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.nomops [ARM64] Unconditionally disable Memory Copy and Memory 570 Set instructions support 571 572 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 573 Monitoring support 574 575 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 576 support 577 578 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 579 support 580 581 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 582 Extension support 583 584 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 585 Extension support 586 587 ataflop= [HW,M68k] 588 589 atarimouse= [HW,MOUSE] Atari Mouse 590 591 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 592 EzKey and similar keyboards 593 594 atkbd.reset= [HW] Reset keyboard during initialization 595 596 atkbd.set= [HW] Select keyboard code set 597 Format: <int> (2 = AT (default), 3 = PS/2) 598 599 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 600 keyboards 601 602 atkbd.softraw= [HW] Choose between synthetic and real raw mode 603 Format: <bool> (0 = real, 1 = synthetic (default)) 604 605 atkbd.softrepeat= [HW] 606 Use software keyboard repeat 607 608 audit= [KNL] Enable the audit sub-system 609 Format: { "0" | "1" | "off" | "on" } 610 0 | off - kernel audit is disabled and can not be 611 enabled until the next reboot 612 unset - kernel audit is initialized but disabled and 613 will be fully enabled by the userspace auditd. 614 1 | on - kernel audit is initialized and partially 615 enabled, storing at most audit_backlog_limit 616 messages in RAM until it is fully enabled by the 617 userspace auditd. 618 Default: unset 619 620 audit_backlog_limit= [KNL] Set the audit queue size limit. 621 Format: <int> (must be >=0) 622 Default: 64 623 624 bau= [X86_UV] Enable the BAU on SGI UV. The default 625 behavior is to disable the BAU (i.e. bau=0). 626 Format: { "0" | "1" } 627 0 - Disable the BAU. 628 1 - Enable the BAU. 629 unset - Disable the BAU. 630 631 bdev_allow_write_mounted= 632 Format: <bool> 633 Control the ability to open a mounted block device 634 for writing, i.e., allow / disallow writes that bypass 635 the FS. This was implemented as a means to prevent 636 fuzzers from crashing the kernel by overwriting the 637 metadata underneath a mounted FS without its awareness. 638 This also prevents destructive formatting of mounted 639 filesystems by naive storage tooling that don't use 640 O_EXCL. Default is Y and can be changed through the 641 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 642 643 bert_disable [ACPI] 644 Disable BERT OS support on buggy BIOSes. 645 646 bgrt_disable [ACPI,X86,EARLY] 647 Disable BGRT to avoid flickering OEM logo. 648 649 blkdevparts= Manual partition parsing of block device(s) for 650 embedded devices based on command line input. 651 See Documentation/block/cmdline-partition.rst 652 653 boot_delay= [KNL,EARLY] 654 Milliseconds to delay each printk during boot. 655 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 656 and you may also have to specify "lpj=". Boot_delay 657 values larger than 10 seconds (10000) are assumed 658 erroneous and ignored. 659 Format: integer 660 661 bootconfig [KNL,EARLY] 662 Extended command line options can be added to an initrd 663 and this will cause the kernel to look for it. 664 665 See Documentation/admin-guide/bootconfig.rst 666 667 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 668 bttv.radio= Most important insmod options are available as 669 kernel args too. 670 bttv.pll= See Documentation/admin-guide/media/bttv.rst 671 bttv.tuner= 672 673 bulk_remove=off [PPC] This parameter disables the use of the pSeries 674 firmware feature for flushing multiple hpte entries 675 at a time. 676 677 c101= [NET] Moxa C101 synchronous serial card 678 679 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 680 Sometimes CPU hardware bugs make them report the cache 681 size incorrectly. The kernel will attempt work arounds 682 to fix known problems, but for some CPUs it is not 683 possible to determine what the correct size should be. 684 This option provides an override for these situations. 685 686 carrier_timeout= 687 [NET] Specifies amount of time (in seconds) that 688 the kernel should wait for a network carrier. By default 689 it waits 120 seconds. 690 691 ca_keys= [KEYS] This parameter identifies a specific key(s) on 692 the system trusted keyring to be used for certificate 693 trust validation. 694 format: { id:<keyid> | builtin } 695 696 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 697 algorithm. Accepted values range from 0 to 7 698 inclusive. See arch/mips/include/asm/pgtable-bits.h 699 for platform specific values (SB1, Loongson3 and 700 others). 701 702 ccw_timeout_log [S390] 703 See Documentation/arch/s390/common_io.rst for details. 704 705 cfi= [X86-64] Set Control Flow Integrity checking features 706 when CONFIG_FINEIBT is enabled. 707 Format: feature[,feature...] 708 Default: auto 709 710 auto: Use FineIBT if IBT available, otherwise kCFI. 711 Under FineIBT, enable "paranoid" mode when 712 FRED is not available. 713 off: Turn off CFI checking. 714 kcfi: Use kCFI (disable FineIBT). 715 fineibt: Use FineIBT (even if IBT not available). 716 norand: Do not re-randomize CFI hashes. 717 paranoid: Add caller hash checking under FineIBT. 718 bhi: Enable register poisoning to stop speculation 719 across FineIBT. (Disabled by default.) 720 warn: Do not enforce CFI checking: warn only. 721 debug: Report CFI initialization details. 722 723 cgroup_disable= [KNL] Disable a particular controller or optional feature 724 Format: {name of the controller(s) or feature(s) to disable} 725 The effects of cgroup_disable=foo are: 726 - foo isn't auto-mounted if you mount all cgroups in 727 a single hierarchy 728 - foo isn't visible as an individually mountable 729 subsystem 730 - if foo is an optional feature then the feature is 731 disabled and corresponding cgroup files are not 732 created 733 {Currently only "memory" controller deal with this and 734 cut the overhead, others just disable the usage. So 735 only cgroup_disable=memory is actually worthy} 736 Specifying "pressure" disables per-cgroup pressure 737 stall information accounting feature 738 739 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 740 Format: { { controller | "all" | "named" } 741 [,{ controller | "all" | "named" }...] } 742 Like cgroup_disable, but only applies to cgroup v1; 743 the blacklisted controllers remain available in cgroup2. 744 "all" blacklists all controllers and "named" disables 745 named mounts. Specifying both "all" and "named" disables 746 all v1 hierarchies. 747 748 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 749 Format: { "true" | "false" } 750 /proc/cgroups lists only v1 controllers by default. 751 This compatibility option enables listing also v2 752 controllers (whose v1 code is not compiled!), so that 753 semi-legacy software can check this file to decide 754 about usage of v2 (sic) controllers. 755 756 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 757 Format: { "true" | "false" } 758 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 759 760 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 761 Format: <string> 762 nosocket -- Disable socket memory accounting. 763 nokmem -- Disable kernel memory accounting. 764 nobpf -- Disable BPF memory accounting. 765 766 check_pages= [MM,EARLY] Enable sanity checking of pages after 767 allocations / before freeing. This adds checks to catch 768 double-frees, use-after-frees, and other sources of 769 page corruption by inspecting page internals (flags, 770 mapcount/refcount, memcg_data, etc.). 771 Format: { "0" | "1" } 772 Default: 0 (1 if CONFIG_DEBUG_VM is set) 773 774 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 775 Format: { "0" | "1" } 776 See security/selinux/Kconfig help text. 777 0 -- check protection applied by kernel (includes 778 any implied execute protection). 779 1 -- check protection requested by application. 780 Default value is set via a kernel config option. 781 Value can be changed at runtime via 782 /sys/fs/selinux/checkreqprot. 783 Setting checkreqprot to 1 is deprecated. 784 785 cio_ignore= [S390] 786 See Documentation/arch/s390/common_io.rst for details. 787 788 clk_ignore_unused 789 [CLK] 790 Prevents the clock framework from automatically gating 791 clocks that have not been explicitly enabled by a Linux 792 device driver but are enabled in hardware at reset or 793 by the bootloader/firmware. Note that this does not 794 force such clocks to be always-on nor does it reserve 795 those clocks in any way. This parameter is useful for 796 debug and development, but should not be needed on a 797 platform with proper driver support. For more 798 information, see Documentation/driver-api/clk.rst. 799 800 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 801 [Deprecated] 802 Forces specified clocksource (if available) to be used 803 when calculating gettimeofday(). If specified 804 clocksource is not available, it defaults to PIT. 805 Format: { pit | tsc | cyclone | pmtmr } 806 807 clocksource= Override the default clocksource 808 Format: <string> 809 Override the default clocksource and use the clocksource 810 with the name specified. 811 Some clocksource names to choose from, depending on 812 the platform: 813 [all] jiffies (this is the base, fallback clocksource) 814 [ACPI] acpi_pm 815 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 816 pxa_timer,timer3,32k_counter,timer0_1 817 [X86-32] pit,hpet,tsc; 818 scx200_hrt on Geode; cyclone on IBM x440 819 [MIPS] MIPS 820 [PARISC] cr16 821 [S390] tod 822 [SH] SuperH 823 [SPARC64] tick 824 [X86-64] hpet,tsc 825 826 clocksource.arm_arch_timer.evtstrm= 827 [ARM,ARM64,EARLY] 828 Format: <bool> 829 Enable/disable the eventstream feature of the ARM 830 architected timer so that code using WFE-based polling 831 loops can be debugged more effectively on production 832 systems. 833 834 clocksource.verify_n_cpus= [KNL] 835 Limit the number of CPUs checked for clocksources 836 marked with CLOCK_SOURCE_VERIFY_PERCPU that 837 are marked unstable due to excessive skew. 838 A negative value says to check all CPUs, while 839 zero says not to check any. Values larger than 840 nr_cpu_ids are silently truncated to nr_cpu_ids. 841 The actual CPUs are chosen randomly, with 842 no replacement if the same CPU is chosen twice. 843 844 clocksource-wdtest.holdoff= [KNL] 845 Set the time in seconds that the clocksource 846 watchdog test waits before commencing its tests. 847 Defaults to zero when built as a module and to 848 10 seconds when built into the kernel. 849 850 cma=nn[MG]@[start[MG][-end[MG]]] 851 [KNL,CMA,EARLY] 852 Sets the size of kernel global memory area for 853 contiguous memory allocations and optionally the 854 placement constraint by the physical address range of 855 memory allocations. A value of 0 disables CMA 856 altogether. For more information, see 857 kernel/dma/contiguous.c 858 859 cma_pernuma=nn[MG] 860 [KNL,CMA,EARLY] 861 Sets the size of kernel per-numa memory area for 862 contiguous memory allocations. A value of 0 disables 863 per-numa CMA altogether. And If this option is not 864 specified, the default value is 0. 865 With per-numa CMA enabled, DMA users on node nid will 866 first try to allocate buffer from the pernuma area 867 which is located in node nid, if the allocation fails, 868 they will fallback to the global default memory area. 869 870 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 871 [KNL,CMA,EARLY] 872 Sets the size of kernel numa memory area for 873 contiguous memory allocations. It will reserve CMA 874 area for the specified node. 875 876 If it is setup together with upper 'cmd_pernuma=' 877 (unlikely), its size setting takes priority for the 878 specified numa nodes. 879 880 With numa CMA enabled, DMA users on node nid will 881 first try to allocate buffer from the numa area 882 which is located in node nid, if the allocation fails, 883 they will fallback to the global default memory area. 884 885 cmo_free_hint= [PPC] Format: { yes | no } 886 Specify whether pages are marked as being inactive 887 when they are freed. This is used in CMO environments 888 to determine OS memory pressure for page stealing by 889 a hypervisor. 890 Default: yes 891 892 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 893 Sets the size of memory pool for coherent, atomic dma 894 allocations, by default set to 256K. 895 896 condev= [HW,S390] console device 897 conmode= 898 899 con3215_drop= [S390,EARLY] 3215 console drop mode. 900 Format: y|n|Y|N|1|0 901 When set to true, drop data on the 3215 console when 902 the console buffer is full. In this case the 903 operator using a 3270 terminal emulator (for example 904 x3270) does not have to enter the clear key for the 905 console output to advance and the kernel to continue. 906 This leads to a much faster boot time when a 3270 907 terminal emulator is active. If no 3270 terminal 908 emulator is used, this parameter has no effect. 909 910 console= [KNL] Output console device and options. 911 912 tty<n> Use the virtual console device <n>. 913 914 ttyS<n>[,options] 915 ttyUSB0[,options] 916 Use the specified serial port. The options are of 917 the form "bbbbpnf", where "bbbb" is the baud rate, 918 "p" is parity ("n", "o", or "e"), "n" is number of 919 bits, and "f" is flow control ("r" for RTS or 920 omit it). Default is "9600n8". 921 922 See Documentation/admin-guide/serial-console.rst for more 923 information. See 924 Documentation/networking/netconsole.rst for an 925 alternative. 926 927 <DEVNAME>:<n>.<n>[,options] 928 Use the specified serial port on the serial core bus. 929 The addressing uses DEVNAME of the physical serial port 930 device, followed by the serial core controller instance, 931 and the serial port instance. The options are the same 932 as documented for the ttyS addressing above. 933 934 The mapping of the serial ports to the tty instances 935 can be viewed with: 936 937 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 938 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 939 940 In the above example, the console can be addressed with 941 console=00:04:0.0. Note that a console addressed this 942 way will only get added when the related device driver 943 is ready. The use of an earlycon parameter in addition to 944 the console may be desired for console output early on. 945 946 uart[8250],io,<addr>[,options] 947 uart[8250],mmio,<addr>[,options] 948 uart[8250],mmio16,<addr>[,options] 949 uart[8250],mmio32,<addr>[,options] 950 uart[8250],0x<addr>[,options] 951 Start an early, polled-mode console on the 8250/16550 952 UART at the specified I/O port or MMIO address, 953 switching to the matching ttyS device later. 954 MMIO inter-register address stride is either 8-bit 955 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 956 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 957 to be equivalent to 'mmio'. 'options' are specified in 958 the same format described for ttyS above; if unspecified, 959 the h/w is not re-initialized. 960 961 hvc<n> Use the hypervisor console device <n>. This is for 962 both Xen and PowerPC hypervisors. 963 964 { null | "" } 965 Use to disable console output, i.e., to have kernel 966 console messages discarded. 967 This must be the only console= parameter used on the 968 kernel command line. 969 970 If the device connected to the port is not a TTY but a braille 971 device, prepend "brl," before the device type, for instance 972 console=brl,ttyS0 973 For now, only VisioBraille is supported. 974 975 console_msg_format= 976 [KNL] Change console messages format 977 default 978 By default we print messages on consoles in 979 "[time stamp] text\n" format (time stamp may not be 980 printed, depending on CONFIG_PRINTK_TIME or 981 `printk_time' param). 982 syslog 983 Switch to syslog format: "<%u>[time stamp] text\n" 984 IOW, each message will have a facility and loglevel 985 prefix. The format is similar to one used by syslog() 986 syscall, or to executing "dmesg -S --raw" or to reading 987 from /proc/kmsg. 988 989 consoleblank= [KNL] The console blank (screen saver) timeout in 990 seconds. A value of 0 disables the blank timer. 991 Defaults to 0. 992 993 coredump_filter= 994 [KNL] Change the default value for 995 /proc/<pid>/coredump_filter. 996 See also Documentation/filesystems/proc.rst. 997 998 coresight_cpu_debug.enable 999 [ARM,ARM64] 1000 Format: <bool> 1001 Enable/disable the CPU sampling based debugging. 1002 0: default value, disable debugging 1003 1: enable debugging at boot time 1004 1005 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1006 Format: 1007 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1008 1009 cpuidle.off=1 [CPU_IDLE] 1010 disable the cpuidle sub-system 1011 1012 cpuidle.governor= 1013 [CPU_IDLE] Name of the cpuidle governor to use. 1014 1015 cpufreq.off=1 [CPU_FREQ] 1016 disable the cpufreq sub-system 1017 1018 cpufreq.default_governor= 1019 [CPU_FREQ] Name of the default cpufreq governor or 1020 policy to use. This governor must be registered in the 1021 kernel before the cpufreq driver probes. 1022 1023 cpu_init_udelay=N 1024 [X86,EARLY] Delay for N microsec between assert and de-assert 1025 of APIC INIT to start processors. This delay occurs 1026 on every CPU online, such as boot, and resume from suspend. 1027 Default: 10000 1028 1029 cpuhp.parallel= 1030 [SMP] Enable/disable parallel bringup of secondary CPUs 1031 Format: <bool> 1032 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1033 the parameter has no effect. 1034 1035 crash_kexec_post_notifiers 1036 Only jump to kdump kernel after running the panic 1037 notifiers and dumping kmsg. This option increases 1038 the risks of a kdump failure, since some panic 1039 notifiers can make the crashed kernel more unstable. 1040 In configurations where kdump may not be reliable, 1041 running the panic notifiers could allow collecting 1042 more data on dmesg, like stack traces from other CPUS 1043 or extra data dumped by panic_print. Note that some 1044 configurations enable this option unconditionally, 1045 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1046 1047 crashkernel=size[KMG][@offset[KMG]] 1048 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1049 upon panic. This parameter reserves the physical 1050 memory region [offset, offset + size] for that kernel 1051 image. If '@offset' is omitted, then a suitable offset 1052 is selected automatically. 1053 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1054 under 4G first, and fall back to reserve region above 1055 4G when '@offset' hasn't been specified. 1056 See Documentation/admin-guide/kdump/kdump.rst for further details. 1057 1058 crashkernel=range1:size1[,range2:size2,...][@offset] 1059 [KNL] Same as above, but depends on the memory 1060 in the running system. The syntax of range is 1061 start-[end] where start and end are both 1062 a memory unit (amount[KMG]). See also 1063 Documentation/admin-guide/kdump/kdump.rst for an example. 1064 1065 crashkernel=size[KMG],high 1066 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1067 above 4G. 1068 Allow kernel to allocate physical memory region from top, 1069 so could be above 4G if system have more than 4G ram 1070 installed. Otherwise memory region will be allocated 1071 below 4G, if available. 1072 It will be ignored if crashkernel=X is specified. 1073 crashkernel=size[KMG],low 1074 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1075 When crashkernel=X,high is passed, kernel could allocate 1076 physical memory region above 4G, that cause second kernel 1077 crash on system that require some amount of low memory, 1078 e.g. swiotlb requires at least 64M+32K low memory, also 1079 enough extra low memory is needed to make sure DMA buffers 1080 for 32-bit devices won't run out. Kernel would try to allocate 1081 default size of memory below 4G automatically. The default 1082 size is platform dependent. 1083 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1084 --> arm64: 128MiB 1085 --> riscv: 128MiB 1086 --> loongarch: 128MiB 1087 This one lets the user specify own low range under 4G 1088 for second kernel instead. 1089 0: to disable low allocation. 1090 It will be ignored when crashkernel=X,high is not used 1091 or memory reserved is below 4G. 1092 crashkernel=size[KMG],cma 1093 [KNL, X86, ARM64, RISCV, PPC] Reserve additional crash 1094 kernel memory from CMA. This reservation is usable by 1095 the first system's userspace memory and kernel movable 1096 allocations (memory balloon, zswap). Pages allocated 1097 from this memory range will not be included in the vmcore 1098 so this should not be used if dumping of userspace memory 1099 is intended and it has to be expected that some movable 1100 kernel pages may be missing from the dump. 1101 1102 A standard crashkernel reservation, as described above, 1103 is still needed to hold the crash kernel and initrd. 1104 1105 This option increases the risk of a kdump failure: DMA 1106 transfers configured by the first kernel may end up 1107 corrupting the second kernel's memory. 1108 1109 This reservation method is intended for systems that 1110 can't afford to sacrifice enough memory for standard 1111 crashkernel reservation and where less reliable and 1112 possibly incomplete kdump is preferable to no kdump at 1113 all. 1114 1115 cryptomgr.notests 1116 [KNL] Disable crypto self-tests 1117 1118 cs89x0_dma= [HW,NET] 1119 Format: <dma> 1120 1121 cs89x0_media= [HW,NET] 1122 Format: { rj45 | aui | bnc } 1123 1124 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1125 function call handling. When switched on, 1126 additional debug data is printed to the console 1127 in case a hanging CPU is detected, and that 1128 CPU is pinged again in order to try to resolve 1129 the hang situation. The default value of this 1130 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1131 Kconfig option. 1132 1133 dasd= [HW,NET] 1134 See header of drivers/s390/block/dasd_devmap.c. 1135 1136 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1137 (one device per port) 1138 Format: <port#>,<type> 1139 See also Documentation/input/devices/joystick-parport.rst 1140 1141 debug [KNL,EARLY] Enable kernel debugging (events log level). 1142 1143 debug_boot_weak_hash 1144 [KNL,EARLY] Enable printing [hashed] pointers early in the 1145 boot sequence. If enabled, we use a weak hash instead 1146 of siphash to hash pointers. Use this option if you are 1147 seeing instances of '(___ptrval___)') and need to see a 1148 value (hashed pointer) instead. Cryptographically 1149 insecure, please do not use on production kernels. 1150 1151 debug_locks_verbose= 1152 [KNL] verbose locking self-tests 1153 Format: <int> 1154 Print debugging info while doing the locking API 1155 self-tests. 1156 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1157 (no extra messages), setting it to -1 (all bits set) 1158 will print _a_lot_ more information - normally only 1159 useful to lockdep developers. 1160 1161 debug_objects [KNL,EARLY] Enable object debugging 1162 1163 debug_guardpage_minorder= 1164 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1165 parameter allows control of the order of pages that will 1166 be intentionally kept free (and hence protected) by the 1167 buddy allocator. Bigger value increase the probability 1168 of catching random memory corruption, but reduce the 1169 amount of memory for normal system use. The maximum 1170 possible value is MAX_PAGE_ORDER/2. Setting this 1171 parameter to 1 or 2 should be enough to identify most 1172 random memory corruption problems caused by bugs in 1173 kernel or driver code when a CPU writes to (or reads 1174 from) a random memory location. Note that there exists 1175 a class of memory corruptions problems caused by buggy 1176 H/W or F/W or by drivers badly programming DMA 1177 (basically when memory is written at bus level and the 1178 CPU MMU is bypassed) which are not detectable by 1179 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1180 help tracking down these problems. 1181 1182 debug_pagealloc= 1183 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1184 enables the feature at boot time. By default, it is 1185 disabled and the system will work mostly the same as a 1186 kernel built without CONFIG_DEBUG_PAGEALLOC. 1187 Note: to get most of debug_pagealloc error reports, it's 1188 useful to also enable the page_owner functionality. 1189 on: enable the feature 1190 1191 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1192 userspace and debugfs internal clients. 1193 Format: { on, off } 1194 on: All functions are enabled. 1195 off: Filesystem is not registered and clients 1196 get a -EPERM as result when trying to register files 1197 or directories within debugfs. 1198 This is equivalent of the runtime functionality if 1199 debugfs was not enabled in the kernel at all. 1200 Default value is set in build-time with a kernel configuration. 1201 1202 debugpat [X86] Enable PAT debugging 1203 1204 default_hugepagesz= 1205 [HW] The size of the default HugeTLB page. This is 1206 the size represented by the legacy /proc/ hugepages 1207 APIs. In addition, this is the default hugetlb size 1208 used for shmget(), mmap() and mounting hugetlbfs 1209 filesystems. If not specified, defaults to the 1210 architecture's default huge page size. Huge page 1211 sizes are architecture dependent. See also 1212 Documentation/admin-guide/mm/hugetlbpage.rst. 1213 Format: size[KMG] 1214 1215 deferred_probe_timeout= 1216 [KNL] Debugging option to set a timeout in seconds for 1217 deferred probe to give up waiting on dependencies to 1218 probe. Only specific dependencies (subsystems or 1219 drivers) that have opted in will be ignored. A timeout 1220 of 0 will timeout at the end of initcalls; a negative 1221 value is treated as an infinite timeout value. If the 1222 timeout hasn't expired, it'll be restarted by each 1223 successful driver registration. This option will also 1224 dump out devices still on the deferred probe list after 1225 retrying. 1226 1227 delayacct [KNL] Enable per-task delay accounting 1228 1229 dell_smm_hwmon.ignore_dmi= 1230 [HW] Continue probing hardware even if DMI data 1231 indicates that the driver is running on unsupported 1232 hardware. 1233 1234 dell_smm_hwmon.force= 1235 [HW] Activate driver even if SMM BIOS signature does 1236 not match list of supported models and enable otherwise 1237 blacklisted features. 1238 1239 dell_smm_hwmon.power_status= 1240 [HW] Report power status in /proc/i8k 1241 (disabled by default). 1242 1243 dell_smm_hwmon.restricted= 1244 [HW] Allow controlling fans only if SYS_ADMIN 1245 capability is set. 1246 1247 dell_smm_hwmon.fan_mult= 1248 [HW] Factor to multiply fan speed with. 1249 1250 dell_smm_hwmon.fan_max= 1251 [HW] Maximum configurable fan speed. 1252 1253 dfltcc= [HW,S390] 1254 Format: { on | off | def_only | inf_only | always } 1255 on: s390 zlib hardware support for compression on 1256 level 1 and decompression (default) 1257 off: No s390 zlib hardware support 1258 def_only: s390 zlib hardware support for deflate 1259 only (compression on level 1) 1260 inf_only: s390 zlib hardware support for inflate 1261 only (decompression) 1262 always: Same as 'on' but ignores the selected compression 1263 level always using hardware support (used for debugging) 1264 1265 dhash_entries= [KNL] 1266 Set number of hash buckets for dentry cache. 1267 1268 disable_1tb_segments [PPC,EARLY] 1269 Disables the use of 1TB hash page table segments. This 1270 causes the kernel to fall back to 256MB segments which 1271 can be useful when debugging issues that require an SLB 1272 miss to occur. 1273 1274 disable= [IPV6] 1275 See Documentation/networking/ipv6.rst. 1276 1277 disable_radix [PPC,EARLY] 1278 Disable RADIX MMU mode on POWER9 1279 1280 disable_tlbie [PPC] 1281 Disable TLBIE instruction. Currently does not work 1282 with KVM, with HASH MMU, or with coherent accelerators. 1283 1284 disable_ddw [PPC/PSERIES,EARLY] 1285 Disable Dynamic DMA Window support. Use this 1286 to workaround buggy firmware. 1287 1288 disable_ipv6= [IPV6] 1289 See Documentation/networking/ipv6.rst. 1290 1291 disable_mtrr_cleanup [X86,EARLY] 1292 The kernel tries to adjust MTRR layout from continuous 1293 to discrete, to make X server driver able to add WB 1294 entry later. This parameter disables that. 1295 1296 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1297 By default the kernel will trim any uncacheable 1298 memory out of your available memory pool based on 1299 MTRR settings. This parameter disables that behavior, 1300 possibly causing your machine to run very slowly. 1301 1302 disable_timer_pin_1 [X86,EARLY] 1303 Disable PIN 1 of APIC timer 1304 Can be useful to work around chipset bugs. 1305 1306 dis_ucode_ldr [X86] Disable the microcode loader. 1307 1308 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1309 this option disables the debugging code at boot. 1310 1311 dma_debug_entries=<number> 1312 This option allows to tune the number of preallocated 1313 entries for DMA-API debugging code. One entry is 1314 required per DMA-API allocation. Use this if the 1315 DMA-API debugging code disables itself because the 1316 architectural default is too low. 1317 1318 dma_debug_driver=<driver_name> 1319 With this option the DMA-API debugging driver 1320 filter feature can be enabled at boot time. Just 1321 pass the driver to filter for as the parameter. 1322 The filter can be disabled or changed to another 1323 driver later using sysfs. 1324 1325 reg_file_data_sampling= 1326 [X86] Controls mitigation for Register File Data 1327 Sampling (RFDS) vulnerability. RFDS is a CPU 1328 vulnerability which may allow userspace to infer 1329 kernel data values previously stored in floating point 1330 registers, vector registers, or integer registers. 1331 RFDS only affects Intel Atom processors. 1332 1333 on: Turns ON the mitigation. 1334 off: Turns OFF the mitigation. 1335 1336 This parameter overrides the compile time default set 1337 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1338 disabled when other VERW based mitigations (like MDS) 1339 are enabled. In order to disable RFDS mitigation all 1340 VERW based mitigations need to be disabled. 1341 1342 For details see: 1343 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1344 1345 dm_verity.keyring_unsealed= 1346 [KNL] When set to 1, leave the dm-verity keyring 1347 unsealed after initialization so userspace can 1348 provision keys. Once the keyring is restricted 1349 it becomes active and is searched during signature 1350 verification. 1351 1352 driver_async_probe= [KNL] 1353 List of driver names to be probed asynchronously. * 1354 matches with all driver names. If * is specified, the 1355 rest of the listed driver names are those that will NOT 1356 match the *. 1357 Format: <driver_name1>,<driver_name2>... 1358 1359 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1360 Broken monitors, graphic adapters, KVMs and EDIDless 1361 panels may send no or incorrect EDID data sets. 1362 This parameter allows to specify an EDID data sets 1363 in the /lib/firmware directory that are used instead. 1364 An EDID data set will only be used for a particular 1365 connector, if its name and a colon are prepended to 1366 the EDID name. Each connector may use a unique EDID 1367 data set by separating the files with a comma. An EDID 1368 data set with no connector name will be used for 1369 any connectors not explicitly specified. 1370 1371 dscc4.setup= [NET] 1372 1373 dt_cpu_ftrs= [PPC,EARLY] 1374 Format: {"off" | "known"} 1375 Control how the dt_cpu_ftrs device-tree binding is 1376 used for CPU feature discovery and setup (if it 1377 exists). 1378 off: Do not use it, fall back to legacy cpu table. 1379 known: Do not pass through unknown features to guests 1380 or userspace, only those that the kernel is aware of. 1381 1382 dump_apple_properties [X86] 1383 Dump name and content of EFI device properties on 1384 x86 Macs. Useful for driver authors to determine 1385 what data is available or for reverse-engineering. 1386 1387 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1388 <module>.dyndbg[="val"] 1389 Enable debug messages at boot time. See 1390 Documentation/admin-guide/dynamic-debug-howto.rst 1391 for details. 1392 1393 early_ioremap_debug [KNL,EARLY] 1394 Enable debug messages in early_ioremap support. This 1395 is useful for tracking down temporary early mappings 1396 which are not unmapped. 1397 1398 earlycon= [KNL,EARLY] Output early console device and options. 1399 1400 When used with no options, the early console is 1401 determined by stdout-path property in device tree's 1402 chosen node or the ACPI SPCR table if supported by 1403 the platform. 1404 1405 cdns,<addr>[,options] 1406 Start an early, polled-mode console on a Cadence 1407 (xuartps) serial port at the specified address. Only 1408 supported option is baud rate. If baud rate is not 1409 specified, the serial port must already be setup and 1410 configured. 1411 1412 uart[8250],io,<addr>[,options[,uartclk]] 1413 uart[8250],mmio,<addr>[,options[,uartclk]] 1414 uart[8250],mmio32,<addr>[,options[,uartclk]] 1415 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1416 uart[8250],0x<addr>[,options] 1417 Start an early, polled-mode console on the 8250/16550 1418 UART at the specified I/O port or MMIO address. 1419 MMIO inter-register address stride is either 8-bit 1420 (mmio) or 32-bit (mmio32 or mmio32be). 1421 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1422 to be equivalent to 'mmio'. 'options' are specified 1423 in the same format described for "console=ttyS<n>"; if 1424 unspecified, the h/w is not initialized. 'uartclk' is 1425 the uart clock frequency; if unspecified, it is set 1426 to 'BASE_BAUD' * 16. 1427 1428 pl011,<addr> 1429 pl011,mmio32,<addr> 1430 Start an early, polled-mode console on a pl011 serial 1431 port at the specified address. The pl011 serial port 1432 must already be setup and configured. Options are not 1433 yet supported. If 'mmio32' is specified, then only 1434 the driver will use only 32-bit accessors to read/write 1435 the device registers. 1436 1437 liteuart,<addr> 1438 Start an early console on a litex serial port at the 1439 specified address. The serial port must already be 1440 setup and configured. Options are not yet supported. 1441 1442 meson,<addr> 1443 Start an early, polled-mode console on a meson serial 1444 port at the specified address. The serial port must 1445 already be setup and configured. Options are not yet 1446 supported. 1447 1448 msm_serial,<addr> 1449 Start an early, polled-mode console on an msm serial 1450 port at the specified address. The serial port 1451 must already be setup and configured. Options are not 1452 yet supported. 1453 1454 msm_serial_dm,<addr> 1455 Start an early, polled-mode console on an msm serial 1456 dm port at the specified address. The serial port 1457 must already be setup and configured. Options are not 1458 yet supported. 1459 1460 owl,<addr> 1461 Start an early, polled-mode console on a serial port 1462 of an Actions Semi SoC, such as S500 or S900, at the 1463 specified address. The serial port must already be 1464 setup and configured. Options are not yet supported. 1465 1466 rda,<addr> 1467 Start an early, polled-mode console on a serial port 1468 of an RDA Micro SoC, such as RDA8810PL, at the 1469 specified address. The serial port must already be 1470 setup and configured. Options are not yet supported. 1471 1472 sbi 1473 Use RISC-V SBI (Supervisor Binary Interface) for early 1474 console. 1475 1476 smh Use ARM semihosting calls for early console. 1477 1478 s3c2410,<addr> 1479 s3c2412,<addr> 1480 s3c2440,<addr> 1481 s3c6400,<addr> 1482 s5pv210,<addr> 1483 exynos4210,<addr> 1484 Use early console provided by serial driver available 1485 on Samsung SoCs, requires selecting proper type and 1486 a correct base address of the selected UART port. The 1487 serial port must already be setup and configured. 1488 Options are not yet supported. 1489 1490 lantiq,<addr> 1491 Start an early, polled-mode console on a lantiq serial 1492 (lqasc) port at the specified address. The serial port 1493 must already be setup and configured. Options are not 1494 yet supported. 1495 1496 lpuart,<addr> 1497 lpuart32,<addr> 1498 Use early console provided by Freescale LP UART driver 1499 found on Freescale Vybrid and QorIQ LS1021A processors. 1500 A valid base address must be provided, and the serial 1501 port must already be setup and configured. 1502 1503 ec_imx21,<addr> 1504 ec_imx6q,<addr> 1505 Start an early, polled-mode, output-only console on the 1506 Freescale i.MX UART at the specified address. The UART 1507 must already be setup and configured. 1508 1509 ar3700_uart,<addr> 1510 Start an early, polled-mode console on the 1511 Armada 3700 serial port at the specified 1512 address. The serial port must already be setup 1513 and configured. Options are not yet supported. 1514 1515 qcom_geni,<addr> 1516 Start an early, polled-mode console on a Qualcomm 1517 Generic Interface (GENI) based serial port at the 1518 specified address. The serial port must already be 1519 setup and configured. Options are not yet supported. 1520 1521 efifb,[options] 1522 Start an early, unaccelerated console on the EFI 1523 memory mapped framebuffer (if available). On cache 1524 coherent non-x86 systems that use system memory for 1525 the framebuffer, pass the 'ram' option so that it is 1526 mapped with the correct attributes. 1527 1528 linflex,<addr> 1529 Use early console provided by Freescale LINFlexD UART 1530 serial driver for NXP S32V234 SoCs. A valid base 1531 address must be provided, and the serial port must 1532 already be setup and configured. 1533 1534 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1535 earlyprintk=vga 1536 earlyprintk=sclp 1537 earlyprintk=xen 1538 earlyprintk=serial[,ttySn[,baudrate]] 1539 earlyprintk=serial[,0x...[,baudrate]] 1540 earlyprintk=ttySn[,baudrate] 1541 earlyprintk=dbgp[debugController#] 1542 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1543 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1544 earlyprintk=xdbc[xhciController#] 1545 earlyprintk=bios 1546 1547 earlyprintk is useful when the kernel crashes before 1548 the normal console is initialized. It is not enabled by 1549 default because it has some cosmetic problems. 1550 1551 Use "nocfg" to skip UART configuration, assume 1552 BIOS/firmware has configured UART correctly. 1553 1554 Append ",keep" to not disable it when the real console 1555 takes over. 1556 1557 Only one of vga, serial, or usb debug port can 1558 be used at a time. 1559 1560 Currently only ttyS0 and ttyS1 may be specified by 1561 name. Other I/O ports may be explicitly specified 1562 on some architectures (x86 and arm at least) by 1563 replacing ttySn with an I/O port address, like this: 1564 earlyprintk=serial,0x1008,115200 1565 You can find the port for a given device in 1566 /proc/tty/driver/serial: 1567 2: uart:ST16650V2 port:00001008 irq:18 ... 1568 1569 Interaction with the standard serial driver is not 1570 very good. 1571 1572 The VGA output is eventually overwritten by 1573 the real console. 1574 1575 The xen option can only be used in Xen domains. 1576 1577 The sclp output can only be used on s390. 1578 1579 The bios output can only be used on SuperH. 1580 1581 The optional "force" to "pciserial" enables use of a 1582 PCI device even when its classcode is not of the 1583 UART class. 1584 1585 edac_report= [HW,EDAC] Control how to report EDAC event 1586 Format: {"on" | "off" | "force"} 1587 on: enable EDAC to report H/W event. May be overridden 1588 by other higher priority error reporting module. 1589 off: disable H/W event reporting through EDAC. 1590 force: enforce the use of EDAC to report H/W event. 1591 default: on. 1592 1593 edd= [EDD] 1594 Format: {"off" | "on" | "skip[mbr]"} 1595 1596 efi= [EFI,EARLY] 1597 Format: { "debug", "disable_early_pci_dma", 1598 "nochunk", "noruntime", "nosoftreserve", 1599 "novamap", "no_disable_early_pci_dma" } 1600 debug: enable misc debug output. 1601 disable_early_pci_dma: disable the busmaster bit on all 1602 PCI bridges while in the EFI boot stub. 1603 nochunk: disable reading files in "chunks" in the EFI 1604 boot stub, as chunking can cause problems with some 1605 firmware implementations. 1606 noruntime : disable EFI runtime services support 1607 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1608 attribute may cause the kernel to reserve the 1609 memory range for a memory mapping driver to 1610 claim. Specify efi=nosoftreserve to disable this 1611 reservation and treat the memory by its base type 1612 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1613 novamap: do not call SetVirtualAddressMap(). 1614 no_disable_early_pci_dma: Leave the busmaster bit set 1615 on all PCI bridges while in the EFI boot stub 1616 1617 efi_no_storage_paranoia [EFI,X86,EARLY] 1618 Using this parameter you can use more than 50% of 1619 your efi variable storage. Use this parameter only if 1620 you are really sure that your UEFI does sane gc and 1621 fulfills the spec otherwise your board may brick. 1622 1623 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1624 that is to be dynamically loaded by Linux. If there are 1625 multiple variables with the same name but with different 1626 vendor GUIDs, all of them will be loaded. See 1627 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1628 1629 1630 eisa_irq_edge= [PARISC,HW] 1631 See header of drivers/parisc/eisa.c. 1632 1633 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1634 Format: ekgdboc=kbd 1635 1636 This is designed to be used in conjunction with 1637 the boot argument: earlyprintk=vga 1638 1639 This parameter works in place of the kgdboc parameter 1640 but can only be used if the backing tty is available 1641 very early in the boot process. For early debugging 1642 via a serial port see kgdboc_earlycon instead. 1643 1644 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1645 Specifies physical address of start of kernel core 1646 image elf header and optionally the size. Generally 1647 kexec loader will pass this option to capture kernel. 1648 See Documentation/admin-guide/kdump/kdump.rst for details. 1649 1650 enable_mtrr_cleanup [X86,EARLY] 1651 The kernel tries to adjust MTRR layout from continuous 1652 to discrete, to make X server driver able to add WB 1653 entry later. This parameter enables that. 1654 1655 enable_timer_pin_1 [X86] 1656 Enable PIN 1 of APIC timer 1657 Can be useful to work around chipset bugs 1658 (in particular on some ATI chipsets). 1659 The kernel tries to set a reasonable default. 1660 1661 enforcing= [SELINUX] Set initial enforcing status. 1662 Format: {"0" | "1"} 1663 See security/selinux/Kconfig help text. 1664 0 -- permissive (log only, no denials). 1665 1 -- enforcing (deny and log). 1666 Default value is 0. 1667 Value can be changed at runtime via 1668 /sys/fs/selinux/enforce. 1669 1670 erst_disable [ACPI] 1671 Disable Error Record Serialization Table (ERST) 1672 support. 1673 1674 ether= [HW,NET] Ethernet cards parameters 1675 This option is obsoleted by the "netdev=" option, which 1676 has equivalent usage. See its documentation for details. 1677 1678 evm= [EVM] 1679 Format: { "fix" } 1680 Permit 'security.evm' to be updated regardless of 1681 current integrity status. 1682 1683 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1684 stages so cover more early boot allocations. 1685 Please note that as side effect some optimizations 1686 might be disabled to achieve that (e.g. parallelized 1687 memory initialization is disabled) so the boot process 1688 might take longer, especially on systems with a lot of 1689 memory. Available with CONFIG_PAGE_EXTENSION=y. 1690 1691 failslab= 1692 fail_usercopy= 1693 fail_page_alloc= 1694 fail_skb_realloc= 1695 fail_make_request=[KNL] 1696 General fault injection mechanism. 1697 Format: <interval>,<probability>,<space>,<times> 1698 See also Documentation/fault-injection/. 1699 1700 fb_tunnels= [NET] 1701 Format: { initns | none } 1702 See Documentation/admin-guide/sysctl/net.rst for 1703 fb_tunnels_only_for_init_ns 1704 1705 floppy= [HW] 1706 See Documentation/admin-guide/blockdev/floppy.rst. 1707 1708 forcepae [X86-32] 1709 Forcefully enable Physical Address Extension (PAE). 1710 Many Pentium M systems disable PAE but may have a 1711 functionally usable PAE implementation. 1712 Warning: use of this parameter will taint the kernel 1713 and may cause unknown problems. 1714 1715 fred= [X86-64] 1716 Enable/disable Flexible Return and Event Delivery. 1717 Format: { on | off } 1718 on: enable FRED when it's present, the default setting. 1719 off: disable FRED. 1720 1721 ftrace=[tracer] 1722 [FTRACE] will set and start the specified tracer 1723 as early as possible in order to facilitate early 1724 boot debugging. 1725 1726 ftrace_boot_snapshot 1727 [FTRACE] On boot up, a snapshot will be taken of the 1728 ftrace ring buffer that can be read at: 1729 /sys/kernel/tracing/snapshot. 1730 This is useful if you need tracing information from kernel 1731 boot up that is likely to be overridden by user space 1732 start up functionality. 1733 1734 Optionally, the snapshot can also be defined for a tracing 1735 instance that was created by the trace_instance= command 1736 line parameter. 1737 1738 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1739 1740 The above will cause the "foo" tracing instance to trigger 1741 a snapshot at the end of boot up. 1742 1743 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1744 ,<instance>=2(orig_cpu)] 1745 [FTRACE] will dump the trace buffers on oops. 1746 If no parameter is passed, ftrace will dump global 1747 buffers of all CPUs, if you pass 2 or orig_cpu, it 1748 will dump only the buffer of the CPU that triggered 1749 the oops, or the specific instance will be dumped if 1750 its name is passed. Multiple instance dump is also 1751 supported, and instances are separated by commas. Each 1752 instance supports only dump on CPU that triggered the 1753 oops by passing 2 or orig_cpu to it. 1754 1755 ftrace_dump_on_oops=foo=orig_cpu 1756 1757 The above will dump only the buffer of "foo" instance 1758 on CPU that triggered the oops. 1759 1760 ftrace_dump_on_oops,foo,bar=orig_cpu 1761 1762 The above will dump global buffer on all CPUs, the 1763 buffer of "foo" instance on all CPUs and the buffer 1764 of "bar" instance on CPU that triggered the oops. 1765 1766 ftrace_filter=[function-list] 1767 [FTRACE] Limit the functions traced by the function 1768 tracer at boot up. function-list is a comma-separated 1769 list of functions. This list can be changed at run 1770 time by the set_ftrace_filter file in the debugfs 1771 tracing directory. 1772 1773 ftrace_notrace=[function-list] 1774 [FTRACE] Do not trace the functions specified in 1775 function-list. This list can be changed at run time 1776 by the set_ftrace_notrace file in the debugfs 1777 tracing directory. 1778 1779 ftrace_graph_filter=[function-list] 1780 [FTRACE] Limit the top level callers functions traced 1781 by the function graph tracer at boot up. 1782 function-list is a comma-separated list of functions 1783 that can be changed at run time by the 1784 set_graph_function file in the debugfs tracing directory. 1785 1786 ftrace_graph_notrace=[function-list] 1787 [FTRACE] Do not trace from the functions specified in 1788 function-list. This list is a comma-separated list of 1789 functions that can be changed at run time by the 1790 set_graph_notrace file in the debugfs tracing directory. 1791 1792 ftrace_graph_max_depth=<uint> 1793 [FTRACE] Used with the function graph tracer. This is 1794 the max depth it will trace into a function. This value 1795 can be changed at run time by the max_graph_depth file 1796 in the tracefs tracing directory. default: 0 (no limit) 1797 1798 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1799 devices by scanning the firmware to infer the 1800 consumer/supplier relationships. This feature is 1801 especially useful when drivers are loaded as modules as 1802 it ensures proper ordering of tasks like device probing 1803 (suppliers first, then consumers), supplier boot state 1804 clean up (only after all consumers have probed), 1805 suspend/resume & runtime PM (consumers first, then 1806 suppliers). 1807 Format: { off | permissive | on | rpm } 1808 off -- Don't create device links from firmware info. 1809 permissive -- Create device links from firmware info 1810 but use it only for ordering boot state clean 1811 up (sync_state() calls). 1812 on -- Create device links from firmware info and use it 1813 to enforce probe and suspend/resume ordering. 1814 rpm -- Like "on", but also use to order runtime PM. 1815 1816 fw_devlink.strict=<bool> 1817 [KNL,EARLY] Treat all inferred dependencies as mandatory 1818 dependencies. This only applies for fw_devlink=on|rpm. 1819 Format: <bool> 1820 1821 fw_devlink.sync_state = 1822 [KNL,EARLY] When all devices that could probe have finished 1823 probing, this parameter controls what to do with 1824 devices that haven't yet received their sync_state() 1825 calls. 1826 Format: { strict | timeout } 1827 strict -- Default. Continue waiting on consumers to 1828 probe successfully. 1829 timeout -- Give up waiting on consumers and call 1830 sync_state() on any devices that haven't yet 1831 received their sync_state() calls after 1832 deferred_probe_timeout has expired or by 1833 late_initcall() if !CONFIG_MODULES. 1834 1835 gamecon.map[2|3]= 1836 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1837 support via parallel port (up to 5 devices per port) 1838 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1839 See also Documentation/input/devices/joystick-parport.rst 1840 1841 gamma= [HW,DRM] 1842 1843 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1844 Format: off | on 1845 default: on 1846 1847 gather_data_sampling= 1848 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1849 mitigation. 1850 1851 Gather Data Sampling is a hardware vulnerability which 1852 allows unprivileged speculative access to data which was 1853 previously stored in vector registers. 1854 1855 This issue is mitigated by default in updated microcode. 1856 The mitigation may have a performance impact but can be 1857 disabled. On systems without the microcode mitigation 1858 disabling AVX serves as a mitigation. 1859 1860 force: Disable AVX to mitigate systems without 1861 microcode mitigation. No effect if the microcode 1862 mitigation is present. Known to cause crashes in 1863 userspace with buggy AVX enumeration. 1864 1865 off: Disable GDS mitigation. 1866 1867 gbpages [X86] Use GB pages for kernel direct mappings. 1868 1869 gcov_persist= [GCOV] When non-zero (default), profiling data for 1870 kernel modules is saved and remains accessible via 1871 debugfs, even when the module is unloaded/reloaded. 1872 When zero, profiling data is discarded and associated 1873 debugfs files are removed at module unload time. 1874 1875 goldfish [X86] Enable the goldfish android emulator platform. 1876 Don't use this when you are not running on the 1877 android emulator 1878 1879 gpio-mockup.gpio_mockup_ranges 1880 [HW] Sets the ranges of gpiochip of for this device. 1881 Format: <start1>,<end1>,<start2>,<end2>... 1882 gpio-mockup.gpio_mockup_named_lines 1883 [HW] Let the driver know GPIO lines should be named. 1884 1885 gpt [EFI] Forces disk with valid GPT signature but 1886 invalid Protective MBR to be treated as GPT. If the 1887 primary GPT is corrupted, it enables the backup/alternate 1888 GPT to be used instead. 1889 1890 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1891 the "Enable 0" bit of the configuration register. 1892 Format: 0 | 1 1893 Default: 0 1894 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1895 the "Enable 0" bit of the configuration register. 1896 Format: 0 | 1 1897 Default: 0 1898 grcan.select= [HW] Select which physical interface to use. 1899 Format: 0 | 1 1900 Default: 0 1901 grcan.txsize= [HW] Sets the size of the tx buffer. 1902 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1903 Default: 1024 1904 grcan.rxsize= [HW] Sets the size of the rx buffer. 1905 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1906 Default: 1024 1907 1908 hardened_usercopy= 1909 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1910 hardening is enabled for this boot. Hardened 1911 usercopy checking is used to protect the kernel 1912 from reading or writing beyond known memory 1913 allocation boundaries as a proactive defense 1914 against bounds-checking flaws in the kernel's 1915 copy_to_user()/copy_from_user() interface. 1916 The default is determined by 1917 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1918 on Perform hardened usercopy checks. 1919 off Disable hardened usercopy checks. 1920 1921 hardlockup_all_cpu_backtrace= 1922 [KNL] Should the hard-lockup detector generate 1923 backtraces on all cpus. 1924 Format: 0 | 1 1925 1926 hash_pointers= 1927 [KNL,EARLY] 1928 By default, when pointers are printed to the console 1929 or buffers via the %p format string, that pointer is 1930 "hashed", i.e. obscured by hashing the pointer value. 1931 This is a security feature that hides actual kernel 1932 addresses from unprivileged users, but it also makes 1933 debugging the kernel more difficult since unequal 1934 pointers can no longer be compared. The choices are: 1935 Format: { auto | always | never } 1936 Default: auto 1937 1938 auto - Hash pointers unless slab_debug is enabled. 1939 always - Always hash pointers (even if slab_debug is 1940 enabled). 1941 never - Never hash pointers. This option should only 1942 be specified when debugging the kernel. Do 1943 not use on production kernels. The boot 1944 param "no_hash_pointers" is an alias for 1945 this mode. 1946 1947 For controlling hashing dynamically at runtime, 1948 use the "kernel.kptr_restrict" sysctl instead. 1949 1950 hashdist= [KNL,NUMA] Large hashes allocated during boot 1951 are distributed across NUMA nodes. Defaults on 1952 for 64-bit NUMA, off otherwise. 1953 Format: 0 | 1 (for off | on) 1954 1955 hd= [EIDE] (E)IDE hard drive subsystem geometry 1956 Format: <cyl>,<head>,<sect> 1957 1958 hest_disable [ACPI] 1959 Disable Hardware Error Source Table (HEST) support; 1960 corresponding firmware-first mode error processing 1961 logic will be disabled. 1962 1963 hibernate= [HIBERNATION] 1964 noresume Don't check if there's a hibernation image 1965 present during boot. 1966 nocompress Don't compress/decompress hibernation images. 1967 no Disable hibernation and resume. 1968 protect_image Turn on image protection during restoration 1969 (that will set all pages holding image data 1970 during restoration read-only). 1971 1972 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1973 used with hibernation. 1974 Format: { lzo | lz4 } 1975 Default: lzo 1976 1977 lzo: Select LZO compression algorithm to 1978 compress/decompress hibernation image. 1979 1980 lz4: Select LZ4 compression algorithm to 1981 compress/decompress hibernation image. 1982 1983 hibernate.pm_test_delay= 1984 [HIBERNATION] 1985 Sets the number of seconds to remain in a hibernation test 1986 mode before resuming the system (see 1987 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 1988 is set. Default value is 5. 1989 1990 hibernate_compression_threads= 1991 [HIBERNATION] 1992 Set the number of threads used for compressing or decompressing 1993 hibernation images. 1994 1995 Format: <integer> 1996 Default: 3 1997 Minimum: 1 1998 Example: hibernate_compression_threads=4 1999 2000 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2001 size of <nn>. This works even on boxes that have no 2002 highmem otherwise. This also works to reduce highmem 2003 size on bigger boxes. 2004 2005 highres= [KNL] Enable/disable high resolution timer mode. 2006 Valid parameters: "on", "off" 2007 Default: "on" 2008 2009 hlt [BUGS=ARM,SH] 2010 2011 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2012 Format: <string> 2013 This allows setting the system's hostname during early 2014 startup. This sets the name returned by gethostname. 2015 Using this parameter to set the hostname makes it 2016 possible to ensure the hostname is correctly set before 2017 any userspace processes run, avoiding the possibility 2018 that a process may call gethostname before the hostname 2019 has been explicitly set, resulting in the calling 2020 process getting an incorrect result. The string must 2021 not exceed the maximum allowed hostname length (usually 2022 64 characters) and will be truncated otherwise. 2023 2024 hpet= [X86-32,HPET] option to control HPET usage 2025 Format: { enable (default) | disable | force | 2026 verbose } 2027 disable: disable HPET and use PIT instead 2028 force: allow force enabled of undocumented chips (ICH4, 2029 VIA, nVidia) 2030 verbose: show contents of HPET registers during setup 2031 2032 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2033 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2034 2035 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2036 If this follows hugepagesz (below), it specifies 2037 the number of pages of hugepagesz to be allocated. 2038 If this is the first HugeTLB parameter on the command 2039 line, it specifies the number of pages to allocate for 2040 the default huge page size. If using node format, the 2041 number of pages to allocate per-node can be specified. 2042 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2043 Format: <integer> or (node format) 2044 <node>:<integer>[,<node>:<integer>] 2045 2046 hugepagesz= 2047 [HW,EARLY] The size of the HugeTLB pages. This is 2048 used in conjunction with hugepages (above) to 2049 allocate huge pages of a specific size at boot. The 2050 pair hugepagesz=X hugepages=Y can be specified once 2051 for each supported huge page size. Huge page sizes 2052 are architecture dependent. See also 2053 Documentation/admin-guide/mm/hugetlbpage.rst. 2054 Format: size[KMG] 2055 2056 hugepage_alloc_threads= 2057 [HW] The number of threads that should be used to 2058 allocate hugepages during boot. This option can be 2059 used to improve system bootup time when allocating 2060 a large amount of huge pages. 2061 The default value is 25% of the available hardware threads. 2062 2063 Note that this parameter only applies to non-gigantic huge pages. 2064 2065 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2066 of gigantic hugepages. Or using node format, the size 2067 of a CMA area per node can be specified. 2068 Format: nn[KMGTPE] or (node format) 2069 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2070 2071 The size must be a multiple of the gigantic page size. 2072 When using node format, this applies to each per-node size. 2073 Missaligned values are dropped with a warning. 2074 2075 Reserve a CMA area of given size and allocate gigantic 2076 hugepages using the CMA allocator. If enabled, the 2077 boot-time allocation of gigantic hugepages is skipped. 2078 2079 hugetlb_cma_only= 2080 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2081 try to allocate from the CMA areas. 2082 2083 This option does nothing if hugetlb_cma= is not also 2084 specified. 2085 2086 hugetlb_free_vmemmap= 2087 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2088 enabled. 2089 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2090 Allows heavy hugetlb users to free up some more 2091 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2092 Format: { on | off (default) } 2093 2094 on: enable HVO 2095 off: disable HVO 2096 2097 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2098 the default is on. 2099 2100 Note that the vmemmap pages may be allocated from the added 2101 memory block itself when memory_hotplug.memmap_on_memory is 2102 enabled, those vmemmap pages cannot be optimized even if this 2103 feature is enabled. Other vmemmap pages not allocated from 2104 the added memory block itself do not be affected. 2105 2106 hung_task_panic= 2107 [KNL] Number of hung tasks to trigger kernel panic. 2108 Format: <int> 2109 2110 When set to a non-zero value, a kernel panic will be triggered if 2111 the number of detected hung tasks reaches this value. 2112 2113 0: don't panic 2114 1: panic immediately on first hung task 2115 N: panic after N hung tasks are detected in a single scan 2116 2117 The default value is controlled by the 2118 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2119 selected by this boot parameter can be changed later by the 2120 kernel.hung_task_panic sysctl. 2121 2122 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2123 terminal devices. Valid values: 0..8 2124 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2125 If specified, z/VM IUCV HVC accepts connections 2126 from listed z/VM user IDs only. 2127 2128 hv_nopvspin [X86,HYPER_V,EARLY] 2129 Disables the paravirt spinlock optimizations 2130 which allow the hypervisor to 'idle' the guest 2131 on lock contention. 2132 2133 hw_protection= [HW] 2134 Format: reboot | shutdown 2135 2136 Hardware protection action taken on critical events like 2137 overtemperature or imminent voltage loss. 2138 2139 i2c_bus= [HW] Override the default board specific I2C bus speed 2140 or register an additional I2C bus that is not 2141 registered from board initialization code. 2142 Format: 2143 <bus_id>,<clkrate> 2144 2145 i2c_touchscreen_props= [HW,ACPI,X86] 2146 Set device-properties for ACPI-enumerated I2C-attached 2147 touchscreen, to e.g. fix coordinates of upside-down 2148 mounted touchscreens. If you need this option please 2149 submit a drivers/platform/x86/touchscreen_dmi.c patch 2150 adding a DMI quirk for this. 2151 2152 Format: 2153 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2154 Where <val> is one of: 2155 Omit "=<val>" entirely Set a boolean device-property 2156 Unsigned number Set a u32 device-property 2157 Anything else Set a string device-property 2158 2159 Examples (split over multiple lines): 2160 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2161 touchscreen-inverted-y 2162 2163 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2164 touchscreen-size-y=1080:touchscreen-inverted-y: 2165 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2166 2167 i8042.debug [HW] Toggle i8042 debug mode 2168 i8042.unmask_kbd_data 2169 [HW] Enable printing of interrupt data from the KBD port 2170 (disabled by default, and as a pre-condition 2171 requires that i8042.debug=1 be enabled) 2172 i8042.direct [HW] Put keyboard port into non-translated mode 2173 i8042.dumbkbd [HW] Pretend that controller can only read data from 2174 keyboard and cannot control its state 2175 (Don't attempt to blink the leds) 2176 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2177 i8042.nokbd [HW] Don't check/create keyboard port 2178 i8042.noloop [HW] Disable the AUX Loopback command while probing 2179 for the AUX port 2180 i8042.nomux [HW] Don't check presence of an active multiplexing 2181 controller 2182 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2183 controllers 2184 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2185 i8042.reset [HW] Reset the controller during init, cleanup and 2186 suspend-to-ram transitions, only during s2r 2187 transitions, or never reset 2188 Format: { 1 | Y | y | 0 | N | n } 2189 1, Y, y: always reset controller 2190 0, N, n: don't ever reset controller 2191 Default: only on s2r transitions on x86; most other 2192 architectures force reset to be always executed 2193 i8042.unlock [HW] Unlock (ignore) the keylock 2194 i8042.kbdreset [HW] Reset device connected to KBD port 2195 i8042.probe_defer 2196 [HW] Allow deferred probing upon i8042 probe errors 2197 2198 i810= [HW,DRM] 2199 2200 i915.invert_brightness= 2201 [DRM] Invert the sense of the variable that is used to 2202 set the brightness of the panel backlight. Normally a 2203 brightness value of 0 indicates backlight switched off, 2204 and the maximum of the brightness value sets the backlight 2205 to maximum brightness. If this parameter is set to 0 2206 (default) and the machine requires it, or this parameter 2207 is set to 1, a brightness value of 0 sets the backlight 2208 to maximum brightness, and the maximum of the brightness 2209 value switches the backlight off. 2210 -1 -- never invert brightness 2211 0 -- machine default 2212 1 -- force brightness inversion 2213 2214 ia32_emulation= [X86-64] 2215 Format: <bool> 2216 When true, allows loading 32-bit programs and executing 32-bit 2217 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2218 boot time. When false, unconditionally disables IA32 emulation. 2219 2220 2221 idle= [X86,EARLY] 2222 Format: idle=poll, idle=halt, idle=nomwait 2223 2224 idle=poll: Don't do power saving in the idle loop 2225 using HLT, but poll for rescheduling event. This will 2226 make the CPUs eat a lot more power, but may be useful 2227 to get slightly better performance in multiprocessor 2228 benchmarks. It also makes some profiling using 2229 performance counters more accurate. Please note that 2230 on systems with MONITOR/MWAIT support (like Intel 2231 EM64T CPUs) this option has no performance advantage 2232 over the normal idle loop. It may also interact badly 2233 with hyperthreading. 2234 2235 idle=halt: Halt is forced to be used for CPU idle. 2236 In such case C2/C3 won't be used again. 2237 2238 idle=nomwait: Disable mwait for CPU C-states 2239 2240 [ARM64,EARLY] 2241 Format: idle=wfi, idle=yield, idle=nop 2242 2243 idle=wfi: Use the WFI (Wait For Interrupt) hint 2244 instruction in the idle loop. This is the default and 2245 allows the CPU to enter a low-power state until an 2246 interrupt arrives. 2247 2248 idle=yield: Use the YIELD hint instruction instead of 2249 WFI. CPUs supporting simultaneous multi-threading (SMT), 2250 can continue executing another thread when the current 2251 thread reaches the idle loop. This will make the CPUs 2252 eat more power, but may be useful to get slightly better 2253 performance in some applications, since the CPUs will 2254 not enter a low-power state. 2255 2256 idle=nop: Do not execute any idle instruction in the 2257 idle loop. This is useful on platforms where WFI 2258 misbehaves, leading to system instability or loss of CPU 2259 state. This will make the CPUs eat more power, but may 2260 give slightly better performance in some applications, 2261 since the CPUs will not enter a low-power state. 2262 2263 idxd.sva= [HW] 2264 Format: <bool> 2265 Allow force disabling of Shared Virtual Memory (SVA) 2266 support for the idxd driver. By default it is set to 2267 true (1). 2268 2269 idxd.tc_override= [HW] 2270 Format: <bool> 2271 Allow override of default traffic class configuration 2272 for the device. By default it is set to false (0). 2273 2274 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2275 Format: { strict | legacy | 2008 | relaxed | emulated } 2276 Default: strict 2277 2278 Choose which programs will be accepted for execution 2279 based on the IEEE 754 NaN encoding(s) supported by 2280 the FPU and the NaN encoding requested with the value 2281 of an ELF file header flag individually set by each 2282 binary. Hardware implementations are permitted to 2283 support either or both of the legacy and the 2008 NaN 2284 encoding mode. 2285 2286 Available settings are as follows: 2287 strict accept binaries that request a NaN encoding 2288 supported by the FPU 2289 legacy only accept legacy-NaN binaries, if supported 2290 by the FPU 2291 2008 only accept 2008-NaN binaries, if supported 2292 by the FPU 2293 relaxed accept any binaries regardless of whether 2294 supported by the FPU 2295 emulated accept any binaries but enable FPU emulator 2296 if binary mode is unsupported by the FPU. 2297 2298 The FPU emulator is always able to support both NaN 2299 encodings, so if no FPU hardware is present or it has 2300 been disabled with 'nofpu', then the settings of 2301 'legacy' and '2008' strap the emulator accordingly, 2302 'relaxed' straps the emulator for both legacy-NaN and 2303 2008-NaN, whereas 'strict' enables legacy-NaN only on 2304 legacy processors and both NaN encodings on MIPS32 or 2305 MIPS64 CPUs. 2306 2307 The setting for ABS.fmt/NEG.fmt instruction execution 2308 mode generally follows that for the NaN encoding, 2309 except where unsupported by hardware. 2310 2311 ignore_loglevel [KNL,EARLY] 2312 Ignore loglevel setting - this will print /all/ 2313 kernel messages to the console. Useful for debugging. 2314 We also add it as printk module parameter, so users 2315 could change it dynamically, usually by 2316 /sys/module/printk/parameters/ignore_loglevel. 2317 2318 ignore_rlimit_data 2319 Ignore RLIMIT_DATA setting for data mappings, 2320 print warning at first misuse. Can be changed via 2321 /sys/module/kernel/parameters/ignore_rlimit_data. 2322 2323 ihash_entries= [KNL] 2324 Set number of hash buckets for inode cache. 2325 2326 ima_appraise= [IMA] appraise integrity measurements 2327 Format: { "off" | "enforce" | "fix" | "log" } 2328 default: "enforce" 2329 2330 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2331 The builtin appraise policy appraises all files 2332 owned by uid=0. 2333 2334 ima_canonical_fmt [IMA] 2335 Use the canonical format for the binary runtime 2336 measurements, instead of host native format. 2337 2338 ima_flush_htable [IMA] 2339 Flush the IMA hash table when deleting all the 2340 staged measurement records, to achieve maximum 2341 memory saving at the cost of having duplicate 2342 records across the staged measurement lists. 2343 2344 ima_hash= [IMA] 2345 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2346 | sha512 | ... } 2347 default: "sha1" 2348 2349 The list of supported hash algorithms is defined 2350 in crypto/hash_info.h. 2351 2352 ima_policy= [IMA] 2353 The builtin policies to load during IMA setup. 2354 Format: "tcb | appraise_tcb | secure_boot | 2355 fail_securely | critical_data" 2356 2357 The "tcb" policy measures all programs exec'd, files 2358 mmap'd for exec, and all files opened with the read 2359 mode bit set by either the effective uid (euid=0) or 2360 uid=0. 2361 2362 The "appraise_tcb" policy appraises the integrity of 2363 all files owned by root. 2364 2365 The "secure_boot" policy appraises the integrity 2366 of files (eg. kexec kernel image, kernel modules, 2367 firmware, policy, etc) based on file signatures. 2368 2369 The "fail_securely" policy forces file signature 2370 verification failure also on privileged mounted 2371 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2372 flag. 2373 2374 The "critical_data" policy measures kernel integrity 2375 critical data. 2376 2377 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2378 Load a policy which meets the needs of the Trusted 2379 Computing Base. This means IMA will measure all 2380 programs exec'd, files mmap'd for exec, and all files 2381 opened for read by uid=0. 2382 2383 ima_template= [IMA] 2384 Select one of defined IMA measurements template formats. 2385 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2386 "ima-sigv2" } 2387 Default: "ima-ng" 2388 2389 ima_template_fmt= 2390 [IMA] Define a custom template format. 2391 Format: { "field1|...|fieldN" } 2392 2393 ima= [IMA] Enable or disable IMA 2394 Format: { "off" | "on" } 2395 Default: "on" 2396 Note that disabling IMA is limited to kdump kernel. 2397 2398 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2399 Target Selection(ITS) bug in Intel CPUs. Updated 2400 microcode is also required for a fix in IBPB. 2401 2402 on: Enable mitigation (default). 2403 off: Disable mitigation. 2404 force: Force the ITS bug and deploy default 2405 mitigation. 2406 vmexit: Only deploy mitigation if CPU is affected by 2407 guest/host isolation part of ITS. 2408 stuff: Deploy RSB-fill mitigation when retpoline is 2409 also deployed. Otherwise, deploy the default 2410 mitigation. 2411 2412 For details see: 2413 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2414 2415 init= [KNL] 2416 Format: <full_path> 2417 Run specified binary instead of /sbin/init as init 2418 process. 2419 2420 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2421 for working out where the kernel is dying during 2422 startup. 2423 2424 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2425 initcall functions. Useful for debugging built-in 2426 modules and initcalls. 2427 2428 initramfs_async= [KNL] 2429 Format: <bool> 2430 Default: 1 2431 This parameter controls whether the initramfs 2432 image is unpacked asynchronously, concurrently 2433 with devices being probed and 2434 initialized. This should normally just work, 2435 but as a debugging aid, one can get the 2436 historical behaviour of the initramfs 2437 unpacking being completed before device_ and 2438 late_ initcalls. 2439 2440 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2441 2442 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2443 load the initrd. If an initrd is compiled in or 2444 specified in the bootparams, it takes priority over this 2445 setting. 2446 Format: ss[KMG],nn[KMG] 2447 Default is 0, 0 2448 2449 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2450 zeroes. 2451 Format: 0 | 1 2452 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2453 2454 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2455 Format: 0 | 1 2456 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2457 2458 init_pkru= [X86] Specify the default memory protection keys rights 2459 register contents for all processes. 0x55555554 by 2460 default (disallow access to all but pkey 0). Can 2461 override in debugfs after boot. 2462 2463 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2464 Format: <irq> 2465 2466 int_pln_enable [X86] Enable power limit notification interrupt 2467 2468 integrity_audit=[IMA] 2469 Format: { "0" | "1" } 2470 0 -- basic integrity auditing messages. (Default) 2471 1 -- additional integrity auditing messages. 2472 2473 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2474 on 2475 Enable intel iommu driver. 2476 off 2477 Disable intel iommu driver. 2478 igfx_off [Default Off] 2479 By default, gfx is mapped as normal device. If a gfx 2480 device has a dedicated DMAR unit, the DMAR unit is 2481 bypassed by not enabling DMAR with this option. In 2482 this case, gfx device will use physical address for 2483 DMA. 2484 strict [Default Off] 2485 Deprecated, equivalent to iommu.strict=1. 2486 sp_off [Default Off] 2487 By default, super page will be supported if Intel IOMMU 2488 has the capability. With this option, super page will 2489 not be supported. 2490 sm_on 2491 Enable the Intel IOMMU scalable mode if the hardware 2492 advertises that it has support for the scalable mode 2493 translation. 2494 sm_off 2495 Disallow use of the Intel IOMMU scalable mode. 2496 tboot_noforce [Default Off] 2497 Do not force the Intel IOMMU enabled under tboot. 2498 By default, tboot will force Intel IOMMU on, which 2499 could harm performance of some high-throughput 2500 devices like 40GBit network cards, even if identity 2501 mapping is enabled. 2502 Note that using this option lowers the security 2503 provided by tboot because it makes the system 2504 vulnerable to DMA attacks. 2505 2506 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2507 0 disables intel_idle and fall back on acpi_idle. 2508 1 to 9 specify maximum depth of C-state. 2509 2510 intel_pstate= [X86,EARLY] 2511 disable 2512 Do not enable intel_pstate as the default 2513 scaling driver for the supported processors 2514 active 2515 Use intel_pstate driver to bypass the scaling 2516 governors layer of cpufreq and provides it own 2517 algorithms for p-state selection. There are two 2518 P-state selection algorithms provided by 2519 intel_pstate in the active mode: powersave and 2520 performance. The way they both operate depends 2521 on whether or not the hardware managed P-states 2522 (HWP) feature has been enabled in the processor 2523 and possibly on the processor model. 2524 passive 2525 Use intel_pstate as a scaling driver, but configure it 2526 to work with generic cpufreq governors (instead of 2527 enabling its internal governor). This mode cannot be 2528 used along with the hardware-managed P-states (HWP) 2529 feature. 2530 force 2531 Enable intel_pstate on systems that prohibit it by default 2532 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2533 instead of acpi-cpufreq may disable platform features, such 2534 as thermal controls and power capping, that rely on ACPI 2535 P-States information being indicated to OSPM and therefore 2536 should be used with caution. This option does not work with 2537 processors that aren't supported by the intel_pstate driver 2538 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2539 no_hwp 2540 Do not enable hardware P state control (HWP) 2541 if available. 2542 hwp_only 2543 Only load intel_pstate on systems which support 2544 hardware P state control (HWP) if available. 2545 support_acpi_ppc 2546 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2547 Description Table, specifies preferred power management 2548 profile as "Enterprise Server" or "Performance Server", 2549 then this feature is turned on by default. 2550 per_cpu_perf_limits 2551 Allow per-logical-CPU P-State performance control limits using 2552 cpufreq sysfs interface 2553 no_cas 2554 Do not enable capacity-aware scheduling (CAS) on 2555 hybrid systems 2556 2557 intremap= [X86-64,Intel-IOMMU,EARLY] 2558 on enable Interrupt Remapping (default) 2559 off disable Interrupt Remapping 2560 nosid disable Source ID checking 2561 no_x2apic_optout 2562 BIOS x2APIC opt-out request will be ignored 2563 nopost disable Interrupt Posting 2564 posted_msi 2565 enable MSIs delivered as posted interrupts 2566 2567 iomem= Disable strict checking of access to MMIO memory 2568 strict regions from userspace. 2569 relaxed 2570 2571 iommu= [X86,EARLY] 2572 2573 off 2574 Don't initialize and use any kind of IOMMU. 2575 2576 force 2577 Force the use of the hardware IOMMU even when 2578 it is not actually needed (e.g. because < 3 GB 2579 memory). 2580 2581 noforce 2582 Don't force hardware IOMMU usage when it is not 2583 needed. (default). 2584 2585 merge 2586 Do scatter-gather (SG) merging. Implies "force" 2587 (experimental). 2588 2589 nomerge 2590 Don't do scatter-gather (SG) merging. 2591 2592 biomerge 2593 Do scatter-gather (SG) merging. Implies "force" 2594 (experimental). [same as "merge"] 2595 2596 panic 2597 Always panic when IOMMU overflows. 2598 2599 nopanic 2600 Don't panic on IOMMU overflows. 2601 2602 pt 2603 Use passththrough mode by default 2604 (Equivalent to iommu.passthrough=1) 2605 2606 nopt 2607 Use translated mode for DMA by default 2608 (Equivalent to iommu.passthrough=0) 2609 2610 soft 2611 Use software bounce buffering (SWIOTLB) (default for 2612 Intel machines). This can be used to prevent the usage 2613 of an available hardware IOMMU. 2614 2615 usedac 2616 Use the DAC on VIA PCI bridge 2617 (default: disable the VIA PCI bridge DAC) 2618 2619 AMD Gart HW IOMMU-specific options: (CONFIG_GART_IOMMU) 2620 2621 <size> 2622 Set the size of the remapping area in bytes. 2623 2624 allowed 2625 Overwrite iommu off workarounds for specific chipsets 2626 2627 force 2628 Overwrite iommu off workarounds for specific chipsets 2629 2630 fullflush 2631 Flush IOMMU on each allocation (default). 2632 2633 nofullflush 2634 Don't use IOMMU fullflush. 2635 2636 memaper[=<order>] 2637 Allocate an own aperture over RAM with size 2638 32MB<<order. (default: order=1, i.e. 64MB) 2639 2640 noaperture 2641 Ask the IOMMU not to touch the aperture for AGP. 2642 2643 noagp 2644 Don't initialize the AGP driver and use full aperture. 2645 2646 iommu= [PPC/POWERNV] 2647 2648 nobypass 2649 Disable IOMMU bypass, using IOMMU for PCI devices. 2650 2651 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2652 Format: { "0" | "1" } 2653 0 - Try to allocate a 32-bit DMA address first, before 2654 falling back to the full range if needed. 2655 1 - Allocate directly from the full usable range, 2656 forcing Dual Address Cycle for PCI cards supporting 2657 greater than 32-bit addressing. 2658 2659 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2660 Format: { "0" | "1" } 2661 0 - Lazy mode. 2662 Request that DMA unmap operations use deferred 2663 invalidation of hardware TLBs, for increased 2664 throughput at the cost of reduced device isolation. 2665 Will fall back to strict mode if not supported by 2666 the relevant IOMMU driver. 2667 1 - Strict mode. 2668 DMA unmap operations invalidate IOMMU hardware TLBs 2669 synchronously. 2670 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2671 Note: on x86, strict mode specified via one of the 2672 legacy driver-specific options takes precedence. 2673 2674 iommu.passthrough= 2675 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2676 Format: { "0" | "1" } 2677 0 - Use IOMMU translation for DMA. 2678 1 - Bypass the IOMMU for DMA. 2679 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2680 2681 iommu.debug_pagealloc= 2682 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2683 parameter enables the feature at boot time. By default, it 2684 is disabled and the system behaves the same way as a kernel 2685 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2686 Format: { "0" | "1" } 2687 0 - Sanitizer disabled. 2688 1 - Sanitizer enabled, expect runtime overhead. 2689 2690 io7= [HW] IO7 for Marvel-based Alpha systems 2691 See comment before marvel_specify_io7 in 2692 arch/alpha/kernel/core_marvel.c. 2693 2694 io_delay= [X86,EARLY] I/O delay method 2695 0x80 2696 Standard port 0x80 based delay 2697 0xed 2698 Alternate port 0xed based delay (needed on some systems) 2699 udelay 2700 Simple two microseconds delay 2701 none 2702 No delay 2703 2704 ip= [IP_PNP] 2705 See Documentation/admin-guide/nfs/nfsroot.rst. 2706 2707 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2708 IPC identifiers from 32,768 to 16,777,216. 2709 2710 ipe.enforce= [IPE] 2711 Format: <bool> 2712 Determine whether IPE starts in permissive (0) or 2713 enforce (1) mode. The default is enforce. 2714 2715 ipe.success_audit= 2716 [IPE] 2717 Format: <bool> 2718 Start IPE with success auditing enabled, emitting 2719 an audit event when a binary is allowed. The default 2720 is 0. 2721 2722 irqaffinity= [SMP] Set the default irq affinity mask 2723 The argument is a cpu list, as described above. 2724 2725 irqchip.gicv2_force_probe= 2726 [ARM,ARM64,EARLY] 2727 Format: <bool> 2728 Force the kernel to look for the second 4kB page 2729 of a GICv2 controller even if the memory range 2730 exposed by the device tree is too small. 2731 2732 irqchip.gicv3_nolpi= 2733 [ARM,ARM64,EARLY] 2734 Force the kernel to ignore the availability of 2735 LPIs (and by consequence ITSs). Intended for system 2736 that use the kernel as a bootloader, and thus want 2737 to let secondary kernels in charge of setting up 2738 LPIs. 2739 2740 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2741 Enables support for pseudo-NMIs in the kernel. This 2742 requires the kernel to be built with 2743 CONFIG_ARM64_PSEUDO_NMI. 2744 2745 irqchip.riscv_imsic_noipi 2746 [RISC-V,EARLY] 2747 Force the kernel to not use IMSIC software injected MSIs 2748 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2749 and thus want to reduce MMIO traps when triggering IPIs 2750 to multiple harts. 2751 2752 irqfixup [HW] 2753 When an interrupt is not handled search all handlers 2754 for it. Intended to get systems with badly broken 2755 firmware running. 2756 2757 irqhandler.duration_warn_us= [KNL] 2758 Warn if an IRQ handler exceeds the specified duration 2759 threshold in microseconds. Useful for identifying 2760 long-running IRQs in the system. 2761 2762 irqpoll [HW] 2763 When an interrupt is not handled search all handlers 2764 for it. Also check all handlers each timer 2765 interrupt. Intended to get systems with badly broken 2766 firmware running. 2767 2768 isapnp= [ISAPNP] 2769 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2770 2771 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2772 Format: [flag-list,]<cpu-list> 2773 2774 Specify one or more CPUs to isolate from disturbances 2775 specified in the flag list (default: domain): 2776 2777 nohz 2778 Disable the tick when a single task runs as well as 2779 disabling other kernel noises like having RCU callbacks 2780 offloaded. This is equivalent to the nohz_full parameter. 2781 2782 A residual 1Hz tick is offloaded to workqueues, which you 2783 need to affine to housekeeping through the global 2784 workqueue's affinity configured via the 2785 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2786 by using the 'domain' flag described below. 2787 2788 NOTE: by default the global workqueue runs on all CPUs, 2789 so to protect individual CPUs the 'cpumask' file has to 2790 be configured manually after bootup. 2791 2792 domain 2793 Isolate from the general SMP balancing and scheduling 2794 algorithms. Note that performing domain isolation this way 2795 is irreversible: it's not possible to bring back a CPU to 2796 the domains once isolated through this boot time 2797 configuration. Use cpusets for a dynamic configuration 2798 which can be altered at runtime. For details see 2799 Documentation/admin-guide/cpu-isolation.rst. 2800 2801 You can move a process onto or off an "isolated" CPU via 2802 the CPU affinity syscalls or cpuset. 2803 <cpu number> begins at 0 and the maximum value is 2804 "number of CPUs in system - 1". 2805 2806 managed_irq 2807 2808 Isolate from being targeted by managed interrupts 2809 which have an interrupt mask containing isolated 2810 CPUs. The affinity of managed interrupts is 2811 handled by the kernel and cannot be changed via 2812 the /proc/irq/* interfaces. 2813 2814 This isolation is best effort and only effective 2815 if the automatically assigned interrupt mask of a 2816 device queue contains isolated and housekeeping 2817 CPUs. If housekeeping CPUs are online then such 2818 interrupts are directed to the housekeeping CPU 2819 so that IO submitted on the housekeeping CPU 2820 cannot disturb the isolated CPU. 2821 2822 If a queue's affinity mask contains only isolated 2823 CPUs then this parameter has no effect on the 2824 interrupt routing decision, though interrupts are 2825 only delivered when tasks running on those 2826 isolated CPUs submit IO. IO submitted on 2827 housekeeping CPUs has no influence on those 2828 queues. 2829 2830 The format of <cpu-list> is described above. 2831 2832 iucv= [HW,NET] 2833 2834 ivrs_ioapic [HW,X86-64] 2835 Provide an override to the IOAPIC-ID<->DEVICE-ID 2836 mapping provided in the IVRS ACPI table. 2837 By default, PCI segment is 0, and can be omitted. 2838 2839 For example, to map IOAPIC-ID decimal 10 to 2840 PCI segment 0x1 and PCI device 00:14.0, 2841 write the parameter as: 2842 ivrs_ioapic=10@0001:00:14.0 2843 2844 Deprecated formats: 2845 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2846 write the parameter as: 2847 ivrs_ioapic[10]=00:14.0 2848 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2849 PCI device 00:14.0 write the parameter as: 2850 ivrs_ioapic[10]=0001:00:14.0 2851 2852 ivrs_hpet [HW,X86-64] 2853 Provide an override to the HPET-ID<->DEVICE-ID 2854 mapping provided in the IVRS ACPI table. 2855 By default, PCI segment is 0, and can be omitted. 2856 2857 For example, to map HPET-ID decimal 10 to 2858 PCI segment 0x1 and PCI device 00:14.0, 2859 write the parameter as: 2860 ivrs_hpet=10@0001:00:14.0 2861 2862 Deprecated formats: 2863 * To map HPET-ID decimal 0 to PCI device 00:14.0 2864 write the parameter as: 2865 ivrs_hpet[0]=00:14.0 2866 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2867 PCI device 00:14.0 write the parameter as: 2868 ivrs_ioapic[10]=0001:00:14.0 2869 2870 ivrs_acpihid [HW,X86-64] 2871 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2872 mapping provided in the IVRS ACPI table. 2873 By default, PCI segment is 0, and can be omitted. 2874 2875 For example, to map UART-HID:UID AMD0020:0 to 2876 PCI segment 0x1 and PCI device ID 00:14.5, 2877 write the parameter as: 2878 ivrs_acpihid=AMD0020:0@0001:00:14.5 2879 2880 Deprecated formats: 2881 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2882 PCI device ID 00:14.5, write the parameter as: 2883 ivrs_acpihid[00:14.5]=AMD0020:0 2884 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2885 PCI device ID 00:14.5, write the parameter as: 2886 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2887 2888 js= [HW,JOY] Analog joystick 2889 See Documentation/input/joydev/joystick.rst. 2890 2891 kasan_multi_shot 2892 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2893 report on every invalid memory access. Without this 2894 parameter KASAN will print report only for the first 2895 invalid access. 2896 2897 keep_bootcon [KNL,EARLY] 2898 Do not unregister boot console at start. This is only 2899 useful for debugging when something happens in the window 2900 between unregistering the boot console and initializing 2901 the real console. 2902 2903 keepinitrd [HW,ARM] See retain_initrd. 2904 2905 kernelcore= [KNL,X86,PPC,EARLY] 2906 Format: nn[KMGTPE] | nn% | "mirror" 2907 This parameter specifies the amount of memory usable by 2908 the kernel for non-movable allocations. The requested 2909 amount is spread evenly throughout all nodes in the 2910 system as ZONE_NORMAL. The remaining memory is used for 2911 movable memory in its own zone, ZONE_MOVABLE. In the 2912 event, a node is too small to have both ZONE_NORMAL and 2913 ZONE_MOVABLE, kernelcore memory will take priority and 2914 other nodes will have a larger ZONE_MOVABLE. 2915 2916 ZONE_MOVABLE is used for the allocation of pages that 2917 may be reclaimed or moved by the page migration 2918 subsystem. Note that allocations like PTEs-from-HighMem 2919 still use the HighMem zone if it exists, and the Normal 2920 zone if it does not. 2921 2922 It is possible to specify the exact amount of memory in 2923 the form of "nn[KMGTPE]", a percentage of total system 2924 memory in the form of "nn%", or "mirror". If "mirror" 2925 option is specified, mirrored (reliable) memory is used 2926 for non-movable allocations and remaining memory is used 2927 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2928 are exclusive, so you cannot specify multiple forms. 2929 2930 kfence.burst= [MM,KFENCE] The number of additional successive 2931 allocations to be attempted through KFENCE for each 2932 sample interval. 2933 Format: <unsigned integer> 2934 Default: 0 2935 2936 kfence.check_on_panic= 2937 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2938 canaries on panic. 2939 Format: <bool> 2940 Default: false 2941 2942 kfence.deferrable= 2943 [MM,KFENCE] Whether to use a deferrable timer to trigger 2944 allocations. This avoids forcing CPU wake-ups if the 2945 system is idle, at the risk of a less predictable 2946 sample interval. 2947 Format: <bool> 2948 Default: CONFIG_KFENCE_DEFERRABLE 2949 2950 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2951 error is detected. 2952 report - print the error report and continue (default). 2953 oops - print the error report and oops. 2954 panic - print the error report and panic. 2955 2956 kfence.sample_interval= 2957 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2958 Format: <unsigned integer> 2959 0 - Disable KFENCE. 2960 >0 - Enabled KFENCE with given sample interval. 2961 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2962 2963 kfence.skip_covered_thresh= 2964 [MM,KFENCE] If pool utilization reaches this threshold 2965 (pool usage%), KFENCE limits currently covered 2966 allocations of the same source from further filling 2967 up the pool. 2968 Format: <unsigned integer> 2969 Default: 75 2970 2971 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2972 Format: <Controller#>[,poll interval] 2973 The controller # is the number of the ehci usb debug 2974 port as it is probed via PCI. The poll interval is 2975 optional and is the number seconds in between 2976 each poll cycle to the debug port in case you need 2977 the functionality for interrupting the kernel with 2978 gdb or control-c on the dbgp connection. When 2979 not using this parameter you use sysrq-g to break into 2980 the kernel debugger. 2981 2982 kgdboc= [KGDB,HW] kgdb over consoles. 2983 Requires a tty driver that supports console polling, 2984 or a supported polling keyboard driver (non-usb). 2985 Serial only format: <serial_device>[,baud] 2986 keyboard only format: kbd 2987 keyboard and serial format: kbd,<serial_device>[,baud] 2988 Optional Kernel mode setting: 2989 kms, kbd format: kms,kbd 2990 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2991 2992 kgdboc_earlycon= [KGDB,HW,EARLY] 2993 If the boot console provides the ability to read 2994 characters and can work in polling mode, you can use 2995 this parameter to tell kgdb to use it as a backend 2996 until the normal console is registered. Intended to 2997 be used together with the kgdboc parameter which 2998 specifies the normal console to transition to. 2999 3000 The name of the early console should be specified 3001 as the value of this parameter. Note that the name of 3002 the early console might be different than the tty 3003 name passed to kgdboc. It's OK to leave the value 3004 blank and the first boot console that implements 3005 read() will be picked. 3006 3007 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3008 kernel debugger at the earliest opportunity. 3009 3010 kho= [KEXEC,EARLY] 3011 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3012 Enables or disables Kexec HandOver. 3013 "0" | "off" | "n" - kexec handover is disabled 3014 "1" | "on" | "y" - kexec handover is enabled 3015 3016 kho_scratch= [KEXEC,EARLY] 3017 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3018 Defines the size of the KHO scratch region. The KHO 3019 scratch regions are physically contiguous memory 3020 ranges that can only be used for non-kernel 3021 allocations. That way, even when memory is heavily 3022 fragmented with handed over memory, the kexeced 3023 kernel will always have enough contiguous ranges to 3024 bootstrap itself. 3025 3026 It is possible to specify the exact amount of 3027 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3028 where the first parameter defines the size of a low 3029 memory scratch area, the second parameter defines 3030 the size of a global scratch area and the third 3031 parameter defines the size of additional per-node 3032 scratch areas. The form "nn%" defines scale factor 3033 (in percents) of memory that was used during boot. 3034 3035 kmac= [MIPS] Korina ethernet MAC address. 3036 Configure the RouterBoard 532 series on-chip 3037 Ethernet adapter MAC address. 3038 3039 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3040 Valid arguments: on, off 3041 Default: on 3042 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3043 the default is off. 3044 3045 kprobe_event=[probe-list] 3046 [FTRACE] Add kprobe events and enable at boot time. 3047 The probe-list is a semicolon delimited list of probe 3048 definitions. Each definition is same as kprobe_events 3049 interface, but the parameters are comma delimited. 3050 For example, to add a kprobe event on vfs_read with 3051 arg1 and arg2, add to the command line; 3052 3053 kprobe_event=p,vfs_read,$arg1,$arg2 3054 3055 See also Documentation/trace/kprobetrace.rst "Kernel 3056 Boot Parameter" section. 3057 3058 kpti= [ARM64,EARLY] Control page table isolation of 3059 user and kernel address spaces. 3060 Default: enabled on cores which need mitigation. 3061 0: force disabled 3062 1: force enabled 3063 3064 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3065 CONFIG_KUNIT to be set to be fully enabled. The 3066 default value can be overridden via 3067 KUNIT_DEFAULT_ENABLED. 3068 Default is 1 (enabled) 3069 3070 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3071 Default is 0 (don't ignore, but inject #GP) 3072 3073 kvm.eager_page_split= 3074 [KVM,X86] Controls whether or not KVM will try to 3075 proactively split all huge pages during dirty logging. 3076 Eager page splitting reduces interruptions to vCPU 3077 execution by eliminating the write-protection faults 3078 and MMU lock contention that would otherwise be 3079 required to split huge pages lazily. 3080 3081 VM workloads that rarely perform writes or that write 3082 only to a small region of VM memory may benefit from 3083 disabling eager page splitting to allow huge pages to 3084 still be used for reads. 3085 3086 The behavior of eager page splitting depends on whether 3087 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3088 disabled, all huge pages in a memslot will be eagerly 3089 split when dirty logging is enabled on that memslot. If 3090 enabled, eager page splitting will be performed during 3091 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3092 cleared. 3093 3094 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3095 3096 Default is Y (on). 3097 3098 kvm.enable_pmu=[KVM,X86] 3099 If enabled, KVM will virtualize PMU functionality based 3100 on the virtual CPU model defined by userspace. This 3101 can be overridden on a per-VM basis via 3102 KVM_CAP_PMU_CAPABILITY. 3103 3104 If disabled, KVM will not virtualize PMU functionality, 3105 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3106 a virtual CPU model that contains PMU assets. 3107 3108 Note, KVM's vPMU support implicitly requires running 3109 with an in-kernel local APIC, e.g. to deliver PMIs to 3110 the guest. Running without an in-kernel local APIC is 3111 not supported, though KVM will allow such a combination 3112 (with severely degraded functionality). 3113 3114 See also enable_mediated_pmu. 3115 3116 Default is Y (on). 3117 3118 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3119 If enabled, KVM will enable virtualization in hardware 3120 when KVM is loaded, and disable virtualization when KVM 3121 is unloaded (if KVM is built as a module). 3122 3123 If disabled, KVM will dynamically enable and disable 3124 virtualization on-demand when creating and destroying 3125 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3126 number of VMs. 3127 3128 Enabling virtualization at module load avoids potential 3129 latency for creation of the 0=>1 VM, as KVM serializes 3130 virtualization enabling across all online CPUs. The 3131 "cost" of enabling virtualization when KVM is loaded, 3132 is that doing so may interfere with using out-of-tree 3133 hypervisors that want to "own" virtualization hardware. 3134 3135 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3136 Default is false (don't support). 3137 3138 kvm.nx_huge_pages= 3139 [KVM] Controls the software workaround for the 3140 X86_BUG_ITLB_MULTIHIT bug. 3141 force : Always deploy workaround. 3142 off : Never deploy workaround. 3143 auto : Deploy workaround based on the presence of 3144 X86_BUG_ITLB_MULTIHIT. 3145 3146 Default is 'auto'. 3147 3148 If the software workaround is enabled for the host, 3149 guests do need not to enable it for nested guests. 3150 3151 kvm.nx_huge_pages_recovery_ratio= 3152 [KVM] Controls how many 4KiB pages are periodically zapped 3153 back to huge pages. 0 disables the recovery, otherwise if 3154 the value is N KVM will zap 1/Nth of the 4KiB pages every 3155 period (see below). The default is 60. 3156 3157 kvm.nx_huge_pages_recovery_period_ms= 3158 [KVM] Controls the time period at which KVM zaps 4KiB pages 3159 back to huge pages. If the value is a non-zero N, KVM will 3160 zap a portion (see ratio above) of the pages every N msecs. 3161 If the value is 0 (the default), KVM will pick a period based 3162 on the ratio, such that a page is zapped after 1 hour on average. 3163 3164 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3165 If enabled, KVM will provide a mediated virtual PMU, 3166 instead of the default perf-based virtual PMU (if 3167 kvm.enable_pmu is true and PMU is enumerated via the 3168 virtual CPU model). 3169 3170 With a perf-based vPMU, KVM operates as a user of perf, 3171 i.e. emulates guest PMU counters using perf events. 3172 KVM-created perf events are managed by perf as regular 3173 (guest-only) events, e.g. are scheduled in/out, contend 3174 for hardware resources, etc. Using a perf-based vPMU 3175 allows guest and host usage of the PMU to co-exist, but 3176 incurs non-trivial overhead and can result in silently 3177 dropped guest events (due to resource contention). 3178 3179 With a mediated vPMU, hardware PMU state is context 3180 switched around the world switch to/from the guest. 3181 KVM mediates which events the guest can utilize, but 3182 gives the guest direct access to all other PMU assets 3183 when possible (KVM may intercept some accesses if the 3184 virtual CPU model provides a subset of hardware PMU 3185 functionality). Using a mediated vPMU significantly 3186 reduces PMU virtualization overhead and eliminates lost 3187 guest events, but is mutually exclusive with using perf 3188 to profile KVM guests and adds latency to most VM-Exits 3189 (to context switch PMU state). 3190 3191 Default is N (off). 3192 3193 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3194 KVM/SVM. Default is 1 (enabled). 3195 3196 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3197 a.k.a. Two-Dimensional Page Tables. Default is 1 3198 (enabled). Disable by KVM if hardware lacks support 3199 for NPT. 3200 3201 kvm-amd.ciphertext_hiding_asids= 3202 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3203 to SNP private memory from reading ciphertext. Instead, 3204 reads will see constant default values (0xff). 3205 3206 If ciphertext hiding is enabled, the joint SEV-ES and 3207 SEV-SNP ASID space is partitioned into separate SEV-ES 3208 and SEV-SNP ASID ranges, with the SEV-SNP range being 3209 [1..max_snp_asid] and the SEV-ES range being 3210 (max_snp_asid..min_sev_asid), where min_sev_asid is 3211 enumerated by CPUID.0x.8000_001F[EDX]. 3212 3213 A non-zero value enables SEV-SNP ciphertext hiding and 3214 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3215 KVM caps the number of SEV-SNP ASIDs at the maximum 3216 possible value, e.g. specifying -1u will assign all 3217 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3218 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3219 max_snp_asid == min_sev_asid-1, will effectively make 3220 SEV-ES unusable. 3221 3222 kvm-arm.mode= 3223 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3224 operation. 3225 3226 none: Forcefully disable KVM. 3227 3228 nvhe: Standard nVHE-based mode, without support for 3229 protected guests. 3230 3231 protected: Mode with support for guests whose state is 3232 kept private from the host, using VHE or 3233 nVHE depending on HW support. 3234 3235 nested: VHE-based mode with support for nested 3236 virtualization. Requires at least ARMv8.4 3237 hardware (with FEAT_NV2). 3238 3239 Defaults to VHE/nVHE based on hardware support. Setting 3240 mode to "protected" will disable kexec and hibernation 3241 for the host. To force nVHE on VHE hardware, add 3242 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3243 command-line. 3244 "nested" and "protected" are experimental and should be 3245 used with extreme caution. 3246 3247 kvm-arm.vgic_v3_group0_trap= 3248 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3249 system registers 3250 3251 kvm-arm.vgic_v3_group1_trap= 3252 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3253 system registers 3254 3255 kvm-arm.vgic_v3_common_trap= 3256 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3257 system registers 3258 3259 kvm-arm.vgic_v4_enable= 3260 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3261 injection of LPIs. 3262 3263 kvm-arm.wfe_trap_policy= 3264 [KVM,ARM] Control when to set WFE instruction trap for 3265 KVM VMs. Traps are allowed but not guaranteed by the 3266 CPU architecture. 3267 3268 trap: set WFE instruction trap 3269 3270 notrap: clear WFE instruction trap 3271 3272 kvm-arm.wfi_trap_policy= 3273 [KVM,ARM] Control when to set WFI instruction trap for 3274 KVM VMs. Traps are allowed but not guaranteed by the 3275 CPU architecture. 3276 3277 trap: set WFI instruction trap 3278 3279 notrap: clear WFI instruction trap 3280 3281 kvm_cma_resv_ratio=n [PPC,EARLY] 3282 Reserves given percentage from system memory area for 3283 contiguous memory allocation for KVM hash pagetable 3284 allocation. 3285 By default it reserves 5% of total system memory. 3286 Format: <integer> 3287 Default: 5 3288 3289 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3290 a.k.a. Two-Dimensional Page Tables. Default is 1 3291 (enabled). Disable by KVM if hardware lacks support 3292 for EPT. 3293 3294 kvm-intel.emulate_invalid_guest_state= 3295 [KVM,Intel] Control whether to emulate invalid guest 3296 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3297 as guest state is never invalid for unrestricted 3298 guests. This param doesn't apply to nested guests (L2), 3299 as KVM never emulates invalid L2 guest state. 3300 Default is 1 (enabled). 3301 3302 kvm-intel.flexpriority= 3303 [KVM,Intel] Control KVM's use of FlexPriority feature 3304 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3305 hardware lacks support for it. 3306 3307 kvm-intel.nested= 3308 [KVM,Intel] Control nested virtualization feature in 3309 KVM/VMX. Default is 1 (enabled). 3310 3311 kvm-intel.unrestricted_guest= 3312 [KVM,Intel] Control KVM's use of unrestricted guest 3313 feature (virtualized real and unpaged mode). Default 3314 is 1 (enabled). Disable by KVM if EPT is disabled or 3315 hardware lacks support for it. 3316 3317 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3318 CVE-2018-3620. 3319 3320 Valid arguments: never, cond, always 3321 3322 always: L1D cache flush on every VMENTER. 3323 cond: Flush L1D on VMENTER only when the code between 3324 VMEXIT and VMENTER can leak host memory. 3325 never: Disables the mitigation 3326 3327 Default is cond (do L1 cache flush in specific instances) 3328 3329 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3330 Identification feature (tagged TLBs). Default is 1 3331 (enabled). Disable by KVM if hardware lacks support 3332 for it. 3333 3334 l1d_flush= [X86,INTEL,EARLY] 3335 Control mitigation for L1D based snooping vulnerability. 3336 3337 Certain CPUs are vulnerable to an exploit against CPU 3338 internal buffers which can forward information to a 3339 disclosure gadget under certain conditions. 3340 3341 In vulnerable processors, the speculatively 3342 forwarded data can be used in a cache side channel 3343 attack, to access data to which the attacker does 3344 not have direct access. 3345 3346 This parameter controls the mitigation. The 3347 options are: 3348 3349 on - enable the interface for the mitigation 3350 3351 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3352 affected CPUs 3353 3354 The kernel PTE inversion protection is unconditionally 3355 enabled and cannot be disabled. 3356 3357 full 3358 Provides all available mitigations for the 3359 L1TF vulnerability. Disables SMT and 3360 enables all mitigations in the 3361 hypervisors, i.e. unconditional L1D flush. 3362 3363 SMT control and L1D flush control via the 3364 sysfs interface is still possible after 3365 boot. Hypervisors will issue a warning 3366 when the first VM is started in a 3367 potentially insecure configuration, 3368 i.e. SMT enabled or L1D flush disabled. 3369 3370 full,force 3371 Same as 'full', but disables SMT and L1D 3372 flush runtime control. Implies the 3373 'nosmt=force' command line option. 3374 (i.e. sysfs control of SMT is disabled.) 3375 3376 flush 3377 Leaves SMT enabled and enables the default 3378 hypervisor mitigation, i.e. conditional 3379 L1D flush. 3380 3381 SMT control and L1D flush control via the 3382 sysfs interface is still possible after 3383 boot. Hypervisors will issue a warning 3384 when the first VM is started in a 3385 potentially insecure configuration, 3386 i.e. SMT enabled or L1D flush disabled. 3387 3388 flush,nosmt 3389 3390 Disables SMT and enables the default 3391 hypervisor mitigation. 3392 3393 SMT control and L1D flush control via the 3394 sysfs interface is still possible after 3395 boot. Hypervisors will issue a warning 3396 when the first VM is started in a 3397 potentially insecure configuration, 3398 i.e. SMT enabled or L1D flush disabled. 3399 3400 flush,nowarn 3401 Same as 'flush', but hypervisors will not 3402 warn when a VM is started in a potentially 3403 insecure configuration. 3404 3405 off 3406 Disables hypervisor mitigations and doesn't 3407 emit any warnings. 3408 It also drops the swap size and available 3409 RAM limit restriction on both hypervisor and 3410 bare metal. 3411 3412 Default is 'flush'. 3413 3414 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3415 3416 l2cr= [PPC] 3417 3418 l3cr= [PPC] 3419 3420 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3421 disabled it. 3422 3423 lapic= [X86,APIC] Do not use TSC deadline 3424 value for LAPIC timer one-shot implementation. Default 3425 back to the programmable timer unit in the LAPIC. 3426 Format: notscdeadline 3427 3428 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3429 in C2 power state. 3430 3431 libata.dma= [LIBATA] DMA control 3432 libata.dma=0 Disable all PATA and SATA DMA 3433 libata.dma=1 PATA and SATA Disk DMA only 3434 libata.dma=2 ATAPI (CDROM) DMA only 3435 libata.dma=4 Compact Flash DMA only 3436 Combinations also work, so libata.dma=3 enables DMA 3437 for disks and CDROMs, but not CFs. 3438 3439 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3440 libata.ignore_hpa=0 keep BIOS limits (default) 3441 libata.ignore_hpa=1 ignore limits, using full disk 3442 3443 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3444 when set. 3445 Format: <int> 3446 3447 libata.force= [LIBATA] Force configurations. The format is a comma- 3448 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3449 PORT and DEVICE are decimal numbers matching port, link 3450 or device. Basically, it matches the ATA ID string 3451 printed on console by libata. If the whole ID part is 3452 omitted, the last PORT and DEVICE values are used. If 3453 ID hasn't been specified yet, the configuration applies 3454 to all ports, links and devices. 3455 3456 If only DEVICE is omitted, the parameter applies to 3457 the port and all links and devices behind it. DEVICE 3458 number of 0 either selects the first device or the 3459 first fan-out link behind PMP device. It does not 3460 select the host link. DEVICE number of 15 selects the 3461 host link and device attached to it. 3462 3463 The VAL specifies the configuration to force. As long 3464 as there is no ambiguity, shortcut notation is allowed. 3465 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3466 The following configurations can be forced. 3467 3468 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3469 Any ID with matching PORT is used. 3470 3471 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3472 3473 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3474 udma[/][16,25,33,44,66,100,133] notation is also 3475 allowed. 3476 3477 * nohrst, nosrst, norst: suppress hard, soft and both 3478 resets. 3479 3480 * rstonce: only attempt one reset during hot-unplug 3481 link recovery. 3482 3483 * [no]dbdelay: Enable or disable the extra 200ms delay 3484 before debouncing a link PHY and device presence 3485 detection. 3486 3487 * [no]ncq: Turn on or off NCQ. 3488 3489 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3490 3491 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3492 3493 * [no]trim: Enable or disable (unqueued) TRIM. 3494 3495 * trim_zero: Indicate that TRIM command zeroes data. 3496 3497 * max_trim_128m: Set 128M maximum trim size limit. 3498 3499 * [no]dma: Turn on or off DMA transfers. 3500 3501 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3502 3503 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3504 commands that are not a multiple of 16 bytes. 3505 3506 * [no]dmalog: Enable or disable the use of the 3507 READ LOG DMA EXT command to access logs. 3508 3509 * [no]iddevlog: Enable or disable access to the 3510 identify device data log. 3511 3512 * [no]logdir: Enable or disable access to the general 3513 purpose log directory. 3514 3515 * max_sec=<sectors>: Set the transfer size limit, in 3516 number of 512-byte sectors, to the value specified in 3517 <sectors>. The value specified in <sectors> has to be 3518 a non-zero positive integer. 3519 3520 * max_sec_128: Set transfer size limit to 128 sectors. 3521 3522 * max_sec_1024: Set or clear transfer size limit to 3523 1024 sectors. 3524 3525 * max_sec_lba48: Set or clear transfer size limit to 3526 65535 sectors. 3527 3528 * external: Mark port as external (hotplug-capable). 3529 3530 * [no]lpm: Enable or disable link power management. 3531 3532 * [no]setxfer: Indicate if transfer speed mode setting 3533 should be skipped. 3534 3535 * [no]fua: Disable or enable FUA (Force Unit Access) 3536 support for devices supporting this feature. 3537 3538 * dump_id: Dump IDENTIFY data. 3539 3540 * disable: Disable this device. 3541 3542 If there are multiple matching configurations changing 3543 the same attribute, the last one is used. 3544 3545 liveupdate= [KNL,EARLY] 3546 Format: <bool> 3547 Enable Live Update Orchestrator (LUO). 3548 Default: off. 3549 3550 lockd.nlm_grace_period=P [NFS] Assign grace period. 3551 Format: <integer> 3552 3553 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3554 Format: <integer> 3555 3556 lockd.nlm_timeout=T [NFS] Assign timeout value. 3557 Format: <integer> 3558 3559 lockd.nlm_udpport=M [NFS] Assign UDP port. 3560 Format: <integer> 3561 3562 lockdown= [SECURITY,EARLY] 3563 { integrity | confidentiality } 3564 Enable the kernel lockdown feature. If set to 3565 integrity, kernel features that allow userland to 3566 modify the running kernel are disabled. If set to 3567 confidentiality, kernel features that allow userland 3568 to extract confidential information from the kernel 3569 are also disabled. 3570 3571 locktorture.acq_writer_lim= [KNL] 3572 Set the time limit in jiffies for a lock 3573 acquisition. Acquisitions exceeding this limit 3574 will result in a splat once they do complete. 3575 3576 locktorture.bind_readers= [KNL] 3577 Specify the list of CPUs to which the readers are 3578 to be bound. 3579 3580 locktorture.bind_writers= [KNL] 3581 Specify the list of CPUs to which the writers are 3582 to be bound. 3583 3584 locktorture.call_rcu_chains= [KNL] 3585 Specify the number of self-propagating call_rcu() 3586 chains to set up. These are used to ensure that 3587 there is a high probability of an RCU grace period 3588 in progress at any given time. Defaults to 0, 3589 which disables these call_rcu() chains. 3590 3591 locktorture.long_hold= [KNL] 3592 Specify the duration in milliseconds for the 3593 occasional long-duration lock hold time. Defaults 3594 to 100 milliseconds. Select 0 to disable. 3595 3596 locktorture.nested_locks= [KNL] 3597 Specify the maximum lock nesting depth that 3598 locktorture is to exercise, up to a limit of 8 3599 (MAX_NESTED_LOCKS). Specify zero to disable. 3600 Note that this parameter is ineffective on types 3601 of locks that do not support nested acquisition. 3602 3603 locktorture.nreaders_stress= [KNL] 3604 Set the number of locking read-acquisition kthreads. 3605 Defaults to being automatically set based on the 3606 number of online CPUs. 3607 3608 locktorture.nwriters_stress= [KNL] 3609 Set the number of locking write-acquisition kthreads. 3610 3611 locktorture.onoff_holdoff= [KNL] 3612 Set time (s) after boot for CPU-hotplug testing. 3613 3614 locktorture.onoff_interval= [KNL] 3615 Set time (s) between CPU-hotplug operations, or 3616 zero to disable CPU-hotplug testing. 3617 3618 locktorture.rt_boost= [KNL] 3619 Do periodic testing of real-time lock priority 3620 boosting. Select 0 to disable, 1 to boost 3621 only rt_mutex, and 2 to boost unconditionally. 3622 Defaults to 2, which might seem to be an 3623 odd choice, but which should be harmless for 3624 non-real-time spinlocks, due to their disabling 3625 of preemption. Note that non-realtime mutexes 3626 disable boosting. 3627 3628 locktorture.rt_boost_factor= [KNL] 3629 Number that determines how often and for how 3630 long priority boosting is exercised. This is 3631 scaled down by the number of writers, so that the 3632 number of boosts per unit time remains roughly 3633 constant as the number of writers increases. 3634 On the other hand, the duration of each boost 3635 increases with the number of writers. 3636 3637 locktorture.shuffle_interval= [KNL] 3638 Set task-shuffle interval (jiffies). Shuffling 3639 tasks allows some CPUs to go into dyntick-idle 3640 mode during the locktorture test. 3641 3642 locktorture.shutdown_secs= [KNL] 3643 Set time (s) after boot system shutdown. This 3644 is useful for hands-off automated testing. 3645 3646 locktorture.stat_interval= [KNL] 3647 Time (s) between statistics printk()s. 3648 3649 locktorture.stutter= [KNL] 3650 Time (s) to stutter testing, for example, 3651 specifying five seconds causes the test to run for 3652 five seconds, wait for five seconds, and so on. 3653 This tests the locking primitive's ability to 3654 transition abruptly to and from idle. 3655 3656 locktorture.torture_type= [KNL] 3657 Specify the locking implementation to test. 3658 3659 locktorture.verbose= [KNL] 3660 Enable additional printk() statements. 3661 3662 locktorture.writer_fifo= [KNL] 3663 Run the write-side locktorture kthreads at 3664 sched_set_fifo() real-time priority. 3665 3666 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3667 Format: <irq> 3668 3669 loglevel= [KNL,EARLY] 3670 All Kernel Messages with a loglevel smaller than the 3671 console loglevel will be printed to the console. It can 3672 also be changed with klogd or other programs. The 3673 loglevels are defined as follows: 3674 3675 0 (KERN_EMERG) system is unusable 3676 1 (KERN_ALERT) action must be taken immediately 3677 2 (KERN_CRIT) critical conditions 3678 3 (KERN_ERR) error conditions 3679 4 (KERN_WARNING) warning conditions 3680 5 (KERN_NOTICE) normal but significant condition 3681 6 (KERN_INFO) informational 3682 7 (KERN_DEBUG) debug-level messages 3683 3684 log_buf_len=n[KMG] [KNL,EARLY] 3685 Sets the size of the printk ring buffer, in bytes. 3686 n must be a power of two and greater than the 3687 minimal size. The minimal size is defined by 3688 LOG_BUF_SHIFT kernel config parameter. There 3689 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3690 parameter that allows to increase the default size 3691 depending on the number of CPUs. See init/Kconfig 3692 for more details. 3693 3694 logo.nologo [FB] Disables display of the built-in Linux logo. 3695 This may be used to provide more screen space for 3696 kernel log messages and is useful when debugging 3697 kernel boot problems. 3698 3699 lp=0 [LP] Specify parallel ports to use, e.g, 3700 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3701 lp=reset first parallel port). 'lp=0' disables the 3702 lp=auto printer driver. 'lp=reset' (which can be 3703 specified in addition to the ports) causes 3704 attached printers to be reset. Using 3705 lp=port1,port2,... specifies the parallel ports 3706 to associate lp devices with, starting with 3707 lp0. A port specification may be 'none' to skip 3708 that lp device, or a parport name such as 3709 'parport0'. Specifying 'lp=auto' instead of a 3710 port specification list means that device IDs 3711 from each port should be examined, to see if 3712 an IEEE 1284-compliant printer is attached; if 3713 so, the driver will manage that printer. 3714 See also header of drivers/char/lp.c. 3715 3716 lpj=n [KNL] 3717 Sets loops_per_jiffy to given constant, thus avoiding 3718 time-consuming boot-time autodetection (up to 250 ms per 3719 CPU). 0 enables autodetection (default). To determine 3720 the correct value for your kernel, boot with normal 3721 autodetection and see what value is printed. Note that 3722 on SMP systems the preset will be applied to all CPUs, 3723 which is likely to cause problems if your CPUs need 3724 significantly divergent settings. An incorrect value 3725 will cause delays in the kernel to be wrong, leading to 3726 unpredictable I/O errors and other breakage. Although 3727 unlikely, in the extreme case this might damage your 3728 hardware. 3729 3730 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3731 3732 lsm=lsm1,...,lsmN 3733 [SECURITY] Choose order of LSM initialization. This 3734 overrides CONFIG_LSM, and the "security=" parameter. 3735 3736 machtype= [Loongson] Share the same kernel image file between 3737 different yeeloong laptops. 3738 Example: machtype=lemote-yeeloong-2f-7inch 3739 3740 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3741 will bring up during bootup. maxcpus=n : n >= 0 limits 3742 the kernel to bring up 'n' processors. Surely after 3743 bootup you can bring up the other plugged cpu by executing 3744 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3745 only takes effect during system bootup. 3746 While n=0 is a special case, it is equivalent to "nosmp", 3747 which also disables the IO APIC. 3748 3749 max_loop= [LOOP] The number of loop block devices that get 3750 (loop.max_loop) unconditionally pre-created at init time. The default 3751 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3752 of statically allocating a predefined number, loop 3753 devices can be requested on-demand with the 3754 /dev/loop-control interface. 3755 3756 mce= [X86-{32,64}] 3757 3758 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3759 3760 off 3761 disable machine check 3762 3763 no_cmci 3764 disable CMCI(Corrected Machine Check Interrupt) that 3765 Intel processor supports. Usually this disablement is 3766 not recommended, but it might be handy if your 3767 hardware is misbehaving. 3768 3769 Note that you'll get more problems without CMCI than 3770 with due to the shared banks, i.e. you might get 3771 duplicated error logs. 3772 3773 dont_log_ce 3774 don't make logs for corrected errors. All events 3775 reported as corrected are silently cleared by OS. This 3776 option will be useful if you have no interest in any 3777 of corrected errors. 3778 3779 ignore_ce 3780 disable features for corrected errors, e.g. 3781 polling timer and CMCI. All events reported as 3782 corrected are not cleared by OS and remained in its 3783 error banks. 3784 3785 Usually this disablement is not recommended, however 3786 if there is an agent checking/clearing corrected 3787 errors (e.g. BIOS or hardware monitoring 3788 applications), conflicting with OS's error handling, 3789 and you cannot deactivate the agent, then this option 3790 will be a help. 3791 3792 no_lmce 3793 do not opt-in to Local MCE delivery. Use legacy method 3794 to broadcast MCEs. 3795 3796 bootlog 3797 enable logging of machine checks left over from 3798 booting. Disabled by default on AMD Fam10h and older 3799 because some BIOS leave bogus ones. 3800 3801 If your BIOS doesn't do that it's a good idea to 3802 enable though to make sure you log even machine check 3803 events that result in a reboot. On Intel systems it is 3804 enabled by default. 3805 3806 nobootlog 3807 disable boot machine check logging. 3808 3809 print_all 3810 print all machine check logs to the console. 3811 3812 monarchtimeout (number) 3813 sets the time in us to wait for other CPUs on machine 3814 checks. 0 to disable. 3815 3816 bios_cmci_threshold 3817 don't overwrite the bios-set CMCI threshold. This boot 3818 option prevents Linux from overwriting the CMCI 3819 threshold set by the bios. Without this option, Linux 3820 always sets the CMCI threshold to 1. Enabling this may 3821 make memory predictive failure analysis less effective 3822 if the bios sets thresholds for memory errors since we 3823 will not see details for all errors. 3824 3825 recovery 3826 force-enable recoverable machine check code paths 3827 3828 Everything else is in sysfs now. 3829 3830 3831 md= [HW] RAID subsystems devices and level 3832 See Documentation/admin-guide/md.rst. 3833 3834 mds= [X86,INTEL,EARLY] 3835 Control mitigation for the Micro-architectural Data 3836 Sampling (MDS) vulnerability. 3837 3838 Certain CPUs are vulnerable to an exploit against CPU 3839 internal buffers which can forward information to a 3840 disclosure gadget under certain conditions. 3841 3842 In vulnerable processors, the speculatively 3843 forwarded data can be used in a cache side channel 3844 attack, to access data to which the attacker does 3845 not have direct access. 3846 3847 This parameter controls the MDS mitigation. The 3848 options are: 3849 3850 full - Enable MDS mitigation on vulnerable CPUs 3851 full,nosmt - Enable MDS mitigation and disable 3852 SMT on vulnerable CPUs 3853 off - Unconditionally disable MDS mitigation 3854 3855 On TAA-affected machines, mds=off can be prevented by 3856 an active TAA mitigation as both vulnerabilities are 3857 mitigated with the same mechanism so in order to disable 3858 this mitigation, you need to specify tsx_async_abort=off 3859 too. 3860 3861 Not specifying this option is equivalent to 3862 mds=full. 3863 3864 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3865 3866 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3867 Must be specified, otherwise memory size will be 0. 3868 3869 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3870 of memory Amount of memory to be used in cases 3871 as follows: 3872 3873 1 for test; 3874 2 when the kernel is not able to see the whole system memory; 3875 3 memory that lies after 'mem=' boundary is excluded from 3876 the hypervisor, then assigned to KVM guests. 3877 4 to limit the memory available for kdump kernel. 3878 3879 [ARC,MICROBLAZE] - the limit applies only to low memory, 3880 high memory is not affected. 3881 3882 [ARM64] - only limits memory covered by the linear 3883 mapping. The NOMAP regions are not affected. 3884 3885 [X86] Work as limiting max address. Use together 3886 with memmap= to avoid physical address space collisions. 3887 Without memmap= PCI devices could be placed at addresses 3888 belonging to unused RAM. 3889 3890 Note that this only takes effects during boot time since 3891 in above case 3, memory may need be hot added after boot 3892 if system memory of hypervisor is not sufficient. 3893 3894 mem=nn[KMG]@ss[KMG] 3895 [ARM,MIPS,EARLY] - override the memory layout 3896 reported by firmware. 3897 Define a memory region of size nn[KMG] starting at 3898 ss[KMG]. 3899 Multiple different regions can be specified with 3900 multiple mem= parameters on the command line. 3901 3902 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3903 memory. 3904 3905 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3906 3907 memchunk=nn[KMG] 3908 [KNL,SH] Allow user to override the default size for 3909 per-device physically contiguous DMA buffers. 3910 3911 memhp_default_state=online/offline/online_kernel/online_movable 3912 [KNL] Set the initial state for the memory hotplug 3913 onlining policy. If not specified, the default value is 3914 set according to the 3915 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3916 options. 3917 See Documentation/admin-guide/mm/memory-hotplug.rst. 3918 3919 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3920 E820 memory map, as specified by the user. 3921 Such memmap=exactmap lines can be constructed based on 3922 BIOS output or other requirements. See the memmap=nn@ss 3923 option description. 3924 3925 memmap=nn[KMG]@ss[KMG] 3926 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3927 Region of memory to be used is from ss to ss+nn. 3928 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3929 which limits max address to nn[KMG]. 3930 Multiple different regions can be specified, 3931 comma delimited. 3932 Example: 3933 memmap=100M@2G,100M#3G,1G!1024G 3934 3935 memmap=nn[KMG]#ss[KMG] 3936 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3937 Region of memory to be marked is from ss to ss+nn. 3938 3939 memmap=nn[KMG]$ss[KMG] 3940 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3941 Region of memory to be reserved is from ss to ss+nn. 3942 Example: Exclude memory from 0x18690000-0x1869ffff 3943 memmap=64K$0x18690000 3944 or 3945 memmap=0x10000$0x18690000 3946 Some bootloaders may need an escape character before '$', 3947 like Grub2, otherwise '$' and the following number 3948 will be eaten. 3949 3950 memmap=nn[KMG]!ss[KMG,EARLY] 3951 [KNL,X86] Mark specific memory as protected. 3952 Region of memory to be used, from ss to ss+nn. 3953 The memory region may be marked as e820 type 12 (0xc) 3954 and is NVDIMM or ADR memory. 3955 3956 memmap=<size>%<offset>-<oldtype>+<newtype> 3957 [KNL,ACPI,EARLY] Convert memory within the specified region 3958 from <oldtype> to <newtype>. If "-<oldtype>" is left 3959 out, the whole region will be marked as <newtype>, 3960 even if previously unavailable. If "+<newtype>" is left 3961 out, matching memory will be removed. Types are 3962 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3963 3 = ACPI, 12 = PRAM. 3964 3965 memory_corruption_check=0/1 [X86,EARLY] 3966 Some BIOSes seem to corrupt the first 64k of 3967 memory when doing things like suspend/resume. 3968 Setting this option will scan the memory 3969 looking for corruption. Enabling this will 3970 both detect corruption and prevent the kernel 3971 from using the memory being corrupted. 3972 However, it's intended as a diagnostic tool; if 3973 repeatable BIOS-originated corruption always 3974 affects the same memory, you can use memmap= 3975 to prevent the kernel from using that memory. 3976 3977 memory_corruption_check_size=size [X86,EARLY] 3978 By default it checks for corruption in the low 3979 64k, making this memory unavailable for normal 3980 use. Use this parameter to scan for 3981 corruption in more or less memory. 3982 3983 memory_corruption_check_period=seconds [X86,EARLY] 3984 By default it checks for corruption every 60 3985 seconds. Use this parameter to check at some 3986 other rate. 0 disables periodic checking. 3987 3988 memory_hotplug.memmap_on_memory 3989 [KNL,X86,ARM] Boolean flag to enable this feature. 3990 Format: {on | off (default)} 3991 When enabled, runtime hotplugged memory will 3992 allocate its internal metadata (struct pages, 3993 those vmemmap pages cannot be optimized even 3994 if hugetlb_free_vmemmap is enabled) from the 3995 hotadded memory which will allow to hotadd a 3996 lot of memory without requiring additional 3997 memory to do so. 3998 This feature is disabled by default because it 3999 has some implication on large (e.g. GB) 4000 allocations in some configurations (e.g. small 4001 memory blocks). 4002 The state of the flag can be read in 4003 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4004 Note that even when enabled, there are a few cases where 4005 the feature is not effective. 4006 4007 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4008 Format: <integer> 4009 default : 0 <disable> 4010 Specifies the number of memtest passes to be 4011 performed. Each pass selects another test 4012 pattern from a given set of patterns. Memtest 4013 fills the memory with this pattern, validates 4014 memory contents and reserves bad memory 4015 regions that are detected. 4016 4017 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4018 Valid arguments: on, off 4019 Default: off 4020 mem_encrypt=on: Activate SME 4021 mem_encrypt=off: Do not activate SME 4022 4023 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4024 for details on when memory encryption can be activated. 4025 4026 mem_sleep_default= [SUSPEND] Default system suspend mode: 4027 s2idle - Suspend-To-Idle 4028 shallow - Power-On Suspend or equivalent (if supported) 4029 deep - Suspend-To-RAM or equivalent (if supported) 4030 See Documentation/admin-guide/pm/sleep-states.rst. 4031 4032 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4033 the BIOS has incorrectly applied a workaround. TinyBIOS 4034 version 0.98 is known to be affected, 0.99 fixes the 4035 problem by letting the user disable the workaround. 4036 4037 mga= [HW,DRM] 4038 4039 microcode= [X86] Control the behavior of the microcode loader. 4040 Available options, comma separated: 4041 4042 base_rev=X - with <X> with format: <u32> 4043 Set the base microcode revision of each thread when in 4044 debug mode. 4045 4046 dis_ucode_ldr: disable the microcode loader 4047 4048 force_minrev: 4049 Enable or disable the microcode minimal revision 4050 enforcement for the runtime microcode loader. 4051 4052 mini2440= [ARM,HW,KNL] 4053 Format:[0..2][b][c][t] 4054 Default: "0tb" 4055 MINI2440 configuration specification: 4056 0 - The attached screen is the 3.5" TFT 4057 1 - The attached screen is the 7" TFT 4058 2 - The VGA Shield is attached (1024x768) 4059 Leaving out the screen size parameter will not load 4060 the TFT driver, and the framebuffer will be left 4061 unconfigured. 4062 b - Enable backlight. The TFT backlight pin will be 4063 linked to the kernel VESA blanking code and a GPIO 4064 LED. This parameter is not necessary when using the 4065 VGA shield. 4066 c - Enable the s3c camera interface. 4067 t - Reserved for enabling touchscreen support. The 4068 touchscreen support is not enabled in the mainstream 4069 kernel as of 2.6.30, a preliminary port can be found 4070 in the "bleeding edge" mini2440 support kernel at 4071 https://repo.or.cz/w/linux-2.6/mini2440.git 4072 4073 mitigations= 4074 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4075 CPU vulnerabilities. This is a set of curated, 4076 arch-independent options, each of which is an 4077 aggregation of existing arch-specific options. 4078 4079 Note, "mitigations" is supported if and only if the 4080 kernel was built with CPU_MITIGATIONS=y. 4081 4082 off 4083 Disable all optional CPU mitigations. This 4084 improves system performance, but it may also 4085 expose users to several CPU vulnerabilities. 4086 Equivalent to: if nokaslr then kpti=0 [ARM64] 4087 gather_data_sampling=off [X86] 4088 indirect_target_selection=off [X86] 4089 kvm.nx_huge_pages=off [X86] 4090 l1tf=off [X86] 4091 mds=off [X86] 4092 mmio_stale_data=off [X86] 4093 no_entry_flush [PPC] 4094 no_uaccess_flush [PPC] 4095 nobp=0 [S390] 4096 nopti [X86,PPC] 4097 nospectre_bhb [ARM64] 4098 nospectre_v1 [X86,PPC] 4099 nospectre_v2 [X86,PPC,S390,ARM64] 4100 reg_file_data_sampling=off [X86] 4101 retbleed=off [X86] 4102 spec_rstack_overflow=off [X86] 4103 spec_store_bypass_disable=off [X86,PPC] 4104 spectre_bhi=off [X86] 4105 spectre_v2_user=off [X86] 4106 srbds=off [X86,INTEL] 4107 ssbd=force-off [ARM64] 4108 tsa=off [X86,AMD] 4109 tsx_async_abort=off [X86] 4110 vmscape=off [X86] 4111 4112 Exceptions: 4113 This does not have any effect on 4114 kvm.nx_huge_pages when 4115 kvm.nx_huge_pages=force. 4116 4117 auto (default) 4118 Mitigate all CPU vulnerabilities, but leave SMT 4119 enabled, even if it's vulnerable. This is for 4120 users who don't want to be surprised by SMT 4121 getting disabled across kernel upgrades, or who 4122 have other ways of avoiding SMT-based attacks. 4123 Equivalent to: (default behavior) 4124 4125 auto,nosmt 4126 Mitigate all CPU vulnerabilities, disabling SMT 4127 if needed. This is for users who always want to 4128 be fully mitigated, even if it means losing SMT. 4129 Equivalent to: l1tf=flush,nosmt [X86] 4130 mds=full,nosmt [X86] 4131 tsx_async_abort=full,nosmt [X86] 4132 mmio_stale_data=full,nosmt [X86] 4133 retbleed=auto,nosmt [X86] 4134 4135 [X86] After one of the above options, additionally 4136 supports attack-vector based controls as documented in 4137 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4138 4139 mminit_loglevel= 4140 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4141 parameter allows control of the logging verbosity for 4142 the additional memory initialisation checks. A value 4143 of 0 disables mminit logging and a level of 4 will 4144 log everything. Information is printed at KERN_DEBUG 4145 so loglevel=8 may also need to be specified. 4146 4147 mmio_stale_data= 4148 [X86,INTEL,EARLY] Control mitigation for the Processor 4149 MMIO Stale Data vulnerabilities. 4150 4151 Processor MMIO Stale Data is a class of 4152 vulnerabilities that may expose data after an MMIO 4153 operation. Exposed data could originate or end in 4154 the same CPU buffers as affected by MDS and TAA. 4155 Therefore, similar to MDS and TAA, the mitigation 4156 is to clear the affected CPU buffers. 4157 4158 This parameter controls the mitigation. The 4159 options are: 4160 4161 full - Enable mitigation on vulnerable CPUs 4162 4163 full,nosmt - Enable mitigation and disable SMT on 4164 vulnerable CPUs. 4165 4166 off - Unconditionally disable mitigation 4167 4168 On MDS or TAA affected machines, 4169 mmio_stale_data=off can be prevented by an active 4170 MDS or TAA mitigation as these vulnerabilities are 4171 mitigated with the same mechanism so in order to 4172 disable this mitigation, you need to specify 4173 mds=off and tsx_async_abort=off too. 4174 4175 Not specifying this option is equivalent to 4176 mmio_stale_data=full. 4177 4178 For details see: 4179 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4180 4181 <module>.async_probe[=<bool>] [KNL] 4182 If no <bool> value is specified or if the value 4183 specified is not a valid <bool>, enable asynchronous 4184 probe on this module. Otherwise, enable/disable 4185 asynchronous probe on this module as indicated by the 4186 <bool> value. See also: module.async_probe 4187 4188 module.async_probe=<bool> 4189 [KNL] When set to true, modules will use async probing 4190 by default. To enable/disable async probing for a 4191 specific module, use the module specific control that 4192 is documented under <module>.async_probe. When both 4193 module.async_probe and <module>.async_probe are 4194 specified, <module>.async_probe takes precedence for 4195 the specific module. 4196 4197 module.enable_dups_trace 4198 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4199 this means that duplicate request_module() calls will 4200 trigger a WARN_ON() instead of a pr_warn(). Note that 4201 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4202 will always be issued and this option does nothing. 4203 module.sig_enforce 4204 [KNL] When CONFIG_MODULE_SIG is set, this means that 4205 modules without (valid) signatures will fail to load. 4206 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4207 is always true, so this option does nothing. 4208 4209 module_blacklist= [KNL] Do not load a comma-separated list of 4210 modules. Useful for debugging problem modules. 4211 4212 mousedev.tap_time= 4213 [MOUSE] Maximum time between finger touching and 4214 leaving touchpad surface for touch to be considered 4215 a tap and be reported as a left button click (for 4216 touchpads working in absolute mode only). 4217 Format: <msecs> 4218 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4219 reporting absolute coordinates, such as tablets 4220 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4221 reporting absolute coordinates, such as tablets 4222 4223 movablecore= [KNL,X86,PPC,EARLY] 4224 Format: nn[KMGTPE] | nn% 4225 This parameter is the complement to kernelcore=, it 4226 specifies the amount of memory used for migratable 4227 allocations. If both kernelcore and movablecore is 4228 specified, then kernelcore will be at *least* the 4229 specified value but may be more. If movablecore on its 4230 own is specified, the administrator must be careful 4231 that the amount of memory usable for all allocations 4232 is not too small. 4233 4234 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4235 NUMA nodes to be movable. This means that the memory 4236 of such nodes will be usable only for movable 4237 allocations which rules out almost all kernel 4238 allocations. Use with caution! 4239 4240 MTD_Partition= [MTD] 4241 Format: <name>,<region-number>,<size>,<offset> 4242 4243 MTD_Region= [MTD] Format: 4244 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4245 4246 mtdparts= [MTD] 4247 See drivers/mtd/parsers/cmdlinepart.c 4248 4249 mtouchusb.raw_coordinates= 4250 [HW] Make the MicroTouch USB driver use raw coordinates 4251 ('y', default) or cooked coordinates ('n') 4252 4253 mtrr=debug [X86,EARLY] 4254 Enable printing debug information related to MTRR 4255 registers at boot time. 4256 4257 mtrr_chunk_size=nn[KMG,X86,EARLY] 4258 used for mtrr cleanup. It is largest continuous chunk 4259 that could hold holes aka. UC entries. 4260 4261 mtrr_gran_size=nn[KMG,X86,EARLY] 4262 Used for mtrr cleanup. It is granularity of mtrr block. 4263 Default is 1. 4264 Large value could prevent small alignment from 4265 using up MTRRs. 4266 4267 mtrr_spare_reg_nr=n [X86,EARLY] 4268 Format: <integer> 4269 Range: 0,7 : spare reg number 4270 Default : 1 4271 Used for mtrr cleanup. It is spare mtrr entries number. 4272 Set to 2 or more if your graphical card needs more. 4273 4274 multitce=off [PPC] This parameter disables the use of the pSeries 4275 firmware feature for updating multiple TCE entries 4276 at a time. 4277 4278 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4279 4280 netdev= [NET] NE2000 ISA network devices parameters 4281 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4282 4283 netpoll.carrier_timeout= 4284 [NET] Specifies amount of time (in seconds) that 4285 netpoll should wait for a carrier. By default netpoll 4286 waits 4 seconds. 4287 4288 nf_conntrack.acct= 4289 [NETFILTER] Enable connection tracking flow accounting 4290 0 to disable accounting 4291 1 to enable accounting 4292 Default value is 0. 4293 4294 nfs.cache_getent= 4295 [NFS] sets the pathname to the program which is used 4296 to update the NFS client cache entries. 4297 4298 nfs.cache_getent_timeout= 4299 [NFS] sets the timeout after which an attempt to 4300 update a cache entry is deemed to have failed. 4301 4302 nfs.callback_nr_threads= 4303 [NFSv4] set the total number of threads that the 4304 NFS client will assign to service NFSv4 callback 4305 requests. 4306 4307 nfs.callback_tcpport= 4308 [NFS] set the TCP port on which the NFSv4 callback 4309 channel should listen. 4310 4311 nfs.delay_retrans= 4312 [NFS] specifies the number of times the NFSv4 client 4313 retries the request before returning an EAGAIN error, 4314 after a reply of NFS4ERR_DELAY from the server. 4315 Only applies if the softerr mount option is enabled, 4316 and the specified value is >= 0. 4317 4318 nfs.idmap_cache_timeout= 4319 [NFS] set the maximum lifetime for idmapper cache 4320 entries. 4321 4322 nfs.max_session_cb_slots= 4323 [NFSv4.1] Sets the maximum number of session 4324 slots the client will assign to the callback 4325 channel. This determines the maximum number of 4326 callbacks the client will process in parallel for 4327 a particular server. 4328 4329 nfs.max_session_slots= 4330 [NFSv4.1] Sets the maximum number of session slots 4331 the client will attempt to negotiate with the server. 4332 This limits the number of simultaneous RPC requests 4333 that the client can send to the NFSv4.1 server. 4334 Note that there is little point in setting this 4335 value higher than the max_tcp_slot_table_limit. 4336 4337 nfs.nfs4_disable_idmapping= 4338 [NFSv4] When set to the default of '1', this option 4339 ensures that both the RPC level authentication 4340 scheme and the NFS level operations agree to use 4341 numeric uids/gids if the mount is using the 4342 'sec=sys' security flavour. In effect it is 4343 disabling idmapping, which can make migration from 4344 legacy NFSv2/v3 systems to NFSv4 easier. 4345 Servers that do not support this mode of operation 4346 will be autodetected by the client, and it will fall 4347 back to using the idmapper. 4348 To turn off this behaviour, set the value to '0'. 4349 4350 nfs.nfs4_unique_id= 4351 [NFS4] Specify an additional fixed unique ident- 4352 ification string that NFSv4 clients can insert into 4353 their nfs_client_id4 string. This is typically a 4354 UUID that is generated at system install time. 4355 4356 nfs.recover_lost_locks= 4357 [NFSv4] Attempt to recover locks that were lost due 4358 to a lease timeout on the server. Please note that 4359 doing this risks data corruption, since there are 4360 no guarantees that the file will remain unchanged 4361 after the locks are lost. 4362 If you want to enable the kernel legacy behaviour of 4363 attempting to recover these locks, then set this 4364 parameter to '1'. 4365 The default parameter value of '0' causes the kernel 4366 not to attempt recovery of lost locks. 4367 4368 nfs.send_implementation_id= 4369 [NFSv4.1] Send client implementation identification 4370 information in exchange_id requests. 4371 If zero, no implementation identification information 4372 will be sent. 4373 The default is to send the implementation identification 4374 information. 4375 4376 nfs4.layoutstats_timer= 4377 [NFSv4.2] Change the rate at which the kernel sends 4378 layoutstats to the pNFS metadata server. 4379 4380 Setting this to value to 0 causes the kernel to use 4381 whatever value is the default set by the layout 4382 driver. A non-zero value sets the minimum interval 4383 in seconds between layoutstats transmissions. 4384 4385 nfsd.inter_copy_offload_enable= 4386 [NFSv4.2] When set to 1, the server will support 4387 server-to-server copies for which this server is 4388 the destination of the copy. 4389 4390 nfsd.nfs4_disable_idmapping= 4391 [NFSv4] When set to the default of '1', the NFSv4 4392 server will return only numeric uids and gids to 4393 clients using auth_sys, and will accept numeric uids 4394 and gids from such clients. This is intended to ease 4395 migration from NFSv2/v3. 4396 4397 nfsd.nfsd4_ssc_umount_timeout= 4398 [NFSv4.2] When used as the destination of a 4399 server-to-server copy, knfsd temporarily mounts 4400 the source server. It caches the mount in case 4401 it will be needed again, and discards it if not 4402 used for the number of milliseconds specified by 4403 this parameter. 4404 4405 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4406 See Documentation/admin-guide/nfs/nfsroot.rst. 4407 4408 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4409 See Documentation/admin-guide/nfs/nfsroot.rst. 4410 4411 nfsrootdebug [NFS] enable nfsroot debugging messages. 4412 See Documentation/admin-guide/nfs/nfsroot.rst. 4413 4414 nmi_backtrace.backtrace_idle [KNL] 4415 Dump stacks even of idle CPUs in response to an 4416 NMI stack-backtrace request. 4417 4418 nmi_debug= [KNL,SH] Specify one or more actions to take 4419 when a NMI is triggered. 4420 Format: [state][,regs][,debounce][,die] 4421 4422 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4423 Format: [panic,][nopanic,][rNNN,][num] 4424 Valid num: 0 or 1 4425 0 - turn hardlockup detector in nmi_watchdog off 4426 1 - turn hardlockup detector in nmi_watchdog on 4427 rNNN - configure the watchdog with raw perf event 0xNNN 4428 4429 When panic is specified, panic when an NMI watchdog 4430 timeout occurs (or 'nopanic' to not panic on an NMI 4431 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4432 To disable both hard and soft lockup detectors, 4433 please see 'nowatchdog'. 4434 This is useful when you use a panic=... timeout and 4435 need the box quickly up again. 4436 4437 These settings can be accessed at runtime via 4438 the nmi_watchdog and hardlockup_panic sysctls. 4439 4440 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4441 Forces kernel to use 3-level paging instead. 4442 4443 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4444 kernel to use 4-level paging instead. 4445 4446 noalign [KNL,ARM] 4447 4448 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4449 IOAPICs that may be present in the system. 4450 4451 noapictimer [APIC,X86] Don't set up the APIC timer 4452 4453 noautogroup Disable scheduler automatic task group creation. 4454 4455 nocache [ARM,EARLY] 4456 4457 no_console_suspend 4458 [HW] Never suspend the console 4459 Disable suspending of consoles during suspend and 4460 hibernate operations. Once disabled, debugging 4461 messages can reach various consoles while the rest 4462 of the system is being put to sleep (ie, while 4463 debugging driver suspend/resume hooks). This may 4464 not work reliably with all consoles, but is known 4465 to work with serial and VGA consoles. 4466 To facilitate more flexible debugging, we also add 4467 console_suspend, a printk module parameter to control 4468 it. Users could use console_suspend (usually 4469 /sys/module/printk/parameters/console_suspend) to 4470 turn on/off it dynamically. 4471 4472 no_debug_objects 4473 [KNL,EARLY] Disable object debugging 4474 4475 nodsp [SH] Disable hardware DSP at boot time. 4476 4477 noefi [EFI,EARLY] Disable EFI runtime services support. 4478 4479 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4480 4481 noexec32 [X86-64] 4482 This affects only 32-bit executables. 4483 noexec32=on: enable non-executable mappings (default) 4484 read doesn't imply executable mappings 4485 noexec32=off: disable non-executable mappings 4486 read implies executable mappings 4487 4488 no_file_caps Tells the kernel not to honor file capabilities. The 4489 only way then for a file to be executed with privilege 4490 is to be setuid root or executed by root. 4491 4492 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4493 4494 nofsgsbase [X86] Disables FSGSBASE instructions. 4495 4496 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4497 register save and restore. The kernel will only save 4498 legacy floating-point registers on task switch. 4499 4500 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4501 4502 no_hash_pointers 4503 [KNL,EARLY] 4504 Alias for "hash_pointers=never". 4505 4506 nohibernate [HIBERNATION] Disable hibernation and resume. 4507 4508 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4509 busy wait in do_idle() and not use the arch_cpu_idle() 4510 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4511 to be effective. This is useful on platforms where the 4512 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4513 correctly or when doing power measurements to evaluate 4514 the impact of the sleep instructions. This is also 4515 useful when using JTAG debugger. 4516 4517 nohpet [X86] Don't use the HPET timer. 4518 4519 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4520 4521 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4522 4523 nohz= [KNL] Boottime enable/disable dynamic ticks 4524 Valid arguments: on, off 4525 Default: on 4526 4527 nohz_full= [KNL,BOOT,SMP,ISOL] 4528 The argument is a cpu list, as described above. 4529 In kernels built with CONFIG_NO_HZ_FULL=y, set 4530 the specified list of CPUs whose tick will be stopped 4531 whenever possible. The boot CPU will be forced outside 4532 the range to maintain the timekeeping. Any CPUs 4533 in this list will have their RCU callbacks offloaded, 4534 just as if they had also been called out in the 4535 rcu_nocbs= boot parameter. 4536 4537 Note that this argument takes precedence over 4538 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4539 4540 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4541 initial RAM disk. Currently this parameter applies to 4542 initrd only, not to initramfs. But it applies to both 4543 in EFI mode. 4544 4545 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4546 remapping. 4547 [Deprecated - use intremap=off] 4548 4549 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4550 4551 noiotrap [SH] Disables trapped I/O port accesses. 4552 4553 noirqdebug [X86-32] Disables the code which attempts to detect and 4554 disable unhandled interrupt sources. 4555 4556 noisapnp [ISAPNP] Disables ISA PnP code. 4557 4558 nokaslr [KNL,EARLY] 4559 When CONFIG_RANDOMIZE_BASE is set, this disables 4560 kernel and module base offset ASLR (Address Space 4561 Layout Randomization). 4562 4563 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4564 fault handling. 4565 4566 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4567 4568 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4569 4570 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4571 4572 nomce [X86-32] Disable Machine Check Exception 4573 4574 nomfgpt [X86-32] Disable Multi-Function General Purpose 4575 Timer usage (for AMD Geode machines). 4576 4577 nomodeset Disable kernel modesetting. Most systems' firmware 4578 sets up a display mode and provides framebuffer memory 4579 for output. With nomodeset, DRM and fbdev drivers will 4580 not load if they could possibly displace the pre- 4581 initialized output. Only the system framebuffer will 4582 be available for use. The respective drivers will not 4583 perform display-mode changes or accelerated rendering. 4584 4585 Useful as error fallback, or for testing and debugging. 4586 4587 nomodule Disable module load 4588 4589 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4590 shutdown the other cpus. Instead use the REBOOT_VECTOR 4591 irq. 4592 4593 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4594 pagetables) support. 4595 4596 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4597 4598 nopku [X86] Disable Memory Protection Keys CPU feature found 4599 in some Intel CPUs. 4600 4601 nopti [X86-64,EARLY] 4602 Equivalent to pti=off 4603 4604 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4605 Disables the PV optimizations forcing the guest to run 4606 as generic guest with no PV drivers. Currently support 4607 XEN HVM, KVM, HYPER_V and VMWARE guest. 4608 4609 nopvspin [X86,XEN,KVM,EARLY] 4610 Disables the qspinlock slow path using PV optimizations 4611 which allow the hypervisor to 'idle' the guest on lock 4612 contention. 4613 4614 norandmaps Don't use address space randomization. Equivalent to 4615 echo 0 > /proc/sys/kernel/randomize_va_space 4616 4617 noresume [SWSUSP] Disables resume and restores original swap 4618 space. 4619 4620 no-scroll [VGA] Disables scrollback. 4621 This is required for the Braillex ib80-piezo Braille 4622 reader made by F.H. Papenmeier (Germany). 4623 4624 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4625 4626 nosmap [PPC,EARLY] 4627 Disable SMAP (Supervisor Mode Access Prevention) 4628 even if it is supported by processor. 4629 4630 nosmep [PPC64s,EARLY] 4631 Disable SMEP (Supervisor Mode Execution Prevention) 4632 even if it is supported by processor. 4633 4634 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4635 and disable the IO APIC. legacy for "maxcpus=0". 4636 4637 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4638 Equivalent to smt=1. 4639 4640 [KNL,LOONGARCH,X86,ARM64,PPC,S390] Disable symmetric multithreading (SMT). 4641 nosmt=force: Force disable SMT, cannot be undone 4642 via the sysfs control file. 4643 4644 nosoftlockup [KNL] Disable the soft-lockup detector. 4645 4646 nospec_store_bypass_disable 4647 [HW,EARLY] Disable all mitigations for the Speculative 4648 Store Bypass vulnerability 4649 4650 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4651 history injection) vulnerability. System may allow data leaks 4652 with this option. 4653 4654 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4655 (bounds check bypass). With this option data leaks are 4656 possible in the system. 4657 4658 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4659 for the Spectre variant 2 (indirect branch 4660 prediction) vulnerability. System may allow data 4661 leaks with this option. 4662 4663 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4664 Disable paravirtualized steal time accounting. steal time 4665 is computed, but won't influence scheduler behaviour 4666 4667 nosync [HW,M68K] Disables sync negotiation for all devices. 4668 4669 no_timer_check [X86,APIC] Disables the code which tests for broken 4670 timer IRQ sources, i.e., the IO-APIC timer. This can 4671 work around problems with incorrect timer 4672 initialization on some boards. 4673 4674 no_uaccess_flush 4675 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4676 4677 novmcoredd [KNL,KDUMP] 4678 Disable device dump. Device dump allows drivers to 4679 append dump data to vmcore so you can collect driver 4680 specified debug info. Drivers can append the data 4681 without any limit and this data is stored in memory, 4682 so this may cause significant memory stress. Disabling 4683 device dump can help save memory but the driver debug 4684 data will be no longer available. This parameter 4685 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4686 is set. 4687 4688 no-vmw-sched-clock 4689 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4690 scheduler clock and use the default one. 4691 4692 nowatchdog [KNL] Disable both lockup detectors, i.e. 4693 soft-lockup and NMI watchdog (hard-lockup). 4694 4695 nowb [ARM,EARLY] 4696 4697 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4698 4699 NOTE: this parameter will be ignored on systems with the 4700 LEGACY_XAPIC_DISABLED bit set in the 4701 IA32_XAPIC_DISABLE_STATUS MSR. 4702 4703 noxsave [BUGS=X86] Disables x86 extended register state save 4704 and restore using xsave. The kernel will fallback to 4705 enabling legacy floating-point and sse state. 4706 4707 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4708 register states. The kernel will fall back to use 4709 xsave to save the states. By using this parameter, 4710 performance of saving the states is degraded because 4711 xsave doesn't support modified optimization while 4712 xsaveopt supports it on xsaveopt enabled systems. 4713 4714 noxsaves [X86] Disables xsaves and xrstors used in saving and 4715 restoring x86 extended register state in compacted 4716 form of xsave area. The kernel will fall back to use 4717 xsaveopt and xrstor to save and restore the states 4718 in standard form of xsave area. By using this 4719 parameter, xsave area per process might occupy more 4720 memory on xsaves enabled systems. 4721 4722 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4723 could support. nr_cpus=n : n >= 1 limits the kernel to 4724 support 'n' processors. It could be larger than the 4725 number of already plugged CPU during bootup, later in 4726 runtime you can physically add extra cpu until it reaches 4727 n. So during boot up some boot time memory for per-cpu 4728 variables need be pre-allocated for later physical cpu 4729 hot plugging. 4730 4731 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4732 4733 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4734 Disable NUMA, Only set up a single NUMA node 4735 spanning all memory. 4736 4737 numa=fake=<size>[MG] 4738 [KNL, ARM64, RISCV, X86, EARLY] 4739 If given as a memory unit, fills all system RAM with 4740 nodes of size interleaved over physical nodes. 4741 4742 numa=fake=<N> 4743 [KNL, ARM64, RISCV, X86, EARLY] 4744 If given as an integer, fills all system RAM with N 4745 fake nodes interleaved over physical nodes. 4746 4747 numa=fake=<N>U 4748 [KNL, ARM64, RISCV, X86, EARLY] 4749 If given as an integer followed by 'U', it will 4750 divide each physical node into N emulated nodes. 4751 4752 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4753 4754 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4755 soft-reserved memory partitioning. 4756 4757 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4758 NUMA balancing. 4759 Allowed values are enable and disable 4760 4761 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4762 'node', 'default' can be specified 4763 This can be set from sysctl after boot. 4764 See Documentation/admin-guide/sysctl/vm.rst for details. 4765 4766 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4767 nvme quirk list. List entries are separated by a 4768 '-' character. 4769 Each entry has the form VendorID:ProductID:quirk_names. 4770 The IDs are 4-digits hex numbers and quirk_names is a 4771 list of quirk names separated by commas. A quirk name 4772 can be prefixed by '^', meaning that the specified 4773 quirk must be disabled. 4774 4775 Example: 4776 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4777 4778 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4779 See Documentation/core-api/debugging-via-ohci1394.rst for more 4780 info. 4781 4782 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4783 Rather than timing out after 20 ms if an EC 4784 command is not properly ACKed, override the length 4785 of the timeout. We have interrupts disabled while 4786 waiting for the ACK, so if this is set too high 4787 interrupts *may* be lost! 4788 4789 omap_mux= [OMAP] Override bootloader pin multiplexing. 4790 Format: <mux_mode0.mode_name=value>... 4791 For example, to override I2C bus2: 4792 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4793 4794 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4795 4796 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4797 4798 boundary - index of last SLC block on Flex-OneNAND. 4799 The remaining blocks are configured as MLC blocks. 4800 lock - Configure if Flex-OneNAND boundary should be locked. 4801 Once locked, the boundary cannot be changed. 4802 1 indicates lock status, 0 indicates unlock status. 4803 4804 oops=panic [KNL,EARLY] 4805 Always panic on oopses. Default is to just kill the 4806 process, but there is a small probability of 4807 deadlocking the machine. 4808 This will also cause panics on machine check exceptions. 4809 Useful together with panic=30 to trigger a reboot. 4810 4811 page_alloc.shuffle= 4812 [KNL] Boolean flag to control whether the page allocator 4813 should randomize its free lists. This parameter can be 4814 used to enable/disable page randomization. The state of 4815 the flag can be read from sysfs at: 4816 /sys/module/page_alloc/parameters/shuffle. 4817 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4818 4819 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4820 Storage of the information about who allocated 4821 each page is disabled in default. With this switch, 4822 we can turn it on. 4823 on: enable the feature 4824 4825 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4826 poisoning on the buddy allocator, available with 4827 CONFIG_PAGE_POISONING=y. 4828 off: turn off poisoning (default) 4829 on: turn on poisoning 4830 4831 page_reporting.page_reporting_order= 4832 [KNL] Minimal page reporting order 4833 Format: <integer> 4834 Adjust the minimal page reporting order. The page 4835 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4836 4837 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4838 timeout > 0: seconds before rebooting 4839 timeout = 0: wait forever 4840 timeout < 0: reboot immediately 4841 Format: <timeout> 4842 4843 panic_on_taint= [KNL,EARLY] 4844 Bitmask for conditionally calling panic() in add_taint() 4845 Format: <hex>[,nousertaint] 4846 Hexadecimal bitmask representing the set of TAINT flags 4847 that will cause the kernel to panic when add_taint() is 4848 called with any of the flags in this set. 4849 The optional switch "nousertaint" can be utilized to 4850 prevent userspace forced crashes by writing to sysctl 4851 /proc/sys/kernel/tainted any flagset matching with the 4852 bitmask set on panic_on_taint. 4853 See Documentation/admin-guide/tainted-kernels.rst for 4854 extra details on the taint flags that users can pick 4855 to compose the bitmask to assign to panic_on_taint. 4856 4857 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4858 on a WARN(). 4859 4860 panic_force_cpu= 4861 [KNL,SMP] Force panic handling to execute on a specific CPU. 4862 Format: <cpu number> 4863 Some platforms require panic handling to occur on a 4864 specific CPU for the crash kernel to function correctly. 4865 This can be due to firmware limitations, interrupt routing 4866 constraints, or platform-specific requirements where only 4867 a particular CPU can safely enter the crash kernel. 4868 When set, panic() will redirect execution to the specified 4869 CPU before proceeding with the normal panic and kexec flow. 4870 If the target CPU is offline or unavailable, panic proceeds 4871 on the current CPU. 4872 This option should only be used for systems with the above 4873 constraints as it might cause the panic operation to be less reliable. 4874 4875 panic_print= Bitmask for printing system info when panic happens. 4876 User can chose combination of the following bits: 4877 bit 0: print all tasks info 4878 bit 1: print system memory info 4879 bit 2: print timer info 4880 bit 3: print locks info if CONFIG_LOCKDEP is on 4881 bit 4: print ftrace buffer 4882 bit 5: replay all kernel messages on consoles at the end of panic 4883 bit 6: print all CPUs backtrace (if available in the arch) 4884 bit 7: print only tasks in uninterruptible (blocked) state 4885 *Be aware* that this option may print a _lot_ of lines, 4886 so there are risks of losing older messages in the log. 4887 Use this option carefully, maybe worth to setup a 4888 bigger log buffer with "log_buf_len" along with this. 4889 4890 panic_sys_info= A comma separated list of extra information to be dumped 4891 on panic. 4892 Format: val[,val...] 4893 Where @val can be any of the following: 4894 4895 tasks: print all tasks info 4896 mem: print system memory info 4897 timers: print timers info 4898 locks: print locks info if CONFIG_LOCKDEP is on 4899 ftrace: print ftrace buffer 4900 all_bt: print all CPUs backtrace (if available in the arch) 4901 blocked_tasks: print only tasks in uninterruptible (blocked) state 4902 4903 This is a human readable alternative to the 'panic_print' option. 4904 4905 panic_console_replay 4906 When panic happens, replay all kernel messages on 4907 consoles at the end of panic. 4908 4909 parkbd.port= [HW] Parallel port number the keyboard adapter is 4910 connected to, default is 0. 4911 Format: <parport#> 4912 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4913 0 for XT, 1 for AT (default is AT). 4914 Format: <mode> 4915 4916 parport= [HW,PPT] Specify parallel ports. 0 disables. 4917 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4918 Use 'auto' to force the driver to use any 4919 IRQ/DMA settings detected (the default is to 4920 ignore detected IRQ/DMA settings because of 4921 possible conflicts). You can specify the base 4922 address, IRQ, and DMA settings; IRQ and DMA 4923 should be numbers, or 'auto' (for using detected 4924 settings on that particular port), or 'nofifo' 4925 (to avoid using a FIFO even if it is detected). 4926 Parallel ports are assigned in the order they 4927 are specified on the command line, starting 4928 with parport0. 4929 4930 parport_init_mode= [HW,PPT] 4931 Configure VIA parallel port to operate in 4932 a specific mode. This is necessary on Pegasos 4933 computer where firmware has no options for setting 4934 up parallel port mode and sets it to spp. 4935 Currently this function knows 686a and 8231 chips. 4936 Format: [spp|ps2|epp|ecp|ecpepp] 4937 4938 pata_legacy.all= [HW,LIBATA] 4939 Format: <int> 4940 Set to non-zero to probe primary and secondary ISA 4941 port ranges on PCI systems where no PCI PATA device 4942 has been found at either range. Disabled by default. 4943 4944 pata_legacy.autospeed= [HW,LIBATA] 4945 Format: <int> 4946 Set to non-zero if a chip is present that snoops speed 4947 changes. Disabled by default. 4948 4949 pata_legacy.ht6560a= [HW,LIBATA] 4950 Format: <int> 4951 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4952 the secondary channel, or both channels respectively. 4953 Disabled by default. 4954 4955 pata_legacy.ht6560b= [HW,LIBATA] 4956 Format: <int> 4957 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4958 the secondary channel, or both channels respectively. 4959 Disabled by default. 4960 4961 pata_legacy.iordy_mask= [HW,LIBATA] 4962 Format: <int> 4963 IORDY enable mask. Set individual bits to allow IORDY 4964 for the respective channel. Bit 0 is for the first 4965 legacy channel handled by this driver, bit 1 is for 4966 the second channel, and so on. The sequence will often 4967 correspond to the primary legacy channel, the secondary 4968 legacy channel, and so on, but the handling of a PCI 4969 bus and the use of other driver options may interfere 4970 with the sequence. By default IORDY is allowed across 4971 all channels. 4972 4973 pata_legacy.opti82c46x= [HW,LIBATA] 4974 Format: <int> 4975 Set to 1, 2, or 3 for Opti 82c611A on the primary 4976 channel, the secondary channel, or both channels 4977 respectively. Disabled by default. 4978 4979 pata_legacy.opti82c611a= [HW,LIBATA] 4980 Format: <int> 4981 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4982 channel, the secondary channel, or both channels 4983 respectively. Disabled by default. 4984 4985 pata_legacy.pio_mask= [HW,LIBATA] 4986 Format: <int> 4987 PIO mode mask for autospeed devices. Set individual 4988 bits to allow the use of the respective PIO modes. 4989 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4990 All modes allowed by default. 4991 4992 pata_legacy.probe_all= [HW,LIBATA] 4993 Format: <int> 4994 Set to non-zero to probe tertiary and further ISA 4995 port ranges on PCI systems. Disabled by default. 4996 4997 pata_legacy.probe_mask= [HW,LIBATA] 4998 Format: <int> 4999 Probe mask for legacy ISA PATA ports. Depending on 5000 platform configuration and the use of other driver 5001 options up to 6 legacy ports are supported: 0x1f0, 5002 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5003 of individual ports can be disabled by setting the 5004 corresponding bits in the mask to 1. Bit 0 is for 5005 the first port in the list above (0x1f0), and so on. 5006 By default all supported ports are probed. 5007 5008 pata_legacy.qdi= [HW,LIBATA] 5009 Format: <int> 5010 Set to non-zero to probe QDI controllers. By default 5011 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5012 5013 pata_legacy.winbond= [HW,LIBATA] 5014 Format: <int> 5015 Set to non-zero to probe Winbond controllers. Use 5016 the standard I/O port (0x130) if 1, otherwise the 5017 value given is the I/O port to use (typically 0x1b0). 5018 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5019 0 otherwise. 5020 5021 pata_platform.pio_mask= [HW,LIBATA] 5022 Format: <int> 5023 Supported PIO mode mask. Set individual bits to allow 5024 the use of the respective PIO modes. Bit 0 is for 5025 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5026 allowed by default. 5027 5028 pause_on_oops=<int> 5029 Halt all CPUs after the first oops has been printed for 5030 the specified number of seconds. This is to be used if 5031 your oopses keep scrolling off the screen. 5032 5033 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5034 5035 Some options herein operate on a specific device 5036 or a set of devices (<pci_dev>). These are 5037 specified in one of the following formats: 5038 5039 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5040 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5041 5042 Note: the first format specifies a PCI 5043 bus/device/function address which may change 5044 if new hardware is inserted, if motherboard 5045 firmware changes, or due to changes caused 5046 by other kernel parameters. If the 5047 domain is left unspecified, it is 5048 taken to be zero. Optionally, a path 5049 to a device through multiple device/function 5050 addresses can be specified after the base 5051 address (this is more robust against 5052 renumbering issues). The second format 5053 selects devices using IDs from the 5054 configuration space which may match multiple 5055 devices in the system. 5056 5057 earlydump dump PCI config space before the kernel 5058 changes anything 5059 off [X86] don't probe for the PCI bus 5060 bios [X86-32] force use of PCI BIOS, don't access 5061 the hardware directly. Use this if your machine 5062 has a non-standard PCI host bridge. 5063 nobios [X86-32] disallow use of PCI BIOS, only direct 5064 hardware access methods are allowed. Use this 5065 if you experience crashes upon bootup and you 5066 suspect they are caused by the BIOS. 5067 conf1 [X86] Force use of PCI Configuration Access 5068 Mechanism 1 (config address in IO port 0xCF8, 5069 data in IO port 0xCFC, both 32-bit). 5070 conf2 [X86] Force use of PCI Configuration Access 5071 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5072 the function, IO port 0xCFA, also 8-bit, sets 5073 bus number. The config space is then accessed 5074 through ports 0xC000-0xCFFF). 5075 See http://wiki.osdev.org/PCI for more info 5076 on the configuration access mechanisms. 5077 noaer [PCIE] If the PCIEAER kernel config parameter is 5078 enabled, this kernel boot option can be used to 5079 disable the use of PCIE advanced error reporting. 5080 nodomains [PCI] Disable support for multiple PCI 5081 root domains (aka PCI segments, in ACPI-speak). 5082 nommconf [X86] Disable use of MMCONFIG for PCI 5083 Configuration 5084 check_enable_amd_mmconf [X86] check for and enable 5085 properly configured MMIO access to PCI 5086 config space on AMD family 10h CPU 5087 nomsi [MSI] If the PCI_MSI kernel config parameter is 5088 enabled, this kernel boot option can be used to 5089 disable the use of MSI interrupts system-wide. 5090 noioapicquirk [APIC] Disable all boot interrupt quirks. 5091 Safety option to keep boot IRQs enabled. This 5092 should never be necessary. 5093 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5094 primary IO-APIC for bridges that cannot disable 5095 boot IRQs. This fixes a source of spurious IRQs 5096 when the system masks IRQs. 5097 noioapicreroute [APIC] Disable workaround that uses the 5098 boot IRQ equivalent of an IRQ that connects to 5099 a chipset where boot IRQs cannot be disabled. 5100 The opposite of ioapicreroute. 5101 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5102 routing table. These calls are known to be buggy 5103 on several machines and they hang the machine 5104 when used, but on other computers it's the only 5105 way to get the interrupt routing table. Try 5106 this option if the kernel is unable to allocate 5107 IRQs or discover secondary PCI buses on your 5108 motherboard. 5109 rom [X86] Assign address space to expansion ROMs. 5110 Use with caution as certain devices share 5111 address decoders between ROMs and other 5112 resources. 5113 norom [X86] Do not assign address space to 5114 expansion ROMs that do not already have 5115 BIOS assigned address ranges. 5116 nobar [X86] Do not assign address space to the 5117 BARs that weren't assigned by the BIOS. 5118 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5119 assigned automatically to PCI devices. You can 5120 make the kernel exclude IRQs of your ISA cards 5121 this way. 5122 pirqaddr=0xAAAAA [X86] Specify the physical address 5123 of the PIRQ table (normally generated 5124 by the BIOS) if it is outside the 5125 F0000h-100000h range. 5126 lastbus=N [X86] Scan all buses thru bus #N. Can be 5127 useful if the kernel is unable to find your 5128 secondary buses and you want to tell it 5129 explicitly which ones they are. 5130 assign-busses [X86] Always assign all PCI bus 5131 numbers ourselves, overriding 5132 whatever the firmware may have done. 5133 usepirqmask [X86] Honor the possible IRQ mask stored 5134 in the BIOS $PIR table. This is needed on 5135 some systems with broken BIOSes, notably 5136 some HP Pavilion N5400 and Omnibook XE3 5137 notebooks. This will have no effect if ACPI 5138 IRQ routing is enabled. 5139 noacpi [X86] Do not use ACPI for IRQ routing 5140 or for PCI scanning. 5141 use_crs [X86] Use PCI host bridge window information 5142 from ACPI. On BIOSes from 2008 or later, this 5143 is enabled by default. If you need to use this, 5144 please report a bug. 5145 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5146 If you need to use this, please report a bug. 5147 use_e820 [X86] Use E820 reservations to exclude parts of 5148 PCI host bridge windows. This is a workaround 5149 for BIOS defects in host bridge _CRS methods. 5150 If you need to use this, please report a bug to 5151 <linux-pci@vger.kernel.org>. 5152 no_e820 [X86] Ignore E820 reservations for PCI host 5153 bridge windows. This is the default on modern 5154 hardware. If you need to use this, please report 5155 a bug to <linux-pci@vger.kernel.org>. 5156 routeirq Do IRQ routing for all PCI devices. 5157 This is normally done in pci_enable_device(), 5158 so this option is a temporary workaround 5159 for broken drivers that don't call it. 5160 skip_isa_align [X86] do not align io start addr, so can 5161 handle more pci cards 5162 noearly [X86] Don't do any early type 1 scanning. 5163 This might help on some broken boards which 5164 machine check when some devices' config space 5165 is read. But various workarounds are disabled 5166 and some IOMMU drivers will not work. 5167 bfsort Sort PCI devices into breadth-first order. 5168 This sorting is done to get a device 5169 order compatible with older (<= 2.4) kernels. 5170 nobfsort Don't sort PCI devices into breadth-first order. 5171 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5172 tuning and use the BIOS-configured MPS defaults. 5173 pcie_bus_safe Set every device's MPS to the largest value 5174 supported by all devices below the root complex. 5175 pcie_bus_perf Set device MPS to the largest allowable MPS 5176 based on its parent bus. Also set MRRS (Max 5177 Read Request Size) to the largest supported 5178 value (no larger than the MPS that the device 5179 or bus can support) for best performance. 5180 pcie_bus_peer2peer Set every device's MPS to 128B, which 5181 every device is guaranteed to support. This 5182 configuration allows peer-to-peer DMA between 5183 any pair of devices, possibly at the cost of 5184 reduced performance. This also guarantees 5185 that hot-added devices will work. 5186 cbiosize=nn[KMG] The fixed amount of bus space which is 5187 reserved for the CardBus bridge's IO window. 5188 The default value is 256 bytes. 5189 cbmemsize=nn[KMG] The fixed amount of bus space which is 5190 reserved for the CardBus bridge's memory 5191 window. The default value is 64 megabytes. 5192 resource_alignment= 5193 Format: 5194 [<order of align>@]<pci_dev>[; ...] 5195 Specifies alignment and device to reassign 5196 aligned memory resources. How to 5197 specify the device is described above. 5198 If <order of align> is not specified, 5199 PAGE_SIZE is used as alignment. 5200 A PCI-PCI bridge can be specified if resource 5201 windows need to be expanded. 5202 To specify the alignment for several 5203 instances of a device, the PCI vendor, 5204 device, subvendor, and subdevice may be 5205 specified, e.g., 12@pci:8086:9c22:103c:198f 5206 for 4096-byte alignment. 5207 ecrc= Enable/disable PCIe ECRC (transaction layer 5208 end-to-end CRC checking). Only effective if 5209 OS has native AER control (either granted by 5210 ACPI _OSC or forced via "pcie_ports=native") 5211 bios: Use BIOS/firmware settings. This is the 5212 the default. 5213 off: Turn ECRC off 5214 on: Turn ECRC on. 5215 hpiosize=nn[KMG] The fixed amount of bus space which is 5216 reserved for hotplug bridge's IO window. 5217 Default size is 256 bytes. 5218 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5219 reserved for hotplug bridge's MMIO window. 5220 Default size is 2 megabytes. 5221 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5222 reserved for hotplug bridge's MMIO_PREF window. 5223 Default size is 2 megabytes. 5224 hpmemsize=nn[KMG] The fixed amount of bus space which is 5225 reserved for hotplug bridge's MMIO and 5226 MMIO_PREF window. 5227 Default size is 2 megabytes. 5228 hpbussize=nn The minimum amount of additional bus numbers 5229 reserved for buses below a hotplug bridge. 5230 Default is 1. 5231 realloc= Enable/disable reallocating PCI bridge resources 5232 if allocations done by BIOS are too small to 5233 accommodate resources required by all child 5234 devices. 5235 off: Turn realloc off 5236 on: Turn realloc on 5237 realloc same as realloc=on 5238 noari do not use PCIe ARI. 5239 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5240 do not use PCIe ATS (and IOMMU device IOTLB). 5241 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5242 only look for one device below a PCIe downstream 5243 port. 5244 big_root_window Try to add a big 64bit memory window to the PCIe 5245 root complex on AMD CPUs. Some GFX hardware 5246 can resize a BAR to allow access to all VRAM. 5247 Adding the window is slightly risky (it may 5248 conflict with unreported devices), so this 5249 taints the kernel. 5250 disable_acs_redir=<pci_dev>[; ...] 5251 Specify one or more PCI devices (in the format 5252 specified above) separated by semicolons. 5253 Each device specified will have the PCI ACS 5254 redirect capabilities forced off which will 5255 allow P2P traffic between devices through 5256 bridges without forcing it upstream. Note: 5257 this removes isolation between devices and 5258 may put more devices in an IOMMU group. 5259 config_acs= 5260 Format: 5261 <ACS flags>@<pci_dev>[; ...] 5262 Specify one or more PCI devices (in the format 5263 specified above) optionally prepended with flags 5264 and separated by semicolons. The respective 5265 capabilities will be enabled, disabled or 5266 unchanged based on what is specified in 5267 flags. 5268 5269 ACS Flags is defined as follows: 5270 bit-0 : ACS Source Validation 5271 bit-1 : ACS Translation Blocking 5272 bit-2 : ACS P2P Request Redirect 5273 bit-3 : ACS P2P Completion Redirect 5274 bit-4 : ACS Upstream Forwarding 5275 bit-5 : ACS P2P Egress Control 5276 bit-6 : ACS Direct Translated P2P 5277 Each bit can be marked as: 5278 '0' – force disabled 5279 '1' – force enabled 5280 'x' – unchanged 5281 For example, 5282 pci=config_acs=10x@pci:0:0 5283 would configure all devices that support 5284 ACS to enable P2P Request Redirect, disable 5285 Translation Blocking, and leave Source 5286 Validation unchanged from whatever power-up 5287 or firmware set it to. 5288 5289 Note: this may remove isolation between devices 5290 and may put more devices in an IOMMU group. 5291 force_floating [S390] Force usage of floating interrupts. 5292 nomio [S390] Do not use MIO instructions. 5293 norid [S390] ignore the RID field and force use of 5294 one PCI domain per PCI function 5295 notph [PCIE] If the PCIE_TPH kernel config parameter 5296 is enabled, this kernel boot option can be used 5297 to disable PCIe TLP Processing Hints support 5298 system-wide. 5299 5300 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5301 Management. 5302 off Don't touch ASPM configuration at all. Leave any 5303 configuration done by firmware unchanged. 5304 force Enable ASPM even on devices that claim not to support it. 5305 WARNING: Forcing ASPM on may cause system lockups. 5306 5307 pcie_ports= [PCIE] PCIe port services handling: 5308 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5309 even if the platform doesn't give the OS permission to 5310 use them. This may cause conflicts if the platform 5311 also tries to use these services. 5312 dpc-native Use native PCIe service for DPC only. May 5313 cause conflicts if firmware uses AER or DPC. 5314 compat Disable native PCIe services (PME, AER, DPC, PCIe 5315 hotplug). 5316 5317 pcie_port_pm= [PCIE] PCIe port power management handling: 5318 off Disable power management of all PCIe ports 5319 force Forcibly enable power management of all PCIe ports 5320 5321 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5322 nomsi Do not use MSI for native PCIe PME signaling (this makes 5323 all PCIe root ports use INTx for all services). 5324 5325 pcmv= [HW,PCMCIA] BadgePAD 4 5326 5327 pd_ignore_unused 5328 [PM] 5329 Keep all power-domains already enabled by bootloader on, 5330 even if no driver has claimed them. This is useful 5331 for debug and development, but should not be 5332 needed on a platform with proper driver support. 5333 5334 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5335 boot time. 5336 Format: { 0 | 1 } 5337 See arch/parisc/kernel/pdc_chassis.c 5338 5339 percpu_alloc= [MM,EARLY] 5340 Select which percpu first chunk allocator to use. 5341 Currently supported values are "embed" and "page". 5342 Archs may support subset or none of the selections. 5343 See comments in mm/percpu.c for details on each 5344 allocator. This parameter is primarily for debugging 5345 and performance comparison. 5346 5347 pirq= [SMP,APIC] Manual mp-table setup 5348 See Documentation/arch/x86/i386/IO-APIC.rst. 5349 5350 plip= [PPT,NET] Parallel port network link 5351 Format: { parport<nr> | timid | 0 } 5352 See also Documentation/admin-guide/parport.rst. 5353 5354 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5355 Override pmtimer IOPort with a hex value. 5356 e.g. pmtmr=0x508 5357 5358 pmu_override= [PPC] Override the PMU. 5359 This option takes over the PMU facility, so it is no 5360 longer usable by perf. Setting this option starts the 5361 PMU counters by setting MMCR0 to 0 (the FC bit is 5362 cleared). If a number is given, then MMCR1 is set to 5363 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5364 remains 0. 5365 5366 pm_async= [PM] 5367 Format: off 5368 This parameter sets the initial value of the 5369 /sys/power/pm_async sysfs knob at boot time. 5370 If set to "off", disables asynchronous suspend and 5371 resume of devices during system-wide power transitions. 5372 This can be useful on platforms where device 5373 dependencies are not well-defined, or for debugging 5374 power management issues. Asynchronous operations are 5375 enabled by default. 5376 5377 5378 pm_debug_messages [SUSPEND,KNL] 5379 Enable suspend/resume debug messages during boot up. 5380 5381 pm.dpm_watchdog_enabled= 5382 [PM] Enable or disable the DPM watchdog. Requires 5383 CONFIG_PM_SLEEP and CONFIG_DPM_WATCHDOG enabled. 5384 Format: <bool> 5385 Default value is set by CONFIG_DPM_WATCHDOG_ENABLED. 5386 5387 pnp.debug=1 [PNP] 5388 Enable PNP debug messages (depends on the 5389 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5390 via /sys/module/pnp/parameters/debug. We always show 5391 current resource usage; turning this on also shows 5392 possible settings and some assignment information. 5393 5394 pnpacpi= [ACPI] 5395 { off } 5396 5397 pnpbios= [ISAPNP] 5398 { on | off | curr | res | no-curr | no-res } 5399 5400 pnp_reserve_irq= 5401 [ISAPNP] Exclude IRQs for the autoconfiguration 5402 5403 pnp_reserve_dma= 5404 [ISAPNP] Exclude DMAs for the autoconfiguration 5405 5406 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5407 Ranges are in pairs (I/O port base and size). 5408 5409 pnp_reserve_mem= 5410 [ISAPNP] Exclude memory regions for the 5411 autoconfiguration. 5412 Ranges are in pairs (memory base and size). 5413 5414 ports= [IP_VS_FTP] IPVS ftp helper module 5415 Default is 21. 5416 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5417 may be specified. 5418 Format: <port>,<port>.... 5419 5420 possible_cpus= [SMP,S390,X86] 5421 Format: <unsigned int> 5422 Set the number of possible CPUs, overriding the 5423 regular discovery mechanisms (such as ACPI/FW, etc). 5424 5425 powersave=off [PPC] This option disables power saving features. 5426 It specifically disables cpuidle and sets the 5427 platform machine description specific power_save 5428 function to NULL. On Idle the CPU just reduces 5429 execution priority. 5430 5431 ppc_strict_facility_enable 5432 [PPC,ENABLE] This option catches any kernel floating point, 5433 Altivec, VSX and SPE outside of regions specifically 5434 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5435 There is some performance impact when enabling this. 5436 5437 ppc_tm= [PPC,EARLY] 5438 Format: {"off"} 5439 Disable Hardware Transactional Memory 5440 5441 preempt= [KNL] 5442 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5443 none - Limited to cond_resched() calls 5444 voluntary - Limited to cond_resched() and might_sleep() calls 5445 full - Any section that isn't explicitly preempt disabled 5446 can be preempted anytime. Tasks will also yield 5447 contended spinlocks (if the critical section isn't 5448 explicitly preempt disabled beyond the lock itself). 5449 lazy - Scheduler controlled. Similar to full but instead 5450 of preempting the task immediately, the task gets 5451 one HZ tick time to yield itself before the 5452 preemption will be forced. One preemption is when the 5453 task returns to user space. 5454 5455 print-fatal-signals= 5456 [KNL] debug: print fatal signals 5457 5458 If enabled, warn about various signal handling 5459 related application anomalies: too many signals, 5460 too many POSIX.1 timers, fatal signals causing a 5461 coredump - etc. 5462 5463 If you hit the warning due to signal overflow, 5464 you might want to try "ulimit -i unlimited". 5465 5466 default: off. 5467 5468 printk.always_kmsg_dump= 5469 Trigger kmsg_dump for cases other than kernel oops or 5470 panics 5471 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5472 default: disabled 5473 5474 printk.console_no_auto_verbose= 5475 Disable console loglevel raise on oops, panic 5476 or lockdep-detected issues (only if lock debug is on). 5477 With an exception to setups with low baudrate on 5478 serial console, keeping this 0 is a good choice 5479 in order to provide more debug information. 5480 Format: <bool> 5481 default: 0 (auto_verbose is enabled) 5482 5483 printk.debug_non_panic_cpus= 5484 Allows storing messages from non-panic CPUs into 5485 the printk log buffer during panic(). They are 5486 flushed to consoles by the panic-CPU on 5487 a best-effort basis. 5488 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5489 Default: disabled 5490 5491 printk.devkmsg={on,off,ratelimit} 5492 Control writing to /dev/kmsg. 5493 on - unlimited logging to /dev/kmsg from userspace 5494 off - logging to /dev/kmsg disabled 5495 ratelimit - ratelimit the logging 5496 Default: ratelimit 5497 5498 printk.time= Show timing data prefixed to each printk message line 5499 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5500 5501 proc_mem.force_override= [KNL] 5502 Format: {always | ptrace | never} 5503 Traditionally /proc/pid/mem allows memory permissions to be 5504 overridden without restrictions. This option may be set to 5505 restrict that. Can be one of: 5506 - 'always': traditional behavior always allows mem overrides. 5507 - 'ptrace': only allow mem overrides for active ptracers. 5508 - 'never': never allow mem overrides. 5509 If not specified, default is the CONFIG_PROC_MEM_* choice. 5510 5511 processor.max_cstate= [HW,ACPI] 5512 Limit processor to maximum C-state 5513 max_cstate=9 overrides any DMI blacklist limit. 5514 5515 processor.nocst [HW,ACPI] 5516 Ignore the _CST method to determine C-states, 5517 instead using the legacy FADT method 5518 5519 profile= [KNL] Enable kernel profiling via /proc/profile 5520 Format: [<profiletype>,]<number> 5521 Param: <profiletype>: "schedule" or "kvm" 5522 [defaults to kernel profiling] 5523 Param: "schedule" - profile schedule points. 5524 Param: "kvm" - profile VM exits. 5525 Param: <number> - step/bucket size as a power of 2 for 5526 statistical time based profiling. 5527 5528 prot_virt= [S390] enable hosting protected virtual machines 5529 isolated from the hypervisor (if hardware supports 5530 that). If enabled, the default kernel base address 5531 might be overridden even when Kernel Address Space 5532 Layout Randomization is disabled. 5533 Format: <bool> 5534 5535 psi= [KNL] Enable or disable pressure stall information 5536 tracking. 5537 Format: <bool> 5538 5539 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5540 probe for; one of (bare|imps|exps|lifebook|any). 5541 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5542 per second. 5543 psmouse.resetafter= [HW,MOUSE] 5544 Try to reset the device after so many bad packets 5545 (0 = never). 5546 psmouse.resolution= 5547 [HW,MOUSE] Set desired mouse resolution, in dpi. 5548 psmouse.smartscroll= 5549 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5550 0 = disabled, 1 = enabled (default). 5551 5552 pstore.backend= Specify the name of the pstore backend to use 5553 5554 pti= [X86-64] Control Page Table Isolation of user and 5555 kernel address spaces. Disabling this feature 5556 removes hardening, but improves performance of 5557 system calls and interrupts. 5558 5559 on - unconditionally enable 5560 off - unconditionally disable 5561 auto - kernel detects whether your CPU model is 5562 vulnerable to issues that PTI mitigates 5563 5564 Not specifying this option is equivalent to pti=auto. 5565 5566 pty.legacy_count= 5567 [KNL] Number of legacy pty's. Overwrites compiled-in 5568 default number. 5569 5570 quiet [KNL,EARLY] Disable most log messages 5571 5572 r128= [HW,DRM] 5573 5574 radix_hcall_invalidate=on [PPC/PSERIES] 5575 Disable RADIX GTSE feature and use hcall for TLB 5576 invalidate. 5577 5578 raid= [HW,RAID] 5579 See Documentation/admin-guide/md.rst. 5580 5581 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5582 See Documentation/admin-guide/blockdev/ramdisk.rst. 5583 5584 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5585 5586 random.trust_cpu=off 5587 [KNL,EARLY] Disable trusting the use of the CPU's 5588 random number generator (if available) to 5589 initialize the kernel's RNG. 5590 5591 random.trust_bootloader=off 5592 [KNL,EARLY] Disable trusting the use of the a seed 5593 passed by the bootloader (if available) to 5594 initialize the kernel's RNG. 5595 5596 randomize_kstack_offset= 5597 [KNL,EARLY] Enable or disable kernel stack offset 5598 randomization, which provides roughly 5 bits of 5599 entropy, frustrating memory corruption attacks 5600 that depend on stack address determinism or 5601 cross-syscall address exposures. This is only 5602 available on architectures that have defined 5603 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5604 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5605 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5606 5607 ras=option[,option,...] [KNL] RAS-specific options 5608 5609 cec_disable [X86] 5610 Disable the Correctable Errors Collector, 5611 see CONFIG_RAS_CEC help text. 5612 5613 rcu_nocbs[=cpu-list] 5614 [KNL] The optional argument is a cpu list, 5615 as described above. 5616 5617 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5618 enable the no-callback CPU mode, which prevents 5619 such CPUs' callbacks from being invoked in 5620 softirq context. Invocation of such CPUs' RCU 5621 callbacks will instead be offloaded to "rcuox/N" 5622 kthreads created for that purpose, where "x" is 5623 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5624 for the kthreads that mediate grace periods; and 5625 "N" is the CPU number. This reduces OS jitter on 5626 the offloaded CPUs, which can be useful for HPC 5627 and real-time workloads. It can also improve 5628 energy efficiency for asymmetric multiprocessors. 5629 5630 If a cpulist is passed as an argument, the specified 5631 list of CPUs is set to no-callback mode from boot. 5632 5633 Otherwise, if the '=' sign and the cpulist 5634 arguments are omitted, no CPU will be set to 5635 no-callback mode from boot but the mode may be 5636 toggled at runtime via cpusets. 5637 5638 Note that this argument takes precedence over 5639 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5640 5641 rcu_nocb_poll [KNL] 5642 Rather than requiring that offloaded CPUs 5643 (specified by rcu_nocbs= above) explicitly 5644 awaken the corresponding "rcuoN" kthreads, 5645 make these kthreads poll for callbacks. 5646 This improves the real-time response for the 5647 offloaded CPUs by relieving them of the need to 5648 wake up the corresponding kthread, but degrades 5649 energy efficiency by requiring that the kthreads 5650 periodically wake up to do the polling. 5651 5652 rcutree.blimit= [KNL] 5653 Set maximum number of finished RCU callbacks to 5654 process in one batch. 5655 5656 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5657 Do only a one-line RCU CPU stall warning when 5658 there is an ongoing too-long CSD-lock wait. 5659 5660 rcutree.do_rcu_barrier= [KNL] 5661 Request a call to rcu_barrier(). This is 5662 throttled so that userspace tests can safely 5663 hammer on the sysfs variable if they so choose. 5664 If triggered before the RCU grace-period machinery 5665 is fully active, this will error out with EAGAIN. 5666 5667 rcutree.dump_tree= [KNL] 5668 Dump the structure of the rcu_node combining tree 5669 out at early boot. This is used for diagnostic 5670 purposes, to verify correct tree setup. 5671 5672 rcutree.gp_cleanup_delay= [KNL] 5673 Set the number of jiffies to delay each step of 5674 RCU grace-period cleanup. 5675 5676 rcutree.gp_init_delay= [KNL] 5677 Set the number of jiffies to delay each step of 5678 RCU grace-period initialization. 5679 5680 rcutree.gp_preinit_delay= [KNL] 5681 Set the number of jiffies to delay each step of 5682 RCU grace-period pre-initialization, that is, 5683 the propagation of recent CPU-hotplug changes up 5684 the rcu_node combining tree. 5685 5686 rcutree.jiffies_till_first_fqs= [KNL] 5687 Set delay from grace-period initialization to 5688 first attempt to force quiescent states. 5689 Units are jiffies, minimum value is zero, 5690 and maximum value is HZ. 5691 5692 rcutree.jiffies_till_next_fqs= [KNL] 5693 Set delay between subsequent attempts to force 5694 quiescent states. Units are jiffies, minimum 5695 value is one, and maximum value is HZ. 5696 5697 rcutree.jiffies_till_sched_qs= [KNL] 5698 Set required age in jiffies for a 5699 given grace period before RCU starts 5700 soliciting quiescent-state help from 5701 rcu_note_context_switch() and cond_resched(). 5702 If not specified, the kernel will calculate 5703 a value based on the most recent settings 5704 of rcutree.jiffies_till_first_fqs 5705 and rcutree.jiffies_till_next_fqs. 5706 This calculated value may be viewed in 5707 rcutree.jiffies_to_sched_qs. Any attempt to set 5708 rcutree.jiffies_to_sched_qs will be cheerfully 5709 overwritten. 5710 5711 rcutree.kthread_prio= [KNL,BOOT] 5712 Set the SCHED_FIFO priority of the RCU per-CPU 5713 kthreads (rcuc/N). This value is also used for 5714 the priority of the RCU boost threads (rcub/N) 5715 and for the RCU grace-period kthreads (rcu_bh, 5716 rcu_preempt, and rcu_sched). If RCU_BOOST is 5717 set, valid values are 1-99 and the default is 1 5718 (the least-favored priority). Otherwise, when 5719 RCU_BOOST is not set, valid values are 0-99 and 5720 the default is zero (non-realtime operation). 5721 When RCU_NOCB_CPU is set, also adjust the 5722 priority of NOCB callback kthreads. 5723 5724 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5725 On callback-offloaded (rcu_nocbs) CPUs, 5726 RCU reduces the lock contention that would 5727 otherwise be caused by callback floods through 5728 use of the ->nocb_bypass list. However, in the 5729 common non-flooded case, RCU queues directly to 5730 the main ->cblist in order to avoid the extra 5731 overhead of the ->nocb_bypass list and its lock. 5732 But if there are too many callbacks queued during 5733 a single jiffy, RCU pre-queues the callbacks into 5734 the ->nocb_bypass queue. The definition of "too 5735 many" is supplied by this kernel boot parameter. 5736 5737 rcutree.nohz_full_patience_delay= [KNL] 5738 On callback-offloaded (rcu_nocbs) CPUs, avoid 5739 disturbing RCU unless the grace period has 5740 reached the specified age in milliseconds. 5741 Defaults to zero. Large values will be capped 5742 at five seconds. All values will be rounded down 5743 to the nearest value representable by jiffies. 5744 5745 rcutree.qhimark= [KNL] 5746 Set threshold of queued RCU callbacks beyond which 5747 batch limiting is disabled. 5748 5749 rcutree.qlowmark= [KNL] 5750 Set threshold of queued RCU callbacks below which 5751 batch limiting is re-enabled. 5752 5753 rcutree.qovld= [KNL] 5754 Set threshold of queued RCU callbacks beyond which 5755 RCU's force-quiescent-state scan will aggressively 5756 enlist help from cond_resched() and sched IPIs to 5757 help CPUs more quickly reach quiescent states. 5758 Set to less than zero to make this be set based 5759 on rcutree.qhimark at boot time and to zero to 5760 disable more aggressive help enlistment. 5761 5762 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5763 Set the page-cache refill delay (in milliseconds) 5764 in response to low-memory conditions. The range 5765 of permitted values is in the range 0:100000. 5766 5767 rcutree.rcu_divisor= [KNL] 5768 Set the shift-right count to use to compute 5769 the callback-invocation batch limit bl from 5770 the number of callbacks queued on this CPU. 5771 The result will be bounded below by the value of 5772 the rcutree.blimit kernel parameter. Every bl 5773 callbacks, the softirq handler will exit in 5774 order to allow the CPU to do other work. 5775 5776 Please note that this callback-invocation batch 5777 limit applies only to non-offloaded callback 5778 invocation. Offloaded callbacks are instead 5779 invoked in the context of an rcuoc kthread, which 5780 scheduler will preempt as it does any other task. 5781 5782 rcutree.rcu_fanout_exact= [KNL] 5783 Disable autobalancing of the rcu_node combining 5784 tree. This is used by rcutorture, and might 5785 possibly be useful for architectures having high 5786 cache-to-cache transfer latencies. 5787 5788 rcutree.rcu_fanout_leaf= [KNL] 5789 Change the number of CPUs assigned to each 5790 leaf rcu_node structure. Useful for very 5791 large systems, which will choose the value 64, 5792 and for NUMA systems with large remote-access 5793 latencies, which will choose a value aligned 5794 with the appropriate hardware boundaries. 5795 5796 rcutree.rcu_min_cached_objs= [KNL] 5797 Minimum number of objects which are cached and 5798 maintained per one CPU. Object size is equal 5799 to PAGE_SIZE. The cache allows to reduce the 5800 pressure to page allocator, also it makes the 5801 whole algorithm to behave better in low memory 5802 condition. 5803 5804 rcutree.rcu_nocb_gp_stride= [KNL] 5805 Set the number of NOCB callback kthreads in 5806 each group, which defaults to the square root 5807 of the number of CPUs. Larger numbers reduce 5808 the wakeup overhead on the global grace-period 5809 kthread, but increases that same overhead on 5810 each group's NOCB grace-period kthread. 5811 5812 rcutree.rcu_kick_kthreads= [KNL] 5813 Cause the grace-period kthread to get an extra 5814 wake_up() if it sleeps three times longer than 5815 it should at force-quiescent-state time. 5816 This wake_up() will be accompanied by a 5817 WARN_ONCE() splat and an ftrace_dump(). 5818 5819 rcutree.rcu_resched_ns= [KNL] 5820 Limit the time spend invoking a batch of RCU 5821 callbacks to the specified number of nanoseconds. 5822 By default, this limit is checked only once 5823 every 32 callbacks in order to limit the pain 5824 inflicted by local_clock() overhead. 5825 5826 rcutree.rcu_unlock_delay= [KNL] 5827 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5828 this specifies an rcu_read_unlock()-time delay 5829 in microseconds. This defaults to zero. 5830 Larger delays increase the probability of 5831 catching RCU pointer leaks, that is, buggy use 5832 of RCU-protected pointers after the relevant 5833 rcu_read_unlock() has completed. 5834 5835 rcutree.sysrq_rcu= [KNL] 5836 Commandeer a sysrq key to dump out Tree RCU's 5837 rcu_node tree with an eye towards determining 5838 why a new grace period has not yet started. 5839 5840 rcutree.use_softirq= [KNL] 5841 If set to zero, move all RCU_SOFTIRQ processing to 5842 per-CPU rcuc kthreads. Defaults to a non-zero 5843 value, meaning that RCU_SOFTIRQ is used by default. 5844 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5845 5846 But note that CONFIG_PREEMPT_RT=y kernels disable 5847 this kernel boot parameter, forcibly setting it 5848 to zero. 5849 5850 rcutree.enable_rcu_lazy= [KNL] 5851 To save power, batch RCU callbacks and flush after 5852 delay, memory pressure or callback list growing too 5853 big. 5854 5855 rcutree.rcu_normal_wake_from_gp= [KNL] 5856 Reduces a latency of synchronize_rcu() call. This approach 5857 maintains its own track of synchronize_rcu() callers, so it 5858 does not interact with regular callbacks because it does not 5859 use a call_rcu[_hurry]() path. Please note, this is for a 5860 normal grace period. 5861 5862 How to disable it: 5863 5864 echo 0 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5865 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=0" 5866 5867 Default is 1 if it is not explicitly disabled by the boot parameter 5868 passing 0. 5869 5870 rcuscale.gp_async= [KNL] 5871 Measure performance of asynchronous 5872 grace-period primitives such as call_rcu(). 5873 5874 rcuscale.gp_async_max= [KNL] 5875 Specify the maximum number of outstanding 5876 callbacks per writer thread. When a writer 5877 thread exceeds this limit, it invokes the 5878 corresponding flavor of rcu_barrier() to allow 5879 previously posted callbacks to drain. 5880 5881 rcuscale.gp_exp= [KNL] 5882 Measure performance of expedited synchronous 5883 grace-period primitives. 5884 5885 rcuscale.holdoff= [KNL] 5886 Set test-start holdoff period. The purpose of 5887 this parameter is to delay the start of the 5888 test until boot completes in order to avoid 5889 interference. 5890 5891 rcuscale.kfree_by_call_rcu= [KNL] 5892 In kernels built with CONFIG_RCU_LAZY=y, test 5893 call_rcu() instead of kfree_rcu(). 5894 5895 rcuscale.kfree_mult= [KNL] 5896 Instead of allocating an object of size kfree_obj, 5897 allocate one of kfree_mult * sizeof(kfree_obj). 5898 Defaults to 1. 5899 5900 rcuscale.kfree_rcu_test= [KNL] 5901 Set to measure performance of kfree_rcu() flooding. 5902 5903 rcuscale.kfree_rcu_test_double= [KNL] 5904 Test the double-argument variant of kfree_rcu(). 5905 If this parameter has the same value as 5906 rcuscale.kfree_rcu_test_single, both the single- 5907 and double-argument variants are tested. 5908 5909 rcuscale.kfree_rcu_test_single= [KNL] 5910 Test the single-argument variant of kfree_rcu(). 5911 If this parameter has the same value as 5912 rcuscale.kfree_rcu_test_double, both the single- 5913 and double-argument variants are tested. 5914 5915 rcuscale.kfree_nthreads= [KNL] 5916 The number of threads running loops of kfree_rcu(). 5917 5918 rcuscale.kfree_alloc_num= [KNL] 5919 Number of allocations and frees done in an iteration. 5920 5921 rcuscale.kfree_loops= [KNL] 5922 Number of loops doing rcuscale.kfree_alloc_num number 5923 of allocations and frees. 5924 5925 rcuscale.minruntime= [KNL] 5926 Set the minimum test run time in seconds. This 5927 does not affect the data-collection interval, 5928 but instead allows better measurement of things 5929 like CPU consumption. 5930 5931 rcuscale.nreaders= [KNL] 5932 Set number of RCU readers. The value -1 selects 5933 N, where N is the number of CPUs. A value 5934 "n" less than -1 selects N-n+1, where N is again 5935 the number of CPUs. For example, -2 selects N 5936 (the number of CPUs), -3 selects N+1, and so on. 5937 A value of "n" less than or equal to -N selects 5938 a single reader. 5939 5940 rcuscale.nwriters= [KNL] 5941 Set number of RCU writers. The values operate 5942 the same as for rcuscale.nreaders. 5943 N, where N is the number of CPUs 5944 5945 rcuscale.scale_type= [KNL] 5946 Specify the RCU implementation to test. 5947 5948 rcuscale.shutdown= [KNL] 5949 Shut the system down after performance tests 5950 complete. This is useful for hands-off automated 5951 testing. 5952 5953 rcuscale.verbose= [KNL] 5954 Enable additional printk() statements. 5955 5956 rcuscale.writer_holdoff= [KNL] 5957 Write-side holdoff between grace periods, 5958 in microseconds. The default of zero says 5959 no holdoff. 5960 5961 rcuscale.writer_holdoff_jiffies= [KNL] 5962 Additional write-side holdoff between grace 5963 periods, but in jiffies. The default of zero 5964 says no holdoff. 5965 5966 rcutorture.fqs_duration= [KNL] 5967 Set duration of force_quiescent_state bursts 5968 in microseconds. 5969 5970 rcutorture.fqs_holdoff= [KNL] 5971 Set holdoff time within force_quiescent_state bursts 5972 in microseconds. 5973 5974 rcutorture.fqs_stutter= [KNL] 5975 Set wait time between force_quiescent_state bursts 5976 in seconds. 5977 5978 rcutorture.fwd_progress= [KNL] 5979 Specifies the number of kthreads to be used 5980 for RCU grace-period forward-progress testing 5981 for the types of RCU supporting this notion. 5982 Defaults to 1 kthread, values less than zero or 5983 greater than the number of CPUs cause the number 5984 of CPUs to be used. 5985 5986 rcutorture.fwd_progress_div= [KNL] 5987 Specify the fraction of a CPU-stall-warning 5988 period to do tight-loop forward-progress testing. 5989 5990 rcutorture.fwd_progress_holdoff= [KNL] 5991 Number of seconds to wait between successive 5992 forward-progress tests. 5993 5994 rcutorture.fwd_progress_need_resched= [KNL] 5995 Enclose cond_resched() calls within checks for 5996 need_resched() during tight-loop forward-progress 5997 testing. 5998 5999 rcutorture.gp_cond= [KNL] 6000 Use conditional/asynchronous update-side 6001 normal-grace-period primitives, if available. 6002 6003 rcutorture.gp_cond_exp= [KNL] 6004 Use conditional/asynchronous update-side 6005 expedited-grace-period primitives, if available. 6006 6007 rcutorture.gp_cond_full= [KNL] 6008 Use conditional/asynchronous update-side 6009 normal-grace-period primitives that also take 6010 concurrent expedited grace periods into account, 6011 if available. 6012 6013 rcutorture.gp_cond_exp_full= [KNL] 6014 Use conditional/asynchronous update-side 6015 expedited-grace-period primitives that also take 6016 concurrent normal grace periods into account, 6017 if available. 6018 6019 rcutorture.gp_cond_wi= [KNL] 6020 Nominal wait interval for normal conditional 6021 grace periods (specified by rcutorture's 6022 gp_cond and gp_cond_full module parameters), 6023 in microseconds. The actual wait interval will 6024 be randomly selected to nanosecond granularity up 6025 to this wait interval. Defaults to 16 jiffies, 6026 for example, 16,000 microseconds on a system 6027 with HZ=1000. 6028 6029 rcutorture.gp_cond_wi_exp= [KNL] 6030 Nominal wait interval for expedited conditional 6031 grace periods (specified by rcutorture's 6032 gp_cond_exp and gp_cond_exp_full module 6033 parameters), in microseconds. The actual wait 6034 interval will be randomly selected to nanosecond 6035 granularity up to this wait interval. Defaults to 6036 128 microseconds. 6037 6038 rcutorture.gp_exp= [KNL] 6039 Use expedited update-side primitives, if available. 6040 6041 rcutorture.gp_normal= [KNL] 6042 Use normal (non-expedited) asynchronous 6043 update-side primitives, if available. 6044 6045 rcutorture.gp_poll= [KNL] 6046 Use polled update-side normal-grace-period 6047 primitives, if available. 6048 6049 rcutorture.gp_poll_exp= [KNL] 6050 Use polled update-side expedited-grace-period 6051 primitives, if available. 6052 6053 rcutorture.gp_poll_full= [KNL] 6054 Use polled update-side normal-grace-period 6055 primitives that also take concurrent expedited 6056 grace periods into account, if available. 6057 6058 rcutorture.gp_poll_exp_full= [KNL] 6059 Use polled update-side expedited-grace-period 6060 primitives that also take concurrent normal 6061 grace periods into account, if available. 6062 6063 rcutorture.gp_poll_wi= [KNL] 6064 Nominal wait interval for normal conditional 6065 grace periods (specified by rcutorture's 6066 gp_poll and gp_poll_full module parameters), 6067 in microseconds. The actual wait interval will 6068 be randomly selected to nanosecond granularity up 6069 to this wait interval. Defaults to 16 jiffies, 6070 for example, 16,000 microseconds on a system 6071 with HZ=1000. 6072 6073 rcutorture.gp_poll_wi_exp= [KNL] 6074 Nominal wait interval for expedited conditional 6075 grace periods (specified by rcutorture's 6076 gp_poll_exp and gp_poll_exp_full module 6077 parameters), in microseconds. The actual wait 6078 interval will be randomly selected to nanosecond 6079 granularity up to this wait interval. Defaults to 6080 128 microseconds. 6081 6082 rcutorture.gp_sync= [KNL] 6083 Use normal (non-expedited) synchronous 6084 update-side primitives, if available. If all 6085 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6086 rcutorture.gp_normal=, and rcutorture.gp_sync= 6087 are zero, rcutorture acts as if is interpreted 6088 they are all non-zero. 6089 6090 rcutorture.gpwrap_lag= [KNL] 6091 Enable grace-period wrap lag testing. Setting 6092 to false prevents the gpwrap lag test from 6093 running. Default is true. 6094 6095 rcutorture.gpwrap_lag_gps= [KNL] 6096 Set the value for grace-period wrap lag during 6097 active lag testing periods. This controls how many 6098 grace periods differences we tolerate between 6099 rdp and rnp's gp_seq before setting overflow flag. 6100 The default is always set to 8. 6101 6102 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6103 Set the total cycle duration for gpwrap lag 6104 testing in minutes. This is the total time for 6105 one complete cycle of active and inactive 6106 testing periods. Default is 30 minutes. 6107 6108 rcutorture.gpwrap_lag_active_mins= [KNL] 6109 Set the duration for which gpwrap lag is active 6110 within each cycle, in minutes. During this time, 6111 the grace-period wrap lag will be set to the 6112 value specified by gpwrap_lag_gps. Default is 6113 5 minutes. 6114 6115 rcutorture.irqreader= [KNL] 6116 Run RCU readers from irq handlers, or, more 6117 accurately, from a timer handler. Not all RCU 6118 flavors take kindly to this sort of thing. 6119 6120 rcutorture.leakpointer= [KNL] 6121 Leak an RCU-protected pointer out of the reader. 6122 This can of course result in splats, and is 6123 intended to test the ability of things like 6124 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6125 such leaks. 6126 6127 rcutorture.n_barrier_cbs= [KNL] 6128 Set callbacks/threads for rcu_barrier() testing. 6129 6130 rcutorture.nfakewriters= [KNL] 6131 Set number of concurrent RCU writers. These just 6132 stress RCU, they don't participate in the actual 6133 test, hence the "fake". 6134 6135 rcutorture.nocbs_nthreads= [KNL] 6136 Set number of RCU callback-offload togglers. 6137 Zero (the default) disables toggling. 6138 6139 rcutorture.nocbs_toggle= [KNL] 6140 Set the delay in milliseconds between successive 6141 callback-offload toggling attempts. 6142 6143 rcutorture.nreaders= [KNL] 6144 Set number of RCU readers. The value -1 selects 6145 N-1, where N is the number of CPUs. A value 6146 "n" less than -1 selects N-n-2, where N is again 6147 the number of CPUs. For example, -2 selects N 6148 (the number of CPUs), -3 selects N+1, and so on. 6149 6150 rcutorture.object_debug= [KNL] 6151 Enable debug-object double-call_rcu() testing. 6152 6153 rcutorture.onoff_holdoff= [KNL] 6154 Set time (s) after boot for CPU-hotplug testing. 6155 6156 rcutorture.onoff_interval= [KNL] 6157 Set time (jiffies) between CPU-hotplug operations, 6158 or zero to disable CPU-hotplug testing. 6159 6160 rcutorture.preempt_duration= [KNL] 6161 Set duration (in milliseconds) of preemptions 6162 by a high-priority FIFO real-time task. Set to 6163 zero (the default) to disable. The CPUs to 6164 preempt are selected randomly from the set that 6165 are online at a given point in time. Races with 6166 CPUs going offline are ignored, with that attempt 6167 at preemption skipped. 6168 6169 rcutorture.preempt_interval= [KNL] 6170 Set interval (in milliseconds, defaulting to one 6171 second) between preemptions by a high-priority 6172 FIFO real-time task. This delay is mediated 6173 by an hrtimer and is further fuzzed to avoid 6174 inadvertent synchronizations. 6175 6176 rcutorture.read_exit_burst= [KNL] 6177 The number of times in a given read-then-exit 6178 episode that a set of read-then-exit kthreads 6179 is spawned. 6180 6181 rcutorture.read_exit_delay= [KNL] 6182 The delay, in seconds, between successive 6183 read-then-exit testing episodes. 6184 6185 rcutorture.reader_flavor= [KNL] 6186 A bit mask indicating which readers to use. 6187 If there is more than one bit set, the readers 6188 are entered from low-order bit up, and are 6189 exited in the opposite order. For SRCU, the 6190 0x1 bit is normal readers, 0x2 NMI-safe readers, 6191 and 0x4 light-weight readers. 6192 6193 rcutorture.shuffle_interval= [KNL] 6194 Set task-shuffle interval (s). Shuffling tasks 6195 allows some CPUs to go into dyntick-idle mode 6196 during the rcutorture test. 6197 6198 rcutorture.shutdown_secs= [KNL] 6199 Set time (s) after boot system shutdown. This 6200 is useful for hands-off automated testing. 6201 6202 rcutorture.stall_cpu= [KNL] 6203 Duration of CPU stall (s) to test RCU CPU stall 6204 warnings, zero to disable. 6205 6206 rcutorture.stall_cpu_block= [KNL] 6207 Sleep while stalling if set. This will result 6208 in warnings from preemptible RCU in addition to 6209 any other stall-related activity. Note that 6210 in kernels built with CONFIG_PREEMPTION=n and 6211 CONFIG_PREEMPT_COUNT=y, this parameter will 6212 cause the CPU to pass through a quiescent state. 6213 Given CONFIG_PREEMPTION=n, this will suppress 6214 RCU CPU stall warnings, but will instead result 6215 in scheduling-while-atomic splats. 6216 6217 Use of this module parameter results in splats. 6218 6219 6220 rcutorture.stall_cpu_holdoff= [KNL] 6221 Time to wait (s) after boot before inducing stall. 6222 6223 rcutorture.stall_cpu_irqsoff= [KNL] 6224 Disable interrupts while stalling if set, but only 6225 on the first stall in the set. 6226 6227 rcutorture.stall_cpu_repeat= [KNL] 6228 Number of times to repeat the stall sequence, 6229 so that rcutorture.stall_cpu_repeat=3 will result 6230 in four stall sequences. 6231 6232 rcutorture.stall_gp_kthread= [KNL] 6233 Duration (s) of forced sleep within RCU 6234 grace-period kthread to test RCU CPU stall 6235 warnings, zero to disable. If both stall_cpu 6236 and stall_gp_kthread are specified, the 6237 kthread is starved first, then the CPU. 6238 6239 rcutorture.stat_interval= [KNL] 6240 Time (s) between statistics printk()s. 6241 6242 rcutorture.stutter= [KNL] 6243 Time (s) to stutter testing, for example, specifying 6244 five seconds causes the test to run for five seconds, 6245 wait for five seconds, and so on. This tests RCU's 6246 ability to transition abruptly to and from idle. 6247 6248 rcutorture.test_boost= [KNL] 6249 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6250 "Maybe" means test if the RCU implementation 6251 under test support RCU priority boosting. 6252 6253 rcutorture.test_boost_duration= [KNL] 6254 Duration (s) of each individual boost test. 6255 6256 rcutorture.test_boost_holdoff= [KNL] 6257 Holdoff time (s) from start of test to the start 6258 of RCU priority-boost testing. Defaults to zero, 6259 that is, no holdoff. 6260 6261 rcutorture.test_boost_interval= [KNL] 6262 Interval (s) between each boost test. 6263 6264 rcutorture.test_no_idle_hz= [KNL] 6265 Test RCU's dyntick-idle handling. See also the 6266 rcutorture.shuffle_interval parameter. 6267 6268 rcutorture.torture_type= [KNL] 6269 Specify the RCU implementation to test. 6270 6271 rcutorture.verbose= [KNL] 6272 Enable additional printk() statements. 6273 6274 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6275 Dump ftrace buffer after reporting RCU CPU 6276 stall warning. 6277 6278 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6279 Provide RCU CPU stall notifiers, but see the 6280 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6281 option's help text. TL;DR: You almost certainly 6282 do not want rcupdate.rcu_cpu_stall_notifiers. 6283 6284 rcupdate.rcu_cpu_stall_suppress= [KNL] 6285 Suppress RCU CPU stall warning messages. 6286 6287 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6288 Suppress RCU CPU stall warning messages and 6289 rcutorture writer stall warnings that occur 6290 during early boot, that is, during the time 6291 before the init task is spawned. 6292 6293 rcupdate.rcu_cpu_stall_timeout= [KNL] 6294 Set timeout for RCU CPU stall warning messages. 6295 The value is in seconds and the maximum allowed 6296 value is 300 seconds. 6297 6298 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6299 Set timeout for expedited RCU CPU stall warning 6300 messages. The value is in milliseconds 6301 and the maximum allowed value is 21000 6302 milliseconds. Please note that this value is 6303 adjusted to an arch timer tick resolution. 6304 Setting this to zero causes the value from 6305 rcupdate.rcu_cpu_stall_timeout to be used (after 6306 conversion from seconds to milliseconds). 6307 6308 rcupdate.rcu_cpu_stall_cputime= [KNL] 6309 Provide statistics on the cputime and count of 6310 interrupts and tasks during the sampling period. For 6311 multiple continuous RCU stalls, all sampling periods 6312 begin at half of the first RCU stall timeout. 6313 6314 rcupdate.rcu_exp_stall_task_details= [KNL] 6315 Print stack dumps of any tasks blocking the 6316 current expedited RCU grace period during an 6317 expedited RCU CPU stall warning. 6318 6319 rcupdate.rcu_expedited= [KNL] 6320 Use expedited grace-period primitives, for 6321 example, synchronize_rcu_expedited() instead 6322 of synchronize_rcu(). This reduces latency, 6323 but can increase CPU utilization, degrade 6324 real-time latency, and degrade energy efficiency. 6325 No effect on CONFIG_TINY_RCU kernels. 6326 6327 rcupdate.rcu_normal= [KNL] 6328 Use only normal grace-period primitives, 6329 for example, synchronize_rcu() instead of 6330 synchronize_rcu_expedited(). This improves 6331 real-time latency, CPU utilization, and 6332 energy efficiency, but can expose users to 6333 increased grace-period latency. This parameter 6334 overrides rcupdate.rcu_expedited. No effect on 6335 CONFIG_TINY_RCU kernels. 6336 6337 rcupdate.rcu_normal_after_boot= [KNL] 6338 Once boot has completed (that is, after 6339 rcu_end_inkernel_boot() has been invoked), use 6340 only normal grace-period primitives. No effect 6341 on CONFIG_TINY_RCU kernels. 6342 6343 But note that CONFIG_PREEMPT_RT=y kernels enables 6344 this kernel boot parameter, forcibly setting 6345 it to the value one, that is, converting any 6346 post-boot attempt at an expedited RCU grace 6347 period to instead use normal non-expedited 6348 grace-period processing. 6349 6350 rcupdate.rcu_task_collapse_lim= [KNL] 6351 Set the maximum number of callbacks present 6352 at the beginning of a grace period that allows 6353 the RCU Tasks flavors to collapse back to using 6354 a single callback queue. This switching only 6355 occurs when rcupdate.rcu_task_enqueue_lim is 6356 set to the default value of -1. 6357 6358 rcupdate.rcu_task_contend_lim= [KNL] 6359 Set the minimum number of callback-queuing-time 6360 lock-contention events per jiffy required to 6361 cause the RCU Tasks flavors to switch to per-CPU 6362 callback queuing. This switching only occurs 6363 when rcupdate.rcu_task_enqueue_lim is set to 6364 the default value of -1. 6365 6366 rcupdate.rcu_task_enqueue_lim= [KNL] 6367 Set the number of callback queues to use for the 6368 RCU Tasks family of RCU flavors. The default 6369 of -1 allows this to be automatically (and 6370 dynamically) adjusted. This parameter is intended 6371 for use in testing. 6372 6373 rcupdate.rcu_task_lazy_lim= [KNL] 6374 Number of callbacks on a given CPU that will 6375 cancel laziness on that CPU. Use -1 to disable 6376 cancellation of laziness, but be advised that 6377 doing so increases the danger of OOM due to 6378 callback flooding. 6379 6380 rcupdate.rcu_task_stall_info= [KNL] 6381 Set initial timeout in jiffies for RCU task stall 6382 informational messages, which give some indication 6383 of the problem for those not patient enough to 6384 wait for ten minutes. Informational messages are 6385 only printed prior to the stall-warning message 6386 for a given grace period. Disable with a value 6387 less than or equal to zero. Defaults to ten 6388 seconds. A change in value does not take effect 6389 until the beginning of the next grace period. 6390 6391 rcupdate.rcu_task_stall_info_mult= [KNL] 6392 Multiplier for time interval between successive 6393 RCU task stall informational messages for a given 6394 RCU tasks grace period. This value is clamped 6395 to one through ten, inclusive. It defaults to 6396 the value three, so that the first informational 6397 message is printed 10 seconds into the grace 6398 period, the second at 40 seconds, the third at 6399 160 seconds, and then the stall warning at 600 6400 seconds would prevent a fourth at 640 seconds. 6401 6402 rcupdate.rcu_task_stall_timeout= [KNL] 6403 Set timeout in jiffies for RCU task stall 6404 warning messages. Disable with a value less 6405 than or equal to zero. Defaults to ten minutes. 6406 A change in value does not take effect until 6407 the beginning of the next grace period. 6408 6409 rcupdate.rcu_tasks_lazy_ms= [KNL] 6410 Set timeout in milliseconds RCU Tasks asynchronous 6411 callback batching for call_rcu_tasks(). 6412 A negative value will take the default. A value 6413 of zero will disable batching. Batching is 6414 always disabled for synchronize_rcu_tasks(). 6415 6416 rcupdate.rcu_self_test= [KNL] 6417 Run the RCU early boot self tests 6418 6419 rdinit= [KNL] 6420 Format: <full_path> 6421 Run specified binary instead of /init from the ramdisk, 6422 used for early userspace startup. See initrd. 6423 6424 rdrand= [X86,EARLY] 6425 force - Override the decision by the kernel to hide the 6426 advertisement of RDRAND support (this affects 6427 certain AMD processors because of buggy BIOS 6428 support, specifically around the suspend/resume 6429 path). 6430 6431 rdt= [HW,X86,RDT] 6432 Turn on/off individual RDT features. List is: 6433 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6434 mba, smba, bmec, abmc, sdciae, energy[:guid], 6435 perf[:guid]. 6436 E.g. to turn on cmt and turn off mba use: 6437 rdt=cmt,!mba 6438 To turn off all energy telemetry monitoring and ensure that 6439 perf telemetry monitoring associated with guid 0x12345 6440 is enabled use: 6441 rdt=!energy,perf:0x12345 6442 6443 reboot= [KNL] 6444 Format (x86 or x86_64): 6445 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6446 [[,]s[mp]#### \ 6447 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6448 [[,]f[orce] 6449 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6450 (prefix with 'panic_' to set mode for panic 6451 reboot only), 6452 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6453 reboot_force is either force or not specified, 6454 reboot_cpu is s[mp]#### with #### being the processor 6455 to be used for rebooting. 6456 6457 acpi 6458 Use the ACPI RESET_REG in the FADT. If ACPI is not 6459 configured or the ACPI reset does not work, the reboot 6460 path attempts the reset using the keyboard controller. 6461 6462 bios 6463 Use the CPU reboot vector for warm reset 6464 6465 cold 6466 Set the cold reboot flag 6467 6468 default 6469 There are some built-in platform specific "quirks" 6470 - you may see: "reboot: <name> series board detected. 6471 Selecting <type> for reboots." In the case where you 6472 think the quirk is in error (e.g. you have newer BIOS, 6473 or newer board) using this option will ignore the 6474 built-in quirk table, and use the generic default 6475 reboot actions. 6476 6477 efi 6478 Use efi reset_system runtime service. If EFI is not 6479 configured or the EFI reset does not work, the reboot 6480 path attempts the reset using the keyboard controller. 6481 6482 force 6483 Don't stop other CPUs on reboot. This can make reboot 6484 more reliable in some cases. 6485 6486 kbd 6487 Use the keyboard controller. cold reset (default) 6488 6489 pci 6490 Use a write to the PCI config space register 0xcf9 to 6491 trigger reboot. 6492 6493 triple 6494 Force a triple fault (init) 6495 6496 warm 6497 Don't set the cold reboot flag 6498 6499 Using warm reset will be much faster especially on big 6500 memory systems because the BIOS will not go through 6501 the memory check. Disadvantage is that not all 6502 hardware will be completely reinitialized on reboot so 6503 there may be boot problems on some systems. 6504 6505 6506 refscale.holdoff= [KNL] 6507 Set test-start holdoff period. The purpose of 6508 this parameter is to delay the start of the 6509 test until boot completes in order to avoid 6510 interference. 6511 6512 refscale.lookup_instances= [KNL] 6513 Number of data elements to use for the forms of 6514 SLAB_TYPESAFE_BY_RCU testing. A negative number 6515 is negated and multiplied by nr_cpu_ids, while 6516 zero specifies nr_cpu_ids. 6517 6518 refscale.loops= [KNL] 6519 Set the number of loops over the synchronization 6520 primitive under test. Increasing this number 6521 reduces noise due to loop start/end overhead, 6522 but the default has already reduced the per-pass 6523 noise to a handful of picoseconds on ca. 2020 6524 x86 laptops. 6525 6526 refscale.nreaders= [KNL] 6527 Set number of readers. The default value of -1 6528 selects N, where N is roughly 75% of the number 6529 of CPUs. A value of zero is an interesting choice. 6530 6531 refscale.nruns= [KNL] 6532 Set number of runs, each of which is dumped onto 6533 the console log. 6534 6535 refscale.readdelay= [KNL] 6536 Set the read-side critical-section duration, 6537 measured in microseconds. 6538 6539 refscale.scale_type= [KNL] 6540 Specify the read-protection implementation to test. 6541 6542 refscale.shutdown= [KNL] 6543 Shut down the system at the end of the performance 6544 test. This defaults to 1 (shut it down) when 6545 refscale is built into the kernel and to 0 (leave 6546 it running) when refscale is built as a module. 6547 6548 refscale.verbose= [KNL] 6549 Enable additional printk() statements. 6550 6551 refscale.verbose_batched= [KNL] 6552 Batch the additional printk() statements. If zero 6553 (the default) or negative, print everything. Otherwise, 6554 print every Nth verbose statement, where N is the value 6555 specified. 6556 6557 regulator_ignore_unused 6558 [REGULATOR] 6559 Prevents regulator framework from disabling regulators 6560 that are unused, due no driver claiming them. This may 6561 be useful for debug and development, but should not be 6562 needed on a platform with proper driver support. 6563 6564 relax_domain_level= 6565 [KNL, SMP] Set scheduler's default relax_domain_level. 6566 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6567 6568 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6569 Format: <base1>,<size1>[,<base2>,<size2>,...] 6570 Reserve I/O ports or memory so the kernel won't use 6571 them. If <base> is less than 0x10000, the region 6572 is assumed to be I/O ports; otherwise it is memory. 6573 6574 reserve_mem= [RAM] 6575 Format: nn[KMG]:<align>:<label> 6576 Reserve physical memory and label it with a name that 6577 other subsystems can use to access it. This is typically 6578 used for systems that do not wipe the RAM, and this command 6579 line will try to reserve the same physical memory on 6580 soft reboots. Note, it is not guaranteed to be the same 6581 location. For example, if anything about the system changes 6582 or if booting a different kernel. It can also fail if KASLR 6583 places the kernel at the location of where the RAM reservation 6584 was from a previous boot, the new reservation will be at a 6585 different location. 6586 Any subsystem using this feature must add a way to verify 6587 that the contents of the physical memory is from a previous 6588 boot, as there may be cases where the memory will not be 6589 located at the same location. 6590 6591 The format is size:align:label for example, to request 6592 12 megabytes of 4096 alignment for ramoops: 6593 6594 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6595 6596 reservetop= [X86-32,EARLY] 6597 Format: nn[KMG] 6598 Reserves a hole at the top of the kernel virtual 6599 address space. 6600 6601 reset_devices [KNL] Force drivers to reset the underlying device 6602 during initialization. 6603 6604 resume= [SWSUSP] 6605 Specify the partition device for software suspend 6606 Format: 6607 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6608 6609 resume_offset= [SWSUSP] 6610 Specify the offset from the beginning of the partition 6611 given by "resume=" at which the swap header is located, 6612 in <PAGE_SIZE> units (needed only for swap files). 6613 See Documentation/power/swsusp-and-swap-files.rst 6614 6615 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6616 read the resume files 6617 6618 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6619 Useful for devices that are detected asynchronously 6620 (e.g. USB and MMC devices). 6621 6622 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6623 be accessible via /sys/firmware/initrd. 6624 6625 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6626 Speculative Code Execution with Return Instructions) 6627 vulnerability. 6628 6629 AMD-based UNRET and IBPB mitigations alone do not stop 6630 sibling threads from influencing the predictions of other 6631 sibling threads. For that reason, STIBP is used on pro- 6632 cessors that support it, and mitigate SMT on processors 6633 that don't. 6634 6635 off - no mitigation 6636 auto - automatically select a mitigation 6637 auto,nosmt - automatically select a mitigation, 6638 disabling SMT if necessary for 6639 the full mitigation (only on Zen1 6640 and older without STIBP). 6641 ibpb - On AMD, mitigate short speculation 6642 windows on basic block boundaries too. 6643 Safe, highest perf impact. It also 6644 enables STIBP if present. Not suitable 6645 on Intel. 6646 ibpb,nosmt - Like "ibpb" above but will disable SMT 6647 when STIBP is not available. This is 6648 the alternative for systems which do not 6649 have STIBP. 6650 unret - Force enable untrained return thunks, 6651 only effective on AMD f15h-f17h based 6652 systems. 6653 unret,nosmt - Like unret, but will disable SMT when STIBP 6654 is not available. This is the alternative for 6655 systems which do not have STIBP. 6656 6657 Selecting 'auto' will choose a mitigation method at run 6658 time according to the CPU. 6659 6660 Not specifying this option is equivalent to retbleed=auto. 6661 6662 rfkill.default_state= 6663 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6664 etc. communication is blocked by default. 6665 1 Unblocked. 6666 6667 rfkill.master_switch_mode= 6668 0 The "airplane mode" button does nothing. 6669 1 The "airplane mode" button toggles between everything 6670 blocked and the previous configuration. 6671 2 The "airplane mode" button toggles between everything 6672 blocked and everything unblocked. 6673 6674 ring3mwait=disable 6675 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6676 CPUs. 6677 6678 riscv_isa_fallback [RISCV,EARLY] 6679 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6680 falling back to detecting extension support by parsing 6681 "riscv,isa" property on devicetree systems when the 6682 replacement properties are not found. See the Kconfig 6683 entry for RISCV_ISA_FALLBACK. 6684 6685 riscv_nousercfi= 6686 all Disable user CFI ABI to userspace even if cpu extension 6687 are available. 6688 bcfi Disable user backward CFI ABI to userspace even if 6689 the shadow stack extension is available. 6690 fcfi Disable user forward CFI ABI to userspace even if the 6691 landing pad extension is available. 6692 6693 ro [KNL] Mount root device read-only on boot 6694 6695 rodata= [KNL,EARLY] 6696 on Mark read-only kernel memory as read-only (default). 6697 off Leave read-only kernel memory writable for debugging. 6698 noalias Mark read-only kernel memory as read-only but retain 6699 writable aliases in the direct map for regions outside 6700 of the kernel image. [arm64] 6701 6702 rockchip.usb_uart 6703 [EARLY] 6704 Enable the uart passthrough on the designated usb port 6705 on Rockchip SoCs. When active, the signals of the 6706 debug-uart get routed to the D+ and D- pins of the usb 6707 port and the regular usb controller gets disabled. 6708 6709 root= [KNL] Root filesystem 6710 Usually this is a block device specifier of some kind, 6711 see the early_lookup_bdev comment in 6712 block/early-lookup.c for details. 6713 Alternatively this can be "ram" for the legacy initial 6714 ramdisk, "nfs" and "cifs" for root on a network file 6715 system, or "mtd" and "ubi" for mounting from raw flash. 6716 6717 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6718 mount the root filesystem 6719 6720 rootflags= [KNL] Set root filesystem mount option string 6721 6722 rseq_slice_ext= [KNL] RSEQ based time slice extension 6723 Format: boolean 6724 Control enablement of RSEQ based time slice extension. 6725 Default is 'on'. 6726 6727 initramfs_options= [KNL] 6728 Specify mount options for the initramfs mount. 6729 6730 rootfstype= [KNL] Set root filesystem type 6731 6732 rootwait [KNL] Wait (indefinitely) for root device to show up. 6733 Useful for devices that are detected asynchronously 6734 (e.g. USB and MMC devices). 6735 6736 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6737 to show up before attempting to mount the root 6738 filesystem. 6739 6740 rproc_mem=nn[KMG][@address] 6741 [KNL,ARM,CMA] Remoteproc physical memory block. 6742 Memory area to be used by remote processor image, 6743 managed by CMA. 6744 6745 rseq_debug= [KNL] Enable or disable restartable sequence 6746 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6747 Format: <bool> 6748 6749 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6750 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6751 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6752 Format: <bool> 6753 6754 rw [KNL] Mount root device read-write on boot 6755 6756 S [KNL] Run init in single mode 6757 6758 s390_iommu= [HW,S390] 6759 Set s390 IOTLB flushing mode 6760 strict 6761 With strict flushing every unmap operation will result 6762 in an IOTLB flush. Default is lazy flushing before 6763 reuse, which is faster. Deprecated, equivalent to 6764 iommu.strict=1. 6765 6766 s390_iommu_aperture= [KNL,S390] 6767 Specifies the size of the per device DMA address space 6768 accessible through the DMA and IOMMU APIs as a decimal 6769 factor of the size of main memory. 6770 The default is 1 meaning that one can concurrently use 6771 as many DMA addresses as physical memory is installed, 6772 if supported by hardware, and thus map all of memory 6773 once. With a value of 2 one can map all of memory twice 6774 and so on. As a special case a factor of 0 imposes no 6775 restrictions other than those given by hardware at the 6776 cost of significant additional memory use for tables. 6777 6778 6779 sched_proxy_exec= [KNL] 6780 Enables or disables "proxy execution" style 6781 solution to mutex-based priority inversion. 6782 Format: <bool> 6783 6784 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6785 6786 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6787 Allowed values are enable and disable. This feature 6788 incurs a small amount of overhead in the scheduler 6789 but is useful for debugging and performance tuning. 6790 6791 sched_thermal_decay_shift= 6792 [Deprecated] 6793 [KNL, SMP] Set a decay shift for scheduler thermal 6794 pressure signal. Thermal pressure signal follows the 6795 default decay period of other scheduler pelt 6796 signals(usually 32 ms but configurable). Setting 6797 sched_thermal_decay_shift will left shift the decay 6798 period for the thermal pressure signal by the shift 6799 value. 6800 i.e. with the default pelt decay period of 32 ms 6801 sched_thermal_decay_shift thermal pressure decay pr 6802 1 64 ms 6803 2 128 ms 6804 and so on. 6805 Format: integer between 0 and 10 6806 Default is 0. 6807 6808 scftorture.holdoff= [KNL] 6809 Number of seconds to hold off before starting 6810 test. Defaults to zero for module insertion and 6811 to 10 seconds for built-in smp_call_function() 6812 tests. 6813 6814 scftorture.longwait= [KNL] 6815 Request ridiculously long waits randomly selected 6816 up to the chosen limit in seconds. Zero (the 6817 default) disables this feature. Please note 6818 that requesting even small non-zero numbers of 6819 seconds can result in RCU CPU stall warnings, 6820 softlockup complaints, and so on. 6821 6822 scftorture.nthreads= [KNL] 6823 Number of kthreads to spawn to invoke the 6824 smp_call_function() family of functions. 6825 The default of -1 specifies a number of kthreads 6826 equal to the number of CPUs. 6827 6828 scftorture.onoff_holdoff= [KNL] 6829 Number seconds to wait after the start of the 6830 test before initiating CPU-hotplug operations. 6831 6832 scftorture.onoff_interval= [KNL] 6833 Number seconds to wait between successive 6834 CPU-hotplug operations. Specifying zero (which 6835 is the default) disables CPU-hotplug operations. 6836 6837 scftorture.shutdown_secs= [KNL] 6838 The number of seconds following the start of the 6839 test after which to shut down the system. The 6840 default of zero avoids shutting down the system. 6841 Non-zero values are useful for automated tests. 6842 6843 scftorture.stat_interval= [KNL] 6844 The number of seconds between outputting the 6845 current test statistics to the console. A value 6846 of zero disables statistics output. 6847 6848 scftorture.stutter_cpus= [KNL] 6849 The number of jiffies to wait between each change 6850 to the set of CPUs under test. 6851 6852 scftorture.use_cpus_read_lock= [KNL] 6853 Use use_cpus_read_lock() instead of the default 6854 preempt_disable() to disable CPU hotplug 6855 while invoking one of the smp_call_function*() 6856 functions. 6857 6858 scftorture.verbose= [KNL] 6859 Enable additional printk() statements. 6860 6861 scftorture.weight_single= [KNL] 6862 The probability weighting to use for the 6863 smp_call_function_single() function with a zero 6864 "wait" parameter. A value of -1 selects the 6865 default if all other weights are -1. However, 6866 if at least one weight has some other value, a 6867 value of -1 will instead select a weight of zero. 6868 6869 scftorture.weight_single_wait= [KNL] 6870 The probability weighting to use for the 6871 smp_call_function_single() function with a 6872 non-zero "wait" parameter. See weight_single. 6873 6874 scftorture.weight_many= [KNL] 6875 The probability weighting to use for the 6876 smp_call_function_many() function with a zero 6877 "wait" parameter. See weight_single. 6878 Note well that setting a high probability for 6879 this weighting can place serious IPI load 6880 on the system. 6881 6882 scftorture.weight_many_wait= [KNL] 6883 The probability weighting to use for the 6884 smp_call_function_many() function with a 6885 non-zero "wait" parameter. See weight_single 6886 and weight_many. 6887 6888 scftorture.weight_all= [KNL] 6889 The probability weighting to use for the 6890 smp_call_function_all() function with a zero 6891 "wait" parameter. See weight_single and 6892 weight_many. 6893 6894 scftorture.weight_all_wait= [KNL] 6895 The probability weighting to use for the 6896 smp_call_function_all() function with a 6897 non-zero "wait" parameter. See weight_single 6898 and weight_many. 6899 6900 sdw_mclk_divider=[SDW] 6901 Specify the MCLK divider for Intel SoundWire buses in 6902 case the BIOS does not provide the clock rate properly. 6903 6904 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6905 xtime_lock contention on larger systems, and/or RCU lock 6906 contention on all systems with CONFIG_MAXSMP set. 6907 Format: { "0" | "1" } 6908 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6909 1 -- enable. 6910 Note: increases power consumption, thus should only be 6911 enabled if running jitter sensitive (HPC/RT) workloads. 6912 6913 security= [SECURITY] Choose a legacy "major" security module to 6914 enable at boot. This has been deprecated by the 6915 "lsm=" parameter. 6916 6917 selinux= [SELINUX] Disable or enable SELinux at boot time. 6918 Format: { "0" | "1" } 6919 See security/selinux/Kconfig help text. 6920 0 -- disable. 6921 1 -- enable. 6922 Default value is 1. 6923 6924 serialnumber [BUGS=X86-32] 6925 6926 sev=option[,option...] [X86-64] 6927 6928 debug 6929 Enable debug messages. 6930 6931 nosnp 6932 Do not enable SEV-SNP (applies to host/hypervisor 6933 only). Setting 'nosnp' avoids the RMP check overhead 6934 in memory accesses when users do not want to run 6935 SEV-SNP guests. 6936 6937 shapers= [NET] 6938 Maximal number of shapers. 6939 6940 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6941 Limit apic dumping. The parameter defines the maximal 6942 number of local apics being dumped. Also it is possible 6943 to set it to "all" by meaning -- no limit here. 6944 Format: { 1 (default) | 2 | ... | all }. 6945 The parameter valid if only apic=debug or 6946 apic=verbose is specified. 6947 Example: apic=debug show_lapic=all 6948 6949 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6950 Enabling slab_debug allows one to determine the 6951 culprit if slab objects become corrupted. Enabling 6952 slab_debug can create guard zones around objects and 6953 may poison objects when not in use. Also tracks the 6954 last alloc / free. For more information see 6955 Documentation/admin-guide/mm/slab.rst. 6956 (slub_debug legacy name also accepted for now) 6957 6958 Using this option implies the "no_hash_pointers" 6959 option which can be undone by adding the 6960 "hash_pointers=always" option. 6961 6962 slab_max_order= [MM] 6963 Determines the maximum allowed order for slabs. 6964 A high setting may cause OOMs due to memory 6965 fragmentation. For more information see 6966 Documentation/admin-guide/mm/slab.rst. 6967 (slub_max_order legacy name also accepted for now) 6968 6969 slab_merge [MM] 6970 Enable merging of slabs with similar size when the 6971 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6972 (slub_merge legacy name also accepted for now) 6973 6974 slab_min_objects= [MM] 6975 The minimum number of objects per slab. SLUB will 6976 increase the slab order up to slab_max_order to 6977 generate a sufficiently large slab able to contain 6978 the number of objects indicated. The higher the number 6979 of objects the smaller the overhead of tracking slabs 6980 and the less frequently locks need to be acquired. 6981 For more information see 6982 Documentation/admin-guide/mm/slab.rst. 6983 (slub_min_objects legacy name also accepted for now) 6984 6985 slab_min_order= [MM] 6986 Determines the minimum page order for slabs. Must be 6987 lower or equal to slab_max_order. For more information see 6988 Documentation/admin-guide/mm/slab.rst. 6989 (slub_min_order legacy name also accepted for now) 6990 6991 slab_nomerge [MM] 6992 Disable merging of slabs with similar size. May be 6993 necessary if there is some reason to distinguish 6994 allocs to different slabs, especially in hardened 6995 environments where the risk of heap overflows and 6996 layout control by attackers can usually be 6997 frustrated by disabling merging. This will reduce 6998 most of the exposure of a heap attack to a single 6999 cache (risks via metadata attacks are mostly 7000 unchanged). Debug options disable merging on their 7001 own. 7002 For more information see 7003 Documentation/admin-guide/mm/slab.rst. 7004 (slub_nomerge legacy name also accepted for now) 7005 7006 slab_strict_numa [MM] 7007 Support memory policies on a per object level 7008 in the slab allocator. The default is for memory 7009 policies to be applied at the folio level when 7010 a new folio is needed or a partial folio is 7011 retrieved from the lists. Increases overhead 7012 in the slab fastpaths but gains more accurate 7013 NUMA kernel object placement which helps with slow 7014 interconnects in NUMA systems. 7015 7016 slram= [HW,MTD] 7017 7018 smart2= [HW] 7019 Format: <io1>[,<io2>[,...,<io8>]] 7020 7021 smp.csd_lock_timeout= [KNL] 7022 Specify the period of time in milliseconds 7023 that smp_call_function() and friends will wait 7024 for a CPU to release the CSD lock. This is 7025 useful when diagnosing bugs involving CPUs 7026 disabling interrupts for extended periods 7027 of time. Defaults to 5,000 milliseconds, and 7028 setting a value of zero disables this feature. 7029 This feature may be more efficiently disabled 7030 using the csdlock_debug- kernel parameter. 7031 7032 smp.panic_on_ipistall= [KNL] 7033 If a csd_lock_timeout extends for more than 7034 the specified number of milliseconds, panic the 7035 system. By default, let CSD-lock acquisition 7036 take as long as they take. Specifying 300,000 7037 for this value provides a 5-minute timeout. 7038 7039 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7040 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7041 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7042 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7043 smsc-ircc2.ircc_irq= [HW] IRQ line 7044 smsc-ircc2.ircc_dma= [HW] DMA channel 7045 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7046 0: Toshiba Satellite 1800 (GP data pin select) 7047 1: Fast pin select (default) 7048 2: ATC IRMode 7049 7050 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7051 (logical CPUs) to use per physical CPU on systems 7052 capable of symmetric multithreading (SMT). Will 7053 be capped to the actual hardware limit. 7054 Format: <integer> 7055 Default: -1 (no limit) 7056 7057 softlockup_panic= 7058 [KNL] Should the soft-lockup detector generate panics. 7059 Format: <int> 7060 7061 A value of non-zero instructs the soft-lockup detector 7062 to panic the machine when a soft-lockup duration exceeds 7063 N thresholds. It is also controlled by the kernel.softlockup_panic 7064 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7065 respective build-time switch to that functionality. 7066 7067 softlockup_all_cpu_backtrace= 7068 [KNL] Should the soft-lockup detector generate 7069 backtraces on all cpus. 7070 Format: 0 | 1 7071 7072 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7073 See Documentation/admin-guide/laptops/sonypi.rst 7074 7075 spectre_bhi= [X86] Control mitigation of Branch History Injection 7076 (BHI) vulnerability. This setting affects the 7077 deployment of the HW BHI control and the SW BHB 7078 clearing sequence. 7079 7080 on - (default) Enable the HW or SW mitigation as 7081 needed. This protects the kernel from 7082 both syscalls and VMs. 7083 vmexit - On systems which don't have the HW mitigation 7084 available, enable the SW mitigation on vmexit 7085 ONLY. On such systems, the host kernel is 7086 protected from VM-originated BHI attacks, but 7087 may still be vulnerable to syscall attacks. 7088 off - Disable the mitigation. 7089 7090 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7091 (indirect branch speculation) vulnerability. 7092 The default operation protects the kernel from 7093 user space attacks. 7094 7095 on - unconditionally enable, implies 7096 spectre_v2_user=on 7097 off - unconditionally disable, implies 7098 spectre_v2_user=off 7099 auto - kernel detects whether your CPU model is 7100 vulnerable 7101 7102 Selecting 'on' will, and 'auto' may, choose a 7103 mitigation method at run time according to the 7104 CPU, the available microcode, the setting of the 7105 CONFIG_MITIGATION_RETPOLINE configuration option, 7106 and the compiler with which the kernel was built. 7107 7108 Selecting 'on' will also enable the mitigation 7109 against user space to user space task attacks. 7110 Selecting specific mitigation does not force enable 7111 user mitigations. 7112 7113 Selecting 'off' will disable both the kernel and 7114 the user space protections. 7115 7116 Specific mitigations can also be selected manually: 7117 7118 retpoline - replace indirect branches 7119 retpoline,generic - Retpolines 7120 retpoline,lfence - LFENCE; indirect branch 7121 retpoline,amd - alias for retpoline,lfence 7122 eibrs - Enhanced/Auto IBRS 7123 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7124 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7125 ibrs - use IBRS to protect kernel 7126 7127 Not specifying this option is equivalent to 7128 spectre_v2=auto. 7129 7130 spectre_v2_user= 7131 [X86] Control mitigation of Spectre variant 2 7132 (indirect branch speculation) vulnerability between 7133 user space tasks 7134 7135 on - Unconditionally enable mitigations. Is 7136 enforced by spectre_v2=on 7137 7138 off - Unconditionally disable mitigations. Is 7139 enforced by spectre_v2=off 7140 7141 prctl - Indirect branch speculation is enabled, 7142 but mitigation can be enabled via prctl 7143 per thread. The mitigation control state 7144 is inherited on fork. 7145 7146 prctl,ibpb 7147 - Like "prctl" above, but only STIBP is 7148 controlled per thread. IBPB is issued 7149 always when switching between different user 7150 space processes. 7151 7152 seccomp 7153 - Same as "prctl" above, but all seccomp 7154 threads will enable the mitigation unless 7155 they explicitly opt out. 7156 7157 seccomp,ibpb 7158 - Like "seccomp" above, but only STIBP is 7159 controlled per thread. IBPB is issued 7160 always when switching between different 7161 user space processes. 7162 7163 auto - Kernel selects the mitigation depending on 7164 the available CPU features and vulnerability. 7165 7166 Default mitigation: "prctl" 7167 7168 Not specifying this option is equivalent to 7169 spectre_v2_user=auto. 7170 7171 spec_rstack_overflow= 7172 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7173 7174 off - Disable mitigation 7175 microcode - Enable microcode mitigation only 7176 safe-ret - Enable sw-only safe RET mitigation (default) 7177 ibpb - Enable mitigation by issuing IBPB on 7178 kernel entry 7179 ibpb-vmexit - Issue IBPB only on VMEXIT 7180 (cloud-specific mitigation) 7181 7182 spec_store_bypass_disable= 7183 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7184 (Speculative Store Bypass vulnerability) 7185 7186 Certain CPUs are vulnerable to an exploit against a 7187 a common industry wide performance optimization known 7188 as "Speculative Store Bypass" in which recent stores 7189 to the same memory location may not be observed by 7190 later loads during speculative execution. The idea 7191 is that such stores are unlikely and that they can 7192 be detected prior to instruction retirement at the 7193 end of a particular speculation execution window. 7194 7195 In vulnerable processors, the speculatively forwarded 7196 store can be used in a cache side channel attack, for 7197 example to read memory to which the attacker does not 7198 directly have access (e.g. inside sandboxed code). 7199 7200 This parameter controls whether the Speculative Store 7201 Bypass optimization is used. 7202 7203 On x86 the options are: 7204 7205 on - Unconditionally disable Speculative Store Bypass 7206 off - Unconditionally enable Speculative Store Bypass 7207 auto - Kernel detects whether the CPU model contains an 7208 implementation of Speculative Store Bypass and 7209 picks the most appropriate mitigation. If the 7210 CPU is not vulnerable, "off" is selected. If the 7211 CPU is vulnerable the default mitigation is 7212 architecture and Kconfig dependent. See below. 7213 prctl - Control Speculative Store Bypass per thread 7214 via prctl. Speculative Store Bypass is enabled 7215 for a process by default. The state of the control 7216 is inherited on fork. 7217 seccomp - Same as "prctl" above, but all seccomp threads 7218 will disable SSB unless they explicitly opt out. 7219 7220 Default mitigations: 7221 X86: "prctl" 7222 7223 On powerpc the options are: 7224 7225 on,auto - On Power8 and Power9 insert a store-forwarding 7226 barrier on kernel entry and exit. On Power7 7227 perform a software flush on kernel entry and 7228 exit. 7229 off - No action. 7230 7231 Not specifying this option is equivalent to 7232 spec_store_bypass_disable=auto. 7233 7234 split_llc= 7235 [X86,EARLY] Split the LLC N-ways 7236 7237 When set, the LLC is split this many ways by matching 7238 'core_id % n'. This is setup before SMP bringup and 7239 used during SMP bringup before it knows the full 7240 topology. If your core count doesn't nicely divide by 7241 the number given, you get to keep the pieces. 7242 7243 This is mostly a debug feature to emulate multiple LLCs 7244 on hardware that only have a single LLC. 7245 7246 split_lock_detect= 7247 [X86] Enable split lock detection or bus lock detection 7248 7249 When enabled (and if hardware support is present), atomic 7250 instructions that access data across cache line 7251 boundaries will result in an alignment check exception 7252 for split lock detection or a debug exception for 7253 bus lock detection. 7254 7255 off - not enabled 7256 7257 warn - the kernel will emit rate-limited warnings 7258 about applications triggering the #AC 7259 exception or the #DB exception. This mode is 7260 the default on CPUs that support split lock 7261 detection or bus lock detection. Default 7262 behavior is by #AC if both features are 7263 enabled in hardware. 7264 7265 fatal - the kernel will send SIGBUS to applications 7266 that trigger the #AC exception or the #DB 7267 exception. Default behavior is by #AC if 7268 both features are enabled in hardware. 7269 7270 ratelimit:N - 7271 Set system wide rate limit to N bus locks 7272 per second for bus lock detection. 7273 0 < N <= 1000. 7274 7275 N/A for split lock detection. 7276 7277 7278 If an #AC exception is hit in the kernel or in 7279 firmware (i.e. not while executing in user mode) 7280 the kernel will oops in either "warn" or "fatal" 7281 mode. 7282 7283 #DB exception for bus lock is triggered only when 7284 CPL > 0. 7285 7286 srbds= [X86,INTEL,EARLY] 7287 Control the Special Register Buffer Data Sampling 7288 (SRBDS) mitigation. 7289 7290 Certain CPUs are vulnerable to an MDS-like 7291 exploit which can leak bits from the random 7292 number generator. 7293 7294 By default, this issue is mitigated by 7295 microcode. However, the microcode fix can cause 7296 the RDRAND and RDSEED instructions to become 7297 much slower. Among other effects, this will 7298 result in reduced throughput from /dev/urandom. 7299 7300 The microcode mitigation can be disabled with 7301 the following option: 7302 7303 off: Disable mitigation and remove 7304 performance impact to RDRAND and RDSEED 7305 7306 srcutree.big_cpu_lim [KNL] 7307 Specifies the number of CPUs constituting a 7308 large system, such that srcu_struct structures 7309 should immediately allocate an srcu_node array. 7310 This kernel-boot parameter defaults to 128, 7311 but takes effect only when the low-order four 7312 bits of srcutree.convert_to_big is equal to 3 7313 (decide at boot). 7314 7315 srcutree.convert_to_big [KNL] 7316 Specifies under what conditions an SRCU tree 7317 srcu_struct structure will be converted to big 7318 form, that is, with an rcu_node tree: 7319 7320 0: Never. 7321 1: At init_srcu_struct() time. 7322 2: When rcutorture decides to. 7323 3: Decide at boot time (default). 7324 0x1X: Above plus if high contention. 7325 7326 Either way, the srcu_node tree will be sized based 7327 on the actual runtime number of CPUs (nr_cpu_ids) 7328 instead of the compile-time CONFIG_NR_CPUS. 7329 7330 srcutree.counter_wrap_check [KNL] 7331 Specifies how frequently to check for 7332 grace-period sequence counter wrap for the 7333 srcu_data structure's ->srcu_gp_seq_needed field. 7334 The greater the number of bits set in this kernel 7335 parameter, the less frequently counter wrap will 7336 be checked for. Note that the bottom two bits 7337 are ignored. 7338 7339 srcutree.exp_holdoff [KNL] 7340 Specifies how many nanoseconds must elapse 7341 since the end of the last SRCU grace period for 7342 a given srcu_struct until the next normal SRCU 7343 grace period will be considered for automatic 7344 expediting. Set to zero to disable automatic 7345 expediting. 7346 7347 srcutree.srcu_max_nodelay [KNL] 7348 Specifies the number of no-delay instances 7349 per jiffy for which the SRCU grace period 7350 worker thread will be rescheduled with zero 7351 delay. Beyond this limit, worker thread will 7352 be rescheduled with a sleep delay of one jiffy. 7353 7354 srcutree.srcu_max_nodelay_phase [KNL] 7355 Specifies the per-grace-period phase, number of 7356 non-sleeping polls of readers. Beyond this limit, 7357 grace period worker thread will be rescheduled 7358 with a sleep delay of one jiffy, between each 7359 rescan of the readers, for a grace period phase. 7360 7361 srcutree.srcu_retry_check_delay [KNL] 7362 Specifies number of microseconds of non-sleeping 7363 delay between each non-sleeping poll of readers. 7364 7365 srcutree.small_contention_lim [KNL] 7366 Specifies the number of update-side contention 7367 events per jiffy will be tolerated before 7368 initiating a conversion of an srcu_struct 7369 structure to big form. Note that the value of 7370 srcutree.convert_to_big must have the 0x10 bit 7371 set for contention-based conversions to occur. 7372 7373 ssbd= [ARM64,HW,EARLY] 7374 Speculative Store Bypass Disable control 7375 7376 On CPUs that are vulnerable to the Speculative 7377 Store Bypass vulnerability and offer a 7378 firmware based mitigation, this parameter 7379 indicates how the mitigation should be used: 7380 7381 force-on: Unconditionally enable mitigation for 7382 for both kernel and userspace 7383 force-off: Unconditionally disable mitigation for 7384 for both kernel and userspace 7385 kernel: Always enable mitigation in the 7386 kernel, and offer a prctl interface 7387 to allow userspace to register its 7388 interest in being mitigated too. 7389 7390 stack_guard_gap= [MM] 7391 override the default stack gap protection. The value 7392 is in page units and it defines how many pages prior 7393 to (for stacks growing down) resp. after (for stacks 7394 growing up) the main stack are reserved for no other 7395 mapping. Default value is 256 pages. 7396 7397 stack_depot_disable= [KNL,EARLY] 7398 Setting this to true through kernel command line will 7399 disable the stack depot thereby saving the static memory 7400 consumed by the stack hash table. By default this is set 7401 to false. 7402 7403 stack_depot_max_pools= [KNL,EARLY] 7404 Specify the maximum number of pools to use for storing 7405 stack traces. Pools are allocated on-demand up to this 7406 limit. Default value is 8191 pools. 7407 7408 stacktrace [FTRACE] 7409 Enable the stack tracer on boot up. 7410 7411 stacktrace_filter=[function-list] 7412 [FTRACE] Limit the functions that the stack tracer 7413 will trace at boot up. function-list is a comma-separated 7414 list of functions. This list can be changed at run 7415 time by the stack_trace_filter file in the debugfs 7416 tracing directory. Note, this enables stack tracing 7417 and the stacktrace above is not needed. 7418 7419 sti= [PARISC,HW] 7420 Format: <num> 7421 Set the STI (builtin display/keyboard on the HP-PARISC 7422 machines) console (graphic card) which should be used 7423 as the initial boot-console. 7424 See also comment in drivers/video/sticore.c. 7425 7426 sti_font= [HW] 7427 See comment in drivers/video/sticore.c. 7428 7429 stifb= [HW] 7430 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7431 7432 strict_sas_size= 7433 [X86] 7434 Format: <bool> 7435 Enable or disable strict sigaltstack size checks 7436 against the required signal frame size which 7437 depends on the supported FPU features. This can 7438 be used to filter out binaries which have 7439 not yet been made aware of AT_MINSIGSTKSZ. 7440 7441 stress_hpt [PPC,EARLY] 7442 Limits the number of kernel HPT entries in the hash 7443 page table to increase the rate of hash page table 7444 faults on kernel addresses. 7445 7446 stress_slb [PPC,EARLY] 7447 Limits the number of kernel SLB entries, and flushes 7448 them frequently to increase the rate of SLB faults 7449 on kernel addresses. 7450 7451 no_slb_preload [PPC,EARLY] 7452 Disables slb preloading for userspace. 7453 7454 sunrpc.min_resvport= 7455 sunrpc.max_resvport= 7456 [NFS,SUNRPC] 7457 SunRPC servers often require that client requests 7458 originate from a privileged port (i.e. a port in the 7459 range 0 < portnr < 1024). 7460 An administrator who wishes to reserve some of these 7461 ports for other uses may adjust the range that the 7462 kernel's sunrpc client considers to be privileged 7463 using these two parameters to set the minimum and 7464 maximum port values. 7465 7466 sunrpc.svc_rpc_per_connection_limit= 7467 [NFS,SUNRPC] 7468 Limit the number of requests that the server will 7469 process in parallel from a single connection. 7470 The default value is 0 (no limit). 7471 7472 sunrpc.pool_mode= 7473 [NFS] 7474 Control how the NFS server code allocates CPUs to 7475 service thread pools. Depending on how many NICs 7476 you have and where their interrupts are bound, this 7477 option will affect which CPUs will do NFS serving. 7478 Note: this parameter cannot be changed while the 7479 NFS server is running. 7480 7481 auto the server chooses an appropriate mode 7482 automatically using heuristics 7483 global a single global pool contains all CPUs 7484 percpu one pool for each CPU 7485 pernode one pool for each NUMA node (equivalent 7486 to global on non-NUMA machines) 7487 7488 sunrpc.tcp_slot_table_entries= 7489 sunrpc.udp_slot_table_entries= 7490 [NFS,SUNRPC] 7491 Sets the upper limit on the number of simultaneous 7492 RPC calls that can be sent from the client to a 7493 server. Increasing these values may allow you to 7494 improve throughput, but will also increase the 7495 amount of memory reserved for use by the client. 7496 7497 suspend.pm_test_delay= 7498 [SUSPEND] 7499 Sets the number of seconds to remain in a suspend test 7500 mode before resuming the system (see 7501 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7502 is set. Default value is 5. 7503 7504 svm= [PPC] 7505 Format: { on | off | y | n | 1 | 0 } 7506 This parameter controls use of the Protected 7507 Execution Facility on pSeries. 7508 7509 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7510 Format: { <int> [,<int>] | force | noforce } 7511 <int> -- Number of I/O TLB slabs 7512 <int> -- Second integer after comma. Number of swiotlb 7513 areas with their own lock. Will be rounded up 7514 to a power of 2. 7515 force -- force using of bounce buffers even if they 7516 wouldn't be automatically used by the kernel 7517 noforce -- Never use bounce buffers (for debugging) 7518 7519 switches= [HW,M68k,EARLY] 7520 7521 sysctl.*= [KNL] 7522 Set a sysctl parameter, right before loading the init 7523 process, as if the value was written to the respective 7524 /proc/sys/... file. Both '.' and '/' are recognized as 7525 separators. Unrecognized parameters and invalid values 7526 are reported in the kernel log. Sysctls registered 7527 later by a loaded module cannot be set this way. 7528 Example: sysctl.vm.swappiness=40 7529 7530 sysrq_always_enabled 7531 [KNL] 7532 Ignore sysrq setting - this boot parameter will 7533 neutralize any effect of /proc/sys/kernel/sysrq. 7534 Useful for debugging. 7535 7536 tcpmhash_entries= [KNL,NET] 7537 Set the number of tcp_metrics_hash slots. 7538 Default value is 8192 or 16384 depending on total 7539 ram pages. This is used to specify the TCP metrics 7540 cache size. See Documentation/networking/ip-sysctl.rst 7541 "tcp_no_metrics_save" section for more details. 7542 7543 tdfx= [HW,DRM] 7544 7545 test_suspend= [SUSPEND] 7546 Format: { "mem" | "standby" | "freeze" }[,N] 7547 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7548 standby suspend) or "freeze" (for suspend type freeze) 7549 as the system sleep state during system startup with 7550 the optional capability to repeat N number of times. 7551 The system is woken from this state using a 7552 wakeup-capable RTC alarm. 7553 7554 thash_entries= [KNL,NET] 7555 Set number of hash buckets for TCP connection 7556 7557 thermal.act= [HW,ACPI] 7558 -1: disable all active trip points in all thermal zones 7559 <degrees C>: override all lowest active trip points 7560 7561 thermal.crt= [HW,ACPI] 7562 -1: disable all critical trip points in all thermal zones 7563 <degrees C>: override all critical trip points 7564 7565 thermal.off= [HW,ACPI] 7566 1: disable ACPI thermal control 7567 7568 thermal.psv= [HW,ACPI] 7569 -1: disable all passive trip points 7570 <degrees C>: override all passive trip points to this 7571 value 7572 7573 thermal.tzp= [HW,ACPI] 7574 Specify global default ACPI thermal zone polling rate 7575 <deci-seconds>: poll all this frequency 7576 0: no polling (default) 7577 7578 thp_anon= [KNL] 7579 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7580 state is one of "always", "madvise", "never" or "inherit". 7581 Control the default behavior of the system with respect 7582 to anonymous transparent hugepages. 7583 Can be used multiple times for multiple anon THP sizes. 7584 See Documentation/admin-guide/mm/transhuge.rst for more 7585 details. 7586 7587 threadirqs [KNL,EARLY] 7588 Force threading of all interrupt handlers except those 7589 marked explicitly IRQF_NO_THREAD. 7590 7591 thp_shmem= [KNL] 7592 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7593 Control the default policy of each hugepage size for the 7594 internal shmem mount. <policy> is one of policies available 7595 for the shmem mount ("always", "inherit", "never", "within_size", 7596 and "advise"). 7597 It can be used multiple times for multiple shmem THP sizes. 7598 See Documentation/admin-guide/mm/transhuge.rst for more 7599 details. 7600 7601 tlbi= [X86-64] 7602 Format: {ipi} 7603 ipi: switch to IPI-based TLB flushing 7604 7605 topology= [S390,EARLY] 7606 Format: {off | on} 7607 Specify if the kernel should make use of the cpu 7608 topology information if the hardware supports this. 7609 The scheduler will make use of this information and 7610 e.g. base its process migration decisions on it. 7611 Default is on. 7612 7613 torture.disable_onoff_at_boot= [KNL] 7614 Prevent the CPU-hotplug component of torturing 7615 until after init has spawned. 7616 7617 torture.ftrace_dump_at_shutdown= [KNL] 7618 Dump the ftrace buffer at torture-test shutdown, 7619 even if there were no errors. This can be a 7620 very costly operation when many torture tests 7621 are running concurrently, especially on systems 7622 with rotating-rust storage. 7623 7624 torture.verbose_sleep_frequency= [KNL] 7625 Specifies how many verbose printk()s should be 7626 emitted between each sleep. The default of zero 7627 disables verbose-printk() sleeping. 7628 7629 torture.verbose_sleep_duration= [KNL] 7630 Duration of each verbose-printk() sleep in jiffies. 7631 7632 tpm.disable_pcr_integrity= [HW,TPM] 7633 Do not protect PCR registers from unintended physical 7634 access, or interposers in the bus by the means of 7635 having an integrity protected session wrapped around 7636 TPM2_PCR_Extend command. Consider this in a situation 7637 where TPM is heavily utilized by IMA, thus protection 7638 causing a major performance hit, and the space where 7639 machines are deployed is by other means guarded. 7640 7641 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7642 Maximum time in milliseconds to retry sending a message 7643 to the TPM service before giving up. This parameter controls 7644 how long the system will continue retrying when the TPM 7645 service is busy. 7646 Format: <unsigned int> 7647 Default: 2000 (2 seconds) 7648 7649 tpm_suspend_pcr=[HW,TPM] 7650 Format: integer pcr id 7651 Specify that at suspend time, the tpm driver 7652 should extend the specified pcr with zeros, 7653 as a workaround for some chips which fail to 7654 flush the last written pcr on TPM_SaveState. 7655 This will guarantee that all the other pcrs 7656 are saved. 7657 7658 tpm_tis.interrupts= [HW,TPM] 7659 Enable interrupts for the MMIO based physical layer 7660 for the FIFO interface. By default it is set to false 7661 (0). For more information about TPM hardware interfaces 7662 defined by Trusted Computing Group (TCG) see 7663 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7664 7665 tp_printk [FTRACE] 7666 Have the tracepoints sent to printk as well as the 7667 tracing ring buffer. This is useful for early boot up 7668 where the system hangs or reboots and does not give the 7669 option for reading the tracing buffer or performing a 7670 ftrace_dump_on_oops. 7671 7672 To turn off having tracepoints sent to printk, 7673 echo 0 > /proc/sys/kernel/tracepoint_printk 7674 Note, echoing 1 into this file without the 7675 tp_printk kernel cmdline option has no effect. 7676 7677 The tp_printk_stop_on_boot (see below) can also be used 7678 to stop the printing of events to console at 7679 late_initcall_sync. 7680 7681 ** CAUTION ** 7682 7683 Having tracepoints sent to printk() and activating high 7684 frequency tracepoints such as irq or sched, can cause 7685 the system to live lock. 7686 7687 tp_printk_stop_on_boot [FTRACE] 7688 When tp_printk (above) is set, it can cause a lot of noise 7689 on the console. It may be useful to only include the 7690 printing of events during boot up, as user space may 7691 make the system inoperable. 7692 7693 This command line option will stop the printing of events 7694 to console at the late_initcall_sync() time frame. 7695 7696 trace_buf_size=nn[KMG] 7697 [FTRACE] will set tracing buffer size on each cpu. 7698 7699 trace_clock= [FTRACE] Set the clock used for tracing events 7700 at boot up. 7701 local - Use the per CPU time stamp counter 7702 (converted into nanoseconds). Fast, but 7703 depending on the architecture, may not be 7704 in sync between CPUs. 7705 global - Event time stamps are synchronized across 7706 CPUs. May be slower than the local clock, 7707 but better for some race conditions. 7708 counter - Simple counting of events (1, 2, ..) 7709 note, some counts may be skipped due to the 7710 infrastructure grabbing the clock more than 7711 once per event. 7712 uptime - Use jiffies as the time stamp. 7713 perf - Use the same clock that perf uses. 7714 mono - Use ktime_get_mono_fast_ns() for time stamps. 7715 mono_raw - Use ktime_get_raw_fast_ns() for time 7716 stamps. 7717 boot - Use ktime_get_boot_fast_ns() for time stamps. 7718 Architectures may add more clocks. See 7719 Documentation/trace/ftrace.rst for more details. 7720 7721 trace_event=[event-list] 7722 [FTRACE] Set and start specified trace events in order 7723 to facilitate early boot debugging. The event-list is a 7724 comma-separated list of trace events to enable. See 7725 also Documentation/trace/events.rst 7726 7727 To enable modules, use :mod: keyword: 7728 7729 trace_event=:mod:<module> 7730 7731 The value before :mod: will only enable specific events 7732 that are part of the module. See the above mentioned 7733 document for more information. 7734 7735 trace_instance=[instance-info] 7736 [FTRACE] Create a ring buffer instance early in boot up. 7737 This will be listed in: 7738 7739 /sys/kernel/tracing/instances 7740 7741 Events can be enabled at the time the instance is created 7742 via: 7743 7744 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7745 7746 Note, the "<system*>:" portion is optional if the event is 7747 unique. 7748 7749 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7750 7751 will enable the "sched_switch" event (note, the "sched:" is optional, and 7752 the same thing would happen if it was left off). The irq_handler_entry 7753 event, and all events under the "initcall" system. 7754 7755 Flags can be added to the instance to modify its behavior when it is 7756 created. The flags are separated by '^'. 7757 7758 The available flags are: 7759 7760 traceoff - Have the tracing instance tracing disabled after it is created. 7761 traceprintk - Have trace_printk() write into this trace instance 7762 (note, "printk" and "trace_printk" can also be used) 7763 7764 trace_instance=foo^traceoff^traceprintk,sched,irq 7765 7766 The flags must come before the defined events. 7767 7768 If memory has been reserved (see memmap for x86), the instance 7769 can use that memory: 7770 7771 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7772 7773 The above will create a "boot_map" instance that uses the physical 7774 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7775 instance will be split up accordingly. 7776 7777 Alternatively, the memory can be reserved by the reserve_mem option: 7778 7779 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7780 7781 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7782 and place the ring buffer in this memory. Note that due to KASLR, the 7783 memory may not be the same location each time, which will not preserve 7784 the buffer content. 7785 7786 Also note that the layout of the ring buffer data may change between 7787 kernel versions where the validator will fail and reset the ring buffer 7788 if the layout is not the same as the previous kernel. 7789 7790 If the ring buffer is used for persistent bootups and has events enabled, 7791 it is recommend to disable tracing so that events from a previous boot do not 7792 mix with events of the current boot (unless you are debugging a random crash 7793 at boot up). 7794 7795 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7796 7797 Note, saving the trace buffer across reboots does require that the system 7798 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7799 can force a memory reset on boot which will clear any trace that was stored. 7800 This is just one of many ways that can clear memory. Make sure your system 7801 keeps the content of memory across reboots before relying on this option. 7802 7803 NB: Both the mapped address and size must be page aligned for the architecture. 7804 7805 See also Documentation/trace/debugging.rst 7806 7807 7808 trace_options=[option-list] 7809 [FTRACE] Enable or disable tracer options at boot. 7810 The option-list is a comma delimited list of options 7811 that can be enabled or disabled just as if you were 7812 to echo the option name into 7813 7814 /sys/kernel/tracing/trace_options 7815 7816 For example, to enable stacktrace option (to dump the 7817 stack trace of each event), add to the command line: 7818 7819 trace_options=stacktrace 7820 7821 See also Documentation/trace/ftrace.rst "trace options" 7822 section. 7823 7824 trace_trigger=[trigger-list] 7825 [FTRACE] Add an event trigger on specific events. 7826 Set a trigger on top of a specific event, with an optional 7827 filter. 7828 7829 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7830 Where more than one trigger may be specified that are comma delimited. 7831 7832 For example: 7833 7834 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7835 7836 The above will enable the "stacktrace" trigger on the "sched_switch" 7837 event but only trigger it if the "prev_state" of the "sched_switch" 7838 event is "2" (TASK_UNINTERRUPTIBLE). 7839 7840 See also "Event triggers" in Documentation/trace/events.rst 7841 7842 7843 traceoff_after_boot 7844 [FTRACE] Sometimes tracing is used to debug issues 7845 during the boot process. Since the trace buffer has a 7846 limited amount of storage, it may be prudent to 7847 disable tracing after the boot is finished, otherwise 7848 the critical information may be overwritten. With this 7849 option, the main tracing buffer will be turned off at 7850 the end of the boot process. 7851 7852 traceoff_on_warning 7853 [FTRACE] enable this option to disable tracing when a 7854 warning is hit. This turns off "tracing_on". Tracing can 7855 be enabled again by echoing '1' into the "tracing_on" 7856 file located in /sys/kernel/tracing/ 7857 7858 This option is useful, as it disables the trace before 7859 the WARNING dump is called, which prevents the trace to 7860 be filled with content caused by the warning output. 7861 7862 This option can also be set at run time via the sysctl 7863 option: kernel/traceoff_on_warning 7864 7865 transparent_hugepage= 7866 [KNL] 7867 Format: [always|madvise|never] 7868 Can be used to control the default behavior of the system 7869 with respect to transparent hugepages. 7870 See Documentation/admin-guide/mm/transhuge.rst 7871 for more details. 7872 7873 transparent_hugepage_shmem= [KNL] 7874 Format: [always|within_size|advise|never|deny|force] 7875 Can be used to control the hugepage allocation policy for 7876 the internal shmem mount. 7877 See Documentation/admin-guide/mm/transhuge.rst 7878 for more details. 7879 7880 transparent_hugepage_tmpfs= [KNL] 7881 Format: [always|within_size|advise|never] 7882 Can be used to control the default hugepage allocation policy 7883 for the tmpfs mount. 7884 See Documentation/admin-guide/mm/transhuge.rst 7885 for more details. 7886 7887 trusted.source= [KEYS] 7888 Format: <string> 7889 This parameter identifies the trust source as a backend 7890 for trusted keys implementation. Supported trust 7891 sources: 7892 - "tpm" 7893 - "tee" 7894 - "caam" 7895 - "dcp" 7896 - "pkwm" 7897 If not specified then it defaults to iterating through 7898 the trust source list starting with TPM and assigns the 7899 first trust source as a backend which is initialized 7900 successfully during iteration. 7901 7902 trusted.debug= [KEYS] 7903 Format: <bool> 7904 Enable trusted keys debug traces at runtime when 7905 CONFIG_TRUSTED_KEYS_DEBUG=y. 7906 7907 To make the traces visible after enabling the option, 7908 use trusted.dyndbg='+p' as needed. By convention, 7909 the subsystem uses pr_debug() for these traces. 7910 7911 SAFETY: The traces can leak sensitive data, so be 7912 cautious before enabling this. They remain inactive 7913 unless this parameter is set this option to a true 7914 value. 7915 7916 Default: false 7917 7918 trusted.rng= [KEYS] 7919 Format: <string> 7920 The RNG used to generate key material for trusted keys. 7921 Can be one of: 7922 - "kernel" 7923 - the same value as trusted.source: "tpm" or "tee" 7924 - "default" 7925 If not specified, "default" is used. In this case, 7926 the RNG's choice is left to each individual trust source. 7927 7928 trusted.dcp_use_otp_key 7929 This is intended to be used in combination with 7930 trusted.source=dcp and will select the DCP OTP key 7931 instead of the DCP UNIQUE key blob encryption. 7932 7933 trusted.dcp_skip_zk_test 7934 This is intended to be used in combination with 7935 trusted.source=dcp and will disable the check if the 7936 blob key is all zeros. This is helpful for situations where 7937 having this key zero'ed is acceptable. E.g. in testing 7938 scenarios. 7939 7940 tsa= [X86] Control mitigation for Transient Scheduler 7941 Attacks on AMD CPUs. Search the following in your 7942 favourite search engine for more details: 7943 7944 "Technical guidance for mitigating transient scheduler 7945 attacks". 7946 7947 off - disable the mitigation 7948 on - enable the mitigation (default) 7949 user - mitigate only user/kernel transitions 7950 vm - mitigate only guest/host transitions 7951 7952 7953 tsc= Disable clocksource stability checks for TSC. 7954 Format: <string> 7955 [x86] reliable: mark tsc clocksource as reliable, this 7956 disables clocksource verification at runtime, as well 7957 as the stability checks done at bootup. Used to enable 7958 high-resolution timer mode on older hardware, and in 7959 virtualized environment. 7960 [x86] noirqtime: Do not use TSC to do irq accounting. 7961 Used to run time disable IRQ_TIME_ACCOUNTING on any 7962 platforms where RDTSC is slow and this accounting 7963 can add overhead. 7964 [x86] unstable: mark the TSC clocksource as unstable, this 7965 marks the TSC unconditionally unstable at bootup and 7966 avoids any further wobbles once the TSC watchdog notices. 7967 [x86] nowatchdog: disable clocksource watchdog. Used 7968 in situations with strict latency requirements (where 7969 interruptions from clocksource watchdog are not 7970 acceptable). 7971 [x86] recalibrate: force recalibration against a HW timer 7972 (HPET or PM timer) on systems whose TSC frequency was 7973 obtained from HW or FW using either an MSR or CPUID(0x15). 7974 Warn if the difference is more than 500 ppm. 7975 [x86] watchdog: Enforce the clocksource watchdog on TSC 7976 7977 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7978 value instead. Useful when the early TSC frequency discovery 7979 procedure is not reliable, such as on overclocked systems 7980 with CPUID.16h support and partial CPUID.15h support. 7981 Format: <unsigned int> 7982 7983 tsx= [X86] Control Transactional Synchronization 7984 Extensions (TSX) feature in Intel processors that 7985 support TSX control. 7986 7987 This parameter controls the TSX feature. The options are: 7988 7989 on - Enable TSX on the system. Although there are 7990 mitigations for all known security vulnerabilities, 7991 TSX has been known to be an accelerator for 7992 several previous speculation-related CVEs, and 7993 so there may be unknown security risks associated 7994 with leaving it enabled. 7995 7996 off - Disable TSX on the system. (Note that this 7997 option takes effect only on newer CPUs which are 7998 not vulnerable to MDS, i.e., have 7999 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 8000 the new IA32_TSX_CTRL MSR through a microcode 8001 update. This new MSR allows for the reliable 8002 deactivation of the TSX functionality.) 8003 8004 auto - Disable TSX if X86_BUG_TAA is present, 8005 otherwise enable TSX on the system. 8006 8007 Not specifying this option is equivalent to tsx=off. 8008 8009 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8010 for more details. 8011 8012 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 8013 Abort (TAA) vulnerability. 8014 8015 Similar to Micro-architectural Data Sampling (MDS) 8016 certain CPUs that support Transactional 8017 Synchronization Extensions (TSX) are vulnerable to an 8018 exploit against CPU internal buffers which can forward 8019 information to a disclosure gadget under certain 8020 conditions. 8021 8022 In vulnerable processors, the speculatively forwarded 8023 data can be used in a cache side channel attack, to 8024 access data to which the attacker does not have direct 8025 access. 8026 8027 This parameter controls the TAA mitigation. The 8028 options are: 8029 8030 full - Enable TAA mitigation on vulnerable CPUs 8031 if TSX is enabled. 8032 8033 full,nosmt - Enable TAA mitigation and disable SMT on 8034 vulnerable CPUs. If TSX is disabled, SMT 8035 is not disabled because CPU is not 8036 vulnerable to cross-thread TAA attacks. 8037 off - Unconditionally disable TAA mitigation 8038 8039 On MDS-affected machines, tsx_async_abort=off can be 8040 prevented by an active MDS mitigation as both vulnerabilities 8041 are mitigated with the same mechanism so in order to disable 8042 this mitigation, you need to specify mds=off too. 8043 8044 Not specifying this option is equivalent to 8045 tsx_async_abort=full. On CPUs which are MDS affected 8046 and deploy MDS mitigation, TAA mitigation is not 8047 required and doesn't provide any additional 8048 mitigation. 8049 8050 For details see: 8051 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8052 8053 turbografx.map[2|3]= [HW,JOY] 8054 TurboGraFX parallel port interface 8055 Format: 8056 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8057 See also Documentation/input/devices/joystick-parport.rst 8058 8059 udbg-immortal [PPC] When debugging early kernel crashes that 8060 happen after console_init() and before a proper 8061 console driver takes over, this boot options might 8062 help "seeing" what's going on. 8063 8064 uhash_entries= [KNL,NET] 8065 Set number of hash buckets for UDP/UDP-Lite connections 8066 8067 uhci-hcd.ignore_oc= 8068 [USB] Ignore overcurrent events (default N). 8069 Some badly-designed motherboards generate lots of 8070 bogus events, for ports that aren't wired to 8071 anything. Set this parameter to avoid log spamming. 8072 Note that genuine overcurrent events won't be 8073 reported either. 8074 8075 unaligned_scalar_speed= 8076 [RISCV] 8077 Format: {slow | fast | unsupported} 8078 Allow skipping scalar unaligned access speed tests. This 8079 is useful for testing alternative code paths and to skip 8080 the tests in environments where they run too slowly. All 8081 CPUs must have the same scalar unaligned access speed. 8082 8083 unaligned_vector_speed= 8084 [RISCV] 8085 Format: {slow | fast | unsupported} 8086 Allow skipping vector unaligned access speed tests. This 8087 is useful for testing alternative code paths and to skip 8088 the tests in environments where they run too slowly. All 8089 CPUs must have the same vector unaligned access speed. 8090 8091 unknown_nmi_panic 8092 [X86] Cause panic on unknown NMI. 8093 8094 unwind_debug [X86-64,EARLY] 8095 Enable unwinder debug output. This can be 8096 useful for debugging certain unwinder error 8097 conditions, including corrupt stacks and 8098 bad/missing unwinder metadata. 8099 8100 usbcore.authorized_default= 8101 [USB] Default USB device authorization: 8102 (default -1 = authorized (same as 1), 8103 0 = not authorized, 1 = authorized, 2 = authorized 8104 if device connected to internal port) 8105 8106 usbcore.autosuspend= 8107 [USB] The autosuspend time delay (in seconds) used 8108 for newly-detected USB devices (default 2). This 8109 is the time required before an idle device will be 8110 autosuspended. Devices for which the delay is set 8111 to a negative value won't be autosuspended at all. 8112 8113 usbcore.usbfs_snoop= 8114 [USB] Set to log all usbfs traffic (default 0 = off). 8115 8116 usbcore.usbfs_snoop_max= 8117 [USB] Maximum number of bytes to snoop in each URB 8118 (default = 65536). 8119 8120 usbcore.blinkenlights= 8121 [USB] Set to cycle leds on hubs (default 0 = off). 8122 8123 usbcore.old_scheme_first= 8124 [USB] Start with the old device initialization 8125 scheme (default 0 = off). 8126 8127 usbcore.usbfs_memory_mb= 8128 [USB] Memory limit (in MB) for buffers allocated by 8129 usbfs (default = 16, 0 = max = 2047). 8130 8131 usbcore.use_both_schemes= 8132 [USB] Try the other device initialization scheme 8133 if the first one fails (default 1 = enabled). 8134 8135 usbcore.initial_descriptor_timeout= 8136 [USB] Specifies timeout for the initial 64-byte 8137 USB_REQ_GET_DESCRIPTOR request in milliseconds 8138 (default 5000 = 5.0 seconds). 8139 8140 usbcore.nousb [USB] Disable the USB subsystem 8141 8142 usbcore.quirks= 8143 [USB] A list of quirk entries to augment the built-in 8144 usb core quirk list. List entries are separated by 8145 commas. Each entry has the form 8146 VendorID:ProductID:Flags. The IDs are 4-digit hex 8147 numbers and Flags is a set of letters. Each letter 8148 will change the built-in quirk; setting it if it is 8149 clear and clearing it if it is set. The letters have 8150 the following meanings: 8151 a = USB_QUIRK_STRING_FETCH_255 (string 8152 descriptors must not be fetched using 8153 a 255-byte read); 8154 b = USB_QUIRK_RESET_RESUME (device can't resume 8155 correctly so reset it instead); 8156 c = USB_QUIRK_NO_SET_INTF (device can't handle 8157 Set-Interface requests); 8158 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8159 handle its Configuration or Interface 8160 strings); 8161 e = USB_QUIRK_RESET (device can't be reset 8162 (e.g morph devices), don't use reset); 8163 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8164 more interface descriptions than the 8165 bNumInterfaces count, and can't handle 8166 talking to these interfaces); 8167 g = USB_QUIRK_DELAY_INIT (device needs a pause 8168 during initialization, after we read 8169 the device descriptor); 8170 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8171 high speed and super speed interrupt 8172 endpoints, the USB 2.0 and USB 3.0 spec 8173 require the interval in microframes (1 8174 microframe = 125 microseconds) to be 8175 calculated as interval = 2 ^ 8176 (bInterval-1). 8177 Devices with this quirk report their 8178 bInterval as the result of this 8179 calculation instead of the exponent 8180 variable used in the calculation); 8181 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8182 handle device_qualifier descriptor 8183 requests); 8184 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8185 generates spurious wakeup, ignore 8186 remote wakeup capability); 8187 k = USB_QUIRK_NO_LPM (device can't handle Link 8188 Power Management); 8189 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8190 (Device reports its bInterval as linear 8191 frames instead of the USB 2.0 8192 calculation); 8193 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8194 to be disconnected before suspend to 8195 prevent spurious wakeup); 8196 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8197 pause after every control message); 8198 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8199 delay after resetting its port); 8200 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8201 (Reduce timeout of the SET_ADDRESS 8202 request from 5000 ms to 500 ms); 8203 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8204 claims zero configurations, 8205 forcing to 1); 8206 r = USB_QUIRK_WINDOWS_CONFIG_REQ_SIZE (Device 8207 fails during initialization when asked for 8208 9-bytes configuration descriptor request. 8209 Ask for 255-bytes request instead to mirror 8210 Windows' behavior); 8211 Example: quirks=0781:5580:bk,0a5c:5834:gij 8212 8213 usbhid.mousepoll= 8214 [USBHID] The interval which mice are to be polled at. 8215 8216 usbhid.jspoll= 8217 [USBHID] The interval which joysticks are to be polled at. 8218 8219 usbhid.kbpoll= 8220 [USBHID] The interval which keyboards are to be polled at. 8221 8222 usb-storage.delay_use= 8223 [UMS] The delay in seconds before a new device is 8224 scanned for Logical Units (default 1). 8225 Optionally the delay in milliseconds if the value has 8226 suffix with "ms". 8227 Example: delay_use=2567ms 8228 8229 usb-storage.quirks= 8230 [UMS] A list of quirks entries to supplement or 8231 override the built-in unusual_devs list. List 8232 entries are separated by commas. Each entry has 8233 the form VID:PID:Flags where VID and PID are Vendor 8234 and Product ID values (4-digit hex numbers) and 8235 Flags is a set of characters, each corresponding 8236 to a common usb-storage quirk flag as follows: 8237 a = SANE_SENSE (collect more than 18 bytes 8238 of sense data, not on uas); 8239 b = BAD_SENSE (don't collect more than 18 8240 bytes of sense data, not on uas); 8241 c = FIX_CAPACITY (decrease the reported 8242 device capacity by one sector); 8243 d = NO_READ_DISC_INFO (don't use 8244 READ_DISC_INFO command, not on uas); 8245 e = NO_READ_CAPACITY_16 (don't use 8246 READ_CAPACITY_16 command); 8247 f = NO_REPORT_OPCODES (don't use report opcodes 8248 command, uas only); 8249 g = MAX_SECTORS_240 (don't transfer more than 8250 240 sectors at a time, uas only); 8251 h = CAPACITY_HEURISTICS (decrease the 8252 reported device capacity by one 8253 sector if the number is odd); 8254 i = IGNORE_DEVICE (don't bind to this 8255 device); 8256 j = NO_REPORT_LUNS (don't use report luns 8257 command, uas only); 8258 k = NO_SAME (do not use WRITE_SAME, uas only) 8259 l = NOT_LOCKABLE (don't try to lock and 8260 unlock ejectable media, not on uas); 8261 m = MAX_SECTORS_64 (don't transfer more 8262 than 64 sectors = 32 KB at a time, 8263 not on uas); 8264 n = INITIAL_READ10 (force a retry of the 8265 initial READ(10) command, not on uas); 8266 o = CAPACITY_OK (accept the capacity 8267 reported by the device, not on uas); 8268 p = WRITE_CACHE (the device cache is ON 8269 by default, not on uas); 8270 r = IGNORE_RESIDUE (the device reports 8271 bogus residue values, not on uas); 8272 s = SINGLE_LUN (the device has only one 8273 Logical Unit); 8274 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8275 commands, uas only); 8276 u = IGNORE_UAS (don't bind to the uas driver); 8277 w = NO_WP_DETECT (don't test whether the 8278 medium is write-protected). 8279 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8280 even if the device claims no cache, 8281 not on uas) 8282 Example: quirks=0419:aaf5:rl,0421:0433:rc 8283 8284 user_debug= [KNL,ARM] 8285 Format: <int> 8286 See arch/arm/Kconfig.debug help text. 8287 1 - undefined instruction events 8288 2 - system calls 8289 4 - invalid data aborts 8290 8 - SIGSEGV faults 8291 16 - SIGBUS faults 8292 Example: user_debug=31 8293 8294 vdso= [X86,SH,SPARC] 8295 On X86_32, this is an alias for vdso32=. Otherwise: 8296 8297 vdso=1: enable VDSO (the default) 8298 vdso=0: disable VDSO mapping 8299 8300 vdso32= [X86] Control the 32-bit vDSO 8301 vdso32=1: enable 32-bit VDSO 8302 vdso32=0 or vdso32=2: disable 32-bit VDSO 8303 8304 See the help text for CONFIG_COMPAT_VDSO for more 8305 details. If CONFIG_COMPAT_VDSO is set, the default is 8306 vdso32=0; otherwise, the default is vdso32=1. 8307 8308 For compatibility with older kernels, vdso32=2 is an 8309 alias for vdso32=0. 8310 8311 Try vdso32=0 if you encounter an error that says: 8312 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8313 8314 video= [FB,EARLY] Frame buffer configuration 8315 See Documentation/fb/modedb.rst. 8316 8317 video.brightness_switch_enabled= [ACPI] 8318 Format: [0|1] 8319 If set to 1, on receiving an ACPI notify event 8320 generated by hotkey, video driver will adjust brightness 8321 level and then send out the event to user space through 8322 the allocated input device. If set to 0, video driver 8323 will only send out the event without touching backlight 8324 brightness level. 8325 default: 1 8326 8327 virtio_mmio.device= 8328 [VMMIO] Memory mapped virtio (platform) device. 8329 8330 <size>@<baseaddr>:<irq>[:<id>] 8331 where: 8332 <size> := size (can use standard suffixes 8333 like K, M and G) 8334 <baseaddr> := physical base address 8335 <irq> := interrupt number (as passed to 8336 request_irq()) 8337 <id> := (optional) platform device id 8338 example: 8339 virtio_mmio.device=1K@0x100b0000:48:7 8340 8341 Can be used multiple times for multiple devices. 8342 8343 vga= [BOOT,X86-32] Select a particular video mode 8344 See Documentation/arch/x86/boot.rst and 8345 Documentation/admin-guide/svga.rst. 8346 Use vga=ask for menu. 8347 This is actually a boot loader parameter; the value is 8348 passed to the kernel using a special protocol. 8349 8350 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8351 May slow down system boot speed, especially when 8352 enabled on systems with a large amount of memory. 8353 All options are enabled by default, and this 8354 interface is meant to allow for selectively 8355 enabling or disabling specific virtual memory 8356 debugging features. 8357 8358 Available options are: 8359 P Enable page structure init time poisoning 8360 - Disable all of the above options 8361 8362 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8363 exact size of <nn>. This can be used to increase 8364 the minimum size (128MB on x86, arm32 platforms). 8365 It can also be used to decrease the size and leave more room 8366 for directly mapped kernel RAM. Note that this parameter does 8367 not exist on many other platforms (including arm64, alpha, 8368 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8369 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8370 8371 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8372 Sets the memory size reserved for contiguous memory 8373 allocations for the vmcp device driver. 8374 8375 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8376 Format: <command> 8377 8378 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8379 Format: <command> 8380 8381 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8382 Format: <command> 8383 8384 vmscape= [X86] Controls mitigation for VMscape attacks. 8385 VMscape attacks can leak information from a userspace 8386 hypervisor to a guest via speculative side-channels. 8387 8388 off - disable the mitigation 8389 ibpb - use Indirect Branch Prediction Barrier 8390 (IBPB) mitigation (default) 8391 force - force vulnerability detection even on 8392 unaffected processors 8393 8394 vsyscall= [X86-64,EARLY] 8395 Controls the behavior of vsyscalls (i.e. calls to 8396 fixed addresses of 0xffffffffff600x00 from legacy 8397 code). Most statically-linked binaries and older 8398 versions of glibc use these calls. Because these 8399 functions are at fixed addresses, they make nice 8400 targets for exploits that can control RIP. 8401 8402 emulate Vsyscalls turn into traps and are emulated 8403 reasonably safely. The vsyscall page is 8404 readable. This disables the Linear 8405 Address Space Separation (LASS) security 8406 feature and makes the system less secure. 8407 8408 xonly [default] Vsyscalls turn into traps and are 8409 emulated reasonably safely. The vsyscall 8410 page is not readable. 8411 8412 none Vsyscalls don't work at all. This makes 8413 them quite hard to use for exploits but 8414 might break your system. 8415 8416 vt.color= [VT] Default text color. 8417 Format: 0xYX, X = foreground, Y = background. 8418 Default: 0x07 = light gray on black. 8419 8420 vt.cur_default= [VT] Default cursor shape. 8421 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8422 the parameters of the <Esc>[?A;B;Cc escape sequence; 8423 see vga-softcursor.rst. Default: 2 = underline. 8424 8425 vt.default_blu= [VT] 8426 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8427 Change the default blue palette of the console. 8428 This is a 16-member array composed of values 8429 ranging from 0-255. 8430 8431 vt.default_grn= [VT] 8432 Format: <green0>,<green1>,<green2>,...,<green15> 8433 Change the default green palette of the console. 8434 This is a 16-member array composed of values 8435 ranging from 0-255. 8436 8437 vt.default_red= [VT] 8438 Format: <red0>,<red1>,<red2>,...,<red15> 8439 Change the default red palette of the console. 8440 This is a 16-member array composed of values 8441 ranging from 0-255. 8442 8443 vt.default_utf8= 8444 [VT] 8445 Format=<0|1> 8446 Set system-wide default UTF-8 mode for all tty's. 8447 Default is 1, i.e. UTF-8 mode is enabled for all 8448 newly opened terminals. 8449 8450 vt.global_cursor_default= 8451 [VT] 8452 Format=<-1|0|1> 8453 Set system-wide default for whether a cursor 8454 is shown on new VTs. Default is -1, 8455 i.e. cursors will be created by default unless 8456 overridden by individual drivers. 0 will hide 8457 cursors, 1 will display them. 8458 8459 vt.italic= [VT] Default color for italic text; 0-15. 8460 Default: 2 = green. 8461 8462 vt.underline= [VT] Default color for underlined text; 0-15. 8463 Default: 3 = cyan. 8464 8465 watchdog timers [HW,WDT] For information on watchdog timers, 8466 see Documentation/watchdog/watchdog-parameters.rst 8467 or other driver-specific files in the 8468 Documentation/watchdog/ directory. 8469 8470 watchdog_thresh= 8471 [KNL] 8472 Set the hard lockup detector stall duration 8473 threshold in seconds. The soft lockup detector 8474 threshold is set to twice the value. A value of 0 8475 disables both lockup detectors. Default is 10 8476 seconds. 8477 8478 workqueue.unbound_cpus= 8479 [KNL,SMP] Specify to constrain one or some CPUs 8480 to use in unbound workqueues. 8481 Format: <cpu-list> 8482 By default, all online CPUs are available for 8483 unbound workqueues. 8484 8485 workqueue.watchdog_thresh= 8486 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8487 warn stall conditions and dump internal state to 8488 help debugging. 0 disables workqueue stall 8489 detection; otherwise, it's the stall threshold 8490 duration in seconds. The default value is 30 and 8491 it can be updated at runtime by writing to the 8492 corresponding sysfs file. 8493 8494 workqueue.panic_on_stall=<uint> 8495 Panic when workqueue stall is detected by 8496 CONFIG_WQ_WATCHDOG. It sets the number times of the 8497 stall to trigger panic. 8498 8499 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8500 which is 0 (disabled) if not configured. 8501 8502 workqueue.panic_on_stall_time=<uint> 8503 Panic when a workqueue stall has been continuous for 8504 the specified number of seconds. Unlike panic_on_stall 8505 which counts accumulated stall events, this triggers 8506 based on the duration of a single continuous stall. 8507 8508 The default is 0, which disables the time-based panic. 8509 8510 workqueue.cpu_intensive_thresh_us= 8511 Per-cpu work items which run for longer than this 8512 threshold are automatically considered CPU intensive 8513 and excluded from concurrency management to prevent 8514 them from noticeably delaying other per-cpu work 8515 items. Default is 10000 (10ms). 8516 8517 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8518 will report the work functions which violate this 8519 threshold repeatedly. They are likely good 8520 candidates for using WQ_UNBOUND workqueues instead. 8521 8522 workqueue.cpu_intensive_warning_thresh=<uint> 8523 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8524 will report the work functions which violate the 8525 intensive_threshold_us repeatedly. In order to prevent 8526 spurious warnings, start printing only after a work 8527 function has violated this threshold number of times. 8528 8529 The default is 4 times. 0 disables the warning. 8530 8531 workqueue.power_efficient 8532 Per-cpu workqueues are generally preferred because 8533 they show better performance thanks to cache 8534 locality; unfortunately, per-cpu workqueues tend to 8535 be more power hungry than unbound workqueues. 8536 8537 Enabling this makes the per-cpu workqueues which 8538 were observed to contribute significantly to power 8539 consumption unbound, leading to measurably lower 8540 power usage at the cost of small performance 8541 overhead. 8542 8543 The default value of this parameter is determined by 8544 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8545 8546 workqueue.default_affinity_scope= 8547 Select the default affinity scope to use for unbound 8548 workqueues. Can be one of "cpu", "smt", "cache", 8549 "cache_shard", "numa" and "system". Default is 8550 "cache_shard". For more 8551 information, see the Affinity Scopes section in 8552 Documentation/core-api/workqueue.rst. 8553 8554 This can be changed after boot by writing to the 8555 matching /sys/module/workqueue/parameters file. All 8556 workqueues with the "default" affinity scope will be 8557 updated accordingly. 8558 8559 workqueue.debug_force_rr_cpu 8560 Workqueue used to implicitly guarantee that work 8561 items queued without explicit CPU specified are put 8562 on the local CPU. This guarantee is no longer true 8563 and while local CPU is still preferred work items 8564 may be put on foreign CPUs. This debug option 8565 forces round-robin CPU selection to flush out 8566 usages which depend on the now broken guarantee. 8567 When enabled, memory and cache locality will be 8568 impacted. 8569 8570 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8571 Type) of ioremap_wc(). 8572 8573 on - Enable writecombine, use WUC for ioremap_wc() 8574 off - Disable writecombine, use SUC for ioremap_wc() 8575 8576 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8577 default x2apic cluster mode on platforms 8578 supporting x2apic. 8579 8580 xen_512gb_limit [KNL,X86-64,XEN] 8581 Restricts the kernel running paravirtualized under Xen 8582 to use only up to 512 GB of RAM. The reason to do so is 8583 crash analysis tools and Xen tools for doing domain 8584 save/restore/migration must be enabled to handle larger 8585 domains. 8586 8587 xen_console_io [XEN,EARLY] 8588 Boolean option to enable/disable the usage of the Xen 8589 console_io hypercalls to read and write to the console. 8590 Mostly useful for debugging and development. 8591 8592 xen_emul_unplug= [HW,X86,XEN,EARLY] 8593 Unplug Xen emulated devices 8594 Format: [unplug0,][unplug1] 8595 ide-disks -- unplug primary master IDE devices 8596 aux-ide-disks -- unplug non-primary-master IDE devices 8597 nics -- unplug network devices 8598 all -- unplug all emulated devices (NICs and IDE disks) 8599 unnecessary -- unplugging emulated devices is 8600 unnecessary even if the host did not respond to 8601 the unplug protocol 8602 never -- do not unplug even if version check succeeds 8603 8604 xen_legacy_crash [X86,XEN,EARLY] 8605 Crash from Xen panic notifier, without executing late 8606 panic() code such as dumping handler. 8607 8608 xen_mc_debug [X86,XEN,EARLY] 8609 Enable multicall debugging when running as a Xen PV guest. 8610 Enabling this feature will reduce performance a little 8611 bit, so it should only be enabled for obtaining extended 8612 debug data in case of multicall errors. 8613 8614 xen_msr_safe= [X86,XEN,EARLY] 8615 Format: <bool> 8616 Select whether to always use non-faulting (safe) MSR 8617 access functions when running as Xen PV guest. The 8618 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8619 8620 xen_nopv [X86] 8621 Disables the PV optimizations forcing the HVM guest to 8622 run as generic HVM guest with no PV drivers. 8623 This option is obsoleted by the "nopv" option, which 8624 has equivalent effect for XEN platform. 8625 8626 xen_no_vector_callback 8627 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8628 event channel interrupts. 8629 8630 xen_scrub_pages= [XEN] 8631 Boolean option to control scrubbing pages before giving them back 8632 to Xen, for use by other domains. Can be also changed at runtime 8633 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8634 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8635 8636 xen_timer_slop= [X86-64,XEN,EARLY] 8637 Set the timer slop (in nanoseconds) for the virtual Xen 8638 timers (default is 100000). This adjusts the minimum 8639 delta of virtualized Xen timers, where lower values 8640 improve timer resolution at the expense of processing 8641 more timer interrupts. 8642 8643 xen.balloon_boot_timeout= [XEN] 8644 The time (in seconds) to wait before giving up to boot 8645 in case initial ballooning fails to free enough memory. 8646 Applies only when running as HVM or PVH guest and 8647 started with less memory configured than allowed at 8648 max. Default is 180. 8649 8650 xen.event_eoi_delay= [XEN] 8651 How long to delay EOI handling in case of event 8652 storms (jiffies). Default is 10. 8653 8654 xen.event_loop_timeout= [XEN] 8655 After which time (jiffies) the event handling loop 8656 should start to delay EOI handling. Default is 2. 8657 8658 xen.fifo_events= [XEN] 8659 Boolean parameter to disable using fifo event handling 8660 even if available. Normally fifo event handling is 8661 preferred over the 2-level event handling, as it is 8662 fairer and the number of possible event channels is 8663 much higher. Default is on (use fifo events). 8664 8665 xirc2ps_cs= [NET,PCMCIA] 8666 Format: 8667 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8668 8669 xive= [PPC] 8670 By default on POWER9 and above, the kernel will 8671 natively use the XIVE interrupt controller. This option 8672 allows the fallback firmware mode to be used: 8673 8674 off Fallback to firmware control of XIVE interrupt 8675 controller on both pseries and powernv 8676 platforms. Only useful on POWER9 and above. 8677 8678 xive.store-eoi=off [PPC] 8679 By default on POWER10 and above, the kernel will use 8680 stores for EOI handling when the XIVE interrupt mode 8681 is active. This option allows the XIVE driver to use 8682 loads instead, as on POWER9. 8683 8684 xhci-hcd.quirks [USB,KNL] 8685 A hex value specifying bitmask with supplemental xhci 8686 host controller quirks. Meaning of each bit can be 8687 consulted in header drivers/usb/host/xhci.h. 8688 8689 xmon [PPC,EARLY] 8690 Format: { early | on | rw | ro | off } 8691 Controls if xmon debugger is enabled. Default is off. 8692 Passing only "xmon" is equivalent to "xmon=early". 8693 early Call xmon as early as possible on boot; xmon 8694 debugger is called from setup_arch(). 8695 on xmon debugger hooks will be installed so xmon 8696 is only called on a kernel crash. Default mode, 8697 i.e. either "ro" or "rw" mode, is controlled 8698 with CONFIG_XMON_DEFAULT_RO_MODE. 8699 rw xmon debugger hooks will be installed so xmon 8700 is called only on a kernel crash, mode is write, 8701 meaning SPR registers, memory and, other data 8702 can be written using xmon commands. 8703 ro same as "rw" option above but SPR registers, 8704 memory, and other data can't be written using 8705 xmon commands. 8706 off xmon is disabled. 8707