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 USBHID USB Human Interface Device support is enabled. 78 V4L Video For Linux support is enabled. 79 VGA The VGA console has been enabled. 80 VMMIO Driver for memory mapped virtio devices is enabled. 81 VT Virtual terminal support is enabled. 82 WDT Watchdog support is enabled. 83 X86-32 X86-32, aka i386 architecture is enabled. 84 X86-64 X86-64 architecture is enabled. 85 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64) 86 X86_UV SGI UV support is enabled. 87 XEN Xen support is enabled 88 XTENSA xtensa architecture is enabled. 89 90In addition, the following text indicates that the option 91 92 BOOT Is a boot loader parameter. 93 BUGS= Relates to possible processor bugs on the said processor. 94 KNL Is a kernel start-up parameter. 95 96 97Kernel parameters 98 99 accept_memory= [MM] 100 Format: { eager | lazy } 101 default: lazy 102 By default, unaccepted memory is accepted lazily to 103 avoid prolonged boot times. The lazy option will add 104 some runtime overhead until all memory is eventually 105 accepted. In most cases the overhead is negligible. 106 For some workloads or for debugging purposes 107 accept_memory=eager can be used to accept all memory 108 at once during boot. 109 110 acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY] 111 Advanced Configuration and Power Interface 112 Format: { force | on | off | strict | noirq | rsdt | 113 copy_dsdt | nospcr } 114 force -- enable ACPI if default was off 115 on -- enable ACPI but allow fallback to DT [arm64,riscv64] 116 off -- disable ACPI if default was on 117 noirq -- do not use ACPI for IRQ routing 118 strict -- Be less tolerant of platforms that are not 119 strictly ACPI specification compliant. 120 rsdt -- prefer RSDT over (default) XSDT 121 copy_dsdt -- copy DSDT to memory 122 nocmcff -- Disable firmware first mode for corrected 123 errors. This disables parsing the HEST CMC error 124 source to check if firmware has set the FF flag. This 125 may result in duplicate corrected error reports. 126 nospcr -- disable console in ACPI SPCR table as 127 default _serial_ console on ARM64 128 spcr -- enable console in ACPI SPCR table as 129 default _serial_ console on x86 130 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 131 "acpi=nospcr" are available 132 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 133 are available 134 135 See also Documentation/power/runtime_pm.rst, pci=noacpi 136 137 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 138 Format: <int> 139 2: use 2nd APIC table, if available 140 1,0: use 1st APIC table 141 default: 0 142 143 acpi_backlight= [HW,ACPI] 144 { vendor | video | native | none } 145 If set to vendor, prefer vendor-specific driver 146 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 147 of the ACPI video.ko driver. 148 If set to video, use the ACPI video.ko driver. 149 If set to native, use the device's native backlight mode. 150 If set to none, disable the ACPI backlight interface. 151 152 acpi_force_32bit_fadt_addr [ACPI,EARLY] 153 force FADT to use 32 bit addresses rather than the 154 64 bit X_* addresses. Some firmware have broken 64 155 bit addresses for force ACPI ignore these and use 156 the older legacy 32 bit addresses. 157 158 acpica_no_return_repair [HW, ACPI] 159 Disable AML predefined validation mechanism 160 This mechanism can repair the evaluation result to make 161 the return objects more ACPI specification compliant. 162 This option is useful for developers to identify the 163 root cause of an AML interpreter issue when the issue 164 has something to do with the repair mechanism. 165 166 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 167 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 168 Format: <int> 169 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 170 debug output. Bits in debug_layer correspond to a 171 _COMPONENT in an ACPI source file, e.g., 172 #define _COMPONENT ACPI_EVENTS 173 Bits in debug_level correspond to a level in 174 ACPI_DEBUG_PRINT statements, e.g., 175 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 176 The debug_level mask defaults to "info". See 177 Documentation/firmware-guide/acpi/debug.rst for more information about 178 debug layers and levels. 179 180 Enable processor driver info messages: 181 acpi.debug_layer=0x20000000 182 Enable AML "Debug" output, i.e., stores to the Debug 183 object while interpreting AML: 184 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 185 Enable all messages related to ACPI hardware: 186 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 187 188 Some values produce so much output that the system is 189 unusable. The "log_buf_len" parameter may be useful 190 if you need to capture more output. 191 192 acpi_enforce_resources= [ACPI] 193 { strict | lax | no } 194 Check for resource conflicts between native drivers 195 and ACPI OperationRegions (SystemIO and SystemMemory 196 only). IO ports and memory declared in ACPI might be 197 used by the ACPI subsystem in arbitrary AML code and 198 can interfere with legacy drivers. 199 strict (default): access to resources claimed by ACPI 200 is denied; legacy drivers trying to access reserved 201 resources will fail to bind to device using them. 202 lax: access to resources claimed by ACPI is allowed; 203 legacy drivers trying to access reserved resources 204 will bind successfully but a warning message is logged. 205 no: ACPI OperationRegions are not marked as reserved, 206 no further checks are performed. 207 208 acpi_force_table_verification [HW,ACPI,EARLY] 209 Enable table checksum verification during early stage. 210 By default, this is disabled due to x86 early mapping 211 size limitation. 212 213 acpi_irq_balance [HW,ACPI] 214 ACPI will balance active IRQs 215 default in APIC mode 216 217 acpi_irq_nobalance [HW,ACPI] 218 ACPI will not move active IRQs (default) 219 default in PIC mode 220 221 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 222 Format: <irq>,<irq>... 223 224 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 225 use by PCI 226 Format: <irq>,<irq>... 227 228 acpi_mask_gpe= [HW,ACPI] 229 Due to the existence of _Lxx/_Exx, some GPEs triggered 230 by unsupported hardware/firmware features can result in 231 GPE floodings that cannot be automatically disabled by 232 the GPE dispatcher. 233 This facility can be used to prevent such uncontrolled 234 GPE floodings. 235 Format: <byte> or <bitmap-list> 236 237 acpi_no_auto_serialize [HW,ACPI] 238 Disable auto-serialization of AML methods 239 AML control methods that contain the opcodes to create 240 named objects will be marked as "Serialized" by the 241 auto-serialization feature. 242 This feature is enabled by default. 243 This option allows to turn off the feature. 244 245 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 246 kernels. 247 248 acpi_no_static_ssdt [HW,ACPI,EARLY] 249 Disable installation of static SSDTs at early boot time 250 By default, SSDTs contained in the RSDT/XSDT will be 251 installed automatically and they will appear under 252 /sys/firmware/acpi/tables. 253 This option turns off this feature. 254 Note that specifying this option does not affect 255 dynamic table installation which will install SSDT 256 tables to /sys/firmware/acpi/tables/dynamic. 257 258 acpi_no_watchdog [HW,ACPI,WDT] 259 Ignore the ACPI-based watchdog interface (WDAT) and let 260 a native driver control the watchdog device instead. 261 262 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 263 Pass the RSDP address to the kernel, mostly used 264 on machines running EFI runtime service to boot the 265 second kernel for kdump. 266 267 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 268 Format: To spoof as Windows 98: ="Microsoft Windows" 269 270 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 271 of 2 which is mandated by ACPI 6) as the supported ACPI 272 specification revision (when using this switch, it may 273 be necessary to carry out a cold reboot _twice_ in a 274 row to make it take effect on the platform firmware). 275 276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 277 acpi_osi="string1" # add string1 278 acpi_osi="!string2" # remove string2 279 acpi_osi=!* # remove all strings 280 acpi_osi=! # disable all built-in OS vendor 281 strings 282 acpi_osi=!! # enable all built-in OS vendor 283 strings 284 acpi_osi= # disable all strings 285 286 'acpi_osi=!' can be used in combination with single or 287 multiple 'acpi_osi="string1"' to support specific OS 288 vendor string(s). Note that such command can only 289 affect the default state of the OS vendor strings, thus 290 it cannot affect the default state of the feature group 291 strings and the current state of the OS vendor strings, 292 specifying it multiple times through kernel command line 293 is meaningless. This command is useful when one do not 294 care about the state of the feature group strings which 295 should be controlled by the OSPM. 296 Examples: 297 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 298 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 299 can make '_OSI("Windows 2000")' TRUE. 300 301 'acpi_osi=' cannot be used in combination with other 302 'acpi_osi=' command lines, the _OSI method will not 303 exist in the ACPI namespace. NOTE that such command can 304 only affect the _OSI support state, thus specifying it 305 multiple times through kernel command line is also 306 meaningless. 307 Examples: 308 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 309 FALSE. 310 311 'acpi_osi=!*' can be used in combination with single or 312 multiple 'acpi_osi="string1"' to support specific 313 string(s). Note that such command can affect the 314 current state of both the OS vendor strings and the 315 feature group strings, thus specifying it multiple times 316 through kernel command line is meaningful. But it may 317 still not able to affect the final state of a string if 318 there are quirks related to this string. This command 319 is useful when one want to control the state of the 320 feature group strings to debug BIOS issues related to 321 the OSPM features. 322 Examples: 323 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 324 '_OSI("Module Device")' FALSE. 325 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 326 '_OSI("Module Device")' TRUE. 327 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 328 equivalent to 329 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 330 and 331 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 332 they all will make '_OSI("Windows 2000")' TRUE. 333 334 acpi_pm_good [X86] 335 Override the pmtimer bug detection: force the kernel 336 to assume that this machine's pmtimer latches its value 337 and always returns good values. 338 339 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 340 Format: { level | edge | high | low } 341 342 acpi_skip_timer_override [HW,ACPI,EARLY] 343 Recognize and ignore IRQ0/pin2 Interrupt Override. 344 For broken nForce2 BIOS resulting in XT-PIC timer. 345 346 acpi_sleep= [HW,ACPI] Sleep options 347 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 348 s4_nohwsig, old_ordering, nonvs, 349 sci_force_enable, nobl } 350 See Documentation/power/video.rst for information on 351 s3_bios and s3_mode. 352 s3_beep is for debugging; it makes the PC's speaker beep 353 as soon as the kernel's real-mode entry point is called. 354 s4_hwsig causes the kernel to check the ACPI hardware 355 signature during resume from hibernation, and gracefully 356 refuse to resume if it has changed. This complies with 357 the ACPI specification but not with reality, since 358 Windows does not do this and many laptops do change it 359 on docking. So the default behaviour is to allow resume 360 and simply warn when the signature changes, unless the 361 s4_hwsig option is enabled. 362 s4_nohwsig prevents ACPI hardware signature from being 363 used (or even warned about) during resume. 364 old_ordering causes the ACPI 1.0 ordering of the _PTS 365 control method, with respect to putting devices into 366 low power states, to be enforced (the ACPI 2.0 ordering 367 of _PTS is used by default). 368 nonvs prevents the kernel from saving/restoring the 369 ACPI NVS memory during suspend/hibernation and resume. 370 sci_force_enable causes the kernel to set SCI_EN directly 371 on resume from S1/S3 (which is against the ACPI spec, 372 but some broken systems don't work without it). 373 nobl causes the internal blacklist of systems known to 374 behave incorrectly in some ways with respect to system 375 suspend and resume to be ignored (use wisely). 376 377 acpi_use_timer_override [HW,ACPI,EARLY] 378 Use timer override. For some broken Nvidia NF5 boards 379 that require a timer override, but don't have HPET 380 381 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 382 kernel's map of available physical RAM. 383 384 agp= [AGP] 385 { off | try_unsupported } 386 off: disable AGP support 387 try_unsupported: try to drive unsupported chipsets 388 (may crash computer or cause data corruption) 389 390 ALSA [HW,ALSA] 391 See Documentation/sound/alsa-configuration.rst 392 393 alignment= [KNL,ARM] 394 Allow the default userspace alignment fault handler 395 behaviour to be specified. Bit 0 enables warnings, 396 bit 1 enables fixups, and bit 2 sends a segfault. 397 398 align_va_addr= [X86-64] 399 Align virtual addresses by clearing slice [14:12] when 400 allocating a VMA at process creation time. This option 401 gives you up to 3% performance improvement on AMD F15h 402 machines (where it is enabled by default) for a 403 CPU-intensive style benchmark, and it can vary highly in 404 a microbenchmark depending on workload and compiler. 405 406 32: only for 32-bit processes 407 64: only for 64-bit processes 408 on: enable for both 32- and 64-bit processes 409 off: disable for both 32- and 64-bit processes 410 411 alloc_snapshot [FTRACE] 412 Allocate the ftrace snapshot buffer on boot up when the 413 main buffer is allocated. This is handy if debugging 414 and you need to use tracing_snapshot() on boot up, and 415 do not want to use tracing_snapshot_alloc() as it needs 416 to be done where GFP_KERNEL allocations are allowed. 417 418 allow_mismatched_32bit_el0 [ARM64,EARLY] 419 Allow execve() of 32-bit applications and setting of the 420 PER_LINUX32 personality on systems where only a strict 421 subset of the CPUs support 32-bit EL0. When this 422 parameter is present, the set of CPUs supporting 32-bit 423 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 424 and hot-unplug operations may be restricted. 425 426 See Documentation/arch/arm64/asymmetric-32bit.rst for more 427 information. 428 429 amd_iommu= [HW,X86-64] 430 Pass parameters to the AMD IOMMU driver in the system. 431 Possible values are: 432 fullflush - Deprecated, equivalent to iommu.strict=1 433 off - do not initialize any AMD IOMMU found in 434 the system 435 force_isolation - Force device isolation for all 436 devices. The IOMMU driver is not 437 allowed anymore to lift isolation 438 requirements as needed. This option 439 does not override iommu=pt 440 force_enable - Force enable the IOMMU on platforms known 441 to be buggy with IOMMU enabled. Use this 442 option with care. 443 pgtbl_v1 - Use v1 page table for DMA-API (Default). 444 pgtbl_v2 - Use v2 page table for DMA-API. 445 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 446 nohugepages - Limit page-sizes used for v1 page-tables 447 to 4 KiB. 448 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 449 to 4KiB/2Mib/1GiB. 450 451 452 amd_iommu_dump= [HW,X86-64] 453 Enable AMD IOMMU driver option to dump the ACPI table 454 for AMD IOMMU. With this option enabled, AMD IOMMU 455 driver will print ACPI tables for AMD IOMMU during 456 IOMMU initialization. 457 458 amd_iommu_intr= [HW,X86-64] 459 Specifies one of the following AMD IOMMU interrupt 460 remapping modes: 461 legacy - Use legacy interrupt remapping mode. 462 vapic - Use virtual APIC mode, which allows IOMMU 463 to inject interrupts directly into guest. 464 This mode requires kvm-amd.avic=1. 465 (Default when IOMMU HW support is present.) 466 467 amd_pstate= [X86,EARLY] 468 disable 469 Do not enable amd_pstate as the default 470 scaling driver for the supported processors 471 passive 472 Use amd_pstate with passive mode as a scaling driver. 473 In this mode autonomous selection is disabled. 474 Driver requests a desired performance level and platform 475 tries to match the same performance level if it is 476 satisfied by guaranteed performance level. 477 active 478 Use amd_pstate_epp driver instance as the scaling driver, 479 driver provides a hint to the hardware if software wants 480 to bias toward performance (0x0) or energy efficiency (0xff) 481 to the CPPC firmware. then CPPC power algorithm will 482 calculate the runtime workload and adjust the realtime cores 483 frequency. 484 guided 485 Activate guided autonomous mode. Driver requests minimum and 486 maximum performance level and the platform autonomously 487 selects a performance level in this range and appropriate 488 to the current workload. 489 490 amd_prefcore= 491 [X86] 492 disable 493 Disable amd-pstate preferred core. 494 495 amijoy.map= [HW,JOY] Amiga joystick support 496 Map of devices attached to JOY0DAT and JOY1DAT 497 Format: <a>,<b> 498 See also Documentation/input/joydev/joystick.rst 499 500 analog.map= [HW,JOY] Analog joystick and gamepad support 501 Specifies type or capabilities of an analog joystick 502 connected to one of 16 gameports 503 Format: <type1>,<type2>,..<type16> 504 505 apc= [HW,SPARC] 506 Power management functions (SPARCstation-4/5 + deriv.) 507 Format: noidle 508 Disable APC CPU standby support. SPARCstation-Fox does 509 not play well with APC CPU idle - disable it if you have 510 APC and your system crashes randomly. 511 512 apic [APIC,X86-64] Use IO-APIC. Default. 513 514 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 515 Change the output verbosity while booting 516 Format: { quiet (default) | verbose | debug } 517 Change the amount of debugging information output 518 when initialising the APIC and IO-APIC components. 519 520 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 521 Format: { bsp (default) | all | none } 522 bsp: External NMI is delivered only to CPU 0 523 all: External NMIs are broadcast to all CPUs as a 524 backup of CPU 0 525 none: External NMI is masked for all CPUs. This is 526 useful so that a dump capture kernel won't be 527 shot down by NMI 528 529 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 530 apicmaintimer. Useful when your PIT timer is totally 531 broken. 532 533 autoconf= [IPV6] 534 See Documentation/networking/ipv6.rst. 535 536 apm= [APM] Advanced Power Management 537 See header of arch/x86/kernel/apm_32.c. 538 539 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 540 Format: { "0" | "1" } 541 See security/apparmor/Kconfig help text 542 0 -- disable. 543 1 -- enable. 544 Default value is set via kernel config option. 545 546 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 547 Format: <io>,<irq>,<nodeID> 548 549 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 550 32 bit applications. 551 552 arm64.nobti [ARM64] Unconditionally disable Branch Target 553 Identification support 554 555 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 556 support 557 558 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 559 Set instructions support 560 561 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 562 Monitoring support 563 564 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 565 support 566 567 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 568 support 569 570 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 571 Extension support 572 573 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 574 Extension support 575 576 ataflop= [HW,M68k] 577 578 atarimouse= [HW,MOUSE] Atari Mouse 579 580 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 581 EzKey and similar keyboards 582 583 atkbd.reset= [HW] Reset keyboard during initialization 584 585 atkbd.set= [HW] Select keyboard code set 586 Format: <int> (2 = AT (default), 3 = PS/2) 587 588 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 589 keyboards 590 591 atkbd.softraw= [HW] Choose between synthetic and real raw mode 592 Format: <bool> (0 = real, 1 = synthetic (default)) 593 594 atkbd.softrepeat= [HW] 595 Use software keyboard repeat 596 597 audit= [KNL] Enable the audit sub-system 598 Format: { "0" | "1" | "off" | "on" } 599 0 | off - kernel audit is disabled and can not be 600 enabled until the next reboot 601 unset - kernel audit is initialized but disabled and 602 will be fully enabled by the userspace auditd. 603 1 | on - kernel audit is initialized and partially 604 enabled, storing at most audit_backlog_limit 605 messages in RAM until it is fully enabled by the 606 userspace auditd. 607 Default: unset 608 609 audit_backlog_limit= [KNL] Set the audit queue size limit. 610 Format: <int> (must be >=0) 611 Default: 64 612 613 bau= [X86_UV] Enable the BAU on SGI UV. The default 614 behavior is to disable the BAU (i.e. bau=0). 615 Format: { "0" | "1" } 616 0 - Disable the BAU. 617 1 - Enable the BAU. 618 unset - Disable the BAU. 619 620 baycom_epp= [HW,AX25] 621 Format: <io>,<mode> 622 623 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 624 Format: <io>,<mode> 625 See header of drivers/net/hamradio/baycom_par.c. 626 627 baycom_ser_fdx= [HW,AX25] 628 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 629 Format: <io>,<irq>,<mode>[,<baud>] 630 See header of drivers/net/hamradio/baycom_ser_fdx.c. 631 632 baycom_ser_hdx= [HW,AX25] 633 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 634 Format: <io>,<irq>,<mode> 635 See header of drivers/net/hamradio/baycom_ser_hdx.c. 636 637 bdev_allow_write_mounted= 638 Format: <bool> 639 Control the ability to open a mounted block device 640 for writing, i.e., allow / disallow writes that bypass 641 the FS. This was implemented as a means to prevent 642 fuzzers from crashing the kernel by overwriting the 643 metadata underneath a mounted FS without its awareness. 644 This also prevents destructive formatting of mounted 645 filesystems by naive storage tooling that don't use 646 O_EXCL. Default is Y and can be changed through the 647 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 648 649 bert_disable [ACPI] 650 Disable BERT OS support on buggy BIOSes. 651 652 bgrt_disable [ACPI,X86,EARLY] 653 Disable BGRT to avoid flickering OEM logo. 654 655 blkdevparts= Manual partition parsing of block device(s) for 656 embedded devices based on command line input. 657 See Documentation/block/cmdline-partition.rst 658 659 boot_delay= [KNL,EARLY] 660 Milliseconds to delay each printk during boot. 661 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 662 and you may also have to specify "lpj=". Boot_delay 663 values larger than 10 seconds (10000) are assumed 664 erroneous and ignored. 665 Format: integer 666 667 bootconfig [KNL,EARLY] 668 Extended command line options can be added to an initrd 669 and this will cause the kernel to look for it. 670 671 See Documentation/admin-guide/bootconfig.rst 672 673 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 674 bttv.radio= Most important insmod options are available as 675 kernel args too. 676 bttv.pll= See Documentation/admin-guide/media/bttv.rst 677 bttv.tuner= 678 679 bulk_remove=off [PPC] This parameter disables the use of the pSeries 680 firmware feature for flushing multiple hpte entries 681 at a time. 682 683 c101= [NET] Moxa C101 synchronous serial card 684 685 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 686 Sometimes CPU hardware bugs make them report the cache 687 size incorrectly. The kernel will attempt work arounds 688 to fix known problems, but for some CPUs it is not 689 possible to determine what the correct size should be. 690 This option provides an override for these situations. 691 692 carrier_timeout= 693 [NET] Specifies amount of time (in seconds) that 694 the kernel should wait for a network carrier. By default 695 it waits 120 seconds. 696 697 ca_keys= [KEYS] This parameter identifies a specific key(s) on 698 the system trusted keyring to be used for certificate 699 trust validation. 700 format: { id:<keyid> | builtin } 701 702 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 703 algorithm. Accepted values range from 0 to 7 704 inclusive. See arch/mips/include/asm/pgtable-bits.h 705 for platform specific values (SB1, Loongson3 and 706 others). 707 708 ccw_timeout_log [S390] 709 See Documentation/arch/s390/common_io.rst for details. 710 711 cfi= [X86-64] Set Control Flow Integrity checking features 712 when CONFIG_FINEIBT is enabled. 713 Format: feature[,feature...] 714 Default: auto 715 716 auto: Use FineIBT if IBT available, otherwise kCFI. 717 Under FineIBT, enable "paranoid" mode when 718 FRED is not available. 719 off: Turn off CFI checking. 720 kcfi: Use kCFI (disable FineIBT). 721 fineibt: Use FineIBT (even if IBT not available). 722 norand: Do not re-randomize CFI hashes. 723 paranoid: Add caller hash checking under FineIBT. 724 bhi: Enable register poisoning to stop speculation 725 across FineIBT. (Disabled by default.) 726 warn: Do not enforce CFI checking: warn only. 727 debug: Report CFI initialization details. 728 729 cgroup_disable= [KNL] Disable a particular controller or optional feature 730 Format: {name of the controller(s) or feature(s) to disable} 731 The effects of cgroup_disable=foo are: 732 - foo isn't auto-mounted if you mount all cgroups in 733 a single hierarchy 734 - foo isn't visible as an individually mountable 735 subsystem 736 - if foo is an optional feature then the feature is 737 disabled and corresponding cgroup files are not 738 created 739 {Currently only "memory" controller deal with this and 740 cut the overhead, others just disable the usage. So 741 only cgroup_disable=memory is actually worthy} 742 Specifying "pressure" disables per-cgroup pressure 743 stall information accounting feature 744 745 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 746 Format: { { controller | "all" | "named" } 747 [,{ controller | "all" | "named" }...] } 748 Like cgroup_disable, but only applies to cgroup v1; 749 the blacklisted controllers remain available in cgroup2. 750 "all" blacklists all controllers and "named" disables 751 named mounts. Specifying both "all" and "named" disables 752 all v1 hierarchies. 753 754 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 755 Format: { "true" | "false" } 756 /proc/cgroups lists only v1 controllers by default. 757 This compatibility option enables listing also v2 758 controllers (whose v1 code is not compiled!), so that 759 semi-legacy software can check this file to decide 760 about usage of v2 (sic) controllers. 761 762 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 763 Format: { "true" | "false" } 764 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 765 766 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 767 Format: <string> 768 nosocket -- Disable socket memory accounting. 769 nokmem -- Disable kernel memory accounting. 770 nobpf -- Disable BPF memory accounting. 771 772 check_pages= [MM,EARLY] Enable sanity checking of pages after 773 allocations / before freeing. This adds checks to catch 774 double-frees, use-after-frees, and other sources of 775 page corruption by inspecting page internals (flags, 776 mapcount/refcount, memcg_data, etc.). 777 Format: { "0" | "1" } 778 Default: 0 (1 if CONFIG_DEBUG_VM is set) 779 780 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 781 Format: { "0" | "1" } 782 See security/selinux/Kconfig help text. 783 0 -- check protection applied by kernel (includes 784 any implied execute protection). 785 1 -- check protection requested by application. 786 Default value is set via a kernel config option. 787 Value can be changed at runtime via 788 /sys/fs/selinux/checkreqprot. 789 Setting checkreqprot to 1 is deprecated. 790 791 cio_ignore= [S390] 792 See Documentation/arch/s390/common_io.rst for details. 793 794 clearcpuid=X[,X...] [X86] 795 Disable CPUID feature X for the kernel. See 796 arch/x86/include/asm/cpufeatures.h for the valid bit 797 numbers X. Note the Linux-specific bits are not necessarily 798 stable over kernel options, but the vendor-specific 799 ones should be. 800 X can also be a string as appearing in the flags: line 801 in /proc/cpuinfo which does not have the above 802 instability issue. However, not all features have names 803 in /proc/cpuinfo. 804 Note that using this option will taint your kernel. 805 Also note that user programs calling CPUID directly 806 or using the feature without checking anything 807 will still see it. This just prevents it from 808 being used by the kernel or shown in /proc/cpuinfo. 809 Also note the kernel might malfunction if you disable 810 some critical bits. 811 812 clk_ignore_unused 813 [CLK] 814 Prevents the clock framework from automatically gating 815 clocks that have not been explicitly enabled by a Linux 816 device driver but are enabled in hardware at reset or 817 by the bootloader/firmware. Note that this does not 818 force such clocks to be always-on nor does it reserve 819 those clocks in any way. This parameter is useful for 820 debug and development, but should not be needed on a 821 platform with proper driver support. For more 822 information, see Documentation/driver-api/clk.rst. 823 824 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 825 [Deprecated] 826 Forces specified clocksource (if available) to be used 827 when calculating gettimeofday(). If specified 828 clocksource is not available, it defaults to PIT. 829 Format: { pit | tsc | cyclone | pmtmr } 830 831 clocksource= Override the default clocksource 832 Format: <string> 833 Override the default clocksource and use the clocksource 834 with the name specified. 835 Some clocksource names to choose from, depending on 836 the platform: 837 [all] jiffies (this is the base, fallback clocksource) 838 [ACPI] acpi_pm 839 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 840 pxa_timer,timer3,32k_counter,timer0_1 841 [X86-32] pit,hpet,tsc; 842 scx200_hrt on Geode; cyclone on IBM x440 843 [MIPS] MIPS 844 [PARISC] cr16 845 [S390] tod 846 [SH] SuperH 847 [SPARC64] tick 848 [X86-64] hpet,tsc 849 850 clocksource.arm_arch_timer.evtstrm= 851 [ARM,ARM64,EARLY] 852 Format: <bool> 853 Enable/disable the eventstream feature of the ARM 854 architected timer so that code using WFE-based polling 855 loops can be debugged more effectively on production 856 systems. 857 858 clocksource.verify_n_cpus= [KNL] 859 Limit the number of CPUs checked for clocksources 860 marked with CLOCK_SOURCE_VERIFY_PERCPU that 861 are marked unstable due to excessive skew. 862 A negative value says to check all CPUs, while 863 zero says not to check any. Values larger than 864 nr_cpu_ids are silently truncated to nr_cpu_ids. 865 The actual CPUs are chosen randomly, with 866 no replacement if the same CPU is chosen twice. 867 868 clocksource-wdtest.holdoff= [KNL] 869 Set the time in seconds that the clocksource 870 watchdog test waits before commencing its tests. 871 Defaults to zero when built as a module and to 872 10 seconds when built into the kernel. 873 874 cma=nn[MG]@[start[MG][-end[MG]]] 875 [KNL,CMA,EARLY] 876 Sets the size of kernel global memory area for 877 contiguous memory allocations and optionally the 878 placement constraint by the physical address range of 879 memory allocations. A value of 0 disables CMA 880 altogether. For more information, see 881 kernel/dma/contiguous.c 882 883 cma_pernuma=nn[MG] 884 [KNL,CMA,EARLY] 885 Sets the size of kernel per-numa memory area for 886 contiguous memory allocations. A value of 0 disables 887 per-numa CMA altogether. And If this option is not 888 specified, the default value is 0. 889 With per-numa CMA enabled, DMA users on node nid will 890 first try to allocate buffer from the pernuma area 891 which is located in node nid, if the allocation fails, 892 they will fallback to the global default memory area. 893 894 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 895 [KNL,CMA,EARLY] 896 Sets the size of kernel numa memory area for 897 contiguous memory allocations. It will reserve CMA 898 area for the specified node. 899 900 With numa CMA enabled, DMA users on node nid will 901 first try to allocate buffer from the numa area 902 which is located in node nid, if the allocation fails, 903 they will fallback to the global default memory area. 904 905 cmo_free_hint= [PPC] Format: { yes | no } 906 Specify whether pages are marked as being inactive 907 when they are freed. This is used in CMO environments 908 to determine OS memory pressure for page stealing by 909 a hypervisor. 910 Default: yes 911 912 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 913 Sets the size of memory pool for coherent, atomic dma 914 allocations, by default set to 256K. 915 916 com20020= [HW,NET] ARCnet - COM20020 chipset 917 Format: 918 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 919 920 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 921 Format: <io>[,<irq>] 922 923 com90xx= [HW,NET] 924 ARCnet - COM90xx chipset (memory-mapped buffers) 925 Format: <io>[,<irq>[,<memstart>]] 926 927 condev= [HW,S390] console device 928 conmode= 929 930 con3215_drop= [S390,EARLY] 3215 console drop mode. 931 Format: y|n|Y|N|1|0 932 When set to true, drop data on the 3215 console when 933 the console buffer is full. In this case the 934 operator using a 3270 terminal emulator (for example 935 x3270) does not have to enter the clear key for the 936 console output to advance and the kernel to continue. 937 This leads to a much faster boot time when a 3270 938 terminal emulator is active. If no 3270 terminal 939 emulator is used, this parameter has no effect. 940 941 console= [KNL] Output console device and options. 942 943 tty<n> Use the virtual console device <n>. 944 945 ttyS<n>[,options] 946 ttyUSB0[,options] 947 Use the specified serial port. The options are of 948 the form "bbbbpnf", where "bbbb" is the baud rate, 949 "p" is parity ("n", "o", or "e"), "n" is number of 950 bits, and "f" is flow control ("r" for RTS or 951 omit it). Default is "9600n8". 952 953 See Documentation/admin-guide/serial-console.rst for more 954 information. See 955 Documentation/networking/netconsole.rst for an 956 alternative. 957 958 <DEVNAME>:<n>.<n>[,options] 959 Use the specified serial port on the serial core bus. 960 The addressing uses DEVNAME of the physical serial port 961 device, followed by the serial core controller instance, 962 and the serial port instance. The options are the same 963 as documented for the ttyS addressing above. 964 965 The mapping of the serial ports to the tty instances 966 can be viewed with: 967 968 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 969 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 970 971 In the above example, the console can be addressed with 972 console=00:04:0.0. Note that a console addressed this 973 way will only get added when the related device driver 974 is ready. The use of an earlycon parameter in addition to 975 the console may be desired for console output early on. 976 977 uart[8250],io,<addr>[,options] 978 uart[8250],mmio,<addr>[,options] 979 uart[8250],mmio16,<addr>[,options] 980 uart[8250],mmio32,<addr>[,options] 981 uart[8250],0x<addr>[,options] 982 Start an early, polled-mode console on the 8250/16550 983 UART at the specified I/O port or MMIO address, 984 switching to the matching ttyS device later. 985 MMIO inter-register address stride is either 8-bit 986 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 987 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 988 to be equivalent to 'mmio'. 'options' are specified in 989 the same format described for ttyS above; if unspecified, 990 the h/w is not re-initialized. 991 992 hvc<n> Use the hypervisor console device <n>. This is for 993 both Xen and PowerPC hypervisors. 994 995 { null | "" } 996 Use to disable console output, i.e., to have kernel 997 console messages discarded. 998 This must be the only console= parameter used on the 999 kernel command line. 1000 1001 If the device connected to the port is not a TTY but a braille 1002 device, prepend "brl," before the device type, for instance 1003 console=brl,ttyS0 1004 For now, only VisioBraille is supported. 1005 1006 console_msg_format= 1007 [KNL] Change console messages format 1008 default 1009 By default we print messages on consoles in 1010 "[time stamp] text\n" format (time stamp may not be 1011 printed, depending on CONFIG_PRINTK_TIME or 1012 `printk_time' param). 1013 syslog 1014 Switch to syslog format: "<%u>[time stamp] text\n" 1015 IOW, each message will have a facility and loglevel 1016 prefix. The format is similar to one used by syslog() 1017 syscall, or to executing "dmesg -S --raw" or to reading 1018 from /proc/kmsg. 1019 1020 consoleblank= [KNL] The console blank (screen saver) timeout in 1021 seconds. A value of 0 disables the blank timer. 1022 Defaults to 0. 1023 1024 coredump_filter= 1025 [KNL] Change the default value for 1026 /proc/<pid>/coredump_filter. 1027 See also Documentation/filesystems/proc.rst. 1028 1029 coresight_cpu_debug.enable 1030 [ARM,ARM64] 1031 Format: <bool> 1032 Enable/disable the CPU sampling based debugging. 1033 0: default value, disable debugging 1034 1: enable debugging at boot time 1035 1036 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1037 Format: 1038 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1039 1040 cpuidle.off=1 [CPU_IDLE] 1041 disable the cpuidle sub-system 1042 1043 cpuidle.governor= 1044 [CPU_IDLE] Name of the cpuidle governor to use. 1045 1046 cpufreq.off=1 [CPU_FREQ] 1047 disable the cpufreq sub-system 1048 1049 cpufreq.default_governor= 1050 [CPU_FREQ] Name of the default cpufreq governor or 1051 policy to use. This governor must be registered in the 1052 kernel before the cpufreq driver probes. 1053 1054 cpu_init_udelay=N 1055 [X86,EARLY] Delay for N microsec between assert and de-assert 1056 of APIC INIT to start processors. This delay occurs 1057 on every CPU online, such as boot, and resume from suspend. 1058 Default: 10000 1059 1060 cpuhp.parallel= 1061 [SMP] Enable/disable parallel bringup of secondary CPUs 1062 Format: <bool> 1063 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1064 the parameter has no effect. 1065 1066 crash_kexec_post_notifiers 1067 Only jump to kdump kernel after running the panic 1068 notifiers and dumping kmsg. This option increases 1069 the risks of a kdump failure, since some panic 1070 notifiers can make the crashed kernel more unstable. 1071 In configurations where kdump may not be reliable, 1072 running the panic notifiers could allow collecting 1073 more data on dmesg, like stack traces from other CPUS 1074 or extra data dumped by panic_print. Note that some 1075 configurations enable this option unconditionally, 1076 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1077 1078 crashkernel=size[KMG][@offset[KMG]] 1079 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1080 upon panic. This parameter reserves the physical 1081 memory region [offset, offset + size] for that kernel 1082 image. If '@offset' is omitted, then a suitable offset 1083 is selected automatically. 1084 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1085 under 4G first, and fall back to reserve region above 1086 4G when '@offset' hasn't been specified. 1087 See Documentation/admin-guide/kdump/kdump.rst for further details. 1088 1089 crashkernel=range1:size1[,range2:size2,...][@offset] 1090 [KNL] Same as above, but depends on the memory 1091 in the running system. The syntax of range is 1092 start-[end] where start and end are both 1093 a memory unit (amount[KMG]). See also 1094 Documentation/admin-guide/kdump/kdump.rst for an example. 1095 1096 crashkernel=size[KMG],high 1097 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1098 above 4G. 1099 Allow kernel to allocate physical memory region from top, 1100 so could be above 4G if system have more than 4G ram 1101 installed. Otherwise memory region will be allocated 1102 below 4G, if available. 1103 It will be ignored if crashkernel=X is specified. 1104 crashkernel=size[KMG],low 1105 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1106 When crashkernel=X,high is passed, kernel could allocate 1107 physical memory region above 4G, that cause second kernel 1108 crash on system that require some amount of low memory, 1109 e.g. swiotlb requires at least 64M+32K low memory, also 1110 enough extra low memory is needed to make sure DMA buffers 1111 for 32-bit devices won't run out. Kernel would try to allocate 1112 default size of memory below 4G automatically. The default 1113 size is platform dependent. 1114 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1115 --> arm64: 128MiB 1116 --> riscv: 128MiB 1117 --> loongarch: 128MiB 1118 This one lets the user specify own low range under 4G 1119 for second kernel instead. 1120 0: to disable low allocation. 1121 It will be ignored when crashkernel=X,high is not used 1122 or memory reserved is below 4G. 1123 crashkernel=size[KMG],cma 1124 [KNL, X86, ppc] Reserve additional crash kernel memory from 1125 CMA. This reservation is usable by the first system's 1126 userspace memory and kernel movable allocations (memory 1127 balloon, zswap). Pages allocated from this memory range 1128 will not be included in the vmcore so this should not 1129 be used if dumping of userspace memory is intended and 1130 it has to be expected that some movable kernel pages 1131 may be missing from the dump. 1132 1133 A standard crashkernel reservation, as described above, 1134 is still needed to hold the crash kernel and initrd. 1135 1136 This option increases the risk of a kdump failure: DMA 1137 transfers configured by the first kernel may end up 1138 corrupting the second kernel's memory. 1139 1140 This reservation method is intended for systems that 1141 can't afford to sacrifice enough memory for standard 1142 crashkernel reservation and where less reliable and 1143 possibly incomplete kdump is preferable to no kdump at 1144 all. 1145 1146 cryptomgr.notests 1147 [KNL] Disable crypto self-tests 1148 1149 cs89x0_dma= [HW,NET] 1150 Format: <dma> 1151 1152 cs89x0_media= [HW,NET] 1153 Format: { rj45 | aui | bnc } 1154 1155 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1156 function call handling. When switched on, 1157 additional debug data is printed to the console 1158 in case a hanging CPU is detected, and that 1159 CPU is pinged again in order to try to resolve 1160 the hang situation. The default value of this 1161 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1162 Kconfig option. 1163 1164 dasd= [HW,NET] 1165 See header of drivers/s390/block/dasd_devmap.c. 1166 1167 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1168 (one device per port) 1169 Format: <port#>,<type> 1170 See also Documentation/input/devices/joystick-parport.rst 1171 1172 debug [KNL,EARLY] Enable kernel debugging (events log level). 1173 1174 debug_boot_weak_hash 1175 [KNL,EARLY] Enable printing [hashed] pointers early in the 1176 boot sequence. If enabled, we use a weak hash instead 1177 of siphash to hash pointers. Use this option if you are 1178 seeing instances of '(___ptrval___)') and need to see a 1179 value (hashed pointer) instead. Cryptographically 1180 insecure, please do not use on production kernels. 1181 1182 debug_locks_verbose= 1183 [KNL] verbose locking self-tests 1184 Format: <int> 1185 Print debugging info while doing the locking API 1186 self-tests. 1187 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1188 (no extra messages), setting it to -1 (all bits set) 1189 will print _a_lot_ more information - normally only 1190 useful to lockdep developers. 1191 1192 debug_objects [KNL,EARLY] Enable object debugging 1193 1194 debug_guardpage_minorder= 1195 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1196 parameter allows control of the order of pages that will 1197 be intentionally kept free (and hence protected) by the 1198 buddy allocator. Bigger value increase the probability 1199 of catching random memory corruption, but reduce the 1200 amount of memory for normal system use. The maximum 1201 possible value is MAX_PAGE_ORDER/2. Setting this 1202 parameter to 1 or 2 should be enough to identify most 1203 random memory corruption problems caused by bugs in 1204 kernel or driver code when a CPU writes to (or reads 1205 from) a random memory location. Note that there exists 1206 a class of memory corruptions problems caused by buggy 1207 H/W or F/W or by drivers badly programming DMA 1208 (basically when memory is written at bus level and the 1209 CPU MMU is bypassed) which are not detectable by 1210 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1211 help tracking down these problems. 1212 1213 debug_pagealloc= 1214 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1215 enables the feature at boot time. By default, it is 1216 disabled and the system will work mostly the same as a 1217 kernel built without CONFIG_DEBUG_PAGEALLOC. 1218 Note: to get most of debug_pagealloc error reports, it's 1219 useful to also enable the page_owner functionality. 1220 on: enable the feature 1221 1222 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1223 userspace and debugfs internal clients. 1224 Format: { on, off } 1225 on: All functions are enabled. 1226 off: Filesystem is not registered and clients 1227 get a -EPERM as result when trying to register files 1228 or directories within debugfs. 1229 This is equivalent of the runtime functionality if 1230 debugfs was not enabled in the kernel at all. 1231 Default value is set in build-time with a kernel configuration. 1232 1233 debugpat [X86] Enable PAT debugging 1234 1235 default_hugepagesz= 1236 [HW] The size of the default HugeTLB page. This is 1237 the size represented by the legacy /proc/ hugepages 1238 APIs. In addition, this is the default hugetlb size 1239 used for shmget(), mmap() and mounting hugetlbfs 1240 filesystems. If not specified, defaults to the 1241 architecture's default huge page size. Huge page 1242 sizes are architecture dependent. See also 1243 Documentation/admin-guide/mm/hugetlbpage.rst. 1244 Format: size[KMG] 1245 1246 deferred_probe_timeout= 1247 [KNL] Debugging option to set a timeout in seconds for 1248 deferred probe to give up waiting on dependencies to 1249 probe. Only specific dependencies (subsystems or 1250 drivers) that have opted in will be ignored. A timeout 1251 of 0 will timeout at the end of initcalls. If the time 1252 out hasn't expired, it'll be restarted by each 1253 successful driver registration. This option will also 1254 dump out devices still on the deferred probe list after 1255 retrying. 1256 1257 delayacct [KNL] Enable per-task delay accounting 1258 1259 dell_smm_hwmon.ignore_dmi= 1260 [HW] Continue probing hardware even if DMI data 1261 indicates that the driver is running on unsupported 1262 hardware. 1263 1264 dell_smm_hwmon.force= 1265 [HW] Activate driver even if SMM BIOS signature does 1266 not match list of supported models and enable otherwise 1267 blacklisted features. 1268 1269 dell_smm_hwmon.power_status= 1270 [HW] Report power status in /proc/i8k 1271 (disabled by default). 1272 1273 dell_smm_hwmon.restricted= 1274 [HW] Allow controlling fans only if SYS_ADMIN 1275 capability is set. 1276 1277 dell_smm_hwmon.fan_mult= 1278 [HW] Factor to multiply fan speed with. 1279 1280 dell_smm_hwmon.fan_max= 1281 [HW] Maximum configurable fan speed. 1282 1283 dfltcc= [HW,S390] 1284 Format: { on | off | def_only | inf_only | always } 1285 on: s390 zlib hardware support for compression on 1286 level 1 and decompression (default) 1287 off: No s390 zlib hardware support 1288 def_only: s390 zlib hardware support for deflate 1289 only (compression on level 1) 1290 inf_only: s390 zlib hardware support for inflate 1291 only (decompression) 1292 always: Same as 'on' but ignores the selected compression 1293 level always using hardware support (used for debugging) 1294 1295 dhash_entries= [KNL] 1296 Set number of hash buckets for dentry cache. 1297 1298 disable_1tb_segments [PPC,EARLY] 1299 Disables the use of 1TB hash page table segments. This 1300 causes the kernel to fall back to 256MB segments which 1301 can be useful when debugging issues that require an SLB 1302 miss to occur. 1303 1304 disable= [IPV6] 1305 See Documentation/networking/ipv6.rst. 1306 1307 disable_radix [PPC,EARLY] 1308 Disable RADIX MMU mode on POWER9 1309 1310 disable_tlbie [PPC] 1311 Disable TLBIE instruction. Currently does not work 1312 with KVM, with HASH MMU, or with coherent accelerators. 1313 1314 disable_ddw [PPC/PSERIES,EARLY] 1315 Disable Dynamic DMA Window support. Use this 1316 to workaround buggy firmware. 1317 1318 disable_ipv6= [IPV6] 1319 See Documentation/networking/ipv6.rst. 1320 1321 disable_mtrr_cleanup [X86,EARLY] 1322 The kernel tries to adjust MTRR layout from continuous 1323 to discrete, to make X server driver able to add WB 1324 entry later. This parameter disables that. 1325 1326 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1327 By default the kernel will trim any uncacheable 1328 memory out of your available memory pool based on 1329 MTRR settings. This parameter disables that behavior, 1330 possibly causing your machine to run very slowly. 1331 1332 disable_timer_pin_1 [X86,EARLY] 1333 Disable PIN 1 of APIC timer 1334 Can be useful to work around chipset bugs. 1335 1336 dis_ucode_ldr [X86] Disable the microcode loader. 1337 1338 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1339 this option disables the debugging code at boot. 1340 1341 dma_debug_entries=<number> 1342 This option allows to tune the number of preallocated 1343 entries for DMA-API debugging code. One entry is 1344 required per DMA-API allocation. Use this if the 1345 DMA-API debugging code disables itself because the 1346 architectural default is too low. 1347 1348 dma_debug_driver=<driver_name> 1349 With this option the DMA-API debugging driver 1350 filter feature can be enabled at boot time. Just 1351 pass the driver to filter for as the parameter. 1352 The filter can be disabled or changed to another 1353 driver later using sysfs. 1354 1355 reg_file_data_sampling= 1356 [X86] Controls mitigation for Register File Data 1357 Sampling (RFDS) vulnerability. RFDS is a CPU 1358 vulnerability which may allow userspace to infer 1359 kernel data values previously stored in floating point 1360 registers, vector registers, or integer registers. 1361 RFDS only affects Intel Atom processors. 1362 1363 on: Turns ON the mitigation. 1364 off: Turns OFF the mitigation. 1365 1366 This parameter overrides the compile time default set 1367 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1368 disabled when other VERW based mitigations (like MDS) 1369 are enabled. In order to disable RFDS mitigation all 1370 VERW based mitigations need to be disabled. 1371 1372 For details see: 1373 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1374 1375 dm_verity.keyring_unsealed= 1376 [KNL] When set to 1, leave the dm-verity keyring 1377 unsealed after initialization so userspace can 1378 provision keys. Once the keyring is restricted 1379 it becomes active and is searched during signature 1380 verification. 1381 1382 driver_async_probe= [KNL] 1383 List of driver names to be probed asynchronously. * 1384 matches with all driver names. If * is specified, the 1385 rest of the listed driver names are those that will NOT 1386 match the *. 1387 Format: <driver_name1>,<driver_name2>... 1388 1389 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1390 Broken monitors, graphic adapters, KVMs and EDIDless 1391 panels may send no or incorrect EDID data sets. 1392 This parameter allows to specify an EDID data sets 1393 in the /lib/firmware directory that are used instead. 1394 An EDID data set will only be used for a particular 1395 connector, if its name and a colon are prepended to 1396 the EDID name. Each connector may use a unique EDID 1397 data set by separating the files with a comma. An EDID 1398 data set with no connector name will be used for 1399 any connectors not explicitly specified. 1400 1401 dscc4.setup= [NET] 1402 1403 dt_cpu_ftrs= [PPC,EARLY] 1404 Format: {"off" | "known"} 1405 Control how the dt_cpu_ftrs device-tree binding is 1406 used for CPU feature discovery and setup (if it 1407 exists). 1408 off: Do not use it, fall back to legacy cpu table. 1409 known: Do not pass through unknown features to guests 1410 or userspace, only those that the kernel is aware of. 1411 1412 dump_apple_properties [X86] 1413 Dump name and content of EFI device properties on 1414 x86 Macs. Useful for driver authors to determine 1415 what data is available or for reverse-engineering. 1416 1417 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1418 <module>.dyndbg[="val"] 1419 Enable debug messages at boot time. See 1420 Documentation/admin-guide/dynamic-debug-howto.rst 1421 for details. 1422 1423 early_ioremap_debug [KNL,EARLY] 1424 Enable debug messages in early_ioremap support. This 1425 is useful for tracking down temporary early mappings 1426 which are not unmapped. 1427 1428 earlycon= [KNL,EARLY] Output early console device and options. 1429 1430 When used with no options, the early console is 1431 determined by stdout-path property in device tree's 1432 chosen node or the ACPI SPCR table if supported by 1433 the platform. 1434 1435 cdns,<addr>[,options] 1436 Start an early, polled-mode console on a Cadence 1437 (xuartps) serial port at the specified address. Only 1438 supported option is baud rate. If baud rate is not 1439 specified, the serial port must already be setup and 1440 configured. 1441 1442 uart[8250],io,<addr>[,options[,uartclk]] 1443 uart[8250],mmio,<addr>[,options[,uartclk]] 1444 uart[8250],mmio32,<addr>[,options[,uartclk]] 1445 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1446 uart[8250],0x<addr>[,options] 1447 Start an early, polled-mode console on the 8250/16550 1448 UART at the specified I/O port or MMIO address. 1449 MMIO inter-register address stride is either 8-bit 1450 (mmio) or 32-bit (mmio32 or mmio32be). 1451 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1452 to be equivalent to 'mmio'. 'options' are specified 1453 in the same format described for "console=ttyS<n>"; if 1454 unspecified, the h/w is not initialized. 'uartclk' is 1455 the uart clock frequency; if unspecified, it is set 1456 to 'BASE_BAUD' * 16. 1457 1458 pl011,<addr> 1459 pl011,mmio32,<addr> 1460 Start an early, polled-mode console on a pl011 serial 1461 port at the specified address. The pl011 serial port 1462 must already be setup and configured. Options are not 1463 yet supported. If 'mmio32' is specified, then only 1464 the driver will use only 32-bit accessors to read/write 1465 the device registers. 1466 1467 liteuart,<addr> 1468 Start an early console on a litex serial port at the 1469 specified address. The serial port must already be 1470 setup and configured. Options are not yet supported. 1471 1472 meson,<addr> 1473 Start an early, polled-mode console on a meson serial 1474 port at the specified address. The serial port must 1475 already be setup and configured. Options are not yet 1476 supported. 1477 1478 msm_serial,<addr> 1479 Start an early, polled-mode console on an msm serial 1480 port at the specified address. The serial port 1481 must already be setup and configured. Options are not 1482 yet supported. 1483 1484 msm_serial_dm,<addr> 1485 Start an early, polled-mode console on an msm serial 1486 dm port at the specified address. The serial port 1487 must already be setup and configured. Options are not 1488 yet supported. 1489 1490 owl,<addr> 1491 Start an early, polled-mode console on a serial port 1492 of an Actions Semi SoC, such as S500 or S900, at the 1493 specified address. The serial port must already be 1494 setup and configured. Options are not yet supported. 1495 1496 rda,<addr> 1497 Start an early, polled-mode console on a serial port 1498 of an RDA Micro SoC, such as RDA8810PL, at the 1499 specified address. The serial port must already be 1500 setup and configured. Options are not yet supported. 1501 1502 sbi 1503 Use RISC-V SBI (Supervisor Binary Interface) for early 1504 console. 1505 1506 smh Use ARM semihosting calls for early console. 1507 1508 s3c2410,<addr> 1509 s3c2412,<addr> 1510 s3c2440,<addr> 1511 s3c6400,<addr> 1512 s5pv210,<addr> 1513 exynos4210,<addr> 1514 Use early console provided by serial driver available 1515 on Samsung SoCs, requires selecting proper type and 1516 a correct base address of the selected UART port. The 1517 serial port must already be setup and configured. 1518 Options are not yet supported. 1519 1520 lantiq,<addr> 1521 Start an early, polled-mode console on a lantiq serial 1522 (lqasc) port at the specified address. The serial port 1523 must already be setup and configured. Options are not 1524 yet supported. 1525 1526 lpuart,<addr> 1527 lpuart32,<addr> 1528 Use early console provided by Freescale LP UART driver 1529 found on Freescale Vybrid and QorIQ LS1021A processors. 1530 A valid base address must be provided, and the serial 1531 port must already be setup and configured. 1532 1533 ec_imx21,<addr> 1534 ec_imx6q,<addr> 1535 Start an early, polled-mode, output-only console on the 1536 Freescale i.MX UART at the specified address. The UART 1537 must already be setup and configured. 1538 1539 ar3700_uart,<addr> 1540 Start an early, polled-mode console on the 1541 Armada 3700 serial port at the specified 1542 address. The serial port must already be setup 1543 and configured. Options are not yet supported. 1544 1545 qcom_geni,<addr> 1546 Start an early, polled-mode console on a Qualcomm 1547 Generic Interface (GENI) based serial port at the 1548 specified address. The serial port must already be 1549 setup and configured. Options are not yet supported. 1550 1551 efifb,[options] 1552 Start an early, unaccelerated console on the EFI 1553 memory mapped framebuffer (if available). On cache 1554 coherent non-x86 systems that use system memory for 1555 the framebuffer, pass the 'ram' option so that it is 1556 mapped with the correct attributes. 1557 1558 linflex,<addr> 1559 Use early console provided by Freescale LINFlexD UART 1560 serial driver for NXP S32V234 SoCs. A valid base 1561 address must be provided, and the serial port must 1562 already be setup and configured. 1563 1564 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1565 earlyprintk=vga 1566 earlyprintk=sclp 1567 earlyprintk=xen 1568 earlyprintk=serial[,ttySn[,baudrate]] 1569 earlyprintk=serial[,0x...[,baudrate]] 1570 earlyprintk=ttySn[,baudrate] 1571 earlyprintk=dbgp[debugController#] 1572 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1573 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1574 earlyprintk=xdbc[xhciController#] 1575 earlyprintk=bios 1576 1577 earlyprintk is useful when the kernel crashes before 1578 the normal console is initialized. It is not enabled by 1579 default because it has some cosmetic problems. 1580 1581 Use "nocfg" to skip UART configuration, assume 1582 BIOS/firmware has configured UART correctly. 1583 1584 Append ",keep" to not disable it when the real console 1585 takes over. 1586 1587 Only one of vga, serial, or usb debug port can 1588 be used at a time. 1589 1590 Currently only ttyS0 and ttyS1 may be specified by 1591 name. Other I/O ports may be explicitly specified 1592 on some architectures (x86 and arm at least) by 1593 replacing ttySn with an I/O port address, like this: 1594 earlyprintk=serial,0x1008,115200 1595 You can find the port for a given device in 1596 /proc/tty/driver/serial: 1597 2: uart:ST16650V2 port:00001008 irq:18 ... 1598 1599 Interaction with the standard serial driver is not 1600 very good. 1601 1602 The VGA output is eventually overwritten by 1603 the real console. 1604 1605 The xen option can only be used in Xen domains. 1606 1607 The sclp output can only be used on s390. 1608 1609 The bios output can only be used on SuperH. 1610 1611 The optional "force" to "pciserial" enables use of a 1612 PCI device even when its classcode is not of the 1613 UART class. 1614 1615 edac_report= [HW,EDAC] Control how to report EDAC event 1616 Format: {"on" | "off" | "force"} 1617 on: enable EDAC to report H/W event. May be overridden 1618 by other higher priority error reporting module. 1619 off: disable H/W event reporting through EDAC. 1620 force: enforce the use of EDAC to report H/W event. 1621 default: on. 1622 1623 edd= [EDD] 1624 Format: {"off" | "on" | "skip[mbr]"} 1625 1626 efi= [EFI,EARLY] 1627 Format: { "debug", "disable_early_pci_dma", 1628 "nochunk", "noruntime", "nosoftreserve", 1629 "novamap", "no_disable_early_pci_dma" } 1630 debug: enable misc debug output. 1631 disable_early_pci_dma: disable the busmaster bit on all 1632 PCI bridges while in the EFI boot stub. 1633 nochunk: disable reading files in "chunks" in the EFI 1634 boot stub, as chunking can cause problems with some 1635 firmware implementations. 1636 noruntime : disable EFI runtime services support 1637 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1638 attribute may cause the kernel to reserve the 1639 memory range for a memory mapping driver to 1640 claim. Specify efi=nosoftreserve to disable this 1641 reservation and treat the memory by its base type 1642 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1643 novamap: do not call SetVirtualAddressMap(). 1644 no_disable_early_pci_dma: Leave the busmaster bit set 1645 on all PCI bridges while in the EFI boot stub 1646 1647 efi_no_storage_paranoia [EFI,X86,EARLY] 1648 Using this parameter you can use more than 50% of 1649 your efi variable storage. Use this parameter only if 1650 you are really sure that your UEFI does sane gc and 1651 fulfills the spec otherwise your board may brick. 1652 1653 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1654 that is to be dynamically loaded by Linux. If there are 1655 multiple variables with the same name but with different 1656 vendor GUIDs, all of them will be loaded. See 1657 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1658 1659 1660 eisa_irq_edge= [PARISC,HW] 1661 See header of drivers/parisc/eisa.c. 1662 1663 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1664 Format: ekgdboc=kbd 1665 1666 This is designed to be used in conjunction with 1667 the boot argument: earlyprintk=vga 1668 1669 This parameter works in place of the kgdboc parameter 1670 but can only be used if the backing tty is available 1671 very early in the boot process. For early debugging 1672 via a serial port see kgdboc_earlycon instead. 1673 1674 elanfreq= [X86-32] 1675 See comment before function elanfreq_setup() in 1676 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1677 1678 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1679 Specifies physical address of start of kernel core 1680 image elf header and optionally the size. Generally 1681 kexec loader will pass this option to capture kernel. 1682 See Documentation/admin-guide/kdump/kdump.rst for details. 1683 1684 enable_mtrr_cleanup [X86,EARLY] 1685 The kernel tries to adjust MTRR layout from continuous 1686 to discrete, to make X server driver able to add WB 1687 entry later. This parameter enables that. 1688 1689 enable_timer_pin_1 [X86] 1690 Enable PIN 1 of APIC timer 1691 Can be useful to work around chipset bugs 1692 (in particular on some ATI chipsets). 1693 The kernel tries to set a reasonable default. 1694 1695 enforcing= [SELINUX] Set initial enforcing status. 1696 Format: {"0" | "1"} 1697 See security/selinux/Kconfig help text. 1698 0 -- permissive (log only, no denials). 1699 1 -- enforcing (deny and log). 1700 Default value is 0. 1701 Value can be changed at runtime via 1702 /sys/fs/selinux/enforce. 1703 1704 erst_disable [ACPI] 1705 Disable Error Record Serialization Table (ERST) 1706 support. 1707 1708 ether= [HW,NET] Ethernet cards parameters 1709 This option is obsoleted by the "netdev=" option, which 1710 has equivalent usage. See its documentation for details. 1711 1712 evm= [EVM] 1713 Format: { "fix" } 1714 Permit 'security.evm' to be updated regardless of 1715 current integrity status. 1716 1717 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1718 stages so cover more early boot allocations. 1719 Please note that as side effect some optimizations 1720 might be disabled to achieve that (e.g. parallelized 1721 memory initialization is disabled) so the boot process 1722 might take longer, especially on systems with a lot of 1723 memory. Available with CONFIG_PAGE_EXTENSION=y. 1724 1725 failslab= 1726 fail_usercopy= 1727 fail_page_alloc= 1728 fail_skb_realloc= 1729 fail_make_request=[KNL] 1730 General fault injection mechanism. 1731 Format: <interval>,<probability>,<space>,<times> 1732 See also Documentation/fault-injection/. 1733 1734 fb_tunnels= [NET] 1735 Format: { initns | none } 1736 See Documentation/admin-guide/sysctl/net.rst for 1737 fb_tunnels_only_for_init_ns 1738 1739 floppy= [HW] 1740 See Documentation/admin-guide/blockdev/floppy.rst. 1741 1742 forcepae [X86-32] 1743 Forcefully enable Physical Address Extension (PAE). 1744 Many Pentium M systems disable PAE but may have a 1745 functionally usable PAE implementation. 1746 Warning: use of this parameter will taint the kernel 1747 and may cause unknown problems. 1748 1749 fred= [X86-64] 1750 Enable/disable Flexible Return and Event Delivery. 1751 Format: { on | off } 1752 on: enable FRED when it's present. 1753 off: disable FRED, the default setting. 1754 1755 ftrace=[tracer] 1756 [FTRACE] will set and start the specified tracer 1757 as early as possible in order to facilitate early 1758 boot debugging. 1759 1760 ftrace_boot_snapshot 1761 [FTRACE] On boot up, a snapshot will be taken of the 1762 ftrace ring buffer that can be read at: 1763 /sys/kernel/tracing/snapshot. 1764 This is useful if you need tracing information from kernel 1765 boot up that is likely to be overridden by user space 1766 start up functionality. 1767 1768 Optionally, the snapshot can also be defined for a tracing 1769 instance that was created by the trace_instance= command 1770 line parameter. 1771 1772 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1773 1774 The above will cause the "foo" tracing instance to trigger 1775 a snapshot at the end of boot up. 1776 1777 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1778 ,<instance>=2(orig_cpu)] 1779 [FTRACE] will dump the trace buffers on oops. 1780 If no parameter is passed, ftrace will dump global 1781 buffers of all CPUs, if you pass 2 or orig_cpu, it 1782 will dump only the buffer of the CPU that triggered 1783 the oops, or the specific instance will be dumped if 1784 its name is passed. Multiple instance dump is also 1785 supported, and instances are separated by commas. Each 1786 instance supports only dump on CPU that triggered the 1787 oops by passing 2 or orig_cpu to it. 1788 1789 ftrace_dump_on_oops=foo=orig_cpu 1790 1791 The above will dump only the buffer of "foo" instance 1792 on CPU that triggered the oops. 1793 1794 ftrace_dump_on_oops,foo,bar=orig_cpu 1795 1796 The above will dump global buffer on all CPUs, the 1797 buffer of "foo" instance on all CPUs and the buffer 1798 of "bar" instance on CPU that triggered the oops. 1799 1800 ftrace_filter=[function-list] 1801 [FTRACE] Limit the functions traced by the function 1802 tracer at boot up. function-list is a comma-separated 1803 list of functions. This list can be changed at run 1804 time by the set_ftrace_filter file in the debugfs 1805 tracing directory. 1806 1807 ftrace_notrace=[function-list] 1808 [FTRACE] Do not trace the functions specified in 1809 function-list. This list can be changed at run time 1810 by the set_ftrace_notrace file in the debugfs 1811 tracing directory. 1812 1813 ftrace_graph_filter=[function-list] 1814 [FTRACE] Limit the top level callers functions traced 1815 by the function graph tracer at boot up. 1816 function-list is a comma-separated list of functions 1817 that can be changed at run time by the 1818 set_graph_function file in the debugfs tracing directory. 1819 1820 ftrace_graph_notrace=[function-list] 1821 [FTRACE] Do not trace from the functions specified in 1822 function-list. This list is a comma-separated list of 1823 functions that can be changed at run time by the 1824 set_graph_notrace file in the debugfs tracing directory. 1825 1826 ftrace_graph_max_depth=<uint> 1827 [FTRACE] Used with the function graph tracer. This is 1828 the max depth it will trace into a function. This value 1829 can be changed at run time by the max_graph_depth file 1830 in the tracefs tracing directory. default: 0 (no limit) 1831 1832 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1833 devices by scanning the firmware to infer the 1834 consumer/supplier relationships. This feature is 1835 especially useful when drivers are loaded as modules as 1836 it ensures proper ordering of tasks like device probing 1837 (suppliers first, then consumers), supplier boot state 1838 clean up (only after all consumers have probed), 1839 suspend/resume & runtime PM (consumers first, then 1840 suppliers). 1841 Format: { off | permissive | on | rpm } 1842 off -- Don't create device links from firmware info. 1843 permissive -- Create device links from firmware info 1844 but use it only for ordering boot state clean 1845 up (sync_state() calls). 1846 on -- Create device links from firmware info and use it 1847 to enforce probe and suspend/resume ordering. 1848 rpm -- Like "on", but also use to order runtime PM. 1849 1850 fw_devlink.strict=<bool> 1851 [KNL,EARLY] Treat all inferred dependencies as mandatory 1852 dependencies. This only applies for fw_devlink=on|rpm. 1853 Format: <bool> 1854 1855 fw_devlink.sync_state = 1856 [KNL,EARLY] When all devices that could probe have finished 1857 probing, this parameter controls what to do with 1858 devices that haven't yet received their sync_state() 1859 calls. 1860 Format: { strict | timeout } 1861 strict -- Default. Continue waiting on consumers to 1862 probe successfully. 1863 timeout -- Give up waiting on consumers and call 1864 sync_state() on any devices that haven't yet 1865 received their sync_state() calls after 1866 deferred_probe_timeout has expired or by 1867 late_initcall() if !CONFIG_MODULES. 1868 1869 gamecon.map[2|3]= 1870 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1871 support via parallel port (up to 5 devices per port) 1872 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1873 See also Documentation/input/devices/joystick-parport.rst 1874 1875 gamma= [HW,DRM] 1876 1877 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1878 Format: off | on 1879 default: on 1880 1881 gather_data_sampling= 1882 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1883 mitigation. 1884 1885 Gather Data Sampling is a hardware vulnerability which 1886 allows unprivileged speculative access to data which was 1887 previously stored in vector registers. 1888 1889 This issue is mitigated by default in updated microcode. 1890 The mitigation may have a performance impact but can be 1891 disabled. On systems without the microcode mitigation 1892 disabling AVX serves as a mitigation. 1893 1894 force: Disable AVX to mitigate systems without 1895 microcode mitigation. No effect if the microcode 1896 mitigation is present. Known to cause crashes in 1897 userspace with buggy AVX enumeration. 1898 1899 off: Disable GDS mitigation. 1900 1901 gbpages [X86] Use GB pages for kernel direct mappings. 1902 1903 gcov_persist= [GCOV] When non-zero (default), profiling data for 1904 kernel modules is saved and remains accessible via 1905 debugfs, even when the module is unloaded/reloaded. 1906 When zero, profiling data is discarded and associated 1907 debugfs files are removed at module unload time. 1908 1909 goldfish [X86] Enable the goldfish android emulator platform. 1910 Don't use this when you are not running on the 1911 android emulator 1912 1913 gpio-mockup.gpio_mockup_ranges 1914 [HW] Sets the ranges of gpiochip of for this device. 1915 Format: <start1>,<end1>,<start2>,<end2>... 1916 gpio-mockup.gpio_mockup_named_lines 1917 [HW] Let the driver know GPIO lines should be named. 1918 1919 gpt [EFI] Forces disk with valid GPT signature but 1920 invalid Protective MBR to be treated as GPT. If the 1921 primary GPT is corrupted, it enables the backup/alternate 1922 GPT to be used instead. 1923 1924 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1925 the "Enable 0" bit of the configuration register. 1926 Format: 0 | 1 1927 Default: 0 1928 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1929 the "Enable 0" bit of the configuration register. 1930 Format: 0 | 1 1931 Default: 0 1932 grcan.select= [HW] Select which physical interface to use. 1933 Format: 0 | 1 1934 Default: 0 1935 grcan.txsize= [HW] Sets the size of the tx buffer. 1936 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1937 Default: 1024 1938 grcan.rxsize= [HW] Sets the size of the rx buffer. 1939 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1940 Default: 1024 1941 1942 hardened_usercopy= 1943 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1944 hardening is enabled for this boot. Hardened 1945 usercopy checking is used to protect the kernel 1946 from reading or writing beyond known memory 1947 allocation boundaries as a proactive defense 1948 against bounds-checking flaws in the kernel's 1949 copy_to_user()/copy_from_user() interface. 1950 The default is determined by 1951 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1952 on Perform hardened usercopy checks. 1953 off Disable hardened usercopy checks. 1954 1955 hardlockup_all_cpu_backtrace= 1956 [KNL] Should the hard-lockup detector generate 1957 backtraces on all cpus. 1958 Format: 0 | 1 1959 1960 hash_pointers= 1961 [KNL,EARLY] 1962 By default, when pointers are printed to the console 1963 or buffers via the %p format string, that pointer is 1964 "hashed", i.e. obscured by hashing the pointer value. 1965 This is a security feature that hides actual kernel 1966 addresses from unprivileged users, but it also makes 1967 debugging the kernel more difficult since unequal 1968 pointers can no longer be compared. The choices are: 1969 Format: { auto | always | never } 1970 Default: auto 1971 1972 auto - Hash pointers unless slab_debug is enabled. 1973 always - Always hash pointers (even if slab_debug is 1974 enabled). 1975 never - Never hash pointers. This option should only 1976 be specified when debugging the kernel. Do 1977 not use on production kernels. The boot 1978 param "no_hash_pointers" is an alias for 1979 this mode. 1980 1981 For controlling hashing dynamically at runtime, 1982 use the "kernel.kptr_restrict" sysctl instead. 1983 1984 hashdist= [KNL,NUMA] Large hashes allocated during boot 1985 are distributed across NUMA nodes. Defaults on 1986 for 64-bit NUMA, off otherwise. 1987 Format: 0 | 1 (for off | on) 1988 1989 hd= [EIDE] (E)IDE hard drive subsystem geometry 1990 Format: <cyl>,<head>,<sect> 1991 1992 hest_disable [ACPI] 1993 Disable Hardware Error Source Table (HEST) support; 1994 corresponding firmware-first mode error processing 1995 logic will be disabled. 1996 1997 hibernate= [HIBERNATION] 1998 noresume Don't check if there's a hibernation image 1999 present during boot. 2000 nocompress Don't compress/decompress hibernation images. 2001 no Disable hibernation and resume. 2002 protect_image Turn on image protection during restoration 2003 (that will set all pages holding image data 2004 during restoration read-only). 2005 2006 hibernate.compressor= [HIBERNATION] Compression algorithm to be 2007 used with hibernation. 2008 Format: { lzo | lz4 } 2009 Default: lzo 2010 2011 lzo: Select LZO compression algorithm to 2012 compress/decompress hibernation image. 2013 2014 lz4: Select LZ4 compression algorithm to 2015 compress/decompress hibernation image. 2016 2017 hibernate.pm_test_delay= 2018 [HIBERNATION] 2019 Sets the number of seconds to remain in a hibernation test 2020 mode before resuming the system (see 2021 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2022 is set. Default value is 5. 2023 2024 hibernate_compression_threads= 2025 [HIBERNATION] 2026 Set the number of threads used for compressing or decompressing 2027 hibernation images. 2028 2029 Format: <integer> 2030 Default: 3 2031 Minimum: 1 2032 Example: hibernate_compression_threads=4 2033 2034 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2035 size of <nn>. This works even on boxes that have no 2036 highmem otherwise. This also works to reduce highmem 2037 size on bigger boxes. 2038 2039 highres= [KNL] Enable/disable high resolution timer mode. 2040 Valid parameters: "on", "off" 2041 Default: "on" 2042 2043 hlt [BUGS=ARM,SH] 2044 2045 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2046 Format: <string> 2047 This allows setting the system's hostname during early 2048 startup. This sets the name returned by gethostname. 2049 Using this parameter to set the hostname makes it 2050 possible to ensure the hostname is correctly set before 2051 any userspace processes run, avoiding the possibility 2052 that a process may call gethostname before the hostname 2053 has been explicitly set, resulting in the calling 2054 process getting an incorrect result. The string must 2055 not exceed the maximum allowed hostname length (usually 2056 64 characters) and will be truncated otherwise. 2057 2058 hpet= [X86-32,HPET] option to control HPET usage 2059 Format: { enable (default) | disable | force | 2060 verbose } 2061 disable: disable HPET and use PIT instead 2062 force: allow force enabled of undocumented chips (ICH4, 2063 VIA, nVidia) 2064 verbose: show contents of HPET registers during setup 2065 2066 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2067 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2068 2069 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2070 If this follows hugepagesz (below), it specifies 2071 the number of pages of hugepagesz to be allocated. 2072 If this is the first HugeTLB parameter on the command 2073 line, it specifies the number of pages to allocate for 2074 the default huge page size. If using node format, the 2075 number of pages to allocate per-node can be specified. 2076 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2077 Format: <integer> or (node format) 2078 <node>:<integer>[,<node>:<integer>] 2079 2080 hugepagesz= 2081 [HW,EARLY] The size of the HugeTLB pages. This is 2082 used in conjunction with hugepages (above) to 2083 allocate huge pages of a specific size at boot. The 2084 pair hugepagesz=X hugepages=Y can be specified once 2085 for each supported huge page size. Huge page sizes 2086 are architecture dependent. See also 2087 Documentation/admin-guide/mm/hugetlbpage.rst. 2088 Format: size[KMG] 2089 2090 hugepage_alloc_threads= 2091 [HW] The number of threads that should be used to 2092 allocate hugepages during boot. This option can be 2093 used to improve system bootup time when allocating 2094 a large amount of huge pages. 2095 The default value is 25% of the available hardware threads. 2096 2097 Note that this parameter only applies to non-gigantic huge pages. 2098 2099 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2100 of gigantic hugepages. Or using node format, the size 2101 of a CMA area per node can be specified. 2102 Format: nn[KMGTPE] or (node format) 2103 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2104 2105 Reserve a CMA area of given size and allocate gigantic 2106 hugepages using the CMA allocator. If enabled, the 2107 boot-time allocation of gigantic hugepages is skipped. 2108 2109 hugetlb_cma_only= 2110 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2111 try to allocate from the CMA areas. 2112 2113 This option does nothing if hugetlb_cma= is not also 2114 specified. 2115 2116 hugetlb_free_vmemmap= 2117 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2118 enabled. 2119 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2120 Allows heavy hugetlb users to free up some more 2121 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2122 Format: { on | off (default) } 2123 2124 on: enable HVO 2125 off: disable HVO 2126 2127 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2128 the default is on. 2129 2130 Note that the vmemmap pages may be allocated from the added 2131 memory block itself when memory_hotplug.memmap_on_memory is 2132 enabled, those vmemmap pages cannot be optimized even if this 2133 feature is enabled. Other vmemmap pages not allocated from 2134 the added memory block itself do not be affected. 2135 2136 hung_task_panic= 2137 [KNL] Number of hung tasks to trigger kernel panic. 2138 Format: <int> 2139 2140 When set to a non-zero value, a kernel panic will be triggered if 2141 the number of detected hung tasks reaches this value. 2142 2143 0: don't panic 2144 1: panic immediately on first hung task 2145 N: panic after N hung tasks are detected in a single scan 2146 2147 The default value is controlled by the 2148 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2149 selected by this boot parameter can be changed later by the 2150 kernel.hung_task_panic sysctl. 2151 2152 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2153 terminal devices. Valid values: 0..8 2154 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2155 If specified, z/VM IUCV HVC accepts connections 2156 from listed z/VM user IDs only. 2157 2158 hv_nopvspin [X86,HYPER_V,EARLY] 2159 Disables the paravirt spinlock optimizations 2160 which allow the hypervisor to 'idle' the guest 2161 on lock contention. 2162 2163 hw_protection= [HW] 2164 Format: reboot | shutdown 2165 2166 Hardware protection action taken on critical events like 2167 overtemperature or imminent voltage loss. 2168 2169 i2c_bus= [HW] Override the default board specific I2C bus speed 2170 or register an additional I2C bus that is not 2171 registered from board initialization code. 2172 Format: 2173 <bus_id>,<clkrate> 2174 2175 i2c_touchscreen_props= [HW,ACPI,X86] 2176 Set device-properties for ACPI-enumerated I2C-attached 2177 touchscreen, to e.g. fix coordinates of upside-down 2178 mounted touchscreens. If you need this option please 2179 submit a drivers/platform/x86/touchscreen_dmi.c patch 2180 adding a DMI quirk for this. 2181 2182 Format: 2183 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2184 Where <val> is one of: 2185 Omit "=<val>" entirely Set a boolean device-property 2186 Unsigned number Set a u32 device-property 2187 Anything else Set a string device-property 2188 2189 Examples (split over multiple lines): 2190 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2191 touchscreen-inverted-y 2192 2193 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2194 touchscreen-size-y=1080:touchscreen-inverted-y: 2195 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2196 2197 i8042.debug [HW] Toggle i8042 debug mode 2198 i8042.unmask_kbd_data 2199 [HW] Enable printing of interrupt data from the KBD port 2200 (disabled by default, and as a pre-condition 2201 requires that i8042.debug=1 be enabled) 2202 i8042.direct [HW] Put keyboard port into non-translated mode 2203 i8042.dumbkbd [HW] Pretend that controller can only read data from 2204 keyboard and cannot control its state 2205 (Don't attempt to blink the leds) 2206 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2207 i8042.nokbd [HW] Don't check/create keyboard port 2208 i8042.noloop [HW] Disable the AUX Loopback command while probing 2209 for the AUX port 2210 i8042.nomux [HW] Don't check presence of an active multiplexing 2211 controller 2212 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2213 controllers 2214 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2215 i8042.reset [HW] Reset the controller during init, cleanup and 2216 suspend-to-ram transitions, only during s2r 2217 transitions, or never reset 2218 Format: { 1 | Y | y | 0 | N | n } 2219 1, Y, y: always reset controller 2220 0, N, n: don't ever reset controller 2221 Default: only on s2r transitions on x86; most other 2222 architectures force reset to be always executed 2223 i8042.unlock [HW] Unlock (ignore) the keylock 2224 i8042.kbdreset [HW] Reset device connected to KBD port 2225 i8042.probe_defer 2226 [HW] Allow deferred probing upon i8042 probe errors 2227 2228 i810= [HW,DRM] 2229 2230 i915.invert_brightness= 2231 [DRM] Invert the sense of the variable that is used to 2232 set the brightness of the panel backlight. Normally a 2233 brightness value of 0 indicates backlight switched off, 2234 and the maximum of the brightness value sets the backlight 2235 to maximum brightness. If this parameter is set to 0 2236 (default) and the machine requires it, or this parameter 2237 is set to 1, a brightness value of 0 sets the backlight 2238 to maximum brightness, and the maximum of the brightness 2239 value switches the backlight off. 2240 -1 -- never invert brightness 2241 0 -- machine default 2242 1 -- force brightness inversion 2243 2244 ia32_emulation= [X86-64] 2245 Format: <bool> 2246 When true, allows loading 32-bit programs and executing 32-bit 2247 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2248 boot time. When false, unconditionally disables IA32 emulation. 2249 2250 icn= [HW,ISDN] 2251 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2252 2253 2254 idle= [X86,EARLY] 2255 Format: idle=poll, idle=halt, idle=nomwait 2256 2257 idle=poll: Don't do power saving in the idle loop 2258 using HLT, but poll for rescheduling event. This will 2259 make the CPUs eat a lot more power, but may be useful 2260 to get slightly better performance in multiprocessor 2261 benchmarks. It also makes some profiling using 2262 performance counters more accurate. Please note that 2263 on systems with MONITOR/MWAIT support (like Intel 2264 EM64T CPUs) this option has no performance advantage 2265 over the normal idle loop. It may also interact badly 2266 with hyperthreading. 2267 2268 idle=halt: Halt is forced to be used for CPU idle. 2269 In such case C2/C3 won't be used again. 2270 2271 idle=nomwait: Disable mwait for CPU C-states 2272 2273 idxd.sva= [HW] 2274 Format: <bool> 2275 Allow force disabling of Shared Virtual Memory (SVA) 2276 support for the idxd driver. By default it is set to 2277 true (1). 2278 2279 idxd.tc_override= [HW] 2280 Format: <bool> 2281 Allow override of default traffic class configuration 2282 for the device. By default it is set to false (0). 2283 2284 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2285 Format: { strict | legacy | 2008 | relaxed | emulated } 2286 Default: strict 2287 2288 Choose which programs will be accepted for execution 2289 based on the IEEE 754 NaN encoding(s) supported by 2290 the FPU and the NaN encoding requested with the value 2291 of an ELF file header flag individually set by each 2292 binary. Hardware implementations are permitted to 2293 support either or both of the legacy and the 2008 NaN 2294 encoding mode. 2295 2296 Available settings are as follows: 2297 strict accept binaries that request a NaN encoding 2298 supported by the FPU 2299 legacy only accept legacy-NaN binaries, if supported 2300 by the FPU 2301 2008 only accept 2008-NaN binaries, if supported 2302 by the FPU 2303 relaxed accept any binaries regardless of whether 2304 supported by the FPU 2305 emulated accept any binaries but enable FPU emulator 2306 if binary mode is unsupported by the FPU. 2307 2308 The FPU emulator is always able to support both NaN 2309 encodings, so if no FPU hardware is present or it has 2310 been disabled with 'nofpu', then the settings of 2311 'legacy' and '2008' strap the emulator accordingly, 2312 'relaxed' straps the emulator for both legacy-NaN and 2313 2008-NaN, whereas 'strict' enables legacy-NaN only on 2314 legacy processors and both NaN encodings on MIPS32 or 2315 MIPS64 CPUs. 2316 2317 The setting for ABS.fmt/NEG.fmt instruction execution 2318 mode generally follows that for the NaN encoding, 2319 except where unsupported by hardware. 2320 2321 ignore_loglevel [KNL,EARLY] 2322 Ignore loglevel setting - this will print /all/ 2323 kernel messages to the console. Useful for debugging. 2324 We also add it as printk module parameter, so users 2325 could change it dynamically, usually by 2326 /sys/module/printk/parameters/ignore_loglevel. 2327 2328 ignore_rlimit_data 2329 Ignore RLIMIT_DATA setting for data mappings, 2330 print warning at first misuse. Can be changed via 2331 /sys/module/kernel/parameters/ignore_rlimit_data. 2332 2333 ihash_entries= [KNL] 2334 Set number of hash buckets for inode cache. 2335 2336 ima_appraise= [IMA] appraise integrity measurements 2337 Format: { "off" | "enforce" | "fix" | "log" } 2338 default: "enforce" 2339 2340 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2341 The builtin appraise policy appraises all files 2342 owned by uid=0. 2343 2344 ima_canonical_fmt [IMA] 2345 Use the canonical format for the binary runtime 2346 measurements, instead of host native format. 2347 2348 ima_hash= [IMA] 2349 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2350 | sha512 | ... } 2351 default: "sha1" 2352 2353 The list of supported hash algorithms is defined 2354 in crypto/hash_info.h. 2355 2356 ima_policy= [IMA] 2357 The builtin policies to load during IMA setup. 2358 Format: "tcb | appraise_tcb | secure_boot | 2359 fail_securely | critical_data" 2360 2361 The "tcb" policy measures all programs exec'd, files 2362 mmap'd for exec, and all files opened with the read 2363 mode bit set by either the effective uid (euid=0) or 2364 uid=0. 2365 2366 The "appraise_tcb" policy appraises the integrity of 2367 all files owned by root. 2368 2369 The "secure_boot" policy appraises the integrity 2370 of files (eg. kexec kernel image, kernel modules, 2371 firmware, policy, etc) based on file signatures. 2372 2373 The "fail_securely" policy forces file signature 2374 verification failure also on privileged mounted 2375 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2376 flag. 2377 2378 The "critical_data" policy measures kernel integrity 2379 critical data. 2380 2381 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2382 Load a policy which meets the needs of the Trusted 2383 Computing Base. This means IMA will measure all 2384 programs exec'd, files mmap'd for exec, and all files 2385 opened for read by uid=0. 2386 2387 ima_template= [IMA] 2388 Select one of defined IMA measurements template formats. 2389 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2390 "ima-sigv2" } 2391 Default: "ima-ng" 2392 2393 ima_template_fmt= 2394 [IMA] Define a custom template format. 2395 Format: { "field1|...|fieldN" } 2396 2397 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2398 Format: <min_file_size> 2399 Set the minimal file size for using asynchronous hash. 2400 If left unspecified, ahash usage is disabled. 2401 2402 ahash performance varies for different data sizes on 2403 different crypto accelerators. This option can be used 2404 to achieve the best performance for a particular HW. 2405 2406 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2407 Format: <bufsize> 2408 Set hashing buffer size. Default: 4k. 2409 2410 ahash performance varies for different chunk sizes on 2411 different crypto accelerators. This option can be used 2412 to achieve best performance for particular HW. 2413 2414 ima= [IMA] Enable or disable IMA 2415 Format: { "off" | "on" } 2416 Default: "on" 2417 Note that disabling IMA is limited to kdump kernel. 2418 2419 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2420 Target Selection(ITS) bug in Intel CPUs. Updated 2421 microcode is also required for a fix in IBPB. 2422 2423 on: Enable mitigation (default). 2424 off: Disable mitigation. 2425 force: Force the ITS bug and deploy default 2426 mitigation. 2427 vmexit: Only deploy mitigation if CPU is affected by 2428 guest/host isolation part of ITS. 2429 stuff: Deploy RSB-fill mitigation when retpoline is 2430 also deployed. Otherwise, deploy the default 2431 mitigation. 2432 2433 For details see: 2434 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2435 2436 init= [KNL] 2437 Format: <full_path> 2438 Run specified binary instead of /sbin/init as init 2439 process. 2440 2441 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2442 for working out where the kernel is dying during 2443 startup. 2444 2445 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2446 initcall functions. Useful for debugging built-in 2447 modules and initcalls. 2448 2449 initramfs_async= [KNL] 2450 Format: <bool> 2451 Default: 1 2452 This parameter controls whether the initramfs 2453 image is unpacked asynchronously, concurrently 2454 with devices being probed and 2455 initialized. This should normally just work, 2456 but as a debugging aid, one can get the 2457 historical behaviour of the initramfs 2458 unpacking being completed before device_ and 2459 late_ initcalls. 2460 2461 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2462 2463 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2464 load the initrd. If an initrd is compiled in or 2465 specified in the bootparams, it takes priority over this 2466 setting. 2467 Format: ss[KMG],nn[KMG] 2468 Default is 0, 0 2469 2470 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2471 zeroes. 2472 Format: 0 | 1 2473 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2474 2475 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2476 Format: 0 | 1 2477 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2478 2479 init_pkru= [X86] Specify the default memory protection keys rights 2480 register contents for all processes. 0x55555554 by 2481 default (disallow access to all but pkey 0). Can 2482 override in debugfs after boot. 2483 2484 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2485 Format: <irq> 2486 2487 int_pln_enable [X86] Enable power limit notification interrupt 2488 2489 integrity_audit=[IMA] 2490 Format: { "0" | "1" } 2491 0 -- basic integrity auditing messages. (Default) 2492 1 -- additional integrity auditing messages. 2493 2494 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2495 on 2496 Enable intel iommu driver. 2497 off 2498 Disable intel iommu driver. 2499 igfx_off [Default Off] 2500 By default, gfx is mapped as normal device. If a gfx 2501 device has a dedicated DMAR unit, the DMAR unit is 2502 bypassed by not enabling DMAR with this option. In 2503 this case, gfx device will use physical address for 2504 DMA. 2505 strict [Default Off] 2506 Deprecated, equivalent to iommu.strict=1. 2507 sp_off [Default Off] 2508 By default, super page will be supported if Intel IOMMU 2509 has the capability. With this option, super page will 2510 not be supported. 2511 sm_on 2512 Enable the Intel IOMMU scalable mode if the hardware 2513 advertises that it has support for the scalable mode 2514 translation. 2515 sm_off 2516 Disallow use of the Intel IOMMU scalable mode. 2517 tboot_noforce [Default Off] 2518 Do not force the Intel IOMMU enabled under tboot. 2519 By default, tboot will force Intel IOMMU on, which 2520 could harm performance of some high-throughput 2521 devices like 40GBit network cards, even if identity 2522 mapping is enabled. 2523 Note that using this option lowers the security 2524 provided by tboot because it makes the system 2525 vulnerable to DMA attacks. 2526 2527 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2528 0 disables intel_idle and fall back on acpi_idle. 2529 1 to 9 specify maximum depth of C-state. 2530 2531 intel_pstate= [X86,EARLY] 2532 disable 2533 Do not enable intel_pstate as the default 2534 scaling driver for the supported processors 2535 active 2536 Use intel_pstate driver to bypass the scaling 2537 governors layer of cpufreq and provides it own 2538 algorithms for p-state selection. There are two 2539 P-state selection algorithms provided by 2540 intel_pstate in the active mode: powersave and 2541 performance. The way they both operate depends 2542 on whether or not the hardware managed P-states 2543 (HWP) feature has been enabled in the processor 2544 and possibly on the processor model. 2545 passive 2546 Use intel_pstate as a scaling driver, but configure it 2547 to work with generic cpufreq governors (instead of 2548 enabling its internal governor). This mode cannot be 2549 used along with the hardware-managed P-states (HWP) 2550 feature. 2551 force 2552 Enable intel_pstate on systems that prohibit it by default 2553 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2554 instead of acpi-cpufreq may disable platform features, such 2555 as thermal controls and power capping, that rely on ACPI 2556 P-States information being indicated to OSPM and therefore 2557 should be used with caution. This option does not work with 2558 processors that aren't supported by the intel_pstate driver 2559 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2560 no_hwp 2561 Do not enable hardware P state control (HWP) 2562 if available. 2563 hwp_only 2564 Only load intel_pstate on systems which support 2565 hardware P state control (HWP) if available. 2566 support_acpi_ppc 2567 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2568 Description Table, specifies preferred power management 2569 profile as "Enterprise Server" or "Performance Server", 2570 then this feature is turned on by default. 2571 per_cpu_perf_limits 2572 Allow per-logical-CPU P-State performance control limits using 2573 cpufreq sysfs interface 2574 no_cas 2575 Do not enable capacity-aware scheduling (CAS) on 2576 hybrid systems 2577 2578 intremap= [X86-64,Intel-IOMMU,EARLY] 2579 on enable Interrupt Remapping (default) 2580 off disable Interrupt Remapping 2581 nosid disable Source ID checking 2582 no_x2apic_optout 2583 BIOS x2APIC opt-out request will be ignored 2584 nopost disable Interrupt Posting 2585 posted_msi 2586 enable MSIs delivered as posted interrupts 2587 2588 iomem= Disable strict checking of access to MMIO memory 2589 strict regions from userspace. 2590 relaxed 2591 2592 iommu= [X86,EARLY] 2593 2594 off 2595 Don't initialize and use any kind of IOMMU. 2596 2597 force 2598 Force the use of the hardware IOMMU even when 2599 it is not actually needed (e.g. because < 3 GB 2600 memory). 2601 2602 noforce 2603 Don't force hardware IOMMU usage when it is not 2604 needed. (default). 2605 2606 biomerge 2607 panic 2608 nopanic 2609 merge 2610 nomerge 2611 2612 soft 2613 Use software bounce buffering (SWIOTLB) (default for 2614 Intel machines). This can be used to prevent the usage 2615 of an available hardware IOMMU. 2616 2617 [X86] 2618 pt 2619 [X86] 2620 nopt 2621 [PPC/POWERNV] 2622 nobypass 2623 Disable IOMMU bypass, using IOMMU for PCI devices. 2624 2625 [X86] 2626 AMD Gart HW IOMMU-specific options: 2627 2628 <size> 2629 Set the size of the remapping area in bytes. 2630 2631 allowed 2632 Overwrite iommu off workarounds for specific chipsets 2633 2634 fullflush 2635 Flush IOMMU on each allocation (default). 2636 2637 nofullflush 2638 Don't use IOMMU fullflush. 2639 2640 memaper[=<order>] 2641 Allocate an own aperture over RAM with size 2642 32MB<<order. (default: order=1, i.e. 64MB) 2643 2644 merge 2645 Do scatter-gather (SG) merging. Implies "force" 2646 (experimental). 2647 2648 nomerge 2649 Don't do scatter-gather (SG) merging. 2650 2651 noaperture 2652 Ask the IOMMU not to touch the aperture for AGP. 2653 2654 noagp 2655 Don't initialize the AGP driver and use full aperture. 2656 2657 panic 2658 Always panic when IOMMU overflows. 2659 2660 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2661 Format: { "0" | "1" } 2662 0 - Try to allocate a 32-bit DMA address first, before 2663 falling back to the full range if needed. 2664 1 - Allocate directly from the full usable range, 2665 forcing Dual Address Cycle for PCI cards supporting 2666 greater than 32-bit addressing. 2667 2668 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2669 Format: { "0" | "1" } 2670 0 - Lazy mode. 2671 Request that DMA unmap operations use deferred 2672 invalidation of hardware TLBs, for increased 2673 throughput at the cost of reduced device isolation. 2674 Will fall back to strict mode if not supported by 2675 the relevant IOMMU driver. 2676 1 - Strict mode. 2677 DMA unmap operations invalidate IOMMU hardware TLBs 2678 synchronously. 2679 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2680 Note: on x86, strict mode specified via one of the 2681 legacy driver-specific options takes precedence. 2682 2683 iommu.passthrough= 2684 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2685 Format: { "0" | "1" } 2686 0 - Use IOMMU translation for DMA. 2687 1 - Bypass the IOMMU for DMA. 2688 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2689 2690 iommu.debug_pagealloc= 2691 [KNL,EARLY] When CONFIG_IOMMU_DEBUG_PAGEALLOC is set, this 2692 parameter enables the feature at boot time. By default, it 2693 is disabled and the system behaves the same way as a kernel 2694 built without CONFIG_IOMMU_DEBUG_PAGEALLOC. 2695 Format: { "0" | "1" } 2696 0 - Sanitizer disabled. 2697 1 - Sanitizer enabled, expect runtime overhead. 2698 2699 io7= [HW] IO7 for Marvel-based Alpha systems 2700 See comment before marvel_specify_io7 in 2701 arch/alpha/kernel/core_marvel.c. 2702 2703 io_delay= [X86,EARLY] I/O delay method 2704 0x80 2705 Standard port 0x80 based delay 2706 0xed 2707 Alternate port 0xed based delay (needed on some systems) 2708 udelay 2709 Simple two microseconds delay 2710 none 2711 No delay 2712 2713 ip= [IP_PNP] 2714 See Documentation/admin-guide/nfs/nfsroot.rst. 2715 2716 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2717 IPC identifiers from 32,768 to 16,777,216. 2718 2719 ipe.enforce= [IPE] 2720 Format: <bool> 2721 Determine whether IPE starts in permissive (0) or 2722 enforce (1) mode. The default is enforce. 2723 2724 ipe.success_audit= 2725 [IPE] 2726 Format: <bool> 2727 Start IPE with success auditing enabled, emitting 2728 an audit event when a binary is allowed. The default 2729 is 0. 2730 2731 irqaffinity= [SMP] Set the default irq affinity mask 2732 The argument is a cpu list, as described above. 2733 2734 irqchip.gicv2_force_probe= 2735 [ARM,ARM64,EARLY] 2736 Format: <bool> 2737 Force the kernel to look for the second 4kB page 2738 of a GICv2 controller even if the memory range 2739 exposed by the device tree is too small. 2740 2741 irqchip.gicv3_nolpi= 2742 [ARM,ARM64,EARLY] 2743 Force the kernel to ignore the availability of 2744 LPIs (and by consequence ITSs). Intended for system 2745 that use the kernel as a bootloader, and thus want 2746 to let secondary kernels in charge of setting up 2747 LPIs. 2748 2749 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2750 Enables support for pseudo-NMIs in the kernel. This 2751 requires the kernel to be built with 2752 CONFIG_ARM64_PSEUDO_NMI. 2753 2754 irqchip.riscv_imsic_noipi 2755 [RISC-V,EARLY] 2756 Force the kernel to not use IMSIC software injected MSIs 2757 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2758 and thus want to reduce MMIO traps when triggering IPIs 2759 to multiple harts. 2760 2761 irqfixup [HW] 2762 When an interrupt is not handled search all handlers 2763 for it. Intended to get systems with badly broken 2764 firmware running. 2765 2766 irqhandler.duration_warn_us= [KNL] 2767 Warn if an IRQ handler exceeds the specified duration 2768 threshold in microseconds. Useful for identifying 2769 long-running IRQs in the system. 2770 2771 irqpoll [HW] 2772 When an interrupt is not handled search all handlers 2773 for it. Also check all handlers each timer 2774 interrupt. Intended to get systems with badly broken 2775 firmware running. 2776 2777 isapnp= [ISAPNP] 2778 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2779 2780 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2781 [Deprecated - use cpusets instead] 2782 Format: [flag-list,]<cpu-list> 2783 2784 Specify one or more CPUs to isolate from disturbances 2785 specified in the flag list (default: domain): 2786 2787 nohz 2788 Disable the tick when a single task runs as well as 2789 disabling other kernel noises like having RCU callbacks 2790 offloaded. This is equivalent to the nohz_full parameter. 2791 2792 A residual 1Hz tick is offloaded to workqueues, which you 2793 need to affine to housekeeping through the global 2794 workqueue's affinity configured via the 2795 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2796 by using the 'domain' flag described below. 2797 2798 NOTE: by default the global workqueue runs on all CPUs, 2799 so to protect individual CPUs the 'cpumask' file has to 2800 be configured manually after bootup. 2801 2802 domain 2803 Isolate from the general SMP balancing and scheduling 2804 algorithms. Note that performing domain isolation this way 2805 is irreversible: it's not possible to bring back a CPU to 2806 the domains once isolated through isolcpus. It's strongly 2807 advised to use cpusets instead to disable scheduler load 2808 balancing through the "cpuset.sched_load_balance" file. 2809 It offers a much more flexible interface where CPUs can 2810 move in and out of an isolated set anytime. 2811 2812 You can move a process onto or off an "isolated" CPU via 2813 the CPU affinity syscalls or cpuset. 2814 <cpu number> begins at 0 and the maximum value is 2815 "number of CPUs in system - 1". 2816 2817 managed_irq 2818 2819 Isolate from being targeted by managed interrupts 2820 which have an interrupt mask containing isolated 2821 CPUs. The affinity of managed interrupts is 2822 handled by the kernel and cannot be changed via 2823 the /proc/irq/* interfaces. 2824 2825 This isolation is best effort and only effective 2826 if the automatically assigned interrupt mask of a 2827 device queue contains isolated and housekeeping 2828 CPUs. If housekeeping CPUs are online then such 2829 interrupts are directed to the housekeeping CPU 2830 so that IO submitted on the housekeeping CPU 2831 cannot disturb the isolated CPU. 2832 2833 If a queue's affinity mask contains only isolated 2834 CPUs then this parameter has no effect on the 2835 interrupt routing decision, though interrupts are 2836 only delivered when tasks running on those 2837 isolated CPUs submit IO. IO submitted on 2838 housekeeping CPUs has no influence on those 2839 queues. 2840 2841 The format of <cpu-list> is described above. 2842 2843 iucv= [HW,NET] 2844 2845 ivrs_ioapic [HW,X86-64] 2846 Provide an override to the IOAPIC-ID<->DEVICE-ID 2847 mapping provided in the IVRS ACPI table. 2848 By default, PCI segment is 0, and can be omitted. 2849 2850 For example, to map IOAPIC-ID decimal 10 to 2851 PCI segment 0x1 and PCI device 00:14.0, 2852 write the parameter as: 2853 ivrs_ioapic=10@0001:00:14.0 2854 2855 Deprecated formats: 2856 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2857 write the parameter as: 2858 ivrs_ioapic[10]=00:14.0 2859 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2860 PCI device 00:14.0 write the parameter as: 2861 ivrs_ioapic[10]=0001:00:14.0 2862 2863 ivrs_hpet [HW,X86-64] 2864 Provide an override to the HPET-ID<->DEVICE-ID 2865 mapping provided in the IVRS ACPI table. 2866 By default, PCI segment is 0, and can be omitted. 2867 2868 For example, to map HPET-ID decimal 10 to 2869 PCI segment 0x1 and PCI device 00:14.0, 2870 write the parameter as: 2871 ivrs_hpet=10@0001:00:14.0 2872 2873 Deprecated formats: 2874 * To map HPET-ID decimal 0 to PCI device 00:14.0 2875 write the parameter as: 2876 ivrs_hpet[0]=00:14.0 2877 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2878 PCI device 00:14.0 write the parameter as: 2879 ivrs_ioapic[10]=0001:00:14.0 2880 2881 ivrs_acpihid [HW,X86-64] 2882 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2883 mapping provided in the IVRS ACPI table. 2884 By default, PCI segment is 0, and can be omitted. 2885 2886 For example, to map UART-HID:UID AMD0020:0 to 2887 PCI segment 0x1 and PCI device ID 00:14.5, 2888 write the parameter as: 2889 ivrs_acpihid=AMD0020:0@0001:00:14.5 2890 2891 Deprecated formats: 2892 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2893 PCI device ID 00:14.5, write the parameter as: 2894 ivrs_acpihid[00:14.5]=AMD0020:0 2895 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2896 PCI device ID 00:14.5, write the parameter as: 2897 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2898 2899 js= [HW,JOY] Analog joystick 2900 See Documentation/input/joydev/joystick.rst. 2901 2902 kasan_multi_shot 2903 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2904 report on every invalid memory access. Without this 2905 parameter KASAN will print report only for the first 2906 invalid access. 2907 2908 keep_bootcon [KNL,EARLY] 2909 Do not unregister boot console at start. This is only 2910 useful for debugging when something happens in the window 2911 between unregistering the boot console and initializing 2912 the real console. 2913 2914 keepinitrd [HW,ARM] See retain_initrd. 2915 2916 kernelcore= [KNL,X86,PPC,EARLY] 2917 Format: nn[KMGTPE] | nn% | "mirror" 2918 This parameter specifies the amount of memory usable by 2919 the kernel for non-movable allocations. The requested 2920 amount is spread evenly throughout all nodes in the 2921 system as ZONE_NORMAL. The remaining memory is used for 2922 movable memory in its own zone, ZONE_MOVABLE. In the 2923 event, a node is too small to have both ZONE_NORMAL and 2924 ZONE_MOVABLE, kernelcore memory will take priority and 2925 other nodes will have a larger ZONE_MOVABLE. 2926 2927 ZONE_MOVABLE is used for the allocation of pages that 2928 may be reclaimed or moved by the page migration 2929 subsystem. Note that allocations like PTEs-from-HighMem 2930 still use the HighMem zone if it exists, and the Normal 2931 zone if it does not. 2932 2933 It is possible to specify the exact amount of memory in 2934 the form of "nn[KMGTPE]", a percentage of total system 2935 memory in the form of "nn%", or "mirror". If "mirror" 2936 option is specified, mirrored (reliable) memory is used 2937 for non-movable allocations and remaining memory is used 2938 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2939 are exclusive, so you cannot specify multiple forms. 2940 2941 kfence.burst= [MM,KFENCE] The number of additional successive 2942 allocations to be attempted through KFENCE for each 2943 sample interval. 2944 Format: <unsigned integer> 2945 Default: 0 2946 2947 kfence.check_on_panic= 2948 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2949 canaries on panic. 2950 Format: <bool> 2951 Default: false 2952 2953 kfence.deferrable= 2954 [MM,KFENCE] Whether to use a deferrable timer to trigger 2955 allocations. This avoids forcing CPU wake-ups if the 2956 system is idle, at the risk of a less predictable 2957 sample interval. 2958 Format: <bool> 2959 Default: CONFIG_KFENCE_DEFERRABLE 2960 2961 kfence.sample_interval= 2962 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2963 Format: <unsigned integer> 2964 0 - Disable KFENCE. 2965 >0 - Enabled KFENCE with given sample interval. 2966 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2967 2968 kfence.skip_covered_thresh= 2969 [MM,KFENCE] If pool utilization reaches this threshold 2970 (pool usage%), KFENCE limits currently covered 2971 allocations of the same source from further filling 2972 up the pool. 2973 Format: <unsigned integer> 2974 Default: 75 2975 2976 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2977 Format: <Controller#>[,poll interval] 2978 The controller # is the number of the ehci usb debug 2979 port as it is probed via PCI. The poll interval is 2980 optional and is the number seconds in between 2981 each poll cycle to the debug port in case you need 2982 the functionality for interrupting the kernel with 2983 gdb or control-c on the dbgp connection. When 2984 not using this parameter you use sysrq-g to break into 2985 the kernel debugger. 2986 2987 kgdboc= [KGDB,HW] kgdb over consoles. 2988 Requires a tty driver that supports console polling, 2989 or a supported polling keyboard driver (non-usb). 2990 Serial only format: <serial_device>[,baud] 2991 keyboard only format: kbd 2992 keyboard and serial format: kbd,<serial_device>[,baud] 2993 Optional Kernel mode setting: 2994 kms, kbd format: kms,kbd 2995 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2996 2997 kgdboc_earlycon= [KGDB,HW,EARLY] 2998 If the boot console provides the ability to read 2999 characters and can work in polling mode, you can use 3000 this parameter to tell kgdb to use it as a backend 3001 until the normal console is registered. Intended to 3002 be used together with the kgdboc parameter which 3003 specifies the normal console to transition to. 3004 3005 The name of the early console should be specified 3006 as the value of this parameter. Note that the name of 3007 the early console might be different than the tty 3008 name passed to kgdboc. It's OK to leave the value 3009 blank and the first boot console that implements 3010 read() will be picked. 3011 3012 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 3013 kernel debugger at the earliest opportunity. 3014 3015 kho= [KEXEC,EARLY] 3016 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 3017 Enables or disables Kexec HandOver. 3018 "0" | "off" | "n" - kexec handover is disabled 3019 "1" | "on" | "y" - kexec handover is enabled 3020 3021 kho_scratch= [KEXEC,EARLY] 3022 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3023 Defines the size of the KHO scratch region. The KHO 3024 scratch regions are physically contiguous memory 3025 ranges that can only be used for non-kernel 3026 allocations. That way, even when memory is heavily 3027 fragmented with handed over memory, the kexeced 3028 kernel will always have enough contiguous ranges to 3029 bootstrap itself. 3030 3031 It is possible to specify the exact amount of 3032 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3033 where the first parameter defines the size of a low 3034 memory scratch area, the second parameter defines 3035 the size of a global scratch area and the third 3036 parameter defines the size of additional per-node 3037 scratch areas. The form "nn%" defines scale factor 3038 (in percents) of memory that was used during boot. 3039 3040 kmac= [MIPS] Korina ethernet MAC address. 3041 Configure the RouterBoard 532 series on-chip 3042 Ethernet adapter MAC address. 3043 3044 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3045 Valid arguments: on, off 3046 Default: on 3047 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3048 the default is off. 3049 3050 kprobe_event=[probe-list] 3051 [FTRACE] Add kprobe events and enable at boot time. 3052 The probe-list is a semicolon delimited list of probe 3053 definitions. Each definition is same as kprobe_events 3054 interface, but the parameters are comma delimited. 3055 For example, to add a kprobe event on vfs_read with 3056 arg1 and arg2, add to the command line; 3057 3058 kprobe_event=p,vfs_read,$arg1,$arg2 3059 3060 See also Documentation/trace/kprobetrace.rst "Kernel 3061 Boot Parameter" section. 3062 3063 kpti= [ARM64,EARLY] Control page table isolation of 3064 user and kernel address spaces. 3065 Default: enabled on cores which need mitigation. 3066 0: force disabled 3067 1: force enabled 3068 3069 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3070 CONFIG_KUNIT to be set to be fully enabled. The 3071 default value can be overridden via 3072 KUNIT_DEFAULT_ENABLED. 3073 Default is 1 (enabled) 3074 3075 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3076 Default is 0 (don't ignore, but inject #GP) 3077 3078 kvm.eager_page_split= 3079 [KVM,X86] Controls whether or not KVM will try to 3080 proactively split all huge pages during dirty logging. 3081 Eager page splitting reduces interruptions to vCPU 3082 execution by eliminating the write-protection faults 3083 and MMU lock contention that would otherwise be 3084 required to split huge pages lazily. 3085 3086 VM workloads that rarely perform writes or that write 3087 only to a small region of VM memory may benefit from 3088 disabling eager page splitting to allow huge pages to 3089 still be used for reads. 3090 3091 The behavior of eager page splitting depends on whether 3092 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3093 disabled, all huge pages in a memslot will be eagerly 3094 split when dirty logging is enabled on that memslot. If 3095 enabled, eager page splitting will be performed during 3096 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3097 cleared. 3098 3099 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3100 3101 Default is Y (on). 3102 3103 kvm.enable_pmu=[KVM,X86] 3104 If enabled, KVM will virtualize PMU functionality based 3105 on the virtual CPU model defined by userspace. This 3106 can be overridden on a per-VM basis via 3107 KVM_CAP_PMU_CAPABILITY. 3108 3109 If disabled, KVM will not virtualize PMU functionality, 3110 e.g. MSRs, PMCs, PMIs, etc., even if userspace defines 3111 a virtual CPU model that contains PMU assets. 3112 3113 Note, KVM's vPMU support implicitly requires running 3114 with an in-kernel local APIC, e.g. to deliver PMIs to 3115 the guest. Running without an in-kernel local APIC is 3116 not supported, though KVM will allow such a combination 3117 (with severely degraded functionality). 3118 3119 See also enable_mediated_pmu. 3120 3121 Default is Y (on). 3122 3123 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3124 If enabled, KVM will enable virtualization in hardware 3125 when KVM is loaded, and disable virtualization when KVM 3126 is unloaded (if KVM is built as a module). 3127 3128 If disabled, KVM will dynamically enable and disable 3129 virtualization on-demand when creating and destroying 3130 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3131 number of VMs. 3132 3133 Enabling virtualization at module load avoids potential 3134 latency for creation of the 0=>1 VM, as KVM serializes 3135 virtualization enabling across all online CPUs. The 3136 "cost" of enabling virtualization when KVM is loaded, 3137 is that doing so may interfere with using out-of-tree 3138 hypervisors that want to "own" virtualization hardware. 3139 3140 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3141 Default is false (don't support). 3142 3143 kvm.nx_huge_pages= 3144 [KVM] Controls the software workaround for the 3145 X86_BUG_ITLB_MULTIHIT bug. 3146 force : Always deploy workaround. 3147 off : Never deploy workaround. 3148 auto : Deploy workaround based on the presence of 3149 X86_BUG_ITLB_MULTIHIT. 3150 3151 Default is 'auto'. 3152 3153 If the software workaround is enabled for the host, 3154 guests do need not to enable it for nested guests. 3155 3156 kvm.nx_huge_pages_recovery_ratio= 3157 [KVM] Controls how many 4KiB pages are periodically zapped 3158 back to huge pages. 0 disables the recovery, otherwise if 3159 the value is N KVM will zap 1/Nth of the 4KiB pages every 3160 period (see below). The default is 60. 3161 3162 kvm.nx_huge_pages_recovery_period_ms= 3163 [KVM] Controls the time period at which KVM zaps 4KiB pages 3164 back to huge pages. If the value is a non-zero N, KVM will 3165 zap a portion (see ratio above) of the pages every N msecs. 3166 If the value is 0 (the default), KVM will pick a period based 3167 on the ratio, such that a page is zapped after 1 hour on average. 3168 3169 kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] 3170 If enabled, KVM will provide a mediated virtual PMU, 3171 instead of the default perf-based virtual PMU (if 3172 kvm.enable_pmu is true and PMU is enumerated via the 3173 virtual CPU model). 3174 3175 With a perf-based vPMU, KVM operates as a user of perf, 3176 i.e. emulates guest PMU counters using perf events. 3177 KVM-created perf events are managed by perf as regular 3178 (guest-only) events, e.g. are scheduled in/out, contend 3179 for hardware resources, etc. Using a perf-based vPMU 3180 allows guest and host usage of the PMU to co-exist, but 3181 incurs non-trivial overhead and can result in silently 3182 dropped guest events (due to resource contention). 3183 3184 With a mediated vPMU, hardware PMU state is context 3185 switched around the world switch to/from the guest. 3186 KVM mediates which events the guest can utilize, but 3187 gives the guest direct access to all other PMU assets 3188 when possible (KVM may intercept some accesses if the 3189 virtual CPU model provides a subset of hardware PMU 3190 functionality). Using a mediated vPMU significantly 3191 reduces PMU virtualization overhead and eliminates lost 3192 guest events, but is mutually exclusive with using perf 3193 to profile KVM guests and adds latency to most VM-Exits 3194 (to context switch PMU state). 3195 3196 Default is N (off). 3197 3198 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3199 KVM/SVM. Default is 1 (enabled). 3200 3201 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3202 a.k.a. Two-Dimensional Page Tables. Default is 1 3203 (enabled). Disable by KVM if hardware lacks support 3204 for NPT. 3205 3206 kvm-amd.ciphertext_hiding_asids= 3207 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3208 to SNP private memory from reading ciphertext. Instead, 3209 reads will see constant default values (0xff). 3210 3211 If ciphertext hiding is enabled, the joint SEV-ES and 3212 SEV-SNP ASID space is partitioned into separate SEV-ES 3213 and SEV-SNP ASID ranges, with the SEV-SNP range being 3214 [1..max_snp_asid] and the SEV-ES range being 3215 (max_snp_asid..min_sev_asid), where min_sev_asid is 3216 enumerated by CPUID.0x.8000_001F[EDX]. 3217 3218 A non-zero value enables SEV-SNP ciphertext hiding and 3219 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3220 KVM caps the number of SEV-SNP ASIDs at the maximum 3221 possible value, e.g. specifying -1u will assign all 3222 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3223 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3224 max_snp_asid == min_sev_asid-1, will effectively make 3225 SEV-ES unusable. 3226 3227 kvm-arm.mode= 3228 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3229 operation. 3230 3231 none: Forcefully disable KVM. 3232 3233 nvhe: Standard nVHE-based mode, without support for 3234 protected guests. 3235 3236 protected: Mode with support for guests whose state is 3237 kept private from the host, using VHE or 3238 nVHE depending on HW support. 3239 3240 nested: VHE-based mode with support for nested 3241 virtualization. Requires at least ARMv8.4 3242 hardware (with FEAT_NV2). 3243 3244 Defaults to VHE/nVHE based on hardware support. Setting 3245 mode to "protected" will disable kexec and hibernation 3246 for the host. To force nVHE on VHE hardware, add 3247 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3248 command-line. 3249 "nested" is experimental and should be used with 3250 extreme caution. 3251 3252 kvm-arm.vgic_v3_group0_trap= 3253 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3254 system registers 3255 3256 kvm-arm.vgic_v3_group1_trap= 3257 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3258 system registers 3259 3260 kvm-arm.vgic_v3_common_trap= 3261 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3262 system registers 3263 3264 kvm-arm.vgic_v4_enable= 3265 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3266 injection of LPIs. 3267 3268 kvm-arm.wfe_trap_policy= 3269 [KVM,ARM] Control when to set WFE instruction trap for 3270 KVM VMs. Traps are allowed but not guaranteed by the 3271 CPU architecture. 3272 3273 trap: set WFE instruction trap 3274 3275 notrap: clear WFE instruction trap 3276 3277 kvm-arm.wfi_trap_policy= 3278 [KVM,ARM] Control when to set WFI instruction trap for 3279 KVM VMs. Traps are allowed but not guaranteed by the 3280 CPU architecture. 3281 3282 trap: set WFI instruction trap 3283 3284 notrap: clear WFI instruction trap 3285 3286 kvm_cma_resv_ratio=n [PPC,EARLY] 3287 Reserves given percentage from system memory area for 3288 contiguous memory allocation for KVM hash pagetable 3289 allocation. 3290 By default it reserves 5% of total system memory. 3291 Format: <integer> 3292 Default: 5 3293 3294 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3295 a.k.a. Two-Dimensional Page Tables. Default is 1 3296 (enabled). Disable by KVM if hardware lacks support 3297 for EPT. 3298 3299 kvm-intel.emulate_invalid_guest_state= 3300 [KVM,Intel] Control whether to emulate invalid guest 3301 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3302 as guest state is never invalid for unrestricted 3303 guests. This param doesn't apply to nested guests (L2), 3304 as KVM never emulates invalid L2 guest state. 3305 Default is 1 (enabled). 3306 3307 kvm-intel.flexpriority= 3308 [KVM,Intel] Control KVM's use of FlexPriority feature 3309 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3310 hardware lacks support for it. 3311 3312 kvm-intel.nested= 3313 [KVM,Intel] Control nested virtualization feature in 3314 KVM/VMX. Default is 1 (enabled). 3315 3316 kvm-intel.unrestricted_guest= 3317 [KVM,Intel] Control KVM's use of unrestricted guest 3318 feature (virtualized real and unpaged mode). Default 3319 is 1 (enabled). Disable by KVM if EPT is disabled or 3320 hardware lacks support for it. 3321 3322 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3323 CVE-2018-3620. 3324 3325 Valid arguments: never, cond, always 3326 3327 always: L1D cache flush on every VMENTER. 3328 cond: Flush L1D on VMENTER only when the code between 3329 VMEXIT and VMENTER can leak host memory. 3330 never: Disables the mitigation 3331 3332 Default is cond (do L1 cache flush in specific instances) 3333 3334 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3335 Identification feature (tagged TLBs). Default is 1 3336 (enabled). Disable by KVM if hardware lacks support 3337 for it. 3338 3339 l1d_flush= [X86,INTEL,EARLY] 3340 Control mitigation for L1D based snooping vulnerability. 3341 3342 Certain CPUs are vulnerable to an exploit against CPU 3343 internal buffers which can forward information to a 3344 disclosure gadget under certain conditions. 3345 3346 In vulnerable processors, the speculatively 3347 forwarded data can be used in a cache side channel 3348 attack, to access data to which the attacker does 3349 not have direct access. 3350 3351 This parameter controls the mitigation. The 3352 options are: 3353 3354 on - enable the interface for the mitigation 3355 3356 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3357 affected CPUs 3358 3359 The kernel PTE inversion protection is unconditionally 3360 enabled and cannot be disabled. 3361 3362 full 3363 Provides all available mitigations for the 3364 L1TF vulnerability. Disables SMT and 3365 enables all mitigations in the 3366 hypervisors, i.e. unconditional L1D flush. 3367 3368 SMT control and L1D flush control via the 3369 sysfs interface is still possible after 3370 boot. Hypervisors will issue a warning 3371 when the first VM is started in a 3372 potentially insecure configuration, 3373 i.e. SMT enabled or L1D flush disabled. 3374 3375 full,force 3376 Same as 'full', but disables SMT and L1D 3377 flush runtime control. Implies the 3378 'nosmt=force' command line option. 3379 (i.e. sysfs control of SMT is disabled.) 3380 3381 flush 3382 Leaves SMT enabled and enables the default 3383 hypervisor mitigation, i.e. conditional 3384 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 flush,nosmt 3394 3395 Disables SMT and enables the default 3396 hypervisor mitigation. 3397 3398 SMT control and L1D flush control via the 3399 sysfs interface is still possible after 3400 boot. Hypervisors will issue a warning 3401 when the first VM is started in a 3402 potentially insecure configuration, 3403 i.e. SMT enabled or L1D flush disabled. 3404 3405 flush,nowarn 3406 Same as 'flush', but hypervisors will not 3407 warn when a VM is started in a potentially 3408 insecure configuration. 3409 3410 off 3411 Disables hypervisor mitigations and doesn't 3412 emit any warnings. 3413 It also drops the swap size and available 3414 RAM limit restriction on both hypervisor and 3415 bare metal. 3416 3417 Default is 'flush'. 3418 3419 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3420 3421 l2cr= [PPC] 3422 3423 l3cr= [PPC] 3424 3425 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3426 disabled it. 3427 3428 lapic= [X86,APIC] Do not use TSC deadline 3429 value for LAPIC timer one-shot implementation. Default 3430 back to the programmable timer unit in the LAPIC. 3431 Format: notscdeadline 3432 3433 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3434 in C2 power state. 3435 3436 libata.dma= [LIBATA] DMA control 3437 libata.dma=0 Disable all PATA and SATA DMA 3438 libata.dma=1 PATA and SATA Disk DMA only 3439 libata.dma=2 ATAPI (CDROM) DMA only 3440 libata.dma=4 Compact Flash DMA only 3441 Combinations also work, so libata.dma=3 enables DMA 3442 for disks and CDROMs, but not CFs. 3443 3444 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3445 libata.ignore_hpa=0 keep BIOS limits (default) 3446 libata.ignore_hpa=1 ignore limits, using full disk 3447 3448 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3449 when set. 3450 Format: <int> 3451 3452 libata.force= [LIBATA] Force configurations. The format is a comma- 3453 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3454 PORT and DEVICE are decimal numbers matching port, link 3455 or device. Basically, it matches the ATA ID string 3456 printed on console by libata. If the whole ID part is 3457 omitted, the last PORT and DEVICE values are used. If 3458 ID hasn't been specified yet, the configuration applies 3459 to all ports, links and devices. 3460 3461 If only DEVICE is omitted, the parameter applies to 3462 the port and all links and devices behind it. DEVICE 3463 number of 0 either selects the first device or the 3464 first fan-out link behind PMP device. It does not 3465 select the host link. DEVICE number of 15 selects the 3466 host link and device attached to it. 3467 3468 The VAL specifies the configuration to force. As long 3469 as there is no ambiguity, shortcut notation is allowed. 3470 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3471 The following configurations can be forced. 3472 3473 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3474 Any ID with matching PORT is used. 3475 3476 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3477 3478 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3479 udma[/][16,25,33,44,66,100,133] notation is also 3480 allowed. 3481 3482 * nohrst, nosrst, norst: suppress hard, soft and both 3483 resets. 3484 3485 * rstonce: only attempt one reset during hot-unplug 3486 link recovery. 3487 3488 * [no]dbdelay: Enable or disable the extra 200ms delay 3489 before debouncing a link PHY and device presence 3490 detection. 3491 3492 * [no]ncq: Turn on or off NCQ. 3493 3494 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3495 3496 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3497 3498 * [no]trim: Enable or disable (unqueued) TRIM. 3499 3500 * trim_zero: Indicate that TRIM command zeroes data. 3501 3502 * max_trim_128m: Set 128M maximum trim size limit. 3503 3504 * [no]dma: Turn on or off DMA transfers. 3505 3506 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3507 3508 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3509 commands that are not a multiple of 16 bytes. 3510 3511 * [no]dmalog: Enable or disable the use of the 3512 READ LOG DMA EXT command to access logs. 3513 3514 * [no]iddevlog: Enable or disable access to the 3515 identify device data log. 3516 3517 * [no]logdir: Enable or disable access to the general 3518 purpose log directory. 3519 3520 * max_sec=<sectors>: Set the transfer size limit, in 3521 number of 512-byte sectors, to the value specified in 3522 <sectors>. The value specified in <sectors> has to be 3523 a non-zero positive integer. 3524 3525 * max_sec_128: Set transfer size limit to 128 sectors. 3526 3527 * max_sec_1024: Set or clear transfer size limit to 3528 1024 sectors. 3529 3530 * max_sec_lba48: Set or clear transfer size limit to 3531 65535 sectors. 3532 3533 * external: Mark port as external (hotplug-capable). 3534 3535 * [no]lpm: Enable or disable link power management. 3536 3537 * [no]setxfer: Indicate if transfer speed mode setting 3538 should be skipped. 3539 3540 * [no]fua: Disable or enable FUA (Force Unit Access) 3541 support for devices supporting this feature. 3542 3543 * dump_id: Dump IDENTIFY data. 3544 3545 * disable: Disable this device. 3546 3547 If there are multiple matching configurations changing 3548 the same attribute, the last one is used. 3549 3550 liveupdate= [KNL,EARLY] 3551 Format: <bool> 3552 Enable Live Update Orchestrator (LUO). 3553 Default: off. 3554 3555 lockd.nlm_grace_period=P [NFS] Assign grace period. 3556 Format: <integer> 3557 3558 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3559 Format: <integer> 3560 3561 lockd.nlm_timeout=T [NFS] Assign timeout value. 3562 Format: <integer> 3563 3564 lockd.nlm_udpport=M [NFS] Assign UDP port. 3565 Format: <integer> 3566 3567 lockdown= [SECURITY,EARLY] 3568 { integrity | confidentiality } 3569 Enable the kernel lockdown feature. If set to 3570 integrity, kernel features that allow userland to 3571 modify the running kernel are disabled. If set to 3572 confidentiality, kernel features that allow userland 3573 to extract confidential information from the kernel 3574 are also disabled. 3575 3576 locktorture.acq_writer_lim= [KNL] 3577 Set the time limit in jiffies for a lock 3578 acquisition. Acquisitions exceeding this limit 3579 will result in a splat once they do complete. 3580 3581 locktorture.bind_readers= [KNL] 3582 Specify the list of CPUs to which the readers are 3583 to be bound. 3584 3585 locktorture.bind_writers= [KNL] 3586 Specify the list of CPUs to which the writers are 3587 to be bound. 3588 3589 locktorture.call_rcu_chains= [KNL] 3590 Specify the number of self-propagating call_rcu() 3591 chains to set up. These are used to ensure that 3592 there is a high probability of an RCU grace period 3593 in progress at any given time. Defaults to 0, 3594 which disables these call_rcu() chains. 3595 3596 locktorture.long_hold= [KNL] 3597 Specify the duration in milliseconds for the 3598 occasional long-duration lock hold time. Defaults 3599 to 100 milliseconds. Select 0 to disable. 3600 3601 locktorture.nested_locks= [KNL] 3602 Specify the maximum lock nesting depth that 3603 locktorture is to exercise, up to a limit of 8 3604 (MAX_NESTED_LOCKS). Specify zero to disable. 3605 Note that this parameter is ineffective on types 3606 of locks that do not support nested acquisition. 3607 3608 locktorture.nreaders_stress= [KNL] 3609 Set the number of locking read-acquisition kthreads. 3610 Defaults to being automatically set based on the 3611 number of online CPUs. 3612 3613 locktorture.nwriters_stress= [KNL] 3614 Set the number of locking write-acquisition kthreads. 3615 3616 locktorture.onoff_holdoff= [KNL] 3617 Set time (s) after boot for CPU-hotplug testing. 3618 3619 locktorture.onoff_interval= [KNL] 3620 Set time (s) between CPU-hotplug operations, or 3621 zero to disable CPU-hotplug testing. 3622 3623 locktorture.rt_boost= [KNL] 3624 Do periodic testing of real-time lock priority 3625 boosting. Select 0 to disable, 1 to boost 3626 only rt_mutex, and 2 to boost unconditionally. 3627 Defaults to 2, which might seem to be an 3628 odd choice, but which should be harmless for 3629 non-real-time spinlocks, due to their disabling 3630 of preemption. Note that non-realtime mutexes 3631 disable boosting. 3632 3633 locktorture.rt_boost_factor= [KNL] 3634 Number that determines how often and for how 3635 long priority boosting is exercised. This is 3636 scaled down by the number of writers, so that the 3637 number of boosts per unit time remains roughly 3638 constant as the number of writers increases. 3639 On the other hand, the duration of each boost 3640 increases with the number of writers. 3641 3642 locktorture.shuffle_interval= [KNL] 3643 Set task-shuffle interval (jiffies). Shuffling 3644 tasks allows some CPUs to go into dyntick-idle 3645 mode during the locktorture test. 3646 3647 locktorture.shutdown_secs= [KNL] 3648 Set time (s) after boot system shutdown. This 3649 is useful for hands-off automated testing. 3650 3651 locktorture.stat_interval= [KNL] 3652 Time (s) between statistics printk()s. 3653 3654 locktorture.stutter= [KNL] 3655 Time (s) to stutter testing, for example, 3656 specifying five seconds causes the test to run for 3657 five seconds, wait for five seconds, and so on. 3658 This tests the locking primitive's ability to 3659 transition abruptly to and from idle. 3660 3661 locktorture.torture_type= [KNL] 3662 Specify the locking implementation to test. 3663 3664 locktorture.verbose= [KNL] 3665 Enable additional printk() statements. 3666 3667 locktorture.writer_fifo= [KNL] 3668 Run the write-side locktorture kthreads at 3669 sched_set_fifo() real-time priority. 3670 3671 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3672 Format: <irq> 3673 3674 loglevel= [KNL,EARLY] 3675 All Kernel Messages with a loglevel smaller than the 3676 console loglevel will be printed to the console. It can 3677 also be changed with klogd or other programs. The 3678 loglevels are defined as follows: 3679 3680 0 (KERN_EMERG) system is unusable 3681 1 (KERN_ALERT) action must be taken immediately 3682 2 (KERN_CRIT) critical conditions 3683 3 (KERN_ERR) error conditions 3684 4 (KERN_WARNING) warning conditions 3685 5 (KERN_NOTICE) normal but significant condition 3686 6 (KERN_INFO) informational 3687 7 (KERN_DEBUG) debug-level messages 3688 3689 log_buf_len=n[KMG] [KNL,EARLY] 3690 Sets the size of the printk ring buffer, in bytes. 3691 n must be a power of two and greater than the 3692 minimal size. The minimal size is defined by 3693 LOG_BUF_SHIFT kernel config parameter. There 3694 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3695 parameter that allows to increase the default size 3696 depending on the number of CPUs. See init/Kconfig 3697 for more details. 3698 3699 logo.nologo [FB] Disables display of the built-in Linux logo. 3700 This may be used to provide more screen space for 3701 kernel log messages and is useful when debugging 3702 kernel boot problems. 3703 3704 lp=0 [LP] Specify parallel ports to use, e.g, 3705 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3706 lp=reset first parallel port). 'lp=0' disables the 3707 lp=auto printer driver. 'lp=reset' (which can be 3708 specified in addition to the ports) causes 3709 attached printers to be reset. Using 3710 lp=port1,port2,... specifies the parallel ports 3711 to associate lp devices with, starting with 3712 lp0. A port specification may be 'none' to skip 3713 that lp device, or a parport name such as 3714 'parport0'. Specifying 'lp=auto' instead of a 3715 port specification list means that device IDs 3716 from each port should be examined, to see if 3717 an IEEE 1284-compliant printer is attached; if 3718 so, the driver will manage that printer. 3719 See also header of drivers/char/lp.c. 3720 3721 lpj=n [KNL] 3722 Sets loops_per_jiffy to given constant, thus avoiding 3723 time-consuming boot-time autodetection (up to 250 ms per 3724 CPU). 0 enables autodetection (default). To determine 3725 the correct value for your kernel, boot with normal 3726 autodetection and see what value is printed. Note that 3727 on SMP systems the preset will be applied to all CPUs, 3728 which is likely to cause problems if your CPUs need 3729 significantly divergent settings. An incorrect value 3730 will cause delays in the kernel to be wrong, leading to 3731 unpredictable I/O errors and other breakage. Although 3732 unlikely, in the extreme case this might damage your 3733 hardware. 3734 3735 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3736 3737 lsm=lsm1,...,lsmN 3738 [SECURITY] Choose order of LSM initialization. This 3739 overrides CONFIG_LSM, and the "security=" parameter. 3740 3741 machtype= [Loongson] Share the same kernel image file between 3742 different yeeloong laptops. 3743 Example: machtype=lemote-yeeloong-2f-7inch 3744 3745 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3746 will bring up during bootup. maxcpus=n : n >= 0 limits 3747 the kernel to bring up 'n' processors. Surely after 3748 bootup you can bring up the other plugged cpu by executing 3749 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3750 only takes effect during system bootup. 3751 While n=0 is a special case, it is equivalent to "nosmp", 3752 which also disables the IO APIC. 3753 3754 max_loop= [LOOP] The number of loop block devices that get 3755 (loop.max_loop) unconditionally pre-created at init time. The default 3756 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3757 of statically allocating a predefined number, loop 3758 devices can be requested on-demand with the 3759 /dev/loop-control interface. 3760 3761 mce= [X86-{32,64}] 3762 3763 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3764 3765 off 3766 disable machine check 3767 3768 no_cmci 3769 disable CMCI(Corrected Machine Check Interrupt) that 3770 Intel processor supports. Usually this disablement is 3771 not recommended, but it might be handy if your 3772 hardware is misbehaving. 3773 3774 Note that you'll get more problems without CMCI than 3775 with due to the shared banks, i.e. you might get 3776 duplicated error logs. 3777 3778 dont_log_ce 3779 don't make logs for corrected errors. All events 3780 reported as corrected are silently cleared by OS. This 3781 option will be useful if you have no interest in any 3782 of corrected errors. 3783 3784 ignore_ce 3785 disable features for corrected errors, e.g. 3786 polling timer and CMCI. All events reported as 3787 corrected are not cleared by OS and remained in its 3788 error banks. 3789 3790 Usually this disablement is not recommended, however 3791 if there is an agent checking/clearing corrected 3792 errors (e.g. BIOS or hardware monitoring 3793 applications), conflicting with OS's error handling, 3794 and you cannot deactivate the agent, then this option 3795 will be a help. 3796 3797 no_lmce 3798 do not opt-in to Local MCE delivery. Use legacy method 3799 to broadcast MCEs. 3800 3801 bootlog 3802 enable logging of machine checks left over from 3803 booting. Disabled by default on AMD Fam10h and older 3804 because some BIOS leave bogus ones. 3805 3806 If your BIOS doesn't do that it's a good idea to 3807 enable though to make sure you log even machine check 3808 events that result in a reboot. On Intel systems it is 3809 enabled by default. 3810 3811 nobootlog 3812 disable boot machine check logging. 3813 3814 monarchtimeout (number) 3815 sets the time in us to wait for other CPUs on machine 3816 checks. 0 to disable. 3817 3818 bios_cmci_threshold 3819 don't overwrite the bios-set CMCI threshold. This boot 3820 option prevents Linux from overwriting the CMCI 3821 threshold set by the bios. Without this option, Linux 3822 always sets the CMCI threshold to 1. Enabling this may 3823 make memory predictive failure analysis less effective 3824 if the bios sets thresholds for memory errors since we 3825 will not see details for all errors. 3826 3827 recovery 3828 force-enable recoverable machine check code paths 3829 3830 Everything else is in sysfs now. 3831 3832 3833 md= [HW] RAID subsystems devices and level 3834 See Documentation/admin-guide/md.rst. 3835 3836 mdacon= [MDA] 3837 Format: <first>,<last> 3838 Specifies range of consoles to be captured by the MDA. 3839 3840 mds= [X86,INTEL,EARLY] 3841 Control mitigation for the Micro-architectural Data 3842 Sampling (MDS) vulnerability. 3843 3844 Certain CPUs are vulnerable to an exploit against CPU 3845 internal buffers which can forward information to a 3846 disclosure gadget under certain conditions. 3847 3848 In vulnerable processors, the speculatively 3849 forwarded data can be used in a cache side channel 3850 attack, to access data to which the attacker does 3851 not have direct access. 3852 3853 This parameter controls the MDS mitigation. The 3854 options are: 3855 3856 full - Enable MDS mitigation on vulnerable CPUs 3857 full,nosmt - Enable MDS mitigation and disable 3858 SMT on vulnerable CPUs 3859 off - Unconditionally disable MDS mitigation 3860 3861 On TAA-affected machines, mds=off can be prevented by 3862 an active TAA mitigation as both vulnerabilities are 3863 mitigated with the same mechanism so in order to disable 3864 this mitigation, you need to specify tsx_async_abort=off 3865 too. 3866 3867 Not specifying this option is equivalent to 3868 mds=full. 3869 3870 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3871 3872 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3873 Must be specified, otherwise memory size will be 0. 3874 3875 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3876 of memory Amount of memory to be used in cases 3877 as follows: 3878 3879 1 for test; 3880 2 when the kernel is not able to see the whole system memory; 3881 3 memory that lies after 'mem=' boundary is excluded from 3882 the hypervisor, then assigned to KVM guests. 3883 4 to limit the memory available for kdump kernel. 3884 3885 [ARC,MICROBLAZE] - the limit applies only to low memory, 3886 high memory is not affected. 3887 3888 [ARM64] - only limits memory covered by the linear 3889 mapping. The NOMAP regions are not affected. 3890 3891 [X86] Work as limiting max address. Use together 3892 with memmap= to avoid physical address space collisions. 3893 Without memmap= PCI devices could be placed at addresses 3894 belonging to unused RAM. 3895 3896 Note that this only takes effects during boot time since 3897 in above case 3, memory may need be hot added after boot 3898 if system memory of hypervisor is not sufficient. 3899 3900 mem=nn[KMG]@ss[KMG] 3901 [ARM,MIPS,EARLY] - override the memory layout 3902 reported by firmware. 3903 Define a memory region of size nn[KMG] starting at 3904 ss[KMG]. 3905 Multiple different regions can be specified with 3906 multiple mem= parameters on the command line. 3907 3908 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3909 memory. 3910 3911 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3912 3913 memchunk=nn[KMG] 3914 [KNL,SH] Allow user to override the default size for 3915 per-device physically contiguous DMA buffers. 3916 3917 memhp_default_state=online/offline/online_kernel/online_movable 3918 [KNL] Set the initial state for the memory hotplug 3919 onlining policy. If not specified, the default value is 3920 set according to the 3921 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3922 options. 3923 See Documentation/admin-guide/mm/memory-hotplug.rst. 3924 3925 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3926 E820 memory map, as specified by the user. 3927 Such memmap=exactmap lines can be constructed based on 3928 BIOS output or other requirements. See the memmap=nn@ss 3929 option description. 3930 3931 memmap=nn[KMG]@ss[KMG] 3932 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3933 Region of memory to be used is from ss to ss+nn. 3934 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3935 which limits max address to nn[KMG]. 3936 Multiple different regions can be specified, 3937 comma delimited. 3938 Example: 3939 memmap=100M@2G,100M#3G,1G!1024G 3940 3941 memmap=nn[KMG]#ss[KMG] 3942 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3943 Region of memory to be marked is from ss to ss+nn. 3944 3945 memmap=nn[KMG]$ss[KMG] 3946 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3947 Region of memory to be reserved is from ss to ss+nn. 3948 Example: Exclude memory from 0x18690000-0x1869ffff 3949 memmap=64K$0x18690000 3950 or 3951 memmap=0x10000$0x18690000 3952 Some bootloaders may need an escape character before '$', 3953 like Grub2, otherwise '$' and the following number 3954 will be eaten. 3955 3956 memmap=nn[KMG]!ss[KMG,EARLY] 3957 [KNL,X86] Mark specific memory as protected. 3958 Region of memory to be used, from ss to ss+nn. 3959 The memory region may be marked as e820 type 12 (0xc) 3960 and is NVDIMM or ADR memory. 3961 3962 memmap=<size>%<offset>-<oldtype>+<newtype> 3963 [KNL,ACPI,EARLY] Convert memory within the specified region 3964 from <oldtype> to <newtype>. If "-<oldtype>" is left 3965 out, the whole region will be marked as <newtype>, 3966 even if previously unavailable. If "+<newtype>" is left 3967 out, matching memory will be removed. Types are 3968 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3969 3 = ACPI, 12 = PRAM. 3970 3971 memory_corruption_check=0/1 [X86,EARLY] 3972 Some BIOSes seem to corrupt the first 64k of 3973 memory when doing things like suspend/resume. 3974 Setting this option will scan the memory 3975 looking for corruption. Enabling this will 3976 both detect corruption and prevent the kernel 3977 from using the memory being corrupted. 3978 However, it's intended as a diagnostic tool; if 3979 repeatable BIOS-originated corruption always 3980 affects the same memory, you can use memmap= 3981 to prevent the kernel from using that memory. 3982 3983 memory_corruption_check_size=size [X86,EARLY] 3984 By default it checks for corruption in the low 3985 64k, making this memory unavailable for normal 3986 use. Use this parameter to scan for 3987 corruption in more or less memory. 3988 3989 memory_corruption_check_period=seconds [X86,EARLY] 3990 By default it checks for corruption every 60 3991 seconds. Use this parameter to check at some 3992 other rate. 0 disables periodic checking. 3993 3994 memory_hotplug.memmap_on_memory 3995 [KNL,X86,ARM] Boolean flag to enable this feature. 3996 Format: {on | off (default)} 3997 When enabled, runtime hotplugged memory will 3998 allocate its internal metadata (struct pages, 3999 those vmemmap pages cannot be optimized even 4000 if hugetlb_free_vmemmap is enabled) from the 4001 hotadded memory which will allow to hotadd a 4002 lot of memory without requiring additional 4003 memory to do so. 4004 This feature is disabled by default because it 4005 has some implication on large (e.g. GB) 4006 allocations in some configurations (e.g. small 4007 memory blocks). 4008 The state of the flag can be read in 4009 /sys/module/memory_hotplug/parameters/memmap_on_memory. 4010 Note that even when enabled, there are a few cases where 4011 the feature is not effective. 4012 4013 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 4014 Format: <integer> 4015 default : 0 <disable> 4016 Specifies the number of memtest passes to be 4017 performed. Each pass selects another test 4018 pattern from a given set of patterns. Memtest 4019 fills the memory with this pattern, validates 4020 memory contents and reserves bad memory 4021 regions that are detected. 4022 4023 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 4024 Valid arguments: on, off 4025 Default: off 4026 mem_encrypt=on: Activate SME 4027 mem_encrypt=off: Do not activate SME 4028 4029 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 4030 for details on when memory encryption can be activated. 4031 4032 mem_sleep_default= [SUSPEND] Default system suspend mode: 4033 s2idle - Suspend-To-Idle 4034 shallow - Power-On Suspend or equivalent (if supported) 4035 deep - Suspend-To-RAM or equivalent (if supported) 4036 See Documentation/admin-guide/pm/sleep-states.rst. 4037 4038 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 4039 the BIOS has incorrectly applied a workaround. TinyBIOS 4040 version 0.98 is known to be affected, 0.99 fixes the 4041 problem by letting the user disable the workaround. 4042 4043 mga= [HW,DRM] 4044 4045 microcode= [X86] Control the behavior of the microcode loader. 4046 Available options, comma separated: 4047 4048 base_rev=X - with <X> with format: <u32> 4049 Set the base microcode revision of each thread when in 4050 debug mode. 4051 4052 dis_ucode_ldr: disable the microcode loader 4053 4054 force_minrev: 4055 Enable or disable the microcode minimal revision 4056 enforcement for the runtime microcode loader. 4057 4058 mini2440= [ARM,HW,KNL] 4059 Format:[0..2][b][c][t] 4060 Default: "0tb" 4061 MINI2440 configuration specification: 4062 0 - The attached screen is the 3.5" TFT 4063 1 - The attached screen is the 7" TFT 4064 2 - The VGA Shield is attached (1024x768) 4065 Leaving out the screen size parameter will not load 4066 the TFT driver, and the framebuffer will be left 4067 unconfigured. 4068 b - Enable backlight. The TFT backlight pin will be 4069 linked to the kernel VESA blanking code and a GPIO 4070 LED. This parameter is not necessary when using the 4071 VGA shield. 4072 c - Enable the s3c camera interface. 4073 t - Reserved for enabling touchscreen support. The 4074 touchscreen support is not enabled in the mainstream 4075 kernel as of 2.6.30, a preliminary port can be found 4076 in the "bleeding edge" mini2440 support kernel at 4077 https://repo.or.cz/w/linux-2.6/mini2440.git 4078 4079 mitigations= 4080 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4081 CPU vulnerabilities. This is a set of curated, 4082 arch-independent options, each of which is an 4083 aggregation of existing arch-specific options. 4084 4085 Note, "mitigations" is supported if and only if the 4086 kernel was built with CPU_MITIGATIONS=y. 4087 4088 off 4089 Disable all optional CPU mitigations. This 4090 improves system performance, but it may also 4091 expose users to several CPU vulnerabilities. 4092 Equivalent to: if nokaslr then kpti=0 [ARM64] 4093 gather_data_sampling=off [X86] 4094 indirect_target_selection=off [X86] 4095 kvm.nx_huge_pages=off [X86] 4096 l1tf=off [X86] 4097 mds=off [X86] 4098 mmio_stale_data=off [X86] 4099 no_entry_flush [PPC] 4100 no_uaccess_flush [PPC] 4101 nobp=0 [S390] 4102 nopti [X86,PPC] 4103 nospectre_bhb [ARM64] 4104 nospectre_v1 [X86,PPC] 4105 nospectre_v2 [X86,PPC,S390,ARM64] 4106 reg_file_data_sampling=off [X86] 4107 retbleed=off [X86] 4108 spec_rstack_overflow=off [X86] 4109 spec_store_bypass_disable=off [X86,PPC] 4110 spectre_bhi=off [X86] 4111 spectre_v2_user=off [X86] 4112 srbds=off [X86,INTEL] 4113 ssbd=force-off [ARM64] 4114 tsa=off [X86,AMD] 4115 tsx_async_abort=off [X86] 4116 vmscape=off [X86] 4117 4118 Exceptions: 4119 This does not have any effect on 4120 kvm.nx_huge_pages when 4121 kvm.nx_huge_pages=force. 4122 4123 auto (default) 4124 Mitigate all CPU vulnerabilities, but leave SMT 4125 enabled, even if it's vulnerable. This is for 4126 users who don't want to be surprised by SMT 4127 getting disabled across kernel upgrades, or who 4128 have other ways of avoiding SMT-based attacks. 4129 Equivalent to: (default behavior) 4130 4131 auto,nosmt 4132 Mitigate all CPU vulnerabilities, disabling SMT 4133 if needed. This is for users who always want to 4134 be fully mitigated, even if it means losing SMT. 4135 Equivalent to: l1tf=flush,nosmt [X86] 4136 mds=full,nosmt [X86] 4137 tsx_async_abort=full,nosmt [X86] 4138 mmio_stale_data=full,nosmt [X86] 4139 retbleed=auto,nosmt [X86] 4140 4141 [X86] After one of the above options, additionally 4142 supports attack-vector based controls as documented in 4143 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4144 4145 mminit_loglevel= 4146 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4147 parameter allows control of the logging verbosity for 4148 the additional memory initialisation checks. A value 4149 of 0 disables mminit logging and a level of 4 will 4150 log everything. Information is printed at KERN_DEBUG 4151 so loglevel=8 may also need to be specified. 4152 4153 mmio_stale_data= 4154 [X86,INTEL,EARLY] Control mitigation for the Processor 4155 MMIO Stale Data vulnerabilities. 4156 4157 Processor MMIO Stale Data is a class of 4158 vulnerabilities that may expose data after an MMIO 4159 operation. Exposed data could originate or end in 4160 the same CPU buffers as affected by MDS and TAA. 4161 Therefore, similar to MDS and TAA, the mitigation 4162 is to clear the affected CPU buffers. 4163 4164 This parameter controls the mitigation. The 4165 options are: 4166 4167 full - Enable mitigation on vulnerable CPUs 4168 4169 full,nosmt - Enable mitigation and disable SMT on 4170 vulnerable CPUs. 4171 4172 off - Unconditionally disable mitigation 4173 4174 On MDS or TAA affected machines, 4175 mmio_stale_data=off can be prevented by an active 4176 MDS or TAA mitigation as these vulnerabilities are 4177 mitigated with the same mechanism so in order to 4178 disable this mitigation, you need to specify 4179 mds=off and tsx_async_abort=off too. 4180 4181 Not specifying this option is equivalent to 4182 mmio_stale_data=full. 4183 4184 For details see: 4185 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4186 4187 <module>.async_probe[=<bool>] [KNL] 4188 If no <bool> value is specified or if the value 4189 specified is not a valid <bool>, enable asynchronous 4190 probe on this module. Otherwise, enable/disable 4191 asynchronous probe on this module as indicated by the 4192 <bool> value. See also: module.async_probe 4193 4194 module.async_probe=<bool> 4195 [KNL] When set to true, modules will use async probing 4196 by default. To enable/disable async probing for a 4197 specific module, use the module specific control that 4198 is documented under <module>.async_probe. When both 4199 module.async_probe and <module>.async_probe are 4200 specified, <module>.async_probe takes precedence for 4201 the specific module. 4202 4203 module.enable_dups_trace 4204 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4205 this means that duplicate request_module() calls will 4206 trigger a WARN_ON() instead of a pr_warn(). Note that 4207 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4208 will always be issued and this option does nothing. 4209 module.sig_enforce 4210 [KNL] When CONFIG_MODULE_SIG is set, this means that 4211 modules without (valid) signatures will fail to load. 4212 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4213 is always true, so this option does nothing. 4214 4215 module_blacklist= [KNL] Do not load a comma-separated list of 4216 modules. Useful for debugging problem modules. 4217 4218 mousedev.tap_time= 4219 [MOUSE] Maximum time between finger touching and 4220 leaving touchpad surface for touch to be considered 4221 a tap and be reported as a left button click (for 4222 touchpads working in absolute mode only). 4223 Format: <msecs> 4224 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4225 reporting absolute coordinates, such as tablets 4226 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4227 reporting absolute coordinates, such as tablets 4228 4229 movablecore= [KNL,X86,PPC,EARLY] 4230 Format: nn[KMGTPE] | nn% 4231 This parameter is the complement to kernelcore=, it 4232 specifies the amount of memory used for migratable 4233 allocations. If both kernelcore and movablecore is 4234 specified, then kernelcore will be at *least* the 4235 specified value but may be more. If movablecore on its 4236 own is specified, the administrator must be careful 4237 that the amount of memory usable for all allocations 4238 is not too small. 4239 4240 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4241 NUMA nodes to be movable. This means that the memory 4242 of such nodes will be usable only for movable 4243 allocations which rules out almost all kernel 4244 allocations. Use with caution! 4245 4246 MTD_Partition= [MTD] 4247 Format: <name>,<region-number>,<size>,<offset> 4248 4249 MTD_Region= [MTD] Format: 4250 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4251 4252 mtdparts= [MTD] 4253 See drivers/mtd/parsers/cmdlinepart.c 4254 4255 mtouchusb.raw_coordinates= 4256 [HW] Make the MicroTouch USB driver use raw coordinates 4257 ('y', default) or cooked coordinates ('n') 4258 4259 mtrr=debug [X86,EARLY] 4260 Enable printing debug information related to MTRR 4261 registers at boot time. 4262 4263 mtrr_chunk_size=nn[KMG,X86,EARLY] 4264 used for mtrr cleanup. It is largest continuous chunk 4265 that could hold holes aka. UC entries. 4266 4267 mtrr_gran_size=nn[KMG,X86,EARLY] 4268 Used for mtrr cleanup. It is granularity of mtrr block. 4269 Default is 1. 4270 Large value could prevent small alignment from 4271 using up MTRRs. 4272 4273 mtrr_spare_reg_nr=n [X86,EARLY] 4274 Format: <integer> 4275 Range: 0,7 : spare reg number 4276 Default : 1 4277 Used for mtrr cleanup. It is spare mtrr entries number. 4278 Set to 2 or more if your graphical card needs more. 4279 4280 multitce=off [PPC] This parameter disables the use of the pSeries 4281 firmware feature for updating multiple TCE entries 4282 at a time. 4283 4284 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4285 4286 netdev= [NET] Network devices parameters 4287 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4288 Note that mem_start is often overloaded to mean 4289 something different and driver-specific. 4290 This usage is only documented in each driver source 4291 file if at all. 4292 4293 netpoll.carrier_timeout= 4294 [NET] Specifies amount of time (in seconds) that 4295 netpoll should wait for a carrier. By default netpoll 4296 waits 4 seconds. 4297 4298 nf_conntrack.acct= 4299 [NETFILTER] Enable connection tracking flow accounting 4300 0 to disable accounting 4301 1 to enable accounting 4302 Default value is 0. 4303 4304 nfs.cache_getent= 4305 [NFS] sets the pathname to the program which is used 4306 to update the NFS client cache entries. 4307 4308 nfs.cache_getent_timeout= 4309 [NFS] sets the timeout after which an attempt to 4310 update a cache entry is deemed to have failed. 4311 4312 nfs.callback_nr_threads= 4313 [NFSv4] set the total number of threads that the 4314 NFS client will assign to service NFSv4 callback 4315 requests. 4316 4317 nfs.callback_tcpport= 4318 [NFS] set the TCP port on which the NFSv4 callback 4319 channel should listen. 4320 4321 nfs.delay_retrans= 4322 [NFS] specifies the number of times the NFSv4 client 4323 retries the request before returning an EAGAIN error, 4324 after a reply of NFS4ERR_DELAY from the server. 4325 Only applies if the softerr mount option is enabled, 4326 and the specified value is >= 0. 4327 4328 nfs.enable_ino64= 4329 [NFS] enable 64-bit inode numbers. 4330 If zero, the NFS client will fake up a 32-bit inode 4331 number for the readdir() and stat() syscalls instead 4332 of returning the full 64-bit number. 4333 The default is to return 64-bit inode numbers. 4334 4335 nfs.idmap_cache_timeout= 4336 [NFS] set the maximum lifetime for idmapper cache 4337 entries. 4338 4339 nfs.max_session_cb_slots= 4340 [NFSv4.1] Sets the maximum number of session 4341 slots the client will assign to the callback 4342 channel. This determines the maximum number of 4343 callbacks the client will process in parallel for 4344 a particular server. 4345 4346 nfs.max_session_slots= 4347 [NFSv4.1] Sets the maximum number of session slots 4348 the client will attempt to negotiate with the server. 4349 This limits the number of simultaneous RPC requests 4350 that the client can send to the NFSv4.1 server. 4351 Note that there is little point in setting this 4352 value higher than the max_tcp_slot_table_limit. 4353 4354 nfs.nfs4_disable_idmapping= 4355 [NFSv4] When set to the default of '1', this option 4356 ensures that both the RPC level authentication 4357 scheme and the NFS level operations agree to use 4358 numeric uids/gids if the mount is using the 4359 'sec=sys' security flavour. In effect it is 4360 disabling idmapping, which can make migration from 4361 legacy NFSv2/v3 systems to NFSv4 easier. 4362 Servers that do not support this mode of operation 4363 will be autodetected by the client, and it will fall 4364 back to using the idmapper. 4365 To turn off this behaviour, set the value to '0'. 4366 4367 nfs.nfs4_unique_id= 4368 [NFS4] Specify an additional fixed unique ident- 4369 ification string that NFSv4 clients can insert into 4370 their nfs_client_id4 string. This is typically a 4371 UUID that is generated at system install time. 4372 4373 nfs.recover_lost_locks= 4374 [NFSv4] Attempt to recover locks that were lost due 4375 to a lease timeout on the server. Please note that 4376 doing this risks data corruption, since there are 4377 no guarantees that the file will remain unchanged 4378 after the locks are lost. 4379 If you want to enable the kernel legacy behaviour of 4380 attempting to recover these locks, then set this 4381 parameter to '1'. 4382 The default parameter value of '0' causes the kernel 4383 not to attempt recovery of lost locks. 4384 4385 nfs.send_implementation_id= 4386 [NFSv4.1] Send client implementation identification 4387 information in exchange_id requests. 4388 If zero, no implementation identification information 4389 will be sent. 4390 The default is to send the implementation identification 4391 information. 4392 4393 nfs4.layoutstats_timer= 4394 [NFSv4.2] Change the rate at which the kernel sends 4395 layoutstats to the pNFS metadata server. 4396 4397 Setting this to value to 0 causes the kernel to use 4398 whatever value is the default set by the layout 4399 driver. A non-zero value sets the minimum interval 4400 in seconds between layoutstats transmissions. 4401 4402 nfsd.inter_copy_offload_enable= 4403 [NFSv4.2] When set to 1, the server will support 4404 server-to-server copies for which this server is 4405 the destination of the copy. 4406 4407 nfsd.nfs4_disable_idmapping= 4408 [NFSv4] When set to the default of '1', the NFSv4 4409 server will return only numeric uids and gids to 4410 clients using auth_sys, and will accept numeric uids 4411 and gids from such clients. This is intended to ease 4412 migration from NFSv2/v3. 4413 4414 nfsd.nfsd4_ssc_umount_timeout= 4415 [NFSv4.2] When used as the destination of a 4416 server-to-server copy, knfsd temporarily mounts 4417 the source server. It caches the mount in case 4418 it will be needed again, and discards it if not 4419 used for the number of milliseconds specified by 4420 this parameter. 4421 4422 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4423 See Documentation/admin-guide/nfs/nfsroot.rst. 4424 4425 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4426 See Documentation/admin-guide/nfs/nfsroot.rst. 4427 4428 nfsrootdebug [NFS] enable nfsroot debugging messages. 4429 See Documentation/admin-guide/nfs/nfsroot.rst. 4430 4431 nmi_backtrace.backtrace_idle [KNL] 4432 Dump stacks even of idle CPUs in response to an 4433 NMI stack-backtrace request. 4434 4435 nmi_debug= [KNL,SH] Specify one or more actions to take 4436 when a NMI is triggered. 4437 Format: [state][,regs][,debounce][,die] 4438 4439 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4440 Format: [panic,][nopanic,][rNNN,][num] 4441 Valid num: 0 or 1 4442 0 - turn hardlockup detector in nmi_watchdog off 4443 1 - turn hardlockup detector in nmi_watchdog on 4444 rNNN - configure the watchdog with raw perf event 0xNNN 4445 4446 When panic is specified, panic when an NMI watchdog 4447 timeout occurs (or 'nopanic' to not panic on an NMI 4448 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4449 To disable both hard and soft lockup detectors, 4450 please see 'nowatchdog'. 4451 This is useful when you use a panic=... timeout and 4452 need the box quickly up again. 4453 4454 These settings can be accessed at runtime via 4455 the nmi_watchdog and hardlockup_panic sysctls. 4456 4457 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4458 emulation library even if a 387 maths coprocessor 4459 is present. 4460 4461 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4462 Forces kernel to use 3-level paging instead. 4463 4464 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4465 kernel to use 4-level paging instead. 4466 4467 noalign [KNL,ARM] 4468 4469 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4470 IOAPICs that may be present in the system. 4471 4472 noapictimer [APIC,X86] Don't set up the APIC timer 4473 4474 noautogroup Disable scheduler automatic task group creation. 4475 4476 nocache [ARM,EARLY] 4477 4478 no_console_suspend 4479 [HW] Never suspend the console 4480 Disable suspending of consoles during suspend and 4481 hibernate operations. Once disabled, debugging 4482 messages can reach various consoles while the rest 4483 of the system is being put to sleep (ie, while 4484 debugging driver suspend/resume hooks). This may 4485 not work reliably with all consoles, but is known 4486 to work with serial and VGA consoles. 4487 To facilitate more flexible debugging, we also add 4488 console_suspend, a printk module parameter to control 4489 it. Users could use console_suspend (usually 4490 /sys/module/printk/parameters/console_suspend) to 4491 turn on/off it dynamically. 4492 4493 no_debug_objects 4494 [KNL,EARLY] Disable object debugging 4495 4496 nodsp [SH] Disable hardware DSP at boot time. 4497 4498 noefi [EFI,EARLY] Disable EFI runtime services support. 4499 4500 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4501 4502 noexec32 [X86-64] 4503 This affects only 32-bit executables. 4504 noexec32=on: enable non-executable mappings (default) 4505 read doesn't imply executable mappings 4506 noexec32=off: disable non-executable mappings 4507 read implies executable mappings 4508 4509 no_file_caps Tells the kernel not to honor file capabilities. The 4510 only way then for a file to be executed with privilege 4511 is to be setuid root or executed by root. 4512 4513 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4514 4515 nofsgsbase [X86] Disables FSGSBASE instructions. 4516 4517 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4518 register save and restore. The kernel will only save 4519 legacy floating-point registers on task switch. 4520 4521 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4522 4523 no_hash_pointers 4524 [KNL,EARLY] 4525 Alias for "hash_pointers=never". 4526 4527 nohibernate [HIBERNATION] Disable hibernation and resume. 4528 4529 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4530 busy wait in do_idle() and not use the arch_cpu_idle() 4531 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4532 to be effective. This is useful on platforms where the 4533 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4534 correctly or when doing power measurements to evaluate 4535 the impact of the sleep instructions. This is also 4536 useful when using JTAG debugger. 4537 4538 nohpet [X86] Don't use the HPET timer. 4539 4540 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4541 4542 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4543 4544 nohz= [KNL] Boottime enable/disable dynamic ticks 4545 Valid arguments: on, off 4546 Default: on 4547 4548 nohz_full= [KNL,BOOT,SMP,ISOL] 4549 The argument is a cpu list, as described above. 4550 In kernels built with CONFIG_NO_HZ_FULL=y, set 4551 the specified list of CPUs whose tick will be stopped 4552 whenever possible. The boot CPU will be forced outside 4553 the range to maintain the timekeeping. Any CPUs 4554 in this list will have their RCU callbacks offloaded, 4555 just as if they had also been called out in the 4556 rcu_nocbs= boot parameter. 4557 4558 Note that this argument takes precedence over 4559 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4560 4561 noinitrd [Deprecated,RAM] Tells the kernel not to load any configured 4562 initial RAM disk. Currently this parameter applies to 4563 initrd only, not to initramfs. But it applies to both 4564 in EFI mode. 4565 4566 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4567 remapping. 4568 [Deprecated - use intremap=off] 4569 4570 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4571 4572 noiotrap [SH] Disables trapped I/O port accesses. 4573 4574 noirqdebug [X86-32] Disables the code which attempts to detect and 4575 disable unhandled interrupt sources. 4576 4577 noisapnp [ISAPNP] Disables ISA PnP code. 4578 4579 nokaslr [KNL,EARLY] 4580 When CONFIG_RANDOMIZE_BASE is set, this disables 4581 kernel and module base offset ASLR (Address Space 4582 Layout Randomization). 4583 4584 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4585 fault handling. 4586 4587 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4588 4589 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4590 4591 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4592 4593 nomce [X86-32] Disable Machine Check Exception 4594 4595 nomfgpt [X86-32] Disable Multi-Function General Purpose 4596 Timer usage (for AMD Geode machines). 4597 4598 nomodeset Disable kernel modesetting. Most systems' firmware 4599 sets up a display mode and provides framebuffer memory 4600 for output. With nomodeset, DRM and fbdev drivers will 4601 not load if they could possibly displace the pre- 4602 initialized output. Only the system framebuffer will 4603 be available for use. The respective drivers will not 4604 perform display-mode changes or accelerated rendering. 4605 4606 Useful as error fallback, or for testing and debugging. 4607 4608 nomodule Disable module load 4609 4610 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4611 shutdown the other cpus. Instead use the REBOOT_VECTOR 4612 irq. 4613 4614 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4615 pagetables) support. 4616 4617 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4618 4619 nopku [X86] Disable Memory Protection Keys CPU feature found 4620 in some Intel CPUs. 4621 4622 nopti [X86-64,EARLY] 4623 Equivalent to pti=off 4624 4625 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4626 Disables the PV optimizations forcing the guest to run 4627 as generic guest with no PV drivers. Currently support 4628 XEN HVM, KVM, HYPER_V and VMWARE guest. 4629 4630 nopvspin [X86,XEN,KVM,EARLY] 4631 Disables the qspinlock slow path using PV optimizations 4632 which allow the hypervisor to 'idle' the guest on lock 4633 contention. 4634 4635 norandmaps Don't use address space randomization. Equivalent to 4636 echo 0 > /proc/sys/kernel/randomize_va_space 4637 4638 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4639 with UP alternatives 4640 4641 noresume [SWSUSP] Disables resume and restores original swap 4642 space. 4643 4644 no-scroll [VGA] Disables scrollback. 4645 This is required for the Braillex ib80-piezo Braille 4646 reader made by F.H. Papenmeier (Germany). 4647 4648 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4649 4650 nosmap [PPC,EARLY] 4651 Disable SMAP (Supervisor Mode Access Prevention) 4652 even if it is supported by processor. 4653 4654 nosmep [PPC64s,EARLY] 4655 Disable SMEP (Supervisor Mode Execution Prevention) 4656 even if it is supported by processor. 4657 4658 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4659 and disable the IO APIC. legacy for "maxcpus=0". 4660 4661 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4662 Equivalent to smt=1. 4663 4664 [KNL,LOONGARCH,X86,PPC,S390] Disable symmetric multithreading (SMT). 4665 nosmt=force: Force disable SMT, cannot be undone 4666 via the sysfs control file. 4667 4668 nosoftlockup [KNL] Disable the soft-lockup detector. 4669 4670 nospec_store_bypass_disable 4671 [HW,EARLY] Disable all mitigations for the Speculative 4672 Store Bypass vulnerability 4673 4674 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4675 history injection) vulnerability. System may allow data leaks 4676 with this option. 4677 4678 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4679 (bounds check bypass). With this option data leaks are 4680 possible in the system. 4681 4682 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4683 for the Spectre variant 2 (indirect branch 4684 prediction) vulnerability. System may allow data 4685 leaks with this option. 4686 4687 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4688 Disable paravirtualized steal time accounting. steal time 4689 is computed, but won't influence scheduler behaviour 4690 4691 nosync [HW,M68K] Disables sync negotiation for all devices. 4692 4693 no_timer_check [X86,APIC] Disables the code which tests for broken 4694 timer IRQ sources, i.e., the IO-APIC timer. This can 4695 work around problems with incorrect timer 4696 initialization on some boards. 4697 4698 no_uaccess_flush 4699 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4700 4701 novmcoredd [KNL,KDUMP] 4702 Disable device dump. Device dump allows drivers to 4703 append dump data to vmcore so you can collect driver 4704 specified debug info. Drivers can append the data 4705 without any limit and this data is stored in memory, 4706 so this may cause significant memory stress. Disabling 4707 device dump can help save memory but the driver debug 4708 data will be no longer available. This parameter 4709 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4710 is set. 4711 4712 no-vmw-sched-clock 4713 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4714 scheduler clock and use the default one. 4715 4716 nowatchdog [KNL] Disable both lockup detectors, i.e. 4717 soft-lockup and NMI watchdog (hard-lockup). 4718 4719 nowb [ARM,EARLY] 4720 4721 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4722 4723 NOTE: this parameter will be ignored on systems with the 4724 LEGACY_XAPIC_DISABLED bit set in the 4725 IA32_XAPIC_DISABLE_STATUS MSR. 4726 4727 noxsave [BUGS=X86] Disables x86 extended register state save 4728 and restore using xsave. The kernel will fallback to 4729 enabling legacy floating-point and sse state. 4730 4731 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4732 register states. The kernel will fall back to use 4733 xsave to save the states. By using this parameter, 4734 performance of saving the states is degraded because 4735 xsave doesn't support modified optimization while 4736 xsaveopt supports it on xsaveopt enabled systems. 4737 4738 noxsaves [X86] Disables xsaves and xrstors used in saving and 4739 restoring x86 extended register state in compacted 4740 form of xsave area. The kernel will fall back to use 4741 xsaveopt and xrstor to save and restore the states 4742 in standard form of xsave area. By using this 4743 parameter, xsave area per process might occupy more 4744 memory on xsaves enabled systems. 4745 4746 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4747 could support. nr_cpus=n : n >= 1 limits the kernel to 4748 support 'n' processors. It could be larger than the 4749 number of already plugged CPU during bootup, later in 4750 runtime you can physically add extra cpu until it reaches 4751 n. So during boot up some boot time memory for per-cpu 4752 variables need be pre-allocated for later physical cpu 4753 hot plugging. 4754 4755 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4756 4757 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4758 Disable NUMA, Only set up a single NUMA node 4759 spanning all memory. 4760 4761 numa=fake=<size>[MG] 4762 [KNL, ARM64, RISCV, X86, EARLY] 4763 If given as a memory unit, fills all system RAM with 4764 nodes of size interleaved over physical nodes. 4765 4766 numa=fake=<N> 4767 [KNL, ARM64, RISCV, X86, EARLY] 4768 If given as an integer, fills all system RAM with N 4769 fake nodes interleaved over physical nodes. 4770 4771 numa=fake=<N>U 4772 [KNL, ARM64, RISCV, X86, EARLY] 4773 If given as an integer followed by 'U', it will 4774 divide each physical node into N emulated nodes. 4775 4776 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4777 4778 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4779 soft-reserved memory partitioning. 4780 4781 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4782 NUMA balancing. 4783 Allowed values are enable and disable 4784 4785 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4786 'node', 'default' can be specified 4787 This can be set from sysctl after boot. 4788 See Documentation/admin-guide/sysctl/vm.rst for details. 4789 4790 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4791 See Documentation/core-api/debugging-via-ohci1394.rst for more 4792 info. 4793 4794 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4795 Rather than timing out after 20 ms if an EC 4796 command is not properly ACKed, override the length 4797 of the timeout. We have interrupts disabled while 4798 waiting for the ACK, so if this is set too high 4799 interrupts *may* be lost! 4800 4801 omap_mux= [OMAP] Override bootloader pin multiplexing. 4802 Format: <mux_mode0.mode_name=value>... 4803 For example, to override I2C bus2: 4804 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4805 4806 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4807 4808 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4809 4810 boundary - index of last SLC block on Flex-OneNAND. 4811 The remaining blocks are configured as MLC blocks. 4812 lock - Configure if Flex-OneNAND boundary should be locked. 4813 Once locked, the boundary cannot be changed. 4814 1 indicates lock status, 0 indicates unlock status. 4815 4816 oops=panic [KNL,EARLY] 4817 Always panic on oopses. Default is to just kill the 4818 process, but there is a small probability of 4819 deadlocking the machine. 4820 This will also cause panics on machine check exceptions. 4821 Useful together with panic=30 to trigger a reboot. 4822 4823 page_alloc.shuffle= 4824 [KNL] Boolean flag to control whether the page allocator 4825 should randomize its free lists. This parameter can be 4826 used to enable/disable page randomization. The state of 4827 the flag can be read from sysfs at: 4828 /sys/module/page_alloc/parameters/shuffle. 4829 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4830 4831 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4832 Storage of the information about who allocated 4833 each page is disabled in default. With this switch, 4834 we can turn it on. 4835 on: enable the feature 4836 4837 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4838 poisoning on the buddy allocator, available with 4839 CONFIG_PAGE_POISONING=y. 4840 off: turn off poisoning (default) 4841 on: turn on poisoning 4842 4843 page_reporting.page_reporting_order= 4844 [KNL] Minimal page reporting order 4845 Format: <integer> 4846 Adjust the minimal page reporting order. The page 4847 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4848 4849 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4850 timeout > 0: seconds before rebooting 4851 timeout = 0: wait forever 4852 timeout < 0: reboot immediately 4853 Format: <timeout> 4854 4855 panic_on_taint= [KNL,EARLY] 4856 Bitmask for conditionally calling panic() in add_taint() 4857 Format: <hex>[,nousertaint] 4858 Hexadecimal bitmask representing the set of TAINT flags 4859 that will cause the kernel to panic when add_taint() is 4860 called with any of the flags in this set. 4861 The optional switch "nousertaint" can be utilized to 4862 prevent userspace forced crashes by writing to sysctl 4863 /proc/sys/kernel/tainted any flagset matching with the 4864 bitmask set on panic_on_taint. 4865 See Documentation/admin-guide/tainted-kernels.rst for 4866 extra details on the taint flags that users can pick 4867 to compose the bitmask to assign to panic_on_taint. 4868 4869 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4870 on a WARN(). 4871 4872 panic_force_cpu= 4873 [KNL,SMP] Force panic handling to execute on a specific CPU. 4874 Format: <cpu number> 4875 Some platforms require panic handling to occur on a 4876 specific CPU for the crash kernel to function correctly. 4877 This can be due to firmware limitations, interrupt routing 4878 constraints, or platform-specific requirements where only 4879 a particular CPU can safely enter the crash kernel. 4880 When set, panic() will redirect execution to the specified 4881 CPU before proceeding with the normal panic and kexec flow. 4882 If the target CPU is offline or unavailable, panic proceeds 4883 on the current CPU. 4884 This option should only be used for systems with the above 4885 constraints as it might cause the panic operation to be less reliable. 4886 4887 panic_print= Bitmask for printing system info when panic happens. 4888 User can chose combination of the following bits: 4889 bit 0: print all tasks info 4890 bit 1: print system memory info 4891 bit 2: print timer info 4892 bit 3: print locks info if CONFIG_LOCKDEP is on 4893 bit 4: print ftrace buffer 4894 bit 5: replay all kernel messages on consoles at the end of panic 4895 bit 6: print all CPUs backtrace (if available in the arch) 4896 bit 7: print only tasks in uninterruptible (blocked) state 4897 *Be aware* that this option may print a _lot_ of lines, 4898 so there are risks of losing older messages in the log. 4899 Use this option carefully, maybe worth to setup a 4900 bigger log buffer with "log_buf_len" along with this. 4901 4902 panic_sys_info= A comma separated list of extra information to be dumped 4903 on panic. 4904 Format: val[,val...] 4905 Where @val can be any of the following: 4906 4907 tasks: print all tasks info 4908 mem: print system memory info 4909 timers: print timers info 4910 locks: print locks info if CONFIG_LOCKDEP is on 4911 ftrace: print ftrace buffer 4912 all_bt: print all CPUs backtrace (if available in the arch) 4913 blocked_tasks: print only tasks in uninterruptible (blocked) state 4914 4915 This is a human readable alternative to the 'panic_print' option. 4916 4917 panic_console_replay 4918 When panic happens, replay all kernel messages on 4919 consoles at the end of panic. 4920 4921 parkbd.port= [HW] Parallel port number the keyboard adapter is 4922 connected to, default is 0. 4923 Format: <parport#> 4924 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4925 0 for XT, 1 for AT (default is AT). 4926 Format: <mode> 4927 4928 parport= [HW,PPT] Specify parallel ports. 0 disables. 4929 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4930 Use 'auto' to force the driver to use any 4931 IRQ/DMA settings detected (the default is to 4932 ignore detected IRQ/DMA settings because of 4933 possible conflicts). You can specify the base 4934 address, IRQ, and DMA settings; IRQ and DMA 4935 should be numbers, or 'auto' (for using detected 4936 settings on that particular port), or 'nofifo' 4937 (to avoid using a FIFO even if it is detected). 4938 Parallel ports are assigned in the order they 4939 are specified on the command line, starting 4940 with parport0. 4941 4942 parport_init_mode= [HW,PPT] 4943 Configure VIA parallel port to operate in 4944 a specific mode. This is necessary on Pegasos 4945 computer where firmware has no options for setting 4946 up parallel port mode and sets it to spp. 4947 Currently this function knows 686a and 8231 chips. 4948 Format: [spp|ps2|epp|ecp|ecpepp] 4949 4950 pata_legacy.all= [HW,LIBATA] 4951 Format: <int> 4952 Set to non-zero to probe primary and secondary ISA 4953 port ranges on PCI systems where no PCI PATA device 4954 has been found at either range. Disabled by default. 4955 4956 pata_legacy.autospeed= [HW,LIBATA] 4957 Format: <int> 4958 Set to non-zero if a chip is present that snoops speed 4959 changes. Disabled by default. 4960 4961 pata_legacy.ht6560a= [HW,LIBATA] 4962 Format: <int> 4963 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4964 the secondary channel, or both channels respectively. 4965 Disabled by default. 4966 4967 pata_legacy.ht6560b= [HW,LIBATA] 4968 Format: <int> 4969 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4970 the secondary channel, or both channels respectively. 4971 Disabled by default. 4972 4973 pata_legacy.iordy_mask= [HW,LIBATA] 4974 Format: <int> 4975 IORDY enable mask. Set individual bits to allow IORDY 4976 for the respective channel. Bit 0 is for the first 4977 legacy channel handled by this driver, bit 1 is for 4978 the second channel, and so on. The sequence will often 4979 correspond to the primary legacy channel, the secondary 4980 legacy channel, and so on, but the handling of a PCI 4981 bus and the use of other driver options may interfere 4982 with the sequence. By default IORDY is allowed across 4983 all channels. 4984 4985 pata_legacy.opti82c46x= [HW,LIBATA] 4986 Format: <int> 4987 Set to 1, 2, or 3 for Opti 82c611A on the primary 4988 channel, the secondary channel, or both channels 4989 respectively. Disabled by default. 4990 4991 pata_legacy.opti82c611a= [HW,LIBATA] 4992 Format: <int> 4993 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4994 channel, the secondary channel, or both channels 4995 respectively. Disabled by default. 4996 4997 pata_legacy.pio_mask= [HW,LIBATA] 4998 Format: <int> 4999 PIO mode mask for autospeed devices. Set individual 5000 bits to allow the use of the respective PIO modes. 5001 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 5002 All modes allowed by default. 5003 5004 pata_legacy.probe_all= [HW,LIBATA] 5005 Format: <int> 5006 Set to non-zero to probe tertiary and further ISA 5007 port ranges on PCI systems. Disabled by default. 5008 5009 pata_legacy.probe_mask= [HW,LIBATA] 5010 Format: <int> 5011 Probe mask for legacy ISA PATA ports. Depending on 5012 platform configuration and the use of other driver 5013 options up to 6 legacy ports are supported: 0x1f0, 5014 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 5015 of individual ports can be disabled by setting the 5016 corresponding bits in the mask to 1. Bit 0 is for 5017 the first port in the list above (0x1f0), and so on. 5018 By default all supported ports are probed. 5019 5020 pata_legacy.qdi= [HW,LIBATA] 5021 Format: <int> 5022 Set to non-zero to probe QDI controllers. By default 5023 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 5024 5025 pata_legacy.winbond= [HW,LIBATA] 5026 Format: <int> 5027 Set to non-zero to probe Winbond controllers. Use 5028 the standard I/O port (0x130) if 1, otherwise the 5029 value given is the I/O port to use (typically 0x1b0). 5030 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 5031 0 otherwise. 5032 5033 pata_platform.pio_mask= [HW,LIBATA] 5034 Format: <int> 5035 Supported PIO mode mask. Set individual bits to allow 5036 the use of the respective PIO modes. Bit 0 is for 5037 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 5038 allowed by default. 5039 5040 pause_on_oops=<int> 5041 Halt all CPUs after the first oops has been printed for 5042 the specified number of seconds. This is to be used if 5043 your oopses keep scrolling off the screen. 5044 5045 pcbit= [HW,ISDN] 5046 5047 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 5048 5049 Some options herein operate on a specific device 5050 or a set of devices (<pci_dev>). These are 5051 specified in one of the following formats: 5052 5053 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 5054 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 5055 5056 Note: the first format specifies a PCI 5057 bus/device/function address which may change 5058 if new hardware is inserted, if motherboard 5059 firmware changes, or due to changes caused 5060 by other kernel parameters. If the 5061 domain is left unspecified, it is 5062 taken to be zero. Optionally, a path 5063 to a device through multiple device/function 5064 addresses can be specified after the base 5065 address (this is more robust against 5066 renumbering issues). The second format 5067 selects devices using IDs from the 5068 configuration space which may match multiple 5069 devices in the system. 5070 5071 earlydump dump PCI config space before the kernel 5072 changes anything 5073 off [X86] don't probe for the PCI bus 5074 bios [X86-32] force use of PCI BIOS, don't access 5075 the hardware directly. Use this if your machine 5076 has a non-standard PCI host bridge. 5077 nobios [X86-32] disallow use of PCI BIOS, only direct 5078 hardware access methods are allowed. Use this 5079 if you experience crashes upon bootup and you 5080 suspect they are caused by the BIOS. 5081 conf1 [X86] Force use of PCI Configuration Access 5082 Mechanism 1 (config address in IO port 0xCF8, 5083 data in IO port 0xCFC, both 32-bit). 5084 conf2 [X86] Force use of PCI Configuration Access 5085 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 5086 the function, IO port 0xCFA, also 8-bit, sets 5087 bus number. The config space is then accessed 5088 through ports 0xC000-0xCFFF). 5089 See http://wiki.osdev.org/PCI for more info 5090 on the configuration access mechanisms. 5091 noaer [PCIE] If the PCIEAER kernel config parameter is 5092 enabled, this kernel boot option can be used to 5093 disable the use of PCIE advanced error reporting. 5094 nodomains [PCI] Disable support for multiple PCI 5095 root domains (aka PCI segments, in ACPI-speak). 5096 nommconf [X86] Disable use of MMCONFIG for PCI 5097 Configuration 5098 check_enable_amd_mmconf [X86] check for and enable 5099 properly configured MMIO access to PCI 5100 config space on AMD family 10h CPU 5101 nomsi [MSI] If the PCI_MSI kernel config parameter is 5102 enabled, this kernel boot option can be used to 5103 disable the use of MSI interrupts system-wide. 5104 noioapicquirk [APIC] Disable all boot interrupt quirks. 5105 Safety option to keep boot IRQs enabled. This 5106 should never be necessary. 5107 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5108 primary IO-APIC for bridges that cannot disable 5109 boot IRQs. This fixes a source of spurious IRQs 5110 when the system masks IRQs. 5111 noioapicreroute [APIC] Disable workaround that uses the 5112 boot IRQ equivalent of an IRQ that connects to 5113 a chipset where boot IRQs cannot be disabled. 5114 The opposite of ioapicreroute. 5115 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5116 routing table. These calls are known to be buggy 5117 on several machines and they hang the machine 5118 when used, but on other computers it's the only 5119 way to get the interrupt routing table. Try 5120 this option if the kernel is unable to allocate 5121 IRQs or discover secondary PCI buses on your 5122 motherboard. 5123 rom [X86] Assign address space to expansion ROMs. 5124 Use with caution as certain devices share 5125 address decoders between ROMs and other 5126 resources. 5127 norom [X86] Do not assign address space to 5128 expansion ROMs that do not already have 5129 BIOS assigned address ranges. 5130 nobar [X86] Do not assign address space to the 5131 BARs that weren't assigned by the BIOS. 5132 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5133 assigned automatically to PCI devices. You can 5134 make the kernel exclude IRQs of your ISA cards 5135 this way. 5136 pirqaddr=0xAAAAA [X86] Specify the physical address 5137 of the PIRQ table (normally generated 5138 by the BIOS) if it is outside the 5139 F0000h-100000h range. 5140 lastbus=N [X86] Scan all buses thru bus #N. Can be 5141 useful if the kernel is unable to find your 5142 secondary buses and you want to tell it 5143 explicitly which ones they are. 5144 assign-busses [X86] Always assign all PCI bus 5145 numbers ourselves, overriding 5146 whatever the firmware may have done. 5147 usepirqmask [X86] Honor the possible IRQ mask stored 5148 in the BIOS $PIR table. This is needed on 5149 some systems with broken BIOSes, notably 5150 some HP Pavilion N5400 and Omnibook XE3 5151 notebooks. This will have no effect if ACPI 5152 IRQ routing is enabled. 5153 noacpi [X86] Do not use ACPI for IRQ routing 5154 or for PCI scanning. 5155 use_crs [X86] Use PCI host bridge window information 5156 from ACPI. On BIOSes from 2008 or later, this 5157 is enabled by default. If you need to use this, 5158 please report a bug. 5159 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5160 If you need to use this, please report a bug. 5161 use_e820 [X86] Use E820 reservations to exclude parts of 5162 PCI host bridge windows. This is a workaround 5163 for BIOS defects in host bridge _CRS methods. 5164 If you need to use this, please report a bug to 5165 <linux-pci@vger.kernel.org>. 5166 no_e820 [X86] Ignore E820 reservations for PCI host 5167 bridge windows. This is the default on modern 5168 hardware. If you need to use this, please report 5169 a bug to <linux-pci@vger.kernel.org>. 5170 routeirq Do IRQ routing for all PCI devices. 5171 This is normally done in pci_enable_device(), 5172 so this option is a temporary workaround 5173 for broken drivers that don't call it. 5174 skip_isa_align [X86] do not align io start addr, so can 5175 handle more pci cards 5176 noearly [X86] Don't do any early type 1 scanning. 5177 This might help on some broken boards which 5178 machine check when some devices' config space 5179 is read. But various workarounds are disabled 5180 and some IOMMU drivers will not work. 5181 bfsort Sort PCI devices into breadth-first order. 5182 This sorting is done to get a device 5183 order compatible with older (<= 2.4) kernels. 5184 nobfsort Don't sort PCI devices into breadth-first order. 5185 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5186 tuning and use the BIOS-configured MPS defaults. 5187 pcie_bus_safe Set every device's MPS to the largest value 5188 supported by all devices below the root complex. 5189 pcie_bus_perf Set device MPS to the largest allowable MPS 5190 based on its parent bus. Also set MRRS (Max 5191 Read Request Size) to the largest supported 5192 value (no larger than the MPS that the device 5193 or bus can support) for best performance. 5194 pcie_bus_peer2peer Set every device's MPS to 128B, which 5195 every device is guaranteed to support. This 5196 configuration allows peer-to-peer DMA between 5197 any pair of devices, possibly at the cost of 5198 reduced performance. This also guarantees 5199 that hot-added devices will work. 5200 cbiosize=nn[KMG] The fixed amount of bus space which is 5201 reserved for the CardBus bridge's IO window. 5202 The default value is 256 bytes. 5203 cbmemsize=nn[KMG] The fixed amount of bus space which is 5204 reserved for the CardBus bridge's memory 5205 window. The default value is 64 megabytes. 5206 resource_alignment= 5207 Format: 5208 [<order of align>@]<pci_dev>[; ...] 5209 Specifies alignment and device to reassign 5210 aligned memory resources. How to 5211 specify the device is described above. 5212 If <order of align> is not specified, 5213 PAGE_SIZE is used as alignment. 5214 A PCI-PCI bridge can be specified if resource 5215 windows need to be expanded. 5216 To specify the alignment for several 5217 instances of a device, the PCI vendor, 5218 device, subvendor, and subdevice may be 5219 specified, e.g., 12@pci:8086:9c22:103c:198f 5220 for 4096-byte alignment. 5221 ecrc= Enable/disable PCIe ECRC (transaction layer 5222 end-to-end CRC checking). Only effective if 5223 OS has native AER control (either granted by 5224 ACPI _OSC or forced via "pcie_ports=native") 5225 bios: Use BIOS/firmware settings. This is the 5226 the default. 5227 off: Turn ECRC off 5228 on: Turn ECRC on. 5229 hpiosize=nn[KMG] The fixed amount of bus space which is 5230 reserved for hotplug bridge's IO window. 5231 Default size is 256 bytes. 5232 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5233 reserved for hotplug bridge's MMIO window. 5234 Default size is 2 megabytes. 5235 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5236 reserved for hotplug bridge's MMIO_PREF window. 5237 Default size is 2 megabytes. 5238 hpmemsize=nn[KMG] The fixed amount of bus space which is 5239 reserved for hotplug bridge's MMIO and 5240 MMIO_PREF window. 5241 Default size is 2 megabytes. 5242 hpbussize=nn The minimum amount of additional bus numbers 5243 reserved for buses below a hotplug bridge. 5244 Default is 1. 5245 realloc= Enable/disable reallocating PCI bridge resources 5246 if allocations done by BIOS are too small to 5247 accommodate resources required by all child 5248 devices. 5249 off: Turn realloc off 5250 on: Turn realloc on 5251 realloc same as realloc=on 5252 noari do not use PCIe ARI. 5253 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5254 do not use PCIe ATS (and IOMMU device IOTLB). 5255 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5256 only look for one device below a PCIe downstream 5257 port. 5258 big_root_window Try to add a big 64bit memory window to the PCIe 5259 root complex on AMD CPUs. Some GFX hardware 5260 can resize a BAR to allow access to all VRAM. 5261 Adding the window is slightly risky (it may 5262 conflict with unreported devices), so this 5263 taints the kernel. 5264 disable_acs_redir=<pci_dev>[; ...] 5265 Specify one or more PCI devices (in the format 5266 specified above) separated by semicolons. 5267 Each device specified will have the PCI ACS 5268 redirect capabilities forced off which will 5269 allow P2P traffic between devices through 5270 bridges without forcing it upstream. Note: 5271 this removes isolation between devices and 5272 may put more devices in an IOMMU group. 5273 config_acs= 5274 Format: 5275 <ACS flags>@<pci_dev>[; ...] 5276 Specify one or more PCI devices (in the format 5277 specified above) optionally prepended with flags 5278 and separated by semicolons. The respective 5279 capabilities will be enabled, disabled or 5280 unchanged based on what is specified in 5281 flags. 5282 5283 ACS Flags is defined as follows: 5284 bit-0 : ACS Source Validation 5285 bit-1 : ACS Translation Blocking 5286 bit-2 : ACS P2P Request Redirect 5287 bit-3 : ACS P2P Completion Redirect 5288 bit-4 : ACS Upstream Forwarding 5289 bit-5 : ACS P2P Egress Control 5290 bit-6 : ACS Direct Translated P2P 5291 Each bit can be marked as: 5292 '0' – force disabled 5293 '1' – force enabled 5294 'x' – unchanged 5295 For example, 5296 pci=config_acs=10x@pci:0:0 5297 would configure all devices that support 5298 ACS to enable P2P Request Redirect, disable 5299 Translation Blocking, and leave Source 5300 Validation unchanged from whatever power-up 5301 or firmware set it to. 5302 5303 Note: this may remove isolation between devices 5304 and may put more devices in an IOMMU group. 5305 force_floating [S390] Force usage of floating interrupts. 5306 nomio [S390] Do not use MIO instructions. 5307 norid [S390] ignore the RID field and force use of 5308 one PCI domain per PCI function 5309 notph [PCIE] If the PCIE_TPH kernel config parameter 5310 is enabled, this kernel boot option can be used 5311 to disable PCIe TLP Processing Hints support 5312 system-wide. 5313 5314 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5315 Management. 5316 off Don't touch ASPM configuration at all. Leave any 5317 configuration done by firmware unchanged. 5318 force Enable ASPM even on devices that claim not to support it. 5319 WARNING: Forcing ASPM on may cause system lockups. 5320 5321 pcie_ports= [PCIE] PCIe port services handling: 5322 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5323 even if the platform doesn't give the OS permission to 5324 use them. This may cause conflicts if the platform 5325 also tries to use these services. 5326 dpc-native Use native PCIe service for DPC only. May 5327 cause conflicts if firmware uses AER or DPC. 5328 compat Disable native PCIe services (PME, AER, DPC, PCIe 5329 hotplug). 5330 5331 pcie_port_pm= [PCIE] PCIe port power management handling: 5332 off Disable power management of all PCIe ports 5333 force Forcibly enable power management of all PCIe ports 5334 5335 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5336 nomsi Do not use MSI for native PCIe PME signaling (this makes 5337 all PCIe root ports use INTx for all services). 5338 5339 pcmv= [HW,PCMCIA] BadgePAD 4 5340 5341 pd_ignore_unused 5342 [PM] 5343 Keep all power-domains already enabled by bootloader on, 5344 even if no driver has claimed them. This is useful 5345 for debug and development, but should not be 5346 needed on a platform with proper driver support. 5347 5348 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5349 boot time. 5350 Format: { 0 | 1 } 5351 See arch/parisc/kernel/pdc_chassis.c 5352 5353 percpu_alloc= [MM,EARLY] 5354 Select which percpu first chunk allocator to use. 5355 Currently supported values are "embed" and "page". 5356 Archs may support subset or none of the selections. 5357 See comments in mm/percpu.c for details on each 5358 allocator. This parameter is primarily for debugging 5359 and performance comparison. 5360 5361 pirq= [SMP,APIC] Manual mp-table setup 5362 See Documentation/arch/x86/i386/IO-APIC.rst. 5363 5364 plip= [PPT,NET] Parallel port network link 5365 Format: { parport<nr> | timid | 0 } 5366 See also Documentation/admin-guide/parport.rst. 5367 5368 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5369 Override pmtimer IOPort with a hex value. 5370 e.g. pmtmr=0x508 5371 5372 pmu_override= [PPC] Override the PMU. 5373 This option takes over the PMU facility, so it is no 5374 longer usable by perf. Setting this option starts the 5375 PMU counters by setting MMCR0 to 0 (the FC bit is 5376 cleared). If a number is given, then MMCR1 is set to 5377 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5378 remains 0. 5379 5380 pm_async= [PM] 5381 Format: off 5382 This parameter sets the initial value of the 5383 /sys/power/pm_async sysfs knob at boot time. 5384 If set to "off", disables asynchronous suspend and 5385 resume of devices during system-wide power transitions. 5386 This can be useful on platforms where device 5387 dependencies are not well-defined, or for debugging 5388 power management issues. Asynchronous operations are 5389 enabled by default. 5390 5391 5392 pm_debug_messages [SUSPEND,KNL] 5393 Enable suspend/resume debug messages during boot up. 5394 5395 pnp.debug=1 [PNP] 5396 Enable PNP debug messages (depends on the 5397 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5398 via /sys/module/pnp/parameters/debug. We always show 5399 current resource usage; turning this on also shows 5400 possible settings and some assignment information. 5401 5402 pnpacpi= [ACPI] 5403 { off } 5404 5405 pnpbios= [ISAPNP] 5406 { on | off | curr | res | no-curr | no-res } 5407 5408 pnp_reserve_irq= 5409 [ISAPNP] Exclude IRQs for the autoconfiguration 5410 5411 pnp_reserve_dma= 5412 [ISAPNP] Exclude DMAs for the autoconfiguration 5413 5414 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5415 Ranges are in pairs (I/O port base and size). 5416 5417 pnp_reserve_mem= 5418 [ISAPNP] Exclude memory regions for the 5419 autoconfiguration. 5420 Ranges are in pairs (memory base and size). 5421 5422 ports= [IP_VS_FTP] IPVS ftp helper module 5423 Default is 21. 5424 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5425 may be specified. 5426 Format: <port>,<port>.... 5427 5428 possible_cpus= [SMP,S390,X86] 5429 Format: <unsigned int> 5430 Set the number of possible CPUs, overriding the 5431 regular discovery mechanisms (such as ACPI/FW, etc). 5432 5433 powersave=off [PPC] This option disables power saving features. 5434 It specifically disables cpuidle and sets the 5435 platform machine description specific power_save 5436 function to NULL. On Idle the CPU just reduces 5437 execution priority. 5438 5439 ppc_strict_facility_enable 5440 [PPC,ENABLE] This option catches any kernel floating point, 5441 Altivec, VSX and SPE outside of regions specifically 5442 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5443 There is some performance impact when enabling this. 5444 5445 ppc_tm= [PPC,EARLY] 5446 Format: {"off"} 5447 Disable Hardware Transactional Memory 5448 5449 preempt= [KNL] 5450 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5451 none - Limited to cond_resched() calls 5452 voluntary - Limited to cond_resched() and might_sleep() calls 5453 full - Any section that isn't explicitly preempt disabled 5454 can be preempted anytime. Tasks will also yield 5455 contended spinlocks (if the critical section isn't 5456 explicitly preempt disabled beyond the lock itself). 5457 lazy - Scheduler controlled. Similar to full but instead 5458 of preempting the task immediately, the task gets 5459 one HZ tick time to yield itself before the 5460 preemption will be forced. One preemption is when the 5461 task returns to user space. 5462 5463 print-fatal-signals= 5464 [KNL] debug: print fatal signals 5465 5466 If enabled, warn about various signal handling 5467 related application anomalies: too many signals, 5468 too many POSIX.1 timers, fatal signals causing a 5469 coredump - etc. 5470 5471 If you hit the warning due to signal overflow, 5472 you might want to try "ulimit -i unlimited". 5473 5474 default: off. 5475 5476 printk.always_kmsg_dump= 5477 Trigger kmsg_dump for cases other than kernel oops or 5478 panics 5479 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5480 default: disabled 5481 5482 printk.console_no_auto_verbose= 5483 Disable console loglevel raise on oops, panic 5484 or lockdep-detected issues (only if lock debug is on). 5485 With an exception to setups with low baudrate on 5486 serial console, keeping this 0 is a good choice 5487 in order to provide more debug information. 5488 Format: <bool> 5489 default: 0 (auto_verbose is enabled) 5490 5491 printk.debug_non_panic_cpus= 5492 Allows storing messages from non-panic CPUs into 5493 the printk log buffer during panic(). They are 5494 flushed to consoles by the panic-CPU on 5495 a best-effort basis. 5496 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5497 Default: disabled 5498 5499 printk.devkmsg={on,off,ratelimit} 5500 Control writing to /dev/kmsg. 5501 on - unlimited logging to /dev/kmsg from userspace 5502 off - logging to /dev/kmsg disabled 5503 ratelimit - ratelimit the logging 5504 Default: ratelimit 5505 5506 printk.time= Show timing data prefixed to each printk message line 5507 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5508 5509 proc_mem.force_override= [KNL] 5510 Format: {always | ptrace | never} 5511 Traditionally /proc/pid/mem allows memory permissions to be 5512 overridden without restrictions. This option may be set to 5513 restrict that. Can be one of: 5514 - 'always': traditional behavior always allows mem overrides. 5515 - 'ptrace': only allow mem overrides for active ptracers. 5516 - 'never': never allow mem overrides. 5517 If not specified, default is the CONFIG_PROC_MEM_* choice. 5518 5519 processor.max_cstate= [HW,ACPI] 5520 Limit processor to maximum C-state 5521 max_cstate=9 overrides any DMI blacklist limit. 5522 5523 processor.nocst [HW,ACPI] 5524 Ignore the _CST method to determine C-states, 5525 instead using the legacy FADT method 5526 5527 profile= [KNL] Enable kernel profiling via /proc/profile 5528 Format: [<profiletype>,]<number> 5529 Param: <profiletype>: "schedule" or "kvm" 5530 [defaults to kernel profiling] 5531 Param: "schedule" - profile schedule points. 5532 Param: "kvm" - profile VM exits. 5533 Param: <number> - step/bucket size as a power of 2 for 5534 statistical time based profiling. 5535 5536 prot_virt= [S390] enable hosting protected virtual machines 5537 isolated from the hypervisor (if hardware supports 5538 that). If enabled, the default kernel base address 5539 might be overridden even when Kernel Address Space 5540 Layout Randomization is disabled. 5541 Format: <bool> 5542 5543 psi= [KNL] Enable or disable pressure stall information 5544 tracking. 5545 Format: <bool> 5546 5547 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5548 probe for; one of (bare|imps|exps|lifebook|any). 5549 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5550 per second. 5551 psmouse.resetafter= [HW,MOUSE] 5552 Try to reset the device after so many bad packets 5553 (0 = never). 5554 psmouse.resolution= 5555 [HW,MOUSE] Set desired mouse resolution, in dpi. 5556 psmouse.smartscroll= 5557 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5558 0 = disabled, 1 = enabled (default). 5559 5560 pstore.backend= Specify the name of the pstore backend to use 5561 5562 pti= [X86-64] Control Page Table Isolation of user and 5563 kernel address spaces. Disabling this feature 5564 removes hardening, but improves performance of 5565 system calls and interrupts. 5566 5567 on - unconditionally enable 5568 off - unconditionally disable 5569 auto - kernel detects whether your CPU model is 5570 vulnerable to issues that PTI mitigates 5571 5572 Not specifying this option is equivalent to pti=auto. 5573 5574 pty.legacy_count= 5575 [KNL] Number of legacy pty's. Overwrites compiled-in 5576 default number. 5577 5578 quiet [KNL,EARLY] Disable most log messages 5579 5580 r128= [HW,DRM] 5581 5582 radix_hcall_invalidate=on [PPC/PSERIES] 5583 Disable RADIX GTSE feature and use hcall for TLB 5584 invalidate. 5585 5586 raid= [HW,RAID] 5587 See Documentation/admin-guide/md.rst. 5588 5589 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5590 See Documentation/admin-guide/blockdev/ramdisk.rst. 5591 5592 ramdisk_start= [Deprecated,RAM] RAM disk image start address 5593 5594 random.trust_cpu=off 5595 [KNL,EARLY] Disable trusting the use of the CPU's 5596 random number generator (if available) to 5597 initialize the kernel's RNG. 5598 5599 random.trust_bootloader=off 5600 [KNL,EARLY] Disable trusting the use of the a seed 5601 passed by the bootloader (if available) to 5602 initialize the kernel's RNG. 5603 5604 randomize_kstack_offset= 5605 [KNL,EARLY] Enable or disable kernel stack offset 5606 randomization, which provides roughly 5 bits of 5607 entropy, frustrating memory corruption attacks 5608 that depend on stack address determinism or 5609 cross-syscall address exposures. This is only 5610 available on architectures that have defined 5611 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5612 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5613 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5614 5615 ras=option[,option,...] [KNL] RAS-specific options 5616 5617 cec_disable [X86] 5618 Disable the Correctable Errors Collector, 5619 see CONFIG_RAS_CEC help text. 5620 5621 rcu_nocbs[=cpu-list] 5622 [KNL] The optional argument is a cpu list, 5623 as described above. 5624 5625 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5626 enable the no-callback CPU mode, which prevents 5627 such CPUs' callbacks from being invoked in 5628 softirq context. Invocation of such CPUs' RCU 5629 callbacks will instead be offloaded to "rcuox/N" 5630 kthreads created for that purpose, where "x" is 5631 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5632 for the kthreads that mediate grace periods; and 5633 "N" is the CPU number. This reduces OS jitter on 5634 the offloaded CPUs, which can be useful for HPC 5635 and real-time workloads. It can also improve 5636 energy efficiency for asymmetric multiprocessors. 5637 5638 If a cpulist is passed as an argument, the specified 5639 list of CPUs is set to no-callback mode from boot. 5640 5641 Otherwise, if the '=' sign and the cpulist 5642 arguments are omitted, no CPU will be set to 5643 no-callback mode from boot but the mode may be 5644 toggled at runtime via cpusets. 5645 5646 Note that this argument takes precedence over 5647 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5648 5649 rcu_nocb_poll [KNL] 5650 Rather than requiring that offloaded CPUs 5651 (specified by rcu_nocbs= above) explicitly 5652 awaken the corresponding "rcuoN" kthreads, 5653 make these kthreads poll for callbacks. 5654 This improves the real-time response for the 5655 offloaded CPUs by relieving them of the need to 5656 wake up the corresponding kthread, but degrades 5657 energy efficiency by requiring that the kthreads 5658 periodically wake up to do the polling. 5659 5660 rcutree.blimit= [KNL] 5661 Set maximum number of finished RCU callbacks to 5662 process in one batch. 5663 5664 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5665 Do only a one-line RCU CPU stall warning when 5666 there is an ongoing too-long CSD-lock wait. 5667 5668 rcutree.do_rcu_barrier= [KNL] 5669 Request a call to rcu_barrier(). This is 5670 throttled so that userspace tests can safely 5671 hammer on the sysfs variable if they so choose. 5672 If triggered before the RCU grace-period machinery 5673 is fully active, this will error out with EAGAIN. 5674 5675 rcutree.dump_tree= [KNL] 5676 Dump the structure of the rcu_node combining tree 5677 out at early boot. This is used for diagnostic 5678 purposes, to verify correct tree setup. 5679 5680 rcutree.gp_cleanup_delay= [KNL] 5681 Set the number of jiffies to delay each step of 5682 RCU grace-period cleanup. 5683 5684 rcutree.gp_init_delay= [KNL] 5685 Set the number of jiffies to delay each step of 5686 RCU grace-period initialization. 5687 5688 rcutree.gp_preinit_delay= [KNL] 5689 Set the number of jiffies to delay each step of 5690 RCU grace-period pre-initialization, that is, 5691 the propagation of recent CPU-hotplug changes up 5692 the rcu_node combining tree. 5693 5694 rcutree.jiffies_till_first_fqs= [KNL] 5695 Set delay from grace-period initialization to 5696 first attempt to force quiescent states. 5697 Units are jiffies, minimum value is zero, 5698 and maximum value is HZ. 5699 5700 rcutree.jiffies_till_next_fqs= [KNL] 5701 Set delay between subsequent attempts to force 5702 quiescent states. Units are jiffies, minimum 5703 value is one, and maximum value is HZ. 5704 5705 rcutree.jiffies_till_sched_qs= [KNL] 5706 Set required age in jiffies for a 5707 given grace period before RCU starts 5708 soliciting quiescent-state help from 5709 rcu_note_context_switch() and cond_resched(). 5710 If not specified, the kernel will calculate 5711 a value based on the most recent settings 5712 of rcutree.jiffies_till_first_fqs 5713 and rcutree.jiffies_till_next_fqs. 5714 This calculated value may be viewed in 5715 rcutree.jiffies_to_sched_qs. Any attempt to set 5716 rcutree.jiffies_to_sched_qs will be cheerfully 5717 overwritten. 5718 5719 rcutree.kthread_prio= [KNL,BOOT] 5720 Set the SCHED_FIFO priority of the RCU per-CPU 5721 kthreads (rcuc/N). This value is also used for 5722 the priority of the RCU boost threads (rcub/N) 5723 and for the RCU grace-period kthreads (rcu_bh, 5724 rcu_preempt, and rcu_sched). If RCU_BOOST is 5725 set, valid values are 1-99 and the default is 1 5726 (the least-favored priority). Otherwise, when 5727 RCU_BOOST is not set, valid values are 0-99 and 5728 the default is zero (non-realtime operation). 5729 When RCU_NOCB_CPU is set, also adjust the 5730 priority of NOCB callback kthreads. 5731 5732 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5733 On callback-offloaded (rcu_nocbs) CPUs, 5734 RCU reduces the lock contention that would 5735 otherwise be caused by callback floods through 5736 use of the ->nocb_bypass list. However, in the 5737 common non-flooded case, RCU queues directly to 5738 the main ->cblist in order to avoid the extra 5739 overhead of the ->nocb_bypass list and its lock. 5740 But if there are too many callbacks queued during 5741 a single jiffy, RCU pre-queues the callbacks into 5742 the ->nocb_bypass queue. The definition of "too 5743 many" is supplied by this kernel boot parameter. 5744 5745 rcutree.nohz_full_patience_delay= [KNL] 5746 On callback-offloaded (rcu_nocbs) CPUs, avoid 5747 disturbing RCU unless the grace period has 5748 reached the specified age in milliseconds. 5749 Defaults to zero. Large values will be capped 5750 at five seconds. All values will be rounded down 5751 to the nearest value representable by jiffies. 5752 5753 rcutree.qhimark= [KNL] 5754 Set threshold of queued RCU callbacks beyond which 5755 batch limiting is disabled. 5756 5757 rcutree.qlowmark= [KNL] 5758 Set threshold of queued RCU callbacks below which 5759 batch limiting is re-enabled. 5760 5761 rcutree.qovld= [KNL] 5762 Set threshold of queued RCU callbacks beyond which 5763 RCU's force-quiescent-state scan will aggressively 5764 enlist help from cond_resched() and sched IPIs to 5765 help CPUs more quickly reach quiescent states. 5766 Set to less than zero to make this be set based 5767 on rcutree.qhimark at boot time and to zero to 5768 disable more aggressive help enlistment. 5769 5770 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5771 Set the page-cache refill delay (in milliseconds) 5772 in response to low-memory conditions. The range 5773 of permitted values is in the range 0:100000. 5774 5775 rcutree.rcu_divisor= [KNL] 5776 Set the shift-right count to use to compute 5777 the callback-invocation batch limit bl from 5778 the number of callbacks queued on this CPU. 5779 The result will be bounded below by the value of 5780 the rcutree.blimit kernel parameter. Every bl 5781 callbacks, the softirq handler will exit in 5782 order to allow the CPU to do other work. 5783 5784 Please note that this callback-invocation batch 5785 limit applies only to non-offloaded callback 5786 invocation. Offloaded callbacks are instead 5787 invoked in the context of an rcuoc kthread, which 5788 scheduler will preempt as it does any other task. 5789 5790 rcutree.rcu_fanout_exact= [KNL] 5791 Disable autobalancing of the rcu_node combining 5792 tree. This is used by rcutorture, and might 5793 possibly be useful for architectures having high 5794 cache-to-cache transfer latencies. 5795 5796 rcutree.rcu_fanout_leaf= [KNL] 5797 Change the number of CPUs assigned to each 5798 leaf rcu_node structure. Useful for very 5799 large systems, which will choose the value 64, 5800 and for NUMA systems with large remote-access 5801 latencies, which will choose a value aligned 5802 with the appropriate hardware boundaries. 5803 5804 rcutree.rcu_min_cached_objs= [KNL] 5805 Minimum number of objects which are cached and 5806 maintained per one CPU. Object size is equal 5807 to PAGE_SIZE. The cache allows to reduce the 5808 pressure to page allocator, also it makes the 5809 whole algorithm to behave better in low memory 5810 condition. 5811 5812 rcutree.rcu_nocb_gp_stride= [KNL] 5813 Set the number of NOCB callback kthreads in 5814 each group, which defaults to the square root 5815 of the number of CPUs. Larger numbers reduce 5816 the wakeup overhead on the global grace-period 5817 kthread, but increases that same overhead on 5818 each group's NOCB grace-period kthread. 5819 5820 rcutree.rcu_kick_kthreads= [KNL] 5821 Cause the grace-period kthread to get an extra 5822 wake_up() if it sleeps three times longer than 5823 it should at force-quiescent-state time. 5824 This wake_up() will be accompanied by a 5825 WARN_ONCE() splat and an ftrace_dump(). 5826 5827 rcutree.rcu_resched_ns= [KNL] 5828 Limit the time spend invoking a batch of RCU 5829 callbacks to the specified number of nanoseconds. 5830 By default, this limit is checked only once 5831 every 32 callbacks in order to limit the pain 5832 inflicted by local_clock() overhead. 5833 5834 rcutree.rcu_unlock_delay= [KNL] 5835 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5836 this specifies an rcu_read_unlock()-time delay 5837 in microseconds. This defaults to zero. 5838 Larger delays increase the probability of 5839 catching RCU pointer leaks, that is, buggy use 5840 of RCU-protected pointers after the relevant 5841 rcu_read_unlock() has completed. 5842 5843 rcutree.sysrq_rcu= [KNL] 5844 Commandeer a sysrq key to dump out Tree RCU's 5845 rcu_node tree with an eye towards determining 5846 why a new grace period has not yet started. 5847 5848 rcutree.use_softirq= [KNL] 5849 If set to zero, move all RCU_SOFTIRQ processing to 5850 per-CPU rcuc kthreads. Defaults to a non-zero 5851 value, meaning that RCU_SOFTIRQ is used by default. 5852 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5853 5854 But note that CONFIG_PREEMPT_RT=y kernels disable 5855 this kernel boot parameter, forcibly setting it 5856 to zero. 5857 5858 rcutree.enable_rcu_lazy= [KNL] 5859 To save power, batch RCU callbacks and flush after 5860 delay, memory pressure or callback list growing too 5861 big. 5862 5863 rcutree.rcu_normal_wake_from_gp= [KNL] 5864 Reduces a latency of synchronize_rcu() call. This approach 5865 maintains its own track of synchronize_rcu() callers, so it 5866 does not interact with regular callbacks because it does not 5867 use a call_rcu[_hurry]() path. Please note, this is for a 5868 normal grace period. 5869 5870 How to enable it: 5871 5872 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5873 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5874 5875 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5876 disabled by the boot parameter passing 0. 5877 5878 rcuscale.gp_async= [KNL] 5879 Measure performance of asynchronous 5880 grace-period primitives such as call_rcu(). 5881 5882 rcuscale.gp_async_max= [KNL] 5883 Specify the maximum number of outstanding 5884 callbacks per writer thread. When a writer 5885 thread exceeds this limit, it invokes the 5886 corresponding flavor of rcu_barrier() to allow 5887 previously posted callbacks to drain. 5888 5889 rcuscale.gp_exp= [KNL] 5890 Measure performance of expedited synchronous 5891 grace-period primitives. 5892 5893 rcuscale.holdoff= [KNL] 5894 Set test-start holdoff period. The purpose of 5895 this parameter is to delay the start of the 5896 test until boot completes in order to avoid 5897 interference. 5898 5899 rcuscale.kfree_by_call_rcu= [KNL] 5900 In kernels built with CONFIG_RCU_LAZY=y, test 5901 call_rcu() instead of kfree_rcu(). 5902 5903 rcuscale.kfree_mult= [KNL] 5904 Instead of allocating an object of size kfree_obj, 5905 allocate one of kfree_mult * sizeof(kfree_obj). 5906 Defaults to 1. 5907 5908 rcuscale.kfree_rcu_test= [KNL] 5909 Set to measure performance of kfree_rcu() flooding. 5910 5911 rcuscale.kfree_rcu_test_double= [KNL] 5912 Test the double-argument variant of kfree_rcu(). 5913 If this parameter has the same value as 5914 rcuscale.kfree_rcu_test_single, both the single- 5915 and double-argument variants are tested. 5916 5917 rcuscale.kfree_rcu_test_single= [KNL] 5918 Test the single-argument variant of kfree_rcu(). 5919 If this parameter has the same value as 5920 rcuscale.kfree_rcu_test_double, both the single- 5921 and double-argument variants are tested. 5922 5923 rcuscale.kfree_nthreads= [KNL] 5924 The number of threads running loops of kfree_rcu(). 5925 5926 rcuscale.kfree_alloc_num= [KNL] 5927 Number of allocations and frees done in an iteration. 5928 5929 rcuscale.kfree_loops= [KNL] 5930 Number of loops doing rcuscale.kfree_alloc_num number 5931 of allocations and frees. 5932 5933 rcuscale.minruntime= [KNL] 5934 Set the minimum test run time in seconds. This 5935 does not affect the data-collection interval, 5936 but instead allows better measurement of things 5937 like CPU consumption. 5938 5939 rcuscale.nreaders= [KNL] 5940 Set number of RCU readers. The value -1 selects 5941 N, where N is the number of CPUs. A value 5942 "n" less than -1 selects N-n+1, where N is again 5943 the number of CPUs. For example, -2 selects N 5944 (the number of CPUs), -3 selects N+1, and so on. 5945 A value of "n" less than or equal to -N selects 5946 a single reader. 5947 5948 rcuscale.nwriters= [KNL] 5949 Set number of RCU writers. The values operate 5950 the same as for rcuscale.nreaders. 5951 N, where N is the number of CPUs 5952 5953 rcuscale.scale_type= [KNL] 5954 Specify the RCU implementation to test. 5955 5956 rcuscale.shutdown= [KNL] 5957 Shut the system down after performance tests 5958 complete. This is useful for hands-off automated 5959 testing. 5960 5961 rcuscale.verbose= [KNL] 5962 Enable additional printk() statements. 5963 5964 rcuscale.writer_holdoff= [KNL] 5965 Write-side holdoff between grace periods, 5966 in microseconds. The default of zero says 5967 no holdoff. 5968 5969 rcuscale.writer_holdoff_jiffies= [KNL] 5970 Additional write-side holdoff between grace 5971 periods, but in jiffies. The default of zero 5972 says no holdoff. 5973 5974 rcutorture.fqs_duration= [KNL] 5975 Set duration of force_quiescent_state bursts 5976 in microseconds. 5977 5978 rcutorture.fqs_holdoff= [KNL] 5979 Set holdoff time within force_quiescent_state bursts 5980 in microseconds. 5981 5982 rcutorture.fqs_stutter= [KNL] 5983 Set wait time between force_quiescent_state bursts 5984 in seconds. 5985 5986 rcutorture.fwd_progress= [KNL] 5987 Specifies the number of kthreads to be used 5988 for RCU grace-period forward-progress testing 5989 for the types of RCU supporting this notion. 5990 Defaults to 1 kthread, values less than zero or 5991 greater than the number of CPUs cause the number 5992 of CPUs to be used. 5993 5994 rcutorture.fwd_progress_div= [KNL] 5995 Specify the fraction of a CPU-stall-warning 5996 period to do tight-loop forward-progress testing. 5997 5998 rcutorture.fwd_progress_holdoff= [KNL] 5999 Number of seconds to wait between successive 6000 forward-progress tests. 6001 6002 rcutorture.fwd_progress_need_resched= [KNL] 6003 Enclose cond_resched() calls within checks for 6004 need_resched() during tight-loop forward-progress 6005 testing. 6006 6007 rcutorture.gp_cond= [KNL] 6008 Use conditional/asynchronous update-side 6009 normal-grace-period primitives, if available. 6010 6011 rcutorture.gp_cond_exp= [KNL] 6012 Use conditional/asynchronous update-side 6013 expedited-grace-period primitives, if available. 6014 6015 rcutorture.gp_cond_full= [KNL] 6016 Use conditional/asynchronous update-side 6017 normal-grace-period primitives that also take 6018 concurrent expedited grace periods into account, 6019 if available. 6020 6021 rcutorture.gp_cond_exp_full= [KNL] 6022 Use conditional/asynchronous update-side 6023 expedited-grace-period primitives that also take 6024 concurrent normal grace periods into account, 6025 if available. 6026 6027 rcutorture.gp_cond_wi= [KNL] 6028 Nominal wait interval for normal conditional 6029 grace periods (specified by rcutorture's 6030 gp_cond and gp_cond_full module parameters), 6031 in microseconds. The actual wait interval will 6032 be randomly selected to nanosecond granularity up 6033 to this wait interval. Defaults to 16 jiffies, 6034 for example, 16,000 microseconds on a system 6035 with HZ=1000. 6036 6037 rcutorture.gp_cond_wi_exp= [KNL] 6038 Nominal wait interval for expedited conditional 6039 grace periods (specified by rcutorture's 6040 gp_cond_exp and gp_cond_exp_full module 6041 parameters), in microseconds. The actual wait 6042 interval will be randomly selected to nanosecond 6043 granularity up to this wait interval. Defaults to 6044 128 microseconds. 6045 6046 rcutorture.gp_exp= [KNL] 6047 Use expedited update-side primitives, if available. 6048 6049 rcutorture.gp_normal= [KNL] 6050 Use normal (non-expedited) asynchronous 6051 update-side primitives, if available. 6052 6053 rcutorture.gp_poll= [KNL] 6054 Use polled update-side normal-grace-period 6055 primitives, if available. 6056 6057 rcutorture.gp_poll_exp= [KNL] 6058 Use polled update-side expedited-grace-period 6059 primitives, if available. 6060 6061 rcutorture.gp_poll_full= [KNL] 6062 Use polled update-side normal-grace-period 6063 primitives that also take concurrent expedited 6064 grace periods into account, if available. 6065 6066 rcutorture.gp_poll_exp_full= [KNL] 6067 Use polled update-side expedited-grace-period 6068 primitives that also take concurrent normal 6069 grace periods into account, if available. 6070 6071 rcutorture.gp_poll_wi= [KNL] 6072 Nominal wait interval for normal conditional 6073 grace periods (specified by rcutorture's 6074 gp_poll and gp_poll_full module parameters), 6075 in microseconds. The actual wait interval will 6076 be randomly selected to nanosecond granularity up 6077 to this wait interval. Defaults to 16 jiffies, 6078 for example, 16,000 microseconds on a system 6079 with HZ=1000. 6080 6081 rcutorture.gp_poll_wi_exp= [KNL] 6082 Nominal wait interval for expedited conditional 6083 grace periods (specified by rcutorture's 6084 gp_poll_exp and gp_poll_exp_full module 6085 parameters), in microseconds. The actual wait 6086 interval will be randomly selected to nanosecond 6087 granularity up to this wait interval. Defaults to 6088 128 microseconds. 6089 6090 rcutorture.gp_sync= [KNL] 6091 Use normal (non-expedited) synchronous 6092 update-side primitives, if available. If all 6093 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6094 rcutorture.gp_normal=, and rcutorture.gp_sync= 6095 are zero, rcutorture acts as if is interpreted 6096 they are all non-zero. 6097 6098 rcutorture.gpwrap_lag= [KNL] 6099 Enable grace-period wrap lag testing. Setting 6100 to false prevents the gpwrap lag test from 6101 running. Default is true. 6102 6103 rcutorture.gpwrap_lag_gps= [KNL] 6104 Set the value for grace-period wrap lag during 6105 active lag testing periods. This controls how many 6106 grace periods differences we tolerate between 6107 rdp and rnp's gp_seq before setting overflow flag. 6108 The default is always set to 8. 6109 6110 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6111 Set the total cycle duration for gpwrap lag 6112 testing in minutes. This is the total time for 6113 one complete cycle of active and inactive 6114 testing periods. Default is 30 minutes. 6115 6116 rcutorture.gpwrap_lag_active_mins= [KNL] 6117 Set the duration for which gpwrap lag is active 6118 within each cycle, in minutes. During this time, 6119 the grace-period wrap lag will be set to the 6120 value specified by gpwrap_lag_gps. Default is 6121 5 minutes. 6122 6123 rcutorture.irqreader= [KNL] 6124 Run RCU readers from irq handlers, or, more 6125 accurately, from a timer handler. Not all RCU 6126 flavors take kindly to this sort of thing. 6127 6128 rcutorture.leakpointer= [KNL] 6129 Leak an RCU-protected pointer out of the reader. 6130 This can of course result in splats, and is 6131 intended to test the ability of things like 6132 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6133 such leaks. 6134 6135 rcutorture.n_barrier_cbs= [KNL] 6136 Set callbacks/threads for rcu_barrier() testing. 6137 6138 rcutorture.nfakewriters= [KNL] 6139 Set number of concurrent RCU writers. These just 6140 stress RCU, they don't participate in the actual 6141 test, hence the "fake". 6142 6143 rcutorture.nocbs_nthreads= [KNL] 6144 Set number of RCU callback-offload togglers. 6145 Zero (the default) disables toggling. 6146 6147 rcutorture.nocbs_toggle= [KNL] 6148 Set the delay in milliseconds between successive 6149 callback-offload toggling attempts. 6150 6151 rcutorture.nreaders= [KNL] 6152 Set number of RCU readers. The value -1 selects 6153 N-1, where N is the number of CPUs. A value 6154 "n" less than -1 selects N-n-2, where N is again 6155 the number of CPUs. For example, -2 selects N 6156 (the number of CPUs), -3 selects N+1, and so on. 6157 6158 rcutorture.object_debug= [KNL] 6159 Enable debug-object double-call_rcu() testing. 6160 6161 rcutorture.onoff_holdoff= [KNL] 6162 Set time (s) after boot for CPU-hotplug testing. 6163 6164 rcutorture.onoff_interval= [KNL] 6165 Set time (jiffies) between CPU-hotplug operations, 6166 or zero to disable CPU-hotplug testing. 6167 6168 rcutorture.preempt_duration= [KNL] 6169 Set duration (in milliseconds) of preemptions 6170 by a high-priority FIFO real-time task. Set to 6171 zero (the default) to disable. The CPUs to 6172 preempt are selected randomly from the set that 6173 are online at a given point in time. Races with 6174 CPUs going offline are ignored, with that attempt 6175 at preemption skipped. 6176 6177 rcutorture.preempt_interval= [KNL] 6178 Set interval (in milliseconds, defaulting to one 6179 second) between preemptions by a high-priority 6180 FIFO real-time task. This delay is mediated 6181 by an hrtimer and is further fuzzed to avoid 6182 inadvertent synchronizations. 6183 6184 rcutorture.read_exit_burst= [KNL] 6185 The number of times in a given read-then-exit 6186 episode that a set of read-then-exit kthreads 6187 is spawned. 6188 6189 rcutorture.read_exit_delay= [KNL] 6190 The delay, in seconds, between successive 6191 read-then-exit testing episodes. 6192 6193 rcutorture.reader_flavor= [KNL] 6194 A bit mask indicating which readers to use. 6195 If there is more than one bit set, the readers 6196 are entered from low-order bit up, and are 6197 exited in the opposite order. For SRCU, the 6198 0x1 bit is normal readers, 0x2 NMI-safe readers, 6199 and 0x4 light-weight readers. 6200 6201 rcutorture.shuffle_interval= [KNL] 6202 Set task-shuffle interval (s). Shuffling tasks 6203 allows some CPUs to go into dyntick-idle mode 6204 during the rcutorture test. 6205 6206 rcutorture.shutdown_secs= [KNL] 6207 Set time (s) after boot system shutdown. This 6208 is useful for hands-off automated testing. 6209 6210 rcutorture.stall_cpu= [KNL] 6211 Duration of CPU stall (s) to test RCU CPU stall 6212 warnings, zero to disable. 6213 6214 rcutorture.stall_cpu_block= [KNL] 6215 Sleep while stalling if set. This will result 6216 in warnings from preemptible RCU in addition to 6217 any other stall-related activity. Note that 6218 in kernels built with CONFIG_PREEMPTION=n and 6219 CONFIG_PREEMPT_COUNT=y, this parameter will 6220 cause the CPU to pass through a quiescent state. 6221 Given CONFIG_PREEMPTION=n, this will suppress 6222 RCU CPU stall warnings, but will instead result 6223 in scheduling-while-atomic splats. 6224 6225 Use of this module parameter results in splats. 6226 6227 6228 rcutorture.stall_cpu_holdoff= [KNL] 6229 Time to wait (s) after boot before inducing stall. 6230 6231 rcutorture.stall_cpu_irqsoff= [KNL] 6232 Disable interrupts while stalling if set, but only 6233 on the first stall in the set. 6234 6235 rcutorture.stall_cpu_repeat= [KNL] 6236 Number of times to repeat the stall sequence, 6237 so that rcutorture.stall_cpu_repeat=3 will result 6238 in four stall sequences. 6239 6240 rcutorture.stall_gp_kthread= [KNL] 6241 Duration (s) of forced sleep within RCU 6242 grace-period kthread to test RCU CPU stall 6243 warnings, zero to disable. If both stall_cpu 6244 and stall_gp_kthread are specified, the 6245 kthread is starved first, then the CPU. 6246 6247 rcutorture.stat_interval= [KNL] 6248 Time (s) between statistics printk()s. 6249 6250 rcutorture.stutter= [KNL] 6251 Time (s) to stutter testing, for example, specifying 6252 five seconds causes the test to run for five seconds, 6253 wait for five seconds, and so on. This tests RCU's 6254 ability to transition abruptly to and from idle. 6255 6256 rcutorture.test_boost= [KNL] 6257 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6258 "Maybe" means test if the RCU implementation 6259 under test support RCU priority boosting. 6260 6261 rcutorture.test_boost_duration= [KNL] 6262 Duration (s) of each individual boost test. 6263 6264 rcutorture.test_boost_holdoff= [KNL] 6265 Holdoff time (s) from start of test to the start 6266 of RCU priority-boost testing. Defaults to zero, 6267 that is, no holdoff. 6268 6269 rcutorture.test_boost_interval= [KNL] 6270 Interval (s) between each boost test. 6271 6272 rcutorture.test_no_idle_hz= [KNL] 6273 Test RCU's dyntick-idle handling. See also the 6274 rcutorture.shuffle_interval parameter. 6275 6276 rcutorture.torture_type= [KNL] 6277 Specify the RCU implementation to test. 6278 6279 rcutorture.verbose= [KNL] 6280 Enable additional printk() statements. 6281 6282 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6283 Dump ftrace buffer after reporting RCU CPU 6284 stall warning. 6285 6286 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6287 Provide RCU CPU stall notifiers, but see the 6288 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6289 option's help text. TL;DR: You almost certainly 6290 do not want rcupdate.rcu_cpu_stall_notifiers. 6291 6292 rcupdate.rcu_cpu_stall_suppress= [KNL] 6293 Suppress RCU CPU stall warning messages. 6294 6295 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6296 Suppress RCU CPU stall warning messages and 6297 rcutorture writer stall warnings that occur 6298 during early boot, that is, during the time 6299 before the init task is spawned. 6300 6301 rcupdate.rcu_cpu_stall_timeout= [KNL] 6302 Set timeout for RCU CPU stall warning messages. 6303 The value is in seconds and the maximum allowed 6304 value is 300 seconds. 6305 6306 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6307 Set timeout for expedited RCU CPU stall warning 6308 messages. The value is in milliseconds 6309 and the maximum allowed value is 21000 6310 milliseconds. Please note that this value is 6311 adjusted to an arch timer tick resolution. 6312 Setting this to zero causes the value from 6313 rcupdate.rcu_cpu_stall_timeout to be used (after 6314 conversion from seconds to milliseconds). 6315 6316 rcupdate.rcu_cpu_stall_cputime= [KNL] 6317 Provide statistics on the cputime and count of 6318 interrupts and tasks during the sampling period. For 6319 multiple continuous RCU stalls, all sampling periods 6320 begin at half of the first RCU stall timeout. 6321 6322 rcupdate.rcu_exp_stall_task_details= [KNL] 6323 Print stack dumps of any tasks blocking the 6324 current expedited RCU grace period during an 6325 expedited RCU CPU stall warning. 6326 6327 rcupdate.rcu_expedited= [KNL] 6328 Use expedited grace-period primitives, for 6329 example, synchronize_rcu_expedited() instead 6330 of synchronize_rcu(). This reduces latency, 6331 but can increase CPU utilization, degrade 6332 real-time latency, and degrade energy efficiency. 6333 No effect on CONFIG_TINY_RCU kernels. 6334 6335 rcupdate.rcu_normal= [KNL] 6336 Use only normal grace-period primitives, 6337 for example, synchronize_rcu() instead of 6338 synchronize_rcu_expedited(). This improves 6339 real-time latency, CPU utilization, and 6340 energy efficiency, but can expose users to 6341 increased grace-period latency. This parameter 6342 overrides rcupdate.rcu_expedited. No effect on 6343 CONFIG_TINY_RCU kernels. 6344 6345 rcupdate.rcu_normal_after_boot= [KNL] 6346 Once boot has completed (that is, after 6347 rcu_end_inkernel_boot() has been invoked), use 6348 only normal grace-period primitives. No effect 6349 on CONFIG_TINY_RCU kernels. 6350 6351 But note that CONFIG_PREEMPT_RT=y kernels enables 6352 this kernel boot parameter, forcibly setting 6353 it to the value one, that is, converting any 6354 post-boot attempt at an expedited RCU grace 6355 period to instead use normal non-expedited 6356 grace-period processing. 6357 6358 rcupdate.rcu_task_collapse_lim= [KNL] 6359 Set the maximum number of callbacks present 6360 at the beginning of a grace period that allows 6361 the RCU Tasks flavors to collapse back to using 6362 a single callback queue. This switching only 6363 occurs when rcupdate.rcu_task_enqueue_lim is 6364 set to the default value of -1. 6365 6366 rcupdate.rcu_task_contend_lim= [KNL] 6367 Set the minimum number of callback-queuing-time 6368 lock-contention events per jiffy required to 6369 cause the RCU Tasks flavors to switch to per-CPU 6370 callback queuing. This switching only occurs 6371 when rcupdate.rcu_task_enqueue_lim is set to 6372 the default value of -1. 6373 6374 rcupdate.rcu_task_enqueue_lim= [KNL] 6375 Set the number of callback queues to use for the 6376 RCU Tasks family of RCU flavors. The default 6377 of -1 allows this to be automatically (and 6378 dynamically) adjusted. This parameter is intended 6379 for use in testing. 6380 6381 rcupdate.rcu_task_lazy_lim= [KNL] 6382 Number of callbacks on a given CPU that will 6383 cancel laziness on that CPU. Use -1 to disable 6384 cancellation of laziness, but be advised that 6385 doing so increases the danger of OOM due to 6386 callback flooding. 6387 6388 rcupdate.rcu_task_stall_info= [KNL] 6389 Set initial timeout in jiffies for RCU task stall 6390 informational messages, which give some indication 6391 of the problem for those not patient enough to 6392 wait for ten minutes. Informational messages are 6393 only printed prior to the stall-warning message 6394 for a given grace period. Disable with a value 6395 less than or equal to zero. Defaults to ten 6396 seconds. A change in value does not take effect 6397 until the beginning of the next grace period. 6398 6399 rcupdate.rcu_task_stall_info_mult= [KNL] 6400 Multiplier for time interval between successive 6401 RCU task stall informational messages for a given 6402 RCU tasks grace period. This value is clamped 6403 to one through ten, inclusive. It defaults to 6404 the value three, so that the first informational 6405 message is printed 10 seconds into the grace 6406 period, the second at 40 seconds, the third at 6407 160 seconds, and then the stall warning at 600 6408 seconds would prevent a fourth at 640 seconds. 6409 6410 rcupdate.rcu_task_stall_timeout= [KNL] 6411 Set timeout in jiffies for RCU task stall 6412 warning messages. Disable with a value less 6413 than or equal to zero. Defaults to ten minutes. 6414 A change in value does not take effect until 6415 the beginning of the next grace period. 6416 6417 rcupdate.rcu_tasks_lazy_ms= [KNL] 6418 Set timeout in milliseconds RCU Tasks asynchronous 6419 callback batching for call_rcu_tasks(). 6420 A negative value will take the default. A value 6421 of zero will disable batching. Batching is 6422 always disabled for synchronize_rcu_tasks(). 6423 6424 rcupdate.rcu_self_test= [KNL] 6425 Run the RCU early boot self tests 6426 6427 rdinit= [KNL] 6428 Format: <full_path> 6429 Run specified binary instead of /init from the ramdisk, 6430 used for early userspace startup. See initrd. 6431 6432 rdrand= [X86,EARLY] 6433 force - Override the decision by the kernel to hide the 6434 advertisement of RDRAND support (this affects 6435 certain AMD processors because of buggy BIOS 6436 support, specifically around the suspend/resume 6437 path). 6438 6439 rdt= [HW,X86,RDT] 6440 Turn on/off individual RDT features. List is: 6441 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6442 mba, smba, bmec, abmc, sdciae, energy[:guid], 6443 perf[:guid]. 6444 E.g. to turn on cmt and turn off mba use: 6445 rdt=cmt,!mba 6446 To turn off all energy telemetry monitoring and ensure that 6447 perf telemetry monitoring associated with guid 0x12345 6448 is enabled use: 6449 rdt=!energy,perf:0x12345 6450 6451 reboot= [KNL] 6452 Format (x86 or x86_64): 6453 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6454 [[,]s[mp]#### \ 6455 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6456 [[,]f[orce] 6457 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6458 (prefix with 'panic_' to set mode for panic 6459 reboot only), 6460 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6461 reboot_force is either force or not specified, 6462 reboot_cpu is s[mp]#### with #### being the processor 6463 to be used for rebooting. 6464 6465 acpi 6466 Use the ACPI RESET_REG in the FADT. If ACPI is not 6467 configured or the ACPI reset does not work, the reboot 6468 path attempts the reset using the keyboard controller. 6469 6470 bios 6471 Use the CPU reboot vector for warm reset 6472 6473 cold 6474 Set the cold reboot flag 6475 6476 default 6477 There are some built-in platform specific "quirks" 6478 - you may see: "reboot: <name> series board detected. 6479 Selecting <type> for reboots." In the case where you 6480 think the quirk is in error (e.g. you have newer BIOS, 6481 or newer board) using this option will ignore the 6482 built-in quirk table, and use the generic default 6483 reboot actions. 6484 6485 efi 6486 Use efi reset_system runtime service. If EFI is not 6487 configured or the EFI reset does not work, the reboot 6488 path attempts the reset using the keyboard controller. 6489 6490 force 6491 Don't stop other CPUs on reboot. This can make reboot 6492 more reliable in some cases. 6493 6494 kbd 6495 Use the keyboard controller. cold reset (default) 6496 6497 pci 6498 Use a write to the PCI config space register 0xcf9 to 6499 trigger reboot. 6500 6501 triple 6502 Force a triple fault (init) 6503 6504 warm 6505 Don't set the cold reboot flag 6506 6507 Using warm reset will be much faster especially on big 6508 memory systems because the BIOS will not go through 6509 the memory check. Disadvantage is that not all 6510 hardware will be completely reinitialized on reboot so 6511 there may be boot problems on some systems. 6512 6513 6514 refscale.holdoff= [KNL] 6515 Set test-start holdoff period. The purpose of 6516 this parameter is to delay the start of the 6517 test until boot completes in order to avoid 6518 interference. 6519 6520 refscale.lookup_instances= [KNL] 6521 Number of data elements to use for the forms of 6522 SLAB_TYPESAFE_BY_RCU testing. A negative number 6523 is negated and multiplied by nr_cpu_ids, while 6524 zero specifies nr_cpu_ids. 6525 6526 refscale.loops= [KNL] 6527 Set the number of loops over the synchronization 6528 primitive under test. Increasing this number 6529 reduces noise due to loop start/end overhead, 6530 but the default has already reduced the per-pass 6531 noise to a handful of picoseconds on ca. 2020 6532 x86 laptops. 6533 6534 refscale.nreaders= [KNL] 6535 Set number of readers. The default value of -1 6536 selects N, where N is roughly 75% of the number 6537 of CPUs. A value of zero is an interesting choice. 6538 6539 refscale.nruns= [KNL] 6540 Set number of runs, each of which is dumped onto 6541 the console log. 6542 6543 refscale.readdelay= [KNL] 6544 Set the read-side critical-section duration, 6545 measured in microseconds. 6546 6547 refscale.scale_type= [KNL] 6548 Specify the read-protection implementation to test. 6549 6550 refscale.shutdown= [KNL] 6551 Shut down the system at the end of the performance 6552 test. This defaults to 1 (shut it down) when 6553 refscale is built into the kernel and to 0 (leave 6554 it running) when refscale is built as a module. 6555 6556 refscale.verbose= [KNL] 6557 Enable additional printk() statements. 6558 6559 refscale.verbose_batched= [KNL] 6560 Batch the additional printk() statements. If zero 6561 (the default) or negative, print everything. Otherwise, 6562 print every Nth verbose statement, where N is the value 6563 specified. 6564 6565 regulator_ignore_unused 6566 [REGULATOR] 6567 Prevents regulator framework from disabling regulators 6568 that are unused, due no driver claiming them. This may 6569 be useful for debug and development, but should not be 6570 needed on a platform with proper driver support. 6571 6572 relax_domain_level= 6573 [KNL, SMP] Set scheduler's default relax_domain_level. 6574 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6575 6576 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6577 Format: <base1>,<size1>[,<base2>,<size2>,...] 6578 Reserve I/O ports or memory so the kernel won't use 6579 them. If <base> is less than 0x10000, the region 6580 is assumed to be I/O ports; otherwise it is memory. 6581 6582 reserve_mem= [RAM] 6583 Format: nn[KMG]:<align>:<label> 6584 Reserve physical memory and label it with a name that 6585 other subsystems can use to access it. This is typically 6586 used for systems that do not wipe the RAM, and this command 6587 line will try to reserve the same physical memory on 6588 soft reboots. Note, it is not guaranteed to be the same 6589 location. For example, if anything about the system changes 6590 or if booting a different kernel. It can also fail if KASLR 6591 places the kernel at the location of where the RAM reservation 6592 was from a previous boot, the new reservation will be at a 6593 different location. 6594 Any subsystem using this feature must add a way to verify 6595 that the contents of the physical memory is from a previous 6596 boot, as there may be cases where the memory will not be 6597 located at the same location. 6598 6599 The format is size:align:label for example, to request 6600 12 megabytes of 4096 alignment for ramoops: 6601 6602 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6603 6604 reservetop= [X86-32,EARLY] 6605 Format: nn[KMG] 6606 Reserves a hole at the top of the kernel virtual 6607 address space. 6608 6609 reset_devices [KNL] Force drivers to reset the underlying device 6610 during initialization. 6611 6612 resume= [SWSUSP] 6613 Specify the partition device for software suspend 6614 Format: 6615 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6616 6617 resume_offset= [SWSUSP] 6618 Specify the offset from the beginning of the partition 6619 given by "resume=" at which the swap header is located, 6620 in <PAGE_SIZE> units (needed only for swap files). 6621 See Documentation/power/swsusp-and-swap-files.rst 6622 6623 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6624 read the resume files 6625 6626 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6627 Useful for devices that are detected asynchronously 6628 (e.g. USB and MMC devices). 6629 6630 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6631 be accessible via /sys/firmware/initrd. 6632 6633 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6634 Speculative Code Execution with Return Instructions) 6635 vulnerability. 6636 6637 AMD-based UNRET and IBPB mitigations alone do not stop 6638 sibling threads from influencing the predictions of other 6639 sibling threads. For that reason, STIBP is used on pro- 6640 cessors that support it, and mitigate SMT on processors 6641 that don't. 6642 6643 off - no mitigation 6644 auto - automatically select a mitigation 6645 auto,nosmt - automatically select a mitigation, 6646 disabling SMT if necessary for 6647 the full mitigation (only on Zen1 6648 and older without STIBP). 6649 ibpb - On AMD, mitigate short speculation 6650 windows on basic block boundaries too. 6651 Safe, highest perf impact. It also 6652 enables STIBP if present. Not suitable 6653 on Intel. 6654 ibpb,nosmt - Like "ibpb" above but will disable SMT 6655 when STIBP is not available. This is 6656 the alternative for systems which do not 6657 have STIBP. 6658 unret - Force enable untrained return thunks, 6659 only effective on AMD f15h-f17h based 6660 systems. 6661 unret,nosmt - Like unret, but will disable SMT when STIBP 6662 is not available. This is the alternative for 6663 systems which do not have STIBP. 6664 6665 Selecting 'auto' will choose a mitigation method at run 6666 time according to the CPU. 6667 6668 Not specifying this option is equivalent to retbleed=auto. 6669 6670 rfkill.default_state= 6671 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6672 etc. communication is blocked by default. 6673 1 Unblocked. 6674 6675 rfkill.master_switch_mode= 6676 0 The "airplane mode" button does nothing. 6677 1 The "airplane mode" button toggles between everything 6678 blocked and the previous configuration. 6679 2 The "airplane mode" button toggles between everything 6680 blocked and everything unblocked. 6681 6682 ring3mwait=disable 6683 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6684 CPUs. 6685 6686 riscv_isa_fallback [RISCV,EARLY] 6687 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6688 falling back to detecting extension support by parsing 6689 "riscv,isa" property on devicetree systems when the 6690 replacement properties are not found. See the Kconfig 6691 entry for RISCV_ISA_FALLBACK. 6692 6693 riscv_nousercfi= 6694 all Disable user CFI ABI to userspace even if cpu extension 6695 are available. 6696 bcfi Disable user backward CFI ABI to userspace even if 6697 the shadow stack extension is available. 6698 fcfi Disable user forward CFI ABI to userspace even if the 6699 landing pad extension is available. 6700 6701 ro [KNL] Mount root device read-only on boot 6702 6703 rodata= [KNL,EARLY] 6704 on Mark read-only kernel memory as read-only (default). 6705 off Leave read-only kernel memory writable for debugging. 6706 noalias Mark read-only kernel memory as read-only but retain 6707 writable aliases in the direct map for regions outside 6708 of the kernel image. [arm64] 6709 6710 rockchip.usb_uart 6711 [EARLY] 6712 Enable the uart passthrough on the designated usb port 6713 on Rockchip SoCs. When active, the signals of the 6714 debug-uart get routed to the D+ and D- pins of the usb 6715 port and the regular usb controller gets disabled. 6716 6717 root= [KNL] Root filesystem 6718 Usually this is a block device specifier of some kind, 6719 see the early_lookup_bdev comment in 6720 block/early-lookup.c for details. 6721 Alternatively this can be "ram" for the legacy initial 6722 ramdisk, "nfs" and "cifs" for root on a network file 6723 system, or "mtd" and "ubi" for mounting from raw flash. 6724 6725 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6726 mount the root filesystem 6727 6728 rootflags= [KNL] Set root filesystem mount option string 6729 6730 rseq_slice_ext= [KNL] RSEQ based time slice extension 6731 Format: boolean 6732 Control enablement of RSEQ based time slice extension. 6733 Default is 'on'. 6734 6735 initramfs_options= [KNL] 6736 Specify mount options for for the initramfs mount. 6737 6738 rootfstype= [KNL] Set root filesystem type 6739 6740 rootwait [KNL] Wait (indefinitely) for root device to show up. 6741 Useful for devices that are detected asynchronously 6742 (e.g. USB and MMC devices). 6743 6744 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6745 to show up before attempting to mount the root 6746 filesystem. 6747 6748 rproc_mem=nn[KMG][@address] 6749 [KNL,ARM,CMA] Remoteproc physical memory block. 6750 Memory area to be used by remote processor image, 6751 managed by CMA. 6752 6753 rseq_debug= [KNL] Enable or disable restartable sequence 6754 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6755 Format: <bool> 6756 6757 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6758 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6759 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6760 Format: <bool> 6761 6762 rw [KNL] Mount root device read-write on boot 6763 6764 S [KNL] Run init in single mode 6765 6766 s390_iommu= [HW,S390] 6767 Set s390 IOTLB flushing mode 6768 strict 6769 With strict flushing every unmap operation will result 6770 in an IOTLB flush. Default is lazy flushing before 6771 reuse, which is faster. Deprecated, equivalent to 6772 iommu.strict=1. 6773 6774 s390_iommu_aperture= [KNL,S390] 6775 Specifies the size of the per device DMA address space 6776 accessible through the DMA and IOMMU APIs as a decimal 6777 factor of the size of main memory. 6778 The default is 1 meaning that one can concurrently use 6779 as many DMA addresses as physical memory is installed, 6780 if supported by hardware, and thus map all of memory 6781 once. With a value of 2 one can map all of memory twice 6782 and so on. As a special case a factor of 0 imposes no 6783 restrictions other than those given by hardware at the 6784 cost of significant additional memory use for tables. 6785 6786 sa1100ir [NET] 6787 See drivers/net/irda/sa1100_ir.c. 6788 6789 sched_proxy_exec= [KNL] 6790 Enables or disables "proxy execution" style 6791 solution to mutex-based priority inversion. 6792 Format: <bool> 6793 6794 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6795 6796 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6797 Allowed values are enable and disable. This feature 6798 incurs a small amount of overhead in the scheduler 6799 but is useful for debugging and performance tuning. 6800 6801 sched_thermal_decay_shift= 6802 [Deprecated] 6803 [KNL, SMP] Set a decay shift for scheduler thermal 6804 pressure signal. Thermal pressure signal follows the 6805 default decay period of other scheduler pelt 6806 signals(usually 32 ms but configurable). Setting 6807 sched_thermal_decay_shift will left shift the decay 6808 period for the thermal pressure signal by the shift 6809 value. 6810 i.e. with the default pelt decay period of 32 ms 6811 sched_thermal_decay_shift thermal pressure decay pr 6812 1 64 ms 6813 2 128 ms 6814 and so on. 6815 Format: integer between 0 and 10 6816 Default is 0. 6817 6818 scftorture.holdoff= [KNL] 6819 Number of seconds to hold off before starting 6820 test. Defaults to zero for module insertion and 6821 to 10 seconds for built-in smp_call_function() 6822 tests. 6823 6824 scftorture.longwait= [KNL] 6825 Request ridiculously long waits randomly selected 6826 up to the chosen limit in seconds. Zero (the 6827 default) disables this feature. Please note 6828 that requesting even small non-zero numbers of 6829 seconds can result in RCU CPU stall warnings, 6830 softlockup complaints, and so on. 6831 6832 scftorture.nthreads= [KNL] 6833 Number of kthreads to spawn to invoke the 6834 smp_call_function() family of functions. 6835 The default of -1 specifies a number of kthreads 6836 equal to the number of CPUs. 6837 6838 scftorture.onoff_holdoff= [KNL] 6839 Number seconds to wait after the start of the 6840 test before initiating CPU-hotplug operations. 6841 6842 scftorture.onoff_interval= [KNL] 6843 Number seconds to wait between successive 6844 CPU-hotplug operations. Specifying zero (which 6845 is the default) disables CPU-hotplug operations. 6846 6847 scftorture.shutdown_secs= [KNL] 6848 The number of seconds following the start of the 6849 test after which to shut down the system. The 6850 default of zero avoids shutting down the system. 6851 Non-zero values are useful for automated tests. 6852 6853 scftorture.stat_interval= [KNL] 6854 The number of seconds between outputting the 6855 current test statistics to the console. A value 6856 of zero disables statistics output. 6857 6858 scftorture.stutter_cpus= [KNL] 6859 The number of jiffies to wait between each change 6860 to the set of CPUs under test. 6861 6862 scftorture.use_cpus_read_lock= [KNL] 6863 Use use_cpus_read_lock() instead of the default 6864 preempt_disable() to disable CPU hotplug 6865 while invoking one of the smp_call_function*() 6866 functions. 6867 6868 scftorture.verbose= [KNL] 6869 Enable additional printk() statements. 6870 6871 scftorture.weight_single= [KNL] 6872 The probability weighting to use for the 6873 smp_call_function_single() function with a zero 6874 "wait" parameter. A value of -1 selects the 6875 default if all other weights are -1. However, 6876 if at least one weight has some other value, a 6877 value of -1 will instead select a weight of zero. 6878 6879 scftorture.weight_single_wait= [KNL] 6880 The probability weighting to use for the 6881 smp_call_function_single() function with a 6882 non-zero "wait" parameter. See weight_single. 6883 6884 scftorture.weight_many= [KNL] 6885 The probability weighting to use for the 6886 smp_call_function_many() function with a zero 6887 "wait" parameter. See weight_single. 6888 Note well that setting a high probability for 6889 this weighting can place serious IPI load 6890 on the system. 6891 6892 scftorture.weight_many_wait= [KNL] 6893 The probability weighting to use for the 6894 smp_call_function_many() function with a 6895 non-zero "wait" parameter. See weight_single 6896 and weight_many. 6897 6898 scftorture.weight_all= [KNL] 6899 The probability weighting to use for the 6900 smp_call_function_all() function with a zero 6901 "wait" parameter. See weight_single and 6902 weight_many. 6903 6904 scftorture.weight_all_wait= [KNL] 6905 The probability weighting to use for the 6906 smp_call_function_all() function with a 6907 non-zero "wait" parameter. See weight_single 6908 and weight_many. 6909 6910 sdw_mclk_divider=[SDW] 6911 Specify the MCLK divider for Intel SoundWire buses in 6912 case the BIOS does not provide the clock rate properly. 6913 6914 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6915 xtime_lock contention on larger systems, and/or RCU lock 6916 contention on all systems with CONFIG_MAXSMP set. 6917 Format: { "0" | "1" } 6918 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6919 1 -- enable. 6920 Note: increases power consumption, thus should only be 6921 enabled if running jitter sensitive (HPC/RT) workloads. 6922 6923 security= [SECURITY] Choose a legacy "major" security module to 6924 enable at boot. This has been deprecated by the 6925 "lsm=" parameter. 6926 6927 selinux= [SELINUX] Disable or enable SELinux at boot time. 6928 Format: { "0" | "1" } 6929 See security/selinux/Kconfig help text. 6930 0 -- disable. 6931 1 -- enable. 6932 Default value is 1. 6933 6934 serialnumber [BUGS=X86-32] 6935 6936 sev=option[,option...] [X86-64] 6937 6938 debug 6939 Enable debug messages. 6940 6941 nosnp 6942 Do not enable SEV-SNP (applies to host/hypervisor 6943 only). Setting 'nosnp' avoids the RMP check overhead 6944 in memory accesses when users do not want to run 6945 SEV-SNP guests. 6946 6947 shapers= [NET] 6948 Maximal number of shapers. 6949 6950 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6951 Limit apic dumping. The parameter defines the maximal 6952 number of local apics being dumped. Also it is possible 6953 to set it to "all" by meaning -- no limit here. 6954 Format: { 1 (default) | 2 | ... | all }. 6955 The parameter valid if only apic=debug or 6956 apic=verbose is specified. 6957 Example: apic=debug show_lapic=all 6958 6959 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6960 Enabling slab_debug allows one to determine the 6961 culprit if slab objects become corrupted. Enabling 6962 slab_debug can create guard zones around objects and 6963 may poison objects when not in use. Also tracks the 6964 last alloc / free. For more information see 6965 Documentation/admin-guide/mm/slab.rst. 6966 (slub_debug legacy name also accepted for now) 6967 6968 Using this option implies the "no_hash_pointers" 6969 option which can be undone by adding the 6970 "hash_pointers=always" option. 6971 6972 slab_max_order= [MM] 6973 Determines the maximum allowed order for slabs. 6974 A high setting may cause OOMs due to memory 6975 fragmentation. For more information see 6976 Documentation/admin-guide/mm/slab.rst. 6977 (slub_max_order legacy name also accepted for now) 6978 6979 slab_merge [MM] 6980 Enable merging of slabs with similar size when the 6981 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6982 (slub_merge legacy name also accepted for now) 6983 6984 slab_min_objects= [MM] 6985 The minimum number of objects per slab. SLUB will 6986 increase the slab order up to slab_max_order to 6987 generate a sufficiently large slab able to contain 6988 the number of objects indicated. The higher the number 6989 of objects the smaller the overhead of tracking slabs 6990 and the less frequently locks need to be acquired. 6991 For more information see 6992 Documentation/admin-guide/mm/slab.rst. 6993 (slub_min_objects legacy name also accepted for now) 6994 6995 slab_min_order= [MM] 6996 Determines the minimum page order for slabs. Must be 6997 lower or equal to slab_max_order. For more information see 6998 Documentation/admin-guide/mm/slab.rst. 6999 (slub_min_order legacy name also accepted for now) 7000 7001 slab_nomerge [MM] 7002 Disable merging of slabs with similar size. May be 7003 necessary if there is some reason to distinguish 7004 allocs to different slabs, especially in hardened 7005 environments where the risk of heap overflows and 7006 layout control by attackers can usually be 7007 frustrated by disabling merging. This will reduce 7008 most of the exposure of a heap attack to a single 7009 cache (risks via metadata attacks are mostly 7010 unchanged). Debug options disable merging on their 7011 own. 7012 For more information see 7013 Documentation/admin-guide/mm/slab.rst. 7014 (slub_nomerge legacy name also accepted for now) 7015 7016 slab_strict_numa [MM] 7017 Support memory policies on a per object level 7018 in the slab allocator. The default is for memory 7019 policies to be applied at the folio level when 7020 a new folio is needed or a partial folio is 7021 retrieved from the lists. Increases overhead 7022 in the slab fastpaths but gains more accurate 7023 NUMA kernel object placement which helps with slow 7024 interconnects in NUMA systems. 7025 7026 slram= [HW,MTD] 7027 7028 smart2= [HW] 7029 Format: <io1>[,<io2>[,...,<io8>]] 7030 7031 smp.csd_lock_timeout= [KNL] 7032 Specify the period of time in milliseconds 7033 that smp_call_function() and friends will wait 7034 for a CPU to release the CSD lock. This is 7035 useful when diagnosing bugs involving CPUs 7036 disabling interrupts for extended periods 7037 of time. Defaults to 5,000 milliseconds, and 7038 setting a value of zero disables this feature. 7039 This feature may be more efficiently disabled 7040 using the csdlock_debug- kernel parameter. 7041 7042 smp.panic_on_ipistall= [KNL] 7043 If a csd_lock_timeout extends for more than 7044 the specified number of milliseconds, panic the 7045 system. By default, let CSD-lock acquisition 7046 take as long as they take. Specifying 300,000 7047 for this value provides a 5-minute timeout. 7048 7049 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 7050 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 7051 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 7052 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 7053 smsc-ircc2.ircc_irq= [HW] IRQ line 7054 smsc-ircc2.ircc_dma= [HW] DMA channel 7055 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 7056 0: Toshiba Satellite 1800 (GP data pin select) 7057 1: Fast pin select (default) 7058 2: ATC IRMode 7059 7060 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 7061 (logical CPUs) to use per physical CPU on systems 7062 capable of symmetric multithreading (SMT). Will 7063 be capped to the actual hardware limit. 7064 Format: <integer> 7065 Default: -1 (no limit) 7066 7067 softlockup_panic= 7068 [KNL] Should the soft-lockup detector generate panics. 7069 Format: <int> 7070 7071 A value of non-zero instructs the soft-lockup detector 7072 to panic the machine when a soft-lockup duration exceeds 7073 N thresholds. It is also controlled by the kernel.softlockup_panic 7074 sysctl and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 7075 respective build-time switch to that functionality. 7076 7077 softlockup_all_cpu_backtrace= 7078 [KNL] Should the soft-lockup detector generate 7079 backtraces on all cpus. 7080 Format: 0 | 1 7081 7082 sonypi.*= [HW] Sony Programmable I/O Control Device driver 7083 See Documentation/admin-guide/laptops/sonypi.rst 7084 7085 spectre_bhi= [X86] Control mitigation of Branch History Injection 7086 (BHI) vulnerability. This setting affects the 7087 deployment of the HW BHI control and the SW BHB 7088 clearing sequence. 7089 7090 on - (default) Enable the HW or SW mitigation as 7091 needed. This protects the kernel from 7092 both syscalls and VMs. 7093 vmexit - On systems which don't have the HW mitigation 7094 available, enable the SW mitigation on vmexit 7095 ONLY. On such systems, the host kernel is 7096 protected from VM-originated BHI attacks, but 7097 may still be vulnerable to syscall attacks. 7098 off - Disable the mitigation. 7099 7100 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7101 (indirect branch speculation) vulnerability. 7102 The default operation protects the kernel from 7103 user space attacks. 7104 7105 on - unconditionally enable, implies 7106 spectre_v2_user=on 7107 off - unconditionally disable, implies 7108 spectre_v2_user=off 7109 auto - kernel detects whether your CPU model is 7110 vulnerable 7111 7112 Selecting 'on' will, and 'auto' may, choose a 7113 mitigation method at run time according to the 7114 CPU, the available microcode, the setting of the 7115 CONFIG_MITIGATION_RETPOLINE configuration option, 7116 and the compiler with which the kernel was built. 7117 7118 Selecting 'on' will also enable the mitigation 7119 against user space to user space task attacks. 7120 Selecting specific mitigation does not force enable 7121 user mitigations. 7122 7123 Selecting 'off' will disable both the kernel and 7124 the user space protections. 7125 7126 Specific mitigations can also be selected manually: 7127 7128 retpoline - replace indirect branches 7129 retpoline,generic - Retpolines 7130 retpoline,lfence - LFENCE; indirect branch 7131 retpoline,amd - alias for retpoline,lfence 7132 eibrs - Enhanced/Auto IBRS 7133 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7134 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7135 ibrs - use IBRS to protect kernel 7136 7137 Not specifying this option is equivalent to 7138 spectre_v2=auto. 7139 7140 spectre_v2_user= 7141 [X86] Control mitigation of Spectre variant 2 7142 (indirect branch speculation) vulnerability between 7143 user space tasks 7144 7145 on - Unconditionally enable mitigations. Is 7146 enforced by spectre_v2=on 7147 7148 off - Unconditionally disable mitigations. Is 7149 enforced by spectre_v2=off 7150 7151 prctl - Indirect branch speculation is enabled, 7152 but mitigation can be enabled via prctl 7153 per thread. The mitigation control state 7154 is inherited on fork. 7155 7156 prctl,ibpb 7157 - Like "prctl" above, but only STIBP is 7158 controlled per thread. IBPB is issued 7159 always when switching between different user 7160 space processes. 7161 7162 seccomp 7163 - Same as "prctl" above, but all seccomp 7164 threads will enable the mitigation unless 7165 they explicitly opt out. 7166 7167 seccomp,ibpb 7168 - Like "seccomp" above, but only STIBP is 7169 controlled per thread. IBPB is issued 7170 always when switching between different 7171 user space processes. 7172 7173 auto - Kernel selects the mitigation depending on 7174 the available CPU features and vulnerability. 7175 7176 Default mitigation: "prctl" 7177 7178 Not specifying this option is equivalent to 7179 spectre_v2_user=auto. 7180 7181 spec_rstack_overflow= 7182 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7183 7184 off - Disable mitigation 7185 microcode - Enable microcode mitigation only 7186 safe-ret - Enable sw-only safe RET mitigation (default) 7187 ibpb - Enable mitigation by issuing IBPB on 7188 kernel entry 7189 ibpb-vmexit - Issue IBPB only on VMEXIT 7190 (cloud-specific mitigation) 7191 7192 spec_store_bypass_disable= 7193 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7194 (Speculative Store Bypass vulnerability) 7195 7196 Certain CPUs are vulnerable to an exploit against a 7197 a common industry wide performance optimization known 7198 as "Speculative Store Bypass" in which recent stores 7199 to the same memory location may not be observed by 7200 later loads during speculative execution. The idea 7201 is that such stores are unlikely and that they can 7202 be detected prior to instruction retirement at the 7203 end of a particular speculation execution window. 7204 7205 In vulnerable processors, the speculatively forwarded 7206 store can be used in a cache side channel attack, for 7207 example to read memory to which the attacker does not 7208 directly have access (e.g. inside sandboxed code). 7209 7210 This parameter controls whether the Speculative Store 7211 Bypass optimization is used. 7212 7213 On x86 the options are: 7214 7215 on - Unconditionally disable Speculative Store Bypass 7216 off - Unconditionally enable Speculative Store Bypass 7217 auto - Kernel detects whether the CPU model contains an 7218 implementation of Speculative Store Bypass and 7219 picks the most appropriate mitigation. If the 7220 CPU is not vulnerable, "off" is selected. If the 7221 CPU is vulnerable the default mitigation is 7222 architecture and Kconfig dependent. See below. 7223 prctl - Control Speculative Store Bypass per thread 7224 via prctl. Speculative Store Bypass is enabled 7225 for a process by default. The state of the control 7226 is inherited on fork. 7227 seccomp - Same as "prctl" above, but all seccomp threads 7228 will disable SSB unless they explicitly opt out. 7229 7230 Default mitigations: 7231 X86: "prctl" 7232 7233 On powerpc the options are: 7234 7235 on,auto - On Power8 and Power9 insert a store-forwarding 7236 barrier on kernel entry and exit. On Power7 7237 perform a software flush on kernel entry and 7238 exit. 7239 off - No action. 7240 7241 Not specifying this option is equivalent to 7242 spec_store_bypass_disable=auto. 7243 7244 split_lock_detect= 7245 [X86] Enable split lock detection or bus lock detection 7246 7247 When enabled (and if hardware support is present), atomic 7248 instructions that access data across cache line 7249 boundaries will result in an alignment check exception 7250 for split lock detection or a debug exception for 7251 bus lock detection. 7252 7253 off - not enabled 7254 7255 warn - the kernel will emit rate-limited warnings 7256 about applications triggering the #AC 7257 exception or the #DB exception. This mode is 7258 the default on CPUs that support split lock 7259 detection or bus lock detection. Default 7260 behavior is by #AC if both features are 7261 enabled in hardware. 7262 7263 fatal - the kernel will send SIGBUS to applications 7264 that trigger the #AC exception or the #DB 7265 exception. Default behavior is by #AC if 7266 both features are enabled in hardware. 7267 7268 ratelimit:N - 7269 Set system wide rate limit to N bus locks 7270 per second for bus lock detection. 7271 0 < N <= 1000. 7272 7273 N/A for split lock detection. 7274 7275 7276 If an #AC exception is hit in the kernel or in 7277 firmware (i.e. not while executing in user mode) 7278 the kernel will oops in either "warn" or "fatal" 7279 mode. 7280 7281 #DB exception for bus lock is triggered only when 7282 CPL > 0. 7283 7284 srbds= [X86,INTEL,EARLY] 7285 Control the Special Register Buffer Data Sampling 7286 (SRBDS) mitigation. 7287 7288 Certain CPUs are vulnerable to an MDS-like 7289 exploit which can leak bits from the random 7290 number generator. 7291 7292 By default, this issue is mitigated by 7293 microcode. However, the microcode fix can cause 7294 the RDRAND and RDSEED instructions to become 7295 much slower. Among other effects, this will 7296 result in reduced throughput from /dev/urandom. 7297 7298 The microcode mitigation can be disabled with 7299 the following option: 7300 7301 off: Disable mitigation and remove 7302 performance impact to RDRAND and RDSEED 7303 7304 srcutree.big_cpu_lim [KNL] 7305 Specifies the number of CPUs constituting a 7306 large system, such that srcu_struct structures 7307 should immediately allocate an srcu_node array. 7308 This kernel-boot parameter defaults to 128, 7309 but takes effect only when the low-order four 7310 bits of srcutree.convert_to_big is equal to 3 7311 (decide at boot). 7312 7313 srcutree.convert_to_big [KNL] 7314 Specifies under what conditions an SRCU tree 7315 srcu_struct structure will be converted to big 7316 form, that is, with an rcu_node tree: 7317 7318 0: Never. 7319 1: At init_srcu_struct() time. 7320 2: When rcutorture decides to. 7321 3: Decide at boot time (default). 7322 0x1X: Above plus if high contention. 7323 7324 Either way, the srcu_node tree will be sized based 7325 on the actual runtime number of CPUs (nr_cpu_ids) 7326 instead of the compile-time CONFIG_NR_CPUS. 7327 7328 srcutree.counter_wrap_check [KNL] 7329 Specifies how frequently to check for 7330 grace-period sequence counter wrap for the 7331 srcu_data structure's ->srcu_gp_seq_needed field. 7332 The greater the number of bits set in this kernel 7333 parameter, the less frequently counter wrap will 7334 be checked for. Note that the bottom two bits 7335 are ignored. 7336 7337 srcutree.exp_holdoff [KNL] 7338 Specifies how many nanoseconds must elapse 7339 since the end of the last SRCU grace period for 7340 a given srcu_struct until the next normal SRCU 7341 grace period will be considered for automatic 7342 expediting. Set to zero to disable automatic 7343 expediting. 7344 7345 srcutree.srcu_max_nodelay [KNL] 7346 Specifies the number of no-delay instances 7347 per jiffy for which the SRCU grace period 7348 worker thread will be rescheduled with zero 7349 delay. Beyond this limit, worker thread will 7350 be rescheduled with a sleep delay of one jiffy. 7351 7352 srcutree.srcu_max_nodelay_phase [KNL] 7353 Specifies the per-grace-period phase, number of 7354 non-sleeping polls of readers. Beyond this limit, 7355 grace period worker thread will be rescheduled 7356 with a sleep delay of one jiffy, between each 7357 rescan of the readers, for a grace period phase. 7358 7359 srcutree.srcu_retry_check_delay [KNL] 7360 Specifies number of microseconds of non-sleeping 7361 delay between each non-sleeping poll of readers. 7362 7363 srcutree.small_contention_lim [KNL] 7364 Specifies the number of update-side contention 7365 events per jiffy will be tolerated before 7366 initiating a conversion of an srcu_struct 7367 structure to big form. Note that the value of 7368 srcutree.convert_to_big must have the 0x10 bit 7369 set for contention-based conversions to occur. 7370 7371 ssbd= [ARM64,HW,EARLY] 7372 Speculative Store Bypass Disable control 7373 7374 On CPUs that are vulnerable to the Speculative 7375 Store Bypass vulnerability and offer a 7376 firmware based mitigation, this parameter 7377 indicates how the mitigation should be used: 7378 7379 force-on: Unconditionally enable mitigation for 7380 for both kernel and userspace 7381 force-off: Unconditionally disable mitigation for 7382 for both kernel and userspace 7383 kernel: Always enable mitigation in the 7384 kernel, and offer a prctl interface 7385 to allow userspace to register its 7386 interest in being mitigated too. 7387 7388 stack_guard_gap= [MM] 7389 override the default stack gap protection. The value 7390 is in page units and it defines how many pages prior 7391 to (for stacks growing down) resp. after (for stacks 7392 growing up) the main stack are reserved for no other 7393 mapping. Default value is 256 pages. 7394 7395 stack_depot_disable= [KNL,EARLY] 7396 Setting this to true through kernel command line will 7397 disable the stack depot thereby saving the static memory 7398 consumed by the stack hash table. By default this is set 7399 to false. 7400 7401 stack_depot_max_pools= [KNL,EARLY] 7402 Specify the maximum number of pools to use for storing 7403 stack traces. Pools are allocated on-demand up to this 7404 limit. Default value is 8191 pools. 7405 7406 stacktrace [FTRACE] 7407 Enable the stack tracer on boot up. 7408 7409 stacktrace_filter=[function-list] 7410 [FTRACE] Limit the functions that the stack tracer 7411 will trace at boot up. function-list is a comma-separated 7412 list of functions. This list can be changed at run 7413 time by the stack_trace_filter file in the debugfs 7414 tracing directory. Note, this enables stack tracing 7415 and the stacktrace above is not needed. 7416 7417 sti= [PARISC,HW] 7418 Format: <num> 7419 Set the STI (builtin display/keyboard on the HP-PARISC 7420 machines) console (graphic card) which should be used 7421 as the initial boot-console. 7422 See also comment in drivers/video/console/sticore.c. 7423 7424 sti_font= [HW] 7425 See comment in drivers/video/console/sticore.c. 7426 7427 stifb= [HW] 7428 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7429 7430 strict_sas_size= 7431 [X86] 7432 Format: <bool> 7433 Enable or disable strict sigaltstack size checks 7434 against the required signal frame size which 7435 depends on the supported FPU features. This can 7436 be used to filter out binaries which have 7437 not yet been made aware of AT_MINSIGSTKSZ. 7438 7439 stress_hpt [PPC,EARLY] 7440 Limits the number of kernel HPT entries in the hash 7441 page table to increase the rate of hash page table 7442 faults on kernel addresses. 7443 7444 stress_slb [PPC,EARLY] 7445 Limits the number of kernel SLB entries, and flushes 7446 them frequently to increase the rate of SLB faults 7447 on kernel addresses. 7448 7449 no_slb_preload [PPC,EARLY] 7450 Disables slb preloading for userspace. 7451 7452 sunrpc.min_resvport= 7453 sunrpc.max_resvport= 7454 [NFS,SUNRPC] 7455 SunRPC servers often require that client requests 7456 originate from a privileged port (i.e. a port in the 7457 range 0 < portnr < 1024). 7458 An administrator who wishes to reserve some of these 7459 ports for other uses may adjust the range that the 7460 kernel's sunrpc client considers to be privileged 7461 using these two parameters to set the minimum and 7462 maximum port values. 7463 7464 sunrpc.svc_rpc_per_connection_limit= 7465 [NFS,SUNRPC] 7466 Limit the number of requests that the server will 7467 process in parallel from a single connection. 7468 The default value is 0 (no limit). 7469 7470 sunrpc.pool_mode= 7471 [NFS] 7472 Control how the NFS server code allocates CPUs to 7473 service thread pools. Depending on how many NICs 7474 you have and where their interrupts are bound, this 7475 option will affect which CPUs will do NFS serving. 7476 Note: this parameter cannot be changed while the 7477 NFS server is running. 7478 7479 auto the server chooses an appropriate mode 7480 automatically using heuristics 7481 global a single global pool contains all CPUs 7482 percpu one pool for each CPU 7483 pernode one pool for each NUMA node (equivalent 7484 to global on non-NUMA machines) 7485 7486 sunrpc.tcp_slot_table_entries= 7487 sunrpc.udp_slot_table_entries= 7488 [NFS,SUNRPC] 7489 Sets the upper limit on the number of simultaneous 7490 RPC calls that can be sent from the client to a 7491 server. Increasing these values may allow you to 7492 improve throughput, but will also increase the 7493 amount of memory reserved for use by the client. 7494 7495 suspend.pm_test_delay= 7496 [SUSPEND] 7497 Sets the number of seconds to remain in a suspend test 7498 mode before resuming the system (see 7499 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7500 is set. Default value is 5. 7501 7502 svm= [PPC] 7503 Format: { on | off | y | n | 1 | 0 } 7504 This parameter controls use of the Protected 7505 Execution Facility on pSeries. 7506 7507 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7508 Format: { <int> [,<int>] | force | noforce } 7509 <int> -- Number of I/O TLB slabs 7510 <int> -- Second integer after comma. Number of swiotlb 7511 areas with their own lock. Will be rounded up 7512 to a power of 2. 7513 force -- force using of bounce buffers even if they 7514 wouldn't be automatically used by the kernel 7515 noforce -- Never use bounce buffers (for debugging) 7516 7517 switches= [HW,M68k,EARLY] 7518 7519 sysctl.*= [KNL] 7520 Set a sysctl parameter, right before loading the init 7521 process, as if the value was written to the respective 7522 /proc/sys/... file. Both '.' and '/' are recognized as 7523 separators. Unrecognized parameters and invalid values 7524 are reported in the kernel log. Sysctls registered 7525 later by a loaded module cannot be set this way. 7526 Example: sysctl.vm.swappiness=40 7527 7528 sysrq_always_enabled 7529 [KNL] 7530 Ignore sysrq setting - this boot parameter will 7531 neutralize any effect of /proc/sys/kernel/sysrq. 7532 Useful for debugging. 7533 7534 tcpmhash_entries= [KNL,NET] 7535 Set the number of tcp_metrics_hash slots. 7536 Default value is 8192 or 16384 depending on total 7537 ram pages. This is used to specify the TCP metrics 7538 cache size. See Documentation/networking/ip-sysctl.rst 7539 "tcp_no_metrics_save" section for more details. 7540 7541 tdfx= [HW,DRM] 7542 7543 test_suspend= [SUSPEND] 7544 Format: { "mem" | "standby" | "freeze" }[,N] 7545 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7546 standby suspend) or "freeze" (for suspend type freeze) 7547 as the system sleep state during system startup with 7548 the optional capability to repeat N number of times. 7549 The system is woken from this state using a 7550 wakeup-capable RTC alarm. 7551 7552 thash_entries= [KNL,NET] 7553 Set number of hash buckets for TCP connection 7554 7555 thermal.act= [HW,ACPI] 7556 -1: disable all active trip points in all thermal zones 7557 <degrees C>: override all lowest active trip points 7558 7559 thermal.crt= [HW,ACPI] 7560 -1: disable all critical trip points in all thermal zones 7561 <degrees C>: override all critical trip points 7562 7563 thermal.off= [HW,ACPI] 7564 1: disable ACPI thermal control 7565 7566 thermal.psv= [HW,ACPI] 7567 -1: disable all passive trip points 7568 <degrees C>: override all passive trip points to this 7569 value 7570 7571 thermal.tzp= [HW,ACPI] 7572 Specify global default ACPI thermal zone polling rate 7573 <deci-seconds>: poll all this frequency 7574 0: no polling (default) 7575 7576 thp_anon= [KNL] 7577 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7578 state is one of "always", "madvise", "never" or "inherit". 7579 Control the default behavior of the system with respect 7580 to anonymous transparent hugepages. 7581 Can be used multiple times for multiple anon THP sizes. 7582 See Documentation/admin-guide/mm/transhuge.rst for more 7583 details. 7584 7585 threadirqs [KNL,EARLY] 7586 Force threading of all interrupt handlers except those 7587 marked explicitly IRQF_NO_THREAD. 7588 7589 thp_shmem= [KNL] 7590 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7591 Control the default policy of each hugepage size for the 7592 internal shmem mount. <policy> is one of policies available 7593 for the shmem mount ("always", "inherit", "never", "within_size", 7594 and "advise"). 7595 It can be used multiple times for multiple shmem THP sizes. 7596 See Documentation/admin-guide/mm/transhuge.rst for more 7597 details. 7598 7599 topology= [S390,EARLY] 7600 Format: {off | on} 7601 Specify if the kernel should make use of the cpu 7602 topology information if the hardware supports this. 7603 The scheduler will make use of this information and 7604 e.g. base its process migration decisions on it. 7605 Default is on. 7606 7607 torture.disable_onoff_at_boot= [KNL] 7608 Prevent the CPU-hotplug component of torturing 7609 until after init has spawned. 7610 7611 torture.ftrace_dump_at_shutdown= [KNL] 7612 Dump the ftrace buffer at torture-test shutdown, 7613 even if there were no errors. This can be a 7614 very costly operation when many torture tests 7615 are running concurrently, especially on systems 7616 with rotating-rust storage. 7617 7618 torture.verbose_sleep_frequency= [KNL] 7619 Specifies how many verbose printk()s should be 7620 emitted between each sleep. The default of zero 7621 disables verbose-printk() sleeping. 7622 7623 torture.verbose_sleep_duration= [KNL] 7624 Duration of each verbose-printk() sleep in jiffies. 7625 7626 tpm.disable_pcr_integrity= [HW,TPM] 7627 Do not protect PCR registers from unintended physical 7628 access, or interposers in the bus by the means of 7629 having an integrity protected session wrapped around 7630 TPM2_PCR_Extend command. Consider this in a situation 7631 where TPM is heavily utilized by IMA, thus protection 7632 causing a major performance hit, and the space where 7633 machines are deployed is by other means guarded. 7634 7635 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7636 Maximum time in milliseconds to retry sending a message 7637 to the TPM service before giving up. This parameter controls 7638 how long the system will continue retrying when the TPM 7639 service is busy. 7640 Format: <unsigned int> 7641 Default: 2000 (2 seconds) 7642 7643 tpm_suspend_pcr=[HW,TPM] 7644 Format: integer pcr id 7645 Specify that at suspend time, the tpm driver 7646 should extend the specified pcr with zeros, 7647 as a workaround for some chips which fail to 7648 flush the last written pcr on TPM_SaveState. 7649 This will guarantee that all the other pcrs 7650 are saved. 7651 7652 tpm_tis.interrupts= [HW,TPM] 7653 Enable interrupts for the MMIO based physical layer 7654 for the FIFO interface. By default it is set to false 7655 (0). For more information about TPM hardware interfaces 7656 defined by Trusted Computing Group (TCG) see 7657 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7658 7659 tp_printk [FTRACE] 7660 Have the tracepoints sent to printk as well as the 7661 tracing ring buffer. This is useful for early boot up 7662 where the system hangs or reboots and does not give the 7663 option for reading the tracing buffer or performing a 7664 ftrace_dump_on_oops. 7665 7666 To turn off having tracepoints sent to printk, 7667 echo 0 > /proc/sys/kernel/tracepoint_printk 7668 Note, echoing 1 into this file without the 7669 tp_printk kernel cmdline option has no effect. 7670 7671 The tp_printk_stop_on_boot (see below) can also be used 7672 to stop the printing of events to console at 7673 late_initcall_sync. 7674 7675 ** CAUTION ** 7676 7677 Having tracepoints sent to printk() and activating high 7678 frequency tracepoints such as irq or sched, can cause 7679 the system to live lock. 7680 7681 tp_printk_stop_on_boot [FTRACE] 7682 When tp_printk (above) is set, it can cause a lot of noise 7683 on the console. It may be useful to only include the 7684 printing of events during boot up, as user space may 7685 make the system inoperable. 7686 7687 This command line option will stop the printing of events 7688 to console at the late_initcall_sync() time frame. 7689 7690 trace_buf_size=nn[KMG] 7691 [FTRACE] will set tracing buffer size on each cpu. 7692 7693 trace_clock= [FTRACE] Set the clock used for tracing events 7694 at boot up. 7695 local - Use the per CPU time stamp counter 7696 (converted into nanoseconds). Fast, but 7697 depending on the architecture, may not be 7698 in sync between CPUs. 7699 global - Event time stamps are synchronized across 7700 CPUs. May be slower than the local clock, 7701 but better for some race conditions. 7702 counter - Simple counting of events (1, 2, ..) 7703 note, some counts may be skipped due to the 7704 infrastructure grabbing the clock more than 7705 once per event. 7706 uptime - Use jiffies as the time stamp. 7707 perf - Use the same clock that perf uses. 7708 mono - Use ktime_get_mono_fast_ns() for time stamps. 7709 mono_raw - Use ktime_get_raw_fast_ns() for time 7710 stamps. 7711 boot - Use ktime_get_boot_fast_ns() for time stamps. 7712 Architectures may add more clocks. See 7713 Documentation/trace/ftrace.rst for more details. 7714 7715 trace_event=[event-list] 7716 [FTRACE] Set and start specified trace events in order 7717 to facilitate early boot debugging. The event-list is a 7718 comma-separated list of trace events to enable. See 7719 also Documentation/trace/events.rst 7720 7721 To enable modules, use :mod: keyword: 7722 7723 trace_event=:mod:<module> 7724 7725 The value before :mod: will only enable specific events 7726 that are part of the module. See the above mentioned 7727 document for more information. 7728 7729 trace_instance=[instance-info] 7730 [FTRACE] Create a ring buffer instance early in boot up. 7731 This will be listed in: 7732 7733 /sys/kernel/tracing/instances 7734 7735 Events can be enabled at the time the instance is created 7736 via: 7737 7738 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7739 7740 Note, the "<system*>:" portion is optional if the event is 7741 unique. 7742 7743 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7744 7745 will enable the "sched_switch" event (note, the "sched:" is optional, and 7746 the same thing would happen if it was left off). The irq_handler_entry 7747 event, and all events under the "initcall" system. 7748 7749 Flags can be added to the instance to modify its behavior when it is 7750 created. The flags are separated by '^'. 7751 7752 The available flags are: 7753 7754 traceoff - Have the tracing instance tracing disabled after it is created. 7755 traceprintk - Have trace_printk() write into this trace instance 7756 (note, "printk" and "trace_printk" can also be used) 7757 7758 trace_instance=foo^traceoff^traceprintk,sched,irq 7759 7760 The flags must come before the defined events. 7761 7762 If memory has been reserved (see memmap for x86), the instance 7763 can use that memory: 7764 7765 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7766 7767 The above will create a "boot_map" instance that uses the physical 7768 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7769 instance will be split up accordingly. 7770 7771 Alternatively, the memory can be reserved by the reserve_mem option: 7772 7773 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7774 7775 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7776 and place the ring buffer in this memory. Note that due to KASLR, the 7777 memory may not be the same location each time, which will not preserve 7778 the buffer content. 7779 7780 Also note that the layout of the ring buffer data may change between 7781 kernel versions where the validator will fail and reset the ring buffer 7782 if the layout is not the same as the previous kernel. 7783 7784 If the ring buffer is used for persistent bootups and has events enabled, 7785 it is recommend to disable tracing so that events from a previous boot do not 7786 mix with events of the current boot (unless you are debugging a random crash 7787 at boot up). 7788 7789 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7790 7791 Note, saving the trace buffer across reboots does require that the system 7792 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7793 can force a memory reset on boot which will clear any trace that was stored. 7794 This is just one of many ways that can clear memory. Make sure your system 7795 keeps the content of memory across reboots before relying on this option. 7796 7797 NB: Both the mapped address and size must be page aligned for the architecture. 7798 7799 See also Documentation/trace/debugging.rst 7800 7801 7802 trace_options=[option-list] 7803 [FTRACE] Enable or disable tracer options at boot. 7804 The option-list is a comma delimited list of options 7805 that can be enabled or disabled just as if you were 7806 to echo the option name into 7807 7808 /sys/kernel/tracing/trace_options 7809 7810 For example, to enable stacktrace option (to dump the 7811 stack trace of each event), add to the command line: 7812 7813 trace_options=stacktrace 7814 7815 See also Documentation/trace/ftrace.rst "trace options" 7816 section. 7817 7818 trace_trigger=[trigger-list] 7819 [FTRACE] Add an event trigger on specific events. 7820 Set a trigger on top of a specific event, with an optional 7821 filter. 7822 7823 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7824 Where more than one trigger may be specified that are comma delimited. 7825 7826 For example: 7827 7828 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7829 7830 The above will enable the "stacktrace" trigger on the "sched_switch" 7831 event but only trigger it if the "prev_state" of the "sched_switch" 7832 event is "2" (TASK_UNINTERRUPTIBLE). 7833 7834 See also "Event triggers" in Documentation/trace/events.rst 7835 7836 7837 traceoff_after_boot 7838 [FTRACE] Sometimes tracing is used to debug issues 7839 during the boot process. Since the trace buffer has a 7840 limited amount of storage, it may be prudent to 7841 disable tracing after the boot is finished, otherwise 7842 the critical information may be overwritten. With this 7843 option, the main tracing buffer will be turned off at 7844 the end of the boot process. 7845 7846 traceoff_on_warning 7847 [FTRACE] enable this option to disable tracing when a 7848 warning is hit. This turns off "tracing_on". Tracing can 7849 be enabled again by echoing '1' into the "tracing_on" 7850 file located in /sys/kernel/tracing/ 7851 7852 This option is useful, as it disables the trace before 7853 the WARNING dump is called, which prevents the trace to 7854 be filled with content caused by the warning output. 7855 7856 This option can also be set at run time via the sysctl 7857 option: kernel/traceoff_on_warning 7858 7859 transparent_hugepage= 7860 [KNL] 7861 Format: [always|madvise|never] 7862 Can be used to control the default behavior of the system 7863 with respect to transparent hugepages. 7864 See Documentation/admin-guide/mm/transhuge.rst 7865 for more details. 7866 7867 transparent_hugepage_shmem= [KNL] 7868 Format: [always|within_size|advise|never|deny|force] 7869 Can be used to control the hugepage allocation policy for 7870 the internal shmem mount. 7871 See Documentation/admin-guide/mm/transhuge.rst 7872 for more details. 7873 7874 transparent_hugepage_tmpfs= [KNL] 7875 Format: [always|within_size|advise|never] 7876 Can be used to control the default hugepage allocation policy 7877 for the tmpfs mount. 7878 See Documentation/admin-guide/mm/transhuge.rst 7879 for more details. 7880 7881 trusted.source= [KEYS] 7882 Format: <string> 7883 This parameter identifies the trust source as a backend 7884 for trusted keys implementation. Supported trust 7885 sources: 7886 - "tpm" 7887 - "tee" 7888 - "caam" 7889 - "dcp" 7890 - "pkwm" 7891 If not specified then it defaults to iterating through 7892 the trust source list starting with TPM and assigns the 7893 first trust source as a backend which is initialized 7894 successfully during iteration. 7895 7896 trusted.rng= [KEYS] 7897 Format: <string> 7898 The RNG used to generate key material for trusted keys. 7899 Can be one of: 7900 - "kernel" 7901 - the same value as trusted.source: "tpm" or "tee" 7902 - "default" 7903 If not specified, "default" is used. In this case, 7904 the RNG's choice is left to each individual trust source. 7905 7906 trusted.dcp_use_otp_key 7907 This is intended to be used in combination with 7908 trusted.source=dcp and will select the DCP OTP key 7909 instead of the DCP UNIQUE key blob encryption. 7910 7911 trusted.dcp_skip_zk_test 7912 This is intended to be used in combination with 7913 trusted.source=dcp and will disable the check if the 7914 blob key is all zeros. This is helpful for situations where 7915 having this key zero'ed is acceptable. E.g. in testing 7916 scenarios. 7917 7918 tsa= [X86] Control mitigation for Transient Scheduler 7919 Attacks on AMD CPUs. Search the following in your 7920 favourite search engine for more details: 7921 7922 "Technical guidance for mitigating transient scheduler 7923 attacks". 7924 7925 off - disable the mitigation 7926 on - enable the mitigation (default) 7927 user - mitigate only user/kernel transitions 7928 vm - mitigate only guest/host transitions 7929 7930 7931 tsc= Disable clocksource stability checks for TSC. 7932 Format: <string> 7933 [x86] reliable: mark tsc clocksource as reliable, this 7934 disables clocksource verification at runtime, as well 7935 as the stability checks done at bootup. Used to enable 7936 high-resolution timer mode on older hardware, and in 7937 virtualized environment. 7938 [x86] noirqtime: Do not use TSC to do irq accounting. 7939 Used to run time disable IRQ_TIME_ACCOUNTING on any 7940 platforms where RDTSC is slow and this accounting 7941 can add overhead. 7942 [x86] unstable: mark the TSC clocksource as unstable, this 7943 marks the TSC unconditionally unstable at bootup and 7944 avoids any further wobbles once the TSC watchdog notices. 7945 [x86] nowatchdog: disable clocksource watchdog. Used 7946 in situations with strict latency requirements (where 7947 interruptions from clocksource watchdog are not 7948 acceptable). 7949 [x86] recalibrate: force recalibration against a HW timer 7950 (HPET or PM timer) on systems whose TSC frequency was 7951 obtained from HW or FW using either an MSR or CPUID(0x15). 7952 Warn if the difference is more than 500 ppm. 7953 [x86] watchdog: Use TSC as the watchdog clocksource with 7954 which to check other HW timers (HPET or PM timer), but 7955 only on systems where TSC has been deemed trustworthy. 7956 This will be suppressed by an earlier tsc=nowatchdog and 7957 can be overridden by a later tsc=nowatchdog. A console 7958 message will flag any such suppression or overriding. 7959 7960 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7961 value instead. Useful when the early TSC frequency discovery 7962 procedure is not reliable, such as on overclocked systems 7963 with CPUID.16h support and partial CPUID.15h support. 7964 Format: <unsigned int> 7965 7966 tsx= [X86] Control Transactional Synchronization 7967 Extensions (TSX) feature in Intel processors that 7968 support TSX control. 7969 7970 This parameter controls the TSX feature. The options are: 7971 7972 on - Enable TSX on the system. Although there are 7973 mitigations for all known security vulnerabilities, 7974 TSX has been known to be an accelerator for 7975 several previous speculation-related CVEs, and 7976 so there may be unknown security risks associated 7977 with leaving it enabled. 7978 7979 off - Disable TSX on the system. (Note that this 7980 option takes effect only on newer CPUs which are 7981 not vulnerable to MDS, i.e., have 7982 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7983 the new IA32_TSX_CTRL MSR through a microcode 7984 update. This new MSR allows for the reliable 7985 deactivation of the TSX functionality.) 7986 7987 auto - Disable TSX if X86_BUG_TAA is present, 7988 otherwise enable TSX on the system. 7989 7990 Not specifying this option is equivalent to tsx=off. 7991 7992 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7993 for more details. 7994 7995 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7996 Abort (TAA) vulnerability. 7997 7998 Similar to Micro-architectural Data Sampling (MDS) 7999 certain CPUs that support Transactional 8000 Synchronization Extensions (TSX) are vulnerable to an 8001 exploit against CPU internal buffers which can forward 8002 information to a disclosure gadget under certain 8003 conditions. 8004 8005 In vulnerable processors, the speculatively forwarded 8006 data can be used in a cache side channel attack, to 8007 access data to which the attacker does not have direct 8008 access. 8009 8010 This parameter controls the TAA mitigation. The 8011 options are: 8012 8013 full - Enable TAA mitigation on vulnerable CPUs 8014 if TSX is enabled. 8015 8016 full,nosmt - Enable TAA mitigation and disable SMT on 8017 vulnerable CPUs. If TSX is disabled, SMT 8018 is not disabled because CPU is not 8019 vulnerable to cross-thread TAA attacks. 8020 off - Unconditionally disable TAA mitigation 8021 8022 On MDS-affected machines, tsx_async_abort=off can be 8023 prevented by an active MDS mitigation as both vulnerabilities 8024 are mitigated with the same mechanism so in order to disable 8025 this mitigation, you need to specify mds=off too. 8026 8027 Not specifying this option is equivalent to 8028 tsx_async_abort=full. On CPUs which are MDS affected 8029 and deploy MDS mitigation, TAA mitigation is not 8030 required and doesn't provide any additional 8031 mitigation. 8032 8033 For details see: 8034 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 8035 8036 turbografx.map[2|3]= [HW,JOY] 8037 TurboGraFX parallel port interface 8038 Format: 8039 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 8040 See also Documentation/input/devices/joystick-parport.rst 8041 8042 udbg-immortal [PPC] When debugging early kernel crashes that 8043 happen after console_init() and before a proper 8044 console driver takes over, this boot options might 8045 help "seeing" what's going on. 8046 8047 uhash_entries= [KNL,NET] 8048 Set number of hash buckets for UDP/UDP-Lite connections 8049 8050 uhci-hcd.ignore_oc= 8051 [USB] Ignore overcurrent events (default N). 8052 Some badly-designed motherboards generate lots of 8053 bogus events, for ports that aren't wired to 8054 anything. Set this parameter to avoid log spamming. 8055 Note that genuine overcurrent events won't be 8056 reported either. 8057 8058 unaligned_scalar_speed= 8059 [RISCV] 8060 Format: {slow | fast | unsupported} 8061 Allow skipping scalar unaligned access speed tests. This 8062 is useful for testing alternative code paths and to skip 8063 the tests in environments where they run too slowly. All 8064 CPUs must have the same scalar unaligned access speed. 8065 8066 unaligned_vector_speed= 8067 [RISCV] 8068 Format: {slow | fast | unsupported} 8069 Allow skipping vector unaligned access speed tests. This 8070 is useful for testing alternative code paths and to skip 8071 the tests in environments where they run too slowly. All 8072 CPUs must have the same vector unaligned access speed. 8073 8074 unknown_nmi_panic 8075 [X86] Cause panic on unknown NMI. 8076 8077 unwind_debug [X86-64,EARLY] 8078 Enable unwinder debug output. This can be 8079 useful for debugging certain unwinder error 8080 conditions, including corrupt stacks and 8081 bad/missing unwinder metadata. 8082 8083 usbcore.authorized_default= 8084 [USB] Default USB device authorization: 8085 (default -1 = authorized (same as 1), 8086 0 = not authorized, 1 = authorized, 2 = authorized 8087 if device connected to internal port) 8088 8089 usbcore.autosuspend= 8090 [USB] The autosuspend time delay (in seconds) used 8091 for newly-detected USB devices (default 2). This 8092 is the time required before an idle device will be 8093 autosuspended. Devices for which the delay is set 8094 to a negative value won't be autosuspended at all. 8095 8096 usbcore.usbfs_snoop= 8097 [USB] Set to log all usbfs traffic (default 0 = off). 8098 8099 usbcore.usbfs_snoop_max= 8100 [USB] Maximum number of bytes to snoop in each URB 8101 (default = 65536). 8102 8103 usbcore.blinkenlights= 8104 [USB] Set to cycle leds on hubs (default 0 = off). 8105 8106 usbcore.old_scheme_first= 8107 [USB] Start with the old device initialization 8108 scheme (default 0 = off). 8109 8110 usbcore.usbfs_memory_mb= 8111 [USB] Memory limit (in MB) for buffers allocated by 8112 usbfs (default = 16, 0 = max = 2047). 8113 8114 usbcore.use_both_schemes= 8115 [USB] Try the other device initialization scheme 8116 if the first one fails (default 1 = enabled). 8117 8118 usbcore.initial_descriptor_timeout= 8119 [USB] Specifies timeout for the initial 64-byte 8120 USB_REQ_GET_DESCRIPTOR request in milliseconds 8121 (default 5000 = 5.0 seconds). 8122 8123 usbcore.nousb [USB] Disable the USB subsystem 8124 8125 usbcore.quirks= 8126 [USB] A list of quirk entries to augment the built-in 8127 usb core quirk list. List entries are separated by 8128 commas. Each entry has the form 8129 VendorID:ProductID:Flags. The IDs are 4-digit hex 8130 numbers and Flags is a set of letters. Each letter 8131 will change the built-in quirk; setting it if it is 8132 clear and clearing it if it is set. The letters have 8133 the following meanings: 8134 a = USB_QUIRK_STRING_FETCH_255 (string 8135 descriptors must not be fetched using 8136 a 255-byte read); 8137 b = USB_QUIRK_RESET_RESUME (device can't resume 8138 correctly so reset it instead); 8139 c = USB_QUIRK_NO_SET_INTF (device can't handle 8140 Set-Interface requests); 8141 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8142 handle its Configuration or Interface 8143 strings); 8144 e = USB_QUIRK_RESET (device can't be reset 8145 (e.g morph devices), don't use reset); 8146 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8147 more interface descriptions than the 8148 bNumInterfaces count, and can't handle 8149 talking to these interfaces); 8150 g = USB_QUIRK_DELAY_INIT (device needs a pause 8151 during initialization, after we read 8152 the device descriptor); 8153 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8154 high speed and super speed interrupt 8155 endpoints, the USB 2.0 and USB 3.0 spec 8156 require the interval in microframes (1 8157 microframe = 125 microseconds) to be 8158 calculated as interval = 2 ^ 8159 (bInterval-1). 8160 Devices with this quirk report their 8161 bInterval as the result of this 8162 calculation instead of the exponent 8163 variable used in the calculation); 8164 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8165 handle device_qualifier descriptor 8166 requests); 8167 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8168 generates spurious wakeup, ignore 8169 remote wakeup capability); 8170 k = USB_QUIRK_NO_LPM (device can't handle Link 8171 Power Management); 8172 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8173 (Device reports its bInterval as linear 8174 frames instead of the USB 2.0 8175 calculation); 8176 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8177 to be disconnected before suspend to 8178 prevent spurious wakeup); 8179 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8180 pause after every control message); 8181 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8182 delay after resetting its port); 8183 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8184 (Reduce timeout of the SET_ADDRESS 8185 request from 5000 ms to 500 ms); 8186 Example: quirks=0781:5580:bk,0a5c:5834:gij 8187 8188 usbhid.mousepoll= 8189 [USBHID] The interval which mice are to be polled at. 8190 8191 usbhid.jspoll= 8192 [USBHID] The interval which joysticks are to be polled at. 8193 8194 usbhid.kbpoll= 8195 [USBHID] The interval which keyboards are to be polled at. 8196 8197 usb-storage.delay_use= 8198 [UMS] The delay in seconds before a new device is 8199 scanned for Logical Units (default 1). 8200 Optionally the delay in milliseconds if the value has 8201 suffix with "ms". 8202 Example: delay_use=2567ms 8203 8204 usb-storage.quirks= 8205 [UMS] A list of quirks entries to supplement or 8206 override the built-in unusual_devs list. List 8207 entries are separated by commas. Each entry has 8208 the form VID:PID:Flags where VID and PID are Vendor 8209 and Product ID values (4-digit hex numbers) and 8210 Flags is a set of characters, each corresponding 8211 to a common usb-storage quirk flag as follows: 8212 a = SANE_SENSE (collect more than 18 bytes 8213 of sense data, not on uas); 8214 b = BAD_SENSE (don't collect more than 18 8215 bytes of sense data, not on uas); 8216 c = FIX_CAPACITY (decrease the reported 8217 device capacity by one sector); 8218 d = NO_READ_DISC_INFO (don't use 8219 READ_DISC_INFO command, not on uas); 8220 e = NO_READ_CAPACITY_16 (don't use 8221 READ_CAPACITY_16 command); 8222 f = NO_REPORT_OPCODES (don't use report opcodes 8223 command, uas only); 8224 g = MAX_SECTORS_240 (don't transfer more than 8225 240 sectors at a time, uas only); 8226 h = CAPACITY_HEURISTICS (decrease the 8227 reported device capacity by one 8228 sector if the number is odd); 8229 i = IGNORE_DEVICE (don't bind to this 8230 device); 8231 j = NO_REPORT_LUNS (don't use report luns 8232 command, uas only); 8233 k = NO_SAME (do not use WRITE_SAME, uas only) 8234 l = NOT_LOCKABLE (don't try to lock and 8235 unlock ejectable media, not on uas); 8236 m = MAX_SECTORS_64 (don't transfer more 8237 than 64 sectors = 32 KB at a time, 8238 not on uas); 8239 n = INITIAL_READ10 (force a retry of the 8240 initial READ(10) command, not on uas); 8241 o = CAPACITY_OK (accept the capacity 8242 reported by the device, not on uas); 8243 p = WRITE_CACHE (the device cache is ON 8244 by default, not on uas); 8245 r = IGNORE_RESIDUE (the device reports 8246 bogus residue values, not on uas); 8247 s = SINGLE_LUN (the device has only one 8248 Logical Unit); 8249 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8250 commands, uas only); 8251 u = IGNORE_UAS (don't bind to the uas driver); 8252 w = NO_WP_DETECT (don't test whether the 8253 medium is write-protected). 8254 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8255 even if the device claims no cache, 8256 not on uas) 8257 Example: quirks=0419:aaf5:rl,0421:0433:rc 8258 8259 user_debug= [KNL,ARM] 8260 Format: <int> 8261 See arch/arm/Kconfig.debug help text. 8262 1 - undefined instruction events 8263 2 - system calls 8264 4 - invalid data aborts 8265 8 - SIGSEGV faults 8266 16 - SIGBUS faults 8267 Example: user_debug=31 8268 8269 vdso= [X86,SH,SPARC] 8270 On X86_32, this is an alias for vdso32=. Otherwise: 8271 8272 vdso=1: enable VDSO (the default) 8273 vdso=0: disable VDSO mapping 8274 8275 vdso32= [X86] Control the 32-bit vDSO 8276 vdso32=1: enable 32-bit VDSO 8277 vdso32=0 or vdso32=2: disable 32-bit VDSO 8278 8279 See the help text for CONFIG_COMPAT_VDSO for more 8280 details. If CONFIG_COMPAT_VDSO is set, the default is 8281 vdso32=0; otherwise, the default is vdso32=1. 8282 8283 For compatibility with older kernels, vdso32=2 is an 8284 alias for vdso32=0. 8285 8286 Try vdso32=0 if you encounter an error that says: 8287 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8288 8289 video= [FB,EARLY] Frame buffer configuration 8290 See Documentation/fb/modedb.rst. 8291 8292 video.brightness_switch_enabled= [ACPI] 8293 Format: [0|1] 8294 If set to 1, on receiving an ACPI notify event 8295 generated by hotkey, video driver will adjust brightness 8296 level and then send out the event to user space through 8297 the allocated input device. If set to 0, video driver 8298 will only send out the event without touching backlight 8299 brightness level. 8300 default: 1 8301 8302 virtio_mmio.device= 8303 [VMMIO] Memory mapped virtio (platform) device. 8304 8305 <size>@<baseaddr>:<irq>[:<id>] 8306 where: 8307 <size> := size (can use standard suffixes 8308 like K, M and G) 8309 <baseaddr> := physical base address 8310 <irq> := interrupt number (as passed to 8311 request_irq()) 8312 <id> := (optional) platform device id 8313 example: 8314 virtio_mmio.device=1K@0x100b0000:48:7 8315 8316 Can be used multiple times for multiple devices. 8317 8318 vga= [BOOT,X86-32] Select a particular video mode 8319 See Documentation/arch/x86/boot.rst and 8320 Documentation/admin-guide/svga.rst. 8321 Use vga=ask for menu. 8322 This is actually a boot loader parameter; the value is 8323 passed to the kernel using a special protocol. 8324 8325 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8326 May slow down system boot speed, especially when 8327 enabled on systems with a large amount of memory. 8328 All options are enabled by default, and this 8329 interface is meant to allow for selectively 8330 enabling or disabling specific virtual memory 8331 debugging features. 8332 8333 Available options are: 8334 P Enable page structure init time poisoning 8335 - Disable all of the above options 8336 8337 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8338 exact size of <nn>. This can be used to increase 8339 the minimum size (128MB on x86, arm32 platforms). 8340 It can also be used to decrease the size and leave more room 8341 for directly mapped kernel RAM. Note that this parameter does 8342 not exist on many other platforms (including arm64, alpha, 8343 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8344 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8345 8346 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8347 Sets the memory size reserved for contiguous memory 8348 allocations for the vmcp device driver. 8349 8350 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8351 Format: <command> 8352 8353 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8354 Format: <command> 8355 8356 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8357 Format: <command> 8358 8359 vmscape= [X86] Controls mitigation for VMscape attacks. 8360 VMscape attacks can leak information from a userspace 8361 hypervisor to a guest via speculative side-channels. 8362 8363 off - disable the mitigation 8364 ibpb - use Indirect Branch Prediction Barrier 8365 (IBPB) mitigation (default) 8366 force - force vulnerability detection even on 8367 unaffected processors 8368 8369 vsyscall= [X86-64,EARLY] 8370 Controls the behavior of vsyscalls (i.e. calls to 8371 fixed addresses of 0xffffffffff600x00 from legacy 8372 code). Most statically-linked binaries and older 8373 versions of glibc use these calls. Because these 8374 functions are at fixed addresses, they make nice 8375 targets for exploits that can control RIP. 8376 8377 emulate Vsyscalls turn into traps and are emulated 8378 reasonably safely. The vsyscall page is 8379 readable. 8380 8381 xonly [default] Vsyscalls turn into traps and are 8382 emulated reasonably safely. The vsyscall 8383 page is not readable. 8384 8385 none Vsyscalls don't work at all. This makes 8386 them quite hard to use for exploits but 8387 might break your system. 8388 8389 vt.color= [VT] Default text color. 8390 Format: 0xYX, X = foreground, Y = background. 8391 Default: 0x07 = light gray on black. 8392 8393 vt.cur_default= [VT] Default cursor shape. 8394 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8395 the parameters of the <Esc>[?A;B;Cc escape sequence; 8396 see vga-softcursor.rst. Default: 2 = underline. 8397 8398 vt.default_blu= [VT] 8399 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8400 Change the default blue palette of the console. 8401 This is a 16-member array composed of values 8402 ranging from 0-255. 8403 8404 vt.default_grn= [VT] 8405 Format: <green0>,<green1>,<green2>,...,<green15> 8406 Change the default green palette of the console. 8407 This is a 16-member array composed of values 8408 ranging from 0-255. 8409 8410 vt.default_red= [VT] 8411 Format: <red0>,<red1>,<red2>,...,<red15> 8412 Change the default red palette of the console. 8413 This is a 16-member array composed of values 8414 ranging from 0-255. 8415 8416 vt.default_utf8= 8417 [VT] 8418 Format=<0|1> 8419 Set system-wide default UTF-8 mode for all tty's. 8420 Default is 1, i.e. UTF-8 mode is enabled for all 8421 newly opened terminals. 8422 8423 vt.global_cursor_default= 8424 [VT] 8425 Format=<-1|0|1> 8426 Set system-wide default for whether a cursor 8427 is shown on new VTs. Default is -1, 8428 i.e. cursors will be created by default unless 8429 overridden by individual drivers. 0 will hide 8430 cursors, 1 will display them. 8431 8432 vt.italic= [VT] Default color for italic text; 0-15. 8433 Default: 2 = green. 8434 8435 vt.underline= [VT] Default color for underlined text; 0-15. 8436 Default: 3 = cyan. 8437 8438 watchdog timers [HW,WDT] For information on watchdog timers, 8439 see Documentation/watchdog/watchdog-parameters.rst 8440 or other driver-specific files in the 8441 Documentation/watchdog/ directory. 8442 8443 watchdog_thresh= 8444 [KNL] 8445 Set the hard lockup detector stall duration 8446 threshold in seconds. The soft lockup detector 8447 threshold is set to twice the value. A value of 0 8448 disables both lockup detectors. Default is 10 8449 seconds. 8450 8451 workqueue.unbound_cpus= 8452 [KNL,SMP] Specify to constrain one or some CPUs 8453 to use in unbound workqueues. 8454 Format: <cpu-list> 8455 By default, all online CPUs are available for 8456 unbound workqueues. 8457 8458 workqueue.watchdog_thresh= 8459 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8460 warn stall conditions and dump internal state to 8461 help debugging. 0 disables workqueue stall 8462 detection; otherwise, it's the stall threshold 8463 duration in seconds. The default value is 30 and 8464 it can be updated at runtime by writing to the 8465 corresponding sysfs file. 8466 8467 workqueue.panic_on_stall=<uint> 8468 Panic when workqueue stall is detected by 8469 CONFIG_WQ_WATCHDOG. It sets the number times of the 8470 stall to trigger panic. 8471 8472 The default is set by CONFIG_BOOTPARAM_WQ_STALL_PANIC, 8473 which is 0 (disabled) if not configured. 8474 8475 workqueue.panic_on_stall_time=<uint> 8476 Panic when a workqueue stall has been continuous for 8477 the specified number of seconds. Unlike panic_on_stall 8478 which counts accumulated stall events, this triggers 8479 based on the duration of a single continuous stall. 8480 8481 The default is 0, which disables the time-based panic. 8482 8483 workqueue.cpu_intensive_thresh_us= 8484 Per-cpu work items which run for longer than this 8485 threshold are automatically considered CPU intensive 8486 and excluded from concurrency management to prevent 8487 them from noticeably delaying other per-cpu work 8488 items. Default is 10000 (10ms). 8489 8490 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8491 will report the work functions which violate this 8492 threshold repeatedly. They are likely good 8493 candidates for using WQ_UNBOUND workqueues instead. 8494 8495 workqueue.cpu_intensive_warning_thresh=<uint> 8496 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8497 will report the work functions which violate the 8498 intensive_threshold_us repeatedly. In order to prevent 8499 spurious warnings, start printing only after a work 8500 function has violated this threshold number of times. 8501 8502 The default is 4 times. 0 disables the warning. 8503 8504 workqueue.power_efficient 8505 Per-cpu workqueues are generally preferred because 8506 they show better performance thanks to cache 8507 locality; unfortunately, per-cpu workqueues tend to 8508 be more power hungry than unbound workqueues. 8509 8510 Enabling this makes the per-cpu workqueues which 8511 were observed to contribute significantly to power 8512 consumption unbound, leading to measurably lower 8513 power usage at the cost of small performance 8514 overhead. 8515 8516 The default value of this parameter is determined by 8517 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8518 8519 workqueue.default_affinity_scope= 8520 Select the default affinity scope to use for unbound 8521 workqueues. Can be one of "cpu", "smt", "cache", 8522 "numa" and "system". Default is "cache". For more 8523 information, see the Affinity Scopes section in 8524 Documentation/core-api/workqueue.rst. 8525 8526 This can be changed after boot by writing to the 8527 matching /sys/module/workqueue/parameters file. All 8528 workqueues with the "default" affinity scope will be 8529 updated accordingly. 8530 8531 workqueue.debug_force_rr_cpu 8532 Workqueue used to implicitly guarantee that work 8533 items queued without explicit CPU specified are put 8534 on the local CPU. This guarantee is no longer true 8535 and while local CPU is still preferred work items 8536 may be put on foreign CPUs. This debug option 8537 forces round-robin CPU selection to flush out 8538 usages which depend on the now broken guarantee. 8539 When enabled, memory and cache locality will be 8540 impacted. 8541 8542 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8543 Type) of ioremap_wc(). 8544 8545 on - Enable writecombine, use WUC for ioremap_wc() 8546 off - Disable writecombine, use SUC for ioremap_wc() 8547 8548 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8549 default x2apic cluster mode on platforms 8550 supporting x2apic. 8551 8552 xen_512gb_limit [KNL,X86-64,XEN] 8553 Restricts the kernel running paravirtualized under Xen 8554 to use only up to 512 GB of RAM. The reason to do so is 8555 crash analysis tools and Xen tools for doing domain 8556 save/restore/migration must be enabled to handle larger 8557 domains. 8558 8559 xen_console_io [XEN,EARLY] 8560 Boolean option to enable/disable the usage of the Xen 8561 console_io hypercalls to read and write to the console. 8562 Mostly useful for debugging and development. 8563 8564 xen_emul_unplug= [HW,X86,XEN,EARLY] 8565 Unplug Xen emulated devices 8566 Format: [unplug0,][unplug1] 8567 ide-disks -- unplug primary master IDE devices 8568 aux-ide-disks -- unplug non-primary-master IDE devices 8569 nics -- unplug network devices 8570 all -- unplug all emulated devices (NICs and IDE disks) 8571 unnecessary -- unplugging emulated devices is 8572 unnecessary even if the host did not respond to 8573 the unplug protocol 8574 never -- do not unplug even if version check succeeds 8575 8576 xen_legacy_crash [X86,XEN,EARLY] 8577 Crash from Xen panic notifier, without executing late 8578 panic() code such as dumping handler. 8579 8580 xen_mc_debug [X86,XEN,EARLY] 8581 Enable multicall debugging when running as a Xen PV guest. 8582 Enabling this feature will reduce performance a little 8583 bit, so it should only be enabled for obtaining extended 8584 debug data in case of multicall errors. 8585 8586 xen_msr_safe= [X86,XEN,EARLY] 8587 Format: <bool> 8588 Select whether to always use non-faulting (safe) MSR 8589 access functions when running as Xen PV guest. The 8590 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8591 8592 xen_nopv [X86] 8593 Disables the PV optimizations forcing the HVM guest to 8594 run as generic HVM guest with no PV drivers. 8595 This option is obsoleted by the "nopv" option, which 8596 has equivalent effect for XEN platform. 8597 8598 xen_no_vector_callback 8599 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8600 event channel interrupts. 8601 8602 xen_scrub_pages= [XEN] 8603 Boolean option to control scrubbing pages before giving them back 8604 to Xen, for use by other domains. Can be also changed at runtime 8605 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8606 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8607 8608 xen_timer_slop= [X86-64,XEN,EARLY] 8609 Set the timer slop (in nanoseconds) for the virtual Xen 8610 timers (default is 100000). This adjusts the minimum 8611 delta of virtualized Xen timers, where lower values 8612 improve timer resolution at the expense of processing 8613 more timer interrupts. 8614 8615 xen.balloon_boot_timeout= [XEN] 8616 The time (in seconds) to wait before giving up to boot 8617 in case initial ballooning fails to free enough memory. 8618 Applies only when running as HVM or PVH guest and 8619 started with less memory configured than allowed at 8620 max. Default is 180. 8621 8622 xen.event_eoi_delay= [XEN] 8623 How long to delay EOI handling in case of event 8624 storms (jiffies). Default is 10. 8625 8626 xen.event_loop_timeout= [XEN] 8627 After which time (jiffies) the event handling loop 8628 should start to delay EOI handling. Default is 2. 8629 8630 xen.fifo_events= [XEN] 8631 Boolean parameter to disable using fifo event handling 8632 even if available. Normally fifo event handling is 8633 preferred over the 2-level event handling, as it is 8634 fairer and the number of possible event channels is 8635 much higher. Default is on (use fifo events). 8636 8637 xirc2ps_cs= [NET,PCMCIA] 8638 Format: 8639 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8640 8641 xive= [PPC] 8642 By default on POWER9 and above, the kernel will 8643 natively use the XIVE interrupt controller. This option 8644 allows the fallback firmware mode to be used: 8645 8646 off Fallback to firmware control of XIVE interrupt 8647 controller on both pseries and powernv 8648 platforms. Only useful on POWER9 and above. 8649 8650 xive.store-eoi=off [PPC] 8651 By default on POWER10 and above, the kernel will use 8652 stores for EOI handling when the XIVE interrupt mode 8653 is active. This option allows the XIVE driver to use 8654 loads instead, as on POWER9. 8655 8656 xhci-hcd.quirks [USB,KNL] 8657 A hex value specifying bitmask with supplemental xhci 8658 host controller quirks. Meaning of each bit can be 8659 consulted in header drivers/usb/host/xhci.h. 8660 8661 xmon [PPC,EARLY] 8662 Format: { early | on | rw | ro | off } 8663 Controls if xmon debugger is enabled. Default is off. 8664 Passing only "xmon" is equivalent to "xmon=early". 8665 early Call xmon as early as possible on boot; xmon 8666 debugger is called from setup_arch(). 8667 on xmon debugger hooks will be installed so xmon 8668 is only called on a kernel crash. Default mode, 8669 i.e. either "ro" or "rw" mode, is controlled 8670 with CONFIG_XMON_DEFAULT_RO_MODE. 8671 rw xmon debugger hooks will be installed so xmon 8672 is called only on a kernel crash, mode is write, 8673 meaning SPR registers, memory and, other data 8674 can be written using xmon commands. 8675 ro same as "rw" option above but SPR registers, 8676 memory, and other data can't be written using 8677 xmon commands. 8678 off xmon is disabled. 8679