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 AX25 Appropriate AX.25 support is enabled. 10 CLK Common clock infrastructure is enabled. 11 CMA Contiguous Memory Area support is enabled. 12 DRM Direct Rendering Management support is enabled. 13 DYNAMIC_DEBUG Build in debug messages and enable them at runtime 14 EARLY Parameter processed too early to be embedded in initrd. 15 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled 16 EFI EFI Partitioning (GPT) is enabled 17 EVM Extended Verification Module 18 FB The frame buffer device is enabled. 19 FTRACE Function tracing enabled. 20 GCOV GCOV profiling is enabled. 21 HIBERNATION HIBERNATION is enabled. 22 HW Appropriate hardware is enabled. 23 HYPER_V HYPERV support is enabled. 24 IMA Integrity measurement architecture is enabled. 25 IP_PNP IP DHCP, BOOTP, or RARP is enabled. 26 IPV6 IPv6 support is enabled. 27 ISAPNP ISA PnP code is enabled. 28 ISDN Appropriate ISDN support is enabled. 29 ISOL CPU Isolation is enabled. 30 JOY Appropriate joystick support is enabled. 31 KGDB Kernel debugger support is enabled. 32 KVM Kernel Virtual Machine support is enabled. 33 LIBATA Libata driver is enabled 34 LOONGARCH LoongArch architecture is enabled. 35 LOOP Loopback device support is enabled. 36 LP Printer support is enabled. 37 M68k M68k architecture is enabled. 38 These options have more detailed description inside of 39 Documentation/arch/m68k/kernel-options.rst. 40 MDA MDA console support is enabled. 41 MIPS MIPS architecture is enabled. 42 MOUSE Appropriate mouse support is enabled. 43 MSI Message Signaled Interrupts (PCI). 44 MTD MTD (Memory Technology Device) support is enabled. 45 NET Appropriate network support is enabled. 46 NFS Appropriate NFS support is enabled. 47 NUMA NUMA support is enabled. 48 OF Devicetree is enabled. 49 PARISC The PA-RISC architecture is enabled. 50 PCI PCI bus support is enabled. 51 PCIE PCI Express support is enabled. 52 PCMCIA The PCMCIA subsystem is enabled. 53 PNP Plug & Play support is enabled. 54 PPC PowerPC architecture is enabled. 55 PPT Parallel port support is enabled. 56 PS2 Appropriate PS/2 support is enabled. 57 PV_OPS A paravirtualized kernel is enabled. 58 RAM RAM disk support is enabled. 59 RDT Intel Resource Director Technology. 60 RISCV RISCV architecture is enabled. 61 S390 S390 architecture is enabled. 62 SCSI Appropriate SCSI support is enabled. 63 A lot of drivers have their options described inside 64 the Documentation/scsi/ sub-directory. 65 SDW SoundWire support is enabled. 66 SECURITY Different security models are enabled. 67 SELINUX SELinux support is enabled. 68 SERIAL Serial support is enabled. 69 SH SuperH architecture is enabled. 70 SMP The kernel is an SMP kernel. 71 SPARC Sparc architecture is enabled. 72 SUSPEND System suspend states are enabled. 73 SWSUSP Software suspend (hibernation) is enabled. 74 TPM TPM drivers are enabled. 75 UMS USB Mass Storage support is enabled. 76 USB USB support is enabled. 77 NVME NVMe support is enabled 78 USBHID USB Human Interface Device support is enabled. 79 V4L Video For Linux support is enabled. 80 VGA The VGA console has been enabled. 81 VMMIO Driver for memory mapped virtio devices is enabled. 82 VT Virtual terminal support is enabled. 83 WDT Watchdog support is enabled. 84 X86-32 X86-32, aka i386 architecture is enabled. 85 X86-64 X86-64 architecture is enabled. 86 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 87 X86_UV SGI UV support is enabled. 88 XEN Xen support is enabled 89 XTENSA xtensa architecture is enabled. 90 91In addition, the following text indicates that the option 92 93 BOOT Is a boot loader parameter. 94 BUGS= Relates to possible processor bugs on the said processor. 95 KNL Is a kernel start-up parameter. 96 97 98Kernel parameters 99 100 accept_memory= [MM] 101 Format: { eager | lazy } 102 default: lazy 103 By default, unaccepted memory is accepted lazily to 104 avoid prolonged boot times. The lazy option will add 105 some runtime overhead until all memory is eventually 106 accepted. In most cases the overhead is negligible. 107 For some workloads or for debugging purposes 108 accept_memory=eager can be used to accept all memory 109 at once during boot. 110 111 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 112 Advanced Configuration and Power Interface 113 Format: { force | on | off | strict | noirq | rsdt | 114 copy_dsdt | nospcr } 115 force -- enable ACPI if default was off 116 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 117 off -- disable ACPI if default was on 118 noirq -- do not use ACPI for IRQ routing 119 strict -- Be less tolerant of platforms that are not 120 strictly ACPI specification compliant. 121 rsdt -- prefer RSDT over (default) XSDT 122 copy_dsdt -- copy DSDT to memory 123 nocmcff -- Disable firmware first mode for corrected 124 errors. This disables parsing the HEST CMC error 125 source to check if firmware has set the FF flag. This 126 may result in duplicate corrected error reports. 127 nospcr -- disable console in ACPI SPCR table as 128 default _serial_ console on ARM64 129 spcr -- enable console in ACPI SPCR table as 130 default _serial_ console on x86 131 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 132 "acpi=nospcr" are available 133 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 134 are available 135 136 See also Documentation/power/runtime_pm.rst, pci=noacpi 137 138 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 139 Format: <int> 140 2: use 2nd APIC table, if available 141 1,0: use 1st APIC table 142 default: 0 143 144 acpi_backlight= [HW,ACPI] 145 { vendor | video | native | none } 146 If set to vendor, prefer vendor-specific driver 147 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 148 of the ACPI video.ko driver. 149 If set to video, use the ACPI video.ko driver. 150 If set to native, use the device's native backlight mode. 151 If set to none, disable the ACPI backlight interface. 152 153 acpi_force_32bit_fadt_addr [ACPI,EARLY] 154 force FADT to use 32 bit addresses rather than the 155 64 bit X_* addresses. Some firmware have broken 64 156 bit addresses for force ACPI ignore these and use 157 the older legacy 32 bit addresses. 158 159 acpica_no_return_repair [HW, ACPI] 160 Disable AML predefined validation mechanism 161 This mechanism can repair the evaluation result to make 162 the return objects more ACPI specification compliant. 163 This option is useful for developers to identify the 164 root cause of an AML interpreter issue when the issue 165 has something to do with the repair mechanism. 166 167 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 168 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 169 Format: <int> 170 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 171 debug output. Bits in debug_layer correspond to a 172 _COMPONENT in an ACPI source file, e.g., 173 #define _COMPONENT ACPI_EVENTS 174 Bits in debug_level correspond to a level in 175 ACPI_DEBUG_PRINT statements, e.g., 176 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 177 The debug_level mask defaults to "info". See 178 Documentation/firmware-guide/acpi/debug.rst for more information about 179 debug layers and levels. 180 181 Enable processor driver info messages: 182 acpi.debug_layer=0x20000000 183 Enable AML "Debug" output, i.e., stores to the Debug 184 object while interpreting AML: 185 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 186 Enable all messages related to ACPI hardware: 187 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 188 189 Some values produce so much output that the system is 190 unusable. The "log_buf_len" parameter may be useful 191 if you need to capture more output. 192 193 acpi.poweroff_on_fatal= [ACPI] 194 {0 | 1} 195 Causes the system to poweroff when the ACPI bytecode signals 196 a fatal error. The default value of this setting is 1. 197 Overriding this value should only be done for diagnosing 198 ACPI firmware problems, as the system might behave erratically 199 after having encountered a fatal ACPI error. 200 201 acpi_enforce_resources= [ACPI] 202 { strict | lax | no } 203 Check for resource conflicts between native drivers 204 and ACPI OperationRegions (SystemIO and SystemMemory 205 only). IO ports and memory declared in ACPI might be 206 used by the ACPI subsystem in arbitrary AML code and 207 can interfere with legacy drivers. 208 strict (default): access to resources claimed by ACPI 209 is denied; legacy drivers trying to access reserved 210 resources will fail to bind to device using them. 211 lax: access to resources claimed by ACPI is allowed; 212 legacy drivers trying to access reserved resources 213 will bind successfully but a warning message is logged. 214 no: ACPI OperationRegions are not marked as reserved, 215 no further checks are performed. 216 217 acpi_force_table_verification [HW,ACPI,EARLY] 218 Enable table checksum verification during early stage. 219 By default, this is disabled due to x86 early mapping 220 size limitation. 221 222 acpi_irq_balance [HW,ACPI] 223 ACPI will balance active IRQs 224 default in APIC mode 225 226 acpi_irq_nobalance [HW,ACPI] 227 ACPI will not move active IRQs (default) 228 default in PIC mode 229 230 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 231 Format: <irq>,<irq>... 232 233 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 234 use by PCI 235 Format: <irq>,<irq>... 236 237 acpi_mask_gpe= [HW,ACPI] 238 Due to the existence of _Lxx/_Exx, some GPEs triggered 239 by unsupported hardware/firmware features can result in 240 GPE floodings that cannot be automatically disabled by 241 the GPE dispatcher. 242 This facility can be used to prevent such uncontrolled 243 GPE floodings. 244 Format: <byte> or <bitmap-list> 245 246 acpi_no_auto_serialize [HW,ACPI] 247 Disable auto-serialization of AML methods 248 AML control methods that contain the opcodes to create 249 named objects will be marked as "Serialized" by the 250 auto-serialization feature. 251 This feature is enabled by default. 252 This option allows to turn off the feature. 253 254 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 255 kernels. 256 257 acpi_no_static_ssdt [HW,ACPI,EARLY] 258 Disable installation of static SSDTs at early boot time 259 By default, SSDTs contained in the RSDT/XSDT will be 260 installed automatically and they will appear under 261 /sys/firmware/acpi/tables. 262 This option turns off this feature. 263 Note that specifying this option does not affect 264 dynamic table installation which will install SSDT 265 tables to /sys/firmware/acpi/tables/dynamic. 266 267 acpi_no_watchdog [HW,ACPI,WDT] 268 Ignore the ACPI-based watchdog interface (WDAT) and let 269 a native driver control the watchdog device instead. 270 271 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 272 Pass the RSDP address to the kernel, mostly used 273 on machines running EFI runtime service to boot the 274 second kernel for kdump. 275 276 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 277 Format: To spoof as Windows 98: ="Microsoft Windows" 278 279 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 280 of 2 which is mandated by ACPI 6) as the supported ACPI 281 specification revision (when using this switch, it may 282 be necessary to carry out a cold reboot _twice_ in a 283 row to make it take effect on the platform firmware). 284 285 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 286 acpi_osi="string1" # add string1 287 acpi_osi="!string2" # remove string2 288 acpi_osi=!* # remove all strings 289 acpi_osi=! # disable all built-in OS vendor 290 strings 291 acpi_osi=!! # enable all built-in OS vendor 292 strings 293 acpi_osi= # disable all strings 294 295 'acpi_osi=!' can be used in combination with single or 296 multiple 'acpi_osi="string1"' to support specific OS 297 vendor string(s). Note that such command can only 298 affect the default state of the OS vendor strings, thus 299 it cannot affect the default state of the feature group 300 strings and the current state of the OS vendor strings, 301 specifying it multiple times through kernel command line 302 is meaningless. This command is useful when one do not 303 care about the state of the feature group strings which 304 should be controlled by the OSPM. 305 Examples: 306 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 307 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 308 can make '_OSI("Windows 2000")' TRUE. 309 310 'acpi_osi=' cannot be used in combination with other 311 'acpi_osi=' command lines, the _OSI method will not 312 exist in the ACPI namespace. NOTE that such command can 313 only affect the _OSI support state, thus specifying it 314 multiple times through kernel command line is also 315 meaningless. 316 Examples: 317 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 318 FALSE. 319 320 'acpi_osi=!*' can be used in combination with single or 321 multiple 'acpi_osi="string1"' to support specific 322 string(s). Note that such command can affect the 323 current state of both the OS vendor strings and the 324 feature group strings, thus specifying it multiple times 325 through kernel command line is meaningful. But it may 326 still not able to affect the final state of a string if 327 there are quirks related to this string. This command 328 is useful when one want to control the state of the 329 feature group strings to debug BIOS issues related to 330 the OSPM features. 331 Examples: 332 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 333 '_OSI("Module Device")' FALSE. 334 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 335 '_OSI("Module Device")' TRUE. 336 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 337 equivalent to 338 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 339 and 340 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 341 they all will make '_OSI("Windows 2000")' TRUE. 342 343 acpi_pm_good [X86] 344 Override the pmtimer bug detection: force the kernel 345 to assume that this machine's pmtimer latches its value 346 and always returns good values. 347 348 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 349 Format: { level | edge | high | low } 350 351 acpi_skip_timer_override [HW,ACPI,EARLY] 352 Recognize and ignore IRQ0/pin2 Interrupt Override. 353 For broken nForce2 BIOS resulting in XT-PIC timer. 354 355 acpi_sleep= [HW,ACPI] Sleep options 356 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 357 s4_nohwsig, old_ordering, nonvs, 358 sci_force_enable, nobl } 359 See Documentation/power/video.rst for information on 360 s3_bios and s3_mode. 361 s3_beep is for debugging; it makes the PC's speaker beep 362 as soon as the kernel's real-mode entry point is called. 363 s4_hwsig causes the kernel to check the ACPI hardware 364 signature during resume from hibernation, and gracefully 365 refuse to resume if it has changed. This complies with 366 the ACPI specification but not with reality, since 367 Windows does not do this and many laptops do change it 368 on docking. So the default behaviour is to allow resume 369 and simply warn when the signature changes, unless the 370 s4_hwsig option is enabled. 371 s4_nohwsig prevents ACPI hardware signature from being 372 used (or even warned about) during resume. 373 old_ordering causes the ACPI 1.0 ordering of the _PTS 374 control method, with respect to putting devices into 375 low power states, to be enforced (the ACPI 2.0 ordering 376 of _PTS is used by default). 377 nonvs prevents the kernel from saving/restoring the 378 ACPI NVS memory during suspend/hibernation and resume. 379 sci_force_enable causes the kernel to set SCI_EN directly 380 on resume from S1/S3 (which is against the ACPI spec, 381 but some broken systems don't work without it). 382 nobl causes the internal blacklist of systems known to 383 behave incorrectly in some ways with respect to system 384 suspend and resume to be ignored (use wisely). 385 386 acpi_use_timer_override [HW,ACPI,EARLY] 387 Use timer override. For some broken Nvidia NF5 boards 388 that require a timer override, but don't have HPET 389 390 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 391 kernel's map of available physical RAM. 392 393 agp= [AGP] 394 { off | try_unsupported } 395 off: disable AGP support 396 try_unsupported: try to drive unsupported chipsets 397 (may crash computer or cause data corruption) 398 399 ALSA [HW,ALSA] 400 See Documentation/sound/alsa-configuration.rst 401 402 alignment= [KNL,ARM] 403 Allow the default userspace alignment fault handler 404 behaviour to be specified. Bit 0 enables warnings, 405 bit 1 enables fixups, and bit 2 sends a segfault. 406 407 align_va_addr= [X86-64] 408 Align virtual addresses by clearing slice [14:12] when 409 allocating a VMA at process creation time. This option 410 gives you up to 3% performance improvement on AMD F15h 411 machines (where it is enabled by default) for a 412 CPU-intensive style benchmark, and it can vary highly in 413 a microbenchmark depending on workload and compiler. 414 415 32: only for 32-bit processes 416 64: only for 64-bit processes 417 on: enable for both 32- and 64-bit processes 418 off: disable for both 32- and 64-bit processes 419 420 alloc_snapshot [FTRACE] 421 Allocate the ftrace snapshot buffer on boot up when the 422 main buffer is allocated. This is handy if debugging 423 and you need to use tracing_snapshot() on boot up, and 424 do not want to use tracing_snapshot_alloc() as it needs 425 to be done where GFP_KERNEL allocations are allowed. 426 427 allow_mismatched_32bit_el0 [ARM64,EARLY] 428 Allow execve() of 32-bit applications and setting of the 429 PER_LINUX32 personality on systems where only a strict 430 subset of the CPUs support 32-bit EL0. When this 431 parameter is present, the set of CPUs supporting 32-bit 432 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 433 and hot-unplug operations may be restricted. 434 435 See Documentation/arch/arm64/asymmetric-32bit.rst for more 436 information. 437 438 amd_iommu= [HW,X86-64] 439 Pass parameters to the AMD IOMMU driver in the system. 440 Possible values are: 441 fullflush - Deprecated, equivalent to iommu.strict=1 442 off - do not initialize any AMD IOMMU found in 443 the system 444 force_isolation - Force device isolation for all 445 devices. The IOMMU driver is not 446 allowed anymore to lift isolation 447 requirements as needed. This option 448 does not override iommu=pt 449 force_enable - Force enable the IOMMU on platforms known 450 to be buggy with IOMMU enabled. Use this 451 option with care. 452 pgtbl_v1 - Use v1 page table for DMA-API (Default). 453 pgtbl_v2 - Use v2 page table for DMA-API. 454 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 455 nohugepages - Limit page-sizes used for v1 page-tables 456 to 4 KiB. 457 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 458 to 4KiB/2Mib/1GiB. 459 460 461 amd_iommu_dump= [HW,X86-64] 462 Enable AMD IOMMU driver option to dump the ACPI table 463 for AMD IOMMU. With this option enabled, AMD IOMMU 464 driver will print ACPI tables for AMD IOMMU during 465 IOMMU initialization. 466 467 amd_iommu_intr= [HW,X86-64] 468 Specifies one of the following AMD IOMMU interrupt 469 remapping modes: 470 legacy - Use legacy interrupt remapping mode. 471 vapic - Use virtual APIC mode, which allows IOMMU 472 to inject interrupts directly into guest. 473 This mode requires kvm-amd.avic=1. 474 (Default when IOMMU HW support is present.) 475 476 amd_pstate= [X86,EARLY] 477 disable 478 Do not enable amd_pstate as the default 479 scaling driver for the supported processors 480 passive 481 Use amd_pstate with passive mode as a scaling driver. 482 In this mode autonomous selection is disabled. 483 Driver requests a desired performance level and platform 484 tries to match the same performance level if it is 485 satisfied by guaranteed performance level. 486 active 487 Use amd_pstate_epp driver instance as the scaling driver, 488 driver provides a hint to the hardware if software wants 489 to bias toward performance (0x0) or energy efficiency (0xff) 490 to the CPPC firmware. then CPPC power algorithm will 491 calculate the runtime workload and adjust the realtime cores 492 frequency. 493 guided 494 Activate guided autonomous mode. Driver requests minimum and 495 maximum performance level and the platform autonomously 496 selects a performance level in this range and appropriate 497 to the current workload. 498 499 amd_prefcore= 500 [X86] 501 disable 502 Disable amd-pstate preferred core. 503 504 amd_dynamic_epp= 505 [X86] 506 disable 507 Disable amd-pstate dynamic EPP. 508 enable 509 Enable amd-pstate dynamic EPP. 510 511 amijoy.map= [HW,JOY] Amiga joystick support 512 Map of devices attached to JOY0DAT and JOY1DAT 513 Format: <a>,<b> 514 See also Documentation/input/joydev/joystick.rst 515 516 analog.map= [HW,JOY] Analog joystick and gamepad support 517 Specifies type or capabilities of an analog joystick 518 connected to one of 16 gameports 519 Format: <type1>,<type2>,..<type16> 520 521 apc= [HW,SPARC] 522 Power management functions (SPARCstation-4/5 + deriv.) 523 Format: noidle 524 Disable APC CPU standby support. SPARCstation-Fox does 525 not play well with APC CPU idle - disable it if you have 526 APC and your system crashes randomly. 527 528 apic [APIC,X86-64] Use IO-APIC. Default. 529 530 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 531 Change the output verbosity while booting 532 Format: { quiet (default) | verbose | debug } 533 Change the amount of debugging information output 534 when initialising the APIC and IO-APIC components. 535 536 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 537 Format: { bsp (default) | all | none } 538 bsp: External NMI is delivered only to CPU 0 539 all: External NMIs are broadcast to all CPUs as a 540 backup of CPU 0 541 none: External NMI is masked for all CPUs. This is 542 useful so that a dump capture kernel won't be 543 shot down by NMI 544 545 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 546 apicmaintimer. Useful when your PIT timer is totally 547 broken. 548 549 autoconf= [IPV6] 550 See Documentation/networking/ipv6.rst. 551 552 apm= [APM] Advanced Power Management 553 See header of arch/x86/kernel/apm_32.c. 554 555 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 556 Format: { "0" | "1" } 557 See security/apparmor/Kconfig help text 558 0 -- disable. 559 1 -- enable. 560 Default value is set via kernel config option. 561 562 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 563 Format: <io>,<irq>,<nodeID> 564 565 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 566 32 bit applications. 567 568 arm64.nobti [ARM64] Unconditionally disable Branch Target 569 Identification support 570 571 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 572 support 573 574 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 575 Set instructions support 576 577 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 578 Monitoring support 579 580 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 581 support 582 583 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 584 support 585 586 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 587 Extension support 588 589 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 590 Extension support 591 592 ataflop= [HW,M68k] 593 594 atarimouse= [HW,MOUSE] Atari Mouse 595 596 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 597 EzKey and similar keyboards 598 599 atkbd.reset= [HW] Reset keyboard during initialization 600 601 atkbd.set= [HW] Select keyboard code set 602 Format: <int> (2 = AT (default), 3 = PS/2) 603 604 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 605 keyboards 606 607 atkbd.softraw= [HW] Choose between synthetic and real raw mode 608 Format: <bool> (0 = real, 1 = synthetic (default)) 609 610 atkbd.softrepeat= [HW] 611 Use software keyboard repeat 612 613 audit= [KNL] Enable the audit sub-system 614 Format: { "0" | "1" | "off" | "on" } 615 0 | off - kernel audit is disabled and can not be 616 enabled until the next reboot 617 unset - kernel audit is initialized but disabled and 618 will be fully enabled by the userspace auditd. 619 1 | on - kernel audit is initialized and partially 620 enabled, storing at most audit_backlog_limit 621 messages in RAM until it is fully enabled by the 622 userspace auditd. 623 Default: unset 624 625 audit_backlog_limit= [KNL] Set the audit queue size limit. 626 Format: <int> (must be >=0) 627 Default: 64 628 629 bau= [X86_UV] Enable the BAU on SGI UV. The default 630 behavior is to disable the BAU (i.e. bau=0). 631 Format: { "0" | "1" } 632 0 - Disable the BAU. 633 1 - Enable the BAU. 634 unset - Disable the BAU. 635 636 baycom_epp= [HW,AX25] 637 Format: <io>,<mode> 638 639 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 640 Format: <io>,<mode> 641 See header of drivers/net/hamradio/baycom_par.c. 642 643 baycom_ser_fdx= [HW,AX25] 644 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 645 Format: <io>,<irq>,<mode>[,<baud>] 646 See header of drivers/net/hamradio/baycom_ser_fdx.c. 647 648 baycom_ser_hdx= [HW,AX25] 649 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 650 Format: <io>,<irq>,<mode> 651 See header of drivers/net/hamradio/baycom_ser_hdx.c. 652 653 bdev_allow_write_mounted= 654 Format: <bool> 655 Control the ability to open a mounted block device 656 for writing, i.e., allow / disallow writes that bypass 657 the FS. This was implemented as a means to prevent 658 fuzzers from crashing the kernel by overwriting the 659 metadata underneath a mounted FS without its awareness. 660 This also prevents destructive formatting of mounted 661 filesystems by naive storage tooling that don't use 662 O_EXCL. Default is Y and can be changed through the 663 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 664 665 bert_disable [ACPI] 666 Disable BERT OS support on buggy BIOSes. 667 668 bgrt_disable [ACPI,X86,EARLY] 669 Disable BGRT to avoid flickering OEM logo. 670 671 blkdevparts= Manual partition parsing of block device(s) for 672 embedded devices based on command line input. 673 See Documentation/block/cmdline-partition.rst 674 675 boot_delay= [KNL,EARLY] 676 Milliseconds to delay each printk during boot. 677 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 678 and you may also have to specify "lpj=". Boot_delay 679 values larger than 10 seconds (10000) are assumed 680 erroneous and ignored. 681 Format: integer 682 683 bootconfig [KNL,EARLY] 684 Extended command line options can be added to an initrd 685 and this will cause the kernel to look for it. 686 687 See Documentation/admin-guide/bootconfig.rst 688 689 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 690 bttv.radio= Most important insmod options are available as 691 kernel args too. 692 bttv.pll= See Documentation/admin-guide/media/bttv.rst 693 bttv.tuner= 694 695 bulk_remove=off [PPC] This parameter disables the use of the pSeries 696 firmware feature for flushing multiple hpte entries 697 at a time. 698 699 c101= [NET] Moxa C101 synchronous serial card 700 701 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 702 Sometimes CPU hardware bugs make them report the cache 703 size incorrectly. The kernel will attempt work arounds 704 to fix known problems, but for some CPUs it is not 705 possible to determine what the correct size should be. 706 This option provides an override for these situations. 707 708 carrier_timeout= 709 [NET] Specifies amount of time (in seconds) that 710 the kernel should wait for a network carrier. By default 711 it waits 120 seconds. 712 713 ca_keys= [KEYS] This parameter identifies a specific key(s) on 714 the system trusted keyring to be used for certificate 715 trust validation. 716 format: { id:<keyid> | builtin } 717 718 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 719 algorithm. Accepted values range from 0 to 7 720 inclusive. See arch/mips/include/asm/pgtable-bits.h 721 for platform specific values (SB1, Loongson3 and 722 others). 723 724 ccw_timeout_log [S390] 725 See Documentation/arch/s390/common_io.rst for details. 726 727 cfi= [X86-64] Set Control Flow Integrity checking features 728 when CONFIG_FINEIBT is enabled. 729 Format: feature[,feature...] 730 Default: auto 731 732 auto: Use FineIBT if IBT available, otherwise kCFI. 733 Under FineIBT, enable "paranoid" mode when 734 FRED is not available. 735 off: Turn off CFI checking. 736 kcfi: Use kCFI (disable FineIBT). 737 fineibt: Use FineIBT (even if IBT not available). 738 norand: Do not re-randomize CFI hashes. 739 paranoid: Add caller hash checking under FineIBT. 740 bhi: Enable register poisoning to stop speculation 741 across FineIBT. (Disabled by default.) 742 warn: Do not enforce CFI checking: warn only. 743 debug: Report CFI initialization details. 744 745 cgroup_disable= [KNL] Disable a particular controller or optional feature 746 Format: {name of the controller(s) or feature(s) to disable} 747 The effects of cgroup_disable=foo are: 748 - foo isn't auto-mounted if you mount all cgroups in 749 a single hierarchy 750 - foo isn't visible as an individually mountable 751 subsystem 752 - if foo is an optional feature then the feature is 753 disabled and corresponding cgroup files are not 754 created 755 {Currently only "memory" controller deal with this and 756 cut the overhead, others just disable the usage. So 757 only cgroup_disable=memory is actually worthy} 758 Specifying "pressure" disables per-cgroup pressure 759 stall information accounting feature 760 761 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 762 Format: { { controller | "all" | "named" } 763 [,{ controller | "all" | "named" }...] } 764 Like cgroup_disable, but only applies to cgroup v1; 765 the blacklisted controllers remain available in cgroup2. 766 "all" blacklists all controllers and "named" disables 767 named mounts. Specifying both "all" and "named" disables 768 all v1 hierarchies. 769 770 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 771 Format: { "true" | "false" } 772 /proc/cgroups lists only v1 controllers by default. 773 This compatibility option enables listing also v2 774 controllers (whose v1 code is not compiled!), so that 775 semi-legacy software can check this file to decide 776 about usage of v2 (sic) controllers. 777 778 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 779 Format: { "true" | "false" } 780 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 781 782 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 783 Format: <string> 784 nosocket -- Disable socket memory accounting. 785 nokmem -- Disable kernel memory accounting. 786 nobpf -- Disable BPF memory accounting. 787 788 check_pages= [MM,EARLY] Enable sanity checking of pages after 789 allocations / before freeing. This adds checks to catch 790 double-frees, use-after-frees, and other sources of 791 page corruption by inspecting page internals (flags, 792 mapcount/refcount, memcg_data, etc.). 793 Format: { "0" | "1" } 794 Default: 0 (1 if CONFIG_DEBUG_VM is set) 795 796 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 797 Format: { "0" | "1" } 798 See security/selinux/Kconfig help text. 799 0 -- check protection applied by kernel (includes 800 any implied execute protection). 801 1 -- check protection requested by application. 802 Default value is set via a kernel config option. 803 Value can be changed at runtime via 804 /sys/fs/selinux/checkreqprot. 805 Setting checkreqprot to 1 is deprecated. 806 807 cio_ignore= [S390] 808 See Documentation/arch/s390/common_io.rst for details. 809 810 clearcpuid=X[,X...] [X86] 811 Disable CPUID feature X for the kernel. See 812 arch/x86/include/asm/cpufeatures.h for the valid bit 813 numbers X. Note the Linux-specific bits are not necessarily 814 stable over kernel options, but the vendor-specific 815 ones should be. 816 X can also be a string as appearing in the flags: line 817 in /proc/cpuinfo which does not have the above 818 instability issue. However, not all features have names 819 in /proc/cpuinfo. 820 Note that using this option will taint your kernel. 821 Also note that user programs calling CPUID directly 822 or using the feature without checking anything 823 will still see it. This just prevents it from 824 being used by the kernel or shown in /proc/cpuinfo. 825 Also note the kernel might malfunction if you disable 826 some critical bits. 827 828 clk_ignore_unused 829 [CLK] 830 Prevents the clock framework from automatically gating 831 clocks that have not been explicitly enabled by a Linux 832 device driver but are enabled in hardware at reset or 833 by the bootloader/firmware. Note that this does not 834 force such clocks to be always-on nor does it reserve 835 those clocks in any way. This parameter is useful for 836 debug and development, but should not be needed on a 837 platform with proper driver support. For more 838 information, see Documentation/driver-api/clk.rst. 839 840 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 841 [Deprecated] 842 Forces specified clocksource (if available) to be used 843 when calculating gettimeofday(). If specified 844 clocksource is not available, it defaults to PIT. 845 Format: { pit | tsc | cyclone | pmtmr } 846 847 clocksource= Override the default clocksource 848 Format: <string> 849 Override the default clocksource and use the clocksource 850 with the name specified. 851 Some clocksource names to choose from, depending on 852 the platform: 853 [all] jiffies (this is the base, fallback clocksource) 854 [ACPI] acpi_pm 855 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 856 pxa_timer,timer3,32k_counter,timer0_1 857 [X86-32] pit,hpet,tsc; 858 scx200_hrt on Geode; cyclone on IBM x440 859 [MIPS] MIPS 860 [PARISC] cr16 861 [S390] tod 862 [SH] SuperH 863 [SPARC64] tick 864 [X86-64] hpet,tsc 865 866 clocksource.arm_arch_timer.evtstrm= 867 [ARM,ARM64,EARLY] 868 Format: <bool> 869 Enable/disable the eventstream feature of the ARM 870 architected timer so that code using WFE-based polling 871 loops can be debugged more effectively on production 872 systems. 873 874 clocksource.verify_n_cpus= [KNL] 875 Limit the number of CPUs checked for clocksources 876 marked with CLOCK_SOURCE_VERIFY_PERCPU that 877 are marked unstable due to excessive skew. 878 A negative value says to check all CPUs, while 879 zero says not to check any. Values larger than 880 nr_cpu_ids are silently truncated to nr_cpu_ids. 881 The actual CPUs are chosen randomly, with 882 no replacement if the same CPU is chosen twice. 883 884 clocksource-wdtest.holdoff= [KNL] 885 Set the time in seconds that the clocksource 886 watchdog test waits before commencing its tests. 887 Defaults to zero when built as a module and to 888 10 seconds when built into the kernel. 889 890 cma=nn[MG]@[start[MG][-end[MG]]] 891 [KNL,CMA,EARLY] 892 Sets the size of kernel global memory area for 893 contiguous memory allocations and optionally the 894 placement constraint by the physical address range of 895 memory allocations. A value of 0 disables CMA 896 altogether. For more information, see 897 kernel/dma/contiguous.c 898 899 cma_pernuma=nn[MG] 900 [KNL,CMA,EARLY] 901 Sets the size of kernel per-numa memory area for 902 contiguous memory allocations. A value of 0 disables 903 per-numa CMA altogether. And If this option is not 904 specified, the default value is 0. 905 With per-numa CMA enabled, DMA users on node nid will 906 first try to allocate buffer from the pernuma area 907 which is located in node nid, if the allocation fails, 908 they will fallback to the global default memory area. 909 910 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 911 [KNL,CMA,EARLY] 912 Sets the size of kernel numa memory area for 913 contiguous memory allocations. It will reserve CMA 914 area for the specified node. 915 916 With numa CMA enabled, DMA users on node nid will 917 first try to allocate buffer from the numa area 918 which is located in node nid, if the allocation fails, 919 they will fallback to the global default memory area. 920 921 cmo_free_hint= [PPC] Format: { yes | no } 922 Specify whether pages are marked as being inactive 923 when they are freed. This is used in CMO environments 924 to determine OS memory pressure for page stealing by 925 a hypervisor. 926 Default: yes 927 928 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 929 Sets the size of memory pool for coherent, atomic dma 930 allocations, by default set to 256K. 931 932 com20020= [HW,NET] ARCnet - COM20020 chipset 933 Format: 934 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 935 936 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 937 Format: <io>[,<irq>] 938 939 com90xx= [HW,NET] 940 ARCnet - COM90xx chipset (memory-mapped buffers) 941 Format: <io>[,<irq>[,<memstart>]] 942 943 condev= [HW,S390] console device 944 conmode= 945 946 con3215_drop= [S390,EARLY] 3215 console drop mode. 947 Format: y|n|Y|N|1|0 948 When set to true, drop data on the 3215 console when 949 the console buffer is full. In this case the 950 operator using a 3270 terminal emulator (for example 951 x3270) does not have to enter the clear key for the 952 console output to advance and the kernel to continue. 953 This leads to a much faster boot time when a 3270 954 terminal emulator is active. If no 3270 terminal 955 emulator is used, this parameter has no effect. 956 957 console= [KNL] Output console device and options. 958 959 tty<n> Use the virtual console device <n>. 960 961 ttyS<n>[,options] 962 ttyUSB0[,options] 963 Use the specified serial port. The options are of 964 the form "bbbbpnf", where "bbbb" is the baud rate, 965 "p" is parity ("n", "o", or "e"), "n" is number of 966 bits, and "f" is flow control ("r" for RTS or 967 omit it). Default is "9600n8". 968 969 See Documentation/admin-guide/serial-console.rst for more 970 information. See 971 Documentation/networking/netconsole.rst for an 972 alternative. 973 974 <DEVNAME>:<n>.<n>[,options] 975 Use the specified serial port on the serial core bus. 976 The addressing uses DEVNAME of the physical serial port 977 device, followed by the serial core controller instance, 978 and the serial port instance. The options are the same 979 as documented for the ttyS addressing above. 980 981 The mapping of the serial ports to the tty instances 982 can be viewed with: 983 984 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 985 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 986 987 In the above example, the console can be addressed with 988 console=00:04:0.0. Note that a console addressed this 989 way will only get added when the related device driver 990 is ready. The use of an earlycon parameter in addition to 991 the console may be desired for console output early on. 992 993 uart[8250],io,<addr>[,options] 994 uart[8250],mmio,<addr>[,options] 995 uart[8250],mmio16,<addr>[,options] 996 uart[8250],mmio32,<addr>[,options] 997 uart[8250],0x<addr>[,options] 998 Start an early, polled-mode console on the 8250/16550 999 UART at the specified I/O port or MMIO address, 1000 switching to the matching ttyS device later. 1001 MMIO inter-register address stride is either 8-bit 1002 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 1003 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 1004 to be equivalent to 'mmio'. 'options' are specified in 1005 the same format described for ttyS above; if unspecified, 1006 the h/w is not re-initialized. 1007 1008 hvc<n> Use the hypervisor console device <n>. This is for 1009 both Xen and PowerPC hypervisors. 1010 1011 { null | "" } 1012 Use to disable console output, i.e., to have kernel 1013 console messages discarded. 1014 This must be the only console= parameter used on the 1015 kernel command line. 1016 1017 If the device connected to the port is not a TTY but a braille 1018 device, prepend "brl," before the device type, for instance 1019 console=brl,ttyS0 1020 For now, only VisioBraille is supported. 1021 1022 console_msg_format= 1023 [KNL] Change console messages format 1024 default 1025 By default we print messages on consoles in 1026 "[time stamp] text\n" format (time stamp may not be 1027 printed, depending on CONFIG_PRINTK_TIME or 1028 `printk_time' param). 1029 syslog 1030 Switch to syslog format: "<%u>[time stamp] text\n" 1031 IOW, each message will have a facility and loglevel 1032 prefix. The format is similar to one used by syslog() 1033 syscall, or to executing "dmesg -S --raw" or to reading 1034 from /proc/kmsg. 1035 1036 consoleblank= [KNL] The console blank (screen saver) timeout in 1037 seconds. A value of 0 disables the blank timer. 1038 Defaults to 0. 1039 1040 coredump_filter= 1041 [KNL] Change the default value for 1042 /proc/<pid>/coredump_filter. 1043 See also Documentation/filesystems/proc.rst. 1044 1045 coresight_cpu_debug.enable 1046 [ARM,ARM64] 1047 Format: <bool> 1048 Enable/disable the CPU sampling based debugging. 1049 0: default value, disable debugging 1050 1: enable debugging at boot time 1051 1052 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1053 Format: 1054 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1055 1056 cpuidle.off=1 [CPU_IDLE] 1057 disable the cpuidle sub-system 1058 1059 cpuidle.governor= 1060 [CPU_IDLE] Name of the cpuidle governor to use. 1061 1062 cpufreq.off=1 [CPU_FREQ] 1063 disable the cpufreq sub-system 1064 1065 cpufreq.default_governor= 1066 [CPU_FREQ] Name of the default cpufreq governor or 1067 policy to use. This governor must be registered in the 1068 kernel before the cpufreq driver probes. 1069 1070 cpu_init_udelay=N 1071 [X86,EARLY] Delay for N microsec between assert and de-assert 1072 of APIC INIT to start processors. This delay occurs 1073 on every CPU online, such as boot, and resume from suspend. 1074 Default: 10000 1075 1076 cpuhp.parallel= 1077 [SMP] Enable/disable parallel bringup of secondary CPUs 1078 Format: <bool> 1079 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1080 the parameter has no effect. 1081 1082 crash_kexec_post_notifiers 1083 Only jump to kdump kernel after running the panic 1084 notifiers and dumping kmsg. This option increases 1085 the risks of a kdump failure, since some panic 1086 notifiers can make the crashed kernel more unstable. 1087 In configurations where kdump may not be reliable, 1088 running the panic notifiers could allow collecting 1089 more data on dmesg, like stack traces from other CPUS 1090 or extra data dumped by panic_print. Note that some 1091 configurations enable this option unconditionally, 1092 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1093 1094 crashkernel=size[KMG][@offset[KMG]] 1095 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1096 upon panic. This parameter reserves the physical 1097 memory region [offset, offset + size] for that kernel 1098 image. If '@offset' is omitted, then a suitable offset 1099 is selected automatically. 1100 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1101 under 4G first, and fall back to reserve region above 1102 4G when '@offset' hasn't been specified. 1103 See Documentation/admin-guide/kdump/kdump.rst for further details. 1104 1105 crashkernel=range1:size1[,range2:size2,...][@offset] 1106 [KNL] Same as above, but depends on the memory 1107 in the running system. The syntax of range is 1108 start-[end] where start and end are both 1109 a memory unit (amount[KMG]). See also 1110 Documentation/admin-guide/kdump/kdump.rst for an example. 1111 1112 crashkernel=size[KMG],high 1113 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1114 above 4G. 1115 Allow kernel to allocate physical memory region from top, 1116 so could be above 4G if system have more than 4G ram 1117 installed. Otherwise memory region will be allocated 1118 below 4G, if available. 1119 It will be ignored if crashkernel=X is specified. 1120 crashkernel=size[KMG],low 1121 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1122 When crashkernel=X,high is passed, kernel could allocate 1123 physical memory region above 4G, that cause second kernel 1124 crash on system that require some amount of low memory, 1125 e.g. swiotlb requires at least 64M+32K low memory, also 1126 enough extra low memory is needed to make sure DMA buffers 1127 for 32-bit devices won't run out. Kernel would try to allocate 1128 default size of memory below 4G automatically. The default 1129 size is platform dependent. 1130 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1131 --> arm64: 128MiB 1132 --> riscv: 128MiB 1133 --> loongarch: 128MiB 1134 This one lets the user specify own low range under 4G 1135 for second kernel instead. 1136 0: to disable low allocation. 1137 It will be ignored when crashkernel=X,high is not used 1138 or memory reserved is below 4G. 1139 crashkernel=size[KMG],cma 1140 [KNL, X86, ppc] Reserve additional crash kernel memory from 1141 CMA. This reservation is usable by the first system's 1142 userspace memory and kernel movable allocations (memory 1143 balloon, zswap). Pages allocated from this memory range 1144 will not be included in the vmcore so this should not 1145 be used if dumping of userspace memory is intended and 1146 it has to be expected that some movable kernel pages 1147 may be missing from the dump. 1148 1149 A standard crashkernel reservation, as described above, 1150 is still needed to hold the crash kernel and initrd. 1151 1152 This option increases the risk of a kdump failure: DMA 1153 transfers configured by the first kernel may end up 1154 corrupting the second kernel's memory. 1155 1156 This reservation method is intended for systems that 1157 can't afford to sacrifice enough memory for standard 1158 crashkernel reservation and where less reliable and 1159 possibly incomplete kdump is preferable to no kdump at 1160 all. 1161 1162 cryptomgr.notests 1163 [KNL] Disable crypto self-tests 1164 1165 cs89x0_dma= [HW,NET] 1166 Format: <dma> 1167 1168 cs89x0_media= [HW,NET] 1169 Format: { rj45 | aui | bnc } 1170 1171 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1172 function call handling. When switched on, 1173 additional debug data is printed to the console 1174 in case a hanging CPU is detected, and that 1175 CPU is pinged again in order to try to resolve 1176 the hang situation. The default value of this 1177 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1178 Kconfig option. 1179 1180 dasd= [HW,NET] 1181 See header of drivers/s390/block/dasd_devmap.c. 1182 1183 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1184 (one device per port) 1185 Format: <port#>,<type> 1186 See also Documentation/input/devices/joystick-parport.rst 1187 1188 debug [KNL,EARLY] Enable kernel debugging (events log level). 1189 1190 debug_boot_weak_hash 1191 [KNL,EARLY] Enable printing [hashed] pointers early in the 1192 boot sequence. If enabled, we use a weak hash instead 1193 of siphash to hash pointers. Use this option if you are 1194 seeing instances of '(___ptrval___)') and need to see a 1195 value (hashed pointer) instead. Cryptographically 1196 insecure, please do not use on production kernels. 1197 1198 debug_locks_verbose= 1199 [KNL] verbose locking self-tests 1200 Format: <int> 1201 Print debugging info while doing the locking API 1202 self-tests. 1203 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1204 (no extra messages), setting it to -1 (all bits set) 1205 will print _a_lot_ more information - normally only 1206 useful to lockdep developers. 1207 1208 debug_objects [KNL,EARLY] Enable object debugging 1209 1210 debug_guardpage_minorder= 1211 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1212 parameter allows control of the order of pages that will 1213 be intentionally kept free (and hence protected) by the 1214 buddy allocator. Bigger value increase the probability 1215 of catching random memory corruption, but reduce the 1216 amount of memory for normal system use. The maximum 1217 possible value is MAX_PAGE_ORDER/2. Setting this 1218 parameter to 1 or 2 should be enough to identify most 1219 random memory corruption problems caused by bugs in 1220 kernel or driver code when a CPU writes to (or reads 1221 from) a random memory location. Note that there exists 1222 a class of memory corruptions problems caused by buggy 1223 H/W or F/W or by drivers badly programming DMA 1224 (basically when memory is written at bus level and the 1225 CPU MMU is bypassed) which are not detectable by 1226 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1227 help tracking down these problems. 1228 1229 debug_pagealloc= 1230 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1231 enables the feature at boot time. By default, it is 1232 disabled and the system will work mostly the same as a 1233 kernel built without CONFIG_DEBUG_PAGEALLOC. 1234 Note: to get most of debug_pagealloc error reports, it's 1235 useful to also enable the page_owner functionality. 1236 on: enable the feature 1237 1238 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1239 userspace and debugfs internal clients. 1240 Format: { on, off } 1241 on: All functions are enabled. 1242 off: Filesystem is not registered and clients 1243 get a -EPERM as result when trying to register files 1244 or directories within debugfs. 1245 This is equivalent of the runtime functionality if 1246 debugfs was not enabled in the kernel at all. 1247 Default value is set in build-time with a kernel configuration. 1248 1249 debugpat [X86] Enable PAT debugging 1250 1251 default_hugepagesz= 1252 [HW] The size of the default HugeTLB page. This is 1253 the size represented by the legacy /proc/ hugepages 1254 APIs. In addition, this is the default hugetlb size 1255 used for shmget(), mmap() and mounting hugetlbfs 1256 filesystems. If not specified, defaults to the 1257 architecture's default huge page size. Huge page 1258 sizes are architecture dependent. See also 1259 Documentation/admin-guide/mm/hugetlbpage.rst. 1260 Format: size[KMG] 1261 1262 deferred_probe_timeout= 1263 [KNL] Debugging option to set a timeout in seconds for 1264 deferred probe to give up waiting on dependencies to 1265 probe. Only specific dependencies (subsystems or 1266 drivers) that have opted in will be ignored. A timeout 1267 of 0 will timeout at the end of initcalls. If the time 1268 out hasn't expired, it'll be restarted by each 1269 successful driver registration. This option will also 1270 dump out devices still on the deferred probe list after 1271 retrying. 1272 1273 delayacct [KNL] Enable per-task delay accounting 1274 1275 dell_smm_hwmon.ignore_dmi= 1276 [HW] Continue probing hardware even if DMI data 1277 indicates that the driver is running on unsupported 1278 hardware. 1279 1280 dell_smm_hwmon.force= 1281 [HW] Activate driver even if SMM BIOS signature does 1282 not match list of supported models and enable otherwise 1283 blacklisted features. 1284 1285 dell_smm_hwmon.power_status= 1286 [HW] Report power status in /proc/i8k 1287 (disabled by default). 1288 1289 dell_smm_hwmon.restricted= 1290 [HW] Allow controlling fans only if SYS_ADMIN 1291 capability is set. 1292 1293 dell_smm_hwmon.fan_mult= 1294 [HW] Factor to multiply fan speed with. 1295 1296 dell_smm_hwmon.fan_max= 1297 [HW] Maximum configurable fan speed. 1298 1299 dfltcc= [HW,S390] 1300 Format: { on | off | def_only | inf_only | always } 1301 on: s390 zlib hardware support for compression on 1302 level 1 and decompression (default) 1303 off: No s390 zlib hardware support 1304 def_only: s390 zlib hardware support for deflate 1305 only (compression on level 1) 1306 inf_only: s390 zlib hardware support for inflate 1307 only (decompression) 1308 always: Same as 'on' but ignores the selected compression 1309 level always using hardware support (used for debugging) 1310 1311 dhash_entries= [KNL] 1312 Set number of hash buckets for dentry cache. 1313 1314 disable_1tb_segments [PPC,EARLY] 1315 Disables the use of 1TB hash page table segments. This 1316 causes the kernel to fall back to 256MB segments which 1317 can be useful when debugging issues that require an SLB 1318 miss to occur. 1319 1320 disable= [IPV6] 1321 See Documentation/networking/ipv6.rst. 1322 1323 disable_radix [PPC,EARLY] 1324 Disable RADIX MMU mode on POWER9 1325 1326 disable_tlbie [PPC] 1327 Disable TLBIE instruction. Currently does not work 1328 with KVM, with HASH MMU, or with coherent accelerators. 1329 1330 disable_ddw [PPC/PSERIES,EARLY] 1331 Disable Dynamic DMA Window support. Use this 1332 to workaround buggy firmware. 1333 1334 disable_ipv6= [IPV6] 1335 See Documentation/networking/ipv6.rst. 1336 1337 disable_mtrr_cleanup [X86,EARLY] 1338 The kernel tries to adjust MTRR layout from continuous 1339 to discrete, to make X server driver able to add WB 1340 entry later. This parameter disables that. 1341 1342 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1343 By default the kernel will trim any uncacheable 1344 memory out of your available memory pool based on 1345 MTRR settings. This parameter disables that behavior, 1346 possibly causing your machine to run very slowly. 1347 1348 disable_timer_pin_1 [X86,EARLY] 1349 Disable PIN 1 of APIC timer 1350 Can be useful to work around chipset bugs. 1351 1352 dis_ucode_ldr [X86] Disable the microcode loader. 1353 1354 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1355 this option disables the debugging code at boot. 1356 1357 dma_debug_entries=<number> 1358 This option allows to tune the number of preallocated 1359 entries for DMA-API debugging code. One entry is 1360 required per DMA-API allocation. Use this if the 1361 DMA-API debugging code disables itself because the 1362 architectural default is too low. 1363 1364 dma_debug_driver=<driver_name> 1365 With this option the DMA-API debugging driver 1366 filter feature can be enabled at boot time. Just 1367 pass the driver to filter for as the parameter. 1368 The filter can be disabled or changed to another 1369 driver later using sysfs. 1370 1371 reg_file_data_sampling= 1372 [X86] Controls mitigation for Register File Data 1373 Sampling (RFDS) vulnerability. RFDS is a CPU 1374 vulnerability which may allow userspace to infer 1375 kernel data values previously stored in floating point 1376 registers, vector registers, or integer registers. 1377 RFDS only affects Intel Atom processors. 1378 1379 on: Turns ON the mitigation. 1380 off: Turns OFF the mitigation. 1381 1382 This parameter overrides the compile time default set 1383 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1384 disabled when other VERW based mitigations (like MDS) 1385 are enabled. In order to disable RFDS mitigation all 1386 VERW based mitigations need to be disabled. 1387 1388 For details see: 1389 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1390 1391 dm_verity.keyring_unsealed= 1392 [KNL] When set to 1, leave the dm-verity keyring 1393 unsealed after initialization so userspace can 1394 provision keys. Once the keyring is restricted 1395 it becomes active and is searched during signature 1396 verification. 1397 1398 driver_async_probe= [KNL] 1399 List of driver names to be probed asynchronously. * 1400 matches with all driver names. If * is specified, the 1401 rest of the listed driver names are those that will NOT 1402 match the *. 1403 Format: <driver_name1>,<driver_name2>... 1404 1405 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1406 Broken monitors, graphic adapters, KVMs and EDIDless 1407 panels may send no or incorrect EDID data sets. 1408 This parameter allows to specify an EDID data sets 1409 in the /lib/firmware directory that are used instead. 1410 An EDID data set will only be used for a particular 1411 connector, if its name and a colon are prepended to 1412 the EDID name. Each connector may use a unique EDID 1413 data set by separating the files with a comma. An EDID 1414 data set with no connector name will be used for 1415 any connectors not explicitly specified. 1416 1417 dscc4.setup= [NET] 1418 1419 dt_cpu_ftrs= [PPC,EARLY] 1420 Format: {"off" | "known"} 1421 Control how the dt_cpu_ftrs device-tree binding is 1422 used for CPU feature discovery and setup (if it 1423 exists). 1424 off: Do not use it, fall back to legacy cpu table. 1425 known: Do not pass through unknown features to guests 1426 or userspace, only those that the kernel is aware of. 1427 1428 dump_apple_properties [X86] 1429 Dump name and content of EFI device properties on 1430 x86 Macs. Useful for driver authors to determine 1431 what data is available or for reverse-engineering. 1432 1433 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1434 <module>.dyndbg[="val"] 1435 Enable debug messages at boot time. See 1436 Documentation/admin-guide/dynamic-debug-howto.rst 1437 for details. 1438 1439 early_ioremap_debug [KNL,EARLY] 1440 Enable debug messages in early_ioremap support. This 1441 is useful for tracking down temporary early mappings 1442 which are not unmapped. 1443 1444 earlycon= [KNL,EARLY] Output early console device and options. 1445 1446 When used with no options, the early console is 1447 determined by stdout-path property in device tree's 1448 chosen node or the ACPI SPCR table if supported by 1449 the platform. 1450 1451 cdns,<addr>[,options] 1452 Start an early, polled-mode console on a Cadence 1453 (xuartps) serial port at the specified address. Only 1454 supported option is baud rate. If baud rate is not 1455 specified, the serial port must already be setup and 1456 configured. 1457 1458 uart[8250],io,<addr>[,options[,uartclk]] 1459 uart[8250],mmio,<addr>[,options[,uartclk]] 1460 uart[8250],mmio32,<addr>[,options[,uartclk]] 1461 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1462 uart[8250],0x<addr>[,options] 1463 Start an early, polled-mode console on the 8250/16550 1464 UART at the specified I/O port or MMIO address. 1465 MMIO inter-register address stride is either 8-bit 1466 (mmio) or 32-bit (mmio32 or mmio32be). 1467 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1468 to be equivalent to 'mmio'. 'options' are specified 1469 in the same format described for "console=ttyS<n>"; if 1470 unspecified, the h/w is not initialized. 'uartclk' is 1471 the uart clock frequency; if unspecified, it is set 1472 to 'BASE_BAUD' * 16. 1473 1474 pl011,<addr> 1475 pl011,mmio32,<addr> 1476 Start an early, polled-mode console on a pl011 serial 1477 port at the specified address. The pl011 serial port 1478 must already be setup and configured. Options are not 1479 yet supported. If 'mmio32' is specified, then only 1480 the driver will use only 32-bit accessors to read/write 1481 the device registers. 1482 1483 liteuart,<addr> 1484 Start an early console on a litex serial port at the 1485 specified address. The serial port must already be 1486 setup and configured. Options are not yet supported. 1487 1488 meson,<addr> 1489 Start an early, polled-mode console on a meson serial 1490 port at the specified address. The serial port must 1491 already be setup and configured. Options are not yet 1492 supported. 1493 1494 msm_serial,<addr> 1495 Start an early, polled-mode console on an msm serial 1496 port at the specified address. The serial port 1497 must already be setup and configured. Options are not 1498 yet supported. 1499 1500 msm_serial_dm,<addr> 1501 Start an early, polled-mode console on an msm serial 1502 dm port at the specified address. The serial port 1503 must already be setup and configured. Options are not 1504 yet supported. 1505 1506 owl,<addr> 1507 Start an early, polled-mode console on a serial port 1508 of an Actions Semi SoC, such as S500 or S900, at the 1509 specified address. The serial port must already be 1510 setup and configured. Options are not yet supported. 1511 1512 rda,<addr> 1513 Start an early, polled-mode console on a serial port 1514 of an RDA Micro SoC, such as RDA8810PL, at the 1515 specified address. The serial port must already be 1516 setup and configured. Options are not yet supported. 1517 1518 sbi 1519 Use RISC-V SBI (Supervisor Binary Interface) for early 1520 console. 1521 1522 smh Use ARM semihosting calls for early console. 1523 1524 s3c2410,<addr> 1525 s3c2412,<addr> 1526 s3c2440,<addr> 1527 s3c6400,<addr> 1528 s5pv210,<addr> 1529 exynos4210,<addr> 1530 Use early console provided by serial driver available 1531 on Samsung SoCs, requires selecting proper type and 1532 a correct base address of the selected UART port. The 1533 serial port must already be setup and configured. 1534 Options are not yet supported. 1535 1536 lantiq,<addr> 1537 Start an early, polled-mode console on a lantiq serial 1538 (lqasc) port at the specified address. The serial port 1539 must already be setup and configured. Options are not 1540 yet supported. 1541 1542 lpuart,<addr> 1543 lpuart32,<addr> 1544 Use early console provided by Freescale LP UART driver 1545 found on Freescale Vybrid and QorIQ LS1021A processors. 1546 A valid base address must be provided, and the serial 1547 port must already be setup and configured. 1548 1549 ec_imx21,<addr> 1550 ec_imx6q,<addr> 1551 Start an early, polled-mode, output-only console on the 1552 Freescale i.MX UART at the specified address. The UART 1553 must already be setup and configured. 1554 1555 ar3700_uart,<addr> 1556 Start an early, polled-mode console on the 1557 Armada 3700 serial port at the specified 1558 address. The serial port must already be setup 1559 and configured. Options are not yet supported. 1560 1561 qcom_geni,<addr> 1562 Start an early, polled-mode console on a Qualcomm 1563 Generic Interface (GENI) based serial port at the 1564 specified address. The serial port must already be 1565 setup and configured. Options are not yet supported. 1566 1567 efifb,[options] 1568 Start an early, unaccelerated console on the EFI 1569 memory mapped framebuffer (if available). On cache 1570 coherent non-x86 systems that use system memory for 1571 the framebuffer, pass the 'ram' option so that it is 1572 mapped with the correct attributes. 1573 1574 linflex,<addr> 1575 Use early console provided by Freescale LINFlexD UART 1576 serial driver for NXP S32V234 SoCs. A valid base 1577 address must be provided, and the serial port must 1578 already be setup and configured. 1579 1580 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1581 earlyprintk=vga 1582 earlyprintk=sclp 1583 earlyprintk=xen 1584 earlyprintk=serial[,ttySn[,baudrate]] 1585 earlyprintk=serial[,0x...[,baudrate]] 1586 earlyprintk=ttySn[,baudrate] 1587 earlyprintk=dbgp[debugController#] 1588 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1589 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1590 earlyprintk=xdbc[xhciController#] 1591 earlyprintk=bios 1592 1593 earlyprintk is useful when the kernel crashes before 1594 the normal console is initialized. It is not enabled by 1595 default because it has some cosmetic problems. 1596 1597 Use "nocfg" to skip UART configuration, assume 1598 BIOS/firmware has configured UART correctly. 1599 1600 Append ",keep" to not disable it when the real console 1601 takes over. 1602 1603 Only one of vga, serial, or usb debug port can 1604 be used at a time. 1605 1606 Currently only ttyS0 and ttyS1 may be specified by 1607 name. Other I/O ports may be explicitly specified 1608 on some architectures (x86 and arm at least) by 1609 replacing ttySn with an I/O port address, like this: 1610 earlyprintk=serial,0x1008,115200 1611 You can find the port for a given device in 1612 /proc/tty/driver/serial: 1613 2: uart:ST16650V2 port:00001008 irq:18 ... 1614 1615 Interaction with the standard serial driver is not 1616 very good. 1617 1618 The VGA output is eventually overwritten by 1619 the real console. 1620 1621 The xen option can only be used in Xen domains. 1622 1623 The sclp output can only be used on s390. 1624 1625 The bios output can only be used on SuperH. 1626 1627 The optional "force" to "pciserial" enables use of a 1628 PCI device even when its classcode is not of the 1629 UART class. 1630 1631 edac_report= [HW,EDAC] Control how to report EDAC event 1632 Format: {"on" | "off" | "force"} 1633 on: enable EDAC to report H/W event. May be overridden 1634 by other higher priority error reporting module. 1635 off: disable H/W event reporting through EDAC. 1636 force: enforce the use of EDAC to report H/W event. 1637 default: on. 1638 1639 edd= [EDD] 1640 Format: {"off" | "on" | "skip[mbr]"} 1641 1642 efi= [EFI,EARLY] 1643 Format: { "debug", "disable_early_pci_dma", 1644 "nochunk", "noruntime", "nosoftreserve", 1645 "novamap", "no_disable_early_pci_dma" } 1646 debug: enable misc debug output. 1647 disable_early_pci_dma: disable the busmaster bit on all 1648 PCI bridges while in the EFI boot stub. 1649 nochunk: disable reading files in "chunks" in the EFI 1650 boot stub, as chunking can cause problems with some 1651 firmware implementations. 1652 noruntime : disable EFI runtime services support 1653 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1654 attribute may cause the kernel to reserve the 1655 memory range for a memory mapping driver to 1656 claim. Specify efi=nosoftreserve to disable this 1657 reservation and treat the memory by its base type 1658 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1659 novamap: do not call SetVirtualAddressMap(). 1660 no_disable_early_pci_dma: Leave the busmaster bit set 1661 on all PCI bridges while in the EFI boot stub 1662 1663 efi_no_storage_paranoia [EFI,X86,EARLY] 1664 Using this parameter you can use more than 50% of 1665 your efi variable storage. Use this parameter only if 1666 you are really sure that your UEFI does sane gc and 1667 fulfills the spec otherwise your board may brick. 1668 1669 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1670 that is to be dynamically loaded by Linux. If there are 1671 multiple variables with the same name but with different 1672 vendor GUIDs, all of them will be loaded. See 1673 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1674 1675 1676 eisa_irq_edge= [PARISC,HW] 1677 See header of drivers/parisc/eisa.c. 1678 1679 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1680 Format: ekgdboc=kbd 1681 1682 This is designed to be used in conjunction with 1683 the boot argument: earlyprintk=vga 1684 1685 This parameter works in place of the kgdboc parameter 1686 but can only be used if the backing tty is available 1687 very early in the boot process. For early debugging 1688 via a serial port see kgdboc_earlycon instead. 1689 1690 elanfreq= [X86-32] 1691 See comment before function elanfreq_setup() in 1692 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1693 1694 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1695 Specifies physical address of start of kernel core 1696 image elf header and optionally the size. Generally 1697 kexec loader will pass this option to capture kernel. 1698 See Documentation/admin-guide/kdump/kdump.rst for details. 1699 1700 enable_mtrr_cleanup [X86,EARLY] 1701 The kernel tries to adjust MTRR layout from continuous 1702 to discrete, to make X server driver able to add WB 1703 entry later. This parameter enables that. 1704 1705 enable_timer_pin_1 [X86] 1706 Enable PIN 1 of APIC timer 1707 Can be useful to work around chipset bugs 1708 (in particular on some ATI chipsets). 1709 The kernel tries to set a reasonable default. 1710 1711 enforcing= [SELINUX] Set initial enforcing status. 1712 Format: {"0" | "1"} 1713 See security/selinux/Kconfig help text. 1714 0 -- permissive (log only, no denials). 1715 1 -- enforcing (deny and log). 1716 Default value is 0. 1717 Value can be changed at runtime via 1718 /sys/fs/selinux/enforce. 1719 1720 erst_disable [ACPI] 1721 Disable Error Record Serialization Table (ERST) 1722 support. 1723 1724 ether= [HW,NET] Ethernet cards parameters 1725 This option is obsoleted by the "netdev=" option, which 1726 has equivalent usage. See its documentation for details. 1727 1728 evm= [EVM] 1729 Format: { "fix" } 1730 Permit 'security.evm' to be updated regardless of 1731 current integrity status. 1732 1733 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1734 stages so cover more early boot allocations. 1735 Please note that as side effect some optimizations 1736 might be disabled to achieve that (e.g. parallelized 1737 memory initialization is disabled) so the boot process 1738 might take longer, especially on systems with a lot of 1739 memory. Available with CONFIG_PAGE_EXTENSION=y. 1740 1741 failslab= 1742 fail_usercopy= 1743 fail_page_alloc= 1744 fail_skb_realloc= 1745 fail_make_request=[KNL] 1746 General fault injection mechanism. 1747 Format: <interval>,<probability>,<space>,<times> 1748 See also Documentation/fault-injection/. 1749 1750 fb_tunnels= [NET] 1751 Format: { initns | none } 1752 See Documentation/admin-guide/sysctl/net.rst for 1753 fb_tunnels_only_for_init_ns 1754 1755 floppy= [HW] 1756 See Documentation/admin-guide/blockdev/floppy.rst. 1757 1758 forcepae [X86-32] 1759 Forcefully enable Physical Address Extension (PAE). 1760 Many Pentium M systems disable PAE but may have a 1761 functionally usable PAE implementation. 1762 Warning: use of this parameter will taint the kernel 1763 and may cause unknown problems. 1764 1765 fred= [X86-64] 1766 Enable/disable Flexible Return and Event Delivery. 1767 Format: { on | off } 1768 on: enable FRED when it's present, the default setting. 1769 off: disable FRED. 1770 1771 ftrace=[tracer] 1772 [FTRACE] will set and start the specified tracer 1773 as early as possible in order to facilitate early 1774 boot debugging. 1775 1776 ftrace_boot_snapshot 1777 [FTRACE] On boot up, a snapshot will be taken of the 1778 ftrace ring buffer that can be read at: 1779 /sys/kernel/tracing/snapshot. 1780 This is useful if you need tracing information from kernel 1781 boot up that is likely to be overridden by user space 1782 start up functionality. 1783 1784 Optionally, the snapshot can also be defined for a tracing 1785 instance that was created by the trace_instance= command 1786 line parameter. 1787 1788 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1789 1790 The above will cause the "foo" tracing instance to trigger 1791 a snapshot at the end of boot up. 1792 1793 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1794 ,<instance>=2(orig_cpu)] 1795 [FTRACE] will dump the trace buffers on oops. 1796 If no parameter is passed, ftrace will dump global 1797 buffers of all CPUs, if you pass 2 or orig_cpu, it 1798 will dump only the buffer of the CPU that triggered 1799 the oops, or the specific instance will be dumped if 1800 its name is passed. Multiple instance dump is also 1801 supported, and instances are separated by commas. Each 1802 instance supports only dump on CPU that triggered the 1803 oops by passing 2 or orig_cpu to it. 1804 1805 ftrace_dump_on_oops=foo=orig_cpu 1806 1807 The above will dump only the buffer of "foo" instance 1808 on CPU that triggered the oops. 1809 1810 ftrace_dump_on_oops,foo,bar=orig_cpu 1811 1812 The above will dump global buffer on all CPUs, the 1813 buffer of "foo" instance on all CPUs and the buffer 1814 of "bar" instance on CPU that triggered the oops. 1815 1816 ftrace_filter=[function-list] 1817 [FTRACE] Limit the functions traced by the function 1818 tracer at boot up. function-list is a comma-separated 1819 list of functions. This list can be changed at run 1820 time by the set_ftrace_filter file in the debugfs 1821 tracing directory. 1822 1823 ftrace_notrace=[function-list] 1824 [FTRACE] Do not trace the functions specified in 1825 function-list. This list can be changed at run time 1826 by the set_ftrace_notrace file in the debugfs 1827 tracing directory. 1828 1829 ftrace_graph_filter=[function-list] 1830 [FTRACE] Limit the top level callers functions traced 1831 by the function graph tracer at boot up. 1832 function-list is a comma-separated list of functions 1833 that can be changed at run time by the 1834 set_graph_function file in the debugfs tracing directory. 1835 1836 ftrace_graph_notrace=[function-list] 1837 [FTRACE] Do not trace from the functions specified in 1838 function-list. This list is a comma-separated list of 1839 functions that can be changed at run time by the 1840 set_graph_notrace file in the debugfs tracing directory. 1841 1842 ftrace_graph_max_depth=<uint> 1843 [FTRACE] Used with the function graph tracer. This is 1844 the max depth it will trace into a function. This value 1845 can be changed at run time by the max_graph_depth file 1846 in the tracefs tracing directory. default: 0 (no limit) 1847 1848 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1849 devices by scanning the firmware to infer the 1850 consumer/supplier relationships. This feature is 1851 especially useful when drivers are loaded as modules as 1852 it ensures proper ordering of tasks like device probing 1853 (suppliers first, then consumers), supplier boot state 1854 clean up (only after all consumers have probed), 1855 suspend/resume & runtime PM (consumers first, then 1856 suppliers). 1857 Format: { off | permissive | on | rpm } 1858 off -- Don't create device links from firmware info. 1859 permissive -- Create device links from firmware info 1860 but use it only for ordering boot state clean 1861 up (sync_state() calls). 1862 on -- Create device links from firmware info and use it 1863 to enforce probe and suspend/resume ordering. 1864 rpm -- Like "on", but also use to order runtime PM. 1865 1866 fw_devlink.strict=<bool> 1867 [KNL,EARLY] Treat all inferred dependencies as mandatory 1868 dependencies. This only applies for fw_devlink=on|rpm. 1869 Format: <bool> 1870 1871 fw_devlink.sync_state = 1872 [KNL,EARLY] When all devices that could probe have finished 1873 probing, this parameter controls what to do with 1874 devices that haven't yet received their sync_state() 1875 calls. 1876 Format: { strict | timeout } 1877 strict -- Default. Continue waiting on consumers to 1878 probe successfully. 1879 timeout -- Give up waiting on consumers and call 1880 sync_state() on any devices that haven't yet 1881 received their sync_state() calls after 1882 deferred_probe_timeout has expired or by 1883 late_initcall() if !CONFIG_MODULES. 1884 1885 gamecon.map[2|3]= 1886 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1887 support via parallel port (up to 5 devices per port) 1888 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1889 See also Documentation/input/devices/joystick-parport.rst 1890 1891 gamma= [HW,DRM] 1892 1893 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1894 Format: off | on 1895 default: on 1896 1897 gather_data_sampling= 1898 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1899 mitigation. 1900 1901 Gather Data Sampling is a hardware vulnerability which 1902 allows unprivileged speculative access to data which was 1903 previously stored in vector registers. 1904 1905 This issue is mitigated by default in updated microcode. 1906 The mitigation may have a performance impact but can be 1907 disabled. On systems without the microcode mitigation 1908 disabling AVX serves as a mitigation. 1909 1910 force: Disable AVX to mitigate systems without 1911 microcode mitigation. No effect if the microcode 1912 mitigation is present. Known to cause crashes in 1913 userspace with buggy AVX enumeration. 1914 1915 off: Disable GDS mitigation. 1916 1917 gbpages [X86] Use GB pages for kernel direct mappings. 1918 1919 gcov_persist= [GCOV] When non-zero (default), profiling data for 1920 kernel modules is saved and remains accessible via 1921 debugfs, even when the module is unloaded/reloaded. 1922 When zero, profiling data is discarded and associated 1923 debugfs files are removed at module unload time. 1924 1925 goldfish [X86] Enable the goldfish android emulator platform. 1926 Don't use this when you are not running on the 1927 android emulator 1928 1929 gpio-mockup.gpio_mockup_ranges 1930 [HW] Sets the ranges of gpiochip of for this device. 1931 Format: <start1>,<end1>,<start2>,<end2>... 1932 gpio-mockup.gpio_mockup_named_lines 1933 [HW] Let the driver know GPIO lines should be named. 1934 1935 gpt [EFI] Forces disk with valid GPT signature but 1936 invalid Protective MBR to be treated as GPT. If the 1937 primary GPT is corrupted, it enables the backup/alternate 1938 GPT to be used instead. 1939 1940 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1941 the "Enable 0" bit of the configuration register. 1942 Format: 0 | 1 1943 Default: 0 1944 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1945 the "Enable 0" bit of the configuration register. 1946 Format: 0 | 1 1947 Default: 0 1948 grcan.select= [HW] Select which physical interface to use. 1949 Format: 0 | 1 1950 Default: 0 1951 grcan.txsize= [HW] Sets the size of the tx buffer. 1952 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1953 Default: 1024 1954 grcan.rxsize= [HW] Sets the size of the rx buffer. 1955 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1956 Default: 1024 1957 1958 hardened_usercopy= 1959 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1960 hardening is enabled for this boot. Hardened 1961 usercopy checking is used to protect the kernel 1962 from reading or writing beyond known memory 1963 allocation boundaries as a proactive defense 1964 against bounds-checking flaws in the kernel's 1965 copy_to_user()/copy_from_user() interface. 1966 The default is determined by 1967 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1968 on Perform hardened usercopy checks. 1969 off Disable hardened usercopy checks. 1970 1971 hardlockup_all_cpu_backtrace= 1972 [KNL] Should the hard-lockup detector generate 1973 backtraces on all cpus. 1974 Format: 0 | 1 1975 1976 hash_pointers= 1977 [KNL,EARLY] 1978 By default, when pointers are printed to the console 1979 or buffers via the %p format string, that pointer is 1980 "hashed", i.e. obscured by hashing the pointer value. 1981 This is a security feature that hides actual kernel 1982 addresses from unprivileged users, but it also makes 1983 debugging the kernel more difficult since unequal 1984 pointers can no longer be compared. The choices are: 1985 Format: { auto | always | never } 1986 Default: auto 1987 1988 auto - Hash pointers unless slab_debug is enabled. 1989 always - Always hash pointers (even if slab_debug is 1990 enabled). 1991 never - Never hash pointers. This option should only 1992 be specified when debugging the kernel. Do 1993 not use on production kernels. The boot 1994 param "no_hash_pointers" is an alias for 1995 this mode. 1996 1997 For controlling hashing dynamically at runtime, 1998 use the "kernel.kptr_restrict" sysctl instead. 1999 2000 hashdist= [KNL,NUMA] Large hashes allocated during boot 2001 are distributed across NUMA nodes. Defaults on 2002 for 64-bit NUMA, off otherwise. 2003 Format: 0 | 1 (for off | on) 2004 2005 hd= [EIDE] (E)IDE hard drive subsystem geometry 2006 Format: <cyl>,<head>,<sect> 2007 2008 hest_disable [ACPI] 2009 Disable Hardware Error Source Table (HEST) support; 2010 corresponding firmware-first mode error processing 2011 logic will be disabled. 2012 2013 hibernate= [HIBERNATION] 2014 noresume Don't check if there's a hibernation image 2015 present during boot. 2016 nocompress Don't compress/decompress hibernation images. 2017 no Disable hibernation and resume. 2018 protect_image Turn on image protection during restoration 2019 (that will set all pages holding image data 2020 during restoration read-only). 2021 2022 hibernate.compressor= [HIBERNATION] Compression algorithm to be 2023 used with hibernation. 2024 Format: { lzo | lz4 } 2025 Default: lzo 2026 2027 lzo: Select LZO compression algorithm to 2028 compress/decompress hibernation image. 2029 2030 lz4: Select LZ4 compression algorithm to 2031 compress/decompress hibernation image. 2032 2033 hibernate.pm_test_delay= 2034 [HIBERNATION] 2035 Sets the number of seconds to remain in a hibernation test 2036 mode before resuming the system (see 2037 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2038 is set. Default value is 5. 2039 2040 hibernate_compression_threads= 2041 [HIBERNATION] 2042 Set the number of threads used for compressing or decompressing 2043 hibernation images. 2044 2045 Format: <integer> 2046 Default: 3 2047 Minimum: 1 2048 Example: hibernate_compression_threads=4 2049 2050 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2051 size of <nn>. This works even on boxes that have no 2052 highmem otherwise. This also works to reduce highmem 2053 size on bigger boxes. 2054 2055 highres= [KNL] Enable/disable high resolution timer mode. 2056 Valid parameters: "on", "off" 2057 Default: "on" 2058 2059 hlt [BUGS=ARM,SH] 2060 2061 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2062 Format: <string> 2063 This allows setting the system's hostname during early 2064 startup. This sets the name returned by gethostname. 2065 Using this parameter to set the hostname makes it 2066 possible to ensure the hostname is correctly set before 2067 any userspace processes run, avoiding the possibility 2068 that a process may call gethostname before the hostname 2069 has been explicitly set, resulting in the calling 2070 process getting an incorrect result. The string must 2071 not exceed the maximum allowed hostname length (usually 2072 64 characters) and will be truncated otherwise. 2073 2074 hpet= [X86-32,HPET] option to control HPET usage 2075 Format: { enable (default) | disable | force | 2076 verbose } 2077 disable: disable HPET and use PIT instead 2078 force: allow force enabled of undocumented chips (ICH4, 2079 VIA, nVidia) 2080 verbose: show contents of HPET registers during setup 2081 2082 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2083 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2084 2085 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2086 If this follows hugepagesz (below), it specifies 2087 the number of pages of hugepagesz to be allocated. 2088 If this is the first HugeTLB parameter on the command 2089 line, it specifies the number of pages to allocate for 2090 the default huge page size. If using node format, the 2091 number of pages to allocate per-node can be specified. 2092 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2093 Format: <integer> or (node format) 2094 <node>:<integer>[,<node>:<integer>] 2095 2096 hugepagesz= 2097 [HW,EARLY] The size of the HugeTLB pages. This is 2098 used in conjunction with hugepages (above) to 2099 allocate huge pages of a specific size at boot. The 2100 pair hugepagesz=X hugepages=Y can be specified once 2101 for each supported huge page size. Huge page sizes 2102 are architecture dependent. See also 2103 Documentation/admin-guide/mm/hugetlbpage.rst. 2104 Format: size[KMG] 2105 2106 hugepage_alloc_threads= 2107 [HW] The number of threads that should be used to 2108 allocate hugepages during boot. This option can be 2109 used to improve system bootup time when allocating 2110 a large amount of huge pages. 2111 The default value is 25% of the available hardware threads. 2112 2113 Note that this parameter only applies to non-gigantic huge pages. 2114 2115 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2116 of gigantic hugepages. Or using node format, the size 2117 of a CMA area per node can be specified. 2118 Format: nn[KMGTPE] or (node format) 2119 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2120 2121 Reserve a CMA area of given size and allocate gigantic 2122 hugepages using the CMA allocator. If enabled, the 2123 boot-time allocation of gigantic hugepages is skipped. 2124 2125 hugetlb_cma_only= 2126 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2127 try to allocate from the CMA areas. 2128 2129 This option does nothing if hugetlb_cma= is not also 2130 specified. 2131 2132 hugetlb_free_vmemmap= 2133 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2134 enabled. 2135 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2136 Allows heavy hugetlb users to free up some more 2137 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2138 Format: { on | off (default) } 2139 2140 on: enable HVO 2141 off: disable HVO 2142 2143 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2144 the default is on. 2145 2146 Note that the vmemmap pages may be allocated from the added 2147 memory block itself when memory_hotplug.memmap_on_memory is 2148 enabled, those vmemmap pages cannot be optimized even if this 2149 feature is enabled. Other vmemmap pages not allocated from 2150 the added memory block itself do not be affected. 2151 2152 hung_task_panic= 2153 [KNL] Number of hung tasks to trigger kernel panic. 2154 Format: <int> 2155 2156 When set to a non-zero value, a kernel panic will be triggered if 2157 the number of detected hung tasks reaches this value. 2158 2159 0: don't panic 2160 1: panic immediately on first hung task 2161 N: panic after N hung tasks are detected in a single scan 2162 2163 The default value is controlled by the 2164 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2165 selected by this boot parameter can be changed later by the 2166 kernel.hung_task_panic sysctl. 2167 2168 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2169 terminal devices. Valid values: 0..8 2170 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2171 If specified, z/VM IUCV HVC accepts connections 2172 from listed z/VM user IDs only. 2173 2174 hv_nopvspin [X86,HYPER_V,EARLY] 2175 Disables the paravirt spinlock optimizations 2176 which allow the hypervisor to 'idle' the guest 2177 on lock contention. 2178 2179 hw_protection= [HW] 2180 Format: reboot | shutdown 2181 2182 Hardware protection action taken on critical events like 2183 overtemperature or imminent voltage loss. 2184 2185 i2c_bus= [HW] Override the default board specific I2C bus speed 2186 or register an additional I2C bus that is not 2187 registered from board initialization code. 2188 Format: 2189 <bus_id>,<clkrate> 2190 2191 i2c_touchscreen_props= [HW,ACPI,X86] 2192 Set device-properties for ACPI-enumerated I2C-attached 2193 touchscreen, to e.g. fix coordinates of upside-down 2194 mounted touchscreens. If you need this option please 2195 submit a drivers/platform/x86/touchscreen_dmi.c patch 2196 adding a DMI quirk for this. 2197 2198 Format: 2199 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2200 Where <val> is one of: 2201 Omit "=<val>" entirely Set a boolean device-property 2202 Unsigned number Set a u32 device-property 2203 Anything else Set a string device-property 2204 2205 Examples (split over multiple lines): 2206 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2207 touchscreen-inverted-y 2208 2209 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2210 touchscreen-size-y=1080:touchscreen-inverted-y: 2211 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2212 2213 i8042.debug [HW] Toggle i8042 debug mode 2214 i8042.unmask_kbd_data 2215 [HW] Enable printing of interrupt data from the KBD port 2216 (disabled by default, and as a pre-condition 2217 requires that i8042.debug=1 be enabled) 2218 i8042.direct [HW] Put keyboard port into non-translated mode 2219 i8042.dumbkbd [HW] Pretend that controller can only read data from 2220 keyboard and cannot control its state 2221 (Don't attempt to blink the leds) 2222 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2223 i8042.nokbd [HW] Don't check/create keyboard port 2224 i8042.noloop [HW] Disable the AUX Loopback command while probing 2225 for the AUX port 2226 i8042.nomux [HW] Don't check presence of an active multiplexing 2227 controller 2228 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2229 controllers 2230 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2231 i8042.reset [HW] Reset the controller during init, cleanup and 2232 suspend-to-ram transitions, only during s2r 2233 transitions, or never reset 2234 Format: { 1 | Y | y | 0 | N | n } 2235 1, Y, y: always reset controller 2236 0, N, n: don't ever reset controller 2237 Default: only on s2r transitions on x86; most other 2238 architectures force reset to be always executed 2239 i8042.unlock [HW] Unlock (ignore) the keylock 2240 i8042.kbdreset [HW] Reset device connected to KBD port 2241 i8042.probe_defer 2242 [HW] Allow deferred probing upon i8042 probe errors 2243 2244 i810= [HW,DRM] 2245 2246 i915.invert_brightness= 2247 [DRM] Invert the sense of the variable that is used to 2248 set the brightness of the panel backlight. Normally a 2249 brightness value of 0 indicates backlight switched off, 2250 and the maximum of the brightness value sets the backlight 2251 to maximum brightness. If this parameter is set to 0 2252 (default) and the machine requires it, or this parameter 2253 is set to 1, a brightness value of 0 sets the backlight 2254 to maximum brightness, and the maximum of the brightness 2255 value switches the backlight off. 2256 -1 -- never invert brightness 2257 0 -- machine default 2258 1 -- force brightness inversion 2259 2260 ia32_emulation= [X86-64] 2261 Format: <bool> 2262 When true, allows loading 32-bit programs and executing 32-bit 2263 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2264 boot time. When false, unconditionally disables IA32 emulation. 2265 2266 icn= [HW,ISDN] 2267 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2268 2269 2270 idle= [X86,EARLY] 2271 Format: idle=poll, idle=halt, idle=nomwait 2272 2273 idle=poll: Don't do power saving in the idle loop 2274 using HLT, but poll for rescheduling event. This will 2275 make the CPUs eat a lot more power, but may be useful 2276 to get slightly better performance in multiprocessor 2277 benchmarks. It also makes some profiling using 2278 performance counters more accurate. Please note that 2279 on systems with MONITOR/MWAIT support (like Intel 2280 EM64T CPUs) this option has no performance advantage 2281 over the normal idle loop. It may also interact badly 2282 with hyperthreading. 2283 2284 idle=halt: Halt is forced to be used for CPU idle. 2285 In such case C2/C3 won't be used again. 2286 2287 idle=nomwait: Disable mwait for CPU C-states 2288 2289 idxd.sva= [HW] 2290 Format: <bool> 2291 Allow force disabling of Shared Virtual Memory (SVA) 2292 support for the idxd driver. By default it is set to 2293 true (1). 2294 2295 idxd.tc_override= [HW] 2296 Format: <bool> 2297 Allow override of default traffic class configuration 2298 for the device. By default it is set to false (0). 2299 2300 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2301 Format: { strict | legacy | 2008 | relaxed | emulated } 2302 Default: strict 2303 2304 Choose which programs will be accepted for execution 2305 based on the IEEE 754 NaN encoding(s) supported by 2306 the FPU and the NaN encoding requested with the value 2307 of an ELF file header flag individually set by each 2308 binary. Hardware implementations are permitted to 2309 support either or both of the legacy and the 2008 NaN 2310 encoding mode. 2311 2312 Available settings are as follows: 2313 strict accept binaries that request a NaN encoding 2314 supported by the FPU 2315 legacy only accept legacy-NaN binaries, if supported 2316 by the FPU 2317 2008 only accept 2008-NaN binaries, if supported 2318 by the FPU 2319 relaxed accept any binaries regardless of whether 2320 supported by the FPU 2321 emulated accept any binaries but enable FPU emulator 2322 if binary mode is unsupported by the FPU. 2323 2324 The FPU emulator is always able to support both NaN 2325 encodings, so if no FPU hardware is present or it has 2326 been disabled with 'nofpu', then the settings of 2327 'legacy' and '2008' strap the emulator accordingly, 2328 'relaxed' straps the emulator for both legacy-NaN and 2329 2008-NaN, whereas 'strict' enables legacy-NaN only on 2330 legacy processors and both NaN encodings on MIPS32 or 2331 MIPS64 CPUs. 2332 2333 The setting for ABS.fmt/NEG.fmt instruction execution 2334 mode generally follows that for the NaN encoding, 2335 except where unsupported by hardware. 2336 2337 ignore_loglevel [KNL,EARLY] 2338 Ignore loglevel setting - this will print /all/ 2339 kernel messages to the console. Useful for debugging. 2340 We also add it as printk module parameter, so users 2341 could change it dynamically, usually by 2342 /sys/module/printk/parameters/ignore_loglevel. 2343 2344 ignore_rlimit_data 2345 Ignore RLIMIT_DATA setting for data mappings, 2346 print warning at first misuse. Can be changed via 2347 /sys/module/kernel/parameters/ignore_rlimit_data. 2348 2349 ihash_entries= [KNL] 2350 Set number of hash buckets for inode cache. 2351 2352 ima_appraise= [IMA] appraise integrity measurements 2353 Format: { "off" | "enforce" | "fix" | "log" } 2354 default: "enforce" 2355 2356 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2357 The builtin appraise policy appraises all files 2358 owned by uid=0. 2359 2360 ima_canonical_fmt [IMA] 2361 Use the canonical format for the binary runtime 2362 measurements, instead of host native format. 2363 2364 ima_hash= [IMA] 2365 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2366 | sha512 | ... } 2367 default: "sha1" 2368 2369 The list of supported hash algorithms is defined 2370 in crypto/hash_info.h. 2371 2372 ima_policy= [IMA] 2373 The builtin policies to load during IMA setup. 2374 Format: "tcb | appraise_tcb | secure_boot | 2375 fail_securely | critical_data" 2376 2377 The "tcb" policy measures all programs exec'd, files 2378 mmap'd for exec, and all files opened with the read 2379 mode bit set by either the effective uid (euid=0) or 2380 uid=0. 2381 2382 The "appraise_tcb" policy appraises the integrity of 2383 all files owned by root. 2384 2385 The "secure_boot" policy appraises the integrity 2386 of files (eg. kexec kernel image, kernel modules, 2387 firmware, policy, etc) based on file signatures. 2388 2389 The "fail_securely" policy forces file signature 2390 verification failure also on privileged mounted 2391 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2392 flag. 2393 2394 The "critical_data" policy measures kernel integrity 2395 critical data. 2396 2397 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2398 Load a policy which meets the needs of the Trusted 2399 Computing Base. This means IMA will measure all 2400 programs exec'd, files mmap'd for exec, and all files 2401 opened for read by uid=0. 2402 2403 ima_template= [IMA] 2404 Select one of defined IMA measurements template formats. 2405 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2406 "ima-sigv2" } 2407 Default: "ima-ng" 2408 2409 ima_template_fmt= 2410 [IMA] Define a custom template format. 2411 Format: { "field1|...|fieldN" } 2412 2413 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2414 Format: <min_file_size> 2415 Set the minimal file size for using asynchronous hash. 2416 If left unspecified, ahash usage is disabled. 2417 2418 ahash performance varies for different data sizes on 2419 different crypto accelerators. This option can be used 2420 to achieve the best performance for a particular HW. 2421 2422 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2423 Format: <bufsize> 2424 Set hashing buffer size. Default: 4k. 2425 2426 ahash performance varies for different chunk sizes on 2427 different crypto accelerators. This option can be used 2428 to achieve best performance for particular HW. 2429 2430 ima= [IMA] Enable or disable IMA 2431 Format: { "off" | "on" } 2432 Default: "on" 2433 Note that disabling IMA is limited to kdump kernel. 2434 2435 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2436 Target Selection(ITS) bug in Intel CPUs. Updated 2437 microcode is also required for a fix in IBPB. 2438 2439 on: Enable mitigation (default). 2440 off: Disable mitigation. 2441 force: Force the ITS bug and deploy default 2442 mitigation. 2443 vmexit: Only deploy mitigation if CPU is affected by 2444 guest/host isolation part of ITS. 2445 stuff: Deploy RSB-fill mitigation when retpoline is 2446 also deployed. Otherwise, deploy the default 2447 mitigation. 2448 2449 For details see: 2450 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2451 2452 init= [KNL] 2453 Format: <full_path> 2454 Run specified binary instead of /sbin/init as init 2455 process. 2456 2457 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2458 for working out where the kernel is dying during 2459 startup. 2460 2461 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2462 initcall functions. Useful for debugging built-in 2463 modules and initcalls. 2464 2465 initramfs_async= [KNL] 2466 Format: <bool> 2467 Default: 1 2468 This parameter controls whether the initramfs 2469 image is unpacked asynchronously, concurrently 2470 with devices being probed and 2471 initialized. This should normally just work, 2472 but as a debugging aid, one can get the 2473 historical behaviour of the initramfs 2474 unpacking being completed before device_ and 2475 late_ initcalls. 2476 2477 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2478 2479 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2480 load the initrd. If an initrd is compiled in or 2481 specified in the bootparams, it takes priority over this 2482 setting. 2483 Format: ss[KMG],nn[KMG] 2484 Default is 0, 0 2485 2486 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2487 zeroes. 2488 Format: 0 | 1 2489 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2490 2491 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2492 Format: 0 | 1 2493 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2494 2495 init_pkru= [X86] Specify the default memory protection keys rights 2496 register contents for all processes. 0x55555554 by 2497 default (disallow access to all but pkey 0). Can 2498 override in debugfs after boot. 2499 2500 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2501 Format: <irq> 2502 2503 int_pln_enable [X86] Enable power limit notification interrupt 2504 2505 integrity_audit=[IMA] 2506 Format: { "0" | "1" } 2507 0 -- basic integrity auditing messages. (Default) 2508 1 -- additional integrity auditing messages. 2509 2510 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2511 on 2512 Enable intel iommu driver. 2513 off 2514 Disable intel iommu driver. 2515 igfx_off [Default Off] 2516 By default, gfx is mapped as normal device. If a gfx 2517 device has a dedicated DMAR unit, the DMAR unit is 2518 bypassed by not enabling DMAR with this option. In 2519 this case, gfx device will use physical address for 2520 DMA. 2521 strict [Default Off] 2522 Deprecated, equivalent to iommu.strict=1. 2523 sp_off [Default Off] 2524 By default, super page will be supported if Intel IOMMU 2525 has the capability. With this option, super page will 2526 not be supported. 2527 sm_on 2528 Enable the Intel IOMMU scalable mode if the hardware 2529 advertises that it has support for the scalable mode 2530 translation. 2531 sm_off 2532 Disallow use of the Intel IOMMU scalable mode. 2533 tboot_noforce [Default Off] 2534 Do not force the Intel IOMMU enabled under tboot. 2535 By default, tboot will force Intel IOMMU on, which 2536 could harm performance of some high-throughput 2537 devices like 40GBit network cards, even if identity 2538 mapping is enabled. 2539 Note that using this option lowers the security 2540 provided by tboot because it makes the system 2541 vulnerable to DMA attacks. 2542 2543 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2544 0 disables intel_idle and fall back on acpi_idle. 2545 1 to 9 specify maximum depth of C-state. 2546 2547 intel_pstate= [X86,EARLY] 2548 disable 2549 Do not enable intel_pstate as the default 2550 scaling driver for the supported processors 2551 active 2552 Use intel_pstate driver to bypass the scaling 2553 governors layer of cpufreq and provides it own 2554 algorithms for p-state selection. There are two 2555 P-state selection algorithms provided by 2556 intel_pstate in the active mode: powersave and 2557 performance. The way they both operate depends 2558 on whether or not the hardware managed P-states 2559 (HWP) feature has been enabled in the processor 2560 and possibly on the processor model. 2561 passive 2562 Use intel_pstate as a scaling driver, but configure it 2563 to work with generic cpufreq governors (instead of 2564 enabling its internal governor). This mode cannot be 2565 used along with the hardware-managed P-states (HWP) 2566 feature. 2567 force 2568 Enable intel_pstate on systems that prohibit it by default 2569 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2570 instead of acpi-cpufreq may disable platform features, such 2571 as thermal controls and power capping, that rely on ACPI 2572 P-States information being indicated to OSPM and therefore 2573 should be used with caution. This option does not work with 2574 processors that aren't supported by the intel_pstate driver 2575 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2576 no_hwp 2577 Do not enable hardware P state control (HWP) 2578 if available. 2579 hwp_only 2580 Only load intel_pstate on systems which support 2581 hardware P state control (HWP) if available. 2582 support_acpi_ppc 2583 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2584 Description Table, specifies preferred power management 2585 profile as "Enterprise Server" or "Performance Server", 2586 then this feature is turned on by default. 2587 per_cpu_perf_limits 2588 Allow per-logical-CPU P-State performance control limits using 2589 cpufreq sysfs interface 2590 no_cas 2591 Do not enable capacity-aware scheduling (CAS) on 2592 hybrid systems 2593 2594 intremap= [X86-64,Intel-IOMMU,EARLY] 2595 on enable Interrupt Remapping (default) 2596 off disable Interrupt Remapping 2597 nosid disable Source ID checking 2598 no_x2apic_optout 2599 BIOS x2APIC opt-out request will be ignored 2600 nopost disable Interrupt Posting 2601 posted_msi 2602 enable MSIs delivered as posted interrupts 2603 2604 iomem= Disable strict checking of access to MMIO memory 2605 strict regions from userspace. 2606 relaxed 2607 2608 iommu= [X86,EARLY] 2609 2610 off 2611 Don't initialize and use any kind of IOMMU. 2612 2613 force 2614 Force the use of the hardware IOMMU even when 2615 it is not actually needed (e.g. because < 3 GB 2616 memory). 2617 2618 noforce 2619 Don't force hardware IOMMU usage when it is not 2620 needed. (default). 2621 2622 biomerge 2623 panic 2624 nopanic 2625 merge 2626 nomerge 2627 2628 soft 2629 Use software bounce buffering (SWIOTLB) (default for 2630 Intel machines). This can be used to prevent the usage 2631 of an available hardware IOMMU. 2632 2633 pt 2634 nopt 2635 nobypass [PPC/POWERNV] 2636 Disable IOMMU bypass, using IOMMU for PCI devices. 2637 2638 AMD Gart HW IOMMU-specific options: 2639 2640 <size> 2641 Set the size of the remapping area in bytes. 2642 2643 allowed 2644 Overwrite iommu off workarounds for specific chipsets 2645 2646 fullflush 2647 Flush IOMMU on each allocation (default). 2648 2649 nofullflush 2650 Don't use IOMMU fullflush. 2651 2652 memaper[=<order>] 2653 Allocate an own aperture over RAM with size 2654 32MB<<order. (default: order=1, i.e. 64MB) 2655 2656 merge 2657 Do scatter-gather (SG) merging. Implies "force" 2658 (experimental). 2659 2660 nomerge 2661 Don't do scatter-gather (SG) merging. 2662 2663 noaperture 2664 Ask the IOMMU not to touch the aperture for AGP. 2665 2666 noagp 2667 Don't initialize the AGP driver and use full aperture. 2668 2669 panic 2670 Always panic when IOMMU overflows. 2671 2672 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2673 Format: { "0" | "1" } 2674 0 - Try to allocate a 32-bit DMA address first, before 2675 falling back to the full range if needed. 2676 1 - Allocate directly from the full usable range, 2677 forcing Dual Address Cycle for PCI cards supporting 2678 greater than 32-bit addressing. 2679 2680 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2681 Format: { "0" | "1" } 2682 0 - Lazy mode. 2683 Request that DMA unmap operations use deferred 2684 invalidation of hardware TLBs, for increased 2685 throughput at the cost of reduced device isolation. 2686 Will fall back to strict mode if not supported by 2687 the relevant IOMMU driver. 2688 1 - Strict mode. 2689 DMA unmap operations invalidate IOMMU hardware TLBs 2690 synchronously. 2691 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2692 Note: on x86, strict mode specified via one of the 2693 legacy driver-specific options takes precedence. 2694 2695 iommu.passthrough= 2696 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2697 Format: { "0" | "1" } 2698 0 - Use IOMMU translation for DMA. 2699 1 - Bypass the IOMMU for DMA. 2700 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2701 2702 iommu.debug_pagealloc= 2703 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2704 parameter enables the feature at boot time. By default, it 2705 is disabled and the system behaves the same way as a kernel 2706 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2707 Format: { "0" | "1" } 2708 0 - Sanitizer disabled. 2709 1 - Sanitizer enabled, expect runtime overhead. 2710 2711 io7= [HW] IO7 for Marvel-based Alpha systems 2712 See comment before marvel_specify_io7 in 2713 arch/alpha/kernel/core_marvel.c. 2714 2715 io_delay= [X86,EARLY] I/O delay method 2716 0x80 2717 Standard port 0x80 based delay 2718 0xed 2719 Alternate port 0xed based delay (needed on some systems) 2720 udelay 2721 Simple two microseconds delay 2722 none 2723 No delay 2724 2725 ip= [IP_PNP] 2726 See Documentation/admin-guide/nfs/nfsroot.rst. 2727 2728 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2729 IPC identifiers from 32,768 to 16,777,216. 2730 2731 ipe.enforce= [IPE] 2732 Format: <bool> 2733 Determine whether IPE starts in permissive (0) or 2734 enforce (1) mode. The default is enforce. 2735 2736 ipe.success_audit= 2737 [IPE] 2738 Format: <bool> 2739 Start IPE with success auditing enabled, emitting 2740 an audit event when a binary is allowed. The default 2741 is 0. 2742 2743 irqaffinity= [SMP] Set the default irq affinity mask 2744 The argument is a cpu list, as described above. 2745 2746 irqchip.gicv2_force_probe= 2747 [ARM,ARM64,EARLY] 2748 Format: <bool> 2749 Force the kernel to look for the second 4kB page 2750 of a GICv2 controller even if the memory range 2751 exposed by the device tree is too small. 2752 2753 irqchip.gicv3_nolpi= 2754 [ARM,ARM64,EARLY] 2755 Force the kernel to ignore the availability of 2756 LPIs (and by consequence ITSs). Intended for system 2757 that use the kernel as a bootloader, and thus want 2758 to let secondary kernels in charge of setting up 2759 LPIs. 2760 2761 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2762 Enables support for pseudo-NMIs in the kernel. This 2763 requires the kernel to be built with 2764 CONFIG_ARM64_PSEUDO_NMI. 2765 2766 irqchip.riscv_imsic_noipi 2767 [RISC-V,EARLY] 2768 Force the kernel to not use IMSIC software injected MSIs 2769 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2770 and thus want to reduce MMIO traps when triggering IPIs 2771 to multiple harts. 2772 2773 irqfixup [HW] 2774 When an interrupt is not handled search all handlers 2775 for it. Intended to get systems with badly broken 2776 firmware running. 2777 2778 irqhandler.duration_warn_us= [KNL] 2779 Warn if an IRQ handler exceeds the specified duration 2780 threshold in microseconds. Useful for identifying 2781 long-running IRQs in the system. 2782 2783 irqpoll [HW] 2784 When an interrupt is not handled search all handlers 2785 for it. Also check all handlers each timer 2786 interrupt. Intended to get systems with badly broken 2787 firmware running. 2788 2789 isapnp= [ISAPNP] 2790 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2791 2792 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2793 [Deprecated - use cpusets instead] 2794 Format: [flag-list,]<cpu-list> 2795 2796 Specify one or more CPUs to isolate from disturbances 2797 specified in the flag list (default: domain): 2798 2799 nohz 2800 Disable the tick when a single task runs as well as 2801 disabling other kernel noises like having RCU callbacks 2802 offloaded. This is equivalent to the nohz_full parameter. 2803 2804 A residual 1Hz tick is offloaded to workqueues, which you 2805 need to affine to housekeeping through the global 2806 workqueue's affinity configured via the 2807 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2808 by using the 'domain' flag described below. 2809 2810 NOTE: by default the global workqueue runs on all CPUs, 2811 so to protect individual CPUs the 'cpumask' file has to 2812 be configured manually after bootup. 2813 2814 domain 2815 Isolate from the general SMP balancing and scheduling 2816 algorithms. Note that performing domain isolation this way 2817 is irreversible: it's not possible to bring back a CPU to 2818 the domains once isolated through isolcpus. It's strongly 2819 advised to use cpusets instead to disable scheduler load 2820 balancing through the "cpuset.sched_load_balance" file. 2821 It offers a much more flexible interface where CPUs can 2822 move in and out of an isolated set anytime. 2823 2824 You can move a process onto or off an "isolated" CPU via 2825 the CPU affinity syscalls or cpuset. 2826 <cpu number> begins at 0 and the maximum value is 2827 "number of CPUs in system - 1". 2828 2829 managed_irq 2830 2831 Isolate from being targeted by managed interrupts 2832 which have an interrupt mask containing isolated 2833 CPUs. The affinity of managed interrupts is 2834 handled by the kernel and cannot be changed via 2835 the /proc/irq/* interfaces. 2836 2837 This isolation is best effort and only effective 2838 if the automatically assigned interrupt mask of a 2839 device queue contains isolated and housekeeping 2840 CPUs. If housekeeping CPUs are online then such 2841 interrupts are directed to the housekeeping CPU 2842 so that IO submitted on the housekeeping CPU 2843 cannot disturb the isolated CPU. 2844 2845 If a queue's affinity mask contains only isolated 2846 CPUs then this parameter has no effect on the 2847 interrupt routing decision, though interrupts are 2848 only delivered when tasks running on those 2849 isolated CPUs submit IO. IO submitted on 2850 housekeeping CPUs has no influence on those 2851 queues. 2852 2853 The format of <cpu-list> is described above. 2854 2855 iucv= [HW,NET] 2856 2857 ivrs_ioapic [HW,X86-64] 2858 Provide an override to the IOAPIC-ID<->DEVICE-ID 2859 mapping provided in the IVRS ACPI table. 2860 By default, PCI segment is 0, and can be omitted. 2861 2862 For example, to map IOAPIC-ID decimal 10 to 2863 PCI segment 0x1 and PCI device 00:14.0, 2864 write the parameter as: 2865 ivrs_ioapic=10@0001:00:14.0 2866 2867 Deprecated formats: 2868 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2869 write the parameter as: 2870 ivrs_ioapic[10]=00:14.0 2871 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2872 PCI device 00:14.0 write the parameter as: 2873 ivrs_ioapic[10]=0001:00:14.0 2874 2875 ivrs_hpet [HW,X86-64] 2876 Provide an override to the HPET-ID<->DEVICE-ID 2877 mapping provided in the IVRS ACPI table. 2878 By default, PCI segment is 0, and can be omitted. 2879 2880 For example, to map HPET-ID decimal 10 to 2881 PCI segment 0x1 and PCI device 00:14.0, 2882 write the parameter as: 2883 ivrs_hpet=10@0001:00:14.0 2884 2885 Deprecated formats: 2886 * To map HPET-ID decimal 0 to PCI device 00:14.0 2887 write the parameter as: 2888 ivrs_hpet[0]=00:14.0 2889 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2890 PCI device 00:14.0 write the parameter as: 2891 ivrs_ioapic[10]=0001:00:14.0 2892 2893 ivrs_acpihid [HW,X86-64] 2894 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2895 mapping provided in the IVRS ACPI table. 2896 By default, PCI segment is 0, and can be omitted. 2897 2898 For example, to map UART-HID:UID AMD0020:0 to 2899 PCI segment 0x1 and PCI device ID 00:14.5, 2900 write the parameter as: 2901 ivrs_acpihid=AMD0020:0@0001:00:14.5 2902 2903 Deprecated formats: 2904 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2905 PCI device ID 00:14.5, write the parameter as: 2906 ivrs_acpihid[00:14.5]=AMD0020:0 2907 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2908 PCI device ID 00:14.5, write the parameter as: 2909 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2910 2911 js= [HW,JOY] Analog joystick 2912 See Documentation/input/joydev/joystick.rst. 2913 2914 kasan_multi_shot 2915 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2916 report on every invalid memory access. Without this 2917 parameter KASAN will print report only for the first 2918 invalid access. 2919 2920 keep_bootcon [KNL,EARLY] 2921 Do not unregister boot console at start. This is only 2922 useful for debugging when something happens in the window 2923 between unregistering the boot console and initializing 2924 the real console. 2925 2926 keepinitrd [HW,ARM] See retain_initrd. 2927 2928 kernelcore= [KNL,X86,PPC,EARLY] 2929 Format: nn[KMGTPE] | nn% | "mirror" 2930 This parameter specifies the amount of memory usable by 2931 the kernel for non-movable allocations. The requested 2932 amount is spread evenly throughout all nodes in the 2933 system as ZONE_NORMAL. The remaining memory is used for 2934 movable memory in its own zone, ZONE_MOVABLE. In the 2935 event, a node is too small to have both ZONE_NORMAL and 2936 ZONE_MOVABLE, kernelcore memory will take priority and 2937 other nodes will have a larger ZONE_MOVABLE. 2938 2939 ZONE_MOVABLE is used for the allocation of pages that 2940 may be reclaimed or moved by the page migration 2941 subsystem. Note that allocations like PTEs-from-HighMem 2942 still use the HighMem zone if it exists, and the Normal 2943 zone if it does not. 2944 2945 It is possible to specify the exact amount of memory in 2946 the form of "nn[KMGTPE]", a percentage of total system 2947 memory in the form of "nn%", or "mirror". If "mirror" 2948 option is specified, mirrored (reliable) memory is used 2949 for non-movable allocations and remaining memory is used 2950 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2951 are exclusive, so you cannot specify multiple forms. 2952 2953 kfence.burst= [MM,KFENCE] The number of additional successive 2954 allocations to be attempted through KFENCE for each 2955 sample interval. 2956 Format: <unsigned integer> 2957 Default: 0 2958 2959 kfence.check_on_panic= 2960 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2961 canaries on panic. 2962 Format: <bool> 2963 Default: false 2964 2965 kfence.deferrable= 2966 [MM,KFENCE] Whether to use a deferrable timer to trigger 2967 allocations. This avoids forcing CPU wake-ups if the 2968 system is idle, at the risk of a less predictable 2969 sample interval. 2970 Format: <bool> 2971 Default: CONFIG_KFENCE_DEFERRABLE 2972 2973 kfence.fault= [MM,KFENCE] Controls the behavior when a KFENCE 2974 error is detected. 2975 report - print the error report and continue (default). 2976 oops - print the error report and oops. 2977 panic - print the error report and panic. 2978 2979 kfence.sample_interval= 2980 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2981 Format: <unsigned integer> 2982 0 - Disable KFENCE. 2983 >0 - Enabled KFENCE with given sample interval. 2984 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2985 2986 kfence.skip_covered_thresh= 2987 [MM,KFENCE] If pool utilization reaches this threshold 2988 (pool usage%), KFENCE limits currently covered 2989 allocations of the same source from further filling 2990 up the pool. 2991 Format: <unsigned integer> 2992 Default: 75 2993 2994 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2995 Format: <Controller#>[,poll interval] 2996 The controller # is the number of the ehci usb debug 2997 port as it is probed via PCI. The poll interval is 2998 optional and is the number seconds in between 2999 each poll cycle to the debug port in case you need 3000 the functionality for interrupting the kernel with 3001 gdb or control-c on the dbgp connection. When 3002 not using this parameter you use sysrq-g to break into 3003 the kernel debugger. 3004 3005 kgdboc= [KGDB,HW] kgdb over consoles. 3006 Requires a tty driver that supports console polling, 3007 or a supported polling keyboard driver (non-usb). 3008 Serial only format: <serial_device>[,baud] 3009 keyboard only format: kbd 3010 keyboard and serial format: kbd,<serial_device>[,baud] 3011 Optional Kernel mode setting: 3012 kms, kbd format: kms,kbd 3013 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 3014 3015 kgdboc_earlycon= [KGDB,HW,EARLY] 3016 If the boot console provides the ability to read 3017 characters and can work in polling mode, you can use 3018 this parameter to tell kgdb to use it as a backend 3019 until the normal console is registered. Intended to 3020 be used together with the kgdboc parameter which 3021 specifies the normal console to transition to. 3022 3023 The name of the early console should be specified 3024 as the value of this parameter. Note that the name of 3025 the early console might be different than the tty 3026 name passed to kgdboc. It's OK to leave the value 3027 blank and the first boot console that implements 3028 read() will be picked. 3029 3030 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3031 kernel debugger at the earliest opportunity. 3032 3033 kho= [KEXEC,EARLY] 3034 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3035 Enables or disables Kexec HandOver. 3036 "0" | "off" | "n" - kexec handover is disabled 3037 "1" | "on" | "y" - kexec handover is enabled 3038 3039 kho_scratch= [KEXEC,EARLY] 3040 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3041 Defines the size of the KHO scratch region. The KHO 3042 scratch regions are physically contiguous memory 3043 ranges that can only be used for non-kernel 3044 allocations. That way, even when memory is heavily 3045 fragmented with handed over memory, the kexeced 3046 kernel will always have enough contiguous ranges to 3047 bootstrap itself. 3048 3049 It is possible to specify the exact amount of 3050 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3051 where the first parameter defines the size of a low 3052 memory scratch area, the second parameter defines 3053 the size of a global scratch area and the third 3054 parameter defines the size of additional per-node 3055 scratch areas. The form "nn%" defines scale factor 3056 (in percents) of memory that was used during boot. 3057 3058 kmac= [MIPS] Korina ethernet MAC address. 3059 Configure the RouterBoard 532 series on-chip 3060 Ethernet adapter MAC address. 3061 3062 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3063 Valid arguments: on, off 3064 Default: on 3065 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3066 the default is off. 3067 3068 kprobe_event=[probe-list] 3069 [FTRACE] Add kprobe events and enable at boot time. 3070 The probe-list is a semicolon delimited list of probe 3071 definitions. Each definition is same as kprobe_events 3072 interface, but the parameters are comma delimited. 3073 For example, to add a kprobe event on vfs_read with 3074 arg1 and arg2, add to the command line; 3075 3076 kprobe_event=p,vfs_read,$arg1,$arg2 3077 3078 See also Documentation/trace/kprobetrace.rst "Kernel 3079 Boot Parameter" section. 3080 3081 kpti= [ARM64,EARLY] Control page table isolation of 3082 user and kernel address spaces. 3083 Default: enabled on cores which need mitigation. 3084 0: force disabled 3085 1: force enabled 3086 3087 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3088 CONFIG_KUNIT to be set to be fully enabled. The 3089 default value can be overridden via 3090 KUNIT_DEFAULT_ENABLED. 3091 Default is 1 (enabled) 3092 3093 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3094 Default is 0 (don't ignore, but inject #GP) 3095 3096 kvm.eager_page_split= 3097 [KVM,X86] Controls whether or not KVM will try to 3098 proactively split all huge pages during dirty logging. 3099 Eager page splitting reduces interruptions to vCPU 3100 execution by eliminating the write-protection faults 3101 and MMU lock contention that would otherwise be 3102 required to split huge pages lazily. 3103 3104 VM workloads that rarely perform writes or that write 3105 only to a small region of VM memory may benefit from 3106 disabling eager page splitting to allow huge pages to 3107 still be used for reads. 3108 3109 The behavior of eager page splitting depends on whether 3110 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3111 disabled, all huge pages in a memslot will be eagerly 3112 split when dirty logging is enabled on that memslot. If 3113 enabled, eager page splitting will be performed during 3114 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3115 cleared. 3116 3117 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3118 3119 Default is Y (on). 3120 3121 kvm.enable_pmu=[KVM,X86] 3122 If enabled, KVM will virtualize PMU functionality based 3123 on the virtual CPU model defined by userspace. This 3124 can be overridden on a per-VM basis via 3125 KVM_CAP_PMU_CAPABILITY. 3126 3127 If disabled, KVM will not virtualize PMU functionality, 3128 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3129 a virtual CPU model that contains PMU assets. 3130 3131 Note, KVM's vPMU support implicitly requires running 3132 with an in-kernel local APIC, e.g. to deliver PMIs to 3133 the guest. Running without an in-kernel local APIC is 3134 not supported, though KVM will allow such a combination 3135 (with severely degraded functionality). 3136 3137 See also enable_mediated_pmu. 3138 3139 Default is Y (on). 3140 3141 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3142 If enabled, KVM will enable virtualization in hardware 3143 when KVM is loaded, and disable virtualization when KVM 3144 is unloaded (if KVM is built as a module). 3145 3146 If disabled, KVM will dynamically enable and disable 3147 virtualization on-demand when creating and destroying 3148 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3149 number of VMs. 3150 3151 Enabling virtualization at module load avoids potential 3152 latency for creation of the 0=>1 VM, as KVM serializes 3153 virtualization enabling across all online CPUs. The 3154 "cost" of enabling virtualization when KVM is loaded, 3155 is that doing so may interfere with using out-of-tree 3156 hypervisors that want to "own" virtualization hardware. 3157 3158 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3159 Default is false (don't support). 3160 3161 kvm.nx_huge_pages= 3162 [KVM] Controls the software workaround for the 3163 X86_BUG_ITLB_MULTIHIT bug. 3164 force : Always deploy workaround. 3165 off : Never deploy workaround. 3166 auto : Deploy workaround based on the presence of 3167 X86_BUG_ITLB_MULTIHIT. 3168 3169 Default is 'auto'. 3170 3171 If the software workaround is enabled for the host, 3172 guests do need not to enable it for nested guests. 3173 3174 kvm.nx_huge_pages_recovery_ratio= 3175 [KVM] Controls how many 4KiB pages are periodically zapped 3176 back to huge pages. 0 disables the recovery, otherwise if 3177 the value is N KVM will zap 1/Nth of the 4KiB pages every 3178 period (see below). The default is 60. 3179 3180 kvm.nx_huge_pages_recovery_period_ms= 3181 [KVM] Controls the time period at which KVM zaps 4KiB pages 3182 back to huge pages. If the value is a non-zero N, KVM will 3183 zap a portion (see ratio above) of the pages every N msecs. 3184 If the value is 0 (the default), KVM will pick a period based 3185 on the ratio, such that a page is zapped after 1 hour on average. 3186 3187 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3188 If enabled, KVM will provide a mediated virtual PMU, 3189 instead of the default perf-based virtual PMU (if 3190 kvm.enable_pmu is true and PMU is enumerated via the 3191 virtual CPU model). 3192 3193 With a perf-based vPMU, KVM operates as a user of perf, 3194 i.e. emulates guest PMU counters using perf events. 3195 KVM-created perf events are managed by perf as regular 3196 (guest-only) events, e.g. are scheduled in/out, contend 3197 for hardware resources, etc. Using a perf-based vPMU 3198 allows guest and host usage of the PMU to co-exist, but 3199 incurs non-trivial overhead and can result in silently 3200 dropped guest events (due to resource contention). 3201 3202 With a mediated vPMU, hardware PMU state is context 3203 switched around the world switch to/from the guest. 3204 KVM mediates which events the guest can utilize, but 3205 gives the guest direct access to all other PMU assets 3206 when possible (KVM may intercept some accesses if the 3207 virtual CPU model provides a subset of hardware PMU 3208 functionality). Using a mediated vPMU significantly 3209 reduces PMU virtualization overhead and eliminates lost 3210 guest events, but is mutually exclusive with using perf 3211 to profile KVM guests and adds latency to most VM-Exits 3212 (to context switch PMU state). 3213 3214 Default is N (off). 3215 3216 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3217 KVM/SVM. Default is 1 (enabled). 3218 3219 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3220 a.k.a. Two-Dimensional Page Tables. Default is 1 3221 (enabled). Disable by KVM if hardware lacks support 3222 for NPT. 3223 3224 kvm-amd.ciphertext_hiding_asids= 3225 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3226 to SNP private memory from reading ciphertext. Instead, 3227 reads will see constant default values (0xff). 3228 3229 If ciphertext hiding is enabled, the joint SEV-ES and 3230 SEV-SNP ASID space is partitioned into separate SEV-ES 3231 and SEV-SNP ASID ranges, with the SEV-SNP range being 3232 [1..max_snp_asid] and the SEV-ES range being 3233 (max_snp_asid..min_sev_asid), where min_sev_asid is 3234 enumerated by CPUID.0x.8000_001F[EDX]. 3235 3236 A non-zero value enables SEV-SNP ciphertext hiding and 3237 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3238 KVM caps the number of SEV-SNP ASIDs at the maximum 3239 possible value, e.g. specifying -1u will assign all 3240 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3241 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3242 max_snp_asid == min_sev_asid-1, will effectively make 3243 SEV-ES unusable. 3244 3245 kvm-arm.mode= 3246 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3247 operation. 3248 3249 none: Forcefully disable KVM. 3250 3251 nvhe: Standard nVHE-based mode, without support for 3252 protected guests. 3253 3254 protected: Mode with support for guests whose state is 3255 kept private from the host, using VHE or 3256 nVHE depending on HW support. 3257 3258 nested: VHE-based mode with support for nested 3259 virtualization. Requires at least ARMv8.4 3260 hardware (with FEAT_NV2). 3261 3262 Defaults to VHE/nVHE based on hardware support. Setting 3263 mode to "protected" will disable kexec and hibernation 3264 for the host. To force nVHE on VHE hardware, add 3265 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3266 command-line. 3267 "nested" is experimental and should be used with 3268 extreme caution. 3269 3270 kvm-arm.vgic_v3_group0_trap= 3271 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3272 system registers 3273 3274 kvm-arm.vgic_v3_group1_trap= 3275 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3276 system registers 3277 3278 kvm-arm.vgic_v3_common_trap= 3279 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3280 system registers 3281 3282 kvm-arm.vgic_v4_enable= 3283 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3284 injection of LPIs. 3285 3286 kvm-arm.wfe_trap_policy= 3287 [KVM,ARM] Control when to set WFE instruction trap for 3288 KVM VMs. Traps are allowed but not guaranteed by the 3289 CPU architecture. 3290 3291 trap: set WFE instruction trap 3292 3293 notrap: clear WFE instruction trap 3294 3295 kvm-arm.wfi_trap_policy= 3296 [KVM,ARM] Control when to set WFI instruction trap for 3297 KVM VMs. Traps are allowed but not guaranteed by the 3298 CPU architecture. 3299 3300 trap: set WFI instruction trap 3301 3302 notrap: clear WFI instruction trap 3303 3304 kvm_cma_resv_ratio=n [PPC,EARLY] 3305 Reserves given percentage from system memory area for 3306 contiguous memory allocation for KVM hash pagetable 3307 allocation. 3308 By default it reserves 5% of total system memory. 3309 Format: <integer> 3310 Default: 5 3311 3312 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3313 a.k.a. Two-Dimensional Page Tables. Default is 1 3314 (enabled). Disable by KVM if hardware lacks support 3315 for EPT. 3316 3317 kvm-intel.emulate_invalid_guest_state= 3318 [KVM,Intel] Control whether to emulate invalid guest 3319 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3320 as guest state is never invalid for unrestricted 3321 guests. This param doesn't apply to nested guests (L2), 3322 as KVM never emulates invalid L2 guest state. 3323 Default is 1 (enabled). 3324 3325 kvm-intel.flexpriority= 3326 [KVM,Intel] Control KVM's use of FlexPriority feature 3327 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3328 hardware lacks support for it. 3329 3330 kvm-intel.nested= 3331 [KVM,Intel] Control nested virtualization feature in 3332 KVM/VMX. Default is 1 (enabled). 3333 3334 kvm-intel.unrestricted_guest= 3335 [KVM,Intel] Control KVM's use of unrestricted guest 3336 feature (virtualized real and unpaged mode). Default 3337 is 1 (enabled). Disable by KVM if EPT is disabled or 3338 hardware lacks support for it. 3339 3340 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3341 CVE-2018-3620. 3342 3343 Valid arguments: never, cond, always 3344 3345 always: L1D cache flush on every VMENTER. 3346 cond: Flush L1D on VMENTER only when the code between 3347 VMEXIT and VMENTER can leak host memory. 3348 never: Disables the mitigation 3349 3350 Default is cond (do L1 cache flush in specific instances) 3351 3352 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3353 Identification feature (tagged TLBs). Default is 1 3354 (enabled). Disable by KVM if hardware lacks support 3355 for it. 3356 3357 l1d_flush= [X86,INTEL,EARLY] 3358 Control mitigation for L1D based snooping vulnerability. 3359 3360 Certain CPUs are vulnerable to an exploit against CPU 3361 internal buffers which can forward information to a 3362 disclosure gadget under certain conditions. 3363 3364 In vulnerable processors, the speculatively 3365 forwarded data can be used in a cache side channel 3366 attack, to access data to which the attacker does 3367 not have direct access. 3368 3369 This parameter controls the mitigation. The 3370 options are: 3371 3372 on - enable the interface for the mitigation 3373 3374 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3375 affected CPUs 3376 3377 The kernel PTE inversion protection is unconditionally 3378 enabled and cannot be disabled. 3379 3380 full 3381 Provides all available mitigations for the 3382 L1TF vulnerability. Disables SMT and 3383 enables all mitigations in the 3384 hypervisors, i.e. unconditional L1D flush. 3385 3386 SMT control and L1D flush control via the 3387 sysfs interface is still possible after 3388 boot. Hypervisors will issue a warning 3389 when the first VM is started in a 3390 potentially insecure configuration, 3391 i.e. SMT enabled or L1D flush disabled. 3392 3393 full,force 3394 Same as 'full', but disables SMT and L1D 3395 flush runtime control. Implies the 3396 'nosmt=force' command line option. 3397 (i.e. sysfs control of SMT is disabled.) 3398 3399 flush 3400 Leaves SMT enabled and enables the default 3401 hypervisor mitigation, i.e. conditional 3402 L1D flush. 3403 3404 SMT control and L1D flush control via the 3405 sysfs interface is still possible after 3406 boot. Hypervisors will issue a warning 3407 when the first VM is started in a 3408 potentially insecure configuration, 3409 i.e. SMT enabled or L1D flush disabled. 3410 3411 flush,nosmt 3412 3413 Disables SMT and enables the default 3414 hypervisor mitigation. 3415 3416 SMT control and L1D flush control via the 3417 sysfs interface is still possible after 3418 boot. Hypervisors will issue a warning 3419 when the first VM is started in a 3420 potentially insecure configuration, 3421 i.e. SMT enabled or L1D flush disabled. 3422 3423 flush,nowarn 3424 Same as 'flush', but hypervisors will not 3425 warn when a VM is started in a potentially 3426 insecure configuration. 3427 3428 off 3429 Disables hypervisor mitigations and doesn't 3430 emit any warnings. 3431 It also drops the swap size and available 3432 RAM limit restriction on both hypervisor and 3433 bare metal. 3434 3435 Default is 'flush'. 3436 3437 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3438 3439 l2cr= [PPC] 3440 3441 l3cr= [PPC] 3442 3443 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3444 disabled it. 3445 3446 lapic= [X86,APIC] Do not use TSC deadline 3447 value for LAPIC timer one-shot implementation. Default 3448 back to the programmable timer unit in the LAPIC. 3449 Format: notscdeadline 3450 3451 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3452 in C2 power state. 3453 3454 libata.dma= [LIBATA] DMA control 3455 libata.dma=0 Disable all PATA and SATA DMA 3456 libata.dma=1 PATA and SATA Disk DMA only 3457 libata.dma=2 ATAPI (CDROM) DMA only 3458 libata.dma=4 Compact Flash DMA only 3459 Combinations also work, so libata.dma=3 enables DMA 3460 for disks and CDROMs, but not CFs. 3461 3462 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3463 libata.ignore_hpa=0 keep BIOS limits (default) 3464 libata.ignore_hpa=1 ignore limits, using full disk 3465 3466 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3467 when set. 3468 Format: <int> 3469 3470 libata.force= [LIBATA] Force configurations. The format is a comma- 3471 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3472 PORT and DEVICE are decimal numbers matching port, link 3473 or device. Basically, it matches the ATA ID string 3474 printed on console by libata. If the whole ID part is 3475 omitted, the last PORT and DEVICE values are used. If 3476 ID hasn't been specified yet, the configuration applies 3477 to all ports, links and devices. 3478 3479 If only DEVICE is omitted, the parameter applies to 3480 the port and all links and devices behind it. DEVICE 3481 number of 0 either selects the first device or the 3482 first fan-out link behind PMP device. It does not 3483 select the host link. DEVICE number of 15 selects the 3484 host link and device attached to it. 3485 3486 The VAL specifies the configuration to force. As long 3487 as there is no ambiguity, shortcut notation is allowed. 3488 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3489 The following configurations can be forced. 3490 3491 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3492 Any ID with matching PORT is used. 3493 3494 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3495 3496 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3497 udma[/][16,25,33,44,66,100,133] notation is also 3498 allowed. 3499 3500 * nohrst, nosrst, norst: suppress hard, soft and both 3501 resets. 3502 3503 * rstonce: only attempt one reset during hot-unplug 3504 link recovery. 3505 3506 * [no]dbdelay: Enable or disable the extra 200ms delay 3507 before debouncing a link PHY and device presence 3508 detection. 3509 3510 * [no]ncq: Turn on or off NCQ. 3511 3512 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3513 3514 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3515 3516 * [no]trim: Enable or disable (unqueued) TRIM. 3517 3518 * trim_zero: Indicate that TRIM command zeroes data. 3519 3520 * max_trim_128m: Set 128M maximum trim size limit. 3521 3522 * [no]dma: Turn on or off DMA transfers. 3523 3524 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3525 3526 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3527 commands that are not a multiple of 16 bytes. 3528 3529 * [no]dmalog: Enable or disable the use of the 3530 READ LOG DMA EXT command to access logs. 3531 3532 * [no]iddevlog: Enable or disable access to the 3533 identify device data log. 3534 3535 * [no]logdir: Enable or disable access to the general 3536 purpose log directory. 3537 3538 * max_sec=<sectors>: Set the transfer size limit, in 3539 number of 512-byte sectors, to the value specified in 3540 <sectors>. The value specified in <sectors> has to be 3541 a non-zero positive integer. 3542 3543 * max_sec_128: Set transfer size limit to 128 sectors. 3544 3545 * max_sec_1024: Set or clear transfer size limit to 3546 1024 sectors. 3547 3548 * max_sec_lba48: Set or clear transfer size limit to 3549 65535 sectors. 3550 3551 * external: Mark port as external (hotplug-capable). 3552 3553 * [no]lpm: Enable or disable link power management. 3554 3555 * [no]setxfer: Indicate if transfer speed mode setting 3556 should be skipped. 3557 3558 * [no]fua: Disable or enable FUA (Force Unit Access) 3559 support for devices supporting this feature. 3560 3561 * dump_id: Dump IDENTIFY data. 3562 3563 * disable: Disable this device. 3564 3565 If there are multiple matching configurations changing 3566 the same attribute, the last one is used. 3567 3568 liveupdate= [KNL,EARLY] 3569 Format: <bool> 3570 Enable Live Update Orchestrator (LUO). 3571 Default: off. 3572 3573 lockd.nlm_grace_period=P [NFS] Assign grace period. 3574 Format: <integer> 3575 3576 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3577 Format: <integer> 3578 3579 lockd.nlm_timeout=T [NFS] Assign timeout value. 3580 Format: <integer> 3581 3582 lockd.nlm_udpport=M [NFS] Assign UDP port. 3583 Format: <integer> 3584 3585 lockdown= [SECURITY,EARLY] 3586 { integrity | confidentiality } 3587 Enable the kernel lockdown feature. If set to 3588 integrity, kernel features that allow userland to 3589 modify the running kernel are disabled. If set to 3590 confidentiality, kernel features that allow userland 3591 to extract confidential information from the kernel 3592 are also disabled. 3593 3594 locktorture.acq_writer_lim= [KNL] 3595 Set the time limit in jiffies for a lock 3596 acquisition. Acquisitions exceeding this limit 3597 will result in a splat once they do complete. 3598 3599 locktorture.bind_readers= [KNL] 3600 Specify the list of CPUs to which the readers are 3601 to be bound. 3602 3603 locktorture.bind_writers= [KNL] 3604 Specify the list of CPUs to which the writers are 3605 to be bound. 3606 3607 locktorture.call_rcu_chains= [KNL] 3608 Specify the number of self-propagating call_rcu() 3609 chains to set up. These are used to ensure that 3610 there is a high probability of an RCU grace period 3611 in progress at any given time. Defaults to 0, 3612 which disables these call_rcu() chains. 3613 3614 locktorture.long_hold= [KNL] 3615 Specify the duration in milliseconds for the 3616 occasional long-duration lock hold time. Defaults 3617 to 100 milliseconds. Select 0 to disable. 3618 3619 locktorture.nested_locks= [KNL] 3620 Specify the maximum lock nesting depth that 3621 locktorture is to exercise, up to a limit of 8 3622 (MAX_NESTED_LOCKS). Specify zero to disable. 3623 Note that this parameter is ineffective on types 3624 of locks that do not support nested acquisition. 3625 3626 locktorture.nreaders_stress= [KNL] 3627 Set the number of locking read-acquisition kthreads. 3628 Defaults to being automatically set based on the 3629 number of online CPUs. 3630 3631 locktorture.nwriters_stress= [KNL] 3632 Set the number of locking write-acquisition kthreads. 3633 3634 locktorture.onoff_holdoff= [KNL] 3635 Set time (s) after boot for CPU-hotplug testing. 3636 3637 locktorture.onoff_interval= [KNL] 3638 Set time (s) between CPU-hotplug operations, or 3639 zero to disable CPU-hotplug testing. 3640 3641 locktorture.rt_boost= [KNL] 3642 Do periodic testing of real-time lock priority 3643 boosting. Select 0 to disable, 1 to boost 3644 only rt_mutex, and 2 to boost unconditionally. 3645 Defaults to 2, which might seem to be an 3646 odd choice, but which should be harmless for 3647 non-real-time spinlocks, due to their disabling 3648 of preemption. Note that non-realtime mutexes 3649 disable boosting. 3650 3651 locktorture.rt_boost_factor= [KNL] 3652 Number that determines how often and for how 3653 long priority boosting is exercised. This is 3654 scaled down by the number of writers, so that the 3655 number of boosts per unit time remains roughly 3656 constant as the number of writers increases. 3657 On the other hand, the duration of each boost 3658 increases with the number of writers. 3659 3660 locktorture.shuffle_interval= [KNL] 3661 Set task-shuffle interval (jiffies). Shuffling 3662 tasks allows some CPUs to go into dyntick-idle 3663 mode during the locktorture test. 3664 3665 locktorture.shutdown_secs= [KNL] 3666 Set time (s) after boot system shutdown. This 3667 is useful for hands-off automated testing. 3668 3669 locktorture.stat_interval= [KNL] 3670 Time (s) between statistics printk()s. 3671 3672 locktorture.stutter= [KNL] 3673 Time (s) to stutter testing, for example, 3674 specifying five seconds causes the test to run for 3675 five seconds, wait for five seconds, and so on. 3676 This tests the locking primitive's ability to 3677 transition abruptly to and from idle. 3678 3679 locktorture.torture_type= [KNL] 3680 Specify the locking implementation to test. 3681 3682 locktorture.verbose= [KNL] 3683 Enable additional printk() statements. 3684 3685 locktorture.writer_fifo= [KNL] 3686 Run the write-side locktorture kthreads at 3687 sched_set_fifo() real-time priority. 3688 3689 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3690 Format: <irq> 3691 3692 loglevel= [KNL,EARLY] 3693 All Kernel Messages with a loglevel smaller than the 3694 console loglevel will be printed to the console. It can 3695 also be changed with klogd or other programs. The 3696 loglevels are defined as follows: 3697 3698 0 (KERN_EMERG) system is unusable 3699 1 (KERN_ALERT) action must be taken immediately 3700 2 (KERN_CRIT) critical conditions 3701 3 (KERN_ERR) error conditions 3702 4 (KERN_WARNING) warning conditions 3703 5 (KERN_NOTICE) normal but significant condition 3704 6 (KERN_INFO) informational 3705 7 (KERN_DEBUG) debug-level messages 3706 3707 log_buf_len=n[KMG] [KNL,EARLY] 3708 Sets the size of the printk ring buffer, in bytes. 3709 n must be a power of two and greater than the 3710 minimal size. The minimal size is defined by 3711 LOG_BUF_SHIFT kernel config parameter. There 3712 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3713 parameter that allows to increase the default size 3714 depending on the number of CPUs. See init/Kconfig 3715 for more details. 3716 3717 logo.nologo [FB] Disables display of the built-in Linux logo. 3718 This may be used to provide more screen space for 3719 kernel log messages and is useful when debugging 3720 kernel boot problems. 3721 3722 lp=0 [LP] Specify parallel ports to use, e.g, 3723 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3724 lp=reset first parallel port). 'lp=0' disables the 3725 lp=auto printer driver. 'lp=reset' (which can be 3726 specified in addition to the ports) causes 3727 attached printers to be reset. Using 3728 lp=port1,port2,... specifies the parallel ports 3729 to associate lp devices with, starting with 3730 lp0. A port specification may be 'none' to skip 3731 that lp device, or a parport name such as 3732 'parport0'. Specifying 'lp=auto' instead of a 3733 port specification list means that device IDs 3734 from each port should be examined, to see if 3735 an IEEE 1284-compliant printer is attached; if 3736 so, the driver will manage that printer. 3737 See also header of drivers/char/lp.c. 3738 3739 lpj=n [KNL] 3740 Sets loops_per_jiffy to given constant, thus avoiding 3741 time-consuming boot-time autodetection (up to 250 ms per 3742 CPU). 0 enables autodetection (default). To determine 3743 the correct value for your kernel, boot with normal 3744 autodetection and see what value is printed. Note that 3745 on SMP systems the preset will be applied to all CPUs, 3746 which is likely to cause problems if your CPUs need 3747 significantly divergent settings. An incorrect value 3748 will cause delays in the kernel to be wrong, leading to 3749 unpredictable I/O errors and other breakage. Although 3750 unlikely, in the extreme case this might damage your 3751 hardware. 3752 3753 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3754 3755 lsm=lsm1,...,lsmN 3756 [SECURITY] Choose order of LSM initialization. This 3757 overrides CONFIG_LSM, and the "security=" parameter. 3758 3759 machtype= [Loongson] Share the same kernel image file between 3760 different yeeloong laptops. 3761 Example: machtype=lemote-yeeloong-2f-7inch 3762 3763 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3764 will bring up during bootup. maxcpus=n : n >= 0 limits 3765 the kernel to bring up 'n' processors. Surely after 3766 bootup you can bring up the other plugged cpu by executing 3767 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3768 only takes effect during system bootup. 3769 While n=0 is a special case, it is equivalent to "nosmp", 3770 which also disables the IO APIC. 3771 3772 max_loop= [LOOP] The number of loop block devices that get 3773 (loop.max_loop) unconditionally pre-created at init time. The default 3774 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3775 of statically allocating a predefined number, loop 3776 devices can be requested on-demand with the 3777 /dev/loop-control interface. 3778 3779 mce= [X86-{32,64}] 3780 3781 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3782 3783 off 3784 disable machine check 3785 3786 no_cmci 3787 disable CMCI(Corrected Machine Check Interrupt) that 3788 Intel processor supports. Usually this disablement is 3789 not recommended, but it might be handy if your 3790 hardware is misbehaving. 3791 3792 Note that you'll get more problems without CMCI than 3793 with due to the shared banks, i.e. you might get 3794 duplicated error logs. 3795 3796 dont_log_ce 3797 don't make logs for corrected errors. All events 3798 reported as corrected are silently cleared by OS. This 3799 option will be useful if you have no interest in any 3800 of corrected errors. 3801 3802 ignore_ce 3803 disable features for corrected errors, e.g. 3804 polling timer and CMCI. All events reported as 3805 corrected are not cleared by OS and remained in its 3806 error banks. 3807 3808 Usually this disablement is not recommended, however 3809 if there is an agent checking/clearing corrected 3810 errors (e.g. BIOS or hardware monitoring 3811 applications), conflicting with OS's error handling, 3812 and you cannot deactivate the agent, then this option 3813 will be a help. 3814 3815 no_lmce 3816 do not opt-in to Local MCE delivery. Use legacy method 3817 to broadcast MCEs. 3818 3819 bootlog 3820 enable logging of machine checks left over from 3821 booting. Disabled by default on AMD Fam10h and older 3822 because some BIOS leave bogus ones. 3823 3824 If your BIOS doesn't do that it's a good idea to 3825 enable though to make sure you log even machine check 3826 events that result in a reboot. On Intel systems it is 3827 enabled by default. 3828 3829 nobootlog 3830 disable boot machine check logging. 3831 3832 monarchtimeout (number) 3833 sets the time in us to wait for other CPUs on machine 3834 checks. 0 to disable. 3835 3836 bios_cmci_threshold 3837 don't overwrite the bios-set CMCI threshold. This boot 3838 option prevents Linux from overwriting the CMCI 3839 threshold set by the bios. Without this option, Linux 3840 always sets the CMCI threshold to 1. Enabling this may 3841 make memory predictive failure analysis less effective 3842 if the bios sets thresholds for memory errors since we 3843 will not see details for all errors. 3844 3845 recovery 3846 force-enable recoverable machine check code paths 3847 3848 Everything else is in sysfs now. 3849 3850 3851 md= [HW] RAID subsystems devices and level 3852 See Documentation/admin-guide/md.rst. 3853 3854 mdacon= [MDA] 3855 Format: <first>,<last> 3856 Specifies range of consoles to be captured by the MDA. 3857 3858 mds= [X86,INTEL,EARLY] 3859 Control mitigation for the Micro-architectural Data 3860 Sampling (MDS) vulnerability. 3861 3862 Certain CPUs are vulnerable to an exploit against CPU 3863 internal buffers which can forward information to a 3864 disclosure gadget under certain conditions. 3865 3866 In vulnerable processors, the speculatively 3867 forwarded data can be used in a cache side channel 3868 attack, to access data to which the attacker does 3869 not have direct access. 3870 3871 This parameter controls the MDS mitigation. The 3872 options are: 3873 3874 full - Enable MDS mitigation on vulnerable CPUs 3875 full,nosmt - Enable MDS mitigation and disable 3876 SMT on vulnerable CPUs 3877 off - Unconditionally disable MDS mitigation 3878 3879 On TAA-affected machines, mds=off can be prevented by 3880 an active TAA mitigation as both vulnerabilities are 3881 mitigated with the same mechanism so in order to disable 3882 this mitigation, you need to specify tsx_async_abort=off 3883 too. 3884 3885 Not specifying this option is equivalent to 3886 mds=full. 3887 3888 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3889 3890 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3891 Must be specified, otherwise memory size will be 0. 3892 3893 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3894 of memory Amount of memory to be used in cases 3895 as follows: 3896 3897 1 for test; 3898 2 when the kernel is not able to see the whole system memory; 3899 3 memory that lies after 'mem=' boundary is excluded from 3900 the hypervisor, then assigned to KVM guests. 3901 4 to limit the memory available for kdump kernel. 3902 3903 [ARC,MICROBLAZE] - the limit applies only to low memory, 3904 high memory is not affected. 3905 3906 [ARM64] - only limits memory covered by the linear 3907 mapping. The NOMAP regions are not affected. 3908 3909 [X86] Work as limiting max address. Use together 3910 with memmap= to avoid physical address space collisions. 3911 Without memmap= PCI devices could be placed at addresses 3912 belonging to unused RAM. 3913 3914 Note that this only takes effects during boot time since 3915 in above case 3, memory may need be hot added after boot 3916 if system memory of hypervisor is not sufficient. 3917 3918 mem=nn[KMG]@ss[KMG] 3919 [ARM,MIPS,EARLY] - override the memory layout 3920 reported by firmware. 3921 Define a memory region of size nn[KMG] starting at 3922 ss[KMG]. 3923 Multiple different regions can be specified with 3924 multiple mem= parameters on the command line. 3925 3926 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3927 memory. 3928 3929 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3930 3931 memchunk=nn[KMG] 3932 [KNL,SH] Allow user to override the default size for 3933 per-device physically contiguous DMA buffers. 3934 3935 memhp_default_state=online/offline/online_kernel/online_movable 3936 [KNL] Set the initial state for the memory hotplug 3937 onlining policy. If not specified, the default value is 3938 set according to the 3939 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3940 options. 3941 See Documentation/admin-guide/mm/memory-hotplug.rst. 3942 3943 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3944 E820 memory map, as specified by the user. 3945 Such memmap=exactmap lines can be constructed based on 3946 BIOS output or other requirements. See the memmap=nn@ss 3947 option description. 3948 3949 memmap=nn[KMG]@ss[KMG] 3950 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3951 Region of memory to be used is from ss to ss+nn. 3952 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3953 which limits max address to nn[KMG]. 3954 Multiple different regions can be specified, 3955 comma delimited. 3956 Example: 3957 memmap=100M@2G,100M#3G,1G!1024G 3958 3959 memmap=nn[KMG]#ss[KMG] 3960 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3961 Region of memory to be marked is from ss to ss+nn. 3962 3963 memmap=nn[KMG]$ss[KMG] 3964 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3965 Region of memory to be reserved is from ss to ss+nn. 3966 Example: Exclude memory from 0x18690000-0x1869ffff 3967 memmap=64K$0x18690000 3968 or 3969 memmap=0x10000$0x18690000 3970 Some bootloaders may need an escape character before '$', 3971 like Grub2, otherwise '$' and the following number 3972 will be eaten. 3973 3974 memmap=nn[KMG]!ss[KMG,EARLY] 3975 [KNL,X86] Mark specific memory as protected. 3976 Region of memory to be used, from ss to ss+nn. 3977 The memory region may be marked as e820 type 12 (0xc) 3978 and is NVDIMM or ADR memory. 3979 3980 memmap=<size>%<offset>-<oldtype>+<newtype> 3981 [KNL,ACPI,EARLY] Convert memory within the specified region 3982 from <oldtype> to <newtype>. If "-<oldtype>" is left 3983 out, the whole region will be marked as <newtype>, 3984 even if previously unavailable. If "+<newtype>" is left 3985 out, matching memory will be removed. Types are 3986 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3987 3 = ACPI, 12 = PRAM. 3988 3989 memory_corruption_check=0/1 [X86,EARLY] 3990 Some BIOSes seem to corrupt the first 64k of 3991 memory when doing things like suspend/resume. 3992 Setting this option will scan the memory 3993 looking for corruption. Enabling this will 3994 both detect corruption and prevent the kernel 3995 from using the memory being corrupted. 3996 However, it's intended as a diagnostic tool; if 3997 repeatable BIOS-originated corruption always 3998 affects the same memory, you can use memmap= 3999 to prevent the kernel from using that memory. 4000 4001 memory_corruption_check_size=size [X86,EARLY] 4002 By default it checks for corruption in the low 4003 64k, making this memory unavailable for normal 4004 use. Use this parameter to scan for 4005 corruption in more or less memory. 4006 4007 memory_corruption_check_period=seconds [X86,EARLY] 4008 By default it checks for corruption every 60 4009 seconds. Use this parameter to check at some 4010 other rate. 0 disables periodic checking. 4011 4012 memory_hotplug.memmap_on_memory 4013 [KNL,X86,ARM] Boolean flag to enable this feature. 4014 Format: {on | off (default)} 4015 When enabled, runtime hotplugged memory will 4016 allocate its internal metadata (struct pages, 4017 those vmemmap pages cannot be optimized even 4018 if hugetlb_free_vmemmap is enabled) from the 4019 hotadded memory which will allow to hotadd a 4020 lot of memory without requiring additional 4021 memory to do so. 4022 This feature is disabled by default because it 4023 has some implication on large (e.g. GB) 4024 allocations in some configurations (e.g. small 4025 memory blocks). 4026 The state of the flag can be read in 4027 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4028 Note that even when enabled, there are a few cases where 4029 the feature is not effective. 4030 4031 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4032 Format: <integer> 4033 default : 0 <disable> 4034 Specifies the number of memtest passes to be 4035 performed. Each pass selects another test 4036 pattern from a given set of patterns. Memtest 4037 fills the memory with this pattern, validates 4038 memory contents and reserves bad memory 4039 regions that are detected. 4040 4041 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4042 Valid arguments: on, off 4043 Default: off 4044 mem_encrypt=on: Activate SME 4045 mem_encrypt=off: Do not activate SME 4046 4047 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4048 for details on when memory encryption can be activated. 4049 4050 mem_sleep_default= [SUSPEND] Default system suspend mode: 4051 s2idle - Suspend-To-Idle 4052 shallow - Power-On Suspend or equivalent (if supported) 4053 deep - Suspend-To-RAM or equivalent (if supported) 4054 See Documentation/admin-guide/pm/sleep-states.rst. 4055 4056 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4057 the BIOS has incorrectly applied a workaround. TinyBIOS 4058 version 0.98 is known to be affected, 0.99 fixes the 4059 problem by letting the user disable the workaround. 4060 4061 mga= [HW,DRM] 4062 4063 microcode= [X86] Control the behavior of the microcode loader. 4064 Available options, comma separated: 4065 4066 base_rev=X - with <X> with format: <u32> 4067 Set the base microcode revision of each thread when in 4068 debug mode. 4069 4070 dis_ucode_ldr: disable the microcode loader 4071 4072 force_minrev: 4073 Enable or disable the microcode minimal revision 4074 enforcement for the runtime microcode loader. 4075 4076 mini2440= [ARM,HW,KNL] 4077 Format:[0..2][b][c][t] 4078 Default: "0tb" 4079 MINI2440 configuration specification: 4080 0 - The attached screen is the 3.5" TFT 4081 1 - The attached screen is the 7" TFT 4082 2 - The VGA Shield is attached (1024x768) 4083 Leaving out the screen size parameter will not load 4084 the TFT driver, and the framebuffer will be left 4085 unconfigured. 4086 b - Enable backlight. The TFT backlight pin will be 4087 linked to the kernel VESA blanking code and a GPIO 4088 LED. This parameter is not necessary when using the 4089 VGA shield. 4090 c - Enable the s3c camera interface. 4091 t - Reserved for enabling touchscreen support. The 4092 touchscreen support is not enabled in the mainstream 4093 kernel as of 2.6.30, a preliminary port can be found 4094 in the "bleeding edge" mini2440 support kernel at 4095 https://repo.or.cz/w/linux-2.6/mini2440.git 4096 4097 mitigations= 4098 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4099 CPU vulnerabilities. This is a set of curated, 4100 arch-independent options, each of which is an 4101 aggregation of existing arch-specific options. 4102 4103 Note, "mitigations" is supported if and only if the 4104 kernel was built with CPU_MITIGATIONS=y. 4105 4106 off 4107 Disable all optional CPU mitigations. This 4108 improves system performance, but it may also 4109 expose users to several CPU vulnerabilities. 4110 Equivalent to: if nokaslr then kpti=0 [ARM64] 4111 gather_data_sampling=off [X86] 4112 indirect_target_selection=off [X86] 4113 kvm.nx_huge_pages=off [X86] 4114 l1tf=off [X86] 4115 mds=off [X86] 4116 mmio_stale_data=off [X86] 4117 no_entry_flush [PPC] 4118 no_uaccess_flush [PPC] 4119 nobp=0 [S390] 4120 nopti [X86,PPC] 4121 nospectre_bhb [ARM64] 4122 nospectre_v1 [X86,PPC] 4123 nospectre_v2 [X86,PPC,S390,ARM64] 4124 reg_file_data_sampling=off [X86] 4125 retbleed=off [X86] 4126 spec_rstack_overflow=off [X86] 4127 spec_store_bypass_disable=off [X86,PPC] 4128 spectre_bhi=off [X86] 4129 spectre_v2_user=off [X86] 4130 srbds=off [X86,INTEL] 4131 ssbd=force-off [ARM64] 4132 tsa=off [X86,AMD] 4133 tsx_async_abort=off [X86] 4134 vmscape=off [X86] 4135 4136 Exceptions: 4137 This does not have any effect on 4138 kvm.nx_huge_pages when 4139 kvm.nx_huge_pages=force. 4140 4141 auto (default) 4142 Mitigate all CPU vulnerabilities, but leave SMT 4143 enabled, even if it's vulnerable. This is for 4144 users who don't want to be surprised by SMT 4145 getting disabled across kernel upgrades, or who 4146 have other ways of avoiding SMT-based attacks. 4147 Equivalent to: (default behavior) 4148 4149 auto,nosmt 4150 Mitigate all CPU vulnerabilities, disabling SMT 4151 if needed. This is for users who always want to 4152 be fully mitigated, even if it means losing SMT. 4153 Equivalent to: l1tf=flush,nosmt [X86] 4154 mds=full,nosmt [X86] 4155 tsx_async_abort=full,nosmt [X86] 4156 mmio_stale_data=full,nosmt [X86] 4157 retbleed=auto,nosmt [X86] 4158 4159 [X86] After one of the above options, additionally 4160 supports attack-vector based controls as documented in 4161 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4162 4163 mminit_loglevel= 4164 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4165 parameter allows control of the logging verbosity for 4166 the additional memory initialisation checks. A value 4167 of 0 disables mminit logging and a level of 4 will 4168 log everything. Information is printed at KERN_DEBUG 4169 so loglevel=8 may also need to be specified. 4170 4171 mmio_stale_data= 4172 [X86,INTEL,EARLY] Control mitigation for the Processor 4173 MMIO Stale Data vulnerabilities. 4174 4175 Processor MMIO Stale Data is a class of 4176 vulnerabilities that may expose data after an MMIO 4177 operation. Exposed data could originate or end in 4178 the same CPU buffers as affected by MDS and TAA. 4179 Therefore, similar to MDS and TAA, the mitigation 4180 is to clear the affected CPU buffers. 4181 4182 This parameter controls the mitigation. The 4183 options are: 4184 4185 full - Enable mitigation on vulnerable CPUs 4186 4187 full,nosmt - Enable mitigation and disable SMT on 4188 vulnerable CPUs. 4189 4190 off - Unconditionally disable mitigation 4191 4192 On MDS or TAA affected machines, 4193 mmio_stale_data=off can be prevented by an active 4194 MDS or TAA mitigation as these vulnerabilities are 4195 mitigated with the same mechanism so in order to 4196 disable this mitigation, you need to specify 4197 mds=off and tsx_async_abort=off too. 4198 4199 Not specifying this option is equivalent to 4200 mmio_stale_data=full. 4201 4202 For details see: 4203 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4204 4205 <module>.async_probe[=<bool>] [KNL] 4206 If no <bool> value is specified or if the value 4207 specified is not a valid <bool>, enable asynchronous 4208 probe on this module. Otherwise, enable/disable 4209 asynchronous probe on this module as indicated by the 4210 <bool> value. See also: module.async_probe 4211 4212 module.async_probe=<bool> 4213 [KNL] When set to true, modules will use async probing 4214 by default. To enable/disable async probing for a 4215 specific module, use the module specific control that 4216 is documented under <module>.async_probe. When both 4217 module.async_probe and <module>.async_probe are 4218 specified, <module>.async_probe takes precedence for 4219 the specific module. 4220 4221 module.enable_dups_trace 4222 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4223 this means that duplicate request_module() calls will 4224 trigger a WARN_ON() instead of a pr_warn(). Note that 4225 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4226 will always be issued and this option does nothing. 4227 module.sig_enforce 4228 [KNL] When CONFIG_MODULE_SIG is set, this means that 4229 modules without (valid) signatures will fail to load. 4230 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4231 is always true, so this option does nothing. 4232 4233 module_blacklist= [KNL] Do not load a comma-separated list of 4234 modules. Useful for debugging problem modules. 4235 4236 mousedev.tap_time= 4237 [MOUSE] Maximum time between finger touching and 4238 leaving touchpad surface for touch to be considered 4239 a tap and be reported as a left button click (for 4240 touchpads working in absolute mode only). 4241 Format: <msecs> 4242 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4243 reporting absolute coordinates, such as tablets 4244 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4245 reporting absolute coordinates, such as tablets 4246 4247 movablecore= [KNL,X86,PPC,EARLY] 4248 Format: nn[KMGTPE] | nn% 4249 This parameter is the complement to kernelcore=, it 4250 specifies the amount of memory used for migratable 4251 allocations. If both kernelcore and movablecore is 4252 specified, then kernelcore will be at *least* the 4253 specified value but may be more. If movablecore on its 4254 own is specified, the administrator must be careful 4255 that the amount of memory usable for all allocations 4256 is not too small. 4257 4258 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4259 NUMA nodes to be movable. This means that the memory 4260 of such nodes will be usable only for movable 4261 allocations which rules out almost all kernel 4262 allocations. Use with caution! 4263 4264 MTD_Partition= [MTD] 4265 Format: <name>,<region-number>,<size>,<offset> 4266 4267 MTD_Region= [MTD] Format: 4268 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4269 4270 mtdparts= [MTD] 4271 See drivers/mtd/parsers/cmdlinepart.c 4272 4273 mtouchusb.raw_coordinates= 4274 [HW] Make the MicroTouch USB driver use raw coordinates 4275 ('y', default) or cooked coordinates ('n') 4276 4277 mtrr=debug [X86,EARLY] 4278 Enable printing debug information related to MTRR 4279 registers at boot time. 4280 4281 mtrr_chunk_size=nn[KMG,X86,EARLY] 4282 used for mtrr cleanup. It is largest continuous chunk 4283 that could hold holes aka. UC entries. 4284 4285 mtrr_gran_size=nn[KMG,X86,EARLY] 4286 Used for mtrr cleanup. It is granularity of mtrr block. 4287 Default is 1. 4288 Large value could prevent small alignment from 4289 using up MTRRs. 4290 4291 mtrr_spare_reg_nr=n [X86,EARLY] 4292 Format: <integer> 4293 Range: 0,7 : spare reg number 4294 Default : 1 4295 Used for mtrr cleanup. It is spare mtrr entries number. 4296 Set to 2 or more if your graphical card needs more. 4297 4298 multitce=off [PPC] This parameter disables the use of the pSeries 4299 firmware feature for updating multiple TCE entries 4300 at a time. 4301 4302 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4303 4304 netdev= [NET] Network devices parameters 4305 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4306 Note that mem_start is often overloaded to mean 4307 something different and driver-specific. 4308 This usage is only documented in each driver source 4309 file if at all. 4310 4311 netpoll.carrier_timeout= 4312 [NET] Specifies amount of time (in seconds) that 4313 netpoll should wait for a carrier. By default netpoll 4314 waits 4 seconds. 4315 4316 nf_conntrack.acct= 4317 [NETFILTER] Enable connection tracking flow accounting 4318 0 to disable accounting 4319 1 to enable accounting 4320 Default value is 0. 4321 4322 nfs.cache_getent= 4323 [NFS] sets the pathname to the program which is used 4324 to update the NFS client cache entries. 4325 4326 nfs.cache_getent_timeout= 4327 [NFS] sets the timeout after which an attempt to 4328 update a cache entry is deemed to have failed. 4329 4330 nfs.callback_nr_threads= 4331 [NFSv4] set the total number of threads that the 4332 NFS client will assign to service NFSv4 callback 4333 requests. 4334 4335 nfs.callback_tcpport= 4336 [NFS] set the TCP port on which the NFSv4 callback 4337 channel should listen. 4338 4339 nfs.delay_retrans= 4340 [NFS] specifies the number of times the NFSv4 client 4341 retries the request before returning an EAGAIN error, 4342 after a reply of NFS4ERR_DELAY from the server. 4343 Only applies if the softerr mount option is enabled, 4344 and the specified value is >= 0. 4345 4346 nfs.enable_ino64= 4347 [NFS] enable 64-bit inode numbers. 4348 If zero, the NFS client will fake up a 32-bit inode 4349 number for the readdir() and stat() syscalls instead 4350 of returning the full 64-bit number. 4351 The default is to return 64-bit inode numbers. 4352 4353 nfs.idmap_cache_timeout= 4354 [NFS] set the maximum lifetime for idmapper cache 4355 entries. 4356 4357 nfs.max_session_cb_slots= 4358 [NFSv4.1] Sets the maximum number of session 4359 slots the client will assign to the callback 4360 channel. This determines the maximum number of 4361 callbacks the client will process in parallel for 4362 a particular server. 4363 4364 nfs.max_session_slots= 4365 [NFSv4.1] Sets the maximum number of session slots 4366 the client will attempt to negotiate with the server. 4367 This limits the number of simultaneous RPC requests 4368 that the client can send to the NFSv4.1 server. 4369 Note that there is little point in setting this 4370 value higher than the max_tcp_slot_table_limit. 4371 4372 nfs.nfs4_disable_idmapping= 4373 [NFSv4] When set to the default of '1', this option 4374 ensures that both the RPC level authentication 4375 scheme and the NFS level operations agree to use 4376 numeric uids/gids if the mount is using the 4377 'sec=sys' security flavour. In effect it is 4378 disabling idmapping, which can make migration from 4379 legacy NFSv2/v3 systems to NFSv4 easier. 4380 Servers that do not support this mode of operation 4381 will be autodetected by the client, and it will fall 4382 back to using the idmapper. 4383 To turn off this behaviour, set the value to '0'. 4384 4385 nfs.nfs4_unique_id= 4386 [NFS4] Specify an additional fixed unique ident- 4387 ification string that NFSv4 clients can insert into 4388 their nfs_client_id4 string. This is typically a 4389 UUID that is generated at system install time. 4390 4391 nfs.recover_lost_locks= 4392 [NFSv4] Attempt to recover locks that were lost due 4393 to a lease timeout on the server. Please note that 4394 doing this risks data corruption, since there are 4395 no guarantees that the file will remain unchanged 4396 after the locks are lost. 4397 If you want to enable the kernel legacy behaviour of 4398 attempting to recover these locks, then set this 4399 parameter to '1'. 4400 The default parameter value of '0' causes the kernel 4401 not to attempt recovery of lost locks. 4402 4403 nfs.send_implementation_id= 4404 [NFSv4.1] Send client implementation identification 4405 information in exchange_id requests. 4406 If zero, no implementation identification information 4407 will be sent. 4408 The default is to send the implementation identification 4409 information. 4410 4411 nfs4.layoutstats_timer= 4412 [NFSv4.2] Change the rate at which the kernel sends 4413 layoutstats to the pNFS metadata server. 4414 4415 Setting this to value to 0 causes the kernel to use 4416 whatever value is the default set by the layout 4417 driver. A non-zero value sets the minimum interval 4418 in seconds between layoutstats transmissions. 4419 4420 nfsd.inter_copy_offload_enable= 4421 [NFSv4.2] When set to 1, the server will support 4422 server-to-server copies for which this server is 4423 the destination of the copy. 4424 4425 nfsd.nfs4_disable_idmapping= 4426 [NFSv4] When set to the default of '1', the NFSv4 4427 server will return only numeric uids and gids to 4428 clients using auth_sys, and will accept numeric uids 4429 and gids from such clients. This is intended to ease 4430 migration from NFSv2/v3. 4431 4432 nfsd.nfsd4_ssc_umount_timeout= 4433 [NFSv4.2] When used as the destination of a 4434 server-to-server copy, knfsd temporarily mounts 4435 the source server. It caches the mount in case 4436 it will be needed again, and discards it if not 4437 used for the number of milliseconds specified by 4438 this parameter. 4439 4440 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4441 See Documentation/admin-guide/nfs/nfsroot.rst. 4442 4443 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4444 See Documentation/admin-guide/nfs/nfsroot.rst. 4445 4446 nfsrootdebug [NFS] enable nfsroot debugging messages. 4447 See Documentation/admin-guide/nfs/nfsroot.rst. 4448 4449 nmi_backtrace.backtrace_idle [KNL] 4450 Dump stacks even of idle CPUs in response to an 4451 NMI stack-backtrace request. 4452 4453 nmi_debug= [KNL,SH] Specify one or more actions to take 4454 when a NMI is triggered. 4455 Format: [state][,regs][,debounce][,die] 4456 4457 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4458 Format: [panic,][nopanic,][rNNN,][num] 4459 Valid num: 0 or 1 4460 0 - turn hardlockup detector in nmi_watchdog off 4461 1 - turn hardlockup detector in nmi_watchdog on 4462 rNNN - configure the watchdog with raw perf event 0xNNN 4463 4464 When panic is specified, panic when an NMI watchdog 4465 timeout occurs (or 'nopanic' to not panic on an NMI 4466 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4467 To disable both hard and soft lockup detectors, 4468 please see 'nowatchdog'. 4469 This is useful when you use a panic=... timeout and 4470 need the box quickly up again. 4471 4472 These settings can be accessed at runtime via 4473 the nmi_watchdog and hardlockup_panic sysctls. 4474 4475 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4476 emulation library even if a 387 maths coprocessor 4477 is present. 4478 4479 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4480 Forces kernel to use 3-level paging instead. 4481 4482 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4483 kernel to use 4-level paging instead. 4484 4485 noalign [KNL,ARM] 4486 4487 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4488 IOAPICs that may be present in the system. 4489 4490 noapictimer [APIC,X86] Don't set up the APIC timer 4491 4492 noautogroup Disable scheduler automatic task group creation. 4493 4494 nocache [ARM,EARLY] 4495 4496 no_console_suspend 4497 [HW] Never suspend the console 4498 Disable suspending of consoles during suspend and 4499 hibernate operations. Once disabled, debugging 4500 messages can reach various consoles while the rest 4501 of the system is being put to sleep (ie, while 4502 debugging driver suspend/resume hooks). This may 4503 not work reliably with all consoles, but is known 4504 to work with serial and VGA consoles. 4505 To facilitate more flexible debugging, we also add 4506 console_suspend, a printk module parameter to control 4507 it. Users could use console_suspend (usually 4508 /sys/module/printk/parameters/console_suspend) to 4509 turn on/off it dynamically. 4510 4511 no_debug_objects 4512 [KNL,EARLY] Disable object debugging 4513 4514 nodsp [SH] Disable hardware DSP at boot time. 4515 4516 noefi [EFI,EARLY] Disable EFI runtime services support. 4517 4518 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4519 4520 noexec32 [X86-64] 4521 This affects only 32-bit executables. 4522 noexec32=on: enable non-executable mappings (default) 4523 read doesn't imply executable mappings 4524 noexec32=off: disable non-executable mappings 4525 read implies executable mappings 4526 4527 no_file_caps Tells the kernel not to honor file capabilities. The 4528 only way then for a file to be executed with privilege 4529 is to be setuid root or executed by root. 4530 4531 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4532 4533 nofsgsbase [X86] Disables FSGSBASE instructions. 4534 4535 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4536 register save and restore. The kernel will only save 4537 legacy floating-point registers on task switch. 4538 4539 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4540 4541 no_hash_pointers 4542 [KNL,EARLY] 4543 Alias for "hash_pointers=never". 4544 4545 nohibernate [HIBERNATION] Disable hibernation and resume. 4546 4547 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4548 busy wait in do_idle() and not use the arch_cpu_idle() 4549 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4550 to be effective. This is useful on platforms where the 4551 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4552 correctly or when doing power measurements to evaluate 4553 the impact of the sleep instructions. This is also 4554 useful when using JTAG debugger. 4555 4556 nohpet [X86] Don't use the HPET timer. 4557 4558 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4559 4560 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4561 4562 nohz= [KNL] Boottime enable/disable dynamic ticks 4563 Valid arguments: on, off 4564 Default: on 4565 4566 nohz_full= [KNL,BOOT,SMP,ISOL] 4567 The argument is a cpu list, as described above. 4568 In kernels built with CONFIG_NO_HZ_FULL=y, set 4569 the specified list of CPUs whose tick will be stopped 4570 whenever possible. The boot CPU will be forced outside 4571 the range to maintain the timekeeping. Any CPUs 4572 in this list will have their RCU callbacks offloaded, 4573 just as if they had also been called out in the 4574 rcu_nocbs= boot parameter. 4575 4576 Note that this argument takes precedence over 4577 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4578 4579 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4580 initial RAM disk. Currently this parameter applies to 4581 initrd only, not to initramfs. But it applies to both 4582 in EFI mode. 4583 4584 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4585 remapping. 4586 [Deprecated - use intremap=off] 4587 4588 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4589 4590 noiotrap [SH] Disables trapped I/O port accesses. 4591 4592 noirqdebug [X86-32] Disables the code which attempts to detect and 4593 disable unhandled interrupt sources. 4594 4595 noisapnp [ISAPNP] Disables ISA PnP code. 4596 4597 nokaslr [KNL,EARLY] 4598 When CONFIG_RANDOMIZE_BASE is set, this disables 4599 kernel and module base offset ASLR (Address Space 4600 Layout Randomization). 4601 4602 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4603 fault handling. 4604 4605 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4606 4607 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4608 4609 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4610 4611 nomce [X86-32] Disable Machine Check Exception 4612 4613 nomfgpt [X86-32] Disable Multi-Function General Purpose 4614 Timer usage (for AMD Geode machines). 4615 4616 nomodeset Disable kernel modesetting. Most systems' firmware 4617 sets up a display mode and provides framebuffer memory 4618 for output. With nomodeset, DRM and fbdev drivers will 4619 not load if they could possibly displace the pre- 4620 initialized output. Only the system framebuffer will 4621 be available for use. The respective drivers will not 4622 perform display-mode changes or accelerated rendering. 4623 4624 Useful as error fallback, or for testing and debugging. 4625 4626 nomodule Disable module load 4627 4628 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4629 shutdown the other cpus. Instead use the REBOOT_VECTOR 4630 irq. 4631 4632 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4633 pagetables) support. 4634 4635 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4636 4637 nopku [X86] Disable Memory Protection Keys CPU feature found 4638 in some Intel CPUs. 4639 4640 nopti [X86-64,EARLY] 4641 Equivalent to pti=off 4642 4643 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4644 Disables the PV optimizations forcing the guest to run 4645 as generic guest with no PV drivers. Currently support 4646 XEN HVM, KVM, HYPER_V and VMWARE guest. 4647 4648 nopvspin [X86,XEN,KVM,EARLY] 4649 Disables the qspinlock slow path using PV optimizations 4650 which allow the hypervisor to 'idle' the guest on lock 4651 contention. 4652 4653 norandmaps Don't use address space randomization. Equivalent to 4654 echo 0 > /proc/sys/kernel/randomize_va_space 4655 4656 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4657 with UP alternatives 4658 4659 noresume [SWSUSP] Disables resume and restores original swap 4660 space. 4661 4662 no-scroll [VGA] Disables scrollback. 4663 This is required for the Braillex ib80-piezo Braille 4664 reader made by F.H. Papenmeier (Germany). 4665 4666 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4667 4668 nosmap [PPC,EARLY] 4669 Disable SMAP (Supervisor Mode Access Prevention) 4670 even if it is supported by processor. 4671 4672 nosmep [PPC64s,EARLY] 4673 Disable SMEP (Supervisor Mode Execution Prevention) 4674 even if it is supported by processor. 4675 4676 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4677 and disable the IO APIC. legacy for "maxcpus=0". 4678 4679 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4680 Equivalent to smt=1. 4681 4682 [KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT). 4683 nosmt=force: Force disable SMT, cannot be undone 4684 via the sysfs control file. 4685 4686 nosoftlockup [KNL] Disable the soft-lockup detector. 4687 4688 nospec_store_bypass_disable 4689 [HW,EARLY] Disable all mitigations for the Speculative 4690 Store Bypass vulnerability 4691 4692 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4693 history injection) vulnerability. System may allow data leaks 4694 with this option. 4695 4696 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4697 (bounds check bypass). With this option data leaks are 4698 possible in the system. 4699 4700 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4701 for the Spectre variant 2 (indirect branch 4702 prediction) vulnerability. System may allow data 4703 leaks with this option. 4704 4705 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4706 Disable paravirtualized steal time accounting. steal time 4707 is computed, but won't influence scheduler behaviour 4708 4709 nosync [HW,M68K] Disables sync negotiation for all devices. 4710 4711 no_timer_check [X86,APIC] Disables the code which tests for broken 4712 timer IRQ sources, i.e., the IO-APIC timer. This can 4713 work around problems with incorrect timer 4714 initialization on some boards. 4715 4716 no_uaccess_flush 4717 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4718 4719 novmcoredd [KNL,KDUMP] 4720 Disable device dump. Device dump allows drivers to 4721 append dump data to vmcore so you can collect driver 4722 specified debug info. Drivers can append the data 4723 without any limit and this data is stored in memory, 4724 so this may cause significant memory stress. Disabling 4725 device dump can help save memory but the driver debug 4726 data will be no longer available. This parameter 4727 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4728 is set. 4729 4730 no-vmw-sched-clock 4731 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4732 scheduler clock and use the default one. 4733 4734 nowatchdog [KNL] Disable both lockup detectors, i.e. 4735 soft-lockup and NMI watchdog (hard-lockup). 4736 4737 nowb [ARM,EARLY] 4738 4739 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4740 4741 NOTE: this parameter will be ignored on systems with the 4742 LEGACY_XAPIC_DISABLED bit set in the 4743 IA32_XAPIC_DISABLE_STATUS MSR. 4744 4745 noxsave [BUGS=X86] Disables x86 extended register state save 4746 and restore using xsave. The kernel will fallback to 4747 enabling legacy floating-point and sse state. 4748 4749 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4750 register states. The kernel will fall back to use 4751 xsave to save the states. By using this parameter, 4752 performance of saving the states is degraded because 4753 xsave doesn't support modified optimization while 4754 xsaveopt supports it on xsaveopt enabled systems. 4755 4756 noxsaves [X86] Disables xsaves and xrstors used in saving and 4757 restoring x86 extended register state in compacted 4758 form of xsave area. The kernel will fall back to use 4759 xsaveopt and xrstor to save and restore the states 4760 in standard form of xsave area. By using this 4761 parameter, xsave area per process might occupy more 4762 memory on xsaves enabled systems. 4763 4764 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4765 could support. nr_cpus=n : n >= 1 limits the kernel to 4766 support 'n' processors. It could be larger than the 4767 number of already plugged CPU during bootup, later in 4768 runtime you can physically add extra cpu until it reaches 4769 n. So during boot up some boot time memory for per-cpu 4770 variables need be pre-allocated for later physical cpu 4771 hot plugging. 4772 4773 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4774 4775 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4776 Disable NUMA, Only set up a single NUMA node 4777 spanning all memory. 4778 4779 numa=fake=<size>[MG] 4780 [KNL, ARM64, RISCV, X86, EARLY] 4781 If given as a memory unit, fills all system RAM with 4782 nodes of size interleaved over physical nodes. 4783 4784 numa=fake=<N> 4785 [KNL, ARM64, RISCV, X86, EARLY] 4786 If given as an integer, fills all system RAM with N 4787 fake nodes interleaved over physical nodes. 4788 4789 numa=fake=<N>U 4790 [KNL, ARM64, RISCV, X86, EARLY] 4791 If given as an integer followed by 'U', it will 4792 divide each physical node into N emulated nodes. 4793 4794 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4795 4796 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4797 soft-reserved memory partitioning. 4798 4799 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4800 NUMA balancing. 4801 Allowed values are enable and disable 4802 4803 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4804 'node', 'default' can be specified 4805 This can be set from sysctl after boot. 4806 See Documentation/admin-guide/sysctl/vm.rst for details. 4807 4808 nvme.quirks= [NVME] A list of quirk entries to augment the built-in 4809 nvme quirk list. List entries are separated by a 4810 '-' character. 4811 Each entry has the form VendorID:ProductID:quirk_names. 4812 The IDs are 4-digits hex numbers and quirk_names is a 4813 list of quirk names separated by commas. A quirk name 4814 can be prefixed by '^', meaning that the specified 4815 quirk must be disabled. 4816 4817 Example: 4818 nvme.quirks=7710:2267:bogus_nid,^identify_cns-9900:7711:broken_msi 4819 4820 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4821 See Documentation/core-api/debugging-via-ohci1394.rst for more 4822 info. 4823 4824 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4825 Rather than timing out after 20 ms if an EC 4826 command is not properly ACKed, override the length 4827 of the timeout. We have interrupts disabled while 4828 waiting for the ACK, so if this is set too high 4829 interrupts *may* be lost! 4830 4831 omap_mux= [OMAP] Override bootloader pin multiplexing. 4832 Format: <mux_mode0.mode_name=value>... 4833 For example, to override I2C bus2: 4834 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4835 4836 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4837 4838 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4839 4840 boundary - index of last SLC block on Flex-OneNAND. 4841 The remaining blocks are configured as MLC blocks. 4842 lock - Configure if Flex-OneNAND boundary should be locked. 4843 Once locked, the boundary cannot be changed. 4844 1 indicates lock status, 0 indicates unlock status. 4845 4846 oops=panic [KNL,EARLY] 4847 Always panic on oopses. Default is to just kill the 4848 process, but there is a small probability of 4849 deadlocking the machine. 4850 This will also cause panics on machine check exceptions. 4851 Useful together with panic=30 to trigger a reboot. 4852 4853 page_alloc.shuffle= 4854 [KNL] Boolean flag to control whether the page allocator 4855 should randomize its free lists. This parameter can be 4856 used to enable/disable page randomization. The state of 4857 the flag can be read from sysfs at: 4858 /sys/module/page_alloc/parameters/shuffle. 4859 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4860 4861 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4862 Storage of the information about who allocated 4863 each page is disabled in default. With this switch, 4864 we can turn it on. 4865 on: enable the feature 4866 4867 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4868 poisoning on the buddy allocator, available with 4869 CONFIG_PAGE_POISONING=y. 4870 off: turn off poisoning (default) 4871 on: turn on poisoning 4872 4873 page_reporting.page_reporting_order= 4874 [KNL] Minimal page reporting order 4875 Format: <integer> 4876 Adjust the minimal page reporting order. The page 4877 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4878 4879 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4880 timeout > 0: seconds before rebooting 4881 timeout = 0: wait forever 4882 timeout < 0: reboot immediately 4883 Format: <timeout> 4884 4885 panic_on_taint= [KNL,EARLY] 4886 Bitmask for conditionally calling panic() in add_taint() 4887 Format: <hex>[,nousertaint] 4888 Hexadecimal bitmask representing the set of TAINT flags 4889 that will cause the kernel to panic when add_taint() is 4890 called with any of the flags in this set. 4891 The optional switch "nousertaint" can be utilized to 4892 prevent userspace forced crashes by writing to sysctl 4893 /proc/sys/kernel/tainted any flagset matching with the 4894 bitmask set on panic_on_taint. 4895 See Documentation/admin-guide/tainted-kernels.rst for 4896 extra details on the taint flags that users can pick 4897 to compose the bitmask to assign to panic_on_taint. 4898 4899 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4900 on a WARN(). 4901 4902 panic_force_cpu= 4903 [KNL,SMP] Force panic handling to execute on a specific CPU. 4904 Format: <cpu number> 4905 Some platforms require panic handling to occur on a 4906 specific CPU for the crash kernel to function correctly. 4907 This can be due to firmware limitations, interrupt routing 4908 constraints, or platform-specific requirements where only 4909 a particular CPU can safely enter the crash kernel. 4910 When set, panic() will redirect execution to the specified 4911 CPU before proceeding with the normal panic and kexec flow. 4912 If the target CPU is offline or unavailable, panic proceeds 4913 on the current CPU. 4914 This option should only be used for systems with the above 4915 constraints as it might cause the panic operation to be less reliable. 4916 4917 panic_print= Bitmask for printing system info when panic happens. 4918 User can chose combination of the following bits: 4919 bit 0: print all tasks info 4920 bit 1: print system memory info 4921 bit 2: print timer info 4922 bit 3: print locks info if CONFIG_LOCKDEP is on 4923 bit 4: print ftrace buffer 4924 bit 5: replay all kernel messages on consoles at the end of panic 4925 bit 6: print all CPUs backtrace (if available in the arch) 4926 bit 7: print only tasks in uninterruptible (blocked) state 4927 *Be aware* that this option may print a _lot_ of lines, 4928 so there are risks of losing older messages in the log. 4929 Use this option carefully, maybe worth to setup a 4930 bigger log buffer with "log_buf_len" along with this. 4931 4932 panic_sys_info= A comma separated list of extra information to be dumped 4933 on panic. 4934 Format: val[,val...] 4935 Where @val can be any of the following: 4936 4937 tasks: print all tasks info 4938 mem: print system memory info 4939 timers: print timers info 4940 locks: print locks info if CONFIG_LOCKDEP is on 4941 ftrace: print ftrace buffer 4942 all_bt: print all CPUs backtrace (if available in the arch) 4943 blocked_tasks: print only tasks in uninterruptible (blocked) state 4944 4945 This is a human readable alternative to the 'panic_print' option. 4946 4947 panic_console_replay 4948 When panic happens, replay all kernel messages on 4949 consoles at the end of panic. 4950 4951 parkbd.port= [HW] Parallel port number the keyboard adapter is 4952 connected to, default is 0. 4953 Format: <parport#> 4954 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4955 0 for XT, 1 for AT (default is AT). 4956 Format: <mode> 4957 4958 parport= [HW,PPT] Specify parallel ports. 0 disables. 4959 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4960 Use 'auto' to force the driver to use any 4961 IRQ/DMA settings detected (the default is to 4962 ignore detected IRQ/DMA settings because of 4963 possible conflicts). You can specify the base 4964 address, IRQ, and DMA settings; IRQ and DMA 4965 should be numbers, or 'auto' (for using detected 4966 settings on that particular port), or 'nofifo' 4967 (to avoid using a FIFO even if it is detected). 4968 Parallel ports are assigned in the order they 4969 are specified on the command line, starting 4970 with parport0. 4971 4972 parport_init_mode= [HW,PPT] 4973 Configure VIA parallel port to operate in 4974 a specific mode. This is necessary on Pegasos 4975 computer where firmware has no options for setting 4976 up parallel port mode and sets it to spp. 4977 Currently this function knows 686a and 8231 chips. 4978 Format: [spp|ps2|epp|ecp|ecpepp] 4979 4980 pata_legacy.all= [HW,LIBATA] 4981 Format: <int> 4982 Set to non-zero to probe primary and secondary ISA 4983 port ranges on PCI systems where no PCI PATA device 4984 has been found at either range. Disabled by default. 4985 4986 pata_legacy.autospeed= [HW,LIBATA] 4987 Format: <int> 4988 Set to non-zero if a chip is present that snoops speed 4989 changes. Disabled by default. 4990 4991 pata_legacy.ht6560a= [HW,LIBATA] 4992 Format: <int> 4993 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4994 the secondary channel, or both channels respectively. 4995 Disabled by default. 4996 4997 pata_legacy.ht6560b= [HW,LIBATA] 4998 Format: <int> 4999 Set to 1, 2, or 3 for HT 6560B on the primary channel, 5000 the secondary channel, or both channels respectively. 5001 Disabled by default. 5002 5003 pata_legacy.iordy_mask= [HW,LIBATA] 5004 Format: <int> 5005 IORDY enable mask. Set individual bits to allow IORDY 5006 for the respective channel. Bit 0 is for the first 5007 legacy channel handled by this driver, bit 1 is for 5008 the second channel, and so on. The sequence will often 5009 correspond to the primary legacy channel, the secondary 5010 legacy channel, and so on, but the handling of a PCI 5011 bus and the use of other driver options may interfere 5012 with the sequence. By default IORDY is allowed across 5013 all channels. 5014 5015 pata_legacy.opti82c46x= [HW,LIBATA] 5016 Format: <int> 5017 Set to 1, 2, or 3 for Opti 82c611A on the primary 5018 channel, the secondary channel, or both channels 5019 respectively. Disabled by default. 5020 5021 pata_legacy.opti82c611a= [HW,LIBATA] 5022 Format: <int> 5023 Set to 1, 2, or 3 for Opti 82c465MV on the primary 5024 channel, the secondary channel, or both channels 5025 respectively. Disabled by default. 5026 5027 pata_legacy.pio_mask= [HW,LIBATA] 5028 Format: <int> 5029 PIO mode mask for autospeed devices. Set individual 5030 bits to allow the use of the respective PIO modes. 5031 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 5032 All modes allowed by default. 5033 5034 pata_legacy.probe_all= [HW,LIBATA] 5035 Format: <int> 5036 Set to non-zero to probe tertiary and further ISA 5037 port ranges on PCI systems. Disabled by default. 5038 5039 pata_legacy.probe_mask= [HW,LIBATA] 5040 Format: <int> 5041 Probe mask for legacy ISA PATA ports. Depending on 5042 platform configuration and the use of other driver 5043 options up to 6 legacy ports are supported: 0x1f0, 5044 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5045 of individual ports can be disabled by setting the 5046 corresponding bits in the mask to 1. Bit 0 is for 5047 the first port in the list above (0x1f0), and so on. 5048 By default all supported ports are probed. 5049 5050 pata_legacy.qdi= [HW,LIBATA] 5051 Format: <int> 5052 Set to non-zero to probe QDI controllers. By default 5053 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5054 5055 pata_legacy.winbond= [HW,LIBATA] 5056 Format: <int> 5057 Set to non-zero to probe Winbond controllers. Use 5058 the standard I/O port (0x130) if 1, otherwise the 5059 value given is the I/O port to use (typically 0x1b0). 5060 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5061 0 otherwise. 5062 5063 pata_platform.pio_mask= [HW,LIBATA] 5064 Format: <int> 5065 Supported PIO mode mask. Set individual bits to allow 5066 the use of the respective PIO modes. Bit 0 is for 5067 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5068 allowed by default. 5069 5070 pause_on_oops=<int> 5071 Halt all CPUs after the first oops has been printed for 5072 the specified number of seconds. This is to be used if 5073 your oopses keep scrolling off the screen. 5074 5075 pcbit= [HW,ISDN] 5076 5077 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5078 5079 Some options herein operate on a specific device 5080 or a set of devices (<pci_dev>). These are 5081 specified in one of the following formats: 5082 5083 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5084 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5085 5086 Note: the first format specifies a PCI 5087 bus/device/function address which may change 5088 if new hardware is inserted, if motherboard 5089 firmware changes, or due to changes caused 5090 by other kernel parameters. If the 5091 domain is left unspecified, it is 5092 taken to be zero. Optionally, a path 5093 to a device through multiple device/function 5094 addresses can be specified after the base 5095 address (this is more robust against 5096 renumbering issues). The second format 5097 selects devices using IDs from the 5098 configuration space which may match multiple 5099 devices in the system. 5100 5101 earlydump dump PCI config space before the kernel 5102 changes anything 5103 off [X86] don't probe for the PCI bus 5104 bios [X86-32] force use of PCI BIOS, don't access 5105 the hardware directly. Use this if your machine 5106 has a non-standard PCI host bridge. 5107 nobios [X86-32] disallow use of PCI BIOS, only direct 5108 hardware access methods are allowed. Use this 5109 if you experience crashes upon bootup and you 5110 suspect they are caused by the BIOS. 5111 conf1 [X86] Force use of PCI Configuration Access 5112 Mechanism 1 (config address in IO port 0xCF8, 5113 data in IO port 0xCFC, both 32-bit). 5114 conf2 [X86] Force use of PCI Configuration Access 5115 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5116 the function, IO port 0xCFA, also 8-bit, sets 5117 bus number. The config space is then accessed 5118 through ports 0xC000-0xCFFF). 5119 See http://wiki.osdev.org/PCI for more info 5120 on the configuration access mechanisms. 5121 noaer [PCIE] If the PCIEAER kernel config parameter is 5122 enabled, this kernel boot option can be used to 5123 disable the use of PCIE advanced error reporting. 5124 nodomains [PCI] Disable support for multiple PCI 5125 root domains (aka PCI segments, in ACPI-speak). 5126 nommconf [X86] Disable use of MMCONFIG for PCI 5127 Configuration 5128 check_enable_amd_mmconf [X86] check for and enable 5129 properly configured MMIO access to PCI 5130 config space on AMD family 10h CPU 5131 nomsi [MSI] If the PCI_MSI kernel config parameter is 5132 enabled, this kernel boot option can be used to 5133 disable the use of MSI interrupts system-wide. 5134 noioapicquirk [APIC] Disable all boot interrupt quirks. 5135 Safety option to keep boot IRQs enabled. This 5136 should never be necessary. 5137 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5138 primary IO-APIC for bridges that cannot disable 5139 boot IRQs. This fixes a source of spurious IRQs 5140 when the system masks IRQs. 5141 noioapicreroute [APIC] Disable workaround that uses the 5142 boot IRQ equivalent of an IRQ that connects to 5143 a chipset where boot IRQs cannot be disabled. 5144 The opposite of ioapicreroute. 5145 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5146 routing table. These calls are known to be buggy 5147 on several machines and they hang the machine 5148 when used, but on other computers it's the only 5149 way to get the interrupt routing table. Try 5150 this option if the kernel is unable to allocate 5151 IRQs or discover secondary PCI buses on your 5152 motherboard. 5153 rom [X86] Assign address space to expansion ROMs. 5154 Use with caution as certain devices share 5155 address decoders between ROMs and other 5156 resources. 5157 norom [X86] Do not assign address space to 5158 expansion ROMs that do not already have 5159 BIOS assigned address ranges. 5160 nobar [X86] Do not assign address space to the 5161 BARs that weren't assigned by the BIOS. 5162 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5163 assigned automatically to PCI devices. You can 5164 make the kernel exclude IRQs of your ISA cards 5165 this way. 5166 pirqaddr=0xAAAAA [X86] Specify the physical address 5167 of the PIRQ table (normally generated 5168 by the BIOS) if it is outside the 5169 F0000h-100000h range. 5170 lastbus=N [X86] Scan all buses thru bus #N. Can be 5171 useful if the kernel is unable to find your 5172 secondary buses and you want to tell it 5173 explicitly which ones they are. 5174 assign-busses [X86] Always assign all PCI bus 5175 numbers ourselves, overriding 5176 whatever the firmware may have done. 5177 usepirqmask [X86] Honor the possible IRQ mask stored 5178 in the BIOS $PIR table. This is needed on 5179 some systems with broken BIOSes, notably 5180 some HP Pavilion N5400 and Omnibook XE3 5181 notebooks. This will have no effect if ACPI 5182 IRQ routing is enabled. 5183 noacpi [X86] Do not use ACPI for IRQ routing 5184 or for PCI scanning. 5185 use_crs [X86] Use PCI host bridge window information 5186 from ACPI. On BIOSes from 2008 or later, this 5187 is enabled by default. If you need to use this, 5188 please report a bug. 5189 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5190 If you need to use this, please report a bug. 5191 use_e820 [X86] Use E820 reservations to exclude parts of 5192 PCI host bridge windows. This is a workaround 5193 for BIOS defects in host bridge _CRS methods. 5194 If you need to use this, please report a bug to 5195 <linux-pci@vger.kernel.org>. 5196 no_e820 [X86] Ignore E820 reservations for PCI host 5197 bridge windows. This is the default on modern 5198 hardware. If you need to use this, please report 5199 a bug to <linux-pci@vger.kernel.org>. 5200 routeirq Do IRQ routing for all PCI devices. 5201 This is normally done in pci_enable_device(), 5202 so this option is a temporary workaround 5203 for broken drivers that don't call it. 5204 skip_isa_align [X86] do not align io start addr, so can 5205 handle more pci cards 5206 noearly [X86] Don't do any early type 1 scanning. 5207 This might help on some broken boards which 5208 machine check when some devices' config space 5209 is read. But various workarounds are disabled 5210 and some IOMMU drivers will not work. 5211 bfsort Sort PCI devices into breadth-first order. 5212 This sorting is done to get a device 5213 order compatible with older (<= 2.4) kernels. 5214 nobfsort Don't sort PCI devices into breadth-first order. 5215 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5216 tuning and use the BIOS-configured MPS defaults. 5217 pcie_bus_safe Set every device's MPS to the largest value 5218 supported by all devices below the root complex. 5219 pcie_bus_perf Set device MPS to the largest allowable MPS 5220 based on its parent bus. Also set MRRS (Max 5221 Read Request Size) to the largest supported 5222 value (no larger than the MPS that the device 5223 or bus can support) for best performance. 5224 pcie_bus_peer2peer Set every device's MPS to 128B, which 5225 every device is guaranteed to support. This 5226 configuration allows peer-to-peer DMA between 5227 any pair of devices, possibly at the cost of 5228 reduced performance. This also guarantees 5229 that hot-added devices will work. 5230 cbiosize=nn[KMG] The fixed amount of bus space which is 5231 reserved for the CardBus bridge's IO window. 5232 The default value is 256 bytes. 5233 cbmemsize=nn[KMG] The fixed amount of bus space which is 5234 reserved for the CardBus bridge's memory 5235 window. The default value is 64 megabytes. 5236 resource_alignment= 5237 Format: 5238 [<order of align>@]<pci_dev>[; ...] 5239 Specifies alignment and device to reassign 5240 aligned memory resources. How to 5241 specify the device is described above. 5242 If <order of align> is not specified, 5243 PAGE_SIZE is used as alignment. 5244 A PCI-PCI bridge can be specified if resource 5245 windows need to be expanded. 5246 To specify the alignment for several 5247 instances of a device, the PCI vendor, 5248 device, subvendor, and subdevice may be 5249 specified, e.g., 12@pci:8086:9c22:103c:198f 5250 for 4096-byte alignment. 5251 ecrc= Enable/disable PCIe ECRC (transaction layer 5252 end-to-end CRC checking). Only effective if 5253 OS has native AER control (either granted by 5254 ACPI _OSC or forced via "pcie_ports=native") 5255 bios: Use BIOS/firmware settings. This is the 5256 the default. 5257 off: Turn ECRC off 5258 on: Turn ECRC on. 5259 hpiosize=nn[KMG] The fixed amount of bus space which is 5260 reserved for hotplug bridge's IO window. 5261 Default size is 256 bytes. 5262 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5263 reserved for hotplug bridge's MMIO window. 5264 Default size is 2 megabytes. 5265 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5266 reserved for hotplug bridge's MMIO_PREF window. 5267 Default size is 2 megabytes. 5268 hpmemsize=nn[KMG] The fixed amount of bus space which is 5269 reserved for hotplug bridge's MMIO and 5270 MMIO_PREF window. 5271 Default size is 2 megabytes. 5272 hpbussize=nn The minimum amount of additional bus numbers 5273 reserved for buses below a hotplug bridge. 5274 Default is 1. 5275 realloc= Enable/disable reallocating PCI bridge resources 5276 if allocations done by BIOS are too small to 5277 accommodate resources required by all child 5278 devices. 5279 off: Turn realloc off 5280 on: Turn realloc on 5281 realloc same as realloc=on 5282 noari do not use PCIe ARI. 5283 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5284 do not use PCIe ATS (and IOMMU device IOTLB). 5285 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5286 only look for one device below a PCIe downstream 5287 port. 5288 big_root_window Try to add a big 64bit memory window to the PCIe 5289 root complex on AMD CPUs. Some GFX hardware 5290 can resize a BAR to allow access to all VRAM. 5291 Adding the window is slightly risky (it may 5292 conflict with unreported devices), so this 5293 taints the kernel. 5294 disable_acs_redir=<pci_dev>[; ...] 5295 Specify one or more PCI devices (in the format 5296 specified above) separated by semicolons. 5297 Each device specified will have the PCI ACS 5298 redirect capabilities forced off which will 5299 allow P2P traffic between devices through 5300 bridges without forcing it upstream. Note: 5301 this removes isolation between devices and 5302 may put more devices in an IOMMU group. 5303 config_acs= 5304 Format: 5305 <ACS flags>@<pci_dev>[; ...] 5306 Specify one or more PCI devices (in the format 5307 specified above) optionally prepended with flags 5308 and separated by semicolons. The respective 5309 capabilities will be enabled, disabled or 5310 unchanged based on what is specified in 5311 flags. 5312 5313 ACS Flags is defined as follows: 5314 bit-0 : ACS Source Validation 5315 bit-1 : ACS Translation Blocking 5316 bit-2 : ACS P2P Request Redirect 5317 bit-3 : ACS P2P Completion Redirect 5318 bit-4 : ACS Upstream Forwarding 5319 bit-5 : ACS P2P Egress Control 5320 bit-6 : ACS Direct Translated P2P 5321 Each bit can be marked as: 5322 '0' – force disabled 5323 '1' – force enabled 5324 'x' – unchanged 5325 For example, 5326 pci=config_acs=10x@pci:0:0 5327 would configure all devices that support 5328 ACS to enable P2P Request Redirect, disable 5329 Translation Blocking, and leave Source 5330 Validation unchanged from whatever power-up 5331 or firmware set it to. 5332 5333 Note: this may remove isolation between devices 5334 and may put more devices in an IOMMU group. 5335 force_floating [S390] Force usage of floating interrupts. 5336 nomio [S390] Do not use MIO instructions. 5337 norid [S390] ignore the RID field and force use of 5338 one PCI domain per PCI function 5339 notph [PCIE] If the PCIE_TPH kernel config parameter 5340 is enabled, this kernel boot option can be used 5341 to disable PCIe TLP Processing Hints support 5342 system-wide. 5343 5344 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5345 Management. 5346 off Don't touch ASPM configuration at all. Leave any 5347 configuration done by firmware unchanged. 5348 force Enable ASPM even on devices that claim not to support it. 5349 WARNING: Forcing ASPM on may cause system lockups. 5350 5351 pcie_ports= [PCIE] PCIe port services handling: 5352 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5353 even if the platform doesn't give the OS permission to 5354 use them. This may cause conflicts if the platform 5355 also tries to use these services. 5356 dpc-native Use native PCIe service for DPC only. May 5357 cause conflicts if firmware uses AER or DPC. 5358 compat Disable native PCIe services (PME, AER, DPC, PCIe 5359 hotplug). 5360 5361 pcie_port_pm= [PCIE] PCIe port power management handling: 5362 off Disable power management of all PCIe ports 5363 force Forcibly enable power management of all PCIe ports 5364 5365 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5366 nomsi Do not use MSI for native PCIe PME signaling (this makes 5367 all PCIe root ports use INTx for all services). 5368 5369 pcmv= [HW,PCMCIA] BadgePAD 4 5370 5371 pd_ignore_unused 5372 [PM] 5373 Keep all power-domains already enabled by bootloader on, 5374 even if no driver has claimed them. This is useful 5375 for debug and development, but should not be 5376 needed on a platform with proper driver support. 5377 5378 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5379 boot time. 5380 Format: { 0 | 1 } 5381 See arch/parisc/kernel/pdc_chassis.c 5382 5383 percpu_alloc= [MM,EARLY] 5384 Select which percpu first chunk allocator to use. 5385 Currently supported values are "embed" and "page". 5386 Archs may support subset or none of the selections. 5387 See comments in mm/percpu.c for details on each 5388 allocator. This parameter is primarily for debugging 5389 and performance comparison. 5390 5391 pirq= [SMP,APIC] Manual mp-table setup 5392 See Documentation/arch/x86/i386/IO-APIC.rst. 5393 5394 plip= [PPT,NET] Parallel port network link 5395 Format: { parport<nr> | timid | 0 } 5396 See also Documentation/admin-guide/parport.rst. 5397 5398 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5399 Override pmtimer IOPort with a hex value. 5400 e.g. pmtmr=0x508 5401 5402 pmu_override= [PPC] Override the PMU. 5403 This option takes over the PMU facility, so it is no 5404 longer usable by perf. Setting this option starts the 5405 PMU counters by setting MMCR0 to 0 (the FC bit is 5406 cleared). If a number is given, then MMCR1 is set to 5407 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5408 remains 0. 5409 5410 pm_async= [PM] 5411 Format: off 5412 This parameter sets the initial value of the 5413 /sys/power/pm_async sysfs knob at boot time. 5414 If set to "off", disables asynchronous suspend and 5415 resume of devices during system-wide power transitions. 5416 This can be useful on platforms where device 5417 dependencies are not well-defined, or for debugging 5418 power management issues. Asynchronous operations are 5419 enabled by default. 5420 5421 5422 pm_debug_messages [SUSPEND,KNL] 5423 Enable suspend/resume debug messages during boot up. 5424 5425 pnp.debug=1 [PNP] 5426 Enable PNP debug messages (depends on the 5427 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5428 via /sys/module/pnp/parameters/debug. We always show 5429 current resource usage; turning this on also shows 5430 possible settings and some assignment information. 5431 5432 pnpacpi= [ACPI] 5433 { off } 5434 5435 pnpbios= [ISAPNP] 5436 { on | off | curr | res | no-curr | no-res } 5437 5438 pnp_reserve_irq= 5439 [ISAPNP] Exclude IRQs for the autoconfiguration 5440 5441 pnp_reserve_dma= 5442 [ISAPNP] Exclude DMAs for the autoconfiguration 5443 5444 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5445 Ranges are in pairs (I/O port base and size). 5446 5447 pnp_reserve_mem= 5448 [ISAPNP] Exclude memory regions for the 5449 autoconfiguration. 5450 Ranges are in pairs (memory base and size). 5451 5452 ports= [IP_VS_FTP] IPVS ftp helper module 5453 Default is 21. 5454 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5455 may be specified. 5456 Format: <port>,<port>.... 5457 5458 possible_cpus= [SMP,S390,X86] 5459 Format: <unsigned int> 5460 Set the number of possible CPUs, overriding the 5461 regular discovery mechanisms (such as ACPI/FW, etc). 5462 5463 powersave=off [PPC] This option disables power saving features. 5464 It specifically disables cpuidle and sets the 5465 platform machine description specific power_save 5466 function to NULL. On Idle the CPU just reduces 5467 execution priority. 5468 5469 ppc_strict_facility_enable 5470 [PPC,ENABLE] This option catches any kernel floating point, 5471 Altivec, VSX and SPE outside of regions specifically 5472 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5473 There is some performance impact when enabling this. 5474 5475 ppc_tm= [PPC,EARLY] 5476 Format: {"off"} 5477 Disable Hardware Transactional Memory 5478 5479 preempt= [KNL] 5480 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5481 none - Limited to cond_resched() calls 5482 voluntary - Limited to cond_resched() and might_sleep() calls 5483 full - Any section that isn't explicitly preempt disabled 5484 can be preempted anytime. Tasks will also yield 5485 contended spinlocks (if the critical section isn't 5486 explicitly preempt disabled beyond the lock itself). 5487 lazy - Scheduler controlled. Similar to full but instead 5488 of preempting the task immediately, the task gets 5489 one HZ tick time to yield itself before the 5490 preemption will be forced. One preemption is when the 5491 task returns to user space. 5492 5493 print-fatal-signals= 5494 [KNL] debug: print fatal signals 5495 5496 If enabled, warn about various signal handling 5497 related application anomalies: too many signals, 5498 too many POSIX.1 timers, fatal signals causing a 5499 coredump - etc. 5500 5501 If you hit the warning due to signal overflow, 5502 you might want to try "ulimit -i unlimited". 5503 5504 default: off. 5505 5506 printk.always_kmsg_dump= 5507 Trigger kmsg_dump for cases other than kernel oops or 5508 panics 5509 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5510 default: disabled 5511 5512 printk.console_no_auto_verbose= 5513 Disable console loglevel raise on oops, panic 5514 or lockdep-detected issues (only if lock debug is on). 5515 With an exception to setups with low baudrate on 5516 serial console, keeping this 0 is a good choice 5517 in order to provide more debug information. 5518 Format: <bool> 5519 default: 0 (auto_verbose is enabled) 5520 5521 printk.debug_non_panic_cpus= 5522 Allows storing messages from non-panic CPUs into 5523 the printk log buffer during panic(). They are 5524 flushed to consoles by the panic-CPU on 5525 a best-effort basis. 5526 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5527 Default: disabled 5528 5529 printk.devkmsg={on,off,ratelimit} 5530 Control writing to /dev/kmsg. 5531 on - unlimited logging to /dev/kmsg from userspace 5532 off - logging to /dev/kmsg disabled 5533 ratelimit - ratelimit the logging 5534 Default: ratelimit 5535 5536 printk.time= Show timing data prefixed to each printk message line 5537 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5538 5539 proc_mem.force_override= [KNL] 5540 Format: {always | ptrace | never} 5541 Traditionally /proc/pid/mem allows memory permissions to be 5542 overridden without restrictions. This option may be set to 5543 restrict that. Can be one of: 5544 - 'always': traditional behavior always allows mem overrides. 5545 - 'ptrace': only allow mem overrides for active ptracers. 5546 - 'never': never allow mem overrides. 5547 If not specified, default is the CONFIG_PROC_MEM_* choice. 5548 5549 processor.max_cstate= [HW,ACPI] 5550 Limit processor to maximum C-state 5551 max_cstate=9 overrides any DMI blacklist limit. 5552 5553 processor.nocst [HW,ACPI] 5554 Ignore the _CST method to determine C-states, 5555 instead using the legacy FADT method 5556 5557 profile= [KNL] Enable kernel profiling via /proc/profile 5558 Format: [<profiletype>,]<number> 5559 Param: <profiletype>: "schedule" or "kvm" 5560 [defaults to kernel profiling] 5561 Param: "schedule" - profile schedule points. 5562 Param: "kvm" - profile VM exits. 5563 Param: <number> - step/bucket size as a power of 2 for 5564 statistical time based profiling. 5565 5566 prot_virt= [S390] enable hosting protected virtual machines 5567 isolated from the hypervisor (if hardware supports 5568 that). If enabled, the default kernel base address 5569 might be overridden even when Kernel Address Space 5570 Layout Randomization is disabled. 5571 Format: <bool> 5572 5573 psi= [KNL] Enable or disable pressure stall information 5574 tracking. 5575 Format: <bool> 5576 5577 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5578 probe for; one of (bare|imps|exps|lifebook|any). 5579 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5580 per second. 5581 psmouse.resetafter= [HW,MOUSE] 5582 Try to reset the device after so many bad packets 5583 (0 = never). 5584 psmouse.resolution= 5585 [HW,MOUSE] Set desired mouse resolution, in dpi. 5586 psmouse.smartscroll= 5587 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5588 0 = disabled, 1 = enabled (default). 5589 5590 pstore.backend= Specify the name of the pstore backend to use 5591 5592 pti= [X86-64] Control Page Table Isolation of user and 5593 kernel address spaces. Disabling this feature 5594 removes hardening, but improves performance of 5595 system calls and interrupts. 5596 5597 on - unconditionally enable 5598 off - unconditionally disable 5599 auto - kernel detects whether your CPU model is 5600 vulnerable to issues that PTI mitigates 5601 5602 Not specifying this option is equivalent to pti=auto. 5603 5604 pty.legacy_count= 5605 [KNL] Number of legacy pty's. Overwrites compiled-in 5606 default number. 5607 5608 quiet [KNL,EARLY] Disable most log messages 5609 5610 r128= [HW,DRM] 5611 5612 radix_hcall_invalidate=on [PPC/PSERIES] 5613 Disable RADIX GTSE feature and use hcall for TLB 5614 invalidate. 5615 5616 raid= [HW,RAID] 5617 See Documentation/admin-guide/md.rst. 5618 5619 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5620 See Documentation/admin-guide/blockdev/ramdisk.rst. 5621 5622 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5623 5624 random.trust_cpu=off 5625 [KNL,EARLY] Disable trusting the use of the CPU's 5626 random number generator (if available) to 5627 initialize the kernel's RNG. 5628 5629 random.trust_bootloader=off 5630 [KNL,EARLY] Disable trusting the use of the a seed 5631 passed by the bootloader (if available) to 5632 initialize the kernel's RNG. 5633 5634 randomize_kstack_offset= 5635 [KNL,EARLY] Enable or disable kernel stack offset 5636 randomization, which provides roughly 5 bits of 5637 entropy, frustrating memory corruption attacks 5638 that depend on stack address determinism or 5639 cross-syscall address exposures. This is only 5640 available on architectures that have defined 5641 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5642 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5643 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5644 5645 ras=option[,option,...] [KNL] RAS-specific options 5646 5647 cec_disable [X86] 5648 Disable the Correctable Errors Collector, 5649 see CONFIG_RAS_CEC help text. 5650 5651 rcu_nocbs[=cpu-list] 5652 [KNL] The optional argument is a cpu list, 5653 as described above. 5654 5655 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5656 enable the no-callback CPU mode, which prevents 5657 such CPUs' callbacks from being invoked in 5658 softirq context. Invocation of such CPUs' RCU 5659 callbacks will instead be offloaded to "rcuox/N" 5660 kthreads created for that purpose, where "x" is 5661 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5662 for the kthreads that mediate grace periods; and 5663 "N" is the CPU number. This reduces OS jitter on 5664 the offloaded CPUs, which can be useful for HPC 5665 and real-time workloads. It can also improve 5666 energy efficiency for asymmetric multiprocessors. 5667 5668 If a cpulist is passed as an argument, the specified 5669 list of CPUs is set to no-callback mode from boot. 5670 5671 Otherwise, if the '=' sign and the cpulist 5672 arguments are omitted, no CPU will be set to 5673 no-callback mode from boot but the mode may be 5674 toggled at runtime via cpusets. 5675 5676 Note that this argument takes precedence over 5677 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5678 5679 rcu_nocb_poll [KNL] 5680 Rather than requiring that offloaded CPUs 5681 (specified by rcu_nocbs= above) explicitly 5682 awaken the corresponding "rcuoN" kthreads, 5683 make these kthreads poll for callbacks. 5684 This improves the real-time response for the 5685 offloaded CPUs by relieving them of the need to 5686 wake up the corresponding kthread, but degrades 5687 energy efficiency by requiring that the kthreads 5688 periodically wake up to do the polling. 5689 5690 rcutree.blimit= [KNL] 5691 Set maximum number of finished RCU callbacks to 5692 process in one batch. 5693 5694 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5695 Do only a one-line RCU CPU stall warning when 5696 there is an ongoing too-long CSD-lock wait. 5697 5698 rcutree.do_rcu_barrier= [KNL] 5699 Request a call to rcu_barrier(). This is 5700 throttled so that userspace tests can safely 5701 hammer on the sysfs variable if they so choose. 5702 If triggered before the RCU grace-period machinery 5703 is fully active, this will error out with EAGAIN. 5704 5705 rcutree.dump_tree= [KNL] 5706 Dump the structure of the rcu_node combining tree 5707 out at early boot. This is used for diagnostic 5708 purposes, to verify correct tree setup. 5709 5710 rcutree.gp_cleanup_delay= [KNL] 5711 Set the number of jiffies to delay each step of 5712 RCU grace-period cleanup. 5713 5714 rcutree.gp_init_delay= [KNL] 5715 Set the number of jiffies to delay each step of 5716 RCU grace-period initialization. 5717 5718 rcutree.gp_preinit_delay= [KNL] 5719 Set the number of jiffies to delay each step of 5720 RCU grace-period pre-initialization, that is, 5721 the propagation of recent CPU-hotplug changes up 5722 the rcu_node combining tree. 5723 5724 rcutree.jiffies_till_first_fqs= [KNL] 5725 Set delay from grace-period initialization to 5726 first attempt to force quiescent states. 5727 Units are jiffies, minimum value is zero, 5728 and maximum value is HZ. 5729 5730 rcutree.jiffies_till_next_fqs= [KNL] 5731 Set delay between subsequent attempts to force 5732 quiescent states. Units are jiffies, minimum 5733 value is one, and maximum value is HZ. 5734 5735 rcutree.jiffies_till_sched_qs= [KNL] 5736 Set required age in jiffies for a 5737 given grace period before RCU starts 5738 soliciting quiescent-state help from 5739 rcu_note_context_switch() and cond_resched(). 5740 If not specified, the kernel will calculate 5741 a value based on the most recent settings 5742 of rcutree.jiffies_till_first_fqs 5743 and rcutree.jiffies_till_next_fqs. 5744 This calculated value may be viewed in 5745 rcutree.jiffies_to_sched_qs. Any attempt to set 5746 rcutree.jiffies_to_sched_qs will be cheerfully 5747 overwritten. 5748 5749 rcutree.kthread_prio= [KNL,BOOT] 5750 Set the SCHED_FIFO priority of the RCU per-CPU 5751 kthreads (rcuc/N). This value is also used for 5752 the priority of the RCU boost threads (rcub/N) 5753 and for the RCU grace-period kthreads (rcu_bh, 5754 rcu_preempt, and rcu_sched). If RCU_BOOST is 5755 set, valid values are 1-99 and the default is 1 5756 (the least-favored priority). Otherwise, when 5757 RCU_BOOST is not set, valid values are 0-99 and 5758 the default is zero (non-realtime operation). 5759 When RCU_NOCB_CPU is set, also adjust the 5760 priority of NOCB callback kthreads. 5761 5762 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5763 On callback-offloaded (rcu_nocbs) CPUs, 5764 RCU reduces the lock contention that would 5765 otherwise be caused by callback floods through 5766 use of the ->nocb_bypass list. However, in the 5767 common non-flooded case, RCU queues directly to 5768 the main ->cblist in order to avoid the extra 5769 overhead of the ->nocb_bypass list and its lock. 5770 But if there are too many callbacks queued during 5771 a single jiffy, RCU pre-queues the callbacks into 5772 the ->nocb_bypass queue. The definition of "too 5773 many" is supplied by this kernel boot parameter. 5774 5775 rcutree.nohz_full_patience_delay= [KNL] 5776 On callback-offloaded (rcu_nocbs) CPUs, avoid 5777 disturbing RCU unless the grace period has 5778 reached the specified age in milliseconds. 5779 Defaults to zero. Large values will be capped 5780 at five seconds. All values will be rounded down 5781 to the nearest value representable by jiffies. 5782 5783 rcutree.qhimark= [KNL] 5784 Set threshold of queued RCU callbacks beyond which 5785 batch limiting is disabled. 5786 5787 rcutree.qlowmark= [KNL] 5788 Set threshold of queued RCU callbacks below which 5789 batch limiting is re-enabled. 5790 5791 rcutree.qovld= [KNL] 5792 Set threshold of queued RCU callbacks beyond which 5793 RCU's force-quiescent-state scan will aggressively 5794 enlist help from cond_resched() and sched IPIs to 5795 help CPUs more quickly reach quiescent states. 5796 Set to less than zero to make this be set based 5797 on rcutree.qhimark at boot time and to zero to 5798 disable more aggressive help enlistment. 5799 5800 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5801 Set the page-cache refill delay (in milliseconds) 5802 in response to low-memory conditions. The range 5803 of permitted values is in the range 0:100000. 5804 5805 rcutree.rcu_divisor= [KNL] 5806 Set the shift-right count to use to compute 5807 the callback-invocation batch limit bl from 5808 the number of callbacks queued on this CPU. 5809 The result will be bounded below by the value of 5810 the rcutree.blimit kernel parameter. Every bl 5811 callbacks, the softirq handler will exit in 5812 order to allow the CPU to do other work. 5813 5814 Please note that this callback-invocation batch 5815 limit applies only to non-offloaded callback 5816 invocation. Offloaded callbacks are instead 5817 invoked in the context of an rcuoc kthread, which 5818 scheduler will preempt as it does any other task. 5819 5820 rcutree.rcu_fanout_exact= [KNL] 5821 Disable autobalancing of the rcu_node combining 5822 tree. This is used by rcutorture, and might 5823 possibly be useful for architectures having high 5824 cache-to-cache transfer latencies. 5825 5826 rcutree.rcu_fanout_leaf= [KNL] 5827 Change the number of CPUs assigned to each 5828 leaf rcu_node structure. Useful for very 5829 large systems, which will choose the value 64, 5830 and for NUMA systems with large remote-access 5831 latencies, which will choose a value aligned 5832 with the appropriate hardware boundaries. 5833 5834 rcutree.rcu_min_cached_objs= [KNL] 5835 Minimum number of objects which are cached and 5836 maintained per one CPU. Object size is equal 5837 to PAGE_SIZE. The cache allows to reduce the 5838 pressure to page allocator, also it makes the 5839 whole algorithm to behave better in low memory 5840 condition. 5841 5842 rcutree.rcu_nocb_gp_stride= [KNL] 5843 Set the number of NOCB callback kthreads in 5844 each group, which defaults to the square root 5845 of the number of CPUs. Larger numbers reduce 5846 the wakeup overhead on the global grace-period 5847 kthread, but increases that same overhead on 5848 each group's NOCB grace-period kthread. 5849 5850 rcutree.rcu_kick_kthreads= [KNL] 5851 Cause the grace-period kthread to get an extra 5852 wake_up() if it sleeps three times longer than 5853 it should at force-quiescent-state time. 5854 This wake_up() will be accompanied by a 5855 WARN_ONCE() splat and an ftrace_dump(). 5856 5857 rcutree.rcu_resched_ns= [KNL] 5858 Limit the time spend invoking a batch of RCU 5859 callbacks to the specified number of nanoseconds. 5860 By default, this limit is checked only once 5861 every 32 callbacks in order to limit the pain 5862 inflicted by local_clock() overhead. 5863 5864 rcutree.rcu_unlock_delay= [KNL] 5865 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5866 this specifies an rcu_read_unlock()-time delay 5867 in microseconds. This defaults to zero. 5868 Larger delays increase the probability of 5869 catching RCU pointer leaks, that is, buggy use 5870 of RCU-protected pointers after the relevant 5871 rcu_read_unlock() has completed. 5872 5873 rcutree.sysrq_rcu= [KNL] 5874 Commandeer a sysrq key to dump out Tree RCU's 5875 rcu_node tree with an eye towards determining 5876 why a new grace period has not yet started. 5877 5878 rcutree.use_softirq= [KNL] 5879 If set to zero, move all RCU_SOFTIRQ processing to 5880 per-CPU rcuc kthreads. Defaults to a non-zero 5881 value, meaning that RCU_SOFTIRQ is used by default. 5882 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5883 5884 But note that CONFIG_PREEMPT_RT=y kernels disable 5885 this kernel boot parameter, forcibly setting it 5886 to zero. 5887 5888 rcutree.enable_rcu_lazy= [KNL] 5889 To save power, batch RCU callbacks and flush after 5890 delay, memory pressure or callback list growing too 5891 big. 5892 5893 rcutree.rcu_normal_wake_from_gp= [KNL] 5894 Reduces a latency of synchronize_rcu() call. This approach 5895 maintains its own track of synchronize_rcu() callers, so it 5896 does not interact with regular callbacks because it does not 5897 use a call_rcu[_hurry]() path. Please note, this is for a 5898 normal grace period. 5899 5900 How to enable it: 5901 5902 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5903 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5904 5905 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5906 disabled by the boot parameter passing 0. 5907 5908 rcuscale.gp_async= [KNL] 5909 Measure performance of asynchronous 5910 grace-period primitives such as call_rcu(). 5911 5912 rcuscale.gp_async_max= [KNL] 5913 Specify the maximum number of outstanding 5914 callbacks per writer thread. When a writer 5915 thread exceeds this limit, it invokes the 5916 corresponding flavor of rcu_barrier() to allow 5917 previously posted callbacks to drain. 5918 5919 rcuscale.gp_exp= [KNL] 5920 Measure performance of expedited synchronous 5921 grace-period primitives. 5922 5923 rcuscale.holdoff= [KNL] 5924 Set test-start holdoff period. The purpose of 5925 this parameter is to delay the start of the 5926 test until boot completes in order to avoid 5927 interference. 5928 5929 rcuscale.kfree_by_call_rcu= [KNL] 5930 In kernels built with CONFIG_RCU_LAZY=y, test 5931 call_rcu() instead of kfree_rcu(). 5932 5933 rcuscale.kfree_mult= [KNL] 5934 Instead of allocating an object of size kfree_obj, 5935 allocate one of kfree_mult * sizeof(kfree_obj). 5936 Defaults to 1. 5937 5938 rcuscale.kfree_rcu_test= [KNL] 5939 Set to measure performance of kfree_rcu() flooding. 5940 5941 rcuscale.kfree_rcu_test_double= [KNL] 5942 Test the double-argument variant of kfree_rcu(). 5943 If this parameter has the same value as 5944 rcuscale.kfree_rcu_test_single, both the single- 5945 and double-argument variants are tested. 5946 5947 rcuscale.kfree_rcu_test_single= [KNL] 5948 Test the single-argument variant of kfree_rcu(). 5949 If this parameter has the same value as 5950 rcuscale.kfree_rcu_test_double, both the single- 5951 and double-argument variants are tested. 5952 5953 rcuscale.kfree_nthreads= [KNL] 5954 The number of threads running loops of kfree_rcu(). 5955 5956 rcuscale.kfree_alloc_num= [KNL] 5957 Number of allocations and frees done in an iteration. 5958 5959 rcuscale.kfree_loops= [KNL] 5960 Number of loops doing rcuscale.kfree_alloc_num number 5961 of allocations and frees. 5962 5963 rcuscale.minruntime= [KNL] 5964 Set the minimum test run time in seconds. This 5965 does not affect the data-collection interval, 5966 but instead allows better measurement of things 5967 like CPU consumption. 5968 5969 rcuscale.nreaders= [KNL] 5970 Set number of RCU readers. The value -1 selects 5971 N, where N is the number of CPUs. A value 5972 "n" less than -1 selects N-n+1, where N is again 5973 the number of CPUs. For example, -2 selects N 5974 (the number of CPUs), -3 selects N+1, and so on. 5975 A value of "n" less than or equal to -N selects 5976 a single reader. 5977 5978 rcuscale.nwriters= [KNL] 5979 Set number of RCU writers. The values operate 5980 the same as for rcuscale.nreaders. 5981 N, where N is the number of CPUs 5982 5983 rcuscale.scale_type= [KNL] 5984 Specify the RCU implementation to test. 5985 5986 rcuscale.shutdown= [KNL] 5987 Shut the system down after performance tests 5988 complete. This is useful for hands-off automated 5989 testing. 5990 5991 rcuscale.verbose= [KNL] 5992 Enable additional printk() statements. 5993 5994 rcuscale.writer_holdoff= [KNL] 5995 Write-side holdoff between grace periods, 5996 in microseconds. The default of zero says 5997 no holdoff. 5998 5999 rcuscale.writer_holdoff_jiffies= [KNL] 6000 Additional write-side holdoff between grace 6001 periods, but in jiffies. The default of zero 6002 says no holdoff. 6003 6004 rcutorture.fqs_duration= [KNL] 6005 Set duration of force_quiescent_state bursts 6006 in microseconds. 6007 6008 rcutorture.fqs_holdoff= [KNL] 6009 Set holdoff time within force_quiescent_state bursts 6010 in microseconds. 6011 6012 rcutorture.fqs_stutter= [KNL] 6013 Set wait time between force_quiescent_state bursts 6014 in seconds. 6015 6016 rcutorture.fwd_progress= [KNL] 6017 Specifies the number of kthreads to be used 6018 for RCU grace-period forward-progress testing 6019 for the types of RCU supporting this notion. 6020 Defaults to 1 kthread, values less than zero or 6021 greater than the number of CPUs cause the number 6022 of CPUs to be used. 6023 6024 rcutorture.fwd_progress_div= [KNL] 6025 Specify the fraction of a CPU-stall-warning 6026 period to do tight-loop forward-progress testing. 6027 6028 rcutorture.fwd_progress_holdoff= [KNL] 6029 Number of seconds to wait between successive 6030 forward-progress tests. 6031 6032 rcutorture.fwd_progress_need_resched= [KNL] 6033 Enclose cond_resched() calls within checks for 6034 need_resched() during tight-loop forward-progress 6035 testing. 6036 6037 rcutorture.gp_cond= [KNL] 6038 Use conditional/asynchronous update-side 6039 normal-grace-period primitives, if available. 6040 6041 rcutorture.gp_cond_exp= [KNL] 6042 Use conditional/asynchronous update-side 6043 expedited-grace-period primitives, if available. 6044 6045 rcutorture.gp_cond_full= [KNL] 6046 Use conditional/asynchronous update-side 6047 normal-grace-period primitives that also take 6048 concurrent expedited grace periods into account, 6049 if available. 6050 6051 rcutorture.gp_cond_exp_full= [KNL] 6052 Use conditional/asynchronous update-side 6053 expedited-grace-period primitives that also take 6054 concurrent normal grace periods into account, 6055 if available. 6056 6057 rcutorture.gp_cond_wi= [KNL] 6058 Nominal wait interval for normal conditional 6059 grace periods (specified by rcutorture's 6060 gp_cond and gp_cond_full module parameters), 6061 in microseconds. The actual wait interval will 6062 be randomly selected to nanosecond granularity up 6063 to this wait interval. Defaults to 16 jiffies, 6064 for example, 16,000 microseconds on a system 6065 with HZ=1000. 6066 6067 rcutorture.gp_cond_wi_exp= [KNL] 6068 Nominal wait interval for expedited conditional 6069 grace periods (specified by rcutorture's 6070 gp_cond_exp and gp_cond_exp_full module 6071 parameters), in microseconds. The actual wait 6072 interval will be randomly selected to nanosecond 6073 granularity up to this wait interval. Defaults to 6074 128 microseconds. 6075 6076 rcutorture.gp_exp= [KNL] 6077 Use expedited update-side primitives, if available. 6078 6079 rcutorture.gp_normal= [KNL] 6080 Use normal (non-expedited) asynchronous 6081 update-side primitives, if available. 6082 6083 rcutorture.gp_poll= [KNL] 6084 Use polled update-side normal-grace-period 6085 primitives, if available. 6086 6087 rcutorture.gp_poll_exp= [KNL] 6088 Use polled update-side expedited-grace-period 6089 primitives, if available. 6090 6091 rcutorture.gp_poll_full= [KNL] 6092 Use polled update-side normal-grace-period 6093 primitives that also take concurrent expedited 6094 grace periods into account, if available. 6095 6096 rcutorture.gp_poll_exp_full= [KNL] 6097 Use polled update-side expedited-grace-period 6098 primitives that also take concurrent normal 6099 grace periods into account, if available. 6100 6101 rcutorture.gp_poll_wi= [KNL] 6102 Nominal wait interval for normal conditional 6103 grace periods (specified by rcutorture's 6104 gp_poll and gp_poll_full module parameters), 6105 in microseconds. The actual wait interval will 6106 be randomly selected to nanosecond granularity up 6107 to this wait interval. Defaults to 16 jiffies, 6108 for example, 16,000 microseconds on a system 6109 with HZ=1000. 6110 6111 rcutorture.gp_poll_wi_exp= [KNL] 6112 Nominal wait interval for expedited conditional 6113 grace periods (specified by rcutorture's 6114 gp_poll_exp and gp_poll_exp_full module 6115 parameters), in microseconds. The actual wait 6116 interval will be randomly selected to nanosecond 6117 granularity up to this wait interval. Defaults to 6118 128 microseconds. 6119 6120 rcutorture.gp_sync= [KNL] 6121 Use normal (non-expedited) synchronous 6122 update-side primitives, if available. If all 6123 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6124 rcutorture.gp_normal=, and rcutorture.gp_sync= 6125 are zero, rcutorture acts as if is interpreted 6126 they are all non-zero. 6127 6128 rcutorture.gpwrap_lag= [KNL] 6129 Enable grace-period wrap lag testing. Setting 6130 to false prevents the gpwrap lag test from 6131 running. Default is true. 6132 6133 rcutorture.gpwrap_lag_gps= [KNL] 6134 Set the value for grace-period wrap lag during 6135 active lag testing periods. This controls how many 6136 grace periods differences we tolerate between 6137 rdp and rnp's gp_seq before setting overflow flag. 6138 The default is always set to 8. 6139 6140 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6141 Set the total cycle duration for gpwrap lag 6142 testing in minutes. This is the total time for 6143 one complete cycle of active and inactive 6144 testing periods. Default is 30 minutes. 6145 6146 rcutorture.gpwrap_lag_active_mins= [KNL] 6147 Set the duration for which gpwrap lag is active 6148 within each cycle, in minutes. During this time, 6149 the grace-period wrap lag will be set to the 6150 value specified by gpwrap_lag_gps. Default is 6151 5 minutes. 6152 6153 rcutorture.irqreader= [KNL] 6154 Run RCU readers from irq handlers, or, more 6155 accurately, from a timer handler. Not all RCU 6156 flavors take kindly to this sort of thing. 6157 6158 rcutorture.leakpointer= [KNL] 6159 Leak an RCU-protected pointer out of the reader. 6160 This can of course result in splats, and is 6161 intended to test the ability of things like 6162 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6163 such leaks. 6164 6165 rcutorture.n_barrier_cbs= [KNL] 6166 Set callbacks/threads for rcu_barrier() testing. 6167 6168 rcutorture.nfakewriters= [KNL] 6169 Set number of concurrent RCU writers. These just 6170 stress RCU, they don't participate in the actual 6171 test, hence the "fake". 6172 6173 rcutorture.nocbs_nthreads= [KNL] 6174 Set number of RCU callback-offload togglers. 6175 Zero (the default) disables toggling. 6176 6177 rcutorture.nocbs_toggle= [KNL] 6178 Set the delay in milliseconds between successive 6179 callback-offload toggling attempts. 6180 6181 rcutorture.nreaders= [KNL] 6182 Set number of RCU readers. The value -1 selects 6183 N-1, where N is the number of CPUs. A value 6184 "n" less than -1 selects N-n-2, where N is again 6185 the number of CPUs. For example, -2 selects N 6186 (the number of CPUs), -3 selects N+1, and so on. 6187 6188 rcutorture.object_debug= [KNL] 6189 Enable debug-object double-call_rcu() testing. 6190 6191 rcutorture.onoff_holdoff= [KNL] 6192 Set time (s) after boot for CPU-hotplug testing. 6193 6194 rcutorture.onoff_interval= [KNL] 6195 Set time (jiffies) between CPU-hotplug operations, 6196 or zero to disable CPU-hotplug testing. 6197 6198 rcutorture.preempt_duration= [KNL] 6199 Set duration (in milliseconds) of preemptions 6200 by a high-priority FIFO real-time task. Set to 6201 zero (the default) to disable. The CPUs to 6202 preempt are selected randomly from the set that 6203 are online at a given point in time. Races with 6204 CPUs going offline are ignored, with that attempt 6205 at preemption skipped. 6206 6207 rcutorture.preempt_interval= [KNL] 6208 Set interval (in milliseconds, defaulting to one 6209 second) between preemptions by a high-priority 6210 FIFO real-time task. This delay is mediated 6211 by an hrtimer and is further fuzzed to avoid 6212 inadvertent synchronizations. 6213 6214 rcutorture.read_exit_burst= [KNL] 6215 The number of times in a given read-then-exit 6216 episode that a set of read-then-exit kthreads 6217 is spawned. 6218 6219 rcutorture.read_exit_delay= [KNL] 6220 The delay, in seconds, between successive 6221 read-then-exit testing episodes. 6222 6223 rcutorture.reader_flavor= [KNL] 6224 A bit mask indicating which readers to use. 6225 If there is more than one bit set, the readers 6226 are entered from low-order bit up, and are 6227 exited in the opposite order. For SRCU, the 6228 0x1 bit is normal readers, 0x2 NMI-safe readers, 6229 and 0x4 light-weight readers. 6230 6231 rcutorture.shuffle_interval= [KNL] 6232 Set task-shuffle interval (s). Shuffling tasks 6233 allows some CPUs to go into dyntick-idle mode 6234 during the rcutorture test. 6235 6236 rcutorture.shutdown_secs= [KNL] 6237 Set time (s) after boot system shutdown. This 6238 is useful for hands-off automated testing. 6239 6240 rcutorture.stall_cpu= [KNL] 6241 Duration of CPU stall (s) to test RCU CPU stall 6242 warnings, zero to disable. 6243 6244 rcutorture.stall_cpu_block= [KNL] 6245 Sleep while stalling if set. This will result 6246 in warnings from preemptible RCU in addition to 6247 any other stall-related activity. Note that 6248 in kernels built with CONFIG_PREEMPTION=n and 6249 CONFIG_PREEMPT_COUNT=y, this parameter will 6250 cause the CPU to pass through a quiescent state. 6251 Given CONFIG_PREEMPTION=n, this will suppress 6252 RCU CPU stall warnings, but will instead result 6253 in scheduling-while-atomic splats. 6254 6255 Use of this module parameter results in splats. 6256 6257 6258 rcutorture.stall_cpu_holdoff= [KNL] 6259 Time to wait (s) after boot before inducing stall. 6260 6261 rcutorture.stall_cpu_irqsoff= [KNL] 6262 Disable interrupts while stalling if set, but only 6263 on the first stall in the set. 6264 6265 rcutorture.stall_cpu_repeat= [KNL] 6266 Number of times to repeat the stall sequence, 6267 so that rcutorture.stall_cpu_repeat=3 will result 6268 in four stall sequences. 6269 6270 rcutorture.stall_gp_kthread= [KNL] 6271 Duration (s) of forced sleep within RCU 6272 grace-period kthread to test RCU CPU stall 6273 warnings, zero to disable. If both stall_cpu 6274 and stall_gp_kthread are specified, the 6275 kthread is starved first, then the CPU. 6276 6277 rcutorture.stat_interval= [KNL] 6278 Time (s) between statistics printk()s. 6279 6280 rcutorture.stutter= [KNL] 6281 Time (s) to stutter testing, for example, specifying 6282 five seconds causes the test to run for five seconds, 6283 wait for five seconds, and so on. This tests RCU's 6284 ability to transition abruptly to and from idle. 6285 6286 rcutorture.test_boost= [KNL] 6287 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6288 "Maybe" means test if the RCU implementation 6289 under test support RCU priority boosting. 6290 6291 rcutorture.test_boost_duration= [KNL] 6292 Duration (s) of each individual boost test. 6293 6294 rcutorture.test_boost_holdoff= [KNL] 6295 Holdoff time (s) from start of test to the start 6296 of RCU priority-boost testing. Defaults to zero, 6297 that is, no holdoff. 6298 6299 rcutorture.test_boost_interval= [KNL] 6300 Interval (s) between each boost test. 6301 6302 rcutorture.test_no_idle_hz= [KNL] 6303 Test RCU's dyntick-idle handling. See also the 6304 rcutorture.shuffle_interval parameter. 6305 6306 rcutorture.torture_type= [KNL] 6307 Specify the RCU implementation to test. 6308 6309 rcutorture.verbose= [KNL] 6310 Enable additional printk() statements. 6311 6312 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6313 Dump ftrace buffer after reporting RCU CPU 6314 stall warning. 6315 6316 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6317 Provide RCU CPU stall notifiers, but see the 6318 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6319 option's help text. TL;DR: You almost certainly 6320 do not want rcupdate.rcu_cpu_stall_notifiers. 6321 6322 rcupdate.rcu_cpu_stall_suppress= [KNL] 6323 Suppress RCU CPU stall warning messages. 6324 6325 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6326 Suppress RCU CPU stall warning messages and 6327 rcutorture writer stall warnings that occur 6328 during early boot, that is, during the time 6329 before the init task is spawned. 6330 6331 rcupdate.rcu_cpu_stall_timeout= [KNL] 6332 Set timeout for RCU CPU stall warning messages. 6333 The value is in seconds and the maximum allowed 6334 value is 300 seconds. 6335 6336 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6337 Set timeout for expedited RCU CPU stall warning 6338 messages. The value is in milliseconds 6339 and the maximum allowed value is 21000 6340 milliseconds. Please note that this value is 6341 adjusted to an arch timer tick resolution. 6342 Setting this to zero causes the value from 6343 rcupdate.rcu_cpu_stall_timeout to be used (after 6344 conversion from seconds to milliseconds). 6345 6346 rcupdate.rcu_cpu_stall_cputime= [KNL] 6347 Provide statistics on the cputime and count of 6348 interrupts and tasks during the sampling period. For 6349 multiple continuous RCU stalls, all sampling periods 6350 begin at half of the first RCU stall timeout. 6351 6352 rcupdate.rcu_exp_stall_task_details= [KNL] 6353 Print stack dumps of any tasks blocking the 6354 current expedited RCU grace period during an 6355 expedited RCU CPU stall warning. 6356 6357 rcupdate.rcu_expedited= [KNL] 6358 Use expedited grace-period primitives, for 6359 example, synchronize_rcu_expedited() instead 6360 of synchronize_rcu(). This reduces latency, 6361 but can increase CPU utilization, degrade 6362 real-time latency, and degrade energy efficiency. 6363 No effect on CONFIG_TINY_RCU kernels. 6364 6365 rcupdate.rcu_normal= [KNL] 6366 Use only normal grace-period primitives, 6367 for example, synchronize_rcu() instead of 6368 synchronize_rcu_expedited(). This improves 6369 real-time latency, CPU utilization, and 6370 energy efficiency, but can expose users to 6371 increased grace-period latency. This parameter 6372 overrides rcupdate.rcu_expedited. No effect on 6373 CONFIG_TINY_RCU kernels. 6374 6375 rcupdate.rcu_normal_after_boot= [KNL] 6376 Once boot has completed (that is, after 6377 rcu_end_inkernel_boot() has been invoked), use 6378 only normal grace-period primitives. No effect 6379 on CONFIG_TINY_RCU kernels. 6380 6381 But note that CONFIG_PREEMPT_RT=y kernels enables 6382 this kernel boot parameter, forcibly setting 6383 it to the value one, that is, converting any 6384 post-boot attempt at an expedited RCU grace 6385 period to instead use normal non-expedited 6386 grace-period processing. 6387 6388 rcupdate.rcu_task_collapse_lim= [KNL] 6389 Set the maximum number of callbacks present 6390 at the beginning of a grace period that allows 6391 the RCU Tasks flavors to collapse back to using 6392 a single callback queue. This switching only 6393 occurs when rcupdate.rcu_task_enqueue_lim is 6394 set to the default value of -1. 6395 6396 rcupdate.rcu_task_contend_lim= [KNL] 6397 Set the minimum number of callback-queuing-time 6398 lock-contention events per jiffy required to 6399 cause the RCU Tasks flavors to switch to per-CPU 6400 callback queuing. This switching only occurs 6401 when rcupdate.rcu_task_enqueue_lim is set to 6402 the default value of -1. 6403 6404 rcupdate.rcu_task_enqueue_lim= [KNL] 6405 Set the number of callback queues to use for the 6406 RCU Tasks family of RCU flavors. The default 6407 of -1 allows this to be automatically (and 6408 dynamically) adjusted. This parameter is intended 6409 for use in testing. 6410 6411 rcupdate.rcu_task_lazy_lim= [KNL] 6412 Number of callbacks on a given CPU that will 6413 cancel laziness on that CPU. Use -1 to disable 6414 cancellation of laziness, but be advised that 6415 doing so increases the danger of OOM due to 6416 callback flooding. 6417 6418 rcupdate.rcu_task_stall_info= [KNL] 6419 Set initial timeout in jiffies for RCU task stall 6420 informational messages, which give some indication 6421 of the problem for those not patient enough to 6422 wait for ten minutes. Informational messages are 6423 only printed prior to the stall-warning message 6424 for a given grace period. Disable with a value 6425 less than or equal to zero. Defaults to ten 6426 seconds. A change in value does not take effect 6427 until the beginning of the next grace period. 6428 6429 rcupdate.rcu_task_stall_info_mult= [KNL] 6430 Multiplier for time interval between successive 6431 RCU task stall informational messages for a given 6432 RCU tasks grace period. This value is clamped 6433 to one through ten, inclusive. It defaults to 6434 the value three, so that the first informational 6435 message is printed 10 seconds into the grace 6436 period, the second at 40 seconds, the third at 6437 160 seconds, and then the stall warning at 600 6438 seconds would prevent a fourth at 640 seconds. 6439 6440 rcupdate.rcu_task_stall_timeout= [KNL] 6441 Set timeout in jiffies for RCU task stall 6442 warning messages. Disable with a value less 6443 than or equal to zero. Defaults to ten minutes. 6444 A change in value does not take effect until 6445 the beginning of the next grace period. 6446 6447 rcupdate.rcu_tasks_lazy_ms= [KNL] 6448 Set timeout in milliseconds RCU Tasks asynchronous 6449 callback batching for call_rcu_tasks(). 6450 A negative value will take the default. A value 6451 of zero will disable batching. Batching is 6452 always disabled for synchronize_rcu_tasks(). 6453 6454 rcupdate.rcu_self_test= [KNL] 6455 Run the RCU early boot self tests 6456 6457 rdinit= [KNL] 6458 Format: <full_path> 6459 Run specified binary instead of /init from the ramdisk, 6460 used for early userspace startup. See initrd. 6461 6462 rdrand= [X86,EARLY] 6463 force - Override the decision by the kernel to hide the 6464 advertisement of RDRAND support (this affects 6465 certain AMD processors because of buggy BIOS 6466 support, specifically around the suspend/resume 6467 path). 6468 6469 rdt= [HW,X86,RDT] 6470 Turn on/off individual RDT features. List is: 6471 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6472 mba, smba, bmec, abmc, sdciae, energy[:guid], 6473 perf[:guid]. 6474 E.g. to turn on cmt and turn off mba use: 6475 rdt=cmt,!mba 6476 To turn off all energy telemetry monitoring and ensure that 6477 perf telemetry monitoring associated with guid 0x12345 6478 is enabled use: 6479 rdt=!energy,perf:0x12345 6480 6481 reboot= [KNL] 6482 Format (x86 or x86_64): 6483 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6484 [[,]s[mp]#### \ 6485 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6486 [[,]f[orce] 6487 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6488 (prefix with 'panic_' to set mode for panic 6489 reboot only), 6490 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6491 reboot_force is either force or not specified, 6492 reboot_cpu is s[mp]#### with #### being the processor 6493 to be used for rebooting. 6494 6495 acpi 6496 Use the ACPI RESET_REG in the FADT. If ACPI is not 6497 configured or the ACPI reset does not work, the reboot 6498 path attempts the reset using the keyboard controller. 6499 6500 bios 6501 Use the CPU reboot vector for warm reset 6502 6503 cold 6504 Set the cold reboot flag 6505 6506 default 6507 There are some built-in platform specific "quirks" 6508 - you may see: "reboot: <name> series board detected. 6509 Selecting <type> for reboots." In the case where you 6510 think the quirk is in error (e.g. you have newer BIOS, 6511 or newer board) using this option will ignore the 6512 built-in quirk table, and use the generic default 6513 reboot actions. 6514 6515 efi 6516 Use efi reset_system runtime service. If EFI is not 6517 configured or the EFI reset does not work, the reboot 6518 path attempts the reset using the keyboard controller. 6519 6520 force 6521 Don't stop other CPUs on reboot. This can make reboot 6522 more reliable in some cases. 6523 6524 kbd 6525 Use the keyboard controller. cold reset (default) 6526 6527 pci 6528 Use a write to the PCI config space register 0xcf9 to 6529 trigger reboot. 6530 6531 triple 6532 Force a triple fault (init) 6533 6534 warm 6535 Don't set the cold reboot flag 6536 6537 Using warm reset will be much faster especially on big 6538 memory systems because the BIOS will not go through 6539 the memory check. Disadvantage is that not all 6540 hardware will be completely reinitialized on reboot so 6541 there may be boot problems on some systems. 6542 6543 6544 refscale.holdoff= [KNL] 6545 Set test-start holdoff period. The purpose of 6546 this parameter is to delay the start of the 6547 test until boot completes in order to avoid 6548 interference. 6549 6550 refscale.lookup_instances= [KNL] 6551 Number of data elements to use for the forms of 6552 SLAB_TYPESAFE_BY_RCU testing. A negative number 6553 is negated and multiplied by nr_cpu_ids, while 6554 zero specifies nr_cpu_ids. 6555 6556 refscale.loops= [KNL] 6557 Set the number of loops over the synchronization 6558 primitive under test. Increasing this number 6559 reduces noise due to loop start/end overhead, 6560 but the default has already reduced the per-pass 6561 noise to a handful of picoseconds on ca. 2020 6562 x86 laptops. 6563 6564 refscale.nreaders= [KNL] 6565 Set number of readers. The default value of -1 6566 selects N, where N is roughly 75% of the number 6567 of CPUs. A value of zero is an interesting choice. 6568 6569 refscale.nruns= [KNL] 6570 Set number of runs, each of which is dumped onto 6571 the console log. 6572 6573 refscale.readdelay= [KNL] 6574 Set the read-side critical-section duration, 6575 measured in microseconds. 6576 6577 refscale.scale_type= [KNL] 6578 Specify the read-protection implementation to test. 6579 6580 refscale.shutdown= [KNL] 6581 Shut down the system at the end of the performance 6582 test. This defaults to 1 (shut it down) when 6583 refscale is built into the kernel and to 0 (leave 6584 it running) when refscale is built as a module. 6585 6586 refscale.verbose= [KNL] 6587 Enable additional printk() statements. 6588 6589 refscale.verbose_batched= [KNL] 6590 Batch the additional printk() statements. If zero 6591 (the default) or negative, print everything. Otherwise, 6592 print every Nth verbose statement, where N is the value 6593 specified. 6594 6595 regulator_ignore_unused 6596 [REGULATOR] 6597 Prevents regulator framework from disabling regulators 6598 that are unused, due no driver claiming them. This may 6599 be useful for debug and development, but should not be 6600 needed on a platform with proper driver support. 6601 6602 relax_domain_level= 6603 [KNL, SMP] Set scheduler's default relax_domain_level. 6604 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6605 6606 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6607 Format: <base1>,<size1>[,<base2>,<size2>,...] 6608 Reserve I/O ports or memory so the kernel won't use 6609 them. If <base> is less than 0x10000, the region 6610 is assumed to be I/O ports; otherwise it is memory. 6611 6612 reserve_mem= [RAM] 6613 Format: nn[KMG]:<align>:<label> 6614 Reserve physical memory and label it with a name that 6615 other subsystems can use to access it. This is typically 6616 used for systems that do not wipe the RAM, and this command 6617 line will try to reserve the same physical memory on 6618 soft reboots. Note, it is not guaranteed to be the same 6619 location. For example, if anything about the system changes 6620 or if booting a different kernel. It can also fail if KASLR 6621 places the kernel at the location of where the RAM reservation 6622 was from a previous boot, the new reservation will be at a 6623 different location. 6624 Any subsystem using this feature must add a way to verify 6625 that the contents of the physical memory is from a previous 6626 boot, as there may be cases where the memory will not be 6627 located at the same location. 6628 6629 The format is size:align:label for example, to request 6630 12 megabytes of 4096 alignment for ramoops: 6631 6632 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6633 6634 reservetop= [X86-32,EARLY] 6635 Format: nn[KMG] 6636 Reserves a hole at the top of the kernel virtual 6637 address space. 6638 6639 reset_devices [KNL] Force drivers to reset the underlying device 6640 during initialization. 6641 6642 resume= [SWSUSP] 6643 Specify the partition device for software suspend 6644 Format: 6645 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6646 6647 resume_offset= [SWSUSP] 6648 Specify the offset from the beginning of the partition 6649 given by "resume=" at which the swap header is located, 6650 in <PAGE_SIZE> units (needed only for swap files). 6651 See Documentation/power/swsusp-and-swap-files.rst 6652 6653 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6654 read the resume files 6655 6656 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6657 Useful for devices that are detected asynchronously 6658 (e.g. USB and MMC devices). 6659 6660 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6661 be accessible via /sys/firmware/initrd. 6662 6663 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6664 Speculative Code Execution with Return Instructions) 6665 vulnerability. 6666 6667 AMD-based UNRET and IBPB mitigations alone do not stop 6668 sibling threads from influencing the predictions of other 6669 sibling threads. For that reason, STIBP is used on pro- 6670 cessors that support it, and mitigate SMT on processors 6671 that don't. 6672 6673 off - no mitigation 6674 auto - automatically select a mitigation 6675 auto,nosmt - automatically select a mitigation, 6676 disabling SMT if necessary for 6677 the full mitigation (only on Zen1 6678 and older without STIBP). 6679 ibpb - On AMD, mitigate short speculation 6680 windows on basic block boundaries too. 6681 Safe, highest perf impact. It also 6682 enables STIBP if present. Not suitable 6683 on Intel. 6684 ibpb,nosmt - Like "ibpb" above but will disable SMT 6685 when STIBP is not available. This is 6686 the alternative for systems which do not 6687 have STIBP. 6688 unret - Force enable untrained return thunks, 6689 only effective on AMD f15h-f17h based 6690 systems. 6691 unret,nosmt - Like unret, but will disable SMT when STIBP 6692 is not available. This is the alternative for 6693 systems which do not have STIBP. 6694 6695 Selecting 'auto' will choose a mitigation method at run 6696 time according to the CPU. 6697 6698 Not specifying this option is equivalent to retbleed=auto. 6699 6700 rfkill.default_state= 6701 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6702 etc. communication is blocked by default. 6703 1 Unblocked. 6704 6705 rfkill.master_switch_mode= 6706 0 The "airplane mode" button does nothing. 6707 1 The "airplane mode" button toggles between everything 6708 blocked and the previous configuration. 6709 2 The "airplane mode" button toggles between everything 6710 blocked and everything unblocked. 6711 6712 ring3mwait=disable 6713 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6714 CPUs. 6715 6716 riscv_isa_fallback [RISCV,EARLY] 6717 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6718 falling back to detecting extension support by parsing 6719 "riscv,isa" property on devicetree systems when the 6720 replacement properties are not found. See the Kconfig 6721 entry for RISCV_ISA_FALLBACK. 6722 6723 riscv_nousercfi= 6724 all Disable user CFI ABI to userspace even if cpu extension 6725 are available. 6726 bcfi Disable user backward CFI ABI to userspace even if 6727 the shadow stack extension is available. 6728 fcfi Disable user forward CFI ABI to userspace even if the 6729 landing pad extension is available. 6730 6731 ro [KNL] Mount root device read-only on boot 6732 6733 rodata= [KNL,EARLY] 6734 on Mark read-only kernel memory as read-only (default). 6735 off Leave read-only kernel memory writable for debugging. 6736 noalias Mark read-only kernel memory as read-only but retain 6737 writable aliases in the direct map for regions outside 6738 of the kernel image. [arm64] 6739 6740 rockchip.usb_uart 6741 [EARLY] 6742 Enable the uart passthrough on the designated usb port 6743 on Rockchip SoCs. When active, the signals of the 6744 debug-uart get routed to the D+ and D- pins of the usb 6745 port and the regular usb controller gets disabled. 6746 6747 root= [KNL] Root filesystem 6748 Usually this is a block device specifier of some kind, 6749 see the early_lookup_bdev comment in 6750 block/early-lookup.c for details. 6751 Alternatively this can be "ram" for the legacy initial 6752 ramdisk, "nfs" and "cifs" for root on a network file 6753 system, or "mtd" and "ubi" for mounting from raw flash. 6754 6755 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6756 mount the root filesystem 6757 6758 rootflags= [KNL] Set root filesystem mount option string 6759 6760 rseq_slice_ext= [KNL] RSEQ based time slice extension 6761 Format: boolean 6762 Control enablement of RSEQ based time slice extension. 6763 Default is 'on'. 6764 6765 initramfs_options= [KNL] 6766 Specify mount options for the initramfs mount. 6767 6768 rootfstype= [KNL] Set root filesystem type 6769 6770 rootwait [KNL] Wait (indefinitely) for root device to show up. 6771 Useful for devices that are detected asynchronously 6772 (e.g. USB and MMC devices). 6773 6774 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6775 to show up before attempting to mount the root 6776 filesystem. 6777 6778 rproc_mem=nn[KMG][@address] 6779 [KNL,ARM,CMA] Remoteproc physical memory block. 6780 Memory area to be used by remote processor image, 6781 managed by CMA. 6782 6783 rseq_debug= [KNL] Enable or disable restartable sequence 6784 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6785 Format: <bool> 6786 6787 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6788 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6789 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6790 Format: <bool> 6791 6792 rw [KNL] Mount root device read-write on boot 6793 6794 S [KNL] Run init in single mode 6795 6796 s390_iommu= [HW,S390] 6797 Set s390 IOTLB flushing mode 6798 strict 6799 With strict flushing every unmap operation will result 6800 in an IOTLB flush. Default is lazy flushing before 6801 reuse, which is faster. Deprecated, equivalent to 6802 iommu.strict=1. 6803 6804 s390_iommu_aperture= [KNL,S390] 6805 Specifies the size of the per device DMA address space 6806 accessible through the DMA and IOMMU APIs as a decimal 6807 factor of the size of main memory. 6808 The default is 1 meaning that one can concurrently use 6809 as many DMA addresses as physical memory is installed, 6810 if supported by hardware, and thus map all of memory 6811 once. With a value of 2 one can map all of memory twice 6812 and so on. As a special case a factor of 0 imposes no 6813 restrictions other than those given by hardware at the 6814 cost of significant additional memory use for tables. 6815 6816 sa1100ir [NET] 6817 See drivers/net/irda/sa1100_ir.c. 6818 6819 sched_proxy_exec= [KNL] 6820 Enables or disables "proxy execution" style 6821 solution to mutex-based priority inversion. 6822 Format: <bool> 6823 6824 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6825 6826 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6827 Allowed values are enable and disable. This feature 6828 incurs a small amount of overhead in the scheduler 6829 but is useful for debugging and performance tuning. 6830 6831 sched_thermal_decay_shift= 6832 [Deprecated] 6833 [KNL, SMP] Set a decay shift for scheduler thermal 6834 pressure signal. Thermal pressure signal follows the 6835 default decay period of other scheduler pelt 6836 signals(usually 32 ms but configurable). Setting 6837 sched_thermal_decay_shift will left shift the decay 6838 period for the thermal pressure signal by the shift 6839 value. 6840 i.e. with the default pelt decay period of 32 ms 6841 sched_thermal_decay_shift thermal pressure decay pr 6842 1 64 ms 6843 2 128 ms 6844 and so on. 6845 Format: integer between 0 and 10 6846 Default is 0. 6847 6848 scftorture.holdoff= [KNL] 6849 Number of seconds to hold off before starting 6850 test. Defaults to zero for module insertion and 6851 to 10 seconds for built-in smp_call_function() 6852 tests. 6853 6854 scftorture.longwait= [KNL] 6855 Request ridiculously long waits randomly selected 6856 up to the chosen limit in seconds. Zero (the 6857 default) disables this feature. Please note 6858 that requesting even small non-zero numbers of 6859 seconds can result in RCU CPU stall warnings, 6860 softlockup complaints, and so on. 6861 6862 scftorture.nthreads= [KNL] 6863 Number of kthreads to spawn to invoke the 6864 smp_call_function() family of functions. 6865 The default of -1 specifies a number of kthreads 6866 equal to the number of CPUs. 6867 6868 scftorture.onoff_holdoff= [KNL] 6869 Number seconds to wait after the start of the 6870 test before initiating CPU-hotplug operations. 6871 6872 scftorture.onoff_interval= [KNL] 6873 Number seconds to wait between successive 6874 CPU-hotplug operations. Specifying zero (which 6875 is the default) disables CPU-hotplug operations. 6876 6877 scftorture.shutdown_secs= [KNL] 6878 The number of seconds following the start of the 6879 test after which to shut down the system. The 6880 default of zero avoids shutting down the system. 6881 Non-zero values are useful for automated tests. 6882 6883 scftorture.stat_interval= [KNL] 6884 The number of seconds between outputting the 6885 current test statistics to the console. A value 6886 of zero disables statistics output. 6887 6888 scftorture.stutter_cpus= [KNL] 6889 The number of jiffies to wait between each change 6890 to the set of CPUs under test. 6891 6892 scftorture.use_cpus_read_lock= [KNL] 6893 Use use_cpus_read_lock() instead of the default 6894 preempt_disable() to disable CPU hotplug 6895 while invoking one of the smp_call_function*() 6896 functions. 6897 6898 scftorture.verbose= [KNL] 6899 Enable additional printk() statements. 6900 6901 scftorture.weight_single= [KNL] 6902 The probability weighting to use for the 6903 smp_call_function_single() function with a zero 6904 "wait" parameter. A value of -1 selects the 6905 default if all other weights are -1. However, 6906 if at least one weight has some other value, a 6907 value of -1 will instead select a weight of zero. 6908 6909 scftorture.weight_single_wait= [KNL] 6910 The probability weighting to use for the 6911 smp_call_function_single() function with a 6912 non-zero "wait" parameter. See weight_single. 6913 6914 scftorture.weight_many= [KNL] 6915 The probability weighting to use for the 6916 smp_call_function_many() function with a zero 6917 "wait" parameter. See weight_single. 6918 Note well that setting a high probability for 6919 this weighting can place serious IPI load 6920 on the system. 6921 6922 scftorture.weight_many_wait= [KNL] 6923 The probability weighting to use for the 6924 smp_call_function_many() function with a 6925 non-zero "wait" parameter. See weight_single 6926 and weight_many. 6927 6928 scftorture.weight_all= [KNL] 6929 The probability weighting to use for the 6930 smp_call_function_all() function with a zero 6931 "wait" parameter. See weight_single and 6932 weight_many. 6933 6934 scftorture.weight_all_wait= [KNL] 6935 The probability weighting to use for the 6936 smp_call_function_all() function with a 6937 non-zero "wait" parameter. See weight_single 6938 and weight_many. 6939 6940 sdw_mclk_divider=[SDW] 6941 Specify the MCLK divider for Intel SoundWire buses in 6942 case the BIOS does not provide the clock rate properly. 6943 6944 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6945 xtime_lock contention on larger systems, and/or RCU lock 6946 contention on all systems with CONFIG_MAXSMP set. 6947 Format: { "0" | "1" } 6948 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6949 1 -- enable. 6950 Note: increases power consumption, thus should only be 6951 enabled if running jitter sensitive (HPC/RT) workloads. 6952 6953 security= [SECURITY] Choose a legacy "major" security module to 6954 enable at boot. This has been deprecated by the 6955 "lsm=" parameter. 6956 6957 selinux= [SELINUX] Disable or enable SELinux at boot time. 6958 Format: { "0" | "1" } 6959 See security/selinux/Kconfig help text. 6960 0 -- disable. 6961 1 -- enable. 6962 Default value is 1. 6963 6964 serialnumber [BUGS=X86-32] 6965 6966 sev=option[,option...] [X86-64] 6967 6968 debug 6969 Enable debug messages. 6970 6971 nosnp 6972 Do not enable SEV-SNP (applies to host/hypervisor 6973 only). Setting 'nosnp' avoids the RMP check overhead 6974 in memory accesses when users do not want to run 6975 SEV-SNP guests. 6976 6977 shapers= [NET] 6978 Maximal number of shapers. 6979 6980 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6981 Limit apic dumping. The parameter defines the maximal 6982 number of local apics being dumped. Also it is possible 6983 to set it to "all" by meaning -- no limit here. 6984 Format: { 1 (default) | 2 | ... | all }. 6985 The parameter valid if only apic=debug or 6986 apic=verbose is specified. 6987 Example: apic=debug show_lapic=all 6988 6989 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6990 Enabling slab_debug allows one to determine the 6991 culprit if slab objects become corrupted. Enabling 6992 slab_debug can create guard zones around objects and 6993 may poison objects when not in use. Also tracks the 6994 last alloc / free. For more information see 6995 Documentation/admin-guide/mm/slab.rst. 6996 (slub_debug legacy name also accepted for now) 6997 6998 Using this option implies the "no_hash_pointers" 6999 option which can be undone by adding the 7000 "hash_pointers=always" option. 7001 7002 slab_max_order= [MM] 7003 Determines the maximum allowed order for slabs. 7004 A high setting may cause OOMs due to memory 7005 fragmentation. For more information see 7006 Documentation/admin-guide/mm/slab.rst. 7007 (slub_max_order legacy name also accepted for now) 7008 7009 slab_merge [MM] 7010 Enable merging of slabs with similar size when the 7011 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 7012 (slub_merge legacy name also accepted for now) 7013 7014 slab_min_objects= [MM] 7015 The minimum number of objects per slab. SLUB will 7016 increase the slab order up to slab_max_order to 7017 generate a sufficiently large slab able to contain 7018 the number of objects indicated. The higher the number 7019 of objects the smaller the overhead of tracking slabs 7020 and the less frequently locks need to be acquired. 7021 For more information see 7022 Documentation/admin-guide/mm/slab.rst. 7023 (slub_min_objects legacy name also accepted for now) 7024 7025 slab_min_order= [MM] 7026 Determines the minimum page order for slabs. Must be 7027 lower or equal to slab_max_order. For more information see 7028 Documentation/admin-guide/mm/slab.rst. 7029 (slub_min_order legacy name also accepted for now) 7030 7031 slab_nomerge [MM] 7032 Disable merging of slabs with similar size. May be 7033 necessary if there is some reason to distinguish 7034 allocs to different slabs, especially in hardened 7035 environments where the risk of heap overflows and 7036 layout control by attackers can usually be 7037 frustrated by disabling merging. This will reduce 7038 most of the exposure of a heap attack to a single 7039 cache (risks via metadata attacks are mostly 7040 unchanged). Debug options disable merging on their 7041 own. 7042 For more information see 7043 Documentation/admin-guide/mm/slab.rst. 7044 (slub_nomerge legacy name also accepted for now) 7045 7046 slab_strict_numa [MM] 7047 Support memory policies on a per object level 7048 in the slab allocator. The default is for memory 7049 policies to be applied at the folio level when 7050 a new folio is needed or a partial folio is 7051 retrieved from the lists. Increases overhead 7052 in the slab fastpaths but gains more accurate 7053 NUMA kernel object placement which helps with slow 7054 interconnects in NUMA systems. 7055 7056 slram= [HW,MTD] 7057 7058 smart2= [HW] 7059 Format: <io1>[,<io2>[,...,<io8>]] 7060 7061 smp.csd_lock_timeout= [KNL] 7062 Specify the period of time in milliseconds 7063 that smp_call_function() and friends will wait 7064 for a CPU to release the CSD lock. This is 7065 useful when diagnosing bugs involving CPUs 7066 disabling interrupts for extended periods 7067 of time. Defaults to 5,000 milliseconds, and 7068 setting a value of zero disables this feature. 7069 This feature may be more efficiently disabled 7070 using the csdlock_debug- kernel parameter. 7071 7072 smp.panic_on_ipistall= [KNL] 7073 If a csd_lock_timeout extends for more than 7074 the specified number of milliseconds, panic the 7075 system. By default, let CSD-lock acquisition 7076 take as long as they take. Specifying 300,000 7077 for this value provides a 5-minute timeout. 7078 7079 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7080 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7081 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7082 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7083 smsc-ircc2.ircc_irq= [HW] IRQ line 7084 smsc-ircc2.ircc_dma= [HW] DMA channel 7085 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7086 0: Toshiba Satellite 1800 (GP data pin select) 7087 1: Fast pin select (default) 7088 2: ATC IRMode 7089 7090 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7091 (logical CPUs) to use per physical CPU on systems 7092 capable of symmetric multithreading (SMT). Will 7093 be capped to the actual hardware limit. 7094 Format: <integer> 7095 Default: -1 (no limit) 7096 7097 softlockup_panic= 7098 [KNL] Should the soft-lockup detector generate panics. 7099 Format: <int> 7100 7101 A value of non-zero instructs the soft-lockup detector 7102 to panic the machine when a soft-lockup duration exceeds 7103 N thresholds. It is also controlled by the kernel.softlockup_panic 7104 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7105 respective build-time switch to that functionality. 7106 7107 softlockup_all_cpu_backtrace= 7108 [KNL] Should the soft-lockup detector generate 7109 backtraces on all cpus. 7110 Format: 0 | 1 7111 7112 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7113 See Documentation/admin-guide/laptops/sonypi.rst 7114 7115 spectre_bhi= [X86] Control mitigation of Branch History Injection 7116 (BHI) vulnerability. This setting affects the 7117 deployment of the HW BHI control and the SW BHB 7118 clearing sequence. 7119 7120 on - (default) Enable the HW or SW mitigation as 7121 needed. This protects the kernel from 7122 both syscalls and VMs. 7123 vmexit - On systems which don't have the HW mitigation 7124 available, enable the SW mitigation on vmexit 7125 ONLY. On such systems, the host kernel is 7126 protected from VM-originated BHI attacks, but 7127 may still be vulnerable to syscall attacks. 7128 off - Disable the mitigation. 7129 7130 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7131 (indirect branch speculation) vulnerability. 7132 The default operation protects the kernel from 7133 user space attacks. 7134 7135 on - unconditionally enable, implies 7136 spectre_v2_user=on 7137 off - unconditionally disable, implies 7138 spectre_v2_user=off 7139 auto - kernel detects whether your CPU model is 7140 vulnerable 7141 7142 Selecting 'on' will, and 'auto' may, choose a 7143 mitigation method at run time according to the 7144 CPU, the available microcode, the setting of the 7145 CONFIG_MITIGATION_RETPOLINE configuration option, 7146 and the compiler with which the kernel was built. 7147 7148 Selecting 'on' will also enable the mitigation 7149 against user space to user space task attacks. 7150 Selecting specific mitigation does not force enable 7151 user mitigations. 7152 7153 Selecting 'off' will disable both the kernel and 7154 the user space protections. 7155 7156 Specific mitigations can also be selected manually: 7157 7158 retpoline - replace indirect branches 7159 retpoline,generic - Retpolines 7160 retpoline,lfence - LFENCE; indirect branch 7161 retpoline,amd - alias for retpoline,lfence 7162 eibrs - Enhanced/Auto IBRS 7163 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7164 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7165 ibrs - use IBRS to protect kernel 7166 7167 Not specifying this option is equivalent to 7168 spectre_v2=auto. 7169 7170 spectre_v2_user= 7171 [X86] Control mitigation of Spectre variant 2 7172 (indirect branch speculation) vulnerability between 7173 user space tasks 7174 7175 on - Unconditionally enable mitigations. Is 7176 enforced by spectre_v2=on 7177 7178 off - Unconditionally disable mitigations. Is 7179 enforced by spectre_v2=off 7180 7181 prctl - Indirect branch speculation is enabled, 7182 but mitigation can be enabled via prctl 7183 per thread. The mitigation control state 7184 is inherited on fork. 7185 7186 prctl,ibpb 7187 - Like "prctl" above, but only STIBP is 7188 controlled per thread. IBPB is issued 7189 always when switching between different user 7190 space processes. 7191 7192 seccomp 7193 - Same as "prctl" above, but all seccomp 7194 threads will enable the mitigation unless 7195 they explicitly opt out. 7196 7197 seccomp,ibpb 7198 - Like "seccomp" above, but only STIBP is 7199 controlled per thread. IBPB is issued 7200 always when switching between different 7201 user space processes. 7202 7203 auto - Kernel selects the mitigation depending on 7204 the available CPU features and vulnerability. 7205 7206 Default mitigation: "prctl" 7207 7208 Not specifying this option is equivalent to 7209 spectre_v2_user=auto. 7210 7211 spec_rstack_overflow= 7212 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7213 7214 off - Disable mitigation 7215 microcode - Enable microcode mitigation only 7216 safe-ret - Enable sw-only safe RET mitigation (default) 7217 ibpb - Enable mitigation by issuing IBPB on 7218 kernel entry 7219 ibpb-vmexit - Issue IBPB only on VMEXIT 7220 (cloud-specific mitigation) 7221 7222 spec_store_bypass_disable= 7223 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7224 (Speculative Store Bypass vulnerability) 7225 7226 Certain CPUs are vulnerable to an exploit against a 7227 a common industry wide performance optimization known 7228 as "Speculative Store Bypass" in which recent stores 7229 to the same memory location may not be observed by 7230 later loads during speculative execution. The idea 7231 is that such stores are unlikely and that they can 7232 be detected prior to instruction retirement at the 7233 end of a particular speculation execution window. 7234 7235 In vulnerable processors, the speculatively forwarded 7236 store can be used in a cache side channel attack, for 7237 example to read memory to which the attacker does not 7238 directly have access (e.g. inside sandboxed code). 7239 7240 This parameter controls whether the Speculative Store 7241 Bypass optimization is used. 7242 7243 On x86 the options are: 7244 7245 on - Unconditionally disable Speculative Store Bypass 7246 off - Unconditionally enable Speculative Store Bypass 7247 auto - Kernel detects whether the CPU model contains an 7248 implementation of Speculative Store Bypass and 7249 picks the most appropriate mitigation. If the 7250 CPU is not vulnerable, "off" is selected. If the 7251 CPU is vulnerable the default mitigation is 7252 architecture and Kconfig dependent. See below. 7253 prctl - Control Speculative Store Bypass per thread 7254 via prctl. Speculative Store Bypass is enabled 7255 for a process by default. The state of the control 7256 is inherited on fork. 7257 seccomp - Same as "prctl" above, but all seccomp threads 7258 will disable SSB unless they explicitly opt out. 7259 7260 Default mitigations: 7261 X86: "prctl" 7262 7263 On powerpc the options are: 7264 7265 on,auto - On Power8 and Power9 insert a store-forwarding 7266 barrier on kernel entry and exit. On Power7 7267 perform a software flush on kernel entry and 7268 exit. 7269 off - No action. 7270 7271 Not specifying this option is equivalent to 7272 spec_store_bypass_disable=auto. 7273 7274 split_lock_detect= 7275 [X86] Enable split lock detection or bus lock detection 7276 7277 When enabled (and if hardware support is present), atomic 7278 instructions that access data across cache line 7279 boundaries will result in an alignment check exception 7280 for split lock detection or a debug exception for 7281 bus lock detection. 7282 7283 off - not enabled 7284 7285 warn - the kernel will emit rate-limited warnings 7286 about applications triggering the #AC 7287 exception or the #DB exception. This mode is 7288 the default on CPUs that support split lock 7289 detection or bus lock detection. Default 7290 behavior is by #AC if both features are 7291 enabled in hardware. 7292 7293 fatal - the kernel will send SIGBUS to applications 7294 that trigger the #AC exception or the #DB 7295 exception. Default behavior is by #AC if 7296 both features are enabled in hardware. 7297 7298 ratelimit:N - 7299 Set system wide rate limit to N bus locks 7300 per second for bus lock detection. 7301 0 < N <= 1000. 7302 7303 N/A for split lock detection. 7304 7305 7306 If an #AC exception is hit in the kernel or in 7307 firmware (i.e. not while executing in user mode) 7308 the kernel will oops in either "warn" or "fatal" 7309 mode. 7310 7311 #DB exception for bus lock is triggered only when 7312 CPL > 0. 7313 7314 srbds= [X86,INTEL,EARLY] 7315 Control the Special Register Buffer Data Sampling 7316 (SRBDS) mitigation. 7317 7318 Certain CPUs are vulnerable to an MDS-like 7319 exploit which can leak bits from the random 7320 number generator. 7321 7322 By default, this issue is mitigated by 7323 microcode. However, the microcode fix can cause 7324 the RDRAND and RDSEED instructions to become 7325 much slower. Among other effects, this will 7326 result in reduced throughput from /dev/urandom. 7327 7328 The microcode mitigation can be disabled with 7329 the following option: 7330 7331 off: Disable mitigation and remove 7332 performance impact to RDRAND and RDSEED 7333 7334 srcutree.big_cpu_lim [KNL] 7335 Specifies the number of CPUs constituting a 7336 large system, such that srcu_struct structures 7337 should immediately allocate an srcu_node array. 7338 This kernel-boot parameter defaults to 128, 7339 but takes effect only when the low-order four 7340 bits of srcutree.convert_to_big is equal to 3 7341 (decide at boot). 7342 7343 srcutree.convert_to_big [KNL] 7344 Specifies under what conditions an SRCU tree 7345 srcu_struct structure will be converted to big 7346 form, that is, with an rcu_node tree: 7347 7348 0: Never. 7349 1: At init_srcu_struct() time. 7350 2: When rcutorture decides to. 7351 3: Decide at boot time (default). 7352 0x1X: Above plus if high contention. 7353 7354 Either way, the srcu_node tree will be sized based 7355 on the actual runtime number of CPUs (nr_cpu_ids) 7356 instead of the compile-time CONFIG_NR_CPUS. 7357 7358 srcutree.counter_wrap_check [KNL] 7359 Specifies how frequently to check for 7360 grace-period sequence counter wrap for the 7361 srcu_data structure's ->srcu_gp_seq_needed field. 7362 The greater the number of bits set in this kernel 7363 parameter, the less frequently counter wrap will 7364 be checked for. Note that the bottom two bits 7365 are ignored. 7366 7367 srcutree.exp_holdoff [KNL] 7368 Specifies how many nanoseconds must elapse 7369 since the end of the last SRCU grace period for 7370 a given srcu_struct until the next normal SRCU 7371 grace period will be considered for automatic 7372 expediting. Set to zero to disable automatic 7373 expediting. 7374 7375 srcutree.srcu_max_nodelay [KNL] 7376 Specifies the number of no-delay instances 7377 per jiffy for which the SRCU grace period 7378 worker thread will be rescheduled with zero 7379 delay. Beyond this limit, worker thread will 7380 be rescheduled with a sleep delay of one jiffy. 7381 7382 srcutree.srcu_max_nodelay_phase [KNL] 7383 Specifies the per-grace-period phase, number of 7384 non-sleeping polls of readers. Beyond this limit, 7385 grace period worker thread will be rescheduled 7386 with a sleep delay of one jiffy, between each 7387 rescan of the readers, for a grace period phase. 7388 7389 srcutree.srcu_retry_check_delay [KNL] 7390 Specifies number of microseconds of non-sleeping 7391 delay between each non-sleeping poll of readers. 7392 7393 srcutree.small_contention_lim [KNL] 7394 Specifies the number of update-side contention 7395 events per jiffy will be tolerated before 7396 initiating a conversion of an srcu_struct 7397 structure to big form. Note that the value of 7398 srcutree.convert_to_big must have the 0x10 bit 7399 set for contention-based conversions to occur. 7400 7401 ssbd= [ARM64,HW,EARLY] 7402 Speculative Store Bypass Disable control 7403 7404 On CPUs that are vulnerable to the Speculative 7405 Store Bypass vulnerability and offer a 7406 firmware based mitigation, this parameter 7407 indicates how the mitigation should be used: 7408 7409 force-on: Unconditionally enable mitigation for 7410 for both kernel and userspace 7411 force-off: Unconditionally disable mitigation for 7412 for both kernel and userspace 7413 kernel: Always enable mitigation in the 7414 kernel, and offer a prctl interface 7415 to allow userspace to register its 7416 interest in being mitigated too. 7417 7418 stack_guard_gap= [MM] 7419 override the default stack gap protection. The value 7420 is in page units and it defines how many pages prior 7421 to (for stacks growing down) resp. after (for stacks 7422 growing up) the main stack are reserved for no other 7423 mapping. Default value is 256 pages. 7424 7425 stack_depot_disable= [KNL,EARLY] 7426 Setting this to true through kernel command line will 7427 disable the stack depot thereby saving the static memory 7428 consumed by the stack hash table. By default this is set 7429 to false. 7430 7431 stack_depot_max_pools= [KNL,EARLY] 7432 Specify the maximum number of pools to use for storing 7433 stack traces. Pools are allocated on-demand up to this 7434 limit. Default value is 8191 pools. 7435 7436 stacktrace [FTRACE] 7437 Enable the stack tracer on boot up. 7438 7439 stacktrace_filter=[function-list] 7440 [FTRACE] Limit the functions that the stack tracer 7441 will trace at boot up. function-list is a comma-separated 7442 list of functions. This list can be changed at run 7443 time by the stack_trace_filter file in the debugfs 7444 tracing directory. Note, this enables stack tracing 7445 and the stacktrace above is not needed. 7446 7447 sti= [PARISC,HW] 7448 Format: <num> 7449 Set the STI (builtin display/keyboard on the HP-PARISC 7450 machines) console (graphic card) which should be used 7451 as the initial boot-console. 7452 See also comment in drivers/video/console/sticore.c. 7453 7454 sti_font= [HW] 7455 See comment in drivers/video/console/sticore.c. 7456 7457 stifb= [HW] 7458 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7459 7460 strict_sas_size= 7461 [X86] 7462 Format: <bool> 7463 Enable or disable strict sigaltstack size checks 7464 against the required signal frame size which 7465 depends on the supported FPU features. This can 7466 be used to filter out binaries which have 7467 not yet been made aware of AT_MINSIGSTKSZ. 7468 7469 stress_hpt [PPC,EARLY] 7470 Limits the number of kernel HPT entries in the hash 7471 page table to increase the rate of hash page table 7472 faults on kernel addresses. 7473 7474 stress_slb [PPC,EARLY] 7475 Limits the number of kernel SLB entries, and flushes 7476 them frequently to increase the rate of SLB faults 7477 on kernel addresses. 7478 7479 no_slb_preload [PPC,EARLY] 7480 Disables slb preloading for userspace. 7481 7482 sunrpc.min_resvport= 7483 sunrpc.max_resvport= 7484 [NFS,SUNRPC] 7485 SunRPC servers often require that client requests 7486 originate from a privileged port (i.e. a port in the 7487 range 0 < portnr < 1024). 7488 An administrator who wishes to reserve some of these 7489 ports for other uses may adjust the range that the 7490 kernel's sunrpc client considers to be privileged 7491 using these two parameters to set the minimum and 7492 maximum port values. 7493 7494 sunrpc.svc_rpc_per_connection_limit= 7495 [NFS,SUNRPC] 7496 Limit the number of requests that the server will 7497 process in parallel from a single connection. 7498 The default value is 0 (no limit). 7499 7500 sunrpc.pool_mode= 7501 [NFS] 7502 Control how the NFS server code allocates CPUs to 7503 service thread pools. Depending on how many NICs 7504 you have and where their interrupts are bound, this 7505 option will affect which CPUs will do NFS serving. 7506 Note: this parameter cannot be changed while the 7507 NFS server is running. 7508 7509 auto the server chooses an appropriate mode 7510 automatically using heuristics 7511 global a single global pool contains all CPUs 7512 percpu one pool for each CPU 7513 pernode one pool for each NUMA node (equivalent 7514 to global on non-NUMA machines) 7515 7516 sunrpc.tcp_slot_table_entries= 7517 sunrpc.udp_slot_table_entries= 7518 [NFS,SUNRPC] 7519 Sets the upper limit on the number of simultaneous 7520 RPC calls that can be sent from the client to a 7521 server. Increasing these values may allow you to 7522 improve throughput, but will also increase the 7523 amount of memory reserved for use by the client. 7524 7525 suspend.pm_test_delay= 7526 [SUSPEND] 7527 Sets the number of seconds to remain in a suspend test 7528 mode before resuming the system (see 7529 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7530 is set. Default value is 5. 7531 7532 svm= [PPC] 7533 Format: { on | off | y | n | 1 | 0 } 7534 This parameter controls use of the Protected 7535 Execution Facility on pSeries. 7536 7537 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7538 Format: { <int> [,<int>] | force | noforce } 7539 <int> -- Number of I/O TLB slabs 7540 <int> -- Second integer after comma. Number of swiotlb 7541 areas with their own lock. Will be rounded up 7542 to a power of 2. 7543 force -- force using of bounce buffers even if they 7544 wouldn't be automatically used by the kernel 7545 noforce -- Never use bounce buffers (for debugging) 7546 7547 switches= [HW,M68k,EARLY] 7548 7549 sysctl.*= [KNL] 7550 Set a sysctl parameter, right before loading the init 7551 process, as if the value was written to the respective 7552 /proc/sys/... file. Both '.' and '/' are recognized as 7553 separators. Unrecognized parameters and invalid values 7554 are reported in the kernel log. Sysctls registered 7555 later by a loaded module cannot be set this way. 7556 Example: sysctl.vm.swappiness=40 7557 7558 sysrq_always_enabled 7559 [KNL] 7560 Ignore sysrq setting - this boot parameter will 7561 neutralize any effect of /proc/sys/kernel/sysrq. 7562 Useful for debugging. 7563 7564 tcpmhash_entries= [KNL,NET] 7565 Set the number of tcp_metrics_hash slots. 7566 Default value is 8192 or 16384 depending on total 7567 ram pages. This is used to specify the TCP metrics 7568 cache size. See Documentation/networking/ip-sysctl.rst 7569 "tcp_no_metrics_save" section for more details. 7570 7571 tdfx= [HW,DRM] 7572 7573 test_suspend= [SUSPEND] 7574 Format: { "mem" | "standby" | "freeze" }[,N] 7575 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7576 standby suspend) or "freeze" (for suspend type freeze) 7577 as the system sleep state during system startup with 7578 the optional capability to repeat N number of times. 7579 The system is woken from this state using a 7580 wakeup-capable RTC alarm. 7581 7582 thash_entries= [KNL,NET] 7583 Set number of hash buckets for TCP connection 7584 7585 thermal.act= [HW,ACPI] 7586 -1: disable all active trip points in all thermal zones 7587 <degrees C>: override all lowest active trip points 7588 7589 thermal.crt= [HW,ACPI] 7590 -1: disable all critical trip points in all thermal zones 7591 <degrees C>: override all critical trip points 7592 7593 thermal.off= [HW,ACPI] 7594 1: disable ACPI thermal control 7595 7596 thermal.psv= [HW,ACPI] 7597 -1: disable all passive trip points 7598 <degrees C>: override all passive trip points to this 7599 value 7600 7601 thermal.tzp= [HW,ACPI] 7602 Specify global default ACPI thermal zone polling rate 7603 <deci-seconds>: poll all this frequency 7604 0: no polling (default) 7605 7606 thp_anon= [KNL] 7607 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7608 state is one of "always", "madvise", "never" or "inherit". 7609 Control the default behavior of the system with respect 7610 to anonymous transparent hugepages. 7611 Can be used multiple times for multiple anon THP sizes. 7612 See Documentation/admin-guide/mm/transhuge.rst for more 7613 details. 7614 7615 threadirqs [KNL,EARLY] 7616 Force threading of all interrupt handlers except those 7617 marked explicitly IRQF_NO_THREAD. 7618 7619 thp_shmem= [KNL] 7620 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7621 Control the default policy of each hugepage size for the 7622 internal shmem mount. <policy> is one of policies available 7623 for the shmem mount ("always", "inherit", "never", "within_size", 7624 and "advise"). 7625 It can be used multiple times for multiple shmem THP sizes. 7626 See Documentation/admin-guide/mm/transhuge.rst for more 7627 details. 7628 7629 topology= [S390,EARLY] 7630 Format: {off | on} 7631 Specify if the kernel should make use of the cpu 7632 topology information if the hardware supports this. 7633 The scheduler will make use of this information and 7634 e.g. base its process migration decisions on it. 7635 Default is on. 7636 7637 torture.disable_onoff_at_boot= [KNL] 7638 Prevent the CPU-hotplug component of torturing 7639 until after init has spawned. 7640 7641 torture.ftrace_dump_at_shutdown= [KNL] 7642 Dump the ftrace buffer at torture-test shutdown, 7643 even if there were no errors. This can be a 7644 very costly operation when many torture tests 7645 are running concurrently, especially on systems 7646 with rotating-rust storage. 7647 7648 torture.verbose_sleep_frequency= [KNL] 7649 Specifies how many verbose printk()s should be 7650 emitted between each sleep. The default of zero 7651 disables verbose-printk() sleeping. 7652 7653 torture.verbose_sleep_duration= [KNL] 7654 Duration of each verbose-printk() sleep in jiffies. 7655 7656 tpm.disable_pcr_integrity= [HW,TPM] 7657 Do not protect PCR registers from unintended physical 7658 access, or interposers in the bus by the means of 7659 having an integrity protected session wrapped around 7660 TPM2_PCR_Extend command. Consider this in a situation 7661 where TPM is heavily utilized by IMA, thus protection 7662 causing a major performance hit, and the space where 7663 machines are deployed is by other means guarded. 7664 7665 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7666 Maximum time in milliseconds to retry sending a message 7667 to the TPM service before giving up. This parameter controls 7668 how long the system will continue retrying when the TPM 7669 service is busy. 7670 Format: <unsigned int> 7671 Default: 2000 (2 seconds) 7672 7673 tpm_suspend_pcr=[HW,TPM] 7674 Format: integer pcr id 7675 Specify that at suspend time, the tpm driver 7676 should extend the specified pcr with zeros, 7677 as a workaround for some chips which fail to 7678 flush the last written pcr on TPM_SaveState. 7679 This will guarantee that all the other pcrs 7680 are saved. 7681 7682 tpm_tis.interrupts= [HW,TPM] 7683 Enable interrupts for the MMIO based physical layer 7684 for the FIFO interface. By default it is set to false 7685 (0). For more information about TPM hardware interfaces 7686 defined by Trusted Computing Group (TCG) see 7687 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7688 7689 tp_printk [FTRACE] 7690 Have the tracepoints sent to printk as well as the 7691 tracing ring buffer. This is useful for early boot up 7692 where the system hangs or reboots and does not give the 7693 option for reading the tracing buffer or performing a 7694 ftrace_dump_on_oops. 7695 7696 To turn off having tracepoints sent to printk, 7697 echo 0 > /proc/sys/kernel/tracepoint_printk 7698 Note, echoing 1 into this file without the 7699 tp_printk kernel cmdline option has no effect. 7700 7701 The tp_printk_stop_on_boot (see below) can also be used 7702 to stop the printing of events to console at 7703 late_initcall_sync. 7704 7705 ** CAUTION ** 7706 7707 Having tracepoints sent to printk() and activating high 7708 frequency tracepoints such as irq or sched, can cause 7709 the system to live lock. 7710 7711 tp_printk_stop_on_boot [FTRACE] 7712 When tp_printk (above) is set, it can cause a lot of noise 7713 on the console. It may be useful to only include the 7714 printing of events during boot up, as user space may 7715 make the system inoperable. 7716 7717 This command line option will stop the printing of events 7718 to console at the late_initcall_sync() time frame. 7719 7720 trace_buf_size=nn[KMG] 7721 [FTRACE] will set tracing buffer size on each cpu. 7722 7723 trace_clock= [FTRACE] Set the clock used for tracing events 7724 at boot up. 7725 local - Use the per CPU time stamp counter 7726 (converted into nanoseconds). Fast, but 7727 depending on the architecture, may not be 7728 in sync between CPUs. 7729 global - Event time stamps are synchronized across 7730 CPUs. May be slower than the local clock, 7731 but better for some race conditions. 7732 counter - Simple counting of events (1, 2, ..) 7733 note, some counts may be skipped due to the 7734 infrastructure grabbing the clock more than 7735 once per event. 7736 uptime - Use jiffies as the time stamp. 7737 perf - Use the same clock that perf uses. 7738 mono - Use ktime_get_mono_fast_ns() for time stamps. 7739 mono_raw - Use ktime_get_raw_fast_ns() for time 7740 stamps. 7741 boot - Use ktime_get_boot_fast_ns() for time stamps. 7742 Architectures may add more clocks. See 7743 Documentation/trace/ftrace.rst for more details. 7744 7745 trace_event=[event-list] 7746 [FTRACE] Set and start specified trace events in order 7747 to facilitate early boot debugging. The event-list is a 7748 comma-separated list of trace events to enable. See 7749 also Documentation/trace/events.rst 7750 7751 To enable modules, use :mod: keyword: 7752 7753 trace_event=:mod:<module> 7754 7755 The value before :mod: will only enable specific events 7756 that are part of the module. See the above mentioned 7757 document for more information. 7758 7759 trace_instance=[instance-info] 7760 [FTRACE] Create a ring buffer instance early in boot up. 7761 This will be listed in: 7762 7763 /sys/kernel/tracing/instances 7764 7765 Events can be enabled at the time the instance is created 7766 via: 7767 7768 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7769 7770 Note, the "<system*>:" portion is optional if the event is 7771 unique. 7772 7773 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7774 7775 will enable the "sched_switch" event (note, the "sched:" is optional, and 7776 the same thing would happen if it was left off). The irq_handler_entry 7777 event, and all events under the "initcall" system. 7778 7779 Flags can be added to the instance to modify its behavior when it is 7780 created. The flags are separated by '^'. 7781 7782 The available flags are: 7783 7784 traceoff - Have the tracing instance tracing disabled after it is created. 7785 traceprintk - Have trace_printk() write into this trace instance 7786 (note, "printk" and "trace_printk" can also be used) 7787 7788 trace_instance=foo^traceoff^traceprintk,sched,irq 7789 7790 The flags must come before the defined events. 7791 7792 If memory has been reserved (see memmap for x86), the instance 7793 can use that memory: 7794 7795 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7796 7797 The above will create a "boot_map" instance that uses the physical 7798 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7799 instance will be split up accordingly. 7800 7801 Alternatively, the memory can be reserved by the reserve_mem option: 7802 7803 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7804 7805 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7806 and place the ring buffer in this memory. Note that due to KASLR, the 7807 memory may not be the same location each time, which will not preserve 7808 the buffer content. 7809 7810 Also note that the layout of the ring buffer data may change between 7811 kernel versions where the validator will fail and reset the ring buffer 7812 if the layout is not the same as the previous kernel. 7813 7814 If the ring buffer is used for persistent bootups and has events enabled, 7815 it is recommend to disable tracing so that events from a previous boot do not 7816 mix with events of the current boot (unless you are debugging a random crash 7817 at boot up). 7818 7819 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7820 7821 Note, saving the trace buffer across reboots does require that the system 7822 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7823 can force a memory reset on boot which will clear any trace that was stored. 7824 This is just one of many ways that can clear memory. Make sure your system 7825 keeps the content of memory across reboots before relying on this option. 7826 7827 NB: Both the mapped address and size must be page aligned for the architecture. 7828 7829 See also Documentation/trace/debugging.rst 7830 7831 7832 trace_options=[option-list] 7833 [FTRACE] Enable or disable tracer options at boot. 7834 The option-list is a comma delimited list of options 7835 that can be enabled or disabled just as if you were 7836 to echo the option name into 7837 7838 /sys/kernel/tracing/trace_options 7839 7840 For example, to enable stacktrace option (to dump the 7841 stack trace of each event), add to the command line: 7842 7843 trace_options=stacktrace 7844 7845 See also Documentation/trace/ftrace.rst "trace options" 7846 section. 7847 7848 trace_trigger=[trigger-list] 7849 [FTRACE] Add an event trigger on specific events. 7850 Set a trigger on top of a specific event, with an optional 7851 filter. 7852 7853 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7854 Where more than one trigger may be specified that are comma delimited. 7855 7856 For example: 7857 7858 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7859 7860 The above will enable the "stacktrace" trigger on the "sched_switch" 7861 event but only trigger it if the "prev_state" of the "sched_switch" 7862 event is "2" (TASK_UNINTERRUPTIBLE). 7863 7864 See also "Event triggers" in Documentation/trace/events.rst 7865 7866 7867 traceoff_after_boot 7868 [FTRACE] Sometimes tracing is used to debug issues 7869 during the boot process. Since the trace buffer has a 7870 limited amount of storage, it may be prudent to 7871 disable tracing after the boot is finished, otherwise 7872 the critical information may be overwritten. With this 7873 option, the main tracing buffer will be turned off at 7874 the end of the boot process. 7875 7876 traceoff_on_warning 7877 [FTRACE] enable this option to disable tracing when a 7878 warning is hit. This turns off "tracing_on". Tracing can 7879 be enabled again by echoing '1' into the "tracing_on" 7880 file located in /sys/kernel/tracing/ 7881 7882 This option is useful, as it disables the trace before 7883 the WARNING dump is called, which prevents the trace to 7884 be filled with content caused by the warning output. 7885 7886 This option can also be set at run time via the sysctl 7887 option: kernel/traceoff_on_warning 7888 7889 transparent_hugepage= 7890 [KNL] 7891 Format: [always|madvise|never] 7892 Can be used to control the default behavior of the system 7893 with respect to transparent hugepages. 7894 See Documentation/admin-guide/mm/transhuge.rst 7895 for more details. 7896 7897 transparent_hugepage_shmem= [KNL] 7898 Format: [always|within_size|advise|never|deny|force] 7899 Can be used to control the hugepage allocation policy for 7900 the internal shmem mount. 7901 See Documentation/admin-guide/mm/transhuge.rst 7902 for more details. 7903 7904 transparent_hugepage_tmpfs= [KNL] 7905 Format: [always|within_size|advise|never] 7906 Can be used to control the default hugepage allocation policy 7907 for the tmpfs mount. 7908 See Documentation/admin-guide/mm/transhuge.rst 7909 for more details. 7910 7911 trusted.source= [KEYS] 7912 Format: <string> 7913 This parameter identifies the trust source as a backend 7914 for trusted keys implementation. Supported trust 7915 sources: 7916 - "tpm" 7917 - "tee" 7918 - "caam" 7919 - "dcp" 7920 - "pkwm" 7921 If not specified then it defaults to iterating through 7922 the trust source list starting with TPM and assigns the 7923 first trust source as a backend which is initialized 7924 successfully during iteration. 7925 7926 trusted.rng= [KEYS] 7927 Format: <string> 7928 The RNG used to generate key material for trusted keys. 7929 Can be one of: 7930 - "kernel" 7931 - the same value as trusted.source: "tpm" or "tee" 7932 - "default" 7933 If not specified, "default" is used. In this case, 7934 the RNG's choice is left to each individual trust source. 7935 7936 trusted.dcp_use_otp_key 7937 This is intended to be used in combination with 7938 trusted.source=dcp and will select the DCP OTP key 7939 instead of the DCP UNIQUE key blob encryption. 7940 7941 trusted.dcp_skip_zk_test 7942 This is intended to be used in combination with 7943 trusted.source=dcp and will disable the check if the 7944 blob key is all zeros. This is helpful for situations where 7945 having this key zero'ed is acceptable. E.g. in testing 7946 scenarios. 7947 7948 tsa= [X86] Control mitigation for Transient Scheduler 7949 Attacks on AMD CPUs. Search the following in your 7950 favourite search engine for more details: 7951 7952 "Technical guidance for mitigating transient scheduler 7953 attacks". 7954 7955 off - disable the mitigation 7956 on - enable the mitigation (default) 7957 user - mitigate only user/kernel transitions 7958 vm - mitigate only guest/host transitions 7959 7960 7961 tsc= Disable clocksource stability checks for TSC. 7962 Format: <string> 7963 [x86] reliable: mark tsc clocksource as reliable, this 7964 disables clocksource verification at runtime, as well 7965 as the stability checks done at bootup. Used to enable 7966 high-resolution timer mode on older hardware, and in 7967 virtualized environment. 7968 [x86] noirqtime: Do not use TSC to do irq accounting. 7969 Used to run time disable IRQ_TIME_ACCOUNTING on any 7970 platforms where RDTSC is slow and this accounting 7971 can add overhead. 7972 [x86] unstable: mark the TSC clocksource as unstable, this 7973 marks the TSC unconditionally unstable at bootup and 7974 avoids any further wobbles once the TSC watchdog notices. 7975 [x86] nowatchdog: disable clocksource watchdog. Used 7976 in situations with strict latency requirements (where 7977 interruptions from clocksource watchdog are not 7978 acceptable). 7979 [x86] recalibrate: force recalibration against a HW timer 7980 (HPET or PM timer) on systems whose TSC frequency was 7981 obtained from HW or FW using either an MSR or CPUID(0x15). 7982 Warn if the difference is more than 500 ppm. 7983 [x86] watchdog: Enforce the clocksource watchdog on TSC 7984 7985 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7986 value instead. Useful when the early TSC frequency discovery 7987 procedure is not reliable, such as on overclocked systems 7988 with CPUID.16h support and partial CPUID.15h support. 7989 Format: <unsigned int> 7990 7991 tsx= [X86] Control Transactional Synchronization 7992 Extensions (TSX) feature in Intel processors that 7993 support TSX control. 7994 7995 This parameter controls the TSX feature. The options are: 7996 7997 on - Enable TSX on the system. Although there are 7998 mitigations for all known security vulnerabilities, 7999 TSX has been known to be an accelerator for 8000 several previous speculation-related CVEs, and 8001 so there may be unknown security risks associated 8002 with leaving it enabled. 8003 8004 off - Disable TSX on the system. (Note that this 8005 option takes effect only on newer CPUs which are 8006 not vulnerable to MDS, i.e., have 8007 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 8008 the new IA32_TSX_CTRL MSR through a microcode 8009 update. This new MSR allows for the reliable 8010 deactivation of the TSX functionality.) 8011 8012 auto - Disable TSX if X86_BUG_TAA is present, 8013 otherwise enable TSX on the system. 8014 8015 Not specifying this option is equivalent to tsx=off. 8016 8017 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8018 for more details. 8019 8020 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 8021 Abort (TAA) vulnerability. 8022 8023 Similar to Micro-architectural Data Sampling (MDS) 8024 certain CPUs that support Transactional 8025 Synchronization Extensions (TSX) are vulnerable to an 8026 exploit against CPU internal buffers which can forward 8027 information to a disclosure gadget under certain 8028 conditions. 8029 8030 In vulnerable processors, the speculatively forwarded 8031 data can be used in a cache side channel attack, to 8032 access data to which the attacker does not have direct 8033 access. 8034 8035 This parameter controls the TAA mitigation. The 8036 options are: 8037 8038 full - Enable TAA mitigation on vulnerable CPUs 8039 if TSX is enabled. 8040 8041 full,nosmt - Enable TAA mitigation and disable SMT on 8042 vulnerable CPUs. If TSX is disabled, SMT 8043 is not disabled because CPU is not 8044 vulnerable to cross-thread TAA attacks. 8045 off - Unconditionally disable TAA mitigation 8046 8047 On MDS-affected machines, tsx_async_abort=off can be 8048 prevented by an active MDS mitigation as both vulnerabilities 8049 are mitigated with the same mechanism so in order to disable 8050 this mitigation, you need to specify mds=off too. 8051 8052 Not specifying this option is equivalent to 8053 tsx_async_abort=full. On CPUs which are MDS affected 8054 and deploy MDS mitigation, TAA mitigation is not 8055 required and doesn't provide any additional 8056 mitigation. 8057 8058 For details see: 8059 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8060 8061 turbografx.map[2|3]= [HW,JOY] 8062 TurboGraFX parallel port interface 8063 Format: 8064 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8065 See also Documentation/input/devices/joystick-parport.rst 8066 8067 udbg-immortal [PPC] When debugging early kernel crashes that 8068 happen after console_init() and before a proper 8069 console driver takes over, this boot options might 8070 help "seeing" what's going on. 8071 8072 uhash_entries= [KNL,NET] 8073 Set number of hash buckets for UDP/UDP-Lite connections 8074 8075 uhci-hcd.ignore_oc= 8076 [USB] Ignore overcurrent events (default N). 8077 Some badly-designed motherboards generate lots of 8078 bogus events, for ports that aren't wired to 8079 anything. Set this parameter to avoid log spamming. 8080 Note that genuine overcurrent events won't be 8081 reported either. 8082 8083 unaligned_scalar_speed= 8084 [RISCV] 8085 Format: {slow | fast | unsupported} 8086 Allow skipping scalar 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 scalar unaligned access speed. 8090 8091 unaligned_vector_speed= 8092 [RISCV] 8093 Format: {slow | fast | unsupported} 8094 Allow skipping vector unaligned access speed tests. This 8095 is useful for testing alternative code paths and to skip 8096 the tests in environments where they run too slowly. All 8097 CPUs must have the same vector unaligned access speed. 8098 8099 unknown_nmi_panic 8100 [X86] Cause panic on unknown NMI. 8101 8102 unwind_debug [X86-64,EARLY] 8103 Enable unwinder debug output. This can be 8104 useful for debugging certain unwinder error 8105 conditions, including corrupt stacks and 8106 bad/missing unwinder metadata. 8107 8108 usbcore.authorized_default= 8109 [USB] Default USB device authorization: 8110 (default -1 = authorized (same as 1), 8111 0 = not authorized, 1 = authorized, 2 = authorized 8112 if device connected to internal port) 8113 8114 usbcore.autosuspend= 8115 [USB] The autosuspend time delay (in seconds) used 8116 for newly-detected USB devices (default 2). This 8117 is the time required before an idle device will be 8118 autosuspended. Devices for which the delay is set 8119 to a negative value won't be autosuspended at all. 8120 8121 usbcore.usbfs_snoop= 8122 [USB] Set to log all usbfs traffic (default 0 = off). 8123 8124 usbcore.usbfs_snoop_max= 8125 [USB] Maximum number of bytes to snoop in each URB 8126 (default = 65536). 8127 8128 usbcore.blinkenlights= 8129 [USB] Set to cycle leds on hubs (default 0 = off). 8130 8131 usbcore.old_scheme_first= 8132 [USB] Start with the old device initialization 8133 scheme (default 0 = off). 8134 8135 usbcore.usbfs_memory_mb= 8136 [USB] Memory limit (in MB) for buffers allocated by 8137 usbfs (default = 16, 0 = max = 2047). 8138 8139 usbcore.use_both_schemes= 8140 [USB] Try the other device initialization scheme 8141 if the first one fails (default 1 = enabled). 8142 8143 usbcore.initial_descriptor_timeout= 8144 [USB] Specifies timeout for the initial 64-byte 8145 USB_REQ_GET_DESCRIPTOR request in milliseconds 8146 (default 5000 = 5.0 seconds). 8147 8148 usbcore.nousb [USB] Disable the USB subsystem 8149 8150 usbcore.quirks= 8151 [USB] A list of quirk entries to augment the built-in 8152 usb core quirk list. List entries are separated by 8153 commas. Each entry has the form 8154 VendorID:ProductID:Flags. The IDs are 4-digit hex 8155 numbers and Flags is a set of letters. Each letter 8156 will change the built-in quirk; setting it if it is 8157 clear and clearing it if it is set. The letters have 8158 the following meanings: 8159 a = USB_QUIRK_STRING_FETCH_255 (string 8160 descriptors must not be fetched using 8161 a 255-byte read); 8162 b = USB_QUIRK_RESET_RESUME (device can't resume 8163 correctly so reset it instead); 8164 c = USB_QUIRK_NO_SET_INTF (device can't handle 8165 Set-Interface requests); 8166 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8167 handle its Configuration or Interface 8168 strings); 8169 e = USB_QUIRK_RESET (device can't be reset 8170 (e.g morph devices), don't use reset); 8171 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8172 more interface descriptions than the 8173 bNumInterfaces count, and can't handle 8174 talking to these interfaces); 8175 g = USB_QUIRK_DELAY_INIT (device needs a pause 8176 during initialization, after we read 8177 the device descriptor); 8178 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8179 high speed and super speed interrupt 8180 endpoints, the USB 2.0 and USB 3.0 spec 8181 require the interval in microframes (1 8182 microframe = 125 microseconds) to be 8183 calculated as interval = 2 ^ 8184 (bInterval-1). 8185 Devices with this quirk report their 8186 bInterval as the result of this 8187 calculation instead of the exponent 8188 variable used in the calculation); 8189 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8190 handle device_qualifier descriptor 8191 requests); 8192 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8193 generates spurious wakeup, ignore 8194 remote wakeup capability); 8195 k = USB_QUIRK_NO_LPM (device can't handle Link 8196 Power Management); 8197 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8198 (Device reports its bInterval as linear 8199 frames instead of the USB 2.0 8200 calculation); 8201 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8202 to be disconnected before suspend to 8203 prevent spurious wakeup); 8204 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8205 pause after every control message); 8206 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8207 delay after resetting its port); 8208 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8209 (Reduce timeout of the SET_ADDRESS 8210 request from 5000 ms to 500 ms); 8211 q = USB_QUIRK_FORCE_ONE_CONFIG (Device 8212 claims zero configurations, 8213 forcing to 1); 8214 Example: quirks=0781:5580:bk,0a5c:5834:gij 8215 8216 usbhid.mousepoll= 8217 [USBHID] The interval which mice are to be polled at. 8218 8219 usbhid.jspoll= 8220 [USBHID] The interval which joysticks are to be polled at. 8221 8222 usbhid.kbpoll= 8223 [USBHID] The interval which keyboards are to be polled at. 8224 8225 usb-storage.delay_use= 8226 [UMS] The delay in seconds before a new device is 8227 scanned for Logical Units (default 1). 8228 Optionally the delay in milliseconds if the value has 8229 suffix with "ms". 8230 Example: delay_use=2567ms 8231 8232 usb-storage.quirks= 8233 [UMS] A list of quirks entries to supplement or 8234 override the built-in unusual_devs list. List 8235 entries are separated by commas. Each entry has 8236 the form VID:PID:Flags where VID and PID are Vendor 8237 and Product ID values (4-digit hex numbers) and 8238 Flags is a set of characters, each corresponding 8239 to a common usb-storage quirk flag as follows: 8240 a = SANE_SENSE (collect more than 18 bytes 8241 of sense data, not on uas); 8242 b = BAD_SENSE (don't collect more than 18 8243 bytes of sense data, not on uas); 8244 c = FIX_CAPACITY (decrease the reported 8245 device capacity by one sector); 8246 d = NO_READ_DISC_INFO (don't use 8247 READ_DISC_INFO command, not on uas); 8248 e = NO_READ_CAPACITY_16 (don't use 8249 READ_CAPACITY_16 command); 8250 f = NO_REPORT_OPCODES (don't use report opcodes 8251 command, uas only); 8252 g = MAX_SECTORS_240 (don't transfer more than 8253 240 sectors at a time, uas only); 8254 h = CAPACITY_HEURISTICS (decrease the 8255 reported device capacity by one 8256 sector if the number is odd); 8257 i = IGNORE_DEVICE (don't bind to this 8258 device); 8259 j = NO_REPORT_LUNS (don't use report luns 8260 command, uas only); 8261 k = NO_SAME (do not use WRITE_SAME, uas only) 8262 l = NOT_LOCKABLE (don't try to lock and 8263 unlock ejectable media, not on uas); 8264 m = MAX_SECTORS_64 (don't transfer more 8265 than 64 sectors = 32 KB at a time, 8266 not on uas); 8267 n = INITIAL_READ10 (force a retry of the 8268 initial READ(10) command, not on uas); 8269 o = CAPACITY_OK (accept the capacity 8270 reported by the device, not on uas); 8271 p = WRITE_CACHE (the device cache is ON 8272 by default, not on uas); 8273 r = IGNORE_RESIDUE (the device reports 8274 bogus residue values, not on uas); 8275 s = SINGLE_LUN (the device has only one 8276 Logical Unit); 8277 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8278 commands, uas only); 8279 u = IGNORE_UAS (don't bind to the uas driver); 8280 w = NO_WP_DETECT (don't test whether the 8281 medium is write-protected). 8282 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8283 even if the device claims no cache, 8284 not on uas) 8285 Example: quirks=0419:aaf5:rl,0421:0433:rc 8286 8287 user_debug= [KNL,ARM] 8288 Format: <int> 8289 See arch/arm/Kconfig.debug help text. 8290 1 - undefined instruction events 8291 2 - system calls 8292 4 - invalid data aborts 8293 8 - SIGSEGV faults 8294 16 - SIGBUS faults 8295 Example: user_debug=31 8296 8297 vdso= [X86,SH,SPARC] 8298 On X86_32, this is an alias for vdso32=. Otherwise: 8299 8300 vdso=1: enable VDSO (the default) 8301 vdso=0: disable VDSO mapping 8302 8303 vdso32= [X86] Control the 32-bit vDSO 8304 vdso32=1: enable 32-bit VDSO 8305 vdso32=0 or vdso32=2: disable 32-bit VDSO 8306 8307 See the help text for CONFIG_COMPAT_VDSO for more 8308 details. If CONFIG_COMPAT_VDSO is set, the default is 8309 vdso32=0; otherwise, the default is vdso32=1. 8310 8311 For compatibility with older kernels, vdso32=2 is an 8312 alias for vdso32=0. 8313 8314 Try vdso32=0 if you encounter an error that says: 8315 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8316 8317 video= [FB,EARLY] Frame buffer configuration 8318 See Documentation/fb/modedb.rst. 8319 8320 video.brightness_switch_enabled= [ACPI] 8321 Format: [0|1] 8322 If set to 1, on receiving an ACPI notify event 8323 generated by hotkey, video driver will adjust brightness 8324 level and then send out the event to user space through 8325 the allocated input device. If set to 0, video driver 8326 will only send out the event without touching backlight 8327 brightness level. 8328 default: 1 8329 8330 virtio_mmio.device= 8331 [VMMIO] Memory mapped virtio (platform) device. 8332 8333 <size>@<baseaddr>:<irq>[:<id>] 8334 where: 8335 <size> := size (can use standard suffixes 8336 like K, M and G) 8337 <baseaddr> := physical base address 8338 <irq> := interrupt number (as passed to 8339 request_irq()) 8340 <id> := (optional) platform device id 8341 example: 8342 virtio_mmio.device=1K@0x100b0000:48:7 8343 8344 Can be used multiple times for multiple devices. 8345 8346 vga= [BOOT,X86-32] Select a particular video mode 8347 See Documentation/arch/x86/boot.rst and 8348 Documentation/admin-guide/svga.rst. 8349 Use vga=ask for menu. 8350 This is actually a boot loader parameter; the value is 8351 passed to the kernel using a special protocol. 8352 8353 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8354 May slow down system boot speed, especially when 8355 enabled on systems with a large amount of memory. 8356 All options are enabled by default, and this 8357 interface is meant to allow for selectively 8358 enabling or disabling specific virtual memory 8359 debugging features. 8360 8361 Available options are: 8362 P Enable page structure init time poisoning 8363 - Disable all of the above options 8364 8365 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8366 exact size of <nn>. This can be used to increase 8367 the minimum size (128MB on x86, arm32 platforms). 8368 It can also be used to decrease the size and leave more room 8369 for directly mapped kernel RAM. Note that this parameter does 8370 not exist on many other platforms (including arm64, alpha, 8371 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8372 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8373 8374 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8375 Sets the memory size reserved for contiguous memory 8376 allocations for the vmcp device driver. 8377 8378 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8379 Format: <command> 8380 8381 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8382 Format: <command> 8383 8384 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8385 Format: <command> 8386 8387 vmscape= [X86] Controls mitigation for VMscape attacks. 8388 VMscape attacks can leak information from a userspace 8389 hypervisor to a guest via speculative side-channels. 8390 8391 off - disable the mitigation 8392 ibpb - use Indirect Branch Prediction Barrier 8393 (IBPB) mitigation (default) 8394 force - force vulnerability detection even on 8395 unaffected processors 8396 8397 vsyscall= [X86-64,EARLY] 8398 Controls the behavior of vsyscalls (i.e. calls to 8399 fixed addresses of 0xffffffffff600x00 from legacy 8400 code). Most statically-linked binaries and older 8401 versions of glibc use these calls. Because these 8402 functions are at fixed addresses, they make nice 8403 targets for exploits that can control RIP. 8404 8405 emulate Vsyscalls turn into traps and are emulated 8406 reasonably safely. The vsyscall page is 8407 readable. This disables the Linear 8408 Address Space Separation (LASS) security 8409 feature and makes the system less secure. 8410 8411 xonly [default] Vsyscalls turn into traps and are 8412 emulated reasonably safely. The vsyscall 8413 page is not readable. 8414 8415 none Vsyscalls don't work at all. This makes 8416 them quite hard to use for exploits but 8417 might break your system. 8418 8419 vt.color= [VT] Default text color. 8420 Format: 0xYX, X = foreground, Y = background. 8421 Default: 0x07 = light gray on black. 8422 8423 vt.cur_default= [VT] Default cursor shape. 8424 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8425 the parameters of the <Esc>[?A;B;Cc escape sequence; 8426 see vga-softcursor.rst. Default: 2 = underline. 8427 8428 vt.default_blu= [VT] 8429 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8430 Change the default blue palette of the console. 8431 This is a 16-member array composed of values 8432 ranging from 0-255. 8433 8434 vt.default_grn= [VT] 8435 Format: <green0>,<green1>,<green2>,...,<green15> 8436 Change the default green palette of the console. 8437 This is a 16-member array composed of values 8438 ranging from 0-255. 8439 8440 vt.default_red= [VT] 8441 Format: <red0>,<red1>,<red2>,...,<red15> 8442 Change the default red palette of the console. 8443 This is a 16-member array composed of values 8444 ranging from 0-255. 8445 8446 vt.default_utf8= 8447 [VT] 8448 Format=<0|1> 8449 Set system-wide default UTF-8 mode for all tty's. 8450 Default is 1, i.e. UTF-8 mode is enabled for all 8451 newly opened terminals. 8452 8453 vt.global_cursor_default= 8454 [VT] 8455 Format=<-1|0|1> 8456 Set system-wide default for whether a cursor 8457 is shown on new VTs. Default is -1, 8458 i.e. cursors will be created by default unless 8459 overridden by individual drivers. 0 will hide 8460 cursors, 1 will display them. 8461 8462 vt.italic= [VT] Default color for italic text; 0-15. 8463 Default: 2 = green. 8464 8465 vt.underline= [VT] Default color for underlined text; 0-15. 8466 Default: 3 = cyan. 8467 8468 watchdog timers [HW,WDT] For information on watchdog timers, 8469 see Documentation/watchdog/watchdog-parameters.rst 8470 or other driver-specific files in the 8471 Documentation/watchdog/ directory. 8472 8473 watchdog_thresh= 8474 [KNL] 8475 Set the hard lockup detector stall duration 8476 threshold in seconds. The soft lockup detector 8477 threshold is set to twice the value. A value of 0 8478 disables both lockup detectors. Default is 10 8479 seconds. 8480 8481 workqueue.unbound_cpus= 8482 [KNL,SMP] Specify to constrain one or some CPUs 8483 to use in unbound workqueues. 8484 Format: <cpu-list> 8485 By default, all online CPUs are available for 8486 unbound workqueues. 8487 8488 workqueue.watchdog_thresh= 8489 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8490 warn stall conditions and dump internal state to 8491 help debugging. 0 disables workqueue stall 8492 detection; otherwise, it's the stall threshold 8493 duration in seconds. The default value is 30 and 8494 it can be updated at runtime by writing to the 8495 corresponding sysfs file. 8496 8497 workqueue.panic_on_stall=<uint> 8498 Panic when workqueue stall is detected by 8499 CONFIG_WQ_WATCHDOG. It sets the number times of the 8500 stall to trigger panic. 8501 8502 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8503 which is 0 (disabled) if not configured. 8504 8505 workqueue.panic_on_stall_time=<uint> 8506 Panic when a workqueue stall has been continuous for 8507 the specified number of seconds. Unlike panic_on_stall 8508 which counts accumulated stall events, this triggers 8509 based on the duration of a single continuous stall. 8510 8511 The default is 0, which disables the time-based panic. 8512 8513 workqueue.cpu_intensive_thresh_us= 8514 Per-cpu work items which run for longer than this 8515 threshold are automatically considered CPU intensive 8516 and excluded from concurrency management to prevent 8517 them from noticeably delaying other per-cpu work 8518 items. Default is 10000 (10ms). 8519 8520 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8521 will report the work functions which violate this 8522 threshold repeatedly. They are likely good 8523 candidates for using WQ_UNBOUND workqueues instead. 8524 8525 workqueue.cpu_intensive_warning_thresh=<uint> 8526 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8527 will report the work functions which violate the 8528 intensive_threshold_us repeatedly. In order to prevent 8529 spurious warnings, start printing only after a work 8530 function has violated this threshold number of times. 8531 8532 The default is 4 times. 0 disables the warning. 8533 8534 workqueue.power_efficient 8535 Per-cpu workqueues are generally preferred because 8536 they show better performance thanks to cache 8537 locality; unfortunately, per-cpu workqueues tend to 8538 be more power hungry than unbound workqueues. 8539 8540 Enabling this makes the per-cpu workqueues which 8541 were observed to contribute significantly to power 8542 consumption unbound, leading to measurably lower 8543 power usage at the cost of small performance 8544 overhead. 8545 8546 The default value of this parameter is determined by 8547 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8548 8549 workqueue.default_affinity_scope= 8550 Select the default affinity scope to use for unbound 8551 workqueues. Can be one of "cpu", "smt", "cache", 8552 "cache_shard", "numa" and "system". Default is 8553 "cache_shard". For more 8554 information, see the Affinity Scopes section in 8555 Documentation/core-api/workqueue.rst. 8556 8557 This can be changed after boot by writing to the 8558 matching /sys/module/workqueue/parameters file. All 8559 workqueues with the "default" affinity scope will be 8560 updated accordingly. 8561 8562 workqueue.debug_force_rr_cpu 8563 Workqueue used to implicitly guarantee that work 8564 items queued without explicit CPU specified are put 8565 on the local CPU. This guarantee is no longer true 8566 and while local CPU is still preferred work items 8567 may be put on foreign CPUs. This debug option 8568 forces round-robin CPU selection to flush out 8569 usages which depend on the now broken guarantee. 8570 When enabled, memory and cache locality will be 8571 impacted. 8572 8573 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8574 Type) of ioremap_wc(). 8575 8576 on - Enable writecombine, use WUC for ioremap_wc() 8577 off - Disable writecombine, use SUC for ioremap_wc() 8578 8579 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8580 default x2apic cluster mode on platforms 8581 supporting x2apic. 8582 8583 xen_512gb_limit [KNL,X86-64,XEN] 8584 Restricts the kernel running paravirtualized under Xen 8585 to use only up to 512 GB of RAM. The reason to do so is 8586 crash analysis tools and Xen tools for doing domain 8587 save/restore/migration must be enabled to handle larger 8588 domains. 8589 8590 xen_console_io [XEN,EARLY] 8591 Boolean option to enable/disable the usage of the Xen 8592 console_io hypercalls to read and write to the console. 8593 Mostly useful for debugging and development. 8594 8595 xen_emul_unplug= [HW,X86,XEN,EARLY] 8596 Unplug Xen emulated devices 8597 Format: [unplug0,][unplug1] 8598 ide-disks -- unplug primary master IDE devices 8599 aux-ide-disks -- unplug non-primary-master IDE devices 8600 nics -- unplug network devices 8601 all -- unplug all emulated devices (NICs and IDE disks) 8602 unnecessary -- unplugging emulated devices is 8603 unnecessary even if the host did not respond to 8604 the unplug protocol 8605 never -- do not unplug even if version check succeeds 8606 8607 xen_legacy_crash [X86,XEN,EARLY] 8608 Crash from Xen panic notifier, without executing late 8609 panic() code such as dumping handler. 8610 8611 xen_mc_debug [X86,XEN,EARLY] 8612 Enable multicall debugging when running as a Xen PV guest. 8613 Enabling this feature will reduce performance a little 8614 bit, so it should only be enabled for obtaining extended 8615 debug data in case of multicall errors. 8616 8617 xen_msr_safe= [X86,XEN,EARLY] 8618 Format: <bool> 8619 Select whether to always use non-faulting (safe) MSR 8620 access functions when running as Xen PV guest. The 8621 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8622 8623 xen_nopv [X86] 8624 Disables the PV optimizations forcing the HVM guest to 8625 run as generic HVM guest with no PV drivers. 8626 This option is obsoleted by the "nopv" option, which 8627 has equivalent effect for XEN platform. 8628 8629 xen_no_vector_callback 8630 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8631 event channel interrupts. 8632 8633 xen_scrub_pages= [XEN] 8634 Boolean option to control scrubbing pages before giving them back 8635 to Xen, for use by other domains. Can be also changed at runtime 8636 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8637 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8638 8639 xen_timer_slop= [X86-64,XEN,EARLY] 8640 Set the timer slop (in nanoseconds) for the virtual Xen 8641 timers (default is 100000). This adjusts the minimum 8642 delta of virtualized Xen timers, where lower values 8643 improve timer resolution at the expense of processing 8644 more timer interrupts. 8645 8646 xen.balloon_boot_timeout= [XEN] 8647 The time (in seconds) to wait before giving up to boot 8648 in case initial ballooning fails to free enough memory. 8649 Applies only when running as HVM or PVH guest and 8650 started with less memory configured than allowed at 8651 max. Default is 180. 8652 8653 xen.event_eoi_delay= [XEN] 8654 How long to delay EOI handling in case of event 8655 storms (jiffies). Default is 10. 8656 8657 xen.event_loop_timeout= [XEN] 8658 After which time (jiffies) the event handling loop 8659 should start to delay EOI handling. Default is 2. 8660 8661 xen.fifo_events= [XEN] 8662 Boolean parameter to disable using fifo event handling 8663 even if available. Normally fifo event handling is 8664 preferred over the 2-level event handling, as it is 8665 fairer and the number of possible event channels is 8666 much higher. Default is on (use fifo events). 8667 8668 xirc2ps_cs= [NET,PCMCIA] 8669 Format: 8670 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8671 8672 xive= [PPC] 8673 By default on POWER9 and above, the kernel will 8674 natively use the XIVE interrupt controller. This option 8675 allows the fallback firmware mode to be used: 8676 8677 off Fallback to firmware control of XIVE interrupt 8678 controller on both pseries and powernv 8679 platforms. Only useful on POWER9 and above. 8680 8681 xive.store-eoi=off [PPC] 8682 By default on POWER10 and above, the kernel will use 8683 stores for EOI handling when the XIVE interrupt mode 8684 is active. This option allows the XIVE driver to use 8685 loads instead, as on POWER9. 8686 8687 xhci-hcd.quirks [USB,KNL] 8688 A hex value specifying bitmask with supplemental xhci 8689 host controller quirks. Meaning of each bit can be 8690 consulted in header drivers/usb/host/xhci.h. 8691 8692 xmon [PPC,EARLY] 8693 Format: { early | on | rw | ro | off } 8694 Controls if xmon debugger is enabled. Default is off. 8695 Passing only "xmon" is equivalent to "xmon=early". 8696 early Call xmon as early as possible on boot; xmon 8697 debugger is called from setup_arch(). 8698 on xmon debugger hooks will be installed so xmon 8699 is only called on a kernel crash. Default mode, 8700 i.e. either "ro" or "rw" mode, is controlled 8701 with CONFIG_XMON_DEFAULT_RO_MODE. 8702 rw xmon debugger hooks will be installed so xmon 8703 is called only on a kernel crash, mode is write, 8704 meaning SPR registers, memory and, other data 8705 can be written using xmon commands. 8706 ro same as "rw" option above but SPR registers, 8707 memory, and other data can't be written using 8708 xmon commands. 8709 off xmon is disabled. 8710