1 ACPI ACPI support is enabled. 2 AGP AGP (Accelerated Graphics Port) is enabled. 3 ALSA ALSA sound support is enabled. 4 APIC APIC support is enabled. 5 APM Advanced Power Management support is enabled. 6 APPARMOR AppArmor support is enabled. 7 ARM ARM architecture is enabled. 8 ARM64 ARM64 architecture is enabled. 9 CLK Common clock infrastructure is enabled. 10 CMA Contiguous Memory Area support is enabled. 11 DRM Direct Rendering Management support is enabled. 12 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 13 EARLY Parameter processed too early to be embedded in initrd. 14 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 15 EFI EFI Partitioning (GPT) is enabled 16 EVM Extended Verification Module 17 FB The frame buffer device is enabled. 18 FTRACE Function tracing enabled. 19 GCOV GCOV profiling is enabled. 20 HIBERNATION HIBERNATION is enabled. 21 HW Appropriate hardware is enabled. 22 HYPER_V HYPERV support is enabled. 23 IMA Integrity measurement architecture is enabled. 24 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 25 IPV6 IPv6 support is enabled. 26 ISAPNP ISA PnP code is enabled. 27 ISOL CPU Isolation is enabled. 28 JOY Appropriate joystick support is enabled. 29 KGDB Kernel debugger support is enabled. 30 KVM Kernel Virtual Machine support is enabled. 31 LIBATA Libata driver is enabled 32 LOONGARCH LoongArch architecture is enabled. 33 LOOP Loopback device support is enabled. 34 LP Printer support is enabled. 35 M68k M68k architecture is enabled. 36 These options have more detailed description inside of 37 Documentation/arch/m68k/kernel-options.rst. 38 MIPS MIPS architecture is enabled. 39 MOUSE Appropriate mouse support is enabled. 40 MSI Message Signaled Interrupts (PCI). 41 MTD MTD (Memory Technology Device) support is enabled. 42 NET Appropriate network support is enabled. 43 NFS Appropriate NFS support is enabled. 44 NUMA NUMA support is enabled. 45 OF Devicetree is enabled. 46 PARISC The PA-RISC architecture is enabled. 47 PCI PCI bus support is enabled. 48 PCIE PCI Express support is enabled. 49 PCMCIA The PCMCIA subsystem is enabled. 50 PM Power Management support is enabled. 51 PNP Plug & Play support is enabled. 52 PPC PowerPC architecture is enabled. 53 PPT Parallel port support is enabled. 54 PS2 Appropriate PS/2 support is enabled. 55 PV_OPS A paravirtualized kernel is enabled. 56 RAM RAM disk support is enabled. 57 RDT Intel Resource Director Technology. 58 RISCV RISCV architecture is enabled. 59 S390 S390 architecture is enabled. 60 SCSI Appropriate SCSI support is enabled. 61 A lot of drivers have their options described inside 62 the Documentation/scsi/ sub-directory. 63 SDW SoundWire support is enabled. 64 SECURITY Different security models are enabled. 65 SELINUX SELinux support is enabled. 66 SERIAL Serial support is enabled. 67 SH SuperH architecture is enabled. 68 SMP The kernel is an SMP kernel. 69 SPARC Sparc architecture is enabled. 70 SUSPEND System suspend states are enabled. 71 SWSUSP Software suspend (hibernation) is enabled. 72 TPM TPM drivers are enabled. 73 UMS USB Mass Storage support is enabled. 74 USB USB support is enabled. 75 NVME NVMe support is enabled 76 USBHID USB Human Interface Device support is enabled. 77 V4L Video For Linux support is enabled. 78 VGA The VGA console has been enabled. 79 VMMIO Driver for memory mapped virtio devices is enabled. 80 VT Virtual terminal support is enabled. 81 WDT Watchdog support is enabled. 82 X86-32 X86-32, aka i386 architecture is enabled. 83 X86-64 X86-64 architecture is enabled. 84 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 85 X86_UV SGI UV support is enabled. 86 XEN Xen support is enabled 87 XTENSA xtensa architecture is enabled. 88 89In addition, the following text indicates that the option 90 91 BOOT Is a boot loader parameter. 92 BUGS= Relates to possible processor bugs on the said processor. 93 KNL Is a kernel start-up parameter. 94 95 96Kernel parameters 97 98 accept_memory= [MM] 99 Format: { eager | lazy } 100 default: lazy 101 By default, unaccepted memory is accepted lazily to 102 avoid prolonged boot times. The lazy option will add 103 some runtime overhead until all memory is eventually 104 accepted. In most cases the overhead is negligible. 105 For some workloads or for debugging purposes 106 accept_memory=eager can be used to accept all memory 107 at once during boot. 108 109 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 110 Advanced Configuration and Power Interface 111 Format: { force | on | off | strict | noirq | rsdt | 112 copy_dsdt | nospcr } 113 force -- enable ACPI if default was off 114 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 115 off -- disable ACPI if default was on 116 noirq -- do not use ACPI for IRQ routing 117 strict -- Be less tolerant of platforms that are not 118 strictly ACPI specification compliant. 119 rsdt -- prefer RSDT over (default) XSDT 120 copy_dsdt -- copy DSDT to memory 121 nocmcff -- Disable firmware first mode for corrected 122 errors. This disables parsing the HEST CMC error 123 source to check if firmware has set the FF flag. This 124 may result in duplicate corrected error reports. 125 nospcr -- disable console in ACPI SPCR table as 126 default _serial_ console on ARM64 127 spcr -- enable console in ACPI SPCR table as 128 default _serial_ console on x86 129 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 130 "acpi=nospcr" are available 131 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 132 are available 133 134 See also Documentation/power/runtime_pm.rst, pci=noacpi 135 136 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 137 Format: <int> 138 2: use 2nd APIC table, if available 139 1,0: use 1st APIC table 140 default: 0 141 142 acpi_backlight= [HW,ACPI] 143 { vendor | video | native | none } 144 If set to vendor, prefer vendor-specific driver 145 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 146 of the ACPI video.ko driver. 147 If set to video, use the ACPI video.ko driver. 148 If set to native, use the device's native backlight mode. 149 If set to none, disable the ACPI backlight interface. 150 151 acpi_force_32bit_fadt_addr [ACPI,EARLY] 152 force FADT to use 32 bit addresses rather than the 153 64 bit X_* addresses. Some firmware have broken 64 154 bit addresses for force ACPI ignore these and use 155 the older legacy 32 bit addresses. 156 157 acpica_no_return_repair [HW, ACPI] 158 Disable AML predefined validation mechanism 159 This mechanism can repair the evaluation result to make 160 the return objects more ACPI specification compliant. 161 This option is useful for developers to identify the 162 root cause of an AML interpreter issue when the issue 163 has something to do with the repair mechanism. 164 165 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 166 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 167 Format: <int> 168 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 169 debug output. Bits in debug_layer correspond to a 170 _COMPONENT in an ACPI source file, e.g., 171 #define _COMPONENT ACPI_EVENTS 172 Bits in debug_level correspond to a level in 173 ACPI_DEBUG_PRINT statements, e.g., 174 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 175 The debug_level mask defaults to "info". See 176 Documentation/firmware-guide/acpi/debug.rst for more information about 177 debug layers and levels. 178 179 Enable processor driver info messages: 180 acpi.debug_layer=0x20000000 181 Enable AML "Debug" output, i.e., stores to the Debug 182 object while interpreting AML: 183 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 184 Enable all messages related to ACPI hardware: 185 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 186 187 Some values produce so much output that the system is 188 unusable. The "log_buf_len" parameter may be useful 189 if you need to capture more output. 190 191 acpi.poweroff_on_fatal= [ACPI] 192 {0 | 1} 193 Causes the system to poweroff when the ACPI bytecode signals 194 a fatal error. The default value of this setting is 1. 195 Overriding this value should only be done for diagnosing 196 ACPI firmware problems, as the system might behave erratically 197 after having encountered a fatal ACPI error. 198 199 acpi_enforce_resources= [ACPI] 200 { strict | lax | no } 201 Check for resource conflicts between native drivers 202 and ACPI OperationRegions (SystemIO and SystemMemory 203 only). IO ports and memory declared in ACPI might be 204 used by the ACPI subsystem in arbitrary AML code and 205 can interfere with legacy drivers. 206 strict (default): access to resources claimed by ACPI 207 is denied; legacy drivers trying to access reserved 208 resources will fail to bind to device using them. 209 lax: access to resources claimed by ACPI is allowed; 210 legacy drivers trying to access reserved resources 211 will bind successfully but a warning message is logged. 212 no: ACPI OperationRegions are not marked as reserved, 213 no further checks are performed. 214 215 acpi_force_table_verification [HW,ACPI,EARLY] 216 Enable table checksum verification during early stage. 217 By default, this is disabled due to x86 early mapping 218 size limitation. 219 220 acpi_irq_balance [HW,ACPI] 221 ACPI will balance active IRQs 222 default in APIC mode 223 224 acpi_irq_nobalance [HW,ACPI] 225 ACPI will not move active IRQs (default) 226 default in PIC mode 227 228 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 229 Format: <irq>,<irq>... 230 231 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 232 use by PCI 233 Format: <irq>,<irq>... 234 235 acpi_mask_gpe= [HW,ACPI] 236 Due to the existence of _Lxx/_Exx, some GPEs triggered 237 by unsupported hardware/firmware features can result in 238 GPE floodings that cannot be automatically disabled by 239 the GPE dispatcher. 240 This facility can be used to prevent such uncontrolled 241 GPE floodings. 242 Format: <byte> or <bitmap-list> 243 244 acpi_no_auto_serialize [HW,ACPI] 245 Disable auto-serialization of AML methods 246 AML control methods that contain the opcodes to create 247 named objects will be marked as "Serialized" by the 248 auto-serialization feature. 249 This feature is enabled by default. 250 This option allows to turn off the feature. 251 252 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 253 kernels. 254 255 acpi_no_static_ssdt [HW,ACPI,EARLY] 256 Disable installation of static SSDTs at early boot time 257 By default, SSDTs contained in the RSDT/XSDT will be 258 installed automatically and they will appear under 259 /sys/firmware/acpi/tables. 260 This option turns off this feature. 261 Note that specifying this option does not affect 262 dynamic table installation which will install SSDT 263 tables to /sys/firmware/acpi/tables/dynamic. 264 265 acpi_no_watchdog [HW,ACPI,WDT] 266 Ignore the ACPI-based watchdog interface (WDAT) and let 267 a native driver control the watchdog device instead. 268 269 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 270 Pass the RSDP address to the kernel, mostly used 271 on machines running EFI runtime service to boot the 272 second kernel for kdump. 273 274 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 275 Format: To spoof as Windows 98: ="Microsoft Windows" 276 277 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 278 of 2 which is mandated by ACPI 6) as the supported ACPI 279 specification revision (when using this switch, it may 280 be necessary to carry out a cold reboot _twice_ in a 281 row to make it take effect on the platform firmware). 282 283 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 284 acpi_osi="string1" # add string1 285 acpi_osi="!string2" # remove string2 286 acpi_osi=!* # remove all strings 287 acpi_osi=! # disable all built-in OS vendor 288 strings 289 acpi_osi=!! # enable all built-in OS vendor 290 strings 291 acpi_osi= # disable all strings 292 293 'acpi_osi=!' can be used in combination with single or 294 multiple 'acpi_osi="string1"' to support specific OS 295 vendor string(s). Note that such command can only 296 affect the default state of the OS vendor strings, thus 297 it cannot affect the default state of the feature group 298 strings and the current state of the OS vendor strings, 299 specifying it multiple times through kernel command line 300 is meaningless. This command is useful when one do not 301 care about the state of the feature group strings which 302 should be controlled by the OSPM. 303 Examples: 304 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 305 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 306 can make '_OSI("Windows 2000")' TRUE. 307 308 'acpi_osi=' cannot be used in combination with other 309 'acpi_osi=' command lines, the _OSI method will not 310 exist in the ACPI namespace. NOTE that such command can 311 only affect the _OSI support state, thus specifying it 312 multiple times through kernel command line is also 313 meaningless. 314 Examples: 315 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 316 FALSE. 317 318 'acpi_osi=!*' can be used in combination with single or 319 multiple 'acpi_osi="string1"' to support specific 320 string(s). Note that such command can affect the 321 current state of both the OS vendor strings and the 322 feature group strings, thus specifying it multiple times 323 through kernel command line is meaningful. But it may 324 still not able to affect the final state of a string if 325 there are quirks related to this string. This command 326 is useful when one want to control the state of the 327 feature group strings to debug BIOS issues related to 328 the OSPM features. 329 Examples: 330 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 331 '_OSI("Module Device")' FALSE. 332 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 333 '_OSI("Module Device")' TRUE. 334 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 335 equivalent to 336 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 337 and 338 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 339 they all will make '_OSI("Windows 2000")' TRUE. 340 341 acpi_pm_good [X86] 342 Override the pmtimer bug detection: force the kernel 343 to assume that this machine's pmtimer latches its value 344 and always returns good values. 345 346 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 347 Format: { level | edge | high | low } 348 349 acpi_skip_timer_override [HW,ACPI,EARLY] 350 Recognize and ignore IRQ0/pin2 Interrupt Override. 351 For broken nForce2 BIOS resulting in XT-PIC timer. 352 353 acpi_sleep= [HW,ACPI] Sleep options 354 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 355 s4_nohwsig, old_ordering, nonvs, 356 sci_force_enable, nobl } 357 See Documentation/power/video.rst for information on 358 s3_bios and s3_mode. 359 s3_beep is for debugging; it makes the PC's speaker beep 360 as soon as the kernel's real-mode entry point is called. 361 s4_hwsig causes the kernel to check the ACPI hardware 362 signature during resume from hibernation, and gracefully 363 refuse to resume if it has changed. This complies with 364 the ACPI specification but not with reality, since 365 Windows does not do this and many laptops do change it 366 on docking. So the default behaviour is to allow resume 367 and simply warn when the signature changes, unless the 368 s4_hwsig option is enabled. 369 s4_nohwsig prevents ACPI hardware signature from being 370 used (or even warned about) during resume. 371 old_ordering causes the ACPI 1.0 ordering of the _PTS 372 control method, with respect to putting devices into 373 low power states, to be enforced (the ACPI 2.0 ordering 374 of _PTS is used by default). 375 nonvs prevents the kernel from saving/restoring the 376 ACPI NVS memory during suspend/hibernation and resume. 377 sci_force_enable causes the kernel to set SCI_EN directly 378 on resume from S1/S3 (which is against the ACPI spec, 379 but some broken systems don't work without it). 380 nobl causes the internal blacklist of systems known to 381 behave incorrectly in some ways with respect to system 382 suspend and resume to be ignored (use wisely). 383 384 acpi_use_timer_override [HW,ACPI,EARLY] 385 Use timer override. For some broken Nvidia NF5 boards 386 that require a timer override, but don't have HPET 387 388 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 389 kernel's map of available physical RAM. 390 391 agp= [AGP] 392 { off | try_unsupported } 393 off: disable AGP support 394 try_unsupported: try to drive unsupported chipsets 395 (may crash computer or cause data corruption) 396 397 ALSA [HW,ALSA] 398 See Documentation/sound/alsa-configuration.rst 399 400 alignment= [KNL,ARM] 401 Allow the default userspace alignment fault handler 402 behaviour to be specified. Bit 0 enables warnings, 403 bit 1 enables fixups, and bit 2 sends a segfault. 404 405 align_va_addr= [X86-64] 406 Align virtual addresses by clearing slice [14:12] when 407 allocating a VMA at process creation time. This option 408 gives you up to 3% performance improvement on AMD F15h 409 machines (where it is enabled by default) for a 410 CPU-intensive style benchmark, and it can vary highly in 411 a microbenchmark depending on workload and compiler. 412 413 32: only for 32-bit processes 414 64: only for 64-bit processes 415 on: enable for both 32- and 64-bit processes 416 off: disable for both 32- and 64-bit processes 417 418 alloc_snapshot [FTRACE] 419 Allocate the ftrace snapshot buffer on boot up when the 420 main buffer is allocated. This is handy if debugging 421 and you need to use tracing_snapshot() on boot up, and 422 do not want to use tracing_snapshot_alloc() as it needs 423 to be done where GFP_KERNEL allocations are allowed. 424 425 allow_mismatched_32bit_el0 [ARM64,EARLY] 426 Allow execve() of 32-bit applications and setting of the 427 PER_LINUX32 personality on systems where only a strict 428 subset of the CPUs support 32-bit EL0. When this 429 parameter is present, the set of CPUs supporting 32-bit 430 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 431 and hot-unplug operations may be restricted. 432 433 See Documentation/arch/arm64/asymmetric-32bit.rst for more 434 information. 435 436 amd_iommu= [HW,X86-64] 437 Pass parameters to the AMD IOMMU driver in the system. 438 Possible values are: 439 fullflush - Deprecated, equivalent to iommu.strict=1 440 off - do not initialize any AMD IOMMU found in 441 the system 442 force_isolation - Force device isolation for all 443 devices. The IOMMU driver is not 444 allowed anymore to lift isolation 445 requirements as needed. This option 446 does not override iommu=pt 447 force_enable - Force enable the IOMMU on platforms known 448 to be buggy with IOMMU enabled. Use this 449 option with care. 450 pgtbl_v1 - Use v1 page table for DMA-API (Default). 451 pgtbl_v2 - Use v2 page table for DMA-API. 452 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 453 nohugepages - Limit page-sizes used for v1 page-tables 454 to 4 KiB. 455 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 456 to 4KiB/2Mib/1GiB. 457 458 459 amd_iommu_dump= [HW,X86-64] 460 Enable AMD IOMMU driver option to dump the ACPI table 461 for AMD IOMMU. With this option enabled, AMD IOMMU 462 driver will print ACPI tables for AMD IOMMU during 463 IOMMU initialization. 464 465 amd_iommu_intr= [HW,X86-64] 466 Specifies one of the following AMD IOMMU interrupt 467 remapping modes: 468 legacy - Use legacy interrupt remapping mode. 469 vapic - Use virtual APIC mode, which allows IOMMU 470 to inject interrupts directly into guest. 471 This mode requires kvm-amd.avic=1. 472 (Default when IOMMU HW support is present.) 473 474 amd_pstate= [X86,EARLY] 475 disable 476 Do not enable amd_pstate as the default 477 scaling driver for the supported processors 478 passive 479 Use amd_pstate with passive mode as a scaling driver. 480 In this mode autonomous selection is disabled. 481 Driver requests a desired performance level and platform 482 tries to match the same performance level if it is 483 satisfied by guaranteed performance level. 484 active 485 Use amd_pstate_epp driver instance as the scaling driver, 486 driver provides a hint to the hardware if software wants 487 to bias toward performance (0x0) or energy efficiency (0xff) 488 to the CPPC firmware. then CPPC power algorithm will 489 calculate the runtime workload and adjust the realtime cores 490 frequency. 491 guided 492 Activate guided autonomous mode. Driver requests minimum and 493 maximum performance level and the platform autonomously 494 selects a performance level in this range and appropriate 495 to the current workload. 496 497 amd_prefcore= 498 [X86] 499 disable 500 Disable amd-pstate preferred core. 501 502 amd_dynamic_epp= 503 [X86] 504 disable 505 Disable amd-pstate dynamic EPP. 506 enable 507 Enable amd-pstate dynamic EPP. 508 509 amijoy.map= [HW,JOY] Amiga joystick support 510 Map of devices attached to JOY0DAT and JOY1DAT 511 Format: <a>,<b> 512 See also Documentation/input/joydev/joystick.rst 513 514 analog.map= [HW,JOY] Analog joystick and gamepad support 515 Specifies type or capabilities of an analog joystick 516 connected to one of 16 gameports 517 Format: <type1>,<type2>,..<type16> 518 519 apc= [HW,SPARC] 520 Power management functions (SPARCstation-4/5 + deriv.) 521 Format: noidle 522 Disable APC CPU standby support. SPARCstation-Fox does 523 not play well with APC CPU idle - disable it if you have 524 APC and your system crashes randomly. 525 526 apic [APIC,X86-64] Use IO-APIC. Default. 527 528 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 529 Change the output verbosity while booting 530 Format: { quiet (default) | verbose | debug } 531 Change the amount of debugging information output 532 when initialising the APIC and IO-APIC components. 533 534 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 535 Format: { bsp (default) | all | none } 536 bsp: External NMI is delivered only to CPU 0 537 all: External NMIs are broadcast to all CPUs as a 538 backup of CPU 0 539 none: External NMI is masked for all CPUs. This is 540 useful so that a dump capture kernel won't be 541 shot down by NMI 542 543 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 544 apicmaintimer. Useful when your PIT timer is totally 545 broken. 546 547 autoconf= [IPV6] 548 See Documentation/networking/ipv6.rst. 549 550 apm= [APM] Advanced Power Management 551 See header of arch/x86/kernel/apm_32.c. 552 553 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 554 Format: { "0" | "1" } 555 See security/apparmor/Kconfig help text 556 0 -- disable. 557 1 -- enable. 558 Default value is set via kernel config option. 559 560 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 561 32 bit applications. 562 563 arm64.nobti [ARM64] Unconditionally disable Branch Target 564 Identification support 565 566 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 567 support 568 569 arm64.nohaft [ARM64] Unconditionally disable Hardware managed Access 570 Flag for Table descriptors support 571 572 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 573 Set instructions support 574 575 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 576 Monitoring support 577 578 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 579 support 580 581 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 582 support 583 584 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 585 Extension support 586 587 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 588 Extension support 589 590 ataflop= [HW,M68k] 591 592 atarimouse= [HW,MOUSE] Atari Mouse 593 594 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 595 EzKey and similar keyboards 596 597 atkbd.reset= [HW] Reset keyboard during initialization 598 599 atkbd.set= [HW] Select keyboard code set 600 Format: <int> (2 = AT (default), 3 = PS/2) 601 602 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 603 keyboards 604 605 atkbd.softraw= [HW] Choose between synthetic and real raw mode 606 Format: <bool> (0 = real, 1 = synthetic (default)) 607 608 atkbd.softrepeat= [HW] 609 Use software keyboard repeat 610 611 audit= [KNL] Enable the audit sub-system 612 Format: { "0" | "1" | "off" | "on" } 613 0 | off - kernel audit is disabled and can not be 614 enabled until the next reboot 615 unset - kernel audit is initialized but disabled and 616 will be fully enabled by the userspace auditd. 617 1 | on - kernel audit is initialized and partially 618 enabled, storing at most audit_backlog_limit 619 messages in RAM until it is fully enabled by the 620 userspace auditd. 621 Default: unset 622 623 audit_backlog_limit= [KNL] Set the audit queue size limit. 624 Format: <int> (must be >=0) 625 Default: 64 626 627 bau= [X86_UV] Enable the BAU on SGI UV. The default 628 behavior is to disable the BAU (i.e. bau=0). 629 Format: { "0" | "1" } 630 0 - Disable the BAU. 631 1 - Enable the BAU. 632 unset - Disable the BAU. 633 634 bdev_allow_write_mounted= 635 Format: <bool> 636 Control the ability to open a mounted block device 637 for writing, i.e., allow / disallow writes that bypass 638 the FS. This was implemented as a means to prevent 639 fuzzers from crashing the kernel by overwriting the 640 metadata underneath a mounted FS without its awareness. 641 This also prevents destructive formatting of mounted 642 filesystems by naive storage tooling that don't use 643 O_EXCL. Default is Y and can be changed through the 644 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 645 646 bert_disable [ACPI] 647 Disable BERT OS support on buggy BIOSes. 648 649 bgrt_disable [ACPI,X86,EARLY] 650 Disable BGRT to avoid flickering OEM logo. 651 652 blkdevparts= Manual partition parsing of block device(s) for 653 embedded devices based on command line input. 654 See Documentation/block/cmdline-partition.rst 655 656 boot_delay= [KNL,EARLY] 657 Milliseconds to delay each printk during boot. 658 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 659 and you may also have to specify "lpj=". Boot_delay 660 values larger than 10 seconds (10000) are assumed 661 erroneous and ignored. 662 Format: integer 663 664 bootconfig [KNL,EARLY] 665 Extended command line options can be added to an initrd 666 and this will cause the kernel to look for it. 667 668 See Documentation/admin-guide/bootconfig.rst 669 670 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 671 bttv.radio= Most important insmod options are available as 672 kernel args too. 673 bttv.pll= See Documentation/admin-guide/media/bttv.rst 674 bttv.tuner= 675 676 bulk_remove=off [PPC] This parameter disables the use of the pSeries 677 firmware feature for flushing multiple hpte entries 678 at a time. 679 680 c101= [NET] Moxa C101 synchronous serial card 681 682 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 683 Sometimes CPU hardware bugs make them report the cache 684 size incorrectly. The kernel will attempt work arounds 685 to fix known problems, but for some CPUs it is not 686 possible to determine what the correct size should be. 687 This option provides an override for these situations. 688 689 carrier_timeout= 690 [NET] Specifies amount of time (in seconds) that 691 the kernel should wait for a network carrier. By default 692 it waits 120 seconds. 693 694 ca_keys= [KEYS] This parameter identifies a specific key(s) on 695 the system trusted keyring to be used for certificate 696 trust validation. 697 format: { id:<keyid> | builtin } 698 699 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 700 algorithm. Accepted values range from 0 to 7 701 inclusive. See arch/mips/include/asm/pgtable-bits.h 702 for platform specific values (SB1, Loongson3 and 703 others). 704 705 ccw_timeout_log [S390] 706 See Documentation/arch/s390/common_io.rst for details. 707 708 cfi= [X86-64] Set Control Flow Integrity checking features 709 when CONFIG_FINEIBT is enabled. 710 Format: feature[,feature...] 711 Default: auto 712 713 auto: Use FineIBT if IBT available, otherwise kCFI. 714 Under FineIBT, enable "paranoid" mode when 715 FRED is not available. 716 off: Turn off CFI checking. 717 kcfi: Use kCFI (disable FineIBT). 718 fineibt: Use FineIBT (even if IBT not available). 719 norand: Do not re-randomize CFI hashes. 720 paranoid: Add caller hash checking under FineIBT. 721 bhi: Enable register poisoning to stop speculation 722 across FineIBT. (Disabled by default.) 723 warn: Do not enforce CFI checking: warn only. 724 debug: Report CFI initialization details. 725 726 cgroup_disable= [KNL] Disable a particular controller or optional feature 727 Format: {name of the controller(s) or feature(s) to disable} 728 The effects of cgroup_disable=foo are: 729 - foo isn't auto-mounted if you mount all cgroups in 730 a single hierarchy 731 - foo isn't visible as an individually mountable 732 subsystem 733 - if foo is an optional feature then the feature is 734 disabled and corresponding cgroup files are not 735 created 736 {Currently only "memory" controller deal with this and 737 cut the overhead, others just disable the usage. So 738 only cgroup_disable=memory is actually worthy} 739 Specifying "pressure" disables per-cgroup pressure 740 stall information accounting feature 741 742 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 743 Format: { { controller | "all" | "named" } 744 [,{ controller | "all" | "named" }...] } 745 Like cgroup_disable, but only applies to cgroup v1; 746 the blacklisted controllers remain available in cgroup2. 747 "all" blacklists all controllers and "named" disables 748 named mounts. Specifying both "all" and "named" disables 749 all v1 hierarchies. 750 751 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 752 Format: { "true" | "false" } 753 /proc/cgroups lists only v1 controllers by default. 754 This compatibility option enables listing also v2 755 controllers (whose v1 code is not compiled!), so that 756 semi-legacy software can check this file to decide 757 about usage of v2 (sic) controllers. 758 759 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 760 Format: { "true" | "false" } 761 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 762 763 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 764 Format: <string> 765 nosocket -- Disable socket memory accounting. 766 nokmem -- Disable kernel memory accounting. 767 nobpf -- Disable BPF memory accounting. 768 769 check_pages= [MM,EARLY] Enable sanity checking of pages after 770 allocations / before freeing. This adds checks to catch 771 double-frees, use-after-frees, and other sources of 772 page corruption by inspecting page internals (flags, 773 mapcount/refcount, memcg_data, etc.). 774 Format: { "0" | "1" } 775 Default: 0 (1 if CONFIG_DEBUG_VM is set) 776 777 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 778 Format: { "0" | "1" } 779 See security/selinux/Kconfig help text. 780 0 -- check protection applied by kernel (includes 781 any implied execute protection). 782 1 -- check protection requested by application. 783 Default value is set via a kernel config option. 784 Value can be changed at runtime via 785 /sys/fs/selinux/checkreqprot. 786 Setting checkreqprot to 1 is deprecated. 787 788 cio_ignore= [S390] 789 See Documentation/arch/s390/common_io.rst for details. 790 791 clk_ignore_unused 792 [CLK] 793 Prevents the clock framework from automatically gating 794 clocks that have not been explicitly enabled by a Linux 795 device driver but are enabled in hardware at reset or 796 by the bootloader/firmware. Note that this does not 797 force such clocks to be always-on nor does it reserve 798 those clocks in any way. This parameter is useful for 799 debug and development, but should not be needed on a 800 platform with proper driver support. For more 801 information, see Documentation/driver-api/clk.rst. 802 803 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 804 [Deprecated] 805 Forces specified clocksource (if available) to be used 806 when calculating gettimeofday(). If specified 807 clocksource is not available, it defaults to PIT. 808 Format: { pit | tsc | cyclone | pmtmr } 809 810 clocksource= Override the default clocksource 811 Format: <string> 812 Override the default clocksource and use the clocksource 813 with the name specified. 814 Some clocksource names to choose from, depending on 815 the platform: 816 [all] jiffies (this is the base, fallback clocksource) 817 [ACPI] acpi_pm 818 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 819 pxa_timer,timer3,32k_counter,timer0_1 820 [X86-32] pit,hpet,tsc; 821 scx200_hrt on Geode; cyclone on IBM x440 822 [MIPS] MIPS 823 [PARISC] cr16 824 [S390] tod 825 [SH] SuperH 826 [SPARC64] tick 827 [X86-64] hpet,tsc 828 829 clocksource.arm_arch_timer.evtstrm= 830 [ARM,ARM64,EARLY] 831 Format: <bool> 832 Enable/disable the eventstream feature of the ARM 833 architected timer so that code using WFE-based polling 834 loops can be debugged more effectively on production 835 systems. 836 837 clocksource.verify_n_cpus= [KNL] 838 Limit the number of CPUs checked for clocksources 839 marked with CLOCK_SOURCE_VERIFY_PERCPU that 840 are marked unstable due to excessive skew. 841 A negative value says to check all CPUs, while 842 zero says not to check any. Values larger than 843 nr_cpu_ids are silently truncated to nr_cpu_ids. 844 The actual CPUs are chosen randomly, with 845 no replacement if the same CPU is chosen twice. 846 847 clocksource-wdtest.holdoff= [KNL] 848 Set the time in seconds that the clocksource 849 watchdog test waits before commencing its tests. 850 Defaults to zero when built as a module and to 851 10 seconds when built into the kernel. 852 853 cma=nn[MG]@[start[MG][-end[MG]]] 854 [KNL,CMA,EARLY] 855 Sets the size of kernel global memory area for 856 contiguous memory allocations and optionally the 857 placement constraint by the physical address range of 858 memory allocations. A value of 0 disables CMA 859 altogether. For more information, see 860 kernel/dma/contiguous.c 861 862 cma_pernuma=nn[MG] 863 [KNL,CMA,EARLY] 864 Sets the size of kernel per-numa memory area for 865 contiguous memory allocations. A value of 0 disables 866 per-numa CMA altogether. And If this option is not 867 specified, the default value is 0. 868 With per-numa CMA enabled, DMA users on node nid will 869 first try to allocate buffer from the pernuma area 870 which is located in node nid, if the allocation fails, 871 they will fallback to the global default memory area. 872 873 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 874 [KNL,CMA,EARLY] 875 Sets the size of kernel numa memory area for 876 contiguous memory allocations. It will reserve CMA 877 area for the specified node. 878 879 If it is setup together with upper 'cmd_pernuma=' 880 (unlikely), its size setting takes priority for the 881 specified numa nodes. 882 883 With numa CMA enabled, DMA users on node nid will 884 first try to allocate buffer from the numa area 885 which is located in node nid, if the allocation fails, 886 they will fallback to the global default memory area. 887 888 cmo_free_hint= [PPC] Format: { yes | no } 889 Specify whether pages are marked as being inactive 890 when they are freed. This is used in CMO environments 891 to determine OS memory pressure for page stealing by 892 a hypervisor. 893 Default: yes 894 895 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 896 Sets the size of memory pool for coherent, atomic dma 897 allocations, by default set to 256K. 898 899 condev= [HW,S390] console device 900 conmode= 901 902 con3215_drop= [S390,EARLY] 3215 console drop mode. 903 Format: y|n|Y|N|1|0 904 When set to true, drop data on the 3215 console when 905 the console buffer is full. In this case the 906 operator using a 3270 terminal emulator (for example 907 x3270) does not have to enter the clear key for the 908 console output to advance and the kernel to continue. 909 This leads to a much faster boot time when a 3270 910 terminal emulator is active. If no 3270 terminal 911 emulator is used, this parameter has no effect. 912 913 console= [KNL] Output console device and options. 914 915 tty<n> Use the virtual console device <n>. 916 917 ttyS<n>[,options] 918 ttyUSB0[,options] 919 Use the specified serial port. The options are of 920 the form "bbbbpnf", where "bbbb" is the baud rate, 921 "p" is parity ("n", "o", or "e"), "n" is number of 922 bits, and "f" is flow control ("r" for RTS or 923 omit it). Default is "9600n8". 924 925 See Documentation/admin-guide/serial-console.rst for more 926 information. See 927 Documentation/networking/netconsole.rst for an 928 alternative. 929 930 <DEVNAME>:<n>.<n>[,options] 931 Use the specified serial port on the serial core bus. 932 The addressing uses DEVNAME of the physical serial port 933 device, followed by the serial core controller instance, 934 and the serial port instance. The options are the same 935 as documented for the ttyS addressing above. 936 937 The mapping of the serial ports to the tty instances 938 can be viewed with: 939 940 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 941 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 942 943 In the above example, the console can be addressed with 944 console=00:04:0.0. Note that a console addressed this 945 way will only get added when the related device driver 946 is ready. The use of an earlycon parameter in addition to 947 the console may be desired for console output early on. 948 949 uart[8250],io,<addr>[,options] 950 uart[8250],mmio,<addr>[,options] 951 uart[8250],mmio16,<addr>[,options] 952 uart[8250],mmio32,<addr>[,options] 953 uart[8250],0x<addr>[,options] 954 Start an early, polled-mode console on the 8250/16550 955 UART at the specified I/O port or MMIO address, 956 switching to the matching ttyS device later. 957 MMIO inter-register address stride is either 8-bit 958 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 959 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 960 to be equivalent to 'mmio'. 'options' are specified in 961 the same format described for ttyS above; if unspecified, 962 the h/w is not re-initialized. 963 964 hvc<n> Use the hypervisor console device <n>. This is for 965 both Xen and PowerPC hypervisors. 966 967 { null | "" } 968 Use to disable console output, i.e., to have kernel 969 console messages discarded. 970 This must be the only console= parameter used on the 971 kernel command line. 972 973 If the device connected to the port is not a TTY but a braille 974 device, prepend "brl," before the device type, for instance 975 console=brl,ttyS0 976 For now, only VisioBraille is supported. 977 978 console_msg_format= 979 [KNL] Change console messages format 980 default 981 By default we print messages on consoles in 982 "[time stamp] text\n" format (time stamp may not be 983 printed, depending on CONFIG_PRINTK_TIME or 984 `printk_time' param). 985 syslog 986 Switch to syslog format: "<%u>[time stamp] text\n" 987 IOW, each message will have a facility and loglevel 988 prefix. The format is similar to one used by syslog() 989 syscall, or to executing "dmesg -S --raw" or to reading 990 from /proc/kmsg. 991 992 consoleblank= [KNL] The console blank (screen saver) timeout in 993 seconds. A value of 0 disables the blank timer. 994 Defaults to 0. 995 996 coredump_filter= 997 [KNL] Change the default value for 998 /proc/<pid>/coredump_filter. 999 See also Documentation/filesystems/proc.rst. 1000 1001 coresight_cpu_debug.enable 1002 [ARM,ARM64] 1003 Format: <bool> 1004 Enable/disable the CPU sampling based debugging. 1005 0: default value, disable debugging 1006 1: enable debugging at boot time 1007 1008 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1009 Format: 1010 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1011 1012 cpuidle.off=1 [CPU_IDLE] 1013 disable the cpuidle sub-system 1014 1015 cpuidle.governor= 1016 [CPU_IDLE] Name of the cpuidle governor to use. 1017 1018 cpufreq.off=1 [CPU_FREQ] 1019 disable the cpufreq sub-system 1020 1021 cpufreq.default_governor= 1022 [CPU_FREQ] Name of the default cpufreq governor or 1023 policy to use. This governor must be registered in the 1024 kernel before the cpufreq driver probes. 1025 1026 cpu_init_udelay=N 1027 [X86,EARLY] Delay for N microsec between assert and de-assert 1028 of APIC INIT to start processors. This delay occurs 1029 on every CPU online, such as boot, and resume from suspend. 1030 Default: 10000 1031 1032 cpuhp.parallel= 1033 [SMP] Enable/disable parallel bringup of secondary CPUs 1034 Format: <bool> 1035 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1036 the parameter has no effect. 1037 1038 crash_kexec_post_notifiers 1039 Only jump to kdump kernel after running the panic 1040 notifiers and dumping kmsg. This option increases 1041 the risks of a kdump failure, since some panic 1042 notifiers can make the crashed kernel more unstable. 1043 In configurations where kdump may not be reliable, 1044 running the panic notifiers could allow collecting 1045 more data on dmesg, like stack traces from other CPUS 1046 or extra data dumped by panic_print. Note that some 1047 configurations enable this option unconditionally, 1048 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1049 1050 crashkernel=size[KMG][@offset[KMG]] 1051 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1052 upon panic. This parameter reserves the physical 1053 memory region [offset, offset + size] for that kernel 1054 image. If '@offset' is omitted, then a suitable offset 1055 is selected automatically. 1056 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1057 under 4G first, and fall back to reserve region above 1058 4G when '@offset' hasn't been specified. 1059 See Documentation/admin-guide/kdump/kdump.rst for further details. 1060 1061 crashkernel=range1:size1[,range2:size2,...][@offset] 1062 [KNL] Same as above, but depends on the memory 1063 in the running system. The syntax of range is 1064 start-[end] where start and end are both 1065 a memory unit (amount[KMG]). See also 1066 Documentation/admin-guide/kdump/kdump.rst for an example. 1067 1068 crashkernel=size[KMG],high 1069 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1070 above 4G. 1071 Allow kernel to allocate physical memory region from top, 1072 so could be above 4G if system have more than 4G ram 1073 installed. Otherwise memory region will be allocated 1074 below 4G, if available. 1075 It will be ignored if crashkernel=X is specified. 1076 crashkernel=size[KMG],low 1077 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1078 When crashkernel=X,high is passed, kernel could allocate 1079 physical memory region above 4G, that cause second kernel 1080 crash on system that require some amount of low memory, 1081 e.g. swiotlb requires at least 64M+32K low memory, also 1082 enough extra low memory is needed to make sure DMA buffers 1083 for 32-bit devices won't run out. Kernel would try to allocate 1084 default size of memory below 4G automatically. The default 1085 size is platform dependent. 1086 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1087 --> arm64: 128MiB 1088 --> riscv: 128MiB 1089 --> loongarch: 128MiB 1090 This one lets the user specify own low range under 4G 1091 for second kernel instead. 1092 0: to disable low allocation. 1093 It will be ignored when crashkernel=X,high is not used 1094 or memory reserved is below 4G. 1095 crashkernel=size[KMG],cma 1096 [KNL, X86, ARM64, RISCV, PPC] Reserve additional crash 1097 kernel memory from CMA. This reservation is usable by 1098 the first system's userspace memory and kernel movable 1099 allocations (memory balloon, zswap). Pages allocated 1100 from this memory range will not be included in the vmcore 1101 so this should not be used if dumping of userspace memory 1102 is intended and it has to be expected that some movable 1103 kernel pages may be missing from the dump. 1104 1105 A standard crashkernel reservation, as described above, 1106 is still needed to hold the crash kernel and initrd. 1107 1108 This option increases the risk of a kdump failure: DMA 1109 transfers configured by the first kernel may end up 1110 corrupting the second kernel's memory. 1111 1112 This reservation method is intended for systems that 1113 can't afford to sacrifice enough memory for standard 1114 crashkernel reservation and where less reliable and 1115 possibly incomplete kdump is preferable to no kdump at 1116 all. 1117 1118 cryptomgr.notests 1119 [KNL] Disable crypto self-tests 1120 1121 cs89x0_dma= [HW,NET] 1122 Format: <dma> 1123 1124 cs89x0_media= [HW,NET] 1125 Format: { rj45 | aui | bnc } 1126 1127 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1128 function call handling. When switched on, 1129 additional debug data is printed to the console 1130 in case a hanging CPU is detected, and that 1131 CPU is pinged again in order to try to resolve 1132 the hang situation. The default value of this 1133 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1134 Kconfig option. 1135 1136 dasd= [HW,NET] 1137 See header of drivers/s390/block/dasd_devmap.c. 1138 1139 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1140 (one device per port) 1141 Format: <port#>,<type> 1142 See also Documentation/input/devices/joystick-parport.rst 1143 1144 debug [KNL,EARLY] Enable kernel debugging (events log level). 1145 1146 debug_boot_weak_hash 1147 [KNL,EARLY] Enable printing [hashed] pointers early in the 1148 boot sequence. If enabled, we use a weak hash instead 1149 of siphash to hash pointers. Use this option if you are 1150 seeing instances of '(___ptrval___)') and need to see a 1151 value (hashed pointer) instead. Cryptographically 1152 insecure, please do not use on production kernels. 1153 1154 debug_locks_verbose= 1155 [KNL] verbose locking self-tests 1156 Format: <int> 1157 Print debugging info while doing the locking API 1158 self-tests. 1159 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1160 (no extra messages), setting it to -1 (all bits set) 1161 will print _a_lot_ more information - normally only 1162 useful to lockdep developers. 1163 1164 debug_objects [KNL,EARLY] Enable object debugging 1165 1166 debug_guardpage_minorder= 1167 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1168 parameter allows control of the order of pages that will 1169 be intentionally kept free (and hence protected) by the 1170 buddy allocator. Bigger value increase the probability 1171 of catching random memory corruption, but reduce the 1172 amount of memory for normal system use. The maximum 1173 possible value is MAX_PAGE_ORDER/2. Setting this 1174 parameter to 1 or 2 should be enough to identify most 1175 random memory corruption problems caused by bugs in 1176 kernel or driver code when a CPU writes to (or reads 1177 from) a random memory location. Note that there exists 1178 a class of memory corruptions problems caused by buggy 1179 H/W or F/W or by drivers badly programming DMA 1180 (basically when memory is written at bus level and the 1181 CPU MMU is bypassed) which are not detectable by 1182 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1183 help tracking down these problems. 1184 1185 debug_pagealloc= 1186 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1187 enables the feature at boot time. By default, it is 1188 disabled and the system will work mostly the same as a 1189 kernel built without CONFIG_DEBUG_PAGEALLOC. 1190 Note: to get most of debug_pagealloc error reports, it's 1191 useful to also enable the page_owner functionality. 1192 on: enable the feature 1193 1194 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1195 userspace and debugfs internal clients. 1196 Format: { on, off } 1197 on: All functions are enabled. 1198 off: Filesystem is not registered and clients 1199 get a -EPERM as result when trying to register files 1200 or directories within debugfs. 1201 This is equivalent of the runtime functionality if 1202 debugfs was not enabled in the kernel at all. 1203 Default value is set in build-time with a kernel configuration. 1204 1205 debugpat [X86] Enable PAT debugging 1206 1207 default_hugepagesz= 1208 [HW] The size of the default HugeTLB page. This is 1209 the size represented by the legacy /proc/ hugepages 1210 APIs. In addition, this is the default hugetlb size 1211 used for shmget(), mmap() and mounting hugetlbfs 1212 filesystems. If not specified, defaults to the 1213 architecture's default huge page size. Huge page 1214 sizes are architecture dependent. See also 1215 Documentation/admin-guide/mm/hugetlbpage.rst. 1216 Format: size[KMG] 1217 1218 deferred_probe_timeout= 1219 [KNL] Debugging option to set a timeout in seconds for 1220 deferred probe to give up waiting on dependencies to 1221 probe. Only specific dependencies (subsystems or 1222 drivers) that have opted in will be ignored. A timeout 1223 of 0 will timeout at the end of initcalls; a negative 1224 value is treated as an infinite timeout value. If the 1225 timeout hasn't expired, it'll be restarted by each 1226 successful driver registration. This option will also 1227 dump out devices still on the deferred probe list after 1228 retrying. 1229 1230 delayacct [KNL] Enable per-task delay accounting 1231 1232 dell_smm_hwmon.ignore_dmi= 1233 [HW] Continue probing hardware even if DMI data 1234 indicates that the driver is running on unsupported 1235 hardware. 1236 1237 dell_smm_hwmon.force= 1238 [HW] Activate driver even if SMM BIOS signature does 1239 not match list of supported models and enable otherwise 1240 blacklisted features. 1241 1242 dell_smm_hwmon.power_status= 1243 [HW] Report power status in /proc/i8k 1244 (disabled by default). 1245 1246 dell_smm_hwmon.restricted= 1247 [HW] Allow controlling fans only if SYS_ADMIN 1248 capability is set. 1249 1250 dell_smm_hwmon.fan_mult= 1251 [HW] Factor to multiply fan speed with. 1252 1253 dell_smm_hwmon.fan_max= 1254 [HW] Maximum configurable fan speed. 1255 1256 dfltcc= [HW,S390] 1257 Format: { on | off | def_only | inf_only | always } 1258 on: s390 zlib hardware support for compression on 1259 level 1 and decompression (default) 1260 off: No s390 zlib hardware support 1261 def_only: s390 zlib hardware support for deflate 1262 only (compression on level 1) 1263 inf_only: s390 zlib hardware support for inflate 1264 only (decompression) 1265 always: Same as 'on' but ignores the selected compression 1266 level always using hardware support (used for debugging) 1267 1268 dhash_entries= [KNL] 1269 Set number of hash buckets for dentry cache. 1270 1271 disable_1tb_segments [PPC,EARLY] 1272 Disables the use of 1TB hash page table segments. This 1273 causes the kernel to fall back to 256MB segments which 1274 can be useful when debugging issues that require an SLB 1275 miss to occur. 1276 1277 disable= [IPV6] 1278 See Documentation/networking/ipv6.rst. 1279 1280 disable_radix [PPC,EARLY] 1281 Disable RADIX MMU mode on POWER9 1282 1283 disable_tlbie [PPC] 1284 Disable TLBIE instruction. Currently does not work 1285 with KVM, with HASH MMU, or with coherent accelerators. 1286 1287 disable_ddw [PPC/PSERIES,EARLY] 1288 Disable Dynamic DMA Window support. Use this 1289 to workaround buggy firmware. 1290 1291 disable_ipv6= [IPV6] 1292 See Documentation/networking/ipv6.rst. 1293 1294 disable_mtrr_cleanup [X86,EARLY] 1295 The kernel tries to adjust MTRR layout from continuous 1296 to discrete, to make X server driver able to add WB 1297 entry later. This parameter disables that. 1298 1299 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1300 By default the kernel will trim any uncacheable 1301 memory out of your available memory pool based on 1302 MTRR settings. This parameter disables that behavior, 1303 possibly causing your machine to run very slowly. 1304 1305 disable_timer_pin_1 [X86,EARLY] 1306 Disable PIN 1 of APIC timer 1307 Can be useful to work around chipset bugs. 1308 1309 dis_ucode_ldr [X86] Disable the microcode loader. 1310 1311 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1312 this option disables the debugging code at boot. 1313 1314 dma_debug_entries=<number> 1315 This option allows to tune the number of preallocated 1316 entries for DMA-API debugging code. One entry is 1317 required per DMA-API allocation. Use this if the 1318 DMA-API debugging code disables itself because the 1319 architectural default is too low. 1320 1321 dma_debug_driver=<driver_name> 1322 With this option the DMA-API debugging driver 1323 filter feature can be enabled at boot time. Just 1324 pass the driver to filter for as the parameter. 1325 The filter can be disabled or changed to another 1326 driver later using sysfs. 1327 1328 reg_file_data_sampling= 1329 [X86] Controls mitigation for Register File Data 1330 Sampling (RFDS) vulnerability. RFDS is a CPU 1331 vulnerability which may allow userspace to infer 1332 kernel data values previously stored in floating point 1333 registers, vector registers, or integer registers. 1334 RFDS only affects Intel Atom processors. 1335 1336 on: Turns ON the mitigation. 1337 off: Turns OFF the mitigation. 1338 1339 This parameter overrides the compile time default set 1340 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1341 disabled when other VERW based mitigations (like MDS) 1342 are enabled. In order to disable RFDS mitigation all 1343 VERW based mitigations need to be disabled. 1344 1345 For details see: 1346 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1347 1348 dm_verity.keyring_unsealed= 1349 [KNL] When set to 1, leave the dm-verity keyring 1350 unsealed after initialization so userspace can 1351 provision keys. Once the keyring is restricted 1352 it becomes active and is searched during signature 1353 verification. 1354 1355 driver_async_probe= [KNL] 1356 List of driver names to be probed asynchronously. * 1357 matches with all driver names. If * is specified, the 1358 rest of the listed driver names are those that will NOT 1359 match the *. 1360 Format: <driver_name1>,<driver_name2>... 1361 1362 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1363 Broken monitors, graphic adapters, KVMs and EDIDless 1364 panels may send no or incorrect EDID data sets. 1365 This parameter allows to specify an EDID data sets 1366 in the /lib/firmware directory that are used instead. 1367 An EDID data set will only be used for a particular 1368 connector, if its name and a colon are prepended to 1369 the EDID name. Each connector may use a unique EDID 1370 data set by separating the files with a comma. An EDID 1371 data set with no connector name will be used for 1372 any connectors not explicitly specified. 1373 1374 dscc4.setup= [NET] 1375 1376 dt_cpu_ftrs= [PPC,EARLY] 1377 Format: {"off" | "known"} 1378 Control how the dt_cpu_ftrs device-tree binding is 1379 used for CPU feature discovery and setup (if it 1380 exists). 1381 off: Do not use it, fall back to legacy cpu table. 1382 known: Do not pass through unknown features to guests 1383 or userspace, only those that the kernel is aware of. 1384 1385 dump_apple_properties [X86] 1386 Dump name and content of EFI device properties on 1387 x86 Macs. Useful for driver authors to determine 1388 what data is available or for reverse-engineering. 1389 1390 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1391 <module>.dyndbg[="val"] 1392 Enable debug messages at boot time. See 1393 Documentation/admin-guide/dynamic-debug-howto.rst 1394 for details. 1395 1396 early_ioremap_debug [KNL,EARLY] 1397 Enable debug messages in early_ioremap support. This 1398 is useful for tracking down temporary early mappings 1399 which are not unmapped. 1400 1401 earlycon= [KNL,EARLY] Output early console device and options. 1402 1403 When used with no options, the early console is 1404 determined by stdout-path property in device tree's 1405 chosen node or the ACPI SPCR table if supported by 1406 the platform. 1407 1408 cdns,<addr>[,options] 1409 Start an early, polled-mode console on a Cadence 1410 (xuartps) serial port at the specified address. Only 1411 supported option is baud rate. If baud rate is not 1412 specified, the serial port must already be setup and 1413 configured. 1414 1415 uart[8250],io,<addr>[,options[,uartclk]] 1416 uart[8250],mmio,<addr>[,options[,uartclk]] 1417 uart[8250],mmio32,<addr>[,options[,uartclk]] 1418 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1419 uart[8250],0x<addr>[,options] 1420 Start an early, polled-mode console on the 8250/16550 1421 UART at the specified I/O port or MMIO address. 1422 MMIO inter-register address stride is either 8-bit 1423 (mmio) or 32-bit (mmio32 or mmio32be). 1424 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1425 to be equivalent to 'mmio'. 'options' are specified 1426 in the same format described for "console=ttyS<n>"; if 1427 unspecified, the h/w is not initialized. 'uartclk' is 1428 the uart clock frequency; if unspecified, it is set 1429 to 'BASE_BAUD' * 16. 1430 1431 pl011,<addr> 1432 pl011,mmio32,<addr> 1433 Start an early, polled-mode console on a pl011 serial 1434 port at the specified address. The pl011 serial port 1435 must already be setup and configured. Options are not 1436 yet supported. If 'mmio32' is specified, then only 1437 the driver will use only 32-bit accessors to read/write 1438 the device registers. 1439 1440 liteuart,<addr> 1441 Start an early console on a litex serial port at the 1442 specified address. The serial port must already be 1443 setup and configured. Options are not yet supported. 1444 1445 meson,<addr> 1446 Start an early, polled-mode console on a meson serial 1447 port at the specified address. The serial port must 1448 already be setup and configured. Options are not yet 1449 supported. 1450 1451 msm_serial,<addr> 1452 Start an early, polled-mode console on an msm serial 1453 port at the specified address. The serial port 1454 must already be setup and configured. Options are not 1455 yet supported. 1456 1457 msm_serial_dm,<addr> 1458 Start an early, polled-mode console on an msm serial 1459 dm port at the specified address. The serial port 1460 must already be setup and configured. Options are not 1461 yet supported. 1462 1463 owl,<addr> 1464 Start an early, polled-mode console on a serial port 1465 of an Actions Semi SoC, such as S500 or S900, at the 1466 specified address. The serial port must already be 1467 setup and configured. Options are not yet supported. 1468 1469 rda,<addr> 1470 Start an early, polled-mode console on a serial port 1471 of an RDA Micro SoC, such as RDA8810PL, at the 1472 specified address. The serial port must already be 1473 setup and configured. Options are not yet supported. 1474 1475 sbi 1476 Use RISC-V SBI (Supervisor Binary Interface) for early 1477 console. 1478 1479 smh Use ARM semihosting calls for early console. 1480 1481 s3c2410,<addr> 1482 s3c2412,<addr> 1483 s3c2440,<addr> 1484 s3c6400,<addr> 1485 s5pv210,<addr> 1486 exynos4210,<addr> 1487 Use early console provided by serial driver available 1488 on Samsung SoCs, requires selecting proper type and 1489 a correct base address of the selected UART port. The 1490 serial port must already be setup and configured. 1491 Options are not yet supported. 1492 1493 lantiq,<addr> 1494 Start an early, polled-mode console on a lantiq serial 1495 (lqasc) port at the specified address. The serial port 1496 must already be setup and configured. Options are not 1497 yet supported. 1498 1499 lpuart,<addr> 1500 lpuart32,<addr> 1501 Use early console provided by Freescale LP UART driver 1502 found on Freescale Vybrid and QorIQ LS1021A processors. 1503 A valid base address must be provided, and the serial 1504 port must already be setup and configured. 1505 1506 ec_imx21,<addr> 1507 ec_imx6q,<addr> 1508 Start an early, polled-mode, output-only console on the 1509 Freescale i.MX UART at the specified address. The UART 1510 must already be setup and configured. 1511 1512 ar3700_uart,<addr> 1513 Start an early, polled-mode console on the 1514 Armada 3700 serial port at the specified 1515 address. The serial port must already be setup 1516 and configured. Options are not yet supported. 1517 1518 qcom_geni,<addr> 1519 Start an early, polled-mode console on a Qualcomm 1520 Generic Interface (GENI) based serial port at the 1521 specified address. The serial port must already be 1522 setup and configured. Options are not yet supported. 1523 1524 efifb,[options] 1525 Start an early, unaccelerated console on the EFI 1526 memory mapped framebuffer (if available). On cache 1527 coherent non-x86 systems that use system memory for 1528 the framebuffer, pass the 'ram' option so that it is 1529 mapped with the correct attributes. 1530 1531 linflex,<addr> 1532 Use early console provided by Freescale LINFlexD UART 1533 serial driver for NXP S32V234 SoCs. A valid base 1534 address must be provided, and the serial port must 1535 already be setup and configured. 1536 1537 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1538 earlyprintk=vga 1539 earlyprintk=sclp 1540 earlyprintk=xen 1541 earlyprintk=serial[,ttySn[,baudrate]] 1542 earlyprintk=serial[,0x...[,baudrate]] 1543 earlyprintk=ttySn[,baudrate] 1544 earlyprintk=dbgp[debugController#] 1545 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1546 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1547 earlyprintk=xdbc[xhciController#] 1548 earlyprintk=bios 1549 1550 earlyprintk is useful when the kernel crashes before 1551 the normal console is initialized. It is not enabled by 1552 default because it has some cosmetic problems. 1553 1554 Use "nocfg" to skip UART configuration, assume 1555 BIOS/firmware has configured UART correctly. 1556 1557 Append ",keep" to not disable it when the real console 1558 takes over. 1559 1560 Only one of vga, serial, or usb debug port can 1561 be used at a time. 1562 1563 Currently only ttyS0 and ttyS1 may be specified by 1564 name. Other I/O ports may be explicitly specified 1565 on some architectures (x86 and arm at least) by 1566 replacing ttySn with an I/O port address, like this: 1567 earlyprintk=serial,0x1008,115200 1568 You can find the port for a given device in 1569 /proc/tty/driver/serial: 1570 2: uart:ST16650V2 port:00001008 irq:18 ... 1571 1572 Interaction with the standard serial driver is not 1573 very good. 1574 1575 The VGA output is eventually overwritten by 1576 the real console. 1577 1578 The xen option can only be used in Xen domains. 1579 1580 The sclp output can only be used on s390. 1581 1582 The bios output can only be used on SuperH. 1583 1584 The optional "force" to "pciserial" enables use of a 1585 PCI device even when its classcode is not of the 1586 UART class. 1587 1588 edac_report= [HW,EDAC] Control how to report EDAC event 1589 Format: {"on" | "off" | "force"} 1590 on: enable EDAC to report H/W event. May be overridden 1591 by other higher priority error reporting module. 1592 off: disable H/W event reporting through EDAC. 1593 force: enforce the use of EDAC to report H/W event. 1594 default: on. 1595 1596 edd= [EDD] 1597 Format: {"off" | "on" | "skip[mbr]"} 1598 1599 efi= [EFI,EARLY] 1600 Format: { "debug", "disable_early_pci_dma", 1601 "nochunk", "noruntime", "nosoftreserve", 1602 "novamap", "no_disable_early_pci_dma" } 1603 debug: enable misc debug output. 1604 disable_early_pci_dma: disable the busmaster bit on all 1605 PCI bridges while in the EFI boot stub. 1606 nochunk: disable reading files in "chunks" in the EFI 1607 boot stub, as chunking can cause problems with some 1608 firmware implementations. 1609 noruntime : disable EFI runtime services support 1610 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1611 attribute may cause the kernel to reserve the 1612 memory range for a memory mapping driver to 1613 claim. Specify efi=nosoftreserve to disable this 1614 reservation and treat the memory by its base type 1615 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1616 novamap: do not call SetVirtualAddressMap(). 1617 no_disable_early_pci_dma: Leave the busmaster bit set 1618 on all PCI bridges while in the EFI boot stub 1619 1620 efi_no_storage_paranoia [EFI,X86,EARLY] 1621 The kernel reserves 5KB of EFI variable storage for 1622 safety, because some UEFI implementation may fail to 1623 boot if there's insufficient space in the EFI variable 1624 storage. 1625 1626 Using this parameter, you can use the 5KB reservation 1627 in the EFI variable storage. 1628 1629 However, Use this parameter only if you are really 1630 sure that your UEFI does sane gc and fulfills the spec 1631 otherwise your board may brick. 1632 1633 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1634 that is to be dynamically loaded by Linux. If there are 1635 multiple variables with the same name but with different 1636 vendor GUIDs, all of them will be loaded. See 1637 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1638 1639 1640 eisa_irq_edge= [PARISC,HW] 1641 See header of drivers/parisc/eisa.c. 1642 1643 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1644 Format: ekgdboc=kbd 1645 1646 This is designed to be used in conjunction with 1647 the boot argument: earlyprintk=vga 1648 1649 This parameter works in place of the kgdboc parameter 1650 but can only be used if the backing tty is available 1651 very early in the boot process. For early debugging 1652 via a serial port see kgdboc_earlycon instead. 1653 1654 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1655 Specifies physical address of start of kernel core 1656 image elf header and optionally the size. Generally 1657 kexec loader will pass this option to capture kernel. 1658 See Documentation/admin-guide/kdump/kdump.rst for details. 1659 1660 enable_mtrr_cleanup [X86,EARLY] 1661 The kernel tries to adjust MTRR layout from continuous 1662 to discrete, to make X server driver able to add WB 1663 entry later. This parameter enables that. 1664 1665 enable_timer_pin_1 [X86] 1666 Enable PIN 1 of APIC timer 1667 Can be useful to work around chipset bugs 1668 (in particular on some ATI chipsets). 1669 The kernel tries to set a reasonable default. 1670 1671 enforcing= [SELINUX] Set initial enforcing status. 1672 Format: {"0" | "1"} 1673 See security/selinux/Kconfig help text. 1674 0 -- permissive (log only, no denials). 1675 1 -- enforcing (deny and log). 1676 Default value is 0. 1677 Value can be changed at runtime via 1678 /sys/fs/selinux/enforce. 1679 1680 erst_disable [ACPI] 1681 Disable Error Record Serialization Table (ERST) 1682 support. 1683 1684 ether= [HW,NET] Ethernet cards parameters 1685 This option is obsoleted by the "netdev=" option, which 1686 has equivalent usage. See its documentation for details. 1687 1688 evm= [EVM] 1689 Format: { "fix" } 1690 Permit 'security.evm' to be updated regardless of 1691 current integrity status. 1692 1693 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1694 stages so cover more early boot allocations. 1695 Please note that as side effect some optimizations 1696 might be disabled to achieve that (e.g. parallelized 1697 memory initialization is disabled) so the boot process 1698 might take longer, especially on systems with a lot of 1699 memory. Available with CONFIG_PAGE_EXTENSION=y. 1700 1701 failslab= 1702 fail_usercopy= 1703 fail_page_alloc= 1704 fail_skb_realloc= 1705 fail_make_request=[KNL] 1706 General fault injection mechanism. 1707 Format: <interval>,<probability>,<space>,<times> 1708 See also Documentation/fault-injection/. 1709 1710 fb_tunnels= [NET] 1711 Format: { initns | none } 1712 See Documentation/admin-guide/sysctl/net.rst for 1713 fb_tunnels_only_for_init_ns 1714 1715 floppy= [HW] 1716 See Documentation/admin-guide/blockdev/floppy.rst. 1717 1718 forcepae [X86-32] 1719 Forcefully enable Physical Address Extension (PAE). 1720 Many Pentium M systems disable PAE but may have a 1721 functionally usable PAE implementation. 1722 Warning: use of this parameter will taint the kernel 1723 and may cause unknown problems. 1724 1725 fred= [X86-64] 1726 Enable/disable Flexible Return and Event Delivery. 1727 Format: { on | off } 1728 on: enable FRED when it's present, the default setting. 1729 off: disable FRED. 1730 1731 ftrace=[tracer] 1732 [FTRACE] will set and start the specified tracer 1733 as early as possible in order to facilitate early 1734 boot debugging. 1735 1736 ftrace_boot_snapshot 1737 [FTRACE] On boot up, a snapshot will be taken of the 1738 ftrace ring buffer that can be read at: 1739 /sys/kernel/tracing/snapshot. 1740 This is useful if you need tracing information from kernel 1741 boot up that is likely to be overridden by user space 1742 start up functionality. 1743 1744 Optionally, the snapshot can also be defined for a tracing 1745 instance that was created by the trace_instance= command 1746 line parameter. 1747 1748 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1749 1750 The above will cause the "foo" tracing instance to trigger 1751 a snapshot at the end of boot up. 1752 1753 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1754 ,<instance>=2(orig_cpu)] 1755 [FTRACE] will dump the trace buffers on oops. 1756 If no parameter is passed, ftrace will dump global 1757 buffers of all CPUs, if you pass 2 or orig_cpu, it 1758 will dump only the buffer of the CPU that triggered 1759 the oops, or the specific instance will be dumped if 1760 its name is passed. Multiple instance dump is also 1761 supported, and instances are separated by commas. Each 1762 instance supports only dump on CPU that triggered the 1763 oops by passing 2 or orig_cpu to it. 1764 1765 ftrace_dump_on_oops=foo=orig_cpu 1766 1767 The above will dump only the buffer of "foo" instance 1768 on CPU that triggered the oops. 1769 1770 ftrace_dump_on_oops,foo,bar=orig_cpu 1771 1772 The above will dump global buffer on all CPUs, the 1773 buffer of "foo" instance on all CPUs and the buffer 1774 of "bar" instance on CPU that triggered the oops. 1775 1776 ftrace_filter=[function-list] 1777 [FTRACE] Limit the functions traced by the function 1778 tracer at boot up. function-list is a comma-separated 1779 list of functions. This list can be changed at run 1780 time by the set_ftrace_filter file in the debugfs 1781 tracing directory. 1782 1783 ftrace_notrace=[function-list] 1784 [FTRACE] Do not trace the functions specified in 1785 function-list. This list can be changed at run time 1786 by the set_ftrace_notrace file in the debugfs 1787 tracing directory. 1788 1789 ftrace_graph_filter=[function-list] 1790 [FTRACE] Limit the top level callers functions traced 1791 by the function graph tracer at boot up. 1792 function-list is a comma-separated list of functions 1793 that can be changed at run time by the 1794 set_graph_function file in the debugfs tracing directory. 1795 1796 ftrace_graph_notrace=[function-list] 1797 [FTRACE] Do not trace from the functions specified in 1798 function-list. This list is a comma-separated list of 1799 functions that can be changed at run time by the 1800 set_graph_notrace file in the debugfs tracing directory. 1801 1802 ftrace_graph_max_depth=<uint> 1803 [FTRACE] Used with the function graph tracer. This is 1804 the max depth it will trace into a function. This value 1805 can be changed at run time by the max_graph_depth file 1806 in the tracefs tracing directory. default: 0 (no limit) 1807 1808 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1809 devices by scanning the firmware to infer the 1810 consumer/supplier relationships. This feature is 1811 especially useful when drivers are loaded as modules as 1812 it ensures proper ordering of tasks like device probing 1813 (suppliers first, then consumers), supplier boot state 1814 clean up (only after all consumers have probed), 1815 suspend/resume & runtime PM (consumers first, then 1816 suppliers). 1817 Format: { off | permissive | on | rpm } 1818 off -- Don't create device links from firmware info. 1819 permissive -- Create device links from firmware info 1820 but use it only for ordering boot state clean 1821 up (sync_state() calls). 1822 on -- Create device links from firmware info and use it 1823 to enforce probe and suspend/resume ordering. 1824 rpm -- Like "on", but also use to order runtime PM. 1825 1826 fw_devlink.strict=<bool> 1827 [KNL,EARLY] Treat all inferred dependencies as mandatory 1828 dependencies. This only applies for fw_devlink=on|rpm. 1829 Format: <bool> 1830 1831 fw_devlink.sync_state = 1832 [KNL,EARLY] When all devices that could probe have finished 1833 probing, this parameter controls what to do with 1834 devices that haven't yet received their sync_state() 1835 calls. 1836 Format: { strict | timeout } 1837 strict -- Default. Continue waiting on consumers to 1838 probe successfully. 1839 timeout -- Give up waiting on consumers and call 1840 sync_state() on any devices that haven't yet 1841 received their sync_state() calls after 1842 deferred_probe_timeout has expired or by 1843 late_initcall() if !CONFIG_MODULES. 1844 1845 gamecon.map[2|3]= 1846 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1847 support via parallel port (up to 5 devices per port) 1848 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1849 See also Documentation/input/devices/joystick-parport.rst 1850 1851 gamma= [HW,DRM] 1852 1853 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1854 Format: off | on 1855 default: on 1856 1857 gather_data_sampling= 1858 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1859 mitigation. 1860 1861 Gather Data Sampling is a hardware vulnerability which 1862 allows unprivileged speculative access to data which was 1863 previously stored in vector registers. 1864 1865 This issue is mitigated by default in updated microcode. 1866 The mitigation may have a performance impact but can be 1867 disabled. On systems without the microcode mitigation 1868 disabling AVX serves as a mitigation. 1869 1870 force: Disable AVX to mitigate systems without 1871 microcode mitigation. No effect if the microcode 1872 mitigation is present. Known to cause crashes in 1873 userspace with buggy AVX enumeration. 1874 1875 off: Disable GDS mitigation. 1876 1877 gbpages [X86] Use GB pages for kernel direct mappings. 1878 1879 gcov_persist= [GCOV] When non-zero (default), profiling data for 1880 kernel modules is saved and remains accessible via 1881 debugfs, even when the module is unloaded/reloaded. 1882 When zero, profiling data is discarded and associated 1883 debugfs files are removed at module unload time. 1884 1885 goldfish [X86] Enable the goldfish android emulator platform. 1886 Don't use this when you are not running on the 1887 android emulator 1888 1889 gpio-mockup.gpio_mockup_ranges 1890 [HW] Sets the ranges of gpiochip of for this device. 1891 Format: <start1>,<end1>,<start2>,<end2>... 1892 gpio-mockup.gpio_mockup_named_lines 1893 [HW] Let the driver know GPIO lines should be named. 1894 1895 gpt [EFI] Forces disk with valid GPT signature but 1896 invalid Protective MBR to be treated as GPT. If the 1897 primary GPT is corrupted, it enables the backup/alternate 1898 GPT to be used instead. 1899 1900 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1901 the "Enable 0" bit of the configuration register. 1902 Format: 0 | 1 1903 Default: 0 1904 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1905 the "Enable 0" bit of the configuration register. 1906 Format: 0 | 1 1907 Default: 0 1908 grcan.select= [HW] Select which physical interface to use. 1909 Format: 0 | 1 1910 Default: 0 1911 grcan.txsize= [HW] Sets the size of the tx buffer. 1912 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1913 Default: 1024 1914 grcan.rxsize= [HW] Sets the size of the rx buffer. 1915 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1916 Default: 1024 1917 1918 hardened_usercopy= 1919 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1920 hardening is enabled for this boot. Hardened 1921 usercopy checking is used to protect the kernel 1922 from reading or writing beyond known memory 1923 allocation boundaries as a proactive defense 1924 against bounds-checking flaws in the kernel's 1925 copy_to_user()/copy_from_user() interface. 1926 The default is determined by 1927 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1928 on Perform hardened usercopy checks. 1929 off Disable hardened usercopy checks. 1930 1931 hardlockup_all_cpu_backtrace= 1932 [KNL] Should the hard-lockup detector generate 1933 backtraces on all cpus. 1934 Format: 0 | 1 1935 1936 hash_pointers= 1937 [KNL,EARLY] 1938 By default, when pointers are printed to the console 1939 or buffers via the %p format string, that pointer is 1940 "hashed", i.e. obscured by hashing the pointer value. 1941 This is a security feature that hides actual kernel 1942 addresses from unprivileged users, but it also makes 1943 debugging the kernel more difficult since unequal 1944 pointers can no longer be compared. The choices are: 1945 Format: { auto | always | never } 1946 Default: auto 1947 1948 auto - Hash pointers unless slab_debug is enabled. 1949 always - Always hash pointers (even if slab_debug is 1950 enabled). 1951 never - Never hash pointers. This option should only 1952 be specified when debugging the kernel. Do 1953 not use on production kernels. The boot 1954 param "no_hash_pointers" is an alias for 1955 this mode. 1956 1957 For controlling hashing dynamically at runtime, 1958 use the "kernel.kptr_restrict" sysctl instead. 1959 1960 hashdist= [KNL,NUMA] Large hashes allocated during boot 1961 are distributed across NUMA nodes. Defaults on 1962 for 64-bit NUMA, off otherwise. 1963 Format: 0 | 1 (for off | on) 1964 1965 hd= [EIDE] (E)IDE hard drive subsystem geometry 1966 Format: <cyl>,<head>,<sect> 1967 1968 hest_disable [ACPI] 1969 Disable Hardware Error Source Table (HEST) support; 1970 corresponding firmware-first mode error processing 1971 logic will be disabled. 1972 1973 hibernate= [HIBERNATION] 1974 noresume Don't check if there's a hibernation image 1975 present during boot. 1976 nocompress Don't compress/decompress hibernation images. 1977 no Disable hibernation and resume. 1978 protect_image Turn on image protection during restoration 1979 (that will set all pages holding image data 1980 during restoration read-only). 1981 1982 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1983 used with hibernation. 1984 Format: { lzo | lz4 } 1985 Default: lzo 1986 1987 lzo: Select LZO compression algorithm to 1988 compress/decompress hibernation image. 1989 1990 lz4: Select LZ4 compression algorithm to 1991 compress/decompress hibernation image. 1992 1993 hibernate.pm_test_delay= 1994 [HIBERNATION] 1995 Sets the number of seconds to remain in a hibernation test 1996 mode before resuming the system (see 1997 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 1998 is set. Default value is 5. 1999 2000 hibernate_compression_threads= 2001 [HIBERNATION] 2002 Set the number of threads used for compressing or decompressing 2003 hibernation images. 2004 2005 Format: <integer> 2006 Default: 3 2007 Minimum: 1 2008 Example: hibernate_compression_threads=4 2009 2010 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2011 size of <nn>. This works even on boxes that have no 2012 highmem otherwise. This also works to reduce highmem 2013 size on bigger boxes. 2014 2015 highres= [KNL] Enable/disable high resolution timer mode. 2016 Valid parameters: "on", "off" 2017 Default: "on" 2018 2019 hlt [BUGS=ARM,SH] 2020 2021 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2022 Format: <string> 2023 This allows setting the system's hostname during early 2024 startup. This sets the name returned by gethostname. 2025 Using this parameter to set the hostname makes it 2026 possible to ensure the hostname is correctly set before 2027 any userspace processes run, avoiding the possibility 2028 that a process may call gethostname before the hostname 2029 has been explicitly set, resulting in the calling 2030 process getting an incorrect result. The string must 2031 not exceed the maximum allowed hostname length (usually 2032 64 characters) and will be truncated otherwise. 2033 2034 hpet= [X86-32,HPET] option to control HPET usage 2035 Format: { enable (default) | disable | force | 2036 verbose } 2037 disable: disable HPET and use PIT instead 2038 force: allow force enabled of undocumented chips (ICH4, 2039 VIA, nVidia) 2040 verbose: show contents of HPET registers during setup 2041 2042 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2043 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2044 2045 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2046 If this follows hugepagesz (below), it specifies 2047 the number of pages of hugepagesz to be allocated. 2048 If this is the first HugeTLB parameter on the command 2049 line, it specifies the number of pages to allocate for 2050 the default huge page size. If using node format, the 2051 number of pages to allocate per-node can be specified. 2052 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2053 Format: <integer> or (node format) 2054 <node>:<integer>[,<node>:<integer>] 2055 2056 hugepagesz= 2057 [HW,EARLY] The size of the HugeTLB pages. This is 2058 used in conjunction with hugepages (above) to 2059 allocate huge pages of a specific size at boot. The 2060 pair hugepagesz=X hugepages=Y can be specified once 2061 for each supported huge page size. Huge page sizes 2062 are architecture dependent. See also 2063 Documentation/admin-guide/mm/hugetlbpage.rst. 2064 Format: size[KMG] 2065 2066 hugepage_alloc_threads= 2067 [HW] The number of threads that should be used to 2068 allocate hugepages during boot. This option can be 2069 used to improve system bootup time when allocating 2070 a large amount of huge pages. 2071 The default value is 25% of the available hardware threads. 2072 2073 Note that this parameter only applies to non-gigantic huge pages. 2074 2075 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2076 of gigantic hugepages. Or using node format, the size 2077 of a CMA area per node can be specified. 2078 Format: nn[KMGTPE] or (node format) 2079 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2080 2081 The size must be a multiple of the gigantic page size. 2082 When using node format, this applies to each per-node size. 2083 Missaligned values are dropped with a warning. 2084 2085 Reserve a CMA area of given size and allocate gigantic 2086 hugepages using the CMA allocator. If enabled, the 2087 boot-time allocation of gigantic hugepages is skipped. 2088 2089 hugetlb_cma_only= 2090 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2091 try to allocate from the CMA areas. 2092 2093 This option does nothing if hugetlb_cma= is not also 2094 specified. 2095 2096 hugetlb_free_vmemmap= 2097 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2098 enabled. 2099 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2100 Allows heavy hugetlb users to free up some more 2101 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2102 Format: { on | off (default) } 2103 2104 on: enable HVO 2105 off: disable HVO 2106 2107 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2108 the default is on. 2109 2110 Note that the vmemmap pages may be allocated from the added 2111 memory block itself when memory_hotplug.memmap_on_memory is 2112 enabled, those vmemmap pages cannot be optimized even if this 2113 feature is enabled. Other vmemmap pages not allocated from 2114 the added memory block itself do not be affected. 2115 2116 hung_task_panic= 2117 [KNL] Number of hung tasks to trigger kernel panic. 2118 Format: <int> 2119 2120 When set to a non-zero value, a kernel panic will be triggered if 2121 the number of detected hung tasks reaches this value. 2122 2123 0: don't panic 2124 1: panic immediately on first hung task 2125 N: panic after N hung tasks are detected in a single scan 2126 2127 The default value is controlled by the 2128 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2129 selected by this boot parameter can be changed later by the 2130 kernel.hung_task_panic sysctl. 2131 2132 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2133 terminal devices. Valid values: 0..8 2134 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2135 If specified, z/VM IUCV HVC accepts connections 2136 from listed z/VM user IDs only. 2137 2138 hv_nopvspin [X86,HYPER_V,EARLY] 2139 Disables the paravirt spinlock optimizations 2140 which allow the hypervisor to 'idle' the guest 2141 on lock contention. 2142 2143 hw_protection= [HW] 2144 Format: reboot | shutdown 2145 2146 Hardware protection action taken on critical events like 2147 overtemperature or imminent voltage loss. 2148 2149 i2c_bus= [HW] Override the default board specific I2C bus speed 2150 or register an additional I2C bus that is not 2151 registered from board initialization code. 2152 Format: 2153 <bus_id>,<clkrate> 2154 2155 i2c_touchscreen_props= [HW,ACPI,X86] 2156 Set device-properties for ACPI-enumerated I2C-attached 2157 touchscreen, to e.g. fix coordinates of upside-down 2158 mounted touchscreens. If you need this option please 2159 submit a drivers/platform/x86/touchscreen_dmi.c patch 2160 adding a DMI quirk for this. 2161 2162 Format: 2163 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2164 Where <val> is one of: 2165 Omit "=<val>" entirely Set a boolean device-property 2166 Unsigned number Set a u32 device-property 2167 Anything else Set a string device-property 2168 2169 Examples (split over multiple lines): 2170 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2171 touchscreen-inverted-y 2172 2173 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2174 touchscreen-size-y=1080:touchscreen-inverted-y: 2175 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2176 2177 i8042.debug [HW] Toggle i8042 debug mode 2178 i8042.unmask_kbd_data 2179 [HW] Enable printing of interrupt data from the KBD port 2180 (disabled by default, and as a pre-condition 2181 requires that i8042.debug=1 be enabled) 2182 i8042.direct [HW] Put keyboard port into non-translated mode 2183 i8042.dumbkbd [HW] Pretend that controller can only read data from 2184 keyboard and cannot control its state 2185 (Don't attempt to blink the leds) 2186 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2187 i8042.nokbd [HW] Don't check/create keyboard port 2188 i8042.noloop [HW] Disable the AUX Loopback command while probing 2189 for the AUX port 2190 i8042.nomux [HW] Don't check presence of an active multiplexing 2191 controller 2192 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2193 controllers 2194 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2195 i8042.reset [HW] Reset the controller during init, cleanup and 2196 suspend-to-ram transitions, only during s2r 2197 transitions, or never reset 2198 Format: { 1 | Y | y | 0 | N | n } 2199 1, Y, y: always reset controller 2200 0, N, n: don't ever reset controller 2201 Default: only on s2r transitions on x86; most other 2202 architectures force reset to be always executed 2203 i8042.unlock [HW] Unlock (ignore) the keylock 2204 i8042.kbdreset [HW] Reset device connected to KBD port 2205 i8042.probe_defer 2206 [HW] Allow deferred probing upon i8042 probe errors 2207 2208 i810= [HW,DRM] 2209 2210 i915.invert_brightness= 2211 [DRM] Invert the sense of the variable that is used to 2212 set the brightness of the panel backlight. Normally a 2213 brightness value of 0 indicates backlight switched off, 2214 and the maximum of the brightness value sets the backlight 2215 to maximum brightness. If this parameter is set to 0 2216 (default) and the machine requires it, or this parameter 2217 is set to 1, a brightness value of 0 sets the backlight 2218 to maximum brightness, and the maximum of the brightness 2219 value switches the backlight off. 2220 -1 -- never invert brightness 2221 0 -- machine default 2222 1 -- force brightness inversion 2223 2224 ia32_emulation= [X86-64] 2225 Format: <bool> 2226 When true, allows loading 32-bit programs and executing 32-bit 2227 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2228 boot time. When false, unconditionally disables IA32 emulation. 2229 2230 2231 idle= [X86,EARLY] 2232 Format: idle=poll, idle=halt, idle=nomwait 2233 2234 idle=poll: Don't do power saving in the idle loop 2235 using HLT, but poll for rescheduling event. This will 2236 make the CPUs eat a lot more power, but may be useful 2237 to get slightly better performance in multiprocessor 2238 benchmarks. It also makes some profiling using 2239 performance counters more accurate. Please note that 2240 on systems with MONITOR/MWAIT support (like Intel 2241 EM64T CPUs) this option has no performance advantage 2242 over the normal idle loop. It may also interact badly 2243 with hyperthreading. 2244 2245 idle=halt: Halt is forced to be used for CPU idle. 2246 In such case C2/C3 won't be used again. 2247 2248 idle=nomwait: Disable mwait for CPU C-states 2249 2250 [ARM64,EARLY] 2251 Format: idle=wfi, idle=yield, idle=nop 2252 2253 idle=wfi: Use the WFI (Wait For Interrupt) hint 2254 instruction in the idle loop. This is the default and 2255 allows the CPU to enter a low-power state until an 2256 interrupt arrives. 2257 2258 idle=yield: Use the YIELD hint instruction instead of 2259 WFI. CPUs supporting simultaneous multi-threading (SMT), 2260 can continue executing another thread when the current 2261 thread reaches the idle loop. This will make the CPUs 2262 eat more power, but may be useful to get slightly better 2263 performance in some applications, since the CPUs will 2264 not enter a low-power state. 2265 2266 idle=nop: Do not execute any idle instruction in the 2267 idle loop. This is useful on platforms where WFI 2268 misbehaves, leading to system instability or loss of CPU 2269 state. This will make the CPUs eat more power, but may 2270 give slightly better performance in some applications, 2271 since the CPUs will not enter a low-power state. 2272 2273 idxd.sva= [HW] 2274 Format: <bool> 2275 Allow force disabling of Shared Virtual Memory (SVA) 2276 support for the idxd driver. By default it is set to 2277 true (1). 2278 2279 idxd.tc_override= [HW] 2280 Format: <bool> 2281 Allow override of default traffic class configuration 2282 for the device. By default it is set to false (0). 2283 2284 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2285 Format: { strict | legacy | 2008 | relaxed | emulated } 2286 Default: strict 2287 2288 Choose which programs will be accepted for execution 2289 based on the IEEE 754 NaN encoding(s) supported by 2290 the FPU and the NaN encoding requested with the value 2291 of an ELF file header flag individually set by each 2292 binary. Hardware implementations are permitted to 2293 support either or both of the legacy and the 2008 NaN 2294 encoding mode. 2295 2296 Available settings are as follows: 2297 strict accept binaries that request a NaN encoding 2298 supported by the FPU 2299 legacy only accept legacy-NaN binaries, if supported 2300 by the FPU 2301 2008 only accept 2008-NaN binaries, if supported 2302 by the FPU 2303 relaxed accept any binaries regardless of whether 2304 supported by the FPU 2305 emulated accept any binaries but enable FPU emulator 2306 if binary mode is unsupported by the FPU. 2307 2308 The FPU emulator is always able to support both NaN 2309 encodings, so if no FPU hardware is present or it has 2310 been disabled with 'nofpu', then the settings of 2311 'legacy' and '2008' strap the emulator accordingly, 2312 'relaxed' straps the emulator for both legacy-NaN and 2313 2008-NaN, whereas 'strict' enables legacy-NaN only on 2314 legacy processors and both NaN encodings on MIPS32 or 2315 MIPS64 CPUs. 2316 2317 The setting for ABS.fmt/NEG.fmt instruction execution 2318 mode generally follows that for the NaN encoding, 2319 except where unsupported by hardware. 2320 2321 ignore_loglevel [KNL,EARLY] 2322 Ignore loglevel setting - this will print /all/ 2323 kernel messages to the console. Useful for debugging. 2324 We also add it as printk module parameter, so users 2325 could change it dynamically, usually by 2326 /sys/module/printk/parameters/ignore_loglevel. 2327 2328 ignore_rlimit_data 2329 Ignore RLIMIT_DATA setting for data mappings, 2330 print warning at first misuse. Can be changed via 2331 /sys/module/kernel/parameters/ignore_rlimit_data. 2332 2333 ihash_entries= [KNL] 2334 Set number of hash buckets for inode cache. 2335 2336 ima_appraise= [IMA] appraise integrity measurements 2337 Format: { "off" | "enforce" | "fix" | "log" } 2338 default: "enforce" 2339 2340 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2341 The builtin appraise policy appraises all files 2342 owned by uid=0. 2343 2344 ima_canonical_fmt [IMA] 2345 Use the canonical format for the binary runtime 2346 measurements, instead of host native format. 2347 2348 ima_flush_htable [IMA] 2349 Flush the IMA hash table when deleting all the 2350 staged measurement records, to achieve maximum 2351 memory saving at the cost of having duplicate 2352 records across the staged measurement lists. 2353 2354 ima_hash= [IMA] 2355 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2356 | sha512 | ... } 2357 default: "sha1" 2358 2359 The list of supported hash algorithms is defined 2360 in crypto/hash_info.h. 2361 2362 ima_policy= [IMA] 2363 The builtin policies to load during IMA setup. 2364 Format: "tcb | appraise_tcb | secure_boot | 2365 fail_securely | critical_data" 2366 2367 The "tcb" policy measures all programs exec'd, files 2368 mmap'd for exec, and all files opened with the read 2369 mode bit set by either the effective uid (euid=0) or 2370 uid=0. 2371 2372 The "appraise_tcb" policy appraises the integrity of 2373 all files owned by root. 2374 2375 The "secure_boot" policy appraises the integrity 2376 of files (eg. kexec kernel image, kernel modules, 2377 firmware, policy, etc) based on file signatures. 2378 2379 The "fail_securely" policy forces file signature 2380 verification failure also on privileged mounted 2381 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2382 flag. 2383 2384 The "critical_data" policy measures kernel integrity 2385 critical data. 2386 2387 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2388 Load a policy which meets the needs of the Trusted 2389 Computing Base. This means IMA will measure all 2390 programs exec'd, files mmap'd for exec, and all files 2391 opened for read by uid=0. 2392 2393 ima_template= [IMA] 2394 Select one of defined IMA measurements template formats. 2395 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2396 "ima-sigv2" } 2397 Default: "ima-ng" 2398 2399 ima_template_fmt= 2400 [IMA] Define a custom template format. 2401 Format: { "field1|...|fieldN" } 2402 2403 ima= [IMA] Enable or disable IMA 2404 Format: { "off" | "on" } 2405 Default: "on" 2406 Note that disabling IMA is limited to kdump kernel. 2407 2408 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2409 Target Selection(ITS) bug in Intel CPUs. Updated 2410 microcode is also required for a fix in IBPB. 2411 2412 on: Enable mitigation (default). 2413 off: Disable mitigation. 2414 force: Force the ITS bug and deploy default 2415 mitigation. 2416 vmexit: Only deploy mitigation if CPU is affected by 2417 guest/host isolation part of ITS. 2418 stuff: Deploy RSB-fill mitigation when retpoline is 2419 also deployed. Otherwise, deploy the default 2420 mitigation. 2421 2422 For details see: 2423 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2424 2425 init= [KNL] 2426 Format: <full_path> 2427 Run specified binary instead of /sbin/init as init 2428 process. 2429 2430 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2431 for working out where the kernel is dying during 2432 startup. 2433 2434 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2435 initcall functions. Useful for debugging built-in 2436 modules and initcalls. 2437 2438 initramfs_async= [KNL] 2439 Format: <bool> 2440 Default: 1 2441 This parameter controls whether the initramfs 2442 image is unpacked asynchronously, concurrently 2443 with devices being probed and 2444 initialized. This should normally just work, 2445 but as a debugging aid, one can get the 2446 historical behaviour of the initramfs 2447 unpacking being completed before device_ and 2448 late_ initcalls. 2449 2450 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2451 2452 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2453 load the initrd. If an initrd is compiled in or 2454 specified in the bootparams, it takes priority over this 2455 setting. 2456 Format: ss[KMG],nn[KMG] 2457 Default is 0, 0 2458 2459 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2460 zeroes. 2461 Format: 0 | 1 2462 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2463 2464 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2465 Format: 0 | 1 2466 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2467 2468 init_pkru= [X86] Specify the default memory protection keys rights 2469 register contents for all processes. 0x55555554 by 2470 default (disallow access to all but pkey 0). Can 2471 override in debugfs after boot. 2472 2473 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2474 Format: <irq> 2475 2476 int_pln_enable [X86] Enable power limit notification interrupt 2477 2478 integrity_audit=[IMA] 2479 Format: { "0" | "1" } 2480 0 -- basic integrity auditing messages. (Default) 2481 1 -- additional integrity auditing messages. 2482 2483 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2484 on 2485 Enable intel iommu driver. 2486 off 2487 Disable intel iommu driver. 2488 igfx_off [Default Off] 2489 By default, gfx is mapped as normal device. If a gfx 2490 device has a dedicated DMAR unit, the DMAR unit is 2491 bypassed by not enabling DMAR with this option. In 2492 this case, gfx device will use physical address for 2493 DMA. 2494 strict [Default Off] 2495 Deprecated, equivalent to iommu.strict=1. 2496 sp_off [Default Off] 2497 By default, super page will be supported if Intel IOMMU 2498 has the capability. With this option, super page will 2499 not be supported. 2500 sm_on 2501 Enable the Intel IOMMU scalable mode if the hardware 2502 advertises that it has support for the scalable mode 2503 translation. 2504 sm_off 2505 Disallow use of the Intel IOMMU scalable mode. 2506 tboot_noforce [Default Off] 2507 Do not force the Intel IOMMU enabled under tboot. 2508 By default, tboot will force Intel IOMMU on, which 2509 could harm performance of some high-throughput 2510 devices like 40GBit network cards, even if identity 2511 mapping is enabled. 2512 Note that using this option lowers the security 2513 provided by tboot because it makes the system 2514 vulnerable to DMA attacks. 2515 2516 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2517 0 disables intel_idle and fall back on acpi_idle. 2518 1 to 9 specify maximum depth of C-state. 2519 2520 intel_pstate= [X86,EARLY] 2521 disable 2522 Do not enable intel_pstate as the default 2523 scaling driver for the supported processors 2524 active 2525 Use intel_pstate driver to bypass the scaling 2526 governors layer of cpufreq and provides it own 2527 algorithms for p-state selection. There are two 2528 P-state selection algorithms provided by 2529 intel_pstate in the active mode: powersave and 2530 performance. The way they both operate depends 2531 on whether or not the hardware managed P-states 2532 (HWP) feature has been enabled in the processor 2533 and possibly on the processor model. 2534 passive 2535 Use intel_pstate as a scaling driver, but configure it 2536 to work with generic cpufreq governors (instead of 2537 enabling its internal governor). This mode cannot be 2538 used along with the hardware-managed P-states (HWP) 2539 feature. 2540 force 2541 Enable intel_pstate on systems that prohibit it by default 2542 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2543 instead of acpi-cpufreq may disable platform features, such 2544 as thermal controls and power capping, that rely on ACPI 2545 P-States information being indicated to OSPM and therefore 2546 should be used with caution. This option does not work with 2547 processors that aren't supported by the intel_pstate driver 2548 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2549 no_hwp 2550 Do not enable hardware P state control (HWP) 2551 if available. 2552 hwp_only 2553 Only load intel_pstate on systems which support 2554 hardware P state control (HWP) if available. 2555 support_acpi_ppc 2556 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2557 Description Table, specifies preferred power management 2558 profile as "Enterprise Server" or "Performance Server", 2559 then this feature is turned on by default. 2560 per_cpu_perf_limits 2561 Allow per-logical-CPU P-State performance control limits using 2562 cpufreq sysfs interface 2563 no_cas 2564 Do not enable capacity-aware scheduling (CAS) on 2565 hybrid systems 2566 2567 intremap= [X86-64,Intel-IOMMU,EARLY] 2568 on enable Interrupt Remapping (default) 2569 off disable Interrupt Remapping 2570 nosid disable Source ID checking 2571 no_x2apic_optout 2572 BIOS x2APIC opt-out request will be ignored 2573 nopost disable Interrupt Posting 2574 posted_msi 2575 enable MSIs delivered as posted interrupts 2576 2577 iomem= Disable strict checking of access to MMIO memory 2578 strict regions from userspace. 2579 relaxed 2580 2581 iommu= [X86,EARLY] 2582 2583 off 2584 Don't initialize and use any kind of IOMMU. 2585 2586 force 2587 Force the use of the hardware IOMMU even when 2588 it is not actually needed (e.g. because < 3 GB 2589 memory). 2590 2591 noforce 2592 Don't force hardware IOMMU usage when it is not 2593 needed. (default). 2594 2595 merge 2596 Do scatter-gather (SG) merging. Implies "force" 2597 (experimental). 2598 2599 nomerge 2600 Don't do scatter-gather (SG) merging. 2601 2602 biomerge 2603 Do scatter-gather (SG) merging. Implies "force" 2604 (experimental). [same as "merge"] 2605 2606 panic 2607 Always panic when IOMMU overflows. 2608 2609 nopanic 2610 Don't panic on IOMMU overflows. 2611 2612 pt 2613 Use passththrough mode by default 2614 (Equivalent to iommu.passthrough=1) 2615 2616 nopt 2617 Use translated mode for DMA by default 2618 (Equivalent to iommu.passthrough=0) 2619 2620 soft 2621 Use software bounce buffering (SWIOTLB) (default for 2622 Intel machines). This can be used to prevent the usage 2623 of an available hardware IOMMU. 2624 2625 usedac 2626 Use the DAC on VIA PCI bridge 2627 (default: disable the VIA PCI bridge DAC) 2628 2629 AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU) 2630 2631 <size> 2632 Set the size of the remapping area in bytes. 2633 2634 allowed 2635 Overwrite iommu off workarounds for specific chipsets 2636 2637 force 2638 Overwrite iommu off workarounds for specific chipsets 2639 2640 fullflush 2641 Flush IOMMU on each allocation (default). 2642 2643 nofullflush 2644 Don't use IOMMU fullflush. 2645 2646 memaper[=<order>] 2647 Allocate an own aperture over RAM with size 2648 32MB<<order. (default: order=1, i.e. 64MB) 2649 2650 noaperture 2651 Ask the IOMMU not to touch the aperture for AGP. 2652 2653 noagp 2654 Don't initialize the AGP driver and use full aperture. 2655 2656 iommu= [PPC/POWERNV] 2657 2658 nobypass 2659 Disable IOMMU bypass, using IOMMU for PCI devices. 2660 2661 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2662 Format: { "0" | "1" } 2663 0 - Try to allocate a 32-bit DMA address first, before 2664 falling back to the full range if needed. 2665 1 - Allocate directly from the full usable range, 2666 forcing Dual Address Cycle for PCI cards supporting 2667 greater than 32-bit addressing. 2668 2669 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2670 Format: { "0" | "1" } 2671 0 - Lazy mode. 2672 Request that DMA unmap operations use deferred 2673 invalidation of hardware TLBs, for increased 2674 throughput at the cost of reduced device isolation. 2675 Will fall back to strict mode if not supported by 2676 the relevant IOMMU driver. 2677 1 - Strict mode. 2678 DMA unmap operations invalidate IOMMU hardware TLBs 2679 synchronously. 2680 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2681 Note: on x86, strict mode specified via one of the 2682 legacy driver-specific options takes precedence. 2683 2684 iommu.passthrough= 2685 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2686 Format: { "0" | "1" } 2687 0 - Use IOMMU translation for DMA. 2688 1 - Bypass the IOMMU for DMA. 2689 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2690 2691 iommu.debug_pagealloc= 2692 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2693 parameter enables the feature at boot time. By default, it 2694 is disabled and the system behaves the same way as a kernel 2695 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2696 Format: { "0" | "1" } 2697 0 - Sanitizer disabled. 2698 1 - Sanitizer enabled, expect runtime overhead. 2699 2700 io7= [HW] IO7 for Marvel-based Alpha systems 2701 See comment before marvel_specify_io7 in 2702 arch/alpha/kernel/core_marvel.c. 2703 2704 io_delay= [X86,EARLY] I/O delay method 2705 0x80 2706 Standard port 0x80 based delay 2707 0xed 2708 Alternate port 0xed based delay (needed on some systems) 2709 udelay 2710 Simple two microseconds delay 2711 none 2712 No delay 2713 2714 ip= [IP_PNP] 2715 See Documentation/admin-guide/nfs/nfsroot.rst. 2716 2717 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2718 IPC identifiers from 32,768 to 16,777,216. 2719 2720 ipe.enforce= [IPE] 2721 Format: <bool> 2722 Determine whether IPE starts in permissive (0) or 2723 enforce (1) mode. The default is enforce. 2724 2725 ipe.success_audit= 2726 [IPE] 2727 Format: <bool> 2728 Start IPE with success auditing enabled, emitting 2729 an audit event when a binary is allowed. The default 2730 is 0. 2731 2732 irqaffinity= [SMP] Set the default irq affinity mask 2733 The argument is a cpu list, as described above. 2734 2735 irqchip.gicv2_force_probe= 2736 [ARM,ARM64,EARLY] 2737 Format: <bool> 2738 Force the kernel to look for the second 4kB page 2739 of a GICv2 controller even if the memory range 2740 exposed by the device tree is too small. 2741 2742 irqchip.gicv3_nolpi= 2743 [ARM,ARM64,EARLY] 2744 Force the kernel to ignore the availability of 2745 LPIs (and by consequence ITSs). Intended for system 2746 that use the kernel as a bootloader, and thus want 2747 to let secondary kernels in charge of setting up 2748 LPIs. 2749 2750 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2751 Enables support for pseudo-NMIs in the kernel. This 2752 requires the kernel to be built with 2753 CONFIG_ARM64_PSEUDO_NMI. 2754 2755 irqchip.riscv_imsic_noipi 2756 [RISC-V,EARLY] 2757 Force the kernel to not use IMSIC software injected MSIs 2758 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2759 and thus want to reduce MMIO traps when triggering IPIs 2760 to multiple harts. 2761 2762 irqfixup [HW] 2763 When an interrupt is not handled search all handlers 2764 for it. Intended to get systems with badly broken 2765 firmware running. 2766 2767 irqhandler.duration_warn_us= [KNL] 2768 Warn if an IRQ handler exceeds the specified duration 2769 threshold in microseconds. Useful for identifying 2770 long-running IRQs in the system. 2771 2772 irqpoll [HW] 2773 When an interrupt is not handled search all handlers 2774 for it. Also check all handlers each timer 2775 interrupt. Intended to get systems with badly broken 2776 firmware running. 2777 2778 isapnp= [ISAPNP] 2779 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2780 2781 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2782 Format: [flag-list,]<cpu-list> 2783 2784 Specify one or more CPUs to isolate from disturbances 2785 specified in the flag list (default: domain): 2786 2787 nohz 2788 Disable the tick when a single task runs as well as 2789 disabling other kernel noises like having RCU callbacks 2790 offloaded. This is equivalent to the nohz_full parameter. 2791 2792 A residual 1Hz tick is offloaded to workqueues, which you 2793 need to affine to housekeeping through the global 2794 workqueue's affinity configured via the 2795 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2796 by using the 'domain' flag described below. 2797 2798 NOTE: by default the global workqueue runs on all CPUs, 2799 so to protect individual CPUs the 'cpumask' file has to 2800 be configured manually after bootup. 2801 2802 domain 2803 Isolate from the general SMP balancing and scheduling 2804 algorithms. Note that performing domain isolation this way 2805 is irreversible: it's not possible to bring back a CPU to 2806 the domains once isolated through this boot time 2807 configuration. Use cpusets for a dynamic configuration 2808 which can be altered at runtime. For details see 2809 Documentation/admin-guide/cpu-isolation.rst. 2810 2811 You can move a process onto or off an "isolated" CPU via 2812 the CPU affinity syscalls or cpuset. 2813 <cpu number> begins at 0 and the maximum value is 2814 "number of CPUs in system - 1". 2815 2816 managed_irq 2817 2818 Isolate from being targeted by managed interrupts 2819 which have an interrupt mask containing isolated 2820 CPUs. The affinity of managed interrupts is 2821 handled by the kernel and cannot be changed via 2822 the /proc/irq/* interfaces. 2823 2824 This isolation is best effort and only effective 2825 if the automatically assigned interrupt mask of a 2826 device queue contains isolated and housekeeping 2827 CPUs. If housekeeping CPUs are online then such 2828 interrupts are directed to the housekeeping CPU 2829 so that IO submitted on the housekeeping CPU 2830 cannot disturb the isolated CPU. 2831 2832 If a queue's affinity mask contains only isolated 2833 CPUs then this parameter has no effect on the 2834 interrupt routing decision, though interrupts are 2835 only delivered when tasks running on those 2836 isolated CPUs submit IO. IO submitted on 2837 housekeeping CPUs has no influence on those 2838 queues. 2839 2840 The format of <cpu-list> is described above. 2841 2842 iucv= [HW,NET] 2843 2844 ivrs_ioapic [HW,X86-64] 2845 Provide an override to the IOAPIC-ID<->DEVICE-ID 2846 mapping provided in the IVRS ACPI table. 2847 By default, PCI segment is 0, and can be omitted. 2848 2849 For example, to map IOAPIC-ID decimal 10 to 2850 PCI segment 0x1 and PCI device 00:14.0, 2851 write the parameter as: 2852 ivrs_ioapic=10@0001:00:14.0 2853 2854 Deprecated formats: 2855 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2856 write the parameter as: 2857 ivrs_ioapic[10]=00:14.0 2858 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2859 PCI device 00:14.0 write the parameter as: 2860 ivrs_ioapic[10]=0001:00:14.0 2861 2862 ivrs_hpet [HW,X86-64] 2863 Provide an override to the HPET-ID<->DEVICE-ID 2864 mapping provided in the IVRS ACPI table. 2865 By default, PCI segment is 0, and can be omitted. 2866 2867 For example, to map HPET-ID decimal 10 to 2868 PCI segment 0x1 and PCI device 00:14.0, 2869 write the parameter as: 2870 ivrs_hpet=10@0001:00:14.0 2871 2872 Deprecated formats: 2873 * To map HPET-ID decimal 0 to PCI device 00:14.0 2874 write the parameter as: 2875 ivrs_hpet[0]=00:14.0 2876 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2877 PCI device 00:14.0 write the parameter as: 2878 ivrs_ioapic[10]=0001:00:14.0 2879 2880 ivrs_acpihid [HW,X86-64] 2881 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2882 mapping provided in the IVRS ACPI table. 2883 By default, PCI segment is 0, and can be omitted. 2884 2885 For example, to map UART-HID:UID AMD0020:0 to 2886 PCI segment 0x1 and PCI device ID 00:14.5, 2887 write the parameter as: 2888 ivrs_acpihid=AMD0020:0@0001:00:14.5 2889 2890 Deprecated formats: 2891 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2892 PCI device ID 00:14.5, write the parameter as: 2893 ivrs_acpihid[00:14.5]=AMD0020:0 2894 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2895 PCI device ID 00:14.5, write the parameter as: 2896 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2897 2898 js= [HW,JOY] Analog joystick 2899 See Documentation/input/joydev/joystick.rst. 2900 2901 kasan_multi_shot 2902 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2903 report on every invalid memory access. Without this 2904 parameter KASAN will print report only for the first 2905 invalid access. 2906 2907 keep_bootcon [KNL,EARLY] 2908 Do not unregister boot console at start. This is only 2909 useful for debugging when something happens in the window 2910 between unregistering the boot console and initializing 2911 the real console. 2912 2913 keepinitrd [HW,ARM] See retain_initrd. 2914 2915 kernelcore= [KNL,X86,PPC,EARLY] 2916 Format: nn[KMGTPE] | nn% | "mirror" 2917 This parameter specifies the amount of memory usable by 2918 the kernel for non-movable allocations. The requested 2919 amount is spread evenly throughout all nodes in the 2920 system as ZONE_NORMAL. The remaining memory is used for 2921 movable memory in its own zone, ZONE_MOVABLE. In the 2922 event, a node is too small to have both ZONE_NORMAL and 2923 ZONE_MOVABLE, kernelcore memory will take priority and 2924 other nodes will have a larger ZONE_MOVABLE. 2925 2926 ZONE_MOVABLE is used for the allocation of pages that 2927 may be reclaimed or moved by the page migration 2928 subsystem. Note that allocations like PTEs-from-HighMem 2929 still use the HighMem zone if it exists, and the Normal 2930 zone if it does not. 2931 2932 It is possible to specify the exact amount of memory in 2933 the form of "nn[KMGTPE]", a percentage of total system 2934 memory in the form of "nn%", or "mirror". If "mirror" 2935 option is specified, mirrored (reliable) memory is used 2936 for non-movable allocations and remaining memory is used 2937 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2938 are exclusive, so you cannot specify multiple forms. 2939 2940 kfence.burst= [MM,KFENCE] The number of additional successive 2941 allocations to be attempted through KFENCE for each 2942 sample interval. 2943 Format: <unsigned integer> 2944 Default: 0 2945 2946 kfence.check_on_panic= 2947 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2948 canaries on panic. 2949 Format: <bool> 2950 Default: false 2951 2952 kfence.deferrable= 2953 [MM,KFENCE] Whether to use a deferrable timer to trigger 2954 allocations. This avoids forcing CPU wake-ups if the 2955 system is idle, at the risk of a less predictable 2956 sample interval. 2957 Format: <bool> 2958 Default: CONFIG_KFENCE_DEFERRABLE 2959 2960 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2961 error is detected. 2962 report - print the error report and continue (default). 2963 oops - print the error report and oops. 2964 panic - print the error report and panic. 2965 2966 kfence.sample_interval= 2967 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2968 Format: <unsigned integer> 2969 0 - Disable KFENCE. 2970 >0 - Enabled KFENCE with given sample interval. 2971 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2972 2973 kfence.skip_covered_thresh= 2974 [MM,KFENCE] If pool utilization reaches this threshold 2975 (pool usage%), KFENCE limits currently covered 2976 allocations of the same source from further filling 2977 up the pool. 2978 Format: <unsigned integer> 2979 Default: 75 2980 2981 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2982 Format: <Controller#>[,poll interval] 2983 The controller # is the number of the ehci usb debug 2984 port as it is probed via PCI. The poll interval is 2985 optional and is the number seconds in between 2986 each poll cycle to the debug port in case you need 2987 the functionality for interrupting the kernel with 2988 gdb or control-c on the dbgp connection. When 2989 not using this parameter you use sysrq-g to break into 2990 the kernel debugger. 2991 2992 kgdboc= [KGDB,HW] kgdb over consoles. 2993 Requires a tty driver that supports console polling, 2994 or a supported polling keyboard driver (non-usb). 2995 Serial only format: <serial_device>[,baud] 2996 keyboard only format: kbd 2997 keyboard and serial format: kbd,<serial_device>[,baud] 2998 Optional Kernel mode setting: 2999 kms, kbd format: kms,kbd 3000 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 3001 3002 kgdboc_earlycon= [KGDB,HW,EARLY] 3003 If the boot console provides the ability to read 3004 characters and can work in polling mode, you can use 3005 this parameter to tell kgdb to use it as a backend 3006 until the normal console is registered. Intended to 3007 be used together with the kgdboc parameter which 3008 specifies the normal console to transition to. 3009 3010 The name of the early console should be specified 3011 as the value of this parameter. Note that the name of 3012 the early console might be different than the tty 3013 name passed to kgdboc. It's OK to leave the value 3014 blank and the first boot console that implements 3015 read() will be picked. 3016 3017 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3018 kernel debugger at the earliest opportunity. 3019 3020 kho= [KEXEC,EARLY] 3021 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3022 Enables or disables Kexec HandOver. 3023 "0" | "off" | "n" - kexec handover is disabled 3024 "1" | "on" | "y" - kexec handover is enabled 3025 3026 kho_scratch= [KEXEC,EARLY] 3027 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3028 Defines the size of the KHO scratch region. The KHO 3029 scratch regions are physically contiguous memory 3030 ranges that can only be used for non-kernel 3031 allocations. That way, even when memory is heavily 3032 fragmented with handed over memory, the kexeced 3033 kernel will always have enough contiguous ranges to 3034 bootstrap itself. 3035 3036 It is possible to specify the exact amount of 3037 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3038 where the first parameter defines the size of a low 3039 memory scratch area, the second parameter defines 3040 the size of a global scratch area and the third 3041 parameter defines the size of additional per-node 3042 scratch areas. The form "nn%" defines scale factor 3043 (in percents) of memory that was used during boot. 3044 3045 kmac= [MIPS] Korina ethernet MAC address. 3046 Configure the RouterBoard 532 series on-chip 3047 Ethernet adapter MAC address. 3048 3049 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3050 Valid arguments: on, off 3051 Default: on 3052 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3053 the default is off. 3054 3055 kprobe_event=[probe-list] 3056 [FTRACE] Add kprobe events and enable at boot time. 3057 The probe-list is a semicolon delimited list of probe 3058 definitions. Each definition is same as kprobe_events 3059 interface, but the parameters are comma delimited. 3060 For example, to add a kprobe event on vfs_read with 3061 arg1 and arg2, add to the command line; 3062 3063 kprobe_event=p,vfs_read,$arg1,$arg2 3064 3065 See also Documentation/trace/kprobetrace.rst "Kernel 3066 Boot Parameter" section. 3067 3068 kpti= [ARM64,EARLY] Control page table isolation of 3069 user and kernel address spaces. 3070 Default: enabled on cores which need mitigation. 3071 0: force disabled 3072 1: force enabled 3073 3074 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3075 CONFIG_KUNIT to be set to be fully enabled. The 3076 default value can be overridden via 3077 KUNIT_DEFAULT_ENABLED. 3078 Default is 1 (enabled) 3079 3080 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3081 Default is 0 (don't ignore, but inject #GP) 3082 3083 kvm.eager_page_split= 3084 [KVM,X86,RISCV] Controls whether or not KVM will try to 3085 proactively split all huge pages during dirty logging. 3086 Eager page splitting reduces interruptions to vCPU 3087 execution by eliminating the write-protection faults 3088 and MMU lock contention that would otherwise be 3089 required to split huge pages lazily. 3090 3091 VM workloads that rarely perform writes or that write 3092 only to a small region of VM memory may benefit from 3093 disabling eager page splitting to allow huge pages to 3094 still be used for reads. 3095 3096 The behavior of eager page splitting depends on whether 3097 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3098 disabled, all huge pages in a memslot will be eagerly 3099 split when dirty logging is enabled on that memslot. If 3100 enabled, eager page splitting will be performed during 3101 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3102 cleared. 3103 3104 On x86, eager page splitting is only supported when 3105 kvm.tdp_mmu=Y. 3106 3107 On RISCV, eager page splitting is supported by default. 3108 3109 Default is Y (on). 3110 3111 kvm.enable_pmu=[KVM,X86] 3112 If enabled, KVM will virtualize PMU functionality based 3113 on the virtual CPU model defined by userspace. This 3114 can be overridden on a per-VM basis via 3115 KVM_CAP_PMU_CAPABILITY. 3116 3117 If disabled, KVM will not virtualize PMU functionality, 3118 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3119 a virtual CPU model that contains PMU assets. 3120 3121 Note, KVM's vPMU support implicitly requires running 3122 with an in-kernel local APIC, e.g. to deliver PMIs to 3123 the guest. Running without an in-kernel local APIC is 3124 not supported, though KVM will allow such a combination 3125 (with severely degraded functionality). 3126 3127 See also enable_mediated_pmu. 3128 3129 Default is Y (on). 3130 3131 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3132 If enabled, KVM will enable virtualization in hardware 3133 when KVM is loaded, and disable virtualization when KVM 3134 is unloaded (if KVM is built as a module). 3135 3136 If disabled, KVM will dynamically enable and disable 3137 virtualization on-demand when creating and destroying 3138 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3139 number of VMs. 3140 3141 Enabling virtualization at module load avoids potential 3142 latency for creation of the 0=>1 VM, as KVM serializes 3143 virtualization enabling across all online CPUs. The 3144 "cost" of enabling virtualization when KVM is loaded, 3145 is that doing so may interfere with using out-of-tree 3146 hypervisors that want to "own" virtualization hardware. 3147 3148 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3149 Default is false (don't support). 3150 3151 kvm.nx_huge_pages= 3152 [KVM] Controls the software workaround for the 3153 X86_BUG_ITLB_MULTIHIT bug. 3154 force : Always deploy workaround. 3155 off : Never deploy workaround. 3156 auto : Deploy workaround based on the presence of 3157 X86_BUG_ITLB_MULTIHIT. 3158 3159 Default is 'auto'. 3160 3161 If the software workaround is enabled for the host, 3162 guests do need not to enable it for nested guests. 3163 3164 kvm.nx_huge_pages_recovery_ratio= 3165 [KVM] Controls how many 4KiB pages are periodically zapped 3166 back to huge pages. 0 disables the recovery, otherwise if 3167 the value is N KVM will zap 1/Nth of the 4KiB pages every 3168 period (see below). The default is 60. 3169 3170 kvm.nx_huge_pages_recovery_period_ms= 3171 [KVM] Controls the time period at which KVM zaps 4KiB pages 3172 back to huge pages. If the value is a non-zero N, KVM will 3173 zap a portion (see ratio above) of the pages every N msecs. 3174 If the value is 0 (the default), KVM will pick a period based 3175 on the ratio, such that a page is zapped after 1 hour on average. 3176 3177 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3178 If enabled, KVM will provide a mediated virtual PMU, 3179 instead of the default perf-based virtual PMU (if 3180 kvm.enable_pmu is true and PMU is enumerated via the 3181 virtual CPU model). 3182 3183 With a perf-based vPMU, KVM operates as a user of perf, 3184 i.e. emulates guest PMU counters using perf events. 3185 KVM-created perf events are managed by perf as regular 3186 (guest-only) events, e.g. are scheduled in/out, contend 3187 for hardware resources, etc. Using a perf-based vPMU 3188 allows guest and host usage of the PMU to co-exist, but 3189 incurs non-trivial overhead and can result in silently 3190 dropped guest events (due to resource contention). 3191 3192 With a mediated vPMU, hardware PMU state is context 3193 switched around the world switch to/from the guest. 3194 KVM mediates which events the guest can utilize, but 3195 gives the guest direct access to all other PMU assets 3196 when possible (KVM may intercept some accesses if the 3197 virtual CPU model provides a subset of hardware PMU 3198 functionality). Using a mediated vPMU significantly 3199 reduces PMU virtualization overhead and eliminates lost 3200 guest events, but is mutually exclusive with using perf 3201 to profile KVM guests and adds latency to most VM-Exits 3202 (to context switch PMU state). 3203 3204 Default is N (off). 3205 3206 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3207 KVM/SVM. Default is 1 (enabled). 3208 3209 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3210 a.k.a. Two-Dimensional Page Tables. Default is 1 3211 (enabled). Disable by KVM if hardware lacks support 3212 for NPT. 3213 3214 kvm-amd.ciphertext_hiding_asids= 3215 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3216 to SNP private memory from reading ciphertext. Instead, 3217 reads will see constant default values (0xff). 3218 3219 If ciphertext hiding is enabled, the joint SEV-ES and 3220 SEV-SNP ASID space is partitioned into separate SEV-ES 3221 and SEV-SNP ASID ranges, with the SEV-SNP range being 3222 [1..max_snp_asid] and the SEV-ES range being 3223 (max_snp_asid..min_sev_asid), where min_sev_asid is 3224 enumerated by CPUID.0x.8000_001F[EDX]. 3225 3226 A non-zero value enables SEV-SNP ciphertext hiding and 3227 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3228 KVM caps the number of SEV-SNP ASIDs at the maximum 3229 possible value, e.g. specifying -1u will assign all 3230 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3231 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3232 max_snp_asid == min_sev_asid-1, will effectively make 3233 SEV-ES unusable. 3234 3235 kvm-arm.mode= 3236 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3237 operation. 3238 3239 none: Forcefully disable KVM. 3240 3241 nvhe: Standard nVHE-based mode, without support for 3242 protected guests. 3243 3244 protected: Mode with support for guests whose state is 3245 kept private from the host, using VHE or 3246 nVHE depending on HW support. 3247 3248 nested: VHE-based mode with support for nested 3249 virtualization. Requires at least ARMv8.4 3250 hardware (with FEAT_NV2). 3251 3252 Defaults to VHE/nVHE based on hardware support. Setting 3253 mode to "protected" will disable kexec and hibernation 3254 for the host. To force nVHE on VHE hardware, add 3255 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3256 command-line. 3257 "nested" and "protected" are experimental and should be 3258 used with extreme caution. 3259 3260 kvm-arm.vgic_v3_group0_trap= 3261 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3262 system registers 3263 3264 kvm-arm.vgic_v3_group1_trap= 3265 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3266 system registers 3267 3268 kvm-arm.vgic_v3_common_trap= 3269 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3270 system registers 3271 3272 kvm-arm.vgic_v4_enable= 3273 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3274 injection of LPIs. 3275 3276 kvm-arm.wfe_trap_policy= 3277 [KVM,ARM] Control when to set WFE instruction trap for 3278 KVM VMs. Traps are allowed but not guaranteed by the 3279 CPU architecture. 3280 3281 trap: set WFE instruction trap 3282 3283 notrap: clear WFE instruction trap 3284 3285 kvm-arm.wfi_trap_policy= 3286 [KVM,ARM] Control when to set WFI instruction trap for 3287 KVM VMs. Traps are allowed but not guaranteed by the 3288 CPU architecture. 3289 3290 trap: set WFI instruction trap 3291 3292 notrap: clear WFI instruction trap 3293 3294 kvm_cma_resv_ratio=n [PPC,EARLY] 3295 Reserves given percentage from system memory area for 3296 contiguous memory allocation for KVM hash pagetable 3297 allocation. 3298 By default it reserves 5% of total system memory. 3299 Format: <integer> 3300 Default: 5 3301 3302 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3303 a.k.a. Two-Dimensional Page Tables. Default is 1 3304 (enabled). Disable by KVM if hardware lacks support 3305 for EPT. 3306 3307 kvm-intel.emulate_invalid_guest_state= 3308 [KVM,Intel] Control whether to emulate invalid guest 3309 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3310 as guest state is never invalid for unrestricted 3311 guests. This param doesn't apply to nested guests (L2), 3312 as KVM never emulates invalid L2 guest state. 3313 Default is 1 (enabled). 3314 3315 kvm-intel.flexpriority= 3316 [KVM,Intel] Control KVM's use of FlexPriority feature 3317 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3318 hardware lacks support for it. 3319 3320 kvm-intel.nested= 3321 [KVM,Intel] Control nested virtualization feature in 3322 KVM/VMX. Default is 1 (enabled). 3323 3324 kvm-intel.unrestricted_guest= 3325 [KVM,Intel] Control KVM's use of unrestricted guest 3326 feature (virtualized real and unpaged mode). Default 3327 is 1 (enabled). Disable by KVM if EPT is disabled or 3328 hardware lacks support for it. 3329 3330 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3331 CVE-2018-3620. 3332 3333 Valid arguments: never, cond, always 3334 3335 always: L1D cache flush on every VMENTER. 3336 cond: Flush L1D on VMENTER only when the code between 3337 VMEXIT and VMENTER can leak host memory. 3338 never: Disables the mitigation 3339 3340 Default is cond (do L1 cache flush in specific instances) 3341 3342 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3343 Identification feature (tagged TLBs). Default is 1 3344 (enabled). Disable by KVM if hardware lacks support 3345 for it. 3346 3347 l1d_flush= [X86,INTEL,EARLY] 3348 Control mitigation for L1D based snooping vulnerability. 3349 3350 Certain CPUs are vulnerable to an exploit against CPU 3351 internal buffers which can forward information to a 3352 disclosure gadget under certain conditions. 3353 3354 In vulnerable processors, the speculatively 3355 forwarded data can be used in a cache side channel 3356 attack, to access data to which the attacker does 3357 not have direct access. 3358 3359 This parameter controls the mitigation. The 3360 options are: 3361 3362 on - enable the interface for the mitigation 3363 3364 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3365 affected CPUs 3366 3367 The kernel PTE inversion protection is unconditionally 3368 enabled and cannot be disabled. 3369 3370 full 3371 Provides all available mitigations for the 3372 L1TF vulnerability. Disables SMT and 3373 enables all mitigations in the 3374 hypervisors, i.e. unconditional L1D flush. 3375 3376 SMT control and L1D flush control via the 3377 sysfs interface is still possible after 3378 boot. Hypervisors will issue a warning 3379 when the first VM is started in a 3380 potentially insecure configuration, 3381 i.e. SMT enabled or L1D flush disabled. 3382 3383 full,force 3384 Same as 'full', but disables SMT and L1D 3385 flush runtime control. Implies the 3386 'nosmt=force' command line option. 3387 (i.e. sysfs control of SMT is disabled.) 3388 3389 flush 3390 Leaves SMT enabled and enables the default 3391 hypervisor mitigation, i.e. conditional 3392 L1D flush. 3393 3394 SMT control and L1D flush control via the 3395 sysfs interface is still possible after 3396 boot. Hypervisors will issue a warning 3397 when the first VM is started in a 3398 potentially insecure configuration, 3399 i.e. SMT enabled or L1D flush disabled. 3400 3401 flush,nosmt 3402 3403 Disables SMT and enables the default 3404 hypervisor mitigation. 3405 3406 SMT control and L1D flush control via the 3407 sysfs interface is still possible after 3408 boot. Hypervisors will issue a warning 3409 when the first VM is started in a 3410 potentially insecure configuration, 3411 i.e. SMT enabled or L1D flush disabled. 3412 3413 flush,nowarn 3414 Same as 'flush', but hypervisors will not 3415 warn when a VM is started in a potentially 3416 insecure configuration. 3417 3418 off 3419 Disables hypervisor mitigations and doesn't 3420 emit any warnings. 3421 It also drops the swap size and available 3422 RAM limit restriction on both hypervisor and 3423 bare metal. 3424 3425 Default is 'flush'. 3426 3427 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3428 3429 l2cr= [PPC] 3430 3431 l3cr= [PPC] 3432 3433 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3434 disabled it. 3435 3436 lapic= [X86,APIC] Do not use TSC deadline 3437 value for LAPIC timer one-shot implementation. Default 3438 back to the programmable timer unit in the LAPIC. 3439 Format: notscdeadline 3440 3441 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3442 in C2 power state. 3443 3444 libata.dma= [LIBATA] DMA control 3445 libata.dma=0 Disable all PATA and SATA DMA 3446 libata.dma=1 PATA and SATA Disk DMA only 3447 libata.dma=2 ATAPI (CDROM) DMA only 3448 libata.dma=4 Compact Flash DMA only 3449 Combinations also work, so libata.dma=3 enables DMA 3450 for disks and CDROMs, but not CFs. 3451 3452 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3453 libata.ignore_hpa=0 keep BIOS limits (default) 3454 libata.ignore_hpa=1 ignore limits, using full disk 3455 3456 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3457 when set. 3458 Format: <int> 3459 3460 libata.force= [LIBATA] Force configurations. The format is a comma- 3461 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3462 PORT and DEVICE are decimal numbers matching port, link 3463 or device. Basically, it matches the ATA ID string 3464 printed on console by libata. If the whole ID part is 3465 omitted, the last PORT and DEVICE values are used. If 3466 ID hasn't been specified yet, the configuration applies 3467 to all ports, links and devices. 3468 3469 If only DEVICE is omitted, the parameter applies to 3470 the port and all links and devices behind it. DEVICE 3471 number of 0 either selects the first device or the 3472 first fan-out link behind PMP device. It does not 3473 select the host link. DEVICE number of 15 selects the 3474 host link and device attached to it. 3475 3476 The VAL specifies the configuration to force. As long 3477 as there is no ambiguity, shortcut notation is allowed. 3478 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3479 The following configurations can be forced. 3480 3481 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3482 Any ID with matching PORT is used. 3483 3484 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3485 3486 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3487 udma[/][16,25,33,44,66,100,133] notation is also 3488 allowed. 3489 3490 * nohrst, nosrst, norst: suppress hard, soft and both 3491 resets. 3492 3493 * rstonce: only attempt one reset during hot-unplug 3494 link recovery. 3495 3496 * [no]dbdelay: Enable or disable the extra 200ms delay 3497 before debouncing a link PHY and device presence 3498 detection. 3499 3500 * [no]ncq: Turn on or off NCQ. 3501 3502 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3503 3504 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3505 3506 * [no]trim: Enable or disable (unqueued) TRIM. 3507 3508 * trim_zero: Indicate that TRIM command zeroes data. 3509 3510 * max_trim_128m: Set 128M maximum trim size limit. 3511 3512 * [no]dma: Turn on or off DMA transfers. 3513 3514 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3515 3516 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3517 commands that are not a multiple of 16 bytes. 3518 3519 * [no]dmalog: Enable or disable the use of the 3520 READ LOG DMA EXT command to access logs. 3521 3522 * [no]iddevlog: Enable or disable access to the 3523 identify device data log. 3524 3525 * [no]logdir: Enable or disable access to the general 3526 purpose log directory. 3527 3528 * max_sec=<sectors>: Set the transfer size limit, in 3529 number of 512-byte sectors, to the value specified in 3530 <sectors>. The value specified in <sectors> has to be 3531 a non-zero positive integer. 3532 3533 * max_sec_128: Set transfer size limit to 128 sectors. 3534 3535 * max_sec_1024: Set or clear transfer size limit to 3536 1024 sectors. 3537 3538 * max_sec_lba48: Set or clear transfer size limit to 3539 65535 sectors. 3540 3541 * external: Mark port as external (hotplug-capable). 3542 3543 * [no]lpm: Enable or disable link power management. 3544 3545 * [no]setxfer: Indicate if transfer speed mode setting 3546 should be skipped. 3547 3548 * [no]fua: Disable or enable FUA (Force Unit Access) 3549 support for devices supporting this feature. 3550 3551 * dump_id: Dump IDENTIFY data. 3552 3553 * disable: Disable this device. 3554 3555 If there are multiple matching configurations changing 3556 the same attribute, the last one is used. 3557 3558 liveupdate= [KNL,EARLY] 3559 Format: <bool> 3560 Enable Live Update Orchestrator (LUO). 3561 Default: off. 3562 3563 lockd.nlm_grace_period=P [NFS] Assign grace period. 3564 Format: <integer> 3565 3566 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3567 Format: <integer> 3568 3569 lockd.nlm_timeout=T [NFS] Assign timeout value. 3570 Format: <integer> 3571 3572 lockd.nlm_udpport=M [NFS] Assign UDP port. 3573 Format: <integer> 3574 3575 lockdown= [SECURITY,EARLY] 3576 { integrity | confidentiality } 3577 Enable the kernel lockdown feature. If set to 3578 integrity, kernel features that allow userland to 3579 modify the running kernel are disabled. If set to 3580 confidentiality, kernel features that allow userland 3581 to extract confidential information from the kernel 3582 are also disabled. 3583 3584 locktorture.acq_writer_lim= [KNL] 3585 Set the time limit in jiffies for a lock 3586 acquisition. Acquisitions exceeding this limit 3587 will result in a splat once they do complete. 3588 3589 locktorture.bind_readers= [KNL] 3590 Specify the list of CPUs to which the readers are 3591 to be bound. 3592 3593 locktorture.bind_writers= [KNL] 3594 Specify the list of CPUs to which the writers are 3595 to be bound. 3596 3597 locktorture.call_rcu_chains= [KNL] 3598 Specify the number of self-propagating call_rcu() 3599 chains to set up. These are used to ensure that 3600 there is a high probability of an RCU grace period 3601 in progress at any given time. Defaults to 0, 3602 which disables these call_rcu() chains. 3603 3604 locktorture.long_hold= [KNL] 3605 Specify the duration in milliseconds for the 3606 occasional long-duration lock hold time. Defaults 3607 to 100 milliseconds. Select 0 to disable. 3608 3609 locktorture.nested_locks= [KNL] 3610 Specify the maximum lock nesting depth that 3611 locktorture is to exercise, up to a limit of 8 3612 (MAX_NESTED_LOCKS). Specify zero to disable. 3613 Note that this parameter is ineffective on types 3614 of locks that do not support nested acquisition. 3615 3616 locktorture.nreaders_stress= [KNL] 3617 Set the number of locking read-acquisition kthreads. 3618 Defaults to being automatically set based on the 3619 number of online CPUs. 3620 3621 locktorture.nwriters_stress= [KNL] 3622 Set the number of locking write-acquisition kthreads. 3623 3624 locktorture.onoff_holdoff= [KNL] 3625 Set time (s) after boot for CPU-hotplug testing. 3626 3627 locktorture.onoff_interval= [KNL] 3628 Set time (s) between CPU-hotplug operations, or 3629 zero to disable CPU-hotplug testing. 3630 3631 locktorture.rt_boost= [KNL] 3632 Do periodic testing of real-time lock priority 3633 boosting. Select 0 to disable, 1 to boost 3634 only rt_mutex, and 2 to boost unconditionally. 3635 Defaults to 2, which might seem to be an 3636 odd choice, but which should be harmless for 3637 non-real-time spinlocks, due to their disabling 3638 of preemption. Note that non-realtime mutexes 3639 disable boosting. 3640 3641 locktorture.rt_boost_factor= [KNL] 3642 Number that determines how often and for how 3643 long priority boosting is exercised. This is 3644 scaled down by the number of writers, so that the 3645 number of boosts per unit time remains roughly 3646 constant as the number of writers increases. 3647 On the other hand, the duration of each boost 3648 increases with the number of writers. 3649 3650 locktorture.shuffle_interval= [KNL] 3651 Set task-shuffle interval (jiffies). Shuffling 3652 tasks allows some CPUs to go into dyntick-idle 3653 mode during the locktorture test. 3654 3655 locktorture.shutdown_secs= [KNL] 3656 Set time (s) after boot system shutdown. This 3657 is useful for hands-off automated testing. 3658 3659 locktorture.stat_interval= [KNL] 3660 Time (s) between statistics printk()s. 3661 3662 locktorture.stutter= [KNL] 3663 Time (s) to stutter testing, for example, 3664 specifying five seconds causes the test to run for 3665 five seconds, wait for five seconds, and so on. 3666 This tests the locking primitive's ability to 3667 transition abruptly to and from idle. 3668 3669 locktorture.torture_type= [KNL] 3670 Specify the locking implementation to test. 3671 3672 locktorture.verbose= [KNL] 3673 Enable additional printk() statements. 3674 3675 locktorture.writer_fifo= [KNL] 3676 Run the write-side locktorture kthreads at 3677 sched_set_fifo() real-time priority. 3678 3679 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3680 Format: <irq> 3681 3682 loglevel= [KNL,EARLY] 3683 All Kernel Messages with a loglevel smaller than the 3684 console loglevel will be printed to the console. It can 3685 also be changed with klogd or other programs. The 3686 loglevels are defined as follows: 3687 3688 0 (KERN_EMERG) system is unusable 3689 1 (KERN_ALERT) action must be taken immediately 3690 2 (KERN_CRIT) critical conditions 3691 3 (KERN_ERR) error conditions 3692 4 (KERN_WARNING) warning conditions 3693 5 (KERN_NOTICE) normal but significant condition 3694 6 (KERN_INFO) informational 3695 7 (KERN_DEBUG) debug-level messages 3696 3697 log_buf_len=n[KMG] [KNL,EARLY] 3698 Sets the size of the printk ring buffer, in bytes. 3699 n must be a power of two and greater than the 3700 minimal size. The minimal size is defined by 3701 LOG_BUF_SHIFT kernel config parameter. There 3702 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3703 parameter that allows to increase the default size 3704 depending on the number of CPUs. See init/Kconfig 3705 for more details. 3706 3707 logo.nologo [FB] Disables display of the built-in Linux logo. 3708 This may be used to provide more screen space for 3709 kernel log messages and is useful when debugging 3710 kernel boot problems. 3711 3712 lp=0 [LP] Specify parallel ports to use, e.g, 3713 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3714 lp=reset first parallel port). 'lp=0' disables the 3715 lp=auto printer driver. 'lp=reset' (which can be 3716 specified in addition to the ports) causes 3717 attached printers to be reset. Using 3718 lp=port1,port2,... specifies the parallel ports 3719 to associate lp devices with, starting with 3720 lp0. A port specification may be 'none' to skip 3721 that lp device, or a parport name such as 3722 'parport0'. Specifying 'lp=auto' instead of a 3723 port specification list means that device IDs 3724 from each port should be examined, to see if 3725 an IEEE 1284-compliant printer is attached; if 3726 so, the driver will manage that printer. 3727 See also header of drivers/char/lp.c. 3728 3729 lpj=n [KNL] 3730 Sets loops_per_jiffy to given constant, thus avoiding 3731 time-consuming boot-time autodetection (up to 250 ms per 3732 CPU). 0 enables autodetection (default). To determine 3733 the correct value for your kernel, boot with normal 3734 autodetection and see what value is printed. Note that 3735 on SMP systems the preset will be applied to all CPUs, 3736 which is likely to cause problems if your CPUs need 3737 significantly divergent settings. An incorrect value 3738 will cause delays in the kernel to be wrong, leading to 3739 unpredictable I/O errors and other breakage. Although 3740 unlikely, in the extreme case this might damage your 3741 hardware. 3742 3743 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3744 3745 lsm=lsm1,...,lsmN 3746 [SECURITY] Choose order of LSM initialization. This 3747 overrides CONFIG_LSM, and the "security=" parameter. 3748 3749 machtype= [Loongson] Share the same kernel image file between 3750 different yeeloong laptops. 3751 Example: machtype=lemote-yeeloong-2f-7inch 3752 3753 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3754 will bring up during bootup. maxcpus=n : n >= 0 limits 3755 the kernel to bring up 'n' processors. Surely after 3756 bootup you can bring up the other plugged cpu by executing 3757 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3758 only takes effect during system bootup. 3759 While n=0 is a special case, it is equivalent to "nosmp", 3760 which also disables the IO APIC. 3761 3762 max_loop= [LOOP] The number of loop block devices that get 3763 (loop.max_loop) unconditionally pre-created at init time. The default 3764 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3765 of statically allocating a predefined number, loop 3766 devices can be requested on-demand with the 3767 /dev/loop-control interface. 3768 3769 mce= [X86-{32,64}] 3770 3771 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3772 3773 off 3774 disable machine check 3775 3776 no_cmci 3777 disable CMCI(Corrected Machine Check Interrupt) that 3778 Intel processor supports. Usually this disablement is 3779 not recommended, but it might be handy if your 3780 hardware is misbehaving. 3781 3782 Note that you'll get more problems without CMCI than 3783 with due to the shared banks, i.e. you might get 3784 duplicated error logs. 3785 3786 dont_log_ce 3787 don't make logs for corrected errors. All events 3788 reported as corrected are silently cleared by OS. This 3789 option will be useful if you have no interest in any 3790 of corrected errors. 3791 3792 ignore_ce 3793 disable features for corrected errors, e.g. 3794 polling timer and CMCI. All events reported as 3795 corrected are not cleared by OS and remained in its 3796 error banks. 3797 3798 Usually this disablement is not recommended, however 3799 if there is an agent checking/clearing corrected 3800 errors (e.g. BIOS or hardware monitoring 3801 applications), conflicting with OS's error handling, 3802 and you cannot deactivate the agent, then this option 3803 will be a help. 3804 3805 no_lmce 3806 do not opt-in to Local MCE delivery. Use legacy method 3807 to broadcast MCEs. 3808 3809 bootlog 3810 enable logging of machine checks left over from 3811 booting. Disabled by default on AMD Fam10h and older 3812 because some BIOS leave bogus ones. 3813 3814 If your BIOS doesn't do that it's a good idea to 3815 enable though to make sure you log even machine check 3816 events that result in a reboot. On Intel systems it is 3817 enabled by default. 3818 3819 nobootlog 3820 disable boot machine check logging. 3821 3822 print_all 3823 print all machine check logs to the console. 3824 3825 monarchtimeout (number) 3826 sets the time in us to wait for other CPUs on machine 3827 checks. 0 to disable. 3828 3829 bios_cmci_threshold 3830 don't overwrite the bios-set CMCI threshold. This boot 3831 option prevents Linux from overwriting the CMCI 3832 threshold set by the bios. Without this option, Linux 3833 always sets the CMCI threshold to 1. Enabling this may 3834 make memory predictive failure analysis less effective 3835 if the bios sets thresholds for memory errors since we 3836 will not see details for all errors. 3837 3838 recovery 3839 force-enable recoverable machine check code paths 3840 3841 Everything else is in sysfs now. 3842 3843 3844 md= [HW] RAID subsystems devices and level 3845 See Documentation/admin-guide/md.rst. 3846 3847 mds= [X86,INTEL,EARLY] 3848 Control mitigation for the Micro-architectural Data 3849 Sampling (MDS) vulnerability. 3850 3851 Certain CPUs are vulnerable to an exploit against CPU 3852 internal buffers which can forward information to a 3853 disclosure gadget under certain conditions. 3854 3855 In vulnerable processors, the speculatively 3856 forwarded data can be used in a cache side channel 3857 attack, to access data to which the attacker does 3858 not have direct access. 3859 3860 This parameter controls the MDS mitigation. The 3861 options are: 3862 3863 full - Enable MDS mitigation on vulnerable CPUs 3864 full,nosmt - Enable MDS mitigation and disable 3865 SMT on vulnerable CPUs 3866 off - Unconditionally disable MDS mitigation 3867 3868 On TAA-affected machines, mds=off can be prevented by 3869 an active TAA mitigation as both vulnerabilities are 3870 mitigated with the same mechanism so in order to disable 3871 this mitigation, you need to specify tsx_async_abort=off 3872 too. 3873 3874 Not specifying this option is equivalent to 3875 mds=full. 3876 3877 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3878 3879 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3880 Must be specified, otherwise memory size will be 0. 3881 3882 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3883 of memory Amount of memory to be used in cases 3884 as follows: 3885 3886 1 for test; 3887 2 when the kernel is not able to see the whole system memory; 3888 3 memory that lies after 'mem=' boundary is excluded from 3889 the hypervisor, then assigned to KVM guests. 3890 4 to limit the memory available for kdump kernel. 3891 3892 [ARC,MICROBLAZE] - the limit applies only to low memory, 3893 high memory is not affected. 3894 3895 [ARM64] - only limits memory covered by the linear 3896 mapping. The NOMAP regions are not affected. 3897 3898 [X86] Work as limiting max address. Use together 3899 with memmap= to avoid physical address space collisions. 3900 Without memmap= PCI devices could be placed at addresses 3901 belonging to unused RAM. 3902 3903 Note that this only takes effects during boot time since 3904 in above case 3, memory may need be hot added after boot 3905 if system memory of hypervisor is not sufficient. 3906 3907 mem=nn[KMG]@ss[KMG] 3908 [ARM,MIPS,EARLY] - override the memory layout 3909 reported by firmware. 3910 Define a memory region of size nn[KMG] starting at 3911 ss[KMG]. 3912 Multiple different regions can be specified with 3913 multiple mem= parameters on the command line. 3914 3915 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3916 memory. 3917 3918 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3919 3920 memchunk=nn[KMG] 3921 [KNL,SH] Allow user to override the default size for 3922 per-device physically contiguous DMA buffers. 3923 3924 memhp_default_state=online/offline/online_kernel/online_movable 3925 [KNL] Set the initial state for the memory hotplug 3926 onlining policy. If not specified, the default value is 3927 set according to the 3928 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3929 options. 3930 See Documentation/admin-guide/mm/memory-hotplug.rst. 3931 3932 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3933 E820 memory map, as specified by the user. 3934 Such memmap=exactmap lines can be constructed based on 3935 BIOS output or other requirements. See the memmap=nn@ss 3936 option description. 3937 3938 memmap=nn[KMG]@ss[KMG] 3939 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3940 Region of memory to be used is from ss to ss+nn. 3941 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3942 which limits max address to nn[KMG]. 3943 Multiple different regions can be specified, 3944 comma delimited. 3945 Example: 3946 memmap=100M@2G,100M#3G,1G!1024G 3947 3948 memmap=nn[KMG]#ss[KMG] 3949 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3950 Region of memory to be marked is from ss to ss+nn. 3951 3952 memmap=nn[KMG]$ss[KMG] 3953 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3954 Region of memory to be reserved is from ss to ss+nn. 3955 Example: Exclude memory from 0x18690000-0x1869ffff 3956 memmap=64K$0x18690000 3957 or 3958 memmap=0x10000$0x18690000 3959 Some bootloaders may need an escape character before '$', 3960 like Grub2, otherwise '$' and the following number 3961 will be eaten. 3962 3963 memmap=nn[KMG]!ss[KMG,EARLY] 3964 [KNL,X86] Mark specific memory as protected. 3965 Region of memory to be used, from ss to ss+nn. 3966 The memory region may be marked as e820 type 12 (0xc) 3967 and is NVDIMM or ADR memory. 3968 3969 memmap=<size>%<offset>-<oldtype>+<newtype> 3970 [KNL,ACPI,EARLY] Convert memory within the specified region 3971 from <oldtype> to <newtype>. If "-<oldtype>" is left 3972 out, the whole region will be marked as <newtype>, 3973 even if previously unavailable. If "+<newtype>" is left 3974 out, matching memory will be removed. Types are 3975 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3976 3 = ACPI, 12 = PRAM. 3977 3978 memory_corruption_check=0/1 [X86,EARLY] 3979 Some BIOSes seem to corrupt the first 64k of 3980 memory when doing things like suspend/resume. 3981 Setting this option will scan the memory 3982 looking for corruption. Enabling this will 3983 both detect corruption and prevent the kernel 3984 from using the memory being corrupted. 3985 However, it's intended as a diagnostic tool; if 3986 repeatable BIOS-originated corruption always 3987 affects the same memory, you can use memmap= 3988 to prevent the kernel from using that memory. 3989 3990 memory_corruption_check_size=size [X86,EARLY] 3991 By default it checks for corruption in the low 3992 64k, making this memory unavailable for normal 3993 use. Use this parameter to scan for 3994 corruption in more or less memory. 3995 3996 memory_corruption_check_period=seconds [X86,EARLY] 3997 By default it checks for corruption every 60 3998 seconds. Use this parameter to check at some 3999 other rate. 0 disables periodic checking. 4000 4001 memory_hotplug.memmap_on_memory 4002 [KNL,X86,ARM] Boolean flag to enable this feature. 4003 Format: {on | off (default)} 4004 When enabled, runtime hotplugged memory will 4005 allocate its internal metadata (struct pages, 4006 those vmemmap pages cannot be optimized even 4007 if hugetlb_free_vmemmap is enabled) from the 4008 hotadded memory which will allow to hotadd a 4009 lot of memory without requiring additional 4010 memory to do so. 4011 This feature is disabled by default because it 4012 has some implication on large (e.g. GB) 4013 allocations in some configurations (e.g. small 4014 memory blocks). 4015 The state of the flag can be read in 4016 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4017 Note that even when enabled, there are a few cases where 4018 the feature is not effective. 4019 4020 mempool_debug [MM] 4021 Enable mempool debugging. This enables element 4022 poison checking when freeing elements back to the 4023 pool. Useful for debugging mempool corruption. 4024 4025 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4026 Format: <integer> 4027 default : 0 <disable> 4028 Specifies the number of memtest passes to be 4029 performed. Each pass selects another test 4030 pattern from a given set of patterns. Memtest 4031 fills the memory with this pattern, validates 4032 memory contents and reserves bad memory 4033 regions that are detected. 4034 4035 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4036 Valid arguments: on, off 4037 Default: off 4038 mem_encrypt=on: Activate SME 4039 mem_encrypt=off: Do not activate SME 4040 4041 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4042 for details on when memory encryption can be activated. 4043 4044 mem_sleep_default= [SUSPEND] Default system suspend mode: 4045 s2idle - Suspend-To-Idle 4046 shallow - Power-On Suspend or equivalent (if supported) 4047 deep - Suspend-To-RAM or equivalent (if supported) 4048 See Documentation/admin-guide/pm/sleep-states.rst. 4049 4050 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4051 the BIOS has incorrectly applied a workaround. TinyBIOS 4052 version 0.98 is known to be affected, 0.99 fixes the 4053 problem by letting the user disable the workaround. 4054 4055 mga= [HW,DRM] 4056 4057 microcode= [X86] Control the behavior of the microcode loader. 4058 Available options, comma separated: 4059 4060 base_rev=X - with <X> with format: <u32> 4061 Set the base microcode revision of each thread when in 4062 debug mode. 4063 4064 dis_ucode_ldr: disable the microcode loader 4065 4066 force_minrev: 4067 Enable or disable the microcode minimal revision 4068 enforcement for the runtime microcode loader. 4069 4070 mini2440= [ARM,HW,KNL] 4071 Format:[0..2][b][c][t] 4072 Default: "0tb" 4073 MINI2440 configuration specification: 4074 0 - The attached screen is the 3.5" TFT 4075 1 - The attached screen is the 7" TFT 4076 2 - The VGA Shield is attached (1024x768) 4077 Leaving out the screen size parameter will not load 4078 the TFT driver, and the framebuffer will be left 4079 unconfigured. 4080 b - Enable backlight. The TFT backlight pin will be 4081 linked to the kernel VESA blanking code and a GPIO 4082 LED. This parameter is not necessary when using the 4083 VGA shield. 4084 c - Enable the s3c camera interface. 4085 t - Reserved for enabling touchscreen support. The 4086 touchscreen support is not enabled in the mainstream 4087 kernel as of 2.6.30, a preliminary port can be found 4088 in the "bleeding edge" mini2440 support kernel at 4089 https://repo.or.cz/w/linux-2.6/mini2440.git 4090 4091 mitigations= 4092 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4093 CPU vulnerabilities. This is a set of curated, 4094 arch-independent options, each of which is an 4095 aggregation of existing arch-specific options. 4096 4097 Note, "mitigations" is supported if and only if the 4098 kernel was built with CPU_MITIGATIONS=y. 4099 4100 off 4101 Disable all optional CPU mitigations. This 4102 improves system performance, but it may also 4103 expose users to several CPU vulnerabilities. 4104 Equivalent to: if nokaslr then kpti=0 [ARM64] 4105 gather_data_sampling=off [X86] 4106 indirect_target_selection=off [X86] 4107 kvm.nx_huge_pages=off [X86] 4108 l1tf=off [X86] 4109 mds=off [X86] 4110 mmio_stale_data=off [X86] 4111 no_entry_flush [PPC] 4112 no_uaccess_flush [PPC] 4113 nobp=0 [S390] 4114 nopti [X86,PPC] 4115 nospectre_bhb [ARM64] 4116 nospectre_v1 [X86,PPC] 4117 nospectre_v2 [X86,PPC,S390,ARM64] 4118 reg_file_data_sampling=off [X86] 4119 retbleed=off [X86] 4120 spec_rstack_overflow=off [X86] 4121 spec_store_bypass_disable=off [X86,PPC] 4122 spectre_bhi=off [X86] 4123 spectre_v2_user=off [X86] 4124 srbds=off [X86,INTEL] 4125 ssbd=force-off [ARM64] 4126 tsa=off [X86,AMD] 4127 tsx_async_abort=off [X86] 4128 vmscape=off [X86] 4129 4130 Exceptions: 4131 This does not have any effect on 4132 kvm.nx_huge_pages when 4133 kvm.nx_huge_pages=force. 4134 4135 auto (default) 4136 Mitigate all CPU vulnerabilities, but leave SMT 4137 enabled, even if it's vulnerable. This is for 4138 users who don't want to be surprised by SMT 4139 getting disabled across kernel upgrades, or who 4140 have other ways of avoiding SMT-based attacks. 4141 Equivalent to: (default behavior) 4142 4143 auto,nosmt 4144 Mitigate all CPU vulnerabilities, disabling SMT 4145 if needed. This is for users who always want to 4146 be fully mitigated, even if it means losing SMT. 4147 Equivalent to: l1tf=flush,nosmt [X86] 4148 mds=full,nosmt [X86] 4149 tsx_async_abort=full,nosmt [X86] 4150 mmio_stale_data=full,nosmt [X86] 4151 retbleed=auto,nosmt [X86] 4152 4153 [X86] After one of the above options, additionally 4154 supports attack-vector based controls as documented in 4155 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4156 4157 mminit_loglevel= 4158 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4159 parameter allows control of the logging verbosity for 4160 the additional memory initialisation checks. A value 4161 of 0 disables mminit logging and a level of 4 will 4162 log everything. Information is printed at KERN_DEBUG 4163 so loglevel=8 may also need to be specified. 4164 4165 mmio_stale_data= 4166 [X86,INTEL,EARLY] Control mitigation for the Processor 4167 MMIO Stale Data vulnerabilities. 4168 4169 Processor MMIO Stale Data is a class of 4170 vulnerabilities that may expose data after an MMIO 4171 operation. Exposed data could originate or end in 4172 the same CPU buffers as affected by MDS and TAA. 4173 Therefore, similar to MDS and TAA, the mitigation 4174 is to clear the affected CPU buffers. 4175 4176 This parameter controls the mitigation. The 4177 options are: 4178 4179 full - Enable mitigation on vulnerable CPUs 4180 4181 full,nosmt - Enable mitigation and disable SMT on 4182 vulnerable CPUs. 4183 4184 off - Unconditionally disable mitigation 4185 4186 On MDS or TAA affected machines, 4187 mmio_stale_data=off can be prevented by an active 4188 MDS or TAA mitigation as these vulnerabilities are 4189 mitigated with the same mechanism so in order to 4190 disable this mitigation, you need to specify 4191 mds=off and tsx_async_abort=off too. 4192 4193 Not specifying this option is equivalent to 4194 mmio_stale_data=full. 4195 4196 For details see: 4197 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4198 4199 <module>.async_probe[=<bool>] [KNL] 4200 If no <bool> value is specified or if the value 4201 specified is not a valid <bool>, enable asynchronous 4202 probe on this module. Otherwise, enable/disable 4203 asynchronous probe on this module as indicated by the 4204 <bool> value. See also: module.async_probe 4205 4206 module.async_probe=<bool> 4207 [KNL] When set to true, modules will use async probing 4208 by default. To enable/disable async probing for a 4209 specific module, use the module specific control that 4210 is documented under <module>.async_probe. When both 4211 module.async_probe and <module>.async_probe are 4212 specified, <module>.async_probe takes precedence for 4213 the specific module. 4214 4215 module.enable_dups_trace 4216 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4217 this means that duplicate request_module() calls will 4218 trigger a WARN_ON() instead of a pr_warn(). Note that 4219 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4220 will always be issued and this option does nothing. 4221 module.sig_enforce 4222 [KNL] When CONFIG_MODULE_SIG is set, this means that 4223 modules without (valid) signatures will fail to load. 4224 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4225 is always true, so this option does nothing. 4226 4227 module_blacklist= [KNL] Do not load a comma-separated list of 4228 modules. Useful for debugging problem modules. 4229 4230 mousedev.tap_time= 4231 [MOUSE] Maximum time between finger touching and 4232 leaving touchpad surface for touch to be considered 4233 a tap and be reported as a left button click (for 4234 touchpads working in absolute mode only). 4235 Format: <msecs> 4236 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4237 reporting absolute coordinates, such as tablets 4238 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4239 reporting absolute coordinates, such as tablets 4240 4241 movablecore= [KNL,X86,PPC,EARLY] 4242 Format: nn[KMGTPE] | nn% 4243 This parameter is the complement to kernelcore=, it 4244 specifies the amount of memory used for migratable 4245 allocations. If both kernelcore and movablecore is 4246 specified, then kernelcore will be at *least* the 4247 specified value but may be more. If movablecore on its 4248 own is specified, the administrator must be careful 4249 that the amount of memory usable for all allocations 4250 is not too small. 4251 4252 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4253 NUMA nodes to be movable. This means that the memory 4254 of such nodes will be usable only for movable 4255 allocations which rules out almost all kernel 4256 allocations. Use with caution! 4257 4258 MTD_Partition= [MTD] 4259 Format: <name>,<region-number>,<size>,<offset> 4260 4261 MTD_Region= [MTD] Format: 4262 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4263 4264 mtdparts= [MTD] 4265 See drivers/mtd/parsers/cmdlinepart.c 4266 4267 mtouchusb.raw_coordinates= 4268 [HW] Make the MicroTouch USB driver use raw coordinates 4269 ('y', default) or cooked coordinates ('n') 4270 4271 mtrr=debug [X86,EARLY] 4272 Enable printing debug information related to MTRR 4273 registers at boot time. 4274 4275 mtrr_chunk_size=nn[KMG,X86,EARLY] 4276 used for mtrr cleanup. It is largest continuous chunk 4277 that could hold holes aka. UC entries. 4278 4279 mtrr_gran_size=nn[KMG,X86,EARLY] 4280 Used for mtrr cleanup. It is granularity of mtrr block. 4281 Default is 1. 4282 Large value could prevent small alignment from 4283 using up MTRRs. 4284 4285 mtrr_spare_reg_nr=n [X86,EARLY] 4286 Format: <integer> 4287 Range: 0,7 : spare reg number 4288 Default : 1 4289 Used for mtrr cleanup. It is spare mtrr entries number. 4290 Set to 2 or more if your graphical card needs more. 4291 4292 multitce=off [PPC] This parameter disables the use of the pSeries 4293 firmware feature for updating multiple TCE entries 4294 at a time. 4295 4296 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4297 4298 netdev= [NET] NE2000 ISA network devices parameters 4299 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4300 4301 netpoll.carrier_timeout= 4302 [NET] Specifies amount of time (in seconds) that 4303 netpoll should wait for a carrier. By default netpoll 4304 waits 4 seconds. 4305 4306 nf_conntrack.acct= 4307 [NETFILTER] Enable connection tracking flow accounting 4308 0 to disable accounting 4309 1 to enable accounting 4310 Default value is 0. 4311 4312 nfs.cache_getent= 4313 [NFS] sets the pathname to the program which is used 4314 to update the NFS client cache entries. 4315 4316 nfs.cache_getent_timeout= 4317 [NFS] sets the timeout after which an attempt to 4318 update a cache entry is deemed to have failed. 4319 4320 nfs.callback_nr_threads= 4321 [NFSv4] set the total number of threads that the 4322 NFS client will assign to service NFSv4 callback 4323 requests. 4324 4325 nfs.callback_tcpport= 4326 [NFS] set the TCP port on which the NFSv4 callback 4327 channel should listen. 4328 4329 nfs.delay_retrans= 4330 [NFS] specifies the number of times the NFSv4 client 4331 retries the request before returning an EAGAIN error, 4332 after a reply of NFS4ERR_DELAY from the server. 4333 Only applies if the softerr mount option is enabled, 4334 and the specified value is >= 0. 4335 4336 nfs.idmap_cache_timeout= 4337 [NFS] set the maximum lifetime for idmapper cache 4338 entries. 4339 4340 nfs.max_session_cb_slots= 4341 [NFSv4.1] Sets the maximum number of session 4342 slots the client will assign to the callback 4343 channel. This determines the maximum number of 4344 callbacks the client will process in parallel for 4345 a particular server. 4346 4347 nfs.max_session_slots= 4348 [NFSv4.1] Sets the maximum number of session slots 4349 the client will attempt to negotiate with the server. 4350 This limits the number of simultaneous RPC requests 4351 that the client can send to the NFSv4.1 server. 4352 Note that there is little point in setting this 4353 value higher than the max_tcp_slot_table_limit. 4354 4355 nfs.nfs4_disable_idmapping= 4356 [NFSv4] When set to the default of '1', this option 4357 ensures that both the RPC level authentication 4358 scheme and the NFS level operations agree to use 4359 numeric uids/gids if the mount is using the 4360 'sec=sys' security flavour. In effect it is 4361 disabling idmapping, which can make migration from 4362 legacy NFSv2/v3 systems to NFSv4 easier. 4363 Servers that do not support this mode of operation 4364 will be autodetected by the client, and it will fall 4365 back to using the idmapper. 4366 To turn off this behaviour, set the value to '0'. 4367 4368 nfs.nfs4_unique_id= 4369 [NFS4] Specify an additional fixed unique ident- 4370 ification string that NFSv4 clients can insert into 4371 their nfs_client_id4 string. This is typically a 4372 UUID that is generated at system install time. 4373 4374 nfs.recover_lost_locks= 4375 [NFSv4] Attempt to recover locks that were lost due 4376 to a lease timeout on the server. Please note that 4377 doing this risks data corruption, since there are 4378 no guarantees that the file will remain unchanged 4379 after the locks are lost. 4380 If you want to enable the kernel legacy behaviour of 4381 attempting to recover these locks, then set this 4382 parameter to '1'. 4383 The default parameter value of '0' causes the kernel 4384 not to attempt recovery of lost locks. 4385 4386 nfs.send_implementation_id= 4387 [NFSv4.1] Send client implementation identification 4388 information in exchange_id requests. 4389 If zero, no implementation identification information 4390 will be sent. 4391 The default is to send the implementation identification 4392 information. 4393 4394 nfs4.layoutstats_timer= 4395 [NFSv4.2] Change the rate at which the kernel sends 4396 layoutstats to the pNFS metadata server. 4397 4398 Setting this to value to 0 causes the kernel to use 4399 whatever value is the default set by the layout 4400 driver. A non-zero value sets the minimum interval 4401 in seconds between layoutstats transmissions. 4402 4403 nfsd.inter_copy_offload_enable= 4404 [NFSv4.2] When set to 1, the server will support 4405 server-to-server copies for which this server is 4406 the destination of the copy. 4407 4408 nfsd.nfs4_disable_idmapping= 4409 [NFSv4] When set to the default of '1', the NFSv4 4410 server will return only numeric uids and gids to 4411 clients using auth_sys, and will accept numeric uids 4412 and gids from such clients. This is intended to ease 4413 migration from NFSv2/v3. 4414 4415 nfsd.nfsd4_ssc_umount_timeout= 4416 [NFSv4.2] When used as the destination of a 4417 server-to-server copy, knfsd temporarily mounts 4418 the source server. It caches the mount in case 4419 it will be needed again, and discards it if not 4420 used for the number of milliseconds specified by 4421 this parameter. 4422 4423 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4424 See Documentation/admin-guide/nfs/nfsroot.rst. 4425 4426 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4427 See Documentation/admin-guide/nfs/nfsroot.rst. 4428 4429 nfsrootdebug [NFS] enable nfsroot debugging messages. 4430 See Documentation/admin-guide/nfs/nfsroot.rst. 4431 4432 nmi_backtrace.backtrace_idle [KNL] 4433 Dump stacks even of idle CPUs in response to an 4434 NMI stack-backtrace request. 4435 4436 nmi_debug= [KNL,SH] Specify one or more actions to take 4437 when a NMI is triggered. 4438 Format: [state][,regs][,debounce][,die] 4439 4440 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4441 Format: [panic,][nopanic,][rNNN,][num] 4442 Valid num: 0 or 1 4443 0 - turn hardlockup detector in nmi_watchdog off 4444 1 - turn hardlockup detector in nmi_watchdog on 4445 rNNN - configure the watchdog with raw perf event 0xNNN 4446 4447 When panic is specified, panic when an NMI watchdog 4448 timeout occurs (or 'nopanic' to not panic on an NMI 4449 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4450 To disable both hard and soft lockup detectors, 4451 please see 'nowatchdog'. 4452 This is useful when you use a panic=... timeout and 4453 need the box quickly up again. 4454 4455 These settings can be accessed at runtime via 4456 the nmi_watchdog and hardlockup_panic sysctls. 4457 4458 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4459 Forces kernel to use 3-level paging instead. 4460 4461 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4462 kernel to use 4-level paging instead. 4463 4464 noalign [KNL,ARM] 4465 4466 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4467 IOAPICs that may be present in the system. 4468 4469 noapictimer [APIC,X86] Don't set up the APIC timer 4470 4471 noautogroup Disable scheduler automatic task group creation. 4472 4473 nocache [ARM,EARLY] 4474 4475 no_console_suspend 4476 [HW] Never suspend the console 4477 Disable suspending of consoles during suspend and 4478 hibernate operations. Once disabled, debugging 4479 messages can reach various consoles while the rest 4480 of the system is being put to sleep (ie, while 4481 debugging driver suspend/resume hooks). This may 4482 not work reliably with all consoles, but is known 4483 to work with serial and VGA consoles. 4484 To facilitate more flexible debugging, we also add 4485 console_suspend, a printk module parameter to control 4486 it. Users could use console_suspend (usually 4487 /sys/module/printk/parameters/console_suspend) to 4488 turn on/off it dynamically. 4489 4490 no_debug_objects 4491 [KNL,EARLY] Disable object debugging 4492 4493 nodsp [SH] Disable hardware DSP at boot time. 4494 4495 noefi [EFI,EARLY] Disable EFI runtime services support. 4496 4497 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4498 4499 noexec32 [X86-64] 4500 This affects only 32-bit executables. 4501 noexec32=on: enable non-executable mappings (default) 4502 read doesn't imply executable mappings 4503 noexec32=off: disable non-executable mappings 4504 read implies executable mappings 4505 4506 no_file_caps Tells the kernel not to honor file capabilities. The 4507 only way then for a file to be executed with privilege 4508 is to be setuid root or executed by root. 4509 4510 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4511 4512 nofsgsbase [X86] Disables FSGSBASE instructions. 4513 4514 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4515 register save and restore. The kernel will only save 4516 legacy floating-point registers on task switch. 4517 4518 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4519 4520 no_hash_pointers 4521 [KNL,EARLY] 4522 Alias for "hash_pointers=never". 4523 4524 nohibernate [HIBERNATION] Disable hibernation and resume. 4525 4526 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4527 busy wait in do_idle() and not use the arch_cpu_idle() 4528 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4529 to be effective. This is useful on platforms where the 4530 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4531 correctly or when doing power measurements to evaluate 4532 the impact of the sleep instructions. This is also 4533 useful when using JTAG debugger. 4534 4535 nohpet [X86] Don't use the HPET timer. 4536 4537 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4538 4539 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4540 4541 nohz= [KNL] Boottime enable/disable dynamic ticks 4542 Valid arguments: on, off 4543 Default: on 4544 4545 nohz_full= [KNL,BOOT,SMP,ISOL] 4546 The argument is a cpu list, as described above. 4547 In kernels built with CONFIG_NO_HZ_FULL=y, set 4548 the specified list of CPUs whose tick will be stopped 4549 whenever possible. The boot CPU will be forced outside 4550 the range to maintain the timekeeping. Any CPUs 4551 in this list will have their RCU callbacks offloaded, 4552 just as if they had also been called out in the 4553 rcu_nocbs= boot parameter. 4554 4555 Note that this argument takes precedence over 4556 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4557 4558 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4559 initial RAM disk. Currently this parameter applies to 4560 initrd only, not to initramfs. But it applies to both 4561 in EFI mode. 4562 4563 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4564 remapping. 4565 [Deprecated - use intremap=off] 4566 4567 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4568 4569 noiotrap [SH] Disables trapped I/O port accesses. 4570 4571 noirqdebug [X86-32] Disables the code which attempts to detect and 4572 disable unhandled interrupt sources. 4573 4574 noisapnp [ISAPNP] Disables ISA PnP code. 4575 4576 nokaslr [KNL,EARLY] 4577 When CONFIG_RANDOMIZE_BASE is set, this disables 4578 kernel and module base offset ASLR (Address Space 4579 Layout Randomization). 4580 4581 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4582 fault handling. 4583 4584 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4585 4586 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4587 4588 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4589 4590 nomce [X86-32] Disable Machine Check Exception 4591 4592 nomfgpt [X86-32] Disable Multi-Function General Purpose 4593 Timer usage (for AMD Geode machines). 4594 4595 nomodeset Disable kernel modesetting. Most systems' firmware 4596 sets up a display mode and provides framebuffer memory 4597 for output. With nomodeset, DRM and fbdev drivers will 4598 not load if they could possibly displace the pre- 4599 initialized output. Only the system framebuffer will 4600 be available for use. The respective drivers will not 4601 perform display-mode changes or accelerated rendering. 4602 4603 Useful as error fallback, or for testing and debugging. 4604 4605 nomodule Disable module load 4606 4607 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4608 shutdown the other cpus. Instead use the REBOOT_VECTOR 4609 irq. 4610 4611 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4612 pagetables) support. 4613 4614 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4615 4616 nopku [X86] Disable Memory Protection Keys CPU feature found 4617 in some Intel CPUs. 4618 4619 nopti [X86-64,EARLY] 4620 Equivalent to pti=off 4621 4622 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4623 Disables the PV optimizations forcing the guest to run 4624 as generic guest with no PV drivers. Currently support 4625 XEN HVM, KVM, HYPER_V and VMWARE guest. 4626 4627 nopvspin [X86,XEN,KVM,EARLY] 4628 Disables the qspinlock slow path using PV optimizations 4629 which allow the hypervisor to 'idle' the guest on lock 4630 contention. 4631 4632 norandmaps Don't use address space randomization. Equivalent to 4633 echo 0 > /proc/sys/kernel/randomize_va_space 4634 4635 noresume [SWSUSP] Disables resume and restores original swap 4636 space. 4637 4638 no-scroll [VGA] Disables scrollback. 4639 This is required for the Braillex ib80-piezo Braille 4640 reader made by F.H. Papenmeier (Germany). 4641 4642 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4643 4644 nosmap [PPC,EARLY] 4645 Disable SMAP (Supervisor Mode Access Prevention) 4646 even if it is supported by processor. 4647 4648 nosmep [PPC64s,EARLY] 4649 Disable SMEP (Supervisor Mode Execution Prevention) 4650 even if it is supported by processor. 4651 4652 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4653 and disable the IO APIC. legacy for "maxcpus=0". 4654 4655 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4656 Equivalent to smt=1. 4657 4658 [KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). 4659 nosmt=force: Force disable SMT, cannot be undone 4660 via the sysfs control file. 4661 4662 nosoftlockup [KNL] Disable the soft-lockup detector. 4663 4664 nospec_store_bypass_disable 4665 [HW,EARLY] Disable all mitigations for the Speculative 4666 Store Bypass vulnerability 4667 4668 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4669 history injection) vulnerability. System may allow data leaks 4670 with this option. 4671 4672 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4673 (bounds check bypass). With this option data leaks are 4674 possible in the system. 4675 4676 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4677 for the Spectre variant 2 (indirect branch 4678 prediction) vulnerability. System may allow data 4679 leaks with this option. 4680 4681 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4682 Disable paravirtualized steal time accounting. steal time 4683 is computed, but won't influence scheduler behaviour 4684 4685 nosync [HW,M68K] Disables sync negotiation for all devices. 4686 4687 no_timer_check [X86,APIC] Disables the code which tests for broken 4688 timer IRQ sources, i.e., the IO-APIC timer. This can 4689 work around problems with incorrect timer 4690 initialization on some boards. 4691 4692 no_uaccess_flush 4693 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4694 4695 novmcoredd [KNL,KDUMP] 4696 Disable device dump. Device dump allows drivers to 4697 append dump data to vmcore so you can collect driver 4698 specified debug info. Drivers can append the data 4699 without any limit and this data is stored in memory, 4700 so this may cause significant memory stress. Disabling 4701 device dump can help save memory but the driver debug 4702 data will be no longer available. This parameter 4703 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4704 is set. 4705 4706 no-vmw-sched-clock 4707 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4708 scheduler clock and use the default one. 4709 4710 nowatchdog [KNL] Disable both lockup detectors, i.e. 4711 soft-lockup and NMI watchdog (hard-lockup). 4712 4713 nowb [ARM,EARLY] 4714 4715 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4716 4717 NOTE: this parameter will be ignored on systems with the 4718 LEGACY_XAPIC_DISABLED bit set in the 4719 IA32_XAPIC_DISABLE_STATUS MSR. 4720 4721 noxsave [BUGS=X86] Disables x86 extended register state save 4722 and restore using xsave. The kernel will fallback to 4723 enabling legacy floating-point and sse state. 4724 4725 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4726 register states. The kernel will fall back to use 4727 xsave to save the states. By using this parameter, 4728 performance of saving the states is degraded because 4729 xsave doesn't support modified optimization while 4730 xsaveopt supports it on xsaveopt enabled systems. 4731 4732 noxsaves [X86] Disables xsaves and xrstors used in saving and 4733 restoring x86 extended register state in compacted 4734 form of xsave area. The kernel will fall back to use 4735 xsaveopt and xrstor to save and restore the states 4736 in standard form of xsave area. By using this 4737 parameter, xsave area per process might occupy more 4738 memory on xsaves enabled systems. 4739 4740 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4741 could support. nr_cpus=n : n >= 1 limits the kernel to 4742 support 'n' processors. It could be larger than the 4743 number of already plugged CPU during bootup, later in 4744 runtime you can physically add extra cpu until it reaches 4745 n. So during boot up some boot time memory for per-cpu 4746 variables need be pre-allocated for later physical cpu 4747 hot plugging. 4748 4749 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4750 4751 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4752 Disable NUMA, Only set up a single NUMA node 4753 spanning all memory. 4754 4755 numa=fake=<size>[MG] 4756 [KNL, ARM64, RISCV, X86, EARLY] 4757 If given as a memory unit, fills all system RAM with 4758 nodes of size interleaved over physical nodes. 4759 4760 numa=fake=<N> 4761 [KNL, ARM64, RISCV, X86, EARLY] 4762 If given as an integer, fills all system RAM with N 4763 fake nodes interleaved over physical nodes. 4764 4765 numa=fake=<N>U 4766 [KNL, ARM64, RISCV, X86, EARLY] 4767 If given as an integer followed by 'U', it will 4768 divide each physical node into N emulated nodes. 4769 4770 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4771 4772 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4773 soft-reserved memory partitioning. 4774 4775 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4776 NUMA balancing. 4777 Allowed values are enable and disable 4778 4779 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4780 'node', 'default' can be specified 4781 This can be set from sysctl after boot. 4782 See Documentation/admin-guide/sysctl/vm.rst for details. 4783 4784 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4785 nvme quirk list. List entries are separated by a 4786 '-' character. 4787 Each entry has the form VendorID:ProductID:quirk_names. 4788 The IDs are 4-digits hex numbers and quirk_names is a 4789 list of quirk names separated by commas. A quirk name 4790 can be prefixed by '^', meaning that the specified 4791 quirk must be disabled. 4792 4793 Example: 4794 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4795 4796 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4797 See Documentation/core-api/debugging-via-ohci1394.rst for more 4798 info. 4799 4800 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4801 Rather than timing out after 20 ms if an EC 4802 command is not properly ACKed, override the length 4803 of the timeout. We have interrupts disabled while 4804 waiting for the ACK, so if this is set too high 4805 interrupts *may* be lost! 4806 4807 omap_mux= [OMAP] Override bootloader pin multiplexing. 4808 Format: <mux_mode0.mode_name=value>... 4809 For example, to override I2C bus2: 4810 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4811 4812 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4813 4814 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4815 4816 boundary - index of last SLC block on Flex-OneNAND. 4817 The remaining blocks are configured as MLC blocks. 4818 lock - Configure if Flex-OneNAND boundary should be locked. 4819 Once locked, the boundary cannot be changed. 4820 1 indicates lock status, 0 indicates unlock status. 4821 4822 oops=panic [KNL,EARLY] 4823 Always panic on oopses. Default is to just kill the 4824 process, but there is a small probability of 4825 deadlocking the machine. 4826 This will also cause panics on machine check exceptions. 4827 Useful together with panic=30 to trigger a reboot. 4828 4829 page_alloc.shuffle= 4830 [KNL] Boolean flag to control whether the page allocator 4831 should randomize its free lists. This parameter can be 4832 used to enable/disable page randomization. The state of 4833 the flag can be read from sysfs at: 4834 /sys/module/page_alloc/parameters/shuffle. 4835 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4836 4837 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4838 Storage of the information about who allocated 4839 each page is disabled in default. With this switch, 4840 we can turn it on. 4841 on: enable the feature 4842 4843 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4844 poisoning on the buddy allocator, available with 4845 CONFIG_PAGE_POISONING=y. 4846 off: turn off poisoning (default) 4847 on: turn on poisoning 4848 4849 page_reporting.page_reporting_order= 4850 [KNL] Minimal page reporting order 4851 Format: <integer> 4852 Adjust the minimal page reporting order. The page 4853 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4854 4855 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4856 timeout > 0: seconds before rebooting 4857 timeout = 0: wait forever 4858 timeout < 0: reboot immediately 4859 Format: <timeout> 4860 4861 panic_on_taint= [KNL,EARLY] 4862 Bitmask for conditionally calling panic() in add_taint() 4863 Format: <hex>[,nousertaint] 4864 Hexadecimal bitmask representing the set of TAINT flags 4865 that will cause the kernel to panic when add_taint() is 4866 called with any of the flags in this set. 4867 The optional switch "nousertaint" can be utilized to 4868 prevent userspace forced crashes by writing to sysctl 4869 /proc/sys/kernel/tainted any flagset matching with the 4870 bitmask set on panic_on_taint. 4871 See Documentation/admin-guide/tainted-kernels.rst for 4872 extra details on the taint flags that users can pick 4873 to compose the bitmask to assign to panic_on_taint. 4874 4875 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4876 on a WARN(). 4877 4878 panic_force_cpu= 4879 [KNL,SMP] Force panic handling to execute on a specific CPU. 4880 Format: <cpu number> 4881 Some platforms require panic handling to occur on a 4882 specific CPU for the crash kernel to function correctly. 4883 This can be due to firmware limitations, interrupt routing 4884 constraints, or platform-specific requirements where only 4885 a particular CPU can safely enter the crash kernel. 4886 When set, panic() will redirect execution to the specified 4887 CPU before proceeding with the normal panic and kexec flow. 4888 If the target CPU is offline or unavailable, panic proceeds 4889 on the current CPU. 4890 This option should only be used for systems with the above 4891 constraints as it might cause the panic operation to be less reliable. 4892 4893 panic_print= Bitmask for printing system info when panic happens. 4894 User can chose combination of the following bits: 4895 bit 0: print all tasks info 4896 bit 1: print system memory info 4897 bit 2: print timer info 4898 bit 3: print locks info if CONFIG_LOCKDEP is on 4899 bit 4: print ftrace buffer 4900 bit 5: replay all kernel messages on consoles at the end of panic 4901 bit 6: print all CPUs backtrace (if available in the arch) 4902 bit 7: print only tasks in uninterruptible (blocked) state 4903 *Be aware* that this option may print a _lot_ of lines, 4904 so there are risks of losing older messages in the log. 4905 Use this option carefully, maybe worth to setup a 4906 bigger log buffer with "log_buf_len" along with this. 4907 4908 panic_sys_info= A comma separated list of extra information to be dumped 4909 on panic. 4910 Format: val[,val...] 4911 Where @val can be any of the following: 4912 4913 tasks: print all tasks info 4914 mem: print system memory info 4915 timers: print timers info 4916 locks: print locks info if CONFIG_LOCKDEP is on 4917 ftrace: print ftrace buffer 4918 all_bt: print all CPUs backtrace (if available in the arch) 4919 blocked_tasks: print only tasks in uninterruptible (blocked) state 4920 4921 This is a human readable alternative to the 'panic_print' option. 4922 4923 panic_console_replay 4924 When panic happens, replay all kernel messages on 4925 consoles at the end of panic. 4926 4927 parkbd.port= [HW] Parallel port number the keyboard adapter is 4928 connected to, default is 0. 4929 Format: <parport#> 4930 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4931 0 for XT, 1 for AT (default is AT). 4932 Format: <mode> 4933 4934 parport= [HW,PPT] Specify parallel ports. 0 disables. 4935 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4936 Use 'auto' to force the driver to use any 4937 IRQ/DMA settings detected (the default is to 4938 ignore detected IRQ/DMA settings because of 4939 possible conflicts). You can specify the base 4940 address, IRQ, and DMA settings; IRQ and DMA 4941 should be numbers, or 'auto' (for using detected 4942 settings on that particular port), or 'nofifo' 4943 (to avoid using a FIFO even if it is detected). 4944 Parallel ports are assigned in the order they 4945 are specified on the command line, starting 4946 with parport0. 4947 4948 parport_init_mode= [HW,PPT] 4949 Configure VIA parallel port to operate in 4950 a specific mode. This is necessary on Pegasos 4951 computer where firmware has no options for setting 4952 up parallel port mode and sets it to spp. 4953 Currently this function knows 686a and 8231 chips. 4954 Format: [spp|ps2|epp|ecp|ecpepp] 4955 4956 pata_legacy.all= [HW,LIBATA] 4957 Format: <int> 4958 Set to non-zero to probe primary and secondary ISA 4959 port ranges on PCI systems where no PCI PATA device 4960 has been found at either range. Disabled by default. 4961 4962 pata_legacy.autospeed= [HW,LIBATA] 4963 Format: <int> 4964 Set to non-zero if a chip is present that snoops speed 4965 changes. Disabled by default. 4966 4967 pata_legacy.ht6560a= [HW,LIBATA] 4968 Format: <int> 4969 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4970 the secondary channel, or both channels respectively. 4971 Disabled by default. 4972 4973 pata_legacy.ht6560b= [HW,LIBATA] 4974 Format: <int> 4975 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4976 the secondary channel, or both channels respectively. 4977 Disabled by default. 4978 4979 pata_legacy.iordy_mask= [HW,LIBATA] 4980 Format: <int> 4981 IORDY enable mask. Set individual bits to allow IORDY 4982 for the respective channel. Bit 0 is for the first 4983 legacy channel handled by this driver, bit 1 is for 4984 the second channel, and so on. The sequence will often 4985 correspond to the primary legacy channel, the secondary 4986 legacy channel, and so on, but the handling of a PCI 4987 bus and the use of other driver options may interfere 4988 with the sequence. By default IORDY is allowed across 4989 all channels. 4990 4991 pata_legacy.opti82c46x= [HW,LIBATA] 4992 Format: <int> 4993 Set to 1, 2, or 3 for Opti 82c611A on the primary 4994 channel, the secondary channel, or both channels 4995 respectively. Disabled by default. 4996 4997 pata_legacy.opti82c611a= [HW,LIBATA] 4998 Format: <int> 4999 Set to 1, 2, or 3 for Opti 82c465MV on the primary 5000 channel, the secondary channel, or both channels 5001 respectively. Disabled by default. 5002 5003 pata_legacy.pio_mask= [HW,LIBATA] 5004 Format: <int> 5005 PIO mode mask for autospeed devices. Set individual 5006 bits to allow the use of the respective PIO modes. 5007 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 5008 All modes allowed by default. 5009 5010 pata_legacy.probe_all= [HW,LIBATA] 5011 Format: <int> 5012 Set to non-zero to probe tertiary and further ISA 5013 port ranges on PCI systems. Disabled by default. 5014 5015 pata_legacy.probe_mask= [HW,LIBATA] 5016 Format: <int> 5017 Probe mask for legacy ISA PATA ports. Depending on 5018 platform configuration and the use of other driver 5019 options up to 6 legacy ports are supported: 0x1f0, 5020 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5021 of individual ports can be disabled by setting the 5022 corresponding bits in the mask to 1. Bit 0 is for 5023 the first port in the list above (0x1f0), and so on. 5024 By default all supported ports are probed. 5025 5026 pata_legacy.qdi= [HW,LIBATA] 5027 Format: <int> 5028 Set to non-zero to probe QDI controllers. By default 5029 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5030 5031 pata_legacy.winbond= [HW,LIBATA] 5032 Format: <int> 5033 Set to non-zero to probe Winbond controllers. Use 5034 the standard I/O port (0x130) if 1, otherwise the 5035 value given is the I/O port to use (typically 0x1b0). 5036 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5037 0 otherwise. 5038 5039 pata_platform.pio_mask= [HW,LIBATA] 5040 Format: <int> 5041 Supported PIO mode mask. Set individual bits to allow 5042 the use of the respective PIO modes. Bit 0 is for 5043 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5044 allowed by default. 5045 5046 pause_on_oops=<int> 5047 Halt all CPUs after the first oops has been printed for 5048 the specified number of seconds. This is to be used if 5049 your oopses keep scrolling off the screen. 5050 5051 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5052 5053 Some options herein operate on a specific device 5054 or a set of devices (<pci_dev>). These are 5055 specified in one of the following formats: 5056 5057 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5058 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5059 5060 Note: the first format specifies a PCI 5061 bus/device/function address which may change 5062 if new hardware is inserted, if motherboard 5063 firmware changes, or due to changes caused 5064 by other kernel parameters. If the 5065 domain is left unspecified, it is 5066 taken to be zero. Optionally, a path 5067 to a device through multiple device/function 5068 addresses can be specified after the base 5069 address (this is more robust against 5070 renumbering issues). The second format 5071 selects devices using IDs from the 5072 configuration space which may match multiple 5073 devices in the system. 5074 5075 earlydump dump PCI config space before the kernel 5076 changes anything 5077 off [X86] don't probe for the PCI bus 5078 bios [X86-32] force use of PCI BIOS, don't access 5079 the hardware directly. Use this if your machine 5080 has a non-standard PCI host bridge. 5081 nobios [X86-32] disallow use of PCI BIOS, only direct 5082 hardware access methods are allowed. Use this 5083 if you experience crashes upon bootup and you 5084 suspect they are caused by the BIOS. 5085 conf1 [X86] Force use of PCI Configuration Access 5086 Mechanism 1 (config address in IO port 0xCF8, 5087 data in IO port 0xCFC, both 32-bit). 5088 conf2 [X86] Force use of PCI Configuration Access 5089 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5090 the function, IO port 0xCFA, also 8-bit, sets 5091 bus number. The config space is then accessed 5092 through ports 0xC000-0xCFFF). 5093 See http://wiki.osdev.org/PCI for more info 5094 on the configuration access mechanisms. 5095 noaer [PCIE] If the PCIEAER kernel config parameter is 5096 enabled, this kernel boot option can be used to 5097 disable the use of PCIE advanced error reporting. 5098 nodomains [PCI] Disable support for multiple PCI 5099 root domains (aka PCI segments, in ACPI-speak). 5100 nommconf [X86] Disable use of MMCONFIG for PCI 5101 Configuration 5102 check_enable_amd_mmconf [X86] check for and enable 5103 properly configured MMIO access to PCI 5104 config space on AMD family 10h CPU 5105 nomsi [MSI] If the PCI_MSI kernel config parameter is 5106 enabled, this kernel boot option can be used to 5107 disable the use of MSI interrupts system-wide. 5108 noioapicquirk [APIC] Disable all boot interrupt quirks. 5109 Safety option to keep boot IRQs enabled. This 5110 should never be necessary. 5111 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5112 primary IO-APIC for bridges that cannot disable 5113 boot IRQs. This fixes a source of spurious IRQs 5114 when the system masks IRQs. 5115 noioapicreroute [APIC] Disable workaround that uses the 5116 boot IRQ equivalent of an IRQ that connects to 5117 a chipset where boot IRQs cannot be disabled. 5118 The opposite of ioapicreroute. 5119 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5120 routing table. These calls are known to be buggy 5121 on several machines and they hang the machine 5122 when used, but on other computers it's the only 5123 way to get the interrupt routing table. Try 5124 this option if the kernel is unable to allocate 5125 IRQs or discover secondary PCI buses on your 5126 motherboard. 5127 rom [X86] Assign address space to expansion ROMs. 5128 Use with caution as certain devices share 5129 address decoders between ROMs and other 5130 resources. 5131 norom [X86] Do not assign address space to 5132 expansion ROMs that do not already have 5133 BIOS assigned address ranges. 5134 nobar [X86] Do not assign address space to the 5135 BARs that weren't assigned by the BIOS. 5136 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5137 assigned automatically to PCI devices. You can 5138 make the kernel exclude IRQs of your ISA cards 5139 this way. 5140 pirqaddr=0xAAAAA [X86] Specify the physical address 5141 of the PIRQ table (normally generated 5142 by the BIOS) if it is outside the 5143 F0000h-100000h range. 5144 lastbus=N [X86] Scan all buses thru bus #N. Can be 5145 useful if the kernel is unable to find your 5146 secondary buses and you want to tell it 5147 explicitly which ones they are. 5148 assign-busses [X86] Always assign all PCI bus 5149 numbers ourselves, overriding 5150 whatever the firmware may have done. 5151 usepirqmask [X86] Honor the possible IRQ mask stored 5152 in the BIOS $PIR table. This is needed on 5153 some systems with broken BIOSes, notably 5154 some HP Pavilion N5400 and Omnibook XE3 5155 notebooks. This will have no effect if ACPI 5156 IRQ routing is enabled. 5157 noacpi [X86] Do not use ACPI for IRQ routing 5158 or for PCI scanning. 5159 use_crs [X86] Use PCI host bridge window information 5160 from ACPI. On BIOSes from 2008 or later, this 5161 is enabled by default. If you need to use this, 5162 please report a bug. 5163 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5164 If you need to use this, please report a bug. 5165 use_e820 [X86] Use E820 reservations to exclude parts of 5166 PCI host bridge windows. This is a workaround 5167 for BIOS defects in host bridge _CRS methods. 5168 If you need to use this, please report a bug to 5169 <linux-pci@vger.kernel.org>. 5170 no_e820 [X86] Ignore E820 reservations for PCI host 5171 bridge windows. This is the default on modern 5172 hardware. If you need to use this, please report 5173 a bug to <linux-pci@vger.kernel.org>. 5174 routeirq Do IRQ routing for all PCI devices. 5175 This is normally done in pci_enable_device(), 5176 so this option is a temporary workaround 5177 for broken drivers that don't call it. 5178 skip_isa_align [X86] do not align io start addr, so can 5179 handle more pci cards 5180 noearly [X86] Don't do any early type 1 scanning. 5181 This might help on some broken boards which 5182 machine check when some devices' config space 5183 is read. But various workarounds are disabled 5184 and some IOMMU drivers will not work. 5185 bfsort Sort PCI devices into breadth-first order. 5186 This sorting is done to get a device 5187 order compatible with older (<= 2.4) kernels. 5188 nobfsort Don't sort PCI devices into breadth-first order. 5189 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5190 tuning and use the BIOS-configured MPS defaults. 5191 pcie_bus_safe Set every device's MPS to the largest value 5192 supported by all devices below the root complex. 5193 pcie_bus_perf Set device MPS to the largest allowable MPS 5194 based on its parent bus. Also set MRRS (Max 5195 Read Request Size) to the largest supported 5196 value (no larger than the MPS that the device 5197 or bus can support) for best performance. 5198 pcie_bus_peer2peer Set every device's MPS to 128B, which 5199 every device is guaranteed to support. This 5200 configuration allows peer-to-peer DMA between 5201 any pair of devices, possibly at the cost of 5202 reduced performance. This also guarantees 5203 that hot-added devices will work. 5204 cbiosize=nn[KMG] The fixed amount of bus space which is 5205 reserved for the CardBus bridge's IO window. 5206 The default value is 256 bytes. 5207 cbmemsize=nn[KMG] The fixed amount of bus space which is 5208 reserved for the CardBus bridge's memory 5209 window. The default value is 64 megabytes. 5210 resource_alignment= 5211 Format: 5212 [<order of align>@]<pci_dev>[; ...] 5213 Specifies alignment and device to reassign 5214 aligned memory resources. How to 5215 specify the device is described above. 5216 If <order of align> is not specified, 5217 PAGE_SIZE is used as alignment. 5218 A PCI-PCI bridge can be specified if resource 5219 windows need to be expanded. 5220 To specify the alignment for several 5221 instances of a device, the PCI vendor, 5222 device, subvendor, and subdevice may be 5223 specified, e.g., 12@pci:8086:9c22:103c:198f 5224 for 4096-byte alignment. 5225 ecrc= Enable/disable PCIe ECRC (transaction layer 5226 end-to-end CRC checking). Only effective if 5227 OS has native AER control (either granted by 5228 ACPI _OSC or forced via "pcie_ports=native") 5229 bios: Use BIOS/firmware settings. This is the 5230 the default. 5231 off: Turn ECRC off 5232 on: Turn ECRC on. 5233 hpiosize=nn[KMG] The fixed amount of bus space which is 5234 reserved for hotplug bridge's IO window. 5235 Default size is 256 bytes. 5236 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5237 reserved for hotplug bridge's MMIO window. 5238 Default size is 2 megabytes. 5239 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5240 reserved for hotplug bridge's MMIO_PREF window. 5241 Default size is 2 megabytes. 5242 hpmemsize=nn[KMG] The fixed amount of bus space which is 5243 reserved for hotplug bridge's MMIO and 5244 MMIO_PREF window. 5245 Default size is 2 megabytes. 5246 hpbussize=nn The minimum amount of additional bus numbers 5247 reserved for buses below a hotplug bridge. 5248 Default is 1. 5249 realloc= Enable/disable reallocating PCI bridge resources 5250 if allocations done by BIOS are too small to 5251 accommodate resources required by all child 5252 devices. 5253 off: Turn realloc off 5254 on: Turn realloc on 5255 realloc same as realloc=on 5256 noari do not use PCIe ARI. 5257 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5258 do not use PCIe ATS (and IOMMU device IOTLB). 5259 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5260 only look for one device below a PCIe downstream 5261 port. 5262 big_root_window Try to add a big 64bit memory window to the PCIe 5263 root complex on AMD CPUs. Some GFX hardware 5264 can resize a BAR to allow access to all VRAM. 5265 Adding the window is slightly risky (it may 5266 conflict with unreported devices), so this 5267 taints the kernel. 5268 disable_acs_redir=<pci_dev>[; ...] 5269 Specify one or more PCI devices (in the format 5270 specified above) separated by semicolons. 5271 Each device specified will have the PCI ACS 5272 redirect capabilities forced off which will 5273 allow P2P traffic between devices through 5274 bridges without forcing it upstream. Note: 5275 this removes isolation between devices and 5276 may put more devices in an IOMMU group. 5277 config_acs= 5278 Format: 5279 <ACS flags>@<pci_dev>[; ...] 5280 Specify one or more PCI devices (in the format 5281 specified above) optionally prepended with flags 5282 and separated by semicolons. The respective 5283 capabilities will be enabled, disabled or 5284 unchanged based on what is specified in 5285 flags. 5286 5287 ACS Flags is defined as follows: 5288 bit-0 : ACS Source Validation 5289 bit-1 : ACS Translation Blocking 5290 bit-2 : ACS P2P Request Redirect 5291 bit-3 : ACS P2P Completion Redirect 5292 bit-4 : ACS Upstream Forwarding 5293 bit-5 : ACS P2P Egress Control 5294 bit-6 : ACS Direct Translated P2P 5295 Each bit can be marked as: 5296 '0' – force disabled 5297 '1' – force enabled 5298 'x' – unchanged 5299 For example, 5300 pci=config_acs=10x@pci:0:0 5301 would configure all devices that support 5302 ACS to enable P2P Request Redirect, disable 5303 Translation Blocking, and leave Source 5304 Validation unchanged from whatever power-up 5305 or firmware set it to. 5306 5307 Note: this may remove isolation between devices 5308 and may put more devices in an IOMMU group. 5309 force_floating [S390] Force usage of floating interrupts. 5310 nomio [S390] Do not use MIO instructions. 5311 norid [S390] ignore the RID field and force use of 5312 one PCI domain per PCI function 5313 notph [PCIE] If the PCIE_TPH kernel config parameter 5314 is enabled, this kernel boot option can be used 5315 to disable PCIe TLP Processing Hints support 5316 system-wide. 5317 5318 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5319 Management. 5320 off Don't touch ASPM configuration at all. Leave any 5321 configuration done by firmware unchanged. 5322 force Enable ASPM even on devices that claim not to support it. 5323 WARNING: Forcing ASPM on may cause system lockups. 5324 5325 pcie_ports= [PCIE] PCIe port services handling: 5326 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5327 even if the platform doesn't give the OS permission to 5328 use them. This may cause conflicts if the platform 5329 also tries to use these services. 5330 dpc-native Use native PCIe service for DPC only. May 5331 cause conflicts if firmware uses AER or DPC. 5332 compat Disable native PCIe services (PME, AER, DPC, PCIe 5333 hotplug). 5334 5335 pcie_port_pm= [PCIE] PCIe port power management handling: 5336 off Disable power management of all PCIe ports 5337 force Forcibly enable power management of all PCIe ports 5338 5339 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5340 nomsi Do not use MSI for native PCIe PME signaling (this makes 5341 all PCIe root ports use INTx for all services). 5342 5343 pcmv= [HW,PCMCIA] BadgePAD 4 5344 5345 pd_ignore_unused 5346 [PM] 5347 Keep all power-domains already enabled by bootloader on, 5348 even if no driver has claimed them. This is useful 5349 for debug and development, but should not be 5350 needed on a platform with proper driver support. 5351 5352 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5353 boot time. 5354 Format: { 0 | 1 } 5355 See arch/parisc/kernel/pdc_chassis.c 5356 5357 percpu_alloc= [MM,EARLY] 5358 Select which percpu first chunk allocator to use. 5359 Currently supported values are "embed" and "page". 5360 Archs may support subset or none of the selections. 5361 See comments in mm/percpu.c for details on each 5362 allocator. This parameter is primarily for debugging 5363 and performance comparison. 5364 5365 pirq= [SMP,APIC] Manual mp-table setup 5366 See Documentation/arch/x86/i386/IO-APIC.rst. 5367 5368 plip= [PPT,NET] Parallel port network link 5369 Format: { parport<nr> | timid | 0 } 5370 See also Documentation/admin-guide/parport.rst. 5371 5372 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5373 Override pmtimer IOPort with a hex value. 5374 e.g. pmtmr=0x508 5375 5376 pmu_override= [PPC] Override the PMU. 5377 This option takes over the PMU facility, so it is no 5378 longer usable by perf. Setting this option starts the 5379 PMU counters by setting MMCR0 to 0 (the FC bit is 5380 cleared). If a number is given, then MMCR1 is set to 5381 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5382 remains 0. 5383 5384 pm_async= [PM] 5385 Format: off 5386 This parameter sets the initial value of the 5387 /sys/power/pm_async sysfs knob at boot time. 5388 If set to "off", disables asynchronous suspend and 5389 resume of devices during system-wide power transitions. 5390 This can be useful on platforms where device 5391 dependencies are not well-defined, or for debugging 5392 power management issues. Asynchronous operations are 5393 enabled by default. 5394 5395 5396 pm_debug_messages [SUSPEND,KNL] 5397 Enable suspend/resume debug messages during boot up. 5398 5399 pm.dpm_watchdog_enabled= 5400 [PM] Enable or disable the DPM watchdog. Requires 5401 CONFIG_PM_SLEEP and CONFIG_DPM_WATCHDOG enabled. 5402 Format: <bool> 5403 Default value is set by CONFIG_DPM_WATCHDOG_ENABLED. 5404 5405 pnp.debug=1 [PNP] 5406 Enable PNP debug messages (depends on the 5407 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5408 via /sys/module/pnp/parameters/debug. We always show 5409 current resource usage; turning this on also shows 5410 possible settings and some assignment information. 5411 5412 pnpacpi= [ACPI] 5413 { off } 5414 5415 pnpbios= [ISAPNP] 5416 { on | off | curr | res | no-curr | no-res } 5417 5418 pnp_reserve_irq= 5419 [ISAPNP] Exclude IRQs for the autoconfiguration 5420 5421 pnp_reserve_dma= 5422 [ISAPNP] Exclude DMAs for the autoconfiguration 5423 5424 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5425 Ranges are in pairs (I/O port base and size). 5426 5427 pnp_reserve_mem= 5428 [ISAPNP] Exclude memory regions for the 5429 autoconfiguration. 5430 Ranges are in pairs (memory base and size). 5431 5432 ports= [IP_VS_FTP] IPVS ftp helper module 5433 Default is 21. 5434 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5435 may be specified. 5436 Format: <port>,<port>.... 5437 5438 possible_cpus= [SMP,S390,X86] 5439 Format: <unsigned int> 5440 Set the number of possible CPUs, overriding the 5441 regular discovery mechanisms (such as ACPI/FW, etc). 5442 5443 powersave=off [PPC] This option disables power saving features. 5444 It specifically disables cpuidle and sets the 5445 platform machine description specific power_save 5446 function to NULL. On Idle the CPU just reduces 5447 execution priority. 5448 5449 ppc_strict_facility_enable 5450 [PPC,ENABLE] This option catches any kernel floating point, 5451 Altivec, VSX and SPE outside of regions specifically 5452 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5453 There is some performance impact when enabling this. 5454 5455 ppc_tm= [PPC,EARLY] 5456 Format: {"off"} 5457 Disable Hardware Transactional Memory 5458 5459 preempt= [KNL] 5460 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5461 none - Limited to cond_resched() calls 5462 voluntary - Limited to cond_resched() and might_sleep() calls 5463 full - Any section that isn't explicitly preempt disabled 5464 can be preempted anytime. Tasks will also yield 5465 contended spinlocks (if the critical section isn't 5466 explicitly preempt disabled beyond the lock itself). 5467 lazy - Scheduler controlled. Similar to full but instead 5468 of preempting the task immediately, the task gets 5469 one HZ tick time to yield itself before the 5470 preemption will be forced. One preemption is when the 5471 task returns to user space. 5472 5473 print-fatal-signals= 5474 [KNL] debug: print fatal signals 5475 5476 If enabled, warn about various signal handling 5477 related application anomalies: too many signals, 5478 too many POSIX.1 timers, fatal signals causing a 5479 coredump - etc. 5480 5481 If you hit the warning due to signal overflow, 5482 you might want to try "ulimit -i unlimited". 5483 5484 default: off. 5485 5486 printk.always_kmsg_dump= 5487 Trigger kmsg_dump for cases other than kernel oops or 5488 panics 5489 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5490 default: disabled 5491 5492 printk.console_no_auto_verbose= 5493 Disable console loglevel raise on oops, panic 5494 or lockdep-detected issues (only if lock debug is on). 5495 With an exception to setups with low baudrate on 5496 serial console, keeping this 0 is a good choice 5497 in order to provide more debug information. 5498 Format: <bool> 5499 default: 0 (auto_verbose is enabled) 5500 5501 printk.debug_non_panic_cpus= 5502 Allows storing messages from non-panic CPUs into 5503 the printk log buffer during panic(). They are 5504 flushed to consoles by the panic-CPU on 5505 a best-effort basis. 5506 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5507 Default: disabled 5508 5509 printk.devkmsg={on,off,ratelimit} 5510 Control writing to /dev/kmsg. 5511 on - unlimited logging to /dev/kmsg from userspace 5512 off - logging to /dev/kmsg disabled 5513 ratelimit - ratelimit the logging 5514 Default: ratelimit 5515 5516 printk.time= Show timing data prefixed to each printk message line 5517 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5518 5519 proc_mem.force_override= [KNL] 5520 Format: {always | ptrace | never} 5521 Traditionally /proc/pid/mem allows memory permissions to be 5522 overridden without restrictions. This option may be set to 5523 restrict that. Can be one of: 5524 - 'always': traditional behavior always allows mem overrides. 5525 - 'ptrace': only allow mem overrides for active ptracers. 5526 - 'never': never allow mem overrides. 5527 If not specified, default is the CONFIG_PROC_MEM_* choice. 5528 5529 processor.max_cstate= [HW,ACPI] 5530 Limit processor to maximum C-state 5531 max_cstate=9 overrides any DMI blacklist limit. 5532 5533 processor.nocst [HW,ACPI] 5534 Ignore the _CST method to determine C-states, 5535 instead using the legacy FADT method 5536 5537 profile= [KNL] Enable kernel profiling via /proc/profile 5538 Format: [<profiletype>,]<number> 5539 Param: <profiletype>: "schedule" or "kvm" 5540 [defaults to kernel profiling] 5541 Param: "schedule" - profile schedule points. 5542 Param: "kvm" - profile VM exits. 5543 Param: <number> - step/bucket size as a power of 2 for 5544 statistical time based profiling. 5545 5546 prot_virt= [S390] enable hosting protected virtual machines 5547 isolated from the hypervisor (if hardware supports 5548 that). If enabled, the default kernel base address 5549 might be overridden even when Kernel Address Space 5550 Layout Randomization is disabled. 5551 Format: <bool> 5552 5553 psi= [KNL] Enable or disable pressure stall information 5554 tracking. 5555 Format: <bool> 5556 5557 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5558 probe for; one of (bare|imps|exps|lifebook|any). 5559 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5560 per second. 5561 psmouse.resetafter= [HW,MOUSE] 5562 Try to reset the device after so many bad packets 5563 (0 = never). 5564 psmouse.resolution= 5565 [HW,MOUSE] Set desired mouse resolution, in dpi. 5566 psmouse.smartscroll= 5567 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5568 0 = disabled, 1 = enabled (default). 5569 5570 pstore.backend= Specify the name of the pstore backend to use 5571 5572 pti= [X86-64] Control Page Table Isolation of user and 5573 kernel address spaces. Disabling this feature 5574 removes hardening, but improves performance of 5575 system calls and interrupts. 5576 5577 on - unconditionally enable 5578 off - unconditionally disable 5579 auto - kernel detects whether your CPU model is 5580 vulnerable to issues that PTI mitigates 5581 5582 Not specifying this option is equivalent to pti=auto. 5583 5584 pty.legacy_count= 5585 [KNL] Number of legacy pty's. Overwrites compiled-in 5586 default number. 5587 5588 quiet [KNL,EARLY] Disable most log messages 5589 5590 r128= [HW,DRM] 5591 5592 radix_hcall_invalidate=on [PPC/PSERIES] 5593 Disable RADIX GTSE feature and use hcall for TLB 5594 invalidate. 5595 5596 raid= [HW,RAID] 5597 See Documentation/admin-guide/md.rst. 5598 5599 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5600 See Documentation/admin-guide/blockdev/ramdisk.rst. 5601 5602 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5603 5604 random.trust_cpu=off 5605 [KNL,EARLY] Disable trusting the use of the CPU's 5606 random number generator (if available) to 5607 initialize the kernel's RNG. 5608 5609 random.trust_bootloader=off 5610 [KNL,EARLY] Disable trusting the use of the a seed 5611 passed by the bootloader (if available) to 5612 initialize the kernel's RNG. 5613 5614 randomize_kstack_offset= 5615 [KNL,EARLY] Enable or disable kernel stack offset 5616 randomization, which provides roughly 5 bits of 5617 entropy, frustrating memory corruption attacks 5618 that depend on stack address determinism or 5619 cross-syscall address exposures. This is only 5620 available on architectures that have defined 5621 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5622 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5623 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5624 5625 ras=option[,option,...] [KNL] RAS-specific options 5626 5627 cec_disable [X86] 5628 Disable the Correctable Errors Collector, 5629 see CONFIG_RAS_CEC help text. 5630 5631 rcu_nocbs[=cpu-list] 5632 [KNL] The optional argument is a cpu list, 5633 as described above. 5634 5635 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5636 enable the no-callback CPU mode, which prevents 5637 such CPUs' callbacks from being invoked in 5638 softirq context. Invocation of such CPUs' RCU 5639 callbacks will instead be offloaded to "rcuox/N" 5640 kthreads created for that purpose, where "x" is 5641 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5642 for the kthreads that mediate grace periods; and 5643 "N" is the CPU number. This reduces OS jitter on 5644 the offloaded CPUs, which can be useful for HPC 5645 and real-time workloads. It can also improve 5646 energy efficiency for asymmetric multiprocessors. 5647 5648 If a cpulist is passed as an argument, the specified 5649 list of CPUs is set to no-callback mode from boot. 5650 5651 Otherwise, if the '=' sign and the cpulist 5652 arguments are omitted, no CPU will be set to 5653 no-callback mode from boot but the mode may be 5654 toggled at runtime via cpusets. 5655 5656 Note that this argument takes precedence over 5657 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5658 5659 rcu_nocb_poll [KNL] 5660 Rather than requiring that offloaded CPUs 5661 (specified by rcu_nocbs= above) explicitly 5662 awaken the corresponding "rcuoN" kthreads, 5663 make these kthreads poll for callbacks. 5664 This improves the real-time response for the 5665 offloaded CPUs by relieving them of the need to 5666 wake up the corresponding kthread, but degrades 5667 energy efficiency by requiring that the kthreads 5668 periodically wake up to do the polling. 5669 5670 rcutree.blimit= [KNL] 5671 Set maximum number of finished RCU callbacks to 5672 process in one batch. 5673 5674 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5675 Do only a one-line RCU CPU stall warning when 5676 there is an ongoing too-long CSD-lock wait. 5677 5678 rcutree.do_rcu_barrier= [KNL] 5679 Request a call to rcu_barrier(). This is 5680 throttled so that userspace tests can safely 5681 hammer on the sysfs variable if they so choose. 5682 If triggered before the RCU grace-period machinery 5683 is fully active, this will error out with EAGAIN. 5684 5685 rcutree.dump_tree= [KNL] 5686 Dump the structure of the rcu_node combining tree 5687 out at early boot. This is used for diagnostic 5688 purposes, to verify correct tree setup. 5689 5690 rcutree.gp_cleanup_delay= [KNL] 5691 Set the number of jiffies to delay each step of 5692 RCU grace-period cleanup. 5693 5694 rcutree.gp_init_delay= [KNL] 5695 Set the number of jiffies to delay each step of 5696 RCU grace-period initialization. 5697 5698 rcutree.gp_preinit_delay= [KNL] 5699 Set the number of jiffies to delay each step of 5700 RCU grace-period pre-initialization, that is, 5701 the propagation of recent CPU-hotplug changes up 5702 the rcu_node combining tree. 5703 5704 rcutree.jiffies_till_first_fqs= [KNL] 5705 Set delay from grace-period initialization to 5706 first attempt to force quiescent states. 5707 Units are jiffies, minimum value is zero, 5708 and maximum value is HZ. 5709 5710 rcutree.jiffies_till_next_fqs= [KNL] 5711 Set delay between subsequent attempts to force 5712 quiescent states. Units are jiffies, minimum 5713 value is one, and maximum value is HZ. 5714 5715 rcutree.jiffies_till_sched_qs= [KNL] 5716 Set required age in jiffies for a 5717 given grace period before RCU starts 5718 soliciting quiescent-state help from 5719 rcu_note_context_switch() and cond_resched(). 5720 If not specified, the kernel will calculate 5721 a value based on the most recent settings 5722 of rcutree.jiffies_till_first_fqs 5723 and rcutree.jiffies_till_next_fqs. 5724 This calculated value may be viewed in 5725 rcutree.jiffies_to_sched_qs. Any attempt to set 5726 rcutree.jiffies_to_sched_qs will be cheerfully 5727 overwritten. 5728 5729 rcutree.kthread_prio= [KNL,BOOT] 5730 Set the SCHED_FIFO priority of the RCU per-CPU 5731 kthreads (rcuc/N). This value is also used for 5732 the priority of the RCU boost threads (rcub/N) 5733 and for the RCU grace-period kthreads (rcu_bh, 5734 rcu_preempt, and rcu_sched). If RCU_BOOST is 5735 set, valid values are 1-99 and the default is 1 5736 (the least-favored priority). Otherwise, when 5737 RCU_BOOST is not set, valid values are 0-99 and 5738 the default is zero (non-realtime operation). 5739 When RCU_NOCB_CPU is set, also adjust the 5740 priority of NOCB callback kthreads. 5741 5742 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5743 On callback-offloaded (rcu_nocbs) CPUs, 5744 RCU reduces the lock contention that would 5745 otherwise be caused by callback floods through 5746 use of the ->nocb_bypass list. However, in the 5747 common non-flooded case, RCU queues directly to 5748 the main ->cblist in order to avoid the extra 5749 overhead of the ->nocb_bypass list and its lock. 5750 But if there are too many callbacks queued during 5751 a single jiffy, RCU pre-queues the callbacks into 5752 the ->nocb_bypass queue. The definition of "too 5753 many" is supplied by this kernel boot parameter. 5754 5755 rcutree.nohz_full_patience_delay= [KNL] 5756 On callback-offloaded (rcu_nocbs) CPUs, avoid 5757 disturbing RCU unless the grace period has 5758 reached the specified age in milliseconds. 5759 Defaults to zero. Large values will be capped 5760 at five seconds. All values will be rounded down 5761 to the nearest value representable by jiffies. 5762 5763 rcutree.qhimark= [KNL] 5764 Set threshold of queued RCU callbacks beyond which 5765 batch limiting is disabled. 5766 5767 rcutree.qlowmark= [KNL] 5768 Set threshold of queued RCU callbacks below which 5769 batch limiting is re-enabled. 5770 5771 rcutree.qovld= [KNL] 5772 Set threshold of queued RCU callbacks beyond which 5773 RCU's force-quiescent-state scan will aggressively 5774 enlist help from cond_resched() and sched IPIs to 5775 help CPUs more quickly reach quiescent states. 5776 Set to less than zero to make this be set based 5777 on rcutree.qhimark at boot time and to zero to 5778 disable more aggressive help enlistment. 5779 5780 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5781 Set the page-cache refill delay (in milliseconds) 5782 in response to low-memory conditions. The range 5783 of permitted values is in the range 0:100000. 5784 5785 rcutree.rcu_divisor= [KNL] 5786 Set the shift-right count to use to compute 5787 the callback-invocation batch limit bl from 5788 the number of callbacks queued on this CPU. 5789 The result will be bounded below by the value of 5790 the rcutree.blimit kernel parameter. Every bl 5791 callbacks, the softirq handler will exit in 5792 order to allow the CPU to do other work. 5793 5794 Please note that this callback-invocation batch 5795 limit applies only to non-offloaded callback 5796 invocation. Offloaded callbacks are instead 5797 invoked in the context of an rcuoc kthread, which 5798 scheduler will preempt as it does any other task. 5799 5800 rcutree.rcu_fanout_exact= [KNL] 5801 Disable autobalancing of the rcu_node combining 5802 tree. This is used by rcutorture, and might 5803 possibly be useful for architectures having high 5804 cache-to-cache transfer latencies. 5805 5806 rcutree.rcu_fanout_leaf= [KNL] 5807 Change the number of CPUs assigned to each 5808 leaf rcu_node structure. Useful for very 5809 large systems, which will choose the value 64, 5810 and for NUMA systems with large remote-access 5811 latencies, which will choose a value aligned 5812 with the appropriate hardware boundaries. 5813 5814 rcutree.rcu_min_cached_objs= [KNL] 5815 Minimum number of objects which are cached and 5816 maintained per one CPU. Object size is equal 5817 to PAGE_SIZE. The cache allows to reduce the 5818 pressure to page allocator, also it makes the 5819 whole algorithm to behave better in low memory 5820 condition. 5821 5822 rcutree.rcu_nocb_gp_stride= [KNL] 5823 Set the number of NOCB callback kthreads in 5824 each group, which defaults to the square root 5825 of the number of CPUs. Larger numbers reduce 5826 the wakeup overhead on the global grace-period 5827 kthread, but increases that same overhead on 5828 each group's NOCB grace-period kthread. 5829 5830 rcutree.rcu_kick_kthreads= [KNL] 5831 Cause the grace-period kthread to get an extra 5832 wake_up() if it sleeps three times longer than 5833 it should at force-quiescent-state time. 5834 This wake_up() will be accompanied by a 5835 WARN_ONCE() splat and an ftrace_dump(). 5836 5837 rcutree.rcu_resched_ns= [KNL] 5838 Limit the time spend invoking a batch of RCU 5839 callbacks to the specified number of nanoseconds. 5840 By default, this limit is checked only once 5841 every 32 callbacks in order to limit the pain 5842 inflicted by local_clock() overhead. 5843 5844 rcutree.rcu_unlock_delay= [KNL] 5845 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5846 this specifies an rcu_read_unlock()-time delay 5847 in microseconds. This defaults to zero. 5848 Larger delays increase the probability of 5849 catching RCU pointer leaks, that is, buggy use 5850 of RCU-protected pointers after the relevant 5851 rcu_read_unlock() has completed. 5852 5853 rcutree.sysrq_rcu= [KNL] 5854 Commandeer a sysrq key to dump out Tree RCU's 5855 rcu_node tree with an eye towards determining 5856 why a new grace period has not yet started. 5857 5858 rcutree.use_softirq= [KNL] 5859 If set to zero, move all RCU_SOFTIRQ processing to 5860 per-CPU rcuc kthreads. Defaults to a non-zero 5861 value, meaning that RCU_SOFTIRQ is used by default. 5862 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5863 5864 But note that CONFIG_PREEMPT_RT=y kernels disable 5865 this kernel boot parameter, forcibly setting it 5866 to zero. 5867 5868 rcutree.enable_rcu_lazy= [KNL] 5869 To save power, batch RCU callbacks and flush after 5870 delay, memory pressure or callback list growing too 5871 big. 5872 5873 rcutree.rcu_normal_wake_from_gp= [KNL] 5874 Reduces a latency of synchronize_rcu() call. This approach 5875 maintains its own track of synchronize_rcu() callers, so it 5876 does not interact with regular callbacks because it does not 5877 use a call_rcu[_hurry]() path. Please note, this is for a 5878 normal grace period. 5879 5880 How to disable it: 5881 5882 echo 0 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5883 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=0" 5884 5885 Default is 1 if it is not explicitly disabled by the boot parameter 5886 passing 0. 5887 5888 rcuscale.gp_async= [KNL] 5889 Measure performance of asynchronous 5890 grace-period primitives such as call_rcu(). 5891 5892 rcuscale.gp_async_max= [KNL] 5893 Specify the maximum number of outstanding 5894 callbacks per writer thread. When a writer 5895 thread exceeds this limit, it invokes the 5896 corresponding flavor of rcu_barrier() to allow 5897 previously posted callbacks to drain. 5898 5899 rcuscale.gp_exp= [KNL] 5900 Measure performance of expedited synchronous 5901 grace-period primitives. 5902 5903 rcuscale.holdoff= [KNL] 5904 Set test-start holdoff period. The purpose of 5905 this parameter is to delay the start of the 5906 test until boot completes in order to avoid 5907 interference. 5908 5909 rcuscale.kfree_by_call_rcu= [KNL] 5910 In kernels built with CONFIG_RCU_LAZY=y, test 5911 call_rcu() instead of kfree_rcu(). 5912 5913 rcuscale.kfree_mult= [KNL] 5914 Instead of allocating an object of size kfree_obj, 5915 allocate one of kfree_mult * sizeof(kfree_obj). 5916 Defaults to 1. 5917 5918 rcuscale.kfree_rcu_test= [KNL] 5919 Set to measure performance of kfree_rcu() flooding. 5920 5921 rcuscale.kfree_rcu_test_double= [KNL] 5922 Test the double-argument variant of kfree_rcu(). 5923 If this parameter has the same value as 5924 rcuscale.kfree_rcu_test_single, both the single- 5925 and double-argument variants are tested. 5926 5927 rcuscale.kfree_rcu_test_single= [KNL] 5928 Test the single-argument variant of kfree_rcu(). 5929 If this parameter has the same value as 5930 rcuscale.kfree_rcu_test_double, both the single- 5931 and double-argument variants are tested. 5932 5933 rcuscale.kfree_nthreads= [KNL] 5934 The number of threads running loops of kfree_rcu(). 5935 5936 rcuscale.kfree_alloc_num= [KNL] 5937 Number of allocations and frees done in an iteration. 5938 5939 rcuscale.kfree_loops= [KNL] 5940 Number of loops doing rcuscale.kfree_alloc_num number 5941 of allocations and frees. 5942 5943 rcuscale.minruntime= [KNL] 5944 Set the minimum test run time in seconds. This 5945 does not affect the data-collection interval, 5946 but instead allows better measurement of things 5947 like CPU consumption. 5948 5949 rcuscale.nreaders= [KNL] 5950 Set number of RCU readers. The value -1 selects 5951 N, where N is the number of CPUs. A value 5952 "n" less than -1 selects N-n+1, where N is again 5953 the number of CPUs. For example, -2 selects N 5954 (the number of CPUs), -3 selects N+1, and so on. 5955 A value of "n" less than or equal to -N selects 5956 a single reader. 5957 5958 rcuscale.nwriters= [KNL] 5959 Set number of RCU writers. The values operate 5960 the same as for rcuscale.nreaders. 5961 N, where N is the number of CPUs 5962 5963 rcuscale.scale_type= [KNL] 5964 Specify the RCU implementation to test. 5965 5966 rcuscale.shutdown= [KNL] 5967 Shut the system down after performance tests 5968 complete. This is useful for hands-off automated 5969 testing. 5970 5971 rcuscale.verbose= [KNL] 5972 Enable additional printk() statements. 5973 5974 rcuscale.writer_holdoff= [KNL] 5975 Write-side holdoff between grace periods, 5976 in microseconds. The default of zero says 5977 no holdoff. 5978 5979 rcuscale.writer_holdoff_jiffies= [KNL] 5980 Additional write-side holdoff between grace 5981 periods, but in jiffies. The default of zero 5982 says no holdoff. 5983 5984 rcutorture.fqs_duration= [KNL] 5985 Set duration of force_quiescent_state bursts 5986 in microseconds. 5987 5988 rcutorture.fqs_holdoff= [KNL] 5989 Set holdoff time within force_quiescent_state bursts 5990 in microseconds. 5991 5992 rcutorture.fqs_stutter= [KNL] 5993 Set wait time between force_quiescent_state bursts 5994 in seconds. 5995 5996 rcutorture.fwd_progress= [KNL] 5997 Specifies the number of kthreads to be used 5998 for RCU grace-period forward-progress testing 5999 for the types of RCU supporting this notion. 6000 Defaults to 1 kthread, values less than zero or 6001 greater than the number of CPUs cause the number 6002 of CPUs to be used. 6003 6004 rcutorture.fwd_progress_div= [KNL] 6005 Specify the fraction of a CPU-stall-warning 6006 period to do tight-loop forward-progress testing. 6007 6008 rcutorture.fwd_progress_holdoff= [KNL] 6009 Number of seconds to wait between successive 6010 forward-progress tests. 6011 6012 rcutorture.fwd_progress_need_resched= [KNL] 6013 Enclose cond_resched() calls within checks for 6014 need_resched() during tight-loop forward-progress 6015 testing. 6016 6017 rcutorture.gp_cond= [KNL] 6018 Use conditional/asynchronous update-side 6019 normal-grace-period primitives, if available. 6020 6021 rcutorture.gp_cond_exp= [KNL] 6022 Use conditional/asynchronous update-side 6023 expedited-grace-period primitives, if available. 6024 6025 rcutorture.gp_cond_full= [KNL] 6026 Use conditional/asynchronous update-side 6027 normal-grace-period primitives that also take 6028 concurrent expedited grace periods into account, 6029 if available. 6030 6031 rcutorture.gp_cond_exp_full= [KNL] 6032 Use conditional/asynchronous update-side 6033 expedited-grace-period primitives that also take 6034 concurrent normal grace periods into account, 6035 if available. 6036 6037 rcutorture.gp_cond_wi= [KNL] 6038 Nominal wait interval for normal conditional 6039 grace periods (specified by rcutorture's 6040 gp_cond and gp_cond_full module parameters), 6041 in microseconds. The actual wait interval will 6042 be randomly selected to nanosecond granularity up 6043 to this wait interval. Defaults to 16 jiffies, 6044 for example, 16,000 microseconds on a system 6045 with HZ=1000. 6046 6047 rcutorture.gp_cond_wi_exp= [KNL] 6048 Nominal wait interval for expedited conditional 6049 grace periods (specified by rcutorture's 6050 gp_cond_exp and gp_cond_exp_full module 6051 parameters), in microseconds. The actual wait 6052 interval will be randomly selected to nanosecond 6053 granularity up to this wait interval. Defaults to 6054 128 microseconds. 6055 6056 rcutorture.gp_exp= [KNL] 6057 Use expedited update-side primitives, if available. 6058 6059 rcutorture.gp_normal= [KNL] 6060 Use normal (non-expedited) asynchronous 6061 update-side primitives, if available. 6062 6063 rcutorture.gp_poll= [KNL] 6064 Use polled update-side normal-grace-period 6065 primitives, if available. 6066 6067 rcutorture.gp_poll_exp= [KNL] 6068 Use polled update-side expedited-grace-period 6069 primitives, if available. 6070 6071 rcutorture.gp_poll_full= [KNL] 6072 Use polled update-side normal-grace-period 6073 primitives that also take concurrent expedited 6074 grace periods into account, if available. 6075 6076 rcutorture.gp_poll_exp_full= [KNL] 6077 Use polled update-side expedited-grace-period 6078 primitives that also take concurrent normal 6079 grace periods into account, if available. 6080 6081 rcutorture.gp_poll_wi= [KNL] 6082 Nominal wait interval for normal conditional 6083 grace periods (specified by rcutorture's 6084 gp_poll and gp_poll_full module parameters), 6085 in microseconds. The actual wait interval will 6086 be randomly selected to nanosecond granularity up 6087 to this wait interval. Defaults to 16 jiffies, 6088 for example, 16,000 microseconds on a system 6089 with HZ=1000. 6090 6091 rcutorture.gp_poll_wi_exp= [KNL] 6092 Nominal wait interval for expedited conditional 6093 grace periods (specified by rcutorture's 6094 gp_poll_exp and gp_poll_exp_full module 6095 parameters), in microseconds. The actual wait 6096 interval will be randomly selected to nanosecond 6097 granularity up to this wait interval. Defaults to 6098 128 microseconds. 6099 6100 rcutorture.gp_sync= [KNL] 6101 Use normal (non-expedited) synchronous 6102 update-side primitives, if available. If all 6103 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6104 rcutorture.gp_normal=, and rcutorture.gp_sync= 6105 are zero, rcutorture acts as if is interpreted 6106 they are all non-zero. 6107 6108 rcutorture.gpwrap_lag= [KNL] 6109 Enable grace-period wrap lag testing. Setting 6110 to false prevents the gpwrap lag test from 6111 running. Default is true. 6112 6113 rcutorture.gpwrap_lag_gps= [KNL] 6114 Set the value for grace-period wrap lag during 6115 active lag testing periods. This controls how many 6116 grace periods differences we tolerate between 6117 rdp and rnp's gp_seq before setting overflow flag. 6118 The default is always set to 8. 6119 6120 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6121 Set the total cycle duration for gpwrap lag 6122 testing in minutes. This is the total time for 6123 one complete cycle of active and inactive 6124 testing periods. Default is 30 minutes. 6125 6126 rcutorture.gpwrap_lag_active_mins= [KNL] 6127 Set the duration for which gpwrap lag is active 6128 within each cycle, in minutes. During this time, 6129 the grace-period wrap lag will be set to the 6130 value specified by gpwrap_lag_gps. Default is 6131 5 minutes. 6132 6133 rcutorture.irqreader= [KNL] 6134 Run RCU readers from irq handlers, or, more 6135 accurately, from a timer handler. Not all RCU 6136 flavors take kindly to this sort of thing. 6137 6138 rcutorture.leakpointer= [KNL] 6139 Leak an RCU-protected pointer out of the reader. 6140 This can of course result in splats, and is 6141 intended to test the ability of things like 6142 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6143 such leaks. 6144 6145 rcutorture.n_barrier_cbs= [KNL] 6146 Set callbacks/threads for rcu_barrier() testing. 6147 6148 rcutorture.nfakewriters= [KNL] 6149 Set number of concurrent RCU writers. These just 6150 stress RCU, they don't participate in the actual 6151 test, hence the "fake". 6152 6153 rcutorture.nocbs_nthreads= [KNL] 6154 Set number of RCU callback-offload togglers. 6155 Zero (the default) disables toggling. 6156 6157 rcutorture.nocbs_toggle= [KNL] 6158 Set the delay in milliseconds between successive 6159 callback-offload toggling attempts. 6160 6161 rcutorture.nreaders= [KNL] 6162 Set number of RCU readers. The value -1 selects 6163 N-1, where N is the number of CPUs. A value 6164 "n" less than -1 selects N-n-2, where N is again 6165 the number of CPUs. For example, -2 selects N 6166 (the number of CPUs), -3 selects N+1, and so on. 6167 6168 rcutorture.nwriters= [KNL] 6169 Set number of RCU writers, which must be either 6170 zero or one. For additional writers, use instead 6171 the rcutorture.nfakewriters parameter. 6172 6173 rcutorture.object_debug= [KNL] 6174 Enable debug-object double-call_rcu() testing. 6175 6176 rcutorture.onoff_holdoff= [KNL] 6177 Set time (s) after boot for CPU-hotplug testing. 6178 6179 rcutorture.onoff_interval= [KNL] 6180 Set time (jiffies) between CPU-hotplug operations, 6181 or zero to disable CPU-hotplug testing. 6182 6183 rcutorture.preempt_duration= [KNL] 6184 Set duration (in milliseconds) of preemptions 6185 by a high-priority FIFO real-time task. Set to 6186 zero (the default) to disable. The CPUs to 6187 preempt are selected randomly from the set that 6188 are online at a given point in time. Races with 6189 CPUs going offline are ignored, with that attempt 6190 at preemption skipped. 6191 6192 rcutorture.preempt_interval= [KNL] 6193 Set interval (in milliseconds, defaulting to one 6194 second) between preemptions by a high-priority 6195 FIFO real-time task. This delay is mediated 6196 by an hrtimer and is further fuzzed to avoid 6197 inadvertent synchronizations. 6198 6199 rcutorture.read_exit_burst= [KNL] 6200 The number of times in a given read-then-exit 6201 episode that a set of read-then-exit kthreads 6202 is spawned. 6203 6204 rcutorture.read_exit_delay= [KNL] 6205 The delay, in seconds, between successive 6206 read-then-exit testing episodes. 6207 6208 rcutorture.reader_flavor= [KNL] 6209 A bit mask indicating which readers to use. 6210 If there is more than one bit set, the readers 6211 are entered from low-order bit up, and are 6212 exited in the opposite order. For SRCU, the 6213 0x1 bit is normal readers, 0x2 NMI-safe readers, 6214 and 0x4 light-weight readers. 6215 6216 rcutorture.shuffle_interval= [KNL] 6217 Set task-shuffle interval (s). Shuffling tasks 6218 allows some CPUs to go into dyntick-idle mode 6219 during the rcutorture test. 6220 6221 rcutorture.shutdown_secs= [KNL] 6222 Set time (s) after boot system shutdown. This 6223 is useful for hands-off automated testing. 6224 6225 rcutorture.stall_cpu= [KNL] 6226 Duration of CPU stall (s) to test RCU CPU stall 6227 warnings, zero to disable. 6228 6229 rcutorture.stall_cpu_block= [KNL] 6230 Sleep while stalling if set. This will result 6231 in warnings from preemptible RCU in addition to 6232 any other stall-related activity. Note that 6233 in kernels built with CONFIG_PREEMPTION=n and 6234 CONFIG_PREEMPT_COUNT=y, this parameter will 6235 cause the CPU to pass through a quiescent state. 6236 Given CONFIG_PREEMPTION=n, this will suppress 6237 RCU CPU stall warnings, but will instead result 6238 in scheduling-while-atomic splats. 6239 6240 Use of this module parameter results in splats. 6241 6242 6243 rcutorture.stall_cpu_holdoff= [KNL] 6244 Time to wait (s) after boot before inducing stall. 6245 6246 rcutorture.stall_cpu_irqsoff= [KNL] 6247 Disable interrupts while stalling if set, but only 6248 on the first stall in the set. 6249 6250 rcutorture.stall_cpu_repeat= [KNL] 6251 Number of times to repeat the stall sequence, 6252 so that rcutorture.stall_cpu_repeat=3 will result 6253 in four stall sequences. 6254 6255 rcutorture.stall_gp_kthread= [KNL] 6256 Duration (s) of forced sleep within RCU 6257 grace-period kthread to test RCU CPU stall 6258 warnings, zero to disable. If both stall_cpu 6259 and stall_gp_kthread are specified, the 6260 kthread is starved first, then the CPU. 6261 6262 rcutorture.stall_only= [KNL] 6263 Shut off all rcutorture kthreads other than the 6264 RCU CPU stall-warning test kthreads. The purpose 6265 of this is to test production applictions' 6266 reactions to CPU stalls, and with minimal 6267 additional overhead. Or you can omit the 6268 stall-warning tests as well and get a heavy 6269 no-op, your choice! 6270 6271 rcutorture.stat_interval= [KNL] 6272 Time (s) between statistics printk()s. 6273 6274 rcutorture.stutter= [KNL] 6275 Time (s) to stutter testing, for example, specifying 6276 five seconds causes the test to run for five seconds, 6277 wait for five seconds, and so on. This tests RCU's 6278 ability to transition abruptly to and from idle. 6279 6280 rcutorture.test_boost= [KNL] 6281 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6282 "Maybe" means test if the RCU implementation 6283 under test support RCU priority boosting. 6284 6285 rcutorture.test_boost_duration= [KNL] 6286 Duration (s) of each individual boost test. 6287 6288 rcutorture.test_boost_holdoff= [KNL] 6289 Holdoff time (s) from start of test to the start 6290 of RCU priority-boost testing. Defaults to zero, 6291 that is, no holdoff. 6292 6293 rcutorture.test_boost_interval= [KNL] 6294 Interval (s) between each boost test. 6295 6296 rcutorture.test_no_idle_hz= [KNL] 6297 Test RCU's dyntick-idle handling. See also the 6298 rcutorture.shuffle_interval parameter. 6299 6300 rcutorture.torture_type= [KNL] 6301 Specify the RCU implementation to test. 6302 6303 rcutorture.verbose= [KNL] 6304 Enable additional printk() statements. 6305 6306 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6307 Dump ftrace buffer after reporting RCU CPU 6308 stall warning. 6309 6310 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6311 Provide RCU CPU stall notifiers, but see the 6312 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6313 option's help text. TL;DR: You almost certainly 6314 do not want rcupdate.rcu_cpu_stall_notifiers. 6315 6316 rcupdate.rcu_cpu_stall_suppress= [KNL] 6317 Suppress RCU CPU stall warning messages. 6318 6319 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6320 Suppress RCU CPU stall warning messages and 6321 rcutorture writer stall warnings that occur 6322 during early boot, that is, during the time 6323 before the init task is spawned. 6324 6325 rcupdate.rcu_cpu_stall_timeout= [KNL] 6326 Set timeout for RCU CPU stall warning messages. 6327 The value is in seconds and the maximum allowed 6328 value is 300 seconds. 6329 6330 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6331 Set timeout for expedited RCU CPU stall warning 6332 messages. The value is in milliseconds 6333 and the maximum allowed value is 21000 6334 milliseconds. Please note that this value is 6335 adjusted to an arch timer tick resolution. 6336 Setting this to zero causes the value from 6337 rcupdate.rcu_cpu_stall_timeout to be used (after 6338 conversion from seconds to milliseconds). 6339 6340 rcupdate.rcu_cpu_stall_cputime= [KNL] 6341 Provide statistics on the cputime and count of 6342 interrupts and tasks during the sampling period. For 6343 multiple continuous RCU stalls, all sampling periods 6344 begin at half of the first RCU stall timeout. 6345 6346 rcupdate.rcu_exp_stall_task_details= [KNL] 6347 Print stack dumps of any tasks blocking the 6348 current expedited RCU grace period during an 6349 expedited RCU CPU stall warning. 6350 6351 rcupdate.rcu_expedited= [KNL] 6352 Use expedited grace-period primitives, for 6353 example, synchronize_rcu_expedited() instead 6354 of synchronize_rcu(). This reduces latency, 6355 but can increase CPU utilization, degrade 6356 real-time latency, and degrade energy efficiency. 6357 No effect on CONFIG_TINY_RCU kernels. 6358 6359 rcupdate.rcu_normal= [KNL] 6360 Use only normal grace-period primitives, 6361 for example, synchronize_rcu() instead of 6362 synchronize_rcu_expedited(). This improves 6363 real-time latency, CPU utilization, and 6364 energy efficiency, but can expose users to 6365 increased grace-period latency. This parameter 6366 overrides rcupdate.rcu_expedited. No effect on 6367 CONFIG_TINY_RCU kernels. 6368 6369 rcupdate.rcu_normal_after_boot= [KNL] 6370 Once boot has completed (that is, after 6371 rcu_end_inkernel_boot() has been invoked), use 6372 only normal grace-period primitives. No effect 6373 on CONFIG_TINY_RCU kernels. 6374 6375 But note that CONFIG_PREEMPT_RT=y kernels enables 6376 this kernel boot parameter, forcibly setting 6377 it to the value one, that is, converting any 6378 post-boot attempt at an expedited RCU grace 6379 period to instead use normal non-expedited 6380 grace-period processing. 6381 6382 rcupdate.rcu_task_collapse_lim= [KNL] 6383 Set the maximum number of callbacks present 6384 at the beginning of a grace period that allows 6385 the RCU Tasks flavors to collapse back to using 6386 a single callback queue. This switching only 6387 occurs when rcupdate.rcu_task_enqueue_lim is 6388 set to the default value of -1. 6389 6390 rcupdate.rcu_task_contend_lim= [KNL] 6391 Set the minimum number of callback-queuing-time 6392 lock-contention events per jiffy required to 6393 cause the RCU Tasks flavors to switch to per-CPU 6394 callback queuing. This switching only occurs 6395 when rcupdate.rcu_task_enqueue_lim is set to 6396 the default value of -1. 6397 6398 rcupdate.rcu_task_enqueue_lim= [KNL] 6399 Set the number of callback queues to use for the 6400 RCU Tasks family of RCU flavors. The default 6401 of -1 allows this to be automatically (and 6402 dynamically) adjusted. This parameter is intended 6403 for use in testing. 6404 6405 rcupdate.rcu_task_lazy_lim= [KNL] 6406 Number of callbacks on a given CPU that will 6407 cancel laziness on that CPU. Use -1 to disable 6408 cancellation of laziness, but be advised that 6409 doing so increases the danger of OOM due to 6410 callback flooding. 6411 6412 rcupdate.rcu_task_stall_info= [KNL] 6413 Set initial timeout in jiffies for RCU task stall 6414 informational messages, which give some indication 6415 of the problem for those not patient enough to 6416 wait for ten minutes. Informational messages are 6417 only printed prior to the stall-warning message 6418 for a given grace period. Disable with a value 6419 less than or equal to zero. Defaults to ten 6420 seconds. A change in value does not take effect 6421 until the beginning of the next grace period. 6422 6423 rcupdate.rcu_task_stall_info_mult= [KNL] 6424 Multiplier for time interval between successive 6425 RCU task stall informational messages for a given 6426 RCU tasks grace period. This value is clamped 6427 to one through ten, inclusive. It defaults to 6428 the value three, so that the first informational 6429 message is printed 10 seconds into the grace 6430 period, the second at 40 seconds, the third at 6431 160 seconds, and then the stall warning at 600 6432 seconds would prevent a fourth at 640 seconds. 6433 6434 rcupdate.rcu_task_stall_timeout= [KNL] 6435 Set timeout in jiffies for RCU task stall 6436 warning messages. Disable with a value less 6437 than or equal to zero. Defaults to ten minutes. 6438 A change in value does not take effect until 6439 the beginning of the next grace period. 6440 6441 rcupdate.rcu_tasks_lazy_ms= [KNL] 6442 Set timeout in milliseconds RCU Tasks asynchronous 6443 callback batching for call_rcu_tasks(). 6444 A negative value will take the default. A value 6445 of zero will disable batching. Batching is 6446 always disabled for synchronize_rcu_tasks(). 6447 6448 rcupdate.rcu_self_test= [KNL] 6449 Run the RCU early boot self tests 6450 6451 rdinit= [KNL] 6452 Format: <full_path> 6453 Run specified binary instead of /init from the ramdisk, 6454 used for early userspace startup. See initrd. 6455 6456 rdrand= [X86,EARLY] 6457 force - Override the decision by the kernel to hide the 6458 advertisement of RDRAND support (this affects 6459 certain AMD processors because of buggy BIOS 6460 support, specifically around the suspend/resume 6461 path). 6462 6463 rdt= [HW,X86,RDT] 6464 Turn on/off individual RDT features. List is: 6465 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6466 mba, smba, bmec, abmc, sdciae, energy[:guid], 6467 perf[:guid]. 6468 E.g. to turn on cmt and turn off mba use: 6469 rdt=cmt,!mba 6470 To turn off all energy telemetry monitoring and ensure that 6471 perf telemetry monitoring associated with guid 0x12345 6472 is enabled use: 6473 rdt=!energy,perf:0x12345 6474 6475 reboot= [KNL] 6476 Format (x86 or x86_64): 6477 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6478 [[,]s[mp]####] \ 6479 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6480 [[,]f[orce]] 6481 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6482 (prefix with 'panic_' to set mode for panic 6483 reboot only), 6484 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6485 reboot_force is either force or not specified, 6486 reboot_cpu is s[mp]#### with #### being the processor 6487 to be used for rebooting. 6488 6489 acpi 6490 Use the ACPI RESET_REG in the FADT. If ACPI is not 6491 configured or the ACPI reset does not work, the reboot 6492 path attempts the reset using the keyboard controller. 6493 6494 bios 6495 Use the CPU reboot vector for warm reset 6496 6497 cold 6498 Set the cold reboot flag 6499 6500 default 6501 There are some built-in platform specific "quirks" 6502 - you may see: "reboot: <name> series board detected. 6503 Selecting <type> for reboots." In the case where you 6504 think the quirk is in error (e.g. you have newer BIOS, 6505 or newer board) using this option will ignore the 6506 built-in quirk table, and use the generic default 6507 reboot actions. 6508 6509 efi 6510 Use efi reset_system runtime service. If EFI is not 6511 configured or the EFI reset does not work, the reboot 6512 path attempts the reset using the keyboard controller. 6513 6514 force 6515 Don't stop other CPUs on reboot. This can make reboot 6516 more reliable in some cases. 6517 6518 kbd 6519 Use the keyboard controller. cold reset (default) 6520 6521 pci 6522 Use a write to the PCI config space register 0xcf9 to 6523 trigger reboot. 6524 6525 triple 6526 Force a triple fault (init) 6527 6528 warm 6529 Don't set the cold reboot flag 6530 6531 Using warm reset will be much faster especially on big 6532 memory systems because the BIOS will not go through 6533 the memory check. Disadvantage is that not all 6534 hardware will be completely reinitialized on reboot so 6535 there may be boot problems on some systems. 6536 6537 6538 refscale.holdoff= [KNL] 6539 Set test-start holdoff period. The purpose of 6540 this parameter is to delay the start of the 6541 test until boot completes in order to avoid 6542 interference. 6543 6544 refscale.lookup_instances= [KNL] 6545 Number of data elements to use for the forms of 6546 SLAB_TYPESAFE_BY_RCU testing. A negative number 6547 is negated and multiplied by nr_cpu_ids, while 6548 zero specifies nr_cpu_ids. 6549 6550 refscale.loops= [KNL] 6551 Set the number of loops over the synchronization 6552 primitive under test. Increasing this number 6553 reduces noise due to loop start/end overhead, 6554 but the default has already reduced the per-pass 6555 noise to a handful of picoseconds on ca. 2020 6556 x86 laptops. 6557 6558 refscale.nreaders= [KNL] 6559 Set number of readers. The default value of -1 6560 selects N, where N is roughly 75% of the number 6561 of CPUs. A value of zero is an interesting choice. 6562 6563 refscale.nruns= [KNL] 6564 Set number of runs, each of which is dumped onto 6565 the console log. 6566 6567 refscale.readdelay= [KNL] 6568 Set the read-side critical-section duration, 6569 measured in microseconds. 6570 6571 refscale.scale_type= [KNL] 6572 Specify the read-protection implementation to test. 6573 6574 refscale.shutdown= [KNL] 6575 Shut down the system at the end of the performance 6576 test. This defaults to 1 (shut it down) when 6577 refscale is built into the kernel and to 0 (leave 6578 it running) when refscale is built as a module. 6579 6580 refscale.verbose= [KNL] 6581 Enable additional printk() statements. 6582 6583 refscale.verbose_batched= [KNL] 6584 Batch the additional printk() statements. If zero 6585 (the default) or negative, print everything. Otherwise, 6586 print every Nth verbose statement, where N is the value 6587 specified. 6588 6589 regulator_ignore_unused 6590 [REGULATOR] 6591 Prevents regulator framework from disabling regulators 6592 that are unused, due no driver claiming them. This may 6593 be useful for debug and development, but should not be 6594 needed on a platform with proper driver support. 6595 6596 relax_domain_level= 6597 [KNL, SMP] Set scheduler's default relax_domain_level. 6598 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6599 6600 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6601 Format: <base1>,<size1>[,<base2>,<size2>,...] 6602 Reserve I/O ports or memory so the kernel won't use 6603 them. If <base> is less than 0x10000, the region 6604 is assumed to be I/O ports; otherwise it is memory. 6605 6606 reserve_mem= [RAM] 6607 Format: nn[KMG]:<align>:<label> 6608 Reserve physical memory and label it with a name that 6609 other subsystems can use to access it. This is typically 6610 used for systems that do not wipe the RAM, and this command 6611 line will try to reserve the same physical memory on 6612 soft reboots. Note, it is not guaranteed to be the same 6613 location. For example, if anything about the system changes 6614 or if booting a different kernel. It can also fail if KASLR 6615 places the kernel at the location of where the RAM reservation 6616 was from a previous boot, the new reservation will be at a 6617 different location. 6618 Any subsystem using this feature must add a way to verify 6619 that the contents of the physical memory is from a previous 6620 boot, as there may be cases where the memory will not be 6621 located at the same location. 6622 6623 The format is size:align:label for example, to request 6624 12 megabytes of 4096 alignment for ramoops: 6625 6626 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6627 6628 reservetop= [X86-32,EARLY] 6629 Format: nn[KMG] 6630 Reserves a hole at the top of the kernel virtual 6631 address space. 6632 6633 reset_devices [KNL] Force drivers to reset the underlying device 6634 during initialization. 6635 6636 resume= [SWSUSP] 6637 Specify the partition device for software suspend 6638 Format: 6639 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6640 6641 resume_offset= [SWSUSP] 6642 Specify the offset from the beginning of the partition 6643 given by "resume=" at which the swap header is located, 6644 in <PAGE_SIZE> units (needed only for swap files). 6645 See Documentation/power/swsusp-and-swap-files.rst 6646 6647 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6648 read the resume files 6649 6650 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6651 Useful for devices that are detected asynchronously 6652 (e.g. USB and MMC devices). 6653 6654 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6655 be accessible via /sys/firmware/initrd. 6656 6657 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6658 Speculative Code Execution with Return Instructions) 6659 vulnerability. 6660 6661 AMD-based UNRET and IBPB mitigations alone do not stop 6662 sibling threads from influencing the predictions of other 6663 sibling threads. For that reason, STIBP is used on pro- 6664 cessors that support it, and mitigate SMT on processors 6665 that don't. 6666 6667 off - no mitigation 6668 auto - automatically select a mitigation 6669 auto,nosmt - automatically select a mitigation, 6670 disabling SMT if necessary for 6671 the full mitigation (only on Zen1 6672 and older without STIBP). 6673 ibpb - On AMD, mitigate short speculation 6674 windows on basic block boundaries too. 6675 Safe, highest perf impact. It also 6676 enables STIBP if present. Not suitable 6677 on Intel. 6678 ibpb,nosmt - Like "ibpb" above but will disable SMT 6679 when STIBP is not available. This is 6680 the alternative for systems which do not 6681 have STIBP. 6682 unret - Force enable untrained return thunks, 6683 only effective on AMD f15h-f17h based 6684 systems. 6685 unret,nosmt - Like unret, but will disable SMT when STIBP 6686 is not available. This is the alternative for 6687 systems which do not have STIBP. 6688 6689 Selecting 'auto' will choose a mitigation method at run 6690 time according to the CPU. 6691 6692 Not specifying this option is equivalent to retbleed=auto. 6693 6694 rfkill.default_state= 6695 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6696 etc. communication is blocked by default. 6697 1 Unblocked. 6698 6699 rfkill.master_switch_mode= 6700 0 The "airplane mode" button does nothing. 6701 1 The "airplane mode" button toggles between everything 6702 blocked and the previous configuration. 6703 2 The "airplane mode" button toggles between everything 6704 blocked and everything unblocked. 6705 6706 ring3mwait=disable 6707 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6708 CPUs. 6709 6710 riscv_isa_fallback [RISCV,EARLY] 6711 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6712 falling back to detecting extension support by parsing 6713 "riscv,isa" property on devicetree systems when the 6714 replacement properties are not found. See the Kconfig 6715 entry for RISCV_ISA_FALLBACK. 6716 6717 riscv_nousercfi= 6718 all Disable user CFI ABI to userspace even if cpu extension 6719 are available. 6720 bcfi Disable user backward CFI ABI to userspace even if 6721 the shadow stack extension is available. 6722 fcfi Disable user forward CFI ABI to userspace even if the 6723 landing pad extension is available. 6724 6725 ro [KNL] Mount root device read-only on boot 6726 6727 rodata= [KNL,EARLY] 6728 on Mark read-only kernel memory as read-only (default). 6729 off Leave read-only kernel memory writable for debugging. 6730 noalias Mark read-only kernel memory as read-only but retain 6731 writable aliases in the direct map for regions outside 6732 of the kernel image. [arm64] 6733 6734 rockchip.usb_uart 6735 [EARLY] 6736 Enable the uart passthrough on the designated usb port 6737 on Rockchip SoCs. When active, the signals of the 6738 debug-uart get routed to the D+ and D- pins of the usb 6739 port and the regular usb controller gets disabled. 6740 6741 root= [KNL] Root filesystem 6742 Usually this is a block device specifier of some kind, 6743 see the early_lookup_bdev comment in 6744 block/early-lookup.c for details. 6745 Alternatively this can be "ram" for the legacy initial 6746 ramdisk, "nfs" and "cifs" for root on a network file 6747 system, or "mtd" and "ubi" for mounting from raw flash. 6748 6749 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6750 mount the root filesystem 6751 6752 rootflags= [KNL] Set root filesystem mount option string 6753 6754 rseq_slice_ext= [KNL] RSEQ based time slice extension 6755 Format: boolean 6756 Control enablement of RSEQ based time slice extension. 6757 Default is 'on'. 6758 6759 initramfs_options= [KNL] 6760 Specify mount options for the initramfs mount. 6761 6762 rootfstype= [KNL] Set root filesystem type 6763 6764 rootwait [KNL] Wait (indefinitely) for root device to show up. 6765 Useful for devices that are detected asynchronously 6766 (e.g. USB and MMC devices). 6767 6768 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6769 to show up before attempting to mount the root 6770 filesystem. 6771 6772 rproc_mem=nn[KMG][@address] 6773 [KNL,ARM,CMA] Remoteproc physical memory block. 6774 Memory area to be used by remote processor image, 6775 managed by CMA. 6776 6777 rseq_debug= [KNL] Enable or disable restartable sequence 6778 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6779 Format: <bool> 6780 6781 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6782 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6783 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6784 Format: <bool> 6785 6786 rw [KNL] Mount root device read-write on boot 6787 6788 S [KNL] Run init in single mode 6789 6790 s390_iommu= [HW,S390] 6791 Set s390 IOTLB flushing mode 6792 strict 6793 With strict flushing every unmap operation will result 6794 in an IOTLB flush. Default is lazy flushing before 6795 reuse, which is faster. Deprecated, equivalent to 6796 iommu.strict=1. 6797 6798 s390_iommu_aperture= [KNL,S390] 6799 Specifies the size of the per device DMA address space 6800 accessible through the DMA and IOMMU APIs as a decimal 6801 factor of the size of main memory. 6802 The default is 1 meaning that one can concurrently use 6803 as many DMA addresses as physical memory is installed, 6804 if supported by hardware, and thus map all of memory 6805 once. With a value of 2 one can map all of memory twice 6806 and so on. As a special case a factor of 0 imposes no 6807 restrictions other than those given by hardware at the 6808 cost of significant additional memory use for tables. 6809 6810 6811 sched_proxy_exec= [KNL] 6812 Enables or disables "proxy execution" style 6813 solution to mutex-based priority inversion. 6814 Format: <bool> 6815 6816 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6817 6818 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6819 Allowed values are enable and disable. This feature 6820 incurs a small amount of overhead in the scheduler 6821 but is useful for debugging and performance tuning. 6822 6823 sched_thermal_decay_shift= 6824 [Deprecated] 6825 [KNL, SMP] Set a decay shift for scheduler thermal 6826 pressure signal. Thermal pressure signal follows the 6827 default decay period of other scheduler pelt 6828 signals(usually 32 ms but configurable). Setting 6829 sched_thermal_decay_shift will left shift the decay 6830 period for the thermal pressure signal by the shift 6831 value. 6832 i.e. with the default pelt decay period of 32 ms 6833 sched_thermal_decay_shift thermal pressure decay pr 6834 1 64 ms 6835 2 128 ms 6836 and so on. 6837 Format: integer between 0 and 10 6838 Default is 0. 6839 6840 scftorture.holdoff= [KNL] 6841 Number of seconds to hold off before starting 6842 test. Defaults to zero for module insertion and 6843 to 10 seconds for built-in smp_call_function() 6844 tests. 6845 6846 scftorture.longwait= [KNL] 6847 Request ridiculously long waits randomly selected 6848 up to the chosen limit in seconds. Zero (the 6849 default) disables this feature. Please note 6850 that requesting even small non-zero numbers of 6851 seconds can result in RCU CPU stall warnings, 6852 softlockup complaints, and so on. 6853 6854 scftorture.nthreads= [KNL] 6855 Number of kthreads to spawn to invoke the 6856 smp_call_function() family of functions. 6857 The default of -1 specifies a number of kthreads 6858 equal to the number of CPUs. 6859 6860 scftorture.onoff_holdoff= [KNL] 6861 Number seconds to wait after the start of the 6862 test before initiating CPU-hotplug operations. 6863 6864 scftorture.onoff_interval= [KNL] 6865 Number seconds to wait between successive 6866 CPU-hotplug operations. Specifying zero (which 6867 is the default) disables CPU-hotplug operations. 6868 6869 scftorture.shutdown_secs= [KNL] 6870 The number of seconds following the start of the 6871 test after which to shut down the system. The 6872 default of zero avoids shutting down the system. 6873 Non-zero values are useful for automated tests. 6874 6875 scftorture.stat_interval= [KNL] 6876 The number of seconds between outputting the 6877 current test statistics to the console. A value 6878 of zero disables statistics output. 6879 6880 scftorture.stutter_cpus= [KNL] 6881 The number of jiffies to wait between each change 6882 to the set of CPUs under test. 6883 6884 scftorture.use_cpus_read_lock= [KNL] 6885 Use use_cpus_read_lock() instead of the default 6886 preempt_disable() to disable CPU hotplug 6887 while invoking one of the smp_call_function*() 6888 functions. 6889 6890 scftorture.verbose= [KNL] 6891 Enable additional printk() statements. 6892 6893 scftorture.weight_single= [KNL] 6894 The probability weighting to use for the 6895 smp_call_function_single() function with a zero 6896 "wait" parameter. A value of -1 selects the 6897 default if all other weights are -1. However, 6898 if at least one weight has some other value, a 6899 value of -1 will instead select a weight of zero. 6900 6901 scftorture.weight_single_wait= [KNL] 6902 The probability weighting to use for the 6903 smp_call_function_single() function with a 6904 non-zero "wait" parameter. See weight_single. 6905 6906 scftorture.weight_many= [KNL] 6907 The probability weighting to use for the 6908 smp_call_function_many() function with a zero 6909 "wait" parameter. See weight_single. 6910 Note well that setting a high probability for 6911 this weighting can place serious IPI load 6912 on the system. 6913 6914 scftorture.weight_many_wait= [KNL] 6915 The probability weighting to use for the 6916 smp_call_function_many() function with a 6917 non-zero "wait" parameter. See weight_single 6918 and weight_many. 6919 6920 scftorture.weight_all= [KNL] 6921 The probability weighting to use for the 6922 smp_call_function_all() function with a zero 6923 "wait" parameter. See weight_single and 6924 weight_many. 6925 6926 scftorture.weight_all_wait= [KNL] 6927 The probability weighting to use for the 6928 smp_call_function_all() function with a 6929 non-zero "wait" parameter. See weight_single 6930 and weight_many. 6931 6932 sdw_mclk_divider=[SDW] 6933 Specify the MCLK divider for Intel SoundWire buses in 6934 case the BIOS does not provide the clock rate properly. 6935 6936 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6937 xtime_lock contention on larger systems, and/or RCU lock 6938 contention on all systems with CONFIG_MAXSMP set. 6939 Format: { "0" | "1" } 6940 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1") 6941 1 -- enable. 6942 Note: increases power consumption, thus should only be 6943 enabled if running jitter sensitive (HPC/RT) workloads. 6944 6945 security= [SECURITY] Choose a legacy "major" security module to 6946 enable at boot. This has been deprecated by the 6947 "lsm=" parameter. 6948 6949 selinux= [SELINUX] Disable or enable SELinux at boot time. 6950 Format: { "0" | "1" } 6951 See security/selinux/Kconfig help text. 6952 0 -- disable. 6953 1 -- enable. 6954 Default value is 1. 6955 6956 serialnumber [BUGS=X86-32] 6957 6958 sev=option[,option...] [X86-64] 6959 6960 debug 6961 Enable debug messages. 6962 6963 nosnp 6964 Do not enable SEV-SNP (applies to host/hypervisor 6965 only). Setting 'nosnp' avoids the RMP check overhead 6966 in memory accesses when users do not want to run 6967 SEV-SNP guests. 6968 6969 shapers= [NET] 6970 Maximal number of shapers. 6971 6972 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6973 Limit apic dumping. The parameter defines the maximal 6974 number of local apics being dumped. Also it is possible 6975 to set it to "all" by meaning -- no limit here. 6976 Format: { 1 (default) | 2 | ... | all }. 6977 The parameter valid if only apic=debug or 6978 apic=verbose is specified. 6979 Example: apic=debug show_lapic=all 6980 6981 slab_debug[=options[,slabs][;[options[,slabs]]...]] [MM] 6982 Enabling slab_debug allows one to determine the 6983 culprit if slab objects become corrupted. Enabling 6984 slab_debug can create guard zones around objects and 6985 may poison objects when not in use. Also tracks the 6986 last alloc / free. For more information see 6987 Documentation/admin-guide/mm/slab.rst. 6988 (slub_debug legacy name also accepted for now) 6989 6990 Using this option implies the "no_hash_pointers" 6991 option which can be undone by adding the 6992 "hash_pointers=always" option. 6993 6994 slab_max_order= [MM] 6995 Determines the maximum allowed order for slabs. 6996 A high setting may cause OOMs due to memory 6997 fragmentation. For more information see 6998 Documentation/admin-guide/mm/slab.rst. 6999 (slub_max_order legacy name also accepted for now) 7000 7001 slab_merge [MM] 7002 Enable merging of slabs with similar size when the 7003 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 7004 (slub_merge legacy name also accepted for now) 7005 7006 slab_min_objects= [MM] 7007 The minimum number of objects per slab. SLUB will 7008 increase the slab order up to slab_max_order to 7009 generate a sufficiently large slab able to contain 7010 the number of objects indicated. The higher the number 7011 of objects the smaller the overhead of tracking slabs 7012 and the less frequently locks need to be acquired. 7013 For more information see 7014 Documentation/admin-guide/mm/slab.rst. 7015 (slub_min_objects legacy name also accepted for now) 7016 7017 slab_min_order= [MM] 7018 Determines the minimum page order for slabs. Must be 7019 lower or equal to slab_max_order. For more information see 7020 Documentation/admin-guide/mm/slab.rst. 7021 (slub_min_order legacy name also accepted for now) 7022 7023 slab_nomerge [MM] 7024 Disable merging of slabs with similar size. May be 7025 necessary if there is some reason to distinguish 7026 allocs to different slabs, especially in hardened 7027 environments where the risk of heap overflows and 7028 layout control by attackers can usually be 7029 frustrated by disabling merging. This will reduce 7030 most of the exposure of a heap attack to a single 7031 cache (risks via metadata attacks are mostly 7032 unchanged). Debug options disable merging on their 7033 own. 7034 For more information see 7035 Documentation/admin-guide/mm/slab.rst. 7036 (slub_nomerge legacy name also accepted for now) 7037 7038 slab_strict_numa [MM] 7039 Support memory policies on a per object level 7040 in the slab allocator. The default is for memory 7041 policies to be applied at the folio level when 7042 a new folio is needed or a partial folio is 7043 retrieved from the lists. Increases overhead 7044 in the slab fastpaths but gains more accurate 7045 NUMA kernel object placement which helps with slow 7046 interconnects in NUMA systems. 7047 7048 slram= [HW,MTD] 7049 7050 smart2= [HW] 7051 Format: <io1>[,<io2>[,...,<io8>]] 7052 7053 smp.csd_lock_timeout= [KNL] 7054 Specify the period of time in milliseconds 7055 that smp_call_function() and friends will wait 7056 for a CPU to release the CSD lock. This is 7057 useful when diagnosing bugs involving CPUs 7058 disabling interrupts for extended periods 7059 of time. Defaults to 5,000 milliseconds, and 7060 setting a value of zero disables this feature. 7061 This feature may be more efficiently disabled 7062 using the csdlock_debug- kernel parameter. 7063 7064 smp.panic_on_ipistall= [KNL] 7065 If a csd_lock_timeout extends for more than 7066 the specified number of milliseconds, panic the 7067 system. By default, let CSD-lock acquisition 7068 take as long as they take. Specifying 300,000 7069 for this value provides a 5-minute timeout. 7070 7071 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7072 (logical CPUs) to use per physical CPU on systems 7073 capable of symmetric multithreading (SMT). Will 7074 be capped to the actual hardware limit. 7075 Format: <integer> 7076 Default: -1 (no limit) 7077 7078 softlockup_panic= 7079 [KNL] Should the soft-lockup detector generate panics. 7080 Format: <int> 7081 7082 A value of non-zero instructs the soft-lockup detector 7083 to panic the machine when a soft-lockup duration exceeds 7084 N thresholds. It is also controlled by the kernel.softlockup_panic 7085 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7086 respective build-time switch to that functionality. 7087 7088 softlockup_all_cpu_backtrace= 7089 [KNL] Should the soft-lockup detector generate 7090 backtraces on all cpus. 7091 Format: 0 | 1 7092 7093 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7094 See Documentation/admin-guide/laptops/sonypi.rst 7095 7096 spectre_bhi= [X86] Control mitigation of Branch History Injection 7097 (BHI) vulnerability. This setting affects the 7098 deployment of the HW BHI control and the SW BHB 7099 clearing sequence. 7100 7101 on - (default) Enable the HW or SW mitigation as 7102 needed. This protects the kernel from 7103 both syscalls and VMs. 7104 vmexit - On systems which don't have the HW mitigation 7105 available, enable the SW mitigation on vmexit 7106 ONLY. On such systems, the host kernel is 7107 protected from VM-originated BHI attacks, but 7108 may still be vulnerable to syscall attacks. 7109 off - Disable the mitigation. 7110 7111 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7112 (indirect branch speculation) vulnerability. 7113 The default operation protects the kernel from 7114 user space attacks. 7115 7116 on - unconditionally enable, implies 7117 spectre_v2_user=on 7118 off - unconditionally disable, implies 7119 spectre_v2_user=off 7120 auto - kernel detects whether your CPU model is 7121 vulnerable 7122 7123 Selecting 'on' will, and 'auto' may, choose a 7124 mitigation method at run time according to the 7125 CPU, the available microcode, the setting of the 7126 CONFIG_MITIGATION_RETPOLINE configuration option, 7127 and the compiler with which the kernel was built. 7128 7129 Selecting 'on' will also enable the mitigation 7130 against user space to user space task attacks. 7131 Selecting specific mitigation does not force enable 7132 user mitigations. 7133 7134 Selecting 'off' will disable both the kernel and 7135 the user space protections. 7136 7137 Specific mitigations can also be selected manually: 7138 7139 retpoline - replace indirect branches 7140 retpoline,generic - Retpolines 7141 retpoline,lfence - LFENCE; indirect branch 7142 retpoline,amd - alias for retpoline,lfence 7143 eibrs - Enhanced/Auto IBRS 7144 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7145 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7146 ibrs - use IBRS to protect kernel 7147 7148 Not specifying this option is equivalent to 7149 spectre_v2=auto. 7150 7151 spectre_v2_user= 7152 [X86] Control mitigation of Spectre variant 2 7153 (indirect branch speculation) vulnerability between 7154 user space tasks 7155 7156 on - Unconditionally enable mitigations. Is 7157 enforced by spectre_v2=on 7158 7159 off - Unconditionally disable mitigations. Is 7160 enforced by spectre_v2=off 7161 7162 prctl - Indirect branch speculation is enabled, 7163 but mitigation can be enabled via prctl 7164 per thread. The mitigation control state 7165 is inherited on fork. 7166 7167 prctl,ibpb 7168 - Like "prctl" above, but only STIBP is 7169 controlled per thread. IBPB is issued 7170 always when switching between different user 7171 space processes. 7172 7173 seccomp 7174 - Same as "prctl" above, but all seccomp 7175 threads will enable the mitigation unless 7176 they explicitly opt out. 7177 7178 seccomp,ibpb 7179 - Like "seccomp" above, but only STIBP is 7180 controlled per thread. IBPB is issued 7181 always when switching between different 7182 user space processes. 7183 7184 auto - Kernel selects the mitigation depending on 7185 the available CPU features and vulnerability. 7186 7187 Default mitigation: "prctl" 7188 7189 Not specifying this option is equivalent to 7190 spectre_v2_user=auto. 7191 7192 spec_rstack_overflow= 7193 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7194 7195 off - Disable mitigation 7196 microcode - Enable microcode mitigation only 7197 safe-ret - Enable sw-only safe RET mitigation (default) 7198 ibpb - Enable mitigation by issuing IBPB on 7199 kernel entry 7200 ibpb-vmexit - Issue IBPB only on VMEXIT 7201 (cloud-specific mitigation) 7202 7203 spec_store_bypass_disable= 7204 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7205 (Speculative Store Bypass vulnerability) 7206 7207 Certain CPUs are vulnerable to an exploit against a 7208 a common industry wide performance optimization known 7209 as "Speculative Store Bypass" in which recent stores 7210 to the same memory location may not be observed by 7211 later loads during speculative execution. The idea 7212 is that such stores are unlikely and that they can 7213 be detected prior to instruction retirement at the 7214 end of a particular speculation execution window. 7215 7216 In vulnerable processors, the speculatively forwarded 7217 store can be used in a cache side channel attack, for 7218 example to read memory to which the attacker does not 7219 directly have access (e.g. inside sandboxed code). 7220 7221 This parameter controls whether the Speculative Store 7222 Bypass optimization is used. 7223 7224 On x86 the options are: 7225 7226 on - Unconditionally disable Speculative Store Bypass 7227 off - Unconditionally enable Speculative Store Bypass 7228 auto - Kernel detects whether the CPU model contains an 7229 implementation of Speculative Store Bypass and 7230 picks the most appropriate mitigation. If the 7231 CPU is not vulnerable, "off" is selected. If the 7232 CPU is vulnerable the default mitigation is 7233 architecture and Kconfig dependent. See below. 7234 prctl - Control Speculative Store Bypass per thread 7235 via prctl. Speculative Store Bypass is enabled 7236 for a process by default. The state of the control 7237 is inherited on fork. 7238 seccomp - Same as "prctl" above, but all seccomp threads 7239 will disable SSB unless they explicitly opt out. 7240 7241 Default mitigations: 7242 X86: "prctl" 7243 7244 On powerpc the options are: 7245 7246 on,auto - On Power8 and Power9 insert a store-forwarding 7247 barrier on kernel entry and exit. On Power7 7248 perform a software flush on kernel entry and 7249 exit. 7250 off - No action. 7251 7252 Not specifying this option is equivalent to 7253 spec_store_bypass_disable=auto. 7254 7255 split_llc= 7256 [X86,EARLY] Split the LLC N-ways 7257 7258 When set, the LLC is split this many ways by matching 7259 'core_id % n'. This is setup before SMP bringup and 7260 used during SMP bringup before it knows the full 7261 topology. If your core count doesn't nicely divide by 7262 the number given, you get to keep the pieces. 7263 7264 This is mostly a debug feature to emulate multiple LLCs 7265 on hardware that only have a single LLC. 7266 7267 split_lock_detect= 7268 [X86] Enable split lock detection or bus lock detection 7269 7270 When enabled (and if hardware support is present), atomic 7271 instructions that access data across cache line 7272 boundaries will result in an alignment check exception 7273 for split lock detection or a debug exception for 7274 bus lock detection. 7275 7276 off - not enabled 7277 7278 warn - the kernel will emit rate-limited warnings 7279 about applications triggering the #AC 7280 exception or the #DB exception. This mode is 7281 the default on CPUs that support split lock 7282 detection or bus lock detection. Default 7283 behavior is by #AC if both features are 7284 enabled in hardware. 7285 7286 fatal - the kernel will send SIGBUS to applications 7287 that trigger the #AC exception or the #DB 7288 exception. Default behavior is by #AC if 7289 both features are enabled in hardware. 7290 7291 ratelimit:N - 7292 Set system wide rate limit to N bus locks 7293 per second for bus lock detection. 7294 0 < N <= 1000. 7295 7296 N/A for split lock detection. 7297 7298 7299 If an #AC exception is hit in the kernel or in 7300 firmware (i.e. not while executing in user mode) 7301 the kernel will oops in either "warn" or "fatal" 7302 mode. 7303 7304 #DB exception for bus lock is triggered only when 7305 CPL > 0. 7306 7307 srbds= [X86,INTEL,EARLY] 7308 Control the Special Register Buffer Data Sampling 7309 (SRBDS) mitigation. 7310 7311 Certain CPUs are vulnerable to an MDS-like 7312 exploit which can leak bits from the random 7313 number generator. 7314 7315 By default, this issue is mitigated by 7316 microcode. However, the microcode fix can cause 7317 the RDRAND and RDSEED instructions to become 7318 much slower. Among other effects, this will 7319 result in reduced throughput from /dev/urandom. 7320 7321 The microcode mitigation can be disabled with 7322 the following option: 7323 7324 off: Disable mitigation and remove 7325 performance impact to RDRAND and RDSEED 7326 7327 srcutree.big_cpu_lim [KNL] 7328 Specifies the number of CPUs constituting a 7329 large system, such that srcu_struct structures 7330 should immediately allocate an srcu_node array. 7331 This kernel-boot parameter defaults to 128, 7332 but takes effect only when the low-order four 7333 bits of srcutree.convert_to_big is equal to 3 7334 (decide at boot). 7335 7336 srcutree.convert_to_big [KNL] 7337 Specifies under what conditions an SRCU tree 7338 srcu_struct structure will be converted to big 7339 form, that is, with an rcu_node tree: 7340 7341 0: Never. 7342 1: At init_srcu_struct() time. 7343 2: When rcutorture decides to. 7344 3: Decide at boot time (default). 7345 0x1X: Above plus if high contention. 7346 7347 Either way, the srcu_node tree will be sized based 7348 on the actual runtime number of CPUs (nr_cpu_ids) 7349 instead of the compile-time CONFIG_NR_CPUS. 7350 7351 srcutree.counter_wrap_check [KNL] 7352 Specifies how frequently to check for 7353 grace-period sequence counter wrap for the 7354 srcu_data structure's ->srcu_gp_seq_needed field. 7355 The greater the number of bits set in this kernel 7356 parameter, the less frequently counter wrap will 7357 be checked for. Note that the bottom two bits 7358 are ignored. 7359 7360 srcutree.exp_holdoff [KNL] 7361 Specifies how many nanoseconds must elapse 7362 since the end of the last SRCU grace period for 7363 a given srcu_struct until the next normal SRCU 7364 grace period will be considered for automatic 7365 expediting. Set to zero to disable automatic 7366 expediting. 7367 7368 srcutree.srcu_max_nodelay [KNL] 7369 Specifies the number of no-delay instances 7370 per jiffy for which the SRCU grace period 7371 worker thread will be rescheduled with zero 7372 delay. Beyond this limit, worker thread will 7373 be rescheduled with a sleep delay of one jiffy. 7374 7375 srcutree.srcu_max_nodelay_phase [KNL] 7376 Specifies the per-grace-period phase, number of 7377 non-sleeping polls of readers. Beyond this limit, 7378 grace period worker thread will be rescheduled 7379 with a sleep delay of one jiffy, between each 7380 rescan of the readers, for a grace period phase. 7381 7382 srcutree.srcu_retry_check_delay [KNL] 7383 Specifies number of microseconds of non-sleeping 7384 delay between each non-sleeping poll of readers. 7385 7386 srcutree.small_contention_lim [KNL] 7387 Specifies the number of update-side contention 7388 events per jiffy will be tolerated before 7389 initiating a conversion of an srcu_struct 7390 structure to big form. Note that the value of 7391 srcutree.convert_to_big must have the 0x10 bit 7392 set for contention-based conversions to occur. 7393 7394 ssbd= [ARM64,HW,EARLY] 7395 Speculative Store Bypass Disable control 7396 7397 On CPUs that are vulnerable to the Speculative 7398 Store Bypass vulnerability and offer a 7399 firmware based mitigation, this parameter 7400 indicates how the mitigation should be used: 7401 7402 force-on: Unconditionally enable mitigation for 7403 for both kernel and userspace 7404 force-off: Unconditionally disable mitigation for 7405 for both kernel and userspace 7406 kernel: Always enable mitigation in the 7407 kernel, and offer a prctl interface 7408 to allow userspace to register its 7409 interest in being mitigated too. 7410 7411 stack_guard_gap= [MM] 7412 override the default stack gap protection. The value 7413 is in page units and it defines how many pages prior 7414 to (for stacks growing down) resp. after (for stacks 7415 growing up) the main stack are reserved for no other 7416 mapping. Default value is 256 pages. 7417 7418 stack_depot_disable= [KNL,EARLY] 7419 Setting this to true through kernel command line will 7420 disable the stack depot thereby saving the static memory 7421 consumed by the stack hash table. By default this is set 7422 to false. 7423 7424 stack_depot_max_pools= [KNL,EARLY] 7425 Specify the maximum number of pools to use for storing 7426 stack traces. Pools are allocated on-demand up to this 7427 limit. Default value is 8191 pools. 7428 7429 stacktrace [FTRACE] 7430 Enable the stack tracer on boot up. 7431 7432 stacktrace_filter=[function-list] 7433 [FTRACE] Limit the functions that the stack tracer 7434 will trace at boot up. function-list is a comma-separated 7435 list of functions. This list can be changed at run 7436 time by the stack_trace_filter file in the debugfs 7437 tracing directory. Note, this enables stack tracing 7438 and the stacktrace above is not needed. 7439 7440 sti= [PARISC,HW] 7441 Format: <num> 7442 Set the STI (builtin display/keyboard on the HP-PARISC 7443 machines) console (graphic card) which should be used 7444 as the initial boot-console. 7445 See also comment in drivers/video/sticore.c. 7446 7447 sti_font= [HW] 7448 See comment in drivers/video/sticore.c. 7449 7450 stifb= [HW] 7451 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7452 7453 strict_sas_size= 7454 [X86] 7455 Format: <bool> 7456 Enable or disable strict sigaltstack size checks 7457 against the required signal frame size which 7458 depends on the supported FPU features. This can 7459 be used to filter out binaries which have 7460 not yet been made aware of AT_MINSIGSTKSZ. 7461 7462 stress_hpt [PPC,EARLY] 7463 Limits the number of kernel HPT entries in the hash 7464 page table to increase the rate of hash page table 7465 faults on kernel addresses. 7466 7467 stress_slb [PPC,EARLY] 7468 Limits the number of kernel SLB entries, and flushes 7469 them frequently to increase the rate of SLB faults 7470 on kernel addresses. 7471 7472 no_slb_preload [PPC,EARLY] 7473 Disables slb preloading for userspace. 7474 7475 sunrpc.min_resvport= 7476 sunrpc.max_resvport= 7477 [NFS,SUNRPC] 7478 SunRPC servers often require that client requests 7479 originate from a privileged port (i.e. a port in the 7480 range 0 < portnr < 1024). 7481 An administrator who wishes to reserve some of these 7482 ports for other uses may adjust the range that the 7483 kernel's sunrpc client considers to be privileged 7484 using these two parameters to set the minimum and 7485 maximum port values. 7486 7487 sunrpc.svc_rpc_per_connection_limit= 7488 [NFS,SUNRPC] 7489 Limit the number of requests that the server will 7490 process in parallel from a single connection. 7491 The default value is 0 (no limit). 7492 7493 sunrpc.pool_mode= 7494 [NFS] 7495 Deprecated. The NFS server now always uses one 7496 service thread pool per NUMA node (equivalent to a 7497 single global pool on non-NUMA machines). All of 7498 the previously accepted values (auto, global, 7499 percpu, pernode) are still accepted for backward 7500 compatibility but are ignored: the mode is always 7501 pernode, and reads always return "pernode". 7502 7503 sunrpc.tcp_slot_table_entries= 7504 sunrpc.udp_slot_table_entries= 7505 [NFS,SUNRPC] 7506 Sets the upper limit on the number of simultaneous 7507 RPC calls that can be sent from the client to a 7508 server. Increasing these values may allow you to 7509 improve throughput, but will also increase the 7510 amount of memory reserved for use by the client. 7511 7512 suspend.pm_test_delay= 7513 [SUSPEND] 7514 Sets the number of seconds to remain in a suspend test 7515 mode before resuming the system (see 7516 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7517 is set. Default value is 5. 7518 7519 svm= [PPC] 7520 Format: { on | off | y | n | 1 | 0 } 7521 This parameter controls use of the Protected 7522 Execution Facility on pSeries. 7523 7524 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7525 Format: { <int> [,<int>] | force | noforce | track_hiwater} 7526 <int> -- Number of I/O TLB slabs 7527 <int> -- Second integer after comma. Number of swiotlb 7528 areas with their own lock. Will be rounded up 7529 to a power of 2. 7530 force -- force using of bounce buffers even if they 7531 wouldn't be automatically used by the kernel 7532 noforce -- Never use bounce buffers (for debugging) 7533 track_hiwater -- Track high watermark of swiotlb buffers. 7534 Only available when CONFIG_DEBUG_FS is set. 7535 7536 switches= [HW,M68k,EARLY] 7537 7538 sysctl.*= [KNL] 7539 Set a sysctl parameter, right before loading the init 7540 process, as if the value was written to the respective 7541 /proc/sys/... file. Both '.' and '/' are recognized as 7542 separators. Unrecognized parameters and invalid values 7543 are reported in the kernel log. Sysctls registered 7544 later by a loaded module cannot be set this way. 7545 Example: sysctl.vm.swappiness=40 7546 7547 sysrq_always_enabled 7548 [KNL] 7549 Ignore sysrq setting - this boot parameter will 7550 neutralize any effect of /proc/sys/kernel/sysrq. 7551 Useful for debugging. 7552 7553 tcpmhash_entries= [KNL,NET] 7554 Set the number of tcp_metrics_hash slots. 7555 Default value is 8192 or 16384 depending on total 7556 ram pages. This is used to specify the TCP metrics 7557 cache size. See Documentation/networking/ip-sysctl.rst 7558 "tcp_no_metrics_save" section for more details. 7559 7560 tdfx= [HW,DRM] 7561 7562 test_suspend= [SUSPEND] 7563 Format: { "mem" | "standby" | "freeze" }[,N] 7564 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7565 standby suspend) or "freeze" (for suspend type freeze) 7566 as the system sleep state during system startup with 7567 the optional capability to repeat N number of times. 7568 The system is woken from this state using a 7569 wakeup-capable RTC alarm. 7570 7571 thash_entries= [KNL,NET] 7572 Set number of hash buckets for TCP connection 7573 7574 thermal.act= [HW,ACPI] 7575 -1: disable all active trip points in all thermal zones 7576 <degrees C>: override all lowest active trip points 7577 7578 thermal.crt= [HW,ACPI] 7579 -1: disable all critical trip points in all thermal zones 7580 <degrees C>: override all critical trip points 7581 7582 thermal.off= [HW,ACPI] 7583 1: disable ACPI thermal control 7584 7585 thermal.psv= [HW,ACPI] 7586 -1: disable all passive trip points 7587 <degrees C>: override all passive trip points to this 7588 value 7589 7590 thermal.tzp= [HW,ACPI] 7591 Specify global default ACPI thermal zone polling rate 7592 <deci-seconds>: poll all this frequency 7593 0: no polling (default) 7594 7595 thp_anon= [KNL] 7596 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7597 state is one of "always", "madvise", "never" or "inherit". 7598 Control the default behavior of the system with respect 7599 to anonymous transparent hugepages. 7600 Can be used multiple times for multiple anon THP sizes. 7601 See Documentation/admin-guide/mm/transhuge.rst for more 7602 details. 7603 7604 threadirqs [KNL,EARLY] 7605 Force threading of all interrupt handlers except those 7606 marked explicitly IRQF_NO_THREAD. 7607 7608 thp_shmem= [KNL] 7609 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7610 Control the default policy of each hugepage size for the 7611 internal shmem mount. <policy> is one of policies available 7612 for the shmem mount ("always", "inherit", "never", "within_size", 7613 and "advise"). 7614 It can be used multiple times for multiple shmem THP sizes. 7615 See Documentation/admin-guide/mm/transhuge.rst for more 7616 details. 7617 7618 tlbi= [X86-64] 7619 Format: {ipi} 7620 ipi: switch to IPI-based TLB flushing 7621 7622 topology= [S390,EARLY] 7623 Format: {off | on} 7624 Specify if the kernel should make use of the cpu 7625 topology information if the hardware supports this. 7626 The scheduler will make use of this information and 7627 e.g. base its process migration decisions on it. 7628 Default is on. 7629 7630 torture.disable_onoff_at_boot= [KNL] 7631 Prevent the CPU-hotplug component of torturing 7632 until after init has spawned. 7633 7634 torture.ftrace_dump_at_shutdown= [KNL] 7635 Dump the ftrace buffer at torture-test shutdown, 7636 even if there were no errors. This can be a 7637 very costly operation when many torture tests 7638 are running concurrently, especially on systems 7639 with rotating-rust storage. 7640 7641 torture.verbose_sleep_frequency= [KNL] 7642 Specifies how many verbose printk()s should be 7643 emitted between each sleep. The default of zero 7644 disables verbose-printk() sleeping. 7645 7646 torture.verbose_sleep_duration= [KNL] 7647 Duration of each verbose-printk() sleep in jiffies. 7648 7649 tpm.disable_pcr_integrity= [HW,TPM] 7650 Do not protect PCR registers from unintended physical 7651 access, or interposers in the bus by the means of 7652 having an integrity protected session wrapped around 7653 TPM2_PCR_Extend command. Consider this in a situation 7654 where TPM is heavily utilized by IMA, thus protection 7655 causing a major performance hit, and the space where 7656 machines are deployed is by other means guarded. 7657 7658 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7659 Maximum time in milliseconds to retry sending a message 7660 to the TPM service before giving up. This parameter controls 7661 how long the system will continue retrying when the TPM 7662 service is busy. 7663 Format: <unsigned int> 7664 Default: 2000 (2 seconds) 7665 7666 tpm_suspend_pcr=[HW,TPM] 7667 Format: integer pcr id 7668 Specify that at suspend time, the tpm driver 7669 should extend the specified pcr with zeros, 7670 as a workaround for some chips which fail to 7671 flush the last written pcr on TPM_SaveState. 7672 This will guarantee that all the other pcrs 7673 are saved. 7674 7675 tpm_tis.interrupts= [HW,TPM] 7676 Enable interrupts for the MMIO based physical layer 7677 for the FIFO interface. By default it is set to false 7678 (0). For more information about TPM hardware interfaces 7679 defined by Trusted Computing Group (TCG) see 7680 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7681 7682 tp_printk [FTRACE] 7683 Have the tracepoints sent to printk as well as the 7684 tracing ring buffer. This is useful for early boot up 7685 where the system hangs or reboots and does not give the 7686 option for reading the tracing buffer or performing a 7687 ftrace_dump_on_oops. 7688 7689 To turn off having tracepoints sent to printk, 7690 echo 0 > /proc/sys/kernel/tracepoint_printk 7691 Note, echoing 1 into this file without the 7692 tp_printk kernel cmdline option has no effect. 7693 7694 The tp_printk_stop_on_boot (see below) can also be used 7695 to stop the printing of events to console at 7696 late_initcall_sync. 7697 7698 ** CAUTION ** 7699 7700 Having tracepoints sent to printk() and activating high 7701 frequency tracepoints such as irq or sched, can cause 7702 the system to live lock. 7703 7704 tp_printk_stop_on_boot [FTRACE] 7705 When tp_printk (above) is set, it can cause a lot of noise 7706 on the console. It may be useful to only include the 7707 printing of events during boot up, as user space may 7708 make the system inoperable. 7709 7710 This command line option will stop the printing of events 7711 to console at the late_initcall_sync() time frame. 7712 7713 trace_buf_size=nn[KMG] 7714 [FTRACE] will set tracing buffer size on each cpu. 7715 7716 trace_clock= [FTRACE] Set the clock used for tracing events 7717 at boot up. 7718 local - Use the per CPU time stamp counter 7719 (converted into nanoseconds). Fast, but 7720 depending on the architecture, may not be 7721 in sync between CPUs. 7722 global - Event time stamps are synchronized across 7723 CPUs. May be slower than the local clock, 7724 but better for some race conditions. 7725 counter - Simple counting of events (1, 2, ..) 7726 note, some counts may be skipped due to the 7727 infrastructure grabbing the clock more than 7728 once per event. 7729 uptime - Use jiffies as the time stamp. 7730 perf - Use the same clock that perf uses. 7731 mono - Use ktime_get_mono_fast_ns() for time stamps. 7732 mono_raw - Use ktime_get_raw_fast_ns() for time 7733 stamps. 7734 boot - Use ktime_get_boot_fast_ns() for time stamps. 7735 Architectures may add more clocks. See 7736 Documentation/trace/ftrace.rst for more details. 7737 7738 trace_event=[event-list] 7739 [FTRACE] Set and start specified trace events in order 7740 to facilitate early boot debugging. The event-list is a 7741 comma-separated list of trace events to enable. See 7742 also Documentation/trace/events.rst 7743 7744 To enable modules, use :mod: keyword: 7745 7746 trace_event=:mod:<module> 7747 7748 The value before :mod: will only enable specific events 7749 that are part of the module. See the above mentioned 7750 document for more information. 7751 7752 trace_instance=[instance-info] 7753 [FTRACE] Create a ring buffer instance early in boot up. 7754 This will be listed in: 7755 7756 /sys/kernel/tracing/instances 7757 7758 Events can be enabled at the time the instance is created 7759 via: 7760 7761 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7762 7763 Note, the "<system*>:" portion is optional if the event is 7764 unique. 7765 7766 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7767 7768 will enable the "sched_switch" event (note, the "sched:" is optional, and 7769 the same thing would happen if it was left off). The irq_handler_entry 7770 event, and all events under the "initcall" system. 7771 7772 Flags can be added to the instance to modify its behavior when it is 7773 created. The flags are separated by '^'. 7774 7775 The available flags are: 7776 7777 traceoff - Have the tracing instance tracing disabled after it is created. 7778 traceprintk - Have trace_printk() write into this trace instance 7779 (note, "printk" and "trace_printk" can also be used) 7780 7781 trace_instance=foo^traceoff^traceprintk,sched,irq 7782 7783 The flags must come before the defined events. 7784 7785 If memory has been reserved (see memmap for x86), the instance 7786 can use that memory: 7787 7788 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7789 7790 The above will create a "boot_map" instance that uses the physical 7791 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7792 instance will be split up accordingly. 7793 7794 Alternatively, the memory can be reserved by the reserve_mem option: 7795 7796 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7797 7798 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7799 and place the ring buffer in this memory. Note that due to KASLR, the 7800 memory may not be the same location each time, which will not preserve 7801 the buffer content. 7802 7803 Also note that the layout of the ring buffer data may change between 7804 kernel versions where the validator will fail and reset the ring buffer 7805 if the layout is not the same as the previous kernel. 7806 7807 If the ring buffer is used for persistent bootups and has events enabled, 7808 it is recommend to disable tracing so that events from a previous boot do not 7809 mix with events of the current boot (unless you are debugging a random crash 7810 at boot up). 7811 7812 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7813 7814 Note, saving the trace buffer across reboots does require that the system 7815 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7816 can force a memory reset on boot which will clear any trace that was stored. 7817 This is just one of many ways that can clear memory. Make sure your system 7818 keeps the content of memory across reboots before relying on this option. 7819 7820 NB: Both the mapped address and size must be page aligned for the architecture. 7821 7822 See also Documentation/trace/debugging.rst 7823 7824 7825 trace_options=[option-list] 7826 [FTRACE] Enable or disable tracer options at boot. 7827 The option-list is a comma delimited list of options 7828 that can be enabled or disabled just as if you were 7829 to echo the option name into 7830 7831 /sys/kernel/tracing/trace_options 7832 7833 For example, to enable stacktrace option (to dump the 7834 stack trace of each event), add to the command line: 7835 7836 trace_options=stacktrace 7837 7838 See also Documentation/trace/ftrace.rst "trace options" 7839 section. 7840 7841 trace_trigger=[trigger-list] 7842 [FTRACE] Add an event trigger on specific events. 7843 Set a trigger on top of a specific event, with an optional 7844 filter. 7845 7846 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7847 Where more than one trigger may be specified that are comma delimited. 7848 7849 For example: 7850 7851 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7852 7853 The above will enable the "stacktrace" trigger on the "sched_switch" 7854 event but only trigger it if the "prev_state" of the "sched_switch" 7855 event is "2" (TASK_UNINTERRUPTIBLE). 7856 7857 See also "Event triggers" in Documentation/trace/events.rst 7858 7859 7860 traceoff_after_boot 7861 [FTRACE] Sometimes tracing is used to debug issues 7862 during the boot process. Since the trace buffer has a 7863 limited amount of storage, it may be prudent to 7864 disable tracing after the boot is finished, otherwise 7865 the critical information may be overwritten. With this 7866 option, the main tracing buffer will be turned off at 7867 the end of the boot process. 7868 7869 traceoff_on_warning 7870 [FTRACE] enable this option to disable tracing when a 7871 warning is hit. This turns off "tracing_on". Tracing can 7872 be enabled again by echoing '1' into the "tracing_on" 7873 file located in /sys/kernel/tracing/ 7874 7875 This option is useful, as it disables the trace before 7876 the WARNING dump is called, which prevents the trace to 7877 be filled with content caused by the warning output. 7878 7879 This option can also be set at run time via the sysctl 7880 option: kernel/traceoff_on_warning 7881 7882 transparent_hugepage= 7883 [KNL] 7884 Format: [always|madvise|never] 7885 Can be used to control the default behavior of the system 7886 with respect to transparent hugepages. 7887 See Documentation/admin-guide/mm/transhuge.rst 7888 for more details. 7889 7890 transparent_hugepage_shmem= [KNL] 7891 Format: [always|within_size|advise|never|deny|force] 7892 Can be used to control the hugepage allocation policy for 7893 the internal shmem mount. 7894 See Documentation/admin-guide/mm/transhuge.rst 7895 for more details. 7896 7897 transparent_hugepage_tmpfs= [KNL] 7898 Format: [always|within_size|advise|never] 7899 Can be used to control the default hugepage allocation policy 7900 for the tmpfs mount. 7901 See Documentation/admin-guide/mm/transhuge.rst 7902 for more details. 7903 7904 trusted.source= [KEYS] 7905 Format: <string> 7906 This parameter identifies the trust source as a backend 7907 for trusted keys implementation. Supported trust 7908 sources: 7909 - "tpm" 7910 - "tee" 7911 - "caam" 7912 - "dcp" 7913 - "pkwm" 7914 If not specified then it defaults to iterating through 7915 the trust source list starting with TPM and assigns the 7916 first trust source as a backend which is initialized 7917 successfully during iteration. 7918 7919 trusted.debug= [KEYS] 7920 Format: <bool> 7921 Enable trusted keys debug traces at runtime when 7922 CONFIG_TRUSTED_KEYS_DEBUG=y. 7923 7924 To make the traces visible after enabling the option, 7925 use trusted.dyndbg='+p' as needed. By convention, 7926 the subsystem uses pr_debug() for these traces. 7927 7928 SAFETY: The traces can leak sensitive data, so be 7929 cautious before enabling this. They remain inactive 7930 unless this parameter is set this option to a true 7931 value. 7932 7933 Default: false 7934 7935 trusted.rng= [KEYS] 7936 Format: <string> 7937 The RNG used to generate key material for trusted keys. 7938 Can be one of: 7939 - "kernel" 7940 - the same value as trusted.source: "tpm" or "tee" 7941 - "default" 7942 If not specified, "default" is used. In this case, 7943 the RNG's choice is left to each individual trust source. 7944 7945 trusted.dcp_use_otp_key 7946 This is intended to be used in combination with 7947 trusted.source=dcp and will select the DCP OTP key 7948 instead of the DCP UNIQUE key blob encryption. 7949 7950 trusted.dcp_skip_zk_test 7951 This is intended to be used in combination with 7952 trusted.source=dcp and will disable the check if the 7953 blob key is all zeros. This is helpful for situations where 7954 having this key zero'ed is acceptable. E.g. in testing 7955 scenarios. 7956 7957 tsa= [X86] Control mitigation for Transient Scheduler 7958 Attacks on AMD CPUs. Search the following in your 7959 favourite search engine for more details: 7960 7961 "Technical guidance for mitigating transient scheduler 7962 attacks". 7963 7964 off - disable the mitigation 7965 on - enable the mitigation (default) 7966 user - mitigate only user/kernel transitions 7967 vm - mitigate only guest/host transitions 7968 7969 7970 tsc= Disable clocksource stability checks for TSC. 7971 Format: <string> 7972 [x86] reliable: mark tsc clocksource as reliable, this 7973 disables clocksource verification at runtime, as well 7974 as the stability checks done at bootup. Used to enable 7975 high-resolution timer mode on older hardware, and in 7976 virtualized environment. 7977 [x86] noirqtime: Do not use TSC to do irq accounting. 7978 Used to run time disable IRQ_TIME_ACCOUNTING on any 7979 platforms where RDTSC is slow and this accounting 7980 can add overhead. 7981 [x86] unstable: mark the TSC clocksource as unstable, this 7982 marks the TSC unconditionally unstable at bootup and 7983 avoids any further wobbles once the TSC watchdog notices. 7984 [x86] nowatchdog: disable clocksource watchdog. Used 7985 in situations with strict latency requirements (where 7986 interruptions from clocksource watchdog are not 7987 acceptable). 7988 [x86] recalibrate: force recalibration against a HW timer 7989 (HPET or PM timer) on systems whose TSC frequency was 7990 obtained from HW or FW using either an MSR or CPUID(0x15). 7991 Warn if the difference is more than 500 ppm. 7992 [x86] watchdog: Enforce the clocksource watchdog on TSC 7993 7994 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7995 value instead. Useful when the early TSC frequency discovery 7996 procedure is not reliable, such as on overclocked systems 7997 with CPUID.16h support and partial CPUID.15h support. 7998 Format: <unsigned int> 7999 8000 tsx= [X86] Control Transactional Synchronization 8001 Extensions (TSX) feature in Intel processors that 8002 support TSX control. 8003 8004 This parameter controls the TSX feature. The options are: 8005 8006 on - Enable TSX on the system. Although there are 8007 mitigations for all known security vulnerabilities, 8008 TSX has been known to be an accelerator for 8009 several previous speculation-related CVEs, and 8010 so there may be unknown security risks associated 8011 with leaving it enabled. 8012 8013 off - Disable TSX on the system. (Note that this 8014 option takes effect only on newer CPUs which are 8015 not vulnerable to MDS, i.e., have 8016 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 8017 the new IA32_TSX_CTRL MSR through a microcode 8018 update. This new MSR allows for the reliable 8019 deactivation of the TSX functionality.) 8020 8021 auto - Disable TSX if X86_BUG_TAA is present, 8022 otherwise enable TSX on the system. 8023 8024 Not specifying this option is equivalent to tsx=off. 8025 8026 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8027 for more details. 8028 8029 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 8030 Abort (TAA) vulnerability. 8031 8032 Similar to Micro-architectural Data Sampling (MDS) 8033 certain CPUs that support Transactional 8034 Synchronization Extensions (TSX) are vulnerable to an 8035 exploit against CPU internal buffers which can forward 8036 information to a disclosure gadget under certain 8037 conditions. 8038 8039 In vulnerable processors, the speculatively forwarded 8040 data can be used in a cache side channel attack, to 8041 access data to which the attacker does not have direct 8042 access. 8043 8044 This parameter controls the TAA mitigation. The 8045 options are: 8046 8047 full - Enable TAA mitigation on vulnerable CPUs 8048 if TSX is enabled. 8049 8050 full,nosmt - Enable TAA mitigation and disable SMT on 8051 vulnerable CPUs. If TSX is disabled, SMT 8052 is not disabled because CPU is not 8053 vulnerable to cross-thread TAA attacks. 8054 off - Unconditionally disable TAA mitigation 8055 8056 On MDS-affected machines, tsx_async_abort=off can be 8057 prevented by an active MDS mitigation as both vulnerabilities 8058 are mitigated with the same mechanism so in order to disable 8059 this mitigation, you need to specify mds=off too. 8060 8061 Not specifying this option is equivalent to 8062 tsx_async_abort=full. On CPUs which are MDS affected 8063 and deploy MDS mitigation, TAA mitigation is not 8064 required and doesn't provide any additional 8065 mitigation. 8066 8067 For details see: 8068 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8069 8070 turbografx.map[2|3]= [HW,JOY] 8071 TurboGraFX parallel port interface 8072 Format: 8073 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8074 See also Documentation/input/devices/joystick-parport.rst 8075 8076 udbg-immortal [PPC] When debugging early kernel crashes that 8077 happen after console_init() and before a proper 8078 console driver takes over, this boot options might 8079 help "seeing" what's going on. 8080 8081 uhash_entries= [KNL,NET] 8082 Set number of hash buckets for UDP/UDP-Lite connections 8083 8084 uhci-hcd.ignore_oc= 8085 [USB] Ignore overcurrent events (default N). 8086 Some badly-designed motherboards generate lots of 8087 bogus events, for ports that aren't wired to 8088 anything. Set this parameter to avoid log spamming. 8089 Note that genuine overcurrent events won't be 8090 reported either. 8091 8092 unaligned_scalar_speed= 8093 [RISCV] 8094 Format: {slow | fast | unsupported} 8095 Allow skipping scalar unaligned access speed tests. This 8096 is useful for testing alternative code paths and to skip 8097 the tests in environments where they run too slowly. All 8098 CPUs must have the same scalar unaligned access speed. 8099 8100 unaligned_vector_speed= 8101 [RISCV] 8102 Format: {slow | fast | unsupported} 8103 Allow skipping vector unaligned access speed tests. This 8104 is useful for testing alternative code paths and to skip 8105 the tests in environments where they run too slowly. All 8106 CPUs must have the same vector unaligned access speed. 8107 8108 unknown_nmi_panic 8109 [X86] Cause panic on unknown NMI. 8110 8111 unwind_debug [X86-64,EARLY] 8112 Enable unwinder debug output. This can be 8113 useful for debugging certain unwinder error 8114 conditions, including corrupt stacks and 8115 bad/missing unwinder metadata. 8116 8117 usbcore.authorized_default= 8118 [USB] Default USB device authorization: 8119 (default -1 = authorized (same as 1), 8120 0 = not authorized, 1 = authorized, 2 = authorized 8121 if device connected to internal port) 8122 8123 usbcore.autosuspend= 8124 [USB] The autosuspend time delay (in seconds) used 8125 for newly-detected USB devices (default 2). This 8126 is the time required before an idle device will be 8127 autosuspended. Devices for which the delay is set 8128 to a negative value won't be autosuspended at all. 8129 8130 usbcore.usbfs_snoop= 8131 [USB] Set to log all usbfs traffic (default 0 = off). 8132 8133 usbcore.usbfs_snoop_max= 8134 [USB] Maximum number of bytes to snoop in each URB 8135 (default = 65536). 8136 8137 usbcore.blinkenlights= 8138 [USB] Set to cycle leds on hubs (default 0 = off). 8139 8140 usbcore.old_scheme_first= 8141 [USB] Start with the old device initialization 8142 scheme (default 0 = off). 8143 8144 usbcore.usbfs_memory_mb= 8145 [USB] Memory limit (in MB) for buffers allocated by 8146 usbfs (default = 16, 0 = max = 2047). 8147 8148 usbcore.use_both_schemes= 8149 [USB] Try the other device initialization scheme 8150 if the first one fails (default 1 = enabled). 8151 8152 usbcore.initial_descriptor_timeout= 8153 [USB] Specifies timeout for the initial 64-byte 8154 USB_REQ_GET_DESCRIPTOR request in milliseconds 8155 (default 5000 = 5.0 seconds). 8156 8157 usbcore.nousb [USB] Disable the USB subsystem 8158 8159 usbcore.quirks= 8160 [USB] A list of quirk entries to augment the built-in 8161 usb core quirk list. List entries are separated by 8162 commas. Each entry has the form 8163 VendorID:ProductID:Flags. The IDs are 4-digit hex 8164 numbers and Flags is a set of letters. Each letter 8165 will change the built-in quirk; setting it if it is 8166 clear and clearing it if it is set. The letters have 8167 the following meanings: 8168 a = USB_QUIRK_STRING_FETCH_255 (string 8169 descriptors must not be fetched using 8170 a 255-byte read); 8171 b = USB_QUIRK_RESET_RESUME (device can't resume 8172 correctly so reset it instead); 8173 c = USB_QUIRK_NO_SET_INTF (device can't handle 8174 Set-Interface requests); 8175 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8176 handle its Configuration or Interface 8177 strings); 8178 e = USB_QUIRK_RESET (device can't be reset 8179 (e.g morph devices), don't use reset); 8180 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8181 more interface descriptions than the 8182 bNumInterfaces count, and can't handle 8183 talking to these interfaces); 8184 g = USB_QUIRK_DELAY_INIT (device needs a pause 8185 during initialization, after we read 8186 the device descriptor); 8187 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8188 high speed and super speed interrupt 8189 endpoints, the USB 2.0 and USB 3.0 spec 8190 require the interval in microframes (1 8191 microframe = 125 microseconds) to be 8192 calculated as interval = 2 ^ 8193 (bInterval-1). 8194 Devices with this quirk report their 8195 bInterval as the result of this 8196 calculation instead of the exponent 8197 variable used in the calculation); 8198 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8199 handle device_qualifier descriptor 8200 requests); 8201 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8202 generates spurious wakeup, ignore 8203 remote wakeup capability); 8204 k = USB_QUIRK_NO_LPM (device can't handle Link 8205 Power Management); 8206 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8207 (Device reports its bInterval as linear 8208 frames instead of the USB 2.0 8209 calculation); 8210 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8211 to be disconnected before suspend to 8212 prevent spurious wakeup); 8213 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8214 pause after every control message); 8215 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8216 delay after resetting its port); 8217 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8218 (Reduce timeout of the SET_ADDRESS 8219 request from 5000 ms to 500 ms); 8220 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8221 claims zero configurations, 8222 forcing to 1); 8223 r = USB_QUIRK_WINDOWS_CONFIG_REQ_SIZE (Device 8224 fails during initialization when asked for 8225 9-bytes configuration descriptor request. 8226 Ask for 255-bytes request instead to mirror 8227 Windows' behavior); 8228 Example: quirks=0781:5580:bk,0a5c:5834:gij 8229 8230 usbhid.mousepoll= 8231 [USBHID] The interval which mice are to be polled at. 8232 8233 usbhid.jspoll= 8234 [USBHID] The interval which joysticks are to be polled at. 8235 8236 usbhid.kbpoll= 8237 [USBHID] The interval which keyboards are to be polled at. 8238 8239 usb-storage.delay_use= 8240 [UMS] The delay in seconds before a new device is 8241 scanned for Logical Units (default 1). 8242 Optionally the delay in milliseconds if the value has 8243 suffix with "ms". 8244 Example: delay_use=2567ms 8245 8246 usb-storage.quirks= 8247 [UMS] A list of quirks entries to supplement or 8248 override the built-in unusual_devs list. List 8249 entries are separated by commas. Each entry has 8250 the form VID:PID:Flags where VID and PID are Vendor 8251 and Product ID values (4-digit hex numbers) and 8252 Flags is a set of characters, each corresponding 8253 to a common usb-storage quirk flag as follows: 8254 a = SANE_SENSE (collect more than 18 bytes 8255 of sense data, not on uas); 8256 b = BAD_SENSE (don't collect more than 18 8257 bytes of sense data, not on uas); 8258 c = FIX_CAPACITY (decrease the reported 8259 device capacity by one sector); 8260 d = NO_READ_DISC_INFO (don't use 8261 READ_DISC_INFO command, not on uas); 8262 e = NO_READ_CAPACITY_16 (don't use 8263 READ_CAPACITY_16 command); 8264 f = NO_REPORT_OPCODES (don't use report opcodes 8265 command, uas only); 8266 g = MAX_SECTORS_240 (don't transfer more than 8267 240 sectors at a time, uas only); 8268 h = CAPACITY_HEURISTICS (decrease the 8269 reported device capacity by one 8270 sector if the number is odd); 8271 i = IGNORE_DEVICE (don't bind to this 8272 device); 8273 j = NO_REPORT_LUNS (don't use report luns 8274 command, uas only); 8275 k = NO_SAME (do not use WRITE_SAME, uas only) 8276 l = NOT_LOCKABLE (don't try to lock and 8277 unlock ejectable media, not on uas); 8278 m = MAX_SECTORS_64 (don't transfer more 8279 than 64 sectors = 32 KB at a time, 8280 not on uas); 8281 n = INITIAL_READ10 (force a retry of the 8282 initial READ(10) command, not on uas); 8283 o = CAPACITY_OK (accept the capacity 8284 reported by the device, not on uas); 8285 p = WRITE_CACHE (the device cache is ON 8286 by default, not on uas); 8287 r = IGNORE_RESIDUE (the device reports 8288 bogus residue values, not on uas); 8289 s = SINGLE_LUN (the device has only one 8290 Logical Unit); 8291 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8292 commands, uas only); 8293 u = IGNORE_UAS (don't bind to the uas driver); 8294 w = NO_WP_DETECT (don't test whether the 8295 medium is write-protected). 8296 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8297 even if the device claims no cache, 8298 not on uas) 8299 Example: quirks=0419:aaf5:rl,0421:0433:rc 8300 8301 user_debug= [KNL,ARM] 8302 Format: <int> 8303 See arch/arm/Kconfig.debug help text. 8304 1 - undefined instruction events 8305 2 - system calls 8306 4 - invalid data aborts 8307 8 - SIGSEGV faults 8308 16 - SIGBUS faults 8309 Example: user_debug=31 8310 8311 vdso= [X86,SH,SPARC] 8312 On X86_32, this is an alias for vdso32=. Otherwise: 8313 8314 vdso=1: enable VDSO (the default) 8315 vdso=0: disable VDSO mapping 8316 8317 vdso32= [X86] Control the 32-bit vDSO 8318 vdso32=1: enable 32-bit VDSO 8319 vdso32=0 or vdso32=2: disable 32-bit VDSO 8320 8321 See the help text for CONFIG_COMPAT_VDSO for more 8322 details. If CONFIG_COMPAT_VDSO is set, the default is 8323 vdso32=0; otherwise, the default is vdso32=1. 8324 8325 For compatibility with older kernels, vdso32=2 is an 8326 alias for vdso32=0. 8327 8328 Try vdso32=0 if you encounter an error that says: 8329 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8330 8331 video= [FB,EARLY] Frame buffer configuration 8332 See Documentation/fb/modedb.rst. 8333 8334 video.brightness_switch_enabled= [ACPI] 8335 Format: [0|1] 8336 If set to 1, on receiving an ACPI notify event 8337 generated by hotkey, video driver will adjust brightness 8338 level and then send out the event to user space through 8339 the allocated input device. If set to 0, video driver 8340 will only send out the event without touching backlight 8341 brightness level. 8342 default: 1 8343 8344 virtio_mmio.device= 8345 [VMMIO] Memory mapped virtio (platform) device. 8346 8347 <size>@<baseaddr>:<irq>[:<id>] 8348 where: 8349 <size> := size (can use standard suffixes 8350 like K, M and G) 8351 <baseaddr> := physical base address 8352 <irq> := interrupt number (as passed to 8353 request_irq()) 8354 <id> := (optional) platform device id 8355 example: 8356 virtio_mmio.device=1K@0x100b0000:48:7 8357 8358 Can be used multiple times for multiple devices. 8359 8360 vga= [BOOT,X86-32] Select a particular video mode 8361 See Documentation/arch/x86/boot.rst and 8362 Documentation/admin-guide/svga.rst. 8363 Use vga=ask for menu. 8364 This is actually a boot loader parameter; the value is 8365 passed to the kernel using a special protocol. 8366 8367 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8368 May slow down system boot speed, especially when 8369 enabled on systems with a large amount of memory. 8370 All options are enabled by default, and this 8371 interface is meant to allow for selectively 8372 enabling or disabling specific virtual memory 8373 debugging features. 8374 8375 Available options are: 8376 P Enable page structure init time poisoning 8377 - Disable all of the above options 8378 8379 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8380 exact size of <nn>. This can be used to increase 8381 the minimum size (128MB on x86, arm32 platforms). 8382 It can also be used to decrease the size and leave more room 8383 for directly mapped kernel RAM. Note that this parameter does 8384 not exist on many other platforms (including arm64, alpha, 8385 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8386 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8387 8388 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8389 Sets the memory size reserved for contiguous memory 8390 allocations for the vmcp device driver. 8391 8392 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8393 Format: <command> 8394 8395 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8396 Format: <command> 8397 8398 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8399 Format: <command> 8400 8401 vmscape= [X86] Controls mitigation for VMscape attacks. 8402 VMscape attacks can leak information from a userspace 8403 hypervisor to a guest via speculative side-channels. 8404 8405 off - disable the mitigation 8406 ibpb - use Indirect Branch Prediction Barrier 8407 (IBPB) mitigation (default) 8408 force - force vulnerability detection even on 8409 unaffected processors 8410 8411 vsyscall= [X86-64,EARLY] 8412 Controls the behavior of vsyscalls (i.e. calls to 8413 fixed addresses of 0xffffffffff600x00 from legacy 8414 code). Most statically-linked binaries and older 8415 versions of glibc use these calls. Because these 8416 functions are at fixed addresses, they make nice 8417 targets for exploits that can control RIP. 8418 8419 emulate Vsyscalls turn into traps and are emulated 8420 reasonably safely. The vsyscall page is 8421 readable. This disables the Linear 8422 Address Space Separation (LASS) security 8423 feature and makes the system less secure. 8424 8425 xonly [default] Vsyscalls turn into traps and are 8426 emulated reasonably safely. The vsyscall 8427 page is not readable. 8428 8429 none Vsyscalls don't work at all. This makes 8430 them quite hard to use for exploits but 8431 might break your system. 8432 8433 vt.color= [VT] Default text color. 8434 Format: 0xYX, X = foreground, Y = background. 8435 Default: 0x07 = light gray on black. 8436 8437 vt.cur_default= [VT] Default cursor shape. 8438 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8439 the parameters of the <Esc>[?A;B;Cc escape sequence; 8440 see vga-softcursor.rst. Default: 2 = underline. 8441 8442 vt.default_blu= [VT] 8443 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8444 Change the default blue palette of the console. 8445 This is a 16-member array composed of values 8446 ranging from 0-255. 8447 8448 vt.default_grn= [VT] 8449 Format: <green0>,<green1>,<green2>,...,<green15> 8450 Change the default green palette of the console. 8451 This is a 16-member array composed of values 8452 ranging from 0-255. 8453 8454 vt.default_red= [VT] 8455 Format: <red0>,<red1>,<red2>,...,<red15> 8456 Change the default red palette of the console. 8457 This is a 16-member array composed of values 8458 ranging from 0-255. 8459 8460 vt.default_utf8= 8461 [VT] 8462 Format=<0|1> 8463 Set system-wide default UTF-8 mode for all tty's. 8464 Default is 1, i.e. UTF-8 mode is enabled for all 8465 newly opened terminals. 8466 8467 vt.global_cursor_default= 8468 [VT] 8469 Format=<-1|0|1> 8470 Set system-wide default for whether a cursor 8471 is shown on new VTs. Default is -1, 8472 i.e. cursors will be created by default unless 8473 overridden by individual drivers. 0 will hide 8474 cursors, 1 will display them. 8475 8476 vt.italic= [VT] Default color for italic text; 0-15. 8477 Default: 2 = green. 8478 8479 vt.underline= [VT] Default color for underlined text; 0-15. 8480 Default: 3 = cyan. 8481 8482 watchdog timers [HW,WDT] For information on watchdog timers, 8483 see Documentation/watchdog/watchdog-parameters.rst 8484 or other driver-specific files in the 8485 Documentation/watchdog/ directory. 8486 8487 watchdog_thresh= 8488 [KNL] 8489 Set the hard lockup detector stall duration 8490 threshold in seconds. The soft lockup detector 8491 threshold is set to twice the value. A value of 0 8492 disables both lockup detectors. Default is 10 8493 seconds. 8494 8495 workqueue.unbound_cpus= 8496 [KNL,SMP] Specify to constrain one or some CPUs 8497 to use in unbound workqueues. 8498 Format: <cpu-list> 8499 By default, all online CPUs are available for 8500 unbound workqueues. 8501 8502 workqueue.watchdog_thresh= 8503 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8504 warn stall conditions and dump internal state to 8505 help debugging. 0 disables workqueue stall 8506 detection; otherwise, it's the stall threshold 8507 duration in seconds. The default value is 30 and 8508 it can be updated at runtime by writing to the 8509 corresponding sysfs file. 8510 8511 workqueue.panic_on_stall=<uint> 8512 Panic when workqueue stall is detected by 8513 CONFIG_WQ_WATCHDOG. It sets the number times of the 8514 stall to trigger panic. 8515 8516 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8517 which is 0 (disabled) if not configured. 8518 8519 workqueue.panic_on_stall_time=<uint> 8520 Panic when a workqueue stall has been continuous for 8521 the specified number of seconds. Unlike panic_on_stall 8522 which counts accumulated stall events, this triggers 8523 based on the duration of a single continuous stall. 8524 8525 The default is 0, which disables the time-based panic. 8526 8527 workqueue.cpu_intensive_thresh_us= 8528 Per-cpu work items which run for longer than this 8529 threshold are automatically considered CPU intensive 8530 and excluded from concurrency management to prevent 8531 them from noticeably delaying other per-cpu work 8532 items. Default is 10000 (10ms). 8533 8534 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8535 will report the work functions which violate this 8536 threshold repeatedly. They are likely good 8537 candidates for using WQ_UNBOUND workqueues instead. 8538 8539 workqueue.cpu_intensive_warning_thresh=<uint> 8540 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8541 will report the work functions which violate the 8542 intensive_threshold_us repeatedly. In order to prevent 8543 spurious warnings, start printing only after a work 8544 function has violated this threshold number of times. 8545 8546 The default is 4 times. 0 disables the warning. 8547 8548 workqueue.power_efficient 8549 Per-cpu workqueues are generally preferred because 8550 they show better performance thanks to cache 8551 locality; unfortunately, per-cpu workqueues tend to 8552 be more power hungry than unbound workqueues. 8553 8554 Enabling this makes the per-cpu workqueues which 8555 were observed to contribute significantly to power 8556 consumption unbound, leading to measurably lower 8557 power usage at the cost of small performance 8558 overhead. 8559 8560 The default value of this parameter is determined by 8561 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8562 8563 workqueue.default_affinity_scope= 8564 Select the default affinity scope to use for unbound 8565 workqueues. Can be one of "cpu", "smt", "cache", 8566 "cache_shard", "numa" and "system". Default is 8567 "cache_shard". For more 8568 information, see the Affinity Scopes section in 8569 Documentation/core-api/workqueue.rst. 8570 8571 This can be changed after boot by writing to the 8572 matching /sys/module/workqueue/parameters file. All 8573 workqueues with the "default" affinity scope will be 8574 updated accordingly. 8575 8576 workqueue.debug_force_rr_cpu 8577 Workqueue used to implicitly guarantee that work 8578 items queued without explicit CPU specified are put 8579 on the local CPU. This guarantee is no longer true 8580 and while local CPU is still preferred work items 8581 may be put on foreign CPUs. This debug option 8582 forces round-robin CPU selection to flush out 8583 usages which depend on the now broken guarantee. 8584 When enabled, memory and cache locality will be 8585 impacted. 8586 8587 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8588 Type) of ioremap_wc(). 8589 8590 on - Enable writecombine, use WUC for ioremap_wc() 8591 off - Disable writecombine, use SUC for ioremap_wc() 8592 8593 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8594 default x2apic cluster mode on platforms 8595 supporting x2apic. 8596 8597 xen_512gb_limit [KNL,X86-64,XEN] 8598 Restricts the kernel running paravirtualized under Xen 8599 to use only up to 512 GB of RAM. The reason to do so is 8600 crash analysis tools and Xen tools for doing domain 8601 save/restore/migration must be enabled to handle larger 8602 domains. 8603 8604 xen_console_io [XEN,EARLY] 8605 Boolean option to enable/disable the usage of the Xen 8606 console_io hypercalls to read and write to the console. 8607 Mostly useful for debugging and development. 8608 8609 xen_emul_unplug= [HW,X86,XEN,EARLY] 8610 Unplug Xen emulated devices 8611 Format: [unplug0,][unplug1] 8612 ide-disks -- unplug primary master IDE devices 8613 aux-ide-disks -- unplug non-primary-master IDE devices 8614 nics -- unplug network devices 8615 all -- unplug all emulated devices (NICs and IDE disks) 8616 unnecessary -- unplugging emulated devices is 8617 unnecessary even if the host did not respond to 8618 the unplug protocol 8619 never -- do not unplug even if version check succeeds 8620 8621 xen_legacy_crash [X86,XEN,EARLY] 8622 Crash from Xen panic notifier, without executing late 8623 panic() code such as dumping handler. 8624 8625 xen_mc_debug [X86,XEN,EARLY] 8626 Enable multicall debugging when running as a Xen PV guest. 8627 Enabling this feature will reduce performance a little 8628 bit, so it should only be enabled for obtaining extended 8629 debug data in case of multicall errors. 8630 8631 xen_msr_safe= [X86,XEN,EARLY] 8632 Format: <bool> 8633 Select whether to always use non-faulting (safe) MSR 8634 access functions when running as Xen PV guest. The 8635 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8636 8637 xen_nopv [X86] 8638 Disables the PV optimizations forcing the HVM guest to 8639 run as generic HVM guest with no PV drivers. 8640 This option is obsoleted by the "nopv" option, which 8641 has equivalent effect for XEN platform. 8642 8643 xen_no_vector_callback 8644 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8645 event channel interrupts. 8646 8647 xen_scrub_pages= [XEN] 8648 Boolean option to control scrubbing pages before giving them back 8649 to Xen, for use by other domains. Can be also changed at runtime 8650 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8651 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8652 8653 xen_timer_slop= [X86-64,XEN,EARLY] 8654 Set the timer slop (in nanoseconds) for the virtual Xen 8655 timers (default is 100000). This adjusts the minimum 8656 delta of virtualized Xen timers, where lower values 8657 improve timer resolution at the expense of processing 8658 more timer interrupts. 8659 8660 xen.balloon_boot_timeout= [XEN] 8661 The time (in seconds) to wait before giving up to boot 8662 in case initial ballooning fails to free enough memory. 8663 Applies only when running as HVM or PVH guest and 8664 started with less memory configured than allowed at 8665 max. Default is 180. 8666 8667 xen.event_eoi_delay= [XEN] 8668 How long to delay EOI handling in case of event 8669 storms (jiffies). Default is 10. 8670 8671 xen.event_loop_timeout= [XEN] 8672 After which time (jiffies) the event handling loop 8673 should start to delay EOI handling. Default is 2. 8674 8675 xen.fifo_events= [XEN] 8676 Boolean parameter to disable using fifo event handling 8677 even if available. Normally fifo event handling is 8678 preferred over the 2-level event handling, as it is 8679 fairer and the number of possible event channels is 8680 much higher. Default is on (use fifo events). 8681 8682 xirc2ps_cs= [NET,PCMCIA] 8683 Format: 8684 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8685 8686 xive= [PPC] 8687 By default on POWER9 and above, the kernel will 8688 natively use the XIVE interrupt controller. This option 8689 allows the fallback firmware mode to be used: 8690 8691 off Fallback to firmware control of XIVE interrupt 8692 controller on both pseries and powernv 8693 platforms. Only useful on POWER9 and above. 8694 8695 xive.store-eoi=off [PPC] 8696 By default on POWER10 and above, the kernel will use 8697 stores for EOI handling when the XIVE interrupt mode 8698 is active. This option allows the XIVE driver to use 8699 loads instead, as on POWER9. 8700 8701 xhci-hcd.quirks [USB,KNL] 8702 A hex value specifying bitmask with supplemental xhci 8703 host controller quirks. Meaning of each bit can be 8704 consulted in header drivers/usb/host/xhci.h. 8705 8706 xmon [PPC,EARLY] 8707 Format: { early | on | rw | ro | off } 8708 Controls if xmon debugger is enabled. Default is off. 8709 Passing only "xmon" is equivalent to "xmon=early". 8710 early Call xmon as early as possible on boot; xmon 8711 debugger is called from setup_arch(). 8712 on xmon debugger hooks will be installed so xmon 8713 is only called on a kernel crash. Default mode, 8714 i.e. either "ro" or "rw" mode, is controlled 8715 with CONFIG_XMON_DEFAULT_RO_MODE. 8716 rw xmon debugger hooks will be installed so xmon 8717 is called only on a kernel crash, mode is write, 8718 meaning SPR registers, memory and, other data 8719 can be written using xmon commands. 8720 ro same as "rw" option above but SPR registers, 8721 memory, and other data can't be written using 8722 xmon commands. 8723 off xmon is disabled. 8724