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 kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port. 2921 Format: <Controller#>[,poll interval] 2922 The controller # is the number of the ehci usb debug 2923 port as it is probed via PCI. The poll interval is 2924 optional and is the number seconds in between 2925 each poll cycle to the debug port in case you need 2926 the functionality for interrupting the kernel with 2927 gdb or control-c on the dbgp connection. When 2928 not using this parameter you use sysrq-g to break into 2929 the kernel debugger. 2930 2931 kgdboc= [KGDB,HW] kgdb over consoles. 2932 Requires a tty driver that supports console polling, 2933 or a supported polling keyboard driver (non-usb). 2934 Serial only format: <serial_device>[,baud] 2935 keyboard only format: kbd 2936 keyboard and serial format: kbd,<serial_device>[,baud] 2937 Optional Kernel mode setting: 2938 kms, kbd format: kms,kbd 2939 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2940 2941 kgdboc_earlycon= [KGDB,HW,EARLY] 2942 If the boot console provides the ability to read 2943 characters and can work in polling mode, you can use 2944 this parameter to tell kgdb to use it as a backend 2945 until the normal console is registered. Intended to 2946 be used together with the kgdboc parameter which 2947 specifies the normal console to transition to. 2948 2949 The name of the early console should be specified 2950 as the value of this parameter. Note that the name of 2951 the early console might be different than the tty 2952 name passed to kgdboc. It's OK to leave the value 2953 blank and the first boot console that implements 2954 read() will be picked. 2955 2956 kgdbwait [KGDB,EARLY] Stop kernel execution and enter the 2957 kernel debugger at the earliest opportunity. 2958 2959 kho= [KEXEC,EARLY] 2960 Format: { "0" | "1" | "off" | "on" | "y" | "n" } 2961 Enables or disables Kexec HandOver. 2962 "0" | "off" | "n" - kexec handover is disabled 2963 "1" | "on" | "y" - kexec handover is enabled 2964 2965 kho_scratch= [KEXEC,EARLY] 2966 Format: ll[KMG],mm[KMG],nn[KMG] | nn% 2967 Defines the size of the KHO scratch region. The KHO 2968 scratch regions are physically contiguous memory 2969 ranges that can only be used for non-kernel 2970 allocations. That way, even when memory is heavily 2971 fragmented with handed over memory, the kexeced 2972 kernel will always have enough contiguous ranges to 2973 bootstrap itself. 2974 2975 It is possible to specify the exact amount of 2976 memory in the form of "ll[KMG],mm[KMG],nn[KMG]" 2977 where the first parameter defines the size of a low 2978 memory scratch area, the second parameter defines 2979 the size of a global scratch area and the third 2980 parameter defines the size of additional per-node 2981 scratch areas. The form "nn%" defines scale factor 2982 (in percents) of memory that was used during boot. 2983 2984 kmac= [MIPS] Korina ethernet MAC address. 2985 Configure the RouterBoard 532 series on-chip 2986 Ethernet adapter MAC address. 2987 2988 kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable 2989 Valid arguments: on, off 2990 Default: on 2991 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2992 the default is off. 2993 2994 kprobe_event=[probe-list] 2995 [FTRACE] Add kprobe events and enable at boot time. 2996 The probe-list is a semicolon delimited list of probe 2997 definitions. Each definition is same as kprobe_events 2998 interface, but the parameters are comma delimited. 2999 For example, to add a kprobe event on vfs_read with 3000 arg1 and arg2, add to the command line; 3001 3002 kprobe_event=p,vfs_read,$arg1,$arg2 3003 3004 See also Documentation/trace/kprobetrace.rst "Kernel 3005 Boot Parameter" section. 3006 3007 kpti= [ARM64,EARLY] Control page table isolation of 3008 user and kernel address spaces. 3009 Default: enabled on cores which need mitigation. 3010 0: force disabled 3011 1: force enabled 3012 3013 kunit.enable= [KUNIT] Enable executing KUnit tests. Requires 3014 CONFIG_KUNIT to be set to be fully enabled. The 3015 default value can be overridden via 3016 KUNIT_DEFAULT_ENABLED. 3017 Default is 1 (enabled) 3018 3019 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 3020 Default is 0 (don't ignore, but inject #GP) 3021 3022 kvm.eager_page_split= 3023 [KVM,X86] Controls whether or not KVM will try to 3024 proactively split all huge pages during dirty logging. 3025 Eager page splitting reduces interruptions to vCPU 3026 execution by eliminating the write-protection faults 3027 and MMU lock contention that would otherwise be 3028 required to split huge pages lazily. 3029 3030 VM workloads that rarely perform writes or that write 3031 only to a small region of VM memory may benefit from 3032 disabling eager page splitting to allow huge pages to 3033 still be used for reads. 3034 3035 The behavior of eager page splitting depends on whether 3036 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 3037 disabled, all huge pages in a memslot will be eagerly 3038 split when dirty logging is enabled on that memslot. If 3039 enabled, eager page splitting will be performed during 3040 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 3041 cleared. 3042 3043 Eager page splitting is only supported when kvm.tdp_mmu=Y. 3044 3045 Default is Y (on). 3046 3047 kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] 3048 If enabled, KVM will enable virtualization in hardware 3049 when KVM is loaded, and disable virtualization when KVM 3050 is unloaded (if KVM is built as a module). 3051 3052 If disabled, KVM will dynamically enable and disable 3053 virtualization on-demand when creating and destroying 3054 VMs, i.e. on the 0=>1 and 1=>0 transitions of the 3055 number of VMs. 3056 3057 Enabling virtualization at module load avoids potential 3058 latency for creation of the 0=>1 VM, as KVM serializes 3059 virtualization enabling across all online CPUs. The 3060 "cost" of enabling virtualization when KVM is loaded, 3061 is that doing so may interfere with using out-of-tree 3062 hypervisors that want to "own" virtualization hardware. 3063 3064 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 3065 Default is false (don't support). 3066 3067 kvm.nx_huge_pages= 3068 [KVM] Controls the software workaround for the 3069 X86_BUG_ITLB_MULTIHIT bug. 3070 force : Always deploy workaround. 3071 off : Never deploy workaround. 3072 auto : Deploy workaround based on the presence of 3073 X86_BUG_ITLB_MULTIHIT. 3074 3075 Default is 'auto'. 3076 3077 If the software workaround is enabled for the host, 3078 guests do need not to enable it for nested guests. 3079 3080 kvm.nx_huge_pages_recovery_ratio= 3081 [KVM] Controls how many 4KiB pages are periodically zapped 3082 back to huge pages. 0 disables the recovery, otherwise if 3083 the value is N KVM will zap 1/Nth of the 4KiB pages every 3084 period (see below). The default is 60. 3085 3086 kvm.nx_huge_pages_recovery_period_ms= 3087 [KVM] Controls the time period at which KVM zaps 4KiB pages 3088 back to huge pages. If the value is a non-zero N, KVM will 3089 zap a portion (see ratio above) of the pages every N msecs. 3090 If the value is 0 (the default), KVM will pick a period based 3091 on the ratio, such that a page is zapped after 1 hour on average. 3092 3093 kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in 3094 KVM/SVM. Default is 1 (enabled). 3095 3096 kvm-amd.npt= [KVM,AMD] Control KVM's use of Nested Page Tables, 3097 a.k.a. Two-Dimensional Page Tables. Default is 1 3098 (enabled). Disable by KVM if hardware lacks support 3099 for NPT. 3100 3101 kvm-amd.ciphertext_hiding_asids= 3102 [KVM,AMD] Ciphertext hiding prevents disallowed accesses 3103 to SNP private memory from reading ciphertext. Instead, 3104 reads will see constant default values (0xff). 3105 3106 If ciphertext hiding is enabled, the joint SEV-ES and 3107 SEV-SNP ASID space is partitioned into separate SEV-ES 3108 and SEV-SNP ASID ranges, with the SEV-SNP range being 3109 [1..max_snp_asid] and the SEV-ES range being 3110 (max_snp_asid..min_sev_asid), where min_sev_asid is 3111 enumerated by CPUID.0x.8000_001F[EDX]. 3112 3113 A non-zero value enables SEV-SNP ciphertext hiding and 3114 adjusts the ASID ranges for SEV-ES and SEV-SNP guests. 3115 KVM caps the number of SEV-SNP ASIDs at the maximum 3116 possible value, e.g. specifying -1u will assign all 3117 joint SEV-ES and SEV-SNP ASIDs to SEV-SNP. Note, 3118 assigning all joint ASIDs to SEV-SNP, i.e. configuring 3119 max_snp_asid == min_sev_asid-1, will effectively make 3120 SEV-ES unusable. 3121 3122 kvm-arm.mode= 3123 [KVM,ARM,EARLY] Select one of KVM/arm64's modes of 3124 operation. 3125 3126 none: Forcefully disable KVM. 3127 3128 nvhe: Standard nVHE-based mode, without support for 3129 protected guests. 3130 3131 protected: Mode with support for guests whose state is 3132 kept private from the host, using VHE or 3133 nVHE depending on HW support. 3134 3135 nested: VHE-based mode with support for nested 3136 virtualization. Requires at least ARMv8.4 3137 hardware (with FEAT_NV2). 3138 3139 Defaults to VHE/nVHE based on hardware support. Setting 3140 mode to "protected" will disable kexec and hibernation 3141 for the host. To force nVHE on VHE hardware, add 3142 "arm64_sw.hvhe=0 id_aa64mmfr1.vh=0" to the 3143 command-line. 3144 "nested" is experimental and should be used with 3145 extreme caution. 3146 3147 kvm-arm.vgic_v3_group0_trap= 3148 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0 3149 system registers 3150 3151 kvm-arm.vgic_v3_group1_trap= 3152 [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1 3153 system registers 3154 3155 kvm-arm.vgic_v3_common_trap= 3156 [KVM,ARM,EARLY] Trap guest accesses to GICv3 common 3157 system registers 3158 3159 kvm-arm.vgic_v4_enable= 3160 [KVM,ARM,EARLY] Allow use of GICv4 for direct 3161 injection of LPIs. 3162 3163 kvm-arm.wfe_trap_policy= 3164 [KVM,ARM] Control when to set WFE instruction trap for 3165 KVM VMs. Traps are allowed but not guaranteed by the 3166 CPU architecture. 3167 3168 trap: set WFE instruction trap 3169 3170 notrap: clear WFE instruction trap 3171 3172 kvm-arm.wfi_trap_policy= 3173 [KVM,ARM] Control when to set WFI instruction trap for 3174 KVM VMs. Traps are allowed but not guaranteed by the 3175 CPU architecture. 3176 3177 trap: set WFI instruction trap 3178 3179 notrap: clear WFI instruction trap 3180 3181 kvm_cma_resv_ratio=n [PPC,EARLY] 3182 Reserves given percentage from system memory area for 3183 contiguous memory allocation for KVM hash pagetable 3184 allocation. 3185 By default it reserves 5% of total system memory. 3186 Format: <integer> 3187 Default: 5 3188 3189 kvm-intel.ept= [KVM,Intel] Control KVM's use of Extended Page Tables, 3190 a.k.a. Two-Dimensional Page Tables. Default is 1 3191 (enabled). Disable by KVM if hardware lacks support 3192 for EPT. 3193 3194 kvm-intel.emulate_invalid_guest_state= 3195 [KVM,Intel] Control whether to emulate invalid guest 3196 state. Ignored if kvm-intel.enable_unrestricted_guest=1, 3197 as guest state is never invalid for unrestricted 3198 guests. This param doesn't apply to nested guests (L2), 3199 as KVM never emulates invalid L2 guest state. 3200 Default is 1 (enabled). 3201 3202 kvm-intel.flexpriority= 3203 [KVM,Intel] Control KVM's use of FlexPriority feature 3204 (TPR shadow). Default is 1 (enabled). Disable by KVM if 3205 hardware lacks support for it. 3206 3207 kvm-intel.nested= 3208 [KVM,Intel] Control nested virtualization feature in 3209 KVM/VMX. Default is 1 (enabled). 3210 3211 kvm-intel.unrestricted_guest= 3212 [KVM,Intel] Control KVM's use of unrestricted guest 3213 feature (virtualized real and unpaged mode). Default 3214 is 1 (enabled). Disable by KVM if EPT is disabled or 3215 hardware lacks support for it. 3216 3217 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 3218 CVE-2018-3620. 3219 3220 Valid arguments: never, cond, always 3221 3222 always: L1D cache flush on every VMENTER. 3223 cond: Flush L1D on VMENTER only when the code between 3224 VMEXIT and VMENTER can leak host memory. 3225 never: Disables the mitigation 3226 3227 Default is cond (do L1 cache flush in specific instances) 3228 3229 kvm-intel.vpid= [KVM,Intel] Control KVM's use of Virtual Processor 3230 Identification feature (tagged TLBs). Default is 1 3231 (enabled). Disable by KVM if hardware lacks support 3232 for it. 3233 3234 l1d_flush= [X86,INTEL,EARLY] 3235 Control mitigation for L1D based snooping vulnerability. 3236 3237 Certain CPUs are vulnerable to an exploit against CPU 3238 internal buffers which can forward information to a 3239 disclosure gadget under certain conditions. 3240 3241 In vulnerable processors, the speculatively 3242 forwarded data can be used in a cache side channel 3243 attack, to access data to which the attacker does 3244 not have direct access. 3245 3246 This parameter controls the mitigation. The 3247 options are: 3248 3249 on - enable the interface for the mitigation 3250 3251 l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on 3252 affected CPUs 3253 3254 The kernel PTE inversion protection is unconditionally 3255 enabled and cannot be disabled. 3256 3257 full 3258 Provides all available mitigations for the 3259 L1TF vulnerability. Disables SMT and 3260 enables all mitigations in the 3261 hypervisors, i.e. unconditional L1D flush. 3262 3263 SMT control and L1D flush control via the 3264 sysfs interface is still possible after 3265 boot. Hypervisors will issue a warning 3266 when the first VM is started in a 3267 potentially insecure configuration, 3268 i.e. SMT enabled or L1D flush disabled. 3269 3270 full,force 3271 Same as 'full', but disables SMT and L1D 3272 flush runtime control. Implies the 3273 'nosmt=force' command line option. 3274 (i.e. sysfs control of SMT is disabled.) 3275 3276 flush 3277 Leaves SMT enabled and enables the default 3278 hypervisor mitigation, i.e. conditional 3279 L1D flush. 3280 3281 SMT control and L1D flush control via the 3282 sysfs interface is still possible after 3283 boot. Hypervisors will issue a warning 3284 when the first VM is started in a 3285 potentially insecure configuration, 3286 i.e. SMT enabled or L1D flush disabled. 3287 3288 flush,nosmt 3289 3290 Disables SMT and enables the default 3291 hypervisor mitigation. 3292 3293 SMT control and L1D flush control via the 3294 sysfs interface is still possible after 3295 boot. Hypervisors will issue a warning 3296 when the first VM is started in a 3297 potentially insecure configuration, 3298 i.e. SMT enabled or L1D flush disabled. 3299 3300 flush,nowarn 3301 Same as 'flush', but hypervisors will not 3302 warn when a VM is started in a potentially 3303 insecure configuration. 3304 3305 off 3306 Disables hypervisor mitigations and doesn't 3307 emit any warnings. 3308 It also drops the swap size and available 3309 RAM limit restriction on both hypervisor and 3310 bare metal. 3311 3312 Default is 'flush'. 3313 3314 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 3315 3316 l2cr= [PPC] 3317 3318 l3cr= [PPC] 3319 3320 lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS 3321 disabled it. 3322 3323 lapic= [X86,APIC] Do not use TSC deadline 3324 value for LAPIC timer one-shot implementation. Default 3325 back to the programmable timer unit in the LAPIC. 3326 Format: notscdeadline 3327 3328 lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer 3329 in C2 power state. 3330 3331 libata.dma= [LIBATA] DMA control 3332 libata.dma=0 Disable all PATA and SATA DMA 3333 libata.dma=1 PATA and SATA Disk DMA only 3334 libata.dma=2 ATAPI (CDROM) DMA only 3335 libata.dma=4 Compact Flash DMA only 3336 Combinations also work, so libata.dma=3 enables DMA 3337 for disks and CDROMs, but not CFs. 3338 3339 libata.ignore_hpa= [LIBATA] Ignore HPA limit 3340 libata.ignore_hpa=0 keep BIOS limits (default) 3341 libata.ignore_hpa=1 ignore limits, using full disk 3342 3343 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 3344 when set. 3345 Format: <int> 3346 3347 libata.force= [LIBATA] Force configurations. The format is a comma- 3348 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 3349 PORT and DEVICE are decimal numbers matching port, link 3350 or device. Basically, it matches the ATA ID string 3351 printed on console by libata. If the whole ID part is 3352 omitted, the last PORT and DEVICE values are used. If 3353 ID hasn't been specified yet, the configuration applies 3354 to all ports, links and devices. 3355 3356 If only DEVICE is omitted, the parameter applies to 3357 the port and all links and devices behind it. DEVICE 3358 number of 0 either selects the first device or the 3359 first fan-out link behind PMP device. It does not 3360 select the host link. DEVICE number of 15 selects the 3361 host link and device attached to it. 3362 3363 The VAL specifies the configuration to force. As long 3364 as there is no ambiguity, shortcut notation is allowed. 3365 For example, both 1.5 and 1.5G would work for 1.5Gbps. 3366 The following configurations can be forced. 3367 3368 * Cable type: 40c, 80c, short40c, unk, ign or sata. 3369 Any ID with matching PORT is used. 3370 3371 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 3372 3373 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 3374 udma[/][16,25,33,44,66,100,133] notation is also 3375 allowed. 3376 3377 * nohrst, nosrst, norst: suppress hard, soft and both 3378 resets. 3379 3380 * rstonce: only attempt one reset during hot-unplug 3381 link recovery. 3382 3383 * [no]dbdelay: Enable or disable the extra 200ms delay 3384 before debouncing a link PHY and device presence 3385 detection. 3386 3387 * [no]ncq: Turn on or off NCQ. 3388 3389 * [no]ncqtrim: Enable or disable queued DSM TRIM. 3390 3391 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 3392 3393 * [no]trim: Enable or disable (unqueued) TRIM. 3394 3395 * trim_zero: Indicate that TRIM command zeroes data. 3396 3397 * max_trim_128m: Set 128M maximum trim size limit. 3398 3399 * [no]dma: Turn on or off DMA transfers. 3400 3401 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 3402 3403 * atapi_mod16_dma: Enable the use of ATAPI DMA for 3404 commands that are not a multiple of 16 bytes. 3405 3406 * [no]dmalog: Enable or disable the use of the 3407 READ LOG DMA EXT command to access logs. 3408 3409 * [no]iddevlog: Enable or disable access to the 3410 identify device data log. 3411 3412 * [no]logdir: Enable or disable access to the general 3413 purpose log directory. 3414 3415 * max_sec_128: Set transfer size limit to 128 sectors. 3416 3417 * max_sec_1024: Set or clear transfer size limit to 3418 1024 sectors. 3419 3420 * max_sec_lba48: Set or clear transfer size limit to 3421 65535 sectors. 3422 3423 * external: Mark port as external (hotplug-capable). 3424 3425 * [no]lpm: Enable or disable link power management. 3426 3427 * [no]setxfer: Indicate if transfer speed mode setting 3428 should be skipped. 3429 3430 * [no]fua: Disable or enable FUA (Force Unit Access) 3431 support for devices supporting this feature. 3432 3433 * dump_id: Dump IDENTIFY data. 3434 3435 * disable: Disable this device. 3436 3437 If there are multiple matching configurations changing 3438 the same attribute, the last one is used. 3439 3440 load_ramdisk= [RAM] [Deprecated] 3441 3442 lockd.nlm_grace_period=P [NFS] Assign grace period. 3443 Format: <integer> 3444 3445 lockd.nlm_tcpport=N [NFS] Assign TCP port. 3446 Format: <integer> 3447 3448 lockd.nlm_timeout=T [NFS] Assign timeout value. 3449 Format: <integer> 3450 3451 lockd.nlm_udpport=M [NFS] Assign UDP port. 3452 Format: <integer> 3453 3454 lockdown= [SECURITY,EARLY] 3455 { integrity | confidentiality } 3456 Enable the kernel lockdown feature. If set to 3457 integrity, kernel features that allow userland to 3458 modify the running kernel are disabled. If set to 3459 confidentiality, kernel features that allow userland 3460 to extract confidential information from the kernel 3461 are also disabled. 3462 3463 locktorture.acq_writer_lim= [KNL] 3464 Set the time limit in jiffies for a lock 3465 acquisition. Acquisitions exceeding this limit 3466 will result in a splat once they do complete. 3467 3468 locktorture.bind_readers= [KNL] 3469 Specify the list of CPUs to which the readers are 3470 to be bound. 3471 3472 locktorture.bind_writers= [KNL] 3473 Specify the list of CPUs to which the writers are 3474 to be bound. 3475 3476 locktorture.call_rcu_chains= [KNL] 3477 Specify the number of self-propagating call_rcu() 3478 chains to set up. These are used to ensure that 3479 there is a high probability of an RCU grace period 3480 in progress at any given time. Defaults to 0, 3481 which disables these call_rcu() chains. 3482 3483 locktorture.long_hold= [KNL] 3484 Specify the duration in milliseconds for the 3485 occasional long-duration lock hold time. Defaults 3486 to 100 milliseconds. Select 0 to disable. 3487 3488 locktorture.nested_locks= [KNL] 3489 Specify the maximum lock nesting depth that 3490 locktorture is to exercise, up to a limit of 8 3491 (MAX_NESTED_LOCKS). Specify zero to disable. 3492 Note that this parameter is ineffective on types 3493 of locks that do not support nested acquisition. 3494 3495 locktorture.nreaders_stress= [KNL] 3496 Set the number of locking read-acquisition kthreads. 3497 Defaults to being automatically set based on the 3498 number of online CPUs. 3499 3500 locktorture.nwriters_stress= [KNL] 3501 Set the number of locking write-acquisition kthreads. 3502 3503 locktorture.onoff_holdoff= [KNL] 3504 Set time (s) after boot for CPU-hotplug testing. 3505 3506 locktorture.onoff_interval= [KNL] 3507 Set time (s) between CPU-hotplug operations, or 3508 zero to disable CPU-hotplug testing. 3509 3510 locktorture.rt_boost= [KNL] 3511 Do periodic testing of real-time lock priority 3512 boosting. Select 0 to disable, 1 to boost 3513 only rt_mutex, and 2 to boost unconditionally. 3514 Defaults to 2, which might seem to be an 3515 odd choice, but which should be harmless for 3516 non-real-time spinlocks, due to their disabling 3517 of preemption. Note that non-realtime mutexes 3518 disable boosting. 3519 3520 locktorture.rt_boost_factor= [KNL] 3521 Number that determines how often and for how 3522 long priority boosting is exercised. This is 3523 scaled down by the number of writers, so that the 3524 number of boosts per unit time remains roughly 3525 constant as the number of writers increases. 3526 On the other hand, the duration of each boost 3527 increases with the number of writers. 3528 3529 locktorture.shuffle_interval= [KNL] 3530 Set task-shuffle interval (jiffies). Shuffling 3531 tasks allows some CPUs to go into dyntick-idle 3532 mode during the locktorture test. 3533 3534 locktorture.shutdown_secs= [KNL] 3535 Set time (s) after boot system shutdown. This 3536 is useful for hands-off automated testing. 3537 3538 locktorture.stat_interval= [KNL] 3539 Time (s) between statistics printk()s. 3540 3541 locktorture.stutter= [KNL] 3542 Time (s) to stutter testing, for example, 3543 specifying five seconds causes the test to run for 3544 five seconds, wait for five seconds, and so on. 3545 This tests the locking primitive's ability to 3546 transition abruptly to and from idle. 3547 3548 locktorture.torture_type= [KNL] 3549 Specify the locking implementation to test. 3550 3551 locktorture.verbose= [KNL] 3552 Enable additional printk() statements. 3553 3554 locktorture.writer_fifo= [KNL] 3555 Run the write-side locktorture kthreads at 3556 sched_set_fifo() real-time priority. 3557 3558 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 3559 Format: <irq> 3560 3561 loglevel= [KNL,EARLY] 3562 All Kernel Messages with a loglevel smaller than the 3563 console loglevel will be printed to the console. It can 3564 also be changed with klogd or other programs. The 3565 loglevels are defined as follows: 3566 3567 0 (KERN_EMERG) system is unusable 3568 1 (KERN_ALERT) action must be taken immediately 3569 2 (KERN_CRIT) critical conditions 3570 3 (KERN_ERR) error conditions 3571 4 (KERN_WARNING) warning conditions 3572 5 (KERN_NOTICE) normal but significant condition 3573 6 (KERN_INFO) informational 3574 7 (KERN_DEBUG) debug-level messages 3575 3576 log_buf_len=n[KMG] [KNL,EARLY] 3577 Sets the size of the printk ring buffer, in bytes. 3578 n must be a power of two and greater than the 3579 minimal size. The minimal size is defined by 3580 LOG_BUF_SHIFT kernel config parameter. There 3581 is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config 3582 parameter that allows to increase the default size 3583 depending on the number of CPUs. See init/Kconfig 3584 for more details. 3585 3586 logo.nologo [FB] Disables display of the built-in Linux logo. 3587 This may be used to provide more screen space for 3588 kernel log messages and is useful when debugging 3589 kernel boot problems. 3590 3591 lp=0 [LP] Specify parallel ports to use, e.g, 3592 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 3593 lp=reset first parallel port). 'lp=0' disables the 3594 lp=auto printer driver. 'lp=reset' (which can be 3595 specified in addition to the ports) causes 3596 attached printers to be reset. Using 3597 lp=port1,port2,... specifies the parallel ports 3598 to associate lp devices with, starting with 3599 lp0. A port specification may be 'none' to skip 3600 that lp device, or a parport name such as 3601 'parport0'. Specifying 'lp=auto' instead of a 3602 port specification list means that device IDs 3603 from each port should be examined, to see if 3604 an IEEE 1284-compliant printer is attached; if 3605 so, the driver will manage that printer. 3606 See also header of drivers/char/lp.c. 3607 3608 lpj=n [KNL] 3609 Sets loops_per_jiffy to given constant, thus avoiding 3610 time-consuming boot-time autodetection (up to 250 ms per 3611 CPU). 0 enables autodetection (default). To determine 3612 the correct value for your kernel, boot with normal 3613 autodetection and see what value is printed. Note that 3614 on SMP systems the preset will be applied to all CPUs, 3615 which is likely to cause problems if your CPUs need 3616 significantly divergent settings. An incorrect value 3617 will cause delays in the kernel to be wrong, leading to 3618 unpredictable I/O errors and other breakage. Although 3619 unlikely, in the extreme case this might damage your 3620 hardware. 3621 3622 lsm.debug [SECURITY] Enable LSM initialization debugging output. 3623 3624 lsm=lsm1,...,lsmN 3625 [SECURITY] Choose order of LSM initialization. This 3626 overrides CONFIG_LSM, and the "security=" parameter. 3627 3628 machtype= [Loongson] Share the same kernel image file between 3629 different yeeloong laptops. 3630 Example: machtype=lemote-yeeloong-2f-7inch 3631 3632 maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 3633 will bring up during bootup. maxcpus=n : n >= 0 limits 3634 the kernel to bring up 'n' processors. Surely after 3635 bootup you can bring up the other plugged cpu by executing 3636 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 3637 only takes effect during system bootup. 3638 While n=0 is a special case, it is equivalent to "nosmp", 3639 which also disables the IO APIC. 3640 3641 max_loop= [LOOP] The number of loop block devices that get 3642 (loop.max_loop) unconditionally pre-created at init time. The default 3643 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 3644 of statically allocating a predefined number, loop 3645 devices can be requested on-demand with the 3646 /dev/loop-control interface. 3647 3648 mce= [X86-{32,64}] 3649 3650 Please see Documentation/arch/x86/x86_64/machinecheck.rst for sysfs runtime tunables. 3651 3652 off 3653 disable machine check 3654 3655 no_cmci 3656 disable CMCI(Corrected Machine Check Interrupt) that 3657 Intel processor supports. Usually this disablement is 3658 not recommended, but it might be handy if your 3659 hardware is misbehaving. 3660 3661 Note that you'll get more problems without CMCI than 3662 with due to the shared banks, i.e. you might get 3663 duplicated error logs. 3664 3665 dont_log_ce 3666 don't make logs for corrected errors. All events 3667 reported as corrected are silently cleared by OS. This 3668 option will be useful if you have no interest in any 3669 of corrected errors. 3670 3671 ignore_ce 3672 disable features for corrected errors, e.g. 3673 polling timer and CMCI. All events reported as 3674 corrected are not cleared by OS and remained in its 3675 error banks. 3676 3677 Usually this disablement is not recommended, however 3678 if there is an agent checking/clearing corrected 3679 errors (e.g. BIOS or hardware monitoring 3680 applications), conflicting with OS's error handling, 3681 and you cannot deactivate the agent, then this option 3682 will be a help. 3683 3684 no_lmce 3685 do not opt-in to Local MCE delivery. Use legacy method 3686 to broadcast MCEs. 3687 3688 bootlog 3689 enable logging of machine checks left over from 3690 booting. Disabled by default on AMD Fam10h and older 3691 because some BIOS leave bogus ones. 3692 3693 If your BIOS doesn't do that it's a good idea to 3694 enable though to make sure you log even machine check 3695 events that result in a reboot. On Intel systems it is 3696 enabled by default. 3697 3698 nobootlog 3699 disable boot machine check logging. 3700 3701 monarchtimeout (number) 3702 sets the time in us to wait for other CPUs on machine 3703 checks. 0 to disable. 3704 3705 bios_cmci_threshold 3706 don't overwrite the bios-set CMCI threshold. This boot 3707 option prevents Linux from overwriting the CMCI 3708 threshold set by the bios. Without this option, Linux 3709 always sets the CMCI threshold to 1. Enabling this may 3710 make memory predictive failure analysis less effective 3711 if the bios sets thresholds for memory errors since we 3712 will not see details for all errors. 3713 3714 recovery 3715 force-enable recoverable machine check code paths 3716 3717 Everything else is in sysfs now. 3718 3719 3720 md= [HW] RAID subsystems devices and level 3721 See Documentation/admin-guide/md.rst. 3722 3723 mdacon= [MDA] 3724 Format: <first>,<last> 3725 Specifies range of consoles to be captured by the MDA. 3726 3727 mds= [X86,INTEL,EARLY] 3728 Control mitigation for the Micro-architectural Data 3729 Sampling (MDS) vulnerability. 3730 3731 Certain CPUs are vulnerable to an exploit against CPU 3732 internal buffers which can forward information to a 3733 disclosure gadget under certain conditions. 3734 3735 In vulnerable processors, the speculatively 3736 forwarded data can be used in a cache side channel 3737 attack, to access data to which the attacker does 3738 not have direct access. 3739 3740 This parameter controls the MDS mitigation. The 3741 options are: 3742 3743 full - Enable MDS mitigation on vulnerable CPUs 3744 full,nosmt - Enable MDS mitigation and disable 3745 SMT on vulnerable CPUs 3746 off - Unconditionally disable MDS mitigation 3747 3748 On TAA-affected machines, mds=off can be prevented by 3749 an active TAA mitigation as both vulnerabilities are 3750 mitigated with the same mechanism so in order to disable 3751 this mitigation, you need to specify tsx_async_abort=off 3752 too. 3753 3754 Not specifying this option is equivalent to 3755 mds=full. 3756 3757 For details see: Documentation/admin-guide/hw-vuln/mds.rst 3758 3759 mem=nn[KMG] [HEXAGON,EARLY] Set the memory size. 3760 Must be specified, otherwise memory size will be 0. 3761 3762 mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount 3763 of memory Amount of memory to be used in cases 3764 as follows: 3765 3766 1 for test; 3767 2 when the kernel is not able to see the whole system memory; 3768 3 memory that lies after 'mem=' boundary is excluded from 3769 the hypervisor, then assigned to KVM guests. 3770 4 to limit the memory available for kdump kernel. 3771 3772 [ARC,MICROBLAZE] - the limit applies only to low memory, 3773 high memory is not affected. 3774 3775 [ARM64] - only limits memory covered by the linear 3776 mapping. The NOMAP regions are not affected. 3777 3778 [X86] Work as limiting max address. Use together 3779 with memmap= to avoid physical address space collisions. 3780 Without memmap= PCI devices could be placed at addresses 3781 belonging to unused RAM. 3782 3783 Note that this only takes effects during boot time since 3784 in above case 3, memory may need be hot added after boot 3785 if system memory of hypervisor is not sufficient. 3786 3787 mem=nn[KMG]@ss[KMG] 3788 [ARM,MIPS,EARLY] - override the memory layout 3789 reported by firmware. 3790 Define a memory region of size nn[KMG] starting at 3791 ss[KMG]. 3792 Multiple different regions can be specified with 3793 multiple mem= parameters on the command line. 3794 3795 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 3796 memory. 3797 3798 memblock=debug [KNL,EARLY] Enable memblock debug messages. 3799 3800 memchunk=nn[KMG] 3801 [KNL,SH] Allow user to override the default size for 3802 per-device physically contiguous DMA buffers. 3803 3804 memhp_default_state=online/offline/online_kernel/online_movable 3805 [KNL] Set the initial state for the memory hotplug 3806 onlining policy. If not specified, the default value is 3807 set according to the 3808 CONFIG_MHP_DEFAULT_ONLINE_TYPE kernel config 3809 options. 3810 See Documentation/admin-guide/mm/memory-hotplug.rst. 3811 3812 memmap=exactmap [KNL,X86,EARLY] Enable setting of an exact 3813 E820 memory map, as specified by the user. 3814 Such memmap=exactmap lines can be constructed based on 3815 BIOS output or other requirements. See the memmap=nn@ss 3816 option description. 3817 3818 memmap=nn[KMG]@ss[KMG] 3819 [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory. 3820 Region of memory to be used is from ss to ss+nn. 3821 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3822 which limits max address to nn[KMG]. 3823 Multiple different regions can be specified, 3824 comma delimited. 3825 Example: 3826 memmap=100M@2G,100M#3G,1G!1024G 3827 3828 memmap=nn[KMG]#ss[KMG] 3829 [KNL,ACPI,EARLY] Mark specific memory as ACPI data. 3830 Region of memory to be marked is from ss to ss+nn. 3831 3832 memmap=nn[KMG]$ss[KMG] 3833 [KNL,ACPI,EARLY] Mark specific memory as reserved. 3834 Region of memory to be reserved is from ss to ss+nn. 3835 Example: Exclude memory from 0x18690000-0x1869ffff 3836 memmap=64K$0x18690000 3837 or 3838 memmap=0x10000$0x18690000 3839 Some bootloaders may need an escape character before '$', 3840 like Grub2, otherwise '$' and the following number 3841 will be eaten. 3842 3843 memmap=nn[KMG]!ss[KMG,EARLY] 3844 [KNL,X86] Mark specific memory as protected. 3845 Region of memory to be used, from ss to ss+nn. 3846 The memory region may be marked as e820 type 12 (0xc) 3847 and is NVDIMM or ADR memory. 3848 3849 memmap=<size>%<offset>-<oldtype>+<newtype> 3850 [KNL,ACPI,EARLY] Convert memory within the specified region 3851 from <oldtype> to <newtype>. If "-<oldtype>" is left 3852 out, the whole region will be marked as <newtype>, 3853 even if previously unavailable. If "+<newtype>" is left 3854 out, matching memory will be removed. Types are 3855 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3856 3 = ACPI, 12 = PRAM. 3857 3858 memory_corruption_check=0/1 [X86,EARLY] 3859 Some BIOSes seem to corrupt the first 64k of 3860 memory when doing things like suspend/resume. 3861 Setting this option will scan the memory 3862 looking for corruption. Enabling this will 3863 both detect corruption and prevent the kernel 3864 from using the memory being corrupted. 3865 However, it's intended as a diagnostic tool; if 3866 repeatable BIOS-originated corruption always 3867 affects the same memory, you can use memmap= 3868 to prevent the kernel from using that memory. 3869 3870 memory_corruption_check_size=size [X86,EARLY] 3871 By default it checks for corruption in the low 3872 64k, making this memory unavailable for normal 3873 use. Use this parameter to scan for 3874 corruption in more or less memory. 3875 3876 memory_corruption_check_period=seconds [X86,EARLY] 3877 By default it checks for corruption every 60 3878 seconds. Use this parameter to check at some 3879 other rate. 0 disables periodic checking. 3880 3881 memory_hotplug.memmap_on_memory 3882 [KNL,X86,ARM] Boolean flag to enable this feature. 3883 Format: {on | off (default)} 3884 When enabled, runtime hotplugged memory will 3885 allocate its internal metadata (struct pages, 3886 those vmemmap pages cannot be optimized even 3887 if hugetlb_free_vmemmap is enabled) from the 3888 hotadded memory which will allow to hotadd a 3889 lot of memory without requiring additional 3890 memory to do so. 3891 This feature is disabled by default because it 3892 has some implication on large (e.g. GB) 3893 allocations in some configurations (e.g. small 3894 memory blocks). 3895 The state of the flag can be read in 3896 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3897 Note that even when enabled, there are a few cases where 3898 the feature is not effective. 3899 3900 memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest 3901 Format: <integer> 3902 default : 0 <disable> 3903 Specifies the number of memtest passes to be 3904 performed. Each pass selects another test 3905 pattern from a given set of patterns. Memtest 3906 fills the memory with this pattern, validates 3907 memory contents and reserves bad memory 3908 regions that are detected. 3909 3910 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3911 Valid arguments: on, off 3912 Default: off 3913 mem_encrypt=on: Activate SME 3914 mem_encrypt=off: Do not activate SME 3915 3916 Refer to Documentation/virt/kvm/x86/amd-memory-encryption.rst 3917 for details on when memory encryption can be activated. 3918 3919 mem_sleep_default= [SUSPEND] Default system suspend mode: 3920 s2idle - Suspend-To-Idle 3921 shallow - Power-On Suspend or equivalent (if supported) 3922 deep - Suspend-To-RAM or equivalent (if supported) 3923 See Documentation/admin-guide/pm/sleep-states.rst. 3924 3925 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3926 the BIOS has incorrectly applied a workaround. TinyBIOS 3927 version 0.98 is known to be affected, 0.99 fixes the 3928 problem by letting the user disable the workaround. 3929 3930 mga= [HW,DRM] 3931 3932 microcode= [X86] Control the behavior of the microcode loader. 3933 Available options, comma separated: 3934 3935 base_rev=X - with <X> with format: <u32> 3936 Set the base microcode revision of each thread when in 3937 debug mode. 3938 3939 dis_ucode_ldr: disable the microcode loader 3940 3941 force_minrev: 3942 Enable or disable the microcode minimal revision 3943 enforcement for the runtime microcode loader. 3944 3945 mini2440= [ARM,HW,KNL] 3946 Format:[0..2][b][c][t] 3947 Default: "0tb" 3948 MINI2440 configuration specification: 3949 0 - The attached screen is the 3.5" TFT 3950 1 - The attached screen is the 7" TFT 3951 2 - The VGA Shield is attached (1024x768) 3952 Leaving out the screen size parameter will not load 3953 the TFT driver, and the framebuffer will be left 3954 unconfigured. 3955 b - Enable backlight. The TFT backlight pin will be 3956 linked to the kernel VESA blanking code and a GPIO 3957 LED. This parameter is not necessary when using the 3958 VGA shield. 3959 c - Enable the s3c camera interface. 3960 t - Reserved for enabling touchscreen support. The 3961 touchscreen support is not enabled in the mainstream 3962 kernel as of 2.6.30, a preliminary port can be found 3963 in the "bleeding edge" mini2440 support kernel at 3964 https://repo.or.cz/w/linux-2.6/mini2440.git 3965 3966 mitigations= 3967 [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for 3968 CPU vulnerabilities. This is a set of curated, 3969 arch-independent options, each of which is an 3970 aggregation of existing arch-specific options. 3971 3972 Note, "mitigations" is supported if and only if the 3973 kernel was built with CPU_MITIGATIONS=y. 3974 3975 off 3976 Disable all optional CPU mitigations. This 3977 improves system performance, but it may also 3978 expose users to several CPU vulnerabilities. 3979 Equivalent to: if nokaslr then kpti=0 [ARM64] 3980 gather_data_sampling=off [X86] 3981 indirect_target_selection=off [X86] 3982 kvm.nx_huge_pages=off [X86] 3983 l1tf=off [X86] 3984 mds=off [X86] 3985 mmio_stale_data=off [X86] 3986 no_entry_flush [PPC] 3987 no_uaccess_flush [PPC] 3988 nobp=0 [S390] 3989 nopti [X86,PPC] 3990 nospectre_bhb [ARM64] 3991 nospectre_v1 [X86,PPC] 3992 nospectre_v2 [X86,PPC,S390,ARM64] 3993 reg_file_data_sampling=off [X86] 3994 retbleed=off [X86] 3995 spec_rstack_overflow=off [X86] 3996 spec_store_bypass_disable=off [X86,PPC] 3997 spectre_bhi=off [X86] 3998 spectre_v2_user=off [X86] 3999 srbds=off [X86,INTEL] 4000 ssbd=force-off [ARM64] 4001 tsa=off [X86,AMD] 4002 tsx_async_abort=off [X86] 4003 vmscape=off [X86] 4004 4005 Exceptions: 4006 This does not have any effect on 4007 kvm.nx_huge_pages when 4008 kvm.nx_huge_pages=force. 4009 4010 auto (default) 4011 Mitigate all CPU vulnerabilities, but leave SMT 4012 enabled, even if it's vulnerable. This is for 4013 users who don't want to be surprised by SMT 4014 getting disabled across kernel upgrades, or who 4015 have other ways of avoiding SMT-based attacks. 4016 Equivalent to: (default behavior) 4017 4018 auto,nosmt 4019 Mitigate all CPU vulnerabilities, disabling SMT 4020 if needed. This is for users who always want to 4021 be fully mitigated, even if it means losing SMT. 4022 Equivalent to: l1tf=flush,nosmt [X86] 4023 mds=full,nosmt [X86] 4024 tsx_async_abort=full,nosmt [X86] 4025 mmio_stale_data=full,nosmt [X86] 4026 retbleed=auto,nosmt [X86] 4027 4028 [X86] After one of the above options, additionally 4029 supports attack-vector based controls as documented in 4030 Documentation/admin-guide/hw-vuln/attack_vector_controls.rst 4031 4032 mminit_loglevel= 4033 [KNL,EARLY] When CONFIG_DEBUG_MEMORY_INIT is set, this 4034 parameter allows control of the logging verbosity for 4035 the additional memory initialisation checks. A value 4036 of 0 disables mminit logging and a level of 4 will 4037 log everything. Information is printed at KERN_DEBUG 4038 so loglevel=8 may also need to be specified. 4039 4040 mmio_stale_data= 4041 [X86,INTEL,EARLY] Control mitigation for the Processor 4042 MMIO Stale Data vulnerabilities. 4043 4044 Processor MMIO Stale Data is a class of 4045 vulnerabilities that may expose data after an MMIO 4046 operation. Exposed data could originate or end in 4047 the same CPU buffers as affected by MDS and TAA. 4048 Therefore, similar to MDS and TAA, the mitigation 4049 is to clear the affected CPU buffers. 4050 4051 This parameter controls the mitigation. The 4052 options are: 4053 4054 full - Enable mitigation on vulnerable CPUs 4055 4056 full,nosmt - Enable mitigation and disable SMT on 4057 vulnerable CPUs. 4058 4059 off - Unconditionally disable mitigation 4060 4061 On MDS or TAA affected machines, 4062 mmio_stale_data=off can be prevented by an active 4063 MDS or TAA mitigation as these vulnerabilities are 4064 mitigated with the same mechanism so in order to 4065 disable this mitigation, you need to specify 4066 mds=off and tsx_async_abort=off too. 4067 4068 Not specifying this option is equivalent to 4069 mmio_stale_data=full. 4070 4071 For details see: 4072 Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst 4073 4074 <module>.async_probe[=<bool>] [KNL] 4075 If no <bool> value is specified or if the value 4076 specified is not a valid <bool>, enable asynchronous 4077 probe on this module. Otherwise, enable/disable 4078 asynchronous probe on this module as indicated by the 4079 <bool> value. See also: module.async_probe 4080 4081 module.async_probe=<bool> 4082 [KNL] When set to true, modules will use async probing 4083 by default. To enable/disable async probing for a 4084 specific module, use the module specific control that 4085 is documented under <module>.async_probe. When both 4086 module.async_probe and <module>.async_probe are 4087 specified, <module>.async_probe takes precedence for 4088 the specific module. 4089 4090 module.enable_dups_trace 4091 [KNL] When CONFIG_MODULE_DEBUG_AUTOLOAD_DUPS is set, 4092 this means that duplicate request_module() calls will 4093 trigger a WARN_ON() instead of a pr_warn(). Note that 4094 if MODULE_DEBUG_AUTOLOAD_DUPS_TRACE is set, WARN_ON()s 4095 will always be issued and this option does nothing. 4096 module.sig_enforce 4097 [KNL] When CONFIG_MODULE_SIG is set, this means that 4098 modules without (valid) signatures will fail to load. 4099 Note that if CONFIG_MODULE_SIG_FORCE is set, that 4100 is always true, so this option does nothing. 4101 4102 module_blacklist= [KNL] Do not load a comma-separated list of 4103 modules. Useful for debugging problem modules. 4104 4105 mousedev.tap_time= 4106 [MOUSE] Maximum time between finger touching and 4107 leaving touchpad surface for touch to be considered 4108 a tap and be reported as a left button click (for 4109 touchpads working in absolute mode only). 4110 Format: <msecs> 4111 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 4112 reporting absolute coordinates, such as tablets 4113 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 4114 reporting absolute coordinates, such as tablets 4115 4116 movablecore= [KNL,X86,PPC,EARLY] 4117 Format: nn[KMGTPE] | nn% 4118 This parameter is the complement to kernelcore=, it 4119 specifies the amount of memory used for migratable 4120 allocations. If both kernelcore and movablecore is 4121 specified, then kernelcore will be at *least* the 4122 specified value but may be more. If movablecore on its 4123 own is specified, the administrator must be careful 4124 that the amount of memory usable for all allocations 4125 is not too small. 4126 4127 movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory 4128 NUMA nodes to be movable. This means that the memory 4129 of such nodes will be usable only for movable 4130 allocations which rules out almost all kernel 4131 allocations. Use with caution! 4132 4133 MTD_Partition= [MTD] 4134 Format: <name>,<region-number>,<size>,<offset> 4135 4136 MTD_Region= [MTD] Format: 4137 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 4138 4139 mtdparts= [MTD] 4140 See drivers/mtd/parsers/cmdlinepart.c 4141 4142 mtouchusb.raw_coordinates= 4143 [HW] Make the MicroTouch USB driver use raw coordinates 4144 ('y', default) or cooked coordinates ('n') 4145 4146 mtrr=debug [X86,EARLY] 4147 Enable printing debug information related to MTRR 4148 registers at boot time. 4149 4150 mtrr_chunk_size=nn[KMG,X86,EARLY] 4151 used for mtrr cleanup. It is largest continuous chunk 4152 that could hold holes aka. UC entries. 4153 4154 mtrr_gran_size=nn[KMG,X86,EARLY] 4155 Used for mtrr cleanup. It is granularity of mtrr block. 4156 Default is 1. 4157 Large value could prevent small alignment from 4158 using up MTRRs. 4159 4160 mtrr_spare_reg_nr=n [X86,EARLY] 4161 Format: <integer> 4162 Range: 0,7 : spare reg number 4163 Default : 1 4164 Used for mtrr cleanup. It is spare mtrr entries number. 4165 Set to 2 or more if your graphical card needs more. 4166 4167 multitce=off [PPC] This parameter disables the use of the pSeries 4168 firmware feature for updating multiple TCE entries 4169 at a time. 4170 4171 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 4172 4173 netdev= [NET] Network devices parameters 4174 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 4175 Note that mem_start is often overloaded to mean 4176 something different and driver-specific. 4177 This usage is only documented in each driver source 4178 file if at all. 4179 4180 netpoll.carrier_timeout= 4181 [NET] Specifies amount of time (in seconds) that 4182 netpoll should wait for a carrier. By default netpoll 4183 waits 4 seconds. 4184 4185 nf_conntrack.acct= 4186 [NETFILTER] Enable connection tracking flow accounting 4187 0 to disable accounting 4188 1 to enable accounting 4189 Default value is 0. 4190 4191 nfs.cache_getent= 4192 [NFS] sets the pathname to the program which is used 4193 to update the NFS client cache entries. 4194 4195 nfs.cache_getent_timeout= 4196 [NFS] sets the timeout after which an attempt to 4197 update a cache entry is deemed to have failed. 4198 4199 nfs.callback_nr_threads= 4200 [NFSv4] set the total number of threads that the 4201 NFS client will assign to service NFSv4 callback 4202 requests. 4203 4204 nfs.callback_tcpport= 4205 [NFS] set the TCP port on which the NFSv4 callback 4206 channel should listen. 4207 4208 nfs.delay_retrans= 4209 [NFS] specifies the number of times the NFSv4 client 4210 retries the request before returning an EAGAIN error, 4211 after a reply of NFS4ERR_DELAY from the server. 4212 Only applies if the softerr mount option is enabled, 4213 and the specified value is >= 0. 4214 4215 nfs.enable_ino64= 4216 [NFS] enable 64-bit inode numbers. 4217 If zero, the NFS client will fake up a 32-bit inode 4218 number for the readdir() and stat() syscalls instead 4219 of returning the full 64-bit number. 4220 The default is to return 64-bit inode numbers. 4221 4222 nfs.idmap_cache_timeout= 4223 [NFS] set the maximum lifetime for idmapper cache 4224 entries. 4225 4226 nfs.max_session_cb_slots= 4227 [NFSv4.1] Sets the maximum number of session 4228 slots the client will assign to the callback 4229 channel. This determines the maximum number of 4230 callbacks the client will process in parallel for 4231 a particular server. 4232 4233 nfs.max_session_slots= 4234 [NFSv4.1] Sets the maximum number of session slots 4235 the client will attempt to negotiate with the server. 4236 This limits the number of simultaneous RPC requests 4237 that the client can send to the NFSv4.1 server. 4238 Note that there is little point in setting this 4239 value higher than the max_tcp_slot_table_limit. 4240 4241 nfs.nfs4_disable_idmapping= 4242 [NFSv4] When set to the default of '1', this option 4243 ensures that both the RPC level authentication 4244 scheme and the NFS level operations agree to use 4245 numeric uids/gids if the mount is using the 4246 'sec=sys' security flavour. In effect it is 4247 disabling idmapping, which can make migration from 4248 legacy NFSv2/v3 systems to NFSv4 easier. 4249 Servers that do not support this mode of operation 4250 will be autodetected by the client, and it will fall 4251 back to using the idmapper. 4252 To turn off this behaviour, set the value to '0'. 4253 4254 nfs.nfs4_unique_id= 4255 [NFS4] Specify an additional fixed unique ident- 4256 ification string that NFSv4 clients can insert into 4257 their nfs_client_id4 string. This is typically a 4258 UUID that is generated at system install time. 4259 4260 nfs.recover_lost_locks= 4261 [NFSv4] Attempt to recover locks that were lost due 4262 to a lease timeout on the server. Please note that 4263 doing this risks data corruption, since there are 4264 no guarantees that the file will remain unchanged 4265 after the locks are lost. 4266 If you want to enable the kernel legacy behaviour of 4267 attempting to recover these locks, then set this 4268 parameter to '1'. 4269 The default parameter value of '0' causes the kernel 4270 not to attempt recovery of lost locks. 4271 4272 nfs.send_implementation_id= 4273 [NFSv4.1] Send client implementation identification 4274 information in exchange_id requests. 4275 If zero, no implementation identification information 4276 will be sent. 4277 The default is to send the implementation identification 4278 information. 4279 4280 nfs4.layoutstats_timer= 4281 [NFSv4.2] Change the rate at which the kernel sends 4282 layoutstats to the pNFS metadata server. 4283 4284 Setting this to value to 0 causes the kernel to use 4285 whatever value is the default set by the layout 4286 driver. A non-zero value sets the minimum interval 4287 in seconds between layoutstats transmissions. 4288 4289 nfsd.inter_copy_offload_enable= 4290 [NFSv4.2] When set to 1, the server will support 4291 server-to-server copies for which this server is 4292 the destination of the copy. 4293 4294 nfsd.nfs4_disable_idmapping= 4295 [NFSv4] When set to the default of '1', the NFSv4 4296 server will return only numeric uids and gids to 4297 clients using auth_sys, and will accept numeric uids 4298 and gids from such clients. This is intended to ease 4299 migration from NFSv2/v3. 4300 4301 nfsd.nfsd4_ssc_umount_timeout= 4302 [NFSv4.2] When used as the destination of a 4303 server-to-server copy, knfsd temporarily mounts 4304 the source server. It caches the mount in case 4305 it will be needed again, and discards it if not 4306 used for the number of milliseconds specified by 4307 this parameter. 4308 4309 nfsaddrs= [NFS] Deprecated. Use ip= instead. 4310 See Documentation/admin-guide/nfs/nfsroot.rst. 4311 4312 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 4313 See Documentation/admin-guide/nfs/nfsroot.rst. 4314 4315 nfsrootdebug [NFS] enable nfsroot debugging messages. 4316 See Documentation/admin-guide/nfs/nfsroot.rst. 4317 4318 nmi_backtrace.backtrace_idle [KNL] 4319 Dump stacks even of idle CPUs in response to an 4320 NMI stack-backtrace request. 4321 4322 nmi_debug= [KNL,SH] Specify one or more actions to take 4323 when a NMI is triggered. 4324 Format: [state][,regs][,debounce][,die] 4325 4326 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 4327 Format: [panic,][nopanic,][rNNN,][num] 4328 Valid num: 0 or 1 4329 0 - turn hardlockup detector in nmi_watchdog off 4330 1 - turn hardlockup detector in nmi_watchdog on 4331 rNNN - configure the watchdog with raw perf event 0xNNN 4332 4333 When panic is specified, panic when an NMI watchdog 4334 timeout occurs (or 'nopanic' to not panic on an NMI 4335 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 4336 To disable both hard and soft lockup detectors, 4337 please see 'nowatchdog'. 4338 This is useful when you use a panic=... timeout and 4339 need the box quickly up again. 4340 4341 These settings can be accessed at runtime via 4342 the nmi_watchdog and hardlockup_panic sysctls. 4343 4344 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 4345 emulation library even if a 387 maths coprocessor 4346 is present. 4347 4348 no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes. 4349 Forces kernel to use 3-level paging instead. 4350 4351 no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces 4352 kernel to use 4-level paging instead. 4353 4354 noalign [KNL,ARM] 4355 4356 noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any 4357 IOAPICs that may be present in the system. 4358 4359 noapictimer [APIC,X86] Don't set up the APIC timer 4360 4361 noautogroup Disable scheduler automatic task group creation. 4362 4363 nocache [ARM,EARLY] 4364 4365 no_console_suspend 4366 [HW] Never suspend the console 4367 Disable suspending of consoles during suspend and 4368 hibernate operations. Once disabled, debugging 4369 messages can reach various consoles while the rest 4370 of the system is being put to sleep (ie, while 4371 debugging driver suspend/resume hooks). This may 4372 not work reliably with all consoles, but is known 4373 to work with serial and VGA consoles. 4374 To facilitate more flexible debugging, we also add 4375 console_suspend, a printk module parameter to control 4376 it. Users could use console_suspend (usually 4377 /sys/module/printk/parameters/console_suspend) to 4378 turn on/off it dynamically. 4379 4380 no_debug_objects 4381 [KNL,EARLY] Disable object debugging 4382 4383 nodsp [SH] Disable hardware DSP at boot time. 4384 4385 noefi [EFI,EARLY] Disable EFI runtime services support. 4386 4387 no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel. 4388 4389 noexec32 [X86-64] 4390 This affects only 32-bit executables. 4391 noexec32=on: enable non-executable mappings (default) 4392 read doesn't imply executable mappings 4393 noexec32=off: disable non-executable mappings 4394 read implies executable mappings 4395 4396 no_file_caps Tells the kernel not to honor file capabilities. The 4397 only way then for a file to be executed with privilege 4398 is to be setuid root or executed by root. 4399 4400 nofpu [MIPS,SH] Disable hardware FPU at boot time. 4401 4402 nofsgsbase [X86] Disables FSGSBASE instructions. 4403 4404 nofxsr [BUGS=X86-32] Disables x86 floating point extended 4405 register save and restore. The kernel will only save 4406 legacy floating-point registers on task switch. 4407 4408 nogbpages [X86] Do not use GB pages for kernel direct mappings. 4409 4410 no_hash_pointers 4411 [KNL,EARLY] 4412 Alias for "hash_pointers=never". 4413 4414 nohibernate [HIBERNATION] Disable hibernation and resume. 4415 4416 nohlt [ARM,ARM64,MICROBLAZE,MIPS,PPC,RISCV,SH] Forces the kernel to 4417 busy wait in do_idle() and not use the arch_cpu_idle() 4418 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 4419 to be effective. This is useful on platforms where the 4420 sleep(SH) or wfi(ARM,ARM64) instructions do not work 4421 correctly or when doing power measurements to evaluate 4422 the impact of the sleep instructions. This is also 4423 useful when using JTAG debugger. 4424 4425 nohpet [X86] Don't use the HPET timer. 4426 4427 nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings. 4428 4429 nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings. 4430 4431 nohz= [KNL] Boottime enable/disable dynamic ticks 4432 Valid arguments: on, off 4433 Default: on 4434 4435 nohz_full= [KNL,BOOT,SMP,ISOL] 4436 The argument is a cpu list, as described above. 4437 In kernels built with CONFIG_NO_HZ_FULL=y, set 4438 the specified list of CPUs whose tick will be stopped 4439 whenever possible. The boot CPU will be forced outside 4440 the range to maintain the timekeeping. Any CPUs 4441 in this list will have their RCU callbacks offloaded, 4442 just as if they had also been called out in the 4443 rcu_nocbs= boot parameter. 4444 4445 Note that this argument takes precedence over 4446 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 4447 4448 noinitrd [RAM] Tells the kernel not to load any configured 4449 initial RAM disk. 4450 4451 nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt 4452 remapping. 4453 [Deprecated - use intremap=off] 4454 4455 noinvpcid [X86,EARLY] Disable the INVPCID cpu feature. 4456 4457 noiotrap [SH] Disables trapped I/O port accesses. 4458 4459 noirqdebug [X86-32] Disables the code which attempts to detect and 4460 disable unhandled interrupt sources. 4461 4462 noisapnp [ISAPNP] Disables ISA PnP code. 4463 4464 nokaslr [KNL,EARLY] 4465 When CONFIG_RANDOMIZE_BASE is set, this disables 4466 kernel and module base offset ASLR (Address Space 4467 Layout Randomization). 4468 4469 no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page 4470 fault handling. 4471 4472 no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver 4473 4474 nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC. 4475 4476 nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer. 4477 4478 nomce [X86-32] Disable Machine Check Exception 4479 4480 nomfgpt [X86-32] Disable Multi-Function General Purpose 4481 Timer usage (for AMD Geode machines). 4482 4483 nomodeset Disable kernel modesetting. Most systems' firmware 4484 sets up a display mode and provides framebuffer memory 4485 for output. With nomodeset, DRM and fbdev drivers will 4486 not load if they could possibly displace the pre- 4487 initialized output. Only the system framebuffer will 4488 be available for use. The respective drivers will not 4489 perform display-mode changes or accelerated rendering. 4490 4491 Useful as error fallback, or for testing and debugging. 4492 4493 nomodule Disable module load 4494 4495 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 4496 shutdown the other cpus. Instead use the REBOOT_VECTOR 4497 irq. 4498 4499 nopat [X86,EARLY] Disable PAT (page attribute table extension of 4500 pagetables) support. 4501 4502 nopcid [X86-64,EARLY] Disable the PCID cpu feature. 4503 4504 nopku [X86] Disable Memory Protection Keys CPU feature found 4505 in some Intel CPUs. 4506 4507 nopti [X86-64,EARLY] 4508 Equivalent to pti=off 4509 4510 nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY] 4511 Disables the PV optimizations forcing the guest to run 4512 as generic guest with no PV drivers. Currently support 4513 XEN HVM, KVM, HYPER_V and VMWARE guest. 4514 4515 nopvspin [X86,XEN,KVM,EARLY] 4516 Disables the qspinlock slow path using PV optimizations 4517 which allow the hypervisor to 'idle' the guest on lock 4518 contention. 4519 4520 norandmaps Don't use address space randomization. Equivalent to 4521 echo 0 > /proc/sys/kernel/randomize_va_space 4522 4523 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 4524 with UP alternatives 4525 4526 noresume [SWSUSP] Disables resume and restores original swap 4527 space. 4528 4529 no-scroll [VGA] Disables scrollback. 4530 This is required for the Braillex ib80-piezo Braille 4531 reader made by F.H. Papenmeier (Germany). 4532 4533 nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support. 4534 4535 nosmap [PPC,EARLY] 4536 Disable SMAP (Supervisor Mode Access Prevention) 4537 even if it is supported by processor. 4538 4539 nosmep [PPC64s,EARLY] 4540 Disable SMEP (Supervisor Mode Execution Prevention) 4541 even if it is supported by processor. 4542 4543 nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel, 4544 and disable the IO APIC. legacy for "maxcpus=0". 4545 4546 nosmt [KNL,MIPS,PPC,EARLY] Disable symmetric multithreading (SMT). 4547 Equivalent to smt=1. 4548 4549 [KNL,X86,PPC,S390] Disable symmetric multithreading (SMT). 4550 nosmt=force: Force disable SMT, cannot be undone 4551 via the sysfs control file. 4552 4553 nosoftlockup [KNL] Disable the soft-lockup detector. 4554 4555 nospec_store_bypass_disable 4556 [HW,EARLY] Disable all mitigations for the Speculative 4557 Store Bypass vulnerability 4558 4559 nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch 4560 history injection) vulnerability. System may allow data leaks 4561 with this option. 4562 4563 nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1 4564 (bounds check bypass). With this option data leaks are 4565 possible in the system. 4566 4567 nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations 4568 for the Spectre variant 2 (indirect branch 4569 prediction) vulnerability. System may allow data 4570 leaks with this option. 4571 4572 no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,LOONGARCH,EARLY] 4573 Disable paravirtualized steal time accounting. steal time 4574 is computed, but won't influence scheduler behaviour 4575 4576 nosync [HW,M68K] Disables sync negotiation for all devices. 4577 4578 no_timer_check [X86,APIC] Disables the code which tests for broken 4579 timer IRQ sources, i.e., the IO-APIC timer. This can 4580 work around problems with incorrect timer 4581 initialization on some boards. 4582 4583 no_uaccess_flush 4584 [PPC,EARLY] Don't flush the L1-D cache after accessing user data. 4585 4586 novmcoredd [KNL,KDUMP] 4587 Disable device dump. Device dump allows drivers to 4588 append dump data to vmcore so you can collect driver 4589 specified debug info. Drivers can append the data 4590 without any limit and this data is stored in memory, 4591 so this may cause significant memory stress. Disabling 4592 device dump can help save memory but the driver debug 4593 data will be no longer available. This parameter 4594 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 4595 is set. 4596 4597 no-vmw-sched-clock 4598 [X86,PV_OPS,EARLY] Disable paravirtualized VMware 4599 scheduler clock and use the default one. 4600 4601 nowatchdog [KNL] Disable both lockup detectors, i.e. 4602 soft-lockup and NMI watchdog (hard-lockup). 4603 4604 nowb [ARM,EARLY] 4605 4606 nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode. 4607 4608 NOTE: this parameter will be ignored on systems with the 4609 LEGACY_XAPIC_DISABLED bit set in the 4610 IA32_XAPIC_DISABLE_STATUS MSR. 4611 4612 noxsave [BUGS=X86] Disables x86 extended register state save 4613 and restore using xsave. The kernel will fallback to 4614 enabling legacy floating-point and sse state. 4615 4616 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 4617 register states. The kernel will fall back to use 4618 xsave to save the states. By using this parameter, 4619 performance of saving the states is degraded because 4620 xsave doesn't support modified optimization while 4621 xsaveopt supports it on xsaveopt enabled systems. 4622 4623 noxsaves [X86] Disables xsaves and xrstors used in saving and 4624 restoring x86 extended register state in compacted 4625 form of xsave area. The kernel will fall back to use 4626 xsaveopt and xrstor to save and restore the states 4627 in standard form of xsave area. By using this 4628 parameter, xsave area per process might occupy more 4629 memory on xsaves enabled systems. 4630 4631 nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel 4632 could support. nr_cpus=n : n >= 1 limits the kernel to 4633 support 'n' processors. It could be larger than the 4634 number of already plugged CPU during bootup, later in 4635 runtime you can physically add extra cpu until it reaches 4636 n. So during boot up some boot time memory for per-cpu 4637 variables need be pre-allocated for later physical cpu 4638 hot plugging. 4639 4640 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 4641 4642 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY] 4643 Disable NUMA, Only set up a single NUMA node 4644 spanning all memory. 4645 4646 numa=fake=<size>[MG] 4647 [KNL, ARM64, RISCV, X86, EARLY] 4648 If given as a memory unit, fills all system RAM with 4649 nodes of size interleaved over physical nodes. 4650 4651 numa=fake=<N> 4652 [KNL, ARM64, RISCV, X86, EARLY] 4653 If given as an integer, fills all system RAM with N 4654 fake nodes interleaved over physical nodes. 4655 4656 numa=fake=<N>U 4657 [KNL, ARM64, RISCV, X86, EARLY] 4658 If given as an integer followed by 'U', it will 4659 divide each physical node into N emulated nodes. 4660 4661 numa=noacpi [X86] Don't parse the SRAT table for NUMA setup 4662 4663 numa=nohmat [X86] Don't parse the HMAT table for NUMA setup, or 4664 soft-reserved memory partitioning. 4665 4666 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 4667 NUMA balancing. 4668 Allowed values are enable and disable 4669 4670 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 4671 'node', 'default' can be specified 4672 This can be set from sysctl after boot. 4673 See Documentation/admin-guide/sysctl/vm.rst for details. 4674 4675 ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver. 4676 See Documentation/core-api/debugging-via-ohci1394.rst for more 4677 info. 4678 4679 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 4680 Rather than timing out after 20 ms if an EC 4681 command is not properly ACKed, override the length 4682 of the timeout. We have interrupts disabled while 4683 waiting for the ACK, so if this is set too high 4684 interrupts *may* be lost! 4685 4686 omap_mux= [OMAP] Override bootloader pin multiplexing. 4687 Format: <mux_mode0.mode_name=value>... 4688 For example, to override I2C bus2: 4689 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 4690 4691 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 4692 4693 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 4694 4695 boundary - index of last SLC block on Flex-OneNAND. 4696 The remaining blocks are configured as MLC blocks. 4697 lock - Configure if Flex-OneNAND boundary should be locked. 4698 Once locked, the boundary cannot be changed. 4699 1 indicates lock status, 0 indicates unlock status. 4700 4701 oops=panic [KNL,EARLY] 4702 Always panic on oopses. Default is to just kill the 4703 process, but there is a small probability of 4704 deadlocking the machine. 4705 This will also cause panics on machine check exceptions. 4706 Useful together with panic=30 to trigger a reboot. 4707 4708 page_alloc.shuffle= 4709 [KNL] Boolean flag to control whether the page allocator 4710 should randomize its free lists. This parameter can be 4711 used to enable/disable page randomization. The state of 4712 the flag can be read from sysfs at: 4713 /sys/module/page_alloc/parameters/shuffle. 4714 This parameter is only available if CONFIG_SHUFFLE_PAGE_ALLOCATOR=y. 4715 4716 page_owner= [KNL,EARLY] Boot-time page_owner enabling option. 4717 Storage of the information about who allocated 4718 each page is disabled in default. With this switch, 4719 we can turn it on. 4720 on: enable the feature 4721 4722 page_poison= [KNL,EARLY] Boot-time parameter changing the state of 4723 poisoning on the buddy allocator, available with 4724 CONFIG_PAGE_POISONING=y. 4725 off: turn off poisoning (default) 4726 on: turn on poisoning 4727 4728 page_reporting.page_reporting_order= 4729 [KNL] Minimal page reporting order 4730 Format: <integer> 4731 Adjust the minimal page reporting order. The page 4732 reporting is disabled when it exceeds MAX_PAGE_ORDER. 4733 4734 panic= [KNL] Kernel behaviour on panic: delay <timeout> 4735 timeout > 0: seconds before rebooting 4736 timeout = 0: wait forever 4737 timeout < 0: reboot immediately 4738 Format: <timeout> 4739 4740 panic_on_taint= [KNL,EARLY] 4741 Bitmask for conditionally calling panic() in add_taint() 4742 Format: <hex>[,nousertaint] 4743 Hexadecimal bitmask representing the set of TAINT flags 4744 that will cause the kernel to panic when add_taint() is 4745 called with any of the flags in this set. 4746 The optional switch "nousertaint" can be utilized to 4747 prevent userspace forced crashes by writing to sysctl 4748 /proc/sys/kernel/tainted any flagset matching with the 4749 bitmask set on panic_on_taint. 4750 See Documentation/admin-guide/tainted-kernels.rst for 4751 extra details on the taint flags that users can pick 4752 to compose the bitmask to assign to panic_on_taint. 4753 4754 panic_on_warn=1 panic() instead of WARN(). Useful to cause kdump 4755 on a WARN(). 4756 4757 panic_print= Bitmask for printing system info when panic happens. 4758 User can chose combination of the following bits: 4759 bit 0: print all tasks info 4760 bit 1: print system memory info 4761 bit 2: print timer info 4762 bit 3: print locks info if CONFIG_LOCKDEP is on 4763 bit 4: print ftrace buffer 4764 bit 5: replay all kernel messages on consoles at the end of panic 4765 bit 6: print all CPUs backtrace (if available in the arch) 4766 bit 7: print only tasks in uninterruptible (blocked) state 4767 *Be aware* that this option may print a _lot_ of lines, 4768 so there are risks of losing older messages in the log. 4769 Use this option carefully, maybe worth to setup a 4770 bigger log buffer with "log_buf_len" along with this. 4771 4772 panic_sys_info= A comma separated list of extra information to be dumped 4773 on panic. 4774 Format: val[,val...] 4775 Where @val can be any of the following: 4776 4777 tasks: print all tasks info 4778 mem: print system memory info 4779 timers: print timers info 4780 locks: print locks info if CONFIG_LOCKDEP is on 4781 ftrace: print ftrace buffer 4782 all_bt: print all CPUs backtrace (if available in the arch) 4783 blocked_tasks: print only tasks in uninterruptible (blocked) state 4784 4785 This is a human readable alternative to the 'panic_print' option. 4786 4787 panic_console_replay 4788 When panic happens, replay all kernel messages on 4789 consoles at the end of panic. 4790 4791 parkbd.port= [HW] Parallel port number the keyboard adapter is 4792 connected to, default is 0. 4793 Format: <parport#> 4794 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 4795 0 for XT, 1 for AT (default is AT). 4796 Format: <mode> 4797 4798 parport= [HW,PPT] Specify parallel ports. 0 disables. 4799 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 4800 Use 'auto' to force the driver to use any 4801 IRQ/DMA settings detected (the default is to 4802 ignore detected IRQ/DMA settings because of 4803 possible conflicts). You can specify the base 4804 address, IRQ, and DMA settings; IRQ and DMA 4805 should be numbers, or 'auto' (for using detected 4806 settings on that particular port), or 'nofifo' 4807 (to avoid using a FIFO even if it is detected). 4808 Parallel ports are assigned in the order they 4809 are specified on the command line, starting 4810 with parport0. 4811 4812 parport_init_mode= [HW,PPT] 4813 Configure VIA parallel port to operate in 4814 a specific mode. This is necessary on Pegasos 4815 computer where firmware has no options for setting 4816 up parallel port mode and sets it to spp. 4817 Currently this function knows 686a and 8231 chips. 4818 Format: [spp|ps2|epp|ecp|ecpepp] 4819 4820 pata_legacy.all= [HW,LIBATA] 4821 Format: <int> 4822 Set to non-zero to probe primary and secondary ISA 4823 port ranges on PCI systems where no PCI PATA device 4824 has been found at either range. Disabled by default. 4825 4826 pata_legacy.autospeed= [HW,LIBATA] 4827 Format: <int> 4828 Set to non-zero if a chip is present that snoops speed 4829 changes. Disabled by default. 4830 4831 pata_legacy.ht6560a= [HW,LIBATA] 4832 Format: <int> 4833 Set to 1, 2, or 3 for HT 6560A on the primary channel, 4834 the secondary channel, or both channels respectively. 4835 Disabled by default. 4836 4837 pata_legacy.ht6560b= [HW,LIBATA] 4838 Format: <int> 4839 Set to 1, 2, or 3 for HT 6560B on the primary channel, 4840 the secondary channel, or both channels respectively. 4841 Disabled by default. 4842 4843 pata_legacy.iordy_mask= [HW,LIBATA] 4844 Format: <int> 4845 IORDY enable mask. Set individual bits to allow IORDY 4846 for the respective channel. Bit 0 is for the first 4847 legacy channel handled by this driver, bit 1 is for 4848 the second channel, and so on. The sequence will often 4849 correspond to the primary legacy channel, the secondary 4850 legacy channel, and so on, but the handling of a PCI 4851 bus and the use of other driver options may interfere 4852 with the sequence. By default IORDY is allowed across 4853 all channels. 4854 4855 pata_legacy.opti82c46x= [HW,LIBATA] 4856 Format: <int> 4857 Set to 1, 2, or 3 for Opti 82c611A on the primary 4858 channel, the secondary channel, or both channels 4859 respectively. Disabled by default. 4860 4861 pata_legacy.opti82c611a= [HW,LIBATA] 4862 Format: <int> 4863 Set to 1, 2, or 3 for Opti 82c465MV on the primary 4864 channel, the secondary channel, or both channels 4865 respectively. Disabled by default. 4866 4867 pata_legacy.pio_mask= [HW,LIBATA] 4868 Format: <int> 4869 PIO mode mask for autospeed devices. Set individual 4870 bits to allow the use of the respective PIO modes. 4871 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 4872 All modes allowed by default. 4873 4874 pata_legacy.probe_all= [HW,LIBATA] 4875 Format: <int> 4876 Set to non-zero to probe tertiary and further ISA 4877 port ranges on PCI systems. Disabled by default. 4878 4879 pata_legacy.probe_mask= [HW,LIBATA] 4880 Format: <int> 4881 Probe mask for legacy ISA PATA ports. Depending on 4882 platform configuration and the use of other driver 4883 options up to 6 legacy ports are supported: 0x1f0, 4884 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 4885 of individual ports can be disabled by setting the 4886 corresponding bits in the mask to 1. Bit 0 is for 4887 the first port in the list above (0x1f0), and so on. 4888 By default all supported ports are probed. 4889 4890 pata_legacy.qdi= [HW,LIBATA] 4891 Format: <int> 4892 Set to non-zero to probe QDI controllers. By default 4893 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 4894 4895 pata_legacy.winbond= [HW,LIBATA] 4896 Format: <int> 4897 Set to non-zero to probe Winbond controllers. Use 4898 the standard I/O port (0x130) if 1, otherwise the 4899 value given is the I/O port to use (typically 0x1b0). 4900 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 4901 0 otherwise. 4902 4903 pata_platform.pio_mask= [HW,LIBATA] 4904 Format: <int> 4905 Supported PIO mode mask. Set individual bits to allow 4906 the use of the respective PIO modes. Bit 0 is for 4907 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 4908 allowed by default. 4909 4910 pause_on_oops=<int> 4911 Halt all CPUs after the first oops has been printed for 4912 the specified number of seconds. This is to be used if 4913 your oopses keep scrolling off the screen. 4914 4915 pcbit= [HW,ISDN] 4916 4917 pci=option[,option...] [PCI,EARLY] various PCI subsystem options. 4918 4919 Some options herein operate on a specific device 4920 or a set of devices (<pci_dev>). These are 4921 specified in one of the following formats: 4922 4923 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 4924 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 4925 4926 Note: the first format specifies a PCI 4927 bus/device/function address which may change 4928 if new hardware is inserted, if motherboard 4929 firmware changes, or due to changes caused 4930 by other kernel parameters. If the 4931 domain is left unspecified, it is 4932 taken to be zero. Optionally, a path 4933 to a device through multiple device/function 4934 addresses can be specified after the base 4935 address (this is more robust against 4936 renumbering issues). The second format 4937 selects devices using IDs from the 4938 configuration space which may match multiple 4939 devices in the system. 4940 4941 earlydump dump PCI config space before the kernel 4942 changes anything 4943 off [X86] don't probe for the PCI bus 4944 bios [X86-32] force use of PCI BIOS, don't access 4945 the hardware directly. Use this if your machine 4946 has a non-standard PCI host bridge. 4947 nobios [X86-32] disallow use of PCI BIOS, only direct 4948 hardware access methods are allowed. Use this 4949 if you experience crashes upon bootup and you 4950 suspect they are caused by the BIOS. 4951 conf1 [X86] Force use of PCI Configuration Access 4952 Mechanism 1 (config address in IO port 0xCF8, 4953 data in IO port 0xCFC, both 32-bit). 4954 conf2 [X86] Force use of PCI Configuration Access 4955 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4956 the function, IO port 0xCFA, also 8-bit, sets 4957 bus number. The config space is then accessed 4958 through ports 0xC000-0xCFFF). 4959 See http://wiki.osdev.org/PCI for more info 4960 on the configuration access mechanisms. 4961 noaer [PCIE] If the PCIEAER kernel config parameter is 4962 enabled, this kernel boot option can be used to 4963 disable the use of PCIE advanced error reporting. 4964 nodomains [PCI] Disable support for multiple PCI 4965 root domains (aka PCI segments, in ACPI-speak). 4966 nommconf [X86] Disable use of MMCONFIG for PCI 4967 Configuration 4968 check_enable_amd_mmconf [X86] check for and enable 4969 properly configured MMIO access to PCI 4970 config space on AMD family 10h CPU 4971 nomsi [MSI] If the PCI_MSI kernel config parameter is 4972 enabled, this kernel boot option can be used to 4973 disable the use of MSI interrupts system-wide. 4974 noioapicquirk [APIC] Disable all boot interrupt quirks. 4975 Safety option to keep boot IRQs enabled. This 4976 should never be necessary. 4977 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4978 primary IO-APIC for bridges that cannot disable 4979 boot IRQs. This fixes a source of spurious IRQs 4980 when the system masks IRQs. 4981 noioapicreroute [APIC] Disable workaround that uses the 4982 boot IRQ equivalent of an IRQ that connects to 4983 a chipset where boot IRQs cannot be disabled. 4984 The opposite of ioapicreroute. 4985 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4986 routing table. These calls are known to be buggy 4987 on several machines and they hang the machine 4988 when used, but on other computers it's the only 4989 way to get the interrupt routing table. Try 4990 this option if the kernel is unable to allocate 4991 IRQs or discover secondary PCI buses on your 4992 motherboard. 4993 rom [X86] Assign address space to expansion ROMs. 4994 Use with caution as certain devices share 4995 address decoders between ROMs and other 4996 resources. 4997 norom [X86] Do not assign address space to 4998 expansion ROMs that do not already have 4999 BIOS assigned address ranges. 5000 nobar [X86] Do not assign address space to the 5001 BARs that weren't assigned by the BIOS. 5002 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 5003 assigned automatically to PCI devices. You can 5004 make the kernel exclude IRQs of your ISA cards 5005 this way. 5006 pirqaddr=0xAAAAA [X86] Specify the physical address 5007 of the PIRQ table (normally generated 5008 by the BIOS) if it is outside the 5009 F0000h-100000h range. 5010 lastbus=N [X86] Scan all buses thru bus #N. Can be 5011 useful if the kernel is unable to find your 5012 secondary buses and you want to tell it 5013 explicitly which ones they are. 5014 assign-busses [X86] Always assign all PCI bus 5015 numbers ourselves, overriding 5016 whatever the firmware may have done. 5017 usepirqmask [X86] Honor the possible IRQ mask stored 5018 in the BIOS $PIR table. This is needed on 5019 some systems with broken BIOSes, notably 5020 some HP Pavilion N5400 and Omnibook XE3 5021 notebooks. This will have no effect if ACPI 5022 IRQ routing is enabled. 5023 noacpi [X86] Do not use ACPI for IRQ routing 5024 or for PCI scanning. 5025 use_crs [X86] Use PCI host bridge window information 5026 from ACPI. On BIOSes from 2008 or later, this 5027 is enabled by default. If you need to use this, 5028 please report a bug. 5029 nocrs [X86] Ignore PCI host bridge windows from ACPI. 5030 If you need to use this, please report a bug. 5031 use_e820 [X86] Use E820 reservations to exclude parts of 5032 PCI host bridge windows. This is a workaround 5033 for BIOS defects in host bridge _CRS methods. 5034 If you need to use this, please report a bug to 5035 <linux-pci@vger.kernel.org>. 5036 no_e820 [X86] Ignore E820 reservations for PCI host 5037 bridge windows. This is the default on modern 5038 hardware. If you need to use this, please report 5039 a bug to <linux-pci@vger.kernel.org>. 5040 routeirq Do IRQ routing for all PCI devices. 5041 This is normally done in pci_enable_device(), 5042 so this option is a temporary workaround 5043 for broken drivers that don't call it. 5044 skip_isa_align [X86] do not align io start addr, so can 5045 handle more pci cards 5046 noearly [X86] Don't do any early type 1 scanning. 5047 This might help on some broken boards which 5048 machine check when some devices' config space 5049 is read. But various workarounds are disabled 5050 and some IOMMU drivers will not work. 5051 bfsort Sort PCI devices into breadth-first order. 5052 This sorting is done to get a device 5053 order compatible with older (<= 2.4) kernels. 5054 nobfsort Don't sort PCI devices into breadth-first order. 5055 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 5056 tuning and use the BIOS-configured MPS defaults. 5057 pcie_bus_safe Set every device's MPS to the largest value 5058 supported by all devices below the root complex. 5059 pcie_bus_perf Set device MPS to the largest allowable MPS 5060 based on its parent bus. Also set MRRS (Max 5061 Read Request Size) to the largest supported 5062 value (no larger than the MPS that the device 5063 or bus can support) for best performance. 5064 pcie_bus_peer2peer Set every device's MPS to 128B, which 5065 every device is guaranteed to support. This 5066 configuration allows peer-to-peer DMA between 5067 any pair of devices, possibly at the cost of 5068 reduced performance. This also guarantees 5069 that hot-added devices will work. 5070 cbiosize=nn[KMG] The fixed amount of bus space which is 5071 reserved for the CardBus bridge's IO window. 5072 The default value is 256 bytes. 5073 cbmemsize=nn[KMG] The fixed amount of bus space which is 5074 reserved for the CardBus bridge's memory 5075 window. The default value is 64 megabytes. 5076 resource_alignment= 5077 Format: 5078 [<order of align>@]<pci_dev>[; ...] 5079 Specifies alignment and device to reassign 5080 aligned memory resources. How to 5081 specify the device is described above. 5082 If <order of align> is not specified, 5083 PAGE_SIZE is used as alignment. 5084 A PCI-PCI bridge can be specified if resource 5085 windows need to be expanded. 5086 To specify the alignment for several 5087 instances of a device, the PCI vendor, 5088 device, subvendor, and subdevice may be 5089 specified, e.g., 12@pci:8086:9c22:103c:198f 5090 for 4096-byte alignment. 5091 ecrc= Enable/disable PCIe ECRC (transaction layer 5092 end-to-end CRC checking). Only effective if 5093 OS has native AER control (either granted by 5094 ACPI _OSC or forced via "pcie_ports=native") 5095 bios: Use BIOS/firmware settings. This is the 5096 the default. 5097 off: Turn ECRC off 5098 on: Turn ECRC on. 5099 hpiosize=nn[KMG] The fixed amount of bus space which is 5100 reserved for hotplug bridge's IO window. 5101 Default size is 256 bytes. 5102 hpmmiosize=nn[KMG] The fixed amount of bus space which is 5103 reserved for hotplug bridge's MMIO window. 5104 Default size is 2 megabytes. 5105 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 5106 reserved for hotplug bridge's MMIO_PREF window. 5107 Default size is 2 megabytes. 5108 hpmemsize=nn[KMG] The fixed amount of bus space which is 5109 reserved for hotplug bridge's MMIO and 5110 MMIO_PREF window. 5111 Default size is 2 megabytes. 5112 hpbussize=nn The minimum amount of additional bus numbers 5113 reserved for buses below a hotplug bridge. 5114 Default is 1. 5115 realloc= Enable/disable reallocating PCI bridge resources 5116 if allocations done by BIOS are too small to 5117 accommodate resources required by all child 5118 devices. 5119 off: Turn realloc off 5120 on: Turn realloc on 5121 realloc same as realloc=on 5122 noari do not use PCIe ARI. 5123 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 5124 do not use PCIe ATS (and IOMMU device IOTLB). 5125 pcie_scan_all Scan all possible PCIe devices. Otherwise we 5126 only look for one device below a PCIe downstream 5127 port. 5128 big_root_window Try to add a big 64bit memory window to the PCIe 5129 root complex on AMD CPUs. Some GFX hardware 5130 can resize a BAR to allow access to all VRAM. 5131 Adding the window is slightly risky (it may 5132 conflict with unreported devices), so this 5133 taints the kernel. 5134 disable_acs_redir=<pci_dev>[; ...] 5135 Specify one or more PCI devices (in the format 5136 specified above) separated by semicolons. 5137 Each device specified will have the PCI ACS 5138 redirect capabilities forced off which will 5139 allow P2P traffic between devices through 5140 bridges without forcing it upstream. Note: 5141 this removes isolation between devices and 5142 may put more devices in an IOMMU group. 5143 config_acs= 5144 Format: 5145 <ACS flags>@<pci_dev>[; ...] 5146 Specify one or more PCI devices (in the format 5147 specified above) optionally prepended with flags 5148 and separated by semicolons. The respective 5149 capabilities will be enabled, disabled or 5150 unchanged based on what is specified in 5151 flags. 5152 5153 ACS Flags is defined as follows: 5154 bit-0 : ACS Source Validation 5155 bit-1 : ACS Translation Blocking 5156 bit-2 : ACS P2P Request Redirect 5157 bit-3 : ACS P2P Completion Redirect 5158 bit-4 : ACS Upstream Forwarding 5159 bit-5 : ACS P2P Egress Control 5160 bit-6 : ACS Direct Translated P2P 5161 Each bit can be marked as: 5162 '0' – force disabled 5163 '1' – force enabled 5164 'x' – unchanged 5165 For example, 5166 pci=config_acs=10x@pci:0:0 5167 would configure all devices that support 5168 ACS to enable P2P Request Redirect, disable 5169 Translation Blocking, and leave Source 5170 Validation unchanged from whatever power-up 5171 or firmware set it to. 5172 5173 Note: this may remove isolation between devices 5174 and may put more devices in an IOMMU group. 5175 force_floating [S390] Force usage of floating interrupts. 5176 nomio [S390] Do not use MIO instructions. 5177 norid [S390] ignore the RID field and force use of 5178 one PCI domain per PCI function 5179 notph [PCIE] If the PCIE_TPH kernel config parameter 5180 is enabled, this kernel boot option can be used 5181 to disable PCIe TLP Processing Hints support 5182 system-wide. 5183 5184 pcie_aspm= [PCIE] Forcibly enable or ignore PCIe Active State Power 5185 Management. 5186 off Don't touch ASPM configuration at all. Leave any 5187 configuration done by firmware unchanged. 5188 force Enable ASPM even on devices that claim not to support it. 5189 WARNING: Forcing ASPM on may cause system lockups. 5190 5191 pcie_ports= [PCIE] PCIe port services handling: 5192 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 5193 even if the platform doesn't give the OS permission to 5194 use them. This may cause conflicts if the platform 5195 also tries to use these services. 5196 dpc-native Use native PCIe service for DPC only. May 5197 cause conflicts if firmware uses AER or DPC. 5198 compat Disable native PCIe services (PME, AER, DPC, PCIe 5199 hotplug). 5200 5201 pcie_port_pm= [PCIE] PCIe port power management handling: 5202 off Disable power management of all PCIe ports 5203 force Forcibly enable power management of all PCIe ports 5204 5205 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 5206 nomsi Do not use MSI for native PCIe PME signaling (this makes 5207 all PCIe root ports use INTx for all services). 5208 5209 pcmv= [HW,PCMCIA] BadgePAD 4 5210 5211 pd_ignore_unused 5212 [PM] 5213 Keep all power-domains already enabled by bootloader on, 5214 even if no driver has claimed them. This is useful 5215 for debug and development, but should not be 5216 needed on a platform with proper driver support. 5217 5218 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 5219 boot time. 5220 Format: { 0 | 1 } 5221 See arch/parisc/kernel/pdc_chassis.c 5222 5223 percpu_alloc= [MM,EARLY] 5224 Select which percpu first chunk allocator to use. 5225 Currently supported values are "embed" and "page". 5226 Archs may support subset or none of the selections. 5227 See comments in mm/percpu.c for details on each 5228 allocator. This parameter is primarily for debugging 5229 and performance comparison. 5230 5231 pirq= [SMP,APIC] Manual mp-table setup 5232 See Documentation/arch/x86/i386/IO-APIC.rst. 5233 5234 plip= [PPT,NET] Parallel port network link 5235 Format: { parport<nr> | timid | 0 } 5236 See also Documentation/admin-guide/parport.rst. 5237 5238 pmtmr= [X86] Manual setup of pmtmr I/O Port. 5239 Override pmtimer IOPort with a hex value. 5240 e.g. pmtmr=0x508 5241 5242 pmu_override= [PPC] Override the PMU. 5243 This option takes over the PMU facility, so it is no 5244 longer usable by perf. Setting this option starts the 5245 PMU counters by setting MMCR0 to 0 (the FC bit is 5246 cleared). If a number is given, then MMCR1 is set to 5247 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 5248 remains 0. 5249 5250 pm_async= [PM] 5251 Format: off 5252 This parameter sets the initial value of the 5253 /sys/power/pm_async sysfs knob at boot time. 5254 If set to "off", disables asynchronous suspend and 5255 resume of devices during system-wide power transitions. 5256 This can be useful on platforms where device 5257 dependencies are not well-defined, or for debugging 5258 power management issues. Asynchronous operations are 5259 enabled by default. 5260 5261 5262 pm_debug_messages [SUSPEND,KNL] 5263 Enable suspend/resume debug messages during boot up. 5264 5265 pnp.debug=1 [PNP] 5266 Enable PNP debug messages (depends on the 5267 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 5268 via /sys/module/pnp/parameters/debug. We always show 5269 current resource usage; turning this on also shows 5270 possible settings and some assignment information. 5271 5272 pnpacpi= [ACPI] 5273 { off } 5274 5275 pnpbios= [ISAPNP] 5276 { on | off | curr | res | no-curr | no-res } 5277 5278 pnp_reserve_irq= 5279 [ISAPNP] Exclude IRQs for the autoconfiguration 5280 5281 pnp_reserve_dma= 5282 [ISAPNP] Exclude DMAs for the autoconfiguration 5283 5284 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 5285 Ranges are in pairs (I/O port base and size). 5286 5287 pnp_reserve_mem= 5288 [ISAPNP] Exclude memory regions for the 5289 autoconfiguration. 5290 Ranges are in pairs (memory base and size). 5291 5292 ports= [IP_VS_FTP] IPVS ftp helper module 5293 Default is 21. 5294 Up to 8 (IP_VS_APP_MAX_PORTS) ports 5295 may be specified. 5296 Format: <port>,<port>.... 5297 5298 possible_cpus= [SMP,S390,X86] 5299 Format: <unsigned int> 5300 Set the number of possible CPUs, overriding the 5301 regular discovery mechanisms (such as ACPI/FW, etc). 5302 5303 powersave=off [PPC] This option disables power saving features. 5304 It specifically disables cpuidle and sets the 5305 platform machine description specific power_save 5306 function to NULL. On Idle the CPU just reduces 5307 execution priority. 5308 5309 ppc_strict_facility_enable 5310 [PPC,ENABLE] This option catches any kernel floating point, 5311 Altivec, VSX and SPE outside of regions specifically 5312 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 5313 There is some performance impact when enabling this. 5314 5315 ppc_tm= [PPC,EARLY] 5316 Format: {"off"} 5317 Disable Hardware Transactional Memory 5318 5319 preempt= [KNL] 5320 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 5321 none - Limited to cond_resched() calls 5322 voluntary - Limited to cond_resched() and might_sleep() calls 5323 full - Any section that isn't explicitly preempt disabled 5324 can be preempted anytime. Tasks will also yield 5325 contended spinlocks (if the critical section isn't 5326 explicitly preempt disabled beyond the lock itself). 5327 lazy - Scheduler controlled. Similar to full but instead 5328 of preempting the task immediately, the task gets 5329 one HZ tick time to yield itself before the 5330 preemption will be forced. One preemption is when the 5331 task returns to user space. 5332 5333 print-fatal-signals= 5334 [KNL] debug: print fatal signals 5335 5336 If enabled, warn about various signal handling 5337 related application anomalies: too many signals, 5338 too many POSIX.1 timers, fatal signals causing a 5339 coredump - etc. 5340 5341 If you hit the warning due to signal overflow, 5342 you might want to try "ulimit -i unlimited". 5343 5344 default: off. 5345 5346 printk.always_kmsg_dump= 5347 Trigger kmsg_dump for cases other than kernel oops or 5348 panics 5349 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5350 default: disabled 5351 5352 printk.console_no_auto_verbose= 5353 Disable console loglevel raise on oops, panic 5354 or lockdep-detected issues (only if lock debug is on). 5355 With an exception to setups with low baudrate on 5356 serial console, keeping this 0 is a good choice 5357 in order to provide more debug information. 5358 Format: <bool> 5359 default: 0 (auto_verbose is enabled) 5360 5361 printk.debug_non_panic_cpus= 5362 Allows storing messages from non-panic CPUs into 5363 the printk log buffer during panic(). They are 5364 flushed to consoles by the panic-CPU on 5365 a best-effort basis. 5366 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5367 Default: disabled 5368 5369 printk.devkmsg={on,off,ratelimit} 5370 Control writing to /dev/kmsg. 5371 on - unlimited logging to /dev/kmsg from userspace 5372 off - logging to /dev/kmsg disabled 5373 ratelimit - ratelimit the logging 5374 Default: ratelimit 5375 5376 printk.time= Show timing data prefixed to each printk message line 5377 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5378 5379 proc_mem.force_override= [KNL] 5380 Format: {always | ptrace | never} 5381 Traditionally /proc/pid/mem allows memory permissions to be 5382 overridden without restrictions. This option may be set to 5383 restrict that. Can be one of: 5384 - 'always': traditional behavior always allows mem overrides. 5385 - 'ptrace': only allow mem overrides for active ptracers. 5386 - 'never': never allow mem overrides. 5387 If not specified, default is the CONFIG_PROC_MEM_* choice. 5388 5389 processor.max_cstate= [HW,ACPI] 5390 Limit processor to maximum C-state 5391 max_cstate=9 overrides any DMI blacklist limit. 5392 5393 processor.nocst [HW,ACPI] 5394 Ignore the _CST method to determine C-states, 5395 instead using the legacy FADT method 5396 5397 profile= [KNL] Enable kernel profiling via /proc/profile 5398 Format: [<profiletype>,]<number> 5399 Param: <profiletype>: "schedule" or "kvm" 5400 [defaults to kernel profiling] 5401 Param: "schedule" - profile schedule points. 5402 Param: "kvm" - profile VM exits. 5403 Param: <number> - step/bucket size as a power of 2 for 5404 statistical time based profiling. 5405 5406 prompt_ramdisk= [RAM] [Deprecated] 5407 5408 prot_virt= [S390] enable hosting protected virtual machines 5409 isolated from the hypervisor (if hardware supports 5410 that). If enabled, the default kernel base address 5411 might be overridden even when Kernel Address Space 5412 Layout Randomization is disabled. 5413 Format: <bool> 5414 5415 psi= [KNL] Enable or disable pressure stall information 5416 tracking. 5417 Format: <bool> 5418 5419 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 5420 probe for; one of (bare|imps|exps|lifebook|any). 5421 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 5422 per second. 5423 psmouse.resetafter= [HW,MOUSE] 5424 Try to reset the device after so many bad packets 5425 (0 = never). 5426 psmouse.resolution= 5427 [HW,MOUSE] Set desired mouse resolution, in dpi. 5428 psmouse.smartscroll= 5429 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 5430 0 = disabled, 1 = enabled (default). 5431 5432 pstore.backend= Specify the name of the pstore backend to use 5433 5434 pti= [X86-64] Control Page Table Isolation of user and 5435 kernel address spaces. Disabling this feature 5436 removes hardening, but improves performance of 5437 system calls and interrupts. 5438 5439 on - unconditionally enable 5440 off - unconditionally disable 5441 auto - kernel detects whether your CPU model is 5442 vulnerable to issues that PTI mitigates 5443 5444 Not specifying this option is equivalent to pti=auto. 5445 5446 pty.legacy_count= 5447 [KNL] Number of legacy pty's. Overwrites compiled-in 5448 default number. 5449 5450 quiet [KNL,EARLY] Disable most log messages 5451 5452 r128= [HW,DRM] 5453 5454 radix_hcall_invalidate=on [PPC/PSERIES] 5455 Disable RADIX GTSE feature and use hcall for TLB 5456 invalidate. 5457 5458 raid= [HW,RAID] 5459 See Documentation/admin-guide/md.rst. 5460 5461 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 5462 See Documentation/admin-guide/blockdev/ramdisk.rst. 5463 5464 ramdisk_start= [RAM] RAM disk image start address 5465 5466 random.trust_cpu=off 5467 [KNL,EARLY] Disable trusting the use of the CPU's 5468 random number generator (if available) to 5469 initialize the kernel's RNG. 5470 5471 random.trust_bootloader=off 5472 [KNL,EARLY] Disable trusting the use of the a seed 5473 passed by the bootloader (if available) to 5474 initialize the kernel's RNG. 5475 5476 randomize_kstack_offset= 5477 [KNL,EARLY] Enable or disable kernel stack offset 5478 randomization, which provides roughly 5 bits of 5479 entropy, frustrating memory corruption attacks 5480 that depend on stack address determinism or 5481 cross-syscall address exposures. This is only 5482 available on architectures that have defined 5483 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 5484 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 5485 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 5486 5487 ras=option[,option,...] [KNL] RAS-specific options 5488 5489 cec_disable [X86] 5490 Disable the Correctable Errors Collector, 5491 see CONFIG_RAS_CEC help text. 5492 5493 rcu_nocbs[=cpu-list] 5494 [KNL] The optional argument is a cpu list, 5495 as described above. 5496 5497 In kernels built with CONFIG_RCU_NOCB_CPU=y, 5498 enable the no-callback CPU mode, which prevents 5499 such CPUs' callbacks from being invoked in 5500 softirq context. Invocation of such CPUs' RCU 5501 callbacks will instead be offloaded to "rcuox/N" 5502 kthreads created for that purpose, where "x" is 5503 "p" for RCU-preempt, "s" for RCU-sched, and "g" 5504 for the kthreads that mediate grace periods; and 5505 "N" is the CPU number. This reduces OS jitter on 5506 the offloaded CPUs, which can be useful for HPC 5507 and real-time workloads. It can also improve 5508 energy efficiency for asymmetric multiprocessors. 5509 5510 If a cpulist is passed as an argument, the specified 5511 list of CPUs is set to no-callback mode from boot. 5512 5513 Otherwise, if the '=' sign and the cpulist 5514 arguments are omitted, no CPU will be set to 5515 no-callback mode from boot but the mode may be 5516 toggled at runtime via cpusets. 5517 5518 Note that this argument takes precedence over 5519 the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option. 5520 5521 rcu_nocb_poll [KNL] 5522 Rather than requiring that offloaded CPUs 5523 (specified by rcu_nocbs= above) explicitly 5524 awaken the corresponding "rcuoN" kthreads, 5525 make these kthreads poll for callbacks. 5526 This improves the real-time response for the 5527 offloaded CPUs by relieving them of the need to 5528 wake up the corresponding kthread, but degrades 5529 energy efficiency by requiring that the kthreads 5530 periodically wake up to do the polling. 5531 5532 rcutree.blimit= [KNL] 5533 Set maximum number of finished RCU callbacks to 5534 process in one batch. 5535 5536 rcutree.csd_lock_suppress_rcu_stall= [KNL] 5537 Do only a one-line RCU CPU stall warning when 5538 there is an ongoing too-long CSD-lock wait. 5539 5540 rcutree.do_rcu_barrier= [KNL] 5541 Request a call to rcu_barrier(). This is 5542 throttled so that userspace tests can safely 5543 hammer on the sysfs variable if they so choose. 5544 If triggered before the RCU grace-period machinery 5545 is fully active, this will error out with EAGAIN. 5546 5547 rcutree.dump_tree= [KNL] 5548 Dump the structure of the rcu_node combining tree 5549 out at early boot. This is used for diagnostic 5550 purposes, to verify correct tree setup. 5551 5552 rcutree.gp_cleanup_delay= [KNL] 5553 Set the number of jiffies to delay each step of 5554 RCU grace-period cleanup. 5555 5556 rcutree.gp_init_delay= [KNL] 5557 Set the number of jiffies to delay each step of 5558 RCU grace-period initialization. 5559 5560 rcutree.gp_preinit_delay= [KNL] 5561 Set the number of jiffies to delay each step of 5562 RCU grace-period pre-initialization, that is, 5563 the propagation of recent CPU-hotplug changes up 5564 the rcu_node combining tree. 5565 5566 rcutree.jiffies_till_first_fqs= [KNL] 5567 Set delay from grace-period initialization to 5568 first attempt to force quiescent states. 5569 Units are jiffies, minimum value is zero, 5570 and maximum value is HZ. 5571 5572 rcutree.jiffies_till_next_fqs= [KNL] 5573 Set delay between subsequent attempts to force 5574 quiescent states. Units are jiffies, minimum 5575 value is one, and maximum value is HZ. 5576 5577 rcutree.jiffies_till_sched_qs= [KNL] 5578 Set required age in jiffies for a 5579 given grace period before RCU starts 5580 soliciting quiescent-state help from 5581 rcu_note_context_switch() and cond_resched(). 5582 If not specified, the kernel will calculate 5583 a value based on the most recent settings 5584 of rcutree.jiffies_till_first_fqs 5585 and rcutree.jiffies_till_next_fqs. 5586 This calculated value may be viewed in 5587 rcutree.jiffies_to_sched_qs. Any attempt to set 5588 rcutree.jiffies_to_sched_qs will be cheerfully 5589 overwritten. 5590 5591 rcutree.kthread_prio= [KNL,BOOT] 5592 Set the SCHED_FIFO priority of the RCU per-CPU 5593 kthreads (rcuc/N). This value is also used for 5594 the priority of the RCU boost threads (rcub/N) 5595 and for the RCU grace-period kthreads (rcu_bh, 5596 rcu_preempt, and rcu_sched). If RCU_BOOST is 5597 set, valid values are 1-99 and the default is 1 5598 (the least-favored priority). Otherwise, when 5599 RCU_BOOST is not set, valid values are 0-99 and 5600 the default is zero (non-realtime operation). 5601 When RCU_NOCB_CPU is set, also adjust the 5602 priority of NOCB callback kthreads. 5603 5604 rcutree.nocb_nobypass_lim_per_jiffy= [KNL] 5605 On callback-offloaded (rcu_nocbs) CPUs, 5606 RCU reduces the lock contention that would 5607 otherwise be caused by callback floods through 5608 use of the ->nocb_bypass list. However, in the 5609 common non-flooded case, RCU queues directly to 5610 the main ->cblist in order to avoid the extra 5611 overhead of the ->nocb_bypass list and its lock. 5612 But if there are too many callbacks queued during 5613 a single jiffy, RCU pre-queues the callbacks into 5614 the ->nocb_bypass queue. The definition of "too 5615 many" is supplied by this kernel boot parameter. 5616 5617 rcutree.nohz_full_patience_delay= [KNL] 5618 On callback-offloaded (rcu_nocbs) CPUs, avoid 5619 disturbing RCU unless the grace period has 5620 reached the specified age in milliseconds. 5621 Defaults to zero. Large values will be capped 5622 at five seconds. All values will be rounded down 5623 to the nearest value representable by jiffies. 5624 5625 rcutree.qhimark= [KNL] 5626 Set threshold of queued RCU callbacks beyond which 5627 batch limiting is disabled. 5628 5629 rcutree.qlowmark= [KNL] 5630 Set threshold of queued RCU callbacks below which 5631 batch limiting is re-enabled. 5632 5633 rcutree.qovld= [KNL] 5634 Set threshold of queued RCU callbacks beyond which 5635 RCU's force-quiescent-state scan will aggressively 5636 enlist help from cond_resched() and sched IPIs to 5637 help CPUs more quickly reach quiescent states. 5638 Set to less than zero to make this be set based 5639 on rcutree.qhimark at boot time and to zero to 5640 disable more aggressive help enlistment. 5641 5642 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 5643 Set the page-cache refill delay (in milliseconds) 5644 in response to low-memory conditions. The range 5645 of permitted values is in the range 0:100000. 5646 5647 rcutree.rcu_divisor= [KNL] 5648 Set the shift-right count to use to compute 5649 the callback-invocation batch limit bl from 5650 the number of callbacks queued on this CPU. 5651 The result will be bounded below by the value of 5652 the rcutree.blimit kernel parameter. Every bl 5653 callbacks, the softirq handler will exit in 5654 order to allow the CPU to do other work. 5655 5656 Please note that this callback-invocation batch 5657 limit applies only to non-offloaded callback 5658 invocation. Offloaded callbacks are instead 5659 invoked in the context of an rcuoc kthread, which 5660 scheduler will preempt as it does any other task. 5661 5662 rcutree.rcu_fanout_exact= [KNL] 5663 Disable autobalancing of the rcu_node combining 5664 tree. This is used by rcutorture, and might 5665 possibly be useful for architectures having high 5666 cache-to-cache transfer latencies. 5667 5668 rcutree.rcu_fanout_leaf= [KNL] 5669 Change the number of CPUs assigned to each 5670 leaf rcu_node structure. Useful for very 5671 large systems, which will choose the value 64, 5672 and for NUMA systems with large remote-access 5673 latencies, which will choose a value aligned 5674 with the appropriate hardware boundaries. 5675 5676 rcutree.rcu_min_cached_objs= [KNL] 5677 Minimum number of objects which are cached and 5678 maintained per one CPU. Object size is equal 5679 to PAGE_SIZE. The cache allows to reduce the 5680 pressure to page allocator, also it makes the 5681 whole algorithm to behave better in low memory 5682 condition. 5683 5684 rcutree.rcu_nocb_gp_stride= [KNL] 5685 Set the number of NOCB callback kthreads in 5686 each group, which defaults to the square root 5687 of the number of CPUs. Larger numbers reduce 5688 the wakeup overhead on the global grace-period 5689 kthread, but increases that same overhead on 5690 each group's NOCB grace-period kthread. 5691 5692 rcutree.rcu_kick_kthreads= [KNL] 5693 Cause the grace-period kthread to get an extra 5694 wake_up() if it sleeps three times longer than 5695 it should at force-quiescent-state time. 5696 This wake_up() will be accompanied by a 5697 WARN_ONCE() splat and an ftrace_dump(). 5698 5699 rcutree.rcu_resched_ns= [KNL] 5700 Limit the time spend invoking a batch of RCU 5701 callbacks to the specified number of nanoseconds. 5702 By default, this limit is checked only once 5703 every 32 callbacks in order to limit the pain 5704 inflicted by local_clock() overhead. 5705 5706 rcutree.rcu_unlock_delay= [KNL] 5707 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 5708 this specifies an rcu_read_unlock()-time delay 5709 in microseconds. This defaults to zero. 5710 Larger delays increase the probability of 5711 catching RCU pointer leaks, that is, buggy use 5712 of RCU-protected pointers after the relevant 5713 rcu_read_unlock() has completed. 5714 5715 rcutree.sysrq_rcu= [KNL] 5716 Commandeer a sysrq key to dump out Tree RCU's 5717 rcu_node tree with an eye towards determining 5718 why a new grace period has not yet started. 5719 5720 rcutree.use_softirq= [KNL] 5721 If set to zero, move all RCU_SOFTIRQ processing to 5722 per-CPU rcuc kthreads. Defaults to a non-zero 5723 value, meaning that RCU_SOFTIRQ is used by default. 5724 Specify rcutree.use_softirq=0 to use rcuc kthreads. 5725 5726 But note that CONFIG_PREEMPT_RT=y kernels disable 5727 this kernel boot parameter, forcibly setting it 5728 to zero. 5729 5730 rcutree.enable_rcu_lazy= [KNL] 5731 To save power, batch RCU callbacks and flush after 5732 delay, memory pressure or callback list growing too 5733 big. 5734 5735 rcutree.rcu_normal_wake_from_gp= [KNL] 5736 Reduces a latency of synchronize_rcu() call. This approach 5737 maintains its own track of synchronize_rcu() callers, so it 5738 does not interact with regular callbacks because it does not 5739 use a call_rcu[_hurry]() path. Please note, this is for a 5740 normal grace period. 5741 5742 How to enable it: 5743 5744 echo 1 > /sys/module/rcutree/parameters/rcu_normal_wake_from_gp 5745 or pass a boot parameter "rcutree.rcu_normal_wake_from_gp=1" 5746 5747 Default is 1 if num_possible_cpus() <= 16 and it is not explicitly 5748 disabled by the boot parameter passing 0. 5749 5750 rcuscale.gp_async= [KNL] 5751 Measure performance of asynchronous 5752 grace-period primitives such as call_rcu(). 5753 5754 rcuscale.gp_async_max= [KNL] 5755 Specify the maximum number of outstanding 5756 callbacks per writer thread. When a writer 5757 thread exceeds this limit, it invokes the 5758 corresponding flavor of rcu_barrier() to allow 5759 previously posted callbacks to drain. 5760 5761 rcuscale.gp_exp= [KNL] 5762 Measure performance of expedited synchronous 5763 grace-period primitives. 5764 5765 rcuscale.holdoff= [KNL] 5766 Set test-start holdoff period. The purpose of 5767 this parameter is to delay the start of the 5768 test until boot completes in order to avoid 5769 interference. 5770 5771 rcuscale.kfree_by_call_rcu= [KNL] 5772 In kernels built with CONFIG_RCU_LAZY=y, test 5773 call_rcu() instead of kfree_rcu(). 5774 5775 rcuscale.kfree_mult= [KNL] 5776 Instead of allocating an object of size kfree_obj, 5777 allocate one of kfree_mult * sizeof(kfree_obj). 5778 Defaults to 1. 5779 5780 rcuscale.kfree_rcu_test= [KNL] 5781 Set to measure performance of kfree_rcu() flooding. 5782 5783 rcuscale.kfree_rcu_test_double= [KNL] 5784 Test the double-argument variant of kfree_rcu(). 5785 If this parameter has the same value as 5786 rcuscale.kfree_rcu_test_single, both the single- 5787 and double-argument variants are tested. 5788 5789 rcuscale.kfree_rcu_test_single= [KNL] 5790 Test the single-argument variant of kfree_rcu(). 5791 If this parameter has the same value as 5792 rcuscale.kfree_rcu_test_double, both the single- 5793 and double-argument variants are tested. 5794 5795 rcuscale.kfree_nthreads= [KNL] 5796 The number of threads running loops of kfree_rcu(). 5797 5798 rcuscale.kfree_alloc_num= [KNL] 5799 Number of allocations and frees done in an iteration. 5800 5801 rcuscale.kfree_loops= [KNL] 5802 Number of loops doing rcuscale.kfree_alloc_num number 5803 of allocations and frees. 5804 5805 rcuscale.minruntime= [KNL] 5806 Set the minimum test run time in seconds. This 5807 does not affect the data-collection interval, 5808 but instead allows better measurement of things 5809 like CPU consumption. 5810 5811 rcuscale.nreaders= [KNL] 5812 Set number of RCU readers. The value -1 selects 5813 N, where N is the number of CPUs. A value 5814 "n" less than -1 selects N-n+1, where N is again 5815 the number of CPUs. For example, -2 selects N 5816 (the number of CPUs), -3 selects N+1, and so on. 5817 A value of "n" less than or equal to -N selects 5818 a single reader. 5819 5820 rcuscale.nwriters= [KNL] 5821 Set number of RCU writers. The values operate 5822 the same as for rcuscale.nreaders. 5823 N, where N is the number of CPUs 5824 5825 rcuscale.scale_type= [KNL] 5826 Specify the RCU implementation to test. 5827 5828 rcuscale.shutdown= [KNL] 5829 Shut the system down after performance tests 5830 complete. This is useful for hands-off automated 5831 testing. 5832 5833 rcuscale.verbose= [KNL] 5834 Enable additional printk() statements. 5835 5836 rcuscale.writer_holdoff= [KNL] 5837 Write-side holdoff between grace periods, 5838 in microseconds. The default of zero says 5839 no holdoff. 5840 5841 rcuscale.writer_holdoff_jiffies= [KNL] 5842 Additional write-side holdoff between grace 5843 periods, but in jiffies. The default of zero 5844 says no holdoff. 5845 5846 rcutorture.fqs_duration= [KNL] 5847 Set duration of force_quiescent_state bursts 5848 in microseconds. 5849 5850 rcutorture.fqs_holdoff= [KNL] 5851 Set holdoff time within force_quiescent_state bursts 5852 in microseconds. 5853 5854 rcutorture.fqs_stutter= [KNL] 5855 Set wait time between force_quiescent_state bursts 5856 in seconds. 5857 5858 rcutorture.fwd_progress= [KNL] 5859 Specifies the number of kthreads to be used 5860 for RCU grace-period forward-progress testing 5861 for the types of RCU supporting this notion. 5862 Defaults to 1 kthread, values less than zero or 5863 greater than the number of CPUs cause the number 5864 of CPUs to be used. 5865 5866 rcutorture.fwd_progress_div= [KNL] 5867 Specify the fraction of a CPU-stall-warning 5868 period to do tight-loop forward-progress testing. 5869 5870 rcutorture.fwd_progress_holdoff= [KNL] 5871 Number of seconds to wait between successive 5872 forward-progress tests. 5873 5874 rcutorture.fwd_progress_need_resched= [KNL] 5875 Enclose cond_resched() calls within checks for 5876 need_resched() during tight-loop forward-progress 5877 testing. 5878 5879 rcutorture.gp_cond= [KNL] 5880 Use conditional/asynchronous update-side 5881 normal-grace-period primitives, if available. 5882 5883 rcutorture.gp_cond_exp= [KNL] 5884 Use conditional/asynchronous update-side 5885 expedited-grace-period primitives, if available. 5886 5887 rcutorture.gp_cond_full= [KNL] 5888 Use conditional/asynchronous update-side 5889 normal-grace-period primitives that also take 5890 concurrent expedited grace periods into account, 5891 if available. 5892 5893 rcutorture.gp_cond_exp_full= [KNL] 5894 Use conditional/asynchronous update-side 5895 expedited-grace-period primitives that also take 5896 concurrent normal grace periods into account, 5897 if available. 5898 5899 rcutorture.gp_cond_wi= [KNL] 5900 Nominal wait interval for normal conditional 5901 grace periods (specified by rcutorture's 5902 gp_cond and gp_cond_full module parameters), 5903 in microseconds. The actual wait interval will 5904 be randomly selected to nanosecond granularity up 5905 to this wait interval. Defaults to 16 jiffies, 5906 for example, 16,000 microseconds on a system 5907 with HZ=1000. 5908 5909 rcutorture.gp_cond_wi_exp= [KNL] 5910 Nominal wait interval for expedited conditional 5911 grace periods (specified by rcutorture's 5912 gp_cond_exp and gp_cond_exp_full module 5913 parameters), in microseconds. The actual wait 5914 interval will be randomly selected to nanosecond 5915 granularity up to this wait interval. Defaults to 5916 128 microseconds. 5917 5918 rcutorture.gp_exp= [KNL] 5919 Use expedited update-side primitives, if available. 5920 5921 rcutorture.gp_normal= [KNL] 5922 Use normal (non-expedited) asynchronous 5923 update-side primitives, if available. 5924 5925 rcutorture.gp_poll= [KNL] 5926 Use polled update-side normal-grace-period 5927 primitives, if available. 5928 5929 rcutorture.gp_poll_exp= [KNL] 5930 Use polled update-side expedited-grace-period 5931 primitives, if available. 5932 5933 rcutorture.gp_poll_full= [KNL] 5934 Use polled update-side normal-grace-period 5935 primitives that also take concurrent expedited 5936 grace periods into account, if available. 5937 5938 rcutorture.gp_poll_exp_full= [KNL] 5939 Use polled update-side expedited-grace-period 5940 primitives that also take concurrent normal 5941 grace periods into account, if available. 5942 5943 rcutorture.gp_poll_wi= [KNL] 5944 Nominal wait interval for normal conditional 5945 grace periods (specified by rcutorture's 5946 gp_poll and gp_poll_full module parameters), 5947 in microseconds. The actual wait interval will 5948 be randomly selected to nanosecond granularity up 5949 to this wait interval. Defaults to 16 jiffies, 5950 for example, 16,000 microseconds on a system 5951 with HZ=1000. 5952 5953 rcutorture.gp_poll_wi_exp= [KNL] 5954 Nominal wait interval for expedited conditional 5955 grace periods (specified by rcutorture's 5956 gp_poll_exp and gp_poll_exp_full module 5957 parameters), in microseconds. The actual wait 5958 interval will be randomly selected to nanosecond 5959 granularity up to this wait interval. Defaults to 5960 128 microseconds. 5961 5962 rcutorture.gp_sync= [KNL] 5963 Use normal (non-expedited) synchronous 5964 update-side primitives, if available. If all 5965 of rcutorture.gp_cond=, rcutorture.gp_exp=, 5966 rcutorture.gp_normal=, and rcutorture.gp_sync= 5967 are zero, rcutorture acts as if is interpreted 5968 they are all non-zero. 5969 5970 rcutorture.gpwrap_lag= [KNL] 5971 Enable grace-period wrap lag testing. Setting 5972 to false prevents the gpwrap lag test from 5973 running. Default is true. 5974 5975 rcutorture.gpwrap_lag_gps= [KNL] 5976 Set the value for grace-period wrap lag during 5977 active lag testing periods. This controls how many 5978 grace periods differences we tolerate between 5979 rdp and rnp's gp_seq before setting overflow flag. 5980 The default is always set to 8. 5981 5982 rcutorture.gpwrap_lag_cycle_mins= [KNL] 5983 Set the total cycle duration for gpwrap lag 5984 testing in minutes. This is the total time for 5985 one complete cycle of active and inactive 5986 testing periods. Default is 30 minutes. 5987 5988 rcutorture.gpwrap_lag_active_mins= [KNL] 5989 Set the duration for which gpwrap lag is active 5990 within each cycle, in minutes. During this time, 5991 the grace-period wrap lag will be set to the 5992 value specified by gpwrap_lag_gps. Default is 5993 5 minutes. 5994 5995 rcutorture.irqreader= [KNL] 5996 Run RCU readers from irq handlers, or, more 5997 accurately, from a timer handler. Not all RCU 5998 flavors take kindly to this sort of thing. 5999 6000 rcutorture.leakpointer= [KNL] 6001 Leak an RCU-protected pointer out of the reader. 6002 This can of course result in splats, and is 6003 intended to test the ability of things like 6004 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 6005 such leaks. 6006 6007 rcutorture.n_barrier_cbs= [KNL] 6008 Set callbacks/threads for rcu_barrier() testing. 6009 6010 rcutorture.nfakewriters= [KNL] 6011 Set number of concurrent RCU writers. These just 6012 stress RCU, they don't participate in the actual 6013 test, hence the "fake". 6014 6015 rcutorture.nocbs_nthreads= [KNL] 6016 Set number of RCU callback-offload togglers. 6017 Zero (the default) disables toggling. 6018 6019 rcutorture.nocbs_toggle= [KNL] 6020 Set the delay in milliseconds between successive 6021 callback-offload toggling attempts. 6022 6023 rcutorture.nreaders= [KNL] 6024 Set number of RCU readers. The value -1 selects 6025 N-1, where N is the number of CPUs. A value 6026 "n" less than -1 selects N-n-2, where N is again 6027 the number of CPUs. For example, -2 selects N 6028 (the number of CPUs), -3 selects N+1, and so on. 6029 6030 rcutorture.object_debug= [KNL] 6031 Enable debug-object double-call_rcu() testing. 6032 6033 rcutorture.onoff_holdoff= [KNL] 6034 Set time (s) after boot for CPU-hotplug testing. 6035 6036 rcutorture.onoff_interval= [KNL] 6037 Set time (jiffies) between CPU-hotplug operations, 6038 or zero to disable CPU-hotplug testing. 6039 6040 rcutorture.preempt_duration= [KNL] 6041 Set duration (in milliseconds) of preemptions 6042 by a high-priority FIFO real-time task. Set to 6043 zero (the default) to disable. The CPUs to 6044 preempt are selected randomly from the set that 6045 are online at a given point in time. Races with 6046 CPUs going offline are ignored, with that attempt 6047 at preemption skipped. 6048 6049 rcutorture.preempt_interval= [KNL] 6050 Set interval (in milliseconds, defaulting to one 6051 second) between preemptions by a high-priority 6052 FIFO real-time task. This delay is mediated 6053 by an hrtimer and is further fuzzed to avoid 6054 inadvertent synchronizations. 6055 6056 rcutorture.read_exit_burst= [KNL] 6057 The number of times in a given read-then-exit 6058 episode that a set of read-then-exit kthreads 6059 is spawned. 6060 6061 rcutorture.read_exit_delay= [KNL] 6062 The delay, in seconds, between successive 6063 read-then-exit testing episodes. 6064 6065 rcutorture.reader_flavor= [KNL] 6066 A bit mask indicating which readers to use. 6067 If there is more than one bit set, the readers 6068 are entered from low-order bit up, and are 6069 exited in the opposite order. For SRCU, the 6070 0x1 bit is normal readers, 0x2 NMI-safe readers, 6071 and 0x4 light-weight readers. 6072 6073 rcutorture.shuffle_interval= [KNL] 6074 Set task-shuffle interval (s). Shuffling tasks 6075 allows some CPUs to go into dyntick-idle mode 6076 during the rcutorture test. 6077 6078 rcutorture.shutdown_secs= [KNL] 6079 Set time (s) after boot system shutdown. This 6080 is useful for hands-off automated testing. 6081 6082 rcutorture.stall_cpu= [KNL] 6083 Duration of CPU stall (s) to test RCU CPU stall 6084 warnings, zero to disable. 6085 6086 rcutorture.stall_cpu_block= [KNL] 6087 Sleep while stalling if set. This will result 6088 in warnings from preemptible RCU in addition to 6089 any other stall-related activity. Note that 6090 in kernels built with CONFIG_PREEMPTION=n and 6091 CONFIG_PREEMPT_COUNT=y, this parameter will 6092 cause the CPU to pass through a quiescent state. 6093 Given CONFIG_PREEMPTION=n, this will suppress 6094 RCU CPU stall warnings, but will instead result 6095 in scheduling-while-atomic splats. 6096 6097 Use of this module parameter results in splats. 6098 6099 6100 rcutorture.stall_cpu_holdoff= [KNL] 6101 Time to wait (s) after boot before inducing stall. 6102 6103 rcutorture.stall_cpu_irqsoff= [KNL] 6104 Disable interrupts while stalling if set, but only 6105 on the first stall in the set. 6106 6107 rcutorture.stall_cpu_repeat= [KNL] 6108 Number of times to repeat the stall sequence, 6109 so that rcutorture.stall_cpu_repeat=3 will result 6110 in four stall sequences. 6111 6112 rcutorture.stall_gp_kthread= [KNL] 6113 Duration (s) of forced sleep within RCU 6114 grace-period kthread to test RCU CPU stall 6115 warnings, zero to disable. If both stall_cpu 6116 and stall_gp_kthread are specified, the 6117 kthread is starved first, then the CPU. 6118 6119 rcutorture.stat_interval= [KNL] 6120 Time (s) between statistics printk()s. 6121 6122 rcutorture.stutter= [KNL] 6123 Time (s) to stutter testing, for example, specifying 6124 five seconds causes the test to run for five seconds, 6125 wait for five seconds, and so on. This tests RCU's 6126 ability to transition abruptly to and from idle. 6127 6128 rcutorture.test_boost= [KNL] 6129 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 6130 "Maybe" means test if the RCU implementation 6131 under test support RCU priority boosting. 6132 6133 rcutorture.test_boost_duration= [KNL] 6134 Duration (s) of each individual boost test. 6135 6136 rcutorture.test_boost_holdoff= [KNL] 6137 Holdoff time (s) from start of test to the start 6138 of RCU priority-boost testing. Defaults to zero, 6139 that is, no holdoff. 6140 6141 rcutorture.test_boost_interval= [KNL] 6142 Interval (s) between each boost test. 6143 6144 rcutorture.test_no_idle_hz= [KNL] 6145 Test RCU's dyntick-idle handling. See also the 6146 rcutorture.shuffle_interval parameter. 6147 6148 rcutorture.torture_type= [KNL] 6149 Specify the RCU implementation to test. 6150 6151 rcutorture.verbose= [KNL] 6152 Enable additional printk() statements. 6153 6154 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 6155 Dump ftrace buffer after reporting RCU CPU 6156 stall warning. 6157 6158 rcupdate.rcu_cpu_stall_notifiers= [KNL] 6159 Provide RCU CPU stall notifiers, but see the 6160 warnings in the RCU_CPU_STALL_NOTIFIER Kconfig 6161 option's help text. TL;DR: You almost certainly 6162 do not want rcupdate.rcu_cpu_stall_notifiers. 6163 6164 rcupdate.rcu_cpu_stall_suppress= [KNL] 6165 Suppress RCU CPU stall warning messages. 6166 6167 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 6168 Suppress RCU CPU stall warning messages and 6169 rcutorture writer stall warnings that occur 6170 during early boot, that is, during the time 6171 before the init task is spawned. 6172 6173 rcupdate.rcu_cpu_stall_timeout= [KNL] 6174 Set timeout for RCU CPU stall warning messages. 6175 The value is in seconds and the maximum allowed 6176 value is 300 seconds. 6177 6178 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 6179 Set timeout for expedited RCU CPU stall warning 6180 messages. The value is in milliseconds 6181 and the maximum allowed value is 21000 6182 milliseconds. Please note that this value is 6183 adjusted to an arch timer tick resolution. 6184 Setting this to zero causes the value from 6185 rcupdate.rcu_cpu_stall_timeout to be used (after 6186 conversion from seconds to milliseconds). 6187 6188 rcupdate.rcu_cpu_stall_cputime= [KNL] 6189 Provide statistics on the cputime and count of 6190 interrupts and tasks during the sampling period. For 6191 multiple continuous RCU stalls, all sampling periods 6192 begin at half of the first RCU stall timeout. 6193 6194 rcupdate.rcu_exp_stall_task_details= [KNL] 6195 Print stack dumps of any tasks blocking the 6196 current expedited RCU grace period during an 6197 expedited RCU CPU stall warning. 6198 6199 rcupdate.rcu_expedited= [KNL] 6200 Use expedited grace-period primitives, for 6201 example, synchronize_rcu_expedited() instead 6202 of synchronize_rcu(). This reduces latency, 6203 but can increase CPU utilization, degrade 6204 real-time latency, and degrade energy efficiency. 6205 No effect on CONFIG_TINY_RCU kernels. 6206 6207 rcupdate.rcu_normal= [KNL] 6208 Use only normal grace-period primitives, 6209 for example, synchronize_rcu() instead of 6210 synchronize_rcu_expedited(). This improves 6211 real-time latency, CPU utilization, and 6212 energy efficiency, but can expose users to 6213 increased grace-period latency. This parameter 6214 overrides rcupdate.rcu_expedited. No effect on 6215 CONFIG_TINY_RCU kernels. 6216 6217 rcupdate.rcu_normal_after_boot= [KNL] 6218 Once boot has completed (that is, after 6219 rcu_end_inkernel_boot() has been invoked), use 6220 only normal grace-period primitives. No effect 6221 on CONFIG_TINY_RCU kernels. 6222 6223 But note that CONFIG_PREEMPT_RT=y kernels enables 6224 this kernel boot parameter, forcibly setting 6225 it to the value one, that is, converting any 6226 post-boot attempt at an expedited RCU grace 6227 period to instead use normal non-expedited 6228 grace-period processing. 6229 6230 rcupdate.rcu_task_collapse_lim= [KNL] 6231 Set the maximum number of callbacks present 6232 at the beginning of a grace period that allows 6233 the RCU Tasks flavors to collapse back to using 6234 a single callback queue. This switching only 6235 occurs when rcupdate.rcu_task_enqueue_lim is 6236 set to the default value of -1. 6237 6238 rcupdate.rcu_task_contend_lim= [KNL] 6239 Set the minimum number of callback-queuing-time 6240 lock-contention events per jiffy required to 6241 cause the RCU Tasks flavors to switch to per-CPU 6242 callback queuing. This switching only occurs 6243 when rcupdate.rcu_task_enqueue_lim is set to 6244 the default value of -1. 6245 6246 rcupdate.rcu_task_enqueue_lim= [KNL] 6247 Set the number of callback queues to use for the 6248 RCU Tasks family of RCU flavors. The default 6249 of -1 allows this to be automatically (and 6250 dynamically) adjusted. This parameter is intended 6251 for use in testing. 6252 6253 rcupdate.rcu_task_ipi_delay= [KNL] 6254 Set time in jiffies during which RCU tasks will 6255 avoid sending IPIs, starting with the beginning 6256 of a given grace period. Setting a large 6257 number avoids disturbing real-time workloads, 6258 but lengthens grace periods. 6259 6260 rcupdate.rcu_task_lazy_lim= [KNL] 6261 Number of callbacks on a given CPU that will 6262 cancel laziness on that CPU. Use -1 to disable 6263 cancellation of laziness, but be advised that 6264 doing so increases the danger of OOM due to 6265 callback flooding. 6266 6267 rcupdate.rcu_task_stall_info= [KNL] 6268 Set initial timeout in jiffies for RCU task stall 6269 informational messages, which give some indication 6270 of the problem for those not patient enough to 6271 wait for ten minutes. Informational messages are 6272 only printed prior to the stall-warning message 6273 for a given grace period. Disable with a value 6274 less than or equal to zero. Defaults to ten 6275 seconds. A change in value does not take effect 6276 until the beginning of the next grace period. 6277 6278 rcupdate.rcu_task_stall_info_mult= [KNL] 6279 Multiplier for time interval between successive 6280 RCU task stall informational messages for a given 6281 RCU tasks grace period. This value is clamped 6282 to one through ten, inclusive. It defaults to 6283 the value three, so that the first informational 6284 message is printed 10 seconds into the grace 6285 period, the second at 40 seconds, the third at 6286 160 seconds, and then the stall warning at 600 6287 seconds would prevent a fourth at 640 seconds. 6288 6289 rcupdate.rcu_task_stall_timeout= [KNL] 6290 Set timeout in jiffies for RCU task stall 6291 warning messages. Disable with a value less 6292 than or equal to zero. Defaults to ten minutes. 6293 A change in value does not take effect until 6294 the beginning of the next grace period. 6295 6296 rcupdate.rcu_tasks_lazy_ms= [KNL] 6297 Set timeout in milliseconds RCU Tasks asynchronous 6298 callback batching for call_rcu_tasks(). 6299 A negative value will take the default. A value 6300 of zero will disable batching. Batching is 6301 always disabled for synchronize_rcu_tasks(). 6302 6303 rcupdate.rcu_tasks_trace_lazy_ms= [KNL] 6304 Set timeout in milliseconds RCU Tasks 6305 Trace asynchronous callback batching for 6306 call_rcu_tasks_trace(). A negative value 6307 will take the default. A value of zero will 6308 disable batching. Batching is always disabled 6309 for synchronize_rcu_tasks_trace(). 6310 6311 rcupdate.rcu_self_test= [KNL] 6312 Run the RCU early boot self tests 6313 6314 rdinit= [KNL] 6315 Format: <full_path> 6316 Run specified binary instead of /init from the ramdisk, 6317 used for early userspace startup. See initrd. 6318 6319 rdrand= [X86,EARLY] 6320 force - Override the decision by the kernel to hide the 6321 advertisement of RDRAND support (this affects 6322 certain AMD processors because of buggy BIOS 6323 support, specifically around the suspend/resume 6324 path). 6325 6326 rdt= [HW,X86,RDT] 6327 Turn on/off individual RDT features. List is: 6328 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 6329 mba, smba, bmec, abmc, sdciae. 6330 E.g. to turn on cmt and turn off mba use: 6331 rdt=cmt,!mba 6332 6333 reboot= [KNL] 6334 Format (x86 or x86_64): 6335 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 6336 [[,]s[mp]#### \ 6337 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 6338 [[,]f[orce] 6339 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 6340 (prefix with 'panic_' to set mode for panic 6341 reboot only), 6342 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 6343 reboot_force is either force or not specified, 6344 reboot_cpu is s[mp]#### with #### being the processor 6345 to be used for rebooting. 6346 6347 acpi 6348 Use the ACPI RESET_REG in the FADT. If ACPI is not 6349 configured or the ACPI reset does not work, the reboot 6350 path attempts the reset using the keyboard controller. 6351 6352 bios 6353 Use the CPU reboot vector for warm reset 6354 6355 cold 6356 Set the cold reboot flag 6357 6358 default 6359 There are some built-in platform specific "quirks" 6360 - you may see: "reboot: <name> series board detected. 6361 Selecting <type> for reboots." In the case where you 6362 think the quirk is in error (e.g. you have newer BIOS, 6363 or newer board) using this option will ignore the 6364 built-in quirk table, and use the generic default 6365 reboot actions. 6366 6367 efi 6368 Use efi reset_system runtime service. If EFI is not 6369 configured or the EFI reset does not work, the reboot 6370 path attempts the reset using the keyboard controller. 6371 6372 force 6373 Don't stop other CPUs on reboot. This can make reboot 6374 more reliable in some cases. 6375 6376 kbd 6377 Use the keyboard controller. cold reset (default) 6378 6379 pci 6380 Use a write to the PCI config space register 0xcf9 to 6381 trigger reboot. 6382 6383 triple 6384 Force a triple fault (init) 6385 6386 warm 6387 Don't set the cold reboot flag 6388 6389 Using warm reset will be much faster especially on big 6390 memory systems because the BIOS will not go through 6391 the memory check. Disadvantage is that not all 6392 hardware will be completely reinitialized on reboot so 6393 there may be boot problems on some systems. 6394 6395 6396 refscale.holdoff= [KNL] 6397 Set test-start holdoff period. The purpose of 6398 this parameter is to delay the start of the 6399 test until boot completes in order to avoid 6400 interference. 6401 6402 refscale.lookup_instances= [KNL] 6403 Number of data elements to use for the forms of 6404 SLAB_TYPESAFE_BY_RCU testing. A negative number 6405 is negated and multiplied by nr_cpu_ids, while 6406 zero specifies nr_cpu_ids. 6407 6408 refscale.loops= [KNL] 6409 Set the number of loops over the synchronization 6410 primitive under test. Increasing this number 6411 reduces noise due to loop start/end overhead, 6412 but the default has already reduced the per-pass 6413 noise to a handful of picoseconds on ca. 2020 6414 x86 laptops. 6415 6416 refscale.nreaders= [KNL] 6417 Set number of readers. The default value of -1 6418 selects N, where N is roughly 75% of the number 6419 of CPUs. A value of zero is an interesting choice. 6420 6421 refscale.nruns= [KNL] 6422 Set number of runs, each of which is dumped onto 6423 the console log. 6424 6425 refscale.readdelay= [KNL] 6426 Set the read-side critical-section duration, 6427 measured in microseconds. 6428 6429 refscale.scale_type= [KNL] 6430 Specify the read-protection implementation to test. 6431 6432 refscale.shutdown= [KNL] 6433 Shut down the system at the end of the performance 6434 test. This defaults to 1 (shut it down) when 6435 refscale is built into the kernel and to 0 (leave 6436 it running) when refscale is built as a module. 6437 6438 refscale.verbose= [KNL] 6439 Enable additional printk() statements. 6440 6441 refscale.verbose_batched= [KNL] 6442 Batch the additional printk() statements. If zero 6443 (the default) or negative, print everything. Otherwise, 6444 print every Nth verbose statement, where N is the value 6445 specified. 6446 6447 regulator_ignore_unused 6448 [REGULATOR] 6449 Prevents regulator framework from disabling regulators 6450 that are unused, due no driver claiming them. This may 6451 be useful for debug and development, but should not be 6452 needed on a platform with proper driver support. 6453 6454 relax_domain_level= 6455 [KNL, SMP] Set scheduler's default relax_domain_level. 6456 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 6457 6458 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 6459 Format: <base1>,<size1>[,<base2>,<size2>,...] 6460 Reserve I/O ports or memory so the kernel won't use 6461 them. If <base> is less than 0x10000, the region 6462 is assumed to be I/O ports; otherwise it is memory. 6463 6464 reserve_mem= [RAM] 6465 Format: nn[KMG]:<align>:<label> 6466 Reserve physical memory and label it with a name that 6467 other subsystems can use to access it. This is typically 6468 used for systems that do not wipe the RAM, and this command 6469 line will try to reserve the same physical memory on 6470 soft reboots. Note, it is not guaranteed to be the same 6471 location. For example, if anything about the system changes 6472 or if booting a different kernel. It can also fail if KASLR 6473 places the kernel at the location of where the RAM reservation 6474 was from a previous boot, the new reservation will be at a 6475 different location. 6476 Any subsystem using this feature must add a way to verify 6477 that the contents of the physical memory is from a previous 6478 boot, as there may be cases where the memory will not be 6479 located at the same location. 6480 6481 The format is size:align:label for example, to request 6482 12 megabytes of 4096 alignment for ramoops: 6483 6484 reserve_mem=12M:4096:oops ramoops.mem_name=oops 6485 6486 reservetop= [X86-32,EARLY] 6487 Format: nn[KMG] 6488 Reserves a hole at the top of the kernel virtual 6489 address space. 6490 6491 reset_devices [KNL] Force drivers to reset the underlying device 6492 during initialization. 6493 6494 resume= [SWSUSP] 6495 Specify the partition device for software suspend 6496 Format: 6497 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 6498 6499 resume_offset= [SWSUSP] 6500 Specify the offset from the beginning of the partition 6501 given by "resume=" at which the swap header is located, 6502 in <PAGE_SIZE> units (needed only for swap files). 6503 See Documentation/power/swsusp-and-swap-files.rst 6504 6505 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 6506 read the resume files 6507 6508 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 6509 Useful for devices that are detected asynchronously 6510 (e.g. USB and MMC devices). 6511 6512 retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will 6513 be accessible via /sys/firmware/initrd. 6514 6515 retbleed= [X86] Control mitigation of RETBleed (Arbitrary 6516 Speculative Code Execution with Return Instructions) 6517 vulnerability. 6518 6519 AMD-based UNRET and IBPB mitigations alone do not stop 6520 sibling threads from influencing the predictions of other 6521 sibling threads. For that reason, STIBP is used on pro- 6522 cessors that support it, and mitigate SMT on processors 6523 that don't. 6524 6525 off - no mitigation 6526 auto - automatically select a mitigation 6527 auto,nosmt - automatically select a mitigation, 6528 disabling SMT if necessary for 6529 the full mitigation (only on Zen1 6530 and older without STIBP). 6531 ibpb - On AMD, mitigate short speculation 6532 windows on basic block boundaries too. 6533 Safe, highest perf impact. It also 6534 enables STIBP if present. Not suitable 6535 on Intel. 6536 ibpb,nosmt - Like "ibpb" above but will disable SMT 6537 when STIBP is not available. This is 6538 the alternative for systems which do not 6539 have STIBP. 6540 unret - Force enable untrained return thunks, 6541 only effective on AMD f15h-f17h based 6542 systems. 6543 unret,nosmt - Like unret, but will disable SMT when STIBP 6544 is not available. This is the alternative for 6545 systems which do not have STIBP. 6546 6547 Selecting 'auto' will choose a mitigation method at run 6548 time according to the CPU. 6549 6550 Not specifying this option is equivalent to retbleed=auto. 6551 6552 rfkill.default_state= 6553 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 6554 etc. communication is blocked by default. 6555 1 Unblocked. 6556 6557 rfkill.master_switch_mode= 6558 0 The "airplane mode" button does nothing. 6559 1 The "airplane mode" button toggles between everything 6560 blocked and the previous configuration. 6561 2 The "airplane mode" button toggles between everything 6562 blocked and everything unblocked. 6563 6564 ring3mwait=disable 6565 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 6566 CPUs. 6567 6568 riscv_isa_fallback [RISCV,EARLY] 6569 When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit 6570 falling back to detecting extension support by parsing 6571 "riscv,isa" property on devicetree systems when the 6572 replacement properties are not found. See the Kconfig 6573 entry for RISCV_ISA_FALLBACK. 6574 6575 ro [KNL] Mount root device read-only on boot 6576 6577 rodata= [KNL,EARLY] 6578 on Mark read-only kernel memory as read-only (default). 6579 off Leave read-only kernel memory writable for debugging. 6580 noalias Mark read-only kernel memory as read-only but retain 6581 writable aliases in the direct map for regions outside 6582 of the kernel image. [arm64] 6583 6584 rockchip.usb_uart 6585 [EARLY] 6586 Enable the uart passthrough on the designated usb port 6587 on Rockchip SoCs. When active, the signals of the 6588 debug-uart get routed to the D+ and D- pins of the usb 6589 port and the regular usb controller gets disabled. 6590 6591 root= [KNL] Root filesystem 6592 Usually this is a block device specifier of some kind, 6593 see the early_lookup_bdev comment in 6594 block/early-lookup.c for details. 6595 Alternatively this can be "ram" for the legacy initial 6596 ramdisk, "nfs" and "cifs" for root on a network file 6597 system, or "mtd" and "ubi" for mounting from raw flash. 6598 6599 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 6600 mount the root filesystem 6601 6602 rootflags= [KNL] Set root filesystem mount option string 6603 6604 initramfs_options= [KNL] 6605 Specify mount options for for the initramfs mount. 6606 6607 rootfstype= [KNL] Set root filesystem type 6608 6609 rootwait [KNL] Wait (indefinitely) for root device to show up. 6610 Useful for devices that are detected asynchronously 6611 (e.g. USB and MMC devices). 6612 6613 rootwait= [KNL] Maximum time (in seconds) to wait for root device 6614 to show up before attempting to mount the root 6615 filesystem. 6616 6617 rproc_mem=nn[KMG][@address] 6618 [KNL,ARM,CMA] Remoteproc physical memory block. 6619 Memory area to be used by remote processor image, 6620 managed by CMA. 6621 6622 rseq_debug= [KNL] Enable or disable restartable sequence 6623 debug mode. Defaults to CONFIG_RSEQ_DEBUG_DEFAULT_ENABLE. 6624 Format: <bool> 6625 6626 rt_group_sched= [KNL] Enable or disable SCHED_RR/FIFO group scheduling 6627 when CONFIG_RT_GROUP_SCHED=y. Defaults to 6628 !CONFIG_RT_GROUP_SCHED_DEFAULT_DISABLED. 6629 Format: <bool> 6630 6631 rw [KNL] Mount root device read-write on boot 6632 6633 S [KNL] Run init in single mode 6634 6635 s390_iommu= [HW,S390] 6636 Set s390 IOTLB flushing mode 6637 strict 6638 With strict flushing every unmap operation will result 6639 in an IOTLB flush. Default is lazy flushing before 6640 reuse, which is faster. Deprecated, equivalent to 6641 iommu.strict=1. 6642 6643 s390_iommu_aperture= [KNL,S390] 6644 Specifies the size of the per device DMA address space 6645 accessible through the DMA and IOMMU APIs as a decimal 6646 factor of the size of main memory. 6647 The default is 1 meaning that one can concurrently use 6648 as many DMA addresses as physical memory is installed, 6649 if supported by hardware, and thus map all of memory 6650 once. With a value of 2 one can map all of memory twice 6651 and so on. As a special case a factor of 0 imposes no 6652 restrictions other than those given by hardware at the 6653 cost of significant additional memory use for tables. 6654 6655 sa1100ir [NET] 6656 See drivers/net/irda/sa1100_ir.c. 6657 6658 sched_proxy_exec= [KNL] 6659 Enables or disables "proxy execution" style 6660 solution to mutex-based priority inversion. 6661 Format: <bool> 6662 6663 sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages. 6664 6665 schedstats= [KNL,X86] Enable or disable scheduled statistics. 6666 Allowed values are enable and disable. This feature 6667 incurs a small amount of overhead in the scheduler 6668 but is useful for debugging and performance tuning. 6669 6670 sched_thermal_decay_shift= 6671 [Deprecated] 6672 [KNL, SMP] Set a decay shift for scheduler thermal 6673 pressure signal. Thermal pressure signal follows the 6674 default decay period of other scheduler pelt 6675 signals(usually 32 ms but configurable). Setting 6676 sched_thermal_decay_shift will left shift the decay 6677 period for the thermal pressure signal by the shift 6678 value. 6679 i.e. with the default pelt decay period of 32 ms 6680 sched_thermal_decay_shift thermal pressure decay pr 6681 1 64 ms 6682 2 128 ms 6683 and so on. 6684 Format: integer between 0 and 10 6685 Default is 0. 6686 6687 scftorture.holdoff= [KNL] 6688 Number of seconds to hold off before starting 6689 test. Defaults to zero for module insertion and 6690 to 10 seconds for built-in smp_call_function() 6691 tests. 6692 6693 scftorture.longwait= [KNL] 6694 Request ridiculously long waits randomly selected 6695 up to the chosen limit in seconds. Zero (the 6696 default) disables this feature. Please note 6697 that requesting even small non-zero numbers of 6698 seconds can result in RCU CPU stall warnings, 6699 softlockup complaints, and so on. 6700 6701 scftorture.nthreads= [KNL] 6702 Number of kthreads to spawn to invoke the 6703 smp_call_function() family of functions. 6704 The default of -1 specifies a number of kthreads 6705 equal to the number of CPUs. 6706 6707 scftorture.onoff_holdoff= [KNL] 6708 Number seconds to wait after the start of the 6709 test before initiating CPU-hotplug operations. 6710 6711 scftorture.onoff_interval= [KNL] 6712 Number seconds to wait between successive 6713 CPU-hotplug operations. Specifying zero (which 6714 is the default) disables CPU-hotplug operations. 6715 6716 scftorture.shutdown_secs= [KNL] 6717 The number of seconds following the start of the 6718 test after which to shut down the system. The 6719 default of zero avoids shutting down the system. 6720 Non-zero values are useful for automated tests. 6721 6722 scftorture.stat_interval= [KNL] 6723 The number of seconds between outputting the 6724 current test statistics to the console. A value 6725 of zero disables statistics output. 6726 6727 scftorture.stutter_cpus= [KNL] 6728 The number of jiffies to wait between each change 6729 to the set of CPUs under test. 6730 6731 scftorture.use_cpus_read_lock= [KNL] 6732 Use use_cpus_read_lock() instead of the default 6733 preempt_disable() to disable CPU hotplug 6734 while invoking one of the smp_call_function*() 6735 functions. 6736 6737 scftorture.verbose= [KNL] 6738 Enable additional printk() statements. 6739 6740 scftorture.weight_single= [KNL] 6741 The probability weighting to use for the 6742 smp_call_function_single() function with a zero 6743 "wait" parameter. A value of -1 selects the 6744 default if all other weights are -1. However, 6745 if at least one weight has some other value, a 6746 value of -1 will instead select a weight of zero. 6747 6748 scftorture.weight_single_wait= [KNL] 6749 The probability weighting to use for the 6750 smp_call_function_single() function with a 6751 non-zero "wait" parameter. See weight_single. 6752 6753 scftorture.weight_many= [KNL] 6754 The probability weighting to use for the 6755 smp_call_function_many() function with a zero 6756 "wait" parameter. See weight_single. 6757 Note well that setting a high probability for 6758 this weighting can place serious IPI load 6759 on the system. 6760 6761 scftorture.weight_many_wait= [KNL] 6762 The probability weighting to use for the 6763 smp_call_function_many() function with a 6764 non-zero "wait" parameter. See weight_single 6765 and weight_many. 6766 6767 scftorture.weight_all= [KNL] 6768 The probability weighting to use for the 6769 smp_call_function_all() function with a zero 6770 "wait" parameter. See weight_single and 6771 weight_many. 6772 6773 scftorture.weight_all_wait= [KNL] 6774 The probability weighting to use for the 6775 smp_call_function_all() function with a 6776 non-zero "wait" parameter. See weight_single 6777 and weight_many. 6778 6779 sdw_mclk_divider=[SDW] 6780 Specify the MCLK divider for Intel SoundWire buses in 6781 case the BIOS does not provide the clock rate properly. 6782 6783 skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate 6784 xtime_lock contention on larger systems, and/or RCU lock 6785 contention on all systems with CONFIG_MAXSMP set. 6786 Format: { "0" | "1" } 6787 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 6788 1 -- enable. 6789 Note: increases power consumption, thus should only be 6790 enabled if running jitter sensitive (HPC/RT) workloads. 6791 6792 security= [SECURITY] Choose a legacy "major" security module to 6793 enable at boot. This has been deprecated by the 6794 "lsm=" parameter. 6795 6796 selinux= [SELINUX] Disable or enable SELinux at boot time. 6797 Format: { "0" | "1" } 6798 See security/selinux/Kconfig help text. 6799 0 -- disable. 6800 1 -- enable. 6801 Default value is 1. 6802 6803 serialnumber [BUGS=X86-32] 6804 6805 sev=option[,option...] [X86-64] 6806 6807 debug 6808 Enable debug messages. 6809 6810 nosnp 6811 Do not enable SEV-SNP (applies to host/hypervisor 6812 only). Setting 'nosnp' avoids the RMP check overhead 6813 in memory accesses when users do not want to run 6814 SEV-SNP guests. 6815 6816 shapers= [NET] 6817 Maximal number of shapers. 6818 6819 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 6820 Limit apic dumping. The parameter defines the maximal 6821 number of local apics being dumped. Also it is possible 6822 to set it to "all" by meaning -- no limit here. 6823 Format: { 1 (default) | 2 | ... | all }. 6824 The parameter valid if only apic=debug or 6825 apic=verbose is specified. 6826 Example: apic=debug show_lapic=all 6827 6828 slab_debug[=options[,slabs][;[options[,slabs]]...] [MM] 6829 Enabling slab_debug allows one to determine the 6830 culprit if slab objects become corrupted. Enabling 6831 slab_debug can create guard zones around objects and 6832 may poison objects when not in use. Also tracks the 6833 last alloc / free. For more information see 6834 Documentation/admin-guide/mm/slab.rst. 6835 (slub_debug legacy name also accepted for now) 6836 6837 Using this option implies the "no_hash_pointers" 6838 option which can be undone by adding the 6839 "hash_pointers=always" option. 6840 6841 slab_max_order= [MM] 6842 Determines the maximum allowed order for slabs. 6843 A high setting may cause OOMs due to memory 6844 fragmentation. For more information see 6845 Documentation/admin-guide/mm/slab.rst. 6846 (slub_max_order legacy name also accepted for now) 6847 6848 slab_merge [MM] 6849 Enable merging of slabs with similar size when the 6850 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 6851 (slub_merge legacy name also accepted for now) 6852 6853 slab_min_objects= [MM] 6854 The minimum number of objects per slab. SLUB will 6855 increase the slab order up to slab_max_order to 6856 generate a sufficiently large slab able to contain 6857 the number of objects indicated. The higher the number 6858 of objects the smaller the overhead of tracking slabs 6859 and the less frequently locks need to be acquired. 6860 For more information see 6861 Documentation/admin-guide/mm/slab.rst. 6862 (slub_min_objects legacy name also accepted for now) 6863 6864 slab_min_order= [MM] 6865 Determines the minimum page order for slabs. Must be 6866 lower or equal to slab_max_order. For more information see 6867 Documentation/admin-guide/mm/slab.rst. 6868 (slub_min_order legacy name also accepted for now) 6869 6870 slab_nomerge [MM] 6871 Disable merging of slabs with similar size. May be 6872 necessary if there is some reason to distinguish 6873 allocs to different slabs, especially in hardened 6874 environments where the risk of heap overflows and 6875 layout control by attackers can usually be 6876 frustrated by disabling merging. This will reduce 6877 most of the exposure of a heap attack to a single 6878 cache (risks via metadata attacks are mostly 6879 unchanged). Debug options disable merging on their 6880 own. 6881 For more information see 6882 Documentation/admin-guide/mm/slab.rst. 6883 (slub_nomerge legacy name also accepted for now) 6884 6885 slab_strict_numa [MM] 6886 Support memory policies on a per object level 6887 in the slab allocator. The default is for memory 6888 policies to be applied at the folio level when 6889 a new folio is needed or a partial folio is 6890 retrieved from the lists. Increases overhead 6891 in the slab fastpaths but gains more accurate 6892 NUMA kernel object placement which helps with slow 6893 interconnects in NUMA systems. 6894 6895 slram= [HW,MTD] 6896 6897 smart2= [HW] 6898 Format: <io1>[,<io2>[,...,<io8>]] 6899 6900 smp.csd_lock_timeout= [KNL] 6901 Specify the period of time in milliseconds 6902 that smp_call_function() and friends will wait 6903 for a CPU to release the CSD lock. This is 6904 useful when diagnosing bugs involving CPUs 6905 disabling interrupts for extended periods 6906 of time. Defaults to 5,000 milliseconds, and 6907 setting a value of zero disables this feature. 6908 This feature may be more efficiently disabled 6909 using the csdlock_debug- kernel parameter. 6910 6911 smp.panic_on_ipistall= [KNL] 6912 If a csd_lock_timeout extends for more than 6913 the specified number of milliseconds, panic the 6914 system. By default, let CSD-lock acquisition 6915 take as long as they take. Specifying 300,000 6916 for this value provides a 5-minute timeout. 6917 6918 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 6919 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 6920 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 6921 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 6922 smsc-ircc2.ircc_irq= [HW] IRQ line 6923 smsc-ircc2.ircc_dma= [HW] DMA channel 6924 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 6925 0: Toshiba Satellite 1800 (GP data pin select) 6926 1: Fast pin select (default) 6927 2: ATC IRMode 6928 6929 smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads 6930 (logical CPUs) to use per physical CPU on systems 6931 capable of symmetric multithreading (SMT). Will 6932 be capped to the actual hardware limit. 6933 Format: <integer> 6934 Default: -1 (no limit) 6935 6936 softlockup_panic= 6937 [KNL] Should the soft-lockup detector generate panics. 6938 Format: 0 | 1 6939 6940 A value of 1 instructs the soft-lockup detector 6941 to panic the machine when a soft-lockup occurs. It is 6942 also controlled by the kernel.softlockup_panic sysctl 6943 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 6944 respective build-time switch to that functionality. 6945 6946 softlockup_all_cpu_backtrace= 6947 [KNL] Should the soft-lockup detector generate 6948 backtraces on all cpus. 6949 Format: 0 | 1 6950 6951 sonypi.*= [HW] Sony Programmable I/O Control Device driver 6952 See Documentation/admin-guide/laptops/sonypi.rst 6953 6954 spectre_bhi= [X86] Control mitigation of Branch History Injection 6955 (BHI) vulnerability. This setting affects the 6956 deployment of the HW BHI control and the SW BHB 6957 clearing sequence. 6958 6959 on - (default) Enable the HW or SW mitigation as 6960 needed. This protects the kernel from 6961 both syscalls and VMs. 6962 vmexit - On systems which don't have the HW mitigation 6963 available, enable the SW mitigation on vmexit 6964 ONLY. On such systems, the host kernel is 6965 protected from VM-originated BHI attacks, but 6966 may still be vulnerable to syscall attacks. 6967 off - Disable the mitigation. 6968 6969 spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2 6970 (indirect branch speculation) vulnerability. 6971 The default operation protects the kernel from 6972 user space attacks. 6973 6974 on - unconditionally enable, implies 6975 spectre_v2_user=on 6976 off - unconditionally disable, implies 6977 spectre_v2_user=off 6978 auto - kernel detects whether your CPU model is 6979 vulnerable 6980 6981 Selecting 'on' will, and 'auto' may, choose a 6982 mitigation method at run time according to the 6983 CPU, the available microcode, the setting of the 6984 CONFIG_MITIGATION_RETPOLINE configuration option, 6985 and the compiler with which the kernel was built. 6986 6987 Selecting 'on' will also enable the mitigation 6988 against user space to user space task attacks. 6989 Selecting specific mitigation does not force enable 6990 user mitigations. 6991 6992 Selecting 'off' will disable both the kernel and 6993 the user space protections. 6994 6995 Specific mitigations can also be selected manually: 6996 6997 retpoline - replace indirect branches 6998 retpoline,generic - Retpolines 6999 retpoline,lfence - LFENCE; indirect branch 7000 retpoline,amd - alias for retpoline,lfence 7001 eibrs - Enhanced/Auto IBRS 7002 eibrs,retpoline - Enhanced/Auto IBRS + Retpolines 7003 eibrs,lfence - Enhanced/Auto IBRS + LFENCE 7004 ibrs - use IBRS to protect kernel 7005 7006 Not specifying this option is equivalent to 7007 spectre_v2=auto. 7008 7009 spectre_v2_user= 7010 [X86] Control mitigation of Spectre variant 2 7011 (indirect branch speculation) vulnerability between 7012 user space tasks 7013 7014 on - Unconditionally enable mitigations. Is 7015 enforced by spectre_v2=on 7016 7017 off - Unconditionally disable mitigations. Is 7018 enforced by spectre_v2=off 7019 7020 prctl - Indirect branch speculation is enabled, 7021 but mitigation can be enabled via prctl 7022 per thread. The mitigation control state 7023 is inherited on fork. 7024 7025 prctl,ibpb 7026 - Like "prctl" above, but only STIBP is 7027 controlled per thread. IBPB is issued 7028 always when switching between different user 7029 space processes. 7030 7031 seccomp 7032 - Same as "prctl" above, but all seccomp 7033 threads will enable the mitigation unless 7034 they explicitly opt out. 7035 7036 seccomp,ibpb 7037 - Like "seccomp" above, but only STIBP is 7038 controlled per thread. IBPB is issued 7039 always when switching between different 7040 user space processes. 7041 7042 auto - Kernel selects the mitigation depending on 7043 the available CPU features and vulnerability. 7044 7045 Default mitigation: "prctl" 7046 7047 Not specifying this option is equivalent to 7048 spectre_v2_user=auto. 7049 7050 spec_rstack_overflow= 7051 [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs 7052 7053 off - Disable mitigation 7054 microcode - Enable microcode mitigation only 7055 safe-ret - Enable sw-only safe RET mitigation (default) 7056 ibpb - Enable mitigation by issuing IBPB on 7057 kernel entry 7058 ibpb-vmexit - Issue IBPB only on VMEXIT 7059 (cloud-specific mitigation) 7060 7061 spec_store_bypass_disable= 7062 [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation 7063 (Speculative Store Bypass vulnerability) 7064 7065 Certain CPUs are vulnerable to an exploit against a 7066 a common industry wide performance optimization known 7067 as "Speculative Store Bypass" in which recent stores 7068 to the same memory location may not be observed by 7069 later loads during speculative execution. The idea 7070 is that such stores are unlikely and that they can 7071 be detected prior to instruction retirement at the 7072 end of a particular speculation execution window. 7073 7074 In vulnerable processors, the speculatively forwarded 7075 store can be used in a cache side channel attack, for 7076 example to read memory to which the attacker does not 7077 directly have access (e.g. inside sandboxed code). 7078 7079 This parameter controls whether the Speculative Store 7080 Bypass optimization is used. 7081 7082 On x86 the options are: 7083 7084 on - Unconditionally disable Speculative Store Bypass 7085 off - Unconditionally enable Speculative Store Bypass 7086 auto - Kernel detects whether the CPU model contains an 7087 implementation of Speculative Store Bypass and 7088 picks the most appropriate mitigation. If the 7089 CPU is not vulnerable, "off" is selected. If the 7090 CPU is vulnerable the default mitigation is 7091 architecture and Kconfig dependent. See below. 7092 prctl - Control Speculative Store Bypass per thread 7093 via prctl. Speculative Store Bypass is enabled 7094 for a process by default. The state of the control 7095 is inherited on fork. 7096 seccomp - Same as "prctl" above, but all seccomp threads 7097 will disable SSB unless they explicitly opt out. 7098 7099 Default mitigations: 7100 X86: "prctl" 7101 7102 On powerpc the options are: 7103 7104 on,auto - On Power8 and Power9 insert a store-forwarding 7105 barrier on kernel entry and exit. On Power7 7106 perform a software flush on kernel entry and 7107 exit. 7108 off - No action. 7109 7110 Not specifying this option is equivalent to 7111 spec_store_bypass_disable=auto. 7112 7113 split_lock_detect= 7114 [X86] Enable split lock detection or bus lock detection 7115 7116 When enabled (and if hardware support is present), atomic 7117 instructions that access data across cache line 7118 boundaries will result in an alignment check exception 7119 for split lock detection or a debug exception for 7120 bus lock detection. 7121 7122 off - not enabled 7123 7124 warn - the kernel will emit rate-limited warnings 7125 about applications triggering the #AC 7126 exception or the #DB exception. This mode is 7127 the default on CPUs that support split lock 7128 detection or bus lock detection. Default 7129 behavior is by #AC if both features are 7130 enabled in hardware. 7131 7132 fatal - the kernel will send SIGBUS to applications 7133 that trigger the #AC exception or the #DB 7134 exception. Default behavior is by #AC if 7135 both features are enabled in hardware. 7136 7137 ratelimit:N - 7138 Set system wide rate limit to N bus locks 7139 per second for bus lock detection. 7140 0 < N <= 1000. 7141 7142 N/A for split lock detection. 7143 7144 7145 If an #AC exception is hit in the kernel or in 7146 firmware (i.e. not while executing in user mode) 7147 the kernel will oops in either "warn" or "fatal" 7148 mode. 7149 7150 #DB exception for bus lock is triggered only when 7151 CPL > 0. 7152 7153 srbds= [X86,INTEL,EARLY] 7154 Control the Special Register Buffer Data Sampling 7155 (SRBDS) mitigation. 7156 7157 Certain CPUs are vulnerable to an MDS-like 7158 exploit which can leak bits from the random 7159 number generator. 7160 7161 By default, this issue is mitigated by 7162 microcode. However, the microcode fix can cause 7163 the RDRAND and RDSEED instructions to become 7164 much slower. Among other effects, this will 7165 result in reduced throughput from /dev/urandom. 7166 7167 The microcode mitigation can be disabled with 7168 the following option: 7169 7170 off: Disable mitigation and remove 7171 performance impact to RDRAND and RDSEED 7172 7173 srcutree.big_cpu_lim [KNL] 7174 Specifies the number of CPUs constituting a 7175 large system, such that srcu_struct structures 7176 should immediately allocate an srcu_node array. 7177 This kernel-boot parameter defaults to 128, 7178 but takes effect only when the low-order four 7179 bits of srcutree.convert_to_big is equal to 3 7180 (decide at boot). 7181 7182 srcutree.convert_to_big [KNL] 7183 Specifies under what conditions an SRCU tree 7184 srcu_struct structure will be converted to big 7185 form, that is, with an rcu_node tree: 7186 7187 0: Never. 7188 1: At init_srcu_struct() time. 7189 2: When rcutorture decides to. 7190 3: Decide at boot time (default). 7191 0x1X: Above plus if high contention. 7192 7193 Either way, the srcu_node tree will be sized based 7194 on the actual runtime number of CPUs (nr_cpu_ids) 7195 instead of the compile-time CONFIG_NR_CPUS. 7196 7197 srcutree.counter_wrap_check [KNL] 7198 Specifies how frequently to check for 7199 grace-period sequence counter wrap for the 7200 srcu_data structure's ->srcu_gp_seq_needed field. 7201 The greater the number of bits set in this kernel 7202 parameter, the less frequently counter wrap will 7203 be checked for. Note that the bottom two bits 7204 are ignored. 7205 7206 srcutree.exp_holdoff [KNL] 7207 Specifies how many nanoseconds must elapse 7208 since the end of the last SRCU grace period for 7209 a given srcu_struct until the next normal SRCU 7210 grace period will be considered for automatic 7211 expediting. Set to zero to disable automatic 7212 expediting. 7213 7214 srcutree.srcu_max_nodelay [KNL] 7215 Specifies the number of no-delay instances 7216 per jiffy for which the SRCU grace period 7217 worker thread will be rescheduled with zero 7218 delay. Beyond this limit, worker thread will 7219 be rescheduled with a sleep delay of one jiffy. 7220 7221 srcutree.srcu_max_nodelay_phase [KNL] 7222 Specifies the per-grace-period phase, number of 7223 non-sleeping polls of readers. Beyond this limit, 7224 grace period worker thread will be rescheduled 7225 with a sleep delay of one jiffy, between each 7226 rescan of the readers, for a grace period phase. 7227 7228 srcutree.srcu_retry_check_delay [KNL] 7229 Specifies number of microseconds of non-sleeping 7230 delay between each non-sleeping poll of readers. 7231 7232 srcutree.small_contention_lim [KNL] 7233 Specifies the number of update-side contention 7234 events per jiffy will be tolerated before 7235 initiating a conversion of an srcu_struct 7236 structure to big form. Note that the value of 7237 srcutree.convert_to_big must have the 0x10 bit 7238 set for contention-based conversions to occur. 7239 7240 ssbd= [ARM64,HW,EARLY] 7241 Speculative Store Bypass Disable control 7242 7243 On CPUs that are vulnerable to the Speculative 7244 Store Bypass vulnerability and offer a 7245 firmware based mitigation, this parameter 7246 indicates how the mitigation should be used: 7247 7248 force-on: Unconditionally enable mitigation for 7249 for both kernel and userspace 7250 force-off: Unconditionally disable mitigation for 7251 for both kernel and userspace 7252 kernel: Always enable mitigation in the 7253 kernel, and offer a prctl interface 7254 to allow userspace to register its 7255 interest in being mitigated too. 7256 7257 stack_guard_gap= [MM] 7258 override the default stack gap protection. The value 7259 is in page units and it defines how many pages prior 7260 to (for stacks growing down) resp. after (for stacks 7261 growing up) the main stack are reserved for no other 7262 mapping. Default value is 256 pages. 7263 7264 stack_depot_disable= [KNL,EARLY] 7265 Setting this to true through kernel command line will 7266 disable the stack depot thereby saving the static memory 7267 consumed by the stack hash table. By default this is set 7268 to false. 7269 7270 stack_depot_max_pools= [KNL,EARLY] 7271 Specify the maximum number of pools to use for storing 7272 stack traces. Pools are allocated on-demand up to this 7273 limit. Default value is 8191 pools. 7274 7275 stacktrace [FTRACE] 7276 Enable the stack tracer on boot up. 7277 7278 stacktrace_filter=[function-list] 7279 [FTRACE] Limit the functions that the stack tracer 7280 will trace at boot up. function-list is a comma-separated 7281 list of functions. This list can be changed at run 7282 time by the stack_trace_filter file in the debugfs 7283 tracing directory. Note, this enables stack tracing 7284 and the stacktrace above is not needed. 7285 7286 sti= [PARISC,HW] 7287 Format: <num> 7288 Set the STI (builtin display/keyboard on the HP-PARISC 7289 machines) console (graphic card) which should be used 7290 as the initial boot-console. 7291 See also comment in drivers/video/console/sticore.c. 7292 7293 sti_font= [HW] 7294 See comment in drivers/video/console/sticore.c. 7295 7296 stifb= [HW] 7297 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 7298 7299 strict_sas_size= 7300 [X86] 7301 Format: <bool> 7302 Enable or disable strict sigaltstack size checks 7303 against the required signal frame size which 7304 depends on the supported FPU features. This can 7305 be used to filter out binaries which have 7306 not yet been made aware of AT_MINSIGSTKSZ. 7307 7308 stress_hpt [PPC,EARLY] 7309 Limits the number of kernel HPT entries in the hash 7310 page table to increase the rate of hash page table 7311 faults on kernel addresses. 7312 7313 stress_slb [PPC,EARLY] 7314 Limits the number of kernel SLB entries, and flushes 7315 them frequently to increase the rate of SLB faults 7316 on kernel addresses. 7317 7318 no_slb_preload [PPC,EARLY] 7319 Disables slb preloading for userspace. 7320 7321 sunrpc.min_resvport= 7322 sunrpc.max_resvport= 7323 [NFS,SUNRPC] 7324 SunRPC servers often require that client requests 7325 originate from a privileged port (i.e. a port in the 7326 range 0 < portnr < 1024). 7327 An administrator who wishes to reserve some of these 7328 ports for other uses may adjust the range that the 7329 kernel's sunrpc client considers to be privileged 7330 using these two parameters to set the minimum and 7331 maximum port values. 7332 7333 sunrpc.svc_rpc_per_connection_limit= 7334 [NFS,SUNRPC] 7335 Limit the number of requests that the server will 7336 process in parallel from a single connection. 7337 The default value is 0 (no limit). 7338 7339 sunrpc.pool_mode= 7340 [NFS] 7341 Control how the NFS server code allocates CPUs to 7342 service thread pools. Depending on how many NICs 7343 you have and where their interrupts are bound, this 7344 option will affect which CPUs will do NFS serving. 7345 Note: this parameter cannot be changed while the 7346 NFS server is running. 7347 7348 auto the server chooses an appropriate mode 7349 automatically using heuristics 7350 global a single global pool contains all CPUs 7351 percpu one pool for each CPU 7352 pernode one pool for each NUMA node (equivalent 7353 to global on non-NUMA machines) 7354 7355 sunrpc.tcp_slot_table_entries= 7356 sunrpc.udp_slot_table_entries= 7357 [NFS,SUNRPC] 7358 Sets the upper limit on the number of simultaneous 7359 RPC calls that can be sent from the client to a 7360 server. Increasing these values may allow you to 7361 improve throughput, but will also increase the 7362 amount of memory reserved for use by the client. 7363 7364 suspend.pm_test_delay= 7365 [SUSPEND] 7366 Sets the number of seconds to remain in a suspend test 7367 mode before resuming the system (see 7368 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 7369 is set. Default value is 5. 7370 7371 svm= [PPC] 7372 Format: { on | off | y | n | 1 | 0 } 7373 This parameter controls use of the Protected 7374 Execution Facility on pSeries. 7375 7376 swiotlb= [ARM,PPC,MIPS,X86,S390,EARLY] 7377 Format: { <int> [,<int>] | force | noforce } 7378 <int> -- Number of I/O TLB slabs 7379 <int> -- Second integer after comma. Number of swiotlb 7380 areas with their own lock. Will be rounded up 7381 to a power of 2. 7382 force -- force using of bounce buffers even if they 7383 wouldn't be automatically used by the kernel 7384 noforce -- Never use bounce buffers (for debugging) 7385 7386 switches= [HW,M68k,EARLY] 7387 7388 sysctl.*= [KNL] 7389 Set a sysctl parameter, right before loading the init 7390 process, as if the value was written to the respective 7391 /proc/sys/... file. Both '.' and '/' are recognized as 7392 separators. Unrecognized parameters and invalid values 7393 are reported in the kernel log. Sysctls registered 7394 later by a loaded module cannot be set this way. 7395 Example: sysctl.vm.swappiness=40 7396 7397 sysrq_always_enabled 7398 [KNL] 7399 Ignore sysrq setting - this boot parameter will 7400 neutralize any effect of /proc/sys/kernel/sysrq. 7401 Useful for debugging. 7402 7403 tcpmhash_entries= [KNL,NET] 7404 Set the number of tcp_metrics_hash slots. 7405 Default value is 8192 or 16384 depending on total 7406 ram pages. This is used to specify the TCP metrics 7407 cache size. See Documentation/networking/ip-sysctl.rst 7408 "tcp_no_metrics_save" section for more details. 7409 7410 tdfx= [HW,DRM] 7411 7412 test_suspend= [SUSPEND] 7413 Format: { "mem" | "standby" | "freeze" }[,N] 7414 Specify "mem" (for Suspend-to-RAM) or "standby" (for 7415 standby suspend) or "freeze" (for suspend type freeze) 7416 as the system sleep state during system startup with 7417 the optional capability to repeat N number of times. 7418 The system is woken from this state using a 7419 wakeup-capable RTC alarm. 7420 7421 thash_entries= [KNL,NET] 7422 Set number of hash buckets for TCP connection 7423 7424 thermal.act= [HW,ACPI] 7425 -1: disable all active trip points in all thermal zones 7426 <degrees C>: override all lowest active trip points 7427 7428 thermal.crt= [HW,ACPI] 7429 -1: disable all critical trip points in all thermal zones 7430 <degrees C>: override all critical trip points 7431 7432 thermal.off= [HW,ACPI] 7433 1: disable ACPI thermal control 7434 7435 thermal.psv= [HW,ACPI] 7436 -1: disable all passive trip points 7437 <degrees C>: override all passive trip points to this 7438 value 7439 7440 thermal.tzp= [HW,ACPI] 7441 Specify global default ACPI thermal zone polling rate 7442 <deci-seconds>: poll all this frequency 7443 0: no polling (default) 7444 7445 thp_anon= [KNL] 7446 Format: <size>[KMG],<size>[KMG]:<state>;<size>[KMG]-<size>[KMG]:<state> 7447 state is one of "always", "madvise", "never" or "inherit". 7448 Control the default behavior of the system with respect 7449 to anonymous transparent hugepages. 7450 Can be used multiple times for multiple anon THP sizes. 7451 See Documentation/admin-guide/mm/transhuge.rst for more 7452 details. 7453 7454 threadirqs [KNL,EARLY] 7455 Force threading of all interrupt handlers except those 7456 marked explicitly IRQF_NO_THREAD. 7457 7458 thp_shmem= [KNL] 7459 Format: <size>[KMG],<size>[KMG]:<policy>;<size>[KMG]-<size>[KMG]:<policy> 7460 Control the default policy of each hugepage size for the 7461 internal shmem mount. <policy> is one of policies available 7462 for the shmem mount ("always", "inherit", "never", "within_size", 7463 and "advise"). 7464 It can be used multiple times for multiple shmem THP sizes. 7465 See Documentation/admin-guide/mm/transhuge.rst for more 7466 details. 7467 7468 topology= [S390,EARLY] 7469 Format: {off | on} 7470 Specify if the kernel should make use of the cpu 7471 topology information if the hardware supports this. 7472 The scheduler will make use of this information and 7473 e.g. base its process migration decisions on it. 7474 Default is on. 7475 7476 torture.disable_onoff_at_boot= [KNL] 7477 Prevent the CPU-hotplug component of torturing 7478 until after init has spawned. 7479 7480 torture.ftrace_dump_at_shutdown= [KNL] 7481 Dump the ftrace buffer at torture-test shutdown, 7482 even if there were no errors. This can be a 7483 very costly operation when many torture tests 7484 are running concurrently, especially on systems 7485 with rotating-rust storage. 7486 7487 torture.verbose_sleep_frequency= [KNL] 7488 Specifies how many verbose printk()s should be 7489 emitted between each sleep. The default of zero 7490 disables verbose-printk() sleeping. 7491 7492 torture.verbose_sleep_duration= [KNL] 7493 Duration of each verbose-printk() sleep in jiffies. 7494 7495 tpm.disable_pcr_integrity= [HW,TPM] 7496 Do not protect PCR registers from unintended physical 7497 access, or interposers in the bus by the means of 7498 having an integrity protected session wrapped around 7499 TPM2_PCR_Extend command. Consider this in a situation 7500 where TPM is heavily utilized by IMA, thus protection 7501 causing a major performance hit, and the space where 7502 machines are deployed is by other means guarded. 7503 7504 tpm_crb_ffa.busy_timeout_ms= [ARM64,TPM] 7505 Maximum time in milliseconds to retry sending a message 7506 to the TPM service before giving up. This parameter controls 7507 how long the system will continue retrying when the TPM 7508 service is busy. 7509 Format: <unsigned int> 7510 Default: 2000 (2 seconds) 7511 7512 tpm_suspend_pcr=[HW,TPM] 7513 Format: integer pcr id 7514 Specify that at suspend time, the tpm driver 7515 should extend the specified pcr with zeros, 7516 as a workaround for some chips which fail to 7517 flush the last written pcr on TPM_SaveState. 7518 This will guarantee that all the other pcrs 7519 are saved. 7520 7521 tpm_tis.interrupts= [HW,TPM] 7522 Enable interrupts for the MMIO based physical layer 7523 for the FIFO interface. By default it is set to false 7524 (0). For more information about TPM hardware interfaces 7525 defined by Trusted Computing Group (TCG) see 7526 https://trustedcomputinggroup.org/resource/pc-client-platform-tpm-profile-ptp-specification/ 7527 7528 tp_printk [FTRACE] 7529 Have the tracepoints sent to printk as well as the 7530 tracing ring buffer. This is useful for early boot up 7531 where the system hangs or reboots and does not give the 7532 option for reading the tracing buffer or performing a 7533 ftrace_dump_on_oops. 7534 7535 To turn off having tracepoints sent to printk, 7536 echo 0 > /proc/sys/kernel/tracepoint_printk 7537 Note, echoing 1 into this file without the 7538 tp_printk kernel cmdline option has no effect. 7539 7540 The tp_printk_stop_on_boot (see below) can also be used 7541 to stop the printing of events to console at 7542 late_initcall_sync. 7543 7544 ** CAUTION ** 7545 7546 Having tracepoints sent to printk() and activating high 7547 frequency tracepoints such as irq or sched, can cause 7548 the system to live lock. 7549 7550 tp_printk_stop_on_boot [FTRACE] 7551 When tp_printk (above) is set, it can cause a lot of noise 7552 on the console. It may be useful to only include the 7553 printing of events during boot up, as user space may 7554 make the system inoperable. 7555 7556 This command line option will stop the printing of events 7557 to console at the late_initcall_sync() time frame. 7558 7559 trace_buf_size=nn[KMG] 7560 [FTRACE] will set tracing buffer size on each cpu. 7561 7562 trace_clock= [FTRACE] Set the clock used for tracing events 7563 at boot up. 7564 local - Use the per CPU time stamp counter 7565 (converted into nanoseconds). Fast, but 7566 depending on the architecture, may not be 7567 in sync between CPUs. 7568 global - Event time stamps are synchronized across 7569 CPUs. May be slower than the local clock, 7570 but better for some race conditions. 7571 counter - Simple counting of events (1, 2, ..) 7572 note, some counts may be skipped due to the 7573 infrastructure grabbing the clock more than 7574 once per event. 7575 uptime - Use jiffies as the time stamp. 7576 perf - Use the same clock that perf uses. 7577 mono - Use ktime_get_mono_fast_ns() for time stamps. 7578 mono_raw - Use ktime_get_raw_fast_ns() for time 7579 stamps. 7580 boot - Use ktime_get_boot_fast_ns() for time stamps. 7581 Architectures may add more clocks. See 7582 Documentation/trace/ftrace.rst for more details. 7583 7584 trace_event=[event-list] 7585 [FTRACE] Set and start specified trace events in order 7586 to facilitate early boot debugging. The event-list is a 7587 comma-separated list of trace events to enable. See 7588 also Documentation/trace/events.rst 7589 7590 To enable modules, use :mod: keyword: 7591 7592 trace_event=:mod:<module> 7593 7594 The value before :mod: will only enable specific events 7595 that are part of the module. See the above mentioned 7596 document for more information. 7597 7598 trace_instance=[instance-info] 7599 [FTRACE] Create a ring buffer instance early in boot up. 7600 This will be listed in: 7601 7602 /sys/kernel/tracing/instances 7603 7604 Events can be enabled at the time the instance is created 7605 via: 7606 7607 trace_instance=<name>,<system1>:<event1>,<system2>:<event2> 7608 7609 Note, the "<system*>:" portion is optional if the event is 7610 unique. 7611 7612 trace_instance=foo,sched:sched_switch,irq_handler_entry,initcall 7613 7614 will enable the "sched_switch" event (note, the "sched:" is optional, and 7615 the same thing would happen if it was left off). The irq_handler_entry 7616 event, and all events under the "initcall" system. 7617 7618 Flags can be added to the instance to modify its behavior when it is 7619 created. The flags are separated by '^'. 7620 7621 The available flags are: 7622 7623 traceoff - Have the tracing instance tracing disabled after it is created. 7624 traceprintk - Have trace_printk() write into this trace instance 7625 (note, "printk" and "trace_printk" can also be used) 7626 7627 trace_instance=foo^traceoff^traceprintk,sched,irq 7628 7629 The flags must come before the defined events. 7630 7631 If memory has been reserved (see memmap for x86), the instance 7632 can use that memory: 7633 7634 memmap=12M$0x284500000 trace_instance=boot_map@0x284500000:12M 7635 7636 The above will create a "boot_map" instance that uses the physical 7637 memory at 0x284500000 that is 12Megs. The per CPU buffers of that 7638 instance will be split up accordingly. 7639 7640 Alternatively, the memory can be reserved by the reserve_mem option: 7641 7642 reserve_mem=12M:4096:trace trace_instance=boot_map@trace 7643 7644 This will reserve 12 megabytes at boot up with a 4096 byte alignment 7645 and place the ring buffer in this memory. Note that due to KASLR, the 7646 memory may not be the same location each time, which will not preserve 7647 the buffer content. 7648 7649 Also note that the layout of the ring buffer data may change between 7650 kernel versions where the validator will fail and reset the ring buffer 7651 if the layout is not the same as the previous kernel. 7652 7653 If the ring buffer is used for persistent bootups and has events enabled, 7654 it is recommend to disable tracing so that events from a previous boot do not 7655 mix with events of the current boot (unless you are debugging a random crash 7656 at boot up). 7657 7658 reserve_mem=12M:4096:trace trace_instance=boot_map^traceoff^traceprintk@trace,sched,irq 7659 7660 Note, saving the trace buffer across reboots does require that the system 7661 is set up to not wipe memory. For instance, CONFIG_RESET_ATTACK_MITIGATION 7662 can force a memory reset on boot which will clear any trace that was stored. 7663 This is just one of many ways that can clear memory. Make sure your system 7664 keeps the content of memory across reboots before relying on this option. 7665 7666 NB: Both the mapped address and size must be page aligned for the architecture. 7667 7668 See also Documentation/trace/debugging.rst 7669 7670 7671 trace_options=[option-list] 7672 [FTRACE] Enable or disable tracer options at boot. 7673 The option-list is a comma delimited list of options 7674 that can be enabled or disabled just as if you were 7675 to echo the option name into 7676 7677 /sys/kernel/tracing/trace_options 7678 7679 For example, to enable stacktrace option (to dump the 7680 stack trace of each event), add to the command line: 7681 7682 trace_options=stacktrace 7683 7684 See also Documentation/trace/ftrace.rst "trace options" 7685 section. 7686 7687 trace_trigger=[trigger-list] 7688 [FTRACE] Add an event trigger on specific events. 7689 Set a trigger on top of a specific event, with an optional 7690 filter. 7691 7692 The format is "trace_trigger=<event>.<trigger>[ if <filter>],..." 7693 Where more than one trigger may be specified that are comma delimited. 7694 7695 For example: 7696 7697 trace_trigger="sched_switch.stacktrace if prev_state == 2" 7698 7699 The above will enable the "stacktrace" trigger on the "sched_switch" 7700 event but only trigger it if the "prev_state" of the "sched_switch" 7701 event is "2" (TASK_UNINTERRUPTIBLE). 7702 7703 See also "Event triggers" in Documentation/trace/events.rst 7704 7705 7706 traceoff_after_boot 7707 [FTRACE] Sometimes tracing is used to debug issues 7708 during the boot process. Since the trace buffer has a 7709 limited amount of storage, it may be prudent to 7710 disable tracing after the boot is finished, otherwise 7711 the critical information may be overwritten. With this 7712 option, the main tracing buffer will be turned off at 7713 the end of the boot process. 7714 7715 traceoff_on_warning 7716 [FTRACE] enable this option to disable tracing when a 7717 warning is hit. This turns off "tracing_on". Tracing can 7718 be enabled again by echoing '1' into the "tracing_on" 7719 file located in /sys/kernel/tracing/ 7720 7721 This option is useful, as it disables the trace before 7722 the WARNING dump is called, which prevents the trace to 7723 be filled with content caused by the warning output. 7724 7725 This option can also be set at run time via the sysctl 7726 option: kernel/traceoff_on_warning 7727 7728 transparent_hugepage= 7729 [KNL] 7730 Format: [always|madvise|never] 7731 Can be used to control the default behavior of the system 7732 with respect to transparent hugepages. 7733 See Documentation/admin-guide/mm/transhuge.rst 7734 for more details. 7735 7736 transparent_hugepage_shmem= [KNL] 7737 Format: [always|within_size|advise|never|deny|force] 7738 Can be used to control the hugepage allocation policy for 7739 the internal shmem mount. 7740 See Documentation/admin-guide/mm/transhuge.rst 7741 for more details. 7742 7743 transparent_hugepage_tmpfs= [KNL] 7744 Format: [always|within_size|advise|never] 7745 Can be used to control the default hugepage allocation policy 7746 for the tmpfs mount. 7747 See Documentation/admin-guide/mm/transhuge.rst 7748 for more details. 7749 7750 trusted.source= [KEYS] 7751 Format: <string> 7752 This parameter identifies the trust source as a backend 7753 for trusted keys implementation. Supported trust 7754 sources: 7755 - "tpm" 7756 - "tee" 7757 - "caam" 7758 - "dcp" 7759 If not specified then it defaults to iterating through 7760 the trust source list starting with TPM and assigns the 7761 first trust source as a backend which is initialized 7762 successfully during iteration. 7763 7764 trusted.rng= [KEYS] 7765 Format: <string> 7766 The RNG used to generate key material for trusted keys. 7767 Can be one of: 7768 - "kernel" 7769 - the same value as trusted.source: "tpm" or "tee" 7770 - "default" 7771 If not specified, "default" is used. In this case, 7772 the RNG's choice is left to each individual trust source. 7773 7774 trusted.dcp_use_otp_key 7775 This is intended to be used in combination with 7776 trusted.source=dcp and will select the DCP OTP key 7777 instead of the DCP UNIQUE key blob encryption. 7778 7779 trusted.dcp_skip_zk_test 7780 This is intended to be used in combination with 7781 trusted.source=dcp and will disable the check if the 7782 blob key is all zeros. This is helpful for situations where 7783 having this key zero'ed is acceptable. E.g. in testing 7784 scenarios. 7785 7786 tsa= [X86] Control mitigation for Transient Scheduler 7787 Attacks on AMD CPUs. Search the following in your 7788 favourite search engine for more details: 7789 7790 "Technical guidance for mitigating transient scheduler 7791 attacks". 7792 7793 off - disable the mitigation 7794 on - enable the mitigation (default) 7795 user - mitigate only user/kernel transitions 7796 vm - mitigate only guest/host transitions 7797 7798 7799 tsc= Disable clocksource stability checks for TSC. 7800 Format: <string> 7801 [x86] reliable: mark tsc clocksource as reliable, this 7802 disables clocksource verification at runtime, as well 7803 as the stability checks done at bootup. Used to enable 7804 high-resolution timer mode on older hardware, and in 7805 virtualized environment. 7806 [x86] noirqtime: Do not use TSC to do irq accounting. 7807 Used to run time disable IRQ_TIME_ACCOUNTING on any 7808 platforms where RDTSC is slow and this accounting 7809 can add overhead. 7810 [x86] unstable: mark the TSC clocksource as unstable, this 7811 marks the TSC unconditionally unstable at bootup and 7812 avoids any further wobbles once the TSC watchdog notices. 7813 [x86] nowatchdog: disable clocksource watchdog. Used 7814 in situations with strict latency requirements (where 7815 interruptions from clocksource watchdog are not 7816 acceptable). 7817 [x86] recalibrate: force recalibration against a HW timer 7818 (HPET or PM timer) on systems whose TSC frequency was 7819 obtained from HW or FW using either an MSR or CPUID(0x15). 7820 Warn if the difference is more than 500 ppm. 7821 [x86] watchdog: Use TSC as the watchdog clocksource with 7822 which to check other HW timers (HPET or PM timer), but 7823 only on systems where TSC has been deemed trustworthy. 7824 This will be suppressed by an earlier tsc=nowatchdog and 7825 can be overridden by a later tsc=nowatchdog. A console 7826 message will flag any such suppression or overriding. 7827 7828 tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given 7829 value instead. Useful when the early TSC frequency discovery 7830 procedure is not reliable, such as on overclocked systems 7831 with CPUID.16h support and partial CPUID.15h support. 7832 Format: <unsigned int> 7833 7834 tsx= [X86] Control Transactional Synchronization 7835 Extensions (TSX) feature in Intel processors that 7836 support TSX control. 7837 7838 This parameter controls the TSX feature. The options are: 7839 7840 on - Enable TSX on the system. Although there are 7841 mitigations for all known security vulnerabilities, 7842 TSX has been known to be an accelerator for 7843 several previous speculation-related CVEs, and 7844 so there may be unknown security risks associated 7845 with leaving it enabled. 7846 7847 off - Disable TSX on the system. (Note that this 7848 option takes effect only on newer CPUs which are 7849 not vulnerable to MDS, i.e., have 7850 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 7851 the new IA32_TSX_CTRL MSR through a microcode 7852 update. This new MSR allows for the reliable 7853 deactivation of the TSX functionality.) 7854 7855 auto - Disable TSX if X86_BUG_TAA is present, 7856 otherwise enable TSX on the system. 7857 7858 Not specifying this option is equivalent to tsx=off. 7859 7860 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7861 for more details. 7862 7863 tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async 7864 Abort (TAA) vulnerability. 7865 7866 Similar to Micro-architectural Data Sampling (MDS) 7867 certain CPUs that support Transactional 7868 Synchronization Extensions (TSX) are vulnerable to an 7869 exploit against CPU internal buffers which can forward 7870 information to a disclosure gadget under certain 7871 conditions. 7872 7873 In vulnerable processors, the speculatively forwarded 7874 data can be used in a cache side channel attack, to 7875 access data to which the attacker does not have direct 7876 access. 7877 7878 This parameter controls the TAA mitigation. The 7879 options are: 7880 7881 full - Enable TAA mitigation on vulnerable CPUs 7882 if TSX is enabled. 7883 7884 full,nosmt - Enable TAA mitigation and disable SMT on 7885 vulnerable CPUs. If TSX is disabled, SMT 7886 is not disabled because CPU is not 7887 vulnerable to cross-thread TAA attacks. 7888 off - Unconditionally disable TAA mitigation 7889 7890 On MDS-affected machines, tsx_async_abort=off can be 7891 prevented by an active MDS mitigation as both vulnerabilities 7892 are mitigated with the same mechanism so in order to disable 7893 this mitigation, you need to specify mds=off too. 7894 7895 Not specifying this option is equivalent to 7896 tsx_async_abort=full. On CPUs which are MDS affected 7897 and deploy MDS mitigation, TAA mitigation is not 7898 required and doesn't provide any additional 7899 mitigation. 7900 7901 For details see: 7902 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 7903 7904 turbografx.map[2|3]= [HW,JOY] 7905 TurboGraFX parallel port interface 7906 Format: 7907 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 7908 See also Documentation/input/devices/joystick-parport.rst 7909 7910 udbg-immortal [PPC] When debugging early kernel crashes that 7911 happen after console_init() and before a proper 7912 console driver takes over, this boot options might 7913 help "seeing" what's going on. 7914 7915 uhash_entries= [KNL,NET] 7916 Set number of hash buckets for UDP/UDP-Lite connections 7917 7918 uhci-hcd.ignore_oc= 7919 [USB] Ignore overcurrent events (default N). 7920 Some badly-designed motherboards generate lots of 7921 bogus events, for ports that aren't wired to 7922 anything. Set this parameter to avoid log spamming. 7923 Note that genuine overcurrent events won't be 7924 reported either. 7925 7926 unaligned_scalar_speed= 7927 [RISCV] 7928 Format: {slow | fast | unsupported} 7929 Allow skipping scalar unaligned access speed tests. This 7930 is useful for testing alternative code paths and to skip 7931 the tests in environments where they run too slowly. All 7932 CPUs must have the same scalar unaligned access speed. 7933 7934 unaligned_vector_speed= 7935 [RISCV] 7936 Format: {slow | fast | unsupported} 7937 Allow skipping vector unaligned access speed tests. This 7938 is useful for testing alternative code paths and to skip 7939 the tests in environments where they run too slowly. All 7940 CPUs must have the same vector unaligned access speed. 7941 7942 unknown_nmi_panic 7943 [X86] Cause panic on unknown NMI. 7944 7945 unwind_debug [X86-64,EARLY] 7946 Enable unwinder debug output. This can be 7947 useful for debugging certain unwinder error 7948 conditions, including corrupt stacks and 7949 bad/missing unwinder metadata. 7950 7951 usbcore.authorized_default= 7952 [USB] Default USB device authorization: 7953 (default -1 = authorized (same as 1), 7954 0 = not authorized, 1 = authorized, 2 = authorized 7955 if device connected to internal port) 7956 7957 usbcore.autosuspend= 7958 [USB] The autosuspend time delay (in seconds) used 7959 for newly-detected USB devices (default 2). This 7960 is the time required before an idle device will be 7961 autosuspended. Devices for which the delay is set 7962 to a negative value won't be autosuspended at all. 7963 7964 usbcore.usbfs_snoop= 7965 [USB] Set to log all usbfs traffic (default 0 = off). 7966 7967 usbcore.usbfs_snoop_max= 7968 [USB] Maximum number of bytes to snoop in each URB 7969 (default = 65536). 7970 7971 usbcore.blinkenlights= 7972 [USB] Set to cycle leds on hubs (default 0 = off). 7973 7974 usbcore.old_scheme_first= 7975 [USB] Start with the old device initialization 7976 scheme (default 0 = off). 7977 7978 usbcore.usbfs_memory_mb= 7979 [USB] Memory limit (in MB) for buffers allocated by 7980 usbfs (default = 16, 0 = max = 2047). 7981 7982 usbcore.use_both_schemes= 7983 [USB] Try the other device initialization scheme 7984 if the first one fails (default 1 = enabled). 7985 7986 usbcore.initial_descriptor_timeout= 7987 [USB] Specifies timeout for the initial 64-byte 7988 USB_REQ_GET_DESCRIPTOR request in milliseconds 7989 (default 5000 = 5.0 seconds). 7990 7991 usbcore.nousb [USB] Disable the USB subsystem 7992 7993 usbcore.quirks= 7994 [USB] A list of quirk entries to augment the built-in 7995 usb core quirk list. List entries are separated by 7996 commas. Each entry has the form 7997 VendorID:ProductID:Flags. The IDs are 4-digit hex 7998 numbers and Flags is a set of letters. Each letter 7999 will change the built-in quirk; setting it if it is 8000 clear and clearing it if it is set. The letters have 8001 the following meanings: 8002 a = USB_QUIRK_STRING_FETCH_255 (string 8003 descriptors must not be fetched using 8004 a 255-byte read); 8005 b = USB_QUIRK_RESET_RESUME (device can't resume 8006 correctly so reset it instead); 8007 c = USB_QUIRK_NO_SET_INTF (device can't handle 8008 Set-Interface requests); 8009 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 8010 handle its Configuration or Interface 8011 strings); 8012 e = USB_QUIRK_RESET (device can't be reset 8013 (e.g morph devices), don't use reset); 8014 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 8015 more interface descriptions than the 8016 bNumInterfaces count, and can't handle 8017 talking to these interfaces); 8018 g = USB_QUIRK_DELAY_INIT (device needs a pause 8019 during initialization, after we read 8020 the device descriptor); 8021 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 8022 high speed and super speed interrupt 8023 endpoints, the USB 2.0 and USB 3.0 spec 8024 require the interval in microframes (1 8025 microframe = 125 microseconds) to be 8026 calculated as interval = 2 ^ 8027 (bInterval-1). 8028 Devices with this quirk report their 8029 bInterval as the result of this 8030 calculation instead of the exponent 8031 variable used in the calculation); 8032 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 8033 handle device_qualifier descriptor 8034 requests); 8035 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 8036 generates spurious wakeup, ignore 8037 remote wakeup capability); 8038 k = USB_QUIRK_NO_LPM (device can't handle Link 8039 Power Management); 8040 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 8041 (Device reports its bInterval as linear 8042 frames instead of the USB 2.0 8043 calculation); 8044 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 8045 to be disconnected before suspend to 8046 prevent spurious wakeup); 8047 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 8048 pause after every control message); 8049 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 8050 delay after resetting its port); 8051 p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT 8052 (Reduce timeout of the SET_ADDRESS 8053 request from 5000 ms to 500 ms); 8054 Example: quirks=0781:5580:bk,0a5c:5834:gij 8055 8056 usbhid.mousepoll= 8057 [USBHID] The interval which mice are to be polled at. 8058 8059 usbhid.jspoll= 8060 [USBHID] The interval which joysticks are to be polled at. 8061 8062 usbhid.kbpoll= 8063 [USBHID] The interval which keyboards are to be polled at. 8064 8065 usb-storage.delay_use= 8066 [UMS] The delay in seconds before a new device is 8067 scanned for Logical Units (default 1). 8068 Optionally the delay in milliseconds if the value has 8069 suffix with "ms". 8070 Example: delay_use=2567ms 8071 8072 usb-storage.quirks= 8073 [UMS] A list of quirks entries to supplement or 8074 override the built-in unusual_devs list. List 8075 entries are separated by commas. Each entry has 8076 the form VID:PID:Flags where VID and PID are Vendor 8077 and Product ID values (4-digit hex numbers) and 8078 Flags is a set of characters, each corresponding 8079 to a common usb-storage quirk flag as follows: 8080 a = SANE_SENSE (collect more than 18 bytes 8081 of sense data, not on uas); 8082 b = BAD_SENSE (don't collect more than 18 8083 bytes of sense data, not on uas); 8084 c = FIX_CAPACITY (decrease the reported 8085 device capacity by one sector); 8086 d = NO_READ_DISC_INFO (don't use 8087 READ_DISC_INFO command, not on uas); 8088 e = NO_READ_CAPACITY_16 (don't use 8089 READ_CAPACITY_16 command); 8090 f = NO_REPORT_OPCODES (don't use report opcodes 8091 command, uas only); 8092 g = MAX_SECTORS_240 (don't transfer more than 8093 240 sectors at a time, uas only); 8094 h = CAPACITY_HEURISTICS (decrease the 8095 reported device capacity by one 8096 sector if the number is odd); 8097 i = IGNORE_DEVICE (don't bind to this 8098 device); 8099 j = NO_REPORT_LUNS (don't use report luns 8100 command, uas only); 8101 k = NO_SAME (do not use WRITE_SAME, uas only) 8102 l = NOT_LOCKABLE (don't try to lock and 8103 unlock ejectable media, not on uas); 8104 m = MAX_SECTORS_64 (don't transfer more 8105 than 64 sectors = 32 KB at a time, 8106 not on uas); 8107 n = INITIAL_READ10 (force a retry of the 8108 initial READ(10) command, not on uas); 8109 o = CAPACITY_OK (accept the capacity 8110 reported by the device, not on uas); 8111 p = WRITE_CACHE (the device cache is ON 8112 by default, not on uas); 8113 r = IGNORE_RESIDUE (the device reports 8114 bogus residue values, not on uas); 8115 s = SINGLE_LUN (the device has only one 8116 Logical Unit); 8117 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 8118 commands, uas only); 8119 u = IGNORE_UAS (don't bind to the uas driver); 8120 w = NO_WP_DETECT (don't test whether the 8121 medium is write-protected). 8122 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 8123 even if the device claims no cache, 8124 not on uas) 8125 Example: quirks=0419:aaf5:rl,0421:0433:rc 8126 8127 user_debug= [KNL,ARM] 8128 Format: <int> 8129 See arch/arm/Kconfig.debug help text. 8130 1 - undefined instruction events 8131 2 - system calls 8132 4 - invalid data aborts 8133 8 - SIGSEGV faults 8134 16 - SIGBUS faults 8135 Example: user_debug=31 8136 8137 vdso= [X86,SH,SPARC] 8138 On X86_32, this is an alias for vdso32=. Otherwise: 8139 8140 vdso=1: enable VDSO (the default) 8141 vdso=0: disable VDSO mapping 8142 8143 vdso32= [X86] Control the 32-bit vDSO 8144 vdso32=1: enable 32-bit VDSO 8145 vdso32=0 or vdso32=2: disable 32-bit VDSO 8146 8147 See the help text for CONFIG_COMPAT_VDSO for more 8148 details. If CONFIG_COMPAT_VDSO is set, the default is 8149 vdso32=0; otherwise, the default is vdso32=1. 8150 8151 For compatibility with older kernels, vdso32=2 is an 8152 alias for vdso32=0. 8153 8154 Try vdso32=0 if you encounter an error that says: 8155 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 8156 8157 video= [FB,EARLY] Frame buffer configuration 8158 See Documentation/fb/modedb.rst. 8159 8160 video.brightness_switch_enabled= [ACPI] 8161 Format: [0|1] 8162 If set to 1, on receiving an ACPI notify event 8163 generated by hotkey, video driver will adjust brightness 8164 level and then send out the event to user space through 8165 the allocated input device. If set to 0, video driver 8166 will only send out the event without touching backlight 8167 brightness level. 8168 default: 1 8169 8170 virtio_mmio.device= 8171 [VMMIO] Memory mapped virtio (platform) device. 8172 8173 <size>@<baseaddr>:<irq>[:<id>] 8174 where: 8175 <size> := size (can use standard suffixes 8176 like K, M and G) 8177 <baseaddr> := physical base address 8178 <irq> := interrupt number (as passed to 8179 request_irq()) 8180 <id> := (optional) platform device id 8181 example: 8182 virtio_mmio.device=1K@0x100b0000:48:7 8183 8184 Can be used multiple times for multiple devices. 8185 8186 vga= [BOOT,X86-32] Select a particular video mode 8187 See Documentation/arch/x86/boot.rst and 8188 Documentation/admin-guide/svga.rst. 8189 Use vga=ask for menu. 8190 This is actually a boot loader parameter; the value is 8191 passed to the kernel using a special protocol. 8192 8193 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 8194 May slow down system boot speed, especially when 8195 enabled on systems with a large amount of memory. 8196 All options are enabled by default, and this 8197 interface is meant to allow for selectively 8198 enabling or disabling specific virtual memory 8199 debugging features. 8200 8201 Available options are: 8202 P Enable page structure init time poisoning 8203 - Disable all of the above options 8204 8205 vmalloc=nn[KMG] [KNL,BOOT,EARLY] Forces the vmalloc area to have an 8206 exact size of <nn>. This can be used to increase 8207 the minimum size (128MB on x86, arm32 platforms). 8208 It can also be used to decrease the size and leave more room 8209 for directly mapped kernel RAM. Note that this parameter does 8210 not exist on many other platforms (including arm64, alpha, 8211 loongarch, arc, csky, hexagon, microblaze, mips, nios2, openrisc, 8212 parisc, m64k, powerpc, riscv, sh, um, xtensa, s390, sparc). 8213 8214 vmcp_cma=nn[MG] [KNL,S390,EARLY] 8215 Sets the memory size reserved for contiguous memory 8216 allocations for the vmcp device driver. 8217 8218 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 8219 Format: <command> 8220 8221 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 8222 Format: <command> 8223 8224 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 8225 Format: <command> 8226 8227 vmscape= [X86] Controls mitigation for VMscape attacks. 8228 VMscape attacks can leak information from a userspace 8229 hypervisor to a guest via speculative side-channels. 8230 8231 off - disable the mitigation 8232 ibpb - use Indirect Branch Prediction Barrier 8233 (IBPB) mitigation (default) 8234 force - force vulnerability detection even on 8235 unaffected processors 8236 8237 vsyscall= [X86-64,EARLY] 8238 Controls the behavior of vsyscalls (i.e. calls to 8239 fixed addresses of 0xffffffffff600x00 from legacy 8240 code). Most statically-linked binaries and older 8241 versions of glibc use these calls. Because these 8242 functions are at fixed addresses, they make nice 8243 targets for exploits that can control RIP. 8244 8245 emulate Vsyscalls turn into traps and are emulated 8246 reasonably safely. The vsyscall page is 8247 readable. 8248 8249 xonly [default] Vsyscalls turn into traps and are 8250 emulated reasonably safely. The vsyscall 8251 page is not readable. 8252 8253 none Vsyscalls don't work at all. This makes 8254 them quite hard to use for exploits but 8255 might break your system. 8256 8257 vt.color= [VT] Default text color. 8258 Format: 0xYX, X = foreground, Y = background. 8259 Default: 0x07 = light gray on black. 8260 8261 vt.cur_default= [VT] Default cursor shape. 8262 Format: 0xCCBBAA, where AA, BB, and CC are the same as 8263 the parameters of the <Esc>[?A;B;Cc escape sequence; 8264 see vga-softcursor.rst. Default: 2 = underline. 8265 8266 vt.default_blu= [VT] 8267 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 8268 Change the default blue palette of the console. 8269 This is a 16-member array composed of values 8270 ranging from 0-255. 8271 8272 vt.default_grn= [VT] 8273 Format: <green0>,<green1>,<green2>,...,<green15> 8274 Change the default green palette of the console. 8275 This is a 16-member array composed of values 8276 ranging from 0-255. 8277 8278 vt.default_red= [VT] 8279 Format: <red0>,<red1>,<red2>,...,<red15> 8280 Change the default red palette of the console. 8281 This is a 16-member array composed of values 8282 ranging from 0-255. 8283 8284 vt.default_utf8= 8285 [VT] 8286 Format=<0|1> 8287 Set system-wide default UTF-8 mode for all tty's. 8288 Default is 1, i.e. UTF-8 mode is enabled for all 8289 newly opened terminals. 8290 8291 vt.global_cursor_default= 8292 [VT] 8293 Format=<-1|0|1> 8294 Set system-wide default for whether a cursor 8295 is shown on new VTs. Default is -1, 8296 i.e. cursors will be created by default unless 8297 overridden by individual drivers. 0 will hide 8298 cursors, 1 will display them. 8299 8300 vt.italic= [VT] Default color for italic text; 0-15. 8301 Default: 2 = green. 8302 8303 vt.underline= [VT] Default color for underlined text; 0-15. 8304 Default: 3 = cyan. 8305 8306 watchdog timers [HW,WDT] For information on watchdog timers, 8307 see Documentation/watchdog/watchdog-parameters.rst 8308 or other driver-specific files in the 8309 Documentation/watchdog/ directory. 8310 8311 watchdog_thresh= 8312 [KNL] 8313 Set the hard lockup detector stall duration 8314 threshold in seconds. The soft lockup detector 8315 threshold is set to twice the value. A value of 0 8316 disables both lockup detectors. Default is 10 8317 seconds. 8318 8319 workqueue.unbound_cpus= 8320 [KNL,SMP] Specify to constrain one or some CPUs 8321 to use in unbound workqueues. 8322 Format: <cpu-list> 8323 By default, all online CPUs are available for 8324 unbound workqueues. 8325 8326 workqueue.watchdog_thresh= 8327 If CONFIG_WQ_WATCHDOG is configured, workqueue can 8328 warn stall conditions and dump internal state to 8329 help debugging. 0 disables workqueue stall 8330 detection; otherwise, it's the stall threshold 8331 duration in seconds. The default value is 30 and 8332 it can be updated at runtime by writing to the 8333 corresponding sysfs file. 8334 8335 workqueue.panic_on_stall=<uint> 8336 Panic when workqueue stall is detected by 8337 CONFIG_WQ_WATCHDOG. It sets the number times of the 8338 stall to trigger panic. 8339 8340 The default is 0, which disables the panic on stall. 8341 8342 workqueue.cpu_intensive_thresh_us= 8343 Per-cpu work items which run for longer than this 8344 threshold are automatically considered CPU intensive 8345 and excluded from concurrency management to prevent 8346 them from noticeably delaying other per-cpu work 8347 items. Default is 10000 (10ms). 8348 8349 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8350 will report the work functions which violate this 8351 threshold repeatedly. They are likely good 8352 candidates for using WQ_UNBOUND workqueues instead. 8353 8354 workqueue.cpu_intensive_warning_thresh=<uint> 8355 If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel 8356 will report the work functions which violate the 8357 intensive_threshold_us repeatedly. In order to prevent 8358 spurious warnings, start printing only after a work 8359 function has violated this threshold number of times. 8360 8361 The default is 4 times. 0 disables the warning. 8362 8363 workqueue.power_efficient 8364 Per-cpu workqueues are generally preferred because 8365 they show better performance thanks to cache 8366 locality; unfortunately, per-cpu workqueues tend to 8367 be more power hungry than unbound workqueues. 8368 8369 Enabling this makes the per-cpu workqueues which 8370 were observed to contribute significantly to power 8371 consumption unbound, leading to measurably lower 8372 power usage at the cost of small performance 8373 overhead. 8374 8375 The default value of this parameter is determined by 8376 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 8377 8378 workqueue.default_affinity_scope= 8379 Select the default affinity scope to use for unbound 8380 workqueues. Can be one of "cpu", "smt", "cache", 8381 "numa" and "system". Default is "cache". For more 8382 information, see the Affinity Scopes section in 8383 Documentation/core-api/workqueue.rst. 8384 8385 This can be changed after boot by writing to the 8386 matching /sys/module/workqueue/parameters file. All 8387 workqueues with the "default" affinity scope will be 8388 updated accordingly. 8389 8390 workqueue.debug_force_rr_cpu 8391 Workqueue used to implicitly guarantee that work 8392 items queued without explicit CPU specified are put 8393 on the local CPU. This guarantee is no longer true 8394 and while local CPU is still preferred work items 8395 may be put on foreign CPUs. This debug option 8396 forces round-robin CPU selection to flush out 8397 usages which depend on the now broken guarantee. 8398 When enabled, memory and cache locality will be 8399 impacted. 8400 8401 writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access 8402 Type) of ioremap_wc(). 8403 8404 on - Enable writecombine, use WUC for ioremap_wc() 8405 off - Disable writecombine, use SUC for ioremap_wc() 8406 8407 x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of 8408 default x2apic cluster mode on platforms 8409 supporting x2apic. 8410 8411 xen_512gb_limit [KNL,X86-64,XEN] 8412 Restricts the kernel running paravirtualized under Xen 8413 to use only up to 512 GB of RAM. The reason to do so is 8414 crash analysis tools and Xen tools for doing domain 8415 save/restore/migration must be enabled to handle larger 8416 domains. 8417 8418 xen_emul_unplug= [HW,X86,XEN,EARLY] 8419 Unplug Xen emulated devices 8420 Format: [unplug0,][unplug1] 8421 ide-disks -- unplug primary master IDE devices 8422 aux-ide-disks -- unplug non-primary-master IDE devices 8423 nics -- unplug network devices 8424 all -- unplug all emulated devices (NICs and IDE disks) 8425 unnecessary -- unplugging emulated devices is 8426 unnecessary even if the host did not respond to 8427 the unplug protocol 8428 never -- do not unplug even if version check succeeds 8429 8430 xen_legacy_crash [X86,XEN,EARLY] 8431 Crash from Xen panic notifier, without executing late 8432 panic() code such as dumping handler. 8433 8434 xen_mc_debug [X86,XEN,EARLY] 8435 Enable multicall debugging when running as a Xen PV guest. 8436 Enabling this feature will reduce performance a little 8437 bit, so it should only be enabled for obtaining extended 8438 debug data in case of multicall errors. 8439 8440 xen_msr_safe= [X86,XEN,EARLY] 8441 Format: <bool> 8442 Select whether to always use non-faulting (safe) MSR 8443 access functions when running as Xen PV guest. The 8444 default value is controlled by CONFIG_XEN_PV_MSR_SAFE. 8445 8446 xen_nopv [X86] 8447 Disables the PV optimizations forcing the HVM guest to 8448 run as generic HVM guest with no PV drivers. 8449 This option is obsoleted by the "nopv" option, which 8450 has equivalent effect for XEN platform. 8451 8452 xen_no_vector_callback 8453 [KNL,X86,XEN,EARLY] Disable the vector callback for Xen 8454 event channel interrupts. 8455 8456 xen_scrub_pages= [XEN] 8457 Boolean option to control scrubbing pages before giving them back 8458 to Xen, for use by other domains. Can be also changed at runtime 8459 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 8460 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 8461 8462 xen_timer_slop= [X86-64,XEN,EARLY] 8463 Set the timer slop (in nanoseconds) for the virtual Xen 8464 timers (default is 100000). This adjusts the minimum 8465 delta of virtualized Xen timers, where lower values 8466 improve timer resolution at the expense of processing 8467 more timer interrupts. 8468 8469 xen.balloon_boot_timeout= [XEN] 8470 The time (in seconds) to wait before giving up to boot 8471 in case initial ballooning fails to free enough memory. 8472 Applies only when running as HVM or PVH guest and 8473 started with less memory configured than allowed at 8474 max. Default is 180. 8475 8476 xen.event_eoi_delay= [XEN] 8477 How long to delay EOI handling in case of event 8478 storms (jiffies). Default is 10. 8479 8480 xen.event_loop_timeout= [XEN] 8481 After which time (jiffies) the event handling loop 8482 should start to delay EOI handling. Default is 2. 8483 8484 xen.fifo_events= [XEN] 8485 Boolean parameter to disable using fifo event handling 8486 even if available. Normally fifo event handling is 8487 preferred over the 2-level event handling, as it is 8488 fairer and the number of possible event channels is 8489 much higher. Default is on (use fifo events). 8490 8491 xirc2ps_cs= [NET,PCMCIA] 8492 Format: 8493 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 8494 8495 xive= [PPC] 8496 By default on POWER9 and above, the kernel will 8497 natively use the XIVE interrupt controller. This option 8498 allows the fallback firmware mode to be used: 8499 8500 off Fallback to firmware control of XIVE interrupt 8501 controller on both pseries and powernv 8502 platforms. Only useful on POWER9 and above. 8503 8504 xive.store-eoi=off [PPC] 8505 By default on POWER10 and above, the kernel will use 8506 stores for EOI handling when the XIVE interrupt mode 8507 is active. This option allows the XIVE driver to use 8508 loads instead, as on POWER9. 8509 8510 xhci-hcd.quirks [USB,KNL] 8511 A hex value specifying bitmask with supplemental xhci 8512 host controller quirks. Meaning of each bit can be 8513 consulted in header drivers/usb/host/xhci.h. 8514 8515 xmon [PPC,EARLY] 8516 Format: { early | on | rw | ro | off } 8517 Controls if xmon debugger is enabled. Default is off. 8518 Passing only "xmon" is equivalent to "xmon=early". 8519 early Call xmon as early as possible on boot; xmon 8520 debugger is called from setup_arch(). 8521 on xmon debugger hooks will be installed so xmon 8522 is only called on a kernel crash. Default mode, 8523 i.e. either "ro" or "rw" mode, is controlled 8524 with CONFIG_XMON_DEFAULT_RO_MODE. 8525 rw xmon debugger hooks will be installed so xmon 8526 is called only on a kernel crash, mode is write, 8527 meaning SPR registers, memory and, other data 8528 can be written using xmon commands. 8529 ro same as "rw" option above but SPR registers, 8530 memory, and other data can't be written using 8531 xmon commands. 8532 off xmon is disabled. 8533