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 [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 include/linux/dma-contiguous.h 601 602 cmo_free_hint= [PPC] Format: { yes | no } 603 Specify whether pages are marked as being inactive 604 when they are freed. This is used in CMO environments 605 to determine OS memory pressure for page stealing by 606 a hypervisor. 607 Default: yes 608 609 coherent_pool=nn[KMG] [ARM,KNL] 610 Sets the size of memory pool for coherent, atomic dma 611 allocations, by default set to 256K. 612 613 com20020= [HW,NET] ARCnet - COM20020 chipset 614 Format: 615 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 616 617 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 618 Format: <io>[,<irq>] 619 620 com90xx= [HW,NET] 621 ARCnet - COM90xx chipset (memory-mapped buffers) 622 Format: <io>[,<irq>[,<memstart>]] 623 624 condev= [HW,S390] console device 625 conmode= 626 627 console= [KNL] Output console device and options. 628 629 tty<n> Use the virtual console device <n>. 630 631 ttyS<n>[,options] 632 ttyUSB0[,options] 633 Use the specified serial port. The options are of 634 the form "bbbbpnf", where "bbbb" is the baud rate, 635 "p" is parity ("n", "o", or "e"), "n" is number of 636 bits, and "f" is flow control ("r" for RTS or 637 omit it). Default is "9600n8". 638 639 See Documentation/admin-guide/serial-console.rst for more 640 information. See 641 Documentation/networking/netconsole.rst for an 642 alternative. 643 644 uart[8250],io,<addr>[,options] 645 uart[8250],mmio,<addr>[,options] 646 uart[8250],mmio16,<addr>[,options] 647 uart[8250],mmio32,<addr>[,options] 648 uart[8250],0x<addr>[,options] 649 Start an early, polled-mode console on the 8250/16550 650 UART at the specified I/O port or MMIO address, 651 switching to the matching ttyS device later. 652 MMIO inter-register address stride is either 8-bit 653 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 655 to be equivalent to 'mmio'. 'options' are specified in 656 the same format described for ttyS above; if unspecified, 657 the h/w is not re-initialized. 658 659 hvc<n> Use the hypervisor console device <n>. This is for 660 both Xen and PowerPC hypervisors. 661 662 If the device connected to the port is not a TTY but a braille 663 device, prepend "brl," before the device type, for instance 664 console=brl,ttyS0 665 For now, only VisioBraille is supported. 666 667 console_msg_format= 668 [KNL] Change console messages format 669 default 670 By default we print messages on consoles in 671 "[time stamp] text\n" format (time stamp may not be 672 printed, depending on CONFIG_PRINTK_TIME or 673 `printk_time' param). 674 syslog 675 Switch to syslog format: "<%u>[time stamp] text\n" 676 IOW, each message will have a facility and loglevel 677 prefix. The format is similar to one used by syslog() 678 syscall, or to executing "dmesg -S --raw" or to reading 679 from /proc/kmsg. 680 681 consoleblank= [KNL] The console blank (screen saver) timeout in 682 seconds. A value of 0 disables the blank timer. 683 Defaults to 0. 684 685 coredump_filter= 686 [KNL] Change the default value for 687 /proc/<pid>/coredump_filter. 688 See also Documentation/filesystems/proc.rst. 689 690 coresight_cpu_debug.enable 691 [ARM,ARM64] 692 Format: <bool> 693 Enable/disable the CPU sampling based debugging. 694 0: default value, disable debugging 695 1: enable debugging at boot time 696 697 cpuidle.off=1 [CPU_IDLE] 698 disable the cpuidle sub-system 699 700 cpuidle.governor= 701 [CPU_IDLE] Name of the cpuidle governor to use. 702 703 cpufreq.off=1 [CPU_FREQ] 704 disable the cpufreq sub-system 705 706 cpufreq.default_governor= 707 [CPU_FREQ] Name of the default cpufreq governor or 708 policy to use. This governor must be registered in the 709 kernel before the cpufreq driver probes. 710 711 cpu_init_udelay=N 712 [X86] Delay for N microsec between assert and de-assert 713 of APIC INIT to start processors. This delay occurs 714 on every CPU online, such as boot, and resume from suspend. 715 Default: 10000 716 717 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 718 Format: 719 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 720 721 crashkernel=size[KMG][@offset[KMG]] 722 [KNL] Using kexec, Linux can switch to a 'crash kernel' 723 upon panic. This parameter reserves the physical 724 memory region [offset, offset + size] for that kernel 725 image. If '@offset' is omitted, then a suitable offset 726 is selected automatically. 727 [KNL, X86-64] Select a region under 4G first, and 728 fall back to reserve region above 4G when '@offset' 729 hasn't been specified. 730 See Documentation/admin-guide/kdump/kdump.rst for further details. 731 732 crashkernel=range1:size1[,range2:size2,...][@offset] 733 [KNL] Same as above, but depends on the memory 734 in the running system. The syntax of range is 735 start-[end] where start and end are both 736 a memory unit (amount[KMG]). See also 737 Documentation/admin-guide/kdump/kdump.rst for an example. 738 739 crashkernel=size[KMG],high 740 [KNL, X86-64] range could be above 4G. Allow kernel 741 to allocate physical memory region from top, so could 742 be above 4G if system have more than 4G ram installed. 743 Otherwise memory region will be allocated below 4G, if 744 available. 745 It will be ignored if crashkernel=X is specified. 746 crashkernel=size[KMG],low 747 [KNL, X86-64] range under 4G. When crashkernel=X,high 748 is passed, kernel could allocate physical memory region 749 above 4G, that cause second kernel crash on system 750 that require some amount of low memory, e.g. swiotlb 751 requires at least 64M+32K low memory, also enough extra 752 low memory is needed to make sure DMA buffers for 32-bit 753 devices won't run out. Kernel would try to allocate at 754 at least 256M below 4G automatically. 755 This one let user to specify own low range under 4G 756 for second kernel instead. 757 0: to disable low allocation. 758 It will be ignored when crashkernel=X,high is not used 759 or memory reserved is below 4G. 760 761 cryptomgr.notests 762 [KNL] Disable crypto self-tests 763 764 cs89x0_dma= [HW,NET] 765 Format: <dma> 766 767 cs89x0_media= [HW,NET] 768 Format: { rj45 | aui | bnc } 769 770 dasd= [HW,NET] 771 See header of drivers/s390/block/dasd_devmap.c. 772 773 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 774 (one device per port) 775 Format: <port#>,<type> 776 See also Documentation/input/devices/joystick-parport.rst 777 778 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 779 time. See 780 Documentation/admin-guide/dynamic-debug-howto.rst for 781 details. Deprecated, see dyndbg. 782 783 debug [KNL] Enable kernel debugging (events log level). 784 785 debug_boot_weak_hash 786 [KNL] Enable printing [hashed] pointers early in the 787 boot sequence. If enabled, we use a weak hash instead 788 of siphash to hash pointers. Use this option if you are 789 seeing instances of '(___ptrval___)') and need to see a 790 value (hashed pointer) instead. Cryptographically 791 insecure, please do not use on production kernels. 792 793 debug_locks_verbose= 794 [KNL] verbose self-tests 795 Format=<0|1> 796 Print debugging info while doing the locking API 797 self-tests. 798 We default to 0 (no extra messages), setting it to 799 1 will print _a lot_ more information - normally 800 only useful to kernel developers. 801 802 debug_objects [KNL] Enable object debugging 803 804 no_debug_objects 805 [KNL] Disable object debugging 806 807 debug_guardpage_minorder= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 809 parameter allows control of the order of pages that will 810 be intentionally kept free (and hence protected) by the 811 buddy allocator. Bigger value increase the probability 812 of catching random memory corruption, but reduce the 813 amount of memory for normal system use. The maximum 814 possible value is MAX_ORDER/2. Setting this parameter 815 to 1 or 2 should be enough to identify most random 816 memory corruption problems caused by bugs in kernel or 817 driver code when a CPU writes to (or reads from) a 818 random memory location. Note that there exists a class 819 of memory corruptions problems caused by buggy H/W or 820 F/W or by drivers badly programing DMA (basically when 821 memory is written at bus level and the CPU MMU is 822 bypassed) which are not detectable by 823 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 824 tracking down these problems. 825 826 debug_pagealloc= 827 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 828 enables the feature at boot time. By default, it is 829 disabled and the system will work mostly the same as a 830 kernel built without CONFIG_DEBUG_PAGEALLOC. 831 Note: to get most of debug_pagealloc error reports, it's 832 useful to also enable the page_owner functionality. 833 on: enable the feature 834 835 debugfs= [KNL] This parameter enables what is exposed to userspace 836 and debugfs internal clients. 837 Format: { on, no-mount, off } 838 on: All functions are enabled. 839 no-mount: 840 Filesystem is not registered but kernel clients can 841 access APIs and a crashkernel can be used to read 842 its content. There is nothing to mount. 843 off: Filesystem is not registered and clients 844 get a -EPERM as result when trying to register files 845 or directories within debugfs. 846 This is equivalent of the runtime functionality if 847 debugfs was not enabled in the kernel at all. 848 Default value is set in build-time with a kernel configuration. 849 850 debugpat [X86] Enable PAT debugging 851 852 decnet.addr= [HW,NET] 853 Format: <area>[,<node>] 854 See also Documentation/networking/decnet.rst. 855 856 default_hugepagesz= 857 [HW] The size of the default HugeTLB page. This is 858 the size represented by the legacy /proc/ hugepages 859 APIs. In addition, this is the default hugetlb size 860 used for shmget(), mmap() and mounting hugetlbfs 861 filesystems. If not specified, defaults to the 862 architecture's default huge page size. Huge page 863 sizes are architecture dependent. See also 864 Documentation/admin-guide/mm/hugetlbpage.rst. 865 Format: size[KMG] 866 867 deferred_probe_timeout= 868 [KNL] Debugging option to set a timeout in seconds for 869 deferred probe to give up waiting on dependencies to 870 probe. Only specific dependencies (subsystems or 871 drivers) that have opted in will be ignored. A timeout of 0 872 will timeout at the end of initcalls. This option will also 873 dump out devices still on the deferred probe list after 874 retrying. 875 876 dfltcc= [HW,S390] 877 Format: { on | off | def_only | inf_only | always } 878 on: s390 zlib hardware support for compression on 879 level 1 and decompression (default) 880 off: No s390 zlib hardware support 881 def_only: s390 zlib hardware support for deflate 882 only (compression on level 1) 883 inf_only: s390 zlib hardware support for inflate 884 only (decompression) 885 always: Same as 'on' but ignores the selected compression 886 level always using hardware support (used for debugging) 887 888 dhash_entries= [KNL] 889 Set number of hash buckets for dentry cache. 890 891 disable_1tb_segments [PPC] 892 Disables the use of 1TB hash page table segments. This 893 causes the kernel to fall back to 256MB segments which 894 can be useful when debugging issues that require an SLB 895 miss to occur. 896 897 stress_slb [PPC] 898 Limits the number of kernel SLB entries, and flushes 899 them frequently to increase the rate of SLB faults 900 on kernel addresses. 901 902 disable= [IPV6] 903 See Documentation/networking/ipv6.rst. 904 905 hardened_usercopy= 906 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 907 hardening is enabled for this boot. Hardened 908 usercopy checking is used to protect the kernel 909 from reading or writing beyond known memory 910 allocation boundaries as a proactive defense 911 against bounds-checking flaws in the kernel's 912 copy_to_user()/copy_from_user() interface. 913 on Perform hardened usercopy checks (default). 914 off Disable hardened usercopy checks. 915 916 disable_radix [PPC] 917 Disable RADIX MMU mode on POWER9 918 919 radix_hcall_invalidate=on [PPC/PSERIES] 920 Disable RADIX GTSE feature and use hcall for TLB 921 invalidate. 922 923 disable_tlbie [PPC] 924 Disable TLBIE instruction. Currently does not work 925 with KVM, with HASH MMU, or with coherent accelerators. 926 927 disable_cpu_apicid= [X86,APIC,SMP] 928 Format: <int> 929 The number of initial APIC ID for the 930 corresponding CPU to be disabled at boot, 931 mostly used for the kdump 2nd kernel to 932 disable BSP to wake up multiple CPUs without 933 causing system reset or hang due to sending 934 INIT from AP to BSP. 935 936 perf_v4_pmi= [X86,INTEL] 937 Format: <bool> 938 Disable Intel PMU counter freezing feature. 939 The feature only exists starting from 940 Arch Perfmon v4 (Skylake and newer). 941 942 disable_ddw [PPC/PSERIES] 943 Disable Dynamic DMA Window support. Use this 944 to workaround buggy firmware. 945 946 disable_ipv6= [IPV6] 947 See Documentation/networking/ipv6.rst. 948 949 disable_mtrr_cleanup [X86] 950 The kernel tries to adjust MTRR layout from continuous 951 to discrete, to make X server driver able to add WB 952 entry later. This parameter disables that. 953 954 disable_mtrr_trim [X86, Intel and AMD only] 955 By default the kernel will trim any uncacheable 956 memory out of your available memory pool based on 957 MTRR settings. This parameter disables that behavior, 958 possibly causing your machine to run very slowly. 959 960 disable_timer_pin_1 [X86] 961 Disable PIN 1 of APIC timer 962 Can be useful to work around chipset bugs. 963 964 dis_ucode_ldr [X86] Disable the microcode loader. 965 966 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 967 this option disables the debugging code at boot. 968 969 dma_debug_entries=<number> 970 This option allows to tune the number of preallocated 971 entries for DMA-API debugging code. One entry is 972 required per DMA-API allocation. Use this if the 973 DMA-API debugging code disables itself because the 974 architectural default is too low. 975 976 dma_debug_driver=<driver_name> 977 With this option the DMA-API debugging driver 978 filter feature can be enabled at boot time. Just 979 pass the driver to filter for as the parameter. 980 The filter can be disabled or changed to another 981 driver later using sysfs. 982 983 driver_async_probe= [KNL] 984 List of driver names to be probed asynchronously. 985 Format: <driver_name1>,<driver_name2>... 986 987 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 988 Broken monitors, graphic adapters, KVMs and EDIDless 989 panels may send no or incorrect EDID data sets. 990 This parameter allows to specify an EDID data sets 991 in the /lib/firmware directory that are used instead. 992 Generic built-in EDID data sets are used, if one of 993 edid/1024x768.bin, edid/1280x1024.bin, 994 edid/1680x1050.bin, or edid/1920x1080.bin is given 995 and no file with the same name exists. Details and 996 instructions how to build your own EDID data are 997 available in Documentation/admin-guide/edid.rst. An EDID 998 data set will only be used for a particular connector, 999 if its name and a colon are prepended to the EDID 1000 name. Each connector may use a unique EDID data 1001 set by separating the files with a comma. An EDID 1002 data set with no connector name will be used for 1003 any connectors not explicitly specified. 1004 1005 dscc4.setup= [NET] 1006 1007 dt_cpu_ftrs= [PPC] 1008 Format: {"off" | "known"} 1009 Control how the dt_cpu_ftrs device-tree binding is 1010 used for CPU feature discovery and setup (if it 1011 exists). 1012 off: Do not use it, fall back to legacy cpu table. 1013 known: Do not pass through unknown features to guests 1014 or userspace, only those that the kernel is aware of. 1015 1016 dump_apple_properties [X86] 1017 Dump name and content of EFI device properties on 1018 x86 Macs. Useful for driver authors to determine 1019 what data is available or for reverse-engineering. 1020 1021 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1022 <module>.dyndbg[="val"] 1023 Enable debug messages at boot time. See 1024 Documentation/admin-guide/dynamic-debug-howto.rst 1025 for details. 1026 1027 nopku [X86] Disable Memory Protection Keys CPU feature found 1028 in some Intel CPUs. 1029 1030 <module>.async_probe [KNL] 1031 Enable asynchronous probe on this module. 1032 1033 early_ioremap_debug [KNL] 1034 Enable debug messages in early_ioremap support. This 1035 is useful for tracking down temporary early mappings 1036 which are not unmapped. 1037 1038 earlycon= [KNL] Output early console device and options. 1039 1040 When used with no options, the early console is 1041 determined by stdout-path property in device tree's 1042 chosen node or the ACPI SPCR table if supported by 1043 the platform. 1044 1045 cdns,<addr>[,options] 1046 Start an early, polled-mode console on a Cadence 1047 (xuartps) serial port at the specified address. Only 1048 supported option is baud rate. If baud rate is not 1049 specified, the serial port must already be setup and 1050 configured. 1051 1052 uart[8250],io,<addr>[,options] 1053 uart[8250],mmio,<addr>[,options] 1054 uart[8250],mmio32,<addr>[,options] 1055 uart[8250],mmio32be,<addr>[,options] 1056 uart[8250],0x<addr>[,options] 1057 Start an early, polled-mode console on the 8250/16550 1058 UART at the specified I/O port or MMIO address. 1059 MMIO inter-register address stride is either 8-bit 1060 (mmio) or 32-bit (mmio32 or mmio32be). 1061 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1062 to be equivalent to 'mmio'. 'options' are specified 1063 in the same format described for "console=ttyS<n>"; if 1064 unspecified, the h/w is not initialized. 1065 1066 pl011,<addr> 1067 pl011,mmio32,<addr> 1068 Start an early, polled-mode console on a pl011 serial 1069 port at the specified address. The pl011 serial port 1070 must already be setup and configured. Options are not 1071 yet supported. If 'mmio32' is specified, then only 1072 the driver will use only 32-bit accessors to read/write 1073 the device registers. 1074 1075 meson,<addr> 1076 Start an early, polled-mode console on a meson serial 1077 port at the specified address. The serial port must 1078 already be setup and configured. Options are not yet 1079 supported. 1080 1081 msm_serial,<addr> 1082 Start an early, polled-mode console on an msm serial 1083 port at the specified address. The serial port 1084 must already be setup and configured. Options are not 1085 yet supported. 1086 1087 msm_serial_dm,<addr> 1088 Start an early, polled-mode console on an msm serial 1089 dm port at the specified address. The serial port 1090 must already be setup and configured. Options are not 1091 yet supported. 1092 1093 owl,<addr> 1094 Start an early, polled-mode console on a serial port 1095 of an Actions Semi SoC, such as S500 or S900, at the 1096 specified address. The serial port must already be 1097 setup and configured. Options are not yet supported. 1098 1099 rda,<addr> 1100 Start an early, polled-mode console on a serial port 1101 of an RDA Micro SoC, such as RDA8810PL, at the 1102 specified address. The serial port must already be 1103 setup and configured. Options are not yet supported. 1104 1105 sbi 1106 Use RISC-V SBI (Supervisor Binary Interface) for early 1107 console. 1108 1109 smh Use ARM semihosting calls for early console. 1110 1111 s3c2410,<addr> 1112 s3c2412,<addr> 1113 s3c2440,<addr> 1114 s3c6400,<addr> 1115 s5pv210,<addr> 1116 exynos4210,<addr> 1117 Use early console provided by serial driver available 1118 on Samsung SoCs, requires selecting proper type and 1119 a correct base address of the selected UART port. The 1120 serial port must already be setup and configured. 1121 Options are not yet supported. 1122 1123 lantiq,<addr> 1124 Start an early, polled-mode console on a lantiq serial 1125 (lqasc) port at the specified address. The serial port 1126 must already be setup and configured. Options are not 1127 yet supported. 1128 1129 lpuart,<addr> 1130 lpuart32,<addr> 1131 Use early console provided by Freescale LP UART driver 1132 found on Freescale Vybrid and QorIQ LS1021A processors. 1133 A valid base address must be provided, and the serial 1134 port must already be setup and configured. 1135 1136 ec_imx21,<addr> 1137 ec_imx6q,<addr> 1138 Start an early, polled-mode, output-only console on the 1139 Freescale i.MX UART at the specified address. The UART 1140 must already be setup and configured. 1141 1142 ar3700_uart,<addr> 1143 Start an early, polled-mode console on the 1144 Armada 3700 serial port at the specified 1145 address. The serial port must already be setup 1146 and configured. Options are not yet supported. 1147 1148 qcom_geni,<addr> 1149 Start an early, polled-mode console on a Qualcomm 1150 Generic Interface (GENI) based serial port at the 1151 specified address. The serial port must already be 1152 setup and configured. Options are not yet supported. 1153 1154 efifb,[options] 1155 Start an early, unaccelerated console on the EFI 1156 memory mapped framebuffer (if available). On cache 1157 coherent non-x86 systems that use system memory for 1158 the framebuffer, pass the 'ram' option so that it is 1159 mapped with the correct attributes. 1160 1161 linflex,<addr> 1162 Use early console provided by Freescale LINFlexD UART 1163 serial driver for NXP S32V234 SoCs. A valid base 1164 address must be provided, and the serial port must 1165 already be setup and configured. 1166 1167 earlyprintk= [X86,SH,ARM,M68k,S390] 1168 earlyprintk=vga 1169 earlyprintk=sclp 1170 earlyprintk=xen 1171 earlyprintk=serial[,ttySn[,baudrate]] 1172 earlyprintk=serial[,0x...[,baudrate]] 1173 earlyprintk=ttySn[,baudrate] 1174 earlyprintk=dbgp[debugController#] 1175 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1176 earlyprintk=xdbc[xhciController#] 1177 1178 earlyprintk is useful when the kernel crashes before 1179 the normal console is initialized. It is not enabled by 1180 default because it has some cosmetic problems. 1181 1182 Append ",keep" to not disable it when the real console 1183 takes over. 1184 1185 Only one of vga, efi, serial, or usb debug port can 1186 be used at a time. 1187 1188 Currently only ttyS0 and ttyS1 may be specified by 1189 name. Other I/O ports may be explicitly specified 1190 on some architectures (x86 and arm at least) by 1191 replacing ttySn with an I/O port address, like this: 1192 earlyprintk=serial,0x1008,115200 1193 You can find the port for a given device in 1194 /proc/tty/driver/serial: 1195 2: uart:ST16650V2 port:00001008 irq:18 ... 1196 1197 Interaction with the standard serial driver is not 1198 very good. 1199 1200 The VGA and EFI output is eventually overwritten by 1201 the real console. 1202 1203 The xen output can only be used by Xen PV guests. 1204 1205 The sclp output can only be used on s390. 1206 1207 The optional "force" to "pciserial" enables use of a 1208 PCI device even when its classcode is not of the 1209 UART class. 1210 1211 edac_report= [HW,EDAC] Control how to report EDAC event 1212 Format: {"on" | "off" | "force"} 1213 on: enable EDAC to report H/W event. May be overridden 1214 by other higher priority error reporting module. 1215 off: disable H/W event reporting through EDAC. 1216 force: enforce the use of EDAC to report H/W event. 1217 default: on. 1218 1219 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1220 ekgdboc=kbd 1221 1222 This is designed to be used in conjunction with 1223 the boot argument: earlyprintk=vga 1224 1225 This parameter works in place of the kgdboc parameter 1226 but can only be used if the backing tty is available 1227 very early in the boot process. For early debugging 1228 via a serial port see kgdboc_earlycon instead. 1229 1230 edd= [EDD] 1231 Format: {"off" | "on" | "skip[mbr]"} 1232 1233 efi= [EFI] 1234 Format: { "debug", "disable_early_pci_dma", 1235 "nochunk", "noruntime", "nosoftreserve", 1236 "novamap", "no_disable_early_pci_dma", 1237 "old_map" } 1238 debug: enable misc debug output. 1239 disable_early_pci_dma: disable the busmaster bit on all 1240 PCI bridges while in the EFI boot stub. 1241 nochunk: disable reading files in "chunks" in the EFI 1242 boot stub, as chunking can cause problems with some 1243 firmware implementations. 1244 noruntime : disable EFI runtime services support 1245 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1246 attribute may cause the kernel to reserve the 1247 memory range for a memory mapping driver to 1248 claim. Specify efi=nosoftreserve to disable this 1249 reservation and treat the memory by its base type 1250 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1251 novamap: do not call SetVirtualAddressMap(). 1252 no_disable_early_pci_dma: Leave the busmaster bit set 1253 on all PCI bridges while in the EFI boot stub 1254 old_map [X86-64]: switch to the old ioremap-based EFI 1255 runtime services mapping. [Needs CONFIG_X86_UV=y] 1256 1257 efi_no_storage_paranoia [EFI; X86] 1258 Using this parameter you can use more than 50% of 1259 your efi variable storage. Use this parameter only if 1260 you are really sure that your UEFI does sane gc and 1261 fulfills the spec otherwise your board may brick. 1262 1263 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1264 Add arbitrary attribute to specific memory range by 1265 updating original EFI memory map. 1266 Region of memory which aa attribute is added to is 1267 from ss to ss+nn. 1268 1269 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1270 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1271 attribute is added to range 0x100000000-0x180000000 and 1272 0x10a0000000-0x1120000000. 1273 1274 If efi_fake_mem=8G@9G:0x40000 is specified, the 1275 EFI_MEMORY_SP(0x40000) attribute is added to 1276 range 0x240000000-0x43fffffff. 1277 1278 Using this parameter you can do debugging of EFI memmap 1279 related features. For example, you can do debugging of 1280 Address Range Mirroring feature even if your box 1281 doesn't support it, or mark specific memory as 1282 "soft reserved". 1283 1284 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1285 that is to be dynamically loaded by Linux. If there are 1286 multiple variables with the same name but with different 1287 vendor GUIDs, all of them will be loaded. See 1288 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1289 1290 1291 eisa_irq_edge= [PARISC,HW] 1292 See header of drivers/parisc/eisa.c. 1293 1294 elanfreq= [X86-32] 1295 See comment before function elanfreq_setup() in 1296 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1297 1298 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1299 Specifies physical address of start of kernel core 1300 image elf header and optionally the size. Generally 1301 kexec loader will pass this option to capture kernel. 1302 See Documentation/admin-guide/kdump/kdump.rst for details. 1303 1304 enable_mtrr_cleanup [X86] 1305 The kernel tries to adjust MTRR layout from continuous 1306 to discrete, to make X server driver able to add WB 1307 entry later. This parameter enables that. 1308 1309 enable_timer_pin_1 [X86] 1310 Enable PIN 1 of APIC timer 1311 Can be useful to work around chipset bugs 1312 (in particular on some ATI chipsets). 1313 The kernel tries to set a reasonable default. 1314 1315 enforcing [SELINUX] Set initial enforcing status. 1316 Format: {"0" | "1"} 1317 See security/selinux/Kconfig help text. 1318 0 -- permissive (log only, no denials). 1319 1 -- enforcing (deny and log). 1320 Default value is 0. 1321 Value can be changed at runtime via 1322 /sys/fs/selinux/enforce. 1323 1324 erst_disable [ACPI] 1325 Disable Error Record Serialization Table (ERST) 1326 support. 1327 1328 ether= [HW,NET] Ethernet cards parameters 1329 This option is obsoleted by the "netdev=" option, which 1330 has equivalent usage. See its documentation for details. 1331 1332 evm= [EVM] 1333 Format: { "fix" } 1334 Permit 'security.evm' to be updated regardless of 1335 current integrity status. 1336 1337 failslab= 1338 fail_page_alloc= 1339 fail_make_request=[KNL] 1340 General fault injection mechanism. 1341 Format: <interval>,<probability>,<space>,<times> 1342 See also Documentation/fault-injection/. 1343 1344 floppy= [HW] 1345 See Documentation/admin-guide/blockdev/floppy.rst. 1346 1347 force_pal_cache_flush 1348 [IA-64] Avoid check_sal_cache_flush which may hang on 1349 buggy SAL_CACHE_FLUSH implementations. Using this 1350 parameter will force ia64_sal_cache_flush to call 1351 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1352 1353 forcepae [X86-32] 1354 Forcefully enable Physical Address Extension (PAE). 1355 Many Pentium M systems disable PAE but may have a 1356 functionally usable PAE implementation. 1357 Warning: use of this parameter will taint the kernel 1358 and may cause unknown problems. 1359 1360 ftrace=[tracer] 1361 [FTRACE] will set and start the specified tracer 1362 as early as possible in order to facilitate early 1363 boot debugging. 1364 1365 ftrace_dump_on_oops[=orig_cpu] 1366 [FTRACE] will dump the trace buffers on oops. 1367 If no parameter is passed, ftrace will dump 1368 buffers of all CPUs, but if you pass orig_cpu, it will 1369 dump only the buffer of the CPU that triggered the 1370 oops. 1371 1372 ftrace_filter=[function-list] 1373 [FTRACE] Limit the functions traced by the function 1374 tracer at boot up. function-list is a comma separated 1375 list of functions. This list can be changed at run 1376 time by the set_ftrace_filter file in the debugfs 1377 tracing directory. 1378 1379 ftrace_notrace=[function-list] 1380 [FTRACE] Do not trace the functions specified in 1381 function-list. This list can be changed at run time 1382 by the set_ftrace_notrace file in the debugfs 1383 tracing directory. 1384 1385 ftrace_graph_filter=[function-list] 1386 [FTRACE] Limit the top level callers functions traced 1387 by the function graph tracer at boot up. 1388 function-list is a comma separated list of functions 1389 that can be changed at run time by the 1390 set_graph_function file in the debugfs tracing directory. 1391 1392 ftrace_graph_notrace=[function-list] 1393 [FTRACE] Do not trace from the functions specified in 1394 function-list. This list is a comma separated list of 1395 functions that can be changed at run time by the 1396 set_graph_notrace file in the debugfs tracing directory. 1397 1398 ftrace_graph_max_depth=<uint> 1399 [FTRACE] Used with the function graph tracer. This is 1400 the max depth it will trace into a function. This value 1401 can be changed at run time by the max_graph_depth file 1402 in the tracefs tracing directory. default: 0 (no limit) 1403 1404 fw_devlink= [KNL] Create device links between consumer and supplier 1405 devices by scanning the firmware to infer the 1406 consumer/supplier relationships. This feature is 1407 especially useful when drivers are loaded as modules as 1408 it ensures proper ordering of tasks like device probing 1409 (suppliers first, then consumers), supplier boot state 1410 clean up (only after all consumers have probed), 1411 suspend/resume & runtime PM (consumers first, then 1412 suppliers). 1413 Format: { off | permissive | on | rpm } 1414 off -- Don't create device links from firmware info. 1415 permissive -- Create device links from firmware info 1416 but use it only for ordering boot state clean 1417 up (sync_state() calls). 1418 on -- Create device links from firmware info and use it 1419 to enforce probe and suspend/resume ordering. 1420 rpm -- Like "on", but also use to order runtime PM. 1421 1422 gamecon.map[2|3]= 1423 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1424 support via parallel port (up to 5 devices per port) 1425 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1426 See also Documentation/input/devices/joystick-parport.rst 1427 1428 gamma= [HW,DRM] 1429 1430 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1431 Format: off | on 1432 default: on 1433 1434 gcov_persist= [GCOV] When non-zero (default), profiling data for 1435 kernel modules is saved and remains accessible via 1436 debugfs, even when the module is unloaded/reloaded. 1437 When zero, profiling data is discarded and associated 1438 debugfs files are removed at module unload time. 1439 1440 goldfish [X86] Enable the goldfish android emulator platform. 1441 Don't use this when you are not running on the 1442 android emulator 1443 1444 gpt [EFI] Forces disk with valid GPT signature but 1445 invalid Protective MBR to be treated as GPT. If the 1446 primary GPT is corrupted, it enables the backup/alternate 1447 GPT to be used instead. 1448 1449 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1450 the "Enable 0" bit of the configuration register. 1451 Format: 0 | 1 1452 Default: 0 1453 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1454 the "Enable 0" bit of the configuration register. 1455 Format: 0 | 1 1456 Default: 0 1457 grcan.select= [HW] Select which physical interface to use. 1458 Format: 0 | 1 1459 Default: 0 1460 grcan.txsize= [HW] Sets the size of the tx buffer. 1461 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1462 Default: 1024 1463 grcan.rxsize= [HW] Sets the size of the rx buffer. 1464 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1465 Default: 1024 1466 1467 gpio-mockup.gpio_mockup_ranges 1468 [HW] Sets the ranges of gpiochip of for this device. 1469 Format: <start1>,<end1>,<start2>,<end2>... 1470 1471 hardlockup_all_cpu_backtrace= 1472 [KNL] Should the hard-lockup detector generate 1473 backtraces on all cpus. 1474 Format: 0 | 1 1475 1476 hashdist= [KNL,NUMA] Large hashes allocated during boot 1477 are distributed across NUMA nodes. Defaults on 1478 for 64-bit NUMA, off otherwise. 1479 Format: 0 | 1 (for off | on) 1480 1481 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1482 1483 hd= [EIDE] (E)IDE hard drive subsystem geometry 1484 Format: <cyl>,<head>,<sect> 1485 1486 hest_disable [ACPI] 1487 Disable Hardware Error Source Table (HEST) support; 1488 corresponding firmware-first mode error processing 1489 logic will be disabled. 1490 1491 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1492 size of <nn>. This works even on boxes that have no 1493 highmem otherwise. This also works to reduce highmem 1494 size on bigger boxes. 1495 1496 highres= [KNL] Enable/disable high resolution timer mode. 1497 Valid parameters: "on", "off" 1498 Default: "on" 1499 1500 hlt [BUGS=ARM,SH] 1501 1502 hpet= [X86-32,HPET] option to control HPET usage 1503 Format: { enable (default) | disable | force | 1504 verbose } 1505 disable: disable HPET and use PIT instead 1506 force: allow force enabled of undocumented chips (ICH4, 1507 VIA, nVidia) 1508 verbose: show contents of HPET registers during setup 1509 1510 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1511 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1512 1513 hugetlb_cma= [HW] The size of a cma area used for allocation 1514 of gigantic hugepages. 1515 Format: nn[KMGTPE] 1516 1517 Reserve a cma area of given size and allocate gigantic 1518 hugepages using the cma allocator. If enabled, the 1519 boot-time allocation of gigantic hugepages is skipped. 1520 1521 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1522 If this follows hugepagesz (below), it specifies 1523 the number of pages of hugepagesz to be allocated. 1524 If this is the first HugeTLB parameter on the command 1525 line, it specifies the number of pages to allocate for 1526 the default huge page size. See also 1527 Documentation/admin-guide/mm/hugetlbpage.rst. 1528 Format: <integer> 1529 1530 hugepagesz= 1531 [HW] The size of the HugeTLB pages. This is used in 1532 conjunction with hugepages (above) to allocate huge 1533 pages of a specific size at boot. The pair 1534 hugepagesz=X hugepages=Y can be specified once for 1535 each supported huge page size. Huge page sizes are 1536 architecture dependent. See also 1537 Documentation/admin-guide/mm/hugetlbpage.rst. 1538 Format: size[KMG] 1539 1540 hung_task_panic= 1541 [KNL] Should the hung task detector generate panics. 1542 Format: 0 | 1 1543 1544 A value of 1 instructs the kernel to panic when a 1545 hung task is detected. The default value is controlled 1546 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1547 option. The value selected by this boot parameter can 1548 be changed later by the kernel.hung_task_panic sysctl. 1549 1550 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1551 terminal devices. Valid values: 0..8 1552 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1553 If specified, z/VM IUCV HVC accepts connections 1554 from listed z/VM user IDs only. 1555 1556 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1557 which allow the hypervisor to 'idle' the 1558 guest on lock contention. 1559 1560 keep_bootcon [KNL] 1561 Do not unregister boot console at start. This is only 1562 useful for debugging when something happens in the window 1563 between unregistering the boot console and initializing 1564 the real console. 1565 1566 i2c_bus= [HW] Override the default board specific I2C bus speed 1567 or register an additional I2C bus that is not 1568 registered from board initialization code. 1569 Format: 1570 <bus_id>,<clkrate> 1571 1572 i8042.debug [HW] Toggle i8042 debug mode 1573 i8042.unmask_kbd_data 1574 [HW] Enable printing of interrupt data from the KBD port 1575 (disabled by default, and as a pre-condition 1576 requires that i8042.debug=1 be enabled) 1577 i8042.direct [HW] Put keyboard port into non-translated mode 1578 i8042.dumbkbd [HW] Pretend that controller can only read data from 1579 keyboard and cannot control its state 1580 (Don't attempt to blink the leds) 1581 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1582 i8042.nokbd [HW] Don't check/create keyboard port 1583 i8042.noloop [HW] Disable the AUX Loopback command while probing 1584 for the AUX port 1585 i8042.nomux [HW] Don't check presence of an active multiplexing 1586 controller 1587 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1588 controllers 1589 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1590 i8042.reset [HW] Reset the controller during init, cleanup and 1591 suspend-to-ram transitions, only during s2r 1592 transitions, or never reset 1593 Format: { 1 | Y | y | 0 | N | n } 1594 1, Y, y: always reset controller 1595 0, N, n: don't ever reset controller 1596 Default: only on s2r transitions on x86; most other 1597 architectures force reset to be always executed 1598 i8042.unlock [HW] Unlock (ignore) the keylock 1599 i8042.kbdreset [HW] Reset device connected to KBD port 1600 1601 i810= [HW,DRM] 1602 1603 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1604 indicates that the driver is running on unsupported 1605 hardware. 1606 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1607 does not match list of supported models. 1608 i8k.power_status 1609 [HW] Report power status in /proc/i8k 1610 (disabled by default) 1611 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1612 capability is set. 1613 1614 i915.invert_brightness= 1615 [DRM] Invert the sense of the variable that is used to 1616 set the brightness of the panel backlight. Normally a 1617 brightness value of 0 indicates backlight switched off, 1618 and the maximum of the brightness value sets the backlight 1619 to maximum brightness. If this parameter is set to 0 1620 (default) and the machine requires it, or this parameter 1621 is set to 1, a brightness value of 0 sets the backlight 1622 to maximum brightness, and the maximum of the brightness 1623 value switches the backlight off. 1624 -1 -- never invert brightness 1625 0 -- machine default 1626 1 -- force brightness inversion 1627 1628 icn= [HW,ISDN] 1629 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1630 1631 ide-core.nodma= [HW] (E)IDE subsystem 1632 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1633 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1634 .cdrom .chs .ignore_cable are additional options 1635 See Documentation/ide/ide.rst. 1636 1637 ide-generic.probe-mask= [HW] (E)IDE subsystem 1638 Format: <int> 1639 Probe mask for legacy ISA IDE ports. Depending on 1640 platform up to 6 ports are supported, enabled by 1641 setting corresponding bits in the mask to 1. The 1642 default value is 0x0, which has a special meaning. 1643 On systems that have PCI, it triggers scanning the 1644 PCI bus for the first and the second port, which 1645 are then probed. On systems without PCI the value 1646 of 0x0 enables probing the two first ports as if it 1647 was 0x3. 1648 1649 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1650 Claim all unknown PCI IDE storage controllers. 1651 1652 idle= [X86] 1653 Format: idle=poll, idle=halt, idle=nomwait 1654 Poll forces a polling idle loop that can slightly 1655 improve the performance of waking up a idle CPU, but 1656 will use a lot of power and make the system run hot. 1657 Not recommended. 1658 idle=halt: Halt is forced to be used for CPU idle. 1659 In such case C2/C3 won't be used again. 1660 idle=nomwait: Disable mwait for CPU C-states 1661 1662 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1663 Format: { strict | legacy | 2008 | relaxed } 1664 Default: strict 1665 1666 Choose which programs will be accepted for execution 1667 based on the IEEE 754 NaN encoding(s) supported by 1668 the FPU and the NaN encoding requested with the value 1669 of an ELF file header flag individually set by each 1670 binary. Hardware implementations are permitted to 1671 support either or both of the legacy and the 2008 NaN 1672 encoding mode. 1673 1674 Available settings are as follows: 1675 strict accept binaries that request a NaN encoding 1676 supported by the FPU 1677 legacy only accept legacy-NaN binaries, if supported 1678 by the FPU 1679 2008 only accept 2008-NaN binaries, if supported 1680 by the FPU 1681 relaxed accept any binaries regardless of whether 1682 supported by the FPU 1683 1684 The FPU emulator is always able to support both NaN 1685 encodings, so if no FPU hardware is present or it has 1686 been disabled with 'nofpu', then the settings of 1687 'legacy' and '2008' strap the emulator accordingly, 1688 'relaxed' straps the emulator for both legacy-NaN and 1689 2008-NaN, whereas 'strict' enables legacy-NaN only on 1690 legacy processors and both NaN encodings on MIPS32 or 1691 MIPS64 CPUs. 1692 1693 The setting for ABS.fmt/NEG.fmt instruction execution 1694 mode generally follows that for the NaN encoding, 1695 except where unsupported by hardware. 1696 1697 ignore_loglevel [KNL] 1698 Ignore loglevel setting - this will print /all/ 1699 kernel messages to the console. Useful for debugging. 1700 We also add it as printk module parameter, so users 1701 could change it dynamically, usually by 1702 /sys/module/printk/parameters/ignore_loglevel. 1703 1704 ignore_rlimit_data 1705 Ignore RLIMIT_DATA setting for data mappings, 1706 print warning at first misuse. Can be changed via 1707 /sys/module/kernel/parameters/ignore_rlimit_data. 1708 1709 ihash_entries= [KNL] 1710 Set number of hash buckets for inode cache. 1711 1712 ima_appraise= [IMA] appraise integrity measurements 1713 Format: { "off" | "enforce" | "fix" | "log" } 1714 default: "enforce" 1715 1716 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1717 The builtin appraise policy appraises all files 1718 owned by uid=0. 1719 1720 ima_canonical_fmt [IMA] 1721 Use the canonical format for the binary runtime 1722 measurements, instead of host native format. 1723 1724 ima_hash= [IMA] 1725 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1726 | sha512 | ... } 1727 default: "sha1" 1728 1729 The list of supported hash algorithms is defined 1730 in crypto/hash_info.h. 1731 1732 ima_policy= [IMA] 1733 The builtin policies to load during IMA setup. 1734 Format: "tcb | appraise_tcb | secure_boot | 1735 fail_securely" 1736 1737 The "tcb" policy measures all programs exec'd, files 1738 mmap'd for exec, and all files opened with the read 1739 mode bit set by either the effective uid (euid=0) or 1740 uid=0. 1741 1742 The "appraise_tcb" policy appraises the integrity of 1743 all files owned by root. 1744 1745 The "secure_boot" policy appraises the integrity 1746 of files (eg. kexec kernel image, kernel modules, 1747 firmware, policy, etc) based on file signatures. 1748 1749 The "fail_securely" policy forces file signature 1750 verification failure also on privileged mounted 1751 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1752 flag. 1753 1754 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1755 Load a policy which meets the needs of the Trusted 1756 Computing Base. This means IMA will measure all 1757 programs exec'd, files mmap'd for exec, and all files 1758 opened for read by uid=0. 1759 1760 ima_template= [IMA] 1761 Select one of defined IMA measurements template formats. 1762 Formats: { "ima" | "ima-ng" | "ima-sig" } 1763 Default: "ima-ng" 1764 1765 ima_template_fmt= 1766 [IMA] Define a custom template format. 1767 Format: { "field1|...|fieldN" } 1768 1769 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1770 Format: <min_file_size> 1771 Set the minimal file size for using asynchronous hash. 1772 If left unspecified, ahash usage is disabled. 1773 1774 ahash performance varies for different data sizes on 1775 different crypto accelerators. This option can be used 1776 to achieve the best performance for a particular HW. 1777 1778 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1779 Format: <bufsize> 1780 Set hashing buffer size. Default: 4k. 1781 1782 ahash performance varies for different chunk sizes on 1783 different crypto accelerators. This option can be used 1784 to achieve best performance for particular HW. 1785 1786 init= [KNL] 1787 Format: <full_path> 1788 Run specified binary instead of /sbin/init as init 1789 process. 1790 1791 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1792 for working out where the kernel is dying during 1793 startup. 1794 1795 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1796 initcall functions. Useful for debugging built-in 1797 modules and initcalls. 1798 1799 initrd= [BOOT] Specify the location of the initial ramdisk 1800 1801 initrdmem= [KNL] Specify a physical address and size from which to 1802 load the initrd. If an initrd is compiled in or 1803 specified in the bootparams, it takes priority over this 1804 setting. 1805 Format: ss[KMG],nn[KMG] 1806 Default is 0, 0 1807 1808 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1809 zeroes. 1810 Format: 0 | 1 1811 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1812 1813 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1814 Format: 0 | 1 1815 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1816 1817 init_pkru= [X86] Specify the default memory protection keys rights 1818 register contents for all processes. 0x55555554 by 1819 default (disallow access to all but pkey 0). Can 1820 override in debugfs after boot. 1821 1822 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1823 Format: <irq> 1824 1825 int_pln_enable [X86] Enable power limit notification interrupt 1826 1827 integrity_audit=[IMA] 1828 Format: { "0" | "1" } 1829 0 -- basic integrity auditing messages. (Default) 1830 1 -- additional integrity auditing messages. 1831 1832 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1833 on 1834 Enable intel iommu driver. 1835 off 1836 Disable intel iommu driver. 1837 igfx_off [Default Off] 1838 By default, gfx is mapped as normal device. If a gfx 1839 device has a dedicated DMAR unit, the DMAR unit is 1840 bypassed by not enabling DMAR with this option. In 1841 this case, gfx device will use physical address for 1842 DMA. 1843 forcedac [X86-64] 1844 With this option iommu will not optimize to look 1845 for io virtual address below 32-bit forcing dual 1846 address cycle on pci bus for cards supporting greater 1847 than 32-bit addressing. The default is to look 1848 for translation below 32-bit and if not available 1849 then look in the higher range. 1850 strict [Default Off] 1851 With this option on every unmap_single operation will 1852 result in a hardware IOTLB flush operation as opposed 1853 to batching them for performance. 1854 sp_off [Default Off] 1855 By default, super page will be supported if Intel IOMMU 1856 has the capability. With this option, super page will 1857 not be supported. 1858 sm_on [Default Off] 1859 By default, scalable mode will be disabled even if the 1860 hardware advertises that it has support for the scalable 1861 mode translation. With this option set, scalable mode 1862 will be used on hardware which claims to support it. 1863 tboot_noforce [Default Off] 1864 Do not force the Intel IOMMU enabled under tboot. 1865 By default, tboot will force Intel IOMMU on, which 1866 could harm performance of some high-throughput 1867 devices like 40GBit network cards, even if identity 1868 mapping is enabled. 1869 Note that using this option lowers the security 1870 provided by tboot because it makes the system 1871 vulnerable to DMA attacks. 1872 nobounce [Default off] 1873 Disable bounce buffer for untrusted devices such as 1874 the Thunderbolt devices. This will treat the untrusted 1875 devices as the trusted ones, hence might expose security 1876 risks of DMA attacks. 1877 1878 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1879 0 disables intel_idle and fall back on acpi_idle. 1880 1 to 9 specify maximum depth of C-state. 1881 1882 intel_pstate= [X86] 1883 disable 1884 Do not enable intel_pstate as the default 1885 scaling driver for the supported processors 1886 passive 1887 Use intel_pstate as a scaling driver, but configure it 1888 to work with generic cpufreq governors (instead of 1889 enabling its internal governor). This mode cannot be 1890 used along with the hardware-managed P-states (HWP) 1891 feature. 1892 force 1893 Enable intel_pstate on systems that prohibit it by default 1894 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1895 instead of acpi-cpufreq may disable platform features, such 1896 as thermal controls and power capping, that rely on ACPI 1897 P-States information being indicated to OSPM and therefore 1898 should be used with caution. This option does not work with 1899 processors that aren't supported by the intel_pstate driver 1900 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1901 no_hwp 1902 Do not enable hardware P state control (HWP) 1903 if available. 1904 hwp_only 1905 Only load intel_pstate on systems which support 1906 hardware P state control (HWP) if available. 1907 support_acpi_ppc 1908 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1909 Description Table, specifies preferred power management 1910 profile as "Enterprise Server" or "Performance Server", 1911 then this feature is turned on by default. 1912 per_cpu_perf_limits 1913 Allow per-logical-CPU P-State performance control limits using 1914 cpufreq sysfs interface 1915 1916 intremap= [X86-64, Intel-IOMMU] 1917 on enable Interrupt Remapping (default) 1918 off disable Interrupt Remapping 1919 nosid disable Source ID checking 1920 no_x2apic_optout 1921 BIOS x2APIC opt-out request will be ignored 1922 nopost disable Interrupt Posting 1923 1924 iomem= Disable strict checking of access to MMIO memory 1925 strict regions from userspace. 1926 relaxed 1927 1928 iommu= [X86] 1929 off 1930 force 1931 noforce 1932 biomerge 1933 panic 1934 nopanic 1935 merge 1936 nomerge 1937 soft 1938 pt [X86] 1939 nopt [X86] 1940 nobypass [PPC/POWERNV] 1941 Disable IOMMU bypass, using IOMMU for PCI devices. 1942 1943 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1944 Format: { "0" | "1" } 1945 0 - Lazy mode. 1946 Request that DMA unmap operations use deferred 1947 invalidation of hardware TLBs, for increased 1948 throughput at the cost of reduced device isolation. 1949 Will fall back to strict mode if not supported by 1950 the relevant IOMMU driver. 1951 1 - Strict mode (default). 1952 DMA unmap operations invalidate IOMMU hardware TLBs 1953 synchronously. 1954 1955 iommu.passthrough= 1956 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1957 Format: { "0" | "1" } 1958 0 - Use IOMMU translation for DMA. 1959 1 - Bypass the IOMMU for DMA. 1960 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1961 1962 io7= [HW] IO7 for Marvel-based Alpha systems 1963 See comment before marvel_specify_io7 in 1964 arch/alpha/kernel/core_marvel.c. 1965 1966 io_delay= [X86] I/O delay method 1967 0x80 1968 Standard port 0x80 based delay 1969 0xed 1970 Alternate port 0xed based delay (needed on some systems) 1971 udelay 1972 Simple two microseconds delay 1973 none 1974 No delay 1975 1976 ip= [IP_PNP] 1977 See Documentation/admin-guide/nfs/nfsroot.rst. 1978 1979 ipcmni_extend [KNL] Extend the maximum number of unique System V 1980 IPC identifiers from 32,768 to 16,777,216. 1981 1982 irqaffinity= [SMP] Set the default irq affinity mask 1983 The argument is a cpu list, as described above. 1984 1985 irqchip.gicv2_force_probe= 1986 [ARM, ARM64] 1987 Format: <bool> 1988 Force the kernel to look for the second 4kB page 1989 of a GICv2 controller even if the memory range 1990 exposed by the device tree is too small. 1991 1992 irqchip.gicv3_nolpi= 1993 [ARM, ARM64] 1994 Force the kernel to ignore the availability of 1995 LPIs (and by consequence ITSs). Intended for system 1996 that use the kernel as a bootloader, and thus want 1997 to let secondary kernels in charge of setting up 1998 LPIs. 1999 2000 irqchip.gicv3_pseudo_nmi= [ARM64] 2001 Enables support for pseudo-NMIs in the kernel. This 2002 requires the kernel to be built with 2003 CONFIG_ARM64_PSEUDO_NMI. 2004 2005 irqfixup [HW] 2006 When an interrupt is not handled search all handlers 2007 for it. Intended to get systems with badly broken 2008 firmware running. 2009 2010 irqpoll [HW] 2011 When an interrupt is not handled search all handlers 2012 for it. Also check all handlers each timer 2013 interrupt. Intended to get systems with badly broken 2014 firmware running. 2015 2016 isapnp= [ISAPNP] 2017 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2018 2019 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2020 [Deprecated - use cpusets instead] 2021 Format: [flag-list,]<cpu-list> 2022 2023 Specify one or more CPUs to isolate from disturbances 2024 specified in the flag list (default: domain): 2025 2026 nohz 2027 Disable the tick when a single task runs. 2028 2029 A residual 1Hz tick is offloaded to workqueues, which you 2030 need to affine to housekeeping through the global 2031 workqueue's affinity configured via the 2032 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2033 by using the 'domain' flag described below. 2034 2035 NOTE: by default the global workqueue runs on all CPUs, 2036 so to protect individual CPUs the 'cpumask' file has to 2037 be configured manually after bootup. 2038 2039 domain 2040 Isolate from the general SMP balancing and scheduling 2041 algorithms. Note that performing domain isolation this way 2042 is irreversible: it's not possible to bring back a CPU to 2043 the domains once isolated through isolcpus. It's strongly 2044 advised to use cpusets instead to disable scheduler load 2045 balancing through the "cpuset.sched_load_balance" file. 2046 It offers a much more flexible interface where CPUs can 2047 move in and out of an isolated set anytime. 2048 2049 You can move a process onto or off an "isolated" CPU via 2050 the CPU affinity syscalls or cpuset. 2051 <cpu number> begins at 0 and the maximum value is 2052 "number of CPUs in system - 1". 2053 2054 managed_irq 2055 2056 Isolate from being targeted by managed interrupts 2057 which have an interrupt mask containing isolated 2058 CPUs. The affinity of managed interrupts is 2059 handled by the kernel and cannot be changed via 2060 the /proc/irq/* interfaces. 2061 2062 This isolation is best effort and only effective 2063 if the automatically assigned interrupt mask of a 2064 device queue contains isolated and housekeeping 2065 CPUs. If housekeeping CPUs are online then such 2066 interrupts are directed to the housekeeping CPU 2067 so that IO submitted on the housekeeping CPU 2068 cannot disturb the isolated CPU. 2069 2070 If a queue's affinity mask contains only isolated 2071 CPUs then this parameter has no effect on the 2072 interrupt routing decision, though interrupts are 2073 only delivered when tasks running on those 2074 isolated CPUs submit IO. IO submitted on 2075 housekeeping CPUs has no influence on those 2076 queues. 2077 2078 The format of <cpu-list> is described above. 2079 2080 iucv= [HW,NET] 2081 2082 ivrs_ioapic [HW,X86-64] 2083 Provide an override to the IOAPIC-ID<->DEVICE-ID 2084 mapping provided in the IVRS ACPI table. For 2085 example, to map IOAPIC-ID decimal 10 to 2086 PCI device 00:14.0 write the parameter as: 2087 ivrs_ioapic[10]=00:14.0 2088 2089 ivrs_hpet [HW,X86-64] 2090 Provide an override to the HPET-ID<->DEVICE-ID 2091 mapping provided in the IVRS ACPI table. For 2092 example, to map HPET-ID decimal 0 to 2093 PCI device 00:14.0 write the parameter as: 2094 ivrs_hpet[0]=00:14.0 2095 2096 ivrs_acpihid [HW,X86-64] 2097 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2098 mapping provided in the IVRS ACPI table. For 2099 example, to map UART-HID:UID AMD0020:0 to 2100 PCI device 00:14.5 write the parameter as: 2101 ivrs_acpihid[00:14.5]=AMD0020:0 2102 2103 js= [HW,JOY] Analog joystick 2104 See Documentation/input/joydev/joystick.rst. 2105 2106 nokaslr [KNL] 2107 When CONFIG_RANDOMIZE_BASE is set, this disables 2108 kernel and module base offset ASLR (Address Space 2109 Layout Randomization). 2110 2111 kasan_multi_shot 2112 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2113 report on every invalid memory access. Without this 2114 parameter KASAN will print report only for the first 2115 invalid access. 2116 2117 keepinitrd [HW,ARM] 2118 2119 kernelcore= [KNL,X86,IA-64,PPC] 2120 Format: nn[KMGTPE] | nn% | "mirror" 2121 This parameter specifies the amount of memory usable by 2122 the kernel for non-movable allocations. The requested 2123 amount is spread evenly throughout all nodes in the 2124 system as ZONE_NORMAL. The remaining memory is used for 2125 movable memory in its own zone, ZONE_MOVABLE. In the 2126 event, a node is too small to have both ZONE_NORMAL and 2127 ZONE_MOVABLE, kernelcore memory will take priority and 2128 other nodes will have a larger ZONE_MOVABLE. 2129 2130 ZONE_MOVABLE is used for the allocation of pages that 2131 may be reclaimed or moved by the page migration 2132 subsystem. Note that allocations like PTEs-from-HighMem 2133 still use the HighMem zone if it exists, and the Normal 2134 zone if it does not. 2135 2136 It is possible to specify the exact amount of memory in 2137 the form of "nn[KMGTPE]", a percentage of total system 2138 memory in the form of "nn%", or "mirror". If "mirror" 2139 option is specified, mirrored (reliable) memory is used 2140 for non-movable allocations and remaining memory is used 2141 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2142 are exclusive, so you cannot specify multiple forms. 2143 2144 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2145 Format: <Controller#>[,poll interval] 2146 The controller # is the number of the ehci usb debug 2147 port as it is probed via PCI. The poll interval is 2148 optional and is the number seconds in between 2149 each poll cycle to the debug port in case you need 2150 the functionality for interrupting the kernel with 2151 gdb or control-c on the dbgp connection. When 2152 not using this parameter you use sysrq-g to break into 2153 the kernel debugger. 2154 2155 kgdboc= [KGDB,HW] kgdb over consoles. 2156 Requires a tty driver that supports console polling, 2157 or a supported polling keyboard driver (non-usb). 2158 Serial only format: <serial_device>[,baud] 2159 keyboard only format: kbd 2160 keyboard and serial format: kbd,<serial_device>[,baud] 2161 Optional Kernel mode setting: 2162 kms, kbd format: kms,kbd 2163 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2164 2165 kgdboc_earlycon= [KGDB,HW] 2166 If the boot console provides the ability to read 2167 characters and can work in polling mode, you can use 2168 this parameter to tell kgdb to use it as a backend 2169 until the normal console is registered. Intended to 2170 be used together with the kgdboc parameter which 2171 specifies the normal console to transition to. 2172 2173 The name of the early console should be specified 2174 as the value of this parameter. Note that the name of 2175 the early console might be different than the tty 2176 name passed to kgdboc. It's OK to leave the value 2177 blank and the first boot console that implements 2178 read() will be picked. 2179 2180 kgdbwait [KGDB] Stop kernel execution and enter the 2181 kernel debugger at the earliest opportunity. 2182 2183 kmac= [MIPS] Korina ethernet MAC address. 2184 Configure the RouterBoard 532 series on-chip 2185 Ethernet adapter MAC address. 2186 2187 kmemleak= [KNL] Boot-time kmemleak enable/disable 2188 Valid arguments: on, off 2189 Default: on 2190 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2191 the default is off. 2192 2193 kprobe_event=[probe-list] 2194 [FTRACE] Add kprobe events and enable at boot time. 2195 The probe-list is a semicolon delimited list of probe 2196 definitions. Each definition is same as kprobe_events 2197 interface, but the parameters are comma delimited. 2198 For example, to add a kprobe event on vfs_read with 2199 arg1 and arg2, add to the command line; 2200 2201 kprobe_event=p,vfs_read,$arg1,$arg2 2202 2203 See also Documentation/trace/kprobetrace.rst "Kernel 2204 Boot Parameter" section. 2205 2206 kpti= [ARM64] Control page table isolation of user 2207 and kernel address spaces. 2208 Default: enabled on cores which need mitigation. 2209 0: force disabled 2210 1: force enabled 2211 2212 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2213 Default is 0 (don't ignore, but inject #GP) 2214 2215 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2216 Default is false (don't support). 2217 2218 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2219 KVM MMU at runtime. 2220 Default is 0 (off) 2221 2222 kvm.nx_huge_pages= 2223 [KVM] Controls the software workaround for the 2224 X86_BUG_ITLB_MULTIHIT bug. 2225 force : Always deploy workaround. 2226 off : Never deploy workaround. 2227 auto : Deploy workaround based on the presence of 2228 X86_BUG_ITLB_MULTIHIT. 2229 2230 Default is 'auto'. 2231 2232 If the software workaround is enabled for the host, 2233 guests do need not to enable it for nested guests. 2234 2235 kvm.nx_huge_pages_recovery_ratio= 2236 [KVM] Controls how many 4KiB pages are periodically zapped 2237 back to huge pages. 0 disables the recovery, otherwise if 2238 the value is N KVM will zap 1/Nth of the 4KiB pages every 2239 minute. The default is 60. 2240 2241 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2242 Default is 1 (enabled) 2243 2244 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2245 for all guests. 2246 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2247 2248 kvm-arm.vgic_v3_group0_trap= 2249 [KVM,ARM] Trap guest accesses to GICv3 group-0 2250 system registers 2251 2252 kvm-arm.vgic_v3_group1_trap= 2253 [KVM,ARM] Trap guest accesses to GICv3 group-1 2254 system registers 2255 2256 kvm-arm.vgic_v3_common_trap= 2257 [KVM,ARM] Trap guest accesses to GICv3 common 2258 system registers 2259 2260 kvm-arm.vgic_v4_enable= 2261 [KVM,ARM] Allow use of GICv4 for direct injection of 2262 LPIs. 2263 2264 kvm_cma_resv_ratio=n [PPC] 2265 Reserves given percentage from system memory area for 2266 contiguous memory allocation for KVM hash pagetable 2267 allocation. 2268 By default it reserves 5% of total system memory. 2269 Format: <integer> 2270 Default: 5 2271 2272 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2273 (virtualized MMU) support on capable Intel chips. 2274 Default is 1 (enabled) 2275 2276 kvm-intel.emulate_invalid_guest_state= 2277 [KVM,Intel] Enable emulation of invalid guest states 2278 Default is 0 (disabled) 2279 2280 kvm-intel.flexpriority= 2281 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2282 Default is 1 (enabled) 2283 2284 kvm-intel.nested= 2285 [KVM,Intel] Enable VMX nesting (nVMX). 2286 Default is 0 (disabled) 2287 2288 kvm-intel.unrestricted_guest= 2289 [KVM,Intel] Disable unrestricted guest feature 2290 (virtualized real and unpaged mode) on capable 2291 Intel chips. Default is 1 (enabled) 2292 2293 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2294 CVE-2018-3620. 2295 2296 Valid arguments: never, cond, always 2297 2298 always: L1D cache flush on every VMENTER. 2299 cond: Flush L1D on VMENTER only when the code between 2300 VMEXIT and VMENTER can leak host memory. 2301 never: Disables the mitigation 2302 2303 Default is cond (do L1 cache flush in specific instances) 2304 2305 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2306 feature (tagged TLBs) on capable Intel chips. 2307 Default is 1 (enabled) 2308 2309 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2310 affected CPUs 2311 2312 The kernel PTE inversion protection is unconditionally 2313 enabled and cannot be disabled. 2314 2315 full 2316 Provides all available mitigations for the 2317 L1TF vulnerability. Disables SMT and 2318 enables all mitigations in the 2319 hypervisors, i.e. unconditional L1D flush. 2320 2321 SMT control and L1D flush control via the 2322 sysfs interface is still possible after 2323 boot. Hypervisors will issue a warning 2324 when the first VM is started in a 2325 potentially insecure configuration, 2326 i.e. SMT enabled or L1D flush disabled. 2327 2328 full,force 2329 Same as 'full', but disables SMT and L1D 2330 flush runtime control. Implies the 2331 'nosmt=force' command line option. 2332 (i.e. sysfs control of SMT is disabled.) 2333 2334 flush 2335 Leaves SMT enabled and enables the default 2336 hypervisor mitigation, i.e. conditional 2337 L1D flush. 2338 2339 SMT control and L1D flush control via the 2340 sysfs interface is still possible after 2341 boot. Hypervisors will issue a warning 2342 when the first VM is started in a 2343 potentially insecure configuration, 2344 i.e. SMT enabled or L1D flush disabled. 2345 2346 flush,nosmt 2347 2348 Disables SMT and enables the default 2349 hypervisor mitigation. 2350 2351 SMT control and L1D flush control via the 2352 sysfs interface is still possible after 2353 boot. Hypervisors will issue a warning 2354 when the first VM is started in a 2355 potentially insecure configuration, 2356 i.e. SMT enabled or L1D flush disabled. 2357 2358 flush,nowarn 2359 Same as 'flush', but hypervisors will not 2360 warn when a VM is started in a potentially 2361 insecure configuration. 2362 2363 off 2364 Disables hypervisor mitigations and doesn't 2365 emit any warnings. 2366 It also drops the swap size and available 2367 RAM limit restriction on both hypervisor and 2368 bare metal. 2369 2370 Default is 'flush'. 2371 2372 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2373 2374 l2cr= [PPC] 2375 2376 l3cr= [PPC] 2377 2378 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2379 disabled it. 2380 2381 lapic= [X86,APIC] Do not use TSC deadline 2382 value for LAPIC timer one-shot implementation. Default 2383 back to the programmable timer unit in the LAPIC. 2384 Format: notscdeadline 2385 2386 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2387 in C2 power state. 2388 2389 libata.dma= [LIBATA] DMA control 2390 libata.dma=0 Disable all PATA and SATA DMA 2391 libata.dma=1 PATA and SATA Disk DMA only 2392 libata.dma=2 ATAPI (CDROM) DMA only 2393 libata.dma=4 Compact Flash DMA only 2394 Combinations also work, so libata.dma=3 enables DMA 2395 for disks and CDROMs, but not CFs. 2396 2397 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2398 libata.ignore_hpa=0 keep BIOS limits (default) 2399 libata.ignore_hpa=1 ignore limits, using full disk 2400 2401 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2402 when set. 2403 Format: <int> 2404 2405 libata.force= [LIBATA] Force configurations. The format is comma 2406 separated list of "[ID:]VAL" where ID is 2407 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2408 matching port, link or device. Basically, it matches 2409 the ATA ID string printed on console by libata. If 2410 the whole ID part is omitted, the last PORT and DEVICE 2411 values are used. If ID hasn't been specified yet, the 2412 configuration applies to all ports, links and devices. 2413 2414 If only DEVICE is omitted, the parameter applies to 2415 the port and all links and devices behind it. DEVICE 2416 number of 0 either selects the first device or the 2417 first fan-out link behind PMP device. It does not 2418 select the host link. DEVICE number of 15 selects the 2419 host link and device attached to it. 2420 2421 The VAL specifies the configuration to force. As long 2422 as there's no ambiguity shortcut notation is allowed. 2423 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2424 The following configurations can be forced. 2425 2426 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2427 Any ID with matching PORT is used. 2428 2429 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2430 2431 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2432 udma[/][16,25,33,44,66,100,133] notation is also 2433 allowed. 2434 2435 * [no]ncq: Turn on or off NCQ. 2436 2437 * [no]ncqtrim: Turn off queued DSM TRIM. 2438 2439 * nohrst, nosrst, norst: suppress hard, soft 2440 and both resets. 2441 2442 * rstonce: only attempt one reset during 2443 hot-unplug link recovery 2444 2445 * dump_id: dump IDENTIFY data. 2446 2447 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2448 2449 * disable: Disable this device. 2450 2451 If there are multiple matching configurations changing 2452 the same attribute, the last one is used. 2453 2454 memblock=debug [KNL] Enable memblock debug messages. 2455 2456 load_ramdisk= [RAM] [Deprecated] 2457 2458 lockd.nlm_grace_period=P [NFS] Assign grace period. 2459 Format: <integer> 2460 2461 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2462 Format: <integer> 2463 2464 lockd.nlm_timeout=T [NFS] Assign timeout value. 2465 Format: <integer> 2466 2467 lockd.nlm_udpport=M [NFS] Assign UDP port. 2468 Format: <integer> 2469 2470 lockdown= [SECURITY] 2471 { integrity | confidentiality } 2472 Enable the kernel lockdown feature. If set to 2473 integrity, kernel features that allow userland to 2474 modify the running kernel are disabled. If set to 2475 confidentiality, kernel features that allow userland 2476 to extract confidential information from the kernel 2477 are also disabled. 2478 2479 locktorture.nreaders_stress= [KNL] 2480 Set the number of locking read-acquisition kthreads. 2481 Defaults to being automatically set based on the 2482 number of online CPUs. 2483 2484 locktorture.nwriters_stress= [KNL] 2485 Set the number of locking write-acquisition kthreads. 2486 2487 locktorture.onoff_holdoff= [KNL] 2488 Set time (s) after boot for CPU-hotplug testing. 2489 2490 locktorture.onoff_interval= [KNL] 2491 Set time (s) between CPU-hotplug operations, or 2492 zero to disable CPU-hotplug testing. 2493 2494 locktorture.shuffle_interval= [KNL] 2495 Set task-shuffle interval (jiffies). Shuffling 2496 tasks allows some CPUs to go into dyntick-idle 2497 mode during the locktorture test. 2498 2499 locktorture.shutdown_secs= [KNL] 2500 Set time (s) after boot system shutdown. This 2501 is useful for hands-off automated testing. 2502 2503 locktorture.stat_interval= [KNL] 2504 Time (s) between statistics printk()s. 2505 2506 locktorture.stutter= [KNL] 2507 Time (s) to stutter testing, for example, 2508 specifying five seconds causes the test to run for 2509 five seconds, wait for five seconds, and so on. 2510 This tests the locking primitive's ability to 2511 transition abruptly to and from idle. 2512 2513 locktorture.torture_type= [KNL] 2514 Specify the locking implementation to test. 2515 2516 locktorture.verbose= [KNL] 2517 Enable additional printk() statements. 2518 2519 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2520 Format: <irq> 2521 2522 loglevel= All Kernel Messages with a loglevel smaller than the 2523 console loglevel will be printed to the console. It can 2524 also be changed with klogd or other programs. The 2525 loglevels are defined as follows: 2526 2527 0 (KERN_EMERG) system is unusable 2528 1 (KERN_ALERT) action must be taken immediately 2529 2 (KERN_CRIT) critical conditions 2530 3 (KERN_ERR) error conditions 2531 4 (KERN_WARNING) warning conditions 2532 5 (KERN_NOTICE) normal but significant condition 2533 6 (KERN_INFO) informational 2534 7 (KERN_DEBUG) debug-level messages 2535 2536 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2537 in bytes. n must be a power of two and greater 2538 than the minimal size. The minimal size is defined 2539 by LOG_BUF_SHIFT kernel config parameter. There is 2540 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2541 that allows to increase the default size depending on 2542 the number of CPUs. See init/Kconfig for more details. 2543 2544 logo.nologo [FB] Disables display of the built-in Linux logo. 2545 This may be used to provide more screen space for 2546 kernel log messages and is useful when debugging 2547 kernel boot problems. 2548 2549 lp=0 [LP] Specify parallel ports to use, e.g, 2550 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2551 lp=reset first parallel port). 'lp=0' disables the 2552 lp=auto printer driver. 'lp=reset' (which can be 2553 specified in addition to the ports) causes 2554 attached printers to be reset. Using 2555 lp=port1,port2,... specifies the parallel ports 2556 to associate lp devices with, starting with 2557 lp0. A port specification may be 'none' to skip 2558 that lp device, or a parport name such as 2559 'parport0'. Specifying 'lp=auto' instead of a 2560 port specification list means that device IDs 2561 from each port should be examined, to see if 2562 an IEEE 1284-compliant printer is attached; if 2563 so, the driver will manage that printer. 2564 See also header of drivers/char/lp.c. 2565 2566 lpj=n [KNL] 2567 Sets loops_per_jiffy to given constant, thus avoiding 2568 time-consuming boot-time autodetection (up to 250 ms per 2569 CPU). 0 enables autodetection (default). To determine 2570 the correct value for your kernel, boot with normal 2571 autodetection and see what value is printed. Note that 2572 on SMP systems the preset will be applied to all CPUs, 2573 which is likely to cause problems if your CPUs need 2574 significantly divergent settings. An incorrect value 2575 will cause delays in the kernel to be wrong, leading to 2576 unpredictable I/O errors and other breakage. Although 2577 unlikely, in the extreme case this might damage your 2578 hardware. 2579 2580 ltpc= [NET] 2581 Format: <io>,<irq>,<dma> 2582 2583 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2584 2585 lsm=lsm1,...,lsmN 2586 [SECURITY] Choose order of LSM initialization. This 2587 overrides CONFIG_LSM, and the "security=" parameter. 2588 2589 machvec= [IA-64] Force the use of a particular machine-vector 2590 (machvec) in a generic kernel. 2591 Example: machvec=hpzx1 2592 2593 machtype= [Loongson] Share the same kernel image file between 2594 different yeeloong laptops. 2595 Example: machtype=lemote-yeeloong-2f-7inch 2596 2597 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2598 than or equal to this physical address is ignored. 2599 2600 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2601 will bring up during bootup. maxcpus=n : n >= 0 limits 2602 the kernel to bring up 'n' processors. Surely after 2603 bootup you can bring up the other plugged cpu by executing 2604 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2605 only takes effect during system bootup. 2606 While n=0 is a special case, it is equivalent to "nosmp", 2607 which also disables the IO APIC. 2608 2609 max_loop= [LOOP] The number of loop block devices that get 2610 (loop.max_loop) unconditionally pre-created at init time. The default 2611 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2612 of statically allocating a predefined number, loop 2613 devices can be requested on-demand with the 2614 /dev/loop-control interface. 2615 2616 mce [X86-32] Machine Check Exception 2617 2618 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2619 2620 md= [HW] RAID subsystems devices and level 2621 See Documentation/admin-guide/md.rst. 2622 2623 mdacon= [MDA] 2624 Format: <first>,<last> 2625 Specifies range of consoles to be captured by the MDA. 2626 2627 mds= [X86,INTEL] 2628 Control mitigation for the Micro-architectural Data 2629 Sampling (MDS) vulnerability. 2630 2631 Certain CPUs are vulnerable to an exploit against CPU 2632 internal buffers which can forward information to a 2633 disclosure gadget under certain conditions. 2634 2635 In vulnerable processors, the speculatively 2636 forwarded data can be used in a cache side channel 2637 attack, to access data to which the attacker does 2638 not have direct access. 2639 2640 This parameter controls the MDS mitigation. The 2641 options are: 2642 2643 full - Enable MDS mitigation on vulnerable CPUs 2644 full,nosmt - Enable MDS mitigation and disable 2645 SMT on vulnerable CPUs 2646 off - Unconditionally disable MDS mitigation 2647 2648 On TAA-affected machines, mds=off can be prevented by 2649 an active TAA mitigation as both vulnerabilities are 2650 mitigated with the same mechanism so in order to disable 2651 this mitigation, you need to specify tsx_async_abort=off 2652 too. 2653 2654 Not specifying this option is equivalent to 2655 mds=full. 2656 2657 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2658 2659 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2660 Amount of memory to be used in cases as follows: 2661 2662 1 for test; 2663 2 when the kernel is not able to see the whole system memory; 2664 3 memory that lies after 'mem=' boundary is excluded from 2665 the hypervisor, then assigned to KVM guests. 2666 2667 [X86] Work as limiting max address. Use together 2668 with memmap= to avoid physical address space collisions. 2669 Without memmap= PCI devices could be placed at addresses 2670 belonging to unused RAM. 2671 2672 Note that this only takes effects during boot time since 2673 in above case 3, memory may need be hot added after boot 2674 if system memory of hypervisor is not sufficient. 2675 2676 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2677 memory. 2678 2679 memchunk=nn[KMG] 2680 [KNL,SH] Allow user to override the default size for 2681 per-device physically contiguous DMA buffers. 2682 2683 memhp_default_state=online/offline 2684 [KNL] Set the initial state for the memory hotplug 2685 onlining policy. If not specified, the default value is 2686 set according to the 2687 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2688 option. 2689 See Documentation/admin-guide/mm/memory-hotplug.rst. 2690 2691 memmap=exactmap [KNL,X86] Enable setting of an exact 2692 E820 memory map, as specified by the user. 2693 Such memmap=exactmap lines can be constructed based on 2694 BIOS output or other requirements. See the memmap=nn@ss 2695 option description. 2696 2697 memmap=nn[KMG]@ss[KMG] 2698 [KNL] Force usage of a specific region of memory. 2699 Region of memory to be used is from ss to ss+nn. 2700 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2701 which limits max address to nn[KMG]. 2702 Multiple different regions can be specified, 2703 comma delimited. 2704 Example: 2705 memmap=100M@2G,100M#3G,1G!1024G 2706 2707 memmap=nn[KMG]#ss[KMG] 2708 [KNL,ACPI] Mark specific memory as ACPI data. 2709 Region of memory to be marked is from ss to ss+nn. 2710 2711 memmap=nn[KMG]$ss[KMG] 2712 [KNL,ACPI] Mark specific memory as reserved. 2713 Region of memory to be reserved is from ss to ss+nn. 2714 Example: Exclude memory from 0x18690000-0x1869ffff 2715 memmap=64K$0x18690000 2716 or 2717 memmap=0x10000$0x18690000 2718 Some bootloaders may need an escape character before '$', 2719 like Grub2, otherwise '$' and the following number 2720 will be eaten. 2721 2722 memmap=nn[KMG]!ss[KMG] 2723 [KNL,X86] Mark specific memory as protected. 2724 Region of memory to be used, from ss to ss+nn. 2725 The memory region may be marked as e820 type 12 (0xc) 2726 and is NVDIMM or ADR memory. 2727 2728 memmap=<size>%<offset>-<oldtype>+<newtype> 2729 [KNL,ACPI] Convert memory within the specified region 2730 from <oldtype> to <newtype>. If "-<oldtype>" is left 2731 out, the whole region will be marked as <newtype>, 2732 even if previously unavailable. If "+<newtype>" is left 2733 out, matching memory will be removed. Types are 2734 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2735 3 = ACPI, 12 = PRAM. 2736 2737 memory_corruption_check=0/1 [X86] 2738 Some BIOSes seem to corrupt the first 64k of 2739 memory when doing things like suspend/resume. 2740 Setting this option will scan the memory 2741 looking for corruption. Enabling this will 2742 both detect corruption and prevent the kernel 2743 from using the memory being corrupted. 2744 However, its intended as a diagnostic tool; if 2745 repeatable BIOS-originated corruption always 2746 affects the same memory, you can use memmap= 2747 to prevent the kernel from using that memory. 2748 2749 memory_corruption_check_size=size [X86] 2750 By default it checks for corruption in the low 2751 64k, making this memory unavailable for normal 2752 use. Use this parameter to scan for 2753 corruption in more or less memory. 2754 2755 memory_corruption_check_period=seconds [X86] 2756 By default it checks for corruption every 60 2757 seconds. Use this parameter to check at some 2758 other rate. 0 disables periodic checking. 2759 2760 memtest= [KNL,X86,ARM,PPC] Enable memtest 2761 Format: <integer> 2762 default : 0 <disable> 2763 Specifies the number of memtest passes to be 2764 performed. Each pass selects another test 2765 pattern from a given set of patterns. Memtest 2766 fills the memory with this pattern, validates 2767 memory contents and reserves bad memory 2768 regions that are detected. 2769 2770 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2771 Valid arguments: on, off 2772 Default (depends on kernel configuration option): 2773 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2774 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2775 mem_encrypt=on: Activate SME 2776 mem_encrypt=off: Do not activate SME 2777 2778 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2779 for details on when memory encryption can be activated. 2780 2781 mem_sleep_default= [SUSPEND] Default system suspend mode: 2782 s2idle - Suspend-To-Idle 2783 shallow - Power-On Suspend or equivalent (if supported) 2784 deep - Suspend-To-RAM or equivalent (if supported) 2785 See Documentation/admin-guide/pm/sleep-states.rst. 2786 2787 meye.*= [HW] Set MotionEye Camera parameters 2788 See Documentation/admin-guide/media/meye.rst. 2789 2790 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2791 Multi-Function General Purpose Timers on AMD Geode 2792 platforms. 2793 2794 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2795 the BIOS has incorrectly applied a workaround. TinyBIOS 2796 version 0.98 is known to be affected, 0.99 fixes the 2797 problem by letting the user disable the workaround. 2798 2799 mga= [HW,DRM] 2800 2801 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2802 physical address is ignored. 2803 2804 mini2440= [ARM,HW,KNL] 2805 Format:[0..2][b][c][t] 2806 Default: "0tb" 2807 MINI2440 configuration specification: 2808 0 - The attached screen is the 3.5" TFT 2809 1 - The attached screen is the 7" TFT 2810 2 - The VGA Shield is attached (1024x768) 2811 Leaving out the screen size parameter will not load 2812 the TFT driver, and the framebuffer will be left 2813 unconfigured. 2814 b - Enable backlight. The TFT backlight pin will be 2815 linked to the kernel VESA blanking code and a GPIO 2816 LED. This parameter is not necessary when using the 2817 VGA shield. 2818 c - Enable the s3c camera interface. 2819 t - Reserved for enabling touchscreen support. The 2820 touchscreen support is not enabled in the mainstream 2821 kernel as of 2.6.30, a preliminary port can be found 2822 in the "bleeding edge" mini2440 support kernel at 2823 https://repo.or.cz/w/linux-2.6/mini2440.git 2824 2825 mitigations= 2826 [X86,PPC,S390,ARM64] Control optional mitigations for 2827 CPU vulnerabilities. This is a set of curated, 2828 arch-independent options, each of which is an 2829 aggregation of existing arch-specific options. 2830 2831 off 2832 Disable all optional CPU mitigations. This 2833 improves system performance, but it may also 2834 expose users to several CPU vulnerabilities. 2835 Equivalent to: nopti [X86,PPC] 2836 kpti=0 [ARM64] 2837 nospectre_v1 [X86,PPC] 2838 nobp=0 [S390] 2839 nospectre_v2 [X86,PPC,S390,ARM64] 2840 spectre_v2_user=off [X86] 2841 spec_store_bypass_disable=off [X86,PPC] 2842 ssbd=force-off [ARM64] 2843 l1tf=off [X86] 2844 mds=off [X86] 2845 tsx_async_abort=off [X86] 2846 kvm.nx_huge_pages=off [X86] 2847 2848 Exceptions: 2849 This does not have any effect on 2850 kvm.nx_huge_pages when 2851 kvm.nx_huge_pages=force. 2852 2853 auto (default) 2854 Mitigate all CPU vulnerabilities, but leave SMT 2855 enabled, even if it's vulnerable. This is for 2856 users who don't want to be surprised by SMT 2857 getting disabled across kernel upgrades, or who 2858 have other ways of avoiding SMT-based attacks. 2859 Equivalent to: (default behavior) 2860 2861 auto,nosmt 2862 Mitigate all CPU vulnerabilities, disabling SMT 2863 if needed. This is for users who always want to 2864 be fully mitigated, even if it means losing SMT. 2865 Equivalent to: l1tf=flush,nosmt [X86] 2866 mds=full,nosmt [X86] 2867 tsx_async_abort=full,nosmt [X86] 2868 2869 mminit_loglevel= 2870 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2871 parameter allows control of the logging verbosity for 2872 the additional memory initialisation checks. A value 2873 of 0 disables mminit logging and a level of 4 will 2874 log everything. Information is printed at KERN_DEBUG 2875 so loglevel=8 may also need to be specified. 2876 2877 module.sig_enforce 2878 [KNL] When CONFIG_MODULE_SIG is set, this means that 2879 modules without (valid) signatures will fail to load. 2880 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2881 is always true, so this option does nothing. 2882 2883 module_blacklist= [KNL] Do not load a comma-separated list of 2884 modules. Useful for debugging problem modules. 2885 2886 mousedev.tap_time= 2887 [MOUSE] Maximum time between finger touching and 2888 leaving touchpad surface for touch to be considered 2889 a tap and be reported as a left button click (for 2890 touchpads working in absolute mode only). 2891 Format: <msecs> 2892 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2893 reporting absolute coordinates, such as tablets 2894 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2895 reporting absolute coordinates, such as tablets 2896 2897 movablecore= [KNL,X86,IA-64,PPC] 2898 Format: nn[KMGTPE] | nn% 2899 This parameter is the complement to kernelcore=, it 2900 specifies the amount of memory used for migratable 2901 allocations. If both kernelcore and movablecore is 2902 specified, then kernelcore will be at *least* the 2903 specified value but may be more. If movablecore on its 2904 own is specified, the administrator must be careful 2905 that the amount of memory usable for all allocations 2906 is not too small. 2907 2908 movable_node [KNL] Boot-time switch to make hotplugable memory 2909 NUMA nodes to be movable. This means that the memory 2910 of such nodes will be usable only for movable 2911 allocations which rules out almost all kernel 2912 allocations. Use with caution! 2913 2914 MTD_Partition= [MTD] 2915 Format: <name>,<region-number>,<size>,<offset> 2916 2917 MTD_Region= [MTD] Format: 2918 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2919 2920 mtdparts= [MTD] 2921 See drivers/mtd/parsers/cmdlinepart.c 2922 2923 multitce=off [PPC] This parameter disables the use of the pSeries 2924 firmware feature for updating multiple TCE entries 2925 at a time. 2926 2927 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2928 2929 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2930 2931 boundary - index of last SLC block on Flex-OneNAND. 2932 The remaining blocks are configured as MLC blocks. 2933 lock - Configure if Flex-OneNAND boundary should be locked. 2934 Once locked, the boundary cannot be changed. 2935 1 indicates lock status, 0 indicates unlock status. 2936 2937 mtdset= [ARM] 2938 ARM/S3C2412 JIVE boot control 2939 2940 See arch/arm/mach-s3c2412/mach-jive.c 2941 2942 mtouchusb.raw_coordinates= 2943 [HW] Make the MicroTouch USB driver use raw coordinates 2944 ('y', default) or cooked coordinates ('n') 2945 2946 mtrr_chunk_size=nn[KMG] [X86] 2947 used for mtrr cleanup. It is largest continuous chunk 2948 that could hold holes aka. UC entries. 2949 2950 mtrr_gran_size=nn[KMG] [X86] 2951 Used for mtrr cleanup. It is granularity of mtrr block. 2952 Default is 1. 2953 Large value could prevent small alignment from 2954 using up MTRRs. 2955 2956 mtrr_spare_reg_nr=n [X86] 2957 Format: <integer> 2958 Range: 0,7 : spare reg number 2959 Default : 1 2960 Used for mtrr cleanup. It is spare mtrr entries number. 2961 Set to 2 or more if your graphical card needs more. 2962 2963 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2964 2965 netdev= [NET] Network devices parameters 2966 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2967 Note that mem_start is often overloaded to mean 2968 something different and driver-specific. 2969 This usage is only documented in each driver source 2970 file if at all. 2971 2972 nf_conntrack.acct= 2973 [NETFILTER] Enable connection tracking flow accounting 2974 0 to disable accounting 2975 1 to enable accounting 2976 Default value is 0. 2977 2978 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2979 See Documentation/admin-guide/nfs/nfsroot.rst. 2980 2981 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2982 See Documentation/admin-guide/nfs/nfsroot.rst. 2983 2984 nfsrootdebug [NFS] enable nfsroot debugging messages. 2985 See Documentation/admin-guide/nfs/nfsroot.rst. 2986 2987 nfs.callback_nr_threads= 2988 [NFSv4] set the total number of threads that the 2989 NFS client will assign to service NFSv4 callback 2990 requests. 2991 2992 nfs.callback_tcpport= 2993 [NFS] set the TCP port on which the NFSv4 callback 2994 channel should listen. 2995 2996 nfs.cache_getent= 2997 [NFS] sets the pathname to the program which is used 2998 to update the NFS client cache entries. 2999 3000 nfs.cache_getent_timeout= 3001 [NFS] sets the timeout after which an attempt to 3002 update a cache entry is deemed to have failed. 3003 3004 nfs.idmap_cache_timeout= 3005 [NFS] set the maximum lifetime for idmapper cache 3006 entries. 3007 3008 nfs.enable_ino64= 3009 [NFS] enable 64-bit inode numbers. 3010 If zero, the NFS client will fake up a 32-bit inode 3011 number for the readdir() and stat() syscalls instead 3012 of returning the full 64-bit number. 3013 The default is to return 64-bit inode numbers. 3014 3015 nfs.max_session_cb_slots= 3016 [NFSv4.1] Sets the maximum number of session 3017 slots the client will assign to the callback 3018 channel. This determines the maximum number of 3019 callbacks the client will process in parallel for 3020 a particular server. 3021 3022 nfs.max_session_slots= 3023 [NFSv4.1] Sets the maximum number of session slots 3024 the client will attempt to negotiate with the server. 3025 This limits the number of simultaneous RPC requests 3026 that the client can send to the NFSv4.1 server. 3027 Note that there is little point in setting this 3028 value higher than the max_tcp_slot_table_limit. 3029 3030 nfs.nfs4_disable_idmapping= 3031 [NFSv4] When set to the default of '1', this option 3032 ensures that both the RPC level authentication 3033 scheme and the NFS level operations agree to use 3034 numeric uids/gids if the mount is using the 3035 'sec=sys' security flavour. In effect it is 3036 disabling idmapping, which can make migration from 3037 legacy NFSv2/v3 systems to NFSv4 easier. 3038 Servers that do not support this mode of operation 3039 will be autodetected by the client, and it will fall 3040 back to using the idmapper. 3041 To turn off this behaviour, set the value to '0'. 3042 nfs.nfs4_unique_id= 3043 [NFS4] Specify an additional fixed unique ident- 3044 ification string that NFSv4 clients can insert into 3045 their nfs_client_id4 string. This is typically a 3046 UUID that is generated at system install time. 3047 3048 nfs.send_implementation_id = 3049 [NFSv4.1] Send client implementation identification 3050 information in exchange_id requests. 3051 If zero, no implementation identification information 3052 will be sent. 3053 The default is to send the implementation identification 3054 information. 3055 3056 nfs.recover_lost_locks = 3057 [NFSv4] Attempt to recover locks that were lost due 3058 to a lease timeout on the server. Please note that 3059 doing this risks data corruption, since there are 3060 no guarantees that the file will remain unchanged 3061 after the locks are lost. 3062 If you want to enable the kernel legacy behaviour of 3063 attempting to recover these locks, then set this 3064 parameter to '1'. 3065 The default parameter value of '0' causes the kernel 3066 not to attempt recovery of lost locks. 3067 3068 nfs4.layoutstats_timer = 3069 [NFSv4.2] Change the rate at which the kernel sends 3070 layoutstats to the pNFS metadata server. 3071 3072 Setting this to value to 0 causes the kernel to use 3073 whatever value is the default set by the layout 3074 driver. A non-zero value sets the minimum interval 3075 in seconds between layoutstats transmissions. 3076 3077 nfsd.nfs4_disable_idmapping= 3078 [NFSv4] When set to the default of '1', the NFSv4 3079 server will return only numeric uids and gids to 3080 clients using auth_sys, and will accept numeric uids 3081 and gids from such clients. This is intended to ease 3082 migration from NFSv2/v3. 3083 3084 nmi_debug= [KNL,SH] Specify one or more actions to take 3085 when a NMI is triggered. 3086 Format: [state][,regs][,debounce][,die] 3087 3088 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3089 Format: [panic,][nopanic,][num] 3090 Valid num: 0 or 1 3091 0 - turn hardlockup detector in nmi_watchdog off 3092 1 - turn hardlockup detector in nmi_watchdog on 3093 When panic is specified, panic when an NMI watchdog 3094 timeout occurs (or 'nopanic' to not panic on an NMI 3095 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3096 To disable both hard and soft lockup detectors, 3097 please see 'nowatchdog'. 3098 This is useful when you use a panic=... timeout and 3099 need the box quickly up again. 3100 3101 These settings can be accessed at runtime via 3102 the nmi_watchdog and hardlockup_panic sysctls. 3103 3104 netpoll.carrier_timeout= 3105 [NET] Specifies amount of time (in seconds) that 3106 netpoll should wait for a carrier. By default netpoll 3107 waits 4 seconds. 3108 3109 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3110 emulation library even if a 387 maths coprocessor 3111 is present. 3112 3113 no5lvl [X86-64] Disable 5-level paging mode. Forces 3114 kernel to use 4-level paging instead. 3115 3116 nofsgsbase [X86] Disables FSGSBASE instructions. 3117 3118 no_console_suspend 3119 [HW] Never suspend the console 3120 Disable suspending of consoles during suspend and 3121 hibernate operations. Once disabled, debugging 3122 messages can reach various consoles while the rest 3123 of the system is being put to sleep (ie, while 3124 debugging driver suspend/resume hooks). This may 3125 not work reliably with all consoles, but is known 3126 to work with serial and VGA consoles. 3127 To facilitate more flexible debugging, we also add 3128 console_suspend, a printk module parameter to control 3129 it. Users could use console_suspend (usually 3130 /sys/module/printk/parameters/console_suspend) to 3131 turn on/off it dynamically. 3132 3133 novmcoredd [KNL,KDUMP] 3134 Disable device dump. Device dump allows drivers to 3135 append dump data to vmcore so you can collect driver 3136 specified debug info. Drivers can append the data 3137 without any limit and this data is stored in memory, 3138 so this may cause significant memory stress. Disabling 3139 device dump can help save memory but the driver debug 3140 data will be no longer available. This parameter 3141 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3142 is set. 3143 3144 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3145 caches in the slab allocator. Saves per-node memory, 3146 but will impact performance. 3147 3148 noalign [KNL,ARM] 3149 3150 noaltinstr [S390] Disables alternative instructions patching 3151 (CPU alternatives feature). 3152 3153 noapic [SMP,APIC] Tells the kernel to not make use of any 3154 IOAPICs that may be present in the system. 3155 3156 noautogroup Disable scheduler automatic task group creation. 3157 3158 nobats [PPC] Do not use BATs for mapping kernel lowmem 3159 on "Classic" PPC cores. 3160 3161 nocache [ARM] 3162 3163 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3164 3165 nodelayacct [KNL] Disable per-task delay accounting 3166 3167 nodsp [SH] Disable hardware DSP at boot time. 3168 3169 noefi Disable EFI runtime services support. 3170 3171 noexec [IA-64] 3172 3173 noexec [X86] 3174 On X86-32 available only on PAE configured kernels. 3175 noexec=on: enable non-executable mappings (default) 3176 noexec=off: disable non-executable mappings 3177 3178 nosmap [X86,PPC] 3179 Disable SMAP (Supervisor Mode Access Prevention) 3180 even if it is supported by processor. 3181 3182 nosmep [X86,PPC] 3183 Disable SMEP (Supervisor Mode Execution Prevention) 3184 even if it is supported by processor. 3185 3186 noexec32 [X86-64] 3187 This affects only 32-bit executables. 3188 noexec32=on: enable non-executable mappings (default) 3189 read doesn't imply executable mappings 3190 noexec32=off: disable non-executable mappings 3191 read implies executable mappings 3192 3193 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3194 3195 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3196 register save and restore. The kernel will only save 3197 legacy floating-point registers on task switch. 3198 3199 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3200 3201 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3202 Equivalent to smt=1. 3203 3204 [KNL,X86] Disable symmetric multithreading (SMT). 3205 nosmt=force: Force disable SMT, cannot be undone 3206 via the sysfs control file. 3207 3208 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3209 (bounds check bypass). With this option data leaks are 3210 possible in the system. 3211 3212 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3213 the Spectre variant 2 (indirect branch prediction) 3214 vulnerability. System may allow data leaks with this 3215 option. 3216 3217 nospec_store_bypass_disable 3218 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3219 3220 noxsave [BUGS=X86] Disables x86 extended register state save 3221 and restore using xsave. The kernel will fallback to 3222 enabling legacy floating-point and sse state. 3223 3224 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3225 register states. The kernel will fall back to use 3226 xsave to save the states. By using this parameter, 3227 performance of saving the states is degraded because 3228 xsave doesn't support modified optimization while 3229 xsaveopt supports it on xsaveopt enabled systems. 3230 3231 noxsaves [X86] Disables xsaves and xrstors used in saving and 3232 restoring x86 extended register state in compacted 3233 form of xsave area. The kernel will fall back to use 3234 xsaveopt and xrstor to save and restore the states 3235 in standard form of xsave area. By using this 3236 parameter, xsave area per process might occupy more 3237 memory on xsaves enabled systems. 3238 3239 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3240 wfi(ARM) instruction doesn't work correctly and not to 3241 use it. This is also useful when using JTAG debugger. 3242 3243 no_file_caps Tells the kernel not to honor file capabilities. The 3244 only way then for a file to be executed with privilege 3245 is to be setuid root or executed by root. 3246 3247 nohalt [IA-64] Tells the kernel not to use the power saving 3248 function PAL_HALT_LIGHT when idle. This increases 3249 power-consumption. On the positive side, it reduces 3250 interrupt wake-up latency, which may improve performance 3251 in certain environments such as networked servers or 3252 real-time systems. 3253 3254 nohibernate [HIBERNATION] Disable hibernation and resume. 3255 3256 nohz= [KNL] Boottime enable/disable dynamic ticks 3257 Valid arguments: on, off 3258 Default: on 3259 3260 nohz_full= [KNL,BOOT,SMP,ISOL] 3261 The argument is a cpu list, as described above. 3262 In kernels built with CONFIG_NO_HZ_FULL=y, set 3263 the specified list of CPUs whose tick will be stopped 3264 whenever possible. The boot CPU will be forced outside 3265 the range to maintain the timekeeping. Any CPUs 3266 in this list will have their RCU callbacks offloaded, 3267 just as if they had also been called out in the 3268 rcu_nocbs= boot parameter. 3269 3270 noiotrap [SH] Disables trapped I/O port accesses. 3271 3272 noirqdebug [X86-32] Disables the code which attempts to detect and 3273 disable unhandled interrupt sources. 3274 3275 no_timer_check [X86,APIC] Disables the code which tests for 3276 broken timer IRQ sources. 3277 3278 noisapnp [ISAPNP] Disables ISA PnP code. 3279 3280 noinitrd [RAM] Tells the kernel not to load any configured 3281 initial RAM disk. 3282 3283 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3284 remapping. 3285 [Deprecated - use intremap=off] 3286 3287 nointroute [IA-64] 3288 3289 noinvpcid [X86] Disable the INVPCID cpu feature. 3290 3291 nojitter [IA-64] Disables jitter checking for ITC timers. 3292 3293 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3294 3295 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3296 fault handling. 3297 3298 no-vmw-sched-clock 3299 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3300 clock and use the default one. 3301 3302 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3303 accounting. steal time is computed, but won't 3304 influence scheduler behaviour 3305 3306 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3307 3308 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3309 3310 noltlbs [PPC] Do not use large page/tlb entries for kernel 3311 lowmem mapping on PPC40x and PPC8xx 3312 3313 nomca [IA-64] Disable machine check abort handling 3314 3315 nomce [X86-32] Disable Machine Check Exception 3316 3317 nomfgpt [X86-32] Disable Multi-Function General Purpose 3318 Timer usage (for AMD Geode machines). 3319 3320 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3321 shutdown the other cpus. Instead use the REBOOT_VECTOR 3322 irq. 3323 3324 nomodule Disable module load 3325 3326 nopat [X86] Disable PAT (page attribute table extension of 3327 pagetables) support. 3328 3329 nopcid [X86-64] Disable the PCID cpu feature. 3330 3331 norandmaps Don't use address space randomization. Equivalent to 3332 echo 0 > /proc/sys/kernel/randomize_va_space 3333 3334 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3335 with UP alternatives 3336 3337 nordrand [X86] Disable kernel use of the RDRAND and 3338 RDSEED instructions even if they are supported 3339 by the processor. RDRAND and RDSEED are still 3340 available to user space applications. 3341 3342 noresume [SWSUSP] Disables resume and restores original swap 3343 space. 3344 3345 no-scroll [VGA] Disables scrollback. 3346 This is required for the Braillex ib80-piezo Braille 3347 reader made by F.H. Papenmeier (Germany). 3348 3349 nosbagart [IA-64] 3350 3351 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3352 3353 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3354 and disable the IO APIC. legacy for "maxcpus=0". 3355 3356 nosoftlockup [KNL] Disable the soft-lockup detector. 3357 3358 nosync [HW,M68K] Disables sync negotiation for all devices. 3359 3360 nowatchdog [KNL] Disable both lockup detectors, i.e. 3361 soft-lockup and NMI watchdog (hard-lockup). 3362 3363 nowb [ARM] 3364 3365 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3366 3367 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3368 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3369 Some features depend on CPU0. Known dependencies are: 3370 1. Resume from suspend/hibernate depends on CPU0. 3371 Suspend/hibernate will fail if CPU0 is offline and you 3372 need to online CPU0 before suspend/hibernate. 3373 2. PIC interrupts also depend on CPU0. CPU0 can't be 3374 removed if a PIC interrupt is detected. 3375 It's said poweroff/reboot may depend on CPU0 on some 3376 machines although I haven't seen such issues so far 3377 after CPU0 is offline on a few tested machines. 3378 If the dependencies are under your control, you can 3379 turn on cpu0_hotplug. 3380 3381 nps_mtm_hs_ctr= [KNL,ARC] 3382 This parameter sets the maximum duration, in 3383 cycles, each HW thread of the CTOP can run 3384 without interruptions, before HW switches it. 3385 The actual maximum duration is 16 times this 3386 parameter's value. 3387 Format: integer between 1 and 255 3388 Default: 255 3389 3390 nptcg= [IA-64] Override max number of concurrent global TLB 3391 purges which is reported from either PAL_VM_SUMMARY or 3392 SAL PALO. 3393 3394 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3395 could support. nr_cpus=n : n >= 1 limits the kernel to 3396 support 'n' processors. It could be larger than the 3397 number of already plugged CPU during bootup, later in 3398 runtime you can physically add extra cpu until it reaches 3399 n. So during boot up some boot time memory for per-cpu 3400 variables need be pre-allocated for later physical cpu 3401 hot plugging. 3402 3403 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3404 3405 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3406 Allowed values are enable and disable 3407 3408 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3409 'node', 'default' can be specified 3410 This can be set from sysctl after boot. 3411 See Documentation/admin-guide/sysctl/vm.rst for details. 3412 3413 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3414 See Documentation/core-api/debugging-via-ohci1394.rst for more 3415 info. 3416 3417 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3418 Rather than timing out after 20 ms if an EC 3419 command is not properly ACKed, override the length 3420 of the timeout. We have interrupts disabled while 3421 waiting for the ACK, so if this is set too high 3422 interrupts *may* be lost! 3423 3424 omap_mux= [OMAP] Override bootloader pin multiplexing. 3425 Format: <mux_mode0.mode_name=value>... 3426 For example, to override I2C bus2: 3427 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3428 3429 oprofile.timer= [HW] 3430 Use timer interrupt instead of performance counters 3431 3432 oprofile.cpu_type= Force an oprofile cpu type 3433 This might be useful if you have an older oprofile 3434 userland or if you want common events. 3435 Format: { arch_perfmon } 3436 arch_perfmon: [X86] Force use of architectural 3437 perfmon on Intel CPUs instead of the 3438 CPU specific event set. 3439 timer: [X86] Force use of architectural NMI 3440 timer mode (see also oprofile.timer 3441 for generic hr timer mode) 3442 3443 oops=panic Always panic on oopses. Default is to just kill the 3444 process, but there is a small probability of 3445 deadlocking the machine. 3446 This will also cause panics on machine check exceptions. 3447 Useful together with panic=30 to trigger a reboot. 3448 3449 page_alloc.shuffle= 3450 [KNL] Boolean flag to control whether the page allocator 3451 should randomize its free lists. The randomization may 3452 be automatically enabled if the kernel detects it is 3453 running on a platform with a direct-mapped memory-side 3454 cache, and this parameter can be used to 3455 override/disable that behavior. The state of the flag 3456 can be read from sysfs at: 3457 /sys/module/page_alloc/parameters/shuffle. 3458 3459 page_owner= [KNL] Boot-time page_owner enabling option. 3460 Storage of the information about who allocated 3461 each page is disabled in default. With this switch, 3462 we can turn it on. 3463 on: enable the feature 3464 3465 page_poison= [KNL] Boot-time parameter changing the state of 3466 poisoning on the buddy allocator, available with 3467 CONFIG_PAGE_POISONING=y. 3468 off: turn off poisoning (default) 3469 on: turn on poisoning 3470 3471 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3472 timeout > 0: seconds before rebooting 3473 timeout = 0: wait forever 3474 timeout < 0: reboot immediately 3475 Format: <timeout> 3476 3477 panic_print= Bitmask for printing system info when panic happens. 3478 User can chose combination of the following bits: 3479 bit 0: print all tasks info 3480 bit 1: print system memory info 3481 bit 2: print timer info 3482 bit 3: print locks info if CONFIG_LOCKDEP is on 3483 bit 4: print ftrace buffer 3484 bit 5: print all printk messages in buffer 3485 3486 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3487 Format: <hex>[,nousertaint] 3488 Hexadecimal bitmask representing the set of TAINT flags 3489 that will cause the kernel to panic when add_taint() is 3490 called with any of the flags in this set. 3491 The optional switch "nousertaint" can be utilized to 3492 prevent userspace forced crashes by writing to sysctl 3493 /proc/sys/kernel/tainted any flagset matching with the 3494 bitmask set on panic_on_taint. 3495 See Documentation/admin-guide/tainted-kernels.rst for 3496 extra details on the taint flags that users can pick 3497 to compose the bitmask to assign to panic_on_taint. 3498 3499 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3500 on a WARN(). 3501 3502 crash_kexec_post_notifiers 3503 Run kdump after running panic-notifiers and dumping 3504 kmsg. This only for the users who doubt kdump always 3505 succeeds in any situation. 3506 Note that this also increases risks of kdump failure, 3507 because some panic notifiers can make the crashed 3508 kernel more unstable. 3509 3510 parkbd.port= [HW] Parallel port number the keyboard adapter is 3511 connected to, default is 0. 3512 Format: <parport#> 3513 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3514 0 for XT, 1 for AT (default is AT). 3515 Format: <mode> 3516 3517 parport= [HW,PPT] Specify parallel ports. 0 disables. 3518 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3519 Use 'auto' to force the driver to use any 3520 IRQ/DMA settings detected (the default is to 3521 ignore detected IRQ/DMA settings because of 3522 possible conflicts). You can specify the base 3523 address, IRQ, and DMA settings; IRQ and DMA 3524 should be numbers, or 'auto' (for using detected 3525 settings on that particular port), or 'nofifo' 3526 (to avoid using a FIFO even if it is detected). 3527 Parallel ports are assigned in the order they 3528 are specified on the command line, starting 3529 with parport0. 3530 3531 parport_init_mode= [HW,PPT] 3532 Configure VIA parallel port to operate in 3533 a specific mode. This is necessary on Pegasos 3534 computer where firmware has no options for setting 3535 up parallel port mode and sets it to spp. 3536 Currently this function knows 686a and 8231 chips. 3537 Format: [spp|ps2|epp|ecp|ecpepp] 3538 3539 pause_on_oops= 3540 Halt all CPUs after the first oops has been printed for 3541 the specified number of seconds. This is to be used if 3542 your oopses keep scrolling off the screen. 3543 3544 pcbit= [HW,ISDN] 3545 3546 pcd. [PARIDE] 3547 See header of drivers/block/paride/pcd.c. 3548 See also Documentation/admin-guide/blockdev/paride.rst. 3549 3550 pci=option[,option...] [PCI] various PCI subsystem options. 3551 3552 Some options herein operate on a specific device 3553 or a set of devices (<pci_dev>). These are 3554 specified in one of the following formats: 3555 3556 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3557 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3558 3559 Note: the first format specifies a PCI 3560 bus/device/function address which may change 3561 if new hardware is inserted, if motherboard 3562 firmware changes, or due to changes caused 3563 by other kernel parameters. If the 3564 domain is left unspecified, it is 3565 taken to be zero. Optionally, a path 3566 to a device through multiple device/function 3567 addresses can be specified after the base 3568 address (this is more robust against 3569 renumbering issues). The second format 3570 selects devices using IDs from the 3571 configuration space which may match multiple 3572 devices in the system. 3573 3574 earlydump dump PCI config space before the kernel 3575 changes anything 3576 off [X86] don't probe for the PCI bus 3577 bios [X86-32] force use of PCI BIOS, don't access 3578 the hardware directly. Use this if your machine 3579 has a non-standard PCI host bridge. 3580 nobios [X86-32] disallow use of PCI BIOS, only direct 3581 hardware access methods are allowed. Use this 3582 if you experience crashes upon bootup and you 3583 suspect they are caused by the BIOS. 3584 conf1 [X86] Force use of PCI Configuration Access 3585 Mechanism 1 (config address in IO port 0xCF8, 3586 data in IO port 0xCFC, both 32-bit). 3587 conf2 [X86] Force use of PCI Configuration Access 3588 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3589 the function, IO port 0xCFA, also 8-bit, sets 3590 bus number. The config space is then accessed 3591 through ports 0xC000-0xCFFF). 3592 See http://wiki.osdev.org/PCI for more info 3593 on the configuration access mechanisms. 3594 noaer [PCIE] If the PCIEAER kernel config parameter is 3595 enabled, this kernel boot option can be used to 3596 disable the use of PCIE advanced error reporting. 3597 nodomains [PCI] Disable support for multiple PCI 3598 root domains (aka PCI segments, in ACPI-speak). 3599 nommconf [X86] Disable use of MMCONFIG for PCI 3600 Configuration 3601 check_enable_amd_mmconf [X86] check for and enable 3602 properly configured MMIO access to PCI 3603 config space on AMD family 10h CPU 3604 nomsi [MSI] If the PCI_MSI kernel config parameter is 3605 enabled, this kernel boot option can be used to 3606 disable the use of MSI interrupts system-wide. 3607 noioapicquirk [APIC] Disable all boot interrupt quirks. 3608 Safety option to keep boot IRQs enabled. This 3609 should never be necessary. 3610 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3611 primary IO-APIC for bridges that cannot disable 3612 boot IRQs. This fixes a source of spurious IRQs 3613 when the system masks IRQs. 3614 noioapicreroute [APIC] Disable workaround that uses the 3615 boot IRQ equivalent of an IRQ that connects to 3616 a chipset where boot IRQs cannot be disabled. 3617 The opposite of ioapicreroute. 3618 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3619 routing table. These calls are known to be buggy 3620 on several machines and they hang the machine 3621 when used, but on other computers it's the only 3622 way to get the interrupt routing table. Try 3623 this option if the kernel is unable to allocate 3624 IRQs or discover secondary PCI buses on your 3625 motherboard. 3626 rom [X86] Assign address space to expansion ROMs. 3627 Use with caution as certain devices share 3628 address decoders between ROMs and other 3629 resources. 3630 norom [X86] Do not assign address space to 3631 expansion ROMs that do not already have 3632 BIOS assigned address ranges. 3633 nobar [X86] Do not assign address space to the 3634 BARs that weren't assigned by the BIOS. 3635 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3636 assigned automatically to PCI devices. You can 3637 make the kernel exclude IRQs of your ISA cards 3638 this way. 3639 pirqaddr=0xAAAAA [X86] Specify the physical address 3640 of the PIRQ table (normally generated 3641 by the BIOS) if it is outside the 3642 F0000h-100000h range. 3643 lastbus=N [X86] Scan all buses thru bus #N. Can be 3644 useful if the kernel is unable to find your 3645 secondary buses and you want to tell it 3646 explicitly which ones they are. 3647 assign-busses [X86] Always assign all PCI bus 3648 numbers ourselves, overriding 3649 whatever the firmware may have done. 3650 usepirqmask [X86] Honor the possible IRQ mask stored 3651 in the BIOS $PIR table. This is needed on 3652 some systems with broken BIOSes, notably 3653 some HP Pavilion N5400 and Omnibook XE3 3654 notebooks. This will have no effect if ACPI 3655 IRQ routing is enabled. 3656 noacpi [X86] Do not use ACPI for IRQ routing 3657 or for PCI scanning. 3658 use_crs [X86] Use PCI host bridge window information 3659 from ACPI. On BIOSes from 2008 or later, this 3660 is enabled by default. If you need to use this, 3661 please report a bug. 3662 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3663 If you need to use this, please report a bug. 3664 routeirq Do IRQ routing for all PCI devices. 3665 This is normally done in pci_enable_device(), 3666 so this option is a temporary workaround 3667 for broken drivers that don't call it. 3668 skip_isa_align [X86] do not align io start addr, so can 3669 handle more pci cards 3670 noearly [X86] Don't do any early type 1 scanning. 3671 This might help on some broken boards which 3672 machine check when some devices' config space 3673 is read. But various workarounds are disabled 3674 and some IOMMU drivers will not work. 3675 bfsort Sort PCI devices into breadth-first order. 3676 This sorting is done to get a device 3677 order compatible with older (<= 2.4) kernels. 3678 nobfsort Don't sort PCI devices into breadth-first order. 3679 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3680 tuning and use the BIOS-configured MPS defaults. 3681 pcie_bus_safe Set every device's MPS to the largest value 3682 supported by all devices below the root complex. 3683 pcie_bus_perf Set device MPS to the largest allowable MPS 3684 based on its parent bus. Also set MRRS (Max 3685 Read Request Size) to the largest supported 3686 value (no larger than the MPS that the device 3687 or bus can support) for best performance. 3688 pcie_bus_peer2peer Set every device's MPS to 128B, which 3689 every device is guaranteed to support. This 3690 configuration allows peer-to-peer DMA between 3691 any pair of devices, possibly at the cost of 3692 reduced performance. This also guarantees 3693 that hot-added devices will work. 3694 cbiosize=nn[KMG] The fixed amount of bus space which is 3695 reserved for the CardBus bridge's IO window. 3696 The default value is 256 bytes. 3697 cbmemsize=nn[KMG] The fixed amount of bus space which is 3698 reserved for the CardBus bridge's memory 3699 window. The default value is 64 megabytes. 3700 resource_alignment= 3701 Format: 3702 [<order of align>@]<pci_dev>[; ...] 3703 Specifies alignment and device to reassign 3704 aligned memory resources. How to 3705 specify the device is described above. 3706 If <order of align> is not specified, 3707 PAGE_SIZE is used as alignment. 3708 A PCI-PCI bridge can be specified if resource 3709 windows need to be expanded. 3710 To specify the alignment for several 3711 instances of a device, the PCI vendor, 3712 device, subvendor, and subdevice may be 3713 specified, e.g., 12@pci:8086:9c22:103c:198f 3714 for 4096-byte alignment. 3715 ecrc= Enable/disable PCIe ECRC (transaction layer 3716 end-to-end CRC checking). 3717 bios: Use BIOS/firmware settings. This is the 3718 the default. 3719 off: Turn ECRC off 3720 on: Turn ECRC on. 3721 hpiosize=nn[KMG] The fixed amount of bus space which is 3722 reserved for hotplug bridge's IO window. 3723 Default size is 256 bytes. 3724 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3725 reserved for hotplug bridge's MMIO window. 3726 Default size is 2 megabytes. 3727 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3728 reserved for hotplug bridge's MMIO_PREF window. 3729 Default size is 2 megabytes. 3730 hpmemsize=nn[KMG] The fixed amount of bus space which is 3731 reserved for hotplug bridge's MMIO and 3732 MMIO_PREF window. 3733 Default size is 2 megabytes. 3734 hpbussize=nn The minimum amount of additional bus numbers 3735 reserved for buses below a hotplug bridge. 3736 Default is 1. 3737 realloc= Enable/disable reallocating PCI bridge resources 3738 if allocations done by BIOS are too small to 3739 accommodate resources required by all child 3740 devices. 3741 off: Turn realloc off 3742 on: Turn realloc on 3743 realloc same as realloc=on 3744 noari do not use PCIe ARI. 3745 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3746 do not use PCIe ATS (and IOMMU device IOTLB). 3747 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3748 only look for one device below a PCIe downstream 3749 port. 3750 big_root_window Try to add a big 64bit memory window to the PCIe 3751 root complex on AMD CPUs. Some GFX hardware 3752 can resize a BAR to allow access to all VRAM. 3753 Adding the window is slightly risky (it may 3754 conflict with unreported devices), so this 3755 taints the kernel. 3756 disable_acs_redir=<pci_dev>[; ...] 3757 Specify one or more PCI devices (in the format 3758 specified above) separated by semicolons. 3759 Each device specified will have the PCI ACS 3760 redirect capabilities forced off which will 3761 allow P2P traffic between devices through 3762 bridges without forcing it upstream. Note: 3763 this removes isolation between devices and 3764 may put more devices in an IOMMU group. 3765 force_floating [S390] Force usage of floating interrupts. 3766 nomio [S390] Do not use MIO instructions. 3767 norid [S390] ignore the RID field and force use of 3768 one PCI domain per PCI function 3769 3770 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3771 Management. 3772 off Disable ASPM. 3773 force Enable ASPM even on devices that claim not to support it. 3774 WARNING: Forcing ASPM on may cause system lockups. 3775 3776 pcie_ports= [PCIE] PCIe port services handling: 3777 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3778 even if the platform doesn't give the OS permission to 3779 use them. This may cause conflicts if the platform 3780 also tries to use these services. 3781 dpc-native Use native PCIe service for DPC only. May 3782 cause conflicts if firmware uses AER or DPC. 3783 compat Disable native PCIe services (PME, AER, DPC, PCIe 3784 hotplug). 3785 3786 pcie_port_pm= [PCIE] PCIe port power management handling: 3787 off Disable power management of all PCIe ports 3788 force Forcibly enable power management of all PCIe ports 3789 3790 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3791 nomsi Do not use MSI for native PCIe PME signaling (this makes 3792 all PCIe root ports use INTx for all services). 3793 3794 pcmv= [HW,PCMCIA] BadgePAD 4 3795 3796 pd_ignore_unused 3797 [PM] 3798 Keep all power-domains already enabled by bootloader on, 3799 even if no driver has claimed them. This is useful 3800 for debug and development, but should not be 3801 needed on a platform with proper driver support. 3802 3803 pd. [PARIDE] 3804 See Documentation/admin-guide/blockdev/paride.rst. 3805 3806 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3807 boot time. 3808 Format: { 0 | 1 } 3809 See arch/parisc/kernel/pdc_chassis.c 3810 3811 percpu_alloc= Select which percpu first chunk allocator to use. 3812 Currently supported values are "embed" and "page". 3813 Archs may support subset or none of the selections. 3814 See comments in mm/percpu.c for details on each 3815 allocator. This parameter is primarily for debugging 3816 and performance comparison. 3817 3818 pf. [PARIDE] 3819 See Documentation/admin-guide/blockdev/paride.rst. 3820 3821 pg. [PARIDE] 3822 See Documentation/admin-guide/blockdev/paride.rst. 3823 3824 pirq= [SMP,APIC] Manual mp-table setup 3825 See Documentation/x86/i386/IO-APIC.rst. 3826 3827 plip= [PPT,NET] Parallel port network link 3828 Format: { parport<nr> | timid | 0 } 3829 See also Documentation/admin-guide/parport.rst. 3830 3831 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3832 Override pmtimer IOPort with a hex value. 3833 e.g. pmtmr=0x508 3834 3835 pm_debug_messages [SUSPEND,KNL] 3836 Enable suspend/resume debug messages during boot up. 3837 3838 pnp.debug=1 [PNP] 3839 Enable PNP debug messages (depends on the 3840 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3841 via /sys/module/pnp/parameters/debug. We always show 3842 current resource usage; turning this on also shows 3843 possible settings and some assignment information. 3844 3845 pnpacpi= [ACPI] 3846 { off } 3847 3848 pnpbios= [ISAPNP] 3849 { on | off | curr | res | no-curr | no-res } 3850 3851 pnp_reserve_irq= 3852 [ISAPNP] Exclude IRQs for the autoconfiguration 3853 3854 pnp_reserve_dma= 3855 [ISAPNP] Exclude DMAs for the autoconfiguration 3856 3857 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3858 Ranges are in pairs (I/O port base and size). 3859 3860 pnp_reserve_mem= 3861 [ISAPNP] Exclude memory regions for the 3862 autoconfiguration. 3863 Ranges are in pairs (memory base and size). 3864 3865 ports= [IP_VS_FTP] IPVS ftp helper module 3866 Default is 21. 3867 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3868 may be specified. 3869 Format: <port>,<port>.... 3870 3871 powersave=off [PPC] This option disables power saving features. 3872 It specifically disables cpuidle and sets the 3873 platform machine description specific power_save 3874 function to NULL. On Idle the CPU just reduces 3875 execution priority. 3876 3877 ppc_strict_facility_enable 3878 [PPC] This option catches any kernel floating point, 3879 Altivec, VSX and SPE outside of regions specifically 3880 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3881 There is some performance impact when enabling this. 3882 3883 ppc_tm= [PPC] 3884 Format: {"off"} 3885 Disable Hardware Transactional Memory 3886 3887 print-fatal-signals= 3888 [KNL] debug: print fatal signals 3889 3890 If enabled, warn about various signal handling 3891 related application anomalies: too many signals, 3892 too many POSIX.1 timers, fatal signals causing a 3893 coredump - etc. 3894 3895 If you hit the warning due to signal overflow, 3896 you might want to try "ulimit -i unlimited". 3897 3898 default: off. 3899 3900 printk.always_kmsg_dump= 3901 Trigger kmsg_dump for cases other than kernel oops or 3902 panics 3903 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3904 default: disabled 3905 3906 printk.devkmsg={on,off,ratelimit} 3907 Control writing to /dev/kmsg. 3908 on - unlimited logging to /dev/kmsg from userspace 3909 off - logging to /dev/kmsg disabled 3910 ratelimit - ratelimit the logging 3911 Default: ratelimit 3912 3913 printk.time= Show timing data prefixed to each printk message line 3914 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3915 3916 processor.max_cstate= [HW,ACPI] 3917 Limit processor to maximum C-state 3918 max_cstate=9 overrides any DMI blacklist limit. 3919 3920 processor.nocst [HW,ACPI] 3921 Ignore the _CST method to determine C-states, 3922 instead using the legacy FADT method 3923 3924 profile= [KNL] Enable kernel profiling via /proc/profile 3925 Format: [<profiletype>,]<number> 3926 Param: <profiletype>: "schedule", "sleep", or "kvm" 3927 [defaults to kernel profiling] 3928 Param: "schedule" - profile schedule points. 3929 Param: "sleep" - profile D-state sleeping (millisecs). 3930 Requires CONFIG_SCHEDSTATS 3931 Param: "kvm" - profile VM exits. 3932 Param: <number> - step/bucket size as a power of 2 for 3933 statistical time based profiling. 3934 3935 prompt_ramdisk= [RAM] [Deprecated] 3936 3937 prot_virt= [S390] enable hosting protected virtual machines 3938 isolated from the hypervisor (if hardware supports 3939 that). 3940 Format: <bool> 3941 3942 psi= [KNL] Enable or disable pressure stall information 3943 tracking. 3944 Format: <bool> 3945 3946 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3947 probe for; one of (bare|imps|exps|lifebook|any). 3948 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3949 per second. 3950 psmouse.resetafter= [HW,MOUSE] 3951 Try to reset the device after so many bad packets 3952 (0 = never). 3953 psmouse.resolution= 3954 [HW,MOUSE] Set desired mouse resolution, in dpi. 3955 psmouse.smartscroll= 3956 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3957 0 = disabled, 1 = enabled (default). 3958 3959 pstore.backend= Specify the name of the pstore backend to use 3960 3961 pt. [PARIDE] 3962 See Documentation/admin-guide/blockdev/paride.rst. 3963 3964 pti= [X86-64] Control Page Table Isolation of user and 3965 kernel address spaces. Disabling this feature 3966 removes hardening, but improves performance of 3967 system calls and interrupts. 3968 3969 on - unconditionally enable 3970 off - unconditionally disable 3971 auto - kernel detects whether your CPU model is 3972 vulnerable to issues that PTI mitigates 3973 3974 Not specifying this option is equivalent to pti=auto. 3975 3976 nopti [X86-64] 3977 Equivalent to pti=off 3978 3979 pty.legacy_count= 3980 [KNL] Number of legacy pty's. Overwrites compiled-in 3981 default number. 3982 3983 quiet [KNL] Disable most log messages 3984 3985 r128= [HW,DRM] 3986 3987 raid= [HW,RAID] 3988 See Documentation/admin-guide/md.rst. 3989 3990 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3991 See Documentation/admin-guide/blockdev/ramdisk.rst. 3992 3993 ramdisk_start= [RAM] RAM disk image start address 3994 3995 random.trust_cpu={on,off} 3996 [KNL] Enable or disable trusting the use of the 3997 CPU's random number generator (if available) to 3998 fully seed the kernel's CRNG. Default is controlled 3999 by CONFIG_RANDOM_TRUST_CPU. 4000 4001 ras=option[,option,...] [KNL] RAS-specific options 4002 4003 cec_disable [X86] 4004 Disable the Correctable Errors Collector, 4005 see CONFIG_RAS_CEC help text. 4006 4007 rcu_nocbs= [KNL] 4008 The argument is a cpu list, as described above, 4009 except that the string "all" can be used to 4010 specify every CPU on the system. 4011 4012 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4013 the specified list of CPUs to be no-callback CPUs. 4014 Invocation of these CPUs' RCU callbacks will be 4015 offloaded to "rcuox/N" kthreads created for that 4016 purpose, where "x" is "p" for RCU-preempt, and 4017 "s" for RCU-sched, and "N" is the CPU number. 4018 This reduces OS jitter on the offloaded CPUs, 4019 which can be useful for HPC and real-time 4020 workloads. It can also improve energy efficiency 4021 for asymmetric multiprocessors. 4022 4023 rcu_nocb_poll [KNL] 4024 Rather than requiring that offloaded CPUs 4025 (specified by rcu_nocbs= above) explicitly 4026 awaken the corresponding "rcuoN" kthreads, 4027 make these kthreads poll for callbacks. 4028 This improves the real-time response for the 4029 offloaded CPUs by relieving them of the need to 4030 wake up the corresponding kthread, but degrades 4031 energy efficiency by requiring that the kthreads 4032 periodically wake up to do the polling. 4033 4034 rcutree.blimit= [KNL] 4035 Set maximum number of finished RCU callbacks to 4036 process in one batch. 4037 4038 rcutree.dump_tree= [KNL] 4039 Dump the structure of the rcu_node combining tree 4040 out at early boot. This is used for diagnostic 4041 purposes, to verify correct tree setup. 4042 4043 rcutree.gp_cleanup_delay= [KNL] 4044 Set the number of jiffies to delay each step of 4045 RCU grace-period cleanup. 4046 4047 rcutree.gp_init_delay= [KNL] 4048 Set the number of jiffies to delay each step of 4049 RCU grace-period initialization. 4050 4051 rcutree.gp_preinit_delay= [KNL] 4052 Set the number of jiffies to delay each step of 4053 RCU grace-period pre-initialization, that is, 4054 the propagation of recent CPU-hotplug changes up 4055 the rcu_node combining tree. 4056 4057 rcutree.use_softirq= [KNL] 4058 If set to zero, move all RCU_SOFTIRQ processing to 4059 per-CPU rcuc kthreads. Defaults to a non-zero 4060 value, meaning that RCU_SOFTIRQ is used by default. 4061 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4062 4063 rcutree.rcu_fanout_exact= [KNL] 4064 Disable autobalancing of the rcu_node combining 4065 tree. This is used by rcutorture, and might 4066 possibly be useful for architectures having high 4067 cache-to-cache transfer latencies. 4068 4069 rcutree.rcu_fanout_leaf= [KNL] 4070 Change the number of CPUs assigned to each 4071 leaf rcu_node structure. Useful for very 4072 large systems, which will choose the value 64, 4073 and for NUMA systems with large remote-access 4074 latencies, which will choose a value aligned 4075 with the appropriate hardware boundaries. 4076 4077 rcutree.rcu_min_cached_objs= [KNL] 4078 Minimum number of objects which are cached and 4079 maintained per one CPU. Object size is equal 4080 to PAGE_SIZE. The cache allows to reduce the 4081 pressure to page allocator, also it makes the 4082 whole algorithm to behave better in low memory 4083 condition. 4084 4085 rcutree.jiffies_till_first_fqs= [KNL] 4086 Set delay from grace-period initialization to 4087 first attempt to force quiescent states. 4088 Units are jiffies, minimum value is zero, 4089 and maximum value is HZ. 4090 4091 rcutree.jiffies_till_next_fqs= [KNL] 4092 Set delay between subsequent attempts to force 4093 quiescent states. Units are jiffies, minimum 4094 value is one, and maximum value is HZ. 4095 4096 rcutree.jiffies_till_sched_qs= [KNL] 4097 Set required age in jiffies for a 4098 given grace period before RCU starts 4099 soliciting quiescent-state help from 4100 rcu_note_context_switch() and cond_resched(). 4101 If not specified, the kernel will calculate 4102 a value based on the most recent settings 4103 of rcutree.jiffies_till_first_fqs 4104 and rcutree.jiffies_till_next_fqs. 4105 This calculated value may be viewed in 4106 rcutree.jiffies_to_sched_qs. Any attempt to set 4107 rcutree.jiffies_to_sched_qs will be cheerfully 4108 overwritten. 4109 4110 rcutree.kthread_prio= [KNL,BOOT] 4111 Set the SCHED_FIFO priority of the RCU per-CPU 4112 kthreads (rcuc/N). This value is also used for 4113 the priority of the RCU boost threads (rcub/N) 4114 and for the RCU grace-period kthreads (rcu_bh, 4115 rcu_preempt, and rcu_sched). If RCU_BOOST is 4116 set, valid values are 1-99 and the default is 1 4117 (the least-favored priority). Otherwise, when 4118 RCU_BOOST is not set, valid values are 0-99 and 4119 the default is zero (non-realtime operation). 4120 4121 rcutree.rcu_nocb_gp_stride= [KNL] 4122 Set the number of NOCB callback kthreads in 4123 each group, which defaults to the square root 4124 of the number of CPUs. Larger numbers reduce 4125 the wakeup overhead on the global grace-period 4126 kthread, but increases that same overhead on 4127 each group's NOCB grace-period kthread. 4128 4129 rcutree.qhimark= [KNL] 4130 Set threshold of queued RCU callbacks beyond which 4131 batch limiting is disabled. 4132 4133 rcutree.qlowmark= [KNL] 4134 Set threshold of queued RCU callbacks below which 4135 batch limiting is re-enabled. 4136 4137 rcutree.qovld= [KNL] 4138 Set threshold of queued RCU callbacks beyond which 4139 RCU's force-quiescent-state scan will aggressively 4140 enlist help from cond_resched() and sched IPIs to 4141 help CPUs more quickly reach quiescent states. 4142 Set to less than zero to make this be set based 4143 on rcutree.qhimark at boot time and to zero to 4144 disable more aggressive help enlistment. 4145 4146 rcutree.rcu_idle_gp_delay= [KNL] 4147 Set wakeup interval for idle CPUs that have 4148 RCU callbacks (RCU_FAST_NO_HZ=y). 4149 4150 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4151 Set wakeup interval for idle CPUs that have 4152 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4153 Lazy RCU callbacks are those which RCU can 4154 prove do nothing more than free memory. 4155 4156 rcutree.rcu_kick_kthreads= [KNL] 4157 Cause the grace-period kthread to get an extra 4158 wake_up() if it sleeps three times longer than 4159 it should at force-quiescent-state time. 4160 This wake_up() will be accompanied by a 4161 WARN_ONCE() splat and an ftrace_dump(). 4162 4163 rcutree.sysrq_rcu= [KNL] 4164 Commandeer a sysrq key to dump out Tree RCU's 4165 rcu_node tree with an eye towards determining 4166 why a new grace period has not yet started. 4167 4168 rcuperf.gp_async= [KNL] 4169 Measure performance of asynchronous 4170 grace-period primitives such as call_rcu(). 4171 4172 rcuperf.gp_async_max= [KNL] 4173 Specify the maximum number of outstanding 4174 callbacks per writer thread. When a writer 4175 thread exceeds this limit, it invokes the 4176 corresponding flavor of rcu_barrier() to allow 4177 previously posted callbacks to drain. 4178 4179 rcuperf.gp_exp= [KNL] 4180 Measure performance of expedited synchronous 4181 grace-period primitives. 4182 4183 rcuperf.holdoff= [KNL] 4184 Set test-start holdoff period. The purpose of 4185 this parameter is to delay the start of the 4186 test until boot completes in order to avoid 4187 interference. 4188 4189 rcuperf.kfree_rcu_test= [KNL] 4190 Set to measure performance of kfree_rcu() flooding. 4191 4192 rcuperf.kfree_nthreads= [KNL] 4193 The number of threads running loops of kfree_rcu(). 4194 4195 rcuperf.kfree_alloc_num= [KNL] 4196 Number of allocations and frees done in an iteration. 4197 4198 rcuperf.kfree_loops= [KNL] 4199 Number of loops doing rcuperf.kfree_alloc_num number 4200 of allocations and frees. 4201 4202 rcuperf.nreaders= [KNL] 4203 Set number of RCU readers. The value -1 selects 4204 N, where N is the number of CPUs. A value 4205 "n" less than -1 selects N-n+1, where N is again 4206 the number of CPUs. For example, -2 selects N 4207 (the number of CPUs), -3 selects N+1, and so on. 4208 A value of "n" less than or equal to -N selects 4209 a single reader. 4210 4211 rcuperf.nwriters= [KNL] 4212 Set number of RCU writers. The values operate 4213 the same as for rcuperf.nreaders. 4214 N, where N is the number of CPUs 4215 4216 rcuperf.perf_type= [KNL] 4217 Specify the RCU implementation to test. 4218 4219 rcuperf.shutdown= [KNL] 4220 Shut the system down after performance tests 4221 complete. This is useful for hands-off automated 4222 testing. 4223 4224 rcuperf.verbose= [KNL] 4225 Enable additional printk() statements. 4226 4227 rcuperf.writer_holdoff= [KNL] 4228 Write-side holdoff between grace periods, 4229 in microseconds. The default of zero says 4230 no holdoff. 4231 4232 rcutorture.fqs_duration= [KNL] 4233 Set duration of force_quiescent_state bursts 4234 in microseconds. 4235 4236 rcutorture.fqs_holdoff= [KNL] 4237 Set holdoff time within force_quiescent_state bursts 4238 in microseconds. 4239 4240 rcutorture.fqs_stutter= [KNL] 4241 Set wait time between force_quiescent_state bursts 4242 in seconds. 4243 4244 rcutorture.fwd_progress= [KNL] 4245 Enable RCU grace-period forward-progress testing 4246 for the types of RCU supporting this notion. 4247 4248 rcutorture.fwd_progress_div= [KNL] 4249 Specify the fraction of a CPU-stall-warning 4250 period to do tight-loop forward-progress testing. 4251 4252 rcutorture.fwd_progress_holdoff= [KNL] 4253 Number of seconds to wait between successive 4254 forward-progress tests. 4255 4256 rcutorture.fwd_progress_need_resched= [KNL] 4257 Enclose cond_resched() calls within checks for 4258 need_resched() during tight-loop forward-progress 4259 testing. 4260 4261 rcutorture.gp_cond= [KNL] 4262 Use conditional/asynchronous update-side 4263 primitives, if available. 4264 4265 rcutorture.gp_exp= [KNL] 4266 Use expedited update-side primitives, if available. 4267 4268 rcutorture.gp_normal= [KNL] 4269 Use normal (non-expedited) asynchronous 4270 update-side primitives, if available. 4271 4272 rcutorture.gp_sync= [KNL] 4273 Use normal (non-expedited) synchronous 4274 update-side primitives, if available. If all 4275 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4276 rcutorture.gp_normal=, and rcutorture.gp_sync= 4277 are zero, rcutorture acts as if is interpreted 4278 they are all non-zero. 4279 4280 rcutorture.n_barrier_cbs= [KNL] 4281 Set callbacks/threads for rcu_barrier() testing. 4282 4283 rcutorture.nfakewriters= [KNL] 4284 Set number of concurrent RCU writers. These just 4285 stress RCU, they don't participate in the actual 4286 test, hence the "fake". 4287 4288 rcutorture.nreaders= [KNL] 4289 Set number of RCU readers. The value -1 selects 4290 N-1, where N is the number of CPUs. A value 4291 "n" less than -1 selects N-n-2, where N is again 4292 the number of CPUs. For example, -2 selects N 4293 (the number of CPUs), -3 selects N+1, and so on. 4294 4295 rcutorture.object_debug= [KNL] 4296 Enable debug-object double-call_rcu() testing. 4297 4298 rcutorture.onoff_holdoff= [KNL] 4299 Set time (s) after boot for CPU-hotplug testing. 4300 4301 rcutorture.onoff_interval= [KNL] 4302 Set time (jiffies) between CPU-hotplug operations, 4303 or zero to disable CPU-hotplug testing. 4304 4305 rcutorture.read_exit= [KNL] 4306 Set the number of read-then-exit kthreads used 4307 to test the interaction of RCU updaters and 4308 task-exit processing. 4309 4310 rcutorture.read_exit_burst= [KNL] 4311 The number of times in a given read-then-exit 4312 episode that a set of read-then-exit kthreads 4313 is spawned. 4314 4315 rcutorture.read_exit_delay= [KNL] 4316 The delay, in seconds, between successive 4317 read-then-exit testing episodes. 4318 4319 rcutorture.shuffle_interval= [KNL] 4320 Set task-shuffle interval (s). Shuffling tasks 4321 allows some CPUs to go into dyntick-idle mode 4322 during the rcutorture test. 4323 4324 rcutorture.shutdown_secs= [KNL] 4325 Set time (s) after boot system shutdown. This 4326 is useful for hands-off automated testing. 4327 4328 rcutorture.stall_cpu= [KNL] 4329 Duration of CPU stall (s) to test RCU CPU stall 4330 warnings, zero to disable. 4331 4332 rcutorture.stall_cpu_block= [KNL] 4333 Sleep while stalling if set. This will result 4334 in warnings from preemptible RCU in addition 4335 to any other stall-related activity. 4336 4337 rcutorture.stall_cpu_holdoff= [KNL] 4338 Time to wait (s) after boot before inducing stall. 4339 4340 rcutorture.stall_cpu_irqsoff= [KNL] 4341 Disable interrupts while stalling if set. 4342 4343 rcutorture.stall_gp_kthread= [KNL] 4344 Duration (s) of forced sleep within RCU 4345 grace-period kthread to test RCU CPU stall 4346 warnings, zero to disable. If both stall_cpu 4347 and stall_gp_kthread are specified, the 4348 kthread is starved first, then the CPU. 4349 4350 rcutorture.stat_interval= [KNL] 4351 Time (s) between statistics printk()s. 4352 4353 rcutorture.stutter= [KNL] 4354 Time (s) to stutter testing, for example, specifying 4355 five seconds causes the test to run for five seconds, 4356 wait for five seconds, and so on. This tests RCU's 4357 ability to transition abruptly to and from idle. 4358 4359 rcutorture.test_boost= [KNL] 4360 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4361 "Maybe" means test if the RCU implementation 4362 under test support RCU priority boosting. 4363 4364 rcutorture.test_boost_duration= [KNL] 4365 Duration (s) of each individual boost test. 4366 4367 rcutorture.test_boost_interval= [KNL] 4368 Interval (s) between each boost test. 4369 4370 rcutorture.test_no_idle_hz= [KNL] 4371 Test RCU's dyntick-idle handling. See also the 4372 rcutorture.shuffle_interval parameter. 4373 4374 rcutorture.torture_type= [KNL] 4375 Specify the RCU implementation to test. 4376 4377 rcutorture.verbose= [KNL] 4378 Enable additional printk() statements. 4379 4380 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4381 Dump ftrace buffer after reporting RCU CPU 4382 stall warning. 4383 4384 rcupdate.rcu_cpu_stall_suppress= [KNL] 4385 Suppress RCU CPU stall warning messages. 4386 4387 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4388 Suppress RCU CPU stall warning messages and 4389 rcutorture writer stall warnings that occur 4390 during early boot, that is, during the time 4391 before the init task is spawned. 4392 4393 rcupdate.rcu_cpu_stall_timeout= [KNL] 4394 Set timeout for RCU CPU stall warning messages. 4395 4396 rcupdate.rcu_expedited= [KNL] 4397 Use expedited grace-period primitives, for 4398 example, synchronize_rcu_expedited() instead 4399 of synchronize_rcu(). This reduces latency, 4400 but can increase CPU utilization, degrade 4401 real-time latency, and degrade energy efficiency. 4402 No effect on CONFIG_TINY_RCU kernels. 4403 4404 rcupdate.rcu_normal= [KNL] 4405 Use only normal grace-period primitives, 4406 for example, synchronize_rcu() instead of 4407 synchronize_rcu_expedited(). This improves 4408 real-time latency, CPU utilization, and 4409 energy efficiency, but can expose users to 4410 increased grace-period latency. This parameter 4411 overrides rcupdate.rcu_expedited. No effect on 4412 CONFIG_TINY_RCU kernels. 4413 4414 rcupdate.rcu_normal_after_boot= [KNL] 4415 Once boot has completed (that is, after 4416 rcu_end_inkernel_boot() has been invoked), use 4417 only normal grace-period primitives. No effect 4418 on CONFIG_TINY_RCU kernels. 4419 4420 rcupdate.rcu_task_ipi_delay= [KNL] 4421 Set time in jiffies during which RCU tasks will 4422 avoid sending IPIs, starting with the beginning 4423 of a given grace period. Setting a large 4424 number avoids disturbing real-time workloads, 4425 but lengthens grace periods. 4426 4427 rcupdate.rcu_task_stall_timeout= [KNL] 4428 Set timeout in jiffies for RCU task stall warning 4429 messages. Disable with a value less than or equal 4430 to zero. 4431 4432 rcupdate.rcu_self_test= [KNL] 4433 Run the RCU early boot self tests 4434 4435 rdinit= [KNL] 4436 Format: <full_path> 4437 Run specified binary instead of /init from the ramdisk, 4438 used for early userspace startup. See initrd. 4439 4440 rdrand= [X86] 4441 force - Override the decision by the kernel to hide the 4442 advertisement of RDRAND support (this affects 4443 certain AMD processors because of buggy BIOS 4444 support, specifically around the suspend/resume 4445 path). 4446 4447 rdt= [HW,X86,RDT] 4448 Turn on/off individual RDT features. List is: 4449 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4450 mba. 4451 E.g. to turn on cmt and turn off mba use: 4452 rdt=cmt,!mba 4453 4454 reboot= [KNL] 4455 Format (x86 or x86_64): 4456 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4457 [[,]s[mp]#### \ 4458 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4459 [[,]f[orce] 4460 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4461 (prefix with 'panic_' to set mode for panic 4462 reboot only), 4463 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4464 reboot_force is either force or not specified, 4465 reboot_cpu is s[mp]#### with #### being the processor 4466 to be used for rebooting. 4467 4468 refscale.holdoff= [KNL] 4469 Set test-start holdoff period. The purpose of 4470 this parameter is to delay the start of the 4471 test until boot completes in order to avoid 4472 interference. 4473 4474 refscale.loops= [KNL] 4475 Set the number of loops over the synchronization 4476 primitive under test. Increasing this number 4477 reduces noise due to loop start/end overhead, 4478 but the default has already reduced the per-pass 4479 noise to a handful of picoseconds on ca. 2020 4480 x86 laptops. 4481 4482 refscale.nreaders= [KNL] 4483 Set number of readers. The default value of -1 4484 selects N, where N is roughly 75% of the number 4485 of CPUs. A value of zero is an interesting choice. 4486 4487 refscale.nruns= [KNL] 4488 Set number of runs, each of which is dumped onto 4489 the console log. 4490 4491 refscale.readdelay= [KNL] 4492 Set the read-side critical-section duration, 4493 measured in microseconds. 4494 4495 refscale.scale_type= [KNL] 4496 Specify the read-protection implementation to test. 4497 4498 refscale.shutdown= [KNL] 4499 Shut down the system at the end of the performance 4500 test. This defaults to 1 (shut it down) when 4501 rcuperf is built into the kernel and to 0 (leave 4502 it running) when rcuperf is built as a module. 4503 4504 refscale.verbose= [KNL] 4505 Enable additional printk() statements. 4506 4507 relax_domain_level= 4508 [KNL, SMP] Set scheduler's default relax_domain_level. 4509 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4510 4511 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4512 Format: <base1>,<size1>[,<base2>,<size2>,...] 4513 Reserve I/O ports or memory so the kernel won't use 4514 them. If <base> is less than 0x10000, the region 4515 is assumed to be I/O ports; otherwise it is memory. 4516 4517 reservetop= [X86-32] 4518 Format: nn[KMG] 4519 Reserves a hole at the top of the kernel virtual 4520 address space. 4521 4522 reservelow= [X86] 4523 Format: nn[K] 4524 Set the amount of memory to reserve for BIOS at 4525 the bottom of the address space. 4526 4527 reset_devices [KNL] Force drivers to reset the underlying device 4528 during initialization. 4529 4530 resume= [SWSUSP] 4531 Specify the partition device for software suspend 4532 Format: 4533 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4534 4535 resume_offset= [SWSUSP] 4536 Specify the offset from the beginning of the partition 4537 given by "resume=" at which the swap header is located, 4538 in <PAGE_SIZE> units (needed only for swap files). 4539 See Documentation/power/swsusp-and-swap-files.rst 4540 4541 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4542 read the resume files 4543 4544 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4545 Useful for devices that are detected asynchronously 4546 (e.g. USB and MMC devices). 4547 4548 hibernate= [HIBERNATION] 4549 noresume Don't check if there's a hibernation image 4550 present during boot. 4551 nocompress Don't compress/decompress hibernation images. 4552 no Disable hibernation and resume. 4553 protect_image Turn on image protection during restoration 4554 (that will set all pages holding image data 4555 during restoration read-only). 4556 4557 retain_initrd [RAM] Keep initrd memory after extraction 4558 4559 rfkill.default_state= 4560 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4561 etc. communication is blocked by default. 4562 1 Unblocked. 4563 4564 rfkill.master_switch_mode= 4565 0 The "airplane mode" button does nothing. 4566 1 The "airplane mode" button toggles between everything 4567 blocked and the previous configuration. 4568 2 The "airplane mode" button toggles between everything 4569 blocked and everything unblocked. 4570 4571 rhash_entries= [KNL,NET] 4572 Set number of hash buckets for route cache 4573 4574 ring3mwait=disable 4575 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4576 CPUs. 4577 4578 ro [KNL] Mount root device read-only on boot 4579 4580 rodata= [KNL] 4581 on Mark read-only kernel memory as read-only (default). 4582 off Leave read-only kernel memory writable for debugging. 4583 4584 rockchip.usb_uart 4585 Enable the uart passthrough on the designated usb port 4586 on Rockchip SoCs. When active, the signals of the 4587 debug-uart get routed to the D+ and D- pins of the usb 4588 port and the regular usb controller gets disabled. 4589 4590 root= [KNL] Root filesystem 4591 See name_to_dev_t comment in init/do_mounts.c. 4592 4593 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4594 mount the root filesystem 4595 4596 rootflags= [KNL] Set root filesystem mount option string 4597 4598 rootfstype= [KNL] Set root filesystem type 4599 4600 rootwait [KNL] Wait (indefinitely) for root device to show up. 4601 Useful for devices that are detected asynchronously 4602 (e.g. USB and MMC devices). 4603 4604 rproc_mem=nn[KMG][@address] 4605 [KNL,ARM,CMA] Remoteproc physical memory block. 4606 Memory area to be used by remote processor image, 4607 managed by CMA. 4608 4609 rw [KNL] Mount root device read-write on boot 4610 4611 S [KNL] Run init in single mode 4612 4613 s390_iommu= [HW,S390] 4614 Set s390 IOTLB flushing mode 4615 strict 4616 With strict flushing every unmap operation will result in 4617 an IOTLB flush. Default is lazy flushing before reuse, 4618 which is faster. 4619 4620 sa1100ir [NET] 4621 See drivers/net/irda/sa1100_ir.c. 4622 4623 sbni= [NET] Granch SBNI12 leased line adapter 4624 4625 sched_debug [KNL] Enables verbose scheduler debug messages. 4626 4627 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4628 Allowed values are enable and disable. This feature 4629 incurs a small amount of overhead in the scheduler 4630 but is useful for debugging and performance tuning. 4631 4632 sched_thermal_decay_shift= 4633 [KNL, SMP] Set a decay shift for scheduler thermal 4634 pressure signal. Thermal pressure signal follows the 4635 default decay period of other scheduler pelt 4636 signals(usually 32 ms but configurable). Setting 4637 sched_thermal_decay_shift will left shift the decay 4638 period for the thermal pressure signal by the shift 4639 value. 4640 i.e. with the default pelt decay period of 32 ms 4641 sched_thermal_decay_shift thermal pressure decay pr 4642 1 64 ms 4643 2 128 ms 4644 and so on. 4645 Format: integer between 0 and 10 4646 Default is 0. 4647 4648 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4649 xtime_lock contention on larger systems, and/or RCU lock 4650 contention on all systems with CONFIG_MAXSMP set. 4651 Format: { "0" | "1" } 4652 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4653 1 -- enable. 4654 Note: increases power consumption, thus should only be 4655 enabled if running jitter sensitive (HPC/RT) workloads. 4656 4657 security= [SECURITY] Choose a legacy "major" security module to 4658 enable at boot. This has been deprecated by the 4659 "lsm=" parameter. 4660 4661 selinux= [SELINUX] Disable or enable SELinux at boot time. 4662 Format: { "0" | "1" } 4663 See security/selinux/Kconfig help text. 4664 0 -- disable. 4665 1 -- enable. 4666 Default value is 1. 4667 4668 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4669 Format: { "0" | "1" } 4670 See security/apparmor/Kconfig help text 4671 0 -- disable. 4672 1 -- enable. 4673 Default value is set via kernel config option. 4674 4675 serialnumber [BUGS=X86-32] 4676 4677 shapers= [NET] 4678 Maximal number of shapers. 4679 4680 simeth= [IA-64] 4681 simscsi= 4682 4683 slram= [HW,MTD] 4684 4685 slab_nomerge [MM] 4686 Disable merging of slabs with similar size. May be 4687 necessary if there is some reason to distinguish 4688 allocs to different slabs, especially in hardened 4689 environments where the risk of heap overflows and 4690 layout control by attackers can usually be 4691 frustrated by disabling merging. This will reduce 4692 most of the exposure of a heap attack to a single 4693 cache (risks via metadata attacks are mostly 4694 unchanged). Debug options disable merging on their 4695 own. 4696 For more information see Documentation/vm/slub.rst. 4697 4698 slab_max_order= [MM, SLAB] 4699 Determines the maximum allowed order for slabs. 4700 A high setting may cause OOMs due to memory 4701 fragmentation. Defaults to 1 for systems with 4702 more than 32MB of RAM, 0 otherwise. 4703 4704 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4705 Enabling slub_debug allows one to determine the 4706 culprit if slab objects become corrupted. Enabling 4707 slub_debug can create guard zones around objects and 4708 may poison objects when not in use. Also tracks the 4709 last alloc / free. For more information see 4710 Documentation/vm/slub.rst. 4711 4712 slub_memcg_sysfs= [MM, SLUB] 4713 Determines whether to enable sysfs directories for 4714 memory cgroup sub-caches. 1 to enable, 0 to disable. 4715 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4716 Enabling this can lead to a very high number of debug 4717 directories and files being created under 4718 /sys/kernel/slub. 4719 4720 slub_max_order= [MM, SLUB] 4721 Determines the maximum allowed order for slabs. 4722 A high setting may cause OOMs due to memory 4723 fragmentation. For more information see 4724 Documentation/vm/slub.rst. 4725 4726 slub_min_objects= [MM, SLUB] 4727 The minimum number of objects per slab. SLUB will 4728 increase the slab order up to slub_max_order to 4729 generate a sufficiently large slab able to contain 4730 the number of objects indicated. The higher the number 4731 of objects the smaller the overhead of tracking slabs 4732 and the less frequently locks need to be acquired. 4733 For more information see Documentation/vm/slub.rst. 4734 4735 slub_min_order= [MM, SLUB] 4736 Determines the minimum page order for slabs. Must be 4737 lower than slub_max_order. 4738 For more information see Documentation/vm/slub.rst. 4739 4740 slub_nomerge [MM, SLUB] 4741 Same with slab_nomerge. This is supported for legacy. 4742 See slab_nomerge for more information. 4743 4744 smart2= [HW] 4745 Format: <io1>[,<io2>[,...,<io8>]] 4746 4747 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4748 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4749 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4750 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4751 smsc-ircc2.ircc_irq= [HW] IRQ line 4752 smsc-ircc2.ircc_dma= [HW] DMA channel 4753 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4754 0: Toshiba Satellite 1800 (GP data pin select) 4755 1: Fast pin select (default) 4756 2: ATC IRMode 4757 4758 smt [KNL,S390] Set the maximum number of threads (logical 4759 CPUs) to use per physical CPU on systems capable of 4760 symmetric multithreading (SMT). Will be capped to the 4761 actual hardware limit. 4762 Format: <integer> 4763 Default: -1 (no limit) 4764 4765 softlockup_panic= 4766 [KNL] Should the soft-lockup detector generate panics. 4767 Format: 0 | 1 4768 4769 A value of 1 instructs the soft-lockup detector 4770 to panic the machine when a soft-lockup occurs. It is 4771 also controlled by the kernel.softlockup_panic sysctl 4772 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4773 respective build-time switch to that functionality. 4774 4775 softlockup_all_cpu_backtrace= 4776 [KNL] Should the soft-lockup detector generate 4777 backtraces on all cpus. 4778 Format: 0 | 1 4779 4780 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4781 See Documentation/admin-guide/laptops/sonypi.rst 4782 4783 spectre_v2= [X86] Control mitigation of Spectre variant 2 4784 (indirect branch speculation) vulnerability. 4785 The default operation protects the kernel from 4786 user space attacks. 4787 4788 on - unconditionally enable, implies 4789 spectre_v2_user=on 4790 off - unconditionally disable, implies 4791 spectre_v2_user=off 4792 auto - kernel detects whether your CPU model is 4793 vulnerable 4794 4795 Selecting 'on' will, and 'auto' may, choose a 4796 mitigation method at run time according to the 4797 CPU, the available microcode, the setting of the 4798 CONFIG_RETPOLINE configuration option, and the 4799 compiler with which the kernel was built. 4800 4801 Selecting 'on' will also enable the mitigation 4802 against user space to user space task attacks. 4803 4804 Selecting 'off' will disable both the kernel and 4805 the user space protections. 4806 4807 Specific mitigations can also be selected manually: 4808 4809 retpoline - replace indirect branches 4810 retpoline,generic - google's original retpoline 4811 retpoline,amd - AMD-specific minimal thunk 4812 4813 Not specifying this option is equivalent to 4814 spectre_v2=auto. 4815 4816 spectre_v2_user= 4817 [X86] Control mitigation of Spectre variant 2 4818 (indirect branch speculation) vulnerability between 4819 user space tasks 4820 4821 on - Unconditionally enable mitigations. Is 4822 enforced by spectre_v2=on 4823 4824 off - Unconditionally disable mitigations. Is 4825 enforced by spectre_v2=off 4826 4827 prctl - Indirect branch speculation is enabled, 4828 but mitigation can be enabled via prctl 4829 per thread. The mitigation control state 4830 is inherited on fork. 4831 4832 prctl,ibpb 4833 - Like "prctl" above, but only STIBP is 4834 controlled per thread. IBPB is issued 4835 always when switching between different user 4836 space processes. 4837 4838 seccomp 4839 - Same as "prctl" above, but all seccomp 4840 threads will enable the mitigation unless 4841 they explicitly opt out. 4842 4843 seccomp,ibpb 4844 - Like "seccomp" above, but only STIBP is 4845 controlled per thread. IBPB is issued 4846 always when switching between different 4847 user space processes. 4848 4849 auto - Kernel selects the mitigation depending on 4850 the available CPU features and vulnerability. 4851 4852 Default mitigation: 4853 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4854 4855 Not specifying this option is equivalent to 4856 spectre_v2_user=auto. 4857 4858 spec_store_bypass_disable= 4859 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4860 (Speculative Store Bypass vulnerability) 4861 4862 Certain CPUs are vulnerable to an exploit against a 4863 a common industry wide performance optimization known 4864 as "Speculative Store Bypass" in which recent stores 4865 to the same memory location may not be observed by 4866 later loads during speculative execution. The idea 4867 is that such stores are unlikely and that they can 4868 be detected prior to instruction retirement at the 4869 end of a particular speculation execution window. 4870 4871 In vulnerable processors, the speculatively forwarded 4872 store can be used in a cache side channel attack, for 4873 example to read memory to which the attacker does not 4874 directly have access (e.g. inside sandboxed code). 4875 4876 This parameter controls whether the Speculative Store 4877 Bypass optimization is used. 4878 4879 On x86 the options are: 4880 4881 on - Unconditionally disable Speculative Store Bypass 4882 off - Unconditionally enable Speculative Store Bypass 4883 auto - Kernel detects whether the CPU model contains an 4884 implementation of Speculative Store Bypass and 4885 picks the most appropriate mitigation. If the 4886 CPU is not vulnerable, "off" is selected. If the 4887 CPU is vulnerable the default mitigation is 4888 architecture and Kconfig dependent. See below. 4889 prctl - Control Speculative Store Bypass per thread 4890 via prctl. Speculative Store Bypass is enabled 4891 for a process by default. The state of the control 4892 is inherited on fork. 4893 seccomp - Same as "prctl" above, but all seccomp threads 4894 will disable SSB unless they explicitly opt out. 4895 4896 Default mitigations: 4897 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4898 4899 On powerpc the options are: 4900 4901 on,auto - On Power8 and Power9 insert a store-forwarding 4902 barrier on kernel entry and exit. On Power7 4903 perform a software flush on kernel entry and 4904 exit. 4905 off - No action. 4906 4907 Not specifying this option is equivalent to 4908 spec_store_bypass_disable=auto. 4909 4910 spia_io_base= [HW,MTD] 4911 spia_fio_base= 4912 spia_pedr= 4913 spia_peddr= 4914 4915 split_lock_detect= 4916 [X86] Enable split lock detection 4917 4918 When enabled (and if hardware support is present), atomic 4919 instructions that access data across cache line 4920 boundaries will result in an alignment check exception. 4921 4922 off - not enabled 4923 4924 warn - the kernel will emit rate limited warnings 4925 about applications triggering the #AC 4926 exception. This mode is the default on CPUs 4927 that supports split lock detection. 4928 4929 fatal - the kernel will send SIGBUS to applications 4930 that trigger the #AC exception. 4931 4932 If an #AC exception is hit in the kernel or in 4933 firmware (i.e. not while executing in user mode) 4934 the kernel will oops in either "warn" or "fatal" 4935 mode. 4936 4937 srbds= [X86,INTEL] 4938 Control the Special Register Buffer Data Sampling 4939 (SRBDS) mitigation. 4940 4941 Certain CPUs are vulnerable to an MDS-like 4942 exploit which can leak bits from the random 4943 number generator. 4944 4945 By default, this issue is mitigated by 4946 microcode. However, the microcode fix can cause 4947 the RDRAND and RDSEED instructions to become 4948 much slower. Among other effects, this will 4949 result in reduced throughput from /dev/urandom. 4950 4951 The microcode mitigation can be disabled with 4952 the following option: 4953 4954 off: Disable mitigation and remove 4955 performance impact to RDRAND and RDSEED 4956 4957 srcutree.counter_wrap_check [KNL] 4958 Specifies how frequently to check for 4959 grace-period sequence counter wrap for the 4960 srcu_data structure's ->srcu_gp_seq_needed field. 4961 The greater the number of bits set in this kernel 4962 parameter, the less frequently counter wrap will 4963 be checked for. Note that the bottom two bits 4964 are ignored. 4965 4966 srcutree.exp_holdoff [KNL] 4967 Specifies how many nanoseconds must elapse 4968 since the end of the last SRCU grace period for 4969 a given srcu_struct until the next normal SRCU 4970 grace period will be considered for automatic 4971 expediting. Set to zero to disable automatic 4972 expediting. 4973 4974 ssbd= [ARM64,HW] 4975 Speculative Store Bypass Disable control 4976 4977 On CPUs that are vulnerable to the Speculative 4978 Store Bypass vulnerability and offer a 4979 firmware based mitigation, this parameter 4980 indicates how the mitigation should be used: 4981 4982 force-on: Unconditionally enable mitigation for 4983 for both kernel and userspace 4984 force-off: Unconditionally disable mitigation for 4985 for both kernel and userspace 4986 kernel: Always enable mitigation in the 4987 kernel, and offer a prctl interface 4988 to allow userspace to register its 4989 interest in being mitigated too. 4990 4991 stack_guard_gap= [MM] 4992 override the default stack gap protection. The value 4993 is in page units and it defines how many pages prior 4994 to (for stacks growing down) resp. after (for stacks 4995 growing up) the main stack are reserved for no other 4996 mapping. Default value is 256 pages. 4997 4998 stacktrace [FTRACE] 4999 Enabled the stack tracer on boot up. 5000 5001 stacktrace_filter=[function-list] 5002 [FTRACE] Limit the functions that the stack tracer 5003 will trace at boot up. function-list is a comma separated 5004 list of functions. This list can be changed at run 5005 time by the stack_trace_filter file in the debugfs 5006 tracing directory. Note, this enables stack tracing 5007 and the stacktrace above is not needed. 5008 5009 sti= [PARISC,HW] 5010 Format: <num> 5011 Set the STI (builtin display/keyboard on the HP-PARISC 5012 machines) console (graphic card) which should be used 5013 as the initial boot-console. 5014 See also comment in drivers/video/console/sticore.c. 5015 5016 sti_font= [HW] 5017 See comment in drivers/video/console/sticore.c. 5018 5019 stifb= [HW] 5020 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5021 5022 sunrpc.min_resvport= 5023 sunrpc.max_resvport= 5024 [NFS,SUNRPC] 5025 SunRPC servers often require that client requests 5026 originate from a privileged port (i.e. a port in the 5027 range 0 < portnr < 1024). 5028 An administrator who wishes to reserve some of these 5029 ports for other uses may adjust the range that the 5030 kernel's sunrpc client considers to be privileged 5031 using these two parameters to set the minimum and 5032 maximum port values. 5033 5034 sunrpc.svc_rpc_per_connection_limit= 5035 [NFS,SUNRPC] 5036 Limit the number of requests that the server will 5037 process in parallel from a single connection. 5038 The default value is 0 (no limit). 5039 5040 sunrpc.pool_mode= 5041 [NFS] 5042 Control how the NFS server code allocates CPUs to 5043 service thread pools. Depending on how many NICs 5044 you have and where their interrupts are bound, this 5045 option will affect which CPUs will do NFS serving. 5046 Note: this parameter cannot be changed while the 5047 NFS server is running. 5048 5049 auto the server chooses an appropriate mode 5050 automatically using heuristics 5051 global a single global pool contains all CPUs 5052 percpu one pool for each CPU 5053 pernode one pool for each NUMA node (equivalent 5054 to global on non-NUMA machines) 5055 5056 sunrpc.tcp_slot_table_entries= 5057 sunrpc.udp_slot_table_entries= 5058 [NFS,SUNRPC] 5059 Sets the upper limit on the number of simultaneous 5060 RPC calls that can be sent from the client to a 5061 server. Increasing these values may allow you to 5062 improve throughput, but will also increase the 5063 amount of memory reserved for use by the client. 5064 5065 suspend.pm_test_delay= 5066 [SUSPEND] 5067 Sets the number of seconds to remain in a suspend test 5068 mode before resuming the system (see 5069 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5070 is set. Default value is 5. 5071 5072 svm= [PPC] 5073 Format: { on | off | y | n | 1 | 0 } 5074 This parameter controls use of the Protected 5075 Execution Facility on pSeries. 5076 5077 swapaccount=[0|1] 5078 [KNL] Enable accounting of swap in memory resource 5079 controller if no parameter or 1 is given or disable 5080 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5081 5082 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5083 Format: { <int> | force | noforce } 5084 <int> -- Number of I/O TLB slabs 5085 force -- force using of bounce buffers even if they 5086 wouldn't be automatically used by the kernel 5087 noforce -- Never use bounce buffers (for debugging) 5088 5089 switches= [HW,M68k] 5090 5091 sysctl.*= [KNL] 5092 Set a sysctl parameter, right before loading the init 5093 process, as if the value was written to the respective 5094 /proc/sys/... file. Both '.' and '/' are recognized as 5095 separators. Unrecognized parameters and invalid values 5096 are reported in the kernel log. Sysctls registered 5097 later by a loaded module cannot be set this way. 5098 Example: sysctl.vm.swappiness=40 5099 5100 sysfs.deprecated=0|1 [KNL] 5101 Enable/disable old style sysfs layout for old udev 5102 on older distributions. When this option is enabled 5103 very new udev will not work anymore. When this option 5104 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5105 in older udev will not work anymore. 5106 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5107 the kernel configuration. 5108 5109 sysrq_always_enabled 5110 [KNL] 5111 Ignore sysrq setting - this boot parameter will 5112 neutralize any effect of /proc/sys/kernel/sysrq. 5113 Useful for debugging. 5114 5115 tcpmhash_entries= [KNL,NET] 5116 Set the number of tcp_metrics_hash slots. 5117 Default value is 8192 or 16384 depending on total 5118 ram pages. This is used to specify the TCP metrics 5119 cache size. See Documentation/networking/ip-sysctl.rst 5120 "tcp_no_metrics_save" section for more details. 5121 5122 tdfx= [HW,DRM] 5123 5124 test_suspend= [SUSPEND][,N] 5125 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5126 standby suspend) or "freeze" (for suspend type freeze) 5127 as the system sleep state during system startup with 5128 the optional capability to repeat N number of times. 5129 The system is woken from this state using a 5130 wakeup-capable RTC alarm. 5131 5132 thash_entries= [KNL,NET] 5133 Set number of hash buckets for TCP connection 5134 5135 thermal.act= [HW,ACPI] 5136 -1: disable all active trip points in all thermal zones 5137 <degrees C>: override all lowest active trip points 5138 5139 thermal.crt= [HW,ACPI] 5140 -1: disable all critical trip points in all thermal zones 5141 <degrees C>: override all critical trip points 5142 5143 thermal.nocrt= [HW,ACPI] 5144 Set to disable actions on ACPI thermal zone 5145 critical and hot trip points. 5146 5147 thermal.off= [HW,ACPI] 5148 1: disable ACPI thermal control 5149 5150 thermal.psv= [HW,ACPI] 5151 -1: disable all passive trip points 5152 <degrees C>: override all passive trip points to this 5153 value 5154 5155 thermal.tzp= [HW,ACPI] 5156 Specify global default ACPI thermal zone polling rate 5157 <deci-seconds>: poll all this frequency 5158 0: no polling (default) 5159 5160 threadirqs [KNL] 5161 Force threading of all interrupt handlers except those 5162 marked explicitly IRQF_NO_THREAD. 5163 5164 topology= [S390] 5165 Format: {off | on} 5166 Specify if the kernel should make use of the cpu 5167 topology information if the hardware supports this. 5168 The scheduler will make use of this information and 5169 e.g. base its process migration decisions on it. 5170 Default is on. 5171 5172 topology_updates= [KNL, PPC, NUMA] 5173 Format: {off} 5174 Specify if the kernel should ignore (off) 5175 topology updates sent by the hypervisor to this 5176 LPAR. 5177 5178 torture.disable_onoff_at_boot= [KNL] 5179 Prevent the CPU-hotplug component of torturing 5180 until after init has spawned. 5181 5182 torture.ftrace_dump_at_shutdown= [KNL] 5183 Dump the ftrace buffer at torture-test shutdown, 5184 even if there were no errors. This can be a 5185 very costly operation when many torture tests 5186 are running concurrently, especially on systems 5187 with rotating-rust storage. 5188 5189 tp720= [HW,PS2] 5190 5191 tpm_suspend_pcr=[HW,TPM] 5192 Format: integer pcr id 5193 Specify that at suspend time, the tpm driver 5194 should extend the specified pcr with zeros, 5195 as a workaround for some chips which fail to 5196 flush the last written pcr on TPM_SaveState. 5197 This will guarantee that all the other pcrs 5198 are saved. 5199 5200 trace_buf_size=nn[KMG] 5201 [FTRACE] will set tracing buffer size on each cpu. 5202 5203 trace_event=[event-list] 5204 [FTRACE] Set and start specified trace events in order 5205 to facilitate early boot debugging. The event-list is a 5206 comma separated list of trace events to enable. See 5207 also Documentation/trace/events.rst 5208 5209 trace_options=[option-list] 5210 [FTRACE] Enable or disable tracer options at boot. 5211 The option-list is a comma delimited list of options 5212 that can be enabled or disabled just as if you were 5213 to echo the option name into 5214 5215 /sys/kernel/debug/tracing/trace_options 5216 5217 For example, to enable stacktrace option (to dump the 5218 stack trace of each event), add to the command line: 5219 5220 trace_options=stacktrace 5221 5222 See also Documentation/trace/ftrace.rst "trace options" 5223 section. 5224 5225 tp_printk[FTRACE] 5226 Have the tracepoints sent to printk as well as the 5227 tracing ring buffer. This is useful for early boot up 5228 where the system hangs or reboots and does not give the 5229 option for reading the tracing buffer or performing a 5230 ftrace_dump_on_oops. 5231 5232 To turn off having tracepoints sent to printk, 5233 echo 0 > /proc/sys/kernel/tracepoint_printk 5234 Note, echoing 1 into this file without the 5235 tracepoint_printk kernel cmdline option has no effect. 5236 5237 ** CAUTION ** 5238 5239 Having tracepoints sent to printk() and activating high 5240 frequency tracepoints such as irq or sched, can cause 5241 the system to live lock. 5242 5243 traceoff_on_warning 5244 [FTRACE] enable this option to disable tracing when a 5245 warning is hit. This turns off "tracing_on". Tracing can 5246 be enabled again by echoing '1' into the "tracing_on" 5247 file located in /sys/kernel/debug/tracing/ 5248 5249 This option is useful, as it disables the trace before 5250 the WARNING dump is called, which prevents the trace to 5251 be filled with content caused by the warning output. 5252 5253 This option can also be set at run time via the sysctl 5254 option: kernel/traceoff_on_warning 5255 5256 transparent_hugepage= 5257 [KNL] 5258 Format: [always|madvise|never] 5259 Can be used to control the default behavior of the system 5260 with respect to transparent hugepages. 5261 See Documentation/admin-guide/mm/transhuge.rst 5262 for more details. 5263 5264 tsc= Disable clocksource stability checks for TSC. 5265 Format: <string> 5266 [x86] reliable: mark tsc clocksource as reliable, this 5267 disables clocksource verification at runtime, as well 5268 as the stability checks done at bootup. Used to enable 5269 high-resolution timer mode on older hardware, and in 5270 virtualized environment. 5271 [x86] noirqtime: Do not use TSC to do irq accounting. 5272 Used to run time disable IRQ_TIME_ACCOUNTING on any 5273 platforms where RDTSC is slow and this accounting 5274 can add overhead. 5275 [x86] unstable: mark the TSC clocksource as unstable, this 5276 marks the TSC unconditionally unstable at bootup and 5277 avoids any further wobbles once the TSC watchdog notices. 5278 [x86] nowatchdog: disable clocksource watchdog. Used 5279 in situations with strict latency requirements (where 5280 interruptions from clocksource watchdog are not 5281 acceptable). 5282 5283 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5284 value instead. Useful when the early TSC frequency discovery 5285 procedure is not reliable, such as on overclocked systems 5286 with CPUID.16h support and partial CPUID.15h support. 5287 Format: <unsigned int> 5288 5289 tsx= [X86] Control Transactional Synchronization 5290 Extensions (TSX) feature in Intel processors that 5291 support TSX control. 5292 5293 This parameter controls the TSX feature. The options are: 5294 5295 on - Enable TSX on the system. Although there are 5296 mitigations for all known security vulnerabilities, 5297 TSX has been known to be an accelerator for 5298 several previous speculation-related CVEs, and 5299 so there may be unknown security risks associated 5300 with leaving it enabled. 5301 5302 off - Disable TSX on the system. (Note that this 5303 option takes effect only on newer CPUs which are 5304 not vulnerable to MDS, i.e., have 5305 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5306 the new IA32_TSX_CTRL MSR through a microcode 5307 update. This new MSR allows for the reliable 5308 deactivation of the TSX functionality.) 5309 5310 auto - Disable TSX if X86_BUG_TAA is present, 5311 otherwise enable TSX on the system. 5312 5313 Not specifying this option is equivalent to tsx=off. 5314 5315 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5316 for more details. 5317 5318 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5319 Abort (TAA) vulnerability. 5320 5321 Similar to Micro-architectural Data Sampling (MDS) 5322 certain CPUs that support Transactional 5323 Synchronization Extensions (TSX) are vulnerable to an 5324 exploit against CPU internal buffers which can forward 5325 information to a disclosure gadget under certain 5326 conditions. 5327 5328 In vulnerable processors, the speculatively forwarded 5329 data can be used in a cache side channel attack, to 5330 access data to which the attacker does not have direct 5331 access. 5332 5333 This parameter controls the TAA mitigation. The 5334 options are: 5335 5336 full - Enable TAA mitigation on vulnerable CPUs 5337 if TSX is enabled. 5338 5339 full,nosmt - Enable TAA mitigation and disable SMT on 5340 vulnerable CPUs. If TSX is disabled, SMT 5341 is not disabled because CPU is not 5342 vulnerable to cross-thread TAA attacks. 5343 off - Unconditionally disable TAA mitigation 5344 5345 On MDS-affected machines, tsx_async_abort=off can be 5346 prevented by an active MDS mitigation as both vulnerabilities 5347 are mitigated with the same mechanism so in order to disable 5348 this mitigation, you need to specify mds=off too. 5349 5350 Not specifying this option is equivalent to 5351 tsx_async_abort=full. On CPUs which are MDS affected 5352 and deploy MDS mitigation, TAA mitigation is not 5353 required and doesn't provide any additional 5354 mitigation. 5355 5356 For details see: 5357 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5358 5359 turbografx.map[2|3]= [HW,JOY] 5360 TurboGraFX parallel port interface 5361 Format: 5362 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5363 See also Documentation/input/devices/joystick-parport.rst 5364 5365 udbg-immortal [PPC] When debugging early kernel crashes that 5366 happen after console_init() and before a proper 5367 console driver takes over, this boot options might 5368 help "seeing" what's going on. 5369 5370 uhash_entries= [KNL,NET] 5371 Set number of hash buckets for UDP/UDP-Lite connections 5372 5373 uhci-hcd.ignore_oc= 5374 [USB] Ignore overcurrent events (default N). 5375 Some badly-designed motherboards generate lots of 5376 bogus events, for ports that aren't wired to 5377 anything. Set this parameter to avoid log spamming. 5378 Note that genuine overcurrent events won't be 5379 reported either. 5380 5381 unknown_nmi_panic 5382 [X86] Cause panic on unknown NMI. 5383 5384 usbcore.authorized_default= 5385 [USB] Default USB device authorization: 5386 (default -1 = authorized except for wireless USB, 5387 0 = not authorized, 1 = authorized, 2 = authorized 5388 if device connected to internal port) 5389 5390 usbcore.autosuspend= 5391 [USB] The autosuspend time delay (in seconds) used 5392 for newly-detected USB devices (default 2). This 5393 is the time required before an idle device will be 5394 autosuspended. Devices for which the delay is set 5395 to a negative value won't be autosuspended at all. 5396 5397 usbcore.usbfs_snoop= 5398 [USB] Set to log all usbfs traffic (default 0 = off). 5399 5400 usbcore.usbfs_snoop_max= 5401 [USB] Maximum number of bytes to snoop in each URB 5402 (default = 65536). 5403 5404 usbcore.blinkenlights= 5405 [USB] Set to cycle leds on hubs (default 0 = off). 5406 5407 usbcore.old_scheme_first= 5408 [USB] Start with the old device initialization 5409 scheme (default 0 = off). 5410 5411 usbcore.usbfs_memory_mb= 5412 [USB] Memory limit (in MB) for buffers allocated by 5413 usbfs (default = 16, 0 = max = 2047). 5414 5415 usbcore.use_both_schemes= 5416 [USB] Try the other device initialization scheme 5417 if the first one fails (default 1 = enabled). 5418 5419 usbcore.initial_descriptor_timeout= 5420 [USB] Specifies timeout for the initial 64-byte 5421 USB_REQ_GET_DESCRIPTOR request in milliseconds 5422 (default 5000 = 5.0 seconds). 5423 5424 usbcore.nousb [USB] Disable the USB subsystem 5425 5426 usbcore.quirks= 5427 [USB] A list of quirk entries to augment the built-in 5428 usb core quirk list. List entries are separated by 5429 commas. Each entry has the form 5430 VendorID:ProductID:Flags. The IDs are 4-digit hex 5431 numbers and Flags is a set of letters. Each letter 5432 will change the built-in quirk; setting it if it is 5433 clear and clearing it if it is set. The letters have 5434 the following meanings: 5435 a = USB_QUIRK_STRING_FETCH_255 (string 5436 descriptors must not be fetched using 5437 a 255-byte read); 5438 b = USB_QUIRK_RESET_RESUME (device can't resume 5439 correctly so reset it instead); 5440 c = USB_QUIRK_NO_SET_INTF (device can't handle 5441 Set-Interface requests); 5442 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5443 handle its Configuration or Interface 5444 strings); 5445 e = USB_QUIRK_RESET (device can't be reset 5446 (e.g morph devices), don't use reset); 5447 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5448 more interface descriptions than the 5449 bNumInterfaces count, and can't handle 5450 talking to these interfaces); 5451 g = USB_QUIRK_DELAY_INIT (device needs a pause 5452 during initialization, after we read 5453 the device descriptor); 5454 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5455 high speed and super speed interrupt 5456 endpoints, the USB 2.0 and USB 3.0 spec 5457 require the interval in microframes (1 5458 microframe = 125 microseconds) to be 5459 calculated as interval = 2 ^ 5460 (bInterval-1). 5461 Devices with this quirk report their 5462 bInterval as the result of this 5463 calculation instead of the exponent 5464 variable used in the calculation); 5465 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5466 handle device_qualifier descriptor 5467 requests); 5468 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5469 generates spurious wakeup, ignore 5470 remote wakeup capability); 5471 k = USB_QUIRK_NO_LPM (device can't handle Link 5472 Power Management); 5473 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5474 (Device reports its bInterval as linear 5475 frames instead of the USB 2.0 5476 calculation); 5477 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5478 to be disconnected before suspend to 5479 prevent spurious wakeup); 5480 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5481 pause after every control message); 5482 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5483 delay after resetting its port); 5484 Example: quirks=0781:5580:bk,0a5c:5834:gij 5485 5486 usbhid.mousepoll= 5487 [USBHID] The interval which mice are to be polled at. 5488 5489 usbhid.jspoll= 5490 [USBHID] The interval which joysticks are to be polled at. 5491 5492 usbhid.kbpoll= 5493 [USBHID] The interval which keyboards are to be polled at. 5494 5495 usb-storage.delay_use= 5496 [UMS] The delay in seconds before a new device is 5497 scanned for Logical Units (default 1). 5498 5499 usb-storage.quirks= 5500 [UMS] A list of quirks entries to supplement or 5501 override the built-in unusual_devs list. List 5502 entries are separated by commas. Each entry has 5503 the form VID:PID:Flags where VID and PID are Vendor 5504 and Product ID values (4-digit hex numbers) and 5505 Flags is a set of characters, each corresponding 5506 to a common usb-storage quirk flag as follows: 5507 a = SANE_SENSE (collect more than 18 bytes 5508 of sense data, not on uas); 5509 b = BAD_SENSE (don't collect more than 18 5510 bytes of sense data, not on uas); 5511 c = FIX_CAPACITY (decrease the reported 5512 device capacity by one sector); 5513 d = NO_READ_DISC_INFO (don't use 5514 READ_DISC_INFO command, not on uas); 5515 e = NO_READ_CAPACITY_16 (don't use 5516 READ_CAPACITY_16 command); 5517 f = NO_REPORT_OPCODES (don't use report opcodes 5518 command, uas only); 5519 g = MAX_SECTORS_240 (don't transfer more than 5520 240 sectors at a time, uas only); 5521 h = CAPACITY_HEURISTICS (decrease the 5522 reported device capacity by one 5523 sector if the number is odd); 5524 i = IGNORE_DEVICE (don't bind to this 5525 device); 5526 j = NO_REPORT_LUNS (don't use report luns 5527 command, uas only); 5528 l = NOT_LOCKABLE (don't try to lock and 5529 unlock ejectable media, not on uas); 5530 m = MAX_SECTORS_64 (don't transfer more 5531 than 64 sectors = 32 KB at a time, 5532 not on uas); 5533 n = INITIAL_READ10 (force a retry of the 5534 initial READ(10) command, not on uas); 5535 o = CAPACITY_OK (accept the capacity 5536 reported by the device, not on uas); 5537 p = WRITE_CACHE (the device cache is ON 5538 by default, not on uas); 5539 r = IGNORE_RESIDUE (the device reports 5540 bogus residue values, not on uas); 5541 s = SINGLE_LUN (the device has only one 5542 Logical Unit); 5543 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5544 commands, uas only); 5545 u = IGNORE_UAS (don't bind to the uas driver); 5546 w = NO_WP_DETECT (don't test whether the 5547 medium is write-protected). 5548 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5549 even if the device claims no cache, 5550 not on uas) 5551 Example: quirks=0419:aaf5:rl,0421:0433:rc 5552 5553 user_debug= [KNL,ARM] 5554 Format: <int> 5555 See arch/arm/Kconfig.debug help text. 5556 1 - undefined instruction events 5557 2 - system calls 5558 4 - invalid data aborts 5559 8 - SIGSEGV faults 5560 16 - SIGBUS faults 5561 Example: user_debug=31 5562 5563 userpte= 5564 [X86] Flags controlling user PTE allocations. 5565 5566 nohigh = do not allocate PTE pages in 5567 HIGHMEM regardless of setting 5568 of CONFIG_HIGHPTE. 5569 5570 vdso= [X86,SH] 5571 On X86_32, this is an alias for vdso32=. Otherwise: 5572 5573 vdso=1: enable VDSO (the default) 5574 vdso=0: disable VDSO mapping 5575 5576 vdso32= [X86] Control the 32-bit vDSO 5577 vdso32=1: enable 32-bit VDSO 5578 vdso32=0 or vdso32=2: disable 32-bit VDSO 5579 5580 See the help text for CONFIG_COMPAT_VDSO for more 5581 details. If CONFIG_COMPAT_VDSO is set, the default is 5582 vdso32=0; otherwise, the default is vdso32=1. 5583 5584 For compatibility with older kernels, vdso32=2 is an 5585 alias for vdso32=0. 5586 5587 Try vdso32=0 if you encounter an error that says: 5588 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5589 5590 vector= [IA-64,SMP] 5591 vector=percpu: enable percpu vector domain 5592 5593 video= [FB] Frame buffer configuration 5594 See Documentation/fb/modedb.rst. 5595 5596 video.brightness_switch_enabled= [0,1] 5597 If set to 1, on receiving an ACPI notify event 5598 generated by hotkey, video driver will adjust brightness 5599 level and then send out the event to user space through 5600 the allocated input device; If set to 0, video driver 5601 will only send out the event without touching backlight 5602 brightness level. 5603 default: 1 5604 5605 virtio_mmio.device= 5606 [VMMIO] Memory mapped virtio (platform) device. 5607 5608 <size>@<baseaddr>:<irq>[:<id>] 5609 where: 5610 <size> := size (can use standard suffixes 5611 like K, M and G) 5612 <baseaddr> := physical base address 5613 <irq> := interrupt number (as passed to 5614 request_irq()) 5615 <id> := (optional) platform device id 5616 example: 5617 virtio_mmio.device=1K@0x100b0000:48:7 5618 5619 Can be used multiple times for multiple devices. 5620 5621 vga= [BOOT,X86-32] Select a particular video mode 5622 See Documentation/x86/boot.rst and 5623 Documentation/admin-guide/svga.rst. 5624 Use vga=ask for menu. 5625 This is actually a boot loader parameter; the value is 5626 passed to the kernel using a special protocol. 5627 5628 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5629 May slow down system boot speed, especially when 5630 enabled on systems with a large amount of memory. 5631 All options are enabled by default, and this 5632 interface is meant to allow for selectively 5633 enabling or disabling specific virtual memory 5634 debugging features. 5635 5636 Available options are: 5637 P Enable page structure init time poisoning 5638 - Disable all of the above options 5639 5640 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5641 size of <nn>. This can be used to increase the 5642 minimum size (128MB on x86). It can also be used to 5643 decrease the size and leave more room for directly 5644 mapped kernel RAM. 5645 5646 vmcp_cma=nn[MG] [KNL,S390] 5647 Sets the memory size reserved for contiguous memory 5648 allocations for the vmcp device driver. 5649 5650 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5651 Format: <command> 5652 5653 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5654 Format: <command> 5655 5656 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5657 Format: <command> 5658 5659 vsyscall= [X86-64] 5660 Controls the behavior of vsyscalls (i.e. calls to 5661 fixed addresses of 0xffffffffff600x00 from legacy 5662 code). Most statically-linked binaries and older 5663 versions of glibc use these calls. Because these 5664 functions are at fixed addresses, they make nice 5665 targets for exploits that can control RIP. 5666 5667 emulate [default] Vsyscalls turn into traps and are 5668 emulated reasonably safely. The vsyscall 5669 page is readable. 5670 5671 xonly Vsyscalls turn into traps and are 5672 emulated reasonably safely. The vsyscall 5673 page is not readable. 5674 5675 none Vsyscalls don't work at all. This makes 5676 them quite hard to use for exploits but 5677 might break your system. 5678 5679 vt.color= [VT] Default text color. 5680 Format: 0xYX, X = foreground, Y = background. 5681 Default: 0x07 = light gray on black. 5682 5683 vt.cur_default= [VT] Default cursor shape. 5684 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5685 the parameters of the <Esc>[?A;B;Cc escape sequence; 5686 see VGA-softcursor.txt. Default: 2 = underline. 5687 5688 vt.default_blu= [VT] 5689 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5690 Change the default blue palette of the console. 5691 This is a 16-member array composed of values 5692 ranging from 0-255. 5693 5694 vt.default_grn= [VT] 5695 Format: <green0>,<green1>,<green2>,...,<green15> 5696 Change the default green palette of the console. 5697 This is a 16-member array composed of values 5698 ranging from 0-255. 5699 5700 vt.default_red= [VT] 5701 Format: <red0>,<red1>,<red2>,...,<red15> 5702 Change the default red palette of the console. 5703 This is a 16-member array composed of values 5704 ranging from 0-255. 5705 5706 vt.default_utf8= 5707 [VT] 5708 Format=<0|1> 5709 Set system-wide default UTF-8 mode for all tty's. 5710 Default is 1, i.e. UTF-8 mode is enabled for all 5711 newly opened terminals. 5712 5713 vt.global_cursor_default= 5714 [VT] 5715 Format=<-1|0|1> 5716 Set system-wide default for whether a cursor 5717 is shown on new VTs. Default is -1, 5718 i.e. cursors will be created by default unless 5719 overridden by individual drivers. 0 will hide 5720 cursors, 1 will display them. 5721 5722 vt.italic= [VT] Default color for italic text; 0-15. 5723 Default: 2 = green. 5724 5725 vt.underline= [VT] Default color for underlined text; 0-15. 5726 Default: 3 = cyan. 5727 5728 watchdog timers [HW,WDT] For information on watchdog timers, 5729 see Documentation/watchdog/watchdog-parameters.rst 5730 or other driver-specific files in the 5731 Documentation/watchdog/ directory. 5732 5733 watchdog_thresh= 5734 [KNL] 5735 Set the hard lockup detector stall duration 5736 threshold in seconds. The soft lockup detector 5737 threshold is set to twice the value. A value of 0 5738 disables both lockup detectors. Default is 10 5739 seconds. 5740 5741 workqueue.watchdog_thresh= 5742 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5743 warn stall conditions and dump internal state to 5744 help debugging. 0 disables workqueue stall 5745 detection; otherwise, it's the stall threshold 5746 duration in seconds. The default value is 30 and 5747 it can be updated at runtime by writing to the 5748 corresponding sysfs file. 5749 5750 workqueue.disable_numa 5751 By default, all work items queued to unbound 5752 workqueues are affine to the NUMA nodes they're 5753 issued on, which results in better behavior in 5754 general. If NUMA affinity needs to be disabled for 5755 whatever reason, this option can be used. Note 5756 that this also can be controlled per-workqueue for 5757 workqueues visible under /sys/bus/workqueue/. 5758 5759 workqueue.power_efficient 5760 Per-cpu workqueues are generally preferred because 5761 they show better performance thanks to cache 5762 locality; unfortunately, per-cpu workqueues tend to 5763 be more power hungry than unbound workqueues. 5764 5765 Enabling this makes the per-cpu workqueues which 5766 were observed to contribute significantly to power 5767 consumption unbound, leading to measurably lower 5768 power usage at the cost of small performance 5769 overhead. 5770 5771 The default value of this parameter is determined by 5772 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5773 5774 workqueue.debug_force_rr_cpu 5775 Workqueue used to implicitly guarantee that work 5776 items queued without explicit CPU specified are put 5777 on the local CPU. This guarantee is no longer true 5778 and while local CPU is still preferred work items 5779 may be put on foreign CPUs. This debug option 5780 forces round-robin CPU selection to flush out 5781 usages which depend on the now broken guarantee. 5782 When enabled, memory and cache locality will be 5783 impacted. 5784 5785 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5786 default x2apic cluster mode on platforms 5787 supporting x2apic. 5788 5789 x86_intel_mid_timer= [X86-32,APBT] 5790 Choose timer option for x86 Intel MID platform. 5791 Two valid options are apbt timer only and lapic timer 5792 plus one apbt timer for broadcast timer. 5793 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5794 5795 xen_512gb_limit [KNL,X86-64,XEN] 5796 Restricts the kernel running paravirtualized under Xen 5797 to use only up to 512 GB of RAM. The reason to do so is 5798 crash analysis tools and Xen tools for doing domain 5799 save/restore/migration must be enabled to handle larger 5800 domains. 5801 5802 xen_emul_unplug= [HW,X86,XEN] 5803 Unplug Xen emulated devices 5804 Format: [unplug0,][unplug1] 5805 ide-disks -- unplug primary master IDE devices 5806 aux-ide-disks -- unplug non-primary-master IDE devices 5807 nics -- unplug network devices 5808 all -- unplug all emulated devices (NICs and IDE disks) 5809 unnecessary -- unplugging emulated devices is 5810 unnecessary even if the host did not respond to 5811 the unplug protocol 5812 never -- do not unplug even if version check succeeds 5813 5814 xen_legacy_crash [X86,XEN] 5815 Crash from Xen panic notifier, without executing late 5816 panic() code such as dumping handler. 5817 5818 xen_nopvspin [X86,XEN] 5819 Disables the qspinlock slowpath using Xen PV optimizations. 5820 This parameter is obsoleted by "nopvspin" parameter, which 5821 has equivalent effect for XEN platform. 5822 5823 xen_nopv [X86] 5824 Disables the PV optimizations forcing the HVM guest to 5825 run as generic HVM guest with no PV drivers. 5826 This option is obsoleted by the "nopv" option, which 5827 has equivalent effect for XEN platform. 5828 5829 xen_scrub_pages= [XEN] 5830 Boolean option to control scrubbing pages before giving them back 5831 to Xen, for use by other domains. Can be also changed at runtime 5832 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5833 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5834 5835 xen_timer_slop= [X86-64,XEN] 5836 Set the timer slop (in nanoseconds) for the virtual Xen 5837 timers (default is 100000). This adjusts the minimum 5838 delta of virtualized Xen timers, where lower values 5839 improve timer resolution at the expense of processing 5840 more timer interrupts. 5841 5842 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5843 Disables the PV optimizations forcing the guest to run 5844 as generic guest with no PV drivers. Currently support 5845 XEN HVM, KVM, HYPER_V and VMWARE guest. 5846 5847 nopvspin [X86,XEN,KVM] 5848 Disables the qspinlock slow path using PV optimizations 5849 which allow the hypervisor to 'idle' the guest on lock 5850 contention. 5851 5852 xirc2ps_cs= [NET,PCMCIA] 5853 Format: 5854 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5855 5856 xive= [PPC] 5857 By default on POWER9 and above, the kernel will 5858 natively use the XIVE interrupt controller. This option 5859 allows the fallback firmware mode to be used: 5860 5861 off Fallback to firmware control of XIVE interrupt 5862 controller on both pseries and powernv 5863 platforms. Only useful on POWER9 and above. 5864 5865 xhci-hcd.quirks [USB,KNL] 5866 A hex value specifying bitmask with supplemental xhci 5867 host controller quirks. Meaning of each bit can be 5868 consulted in header drivers/usb/host/xhci.h. 5869 5870 xmon [PPC] 5871 Format: { early | on | rw | ro | off } 5872 Controls if xmon debugger is enabled. Default is off. 5873 Passing only "xmon" is equivalent to "xmon=early". 5874 early Call xmon as early as possible on boot; xmon 5875 debugger is called from setup_arch(). 5876 on xmon debugger hooks will be installed so xmon 5877 is only called on a kernel crash. Default mode, 5878 i.e. either "ro" or "rw" mode, is controlled 5879 with CONFIG_XMON_DEFAULT_RO_MODE. 5880 rw xmon debugger hooks will be installed so xmon 5881 is called only on a kernel crash, mode is write, 5882 meaning SPR registers, memory and, other data 5883 can be written using xmon commands. 5884 ro same as "rw" option above but SPR registers, 5885 memory, and other data can't be written using 5886 xmon commands. 5887 off xmon is disabled. 5888