1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM[,BITNUM...] [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [KNL,CMA] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 kernel/dma/contiguous.c 601 602 cma_pernuma=nn[MG] 603 [ARM64,KNL] 604 Sets the size of kernel per-numa memory area for 605 contiguous memory allocations. A value of 0 disables 606 per-numa CMA altogether. And If this option is not 607 specificed, the default value is 0. 608 With per-numa CMA enabled, DMA users on node nid will 609 first try to allocate buffer from the pernuma area 610 which is located in node nid, if the allocation fails, 611 they will fallback to the global default memory area. 612 613 cmo_free_hint= [PPC] Format: { yes | no } 614 Specify whether pages are marked as being inactive 615 when they are freed. This is used in CMO environments 616 to determine OS memory pressure for page stealing by 617 a hypervisor. 618 Default: yes 619 620 coherent_pool=nn[KMG] [ARM,KNL] 621 Sets the size of memory pool for coherent, atomic dma 622 allocations, by default set to 256K. 623 624 com20020= [HW,NET] ARCnet - COM20020 chipset 625 Format: 626 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 627 628 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 629 Format: <io>[,<irq>] 630 631 com90xx= [HW,NET] 632 ARCnet - COM90xx chipset (memory-mapped buffers) 633 Format: <io>[,<irq>[,<memstart>]] 634 635 condev= [HW,S390] console device 636 conmode= 637 638 console= [KNL] Output console device and options. 639 640 tty<n> Use the virtual console device <n>. 641 642 ttyS<n>[,options] 643 ttyUSB0[,options] 644 Use the specified serial port. The options are of 645 the form "bbbbpnf", where "bbbb" is the baud rate, 646 "p" is parity ("n", "o", or "e"), "n" is number of 647 bits, and "f" is flow control ("r" for RTS or 648 omit it). Default is "9600n8". 649 650 See Documentation/admin-guide/serial-console.rst for more 651 information. See 652 Documentation/networking/netconsole.rst for an 653 alternative. 654 655 uart[8250],io,<addr>[,options] 656 uart[8250],mmio,<addr>[,options] 657 uart[8250],mmio16,<addr>[,options] 658 uart[8250],mmio32,<addr>[,options] 659 uart[8250],0x<addr>[,options] 660 Start an early, polled-mode console on the 8250/16550 661 UART at the specified I/O port or MMIO address, 662 switching to the matching ttyS device later. 663 MMIO inter-register address stride is either 8-bit 664 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 665 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 666 to be equivalent to 'mmio'. 'options' are specified in 667 the same format described for ttyS above; if unspecified, 668 the h/w is not re-initialized. 669 670 hvc<n> Use the hypervisor console device <n>. This is for 671 both Xen and PowerPC hypervisors. 672 673 If the device connected to the port is not a TTY but a braille 674 device, prepend "brl," before the device type, for instance 675 console=brl,ttyS0 676 For now, only VisioBraille is supported. 677 678 console_msg_format= 679 [KNL] Change console messages format 680 default 681 By default we print messages on consoles in 682 "[time stamp] text\n" format (time stamp may not be 683 printed, depending on CONFIG_PRINTK_TIME or 684 `printk_time' param). 685 syslog 686 Switch to syslog format: "<%u>[time stamp] text\n" 687 IOW, each message will have a facility and loglevel 688 prefix. The format is similar to one used by syslog() 689 syscall, or to executing "dmesg -S --raw" or to reading 690 from /proc/kmsg. 691 692 consoleblank= [KNL] The console blank (screen saver) timeout in 693 seconds. A value of 0 disables the blank timer. 694 Defaults to 0. 695 696 coredump_filter= 697 [KNL] Change the default value for 698 /proc/<pid>/coredump_filter. 699 See also Documentation/filesystems/proc.rst. 700 701 coresight_cpu_debug.enable 702 [ARM,ARM64] 703 Format: <bool> 704 Enable/disable the CPU sampling based debugging. 705 0: default value, disable debugging 706 1: enable debugging at boot time 707 708 cpuidle.off=1 [CPU_IDLE] 709 disable the cpuidle sub-system 710 711 cpuidle.governor= 712 [CPU_IDLE] Name of the cpuidle governor to use. 713 714 cpufreq.off=1 [CPU_FREQ] 715 disable the cpufreq sub-system 716 717 cpufreq.default_governor= 718 [CPU_FREQ] Name of the default cpufreq governor or 719 policy to use. This governor must be registered in the 720 kernel before the cpufreq driver probes. 721 722 cpu_init_udelay=N 723 [X86] Delay for N microsec between assert and de-assert 724 of APIC INIT to start processors. This delay occurs 725 on every CPU online, such as boot, and resume from suspend. 726 Default: 10000 727 728 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 729 Format: 730 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 731 732 crashkernel=size[KMG][@offset[KMG]] 733 [KNL] Using kexec, Linux can switch to a 'crash kernel' 734 upon panic. This parameter reserves the physical 735 memory region [offset, offset + size] for that kernel 736 image. If '@offset' is omitted, then a suitable offset 737 is selected automatically. 738 [KNL, X86-64] Select a region under 4G first, and 739 fall back to reserve region above 4G when '@offset' 740 hasn't been specified. 741 See Documentation/admin-guide/kdump/kdump.rst for further details. 742 743 crashkernel=range1:size1[,range2:size2,...][@offset] 744 [KNL] Same as above, but depends on the memory 745 in the running system. The syntax of range is 746 start-[end] where start and end are both 747 a memory unit (amount[KMG]). See also 748 Documentation/admin-guide/kdump/kdump.rst for an example. 749 750 crashkernel=size[KMG],high 751 [KNL, X86-64] range could be above 4G. Allow kernel 752 to allocate physical memory region from top, so could 753 be above 4G if system have more than 4G ram installed. 754 Otherwise memory region will be allocated below 4G, if 755 available. 756 It will be ignored if crashkernel=X is specified. 757 crashkernel=size[KMG],low 758 [KNL, X86-64] range under 4G. When crashkernel=X,high 759 is passed, kernel could allocate physical memory region 760 above 4G, that cause second kernel crash on system 761 that require some amount of low memory, e.g. swiotlb 762 requires at least 64M+32K low memory, also enough extra 763 low memory is needed to make sure DMA buffers for 32-bit 764 devices won't run out. Kernel would try to allocate at 765 at least 256M below 4G automatically. 766 This one let user to specify own low range under 4G 767 for second kernel instead. 768 0: to disable low allocation. 769 It will be ignored when crashkernel=X,high is not used 770 or memory reserved is below 4G. 771 772 cryptomgr.notests 773 [KNL] Disable crypto self-tests 774 775 cs89x0_dma= [HW,NET] 776 Format: <dma> 777 778 cs89x0_media= [HW,NET] 779 Format: { rj45 | aui | bnc } 780 781 dasd= [HW,NET] 782 See header of drivers/s390/block/dasd_devmap.c. 783 784 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 785 (one device per port) 786 Format: <port#>,<type> 787 See also Documentation/input/devices/joystick-parport.rst 788 789 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 790 time. See 791 Documentation/admin-guide/dynamic-debug-howto.rst for 792 details. Deprecated, see dyndbg. 793 794 debug [KNL] Enable kernel debugging (events log level). 795 796 debug_boot_weak_hash 797 [KNL] Enable printing [hashed] pointers early in the 798 boot sequence. If enabled, we use a weak hash instead 799 of siphash to hash pointers. Use this option if you are 800 seeing instances of '(___ptrval___)') and need to see a 801 value (hashed pointer) instead. Cryptographically 802 insecure, please do not use on production kernels. 803 804 debug_locks_verbose= 805 [KNL] verbose self-tests 806 Format=<0|1> 807 Print debugging info while doing the locking API 808 self-tests. 809 We default to 0 (no extra messages), setting it to 810 1 will print _a lot_ more information - normally 811 only useful to kernel developers. 812 813 debug_objects [KNL] Enable object debugging 814 815 no_debug_objects 816 [KNL] Disable object debugging 817 818 debug_guardpage_minorder= 819 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 820 parameter allows control of the order of pages that will 821 be intentionally kept free (and hence protected) by the 822 buddy allocator. Bigger value increase the probability 823 of catching random memory corruption, but reduce the 824 amount of memory for normal system use. The maximum 825 possible value is MAX_ORDER/2. Setting this parameter 826 to 1 or 2 should be enough to identify most random 827 memory corruption problems caused by bugs in kernel or 828 driver code when a CPU writes to (or reads from) a 829 random memory location. Note that there exists a class 830 of memory corruptions problems caused by buggy H/W or 831 F/W or by drivers badly programing DMA (basically when 832 memory is written at bus level and the CPU MMU is 833 bypassed) which are not detectable by 834 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 835 tracking down these problems. 836 837 debug_pagealloc= 838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 839 enables the feature at boot time. By default, it is 840 disabled and the system will work mostly the same as a 841 kernel built without CONFIG_DEBUG_PAGEALLOC. 842 Note: to get most of debug_pagealloc error reports, it's 843 useful to also enable the page_owner functionality. 844 on: enable the feature 845 846 debugfs= [KNL] This parameter enables what is exposed to userspace 847 and debugfs internal clients. 848 Format: { on, no-mount, off } 849 on: All functions are enabled. 850 no-mount: 851 Filesystem is not registered but kernel clients can 852 access APIs and a crashkernel can be used to read 853 its content. There is nothing to mount. 854 off: Filesystem is not registered and clients 855 get a -EPERM as result when trying to register files 856 or directories within debugfs. 857 This is equivalent of the runtime functionality if 858 debugfs was not enabled in the kernel at all. 859 Default value is set in build-time with a kernel configuration. 860 861 debugpat [X86] Enable PAT debugging 862 863 decnet.addr= [HW,NET] 864 Format: <area>[,<node>] 865 See also Documentation/networking/decnet.rst. 866 867 default_hugepagesz= 868 [HW] The size of the default HugeTLB page. This is 869 the size represented by the legacy /proc/ hugepages 870 APIs. In addition, this is the default hugetlb size 871 used for shmget(), mmap() and mounting hugetlbfs 872 filesystems. If not specified, defaults to the 873 architecture's default huge page size. Huge page 874 sizes are architecture dependent. See also 875 Documentation/admin-guide/mm/hugetlbpage.rst. 876 Format: size[KMG] 877 878 deferred_probe_timeout= 879 [KNL] Debugging option to set a timeout in seconds for 880 deferred probe to give up waiting on dependencies to 881 probe. Only specific dependencies (subsystems or 882 drivers) that have opted in will be ignored. A timeout of 0 883 will timeout at the end of initcalls. This option will also 884 dump out devices still on the deferred probe list after 885 retrying. 886 887 dfltcc= [HW,S390] 888 Format: { on | off | def_only | inf_only | always } 889 on: s390 zlib hardware support for compression on 890 level 1 and decompression (default) 891 off: No s390 zlib hardware support 892 def_only: s390 zlib hardware support for deflate 893 only (compression on level 1) 894 inf_only: s390 zlib hardware support for inflate 895 only (decompression) 896 always: Same as 'on' but ignores the selected compression 897 level always using hardware support (used for debugging) 898 899 dhash_entries= [KNL] 900 Set number of hash buckets for dentry cache. 901 902 disable_1tb_segments [PPC] 903 Disables the use of 1TB hash page table segments. This 904 causes the kernel to fall back to 256MB segments which 905 can be useful when debugging issues that require an SLB 906 miss to occur. 907 908 stress_slb [PPC] 909 Limits the number of kernel SLB entries, and flushes 910 them frequently to increase the rate of SLB faults 911 on kernel addresses. 912 913 disable= [IPV6] 914 See Documentation/networking/ipv6.rst. 915 916 hardened_usercopy= 917 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 918 hardening is enabled for this boot. Hardened 919 usercopy checking is used to protect the kernel 920 from reading or writing beyond known memory 921 allocation boundaries as a proactive defense 922 against bounds-checking flaws in the kernel's 923 copy_to_user()/copy_from_user() interface. 924 on Perform hardened usercopy checks (default). 925 off Disable hardened usercopy checks. 926 927 disable_radix [PPC] 928 Disable RADIX MMU mode on POWER9 929 930 radix_hcall_invalidate=on [PPC/PSERIES] 931 Disable RADIX GTSE feature and use hcall for TLB 932 invalidate. 933 934 disable_tlbie [PPC] 935 Disable TLBIE instruction. Currently does not work 936 with KVM, with HASH MMU, or with coherent accelerators. 937 938 disable_cpu_apicid= [X86,APIC,SMP] 939 Format: <int> 940 The number of initial APIC ID for the 941 corresponding CPU to be disabled at boot, 942 mostly used for the kdump 2nd kernel to 943 disable BSP to wake up multiple CPUs without 944 causing system reset or hang due to sending 945 INIT from AP to BSP. 946 947 perf_v4_pmi= [X86,INTEL] 948 Format: <bool> 949 Disable Intel PMU counter freezing feature. 950 The feature only exists starting from 951 Arch Perfmon v4 (Skylake and newer). 952 953 disable_ddw [PPC/PSERIES] 954 Disable Dynamic DMA Window support. Use this 955 to workaround buggy firmware. 956 957 disable_ipv6= [IPV6] 958 See Documentation/networking/ipv6.rst. 959 960 disable_mtrr_cleanup [X86] 961 The kernel tries to adjust MTRR layout from continuous 962 to discrete, to make X server driver able to add WB 963 entry later. This parameter disables that. 964 965 disable_mtrr_trim [X86, Intel and AMD only] 966 By default the kernel will trim any uncacheable 967 memory out of your available memory pool based on 968 MTRR settings. This parameter disables that behavior, 969 possibly causing your machine to run very slowly. 970 971 disable_timer_pin_1 [X86] 972 Disable PIN 1 of APIC timer 973 Can be useful to work around chipset bugs. 974 975 dis_ucode_ldr [X86] Disable the microcode loader. 976 977 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 978 this option disables the debugging code at boot. 979 980 dma_debug_entries=<number> 981 This option allows to tune the number of preallocated 982 entries for DMA-API debugging code. One entry is 983 required per DMA-API allocation. Use this if the 984 DMA-API debugging code disables itself because the 985 architectural default is too low. 986 987 dma_debug_driver=<driver_name> 988 With this option the DMA-API debugging driver 989 filter feature can be enabled at boot time. Just 990 pass the driver to filter for as the parameter. 991 The filter can be disabled or changed to another 992 driver later using sysfs. 993 994 driver_async_probe= [KNL] 995 List of driver names to be probed asynchronously. 996 Format: <driver_name1>,<driver_name2>... 997 998 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 999 Broken monitors, graphic adapters, KVMs and EDIDless 1000 panels may send no or incorrect EDID data sets. 1001 This parameter allows to specify an EDID data sets 1002 in the /lib/firmware directory that are used instead. 1003 Generic built-in EDID data sets are used, if one of 1004 edid/1024x768.bin, edid/1280x1024.bin, 1005 edid/1680x1050.bin, or edid/1920x1080.bin is given 1006 and no file with the same name exists. Details and 1007 instructions how to build your own EDID data are 1008 available in Documentation/admin-guide/edid.rst. An EDID 1009 data set will only be used for a particular connector, 1010 if its name and a colon are prepended to the EDID 1011 name. Each connector may use a unique EDID data 1012 set by separating the files with a comma. An EDID 1013 data set with no connector name will be used for 1014 any connectors not explicitly specified. 1015 1016 dscc4.setup= [NET] 1017 1018 dt_cpu_ftrs= [PPC] 1019 Format: {"off" | "known"} 1020 Control how the dt_cpu_ftrs device-tree binding is 1021 used for CPU feature discovery and setup (if it 1022 exists). 1023 off: Do not use it, fall back to legacy cpu table. 1024 known: Do not pass through unknown features to guests 1025 or userspace, only those that the kernel is aware of. 1026 1027 dump_apple_properties [X86] 1028 Dump name and content of EFI device properties on 1029 x86 Macs. Useful for driver authors to determine 1030 what data is available or for reverse-engineering. 1031 1032 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1033 <module>.dyndbg[="val"] 1034 Enable debug messages at boot time. See 1035 Documentation/admin-guide/dynamic-debug-howto.rst 1036 for details. 1037 1038 nopku [X86] Disable Memory Protection Keys CPU feature found 1039 in some Intel CPUs. 1040 1041 <module>.async_probe [KNL] 1042 Enable asynchronous probe on this module. 1043 1044 early_ioremap_debug [KNL] 1045 Enable debug messages in early_ioremap support. This 1046 is useful for tracking down temporary early mappings 1047 which are not unmapped. 1048 1049 earlycon= [KNL] Output early console device and options. 1050 1051 When used with no options, the early console is 1052 determined by stdout-path property in device tree's 1053 chosen node or the ACPI SPCR table if supported by 1054 the platform. 1055 1056 cdns,<addr>[,options] 1057 Start an early, polled-mode console on a Cadence 1058 (xuartps) serial port at the specified address. Only 1059 supported option is baud rate. If baud rate is not 1060 specified, the serial port must already be setup and 1061 configured. 1062 1063 uart[8250],io,<addr>[,options] 1064 uart[8250],mmio,<addr>[,options] 1065 uart[8250],mmio32,<addr>[,options] 1066 uart[8250],mmio32be,<addr>[,options] 1067 uart[8250],0x<addr>[,options] 1068 Start an early, polled-mode console on the 8250/16550 1069 UART at the specified I/O port or MMIO address. 1070 MMIO inter-register address stride is either 8-bit 1071 (mmio) or 32-bit (mmio32 or mmio32be). 1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1073 to be equivalent to 'mmio'. 'options' are specified 1074 in the same format described for "console=ttyS<n>"; if 1075 unspecified, the h/w is not initialized. 1076 1077 pl011,<addr> 1078 pl011,mmio32,<addr> 1079 Start an early, polled-mode console on a pl011 serial 1080 port at the specified address. The pl011 serial port 1081 must already be setup and configured. Options are not 1082 yet supported. If 'mmio32' is specified, then only 1083 the driver will use only 32-bit accessors to read/write 1084 the device registers. 1085 1086 meson,<addr> 1087 Start an early, polled-mode console on a meson serial 1088 port at the specified address. The serial port must 1089 already be setup and configured. Options are not yet 1090 supported. 1091 1092 msm_serial,<addr> 1093 Start an early, polled-mode console on an msm serial 1094 port at the specified address. The serial port 1095 must already be setup and configured. Options are not 1096 yet supported. 1097 1098 msm_serial_dm,<addr> 1099 Start an early, polled-mode console on an msm serial 1100 dm port at the specified address. The serial port 1101 must already be setup and configured. Options are not 1102 yet supported. 1103 1104 owl,<addr> 1105 Start an early, polled-mode console on a serial port 1106 of an Actions Semi SoC, such as S500 or S900, at the 1107 specified address. The serial port must already be 1108 setup and configured. Options are not yet supported. 1109 1110 rda,<addr> 1111 Start an early, polled-mode console on a serial port 1112 of an RDA Micro SoC, such as RDA8810PL, at the 1113 specified address. The serial port must already be 1114 setup and configured. Options are not yet supported. 1115 1116 sbi 1117 Use RISC-V SBI (Supervisor Binary Interface) for early 1118 console. 1119 1120 smh Use ARM semihosting calls for early console. 1121 1122 s3c2410,<addr> 1123 s3c2412,<addr> 1124 s3c2440,<addr> 1125 s3c6400,<addr> 1126 s5pv210,<addr> 1127 exynos4210,<addr> 1128 Use early console provided by serial driver available 1129 on Samsung SoCs, requires selecting proper type and 1130 a correct base address of the selected UART port. The 1131 serial port must already be setup and configured. 1132 Options are not yet supported. 1133 1134 lantiq,<addr> 1135 Start an early, polled-mode console on a lantiq serial 1136 (lqasc) port at the specified address. The serial port 1137 must already be setup and configured. Options are not 1138 yet supported. 1139 1140 lpuart,<addr> 1141 lpuart32,<addr> 1142 Use early console provided by Freescale LP UART driver 1143 found on Freescale Vybrid and QorIQ LS1021A processors. 1144 A valid base address must be provided, and the serial 1145 port must already be setup and configured. 1146 1147 ec_imx21,<addr> 1148 ec_imx6q,<addr> 1149 Start an early, polled-mode, output-only console on the 1150 Freescale i.MX UART at the specified address. The UART 1151 must already be setup and configured. 1152 1153 ar3700_uart,<addr> 1154 Start an early, polled-mode console on the 1155 Armada 3700 serial port at the specified 1156 address. The serial port must already be setup 1157 and configured. Options are not yet supported. 1158 1159 qcom_geni,<addr> 1160 Start an early, polled-mode console on a Qualcomm 1161 Generic Interface (GENI) based serial port at the 1162 specified address. The serial port must already be 1163 setup and configured. Options are not yet supported. 1164 1165 efifb,[options] 1166 Start an early, unaccelerated console on the EFI 1167 memory mapped framebuffer (if available). On cache 1168 coherent non-x86 systems that use system memory for 1169 the framebuffer, pass the 'ram' option so that it is 1170 mapped with the correct attributes. 1171 1172 linflex,<addr> 1173 Use early console provided by Freescale LINFlexD UART 1174 serial driver for NXP S32V234 SoCs. A valid base 1175 address must be provided, and the serial port must 1176 already be setup and configured. 1177 1178 earlyprintk= [X86,SH,ARM,M68k,S390] 1179 earlyprintk=vga 1180 earlyprintk=sclp 1181 earlyprintk=xen 1182 earlyprintk=serial[,ttySn[,baudrate]] 1183 earlyprintk=serial[,0x...[,baudrate]] 1184 earlyprintk=ttySn[,baudrate] 1185 earlyprintk=dbgp[debugController#] 1186 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1187 earlyprintk=xdbc[xhciController#] 1188 1189 earlyprintk is useful when the kernel crashes before 1190 the normal console is initialized. It is not enabled by 1191 default because it has some cosmetic problems. 1192 1193 Append ",keep" to not disable it when the real console 1194 takes over. 1195 1196 Only one of vga, efi, serial, or usb debug port can 1197 be used at a time. 1198 1199 Currently only ttyS0 and ttyS1 may be specified by 1200 name. Other I/O ports may be explicitly specified 1201 on some architectures (x86 and arm at least) by 1202 replacing ttySn with an I/O port address, like this: 1203 earlyprintk=serial,0x1008,115200 1204 You can find the port for a given device in 1205 /proc/tty/driver/serial: 1206 2: uart:ST16650V2 port:00001008 irq:18 ... 1207 1208 Interaction with the standard serial driver is not 1209 very good. 1210 1211 The VGA and EFI output is eventually overwritten by 1212 the real console. 1213 1214 The xen output can only be used by Xen PV guests. 1215 1216 The sclp output can only be used on s390. 1217 1218 The optional "force" to "pciserial" enables use of a 1219 PCI device even when its classcode is not of the 1220 UART class. 1221 1222 edac_report= [HW,EDAC] Control how to report EDAC event 1223 Format: {"on" | "off" | "force"} 1224 on: enable EDAC to report H/W event. May be overridden 1225 by other higher priority error reporting module. 1226 off: disable H/W event reporting through EDAC. 1227 force: enforce the use of EDAC to report H/W event. 1228 default: on. 1229 1230 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1231 ekgdboc=kbd 1232 1233 This is designed to be used in conjunction with 1234 the boot argument: earlyprintk=vga 1235 1236 This parameter works in place of the kgdboc parameter 1237 but can only be used if the backing tty is available 1238 very early in the boot process. For early debugging 1239 via a serial port see kgdboc_earlycon instead. 1240 1241 edd= [EDD] 1242 Format: {"off" | "on" | "skip[mbr]"} 1243 1244 efi= [EFI] 1245 Format: { "debug", "disable_early_pci_dma", 1246 "nochunk", "noruntime", "nosoftreserve", 1247 "novamap", "no_disable_early_pci_dma" } 1248 debug: enable misc debug output. 1249 disable_early_pci_dma: disable the busmaster bit on all 1250 PCI bridges while in the EFI boot stub. 1251 nochunk: disable reading files in "chunks" in the EFI 1252 boot stub, as chunking can cause problems with some 1253 firmware implementations. 1254 noruntime : disable EFI runtime services support 1255 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1256 attribute may cause the kernel to reserve the 1257 memory range for a memory mapping driver to 1258 claim. Specify efi=nosoftreserve to disable this 1259 reservation and treat the memory by its base type 1260 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1261 novamap: do not call SetVirtualAddressMap(). 1262 no_disable_early_pci_dma: Leave the busmaster bit set 1263 on all PCI bridges while in the EFI boot stub 1264 1265 efi_no_storage_paranoia [EFI; X86] 1266 Using this parameter you can use more than 50% of 1267 your efi variable storage. Use this parameter only if 1268 you are really sure that your UEFI does sane gc and 1269 fulfills the spec otherwise your board may brick. 1270 1271 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1272 Add arbitrary attribute to specific memory range by 1273 updating original EFI memory map. 1274 Region of memory which aa attribute is added to is 1275 from ss to ss+nn. 1276 1277 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1278 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1279 attribute is added to range 0x100000000-0x180000000 and 1280 0x10a0000000-0x1120000000. 1281 1282 If efi_fake_mem=8G@9G:0x40000 is specified, the 1283 EFI_MEMORY_SP(0x40000) attribute is added to 1284 range 0x240000000-0x43fffffff. 1285 1286 Using this parameter you can do debugging of EFI memmap 1287 related features. For example, you can do debugging of 1288 Address Range Mirroring feature even if your box 1289 doesn't support it, or mark specific memory as 1290 "soft reserved". 1291 1292 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1293 that is to be dynamically loaded by Linux. If there are 1294 multiple variables with the same name but with different 1295 vendor GUIDs, all of them will be loaded. See 1296 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1297 1298 1299 eisa_irq_edge= [PARISC,HW] 1300 See header of drivers/parisc/eisa.c. 1301 1302 elanfreq= [X86-32] 1303 See comment before function elanfreq_setup() in 1304 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1305 1306 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1307 Specifies physical address of start of kernel core 1308 image elf header and optionally the size. Generally 1309 kexec loader will pass this option to capture kernel. 1310 See Documentation/admin-guide/kdump/kdump.rst for details. 1311 1312 enable_mtrr_cleanup [X86] 1313 The kernel tries to adjust MTRR layout from continuous 1314 to discrete, to make X server driver able to add WB 1315 entry later. This parameter enables that. 1316 1317 enable_timer_pin_1 [X86] 1318 Enable PIN 1 of APIC timer 1319 Can be useful to work around chipset bugs 1320 (in particular on some ATI chipsets). 1321 The kernel tries to set a reasonable default. 1322 1323 enforcing [SELINUX] Set initial enforcing status. 1324 Format: {"0" | "1"} 1325 See security/selinux/Kconfig help text. 1326 0 -- permissive (log only, no denials). 1327 1 -- enforcing (deny and log). 1328 Default value is 0. 1329 Value can be changed at runtime via 1330 /sys/fs/selinux/enforce. 1331 1332 erst_disable [ACPI] 1333 Disable Error Record Serialization Table (ERST) 1334 support. 1335 1336 ether= [HW,NET] Ethernet cards parameters 1337 This option is obsoleted by the "netdev=" option, which 1338 has equivalent usage. See its documentation for details. 1339 1340 evm= [EVM] 1341 Format: { "fix" } 1342 Permit 'security.evm' to be updated regardless of 1343 current integrity status. 1344 1345 failslab= 1346 fail_usercopy= 1347 fail_page_alloc= 1348 fail_make_request=[KNL] 1349 General fault injection mechanism. 1350 Format: <interval>,<probability>,<space>,<times> 1351 See also Documentation/fault-injection/. 1352 1353 floppy= [HW] 1354 See Documentation/admin-guide/blockdev/floppy.rst. 1355 1356 force_pal_cache_flush 1357 [IA-64] Avoid check_sal_cache_flush which may hang on 1358 buggy SAL_CACHE_FLUSH implementations. Using this 1359 parameter will force ia64_sal_cache_flush to call 1360 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1361 1362 forcepae [X86-32] 1363 Forcefully enable Physical Address Extension (PAE). 1364 Many Pentium M systems disable PAE but may have a 1365 functionally usable PAE implementation. 1366 Warning: use of this parameter will taint the kernel 1367 and may cause unknown problems. 1368 1369 ftrace=[tracer] 1370 [FTRACE] will set and start the specified tracer 1371 as early as possible in order to facilitate early 1372 boot debugging. 1373 1374 ftrace_dump_on_oops[=orig_cpu] 1375 [FTRACE] will dump the trace buffers on oops. 1376 If no parameter is passed, ftrace will dump 1377 buffers of all CPUs, but if you pass orig_cpu, it will 1378 dump only the buffer of the CPU that triggered the 1379 oops. 1380 1381 ftrace_filter=[function-list] 1382 [FTRACE] Limit the functions traced by the function 1383 tracer at boot up. function-list is a comma separated 1384 list of functions. This list can be changed at run 1385 time by the set_ftrace_filter file in the debugfs 1386 tracing directory. 1387 1388 ftrace_notrace=[function-list] 1389 [FTRACE] Do not trace the functions specified in 1390 function-list. This list can be changed at run time 1391 by the set_ftrace_notrace file in the debugfs 1392 tracing directory. 1393 1394 ftrace_graph_filter=[function-list] 1395 [FTRACE] Limit the top level callers functions traced 1396 by the function graph tracer at boot up. 1397 function-list is a comma separated list of functions 1398 that can be changed at run time by the 1399 set_graph_function file in the debugfs tracing directory. 1400 1401 ftrace_graph_notrace=[function-list] 1402 [FTRACE] Do not trace from the functions specified in 1403 function-list. This list is a comma separated list of 1404 functions that can be changed at run time by the 1405 set_graph_notrace file in the debugfs tracing directory. 1406 1407 ftrace_graph_max_depth=<uint> 1408 [FTRACE] Used with the function graph tracer. This is 1409 the max depth it will trace into a function. This value 1410 can be changed at run time by the max_graph_depth file 1411 in the tracefs tracing directory. default: 0 (no limit) 1412 1413 fw_devlink= [KNL] Create device links between consumer and supplier 1414 devices by scanning the firmware to infer the 1415 consumer/supplier relationships. This feature is 1416 especially useful when drivers are loaded as modules as 1417 it ensures proper ordering of tasks like device probing 1418 (suppliers first, then consumers), supplier boot state 1419 clean up (only after all consumers have probed), 1420 suspend/resume & runtime PM (consumers first, then 1421 suppliers). 1422 Format: { off | permissive | on | rpm } 1423 off -- Don't create device links from firmware info. 1424 permissive -- Create device links from firmware info 1425 but use it only for ordering boot state clean 1426 up (sync_state() calls). 1427 on -- Create device links from firmware info and use it 1428 to enforce probe and suspend/resume ordering. 1429 rpm -- Like "on", but also use to order runtime PM. 1430 1431 gamecon.map[2|3]= 1432 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1433 support via parallel port (up to 5 devices per port) 1434 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1435 See also Documentation/input/devices/joystick-parport.rst 1436 1437 gamma= [HW,DRM] 1438 1439 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1440 Format: off | on 1441 default: on 1442 1443 gcov_persist= [GCOV] When non-zero (default), profiling data for 1444 kernel modules is saved and remains accessible via 1445 debugfs, even when the module is unloaded/reloaded. 1446 When zero, profiling data is discarded and associated 1447 debugfs files are removed at module unload time. 1448 1449 goldfish [X86] Enable the goldfish android emulator platform. 1450 Don't use this when you are not running on the 1451 android emulator 1452 1453 gpt [EFI] Forces disk with valid GPT signature but 1454 invalid Protective MBR to be treated as GPT. If the 1455 primary GPT is corrupted, it enables the backup/alternate 1456 GPT to be used instead. 1457 1458 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1459 the "Enable 0" bit of the configuration register. 1460 Format: 0 | 1 1461 Default: 0 1462 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1463 the "Enable 0" bit of the configuration register. 1464 Format: 0 | 1 1465 Default: 0 1466 grcan.select= [HW] Select which physical interface to use. 1467 Format: 0 | 1 1468 Default: 0 1469 grcan.txsize= [HW] Sets the size of the tx buffer. 1470 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1471 Default: 1024 1472 grcan.rxsize= [HW] Sets the size of the rx buffer. 1473 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1474 Default: 1024 1475 1476 gpio-mockup.gpio_mockup_ranges 1477 [HW] Sets the ranges of gpiochip of for this device. 1478 Format: <start1>,<end1>,<start2>,<end2>... 1479 1480 hardlockup_all_cpu_backtrace= 1481 [KNL] Should the hard-lockup detector generate 1482 backtraces on all cpus. 1483 Format: 0 | 1 1484 1485 hashdist= [KNL,NUMA] Large hashes allocated during boot 1486 are distributed across NUMA nodes. Defaults on 1487 for 64-bit NUMA, off otherwise. 1488 Format: 0 | 1 (for off | on) 1489 1490 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1491 1492 hd= [EIDE] (E)IDE hard drive subsystem geometry 1493 Format: <cyl>,<head>,<sect> 1494 1495 hest_disable [ACPI] 1496 Disable Hardware Error Source Table (HEST) support; 1497 corresponding firmware-first mode error processing 1498 logic will be disabled. 1499 1500 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1501 size of <nn>. This works even on boxes that have no 1502 highmem otherwise. This also works to reduce highmem 1503 size on bigger boxes. 1504 1505 highres= [KNL] Enable/disable high resolution timer mode. 1506 Valid parameters: "on", "off" 1507 Default: "on" 1508 1509 hlt [BUGS=ARM,SH] 1510 1511 hpet= [X86-32,HPET] option to control HPET usage 1512 Format: { enable (default) | disable | force | 1513 verbose } 1514 disable: disable HPET and use PIT instead 1515 force: allow force enabled of undocumented chips (ICH4, 1516 VIA, nVidia) 1517 verbose: show contents of HPET registers during setup 1518 1519 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1520 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1521 1522 hugetlb_cma= [HW] The size of a cma area used for allocation 1523 of gigantic hugepages. 1524 Format: nn[KMGTPE] 1525 1526 Reserve a cma area of given size and allocate gigantic 1527 hugepages using the cma allocator. If enabled, the 1528 boot-time allocation of gigantic hugepages is skipped. 1529 1530 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1531 If this follows hugepagesz (below), it specifies 1532 the number of pages of hugepagesz to be allocated. 1533 If this is the first HugeTLB parameter on the command 1534 line, it specifies the number of pages to allocate for 1535 the default huge page size. See also 1536 Documentation/admin-guide/mm/hugetlbpage.rst. 1537 Format: <integer> 1538 1539 hugepagesz= 1540 [HW] The size of the HugeTLB pages. This is used in 1541 conjunction with hugepages (above) to allocate huge 1542 pages of a specific size at boot. The pair 1543 hugepagesz=X hugepages=Y can be specified once for 1544 each supported huge page size. Huge page sizes are 1545 architecture dependent. See also 1546 Documentation/admin-guide/mm/hugetlbpage.rst. 1547 Format: size[KMG] 1548 1549 hung_task_panic= 1550 [KNL] Should the hung task detector generate panics. 1551 Format: 0 | 1 1552 1553 A value of 1 instructs the kernel to panic when a 1554 hung task is detected. The default value is controlled 1555 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1556 option. The value selected by this boot parameter can 1557 be changed later by the kernel.hung_task_panic sysctl. 1558 1559 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1560 terminal devices. Valid values: 0..8 1561 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1562 If specified, z/VM IUCV HVC accepts connections 1563 from listed z/VM user IDs only. 1564 1565 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1566 which allow the hypervisor to 'idle' the 1567 guest on lock contention. 1568 1569 keep_bootcon [KNL] 1570 Do not unregister boot console at start. This is only 1571 useful for debugging when something happens in the window 1572 between unregistering the boot console and initializing 1573 the real console. 1574 1575 i2c_bus= [HW] Override the default board specific I2C bus speed 1576 or register an additional I2C bus that is not 1577 registered from board initialization code. 1578 Format: 1579 <bus_id>,<clkrate> 1580 1581 i8042.debug [HW] Toggle i8042 debug mode 1582 i8042.unmask_kbd_data 1583 [HW] Enable printing of interrupt data from the KBD port 1584 (disabled by default, and as a pre-condition 1585 requires that i8042.debug=1 be enabled) 1586 i8042.direct [HW] Put keyboard port into non-translated mode 1587 i8042.dumbkbd [HW] Pretend that controller can only read data from 1588 keyboard and cannot control its state 1589 (Don't attempt to blink the leds) 1590 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1591 i8042.nokbd [HW] Don't check/create keyboard port 1592 i8042.noloop [HW] Disable the AUX Loopback command while probing 1593 for the AUX port 1594 i8042.nomux [HW] Don't check presence of an active multiplexing 1595 controller 1596 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1597 controllers 1598 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1599 i8042.reset [HW] Reset the controller during init, cleanup and 1600 suspend-to-ram transitions, only during s2r 1601 transitions, or never reset 1602 Format: { 1 | Y | y | 0 | N | n } 1603 1, Y, y: always reset controller 1604 0, N, n: don't ever reset controller 1605 Default: only on s2r transitions on x86; most other 1606 architectures force reset to be always executed 1607 i8042.unlock [HW] Unlock (ignore) the keylock 1608 i8042.kbdreset [HW] Reset device connected to KBD port 1609 1610 i810= [HW,DRM] 1611 1612 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1613 indicates that the driver is running on unsupported 1614 hardware. 1615 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1616 does not match list of supported models. 1617 i8k.power_status 1618 [HW] Report power status in /proc/i8k 1619 (disabled by default) 1620 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1621 capability is set. 1622 1623 i915.invert_brightness= 1624 [DRM] Invert the sense of the variable that is used to 1625 set the brightness of the panel backlight. Normally a 1626 brightness value of 0 indicates backlight switched off, 1627 and the maximum of the brightness value sets the backlight 1628 to maximum brightness. If this parameter is set to 0 1629 (default) and the machine requires it, or this parameter 1630 is set to 1, a brightness value of 0 sets the backlight 1631 to maximum brightness, and the maximum of the brightness 1632 value switches the backlight off. 1633 -1 -- never invert brightness 1634 0 -- machine default 1635 1 -- force brightness inversion 1636 1637 icn= [HW,ISDN] 1638 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1639 1640 ide-core.nodma= [HW] (E)IDE subsystem 1641 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1642 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1643 .cdrom .chs .ignore_cable are additional options 1644 See Documentation/ide/ide.rst. 1645 1646 ide-generic.probe-mask= [HW] (E)IDE subsystem 1647 Format: <int> 1648 Probe mask for legacy ISA IDE ports. Depending on 1649 platform up to 6 ports are supported, enabled by 1650 setting corresponding bits in the mask to 1. The 1651 default value is 0x0, which has a special meaning. 1652 On systems that have PCI, it triggers scanning the 1653 PCI bus for the first and the second port, which 1654 are then probed. On systems without PCI the value 1655 of 0x0 enables probing the two first ports as if it 1656 was 0x3. 1657 1658 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1659 Claim all unknown PCI IDE storage controllers. 1660 1661 idle= [X86] 1662 Format: idle=poll, idle=halt, idle=nomwait 1663 Poll forces a polling idle loop that can slightly 1664 improve the performance of waking up a idle CPU, but 1665 will use a lot of power and make the system run hot. 1666 Not recommended. 1667 idle=halt: Halt is forced to be used for CPU idle. 1668 In such case C2/C3 won't be used again. 1669 idle=nomwait: Disable mwait for CPU C-states 1670 1671 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1672 Format: { strict | legacy | 2008 | relaxed } 1673 Default: strict 1674 1675 Choose which programs will be accepted for execution 1676 based on the IEEE 754 NaN encoding(s) supported by 1677 the FPU and the NaN encoding requested with the value 1678 of an ELF file header flag individually set by each 1679 binary. Hardware implementations are permitted to 1680 support either or both of the legacy and the 2008 NaN 1681 encoding mode. 1682 1683 Available settings are as follows: 1684 strict accept binaries that request a NaN encoding 1685 supported by the FPU 1686 legacy only accept legacy-NaN binaries, if supported 1687 by the FPU 1688 2008 only accept 2008-NaN binaries, if supported 1689 by the FPU 1690 relaxed accept any binaries regardless of whether 1691 supported by the FPU 1692 1693 The FPU emulator is always able to support both NaN 1694 encodings, so if no FPU hardware is present or it has 1695 been disabled with 'nofpu', then the settings of 1696 'legacy' and '2008' strap the emulator accordingly, 1697 'relaxed' straps the emulator for both legacy-NaN and 1698 2008-NaN, whereas 'strict' enables legacy-NaN only on 1699 legacy processors and both NaN encodings on MIPS32 or 1700 MIPS64 CPUs. 1701 1702 The setting for ABS.fmt/NEG.fmt instruction execution 1703 mode generally follows that for the NaN encoding, 1704 except where unsupported by hardware. 1705 1706 ignore_loglevel [KNL] 1707 Ignore loglevel setting - this will print /all/ 1708 kernel messages to the console. Useful for debugging. 1709 We also add it as printk module parameter, so users 1710 could change it dynamically, usually by 1711 /sys/module/printk/parameters/ignore_loglevel. 1712 1713 ignore_rlimit_data 1714 Ignore RLIMIT_DATA setting for data mappings, 1715 print warning at first misuse. Can be changed via 1716 /sys/module/kernel/parameters/ignore_rlimit_data. 1717 1718 ihash_entries= [KNL] 1719 Set number of hash buckets for inode cache. 1720 1721 ima_appraise= [IMA] appraise integrity measurements 1722 Format: { "off" | "enforce" | "fix" | "log" } 1723 default: "enforce" 1724 1725 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1726 The builtin appraise policy appraises all files 1727 owned by uid=0. 1728 1729 ima_canonical_fmt [IMA] 1730 Use the canonical format for the binary runtime 1731 measurements, instead of host native format. 1732 1733 ima_hash= [IMA] 1734 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1735 | sha512 | ... } 1736 default: "sha1" 1737 1738 The list of supported hash algorithms is defined 1739 in crypto/hash_info.h. 1740 1741 ima_policy= [IMA] 1742 The builtin policies to load during IMA setup. 1743 Format: "tcb | appraise_tcb | secure_boot | 1744 fail_securely" 1745 1746 The "tcb" policy measures all programs exec'd, files 1747 mmap'd for exec, and all files opened with the read 1748 mode bit set by either the effective uid (euid=0) or 1749 uid=0. 1750 1751 The "appraise_tcb" policy appraises the integrity of 1752 all files owned by root. 1753 1754 The "secure_boot" policy appraises the integrity 1755 of files (eg. kexec kernel image, kernel modules, 1756 firmware, policy, etc) based on file signatures. 1757 1758 The "fail_securely" policy forces file signature 1759 verification failure also on privileged mounted 1760 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1761 flag. 1762 1763 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1764 Load a policy which meets the needs of the Trusted 1765 Computing Base. This means IMA will measure all 1766 programs exec'd, files mmap'd for exec, and all files 1767 opened for read by uid=0. 1768 1769 ima_template= [IMA] 1770 Select one of defined IMA measurements template formats. 1771 Formats: { "ima" | "ima-ng" | "ima-sig" } 1772 Default: "ima-ng" 1773 1774 ima_template_fmt= 1775 [IMA] Define a custom template format. 1776 Format: { "field1|...|fieldN" } 1777 1778 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1779 Format: <min_file_size> 1780 Set the minimal file size for using asynchronous hash. 1781 If left unspecified, ahash usage is disabled. 1782 1783 ahash performance varies for different data sizes on 1784 different crypto accelerators. This option can be used 1785 to achieve the best performance for a particular HW. 1786 1787 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1788 Format: <bufsize> 1789 Set hashing buffer size. Default: 4k. 1790 1791 ahash performance varies for different chunk sizes on 1792 different crypto accelerators. This option can be used 1793 to achieve best performance for particular HW. 1794 1795 init= [KNL] 1796 Format: <full_path> 1797 Run specified binary instead of /sbin/init as init 1798 process. 1799 1800 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1801 for working out where the kernel is dying during 1802 startup. 1803 1804 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1805 initcall functions. Useful for debugging built-in 1806 modules and initcalls. 1807 1808 initrd= [BOOT] Specify the location of the initial ramdisk 1809 1810 initrdmem= [KNL] Specify a physical address and size from which to 1811 load the initrd. If an initrd is compiled in or 1812 specified in the bootparams, it takes priority over this 1813 setting. 1814 Format: ss[KMG],nn[KMG] 1815 Default is 0, 0 1816 1817 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1818 zeroes. 1819 Format: 0 | 1 1820 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1821 1822 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1823 Format: 0 | 1 1824 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1825 1826 init_pkru= [X86] Specify the default memory protection keys rights 1827 register contents for all processes. 0x55555554 by 1828 default (disallow access to all but pkey 0). Can 1829 override in debugfs after boot. 1830 1831 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1832 Format: <irq> 1833 1834 int_pln_enable [X86] Enable power limit notification interrupt 1835 1836 integrity_audit=[IMA] 1837 Format: { "0" | "1" } 1838 0 -- basic integrity auditing messages. (Default) 1839 1 -- additional integrity auditing messages. 1840 1841 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1842 on 1843 Enable intel iommu driver. 1844 off 1845 Disable intel iommu driver. 1846 igfx_off [Default Off] 1847 By default, gfx is mapped as normal device. If a gfx 1848 device has a dedicated DMAR unit, the DMAR unit is 1849 bypassed by not enabling DMAR with this option. In 1850 this case, gfx device will use physical address for 1851 DMA. 1852 forcedac [X86-64] 1853 With this option iommu will not optimize to look 1854 for io virtual address below 32-bit forcing dual 1855 address cycle on pci bus for cards supporting greater 1856 than 32-bit addressing. The default is to look 1857 for translation below 32-bit and if not available 1858 then look in the higher range. 1859 strict [Default Off] 1860 With this option on every unmap_single operation will 1861 result in a hardware IOTLB flush operation as opposed 1862 to batching them for performance. 1863 sp_off [Default Off] 1864 By default, super page will be supported if Intel IOMMU 1865 has the capability. With this option, super page will 1866 not be supported. 1867 sm_on [Default Off] 1868 By default, scalable mode will be disabled even if the 1869 hardware advertises that it has support for the scalable 1870 mode translation. With this option set, scalable mode 1871 will be used on hardware which claims to support it. 1872 tboot_noforce [Default Off] 1873 Do not force the Intel IOMMU enabled under tboot. 1874 By default, tboot will force Intel IOMMU on, which 1875 could harm performance of some high-throughput 1876 devices like 40GBit network cards, even if identity 1877 mapping is enabled. 1878 Note that using this option lowers the security 1879 provided by tboot because it makes the system 1880 vulnerable to DMA attacks. 1881 nobounce [Default off] 1882 Disable bounce buffer for untrusted devices such as 1883 the Thunderbolt devices. This will treat the untrusted 1884 devices as the trusted ones, hence might expose security 1885 risks of DMA attacks. 1886 1887 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1888 0 disables intel_idle and fall back on acpi_idle. 1889 1 to 9 specify maximum depth of C-state. 1890 1891 intel_pstate= [X86] 1892 disable 1893 Do not enable intel_pstate as the default 1894 scaling driver for the supported processors 1895 passive 1896 Use intel_pstate as a scaling driver, but configure it 1897 to work with generic cpufreq governors (instead of 1898 enabling its internal governor). This mode cannot be 1899 used along with the hardware-managed P-states (HWP) 1900 feature. 1901 force 1902 Enable intel_pstate on systems that prohibit it by default 1903 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1904 instead of acpi-cpufreq may disable platform features, such 1905 as thermal controls and power capping, that rely on ACPI 1906 P-States information being indicated to OSPM and therefore 1907 should be used with caution. This option does not work with 1908 processors that aren't supported by the intel_pstate driver 1909 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1910 no_hwp 1911 Do not enable hardware P state control (HWP) 1912 if available. 1913 hwp_only 1914 Only load intel_pstate on systems which support 1915 hardware P state control (HWP) if available. 1916 support_acpi_ppc 1917 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1918 Description Table, specifies preferred power management 1919 profile as "Enterprise Server" or "Performance Server", 1920 then this feature is turned on by default. 1921 per_cpu_perf_limits 1922 Allow per-logical-CPU P-State performance control limits using 1923 cpufreq sysfs interface 1924 1925 intremap= [X86-64, Intel-IOMMU] 1926 on enable Interrupt Remapping (default) 1927 off disable Interrupt Remapping 1928 nosid disable Source ID checking 1929 no_x2apic_optout 1930 BIOS x2APIC opt-out request will be ignored 1931 nopost disable Interrupt Posting 1932 1933 iomem= Disable strict checking of access to MMIO memory 1934 strict regions from userspace. 1935 relaxed 1936 1937 iommu= [X86] 1938 off 1939 force 1940 noforce 1941 biomerge 1942 panic 1943 nopanic 1944 merge 1945 nomerge 1946 soft 1947 pt [X86] 1948 nopt [X86] 1949 nobypass [PPC/POWERNV] 1950 Disable IOMMU bypass, using IOMMU for PCI devices. 1951 1952 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1953 Format: { "0" | "1" } 1954 0 - Lazy mode. 1955 Request that DMA unmap operations use deferred 1956 invalidation of hardware TLBs, for increased 1957 throughput at the cost of reduced device isolation. 1958 Will fall back to strict mode if not supported by 1959 the relevant IOMMU driver. 1960 1 - Strict mode (default). 1961 DMA unmap operations invalidate IOMMU hardware TLBs 1962 synchronously. 1963 1964 iommu.passthrough= 1965 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1966 Format: { "0" | "1" } 1967 0 - Use IOMMU translation for DMA. 1968 1 - Bypass the IOMMU for DMA. 1969 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1970 1971 io7= [HW] IO7 for Marvel-based Alpha systems 1972 See comment before marvel_specify_io7 in 1973 arch/alpha/kernel/core_marvel.c. 1974 1975 io_delay= [X86] I/O delay method 1976 0x80 1977 Standard port 0x80 based delay 1978 0xed 1979 Alternate port 0xed based delay (needed on some systems) 1980 udelay 1981 Simple two microseconds delay 1982 none 1983 No delay 1984 1985 ip= [IP_PNP] 1986 See Documentation/admin-guide/nfs/nfsroot.rst. 1987 1988 ipcmni_extend [KNL] Extend the maximum number of unique System V 1989 IPC identifiers from 32,768 to 16,777,216. 1990 1991 irqaffinity= [SMP] Set the default irq affinity mask 1992 The argument is a cpu list, as described above. 1993 1994 irqchip.gicv2_force_probe= 1995 [ARM, ARM64] 1996 Format: <bool> 1997 Force the kernel to look for the second 4kB page 1998 of a GICv2 controller even if the memory range 1999 exposed by the device tree is too small. 2000 2001 irqchip.gicv3_nolpi= 2002 [ARM, ARM64] 2003 Force the kernel to ignore the availability of 2004 LPIs (and by consequence ITSs). Intended for system 2005 that use the kernel as a bootloader, and thus want 2006 to let secondary kernels in charge of setting up 2007 LPIs. 2008 2009 irqchip.gicv3_pseudo_nmi= [ARM64] 2010 Enables support for pseudo-NMIs in the kernel. This 2011 requires the kernel to be built with 2012 CONFIG_ARM64_PSEUDO_NMI. 2013 2014 irqfixup [HW] 2015 When an interrupt is not handled search all handlers 2016 for it. Intended to get systems with badly broken 2017 firmware running. 2018 2019 irqpoll [HW] 2020 When an interrupt is not handled search all handlers 2021 for it. Also check all handlers each timer 2022 interrupt. Intended to get systems with badly broken 2023 firmware running. 2024 2025 isapnp= [ISAPNP] 2026 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2027 2028 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2029 [Deprecated - use cpusets instead] 2030 Format: [flag-list,]<cpu-list> 2031 2032 Specify one or more CPUs to isolate from disturbances 2033 specified in the flag list (default: domain): 2034 2035 nohz 2036 Disable the tick when a single task runs. 2037 2038 A residual 1Hz tick is offloaded to workqueues, which you 2039 need to affine to housekeeping through the global 2040 workqueue's affinity configured via the 2041 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2042 by using the 'domain' flag described below. 2043 2044 NOTE: by default the global workqueue runs on all CPUs, 2045 so to protect individual CPUs the 'cpumask' file has to 2046 be configured manually after bootup. 2047 2048 domain 2049 Isolate from the general SMP balancing and scheduling 2050 algorithms. Note that performing domain isolation this way 2051 is irreversible: it's not possible to bring back a CPU to 2052 the domains once isolated through isolcpus. It's strongly 2053 advised to use cpusets instead to disable scheduler load 2054 balancing through the "cpuset.sched_load_balance" file. 2055 It offers a much more flexible interface where CPUs can 2056 move in and out of an isolated set anytime. 2057 2058 You can move a process onto or off an "isolated" CPU via 2059 the CPU affinity syscalls or cpuset. 2060 <cpu number> begins at 0 and the maximum value is 2061 "number of CPUs in system - 1". 2062 2063 managed_irq 2064 2065 Isolate from being targeted by managed interrupts 2066 which have an interrupt mask containing isolated 2067 CPUs. The affinity of managed interrupts is 2068 handled by the kernel and cannot be changed via 2069 the /proc/irq/* interfaces. 2070 2071 This isolation is best effort and only effective 2072 if the automatically assigned interrupt mask of a 2073 device queue contains isolated and housekeeping 2074 CPUs. If housekeeping CPUs are online then such 2075 interrupts are directed to the housekeeping CPU 2076 so that IO submitted on the housekeeping CPU 2077 cannot disturb the isolated CPU. 2078 2079 If a queue's affinity mask contains only isolated 2080 CPUs then this parameter has no effect on the 2081 interrupt routing decision, though interrupts are 2082 only delivered when tasks running on those 2083 isolated CPUs submit IO. IO submitted on 2084 housekeeping CPUs has no influence on those 2085 queues. 2086 2087 The format of <cpu-list> is described above. 2088 2089 iucv= [HW,NET] 2090 2091 ivrs_ioapic [HW,X86-64] 2092 Provide an override to the IOAPIC-ID<->DEVICE-ID 2093 mapping provided in the IVRS ACPI table. For 2094 example, to map IOAPIC-ID decimal 10 to 2095 PCI device 00:14.0 write the parameter as: 2096 ivrs_ioapic[10]=00:14.0 2097 2098 ivrs_hpet [HW,X86-64] 2099 Provide an override to the HPET-ID<->DEVICE-ID 2100 mapping provided in the IVRS ACPI table. For 2101 example, to map HPET-ID decimal 0 to 2102 PCI device 00:14.0 write the parameter as: 2103 ivrs_hpet[0]=00:14.0 2104 2105 ivrs_acpihid [HW,X86-64] 2106 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2107 mapping provided in the IVRS ACPI table. For 2108 example, to map UART-HID:UID AMD0020:0 to 2109 PCI device 00:14.5 write the parameter as: 2110 ivrs_acpihid[00:14.5]=AMD0020:0 2111 2112 js= [HW,JOY] Analog joystick 2113 See Documentation/input/joydev/joystick.rst. 2114 2115 nokaslr [KNL] 2116 When CONFIG_RANDOMIZE_BASE is set, this disables 2117 kernel and module base offset ASLR (Address Space 2118 Layout Randomization). 2119 2120 kasan_multi_shot 2121 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2122 report on every invalid memory access. Without this 2123 parameter KASAN will print report only for the first 2124 invalid access. 2125 2126 keepinitrd [HW,ARM] 2127 2128 kernelcore= [KNL,X86,IA-64,PPC] 2129 Format: nn[KMGTPE] | nn% | "mirror" 2130 This parameter specifies the amount of memory usable by 2131 the kernel for non-movable allocations. The requested 2132 amount is spread evenly throughout all nodes in the 2133 system as ZONE_NORMAL. The remaining memory is used for 2134 movable memory in its own zone, ZONE_MOVABLE. In the 2135 event, a node is too small to have both ZONE_NORMAL and 2136 ZONE_MOVABLE, kernelcore memory will take priority and 2137 other nodes will have a larger ZONE_MOVABLE. 2138 2139 ZONE_MOVABLE is used for the allocation of pages that 2140 may be reclaimed or moved by the page migration 2141 subsystem. Note that allocations like PTEs-from-HighMem 2142 still use the HighMem zone if it exists, and the Normal 2143 zone if it does not. 2144 2145 It is possible to specify the exact amount of memory in 2146 the form of "nn[KMGTPE]", a percentage of total system 2147 memory in the form of "nn%", or "mirror". If "mirror" 2148 option is specified, mirrored (reliable) memory is used 2149 for non-movable allocations and remaining memory is used 2150 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2151 are exclusive, so you cannot specify multiple forms. 2152 2153 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2154 Format: <Controller#>[,poll interval] 2155 The controller # is the number of the ehci usb debug 2156 port as it is probed via PCI. The poll interval is 2157 optional and is the number seconds in between 2158 each poll cycle to the debug port in case you need 2159 the functionality for interrupting the kernel with 2160 gdb or control-c on the dbgp connection. When 2161 not using this parameter you use sysrq-g to break into 2162 the kernel debugger. 2163 2164 kgdboc= [KGDB,HW] kgdb over consoles. 2165 Requires a tty driver that supports console polling, 2166 or a supported polling keyboard driver (non-usb). 2167 Serial only format: <serial_device>[,baud] 2168 keyboard only format: kbd 2169 keyboard and serial format: kbd,<serial_device>[,baud] 2170 Optional Kernel mode setting: 2171 kms, kbd format: kms,kbd 2172 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2173 2174 kgdboc_earlycon= [KGDB,HW] 2175 If the boot console provides the ability to read 2176 characters and can work in polling mode, you can use 2177 this parameter to tell kgdb to use it as a backend 2178 until the normal console is registered. Intended to 2179 be used together with the kgdboc parameter which 2180 specifies the normal console to transition to. 2181 2182 The name of the early console should be specified 2183 as the value of this parameter. Note that the name of 2184 the early console might be different than the tty 2185 name passed to kgdboc. It's OK to leave the value 2186 blank and the first boot console that implements 2187 read() will be picked. 2188 2189 kgdbwait [KGDB] Stop kernel execution and enter the 2190 kernel debugger at the earliest opportunity. 2191 2192 kmac= [MIPS] Korina ethernet MAC address. 2193 Configure the RouterBoard 532 series on-chip 2194 Ethernet adapter MAC address. 2195 2196 kmemleak= [KNL] Boot-time kmemleak enable/disable 2197 Valid arguments: on, off 2198 Default: on 2199 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2200 the default is off. 2201 2202 kprobe_event=[probe-list] 2203 [FTRACE] Add kprobe events and enable at boot time. 2204 The probe-list is a semicolon delimited list of probe 2205 definitions. Each definition is same as kprobe_events 2206 interface, but the parameters are comma delimited. 2207 For example, to add a kprobe event on vfs_read with 2208 arg1 and arg2, add to the command line; 2209 2210 kprobe_event=p,vfs_read,$arg1,$arg2 2211 2212 See also Documentation/trace/kprobetrace.rst "Kernel 2213 Boot Parameter" section. 2214 2215 kpti= [ARM64] Control page table isolation of user 2216 and kernel address spaces. 2217 Default: enabled on cores which need mitigation. 2218 0: force disabled 2219 1: force enabled 2220 2221 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2222 Default is 0 (don't ignore, but inject #GP) 2223 2224 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2225 Default is false (don't support). 2226 2227 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2228 KVM MMU at runtime. 2229 Default is 0 (off) 2230 2231 kvm.nx_huge_pages= 2232 [KVM] Controls the software workaround for the 2233 X86_BUG_ITLB_MULTIHIT bug. 2234 force : Always deploy workaround. 2235 off : Never deploy workaround. 2236 auto : Deploy workaround based on the presence of 2237 X86_BUG_ITLB_MULTIHIT. 2238 2239 Default is 'auto'. 2240 2241 If the software workaround is enabled for the host, 2242 guests do need not to enable it for nested guests. 2243 2244 kvm.nx_huge_pages_recovery_ratio= 2245 [KVM] Controls how many 4KiB pages are periodically zapped 2246 back to huge pages. 0 disables the recovery, otherwise if 2247 the value is N KVM will zap 1/Nth of the 4KiB pages every 2248 minute. The default is 60. 2249 2250 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2251 Default is 1 (enabled) 2252 2253 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2254 for all guests. 2255 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2256 2257 kvm-arm.vgic_v3_group0_trap= 2258 [KVM,ARM] Trap guest accesses to GICv3 group-0 2259 system registers 2260 2261 kvm-arm.vgic_v3_group1_trap= 2262 [KVM,ARM] Trap guest accesses to GICv3 group-1 2263 system registers 2264 2265 kvm-arm.vgic_v3_common_trap= 2266 [KVM,ARM] Trap guest accesses to GICv3 common 2267 system registers 2268 2269 kvm-arm.vgic_v4_enable= 2270 [KVM,ARM] Allow use of GICv4 for direct injection of 2271 LPIs. 2272 2273 kvm_cma_resv_ratio=n [PPC] 2274 Reserves given percentage from system memory area for 2275 contiguous memory allocation for KVM hash pagetable 2276 allocation. 2277 By default it reserves 5% of total system memory. 2278 Format: <integer> 2279 Default: 5 2280 2281 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2282 (virtualized MMU) support on capable Intel chips. 2283 Default is 1 (enabled) 2284 2285 kvm-intel.emulate_invalid_guest_state= 2286 [KVM,Intel] Enable emulation of invalid guest states 2287 Default is 0 (disabled) 2288 2289 kvm-intel.flexpriority= 2290 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2291 Default is 1 (enabled) 2292 2293 kvm-intel.nested= 2294 [KVM,Intel] Enable VMX nesting (nVMX). 2295 Default is 0 (disabled) 2296 2297 kvm-intel.unrestricted_guest= 2298 [KVM,Intel] Disable unrestricted guest feature 2299 (virtualized real and unpaged mode) on capable 2300 Intel chips. Default is 1 (enabled) 2301 2302 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2303 CVE-2018-3620. 2304 2305 Valid arguments: never, cond, always 2306 2307 always: L1D cache flush on every VMENTER. 2308 cond: Flush L1D on VMENTER only when the code between 2309 VMEXIT and VMENTER can leak host memory. 2310 never: Disables the mitigation 2311 2312 Default is cond (do L1 cache flush in specific instances) 2313 2314 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2315 feature (tagged TLBs) on capable Intel chips. 2316 Default is 1 (enabled) 2317 2318 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2319 affected CPUs 2320 2321 The kernel PTE inversion protection is unconditionally 2322 enabled and cannot be disabled. 2323 2324 full 2325 Provides all available mitigations for the 2326 L1TF vulnerability. Disables SMT and 2327 enables all mitigations in the 2328 hypervisors, i.e. unconditional L1D flush. 2329 2330 SMT control and L1D flush control via the 2331 sysfs interface is still possible after 2332 boot. Hypervisors will issue a warning 2333 when the first VM is started in a 2334 potentially insecure configuration, 2335 i.e. SMT enabled or L1D flush disabled. 2336 2337 full,force 2338 Same as 'full', but disables SMT and L1D 2339 flush runtime control. Implies the 2340 'nosmt=force' command line option. 2341 (i.e. sysfs control of SMT is disabled.) 2342 2343 flush 2344 Leaves SMT enabled and enables the default 2345 hypervisor mitigation, i.e. conditional 2346 L1D flush. 2347 2348 SMT control and L1D flush control via the 2349 sysfs interface is still possible after 2350 boot. Hypervisors will issue a warning 2351 when the first VM is started in a 2352 potentially insecure configuration, 2353 i.e. SMT enabled or L1D flush disabled. 2354 2355 flush,nosmt 2356 2357 Disables SMT and enables the default 2358 hypervisor mitigation. 2359 2360 SMT control and L1D flush control via the 2361 sysfs interface is still possible after 2362 boot. Hypervisors will issue a warning 2363 when the first VM is started in a 2364 potentially insecure configuration, 2365 i.e. SMT enabled or L1D flush disabled. 2366 2367 flush,nowarn 2368 Same as 'flush', but hypervisors will not 2369 warn when a VM is started in a potentially 2370 insecure configuration. 2371 2372 off 2373 Disables hypervisor mitigations and doesn't 2374 emit any warnings. 2375 It also drops the swap size and available 2376 RAM limit restriction on both hypervisor and 2377 bare metal. 2378 2379 Default is 'flush'. 2380 2381 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2382 2383 l2cr= [PPC] 2384 2385 l3cr= [PPC] 2386 2387 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2388 disabled it. 2389 2390 lapic= [X86,APIC] Do not use TSC deadline 2391 value for LAPIC timer one-shot implementation. Default 2392 back to the programmable timer unit in the LAPIC. 2393 Format: notscdeadline 2394 2395 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2396 in C2 power state. 2397 2398 libata.dma= [LIBATA] DMA control 2399 libata.dma=0 Disable all PATA and SATA DMA 2400 libata.dma=1 PATA and SATA Disk DMA only 2401 libata.dma=2 ATAPI (CDROM) DMA only 2402 libata.dma=4 Compact Flash DMA only 2403 Combinations also work, so libata.dma=3 enables DMA 2404 for disks and CDROMs, but not CFs. 2405 2406 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2407 libata.ignore_hpa=0 keep BIOS limits (default) 2408 libata.ignore_hpa=1 ignore limits, using full disk 2409 2410 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2411 when set. 2412 Format: <int> 2413 2414 libata.force= [LIBATA] Force configurations. The format is comma 2415 separated list of "[ID:]VAL" where ID is 2416 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2417 matching port, link or device. Basically, it matches 2418 the ATA ID string printed on console by libata. If 2419 the whole ID part is omitted, the last PORT and DEVICE 2420 values are used. If ID hasn't been specified yet, the 2421 configuration applies to all ports, links and devices. 2422 2423 If only DEVICE is omitted, the parameter applies to 2424 the port and all links and devices behind it. DEVICE 2425 number of 0 either selects the first device or the 2426 first fan-out link behind PMP device. It does not 2427 select the host link. DEVICE number of 15 selects the 2428 host link and device attached to it. 2429 2430 The VAL specifies the configuration to force. As long 2431 as there's no ambiguity shortcut notation is allowed. 2432 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2433 The following configurations can be forced. 2434 2435 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2436 Any ID with matching PORT is used. 2437 2438 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2439 2440 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2441 udma[/][16,25,33,44,66,100,133] notation is also 2442 allowed. 2443 2444 * [no]ncq: Turn on or off NCQ. 2445 2446 * [no]ncqtrim: Turn off queued DSM TRIM. 2447 2448 * nohrst, nosrst, norst: suppress hard, soft 2449 and both resets. 2450 2451 * rstonce: only attempt one reset during 2452 hot-unplug link recovery 2453 2454 * dump_id: dump IDENTIFY data. 2455 2456 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2457 2458 * disable: Disable this device. 2459 2460 If there are multiple matching configurations changing 2461 the same attribute, the last one is used. 2462 2463 memblock=debug [KNL] Enable memblock debug messages. 2464 2465 load_ramdisk= [RAM] [Deprecated] 2466 2467 lockd.nlm_grace_period=P [NFS] Assign grace period. 2468 Format: <integer> 2469 2470 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2471 Format: <integer> 2472 2473 lockd.nlm_timeout=T [NFS] Assign timeout value. 2474 Format: <integer> 2475 2476 lockd.nlm_udpport=M [NFS] Assign UDP port. 2477 Format: <integer> 2478 2479 lockdown= [SECURITY] 2480 { integrity | confidentiality } 2481 Enable the kernel lockdown feature. If set to 2482 integrity, kernel features that allow userland to 2483 modify the running kernel are disabled. If set to 2484 confidentiality, kernel features that allow userland 2485 to extract confidential information from the kernel 2486 are also disabled. 2487 2488 locktorture.nreaders_stress= [KNL] 2489 Set the number of locking read-acquisition kthreads. 2490 Defaults to being automatically set based on the 2491 number of online CPUs. 2492 2493 locktorture.nwriters_stress= [KNL] 2494 Set the number of locking write-acquisition kthreads. 2495 2496 locktorture.onoff_holdoff= [KNL] 2497 Set time (s) after boot for CPU-hotplug testing. 2498 2499 locktorture.onoff_interval= [KNL] 2500 Set time (s) between CPU-hotplug operations, or 2501 zero to disable CPU-hotplug testing. 2502 2503 locktorture.shuffle_interval= [KNL] 2504 Set task-shuffle interval (jiffies). Shuffling 2505 tasks allows some CPUs to go into dyntick-idle 2506 mode during the locktorture test. 2507 2508 locktorture.shutdown_secs= [KNL] 2509 Set time (s) after boot system shutdown. This 2510 is useful for hands-off automated testing. 2511 2512 locktorture.stat_interval= [KNL] 2513 Time (s) between statistics printk()s. 2514 2515 locktorture.stutter= [KNL] 2516 Time (s) to stutter testing, for example, 2517 specifying five seconds causes the test to run for 2518 five seconds, wait for five seconds, and so on. 2519 This tests the locking primitive's ability to 2520 transition abruptly to and from idle. 2521 2522 locktorture.torture_type= [KNL] 2523 Specify the locking implementation to test. 2524 2525 locktorture.verbose= [KNL] 2526 Enable additional printk() statements. 2527 2528 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2529 Format: <irq> 2530 2531 loglevel= All Kernel Messages with a loglevel smaller than the 2532 console loglevel will be printed to the console. It can 2533 also be changed with klogd or other programs. The 2534 loglevels are defined as follows: 2535 2536 0 (KERN_EMERG) system is unusable 2537 1 (KERN_ALERT) action must be taken immediately 2538 2 (KERN_CRIT) critical conditions 2539 3 (KERN_ERR) error conditions 2540 4 (KERN_WARNING) warning conditions 2541 5 (KERN_NOTICE) normal but significant condition 2542 6 (KERN_INFO) informational 2543 7 (KERN_DEBUG) debug-level messages 2544 2545 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2546 in bytes. n must be a power of two and greater 2547 than the minimal size. The minimal size is defined 2548 by LOG_BUF_SHIFT kernel config parameter. There is 2549 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2550 that allows to increase the default size depending on 2551 the number of CPUs. See init/Kconfig for more details. 2552 2553 logo.nologo [FB] Disables display of the built-in Linux logo. 2554 This may be used to provide more screen space for 2555 kernel log messages and is useful when debugging 2556 kernel boot problems. 2557 2558 lp=0 [LP] Specify parallel ports to use, e.g, 2559 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2560 lp=reset first parallel port). 'lp=0' disables the 2561 lp=auto printer driver. 'lp=reset' (which can be 2562 specified in addition to the ports) causes 2563 attached printers to be reset. Using 2564 lp=port1,port2,... specifies the parallel ports 2565 to associate lp devices with, starting with 2566 lp0. A port specification may be 'none' to skip 2567 that lp device, or a parport name such as 2568 'parport0'. Specifying 'lp=auto' instead of a 2569 port specification list means that device IDs 2570 from each port should be examined, to see if 2571 an IEEE 1284-compliant printer is attached; if 2572 so, the driver will manage that printer. 2573 See also header of drivers/char/lp.c. 2574 2575 lpj=n [KNL] 2576 Sets loops_per_jiffy to given constant, thus avoiding 2577 time-consuming boot-time autodetection (up to 250 ms per 2578 CPU). 0 enables autodetection (default). To determine 2579 the correct value for your kernel, boot with normal 2580 autodetection and see what value is printed. Note that 2581 on SMP systems the preset will be applied to all CPUs, 2582 which is likely to cause problems if your CPUs need 2583 significantly divergent settings. An incorrect value 2584 will cause delays in the kernel to be wrong, leading to 2585 unpredictable I/O errors and other breakage. Although 2586 unlikely, in the extreme case this might damage your 2587 hardware. 2588 2589 ltpc= [NET] 2590 Format: <io>,<irq>,<dma> 2591 2592 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2593 2594 lsm=lsm1,...,lsmN 2595 [SECURITY] Choose order of LSM initialization. This 2596 overrides CONFIG_LSM, and the "security=" parameter. 2597 2598 machvec= [IA-64] Force the use of a particular machine-vector 2599 (machvec) in a generic kernel. 2600 Example: machvec=hpzx1 2601 2602 machtype= [Loongson] Share the same kernel image file between 2603 different yeeloong laptops. 2604 Example: machtype=lemote-yeeloong-2f-7inch 2605 2606 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2607 than or equal to this physical address is ignored. 2608 2609 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2610 will bring up during bootup. maxcpus=n : n >= 0 limits 2611 the kernel to bring up 'n' processors. Surely after 2612 bootup you can bring up the other plugged cpu by executing 2613 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2614 only takes effect during system bootup. 2615 While n=0 is a special case, it is equivalent to "nosmp", 2616 which also disables the IO APIC. 2617 2618 max_loop= [LOOP] The number of loop block devices that get 2619 (loop.max_loop) unconditionally pre-created at init time. The default 2620 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2621 of statically allocating a predefined number, loop 2622 devices can be requested on-demand with the 2623 /dev/loop-control interface. 2624 2625 mce [X86-32] Machine Check Exception 2626 2627 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2628 2629 md= [HW] RAID subsystems devices and level 2630 See Documentation/admin-guide/md.rst. 2631 2632 mdacon= [MDA] 2633 Format: <first>,<last> 2634 Specifies range of consoles to be captured by the MDA. 2635 2636 mds= [X86,INTEL] 2637 Control mitigation for the Micro-architectural Data 2638 Sampling (MDS) vulnerability. 2639 2640 Certain CPUs are vulnerable to an exploit against CPU 2641 internal buffers which can forward information to a 2642 disclosure gadget under certain conditions. 2643 2644 In vulnerable processors, the speculatively 2645 forwarded data can be used in a cache side channel 2646 attack, to access data to which the attacker does 2647 not have direct access. 2648 2649 This parameter controls the MDS mitigation. The 2650 options are: 2651 2652 full - Enable MDS mitigation on vulnerable CPUs 2653 full,nosmt - Enable MDS mitigation and disable 2654 SMT on vulnerable CPUs 2655 off - Unconditionally disable MDS mitigation 2656 2657 On TAA-affected machines, mds=off can be prevented by 2658 an active TAA mitigation as both vulnerabilities are 2659 mitigated with the same mechanism so in order to disable 2660 this mitigation, you need to specify tsx_async_abort=off 2661 too. 2662 2663 Not specifying this option is equivalent to 2664 mds=full. 2665 2666 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2667 2668 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2669 Amount of memory to be used in cases as follows: 2670 2671 1 for test; 2672 2 when the kernel is not able to see the whole system memory; 2673 3 memory that lies after 'mem=' boundary is excluded from 2674 the hypervisor, then assigned to KVM guests. 2675 2676 [X86] Work as limiting max address. Use together 2677 with memmap= to avoid physical address space collisions. 2678 Without memmap= PCI devices could be placed at addresses 2679 belonging to unused RAM. 2680 2681 Note that this only takes effects during boot time since 2682 in above case 3, memory may need be hot added after boot 2683 if system memory of hypervisor is not sufficient. 2684 2685 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2686 memory. 2687 2688 memchunk=nn[KMG] 2689 [KNL,SH] Allow user to override the default size for 2690 per-device physically contiguous DMA buffers. 2691 2692 memhp_default_state=online/offline 2693 [KNL] Set the initial state for the memory hotplug 2694 onlining policy. If not specified, the default value is 2695 set according to the 2696 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2697 option. 2698 See Documentation/admin-guide/mm/memory-hotplug.rst. 2699 2700 memmap=exactmap [KNL,X86] Enable setting of an exact 2701 E820 memory map, as specified by the user. 2702 Such memmap=exactmap lines can be constructed based on 2703 BIOS output or other requirements. See the memmap=nn@ss 2704 option description. 2705 2706 memmap=nn[KMG]@ss[KMG] 2707 [KNL] Force usage of a specific region of memory. 2708 Region of memory to be used is from ss to ss+nn. 2709 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2710 which limits max address to nn[KMG]. 2711 Multiple different regions can be specified, 2712 comma delimited. 2713 Example: 2714 memmap=100M@2G,100M#3G,1G!1024G 2715 2716 memmap=nn[KMG]#ss[KMG] 2717 [KNL,ACPI] Mark specific memory as ACPI data. 2718 Region of memory to be marked is from ss to ss+nn. 2719 2720 memmap=nn[KMG]$ss[KMG] 2721 [KNL,ACPI] Mark specific memory as reserved. 2722 Region of memory to be reserved is from ss to ss+nn. 2723 Example: Exclude memory from 0x18690000-0x1869ffff 2724 memmap=64K$0x18690000 2725 or 2726 memmap=0x10000$0x18690000 2727 Some bootloaders may need an escape character before '$', 2728 like Grub2, otherwise '$' and the following number 2729 will be eaten. 2730 2731 memmap=nn[KMG]!ss[KMG] 2732 [KNL,X86] Mark specific memory as protected. 2733 Region of memory to be used, from ss to ss+nn. 2734 The memory region may be marked as e820 type 12 (0xc) 2735 and is NVDIMM or ADR memory. 2736 2737 memmap=<size>%<offset>-<oldtype>+<newtype> 2738 [KNL,ACPI] Convert memory within the specified region 2739 from <oldtype> to <newtype>. If "-<oldtype>" is left 2740 out, the whole region will be marked as <newtype>, 2741 even if previously unavailable. If "+<newtype>" is left 2742 out, matching memory will be removed. Types are 2743 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2744 3 = ACPI, 12 = PRAM. 2745 2746 memory_corruption_check=0/1 [X86] 2747 Some BIOSes seem to corrupt the first 64k of 2748 memory when doing things like suspend/resume. 2749 Setting this option will scan the memory 2750 looking for corruption. Enabling this will 2751 both detect corruption and prevent the kernel 2752 from using the memory being corrupted. 2753 However, its intended as a diagnostic tool; if 2754 repeatable BIOS-originated corruption always 2755 affects the same memory, you can use memmap= 2756 to prevent the kernel from using that memory. 2757 2758 memory_corruption_check_size=size [X86] 2759 By default it checks for corruption in the low 2760 64k, making this memory unavailable for normal 2761 use. Use this parameter to scan for 2762 corruption in more or less memory. 2763 2764 memory_corruption_check_period=seconds [X86] 2765 By default it checks for corruption every 60 2766 seconds. Use this parameter to check at some 2767 other rate. 0 disables periodic checking. 2768 2769 memtest= [KNL,X86,ARM,PPC] Enable memtest 2770 Format: <integer> 2771 default : 0 <disable> 2772 Specifies the number of memtest passes to be 2773 performed. Each pass selects another test 2774 pattern from a given set of patterns. Memtest 2775 fills the memory with this pattern, validates 2776 memory contents and reserves bad memory 2777 regions that are detected. 2778 2779 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2780 Valid arguments: on, off 2781 Default (depends on kernel configuration option): 2782 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2783 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2784 mem_encrypt=on: Activate SME 2785 mem_encrypt=off: Do not activate SME 2786 2787 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2788 for details on when memory encryption can be activated. 2789 2790 mem_sleep_default= [SUSPEND] Default system suspend mode: 2791 s2idle - Suspend-To-Idle 2792 shallow - Power-On Suspend or equivalent (if supported) 2793 deep - Suspend-To-RAM or equivalent (if supported) 2794 See Documentation/admin-guide/pm/sleep-states.rst. 2795 2796 meye.*= [HW] Set MotionEye Camera parameters 2797 See Documentation/admin-guide/media/meye.rst. 2798 2799 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2800 Multi-Function General Purpose Timers on AMD Geode 2801 platforms. 2802 2803 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2804 the BIOS has incorrectly applied a workaround. TinyBIOS 2805 version 0.98 is known to be affected, 0.99 fixes the 2806 problem by letting the user disable the workaround. 2807 2808 mga= [HW,DRM] 2809 2810 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2811 physical address is ignored. 2812 2813 mini2440= [ARM,HW,KNL] 2814 Format:[0..2][b][c][t] 2815 Default: "0tb" 2816 MINI2440 configuration specification: 2817 0 - The attached screen is the 3.5" TFT 2818 1 - The attached screen is the 7" TFT 2819 2 - The VGA Shield is attached (1024x768) 2820 Leaving out the screen size parameter will not load 2821 the TFT driver, and the framebuffer will be left 2822 unconfigured. 2823 b - Enable backlight. The TFT backlight pin will be 2824 linked to the kernel VESA blanking code and a GPIO 2825 LED. This parameter is not necessary when using the 2826 VGA shield. 2827 c - Enable the s3c camera interface. 2828 t - Reserved for enabling touchscreen support. The 2829 touchscreen support is not enabled in the mainstream 2830 kernel as of 2.6.30, a preliminary port can be found 2831 in the "bleeding edge" mini2440 support kernel at 2832 https://repo.or.cz/w/linux-2.6/mini2440.git 2833 2834 mitigations= 2835 [X86,PPC,S390,ARM64] Control optional mitigations for 2836 CPU vulnerabilities. This is a set of curated, 2837 arch-independent options, each of which is an 2838 aggregation of existing arch-specific options. 2839 2840 off 2841 Disable all optional CPU mitigations. This 2842 improves system performance, but it may also 2843 expose users to several CPU vulnerabilities. 2844 Equivalent to: nopti [X86,PPC] 2845 kpti=0 [ARM64] 2846 nospectre_v1 [X86,PPC] 2847 nobp=0 [S390] 2848 nospectre_v2 [X86,PPC,S390,ARM64] 2849 spectre_v2_user=off [X86] 2850 spec_store_bypass_disable=off [X86,PPC] 2851 ssbd=force-off [ARM64] 2852 l1tf=off [X86] 2853 mds=off [X86] 2854 tsx_async_abort=off [X86] 2855 kvm.nx_huge_pages=off [X86] 2856 2857 Exceptions: 2858 This does not have any effect on 2859 kvm.nx_huge_pages when 2860 kvm.nx_huge_pages=force. 2861 2862 auto (default) 2863 Mitigate all CPU vulnerabilities, but leave SMT 2864 enabled, even if it's vulnerable. This is for 2865 users who don't want to be surprised by SMT 2866 getting disabled across kernel upgrades, or who 2867 have other ways of avoiding SMT-based attacks. 2868 Equivalent to: (default behavior) 2869 2870 auto,nosmt 2871 Mitigate all CPU vulnerabilities, disabling SMT 2872 if needed. This is for users who always want to 2873 be fully mitigated, even if it means losing SMT. 2874 Equivalent to: l1tf=flush,nosmt [X86] 2875 mds=full,nosmt [X86] 2876 tsx_async_abort=full,nosmt [X86] 2877 2878 mminit_loglevel= 2879 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2880 parameter allows control of the logging verbosity for 2881 the additional memory initialisation checks. A value 2882 of 0 disables mminit logging and a level of 4 will 2883 log everything. Information is printed at KERN_DEBUG 2884 so loglevel=8 may also need to be specified. 2885 2886 module.sig_enforce 2887 [KNL] When CONFIG_MODULE_SIG is set, this means that 2888 modules without (valid) signatures will fail to load. 2889 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2890 is always true, so this option does nothing. 2891 2892 module_blacklist= [KNL] Do not load a comma-separated list of 2893 modules. Useful for debugging problem modules. 2894 2895 mousedev.tap_time= 2896 [MOUSE] Maximum time between finger touching and 2897 leaving touchpad surface for touch to be considered 2898 a tap and be reported as a left button click (for 2899 touchpads working in absolute mode only). 2900 Format: <msecs> 2901 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2902 reporting absolute coordinates, such as tablets 2903 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2904 reporting absolute coordinates, such as tablets 2905 2906 movablecore= [KNL,X86,IA-64,PPC] 2907 Format: nn[KMGTPE] | nn% 2908 This parameter is the complement to kernelcore=, it 2909 specifies the amount of memory used for migratable 2910 allocations. If both kernelcore and movablecore is 2911 specified, then kernelcore will be at *least* the 2912 specified value but may be more. If movablecore on its 2913 own is specified, the administrator must be careful 2914 that the amount of memory usable for all allocations 2915 is not too small. 2916 2917 movable_node [KNL] Boot-time switch to make hotplugable memory 2918 NUMA nodes to be movable. This means that the memory 2919 of such nodes will be usable only for movable 2920 allocations which rules out almost all kernel 2921 allocations. Use with caution! 2922 2923 MTD_Partition= [MTD] 2924 Format: <name>,<region-number>,<size>,<offset> 2925 2926 MTD_Region= [MTD] Format: 2927 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2928 2929 mtdparts= [MTD] 2930 See drivers/mtd/parsers/cmdlinepart.c 2931 2932 multitce=off [PPC] This parameter disables the use of the pSeries 2933 firmware feature for updating multiple TCE entries 2934 at a time. 2935 2936 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2937 2938 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2939 2940 boundary - index of last SLC block on Flex-OneNAND. 2941 The remaining blocks are configured as MLC blocks. 2942 lock - Configure if Flex-OneNAND boundary should be locked. 2943 Once locked, the boundary cannot be changed. 2944 1 indicates lock status, 0 indicates unlock status. 2945 2946 mtdset= [ARM] 2947 ARM/S3C2412 JIVE boot control 2948 2949 See arch/arm/mach-s3c2412/mach-jive.c 2950 2951 mtouchusb.raw_coordinates= 2952 [HW] Make the MicroTouch USB driver use raw coordinates 2953 ('y', default) or cooked coordinates ('n') 2954 2955 mtrr_chunk_size=nn[KMG] [X86] 2956 used for mtrr cleanup. It is largest continuous chunk 2957 that could hold holes aka. UC entries. 2958 2959 mtrr_gran_size=nn[KMG] [X86] 2960 Used for mtrr cleanup. It is granularity of mtrr block. 2961 Default is 1. 2962 Large value could prevent small alignment from 2963 using up MTRRs. 2964 2965 mtrr_spare_reg_nr=n [X86] 2966 Format: <integer> 2967 Range: 0,7 : spare reg number 2968 Default : 1 2969 Used for mtrr cleanup. It is spare mtrr entries number. 2970 Set to 2 or more if your graphical card needs more. 2971 2972 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2973 2974 netdev= [NET] Network devices parameters 2975 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2976 Note that mem_start is often overloaded to mean 2977 something different and driver-specific. 2978 This usage is only documented in each driver source 2979 file if at all. 2980 2981 nf_conntrack.acct= 2982 [NETFILTER] Enable connection tracking flow accounting 2983 0 to disable accounting 2984 1 to enable accounting 2985 Default value is 0. 2986 2987 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2988 See Documentation/admin-guide/nfs/nfsroot.rst. 2989 2990 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2991 See Documentation/admin-guide/nfs/nfsroot.rst. 2992 2993 nfsrootdebug [NFS] enable nfsroot debugging messages. 2994 See Documentation/admin-guide/nfs/nfsroot.rst. 2995 2996 nfs.callback_nr_threads= 2997 [NFSv4] set the total number of threads that the 2998 NFS client will assign to service NFSv4 callback 2999 requests. 3000 3001 nfs.callback_tcpport= 3002 [NFS] set the TCP port on which the NFSv4 callback 3003 channel should listen. 3004 3005 nfs.cache_getent= 3006 [NFS] sets the pathname to the program which is used 3007 to update the NFS client cache entries. 3008 3009 nfs.cache_getent_timeout= 3010 [NFS] sets the timeout after which an attempt to 3011 update a cache entry is deemed to have failed. 3012 3013 nfs.idmap_cache_timeout= 3014 [NFS] set the maximum lifetime for idmapper cache 3015 entries. 3016 3017 nfs.enable_ino64= 3018 [NFS] enable 64-bit inode numbers. 3019 If zero, the NFS client will fake up a 32-bit inode 3020 number for the readdir() and stat() syscalls instead 3021 of returning the full 64-bit number. 3022 The default is to return 64-bit inode numbers. 3023 3024 nfs.max_session_cb_slots= 3025 [NFSv4.1] Sets the maximum number of session 3026 slots the client will assign to the callback 3027 channel. This determines the maximum number of 3028 callbacks the client will process in parallel for 3029 a particular server. 3030 3031 nfs.max_session_slots= 3032 [NFSv4.1] Sets the maximum number of session slots 3033 the client will attempt to negotiate with the server. 3034 This limits the number of simultaneous RPC requests 3035 that the client can send to the NFSv4.1 server. 3036 Note that there is little point in setting this 3037 value higher than the max_tcp_slot_table_limit. 3038 3039 nfs.nfs4_disable_idmapping= 3040 [NFSv4] When set to the default of '1', this option 3041 ensures that both the RPC level authentication 3042 scheme and the NFS level operations agree to use 3043 numeric uids/gids if the mount is using the 3044 'sec=sys' security flavour. In effect it is 3045 disabling idmapping, which can make migration from 3046 legacy NFSv2/v3 systems to NFSv4 easier. 3047 Servers that do not support this mode of operation 3048 will be autodetected by the client, and it will fall 3049 back to using the idmapper. 3050 To turn off this behaviour, set the value to '0'. 3051 nfs.nfs4_unique_id= 3052 [NFS4] Specify an additional fixed unique ident- 3053 ification string that NFSv4 clients can insert into 3054 their nfs_client_id4 string. This is typically a 3055 UUID that is generated at system install time. 3056 3057 nfs.send_implementation_id = 3058 [NFSv4.1] Send client implementation identification 3059 information in exchange_id requests. 3060 If zero, no implementation identification information 3061 will be sent. 3062 The default is to send the implementation identification 3063 information. 3064 3065 nfs.recover_lost_locks = 3066 [NFSv4] Attempt to recover locks that were lost due 3067 to a lease timeout on the server. Please note that 3068 doing this risks data corruption, since there are 3069 no guarantees that the file will remain unchanged 3070 after the locks are lost. 3071 If you want to enable the kernel legacy behaviour of 3072 attempting to recover these locks, then set this 3073 parameter to '1'. 3074 The default parameter value of '0' causes the kernel 3075 not to attempt recovery of lost locks. 3076 3077 nfs4.layoutstats_timer = 3078 [NFSv4.2] Change the rate at which the kernel sends 3079 layoutstats to the pNFS metadata server. 3080 3081 Setting this to value to 0 causes the kernel to use 3082 whatever value is the default set by the layout 3083 driver. A non-zero value sets the minimum interval 3084 in seconds between layoutstats transmissions. 3085 3086 nfsd.nfs4_disable_idmapping= 3087 [NFSv4] When set to the default of '1', the NFSv4 3088 server will return only numeric uids and gids to 3089 clients using auth_sys, and will accept numeric uids 3090 and gids from such clients. This is intended to ease 3091 migration from NFSv2/v3. 3092 3093 nmi_debug= [KNL,SH] Specify one or more actions to take 3094 when a NMI is triggered. 3095 Format: [state][,regs][,debounce][,die] 3096 3097 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3098 Format: [panic,][nopanic,][num] 3099 Valid num: 0 or 1 3100 0 - turn hardlockup detector in nmi_watchdog off 3101 1 - turn hardlockup detector in nmi_watchdog on 3102 When panic is specified, panic when an NMI watchdog 3103 timeout occurs (or 'nopanic' to not panic on an NMI 3104 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3105 To disable both hard and soft lockup detectors, 3106 please see 'nowatchdog'. 3107 This is useful when you use a panic=... timeout and 3108 need the box quickly up again. 3109 3110 These settings can be accessed at runtime via 3111 the nmi_watchdog and hardlockup_panic sysctls. 3112 3113 netpoll.carrier_timeout= 3114 [NET] Specifies amount of time (in seconds) that 3115 netpoll should wait for a carrier. By default netpoll 3116 waits 4 seconds. 3117 3118 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3119 emulation library even if a 387 maths coprocessor 3120 is present. 3121 3122 no5lvl [X86-64] Disable 5-level paging mode. Forces 3123 kernel to use 4-level paging instead. 3124 3125 nofsgsbase [X86] Disables FSGSBASE instructions. 3126 3127 no_console_suspend 3128 [HW] Never suspend the console 3129 Disable suspending of consoles during suspend and 3130 hibernate operations. Once disabled, debugging 3131 messages can reach various consoles while the rest 3132 of the system is being put to sleep (ie, while 3133 debugging driver suspend/resume hooks). This may 3134 not work reliably with all consoles, but is known 3135 to work with serial and VGA consoles. 3136 To facilitate more flexible debugging, we also add 3137 console_suspend, a printk module parameter to control 3138 it. Users could use console_suspend (usually 3139 /sys/module/printk/parameters/console_suspend) to 3140 turn on/off it dynamically. 3141 3142 novmcoredd [KNL,KDUMP] 3143 Disable device dump. Device dump allows drivers to 3144 append dump data to vmcore so you can collect driver 3145 specified debug info. Drivers can append the data 3146 without any limit and this data is stored in memory, 3147 so this may cause significant memory stress. Disabling 3148 device dump can help save memory but the driver debug 3149 data will be no longer available. This parameter 3150 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3151 is set. 3152 3153 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3154 caches in the slab allocator. Saves per-node memory, 3155 but will impact performance. 3156 3157 noalign [KNL,ARM] 3158 3159 noaltinstr [S390] Disables alternative instructions patching 3160 (CPU alternatives feature). 3161 3162 noapic [SMP,APIC] Tells the kernel to not make use of any 3163 IOAPICs that may be present in the system. 3164 3165 noautogroup Disable scheduler automatic task group creation. 3166 3167 nobats [PPC] Do not use BATs for mapping kernel lowmem 3168 on "Classic" PPC cores. 3169 3170 nocache [ARM] 3171 3172 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3173 3174 nodelayacct [KNL] Disable per-task delay accounting 3175 3176 nodsp [SH] Disable hardware DSP at boot time. 3177 3178 noefi Disable EFI runtime services support. 3179 3180 noexec [IA-64] 3181 3182 noexec [X86] 3183 On X86-32 available only on PAE configured kernels. 3184 noexec=on: enable non-executable mappings (default) 3185 noexec=off: disable non-executable mappings 3186 3187 nosmap [X86,PPC] 3188 Disable SMAP (Supervisor Mode Access Prevention) 3189 even if it is supported by processor. 3190 3191 nosmep [X86,PPC] 3192 Disable SMEP (Supervisor Mode Execution Prevention) 3193 even if it is supported by processor. 3194 3195 noexec32 [X86-64] 3196 This affects only 32-bit executables. 3197 noexec32=on: enable non-executable mappings (default) 3198 read doesn't imply executable mappings 3199 noexec32=off: disable non-executable mappings 3200 read implies executable mappings 3201 3202 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3203 3204 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3205 register save and restore. The kernel will only save 3206 legacy floating-point registers on task switch. 3207 3208 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3209 3210 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3211 Equivalent to smt=1. 3212 3213 [KNL,X86] Disable symmetric multithreading (SMT). 3214 nosmt=force: Force disable SMT, cannot be undone 3215 via the sysfs control file. 3216 3217 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3218 (bounds check bypass). With this option data leaks are 3219 possible in the system. 3220 3221 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3222 the Spectre variant 2 (indirect branch prediction) 3223 vulnerability. System may allow data leaks with this 3224 option. 3225 3226 nospec_store_bypass_disable 3227 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3228 3229 noxsave [BUGS=X86] Disables x86 extended register state save 3230 and restore using xsave. The kernel will fallback to 3231 enabling legacy floating-point and sse state. 3232 3233 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3234 register states. The kernel will fall back to use 3235 xsave to save the states. By using this parameter, 3236 performance of saving the states is degraded because 3237 xsave doesn't support modified optimization while 3238 xsaveopt supports it on xsaveopt enabled systems. 3239 3240 noxsaves [X86] Disables xsaves and xrstors used in saving and 3241 restoring x86 extended register state in compacted 3242 form of xsave area. The kernel will fall back to use 3243 xsaveopt and xrstor to save and restore the states 3244 in standard form of xsave area. By using this 3245 parameter, xsave area per process might occupy more 3246 memory on xsaves enabled systems. 3247 3248 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3249 wfi(ARM) instruction doesn't work correctly and not to 3250 use it. This is also useful when using JTAG debugger. 3251 3252 no_file_caps Tells the kernel not to honor file capabilities. The 3253 only way then for a file to be executed with privilege 3254 is to be setuid root or executed by root. 3255 3256 nohalt [IA-64] Tells the kernel not to use the power saving 3257 function PAL_HALT_LIGHT when idle. This increases 3258 power-consumption. On the positive side, it reduces 3259 interrupt wake-up latency, which may improve performance 3260 in certain environments such as networked servers or 3261 real-time systems. 3262 3263 nohibernate [HIBERNATION] Disable hibernation and resume. 3264 3265 nohz= [KNL] Boottime enable/disable dynamic ticks 3266 Valid arguments: on, off 3267 Default: on 3268 3269 nohz_full= [KNL,BOOT,SMP,ISOL] 3270 The argument is a cpu list, as described above. 3271 In kernels built with CONFIG_NO_HZ_FULL=y, set 3272 the specified list of CPUs whose tick will be stopped 3273 whenever possible. The boot CPU will be forced outside 3274 the range to maintain the timekeeping. Any CPUs 3275 in this list will have their RCU callbacks offloaded, 3276 just as if they had also been called out in the 3277 rcu_nocbs= boot parameter. 3278 3279 noiotrap [SH] Disables trapped I/O port accesses. 3280 3281 noirqdebug [X86-32] Disables the code which attempts to detect and 3282 disable unhandled interrupt sources. 3283 3284 no_timer_check [X86,APIC] Disables the code which tests for 3285 broken timer IRQ sources. 3286 3287 noisapnp [ISAPNP] Disables ISA PnP code. 3288 3289 noinitrd [RAM] Tells the kernel not to load any configured 3290 initial RAM disk. 3291 3292 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3293 remapping. 3294 [Deprecated - use intremap=off] 3295 3296 nointroute [IA-64] 3297 3298 noinvpcid [X86] Disable the INVPCID cpu feature. 3299 3300 nojitter [IA-64] Disables jitter checking for ITC timers. 3301 3302 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3303 3304 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3305 fault handling. 3306 3307 no-vmw-sched-clock 3308 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3309 clock and use the default one. 3310 3311 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3312 accounting. steal time is computed, but won't 3313 influence scheduler behaviour 3314 3315 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3316 3317 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3318 3319 noltlbs [PPC] Do not use large page/tlb entries for kernel 3320 lowmem mapping on PPC40x and PPC8xx 3321 3322 nomca [IA-64] Disable machine check abort handling 3323 3324 nomce [X86-32] Disable Machine Check Exception 3325 3326 nomfgpt [X86-32] Disable Multi-Function General Purpose 3327 Timer usage (for AMD Geode machines). 3328 3329 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3330 shutdown the other cpus. Instead use the REBOOT_VECTOR 3331 irq. 3332 3333 nomodule Disable module load 3334 3335 nopat [X86] Disable PAT (page attribute table extension of 3336 pagetables) support. 3337 3338 nopcid [X86-64] Disable the PCID cpu feature. 3339 3340 norandmaps Don't use address space randomization. Equivalent to 3341 echo 0 > /proc/sys/kernel/randomize_va_space 3342 3343 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3344 with UP alternatives 3345 3346 nordrand [X86] Disable kernel use of the RDRAND and 3347 RDSEED instructions even if they are supported 3348 by the processor. RDRAND and RDSEED are still 3349 available to user space applications. 3350 3351 noresume [SWSUSP] Disables resume and restores original swap 3352 space. 3353 3354 no-scroll [VGA] Disables scrollback. 3355 This is required for the Braillex ib80-piezo Braille 3356 reader made by F.H. Papenmeier (Germany). 3357 3358 nosbagart [IA-64] 3359 3360 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3361 3362 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3363 and disable the IO APIC. legacy for "maxcpus=0". 3364 3365 nosoftlockup [KNL] Disable the soft-lockup detector. 3366 3367 nosync [HW,M68K] Disables sync negotiation for all devices. 3368 3369 nowatchdog [KNL] Disable both lockup detectors, i.e. 3370 soft-lockup and NMI watchdog (hard-lockup). 3371 3372 nowb [ARM] 3373 3374 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3375 3376 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3377 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3378 Some features depend on CPU0. Known dependencies are: 3379 1. Resume from suspend/hibernate depends on CPU0. 3380 Suspend/hibernate will fail if CPU0 is offline and you 3381 need to online CPU0 before suspend/hibernate. 3382 2. PIC interrupts also depend on CPU0. CPU0 can't be 3383 removed if a PIC interrupt is detected. 3384 It's said poweroff/reboot may depend on CPU0 on some 3385 machines although I haven't seen such issues so far 3386 after CPU0 is offline on a few tested machines. 3387 If the dependencies are under your control, you can 3388 turn on cpu0_hotplug. 3389 3390 nps_mtm_hs_ctr= [KNL,ARC] 3391 This parameter sets the maximum duration, in 3392 cycles, each HW thread of the CTOP can run 3393 without interruptions, before HW switches it. 3394 The actual maximum duration is 16 times this 3395 parameter's value. 3396 Format: integer between 1 and 255 3397 Default: 255 3398 3399 nptcg= [IA-64] Override max number of concurrent global TLB 3400 purges which is reported from either PAL_VM_SUMMARY or 3401 SAL PALO. 3402 3403 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3404 could support. nr_cpus=n : n >= 1 limits the kernel to 3405 support 'n' processors. It could be larger than the 3406 number of already plugged CPU during bootup, later in 3407 runtime you can physically add extra cpu until it reaches 3408 n. So during boot up some boot time memory for per-cpu 3409 variables need be pre-allocated for later physical cpu 3410 hot plugging. 3411 3412 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3413 3414 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3415 Allowed values are enable and disable 3416 3417 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3418 'node', 'default' can be specified 3419 This can be set from sysctl after boot. 3420 See Documentation/admin-guide/sysctl/vm.rst for details. 3421 3422 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3423 See Documentation/core-api/debugging-via-ohci1394.rst for more 3424 info. 3425 3426 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3427 Rather than timing out after 20 ms if an EC 3428 command is not properly ACKed, override the length 3429 of the timeout. We have interrupts disabled while 3430 waiting for the ACK, so if this is set too high 3431 interrupts *may* be lost! 3432 3433 omap_mux= [OMAP] Override bootloader pin multiplexing. 3434 Format: <mux_mode0.mode_name=value>... 3435 For example, to override I2C bus2: 3436 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3437 3438 oprofile.timer= [HW] 3439 Use timer interrupt instead of performance counters 3440 3441 oprofile.cpu_type= Force an oprofile cpu type 3442 This might be useful if you have an older oprofile 3443 userland or if you want common events. 3444 Format: { arch_perfmon } 3445 arch_perfmon: [X86] Force use of architectural 3446 perfmon on Intel CPUs instead of the 3447 CPU specific event set. 3448 timer: [X86] Force use of architectural NMI 3449 timer mode (see also oprofile.timer 3450 for generic hr timer mode) 3451 3452 oops=panic Always panic on oopses. Default is to just kill the 3453 process, but there is a small probability of 3454 deadlocking the machine. 3455 This will also cause panics on machine check exceptions. 3456 Useful together with panic=30 to trigger a reboot. 3457 3458 page_alloc.shuffle= 3459 [KNL] Boolean flag to control whether the page allocator 3460 should randomize its free lists. The randomization may 3461 be automatically enabled if the kernel detects it is 3462 running on a platform with a direct-mapped memory-side 3463 cache, and this parameter can be used to 3464 override/disable that behavior. The state of the flag 3465 can be read from sysfs at: 3466 /sys/module/page_alloc/parameters/shuffle. 3467 3468 page_owner= [KNL] Boot-time page_owner enabling option. 3469 Storage of the information about who allocated 3470 each page is disabled in default. With this switch, 3471 we can turn it on. 3472 on: enable the feature 3473 3474 page_poison= [KNL] Boot-time parameter changing the state of 3475 poisoning on the buddy allocator, available with 3476 CONFIG_PAGE_POISONING=y. 3477 off: turn off poisoning (default) 3478 on: turn on poisoning 3479 3480 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3481 timeout > 0: seconds before rebooting 3482 timeout = 0: wait forever 3483 timeout < 0: reboot immediately 3484 Format: <timeout> 3485 3486 panic_print= Bitmask for printing system info when panic happens. 3487 User can chose combination of the following bits: 3488 bit 0: print all tasks info 3489 bit 1: print system memory info 3490 bit 2: print timer info 3491 bit 3: print locks info if CONFIG_LOCKDEP is on 3492 bit 4: print ftrace buffer 3493 bit 5: print all printk messages in buffer 3494 3495 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3496 Format: <hex>[,nousertaint] 3497 Hexadecimal bitmask representing the set of TAINT flags 3498 that will cause the kernel to panic when add_taint() is 3499 called with any of the flags in this set. 3500 The optional switch "nousertaint" can be utilized to 3501 prevent userspace forced crashes by writing to sysctl 3502 /proc/sys/kernel/tainted any flagset matching with the 3503 bitmask set on panic_on_taint. 3504 See Documentation/admin-guide/tainted-kernels.rst for 3505 extra details on the taint flags that users can pick 3506 to compose the bitmask to assign to panic_on_taint. 3507 3508 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3509 on a WARN(). 3510 3511 crash_kexec_post_notifiers 3512 Run kdump after running panic-notifiers and dumping 3513 kmsg. This only for the users who doubt kdump always 3514 succeeds in any situation. 3515 Note that this also increases risks of kdump failure, 3516 because some panic notifiers can make the crashed 3517 kernel more unstable. 3518 3519 parkbd.port= [HW] Parallel port number the keyboard adapter is 3520 connected to, default is 0. 3521 Format: <parport#> 3522 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3523 0 for XT, 1 for AT (default is AT). 3524 Format: <mode> 3525 3526 parport= [HW,PPT] Specify parallel ports. 0 disables. 3527 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3528 Use 'auto' to force the driver to use any 3529 IRQ/DMA settings detected (the default is to 3530 ignore detected IRQ/DMA settings because of 3531 possible conflicts). You can specify the base 3532 address, IRQ, and DMA settings; IRQ and DMA 3533 should be numbers, or 'auto' (for using detected 3534 settings on that particular port), or 'nofifo' 3535 (to avoid using a FIFO even if it is detected). 3536 Parallel ports are assigned in the order they 3537 are specified on the command line, starting 3538 with parport0. 3539 3540 parport_init_mode= [HW,PPT] 3541 Configure VIA parallel port to operate in 3542 a specific mode. This is necessary on Pegasos 3543 computer where firmware has no options for setting 3544 up parallel port mode and sets it to spp. 3545 Currently this function knows 686a and 8231 chips. 3546 Format: [spp|ps2|epp|ecp|ecpepp] 3547 3548 pause_on_oops= 3549 Halt all CPUs after the first oops has been printed for 3550 the specified number of seconds. This is to be used if 3551 your oopses keep scrolling off the screen. 3552 3553 pcbit= [HW,ISDN] 3554 3555 pcd. [PARIDE] 3556 See header of drivers/block/paride/pcd.c. 3557 See also Documentation/admin-guide/blockdev/paride.rst. 3558 3559 pci=option[,option...] [PCI] various PCI subsystem options. 3560 3561 Some options herein operate on a specific device 3562 or a set of devices (<pci_dev>). These are 3563 specified in one of the following formats: 3564 3565 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3566 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3567 3568 Note: the first format specifies a PCI 3569 bus/device/function address which may change 3570 if new hardware is inserted, if motherboard 3571 firmware changes, or due to changes caused 3572 by other kernel parameters. If the 3573 domain is left unspecified, it is 3574 taken to be zero. Optionally, a path 3575 to a device through multiple device/function 3576 addresses can be specified after the base 3577 address (this is more robust against 3578 renumbering issues). The second format 3579 selects devices using IDs from the 3580 configuration space which may match multiple 3581 devices in the system. 3582 3583 earlydump dump PCI config space before the kernel 3584 changes anything 3585 off [X86] don't probe for the PCI bus 3586 bios [X86-32] force use of PCI BIOS, don't access 3587 the hardware directly. Use this if your machine 3588 has a non-standard PCI host bridge. 3589 nobios [X86-32] disallow use of PCI BIOS, only direct 3590 hardware access methods are allowed. Use this 3591 if you experience crashes upon bootup and you 3592 suspect they are caused by the BIOS. 3593 conf1 [X86] Force use of PCI Configuration Access 3594 Mechanism 1 (config address in IO port 0xCF8, 3595 data in IO port 0xCFC, both 32-bit). 3596 conf2 [X86] Force use of PCI Configuration Access 3597 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3598 the function, IO port 0xCFA, also 8-bit, sets 3599 bus number. The config space is then accessed 3600 through ports 0xC000-0xCFFF). 3601 See http://wiki.osdev.org/PCI for more info 3602 on the configuration access mechanisms. 3603 noaer [PCIE] If the PCIEAER kernel config parameter is 3604 enabled, this kernel boot option can be used to 3605 disable the use of PCIE advanced error reporting. 3606 nodomains [PCI] Disable support for multiple PCI 3607 root domains (aka PCI segments, in ACPI-speak). 3608 nommconf [X86] Disable use of MMCONFIG for PCI 3609 Configuration 3610 check_enable_amd_mmconf [X86] check for and enable 3611 properly configured MMIO access to PCI 3612 config space on AMD family 10h CPU 3613 nomsi [MSI] If the PCI_MSI kernel config parameter is 3614 enabled, this kernel boot option can be used to 3615 disable the use of MSI interrupts system-wide. 3616 noioapicquirk [APIC] Disable all boot interrupt quirks. 3617 Safety option to keep boot IRQs enabled. This 3618 should never be necessary. 3619 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3620 primary IO-APIC for bridges that cannot disable 3621 boot IRQs. This fixes a source of spurious IRQs 3622 when the system masks IRQs. 3623 noioapicreroute [APIC] Disable workaround that uses the 3624 boot IRQ equivalent of an IRQ that connects to 3625 a chipset where boot IRQs cannot be disabled. 3626 The opposite of ioapicreroute. 3627 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3628 routing table. These calls are known to be buggy 3629 on several machines and they hang the machine 3630 when used, but on other computers it's the only 3631 way to get the interrupt routing table. Try 3632 this option if the kernel is unable to allocate 3633 IRQs or discover secondary PCI buses on your 3634 motherboard. 3635 rom [X86] Assign address space to expansion ROMs. 3636 Use with caution as certain devices share 3637 address decoders between ROMs and other 3638 resources. 3639 norom [X86] Do not assign address space to 3640 expansion ROMs that do not already have 3641 BIOS assigned address ranges. 3642 nobar [X86] Do not assign address space to the 3643 BARs that weren't assigned by the BIOS. 3644 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3645 assigned automatically to PCI devices. You can 3646 make the kernel exclude IRQs of your ISA cards 3647 this way. 3648 pirqaddr=0xAAAAA [X86] Specify the physical address 3649 of the PIRQ table (normally generated 3650 by the BIOS) if it is outside the 3651 F0000h-100000h range. 3652 lastbus=N [X86] Scan all buses thru bus #N. Can be 3653 useful if the kernel is unable to find your 3654 secondary buses and you want to tell it 3655 explicitly which ones they are. 3656 assign-busses [X86] Always assign all PCI bus 3657 numbers ourselves, overriding 3658 whatever the firmware may have done. 3659 usepirqmask [X86] Honor the possible IRQ mask stored 3660 in the BIOS $PIR table. This is needed on 3661 some systems with broken BIOSes, notably 3662 some HP Pavilion N5400 and Omnibook XE3 3663 notebooks. This will have no effect if ACPI 3664 IRQ routing is enabled. 3665 noacpi [X86] Do not use ACPI for IRQ routing 3666 or for PCI scanning. 3667 use_crs [X86] Use PCI host bridge window information 3668 from ACPI. On BIOSes from 2008 or later, this 3669 is enabled by default. If you need to use this, 3670 please report a bug. 3671 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3672 If you need to use this, please report a bug. 3673 routeirq Do IRQ routing for all PCI devices. 3674 This is normally done in pci_enable_device(), 3675 so this option is a temporary workaround 3676 for broken drivers that don't call it. 3677 skip_isa_align [X86] do not align io start addr, so can 3678 handle more pci cards 3679 noearly [X86] Don't do any early type 1 scanning. 3680 This might help on some broken boards which 3681 machine check when some devices' config space 3682 is read. But various workarounds are disabled 3683 and some IOMMU drivers will not work. 3684 bfsort Sort PCI devices into breadth-first order. 3685 This sorting is done to get a device 3686 order compatible with older (<= 2.4) kernels. 3687 nobfsort Don't sort PCI devices into breadth-first order. 3688 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3689 tuning and use the BIOS-configured MPS defaults. 3690 pcie_bus_safe Set every device's MPS to the largest value 3691 supported by all devices below the root complex. 3692 pcie_bus_perf Set device MPS to the largest allowable MPS 3693 based on its parent bus. Also set MRRS (Max 3694 Read Request Size) to the largest supported 3695 value (no larger than the MPS that the device 3696 or bus can support) for best performance. 3697 pcie_bus_peer2peer Set every device's MPS to 128B, which 3698 every device is guaranteed to support. This 3699 configuration allows peer-to-peer DMA between 3700 any pair of devices, possibly at the cost of 3701 reduced performance. This also guarantees 3702 that hot-added devices will work. 3703 cbiosize=nn[KMG] The fixed amount of bus space which is 3704 reserved for the CardBus bridge's IO window. 3705 The default value is 256 bytes. 3706 cbmemsize=nn[KMG] The fixed amount of bus space which is 3707 reserved for the CardBus bridge's memory 3708 window. The default value is 64 megabytes. 3709 resource_alignment= 3710 Format: 3711 [<order of align>@]<pci_dev>[; ...] 3712 Specifies alignment and device to reassign 3713 aligned memory resources. How to 3714 specify the device is described above. 3715 If <order of align> is not specified, 3716 PAGE_SIZE is used as alignment. 3717 A PCI-PCI bridge can be specified if resource 3718 windows need to be expanded. 3719 To specify the alignment for several 3720 instances of a device, the PCI vendor, 3721 device, subvendor, and subdevice may be 3722 specified, e.g., 12@pci:8086:9c22:103c:198f 3723 for 4096-byte alignment. 3724 ecrc= Enable/disable PCIe ECRC (transaction layer 3725 end-to-end CRC checking). 3726 bios: Use BIOS/firmware settings. This is the 3727 the default. 3728 off: Turn ECRC off 3729 on: Turn ECRC on. 3730 hpiosize=nn[KMG] The fixed amount of bus space which is 3731 reserved for hotplug bridge's IO window. 3732 Default size is 256 bytes. 3733 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3734 reserved for hotplug bridge's MMIO window. 3735 Default size is 2 megabytes. 3736 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3737 reserved for hotplug bridge's MMIO_PREF window. 3738 Default size is 2 megabytes. 3739 hpmemsize=nn[KMG] The fixed amount of bus space which is 3740 reserved for hotplug bridge's MMIO and 3741 MMIO_PREF window. 3742 Default size is 2 megabytes. 3743 hpbussize=nn The minimum amount of additional bus numbers 3744 reserved for buses below a hotplug bridge. 3745 Default is 1. 3746 realloc= Enable/disable reallocating PCI bridge resources 3747 if allocations done by BIOS are too small to 3748 accommodate resources required by all child 3749 devices. 3750 off: Turn realloc off 3751 on: Turn realloc on 3752 realloc same as realloc=on 3753 noari do not use PCIe ARI. 3754 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3755 do not use PCIe ATS (and IOMMU device IOTLB). 3756 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3757 only look for one device below a PCIe downstream 3758 port. 3759 big_root_window Try to add a big 64bit memory window to the PCIe 3760 root complex on AMD CPUs. Some GFX hardware 3761 can resize a BAR to allow access to all VRAM. 3762 Adding the window is slightly risky (it may 3763 conflict with unreported devices), so this 3764 taints the kernel. 3765 disable_acs_redir=<pci_dev>[; ...] 3766 Specify one or more PCI devices (in the format 3767 specified above) separated by semicolons. 3768 Each device specified will have the PCI ACS 3769 redirect capabilities forced off which will 3770 allow P2P traffic between devices through 3771 bridges without forcing it upstream. Note: 3772 this removes isolation between devices and 3773 may put more devices in an IOMMU group. 3774 force_floating [S390] Force usage of floating interrupts. 3775 nomio [S390] Do not use MIO instructions. 3776 norid [S390] ignore the RID field and force use of 3777 one PCI domain per PCI function 3778 3779 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3780 Management. 3781 off Disable ASPM. 3782 force Enable ASPM even on devices that claim not to support it. 3783 WARNING: Forcing ASPM on may cause system lockups. 3784 3785 pcie_ports= [PCIE] PCIe port services handling: 3786 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3787 even if the platform doesn't give the OS permission to 3788 use them. This may cause conflicts if the platform 3789 also tries to use these services. 3790 dpc-native Use native PCIe service for DPC only. May 3791 cause conflicts if firmware uses AER or DPC. 3792 compat Disable native PCIe services (PME, AER, DPC, PCIe 3793 hotplug). 3794 3795 pcie_port_pm= [PCIE] PCIe port power management handling: 3796 off Disable power management of all PCIe ports 3797 force Forcibly enable power management of all PCIe ports 3798 3799 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3800 nomsi Do not use MSI for native PCIe PME signaling (this makes 3801 all PCIe root ports use INTx for all services). 3802 3803 pcmv= [HW,PCMCIA] BadgePAD 4 3804 3805 pd_ignore_unused 3806 [PM] 3807 Keep all power-domains already enabled by bootloader on, 3808 even if no driver has claimed them. This is useful 3809 for debug and development, but should not be 3810 needed on a platform with proper driver support. 3811 3812 pd. [PARIDE] 3813 See Documentation/admin-guide/blockdev/paride.rst. 3814 3815 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3816 boot time. 3817 Format: { 0 | 1 } 3818 See arch/parisc/kernel/pdc_chassis.c 3819 3820 percpu_alloc= Select which percpu first chunk allocator to use. 3821 Currently supported values are "embed" and "page". 3822 Archs may support subset or none of the selections. 3823 See comments in mm/percpu.c for details on each 3824 allocator. This parameter is primarily for debugging 3825 and performance comparison. 3826 3827 pf. [PARIDE] 3828 See Documentation/admin-guide/blockdev/paride.rst. 3829 3830 pg. [PARIDE] 3831 See Documentation/admin-guide/blockdev/paride.rst. 3832 3833 pirq= [SMP,APIC] Manual mp-table setup 3834 See Documentation/x86/i386/IO-APIC.rst. 3835 3836 plip= [PPT,NET] Parallel port network link 3837 Format: { parport<nr> | timid | 0 } 3838 See also Documentation/admin-guide/parport.rst. 3839 3840 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3841 Override pmtimer IOPort with a hex value. 3842 e.g. pmtmr=0x508 3843 3844 pm_debug_messages [SUSPEND,KNL] 3845 Enable suspend/resume debug messages during boot up. 3846 3847 pnp.debug=1 [PNP] 3848 Enable PNP debug messages (depends on the 3849 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3850 via /sys/module/pnp/parameters/debug. We always show 3851 current resource usage; turning this on also shows 3852 possible settings and some assignment information. 3853 3854 pnpacpi= [ACPI] 3855 { off } 3856 3857 pnpbios= [ISAPNP] 3858 { on | off | curr | res | no-curr | no-res } 3859 3860 pnp_reserve_irq= 3861 [ISAPNP] Exclude IRQs for the autoconfiguration 3862 3863 pnp_reserve_dma= 3864 [ISAPNP] Exclude DMAs for the autoconfiguration 3865 3866 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3867 Ranges are in pairs (I/O port base and size). 3868 3869 pnp_reserve_mem= 3870 [ISAPNP] Exclude memory regions for the 3871 autoconfiguration. 3872 Ranges are in pairs (memory base and size). 3873 3874 ports= [IP_VS_FTP] IPVS ftp helper module 3875 Default is 21. 3876 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3877 may be specified. 3878 Format: <port>,<port>.... 3879 3880 powersave=off [PPC] This option disables power saving features. 3881 It specifically disables cpuidle and sets the 3882 platform machine description specific power_save 3883 function to NULL. On Idle the CPU just reduces 3884 execution priority. 3885 3886 ppc_strict_facility_enable 3887 [PPC] This option catches any kernel floating point, 3888 Altivec, VSX and SPE outside of regions specifically 3889 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3890 There is some performance impact when enabling this. 3891 3892 ppc_tm= [PPC] 3893 Format: {"off"} 3894 Disable Hardware Transactional Memory 3895 3896 print-fatal-signals= 3897 [KNL] debug: print fatal signals 3898 3899 If enabled, warn about various signal handling 3900 related application anomalies: too many signals, 3901 too many POSIX.1 timers, fatal signals causing a 3902 coredump - etc. 3903 3904 If you hit the warning due to signal overflow, 3905 you might want to try "ulimit -i unlimited". 3906 3907 default: off. 3908 3909 printk.always_kmsg_dump= 3910 Trigger kmsg_dump for cases other than kernel oops or 3911 panics 3912 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3913 default: disabled 3914 3915 printk.devkmsg={on,off,ratelimit} 3916 Control writing to /dev/kmsg. 3917 on - unlimited logging to /dev/kmsg from userspace 3918 off - logging to /dev/kmsg disabled 3919 ratelimit - ratelimit the logging 3920 Default: ratelimit 3921 3922 printk.time= Show timing data prefixed to each printk message line 3923 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3924 3925 processor.max_cstate= [HW,ACPI] 3926 Limit processor to maximum C-state 3927 max_cstate=9 overrides any DMI blacklist limit. 3928 3929 processor.nocst [HW,ACPI] 3930 Ignore the _CST method to determine C-states, 3931 instead using the legacy FADT method 3932 3933 profile= [KNL] Enable kernel profiling via /proc/profile 3934 Format: [<profiletype>,]<number> 3935 Param: <profiletype>: "schedule", "sleep", or "kvm" 3936 [defaults to kernel profiling] 3937 Param: "schedule" - profile schedule points. 3938 Param: "sleep" - profile D-state sleeping (millisecs). 3939 Requires CONFIG_SCHEDSTATS 3940 Param: "kvm" - profile VM exits. 3941 Param: <number> - step/bucket size as a power of 2 for 3942 statistical time based profiling. 3943 3944 prompt_ramdisk= [RAM] [Deprecated] 3945 3946 prot_virt= [S390] enable hosting protected virtual machines 3947 isolated from the hypervisor (if hardware supports 3948 that). 3949 Format: <bool> 3950 3951 psi= [KNL] Enable or disable pressure stall information 3952 tracking. 3953 Format: <bool> 3954 3955 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3956 probe for; one of (bare|imps|exps|lifebook|any). 3957 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3958 per second. 3959 psmouse.resetafter= [HW,MOUSE] 3960 Try to reset the device after so many bad packets 3961 (0 = never). 3962 psmouse.resolution= 3963 [HW,MOUSE] Set desired mouse resolution, in dpi. 3964 psmouse.smartscroll= 3965 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3966 0 = disabled, 1 = enabled (default). 3967 3968 pstore.backend= Specify the name of the pstore backend to use 3969 3970 pt. [PARIDE] 3971 See Documentation/admin-guide/blockdev/paride.rst. 3972 3973 pti= [X86-64] Control Page Table Isolation of user and 3974 kernel address spaces. Disabling this feature 3975 removes hardening, but improves performance of 3976 system calls and interrupts. 3977 3978 on - unconditionally enable 3979 off - unconditionally disable 3980 auto - kernel detects whether your CPU model is 3981 vulnerable to issues that PTI mitigates 3982 3983 Not specifying this option is equivalent to pti=auto. 3984 3985 nopti [X86-64] 3986 Equivalent to pti=off 3987 3988 pty.legacy_count= 3989 [KNL] Number of legacy pty's. Overwrites compiled-in 3990 default number. 3991 3992 quiet [KNL] Disable most log messages 3993 3994 r128= [HW,DRM] 3995 3996 raid= [HW,RAID] 3997 See Documentation/admin-guide/md.rst. 3998 3999 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4000 See Documentation/admin-guide/blockdev/ramdisk.rst. 4001 4002 ramdisk_start= [RAM] RAM disk image start address 4003 4004 random.trust_cpu={on,off} 4005 [KNL] Enable or disable trusting the use of the 4006 CPU's random number generator (if available) to 4007 fully seed the kernel's CRNG. Default is controlled 4008 by CONFIG_RANDOM_TRUST_CPU. 4009 4010 ras=option[,option,...] [KNL] RAS-specific options 4011 4012 cec_disable [X86] 4013 Disable the Correctable Errors Collector, 4014 see CONFIG_RAS_CEC help text. 4015 4016 rcu_nocbs= [KNL] 4017 The argument is a cpu list, as described above, 4018 except that the string "all" can be used to 4019 specify every CPU on the system. 4020 4021 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4022 the specified list of CPUs to be no-callback CPUs. 4023 Invocation of these CPUs' RCU callbacks will be 4024 offloaded to "rcuox/N" kthreads created for that 4025 purpose, where "x" is "p" for RCU-preempt, and 4026 "s" for RCU-sched, and "N" is the CPU number. 4027 This reduces OS jitter on the offloaded CPUs, 4028 which can be useful for HPC and real-time 4029 workloads. It can also improve energy efficiency 4030 for asymmetric multiprocessors. 4031 4032 rcu_nocb_poll [KNL] 4033 Rather than requiring that offloaded CPUs 4034 (specified by rcu_nocbs= above) explicitly 4035 awaken the corresponding "rcuoN" kthreads, 4036 make these kthreads poll for callbacks. 4037 This improves the real-time response for the 4038 offloaded CPUs by relieving them of the need to 4039 wake up the corresponding kthread, but degrades 4040 energy efficiency by requiring that the kthreads 4041 periodically wake up to do the polling. 4042 4043 rcutree.blimit= [KNL] 4044 Set maximum number of finished RCU callbacks to 4045 process in one batch. 4046 4047 rcutree.dump_tree= [KNL] 4048 Dump the structure of the rcu_node combining tree 4049 out at early boot. This is used for diagnostic 4050 purposes, to verify correct tree setup. 4051 4052 rcutree.gp_cleanup_delay= [KNL] 4053 Set the number of jiffies to delay each step of 4054 RCU grace-period cleanup. 4055 4056 rcutree.gp_init_delay= [KNL] 4057 Set the number of jiffies to delay each step of 4058 RCU grace-period initialization. 4059 4060 rcutree.gp_preinit_delay= [KNL] 4061 Set the number of jiffies to delay each step of 4062 RCU grace-period pre-initialization, that is, 4063 the propagation of recent CPU-hotplug changes up 4064 the rcu_node combining tree. 4065 4066 rcutree.use_softirq= [KNL] 4067 If set to zero, move all RCU_SOFTIRQ processing to 4068 per-CPU rcuc kthreads. Defaults to a non-zero 4069 value, meaning that RCU_SOFTIRQ is used by default. 4070 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4071 4072 rcutree.rcu_fanout_exact= [KNL] 4073 Disable autobalancing of the rcu_node combining 4074 tree. This is used by rcutorture, and might 4075 possibly be useful for architectures having high 4076 cache-to-cache transfer latencies. 4077 4078 rcutree.rcu_fanout_leaf= [KNL] 4079 Change the number of CPUs assigned to each 4080 leaf rcu_node structure. Useful for very 4081 large systems, which will choose the value 64, 4082 and for NUMA systems with large remote-access 4083 latencies, which will choose a value aligned 4084 with the appropriate hardware boundaries. 4085 4086 rcutree.rcu_min_cached_objs= [KNL] 4087 Minimum number of objects which are cached and 4088 maintained per one CPU. Object size is equal 4089 to PAGE_SIZE. The cache allows to reduce the 4090 pressure to page allocator, also it makes the 4091 whole algorithm to behave better in low memory 4092 condition. 4093 4094 rcutree.jiffies_till_first_fqs= [KNL] 4095 Set delay from grace-period initialization to 4096 first attempt to force quiescent states. 4097 Units are jiffies, minimum value is zero, 4098 and maximum value is HZ. 4099 4100 rcutree.jiffies_till_next_fqs= [KNL] 4101 Set delay between subsequent attempts to force 4102 quiescent states. Units are jiffies, minimum 4103 value is one, and maximum value is HZ. 4104 4105 rcutree.jiffies_till_sched_qs= [KNL] 4106 Set required age in jiffies for a 4107 given grace period before RCU starts 4108 soliciting quiescent-state help from 4109 rcu_note_context_switch() and cond_resched(). 4110 If not specified, the kernel will calculate 4111 a value based on the most recent settings 4112 of rcutree.jiffies_till_first_fqs 4113 and rcutree.jiffies_till_next_fqs. 4114 This calculated value may be viewed in 4115 rcutree.jiffies_to_sched_qs. Any attempt to set 4116 rcutree.jiffies_to_sched_qs will be cheerfully 4117 overwritten. 4118 4119 rcutree.kthread_prio= [KNL,BOOT] 4120 Set the SCHED_FIFO priority of the RCU per-CPU 4121 kthreads (rcuc/N). This value is also used for 4122 the priority of the RCU boost threads (rcub/N) 4123 and for the RCU grace-period kthreads (rcu_bh, 4124 rcu_preempt, and rcu_sched). If RCU_BOOST is 4125 set, valid values are 1-99 and the default is 1 4126 (the least-favored priority). Otherwise, when 4127 RCU_BOOST is not set, valid values are 0-99 and 4128 the default is zero (non-realtime operation). 4129 4130 rcutree.rcu_nocb_gp_stride= [KNL] 4131 Set the number of NOCB callback kthreads in 4132 each group, which defaults to the square root 4133 of the number of CPUs. Larger numbers reduce 4134 the wakeup overhead on the global grace-period 4135 kthread, but increases that same overhead on 4136 each group's NOCB grace-period kthread. 4137 4138 rcutree.qhimark= [KNL] 4139 Set threshold of queued RCU callbacks beyond which 4140 batch limiting is disabled. 4141 4142 rcutree.qlowmark= [KNL] 4143 Set threshold of queued RCU callbacks below which 4144 batch limiting is re-enabled. 4145 4146 rcutree.qovld= [KNL] 4147 Set threshold of queued RCU callbacks beyond which 4148 RCU's force-quiescent-state scan will aggressively 4149 enlist help from cond_resched() and sched IPIs to 4150 help CPUs more quickly reach quiescent states. 4151 Set to less than zero to make this be set based 4152 on rcutree.qhimark at boot time and to zero to 4153 disable more aggressive help enlistment. 4154 4155 rcutree.rcu_idle_gp_delay= [KNL] 4156 Set wakeup interval for idle CPUs that have 4157 RCU callbacks (RCU_FAST_NO_HZ=y). 4158 4159 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4160 Set wakeup interval for idle CPUs that have 4161 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4162 Lazy RCU callbacks are those which RCU can 4163 prove do nothing more than free memory. 4164 4165 rcutree.rcu_kick_kthreads= [KNL] 4166 Cause the grace-period kthread to get an extra 4167 wake_up() if it sleeps three times longer than 4168 it should at force-quiescent-state time. 4169 This wake_up() will be accompanied by a 4170 WARN_ONCE() splat and an ftrace_dump(). 4171 4172 rcutree.sysrq_rcu= [KNL] 4173 Commandeer a sysrq key to dump out Tree RCU's 4174 rcu_node tree with an eye towards determining 4175 why a new grace period has not yet started. 4176 4177 rcuperf.gp_async= [KNL] 4178 Measure performance of asynchronous 4179 grace-period primitives such as call_rcu(). 4180 4181 rcuperf.gp_async_max= [KNL] 4182 Specify the maximum number of outstanding 4183 callbacks per writer thread. When a writer 4184 thread exceeds this limit, it invokes the 4185 corresponding flavor of rcu_barrier() to allow 4186 previously posted callbacks to drain. 4187 4188 rcuperf.gp_exp= [KNL] 4189 Measure performance of expedited synchronous 4190 grace-period primitives. 4191 4192 rcuperf.holdoff= [KNL] 4193 Set test-start holdoff period. The purpose of 4194 this parameter is to delay the start of the 4195 test until boot completes in order to avoid 4196 interference. 4197 4198 rcuperf.kfree_rcu_test= [KNL] 4199 Set to measure performance of kfree_rcu() flooding. 4200 4201 rcuperf.kfree_nthreads= [KNL] 4202 The number of threads running loops of kfree_rcu(). 4203 4204 rcuperf.kfree_alloc_num= [KNL] 4205 Number of allocations and frees done in an iteration. 4206 4207 rcuperf.kfree_loops= [KNL] 4208 Number of loops doing rcuperf.kfree_alloc_num number 4209 of allocations and frees. 4210 4211 rcuperf.nreaders= [KNL] 4212 Set number of RCU readers. The value -1 selects 4213 N, where N is the number of CPUs. A value 4214 "n" less than -1 selects N-n+1, where N is again 4215 the number of CPUs. For example, -2 selects N 4216 (the number of CPUs), -3 selects N+1, and so on. 4217 A value of "n" less than or equal to -N selects 4218 a single reader. 4219 4220 rcuperf.nwriters= [KNL] 4221 Set number of RCU writers. The values operate 4222 the same as for rcuperf.nreaders. 4223 N, where N is the number of CPUs 4224 4225 rcuperf.perf_type= [KNL] 4226 Specify the RCU implementation to test. 4227 4228 rcuperf.shutdown= [KNL] 4229 Shut the system down after performance tests 4230 complete. This is useful for hands-off automated 4231 testing. 4232 4233 rcuperf.verbose= [KNL] 4234 Enable additional printk() statements. 4235 4236 rcuperf.writer_holdoff= [KNL] 4237 Write-side holdoff between grace periods, 4238 in microseconds. The default of zero says 4239 no holdoff. 4240 4241 rcutorture.fqs_duration= [KNL] 4242 Set duration of force_quiescent_state bursts 4243 in microseconds. 4244 4245 rcutorture.fqs_holdoff= [KNL] 4246 Set holdoff time within force_quiescent_state bursts 4247 in microseconds. 4248 4249 rcutorture.fqs_stutter= [KNL] 4250 Set wait time between force_quiescent_state bursts 4251 in seconds. 4252 4253 rcutorture.fwd_progress= [KNL] 4254 Enable RCU grace-period forward-progress testing 4255 for the types of RCU supporting this notion. 4256 4257 rcutorture.fwd_progress_div= [KNL] 4258 Specify the fraction of a CPU-stall-warning 4259 period to do tight-loop forward-progress testing. 4260 4261 rcutorture.fwd_progress_holdoff= [KNL] 4262 Number of seconds to wait between successive 4263 forward-progress tests. 4264 4265 rcutorture.fwd_progress_need_resched= [KNL] 4266 Enclose cond_resched() calls within checks for 4267 need_resched() during tight-loop forward-progress 4268 testing. 4269 4270 rcutorture.gp_cond= [KNL] 4271 Use conditional/asynchronous update-side 4272 primitives, if available. 4273 4274 rcutorture.gp_exp= [KNL] 4275 Use expedited update-side primitives, if available. 4276 4277 rcutorture.gp_normal= [KNL] 4278 Use normal (non-expedited) asynchronous 4279 update-side primitives, if available. 4280 4281 rcutorture.gp_sync= [KNL] 4282 Use normal (non-expedited) synchronous 4283 update-side primitives, if available. If all 4284 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4285 rcutorture.gp_normal=, and rcutorture.gp_sync= 4286 are zero, rcutorture acts as if is interpreted 4287 they are all non-zero. 4288 4289 rcutorture.n_barrier_cbs= [KNL] 4290 Set callbacks/threads for rcu_barrier() testing. 4291 4292 rcutorture.nfakewriters= [KNL] 4293 Set number of concurrent RCU writers. These just 4294 stress RCU, they don't participate in the actual 4295 test, hence the "fake". 4296 4297 rcutorture.nreaders= [KNL] 4298 Set number of RCU readers. The value -1 selects 4299 N-1, where N is the number of CPUs. A value 4300 "n" less than -1 selects N-n-2, where N is again 4301 the number of CPUs. For example, -2 selects N 4302 (the number of CPUs), -3 selects N+1, and so on. 4303 4304 rcutorture.object_debug= [KNL] 4305 Enable debug-object double-call_rcu() testing. 4306 4307 rcutorture.onoff_holdoff= [KNL] 4308 Set time (s) after boot for CPU-hotplug testing. 4309 4310 rcutorture.onoff_interval= [KNL] 4311 Set time (jiffies) between CPU-hotplug operations, 4312 or zero to disable CPU-hotplug testing. 4313 4314 rcutorture.read_exit= [KNL] 4315 Set the number of read-then-exit kthreads used 4316 to test the interaction of RCU updaters and 4317 task-exit processing. 4318 4319 rcutorture.read_exit_burst= [KNL] 4320 The number of times in a given read-then-exit 4321 episode that a set of read-then-exit kthreads 4322 is spawned. 4323 4324 rcutorture.read_exit_delay= [KNL] 4325 The delay, in seconds, between successive 4326 read-then-exit testing episodes. 4327 4328 rcutorture.shuffle_interval= [KNL] 4329 Set task-shuffle interval (s). Shuffling tasks 4330 allows some CPUs to go into dyntick-idle mode 4331 during the rcutorture test. 4332 4333 rcutorture.shutdown_secs= [KNL] 4334 Set time (s) after boot system shutdown. This 4335 is useful for hands-off automated testing. 4336 4337 rcutorture.stall_cpu= [KNL] 4338 Duration of CPU stall (s) to test RCU CPU stall 4339 warnings, zero to disable. 4340 4341 rcutorture.stall_cpu_block= [KNL] 4342 Sleep while stalling if set. This will result 4343 in warnings from preemptible RCU in addition 4344 to any other stall-related activity. 4345 4346 rcutorture.stall_cpu_holdoff= [KNL] 4347 Time to wait (s) after boot before inducing stall. 4348 4349 rcutorture.stall_cpu_irqsoff= [KNL] 4350 Disable interrupts while stalling if set. 4351 4352 rcutorture.stall_gp_kthread= [KNL] 4353 Duration (s) of forced sleep within RCU 4354 grace-period kthread to test RCU CPU stall 4355 warnings, zero to disable. If both stall_cpu 4356 and stall_gp_kthread are specified, the 4357 kthread is starved first, then the CPU. 4358 4359 rcutorture.stat_interval= [KNL] 4360 Time (s) between statistics printk()s. 4361 4362 rcutorture.stutter= [KNL] 4363 Time (s) to stutter testing, for example, specifying 4364 five seconds causes the test to run for five seconds, 4365 wait for five seconds, and so on. This tests RCU's 4366 ability to transition abruptly to and from idle. 4367 4368 rcutorture.test_boost= [KNL] 4369 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4370 "Maybe" means test if the RCU implementation 4371 under test support RCU priority boosting. 4372 4373 rcutorture.test_boost_duration= [KNL] 4374 Duration (s) of each individual boost test. 4375 4376 rcutorture.test_boost_interval= [KNL] 4377 Interval (s) between each boost test. 4378 4379 rcutorture.test_no_idle_hz= [KNL] 4380 Test RCU's dyntick-idle handling. See also the 4381 rcutorture.shuffle_interval parameter. 4382 4383 rcutorture.torture_type= [KNL] 4384 Specify the RCU implementation to test. 4385 4386 rcutorture.verbose= [KNL] 4387 Enable additional printk() statements. 4388 4389 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4390 Dump ftrace buffer after reporting RCU CPU 4391 stall warning. 4392 4393 rcupdate.rcu_cpu_stall_suppress= [KNL] 4394 Suppress RCU CPU stall warning messages. 4395 4396 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4397 Suppress RCU CPU stall warning messages and 4398 rcutorture writer stall warnings that occur 4399 during early boot, that is, during the time 4400 before the init task is spawned. 4401 4402 rcupdate.rcu_cpu_stall_timeout= [KNL] 4403 Set timeout for RCU CPU stall warning messages. 4404 4405 rcupdate.rcu_expedited= [KNL] 4406 Use expedited grace-period primitives, for 4407 example, synchronize_rcu_expedited() instead 4408 of synchronize_rcu(). This reduces latency, 4409 but can increase CPU utilization, degrade 4410 real-time latency, and degrade energy efficiency. 4411 No effect on CONFIG_TINY_RCU kernels. 4412 4413 rcupdate.rcu_normal= [KNL] 4414 Use only normal grace-period primitives, 4415 for example, synchronize_rcu() instead of 4416 synchronize_rcu_expedited(). This improves 4417 real-time latency, CPU utilization, and 4418 energy efficiency, but can expose users to 4419 increased grace-period latency. This parameter 4420 overrides rcupdate.rcu_expedited. No effect on 4421 CONFIG_TINY_RCU kernels. 4422 4423 rcupdate.rcu_normal_after_boot= [KNL] 4424 Once boot has completed (that is, after 4425 rcu_end_inkernel_boot() has been invoked), use 4426 only normal grace-period primitives. No effect 4427 on CONFIG_TINY_RCU kernels. 4428 4429 rcupdate.rcu_task_ipi_delay= [KNL] 4430 Set time in jiffies during which RCU tasks will 4431 avoid sending IPIs, starting with the beginning 4432 of a given grace period. Setting a large 4433 number avoids disturbing real-time workloads, 4434 but lengthens grace periods. 4435 4436 rcupdate.rcu_task_stall_timeout= [KNL] 4437 Set timeout in jiffies for RCU task stall warning 4438 messages. Disable with a value less than or equal 4439 to zero. 4440 4441 rcupdate.rcu_self_test= [KNL] 4442 Run the RCU early boot self tests 4443 4444 rdinit= [KNL] 4445 Format: <full_path> 4446 Run specified binary instead of /init from the ramdisk, 4447 used for early userspace startup. See initrd. 4448 4449 rdrand= [X86] 4450 force - Override the decision by the kernel to hide the 4451 advertisement of RDRAND support (this affects 4452 certain AMD processors because of buggy BIOS 4453 support, specifically around the suspend/resume 4454 path). 4455 4456 rdt= [HW,X86,RDT] 4457 Turn on/off individual RDT features. List is: 4458 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4459 mba. 4460 E.g. to turn on cmt and turn off mba use: 4461 rdt=cmt,!mba 4462 4463 reboot= [KNL] 4464 Format (x86 or x86_64): 4465 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4466 [[,]s[mp]#### \ 4467 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4468 [[,]f[orce] 4469 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4470 (prefix with 'panic_' to set mode for panic 4471 reboot only), 4472 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4473 reboot_force is either force or not specified, 4474 reboot_cpu is s[mp]#### with #### being the processor 4475 to be used for rebooting. 4476 4477 refscale.holdoff= [KNL] 4478 Set test-start holdoff period. The purpose of 4479 this parameter is to delay the start of the 4480 test until boot completes in order to avoid 4481 interference. 4482 4483 refscale.loops= [KNL] 4484 Set the number of loops over the synchronization 4485 primitive under test. Increasing this number 4486 reduces noise due to loop start/end overhead, 4487 but the default has already reduced the per-pass 4488 noise to a handful of picoseconds on ca. 2020 4489 x86 laptops. 4490 4491 refscale.nreaders= [KNL] 4492 Set number of readers. The default value of -1 4493 selects N, where N is roughly 75% of the number 4494 of CPUs. A value of zero is an interesting choice. 4495 4496 refscale.nruns= [KNL] 4497 Set number of runs, each of which is dumped onto 4498 the console log. 4499 4500 refscale.readdelay= [KNL] 4501 Set the read-side critical-section duration, 4502 measured in microseconds. 4503 4504 refscale.scale_type= [KNL] 4505 Specify the read-protection implementation to test. 4506 4507 refscale.shutdown= [KNL] 4508 Shut down the system at the end of the performance 4509 test. This defaults to 1 (shut it down) when 4510 rcuperf is built into the kernel and to 0 (leave 4511 it running) when rcuperf is built as a module. 4512 4513 refscale.verbose= [KNL] 4514 Enable additional printk() statements. 4515 4516 relax_domain_level= 4517 [KNL, SMP] Set scheduler's default relax_domain_level. 4518 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4519 4520 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4521 Format: <base1>,<size1>[,<base2>,<size2>,...] 4522 Reserve I/O ports or memory so the kernel won't use 4523 them. If <base> is less than 0x10000, the region 4524 is assumed to be I/O ports; otherwise it is memory. 4525 4526 reservetop= [X86-32] 4527 Format: nn[KMG] 4528 Reserves a hole at the top of the kernel virtual 4529 address space. 4530 4531 reservelow= [X86] 4532 Format: nn[K] 4533 Set the amount of memory to reserve for BIOS at 4534 the bottom of the address space. 4535 4536 reset_devices [KNL] Force drivers to reset the underlying device 4537 during initialization. 4538 4539 resume= [SWSUSP] 4540 Specify the partition device for software suspend 4541 Format: 4542 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4543 4544 resume_offset= [SWSUSP] 4545 Specify the offset from the beginning of the partition 4546 given by "resume=" at which the swap header is located, 4547 in <PAGE_SIZE> units (needed only for swap files). 4548 See Documentation/power/swsusp-and-swap-files.rst 4549 4550 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4551 read the resume files 4552 4553 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4554 Useful for devices that are detected asynchronously 4555 (e.g. USB and MMC devices). 4556 4557 hibernate= [HIBERNATION] 4558 noresume Don't check if there's a hibernation image 4559 present during boot. 4560 nocompress Don't compress/decompress hibernation images. 4561 no Disable hibernation and resume. 4562 protect_image Turn on image protection during restoration 4563 (that will set all pages holding image data 4564 during restoration read-only). 4565 4566 retain_initrd [RAM] Keep initrd memory after extraction 4567 4568 rfkill.default_state= 4569 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4570 etc. communication is blocked by default. 4571 1 Unblocked. 4572 4573 rfkill.master_switch_mode= 4574 0 The "airplane mode" button does nothing. 4575 1 The "airplane mode" button toggles between everything 4576 blocked and the previous configuration. 4577 2 The "airplane mode" button toggles between everything 4578 blocked and everything unblocked. 4579 4580 rhash_entries= [KNL,NET] 4581 Set number of hash buckets for route cache 4582 4583 ring3mwait=disable 4584 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4585 CPUs. 4586 4587 ro [KNL] Mount root device read-only on boot 4588 4589 rodata= [KNL] 4590 on Mark read-only kernel memory as read-only (default). 4591 off Leave read-only kernel memory writable for debugging. 4592 4593 rockchip.usb_uart 4594 Enable the uart passthrough on the designated usb port 4595 on Rockchip SoCs. When active, the signals of the 4596 debug-uart get routed to the D+ and D- pins of the usb 4597 port and the regular usb controller gets disabled. 4598 4599 root= [KNL] Root filesystem 4600 See name_to_dev_t comment in init/do_mounts.c. 4601 4602 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4603 mount the root filesystem 4604 4605 rootflags= [KNL] Set root filesystem mount option string 4606 4607 rootfstype= [KNL] Set root filesystem type 4608 4609 rootwait [KNL] Wait (indefinitely) for root device to show up. 4610 Useful for devices that are detected asynchronously 4611 (e.g. USB and MMC devices). 4612 4613 rproc_mem=nn[KMG][@address] 4614 [KNL,ARM,CMA] Remoteproc physical memory block. 4615 Memory area to be used by remote processor image, 4616 managed by CMA. 4617 4618 rw [KNL] Mount root device read-write on boot 4619 4620 S [KNL] Run init in single mode 4621 4622 s390_iommu= [HW,S390] 4623 Set s390 IOTLB flushing mode 4624 strict 4625 With strict flushing every unmap operation will result in 4626 an IOTLB flush. Default is lazy flushing before reuse, 4627 which is faster. 4628 4629 sa1100ir [NET] 4630 See drivers/net/irda/sa1100_ir.c. 4631 4632 sbni= [NET] Granch SBNI12 leased line adapter 4633 4634 sched_debug [KNL] Enables verbose scheduler debug messages. 4635 4636 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4637 Allowed values are enable and disable. This feature 4638 incurs a small amount of overhead in the scheduler 4639 but is useful for debugging and performance tuning. 4640 4641 sched_thermal_decay_shift= 4642 [KNL, SMP] Set a decay shift for scheduler thermal 4643 pressure signal. Thermal pressure signal follows the 4644 default decay period of other scheduler pelt 4645 signals(usually 32 ms but configurable). Setting 4646 sched_thermal_decay_shift will left shift the decay 4647 period for the thermal pressure signal by the shift 4648 value. 4649 i.e. with the default pelt decay period of 32 ms 4650 sched_thermal_decay_shift thermal pressure decay pr 4651 1 64 ms 4652 2 128 ms 4653 and so on. 4654 Format: integer between 0 and 10 4655 Default is 0. 4656 4657 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4658 xtime_lock contention on larger systems, and/or RCU lock 4659 contention on all systems with CONFIG_MAXSMP set. 4660 Format: { "0" | "1" } 4661 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4662 1 -- enable. 4663 Note: increases power consumption, thus should only be 4664 enabled if running jitter sensitive (HPC/RT) workloads. 4665 4666 security= [SECURITY] Choose a legacy "major" security module to 4667 enable at boot. This has been deprecated by the 4668 "lsm=" parameter. 4669 4670 selinux= [SELINUX] Disable or enable SELinux at boot time. 4671 Format: { "0" | "1" } 4672 See security/selinux/Kconfig help text. 4673 0 -- disable. 4674 1 -- enable. 4675 Default value is 1. 4676 4677 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4678 Format: { "0" | "1" } 4679 See security/apparmor/Kconfig help text 4680 0 -- disable. 4681 1 -- enable. 4682 Default value is set via kernel config option. 4683 4684 serialnumber [BUGS=X86-32] 4685 4686 shapers= [NET] 4687 Maximal number of shapers. 4688 4689 simeth= [IA-64] 4690 simscsi= 4691 4692 slram= [HW,MTD] 4693 4694 slab_nomerge [MM] 4695 Disable merging of slabs with similar size. May be 4696 necessary if there is some reason to distinguish 4697 allocs to different slabs, especially in hardened 4698 environments where the risk of heap overflows and 4699 layout control by attackers can usually be 4700 frustrated by disabling merging. This will reduce 4701 most of the exposure of a heap attack to a single 4702 cache (risks via metadata attacks are mostly 4703 unchanged). Debug options disable merging on their 4704 own. 4705 For more information see Documentation/vm/slub.rst. 4706 4707 slab_max_order= [MM, SLAB] 4708 Determines the maximum allowed order for slabs. 4709 A high setting may cause OOMs due to memory 4710 fragmentation. Defaults to 1 for systems with 4711 more than 32MB of RAM, 0 otherwise. 4712 4713 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4714 Enabling slub_debug allows one to determine the 4715 culprit if slab objects become corrupted. Enabling 4716 slub_debug can create guard zones around objects and 4717 may poison objects when not in use. Also tracks the 4718 last alloc / free. For more information see 4719 Documentation/vm/slub.rst. 4720 4721 slub_memcg_sysfs= [MM, SLUB] 4722 Determines whether to enable sysfs directories for 4723 memory cgroup sub-caches. 1 to enable, 0 to disable. 4724 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4725 Enabling this can lead to a very high number of debug 4726 directories and files being created under 4727 /sys/kernel/slub. 4728 4729 slub_max_order= [MM, SLUB] 4730 Determines the maximum allowed order for slabs. 4731 A high setting may cause OOMs due to memory 4732 fragmentation. For more information see 4733 Documentation/vm/slub.rst. 4734 4735 slub_min_objects= [MM, SLUB] 4736 The minimum number of objects per slab. SLUB will 4737 increase the slab order up to slub_max_order to 4738 generate a sufficiently large slab able to contain 4739 the number of objects indicated. The higher the number 4740 of objects the smaller the overhead of tracking slabs 4741 and the less frequently locks need to be acquired. 4742 For more information see Documentation/vm/slub.rst. 4743 4744 slub_min_order= [MM, SLUB] 4745 Determines the minimum page order for slabs. Must be 4746 lower than slub_max_order. 4747 For more information see Documentation/vm/slub.rst. 4748 4749 slub_nomerge [MM, SLUB] 4750 Same with slab_nomerge. This is supported for legacy. 4751 See slab_nomerge for more information. 4752 4753 smart2= [HW] 4754 Format: <io1>[,<io2>[,...,<io8>]] 4755 4756 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4757 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4758 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4759 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4760 smsc-ircc2.ircc_irq= [HW] IRQ line 4761 smsc-ircc2.ircc_dma= [HW] DMA channel 4762 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4763 0: Toshiba Satellite 1800 (GP data pin select) 4764 1: Fast pin select (default) 4765 2: ATC IRMode 4766 4767 smt [KNL,S390] Set the maximum number of threads (logical 4768 CPUs) to use per physical CPU on systems capable of 4769 symmetric multithreading (SMT). Will be capped to the 4770 actual hardware limit. 4771 Format: <integer> 4772 Default: -1 (no limit) 4773 4774 softlockup_panic= 4775 [KNL] Should the soft-lockup detector generate panics. 4776 Format: 0 | 1 4777 4778 A value of 1 instructs the soft-lockup detector 4779 to panic the machine when a soft-lockup occurs. It is 4780 also controlled by the kernel.softlockup_panic sysctl 4781 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4782 respective build-time switch to that functionality. 4783 4784 softlockup_all_cpu_backtrace= 4785 [KNL] Should the soft-lockup detector generate 4786 backtraces on all cpus. 4787 Format: 0 | 1 4788 4789 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4790 See Documentation/admin-guide/laptops/sonypi.rst 4791 4792 spectre_v2= [X86] Control mitigation of Spectre variant 2 4793 (indirect branch speculation) vulnerability. 4794 The default operation protects the kernel from 4795 user space attacks. 4796 4797 on - unconditionally enable, implies 4798 spectre_v2_user=on 4799 off - unconditionally disable, implies 4800 spectre_v2_user=off 4801 auto - kernel detects whether your CPU model is 4802 vulnerable 4803 4804 Selecting 'on' will, and 'auto' may, choose a 4805 mitigation method at run time according to the 4806 CPU, the available microcode, the setting of the 4807 CONFIG_RETPOLINE configuration option, and the 4808 compiler with which the kernel was built. 4809 4810 Selecting 'on' will also enable the mitigation 4811 against user space to user space task attacks. 4812 4813 Selecting 'off' will disable both the kernel and 4814 the user space protections. 4815 4816 Specific mitigations can also be selected manually: 4817 4818 retpoline - replace indirect branches 4819 retpoline,generic - google's original retpoline 4820 retpoline,amd - AMD-specific minimal thunk 4821 4822 Not specifying this option is equivalent to 4823 spectre_v2=auto. 4824 4825 spectre_v2_user= 4826 [X86] Control mitigation of Spectre variant 2 4827 (indirect branch speculation) vulnerability between 4828 user space tasks 4829 4830 on - Unconditionally enable mitigations. Is 4831 enforced by spectre_v2=on 4832 4833 off - Unconditionally disable mitigations. Is 4834 enforced by spectre_v2=off 4835 4836 prctl - Indirect branch speculation is enabled, 4837 but mitigation can be enabled via prctl 4838 per thread. The mitigation control state 4839 is inherited on fork. 4840 4841 prctl,ibpb 4842 - Like "prctl" above, but only STIBP is 4843 controlled per thread. IBPB is issued 4844 always when switching between different user 4845 space processes. 4846 4847 seccomp 4848 - Same as "prctl" above, but all seccomp 4849 threads will enable the mitigation unless 4850 they explicitly opt out. 4851 4852 seccomp,ibpb 4853 - Like "seccomp" above, but only STIBP is 4854 controlled per thread. IBPB is issued 4855 always when switching between different 4856 user space processes. 4857 4858 auto - Kernel selects the mitigation depending on 4859 the available CPU features and vulnerability. 4860 4861 Default mitigation: 4862 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4863 4864 Not specifying this option is equivalent to 4865 spectre_v2_user=auto. 4866 4867 spec_store_bypass_disable= 4868 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4869 (Speculative Store Bypass vulnerability) 4870 4871 Certain CPUs are vulnerable to an exploit against a 4872 a common industry wide performance optimization known 4873 as "Speculative Store Bypass" in which recent stores 4874 to the same memory location may not be observed by 4875 later loads during speculative execution. The idea 4876 is that such stores are unlikely and that they can 4877 be detected prior to instruction retirement at the 4878 end of a particular speculation execution window. 4879 4880 In vulnerable processors, the speculatively forwarded 4881 store can be used in a cache side channel attack, for 4882 example to read memory to which the attacker does not 4883 directly have access (e.g. inside sandboxed code). 4884 4885 This parameter controls whether the Speculative Store 4886 Bypass optimization is used. 4887 4888 On x86 the options are: 4889 4890 on - Unconditionally disable Speculative Store Bypass 4891 off - Unconditionally enable Speculative Store Bypass 4892 auto - Kernel detects whether the CPU model contains an 4893 implementation of Speculative Store Bypass and 4894 picks the most appropriate mitigation. If the 4895 CPU is not vulnerable, "off" is selected. If the 4896 CPU is vulnerable the default mitigation is 4897 architecture and Kconfig dependent. See below. 4898 prctl - Control Speculative Store Bypass per thread 4899 via prctl. Speculative Store Bypass is enabled 4900 for a process by default. The state of the control 4901 is inherited on fork. 4902 seccomp - Same as "prctl" above, but all seccomp threads 4903 will disable SSB unless they explicitly opt out. 4904 4905 Default mitigations: 4906 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4907 4908 On powerpc the options are: 4909 4910 on,auto - On Power8 and Power9 insert a store-forwarding 4911 barrier on kernel entry and exit. On Power7 4912 perform a software flush on kernel entry and 4913 exit. 4914 off - No action. 4915 4916 Not specifying this option is equivalent to 4917 spec_store_bypass_disable=auto. 4918 4919 spia_io_base= [HW,MTD] 4920 spia_fio_base= 4921 spia_pedr= 4922 spia_peddr= 4923 4924 split_lock_detect= 4925 [X86] Enable split lock detection 4926 4927 When enabled (and if hardware support is present), atomic 4928 instructions that access data across cache line 4929 boundaries will result in an alignment check exception. 4930 4931 off - not enabled 4932 4933 warn - the kernel will emit rate limited warnings 4934 about applications triggering the #AC 4935 exception. This mode is the default on CPUs 4936 that supports split lock detection. 4937 4938 fatal - the kernel will send SIGBUS to applications 4939 that trigger the #AC exception. 4940 4941 If an #AC exception is hit in the kernel or in 4942 firmware (i.e. not while executing in user mode) 4943 the kernel will oops in either "warn" or "fatal" 4944 mode. 4945 4946 srbds= [X86,INTEL] 4947 Control the Special Register Buffer Data Sampling 4948 (SRBDS) mitigation. 4949 4950 Certain CPUs are vulnerable to an MDS-like 4951 exploit which can leak bits from the random 4952 number generator. 4953 4954 By default, this issue is mitigated by 4955 microcode. However, the microcode fix can cause 4956 the RDRAND and RDSEED instructions to become 4957 much slower. Among other effects, this will 4958 result in reduced throughput from /dev/urandom. 4959 4960 The microcode mitigation can be disabled with 4961 the following option: 4962 4963 off: Disable mitigation and remove 4964 performance impact to RDRAND and RDSEED 4965 4966 srcutree.counter_wrap_check [KNL] 4967 Specifies how frequently to check for 4968 grace-period sequence counter wrap for the 4969 srcu_data structure's ->srcu_gp_seq_needed field. 4970 The greater the number of bits set in this kernel 4971 parameter, the less frequently counter wrap will 4972 be checked for. Note that the bottom two bits 4973 are ignored. 4974 4975 srcutree.exp_holdoff [KNL] 4976 Specifies how many nanoseconds must elapse 4977 since the end of the last SRCU grace period for 4978 a given srcu_struct until the next normal SRCU 4979 grace period will be considered for automatic 4980 expediting. Set to zero to disable automatic 4981 expediting. 4982 4983 ssbd= [ARM64,HW] 4984 Speculative Store Bypass Disable control 4985 4986 On CPUs that are vulnerable to the Speculative 4987 Store Bypass vulnerability and offer a 4988 firmware based mitigation, this parameter 4989 indicates how the mitigation should be used: 4990 4991 force-on: Unconditionally enable mitigation for 4992 for both kernel and userspace 4993 force-off: Unconditionally disable mitigation for 4994 for both kernel and userspace 4995 kernel: Always enable mitigation in the 4996 kernel, and offer a prctl interface 4997 to allow userspace to register its 4998 interest in being mitigated too. 4999 5000 stack_guard_gap= [MM] 5001 override the default stack gap protection. The value 5002 is in page units and it defines how many pages prior 5003 to (for stacks growing down) resp. after (for stacks 5004 growing up) the main stack are reserved for no other 5005 mapping. Default value is 256 pages. 5006 5007 stacktrace [FTRACE] 5008 Enabled the stack tracer on boot up. 5009 5010 stacktrace_filter=[function-list] 5011 [FTRACE] Limit the functions that the stack tracer 5012 will trace at boot up. function-list is a comma separated 5013 list of functions. This list can be changed at run 5014 time by the stack_trace_filter file in the debugfs 5015 tracing directory. Note, this enables stack tracing 5016 and the stacktrace above is not needed. 5017 5018 sti= [PARISC,HW] 5019 Format: <num> 5020 Set the STI (builtin display/keyboard on the HP-PARISC 5021 machines) console (graphic card) which should be used 5022 as the initial boot-console. 5023 See also comment in drivers/video/console/sticore.c. 5024 5025 sti_font= [HW] 5026 See comment in drivers/video/console/sticore.c. 5027 5028 stifb= [HW] 5029 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5030 5031 sunrpc.min_resvport= 5032 sunrpc.max_resvport= 5033 [NFS,SUNRPC] 5034 SunRPC servers often require that client requests 5035 originate from a privileged port (i.e. a port in the 5036 range 0 < portnr < 1024). 5037 An administrator who wishes to reserve some of these 5038 ports for other uses may adjust the range that the 5039 kernel's sunrpc client considers to be privileged 5040 using these two parameters to set the minimum and 5041 maximum port values. 5042 5043 sunrpc.svc_rpc_per_connection_limit= 5044 [NFS,SUNRPC] 5045 Limit the number of requests that the server will 5046 process in parallel from a single connection. 5047 The default value is 0 (no limit). 5048 5049 sunrpc.pool_mode= 5050 [NFS] 5051 Control how the NFS server code allocates CPUs to 5052 service thread pools. Depending on how many NICs 5053 you have and where their interrupts are bound, this 5054 option will affect which CPUs will do NFS serving. 5055 Note: this parameter cannot be changed while the 5056 NFS server is running. 5057 5058 auto the server chooses an appropriate mode 5059 automatically using heuristics 5060 global a single global pool contains all CPUs 5061 percpu one pool for each CPU 5062 pernode one pool for each NUMA node (equivalent 5063 to global on non-NUMA machines) 5064 5065 sunrpc.tcp_slot_table_entries= 5066 sunrpc.udp_slot_table_entries= 5067 [NFS,SUNRPC] 5068 Sets the upper limit on the number of simultaneous 5069 RPC calls that can be sent from the client to a 5070 server. Increasing these values may allow you to 5071 improve throughput, but will also increase the 5072 amount of memory reserved for use by the client. 5073 5074 suspend.pm_test_delay= 5075 [SUSPEND] 5076 Sets the number of seconds to remain in a suspend test 5077 mode before resuming the system (see 5078 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5079 is set. Default value is 5. 5080 5081 svm= [PPC] 5082 Format: { on | off | y | n | 1 | 0 } 5083 This parameter controls use of the Protected 5084 Execution Facility on pSeries. 5085 5086 swapaccount=[0|1] 5087 [KNL] Enable accounting of swap in memory resource 5088 controller if no parameter or 1 is given or disable 5089 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5090 5091 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5092 Format: { <int> | force | noforce } 5093 <int> -- Number of I/O TLB slabs 5094 force -- force using of bounce buffers even if they 5095 wouldn't be automatically used by the kernel 5096 noforce -- Never use bounce buffers (for debugging) 5097 5098 switches= [HW,M68k] 5099 5100 sysctl.*= [KNL] 5101 Set a sysctl parameter, right before loading the init 5102 process, as if the value was written to the respective 5103 /proc/sys/... file. Both '.' and '/' are recognized as 5104 separators. Unrecognized parameters and invalid values 5105 are reported in the kernel log. Sysctls registered 5106 later by a loaded module cannot be set this way. 5107 Example: sysctl.vm.swappiness=40 5108 5109 sysfs.deprecated=0|1 [KNL] 5110 Enable/disable old style sysfs layout for old udev 5111 on older distributions. When this option is enabled 5112 very new udev will not work anymore. When this option 5113 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5114 in older udev will not work anymore. 5115 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5116 the kernel configuration. 5117 5118 sysrq_always_enabled 5119 [KNL] 5120 Ignore sysrq setting - this boot parameter will 5121 neutralize any effect of /proc/sys/kernel/sysrq. 5122 Useful for debugging. 5123 5124 tcpmhash_entries= [KNL,NET] 5125 Set the number of tcp_metrics_hash slots. 5126 Default value is 8192 or 16384 depending on total 5127 ram pages. This is used to specify the TCP metrics 5128 cache size. See Documentation/networking/ip-sysctl.rst 5129 "tcp_no_metrics_save" section for more details. 5130 5131 tdfx= [HW,DRM] 5132 5133 test_suspend= [SUSPEND][,N] 5134 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5135 standby suspend) or "freeze" (for suspend type freeze) 5136 as the system sleep state during system startup with 5137 the optional capability to repeat N number of times. 5138 The system is woken from this state using a 5139 wakeup-capable RTC alarm. 5140 5141 thash_entries= [KNL,NET] 5142 Set number of hash buckets for TCP connection 5143 5144 thermal.act= [HW,ACPI] 5145 -1: disable all active trip points in all thermal zones 5146 <degrees C>: override all lowest active trip points 5147 5148 thermal.crt= [HW,ACPI] 5149 -1: disable all critical trip points in all thermal zones 5150 <degrees C>: override all critical trip points 5151 5152 thermal.nocrt= [HW,ACPI] 5153 Set to disable actions on ACPI thermal zone 5154 critical and hot trip points. 5155 5156 thermal.off= [HW,ACPI] 5157 1: disable ACPI thermal control 5158 5159 thermal.psv= [HW,ACPI] 5160 -1: disable all passive trip points 5161 <degrees C>: override all passive trip points to this 5162 value 5163 5164 thermal.tzp= [HW,ACPI] 5165 Specify global default ACPI thermal zone polling rate 5166 <deci-seconds>: poll all this frequency 5167 0: no polling (default) 5168 5169 threadirqs [KNL] 5170 Force threading of all interrupt handlers except those 5171 marked explicitly IRQF_NO_THREAD. 5172 5173 topology= [S390] 5174 Format: {off | on} 5175 Specify if the kernel should make use of the cpu 5176 topology information if the hardware supports this. 5177 The scheduler will make use of this information and 5178 e.g. base its process migration decisions on it. 5179 Default is on. 5180 5181 topology_updates= [KNL, PPC, NUMA] 5182 Format: {off} 5183 Specify if the kernel should ignore (off) 5184 topology updates sent by the hypervisor to this 5185 LPAR. 5186 5187 torture.disable_onoff_at_boot= [KNL] 5188 Prevent the CPU-hotplug component of torturing 5189 until after init has spawned. 5190 5191 torture.ftrace_dump_at_shutdown= [KNL] 5192 Dump the ftrace buffer at torture-test shutdown, 5193 even if there were no errors. This can be a 5194 very costly operation when many torture tests 5195 are running concurrently, especially on systems 5196 with rotating-rust storage. 5197 5198 tp720= [HW,PS2] 5199 5200 tpm_suspend_pcr=[HW,TPM] 5201 Format: integer pcr id 5202 Specify that at suspend time, the tpm driver 5203 should extend the specified pcr with zeros, 5204 as a workaround for some chips which fail to 5205 flush the last written pcr on TPM_SaveState. 5206 This will guarantee that all the other pcrs 5207 are saved. 5208 5209 trace_buf_size=nn[KMG] 5210 [FTRACE] will set tracing buffer size on each cpu. 5211 5212 trace_event=[event-list] 5213 [FTRACE] Set and start specified trace events in order 5214 to facilitate early boot debugging. The event-list is a 5215 comma separated list of trace events to enable. See 5216 also Documentation/trace/events.rst 5217 5218 trace_options=[option-list] 5219 [FTRACE] Enable or disable tracer options at boot. 5220 The option-list is a comma delimited list of options 5221 that can be enabled or disabled just as if you were 5222 to echo the option name into 5223 5224 /sys/kernel/debug/tracing/trace_options 5225 5226 For example, to enable stacktrace option (to dump the 5227 stack trace of each event), add to the command line: 5228 5229 trace_options=stacktrace 5230 5231 See also Documentation/trace/ftrace.rst "trace options" 5232 section. 5233 5234 tp_printk[FTRACE] 5235 Have the tracepoints sent to printk as well as the 5236 tracing ring buffer. This is useful for early boot up 5237 where the system hangs or reboots and does not give the 5238 option for reading the tracing buffer or performing a 5239 ftrace_dump_on_oops. 5240 5241 To turn off having tracepoints sent to printk, 5242 echo 0 > /proc/sys/kernel/tracepoint_printk 5243 Note, echoing 1 into this file without the 5244 tracepoint_printk kernel cmdline option has no effect. 5245 5246 ** CAUTION ** 5247 5248 Having tracepoints sent to printk() and activating high 5249 frequency tracepoints such as irq or sched, can cause 5250 the system to live lock. 5251 5252 traceoff_on_warning 5253 [FTRACE] enable this option to disable tracing when a 5254 warning is hit. This turns off "tracing_on". Tracing can 5255 be enabled again by echoing '1' into the "tracing_on" 5256 file located in /sys/kernel/debug/tracing/ 5257 5258 This option is useful, as it disables the trace before 5259 the WARNING dump is called, which prevents the trace to 5260 be filled with content caused by the warning output. 5261 5262 This option can also be set at run time via the sysctl 5263 option: kernel/traceoff_on_warning 5264 5265 transparent_hugepage= 5266 [KNL] 5267 Format: [always|madvise|never] 5268 Can be used to control the default behavior of the system 5269 with respect to transparent hugepages. 5270 See Documentation/admin-guide/mm/transhuge.rst 5271 for more details. 5272 5273 tsc= Disable clocksource stability checks for TSC. 5274 Format: <string> 5275 [x86] reliable: mark tsc clocksource as reliable, this 5276 disables clocksource verification at runtime, as well 5277 as the stability checks done at bootup. Used to enable 5278 high-resolution timer mode on older hardware, and in 5279 virtualized environment. 5280 [x86] noirqtime: Do not use TSC to do irq accounting. 5281 Used to run time disable IRQ_TIME_ACCOUNTING on any 5282 platforms where RDTSC is slow and this accounting 5283 can add overhead. 5284 [x86] unstable: mark the TSC clocksource as unstable, this 5285 marks the TSC unconditionally unstable at bootup and 5286 avoids any further wobbles once the TSC watchdog notices. 5287 [x86] nowatchdog: disable clocksource watchdog. Used 5288 in situations with strict latency requirements (where 5289 interruptions from clocksource watchdog are not 5290 acceptable). 5291 5292 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5293 value instead. Useful when the early TSC frequency discovery 5294 procedure is not reliable, such as on overclocked systems 5295 with CPUID.16h support and partial CPUID.15h support. 5296 Format: <unsigned int> 5297 5298 tsx= [X86] Control Transactional Synchronization 5299 Extensions (TSX) feature in Intel processors that 5300 support TSX control. 5301 5302 This parameter controls the TSX feature. The options are: 5303 5304 on - Enable TSX on the system. Although there are 5305 mitigations for all known security vulnerabilities, 5306 TSX has been known to be an accelerator for 5307 several previous speculation-related CVEs, and 5308 so there may be unknown security risks associated 5309 with leaving it enabled. 5310 5311 off - Disable TSX on the system. (Note that this 5312 option takes effect only on newer CPUs which are 5313 not vulnerable to MDS, i.e., have 5314 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5315 the new IA32_TSX_CTRL MSR through a microcode 5316 update. This new MSR allows for the reliable 5317 deactivation of the TSX functionality.) 5318 5319 auto - Disable TSX if X86_BUG_TAA is present, 5320 otherwise enable TSX on the system. 5321 5322 Not specifying this option is equivalent to tsx=off. 5323 5324 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5325 for more details. 5326 5327 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5328 Abort (TAA) vulnerability. 5329 5330 Similar to Micro-architectural Data Sampling (MDS) 5331 certain CPUs that support Transactional 5332 Synchronization Extensions (TSX) are vulnerable to an 5333 exploit against CPU internal buffers which can forward 5334 information to a disclosure gadget under certain 5335 conditions. 5336 5337 In vulnerable processors, the speculatively forwarded 5338 data can be used in a cache side channel attack, to 5339 access data to which the attacker does not have direct 5340 access. 5341 5342 This parameter controls the TAA mitigation. The 5343 options are: 5344 5345 full - Enable TAA mitigation on vulnerable CPUs 5346 if TSX is enabled. 5347 5348 full,nosmt - Enable TAA mitigation and disable SMT on 5349 vulnerable CPUs. If TSX is disabled, SMT 5350 is not disabled because CPU is not 5351 vulnerable to cross-thread TAA attacks. 5352 off - Unconditionally disable TAA mitigation 5353 5354 On MDS-affected machines, tsx_async_abort=off can be 5355 prevented by an active MDS mitigation as both vulnerabilities 5356 are mitigated with the same mechanism so in order to disable 5357 this mitigation, you need to specify mds=off too. 5358 5359 Not specifying this option is equivalent to 5360 tsx_async_abort=full. On CPUs which are MDS affected 5361 and deploy MDS mitigation, TAA mitigation is not 5362 required and doesn't provide any additional 5363 mitigation. 5364 5365 For details see: 5366 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5367 5368 turbografx.map[2|3]= [HW,JOY] 5369 TurboGraFX parallel port interface 5370 Format: 5371 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5372 See also Documentation/input/devices/joystick-parport.rst 5373 5374 udbg-immortal [PPC] When debugging early kernel crashes that 5375 happen after console_init() and before a proper 5376 console driver takes over, this boot options might 5377 help "seeing" what's going on. 5378 5379 uhash_entries= [KNL,NET] 5380 Set number of hash buckets for UDP/UDP-Lite connections 5381 5382 uhci-hcd.ignore_oc= 5383 [USB] Ignore overcurrent events (default N). 5384 Some badly-designed motherboards generate lots of 5385 bogus events, for ports that aren't wired to 5386 anything. Set this parameter to avoid log spamming. 5387 Note that genuine overcurrent events won't be 5388 reported either. 5389 5390 unknown_nmi_panic 5391 [X86] Cause panic on unknown NMI. 5392 5393 usbcore.authorized_default= 5394 [USB] Default USB device authorization: 5395 (default -1 = authorized except for wireless USB, 5396 0 = not authorized, 1 = authorized, 2 = authorized 5397 if device connected to internal port) 5398 5399 usbcore.autosuspend= 5400 [USB] The autosuspend time delay (in seconds) used 5401 for newly-detected USB devices (default 2). This 5402 is the time required before an idle device will be 5403 autosuspended. Devices for which the delay is set 5404 to a negative value won't be autosuspended at all. 5405 5406 usbcore.usbfs_snoop= 5407 [USB] Set to log all usbfs traffic (default 0 = off). 5408 5409 usbcore.usbfs_snoop_max= 5410 [USB] Maximum number of bytes to snoop in each URB 5411 (default = 65536). 5412 5413 usbcore.blinkenlights= 5414 [USB] Set to cycle leds on hubs (default 0 = off). 5415 5416 usbcore.old_scheme_first= 5417 [USB] Start with the old device initialization 5418 scheme (default 0 = off). 5419 5420 usbcore.usbfs_memory_mb= 5421 [USB] Memory limit (in MB) for buffers allocated by 5422 usbfs (default = 16, 0 = max = 2047). 5423 5424 usbcore.use_both_schemes= 5425 [USB] Try the other device initialization scheme 5426 if the first one fails (default 1 = enabled). 5427 5428 usbcore.initial_descriptor_timeout= 5429 [USB] Specifies timeout for the initial 64-byte 5430 USB_REQ_GET_DESCRIPTOR request in milliseconds 5431 (default 5000 = 5.0 seconds). 5432 5433 usbcore.nousb [USB] Disable the USB subsystem 5434 5435 usbcore.quirks= 5436 [USB] A list of quirk entries to augment the built-in 5437 usb core quirk list. List entries are separated by 5438 commas. Each entry has the form 5439 VendorID:ProductID:Flags. The IDs are 4-digit hex 5440 numbers and Flags is a set of letters. Each letter 5441 will change the built-in quirk; setting it if it is 5442 clear and clearing it if it is set. The letters have 5443 the following meanings: 5444 a = USB_QUIRK_STRING_FETCH_255 (string 5445 descriptors must not be fetched using 5446 a 255-byte read); 5447 b = USB_QUIRK_RESET_RESUME (device can't resume 5448 correctly so reset it instead); 5449 c = USB_QUIRK_NO_SET_INTF (device can't handle 5450 Set-Interface requests); 5451 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5452 handle its Configuration or Interface 5453 strings); 5454 e = USB_QUIRK_RESET (device can't be reset 5455 (e.g morph devices), don't use reset); 5456 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5457 more interface descriptions than the 5458 bNumInterfaces count, and can't handle 5459 talking to these interfaces); 5460 g = USB_QUIRK_DELAY_INIT (device needs a pause 5461 during initialization, after we read 5462 the device descriptor); 5463 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5464 high speed and super speed interrupt 5465 endpoints, the USB 2.0 and USB 3.0 spec 5466 require the interval in microframes (1 5467 microframe = 125 microseconds) to be 5468 calculated as interval = 2 ^ 5469 (bInterval-1). 5470 Devices with this quirk report their 5471 bInterval as the result of this 5472 calculation instead of the exponent 5473 variable used in the calculation); 5474 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5475 handle device_qualifier descriptor 5476 requests); 5477 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5478 generates spurious wakeup, ignore 5479 remote wakeup capability); 5480 k = USB_QUIRK_NO_LPM (device can't handle Link 5481 Power Management); 5482 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5483 (Device reports its bInterval as linear 5484 frames instead of the USB 2.0 5485 calculation); 5486 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5487 to be disconnected before suspend to 5488 prevent spurious wakeup); 5489 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5490 pause after every control message); 5491 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5492 delay after resetting its port); 5493 Example: quirks=0781:5580:bk,0a5c:5834:gij 5494 5495 usbhid.mousepoll= 5496 [USBHID] The interval which mice are to be polled at. 5497 5498 usbhid.jspoll= 5499 [USBHID] The interval which joysticks are to be polled at. 5500 5501 usbhid.kbpoll= 5502 [USBHID] The interval which keyboards are to be polled at. 5503 5504 usb-storage.delay_use= 5505 [UMS] The delay in seconds before a new device is 5506 scanned for Logical Units (default 1). 5507 5508 usb-storage.quirks= 5509 [UMS] A list of quirks entries to supplement or 5510 override the built-in unusual_devs list. List 5511 entries are separated by commas. Each entry has 5512 the form VID:PID:Flags where VID and PID are Vendor 5513 and Product ID values (4-digit hex numbers) and 5514 Flags is a set of characters, each corresponding 5515 to a common usb-storage quirk flag as follows: 5516 a = SANE_SENSE (collect more than 18 bytes 5517 of sense data, not on uas); 5518 b = BAD_SENSE (don't collect more than 18 5519 bytes of sense data, not on uas); 5520 c = FIX_CAPACITY (decrease the reported 5521 device capacity by one sector); 5522 d = NO_READ_DISC_INFO (don't use 5523 READ_DISC_INFO command, not on uas); 5524 e = NO_READ_CAPACITY_16 (don't use 5525 READ_CAPACITY_16 command); 5526 f = NO_REPORT_OPCODES (don't use report opcodes 5527 command, uas only); 5528 g = MAX_SECTORS_240 (don't transfer more than 5529 240 sectors at a time, uas only); 5530 h = CAPACITY_HEURISTICS (decrease the 5531 reported device capacity by one 5532 sector if the number is odd); 5533 i = IGNORE_DEVICE (don't bind to this 5534 device); 5535 j = NO_REPORT_LUNS (don't use report luns 5536 command, uas only); 5537 l = NOT_LOCKABLE (don't try to lock and 5538 unlock ejectable media, not on uas); 5539 m = MAX_SECTORS_64 (don't transfer more 5540 than 64 sectors = 32 KB at a time, 5541 not on uas); 5542 n = INITIAL_READ10 (force a retry of the 5543 initial READ(10) command, not on uas); 5544 o = CAPACITY_OK (accept the capacity 5545 reported by the device, not on uas); 5546 p = WRITE_CACHE (the device cache is ON 5547 by default, not on uas); 5548 r = IGNORE_RESIDUE (the device reports 5549 bogus residue values, not on uas); 5550 s = SINGLE_LUN (the device has only one 5551 Logical Unit); 5552 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5553 commands, uas only); 5554 u = IGNORE_UAS (don't bind to the uas driver); 5555 w = NO_WP_DETECT (don't test whether the 5556 medium is write-protected). 5557 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5558 even if the device claims no cache, 5559 not on uas) 5560 Example: quirks=0419:aaf5:rl,0421:0433:rc 5561 5562 user_debug= [KNL,ARM] 5563 Format: <int> 5564 See arch/arm/Kconfig.debug help text. 5565 1 - undefined instruction events 5566 2 - system calls 5567 4 - invalid data aborts 5568 8 - SIGSEGV faults 5569 16 - SIGBUS faults 5570 Example: user_debug=31 5571 5572 userpte= 5573 [X86] Flags controlling user PTE allocations. 5574 5575 nohigh = do not allocate PTE pages in 5576 HIGHMEM regardless of setting 5577 of CONFIG_HIGHPTE. 5578 5579 vdso= [X86,SH] 5580 On X86_32, this is an alias for vdso32=. Otherwise: 5581 5582 vdso=1: enable VDSO (the default) 5583 vdso=0: disable VDSO mapping 5584 5585 vdso32= [X86] Control the 32-bit vDSO 5586 vdso32=1: enable 32-bit VDSO 5587 vdso32=0 or vdso32=2: disable 32-bit VDSO 5588 5589 See the help text for CONFIG_COMPAT_VDSO for more 5590 details. If CONFIG_COMPAT_VDSO is set, the default is 5591 vdso32=0; otherwise, the default is vdso32=1. 5592 5593 For compatibility with older kernels, vdso32=2 is an 5594 alias for vdso32=0. 5595 5596 Try vdso32=0 if you encounter an error that says: 5597 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5598 5599 vector= [IA-64,SMP] 5600 vector=percpu: enable percpu vector domain 5601 5602 video= [FB] Frame buffer configuration 5603 See Documentation/fb/modedb.rst. 5604 5605 video.brightness_switch_enabled= [0,1] 5606 If set to 1, on receiving an ACPI notify event 5607 generated by hotkey, video driver will adjust brightness 5608 level and then send out the event to user space through 5609 the allocated input device; If set to 0, video driver 5610 will only send out the event without touching backlight 5611 brightness level. 5612 default: 1 5613 5614 virtio_mmio.device= 5615 [VMMIO] Memory mapped virtio (platform) device. 5616 5617 <size>@<baseaddr>:<irq>[:<id>] 5618 where: 5619 <size> := size (can use standard suffixes 5620 like K, M and G) 5621 <baseaddr> := physical base address 5622 <irq> := interrupt number (as passed to 5623 request_irq()) 5624 <id> := (optional) platform device id 5625 example: 5626 virtio_mmio.device=1K@0x100b0000:48:7 5627 5628 Can be used multiple times for multiple devices. 5629 5630 vga= [BOOT,X86-32] Select a particular video mode 5631 See Documentation/x86/boot.rst and 5632 Documentation/admin-guide/svga.rst. 5633 Use vga=ask for menu. 5634 This is actually a boot loader parameter; the value is 5635 passed to the kernel using a special protocol. 5636 5637 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5638 May slow down system boot speed, especially when 5639 enabled on systems with a large amount of memory. 5640 All options are enabled by default, and this 5641 interface is meant to allow for selectively 5642 enabling or disabling specific virtual memory 5643 debugging features. 5644 5645 Available options are: 5646 P Enable page structure init time poisoning 5647 - Disable all of the above options 5648 5649 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5650 size of <nn>. This can be used to increase the 5651 minimum size (128MB on x86). It can also be used to 5652 decrease the size and leave more room for directly 5653 mapped kernel RAM. 5654 5655 vmcp_cma=nn[MG] [KNL,S390] 5656 Sets the memory size reserved for contiguous memory 5657 allocations for the vmcp device driver. 5658 5659 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5660 Format: <command> 5661 5662 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5663 Format: <command> 5664 5665 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5666 Format: <command> 5667 5668 vsyscall= [X86-64] 5669 Controls the behavior of vsyscalls (i.e. calls to 5670 fixed addresses of 0xffffffffff600x00 from legacy 5671 code). Most statically-linked binaries and older 5672 versions of glibc use these calls. Because these 5673 functions are at fixed addresses, they make nice 5674 targets for exploits that can control RIP. 5675 5676 emulate [default] Vsyscalls turn into traps and are 5677 emulated reasonably safely. The vsyscall 5678 page is readable. 5679 5680 xonly Vsyscalls turn into traps and are 5681 emulated reasonably safely. The vsyscall 5682 page is not readable. 5683 5684 none Vsyscalls don't work at all. This makes 5685 them quite hard to use for exploits but 5686 might break your system. 5687 5688 vt.color= [VT] Default text color. 5689 Format: 0xYX, X = foreground, Y = background. 5690 Default: 0x07 = light gray on black. 5691 5692 vt.cur_default= [VT] Default cursor shape. 5693 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5694 the parameters of the <Esc>[?A;B;Cc escape sequence; 5695 see VGA-softcursor.txt. Default: 2 = underline. 5696 5697 vt.default_blu= [VT] 5698 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5699 Change the default blue palette of the console. 5700 This is a 16-member array composed of values 5701 ranging from 0-255. 5702 5703 vt.default_grn= [VT] 5704 Format: <green0>,<green1>,<green2>,...,<green15> 5705 Change the default green palette of the console. 5706 This is a 16-member array composed of values 5707 ranging from 0-255. 5708 5709 vt.default_red= [VT] 5710 Format: <red0>,<red1>,<red2>,...,<red15> 5711 Change the default red palette of the console. 5712 This is a 16-member array composed of values 5713 ranging from 0-255. 5714 5715 vt.default_utf8= 5716 [VT] 5717 Format=<0|1> 5718 Set system-wide default UTF-8 mode for all tty's. 5719 Default is 1, i.e. UTF-8 mode is enabled for all 5720 newly opened terminals. 5721 5722 vt.global_cursor_default= 5723 [VT] 5724 Format=<-1|0|1> 5725 Set system-wide default for whether a cursor 5726 is shown on new VTs. Default is -1, 5727 i.e. cursors will be created by default unless 5728 overridden by individual drivers. 0 will hide 5729 cursors, 1 will display them. 5730 5731 vt.italic= [VT] Default color for italic text; 0-15. 5732 Default: 2 = green. 5733 5734 vt.underline= [VT] Default color for underlined text; 0-15. 5735 Default: 3 = cyan. 5736 5737 watchdog timers [HW,WDT] For information on watchdog timers, 5738 see Documentation/watchdog/watchdog-parameters.rst 5739 or other driver-specific files in the 5740 Documentation/watchdog/ directory. 5741 5742 watchdog_thresh= 5743 [KNL] 5744 Set the hard lockup detector stall duration 5745 threshold in seconds. The soft lockup detector 5746 threshold is set to twice the value. A value of 0 5747 disables both lockup detectors. Default is 10 5748 seconds. 5749 5750 workqueue.watchdog_thresh= 5751 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5752 warn stall conditions and dump internal state to 5753 help debugging. 0 disables workqueue stall 5754 detection; otherwise, it's the stall threshold 5755 duration in seconds. The default value is 30 and 5756 it can be updated at runtime by writing to the 5757 corresponding sysfs file. 5758 5759 workqueue.disable_numa 5760 By default, all work items queued to unbound 5761 workqueues are affine to the NUMA nodes they're 5762 issued on, which results in better behavior in 5763 general. If NUMA affinity needs to be disabled for 5764 whatever reason, this option can be used. Note 5765 that this also can be controlled per-workqueue for 5766 workqueues visible under /sys/bus/workqueue/. 5767 5768 workqueue.power_efficient 5769 Per-cpu workqueues are generally preferred because 5770 they show better performance thanks to cache 5771 locality; unfortunately, per-cpu workqueues tend to 5772 be more power hungry than unbound workqueues. 5773 5774 Enabling this makes the per-cpu workqueues which 5775 were observed to contribute significantly to power 5776 consumption unbound, leading to measurably lower 5777 power usage at the cost of small performance 5778 overhead. 5779 5780 The default value of this parameter is determined by 5781 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5782 5783 workqueue.debug_force_rr_cpu 5784 Workqueue used to implicitly guarantee that work 5785 items queued without explicit CPU specified are put 5786 on the local CPU. This guarantee is no longer true 5787 and while local CPU is still preferred work items 5788 may be put on foreign CPUs. This debug option 5789 forces round-robin CPU selection to flush out 5790 usages which depend on the now broken guarantee. 5791 When enabled, memory and cache locality will be 5792 impacted. 5793 5794 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5795 default x2apic cluster mode on platforms 5796 supporting x2apic. 5797 5798 x86_intel_mid_timer= [X86-32,APBT] 5799 Choose timer option for x86 Intel MID platform. 5800 Two valid options are apbt timer only and lapic timer 5801 plus one apbt timer for broadcast timer. 5802 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5803 5804 xen_512gb_limit [KNL,X86-64,XEN] 5805 Restricts the kernel running paravirtualized under Xen 5806 to use only up to 512 GB of RAM. The reason to do so is 5807 crash analysis tools and Xen tools for doing domain 5808 save/restore/migration must be enabled to handle larger 5809 domains. 5810 5811 xen_emul_unplug= [HW,X86,XEN] 5812 Unplug Xen emulated devices 5813 Format: [unplug0,][unplug1] 5814 ide-disks -- unplug primary master IDE devices 5815 aux-ide-disks -- unplug non-primary-master IDE devices 5816 nics -- unplug network devices 5817 all -- unplug all emulated devices (NICs and IDE disks) 5818 unnecessary -- unplugging emulated devices is 5819 unnecessary even if the host did not respond to 5820 the unplug protocol 5821 never -- do not unplug even if version check succeeds 5822 5823 xen_legacy_crash [X86,XEN] 5824 Crash from Xen panic notifier, without executing late 5825 panic() code such as dumping handler. 5826 5827 xen_nopvspin [X86,XEN] 5828 Disables the qspinlock slowpath using Xen PV optimizations. 5829 This parameter is obsoleted by "nopvspin" parameter, which 5830 has equivalent effect for XEN platform. 5831 5832 xen_nopv [X86] 5833 Disables the PV optimizations forcing the HVM guest to 5834 run as generic HVM guest with no PV drivers. 5835 This option is obsoleted by the "nopv" option, which 5836 has equivalent effect for XEN platform. 5837 5838 xen_scrub_pages= [XEN] 5839 Boolean option to control scrubbing pages before giving them back 5840 to Xen, for use by other domains. Can be also changed at runtime 5841 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5842 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5843 5844 xen_timer_slop= [X86-64,XEN] 5845 Set the timer slop (in nanoseconds) for the virtual Xen 5846 timers (default is 100000). This adjusts the minimum 5847 delta of virtualized Xen timers, where lower values 5848 improve timer resolution at the expense of processing 5849 more timer interrupts. 5850 5851 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5852 Disables the PV optimizations forcing the guest to run 5853 as generic guest with no PV drivers. Currently support 5854 XEN HVM, KVM, HYPER_V and VMWARE guest. 5855 5856 nopvspin [X86,XEN,KVM] 5857 Disables the qspinlock slow path using PV optimizations 5858 which allow the hypervisor to 'idle' the guest on lock 5859 contention. 5860 5861 xirc2ps_cs= [NET,PCMCIA] 5862 Format: 5863 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5864 5865 xive= [PPC] 5866 By default on POWER9 and above, the kernel will 5867 natively use the XIVE interrupt controller. This option 5868 allows the fallback firmware mode to be used: 5869 5870 off Fallback to firmware control of XIVE interrupt 5871 controller on both pseries and powernv 5872 platforms. Only useful on POWER9 and above. 5873 5874 xhci-hcd.quirks [USB,KNL] 5875 A hex value specifying bitmask with supplemental xhci 5876 host controller quirks. Meaning of each bit can be 5877 consulted in header drivers/usb/host/xhci.h. 5878 5879 xmon [PPC] 5880 Format: { early | on | rw | ro | off } 5881 Controls if xmon debugger is enabled. Default is off. 5882 Passing only "xmon" is equivalent to "xmon=early". 5883 early Call xmon as early as possible on boot; xmon 5884 debugger is called from setup_arch(). 5885 on xmon debugger hooks will be installed so xmon 5886 is only called on a kernel crash. Default mode, 5887 i.e. either "ro" or "rw" mode, is controlled 5888 with CONFIG_XMON_DEFAULT_RO_MODE. 5889 rw xmon debugger hooks will be installed so xmon 5890 is called only on a kernel crash, mode is write, 5891 meaning SPR registers, memory and, other data 5892 can be written using xmon commands. 5893 ro same as "rw" option above but SPR registers, 5894 memory, and other data can't be written using 5895 xmon commands. 5896 off xmon is disabled. 5897