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] 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 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3105 3106 Default is Y (on). 3107 3108 kvm.enable_pmu=[KVM,X86] 3109 If enabled, KVM will virtualize PMU functionality based 3110 on the virtual CPU model defined by userspace. This 3111 can be overridden on a per-VM basis via 3112 KVM_CAP_PMU_CAPABILITY. 3113 3114 If disabled, KVM will not virtualize PMU functionality, 3115 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3116 a virtual CPU model that contains PMU assets. 3117 3118 Note, KVM's vPMU support implicitly requires running 3119 with an in-kernel local APIC, e.g. to deliver PMIs to 3120 the guest. Running without an in-kernel local APIC is 3121 not supported, though KVM will allow such a combination 3122 (with severely degraded functionality). 3123 3124 See also enable_mediated_pmu. 3125 3126 Default is Y (on). 3127 3128 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3129 If enabled, KVM will enable virtualization in hardware 3130 when KVM is loaded, and disable virtualization when KVM 3131 is unloaded (if KVM is built as a module). 3132 3133 If disabled, KVM will dynamically enable and disable 3134 virtualization on-demand when creating and destroying 3135 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3136 number of VMs. 3137 3138 Enabling virtualization at module load avoids potential 3139 latency for creation of the 0=>1 VM, as KVM serializes 3140 virtualization enabling across all online CPUs. The 3141 "cost" of enabling virtualization when KVM is loaded, 3142 is that doing so may interfere with using out-of-tree 3143 hypervisors that want to "own" virtualization hardware. 3144 3145 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3146 Default is false (don't support). 3147 3148 kvm.nx_huge_pages= 3149 [KVM] Controls the software workaround for the 3150 X86_BUG_ITLB_MULTIHIT bug. 3151 force : Always deploy workaround. 3152 off : Never deploy workaround. 3153 auto : Deploy workaround based on the presence of 3154 X86_BUG_ITLB_MULTIHIT. 3155 3156 Default is 'auto'. 3157 3158 If the software workaround is enabled for the host, 3159 guests do need not to enable it for nested guests. 3160 3161 kvm.nx_huge_pages_recovery_ratio= 3162 [KVM] Controls how many 4KiB pages are periodically zapped 3163 back to huge pages. 0 disables the recovery, otherwise if 3164 the value is N KVM will zap 1/Nth of the 4KiB pages every 3165 period (see below). The default is 60. 3166 3167 kvm.nx_huge_pages_recovery_period_ms= 3168 [KVM] Controls the time period at which KVM zaps 4KiB pages 3169 back to huge pages. If the value is a non-zero N, KVM will 3170 zap a portion (see ratio above) of the pages every N msecs. 3171 If the value is 0 (the default), KVM will pick a period based 3172 on the ratio, such that a page is zapped after 1 hour on average. 3173 3174 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3175 If enabled, KVM will provide a mediated virtual PMU, 3176 instead of the default perf-based virtual PMU (if 3177 kvm.enable_pmu is true and PMU is enumerated via the 3178 virtual CPU model). 3179 3180 With a perf-based vPMU, KVM operates as a user of perf, 3181 i.e. emulates guest PMU counters using perf events. 3182 KVM-created perf events are managed by perf as regular 3183 (guest-only) events, e.g. are scheduled in/out, contend 3184 for hardware resources, etc. Using a perf-based vPMU 3185 allows guest and host usage of the PMU to co-exist, but 3186 incurs non-trivial overhead and can result in silently 3187 dropped guest events (due to resource contention). 3188 3189 With a mediated vPMU, hardware PMU state is context 3190 switched around the world switch to/from the guest. 3191 KVM mediates which events the guest can utilize, but 3192 gives the guest direct access to all other PMU assets 3193 when possible (KVM may intercept some accesses if the 3194 virtual CPU model provides a subset of hardware PMU 3195 functionality). Using a mediated vPMU significantly 3196 reduces PMU virtualization overhead and eliminates lost 3197 guest events, but is mutually exclusive with using perf 3198 to profile KVM guests and adds latency to most VM-Exits 3199 (to context switch PMU state). 3200 3201 Default is N (off). 3202 3203 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3204 KVM/SVM. Default is 1 (enabled). 3205 3206 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3207 a.k.a. Two-Dimensional Page Tables. Default is 1 3208 (enabled). Disable by KVM if hardware lacks support 3209 for NPT. 3210 3211 kvm-amd.ciphertext_hiding_asids= 3212 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3213 to SNP private memory from reading ciphertext. Instead, 3214 reads will see constant default values (0xff). 3215 3216 If ciphertext hiding is enabled, the joint SEV-ES and 3217 SEV-SNP ASID space is partitioned into separate SEV-ES 3218 and SEV-SNP ASID ranges, with the SEV-SNP range being 3219 [1..max_snp_asid] and the SEV-ES range being 3220 (max_snp_asid..min_sev_asid), where min_sev_asid is 3221 enumerated by CPUID.0x.8000_001F[EDX]. 3222 3223 A non-zero value enables SEV-SNP ciphertext hiding and 3224 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3225 KVM caps the number of SEV-SNP ASIDs at the maximum 3226 possible value, e.g. specifying -1u will assign all 3227 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3228 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3229 max_snp_asid == min_sev_asid-1, will effectively make 3230 SEV-ES unusable. 3231 3232 kvm-arm.mode= 3233 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3234 operation. 3235 3236 none: Forcefully disable KVM. 3237 3238 nvhe: Standard nVHE-based mode, without support for 3239 protected guests. 3240 3241 protected: Mode with support for guests whose state is 3242 kept private from the host, using VHE or 3243 nVHE depending on HW support. 3244 3245 nested: VHE-based mode with support for nested 3246 virtualization. Requires at least ARMv8.4 3247 hardware (with FEAT_NV2). 3248 3249 Defaults to VHE/nVHE based on hardware support. Setting 3250 mode to "protected" will disable kexec and hibernation 3251 for the host. To force nVHE on VHE hardware, add 3252 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3253 command-line. 3254 "nested" and "protected" are experimental and should be 3255 used with extreme caution. 3256 3257 kvm-arm.vgic_v3_group0_trap= 3258 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3259 system registers 3260 3261 kvm-arm.vgic_v3_group1_trap= 3262 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3263 system registers 3264 3265 kvm-arm.vgic_v3_common_trap= 3266 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3267 system registers 3268 3269 kvm-arm.vgic_v4_enable= 3270 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3271 injection of LPIs. 3272 3273 kvm-arm.wfe_trap_policy= 3274 [KVM,ARM] Control when to set WFE instruction trap for 3275 KVM VMs. Traps are allowed but not guaranteed by the 3276 CPU architecture. 3277 3278 trap: set WFE instruction trap 3279 3280 notrap: clear WFE instruction trap 3281 3282 kvm-arm.wfi_trap_policy= 3283 [KVM,ARM] Control when to set WFI instruction trap for 3284 KVM VMs. Traps are allowed but not guaranteed by the 3285 CPU architecture. 3286 3287 trap: set WFI instruction trap 3288 3289 notrap: clear WFI instruction trap 3290 3291 kvm_cma_resv_ratio=n [PPC,EARLY] 3292 Reserves given percentage from system memory area for 3293 contiguous memory allocation for KVM hash pagetable 3294 allocation. 3295 By default it reserves 5% of total system memory. 3296 Format: <integer> 3297 Default: 5 3298 3299 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3300 a.k.a. Two-Dimensional Page Tables. Default is 1 3301 (enabled). Disable by KVM if hardware lacks support 3302 for EPT. 3303 3304 kvm-intel.emulate_invalid_guest_state= 3305 [KVM,Intel] Control whether to emulate invalid guest 3306 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3307 as guest state is never invalid for unrestricted 3308 guests. This param doesn't apply to nested guests (L2), 3309 as KVM never emulates invalid L2 guest state. 3310 Default is 1 (enabled). 3311 3312 kvm-intel.flexpriority= 3313 [KVM,Intel] Control KVM's use of FlexPriority feature 3314 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3315 hardware lacks support for it. 3316 3317 kvm-intel.nested= 3318 [KVM,Intel] Control nested virtualization feature in 3319 KVM/VMX. Default is 1 (enabled). 3320 3321 kvm-intel.unrestricted_guest= 3322 [KVM,Intel] Control KVM's use of unrestricted guest 3323 feature (virtualized real and unpaged mode). Default 3324 is 1 (enabled). Disable by KVM if EPT is disabled or 3325 hardware lacks support for it. 3326 3327 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3328 CVE-2018-3620. 3329 3330 Valid arguments: never, cond, always 3331 3332 always: L1D cache flush on every VMENTER. 3333 cond: Flush L1D on VMENTER only when the code between 3334 VMEXIT and VMENTER can leak host memory. 3335 never: Disables the mitigation 3336 3337 Default is cond (do L1 cache flush in specific instances) 3338 3339 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3340 Identification feature (tagged TLBs). Default is 1 3341 (enabled). Disable by KVM if hardware lacks support 3342 for it. 3343 3344 l1d_flush= [X86,INTEL,EARLY] 3345 Control mitigation for L1D based snooping vulnerability. 3346 3347 Certain CPUs are vulnerable to an exploit against CPU 3348 internal buffers which can forward information to a 3349 disclosure gadget under certain conditions. 3350 3351 In vulnerable processors, the speculatively 3352 forwarded data can be used in a cache side channel 3353 attack, to access data to which the attacker does 3354 not have direct access. 3355 3356 This parameter controls the mitigation. The 3357 options are: 3358 3359 on - enable the interface for the mitigation 3360 3361 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3362 affected CPUs 3363 3364 The kernel PTE inversion protection is unconditionally 3365 enabled and cannot be disabled. 3366 3367 full 3368 Provides all available mitigations for the 3369 L1TF vulnerability. Disables SMT and 3370 enables all mitigations in the 3371 hypervisors, i.e. unconditional L1D flush. 3372 3373 SMT control and L1D flush control via the 3374 sysfs interface is still possible after 3375 boot. Hypervisors will issue a warning 3376 when the first VM is started in a 3377 potentially insecure configuration, 3378 i.e. SMT enabled or L1D flush disabled. 3379 3380 full,force 3381 Same as 'full', but disables SMT and L1D 3382 flush runtime control. Implies the 3383 'nosmt=force' command line option. 3384 (i.e. sysfs control of SMT is disabled.) 3385 3386 flush 3387 Leaves SMT enabled and enables the default 3388 hypervisor mitigation, i.e. conditional 3389 L1D flush. 3390 3391 SMT control and L1D flush control via the 3392 sysfs interface is still possible after 3393 boot. Hypervisors will issue a warning 3394 when the first VM is started in a 3395 potentially insecure configuration, 3396 i.e. SMT enabled or L1D flush disabled. 3397 3398 flush,nosmt 3399 3400 Disables SMT and enables the default 3401 hypervisor mitigation. 3402 3403 SMT control and L1D flush control via the 3404 sysfs interface is still possible after 3405 boot. Hypervisors will issue a warning 3406 when the first VM is started in a 3407 potentially insecure configuration, 3408 i.e. SMT enabled or L1D flush disabled. 3409 3410 flush,nowarn 3411 Same as 'flush', but hypervisors will not 3412 warn when a VM is started in a potentially 3413 insecure configuration. 3414 3415 off 3416 Disables hypervisor mitigations and doesn't 3417 emit any warnings. 3418 It also drops the swap size and available 3419 RAM limit restriction on both hypervisor and 3420 bare metal. 3421 3422 Default is 'flush'. 3423 3424 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3425 3426 l2cr= [PPC] 3427 3428 l3cr= [PPC] 3429 3430 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3431 disabled it. 3432 3433 lapic= [X86,APIC] Do not use TSC deadline 3434 value for LAPIC timer one-shot implementation. Default 3435 back to the programmable timer unit in the LAPIC. 3436 Format: notscdeadline 3437 3438 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3439 in C2 power state. 3440 3441 libata.dma= [LIBATA] DMA control 3442 libata.dma=0 Disable all PATA and SATA DMA 3443 libata.dma=1 PATA and SATA Disk DMA only 3444 libata.dma=2 ATAPI (CDROM) DMA only 3445 libata.dma=4 Compact Flash DMA only 3446 Combinations also work, so libata.dma=3 enables DMA 3447 for disks and CDROMs, but not CFs. 3448 3449 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3450 libata.ignore_hpa=0 keep BIOS limits (default) 3451 libata.ignore_hpa=1 ignore limits, using full disk 3452 3453 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3454 when set. 3455 Format: <int> 3456 3457 libata.force= [LIBATA] Force configurations. The format is a comma- 3458 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3459 PORT and DEVICE are decimal numbers matching port, link 3460 or device. Basically, it matches the ATA ID string 3461 printed on console by libata. If the whole ID part is 3462 omitted, the last PORT and DEVICE values are used. If 3463 ID hasn't been specified yet, the configuration applies 3464 to all ports, links and devices. 3465 3466 If only DEVICE is omitted, the parameter applies to 3467 the port and all links and devices behind it. DEVICE 3468 number of 0 either selects the first device or the 3469 first fan-out link behind PMP device. It does not 3470 select the host link. DEVICE number of 15 selects the 3471 host link and device attached to it. 3472 3473 The VAL specifies the configuration to force. As long 3474 as there is no ambiguity, shortcut notation is allowed. 3475 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3476 The following configurations can be forced. 3477 3478 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3479 Any ID with matching PORT is used. 3480 3481 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3482 3483 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3484 udma[/][16,25,33,44,66,100,133] notation is also 3485 allowed. 3486 3487 * nohrst, nosrst, norst: suppress hard, soft and both 3488 resets. 3489 3490 * rstonce: only attempt one reset during hot-unplug 3491 link recovery. 3492 3493 * [no]dbdelay: Enable or disable the extra 200ms delay 3494 before debouncing a link PHY and device presence 3495 detection. 3496 3497 * [no]ncq: Turn on or off NCQ. 3498 3499 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3500 3501 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3502 3503 * [no]trim: Enable or disable (unqueued) TRIM. 3504 3505 * trim_zero: Indicate that TRIM command zeroes data. 3506 3507 * max_trim_128m: Set 128M maximum trim size limit. 3508 3509 * [no]dma: Turn on or off DMA transfers. 3510 3511 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3512 3513 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3514 commands that are not a multiple of 16 bytes. 3515 3516 * [no]dmalog: Enable or disable the use of the 3517 READ LOG DMA EXT command to access logs. 3518 3519 * [no]iddevlog: Enable or disable access to the 3520 identify device data log. 3521 3522 * [no]logdir: Enable or disable access to the general 3523 purpose log directory. 3524 3525 * max_sec=<sectors>: Set the transfer size limit, in 3526 number of 512-byte sectors, to the value specified in 3527 <sectors>. The value specified in <sectors> has to be 3528 a non-zero positive integer. 3529 3530 * max_sec_128: Set transfer size limit to 128 sectors. 3531 3532 * max_sec_1024: Set or clear transfer size limit to 3533 1024 sectors. 3534 3535 * max_sec_lba48: Set or clear transfer size limit to 3536 65535 sectors. 3537 3538 * external: Mark port as external (hotplug-capable). 3539 3540 * [no]lpm: Enable or disable link power management. 3541 3542 * [no]setxfer: Indicate if transfer speed mode setting 3543 should be skipped. 3544 3545 * [no]fua: Disable or enable FUA (Force Unit Access) 3546 support for devices supporting this feature. 3547 3548 * dump_id: Dump IDENTIFY data. 3549 3550 * disable: Disable this device. 3551 3552 If there are multiple matching configurations changing 3553 the same attribute, the last one is used. 3554 3555 liveupdate= [KNL,EARLY] 3556 Format: <bool> 3557 Enable Live Update Orchestrator (LUO). 3558 Default: off. 3559 3560 lockd.nlm_grace_period=P [NFS] Assign grace period. 3561 Format: <integer> 3562 3563 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3564 Format: <integer> 3565 3566 lockd.nlm_timeout=T [NFS] Assign timeout value. 3567 Format: <integer> 3568 3569 lockd.nlm_udpport=M [NFS] Assign UDP port. 3570 Format: <integer> 3571 3572 lockdown= [SECURITY,EARLY] 3573 { integrity | confidentiality } 3574 Enable the kernel lockdown feature. If set to 3575 integrity, kernel features that allow userland to 3576 modify the running kernel are disabled. If set to 3577 confidentiality, kernel features that allow userland 3578 to extract confidential information from the kernel 3579 are also disabled. 3580 3581 locktorture.acq_writer_lim= [KNL] 3582 Set the time limit in jiffies for a lock 3583 acquisition. Acquisitions exceeding this limit 3584 will result in a splat once they do complete. 3585 3586 locktorture.bind_readers= [KNL] 3587 Specify the list of CPUs to which the readers are 3588 to be bound. 3589 3590 locktorture.bind_writers= [KNL] 3591 Specify the list of CPUs to which the writers are 3592 to be bound. 3593 3594 locktorture.call_rcu_chains= [KNL] 3595 Specify the number of self-propagating call_rcu() 3596 chains to set up. These are used to ensure that 3597 there is a high probability of an RCU grace period 3598 in progress at any given time. Defaults to 0, 3599 which disables these call_rcu() chains. 3600 3601 locktorture.long_hold= [KNL] 3602 Specify the duration in milliseconds for the 3603 occasional long-duration lock hold time. Defaults 3604 to 100 milliseconds. Select 0 to disable. 3605 3606 locktorture.nested_locks= [KNL] 3607 Specify the maximum lock nesting depth that 3608 locktorture is to exercise, up to a limit of 8 3609 (MAX_NESTED_LOCKS). Specify zero to disable. 3610 Note that this parameter is ineffective on types 3611 of locks that do not support nested acquisition. 3612 3613 locktorture.nreaders_stress= [KNL] 3614 Set the number of locking read-acquisition kthreads. 3615 Defaults to being automatically set based on the 3616 number of online CPUs. 3617 3618 locktorture.nwriters_stress= [KNL] 3619 Set the number of locking write-acquisition kthreads. 3620 3621 locktorture.onoff_holdoff= [KNL] 3622 Set time (s) after boot for CPU-hotplug testing. 3623 3624 locktorture.onoff_interval= [KNL] 3625 Set time (s) between CPU-hotplug operations, or 3626 zero to disable CPU-hotplug testing. 3627 3628 locktorture.rt_boost= [KNL] 3629 Do periodic testing of real-time lock priority 3630 boosting. Select 0 to disable, 1 to boost 3631 only rt_mutex, and 2 to boost unconditionally. 3632 Defaults to 2, which might seem to be an 3633 odd choice, but which should be harmless for 3634 non-real-time spinlocks, due to their disabling 3635 of preemption. Note that non-realtime mutexes 3636 disable boosting. 3637 3638 locktorture.rt_boost_factor= [KNL] 3639 Number that determines how often and for how 3640 long priority boosting is exercised. This is 3641 scaled down by the number of writers, so that the 3642 number of boosts per unit time remains roughly 3643 constant as the number of writers increases. 3644 On the other hand, the duration of each boost 3645 increases with the number of writers. 3646 3647 locktorture.shuffle_interval= [KNL] 3648 Set task-shuffle interval (jiffies). Shuffling 3649 tasks allows some CPUs to go into dyntick-idle 3650 mode during the locktorture test. 3651 3652 locktorture.shutdown_secs= [KNL] 3653 Set time (s) after boot system shutdown. This 3654 is useful for hands-off automated testing. 3655 3656 locktorture.stat_interval= [KNL] 3657 Time (s) between statistics printk()s. 3658 3659 locktorture.stutter= [KNL] 3660 Time (s) to stutter testing, for example, 3661 specifying five seconds causes the test to run for 3662 five seconds, wait for five seconds, and so on. 3663 This tests the locking primitive's ability to 3664 transition abruptly to and from idle. 3665 3666 locktorture.torture_type= [KNL] 3667 Specify the locking implementation to test. 3668 3669 locktorture.verbose= [KNL] 3670 Enable additional printk() statements. 3671 3672 locktorture.writer_fifo= [KNL] 3673 Run the write-side locktorture kthreads at 3674 sched_set_fifo() real-time priority. 3675 3676 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3677 Format: <irq> 3678 3679 loglevel= [KNL,EARLY] 3680 All Kernel Messages with a loglevel smaller than the 3681 console loglevel will be printed to the console. It can 3682 also be changed with klogd or other programs. The 3683 loglevels are defined as follows: 3684 3685 0 (KERN_EMERG) system is unusable 3686 1 (KERN_ALERT) action must be taken immediately 3687 2 (KERN_CRIT) critical conditions 3688 3 (KERN_ERR) error conditions 3689 4 (KERN_WARNING) warning conditions 3690 5 (KERN_NOTICE) normal but significant condition 3691 6 (KERN_INFO) informational 3692 7 (KERN_DEBUG) debug-level messages 3693 3694 log_buf_len=n[KMG] [KNL,EARLY] 3695 Sets the size of the printk ring buffer, in bytes. 3696 n must be a power of two and greater than the 3697 minimal size. The minimal size is defined by 3698 LOG_BUF_SHIFT kernel config parameter. There 3699 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3700 parameter that allows to increase the default size 3701 depending on the number of CPUs. See init/Kconfig 3702 for more details. 3703 3704 logo.nologo [FB] Disables display of the built-in Linux logo. 3705 This may be used to provide more screen space for 3706 kernel log messages and is useful when debugging 3707 kernel boot problems. 3708 3709 lp=0 [LP] Specify parallel ports to use, e.g, 3710 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3711 lp=reset first parallel port). 'lp=0' disables the 3712 lp=auto printer driver. 'lp=reset' (which can be 3713 specified in addition to the ports) causes 3714 attached printers to be reset. Using 3715 lp=port1,port2,... specifies the parallel ports 3716 to associate lp devices with, starting with 3717 lp0. A port specification may be 'none' to skip 3718 that lp device, or a parport name such as 3719 'parport0'. Specifying 'lp=auto' instead of a 3720 port specification list means that device IDs 3721 from each port should be examined, to see if 3722 an IEEE 1284-compliant printer is attached; if 3723 so, the driver will manage that printer. 3724 See also header of drivers/char/lp.c. 3725 3726 lpj=n [KNL] 3727 Sets loops_per_jiffy to given constant, thus avoiding 3728 time-consuming boot-time autodetection (up to 250 ms per 3729 CPU). 0 enables autodetection (default). To determine 3730 the correct value for your kernel, boot with normal 3731 autodetection and see what value is printed. Note that 3732 on SMP systems the preset will be applied to all CPUs, 3733 which is likely to cause problems if your CPUs need 3734 significantly divergent settings. An incorrect value 3735 will cause delays in the kernel to be wrong, leading to 3736 unpredictable I/O errors and other breakage. Although 3737 unlikely, in the extreme case this might damage your 3738 hardware. 3739 3740 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3741 3742 lsm=lsm1,...,lsmN 3743 [SECURITY] Choose order of LSM initialization. This 3744 overrides CONFIG_LSM, and the "security=" parameter. 3745 3746 machtype= [Loongson] Share the same kernel image file between 3747 different yeeloong laptops. 3748 Example: machtype=lemote-yeeloong-2f-7inch 3749 3750 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3751 will bring up during bootup. maxcpus=n : n >= 0 limits 3752 the kernel to bring up 'n' processors. Surely after 3753 bootup you can bring up the other plugged cpu by executing 3754 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3755 only takes effect during system bootup. 3756 While n=0 is a special case, it is equivalent to "nosmp", 3757 which also disables the IO APIC. 3758 3759 max_loop= [LOOP] The number of loop block devices that get 3760 (loop.max_loop) unconditionally pre-created at init time. The default 3761 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3762 of statically allocating a predefined number, loop 3763 devices can be requested on-demand with the 3764 /dev/loop-control interface. 3765 3766 mce= [X86-{32,64}] 3767 3768 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3769 3770 off 3771 disable machine check 3772 3773 no_cmci 3774 disable CMCI(Corrected Machine Check Interrupt) that 3775 Intel processor supports. Usually this disablement is 3776 not recommended, but it might be handy if your 3777 hardware is misbehaving. 3778 3779 Note that you'll get more problems without CMCI than 3780 with due to the shared banks, i.e. you might get 3781 duplicated error logs. 3782 3783 dont_log_ce 3784 don't make logs for corrected errors. All events 3785 reported as corrected are silently cleared by OS. This 3786 option will be useful if you have no interest in any 3787 of corrected errors. 3788 3789 ignore_ce 3790 disable features for corrected errors, e.g. 3791 polling timer and CMCI. All events reported as 3792 corrected are not cleared by OS and remained in its 3793 error banks. 3794 3795 Usually this disablement is not recommended, however 3796 if there is an agent checking/clearing corrected 3797 errors (e.g. BIOS or hardware monitoring 3798 applications), conflicting with OS's error handling, 3799 and you cannot deactivate the agent, then this option 3800 will be a help. 3801 3802 no_lmce 3803 do not opt-in to Local MCE delivery. Use legacy method 3804 to broadcast MCEs. 3805 3806 bootlog 3807 enable logging of machine checks left over from 3808 booting. Disabled by default on AMD Fam10h and older 3809 because some BIOS leave bogus ones. 3810 3811 If your BIOS doesn't do that it's a good idea to 3812 enable though to make sure you log even machine check 3813 events that result in a reboot. On Intel systems it is 3814 enabled by default. 3815 3816 nobootlog 3817 disable boot machine check logging. 3818 3819 print_all 3820 print all machine check logs to the console. 3821 3822 monarchtimeout (number) 3823 sets the time in us to wait for other CPUs on machine 3824 checks. 0 to disable. 3825 3826 bios_cmci_threshold 3827 don't overwrite the bios-set CMCI threshold. This boot 3828 option prevents Linux from overwriting the CMCI 3829 threshold set by the bios. Without this option, Linux 3830 always sets the CMCI threshold to 1. Enabling this may 3831 make memory predictive failure analysis less effective 3832 if the bios sets thresholds for memory errors since we 3833 will not see details for all errors. 3834 3835 recovery 3836 force-enable recoverable machine check code paths 3837 3838 Everything else is in sysfs now. 3839 3840 3841 md= [HW] RAID subsystems devices and level 3842 See Documentation/admin-guide/md.rst. 3843 3844 mds= [X86,INTEL,EARLY] 3845 Control mitigation for the Micro-architectural Data 3846 Sampling (MDS) vulnerability. 3847 3848 Certain CPUs are vulnerable to an exploit against CPU 3849 internal buffers which can forward information to a 3850 disclosure gadget under certain conditions. 3851 3852 In vulnerable processors, the speculatively 3853 forwarded data can be used in a cache side channel 3854 attack, to access data to which the attacker does 3855 not have direct access. 3856 3857 This parameter controls the MDS mitigation. The 3858 options are: 3859 3860 full - Enable MDS mitigation on vulnerable CPUs 3861 full,nosmt - Enable MDS mitigation and disable 3862 SMT on vulnerable CPUs 3863 off - Unconditionally disable MDS mitigation 3864 3865 On TAA-affected machines, mds=off can be prevented by 3866 an active TAA mitigation as both vulnerabilities are 3867 mitigated with the same mechanism so in order to disable 3868 this mitigation, you need to specify tsx_async_abort=off 3869 too. 3870 3871 Not specifying this option is equivalent to 3872 mds=full. 3873 3874 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3875 3876 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3877 Must be specified, otherwise memory size will be 0. 3878 3879 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3880 of memory Amount of memory to be used in cases 3881 as follows: 3882 3883 1 for test; 3884 2 when the kernel is not able to see the whole system memory; 3885 3 memory that lies after 'mem=' boundary is excluded from 3886 the hypervisor, then assigned to KVM guests. 3887 4 to limit the memory available for kdump kernel. 3888 3889 [ARC,MICROBLAZE] - the limit applies only to low memory, 3890 high memory is not affected. 3891 3892 [ARM64] - only limits memory covered by the linear 3893 mapping. The NOMAP regions are not affected. 3894 3895 [X86] Work as limiting max address. Use together 3896 with memmap= to avoid physical address space collisions. 3897 Without memmap= PCI devices could be placed at addresses 3898 belonging to unused RAM. 3899 3900 Note that this only takes effects during boot time since 3901 in above case 3, memory may need be hot added after boot 3902 if system memory of hypervisor is not sufficient. 3903 3904 mem=nn[KMG]@ss[KMG] 3905 [ARM,MIPS,EARLY] - override the memory layout 3906 reported by firmware. 3907 Define a memory region of size nn[KMG] starting at 3908 ss[KMG]. 3909 Multiple different regions can be specified with 3910 multiple mem= parameters on the command line. 3911 3912 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3913 memory. 3914 3915 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3916 3917 memchunk=nn[KMG] 3918 [KNL,SH] Allow user to override the default size for 3919 per-device physically contiguous DMA buffers. 3920 3921 memhp_default_state=online/offline/online_kernel/online_movable 3922 [KNL] Set the initial state for the memory hotplug 3923 onlining policy. If not specified, the default value is 3924 set according to the 3925 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3926 options. 3927 See Documentation/admin-guide/mm/memory-hotplug.rst. 3928 3929 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3930 E820 memory map, as specified by the user. 3931 Such memmap=exactmap lines can be constructed based on 3932 BIOS output or other requirements. See the memmap=nn@ss 3933 option description. 3934 3935 memmap=nn[KMG]@ss[KMG] 3936 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3937 Region of memory to be used is from ss to ss+nn. 3938 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3939 which limits max address to nn[KMG]. 3940 Multiple different regions can be specified, 3941 comma delimited. 3942 Example: 3943 memmap=100M@2G,100M#3G,1G!1024G 3944 3945 memmap=nn[KMG]#ss[KMG] 3946 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3947 Region of memory to be marked is from ss to ss+nn. 3948 3949 memmap=nn[KMG]$ss[KMG] 3950 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3951 Region of memory to be reserved is from ss to ss+nn. 3952 Example: Exclude memory from 0x18690000-0x1869ffff 3953 memmap=64K$0x18690000 3954 or 3955 memmap=0x10000$0x18690000 3956 Some bootloaders may need an escape character before '$', 3957 like Grub2, otherwise '$' and the following number 3958 will be eaten. 3959 3960 memmap=nn[KMG]!ss[KMG,EARLY] 3961 [KNL,X86] Mark specific memory as protected. 3962 Region of memory to be used, from ss to ss+nn. 3963 The memory region may be marked as e820 type 12 (0xc) 3964 and is NVDIMM or ADR memory. 3965 3966 memmap=<size>%<offset>-<oldtype>+<newtype> 3967 [KNL,ACPI,EARLY] Convert memory within the specified region 3968 from <oldtype> to <newtype>. If "-<oldtype>" is left 3969 out, the whole region will be marked as <newtype>, 3970 even if previously unavailable. If "+<newtype>" is left 3971 out, matching memory will be removed. Types are 3972 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3973 3 = ACPI, 12 = PRAM. 3974 3975 memory_corruption_check=0/1 [X86,EARLY] 3976 Some BIOSes seem to corrupt the first 64k of 3977 memory when doing things like suspend/resume. 3978 Setting this option will scan the memory 3979 looking for corruption. Enabling this will 3980 both detect corruption and prevent the kernel 3981 from using the memory being corrupted. 3982 However, it's intended as a diagnostic tool; if 3983 repeatable BIOS-originated corruption always 3984 affects the same memory, you can use memmap= 3985 to prevent the kernel from using that memory. 3986 3987 memory_corruption_check_size=size [X86,EARLY] 3988 By default it checks for corruption in the low 3989 64k, making this memory unavailable for normal 3990 use. Use this parameter to scan for 3991 corruption in more or less memory. 3992 3993 memory_corruption_check_period=seconds [X86,EARLY] 3994 By default it checks for corruption every 60 3995 seconds. Use this parameter to check at some 3996 other rate. 0 disables periodic checking. 3997 3998 memory_hotplug.memmap_on_memory 3999 [KNL,X86,ARM] Boolean flag to enable this feature. 4000 Format: {on | off (default)} 4001 When enabled, runtime hotplugged memory will 4002 allocate its internal metadata (struct pages, 4003 those vmemmap pages cannot be optimized even 4004 if hugetlb_free_vmemmap is enabled) from the 4005 hotadded memory which will allow to hotadd a 4006 lot of memory without requiring additional 4007 memory to do so. 4008 This feature is disabled by default because it 4009 has some implication on large (e.g. GB) 4010 allocations in some configurations (e.g. small 4011 memory blocks). 4012 The state of the flag can be read in 4013 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4014 Note that even when enabled, there are a few cases where 4015 the feature is not effective. 4016 4017 mempool_debug [MM] 4018 Enable mempool debugging. This enables element 4019 poison checking when freeing elements back to the 4020 pool. Useful for debugging mempool corruption. 4021 4022 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4023 Format: <integer> 4024 default : 0 <disable> 4025 Specifies the number of memtest passes to be 4026 performed. Each pass selects another test 4027 pattern from a given set of patterns. Memtest 4028 fills the memory with this pattern, validates 4029 memory contents and reserves bad memory 4030 regions that are detected. 4031 4032 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4033 Valid arguments: on, off 4034 Default: off 4035 mem_encrypt=on: Activate SME 4036 mem_encrypt=off: Do not activate SME 4037 4038 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4039 for details on when memory encryption can be activated. 4040 4041 mem_sleep_default= [SUSPEND] Default system suspend mode: 4042 s2idle - Suspend-To-Idle 4043 shallow - Power-On Suspend or equivalent (if supported) 4044 deep - Suspend-To-RAM or equivalent (if supported) 4045 See Documentation/admin-guide/pm/sleep-states.rst. 4046 4047 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4048 the BIOS has incorrectly applied a workaround. TinyBIOS 4049 version 0.98 is known to be affected, 0.99 fixes the 4050 problem by letting the user disable the workaround. 4051 4052 mga= [HW,DRM] 4053 4054 microcode= [X86] Control the behavior of the microcode loader. 4055 Available options, comma separated: 4056 4057 base_rev=X - with <X> with format: <u32> 4058 Set the base microcode revision of each thread when in 4059 debug mode. 4060 4061 dis_ucode_ldr: disable the microcode loader 4062 4063 force_minrev: 4064 Enable or disable the microcode minimal revision 4065 enforcement for the runtime microcode loader. 4066 4067 mini2440= [ARM,HW,KNL] 4068 Format:[0..2][b][c][t] 4069 Default: "0tb" 4070 MINI2440 configuration specification: 4071 0 - The attached screen is the 3.5" TFT 4072 1 - The attached screen is the 7" TFT 4073 2 - The VGA Shield is attached (1024x768) 4074 Leaving out the screen size parameter will not load 4075 the TFT driver, and the framebuffer will be left 4076 unconfigured. 4077 b - Enable backlight. The TFT backlight pin will be 4078 linked to the kernel VESA blanking code and a GPIO 4079 LED. This parameter is not necessary when using the 4080 VGA shield. 4081 c - Enable the s3c camera interface. 4082 t - Reserved for enabling touchscreen support. The 4083 touchscreen support is not enabled in the mainstream 4084 kernel as of 2.6.30, a preliminary port can be found 4085 in the "bleeding edge" mini2440 support kernel at 4086 https://repo.or.cz/w/linux-2.6/mini2440.git 4087 4088 mitigations= 4089 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4090 CPU vulnerabilities. This is a set of curated, 4091 arch-independent options, each of which is an 4092 aggregation of existing arch-specific options. 4093 4094 Note, "mitigations" is supported if and only if the 4095 kernel was built with CPU_MITIGATIONS=y. 4096 4097 off 4098 Disable all optional CPU mitigations. This 4099 improves system performance, but it may also 4100 expose users to several CPU vulnerabilities. 4101 Equivalent to: if nokaslr then kpti=0 [ARM64] 4102 gather_data_sampling=off [X86] 4103 indirect_target_selection=off [X86] 4104 kvm.nx_huge_pages=off [X86] 4105 l1tf=off [X86] 4106 mds=off [X86] 4107 mmio_stale_data=off [X86] 4108 no_entry_flush [PPC] 4109 no_uaccess_flush [PPC] 4110 nobp=0 [S390] 4111 nopti [X86,PPC] 4112 nospectre_bhb [ARM64] 4113 nospectre_v1 [X86,PPC] 4114 nospectre_v2 [X86,PPC,S390,ARM64] 4115 reg_file_data_sampling=off [X86] 4116 retbleed=off [X86] 4117 spec_rstack_overflow=off [X86] 4118 spec_store_bypass_disable=off [X86,PPC] 4119 spectre_bhi=off [X86] 4120 spectre_v2_user=off [X86] 4121 srbds=off [X86,INTEL] 4122 ssbd=force-off [ARM64] 4123 tsa=off [X86,AMD] 4124 tsx_async_abort=off [X86] 4125 vmscape=off [X86] 4126 4127 Exceptions: 4128 This does not have any effect on 4129 kvm.nx_huge_pages when 4130 kvm.nx_huge_pages=force. 4131 4132 auto (default) 4133 Mitigate all CPU vulnerabilities, but leave SMT 4134 enabled, even if it's vulnerable. This is for 4135 users who don't want to be surprised by SMT 4136 getting disabled across kernel upgrades, or who 4137 have other ways of avoiding SMT-based attacks. 4138 Equivalent to: (default behavior) 4139 4140 auto,nosmt 4141 Mitigate all CPU vulnerabilities, disabling SMT 4142 if needed. This is for users who always want to 4143 be fully mitigated, even if it means losing SMT. 4144 Equivalent to: l1tf=flush,nosmt [X86] 4145 mds=full,nosmt [X86] 4146 tsx_async_abort=full,nosmt [X86] 4147 mmio_stale_data=full,nosmt [X86] 4148 retbleed=auto,nosmt [X86] 4149 4150 [X86] After one of the above options, additionally 4151 supports attack-vector based controls as documented in 4152 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4153 4154 mminit_loglevel= 4155 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4156 parameter allows control of the logging verbosity for 4157 the additional memory initialisation checks. A value 4158 of 0 disables mminit logging and a level of 4 will 4159 log everything. Information is printed at KERN_DEBUG 4160 so loglevel=8 may also need to be specified. 4161 4162 mmio_stale_data= 4163 [X86,INTEL,EARLY] Control mitigation for the Processor 4164 MMIO Stale Data vulnerabilities. 4165 4166 Processor MMIO Stale Data is a class of 4167 vulnerabilities that may expose data after an MMIO 4168 operation. Exposed data could originate or end in 4169 the same CPU buffers as affected by MDS and TAA. 4170 Therefore, similar to MDS and TAA, the mitigation 4171 is to clear the affected CPU buffers. 4172 4173 This parameter controls the mitigation. The 4174 options are: 4175 4176 full - Enable mitigation on vulnerable CPUs 4177 4178 full,nosmt - Enable mitigation and disable SMT on 4179 vulnerable CPUs. 4180 4181 off - Unconditionally disable mitigation 4182 4183 On MDS or TAA affected machines, 4184 mmio_stale_data=off can be prevented by an active 4185 MDS or TAA mitigation as these vulnerabilities are 4186 mitigated with the same mechanism so in order to 4187 disable this mitigation, you need to specify 4188 mds=off and tsx_async_abort=off too. 4189 4190 Not specifying this option is equivalent to 4191 mmio_stale_data=full. 4192 4193 For details see: 4194 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4195 4196 <module>.async_probe[=<bool>] [KNL] 4197 If no <bool> value is specified or if the value 4198 specified is not a valid <bool>, enable asynchronous 4199 probe on this module. Otherwise, enable/disable 4200 asynchronous probe on this module as indicated by the 4201 <bool> value. See also: module.async_probe 4202 4203 module.async_probe=<bool> 4204 [KNL] When set to true, modules will use async probing 4205 by default. To enable/disable async probing for a 4206 specific module, use the module specific control that 4207 is documented under <module>.async_probe. When both 4208 module.async_probe and <module>.async_probe are 4209 specified, <module>.async_probe takes precedence for 4210 the specific module. 4211 4212 module.enable_dups_trace 4213 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4214 this means that duplicate request_module() calls will 4215 trigger a WARN_ON() instead of a pr_warn(). Note that 4216 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4217 will always be issued and this option does nothing. 4218 module.sig_enforce 4219 [KNL] When CONFIG_MODULE_SIG is set, this means that 4220 modules without (valid) signatures will fail to load. 4221 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4222 is always true, so this option does nothing. 4223 4224 module_blacklist= [KNL] Do not load a comma-separated list of 4225 modules. Useful for debugging problem modules. 4226 4227 mousedev.tap_time= 4228 [MOUSE] Maximum time between finger touching and 4229 leaving touchpad surface for touch to be considered 4230 a tap and be reported as a left button click (for 4231 touchpads working in absolute mode only). 4232 Format: <msecs> 4233 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4234 reporting absolute coordinates, such as tablets 4235 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4236 reporting absolute coordinates, such as tablets 4237 4238 movablecore= [KNL,X86,PPC,EARLY] 4239 Format: nn[KMGTPE] | nn% 4240 This parameter is the complement to kernelcore=, it 4241 specifies the amount of memory used for migratable 4242 allocations. If both kernelcore and movablecore is 4243 specified, then kernelcore will be at *least* the 4244 specified value but may be more. If movablecore on its 4245 own is specified, the administrator must be careful 4246 that the amount of memory usable for all allocations 4247 is not too small. 4248 4249 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4250 NUMA nodes to be movable. This means that the memory 4251 of such nodes will be usable only for movable 4252 allocations which rules out almost all kernel 4253 allocations. Use with caution! 4254 4255 MTD_Partition= [MTD] 4256 Format: <name>,<region-number>,<size>,<offset> 4257 4258 MTD_Region= [MTD] Format: 4259 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4260 4261 mtdparts= [MTD] 4262 See drivers/mtd/parsers/cmdlinepart.c 4263 4264 mtouchusb.raw_coordinates= 4265 [HW] Make the MicroTouch USB driver use raw coordinates 4266 ('y', default) or cooked coordinates ('n') 4267 4268 mtrr=debug [X86,EARLY] 4269 Enable printing debug information related to MTRR 4270 registers at boot time. 4271 4272 mtrr_chunk_size=nn[KMG,X86,EARLY] 4273 used for mtrr cleanup. It is largest continuous chunk 4274 that could hold holes aka. UC entries. 4275 4276 mtrr_gran_size=nn[KMG,X86,EARLY] 4277 Used for mtrr cleanup. It is granularity of mtrr block. 4278 Default is 1. 4279 Large value could prevent small alignment from 4280 using up MTRRs. 4281 4282 mtrr_spare_reg_nr=n [X86,EARLY] 4283 Format: <integer> 4284 Range: 0,7 : spare reg number 4285 Default : 1 4286 Used for mtrr cleanup. It is spare mtrr entries number. 4287 Set to 2 or more if your graphical card needs more. 4288 4289 multitce=off [PPC] This parameter disables the use of the pSeries 4290 firmware feature for updating multiple TCE entries 4291 at a time. 4292 4293 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4294 4295 netdev= [NET] NE2000 ISA network devices parameters 4296 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4297 4298 netpoll.carrier_timeout= 4299 [NET] Specifies amount of time (in seconds) that 4300 netpoll should wait for a carrier. By default netpoll 4301 waits 4 seconds. 4302 4303 nf_conntrack.acct= 4304 [NETFILTER] Enable connection tracking flow accounting 4305 0 to disable accounting 4306 1 to enable accounting 4307 Default value is 0. 4308 4309 nfs.cache_getent= 4310 [NFS] sets the pathname to the program which is used 4311 to update the NFS client cache entries. 4312 4313 nfs.cache_getent_timeout= 4314 [NFS] sets the timeout after which an attempt to 4315 update a cache entry is deemed to have failed. 4316 4317 nfs.callback_nr_threads= 4318 [NFSv4] set the total number of threads that the 4319 NFS client will assign to service NFSv4 callback 4320 requests. 4321 4322 nfs.callback_tcpport= 4323 [NFS] set the TCP port on which the NFSv4 callback 4324 channel should listen. 4325 4326 nfs.delay_retrans= 4327 [NFS] specifies the number of times the NFSv4 client 4328 retries the request before returning an EAGAIN error, 4329 after a reply of NFS4ERR_DELAY from the server. 4330 Only applies if the softerr mount option is enabled, 4331 and the specified value is >= 0. 4332 4333 nfs.idmap_cache_timeout= 4334 [NFS] set the maximum lifetime for idmapper cache 4335 entries. 4336 4337 nfs.max_session_cb_slots= 4338 [NFSv4.1] Sets the maximum number of session 4339 slots the client will assign to the callback 4340 channel. This determines the maximum number of 4341 callbacks the client will process in parallel for 4342 a particular server. 4343 4344 nfs.max_session_slots= 4345 [NFSv4.1] Sets the maximum number of session slots 4346 the client will attempt to negotiate with the server. 4347 This limits the number of simultaneous RPC requests 4348 that the client can send to the NFSv4.1 server. 4349 Note that there is little point in setting this 4350 value higher than the max_tcp_slot_table_limit. 4351 4352 nfs.nfs4_disable_idmapping= 4353 [NFSv4] When set to the default of '1', this option 4354 ensures that both the RPC level authentication 4355 scheme and the NFS level operations agree to use 4356 numeric uids/gids if the mount is using the 4357 'sec=sys' security flavour. In effect it is 4358 disabling idmapping, which can make migration from 4359 legacy NFSv2/v3 systems to NFSv4 easier. 4360 Servers that do not support this mode of operation 4361 will be autodetected by the client, and it will fall 4362 back to using the idmapper. 4363 To turn off this behaviour, set the value to '0'. 4364 4365 nfs.nfs4_unique_id= 4366 [NFS4] Specify an additional fixed unique ident- 4367 ification string that NFSv4 clients can insert into 4368 their nfs_client_id4 string. This is typically a 4369 UUID that is generated at system install time. 4370 4371 nfs.recover_lost_locks= 4372 [NFSv4] Attempt to recover locks that were lost due 4373 to a lease timeout on the server. Please note that 4374 doing this risks data corruption, since there are 4375 no guarantees that the file will remain unchanged 4376 after the locks are lost. 4377 If you want to enable the kernel legacy behaviour of 4378 attempting to recover these locks, then set this 4379 parameter to '1'. 4380 The default parameter value of '0' causes the kernel 4381 not to attempt recovery of lost locks. 4382 4383 nfs.send_implementation_id= 4384 [NFSv4.1] Send client implementation identification 4385 information in exchange_id requests. 4386 If zero, no implementation identification information 4387 will be sent. 4388 The default is to send the implementation identification 4389 information. 4390 4391 nfs4.layoutstats_timer= 4392 [NFSv4.2] Change the rate at which the kernel sends 4393 layoutstats to the pNFS metadata server. 4394 4395 Setting this to value to 0 causes the kernel to use 4396 whatever value is the default set by the layout 4397 driver. A non-zero value sets the minimum interval 4398 in seconds between layoutstats transmissions. 4399 4400 nfsd.inter_copy_offload_enable= 4401 [NFSv4.2] When set to 1, the server will support 4402 server-to-server copies for which this server is 4403 the destination of the copy. 4404 4405 nfsd.nfs4_disable_idmapping= 4406 [NFSv4] When set to the default of '1', the NFSv4 4407 server will return only numeric uids and gids to 4408 clients using auth_sys, and will accept numeric uids 4409 and gids from such clients. This is intended to ease 4410 migration from NFSv2/v3. 4411 4412 nfsd.nfsd4_ssc_umount_timeout= 4413 [NFSv4.2] When used as the destination of a 4414 server-to-server copy, knfsd temporarily mounts 4415 the source server. It caches the mount in case 4416 it will be needed again, and discards it if not 4417 used for the number of milliseconds specified by 4418 this parameter. 4419 4420 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4421 See Documentation/admin-guide/nfs/nfsroot.rst. 4422 4423 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4424 See Documentation/admin-guide/nfs/nfsroot.rst. 4425 4426 nfsrootdebug [NFS] enable nfsroot debugging messages. 4427 See Documentation/admin-guide/nfs/nfsroot.rst. 4428 4429 nmi_backtrace.backtrace_idle [KNL] 4430 Dump stacks even of idle CPUs in response to an 4431 NMI stack-backtrace request. 4432 4433 nmi_debug= [KNL,SH] Specify one or more actions to take 4434 when a NMI is triggered. 4435 Format: [state][,regs][,debounce][,die] 4436 4437 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4438 Format: [panic,][nopanic,][rNNN,][num] 4439 Valid num: 0 or 1 4440 0 - turn hardlockup detector in nmi_watchdog off 4441 1 - turn hardlockup detector in nmi_watchdog on 4442 rNNN - configure the watchdog with raw perf event 0xNNN 4443 4444 When panic is specified, panic when an NMI watchdog 4445 timeout occurs (or 'nopanic' to not panic on an NMI 4446 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4447 To disable both hard and soft lockup detectors, 4448 please see 'nowatchdog'. 4449 This is useful when you use a panic=... timeout and 4450 need the box quickly up again. 4451 4452 These settings can be accessed at runtime via 4453 the nmi_watchdog and hardlockup_panic sysctls. 4454 4455 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4456 Forces kernel to use 3-level paging instead. 4457 4458 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4459 kernel to use 4-level paging instead. 4460 4461 noalign [KNL,ARM] 4462 4463 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4464 IOAPICs that may be present in the system. 4465 4466 noapictimer [APIC,X86] Don't set up the APIC timer 4467 4468 noautogroup Disable scheduler automatic task group creation. 4469 4470 nocache [ARM,EARLY] 4471 4472 no_console_suspend 4473 [HW] Never suspend the console 4474 Disable suspending of consoles during suspend and 4475 hibernate operations. Once disabled, debugging 4476 messages can reach various consoles while the rest 4477 of the system is being put to sleep (ie, while 4478 debugging driver suspend/resume hooks). This may 4479 not work reliably with all consoles, but is known 4480 to work with serial and VGA consoles. 4481 To facilitate more flexible debugging, we also add 4482 console_suspend, a printk module parameter to control 4483 it. Users could use console_suspend (usually 4484 /sys/module/printk/parameters/console_suspend) to 4485 turn on/off it dynamically. 4486 4487 no_debug_objects 4488 [KNL,EARLY] Disable object debugging 4489 4490 nodsp [SH] Disable hardware DSP at boot time. 4491 4492 noefi [EFI,EARLY] Disable EFI runtime services support. 4493 4494 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4495 4496 noexec32 [X86-64] 4497 This affects only 32-bit executables. 4498 noexec32=on: enable non-executable mappings (default) 4499 read doesn't imply executable mappings 4500 noexec32=off: disable non-executable mappings 4501 read implies executable mappings 4502 4503 no_file_caps Tells the kernel not to honor file capabilities. The 4504 only way then for a file to be executed with privilege 4505 is to be setuid root or executed by root. 4506 4507 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4508 4509 nofsgsbase [X86] Disables FSGSBASE instructions. 4510 4511 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4512 register save and restore. The kernel will only save 4513 legacy floating-point registers on task switch. 4514 4515 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4516 4517 no_hash_pointers 4518 [KNL,EARLY] 4519 Alias for "hash_pointers=never". 4520 4521 nohibernate [HIBERNATION] Disable hibernation and resume. 4522 4523 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4524 busy wait in do_idle() and not use the arch_cpu_idle() 4525 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4526 to be effective. This is useful on platforms where the 4527 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4528 correctly or when doing power measurements to evaluate 4529 the impact of the sleep instructions. This is also 4530 useful when using JTAG debugger. 4531 4532 nohpet [X86] Don't use the HPET timer. 4533 4534 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4535 4536 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4537 4538 nohz= [KNL] Boottime enable/disable dynamic ticks 4539 Valid arguments: on, off 4540 Default: on 4541 4542 nohz_full= [KNL,BOOT,SMP,ISOL] 4543 The argument is a cpu list, as described above. 4544 In kernels built with CONFIG_NO_HZ_FULL=y, set 4545 the specified list of CPUs whose tick will be stopped 4546 whenever possible. The boot CPU will be forced outside 4547 the range to maintain the timekeeping. Any CPUs 4548 in this list will have their RCU callbacks offloaded, 4549 just as if they had also been called out in the 4550 rcu_nocbs= boot parameter. 4551 4552 Note that this argument takes precedence over 4553 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4554 4555 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4556 initial RAM disk. Currently this parameter applies to 4557 initrd only, not to initramfs. But it applies to both 4558 in EFI mode. 4559 4560 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4561 remapping. 4562 [Deprecated - use intremap=off] 4563 4564 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4565 4566 noiotrap [SH] Disables trapped I/O port accesses. 4567 4568 noirqdebug [X86-32] Disables the code which attempts to detect and 4569 disable unhandled interrupt sources. 4570 4571 noisapnp [ISAPNP] Disables ISA PnP code. 4572 4573 nokaslr [KNL,EARLY] 4574 When CONFIG_RANDOMIZE_BASE is set, this disables 4575 kernel and module base offset ASLR (Address Space 4576 Layout Randomization). 4577 4578 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4579 fault handling. 4580 4581 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4582 4583 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4584 4585 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4586 4587 nomce [X86-32] Disable Machine Check Exception 4588 4589 nomfgpt [X86-32] Disable Multi-Function General Purpose 4590 Timer usage (for AMD Geode machines). 4591 4592 nomodeset Disable kernel modesetting. Most systems' firmware 4593 sets up a display mode and provides framebuffer memory 4594 for output. With nomodeset, DRM and fbdev drivers will 4595 not load if they could possibly displace the pre- 4596 initialized output. Only the system framebuffer will 4597 be available for use. The respective drivers will not 4598 perform display-mode changes or accelerated rendering. 4599 4600 Useful as error fallback, or for testing and debugging. 4601 4602 nomodule Disable module load 4603 4604 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4605 shutdown the other cpus. Instead use the REBOOT_VECTOR 4606 irq. 4607 4608 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4609 pagetables) support. 4610 4611 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4612 4613 nopku [X86] Disable Memory Protection Keys CPU feature found 4614 in some Intel CPUs. 4615 4616 nopti [X86-64,EARLY] 4617 Equivalent to pti=off 4618 4619 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4620 Disables the PV optimizations forcing the guest to run 4621 as generic guest with no PV drivers. Currently support 4622 XEN HVM, KVM, HYPER_V and VMWARE guest. 4623 4624 nopvspin [X86,XEN,KVM,EARLY] 4625 Disables the qspinlock slow path using PV optimizations 4626 which allow the hypervisor to 'idle' the guest on lock 4627 contention. 4628 4629 norandmaps Don't use address space randomization. Equivalent to 4630 echo 0 > /proc/sys/kernel/randomize_va_space 4631 4632 noresume [SWSUSP] Disables resume and restores original swap 4633 space. 4634 4635 no-scroll [VGA] Disables scrollback. 4636 This is required for the Braillex ib80-piezo Braille 4637 reader made by F.H. Papenmeier (Germany). 4638 4639 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4640 4641 nosmap [PPC,EARLY] 4642 Disable SMAP (Supervisor Mode Access Prevention) 4643 even if it is supported by processor. 4644 4645 nosmep [PPC64s,EARLY] 4646 Disable SMEP (Supervisor Mode Execution Prevention) 4647 even if it is supported by processor. 4648 4649 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4650 and disable the IO APIC. legacy for "maxcpus=0". 4651 4652 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4653 Equivalent to smt=1. 4654 4655 [KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). 4656 nosmt=force: Force disable SMT, cannot be undone 4657 via the sysfs control file. 4658 4659 nosoftlockup [KNL] Disable the soft-lockup detector. 4660 4661 nospec_store_bypass_disable 4662 [HW,EARLY] Disable all mitigations for the Speculative 4663 Store Bypass vulnerability 4664 4665 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4666 history injection) vulnerability. System may allow data leaks 4667 with this option. 4668 4669 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4670 (bounds check bypass). With this option data leaks are 4671 possible in the system. 4672 4673 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4674 for the Spectre variant 2 (indirect branch 4675 prediction) vulnerability. System may allow data 4676 leaks with this option. 4677 4678 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4679 Disable paravirtualized steal time accounting. steal time 4680 is computed, but won't influence scheduler behaviour 4681 4682 nosync [HW,M68K] Disables sync negotiation for all devices. 4683 4684 no_timer_check [X86,APIC] Disables the code which tests for broken 4685 timer IRQ sources, i.e., the IO-APIC timer. This can 4686 work around problems with incorrect timer 4687 initialization on some boards. 4688 4689 no_uaccess_flush 4690 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4691 4692 novmcoredd [KNL,KDUMP] 4693 Disable device dump. Device dump allows drivers to 4694 append dump data to vmcore so you can collect driver 4695 specified debug info. Drivers can append the data 4696 without any limit and this data is stored in memory, 4697 so this may cause significant memory stress. Disabling 4698 device dump can help save memory but the driver debug 4699 data will be no longer available. This parameter 4700 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4701 is set. 4702 4703 no-vmw-sched-clock 4704 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4705 scheduler clock and use the default one. 4706 4707 nowatchdog [KNL] Disable both lockup detectors, i.e. 4708 soft-lockup and NMI watchdog (hard-lockup). 4709 4710 nowb [ARM,EARLY] 4711 4712 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4713 4714 NOTE: this parameter will be ignored on systems with the 4715 LEGACY_XAPIC_DISABLED bit set in the 4716 IA32_XAPIC_DISABLE_STATUS MSR. 4717 4718 noxsave [BUGS=X86] Disables x86 extended register state save 4719 and restore using xsave. The kernel will fallback to 4720 enabling legacy floating-point and sse state. 4721 4722 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4723 register states. The kernel will fall back to use 4724 xsave to save the states. By using this parameter, 4725 performance of saving the states is degraded because 4726 xsave doesn't support modified optimization while 4727 xsaveopt supports it on xsaveopt enabled systems. 4728 4729 noxsaves [X86] Disables xsaves and xrstors used in saving and 4730 restoring x86 extended register state in compacted 4731 form of xsave area. The kernel will fall back to use 4732 xsaveopt and xrstor to save and restore the states 4733 in standard form of xsave area. By using this 4734 parameter, xsave area per process might occupy more 4735 memory on xsaves enabled systems. 4736 4737 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4738 could support. nr_cpus=n : n >= 1 limits the kernel to 4739 support 'n' processors. It could be larger than the 4740 number of already plugged CPU during bootup, later in 4741 runtime you can physically add extra cpu until it reaches 4742 n. So during boot up some boot time memory for per-cpu 4743 variables need be pre-allocated for later physical cpu 4744 hot plugging. 4745 4746 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4747 4748 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4749 Disable NUMA, Only set up a single NUMA node 4750 spanning all memory. 4751 4752 numa=fake=<size>[MG] 4753 [KNL, ARM64, RISCV, X86, EARLY] 4754 If given as a memory unit, fills all system RAM with 4755 nodes of size interleaved over physical nodes. 4756 4757 numa=fake=<N> 4758 [KNL, ARM64, RISCV, X86, EARLY] 4759 If given as an integer, fills all system RAM with N 4760 fake nodes interleaved over physical nodes. 4761 4762 numa=fake=<N>U 4763 [KNL, ARM64, RISCV, X86, EARLY] 4764 If given as an integer followed by 'U', it will 4765 divide each physical node into N emulated nodes. 4766 4767 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4768 4769 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4770 soft-reserved memory partitioning. 4771 4772 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4773 NUMA balancing. 4774 Allowed values are enable and disable 4775 4776 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4777 'node', 'default' can be specified 4778 This can be set from sysctl after boot. 4779 See Documentation/admin-guide/sysctl/vm.rst for details. 4780 4781 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4782 nvme quirk list. List entries are separated by a 4783 '-' character. 4784 Each entry has the form VendorID:ProductID:quirk_names. 4785 The IDs are 4-digits hex numbers and quirk_names is a 4786 list of quirk names separated by commas. A quirk name 4787 can be prefixed by '^', meaning that the specified 4788 quirk must be disabled. 4789 4790 Example: 4791 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4792 4793 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4794 See Documentation/core-api/debugging-via-ohci1394.rst for more 4795 info. 4796 4797 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4798 Rather than timing out after 20 ms if an EC 4799 command is not properly ACKed, override the length 4800 of the timeout. We have interrupts disabled while 4801 waiting for the ACK, so if this is set too high 4802 interrupts *may* be lost! 4803 4804 omap_mux= [OMAP] Override bootloader pin multiplexing. 4805 Format: <mux_mode0.mode_name=value>... 4806 For example, to override I2C bus2: 4807 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4808 4809 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4810 4811 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4812 4813 boundary - index of last SLC block on Flex-OneNAND. 4814 The remaining blocks are configured as MLC blocks. 4815 lock - Configure if Flex-OneNAND boundary should be locked. 4816 Once locked, the boundary cannot be changed. 4817 1 indicates lock status, 0 indicates unlock status. 4818 4819 oops=panic [KNL,EARLY] 4820 Always panic on oopses. Default is to just kill the 4821 process, but there is a small probability of 4822 deadlocking the machine. 4823 This will also cause panics on machine check exceptions. 4824 Useful together with panic=30 to trigger a reboot. 4825 4826 page_alloc.shuffle= 4827 [KNL] Boolean flag to control whether the page allocator 4828 should randomize its free lists. This parameter can be 4829 used to enable/disable page randomization. The state of 4830 the flag can be read from sysfs at: 4831 /sys/module/page_alloc/parameters/shuffle. 4832 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4833 4834 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4835 Storage of the information about who allocated 4836 each page is disabled in default. With this switch, 4837 we can turn it on. 4838 on: enable the feature 4839 4840 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4841 poisoning on the buddy allocator, available with 4842 CONFIG_PAGE_POISONING=y. 4843 off: turn off poisoning (default) 4844 on: turn on poisoning 4845 4846 page_reporting.page_reporting_order= 4847 [KNL] Minimal page reporting order 4848 Format: <integer> 4849 Adjust the minimal page reporting order. The page 4850 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4851 4852 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4853 timeout > 0: seconds before rebooting 4854 timeout = 0: wait forever 4855 timeout < 0: reboot immediately 4856 Format: <timeout> 4857 4858 panic_on_taint= [KNL,EARLY] 4859 Bitmask for conditionally calling panic() in add_taint() 4860 Format: <hex>[,nousertaint] 4861 Hexadecimal bitmask representing the set of TAINT flags 4862 that will cause the kernel to panic when add_taint() is 4863 called with any of the flags in this set. 4864 The optional switch "nousertaint" can be utilized to 4865 prevent userspace forced crashes by writing to sysctl 4866 /proc/sys/kernel/tainted any flagset matching with the 4867 bitmask set on panic_on_taint. 4868 See Documentation/admin-guide/tainted-kernels.rst for 4869 extra details on the taint flags that users can pick 4870 to compose the bitmask to assign to panic_on_taint. 4871 4872 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4873 on a WARN(). 4874 4875 panic_force_cpu= 4876 [KNL,SMP] Force panic handling to execute on a specific CPU. 4877 Format: <cpu number> 4878 Some platforms require panic handling to occur on a 4879 specific CPU for the crash kernel to function correctly. 4880 This can be due to firmware limitations, interrupt routing 4881 constraints, or platform-specific requirements where only 4882 a particular CPU can safely enter the crash kernel. 4883 When set, panic() will redirect execution to the specified 4884 CPU before proceeding with the normal panic and kexec flow. 4885 If the target CPU is offline or unavailable, panic proceeds 4886 on the current CPU. 4887 This option should only be used for systems with the above 4888 constraints as it might cause the panic operation to be less reliable. 4889 4890 panic_print= Bitmask for printing system info when panic happens. 4891 User can chose combination of the following bits: 4892 bit 0: print all tasks info 4893 bit 1: print system memory info 4894 bit 2: print timer info 4895 bit 3: print locks info if CONFIG_LOCKDEP is on 4896 bit 4: print ftrace buffer 4897 bit 5: replay all kernel messages on consoles at the end of panic 4898 bit 6: print all CPUs backtrace (if available in the arch) 4899 bit 7: print only tasks in uninterruptible (blocked) state 4900 *Be aware* that this option may print a _lot_ of lines, 4901 so there are risks of losing older messages in the log. 4902 Use this option carefully, maybe worth to setup a 4903 bigger log buffer with "log_buf_len" along with this. 4904 4905 panic_sys_info= A comma separated list of extra information to be dumped 4906 on panic. 4907 Format: val[,val...] 4908 Where @val can be any of the following: 4909 4910 tasks: print all tasks info 4911 mem: print system memory info 4912 timers: print timers info 4913 locks: print locks info if CONFIG_LOCKDEP is on 4914 ftrace: print ftrace buffer 4915 all_bt: print all CPUs backtrace (if available in the arch) 4916 blocked_tasks: print only tasks in uninterruptible (blocked) state 4917 4918 This is a human readable alternative to the 'panic_print' option. 4919 4920 panic_console_replay 4921 When panic happens, replay all kernel messages on 4922 consoles at the end of panic. 4923 4924 parkbd.port= [HW] Parallel port number the keyboard adapter is 4925 connected to, default is 0. 4926 Format: <parport#> 4927 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4928 0 for XT, 1 for AT (default is AT). 4929 Format: <mode> 4930 4931 parport= [HW,PPT] Specify parallel ports. 0 disables. 4932 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4933 Use 'auto' to force the driver to use any 4934 IRQ/DMA settings detected (the default is to 4935 ignore detected IRQ/DMA settings because of 4936 possible conflicts). You can specify the base 4937 address, IRQ, and DMA settings; IRQ and DMA 4938 should be numbers, or 'auto' (for using detected 4939 settings on that particular port), or 'nofifo' 4940 (to avoid using a FIFO even if it is detected). 4941 Parallel ports are assigned in the order they 4942 are specified on the command line, starting 4943 with parport0. 4944 4945 parport_init_mode= [HW,PPT] 4946 Configure VIA parallel port to operate in 4947 a specific mode. This is necessary on Pegasos 4948 computer where firmware has no options for setting 4949 up parallel port mode and sets it to spp. 4950 Currently this function knows 686a and 8231 chips. 4951 Format: [spp|ps2|epp|ecp|ecpepp] 4952 4953 pata_legacy.all= [HW,LIBATA] 4954 Format: <int> 4955 Set to non-zero to probe primary and secondary ISA 4956 port ranges on PCI systems where no PCI PATA device 4957 has been found at either range. Disabled by default. 4958 4959 pata_legacy.autospeed= [HW,LIBATA] 4960 Format: <int> 4961 Set to non-zero if a chip is present that snoops speed 4962 changes. Disabled by default. 4963 4964 pata_legacy.ht6560a= [HW,LIBATA] 4965 Format: <int> 4966 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4967 the secondary channel, or both channels respectively. 4968 Disabled by default. 4969 4970 pata_legacy.ht6560b= [HW,LIBATA] 4971 Format: <int> 4972 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4973 the secondary channel, or both channels respectively. 4974 Disabled by default. 4975 4976 pata_legacy.iordy_mask= [HW,LIBATA] 4977 Format: <int> 4978 IORDY enable mask. Set individual bits to allow IORDY 4979 for the respective channel. Bit 0 is for the first 4980 legacy channel handled by this driver, bit 1 is for 4981 the second channel, and so on. The sequence will often 4982 correspond to the primary legacy channel, the secondary 4983 legacy channel, and so on, but the handling of a PCI 4984 bus and the use of other driver options may interfere 4985 with the sequence. By default IORDY is allowed across 4986 all channels. 4987 4988 pata_legacy.opti82c46x= [HW,LIBATA] 4989 Format: <int> 4990 Set to 1, 2, or 3 for Opti 82c611A on the primary 4991 channel, the secondary channel, or both channels 4992 respectively. Disabled by default. 4993 4994 pata_legacy.opti82c611a= [HW,LIBATA] 4995 Format: <int> 4996 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4997 channel, the secondary channel, or both channels 4998 respectively. Disabled by default. 4999 5000 pata_legacy.pio_mask= [HW,LIBATA] 5001 Format: <int> 5002 PIO mode mask for autospeed devices. Set individual 5003 bits to allow the use of the respective PIO modes. 5004 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 5005 All modes allowed by default. 5006 5007 pata_legacy.probe_all= [HW,LIBATA] 5008 Format: <int> 5009 Set to non-zero to probe tertiary and further ISA 5010 port ranges on PCI systems. Disabled by default. 5011 5012 pata_legacy.probe_mask= [HW,LIBATA] 5013 Format: <int> 5014 Probe mask for legacy ISA PATA ports. Depending on 5015 platform configuration and the use of other driver 5016 options up to 6 legacy ports are supported: 0x1f0, 5017 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5018 of individual ports can be disabled by setting the 5019 corresponding bits in the mask to 1. Bit 0 is for 5020 the first port in the list above (0x1f0), and so on. 5021 By default all supported ports are probed. 5022 5023 pata_legacy.qdi= [HW,LIBATA] 5024 Format: <int> 5025 Set to non-zero to probe QDI controllers. By default 5026 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5027 5028 pata_legacy.winbond= [HW,LIBATA] 5029 Format: <int> 5030 Set to non-zero to probe Winbond controllers. Use 5031 the standard I/O port (0x130) if 1, otherwise the 5032 value given is the I/O port to use (typically 0x1b0). 5033 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5034 0 otherwise. 5035 5036 pata_platform.pio_mask= [HW,LIBATA] 5037 Format: <int> 5038 Supported PIO mode mask. Set individual bits to allow 5039 the use of the respective PIO modes. Bit 0 is for 5040 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5041 allowed by default. 5042 5043 pause_on_oops=<int> 5044 Halt all CPUs after the first oops has been printed for 5045 the specified number of seconds. This is to be used if 5046 your oopses keep scrolling off the screen. 5047 5048 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5049 5050 Some options herein operate on a specific device 5051 or a set of devices (<pci_dev>). These are 5052 specified in one of the following formats: 5053 5054 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5055 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5056 5057 Note: the first format specifies a PCI 5058 bus/device/function address which may change 5059 if new hardware is inserted, if motherboard 5060 firmware changes, or due to changes caused 5061 by other kernel parameters. If the 5062 domain is left unspecified, it is 5063 taken to be zero. Optionally, a path 5064 to a device through multiple device/function 5065 addresses can be specified after the base 5066 address (this is more robust against 5067 renumbering issues). The second format 5068 selects devices using IDs from the 5069 configuration space which may match multiple 5070 devices in the system. 5071 5072 earlydump dump PCI config space before the kernel 5073 changes anything 5074 off [X86] don't probe for the PCI bus 5075 bios [X86-32] force use of PCI BIOS, don't access 5076 the hardware directly. Use this if your machine 5077 has a non-standard PCI host bridge. 5078 nobios [X86-32] disallow use of PCI BIOS, only direct 5079 hardware access methods are allowed. Use this 5080 if you experience crashes upon bootup and you 5081 suspect they are caused by the BIOS. 5082 conf1 [X86] Force use of PCI Configuration Access 5083 Mechanism 1 (config address in IO port 0xCF8, 5084 data in IO port 0xCFC, both 32-bit). 5085 conf2 [X86] Force use of PCI Configuration Access 5086 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5087 the function, IO port 0xCFA, also 8-bit, sets 5088 bus number. The config space is then accessed 5089 through ports 0xC000-0xCFFF). 5090 See http://wiki.osdev.org/PCI for more info 5091 on the configuration access mechanisms. 5092 noaer [PCIE] If the PCIEAER kernel config parameter is 5093 enabled, this kernel boot option can be used to 5094 disable the use of PCIE advanced error reporting. 5095 nodomains [PCI] Disable support for multiple PCI 5096 root domains (aka PCI segments, in ACPI-speak). 5097 nommconf [X86] Disable use of MMCONFIG for PCI 5098 Configuration 5099 check_enable_amd_mmconf [X86] check for and enable 5100 properly configured MMIO access to PCI 5101 config space on AMD family 10h CPU 5102 nomsi [MSI] If the PCI_MSI kernel config parameter is 5103 enabled, this kernel boot option can be used to 5104 disable the use of MSI interrupts system-wide. 5105 noioapicquirk [APIC] Disable all boot interrupt quirks. 5106 Safety option to keep boot IRQs enabled. This 5107 should never be necessary. 5108 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5109 primary IO-APIC for bridges that cannot disable 5110 boot IRQs. This fixes a source of spurious IRQs 5111 when the system masks IRQs. 5112 noioapicreroute [APIC] Disable workaround that uses the 5113 boot IRQ equivalent of an IRQ that connects to 5114 a chipset where boot IRQs cannot be disabled. 5115 The opposite of ioapicreroute. 5116 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5117 routing table. These calls are known to be buggy 5118 on several machines and they hang the machine 5119 when used, but on other computers it's the only 5120 way to get the interrupt routing table. Try 5121 this option if the kernel is unable to allocate 5122 IRQs or discover secondary PCI buses on your 5123 motherboard. 5124 rom [X86] Assign address space to expansion ROMs. 5125 Use with caution as certain devices share 5126 address decoders between ROMs and other 5127 resources. 5128 norom [X86] Do not assign address space to 5129 expansion ROMs that do not already have 5130 BIOS assigned address ranges. 5131 nobar [X86] Do not assign address space to the 5132 BARs that weren't assigned by the BIOS. 5133 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5134 assigned automatically to PCI devices. You can 5135 make the kernel exclude IRQs of your ISA cards 5136 this way. 5137 pirqaddr=0xAAAAA [X86] Specify the physical address 5138 of the PIRQ table (normally generated 5139 by the BIOS) if it is outside the 5140 F0000h-100000h range. 5141 lastbus=N [X86] Scan all buses thru bus #N. Can be 5142 useful if the kernel is unable to find your 5143 secondary buses and you want to tell it 5144 explicitly which ones they are. 5145 assign-busses [X86] Always assign all PCI bus 5146 numbers ourselves, overriding 5147 whatever the firmware may have done. 5148 usepirqmask [X86] Honor the possible IRQ mask stored 5149 in the BIOS $PIR table. This is needed on 5150 some systems with broken BIOSes, notably 5151 some HP Pavilion N5400 and Omnibook XE3 5152 notebooks. This will have no effect if ACPI 5153 IRQ routing is enabled. 5154 noacpi [X86] Do not use ACPI for IRQ routing 5155 or for PCI scanning. 5156 use_crs [X86] Use PCI host bridge window information 5157 from ACPI. On BIOSes from 2008 or later, this 5158 is enabled by default. If you need to use this, 5159 please report a bug. 5160 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5161 If you need to use this, please report a bug. 5162 use_e820 [X86] Use E820 reservations to exclude parts of 5163 PCI host bridge windows. This is a workaround 5164 for BIOS defects in host bridge _CRS methods. 5165 If you need to use this, please report a bug to 5166 <linux-pci@vger.kernel.org>. 5167 no_e820 [X86] Ignore E820 reservations for PCI host 5168 bridge windows. This is the default on modern 5169 hardware. If you need to use this, please report 5170 a bug to <linux-pci@vger.kernel.org>. 5171 routeirq Do IRQ routing for all PCI devices. 5172 This is normally done in pci_enable_device(), 5173 so this option is a temporary workaround 5174 for broken drivers that don't call it. 5175 skip_isa_align [X86] do not align io start addr, so can 5176 handle more pci cards 5177 noearly [X86] Don't do any early type 1 scanning. 5178 This might help on some broken boards which 5179 machine check when some devices' config space 5180 is read. But various workarounds are disabled 5181 and some IOMMU drivers will not work. 5182 bfsort Sort PCI devices into breadth-first order. 5183 This sorting is done to get a device 5184 order compatible with older (<= 2.4) kernels. 5185 nobfsort Don't sort PCI devices into breadth-first order. 5186 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5187 tuning and use the BIOS-configured MPS defaults. 5188 pcie_bus_safe Set every device's MPS to the largest value 5189 supported by all devices below the root complex. 5190 pcie_bus_perf Set device MPS to the largest allowable MPS 5191 based on its parent bus. Also set MRRS (Max 5192 Read Request Size) to the largest supported 5193 value (no larger than the MPS that the device 5194 or bus can support) for best performance. 5195 pcie_bus_peer2peer Set every device's MPS to 128B, which 5196 every device is guaranteed to support. This 5197 configuration allows peer-to-peer DMA between 5198 any pair of devices, possibly at the cost of 5199 reduced performance. This also guarantees 5200 that hot-added devices will work. 5201 cbiosize=nn[KMG] The fixed amount of bus space which is 5202 reserved for the CardBus bridge's IO window. 5203 The default value is 256 bytes. 5204 cbmemsize=nn[KMG] The fixed amount of bus space which is 5205 reserved for the CardBus bridge's memory 5206 window. The default value is 64 megabytes. 5207 resource_alignment= 5208 Format: 5209 [<order of align>@]<pci_dev>[; ...] 5210 Specifies alignment and device to reassign 5211 aligned memory resources. How to 5212 specify the device is described above. 5213 If <order of align> is not specified, 5214 PAGE_SIZE is used as alignment. 5215 A PCI-PCI bridge can be specified if resource 5216 windows need to be expanded. 5217 To specify the alignment for several 5218 instances of a device, the PCI vendor, 5219 device, subvendor, and subdevice may be 5220 specified, e.g., 12@pci:8086:9c22:103c:198f 5221 for 4096-byte alignment. 5222 ecrc= Enable/disable PCIe ECRC (transaction layer 5223 end-to-end CRC checking). Only effective if 5224 OS has native AER control (either granted by 5225 ACPI _OSC or forced via "pcie_ports=native") 5226 bios: Use BIOS/firmware settings. This is the 5227 the default. 5228 off: Turn ECRC off 5229 on: Turn ECRC on. 5230 hpiosize=nn[KMG] The fixed amount of bus space which is 5231 reserved for hotplug bridge's IO window. 5232 Default size is 256 bytes. 5233 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5234 reserved for hotplug bridge's MMIO window. 5235 Default size is 2 megabytes. 5236 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5237 reserved for hotplug bridge's MMIO_PREF window. 5238 Default size is 2 megabytes. 5239 hpmemsize=nn[KMG] The fixed amount of bus space which is 5240 reserved for hotplug bridge's MMIO and 5241 MMIO_PREF window. 5242 Default size is 2 megabytes. 5243 hpbussize=nn The minimum amount of additional bus numbers 5244 reserved for buses below a hotplug bridge. 5245 Default is 1. 5246 realloc= Enable/disable reallocating PCI bridge resources 5247 if allocations done by BIOS are too small to 5248 accommodate resources required by all child 5249 devices. 5250 off: Turn realloc off 5251 on: Turn realloc on 5252 realloc same as realloc=on 5253 noari do not use PCIe ARI. 5254 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5255 do not use PCIe ATS (and IOMMU device IOTLB). 5256 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5257 only look for one device below a PCIe downstream 5258 port. 5259 big_root_window Try to add a big 64bit memory window to the PCIe 5260 root complex on AMD CPUs. Some GFX hardware 5261 can resize a BAR to allow access to all VRAM. 5262 Adding the window is slightly risky (it may 5263 conflict with unreported devices), so this 5264 taints the kernel. 5265 disable_acs_redir=<pci_dev>[; ...] 5266 Specify one or more PCI devices (in the format 5267 specified above) separated by semicolons. 5268 Each device specified will have the PCI ACS 5269 redirect capabilities forced off which will 5270 allow P2P traffic between devices through 5271 bridges without forcing it upstream. Note: 5272 this removes isolation between devices and 5273 may put more devices in an IOMMU group. 5274 config_acs= 5275 Format: 5276 <ACS flags>@<pci_dev>[; ...] 5277 Specify one or more PCI devices (in the format 5278 specified above) optionally prepended with flags 5279 and separated by semicolons. The respective 5280 capabilities will be enabled, disabled or 5281 unchanged based on what is specified in 5282 flags. 5283 5284 ACS Flags is defined as follows: 5285 bit-0 : ACS Source Validation 5286 bit-1 : ACS Translation Blocking 5287 bit-2 : ACS P2P Request Redirect 5288 bit-3 : ACS P2P Completion Redirect 5289 bit-4 : ACS Upstream Forwarding 5290 bit-5 : ACS P2P Egress Control 5291 bit-6 : ACS Direct Translated P2P 5292 Each bit can be marked as: 5293 '0' – force disabled 5294 '1' – force enabled 5295 'x' – unchanged 5296 For example, 5297 pci=config_acs=10x@pci:0:0 5298 would configure all devices that support 5299 ACS to enable P2P Request Redirect, disable 5300 Translation Blocking, and leave Source 5301 Validation unchanged from whatever power-up 5302 or firmware set it to. 5303 5304 Note: this may remove isolation between devices 5305 and may put more devices in an IOMMU group. 5306 force_floating [S390] Force usage of floating interrupts. 5307 nomio [S390] Do not use MIO instructions. 5308 norid [S390] ignore the RID field and force use of 5309 one PCI domain per PCI function 5310 notph [PCIE] If the PCIE_TPH kernel config parameter 5311 is enabled, this kernel boot option can be used 5312 to disable PCIe TLP Processing Hints support 5313 system-wide. 5314 5315 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5316 Management. 5317 off Don't touch ASPM configuration at all. Leave any 5318 configuration done by firmware unchanged. 5319 force Enable ASPM even on devices that claim not to support it. 5320 WARNING: Forcing ASPM on may cause system lockups. 5321 5322 pcie_ports= [PCIE] PCIe port services handling: 5323 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5324 even if the platform doesn't give the OS permission to 5325 use them. This may cause conflicts if the platform 5326 also tries to use these services. 5327 dpc-native Use native PCIe service for DPC only. May 5328 cause conflicts if firmware uses AER or DPC. 5329 compat Disable native PCIe services (PME, AER, DPC, PCIe 5330 hotplug). 5331 5332 pcie_port_pm= [PCIE] PCIe port power management handling: 5333 off Disable power management of all PCIe ports 5334 force Forcibly enable power management of all PCIe ports 5335 5336 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5337 nomsi Do not use MSI for native PCIe PME signaling (this makes 5338 all PCIe root ports use INTx for all services). 5339 5340 pcmv= [HW,PCMCIA] BadgePAD 4 5341 5342 pd_ignore_unused 5343 [PM] 5344 Keep all power-domains already enabled by bootloader on, 5345 even if no driver has claimed them. This is useful 5346 for debug and development, but should not be 5347 needed on a platform with proper driver support. 5348 5349 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5350 boot time. 5351 Format: { 0 | 1 } 5352 See arch/parisc/kernel/pdc_chassis.c 5353 5354 percpu_alloc= [MM,EARLY] 5355 Select which percpu first chunk allocator to use. 5356 Currently supported values are "embed" and "page". 5357 Archs may support subset or none of the selections. 5358 See comments in mm/percpu.c for details on each 5359 allocator. This parameter is primarily for debugging 5360 and performance comparison. 5361 5362 pirq= [SMP,APIC] Manual mp-table setup 5363 See Documentation/arch/x86/i386/IO-APIC.rst. 5364 5365 plip= [PPT,NET] Parallel port network link 5366 Format: { parport<nr> | timid | 0 } 5367 See also Documentation/admin-guide/parport.rst. 5368 5369 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5370 Override pmtimer IOPort with a hex value. 5371 e.g. pmtmr=0x508 5372 5373 pmu_override= [PPC] Override the PMU. 5374 This option takes over the PMU facility, so it is no 5375 longer usable by perf. Setting this option starts the 5376 PMU counters by setting MMCR0 to 0 (the FC bit is 5377 cleared). If a number is given, then MMCR1 is set to 5378 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5379 remains 0. 5380 5381 pm_async= [PM] 5382 Format: off 5383 This parameter sets the initial value of the 5384 /sys/power/pm_async sysfs knob at boot time. 5385 If set to "off", disables asynchronous suspend and 5386 resume of devices during system-wide power transitions. 5387 This can be useful on platforms where device 5388 dependencies are not well-defined, or for debugging 5389 power management issues. Asynchronous operations are 5390 enabled by default. 5391 5392 5393 pm_debug_messages [SUSPEND,KNL] 5394 Enable suspend/resume debug messages during boot up. 5395 5396 pm.dpm_watchdog_enabled= 5397 [PM] Enable or disable the DPM watchdog. Requires 5398 CONFIG_PM_SLEEP and CONFIG_DPM_WATCHDOG enabled. 5399 Format: <bool> 5400 Default value is set by CONFIG_DPM_WATCHDOG_ENABLED. 5401 5402 pnp.debug=1 [PNP] 5403 Enable PNP debug messages (depends on the 5404 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5405 via /sys/module/pnp/parameters/debug. We always show 5406 current resource usage; turning this on also shows 5407 possible settings and some assignment information. 5408 5409 pnpacpi= [ACPI] 5410 { off } 5411 5412 pnpbios= [ISAPNP] 5413 { on | off | curr | res | no-curr | no-res } 5414 5415 pnp_reserve_irq= 5416 [ISAPNP] Exclude IRQs for the autoconfiguration 5417 5418 pnp_reserve_dma= 5419 [ISAPNP] Exclude DMAs for the autoconfiguration 5420 5421 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5422 Ranges are in pairs (I/O port base and size). 5423 5424 pnp_reserve_mem= 5425 [ISAPNP] Exclude memory regions for the 5426 autoconfiguration. 5427 Ranges are in pairs (memory base and size). 5428 5429 ports= [IP_VS_FTP] IPVS ftp helper module 5430 Default is 21. 5431 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5432 may be specified. 5433 Format: <port>,<port>.... 5434 5435 possible_cpus= [SMP,S390,X86] 5436 Format: <unsigned int> 5437 Set the number of possible CPUs, overriding the 5438 regular discovery mechanisms (such as ACPI/FW, etc). 5439 5440 powersave=off [PPC] This option disables power saving features. 5441 It specifically disables cpuidle and sets the 5442 platform machine description specific power_save 5443 function to NULL. On Idle the CPU just reduces 5444 execution priority. 5445 5446 ppc_strict_facility_enable 5447 [PPC,ENABLE] This option catches any kernel floating point, 5448 Altivec, VSX and SPE outside of regions specifically 5449 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5450 There is some performance impact when enabling this. 5451 5452 ppc_tm= [PPC,EARLY] 5453 Format: {"off"} 5454 Disable Hardware Transactional Memory 5455 5456 preempt= [KNL] 5457 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5458 none - Limited to cond_resched() calls 5459 voluntary - Limited to cond_resched() and might_sleep() calls 5460 full - Any section that isn't explicitly preempt disabled 5461 can be preempted anytime. Tasks will also yield 5462 contended spinlocks (if the critical section isn't 5463 explicitly preempt disabled beyond the lock itself). 5464 lazy - Scheduler controlled. Similar to full but instead 5465 of preempting the task immediately, the task gets 5466 one HZ tick time to yield itself before the 5467 preemption will be forced. One preemption is when the 5468 task returns to user space. 5469 5470 print-fatal-signals= 5471 [KNL] debug: print fatal signals 5472 5473 If enabled, warn about various signal handling 5474 related application anomalies: too many signals, 5475 too many POSIX.1 timers, fatal signals causing a 5476 coredump - etc. 5477 5478 If you hit the warning due to signal overflow, 5479 you might want to try "ulimit -i unlimited". 5480 5481 default: off. 5482 5483 printk.always_kmsg_dump= 5484 Trigger kmsg_dump for cases other than kernel oops or 5485 panics 5486 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5487 default: disabled 5488 5489 printk.console_no_auto_verbose= 5490 Disable console loglevel raise on oops, panic 5491 or lockdep-detected issues (only if lock debug is on). 5492 With an exception to setups with low baudrate on 5493 serial console, keeping this 0 is a good choice 5494 in order to provide more debug information. 5495 Format: <bool> 5496 default: 0 (auto_verbose is enabled) 5497 5498 printk.debug_non_panic_cpus= 5499 Allows storing messages from non-panic CPUs into 5500 the printk log buffer during panic(). They are 5501 flushed to consoles by the panic-CPU on 5502 a best-effort basis. 5503 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5504 Default: disabled 5505 5506 printk.devkmsg={on,off,ratelimit} 5507 Control writing to /dev/kmsg. 5508 on - unlimited logging to /dev/kmsg from userspace 5509 off - logging to /dev/kmsg disabled 5510 ratelimit - ratelimit the logging 5511 Default: ratelimit 5512 5513 printk.time= Show timing data prefixed to each printk message line 5514 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5515 5516 proc_mem.force_override= [KNL] 5517 Format: {always | ptrace | never} 5518 Traditionally /proc/pid/mem allows memory permissions to be 5519 overridden without restrictions. This option may be set to 5520 restrict that. Can be one of: 5521 - 'always': traditional behavior always allows mem overrides. 5522 - 'ptrace': only allow mem overrides for active ptracers. 5523 - 'never': never allow mem overrides. 5524 If not specified, default is the CONFIG_PROC_MEM_* choice. 5525 5526 processor.max_cstate= [HW,ACPI] 5527 Limit processor to maximum C-state 5528 max_cstate=9 overrides any DMI blacklist limit. 5529 5530 processor.nocst [HW,ACPI] 5531 Ignore the _CST method to determine C-states, 5532 instead using the legacy FADT method 5533 5534 profile= [KNL] Enable kernel profiling via /proc/profile 5535 Format: [<profiletype>,]<number> 5536 Param: <profiletype>: "schedule" or "kvm" 5537 [defaults to kernel profiling] 5538 Param: "schedule" - profile schedule points. 5539 Param: "kvm" - profile VM exits. 5540 Param: <number> - step/bucket size as a power of 2 for 5541 statistical time based profiling. 5542 5543 prot_virt= [S390] enable hosting protected virtual machines 5544 isolated from the hypervisor (if hardware supports 5545 that). If enabled, the default kernel base address 5546 might be overridden even when Kernel Address Space 5547 Layout Randomization is disabled. 5548 Format: <bool> 5549 5550 psi= [KNL] Enable or disable pressure stall information 5551 tracking. 5552 Format: <bool> 5553 5554 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5555 probe for; one of (bare|imps|exps|lifebook|any). 5556 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5557 per second. 5558 psmouse.resetafter= [HW,MOUSE] 5559 Try to reset the device after so many bad packets 5560 (0 = never). 5561 psmouse.resolution= 5562 [HW,MOUSE] Set desired mouse resolution, in dpi. 5563 psmouse.smartscroll= 5564 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5565 0 = disabled, 1 = enabled (default). 5566 5567 pstore.backend= Specify the name of the pstore backend to use 5568 5569 pti= [X86-64] Control Page Table Isolation of user and 5570 kernel address spaces. Disabling this feature 5571 removes hardening, but improves performance of 5572 system calls and interrupts. 5573 5574 on - unconditionally enable 5575 off - unconditionally disable 5576 auto - kernel detects whether your CPU model is 5577 vulnerable to issues that PTI mitigates 5578 5579 Not specifying this option is equivalent to pti=auto. 5580 5581 pty.legacy_count= 5582 [KNL] Number of legacy pty's. Overwrites compiled-in 5583 default number. 5584 5585 quiet [KNL,EARLY] Disable most log messages 5586 5587 r128= [HW,DRM] 5588 5589 radix_hcall_invalidate=on [PPC/PSERIES] 5590 Disable RADIX GTSE feature and use hcall for TLB 5591 invalidate. 5592 5593 raid= [HW,RAID] 5594 See Documentation/admin-guide/md.rst. 5595 5596 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5597 See Documentation/admin-guide/blockdev/ramdisk.rst. 5598 5599 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5600 5601 random.trust_cpu=off 5602 [KNL,EARLY] Disable trusting the use of the CPU's 5603 random number generator (if available) to 5604 initialize the kernel's RNG. 5605 5606 random.trust_bootloader=off 5607 [KNL,EARLY] Disable trusting the use of the a seed 5608 passed by the bootloader (if available) to 5609 initialize the kernel's RNG. 5610 5611 randomize_kstack_offset= 5612 [KNL,EARLY] Enable or disable kernel stack offset 5613 randomization, which provides roughly 5 bits of 5614 entropy, frustrating memory corruption attacks 5615 that depend on stack address determinism or 5616 cross-syscall address exposures. This is only 5617 available on architectures that have defined 5618 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5619 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5620 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5621 5622 ras=option[,option,...] [KNL] RAS-specific options 5623 5624 cec_disable [X86] 5625 Disable the Correctable Errors Collector, 5626 see CONFIG_RAS_CEC help text. 5627 5628 rcu_nocbs[=cpu-list] 5629 [KNL] The optional argument is a cpu list, 5630 as described above. 5631 5632 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5633 enable the no-callback CPU mode, which prevents 5634 such CPUs' callbacks from being invoked in 5635 softirq context. Invocation of such CPUs' RCU 5636 callbacks will instead be offloaded to "rcuox/N" 5637 kthreads created for that purpose, where "x" is 5638 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5639 for the kthreads that mediate grace periods; and 5640 "N" is the CPU number. This reduces OS jitter on 5641 the offloaded CPUs, which can be useful for HPC 5642 and real-time workloads. It can also improve 5643 energy efficiency for asymmetric multiprocessors. 5644 5645 If a cpulist is passed as an argument, the specified 5646 list of CPUs is set to no-callback mode from boot. 5647 5648 Otherwise, if the '=' sign and the cpulist 5649 arguments are omitted, no CPU will be set to 5650 no-callback mode from boot but the mode may be 5651 toggled at runtime via cpusets. 5652 5653 Note that this argument takes precedence over 5654 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5655 5656 rcu_nocb_poll [KNL] 5657 Rather than requiring that offloaded CPUs 5658 (specified by rcu_nocbs= above) explicitly 5659 awaken the corresponding "rcuoN" kthreads, 5660 make these kthreads poll for callbacks. 5661 This improves the real-time response for the 5662 offloaded CPUs by relieving them of the need to 5663 wake up the corresponding kthread, but degrades 5664 energy efficiency by requiring that the kthreads 5665 periodically wake up to do the polling. 5666 5667 rcutree.blimit= [KNL] 5668 Set maximum number of finished RCU callbacks to 5669 process in one batch. 5670 5671 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5672 Do only a one-line RCU CPU stall warning when 5673 there is an ongoing too-long CSD-lock wait. 5674 5675 rcutree.do_rcu_barrier= [KNL] 5676 Request a call to rcu_barrier(). This is 5677 throttled so that userspace tests can safely 5678 hammer on the sysfs variable if they so choose. 5679 If triggered before the RCU grace-period machinery 5680 is fully active, this will error out with EAGAIN. 5681 5682 rcutree.dump_tree= [KNL] 5683 Dump the structure of the rcu_node combining tree 5684 out at early boot. This is used for diagnostic 5685 purposes, to verify correct tree setup. 5686 5687 rcutree.gp_cleanup_delay= [KNL] 5688 Set the number of jiffies to delay each step of 5689 RCU grace-period cleanup. 5690 5691 rcutree.gp_init_delay= [KNL] 5692 Set the number of jiffies to delay each step of 5693 RCU grace-period initialization. 5694 5695 rcutree.gp_preinit_delay= [KNL] 5696 Set the number of jiffies to delay each step of 5697 RCU grace-period pre-initialization, that is, 5698 the propagation of recent CPU-hotplug changes up 5699 the rcu_node combining tree. 5700 5701 rcutree.jiffies_till_first_fqs= [KNL] 5702 Set delay from grace-period initialization to 5703 first attempt to force quiescent states. 5704 Units are jiffies, minimum value is zero, 5705 and maximum value is HZ. 5706 5707 rcutree.jiffies_till_next_fqs= [KNL] 5708 Set delay between subsequent attempts to force 5709 quiescent states. Units are jiffies, minimum 5710 value is one, and maximum value is HZ. 5711 5712 rcutree.jiffies_till_sched_qs= [KNL] 5713 Set required age in jiffies for a 5714 given grace period before RCU starts 5715 soliciting quiescent-state help from 5716 rcu_note_context_switch() and cond_resched(). 5717 If not specified, the kernel will calculate 5718 a value based on the most recent settings 5719 of rcutree.jiffies_till_first_fqs 5720 and rcutree.jiffies_till_next_fqs. 5721 This calculated value may be viewed in 5722 rcutree.jiffies_to_sched_qs. Any attempt to set 5723 rcutree.jiffies_to_sched_qs will be cheerfully 5724 overwritten. 5725 5726 rcutree.kthread_prio= [KNL,BOOT] 5727 Set the SCHED_FIFO priority of the RCU per-CPU 5728 kthreads (rcuc/N). This value is also used for 5729 the priority of the RCU boost threads (rcub/N) 5730 and for the RCU grace-period kthreads (rcu_bh, 5731 rcu_preempt, and rcu_sched). If RCU_BOOST is 5732 set, valid values are 1-99 and the default is 1 5733 (the least-favored priority). Otherwise, when 5734 RCU_BOOST is not set, valid values are 0-99 and 5735 the default is zero (non-realtime operation). 5736 When RCU_NOCB_CPU is set, also adjust the 5737 priority of NOCB callback kthreads. 5738 5739 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5740 On callback-offloaded (rcu_nocbs) CPUs, 5741 RCU reduces the lock contention that would 5742 otherwise be caused by callback floods through 5743 use of the ->nocb_bypass list. However, in the 5744 common non-flooded case, RCU queues directly to 5745 the main ->cblist in order to avoid the extra 5746 overhead of the ->nocb_bypass list and its lock. 5747 But if there are too many callbacks queued during 5748 a single jiffy, RCU pre-queues the callbacks into 5749 the ->nocb_bypass queue. The definition of "too 5750 many" is supplied by this kernel boot parameter. 5751 5752 rcutree.nohz_full_patience_delay= [KNL] 5753 On callback-offloaded (rcu_nocbs) CPUs, avoid 5754 disturbing RCU unless the grace period has 5755 reached the specified age in milliseconds. 5756 Defaults to zero. Large values will be capped 5757 at five seconds. All values will be rounded down 5758 to the nearest value representable by jiffies. 5759 5760 rcutree.qhimark= [KNL] 5761 Set threshold of queued RCU callbacks beyond which 5762 batch limiting is disabled. 5763 5764 rcutree.qlowmark= [KNL] 5765 Set threshold of queued RCU callbacks below which 5766 batch limiting is re-enabled. 5767 5768 rcutree.qovld= [KNL] 5769 Set threshold of queued RCU callbacks beyond which 5770 RCU's force-quiescent-state scan will aggressively 5771 enlist help from cond_resched() and sched IPIs to 5772 help CPUs more quickly reach quiescent states. 5773 Set to less than zero to make this be set based 5774 on rcutree.qhimark at boot time and to zero to 5775 disable more aggressive help enlistment. 5776 5777 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5778 Set the page-cache refill delay (in milliseconds) 5779 in response to low-memory conditions. The range 5780 of permitted values is in the range 0:100000. 5781 5782 rcutree.rcu_divisor= [KNL] 5783 Set the shift-right count to use to compute 5784 the callback-invocation batch limit bl from 5785 the number of callbacks queued on this CPU. 5786 The result will be bounded below by the value of 5787 the rcutree.blimit kernel parameter. Every bl 5788 callbacks, the softirq handler will exit in 5789 order to allow the CPU to do other work. 5790 5791 Please note that this callback-invocation batch 5792 limit applies only to non-offloaded callback 5793 invocation. Offloaded callbacks are instead 5794 invoked in the context of an rcuoc kthread, which 5795 scheduler will preempt as it does any other task. 5796 5797 rcutree.rcu_fanout_exact= [KNL] 5798 Disable autobalancing of the rcu_node combining 5799 tree. This is used by rcutorture, and might 5800 possibly be useful for architectures having high 5801 cache-to-cache transfer latencies. 5802 5803 rcutree.rcu_fanout_leaf= [KNL] 5804 Change the number of CPUs assigned to each 5805 leaf rcu_node structure. Useful for very 5806 large systems, which will choose the value 64, 5807 and for NUMA systems with large remote-access 5808 latencies, which will choose a value aligned 5809 with the appropriate hardware boundaries. 5810 5811 rcutree.rcu_min_cached_objs= [KNL] 5812 Minimum number of objects which are cached and 5813 maintained per one CPU. Object size is equal 5814 to PAGE_SIZE. The cache allows to reduce the 5815 pressure to page allocator, also it makes the 5816 whole algorithm to behave better in low memory 5817 condition. 5818 5819 rcutree.rcu_nocb_gp_stride= [KNL] 5820 Set the number of NOCB callback kthreads in 5821 each group, which defaults to the square root 5822 of the number of CPUs. Larger numbers reduce 5823 the wakeup overhead on the global grace-period 5824 kthread, but increases that same overhead on 5825 each group's NOCB grace-period kthread. 5826 5827 rcutree.rcu_kick_kthreads= [KNL] 5828 Cause the grace-period kthread to get an extra 5829 wake_up() if it sleeps three times longer than 5830 it should at force-quiescent-state time. 5831 This wake_up() will be accompanied by a 5832 WARN_ONCE() splat and an ftrace_dump(). 5833 5834 rcutree.rcu_resched_ns= [KNL] 5835 Limit the time spend invoking a batch of RCU 5836 callbacks to the specified number of nanoseconds. 5837 By default, this limit is checked only once 5838 every 32 callbacks in order to limit the pain 5839 inflicted by local_clock() overhead. 5840 5841 rcutree.rcu_unlock_delay= [KNL] 5842 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5843 this specifies an rcu_read_unlock()-time delay 5844 in microseconds. This defaults to zero. 5845 Larger delays increase the probability of 5846 catching RCU pointer leaks, that is, buggy use 5847 of RCU-protected pointers after the relevant 5848 rcu_read_unlock() has completed. 5849 5850 rcutree.sysrq_rcu= [KNL] 5851 Commandeer a sysrq key to dump out Tree RCU's 5852 rcu_node tree with an eye towards determining 5853 why a new grace period has not yet started. 5854 5855 rcutree.use_softirq= [KNL] 5856 If set to zero, move all RCU_SOFTIRQ processing to 5857 per-CPU rcuc kthreads. Defaults to a non-zero 5858 value, meaning that RCU_SOFTIRQ is used by default. 5859 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5860 5861 But note that CONFIG_PREEMPT_RT=y kernels disable 5862 this kernel boot parameter, forcibly setting it 5863 to zero. 5864 5865 rcutree.enable_rcu_lazy= [KNL] 5866 To save power, batch RCU callbacks and flush after 5867 delay, memory pressure or callback list growing too 5868 big. 5869 5870 rcutree.rcu_normal_wake_from_gp= [KNL] 5871 Reduces a latency of synchronize_rcu() call. This approach 5872 maintains its own track of synchronize_rcu() callers, so it 5873 does not interact with regular callbacks because it does not 5874 use a call_rcu[_hurry]() path. Please note, this is for a 5875 normal grace period. 5876 5877 How to disable it: 5878 5879 echo 0 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5880 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=0" 5881 5882 Default is 1 if it is not explicitly disabled by the boot parameter 5883 passing 0. 5884 5885 rcuscale.gp_async= [KNL] 5886 Measure performance of asynchronous 5887 grace-period primitives such as call_rcu(). 5888 5889 rcuscale.gp_async_max= [KNL] 5890 Specify the maximum number of outstanding 5891 callbacks per writer thread. When a writer 5892 thread exceeds this limit, it invokes the 5893 corresponding flavor of rcu_barrier() to allow 5894 previously posted callbacks to drain. 5895 5896 rcuscale.gp_exp= [KNL] 5897 Measure performance of expedited synchronous 5898 grace-period primitives. 5899 5900 rcuscale.holdoff= [KNL] 5901 Set test-start holdoff period. The purpose of 5902 this parameter is to delay the start of the 5903 test until boot completes in order to avoid 5904 interference. 5905 5906 rcuscale.kfree_by_call_rcu= [KNL] 5907 In kernels built with CONFIG_RCU_LAZY=y, test 5908 call_rcu() instead of kfree_rcu(). 5909 5910 rcuscale.kfree_mult= [KNL] 5911 Instead of allocating an object of size kfree_obj, 5912 allocate one of kfree_mult * sizeof(kfree_obj). 5913 Defaults to 1. 5914 5915 rcuscale.kfree_rcu_test= [KNL] 5916 Set to measure performance of kfree_rcu() flooding. 5917 5918 rcuscale.kfree_rcu_test_double= [KNL] 5919 Test the double-argument variant of kfree_rcu(). 5920 If this parameter has the same value as 5921 rcuscale.kfree_rcu_test_single, both the single- 5922 and double-argument variants are tested. 5923 5924 rcuscale.kfree_rcu_test_single= [KNL] 5925 Test the single-argument variant of kfree_rcu(). 5926 If this parameter has the same value as 5927 rcuscale.kfree_rcu_test_double, both the single- 5928 and double-argument variants are tested. 5929 5930 rcuscale.kfree_nthreads= [KNL] 5931 The number of threads running loops of kfree_rcu(). 5932 5933 rcuscale.kfree_alloc_num= [KNL] 5934 Number of allocations and frees done in an iteration. 5935 5936 rcuscale.kfree_loops= [KNL] 5937 Number of loops doing rcuscale.kfree_alloc_num number 5938 of allocations and frees. 5939 5940 rcuscale.minruntime= [KNL] 5941 Set the minimum test run time in seconds. This 5942 does not affect the data-collection interval, 5943 but instead allows better measurement of things 5944 like CPU consumption. 5945 5946 rcuscale.nreaders= [KNL] 5947 Set number of RCU readers. The value -1 selects 5948 N, where N is the number of CPUs. A value 5949 "n" less than -1 selects N-n+1, where N is again 5950 the number of CPUs. For example, -2 selects N 5951 (the number of CPUs), -3 selects N+1, and so on. 5952 A value of "n" less than or equal to -N selects 5953 a single reader. 5954 5955 rcuscale.nwriters= [KNL] 5956 Set number of RCU writers. The values operate 5957 the same as for rcuscale.nreaders. 5958 N, where N is the number of CPUs 5959 5960 rcuscale.scale_type= [KNL] 5961 Specify the RCU implementation to test. 5962 5963 rcuscale.shutdown= [KNL] 5964 Shut the system down after performance tests 5965 complete. This is useful for hands-off automated 5966 testing. 5967 5968 rcuscale.verbose= [KNL] 5969 Enable additional printk() statements. 5970 5971 rcuscale.writer_holdoff= [KNL] 5972 Write-side holdoff between grace periods, 5973 in microseconds. The default of zero says 5974 no holdoff. 5975 5976 rcuscale.writer_holdoff_jiffies= [KNL] 5977 Additional write-side holdoff between grace 5978 periods, but in jiffies. The default of zero 5979 says no holdoff. 5980 5981 rcutorture.fqs_duration= [KNL] 5982 Set duration of force_quiescent_state bursts 5983 in microseconds. 5984 5985 rcutorture.fqs_holdoff= [KNL] 5986 Set holdoff time within force_quiescent_state bursts 5987 in microseconds. 5988 5989 rcutorture.fqs_stutter= [KNL] 5990 Set wait time between force_quiescent_state bursts 5991 in seconds. 5992 5993 rcutorture.fwd_progress= [KNL] 5994 Specifies the number of kthreads to be used 5995 for RCU grace-period forward-progress testing 5996 for the types of RCU supporting this notion. 5997 Defaults to 1 kthread, values less than zero or 5998 greater than the number of CPUs cause the number 5999 of CPUs to be used. 6000 6001 rcutorture.fwd_progress_div= [KNL] 6002 Specify the fraction of a CPU-stall-warning 6003 period to do tight-loop forward-progress testing. 6004 6005 rcutorture.fwd_progress_holdoff= [KNL] 6006 Number of seconds to wait between successive 6007 forward-progress tests. 6008 6009 rcutorture.fwd_progress_need_resched= [KNL] 6010 Enclose cond_resched() calls within checks for 6011 need_resched() during tight-loop forward-progress 6012 testing. 6013 6014 rcutorture.gp_cond= [KNL] 6015 Use conditional/asynchronous update-side 6016 normal-grace-period primitives, if available. 6017 6018 rcutorture.gp_cond_exp= [KNL] 6019 Use conditional/asynchronous update-side 6020 expedited-grace-period primitives, if available. 6021 6022 rcutorture.gp_cond_full= [KNL] 6023 Use conditional/asynchronous update-side 6024 normal-grace-period primitives that also take 6025 concurrent expedited grace periods into account, 6026 if available. 6027 6028 rcutorture.gp_cond_exp_full= [KNL] 6029 Use conditional/asynchronous update-side 6030 expedited-grace-period primitives that also take 6031 concurrent normal grace periods into account, 6032 if available. 6033 6034 rcutorture.gp_cond_wi= [KNL] 6035 Nominal wait interval for normal conditional 6036 grace periods (specified by rcutorture's 6037 gp_cond and gp_cond_full module parameters), 6038 in microseconds. The actual wait interval will 6039 be randomly selected to nanosecond granularity up 6040 to this wait interval. Defaults to 16 jiffies, 6041 for example, 16,000 microseconds on a system 6042 with HZ=1000. 6043 6044 rcutorture.gp_cond_wi_exp= [KNL] 6045 Nominal wait interval for expedited conditional 6046 grace periods (specified by rcutorture's 6047 gp_cond_exp and gp_cond_exp_full module 6048 parameters), in microseconds. The actual wait 6049 interval will be randomly selected to nanosecond 6050 granularity up to this wait interval. Defaults to 6051 128 microseconds. 6052 6053 rcutorture.gp_exp= [KNL] 6054 Use expedited update-side primitives, if available. 6055 6056 rcutorture.gp_normal= [KNL] 6057 Use normal (non-expedited) asynchronous 6058 update-side primitives, if available. 6059 6060 rcutorture.gp_poll= [KNL] 6061 Use polled update-side normal-grace-period 6062 primitives, if available. 6063 6064 rcutorture.gp_poll_exp= [KNL] 6065 Use polled update-side expedited-grace-period 6066 primitives, if available. 6067 6068 rcutorture.gp_poll_full= [KNL] 6069 Use polled update-side normal-grace-period 6070 primitives that also take concurrent expedited 6071 grace periods into account, if available. 6072 6073 rcutorture.gp_poll_exp_full= [KNL] 6074 Use polled update-side expedited-grace-period 6075 primitives that also take concurrent normal 6076 grace periods into account, if available. 6077 6078 rcutorture.gp_poll_wi= [KNL] 6079 Nominal wait interval for normal conditional 6080 grace periods (specified by rcutorture's 6081 gp_poll and gp_poll_full module parameters), 6082 in microseconds. The actual wait interval will 6083 be randomly selected to nanosecond granularity up 6084 to this wait interval. Defaults to 16 jiffies, 6085 for example, 16,000 microseconds on a system 6086 with HZ=1000. 6087 6088 rcutorture.gp_poll_wi_exp= [KNL] 6089 Nominal wait interval for expedited conditional 6090 grace periods (specified by rcutorture's 6091 gp_poll_exp and gp_poll_exp_full module 6092 parameters), in microseconds. The actual wait 6093 interval will be randomly selected to nanosecond 6094 granularity up to this wait interval. Defaults to 6095 128 microseconds. 6096 6097 rcutorture.gp_sync= [KNL] 6098 Use normal (non-expedited) synchronous 6099 update-side primitives, if available. If all 6100 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6101 rcutorture.gp_normal=, and rcutorture.gp_sync= 6102 are zero, rcutorture acts as if is interpreted 6103 they are all non-zero. 6104 6105 rcutorture.gpwrap_lag= [KNL] 6106 Enable grace-period wrap lag testing. Setting 6107 to false prevents the gpwrap lag test from 6108 running. Default is true. 6109 6110 rcutorture.gpwrap_lag_gps= [KNL] 6111 Set the value for grace-period wrap lag during 6112 active lag testing periods. This controls how many 6113 grace periods differences we tolerate between 6114 rdp and rnp's gp_seq before setting overflow flag. 6115 The default is always set to 8. 6116 6117 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6118 Set the total cycle duration for gpwrap lag 6119 testing in minutes. This is the total time for 6120 one complete cycle of active and inactive 6121 testing periods. Default is 30 minutes. 6122 6123 rcutorture.gpwrap_lag_active_mins= [KNL] 6124 Set the duration for which gpwrap lag is active 6125 within each cycle, in minutes. During this time, 6126 the grace-period wrap lag will be set to the 6127 value specified by gpwrap_lag_gps. Default is 6128 5 minutes. 6129 6130 rcutorture.irqreader= [KNL] 6131 Run RCU readers from irq handlers, or, more 6132 accurately, from a timer handler. Not all RCU 6133 flavors take kindly to this sort of thing. 6134 6135 rcutorture.leakpointer= [KNL] 6136 Leak an RCU-protected pointer out of the reader. 6137 This can of course result in splats, and is 6138 intended to test the ability of things like 6139 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6140 such leaks. 6141 6142 rcutorture.n_barrier_cbs= [KNL] 6143 Set callbacks/threads for rcu_barrier() testing. 6144 6145 rcutorture.nfakewriters= [KNL] 6146 Set number of concurrent RCU writers. These just 6147 stress RCU, they don't participate in the actual 6148 test, hence the "fake". 6149 6150 rcutorture.nocbs_nthreads= [KNL] 6151 Set number of RCU callback-offload togglers. 6152 Zero (the default) disables toggling. 6153 6154 rcutorture.nocbs_toggle= [KNL] 6155 Set the delay in milliseconds between successive 6156 callback-offload toggling attempts. 6157 6158 rcutorture.nreaders= [KNL] 6159 Set number of RCU readers. The value -1 selects 6160 N-1, where N is the number of CPUs. A value 6161 "n" less than -1 selects N-n-2, where N is again 6162 the number of CPUs. For example, -2 selects N 6163 (the number of CPUs), -3 selects N+1, and so on. 6164 6165 rcutorture.nwriters= [KNL] 6166 Set number of RCU writers, which must be either 6167 zero or one. For additional writers, use instead 6168 the rcutorture.nfakewriters parameter. 6169 6170 rcutorture.object_debug= [KNL] 6171 Enable debug-object double-call_rcu() testing. 6172 6173 rcutorture.onoff_holdoff= [KNL] 6174 Set time (s) after boot for CPU-hotplug testing. 6175 6176 rcutorture.onoff_interval= [KNL] 6177 Set time (jiffies) between CPU-hotplug operations, 6178 or zero to disable CPU-hotplug testing. 6179 6180 rcutorture.preempt_duration= [KNL] 6181 Set duration (in milliseconds) of preemptions 6182 by a high-priority FIFO real-time task. Set to 6183 zero (the default) to disable. The CPUs to 6184 preempt are selected randomly from the set that 6185 are online at a given point in time. Races with 6186 CPUs going offline are ignored, with that attempt 6187 at preemption skipped. 6188 6189 rcutorture.preempt_interval= [KNL] 6190 Set interval (in milliseconds, defaulting to one 6191 second) between preemptions by a high-priority 6192 FIFO real-time task. This delay is mediated 6193 by an hrtimer and is further fuzzed to avoid 6194 inadvertent synchronizations. 6195 6196 rcutorture.read_exit_burst= [KNL] 6197 The number of times in a given read-then-exit 6198 episode that a set of read-then-exit kthreads 6199 is spawned. 6200 6201 rcutorture.read_exit_delay= [KNL] 6202 The delay, in seconds, between successive 6203 read-then-exit testing episodes. 6204 6205 rcutorture.reader_flavor= [KNL] 6206 A bit mask indicating which readers to use. 6207 If there is more than one bit set, the readers 6208 are entered from low-order bit up, and are 6209 exited in the opposite order. For SRCU, the 6210 0x1 bit is normal readers, 0x2 NMI-safe readers, 6211 and 0x4 light-weight readers. 6212 6213 rcutorture.shuffle_interval= [KNL] 6214 Set task-shuffle interval (s). Shuffling tasks 6215 allows some CPUs to go into dyntick-idle mode 6216 during the rcutorture test. 6217 6218 rcutorture.shutdown_secs= [KNL] 6219 Set time (s) after boot system shutdown. This 6220 is useful for hands-off automated testing. 6221 6222 rcutorture.stall_cpu= [KNL] 6223 Duration of CPU stall (s) to test RCU CPU stall 6224 warnings, zero to disable. 6225 6226 rcutorture.stall_cpu_block= [KNL] 6227 Sleep while stalling if set. This will result 6228 in warnings from preemptible RCU in addition to 6229 any other stall-related activity. Note that 6230 in kernels built with CONFIG_PREEMPTION=n and 6231 CONFIG_PREEMPT_COUNT=y, this parameter will 6232 cause the CPU to pass through a quiescent state. 6233 Given CONFIG_PREEMPTION=n, this will suppress 6234 RCU CPU stall warnings, but will instead result 6235 in scheduling-while-atomic splats. 6236 6237 Use of this module parameter results in splats. 6238 6239 6240 rcutorture.stall_cpu_holdoff= [KNL] 6241 Time to wait (s) after boot before inducing stall. 6242 6243 rcutorture.stall_cpu_irqsoff= [KNL] 6244 Disable interrupts while stalling if set, but only 6245 on the first stall in the set. 6246 6247 rcutorture.stall_cpu_repeat= [KNL] 6248 Number of times to repeat the stall sequence, 6249 so that rcutorture.stall_cpu_repeat=3 will result 6250 in four stall sequences. 6251 6252 rcutorture.stall_gp_kthread= [KNL] 6253 Duration (s) of forced sleep within RCU 6254 grace-period kthread to test RCU CPU stall 6255 warnings, zero to disable. If both stall_cpu 6256 and stall_gp_kthread are specified, the 6257 kthread is starved first, then the CPU. 6258 6259 rcutorture.stall_only= [KNL] 6260 Shut off all rcutorture kthreads other than the 6261 RCU CPU stall-warning test kthreads. The purpose 6262 of this is to test production applictions' 6263 reactions to CPU stalls, and with minimal 6264 additional overhead. Or you can omit the 6265 stall-warning tests as well and get a heavy 6266 no-op, your choice! 6267 6268 rcutorture.stat_interval= [KNL] 6269 Time (s) between statistics printk()s. 6270 6271 rcutorture.stutter= [KNL] 6272 Time (s) to stutter testing, for example, specifying 6273 five seconds causes the test to run for five seconds, 6274 wait for five seconds, and so on. This tests RCU's 6275 ability to transition abruptly to and from idle. 6276 6277 rcutorture.test_boost= [KNL] 6278 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6279 "Maybe" means test if the RCU implementation 6280 under test support RCU priority boosting. 6281 6282 rcutorture.test_boost_duration= [KNL] 6283 Duration (s) of each individual boost test. 6284 6285 rcutorture.test_boost_holdoff= [KNL] 6286 Holdoff time (s) from start of test to the start 6287 of RCU priority-boost testing. Defaults to zero, 6288 that is, no holdoff. 6289 6290 rcutorture.test_boost_interval= [KNL] 6291 Interval (s) between each boost test. 6292 6293 rcutorture.test_no_idle_hz= [KNL] 6294 Test RCU's dyntick-idle handling. See also the 6295 rcutorture.shuffle_interval parameter. 6296 6297 rcutorture.torture_type= [KNL] 6298 Specify the RCU implementation to test. 6299 6300 rcutorture.verbose= [KNL] 6301 Enable additional printk() statements. 6302 6303 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6304 Dump ftrace buffer after reporting RCU CPU 6305 stall warning. 6306 6307 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6308 Provide RCU CPU stall notifiers, but see the 6309 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6310 option's help text. TL;DR: You almost certainly 6311 do not want rcupdate.rcu_cpu_stall_notifiers. 6312 6313 rcupdate.rcu_cpu_stall_suppress= [KNL] 6314 Suppress RCU CPU stall warning messages. 6315 6316 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6317 Suppress RCU CPU stall warning messages and 6318 rcutorture writer stall warnings that occur 6319 during early boot, that is, during the time 6320 before the init task is spawned. 6321 6322 rcupdate.rcu_cpu_stall_timeout= [KNL] 6323 Set timeout for RCU CPU stall warning messages. 6324 The value is in seconds and the maximum allowed 6325 value is 300 seconds. 6326 6327 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6328 Set timeout for expedited RCU CPU stall warning 6329 messages. The value is in milliseconds 6330 and the maximum allowed value is 21000 6331 milliseconds. Please note that this value is 6332 adjusted to an arch timer tick resolution. 6333 Setting this to zero causes the value from 6334 rcupdate.rcu_cpu_stall_timeout to be used (after 6335 conversion from seconds to milliseconds). 6336 6337 rcupdate.rcu_cpu_stall_cputime= [KNL] 6338 Provide statistics on the cputime and count of 6339 interrupts and tasks during the sampling period. For 6340 multiple continuous RCU stalls, all sampling periods 6341 begin at half of the first RCU stall timeout. 6342 6343 rcupdate.rcu_exp_stall_task_details= [KNL] 6344 Print stack dumps of any tasks blocking the 6345 current expedited RCU grace period during an 6346 expedited RCU CPU stall warning. 6347 6348 rcupdate.rcu_expedited= [KNL] 6349 Use expedited grace-period primitives, for 6350 example, synchronize_rcu_expedited() instead 6351 of synchronize_rcu(). This reduces latency, 6352 but can increase CPU utilization, degrade 6353 real-time latency, and degrade energy efficiency. 6354 No effect on CONFIG_TINY_RCU kernels. 6355 6356 rcupdate.rcu_normal= [KNL] 6357 Use only normal grace-period primitives, 6358 for example, synchronize_rcu() instead of 6359 synchronize_rcu_expedited(). This improves 6360 real-time latency, CPU utilization, and 6361 energy efficiency, but can expose users to 6362 increased grace-period latency. This parameter 6363 overrides rcupdate.rcu_expedited. No effect on 6364 CONFIG_TINY_RCU kernels. 6365 6366 rcupdate.rcu_normal_after_boot= [KNL] 6367 Once boot has completed (that is, after 6368 rcu_end_inkernel_boot() has been invoked), use 6369 only normal grace-period primitives. No effect 6370 on CONFIG_TINY_RCU kernels. 6371 6372 But note that CONFIG_PREEMPT_RT=y kernels enables 6373 this kernel boot parameter, forcibly setting 6374 it to the value one, that is, converting any 6375 post-boot attempt at an expedited RCU grace 6376 period to instead use normal non-expedited 6377 grace-period processing. 6378 6379 rcupdate.rcu_task_collapse_lim= [KNL] 6380 Set the maximum number of callbacks present 6381 at the beginning of a grace period that allows 6382 the RCU Tasks flavors to collapse back to using 6383 a single callback queue. This switching only 6384 occurs when rcupdate.rcu_task_enqueue_lim is 6385 set to the default value of -1. 6386 6387 rcupdate.rcu_task_contend_lim= [KNL] 6388 Set the minimum number of callback-queuing-time 6389 lock-contention events per jiffy required to 6390 cause the RCU Tasks flavors to switch to per-CPU 6391 callback queuing. This switching only occurs 6392 when rcupdate.rcu_task_enqueue_lim is set to 6393 the default value of -1. 6394 6395 rcupdate.rcu_task_enqueue_lim= [KNL] 6396 Set the number of callback queues to use for the 6397 RCU Tasks family of RCU flavors. The default 6398 of -1 allows this to be automatically (and 6399 dynamically) adjusted. This parameter is intended 6400 for use in testing. 6401 6402 rcupdate.rcu_task_lazy_lim= [KNL] 6403 Number of callbacks on a given CPU that will 6404 cancel laziness on that CPU. Use -1 to disable 6405 cancellation of laziness, but be advised that 6406 doing so increases the danger of OOM due to 6407 callback flooding. 6408 6409 rcupdate.rcu_task_stall_info= [KNL] 6410 Set initial timeout in jiffies for RCU task stall 6411 informational messages, which give some indication 6412 of the problem for those not patient enough to 6413 wait for ten minutes. Informational messages are 6414 only printed prior to the stall-warning message 6415 for a given grace period. Disable with a value 6416 less than or equal to zero. Defaults to ten 6417 seconds. A change in value does not take effect 6418 until the beginning of the next grace period. 6419 6420 rcupdate.rcu_task_stall_info_mult= [KNL] 6421 Multiplier for time interval between successive 6422 RCU task stall informational messages for a given 6423 RCU tasks grace period. This value is clamped 6424 to one through ten, inclusive. It defaults to 6425 the value three, so that the first informational 6426 message is printed 10 seconds into the grace 6427 period, the second at 40 seconds, the third at 6428 160 seconds, and then the stall warning at 600 6429 seconds would prevent a fourth at 640 seconds. 6430 6431 rcupdate.rcu_task_stall_timeout= [KNL] 6432 Set timeout in jiffies for RCU task stall 6433 warning messages. Disable with a value less 6434 than or equal to zero. Defaults to ten minutes. 6435 A change in value does not take effect until 6436 the beginning of the next grace period. 6437 6438 rcupdate.rcu_tasks_lazy_ms= [KNL] 6439 Set timeout in milliseconds RCU Tasks asynchronous 6440 callback batching for call_rcu_tasks(). 6441 A negative value will take the default. A value 6442 of zero will disable batching. Batching is 6443 always disabled for synchronize_rcu_tasks(). 6444 6445 rcupdate.rcu_self_test= [KNL] 6446 Run the RCU early boot self tests 6447 6448 rdinit= [KNL] 6449 Format: <full_path> 6450 Run specified binary instead of /init from the ramdisk, 6451 used for early userspace startup. See initrd. 6452 6453 rdrand= [X86,EARLY] 6454 force - Override the decision by the kernel to hide the 6455 advertisement of RDRAND support (this affects 6456 certain AMD processors because of buggy BIOS 6457 support, specifically around the suspend/resume 6458 path). 6459 6460 rdt= [HW,X86,RDT] 6461 Turn on/off individual RDT features. List is: 6462 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6463 mba, smba, bmec, abmc, sdciae, energy[:guid], 6464 perf[:guid]. 6465 E.g. to turn on cmt and turn off mba use: 6466 rdt=cmt,!mba 6467 To turn off all energy telemetry monitoring and ensure that 6468 perf telemetry monitoring associated with guid 0x12345 6469 is enabled use: 6470 rdt=!energy,perf:0x12345 6471 6472 reboot= [KNL] 6473 Format (x86 or x86_64): 6474 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6475 [[,]s[mp]####] \ 6476 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6477 [[,]f[orce]] 6478 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6479 (prefix with 'panic_' to set mode for panic 6480 reboot only), 6481 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6482 reboot_force is either force or not specified, 6483 reboot_cpu is s[mp]#### with #### being the processor 6484 to be used for rebooting. 6485 6486 acpi 6487 Use the ACPI RESET_REG in the FADT. If ACPI is not 6488 configured or the ACPI reset does not work, the reboot 6489 path attempts the reset using the keyboard controller. 6490 6491 bios 6492 Use the CPU reboot vector for warm reset 6493 6494 cold 6495 Set the cold reboot flag 6496 6497 default 6498 There are some built-in platform specific "quirks" 6499 - you may see: "reboot: <name> series board detected. 6500 Selecting <type> for reboots." In the case where you 6501 think the quirk is in error (e.g. you have newer BIOS, 6502 or newer board) using this option will ignore the 6503 built-in quirk table, and use the generic default 6504 reboot actions. 6505 6506 efi 6507 Use efi reset_system runtime service. If EFI is not 6508 configured or the EFI reset does not work, the reboot 6509 path attempts the reset using the keyboard controller. 6510 6511 force 6512 Don't stop other CPUs on reboot. This can make reboot 6513 more reliable in some cases. 6514 6515 kbd 6516 Use the keyboard controller. cold reset (default) 6517 6518 pci 6519 Use a write to the PCI config space register 0xcf9 to 6520 trigger reboot. 6521 6522 triple 6523 Force a triple fault (init) 6524 6525 warm 6526 Don't set the cold reboot flag 6527 6528 Using warm reset will be much faster especially on big 6529 memory systems because the BIOS will not go through 6530 the memory check. Disadvantage is that not all 6531 hardware will be completely reinitialized on reboot so 6532 there may be boot problems on some systems. 6533 6534 6535 refscale.holdoff= [KNL] 6536 Set test-start holdoff period. The purpose of 6537 this parameter is to delay the start of the 6538 test until boot completes in order to avoid 6539 interference. 6540 6541 refscale.lookup_instances= [KNL] 6542 Number of data elements to use for the forms of 6543 SLAB_TYPESAFE_BY_RCU testing. A negative number 6544 is negated and multiplied by nr_cpu_ids, while 6545 zero specifies nr_cpu_ids. 6546 6547 refscale.loops= [KNL] 6548 Set the number of loops over the synchronization 6549 primitive under test. Increasing this number 6550 reduces noise due to loop start/end overhead, 6551 but the default has already reduced the per-pass 6552 noise to a handful of picoseconds on ca. 2020 6553 x86 laptops. 6554 6555 refscale.nreaders= [KNL] 6556 Set number of readers. The default value of -1 6557 selects N, where N is roughly 75% of the number 6558 of CPUs. A value of zero is an interesting choice. 6559 6560 refscale.nruns= [KNL] 6561 Set number of runs, each of which is dumped onto 6562 the console log. 6563 6564 refscale.readdelay= [KNL] 6565 Set the read-side critical-section duration, 6566 measured in microseconds. 6567 6568 refscale.scale_type= [KNL] 6569 Specify the read-protection implementation to test. 6570 6571 refscale.shutdown= [KNL] 6572 Shut down the system at the end of the performance 6573 test. This defaults to 1 (shut it down) when 6574 refscale is built into the kernel and to 0 (leave 6575 it running) when refscale is built as a module. 6576 6577 refscale.verbose= [KNL] 6578 Enable additional printk() statements. 6579 6580 refscale.verbose_batched= [KNL] 6581 Batch the additional printk() statements. If zero 6582 (the default) or negative, print everything. Otherwise, 6583 print every Nth verbose statement, where N is the value 6584 specified. 6585 6586 regulator_ignore_unused 6587 [REGULATOR] 6588 Prevents regulator framework from disabling regulators 6589 that are unused, due no driver claiming them. This may 6590 be useful for debug and development, but should not be 6591 needed on a platform with proper driver support. 6592 6593 relax_domain_level= 6594 [KNL, SMP] Set scheduler's default relax_domain_level. 6595 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6596 6597 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6598 Format: <base1>,<size1>[,<base2>,<size2>,...] 6599 Reserve I/O ports or memory so the kernel won't use 6600 them. If <base> is less than 0x10000, the region 6601 is assumed to be I/O ports; otherwise it is memory. 6602 6603 reserve_mem= [RAM] 6604 Format: nn[KMG]:<align>:<label> 6605 Reserve physical memory and label it with a name that 6606 other subsystems can use to access it. This is typically 6607 used for systems that do not wipe the RAM, and this command 6608 line will try to reserve the same physical memory on 6609 soft reboots. Note, it is not guaranteed to be the same 6610 location. For example, if anything about the system changes 6611 or if booting a different kernel. It can also fail if KASLR 6612 places the kernel at the location of where the RAM reservation 6613 was from a previous boot, the new reservation will be at a 6614 different location. 6615 Any subsystem using this feature must add a way to verify 6616 that the contents of the physical memory is from a previous 6617 boot, as there may be cases where the memory will not be 6618 located at the same location. 6619 6620 The format is size:align:label for example, to request 6621 12 megabytes of 4096 alignment for ramoops: 6622 6623 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6624 6625 reservetop= [X86-32,EARLY] 6626 Format: nn[KMG] 6627 Reserves a hole at the top of the kernel virtual 6628 address space. 6629 6630 reset_devices [KNL] Force drivers to reset the underlying device 6631 during initialization. 6632 6633 resume= [SWSUSP] 6634 Specify the partition device for software suspend 6635 Format: 6636 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6637 6638 resume_offset= [SWSUSP] 6639 Specify the offset from the beginning of the partition 6640 given by "resume=" at which the swap header is located, 6641 in <PAGE_SIZE> units (needed only for swap files). 6642 See Documentation/power/swsusp-and-swap-files.rst 6643 6644 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6645 read the resume files 6646 6647 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6648 Useful for devices that are detected asynchronously 6649 (e.g. USB and MMC devices). 6650 6651 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6652 be accessible via /sys/firmware/initrd. 6653 6654 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6655 Speculative Code Execution with Return Instructions) 6656 vulnerability. 6657 6658 AMD-based UNRET and IBPB mitigations alone do not stop 6659 sibling threads from influencing the predictions of other 6660 sibling threads. For that reason, STIBP is used on pro- 6661 cessors that support it, and mitigate SMT on processors 6662 that don't. 6663 6664 off - no mitigation 6665 auto - automatically select a mitigation 6666 auto,nosmt - automatically select a mitigation, 6667 disabling SMT if necessary for 6668 the full mitigation (only on Zen1 6669 and older without STIBP). 6670 ibpb - On AMD, mitigate short speculation 6671 windows on basic block boundaries too. 6672 Safe, highest perf impact. It also 6673 enables STIBP if present. Not suitable 6674 on Intel. 6675 ibpb,nosmt - Like "ibpb" above but will disable SMT 6676 when STIBP is not available. This is 6677 the alternative for systems which do not 6678 have STIBP. 6679 unret - Force enable untrained return thunks, 6680 only effective on AMD f15h-f17h based 6681 systems. 6682 unret,nosmt - Like unret, but will disable SMT when STIBP 6683 is not available. This is the alternative for 6684 systems which do not have STIBP. 6685 6686 Selecting 'auto' will choose a mitigation method at run 6687 time according to the CPU. 6688 6689 Not specifying this option is equivalent to retbleed=auto. 6690 6691 rfkill.default_state= 6692 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6693 etc. communication is blocked by default. 6694 1 Unblocked. 6695 6696 rfkill.master_switch_mode= 6697 0 The "airplane mode" button does nothing. 6698 1 The "airplane mode" button toggles between everything 6699 blocked and the previous configuration. 6700 2 The "airplane mode" button toggles between everything 6701 blocked and everything unblocked. 6702 6703 ring3mwait=disable 6704 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6705 CPUs. 6706 6707 riscv_isa_fallback [RISCV,EARLY] 6708 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6709 falling back to detecting extension support by parsing 6710 "riscv,isa" property on devicetree systems when the 6711 replacement properties are not found. See the Kconfig 6712 entry for RISCV_ISA_FALLBACK. 6713 6714 riscv_nousercfi= 6715 all Disable user CFI ABI to userspace even if cpu extension 6716 are available. 6717 bcfi Disable user backward CFI ABI to userspace even if 6718 the shadow stack extension is available. 6719 fcfi Disable user forward CFI ABI to userspace even if the 6720 landing pad extension is available. 6721 6722 ro [KNL] Mount root device read-only on boot 6723 6724 rodata= [KNL,EARLY] 6725 on Mark read-only kernel memory as read-only (default). 6726 off Leave read-only kernel memory writable for debugging. 6727 noalias Mark read-only kernel memory as read-only but retain 6728 writable aliases in the direct map for regions outside 6729 of the kernel image. [arm64] 6730 6731 rockchip.usb_uart 6732 [EARLY] 6733 Enable the uart passthrough on the designated usb port 6734 on Rockchip SoCs. When active, the signals of the 6735 debug-uart get routed to the D+ and D- pins of the usb 6736 port and the regular usb controller gets disabled. 6737 6738 root= [KNL] Root filesystem 6739 Usually this is a block device specifier of some kind, 6740 see the early_lookup_bdev comment in 6741 block/early-lookup.c for details. 6742 Alternatively this can be "ram" for the legacy initial 6743 ramdisk, "nfs" and "cifs" for root on a network file 6744 system, or "mtd" and "ubi" for mounting from raw flash. 6745 6746 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6747 mount the root filesystem 6748 6749 rootflags= [KNL] Set root filesystem mount option string 6750 6751 rseq_slice_ext= [KNL] RSEQ based time slice extension 6752 Format: boolean 6753 Control enablement of RSEQ based time slice extension. 6754 Default is 'on'. 6755 6756 initramfs_options= [KNL] 6757 Specify mount options for the initramfs mount. 6758 6759 rootfstype= [KNL] Set root filesystem type 6760 6761 rootwait [KNL] Wait (indefinitely) for root device to show up. 6762 Useful for devices that are detected asynchronously 6763 (e.g. USB and MMC devices). 6764 6765 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6766 to show up before attempting to mount the root 6767 filesystem. 6768 6769 rproc_mem=nn[KMG][@address] 6770 [KNL,ARM,CMA] Remoteproc physical memory block. 6771 Memory area to be used by remote processor image, 6772 managed by CMA. 6773 6774 rseq_debug= [KNL] Enable or disable restartable sequence 6775 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6776 Format: <bool> 6777 6778 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6779 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6780 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6781 Format: <bool> 6782 6783 rw [KNL] Mount root device read-write on boot 6784 6785 S [KNL] Run init in single mode 6786 6787 s390_iommu= [HW,S390] 6788 Set s390 IOTLB flushing mode 6789 strict 6790 With strict flushing every unmap operation will result 6791 in an IOTLB flush. Default is lazy flushing before 6792 reuse, which is faster. Deprecated, equivalent to 6793 iommu.strict=1. 6794 6795 s390_iommu_aperture= [KNL,S390] 6796 Specifies the size of the per device DMA address space 6797 accessible through the DMA and IOMMU APIs as a decimal 6798 factor of the size of main memory. 6799 The default is 1 meaning that one can concurrently use 6800 as many DMA addresses as physical memory is installed, 6801 if supported by hardware, and thus map all of memory 6802 once. With a value of 2 one can map all of memory twice 6803 and so on. As a special case a factor of 0 imposes no 6804 restrictions other than those given by hardware at the 6805 cost of significant additional memory use for tables. 6806 6807 6808 sched_proxy_exec= [KNL] 6809 Enables or disables "proxy execution" style 6810 solution to mutex-based priority inversion. 6811 Format: <bool> 6812 6813 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6814 6815 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6816 Allowed values are enable and disable. This feature 6817 incurs a small amount of overhead in the scheduler 6818 but is useful for debugging and performance tuning. 6819 6820 sched_thermal_decay_shift= 6821 [Deprecated] 6822 [KNL, SMP] Set a decay shift for scheduler thermal 6823 pressure signal. Thermal pressure signal follows the 6824 default decay period of other scheduler pelt 6825 signals(usually 32 ms but configurable). Setting 6826 sched_thermal_decay_shift will left shift the decay 6827 period for the thermal pressure signal by the shift 6828 value. 6829 i.e. with the default pelt decay period of 32 ms 6830 sched_thermal_decay_shift thermal pressure decay pr 6831 1 64 ms 6832 2 128 ms 6833 and so on. 6834 Format: integer between 0 and 10 6835 Default is 0. 6836 6837 scftorture.holdoff= [KNL] 6838 Number of seconds to hold off before starting 6839 test. Defaults to zero for module insertion and 6840 to 10 seconds for built-in smp_call_function() 6841 tests. 6842 6843 scftorture.longwait= [KNL] 6844 Request ridiculously long waits randomly selected 6845 up to the chosen limit in seconds. Zero (the 6846 default) disables this feature. Please note 6847 that requesting even small non-zero numbers of 6848 seconds can result in RCU CPU stall warnings, 6849 softlockup complaints, and so on. 6850 6851 scftorture.nthreads= [KNL] 6852 Number of kthreads to spawn to invoke the 6853 smp_call_function() family of functions. 6854 The default of -1 specifies a number of kthreads 6855 equal to the number of CPUs. 6856 6857 scftorture.onoff_holdoff= [KNL] 6858 Number seconds to wait after the start of the 6859 test before initiating CPU-hotplug operations. 6860 6861 scftorture.onoff_interval= [KNL] 6862 Number seconds to wait between successive 6863 CPU-hotplug operations. Specifying zero (which 6864 is the default) disables CPU-hotplug operations. 6865 6866 scftorture.shutdown_secs= [KNL] 6867 The number of seconds following the start of the 6868 test after which to shut down the system. The 6869 default of zero avoids shutting down the system. 6870 Non-zero values are useful for automated tests. 6871 6872 scftorture.stat_interval= [KNL] 6873 The number of seconds between outputting the 6874 current test statistics to the console. A value 6875 of zero disables statistics output. 6876 6877 scftorture.stutter_cpus= [KNL] 6878 The number of jiffies to wait between each change 6879 to the set of CPUs under test. 6880 6881 scftorture.use_cpus_read_lock= [KNL] 6882 Use use_cpus_read_lock() instead of the default 6883 preempt_disable() to disable CPU hotplug 6884 while invoking one of the smp_call_function*() 6885 functions. 6886 6887 scftorture.verbose= [KNL] 6888 Enable additional printk() statements. 6889 6890 scftorture.weight_single= [KNL] 6891 The probability weighting to use for the 6892 smp_call_function_single() function with a zero 6893 "wait" parameter. A value of -1 selects the 6894 default if all other weights are -1. However, 6895 if at least one weight has some other value, a 6896 value of -1 will instead select a weight of zero. 6897 6898 scftorture.weight_single_wait= [KNL] 6899 The probability weighting to use for the 6900 smp_call_function_single() function with a 6901 non-zero "wait" parameter. See weight_single. 6902 6903 scftorture.weight_many= [KNL] 6904 The probability weighting to use for the 6905 smp_call_function_many() function with a zero 6906 "wait" parameter. See weight_single. 6907 Note well that setting a high probability for 6908 this weighting can place serious IPI load 6909 on the system. 6910 6911 scftorture.weight_many_wait= [KNL] 6912 The probability weighting to use for the 6913 smp_call_function_many() function with a 6914 non-zero "wait" parameter. See weight_single 6915 and weight_many. 6916 6917 scftorture.weight_all= [KNL] 6918 The probability weighting to use for the 6919 smp_call_function_all() function with a zero 6920 "wait" parameter. See weight_single and 6921 weight_many. 6922 6923 scftorture.weight_all_wait= [KNL] 6924 The probability weighting to use for the 6925 smp_call_function_all() function with a 6926 non-zero "wait" parameter. See weight_single 6927 and weight_many. 6928 6929 sdw_mclk_divider=[SDW] 6930 Specify the MCLK divider for Intel SoundWire buses in 6931 case the BIOS does not provide the clock rate properly. 6932 6933 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6934 xtime_lock contention on larger systems, and/or RCU lock 6935 contention on all systems with CONFIG_MAXSMP set. 6936 Format: { "0" | "1" } 6937 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1") 6938 1 -- enable. 6939 Note: increases power consumption, thus should only be 6940 enabled if running jitter sensitive (HPC/RT) workloads. 6941 6942 security= [SECURITY] Choose a legacy "major" security module to 6943 enable at boot. This has been deprecated by the 6944 "lsm=" parameter. 6945 6946 selinux= [SELINUX] Disable or enable SELinux at boot time. 6947 Format: { "0" | "1" } 6948 See security/selinux/Kconfig help text. 6949 0 -- disable. 6950 1 -- enable. 6951 Default value is 1. 6952 6953 serialnumber [BUGS=X86-32] 6954 6955 sev=option[,option...] [X86-64] 6956 6957 debug 6958 Enable debug messages. 6959 6960 nosnp 6961 Do not enable SEV-SNP (applies to host/hypervisor 6962 only). Setting 'nosnp' avoids the RMP check overhead 6963 in memory accesses when users do not want to run 6964 SEV-SNP guests. 6965 6966 shapers= [NET] 6967 Maximal number of shapers. 6968 6969 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6970 Limit apic dumping. The parameter defines the maximal 6971 number of local apics being dumped. Also it is possible 6972 to set it to "all" by meaning -- no limit here. 6973 Format: { 1 (default) | 2 | ... | all }. 6974 The parameter valid if only apic=debug or 6975 apic=verbose is specified. 6976 Example: apic=debug show_lapic=all 6977 6978 slab_debug[=options[,slabs][;[options[,slabs]]...]] [MM] 6979 Enabling slab_debug allows one to determine the 6980 culprit if slab objects become corrupted. Enabling 6981 slab_debug can create guard zones around objects and 6982 may poison objects when not in use. Also tracks the 6983 last alloc / free. For more information see 6984 Documentation/admin-guide/mm/slab.rst. 6985 (slub_debug legacy name also accepted for now) 6986 6987 Using this option implies the "no_hash_pointers" 6988 option which can be undone by adding the 6989 "hash_pointers=always" option. 6990 6991 slab_max_order= [MM] 6992 Determines the maximum allowed order for slabs. 6993 A high setting may cause OOMs due to memory 6994 fragmentation. For more information see 6995 Documentation/admin-guide/mm/slab.rst. 6996 (slub_max_order legacy name also accepted for now) 6997 6998 slab_merge [MM] 6999 Enable merging of slabs with similar size when the 7000 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 7001 (slub_merge legacy name also accepted for now) 7002 7003 slab_min_objects= [MM] 7004 The minimum number of objects per slab. SLUB will 7005 increase the slab order up to slab_max_order to 7006 generate a sufficiently large slab able to contain 7007 the number of objects indicated. The higher the number 7008 of objects the smaller the overhead of tracking slabs 7009 and the less frequently locks need to be acquired. 7010 For more information see 7011 Documentation/admin-guide/mm/slab.rst. 7012 (slub_min_objects legacy name also accepted for now) 7013 7014 slab_min_order= [MM] 7015 Determines the minimum page order for slabs. Must be 7016 lower or equal to slab_max_order. For more information see 7017 Documentation/admin-guide/mm/slab.rst. 7018 (slub_min_order legacy name also accepted for now) 7019 7020 slab_nomerge [MM] 7021 Disable merging of slabs with similar size. May be 7022 necessary if there is some reason to distinguish 7023 allocs to different slabs, especially in hardened 7024 environments where the risk of heap overflows and 7025 layout control by attackers can usually be 7026 frustrated by disabling merging. This will reduce 7027 most of the exposure of a heap attack to a single 7028 cache (risks via metadata attacks are mostly 7029 unchanged). Debug options disable merging on their 7030 own. 7031 For more information see 7032 Documentation/admin-guide/mm/slab.rst. 7033 (slub_nomerge legacy name also accepted for now) 7034 7035 slab_strict_numa [MM] 7036 Support memory policies on a per object level 7037 in the slab allocator. The default is for memory 7038 policies to be applied at the folio level when 7039 a new folio is needed or a partial folio is 7040 retrieved from the lists. Increases overhead 7041 in the slab fastpaths but gains more accurate 7042 NUMA kernel object placement which helps with slow 7043 interconnects in NUMA systems. 7044 7045 slram= [HW,MTD] 7046 7047 smart2= [HW] 7048 Format: <io1>[,<io2>[,...,<io8>]] 7049 7050 smp.csd_lock_timeout= [KNL] 7051 Specify the period of time in milliseconds 7052 that smp_call_function() and friends will wait 7053 for a CPU to release the CSD lock. This is 7054 useful when diagnosing bugs involving CPUs 7055 disabling interrupts for extended periods 7056 of time. Defaults to 5,000 milliseconds, and 7057 setting a value of zero disables this feature. 7058 This feature may be more efficiently disabled 7059 using the csdlock_debug- kernel parameter. 7060 7061 smp.panic_on_ipistall= [KNL] 7062 If a csd_lock_timeout extends for more than 7063 the specified number of milliseconds, panic the 7064 system. By default, let CSD-lock acquisition 7065 take as long as they take. Specifying 300,000 7066 for this value provides a 5-minute timeout. 7067 7068 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7069 (logical CPUs) to use per physical CPU on systems 7070 capable of symmetric multithreading (SMT). Will 7071 be capped to the actual hardware limit. 7072 Format: <integer> 7073 Default: -1 (no limit) 7074 7075 softlockup_panic= 7076 [KNL] Should the soft-lockup detector generate panics. 7077 Format: <int> 7078 7079 A value of non-zero instructs the soft-lockup detector 7080 to panic the machine when a soft-lockup duration exceeds 7081 N thresholds. It is also controlled by the kernel.softlockup_panic 7082 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7083 respective build-time switch to that functionality. 7084 7085 softlockup_all_cpu_backtrace= 7086 [KNL] Should the soft-lockup detector generate 7087 backtraces on all cpus. 7088 Format: 0 | 1 7089 7090 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7091 See Documentation/admin-guide/laptops/sonypi.rst 7092 7093 spectre_bhi= [X86] Control mitigation of Branch History Injection 7094 (BHI) vulnerability. This setting affects the 7095 deployment of the HW BHI control and the SW BHB 7096 clearing sequence. 7097 7098 on - (default) Enable the HW or SW mitigation as 7099 needed. This protects the kernel from 7100 both syscalls and VMs. 7101 vmexit - On systems which don't have the HW mitigation 7102 available, enable the SW mitigation on vmexit 7103 ONLY. On such systems, the host kernel is 7104 protected from VM-originated BHI attacks, but 7105 may still be vulnerable to syscall attacks. 7106 off - Disable the mitigation. 7107 7108 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7109 (indirect branch speculation) vulnerability. 7110 The default operation protects the kernel from 7111 user space attacks. 7112 7113 on - unconditionally enable, implies 7114 spectre_v2_user=on 7115 off - unconditionally disable, implies 7116 spectre_v2_user=off 7117 auto - kernel detects whether your CPU model is 7118 vulnerable 7119 7120 Selecting 'on' will, and 'auto' may, choose a 7121 mitigation method at run time according to the 7122 CPU, the available microcode, the setting of the 7123 CONFIG_MITIGATION_RETPOLINE configuration option, 7124 and the compiler with which the kernel was built. 7125 7126 Selecting 'on' will also enable the mitigation 7127 against user space to user space task attacks. 7128 Selecting specific mitigation does not force enable 7129 user mitigations. 7130 7131 Selecting 'off' will disable both the kernel and 7132 the user space protections. 7133 7134 Specific mitigations can also be selected manually: 7135 7136 retpoline - replace indirect branches 7137 retpoline,generic - Retpolines 7138 retpoline,lfence - LFENCE; indirect branch 7139 retpoline,amd - alias for retpoline,lfence 7140 eibrs - Enhanced/Auto IBRS 7141 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7142 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7143 ibrs - use IBRS to protect kernel 7144 7145 Not specifying this option is equivalent to 7146 spectre_v2=auto. 7147 7148 spectre_v2_user= 7149 [X86] Control mitigation of Spectre variant 2 7150 (indirect branch speculation) vulnerability between 7151 user space tasks 7152 7153 on - Unconditionally enable mitigations. Is 7154 enforced by spectre_v2=on 7155 7156 off - Unconditionally disable mitigations. Is 7157 enforced by spectre_v2=off 7158 7159 prctl - Indirect branch speculation is enabled, 7160 but mitigation can be enabled via prctl 7161 per thread. The mitigation control state 7162 is inherited on fork. 7163 7164 prctl,ibpb 7165 - Like "prctl" above, but only STIBP is 7166 controlled per thread. IBPB is issued 7167 always when switching between different user 7168 space processes. 7169 7170 seccomp 7171 - Same as "prctl" above, but all seccomp 7172 threads will enable the mitigation unless 7173 they explicitly opt out. 7174 7175 seccomp,ibpb 7176 - Like "seccomp" above, but only STIBP is 7177 controlled per thread. IBPB is issued 7178 always when switching between different 7179 user space processes. 7180 7181 auto - Kernel selects the mitigation depending on 7182 the available CPU features and vulnerability. 7183 7184 Default mitigation: "prctl" 7185 7186 Not specifying this option is equivalent to 7187 spectre_v2_user=auto. 7188 7189 spec_rstack_overflow= 7190 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7191 7192 off - Disable mitigation 7193 microcode - Enable microcode mitigation only 7194 safe-ret - Enable sw-only safe RET mitigation (default) 7195 ibpb - Enable mitigation by issuing IBPB on 7196 kernel entry 7197 ibpb-vmexit - Issue IBPB only on VMEXIT 7198 (cloud-specific mitigation) 7199 7200 spec_store_bypass_disable= 7201 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7202 (Speculative Store Bypass vulnerability) 7203 7204 Certain CPUs are vulnerable to an exploit against a 7205 a common industry wide performance optimization known 7206 as "Speculative Store Bypass" in which recent stores 7207 to the same memory location may not be observed by 7208 later loads during speculative execution. The idea 7209 is that such stores are unlikely and that they can 7210 be detected prior to instruction retirement at the 7211 end of a particular speculation execution window. 7212 7213 In vulnerable processors, the speculatively forwarded 7214 store can be used in a cache side channel attack, for 7215 example to read memory to which the attacker does not 7216 directly have access (e.g. inside sandboxed code). 7217 7218 This parameter controls whether the Speculative Store 7219 Bypass optimization is used. 7220 7221 On x86 the options are: 7222 7223 on - Unconditionally disable Speculative Store Bypass 7224 off - Unconditionally enable Speculative Store Bypass 7225 auto - Kernel detects whether the CPU model contains an 7226 implementation of Speculative Store Bypass and 7227 picks the most appropriate mitigation. If the 7228 CPU is not vulnerable, "off" is selected. If the 7229 CPU is vulnerable the default mitigation is 7230 architecture and Kconfig dependent. See below. 7231 prctl - Control Speculative Store Bypass per thread 7232 via prctl. Speculative Store Bypass is enabled 7233 for a process by default. The state of the control 7234 is inherited on fork. 7235 seccomp - Same as "prctl" above, but all seccomp threads 7236 will disable SSB unless they explicitly opt out. 7237 7238 Default mitigations: 7239 X86: "prctl" 7240 7241 On powerpc the options are: 7242 7243 on,auto - On Power8 and Power9 insert a store-forwarding 7244 barrier on kernel entry and exit. On Power7 7245 perform a software flush on kernel entry and 7246 exit. 7247 off - No action. 7248 7249 Not specifying this option is equivalent to 7250 spec_store_bypass_disable=auto. 7251 7252 split_llc= 7253 [X86,EARLY] Split the LLC N-ways 7254 7255 When set, the LLC is split this many ways by matching 7256 'core_id % n'. This is setup before SMP bringup and 7257 used during SMP bringup before it knows the full 7258 topology. If your core count doesn't nicely divide by 7259 the number given, you get to keep the pieces. 7260 7261 This is mostly a debug feature to emulate multiple LLCs 7262 on hardware that only have a single LLC. 7263 7264 split_lock_detect= 7265 [X86] Enable split lock detection or bus lock detection 7266 7267 When enabled (and if hardware support is present), atomic 7268 instructions that access data across cache line 7269 boundaries will result in an alignment check exception 7270 for split lock detection or a debug exception for 7271 bus lock detection. 7272 7273 off - not enabled 7274 7275 warn - the kernel will emit rate-limited warnings 7276 about applications triggering the #AC 7277 exception or the #DB exception. This mode is 7278 the default on CPUs that support split lock 7279 detection or bus lock detection. Default 7280 behavior is by #AC if both features are 7281 enabled in hardware. 7282 7283 fatal - the kernel will send SIGBUS to applications 7284 that trigger the #AC exception or the #DB 7285 exception. Default behavior is by #AC if 7286 both features are enabled in hardware. 7287 7288 ratelimit:N - 7289 Set system wide rate limit to N bus locks 7290 per second for bus lock detection. 7291 0 < N <= 1000. 7292 7293 N/A for split lock detection. 7294 7295 7296 If an #AC exception is hit in the kernel or in 7297 firmware (i.e. not while executing in user mode) 7298 the kernel will oops in either "warn" or "fatal" 7299 mode. 7300 7301 #DB exception for bus lock is triggered only when 7302 CPL > 0. 7303 7304 srbds= [X86,INTEL,EARLY] 7305 Control the Special Register Buffer Data Sampling 7306 (SRBDS) mitigation. 7307 7308 Certain CPUs are vulnerable to an MDS-like 7309 exploit which can leak bits from the random 7310 number generator. 7311 7312 By default, this issue is mitigated by 7313 microcode. However, the microcode fix can cause 7314 the RDRAND and RDSEED instructions to become 7315 much slower. Among other effects, this will 7316 result in reduced throughput from /dev/urandom. 7317 7318 The microcode mitigation can be disabled with 7319 the following option: 7320 7321 off: Disable mitigation and remove 7322 performance impact to RDRAND and RDSEED 7323 7324 srcutree.big_cpu_lim [KNL] 7325 Specifies the number of CPUs constituting a 7326 large system, such that srcu_struct structures 7327 should immediately allocate an srcu_node array. 7328 This kernel-boot parameter defaults to 128, 7329 but takes effect only when the low-order four 7330 bits of srcutree.convert_to_big is equal to 3 7331 (decide at boot). 7332 7333 srcutree.convert_to_big [KNL] 7334 Specifies under what conditions an SRCU tree 7335 srcu_struct structure will be converted to big 7336 form, that is, with an rcu_node tree: 7337 7338 0: Never. 7339 1: At init_srcu_struct() time. 7340 2: When rcutorture decides to. 7341 3: Decide at boot time (default). 7342 0x1X: Above plus if high contention. 7343 7344 Either way, the srcu_node tree will be sized based 7345 on the actual runtime number of CPUs (nr_cpu_ids) 7346 instead of the compile-time CONFIG_NR_CPUS. 7347 7348 srcutree.counter_wrap_check [KNL] 7349 Specifies how frequently to check for 7350 grace-period sequence counter wrap for the 7351 srcu_data structure's ->srcu_gp_seq_needed field. 7352 The greater the number of bits set in this kernel 7353 parameter, the less frequently counter wrap will 7354 be checked for. Note that the bottom two bits 7355 are ignored. 7356 7357 srcutree.exp_holdoff [KNL] 7358 Specifies how many nanoseconds must elapse 7359 since the end of the last SRCU grace period for 7360 a given srcu_struct until the next normal SRCU 7361 grace period will be considered for automatic 7362 expediting. Set to zero to disable automatic 7363 expediting. 7364 7365 srcutree.srcu_max_nodelay [KNL] 7366 Specifies the number of no-delay instances 7367 per jiffy for which the SRCU grace period 7368 worker thread will be rescheduled with zero 7369 delay. Beyond this limit, worker thread will 7370 be rescheduled with a sleep delay of one jiffy. 7371 7372 srcutree.srcu_max_nodelay_phase [KNL] 7373 Specifies the per-grace-period phase, number of 7374 non-sleeping polls of readers. Beyond this limit, 7375 grace period worker thread will be rescheduled 7376 with a sleep delay of one jiffy, between each 7377 rescan of the readers, for a grace period phase. 7378 7379 srcutree.srcu_retry_check_delay [KNL] 7380 Specifies number of microseconds of non-sleeping 7381 delay between each non-sleeping poll of readers. 7382 7383 srcutree.small_contention_lim [KNL] 7384 Specifies the number of update-side contention 7385 events per jiffy will be tolerated before 7386 initiating a conversion of an srcu_struct 7387 structure to big form. Note that the value of 7388 srcutree.convert_to_big must have the 0x10 bit 7389 set for contention-based conversions to occur. 7390 7391 ssbd= [ARM64,HW,EARLY] 7392 Speculative Store Bypass Disable control 7393 7394 On CPUs that are vulnerable to the Speculative 7395 Store Bypass vulnerability and offer a 7396 firmware based mitigation, this parameter 7397 indicates how the mitigation should be used: 7398 7399 force-on: Unconditionally enable mitigation for 7400 for both kernel and userspace 7401 force-off: Unconditionally disable mitigation for 7402 for both kernel and userspace 7403 kernel: Always enable mitigation in the 7404 kernel, and offer a prctl interface 7405 to allow userspace to register its 7406 interest in being mitigated too. 7407 7408 stack_guard_gap= [MM] 7409 override the default stack gap protection. The value 7410 is in page units and it defines how many pages prior 7411 to (for stacks growing down) resp. after (for stacks 7412 growing up) the main stack are reserved for no other 7413 mapping. Default value is 256 pages. 7414 7415 stack_depot_disable= [KNL,EARLY] 7416 Setting this to true through kernel command line will 7417 disable the stack depot thereby saving the static memory 7418 consumed by the stack hash table. By default this is set 7419 to false. 7420 7421 stack_depot_max_pools= [KNL,EARLY] 7422 Specify the maximum number of pools to use for storing 7423 stack traces. Pools are allocated on-demand up to this 7424 limit. Default value is 8191 pools. 7425 7426 stacktrace [FTRACE] 7427 Enable the stack tracer on boot up. 7428 7429 stacktrace_filter=[function-list] 7430 [FTRACE] Limit the functions that the stack tracer 7431 will trace at boot up. function-list is a comma-separated 7432 list of functions. This list can be changed at run 7433 time by the stack_trace_filter file in the debugfs 7434 tracing directory. Note, this enables stack tracing 7435 and the stacktrace above is not needed. 7436 7437 sti= [PARISC,HW] 7438 Format: <num> 7439 Set the STI (builtin display/keyboard on the HP-PARISC 7440 machines) console (graphic card) which should be used 7441 as the initial boot-console. 7442 See also comment in drivers/video/sticore.c. 7443 7444 sti_font= [HW] 7445 See comment in drivers/video/sticore.c. 7446 7447 stifb= [HW] 7448 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7449 7450 strict_sas_size= 7451 [X86] 7452 Format: <bool> 7453 Enable or disable strict sigaltstack size checks 7454 against the required signal frame size which 7455 depends on the supported FPU features. This can 7456 be used to filter out binaries which have 7457 not yet been made aware of AT_MINSIGSTKSZ. 7458 7459 stress_hpt [PPC,EARLY] 7460 Limits the number of kernel HPT entries in the hash 7461 page table to increase the rate of hash page table 7462 faults on kernel addresses. 7463 7464 stress_slb [PPC,EARLY] 7465 Limits the number of kernel SLB entries, and flushes 7466 them frequently to increase the rate of SLB faults 7467 on kernel addresses. 7468 7469 no_slb_preload [PPC,EARLY] 7470 Disables slb preloading for userspace. 7471 7472 sunrpc.min_resvport= 7473 sunrpc.max_resvport= 7474 [NFS,SUNRPC] 7475 SunRPC servers often require that client requests 7476 originate from a privileged port (i.e. a port in the 7477 range 0 < portnr < 1024). 7478 An administrator who wishes to reserve some of these 7479 ports for other uses may adjust the range that the 7480 kernel's sunrpc client considers to be privileged 7481 using these two parameters to set the minimum and 7482 maximum port values. 7483 7484 sunrpc.svc_rpc_per_connection_limit= 7485 [NFS,SUNRPC] 7486 Limit the number of requests that the server will 7487 process in parallel from a single connection. 7488 The default value is 0 (no limit). 7489 7490 sunrpc.pool_mode= 7491 [NFS] 7492 Deprecated. The NFS server now always uses one 7493 service thread pool per NUMA node (equivalent to a 7494 single global pool on non-NUMA machines). All of 7495 the previously accepted values (auto, global, 7496 percpu, pernode) are still accepted for backward 7497 compatibility but are ignored: the mode is always 7498 pernode, and reads always return "pernode". 7499 7500 sunrpc.tcp_slot_table_entries= 7501 sunrpc.udp_slot_table_entries= 7502 [NFS,SUNRPC] 7503 Sets the upper limit on the number of simultaneous 7504 RPC calls that can be sent from the client to a 7505 server. Increasing these values may allow you to 7506 improve throughput, but will also increase the 7507 amount of memory reserved for use by the client. 7508 7509 suspend.pm_test_delay= 7510 [SUSPEND] 7511 Sets the number of seconds to remain in a suspend test 7512 mode before resuming the system (see 7513 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7514 is set. Default value is 5. 7515 7516 svm= [PPC] 7517 Format: { on | off | y | n | 1 | 0 } 7518 This parameter controls use of the Protected 7519 Execution Facility on pSeries. 7520 7521 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7522 Format: { <int> [,<int>] | force | noforce | track_hiwater} 7523 <int> -- Number of I/O TLB slabs 7524 <int> -- Second integer after comma. Number of swiotlb 7525 areas with their own lock. Will be rounded up 7526 to a power of 2. 7527 force -- force using of bounce buffers even if they 7528 wouldn't be automatically used by the kernel 7529 noforce -- Never use bounce buffers (for debugging) 7530 track_hiwater -- Track high watermark of swiotlb buffers. 7531 Only available when CONFIG_DEBUG_FS is set. 7532 7533 switches= [HW,M68k,EARLY] 7534 7535 sysctl.*= [KNL] 7536 Set a sysctl parameter, right before loading the init 7537 process, as if the value was written to the respective 7538 /proc/sys/... file. Both '.' and '/' are recognized as 7539 separators. Unrecognized parameters and invalid values 7540 are reported in the kernel log. Sysctls registered 7541 later by a loaded module cannot be set this way. 7542 Example: sysctl.vm.swappiness=40 7543 7544 sysrq_always_enabled 7545 [KNL] 7546 Ignore sysrq setting - this boot parameter will 7547 neutralize any effect of /proc/sys/kernel/sysrq. 7548 Useful for debugging. 7549 7550 tcpmhash_entries= [KNL,NET] 7551 Set the number of tcp_metrics_hash slots. 7552 Default value is 8192 or 16384 depending on total 7553 ram pages. This is used to specify the TCP metrics 7554 cache size. See Documentation/networking/ip-sysctl.rst 7555 "tcp_no_metrics_save" section for more details. 7556 7557 tdfx= [HW,DRM] 7558 7559 test_suspend= [SUSPEND] 7560 Format: { "mem" | "standby" | "freeze" }[,N] 7561 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7562 standby suspend) or "freeze" (for suspend type freeze) 7563 as the system sleep state during system startup with 7564 the optional capability to repeat N number of times. 7565 The system is woken from this state using a 7566 wakeup-capable RTC alarm. 7567 7568 thash_entries= [KNL,NET] 7569 Set number of hash buckets for TCP connection 7570 7571 thermal.act= [HW,ACPI] 7572 -1: disable all active trip points in all thermal zones 7573 <degrees C>: override all lowest active trip points 7574 7575 thermal.crt= [HW,ACPI] 7576 -1: disable all critical trip points in all thermal zones 7577 <degrees C>: override all critical trip points 7578 7579 thermal.off= [HW,ACPI] 7580 1: disable ACPI thermal control 7581 7582 thermal.psv= [HW,ACPI] 7583 -1: disable all passive trip points 7584 <degrees C>: override all passive trip points to this 7585 value 7586 7587 thermal.tzp= [HW,ACPI] 7588 Specify global default ACPI thermal zone polling rate 7589 <deci-seconds>: poll all this frequency 7590 0: no polling (default) 7591 7592 thp_anon= [KNL] 7593 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7594 state is one of "always", "madvise", "never" or "inherit". 7595 Control the default behavior of the system with respect 7596 to anonymous transparent hugepages. 7597 Can be used multiple times for multiple anon THP sizes. 7598 See Documentation/admin-guide/mm/transhuge.rst for more 7599 details. 7600 7601 threadirqs [KNL,EARLY] 7602 Force threading of all interrupt handlers except those 7603 marked explicitly IRQF_NO_THREAD. 7604 7605 thp_shmem= [KNL] 7606 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7607 Control the default policy of each hugepage size for the 7608 internal shmem mount. <policy> is one of policies available 7609 for the shmem mount ("always", "inherit", "never", "within_size", 7610 and "advise"). 7611 It can be used multiple times for multiple shmem THP sizes. 7612 See Documentation/admin-guide/mm/transhuge.rst for more 7613 details. 7614 7615 tlbi= [X86-64] 7616 Format: {ipi} 7617 ipi: switch to IPI-based TLB flushing 7618 7619 topology= [S390,EARLY] 7620 Format: {off | on} 7621 Specify if the kernel should make use of the cpu 7622 topology information if the hardware supports this. 7623 The scheduler will make use of this information and 7624 e.g. base its process migration decisions on it. 7625 Default is on. 7626 7627 torture.disable_onoff_at_boot= [KNL] 7628 Prevent the CPU-hotplug component of torturing 7629 until after init has spawned. 7630 7631 torture.ftrace_dump_at_shutdown= [KNL] 7632 Dump the ftrace buffer at torture-test shutdown, 7633 even if there were no errors. This can be a 7634 very costly operation when many torture tests 7635 are running concurrently, especially on systems 7636 with rotating-rust storage. 7637 7638 torture.verbose_sleep_frequency= [KNL] 7639 Specifies how many verbose printk()s should be 7640 emitted between each sleep. The default of zero 7641 disables verbose-printk() sleeping. 7642 7643 torture.verbose_sleep_duration= [KNL] 7644 Duration of each verbose-printk() sleep in jiffies. 7645 7646 tpm.disable_pcr_integrity= [HW,TPM] 7647 Do not protect PCR registers from unintended physical 7648 access, or interposers in the bus by the means of 7649 having an integrity protected session wrapped around 7650 TPM2_PCR_Extend command. Consider this in a situation 7651 where TPM is heavily utilized by IMA, thus protection 7652 causing a major performance hit, and the space where 7653 machines are deployed is by other means guarded. 7654 7655 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7656 Maximum time in milliseconds to retry sending a message 7657 to the TPM service before giving up. This parameter controls 7658 how long the system will continue retrying when the TPM 7659 service is busy. 7660 Format: <unsigned int> 7661 Default: 2000 (2 seconds) 7662 7663 tpm_suspend_pcr=[HW,TPM] 7664 Format: integer pcr id 7665 Specify that at suspend time, the tpm driver 7666 should extend the specified pcr with zeros, 7667 as a workaround for some chips which fail to 7668 flush the last written pcr on TPM_SaveState. 7669 This will guarantee that all the other pcrs 7670 are saved. 7671 7672 tpm_tis.interrupts= [HW,TPM] 7673 Enable interrupts for the MMIO based physical layer 7674 for the FIFO interface. By default it is set to false 7675 (0). For more information about TPM hardware interfaces 7676 defined by Trusted Computing Group (TCG) see 7677 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7678 7679 tp_printk [FTRACE] 7680 Have the tracepoints sent to printk as well as the 7681 tracing ring buffer. This is useful for early boot up 7682 where the system hangs or reboots and does not give the 7683 option for reading the tracing buffer or performing a 7684 ftrace_dump_on_oops. 7685 7686 To turn off having tracepoints sent to printk, 7687 echo 0 > /proc/sys/kernel/tracepoint_printk 7688 Note, echoing 1 into this file without the 7689 tp_printk kernel cmdline option has no effect. 7690 7691 The tp_printk_stop_on_boot (see below) can also be used 7692 to stop the printing of events to console at 7693 late_initcall_sync. 7694 7695 ** CAUTION ** 7696 7697 Having tracepoints sent to printk() and activating high 7698 frequency tracepoints such as irq or sched, can cause 7699 the system to live lock. 7700 7701 tp_printk_stop_on_boot [FTRACE] 7702 When tp_printk (above) is set, it can cause a lot of noise 7703 on the console. It may be useful to only include the 7704 printing of events during boot up, as user space may 7705 make the system inoperable. 7706 7707 This command line option will stop the printing of events 7708 to console at the late_initcall_sync() time frame. 7709 7710 trace_buf_size=nn[KMG] 7711 [FTRACE] will set tracing buffer size on each cpu. 7712 7713 trace_clock= [FTRACE] Set the clock used for tracing events 7714 at boot up. 7715 local - Use the per CPU time stamp counter 7716 (converted into nanoseconds). Fast, but 7717 depending on the architecture, may not be 7718 in sync between CPUs. 7719 global - Event time stamps are synchronized across 7720 CPUs. May be slower than the local clock, 7721 but better for some race conditions. 7722 counter - Simple counting of events (1, 2, ..) 7723 note, some counts may be skipped due to the 7724 infrastructure grabbing the clock more than 7725 once per event. 7726 uptime - Use jiffies as the time stamp. 7727 perf - Use the same clock that perf uses. 7728 mono - Use ktime_get_mono_fast_ns() for time stamps. 7729 mono_raw - Use ktime_get_raw_fast_ns() for time 7730 stamps. 7731 boot - Use ktime_get_boot_fast_ns() for time stamps. 7732 Architectures may add more clocks. See 7733 Documentation/trace/ftrace.rst for more details. 7734 7735 trace_event=[event-list] 7736 [FTRACE] Set and start specified trace events in order 7737 to facilitate early boot debugging. The event-list is a 7738 comma-separated list of trace events to enable. See 7739 also Documentation/trace/events.rst 7740 7741 To enable modules, use :mod: keyword: 7742 7743 trace_event=:mod:<module> 7744 7745 The value before :mod: will only enable specific events 7746 that are part of the module. See the above mentioned 7747 document for more information. 7748 7749 trace_instance=[instance-info] 7750 [FTRACE] Create a ring buffer instance early in boot up. 7751 This will be listed in: 7752 7753 /sys/kernel/tracing/instances 7754 7755 Events can be enabled at the time the instance is created 7756 via: 7757 7758 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7759 7760 Note, the "<system*>:" portion is optional if the event is 7761 unique. 7762 7763 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7764 7765 will enable the "sched_switch" event (note, the "sched:" is optional, and 7766 the same thing would happen if it was left off). The irq_handler_entry 7767 event, and all events under the "initcall" system. 7768 7769 Flags can be added to the instance to modify its behavior when it is 7770 created. The flags are separated by '^'. 7771 7772 The available flags are: 7773 7774 traceoff - Have the tracing instance tracing disabled after it is created. 7775 traceprintk - Have trace_printk() write into this trace instance 7776 (note, "printk" and "trace_printk" can also be used) 7777 7778 trace_instance=foo^traceoff^traceprintk,sched,irq 7779 7780 The flags must come before the defined events. 7781 7782 If memory has been reserved (see memmap for x86), the instance 7783 can use that memory: 7784 7785 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7786 7787 The above will create a "boot_map" instance that uses the physical 7788 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7789 instance will be split up accordingly. 7790 7791 Alternatively, the memory can be reserved by the reserve_mem option: 7792 7793 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7794 7795 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7796 and place the ring buffer in this memory. Note that due to KASLR, the 7797 memory may not be the same location each time, which will not preserve 7798 the buffer content. 7799 7800 Also note that the layout of the ring buffer data may change between 7801 kernel versions where the validator will fail and reset the ring buffer 7802 if the layout is not the same as the previous kernel. 7803 7804 If the ring buffer is used for persistent bootups and has events enabled, 7805 it is recommend to disable tracing so that events from a previous boot do not 7806 mix with events of the current boot (unless you are debugging a random crash 7807 at boot up). 7808 7809 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7810 7811 Note, saving the trace buffer across reboots does require that the system 7812 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7813 can force a memory reset on boot which will clear any trace that was stored. 7814 This is just one of many ways that can clear memory. Make sure your system 7815 keeps the content of memory across reboots before relying on this option. 7816 7817 NB: Both the mapped address and size must be page aligned for the architecture. 7818 7819 See also Documentation/trace/debugging.rst 7820 7821 7822 trace_options=[option-list] 7823 [FTRACE] Enable or disable tracer options at boot. 7824 The option-list is a comma delimited list of options 7825 that can be enabled or disabled just as if you were 7826 to echo the option name into 7827 7828 /sys/kernel/tracing/trace_options 7829 7830 For example, to enable stacktrace option (to dump the 7831 stack trace of each event), add to the command line: 7832 7833 trace_options=stacktrace 7834 7835 See also Documentation/trace/ftrace.rst "trace options" 7836 section. 7837 7838 trace_trigger=[trigger-list] 7839 [FTRACE] Add an event trigger on specific events. 7840 Set a trigger on top of a specific event, with an optional 7841 filter. 7842 7843 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7844 Where more than one trigger may be specified that are comma delimited. 7845 7846 For example: 7847 7848 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7849 7850 The above will enable the "stacktrace" trigger on the "sched_switch" 7851 event but only trigger it if the "prev_state" of the "sched_switch" 7852 event is "2" (TASK_UNINTERRUPTIBLE). 7853 7854 See also "Event triggers" in Documentation/trace/events.rst 7855 7856 7857 traceoff_after_boot 7858 [FTRACE] Sometimes tracing is used to debug issues 7859 during the boot process. Since the trace buffer has a 7860 limited amount of storage, it may be prudent to 7861 disable tracing after the boot is finished, otherwise 7862 the critical information may be overwritten. With this 7863 option, the main tracing buffer will be turned off at 7864 the end of the boot process. 7865 7866 traceoff_on_warning 7867 [FTRACE] enable this option to disable tracing when a 7868 warning is hit. This turns off "tracing_on". Tracing can 7869 be enabled again by echoing '1' into the "tracing_on" 7870 file located in /sys/kernel/tracing/ 7871 7872 This option is useful, as it disables the trace before 7873 the WARNING dump is called, which prevents the trace to 7874 be filled with content caused by the warning output. 7875 7876 This option can also be set at run time via the sysctl 7877 option: kernel/traceoff_on_warning 7878 7879 transparent_hugepage= 7880 [KNL] 7881 Format: [always|madvise|never] 7882 Can be used to control the default behavior of the system 7883 with respect to transparent hugepages. 7884 See Documentation/admin-guide/mm/transhuge.rst 7885 for more details. 7886 7887 transparent_hugepage_shmem= [KNL] 7888 Format: [always|within_size|advise|never|deny|force] 7889 Can be used to control the hugepage allocation policy for 7890 the internal shmem mount. 7891 See Documentation/admin-guide/mm/transhuge.rst 7892 for more details. 7893 7894 transparent_hugepage_tmpfs= [KNL] 7895 Format: [always|within_size|advise|never] 7896 Can be used to control the default hugepage allocation policy 7897 for the tmpfs mount. 7898 See Documentation/admin-guide/mm/transhuge.rst 7899 for more details. 7900 7901 trusted.source= [KEYS] 7902 Format: <string> 7903 This parameter identifies the trust source as a backend 7904 for trusted keys implementation. Supported trust 7905 sources: 7906 - "tpm" 7907 - "tee" 7908 - "caam" 7909 - "dcp" 7910 - "pkwm" 7911 If not specified then it defaults to iterating through 7912 the trust source list starting with TPM and assigns the 7913 first trust source as a backend which is initialized 7914 successfully during iteration. 7915 7916 trusted.debug= [KEYS] 7917 Format: <bool> 7918 Enable trusted keys debug traces at runtime when 7919 CONFIG_TRUSTED_KEYS_DEBUG=y. 7920 7921 To make the traces visible after enabling the option, 7922 use trusted.dyndbg='+p' as needed. By convention, 7923 the subsystem uses pr_debug() for these traces. 7924 7925 SAFETY: The traces can leak sensitive data, so be 7926 cautious before enabling this. They remain inactive 7927 unless this parameter is set this option to a true 7928 value. 7929 7930 Default: false 7931 7932 trusted.rng= [KEYS] 7933 Format: <string> 7934 The RNG used to generate key material for trusted keys. 7935 Can be one of: 7936 - "kernel" 7937 - the same value as trusted.source: "tpm" or "tee" 7938 - "default" 7939 If not specified, "default" is used. In this case, 7940 the RNG's choice is left to each individual trust source. 7941 7942 trusted.dcp_use_otp_key 7943 This is intended to be used in combination with 7944 trusted.source=dcp and will select the DCP OTP key 7945 instead of the DCP UNIQUE key blob encryption. 7946 7947 trusted.dcp_skip_zk_test 7948 This is intended to be used in combination with 7949 trusted.source=dcp and will disable the check if the 7950 blob key is all zeros. This is helpful for situations where 7951 having this key zero'ed is acceptable. E.g. in testing 7952 scenarios. 7953 7954 tsa= [X86] Control mitigation for Transient Scheduler 7955 Attacks on AMD CPUs. Search the following in your 7956 favourite search engine for more details: 7957 7958 "Technical guidance for mitigating transient scheduler 7959 attacks". 7960 7961 off - disable the mitigation 7962 on - enable the mitigation (default) 7963 user - mitigate only user/kernel transitions 7964 vm - mitigate only guest/host transitions 7965 7966 7967 tsc= Disable clocksource stability checks for TSC. 7968 Format: <string> 7969 [x86] reliable: mark tsc clocksource as reliable, this 7970 disables clocksource verification at runtime, as well 7971 as the stability checks done at bootup. Used to enable 7972 high-resolution timer mode on older hardware, and in 7973 virtualized environment. 7974 [x86] noirqtime: Do not use TSC to do irq accounting. 7975 Used to run time disable IRQ_TIME_ACCOUNTING on any 7976 platforms where RDTSC is slow and this accounting 7977 can add overhead. 7978 [x86] unstable: mark the TSC clocksource as unstable, this 7979 marks the TSC unconditionally unstable at bootup and 7980 avoids any further wobbles once the TSC watchdog notices. 7981 [x86] nowatchdog: disable clocksource watchdog. Used 7982 in situations with strict latency requirements (where 7983 interruptions from clocksource watchdog are not 7984 acceptable). 7985 [x86] recalibrate: force recalibration against a HW timer 7986 (HPET or PM timer) on systems whose TSC frequency was 7987 obtained from HW or FW using either an MSR or CPUID(0x15). 7988 Warn if the difference is more than 500 ppm. 7989 [x86] watchdog: Enforce the clocksource watchdog on TSC 7990 7991 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7992 value instead. Useful when the early TSC frequency discovery 7993 procedure is not reliable, such as on overclocked systems 7994 with CPUID.16h support and partial CPUID.15h support. 7995 Format: <unsigned int> 7996 7997 tsx= [X86] Control Transactional Synchronization 7998 Extensions (TSX) feature in Intel processors that 7999 support TSX control. 8000 8001 This parameter controls the TSX feature. The options are: 8002 8003 on - Enable TSX on the system. Although there are 8004 mitigations for all known security vulnerabilities, 8005 TSX has been known to be an accelerator for 8006 several previous speculation-related CVEs, and 8007 so there may be unknown security risks associated 8008 with leaving it enabled. 8009 8010 off - Disable TSX on the system. (Note that this 8011 option takes effect only on newer CPUs which are 8012 not vulnerable to MDS, i.e., have 8013 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 8014 the new IA32_TSX_CTRL MSR through a microcode 8015 update. This new MSR allows for the reliable 8016 deactivation of the TSX functionality.) 8017 8018 auto - Disable TSX if X86_BUG_TAA is present, 8019 otherwise enable TSX on the system. 8020 8021 Not specifying this option is equivalent to tsx=off. 8022 8023 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8024 for more details. 8025 8026 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 8027 Abort (TAA) vulnerability. 8028 8029 Similar to Micro-architectural Data Sampling (MDS) 8030 certain CPUs that support Transactional 8031 Synchronization Extensions (TSX) are vulnerable to an 8032 exploit against CPU internal buffers which can forward 8033 information to a disclosure gadget under certain 8034 conditions. 8035 8036 In vulnerable processors, the speculatively forwarded 8037 data can be used in a cache side channel attack, to 8038 access data to which the attacker does not have direct 8039 access. 8040 8041 This parameter controls the TAA mitigation. The 8042 options are: 8043 8044 full - Enable TAA mitigation on vulnerable CPUs 8045 if TSX is enabled. 8046 8047 full,nosmt - Enable TAA mitigation and disable SMT on 8048 vulnerable CPUs. If TSX is disabled, SMT 8049 is not disabled because CPU is not 8050 vulnerable to cross-thread TAA attacks. 8051 off - Unconditionally disable TAA mitigation 8052 8053 On MDS-affected machines, tsx_async_abort=off can be 8054 prevented by an active MDS mitigation as both vulnerabilities 8055 are mitigated with the same mechanism so in order to disable 8056 this mitigation, you need to specify mds=off too. 8057 8058 Not specifying this option is equivalent to 8059 tsx_async_abort=full. On CPUs which are MDS affected 8060 and deploy MDS mitigation, TAA mitigation is not 8061 required and doesn't provide any additional 8062 mitigation. 8063 8064 For details see: 8065 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8066 8067 turbografx.map[2|3]= [HW,JOY] 8068 TurboGraFX parallel port interface 8069 Format: 8070 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8071 See also Documentation/input/devices/joystick-parport.rst 8072 8073 udbg-immortal [PPC] When debugging early kernel crashes that 8074 happen after console_init() and before a proper 8075 console driver takes over, this boot options might 8076 help "seeing" what's going on. 8077 8078 uhash_entries= [KNL,NET] 8079 Set number of hash buckets for UDP/UDP-Lite connections 8080 8081 uhci-hcd.ignore_oc= 8082 [USB] Ignore overcurrent events (default N). 8083 Some badly-designed motherboards generate lots of 8084 bogus events, for ports that aren't wired to 8085 anything. Set this parameter to avoid log spamming. 8086 Note that genuine overcurrent events won't be 8087 reported either. 8088 8089 unaligned_scalar_speed= 8090 [RISCV] 8091 Format: {slow | fast | unsupported} 8092 Allow skipping scalar unaligned access speed tests. This 8093 is useful for testing alternative code paths and to skip 8094 the tests in environments where they run too slowly. All 8095 CPUs must have the same scalar unaligned access speed. 8096 8097 unaligned_vector_speed= 8098 [RISCV] 8099 Format: {slow | fast | unsupported} 8100 Allow skipping vector unaligned access speed tests. This 8101 is useful for testing alternative code paths and to skip 8102 the tests in environments where they run too slowly. All 8103 CPUs must have the same vector unaligned access speed. 8104 8105 unknown_nmi_panic 8106 [X86] Cause panic on unknown NMI. 8107 8108 unwind_debug [X86-64,EARLY] 8109 Enable unwinder debug output. This can be 8110 useful for debugging certain unwinder error 8111 conditions, including corrupt stacks and 8112 bad/missing unwinder metadata. 8113 8114 usbcore.authorized_default= 8115 [USB] Default USB device authorization: 8116 (default -1 = authorized (same as 1), 8117 0 = not authorized, 1 = authorized, 2 = authorized 8118 if device connected to internal port) 8119 8120 usbcore.autosuspend= 8121 [USB] The autosuspend time delay (in seconds) used 8122 for newly-detected USB devices (default 2). This 8123 is the time required before an idle device will be 8124 autosuspended. Devices for which the delay is set 8125 to a negative value won't be autosuspended at all. 8126 8127 usbcore.usbfs_snoop= 8128 [USB] Set to log all usbfs traffic (default 0 = off). 8129 8130 usbcore.usbfs_snoop_max= 8131 [USB] Maximum number of bytes to snoop in each URB 8132 (default = 65536). 8133 8134 usbcore.blinkenlights= 8135 [USB] Set to cycle leds on hubs (default 0 = off). 8136 8137 usbcore.old_scheme_first= 8138 [USB] Start with the old device initialization 8139 scheme (default 0 = off). 8140 8141 usbcore.usbfs_memory_mb= 8142 [USB] Memory limit (in MB) for buffers allocated by 8143 usbfs (default = 16, 0 = max = 2047). 8144 8145 usbcore.use_both_schemes= 8146 [USB] Try the other device initialization scheme 8147 if the first one fails (default 1 = enabled). 8148 8149 usbcore.initial_descriptor_timeout= 8150 [USB] Specifies timeout for the initial 64-byte 8151 USB_REQ_GET_DESCRIPTOR request in milliseconds 8152 (default 5000 = 5.0 seconds). 8153 8154 usbcore.nousb [USB] Disable the USB subsystem 8155 8156 usbcore.quirks= 8157 [USB] A list of quirk entries to augment the built-in 8158 usb core quirk list. List entries are separated by 8159 commas. Each entry has the form 8160 VendorID:ProductID:Flags. The IDs are 4-digit hex 8161 numbers and Flags is a set of letters. Each letter 8162 will change the built-in quirk; setting it if it is 8163 clear and clearing it if it is set. The letters have 8164 the following meanings: 8165 a = USB_QUIRK_STRING_FETCH_255 (string 8166 descriptors must not be fetched using 8167 a 255-byte read); 8168 b = USB_QUIRK_RESET_RESUME (device can't resume 8169 correctly so reset it instead); 8170 c = USB_QUIRK_NO_SET_INTF (device can't handle 8171 Set-Interface requests); 8172 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8173 handle its Configuration or Interface 8174 strings); 8175 e = USB_QUIRK_RESET (device can't be reset 8176 (e.g morph devices), don't use reset); 8177 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8178 more interface descriptions than the 8179 bNumInterfaces count, and can't handle 8180 talking to these interfaces); 8181 g = USB_QUIRK_DELAY_INIT (device needs a pause 8182 during initialization, after we read 8183 the device descriptor); 8184 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8185 high speed and super speed interrupt 8186 endpoints, the USB 2.0 and USB 3.0 spec 8187 require the interval in microframes (1 8188 microframe = 125 microseconds) to be 8189 calculated as interval = 2 ^ 8190 (bInterval-1). 8191 Devices with this quirk report their 8192 bInterval as the result of this 8193 calculation instead of the exponent 8194 variable used in the calculation); 8195 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8196 handle device_qualifier descriptor 8197 requests); 8198 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8199 generates spurious wakeup, ignore 8200 remote wakeup capability); 8201 k = USB_QUIRK_NO_LPM (device can't handle Link 8202 Power Management); 8203 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8204 (Device reports its bInterval as linear 8205 frames instead of the USB 2.0 8206 calculation); 8207 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8208 to be disconnected before suspend to 8209 prevent spurious wakeup); 8210 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8211 pause after every control message); 8212 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8213 delay after resetting its port); 8214 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8215 (Reduce timeout of the SET_ADDRESS 8216 request from 5000 ms to 500 ms); 8217 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8218 claims zero configurations, 8219 forcing to 1); 8220 r = USB_QUIRK_WINDOWS_CONFIG_REQ_SIZE (Device 8221 fails during initialization when asked for 8222 9-bytes configuration descriptor request. 8223 Ask for 255-bytes request instead to mirror 8224 Windows' behavior); 8225 Example: quirks=0781:5580:bk,0a5c:5834:gij 8226 8227 usbhid.mousepoll= 8228 [USBHID] The interval which mice are to be polled at. 8229 8230 usbhid.jspoll= 8231 [USBHID] The interval which joysticks are to be polled at. 8232 8233 usbhid.kbpoll= 8234 [USBHID] The interval which keyboards are to be polled at. 8235 8236 usb-storage.delay_use= 8237 [UMS] The delay in seconds before a new device is 8238 scanned for Logical Units (default 1). 8239 Optionally the delay in milliseconds if the value has 8240 suffix with "ms". 8241 Example: delay_use=2567ms 8242 8243 usb-storage.quirks= 8244 [UMS] A list of quirks entries to supplement or 8245 override the built-in unusual_devs list. List 8246 entries are separated by commas. Each entry has 8247 the form VID:PID:Flags where VID and PID are Vendor 8248 and Product ID values (4-digit hex numbers) and 8249 Flags is a set of characters, each corresponding 8250 to a common usb-storage quirk flag as follows: 8251 a = SANE_SENSE (collect more than 18 bytes 8252 of sense data, not on uas); 8253 b = BAD_SENSE (don't collect more than 18 8254 bytes of sense data, not on uas); 8255 c = FIX_CAPACITY (decrease the reported 8256 device capacity by one sector); 8257 d = NO_READ_DISC_INFO (don't use 8258 READ_DISC_INFO command, not on uas); 8259 e = NO_READ_CAPACITY_16 (don't use 8260 READ_CAPACITY_16 command); 8261 f = NO_REPORT_OPCODES (don't use report opcodes 8262 command, uas only); 8263 g = MAX_SECTORS_240 (don't transfer more than 8264 240 sectors at a time, uas only); 8265 h = CAPACITY_HEURISTICS (decrease the 8266 reported device capacity by one 8267 sector if the number is odd); 8268 i = IGNORE_DEVICE (don't bind to this 8269 device); 8270 j = NO_REPORT_LUNS (don't use report luns 8271 command, uas only); 8272 k = NO_SAME (do not use WRITE_SAME, uas only) 8273 l = NOT_LOCKABLE (don't try to lock and 8274 unlock ejectable media, not on uas); 8275 m = MAX_SECTORS_64 (don't transfer more 8276 than 64 sectors = 32 KB at a time, 8277 not on uas); 8278 n = INITIAL_READ10 (force a retry of the 8279 initial READ(10) command, not on uas); 8280 o = CAPACITY_OK (accept the capacity 8281 reported by the device, not on uas); 8282 p = WRITE_CACHE (the device cache is ON 8283 by default, not on uas); 8284 r = IGNORE_RESIDUE (the device reports 8285 bogus residue values, not on uas); 8286 s = SINGLE_LUN (the device has only one 8287 Logical Unit); 8288 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8289 commands, uas only); 8290 u = IGNORE_UAS (don't bind to the uas driver); 8291 w = NO_WP_DETECT (don't test whether the 8292 medium is write-protected). 8293 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8294 even if the device claims no cache, 8295 not on uas) 8296 Example: quirks=0419:aaf5:rl,0421:0433:rc 8297 8298 user_debug= [KNL,ARM] 8299 Format: <int> 8300 See arch/arm/Kconfig.debug help text. 8301 1 - undefined instruction events 8302 2 - system calls 8303 4 - invalid data aborts 8304 8 - SIGSEGV faults 8305 16 - SIGBUS faults 8306 Example: user_debug=31 8307 8308 vdso= [X86,SH,SPARC] 8309 On X86_32, this is an alias for vdso32=. Otherwise: 8310 8311 vdso=1: enable VDSO (the default) 8312 vdso=0: disable VDSO mapping 8313 8314 vdso32= [X86] Control the 32-bit vDSO 8315 vdso32=1: enable 32-bit VDSO 8316 vdso32=0 or vdso32=2: disable 32-bit VDSO 8317 8318 See the help text for CONFIG_COMPAT_VDSO for more 8319 details. If CONFIG_COMPAT_VDSO is set, the default is 8320 vdso32=0; otherwise, the default is vdso32=1. 8321 8322 For compatibility with older kernels, vdso32=2 is an 8323 alias for vdso32=0. 8324 8325 Try vdso32=0 if you encounter an error that says: 8326 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8327 8328 video= [FB,EARLY] Frame buffer configuration 8329 See Documentation/fb/modedb.rst. 8330 8331 video.brightness_switch_enabled= [ACPI] 8332 Format: [0|1] 8333 If set to 1, on receiving an ACPI notify event 8334 generated by hotkey, video driver will adjust brightness 8335 level and then send out the event to user space through 8336 the allocated input device. If set to 0, video driver 8337 will only send out the event without touching backlight 8338 brightness level. 8339 default: 1 8340 8341 virtio_mmio.device= 8342 [VMMIO] Memory mapped virtio (platform) device. 8343 8344 <size>@<baseaddr>:<irq>[:<id>] 8345 where: 8346 <size> := size (can use standard suffixes 8347 like K, M and G) 8348 <baseaddr> := physical base address 8349 <irq> := interrupt number (as passed to 8350 request_irq()) 8351 <id> := (optional) platform device id 8352 example: 8353 virtio_mmio.device=1K@0x100b0000:48:7 8354 8355 Can be used multiple times for multiple devices. 8356 8357 vga= [BOOT,X86-32] Select a particular video mode 8358 See Documentation/arch/x86/boot.rst and 8359 Documentation/admin-guide/svga.rst. 8360 Use vga=ask for menu. 8361 This is actually a boot loader parameter; the value is 8362 passed to the kernel using a special protocol. 8363 8364 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8365 May slow down system boot speed, especially when 8366 enabled on systems with a large amount of memory. 8367 All options are enabled by default, and this 8368 interface is meant to allow for selectively 8369 enabling or disabling specific virtual memory 8370 debugging features. 8371 8372 Available options are: 8373 P Enable page structure init time poisoning 8374 - Disable all of the above options 8375 8376 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8377 exact size of <nn>. This can be used to increase 8378 the minimum size (128MB on x86, arm32 platforms). 8379 It can also be used to decrease the size and leave more room 8380 for directly mapped kernel RAM. Note that this parameter does 8381 not exist on many other platforms (including arm64, alpha, 8382 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8383 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8384 8385 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8386 Sets the memory size reserved for contiguous memory 8387 allocations for the vmcp device driver. 8388 8389 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8390 Format: <command> 8391 8392 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8393 Format: <command> 8394 8395 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8396 Format: <command> 8397 8398 vmscape= [X86] Controls mitigation for VMscape attacks. 8399 VMscape attacks can leak information from a userspace 8400 hypervisor to a guest via speculative side-channels. 8401 8402 off - disable the mitigation 8403 ibpb - use Indirect Branch Prediction Barrier 8404 (IBPB) mitigation (default) 8405 force - force vulnerability detection even on 8406 unaffected processors 8407 8408 vsyscall= [X86-64,EARLY] 8409 Controls the behavior of vsyscalls (i.e. calls to 8410 fixed addresses of 0xffffffffff600x00 from legacy 8411 code). Most statically-linked binaries and older 8412 versions of glibc use these calls. Because these 8413 functions are at fixed addresses, they make nice 8414 targets for exploits that can control RIP. 8415 8416 emulate Vsyscalls turn into traps and are emulated 8417 reasonably safely. The vsyscall page is 8418 readable. This disables the Linear 8419 Address Space Separation (LASS) security 8420 feature and makes the system less secure. 8421 8422 xonly [default] Vsyscalls turn into traps and are 8423 emulated reasonably safely. The vsyscall 8424 page is not readable. 8425 8426 none Vsyscalls don't work at all. This makes 8427 them quite hard to use for exploits but 8428 might break your system. 8429 8430 vt.color= [VT] Default text color. 8431 Format: 0xYX, X = foreground, Y = background. 8432 Default: 0x07 = light gray on black. 8433 8434 vt.cur_default= [VT] Default cursor shape. 8435 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8436 the parameters of the <Esc>[?A;B;Cc escape sequence; 8437 see vga-softcursor.rst. Default: 2 = underline. 8438 8439 vt.default_blu= [VT] 8440 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8441 Change the default blue palette of the console. 8442 This is a 16-member array composed of values 8443 ranging from 0-255. 8444 8445 vt.default_grn= [VT] 8446 Format: <green0>,<green1>,<green2>,...,<green15> 8447 Change the default green palette of the console. 8448 This is a 16-member array composed of values 8449 ranging from 0-255. 8450 8451 vt.default_red= [VT] 8452 Format: <red0>,<red1>,<red2>,...,<red15> 8453 Change the default red palette of the console. 8454 This is a 16-member array composed of values 8455 ranging from 0-255. 8456 8457 vt.default_utf8= 8458 [VT] 8459 Format=<0|1> 8460 Set system-wide default UTF-8 mode for all tty's. 8461 Default is 1, i.e. UTF-8 mode is enabled for all 8462 newly opened terminals. 8463 8464 vt.global_cursor_default= 8465 [VT] 8466 Format=<-1|0|1> 8467 Set system-wide default for whether a cursor 8468 is shown on new VTs. Default is -1, 8469 i.e. cursors will be created by default unless 8470 overridden by individual drivers. 0 will hide 8471 cursors, 1 will display them. 8472 8473 vt.italic= [VT] Default color for italic text; 0-15. 8474 Default: 2 = green. 8475 8476 vt.underline= [VT] Default color for underlined text; 0-15. 8477 Default: 3 = cyan. 8478 8479 watchdog timers [HW,WDT] For information on watchdog timers, 8480 see Documentation/watchdog/watchdog-parameters.rst 8481 or other driver-specific files in the 8482 Documentation/watchdog/ directory. 8483 8484 watchdog_thresh= 8485 [KNL] 8486 Set the hard lockup detector stall duration 8487 threshold in seconds. The soft lockup detector 8488 threshold is set to twice the value. A value of 0 8489 disables both lockup detectors. Default is 10 8490 seconds. 8491 8492 workqueue.unbound_cpus= 8493 [KNL,SMP] Specify to constrain one or some CPUs 8494 to use in unbound workqueues. 8495 Format: <cpu-list> 8496 By default, all online CPUs are available for 8497 unbound workqueues. 8498 8499 workqueue.watchdog_thresh= 8500 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8501 warn stall conditions and dump internal state to 8502 help debugging. 0 disables workqueue stall 8503 detection; otherwise, it's the stall threshold 8504 duration in seconds. The default value is 30 and 8505 it can be updated at runtime by writing to the 8506 corresponding sysfs file. 8507 8508 workqueue.panic_on_stall=<uint> 8509 Panic when workqueue stall is detected by 8510 CONFIG_WQ_WATCHDOG. It sets the number times of the 8511 stall to trigger panic. 8512 8513 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8514 which is 0 (disabled) if not configured. 8515 8516 workqueue.panic_on_stall_time=<uint> 8517 Panic when a workqueue stall has been continuous for 8518 the specified number of seconds. Unlike panic_on_stall 8519 which counts accumulated stall events, this triggers 8520 based on the duration of a single continuous stall. 8521 8522 The default is 0, which disables the time-based panic. 8523 8524 workqueue.cpu_intensive_thresh_us= 8525 Per-cpu work items which run for longer than this 8526 threshold are automatically considered CPU intensive 8527 and excluded from concurrency management to prevent 8528 them from noticeably delaying other per-cpu work 8529 items. Default is 10000 (10ms). 8530 8531 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8532 will report the work functions which violate this 8533 threshold repeatedly. They are likely good 8534 candidates for using WQ_UNBOUND workqueues instead. 8535 8536 workqueue.cpu_intensive_warning_thresh=<uint> 8537 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8538 will report the work functions which violate the 8539 intensive_threshold_us repeatedly. In order to prevent 8540 spurious warnings, start printing only after a work 8541 function has violated this threshold number of times. 8542 8543 The default is 4 times. 0 disables the warning. 8544 8545 workqueue.power_efficient 8546 Per-cpu workqueues are generally preferred because 8547 they show better performance thanks to cache 8548 locality; unfortunately, per-cpu workqueues tend to 8549 be more power hungry than unbound workqueues. 8550 8551 Enabling this makes the per-cpu workqueues which 8552 were observed to contribute significantly to power 8553 consumption unbound, leading to measurably lower 8554 power usage at the cost of small performance 8555 overhead. 8556 8557 The default value of this parameter is determined by 8558 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8559 8560 workqueue.default_affinity_scope= 8561 Select the default affinity scope to use for unbound 8562 workqueues. Can be one of "cpu", "smt", "cache", 8563 "cache_shard", "numa" and "system". Default is 8564 "cache_shard". For more 8565 information, see the Affinity Scopes section in 8566 Documentation/core-api/workqueue.rst. 8567 8568 This can be changed after boot by writing to the 8569 matching /sys/module/workqueue/parameters file. All 8570 workqueues with the "default" affinity scope will be 8571 updated accordingly. 8572 8573 workqueue.debug_force_rr_cpu 8574 Workqueue used to implicitly guarantee that work 8575 items queued without explicit CPU specified are put 8576 on the local CPU. This guarantee is no longer true 8577 and while local CPU is still preferred work items 8578 may be put on foreign CPUs. This debug option 8579 forces round-robin CPU selection to flush out 8580 usages which depend on the now broken guarantee. 8581 When enabled, memory and cache locality will be 8582 impacted. 8583 8584 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8585 Type) of ioremap_wc(). 8586 8587 on - Enable writecombine, use WUC for ioremap_wc() 8588 off - Disable writecombine, use SUC for ioremap_wc() 8589 8590 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8591 default x2apic cluster mode on platforms 8592 supporting x2apic. 8593 8594 xen_512gb_limit [KNL,X86-64,XEN] 8595 Restricts the kernel running paravirtualized under Xen 8596 to use only up to 512 GB of RAM. The reason to do so is 8597 crash analysis tools and Xen tools for doing domain 8598 save/restore/migration must be enabled to handle larger 8599 domains. 8600 8601 xen_console_io [XEN,EARLY] 8602 Boolean option to enable/disable the usage of the Xen 8603 console_io hypercalls to read and write to the console. 8604 Mostly useful for debugging and development. 8605 8606 xen_emul_unplug= [HW,X86,XEN,EARLY] 8607 Unplug Xen emulated devices 8608 Format: [unplug0,][unplug1] 8609 ide-disks -- unplug primary master IDE devices 8610 aux-ide-disks -- unplug non-primary-master IDE devices 8611 nics -- unplug network devices 8612 all -- unplug all emulated devices (NICs and IDE disks) 8613 unnecessary -- unplugging emulated devices is 8614 unnecessary even if the host did not respond to 8615 the unplug protocol 8616 never -- do not unplug even if version check succeeds 8617 8618 xen_legacy_crash [X86,XEN,EARLY] 8619 Crash from Xen panic notifier, without executing late 8620 panic() code such as dumping handler. 8621 8622 xen_mc_debug [X86,XEN,EARLY] 8623 Enable multicall debugging when running as a Xen PV guest. 8624 Enabling this feature will reduce performance a little 8625 bit, so it should only be enabled for obtaining extended 8626 debug data in case of multicall errors. 8627 8628 xen_msr_safe= [X86,XEN,EARLY] 8629 Format: <bool> 8630 Select whether to always use non-faulting (safe) MSR 8631 access functions when running as Xen PV guest. The 8632 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8633 8634 xen_nopv [X86] 8635 Disables the PV optimizations forcing the HVM guest to 8636 run as generic HVM guest with no PV drivers. 8637 This option is obsoleted by the "nopv" option, which 8638 has equivalent effect for XEN platform. 8639 8640 xen_no_vector_callback 8641 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8642 event channel interrupts. 8643 8644 xen_scrub_pages= [XEN] 8645 Boolean option to control scrubbing pages before giving them back 8646 to Xen, for use by other domains. Can be also changed at runtime 8647 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8648 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8649 8650 xen_timer_slop= [X86-64,XEN,EARLY] 8651 Set the timer slop (in nanoseconds) for the virtual Xen 8652 timers (default is 100000). This adjusts the minimum 8653 delta of virtualized Xen timers, where lower values 8654 improve timer resolution at the expense of processing 8655 more timer interrupts. 8656 8657 xen.balloon_boot_timeout= [XEN] 8658 The time (in seconds) to wait before giving up to boot 8659 in case initial ballooning fails to free enough memory. 8660 Applies only when running as HVM or PVH guest and 8661 started with less memory configured than allowed at 8662 max. Default is 180. 8663 8664 xen.event_eoi_delay= [XEN] 8665 How long to delay EOI handling in case of event 8666 storms (jiffies). Default is 10. 8667 8668 xen.event_loop_timeout= [XEN] 8669 After which time (jiffies) the event handling loop 8670 should start to delay EOI handling. Default is 2. 8671 8672 xen.fifo_events= [XEN] 8673 Boolean parameter to disable using fifo event handling 8674 even if available. Normally fifo event handling is 8675 preferred over the 2-level event handling, as it is 8676 fairer and the number of possible event channels is 8677 much higher. Default is on (use fifo events). 8678 8679 xirc2ps_cs= [NET,PCMCIA] 8680 Format: 8681 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8682 8683 xive= [PPC] 8684 By default on POWER9 and above, the kernel will 8685 natively use the XIVE interrupt controller. This option 8686 allows the fallback firmware mode to be used: 8687 8688 off Fallback to firmware control of XIVE interrupt 8689 controller on both pseries and powernv 8690 platforms. Only useful on POWER9 and above. 8691 8692 xive.store-eoi=off [PPC] 8693 By default on POWER10 and above, the kernel will use 8694 stores for EOI handling when the XIVE interrupt mode 8695 is active. This option allows the XIVE driver to use 8696 loads instead, as on POWER9. 8697 8698 xhci-hcd.quirks [USB,KNL] 8699 A hex value specifying bitmask with supplemental xhci 8700 host controller quirks. Meaning of each bit can be 8701 consulted in header drivers/usb/host/xhci.h. 8702 8703 xmon [PPC,EARLY] 8704 Format: { early | on | rw | ro | off } 8705 Controls if xmon debugger is enabled. Default is off. 8706 Passing only "xmon" is equivalent to "xmon=early". 8707 early Call xmon as early as possible on boot; xmon 8708 debugger is called from setup_arch(). 8709 on xmon debugger hooks will be installed so xmon 8710 is only called on a kernel crash. Default mode, 8711 i.e. either "ro" or "rw" mode, is controlled 8712 with CONFIG_XMON_DEFAULT_RO_MODE. 8713 rw xmon debugger hooks will be installed so xmon 8714 is called only on a kernel crash, mode is write, 8715 meaning SPR registers, memory and, other data 8716 can be written using xmon commands. 8717 ro same as "rw" option above but SPR registers, 8718 memory, and other data can't be written using 8719 xmon commands. 8720 off xmon is disabled. 8721