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.txt. 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/media/v4l-drivers/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 [ARM,X86,KNL] 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.txt 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.txt. 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 cpu_init_udelay=N 707 [X86] Delay for N microsec between assert and de-assert 708 of APIC INIT to start processors. This delay occurs 709 on every CPU online, such as boot, and resume from suspend. 710 Default: 10000 711 712 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 713 Format: 714 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 715 716 crashkernel=size[KMG][@offset[KMG]] 717 [KNL] Using kexec, Linux can switch to a 'crash kernel' 718 upon panic. This parameter reserves the physical 719 memory region [offset, offset + size] for that kernel 720 image. If '@offset' is omitted, then a suitable offset 721 is selected automatically. 722 [KNL, x86_64] select a region under 4G first, and 723 fall back to reserve region above 4G when '@offset' 724 hasn't been specified. 725 See Documentation/admin-guide/kdump/kdump.rst for further details. 726 727 crashkernel=range1:size1[,range2:size2,...][@offset] 728 [KNL] Same as above, but depends on the memory 729 in the running system. The syntax of range is 730 start-[end] where start and end are both 731 a memory unit (amount[KMG]). See also 732 Documentation/admin-guide/kdump/kdump.rst for an example. 733 734 crashkernel=size[KMG],high 735 [KNL, x86_64] range could be above 4G. Allow kernel 736 to allocate physical memory region from top, so could 737 be above 4G if system have more than 4G ram installed. 738 Otherwise memory region will be allocated below 4G, if 739 available. 740 It will be ignored if crashkernel=X is specified. 741 crashkernel=size[KMG],low 742 [KNL, x86_64] range under 4G. When crashkernel=X,high 743 is passed, kernel could allocate physical memory region 744 above 4G, that cause second kernel crash on system 745 that require some amount of low memory, e.g. swiotlb 746 requires at least 64M+32K low memory, also enough extra 747 low memory is needed to make sure DMA buffers for 32-bit 748 devices won't run out. Kernel would try to allocate at 749 at least 256M below 4G automatically. 750 This one let user to specify own low range under 4G 751 for second kernel instead. 752 0: to disable low allocation. 753 It will be ignored when crashkernel=X,high is not used 754 or memory reserved is below 4G. 755 756 cryptomgr.notests 757 [KNL] Disable crypto self-tests 758 759 cs89x0_dma= [HW,NET] 760 Format: <dma> 761 762 cs89x0_media= [HW,NET] 763 Format: { rj45 | aui | bnc } 764 765 dasd= [HW,NET] 766 See header of drivers/s390/block/dasd_devmap.c. 767 768 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 769 (one device per port) 770 Format: <port#>,<type> 771 See also Documentation/input/devices/joystick-parport.rst 772 773 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 774 time. See 775 Documentation/admin-guide/dynamic-debug-howto.rst for 776 details. Deprecated, see dyndbg. 777 778 debug [KNL] Enable kernel debugging (events log level). 779 780 debug_boot_weak_hash 781 [KNL] Enable printing [hashed] pointers early in the 782 boot sequence. If enabled, we use a weak hash instead 783 of siphash to hash pointers. Use this option if you are 784 seeing instances of '(___ptrval___)') and need to see a 785 value (hashed pointer) instead. Cryptographically 786 insecure, please do not use on production kernels. 787 788 debug_locks_verbose= 789 [KNL] verbose self-tests 790 Format=<0|1> 791 Print debugging info while doing the locking API 792 self-tests. 793 We default to 0 (no extra messages), setting it to 794 1 will print _a lot_ more information - normally 795 only useful to kernel developers. 796 797 debug_objects [KNL] Enable object debugging 798 799 no_debug_objects 800 [KNL] Disable object debugging 801 802 debug_guardpage_minorder= 803 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 804 parameter allows control of the order of pages that will 805 be intentionally kept free (and hence protected) by the 806 buddy allocator. Bigger value increase the probability 807 of catching random memory corruption, but reduce the 808 amount of memory for normal system use. The maximum 809 possible value is MAX_ORDER/2. Setting this parameter 810 to 1 or 2 should be enough to identify most random 811 memory corruption problems caused by bugs in kernel or 812 driver code when a CPU writes to (or reads from) a 813 random memory location. Note that there exists a class 814 of memory corruptions problems caused by buggy H/W or 815 F/W or by drivers badly programing DMA (basically when 816 memory is written at bus level and the CPU MMU is 817 bypassed) which are not detectable by 818 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 819 tracking down these problems. 820 821 debug_pagealloc= 822 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 823 enables the feature at boot time. By default, it is 824 disabled and the system will work mostly the same as a 825 kernel built without CONFIG_DEBUG_PAGEALLOC. 826 Note: to get most of debug_pagealloc error reports, it's 827 useful to also enable the page_owner functionality. 828 on: enable the feature 829 830 debugpat [X86] Enable PAT debugging 831 832 decnet.addr= [HW,NET] 833 Format: <area>[,<node>] 834 See also Documentation/networking/decnet.txt. 835 836 default_hugepagesz= 837 [same as hugepagesz=] The size of the default 838 HugeTLB page size. This is the size represented by 839 the legacy /proc/ hugepages APIs, used for SHM, and 840 default size when mounting hugetlbfs filesystems. 841 Defaults to the default architecture's huge page size 842 if not specified. 843 844 deferred_probe_timeout= 845 [KNL] Debugging option to set a timeout in seconds for 846 deferred probe to give up waiting on dependencies to 847 probe. Only specific dependencies (subsystems or 848 drivers) that have opted in will be ignored. A timeout of 0 849 will timeout at the end of initcalls. This option will also 850 dump out devices still on the deferred probe list after 851 retrying. 852 853 dfltcc= [HW,S390] 854 Format: { on | off | def_only | inf_only | always } 855 on: s390 zlib hardware support for compression on 856 level 1 and decompression (default) 857 off: No s390 zlib hardware support 858 def_only: s390 zlib hardware support for deflate 859 only (compression on level 1) 860 inf_only: s390 zlib hardware support for inflate 861 only (decompression) 862 always: Same as 'on' but ignores the selected compression 863 level always using hardware support (used for debugging) 864 865 dhash_entries= [KNL] 866 Set number of hash buckets for dentry cache. 867 868 disable_1tb_segments [PPC] 869 Disables the use of 1TB hash page table segments. This 870 causes the kernel to fall back to 256MB segments which 871 can be useful when debugging issues that require an SLB 872 miss to occur. 873 874 disable= [IPV6] 875 See Documentation/networking/ipv6.txt. 876 877 hardened_usercopy= 878 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 879 hardening is enabled for this boot. Hardened 880 usercopy checking is used to protect the kernel 881 from reading or writing beyond known memory 882 allocation boundaries as a proactive defense 883 against bounds-checking flaws in the kernel's 884 copy_to_user()/copy_from_user() interface. 885 on Perform hardened usercopy checks (default). 886 off Disable hardened usercopy checks. 887 888 disable_radix [PPC] 889 Disable RADIX MMU mode on POWER9 890 891 disable_tlbie [PPC] 892 Disable TLBIE instruction. Currently does not work 893 with KVM, with HASH MMU, or with coherent accelerators. 894 895 disable_cpu_apicid= [X86,APIC,SMP] 896 Format: <int> 897 The number of initial APIC ID for the 898 corresponding CPU to be disabled at boot, 899 mostly used for the kdump 2nd kernel to 900 disable BSP to wake up multiple CPUs without 901 causing system reset or hang due to sending 902 INIT from AP to BSP. 903 904 perf_v4_pmi= [X86,INTEL] 905 Format: <bool> 906 Disable Intel PMU counter freezing feature. 907 The feature only exists starting from 908 Arch Perfmon v4 (Skylake and newer). 909 910 disable_ddw [PPC/PSERIES] 911 Disable Dynamic DMA Window support. Use this if 912 to workaround buggy firmware. 913 914 disable_ipv6= [IPV6] 915 See Documentation/networking/ipv6.txt. 916 917 disable_mtrr_cleanup [X86] 918 The kernel tries to adjust MTRR layout from continuous 919 to discrete, to make X server driver able to add WB 920 entry later. This parameter disables that. 921 922 disable_mtrr_trim [X86, Intel and AMD only] 923 By default the kernel will trim any uncacheable 924 memory out of your available memory pool based on 925 MTRR settings. This parameter disables that behavior, 926 possibly causing your machine to run very slowly. 927 928 disable_timer_pin_1 [X86] 929 Disable PIN 1 of APIC timer 930 Can be useful to work around chipset bugs. 931 932 dis_ucode_ldr [X86] Disable the microcode loader. 933 934 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 935 this option disables the debugging code at boot. 936 937 dma_debug_entries=<number> 938 This option allows to tune the number of preallocated 939 entries for DMA-API debugging code. One entry is 940 required per DMA-API allocation. Use this if the 941 DMA-API debugging code disables itself because the 942 architectural default is too low. 943 944 dma_debug_driver=<driver_name> 945 With this option the DMA-API debugging driver 946 filter feature can be enabled at boot time. Just 947 pass the driver to filter for as the parameter. 948 The filter can be disabled or changed to another 949 driver later using sysfs. 950 951 driver_async_probe= [KNL] 952 List of driver names to be probed asynchronously. 953 Format: <driver_name1>,<driver_name2>... 954 955 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 956 Broken monitors, graphic adapters, KVMs and EDIDless 957 panels may send no or incorrect EDID data sets. 958 This parameter allows to specify an EDID data sets 959 in the /lib/firmware directory that are used instead. 960 Generic built-in EDID data sets are used, if one of 961 edid/1024x768.bin, edid/1280x1024.bin, 962 edid/1680x1050.bin, or edid/1920x1080.bin is given 963 and no file with the same name exists. Details and 964 instructions how to build your own EDID data are 965 available in Documentation/driver-api/edid.rst. An EDID 966 data set will only be used for a particular connector, 967 if its name and a colon are prepended to the EDID 968 name. Each connector may use a unique EDID data 969 set by separating the files with a comma. An EDID 970 data set with no connector name will be used for 971 any connectors not explicitly specified. 972 973 dscc4.setup= [NET] 974 975 dt_cpu_ftrs= [PPC] 976 Format: {"off" | "known"} 977 Control how the dt_cpu_ftrs device-tree binding is 978 used for CPU feature discovery and setup (if it 979 exists). 980 off: Do not use it, fall back to legacy cpu table. 981 known: Do not pass through unknown features to guests 982 or userspace, only those that the kernel is aware of. 983 984 dump_apple_properties [X86] 985 Dump name and content of EFI device properties on 986 x86 Macs. Useful for driver authors to determine 987 what data is available or for reverse-engineering. 988 989 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 990 module.dyndbg[="val"] 991 Enable debug messages at boot time. See 992 Documentation/admin-guide/dynamic-debug-howto.rst 993 for details. 994 995 nompx [X86] Disables Intel Memory Protection Extensions. 996 See Documentation/x86/intel_mpx.rst for more 997 information about the feature. 998 999 nopku [X86] Disable Memory Protection Keys CPU feature found 1000 in some Intel CPUs. 1001 1002 module.async_probe [KNL] 1003 Enable asynchronous probe on this module. 1004 1005 early_ioremap_debug [KNL] 1006 Enable debug messages in early_ioremap support. This 1007 is useful for tracking down temporary early mappings 1008 which are not unmapped. 1009 1010 earlycon= [KNL] Output early console device and options. 1011 1012 When used with no options, the early console is 1013 determined by stdout-path property in device tree's 1014 chosen node or the ACPI SPCR table if supported by 1015 the platform. 1016 1017 cdns,<addr>[,options] 1018 Start an early, polled-mode console on a Cadence 1019 (xuartps) serial port at the specified address. Only 1020 supported option is baud rate. If baud rate is not 1021 specified, the serial port must already be setup and 1022 configured. 1023 1024 uart[8250],io,<addr>[,options] 1025 uart[8250],mmio,<addr>[,options] 1026 uart[8250],mmio32,<addr>[,options] 1027 uart[8250],mmio32be,<addr>[,options] 1028 uart[8250],0x<addr>[,options] 1029 Start an early, polled-mode console on the 8250/16550 1030 UART at the specified I/O port or MMIO address. 1031 MMIO inter-register address stride is either 8-bit 1032 (mmio) or 32-bit (mmio32 or mmio32be). 1033 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1034 to be equivalent to 'mmio'. 'options' are specified 1035 in the same format described for "console=ttyS<n>"; if 1036 unspecified, the h/w is not initialized. 1037 1038 pl011,<addr> 1039 pl011,mmio32,<addr> 1040 Start an early, polled-mode console on a pl011 serial 1041 port at the specified address. The pl011 serial port 1042 must already be setup and configured. Options are not 1043 yet supported. If 'mmio32' is specified, then only 1044 the driver will use only 32-bit accessors to read/write 1045 the device registers. 1046 1047 meson,<addr> 1048 Start an early, polled-mode console on a meson serial 1049 port at the specified address. The serial port must 1050 already be setup and configured. Options are not yet 1051 supported. 1052 1053 msm_serial,<addr> 1054 Start an early, polled-mode console on an msm serial 1055 port at the specified address. The serial port 1056 must already be setup and configured. Options are not 1057 yet supported. 1058 1059 msm_serial_dm,<addr> 1060 Start an early, polled-mode console on an msm serial 1061 dm port at the specified address. The serial port 1062 must already be setup and configured. Options are not 1063 yet supported. 1064 1065 owl,<addr> 1066 Start an early, polled-mode console on a serial port 1067 of an Actions Semi SoC, such as S500 or S900, at the 1068 specified address. The serial port must already be 1069 setup and configured. Options are not yet supported. 1070 1071 rda,<addr> 1072 Start an early, polled-mode console on a serial port 1073 of an RDA Micro SoC, such as RDA8810PL, at the 1074 specified address. The serial port must already be 1075 setup and configured. Options are not yet supported. 1076 1077 sbi 1078 Use RISC-V SBI (Supervisor Binary Interface) for early 1079 console. 1080 1081 smh Use ARM semihosting calls for early console. 1082 1083 s3c2410,<addr> 1084 s3c2412,<addr> 1085 s3c2440,<addr> 1086 s3c6400,<addr> 1087 s5pv210,<addr> 1088 exynos4210,<addr> 1089 Use early console provided by serial driver available 1090 on Samsung SoCs, requires selecting proper type and 1091 a correct base address of the selected UART port. The 1092 serial port must already be setup and configured. 1093 Options are not yet supported. 1094 1095 lantiq,<addr> 1096 Start an early, polled-mode console on a lantiq serial 1097 (lqasc) port at the specified address. The serial port 1098 must already be setup and configured. Options are not 1099 yet supported. 1100 1101 lpuart,<addr> 1102 lpuart32,<addr> 1103 Use early console provided by Freescale LP UART driver 1104 found on Freescale Vybrid and QorIQ LS1021A processors. 1105 A valid base address must be provided, and the serial 1106 port must already be setup and configured. 1107 1108 ec_imx21,<addr> 1109 ec_imx6q,<addr> 1110 Start an early, polled-mode, output-only console on the 1111 Freescale i.MX UART at the specified address. The UART 1112 must already be setup and configured. 1113 1114 ar3700_uart,<addr> 1115 Start an early, polled-mode console on the 1116 Armada 3700 serial port at the specified 1117 address. The serial port must already be setup 1118 and configured. Options are not yet supported. 1119 1120 qcom_geni,<addr> 1121 Start an early, polled-mode console on a Qualcomm 1122 Generic Interface (GENI) based serial port at the 1123 specified address. The serial port must already be 1124 setup and configured. Options are not yet supported. 1125 1126 efifb,[options] 1127 Start an early, unaccelerated console on the EFI 1128 memory mapped framebuffer (if available). On cache 1129 coherent non-x86 systems that use system memory for 1130 the framebuffer, pass the 'ram' option so that it is 1131 mapped with the correct attributes. 1132 1133 linflex,<addr> 1134 Use early console provided by Freescale LINFlexD UART 1135 serial driver for NXP S32V234 SoCs. A valid base 1136 address must be provided, and the serial port must 1137 already be setup and configured. 1138 1139 earlyprintk= [X86,SH,ARM,M68k,S390] 1140 earlyprintk=vga 1141 earlyprintk=sclp 1142 earlyprintk=xen 1143 earlyprintk=serial[,ttySn[,baudrate]] 1144 earlyprintk=serial[,0x...[,baudrate]] 1145 earlyprintk=ttySn[,baudrate] 1146 earlyprintk=dbgp[debugController#] 1147 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1148 earlyprintk=xdbc[xhciController#] 1149 1150 earlyprintk is useful when the kernel crashes before 1151 the normal console is initialized. It is not enabled by 1152 default because it has some cosmetic problems. 1153 1154 Append ",keep" to not disable it when the real console 1155 takes over. 1156 1157 Only one of vga, efi, serial, or usb debug port can 1158 be used at a time. 1159 1160 Currently only ttyS0 and ttyS1 may be specified by 1161 name. Other I/O ports may be explicitly specified 1162 on some architectures (x86 and arm at least) by 1163 replacing ttySn with an I/O port address, like this: 1164 earlyprintk=serial,0x1008,115200 1165 You can find the port for a given device in 1166 /proc/tty/driver/serial: 1167 2: uart:ST16650V2 port:00001008 irq:18 ... 1168 1169 Interaction with the standard serial driver is not 1170 very good. 1171 1172 The VGA and EFI output is eventually overwritten by 1173 the real console. 1174 1175 The xen output can only be used by Xen PV guests. 1176 1177 The sclp output can only be used on s390. 1178 1179 The optional "force" to "pciserial" enables use of a 1180 PCI device even when its classcode is not of the 1181 UART class. 1182 1183 edac_report= [HW,EDAC] Control how to report EDAC event 1184 Format: {"on" | "off" | "force"} 1185 on: enable EDAC to report H/W event. May be overridden 1186 by other higher priority error reporting module. 1187 off: disable H/W event reporting through EDAC. 1188 force: enforce the use of EDAC to report H/W event. 1189 default: on. 1190 1191 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1192 ekgdboc=kbd 1193 1194 This is designed to be used in conjunction with 1195 the boot argument: earlyprintk=vga 1196 1197 edd= [EDD] 1198 Format: {"off" | "on" | "skip[mbr]"} 1199 1200 efi= [EFI] 1201 Format: { "old_map", "nochunk", "noruntime", "debug", 1202 "nosoftreserve", "disable_early_pci_dma", 1203 "no_disable_early_pci_dma" } 1204 old_map [X86-64]: switch to the old ioremap-based EFI 1205 runtime services mapping. [Needs CONFIG_X86_UV=y] 1206 nochunk: disable reading files in "chunks" in the EFI 1207 boot stub, as chunking can cause problems with some 1208 firmware implementations. 1209 noruntime : disable EFI runtime services support 1210 debug: enable misc debug output 1211 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1212 attribute may cause the kernel to reserve the 1213 memory range for a memory mapping driver to 1214 claim. Specify efi=nosoftreserve to disable this 1215 reservation and treat the memory by its base type 1216 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1217 disable_early_pci_dma: Disable the busmaster bit on all 1218 PCI bridges while in the EFI boot stub 1219 no_disable_early_pci_dma: Leave the busmaster bit set 1220 on all PCI bridges while in the EFI boot stub 1221 1222 efi_no_storage_paranoia [EFI; X86] 1223 Using this parameter you can use more than 50% of 1224 your efi variable storage. Use this parameter only if 1225 you are really sure that your UEFI does sane gc and 1226 fulfills the spec otherwise your board may brick. 1227 1228 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1229 Add arbitrary attribute to specific memory range by 1230 updating original EFI memory map. 1231 Region of memory which aa attribute is added to is 1232 from ss to ss+nn. 1233 1234 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1235 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1236 attribute is added to range 0x100000000-0x180000000 and 1237 0x10a0000000-0x1120000000. 1238 1239 If efi_fake_mem=8G@9G:0x40000 is specified, the 1240 EFI_MEMORY_SP(0x40000) attribute is added to 1241 range 0x240000000-0x43fffffff. 1242 1243 Using this parameter you can do debugging of EFI memmap 1244 related features. For example, you can do debugging of 1245 Address Range Mirroring feature even if your box 1246 doesn't support it, or mark specific memory as 1247 "soft reserved". 1248 1249 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1250 that is to be dynamically loaded by Linux. If there are 1251 multiple variables with the same name but with different 1252 vendor GUIDs, all of them will be loaded. See 1253 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1254 1255 1256 eisa_irq_edge= [PARISC,HW] 1257 See header of drivers/parisc/eisa.c. 1258 1259 elanfreq= [X86-32] 1260 See comment before function elanfreq_setup() in 1261 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1262 1263 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1264 Specifies physical address of start of kernel core 1265 image elf header and optionally the size. Generally 1266 kexec loader will pass this option to capture kernel. 1267 See Documentation/admin-guide/kdump/kdump.rst for details. 1268 1269 enable_mtrr_cleanup [X86] 1270 The kernel tries to adjust MTRR layout from continuous 1271 to discrete, to make X server driver able to add WB 1272 entry later. This parameter enables that. 1273 1274 enable_timer_pin_1 [X86] 1275 Enable PIN 1 of APIC timer 1276 Can be useful to work around chipset bugs 1277 (in particular on some ATI chipsets). 1278 The kernel tries to set a reasonable default. 1279 1280 enforcing [SELINUX] Set initial enforcing status. 1281 Format: {"0" | "1"} 1282 See security/selinux/Kconfig help text. 1283 0 -- permissive (log only, no denials). 1284 1 -- enforcing (deny and log). 1285 Default value is 0. 1286 Value can be changed at runtime via 1287 /sys/fs/selinux/enforce. 1288 1289 erst_disable [ACPI] 1290 Disable Error Record Serialization Table (ERST) 1291 support. 1292 1293 ether= [HW,NET] Ethernet cards parameters 1294 This option is obsoleted by the "netdev=" option, which 1295 has equivalent usage. See its documentation for details. 1296 1297 evm= [EVM] 1298 Format: { "fix" } 1299 Permit 'security.evm' to be updated regardless of 1300 current integrity status. 1301 1302 failslab= 1303 fail_page_alloc= 1304 fail_make_request=[KNL] 1305 General fault injection mechanism. 1306 Format: <interval>,<probability>,<space>,<times> 1307 See also Documentation/fault-injection/. 1308 1309 floppy= [HW] 1310 See Documentation/admin-guide/blockdev/floppy.rst. 1311 1312 force_pal_cache_flush 1313 [IA-64] Avoid check_sal_cache_flush which may hang on 1314 buggy SAL_CACHE_FLUSH implementations. Using this 1315 parameter will force ia64_sal_cache_flush to call 1316 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1317 1318 forcepae [X86-32] 1319 Forcefully enable Physical Address Extension (PAE). 1320 Many Pentium M systems disable PAE but may have a 1321 functionally usable PAE implementation. 1322 Warning: use of this parameter will taint the kernel 1323 and may cause unknown problems. 1324 1325 ftrace=[tracer] 1326 [FTRACE] will set and start the specified tracer 1327 as early as possible in order to facilitate early 1328 boot debugging. 1329 1330 ftrace_dump_on_oops[=orig_cpu] 1331 [FTRACE] will dump the trace buffers on oops. 1332 If no parameter is passed, ftrace will dump 1333 buffers of all CPUs, but if you pass orig_cpu, it will 1334 dump only the buffer of the CPU that triggered the 1335 oops. 1336 1337 ftrace_filter=[function-list] 1338 [FTRACE] Limit the functions traced by the function 1339 tracer at boot up. function-list is a comma separated 1340 list of functions. This list can be changed at run 1341 time by the set_ftrace_filter file in the debugfs 1342 tracing directory. 1343 1344 ftrace_notrace=[function-list] 1345 [FTRACE] Do not trace the functions specified in 1346 function-list. This list can be changed at run time 1347 by the set_ftrace_notrace file in the debugfs 1348 tracing directory. 1349 1350 ftrace_graph_filter=[function-list] 1351 [FTRACE] Limit the top level callers functions traced 1352 by the function graph tracer at boot up. 1353 function-list is a comma separated list of functions 1354 that can be changed at run time by the 1355 set_graph_function file in the debugfs tracing directory. 1356 1357 ftrace_graph_notrace=[function-list] 1358 [FTRACE] Do not trace from the functions specified in 1359 function-list. This list is a comma separated list of 1360 functions that can be changed at run time by the 1361 set_graph_notrace file in the debugfs tracing directory. 1362 1363 ftrace_graph_max_depth=<uint> 1364 [FTRACE] Used with the function graph tracer. This is 1365 the max depth it will trace into a function. This value 1366 can be changed at run time by the max_graph_depth file 1367 in the tracefs tracing directory. default: 0 (no limit) 1368 1369 fw_devlink= [KNL] Create device links between consumer and supplier 1370 devices by scanning the firmware to infer the 1371 consumer/supplier relationships. This feature is 1372 especially useful when drivers are loaded as modules as 1373 it ensures proper ordering of tasks like device probing 1374 (suppliers first, then consumers), supplier boot state 1375 clean up (only after all consumers have probed), 1376 suspend/resume & runtime PM (consumers first, then 1377 suppliers). 1378 Format: { off | permissive | on | rpm } 1379 off -- Don't create device links from firmware info. 1380 permissive -- Create device links from firmware info 1381 but use it only for ordering boot state clean 1382 up (sync_state() calls). 1383 on -- Create device links from firmware info and use it 1384 to enforce probe and suspend/resume ordering. 1385 rpm -- Like "on", but also use to order runtime PM. 1386 1387 gamecon.map[2|3]= 1388 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1389 support via parallel port (up to 5 devices per port) 1390 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1391 See also Documentation/input/devices/joystick-parport.rst 1392 1393 gamma= [HW,DRM] 1394 1395 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1396 Format: off | on 1397 default: on 1398 1399 gcov_persist= [GCOV] When non-zero (default), profiling data for 1400 kernel modules is saved and remains accessible via 1401 debugfs, even when the module is unloaded/reloaded. 1402 When zero, profiling data is discarded and associated 1403 debugfs files are removed at module unload time. 1404 1405 goldfish [X86] Enable the goldfish android emulator platform. 1406 Don't use this when you are not running on the 1407 android emulator 1408 1409 gpt [EFI] Forces disk with valid GPT signature but 1410 invalid Protective MBR to be treated as GPT. If the 1411 primary GPT is corrupted, it enables the backup/alternate 1412 GPT to be used instead. 1413 1414 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1415 the "Enable 0" bit of the configuration register. 1416 Format: 0 | 1 1417 Default: 0 1418 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1419 the "Enable 0" bit of the configuration register. 1420 Format: 0 | 1 1421 Default: 0 1422 grcan.select= [HW] Select which physical interface to use. 1423 Format: 0 | 1 1424 Default: 0 1425 grcan.txsize= [HW] Sets the size of the tx buffer. 1426 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1427 Default: 1024 1428 grcan.rxsize= [HW] Sets the size of the rx buffer. 1429 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1430 Default: 1024 1431 1432 gpio-mockup.gpio_mockup_ranges 1433 [HW] Sets the ranges of gpiochip of for this device. 1434 Format: <start1>,<end1>,<start2>,<end2>... 1435 1436 hardlockup_all_cpu_backtrace= 1437 [KNL] Should the hard-lockup detector generate 1438 backtraces on all cpus. 1439 Format: <integer> 1440 1441 hashdist= [KNL,NUMA] Large hashes allocated during boot 1442 are distributed across NUMA nodes. Defaults on 1443 for 64-bit NUMA, off otherwise. 1444 Format: 0 | 1 (for off | on) 1445 1446 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1447 1448 hd= [EIDE] (E)IDE hard drive subsystem geometry 1449 Format: <cyl>,<head>,<sect> 1450 1451 hest_disable [ACPI] 1452 Disable Hardware Error Source Table (HEST) support; 1453 corresponding firmware-first mode error processing 1454 logic will be disabled. 1455 1456 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1457 size of <nn>. This works even on boxes that have no 1458 highmem otherwise. This also works to reduce highmem 1459 size on bigger boxes. 1460 1461 highres= [KNL] Enable/disable high resolution timer mode. 1462 Valid parameters: "on", "off" 1463 Default: "on" 1464 1465 hlt [BUGS=ARM,SH] 1466 1467 hpet= [X86-32,HPET] option to control HPET usage 1468 Format: { enable (default) | disable | force | 1469 verbose } 1470 disable: disable HPET and use PIT instead 1471 force: allow force enabled of undocumented chips (ICH4, 1472 VIA, nVidia) 1473 verbose: show contents of HPET registers during setup 1474 1475 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1476 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1477 1478 hugetlb_cma= [HW] The size of a cma area used for allocation 1479 of gigantic hugepages. 1480 Format: nn[KMGTPE] 1481 1482 Reserve a cma area of given size and allocate gigantic 1483 hugepages using the cma allocator. If enabled, the 1484 boot-time allocation of gigantic hugepages is skipped. 1485 1486 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1487 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1488 On x86-64 and powerpc, this option can be specified 1489 multiple times interleaved with hugepages= to reserve 1490 huge pages of different sizes. Valid pages sizes on 1491 x86-64 are 2M (when the CPU supports "pse") and 1G 1492 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1493 1494 hung_task_panic= 1495 [KNL] Should the hung task detector generate panics. 1496 Format: <integer> 1497 1498 A nonzero value instructs the kernel to panic when a 1499 hung task is detected. The default value is controlled 1500 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1501 option. The value selected by this boot parameter can 1502 be changed later by the kernel.hung_task_panic sysctl. 1503 1504 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1505 terminal devices. Valid values: 0..8 1506 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1507 If specified, z/VM IUCV HVC accepts connections 1508 from listed z/VM user IDs only. 1509 1510 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1511 which allow the hypervisor to 'idle' the 1512 guest on lock contention. 1513 1514 keep_bootcon [KNL] 1515 Do not unregister boot console at start. This is only 1516 useful for debugging when something happens in the window 1517 between unregistering the boot console and initializing 1518 the real console. 1519 1520 i2c_bus= [HW] Override the default board specific I2C bus speed 1521 or register an additional I2C bus that is not 1522 registered from board initialization code. 1523 Format: 1524 <bus_id>,<clkrate> 1525 1526 i8042.debug [HW] Toggle i8042 debug mode 1527 i8042.unmask_kbd_data 1528 [HW] Enable printing of interrupt data from the KBD port 1529 (disabled by default, and as a pre-condition 1530 requires that i8042.debug=1 be enabled) 1531 i8042.direct [HW] Put keyboard port into non-translated mode 1532 i8042.dumbkbd [HW] Pretend that controller can only read data from 1533 keyboard and cannot control its state 1534 (Don't attempt to blink the leds) 1535 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1536 i8042.nokbd [HW] Don't check/create keyboard port 1537 i8042.noloop [HW] Disable the AUX Loopback command while probing 1538 for the AUX port 1539 i8042.nomux [HW] Don't check presence of an active multiplexing 1540 controller 1541 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1542 controllers 1543 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1544 i8042.reset [HW] Reset the controller during init, cleanup and 1545 suspend-to-ram transitions, only during s2r 1546 transitions, or never reset 1547 Format: { 1 | Y | y | 0 | N | n } 1548 1, Y, y: always reset controller 1549 0, N, n: don't ever reset controller 1550 Default: only on s2r transitions on x86; most other 1551 architectures force reset to be always executed 1552 i8042.unlock [HW] Unlock (ignore) the keylock 1553 i8042.kbdreset [HW] Reset device connected to KBD port 1554 1555 i810= [HW,DRM] 1556 1557 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1558 indicates that the driver is running on unsupported 1559 hardware. 1560 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1561 does not match list of supported models. 1562 i8k.power_status 1563 [HW] Report power status in /proc/i8k 1564 (disabled by default) 1565 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1566 capability is set. 1567 1568 i915.invert_brightness= 1569 [DRM] Invert the sense of the variable that is used to 1570 set the brightness of the panel backlight. Normally a 1571 brightness value of 0 indicates backlight switched off, 1572 and the maximum of the brightness value sets the backlight 1573 to maximum brightness. If this parameter is set to 0 1574 (default) and the machine requires it, or this parameter 1575 is set to 1, a brightness value of 0 sets the backlight 1576 to maximum brightness, and the maximum of the brightness 1577 value switches the backlight off. 1578 -1 -- never invert brightness 1579 0 -- machine default 1580 1 -- force brightness inversion 1581 1582 icn= [HW,ISDN] 1583 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1584 1585 ide-core.nodma= [HW] (E)IDE subsystem 1586 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1587 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1588 .cdrom .chs .ignore_cable are additional options 1589 See Documentation/ide/ide.rst. 1590 1591 ide-generic.probe-mask= [HW] (E)IDE subsystem 1592 Format: <int> 1593 Probe mask for legacy ISA IDE ports. Depending on 1594 platform up to 6 ports are supported, enabled by 1595 setting corresponding bits in the mask to 1. The 1596 default value is 0x0, which has a special meaning. 1597 On systems that have PCI, it triggers scanning the 1598 PCI bus for the first and the second port, which 1599 are then probed. On systems without PCI the value 1600 of 0x0 enables probing the two first ports as if it 1601 was 0x3. 1602 1603 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1604 Claim all unknown PCI IDE storage controllers. 1605 1606 idle= [X86] 1607 Format: idle=poll, idle=halt, idle=nomwait 1608 Poll forces a polling idle loop that can slightly 1609 improve the performance of waking up a idle CPU, but 1610 will use a lot of power and make the system run hot. 1611 Not recommended. 1612 idle=halt: Halt is forced to be used for CPU idle. 1613 In such case C2/C3 won't be used again. 1614 idle=nomwait: Disable mwait for CPU C-states 1615 1616 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1617 Format: { strict | legacy | 2008 | relaxed } 1618 Default: strict 1619 1620 Choose which programs will be accepted for execution 1621 based on the IEEE 754 NaN encoding(s) supported by 1622 the FPU and the NaN encoding requested with the value 1623 of an ELF file header flag individually set by each 1624 binary. Hardware implementations are permitted to 1625 support either or both of the legacy and the 2008 NaN 1626 encoding mode. 1627 1628 Available settings are as follows: 1629 strict accept binaries that request a NaN encoding 1630 supported by the FPU 1631 legacy only accept legacy-NaN binaries, if supported 1632 by the FPU 1633 2008 only accept 2008-NaN binaries, if supported 1634 by the FPU 1635 relaxed accept any binaries regardless of whether 1636 supported by the FPU 1637 1638 The FPU emulator is always able to support both NaN 1639 encodings, so if no FPU hardware is present or it has 1640 been disabled with 'nofpu', then the settings of 1641 'legacy' and '2008' strap the emulator accordingly, 1642 'relaxed' straps the emulator for both legacy-NaN and 1643 2008-NaN, whereas 'strict' enables legacy-NaN only on 1644 legacy processors and both NaN encodings on MIPS32 or 1645 MIPS64 CPUs. 1646 1647 The setting for ABS.fmt/NEG.fmt instruction execution 1648 mode generally follows that for the NaN encoding, 1649 except where unsupported by hardware. 1650 1651 ignore_loglevel [KNL] 1652 Ignore loglevel setting - this will print /all/ 1653 kernel messages to the console. Useful for debugging. 1654 We also add it as printk module parameter, so users 1655 could change it dynamically, usually by 1656 /sys/module/printk/parameters/ignore_loglevel. 1657 1658 ignore_rlimit_data 1659 Ignore RLIMIT_DATA setting for data mappings, 1660 print warning at first misuse. Can be changed via 1661 /sys/module/kernel/parameters/ignore_rlimit_data. 1662 1663 ihash_entries= [KNL] 1664 Set number of hash buckets for inode cache. 1665 1666 ima_appraise= [IMA] appraise integrity measurements 1667 Format: { "off" | "enforce" | "fix" | "log" } 1668 default: "enforce" 1669 1670 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1671 The builtin appraise policy appraises all files 1672 owned by uid=0. 1673 1674 ima_canonical_fmt [IMA] 1675 Use the canonical format for the binary runtime 1676 measurements, instead of host native format. 1677 1678 ima_hash= [IMA] 1679 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1680 | sha512 | ... } 1681 default: "sha1" 1682 1683 The list of supported hash algorithms is defined 1684 in crypto/hash_info.h. 1685 1686 ima_policy= [IMA] 1687 The builtin policies to load during IMA setup. 1688 Format: "tcb | appraise_tcb | secure_boot | 1689 fail_securely" 1690 1691 The "tcb" policy measures all programs exec'd, files 1692 mmap'd for exec, and all files opened with the read 1693 mode bit set by either the effective uid (euid=0) or 1694 uid=0. 1695 1696 The "appraise_tcb" policy appraises the integrity of 1697 all files owned by root. 1698 1699 The "secure_boot" policy appraises the integrity 1700 of files (eg. kexec kernel image, kernel modules, 1701 firmware, policy, etc) based on file signatures. 1702 1703 The "fail_securely" policy forces file signature 1704 verification failure also on privileged mounted 1705 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1706 flag. 1707 1708 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1709 Load a policy which meets the needs of the Trusted 1710 Computing Base. This means IMA will measure all 1711 programs exec'd, files mmap'd for exec, and all files 1712 opened for read by uid=0. 1713 1714 ima_template= [IMA] 1715 Select one of defined IMA measurements template formats. 1716 Formats: { "ima" | "ima-ng" | "ima-sig" } 1717 Default: "ima-ng" 1718 1719 ima_template_fmt= 1720 [IMA] Define a custom template format. 1721 Format: { "field1|...|fieldN" } 1722 1723 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1724 Format: <min_file_size> 1725 Set the minimal file size for using asynchronous hash. 1726 If left unspecified, ahash usage is disabled. 1727 1728 ahash performance varies for different data sizes on 1729 different crypto accelerators. This option can be used 1730 to achieve the best performance for a particular HW. 1731 1732 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1733 Format: <bufsize> 1734 Set hashing buffer size. Default: 4k. 1735 1736 ahash performance varies for different chunk sizes on 1737 different crypto accelerators. This option can be used 1738 to achieve best performance for particular HW. 1739 1740 init= [KNL] 1741 Format: <full_path> 1742 Run specified binary instead of /sbin/init as init 1743 process. 1744 1745 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1746 for working out where the kernel is dying during 1747 startup. 1748 1749 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1750 initcall functions. Useful for debugging built-in 1751 modules and initcalls. 1752 1753 initrd= [BOOT] Specify the location of the initial ramdisk 1754 1755 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1756 zeroes. 1757 Format: 0 | 1 1758 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1759 1760 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1761 Format: 0 | 1 1762 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1763 1764 init_pkru= [x86] Specify the default memory protection keys rights 1765 register contents for all processes. 0x55555554 by 1766 default (disallow access to all but pkey 0). Can 1767 override in debugfs after boot. 1768 1769 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1770 Format: <irq> 1771 1772 int_pln_enable [x86] Enable power limit notification interrupt 1773 1774 integrity_audit=[IMA] 1775 Format: { "0" | "1" } 1776 0 -- basic integrity auditing messages. (Default) 1777 1 -- additional integrity auditing messages. 1778 1779 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1780 on 1781 Enable intel iommu driver. 1782 off 1783 Disable intel iommu driver. 1784 igfx_off [Default Off] 1785 By default, gfx is mapped as normal device. If a gfx 1786 device has a dedicated DMAR unit, the DMAR unit is 1787 bypassed by not enabling DMAR with this option. In 1788 this case, gfx device will use physical address for 1789 DMA. 1790 forcedac [x86_64] 1791 With this option iommu will not optimize to look 1792 for io virtual address below 32-bit forcing dual 1793 address cycle on pci bus for cards supporting greater 1794 than 32-bit addressing. The default is to look 1795 for translation below 32-bit and if not available 1796 then look in the higher range. 1797 strict [Default Off] 1798 With this option on every unmap_single operation will 1799 result in a hardware IOTLB flush operation as opposed 1800 to batching them for performance. 1801 sp_off [Default Off] 1802 By default, super page will be supported if Intel IOMMU 1803 has the capability. With this option, super page will 1804 not be supported. 1805 sm_on [Default Off] 1806 By default, scalable mode will be disabled even if the 1807 hardware advertises that it has support for the scalable 1808 mode translation. With this option set, scalable mode 1809 will be used on hardware which claims to support it. 1810 tboot_noforce [Default Off] 1811 Do not force the Intel IOMMU enabled under tboot. 1812 By default, tboot will force Intel IOMMU on, which 1813 could harm performance of some high-throughput 1814 devices like 40GBit network cards, even if identity 1815 mapping is enabled. 1816 Note that using this option lowers the security 1817 provided by tboot because it makes the system 1818 vulnerable to DMA attacks. 1819 nobounce [Default off] 1820 Disable bounce buffer for untrusted devices such as 1821 the Thunderbolt devices. This will treat the untrusted 1822 devices as the trusted ones, hence might expose security 1823 risks of DMA attacks. 1824 1825 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1826 0 disables intel_idle and fall back on acpi_idle. 1827 1 to 9 specify maximum depth of C-state. 1828 1829 intel_pstate= [X86] 1830 disable 1831 Do not enable intel_pstate as the default 1832 scaling driver for the supported processors 1833 passive 1834 Use intel_pstate as a scaling driver, but configure it 1835 to work with generic cpufreq governors (instead of 1836 enabling its internal governor). This mode cannot be 1837 used along with the hardware-managed P-states (HWP) 1838 feature. 1839 force 1840 Enable intel_pstate on systems that prohibit it by default 1841 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1842 instead of acpi-cpufreq may disable platform features, such 1843 as thermal controls and power capping, that rely on ACPI 1844 P-States information being indicated to OSPM and therefore 1845 should be used with caution. This option does not work with 1846 processors that aren't supported by the intel_pstate driver 1847 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1848 no_hwp 1849 Do not enable hardware P state control (HWP) 1850 if available. 1851 hwp_only 1852 Only load intel_pstate on systems which support 1853 hardware P state control (HWP) if available. 1854 support_acpi_ppc 1855 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1856 Description Table, specifies preferred power management 1857 profile as "Enterprise Server" or "Performance Server", 1858 then this feature is turned on by default. 1859 per_cpu_perf_limits 1860 Allow per-logical-CPU P-State performance control limits using 1861 cpufreq sysfs interface 1862 1863 intremap= [X86-64, Intel-IOMMU] 1864 on enable Interrupt Remapping (default) 1865 off disable Interrupt Remapping 1866 nosid disable Source ID checking 1867 no_x2apic_optout 1868 BIOS x2APIC opt-out request will be ignored 1869 nopost disable Interrupt Posting 1870 1871 iomem= Disable strict checking of access to MMIO memory 1872 strict regions from userspace. 1873 relaxed 1874 1875 iommu= [x86] 1876 off 1877 force 1878 noforce 1879 biomerge 1880 panic 1881 nopanic 1882 merge 1883 nomerge 1884 soft 1885 pt [x86] 1886 nopt [x86] 1887 nobypass [PPC/POWERNV] 1888 Disable IOMMU bypass, using IOMMU for PCI devices. 1889 1890 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1891 Format: { "0" | "1" } 1892 0 - Lazy mode. 1893 Request that DMA unmap operations use deferred 1894 invalidation of hardware TLBs, for increased 1895 throughput at the cost of reduced device isolation. 1896 Will fall back to strict mode if not supported by 1897 the relevant IOMMU driver. 1898 1 - Strict mode (default). 1899 DMA unmap operations invalidate IOMMU hardware TLBs 1900 synchronously. 1901 1902 iommu.passthrough= 1903 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1904 Format: { "0" | "1" } 1905 0 - Use IOMMU translation for DMA. 1906 1 - Bypass the IOMMU for DMA. 1907 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1908 1909 io7= [HW] IO7 for Marvel based alpha systems 1910 See comment before marvel_specify_io7 in 1911 arch/alpha/kernel/core_marvel.c. 1912 1913 io_delay= [X86] I/O delay method 1914 0x80 1915 Standard port 0x80 based delay 1916 0xed 1917 Alternate port 0xed based delay (needed on some systems) 1918 udelay 1919 Simple two microseconds delay 1920 none 1921 No delay 1922 1923 ip= [IP_PNP] 1924 See Documentation/admin-guide/nfs/nfsroot.rst. 1925 1926 ipcmni_extend [KNL] Extend the maximum number of unique System V 1927 IPC identifiers from 32,768 to 16,777,216. 1928 1929 irqaffinity= [SMP] Set the default irq affinity mask 1930 The argument is a cpu list, as described above. 1931 1932 irqchip.gicv2_force_probe= 1933 [ARM, ARM64] 1934 Format: <bool> 1935 Force the kernel to look for the second 4kB page 1936 of a GICv2 controller even if the memory range 1937 exposed by the device tree is too small. 1938 1939 irqchip.gicv3_nolpi= 1940 [ARM, ARM64] 1941 Force the kernel to ignore the availability of 1942 LPIs (and by consequence ITSs). Intended for system 1943 that use the kernel as a bootloader, and thus want 1944 to let secondary kernels in charge of setting up 1945 LPIs. 1946 1947 irqchip.gicv3_pseudo_nmi= [ARM64] 1948 Enables support for pseudo-NMIs in the kernel. This 1949 requires the kernel to be built with 1950 CONFIG_ARM64_PSEUDO_NMI. 1951 1952 irqfixup [HW] 1953 When an interrupt is not handled search all handlers 1954 for it. Intended to get systems with badly broken 1955 firmware running. 1956 1957 irqpoll [HW] 1958 When an interrupt is not handled search all handlers 1959 for it. Also check all handlers each timer 1960 interrupt. Intended to get systems with badly broken 1961 firmware running. 1962 1963 isapnp= [ISAPNP] 1964 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1965 1966 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1967 [Deprecated - use cpusets instead] 1968 Format: [flag-list,]<cpu-list> 1969 1970 Specify one or more CPUs to isolate from disturbances 1971 specified in the flag list (default: domain): 1972 1973 nohz 1974 Disable the tick when a single task runs. 1975 1976 A residual 1Hz tick is offloaded to workqueues, which you 1977 need to affine to housekeeping through the global 1978 workqueue's affinity configured via the 1979 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1980 by using the 'domain' flag described below. 1981 1982 NOTE: by default the global workqueue runs on all CPUs, 1983 so to protect individual CPUs the 'cpumask' file has to 1984 be configured manually after bootup. 1985 1986 domain 1987 Isolate from the general SMP balancing and scheduling 1988 algorithms. Note that performing domain isolation this way 1989 is irreversible: it's not possible to bring back a CPU to 1990 the domains once isolated through isolcpus. It's strongly 1991 advised to use cpusets instead to disable scheduler load 1992 balancing through the "cpuset.sched_load_balance" file. 1993 It offers a much more flexible interface where CPUs can 1994 move in and out of an isolated set anytime. 1995 1996 You can move a process onto or off an "isolated" CPU via 1997 the CPU affinity syscalls or cpuset. 1998 <cpu number> begins at 0 and the maximum value is 1999 "number of CPUs in system - 1". 2000 2001 managed_irq 2002 2003 Isolate from being targeted by managed interrupts 2004 which have an interrupt mask containing isolated 2005 CPUs. The affinity of managed interrupts is 2006 handled by the kernel and cannot be changed via 2007 the /proc/irq/* interfaces. 2008 2009 This isolation is best effort and only effective 2010 if the automatically assigned interrupt mask of a 2011 device queue contains isolated and housekeeping 2012 CPUs. If housekeeping CPUs are online then such 2013 interrupts are directed to the housekeeping CPU 2014 so that IO submitted on the housekeeping CPU 2015 cannot disturb the isolated CPU. 2016 2017 If a queue's affinity mask contains only isolated 2018 CPUs then this parameter has no effect on the 2019 interrupt routing decision, though interrupts are 2020 only delivered when tasks running on those 2021 isolated CPUs submit IO. IO submitted on 2022 housekeeping CPUs has no influence on those 2023 queues. 2024 2025 The format of <cpu-list> is described above. 2026 2027 iucv= [HW,NET] 2028 2029 ivrs_ioapic [HW,X86_64] 2030 Provide an override to the IOAPIC-ID<->DEVICE-ID 2031 mapping provided in the IVRS ACPI table. For 2032 example, to map IOAPIC-ID decimal 10 to 2033 PCI device 00:14.0 write the parameter as: 2034 ivrs_ioapic[10]=00:14.0 2035 2036 ivrs_hpet [HW,X86_64] 2037 Provide an override to the HPET-ID<->DEVICE-ID 2038 mapping provided in the IVRS ACPI table. For 2039 example, to map HPET-ID decimal 0 to 2040 PCI device 00:14.0 write the parameter as: 2041 ivrs_hpet[0]=00:14.0 2042 2043 ivrs_acpihid [HW,X86_64] 2044 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2045 mapping provided in the IVRS ACPI table. For 2046 example, to map UART-HID:UID AMD0020:0 to 2047 PCI device 00:14.5 write the parameter as: 2048 ivrs_acpihid[00:14.5]=AMD0020:0 2049 2050 js= [HW,JOY] Analog joystick 2051 See Documentation/input/joydev/joystick.rst. 2052 2053 nokaslr [KNL] 2054 When CONFIG_RANDOMIZE_BASE is set, this disables 2055 kernel and module base offset ASLR (Address Space 2056 Layout Randomization). 2057 2058 kasan_multi_shot 2059 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2060 report on every invalid memory access. Without this 2061 parameter KASAN will print report only for the first 2062 invalid access. 2063 2064 keepinitrd [HW,ARM] 2065 2066 kernelcore= [KNL,X86,IA-64,PPC] 2067 Format: nn[KMGTPE] | nn% | "mirror" 2068 This parameter specifies the amount of memory usable by 2069 the kernel for non-movable allocations. The requested 2070 amount is spread evenly throughout all nodes in the 2071 system as ZONE_NORMAL. The remaining memory is used for 2072 movable memory in its own zone, ZONE_MOVABLE. In the 2073 event, a node is too small to have both ZONE_NORMAL and 2074 ZONE_MOVABLE, kernelcore memory will take priority and 2075 other nodes will have a larger ZONE_MOVABLE. 2076 2077 ZONE_MOVABLE is used for the allocation of pages that 2078 may be reclaimed or moved by the page migration 2079 subsystem. Note that allocations like PTEs-from-HighMem 2080 still use the HighMem zone if it exists, and the Normal 2081 zone if it does not. 2082 2083 It is possible to specify the exact amount of memory in 2084 the form of "nn[KMGTPE]", a percentage of total system 2085 memory in the form of "nn%", or "mirror". If "mirror" 2086 option is specified, mirrored (reliable) memory is used 2087 for non-movable allocations and remaining memory is used 2088 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2089 are exclusive, so you cannot specify multiple forms. 2090 2091 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2092 Format: <Controller#>[,poll interval] 2093 The controller # is the number of the ehci usb debug 2094 port as it is probed via PCI. The poll interval is 2095 optional and is the number seconds in between 2096 each poll cycle to the debug port in case you need 2097 the functionality for interrupting the kernel with 2098 gdb or control-c on the dbgp connection. When 2099 not using this parameter you use sysrq-g to break into 2100 the kernel debugger. 2101 2102 kgdboc= [KGDB,HW] kgdb over consoles. 2103 Requires a tty driver that supports console polling, 2104 or a supported polling keyboard driver (non-usb). 2105 Serial only format: <serial_device>[,baud] 2106 keyboard only format: kbd 2107 keyboard and serial format: kbd,<serial_device>[,baud] 2108 Optional Kernel mode setting: 2109 kms, kbd format: kms,kbd 2110 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2111 2112 kgdbwait [KGDB] Stop kernel execution and enter the 2113 kernel debugger at the earliest opportunity. 2114 2115 kmac= [MIPS] korina ethernet MAC address. 2116 Configure the RouterBoard 532 series on-chip 2117 Ethernet adapter MAC address. 2118 2119 kmemleak= [KNL] Boot-time kmemleak enable/disable 2120 Valid arguments: on, off 2121 Default: on 2122 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2123 the default is off. 2124 2125 kprobe_event=[probe-list] 2126 [FTRACE] Add kprobe events and enable at boot time. 2127 The probe-list is a semicolon delimited list of probe 2128 definitions. Each definition is same as kprobe_events 2129 interface, but the parameters are comma delimited. 2130 For example, to add a kprobe event on vfs_read with 2131 arg1 and arg2, add to the command line; 2132 2133 kprobe_event=p,vfs_read,$arg1,$arg2 2134 2135 See also Documentation/trace/kprobetrace.rst "Kernel 2136 Boot Parameter" section. 2137 2138 kpti= [ARM64] Control page table isolation of user 2139 and kernel address spaces. 2140 Default: enabled on cores which need mitigation. 2141 0: force disabled 2142 1: force enabled 2143 2144 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2145 Default is 0 (don't ignore, but inject #GP) 2146 2147 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2148 Default is false (don't support). 2149 2150 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2151 KVM MMU at runtime. 2152 Default is 0 (off) 2153 2154 kvm.nx_huge_pages= 2155 [KVM] Controls the software workaround for the 2156 X86_BUG_ITLB_MULTIHIT bug. 2157 force : Always deploy workaround. 2158 off : Never deploy workaround. 2159 auto : Deploy workaround based on the presence of 2160 X86_BUG_ITLB_MULTIHIT. 2161 2162 Default is 'auto'. 2163 2164 If the software workaround is enabled for the host, 2165 guests do need not to enable it for nested guests. 2166 2167 kvm.nx_huge_pages_recovery_ratio= 2168 [KVM] Controls how many 4KiB pages are periodically zapped 2169 back to huge pages. 0 disables the recovery, otherwise if 2170 the value is N KVM will zap 1/Nth of the 4KiB pages every 2171 minute. The default is 60. 2172 2173 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2174 Default is 1 (enabled) 2175 2176 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2177 for all guests. 2178 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2179 2180 kvm-arm.vgic_v3_group0_trap= 2181 [KVM,ARM] Trap guest accesses to GICv3 group-0 2182 system registers 2183 2184 kvm-arm.vgic_v3_group1_trap= 2185 [KVM,ARM] Trap guest accesses to GICv3 group-1 2186 system registers 2187 2188 kvm-arm.vgic_v3_common_trap= 2189 [KVM,ARM] Trap guest accesses to GICv3 common 2190 system registers 2191 2192 kvm-arm.vgic_v4_enable= 2193 [KVM,ARM] Allow use of GICv4 for direct injection of 2194 LPIs. 2195 2196 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2197 (virtualized MMU) support on capable Intel chips. 2198 Default is 1 (enabled) 2199 2200 kvm-intel.emulate_invalid_guest_state= 2201 [KVM,Intel] Enable emulation of invalid guest states 2202 Default is 0 (disabled) 2203 2204 kvm-intel.flexpriority= 2205 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2206 Default is 1 (enabled) 2207 2208 kvm-intel.nested= 2209 [KVM,Intel] Enable VMX nesting (nVMX). 2210 Default is 0 (disabled) 2211 2212 kvm-intel.unrestricted_guest= 2213 [KVM,Intel] Disable unrestricted guest feature 2214 (virtualized real and unpaged mode) on capable 2215 Intel chips. Default is 1 (enabled) 2216 2217 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2218 CVE-2018-3620. 2219 2220 Valid arguments: never, cond, always 2221 2222 always: L1D cache flush on every VMENTER. 2223 cond: Flush L1D on VMENTER only when the code between 2224 VMEXIT and VMENTER can leak host memory. 2225 never: Disables the mitigation 2226 2227 Default is cond (do L1 cache flush in specific instances) 2228 2229 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2230 feature (tagged TLBs) on capable Intel chips. 2231 Default is 1 (enabled) 2232 2233 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2234 affected CPUs 2235 2236 The kernel PTE inversion protection is unconditionally 2237 enabled and cannot be disabled. 2238 2239 full 2240 Provides all available mitigations for the 2241 L1TF vulnerability. Disables SMT and 2242 enables all mitigations in the 2243 hypervisors, i.e. unconditional L1D flush. 2244 2245 SMT control and L1D flush control via the 2246 sysfs interface is still possible after 2247 boot. Hypervisors will issue a warning 2248 when the first VM is started in a 2249 potentially insecure configuration, 2250 i.e. SMT enabled or L1D flush disabled. 2251 2252 full,force 2253 Same as 'full', but disables SMT and L1D 2254 flush runtime control. Implies the 2255 'nosmt=force' command line option. 2256 (i.e. sysfs control of SMT is disabled.) 2257 2258 flush 2259 Leaves SMT enabled and enables the default 2260 hypervisor mitigation, i.e. conditional 2261 L1D flush. 2262 2263 SMT control and L1D flush control via the 2264 sysfs interface is still possible after 2265 boot. Hypervisors will issue a warning 2266 when the first VM is started in a 2267 potentially insecure configuration, 2268 i.e. SMT enabled or L1D flush disabled. 2269 2270 flush,nosmt 2271 2272 Disables SMT and enables the default 2273 hypervisor mitigation. 2274 2275 SMT control and L1D flush control via the 2276 sysfs interface is still possible after 2277 boot. Hypervisors will issue a warning 2278 when the first VM is started in a 2279 potentially insecure configuration, 2280 i.e. SMT enabled or L1D flush disabled. 2281 2282 flush,nowarn 2283 Same as 'flush', but hypervisors will not 2284 warn when a VM is started in a potentially 2285 insecure configuration. 2286 2287 off 2288 Disables hypervisor mitigations and doesn't 2289 emit any warnings. 2290 It also drops the swap size and available 2291 RAM limit restriction on both hypervisor and 2292 bare metal. 2293 2294 Default is 'flush'. 2295 2296 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2297 2298 l2cr= [PPC] 2299 2300 l3cr= [PPC] 2301 2302 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2303 disabled it. 2304 2305 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2306 value for LAPIC timer one-shot implementation. Default 2307 back to the programmable timer unit in the LAPIC. 2308 2309 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2310 in C2 power state. 2311 2312 libata.dma= [LIBATA] DMA control 2313 libata.dma=0 Disable all PATA and SATA DMA 2314 libata.dma=1 PATA and SATA Disk DMA only 2315 libata.dma=2 ATAPI (CDROM) DMA only 2316 libata.dma=4 Compact Flash DMA only 2317 Combinations also work, so libata.dma=3 enables DMA 2318 for disks and CDROMs, but not CFs. 2319 2320 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2321 libata.ignore_hpa=0 keep BIOS limits (default) 2322 libata.ignore_hpa=1 ignore limits, using full disk 2323 2324 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2325 when set. 2326 Format: <int> 2327 2328 libata.force= [LIBATA] Force configurations. The format is comma 2329 separated list of "[ID:]VAL" where ID is 2330 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2331 matching port, link or device. Basically, it matches 2332 the ATA ID string printed on console by libata. If 2333 the whole ID part is omitted, the last PORT and DEVICE 2334 values are used. If ID hasn't been specified yet, the 2335 configuration applies to all ports, links and devices. 2336 2337 If only DEVICE is omitted, the parameter applies to 2338 the port and all links and devices behind it. DEVICE 2339 number of 0 either selects the first device or the 2340 first fan-out link behind PMP device. It does not 2341 select the host link. DEVICE number of 15 selects the 2342 host link and device attached to it. 2343 2344 The VAL specifies the configuration to force. As long 2345 as there's no ambiguity shortcut notation is allowed. 2346 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2347 The following configurations can be forced. 2348 2349 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2350 Any ID with matching PORT is used. 2351 2352 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2353 2354 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2355 udma[/][16,25,33,44,66,100,133] notation is also 2356 allowed. 2357 2358 * [no]ncq: Turn on or off NCQ. 2359 2360 * [no]ncqtrim: Turn off queued DSM TRIM. 2361 2362 * nohrst, nosrst, norst: suppress hard, soft 2363 and both resets. 2364 2365 * rstonce: only attempt one reset during 2366 hot-unplug link recovery 2367 2368 * dump_id: dump IDENTIFY data. 2369 2370 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2371 2372 * disable: Disable this device. 2373 2374 If there are multiple matching configurations changing 2375 the same attribute, the last one is used. 2376 2377 memblock=debug [KNL] Enable memblock debug messages. 2378 2379 load_ramdisk= [RAM] List of ramdisks to load from floppy 2380 See Documentation/admin-guide/blockdev/ramdisk.rst. 2381 2382 lockd.nlm_grace_period=P [NFS] Assign grace period. 2383 Format: <integer> 2384 2385 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2386 Format: <integer> 2387 2388 lockd.nlm_timeout=T [NFS] Assign timeout value. 2389 Format: <integer> 2390 2391 lockd.nlm_udpport=M [NFS] Assign UDP port. 2392 Format: <integer> 2393 2394 lockdown= [SECURITY] 2395 { integrity | confidentiality } 2396 Enable the kernel lockdown feature. If set to 2397 integrity, kernel features that allow userland to 2398 modify the running kernel are disabled. If set to 2399 confidentiality, kernel features that allow userland 2400 to extract confidential information from the kernel 2401 are also disabled. 2402 2403 locktorture.nreaders_stress= [KNL] 2404 Set the number of locking read-acquisition kthreads. 2405 Defaults to being automatically set based on the 2406 number of online CPUs. 2407 2408 locktorture.nwriters_stress= [KNL] 2409 Set the number of locking write-acquisition kthreads. 2410 2411 locktorture.onoff_holdoff= [KNL] 2412 Set time (s) after boot for CPU-hotplug testing. 2413 2414 locktorture.onoff_interval= [KNL] 2415 Set time (s) between CPU-hotplug operations, or 2416 zero to disable CPU-hotplug testing. 2417 2418 locktorture.shuffle_interval= [KNL] 2419 Set task-shuffle interval (jiffies). Shuffling 2420 tasks allows some CPUs to go into dyntick-idle 2421 mode during the locktorture test. 2422 2423 locktorture.shutdown_secs= [KNL] 2424 Set time (s) after boot system shutdown. This 2425 is useful for hands-off automated testing. 2426 2427 locktorture.stat_interval= [KNL] 2428 Time (s) between statistics printk()s. 2429 2430 locktorture.stutter= [KNL] 2431 Time (s) to stutter testing, for example, 2432 specifying five seconds causes the test to run for 2433 five seconds, wait for five seconds, and so on. 2434 This tests the locking primitive's ability to 2435 transition abruptly to and from idle. 2436 2437 locktorture.torture_type= [KNL] 2438 Specify the locking implementation to test. 2439 2440 locktorture.verbose= [KNL] 2441 Enable additional printk() statements. 2442 2443 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2444 Format: <irq> 2445 2446 loglevel= All Kernel Messages with a loglevel smaller than the 2447 console loglevel will be printed to the console. It can 2448 also be changed with klogd or other programs. The 2449 loglevels are defined as follows: 2450 2451 0 (KERN_EMERG) system is unusable 2452 1 (KERN_ALERT) action must be taken immediately 2453 2 (KERN_CRIT) critical conditions 2454 3 (KERN_ERR) error conditions 2455 4 (KERN_WARNING) warning conditions 2456 5 (KERN_NOTICE) normal but significant condition 2457 6 (KERN_INFO) informational 2458 7 (KERN_DEBUG) debug-level messages 2459 2460 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2461 in bytes. n must be a power of two and greater 2462 than the minimal size. The minimal size is defined 2463 by LOG_BUF_SHIFT kernel config parameter. There is 2464 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2465 that allows to increase the default size depending on 2466 the number of CPUs. See init/Kconfig for more details. 2467 2468 logo.nologo [FB] Disables display of the built-in Linux logo. 2469 This may be used to provide more screen space for 2470 kernel log messages and is useful when debugging 2471 kernel boot problems. 2472 2473 lp=0 [LP] Specify parallel ports to use, e.g, 2474 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2475 lp=reset first parallel port). 'lp=0' disables the 2476 lp=auto printer driver. 'lp=reset' (which can be 2477 specified in addition to the ports) causes 2478 attached printers to be reset. Using 2479 lp=port1,port2,... specifies the parallel ports 2480 to associate lp devices with, starting with 2481 lp0. A port specification may be 'none' to skip 2482 that lp device, or a parport name such as 2483 'parport0'. Specifying 'lp=auto' instead of a 2484 port specification list means that device IDs 2485 from each port should be examined, to see if 2486 an IEEE 1284-compliant printer is attached; if 2487 so, the driver will manage that printer. 2488 See also header of drivers/char/lp.c. 2489 2490 lpj=n [KNL] 2491 Sets loops_per_jiffy to given constant, thus avoiding 2492 time-consuming boot-time autodetection (up to 250 ms per 2493 CPU). 0 enables autodetection (default). To determine 2494 the correct value for your kernel, boot with normal 2495 autodetection and see what value is printed. Note that 2496 on SMP systems the preset will be applied to all CPUs, 2497 which is likely to cause problems if your CPUs need 2498 significantly divergent settings. An incorrect value 2499 will cause delays in the kernel to be wrong, leading to 2500 unpredictable I/O errors and other breakage. Although 2501 unlikely, in the extreme case this might damage your 2502 hardware. 2503 2504 ltpc= [NET] 2505 Format: <io>,<irq>,<dma> 2506 2507 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2508 2509 lsm=lsm1,...,lsmN 2510 [SECURITY] Choose order of LSM initialization. This 2511 overrides CONFIG_LSM, and the "security=" parameter. 2512 2513 machvec= [IA-64] Force the use of a particular machine-vector 2514 (machvec) in a generic kernel. 2515 Example: machvec=hpzx1 2516 2517 machtype= [Loongson] Share the same kernel image file between different 2518 yeeloong laptop. 2519 Example: machtype=lemote-yeeloong-2f-7inch 2520 2521 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2522 than or equal to this physical address is ignored. 2523 2524 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2525 will bring up during bootup. maxcpus=n : n >= 0 limits 2526 the kernel to bring up 'n' processors. Surely after 2527 bootup you can bring up the other plugged cpu by executing 2528 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2529 only takes effect during system bootup. 2530 While n=0 is a special case, it is equivalent to "nosmp", 2531 which also disables the IO APIC. 2532 2533 max_loop= [LOOP] The number of loop block devices that get 2534 (loop.max_loop) unconditionally pre-created at init time. The default 2535 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2536 of statically allocating a predefined number, loop 2537 devices can be requested on-demand with the 2538 /dev/loop-control interface. 2539 2540 mce [X86-32] Machine Check Exception 2541 2542 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2543 2544 md= [HW] RAID subsystems devices and level 2545 See Documentation/admin-guide/md.rst. 2546 2547 mdacon= [MDA] 2548 Format: <first>,<last> 2549 Specifies range of consoles to be captured by the MDA. 2550 2551 mds= [X86,INTEL] 2552 Control mitigation for the Micro-architectural Data 2553 Sampling (MDS) vulnerability. 2554 2555 Certain CPUs are vulnerable to an exploit against CPU 2556 internal buffers which can forward information to a 2557 disclosure gadget under certain conditions. 2558 2559 In vulnerable processors, the speculatively 2560 forwarded data can be used in a cache side channel 2561 attack, to access data to which the attacker does 2562 not have direct access. 2563 2564 This parameter controls the MDS mitigation. The 2565 options are: 2566 2567 full - Enable MDS mitigation on vulnerable CPUs 2568 full,nosmt - Enable MDS mitigation and disable 2569 SMT on vulnerable CPUs 2570 off - Unconditionally disable MDS mitigation 2571 2572 On TAA-affected machines, mds=off can be prevented by 2573 an active TAA mitigation as both vulnerabilities are 2574 mitigated with the same mechanism so in order to disable 2575 this mitigation, you need to specify tsx_async_abort=off 2576 too. 2577 2578 Not specifying this option is equivalent to 2579 mds=full. 2580 2581 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2582 2583 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2584 Amount of memory to be used in cases as follows: 2585 2586 1 for test; 2587 2 when the kernel is not able to see the whole system memory; 2588 3 memory that lies after 'mem=' boundary is excluded from 2589 the hypervisor, then assigned to KVM guests. 2590 2591 [X86] Work as limiting max address. Use together 2592 with memmap= to avoid physical address space collisions. 2593 Without memmap= PCI devices could be placed at addresses 2594 belonging to unused RAM. 2595 2596 Note that this only takes effects during boot time since 2597 in above case 3, memory may need be hot added after boot 2598 if system memory of hypervisor is not sufficient. 2599 2600 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2601 memory. 2602 2603 memchunk=nn[KMG] 2604 [KNL,SH] Allow user to override the default size for 2605 per-device physically contiguous DMA buffers. 2606 2607 memhp_default_state=online/offline 2608 [KNL] Set the initial state for the memory hotplug 2609 onlining policy. If not specified, the default value is 2610 set according to the 2611 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2612 option. 2613 See Documentation/admin-guide/mm/memory-hotplug.rst. 2614 2615 memmap=exactmap [KNL,X86] Enable setting of an exact 2616 E820 memory map, as specified by the user. 2617 Such memmap=exactmap lines can be constructed based on 2618 BIOS output or other requirements. See the memmap=nn@ss 2619 option description. 2620 2621 memmap=nn[KMG]@ss[KMG] 2622 [KNL] Force usage of a specific region of memory. 2623 Region of memory to be used is from ss to ss+nn. 2624 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2625 which limits max address to nn[KMG]. 2626 Multiple different regions can be specified, 2627 comma delimited. 2628 Example: 2629 memmap=100M@2G,100M#3G,1G!1024G 2630 2631 memmap=nn[KMG]#ss[KMG] 2632 [KNL,ACPI] Mark specific memory as ACPI data. 2633 Region of memory to be marked is from ss to ss+nn. 2634 2635 memmap=nn[KMG]$ss[KMG] 2636 [KNL,ACPI] Mark specific memory as reserved. 2637 Region of memory to be reserved is from ss to ss+nn. 2638 Example: Exclude memory from 0x18690000-0x1869ffff 2639 memmap=64K$0x18690000 2640 or 2641 memmap=0x10000$0x18690000 2642 Some bootloaders may need an escape character before '$', 2643 like Grub2, otherwise '$' and the following number 2644 will be eaten. 2645 2646 memmap=nn[KMG]!ss[KMG] 2647 [KNL,X86] Mark specific memory as protected. 2648 Region of memory to be used, from ss to ss+nn. 2649 The memory region may be marked as e820 type 12 (0xc) 2650 and is NVDIMM or ADR memory. 2651 2652 memmap=<size>%<offset>-<oldtype>+<newtype> 2653 [KNL,ACPI] Convert memory within the specified region 2654 from <oldtype> to <newtype>. If "-<oldtype>" is left 2655 out, the whole region will be marked as <newtype>, 2656 even if previously unavailable. If "+<newtype>" is left 2657 out, matching memory will be removed. Types are 2658 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2659 3 = ACPI, 12 = PRAM. 2660 2661 memory_corruption_check=0/1 [X86] 2662 Some BIOSes seem to corrupt the first 64k of 2663 memory when doing things like suspend/resume. 2664 Setting this option will scan the memory 2665 looking for corruption. Enabling this will 2666 both detect corruption and prevent the kernel 2667 from using the memory being corrupted. 2668 However, its intended as a diagnostic tool; if 2669 repeatable BIOS-originated corruption always 2670 affects the same memory, you can use memmap= 2671 to prevent the kernel from using that memory. 2672 2673 memory_corruption_check_size=size [X86] 2674 By default it checks for corruption in the low 2675 64k, making this memory unavailable for normal 2676 use. Use this parameter to scan for 2677 corruption in more or less memory. 2678 2679 memory_corruption_check_period=seconds [X86] 2680 By default it checks for corruption every 60 2681 seconds. Use this parameter to check at some 2682 other rate. 0 disables periodic checking. 2683 2684 memtest= [KNL,X86,ARM,PPC] Enable memtest 2685 Format: <integer> 2686 default : 0 <disable> 2687 Specifies the number of memtest passes to be 2688 performed. Each pass selects another test 2689 pattern from a given set of patterns. Memtest 2690 fills the memory with this pattern, validates 2691 memory contents and reserves bad memory 2692 regions that are detected. 2693 2694 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2695 Valid arguments: on, off 2696 Default (depends on kernel configuration option): 2697 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2698 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2699 mem_encrypt=on: Activate SME 2700 mem_encrypt=off: Do not activate SME 2701 2702 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2703 for details on when memory encryption can be activated. 2704 2705 mem_sleep_default= [SUSPEND] Default system suspend mode: 2706 s2idle - Suspend-To-Idle 2707 shallow - Power-On Suspend or equivalent (if supported) 2708 deep - Suspend-To-RAM or equivalent (if supported) 2709 See Documentation/admin-guide/pm/sleep-states.rst. 2710 2711 meye.*= [HW] Set MotionEye Camera parameters 2712 See Documentation/media/v4l-drivers/meye.rst. 2713 2714 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2715 Multi-Function General Purpose Timers on AMD Geode 2716 platforms. 2717 2718 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2719 the BIOS has incorrectly applied a workaround. TinyBIOS 2720 version 0.98 is known to be affected, 0.99 fixes the 2721 problem by letting the user disable the workaround. 2722 2723 mga= [HW,DRM] 2724 2725 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2726 physical address is ignored. 2727 2728 mini2440= [ARM,HW,KNL] 2729 Format:[0..2][b][c][t] 2730 Default: "0tb" 2731 MINI2440 configuration specification: 2732 0 - The attached screen is the 3.5" TFT 2733 1 - The attached screen is the 7" TFT 2734 2 - The VGA Shield is attached (1024x768) 2735 Leaving out the screen size parameter will not load 2736 the TFT driver, and the framebuffer will be left 2737 unconfigured. 2738 b - Enable backlight. The TFT backlight pin will be 2739 linked to the kernel VESA blanking code and a GPIO 2740 LED. This parameter is not necessary when using the 2741 VGA shield. 2742 c - Enable the s3c camera interface. 2743 t - Reserved for enabling touchscreen support. The 2744 touchscreen support is not enabled in the mainstream 2745 kernel as of 2.6.30, a preliminary port can be found 2746 in the "bleeding edge" mini2440 support kernel at 2747 http://repo.or.cz/w/linux-2.6/mini2440.git 2748 2749 mitigations= 2750 [X86,PPC,S390,ARM64] Control optional mitigations for 2751 CPU vulnerabilities. This is a set of curated, 2752 arch-independent options, each of which is an 2753 aggregation of existing arch-specific options. 2754 2755 off 2756 Disable all optional CPU mitigations. This 2757 improves system performance, but it may also 2758 expose users to several CPU vulnerabilities. 2759 Equivalent to: nopti [X86,PPC] 2760 kpti=0 [ARM64] 2761 nospectre_v1 [X86,PPC] 2762 nobp=0 [S390] 2763 nospectre_v2 [X86,PPC,S390,ARM64] 2764 spectre_v2_user=off [X86] 2765 spec_store_bypass_disable=off [X86,PPC] 2766 ssbd=force-off [ARM64] 2767 l1tf=off [X86] 2768 mds=off [X86] 2769 tsx_async_abort=off [X86] 2770 kvm.nx_huge_pages=off [X86] 2771 2772 Exceptions: 2773 This does not have any effect on 2774 kvm.nx_huge_pages when 2775 kvm.nx_huge_pages=force. 2776 2777 auto (default) 2778 Mitigate all CPU vulnerabilities, but leave SMT 2779 enabled, even if it's vulnerable. This is for 2780 users who don't want to be surprised by SMT 2781 getting disabled across kernel upgrades, or who 2782 have other ways of avoiding SMT-based attacks. 2783 Equivalent to: (default behavior) 2784 2785 auto,nosmt 2786 Mitigate all CPU vulnerabilities, disabling SMT 2787 if needed. This is for users who always want to 2788 be fully mitigated, even if it means losing SMT. 2789 Equivalent to: l1tf=flush,nosmt [X86] 2790 mds=full,nosmt [X86] 2791 tsx_async_abort=full,nosmt [X86] 2792 2793 mminit_loglevel= 2794 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2795 parameter allows control of the logging verbosity for 2796 the additional memory initialisation checks. A value 2797 of 0 disables mminit logging and a level of 4 will 2798 log everything. Information is printed at KERN_DEBUG 2799 so loglevel=8 may also need to be specified. 2800 2801 module.sig_enforce 2802 [KNL] When CONFIG_MODULE_SIG is set, this means that 2803 modules without (valid) signatures will fail to load. 2804 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2805 is always true, so this option does nothing. 2806 2807 module_blacklist= [KNL] Do not load a comma-separated list of 2808 modules. Useful for debugging problem modules. 2809 2810 mousedev.tap_time= 2811 [MOUSE] Maximum time between finger touching and 2812 leaving touchpad surface for touch to be considered 2813 a tap and be reported as a left button click (for 2814 touchpads working in absolute mode only). 2815 Format: <msecs> 2816 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2817 reporting absolute coordinates, such as tablets 2818 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2819 reporting absolute coordinates, such as tablets 2820 2821 movablecore= [KNL,X86,IA-64,PPC] 2822 Format: nn[KMGTPE] | nn% 2823 This parameter is the complement to kernelcore=, it 2824 specifies the amount of memory used for migratable 2825 allocations. If both kernelcore and movablecore is 2826 specified, then kernelcore will be at *least* the 2827 specified value but may be more. If movablecore on its 2828 own is specified, the administrator must be careful 2829 that the amount of memory usable for all allocations 2830 is not too small. 2831 2832 movable_node [KNL] Boot-time switch to make hotplugable memory 2833 NUMA nodes to be movable. This means that the memory 2834 of such nodes will be usable only for movable 2835 allocations which rules out almost all kernel 2836 allocations. Use with caution! 2837 2838 MTD_Partition= [MTD] 2839 Format: <name>,<region-number>,<size>,<offset> 2840 2841 MTD_Region= [MTD] Format: 2842 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2843 2844 mtdparts= [MTD] 2845 See drivers/mtd/parsers/cmdlinepart.c 2846 2847 multitce=off [PPC] This parameter disables the use of the pSeries 2848 firmware feature for updating multiple TCE entries 2849 at a time. 2850 2851 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2852 2853 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2854 2855 boundary - index of last SLC block on Flex-OneNAND. 2856 The remaining blocks are configured as MLC blocks. 2857 lock - Configure if Flex-OneNAND boundary should be locked. 2858 Once locked, the boundary cannot be changed. 2859 1 indicates lock status, 0 indicates unlock status. 2860 2861 mtdset= [ARM] 2862 ARM/S3C2412 JIVE boot control 2863 2864 See arch/arm/mach-s3c2412/mach-jive.c 2865 2866 mtouchusb.raw_coordinates= 2867 [HW] Make the MicroTouch USB driver use raw coordinates 2868 ('y', default) or cooked coordinates ('n') 2869 2870 mtrr_chunk_size=nn[KMG] [X86] 2871 used for mtrr cleanup. It is largest continuous chunk 2872 that could hold holes aka. UC entries. 2873 2874 mtrr_gran_size=nn[KMG] [X86] 2875 Used for mtrr cleanup. It is granularity of mtrr block. 2876 Default is 1. 2877 Large value could prevent small alignment from 2878 using up MTRRs. 2879 2880 mtrr_spare_reg_nr=n [X86] 2881 Format: <integer> 2882 Range: 0,7 : spare reg number 2883 Default : 1 2884 Used for mtrr cleanup. It is spare mtrr entries number. 2885 Set to 2 or more if your graphical card needs more. 2886 2887 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2888 2889 netdev= [NET] Network devices parameters 2890 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2891 Note that mem_start is often overloaded to mean 2892 something different and driver-specific. 2893 This usage is only documented in each driver source 2894 file if at all. 2895 2896 nf_conntrack.acct= 2897 [NETFILTER] Enable connection tracking flow accounting 2898 0 to disable accounting 2899 1 to enable accounting 2900 Default value is 0. 2901 2902 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2903 See Documentation/admin-guide/nfs/nfsroot.rst. 2904 2905 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2906 See Documentation/admin-guide/nfs/nfsroot.rst. 2907 2908 nfsrootdebug [NFS] enable nfsroot debugging messages. 2909 See Documentation/admin-guide/nfs/nfsroot.rst. 2910 2911 nfs.callback_nr_threads= 2912 [NFSv4] set the total number of threads that the 2913 NFS client will assign to service NFSv4 callback 2914 requests. 2915 2916 nfs.callback_tcpport= 2917 [NFS] set the TCP port on which the NFSv4 callback 2918 channel should listen. 2919 2920 nfs.cache_getent= 2921 [NFS] sets the pathname to the program which is used 2922 to update the NFS client cache entries. 2923 2924 nfs.cache_getent_timeout= 2925 [NFS] sets the timeout after which an attempt to 2926 update a cache entry is deemed to have failed. 2927 2928 nfs.idmap_cache_timeout= 2929 [NFS] set the maximum lifetime for idmapper cache 2930 entries. 2931 2932 nfs.enable_ino64= 2933 [NFS] enable 64-bit inode numbers. 2934 If zero, the NFS client will fake up a 32-bit inode 2935 number for the readdir() and stat() syscalls instead 2936 of returning the full 64-bit number. 2937 The default is to return 64-bit inode numbers. 2938 2939 nfs.max_session_cb_slots= 2940 [NFSv4.1] Sets the maximum number of session 2941 slots the client will assign to the callback 2942 channel. This determines the maximum number of 2943 callbacks the client will process in parallel for 2944 a particular server. 2945 2946 nfs.max_session_slots= 2947 [NFSv4.1] Sets the maximum number of session slots 2948 the client will attempt to negotiate with the server. 2949 This limits the number of simultaneous RPC requests 2950 that the client can send to the NFSv4.1 server. 2951 Note that there is little point in setting this 2952 value higher than the max_tcp_slot_table_limit. 2953 2954 nfs.nfs4_disable_idmapping= 2955 [NFSv4] When set to the default of '1', this option 2956 ensures that both the RPC level authentication 2957 scheme and the NFS level operations agree to use 2958 numeric uids/gids if the mount is using the 2959 'sec=sys' security flavour. In effect it is 2960 disabling idmapping, which can make migration from 2961 legacy NFSv2/v3 systems to NFSv4 easier. 2962 Servers that do not support this mode of operation 2963 will be autodetected by the client, and it will fall 2964 back to using the idmapper. 2965 To turn off this behaviour, set the value to '0'. 2966 nfs.nfs4_unique_id= 2967 [NFS4] Specify an additional fixed unique ident- 2968 ification string that NFSv4 clients can insert into 2969 their nfs_client_id4 string. This is typically a 2970 UUID that is generated at system install time. 2971 2972 nfs.send_implementation_id = 2973 [NFSv4.1] Send client implementation identification 2974 information in exchange_id requests. 2975 If zero, no implementation identification information 2976 will be sent. 2977 The default is to send the implementation identification 2978 information. 2979 2980 nfs.recover_lost_locks = 2981 [NFSv4] Attempt to recover locks that were lost due 2982 to a lease timeout on the server. Please note that 2983 doing this risks data corruption, since there are 2984 no guarantees that the file will remain unchanged 2985 after the locks are lost. 2986 If you want to enable the kernel legacy behaviour of 2987 attempting to recover these locks, then set this 2988 parameter to '1'. 2989 The default parameter value of '0' causes the kernel 2990 not to attempt recovery of lost locks. 2991 2992 nfs4.layoutstats_timer = 2993 [NFSv4.2] Change the rate at which the kernel sends 2994 layoutstats to the pNFS metadata server. 2995 2996 Setting this to value to 0 causes the kernel to use 2997 whatever value is the default set by the layout 2998 driver. A non-zero value sets the minimum interval 2999 in seconds between layoutstats transmissions. 3000 3001 nfsd.nfs4_disable_idmapping= 3002 [NFSv4] When set to the default of '1', the NFSv4 3003 server will return only numeric uids and gids to 3004 clients using auth_sys, and will accept numeric uids 3005 and gids from such clients. This is intended to ease 3006 migration from NFSv2/v3. 3007 3008 nmi_debug= [KNL,SH] Specify one or more actions to take 3009 when a NMI is triggered. 3010 Format: [state][,regs][,debounce][,die] 3011 3012 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3013 Format: [panic,][nopanic,][num] 3014 Valid num: 0 or 1 3015 0 - turn hardlockup detector in nmi_watchdog off 3016 1 - turn hardlockup detector in nmi_watchdog on 3017 When panic is specified, panic when an NMI watchdog 3018 timeout occurs (or 'nopanic' to not panic on an NMI 3019 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3020 To disable both hard and soft lockup detectors, 3021 please see 'nowatchdog'. 3022 This is useful when you use a panic=... timeout and 3023 need the box quickly up again. 3024 3025 These settings can be accessed at runtime via 3026 the nmi_watchdog and hardlockup_panic sysctls. 3027 3028 netpoll.carrier_timeout= 3029 [NET] Specifies amount of time (in seconds) that 3030 netpoll should wait for a carrier. By default netpoll 3031 waits 4 seconds. 3032 3033 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3034 emulation library even if a 387 maths coprocessor 3035 is present. 3036 3037 no5lvl [X86-64] Disable 5-level paging mode. Forces 3038 kernel to use 4-level paging instead. 3039 3040 no_console_suspend 3041 [HW] Never suspend the console 3042 Disable suspending of consoles during suspend and 3043 hibernate operations. Once disabled, debugging 3044 messages can reach various consoles while the rest 3045 of the system is being put to sleep (ie, while 3046 debugging driver suspend/resume hooks). This may 3047 not work reliably with all consoles, but is known 3048 to work with serial and VGA consoles. 3049 To facilitate more flexible debugging, we also add 3050 console_suspend, a printk module parameter to control 3051 it. Users could use console_suspend (usually 3052 /sys/module/printk/parameters/console_suspend) to 3053 turn on/off it dynamically. 3054 3055 novmcoredd [KNL,KDUMP] 3056 Disable device dump. Device dump allows drivers to 3057 append dump data to vmcore so you can collect driver 3058 specified debug info. Drivers can append the data 3059 without any limit and this data is stored in memory, 3060 so this may cause significant memory stress. Disabling 3061 device dump can help save memory but the driver debug 3062 data will be no longer available. This parameter 3063 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3064 is set. 3065 3066 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3067 caches in the slab allocator. Saves per-node memory, 3068 but will impact performance. 3069 3070 noalign [KNL,ARM] 3071 3072 noaltinstr [S390] Disables alternative instructions patching 3073 (CPU alternatives feature). 3074 3075 noapic [SMP,APIC] Tells the kernel to not make use of any 3076 IOAPICs that may be present in the system. 3077 3078 noautogroup Disable scheduler automatic task group creation. 3079 3080 nobats [PPC] Do not use BATs for mapping kernel lowmem 3081 on "Classic" PPC cores. 3082 3083 nocache [ARM] 3084 3085 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3086 3087 nodelayacct [KNL] Disable per-task delay accounting 3088 3089 nodsp [SH] Disable hardware DSP at boot time. 3090 3091 noefi Disable EFI runtime services support. 3092 3093 noexec [IA-64] 3094 3095 noexec [X86] 3096 On X86-32 available only on PAE configured kernels. 3097 noexec=on: enable non-executable mappings (default) 3098 noexec=off: disable non-executable mappings 3099 3100 nosmap [X86,PPC] 3101 Disable SMAP (Supervisor Mode Access Prevention) 3102 even if it is supported by processor. 3103 3104 nosmep [X86,PPC] 3105 Disable SMEP (Supervisor Mode Execution Prevention) 3106 even if it is supported by processor. 3107 3108 noexec32 [X86-64] 3109 This affects only 32-bit executables. 3110 noexec32=on: enable non-executable mappings (default) 3111 read doesn't imply executable mappings 3112 noexec32=off: disable non-executable mappings 3113 read implies executable mappings 3114 3115 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3116 3117 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3118 register save and restore. The kernel will only save 3119 legacy floating-point registers on task switch. 3120 3121 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3122 3123 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3124 Equivalent to smt=1. 3125 3126 [KNL,x86] Disable symmetric multithreading (SMT). 3127 nosmt=force: Force disable SMT, cannot be undone 3128 via the sysfs control file. 3129 3130 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3131 (bounds check bypass). With this option data leaks are 3132 possible in the system. 3133 3134 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3135 the Spectre variant 2 (indirect branch prediction) 3136 vulnerability. System may allow data leaks with this 3137 option. 3138 3139 nospec_store_bypass_disable 3140 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3141 3142 noxsave [BUGS=X86] Disables x86 extended register state save 3143 and restore using xsave. The kernel will fallback to 3144 enabling legacy floating-point and sse state. 3145 3146 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3147 register states. The kernel will fall back to use 3148 xsave to save the states. By using this parameter, 3149 performance of saving the states is degraded because 3150 xsave doesn't support modified optimization while 3151 xsaveopt supports it on xsaveopt enabled systems. 3152 3153 noxsaves [X86] Disables xsaves and xrstors used in saving and 3154 restoring x86 extended register state in compacted 3155 form of xsave area. The kernel will fall back to use 3156 xsaveopt and xrstor to save and restore the states 3157 in standard form of xsave area. By using this 3158 parameter, xsave area per process might occupy more 3159 memory on xsaves enabled systems. 3160 3161 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3162 wfi(ARM) instruction doesn't work correctly and not to 3163 use it. This is also useful when using JTAG debugger. 3164 3165 no_file_caps Tells the kernel not to honor file capabilities. The 3166 only way then for a file to be executed with privilege 3167 is to be setuid root or executed by root. 3168 3169 nohalt [IA-64] Tells the kernel not to use the power saving 3170 function PAL_HALT_LIGHT when idle. This increases 3171 power-consumption. On the positive side, it reduces 3172 interrupt wake-up latency, which may improve performance 3173 in certain environments such as networked servers or 3174 real-time systems. 3175 3176 nohibernate [HIBERNATION] Disable hibernation and resume. 3177 3178 nohz= [KNL] Boottime enable/disable dynamic ticks 3179 Valid arguments: on, off 3180 Default: on 3181 3182 nohz_full= [KNL,BOOT,SMP,ISOL] 3183 The argument is a cpu list, as described above. 3184 In kernels built with CONFIG_NO_HZ_FULL=y, set 3185 the specified list of CPUs whose tick will be stopped 3186 whenever possible. The boot CPU will be forced outside 3187 the range to maintain the timekeeping. Any CPUs 3188 in this list will have their RCU callbacks offloaded, 3189 just as if they had also been called out in the 3190 rcu_nocbs= boot parameter. 3191 3192 noiotrap [SH] Disables trapped I/O port accesses. 3193 3194 noirqdebug [X86-32] Disables the code which attempts to detect and 3195 disable unhandled interrupt sources. 3196 3197 no_timer_check [X86,APIC] Disables the code which tests for 3198 broken timer IRQ sources. 3199 3200 noisapnp [ISAPNP] Disables ISA PnP code. 3201 3202 noinitrd [RAM] Tells the kernel not to load any configured 3203 initial RAM disk. 3204 3205 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3206 remapping. 3207 [Deprecated - use intremap=off] 3208 3209 nointroute [IA-64] 3210 3211 noinvpcid [X86] Disable the INVPCID cpu feature. 3212 3213 nojitter [IA-64] Disables jitter checking for ITC timers. 3214 3215 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3216 3217 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3218 fault handling. 3219 3220 no-vmw-sched-clock 3221 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3222 clock and use the default one. 3223 3224 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3225 accounting. steal time is computed, but won't 3226 influence scheduler behaviour 3227 3228 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3229 3230 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3231 3232 noltlbs [PPC] Do not use large page/tlb entries for kernel 3233 lowmem mapping on PPC40x and PPC8xx 3234 3235 nomca [IA-64] Disable machine check abort handling 3236 3237 nomce [X86-32] Disable Machine Check Exception 3238 3239 nomfgpt [X86-32] Disable Multi-Function General Purpose 3240 Timer usage (for AMD Geode machines). 3241 3242 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3243 shutdown the other cpus. Instead use the REBOOT_VECTOR 3244 irq. 3245 3246 nomodule Disable module load 3247 3248 nopat [X86] Disable PAT (page attribute table extension of 3249 pagetables) support. 3250 3251 nopcid [X86-64] Disable the PCID cpu feature. 3252 3253 norandmaps Don't use address space randomization. Equivalent to 3254 echo 0 > /proc/sys/kernel/randomize_va_space 3255 3256 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3257 with UP alternatives 3258 3259 nordrand [X86] Disable kernel use of the RDRAND and 3260 RDSEED instructions even if they are supported 3261 by the processor. RDRAND and RDSEED are still 3262 available to user space applications. 3263 3264 noresume [SWSUSP] Disables resume and restores original swap 3265 space. 3266 3267 no-scroll [VGA] Disables scrollback. 3268 This is required for the Braillex ib80-piezo Braille 3269 reader made by F.H. Papenmeier (Germany). 3270 3271 nosbagart [IA-64] 3272 3273 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3274 3275 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3276 and disable the IO APIC. legacy for "maxcpus=0". 3277 3278 nosoftlockup [KNL] Disable the soft-lockup detector. 3279 3280 nosync [HW,M68K] Disables sync negotiation for all devices. 3281 3282 nowatchdog [KNL] Disable both lockup detectors, i.e. 3283 soft-lockup and NMI watchdog (hard-lockup). 3284 3285 nowb [ARM] 3286 3287 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3288 3289 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3290 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3291 Some features depend on CPU0. Known dependencies are: 3292 1. Resume from suspend/hibernate depends on CPU0. 3293 Suspend/hibernate will fail if CPU0 is offline and you 3294 need to online CPU0 before suspend/hibernate. 3295 2. PIC interrupts also depend on CPU0. CPU0 can't be 3296 removed if a PIC interrupt is detected. 3297 It's said poweroff/reboot may depend on CPU0 on some 3298 machines although I haven't seen such issues so far 3299 after CPU0 is offline on a few tested machines. 3300 If the dependencies are under your control, you can 3301 turn on cpu0_hotplug. 3302 3303 nps_mtm_hs_ctr= [KNL,ARC] 3304 This parameter sets the maximum duration, in 3305 cycles, each HW thread of the CTOP can run 3306 without interruptions, before HW switches it. 3307 The actual maximum duration is 16 times this 3308 parameter's value. 3309 Format: integer between 1 and 255 3310 Default: 255 3311 3312 nptcg= [IA-64] Override max number of concurrent global TLB 3313 purges which is reported from either PAL_VM_SUMMARY or 3314 SAL PALO. 3315 3316 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3317 could support. nr_cpus=n : n >= 1 limits the kernel to 3318 support 'n' processors. It could be larger than the 3319 number of already plugged CPU during bootup, later in 3320 runtime you can physically add extra cpu until it reaches 3321 n. So during boot up some boot time memory for per-cpu 3322 variables need be pre-allocated for later physical cpu 3323 hot plugging. 3324 3325 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3326 3327 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3328 Allowed values are enable and disable 3329 3330 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3331 'node', 'default' can be specified 3332 This can be set from sysctl after boot. 3333 See Documentation/admin-guide/sysctl/vm.rst for details. 3334 3335 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3336 See Documentation/debugging-via-ohci1394.txt for more 3337 info. 3338 3339 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3340 Rather than timing out after 20 ms if an EC 3341 command is not properly ACKed, override the length 3342 of the timeout. We have interrupts disabled while 3343 waiting for the ACK, so if this is set too high 3344 interrupts *may* be lost! 3345 3346 omap_mux= [OMAP] Override bootloader pin multiplexing. 3347 Format: <mux_mode0.mode_name=value>... 3348 For example, to override I2C bus2: 3349 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3350 3351 oprofile.timer= [HW] 3352 Use timer interrupt instead of performance counters 3353 3354 oprofile.cpu_type= Force an oprofile cpu type 3355 This might be useful if you have an older oprofile 3356 userland or if you want common events. 3357 Format: { arch_perfmon } 3358 arch_perfmon: [X86] Force use of architectural 3359 perfmon on Intel CPUs instead of the 3360 CPU specific event set. 3361 timer: [X86] Force use of architectural NMI 3362 timer mode (see also oprofile.timer 3363 for generic hr timer mode) 3364 3365 oops=panic Always panic on oopses. Default is to just kill the 3366 process, but there is a small probability of 3367 deadlocking the machine. 3368 This will also cause panics on machine check exceptions. 3369 Useful together with panic=30 to trigger a reboot. 3370 3371 page_alloc.shuffle= 3372 [KNL] Boolean flag to control whether the page allocator 3373 should randomize its free lists. The randomization may 3374 be automatically enabled if the kernel detects it is 3375 running on a platform with a direct-mapped memory-side 3376 cache, and this parameter can be used to 3377 override/disable that behavior. The state of the flag 3378 can be read from sysfs at: 3379 /sys/module/page_alloc/parameters/shuffle. 3380 3381 page_owner= [KNL] Boot-time page_owner enabling option. 3382 Storage of the information about who allocated 3383 each page is disabled in default. With this switch, 3384 we can turn it on. 3385 on: enable the feature 3386 3387 page_poison= [KNL] Boot-time parameter changing the state of 3388 poisoning on the buddy allocator, available with 3389 CONFIG_PAGE_POISONING=y. 3390 off: turn off poisoning (default) 3391 on: turn on poisoning 3392 3393 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3394 timeout > 0: seconds before rebooting 3395 timeout = 0: wait forever 3396 timeout < 0: reboot immediately 3397 Format: <timeout> 3398 3399 panic_print= Bitmask for printing system info when panic happens. 3400 User can chose combination of the following bits: 3401 bit 0: print all tasks info 3402 bit 1: print system memory info 3403 bit 2: print timer info 3404 bit 3: print locks info if CONFIG_LOCKDEP is on 3405 bit 4: print ftrace buffer 3406 bit 5: print all printk messages in buffer 3407 3408 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3409 on a WARN(). 3410 3411 crash_kexec_post_notifiers 3412 Run kdump after running panic-notifiers and dumping 3413 kmsg. This only for the users who doubt kdump always 3414 succeeds in any situation. 3415 Note that this also increases risks of kdump failure, 3416 because some panic notifiers can make the crashed 3417 kernel more unstable. 3418 3419 parkbd.port= [HW] Parallel port number the keyboard adapter is 3420 connected to, default is 0. 3421 Format: <parport#> 3422 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3423 0 for XT, 1 for AT (default is AT). 3424 Format: <mode> 3425 3426 parport= [HW,PPT] Specify parallel ports. 0 disables. 3427 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3428 Use 'auto' to force the driver to use any 3429 IRQ/DMA settings detected (the default is to 3430 ignore detected IRQ/DMA settings because of 3431 possible conflicts). You can specify the base 3432 address, IRQ, and DMA settings; IRQ and DMA 3433 should be numbers, or 'auto' (for using detected 3434 settings on that particular port), or 'nofifo' 3435 (to avoid using a FIFO even if it is detected). 3436 Parallel ports are assigned in the order they 3437 are specified on the command line, starting 3438 with parport0. 3439 3440 parport_init_mode= [HW,PPT] 3441 Configure VIA parallel port to operate in 3442 a specific mode. This is necessary on Pegasos 3443 computer where firmware has no options for setting 3444 up parallel port mode and sets it to spp. 3445 Currently this function knows 686a and 8231 chips. 3446 Format: [spp|ps2|epp|ecp|ecpepp] 3447 3448 pause_on_oops= 3449 Halt all CPUs after the first oops has been printed for 3450 the specified number of seconds. This is to be used if 3451 your oopses keep scrolling off the screen. 3452 3453 pcbit= [HW,ISDN] 3454 3455 pcd. [PARIDE] 3456 See header of drivers/block/paride/pcd.c. 3457 See also Documentation/admin-guide/blockdev/paride.rst. 3458 3459 pci=option[,option...] [PCI] various PCI subsystem options. 3460 3461 Some options herein operate on a specific device 3462 or a set of devices (<pci_dev>). These are 3463 specified in one of the following formats: 3464 3465 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3466 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3467 3468 Note: the first format specifies a PCI 3469 bus/device/function address which may change 3470 if new hardware is inserted, if motherboard 3471 firmware changes, or due to changes caused 3472 by other kernel parameters. If the 3473 domain is left unspecified, it is 3474 taken to be zero. Optionally, a path 3475 to a device through multiple device/function 3476 addresses can be specified after the base 3477 address (this is more robust against 3478 renumbering issues). The second format 3479 selects devices using IDs from the 3480 configuration space which may match multiple 3481 devices in the system. 3482 3483 earlydump dump PCI config space before the kernel 3484 changes anything 3485 off [X86] don't probe for the PCI bus 3486 bios [X86-32] force use of PCI BIOS, don't access 3487 the hardware directly. Use this if your machine 3488 has a non-standard PCI host bridge. 3489 nobios [X86-32] disallow use of PCI BIOS, only direct 3490 hardware access methods are allowed. Use this 3491 if you experience crashes upon bootup and you 3492 suspect they are caused by the BIOS. 3493 conf1 [X86] Force use of PCI Configuration Access 3494 Mechanism 1 (config address in IO port 0xCF8, 3495 data in IO port 0xCFC, both 32-bit). 3496 conf2 [X86] Force use of PCI Configuration Access 3497 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3498 the function, IO port 0xCFA, also 8-bit, sets 3499 bus number. The config space is then accessed 3500 through ports 0xC000-0xCFFF). 3501 See http://wiki.osdev.org/PCI for more info 3502 on the configuration access mechanisms. 3503 noaer [PCIE] If the PCIEAER kernel config parameter is 3504 enabled, this kernel boot option can be used to 3505 disable the use of PCIE advanced error reporting. 3506 nodomains [PCI] Disable support for multiple PCI 3507 root domains (aka PCI segments, in ACPI-speak). 3508 nommconf [X86] Disable use of MMCONFIG for PCI 3509 Configuration 3510 check_enable_amd_mmconf [X86] check for and enable 3511 properly configured MMIO access to PCI 3512 config space on AMD family 10h CPU 3513 nomsi [MSI] If the PCI_MSI kernel config parameter is 3514 enabled, this kernel boot option can be used to 3515 disable the use of MSI interrupts system-wide. 3516 noioapicquirk [APIC] Disable all boot interrupt quirks. 3517 Safety option to keep boot IRQs enabled. This 3518 should never be necessary. 3519 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3520 primary IO-APIC for bridges that cannot disable 3521 boot IRQs. This fixes a source of spurious IRQs 3522 when the system masks IRQs. 3523 noioapicreroute [APIC] Disable workaround that uses the 3524 boot IRQ equivalent of an IRQ that connects to 3525 a chipset where boot IRQs cannot be disabled. 3526 The opposite of ioapicreroute. 3527 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3528 routing table. These calls are known to be buggy 3529 on several machines and they hang the machine 3530 when used, but on other computers it's the only 3531 way to get the interrupt routing table. Try 3532 this option if the kernel is unable to allocate 3533 IRQs or discover secondary PCI buses on your 3534 motherboard. 3535 rom [X86] Assign address space to expansion ROMs. 3536 Use with caution as certain devices share 3537 address decoders between ROMs and other 3538 resources. 3539 norom [X86] Do not assign address space to 3540 expansion ROMs that do not already have 3541 BIOS assigned address ranges. 3542 nobar [X86] Do not assign address space to the 3543 BARs that weren't assigned by the BIOS. 3544 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3545 assigned automatically to PCI devices. You can 3546 make the kernel exclude IRQs of your ISA cards 3547 this way. 3548 pirqaddr=0xAAAAA [X86] Specify the physical address 3549 of the PIRQ table (normally generated 3550 by the BIOS) if it is outside the 3551 F0000h-100000h range. 3552 lastbus=N [X86] Scan all buses thru bus #N. Can be 3553 useful if the kernel is unable to find your 3554 secondary buses and you want to tell it 3555 explicitly which ones they are. 3556 assign-busses [X86] Always assign all PCI bus 3557 numbers ourselves, overriding 3558 whatever the firmware may have done. 3559 usepirqmask [X86] Honor the possible IRQ mask stored 3560 in the BIOS $PIR table. This is needed on 3561 some systems with broken BIOSes, notably 3562 some HP Pavilion N5400 and Omnibook XE3 3563 notebooks. This will have no effect if ACPI 3564 IRQ routing is enabled. 3565 noacpi [X86] Do not use ACPI for IRQ routing 3566 or for PCI scanning. 3567 use_crs [X86] Use PCI host bridge window information 3568 from ACPI. On BIOSes from 2008 or later, this 3569 is enabled by default. If you need to use this, 3570 please report a bug. 3571 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3572 If you need to use this, please report a bug. 3573 routeirq Do IRQ routing for all PCI devices. 3574 This is normally done in pci_enable_device(), 3575 so this option is a temporary workaround 3576 for broken drivers that don't call it. 3577 skip_isa_align [X86] do not align io start addr, so can 3578 handle more pci cards 3579 noearly [X86] Don't do any early type 1 scanning. 3580 This might help on some broken boards which 3581 machine check when some devices' config space 3582 is read. But various workarounds are disabled 3583 and some IOMMU drivers will not work. 3584 bfsort Sort PCI devices into breadth-first order. 3585 This sorting is done to get a device 3586 order compatible with older (<= 2.4) kernels. 3587 nobfsort Don't sort PCI devices into breadth-first order. 3588 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3589 tuning and use the BIOS-configured MPS defaults. 3590 pcie_bus_safe Set every device's MPS to the largest value 3591 supported by all devices below the root complex. 3592 pcie_bus_perf Set device MPS to the largest allowable MPS 3593 based on its parent bus. Also set MRRS (Max 3594 Read Request Size) to the largest supported 3595 value (no larger than the MPS that the device 3596 or bus can support) for best performance. 3597 pcie_bus_peer2peer Set every device's MPS to 128B, which 3598 every device is guaranteed to support. This 3599 configuration allows peer-to-peer DMA between 3600 any pair of devices, possibly at the cost of 3601 reduced performance. This also guarantees 3602 that hot-added devices will work. 3603 cbiosize=nn[KMG] The fixed amount of bus space which is 3604 reserved for the CardBus bridge's IO window. 3605 The default value is 256 bytes. 3606 cbmemsize=nn[KMG] The fixed amount of bus space which is 3607 reserved for the CardBus bridge's memory 3608 window. The default value is 64 megabytes. 3609 resource_alignment= 3610 Format: 3611 [<order of align>@]<pci_dev>[; ...] 3612 Specifies alignment and device to reassign 3613 aligned memory resources. How to 3614 specify the device is described above. 3615 If <order of align> is not specified, 3616 PAGE_SIZE is used as alignment. 3617 A PCI-PCI bridge can be specified if resource 3618 windows need to be expanded. 3619 To specify the alignment for several 3620 instances of a device, the PCI vendor, 3621 device, subvendor, and subdevice may be 3622 specified, e.g., 12@pci:8086:9c22:103c:198f 3623 for 4096-byte alignment. 3624 ecrc= Enable/disable PCIe ECRC (transaction layer 3625 end-to-end CRC checking). 3626 bios: Use BIOS/firmware settings. This is the 3627 the default. 3628 off: Turn ECRC off 3629 on: Turn ECRC on. 3630 hpiosize=nn[KMG] The fixed amount of bus space which is 3631 reserved for hotplug bridge's IO window. 3632 Default size is 256 bytes. 3633 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3634 reserved for hotplug bridge's MMIO window. 3635 Default size is 2 megabytes. 3636 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3637 reserved for hotplug bridge's MMIO_PREF window. 3638 Default size is 2 megabytes. 3639 hpmemsize=nn[KMG] The fixed amount of bus space which is 3640 reserved for hotplug bridge's MMIO and 3641 MMIO_PREF window. 3642 Default size is 2 megabytes. 3643 hpbussize=nn The minimum amount of additional bus numbers 3644 reserved for buses below a hotplug bridge. 3645 Default is 1. 3646 realloc= Enable/disable reallocating PCI bridge resources 3647 if allocations done by BIOS are too small to 3648 accommodate resources required by all child 3649 devices. 3650 off: Turn realloc off 3651 on: Turn realloc on 3652 realloc same as realloc=on 3653 noari do not use PCIe ARI. 3654 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3655 do not use PCIe ATS (and IOMMU device IOTLB). 3656 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3657 only look for one device below a PCIe downstream 3658 port. 3659 big_root_window Try to add a big 64bit memory window to the PCIe 3660 root complex on AMD CPUs. Some GFX hardware 3661 can resize a BAR to allow access to all VRAM. 3662 Adding the window is slightly risky (it may 3663 conflict with unreported devices), so this 3664 taints the kernel. 3665 disable_acs_redir=<pci_dev>[; ...] 3666 Specify one or more PCI devices (in the format 3667 specified above) separated by semicolons. 3668 Each device specified will have the PCI ACS 3669 redirect capabilities forced off which will 3670 allow P2P traffic between devices through 3671 bridges without forcing it upstream. Note: 3672 this removes isolation between devices and 3673 may put more devices in an IOMMU group. 3674 force_floating [S390] Force usage of floating interrupts. 3675 nomio [S390] Do not use MIO instructions. 3676 3677 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3678 Management. 3679 off Disable ASPM. 3680 force Enable ASPM even on devices that claim not to support it. 3681 WARNING: Forcing ASPM on may cause system lockups. 3682 3683 pcie_ports= [PCIE] PCIe port services handling: 3684 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3685 even if the platform doesn't give the OS permission to 3686 use them. This may cause conflicts if the platform 3687 also tries to use these services. 3688 dpc-native Use native PCIe service for DPC only. May 3689 cause conflicts if firmware uses AER or DPC. 3690 compat Disable native PCIe services (PME, AER, DPC, PCIe 3691 hotplug). 3692 3693 pcie_port_pm= [PCIE] PCIe port power management handling: 3694 off Disable power management of all PCIe ports 3695 force Forcibly enable power management of all PCIe ports 3696 3697 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3698 nomsi Do not use MSI for native PCIe PME signaling (this makes 3699 all PCIe root ports use INTx for all services). 3700 3701 pcmv= [HW,PCMCIA] BadgePAD 4 3702 3703 pd_ignore_unused 3704 [PM] 3705 Keep all power-domains already enabled by bootloader on, 3706 even if no driver has claimed them. This is useful 3707 for debug and development, but should not be 3708 needed on a platform with proper driver support. 3709 3710 pd. [PARIDE] 3711 See Documentation/admin-guide/blockdev/paride.rst. 3712 3713 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3714 boot time. 3715 Format: { 0 | 1 } 3716 See arch/parisc/kernel/pdc_chassis.c 3717 3718 percpu_alloc= Select which percpu first chunk allocator to use. 3719 Currently supported values are "embed" and "page". 3720 Archs may support subset or none of the selections. 3721 See comments in mm/percpu.c for details on each 3722 allocator. This parameter is primarily for debugging 3723 and performance comparison. 3724 3725 pf. [PARIDE] 3726 See Documentation/admin-guide/blockdev/paride.rst. 3727 3728 pg. [PARIDE] 3729 See Documentation/admin-guide/blockdev/paride.rst. 3730 3731 pirq= [SMP,APIC] Manual mp-table setup 3732 See Documentation/x86/i386/IO-APIC.rst. 3733 3734 plip= [PPT,NET] Parallel port network link 3735 Format: { parport<nr> | timid | 0 } 3736 See also Documentation/admin-guide/parport.rst. 3737 3738 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3739 Override pmtimer IOPort with a hex value. 3740 e.g. pmtmr=0x508 3741 3742 pm_debug_messages [SUSPEND,KNL] 3743 Enable suspend/resume debug messages during boot up. 3744 3745 pnp.debug=1 [PNP] 3746 Enable PNP debug messages (depends on the 3747 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3748 via /sys/module/pnp/parameters/debug. We always show 3749 current resource usage; turning this on also shows 3750 possible settings and some assignment information. 3751 3752 pnpacpi= [ACPI] 3753 { off } 3754 3755 pnpbios= [ISAPNP] 3756 { on | off | curr | res | no-curr | no-res } 3757 3758 pnp_reserve_irq= 3759 [ISAPNP] Exclude IRQs for the autoconfiguration 3760 3761 pnp_reserve_dma= 3762 [ISAPNP] Exclude DMAs for the autoconfiguration 3763 3764 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3765 Ranges are in pairs (I/O port base and size). 3766 3767 pnp_reserve_mem= 3768 [ISAPNP] Exclude memory regions for the 3769 autoconfiguration. 3770 Ranges are in pairs (memory base and size). 3771 3772 ports= [IP_VS_FTP] IPVS ftp helper module 3773 Default is 21. 3774 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3775 may be specified. 3776 Format: <port>,<port>.... 3777 3778 powersave=off [PPC] This option disables power saving features. 3779 It specifically disables cpuidle and sets the 3780 platform machine description specific power_save 3781 function to NULL. On Idle the CPU just reduces 3782 execution priority. 3783 3784 ppc_strict_facility_enable 3785 [PPC] This option catches any kernel floating point, 3786 Altivec, VSX and SPE outside of regions specifically 3787 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3788 There is some performance impact when enabling this. 3789 3790 ppc_tm= [PPC] 3791 Format: {"off"} 3792 Disable Hardware Transactional Memory 3793 3794 print-fatal-signals= 3795 [KNL] debug: print fatal signals 3796 3797 If enabled, warn about various signal handling 3798 related application anomalies: too many signals, 3799 too many POSIX.1 timers, fatal signals causing a 3800 coredump - etc. 3801 3802 If you hit the warning due to signal overflow, 3803 you might want to try "ulimit -i unlimited". 3804 3805 default: off. 3806 3807 printk.always_kmsg_dump= 3808 Trigger kmsg_dump for cases other than kernel oops or 3809 panics 3810 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3811 default: disabled 3812 3813 printk.devkmsg={on,off,ratelimit} 3814 Control writing to /dev/kmsg. 3815 on - unlimited logging to /dev/kmsg from userspace 3816 off - logging to /dev/kmsg disabled 3817 ratelimit - ratelimit the logging 3818 Default: ratelimit 3819 3820 printk.time= Show timing data prefixed to each printk message line 3821 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3822 3823 processor.max_cstate= [HW,ACPI] 3824 Limit processor to maximum C-state 3825 max_cstate=9 overrides any DMI blacklist limit. 3826 3827 processor.nocst [HW,ACPI] 3828 Ignore the _CST method to determine C-states, 3829 instead using the legacy FADT method 3830 3831 profile= [KNL] Enable kernel profiling via /proc/profile 3832 Format: [<profiletype>,]<number> 3833 Param: <profiletype>: "schedule", "sleep", or "kvm" 3834 [defaults to kernel profiling] 3835 Param: "schedule" - profile schedule points. 3836 Param: "sleep" - profile D-state sleeping (millisecs). 3837 Requires CONFIG_SCHEDSTATS 3838 Param: "kvm" - profile VM exits. 3839 Param: <number> - step/bucket size as a power of 2 for 3840 statistical time based profiling. 3841 3842 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3843 before loading. 3844 See Documentation/admin-guide/blockdev/ramdisk.rst. 3845 3846 prot_virt= [S390] enable hosting protected virtual machines 3847 isolated from the hypervisor (if hardware supports 3848 that). 3849 Format: <bool> 3850 3851 psi= [KNL] Enable or disable pressure stall information 3852 tracking. 3853 Format: <bool> 3854 3855 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3856 probe for; one of (bare|imps|exps|lifebook|any). 3857 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3858 per second. 3859 psmouse.resetafter= [HW,MOUSE] 3860 Try to reset the device after so many bad packets 3861 (0 = never). 3862 psmouse.resolution= 3863 [HW,MOUSE] Set desired mouse resolution, in dpi. 3864 psmouse.smartscroll= 3865 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3866 0 = disabled, 1 = enabled (default). 3867 3868 pstore.backend= Specify the name of the pstore backend to use 3869 3870 pt. [PARIDE] 3871 See Documentation/admin-guide/blockdev/paride.rst. 3872 3873 pti= [X86_64] Control Page Table Isolation of user and 3874 kernel address spaces. Disabling this feature 3875 removes hardening, but improves performance of 3876 system calls and interrupts. 3877 3878 on - unconditionally enable 3879 off - unconditionally disable 3880 auto - kernel detects whether your CPU model is 3881 vulnerable to issues that PTI mitigates 3882 3883 Not specifying this option is equivalent to pti=auto. 3884 3885 nopti [X86_64] 3886 Equivalent to pti=off 3887 3888 pty.legacy_count= 3889 [KNL] Number of legacy pty's. Overwrites compiled-in 3890 default number. 3891 3892 quiet [KNL] Disable most log messages 3893 3894 r128= [HW,DRM] 3895 3896 raid= [HW,RAID] 3897 See Documentation/admin-guide/md.rst. 3898 3899 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3900 See Documentation/admin-guide/blockdev/ramdisk.rst. 3901 3902 random.trust_cpu={on,off} 3903 [KNL] Enable or disable trusting the use of the 3904 CPU's random number generator (if available) to 3905 fully seed the kernel's CRNG. Default is controlled 3906 by CONFIG_RANDOM_TRUST_CPU. 3907 3908 ras=option[,option,...] [KNL] RAS-specific options 3909 3910 cec_disable [X86] 3911 Disable the Correctable Errors Collector, 3912 see CONFIG_RAS_CEC help text. 3913 3914 rcu_nocbs= [KNL] 3915 The argument is a cpu list, as described above, 3916 except that the string "all" can be used to 3917 specify every CPU on the system. 3918 3919 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3920 the specified list of CPUs to be no-callback CPUs. 3921 Invocation of these CPUs' RCU callbacks will be 3922 offloaded to "rcuox/N" kthreads created for that 3923 purpose, where "x" is "p" for RCU-preempt, and 3924 "s" for RCU-sched, and "N" is the CPU number. 3925 This reduces OS jitter on the offloaded CPUs, 3926 which can be useful for HPC and real-time 3927 workloads. It can also improve energy efficiency 3928 for asymmetric multiprocessors. 3929 3930 rcu_nocb_poll [KNL] 3931 Rather than requiring that offloaded CPUs 3932 (specified by rcu_nocbs= above) explicitly 3933 awaken the corresponding "rcuoN" kthreads, 3934 make these kthreads poll for callbacks. 3935 This improves the real-time response for the 3936 offloaded CPUs by relieving them of the need to 3937 wake up the corresponding kthread, but degrades 3938 energy efficiency by requiring that the kthreads 3939 periodically wake up to do the polling. 3940 3941 rcutree.blimit= [KNL] 3942 Set maximum number of finished RCU callbacks to 3943 process in one batch. 3944 3945 rcutree.dump_tree= [KNL] 3946 Dump the structure of the rcu_node combining tree 3947 out at early boot. This is used for diagnostic 3948 purposes, to verify correct tree setup. 3949 3950 rcutree.gp_cleanup_delay= [KNL] 3951 Set the number of jiffies to delay each step of 3952 RCU grace-period cleanup. 3953 3954 rcutree.gp_init_delay= [KNL] 3955 Set the number of jiffies to delay each step of 3956 RCU grace-period initialization. 3957 3958 rcutree.gp_preinit_delay= [KNL] 3959 Set the number of jiffies to delay each step of 3960 RCU grace-period pre-initialization, that is, 3961 the propagation of recent CPU-hotplug changes up 3962 the rcu_node combining tree. 3963 3964 rcutree.use_softirq= [KNL] 3965 If set to zero, move all RCU_SOFTIRQ processing to 3966 per-CPU rcuc kthreads. Defaults to a non-zero 3967 value, meaning that RCU_SOFTIRQ is used by default. 3968 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3969 3970 rcutree.rcu_fanout_exact= [KNL] 3971 Disable autobalancing of the rcu_node combining 3972 tree. This is used by rcutorture, and might 3973 possibly be useful for architectures having high 3974 cache-to-cache transfer latencies. 3975 3976 rcutree.rcu_fanout_leaf= [KNL] 3977 Change the number of CPUs assigned to each 3978 leaf rcu_node structure. Useful for very 3979 large systems, which will choose the value 64, 3980 and for NUMA systems with large remote-access 3981 latencies, which will choose a value aligned 3982 with the appropriate hardware boundaries. 3983 3984 rcutree.jiffies_till_first_fqs= [KNL] 3985 Set delay from grace-period initialization to 3986 first attempt to force quiescent states. 3987 Units are jiffies, minimum value is zero, 3988 and maximum value is HZ. 3989 3990 rcutree.jiffies_till_next_fqs= [KNL] 3991 Set delay between subsequent attempts to force 3992 quiescent states. Units are jiffies, minimum 3993 value is one, and maximum value is HZ. 3994 3995 rcutree.jiffies_till_sched_qs= [KNL] 3996 Set required age in jiffies for a 3997 given grace period before RCU starts 3998 soliciting quiescent-state help from 3999 rcu_note_context_switch() and cond_resched(). 4000 If not specified, the kernel will calculate 4001 a value based on the most recent settings 4002 of rcutree.jiffies_till_first_fqs 4003 and rcutree.jiffies_till_next_fqs. 4004 This calculated value may be viewed in 4005 rcutree.jiffies_to_sched_qs. Any attempt to set 4006 rcutree.jiffies_to_sched_qs will be cheerfully 4007 overwritten. 4008 4009 rcutree.kthread_prio= [KNL,BOOT] 4010 Set the SCHED_FIFO priority of the RCU per-CPU 4011 kthreads (rcuc/N). This value is also used for 4012 the priority of the RCU boost threads (rcub/N) 4013 and for the RCU grace-period kthreads (rcu_bh, 4014 rcu_preempt, and rcu_sched). If RCU_BOOST is 4015 set, valid values are 1-99 and the default is 1 4016 (the least-favored priority). Otherwise, when 4017 RCU_BOOST is not set, valid values are 0-99 and 4018 the default is zero (non-realtime operation). 4019 4020 rcutree.rcu_nocb_gp_stride= [KNL] 4021 Set the number of NOCB callback kthreads in 4022 each group, which defaults to the square root 4023 of the number of CPUs. Larger numbers reduce 4024 the wakeup overhead on the global grace-period 4025 kthread, but increases that same overhead on 4026 each group's NOCB grace-period kthread. 4027 4028 rcutree.qhimark= [KNL] 4029 Set threshold of queued RCU callbacks beyond which 4030 batch limiting is disabled. 4031 4032 rcutree.qlowmark= [KNL] 4033 Set threshold of queued RCU callbacks below which 4034 batch limiting is re-enabled. 4035 4036 rcutree.qovld= [KNL] 4037 Set threshold of queued RCU callbacks beyond which 4038 RCU's force-quiescent-state scan will aggressively 4039 enlist help from cond_resched() and sched IPIs to 4040 help CPUs more quickly reach quiescent states. 4041 Set to less than zero to make this be set based 4042 on rcutree.qhimark at boot time and to zero to 4043 disable more aggressive help enlistment. 4044 4045 rcutree.rcu_idle_gp_delay= [KNL] 4046 Set wakeup interval for idle CPUs that have 4047 RCU callbacks (RCU_FAST_NO_HZ=y). 4048 4049 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4050 Set wakeup interval for idle CPUs that have 4051 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4052 Lazy RCU callbacks are those which RCU can 4053 prove do nothing more than free memory. 4054 4055 rcutree.rcu_kick_kthreads= [KNL] 4056 Cause the grace-period kthread to get an extra 4057 wake_up() if it sleeps three times longer than 4058 it should at force-quiescent-state time. 4059 This wake_up() will be accompanied by a 4060 WARN_ONCE() splat and an ftrace_dump(). 4061 4062 rcutree.sysrq_rcu= [KNL] 4063 Commandeer a sysrq key to dump out Tree RCU's 4064 rcu_node tree with an eye towards determining 4065 why a new grace period has not yet started. 4066 4067 rcuperf.gp_async= [KNL] 4068 Measure performance of asynchronous 4069 grace-period primitives such as call_rcu(). 4070 4071 rcuperf.gp_async_max= [KNL] 4072 Specify the maximum number of outstanding 4073 callbacks per writer thread. When a writer 4074 thread exceeds this limit, it invokes the 4075 corresponding flavor of rcu_barrier() to allow 4076 previously posted callbacks to drain. 4077 4078 rcuperf.gp_exp= [KNL] 4079 Measure performance of expedited synchronous 4080 grace-period primitives. 4081 4082 rcuperf.holdoff= [KNL] 4083 Set test-start holdoff period. The purpose of 4084 this parameter is to delay the start of the 4085 test until boot completes in order to avoid 4086 interference. 4087 4088 rcuperf.kfree_rcu_test= [KNL] 4089 Set to measure performance of kfree_rcu() flooding. 4090 4091 rcuperf.kfree_nthreads= [KNL] 4092 The number of threads running loops of kfree_rcu(). 4093 4094 rcuperf.kfree_alloc_num= [KNL] 4095 Number of allocations and frees done in an iteration. 4096 4097 rcuperf.kfree_loops= [KNL] 4098 Number of loops doing rcuperf.kfree_alloc_num number 4099 of allocations and frees. 4100 4101 rcuperf.nreaders= [KNL] 4102 Set number of RCU readers. The value -1 selects 4103 N, where N is the number of CPUs. A value 4104 "n" less than -1 selects N-n+1, where N is again 4105 the number of CPUs. For example, -2 selects N 4106 (the number of CPUs), -3 selects N+1, and so on. 4107 A value of "n" less than or equal to -N selects 4108 a single reader. 4109 4110 rcuperf.nwriters= [KNL] 4111 Set number of RCU writers. The values operate 4112 the same as for rcuperf.nreaders. 4113 N, where N is the number of CPUs 4114 4115 rcuperf.perf_type= [KNL] 4116 Specify the RCU implementation to test. 4117 4118 rcuperf.shutdown= [KNL] 4119 Shut the system down after performance tests 4120 complete. This is useful for hands-off automated 4121 testing. 4122 4123 rcuperf.verbose= [KNL] 4124 Enable additional printk() statements. 4125 4126 rcuperf.writer_holdoff= [KNL] 4127 Write-side holdoff between grace periods, 4128 in microseconds. The default of zero says 4129 no holdoff. 4130 4131 rcutorture.fqs_duration= [KNL] 4132 Set duration of force_quiescent_state bursts 4133 in microseconds. 4134 4135 rcutorture.fqs_holdoff= [KNL] 4136 Set holdoff time within force_quiescent_state bursts 4137 in microseconds. 4138 4139 rcutorture.fqs_stutter= [KNL] 4140 Set wait time between force_quiescent_state bursts 4141 in seconds. 4142 4143 rcutorture.fwd_progress= [KNL] 4144 Enable RCU grace-period forward-progress testing 4145 for the types of RCU supporting this notion. 4146 4147 rcutorture.fwd_progress_div= [KNL] 4148 Specify the fraction of a CPU-stall-warning 4149 period to do tight-loop forward-progress testing. 4150 4151 rcutorture.fwd_progress_holdoff= [KNL] 4152 Number of seconds to wait between successive 4153 forward-progress tests. 4154 4155 rcutorture.fwd_progress_need_resched= [KNL] 4156 Enclose cond_resched() calls within checks for 4157 need_resched() during tight-loop forward-progress 4158 testing. 4159 4160 rcutorture.gp_cond= [KNL] 4161 Use conditional/asynchronous update-side 4162 primitives, if available. 4163 4164 rcutorture.gp_exp= [KNL] 4165 Use expedited update-side primitives, if available. 4166 4167 rcutorture.gp_normal= [KNL] 4168 Use normal (non-expedited) asynchronous 4169 update-side primitives, if available. 4170 4171 rcutorture.gp_sync= [KNL] 4172 Use normal (non-expedited) synchronous 4173 update-side primitives, if available. If all 4174 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4175 rcutorture.gp_normal=, and rcutorture.gp_sync= 4176 are zero, rcutorture acts as if is interpreted 4177 they are all non-zero. 4178 4179 rcutorture.n_barrier_cbs= [KNL] 4180 Set callbacks/threads for rcu_barrier() testing. 4181 4182 rcutorture.nfakewriters= [KNL] 4183 Set number of concurrent RCU writers. These just 4184 stress RCU, they don't participate in the actual 4185 test, hence the "fake". 4186 4187 rcutorture.nreaders= [KNL] 4188 Set number of RCU readers. The value -1 selects 4189 N-1, where N is the number of CPUs. A value 4190 "n" less than -1 selects N-n-2, where N is again 4191 the number of CPUs. For example, -2 selects N 4192 (the number of CPUs), -3 selects N+1, and so on. 4193 4194 rcutorture.object_debug= [KNL] 4195 Enable debug-object double-call_rcu() testing. 4196 4197 rcutorture.onoff_holdoff= [KNL] 4198 Set time (s) after boot for CPU-hotplug testing. 4199 4200 rcutorture.onoff_interval= [KNL] 4201 Set time (jiffies) between CPU-hotplug operations, 4202 or zero to disable CPU-hotplug testing. 4203 4204 rcutorture.shuffle_interval= [KNL] 4205 Set task-shuffle interval (s). Shuffling tasks 4206 allows some CPUs to go into dyntick-idle mode 4207 during the rcutorture test. 4208 4209 rcutorture.shutdown_secs= [KNL] 4210 Set time (s) after boot system shutdown. This 4211 is useful for hands-off automated testing. 4212 4213 rcutorture.stall_cpu= [KNL] 4214 Duration of CPU stall (s) to test RCU CPU stall 4215 warnings, zero to disable. 4216 4217 rcutorture.stall_cpu_holdoff= [KNL] 4218 Time to wait (s) after boot before inducing stall. 4219 4220 rcutorture.stall_cpu_irqsoff= [KNL] 4221 Disable interrupts while stalling if set. 4222 4223 rcutorture.stat_interval= [KNL] 4224 Time (s) between statistics printk()s. 4225 4226 rcutorture.stutter= [KNL] 4227 Time (s) to stutter testing, for example, specifying 4228 five seconds causes the test to run for five seconds, 4229 wait for five seconds, and so on. This tests RCU's 4230 ability to transition abruptly to and from idle. 4231 4232 rcutorture.test_boost= [KNL] 4233 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4234 "Maybe" means test if the RCU implementation 4235 under test support RCU priority boosting. 4236 4237 rcutorture.test_boost_duration= [KNL] 4238 Duration (s) of each individual boost test. 4239 4240 rcutorture.test_boost_interval= [KNL] 4241 Interval (s) between each boost test. 4242 4243 rcutorture.test_no_idle_hz= [KNL] 4244 Test RCU's dyntick-idle handling. See also the 4245 rcutorture.shuffle_interval parameter. 4246 4247 rcutorture.torture_type= [KNL] 4248 Specify the RCU implementation to test. 4249 4250 rcutorture.verbose= [KNL] 4251 Enable additional printk() statements. 4252 4253 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4254 Dump ftrace buffer after reporting RCU CPU 4255 stall warning. 4256 4257 rcupdate.rcu_cpu_stall_suppress= [KNL] 4258 Suppress RCU CPU stall warning messages. 4259 4260 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4261 Suppress RCU CPU stall warning messages and 4262 rcutorture writer stall warnings that occur 4263 during early boot, that is, during the time 4264 before the init task is spawned. 4265 4266 rcupdate.rcu_cpu_stall_timeout= [KNL] 4267 Set timeout for RCU CPU stall warning messages. 4268 4269 rcupdate.rcu_expedited= [KNL] 4270 Use expedited grace-period primitives, for 4271 example, synchronize_rcu_expedited() instead 4272 of synchronize_rcu(). This reduces latency, 4273 but can increase CPU utilization, degrade 4274 real-time latency, and degrade energy efficiency. 4275 No effect on CONFIG_TINY_RCU kernels. 4276 4277 rcupdate.rcu_normal= [KNL] 4278 Use only normal grace-period primitives, 4279 for example, synchronize_rcu() instead of 4280 synchronize_rcu_expedited(). This improves 4281 real-time latency, CPU utilization, and 4282 energy efficiency, but can expose users to 4283 increased grace-period latency. This parameter 4284 overrides rcupdate.rcu_expedited. No effect on 4285 CONFIG_TINY_RCU kernels. 4286 4287 rcupdate.rcu_normal_after_boot= [KNL] 4288 Once boot has completed (that is, after 4289 rcu_end_inkernel_boot() has been invoked), use 4290 only normal grace-period primitives. No effect 4291 on CONFIG_TINY_RCU kernels. 4292 4293 rcupdate.rcu_task_stall_timeout= [KNL] 4294 Set timeout in jiffies for RCU task stall warning 4295 messages. Disable with a value less than or equal 4296 to zero. 4297 4298 rcupdate.rcu_self_test= [KNL] 4299 Run the RCU early boot self tests 4300 4301 rdinit= [KNL] 4302 Format: <full_path> 4303 Run specified binary instead of /init from the ramdisk, 4304 used for early userspace startup. See initrd. 4305 4306 rdrand= [X86] 4307 force - Override the decision by the kernel to hide the 4308 advertisement of RDRAND support (this affects 4309 certain AMD processors because of buggy BIOS 4310 support, specifically around the suspend/resume 4311 path). 4312 4313 rdt= [HW,X86,RDT] 4314 Turn on/off individual RDT features. List is: 4315 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4316 mba. 4317 E.g. to turn on cmt and turn off mba use: 4318 rdt=cmt,!mba 4319 4320 reboot= [KNL] 4321 Format (x86 or x86_64): 4322 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4323 [[,]s[mp]#### \ 4324 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4325 [[,]f[orce] 4326 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4327 (prefix with 'panic_' to set mode for panic 4328 reboot only), 4329 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4330 reboot_force is either force or not specified, 4331 reboot_cpu is s[mp]#### with #### being the processor 4332 to be used for rebooting. 4333 4334 relax_domain_level= 4335 [KNL, SMP] Set scheduler's default relax_domain_level. 4336 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4337 4338 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4339 Format: <base1>,<size1>[,<base2>,<size2>,...] 4340 Reserve I/O ports or memory so the kernel won't use 4341 them. If <base> is less than 0x10000, the region 4342 is assumed to be I/O ports; otherwise it is memory. 4343 4344 reservetop= [X86-32] 4345 Format: nn[KMG] 4346 Reserves a hole at the top of the kernel virtual 4347 address space. 4348 4349 reservelow= [X86] 4350 Format: nn[K] 4351 Set the amount of memory to reserve for BIOS at 4352 the bottom of the address space. 4353 4354 reset_devices [KNL] Force drivers to reset the underlying device 4355 during initialization. 4356 4357 resume= [SWSUSP] 4358 Specify the partition device for software suspend 4359 Format: 4360 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4361 4362 resume_offset= [SWSUSP] 4363 Specify the offset from the beginning of the partition 4364 given by "resume=" at which the swap header is located, 4365 in <PAGE_SIZE> units (needed only for swap files). 4366 See Documentation/power/swsusp-and-swap-files.rst 4367 4368 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4369 read the resume files 4370 4371 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4372 Useful for devices that are detected asynchronously 4373 (e.g. USB and MMC devices). 4374 4375 hibernate= [HIBERNATION] 4376 noresume Don't check if there's a hibernation image 4377 present during boot. 4378 nocompress Don't compress/decompress hibernation images. 4379 no Disable hibernation and resume. 4380 protect_image Turn on image protection during restoration 4381 (that will set all pages holding image data 4382 during restoration read-only). 4383 4384 retain_initrd [RAM] Keep initrd memory after extraction 4385 4386 rfkill.default_state= 4387 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4388 etc. communication is blocked by default. 4389 1 Unblocked. 4390 4391 rfkill.master_switch_mode= 4392 0 The "airplane mode" button does nothing. 4393 1 The "airplane mode" button toggles between everything 4394 blocked and the previous configuration. 4395 2 The "airplane mode" button toggles between everything 4396 blocked and everything unblocked. 4397 4398 rhash_entries= [KNL,NET] 4399 Set number of hash buckets for route cache 4400 4401 ring3mwait=disable 4402 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4403 CPUs. 4404 4405 ro [KNL] Mount root device read-only on boot 4406 4407 rodata= [KNL] 4408 on Mark read-only kernel memory as read-only (default). 4409 off Leave read-only kernel memory writable for debugging. 4410 4411 rockchip.usb_uart 4412 Enable the uart passthrough on the designated usb port 4413 on Rockchip SoCs. When active, the signals of the 4414 debug-uart get routed to the D+ and D- pins of the usb 4415 port and the regular usb controller gets disabled. 4416 4417 root= [KNL] Root filesystem 4418 See name_to_dev_t comment in init/do_mounts.c. 4419 4420 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4421 mount the root filesystem 4422 4423 rootflags= [KNL] Set root filesystem mount option string 4424 4425 rootfstype= [KNL] Set root filesystem type 4426 4427 rootwait [KNL] Wait (indefinitely) for root device to show up. 4428 Useful for devices that are detected asynchronously 4429 (e.g. USB and MMC devices). 4430 4431 rproc_mem=nn[KMG][@address] 4432 [KNL,ARM,CMA] Remoteproc physical memory block. 4433 Memory area to be used by remote processor image, 4434 managed by CMA. 4435 4436 rw [KNL] Mount root device read-write on boot 4437 4438 S [KNL] Run init in single mode 4439 4440 s390_iommu= [HW,S390] 4441 Set s390 IOTLB flushing mode 4442 strict 4443 With strict flushing every unmap operation will result in 4444 an IOTLB flush. Default is lazy flushing before reuse, 4445 which is faster. 4446 4447 sa1100ir [NET] 4448 See drivers/net/irda/sa1100_ir.c. 4449 4450 sbni= [NET] Granch SBNI12 leased line adapter 4451 4452 sched_debug [KNL] Enables verbose scheduler debug messages. 4453 4454 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4455 Allowed values are enable and disable. This feature 4456 incurs a small amount of overhead in the scheduler 4457 but is useful for debugging and performance tuning. 4458 4459 sched_thermal_decay_shift= 4460 [KNL, SMP] Set a decay shift for scheduler thermal 4461 pressure signal. Thermal pressure signal follows the 4462 default decay period of other scheduler pelt 4463 signals(usually 32 ms but configurable). Setting 4464 sched_thermal_decay_shift will left shift the decay 4465 period for the thermal pressure signal by the shift 4466 value. 4467 i.e. with the default pelt decay period of 32 ms 4468 sched_thermal_decay_shift thermal pressure decay pr 4469 1 64 ms 4470 2 128 ms 4471 and so on. 4472 Format: integer between 0 and 10 4473 Default is 0. 4474 4475 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4476 xtime_lock contention on larger systems, and/or RCU lock 4477 contention on all systems with CONFIG_MAXSMP set. 4478 Format: { "0" | "1" } 4479 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4480 1 -- enable. 4481 Note: increases power consumption, thus should only be 4482 enabled if running jitter sensitive (HPC/RT) workloads. 4483 4484 security= [SECURITY] Choose a legacy "major" security module to 4485 enable at boot. This has been deprecated by the 4486 "lsm=" parameter. 4487 4488 selinux= [SELINUX] Disable or enable SELinux at boot time. 4489 Format: { "0" | "1" } 4490 See security/selinux/Kconfig help text. 4491 0 -- disable. 4492 1 -- enable. 4493 Default value is 1. 4494 4495 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4496 Format: { "0" | "1" } 4497 See security/apparmor/Kconfig help text 4498 0 -- disable. 4499 1 -- enable. 4500 Default value is set via kernel config option. 4501 4502 serialnumber [BUGS=X86-32] 4503 4504 shapers= [NET] 4505 Maximal number of shapers. 4506 4507 simeth= [IA-64] 4508 simscsi= 4509 4510 slram= [HW,MTD] 4511 4512 slab_nomerge [MM] 4513 Disable merging of slabs with similar size. May be 4514 necessary if there is some reason to distinguish 4515 allocs to different slabs, especially in hardened 4516 environments where the risk of heap overflows and 4517 layout control by attackers can usually be 4518 frustrated by disabling merging. This will reduce 4519 most of the exposure of a heap attack to a single 4520 cache (risks via metadata attacks are mostly 4521 unchanged). Debug options disable merging on their 4522 own. 4523 For more information see Documentation/vm/slub.rst. 4524 4525 slab_max_order= [MM, SLAB] 4526 Determines the maximum allowed order for slabs. 4527 A high setting may cause OOMs due to memory 4528 fragmentation. Defaults to 1 for systems with 4529 more than 32MB of RAM, 0 otherwise. 4530 4531 slub_debug[=options[,slabs]] [MM, SLUB] 4532 Enabling slub_debug allows one to determine the 4533 culprit if slab objects become corrupted. Enabling 4534 slub_debug can create guard zones around objects and 4535 may poison objects when not in use. Also tracks the 4536 last alloc / free. For more information see 4537 Documentation/vm/slub.rst. 4538 4539 slub_memcg_sysfs= [MM, SLUB] 4540 Determines whether to enable sysfs directories for 4541 memory cgroup sub-caches. 1 to enable, 0 to disable. 4542 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4543 Enabling this can lead to a very high number of debug 4544 directories and files being created under 4545 /sys/kernel/slub. 4546 4547 slub_max_order= [MM, SLUB] 4548 Determines the maximum allowed order for slabs. 4549 A high setting may cause OOMs due to memory 4550 fragmentation. For more information see 4551 Documentation/vm/slub.rst. 4552 4553 slub_min_objects= [MM, SLUB] 4554 The minimum number of objects per slab. SLUB will 4555 increase the slab order up to slub_max_order to 4556 generate a sufficiently large slab able to contain 4557 the number of objects indicated. The higher the number 4558 of objects the smaller the overhead of tracking slabs 4559 and the less frequently locks need to be acquired. 4560 For more information see Documentation/vm/slub.rst. 4561 4562 slub_min_order= [MM, SLUB] 4563 Determines the minimum page order for slabs. Must be 4564 lower than slub_max_order. 4565 For more information see Documentation/vm/slub.rst. 4566 4567 slub_nomerge [MM, SLUB] 4568 Same with slab_nomerge. This is supported for legacy. 4569 See slab_nomerge for more information. 4570 4571 smart2= [HW] 4572 Format: <io1>[,<io2>[,...,<io8>]] 4573 4574 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4575 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4576 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4577 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4578 smsc-ircc2.ircc_irq= [HW] IRQ line 4579 smsc-ircc2.ircc_dma= [HW] DMA channel 4580 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4581 0: Toshiba Satellite 1800 (GP data pin select) 4582 1: Fast pin select (default) 4583 2: ATC IRMode 4584 4585 smt [KNL,S390] Set the maximum number of threads (logical 4586 CPUs) to use per physical CPU on systems capable of 4587 symmetric multithreading (SMT). Will be capped to the 4588 actual hardware limit. 4589 Format: <integer> 4590 Default: -1 (no limit) 4591 4592 softlockup_panic= 4593 [KNL] Should the soft-lockup detector generate panics. 4594 Format: <integer> 4595 4596 A nonzero value instructs the soft-lockup detector 4597 to panic the machine when a soft-lockup occurs. It is 4598 also controlled by the kernel.softlockup_panic sysctl 4599 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4600 respective build-time switch to that functionality. 4601 4602 softlockup_all_cpu_backtrace= 4603 [KNL] Should the soft-lockup detector generate 4604 backtraces on all cpus. 4605 Format: <integer> 4606 4607 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4608 See Documentation/admin-guide/laptops/sonypi.rst 4609 4610 spectre_v2= [X86] Control mitigation of Spectre variant 2 4611 (indirect branch speculation) vulnerability. 4612 The default operation protects the kernel from 4613 user space attacks. 4614 4615 on - unconditionally enable, implies 4616 spectre_v2_user=on 4617 off - unconditionally disable, implies 4618 spectre_v2_user=off 4619 auto - kernel detects whether your CPU model is 4620 vulnerable 4621 4622 Selecting 'on' will, and 'auto' may, choose a 4623 mitigation method at run time according to the 4624 CPU, the available microcode, the setting of the 4625 CONFIG_RETPOLINE configuration option, and the 4626 compiler with which the kernel was built. 4627 4628 Selecting 'on' will also enable the mitigation 4629 against user space to user space task attacks. 4630 4631 Selecting 'off' will disable both the kernel and 4632 the user space protections. 4633 4634 Specific mitigations can also be selected manually: 4635 4636 retpoline - replace indirect branches 4637 retpoline,generic - google's original retpoline 4638 retpoline,amd - AMD-specific minimal thunk 4639 4640 Not specifying this option is equivalent to 4641 spectre_v2=auto. 4642 4643 spectre_v2_user= 4644 [X86] Control mitigation of Spectre variant 2 4645 (indirect branch speculation) vulnerability between 4646 user space tasks 4647 4648 on - Unconditionally enable mitigations. Is 4649 enforced by spectre_v2=on 4650 4651 off - Unconditionally disable mitigations. Is 4652 enforced by spectre_v2=off 4653 4654 prctl - Indirect branch speculation is enabled, 4655 but mitigation can be enabled via prctl 4656 per thread. The mitigation control state 4657 is inherited on fork. 4658 4659 prctl,ibpb 4660 - Like "prctl" above, but only STIBP is 4661 controlled per thread. IBPB is issued 4662 always when switching between different user 4663 space processes. 4664 4665 seccomp 4666 - Same as "prctl" above, but all seccomp 4667 threads will enable the mitigation unless 4668 they explicitly opt out. 4669 4670 seccomp,ibpb 4671 - Like "seccomp" above, but only STIBP is 4672 controlled per thread. IBPB is issued 4673 always when switching between different 4674 user space processes. 4675 4676 auto - Kernel selects the mitigation depending on 4677 the available CPU features and vulnerability. 4678 4679 Default mitigation: 4680 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4681 4682 Not specifying this option is equivalent to 4683 spectre_v2_user=auto. 4684 4685 spec_store_bypass_disable= 4686 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4687 (Speculative Store Bypass vulnerability) 4688 4689 Certain CPUs are vulnerable to an exploit against a 4690 a common industry wide performance optimization known 4691 as "Speculative Store Bypass" in which recent stores 4692 to the same memory location may not be observed by 4693 later loads during speculative execution. The idea 4694 is that such stores are unlikely and that they can 4695 be detected prior to instruction retirement at the 4696 end of a particular speculation execution window. 4697 4698 In vulnerable processors, the speculatively forwarded 4699 store can be used in a cache side channel attack, for 4700 example to read memory to which the attacker does not 4701 directly have access (e.g. inside sandboxed code). 4702 4703 This parameter controls whether the Speculative Store 4704 Bypass optimization is used. 4705 4706 On x86 the options are: 4707 4708 on - Unconditionally disable Speculative Store Bypass 4709 off - Unconditionally enable Speculative Store Bypass 4710 auto - Kernel detects whether the CPU model contains an 4711 implementation of Speculative Store Bypass and 4712 picks the most appropriate mitigation. If the 4713 CPU is not vulnerable, "off" is selected. If the 4714 CPU is vulnerable the default mitigation is 4715 architecture and Kconfig dependent. See below. 4716 prctl - Control Speculative Store Bypass per thread 4717 via prctl. Speculative Store Bypass is enabled 4718 for a process by default. The state of the control 4719 is inherited on fork. 4720 seccomp - Same as "prctl" above, but all seccomp threads 4721 will disable SSB unless they explicitly opt out. 4722 4723 Default mitigations: 4724 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4725 4726 On powerpc the options are: 4727 4728 on,auto - On Power8 and Power9 insert a store-forwarding 4729 barrier on kernel entry and exit. On Power7 4730 perform a software flush on kernel entry and 4731 exit. 4732 off - No action. 4733 4734 Not specifying this option is equivalent to 4735 spec_store_bypass_disable=auto. 4736 4737 spia_io_base= [HW,MTD] 4738 spia_fio_base= 4739 spia_pedr= 4740 spia_peddr= 4741 4742 split_lock_detect= 4743 [X86] Enable split lock detection 4744 4745 When enabled (and if hardware support is present), atomic 4746 instructions that access data across cache line 4747 boundaries will result in an alignment check exception. 4748 4749 off - not enabled 4750 4751 warn - the kernel will emit rate limited warnings 4752 about applications triggering the #AC 4753 exception. This mode is the default on CPUs 4754 that supports split lock detection. 4755 4756 fatal - the kernel will send SIGBUS to applications 4757 that trigger the #AC exception. 4758 4759 If an #AC exception is hit in the kernel or in 4760 firmware (i.e. not while executing in user mode) 4761 the kernel will oops in either "warn" or "fatal" 4762 mode. 4763 4764 srcutree.counter_wrap_check [KNL] 4765 Specifies how frequently to check for 4766 grace-period sequence counter wrap for the 4767 srcu_data structure's ->srcu_gp_seq_needed field. 4768 The greater the number of bits set in this kernel 4769 parameter, the less frequently counter wrap will 4770 be checked for. Note that the bottom two bits 4771 are ignored. 4772 4773 srcutree.exp_holdoff [KNL] 4774 Specifies how many nanoseconds must elapse 4775 since the end of the last SRCU grace period for 4776 a given srcu_struct until the next normal SRCU 4777 grace period will be considered for automatic 4778 expediting. Set to zero to disable automatic 4779 expediting. 4780 4781 ssbd= [ARM64,HW] 4782 Speculative Store Bypass Disable control 4783 4784 On CPUs that are vulnerable to the Speculative 4785 Store Bypass vulnerability and offer a 4786 firmware based mitigation, this parameter 4787 indicates how the mitigation should be used: 4788 4789 force-on: Unconditionally enable mitigation for 4790 for both kernel and userspace 4791 force-off: Unconditionally disable mitigation for 4792 for both kernel and userspace 4793 kernel: Always enable mitigation in the 4794 kernel, and offer a prctl interface 4795 to allow userspace to register its 4796 interest in being mitigated too. 4797 4798 stack_guard_gap= [MM] 4799 override the default stack gap protection. The value 4800 is in page units and it defines how many pages prior 4801 to (for stacks growing down) resp. after (for stacks 4802 growing up) the main stack are reserved for no other 4803 mapping. Default value is 256 pages. 4804 4805 stacktrace [FTRACE] 4806 Enabled the stack tracer on boot up. 4807 4808 stacktrace_filter=[function-list] 4809 [FTRACE] Limit the functions that the stack tracer 4810 will trace at boot up. function-list is a comma separated 4811 list of functions. This list can be changed at run 4812 time by the stack_trace_filter file in the debugfs 4813 tracing directory. Note, this enables stack tracing 4814 and the stacktrace above is not needed. 4815 4816 sti= [PARISC,HW] 4817 Format: <num> 4818 Set the STI (builtin display/keyboard on the HP-PARISC 4819 machines) console (graphic card) which should be used 4820 as the initial boot-console. 4821 See also comment in drivers/video/console/sticore.c. 4822 4823 sti_font= [HW] 4824 See comment in drivers/video/console/sticore.c. 4825 4826 stifb= [HW] 4827 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4828 4829 sunrpc.min_resvport= 4830 sunrpc.max_resvport= 4831 [NFS,SUNRPC] 4832 SunRPC servers often require that client requests 4833 originate from a privileged port (i.e. a port in the 4834 range 0 < portnr < 1024). 4835 An administrator who wishes to reserve some of these 4836 ports for other uses may adjust the range that the 4837 kernel's sunrpc client considers to be privileged 4838 using these two parameters to set the minimum and 4839 maximum port values. 4840 4841 sunrpc.svc_rpc_per_connection_limit= 4842 [NFS,SUNRPC] 4843 Limit the number of requests that the server will 4844 process in parallel from a single connection. 4845 The default value is 0 (no limit). 4846 4847 sunrpc.pool_mode= 4848 [NFS] 4849 Control how the NFS server code allocates CPUs to 4850 service thread pools. Depending on how many NICs 4851 you have and where their interrupts are bound, this 4852 option will affect which CPUs will do NFS serving. 4853 Note: this parameter cannot be changed while the 4854 NFS server is running. 4855 4856 auto the server chooses an appropriate mode 4857 automatically using heuristics 4858 global a single global pool contains all CPUs 4859 percpu one pool for each CPU 4860 pernode one pool for each NUMA node (equivalent 4861 to global on non-NUMA machines) 4862 4863 sunrpc.tcp_slot_table_entries= 4864 sunrpc.udp_slot_table_entries= 4865 [NFS,SUNRPC] 4866 Sets the upper limit on the number of simultaneous 4867 RPC calls that can be sent from the client to a 4868 server. Increasing these values may allow you to 4869 improve throughput, but will also increase the 4870 amount of memory reserved for use by the client. 4871 4872 suspend.pm_test_delay= 4873 [SUSPEND] 4874 Sets the number of seconds to remain in a suspend test 4875 mode before resuming the system (see 4876 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4877 is set. Default value is 5. 4878 4879 svm= [PPC] 4880 Format: { on | off | y | n | 1 | 0 } 4881 This parameter controls use of the Protected 4882 Execution Facility on pSeries. 4883 4884 swapaccount=[0|1] 4885 [KNL] Enable accounting of swap in memory resource 4886 controller if no parameter or 1 is given or disable 4887 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4888 4889 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4890 Format: { <int> | force | noforce } 4891 <int> -- Number of I/O TLB slabs 4892 force -- force using of bounce buffers even if they 4893 wouldn't be automatically used by the kernel 4894 noforce -- Never use bounce buffers (for debugging) 4895 4896 switches= [HW,M68k] 4897 4898 sysfs.deprecated=0|1 [KNL] 4899 Enable/disable old style sysfs layout for old udev 4900 on older distributions. When this option is enabled 4901 very new udev will not work anymore. When this option 4902 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4903 in older udev will not work anymore. 4904 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4905 the kernel configuration. 4906 4907 sysrq_always_enabled 4908 [KNL] 4909 Ignore sysrq setting - this boot parameter will 4910 neutralize any effect of /proc/sys/kernel/sysrq. 4911 Useful for debugging. 4912 4913 tcpmhash_entries= [KNL,NET] 4914 Set the number of tcp_metrics_hash slots. 4915 Default value is 8192 or 16384 depending on total 4916 ram pages. This is used to specify the TCP metrics 4917 cache size. See Documentation/networking/ip-sysctl.txt 4918 "tcp_no_metrics_save" section for more details. 4919 4920 tdfx= [HW,DRM] 4921 4922 test_suspend= [SUSPEND][,N] 4923 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4924 standby suspend) or "freeze" (for suspend type freeze) 4925 as the system sleep state during system startup with 4926 the optional capability to repeat N number of times. 4927 The system is woken from this state using a 4928 wakeup-capable RTC alarm. 4929 4930 thash_entries= [KNL,NET] 4931 Set number of hash buckets for TCP connection 4932 4933 thermal.act= [HW,ACPI] 4934 -1: disable all active trip points in all thermal zones 4935 <degrees C>: override all lowest active trip points 4936 4937 thermal.crt= [HW,ACPI] 4938 -1: disable all critical trip points in all thermal zones 4939 <degrees C>: override all critical trip points 4940 4941 thermal.nocrt= [HW,ACPI] 4942 Set to disable actions on ACPI thermal zone 4943 critical and hot trip points. 4944 4945 thermal.off= [HW,ACPI] 4946 1: disable ACPI thermal control 4947 4948 thermal.psv= [HW,ACPI] 4949 -1: disable all passive trip points 4950 <degrees C>: override all passive trip points to this 4951 value 4952 4953 thermal.tzp= [HW,ACPI] 4954 Specify global default ACPI thermal zone polling rate 4955 <deci-seconds>: poll all this frequency 4956 0: no polling (default) 4957 4958 threadirqs [KNL] 4959 Force threading of all interrupt handlers except those 4960 marked explicitly IRQF_NO_THREAD. 4961 4962 topology= [S390] 4963 Format: {off | on} 4964 Specify if the kernel should make use of the cpu 4965 topology information if the hardware supports this. 4966 The scheduler will make use of this information and 4967 e.g. base its process migration decisions on it. 4968 Default is on. 4969 4970 topology_updates= [KNL, PPC, NUMA] 4971 Format: {off} 4972 Specify if the kernel should ignore (off) 4973 topology updates sent by the hypervisor to this 4974 LPAR. 4975 4976 torture.disable_onoff_at_boot= [KNL] 4977 Prevent the CPU-hotplug component of torturing 4978 until after init has spawned. 4979 4980 tp720= [HW,PS2] 4981 4982 tpm_suspend_pcr=[HW,TPM] 4983 Format: integer pcr id 4984 Specify that at suspend time, the tpm driver 4985 should extend the specified pcr with zeros, 4986 as a workaround for some chips which fail to 4987 flush the last written pcr on TPM_SaveState. 4988 This will guarantee that all the other pcrs 4989 are saved. 4990 4991 trace_buf_size=nn[KMG] 4992 [FTRACE] will set tracing buffer size on each cpu. 4993 4994 trace_event=[event-list] 4995 [FTRACE] Set and start specified trace events in order 4996 to facilitate early boot debugging. The event-list is a 4997 comma separated list of trace events to enable. See 4998 also Documentation/trace/events.rst 4999 5000 trace_options=[option-list] 5001 [FTRACE] Enable or disable tracer options at boot. 5002 The option-list is a comma delimited list of options 5003 that can be enabled or disabled just as if you were 5004 to echo the option name into 5005 5006 /sys/kernel/debug/tracing/trace_options 5007 5008 For example, to enable stacktrace option (to dump the 5009 stack trace of each event), add to the command line: 5010 5011 trace_options=stacktrace 5012 5013 See also Documentation/trace/ftrace.rst "trace options" 5014 section. 5015 5016 tp_printk[FTRACE] 5017 Have the tracepoints sent to printk as well as the 5018 tracing ring buffer. This is useful for early boot up 5019 where the system hangs or reboots and does not give the 5020 option for reading the tracing buffer or performing a 5021 ftrace_dump_on_oops. 5022 5023 To turn off having tracepoints sent to printk, 5024 echo 0 > /proc/sys/kernel/tracepoint_printk 5025 Note, echoing 1 into this file without the 5026 tracepoint_printk kernel cmdline option has no effect. 5027 5028 ** CAUTION ** 5029 5030 Having tracepoints sent to printk() and activating high 5031 frequency tracepoints such as irq or sched, can cause 5032 the system to live lock. 5033 5034 traceoff_on_warning 5035 [FTRACE] enable this option to disable tracing when a 5036 warning is hit. This turns off "tracing_on". Tracing can 5037 be enabled again by echoing '1' into the "tracing_on" 5038 file located in /sys/kernel/debug/tracing/ 5039 5040 This option is useful, as it disables the trace before 5041 the WARNING dump is called, which prevents the trace to 5042 be filled with content caused by the warning output. 5043 5044 This option can also be set at run time via the sysctl 5045 option: kernel/traceoff_on_warning 5046 5047 transparent_hugepage= 5048 [KNL] 5049 Format: [always|madvise|never] 5050 Can be used to control the default behavior of the system 5051 with respect to transparent hugepages. 5052 See Documentation/admin-guide/mm/transhuge.rst 5053 for more details. 5054 5055 tsc= Disable clocksource stability checks for TSC. 5056 Format: <string> 5057 [x86] reliable: mark tsc clocksource as reliable, this 5058 disables clocksource verification at runtime, as well 5059 as the stability checks done at bootup. Used to enable 5060 high-resolution timer mode on older hardware, and in 5061 virtualized environment. 5062 [x86] noirqtime: Do not use TSC to do irq accounting. 5063 Used to run time disable IRQ_TIME_ACCOUNTING on any 5064 platforms where RDTSC is slow and this accounting 5065 can add overhead. 5066 [x86] unstable: mark the TSC clocksource as unstable, this 5067 marks the TSC unconditionally unstable at bootup and 5068 avoids any further wobbles once the TSC watchdog notices. 5069 [x86] nowatchdog: disable clocksource watchdog. Used 5070 in situations with strict latency requirements (where 5071 interruptions from clocksource watchdog are not 5072 acceptable). 5073 5074 tsx= [X86] Control Transactional Synchronization 5075 Extensions (TSX) feature in Intel processors that 5076 support TSX control. 5077 5078 This parameter controls the TSX feature. The options are: 5079 5080 on - Enable TSX on the system. Although there are 5081 mitigations for all known security vulnerabilities, 5082 TSX has been known to be an accelerator for 5083 several previous speculation-related CVEs, and 5084 so there may be unknown security risks associated 5085 with leaving it enabled. 5086 5087 off - Disable TSX on the system. (Note that this 5088 option takes effect only on newer CPUs which are 5089 not vulnerable to MDS, i.e., have 5090 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5091 the new IA32_TSX_CTRL MSR through a microcode 5092 update. This new MSR allows for the reliable 5093 deactivation of the TSX functionality.) 5094 5095 auto - Disable TSX if X86_BUG_TAA is present, 5096 otherwise enable TSX on the system. 5097 5098 Not specifying this option is equivalent to tsx=off. 5099 5100 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5101 for more details. 5102 5103 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5104 Abort (TAA) vulnerability. 5105 5106 Similar to Micro-architectural Data Sampling (MDS) 5107 certain CPUs that support Transactional 5108 Synchronization Extensions (TSX) are vulnerable to an 5109 exploit against CPU internal buffers which can forward 5110 information to a disclosure gadget under certain 5111 conditions. 5112 5113 In vulnerable processors, the speculatively forwarded 5114 data can be used in a cache side channel attack, to 5115 access data to which the attacker does not have direct 5116 access. 5117 5118 This parameter controls the TAA mitigation. The 5119 options are: 5120 5121 full - Enable TAA mitigation on vulnerable CPUs 5122 if TSX is enabled. 5123 5124 full,nosmt - Enable TAA mitigation and disable SMT on 5125 vulnerable CPUs. If TSX is disabled, SMT 5126 is not disabled because CPU is not 5127 vulnerable to cross-thread TAA attacks. 5128 off - Unconditionally disable TAA mitigation 5129 5130 On MDS-affected machines, tsx_async_abort=off can be 5131 prevented by an active MDS mitigation as both vulnerabilities 5132 are mitigated with the same mechanism so in order to disable 5133 this mitigation, you need to specify mds=off too. 5134 5135 Not specifying this option is equivalent to 5136 tsx_async_abort=full. On CPUs which are MDS affected 5137 and deploy MDS mitigation, TAA mitigation is not 5138 required and doesn't provide any additional 5139 mitigation. 5140 5141 For details see: 5142 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5143 5144 turbografx.map[2|3]= [HW,JOY] 5145 TurboGraFX parallel port interface 5146 Format: 5147 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5148 See also Documentation/input/devices/joystick-parport.rst 5149 5150 udbg-immortal [PPC] When debugging early kernel crashes that 5151 happen after console_init() and before a proper 5152 console driver takes over, this boot options might 5153 help "seeing" what's going on. 5154 5155 uhash_entries= [KNL,NET] 5156 Set number of hash buckets for UDP/UDP-Lite connections 5157 5158 uhci-hcd.ignore_oc= 5159 [USB] Ignore overcurrent events (default N). 5160 Some badly-designed motherboards generate lots of 5161 bogus events, for ports that aren't wired to 5162 anything. Set this parameter to avoid log spamming. 5163 Note that genuine overcurrent events won't be 5164 reported either. 5165 5166 unknown_nmi_panic 5167 [X86] Cause panic on unknown NMI. 5168 5169 usbcore.authorized_default= 5170 [USB] Default USB device authorization: 5171 (default -1 = authorized except for wireless USB, 5172 0 = not authorized, 1 = authorized, 2 = authorized 5173 if device connected to internal port) 5174 5175 usbcore.autosuspend= 5176 [USB] The autosuspend time delay (in seconds) used 5177 for newly-detected USB devices (default 2). This 5178 is the time required before an idle device will be 5179 autosuspended. Devices for which the delay is set 5180 to a negative value won't be autosuspended at all. 5181 5182 usbcore.usbfs_snoop= 5183 [USB] Set to log all usbfs traffic (default 0 = off). 5184 5185 usbcore.usbfs_snoop_max= 5186 [USB] Maximum number of bytes to snoop in each URB 5187 (default = 65536). 5188 5189 usbcore.blinkenlights= 5190 [USB] Set to cycle leds on hubs (default 0 = off). 5191 5192 usbcore.old_scheme_first= 5193 [USB] Start with the old device initialization 5194 scheme, applies only to low and full-speed devices 5195 (default 0 = off). 5196 5197 usbcore.usbfs_memory_mb= 5198 [USB] Memory limit (in MB) for buffers allocated by 5199 usbfs (default = 16, 0 = max = 2047). 5200 5201 usbcore.use_both_schemes= 5202 [USB] Try the other device initialization scheme 5203 if the first one fails (default 1 = enabled). 5204 5205 usbcore.initial_descriptor_timeout= 5206 [USB] Specifies timeout for the initial 64-byte 5207 USB_REQ_GET_DESCRIPTOR request in milliseconds 5208 (default 5000 = 5.0 seconds). 5209 5210 usbcore.nousb [USB] Disable the USB subsystem 5211 5212 usbcore.quirks= 5213 [USB] A list of quirk entries to augment the built-in 5214 usb core quirk list. List entries are separated by 5215 commas. Each entry has the form 5216 VendorID:ProductID:Flags. The IDs are 4-digit hex 5217 numbers and Flags is a set of letters. Each letter 5218 will change the built-in quirk; setting it if it is 5219 clear and clearing it if it is set. The letters have 5220 the following meanings: 5221 a = USB_QUIRK_STRING_FETCH_255 (string 5222 descriptors must not be fetched using 5223 a 255-byte read); 5224 b = USB_QUIRK_RESET_RESUME (device can't resume 5225 correctly so reset it instead); 5226 c = USB_QUIRK_NO_SET_INTF (device can't handle 5227 Set-Interface requests); 5228 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5229 handle its Configuration or Interface 5230 strings); 5231 e = USB_QUIRK_RESET (device can't be reset 5232 (e.g morph devices), don't use reset); 5233 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5234 more interface descriptions than the 5235 bNumInterfaces count, and can't handle 5236 talking to these interfaces); 5237 g = USB_QUIRK_DELAY_INIT (device needs a pause 5238 during initialization, after we read 5239 the device descriptor); 5240 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5241 high speed and super speed interrupt 5242 endpoints, the USB 2.0 and USB 3.0 spec 5243 require the interval in microframes (1 5244 microframe = 125 microseconds) to be 5245 calculated as interval = 2 ^ 5246 (bInterval-1). 5247 Devices with this quirk report their 5248 bInterval as the result of this 5249 calculation instead of the exponent 5250 variable used in the calculation); 5251 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5252 handle device_qualifier descriptor 5253 requests); 5254 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5255 generates spurious wakeup, ignore 5256 remote wakeup capability); 5257 k = USB_QUIRK_NO_LPM (device can't handle Link 5258 Power Management); 5259 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5260 (Device reports its bInterval as linear 5261 frames instead of the USB 2.0 5262 calculation); 5263 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5264 to be disconnected before suspend to 5265 prevent spurious wakeup); 5266 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5267 pause after every control message); 5268 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5269 delay after resetting its port); 5270 Example: quirks=0781:5580:bk,0a5c:5834:gij 5271 5272 usbhid.mousepoll= 5273 [USBHID] The interval which mice are to be polled at. 5274 5275 usbhid.jspoll= 5276 [USBHID] The interval which joysticks are to be polled at. 5277 5278 usbhid.kbpoll= 5279 [USBHID] The interval which keyboards are to be polled at. 5280 5281 usb-storage.delay_use= 5282 [UMS] The delay in seconds before a new device is 5283 scanned for Logical Units (default 1). 5284 5285 usb-storage.quirks= 5286 [UMS] A list of quirks entries to supplement or 5287 override the built-in unusual_devs list. List 5288 entries are separated by commas. Each entry has 5289 the form VID:PID:Flags where VID and PID are Vendor 5290 and Product ID values (4-digit hex numbers) and 5291 Flags is a set of characters, each corresponding 5292 to a common usb-storage quirk flag as follows: 5293 a = SANE_SENSE (collect more than 18 bytes 5294 of sense data, not on uas); 5295 b = BAD_SENSE (don't collect more than 18 5296 bytes of sense data, not on uas); 5297 c = FIX_CAPACITY (decrease the reported 5298 device capacity by one sector); 5299 d = NO_READ_DISC_INFO (don't use 5300 READ_DISC_INFO command, not on uas); 5301 e = NO_READ_CAPACITY_16 (don't use 5302 READ_CAPACITY_16 command); 5303 f = NO_REPORT_OPCODES (don't use report opcodes 5304 command, uas only); 5305 g = MAX_SECTORS_240 (don't transfer more than 5306 240 sectors at a time, uas only); 5307 h = CAPACITY_HEURISTICS (decrease the 5308 reported device capacity by one 5309 sector if the number is odd); 5310 i = IGNORE_DEVICE (don't bind to this 5311 device); 5312 j = NO_REPORT_LUNS (don't use report luns 5313 command, uas only); 5314 l = NOT_LOCKABLE (don't try to lock and 5315 unlock ejectable media, not on uas); 5316 m = MAX_SECTORS_64 (don't transfer more 5317 than 64 sectors = 32 KB at a time, 5318 not on uas); 5319 n = INITIAL_READ10 (force a retry of the 5320 initial READ(10) command, not on uas); 5321 o = CAPACITY_OK (accept the capacity 5322 reported by the device, not on uas); 5323 p = WRITE_CACHE (the device cache is ON 5324 by default, not on uas); 5325 r = IGNORE_RESIDUE (the device reports 5326 bogus residue values, not on uas); 5327 s = SINGLE_LUN (the device has only one 5328 Logical Unit); 5329 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5330 commands, uas only); 5331 u = IGNORE_UAS (don't bind to the uas driver); 5332 w = NO_WP_DETECT (don't test whether the 5333 medium is write-protected). 5334 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5335 even if the device claims no cache, 5336 not on uas) 5337 Example: quirks=0419:aaf5:rl,0421:0433:rc 5338 5339 user_debug= [KNL,ARM] 5340 Format: <int> 5341 See arch/arm/Kconfig.debug help text. 5342 1 - undefined instruction events 5343 2 - system calls 5344 4 - invalid data aborts 5345 8 - SIGSEGV faults 5346 16 - SIGBUS faults 5347 Example: user_debug=31 5348 5349 userpte= 5350 [X86] Flags controlling user PTE allocations. 5351 5352 nohigh = do not allocate PTE pages in 5353 HIGHMEM regardless of setting 5354 of CONFIG_HIGHPTE. 5355 5356 vdso= [X86,SH] 5357 On X86_32, this is an alias for vdso32=. Otherwise: 5358 5359 vdso=1: enable VDSO (the default) 5360 vdso=0: disable VDSO mapping 5361 5362 vdso32= [X86] Control the 32-bit vDSO 5363 vdso32=1: enable 32-bit VDSO 5364 vdso32=0 or vdso32=2: disable 32-bit VDSO 5365 5366 See the help text for CONFIG_COMPAT_VDSO for more 5367 details. If CONFIG_COMPAT_VDSO is set, the default is 5368 vdso32=0; otherwise, the default is vdso32=1. 5369 5370 For compatibility with older kernels, vdso32=2 is an 5371 alias for vdso32=0. 5372 5373 Try vdso32=0 if you encounter an error that says: 5374 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5375 5376 vector= [IA-64,SMP] 5377 vector=percpu: enable percpu vector domain 5378 5379 video= [FB] Frame buffer configuration 5380 See Documentation/fb/modedb.rst. 5381 5382 video.brightness_switch_enabled= [0,1] 5383 If set to 1, on receiving an ACPI notify event 5384 generated by hotkey, video driver will adjust brightness 5385 level and then send out the event to user space through 5386 the allocated input device; If set to 0, video driver 5387 will only send out the event without touching backlight 5388 brightness level. 5389 default: 1 5390 5391 virtio_mmio.device= 5392 [VMMIO] Memory mapped virtio (platform) device. 5393 5394 <size>@<baseaddr>:<irq>[:<id>] 5395 where: 5396 <size> := size (can use standard suffixes 5397 like K, M and G) 5398 <baseaddr> := physical base address 5399 <irq> := interrupt number (as passed to 5400 request_irq()) 5401 <id> := (optional) platform device id 5402 example: 5403 virtio_mmio.device=1K@0x100b0000:48:7 5404 5405 Can be used multiple times for multiple devices. 5406 5407 vga= [BOOT,X86-32] Select a particular video mode 5408 See Documentation/x86/boot.rst and 5409 Documentation/admin-guide/svga.rst. 5410 Use vga=ask for menu. 5411 This is actually a boot loader parameter; the value is 5412 passed to the kernel using a special protocol. 5413 5414 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5415 May slow down system boot speed, especially when 5416 enabled on systems with a large amount of memory. 5417 All options are enabled by default, and this 5418 interface is meant to allow for selectively 5419 enabling or disabling specific virtual memory 5420 debugging features. 5421 5422 Available options are: 5423 P Enable page structure init time poisoning 5424 - Disable all of the above options 5425 5426 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5427 size of <nn>. This can be used to increase the 5428 minimum size (128MB on x86). It can also be used to 5429 decrease the size and leave more room for directly 5430 mapped kernel RAM. 5431 5432 vmcp_cma=nn[MG] [KNL,S390] 5433 Sets the memory size reserved for contiguous memory 5434 allocations for the vmcp device driver. 5435 5436 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5437 Format: <command> 5438 5439 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5440 Format: <command> 5441 5442 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5443 Format: <command> 5444 5445 vsyscall= [X86-64] 5446 Controls the behavior of vsyscalls (i.e. calls to 5447 fixed addresses of 0xffffffffff600x00 from legacy 5448 code). Most statically-linked binaries and older 5449 versions of glibc use these calls. Because these 5450 functions are at fixed addresses, they make nice 5451 targets for exploits that can control RIP. 5452 5453 emulate [default] Vsyscalls turn into traps and are 5454 emulated reasonably safely. The vsyscall 5455 page is readable. 5456 5457 xonly Vsyscalls turn into traps and are 5458 emulated reasonably safely. The vsyscall 5459 page is not readable. 5460 5461 none Vsyscalls don't work at all. This makes 5462 them quite hard to use for exploits but 5463 might break your system. 5464 5465 vt.color= [VT] Default text color. 5466 Format: 0xYX, X = foreground, Y = background. 5467 Default: 0x07 = light gray on black. 5468 5469 vt.cur_default= [VT] Default cursor shape. 5470 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5471 the parameters of the <Esc>[?A;B;Cc escape sequence; 5472 see VGA-softcursor.txt. Default: 2 = underline. 5473 5474 vt.default_blu= [VT] 5475 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5476 Change the default blue palette of the console. 5477 This is a 16-member array composed of values 5478 ranging from 0-255. 5479 5480 vt.default_grn= [VT] 5481 Format: <green0>,<green1>,<green2>,...,<green15> 5482 Change the default green palette of the console. 5483 This is a 16-member array composed of values 5484 ranging from 0-255. 5485 5486 vt.default_red= [VT] 5487 Format: <red0>,<red1>,<red2>,...,<red15> 5488 Change the default red palette of the console. 5489 This is a 16-member array composed of values 5490 ranging from 0-255. 5491 5492 vt.default_utf8= 5493 [VT] 5494 Format=<0|1> 5495 Set system-wide default UTF-8 mode for all tty's. 5496 Default is 1, i.e. UTF-8 mode is enabled for all 5497 newly opened terminals. 5498 5499 vt.global_cursor_default= 5500 [VT] 5501 Format=<-1|0|1> 5502 Set system-wide default for whether a cursor 5503 is shown on new VTs. Default is -1, 5504 i.e. cursors will be created by default unless 5505 overridden by individual drivers. 0 will hide 5506 cursors, 1 will display them. 5507 5508 vt.italic= [VT] Default color for italic text; 0-15. 5509 Default: 2 = green. 5510 5511 vt.underline= [VT] Default color for underlined text; 0-15. 5512 Default: 3 = cyan. 5513 5514 watchdog timers [HW,WDT] For information on watchdog timers, 5515 see Documentation/watchdog/watchdog-parameters.rst 5516 or other driver-specific files in the 5517 Documentation/watchdog/ directory. 5518 5519 watchdog_thresh= 5520 [KNL] 5521 Set the hard lockup detector stall duration 5522 threshold in seconds. The soft lockup detector 5523 threshold is set to twice the value. A value of 0 5524 disables both lockup detectors. Default is 10 5525 seconds. 5526 5527 workqueue.watchdog_thresh= 5528 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5529 warn stall conditions and dump internal state to 5530 help debugging. 0 disables workqueue stall 5531 detection; otherwise, it's the stall threshold 5532 duration in seconds. The default value is 30 and 5533 it can be updated at runtime by writing to the 5534 corresponding sysfs file. 5535 5536 workqueue.disable_numa 5537 By default, all work items queued to unbound 5538 workqueues are affine to the NUMA nodes they're 5539 issued on, which results in better behavior in 5540 general. If NUMA affinity needs to be disabled for 5541 whatever reason, this option can be used. Note 5542 that this also can be controlled per-workqueue for 5543 workqueues visible under /sys/bus/workqueue/. 5544 5545 workqueue.power_efficient 5546 Per-cpu workqueues are generally preferred because 5547 they show better performance thanks to cache 5548 locality; unfortunately, per-cpu workqueues tend to 5549 be more power hungry than unbound workqueues. 5550 5551 Enabling this makes the per-cpu workqueues which 5552 were observed to contribute significantly to power 5553 consumption unbound, leading to measurably lower 5554 power usage at the cost of small performance 5555 overhead. 5556 5557 The default value of this parameter is determined by 5558 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5559 5560 workqueue.debug_force_rr_cpu 5561 Workqueue used to implicitly guarantee that work 5562 items queued without explicit CPU specified are put 5563 on the local CPU. This guarantee is no longer true 5564 and while local CPU is still preferred work items 5565 may be put on foreign CPUs. This debug option 5566 forces round-robin CPU selection to flush out 5567 usages which depend on the now broken guarantee. 5568 When enabled, memory and cache locality will be 5569 impacted. 5570 5571 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5572 default x2apic cluster mode on platforms 5573 supporting x2apic. 5574 5575 x86_intel_mid_timer= [X86-32,APBT] 5576 Choose timer option for x86 Intel MID platform. 5577 Two valid options are apbt timer only and lapic timer 5578 plus one apbt timer for broadcast timer. 5579 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5580 5581 xen_512gb_limit [KNL,X86-64,XEN] 5582 Restricts the kernel running paravirtualized under Xen 5583 to use only up to 512 GB of RAM. The reason to do so is 5584 crash analysis tools and Xen tools for doing domain 5585 save/restore/migration must be enabled to handle larger 5586 domains. 5587 5588 xen_emul_unplug= [HW,X86,XEN] 5589 Unplug Xen emulated devices 5590 Format: [unplug0,][unplug1] 5591 ide-disks -- unplug primary master IDE devices 5592 aux-ide-disks -- unplug non-primary-master IDE devices 5593 nics -- unplug network devices 5594 all -- unplug all emulated devices (NICs and IDE disks) 5595 unnecessary -- unplugging emulated devices is 5596 unnecessary even if the host did not respond to 5597 the unplug protocol 5598 never -- do not unplug even if version check succeeds 5599 5600 xen_legacy_crash [X86,XEN] 5601 Crash from Xen panic notifier, without executing late 5602 panic() code such as dumping handler. 5603 5604 xen_nopvspin [X86,XEN] 5605 Disables the ticketlock slowpath using Xen PV 5606 optimizations. 5607 5608 xen_nopv [X86] 5609 Disables the PV optimizations forcing the HVM guest to 5610 run as generic HVM guest with no PV drivers. 5611 This option is obsoleted by the "nopv" option, which 5612 has equivalent effect for XEN platform. 5613 5614 xen_scrub_pages= [XEN] 5615 Boolean option to control scrubbing pages before giving them back 5616 to Xen, for use by other domains. Can be also changed at runtime 5617 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5618 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5619 5620 xen_timer_slop= [X86-64,XEN] 5621 Set the timer slop (in nanoseconds) for the virtual Xen 5622 timers (default is 100000). This adjusts the minimum 5623 delta of virtualized Xen timers, where lower values 5624 improve timer resolution at the expense of processing 5625 more timer interrupts. 5626 5627 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5628 Disables the PV optimizations forcing the guest to run 5629 as generic guest with no PV drivers. Currently support 5630 XEN HVM, KVM, HYPER_V and VMWARE guest. 5631 5632 xirc2ps_cs= [NET,PCMCIA] 5633 Format: 5634 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5635 5636 xive= [PPC] 5637 By default on POWER9 and above, the kernel will 5638 natively use the XIVE interrupt controller. This option 5639 allows the fallback firmware mode to be used: 5640 5641 off Fallback to firmware control of XIVE interrupt 5642 controller on both pseries and powernv 5643 platforms. Only useful on POWER9 and above. 5644 5645 xhci-hcd.quirks [USB,KNL] 5646 A hex value specifying bitmask with supplemental xhci 5647 host controller quirks. Meaning of each bit can be 5648 consulted in header drivers/usb/host/xhci.h. 5649 5650 xmon [PPC] 5651 Format: { early | on | rw | ro | off } 5652 Controls if xmon debugger is enabled. Default is off. 5653 Passing only "xmon" is equivalent to "xmon=early". 5654 early Call xmon as early as possible on boot; xmon 5655 debugger is called from setup_arch(). 5656 on xmon debugger hooks will be installed so xmon 5657 is only called on a kernel crash. Default mode, 5658 i.e. either "ro" or "rw" mode, is controlled 5659 with CONFIG_XMON_DEFAULT_RO_MODE. 5660 rw xmon debugger hooks will be installed so xmon 5661 is called only on a kernel crash, mode is write, 5662 meaning SPR registers, memory and, other data 5663 can be written using xmon commands. 5664 ro same as "rw" option above but SPR registers, 5665 memory, and other data can't be written using 5666 xmon commands. 5667 off xmon is disabled. 5668