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 For ARM64, ONLY "acpi=off", "acpi=on", "acpi=force" or 129 "acpi=nospcr" are available 130 For RISCV64, ONLY "acpi=off", "acpi=on" or "acpi=force" 131 are available 132 133 See also Documentation/power/runtime_pm.rst, pci=noacpi 134 135 acpi_apic_instance= [ACPI,IOAPIC,EARLY] 136 Format: <int> 137 2: use 2nd APIC table, if available 138 1,0: use 1st APIC table 139 default: 0 140 141 acpi_backlight= [HW,ACPI] 142 { vendor | video | native | none } 143 If set to vendor, prefer vendor-specific driver 144 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 145 of the ACPI video.ko driver. 146 If set to video, use the ACPI video.ko driver. 147 If set to native, use the device's native backlight mode. 148 If set to none, disable the ACPI backlight interface. 149 150 acpi_force_32bit_fadt_addr [ACPI,EARLY] 151 force FADT to use 32 bit addresses rather than the 152 64 bit X_* addresses. Some firmware have broken 64 153 bit addresses for force ACPI ignore these and use 154 the older legacy 32 bit addresses. 155 156 acpica_no_return_repair [HW, ACPI] 157 Disable AML predefined validation mechanism 158 This mechanism can repair the evaluation result to make 159 the return objects more ACPI specification compliant. 160 This option is useful for developers to identify the 161 root cause of an AML interpreter issue when the issue 162 has something to do with the repair mechanism. 163 164 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 165 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 166 Format: <int> 167 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 168 debug output. Bits in debug_layer correspond to a 169 _COMPONENT in an ACPI source file, e.g., 170 #define _COMPONENT ACPI_EVENTS 171 Bits in debug_level correspond to a level in 172 ACPI_DEBUG_PRINT statements, e.g., 173 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 174 The debug_level mask defaults to "info". See 175 Documentation/firmware-guide/acpi/debug.rst for more information about 176 debug layers and levels. 177 178 Enable processor driver info messages: 179 acpi.debug_layer=0x20000000 180 Enable AML "Debug" output, i.e., stores to the Debug 181 object while interpreting AML: 182 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 183 Enable all messages related to ACPI hardware: 184 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 185 186 Some values produce so much output that the system is 187 unusable. The "log_buf_len" parameter may be useful 188 if you need to capture more output. 189 190 acpi_enforce_resources= [ACPI] 191 { strict | lax | no } 192 Check for resource conflicts between native drivers 193 and ACPI OperationRegions (SystemIO and SystemMemory 194 only). IO ports and memory declared in ACPI might be 195 used by the ACPI subsystem in arbitrary AML code and 196 can interfere with legacy drivers. 197 strict (default): access to resources claimed by ACPI 198 is denied; legacy drivers trying to access reserved 199 resources will fail to bind to device using them. 200 lax: access to resources claimed by ACPI is allowed; 201 legacy drivers trying to access reserved resources 202 will bind successfully but a warning message is logged. 203 no: ACPI OperationRegions are not marked as reserved, 204 no further checks are performed. 205 206 acpi_force_table_verification [HW,ACPI,EARLY] 207 Enable table checksum verification during early stage. 208 By default, this is disabled due to x86 early mapping 209 size limitation. 210 211 acpi_irq_balance [HW,ACPI] 212 ACPI will balance active IRQs 213 default in APIC mode 214 215 acpi_irq_nobalance [HW,ACPI] 216 ACPI will not move active IRQs (default) 217 default in PIC mode 218 219 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 220 Format: <irq>,<irq>... 221 222 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 223 use by PCI 224 Format: <irq>,<irq>... 225 226 acpi_mask_gpe= [HW,ACPI] 227 Due to the existence of _Lxx/_Exx, some GPEs triggered 228 by unsupported hardware/firmware features can result in 229 GPE floodings that cannot be automatically disabled by 230 the GPE dispatcher. 231 This facility can be used to prevent such uncontrolled 232 GPE floodings. 233 Format: <byte> or <bitmap-list> 234 235 acpi_no_auto_serialize [HW,ACPI] 236 Disable auto-serialization of AML methods 237 AML control methods that contain the opcodes to create 238 named objects will be marked as "Serialized" by the 239 auto-serialization feature. 240 This feature is enabled by default. 241 This option allows to turn off the feature. 242 243 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 244 kernels. 245 246 acpi_no_static_ssdt [HW,ACPI,EARLY] 247 Disable installation of static SSDTs at early boot time 248 By default, SSDTs contained in the RSDT/XSDT will be 249 installed automatically and they will appear under 250 /sys/firmware/acpi/tables. 251 This option turns off this feature. 252 Note that specifying this option does not affect 253 dynamic table installation which will install SSDT 254 tables to /sys/firmware/acpi/tables/dynamic. 255 256 acpi_no_watchdog [HW,ACPI,WDT] 257 Ignore the ACPI-based watchdog interface (WDAT) and let 258 a native driver control the watchdog device instead. 259 260 acpi_rsdp= [ACPI,EFI,KEXEC,EARLY] 261 Pass the RSDP address to the kernel, mostly used 262 on machines running EFI runtime service to boot the 263 second kernel for kdump. 264 265 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 266 Format: To spoof as Windows 98: ="Microsoft Windows" 267 268 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 269 of 2 which is mandated by ACPI 6) as the supported ACPI 270 specification revision (when using this switch, it may 271 be necessary to carry out a cold reboot _twice_ in a 272 row to make it take effect on the platform firmware). 273 274 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 275 acpi_osi="string1" # add string1 276 acpi_osi="!string2" # remove string2 277 acpi_osi=!* # remove all strings 278 acpi_osi=! # disable all built-in OS vendor 279 strings 280 acpi_osi=!! # enable all built-in OS vendor 281 strings 282 acpi_osi= # disable all strings 283 284 'acpi_osi=!' can be used in combination with single or 285 multiple 'acpi_osi="string1"' to support specific OS 286 vendor string(s). Note that such command can only 287 affect the default state of the OS vendor strings, thus 288 it cannot affect the default state of the feature group 289 strings and the current state of the OS vendor strings, 290 specifying it multiple times through kernel command line 291 is meaningless. This command is useful when one do not 292 care about the state of the feature group strings which 293 should be controlled by the OSPM. 294 Examples: 295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 297 can make '_OSI("Windows 2000")' TRUE. 298 299 'acpi_osi=' cannot be used in combination with other 300 'acpi_osi=' command lines, the _OSI method will not 301 exist in the ACPI namespace. NOTE that such command can 302 only affect the _OSI support state, thus specifying it 303 multiple times through kernel command line is also 304 meaningless. 305 Examples: 306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 307 FALSE. 308 309 'acpi_osi=!*' can be used in combination with single or 310 multiple 'acpi_osi="string1"' to support specific 311 string(s). Note that such command can affect the 312 current state of both the OS vendor strings and the 313 feature group strings, thus specifying it multiple times 314 through kernel command line is meaningful. But it may 315 still not able to affect the final state of a string if 316 there are quirks related to this string. This command 317 is useful when one want to control the state of the 318 feature group strings to debug BIOS issues related to 319 the OSPM features. 320 Examples: 321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 322 '_OSI("Module Device")' FALSE. 323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 324 '_OSI("Module Device")' TRUE. 325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 326 equivalent to 327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 328 and 329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 330 they all will make '_OSI("Windows 2000")' TRUE. 331 332 acpi_pm_good [X86] 333 Override the pmtimer bug detection: force the kernel 334 to assume that this machine's pmtimer latches its value 335 and always returns good values. 336 337 acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode 338 Format: { level | edge | high | low } 339 340 acpi_skip_timer_override [HW,ACPI,EARLY] 341 Recognize and ignore IRQ0/pin2 Interrupt Override. 342 For broken nForce2 BIOS resulting in XT-PIC timer. 343 344 acpi_sleep= [HW,ACPI] Sleep options 345 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 346 s4_nohwsig, old_ordering, nonvs, 347 sci_force_enable, nobl } 348 See Documentation/power/video.rst for information on 349 s3_bios and s3_mode. 350 s3_beep is for debugging; it makes the PC's speaker beep 351 as soon as the kernel's real-mode entry point is called. 352 s4_hwsig causes the kernel to check the ACPI hardware 353 signature during resume from hibernation, and gracefully 354 refuse to resume if it has changed. This complies with 355 the ACPI specification but not with reality, since 356 Windows does not do this and many laptops do change it 357 on docking. So the default behaviour is to allow resume 358 and simply warn when the signature changes, unless the 359 s4_hwsig option is enabled. 360 s4_nohwsig prevents ACPI hardware signature from being 361 used (or even warned about) during resume. 362 old_ordering causes the ACPI 1.0 ordering of the _PTS 363 control method, with respect to putting devices into 364 low power states, to be enforced (the ACPI 2.0 ordering 365 of _PTS is used by default). 366 nonvs prevents the kernel from saving/restoring the 367 ACPI NVS memory during suspend/hibernation and resume. 368 sci_force_enable causes the kernel to set SCI_EN directly 369 on resume from S1/S3 (which is against the ACPI spec, 370 but some broken systems don't work without it). 371 nobl causes the internal blacklist of systems known to 372 behave incorrectly in some ways with respect to system 373 suspend and resume to be ignored (use wisely). 374 375 acpi_use_timer_override [HW,ACPI,EARLY] 376 Use timer override. For some broken Nvidia NF5 boards 377 that require a timer override, but don't have HPET 378 379 add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in 380 kernel's map of available physical RAM. 381 382 agp= [AGP] 383 { off | try_unsupported } 384 off: disable AGP support 385 try_unsupported: try to drive unsupported chipsets 386 (may crash computer or cause data corruption) 387 388 ALSA [HW,ALSA] 389 See Documentation/sound/alsa-configuration.rst 390 391 alignment= [KNL,ARM] 392 Allow the default userspace alignment fault handler 393 behaviour to be specified. Bit 0 enables warnings, 394 bit 1 enables fixups, and bit 2 sends a segfault. 395 396 align_va_addr= [X86-64] 397 Align virtual addresses by clearing slice [14:12] when 398 allocating a VMA at process creation time. This option 399 gives you up to 3% performance improvement on AMD F15h 400 machines (where it is enabled by default) for a 401 CPU-intensive style benchmark, and it can vary highly in 402 a microbenchmark depending on workload and compiler. 403 404 32: only for 32-bit processes 405 64: only for 64-bit processes 406 on: enable for both 32- and 64-bit processes 407 off: disable for both 32- and 64-bit processes 408 409 alloc_snapshot [FTRACE] 410 Allocate the ftrace snapshot buffer on boot up when the 411 main buffer is allocated. This is handy if debugging 412 and you need to use tracing_snapshot() on boot up, and 413 do not want to use tracing_snapshot_alloc() as it needs 414 to be done where GFP_KERNEL allocations are allowed. 415 416 allow_mismatched_32bit_el0 [ARM64,EARLY] 417 Allow execve() of 32-bit applications and setting of the 418 PER_LINUX32 personality on systems where only a strict 419 subset of the CPUs support 32-bit EL0. When this 420 parameter is present, the set of CPUs supporting 32-bit 421 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 422 and hot-unplug operations may be restricted. 423 424 See Documentation/arch/arm64/asymmetric-32bit.rst for more 425 information. 426 427 amd_iommu= [HW,X86-64] 428 Pass parameters to the AMD IOMMU driver in the system. 429 Possible values are: 430 fullflush - Deprecated, equivalent to iommu.strict=1 431 off - do not initialize any AMD IOMMU found in 432 the system 433 force_isolation - Force device isolation for all 434 devices. The IOMMU driver is not 435 allowed anymore to lift isolation 436 requirements as needed. This option 437 does not override iommu=pt 438 force_enable - Force enable the IOMMU on platforms known 439 to be buggy with IOMMU enabled. Use this 440 option with care. 441 pgtbl_v1 - Use v1 page table for DMA-API (Default). 442 pgtbl_v2 - Use v2 page table for DMA-API. 443 irtcachedis - Disable Interrupt Remapping Table (IRT) caching. 444 nohugepages - Limit page-sizes used for v1 page-tables 445 to 4 KiB. 446 v2_pgsizes_only - Limit page-sizes used for v1 page-tables 447 to 4KiB/2Mib/1GiB. 448 449 450 amd_iommu_dump= [HW,X86-64] 451 Enable AMD IOMMU driver option to dump the ACPI table 452 for AMD IOMMU. With this option enabled, AMD IOMMU 453 driver will print ACPI tables for AMD IOMMU during 454 IOMMU initialization. 455 456 amd_iommu_intr= [HW,X86-64] 457 Specifies one of the following AMD IOMMU interrupt 458 remapping modes: 459 legacy - Use legacy interrupt remapping mode. 460 vapic - Use virtual APIC mode, which allows IOMMU 461 to inject interrupts directly into guest. 462 This mode requires kvm-amd.avic=1. 463 (Default when IOMMU HW support is present.) 464 465 amd_pstate= [X86,EARLY] 466 disable 467 Do not enable amd_pstate as the default 468 scaling driver for the supported processors 469 passive 470 Use amd_pstate with passive mode as a scaling driver. 471 In this mode autonomous selection is disabled. 472 Driver requests a desired performance level and platform 473 tries to match the same performance level if it is 474 satisfied by guaranteed performance level. 475 active 476 Use amd_pstate_epp driver instance as the scaling driver, 477 driver provides a hint to the hardware if software wants 478 to bias toward performance (0x0) or energy efficiency (0xff) 479 to the CPPC firmware. then CPPC power algorithm will 480 calculate the runtime workload and adjust the realtime cores 481 frequency. 482 guided 483 Activate guided autonomous mode. Driver requests minimum and 484 maximum performance level and the platform autonomously 485 selects a performance level in this range and appropriate 486 to the current workload. 487 488 amd_prefcore= 489 [X86] 490 disable 491 Disable amd-pstate preferred core. 492 493 amijoy.map= [HW,JOY] Amiga joystick support 494 Map of devices attached to JOY0DAT and JOY1DAT 495 Format: <a>,<b> 496 See also Documentation/input/joydev/joystick.rst 497 498 analog.map= [HW,JOY] Analog joystick and gamepad support 499 Specifies type or capabilities of an analog joystick 500 connected to one of 16 gameports 501 Format: <type1>,<type2>,..<type16> 502 503 apc= [HW,SPARC] 504 Power management functions (SPARCstation-4/5 + deriv.) 505 Format: noidle 506 Disable APC CPU standby support. SPARCstation-Fox does 507 not play well with APC CPU idle - disable it if you have 508 APC and your system crashes randomly. 509 510 apic [APIC,X86-64] Use IO-APIC. Default. 511 512 apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller 513 Change the output verbosity while booting 514 Format: { quiet (default) | verbose | debug } 515 Change the amount of debugging information output 516 when initialising the APIC and IO-APIC components. 517 518 apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting 519 Format: { bsp (default) | all | none } 520 bsp: External NMI is delivered only to CPU 0 521 all: External NMIs are broadcast to all CPUs as a 522 backup of CPU 0 523 none: External NMI is masked for all CPUs. This is 524 useful so that a dump capture kernel won't be 525 shot down by NMI 526 527 apicpmtimer Do APIC timer calibration using the pmtimer. Implies 528 apicmaintimer. Useful when your PIT timer is totally 529 broken. 530 531 autoconf= [IPV6] 532 See Documentation/networking/ipv6.rst. 533 534 apm= [APM] Advanced Power Management 535 See header of arch/x86/kernel/apm_32.c. 536 537 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 538 Format: { "0" | "1" } 539 See security/apparmor/Kconfig help text 540 0 -- disable. 541 1 -- enable. 542 Default value is set via kernel config option. 543 544 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 545 Format: <io>,<irq>,<nodeID> 546 547 arm64.no32bit_el0 [ARM64] Unconditionally disable the execution of 548 32 bit applications. 549 550 arm64.nobti [ARM64] Unconditionally disable Branch Target 551 Identification support 552 553 arm64.nogcs [ARM64] Unconditionally disable Guarded Control Stack 554 support 555 556 arm64.nomops [ARM64] Unconditionally disable Memory Copy and Memory 557 Set instructions support 558 559 arm64.nompam [ARM64] Unconditionally disable Memory Partitioning And 560 Monitoring support 561 562 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 563 support 564 565 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 566 support 567 568 arm64.nosme [ARM64] Unconditionally disable Scalable Matrix 569 Extension support 570 571 arm64.nosve [ARM64] Unconditionally disable Scalable Vector 572 Extension support 573 574 ataflop= [HW,M68k] 575 576 atarimouse= [HW,MOUSE] Atari Mouse 577 578 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 579 EzKey and similar keyboards 580 581 atkbd.reset= [HW] Reset keyboard during initialization 582 583 atkbd.set= [HW] Select keyboard code set 584 Format: <int> (2 = AT (default), 3 = PS/2) 585 586 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 587 keyboards 588 589 atkbd.softraw= [HW] Choose between synthetic and real raw mode 590 Format: <bool> (0 = real, 1 = synthetic (default)) 591 592 atkbd.softrepeat= [HW] 593 Use software keyboard repeat 594 595 audit= [KNL] Enable the audit sub-system 596 Format: { "0" | "1" | "off" | "on" } 597 0 | off - kernel audit is disabled and can not be 598 enabled until the next reboot 599 unset - kernel audit is initialized but disabled and 600 will be fully enabled by the userspace auditd. 601 1 | on - kernel audit is initialized and partially 602 enabled, storing at most audit_backlog_limit 603 messages in RAM until it is fully enabled by the 604 userspace auditd. 605 Default: unset 606 607 audit_backlog_limit= [KNL] Set the audit queue size limit. 608 Format: <int> (must be >=0) 609 Default: 64 610 611 bau= [X86_UV] Enable the BAU on SGI UV. The default 612 behavior is to disable the BAU (i.e. bau=0). 613 Format: { "0" | "1" } 614 0 - Disable the BAU. 615 1 - Enable the BAU. 616 unset - Disable the BAU. 617 618 baycom_epp= [HW,AX25] 619 Format: <io>,<mode> 620 621 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 622 Format: <io>,<mode> 623 See header of drivers/net/hamradio/baycom_par.c. 624 625 baycom_ser_fdx= [HW,AX25] 626 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 627 Format: <io>,<irq>,<mode>[,<baud>] 628 See header of drivers/net/hamradio/baycom_ser_fdx.c. 629 630 baycom_ser_hdx= [HW,AX25] 631 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 632 Format: <io>,<irq>,<mode> 633 See header of drivers/net/hamradio/baycom_ser_hdx.c. 634 635 bdev_allow_write_mounted= 636 Format: <bool> 637 Control the ability to open a mounted block device 638 for writing, i.e., allow / disallow writes that bypass 639 the FS. This was implemented as a means to prevent 640 fuzzers from crashing the kernel by overwriting the 641 metadata underneath a mounted FS without its awareness. 642 This also prevents destructive formatting of mounted 643 filesystems by naive storage tooling that don't use 644 O_EXCL. Default is Y and can be changed through the 645 Kconfig option CONFIG_BLK_DEV_WRITE_MOUNTED. 646 647 bert_disable [ACPI] 648 Disable BERT OS support on buggy BIOSes. 649 650 bgrt_disable [ACPI,X86,EARLY] 651 Disable BGRT to avoid flickering OEM logo. 652 653 blkdevparts= Manual partition parsing of block device(s) for 654 embedded devices based on command line input. 655 See Documentation/block/cmdline-partition.rst 656 657 boot_delay= [KNL,EARLY] 658 Milliseconds to delay each printk during boot. 659 Only works if CONFIG_BOOT_PRINTK_DELAY is enabled, 660 and you may also have to specify "lpj=". Boot_delay 661 values larger than 10 seconds (10000) are assumed 662 erroneous and ignored. 663 Format: integer 664 665 bootconfig [KNL,EARLY] 666 Extended command line options can be added to an initrd 667 and this will cause the kernel to look for it. 668 669 See Documentation/admin-guide/bootconfig.rst 670 671 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 672 bttv.radio= Most important insmod options are available as 673 kernel args too. 674 bttv.pll= See Documentation/admin-guide/media/bttv.rst 675 bttv.tuner= 676 677 bulk_remove=off [PPC] This parameter disables the use of the pSeries 678 firmware feature for flushing multiple hpte entries 679 at a time. 680 681 c101= [NET] Moxa C101 synchronous serial card 682 683 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 684 Sometimes CPU hardware bugs make them report the cache 685 size incorrectly. The kernel will attempt work arounds 686 to fix known problems, but for some CPUs it is not 687 possible to determine what the correct size should be. 688 This option provides an override for these situations. 689 690 carrier_timeout= 691 [NET] Specifies amount of time (in seconds) that 692 the kernel should wait for a network carrier. By default 693 it waits 120 seconds. 694 695 ca_keys= [KEYS] This parameter identifies a specific key(s) on 696 the system trusted keyring to be used for certificate 697 trust validation. 698 format: { id:<keyid> | builtin } 699 700 cca= [MIPS,EARLY] Override the kernel pages' cache coherency 701 algorithm. Accepted values range from 0 to 7 702 inclusive. See arch/mips/include/asm/pgtable-bits.h 703 for platform specific values (SB1, Loongson3 and 704 others). 705 706 ccw_timeout_log [S390] 707 See Documentation/arch/s390/common_io.rst for details. 708 709 cfi= [X86-64] Set Control Flow Integrity checking features 710 when CONFIG_FINEIBT is enabled. 711 Format: feature[,feature...] 712 Default: auto 713 714 auto: Use FineIBT if IBT available, otherwise kCFI. 715 Under FineIBT, enable "paranoid" mode when 716 FRED is not available. 717 off: Turn off CFI checking. 718 kcfi: Use kCFI (disable FineIBT). 719 fineibt: Use FineIBT (even if IBT not available). 720 norand: Do not re-randomize CFI hashes. 721 paranoid: Add caller hash checking under FineIBT. 722 bhi: Enable register poisoning to stop speculation 723 across FineIBT. (Disabled by default.) 724 warn: Do not enforce CFI checking: warn only. 725 debug: Report CFI initialization details. 726 727 cgroup_disable= [KNL] Disable a particular controller or optional feature 728 Format: {name of the controller(s) or feature(s) to disable} 729 The effects of cgroup_disable=foo are: 730 - foo isn't auto-mounted if you mount all cgroups in 731 a single hierarchy 732 - foo isn't visible as an individually mountable 733 subsystem 734 - if foo is an optional feature then the feature is 735 disabled and corresponding cgroup files are not 736 created 737 {Currently only "memory" controller deal with this and 738 cut the overhead, others just disable the usage. So 739 only cgroup_disable=memory is actually worthy} 740 Specifying "pressure" disables per-cgroup pressure 741 stall information accounting feature 742 743 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 744 Format: { { controller | "all" | "named" } 745 [,{ controller | "all" | "named" }...] } 746 Like cgroup_disable, but only applies to cgroup v1; 747 the blacklisted controllers remain available in cgroup2. 748 "all" blacklists all controllers and "named" disables 749 named mounts. Specifying both "all" and "named" disables 750 all v1 hierarchies. 751 752 cgroup_v1_proc= [KNL] Show also missing controllers in /proc/cgroups 753 Format: { "true" | "false" } 754 /proc/cgroups lists only v1 controllers by default. 755 This compatibility option enables listing also v2 756 controllers (whose v1 code is not compiled!), so that 757 semi-legacy software can check this file to decide 758 about usage of v2 (sic) controllers. 759 760 cgroup_favordynmods= [KNL] Enable or Disable favordynmods. 761 Format: { "true" | "false" } 762 Defaults to the value of CONFIG_CGROUP_FAVOR_DYNMODS. 763 764 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 765 Format: <string> 766 nosocket -- Disable socket memory accounting. 767 nokmem -- Disable kernel memory accounting. 768 nobpf -- Disable BPF memory accounting. 769 770 check_pages= [MM,EARLY] Enable sanity checking of pages after 771 allocations / before freeing. This adds checks to catch 772 double-frees, use-after-frees, and other sources of 773 page corruption by inspecting page internals (flags, 774 mapcount/refcount, memcg_data, etc.). 775 Format: { "0" | "1" } 776 Default: 0 (1 if CONFIG_DEBUG_VM is set) 777 778 checkreqprot= [SELINUX] Set initial checkreqprot flag value. 779 Format: { "0" | "1" } 780 See security/selinux/Kconfig help text. 781 0 -- check protection applied by kernel (includes 782 any implied execute protection). 783 1 -- check protection requested by application. 784 Default value is set via a kernel config option. 785 Value can be changed at runtime via 786 /sys/fs/selinux/checkreqprot. 787 Setting checkreqprot to 1 is deprecated. 788 789 cio_ignore= [S390] 790 See Documentation/arch/s390/common_io.rst for details. 791 792 clearcpuid=X[,X...] [X86] 793 Disable CPUID feature X for the kernel. See 794 arch/x86/include/asm/cpufeatures.h for the valid bit 795 numbers X. Note the Linux-specific bits are not necessarily 796 stable over kernel options, but the vendor-specific 797 ones should be. 798 X can also be a string as appearing in the flags: line 799 in /proc/cpuinfo which does not have the above 800 instability issue. However, not all features have names 801 in /proc/cpuinfo. 802 Note that using this option will taint your kernel. 803 Also note that user programs calling CPUID directly 804 or using the feature without checking anything 805 will still see it. This just prevents it from 806 being used by the kernel or shown in /proc/cpuinfo. 807 Also note the kernel might malfunction if you disable 808 some critical bits. 809 810 clk_ignore_unused 811 [CLK] 812 Prevents the clock framework from automatically gating 813 clocks that have not been explicitly enabled by a Linux 814 device driver but are enabled in hardware at reset or 815 by the bootloader/firmware. Note that this does not 816 force such clocks to be always-on nor does it reserve 817 those clocks in any way. This parameter is useful for 818 debug and development, but should not be needed on a 819 platform with proper driver support. For more 820 information, see Documentation/driver-api/clk.rst. 821 822 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 823 [Deprecated] 824 Forces specified clocksource (if available) to be used 825 when calculating gettimeofday(). If specified 826 clocksource is not available, it defaults to PIT. 827 Format: { pit | tsc | cyclone | pmtmr } 828 829 clocksource= Override the default clocksource 830 Format: <string> 831 Override the default clocksource and use the clocksource 832 with the name specified. 833 Some clocksource names to choose from, depending on 834 the platform: 835 [all] jiffies (this is the base, fallback clocksource) 836 [ACPI] acpi_pm 837 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 838 pxa_timer,timer3,32k_counter,timer0_1 839 [X86-32] pit,hpet,tsc; 840 scx200_hrt on Geode; cyclone on IBM x440 841 [MIPS] MIPS 842 [PARISC] cr16 843 [S390] tod 844 [SH] SuperH 845 [SPARC64] tick 846 [X86-64] hpet,tsc 847 848 clocksource.arm_arch_timer.evtstrm= 849 [ARM,ARM64,EARLY] 850 Format: <bool> 851 Enable/disable the eventstream feature of the ARM 852 architected timer so that code using WFE-based polling 853 loops can be debugged more effectively on production 854 systems. 855 856 clocksource.verify_n_cpus= [KNL] 857 Limit the number of CPUs checked for clocksources 858 marked with CLOCK_SOURCE_VERIFY_PERCPU that 859 are marked unstable due to excessive skew. 860 A negative value says to check all CPUs, while 861 zero says not to check any. Values larger than 862 nr_cpu_ids are silently truncated to nr_cpu_ids. 863 The actual CPUs are chosen randomly, with 864 no replacement if the same CPU is chosen twice. 865 866 clocksource-wdtest.holdoff= [KNL] 867 Set the time in seconds that the clocksource 868 watchdog test waits before commencing its tests. 869 Defaults to zero when built as a module and to 870 10 seconds when built into the kernel. 871 872 cma=nn[MG]@[start[MG][-end[MG]]] 873 [KNL,CMA,EARLY] 874 Sets the size of kernel global memory area for 875 contiguous memory allocations and optionally the 876 placement constraint by the physical address range of 877 memory allocations. A value of 0 disables CMA 878 altogether. For more information, see 879 kernel/dma/contiguous.c 880 881 cma_pernuma=nn[MG] 882 [KNL,CMA,EARLY] 883 Sets the size of kernel per-numa memory area for 884 contiguous memory allocations. A value of 0 disables 885 per-numa CMA altogether. And If this option is not 886 specified, the default value is 0. 887 With per-numa CMA enabled, DMA users on node nid will 888 first try to allocate buffer from the pernuma area 889 which is located in node nid, if the allocation fails, 890 they will fallback to the global default memory area. 891 892 numa_cma=<node>:nn[MG][,<node>:nn[MG]] 893 [KNL,CMA,EARLY] 894 Sets the size of kernel numa memory area for 895 contiguous memory allocations. It will reserve CMA 896 area for the specified node. 897 898 With numa CMA enabled, DMA users on node nid will 899 first try to allocate buffer from the numa area 900 which is located in node nid, if the allocation fails, 901 they will fallback to the global default memory area. 902 903 cmo_free_hint= [PPC] Format: { yes | no } 904 Specify whether pages are marked as being inactive 905 when they are freed. This is used in CMO environments 906 to determine OS memory pressure for page stealing by 907 a hypervisor. 908 Default: yes 909 910 coherent_pool=nn[KMG] [ARM,KNL,EARLY] 911 Sets the size of memory pool for coherent, atomic dma 912 allocations, by default set to 256K. 913 914 com20020= [HW,NET] ARCnet - COM20020 chipset 915 Format: 916 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 917 918 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 919 Format: <io>[,<irq>] 920 921 com90xx= [HW,NET] 922 ARCnet - COM90xx chipset (memory-mapped buffers) 923 Format: <io>[,<irq>[,<memstart>]] 924 925 condev= [HW,S390] console device 926 conmode= 927 928 con3215_drop= [S390,EARLY] 3215 console drop mode. 929 Format: y|n|Y|N|1|0 930 When set to true, drop data on the 3215 console when 931 the console buffer is full. In this case the 932 operator using a 3270 terminal emulator (for example 933 x3270) does not have to enter the clear key for the 934 console output to advance and the kernel to continue. 935 This leads to a much faster boot time when a 3270 936 terminal emulator is active. If no 3270 terminal 937 emulator is used, this parameter has no effect. 938 939 console= [KNL] Output console device and options. 940 941 tty<n> Use the virtual console device <n>. 942 943 ttyS<n>[,options] 944 ttyUSB0[,options] 945 Use the specified serial port. The options are of 946 the form "bbbbpnf", where "bbbb" is the baud rate, 947 "p" is parity ("n", "o", or "e"), "n" is number of 948 bits, and "f" is flow control ("r" for RTS or 949 omit it). Default is "9600n8". 950 951 See Documentation/admin-guide/serial-console.rst for more 952 information. See 953 Documentation/networking/netconsole.rst for an 954 alternative. 955 956 <DEVNAME>:<n>.<n>[,options] 957 Use the specified serial port on the serial core bus. 958 The addressing uses DEVNAME of the physical serial port 959 device, followed by the serial core controller instance, 960 and the serial port instance. The options are the same 961 as documented for the ttyS addressing above. 962 963 The mapping of the serial ports to the tty instances 964 can be viewed with: 965 966 $ ls -d /sys/bus/serial-base/devices/*:*.*/tty/* 967 /sys/bus/serial-base/devices/00:04:0.0/tty/ttyS0 968 969 In the above example, the console can be addressed with 970 console=00:04:0.0. Note that a console addressed this 971 way will only get added when the related device driver 972 is ready. The use of an earlycon parameter in addition to 973 the console may be desired for console output early on. 974 975 uart[8250],io,<addr>[,options] 976 uart[8250],mmio,<addr>[,options] 977 uart[8250],mmio16,<addr>[,options] 978 uart[8250],mmio32,<addr>[,options] 979 uart[8250],0x<addr>[,options] 980 Start an early, polled-mode console on the 8250/16550 981 UART at the specified I/O port or MMIO address, 982 switching to the matching ttyS device later. 983 MMIO inter-register address stride is either 8-bit 984 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 985 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 986 to be equivalent to 'mmio'. 'options' are specified in 987 the same format described for ttyS above; if unspecified, 988 the h/w is not re-initialized. 989 990 hvc<n> Use the hypervisor console device <n>. This is for 991 both Xen and PowerPC hypervisors. 992 993 { null | "" } 994 Use to disable console output, i.e., to have kernel 995 console messages discarded. 996 This must be the only console= parameter used on the 997 kernel command line. 998 999 If the device connected to the port is not a TTY but a braille 1000 device, prepend "brl," before the device type, for instance 1001 console=brl,ttyS0 1002 For now, only VisioBraille is supported. 1003 1004 console_msg_format= 1005 [KNL] Change console messages format 1006 default 1007 By default we print messages on consoles in 1008 "[time stamp] text\n" format (time stamp may not be 1009 printed, depending on CONFIG_PRINTK_TIME or 1010 `printk_time' param). 1011 syslog 1012 Switch to syslog format: "<%u>[time stamp] text\n" 1013 IOW, each message will have a facility and loglevel 1014 prefix. The format is similar to one used by syslog() 1015 syscall, or to executing "dmesg -S --raw" or to reading 1016 from /proc/kmsg. 1017 1018 consoleblank= [KNL] The console blank (screen saver) timeout in 1019 seconds. A value of 0 disables the blank timer. 1020 Defaults to 0. 1021 1022 coredump_filter= 1023 [KNL] Change the default value for 1024 /proc/<pid>/coredump_filter. 1025 See also Documentation/filesystems/proc.rst. 1026 1027 coresight_cpu_debug.enable 1028 [ARM,ARM64] 1029 Format: <bool> 1030 Enable/disable the CPU sampling based debugging. 1031 0: default value, disable debugging 1032 1: enable debugging at boot time 1033 1034 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 1035 Format: 1036 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 1037 1038 cpuidle.off=1 [CPU_IDLE] 1039 disable the cpuidle sub-system 1040 1041 cpuidle.governor= 1042 [CPU_IDLE] Name of the cpuidle governor to use. 1043 1044 cpufreq.off=1 [CPU_FREQ] 1045 disable the cpufreq sub-system 1046 1047 cpufreq.default_governor= 1048 [CPU_FREQ] Name of the default cpufreq governor or 1049 policy to use. This governor must be registered in the 1050 kernel before the cpufreq driver probes. 1051 1052 cpu_init_udelay=N 1053 [X86,EARLY] Delay for N microsec between assert and de-assert 1054 of APIC INIT to start processors. This delay occurs 1055 on every CPU online, such as boot, and resume from suspend. 1056 Default: 10000 1057 1058 cpuhp.parallel= 1059 [SMP] Enable/disable parallel bringup of secondary CPUs 1060 Format: <bool> 1061 Default is enabled if CONFIG_HOTPLUG_PARALLEL=y. Otherwise 1062 the parameter has no effect. 1063 1064 crash_kexec_post_notifiers 1065 Only jump to kdump kernel after running the panic 1066 notifiers and dumping kmsg. This option increases 1067 the risks of a kdump failure, since some panic 1068 notifiers can make the crashed kernel more unstable. 1069 In configurations where kdump may not be reliable, 1070 running the panic notifiers could allow collecting 1071 more data on dmesg, like stack traces from other CPUS 1072 or extra data dumped by panic_print. Note that some 1073 configurations enable this option unconditionally, 1074 like Hyper-V, PowerPC (fadump) and AMD SEV-SNP. 1075 1076 crashkernel=size[KMG][@offset[KMG]] 1077 [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel' 1078 upon panic. This parameter reserves the physical 1079 memory region [offset, offset + size] for that kernel 1080 image. If '@offset' is omitted, then a suitable offset 1081 is selected automatically. 1082 [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region 1083 under 4G first, and fall back to reserve region above 1084 4G when '@offset' hasn't been specified. 1085 See Documentation/admin-guide/kdump/kdump.rst for further details. 1086 1087 crashkernel=range1:size1[,range2:size2,...][@offset] 1088 [KNL] Same as above, but depends on the memory 1089 in the running system. The syntax of range is 1090 start-[end] where start and end are both 1091 a memory unit (amount[KMG]). See also 1092 Documentation/admin-guide/kdump/kdump.rst for an example. 1093 1094 crashkernel=size[KMG],high 1095 [KNL, X86-64, ARM64, RISCV, LoongArch] range could be 1096 above 4G. 1097 Allow kernel to allocate physical memory region from top, 1098 so could be above 4G if system have more than 4G ram 1099 installed. Otherwise memory region will be allocated 1100 below 4G, if available. 1101 It will be ignored if crashkernel=X is specified. 1102 crashkernel=size[KMG],low 1103 [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G. 1104 When crashkernel=X,high is passed, kernel could allocate 1105 physical memory region above 4G, that cause second kernel 1106 crash on system that require some amount of low memory, 1107 e.g. swiotlb requires at least 64M+32K low memory, also 1108 enough extra low memory is needed to make sure DMA buffers 1109 for 32-bit devices won't run out. Kernel would try to allocate 1110 default size of memory below 4G automatically. The default 1111 size is platform dependent. 1112 --> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB) 1113 --> arm64: 128MiB 1114 --> riscv: 128MiB 1115 --> loongarch: 128MiB 1116 This one lets the user specify own low range under 4G 1117 for second kernel instead. 1118 0: to disable low allocation. 1119 It will be ignored when crashkernel=X,high is not used 1120 or memory reserved is below 4G. 1121 crashkernel=size[KMG],cma 1122 [KNL, X86, ppc] Reserve additional crash kernel memory from 1123 CMA. This reservation is usable by the first system's 1124 userspace memory and kernel movable allocations (memory 1125 balloon, zswap). Pages allocated from this memory range 1126 will not be included in the vmcore so this should not 1127 be used if dumping of userspace memory is intended and 1128 it has to be expected that some movable kernel pages 1129 may be missing from the dump. 1130 1131 A standard crashkernel reservation, as described above, 1132 is still needed to hold the crash kernel and initrd. 1133 1134 This option increases the risk of a kdump failure: DMA 1135 transfers configured by the first kernel may end up 1136 corrupting the second kernel's memory. 1137 1138 This reservation method is intended for systems that 1139 can't afford to sacrifice enough memory for standard 1140 crashkernel reservation and where less reliable and 1141 possibly incomplete kdump is preferable to no kdump at 1142 all. 1143 1144 cryptomgr.notests 1145 [KNL] Disable crypto self-tests 1146 1147 cs89x0_dma= [HW,NET] 1148 Format: <dma> 1149 1150 cs89x0_media= [HW,NET] 1151 Format: { rj45 | aui | bnc } 1152 1153 csdlock_debug= [KNL] Enable or disable debug add-ons of cross-CPU 1154 function call handling. When switched on, 1155 additional debug data is printed to the console 1156 in case a hanging CPU is detected, and that 1157 CPU is pinged again in order to try to resolve 1158 the hang situation. The default value of this 1159 option depends on the CSD_LOCK_WAIT_DEBUG_DEFAULT 1160 Kconfig option. 1161 1162 dasd= [HW,NET] 1163 See header of drivers/s390/block/dasd_devmap.c. 1164 1165 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 1166 (one device per port) 1167 Format: <port#>,<type> 1168 See also Documentation/input/devices/joystick-parport.rst 1169 1170 debug [KNL,EARLY] Enable kernel debugging (events log level). 1171 1172 debug_boot_weak_hash 1173 [KNL,EARLY] Enable printing [hashed] pointers early in the 1174 boot sequence. If enabled, we use a weak hash instead 1175 of siphash to hash pointers. Use this option if you are 1176 seeing instances of '(___ptrval___)') and need to see a 1177 value (hashed pointer) instead. Cryptographically 1178 insecure, please do not use on production kernels. 1179 1180 debug_locks_verbose= 1181 [KNL] verbose locking self-tests 1182 Format: <int> 1183 Print debugging info while doing the locking API 1184 self-tests. 1185 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 1186 (no extra messages), setting it to -1 (all bits set) 1187 will print _a_lot_ more information - normally only 1188 useful to lockdep developers. 1189 1190 debug_objects [KNL,EARLY] Enable object debugging 1191 1192 debug_guardpage_minorder= 1193 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this 1194 parameter allows control of the order of pages that will 1195 be intentionally kept free (and hence protected) by the 1196 buddy allocator. Bigger value increase the probability 1197 of catching random memory corruption, but reduce the 1198 amount of memory for normal system use. The maximum 1199 possible value is MAX_PAGE_ORDER/2. Setting this 1200 parameter to 1 or 2 should be enough to identify most 1201 random memory corruption problems caused by bugs in 1202 kernel or driver code when a CPU writes to (or reads 1203 from) a random memory location. Note that there exists 1204 a class of memory corruptions problems caused by buggy 1205 H/W or F/W or by drivers badly programming DMA 1206 (basically when memory is written at bus level and the 1207 CPU MMU is bypassed) which are not detectable by 1208 CONFIG_DEBUG_PAGEALLOC, hence this option will not 1209 help tracking down these problems. 1210 1211 debug_pagealloc= 1212 [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 1213 enables the feature at boot time. By default, it is 1214 disabled and the system will work mostly the same as a 1215 kernel built without CONFIG_DEBUG_PAGEALLOC. 1216 Note: to get most of debug_pagealloc error reports, it's 1217 useful to also enable the page_owner functionality. 1218 on: enable the feature 1219 1220 debugfs= [KNL,EARLY] This parameter enables what is exposed to 1221 userspace and debugfs internal clients. 1222 Format: { on, off } 1223 on: All functions are enabled. 1224 off: Filesystem is not registered and clients 1225 get a -EPERM as result when trying to register files 1226 or directories within debugfs. 1227 This is equivalent of the runtime functionality if 1228 debugfs was not enabled in the kernel at all. 1229 Default value is set in build-time with a kernel configuration. 1230 1231 debugpat [X86] Enable PAT debugging 1232 1233 default_hugepagesz= 1234 [HW] The size of the default HugeTLB page. This is 1235 the size represented by the legacy /proc/ hugepages 1236 APIs. In addition, this is the default hugetlb size 1237 used for shmget(), mmap() and mounting hugetlbfs 1238 filesystems. If not specified, defaults to the 1239 architecture's default huge page size. Huge page 1240 sizes are architecture dependent. See also 1241 Documentation/admin-guide/mm/hugetlbpage.rst. 1242 Format: size[KMG] 1243 1244 deferred_probe_timeout= 1245 [KNL] Debugging option to set a timeout in seconds for 1246 deferred probe to give up waiting on dependencies to 1247 probe. Only specific dependencies (subsystems or 1248 drivers) that have opted in will be ignored. A timeout 1249 of 0 will timeout at the end of initcalls. If the time 1250 out hasn't expired, it'll be restarted by each 1251 successful driver registration. This option will also 1252 dump out devices still on the deferred probe list after 1253 retrying. 1254 1255 delayacct [KNL] Enable per-task delay accounting 1256 1257 dell_smm_hwmon.ignore_dmi= 1258 [HW] Continue probing hardware even if DMI data 1259 indicates that the driver is running on unsupported 1260 hardware. 1261 1262 dell_smm_hwmon.force= 1263 [HW] Activate driver even if SMM BIOS signature does 1264 not match list of supported models and enable otherwise 1265 blacklisted features. 1266 1267 dell_smm_hwmon.power_status= 1268 [HW] Report power status in /proc/i8k 1269 (disabled by default). 1270 1271 dell_smm_hwmon.restricted= 1272 [HW] Allow controlling fans only if SYS_ADMIN 1273 capability is set. 1274 1275 dell_smm_hwmon.fan_mult= 1276 [HW] Factor to multiply fan speed with. 1277 1278 dell_smm_hwmon.fan_max= 1279 [HW] Maximum configurable fan speed. 1280 1281 dfltcc= [HW,S390] 1282 Format: { on | off | def_only | inf_only | always } 1283 on: s390 zlib hardware support for compression on 1284 level 1 and decompression (default) 1285 off: No s390 zlib hardware support 1286 def_only: s390 zlib hardware support for deflate 1287 only (compression on level 1) 1288 inf_only: s390 zlib hardware support for inflate 1289 only (decompression) 1290 always: Same as 'on' but ignores the selected compression 1291 level always using hardware support (used for debugging) 1292 1293 dhash_entries= [KNL] 1294 Set number of hash buckets for dentry cache. 1295 1296 disable_1tb_segments [PPC,EARLY] 1297 Disables the use of 1TB hash page table segments. This 1298 causes the kernel to fall back to 256MB segments which 1299 can be useful when debugging issues that require an SLB 1300 miss to occur. 1301 1302 disable= [IPV6] 1303 See Documentation/networking/ipv6.rst. 1304 1305 disable_radix [PPC,EARLY] 1306 Disable RADIX MMU mode on POWER9 1307 1308 disable_tlbie [PPC] 1309 Disable TLBIE instruction. Currently does not work 1310 with KVM, with HASH MMU, or with coherent accelerators. 1311 1312 disable_ddw [PPC/PSERIES,EARLY] 1313 Disable Dynamic DMA Window support. Use this 1314 to workaround buggy firmware. 1315 1316 disable_ipv6= [IPV6] 1317 See Documentation/networking/ipv6.rst. 1318 1319 disable_mtrr_cleanup [X86,EARLY] 1320 The kernel tries to adjust MTRR layout from continuous 1321 to discrete, to make X server driver able to add WB 1322 entry later. This parameter disables that. 1323 1324 disable_mtrr_trim [X86, Intel and AMD only,EARLY] 1325 By default the kernel will trim any uncacheable 1326 memory out of your available memory pool based on 1327 MTRR settings. This parameter disables that behavior, 1328 possibly causing your machine to run very slowly. 1329 1330 disable_timer_pin_1 [X86,EARLY] 1331 Disable PIN 1 of APIC timer 1332 Can be useful to work around chipset bugs. 1333 1334 dis_ucode_ldr [X86] Disable the microcode loader. 1335 1336 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1337 this option disables the debugging code at boot. 1338 1339 dma_debug_entries=<number> 1340 This option allows to tune the number of preallocated 1341 entries for DMA-API debugging code. One entry is 1342 required per DMA-API allocation. Use this if the 1343 DMA-API debugging code disables itself because the 1344 architectural default is too low. 1345 1346 dma_debug_driver=<driver_name> 1347 With this option the DMA-API debugging driver 1348 filter feature can be enabled at boot time. Just 1349 pass the driver to filter for as the parameter. 1350 The filter can be disabled or changed to another 1351 driver later using sysfs. 1352 1353 reg_file_data_sampling= 1354 [X86] Controls mitigation for Register File Data 1355 Sampling (RFDS) vulnerability. RFDS is a CPU 1356 vulnerability which may allow userspace to infer 1357 kernel data values previously stored in floating point 1358 registers, vector registers, or integer registers. 1359 RFDS only affects Intel Atom processors. 1360 1361 on: Turns ON the mitigation. 1362 off: Turns OFF the mitigation. 1363 1364 This parameter overrides the compile time default set 1365 by CONFIG_MITIGATION_RFDS. Mitigation cannot be 1366 disabled when other VERW based mitigations (like MDS) 1367 are enabled. In order to disable RFDS mitigation all 1368 VERW based mitigations need to be disabled. 1369 1370 For details see: 1371 Documentation/admin-guide/hw-vuln/reg-file-data-sampling.rst 1372 1373 driver_async_probe= [KNL] 1374 List of driver names to be probed asynchronously. * 1375 matches with all driver names. If * is specified, the 1376 rest of the listed driver names are those that will NOT 1377 match the *. 1378 Format: <driver_name1>,<driver_name2>... 1379 1380 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1381 Broken monitors, graphic adapters, KVMs and EDIDless 1382 panels may send no or incorrect EDID data sets. 1383 This parameter allows to specify an EDID data sets 1384 in the /lib/firmware directory that are used instead. 1385 An EDID data set will only be used for a particular 1386 connector, if its name and a colon are prepended to 1387 the EDID name. Each connector may use a unique EDID 1388 data set by separating the files with a comma. An EDID 1389 data set with no connector name will be used for 1390 any connectors not explicitly specified. 1391 1392 dscc4.setup= [NET] 1393 1394 dt_cpu_ftrs= [PPC,EARLY] 1395 Format: {"off" | "known"} 1396 Control how the dt_cpu_ftrs device-tree binding is 1397 used for CPU feature discovery and setup (if it 1398 exists). 1399 off: Do not use it, fall back to legacy cpu table. 1400 known: Do not pass through unknown features to guests 1401 or userspace, only those that the kernel is aware of. 1402 1403 dump_apple_properties [X86] 1404 Dump name and content of EFI device properties on 1405 x86 Macs. Useful for driver authors to determine 1406 what data is available or for reverse-engineering. 1407 1408 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1409 <module>.dyndbg[="val"] 1410 Enable debug messages at boot time. See 1411 Documentation/admin-guide/dynamic-debug-howto.rst 1412 for details. 1413 1414 early_ioremap_debug [KNL,EARLY] 1415 Enable debug messages in early_ioremap support. This 1416 is useful for tracking down temporary early mappings 1417 which are not unmapped. 1418 1419 earlycon= [KNL,EARLY] Output early console device and options. 1420 1421 When used with no options, the early console is 1422 determined by stdout-path property in device tree's 1423 chosen node or the ACPI SPCR table if supported by 1424 the platform. 1425 1426 cdns,<addr>[,options] 1427 Start an early, polled-mode console on a Cadence 1428 (xuartps) serial port at the specified address. Only 1429 supported option is baud rate. If baud rate is not 1430 specified, the serial port must already be setup and 1431 configured. 1432 1433 uart[8250],io,<addr>[,options[,uartclk]] 1434 uart[8250],mmio,<addr>[,options[,uartclk]] 1435 uart[8250],mmio32,<addr>[,options[,uartclk]] 1436 uart[8250],mmio32be,<addr>[,options[,uartclk]] 1437 uart[8250],0x<addr>[,options] 1438 Start an early, polled-mode console on the 8250/16550 1439 UART at the specified I/O port or MMIO address. 1440 MMIO inter-register address stride is either 8-bit 1441 (mmio) or 32-bit (mmio32 or mmio32be). 1442 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1443 to be equivalent to 'mmio'. 'options' are specified 1444 in the same format described for "console=ttyS<n>"; if 1445 unspecified, the h/w is not initialized. 'uartclk' is 1446 the uart clock frequency; if unspecified, it is set 1447 to 'BASE_BAUD' * 16. 1448 1449 pl011,<addr> 1450 pl011,mmio32,<addr> 1451 Start an early, polled-mode console on a pl011 serial 1452 port at the specified address. The pl011 serial port 1453 must already be setup and configured. Options are not 1454 yet supported. If 'mmio32' is specified, then only 1455 the driver will use only 32-bit accessors to read/write 1456 the device registers. 1457 1458 liteuart,<addr> 1459 Start an early console on a litex serial port at the 1460 specified address. The serial port must already be 1461 setup and configured. Options are not yet supported. 1462 1463 meson,<addr> 1464 Start an early, polled-mode console on a meson serial 1465 port at the specified address. The serial port must 1466 already be setup and configured. Options are not yet 1467 supported. 1468 1469 msm_serial,<addr> 1470 Start an early, polled-mode console on an msm serial 1471 port at the specified address. The serial port 1472 must already be setup and configured. Options are not 1473 yet supported. 1474 1475 msm_serial_dm,<addr> 1476 Start an early, polled-mode console on an msm serial 1477 dm port at the specified address. The serial port 1478 must already be setup and configured. Options are not 1479 yet supported. 1480 1481 owl,<addr> 1482 Start an early, polled-mode console on a serial port 1483 of an Actions Semi SoC, such as S500 or S900, at the 1484 specified address. The serial port must already be 1485 setup and configured. Options are not yet supported. 1486 1487 rda,<addr> 1488 Start an early, polled-mode console on a serial port 1489 of an RDA Micro SoC, such as RDA8810PL, at the 1490 specified address. The serial port must already be 1491 setup and configured. Options are not yet supported. 1492 1493 sbi 1494 Use RISC-V SBI (Supervisor Binary Interface) for early 1495 console. 1496 1497 smh Use ARM semihosting calls for early console. 1498 1499 s3c2410,<addr> 1500 s3c2412,<addr> 1501 s3c2440,<addr> 1502 s3c6400,<addr> 1503 s5pv210,<addr> 1504 exynos4210,<addr> 1505 Use early console provided by serial driver available 1506 on Samsung SoCs, requires selecting proper type and 1507 a correct base address of the selected UART port. The 1508 serial port must already be setup and configured. 1509 Options are not yet supported. 1510 1511 lantiq,<addr> 1512 Start an early, polled-mode console on a lantiq serial 1513 (lqasc) port at the specified address. The serial port 1514 must already be setup and configured. Options are not 1515 yet supported. 1516 1517 lpuart,<addr> 1518 lpuart32,<addr> 1519 Use early console provided by Freescale LP UART driver 1520 found on Freescale Vybrid and QorIQ LS1021A processors. 1521 A valid base address must be provided, and the serial 1522 port must already be setup and configured. 1523 1524 ec_imx21,<addr> 1525 ec_imx6q,<addr> 1526 Start an early, polled-mode, output-only console on the 1527 Freescale i.MX UART at the specified address. The UART 1528 must already be setup and configured. 1529 1530 ar3700_uart,<addr> 1531 Start an early, polled-mode console on the 1532 Armada 3700 serial port at the specified 1533 address. The serial port must already be setup 1534 and configured. Options are not yet supported. 1535 1536 qcom_geni,<addr> 1537 Start an early, polled-mode console on a Qualcomm 1538 Generic Interface (GENI) based serial port at the 1539 specified address. The serial port must already be 1540 setup and configured. Options are not yet supported. 1541 1542 efifb,[options] 1543 Start an early, unaccelerated console on the EFI 1544 memory mapped framebuffer (if available). On cache 1545 coherent non-x86 systems that use system memory for 1546 the framebuffer, pass the 'ram' option so that it is 1547 mapped with the correct attributes. 1548 1549 linflex,<addr> 1550 Use early console provided by Freescale LINFlexD UART 1551 serial driver for NXP S32V234 SoCs. A valid base 1552 address must be provided, and the serial port must 1553 already be setup and configured. 1554 1555 earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY] 1556 earlyprintk=vga 1557 earlyprintk=sclp 1558 earlyprintk=xen 1559 earlyprintk=serial[,ttySn[,baudrate]] 1560 earlyprintk=serial[,0x...[,baudrate]] 1561 earlyprintk=ttySn[,baudrate] 1562 earlyprintk=dbgp[debugController#] 1563 earlyprintk=mmio32,membase[,{nocfg|baudrate}] 1564 earlyprintk=pciserial[,force],bus:device.function[,{nocfg|baudrate}] 1565 earlyprintk=xdbc[xhciController#] 1566 earlyprintk=bios 1567 1568 earlyprintk is useful when the kernel crashes before 1569 the normal console is initialized. It is not enabled by 1570 default because it has some cosmetic problems. 1571 1572 Use "nocfg" to skip UART configuration, assume 1573 BIOS/firmware has configured UART correctly. 1574 1575 Append ",keep" to not disable it when the real console 1576 takes over. 1577 1578 Only one of vga, serial, or usb debug port can 1579 be used at a time. 1580 1581 Currently only ttyS0 and ttyS1 may be specified by 1582 name. Other I/O ports may be explicitly specified 1583 on some architectures (x86 and arm at least) by 1584 replacing ttySn with an I/O port address, like this: 1585 earlyprintk=serial,0x1008,115200 1586 You can find the port for a given device in 1587 /proc/tty/driver/serial: 1588 2: uart:ST16650V2 port:00001008 irq:18 ... 1589 1590 Interaction with the standard serial driver is not 1591 very good. 1592 1593 The VGA output is eventually overwritten by 1594 the real console. 1595 1596 The xen option can only be used in Xen domains. 1597 1598 The sclp output can only be used on s390. 1599 1600 The bios output can only be used on SuperH. 1601 1602 The optional "force" to "pciserial" enables use of a 1603 PCI device even when its classcode is not of the 1604 UART class. 1605 1606 edac_report= [HW,EDAC] Control how to report EDAC event 1607 Format: {"on" | "off" | "force"} 1608 on: enable EDAC to report H/W event. May be overridden 1609 by other higher priority error reporting module. 1610 off: disable H/W event reporting through EDAC. 1611 force: enforce the use of EDAC to report H/W event. 1612 default: on. 1613 1614 edd= [EDD] 1615 Format: {"off" | "on" | "skip[mbr]"} 1616 1617 efi= [EFI,EARLY] 1618 Format: { "debug", "disable_early_pci_dma", 1619 "nochunk", "noruntime", "nosoftreserve", 1620 "novamap", "no_disable_early_pci_dma" } 1621 debug: enable misc debug output. 1622 disable_early_pci_dma: disable the busmaster bit on all 1623 PCI bridges while in the EFI boot stub. 1624 nochunk: disable reading files in "chunks" in the EFI 1625 boot stub, as chunking can cause problems with some 1626 firmware implementations. 1627 noruntime : disable EFI runtime services support 1628 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1629 attribute may cause the kernel to reserve the 1630 memory range for a memory mapping driver to 1631 claim. Specify efi=nosoftreserve to disable this 1632 reservation and treat the memory by its base type 1633 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1634 novamap: do not call SetVirtualAddressMap(). 1635 no_disable_early_pci_dma: Leave the busmaster bit set 1636 on all PCI bridges while in the EFI boot stub 1637 1638 efi_no_storage_paranoia [EFI,X86,EARLY] 1639 Using this parameter you can use more than 50% of 1640 your efi variable storage. Use this parameter only if 1641 you are really sure that your UEFI does sane gc and 1642 fulfills the spec otherwise your board may brick. 1643 1644 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1645 that is to be dynamically loaded by Linux. If there are 1646 multiple variables with the same name but with different 1647 vendor GUIDs, all of them will be loaded. See 1648 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1649 1650 1651 eisa_irq_edge= [PARISC,HW] 1652 See header of drivers/parisc/eisa.c. 1653 1654 ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging 1655 Format: ekgdboc=kbd 1656 1657 This is designed to be used in conjunction with 1658 the boot argument: earlyprintk=vga 1659 1660 This parameter works in place of the kgdboc parameter 1661 but can only be used if the backing tty is available 1662 very early in the boot process. For early debugging 1663 via a serial port see kgdboc_earlycon instead. 1664 1665 elanfreq= [X86-32] 1666 See comment before function elanfreq_setup() in 1667 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1668 1669 elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY] 1670 Specifies physical address of start of kernel core 1671 image elf header and optionally the size. Generally 1672 kexec loader will pass this option to capture kernel. 1673 See Documentation/admin-guide/kdump/kdump.rst for details. 1674 1675 enable_mtrr_cleanup [X86,EARLY] 1676 The kernel tries to adjust MTRR layout from continuous 1677 to discrete, to make X server driver able to add WB 1678 entry later. This parameter enables that. 1679 1680 enable_timer_pin_1 [X86] 1681 Enable PIN 1 of APIC timer 1682 Can be useful to work around chipset bugs 1683 (in particular on some ATI chipsets). 1684 The kernel tries to set a reasonable default. 1685 1686 enforcing= [SELINUX] Set initial enforcing status. 1687 Format: {"0" | "1"} 1688 See security/selinux/Kconfig help text. 1689 0 -- permissive (log only, no denials). 1690 1 -- enforcing (deny and log). 1691 Default value is 0. 1692 Value can be changed at runtime via 1693 /sys/fs/selinux/enforce. 1694 1695 erst_disable [ACPI] 1696 Disable Error Record Serialization Table (ERST) 1697 support. 1698 1699 ether= [HW,NET] Ethernet cards parameters 1700 This option is obsoleted by the "netdev=" option, which 1701 has equivalent usage. See its documentation for details. 1702 1703 evm= [EVM] 1704 Format: { "fix" } 1705 Permit 'security.evm' to be updated regardless of 1706 current integrity status. 1707 1708 early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier 1709 stages so cover more early boot allocations. 1710 Please note that as side effect some optimizations 1711 might be disabled to achieve that (e.g. parallelized 1712 memory initialization is disabled) so the boot process 1713 might take longer, especially on systems with a lot of 1714 memory. Available with CONFIG_PAGE_EXTENSION=y. 1715 1716 failslab= 1717 fail_usercopy= 1718 fail_page_alloc= 1719 fail_skb_realloc= 1720 fail_make_request=[KNL] 1721 General fault injection mechanism. 1722 Format: <interval>,<probability>,<space>,<times> 1723 See also Documentation/fault-injection/. 1724 1725 fb_tunnels= [NET] 1726 Format: { initns | none } 1727 See Documentation/admin-guide/sysctl/net.rst for 1728 fb_tunnels_only_for_init_ns 1729 1730 floppy= [HW] 1731 See Documentation/admin-guide/blockdev/floppy.rst. 1732 1733 forcepae [X86-32] 1734 Forcefully enable Physical Address Extension (PAE). 1735 Many Pentium M systems disable PAE but may have a 1736 functionally usable PAE implementation. 1737 Warning: use of this parameter will taint the kernel 1738 and may cause unknown problems. 1739 1740 fred= [X86-64] 1741 Enable/disable Flexible Return and Event Delivery. 1742 Format: { on | off } 1743 on: enable FRED when it's present. 1744 off: disable FRED, the default setting. 1745 1746 ftrace=[tracer] 1747 [FTRACE] will set and start the specified tracer 1748 as early as possible in order to facilitate early 1749 boot debugging. 1750 1751 ftrace_boot_snapshot 1752 [FTRACE] On boot up, a snapshot will be taken of the 1753 ftrace ring buffer that can be read at: 1754 /sys/kernel/tracing/snapshot. 1755 This is useful if you need tracing information from kernel 1756 boot up that is likely to be overridden by user space 1757 start up functionality. 1758 1759 Optionally, the snapshot can also be defined for a tracing 1760 instance that was created by the trace_instance= command 1761 line parameter. 1762 1763 trace_instance=foo,sched_switch ftrace_boot_snapshot=foo 1764 1765 The above will cause the "foo" tracing instance to trigger 1766 a snapshot at the end of boot up. 1767 1768 ftrace_dump_on_oops[=2(orig_cpu) | =<instance>][,<instance> | 1769 ,<instance>=2(orig_cpu)] 1770 [FTRACE] will dump the trace buffers on oops. 1771 If no parameter is passed, ftrace will dump global 1772 buffers of all CPUs, if you pass 2 or orig_cpu, it 1773 will dump only the buffer of the CPU that triggered 1774 the oops, or the specific instance will be dumped if 1775 its name is passed. Multiple instance dump is also 1776 supported, and instances are separated by commas. Each 1777 instance supports only dump on CPU that triggered the 1778 oops by passing 2 or orig_cpu to it. 1779 1780 ftrace_dump_on_oops=foo=orig_cpu 1781 1782 The above will dump only the buffer of "foo" instance 1783 on CPU that triggered the oops. 1784 1785 ftrace_dump_on_oops,foo,bar=orig_cpu 1786 1787 The above will dump global buffer on all CPUs, the 1788 buffer of "foo" instance on all CPUs and the buffer 1789 of "bar" instance on CPU that triggered the oops. 1790 1791 ftrace_filter=[function-list] 1792 [FTRACE] Limit the functions traced by the function 1793 tracer at boot up. function-list is a comma-separated 1794 list of functions. This list can be changed at run 1795 time by the set_ftrace_filter file in the debugfs 1796 tracing directory. 1797 1798 ftrace_notrace=[function-list] 1799 [FTRACE] Do not trace the functions specified in 1800 function-list. This list can be changed at run time 1801 by the set_ftrace_notrace file in the debugfs 1802 tracing directory. 1803 1804 ftrace_graph_filter=[function-list] 1805 [FTRACE] Limit the top level callers functions traced 1806 by the function graph tracer at boot up. 1807 function-list is a comma-separated list of functions 1808 that can be changed at run time by the 1809 set_graph_function file in the debugfs tracing directory. 1810 1811 ftrace_graph_notrace=[function-list] 1812 [FTRACE] Do not trace from the functions specified in 1813 function-list. This list is a comma-separated list of 1814 functions that can be changed at run time by the 1815 set_graph_notrace file in the debugfs tracing directory. 1816 1817 ftrace_graph_max_depth=<uint> 1818 [FTRACE] Used with the function graph tracer. This is 1819 the max depth it will trace into a function. This value 1820 can be changed at run time by the max_graph_depth file 1821 in the tracefs tracing directory. default: 0 (no limit) 1822 1823 fw_devlink= [KNL,EARLY] Create device links between consumer and supplier 1824 devices by scanning the firmware to infer the 1825 consumer/supplier relationships. This feature is 1826 especially useful when drivers are loaded as modules as 1827 it ensures proper ordering of tasks like device probing 1828 (suppliers first, then consumers), supplier boot state 1829 clean up (only after all consumers have probed), 1830 suspend/resume & runtime PM (consumers first, then 1831 suppliers). 1832 Format: { off | permissive | on | rpm } 1833 off -- Don't create device links from firmware info. 1834 permissive -- Create device links from firmware info 1835 but use it only for ordering boot state clean 1836 up (sync_state() calls). 1837 on -- Create device links from firmware info and use it 1838 to enforce probe and suspend/resume ordering. 1839 rpm -- Like "on", but also use to order runtime PM. 1840 1841 fw_devlink.strict=<bool> 1842 [KNL,EARLY] Treat all inferred dependencies as mandatory 1843 dependencies. This only applies for fw_devlink=on|rpm. 1844 Format: <bool> 1845 1846 fw_devlink.sync_state = 1847 [KNL,EARLY] When all devices that could probe have finished 1848 probing, this parameter controls what to do with 1849 devices that haven't yet received their sync_state() 1850 calls. 1851 Format: { strict | timeout } 1852 strict -- Default. Continue waiting on consumers to 1853 probe successfully. 1854 timeout -- Give up waiting on consumers and call 1855 sync_state() on any devices that haven't yet 1856 received their sync_state() calls after 1857 deferred_probe_timeout has expired or by 1858 late_initcall() if !CONFIG_MODULES. 1859 1860 gamecon.map[2|3]= 1861 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1862 support via parallel port (up to 5 devices per port) 1863 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1864 See also Documentation/input/devices/joystick-parport.rst 1865 1866 gamma= [HW,DRM] 1867 1868 gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART 1869 Format: off | on 1870 default: on 1871 1872 gather_data_sampling= 1873 [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS) 1874 mitigation. 1875 1876 Gather Data Sampling is a hardware vulnerability which 1877 allows unprivileged speculative access to data which was 1878 previously stored in vector registers. 1879 1880 This issue is mitigated by default in updated microcode. 1881 The mitigation may have a performance impact but can be 1882 disabled. On systems without the microcode mitigation 1883 disabling AVX serves as a mitigation. 1884 1885 force: Disable AVX to mitigate systems without 1886 microcode mitigation. No effect if the microcode 1887 mitigation is present. Known to cause crashes in 1888 userspace with buggy AVX enumeration. 1889 1890 off: Disable GDS mitigation. 1891 1892 gbpages [X86] Use GB pages for kernel direct mappings. 1893 1894 gcov_persist= [GCOV] When non-zero (default), profiling data for 1895 kernel modules is saved and remains accessible via 1896 debugfs, even when the module is unloaded/reloaded. 1897 When zero, profiling data is discarded and associated 1898 debugfs files are removed at module unload time. 1899 1900 goldfish [X86] Enable the goldfish android emulator platform. 1901 Don't use this when you are not running on the 1902 android emulator 1903 1904 gpio-mockup.gpio_mockup_ranges 1905 [HW] Sets the ranges of gpiochip of for this device. 1906 Format: <start1>,<end1>,<start2>,<end2>... 1907 gpio-mockup.gpio_mockup_named_lines 1908 [HW] Let the driver know GPIO lines should be named. 1909 1910 gpt [EFI] Forces disk with valid GPT signature but 1911 invalid Protective MBR to be treated as GPT. If the 1912 primary GPT is corrupted, it enables the backup/alternate 1913 GPT to be used instead. 1914 1915 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1916 the "Enable 0" bit of the configuration register. 1917 Format: 0 | 1 1918 Default: 0 1919 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1920 the "Enable 0" bit of the configuration register. 1921 Format: 0 | 1 1922 Default: 0 1923 grcan.select= [HW] Select which physical interface to use. 1924 Format: 0 | 1 1925 Default: 0 1926 grcan.txsize= [HW] Sets the size of the tx buffer. 1927 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1928 Default: 1024 1929 grcan.rxsize= [HW] Sets the size of the rx buffer. 1930 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1931 Default: 1024 1932 1933 hardened_usercopy= 1934 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1935 hardening is enabled for this boot. Hardened 1936 usercopy checking is used to protect the kernel 1937 from reading or writing beyond known memory 1938 allocation boundaries as a proactive defense 1939 against bounds-checking flaws in the kernel's 1940 copy_to_user()/copy_from_user() interface. 1941 The default is determined by 1942 CONFIG_HARDENED_USERCOPY_DEFAULT_ON. 1943 on Perform hardened usercopy checks. 1944 off Disable hardened usercopy checks. 1945 1946 hardlockup_all_cpu_backtrace= 1947 [KNL] Should the hard-lockup detector generate 1948 backtraces on all cpus. 1949 Format: 0 | 1 1950 1951 hash_pointers= 1952 [KNL,EARLY] 1953 By default, when pointers are printed to the console 1954 or buffers via the %p format string, that pointer is 1955 "hashed", i.e. obscured by hashing the pointer value. 1956 This is a security feature that hides actual kernel 1957 addresses from unprivileged users, but it also makes 1958 debugging the kernel more difficult since unequal 1959 pointers can no longer be compared. The choices are: 1960 Format: { auto | always | never } 1961 Default: auto 1962 1963 auto - Hash pointers unless slab_debug is enabled. 1964 always - Always hash pointers (even if slab_debug is 1965 enabled). 1966 never - Never hash pointers. This option should only 1967 be specified when debugging the kernel. Do 1968 not use on production kernels. The boot 1969 param "no_hash_pointers" is an alias for 1970 this mode. 1971 1972 hashdist= [KNL,NUMA] Large hashes allocated during boot 1973 are distributed across NUMA nodes. Defaults on 1974 for 64-bit NUMA, off otherwise. 1975 Format: 0 | 1 (for off | on) 1976 1977 hd= [EIDE] (E)IDE hard drive subsystem geometry 1978 Format: <cyl>,<head>,<sect> 1979 1980 hest_disable [ACPI] 1981 Disable Hardware Error Source Table (HEST) support; 1982 corresponding firmware-first mode error processing 1983 logic will be disabled. 1984 1985 hibernate= [HIBERNATION] 1986 noresume Don't check if there's a hibernation image 1987 present during boot. 1988 nocompress Don't compress/decompress hibernation images. 1989 no Disable hibernation and resume. 1990 protect_image Turn on image protection during restoration 1991 (that will set all pages holding image data 1992 during restoration read-only). 1993 1994 hibernate.compressor= [HIBERNATION] Compression algorithm to be 1995 used with hibernation. 1996 Format: { lzo | lz4 } 1997 Default: lzo 1998 1999 lzo: Select LZO compression algorithm to 2000 compress/decompress hibernation image. 2001 2002 lz4: Select LZ4 compression algorithm to 2003 compress/decompress hibernation image. 2004 2005 hibernate.pm_test_delay= 2006 [HIBERNATION] 2007 Sets the number of seconds to remain in a hibernation test 2008 mode before resuming the system (see 2009 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 2010 is set. Default value is 5. 2011 2012 hibernate_compression_threads= 2013 [HIBERNATION] 2014 Set the number of threads used for compressing or decompressing 2015 hibernation images. 2016 2017 Format: <integer> 2018 Default: 3 2019 Minimum: 1 2020 Example: hibernate_compression_threads=4 2021 2022 highmem=nn[KMG] [KNL,BOOT,EARLY] forces the highmem zone to have an exact 2023 size of <nn>. This works even on boxes that have no 2024 highmem otherwise. This also works to reduce highmem 2025 size on bigger boxes. 2026 2027 highres= [KNL] Enable/disable high resolution timer mode. 2028 Valid parameters: "on", "off" 2029 Default: "on" 2030 2031 hlt [BUGS=ARM,SH] 2032 2033 hostname= [KNL,EARLY] Set the hostname (aka UTS nodename). 2034 Format: <string> 2035 This allows setting the system's hostname during early 2036 startup. This sets the name returned by gethostname. 2037 Using this parameter to set the hostname makes it 2038 possible to ensure the hostname is correctly set before 2039 any userspace processes run, avoiding the possibility 2040 that a process may call gethostname before the hostname 2041 has been explicitly set, resulting in the calling 2042 process getting an incorrect result. The string must 2043 not exceed the maximum allowed hostname length (usually 2044 64 characters) and will be truncated otherwise. 2045 2046 hpet= [X86-32,HPET] option to control HPET usage 2047 Format: { enable (default) | disable | force | 2048 verbose } 2049 disable: disable HPET and use PIT instead 2050 force: allow force enabled of undocumented chips (ICH4, 2051 VIA, nVidia) 2052 verbose: show contents of HPET registers during setup 2053 2054 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 2055 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 2056 2057 hugepages= [HW,EARLY] Number of HugeTLB pages to allocate at boot. 2058 If this follows hugepagesz (below), it specifies 2059 the number of pages of hugepagesz to be allocated. 2060 If this is the first HugeTLB parameter on the command 2061 line, it specifies the number of pages to allocate for 2062 the default huge page size. If using node format, the 2063 number of pages to allocate per-node can be specified. 2064 See also Documentation/admin-guide/mm/hugetlbpage.rst. 2065 Format: <integer> or (node format) 2066 <node>:<integer>[,<node>:<integer>] 2067 2068 hugepagesz= 2069 [HW,EARLY] The size of the HugeTLB pages. This is 2070 used in conjunction with hugepages (above) to 2071 allocate huge pages of a specific size at boot. The 2072 pair hugepagesz=X hugepages=Y can be specified once 2073 for each supported huge page size. Huge page sizes 2074 are architecture dependent. See also 2075 Documentation/admin-guide/mm/hugetlbpage.rst. 2076 Format: size[KMG] 2077 2078 hugepage_alloc_threads= 2079 [HW] The number of threads that should be used to 2080 allocate hugepages during boot. This option can be 2081 used to improve system bootup time when allocating 2082 a large amount of huge pages. 2083 The default value is 25% of the available hardware threads. 2084 2085 Note that this parameter only applies to non-gigantic huge pages. 2086 2087 hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation 2088 of gigantic hugepages. Or using node format, the size 2089 of a CMA area per node can be specified. 2090 Format: nn[KMGTPE] or (node format) 2091 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 2092 2093 Reserve a CMA area of given size and allocate gigantic 2094 hugepages using the CMA allocator. If enabled, the 2095 boot-time allocation of gigantic hugepages is skipped. 2096 2097 hugetlb_cma_only= 2098 [HW,CMA,EARLY] When allocating new HugeTLB pages, only 2099 try to allocate from the CMA areas. 2100 2101 This option does nothing if hugetlb_cma= is not also 2102 specified. 2103 2104 hugetlb_free_vmemmap= 2105 [KNL] Requires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 2106 enabled. 2107 Control if HugeTLB Vmemmap Optimization (HVO) is enabled. 2108 Allows heavy hugetlb users to free up some more 2109 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 2110 Format: { on | off (default) } 2111 2112 on: enable HVO 2113 off: disable HVO 2114 2115 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 2116 the default is on. 2117 2118 Note that the vmemmap pages may be allocated from the added 2119 memory block itself when memory_hotplug.memmap_on_memory is 2120 enabled, those vmemmap pages cannot be optimized even if this 2121 feature is enabled. Other vmemmap pages not allocated from 2122 the added memory block itself do not be affected. 2123 2124 hung_task_panic= 2125 [KNL] Number of hung tasks to trigger kernel panic. 2126 Format: <int> 2127 2128 When set to a non-zero value, a kernel panic will be triggered if 2129 the number of detected hung tasks reaches this value. 2130 2131 0: don't panic 2132 1: panic immediately on first hung task 2133 N: panic after N hung tasks are detected in a single scan 2134 2135 The default value is controlled by the 2136 CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time option. The value 2137 selected by this boot parameter can be changed later by the 2138 kernel.hung_task_panic sysctl. 2139 2140 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 2141 terminal devices. Valid values: 0..8 2142 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 2143 If specified, z/VM IUCV HVC accepts connections 2144 from listed z/VM user IDs only. 2145 2146 hv_nopvspin [X86,HYPER_V,EARLY] 2147 Disables the paravirt spinlock optimizations 2148 which allow the hypervisor to 'idle' the guest 2149 on lock contention. 2150 2151 hw_protection= [HW] 2152 Format: reboot | shutdown 2153 2154 Hardware protection action taken on critical events like 2155 overtemperature or imminent voltage loss. 2156 2157 i2c_bus= [HW] Override the default board specific I2C bus speed 2158 or register an additional I2C bus that is not 2159 registered from board initialization code. 2160 Format: 2161 <bus_id>,<clkrate> 2162 2163 i2c_touchscreen_props= [HW,ACPI,X86] 2164 Set device-properties for ACPI-enumerated I2C-attached 2165 touchscreen, to e.g. fix coordinates of upside-down 2166 mounted touchscreens. If you need this option please 2167 submit a drivers/platform/x86/touchscreen_dmi.c patch 2168 adding a DMI quirk for this. 2169 2170 Format: 2171 <ACPI_HW_ID>:<prop_name>=<val>[:prop_name=val][:...] 2172 Where <val> is one of: 2173 Omit "=<val>" entirely Set a boolean device-property 2174 Unsigned number Set a u32 device-property 2175 Anything else Set a string device-property 2176 2177 Examples (split over multiple lines): 2178 i2c_touchscreen_props=GDIX1001:touchscreen-inverted-x: 2179 touchscreen-inverted-y 2180 2181 i2c_touchscreen_props=MSSL1680:touchscreen-size-x=1920: 2182 touchscreen-size-y=1080:touchscreen-inverted-y: 2183 firmware-name=gsl1680-vendor-model.fw:silead,home-button 2184 2185 i8042.debug [HW] Toggle i8042 debug mode 2186 i8042.unmask_kbd_data 2187 [HW] Enable printing of interrupt data from the KBD port 2188 (disabled by default, and as a pre-condition 2189 requires that i8042.debug=1 be enabled) 2190 i8042.direct [HW] Put keyboard port into non-translated mode 2191 i8042.dumbkbd [HW] Pretend that controller can only read data from 2192 keyboard and cannot control its state 2193 (Don't attempt to blink the leds) 2194 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 2195 i8042.nokbd [HW] Don't check/create keyboard port 2196 i8042.noloop [HW] Disable the AUX Loopback command while probing 2197 for the AUX port 2198 i8042.nomux [HW] Don't check presence of an active multiplexing 2199 controller 2200 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 2201 controllers 2202 i8042.notimeout [HW] Ignore timeout condition signalled by controller 2203 i8042.reset [HW] Reset the controller during init, cleanup and 2204 suspend-to-ram transitions, only during s2r 2205 transitions, or never reset 2206 Format: { 1 | Y | y | 0 | N | n } 2207 1, Y, y: always reset controller 2208 0, N, n: don't ever reset controller 2209 Default: only on s2r transitions on x86; most other 2210 architectures force reset to be always executed 2211 i8042.unlock [HW] Unlock (ignore) the keylock 2212 i8042.kbdreset [HW] Reset device connected to KBD port 2213 i8042.probe_defer 2214 [HW] Allow deferred probing upon i8042 probe errors 2215 2216 i810= [HW,DRM] 2217 2218 i915.invert_brightness= 2219 [DRM] Invert the sense of the variable that is used to 2220 set the brightness of the panel backlight. Normally a 2221 brightness value of 0 indicates backlight switched off, 2222 and the maximum of the brightness value sets the backlight 2223 to maximum brightness. If this parameter is set to 0 2224 (default) and the machine requires it, or this parameter 2225 is set to 1, a brightness value of 0 sets the backlight 2226 to maximum brightness, and the maximum of the brightness 2227 value switches the backlight off. 2228 -1 -- never invert brightness 2229 0 -- machine default 2230 1 -- force brightness inversion 2231 2232 ia32_emulation= [X86-64] 2233 Format: <bool> 2234 When true, allows loading 32-bit programs and executing 32-bit 2235 syscalls, essentially overriding IA32_EMULATION_DEFAULT_DISABLED at 2236 boot time. When false, unconditionally disables IA32 emulation. 2237 2238 icn= [HW,ISDN] 2239 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 2240 2241 2242 idle= [X86,EARLY] 2243 Format: idle=poll, idle=halt, idle=nomwait 2244 2245 idle=poll: Don't do power saving in the idle loop 2246 using HLT, but poll for rescheduling event. This will 2247 make the CPUs eat a lot more power, but may be useful 2248 to get slightly better performance in multiprocessor 2249 benchmarks. It also makes some profiling using 2250 performance counters more accurate. Please note that 2251 on systems with MONITOR/MWAIT support (like Intel 2252 EM64T CPUs) this option has no performance advantage 2253 over the normal idle loop. It may also interact badly 2254 with hyperthreading. 2255 2256 idle=halt: Halt is forced to be used for CPU idle. 2257 In such case C2/C3 won't be used again. 2258 2259 idle=nomwait: Disable mwait for CPU C-states 2260 2261 idxd.sva= [HW] 2262 Format: <bool> 2263 Allow force disabling of Shared Virtual Memory (SVA) 2264 support for the idxd driver. By default it is set to 2265 true (1). 2266 2267 idxd.tc_override= [HW] 2268 Format: <bool> 2269 Allow override of default traffic class configuration 2270 for the device. By default it is set to false (0). 2271 2272 ieee754= [MIPS] Select IEEE Std 754 conformance mode 2273 Format: { strict | legacy | 2008 | relaxed | emulated } 2274 Default: strict 2275 2276 Choose which programs will be accepted for execution 2277 based on the IEEE 754 NaN encoding(s) supported by 2278 the FPU and the NaN encoding requested with the value 2279 of an ELF file header flag individually set by each 2280 binary. Hardware implementations are permitted to 2281 support either or both of the legacy and the 2008 NaN 2282 encoding mode. 2283 2284 Available settings are as follows: 2285 strict accept binaries that request a NaN encoding 2286 supported by the FPU 2287 legacy only accept legacy-NaN binaries, if supported 2288 by the FPU 2289 2008 only accept 2008-NaN binaries, if supported 2290 by the FPU 2291 relaxed accept any binaries regardless of whether 2292 supported by the FPU 2293 emulated accept any binaries but enable FPU emulator 2294 if binary mode is unsupported by the FPU. 2295 2296 The FPU emulator is always able to support both NaN 2297 encodings, so if no FPU hardware is present or it has 2298 been disabled with 'nofpu', then the settings of 2299 'legacy' and '2008' strap the emulator accordingly, 2300 'relaxed' straps the emulator for both legacy-NaN and 2301 2008-NaN, whereas 'strict' enables legacy-NaN only on 2302 legacy processors and both NaN encodings on MIPS32 or 2303 MIPS64 CPUs. 2304 2305 The setting for ABS.fmt/NEG.fmt instruction execution 2306 mode generally follows that for the NaN encoding, 2307 except where unsupported by hardware. 2308 2309 ignore_loglevel [KNL,EARLY] 2310 Ignore loglevel setting - this will print /all/ 2311 kernel messages to the console. Useful for debugging. 2312 We also add it as printk module parameter, so users 2313 could change it dynamically, usually by 2314 /sys/module/printk/parameters/ignore_loglevel. 2315 2316 ignore_rlimit_data 2317 Ignore RLIMIT_DATA setting for data mappings, 2318 print warning at first misuse. Can be changed via 2319 /sys/module/kernel/parameters/ignore_rlimit_data. 2320 2321 ihash_entries= [KNL] 2322 Set number of hash buckets for inode cache. 2323 2324 ima_appraise= [IMA] appraise integrity measurements 2325 Format: { "off" | "enforce" | "fix" | "log" } 2326 default: "enforce" 2327 2328 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 2329 The builtin appraise policy appraises all files 2330 owned by uid=0. 2331 2332 ima_canonical_fmt [IMA] 2333 Use the canonical format for the binary runtime 2334 measurements, instead of host native format. 2335 2336 ima_hash= [IMA] 2337 Format: { md5 | sha1 | rmd160 | sha256 | sha384 2338 | sha512 | ... } 2339 default: "sha1" 2340 2341 The list of supported hash algorithms is defined 2342 in crypto/hash_info.h. 2343 2344 ima_policy= [IMA] 2345 The builtin policies to load during IMA setup. 2346 Format: "tcb | appraise_tcb | secure_boot | 2347 fail_securely | critical_data" 2348 2349 The "tcb" policy measures all programs exec'd, files 2350 mmap'd for exec, and all files opened with the read 2351 mode bit set by either the effective uid (euid=0) or 2352 uid=0. 2353 2354 The "appraise_tcb" policy appraises the integrity of 2355 all files owned by root. 2356 2357 The "secure_boot" policy appraises the integrity 2358 of files (eg. kexec kernel image, kernel modules, 2359 firmware, policy, etc) based on file signatures. 2360 2361 The "fail_securely" policy forces file signature 2362 verification failure also on privileged mounted 2363 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 2364 flag. 2365 2366 The "critical_data" policy measures kernel integrity 2367 critical data. 2368 2369 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 2370 Load a policy which meets the needs of the Trusted 2371 Computing Base. This means IMA will measure all 2372 programs exec'd, files mmap'd for exec, and all files 2373 opened for read by uid=0. 2374 2375 ima_template= [IMA] 2376 Select one of defined IMA measurements template formats. 2377 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 2378 "ima-sigv2" } 2379 Default: "ima-ng" 2380 2381 ima_template_fmt= 2382 [IMA] Define a custom template format. 2383 Format: { "field1|...|fieldN" } 2384 2385 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 2386 Format: <min_file_size> 2387 Set the minimal file size for using asynchronous hash. 2388 If left unspecified, ahash usage is disabled. 2389 2390 ahash performance varies for different data sizes on 2391 different crypto accelerators. This option can be used 2392 to achieve the best performance for a particular HW. 2393 2394 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 2395 Format: <bufsize> 2396 Set hashing buffer size. Default: 4k. 2397 2398 ahash performance varies for different chunk sizes on 2399 different crypto accelerators. This option can be used 2400 to achieve best performance for particular HW. 2401 2402 ima= [IMA] Enable or disable IMA 2403 Format: { "off" | "on" } 2404 Default: "on" 2405 Note that disabling IMA is limited to kdump kernel. 2406 2407 indirect_target_selection= [X86,Intel] Mitigation control for Indirect 2408 Target Selection(ITS) bug in Intel CPUs. Updated 2409 microcode is also required for a fix in IBPB. 2410 2411 on: Enable mitigation (default). 2412 off: Disable mitigation. 2413 force: Force the ITS bug and deploy default 2414 mitigation. 2415 vmexit: Only deploy mitigation if CPU is affected by 2416 guest/host isolation part of ITS. 2417 stuff: Deploy RSB-fill mitigation when retpoline is 2418 also deployed. Otherwise, deploy the default 2419 mitigation. 2420 2421 For details see: 2422 Documentation/admin-guide/hw-vuln/indirect-target-selection.rst 2423 2424 init= [KNL] 2425 Format: <full_path> 2426 Run specified binary instead of /sbin/init as init 2427 process. 2428 2429 initcall_debug [KNL] Trace initcalls as they are executed. Useful 2430 for working out where the kernel is dying during 2431 startup. 2432 2433 initcall_blacklist= [KNL] Do not execute a comma-separated list of 2434 initcall functions. Useful for debugging built-in 2435 modules and initcalls. 2436 2437 initramfs_async= [KNL] 2438 Format: <bool> 2439 Default: 1 2440 This parameter controls whether the initramfs 2441 image is unpacked asynchronously, concurrently 2442 with devices being probed and 2443 initialized. This should normally just work, 2444 but as a debugging aid, one can get the 2445 historical behaviour of the initramfs 2446 unpacking being completed before device_ and 2447 late_ initcalls. 2448 2449 initrd= [BOOT,EARLY] Specify the location of the initial ramdisk 2450 2451 initrdmem= [KNL,EARLY] Specify a physical address and size from which to 2452 load the initrd. If an initrd is compiled in or 2453 specified in the bootparams, it takes priority over this 2454 setting. 2455 Format: ss[KMG],nn[KMG] 2456 Default is 0, 0 2457 2458 init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with 2459 zeroes. 2460 Format: 0 | 1 2461 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 2462 2463 init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes. 2464 Format: 0 | 1 2465 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 2466 2467 init_pkru= [X86] Specify the default memory protection keys rights 2468 register contents for all processes. 0x55555554 by 2469 default (disallow access to all but pkey 0). Can 2470 override in debugfs after boot. 2471 2472 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2473 Format: <irq> 2474 2475 int_pln_enable [X86] Enable power limit notification interrupt 2476 2477 integrity_audit=[IMA] 2478 Format: { "0" | "1" } 2479 0 -- basic integrity auditing messages. (Default) 2480 1 -- additional integrity auditing messages. 2481 2482 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2483 on 2484 Enable intel iommu driver. 2485 off 2486 Disable intel iommu driver. 2487 igfx_off [Default Off] 2488 By default, gfx is mapped as normal device. If a gfx 2489 device has a dedicated DMAR unit, the DMAR unit is 2490 bypassed by not enabling DMAR with this option. In 2491 this case, gfx device will use physical address for 2492 DMA. 2493 strict [Default Off] 2494 Deprecated, equivalent to iommu.strict=1. 2495 sp_off [Default Off] 2496 By default, super page will be supported if Intel IOMMU 2497 has the capability. With this option, super page will 2498 not be supported. 2499 sm_on 2500 Enable the Intel IOMMU scalable mode if the hardware 2501 advertises that it has support for the scalable mode 2502 translation. 2503 sm_off 2504 Disallow use of the Intel IOMMU scalable mode. 2505 tboot_noforce [Default Off] 2506 Do not force the Intel IOMMU enabled under tboot. 2507 By default, tboot will force Intel IOMMU on, which 2508 could harm performance of some high-throughput 2509 devices like 40GBit network cards, even if identity 2510 mapping is enabled. 2511 Note that using this option lowers the security 2512 provided by tboot because it makes the system 2513 vulnerable to DMA attacks. 2514 2515 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2516 0 disables intel_idle and fall back on acpi_idle. 2517 1 to 9 specify maximum depth of C-state. 2518 2519 intel_pstate= [X86,EARLY] 2520 disable 2521 Do not enable intel_pstate as the default 2522 scaling driver for the supported processors 2523 active 2524 Use intel_pstate driver to bypass the scaling 2525 governors layer of cpufreq and provides it own 2526 algorithms for p-state selection. There are two 2527 P-state selection algorithms provided by 2528 intel_pstate in the active mode: powersave and 2529 performance. The way they both operate depends 2530 on whether or not the hardware managed P-states 2531 (HWP) feature has been enabled in the processor 2532 and possibly on the processor model. 2533 passive 2534 Use intel_pstate as a scaling driver, but configure it 2535 to work with generic cpufreq governors (instead of 2536 enabling its internal governor). This mode cannot be 2537 used along with the hardware-managed P-states (HWP) 2538 feature. 2539 force 2540 Enable intel_pstate on systems that prohibit it by default 2541 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2542 instead of acpi-cpufreq may disable platform features, such 2543 as thermal controls and power capping, that rely on ACPI 2544 P-States information being indicated to OSPM and therefore 2545 should be used with caution. This option does not work with 2546 processors that aren't supported by the intel_pstate driver 2547 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2548 no_hwp 2549 Do not enable hardware P state control (HWP) 2550 if available. 2551 hwp_only 2552 Only load intel_pstate on systems which support 2553 hardware P state control (HWP) if available. 2554 support_acpi_ppc 2555 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2556 Description Table, specifies preferred power management 2557 profile as "Enterprise Server" or "Performance Server", 2558 then this feature is turned on by default. 2559 per_cpu_perf_limits 2560 Allow per-logical-CPU P-State performance control limits using 2561 cpufreq sysfs interface 2562 no_cas 2563 Do not enable capacity-aware scheduling (CAS) on 2564 hybrid systems 2565 2566 intremap= [X86-64,Intel-IOMMU,EARLY] 2567 on enable Interrupt Remapping (default) 2568 off disable Interrupt Remapping 2569 nosid disable Source ID checking 2570 no_x2apic_optout 2571 BIOS x2APIC opt-out request will be ignored 2572 nopost disable Interrupt Posting 2573 posted_msi 2574 enable MSIs delivered as posted interrupts 2575 2576 iomem= Disable strict checking of access to MMIO memory 2577 strict regions from userspace. 2578 relaxed 2579 2580 iommu= [X86,EARLY] 2581 2582 off 2583 Don't initialize and use any kind of IOMMU. 2584 2585 force 2586 Force the use of the hardware IOMMU even when 2587 it is not actually needed (e.g. because < 3 GB 2588 memory). 2589 2590 noforce 2591 Don't force hardware IOMMU usage when it is not 2592 needed. (default). 2593 2594 biomerge 2595 panic 2596 nopanic 2597 merge 2598 nomerge 2599 2600 soft 2601 Use software bounce buffering (SWIOTLB) (default for 2602 Intel machines). This can be used to prevent the usage 2603 of an available hardware IOMMU. 2604 2605 [X86] 2606 pt 2607 [X86] 2608 nopt 2609 [PPC/POWERNV] 2610 nobypass 2611 Disable IOMMU bypass, using IOMMU for PCI devices. 2612 2613 [X86] 2614 AMD Gart HW IOMMU-specific options: 2615 2616 <size> 2617 Set the size of the remapping area in bytes. 2618 2619 allowed 2620 Overwrite iommu off workarounds for specific chipsets 2621 2622 fullflush 2623 Flush IOMMU on each allocation (default). 2624 2625 nofullflush 2626 Don't use IOMMU fullflush. 2627 2628 memaper[=<order>] 2629 Allocate an own aperture over RAM with size 2630 32MB<<order. (default: order=1, i.e. 64MB) 2631 2632 merge 2633 Do scatter-gather (SG) merging. Implies "force" 2634 (experimental). 2635 2636 nomerge 2637 Don't do scatter-gather (SG) merging. 2638 2639 noaperture 2640 Ask the IOMMU not to touch the aperture for AGP. 2641 2642 noagp 2643 Don't initialize the AGP driver and use full aperture. 2644 2645 panic 2646 Always panic when IOMMU overflows. 2647 2648 iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices. 2649 Format: { "0" | "1" } 2650 0 - Try to allocate a 32-bit DMA address first, before 2651 falling back to the full range if needed. 2652 1 - Allocate directly from the full usable range, 2653 forcing Dual Address Cycle for PCI cards supporting 2654 greater than 32-bit addressing. 2655 2656 iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour 2657 Format: { "0" | "1" } 2658 0 - Lazy mode. 2659 Request that DMA unmap operations use deferred 2660 invalidation of hardware TLBs, for increased 2661 throughput at the cost of reduced device isolation. 2662 Will fall back to strict mode if not supported by 2663 the relevant IOMMU driver. 2664 1 - Strict mode. 2665 DMA unmap operations invalidate IOMMU hardware TLBs 2666 synchronously. 2667 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2668 Note: on x86, strict mode specified via one of the 2669 legacy driver-specific options takes precedence. 2670 2671 iommu.passthrough= 2672 [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default. 2673 Format: { "0" | "1" } 2674 0 - Use IOMMU translation for DMA. 2675 1 - Bypass the IOMMU for DMA. 2676 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2677 2678 io7= [HW] IO7 for Marvel-based Alpha systems 2679 See comment before marvel_specify_io7 in 2680 arch/alpha/kernel/core_marvel.c. 2681 2682 io_delay= [X86,EARLY] I/O delay method 2683 0x80 2684 Standard port 0x80 based delay 2685 0xed 2686 Alternate port 0xed based delay (needed on some systems) 2687 udelay 2688 Simple two microseconds delay 2689 none 2690 No delay 2691 2692 ip= [IP_PNP] 2693 See Documentation/admin-guide/nfs/nfsroot.rst. 2694 2695 ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V 2696 IPC identifiers from 32,768 to 16,777,216. 2697 2698 ipe.enforce= [IPE] 2699 Format: <bool> 2700 Determine whether IPE starts in permissive (0) or 2701 enforce (1) mode. The default is enforce. 2702 2703 ipe.success_audit= 2704 [IPE] 2705 Format: <bool> 2706 Start IPE with success auditing enabled, emitting 2707 an audit event when a binary is allowed. The default 2708 is 0. 2709 2710 irqaffinity= [SMP] Set the default irq affinity mask 2711 The argument is a cpu list, as described above. 2712 2713 irqchip.gicv2_force_probe= 2714 [ARM,ARM64,EARLY] 2715 Format: <bool> 2716 Force the kernel to look for the second 4kB page 2717 of a GICv2 controller even if the memory range 2718 exposed by the device tree is too small. 2719 2720 irqchip.gicv3_nolpi= 2721 [ARM,ARM64,EARLY] 2722 Force the kernel to ignore the availability of 2723 LPIs (and by consequence ITSs). Intended for system 2724 that use the kernel as a bootloader, and thus want 2725 to let secondary kernels in charge of setting up 2726 LPIs. 2727 2728 irqchip.gicv3_pseudo_nmi= [ARM64,EARLY] 2729 Enables support for pseudo-NMIs in the kernel. This 2730 requires the kernel to be built with 2731 CONFIG_ARM64_PSEUDO_NMI. 2732 2733 irqchip.riscv_imsic_noipi 2734 [RISC-V,EARLY] 2735 Force the kernel to not use IMSIC software injected MSIs 2736 as IPIs. Intended for system where IMSIC is trap-n-emulated, 2737 and thus want to reduce MMIO traps when triggering IPIs 2738 to multiple harts. 2739 2740 irqfixup [HW] 2741 When an interrupt is not handled search all handlers 2742 for it. Intended to get systems with badly broken 2743 firmware running. 2744 2745 irqhandler.duration_warn_us= [KNL] 2746 Warn if an IRQ handler exceeds the specified duration 2747 threshold in microseconds. Useful for identifying 2748 long-running IRQs in the system. 2749 2750 irqpoll [HW] 2751 When an interrupt is not handled search all handlers 2752 for it. Also check all handlers each timer 2753 interrupt. Intended to get systems with badly broken 2754 firmware running. 2755 2756 isapnp= [ISAPNP] 2757 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2758 2759 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2760 [Deprecated - use cpusets instead] 2761 Format: [flag-list,]<cpu-list> 2762 2763 Specify one or more CPUs to isolate from disturbances 2764 specified in the flag list (default: domain): 2765 2766 nohz 2767 Disable the tick when a single task runs as well as 2768 disabling other kernel noises like having RCU callbacks 2769 offloaded. This is equivalent to the nohz_full parameter. 2770 2771 A residual 1Hz tick is offloaded to workqueues, which you 2772 need to affine to housekeeping through the global 2773 workqueue's affinity configured via the 2774 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2775 by using the 'domain' flag described below. 2776 2777 NOTE: by default the global workqueue runs on all CPUs, 2778 so to protect individual CPUs the 'cpumask' file has to 2779 be configured manually after bootup. 2780 2781 domain 2782 Isolate from the general SMP balancing and scheduling 2783 algorithms. Note that performing domain isolation this way 2784 is irreversible: it's not possible to bring back a CPU to 2785 the domains once isolated through isolcpus. It's strongly 2786 advised to use cpusets instead to disable scheduler load 2787 balancing through the "cpuset.sched_load_balance" file. 2788 It offers a much more flexible interface where CPUs can 2789 move in and out of an isolated set anytime. 2790 2791 You can move a process onto or off an "isolated" CPU via 2792 the CPU affinity syscalls or cpuset. 2793 <cpu number> begins at 0 and the maximum value is 2794 "number of CPUs in system - 1". 2795 2796 managed_irq 2797 2798 Isolate from being targeted by managed interrupts 2799 which have an interrupt mask containing isolated 2800 CPUs. The affinity of managed interrupts is 2801 handled by the kernel and cannot be changed via 2802 the /proc/irq/* interfaces. 2803 2804 This isolation is best effort and only effective 2805 if the automatically assigned interrupt mask of a 2806 device queue contains isolated and housekeeping 2807 CPUs. If housekeeping CPUs are online then such 2808 interrupts are directed to the housekeeping CPU 2809 so that IO submitted on the housekeeping CPU 2810 cannot disturb the isolated CPU. 2811 2812 If a queue's affinity mask contains only isolated 2813 CPUs then this parameter has no effect on the 2814 interrupt routing decision, though interrupts are 2815 only delivered when tasks running on those 2816 isolated CPUs submit IO. IO submitted on 2817 housekeeping CPUs has no influence on those 2818 queues. 2819 2820 The format of <cpu-list> is described above. 2821 2822 iucv= [HW,NET] 2823 2824 ivrs_ioapic [HW,X86-64] 2825 Provide an override to the IOAPIC-ID<->DEVICE-ID 2826 mapping provided in the IVRS ACPI table. 2827 By default, PCI segment is 0, and can be omitted. 2828 2829 For example, to map IOAPIC-ID decimal 10 to 2830 PCI segment 0x1 and PCI device 00:14.0, 2831 write the parameter as: 2832 ivrs_ioapic=10@0001:00:14.0 2833 2834 Deprecated formats: 2835 * To map IOAPIC-ID decimal 10 to PCI device 00:14.0 2836 write the parameter as: 2837 ivrs_ioapic[10]=00:14.0 2838 * To map IOAPIC-ID decimal 10 to PCI segment 0x1 and 2839 PCI device 00:14.0 write the parameter as: 2840 ivrs_ioapic[10]=0001:00:14.0 2841 2842 ivrs_hpet [HW,X86-64] 2843 Provide an override to the HPET-ID<->DEVICE-ID 2844 mapping provided in the IVRS ACPI table. 2845 By default, PCI segment is 0, and can be omitted. 2846 2847 For example, to map HPET-ID decimal 10 to 2848 PCI segment 0x1 and PCI device 00:14.0, 2849 write the parameter as: 2850 ivrs_hpet=10@0001:00:14.0 2851 2852 Deprecated formats: 2853 * To map HPET-ID decimal 0 to PCI device 00:14.0 2854 write the parameter as: 2855 ivrs_hpet[0]=00:14.0 2856 * To map HPET-ID decimal 10 to PCI segment 0x1 and 2857 PCI device 00:14.0 write the parameter as: 2858 ivrs_ioapic[10]=0001:00:14.0 2859 2860 ivrs_acpihid [HW,X86-64] 2861 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2862 mapping provided in the IVRS ACPI table. 2863 By default, PCI segment is 0, and can be omitted. 2864 2865 For example, to map UART-HID:UID AMD0020:0 to 2866 PCI segment 0x1 and PCI device ID 00:14.5, 2867 write the parameter as: 2868 ivrs_acpihid=AMD0020:0@0001:00:14.5 2869 2870 Deprecated formats: 2871 * To map UART-HID:UID AMD0020:0 to PCI segment is 0, 2872 PCI device ID 00:14.5, write the parameter as: 2873 ivrs_acpihid[00:14.5]=AMD0020:0 2874 * To map UART-HID:UID AMD0020:0 to PCI segment 0x1 and 2875 PCI device ID 00:14.5, write the parameter as: 2876 ivrs_acpihid[0001:00:14.5]=AMD0020:0 2877 2878 js= [HW,JOY] Analog joystick 2879 See Documentation/input/joydev/joystick.rst. 2880 2881 kasan_multi_shot 2882 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2883 report on every invalid memory access. Without this 2884 parameter KASAN will print report only for the first 2885 invalid access. 2886 2887 keep_bootcon [KNL,EARLY] 2888 Do not unregister boot console at start. This is only 2889 useful for debugging when something happens in the window 2890 between unregistering the boot console and initializing 2891 the real console. 2892 2893 keepinitrd [HW,ARM] See retain_initrd. 2894 2895 kernelcore= [KNL,X86,PPC,EARLY] 2896 Format: nn[KMGTPE] | nn% | "mirror" 2897 This parameter specifies the amount of memory usable by 2898 the kernel for non-movable allocations. The requested 2899 amount is spread evenly throughout all nodes in the 2900 system as ZONE_NORMAL. The remaining memory is used for 2901 movable memory in its own zone, ZONE_MOVABLE. In the 2902 event, a node is too small to have both ZONE_NORMAL and 2903 ZONE_MOVABLE, kernelcore memory will take priority and 2904 other nodes will have a larger ZONE_MOVABLE. 2905 2906 ZONE_MOVABLE is used for the allocation of pages that 2907 may be reclaimed or moved by the page migration 2908 subsystem. Note that allocations like PTEs-from-HighMem 2909 still use the HighMem zone if it exists, and the Normal 2910 zone if it does not. 2911 2912 It is possible to specify the exact amount of memory in 2913 the form of "nn[KMGTPE]", a percentage of total system 2914 memory in the form of "nn%", or "mirror". If "mirror" 2915 option is specified, mirrored (reliable) memory is used 2916 for non-movable allocations and remaining memory is used 2917 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2918 are exclusive, so you cannot specify multiple forms. 2919 2920 kfence.burst= [MM,KFENCE] The number of additional successive 2921 allocations to be attempted through KFENCE for each 2922 sample interval. 2923 Format: <unsigned integer> 2924 Default: 0 2925 2926 kfence.check_on_panic= 2927 [MM,KFENCE] Whether to check all KFENCE-managed objects' 2928 canaries on panic. 2929 Format: <bool> 2930 Default: false 2931 2932 kfence.deferrable= 2933 [MM,KFENCE] Whether to use a deferrable timer to trigger 2934 allocations. This avoids forcing CPU wake-ups if the 2935 system is idle, at the risk of a less predictable 2936 sample interval. 2937 Format: <bool> 2938 Default: CONFIG_KFENCE_DEFERRABLE 2939 2940 kfence.sample_interval= 2941 [MM,KFENCE] KFENCE's sample interval in milliseconds. 2942 Format: <unsigned integer> 2943 0 - Disable KFENCE. 2944 >0 - Enabled KFENCE with given sample interval. 2945 Default: CONFIG_KFENCE_SAMPLE_INTERVAL 2946 2947 kfence.skip_covered_thresh= 2948 [MM,KFENCE] If pool utilization reaches this threshold 2949 (pool usage%), KFENCE limits currently covered 2950 allocations of the same source from further filling 2951 up the pool. 2952 Format: <unsigned integer> 2953 Default: 75 2954 2955 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2956 Format: <Controller#>[,poll interval] 2957 The controller # is the number of the ehci usb debug 2958 port as it is probed via PCI. The poll interval is 2959 optional and is the number seconds in between 2960 each poll cycle to the debug port in case you need 2961 the functionality for interrupting the kernel with 2962 gdb or control-c on the dbgp connection. When 2963 not using this parameter you use sysrq-g to break into 2964 the kernel debugger. 2965 2966 kgdboc= [KGDB,HW] kgdb over consoles. 2967 Requires a tty driver that supports console polling, 2968 or a supported polling keyboard driver (non-usb). 2969 Serial only format: <serial_device>[,baud] 2970 keyboard only format: kbd 2971 keyboard and serial format: kbd,<serial_device>[,baud] 2972 Optional Kernel mode setting: 2973 kms, kbd format: kms,kbd 2974 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2975 2976 kgdboc_earlycon= [KGDB,HW,EARLY] 2977 If the boot console provides the ability to read 2978 characters and can work in polling mode, you can use 2979 this parameter to tell kgdb to use it as a backend 2980 until the normal console is registered. Intended to 2981 be used together with the kgdboc parameter which 2982 specifies the normal console to transition to. 2983 2984 The name of the early console should be specified 2985 as the value of this parameter. Note that the name of 2986 the early console might be different than the tty 2987 name passed to kgdboc. It's OK to leave the value 2988 blank and the first boot console that implements 2989 read() will be picked. 2990 2991 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2992 kernel debugger at the earliest opportunity. 2993 2994 kho= [KEXEC,EARLY] 2995 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 2996 Enables or disables Kexec HandOver. 2997 "0" | "off" | "n" - kexec handover is disabled 2998 "1" | "on" | "y" - kexec handover is enabled 2999 3000 kho_scratch= [KEXEC,EARLY] 3001 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 3002 Defines the size of the KHO scratch region. The KHO 3003 scratch regions are physically contiguous memory 3004 ranges that can only be used for non-kernel 3005 allocations. That way, even when memory is heavily 3006 fragmented with handed over memory, the kexeced 3007 kernel will always have enough contiguous ranges to 3008 bootstrap itself. 3009 3010 It is possible to specify the exact amount of 3011 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 3012 where the first parameter defines the size of a low 3013 memory scratch area, the second parameter defines 3014 the size of a global scratch area and the third 3015 parameter defines the size of additional per-node 3016 scratch areas. The form "nn%" defines scale factor 3017 (in percents) of memory that was used during boot. 3018 3019 kmac= [MIPS] Korina ethernet MAC address. 3020 Configure the RouterBoard 532 series on-chip 3021 Ethernet adapter MAC address. 3022 3023 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 3024 Valid arguments: on, off 3025 Default: on 3026 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 3027 the default is off. 3028 3029 kprobe_event=[probe-list] 3030 [FTRACE] Add kprobe events and enable at boot time. 3031 The probe-list is a semicolon delimited list of probe 3032 definitions. Each definition is same as kprobe_events 3033 interface, but the parameters are comma delimited. 3034 For example, to add a kprobe event on vfs_read with 3035 arg1 and arg2, add to the command line; 3036 3037 kprobe_event=p,vfs_read,$arg1,$arg2 3038 3039 See also Documentation/trace/kprobetrace.rst "Kernel 3040 Boot Parameter" section. 3041 3042 kpti= [ARM64,EARLY] Control page table isolation of 3043 user and kernel address spaces. 3044 Default: enabled on cores which need mitigation. 3045 0: force disabled 3046 1: force enabled 3047 3048 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3049 CONFIG_KUNIT to be set to be fully enabled. The 3050 default value can be overridden via 3051 KUNIT_DEFAULT_ENABLED. 3052 Default is 1 (enabled) 3053 3054 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3055 Default is 0 (don't ignore, but inject #GP) 3056 3057 kvm.eager_page_split= 3058 [KVM,X86] Controls whether or not KVM will try to 3059 proactively split all huge pages during dirty logging. 3060 Eager page splitting reduces interruptions to vCPU 3061 execution by eliminating the write-protection faults 3062 and MMU lock contention that would otherwise be 3063 required to split huge pages lazily. 3064 3065 VM workloads that rarely perform writes or that write 3066 only to a small region of VM memory may benefit from 3067 disabling eager page splitting to allow huge pages to 3068 still be used for reads. 3069 3070 The behavior of eager page splitting depends on whether 3071 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3072 disabled, all huge pages in a memslot will be eagerly 3073 split when dirty logging is enabled on that memslot. If 3074 enabled, eager page splitting will be performed during 3075 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3076 cleared. 3077 3078 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3079 3080 Default is Y (on). 3081 3082 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3083 If enabled, KVM will enable virtualization in hardware 3084 when KVM is loaded, and disable virtualization when KVM 3085 is unloaded (if KVM is built as a module). 3086 3087 If disabled, KVM will dynamically enable and disable 3088 virtualization on-demand when creating and destroying 3089 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3090 number of VMs. 3091 3092 Enabling virtualization at module load avoids potential 3093 latency for creation of the 0=>1 VM, as KVM serializes 3094 virtualization enabling across all online CPUs. The 3095 "cost" of enabling virtualization when KVM is loaded, 3096 is that doing so may interfere with using out-of-tree 3097 hypervisors that want to "own" virtualization hardware. 3098 3099 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3100 Default is false (don't support). 3101 3102 kvm.nx_huge_pages= 3103 [KVM] Controls the software workaround for the 3104 X86_BUG_ITLB_MULTIHIT bug. 3105 force : Always deploy workaround. 3106 off : Never deploy workaround. 3107 auto : Deploy workaround based on the presence of 3108 X86_BUG_ITLB_MULTIHIT. 3109 3110 Default is 'auto'. 3111 3112 If the software workaround is enabled for the host, 3113 guests do need not to enable it for nested guests. 3114 3115 kvm.nx_huge_pages_recovery_ratio= 3116 [KVM] Controls how many 4KiB pages are periodically zapped 3117 back to huge pages. 0 disables the recovery, otherwise if 3118 the value is N KVM will zap 1/Nth of the 4KiB pages every 3119 period (see below). The default is 60. 3120 3121 kvm.nx_huge_pages_recovery_period_ms= 3122 [KVM] Controls the time period at which KVM zaps 4KiB pages 3123 back to huge pages. If the value is a non-zero N, KVM will 3124 zap a portion (see ratio above) of the pages every N msecs. 3125 If the value is 0 (the default), KVM will pick a period based 3126 on the ratio, such that a page is zapped after 1 hour on average. 3127 3128 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3129 KVM/SVM. Default is 1 (enabled). 3130 3131 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3132 a.k.a. Two-Dimensional Page Tables. Default is 1 3133 (enabled). Disable by KVM if hardware lacks support 3134 for NPT. 3135 3136 kvm-amd.ciphertext_hiding_asids= 3137 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3138 to SNP private memory from reading ciphertext. Instead, 3139 reads will see constant default values (0xff). 3140 3141 If ciphertext hiding is enabled, the joint SEV-ES and 3142 SEV-SNP ASID space is partitioned into separate SEV-ES 3143 and SEV-SNP ASID ranges, with the SEV-SNP range being 3144 [1..max_snp_asid] and the SEV-ES range being 3145 (max_snp_asid..min_sev_asid), where min_sev_asid is 3146 enumerated by CPUID.0x.8000_001F[EDX]. 3147 3148 A non-zero value enables SEV-SNP ciphertext hiding and 3149 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3150 KVM caps the number of SEV-SNP ASIDs at the maximum 3151 possible value, e.g. specifying -1u will assign all 3152 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3153 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3154 max_snp_asid == min_sev_asid-1, will effectively make 3155 SEV-ES unusable. 3156 3157 kvm-arm.mode= 3158 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3159 operation. 3160 3161 none: Forcefully disable KVM. 3162 3163 nvhe: Standard nVHE-based mode, without support for 3164 protected guests. 3165 3166 protected: Mode with support for guests whose state is 3167 kept private from the host, using VHE or 3168 nVHE depending on HW support. 3169 3170 nested: VHE-based mode with support for nested 3171 virtualization. Requires at least ARMv8.4 3172 hardware (with FEAT_NV2). 3173 3174 Defaults to VHE/nVHE based on hardware support. Setting 3175 mode to "protected" will disable kexec and hibernation 3176 for the host. To force nVHE on VHE hardware, add 3177 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3178 command-line. 3179 "nested" is experimental and should be used with 3180 extreme caution. 3181 3182 kvm-arm.vgic_v3_group0_trap= 3183 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3184 system registers 3185 3186 kvm-arm.vgic_v3_group1_trap= 3187 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3188 system registers 3189 3190 kvm-arm.vgic_v3_common_trap= 3191 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3192 system registers 3193 3194 kvm-arm.vgic_v4_enable= 3195 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3196 injection of LPIs. 3197 3198 kvm-arm.wfe_trap_policy= 3199 [KVM,ARM] Control when to set WFE instruction trap for 3200 KVM VMs. Traps are allowed but not guaranteed by the 3201 CPU architecture. 3202 3203 trap: set WFE instruction trap 3204 3205 notrap: clear WFE instruction trap 3206 3207 kvm-arm.wfi_trap_policy= 3208 [KVM,ARM] Control when to set WFI instruction trap for 3209 KVM VMs. Traps are allowed but not guaranteed by the 3210 CPU architecture. 3211 3212 trap: set WFI instruction trap 3213 3214 notrap: clear WFI instruction trap 3215 3216 kvm_cma_resv_ratio=n [PPC,EARLY] 3217 Reserves given percentage from system memory area for 3218 contiguous memory allocation for KVM hash pagetable 3219 allocation. 3220 By default it reserves 5% of total system memory. 3221 Format: <integer> 3222 Default: 5 3223 3224 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3225 a.k.a. Two-Dimensional Page Tables. Default is 1 3226 (enabled). Disable by KVM if hardware lacks support 3227 for EPT. 3228 3229 kvm-intel.emulate_invalid_guest_state= 3230 [KVM,Intel] Control whether to emulate invalid guest 3231 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3232 as guest state is never invalid for unrestricted 3233 guests. This param doesn't apply to nested guests (L2), 3234 as KVM never emulates invalid L2 guest state. 3235 Default is 1 (enabled). 3236 3237 kvm-intel.flexpriority= 3238 [KVM,Intel] Control KVM's use of FlexPriority feature 3239 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3240 hardware lacks support for it. 3241 3242 kvm-intel.nested= 3243 [KVM,Intel] Control nested virtualization feature in 3244 KVM/VMX. Default is 1 (enabled). 3245 3246 kvm-intel.unrestricted_guest= 3247 [KVM,Intel] Control KVM's use of unrestricted guest 3248 feature (virtualized real and unpaged mode). Default 3249 is 1 (enabled). Disable by KVM if EPT is disabled or 3250 hardware lacks support for it. 3251 3252 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3253 CVE-2018-3620. 3254 3255 Valid arguments: never, cond, always 3256 3257 always: L1D cache flush on every VMENTER. 3258 cond: Flush L1D on VMENTER only when the code between 3259 VMEXIT and VMENTER can leak host memory. 3260 never: Disables the mitigation 3261 3262 Default is cond (do L1 cache flush in specific instances) 3263 3264 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3265 Identification feature (tagged TLBs). Default is 1 3266 (enabled). Disable by KVM if hardware lacks support 3267 for it. 3268 3269 l1d_flush= [X86,INTEL,EARLY] 3270 Control mitigation for L1D based snooping vulnerability. 3271 3272 Certain CPUs are vulnerable to an exploit against CPU 3273 internal buffers which can forward information to a 3274 disclosure gadget under certain conditions. 3275 3276 In vulnerable processors, the speculatively 3277 forwarded data can be used in a cache side channel 3278 attack, to access data to which the attacker does 3279 not have direct access. 3280 3281 This parameter controls the mitigation. The 3282 options are: 3283 3284 on - enable the interface for the mitigation 3285 3286 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3287 affected CPUs 3288 3289 The kernel PTE inversion protection is unconditionally 3290 enabled and cannot be disabled. 3291 3292 full 3293 Provides all available mitigations for the 3294 L1TF vulnerability. Disables SMT and 3295 enables all mitigations in the 3296 hypervisors, i.e. unconditional L1D flush. 3297 3298 SMT control and L1D flush control via the 3299 sysfs interface is still possible after 3300 boot. Hypervisors will issue a warning 3301 when the first VM is started in a 3302 potentially insecure configuration, 3303 i.e. SMT enabled or L1D flush disabled. 3304 3305 full,force 3306 Same as 'full', but disables SMT and L1D 3307 flush runtime control. Implies the 3308 'nosmt=force' command line option. 3309 (i.e. sysfs control of SMT is disabled.) 3310 3311 flush 3312 Leaves SMT enabled and enables the default 3313 hypervisor mitigation, i.e. conditional 3314 L1D flush. 3315 3316 SMT control and L1D flush control via the 3317 sysfs interface is still possible after 3318 boot. Hypervisors will issue a warning 3319 when the first VM is started in a 3320 potentially insecure configuration, 3321 i.e. SMT enabled or L1D flush disabled. 3322 3323 flush,nosmt 3324 3325 Disables SMT and enables the default 3326 hypervisor mitigation. 3327 3328 SMT control and L1D flush control via the 3329 sysfs interface is still possible after 3330 boot. Hypervisors will issue a warning 3331 when the first VM is started in a 3332 potentially insecure configuration, 3333 i.e. SMT enabled or L1D flush disabled. 3334 3335 flush,nowarn 3336 Same as 'flush', but hypervisors will not 3337 warn when a VM is started in a potentially 3338 insecure configuration. 3339 3340 off 3341 Disables hypervisor mitigations and doesn't 3342 emit any warnings. 3343 It also drops the swap size and available 3344 RAM limit restriction on both hypervisor and 3345 bare metal. 3346 3347 Default is 'flush'. 3348 3349 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3350 3351 l2cr= [PPC] 3352 3353 l3cr= [PPC] 3354 3355 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3356 disabled it. 3357 3358 lapic= [X86,APIC] Do not use TSC deadline 3359 value for LAPIC timer one-shot implementation. Default 3360 back to the programmable timer unit in the LAPIC. 3361 Format: notscdeadline 3362 3363 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3364 in C2 power state. 3365 3366 libata.dma= [LIBATA] DMA control 3367 libata.dma=0 Disable all PATA and SATA DMA 3368 libata.dma=1 PATA and SATA Disk DMA only 3369 libata.dma=2 ATAPI (CDROM) DMA only 3370 libata.dma=4 Compact Flash DMA only 3371 Combinations also work, so libata.dma=3 enables DMA 3372 for disks and CDROMs, but not CFs. 3373 3374 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3375 libata.ignore_hpa=0 keep BIOS limits (default) 3376 libata.ignore_hpa=1 ignore limits, using full disk 3377 3378 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3379 when set. 3380 Format: <int> 3381 3382 libata.force= [LIBATA] Force configurations. The format is a comma- 3383 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3384 PORT and DEVICE are decimal numbers matching port, link 3385 or device. Basically, it matches the ATA ID string 3386 printed on console by libata. If the whole ID part is 3387 omitted, the last PORT and DEVICE values are used. If 3388 ID hasn't been specified yet, the configuration applies 3389 to all ports, links and devices. 3390 3391 If only DEVICE is omitted, the parameter applies to 3392 the port and all links and devices behind it. DEVICE 3393 number of 0 either selects the first device or the 3394 first fan-out link behind PMP device. It does not 3395 select the host link. DEVICE number of 15 selects the 3396 host link and device attached to it. 3397 3398 The VAL specifies the configuration to force. As long 3399 as there is no ambiguity, shortcut notation is allowed. 3400 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3401 The following configurations can be forced. 3402 3403 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3404 Any ID with matching PORT is used. 3405 3406 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3407 3408 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3409 udma[/][16,25,33,44,66,100,133] notation is also 3410 allowed. 3411 3412 * nohrst, nosrst, norst: suppress hard, soft and both 3413 resets. 3414 3415 * rstonce: only attempt one reset during hot-unplug 3416 link recovery. 3417 3418 * [no]dbdelay: Enable or disable the extra 200ms delay 3419 before debouncing a link PHY and device presence 3420 detection. 3421 3422 * [no]ncq: Turn on or off NCQ. 3423 3424 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3425 3426 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3427 3428 * [no]trim: Enable or disable (unqueued) TRIM. 3429 3430 * trim_zero: Indicate that TRIM command zeroes data. 3431 3432 * max_trim_128m: Set 128M maximum trim size limit. 3433 3434 * [no]dma: Turn on or off DMA transfers. 3435 3436 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3437 3438 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3439 commands that are not a multiple of 16 bytes. 3440 3441 * [no]dmalog: Enable or disable the use of the 3442 READ LOG DMA EXT command to access logs. 3443 3444 * [no]iddevlog: Enable or disable access to the 3445 identify device data log. 3446 3447 * [no]logdir: Enable or disable access to the general 3448 purpose log directory. 3449 3450 * max_sec_128: Set transfer size limit to 128 sectors. 3451 3452 * max_sec_1024: Set or clear transfer size limit to 3453 1024 sectors. 3454 3455 * max_sec_lba48: Set or clear transfer size limit to 3456 65535 sectors. 3457 3458 * external: Mark port as external (hotplug-capable). 3459 3460 * [no]lpm: Enable or disable link power management. 3461 3462 * [no]setxfer: Indicate if transfer speed mode setting 3463 should be skipped. 3464 3465 * [no]fua: Disable or enable FUA (Force Unit Access) 3466 support for devices supporting this feature. 3467 3468 * dump_id: Dump IDENTIFY data. 3469 3470 * disable: Disable this device. 3471 3472 If there are multiple matching configurations changing 3473 the same attribute, the last one is used. 3474 3475 liveupdate= [KNL,EARLY] 3476 Format: <bool> 3477 Enable Live Update Orchestrator (LUO). 3478 Default: off. 3479 3480 load_ramdisk= [RAM] [Deprecated] 3481 3482 lockd.nlm_grace_period=P [NFS] Assign grace period. 3483 Format: <integer> 3484 3485 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3486 Format: <integer> 3487 3488 lockd.nlm_timeout=T [NFS] Assign timeout value. 3489 Format: <integer> 3490 3491 lockd.nlm_udpport=M [NFS] Assign UDP port. 3492 Format: <integer> 3493 3494 lockdown= [SECURITY,EARLY] 3495 { integrity | confidentiality } 3496 Enable the kernel lockdown feature. If set to 3497 integrity, kernel features that allow userland to 3498 modify the running kernel are disabled. If set to 3499 confidentiality, kernel features that allow userland 3500 to extract confidential information from the kernel 3501 are also disabled. 3502 3503 locktorture.acq_writer_lim= [KNL] 3504 Set the time limit in jiffies for a lock 3505 acquisition. Acquisitions exceeding this limit 3506 will result in a splat once they do complete. 3507 3508 locktorture.bind_readers= [KNL] 3509 Specify the list of CPUs to which the readers are 3510 to be bound. 3511 3512 locktorture.bind_writers= [KNL] 3513 Specify the list of CPUs to which the writers are 3514 to be bound. 3515 3516 locktorture.call_rcu_chains= [KNL] 3517 Specify the number of self-propagating call_rcu() 3518 chains to set up. These are used to ensure that 3519 there is a high probability of an RCU grace period 3520 in progress at any given time. Defaults to 0, 3521 which disables these call_rcu() chains. 3522 3523 locktorture.long_hold= [KNL] 3524 Specify the duration in milliseconds for the 3525 occasional long-duration lock hold time. Defaults 3526 to 100 milliseconds. Select 0 to disable. 3527 3528 locktorture.nested_locks= [KNL] 3529 Specify the maximum lock nesting depth that 3530 locktorture is to exercise, up to a limit of 8 3531 (MAX_NESTED_LOCKS). Specify zero to disable. 3532 Note that this parameter is ineffective on types 3533 of locks that do not support nested acquisition. 3534 3535 locktorture.nreaders_stress= [KNL] 3536 Set the number of locking read-acquisition kthreads. 3537 Defaults to being automatically set based on the 3538 number of online CPUs. 3539 3540 locktorture.nwriters_stress= [KNL] 3541 Set the number of locking write-acquisition kthreads. 3542 3543 locktorture.onoff_holdoff= [KNL] 3544 Set time (s) after boot for CPU-hotplug testing. 3545 3546 locktorture.onoff_interval= [KNL] 3547 Set time (s) between CPU-hotplug operations, or 3548 zero to disable CPU-hotplug testing. 3549 3550 locktorture.rt_boost= [KNL] 3551 Do periodic testing of real-time lock priority 3552 boosting. Select 0 to disable, 1 to boost 3553 only rt_mutex, and 2 to boost unconditionally. 3554 Defaults to 2, which might seem to be an 3555 odd choice, but which should be harmless for 3556 non-real-time spinlocks, due to their disabling 3557 of preemption. Note that non-realtime mutexes 3558 disable boosting. 3559 3560 locktorture.rt_boost_factor= [KNL] 3561 Number that determines how often and for how 3562 long priority boosting is exercised. This is 3563 scaled down by the number of writers, so that the 3564 number of boosts per unit time remains roughly 3565 constant as the number of writers increases. 3566 On the other hand, the duration of each boost 3567 increases with the number of writers. 3568 3569 locktorture.shuffle_interval= [KNL] 3570 Set task-shuffle interval (jiffies). Shuffling 3571 tasks allows some CPUs to go into dyntick-idle 3572 mode during the locktorture test. 3573 3574 locktorture.shutdown_secs= [KNL] 3575 Set time (s) after boot system shutdown. This 3576 is useful for hands-off automated testing. 3577 3578 locktorture.stat_interval= [KNL] 3579 Time (s) between statistics printk()s. 3580 3581 locktorture.stutter= [KNL] 3582 Time (s) to stutter testing, for example, 3583 specifying five seconds causes the test to run for 3584 five seconds, wait for five seconds, and so on. 3585 This tests the locking primitive's ability to 3586 transition abruptly to and from idle. 3587 3588 locktorture.torture_type= [KNL] 3589 Specify the locking implementation to test. 3590 3591 locktorture.verbose= [KNL] 3592 Enable additional printk() statements. 3593 3594 locktorture.writer_fifo= [KNL] 3595 Run the write-side locktorture kthreads at 3596 sched_set_fifo() real-time priority. 3597 3598 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3599 Format: <irq> 3600 3601 loglevel= [KNL,EARLY] 3602 All Kernel Messages with a loglevel smaller than the 3603 console loglevel will be printed to the console. It can 3604 also be changed with klogd or other programs. The 3605 loglevels are defined as follows: 3606 3607 0 (KERN_EMERG) system is unusable 3608 1 (KERN_ALERT) action must be taken immediately 3609 2 (KERN_CRIT) critical conditions 3610 3 (KERN_ERR) error conditions 3611 4 (KERN_WARNING) warning conditions 3612 5 (KERN_NOTICE) normal but significant condition 3613 6 (KERN_INFO) informational 3614 7 (KERN_DEBUG) debug-level messages 3615 3616 log_buf_len=n[KMG] [KNL,EARLY] 3617 Sets the size of the printk ring buffer, in bytes. 3618 n must be a power of two and greater than the 3619 minimal size. The minimal size is defined by 3620 LOG_BUF_SHIFT kernel config parameter. There 3621 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3622 parameter that allows to increase the default size 3623 depending on the number of CPUs. See init/Kconfig 3624 for more details. 3625 3626 logo.nologo [FB] Disables display of the built-in Linux logo. 3627 This may be used to provide more screen space for 3628 kernel log messages and is useful when debugging 3629 kernel boot problems. 3630 3631 lp=0 [LP] Specify parallel ports to use, e.g, 3632 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3633 lp=reset first parallel port). 'lp=0' disables the 3634 lp=auto printer driver. 'lp=reset' (which can be 3635 specified in addition to the ports) causes 3636 attached printers to be reset. Using 3637 lp=port1,port2,... specifies the parallel ports 3638 to associate lp devices with, starting with 3639 lp0. A port specification may be 'none' to skip 3640 that lp device, or a parport name such as 3641 'parport0'. Specifying 'lp=auto' instead of a 3642 port specification list means that device IDs 3643 from each port should be examined, to see if 3644 an IEEE 1284-compliant printer is attached; if 3645 so, the driver will manage that printer. 3646 See also header of drivers/char/lp.c. 3647 3648 lpj=n [KNL] 3649 Sets loops_per_jiffy to given constant, thus avoiding 3650 time-consuming boot-time autodetection (up to 250 ms per 3651 CPU). 0 enables autodetection (default). To determine 3652 the correct value for your kernel, boot with normal 3653 autodetection and see what value is printed. Note that 3654 on SMP systems the preset will be applied to all CPUs, 3655 which is likely to cause problems if your CPUs need 3656 significantly divergent settings. An incorrect value 3657 will cause delays in the kernel to be wrong, leading to 3658 unpredictable I/O errors and other breakage. Although 3659 unlikely, in the extreme case this might damage your 3660 hardware. 3661 3662 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3663 3664 lsm=lsm1,...,lsmN 3665 [SECURITY] Choose order of LSM initialization. This 3666 overrides CONFIG_LSM, and the "security=" parameter. 3667 3668 machtype= [Loongson] Share the same kernel image file between 3669 different yeeloong laptops. 3670 Example: machtype=lemote-yeeloong-2f-7inch 3671 3672 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3673 will bring up during bootup. maxcpus=n : n >= 0 limits 3674 the kernel to bring up 'n' processors. Surely after 3675 bootup you can bring up the other plugged cpu by executing 3676 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3677 only takes effect during system bootup. 3678 While n=0 is a special case, it is equivalent to "nosmp", 3679 which also disables the IO APIC. 3680 3681 max_loop= [LOOP] The number of loop block devices that get 3682 (loop.max_loop) unconditionally pre-created at init time. The default 3683 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3684 of statically allocating a predefined number, loop 3685 devices can be requested on-demand with the 3686 /dev/loop-control interface. 3687 3688 mce= [X86-{32,64}] 3689 3690 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3691 3692 off 3693 disable machine check 3694 3695 no_cmci 3696 disable CMCI(Corrected Machine Check Interrupt) that 3697 Intel processor supports. Usually this disablement is 3698 not recommended, but it might be handy if your 3699 hardware is misbehaving. 3700 3701 Note that you'll get more problems without CMCI than 3702 with due to the shared banks, i.e. you might get 3703 duplicated error logs. 3704 3705 dont_log_ce 3706 don't make logs for corrected errors. All events 3707 reported as corrected are silently cleared by OS. This 3708 option will be useful if you have no interest in any 3709 of corrected errors. 3710 3711 ignore_ce 3712 disable features for corrected errors, e.g. 3713 polling timer and CMCI. All events reported as 3714 corrected are not cleared by OS and remained in its 3715 error banks. 3716 3717 Usually this disablement is not recommended, however 3718 if there is an agent checking/clearing corrected 3719 errors (e.g. BIOS or hardware monitoring 3720 applications), conflicting with OS's error handling, 3721 and you cannot deactivate the agent, then this option 3722 will be a help. 3723 3724 no_lmce 3725 do not opt-in to Local MCE delivery. Use legacy method 3726 to broadcast MCEs. 3727 3728 bootlog 3729 enable logging of machine checks left over from 3730 booting. Disabled by default on AMD Fam10h and older 3731 because some BIOS leave bogus ones. 3732 3733 If your BIOS doesn't do that it's a good idea to 3734 enable though to make sure you log even machine check 3735 events that result in a reboot. On Intel systems it is 3736 enabled by default. 3737 3738 nobootlog 3739 disable boot machine check logging. 3740 3741 monarchtimeout (number) 3742 sets the time in us to wait for other CPUs on machine 3743 checks. 0 to disable. 3744 3745 bios_cmci_threshold 3746 don't overwrite the bios-set CMCI threshold. This boot 3747 option prevents Linux from overwriting the CMCI 3748 threshold set by the bios. Without this option, Linux 3749 always sets the CMCI threshold to 1. Enabling this may 3750 make memory predictive failure analysis less effective 3751 if the bios sets thresholds for memory errors since we 3752 will not see details for all errors. 3753 3754 recovery 3755 force-enable recoverable machine check code paths 3756 3757 Everything else is in sysfs now. 3758 3759 3760 md= [HW] RAID subsystems devices and level 3761 See Documentation/admin-guide/md.rst. 3762 3763 mdacon= [MDA] 3764 Format: <first>,<last> 3765 Specifies range of consoles to be captured by the MDA. 3766 3767 mds= [X86,INTEL,EARLY] 3768 Control mitigation for the Micro-architectural Data 3769 Sampling (MDS) vulnerability. 3770 3771 Certain CPUs are vulnerable to an exploit against CPU 3772 internal buffers which can forward information to a 3773 disclosure gadget under certain conditions. 3774 3775 In vulnerable processors, the speculatively 3776 forwarded data can be used in a cache side channel 3777 attack, to access data to which the attacker does 3778 not have direct access. 3779 3780 This parameter controls the MDS mitigation. The 3781 options are: 3782 3783 full - Enable MDS mitigation on vulnerable CPUs 3784 full,nosmt - Enable MDS mitigation and disable 3785 SMT on vulnerable CPUs 3786 off - Unconditionally disable MDS mitigation 3787 3788 On TAA-affected machines, mds=off can be prevented by 3789 an active TAA mitigation as both vulnerabilities are 3790 mitigated with the same mechanism so in order to disable 3791 this mitigation, you need to specify tsx_async_abort=off 3792 too. 3793 3794 Not specifying this option is equivalent to 3795 mds=full. 3796 3797 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3798 3799 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3800 Must be specified, otherwise memory size will be 0. 3801 3802 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3803 of memory Amount of memory to be used in cases 3804 as follows: 3805 3806 1 for test; 3807 2 when the kernel is not able to see the whole system memory; 3808 3 memory that lies after 'mem=' boundary is excluded from 3809 the hypervisor, then assigned to KVM guests. 3810 4 to limit the memory available for kdump kernel. 3811 3812 [ARC,MICROBLAZE] - the limit applies only to low memory, 3813 high memory is not affected. 3814 3815 [ARM64] - only limits memory covered by the linear 3816 mapping. The NOMAP regions are not affected. 3817 3818 [X86] Work as limiting max address. Use together 3819 with memmap= to avoid physical address space collisions. 3820 Without memmap= PCI devices could be placed at addresses 3821 belonging to unused RAM. 3822 3823 Note that this only takes effects during boot time since 3824 in above case 3, memory may need be hot added after boot 3825 if system memory of hypervisor is not sufficient. 3826 3827 mem=nn[KMG]@ss[KMG] 3828 [ARM,MIPS,EARLY] - override the memory layout 3829 reported by firmware. 3830 Define a memory region of size nn[KMG] starting at 3831 ss[KMG]. 3832 Multiple different regions can be specified with 3833 multiple mem= parameters on the command line. 3834 3835 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3836 memory. 3837 3838 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3839 3840 memchunk=nn[KMG] 3841 [KNL,SH] Allow user to override the default size for 3842 per-device physically contiguous DMA buffers. 3843 3844 memhp_default_state=online/offline/online_kernel/online_movable 3845 [KNL] Set the initial state for the memory hotplug 3846 onlining policy. If not specified, the default value is 3847 set according to the 3848 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3849 options. 3850 See Documentation/admin-guide/mm/memory-hotplug.rst. 3851 3852 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3853 E820 memory map, as specified by the user. 3854 Such memmap=exactmap lines can be constructed based on 3855 BIOS output or other requirements. See the memmap=nn@ss 3856 option description. 3857 3858 memmap=nn[KMG]@ss[KMG] 3859 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3860 Region of memory to be used is from ss to ss+nn. 3861 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3862 which limits max address to nn[KMG]. 3863 Multiple different regions can be specified, 3864 comma delimited. 3865 Example: 3866 memmap=100M@2G,100M#3G,1G!1024G 3867 3868 memmap=nn[KMG]#ss[KMG] 3869 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3870 Region of memory to be marked is from ss to ss+nn. 3871 3872 memmap=nn[KMG]$ss[KMG] 3873 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3874 Region of memory to be reserved is from ss to ss+nn. 3875 Example: Exclude memory from 0x18690000-0x1869ffff 3876 memmap=64K$0x18690000 3877 or 3878 memmap=0x10000$0x18690000 3879 Some bootloaders may need an escape character before '$', 3880 like Grub2, otherwise '$' and the following number 3881 will be eaten. 3882 3883 memmap=nn[KMG]!ss[KMG,EARLY] 3884 [KNL,X86] Mark specific memory as protected. 3885 Region of memory to be used, from ss to ss+nn. 3886 The memory region may be marked as e820 type 12 (0xc) 3887 and is NVDIMM or ADR memory. 3888 3889 memmap=<size>%<offset>-<oldtype>+<newtype> 3890 [KNL,ACPI,EARLY] Convert memory within the specified region 3891 from <oldtype> to <newtype>. If "-<oldtype>" is left 3892 out, the whole region will be marked as <newtype>, 3893 even if previously unavailable. If "+<newtype>" is left 3894 out, matching memory will be removed. Types are 3895 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3896 3 = ACPI, 12 = PRAM. 3897 3898 memory_corruption_check=0/1 [X86,EARLY] 3899 Some BIOSes seem to corrupt the first 64k of 3900 memory when doing things like suspend/resume. 3901 Setting this option will scan the memory 3902 looking for corruption. Enabling this will 3903 both detect corruption and prevent the kernel 3904 from using the memory being corrupted. 3905 However, it's intended as a diagnostic tool; if 3906 repeatable BIOS-originated corruption always 3907 affects the same memory, you can use memmap= 3908 to prevent the kernel from using that memory. 3909 3910 memory_corruption_check_size=size [X86,EARLY] 3911 By default it checks for corruption in the low 3912 64k, making this memory unavailable for normal 3913 use. Use this parameter to scan for 3914 corruption in more or less memory. 3915 3916 memory_corruption_check_period=seconds [X86,EARLY] 3917 By default it checks for corruption every 60 3918 seconds. Use this parameter to check at some 3919 other rate. 0 disables periodic checking. 3920 3921 memory_hotplug.memmap_on_memory 3922 [KNL,X86,ARM] Boolean flag to enable this feature. 3923 Format: {on | off (default)} 3924 When enabled, runtime hotplugged memory will 3925 allocate its internal metadata (struct pages, 3926 those vmemmap pages cannot be optimized even 3927 if hugetlb_free_vmemmap is enabled) from the 3928 hotadded memory which will allow to hotadd a 3929 lot of memory without requiring additional 3930 memory to do so. 3931 This feature is disabled by default because it 3932 has some implication on large (e.g. GB) 3933 allocations in some configurations (e.g. small 3934 memory blocks). 3935 The state of the flag can be read in 3936 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3937 Note that even when enabled, there are a few cases where 3938 the feature is not effective. 3939 3940 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3941 Format: <integer> 3942 default : 0 <disable> 3943 Specifies the number of memtest passes to be 3944 performed. Each pass selects another test 3945 pattern from a given set of patterns. Memtest 3946 fills the memory with this pattern, validates 3947 memory contents and reserves bad memory 3948 regions that are detected. 3949 3950 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3951 Valid arguments: on, off 3952 Default: off 3953 mem_encrypt=on: Activate SME 3954 mem_encrypt=off: Do not activate SME 3955 3956 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3957 for details on when memory encryption can be activated. 3958 3959 mem_sleep_default= [SUSPEND] Default system suspend mode: 3960 s2idle - Suspend-To-Idle 3961 shallow - Power-On Suspend or equivalent (if supported) 3962 deep - Suspend-To-RAM or equivalent (if supported) 3963 See Documentation/admin-guide/pm/sleep-states.rst. 3964 3965 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3966 the BIOS has incorrectly applied a workaround. TinyBIOS 3967 version 0.98 is known to be affected, 0.99 fixes the 3968 problem by letting the user disable the workaround. 3969 3970 mga= [HW,DRM] 3971 3972 microcode= [X86] Control the behavior of the microcode loader. 3973 Available options, comma separated: 3974 3975 base_rev=X - with <X> with format: <u32> 3976 Set the base microcode revision of each thread when in 3977 debug mode. 3978 3979 dis_ucode_ldr: disable the microcode loader 3980 3981 force_minrev: 3982 Enable or disable the microcode minimal revision 3983 enforcement for the runtime microcode loader. 3984 3985 mini2440= [ARM,HW,KNL] 3986 Format:[0..2][b][c][t] 3987 Default: "0tb" 3988 MINI2440 configuration specification: 3989 0 - The attached screen is the 3.5" TFT 3990 1 - The attached screen is the 7" TFT 3991 2 - The VGA Shield is attached (1024x768) 3992 Leaving out the screen size parameter will not load 3993 the TFT driver, and the framebuffer will be left 3994 unconfigured. 3995 b - Enable backlight. The TFT backlight pin will be 3996 linked to the kernel VESA blanking code and a GPIO 3997 LED. This parameter is not necessary when using the 3998 VGA shield. 3999 c - Enable the s3c camera interface. 4000 t - Reserved for enabling touchscreen support. The 4001 touchscreen support is not enabled in the mainstream 4002 kernel as of 2.6.30, a preliminary port can be found 4003 in the "bleeding edge" mini2440 support kernel at 4004 https://repo.or.cz/w/linux-2.6/mini2440.git 4005 4006 mitigations= 4007 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 4008 CPU vulnerabilities. This is a set of curated, 4009 arch-independent options, each of which is an 4010 aggregation of existing arch-specific options. 4011 4012 Note, "mitigations" is supported if and only if the 4013 kernel was built with CPU_MITIGATIONS=y. 4014 4015 off 4016 Disable all optional CPU mitigations. This 4017 improves system performance, but it may also 4018 expose users to several CPU vulnerabilities. 4019 Equivalent to: if nokaslr then kpti=0 [ARM64] 4020 gather_data_sampling=off [X86] 4021 indirect_target_selection=off [X86] 4022 kvm.nx_huge_pages=off [X86] 4023 l1tf=off [X86] 4024 mds=off [X86] 4025 mmio_stale_data=off [X86] 4026 no_entry_flush [PPC] 4027 no_uaccess_flush [PPC] 4028 nobp=0 [S390] 4029 nopti [X86,PPC] 4030 nospectre_bhb [ARM64] 4031 nospectre_v1 [X86,PPC] 4032 nospectre_v2 [X86,PPC,S390,ARM64] 4033 reg_file_data_sampling=off [X86] 4034 retbleed=off [X86] 4035 spec_rstack_overflow=off [X86] 4036 spec_store_bypass_disable=off [X86,PPC] 4037 spectre_bhi=off [X86] 4038 spectre_v2_user=off [X86] 4039 srbds=off [X86,INTEL] 4040 ssbd=force-off [ARM64] 4041 tsx_async_abort=off [X86] 4042 vmscape=off [X86] 4043 4044 Exceptions: 4045 This does not have any effect on 4046 kvm.nx_huge_pages when 4047 kvm.nx_huge_pages=force. 4048 4049 auto (default) 4050 Mitigate all CPU vulnerabilities, but leave SMT 4051 enabled, even if it's vulnerable. This is for 4052 users who don't want to be surprised by SMT 4053 getting disabled across kernel upgrades, or who 4054 have other ways of avoiding SMT-based attacks. 4055 Equivalent to: (default behavior) 4056 4057 auto,nosmt 4058 Mitigate all CPU vulnerabilities, disabling SMT 4059 if needed. This is for users who always want to 4060 be fully mitigated, even if it means losing SMT. 4061 Equivalent to: l1tf=flush,nosmt [X86] 4062 mds=full,nosmt [X86] 4063 tsx_async_abort=full,nosmt [X86] 4064 mmio_stale_data=full,nosmt [X86] 4065 retbleed=auto,nosmt [X86] 4066 4067 [X86] After one of the above options, additionally 4068 supports attack-vector based controls as documented in 4069 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4070 4071 mminit_loglevel= 4072 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4073 parameter allows control of the logging verbosity for 4074 the additional memory initialisation checks. A value 4075 of 0 disables mminit logging and a level of 4 will 4076 log everything. Information is printed at KERN_DEBUG 4077 so loglevel=8 may also need to be specified. 4078 4079 mmio_stale_data= 4080 [X86,INTEL,EARLY] Control mitigation for the Processor 4081 MMIO Stale Data vulnerabilities. 4082 4083 Processor MMIO Stale Data is a class of 4084 vulnerabilities that may expose data after an MMIO 4085 operation. Exposed data could originate or end in 4086 the same CPU buffers as affected by MDS and TAA. 4087 Therefore, similar to MDS and TAA, the mitigation 4088 is to clear the affected CPU buffers. 4089 4090 This parameter controls the mitigation. The 4091 options are: 4092 4093 full - Enable mitigation on vulnerable CPUs 4094 4095 full,nosmt - Enable mitigation and disable SMT on 4096 vulnerable CPUs. 4097 4098 off - Unconditionally disable mitigation 4099 4100 On MDS or TAA affected machines, 4101 mmio_stale_data=off can be prevented by an active 4102 MDS or TAA mitigation as these vulnerabilities are 4103 mitigated with the same mechanism so in order to 4104 disable this mitigation, you need to specify 4105 mds=off and tsx_async_abort=off too. 4106 4107 Not specifying this option is equivalent to 4108 mmio_stale_data=full. 4109 4110 For details see: 4111 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4112 4113 <module>.async_probe[=<bool>] [KNL] 4114 If no <bool> value is specified or if the value 4115 specified is not a valid <bool>, enable asynchronous 4116 probe on this module. Otherwise, enable/disable 4117 asynchronous probe on this module as indicated by the 4118 <bool> value. See also: module.async_probe 4119 4120 module.async_probe=<bool> 4121 [KNL] When set to true, modules will use async probing 4122 by default. To enable/disable async probing for a 4123 specific module, use the module specific control that 4124 is documented under <module>.async_probe. When both 4125 module.async_probe and <module>.async_probe are 4126 specified, <module>.async_probe takes precedence for 4127 the specific module. 4128 4129 module.enable_dups_trace 4130 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4131 this means that duplicate request_module() calls will 4132 trigger a WARN_ON() instead of a pr_warn(). Note that 4133 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4134 will always be issued and this option does nothing. 4135 module.sig_enforce 4136 [KNL] When CONFIG_MODULE_SIG is set, this means that 4137 modules without (valid) signatures will fail to load. 4138 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4139 is always true, so this option does nothing. 4140 4141 module_blacklist= [KNL] Do not load a comma-separated list of 4142 modules. Useful for debugging problem modules. 4143 4144 mousedev.tap_time= 4145 [MOUSE] Maximum time between finger touching and 4146 leaving touchpad surface for touch to be considered 4147 a tap and be reported as a left button click (for 4148 touchpads working in absolute mode only). 4149 Format: <msecs> 4150 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4151 reporting absolute coordinates, such as tablets 4152 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4153 reporting absolute coordinates, such as tablets 4154 4155 movablecore= [KNL,X86,PPC,EARLY] 4156 Format: nn[KMGTPE] | nn% 4157 This parameter is the complement to kernelcore=, it 4158 specifies the amount of memory used for migratable 4159 allocations. If both kernelcore and movablecore is 4160 specified, then kernelcore will be at *least* the 4161 specified value but may be more. If movablecore on its 4162 own is specified, the administrator must be careful 4163 that the amount of memory usable for all allocations 4164 is not too small. 4165 4166 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4167 NUMA nodes to be movable. This means that the memory 4168 of such nodes will be usable only for movable 4169 allocations which rules out almost all kernel 4170 allocations. Use with caution! 4171 4172 MTD_Partition= [MTD] 4173 Format: <name>,<region-number>,<size>,<offset> 4174 4175 MTD_Region= [MTD] Format: 4176 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4177 4178 mtdparts= [MTD] 4179 See drivers/mtd/parsers/cmdlinepart.c 4180 4181 mtouchusb.raw_coordinates= 4182 [HW] Make the MicroTouch USB driver use raw coordinates 4183 ('y', default) or cooked coordinates ('n') 4184 4185 mtrr=debug [X86,EARLY] 4186 Enable printing debug information related to MTRR 4187 registers at boot time. 4188 4189 mtrr_chunk_size=nn[KMG,X86,EARLY] 4190 used for mtrr cleanup. It is largest continuous chunk 4191 that could hold holes aka. UC entries. 4192 4193 mtrr_gran_size=nn[KMG,X86,EARLY] 4194 Used for mtrr cleanup. It is granularity of mtrr block. 4195 Default is 1. 4196 Large value could prevent small alignment from 4197 using up MTRRs. 4198 4199 mtrr_spare_reg_nr=n [X86,EARLY] 4200 Format: <integer> 4201 Range: 0,7 : spare reg number 4202 Default : 1 4203 Used for mtrr cleanup. It is spare mtrr entries number. 4204 Set to 2 or more if your graphical card needs more. 4205 4206 multitce=off [PPC] This parameter disables the use of the pSeries 4207 firmware feature for updating multiple TCE entries 4208 at a time. 4209 4210 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4211 4212 netdev= [NET] Network devices parameters 4213 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4214 Note that mem_start is often overloaded to mean 4215 something different and driver-specific. 4216 This usage is only documented in each driver source 4217 file if at all. 4218 4219 netpoll.carrier_timeout= 4220 [NET] Specifies amount of time (in seconds) that 4221 netpoll should wait for a carrier. By default netpoll 4222 waits 4 seconds. 4223 4224 nf_conntrack.acct= 4225 [NETFILTER] Enable connection tracking flow accounting 4226 0 to disable accounting 4227 1 to enable accounting 4228 Default value is 0. 4229 4230 nfs.cache_getent= 4231 [NFS] sets the pathname to the program which is used 4232 to update the NFS client cache entries. 4233 4234 nfs.cache_getent_timeout= 4235 [NFS] sets the timeout after which an attempt to 4236 update a cache entry is deemed to have failed. 4237 4238 nfs.callback_nr_threads= 4239 [NFSv4] set the total number of threads that the 4240 NFS client will assign to service NFSv4 callback 4241 requests. 4242 4243 nfs.callback_tcpport= 4244 [NFS] set the TCP port on which the NFSv4 callback 4245 channel should listen. 4246 4247 nfs.delay_retrans= 4248 [NFS] specifies the number of times the NFSv4 client 4249 retries the request before returning an EAGAIN error, 4250 after a reply of NFS4ERR_DELAY from the server. 4251 Only applies if the softerr mount option is enabled, 4252 and the specified value is >= 0. 4253 4254 nfs.enable_ino64= 4255 [NFS] enable 64-bit inode numbers. 4256 If zero, the NFS client will fake up a 32-bit inode 4257 number for the readdir() and stat() syscalls instead 4258 of returning the full 64-bit number. 4259 The default is to return 64-bit inode numbers. 4260 4261 nfs.idmap_cache_timeout= 4262 [NFS] set the maximum lifetime for idmapper cache 4263 entries. 4264 4265 nfs.max_session_cb_slots= 4266 [NFSv4.1] Sets the maximum number of session 4267 slots the client will assign to the callback 4268 channel. This determines the maximum number of 4269 callbacks the client will process in parallel for 4270 a particular server. 4271 4272 nfs.max_session_slots= 4273 [NFSv4.1] Sets the maximum number of session slots 4274 the client will attempt to negotiate with the server. 4275 This limits the number of simultaneous RPC requests 4276 that the client can send to the NFSv4.1 server. 4277 Note that there is little point in setting this 4278 value higher than the max_tcp_slot_table_limit. 4279 4280 nfs.nfs4_disable_idmapping= 4281 [NFSv4] When set to the default of '1', this option 4282 ensures that both the RPC level authentication 4283 scheme and the NFS level operations agree to use 4284 numeric uids/gids if the mount is using the 4285 'sec=sys' security flavour. In effect it is 4286 disabling idmapping, which can make migration from 4287 legacy NFSv2/v3 systems to NFSv4 easier. 4288 Servers that do not support this mode of operation 4289 will be autodetected by the client, and it will fall 4290 back to using the idmapper. 4291 To turn off this behaviour, set the value to '0'. 4292 4293 nfs.nfs4_unique_id= 4294 [NFS4] Specify an additional fixed unique ident- 4295 ification string that NFSv4 clients can insert into 4296 their nfs_client_id4 string. This is typically a 4297 UUID that is generated at system install time. 4298 4299 nfs.recover_lost_locks= 4300 [NFSv4] Attempt to recover locks that were lost due 4301 to a lease timeout on the server. Please note that 4302 doing this risks data corruption, since there are 4303 no guarantees that the file will remain unchanged 4304 after the locks are lost. 4305 If you want to enable the kernel legacy behaviour of 4306 attempting to recover these locks, then set this 4307 parameter to '1'. 4308 The default parameter value of '0' causes the kernel 4309 not to attempt recovery of lost locks. 4310 4311 nfs.send_implementation_id= 4312 [NFSv4.1] Send client implementation identification 4313 information in exchange_id requests. 4314 If zero, no implementation identification information 4315 will be sent. 4316 The default is to send the implementation identification 4317 information. 4318 4319 nfs4.layoutstats_timer= 4320 [NFSv4.2] Change the rate at which the kernel sends 4321 layoutstats to the pNFS metadata server. 4322 4323 Setting this to value to 0 causes the kernel to use 4324 whatever value is the default set by the layout 4325 driver. A non-zero value sets the minimum interval 4326 in seconds between layoutstats transmissions. 4327 4328 nfsd.inter_copy_offload_enable= 4329 [NFSv4.2] When set to 1, the server will support 4330 server-to-server copies for which this server is 4331 the destination of the copy. 4332 4333 nfsd.nfs4_disable_idmapping= 4334 [NFSv4] When set to the default of '1', the NFSv4 4335 server will return only numeric uids and gids to 4336 clients using auth_sys, and will accept numeric uids 4337 and gids from such clients. This is intended to ease 4338 migration from NFSv2/v3. 4339 4340 nfsd.nfsd4_ssc_umount_timeout= 4341 [NFSv4.2] When used as the destination of a 4342 server-to-server copy, knfsd temporarily mounts 4343 the source server. It caches the mount in case 4344 it will be needed again, and discards it if not 4345 used for the number of milliseconds specified by 4346 this parameter. 4347 4348 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4349 See Documentation/admin-guide/nfs/nfsroot.rst. 4350 4351 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4352 See Documentation/admin-guide/nfs/nfsroot.rst. 4353 4354 nfsrootdebug [NFS] enable nfsroot debugging messages. 4355 See Documentation/admin-guide/nfs/nfsroot.rst. 4356 4357 nmi_backtrace.backtrace_idle [KNL] 4358 Dump stacks even of idle CPUs in response to an 4359 NMI stack-backtrace request. 4360 4361 nmi_debug= [KNL,SH] Specify one or more actions to take 4362 when a NMI is triggered. 4363 Format: [state][,regs][,debounce][,die] 4364 4365 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4366 Format: [panic,][nopanic,][rNNN,][num] 4367 Valid num: 0 or 1 4368 0 - turn hardlockup detector in nmi_watchdog off 4369 1 - turn hardlockup detector in nmi_watchdog on 4370 rNNN - configure the watchdog with raw perf event 0xNNN 4371 4372 When panic is specified, panic when an NMI watchdog 4373 timeout occurs (or 'nopanic' to not panic on an NMI 4374 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4375 To disable both hard and soft lockup detectors, 4376 please see 'nowatchdog'. 4377 This is useful when you use a panic=... timeout and 4378 need the box quickly up again. 4379 4380 These settings can be accessed at runtime via 4381 the nmi_watchdog and hardlockup_panic sysctls. 4382 4383 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4384 emulation library even if a 387 maths coprocessor 4385 is present. 4386 4387 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4388 Forces kernel to use 3-level paging instead. 4389 4390 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4391 kernel to use 4-level paging instead. 4392 4393 noalign [KNL,ARM] 4394 4395 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4396 IOAPICs that may be present in the system. 4397 4398 noapictimer [APIC,X86] Don't set up the APIC timer 4399 4400 noautogroup Disable scheduler automatic task group creation. 4401 4402 nocache [ARM,EARLY] 4403 4404 no_console_suspend 4405 [HW] Never suspend the console 4406 Disable suspending of consoles during suspend and 4407 hibernate operations. Once disabled, debugging 4408 messages can reach various consoles while the rest 4409 of the system is being put to sleep (ie, while 4410 debugging driver suspend/resume hooks). This may 4411 not work reliably with all consoles, but is known 4412 to work with serial and VGA consoles. 4413 To facilitate more flexible debugging, we also add 4414 console_suspend, a printk module parameter to control 4415 it. Users could use console_suspend (usually 4416 /sys/module/printk/parameters/console_suspend) to 4417 turn on/off it dynamically. 4418 4419 no_debug_objects 4420 [KNL,EARLY] Disable object debugging 4421 4422 nodsp [SH] Disable hardware DSP at boot time. 4423 4424 noefi [EFI,EARLY] Disable EFI runtime services support. 4425 4426 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4427 4428 noexec32 [X86-64] 4429 This affects only 32-bit executables. 4430 noexec32=on: enable non-executable mappings (default) 4431 read doesn't imply executable mappings 4432 noexec32=off: disable non-executable mappings 4433 read implies executable mappings 4434 4435 no_file_caps Tells the kernel not to honor file capabilities. The 4436 only way then for a file to be executed with privilege 4437 is to be setuid root or executed by root. 4438 4439 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4440 4441 nofsgsbase [X86] Disables FSGSBASE instructions. 4442 4443 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4444 register save and restore. The kernel will only save 4445 legacy floating-point registers on task switch. 4446 4447 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4448 4449 no_hash_pointers 4450 [KNL,EARLY] 4451 Alias for "hash_pointers=never". 4452 4453 nohibernate [HIBERNATION] Disable hibernation and resume. 4454 4455 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4456 busy wait in do_idle() and not use the arch_cpu_idle() 4457 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4458 to be effective. This is useful on platforms where the 4459 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4460 correctly or when doing power measurements to evaluate 4461 the impact of the sleep instructions. This is also 4462 useful when using JTAG debugger. 4463 4464 nohpet [X86] Don't use the HPET timer. 4465 4466 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4467 4468 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4469 4470 nohz= [KNL] Boottime enable/disable dynamic ticks 4471 Valid arguments: on, off 4472 Default: on 4473 4474 nohz_full= [KNL,BOOT,SMP,ISOL] 4475 The argument is a cpu list, as described above. 4476 In kernels built with CONFIG_NO_HZ_FULL=y, set 4477 the specified list of CPUs whose tick will be stopped 4478 whenever possible. The boot CPU will be forced outside 4479 the range to maintain the timekeeping. Any CPUs 4480 in this list will have their RCU callbacks offloaded, 4481 just as if they had also been called out in the 4482 rcu_nocbs= boot parameter. 4483 4484 Note that this argument takes precedence over 4485 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4486 4487 noinitrd [RAM] Tells the kernel not to load any configured 4488 initial RAM disk. 4489 4490 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4491 remapping. 4492 [Deprecated - use intremap=off] 4493 4494 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4495 4496 noiotrap [SH] Disables trapped I/O port accesses. 4497 4498 noirqdebug [X86-32] Disables the code which attempts to detect and 4499 disable unhandled interrupt sources. 4500 4501 noisapnp [ISAPNP] Disables ISA PnP code. 4502 4503 nokaslr [KNL,EARLY] 4504 When CONFIG_RANDOMIZE_BASE is set, this disables 4505 kernel and module base offset ASLR (Address Space 4506 Layout Randomization). 4507 4508 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4509 fault handling. 4510 4511 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4512 4513 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4514 4515 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4516 4517 nomce [X86-32] Disable Machine Check Exception 4518 4519 nomfgpt [X86-32] Disable Multi-Function General Purpose 4520 Timer usage (for AMD Geode machines). 4521 4522 nomodeset Disable kernel modesetting. Most systems' firmware 4523 sets up a display mode and provides framebuffer memory 4524 for output. With nomodeset, DRM and fbdev drivers will 4525 not load if they could possibly displace the pre- 4526 initialized output. Only the system framebuffer will 4527 be available for use. The respective drivers will not 4528 perform display-mode changes or accelerated rendering. 4529 4530 Useful as error fallback, or for testing and debugging. 4531 4532 nomodule Disable module load 4533 4534 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4535 shutdown the other cpus. Instead use the REBOOT_VECTOR 4536 irq. 4537 4538 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4539 pagetables) support. 4540 4541 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4542 4543 nopku [X86] Disable Memory Protection Keys CPU feature found 4544 in some Intel CPUs. 4545 4546 nopti [X86-64,EARLY] 4547 Equivalent to pti=off 4548 4549 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4550 Disables the PV optimizations forcing the guest to run 4551 as generic guest with no PV drivers. Currently support 4552 XEN HVM, KVM, HYPER_V and VMWARE guest. 4553 4554 nopvspin [X86,XEN,KVM,EARLY] 4555 Disables the qspinlock slow path using PV optimizations 4556 which allow the hypervisor to 'idle' the guest on lock 4557 contention. 4558 4559 norandmaps Don't use address space randomization. Equivalent to 4560 echo 0 > /proc/sys/kernel/randomize_va_space 4561 4562 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4563 with UP alternatives 4564 4565 noresume [SWSUSP] Disables resume and restores original swap 4566 space. 4567 4568 no-scroll [VGA] Disables scrollback. 4569 This is required for the Braillex ib80-piezo Braille 4570 reader made by F.H. Papenmeier (Germany). 4571 4572 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4573 4574 nosmap [PPC,EARLY] 4575 Disable SMAP (Supervisor Mode Access Prevention) 4576 even if it is supported by processor. 4577 4578 nosmep [PPC64s,EARLY] 4579 Disable SMEP (Supervisor Mode Execution Prevention) 4580 even if it is supported by processor. 4581 4582 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4583 and disable the IO APIC. legacy for "maxcpus=0". 4584 4585 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4586 Equivalent to smt=1. 4587 4588 [KNL,X86,PPC,S390] Disable symmetric multithreading (SMT). 4589 nosmt=force: Force disable SMT, cannot be undone 4590 via the sysfs control file. 4591 4592 nosoftlockup [KNL] Disable the soft-lockup detector. 4593 4594 nospec_store_bypass_disable 4595 [HW,EARLY] Disable all mitigations for the Speculative 4596 Store Bypass vulnerability 4597 4598 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4599 history injection) vulnerability. System may allow data leaks 4600 with this option. 4601 4602 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4603 (bounds check bypass). With this option data leaks are 4604 possible in the system. 4605 4606 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4607 for the Spectre variant 2 (indirect branch 4608 prediction) vulnerability. System may allow data 4609 leaks with this option. 4610 4611 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4612 Disable paravirtualized steal time accounting. steal time 4613 is computed, but won't influence scheduler behaviour 4614 4615 nosync [HW,M68K] Disables sync negotiation for all devices. 4616 4617 no_timer_check [X86,APIC] Disables the code which tests for broken 4618 timer IRQ sources, i.e., the IO-APIC timer. This can 4619 work around problems with incorrect timer 4620 initialization on some boards. 4621 4622 no_uaccess_flush 4623 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4624 4625 novmcoredd [KNL,KDUMP] 4626 Disable device dump. Device dump allows drivers to 4627 append dump data to vmcore so you can collect driver 4628 specified debug info. Drivers can append the data 4629 without any limit and this data is stored in memory, 4630 so this may cause significant memory stress. Disabling 4631 device dump can help save memory but the driver debug 4632 data will be no longer available. This parameter 4633 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4634 is set. 4635 4636 no-vmw-sched-clock 4637 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4638 scheduler clock and use the default one. 4639 4640 nowatchdog [KNL] Disable both lockup detectors, i.e. 4641 soft-lockup and NMI watchdog (hard-lockup). 4642 4643 nowb [ARM,EARLY] 4644 4645 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4646 4647 NOTE: this parameter will be ignored on systems with the 4648 LEGACY_XAPIC_DISABLED bit set in the 4649 IA32_XAPIC_DISABLE_STATUS MSR. 4650 4651 noxsave [BUGS=X86] Disables x86 extended register state save 4652 and restore using xsave. The kernel will fallback to 4653 enabling legacy floating-point and sse state. 4654 4655 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4656 register states. The kernel will fall back to use 4657 xsave to save the states. By using this parameter, 4658 performance of saving the states is degraded because 4659 xsave doesn't support modified optimization while 4660 xsaveopt supports it on xsaveopt enabled systems. 4661 4662 noxsaves [X86] Disables xsaves and xrstors used in saving and 4663 restoring x86 extended register state in compacted 4664 form of xsave area. The kernel will fall back to use 4665 xsaveopt and xrstor to save and restore the states 4666 in standard form of xsave area. By using this 4667 parameter, xsave area per process might occupy more 4668 memory on xsaves enabled systems. 4669 4670 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4671 could support. nr_cpus=n : n >= 1 limits the kernel to 4672 support 'n' processors. It could be larger than the 4673 number of already plugged CPU during bootup, later in 4674 runtime you can physically add extra cpu until it reaches 4675 n. So during boot up some boot time memory for per-cpu 4676 variables need be pre-allocated for later physical cpu 4677 hot plugging. 4678 4679 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4680 4681 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4682 Disable NUMA, Only set up a single NUMA node 4683 spanning all memory. 4684 4685 numa=fake=<size>[MG] 4686 [KNL, ARM64, RISCV, X86, EARLY] 4687 If given as a memory unit, fills all system RAM with 4688 nodes of size interleaved over physical nodes. 4689 4690 numa=fake=<N> 4691 [KNL, ARM64, RISCV, X86, EARLY] 4692 If given as an integer, fills all system RAM with N 4693 fake nodes interleaved over physical nodes. 4694 4695 numa=fake=<N>U 4696 [KNL, ARM64, RISCV, X86, EARLY] 4697 If given as an integer followed by 'U', it will 4698 divide each physical node into N emulated nodes. 4699 4700 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4701 4702 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4703 soft-reserved memory partitioning. 4704 4705 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4706 NUMA balancing. 4707 Allowed values are enable and disable 4708 4709 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4710 'node', 'default' can be specified 4711 This can be set from sysctl after boot. 4712 See Documentation/admin-guide/sysctl/vm.rst for details. 4713 4714 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4715 See Documentation/core-api/debugging-via-ohci1394.rst for more 4716 info. 4717 4718 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4719 Rather than timing out after 20 ms if an EC 4720 command is not properly ACKed, override the length 4721 of the timeout. We have interrupts disabled while 4722 waiting for the ACK, so if this is set too high 4723 interrupts *may* be lost! 4724 4725 omap_mux= [OMAP] Override bootloader pin multiplexing. 4726 Format: <mux_mode0.mode_name=value>... 4727 For example, to override I2C bus2: 4728 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4729 4730 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4731 4732 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4733 4734 boundary - index of last SLC block on Flex-OneNAND. 4735 The remaining blocks are configured as MLC blocks. 4736 lock - Configure if Flex-OneNAND boundary should be locked. 4737 Once locked, the boundary cannot be changed. 4738 1 indicates lock status, 0 indicates unlock status. 4739 4740 oops=panic [KNL,EARLY] 4741 Always panic on oopses. Default is to just kill the 4742 process, but there is a small probability of 4743 deadlocking the machine. 4744 This will also cause panics on machine check exceptions. 4745 Useful together with panic=30 to trigger a reboot. 4746 4747 page_alloc.shuffle= 4748 [KNL] Boolean flag to control whether the page allocator 4749 should randomize its free lists. This parameter can be 4750 used to enable/disable page randomization. The state of 4751 the flag can be read from sysfs at: 4752 /sys/module/page_alloc/parameters/shuffle. 4753 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4754 4755 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4756 Storage of the information about who allocated 4757 each page is disabled in default. With this switch, 4758 we can turn it on. 4759 on: enable the feature 4760 4761 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4762 poisoning on the buddy allocator, available with 4763 CONFIG_PAGE_POISONING=y. 4764 off: turn off poisoning (default) 4765 on: turn on poisoning 4766 4767 page_reporting.page_reporting_order= 4768 [KNL] Minimal page reporting order 4769 Format: <integer> 4770 Adjust the minimal page reporting order. The page 4771 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4772 4773 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4774 timeout > 0: seconds before rebooting 4775 timeout = 0: wait forever 4776 timeout < 0: reboot immediately 4777 Format: <timeout> 4778 4779 panic_on_taint= [KNL,EARLY] 4780 Bitmask for conditionally calling panic() in add_taint() 4781 Format: <hex>[,nousertaint] 4782 Hexadecimal bitmask representing the set of TAINT flags 4783 that will cause the kernel to panic when add_taint() is 4784 called with any of the flags in this set. 4785 The optional switch "nousertaint" can be utilized to 4786 prevent userspace forced crashes by writing to sysctl 4787 /proc/sys/kernel/tainted any flagset matching with the 4788 bitmask set on panic_on_taint. 4789 See Documentation/admin-guide/tainted-kernels.rst for 4790 extra details on the taint flags that users can pick 4791 to compose the bitmask to assign to panic_on_taint. 4792 4793 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4794 on a WARN(). 4795 4796 panic_print= Bitmask for printing system info when panic happens. 4797 User can chose combination of the following bits: 4798 bit 0: print all tasks info 4799 bit 1: print system memory info 4800 bit 2: print timer info 4801 bit 3: print locks info if CONFIG_LOCKDEP is on 4802 bit 4: print ftrace buffer 4803 bit 5: replay all kernel messages on consoles at the end of panic 4804 bit 6: print all CPUs backtrace (if available in the arch) 4805 bit 7: print only tasks in uninterruptible (blocked) state 4806 *Be aware* that this option may print a _lot_ of lines, 4807 so there are risks of losing older messages in the log. 4808 Use this option carefully, maybe worth to setup a 4809 bigger log buffer with "log_buf_len" along with this. 4810 4811 panic_sys_info= A comma separated list of extra information to be dumped 4812 on panic. 4813 Format: val[,val...] 4814 Where @val can be any of the following: 4815 4816 tasks: print all tasks info 4817 mem: print system memory info 4818 timers: print timers info 4819 locks: print locks info if CONFIG_LOCKDEP is on 4820 ftrace: print ftrace buffer 4821 all_bt: print all CPUs backtrace (if available in the arch) 4822 blocked_tasks: print only tasks in uninterruptible (blocked) state 4823 4824 This is a human readable alternative to the 'panic_print' option. 4825 4826 panic_console_replay 4827 When panic happens, replay all kernel messages on 4828 consoles at the end of panic. 4829 4830 parkbd.port= [HW] Parallel port number the keyboard adapter is 4831 connected to, default is 0. 4832 Format: <parport#> 4833 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4834 0 for XT, 1 for AT (default is AT). 4835 Format: <mode> 4836 4837 parport= [HW,PPT] Specify parallel ports. 0 disables. 4838 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4839 Use 'auto' to force the driver to use any 4840 IRQ/DMA settings detected (the default is to 4841 ignore detected IRQ/DMA settings because of 4842 possible conflicts). You can specify the base 4843 address, IRQ, and DMA settings; IRQ and DMA 4844 should be numbers, or 'auto' (for using detected 4845 settings on that particular port), or 'nofifo' 4846 (to avoid using a FIFO even if it is detected). 4847 Parallel ports are assigned in the order they 4848 are specified on the command line, starting 4849 with parport0. 4850 4851 parport_init_mode= [HW,PPT] 4852 Configure VIA parallel port to operate in 4853 a specific mode. This is necessary on Pegasos 4854 computer where firmware has no options for setting 4855 up parallel port mode and sets it to spp. 4856 Currently this function knows 686a and 8231 chips. 4857 Format: [spp|ps2|epp|ecp|ecpepp] 4858 4859 pata_legacy.all= [HW,LIBATA] 4860 Format: <int> 4861 Set to non-zero to probe primary and secondary ISA 4862 port ranges on PCI systems where no PCI PATA device 4863 has been found at either range. Disabled by default. 4864 4865 pata_legacy.autospeed= [HW,LIBATA] 4866 Format: <int> 4867 Set to non-zero if a chip is present that snoops speed 4868 changes. Disabled by default. 4869 4870 pata_legacy.ht6560a= [HW,LIBATA] 4871 Format: <int> 4872 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4873 the secondary channel, or both channels respectively. 4874 Disabled by default. 4875 4876 pata_legacy.ht6560b= [HW,LIBATA] 4877 Format: <int> 4878 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4879 the secondary channel, or both channels respectively. 4880 Disabled by default. 4881 4882 pata_legacy.iordy_mask= [HW,LIBATA] 4883 Format: <int> 4884 IORDY enable mask. Set individual bits to allow IORDY 4885 for the respective channel. Bit 0 is for the first 4886 legacy channel handled by this driver, bit 1 is for 4887 the second channel, and so on. The sequence will often 4888 correspond to the primary legacy channel, the secondary 4889 legacy channel, and so on, but the handling of a PCI 4890 bus and the use of other driver options may interfere 4891 with the sequence. By default IORDY is allowed across 4892 all channels. 4893 4894 pata_legacy.opti82c46x= [HW,LIBATA] 4895 Format: <int> 4896 Set to 1, 2, or 3 for Opti 82c611A on the primary 4897 channel, the secondary channel, or both channels 4898 respectively. Disabled by default. 4899 4900 pata_legacy.opti82c611a= [HW,LIBATA] 4901 Format: <int> 4902 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4903 channel, the secondary channel, or both channels 4904 respectively. Disabled by default. 4905 4906 pata_legacy.pio_mask= [HW,LIBATA] 4907 Format: <int> 4908 PIO mode mask for autospeed devices. Set individual 4909 bits to allow the use of the respective PIO modes. 4910 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4911 All modes allowed by default. 4912 4913 pata_legacy.probe_all= [HW,LIBATA] 4914 Format: <int> 4915 Set to non-zero to probe tertiary and further ISA 4916 port ranges on PCI systems. Disabled by default. 4917 4918 pata_legacy.probe_mask= [HW,LIBATA] 4919 Format: <int> 4920 Probe mask for legacy ISA PATA ports. Depending on 4921 platform configuration and the use of other driver 4922 options up to 6 legacy ports are supported: 0x1f0, 4923 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4924 of individual ports can be disabled by setting the 4925 corresponding bits in the mask to 1. Bit 0 is for 4926 the first port in the list above (0x1f0), and so on. 4927 By default all supported ports are probed. 4928 4929 pata_legacy.qdi= [HW,LIBATA] 4930 Format: <int> 4931 Set to non-zero to probe QDI controllers. By default 4932 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4933 4934 pata_legacy.winbond= [HW,LIBATA] 4935 Format: <int> 4936 Set to non-zero to probe Winbond controllers. Use 4937 the standard I/O port (0x130) if 1, otherwise the 4938 value given is the I/O port to use (typically 0x1b0). 4939 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4940 0 otherwise. 4941 4942 pata_platform.pio_mask= [HW,LIBATA] 4943 Format: <int> 4944 Supported PIO mode mask. Set individual bits to allow 4945 the use of the respective PIO modes. Bit 0 is for 4946 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4947 allowed by default. 4948 4949 pause_on_oops=<int> 4950 Halt all CPUs after the first oops has been printed for 4951 the specified number of seconds. This is to be used if 4952 your oopses keep scrolling off the screen. 4953 4954 pcbit= [HW,ISDN] 4955 4956 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4957 4958 Some options herein operate on a specific device 4959 or a set of devices (<pci_dev>). These are 4960 specified in one of the following formats: 4961 4962 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4963 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4964 4965 Note: the first format specifies a PCI 4966 bus/device/function address which may change 4967 if new hardware is inserted, if motherboard 4968 firmware changes, or due to changes caused 4969 by other kernel parameters. If the 4970 domain is left unspecified, it is 4971 taken to be zero. Optionally, a path 4972 to a device through multiple device/function 4973 addresses can be specified after the base 4974 address (this is more robust against 4975 renumbering issues). The second format 4976 selects devices using IDs from the 4977 configuration space which may match multiple 4978 devices in the system. 4979 4980 earlydump dump PCI config space before the kernel 4981 changes anything 4982 off [X86] don't probe for the PCI bus 4983 bios [X86-32] force use of PCI BIOS, don't access 4984 the hardware directly. Use this if your machine 4985 has a non-standard PCI host bridge. 4986 nobios [X86-32] disallow use of PCI BIOS, only direct 4987 hardware access methods are allowed. Use this 4988 if you experience crashes upon bootup and you 4989 suspect they are caused by the BIOS. 4990 conf1 [X86] Force use of PCI Configuration Access 4991 Mechanism 1 (config address in IO port 0xCF8, 4992 data in IO port 0xCFC, both 32-bit). 4993 conf2 [X86] Force use of PCI Configuration Access 4994 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4995 the function, IO port 0xCFA, also 8-bit, sets 4996 bus number. The config space is then accessed 4997 through ports 0xC000-0xCFFF). 4998 See http://wiki.osdev.org/PCI for more info 4999 on the configuration access mechanisms. 5000 noaer [PCIE] If the PCIEAER kernel config parameter is 5001 enabled, this kernel boot option can be used to 5002 disable the use of PCIE advanced error reporting. 5003 nodomains [PCI] Disable support for multiple PCI 5004 root domains (aka PCI segments, in ACPI-speak). 5005 nommconf [X86] Disable use of MMCONFIG for PCI 5006 Configuration 5007 check_enable_amd_mmconf [X86] check for and enable 5008 properly configured MMIO access to PCI 5009 config space on AMD family 10h CPU 5010 nomsi [MSI] If the PCI_MSI kernel config parameter is 5011 enabled, this kernel boot option can be used to 5012 disable the use of MSI interrupts system-wide. 5013 noioapicquirk [APIC] Disable all boot interrupt quirks. 5014 Safety option to keep boot IRQs enabled. This 5015 should never be necessary. 5016 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 5017 primary IO-APIC for bridges that cannot disable 5018 boot IRQs. This fixes a source of spurious IRQs 5019 when the system masks IRQs. 5020 noioapicreroute [APIC] Disable workaround that uses the 5021 boot IRQ equivalent of an IRQ that connects to 5022 a chipset where boot IRQs cannot be disabled. 5023 The opposite of ioapicreroute. 5024 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 5025 routing table. These calls are known to be buggy 5026 on several machines and they hang the machine 5027 when used, but on other computers it's the only 5028 way to get the interrupt routing table. Try 5029 this option if the kernel is unable to allocate 5030 IRQs or discover secondary PCI buses on your 5031 motherboard. 5032 rom [X86] Assign address space to expansion ROMs. 5033 Use with caution as certain devices share 5034 address decoders between ROMs and other 5035 resources. 5036 norom [X86] Do not assign address space to 5037 expansion ROMs that do not already have 5038 BIOS assigned address ranges. 5039 nobar [X86] Do not assign address space to the 5040 BARs that weren't assigned by the BIOS. 5041 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5042 assigned automatically to PCI devices. You can 5043 make the kernel exclude IRQs of your ISA cards 5044 this way. 5045 pirqaddr=0xAAAAA [X86] Specify the physical address 5046 of the PIRQ table (normally generated 5047 by the BIOS) if it is outside the 5048 F0000h-100000h range. 5049 lastbus=N [X86] Scan all buses thru bus #N. Can be 5050 useful if the kernel is unable to find your 5051 secondary buses and you want to tell it 5052 explicitly which ones they are. 5053 assign-busses [X86] Always assign all PCI bus 5054 numbers ourselves, overriding 5055 whatever the firmware may have done. 5056 usepirqmask [X86] Honor the possible IRQ mask stored 5057 in the BIOS $PIR table. This is needed on 5058 some systems with broken BIOSes, notably 5059 some HP Pavilion N5400 and Omnibook XE3 5060 notebooks. This will have no effect if ACPI 5061 IRQ routing is enabled. 5062 noacpi [X86] Do not use ACPI for IRQ routing 5063 or for PCI scanning. 5064 use_crs [X86] Use PCI host bridge window information 5065 from ACPI. On BIOSes from 2008 or later, this 5066 is enabled by default. If you need to use this, 5067 please report a bug. 5068 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5069 If you need to use this, please report a bug. 5070 use_e820 [X86] Use E820 reservations to exclude parts of 5071 PCI host bridge windows. This is a workaround 5072 for BIOS defects in host bridge _CRS methods. 5073 If you need to use this, please report a bug to 5074 <linux-pci@vger.kernel.org>. 5075 no_e820 [X86] Ignore E820 reservations for PCI host 5076 bridge windows. This is the default on modern 5077 hardware. If you need to use this, please report 5078 a bug to <linux-pci@vger.kernel.org>. 5079 routeirq Do IRQ routing for all PCI devices. 5080 This is normally done in pci_enable_device(), 5081 so this option is a temporary workaround 5082 for broken drivers that don't call it. 5083 skip_isa_align [X86] do not align io start addr, so can 5084 handle more pci cards 5085 noearly [X86] Don't do any early type 1 scanning. 5086 This might help on some broken boards which 5087 machine check when some devices' config space 5088 is read. But various workarounds are disabled 5089 and some IOMMU drivers will not work. 5090 bfsort Sort PCI devices into breadth-first order. 5091 This sorting is done to get a device 5092 order compatible with older (<= 2.4) kernels. 5093 nobfsort Don't sort PCI devices into breadth-first order. 5094 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5095 tuning and use the BIOS-configured MPS defaults. 5096 pcie_bus_safe Set every device's MPS to the largest value 5097 supported by all devices below the root complex. 5098 pcie_bus_perf Set device MPS to the largest allowable MPS 5099 based on its parent bus. Also set MRRS (Max 5100 Read Request Size) to the largest supported 5101 value (no larger than the MPS that the device 5102 or bus can support) for best performance. 5103 pcie_bus_peer2peer Set every device's MPS to 128B, which 5104 every device is guaranteed to support. This 5105 configuration allows peer-to-peer DMA between 5106 any pair of devices, possibly at the cost of 5107 reduced performance. This also guarantees 5108 that hot-added devices will work. 5109 cbiosize=nn[KMG] The fixed amount of bus space which is 5110 reserved for the CardBus bridge's IO window. 5111 The default value is 256 bytes. 5112 cbmemsize=nn[KMG] The fixed amount of bus space which is 5113 reserved for the CardBus bridge's memory 5114 window. The default value is 64 megabytes. 5115 resource_alignment= 5116 Format: 5117 [<order of align>@]<pci_dev>[; ...] 5118 Specifies alignment and device to reassign 5119 aligned memory resources. How to 5120 specify the device is described above. 5121 If <order of align> is not specified, 5122 PAGE_SIZE is used as alignment. 5123 A PCI-PCI bridge can be specified if resource 5124 windows need to be expanded. 5125 To specify the alignment for several 5126 instances of a device, the PCI vendor, 5127 device, subvendor, and subdevice may be 5128 specified, e.g., 12@pci:8086:9c22:103c:198f 5129 for 4096-byte alignment. 5130 ecrc= Enable/disable PCIe ECRC (transaction layer 5131 end-to-end CRC checking). Only effective if 5132 OS has native AER control (either granted by 5133 ACPI _OSC or forced via "pcie_ports=native") 5134 bios: Use BIOS/firmware settings. This is the 5135 the default. 5136 off: Turn ECRC off 5137 on: Turn ECRC on. 5138 hpiosize=nn[KMG] The fixed amount of bus space which is 5139 reserved for hotplug bridge's IO window. 5140 Default size is 256 bytes. 5141 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5142 reserved for hotplug bridge's MMIO window. 5143 Default size is 2 megabytes. 5144 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5145 reserved for hotplug bridge's MMIO_PREF window. 5146 Default size is 2 megabytes. 5147 hpmemsize=nn[KMG] The fixed amount of bus space which is 5148 reserved for hotplug bridge's MMIO and 5149 MMIO_PREF window. 5150 Default size is 2 megabytes. 5151 hpbussize=nn The minimum amount of additional bus numbers 5152 reserved for buses below a hotplug bridge. 5153 Default is 1. 5154 realloc= Enable/disable reallocating PCI bridge resources 5155 if allocations done by BIOS are too small to 5156 accommodate resources required by all child 5157 devices. 5158 off: Turn realloc off 5159 on: Turn realloc on 5160 realloc same as realloc=on 5161 noari do not use PCIe ARI. 5162 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5163 do not use PCIe ATS (and IOMMU device IOTLB). 5164 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5165 only look for one device below a PCIe downstream 5166 port. 5167 big_root_window Try to add a big 64bit memory window to the PCIe 5168 root complex on AMD CPUs. Some GFX hardware 5169 can resize a BAR to allow access to all VRAM. 5170 Adding the window is slightly risky (it may 5171 conflict with unreported devices), so this 5172 taints the kernel. 5173 disable_acs_redir=<pci_dev>[; ...] 5174 Specify one or more PCI devices (in the format 5175 specified above) separated by semicolons. 5176 Each device specified will have the PCI ACS 5177 redirect capabilities forced off which will 5178 allow P2P traffic between devices through 5179 bridges without forcing it upstream. Note: 5180 this removes isolation between devices and 5181 may put more devices in an IOMMU group. 5182 config_acs= 5183 Format: 5184 <ACS flags>@<pci_dev>[; ...] 5185 Specify one or more PCI devices (in the format 5186 specified above) optionally prepended with flags 5187 and separated by semicolons. The respective 5188 capabilities will be enabled, disabled or 5189 unchanged based on what is specified in 5190 flags. 5191 5192 ACS Flags is defined as follows: 5193 bit-0 : ACS Source Validation 5194 bit-1 : ACS Translation Blocking 5195 bit-2 : ACS P2P Request Redirect 5196 bit-3 : ACS P2P Completion Redirect 5197 bit-4 : ACS Upstream Forwarding 5198 bit-5 : ACS P2P Egress Control 5199 bit-6 : ACS Direct Translated P2P 5200 Each bit can be marked as: 5201 '0' – force disabled 5202 '1' – force enabled 5203 'x' – unchanged 5204 For example, 5205 pci=config_acs=10x@pci:0:0 5206 would configure all devices that support 5207 ACS to enable P2P Request Redirect, disable 5208 Translation Blocking, and leave Source 5209 Validation unchanged from whatever power-up 5210 or firmware set it to. 5211 5212 Note: this may remove isolation between devices 5213 and may put more devices in an IOMMU group. 5214 force_floating [S390] Force usage of floating interrupts. 5215 nomio [S390] Do not use MIO instructions. 5216 norid [S390] ignore the RID field and force use of 5217 one PCI domain per PCI function 5218 notph [PCIE] If the PCIE_TPH kernel config parameter 5219 is enabled, this kernel boot option can be used 5220 to disable PCIe TLP Processing Hints support 5221 system-wide. 5222 5223 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5224 Management. 5225 off Don't touch ASPM configuration at all. Leave any 5226 configuration done by firmware unchanged. 5227 force Enable ASPM even on devices that claim not to support it. 5228 WARNING: Forcing ASPM on may cause system lockups. 5229 5230 pcie_ports= [PCIE] PCIe port services handling: 5231 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5232 even if the platform doesn't give the OS permission to 5233 use them. This may cause conflicts if the platform 5234 also tries to use these services. 5235 dpc-native Use native PCIe service for DPC only. May 5236 cause conflicts if firmware uses AER or DPC. 5237 compat Disable native PCIe services (PME, AER, DPC, PCIe 5238 hotplug). 5239 5240 pcie_port_pm= [PCIE] PCIe port power management handling: 5241 off Disable power management of all PCIe ports 5242 force Forcibly enable power management of all PCIe ports 5243 5244 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5245 nomsi Do not use MSI for native PCIe PME signaling (this makes 5246 all PCIe root ports use INTx for all services). 5247 5248 pcmv= [HW,PCMCIA] BadgePAD 4 5249 5250 pd_ignore_unused 5251 [PM] 5252 Keep all power-domains already enabled by bootloader on, 5253 even if no driver has claimed them. This is useful 5254 for debug and development, but should not be 5255 needed on a platform with proper driver support. 5256 5257 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5258 boot time. 5259 Format: { 0 | 1 } 5260 See arch/parisc/kernel/pdc_chassis.c 5261 5262 percpu_alloc= [MM,EARLY] 5263 Select which percpu first chunk allocator to use. 5264 Currently supported values are "embed" and "page". 5265 Archs may support subset or none of the selections. 5266 See comments in mm/percpu.c for details on each 5267 allocator. This parameter is primarily for debugging 5268 and performance comparison. 5269 5270 pirq= [SMP,APIC] Manual mp-table setup 5271 See Documentation/arch/x86/i386/IO-APIC.rst. 5272 5273 plip= [PPT,NET] Parallel port network link 5274 Format: { parport<nr> | timid | 0 } 5275 See also Documentation/admin-guide/parport.rst. 5276 5277 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5278 Override pmtimer IOPort with a hex value. 5279 e.g. pmtmr=0x508 5280 5281 pmu_override= [PPC] Override the PMU. 5282 This option takes over the PMU facility, so it is no 5283 longer usable by perf. Setting this option starts the 5284 PMU counters by setting MMCR0 to 0 (the FC bit is 5285 cleared). If a number is given, then MMCR1 is set to 5286 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5287 remains 0. 5288 5289 pm_async= [PM] 5290 Format: off 5291 This parameter sets the initial value of the 5292 /sys/power/pm_async sysfs knob at boot time. 5293 If set to "off", disables asynchronous suspend and 5294 resume of devices during system-wide power transitions. 5295 This can be useful on platforms where device 5296 dependencies are not well-defined, or for debugging 5297 power management issues. Asynchronous operations are 5298 enabled by default. 5299 5300 5301 pm_debug_messages [SUSPEND,KNL] 5302 Enable suspend/resume debug messages during boot up. 5303 5304 pnp.debug=1 [PNP] 5305 Enable PNP debug messages (depends on the 5306 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5307 via /sys/module/pnp/parameters/debug. We always show 5308 current resource usage; turning this on also shows 5309 possible settings and some assignment information. 5310 5311 pnpacpi= [ACPI] 5312 { off } 5313 5314 pnpbios= [ISAPNP] 5315 { on | off | curr | res | no-curr | no-res } 5316 5317 pnp_reserve_irq= 5318 [ISAPNP] Exclude IRQs for the autoconfiguration 5319 5320 pnp_reserve_dma= 5321 [ISAPNP] Exclude DMAs for the autoconfiguration 5322 5323 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5324 Ranges are in pairs (I/O port base and size). 5325 5326 pnp_reserve_mem= 5327 [ISAPNP] Exclude memory regions for the 5328 autoconfiguration. 5329 Ranges are in pairs (memory base and size). 5330 5331 ports= [IP_VS_FTP] IPVS ftp helper module 5332 Default is 21. 5333 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5334 may be specified. 5335 Format: <port>,<port>.... 5336 5337 possible_cpus= [SMP,S390,X86] 5338 Format: <unsigned int> 5339 Set the number of possible CPUs, overriding the 5340 regular discovery mechanisms (such as ACPI/FW, etc). 5341 5342 powersave=off [PPC] This option disables power saving features. 5343 It specifically disables cpuidle and sets the 5344 platform machine description specific power_save 5345 function to NULL. On Idle the CPU just reduces 5346 execution priority. 5347 5348 ppc_strict_facility_enable 5349 [PPC,ENABLE] This option catches any kernel floating point, 5350 Altivec, VSX and SPE outside of regions specifically 5351 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5352 There is some performance impact when enabling this. 5353 5354 ppc_tm= [PPC,EARLY] 5355 Format: {"off"} 5356 Disable Hardware Transactional Memory 5357 5358 preempt= [KNL] 5359 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5360 none - Limited to cond_resched() calls 5361 voluntary - Limited to cond_resched() and might_sleep() calls 5362 full - Any section that isn't explicitly preempt disabled 5363 can be preempted anytime. Tasks will also yield 5364 contended spinlocks (if the critical section isn't 5365 explicitly preempt disabled beyond the lock itself). 5366 lazy - Scheduler controlled. Similar to full but instead 5367 of preempting the task immediately, the task gets 5368 one HZ tick time to yield itself before the 5369 preemption will be forced. One preemption is when the 5370 task returns to user space. 5371 5372 print-fatal-signals= 5373 [KNL] debug: print fatal signals 5374 5375 If enabled, warn about various signal handling 5376 related application anomalies: too many signals, 5377 too many POSIX.1 timers, fatal signals causing a 5378 coredump - etc. 5379 5380 If you hit the warning due to signal overflow, 5381 you might want to try "ulimit -i unlimited". 5382 5383 default: off. 5384 5385 printk.always_kmsg_dump= 5386 Trigger kmsg_dump for cases other than kernel oops or 5387 panics 5388 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5389 default: disabled 5390 5391 printk.console_no_auto_verbose= 5392 Disable console loglevel raise on oops, panic 5393 or lockdep-detected issues (only if lock debug is on). 5394 With an exception to setups with low baudrate on 5395 serial console, keeping this 0 is a good choice 5396 in order to provide more debug information. 5397 Format: <bool> 5398 default: 0 (auto_verbose is enabled) 5399 5400 printk.debug_non_panic_cpus= 5401 Allows storing messages from non-panic CPUs into 5402 the printk log buffer during panic(). They are 5403 flushed to consoles by the panic-CPU on 5404 a best-effort basis. 5405 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5406 Default: disabled 5407 5408 printk.devkmsg={on,off,ratelimit} 5409 Control writing to /dev/kmsg. 5410 on - unlimited logging to /dev/kmsg from userspace 5411 off - logging to /dev/kmsg disabled 5412 ratelimit - ratelimit the logging 5413 Default: ratelimit 5414 5415 printk.time= Show timing data prefixed to each printk message line 5416 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5417 5418 proc_mem.force_override= [KNL] 5419 Format: {always | ptrace | never} 5420 Traditionally /proc/pid/mem allows memory permissions to be 5421 overridden without restrictions. This option may be set to 5422 restrict that. Can be one of: 5423 - 'always': traditional behavior always allows mem overrides. 5424 - 'ptrace': only allow mem overrides for active ptracers. 5425 - 'never': never allow mem overrides. 5426 If not specified, default is the CONFIG_PROC_MEM_* choice. 5427 5428 processor.max_cstate= [HW,ACPI] 5429 Limit processor to maximum C-state 5430 max_cstate=9 overrides any DMI blacklist limit. 5431 5432 processor.nocst [HW,ACPI] 5433 Ignore the _CST method to determine C-states, 5434 instead using the legacy FADT method 5435 5436 profile= [KNL] Enable kernel profiling via /proc/profile 5437 Format: [<profiletype>,]<number> 5438 Param: <profiletype>: "schedule" or "kvm" 5439 [defaults to kernel profiling] 5440 Param: "schedule" - profile schedule points. 5441 Param: "kvm" - profile VM exits. 5442 Param: <number> - step/bucket size as a power of 2 for 5443 statistical time based profiling. 5444 5445 prompt_ramdisk= [RAM] [Deprecated] 5446 5447 prot_virt= [S390] enable hosting protected virtual machines 5448 isolated from the hypervisor (if hardware supports 5449 that). If enabled, the default kernel base address 5450 might be overridden even when Kernel Address Space 5451 Layout Randomization is disabled. 5452 Format: <bool> 5453 5454 psi= [KNL] Enable or disable pressure stall information 5455 tracking. 5456 Format: <bool> 5457 5458 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5459 probe for; one of (bare|imps|exps|lifebook|any). 5460 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5461 per second. 5462 psmouse.resetafter= [HW,MOUSE] 5463 Try to reset the device after so many bad packets 5464 (0 = never). 5465 psmouse.resolution= 5466 [HW,MOUSE] Set desired mouse resolution, in dpi. 5467 psmouse.smartscroll= 5468 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5469 0 = disabled, 1 = enabled (default). 5470 5471 pstore.backend= Specify the name of the pstore backend to use 5472 5473 pti= [X86-64] Control Page Table Isolation of user and 5474 kernel address spaces. Disabling this feature 5475 removes hardening, but improves performance of 5476 system calls and interrupts. 5477 5478 on - unconditionally enable 5479 off - unconditionally disable 5480 auto - kernel detects whether your CPU model is 5481 vulnerable to issues that PTI mitigates 5482 5483 Not specifying this option is equivalent to pti=auto. 5484 5485 pty.legacy_count= 5486 [KNL] Number of legacy pty's. Overwrites compiled-in 5487 default number. 5488 5489 quiet [KNL,EARLY] Disable most log messages 5490 5491 r128= [HW,DRM] 5492 5493 radix_hcall_invalidate=on [PPC/PSERIES] 5494 Disable RADIX GTSE feature and use hcall for TLB 5495 invalidate. 5496 5497 raid= [HW,RAID] 5498 See Documentation/admin-guide/md.rst. 5499 5500 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5501 See Documentation/admin-guide/blockdev/ramdisk.rst. 5502 5503 ramdisk_start= [RAM] RAM disk image start address 5504 5505 random.trust_cpu=off 5506 [KNL,EARLY] Disable trusting the use of the CPU's 5507 random number generator (if available) to 5508 initialize the kernel's RNG. 5509 5510 random.trust_bootloader=off 5511 [KNL,EARLY] Disable trusting the use of the a seed 5512 passed by the bootloader (if available) to 5513 initialize the kernel's RNG. 5514 5515 randomize_kstack_offset= 5516 [KNL,EARLY] Enable or disable kernel stack offset 5517 randomization, which provides roughly 5 bits of 5518 entropy, frustrating memory corruption attacks 5519 that depend on stack address determinism or 5520 cross-syscall address exposures. This is only 5521 available on architectures that have defined 5522 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5523 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5524 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5525 5526 ras=option[,option,...] [KNL] RAS-specific options 5527 5528 cec_disable [X86] 5529 Disable the Correctable Errors Collector, 5530 see CONFIG_RAS_CEC help text. 5531 5532 rcu_nocbs[=cpu-list] 5533 [KNL] The optional argument is a cpu list, 5534 as described above. 5535 5536 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5537 enable the no-callback CPU mode, which prevents 5538 such CPUs' callbacks from being invoked in 5539 softirq context. Invocation of such CPUs' RCU 5540 callbacks will instead be offloaded to "rcuox/N" 5541 kthreads created for that purpose, where "x" is 5542 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5543 for the kthreads that mediate grace periods; and 5544 "N" is the CPU number. This reduces OS jitter on 5545 the offloaded CPUs, which can be useful for HPC 5546 and real-time workloads. It can also improve 5547 energy efficiency for asymmetric multiprocessors. 5548 5549 If a cpulist is passed as an argument, the specified 5550 list of CPUs is set to no-callback mode from boot. 5551 5552 Otherwise, if the '=' sign and the cpulist 5553 arguments are omitted, no CPU will be set to 5554 no-callback mode from boot but the mode may be 5555 toggled at runtime via cpusets. 5556 5557 Note that this argument takes precedence over 5558 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5559 5560 rcu_nocb_poll [KNL] 5561 Rather than requiring that offloaded CPUs 5562 (specified by rcu_nocbs= above) explicitly 5563 awaken the corresponding "rcuoN" kthreads, 5564 make these kthreads poll for callbacks. 5565 This improves the real-time response for the 5566 offloaded CPUs by relieving them of the need to 5567 wake up the corresponding kthread, but degrades 5568 energy efficiency by requiring that the kthreads 5569 periodically wake up to do the polling. 5570 5571 rcutree.blimit= [KNL] 5572 Set maximum number of finished RCU callbacks to 5573 process in one batch. 5574 5575 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5576 Do only a one-line RCU CPU stall warning when 5577 there is an ongoing too-long CSD-lock wait. 5578 5579 rcutree.do_rcu_barrier= [KNL] 5580 Request a call to rcu_barrier(). This is 5581 throttled so that userspace tests can safely 5582 hammer on the sysfs variable if they so choose. 5583 If triggered before the RCU grace-period machinery 5584 is fully active, this will error out with EAGAIN. 5585 5586 rcutree.dump_tree= [KNL] 5587 Dump the structure of the rcu_node combining tree 5588 out at early boot. This is used for diagnostic 5589 purposes, to verify correct tree setup. 5590 5591 rcutree.gp_cleanup_delay= [KNL] 5592 Set the number of jiffies to delay each step of 5593 RCU grace-period cleanup. 5594 5595 rcutree.gp_init_delay= [KNL] 5596 Set the number of jiffies to delay each step of 5597 RCU grace-period initialization. 5598 5599 rcutree.gp_preinit_delay= [KNL] 5600 Set the number of jiffies to delay each step of 5601 RCU grace-period pre-initialization, that is, 5602 the propagation of recent CPU-hotplug changes up 5603 the rcu_node combining tree. 5604 5605 rcutree.jiffies_till_first_fqs= [KNL] 5606 Set delay from grace-period initialization to 5607 first attempt to force quiescent states. 5608 Units are jiffies, minimum value is zero, 5609 and maximum value is HZ. 5610 5611 rcutree.jiffies_till_next_fqs= [KNL] 5612 Set delay between subsequent attempts to force 5613 quiescent states. Units are jiffies, minimum 5614 value is one, and maximum value is HZ. 5615 5616 rcutree.jiffies_till_sched_qs= [KNL] 5617 Set required age in jiffies for a 5618 given grace period before RCU starts 5619 soliciting quiescent-state help from 5620 rcu_note_context_switch() and cond_resched(). 5621 If not specified, the kernel will calculate 5622 a value based on the most recent settings 5623 of rcutree.jiffies_till_first_fqs 5624 and rcutree.jiffies_till_next_fqs. 5625 This calculated value may be viewed in 5626 rcutree.jiffies_to_sched_qs. Any attempt to set 5627 rcutree.jiffies_to_sched_qs will be cheerfully 5628 overwritten. 5629 5630 rcutree.kthread_prio= [KNL,BOOT] 5631 Set the SCHED_FIFO priority of the RCU per-CPU 5632 kthreads (rcuc/N). This value is also used for 5633 the priority of the RCU boost threads (rcub/N) 5634 and for the RCU grace-period kthreads (rcu_bh, 5635 rcu_preempt, and rcu_sched). If RCU_BOOST is 5636 set, valid values are 1-99 and the default is 1 5637 (the least-favored priority). Otherwise, when 5638 RCU_BOOST is not set, valid values are 0-99 and 5639 the default is zero (non-realtime operation). 5640 When RCU_NOCB_CPU is set, also adjust the 5641 priority of NOCB callback kthreads. 5642 5643 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5644 On callback-offloaded (rcu_nocbs) CPUs, 5645 RCU reduces the lock contention that would 5646 otherwise be caused by callback floods through 5647 use of the ->nocb_bypass list. However, in the 5648 common non-flooded case, RCU queues directly to 5649 the main ->cblist in order to avoid the extra 5650 overhead of the ->nocb_bypass list and its lock. 5651 But if there are too many callbacks queued during 5652 a single jiffy, RCU pre-queues the callbacks into 5653 the ->nocb_bypass queue. The definition of "too 5654 many" is supplied by this kernel boot parameter. 5655 5656 rcutree.nohz_full_patience_delay= [KNL] 5657 On callback-offloaded (rcu_nocbs) CPUs, avoid 5658 disturbing RCU unless the grace period has 5659 reached the specified age in milliseconds. 5660 Defaults to zero. Large values will be capped 5661 at five seconds. All values will be rounded down 5662 to the nearest value representable by jiffies. 5663 5664 rcutree.qhimark= [KNL] 5665 Set threshold of queued RCU callbacks beyond which 5666 batch limiting is disabled. 5667 5668 rcutree.qlowmark= [KNL] 5669 Set threshold of queued RCU callbacks below which 5670 batch limiting is re-enabled. 5671 5672 rcutree.qovld= [KNL] 5673 Set threshold of queued RCU callbacks beyond which 5674 RCU's force-quiescent-state scan will aggressively 5675 enlist help from cond_resched() and sched IPIs to 5676 help CPUs more quickly reach quiescent states. 5677 Set to less than zero to make this be set based 5678 on rcutree.qhimark at boot time and to zero to 5679 disable more aggressive help enlistment. 5680 5681 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5682 Set the page-cache refill delay (in milliseconds) 5683 in response to low-memory conditions. The range 5684 of permitted values is in the range 0:100000. 5685 5686 rcutree.rcu_divisor= [KNL] 5687 Set the shift-right count to use to compute 5688 the callback-invocation batch limit bl from 5689 the number of callbacks queued on this CPU. 5690 The result will be bounded below by the value of 5691 the rcutree.blimit kernel parameter. Every bl 5692 callbacks, the softirq handler will exit in 5693 order to allow the CPU to do other work. 5694 5695 Please note that this callback-invocation batch 5696 limit applies only to non-offloaded callback 5697 invocation. Offloaded callbacks are instead 5698 invoked in the context of an rcuoc kthread, which 5699 scheduler will preempt as it does any other task. 5700 5701 rcutree.rcu_fanout_exact= [KNL] 5702 Disable autobalancing of the rcu_node combining 5703 tree. This is used by rcutorture, and might 5704 possibly be useful for architectures having high 5705 cache-to-cache transfer latencies. 5706 5707 rcutree.rcu_fanout_leaf= [KNL] 5708 Change the number of CPUs assigned to each 5709 leaf rcu_node structure. Useful for very 5710 large systems, which will choose the value 64, 5711 and for NUMA systems with large remote-access 5712 latencies, which will choose a value aligned 5713 with the appropriate hardware boundaries. 5714 5715 rcutree.rcu_min_cached_objs= [KNL] 5716 Minimum number of objects which are cached and 5717 maintained per one CPU. Object size is equal 5718 to PAGE_SIZE. The cache allows to reduce the 5719 pressure to page allocator, also it makes the 5720 whole algorithm to behave better in low memory 5721 condition. 5722 5723 rcutree.rcu_nocb_gp_stride= [KNL] 5724 Set the number of NOCB callback kthreads in 5725 each group, which defaults to the square root 5726 of the number of CPUs. Larger numbers reduce 5727 the wakeup overhead on the global grace-period 5728 kthread, but increases that same overhead on 5729 each group's NOCB grace-period kthread. 5730 5731 rcutree.rcu_kick_kthreads= [KNL] 5732 Cause the grace-period kthread to get an extra 5733 wake_up() if it sleeps three times longer than 5734 it should at force-quiescent-state time. 5735 This wake_up() will be accompanied by a 5736 WARN_ONCE() splat and an ftrace_dump(). 5737 5738 rcutree.rcu_resched_ns= [KNL] 5739 Limit the time spend invoking a batch of RCU 5740 callbacks to the specified number of nanoseconds. 5741 By default, this limit is checked only once 5742 every 32 callbacks in order to limit the pain 5743 inflicted by local_clock() overhead. 5744 5745 rcutree.rcu_unlock_delay= [KNL] 5746 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5747 this specifies an rcu_read_unlock()-time delay 5748 in microseconds. This defaults to zero. 5749 Larger delays increase the probability of 5750 catching RCU pointer leaks, that is, buggy use 5751 of RCU-protected pointers after the relevant 5752 rcu_read_unlock() has completed. 5753 5754 rcutree.sysrq_rcu= [KNL] 5755 Commandeer a sysrq key to dump out Tree RCU's 5756 rcu_node tree with an eye towards determining 5757 why a new grace period has not yet started. 5758 5759 rcutree.use_softirq= [KNL] 5760 If set to zero, move all RCU_SOFTIRQ processing to 5761 per-CPU rcuc kthreads. Defaults to a non-zero 5762 value, meaning that RCU_SOFTIRQ is used by default. 5763 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5764 5765 But note that CONFIG_PREEMPT_RT=y kernels disable 5766 this kernel boot parameter, forcibly setting it 5767 to zero. 5768 5769 rcutree.enable_rcu_lazy= [KNL] 5770 To save power, batch RCU callbacks and flush after 5771 delay, memory pressure or callback list growing too 5772 big. 5773 5774 rcutree.rcu_normal_wake_from_gp= [KNL] 5775 Reduces a latency of synchronize_rcu() call. This approach 5776 maintains its own track of synchronize_rcu() callers, so it 5777 does not interact with regular callbacks because it does not 5778 use a call_rcu[_hurry]() path. Please note, this is for a 5779 normal grace period. 5780 5781 How to enable it: 5782 5783 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5784 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5785 5786 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5787 disabled by the boot parameter passing 0. 5788 5789 rcuscale.gp_async= [KNL] 5790 Measure performance of asynchronous 5791 grace-period primitives such as call_rcu(). 5792 5793 rcuscale.gp_async_max= [KNL] 5794 Specify the maximum number of outstanding 5795 callbacks per writer thread. When a writer 5796 thread exceeds this limit, it invokes the 5797 corresponding flavor of rcu_barrier() to allow 5798 previously posted callbacks to drain. 5799 5800 rcuscale.gp_exp= [KNL] 5801 Measure performance of expedited synchronous 5802 grace-period primitives. 5803 5804 rcuscale.holdoff= [KNL] 5805 Set test-start holdoff period. The purpose of 5806 this parameter is to delay the start of the 5807 test until boot completes in order to avoid 5808 interference. 5809 5810 rcuscale.kfree_by_call_rcu= [KNL] 5811 In kernels built with CONFIG_RCU_LAZY=y, test 5812 call_rcu() instead of kfree_rcu(). 5813 5814 rcuscale.kfree_mult= [KNL] 5815 Instead of allocating an object of size kfree_obj, 5816 allocate one of kfree_mult * sizeof(kfree_obj). 5817 Defaults to 1. 5818 5819 rcuscale.kfree_rcu_test= [KNL] 5820 Set to measure performance of kfree_rcu() flooding. 5821 5822 rcuscale.kfree_rcu_test_double= [KNL] 5823 Test the double-argument variant of kfree_rcu(). 5824 If this parameter has the same value as 5825 rcuscale.kfree_rcu_test_single, both the single- 5826 and double-argument variants are tested. 5827 5828 rcuscale.kfree_rcu_test_single= [KNL] 5829 Test the single-argument variant of kfree_rcu(). 5830 If this parameter has the same value as 5831 rcuscale.kfree_rcu_test_double, both the single- 5832 and double-argument variants are tested. 5833 5834 rcuscale.kfree_nthreads= [KNL] 5835 The number of threads running loops of kfree_rcu(). 5836 5837 rcuscale.kfree_alloc_num= [KNL] 5838 Number of allocations and frees done in an iteration. 5839 5840 rcuscale.kfree_loops= [KNL] 5841 Number of loops doing rcuscale.kfree_alloc_num number 5842 of allocations and frees. 5843 5844 rcuscale.minruntime= [KNL] 5845 Set the minimum test run time in seconds. This 5846 does not affect the data-collection interval, 5847 but instead allows better measurement of things 5848 like CPU consumption. 5849 5850 rcuscale.nreaders= [KNL] 5851 Set number of RCU readers. The value -1 selects 5852 N, where N is the number of CPUs. A value 5853 "n" less than -1 selects N-n+1, where N is again 5854 the number of CPUs. For example, -2 selects N 5855 (the number of CPUs), -3 selects N+1, and so on. 5856 A value of "n" less than or equal to -N selects 5857 a single reader. 5858 5859 rcuscale.nwriters= [KNL] 5860 Set number of RCU writers. The values operate 5861 the same as for rcuscale.nreaders. 5862 N, where N is the number of CPUs 5863 5864 rcuscale.scale_type= [KNL] 5865 Specify the RCU implementation to test. 5866 5867 rcuscale.shutdown= [KNL] 5868 Shut the system down after performance tests 5869 complete. This is useful for hands-off automated 5870 testing. 5871 5872 rcuscale.verbose= [KNL] 5873 Enable additional printk() statements. 5874 5875 rcuscale.writer_holdoff= [KNL] 5876 Write-side holdoff between grace periods, 5877 in microseconds. The default of zero says 5878 no holdoff. 5879 5880 rcuscale.writer_holdoff_jiffies= [KNL] 5881 Additional write-side holdoff between grace 5882 periods, but in jiffies. The default of zero 5883 says no holdoff. 5884 5885 rcutorture.fqs_duration= [KNL] 5886 Set duration of force_quiescent_state bursts 5887 in microseconds. 5888 5889 rcutorture.fqs_holdoff= [KNL] 5890 Set holdoff time within force_quiescent_state bursts 5891 in microseconds. 5892 5893 rcutorture.fqs_stutter= [KNL] 5894 Set wait time between force_quiescent_state bursts 5895 in seconds. 5896 5897 rcutorture.fwd_progress= [KNL] 5898 Specifies the number of kthreads to be used 5899 for RCU grace-period forward-progress testing 5900 for the types of RCU supporting this notion. 5901 Defaults to 1 kthread, values less than zero or 5902 greater than the number of CPUs cause the number 5903 of CPUs to be used. 5904 5905 rcutorture.fwd_progress_div= [KNL] 5906 Specify the fraction of a CPU-stall-warning 5907 period to do tight-loop forward-progress testing. 5908 5909 rcutorture.fwd_progress_holdoff= [KNL] 5910 Number of seconds to wait between successive 5911 forward-progress tests. 5912 5913 rcutorture.fwd_progress_need_resched= [KNL] 5914 Enclose cond_resched() calls within checks for 5915 need_resched() during tight-loop forward-progress 5916 testing. 5917 5918 rcutorture.gp_cond= [KNL] 5919 Use conditional/asynchronous update-side 5920 normal-grace-period primitives, if available. 5921 5922 rcutorture.gp_cond_exp= [KNL] 5923 Use conditional/asynchronous update-side 5924 expedited-grace-period primitives, if available. 5925 5926 rcutorture.gp_cond_full= [KNL] 5927 Use conditional/asynchronous update-side 5928 normal-grace-period primitives that also take 5929 concurrent expedited grace periods into account, 5930 if available. 5931 5932 rcutorture.gp_cond_exp_full= [KNL] 5933 Use conditional/asynchronous update-side 5934 expedited-grace-period primitives that also take 5935 concurrent normal grace periods into account, 5936 if available. 5937 5938 rcutorture.gp_cond_wi= [KNL] 5939 Nominal wait interval for normal conditional 5940 grace periods (specified by rcutorture's 5941 gp_cond and gp_cond_full module parameters), 5942 in microseconds. The actual wait interval will 5943 be randomly selected to nanosecond granularity up 5944 to this wait interval. Defaults to 16 jiffies, 5945 for example, 16,000 microseconds on a system 5946 with HZ=1000. 5947 5948 rcutorture.gp_cond_wi_exp= [KNL] 5949 Nominal wait interval for expedited conditional 5950 grace periods (specified by rcutorture's 5951 gp_cond_exp and gp_cond_exp_full module 5952 parameters), in microseconds. The actual wait 5953 interval will be randomly selected to nanosecond 5954 granularity up to this wait interval. Defaults to 5955 128 microseconds. 5956 5957 rcutorture.gp_exp= [KNL] 5958 Use expedited update-side primitives, if available. 5959 5960 rcutorture.gp_normal= [KNL] 5961 Use normal (non-expedited) asynchronous 5962 update-side primitives, if available. 5963 5964 rcutorture.gp_poll= [KNL] 5965 Use polled update-side normal-grace-period 5966 primitives, if available. 5967 5968 rcutorture.gp_poll_exp= [KNL] 5969 Use polled update-side expedited-grace-period 5970 primitives, if available. 5971 5972 rcutorture.gp_poll_full= [KNL] 5973 Use polled update-side normal-grace-period 5974 primitives that also take concurrent expedited 5975 grace periods into account, if available. 5976 5977 rcutorture.gp_poll_exp_full= [KNL] 5978 Use polled update-side expedited-grace-period 5979 primitives that also take concurrent normal 5980 grace periods into account, if available. 5981 5982 rcutorture.gp_poll_wi= [KNL] 5983 Nominal wait interval for normal conditional 5984 grace periods (specified by rcutorture's 5985 gp_poll and gp_poll_full module parameters), 5986 in microseconds. The actual wait interval will 5987 be randomly selected to nanosecond granularity up 5988 to this wait interval. Defaults to 16 jiffies, 5989 for example, 16,000 microseconds on a system 5990 with HZ=1000. 5991 5992 rcutorture.gp_poll_wi_exp= [KNL] 5993 Nominal wait interval for expedited conditional 5994 grace periods (specified by rcutorture's 5995 gp_poll_exp and gp_poll_exp_full module 5996 parameters), in microseconds. The actual wait 5997 interval will be randomly selected to nanosecond 5998 granularity up to this wait interval. Defaults to 5999 128 microseconds. 6000 6001 rcutorture.gp_sync= [KNL] 6002 Use normal (non-expedited) synchronous 6003 update-side primitives, if available. If all 6004 of rcutorture.gp_cond=, rcutorture.gp_exp=, 6005 rcutorture.gp_normal=, and rcutorture.gp_sync= 6006 are zero, rcutorture acts as if is interpreted 6007 they are all non-zero. 6008 6009 rcutorture.gpwrap_lag= [KNL] 6010 Enable grace-period wrap lag testing. Setting 6011 to false prevents the gpwrap lag test from 6012 running. Default is true. 6013 6014 rcutorture.gpwrap_lag_gps= [KNL] 6015 Set the value for grace-period wrap lag during 6016 active lag testing periods. This controls how many 6017 grace periods differences we tolerate between 6018 rdp and rnp's gp_seq before setting overflow flag. 6019 The default is always set to 8. 6020 6021 rcutorture.gpwrap_lag_cycle_mins= [KNL] 6022 Set the total cycle duration for gpwrap lag 6023 testing in minutes. This is the total time for 6024 one complete cycle of active and inactive 6025 testing periods. Default is 30 minutes. 6026 6027 rcutorture.gpwrap_lag_active_mins= [KNL] 6028 Set the duration for which gpwrap lag is active 6029 within each cycle, in minutes. During this time, 6030 the grace-period wrap lag will be set to the 6031 value specified by gpwrap_lag_gps. Default is 6032 5 minutes. 6033 6034 rcutorture.irqreader= [KNL] 6035 Run RCU readers from irq handlers, or, more 6036 accurately, from a timer handler. Not all RCU 6037 flavors take kindly to this sort of thing. 6038 6039 rcutorture.leakpointer= [KNL] 6040 Leak an RCU-protected pointer out of the reader. 6041 This can of course result in splats, and is 6042 intended to test the ability of things like 6043 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6044 such leaks. 6045 6046 rcutorture.n_barrier_cbs= [KNL] 6047 Set callbacks/threads for rcu_barrier() testing. 6048 6049 rcutorture.nfakewriters= [KNL] 6050 Set number of concurrent RCU writers. These just 6051 stress RCU, they don't participate in the actual 6052 test, hence the "fake". 6053 6054 rcutorture.nocbs_nthreads= [KNL] 6055 Set number of RCU callback-offload togglers. 6056 Zero (the default) disables toggling. 6057 6058 rcutorture.nocbs_toggle= [KNL] 6059 Set the delay in milliseconds between successive 6060 callback-offload toggling attempts. 6061 6062 rcutorture.nreaders= [KNL] 6063 Set number of RCU readers. The value -1 selects 6064 N-1, where N is the number of CPUs. A value 6065 "n" less than -1 selects N-n-2, where N is again 6066 the number of CPUs. For example, -2 selects N 6067 (the number of CPUs), -3 selects N+1, and so on. 6068 6069 rcutorture.object_debug= [KNL] 6070 Enable debug-object double-call_rcu() testing. 6071 6072 rcutorture.onoff_holdoff= [KNL] 6073 Set time (s) after boot for CPU-hotplug testing. 6074 6075 rcutorture.onoff_interval= [KNL] 6076 Set time (jiffies) between CPU-hotplug operations, 6077 or zero to disable CPU-hotplug testing. 6078 6079 rcutorture.preempt_duration= [KNL] 6080 Set duration (in milliseconds) of preemptions 6081 by a high-priority FIFO real-time task. Set to 6082 zero (the default) to disable. The CPUs to 6083 preempt are selected randomly from the set that 6084 are online at a given point in time. Races with 6085 CPUs going offline are ignored, with that attempt 6086 at preemption skipped. 6087 6088 rcutorture.preempt_interval= [KNL] 6089 Set interval (in milliseconds, defaulting to one 6090 second) between preemptions by a high-priority 6091 FIFO real-time task. This delay is mediated 6092 by an hrtimer and is further fuzzed to avoid 6093 inadvertent synchronizations. 6094 6095 rcutorture.read_exit_burst= [KNL] 6096 The number of times in a given read-then-exit 6097 episode that a set of read-then-exit kthreads 6098 is spawned. 6099 6100 rcutorture.read_exit_delay= [KNL] 6101 The delay, in seconds, between successive 6102 read-then-exit testing episodes. 6103 6104 rcutorture.reader_flavor= [KNL] 6105 A bit mask indicating which readers to use. 6106 If there is more than one bit set, the readers 6107 are entered from low-order bit up, and are 6108 exited in the opposite order. For SRCU, the 6109 0x1 bit is normal readers, 0x2 NMI-safe readers, 6110 and 0x4 light-weight readers. 6111 6112 rcutorture.shuffle_interval= [KNL] 6113 Set task-shuffle interval (s). Shuffling tasks 6114 allows some CPUs to go into dyntick-idle mode 6115 during the rcutorture test. 6116 6117 rcutorture.shutdown_secs= [KNL] 6118 Set time (s) after boot system shutdown. This 6119 is useful for hands-off automated testing. 6120 6121 rcutorture.stall_cpu= [KNL] 6122 Duration of CPU stall (s) to test RCU CPU stall 6123 warnings, zero to disable. 6124 6125 rcutorture.stall_cpu_block= [KNL] 6126 Sleep while stalling if set. This will result 6127 in warnings from preemptible RCU in addition to 6128 any other stall-related activity. Note that 6129 in kernels built with CONFIG_PREEMPTION=n and 6130 CONFIG_PREEMPT_COUNT=y, this parameter will 6131 cause the CPU to pass through a quiescent state. 6132 Given CONFIG_PREEMPTION=n, this will suppress 6133 RCU CPU stall warnings, but will instead result 6134 in scheduling-while-atomic splats. 6135 6136 Use of this module parameter results in splats. 6137 6138 6139 rcutorture.stall_cpu_holdoff= [KNL] 6140 Time to wait (s) after boot before inducing stall. 6141 6142 rcutorture.stall_cpu_irqsoff= [KNL] 6143 Disable interrupts while stalling if set, but only 6144 on the first stall in the set. 6145 6146 rcutorture.stall_cpu_repeat= [KNL] 6147 Number of times to repeat the stall sequence, 6148 so that rcutorture.stall_cpu_repeat=3 will result 6149 in four stall sequences. 6150 6151 rcutorture.stall_gp_kthread= [KNL] 6152 Duration (s) of forced sleep within RCU 6153 grace-period kthread to test RCU CPU stall 6154 warnings, zero to disable. If both stall_cpu 6155 and stall_gp_kthread are specified, the 6156 kthread is starved first, then the CPU. 6157 6158 rcutorture.stat_interval= [KNL] 6159 Time (s) between statistics printk()s. 6160 6161 rcutorture.stutter= [KNL] 6162 Time (s) to stutter testing, for example, specifying 6163 five seconds causes the test to run for five seconds, 6164 wait for five seconds, and so on. This tests RCU's 6165 ability to transition abruptly to and from idle. 6166 6167 rcutorture.test_boost= [KNL] 6168 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6169 "Maybe" means test if the RCU implementation 6170 under test support RCU priority boosting. 6171 6172 rcutorture.test_boost_duration= [KNL] 6173 Duration (s) of each individual boost test. 6174 6175 rcutorture.test_boost_holdoff= [KNL] 6176 Holdoff time (s) from start of test to the start 6177 of RCU priority-boost testing. Defaults to zero, 6178 that is, no holdoff. 6179 6180 rcutorture.test_boost_interval= [KNL] 6181 Interval (s) between each boost test. 6182 6183 rcutorture.test_no_idle_hz= [KNL] 6184 Test RCU's dyntick-idle handling. See also the 6185 rcutorture.shuffle_interval parameter. 6186 6187 rcutorture.torture_type= [KNL] 6188 Specify the RCU implementation to test. 6189 6190 rcutorture.verbose= [KNL] 6191 Enable additional printk() statements. 6192 6193 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6194 Dump ftrace buffer after reporting RCU CPU 6195 stall warning. 6196 6197 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6198 Provide RCU CPU stall notifiers, but see the 6199 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6200 option's help text. TL;DR: You almost certainly 6201 do not want rcupdate.rcu_cpu_stall_notifiers. 6202 6203 rcupdate.rcu_cpu_stall_suppress= [KNL] 6204 Suppress RCU CPU stall warning messages. 6205 6206 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6207 Suppress RCU CPU stall warning messages and 6208 rcutorture writer stall warnings that occur 6209 during early boot, that is, during the time 6210 before the init task is spawned. 6211 6212 rcupdate.rcu_cpu_stall_timeout= [KNL] 6213 Set timeout for RCU CPU stall warning messages. 6214 The value is in seconds and the maximum allowed 6215 value is 300 seconds. 6216 6217 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6218 Set timeout for expedited RCU CPU stall warning 6219 messages. The value is in milliseconds 6220 and the maximum allowed value is 21000 6221 milliseconds. Please note that this value is 6222 adjusted to an arch timer tick resolution. 6223 Setting this to zero causes the value from 6224 rcupdate.rcu_cpu_stall_timeout to be used (after 6225 conversion from seconds to milliseconds). 6226 6227 rcupdate.rcu_cpu_stall_cputime= [KNL] 6228 Provide statistics on the cputime and count of 6229 interrupts and tasks during the sampling period. For 6230 multiple continuous RCU stalls, all sampling periods 6231 begin at half of the first RCU stall timeout. 6232 6233 rcupdate.rcu_exp_stall_task_details= [KNL] 6234 Print stack dumps of any tasks blocking the 6235 current expedited RCU grace period during an 6236 expedited RCU CPU stall warning. 6237 6238 rcupdate.rcu_expedited= [KNL] 6239 Use expedited grace-period primitives, for 6240 example, synchronize_rcu_expedited() instead 6241 of synchronize_rcu(). This reduces latency, 6242 but can increase CPU utilization, degrade 6243 real-time latency, and degrade energy efficiency. 6244 No effect on CONFIG_TINY_RCU kernels. 6245 6246 rcupdate.rcu_normal= [KNL] 6247 Use only normal grace-period primitives, 6248 for example, synchronize_rcu() instead of 6249 synchronize_rcu_expedited(). This improves 6250 real-time latency, CPU utilization, and 6251 energy efficiency, but can expose users to 6252 increased grace-period latency. This parameter 6253 overrides rcupdate.rcu_expedited. No effect on 6254 CONFIG_TINY_RCU kernels. 6255 6256 rcupdate.rcu_normal_after_boot= [KNL] 6257 Once boot has completed (that is, after 6258 rcu_end_inkernel_boot() has been invoked), use 6259 only normal grace-period primitives. No effect 6260 on CONFIG_TINY_RCU kernels. 6261 6262 But note that CONFIG_PREEMPT_RT=y kernels enables 6263 this kernel boot parameter, forcibly setting 6264 it to the value one, that is, converting any 6265 post-boot attempt at an expedited RCU grace 6266 period to instead use normal non-expedited 6267 grace-period processing. 6268 6269 rcupdate.rcu_task_collapse_lim= [KNL] 6270 Set the maximum number of callbacks present 6271 at the beginning of a grace period that allows 6272 the RCU Tasks flavors to collapse back to using 6273 a single callback queue. This switching only 6274 occurs when rcupdate.rcu_task_enqueue_lim is 6275 set to the default value of -1. 6276 6277 rcupdate.rcu_task_contend_lim= [KNL] 6278 Set the minimum number of callback-queuing-time 6279 lock-contention events per jiffy required to 6280 cause the RCU Tasks flavors to switch to per-CPU 6281 callback queuing. This switching only occurs 6282 when rcupdate.rcu_task_enqueue_lim is set to 6283 the default value of -1. 6284 6285 rcupdate.rcu_task_enqueue_lim= [KNL] 6286 Set the number of callback queues to use for the 6287 RCU Tasks family of RCU flavors. The default 6288 of -1 allows this to be automatically (and 6289 dynamically) adjusted. This parameter is intended 6290 for use in testing. 6291 6292 rcupdate.rcu_task_ipi_delay= [KNL] 6293 Set time in jiffies during which RCU tasks will 6294 avoid sending IPIs, starting with the beginning 6295 of a given grace period. Setting a large 6296 number avoids disturbing real-time workloads, 6297 but lengthens grace periods. 6298 6299 rcupdate.rcu_task_lazy_lim= [KNL] 6300 Number of callbacks on a given CPU that will 6301 cancel laziness on that CPU. Use -1 to disable 6302 cancellation of laziness, but be advised that 6303 doing so increases the danger of OOM due to 6304 callback flooding. 6305 6306 rcupdate.rcu_task_stall_info= [KNL] 6307 Set initial timeout in jiffies for RCU task stall 6308 informational messages, which give some indication 6309 of the problem for those not patient enough to 6310 wait for ten minutes. Informational messages are 6311 only printed prior to the stall-warning message 6312 for a given grace period. Disable with a value 6313 less than or equal to zero. Defaults to ten 6314 seconds. A change in value does not take effect 6315 until the beginning of the next grace period. 6316 6317 rcupdate.rcu_task_stall_info_mult= [KNL] 6318 Multiplier for time interval between successive 6319 RCU task stall informational messages for a given 6320 RCU tasks grace period. This value is clamped 6321 to one through ten, inclusive. It defaults to 6322 the value three, so that the first informational 6323 message is printed 10 seconds into the grace 6324 period, the second at 40 seconds, the third at 6325 160 seconds, and then the stall warning at 600 6326 seconds would prevent a fourth at 640 seconds. 6327 6328 rcupdate.rcu_task_stall_timeout= [KNL] 6329 Set timeout in jiffies for RCU task stall 6330 warning messages. Disable with a value less 6331 than or equal to zero. Defaults to ten minutes. 6332 A change in value does not take effect until 6333 the beginning of the next grace period. 6334 6335 rcupdate.rcu_tasks_lazy_ms= [KNL] 6336 Set timeout in milliseconds RCU Tasks asynchronous 6337 callback batching for call_rcu_tasks(). 6338 A negative value will take the default. A value 6339 of zero will disable batching. Batching is 6340 always disabled for synchronize_rcu_tasks(). 6341 6342 rcupdate.rcu_tasks_trace_lazy_ms= [KNL] 6343 Set timeout in milliseconds RCU Tasks 6344 Trace asynchronous callback batching for 6345 call_rcu_tasks_trace(). A negative value 6346 will take the default. A value of zero will 6347 disable batching. Batching is always disabled 6348 for synchronize_rcu_tasks_trace(). 6349 6350 rcupdate.rcu_self_test= [KNL] 6351 Run the RCU early boot self tests 6352 6353 rdinit= [KNL] 6354 Format: <full_path> 6355 Run specified binary instead of /init from the ramdisk, 6356 used for early userspace startup. See initrd. 6357 6358 rdrand= [X86,EARLY] 6359 force - Override the decision by the kernel to hide the 6360 advertisement of RDRAND support (this affects 6361 certain AMD processors because of buggy BIOS 6362 support, specifically around the suspend/resume 6363 path). 6364 6365 rdt= [HW,X86,RDT] 6366 Turn on/off individual RDT features. List is: 6367 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6368 mba, smba, bmec, abmc, sdciae. 6369 E.g. to turn on cmt and turn off mba use: 6370 rdt=cmt,!mba 6371 6372 reboot= [KNL] 6373 Format (x86 or x86_64): 6374 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6375 [[,]s[mp]#### \ 6376 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6377 [[,]f[orce] 6378 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6379 (prefix with 'panic_' to set mode for panic 6380 reboot only), 6381 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6382 reboot_force is either force or not specified, 6383 reboot_cpu is s[mp]#### with #### being the processor 6384 to be used for rebooting. 6385 6386 acpi 6387 Use the ACPI RESET_REG in the FADT. If ACPI is not 6388 configured or the ACPI reset does not work, the reboot 6389 path attempts the reset using the keyboard controller. 6390 6391 bios 6392 Use the CPU reboot vector for warm reset 6393 6394 cold 6395 Set the cold reboot flag 6396 6397 default 6398 There are some built-in platform specific "quirks" 6399 - you may see: "reboot: <name> series board detected. 6400 Selecting <type> for reboots." In the case where you 6401 think the quirk is in error (e.g. you have newer BIOS, 6402 or newer board) using this option will ignore the 6403 built-in quirk table, and use the generic default 6404 reboot actions. 6405 6406 efi 6407 Use efi reset_system runtime service. If EFI is not 6408 configured or the EFI reset does not work, the reboot 6409 path attempts the reset using the keyboard controller. 6410 6411 force 6412 Don't stop other CPUs on reboot. This can make reboot 6413 more reliable in some cases. 6414 6415 kbd 6416 Use the keyboard controller. cold reset (default) 6417 6418 pci 6419 Use a write to the PCI config space register 0xcf9 to 6420 trigger reboot. 6421 6422 triple 6423 Force a triple fault (init) 6424 6425 warm 6426 Don't set the cold reboot flag 6427 6428 Using warm reset will be much faster especially on big 6429 memory systems because the BIOS will not go through 6430 the memory check. Disadvantage is that not all 6431 hardware will be completely reinitialized on reboot so 6432 there may be boot problems on some systems. 6433 6434 6435 refscale.holdoff= [KNL] 6436 Set test-start holdoff period. The purpose of 6437 this parameter is to delay the start of the 6438 test until boot completes in order to avoid 6439 interference. 6440 6441 refscale.lookup_instances= [KNL] 6442 Number of data elements to use for the forms of 6443 SLAB_TYPESAFE_BY_RCU testing. A negative number 6444 is negated and multiplied by nr_cpu_ids, while 6445 zero specifies nr_cpu_ids. 6446 6447 refscale.loops= [KNL] 6448 Set the number of loops over the synchronization 6449 primitive under test. Increasing this number 6450 reduces noise due to loop start/end overhead, 6451 but the default has already reduced the per-pass 6452 noise to a handful of picoseconds on ca. 2020 6453 x86 laptops. 6454 6455 refscale.nreaders= [KNL] 6456 Set number of readers. The default value of -1 6457 selects N, where N is roughly 75% of the number 6458 of CPUs. A value of zero is an interesting choice. 6459 6460 refscale.nruns= [KNL] 6461 Set number of runs, each of which is dumped onto 6462 the console log. 6463 6464 refscale.readdelay= [KNL] 6465 Set the read-side critical-section duration, 6466 measured in microseconds. 6467 6468 refscale.scale_type= [KNL] 6469 Specify the read-protection implementation to test. 6470 6471 refscale.shutdown= [KNL] 6472 Shut down the system at the end of the performance 6473 test. This defaults to 1 (shut it down) when 6474 refscale is built into the kernel and to 0 (leave 6475 it running) when refscale is built as a module. 6476 6477 refscale.verbose= [KNL] 6478 Enable additional printk() statements. 6479 6480 refscale.verbose_batched= [KNL] 6481 Batch the additional printk() statements. If zero 6482 (the default) or negative, print everything. Otherwise, 6483 print every Nth verbose statement, where N is the value 6484 specified. 6485 6486 regulator_ignore_unused 6487 [REGULATOR] 6488 Prevents regulator framework from disabling regulators 6489 that are unused, due no driver claiming them. This may 6490 be useful for debug and development, but should not be 6491 needed on a platform with proper driver support. 6492 6493 relax_domain_level= 6494 [KNL, SMP] Set scheduler's default relax_domain_level. 6495 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6496 6497 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6498 Format: <base1>,<size1>[,<base2>,<size2>,...] 6499 Reserve I/O ports or memory so the kernel won't use 6500 them. If <base> is less than 0x10000, the region 6501 is assumed to be I/O ports; otherwise it is memory. 6502 6503 reserve_mem= [RAM] 6504 Format: nn[KMG]:<align>:<label> 6505 Reserve physical memory and label it with a name that 6506 other subsystems can use to access it. This is typically 6507 used for systems that do not wipe the RAM, and this command 6508 line will try to reserve the same physical memory on 6509 soft reboots. Note, it is not guaranteed to be the same 6510 location. For example, if anything about the system changes 6511 or if booting a different kernel. It can also fail if KASLR 6512 places the kernel at the location of where the RAM reservation 6513 was from a previous boot, the new reservation will be at a 6514 different location. 6515 Any subsystem using this feature must add a way to verify 6516 that the contents of the physical memory is from a previous 6517 boot, as there may be cases where the memory will not be 6518 located at the same location. 6519 6520 The format is size:align:label for example, to request 6521 12 megabytes of 4096 alignment for ramoops: 6522 6523 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6524 6525 reservetop= [X86-32,EARLY] 6526 Format: nn[KMG] 6527 Reserves a hole at the top of the kernel virtual 6528 address space. 6529 6530 reset_devices [KNL] Force drivers to reset the underlying device 6531 during initialization. 6532 6533 resume= [SWSUSP] 6534 Specify the partition device for software suspend 6535 Format: 6536 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6537 6538 resume_offset= [SWSUSP] 6539 Specify the offset from the beginning of the partition 6540 given by "resume=" at which the swap header is located, 6541 in <PAGE_SIZE> units (needed only for swap files). 6542 See Documentation/power/swsusp-and-swap-files.rst 6543 6544 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6545 read the resume files 6546 6547 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6548 Useful for devices that are detected asynchronously 6549 (e.g. USB and MMC devices). 6550 6551 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6552 be accessible via /sys/firmware/initrd. 6553 6554 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6555 Speculative Code Execution with Return Instructions) 6556 vulnerability. 6557 6558 AMD-based UNRET and IBPB mitigations alone do not stop 6559 sibling threads from influencing the predictions of other 6560 sibling threads. For that reason, STIBP is used on pro- 6561 cessors that support it, and mitigate SMT on processors 6562 that don't. 6563 6564 off - no mitigation 6565 auto - automatically select a mitigation 6566 auto,nosmt - automatically select a mitigation, 6567 disabling SMT if necessary for 6568 the full mitigation (only on Zen1 6569 and older without STIBP). 6570 ibpb - On AMD, mitigate short speculation 6571 windows on basic block boundaries too. 6572 Safe, highest perf impact. It also 6573 enables STIBP if present. Not suitable 6574 on Intel. 6575 ibpb,nosmt - Like "ibpb" above but will disable SMT 6576 when STIBP is not available. This is 6577 the alternative for systems which do not 6578 have STIBP. 6579 unret - Force enable untrained return thunks, 6580 only effective on AMD f15h-f17h based 6581 systems. 6582 unret,nosmt - Like unret, but will disable SMT when STIBP 6583 is not available. This is the alternative for 6584 systems which do not have STIBP. 6585 6586 Selecting 'auto' will choose a mitigation method at run 6587 time according to the CPU. 6588 6589 Not specifying this option is equivalent to retbleed=auto. 6590 6591 rfkill.default_state= 6592 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6593 etc. communication is blocked by default. 6594 1 Unblocked. 6595 6596 rfkill.master_switch_mode= 6597 0 The "airplane mode" button does nothing. 6598 1 The "airplane mode" button toggles between everything 6599 blocked and the previous configuration. 6600 2 The "airplane mode" button toggles between everything 6601 blocked and everything unblocked. 6602 6603 ring3mwait=disable 6604 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6605 CPUs. 6606 6607 riscv_isa_fallback [RISCV,EARLY] 6608 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6609 falling back to detecting extension support by parsing 6610 "riscv,isa" property on devicetree systems when the 6611 replacement properties are not found. See the Kconfig 6612 entry for RISCV_ISA_FALLBACK. 6613 6614 ro [KNL] Mount root device read-only on boot 6615 6616 rodata= [KNL,EARLY] 6617 on Mark read-only kernel memory as read-only (default). 6618 off Leave read-only kernel memory writable for debugging. 6619 noalias Mark read-only kernel memory as read-only but retain 6620 writable aliases in the direct map for regions outside 6621 of the kernel image. [arm64] 6622 6623 rockchip.usb_uart 6624 [EARLY] 6625 Enable the uart passthrough on the designated usb port 6626 on Rockchip SoCs. When active, the signals of the 6627 debug-uart get routed to the D+ and D- pins of the usb 6628 port and the regular usb controller gets disabled. 6629 6630 root= [KNL] Root filesystem 6631 Usually this is a block device specifier of some kind, 6632 see the early_lookup_bdev comment in 6633 block/early-lookup.c for details. 6634 Alternatively this can be "ram" for the legacy initial 6635 ramdisk, "nfs" and "cifs" for root on a network file 6636 system, or "mtd" and "ubi" for mounting from raw flash. 6637 6638 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6639 mount the root filesystem 6640 6641 rootflags= [KNL] Set root filesystem mount option string 6642 6643 initramfs_options= [KNL] 6644 Specify mount options for for the initramfs mount. 6645 6646 rootfstype= [KNL] Set root filesystem type 6647 6648 rootwait [KNL] Wait (indefinitely) for root device to show up. 6649 Useful for devices that are detected asynchronously 6650 (e.g. USB and MMC devices). 6651 6652 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6653 to show up before attempting to mount the root 6654 filesystem. 6655 6656 rproc_mem=nn[KMG][@address] 6657 [KNL,ARM,CMA] Remoteproc physical memory block. 6658 Memory area to be used by remote processor image, 6659 managed by CMA. 6660 6661 rseq_debug= [KNL] Enable or disable restartable sequence 6662 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6663 Format: <bool> 6664 6665 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6666 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6667 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6668 Format: <bool> 6669 6670 rw [KNL] Mount root device read-write on boot 6671 6672 S [KNL] Run init in single mode 6673 6674 s390_iommu= [HW,S390] 6675 Set s390 IOTLB flushing mode 6676 strict 6677 With strict flushing every unmap operation will result 6678 in an IOTLB flush. Default is lazy flushing before 6679 reuse, which is faster. Deprecated, equivalent to 6680 iommu.strict=1. 6681 6682 s390_iommu_aperture= [KNL,S390] 6683 Specifies the size of the per device DMA address space 6684 accessible through the DMA and IOMMU APIs as a decimal 6685 factor of the size of main memory. 6686 The default is 1 meaning that one can concurrently use 6687 as many DMA addresses as physical memory is installed, 6688 if supported by hardware, and thus map all of memory 6689 once. With a value of 2 one can map all of memory twice 6690 and so on. As a special case a factor of 0 imposes no 6691 restrictions other than those given by hardware at the 6692 cost of significant additional memory use for tables. 6693 6694 sa1100ir [NET] 6695 See drivers/net/irda/sa1100_ir.c. 6696 6697 sched_proxy_exec= [KNL] 6698 Enables or disables "proxy execution" style 6699 solution to mutex-based priority inversion. 6700 Format: <bool> 6701 6702 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6703 6704 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6705 Allowed values are enable and disable. This feature 6706 incurs a small amount of overhead in the scheduler 6707 but is useful for debugging and performance tuning. 6708 6709 sched_thermal_decay_shift= 6710 [Deprecated] 6711 [KNL, SMP] Set a decay shift for scheduler thermal 6712 pressure signal. Thermal pressure signal follows the 6713 default decay period of other scheduler pelt 6714 signals(usually 32 ms but configurable). Setting 6715 sched_thermal_decay_shift will left shift the decay 6716 period for the thermal pressure signal by the shift 6717 value. 6718 i.e. with the default pelt decay period of 32 ms 6719 sched_thermal_decay_shift thermal pressure decay pr 6720 1 64 ms 6721 2 128 ms 6722 and so on. 6723 Format: integer between 0 and 10 6724 Default is 0. 6725 6726 scftorture.holdoff= [KNL] 6727 Number of seconds to hold off before starting 6728 test. Defaults to zero for module insertion and 6729 to 10 seconds for built-in smp_call_function() 6730 tests. 6731 6732 scftorture.longwait= [KNL] 6733 Request ridiculously long waits randomly selected 6734 up to the chosen limit in seconds. Zero (the 6735 default) disables this feature. Please note 6736 that requesting even small non-zero numbers of 6737 seconds can result in RCU CPU stall warnings, 6738 softlockup complaints, and so on. 6739 6740 scftorture.nthreads= [KNL] 6741 Number of kthreads to spawn to invoke the 6742 smp_call_function() family of functions. 6743 The default of -1 specifies a number of kthreads 6744 equal to the number of CPUs. 6745 6746 scftorture.onoff_holdoff= [KNL] 6747 Number seconds to wait after the start of the 6748 test before initiating CPU-hotplug operations. 6749 6750 scftorture.onoff_interval= [KNL] 6751 Number seconds to wait between successive 6752 CPU-hotplug operations. Specifying zero (which 6753 is the default) disables CPU-hotplug operations. 6754 6755 scftorture.shutdown_secs= [KNL] 6756 The number of seconds following the start of the 6757 test after which to shut down the system. The 6758 default of zero avoids shutting down the system. 6759 Non-zero values are useful for automated tests. 6760 6761 scftorture.stat_interval= [KNL] 6762 The number of seconds between outputting the 6763 current test statistics to the console. A value 6764 of zero disables statistics output. 6765 6766 scftorture.stutter_cpus= [KNL] 6767 The number of jiffies to wait between each change 6768 to the set of CPUs under test. 6769 6770 scftorture.use_cpus_read_lock= [KNL] 6771 Use use_cpus_read_lock() instead of the default 6772 preempt_disable() to disable CPU hotplug 6773 while invoking one of the smp_call_function*() 6774 functions. 6775 6776 scftorture.verbose= [KNL] 6777 Enable additional printk() statements. 6778 6779 scftorture.weight_single= [KNL] 6780 The probability weighting to use for the 6781 smp_call_function_single() function with a zero 6782 "wait" parameter. A value of -1 selects the 6783 default if all other weights are -1. However, 6784 if at least one weight has some other value, a 6785 value of -1 will instead select a weight of zero. 6786 6787 scftorture.weight_single_wait= [KNL] 6788 The probability weighting to use for the 6789 smp_call_function_single() function with a 6790 non-zero "wait" parameter. See weight_single. 6791 6792 scftorture.weight_many= [KNL] 6793 The probability weighting to use for the 6794 smp_call_function_many() function with a zero 6795 "wait" parameter. See weight_single. 6796 Note well that setting a high probability for 6797 this weighting can place serious IPI load 6798 on the system. 6799 6800 scftorture.weight_many_wait= [KNL] 6801 The probability weighting to use for the 6802 smp_call_function_many() function with a 6803 non-zero "wait" parameter. See weight_single 6804 and weight_many. 6805 6806 scftorture.weight_all= [KNL] 6807 The probability weighting to use for the 6808 smp_call_function_all() function with a zero 6809 "wait" parameter. See weight_single and 6810 weight_many. 6811 6812 scftorture.weight_all_wait= [KNL] 6813 The probability weighting to use for the 6814 smp_call_function_all() function with a 6815 non-zero "wait" parameter. See weight_single 6816 and weight_many. 6817 6818 sdw_mclk_divider=[SDW] 6819 Specify the MCLK divider for Intel SoundWire buses in 6820 case the BIOS does not provide the clock rate properly. 6821 6822 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6823 xtime_lock contention on larger systems, and/or RCU lock 6824 contention on all systems with CONFIG_MAXSMP set. 6825 Format: { "0" | "1" } 6826 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6827 1 -- enable. 6828 Note: increases power consumption, thus should only be 6829 enabled if running jitter sensitive (HPC/RT) workloads. 6830 6831 security= [SECURITY] Choose a legacy "major" security module to 6832 enable at boot. This has been deprecated by the 6833 "lsm=" parameter. 6834 6835 selinux= [SELINUX] Disable or enable SELinux at boot time. 6836 Format: { "0" | "1" } 6837 See security/selinux/Kconfig help text. 6838 0 -- disable. 6839 1 -- enable. 6840 Default value is 1. 6841 6842 serialnumber [BUGS=X86-32] 6843 6844 sev=option[,option...] [X86-64] 6845 6846 debug 6847 Enable debug messages. 6848 6849 nosnp 6850 Do not enable SEV-SNP (applies to host/hypervisor 6851 only). Setting 'nosnp' avoids the RMP check overhead 6852 in memory accesses when users do not want to run 6853 SEV-SNP guests. 6854 6855 shapers= [NET] 6856 Maximal number of shapers. 6857 6858 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6859 Limit apic dumping. The parameter defines the maximal 6860 number of local apics being dumped. Also it is possible 6861 to set it to "all" by meaning -- no limit here. 6862 Format: { 1 (default) | 2 | ... | all }. 6863 The parameter valid if only apic=debug or 6864 apic=verbose is specified. 6865 Example: apic=debug show_lapic=all 6866 6867 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6868 Enabling slab_debug allows one to determine the 6869 culprit if slab objects become corrupted. Enabling 6870 slab_debug can create guard zones around objects and 6871 may poison objects when not in use. Also tracks the 6872 last alloc / free. For more information see 6873 Documentation/admin-guide/mm/slab.rst. 6874 (slub_debug legacy name also accepted for now) 6875 6876 Using this option implies the "no_hash_pointers" 6877 option which can be undone by adding the 6878 "hash_pointers=always" option. 6879 6880 slab_max_order= [MM] 6881 Determines the maximum allowed order for slabs. 6882 A high setting may cause OOMs due to memory 6883 fragmentation. For more information see 6884 Documentation/admin-guide/mm/slab.rst. 6885 (slub_max_order legacy name also accepted for now) 6886 6887 slab_merge [MM] 6888 Enable merging of slabs with similar size when the 6889 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6890 (slub_merge legacy name also accepted for now) 6891 6892 slab_min_objects= [MM] 6893 The minimum number of objects per slab. SLUB will 6894 increase the slab order up to slab_max_order to 6895 generate a sufficiently large slab able to contain 6896 the number of objects indicated. The higher the number 6897 of objects the smaller the overhead of tracking slabs 6898 and the less frequently locks need to be acquired. 6899 For more information see 6900 Documentation/admin-guide/mm/slab.rst. 6901 (slub_min_objects legacy name also accepted for now) 6902 6903 slab_min_order= [MM] 6904 Determines the minimum page order for slabs. Must be 6905 lower or equal to slab_max_order. For more information see 6906 Documentation/admin-guide/mm/slab.rst. 6907 (slub_min_order legacy name also accepted for now) 6908 6909 slab_nomerge [MM] 6910 Disable merging of slabs with similar size. May be 6911 necessary if there is some reason to distinguish 6912 allocs to different slabs, especially in hardened 6913 environments where the risk of heap overflows and 6914 layout control by attackers can usually be 6915 frustrated by disabling merging. This will reduce 6916 most of the exposure of a heap attack to a single 6917 cache (risks via metadata attacks are mostly 6918 unchanged). Debug options disable merging on their 6919 own. 6920 For more information see 6921 Documentation/admin-guide/mm/slab.rst. 6922 (slub_nomerge legacy name also accepted for now) 6923 6924 slab_strict_numa [MM] 6925 Support memory policies on a per object level 6926 in the slab allocator. The default is for memory 6927 policies to be applied at the folio level when 6928 a new folio is needed or a partial folio is 6929 retrieved from the lists. Increases overhead 6930 in the slab fastpaths but gains more accurate 6931 NUMA kernel object placement which helps with slow 6932 interconnects in NUMA systems. 6933 6934 slram= [HW,MTD] 6935 6936 smart2= [HW] 6937 Format: <io1>[,<io2>[,...,<io8>]] 6938 6939 smp.csd_lock_timeout= [KNL] 6940 Specify the period of time in milliseconds 6941 that smp_call_function() and friends will wait 6942 for a CPU to release the CSD lock. This is 6943 useful when diagnosing bugs involving CPUs 6944 disabling interrupts for extended periods 6945 of time. Defaults to 5,000 milliseconds, and 6946 setting a value of zero disables this feature. 6947 This feature may be more efficiently disabled 6948 using the csdlock_debug- kernel parameter. 6949 6950 smp.panic_on_ipistall= [KNL] 6951 If a csd_lock_timeout extends for more than 6952 the specified number of milliseconds, panic the 6953 system. By default, let CSD-lock acquisition 6954 take as long as they take. Specifying 300,000 6955 for this value provides a 5-minute timeout. 6956 6957 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 6958 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 6959 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 6960 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 6961 smsc-ircc2.ircc_irq= [HW] IRQ line 6962 smsc-ircc2.ircc_dma= [HW] DMA channel 6963 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 6964 0: Toshiba Satellite 1800 (GP data pin select) 6965 1: Fast pin select (default) 6966 2: ATC IRMode 6967 6968 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 6969 (logical CPUs) to use per physical CPU on systems 6970 capable of symmetric multithreading (SMT). Will 6971 be capped to the actual hardware limit. 6972 Format: <integer> 6973 Default: -1 (no limit) 6974 6975 softlockup_panic= 6976 [KNL] Should the soft-lockup detector generate panics. 6977 Format: 0 | 1 6978 6979 A value of 1 instructs the soft-lockup detector 6980 to panic the machine when a soft-lockup occurs. It is 6981 also controlled by the kernel.softlockup_panic sysctl 6982 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 6983 respective build-time switch to that functionality. 6984 6985 softlockup_all_cpu_backtrace= 6986 [KNL] Should the soft-lockup detector generate 6987 backtraces on all cpus. 6988 Format: 0 | 1 6989 6990 sonypi.*= [HW] Sony Programmable I/O Control Device driver 6991 See Documentation/admin-guide/laptops/sonypi.rst 6992 6993 spectre_bhi= [X86] Control mitigation of Branch History Injection 6994 (BHI) vulnerability. This setting affects the 6995 deployment of the HW BHI control and the SW BHB 6996 clearing sequence. 6997 6998 on - (default) Enable the HW or SW mitigation as 6999 needed. This protects the kernel from 7000 both syscalls and VMs. 7001 vmexit - On systems which don't have the HW mitigation 7002 available, enable the SW mitigation on vmexit 7003 ONLY. On such systems, the host kernel is 7004 protected from VM-originated BHI attacks, but 7005 may still be vulnerable to syscall attacks. 7006 off - Disable the mitigation. 7007 7008 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 7009 (indirect branch speculation) vulnerability. 7010 The default operation protects the kernel from 7011 user space attacks. 7012 7013 on - unconditionally enable, implies 7014 spectre_v2_user=on 7015 off - unconditionally disable, implies 7016 spectre_v2_user=off 7017 auto - kernel detects whether your CPU model is 7018 vulnerable 7019 7020 Selecting 'on' will, and 'auto' may, choose a 7021 mitigation method at run time according to the 7022 CPU, the available microcode, the setting of the 7023 CONFIG_MITIGATION_RETPOLINE configuration option, 7024 and the compiler with which the kernel was built. 7025 7026 Selecting 'on' will also enable the mitigation 7027 against user space to user space task attacks. 7028 Selecting specific mitigation does not force enable 7029 user mitigations. 7030 7031 Selecting 'off' will disable both the kernel and 7032 the user space protections. 7033 7034 Specific mitigations can also be selected manually: 7035 7036 retpoline - replace indirect branches 7037 retpoline,generic - Retpolines 7038 retpoline,lfence - LFENCE; indirect branch 7039 retpoline,amd - alias for retpoline,lfence 7040 eibrs - Enhanced/Auto IBRS 7041 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7042 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7043 ibrs - use IBRS to protect kernel 7044 7045 Not specifying this option is equivalent to 7046 spectre_v2=auto. 7047 7048 spectre_v2_user= 7049 [X86] Control mitigation of Spectre variant 2 7050 (indirect branch speculation) vulnerability between 7051 user space tasks 7052 7053 on - Unconditionally enable mitigations. Is 7054 enforced by spectre_v2=on 7055 7056 off - Unconditionally disable mitigations. Is 7057 enforced by spectre_v2=off 7058 7059 prctl - Indirect branch speculation is enabled, 7060 but mitigation can be enabled via prctl 7061 per thread. The mitigation control state 7062 is inherited on fork. 7063 7064 prctl,ibpb 7065 - Like "prctl" above, but only STIBP is 7066 controlled per thread. IBPB is issued 7067 always when switching between different user 7068 space processes. 7069 7070 seccomp 7071 - Same as "prctl" above, but all seccomp 7072 threads will enable the mitigation unless 7073 they explicitly opt out. 7074 7075 seccomp,ibpb 7076 - Like "seccomp" above, but only STIBP is 7077 controlled per thread. IBPB is issued 7078 always when switching between different 7079 user space processes. 7080 7081 auto - Kernel selects the mitigation depending on 7082 the available CPU features and vulnerability. 7083 7084 Default mitigation: "prctl" 7085 7086 Not specifying this option is equivalent to 7087 spectre_v2_user=auto. 7088 7089 spec_rstack_overflow= 7090 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7091 7092 off - Disable mitigation 7093 microcode - Enable microcode mitigation only 7094 safe-ret - Enable sw-only safe RET mitigation (default) 7095 ibpb - Enable mitigation by issuing IBPB on 7096 kernel entry 7097 ibpb-vmexit - Issue IBPB only on VMEXIT 7098 (cloud-specific mitigation) 7099 7100 spec_store_bypass_disable= 7101 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7102 (Speculative Store Bypass vulnerability) 7103 7104 Certain CPUs are vulnerable to an exploit against a 7105 a common industry wide performance optimization known 7106 as "Speculative Store Bypass" in which recent stores 7107 to the same memory location may not be observed by 7108 later loads during speculative execution. The idea 7109 is that such stores are unlikely and that they can 7110 be detected prior to instruction retirement at the 7111 end of a particular speculation execution window. 7112 7113 In vulnerable processors, the speculatively forwarded 7114 store can be used in a cache side channel attack, for 7115 example to read memory to which the attacker does not 7116 directly have access (e.g. inside sandboxed code). 7117 7118 This parameter controls whether the Speculative Store 7119 Bypass optimization is used. 7120 7121 On x86 the options are: 7122 7123 on - Unconditionally disable Speculative Store Bypass 7124 off - Unconditionally enable Speculative Store Bypass 7125 auto - Kernel detects whether the CPU model contains an 7126 implementation of Speculative Store Bypass and 7127 picks the most appropriate mitigation. If the 7128 CPU is not vulnerable, "off" is selected. If the 7129 CPU is vulnerable the default mitigation is 7130 architecture and Kconfig dependent. See below. 7131 prctl - Control Speculative Store Bypass per thread 7132 via prctl. Speculative Store Bypass is enabled 7133 for a process by default. The state of the control 7134 is inherited on fork. 7135 seccomp - Same as "prctl" above, but all seccomp threads 7136 will disable SSB unless they explicitly opt out. 7137 7138 Default mitigations: 7139 X86: "prctl" 7140 7141 On powerpc the options are: 7142 7143 on,auto - On Power8 and Power9 insert a store-forwarding 7144 barrier on kernel entry and exit. On Power7 7145 perform a software flush on kernel entry and 7146 exit. 7147 off - No action. 7148 7149 Not specifying this option is equivalent to 7150 spec_store_bypass_disable=auto. 7151 7152 split_lock_detect= 7153 [X86] Enable split lock detection or bus lock detection 7154 7155 When enabled (and if hardware support is present), atomic 7156 instructions that access data across cache line 7157 boundaries will result in an alignment check exception 7158 for split lock detection or a debug exception for 7159 bus lock detection. 7160 7161 off - not enabled 7162 7163 warn - the kernel will emit rate-limited warnings 7164 about applications triggering the #AC 7165 exception or the #DB exception. This mode is 7166 the default on CPUs that support split lock 7167 detection or bus lock detection. Default 7168 behavior is by #AC if both features are 7169 enabled in hardware. 7170 7171 fatal - the kernel will send SIGBUS to applications 7172 that trigger the #AC exception or the #DB 7173 exception. Default behavior is by #AC if 7174 both features are enabled in hardware. 7175 7176 ratelimit:N - 7177 Set system wide rate limit to N bus locks 7178 per second for bus lock detection. 7179 0 < N <= 1000. 7180 7181 N/A for split lock detection. 7182 7183 7184 If an #AC exception is hit in the kernel or in 7185 firmware (i.e. not while executing in user mode) 7186 the kernel will oops in either "warn" or "fatal" 7187 mode. 7188 7189 #DB exception for bus lock is triggered only when 7190 CPL > 0. 7191 7192 srbds= [X86,INTEL,EARLY] 7193 Control the Special Register Buffer Data Sampling 7194 (SRBDS) mitigation. 7195 7196 Certain CPUs are vulnerable to an MDS-like 7197 exploit which can leak bits from the random 7198 number generator. 7199 7200 By default, this issue is mitigated by 7201 microcode. However, the microcode fix can cause 7202 the RDRAND and RDSEED instructions to become 7203 much slower. Among other effects, this will 7204 result in reduced throughput from /dev/urandom. 7205 7206 The microcode mitigation can be disabled with 7207 the following option: 7208 7209 off: Disable mitigation and remove 7210 performance impact to RDRAND and RDSEED 7211 7212 srcutree.big_cpu_lim [KNL] 7213 Specifies the number of CPUs constituting a 7214 large system, such that srcu_struct structures 7215 should immediately allocate an srcu_node array. 7216 This kernel-boot parameter defaults to 128, 7217 but takes effect only when the low-order four 7218 bits of srcutree.convert_to_big is equal to 3 7219 (decide at boot). 7220 7221 srcutree.convert_to_big [KNL] 7222 Specifies under what conditions an SRCU tree 7223 srcu_struct structure will be converted to big 7224 form, that is, with an rcu_node tree: 7225 7226 0: Never. 7227 1: At init_srcu_struct() time. 7228 2: When rcutorture decides to. 7229 3: Decide at boot time (default). 7230 0x1X: Above plus if high contention. 7231 7232 Either way, the srcu_node tree will be sized based 7233 on the actual runtime number of CPUs (nr_cpu_ids) 7234 instead of the compile-time CONFIG_NR_CPUS. 7235 7236 srcutree.counter_wrap_check [KNL] 7237 Specifies how frequently to check for 7238 grace-period sequence counter wrap for the 7239 srcu_data structure's ->srcu_gp_seq_needed field. 7240 The greater the number of bits set in this kernel 7241 parameter, the less frequently counter wrap will 7242 be checked for. Note that the bottom two bits 7243 are ignored. 7244 7245 srcutree.exp_holdoff [KNL] 7246 Specifies how many nanoseconds must elapse 7247 since the end of the last SRCU grace period for 7248 a given srcu_struct until the next normal SRCU 7249 grace period will be considered for automatic 7250 expediting. Set to zero to disable automatic 7251 expediting. 7252 7253 srcutree.srcu_max_nodelay [KNL] 7254 Specifies the number of no-delay instances 7255 per jiffy for which the SRCU grace period 7256 worker thread will be rescheduled with zero 7257 delay. Beyond this limit, worker thread will 7258 be rescheduled with a sleep delay of one jiffy. 7259 7260 srcutree.srcu_max_nodelay_phase [KNL] 7261 Specifies the per-grace-period phase, number of 7262 non-sleeping polls of readers. Beyond this limit, 7263 grace period worker thread will be rescheduled 7264 with a sleep delay of one jiffy, between each 7265 rescan of the readers, for a grace period phase. 7266 7267 srcutree.srcu_retry_check_delay [KNL] 7268 Specifies number of microseconds of non-sleeping 7269 delay between each non-sleeping poll of readers. 7270 7271 srcutree.small_contention_lim [KNL] 7272 Specifies the number of update-side contention 7273 events per jiffy will be tolerated before 7274 initiating a conversion of an srcu_struct 7275 structure to big form. Note that the value of 7276 srcutree.convert_to_big must have the 0x10 bit 7277 set for contention-based conversions to occur. 7278 7279 ssbd= [ARM64,HW,EARLY] 7280 Speculative Store Bypass Disable control 7281 7282 On CPUs that are vulnerable to the Speculative 7283 Store Bypass vulnerability and offer a 7284 firmware based mitigation, this parameter 7285 indicates how the mitigation should be used: 7286 7287 force-on: Unconditionally enable mitigation for 7288 for both kernel and userspace 7289 force-off: Unconditionally disable mitigation for 7290 for both kernel and userspace 7291 kernel: Always enable mitigation in the 7292 kernel, and offer a prctl interface 7293 to allow userspace to register its 7294 interest in being mitigated too. 7295 7296 stack_guard_gap= [MM] 7297 override the default stack gap protection. The value 7298 is in page units and it defines how many pages prior 7299 to (for stacks growing down) resp. after (for stacks 7300 growing up) the main stack are reserved for no other 7301 mapping. Default value is 256 pages. 7302 7303 stack_depot_disable= [KNL,EARLY] 7304 Setting this to true through kernel command line will 7305 disable the stack depot thereby saving the static memory 7306 consumed by the stack hash table. By default this is set 7307 to false. 7308 7309 stack_depot_max_pools= [KNL,EARLY] 7310 Specify the maximum number of pools to use for storing 7311 stack traces. Pools are allocated on-demand up to this 7312 limit. Default value is 8191 pools. 7313 7314 stacktrace [FTRACE] 7315 Enable the stack tracer on boot up. 7316 7317 stacktrace_filter=[function-list] 7318 [FTRACE] Limit the functions that the stack tracer 7319 will trace at boot up. function-list is a comma-separated 7320 list of functions. This list can be changed at run 7321 time by the stack_trace_filter file in the debugfs 7322 tracing directory. Note, this enables stack tracing 7323 and the stacktrace above is not needed. 7324 7325 sti= [PARISC,HW] 7326 Format: <num> 7327 Set the STI (builtin display/keyboard on the HP-PARISC 7328 machines) console (graphic card) which should be used 7329 as the initial boot-console. 7330 See also comment in drivers/video/console/sticore.c. 7331 7332 sti_font= [HW] 7333 See comment in drivers/video/console/sticore.c. 7334 7335 stifb= [HW] 7336 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7337 7338 strict_sas_size= 7339 [X86] 7340 Format: <bool> 7341 Enable or disable strict sigaltstack size checks 7342 against the required signal frame size which 7343 depends on the supported FPU features. This can 7344 be used to filter out binaries which have 7345 not yet been made aware of AT_MINSIGSTKSZ. 7346 7347 stress_hpt [PPC,EARLY] 7348 Limits the number of kernel HPT entries in the hash 7349 page table to increase the rate of hash page table 7350 faults on kernel addresses. 7351 7352 stress_slb [PPC,EARLY] 7353 Limits the number of kernel SLB entries, and flushes 7354 them frequently to increase the rate of SLB faults 7355 on kernel addresses. 7356 7357 no_slb_preload [PPC,EARLY] 7358 Disables slb preloading for userspace. 7359 7360 sunrpc.min_resvport= 7361 sunrpc.max_resvport= 7362 [NFS,SUNRPC] 7363 SunRPC servers often require that client requests 7364 originate from a privileged port (i.e. a port in the 7365 range 0 < portnr < 1024). 7366 An administrator who wishes to reserve some of these 7367 ports for other uses may adjust the range that the 7368 kernel's sunrpc client considers to be privileged 7369 using these two parameters to set the minimum and 7370 maximum port values. 7371 7372 sunrpc.svc_rpc_per_connection_limit= 7373 [NFS,SUNRPC] 7374 Limit the number of requests that the server will 7375 process in parallel from a single connection. 7376 The default value is 0 (no limit). 7377 7378 sunrpc.pool_mode= 7379 [NFS] 7380 Control how the NFS server code allocates CPUs to 7381 service thread pools. Depending on how many NICs 7382 you have and where their interrupts are bound, this 7383 option will affect which CPUs will do NFS serving. 7384 Note: this parameter cannot be changed while the 7385 NFS server is running. 7386 7387 auto the server chooses an appropriate mode 7388 automatically using heuristics 7389 global a single global pool contains all CPUs 7390 percpu one pool for each CPU 7391 pernode one pool for each NUMA node (equivalent 7392 to global on non-NUMA machines) 7393 7394 sunrpc.tcp_slot_table_entries= 7395 sunrpc.udp_slot_table_entries= 7396 [NFS,SUNRPC] 7397 Sets the upper limit on the number of simultaneous 7398 RPC calls that can be sent from the client to a 7399 server. Increasing these values may allow you to 7400 improve throughput, but will also increase the 7401 amount of memory reserved for use by the client. 7402 7403 suspend.pm_test_delay= 7404 [SUSPEND] 7405 Sets the number of seconds to remain in a suspend test 7406 mode before resuming the system (see 7407 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7408 is set. Default value is 5. 7409 7410 svm= [PPC] 7411 Format: { on | off | y | n | 1 | 0 } 7412 This parameter controls use of the Protected 7413 Execution Facility on pSeries. 7414 7415 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7416 Format: { <int> [,<int>] | force | noforce } 7417 <int> -- Number of I/O TLB slabs 7418 <int> -- Second integer after comma. Number of swiotlb 7419 areas with their own lock. Will be rounded up 7420 to a power of 2. 7421 force -- force using of bounce buffers even if they 7422 wouldn't be automatically used by the kernel 7423 noforce -- Never use bounce buffers (for debugging) 7424 7425 switches= [HW,M68k,EARLY] 7426 7427 sysctl.*= [KNL] 7428 Set a sysctl parameter, right before loading the init 7429 process, as if the value was written to the respective 7430 /proc/sys/... file. Both '.' and '/' are recognized as 7431 separators. Unrecognized parameters and invalid values 7432 are reported in the kernel log. Sysctls registered 7433 later by a loaded module cannot be set this way. 7434 Example: sysctl.vm.swappiness=40 7435 7436 sysrq_always_enabled 7437 [KNL] 7438 Ignore sysrq setting - this boot parameter will 7439 neutralize any effect of /proc/sys/kernel/sysrq. 7440 Useful for debugging. 7441 7442 tcpmhash_entries= [KNL,NET] 7443 Set the number of tcp_metrics_hash slots. 7444 Default value is 8192 or 16384 depending on total 7445 ram pages. This is used to specify the TCP metrics 7446 cache size. See Documentation/networking/ip-sysctl.rst 7447 "tcp_no_metrics_save" section for more details. 7448 7449 tdfx= [HW,DRM] 7450 7451 test_suspend= [SUSPEND] 7452 Format: { "mem" | "standby" | "freeze" }[,N] 7453 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7454 standby suspend) or "freeze" (for suspend type freeze) 7455 as the system sleep state during system startup with 7456 the optional capability to repeat N number of times. 7457 The system is woken from this state using a 7458 wakeup-capable RTC alarm. 7459 7460 thash_entries= [KNL,NET] 7461 Set number of hash buckets for TCP connection 7462 7463 thermal.act= [HW,ACPI] 7464 -1: disable all active trip points in all thermal zones 7465 <degrees C>: override all lowest active trip points 7466 7467 thermal.crt= [HW,ACPI] 7468 -1: disable all critical trip points in all thermal zones 7469 <degrees C>: override all critical trip points 7470 7471 thermal.off= [HW,ACPI] 7472 1: disable ACPI thermal control 7473 7474 thermal.psv= [HW,ACPI] 7475 -1: disable all passive trip points 7476 <degrees C>: override all passive trip points to this 7477 value 7478 7479 thermal.tzp= [HW,ACPI] 7480 Specify global default ACPI thermal zone polling rate 7481 <deci-seconds>: poll all this frequency 7482 0: no polling (default) 7483 7484 thp_anon= [KNL] 7485 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7486 state is one of "always", "madvise", "never" or "inherit". 7487 Control the default behavior of the system with respect 7488 to anonymous transparent hugepages. 7489 Can be used multiple times for multiple anon THP sizes. 7490 See Documentation/admin-guide/mm/transhuge.rst for more 7491 details. 7492 7493 threadirqs [KNL,EARLY] 7494 Force threading of all interrupt handlers except those 7495 marked explicitly IRQF_NO_THREAD. 7496 7497 thp_shmem= [KNL] 7498 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7499 Control the default policy of each hugepage size for the 7500 internal shmem mount. <policy> is one of policies available 7501 for the shmem mount ("always", "inherit", "never", "within_size", 7502 and "advise"). 7503 It can be used multiple times for multiple shmem THP sizes. 7504 See Documentation/admin-guide/mm/transhuge.rst for more 7505 details. 7506 7507 topology= [S390,EARLY] 7508 Format: {off | on} 7509 Specify if the kernel should make use of the cpu 7510 topology information if the hardware supports this. 7511 The scheduler will make use of this information and 7512 e.g. base its process migration decisions on it. 7513 Default is on. 7514 7515 torture.disable_onoff_at_boot= [KNL] 7516 Prevent the CPU-hotplug component of torturing 7517 until after init has spawned. 7518 7519 torture.ftrace_dump_at_shutdown= [KNL] 7520 Dump the ftrace buffer at torture-test shutdown, 7521 even if there were no errors. This can be a 7522 very costly operation when many torture tests 7523 are running concurrently, especially on systems 7524 with rotating-rust storage. 7525 7526 torture.verbose_sleep_frequency= [KNL] 7527 Specifies how many verbose printk()s should be 7528 emitted between each sleep. The default of zero 7529 disables verbose-printk() sleeping. 7530 7531 torture.verbose_sleep_duration= [KNL] 7532 Duration of each verbose-printk() sleep in jiffies. 7533 7534 tpm.disable_pcr_integrity= [HW,TPM] 7535 Do not protect PCR registers from unintended physical 7536 access, or interposers in the bus by the means of 7537 having an integrity protected session wrapped around 7538 TPM2_PCR_Extend command. Consider this in a situation 7539 where TPM is heavily utilized by IMA, thus protection 7540 causing a major performance hit, and the space where 7541 machines are deployed is by other means guarded. 7542 7543 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7544 Maximum time in milliseconds to retry sending a message 7545 to the TPM service before giving up. This parameter controls 7546 how long the system will continue retrying when the TPM 7547 service is busy. 7548 Format: <unsigned int> 7549 Default: 2000 (2 seconds) 7550 7551 tpm_suspend_pcr=[HW,TPM] 7552 Format: integer pcr id 7553 Specify that at suspend time, the tpm driver 7554 should extend the specified pcr with zeros, 7555 as a workaround for some chips which fail to 7556 flush the last written pcr on TPM_SaveState. 7557 This will guarantee that all the other pcrs 7558 are saved. 7559 7560 tpm_tis.interrupts= [HW,TPM] 7561 Enable interrupts for the MMIO based physical layer 7562 for the FIFO interface. By default it is set to false 7563 (0). For more information about TPM hardware interfaces 7564 defined by Trusted Computing Group (TCG) see 7565 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7566 7567 tp_printk [FTRACE] 7568 Have the tracepoints sent to printk as well as the 7569 tracing ring buffer. This is useful for early boot up 7570 where the system hangs or reboots and does not give the 7571 option for reading the tracing buffer or performing a 7572 ftrace_dump_on_oops. 7573 7574 To turn off having tracepoints sent to printk, 7575 echo 0 > /proc/sys/kernel/tracepoint_printk 7576 Note, echoing 1 into this file without the 7577 tp_printk kernel cmdline option has no effect. 7578 7579 The tp_printk_stop_on_boot (see below) can also be used 7580 to stop the printing of events to console at 7581 late_initcall_sync. 7582 7583 ** CAUTION ** 7584 7585 Having tracepoints sent to printk() and activating high 7586 frequency tracepoints such as irq or sched, can cause 7587 the system to live lock. 7588 7589 tp_printk_stop_on_boot [FTRACE] 7590 When tp_printk (above) is set, it can cause a lot of noise 7591 on the console. It may be useful to only include the 7592 printing of events during boot up, as user space may 7593 make the system inoperable. 7594 7595 This command line option will stop the printing of events 7596 to console at the late_initcall_sync() time frame. 7597 7598 trace_buf_size=nn[KMG] 7599 [FTRACE] will set tracing buffer size on each cpu. 7600 7601 trace_clock= [FTRACE] Set the clock used for tracing events 7602 at boot up. 7603 local - Use the per CPU time stamp counter 7604 (converted into nanoseconds). Fast, but 7605 depending on the architecture, may not be 7606 in sync between CPUs. 7607 global - Event time stamps are synchronized across 7608 CPUs. May be slower than the local clock, 7609 but better for some race conditions. 7610 counter - Simple counting of events (1, 2, ..) 7611 note, some counts may be skipped due to the 7612 infrastructure grabbing the clock more than 7613 once per event. 7614 uptime - Use jiffies as the time stamp. 7615 perf - Use the same clock that perf uses. 7616 mono - Use ktime_get_mono_fast_ns() for time stamps. 7617 mono_raw - Use ktime_get_raw_fast_ns() for time 7618 stamps. 7619 boot - Use ktime_get_boot_fast_ns() for time stamps. 7620 Architectures may add more clocks. See 7621 Documentation/trace/ftrace.rst for more details. 7622 7623 trace_event=[event-list] 7624 [FTRACE] Set and start specified trace events in order 7625 to facilitate early boot debugging. The event-list is a 7626 comma-separated list of trace events to enable. See 7627 also Documentation/trace/events.rst 7628 7629 To enable modules, use :mod: keyword: 7630 7631 trace_event=:mod:<module> 7632 7633 The value before :mod: will only enable specific events 7634 that are part of the module. See the above mentioned 7635 document for more information. 7636 7637 trace_instance=[instance-info] 7638 [FTRACE] Create a ring buffer instance early in boot up. 7639 This will be listed in: 7640 7641 /sys/kernel/tracing/instances 7642 7643 Events can be enabled at the time the instance is created 7644 via: 7645 7646 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7647 7648 Note, the "<system*>:" portion is optional if the event is 7649 unique. 7650 7651 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7652 7653 will enable the "sched_switch" event (note, the "sched:" is optional, and 7654 the same thing would happen if it was left off). The irq_handler_entry 7655 event, and all events under the "initcall" system. 7656 7657 Flags can be added to the instance to modify its behavior when it is 7658 created. The flags are separated by '^'. 7659 7660 The available flags are: 7661 7662 traceoff - Have the tracing instance tracing disabled after it is created. 7663 traceprintk - Have trace_printk() write into this trace instance 7664 (note, "printk" and "trace_printk" can also be used) 7665 7666 trace_instance=foo^traceoff^traceprintk,sched,irq 7667 7668 The flags must come before the defined events. 7669 7670 If memory has been reserved (see memmap for x86), the instance 7671 can use that memory: 7672 7673 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7674 7675 The above will create a "boot_map" instance that uses the physical 7676 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7677 instance will be split up accordingly. 7678 7679 Alternatively, the memory can be reserved by the reserve_mem option: 7680 7681 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7682 7683 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7684 and place the ring buffer in this memory. Note that due to KASLR, the 7685 memory may not be the same location each time, which will not preserve 7686 the buffer content. 7687 7688 Also note that the layout of the ring buffer data may change between 7689 kernel versions where the validator will fail and reset the ring buffer 7690 if the layout is not the same as the previous kernel. 7691 7692 If the ring buffer is used for persistent bootups and has events enabled, 7693 it is recommend to disable tracing so that events from a previous boot do not 7694 mix with events of the current boot (unless you are debugging a random crash 7695 at boot up). 7696 7697 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7698 7699 Note, saving the trace buffer across reboots does require that the system 7700 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7701 can force a memory reset on boot which will clear any trace that was stored. 7702 This is just one of many ways that can clear memory. Make sure your system 7703 keeps the content of memory across reboots before relying on this option. 7704 7705 NB: Both the mapped address and size must be page aligned for the architecture. 7706 7707 See also Documentation/trace/debugging.rst 7708 7709 7710 trace_options=[option-list] 7711 [FTRACE] Enable or disable tracer options at boot. 7712 The option-list is a comma delimited list of options 7713 that can be enabled or disabled just as if you were 7714 to echo the option name into 7715 7716 /sys/kernel/tracing/trace_options 7717 7718 For example, to enable stacktrace option (to dump the 7719 stack trace of each event), add to the command line: 7720 7721 trace_options=stacktrace 7722 7723 See also Documentation/trace/ftrace.rst "trace options" 7724 section. 7725 7726 trace_trigger=[trigger-list] 7727 [FTRACE] Add an event trigger on specific events. 7728 Set a trigger on top of a specific event, with an optional 7729 filter. 7730 7731 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7732 Where more than one trigger may be specified that are comma delimited. 7733 7734 For example: 7735 7736 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7737 7738 The above will enable the "stacktrace" trigger on the "sched_switch" 7739 event but only trigger it if the "prev_state" of the "sched_switch" 7740 event is "2" (TASK_UNINTERRUPTIBLE). 7741 7742 See also "Event triggers" in Documentation/trace/events.rst 7743 7744 7745 traceoff_after_boot 7746 [FTRACE] Sometimes tracing is used to debug issues 7747 during the boot process. Since the trace buffer has a 7748 limited amount of storage, it may be prudent to 7749 disable tracing after the boot is finished, otherwise 7750 the critical information may be overwritten. With this 7751 option, the main tracing buffer will be turned off at 7752 the end of the boot process. 7753 7754 traceoff_on_warning 7755 [FTRACE] enable this option to disable tracing when a 7756 warning is hit. This turns off "tracing_on". Tracing can 7757 be enabled again by echoing '1' into the "tracing_on" 7758 file located in /sys/kernel/tracing/ 7759 7760 This option is useful, as it disables the trace before 7761 the WARNING dump is called, which prevents the trace to 7762 be filled with content caused by the warning output. 7763 7764 This option can also be set at run time via the sysctl 7765 option: kernel/traceoff_on_warning 7766 7767 transparent_hugepage= 7768 [KNL] 7769 Format: [always|madvise|never] 7770 Can be used to control the default behavior of the system 7771 with respect to transparent hugepages. 7772 See Documentation/admin-guide/mm/transhuge.rst 7773 for more details. 7774 7775 transparent_hugepage_shmem= [KNL] 7776 Format: [always|within_size|advise|never|deny|force] 7777 Can be used to control the hugepage allocation policy for 7778 the internal shmem mount. 7779 See Documentation/admin-guide/mm/transhuge.rst 7780 for more details. 7781 7782 transparent_hugepage_tmpfs= [KNL] 7783 Format: [always|within_size|advise|never] 7784 Can be used to control the default hugepage allocation policy 7785 for the tmpfs mount. 7786 See Documentation/admin-guide/mm/transhuge.rst 7787 for more details. 7788 7789 trusted.source= [KEYS] 7790 Format: <string> 7791 This parameter identifies the trust source as a backend 7792 for trusted keys implementation. Supported trust 7793 sources: 7794 - "tpm" 7795 - "tee" 7796 - "caam" 7797 - "dcp" 7798 If not specified then it defaults to iterating through 7799 the trust source list starting with TPM and assigns the 7800 first trust source as a backend which is initialized 7801 successfully during iteration. 7802 7803 trusted.rng= [KEYS] 7804 Format: <string> 7805 The RNG used to generate key material for trusted keys. 7806 Can be one of: 7807 - "kernel" 7808 - the same value as trusted.source: "tpm" or "tee" 7809 - "default" 7810 If not specified, "default" is used. In this case, 7811 the RNG's choice is left to each individual trust source. 7812 7813 trusted.dcp_use_otp_key 7814 This is intended to be used in combination with 7815 trusted.source=dcp and will select the DCP OTP key 7816 instead of the DCP UNIQUE key blob encryption. 7817 7818 trusted.dcp_skip_zk_test 7819 This is intended to be used in combination with 7820 trusted.source=dcp and will disable the check if the 7821 blob key is all zeros. This is helpful for situations where 7822 having this key zero'ed is acceptable. E.g. in testing 7823 scenarios. 7824 7825 tsa= [X86] Control mitigation for Transient Scheduler 7826 Attacks on AMD CPUs. Search the following in your 7827 favourite search engine for more details: 7828 7829 "Technical guidance for mitigating transient scheduler 7830 attacks". 7831 7832 off - disable the mitigation 7833 on - enable the mitigation (default) 7834 user - mitigate only user/kernel transitions 7835 vm - mitigate only guest/host transitions 7836 7837 7838 tsc= Disable clocksource stability checks for TSC. 7839 Format: <string> 7840 [x86] reliable: mark tsc clocksource as reliable, this 7841 disables clocksource verification at runtime, as well 7842 as the stability checks done at bootup. Used to enable 7843 high-resolution timer mode on older hardware, and in 7844 virtualized environment. 7845 [x86] noirqtime: Do not use TSC to do irq accounting. 7846 Used to run time disable IRQ_TIME_ACCOUNTING on any 7847 platforms where RDTSC is slow and this accounting 7848 can add overhead. 7849 [x86] unstable: mark the TSC clocksource as unstable, this 7850 marks the TSC unconditionally unstable at bootup and 7851 avoids any further wobbles once the TSC watchdog notices. 7852 [x86] nowatchdog: disable clocksource watchdog. Used 7853 in situations with strict latency requirements (where 7854 interruptions from clocksource watchdog are not 7855 acceptable). 7856 [x86] recalibrate: force recalibration against a HW timer 7857 (HPET or PM timer) on systems whose TSC frequency was 7858 obtained from HW or FW using either an MSR or CPUID(0x15). 7859 Warn if the difference is more than 500 ppm. 7860 [x86] watchdog: Use TSC as the watchdog clocksource with 7861 which to check other HW timers (HPET or PM timer), but 7862 only on systems where TSC has been deemed trustworthy. 7863 This will be suppressed by an earlier tsc=nowatchdog and 7864 can be overridden by a later tsc=nowatchdog. A console 7865 message will flag any such suppression or overriding. 7866 7867 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7868 value instead. Useful when the early TSC frequency discovery 7869 procedure is not reliable, such as on overclocked systems 7870 with CPUID.16h support and partial CPUID.15h support. 7871 Format: <unsigned int> 7872 7873 tsx= [X86] Control Transactional Synchronization 7874 Extensions (TSX) feature in Intel processors that 7875 support TSX control. 7876 7877 This parameter controls the TSX feature. The options are: 7878 7879 on - Enable TSX on the system. Although there are 7880 mitigations for all known security vulnerabilities, 7881 TSX has been known to be an accelerator for 7882 several previous speculation-related CVEs, and 7883 so there may be unknown security risks associated 7884 with leaving it enabled. 7885 7886 off - Disable TSX on the system. (Note that this 7887 option takes effect only on newer CPUs which are 7888 not vulnerable to MDS, i.e., have 7889 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7890 the new IA32_TSX_CTRL MSR through a microcode 7891 update. This new MSR allows for the reliable 7892 deactivation of the TSX functionality.) 7893 7894 auto - Disable TSX if X86_BUG_TAA is present, 7895 otherwise enable TSX on the system. 7896 7897 Not specifying this option is equivalent to tsx=off. 7898 7899 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7900 for more details. 7901 7902 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7903 Abort (TAA) vulnerability. 7904 7905 Similar to Micro-architectural Data Sampling (MDS) 7906 certain CPUs that support Transactional 7907 Synchronization Extensions (TSX) are vulnerable to an 7908 exploit against CPU internal buffers which can forward 7909 information to a disclosure gadget under certain 7910 conditions. 7911 7912 In vulnerable processors, the speculatively forwarded 7913 data can be used in a cache side channel attack, to 7914 access data to which the attacker does not have direct 7915 access. 7916 7917 This parameter controls the TAA mitigation. The 7918 options are: 7919 7920 full - Enable TAA mitigation on vulnerable CPUs 7921 if TSX is enabled. 7922 7923 full,nosmt - Enable TAA mitigation and disable SMT on 7924 vulnerable CPUs. If TSX is disabled, SMT 7925 is not disabled because CPU is not 7926 vulnerable to cross-thread TAA attacks. 7927 off - Unconditionally disable TAA mitigation 7928 7929 On MDS-affected machines, tsx_async_abort=off can be 7930 prevented by an active MDS mitigation as both vulnerabilities 7931 are mitigated with the same mechanism so in order to disable 7932 this mitigation, you need to specify mds=off too. 7933 7934 Not specifying this option is equivalent to 7935 tsx_async_abort=full. On CPUs which are MDS affected 7936 and deploy MDS mitigation, TAA mitigation is not 7937 required and doesn't provide any additional 7938 mitigation. 7939 7940 For details see: 7941 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7942 7943 turbografx.map[2|3]= [HW,JOY] 7944 TurboGraFX parallel port interface 7945 Format: 7946 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 7947 See also Documentation/input/devices/joystick-parport.rst 7948 7949 udbg-immortal [PPC] When debugging early kernel crashes that 7950 happen after console_init() and before a proper 7951 console driver takes over, this boot options might 7952 help "seeing" what's going on. 7953 7954 uhash_entries= [KNL,NET] 7955 Set number of hash buckets for UDP/UDP-Lite connections 7956 7957 uhci-hcd.ignore_oc= 7958 [USB] Ignore overcurrent events (default N). 7959 Some badly-designed motherboards generate lots of 7960 bogus events, for ports that aren't wired to 7961 anything. Set this parameter to avoid log spamming. 7962 Note that genuine overcurrent events won't be 7963 reported either. 7964 7965 unaligned_scalar_speed= 7966 [RISCV] 7967 Format: {slow | fast | unsupported} 7968 Allow skipping scalar unaligned access speed tests. This 7969 is useful for testing alternative code paths and to skip 7970 the tests in environments where they run too slowly. All 7971 CPUs must have the same scalar unaligned access speed. 7972 7973 unaligned_vector_speed= 7974 [RISCV] 7975 Format: {slow | fast | unsupported} 7976 Allow skipping vector unaligned access speed tests. This 7977 is useful for testing alternative code paths and to skip 7978 the tests in environments where they run too slowly. All 7979 CPUs must have the same vector unaligned access speed. 7980 7981 unknown_nmi_panic 7982 [X86] Cause panic on unknown NMI. 7983 7984 unwind_debug [X86-64,EARLY] 7985 Enable unwinder debug output. This can be 7986 useful for debugging certain unwinder error 7987 conditions, including corrupt stacks and 7988 bad/missing unwinder metadata. 7989 7990 usbcore.authorized_default= 7991 [USB] Default USB device authorization: 7992 (default -1 = authorized (same as 1), 7993 0 = not authorized, 1 = authorized, 2 = authorized 7994 if device connected to internal port) 7995 7996 usbcore.autosuspend= 7997 [USB] The autosuspend time delay (in seconds) used 7998 for newly-detected USB devices (default 2). This 7999 is the time required before an idle device will be 8000 autosuspended. Devices for which the delay is set 8001 to a negative value won't be autosuspended at all. 8002 8003 usbcore.usbfs_snoop= 8004 [USB] Set to log all usbfs traffic (default 0 = off). 8005 8006 usbcore.usbfs_snoop_max= 8007 [USB] Maximum number of bytes to snoop in each URB 8008 (default = 65536). 8009 8010 usbcore.blinkenlights= 8011 [USB] Set to cycle leds on hubs (default 0 = off). 8012 8013 usbcore.old_scheme_first= 8014 [USB] Start with the old device initialization 8015 scheme (default 0 = off). 8016 8017 usbcore.usbfs_memory_mb= 8018 [USB] Memory limit (in MB) for buffers allocated by 8019 usbfs (default = 16, 0 = max = 2047). 8020 8021 usbcore.use_both_schemes= 8022 [USB] Try the other device initialization scheme 8023 if the first one fails (default 1 = enabled). 8024 8025 usbcore.initial_descriptor_timeout= 8026 [USB] Specifies timeout for the initial 64-byte 8027 USB_REQ_GET_DESCRIPTOR request in milliseconds 8028 (default 5000 = 5.0 seconds). 8029 8030 usbcore.nousb [USB] Disable the USB subsystem 8031 8032 usbcore.quirks= 8033 [USB] A list of quirk entries to augment the built-in 8034 usb core quirk list. List entries are separated by 8035 commas. Each entry has the form 8036 VendorID:ProductID:Flags. The IDs are 4-digit hex 8037 numbers and Flags is a set of letters. Each letter 8038 will change the built-in quirk; setting it if it is 8039 clear and clearing it if it is set. The letters have 8040 the following meanings: 8041 a = USB_QUIRK_STRING_FETCH_255 (string 8042 descriptors must not be fetched using 8043 a 255-byte read); 8044 b = USB_QUIRK_RESET_RESUME (device can't resume 8045 correctly so reset it instead); 8046 c = USB_QUIRK_NO_SET_INTF (device can't handle 8047 Set-Interface requests); 8048 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8049 handle its Configuration or Interface 8050 strings); 8051 e = USB_QUIRK_RESET (device can't be reset 8052 (e.g morph devices), don't use reset); 8053 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8054 more interface descriptions than the 8055 bNumInterfaces count, and can't handle 8056 talking to these interfaces); 8057 g = USB_QUIRK_DELAY_INIT (device needs a pause 8058 during initialization, after we read 8059 the device descriptor); 8060 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8061 high speed and super speed interrupt 8062 endpoints, the USB 2.0 and USB 3.0 spec 8063 require the interval in microframes (1 8064 microframe = 125 microseconds) to be 8065 calculated as interval = 2 ^ 8066 (bInterval-1). 8067 Devices with this quirk report their 8068 bInterval as the result of this 8069 calculation instead of the exponent 8070 variable used in the calculation); 8071 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8072 handle device_qualifier descriptor 8073 requests); 8074 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8075 generates spurious wakeup, ignore 8076 remote wakeup capability); 8077 k = USB_QUIRK_NO_LPM (device can't handle Link 8078 Power Management); 8079 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8080 (Device reports its bInterval as linear 8081 frames instead of the USB 2.0 8082 calculation); 8083 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8084 to be disconnected before suspend to 8085 prevent spurious wakeup); 8086 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8087 pause after every control message); 8088 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8089 delay after resetting its port); 8090 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8091 (Reduce timeout of the SET_ADDRESS 8092 request from 5000 ms to 500 ms); 8093 Example: quirks=0781:5580:bk,0a5c:5834:gij 8094 8095 usbhid.mousepoll= 8096 [USBHID] The interval which mice are to be polled at. 8097 8098 usbhid.jspoll= 8099 [USBHID] The interval which joysticks are to be polled at. 8100 8101 usbhid.kbpoll= 8102 [USBHID] The interval which keyboards are to be polled at. 8103 8104 usb-storage.delay_use= 8105 [UMS] The delay in seconds before a new device is 8106 scanned for Logical Units (default 1). 8107 Optionally the delay in milliseconds if the value has 8108 suffix with "ms". 8109 Example: delay_use=2567ms 8110 8111 usb-storage.quirks= 8112 [UMS] A list of quirks entries to supplement or 8113 override the built-in unusual_devs list. List 8114 entries are separated by commas. Each entry has 8115 the form VID:PID:Flags where VID and PID are Vendor 8116 and Product ID values (4-digit hex numbers) and 8117 Flags is a set of characters, each corresponding 8118 to a common usb-storage quirk flag as follows: 8119 a = SANE_SENSE (collect more than 18 bytes 8120 of sense data, not on uas); 8121 b = BAD_SENSE (don't collect more than 18 8122 bytes of sense data, not on uas); 8123 c = FIX_CAPACITY (decrease the reported 8124 device capacity by one sector); 8125 d = NO_READ_DISC_INFO (don't use 8126 READ_DISC_INFO command, not on uas); 8127 e = NO_READ_CAPACITY_16 (don't use 8128 READ_CAPACITY_16 command); 8129 f = NO_REPORT_OPCODES (don't use report opcodes 8130 command, uas only); 8131 g = MAX_SECTORS_240 (don't transfer more than 8132 240 sectors at a time, uas only); 8133 h = CAPACITY_HEURISTICS (decrease the 8134 reported device capacity by one 8135 sector if the number is odd); 8136 i = IGNORE_DEVICE (don't bind to this 8137 device); 8138 j = NO_REPORT_LUNS (don't use report luns 8139 command, uas only); 8140 k = NO_SAME (do not use WRITE_SAME, uas only) 8141 l = NOT_LOCKABLE (don't try to lock and 8142 unlock ejectable media, not on uas); 8143 m = MAX_SECTORS_64 (don't transfer more 8144 than 64 sectors = 32 KB at a time, 8145 not on uas); 8146 n = INITIAL_READ10 (force a retry of the 8147 initial READ(10) command, not on uas); 8148 o = CAPACITY_OK (accept the capacity 8149 reported by the device, not on uas); 8150 p = WRITE_CACHE (the device cache is ON 8151 by default, not on uas); 8152 r = IGNORE_RESIDUE (the device reports 8153 bogus residue values, not on uas); 8154 s = SINGLE_LUN (the device has only one 8155 Logical Unit); 8156 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8157 commands, uas only); 8158 u = IGNORE_UAS (don't bind to the uas driver); 8159 w = NO_WP_DETECT (don't test whether the 8160 medium is write-protected). 8161 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8162 even if the device claims no cache, 8163 not on uas) 8164 Example: quirks=0419:aaf5:rl,0421:0433:rc 8165 8166 user_debug= [KNL,ARM] 8167 Format: <int> 8168 See arch/arm/Kconfig.debug help text. 8169 1 - undefined instruction events 8170 2 - system calls 8171 4 - invalid data aborts 8172 8 - SIGSEGV faults 8173 16 - SIGBUS faults 8174 Example: user_debug=31 8175 8176 vdso= [X86,SH,SPARC] 8177 On X86_32, this is an alias for vdso32=. Otherwise: 8178 8179 vdso=1: enable VDSO (the default) 8180 vdso=0: disable VDSO mapping 8181 8182 vdso32= [X86] Control the 32-bit vDSO 8183 vdso32=1: enable 32-bit VDSO 8184 vdso32=0 or vdso32=2: disable 32-bit VDSO 8185 8186 See the help text for CONFIG_COMPAT_VDSO for more 8187 details. If CONFIG_COMPAT_VDSO is set, the default is 8188 vdso32=0; otherwise, the default is vdso32=1. 8189 8190 For compatibility with older kernels, vdso32=2 is an 8191 alias for vdso32=0. 8192 8193 Try vdso32=0 if you encounter an error that says: 8194 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8195 8196 video= [FB,EARLY] Frame buffer configuration 8197 See Documentation/fb/modedb.rst. 8198 8199 video.brightness_switch_enabled= [ACPI] 8200 Format: [0|1] 8201 If set to 1, on receiving an ACPI notify event 8202 generated by hotkey, video driver will adjust brightness 8203 level and then send out the event to user space through 8204 the allocated input device. If set to 0, video driver 8205 will only send out the event without touching backlight 8206 brightness level. 8207 default: 1 8208 8209 virtio_mmio.device= 8210 [VMMIO] Memory mapped virtio (platform) device. 8211 8212 <size>@<baseaddr>:<irq>[:<id>] 8213 where: 8214 <size> := size (can use standard suffixes 8215 like K, M and G) 8216 <baseaddr> := physical base address 8217 <irq> := interrupt number (as passed to 8218 request_irq()) 8219 <id> := (optional) platform device id 8220 example: 8221 virtio_mmio.device=1K@0x100b0000:48:7 8222 8223 Can be used multiple times for multiple devices. 8224 8225 vga= [BOOT,X86-32] Select a particular video mode 8226 See Documentation/arch/x86/boot.rst and 8227 Documentation/admin-guide/svga.rst. 8228 Use vga=ask for menu. 8229 This is actually a boot loader parameter; the value is 8230 passed to the kernel using a special protocol. 8231 8232 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8233 May slow down system boot speed, especially when 8234 enabled on systems with a large amount of memory. 8235 All options are enabled by default, and this 8236 interface is meant to allow for selectively 8237 enabling or disabling specific virtual memory 8238 debugging features. 8239 8240 Available options are: 8241 P Enable page structure init time poisoning 8242 - Disable all of the above options 8243 8244 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8245 exact size of <nn>. This can be used to increase 8246 the minimum size (128MB on x86, arm32 platforms). 8247 It can also be used to decrease the size and leave more room 8248 for directly mapped kernel RAM. Note that this parameter does 8249 not exist on many other platforms (including arm64, alpha, 8250 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8251 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8252 8253 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8254 Sets the memory size reserved for contiguous memory 8255 allocations for the vmcp device driver. 8256 8257 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8258 Format: <command> 8259 8260 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8261 Format: <command> 8262 8263 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8264 Format: <command> 8265 8266 vmscape= [X86] Controls mitigation for VMscape attacks. 8267 VMscape attacks can leak information from a userspace 8268 hypervisor to a guest via speculative side-channels. 8269 8270 off - disable the mitigation 8271 ibpb - use Indirect Branch Prediction Barrier 8272 (IBPB) mitigation (default) 8273 force - force vulnerability detection even on 8274 unaffected processors 8275 8276 vsyscall= [X86-64,EARLY] 8277 Controls the behavior of vsyscalls (i.e. calls to 8278 fixed addresses of 0xffffffffff600x00 from legacy 8279 code). Most statically-linked binaries and older 8280 versions of glibc use these calls. Because these 8281 functions are at fixed addresses, they make nice 8282 targets for exploits that can control RIP. 8283 8284 emulate Vsyscalls turn into traps and are emulated 8285 reasonably safely. The vsyscall page is 8286 readable. 8287 8288 xonly [default] Vsyscalls turn into traps and are 8289 emulated reasonably safely. The vsyscall 8290 page is not readable. 8291 8292 none Vsyscalls don't work at all. This makes 8293 them quite hard to use for exploits but 8294 might break your system. 8295 8296 vt.color= [VT] Default text color. 8297 Format: 0xYX, X = foreground, Y = background. 8298 Default: 0x07 = light gray on black. 8299 8300 vt.cur_default= [VT] Default cursor shape. 8301 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8302 the parameters of the <Esc>[?A;B;Cc escape sequence; 8303 see vga-softcursor.rst. Default: 2 = underline. 8304 8305 vt.default_blu= [VT] 8306 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8307 Change the default blue palette of the console. 8308 This is a 16-member array composed of values 8309 ranging from 0-255. 8310 8311 vt.default_grn= [VT] 8312 Format: <green0>,<green1>,<green2>,...,<green15> 8313 Change the default green palette of the console. 8314 This is a 16-member array composed of values 8315 ranging from 0-255. 8316 8317 vt.default_red= [VT] 8318 Format: <red0>,<red1>,<red2>,...,<red15> 8319 Change the default red palette of the console. 8320 This is a 16-member array composed of values 8321 ranging from 0-255. 8322 8323 vt.default_utf8= 8324 [VT] 8325 Format=<0|1> 8326 Set system-wide default UTF-8 mode for all tty's. 8327 Default is 1, i.e. UTF-8 mode is enabled for all 8328 newly opened terminals. 8329 8330 vt.global_cursor_default= 8331 [VT] 8332 Format=<-1|0|1> 8333 Set system-wide default for whether a cursor 8334 is shown on new VTs. Default is -1, 8335 i.e. cursors will be created by default unless 8336 overridden by individual drivers. 0 will hide 8337 cursors, 1 will display them. 8338 8339 vt.italic= [VT] Default color for italic text; 0-15. 8340 Default: 2 = green. 8341 8342 vt.underline= [VT] Default color for underlined text; 0-15. 8343 Default: 3 = cyan. 8344 8345 watchdog timers [HW,WDT] For information on watchdog timers, 8346 see Documentation/watchdog/watchdog-parameters.rst 8347 or other driver-specific files in the 8348 Documentation/watchdog/ directory. 8349 8350 watchdog_thresh= 8351 [KNL] 8352 Set the hard lockup detector stall duration 8353 threshold in seconds. The soft lockup detector 8354 threshold is set to twice the value. A value of 0 8355 disables both lockup detectors. Default is 10 8356 seconds. 8357 8358 workqueue.unbound_cpus= 8359 [KNL,SMP] Specify to constrain one or some CPUs 8360 to use in unbound workqueues. 8361 Format: <cpu-list> 8362 By default, all online CPUs are available for 8363 unbound workqueues. 8364 8365 workqueue.watchdog_thresh= 8366 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8367 warn stall conditions and dump internal state to 8368 help debugging. 0 disables workqueue stall 8369 detection; otherwise, it's the stall threshold 8370 duration in seconds. The default value is 30 and 8371 it can be updated at runtime by writing to the 8372 corresponding sysfs file. 8373 8374 workqueue.panic_on_stall=<uint> 8375 Panic when workqueue stall is detected by 8376 CONFIG_WQ_WATCHDOG. It sets the number times of the 8377 stall to trigger panic. 8378 8379 The default is 0, which disables the panic on stall. 8380 8381 workqueue.cpu_intensive_thresh_us= 8382 Per-cpu work items which run for longer than this 8383 threshold are automatically considered CPU intensive 8384 and excluded from concurrency management to prevent 8385 them from noticeably delaying other per-cpu work 8386 items. Default is 10000 (10ms). 8387 8388 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8389 will report the work functions which violate this 8390 threshold repeatedly. They are likely good 8391 candidates for using WQ_UNBOUND workqueues instead. 8392 8393 workqueue.cpu_intensive_warning_thresh=<uint> 8394 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8395 will report the work functions which violate the 8396 intensive_threshold_us repeatedly. In order to prevent 8397 spurious warnings, start printing only after a work 8398 function has violated this threshold number of times. 8399 8400 The default is 4 times. 0 disables the warning. 8401 8402 workqueue.power_efficient 8403 Per-cpu workqueues are generally preferred because 8404 they show better performance thanks to cache 8405 locality; unfortunately, per-cpu workqueues tend to 8406 be more power hungry than unbound workqueues. 8407 8408 Enabling this makes the per-cpu workqueues which 8409 were observed to contribute significantly to power 8410 consumption unbound, leading to measurably lower 8411 power usage at the cost of small performance 8412 overhead. 8413 8414 The default value of this parameter is determined by 8415 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8416 8417 workqueue.default_affinity_scope= 8418 Select the default affinity scope to use for unbound 8419 workqueues. Can be one of "cpu", "smt", "cache", 8420 "numa" and "system". Default is "cache". For more 8421 information, see the Affinity Scopes section in 8422 Documentation/core-api/workqueue.rst. 8423 8424 This can be changed after boot by writing to the 8425 matching /sys/module/workqueue/parameters file. All 8426 workqueues with the "default" affinity scope will be 8427 updated accordingly. 8428 8429 workqueue.debug_force_rr_cpu 8430 Workqueue used to implicitly guarantee that work 8431 items queued without explicit CPU specified are put 8432 on the local CPU. This guarantee is no longer true 8433 and while local CPU is still preferred work items 8434 may be put on foreign CPUs. This debug option 8435 forces round-robin CPU selection to flush out 8436 usages which depend on the now broken guarantee. 8437 When enabled, memory and cache locality will be 8438 impacted. 8439 8440 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8441 Type) of ioremap_wc(). 8442 8443 on - Enable writecombine, use WUC for ioremap_wc() 8444 off - Disable writecombine, use SUC for ioremap_wc() 8445 8446 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8447 default x2apic cluster mode on platforms 8448 supporting x2apic. 8449 8450 xen_512gb_limit [KNL,X86-64,XEN] 8451 Restricts the kernel running paravirtualized under Xen 8452 to use only up to 512 GB of RAM. The reason to do so is 8453 crash analysis tools and Xen tools for doing domain 8454 save/restore/migration must be enabled to handle larger 8455 domains. 8456 8457 xen_emul_unplug= [HW,X86,XEN,EARLY] 8458 Unplug Xen emulated devices 8459 Format: [unplug0,][unplug1] 8460 ide-disks -- unplug primary master IDE devices 8461 aux-ide-disks -- unplug non-primary-master IDE devices 8462 nics -- unplug network devices 8463 all -- unplug all emulated devices (NICs and IDE disks) 8464 unnecessary -- unplugging emulated devices is 8465 unnecessary even if the host did not respond to 8466 the unplug protocol 8467 never -- do not unplug even if version check succeeds 8468 8469 xen_legacy_crash [X86,XEN,EARLY] 8470 Crash from Xen panic notifier, without executing late 8471 panic() code such as dumping handler. 8472 8473 xen_mc_debug [X86,XEN,EARLY] 8474 Enable multicall debugging when running as a Xen PV guest. 8475 Enabling this feature will reduce performance a little 8476 bit, so it should only be enabled for obtaining extended 8477 debug data in case of multicall errors. 8478 8479 xen_msr_safe= [X86,XEN,EARLY] 8480 Format: <bool> 8481 Select whether to always use non-faulting (safe) MSR 8482 access functions when running as Xen PV guest. The 8483 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8484 8485 xen_nopv [X86] 8486 Disables the PV optimizations forcing the HVM guest to 8487 run as generic HVM guest with no PV drivers. 8488 This option is obsoleted by the "nopv" option, which 8489 has equivalent effect for XEN platform. 8490 8491 xen_no_vector_callback 8492 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8493 event channel interrupts. 8494 8495 xen_scrub_pages= [XEN] 8496 Boolean option to control scrubbing pages before giving them back 8497 to Xen, for use by other domains. Can be also changed at runtime 8498 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8499 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8500 8501 xen_timer_slop= [X86-64,XEN,EARLY] 8502 Set the timer slop (in nanoseconds) for the virtual Xen 8503 timers (default is 100000). This adjusts the minimum 8504 delta of virtualized Xen timers, where lower values 8505 improve timer resolution at the expense of processing 8506 more timer interrupts. 8507 8508 xen.balloon_boot_timeout= [XEN] 8509 The time (in seconds) to wait before giving up to boot 8510 in case initial ballooning fails to free enough memory. 8511 Applies only when running as HVM or PVH guest and 8512 started with less memory configured than allowed at 8513 max. Default is 180. 8514 8515 xen.event_eoi_delay= [XEN] 8516 How long to delay EOI handling in case of event 8517 storms (jiffies). Default is 10. 8518 8519 xen.event_loop_timeout= [XEN] 8520 After which time (jiffies) the event handling loop 8521 should start to delay EOI handling. Default is 2. 8522 8523 xen.fifo_events= [XEN] 8524 Boolean parameter to disable using fifo event handling 8525 even if available. Normally fifo event handling is 8526 preferred over the 2-level event handling, as it is 8527 fairer and the number of possible event channels is 8528 much higher. Default is on (use fifo events). 8529 8530 xirc2ps_cs= [NET,PCMCIA] 8531 Format: 8532 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8533 8534 xive= [PPC] 8535 By default on POWER9 and above, the kernel will 8536 natively use the XIVE interrupt controller. This option 8537 allows the fallback firmware mode to be used: 8538 8539 off Fallback to firmware control of XIVE interrupt 8540 controller on both pseries and powernv 8541 platforms. Only useful on POWER9 and above. 8542 8543 xive.store-eoi=off [PPC] 8544 By default on POWER10 and above, the kernel will use 8545 stores for EOI handling when the XIVE interrupt mode 8546 is active. This option allows the XIVE driver to use 8547 loads instead, as on POWER9. 8548 8549 xhci-hcd.quirks [USB,KNL] 8550 A hex value specifying bitmask with supplemental xhci 8551 host controller quirks. Meaning of each bit can be 8552 consulted in header drivers/usb/host/xhci.h. 8553 8554 xmon [PPC,EARLY] 8555 Format: { early | on | rw | ro | off } 8556 Controls if xmon debugger is enabled. Default is off. 8557 Passing only "xmon" is equivalent to "xmon=early". 8558 early Call xmon as early as possible on boot; xmon 8559 debugger is called from setup_arch(). 8560 on xmon debugger hooks will be installed so xmon 8561 is only called on a kernel crash. Default mode, 8562 i.e. either "ro" or "rw" mode, is controlled 8563 with CONFIG_XMON_DEFAULT_RO_MODE. 8564 rw xmon debugger hooks will be installed so xmon 8565 is called only on a kernel crash, mode is write, 8566 meaning SPR registers, memory and, other data 8567 can be written using xmon commands. 8568 ro same as "rw" option above but SPR registers, 8569 memory, and other data can't be written using 8570 xmon commands. 8571 off xmon is disabled. 8572