1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [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.rst for an 642 alternative. 643 644 uart[8250],io,<addr>[,options] 645 uart[8250],mmio,<addr>[,options] 646 uart[8250],mmio16,<addr>[,options] 647 uart[8250],mmio32,<addr>[,options] 648 uart[8250],0x<addr>[,options] 649 Start an early, polled-mode console on the 8250/16550 650 UART at the specified I/O port or MMIO address, 651 switching to the matching ttyS device later. 652 MMIO inter-register address stride is either 8-bit 653 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 654 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 655 to be equivalent to 'mmio'. 'options' are specified in 656 the same format described for ttyS above; if unspecified, 657 the h/w is not re-initialized. 658 659 hvc<n> Use the hypervisor console device <n>. This is for 660 both Xen and PowerPC hypervisors. 661 662 If the device connected to the port is not a TTY but a braille 663 device, prepend "brl," before the device type, for instance 664 console=brl,ttyS0 665 For now, only VisioBraille is supported. 666 667 console_msg_format= 668 [KNL] Change console messages format 669 default 670 By default we print messages on consoles in 671 "[time stamp] text\n" format (time stamp may not be 672 printed, depending on CONFIG_PRINTK_TIME or 673 `printk_time' param). 674 syslog 675 Switch to syslog format: "<%u>[time stamp] text\n" 676 IOW, each message will have a facility and loglevel 677 prefix. The format is similar to one used by syslog() 678 syscall, or to executing "dmesg -S --raw" or to reading 679 from /proc/kmsg. 680 681 consoleblank= [KNL] The console blank (screen saver) timeout in 682 seconds. A value of 0 disables the blank timer. 683 Defaults to 0. 684 685 coredump_filter= 686 [KNL] Change the default value for 687 /proc/<pid>/coredump_filter. 688 See also Documentation/filesystems/proc.rst. 689 690 coresight_cpu_debug.enable 691 [ARM,ARM64] 692 Format: <bool> 693 Enable/disable the CPU sampling based debugging. 694 0: default value, disable debugging 695 1: enable debugging at boot time 696 697 cpuidle.off=1 [CPU_IDLE] 698 disable the cpuidle sub-system 699 700 cpuidle.governor= 701 [CPU_IDLE] Name of the cpuidle governor to use. 702 703 cpufreq.off=1 [CPU_FREQ] 704 disable the cpufreq sub-system 705 706 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.rst. 835 836 default_hugepagesz= 837 [HW] The size of the default HugeTLB page. This is 838 the size represented by the legacy /proc/ hugepages 839 APIs. In addition, this is the default hugetlb size 840 used for shmget(), mmap() and mounting hugetlbfs 841 filesystems. If not specified, defaults to the 842 architecture's default huge page size. Huge page 843 sizes are architecture dependent. See also 844 Documentation/admin-guide/mm/hugetlbpage.rst. 845 Format: size[KMG] 846 847 deferred_probe_timeout= 848 [KNL] Debugging option to set a timeout in seconds for 849 deferred probe to give up waiting on dependencies to 850 probe. Only specific dependencies (subsystems or 851 drivers) that have opted in will be ignored. A timeout of 0 852 will timeout at the end of initcalls. This option will also 853 dump out devices still on the deferred probe list after 854 retrying. 855 856 dfltcc= [HW,S390] 857 Format: { on | off | def_only | inf_only | always } 858 on: s390 zlib hardware support for compression on 859 level 1 and decompression (default) 860 off: No s390 zlib hardware support 861 def_only: s390 zlib hardware support for deflate 862 only (compression on level 1) 863 inf_only: s390 zlib hardware support for inflate 864 only (decompression) 865 always: Same as 'on' but ignores the selected compression 866 level always using hardware support (used for debugging) 867 868 dhash_entries= [KNL] 869 Set number of hash buckets for dentry cache. 870 871 disable_1tb_segments [PPC] 872 Disables the use of 1TB hash page table segments. This 873 causes the kernel to fall back to 256MB segments which 874 can be useful when debugging issues that require an SLB 875 miss to occur. 876 877 stress_slb [PPC] 878 Limits the number of kernel SLB entries, and flushes 879 them frequently to increase the rate of SLB faults 880 on kernel addresses. 881 882 disable= [IPV6] 883 See Documentation/networking/ipv6.rst. 884 885 hardened_usercopy= 886 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 887 hardening is enabled for this boot. Hardened 888 usercopy checking is used to protect the kernel 889 from reading or writing beyond known memory 890 allocation boundaries as a proactive defense 891 against bounds-checking flaws in the kernel's 892 copy_to_user()/copy_from_user() interface. 893 on Perform hardened usercopy checks (default). 894 off Disable hardened usercopy checks. 895 896 disable_radix [PPC] 897 Disable RADIX MMU mode on POWER9 898 899 disable_tlbie [PPC] 900 Disable TLBIE instruction. Currently does not work 901 with KVM, with HASH MMU, or with coherent accelerators. 902 903 disable_cpu_apicid= [X86,APIC,SMP] 904 Format: <int> 905 The number of initial APIC ID for the 906 corresponding CPU to be disabled at boot, 907 mostly used for the kdump 2nd kernel to 908 disable BSP to wake up multiple CPUs without 909 causing system reset or hang due to sending 910 INIT from AP to BSP. 911 912 perf_v4_pmi= [X86,INTEL] 913 Format: <bool> 914 Disable Intel PMU counter freezing feature. 915 The feature only exists starting from 916 Arch Perfmon v4 (Skylake and newer). 917 918 disable_ddw [PPC/PSERIES] 919 Disable Dynamic DMA Window support. Use this if 920 to workaround buggy firmware. 921 922 disable_ipv6= [IPV6] 923 See Documentation/networking/ipv6.rst. 924 925 disable_mtrr_cleanup [X86] 926 The kernel tries to adjust MTRR layout from continuous 927 to discrete, to make X server driver able to add WB 928 entry later. This parameter disables that. 929 930 disable_mtrr_trim [X86, Intel and AMD only] 931 By default the kernel will trim any uncacheable 932 memory out of your available memory pool based on 933 MTRR settings. This parameter disables that behavior, 934 possibly causing your machine to run very slowly. 935 936 disable_timer_pin_1 [X86] 937 Disable PIN 1 of APIC timer 938 Can be useful to work around chipset bugs. 939 940 dis_ucode_ldr [X86] Disable the microcode loader. 941 942 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 943 this option disables the debugging code at boot. 944 945 dma_debug_entries=<number> 946 This option allows to tune the number of preallocated 947 entries for DMA-API debugging code. One entry is 948 required per DMA-API allocation. Use this if the 949 DMA-API debugging code disables itself because the 950 architectural default is too low. 951 952 dma_debug_driver=<driver_name> 953 With this option the DMA-API debugging driver 954 filter feature can be enabled at boot time. Just 955 pass the driver to filter for as the parameter. 956 The filter can be disabled or changed to another 957 driver later using sysfs. 958 959 driver_async_probe= [KNL] 960 List of driver names to be probed asynchronously. 961 Format: <driver_name1>,<driver_name2>... 962 963 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 964 Broken monitors, graphic adapters, KVMs and EDIDless 965 panels may send no or incorrect EDID data sets. 966 This parameter allows to specify an EDID data sets 967 in the /lib/firmware directory that are used instead. 968 Generic built-in EDID data sets are used, if one of 969 edid/1024x768.bin, edid/1280x1024.bin, 970 edid/1680x1050.bin, or edid/1920x1080.bin is given 971 and no file with the same name exists. Details and 972 instructions how to build your own EDID data are 973 available in Documentation/admin-guide/edid.rst. An EDID 974 data set will only be used for a particular connector, 975 if its name and a colon are prepended to the EDID 976 name. Each connector may use a unique EDID data 977 set by separating the files with a comma. An EDID 978 data set with no connector name will be used for 979 any connectors not explicitly specified. 980 981 dscc4.setup= [NET] 982 983 dt_cpu_ftrs= [PPC] 984 Format: {"off" | "known"} 985 Control how the dt_cpu_ftrs device-tree binding is 986 used for CPU feature discovery and setup (if it 987 exists). 988 off: Do not use it, fall back to legacy cpu table. 989 known: Do not pass through unknown features to guests 990 or userspace, only those that the kernel is aware of. 991 992 dump_apple_properties [X86] 993 Dump name and content of EFI device properties on 994 x86 Macs. Useful for driver authors to determine 995 what data is available or for reverse-engineering. 996 997 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 998 module.dyndbg[="val"] 999 Enable debug messages at boot time. See 1000 Documentation/admin-guide/dynamic-debug-howto.rst 1001 for details. 1002 1003 nopku [X86] Disable Memory Protection Keys CPU feature found 1004 in some Intel CPUs. 1005 1006 module.async_probe [KNL] 1007 Enable asynchronous probe on this module. 1008 1009 early_ioremap_debug [KNL] 1010 Enable debug messages in early_ioremap support. This 1011 is useful for tracking down temporary early mappings 1012 which are not unmapped. 1013 1014 earlycon= [KNL] Output early console device and options. 1015 1016 When used with no options, the early console is 1017 determined by stdout-path property in device tree's 1018 chosen node or the ACPI SPCR table if supported by 1019 the platform. 1020 1021 cdns,<addr>[,options] 1022 Start an early, polled-mode console on a Cadence 1023 (xuartps) serial port at the specified address. Only 1024 supported option is baud rate. If baud rate is not 1025 specified, the serial port must already be setup and 1026 configured. 1027 1028 uart[8250],io,<addr>[,options] 1029 uart[8250],mmio,<addr>[,options] 1030 uart[8250],mmio32,<addr>[,options] 1031 uart[8250],mmio32be,<addr>[,options] 1032 uart[8250],0x<addr>[,options] 1033 Start an early, polled-mode console on the 8250/16550 1034 UART at the specified I/O port or MMIO address. 1035 MMIO inter-register address stride is either 8-bit 1036 (mmio) or 32-bit (mmio32 or mmio32be). 1037 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1038 to be equivalent to 'mmio'. 'options' are specified 1039 in the same format described for "console=ttyS<n>"; if 1040 unspecified, the h/w is not initialized. 1041 1042 pl011,<addr> 1043 pl011,mmio32,<addr> 1044 Start an early, polled-mode console on a pl011 serial 1045 port at the specified address. The pl011 serial port 1046 must already be setup and configured. Options are not 1047 yet supported. If 'mmio32' is specified, then only 1048 the driver will use only 32-bit accessors to read/write 1049 the device registers. 1050 1051 meson,<addr> 1052 Start an early, polled-mode console on a meson serial 1053 port at the specified address. The serial port must 1054 already be setup and configured. Options are not yet 1055 supported. 1056 1057 msm_serial,<addr> 1058 Start an early, polled-mode console on an msm serial 1059 port at the specified address. The serial port 1060 must already be setup and configured. Options are not 1061 yet supported. 1062 1063 msm_serial_dm,<addr> 1064 Start an early, polled-mode console on an msm serial 1065 dm port at the specified address. The serial port 1066 must already be setup and configured. Options are not 1067 yet supported. 1068 1069 owl,<addr> 1070 Start an early, polled-mode console on a serial port 1071 of an Actions Semi SoC, such as S500 or S900, at the 1072 specified address. The serial port must already be 1073 setup and configured. Options are not yet supported. 1074 1075 rda,<addr> 1076 Start an early, polled-mode console on a serial port 1077 of an RDA Micro SoC, such as RDA8810PL, at the 1078 specified address. The serial port must already be 1079 setup and configured. Options are not yet supported. 1080 1081 sbi 1082 Use RISC-V SBI (Supervisor Binary Interface) for early 1083 console. 1084 1085 smh Use ARM semihosting calls for early console. 1086 1087 s3c2410,<addr> 1088 s3c2412,<addr> 1089 s3c2440,<addr> 1090 s3c6400,<addr> 1091 s5pv210,<addr> 1092 exynos4210,<addr> 1093 Use early console provided by serial driver available 1094 on Samsung SoCs, requires selecting proper type and 1095 a correct base address of the selected UART port. The 1096 serial port must already be setup and configured. 1097 Options are not yet supported. 1098 1099 lantiq,<addr> 1100 Start an early, polled-mode console on a lantiq serial 1101 (lqasc) port at the specified address. The serial port 1102 must already be setup and configured. Options are not 1103 yet supported. 1104 1105 lpuart,<addr> 1106 lpuart32,<addr> 1107 Use early console provided by Freescale LP UART driver 1108 found on Freescale Vybrid and QorIQ LS1021A processors. 1109 A valid base address must be provided, and the serial 1110 port must already be setup and configured. 1111 1112 ec_imx21,<addr> 1113 ec_imx6q,<addr> 1114 Start an early, polled-mode, output-only console on the 1115 Freescale i.MX UART at the specified address. The UART 1116 must already be setup and configured. 1117 1118 ar3700_uart,<addr> 1119 Start an early, polled-mode console on the 1120 Armada 3700 serial port at the specified 1121 address. The serial port must already be setup 1122 and configured. Options are not yet supported. 1123 1124 qcom_geni,<addr> 1125 Start an early, polled-mode console on a Qualcomm 1126 Generic Interface (GENI) based serial port at the 1127 specified address. The serial port must already be 1128 setup and configured. Options are not yet supported. 1129 1130 efifb,[options] 1131 Start an early, unaccelerated console on the EFI 1132 memory mapped framebuffer (if available). On cache 1133 coherent non-x86 systems that use system memory for 1134 the framebuffer, pass the 'ram' option so that it is 1135 mapped with the correct attributes. 1136 1137 linflex,<addr> 1138 Use early console provided by Freescale LINFlexD UART 1139 serial driver for NXP S32V234 SoCs. A valid base 1140 address must be provided, and the serial port must 1141 already be setup and configured. 1142 1143 earlyprintk= [X86,SH,ARM,M68k,S390] 1144 earlyprintk=vga 1145 earlyprintk=sclp 1146 earlyprintk=xen 1147 earlyprintk=serial[,ttySn[,baudrate]] 1148 earlyprintk=serial[,0x...[,baudrate]] 1149 earlyprintk=ttySn[,baudrate] 1150 earlyprintk=dbgp[debugController#] 1151 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1152 earlyprintk=xdbc[xhciController#] 1153 1154 earlyprintk is useful when the kernel crashes before 1155 the normal console is initialized. It is not enabled by 1156 default because it has some cosmetic problems. 1157 1158 Append ",keep" to not disable it when the real console 1159 takes over. 1160 1161 Only one of vga, efi, serial, or usb debug port can 1162 be used at a time. 1163 1164 Currently only ttyS0 and ttyS1 may be specified by 1165 name. Other I/O ports may be explicitly specified 1166 on some architectures (x86 and arm at least) by 1167 replacing ttySn with an I/O port address, like this: 1168 earlyprintk=serial,0x1008,115200 1169 You can find the port for a given device in 1170 /proc/tty/driver/serial: 1171 2: uart:ST16650V2 port:00001008 irq:18 ... 1172 1173 Interaction with the standard serial driver is not 1174 very good. 1175 1176 The VGA and EFI output is eventually overwritten by 1177 the real console. 1178 1179 The xen output can only be used by Xen PV guests. 1180 1181 The sclp output can only be used on s390. 1182 1183 The optional "force" to "pciserial" enables use of a 1184 PCI device even when its classcode is not of the 1185 UART class. 1186 1187 edac_report= [HW,EDAC] Control how to report EDAC event 1188 Format: {"on" | "off" | "force"} 1189 on: enable EDAC to report H/W event. May be overridden 1190 by other higher priority error reporting module. 1191 off: disable H/W event reporting through EDAC. 1192 force: enforce the use of EDAC to report H/W event. 1193 default: on. 1194 1195 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1196 ekgdboc=kbd 1197 1198 This is designed to be used in conjunction with 1199 the boot argument: earlyprintk=vga 1200 1201 This parameter works in place of the kgdboc parameter 1202 but can only be used if the backing tty is available 1203 very early in the boot process. For early debugging 1204 via a serial port see kgdboc_earlycon instead. 1205 1206 edd= [EDD] 1207 Format: {"off" | "on" | "skip[mbr]"} 1208 1209 efi= [EFI] 1210 Format: { "old_map", "nochunk", "noruntime", "debug", 1211 "nosoftreserve", "disable_early_pci_dma", 1212 "no_disable_early_pci_dma" } 1213 old_map [X86-64]: switch to the old ioremap-based EFI 1214 runtime services mapping. [Needs CONFIG_X86_UV=y] 1215 nochunk: disable reading files in "chunks" in the EFI 1216 boot stub, as chunking can cause problems with some 1217 firmware implementations. 1218 noruntime : disable EFI runtime services support 1219 debug: enable misc debug output 1220 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1221 attribute may cause the kernel to reserve the 1222 memory range for a memory mapping driver to 1223 claim. Specify efi=nosoftreserve to disable this 1224 reservation and treat the memory by its base type 1225 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1226 disable_early_pci_dma: Disable the busmaster bit on all 1227 PCI bridges while in the EFI boot stub 1228 no_disable_early_pci_dma: Leave the busmaster bit set 1229 on all PCI bridges while in the EFI boot stub 1230 1231 efi_no_storage_paranoia [EFI; X86] 1232 Using this parameter you can use more than 50% of 1233 your efi variable storage. Use this parameter only if 1234 you are really sure that your UEFI does sane gc and 1235 fulfills the spec otherwise your board may brick. 1236 1237 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1238 Add arbitrary attribute to specific memory range by 1239 updating original EFI memory map. 1240 Region of memory which aa attribute is added to is 1241 from ss to ss+nn. 1242 1243 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1244 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1245 attribute is added to range 0x100000000-0x180000000 and 1246 0x10a0000000-0x1120000000. 1247 1248 If efi_fake_mem=8G@9G:0x40000 is specified, the 1249 EFI_MEMORY_SP(0x40000) attribute is added to 1250 range 0x240000000-0x43fffffff. 1251 1252 Using this parameter you can do debugging of EFI memmap 1253 related features. For example, you can do debugging of 1254 Address Range Mirroring feature even if your box 1255 doesn't support it, or mark specific memory as 1256 "soft reserved". 1257 1258 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1259 that is to be dynamically loaded by Linux. If there are 1260 multiple variables with the same name but with different 1261 vendor GUIDs, all of them will be loaded. See 1262 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1263 1264 1265 eisa_irq_edge= [PARISC,HW] 1266 See header of drivers/parisc/eisa.c. 1267 1268 elanfreq= [X86-32] 1269 See comment before function elanfreq_setup() in 1270 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1271 1272 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1273 Specifies physical address of start of kernel core 1274 image elf header and optionally the size. Generally 1275 kexec loader will pass this option to capture kernel. 1276 See Documentation/admin-guide/kdump/kdump.rst for details. 1277 1278 enable_mtrr_cleanup [X86] 1279 The kernel tries to adjust MTRR layout from continuous 1280 to discrete, to make X server driver able to add WB 1281 entry later. This parameter enables that. 1282 1283 enable_timer_pin_1 [X86] 1284 Enable PIN 1 of APIC timer 1285 Can be useful to work around chipset bugs 1286 (in particular on some ATI chipsets). 1287 The kernel tries to set a reasonable default. 1288 1289 enforcing [SELINUX] Set initial enforcing status. 1290 Format: {"0" | "1"} 1291 See security/selinux/Kconfig help text. 1292 0 -- permissive (log only, no denials). 1293 1 -- enforcing (deny and log). 1294 Default value is 0. 1295 Value can be changed at runtime via 1296 /sys/fs/selinux/enforce. 1297 1298 erst_disable [ACPI] 1299 Disable Error Record Serialization Table (ERST) 1300 support. 1301 1302 ether= [HW,NET] Ethernet cards parameters 1303 This option is obsoleted by the "netdev=" option, which 1304 has equivalent usage. See its documentation for details. 1305 1306 evm= [EVM] 1307 Format: { "fix" } 1308 Permit 'security.evm' to be updated regardless of 1309 current integrity status. 1310 1311 failslab= 1312 fail_page_alloc= 1313 fail_make_request=[KNL] 1314 General fault injection mechanism. 1315 Format: <interval>,<probability>,<space>,<times> 1316 See also Documentation/fault-injection/. 1317 1318 floppy= [HW] 1319 See Documentation/admin-guide/blockdev/floppy.rst. 1320 1321 force_pal_cache_flush 1322 [IA-64] Avoid check_sal_cache_flush which may hang on 1323 buggy SAL_CACHE_FLUSH implementations. Using this 1324 parameter will force ia64_sal_cache_flush to call 1325 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1326 1327 forcepae [X86-32] 1328 Forcefully enable Physical Address Extension (PAE). 1329 Many Pentium M systems disable PAE but may have a 1330 functionally usable PAE implementation. 1331 Warning: use of this parameter will taint the kernel 1332 and may cause unknown problems. 1333 1334 ftrace=[tracer] 1335 [FTRACE] will set and start the specified tracer 1336 as early as possible in order to facilitate early 1337 boot debugging. 1338 1339 ftrace_dump_on_oops[=orig_cpu] 1340 [FTRACE] will dump the trace buffers on oops. 1341 If no parameter is passed, ftrace will dump 1342 buffers of all CPUs, but if you pass orig_cpu, it will 1343 dump only the buffer of the CPU that triggered the 1344 oops. 1345 1346 ftrace_filter=[function-list] 1347 [FTRACE] Limit the functions traced by the function 1348 tracer at boot up. function-list is a comma separated 1349 list of functions. This list can be changed at run 1350 time by the set_ftrace_filter file in the debugfs 1351 tracing directory. 1352 1353 ftrace_notrace=[function-list] 1354 [FTRACE] Do not trace the functions specified in 1355 function-list. This list can be changed at run time 1356 by the set_ftrace_notrace file in the debugfs 1357 tracing directory. 1358 1359 ftrace_graph_filter=[function-list] 1360 [FTRACE] Limit the top level callers functions traced 1361 by the function graph tracer at boot up. 1362 function-list is a comma separated list of functions 1363 that can be changed at run time by the 1364 set_graph_function file in the debugfs tracing directory. 1365 1366 ftrace_graph_notrace=[function-list] 1367 [FTRACE] Do not trace from the functions specified in 1368 function-list. This list is a comma separated list of 1369 functions that can be changed at run time by the 1370 set_graph_notrace file in the debugfs tracing directory. 1371 1372 ftrace_graph_max_depth=<uint> 1373 [FTRACE] Used with the function graph tracer. This is 1374 the max depth it will trace into a function. This value 1375 can be changed at run time by the max_graph_depth file 1376 in the tracefs tracing directory. default: 0 (no limit) 1377 1378 fw_devlink= [KNL] Create device links between consumer and supplier 1379 devices by scanning the firmware to infer the 1380 consumer/supplier relationships. This feature is 1381 especially useful when drivers are loaded as modules as 1382 it ensures proper ordering of tasks like device probing 1383 (suppliers first, then consumers), supplier boot state 1384 clean up (only after all consumers have probed), 1385 suspend/resume & runtime PM (consumers first, then 1386 suppliers). 1387 Format: { off | permissive | on | rpm } 1388 off -- Don't create device links from firmware info. 1389 permissive -- Create device links from firmware info 1390 but use it only for ordering boot state clean 1391 up (sync_state() calls). 1392 on -- Create device links from firmware info and use it 1393 to enforce probe and suspend/resume ordering. 1394 rpm -- Like "on", but also use to order runtime PM. 1395 1396 gamecon.map[2|3]= 1397 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1398 support via parallel port (up to 5 devices per port) 1399 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1400 See also Documentation/input/devices/joystick-parport.rst 1401 1402 gamma= [HW,DRM] 1403 1404 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1405 Format: off | on 1406 default: on 1407 1408 gcov_persist= [GCOV] When non-zero (default), profiling data for 1409 kernel modules is saved and remains accessible via 1410 debugfs, even when the module is unloaded/reloaded. 1411 When zero, profiling data is discarded and associated 1412 debugfs files are removed at module unload time. 1413 1414 goldfish [X86] Enable the goldfish android emulator platform. 1415 Don't use this when you are not running on the 1416 android emulator 1417 1418 gpt [EFI] Forces disk with valid GPT signature but 1419 invalid Protective MBR to be treated as GPT. If the 1420 primary GPT is corrupted, it enables the backup/alternate 1421 GPT to be used instead. 1422 1423 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1424 the "Enable 0" bit of the configuration register. 1425 Format: 0 | 1 1426 Default: 0 1427 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1428 the "Enable 0" bit of the configuration register. 1429 Format: 0 | 1 1430 Default: 0 1431 grcan.select= [HW] Select which physical interface to use. 1432 Format: 0 | 1 1433 Default: 0 1434 grcan.txsize= [HW] Sets the size of the tx buffer. 1435 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1436 Default: 1024 1437 grcan.rxsize= [HW] Sets the size of the rx buffer. 1438 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1439 Default: 1024 1440 1441 gpio-mockup.gpio_mockup_ranges 1442 [HW] Sets the ranges of gpiochip of for this device. 1443 Format: <start1>,<end1>,<start2>,<end2>... 1444 1445 hardlockup_all_cpu_backtrace= 1446 [KNL] Should the hard-lockup detector generate 1447 backtraces on all cpus. 1448 Format: 0 | 1 1449 1450 hashdist= [KNL,NUMA] Large hashes allocated during boot 1451 are distributed across NUMA nodes. Defaults on 1452 for 64-bit NUMA, off otherwise. 1453 Format: 0 | 1 (for off | on) 1454 1455 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1456 1457 hd= [EIDE] (E)IDE hard drive subsystem geometry 1458 Format: <cyl>,<head>,<sect> 1459 1460 hest_disable [ACPI] 1461 Disable Hardware Error Source Table (HEST) support; 1462 corresponding firmware-first mode error processing 1463 logic will be disabled. 1464 1465 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1466 size of <nn>. This works even on boxes that have no 1467 highmem otherwise. This also works to reduce highmem 1468 size on bigger boxes. 1469 1470 highres= [KNL] Enable/disable high resolution timer mode. 1471 Valid parameters: "on", "off" 1472 Default: "on" 1473 1474 hlt [BUGS=ARM,SH] 1475 1476 hpet= [X86-32,HPET] option to control HPET usage 1477 Format: { enable (default) | disable | force | 1478 verbose } 1479 disable: disable HPET and use PIT instead 1480 force: allow force enabled of undocumented chips (ICH4, 1481 VIA, nVidia) 1482 verbose: show contents of HPET registers during setup 1483 1484 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1485 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1486 1487 hugetlb_cma= [HW] The size of a cma area used for allocation 1488 of gigantic hugepages. 1489 Format: nn[KMGTPE] 1490 1491 Reserve a cma area of given size and allocate gigantic 1492 hugepages using the cma allocator. If enabled, the 1493 boot-time allocation of gigantic hugepages is skipped. 1494 1495 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1496 If this follows hugepagesz (below), it specifies 1497 the number of pages of hugepagesz to be allocated. 1498 If this is the first HugeTLB parameter on the command 1499 line, it specifies the number of pages to allocate for 1500 the default huge page size. See also 1501 Documentation/admin-guide/mm/hugetlbpage.rst. 1502 Format: <integer> 1503 1504 hugepagesz= 1505 [HW] The size of the HugeTLB pages. This is used in 1506 conjunction with hugepages (above) to allocate huge 1507 pages of a specific size at boot. The pair 1508 hugepagesz=X hugepages=Y can be specified once for 1509 each supported huge page size. Huge page sizes are 1510 architecture dependent. See also 1511 Documentation/admin-guide/mm/hugetlbpage.rst. 1512 Format: size[KMG] 1513 1514 hung_task_panic= 1515 [KNL] Should the hung task detector generate panics. 1516 Format: 0 | 1 1517 1518 A value of 1 instructs the kernel to panic when a 1519 hung task is detected. The default value is controlled 1520 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1521 option. The value selected by this boot parameter can 1522 be changed later by the kernel.hung_task_panic sysctl. 1523 1524 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1525 terminal devices. Valid values: 0..8 1526 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1527 If specified, z/VM IUCV HVC accepts connections 1528 from listed z/VM user IDs only. 1529 1530 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1531 which allow the hypervisor to 'idle' the 1532 guest on lock contention. 1533 1534 keep_bootcon [KNL] 1535 Do not unregister boot console at start. This is only 1536 useful for debugging when something happens in the window 1537 between unregistering the boot console and initializing 1538 the real console. 1539 1540 i2c_bus= [HW] Override the default board specific I2C bus speed 1541 or register an additional I2C bus that is not 1542 registered from board initialization code. 1543 Format: 1544 <bus_id>,<clkrate> 1545 1546 i8042.debug [HW] Toggle i8042 debug mode 1547 i8042.unmask_kbd_data 1548 [HW] Enable printing of interrupt data from the KBD port 1549 (disabled by default, and as a pre-condition 1550 requires that i8042.debug=1 be enabled) 1551 i8042.direct [HW] Put keyboard port into non-translated mode 1552 i8042.dumbkbd [HW] Pretend that controller can only read data from 1553 keyboard and cannot control its state 1554 (Don't attempt to blink the leds) 1555 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1556 i8042.nokbd [HW] Don't check/create keyboard port 1557 i8042.noloop [HW] Disable the AUX Loopback command while probing 1558 for the AUX port 1559 i8042.nomux [HW] Don't check presence of an active multiplexing 1560 controller 1561 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1562 controllers 1563 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1564 i8042.reset [HW] Reset the controller during init, cleanup and 1565 suspend-to-ram transitions, only during s2r 1566 transitions, or never reset 1567 Format: { 1 | Y | y | 0 | N | n } 1568 1, Y, y: always reset controller 1569 0, N, n: don't ever reset controller 1570 Default: only on s2r transitions on x86; most other 1571 architectures force reset to be always executed 1572 i8042.unlock [HW] Unlock (ignore) the keylock 1573 i8042.kbdreset [HW] Reset device connected to KBD port 1574 1575 i810= [HW,DRM] 1576 1577 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1578 indicates that the driver is running on unsupported 1579 hardware. 1580 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1581 does not match list of supported models. 1582 i8k.power_status 1583 [HW] Report power status in /proc/i8k 1584 (disabled by default) 1585 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1586 capability is set. 1587 1588 i915.invert_brightness= 1589 [DRM] Invert the sense of the variable that is used to 1590 set the brightness of the panel backlight. Normally a 1591 brightness value of 0 indicates backlight switched off, 1592 and the maximum of the brightness value sets the backlight 1593 to maximum brightness. If this parameter is set to 0 1594 (default) and the machine requires it, or this parameter 1595 is set to 1, a brightness value of 0 sets the backlight 1596 to maximum brightness, and the maximum of the brightness 1597 value switches the backlight off. 1598 -1 -- never invert brightness 1599 0 -- machine default 1600 1 -- force brightness inversion 1601 1602 icn= [HW,ISDN] 1603 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1604 1605 ide-core.nodma= [HW] (E)IDE subsystem 1606 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1607 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1608 .cdrom .chs .ignore_cable are additional options 1609 See Documentation/ide/ide.rst. 1610 1611 ide-generic.probe-mask= [HW] (E)IDE subsystem 1612 Format: <int> 1613 Probe mask for legacy ISA IDE ports. Depending on 1614 platform up to 6 ports are supported, enabled by 1615 setting corresponding bits in the mask to 1. The 1616 default value is 0x0, which has a special meaning. 1617 On systems that have PCI, it triggers scanning the 1618 PCI bus for the first and the second port, which 1619 are then probed. On systems without PCI the value 1620 of 0x0 enables probing the two first ports as if it 1621 was 0x3. 1622 1623 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1624 Claim all unknown PCI IDE storage controllers. 1625 1626 idle= [X86] 1627 Format: idle=poll, idle=halt, idle=nomwait 1628 Poll forces a polling idle loop that can slightly 1629 improve the performance of waking up a idle CPU, but 1630 will use a lot of power and make the system run hot. 1631 Not recommended. 1632 idle=halt: Halt is forced to be used for CPU idle. 1633 In such case C2/C3 won't be used again. 1634 idle=nomwait: Disable mwait for CPU C-states 1635 1636 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1637 Format: { strict | legacy | 2008 | relaxed } 1638 Default: strict 1639 1640 Choose which programs will be accepted for execution 1641 based on the IEEE 754 NaN encoding(s) supported by 1642 the FPU and the NaN encoding requested with the value 1643 of an ELF file header flag individually set by each 1644 binary. Hardware implementations are permitted to 1645 support either or both of the legacy and the 2008 NaN 1646 encoding mode. 1647 1648 Available settings are as follows: 1649 strict accept binaries that request a NaN encoding 1650 supported by the FPU 1651 legacy only accept legacy-NaN binaries, if supported 1652 by the FPU 1653 2008 only accept 2008-NaN binaries, if supported 1654 by the FPU 1655 relaxed accept any binaries regardless of whether 1656 supported by the FPU 1657 1658 The FPU emulator is always able to support both NaN 1659 encodings, so if no FPU hardware is present or it has 1660 been disabled with 'nofpu', then the settings of 1661 'legacy' and '2008' strap the emulator accordingly, 1662 'relaxed' straps the emulator for both legacy-NaN and 1663 2008-NaN, whereas 'strict' enables legacy-NaN only on 1664 legacy processors and both NaN encodings on MIPS32 or 1665 MIPS64 CPUs. 1666 1667 The setting for ABS.fmt/NEG.fmt instruction execution 1668 mode generally follows that for the NaN encoding, 1669 except where unsupported by hardware. 1670 1671 ignore_loglevel [KNL] 1672 Ignore loglevel setting - this will print /all/ 1673 kernel messages to the console. Useful for debugging. 1674 We also add it as printk module parameter, so users 1675 could change it dynamically, usually by 1676 /sys/module/printk/parameters/ignore_loglevel. 1677 1678 ignore_rlimit_data 1679 Ignore RLIMIT_DATA setting for data mappings, 1680 print warning at first misuse. Can be changed via 1681 /sys/module/kernel/parameters/ignore_rlimit_data. 1682 1683 ihash_entries= [KNL] 1684 Set number of hash buckets for inode cache. 1685 1686 ima_appraise= [IMA] appraise integrity measurements 1687 Format: { "off" | "enforce" | "fix" | "log" } 1688 default: "enforce" 1689 1690 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1691 The builtin appraise policy appraises all files 1692 owned by uid=0. 1693 1694 ima_canonical_fmt [IMA] 1695 Use the canonical format for the binary runtime 1696 measurements, instead of host native format. 1697 1698 ima_hash= [IMA] 1699 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1700 | sha512 | ... } 1701 default: "sha1" 1702 1703 The list of supported hash algorithms is defined 1704 in crypto/hash_info.h. 1705 1706 ima_policy= [IMA] 1707 The builtin policies to load during IMA setup. 1708 Format: "tcb | appraise_tcb | secure_boot | 1709 fail_securely" 1710 1711 The "tcb" policy measures all programs exec'd, files 1712 mmap'd for exec, and all files opened with the read 1713 mode bit set by either the effective uid (euid=0) or 1714 uid=0. 1715 1716 The "appraise_tcb" policy appraises the integrity of 1717 all files owned by root. 1718 1719 The "secure_boot" policy appraises the integrity 1720 of files (eg. kexec kernel image, kernel modules, 1721 firmware, policy, etc) based on file signatures. 1722 1723 The "fail_securely" policy forces file signature 1724 verification failure also on privileged mounted 1725 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1726 flag. 1727 1728 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1729 Load a policy which meets the needs of the Trusted 1730 Computing Base. This means IMA will measure all 1731 programs exec'd, files mmap'd for exec, and all files 1732 opened for read by uid=0. 1733 1734 ima_template= [IMA] 1735 Select one of defined IMA measurements template formats. 1736 Formats: { "ima" | "ima-ng" | "ima-sig" } 1737 Default: "ima-ng" 1738 1739 ima_template_fmt= 1740 [IMA] Define a custom template format. 1741 Format: { "field1|...|fieldN" } 1742 1743 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1744 Format: <min_file_size> 1745 Set the minimal file size for using asynchronous hash. 1746 If left unspecified, ahash usage is disabled. 1747 1748 ahash performance varies for different data sizes on 1749 different crypto accelerators. This option can be used 1750 to achieve the best performance for a particular HW. 1751 1752 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1753 Format: <bufsize> 1754 Set hashing buffer size. Default: 4k. 1755 1756 ahash performance varies for different chunk sizes on 1757 different crypto accelerators. This option can be used 1758 to achieve best performance for particular HW. 1759 1760 init= [KNL] 1761 Format: <full_path> 1762 Run specified binary instead of /sbin/init as init 1763 process. 1764 1765 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1766 for working out where the kernel is dying during 1767 startup. 1768 1769 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1770 initcall functions. Useful for debugging built-in 1771 modules and initcalls. 1772 1773 initrd= [BOOT] Specify the location of the initial ramdisk 1774 1775 initrdmem= [KNL] Specify a physical address and size from which to 1776 load the initrd. If an initrd is compiled in or 1777 specified in the bootparams, it takes priority over this 1778 setting. 1779 Format: ss[KMG],nn[KMG] 1780 Default is 0, 0 1781 1782 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1783 zeroes. 1784 Format: 0 | 1 1785 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1786 1787 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1788 Format: 0 | 1 1789 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1790 1791 init_pkru= [x86] Specify the default memory protection keys rights 1792 register contents for all processes. 0x55555554 by 1793 default (disallow access to all but pkey 0). Can 1794 override in debugfs after boot. 1795 1796 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1797 Format: <irq> 1798 1799 int_pln_enable [x86] Enable power limit notification interrupt 1800 1801 integrity_audit=[IMA] 1802 Format: { "0" | "1" } 1803 0 -- basic integrity auditing messages. (Default) 1804 1 -- additional integrity auditing messages. 1805 1806 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1807 on 1808 Enable intel iommu driver. 1809 off 1810 Disable intel iommu driver. 1811 igfx_off [Default Off] 1812 By default, gfx is mapped as normal device. If a gfx 1813 device has a dedicated DMAR unit, the DMAR unit is 1814 bypassed by not enabling DMAR with this option. In 1815 this case, gfx device will use physical address for 1816 DMA. 1817 forcedac [x86_64] 1818 With this option iommu will not optimize to look 1819 for io virtual address below 32-bit forcing dual 1820 address cycle on pci bus for cards supporting greater 1821 than 32-bit addressing. The default is to look 1822 for translation below 32-bit and if not available 1823 then look in the higher range. 1824 strict [Default Off] 1825 With this option on every unmap_single operation will 1826 result in a hardware IOTLB flush operation as opposed 1827 to batching them for performance. 1828 sp_off [Default Off] 1829 By default, super page will be supported if Intel IOMMU 1830 has the capability. With this option, super page will 1831 not be supported. 1832 sm_on [Default Off] 1833 By default, scalable mode will be disabled even if the 1834 hardware advertises that it has support for the scalable 1835 mode translation. With this option set, scalable mode 1836 will be used on hardware which claims to support it. 1837 tboot_noforce [Default Off] 1838 Do not force the Intel IOMMU enabled under tboot. 1839 By default, tboot will force Intel IOMMU on, which 1840 could harm performance of some high-throughput 1841 devices like 40GBit network cards, even if identity 1842 mapping is enabled. 1843 Note that using this option lowers the security 1844 provided by tboot because it makes the system 1845 vulnerable to DMA attacks. 1846 nobounce [Default off] 1847 Disable bounce buffer for untrusted devices such as 1848 the Thunderbolt devices. This will treat the untrusted 1849 devices as the trusted ones, hence might expose security 1850 risks of DMA attacks. 1851 1852 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1853 0 disables intel_idle and fall back on acpi_idle. 1854 1 to 9 specify maximum depth of C-state. 1855 1856 intel_pstate= [X86] 1857 disable 1858 Do not enable intel_pstate as the default 1859 scaling driver for the supported processors 1860 passive 1861 Use intel_pstate as a scaling driver, but configure it 1862 to work with generic cpufreq governors (instead of 1863 enabling its internal governor). This mode cannot be 1864 used along with the hardware-managed P-states (HWP) 1865 feature. 1866 force 1867 Enable intel_pstate on systems that prohibit it by default 1868 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1869 instead of acpi-cpufreq may disable platform features, such 1870 as thermal controls and power capping, that rely on ACPI 1871 P-States information being indicated to OSPM and therefore 1872 should be used with caution. This option does not work with 1873 processors that aren't supported by the intel_pstate driver 1874 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1875 no_hwp 1876 Do not enable hardware P state control (HWP) 1877 if available. 1878 hwp_only 1879 Only load intel_pstate on systems which support 1880 hardware P state control (HWP) if available. 1881 support_acpi_ppc 1882 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1883 Description Table, specifies preferred power management 1884 profile as "Enterprise Server" or "Performance Server", 1885 then this feature is turned on by default. 1886 per_cpu_perf_limits 1887 Allow per-logical-CPU P-State performance control limits using 1888 cpufreq sysfs interface 1889 1890 intremap= [X86-64, Intel-IOMMU] 1891 on enable Interrupt Remapping (default) 1892 off disable Interrupt Remapping 1893 nosid disable Source ID checking 1894 no_x2apic_optout 1895 BIOS x2APIC opt-out request will be ignored 1896 nopost disable Interrupt Posting 1897 1898 iomem= Disable strict checking of access to MMIO memory 1899 strict regions from userspace. 1900 relaxed 1901 1902 iommu= [x86] 1903 off 1904 force 1905 noforce 1906 biomerge 1907 panic 1908 nopanic 1909 merge 1910 nomerge 1911 soft 1912 pt [x86] 1913 nopt [x86] 1914 nobypass [PPC/POWERNV] 1915 Disable IOMMU bypass, using IOMMU for PCI devices. 1916 1917 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1918 Format: { "0" | "1" } 1919 0 - Lazy mode. 1920 Request that DMA unmap operations use deferred 1921 invalidation of hardware TLBs, for increased 1922 throughput at the cost of reduced device isolation. 1923 Will fall back to strict mode if not supported by 1924 the relevant IOMMU driver. 1925 1 - Strict mode (default). 1926 DMA unmap operations invalidate IOMMU hardware TLBs 1927 synchronously. 1928 1929 iommu.passthrough= 1930 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1931 Format: { "0" | "1" } 1932 0 - Use IOMMU translation for DMA. 1933 1 - Bypass the IOMMU for DMA. 1934 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1935 1936 io7= [HW] IO7 for Marvel based alpha systems 1937 See comment before marvel_specify_io7 in 1938 arch/alpha/kernel/core_marvel.c. 1939 1940 io_delay= [X86] I/O delay method 1941 0x80 1942 Standard port 0x80 based delay 1943 0xed 1944 Alternate port 0xed based delay (needed on some systems) 1945 udelay 1946 Simple two microseconds delay 1947 none 1948 No delay 1949 1950 ip= [IP_PNP] 1951 See Documentation/admin-guide/nfs/nfsroot.rst. 1952 1953 ipcmni_extend [KNL] Extend the maximum number of unique System V 1954 IPC identifiers from 32,768 to 16,777,216. 1955 1956 irqaffinity= [SMP] Set the default irq affinity mask 1957 The argument is a cpu list, as described above. 1958 1959 irqchip.gicv2_force_probe= 1960 [ARM, ARM64] 1961 Format: <bool> 1962 Force the kernel to look for the second 4kB page 1963 of a GICv2 controller even if the memory range 1964 exposed by the device tree is too small. 1965 1966 irqchip.gicv3_nolpi= 1967 [ARM, ARM64] 1968 Force the kernel to ignore the availability of 1969 LPIs (and by consequence ITSs). Intended for system 1970 that use the kernel as a bootloader, and thus want 1971 to let secondary kernels in charge of setting up 1972 LPIs. 1973 1974 irqchip.gicv3_pseudo_nmi= [ARM64] 1975 Enables support for pseudo-NMIs in the kernel. This 1976 requires the kernel to be built with 1977 CONFIG_ARM64_PSEUDO_NMI. 1978 1979 irqfixup [HW] 1980 When an interrupt is not handled search all handlers 1981 for it. Intended to get systems with badly broken 1982 firmware running. 1983 1984 irqpoll [HW] 1985 When an interrupt is not handled search all handlers 1986 for it. Also check all handlers each timer 1987 interrupt. Intended to get systems with badly broken 1988 firmware running. 1989 1990 isapnp= [ISAPNP] 1991 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1992 1993 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1994 [Deprecated - use cpusets instead] 1995 Format: [flag-list,]<cpu-list> 1996 1997 Specify one or more CPUs to isolate from disturbances 1998 specified in the flag list (default: domain): 1999 2000 nohz 2001 Disable the tick when a single task runs. 2002 2003 A residual 1Hz tick is offloaded to workqueues, which you 2004 need to affine to housekeeping through the global 2005 workqueue's affinity configured via the 2006 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2007 by using the 'domain' flag described below. 2008 2009 NOTE: by default the global workqueue runs on all CPUs, 2010 so to protect individual CPUs the 'cpumask' file has to 2011 be configured manually after bootup. 2012 2013 domain 2014 Isolate from the general SMP balancing and scheduling 2015 algorithms. Note that performing domain isolation this way 2016 is irreversible: it's not possible to bring back a CPU to 2017 the domains once isolated through isolcpus. It's strongly 2018 advised to use cpusets instead to disable scheduler load 2019 balancing through the "cpuset.sched_load_balance" file. 2020 It offers a much more flexible interface where CPUs can 2021 move in and out of an isolated set anytime. 2022 2023 You can move a process onto or off an "isolated" CPU via 2024 the CPU affinity syscalls or cpuset. 2025 <cpu number> begins at 0 and the maximum value is 2026 "number of CPUs in system - 1". 2027 2028 managed_irq 2029 2030 Isolate from being targeted by managed interrupts 2031 which have an interrupt mask containing isolated 2032 CPUs. The affinity of managed interrupts is 2033 handled by the kernel and cannot be changed via 2034 the /proc/irq/* interfaces. 2035 2036 This isolation is best effort and only effective 2037 if the automatically assigned interrupt mask of a 2038 device queue contains isolated and housekeeping 2039 CPUs. If housekeeping CPUs are online then such 2040 interrupts are directed to the housekeeping CPU 2041 so that IO submitted on the housekeeping CPU 2042 cannot disturb the isolated CPU. 2043 2044 If a queue's affinity mask contains only isolated 2045 CPUs then this parameter has no effect on the 2046 interrupt routing decision, though interrupts are 2047 only delivered when tasks running on those 2048 isolated CPUs submit IO. IO submitted on 2049 housekeeping CPUs has no influence on those 2050 queues. 2051 2052 The format of <cpu-list> is described above. 2053 2054 iucv= [HW,NET] 2055 2056 ivrs_ioapic [HW,X86_64] 2057 Provide an override to the IOAPIC-ID<->DEVICE-ID 2058 mapping provided in the IVRS ACPI table. For 2059 example, to map IOAPIC-ID decimal 10 to 2060 PCI device 00:14.0 write the parameter as: 2061 ivrs_ioapic[10]=00:14.0 2062 2063 ivrs_hpet [HW,X86_64] 2064 Provide an override to the HPET-ID<->DEVICE-ID 2065 mapping provided in the IVRS ACPI table. For 2066 example, to map HPET-ID decimal 0 to 2067 PCI device 00:14.0 write the parameter as: 2068 ivrs_hpet[0]=00:14.0 2069 2070 ivrs_acpihid [HW,X86_64] 2071 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2072 mapping provided in the IVRS ACPI table. For 2073 example, to map UART-HID:UID AMD0020:0 to 2074 PCI device 00:14.5 write the parameter as: 2075 ivrs_acpihid[00:14.5]=AMD0020:0 2076 2077 js= [HW,JOY] Analog joystick 2078 See Documentation/input/joydev/joystick.rst. 2079 2080 nokaslr [KNL] 2081 When CONFIG_RANDOMIZE_BASE is set, this disables 2082 kernel and module base offset ASLR (Address Space 2083 Layout Randomization). 2084 2085 kasan_multi_shot 2086 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2087 report on every invalid memory access. Without this 2088 parameter KASAN will print report only for the first 2089 invalid access. 2090 2091 keepinitrd [HW,ARM] 2092 2093 kernelcore= [KNL,X86,IA-64,PPC] 2094 Format: nn[KMGTPE] | nn% | "mirror" 2095 This parameter specifies the amount of memory usable by 2096 the kernel for non-movable allocations. The requested 2097 amount is spread evenly throughout all nodes in the 2098 system as ZONE_NORMAL. The remaining memory is used for 2099 movable memory in its own zone, ZONE_MOVABLE. In the 2100 event, a node is too small to have both ZONE_NORMAL and 2101 ZONE_MOVABLE, kernelcore memory will take priority and 2102 other nodes will have a larger ZONE_MOVABLE. 2103 2104 ZONE_MOVABLE is used for the allocation of pages that 2105 may be reclaimed or moved by the page migration 2106 subsystem. Note that allocations like PTEs-from-HighMem 2107 still use the HighMem zone if it exists, and the Normal 2108 zone if it does not. 2109 2110 It is possible to specify the exact amount of memory in 2111 the form of "nn[KMGTPE]", a percentage of total system 2112 memory in the form of "nn%", or "mirror". If "mirror" 2113 option is specified, mirrored (reliable) memory is used 2114 for non-movable allocations and remaining memory is used 2115 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2116 are exclusive, so you cannot specify multiple forms. 2117 2118 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2119 Format: <Controller#>[,poll interval] 2120 The controller # is the number of the ehci usb debug 2121 port as it is probed via PCI. The poll interval is 2122 optional and is the number seconds in between 2123 each poll cycle to the debug port in case you need 2124 the functionality for interrupting the kernel with 2125 gdb or control-c on the dbgp connection. When 2126 not using this parameter you use sysrq-g to break into 2127 the kernel debugger. 2128 2129 kgdboc= [KGDB,HW] kgdb over consoles. 2130 Requires a tty driver that supports console polling, 2131 or a supported polling keyboard driver (non-usb). 2132 Serial only format: <serial_device>[,baud] 2133 keyboard only format: kbd 2134 keyboard and serial format: kbd,<serial_device>[,baud] 2135 Optional Kernel mode setting: 2136 kms, kbd format: kms,kbd 2137 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2138 2139 kgdboc_earlycon= [KGDB,HW] 2140 If the boot console provides the ability to read 2141 characters and can work in polling mode, you can use 2142 this parameter to tell kgdb to use it as a backend 2143 until the normal console is registered. Intended to 2144 be used together with the kgdboc parameter which 2145 specifies the normal console to transition to. 2146 2147 The name of the early console should be specified 2148 as the value of this parameter. Note that the name of 2149 the early console might be different than the tty 2150 name passed to kgdboc. It's OK to leave the value 2151 blank and the first boot console that implements 2152 read() will be picked. 2153 2154 kgdbwait [KGDB] Stop kernel execution and enter the 2155 kernel debugger at the earliest opportunity. 2156 2157 kmac= [MIPS] korina ethernet MAC address. 2158 Configure the RouterBoard 532 series on-chip 2159 Ethernet adapter MAC address. 2160 2161 kmemleak= [KNL] Boot-time kmemleak enable/disable 2162 Valid arguments: on, off 2163 Default: on 2164 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2165 the default is off. 2166 2167 kprobe_event=[probe-list] 2168 [FTRACE] Add kprobe events and enable at boot time. 2169 The probe-list is a semicolon delimited list of probe 2170 definitions. Each definition is same as kprobe_events 2171 interface, but the parameters are comma delimited. 2172 For example, to add a kprobe event on vfs_read with 2173 arg1 and arg2, add to the command line; 2174 2175 kprobe_event=p,vfs_read,$arg1,$arg2 2176 2177 See also Documentation/trace/kprobetrace.rst "Kernel 2178 Boot Parameter" section. 2179 2180 kpti= [ARM64] Control page table isolation of user 2181 and kernel address spaces. 2182 Default: enabled on cores which need mitigation. 2183 0: force disabled 2184 1: force enabled 2185 2186 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2187 Default is 0 (don't ignore, but inject #GP) 2188 2189 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2190 Default is false (don't support). 2191 2192 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2193 KVM MMU at runtime. 2194 Default is 0 (off) 2195 2196 kvm.nx_huge_pages= 2197 [KVM] Controls the software workaround for the 2198 X86_BUG_ITLB_MULTIHIT bug. 2199 force : Always deploy workaround. 2200 off : Never deploy workaround. 2201 auto : Deploy workaround based on the presence of 2202 X86_BUG_ITLB_MULTIHIT. 2203 2204 Default is 'auto'. 2205 2206 If the software workaround is enabled for the host, 2207 guests do need not to enable it for nested guests. 2208 2209 kvm.nx_huge_pages_recovery_ratio= 2210 [KVM] Controls how many 4KiB pages are periodically zapped 2211 back to huge pages. 0 disables the recovery, otherwise if 2212 the value is N KVM will zap 1/Nth of the 4KiB pages every 2213 minute. The default is 60. 2214 2215 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2216 Default is 1 (enabled) 2217 2218 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2219 for all guests. 2220 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2221 2222 kvm-arm.vgic_v3_group0_trap= 2223 [KVM,ARM] Trap guest accesses to GICv3 group-0 2224 system registers 2225 2226 kvm-arm.vgic_v3_group1_trap= 2227 [KVM,ARM] Trap guest accesses to GICv3 group-1 2228 system registers 2229 2230 kvm-arm.vgic_v3_common_trap= 2231 [KVM,ARM] Trap guest accesses to GICv3 common 2232 system registers 2233 2234 kvm-arm.vgic_v4_enable= 2235 [KVM,ARM] Allow use of GICv4 for direct injection of 2236 LPIs. 2237 2238 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2239 (virtualized MMU) support on capable Intel chips. 2240 Default is 1 (enabled) 2241 2242 kvm-intel.emulate_invalid_guest_state= 2243 [KVM,Intel] Enable emulation of invalid guest states 2244 Default is 0 (disabled) 2245 2246 kvm-intel.flexpriority= 2247 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2248 Default is 1 (enabled) 2249 2250 kvm-intel.nested= 2251 [KVM,Intel] Enable VMX nesting (nVMX). 2252 Default is 0 (disabled) 2253 2254 kvm-intel.unrestricted_guest= 2255 [KVM,Intel] Disable unrestricted guest feature 2256 (virtualized real and unpaged mode) on capable 2257 Intel chips. Default is 1 (enabled) 2258 2259 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2260 CVE-2018-3620. 2261 2262 Valid arguments: never, cond, always 2263 2264 always: L1D cache flush on every VMENTER. 2265 cond: Flush L1D on VMENTER only when the code between 2266 VMEXIT and VMENTER can leak host memory. 2267 never: Disables the mitigation 2268 2269 Default is cond (do L1 cache flush in specific instances) 2270 2271 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2272 feature (tagged TLBs) on capable Intel chips. 2273 Default is 1 (enabled) 2274 2275 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2276 affected CPUs 2277 2278 The kernel PTE inversion protection is unconditionally 2279 enabled and cannot be disabled. 2280 2281 full 2282 Provides all available mitigations for the 2283 L1TF vulnerability. Disables SMT and 2284 enables all mitigations in the 2285 hypervisors, i.e. unconditional L1D flush. 2286 2287 SMT control and L1D flush control via the 2288 sysfs interface is still possible after 2289 boot. Hypervisors will issue a warning 2290 when the first VM is started in a 2291 potentially insecure configuration, 2292 i.e. SMT enabled or L1D flush disabled. 2293 2294 full,force 2295 Same as 'full', but disables SMT and L1D 2296 flush runtime control. Implies the 2297 'nosmt=force' command line option. 2298 (i.e. sysfs control of SMT is disabled.) 2299 2300 flush 2301 Leaves SMT enabled and enables the default 2302 hypervisor mitigation, i.e. conditional 2303 L1D flush. 2304 2305 SMT control and L1D flush control via the 2306 sysfs interface is still possible after 2307 boot. Hypervisors will issue a warning 2308 when the first VM is started in a 2309 potentially insecure configuration, 2310 i.e. SMT enabled or L1D flush disabled. 2311 2312 flush,nosmt 2313 2314 Disables SMT and enables the default 2315 hypervisor mitigation. 2316 2317 SMT control and L1D flush control via the 2318 sysfs interface is still possible after 2319 boot. Hypervisors will issue a warning 2320 when the first VM is started in a 2321 potentially insecure configuration, 2322 i.e. SMT enabled or L1D flush disabled. 2323 2324 flush,nowarn 2325 Same as 'flush', but hypervisors will not 2326 warn when a VM is started in a potentially 2327 insecure configuration. 2328 2329 off 2330 Disables hypervisor mitigations and doesn't 2331 emit any warnings. 2332 It also drops the swap size and available 2333 RAM limit restriction on both hypervisor and 2334 bare metal. 2335 2336 Default is 'flush'. 2337 2338 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2339 2340 l2cr= [PPC] 2341 2342 l3cr= [PPC] 2343 2344 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2345 disabled it. 2346 2347 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2348 value for LAPIC timer one-shot implementation. Default 2349 back to the programmable timer unit in the LAPIC. 2350 2351 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2352 in C2 power state. 2353 2354 libata.dma= [LIBATA] DMA control 2355 libata.dma=0 Disable all PATA and SATA DMA 2356 libata.dma=1 PATA and SATA Disk DMA only 2357 libata.dma=2 ATAPI (CDROM) DMA only 2358 libata.dma=4 Compact Flash DMA only 2359 Combinations also work, so libata.dma=3 enables DMA 2360 for disks and CDROMs, but not CFs. 2361 2362 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2363 libata.ignore_hpa=0 keep BIOS limits (default) 2364 libata.ignore_hpa=1 ignore limits, using full disk 2365 2366 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2367 when set. 2368 Format: <int> 2369 2370 libata.force= [LIBATA] Force configurations. The format is comma 2371 separated list of "[ID:]VAL" where ID is 2372 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2373 matching port, link or device. Basically, it matches 2374 the ATA ID string printed on console by libata. If 2375 the whole ID part is omitted, the last PORT and DEVICE 2376 values are used. If ID hasn't been specified yet, the 2377 configuration applies to all ports, links and devices. 2378 2379 If only DEVICE is omitted, the parameter applies to 2380 the port and all links and devices behind it. DEVICE 2381 number of 0 either selects the first device or the 2382 first fan-out link behind PMP device. It does not 2383 select the host link. DEVICE number of 15 selects the 2384 host link and device attached to it. 2385 2386 The VAL specifies the configuration to force. As long 2387 as there's no ambiguity shortcut notation is allowed. 2388 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2389 The following configurations can be forced. 2390 2391 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2392 Any ID with matching PORT is used. 2393 2394 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2395 2396 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2397 udma[/][16,25,33,44,66,100,133] notation is also 2398 allowed. 2399 2400 * [no]ncq: Turn on or off NCQ. 2401 2402 * [no]ncqtrim: Turn off queued DSM TRIM. 2403 2404 * nohrst, nosrst, norst: suppress hard, soft 2405 and both resets. 2406 2407 * rstonce: only attempt one reset during 2408 hot-unplug link recovery 2409 2410 * dump_id: dump IDENTIFY data. 2411 2412 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2413 2414 * disable: Disable this device. 2415 2416 If there are multiple matching configurations changing 2417 the same attribute, the last one is used. 2418 2419 memblock=debug [KNL] Enable memblock debug messages. 2420 2421 load_ramdisk= [RAM] List of ramdisks to load from floppy 2422 See Documentation/admin-guide/blockdev/ramdisk.rst. 2423 2424 lockd.nlm_grace_period=P [NFS] Assign grace period. 2425 Format: <integer> 2426 2427 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2428 Format: <integer> 2429 2430 lockd.nlm_timeout=T [NFS] Assign timeout value. 2431 Format: <integer> 2432 2433 lockd.nlm_udpport=M [NFS] Assign UDP port. 2434 Format: <integer> 2435 2436 lockdown= [SECURITY] 2437 { integrity | confidentiality } 2438 Enable the kernel lockdown feature. If set to 2439 integrity, kernel features that allow userland to 2440 modify the running kernel are disabled. If set to 2441 confidentiality, kernel features that allow userland 2442 to extract confidential information from the kernel 2443 are also disabled. 2444 2445 locktorture.nreaders_stress= [KNL] 2446 Set the number of locking read-acquisition kthreads. 2447 Defaults to being automatically set based on the 2448 number of online CPUs. 2449 2450 locktorture.nwriters_stress= [KNL] 2451 Set the number of locking write-acquisition kthreads. 2452 2453 locktorture.onoff_holdoff= [KNL] 2454 Set time (s) after boot for CPU-hotplug testing. 2455 2456 locktorture.onoff_interval= [KNL] 2457 Set time (s) between CPU-hotplug operations, or 2458 zero to disable CPU-hotplug testing. 2459 2460 locktorture.shuffle_interval= [KNL] 2461 Set task-shuffle interval (jiffies). Shuffling 2462 tasks allows some CPUs to go into dyntick-idle 2463 mode during the locktorture test. 2464 2465 locktorture.shutdown_secs= [KNL] 2466 Set time (s) after boot system shutdown. This 2467 is useful for hands-off automated testing. 2468 2469 locktorture.stat_interval= [KNL] 2470 Time (s) between statistics printk()s. 2471 2472 locktorture.stutter= [KNL] 2473 Time (s) to stutter testing, for example, 2474 specifying five seconds causes the test to run for 2475 five seconds, wait for five seconds, and so on. 2476 This tests the locking primitive's ability to 2477 transition abruptly to and from idle. 2478 2479 locktorture.torture_type= [KNL] 2480 Specify the locking implementation to test. 2481 2482 locktorture.verbose= [KNL] 2483 Enable additional printk() statements. 2484 2485 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2486 Format: <irq> 2487 2488 loglevel= All Kernel Messages with a loglevel smaller than the 2489 console loglevel will be printed to the console. It can 2490 also be changed with klogd or other programs. The 2491 loglevels are defined as follows: 2492 2493 0 (KERN_EMERG) system is unusable 2494 1 (KERN_ALERT) action must be taken immediately 2495 2 (KERN_CRIT) critical conditions 2496 3 (KERN_ERR) error conditions 2497 4 (KERN_WARNING) warning conditions 2498 5 (KERN_NOTICE) normal but significant condition 2499 6 (KERN_INFO) informational 2500 7 (KERN_DEBUG) debug-level messages 2501 2502 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2503 in bytes. n must be a power of two and greater 2504 than the minimal size. The minimal size is defined 2505 by LOG_BUF_SHIFT kernel config parameter. There is 2506 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2507 that allows to increase the default size depending on 2508 the number of CPUs. See init/Kconfig for more details. 2509 2510 logo.nologo [FB] Disables display of the built-in Linux logo. 2511 This may be used to provide more screen space for 2512 kernel log messages and is useful when debugging 2513 kernel boot problems. 2514 2515 lp=0 [LP] Specify parallel ports to use, e.g, 2516 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2517 lp=reset first parallel port). 'lp=0' disables the 2518 lp=auto printer driver. 'lp=reset' (which can be 2519 specified in addition to the ports) causes 2520 attached printers to be reset. Using 2521 lp=port1,port2,... specifies the parallel ports 2522 to associate lp devices with, starting with 2523 lp0. A port specification may be 'none' to skip 2524 that lp device, or a parport name such as 2525 'parport0'. Specifying 'lp=auto' instead of a 2526 port specification list means that device IDs 2527 from each port should be examined, to see if 2528 an IEEE 1284-compliant printer is attached; if 2529 so, the driver will manage that printer. 2530 See also header of drivers/char/lp.c. 2531 2532 lpj=n [KNL] 2533 Sets loops_per_jiffy to given constant, thus avoiding 2534 time-consuming boot-time autodetection (up to 250 ms per 2535 CPU). 0 enables autodetection (default). To determine 2536 the correct value for your kernel, boot with normal 2537 autodetection and see what value is printed. Note that 2538 on SMP systems the preset will be applied to all CPUs, 2539 which is likely to cause problems if your CPUs need 2540 significantly divergent settings. An incorrect value 2541 will cause delays in the kernel to be wrong, leading to 2542 unpredictable I/O errors and other breakage. Although 2543 unlikely, in the extreme case this might damage your 2544 hardware. 2545 2546 ltpc= [NET] 2547 Format: <io>,<irq>,<dma> 2548 2549 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2550 2551 lsm=lsm1,...,lsmN 2552 [SECURITY] Choose order of LSM initialization. This 2553 overrides CONFIG_LSM, and the "security=" parameter. 2554 2555 machvec= [IA-64] Force the use of a particular machine-vector 2556 (machvec) in a generic kernel. 2557 Example: machvec=hpzx1 2558 2559 machtype= [Loongson] Share the same kernel image file between different 2560 yeeloong laptop. 2561 Example: machtype=lemote-yeeloong-2f-7inch 2562 2563 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2564 than or equal to this physical address is ignored. 2565 2566 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2567 will bring up during bootup. maxcpus=n : n >= 0 limits 2568 the kernel to bring up 'n' processors. Surely after 2569 bootup you can bring up the other plugged cpu by executing 2570 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2571 only takes effect during system bootup. 2572 While n=0 is a special case, it is equivalent to "nosmp", 2573 which also disables the IO APIC. 2574 2575 max_loop= [LOOP] The number of loop block devices that get 2576 (loop.max_loop) unconditionally pre-created at init time. The default 2577 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2578 of statically allocating a predefined number, loop 2579 devices can be requested on-demand with the 2580 /dev/loop-control interface. 2581 2582 mce [X86-32] Machine Check Exception 2583 2584 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2585 2586 md= [HW] RAID subsystems devices and level 2587 See Documentation/admin-guide/md.rst. 2588 2589 mdacon= [MDA] 2590 Format: <first>,<last> 2591 Specifies range of consoles to be captured by the MDA. 2592 2593 mds= [X86,INTEL] 2594 Control mitigation for the Micro-architectural Data 2595 Sampling (MDS) vulnerability. 2596 2597 Certain CPUs are vulnerable to an exploit against CPU 2598 internal buffers which can forward information to a 2599 disclosure gadget under certain conditions. 2600 2601 In vulnerable processors, the speculatively 2602 forwarded data can be used in a cache side channel 2603 attack, to access data to which the attacker does 2604 not have direct access. 2605 2606 This parameter controls the MDS mitigation. The 2607 options are: 2608 2609 full - Enable MDS mitigation on vulnerable CPUs 2610 full,nosmt - Enable MDS mitigation and disable 2611 SMT on vulnerable CPUs 2612 off - Unconditionally disable MDS mitigation 2613 2614 On TAA-affected machines, mds=off can be prevented by 2615 an active TAA mitigation as both vulnerabilities are 2616 mitigated with the same mechanism so in order to disable 2617 this mitigation, you need to specify tsx_async_abort=off 2618 too. 2619 2620 Not specifying this option is equivalent to 2621 mds=full. 2622 2623 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2624 2625 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2626 Amount of memory to be used in cases as follows: 2627 2628 1 for test; 2629 2 when the kernel is not able to see the whole system memory; 2630 3 memory that lies after 'mem=' boundary is excluded from 2631 the hypervisor, then assigned to KVM guests. 2632 2633 [X86] Work as limiting max address. Use together 2634 with memmap= to avoid physical address space collisions. 2635 Without memmap= PCI devices could be placed at addresses 2636 belonging to unused RAM. 2637 2638 Note that this only takes effects during boot time since 2639 in above case 3, memory may need be hot added after boot 2640 if system memory of hypervisor is not sufficient. 2641 2642 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2643 memory. 2644 2645 memchunk=nn[KMG] 2646 [KNL,SH] Allow user to override the default size for 2647 per-device physically contiguous DMA buffers. 2648 2649 memhp_default_state=online/offline 2650 [KNL] Set the initial state for the memory hotplug 2651 onlining policy. If not specified, the default value is 2652 set according to the 2653 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2654 option. 2655 See Documentation/admin-guide/mm/memory-hotplug.rst. 2656 2657 memmap=exactmap [KNL,X86] Enable setting of an exact 2658 E820 memory map, as specified by the user. 2659 Such memmap=exactmap lines can be constructed based on 2660 BIOS output or other requirements. See the memmap=nn@ss 2661 option description. 2662 2663 memmap=nn[KMG]@ss[KMG] 2664 [KNL] Force usage of a specific region of memory. 2665 Region of memory to be used is from ss to ss+nn. 2666 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2667 which limits max address to nn[KMG]. 2668 Multiple different regions can be specified, 2669 comma delimited. 2670 Example: 2671 memmap=100M@2G,100M#3G,1G!1024G 2672 2673 memmap=nn[KMG]#ss[KMG] 2674 [KNL,ACPI] Mark specific memory as ACPI data. 2675 Region of memory to be marked is from ss to ss+nn. 2676 2677 memmap=nn[KMG]$ss[KMG] 2678 [KNL,ACPI] Mark specific memory as reserved. 2679 Region of memory to be reserved is from ss to ss+nn. 2680 Example: Exclude memory from 0x18690000-0x1869ffff 2681 memmap=64K$0x18690000 2682 or 2683 memmap=0x10000$0x18690000 2684 Some bootloaders may need an escape character before '$', 2685 like Grub2, otherwise '$' and the following number 2686 will be eaten. 2687 2688 memmap=nn[KMG]!ss[KMG] 2689 [KNL,X86] Mark specific memory as protected. 2690 Region of memory to be used, from ss to ss+nn. 2691 The memory region may be marked as e820 type 12 (0xc) 2692 and is NVDIMM or ADR memory. 2693 2694 memmap=<size>%<offset>-<oldtype>+<newtype> 2695 [KNL,ACPI] Convert memory within the specified region 2696 from <oldtype> to <newtype>. If "-<oldtype>" is left 2697 out, the whole region will be marked as <newtype>, 2698 even if previously unavailable. If "+<newtype>" is left 2699 out, matching memory will be removed. Types are 2700 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2701 3 = ACPI, 12 = PRAM. 2702 2703 memory_corruption_check=0/1 [X86] 2704 Some BIOSes seem to corrupt the first 64k of 2705 memory when doing things like suspend/resume. 2706 Setting this option will scan the memory 2707 looking for corruption. Enabling this will 2708 both detect corruption and prevent the kernel 2709 from using the memory being corrupted. 2710 However, its intended as a diagnostic tool; if 2711 repeatable BIOS-originated corruption always 2712 affects the same memory, you can use memmap= 2713 to prevent the kernel from using that memory. 2714 2715 memory_corruption_check_size=size [X86] 2716 By default it checks for corruption in the low 2717 64k, making this memory unavailable for normal 2718 use. Use this parameter to scan for 2719 corruption in more or less memory. 2720 2721 memory_corruption_check_period=seconds [X86] 2722 By default it checks for corruption every 60 2723 seconds. Use this parameter to check at some 2724 other rate. 0 disables periodic checking. 2725 2726 memtest= [KNL,X86,ARM,PPC] Enable memtest 2727 Format: <integer> 2728 default : 0 <disable> 2729 Specifies the number of memtest passes to be 2730 performed. Each pass selects another test 2731 pattern from a given set of patterns. Memtest 2732 fills the memory with this pattern, validates 2733 memory contents and reserves bad memory 2734 regions that are detected. 2735 2736 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2737 Valid arguments: on, off 2738 Default (depends on kernel configuration option): 2739 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2740 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2741 mem_encrypt=on: Activate SME 2742 mem_encrypt=off: Do not activate SME 2743 2744 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2745 for details on when memory encryption can be activated. 2746 2747 mem_sleep_default= [SUSPEND] Default system suspend mode: 2748 s2idle - Suspend-To-Idle 2749 shallow - Power-On Suspend or equivalent (if supported) 2750 deep - Suspend-To-RAM or equivalent (if supported) 2751 See Documentation/admin-guide/pm/sleep-states.rst. 2752 2753 meye.*= [HW] Set MotionEye Camera parameters 2754 See Documentation/admin-guide/media/meye.rst. 2755 2756 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2757 Multi-Function General Purpose Timers on AMD Geode 2758 platforms. 2759 2760 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2761 the BIOS has incorrectly applied a workaround. TinyBIOS 2762 version 0.98 is known to be affected, 0.99 fixes the 2763 problem by letting the user disable the workaround. 2764 2765 mga= [HW,DRM] 2766 2767 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2768 physical address is ignored. 2769 2770 mini2440= [ARM,HW,KNL] 2771 Format:[0..2][b][c][t] 2772 Default: "0tb" 2773 MINI2440 configuration specification: 2774 0 - The attached screen is the 3.5" TFT 2775 1 - The attached screen is the 7" TFT 2776 2 - The VGA Shield is attached (1024x768) 2777 Leaving out the screen size parameter will not load 2778 the TFT driver, and the framebuffer will be left 2779 unconfigured. 2780 b - Enable backlight. The TFT backlight pin will be 2781 linked to the kernel VESA blanking code and a GPIO 2782 LED. This parameter is not necessary when using the 2783 VGA shield. 2784 c - Enable the s3c camera interface. 2785 t - Reserved for enabling touchscreen support. The 2786 touchscreen support is not enabled in the mainstream 2787 kernel as of 2.6.30, a preliminary port can be found 2788 in the "bleeding edge" mini2440 support kernel at 2789 http://repo.or.cz/w/linux-2.6/mini2440.git 2790 2791 mitigations= 2792 [X86,PPC,S390,ARM64] Control optional mitigations for 2793 CPU vulnerabilities. This is a set of curated, 2794 arch-independent options, each of which is an 2795 aggregation of existing arch-specific options. 2796 2797 off 2798 Disable all optional CPU mitigations. This 2799 improves system performance, but it may also 2800 expose users to several CPU vulnerabilities. 2801 Equivalent to: nopti [X86,PPC] 2802 kpti=0 [ARM64] 2803 nospectre_v1 [X86,PPC] 2804 nobp=0 [S390] 2805 nospectre_v2 [X86,PPC,S390,ARM64] 2806 spectre_v2_user=off [X86] 2807 spec_store_bypass_disable=off [X86,PPC] 2808 ssbd=force-off [ARM64] 2809 l1tf=off [X86] 2810 mds=off [X86] 2811 tsx_async_abort=off [X86] 2812 kvm.nx_huge_pages=off [X86] 2813 2814 Exceptions: 2815 This does not have any effect on 2816 kvm.nx_huge_pages when 2817 kvm.nx_huge_pages=force. 2818 2819 auto (default) 2820 Mitigate all CPU vulnerabilities, but leave SMT 2821 enabled, even if it's vulnerable. This is for 2822 users who don't want to be surprised by SMT 2823 getting disabled across kernel upgrades, or who 2824 have other ways of avoiding SMT-based attacks. 2825 Equivalent to: (default behavior) 2826 2827 auto,nosmt 2828 Mitigate all CPU vulnerabilities, disabling SMT 2829 if needed. This is for users who always want to 2830 be fully mitigated, even if it means losing SMT. 2831 Equivalent to: l1tf=flush,nosmt [X86] 2832 mds=full,nosmt [X86] 2833 tsx_async_abort=full,nosmt [X86] 2834 2835 mminit_loglevel= 2836 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2837 parameter allows control of the logging verbosity for 2838 the additional memory initialisation checks. A value 2839 of 0 disables mminit logging and a level of 4 will 2840 log everything. Information is printed at KERN_DEBUG 2841 so loglevel=8 may also need to be specified. 2842 2843 module.sig_enforce 2844 [KNL] When CONFIG_MODULE_SIG is set, this means that 2845 modules without (valid) signatures will fail to load. 2846 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2847 is always true, so this option does nothing. 2848 2849 module_blacklist= [KNL] Do not load a comma-separated list of 2850 modules. Useful for debugging problem modules. 2851 2852 mousedev.tap_time= 2853 [MOUSE] Maximum time between finger touching and 2854 leaving touchpad surface for touch to be considered 2855 a tap and be reported as a left button click (for 2856 touchpads working in absolute mode only). 2857 Format: <msecs> 2858 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2859 reporting absolute coordinates, such as tablets 2860 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2861 reporting absolute coordinates, such as tablets 2862 2863 movablecore= [KNL,X86,IA-64,PPC] 2864 Format: nn[KMGTPE] | nn% 2865 This parameter is the complement to kernelcore=, it 2866 specifies the amount of memory used for migratable 2867 allocations. If both kernelcore and movablecore is 2868 specified, then kernelcore will be at *least* the 2869 specified value but may be more. If movablecore on its 2870 own is specified, the administrator must be careful 2871 that the amount of memory usable for all allocations 2872 is not too small. 2873 2874 movable_node [KNL] Boot-time switch to make hotplugable memory 2875 NUMA nodes to be movable. This means that the memory 2876 of such nodes will be usable only for movable 2877 allocations which rules out almost all kernel 2878 allocations. Use with caution! 2879 2880 MTD_Partition= [MTD] 2881 Format: <name>,<region-number>,<size>,<offset> 2882 2883 MTD_Region= [MTD] Format: 2884 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2885 2886 mtdparts= [MTD] 2887 See drivers/mtd/parsers/cmdlinepart.c 2888 2889 multitce=off [PPC] This parameter disables the use of the pSeries 2890 firmware feature for updating multiple TCE entries 2891 at a time. 2892 2893 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2894 2895 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2896 2897 boundary - index of last SLC block on Flex-OneNAND. 2898 The remaining blocks are configured as MLC blocks. 2899 lock - Configure if Flex-OneNAND boundary should be locked. 2900 Once locked, the boundary cannot be changed. 2901 1 indicates lock status, 0 indicates unlock status. 2902 2903 mtdset= [ARM] 2904 ARM/S3C2412 JIVE boot control 2905 2906 See arch/arm/mach-s3c2412/mach-jive.c 2907 2908 mtouchusb.raw_coordinates= 2909 [HW] Make the MicroTouch USB driver use raw coordinates 2910 ('y', default) or cooked coordinates ('n') 2911 2912 mtrr_chunk_size=nn[KMG] [X86] 2913 used for mtrr cleanup. It is largest continuous chunk 2914 that could hold holes aka. UC entries. 2915 2916 mtrr_gran_size=nn[KMG] [X86] 2917 Used for mtrr cleanup. It is granularity of mtrr block. 2918 Default is 1. 2919 Large value could prevent small alignment from 2920 using up MTRRs. 2921 2922 mtrr_spare_reg_nr=n [X86] 2923 Format: <integer> 2924 Range: 0,7 : spare reg number 2925 Default : 1 2926 Used for mtrr cleanup. It is spare mtrr entries number. 2927 Set to 2 or more if your graphical card needs more. 2928 2929 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2930 2931 netdev= [NET] Network devices parameters 2932 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2933 Note that mem_start is often overloaded to mean 2934 something different and driver-specific. 2935 This usage is only documented in each driver source 2936 file if at all. 2937 2938 nf_conntrack.acct= 2939 [NETFILTER] Enable connection tracking flow accounting 2940 0 to disable accounting 2941 1 to enable accounting 2942 Default value is 0. 2943 2944 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2945 See Documentation/admin-guide/nfs/nfsroot.rst. 2946 2947 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2948 See Documentation/admin-guide/nfs/nfsroot.rst. 2949 2950 nfsrootdebug [NFS] enable nfsroot debugging messages. 2951 See Documentation/admin-guide/nfs/nfsroot.rst. 2952 2953 nfs.callback_nr_threads= 2954 [NFSv4] set the total number of threads that the 2955 NFS client will assign to service NFSv4 callback 2956 requests. 2957 2958 nfs.callback_tcpport= 2959 [NFS] set the TCP port on which the NFSv4 callback 2960 channel should listen. 2961 2962 nfs.cache_getent= 2963 [NFS] sets the pathname to the program which is used 2964 to update the NFS client cache entries. 2965 2966 nfs.cache_getent_timeout= 2967 [NFS] sets the timeout after which an attempt to 2968 update a cache entry is deemed to have failed. 2969 2970 nfs.idmap_cache_timeout= 2971 [NFS] set the maximum lifetime for idmapper cache 2972 entries. 2973 2974 nfs.enable_ino64= 2975 [NFS] enable 64-bit inode numbers. 2976 If zero, the NFS client will fake up a 32-bit inode 2977 number for the readdir() and stat() syscalls instead 2978 of returning the full 64-bit number. 2979 The default is to return 64-bit inode numbers. 2980 2981 nfs.max_session_cb_slots= 2982 [NFSv4.1] Sets the maximum number of session 2983 slots the client will assign to the callback 2984 channel. This determines the maximum number of 2985 callbacks the client will process in parallel for 2986 a particular server. 2987 2988 nfs.max_session_slots= 2989 [NFSv4.1] Sets the maximum number of session slots 2990 the client will attempt to negotiate with the server. 2991 This limits the number of simultaneous RPC requests 2992 that the client can send to the NFSv4.1 server. 2993 Note that there is little point in setting this 2994 value higher than the max_tcp_slot_table_limit. 2995 2996 nfs.nfs4_disable_idmapping= 2997 [NFSv4] When set to the default of '1', this option 2998 ensures that both the RPC level authentication 2999 scheme and the NFS level operations agree to use 3000 numeric uids/gids if the mount is using the 3001 'sec=sys' security flavour. In effect it is 3002 disabling idmapping, which can make migration from 3003 legacy NFSv2/v3 systems to NFSv4 easier. 3004 Servers that do not support this mode of operation 3005 will be autodetected by the client, and it will fall 3006 back to using the idmapper. 3007 To turn off this behaviour, set the value to '0'. 3008 nfs.nfs4_unique_id= 3009 [NFS4] Specify an additional fixed unique ident- 3010 ification string that NFSv4 clients can insert into 3011 their nfs_client_id4 string. This is typically a 3012 UUID that is generated at system install time. 3013 3014 nfs.send_implementation_id = 3015 [NFSv4.1] Send client implementation identification 3016 information in exchange_id requests. 3017 If zero, no implementation identification information 3018 will be sent. 3019 The default is to send the implementation identification 3020 information. 3021 3022 nfs.recover_lost_locks = 3023 [NFSv4] Attempt to recover locks that were lost due 3024 to a lease timeout on the server. Please note that 3025 doing this risks data corruption, since there are 3026 no guarantees that the file will remain unchanged 3027 after the locks are lost. 3028 If you want to enable the kernel legacy behaviour of 3029 attempting to recover these locks, then set this 3030 parameter to '1'. 3031 The default parameter value of '0' causes the kernel 3032 not to attempt recovery of lost locks. 3033 3034 nfs4.layoutstats_timer = 3035 [NFSv4.2] Change the rate at which the kernel sends 3036 layoutstats to the pNFS metadata server. 3037 3038 Setting this to value to 0 causes the kernel to use 3039 whatever value is the default set by the layout 3040 driver. A non-zero value sets the minimum interval 3041 in seconds between layoutstats transmissions. 3042 3043 nfsd.nfs4_disable_idmapping= 3044 [NFSv4] When set to the default of '1', the NFSv4 3045 server will return only numeric uids and gids to 3046 clients using auth_sys, and will accept numeric uids 3047 and gids from such clients. This is intended to ease 3048 migration from NFSv2/v3. 3049 3050 nmi_debug= [KNL,SH] Specify one or more actions to take 3051 when a NMI is triggered. 3052 Format: [state][,regs][,debounce][,die] 3053 3054 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3055 Format: [panic,][nopanic,][num] 3056 Valid num: 0 or 1 3057 0 - turn hardlockup detector in nmi_watchdog off 3058 1 - turn hardlockup detector in nmi_watchdog on 3059 When panic is specified, panic when an NMI watchdog 3060 timeout occurs (or 'nopanic' to not panic on an NMI 3061 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3062 To disable both hard and soft lockup detectors, 3063 please see 'nowatchdog'. 3064 This is useful when you use a panic=... timeout and 3065 need the box quickly up again. 3066 3067 These settings can be accessed at runtime via 3068 the nmi_watchdog and hardlockup_panic sysctls. 3069 3070 netpoll.carrier_timeout= 3071 [NET] Specifies amount of time (in seconds) that 3072 netpoll should wait for a carrier. By default netpoll 3073 waits 4 seconds. 3074 3075 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3076 emulation library even if a 387 maths coprocessor 3077 is present. 3078 3079 no5lvl [X86-64] Disable 5-level paging mode. Forces 3080 kernel to use 4-level paging instead. 3081 3082 no_console_suspend 3083 [HW] Never suspend the console 3084 Disable suspending of consoles during suspend and 3085 hibernate operations. Once disabled, debugging 3086 messages can reach various consoles while the rest 3087 of the system is being put to sleep (ie, while 3088 debugging driver suspend/resume hooks). This may 3089 not work reliably with all consoles, but is known 3090 to work with serial and VGA consoles. 3091 To facilitate more flexible debugging, we also add 3092 console_suspend, a printk module parameter to control 3093 it. Users could use console_suspend (usually 3094 /sys/module/printk/parameters/console_suspend) to 3095 turn on/off it dynamically. 3096 3097 novmcoredd [KNL,KDUMP] 3098 Disable device dump. Device dump allows drivers to 3099 append dump data to vmcore so you can collect driver 3100 specified debug info. Drivers can append the data 3101 without any limit and this data is stored in memory, 3102 so this may cause significant memory stress. Disabling 3103 device dump can help save memory but the driver debug 3104 data will be no longer available. This parameter 3105 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3106 is set. 3107 3108 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3109 caches in the slab allocator. Saves per-node memory, 3110 but will impact performance. 3111 3112 noalign [KNL,ARM] 3113 3114 noaltinstr [S390] Disables alternative instructions patching 3115 (CPU alternatives feature). 3116 3117 noapic [SMP,APIC] Tells the kernel to not make use of any 3118 IOAPICs that may be present in the system. 3119 3120 noautogroup Disable scheduler automatic task group creation. 3121 3122 nobats [PPC] Do not use BATs for mapping kernel lowmem 3123 on "Classic" PPC cores. 3124 3125 nocache [ARM] 3126 3127 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3128 3129 nodelayacct [KNL] Disable per-task delay accounting 3130 3131 nodsp [SH] Disable hardware DSP at boot time. 3132 3133 noefi Disable EFI runtime services support. 3134 3135 noexec [IA-64] 3136 3137 noexec [X86] 3138 On X86-32 available only on PAE configured kernels. 3139 noexec=on: enable non-executable mappings (default) 3140 noexec=off: disable non-executable mappings 3141 3142 nosmap [X86,PPC] 3143 Disable SMAP (Supervisor Mode Access Prevention) 3144 even if it is supported by processor. 3145 3146 nosmep [X86,PPC] 3147 Disable SMEP (Supervisor Mode Execution Prevention) 3148 even if it is supported by processor. 3149 3150 noexec32 [X86-64] 3151 This affects only 32-bit executables. 3152 noexec32=on: enable non-executable mappings (default) 3153 read doesn't imply executable mappings 3154 noexec32=off: disable non-executable mappings 3155 read implies executable mappings 3156 3157 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3158 3159 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3160 register save and restore. The kernel will only save 3161 legacy floating-point registers on task switch. 3162 3163 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3164 3165 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3166 Equivalent to smt=1. 3167 3168 [KNL,x86] Disable symmetric multithreading (SMT). 3169 nosmt=force: Force disable SMT, cannot be undone 3170 via the sysfs control file. 3171 3172 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3173 (bounds check bypass). With this option data leaks are 3174 possible in the system. 3175 3176 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3177 the Spectre variant 2 (indirect branch prediction) 3178 vulnerability. System may allow data leaks with this 3179 option. 3180 3181 nospec_store_bypass_disable 3182 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3183 3184 noxsave [BUGS=X86] Disables x86 extended register state save 3185 and restore using xsave. The kernel will fallback to 3186 enabling legacy floating-point and sse state. 3187 3188 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3189 register states. The kernel will fall back to use 3190 xsave to save the states. By using this parameter, 3191 performance of saving the states is degraded because 3192 xsave doesn't support modified optimization while 3193 xsaveopt supports it on xsaveopt enabled systems. 3194 3195 noxsaves [X86] Disables xsaves and xrstors used in saving and 3196 restoring x86 extended register state in compacted 3197 form of xsave area. The kernel will fall back to use 3198 xsaveopt and xrstor to save and restore the states 3199 in standard form of xsave area. By using this 3200 parameter, xsave area per process might occupy more 3201 memory on xsaves enabled systems. 3202 3203 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3204 wfi(ARM) instruction doesn't work correctly and not to 3205 use it. This is also useful when using JTAG debugger. 3206 3207 no_file_caps Tells the kernel not to honor file capabilities. The 3208 only way then for a file to be executed with privilege 3209 is to be setuid root or executed by root. 3210 3211 nohalt [IA-64] Tells the kernel not to use the power saving 3212 function PAL_HALT_LIGHT when idle. This increases 3213 power-consumption. On the positive side, it reduces 3214 interrupt wake-up latency, which may improve performance 3215 in certain environments such as networked servers or 3216 real-time systems. 3217 3218 nohibernate [HIBERNATION] Disable hibernation and resume. 3219 3220 nohz= [KNL] Boottime enable/disable dynamic ticks 3221 Valid arguments: on, off 3222 Default: on 3223 3224 nohz_full= [KNL,BOOT,SMP,ISOL] 3225 The argument is a cpu list, as described above. 3226 In kernels built with CONFIG_NO_HZ_FULL=y, set 3227 the specified list of CPUs whose tick will be stopped 3228 whenever possible. The boot CPU will be forced outside 3229 the range to maintain the timekeeping. Any CPUs 3230 in this list will have their RCU callbacks offloaded, 3231 just as if they had also been called out in the 3232 rcu_nocbs= boot parameter. 3233 3234 noiotrap [SH] Disables trapped I/O port accesses. 3235 3236 noirqdebug [X86-32] Disables the code which attempts to detect and 3237 disable unhandled interrupt sources. 3238 3239 no_timer_check [X86,APIC] Disables the code which tests for 3240 broken timer IRQ sources. 3241 3242 noisapnp [ISAPNP] Disables ISA PnP code. 3243 3244 noinitrd [RAM] Tells the kernel not to load any configured 3245 initial RAM disk. 3246 3247 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3248 remapping. 3249 [Deprecated - use intremap=off] 3250 3251 nointroute [IA-64] 3252 3253 noinvpcid [X86] Disable the INVPCID cpu feature. 3254 3255 nojitter [IA-64] Disables jitter checking for ITC timers. 3256 3257 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3258 3259 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3260 fault handling. 3261 3262 no-vmw-sched-clock 3263 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3264 clock and use the default one. 3265 3266 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3267 accounting. steal time is computed, but won't 3268 influence scheduler behaviour 3269 3270 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3271 3272 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3273 3274 noltlbs [PPC] Do not use large page/tlb entries for kernel 3275 lowmem mapping on PPC40x and PPC8xx 3276 3277 nomca [IA-64] Disable machine check abort handling 3278 3279 nomce [X86-32] Disable Machine Check Exception 3280 3281 nomfgpt [X86-32] Disable Multi-Function General Purpose 3282 Timer usage (for AMD Geode machines). 3283 3284 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3285 shutdown the other cpus. Instead use the REBOOT_VECTOR 3286 irq. 3287 3288 nomodule Disable module load 3289 3290 nopat [X86] Disable PAT (page attribute table extension of 3291 pagetables) support. 3292 3293 nopcid [X86-64] Disable the PCID cpu feature. 3294 3295 norandmaps Don't use address space randomization. Equivalent to 3296 echo 0 > /proc/sys/kernel/randomize_va_space 3297 3298 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3299 with UP alternatives 3300 3301 nordrand [X86] Disable kernel use of the RDRAND and 3302 RDSEED instructions even if they are supported 3303 by the processor. RDRAND and RDSEED are still 3304 available to user space applications. 3305 3306 noresume [SWSUSP] Disables resume and restores original swap 3307 space. 3308 3309 no-scroll [VGA] Disables scrollback. 3310 This is required for the Braillex ib80-piezo Braille 3311 reader made by F.H. Papenmeier (Germany). 3312 3313 nosbagart [IA-64] 3314 3315 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3316 3317 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3318 and disable the IO APIC. legacy for "maxcpus=0". 3319 3320 nosoftlockup [KNL] Disable the soft-lockup detector. 3321 3322 nosync [HW,M68K] Disables sync negotiation for all devices. 3323 3324 nowatchdog [KNL] Disable both lockup detectors, i.e. 3325 soft-lockup and NMI watchdog (hard-lockup). 3326 3327 nowb [ARM] 3328 3329 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3330 3331 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3332 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3333 Some features depend on CPU0. Known dependencies are: 3334 1. Resume from suspend/hibernate depends on CPU0. 3335 Suspend/hibernate will fail if CPU0 is offline and you 3336 need to online CPU0 before suspend/hibernate. 3337 2. PIC interrupts also depend on CPU0. CPU0 can't be 3338 removed if a PIC interrupt is detected. 3339 It's said poweroff/reboot may depend on CPU0 on some 3340 machines although I haven't seen such issues so far 3341 after CPU0 is offline on a few tested machines. 3342 If the dependencies are under your control, you can 3343 turn on cpu0_hotplug. 3344 3345 nps_mtm_hs_ctr= [KNL,ARC] 3346 This parameter sets the maximum duration, in 3347 cycles, each HW thread of the CTOP can run 3348 without interruptions, before HW switches it. 3349 The actual maximum duration is 16 times this 3350 parameter's value. 3351 Format: integer between 1 and 255 3352 Default: 255 3353 3354 nptcg= [IA-64] Override max number of concurrent global TLB 3355 purges which is reported from either PAL_VM_SUMMARY or 3356 SAL PALO. 3357 3358 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3359 could support. nr_cpus=n : n >= 1 limits the kernel to 3360 support 'n' processors. It could be larger than the 3361 number of already plugged CPU during bootup, later in 3362 runtime you can physically add extra cpu until it reaches 3363 n. So during boot up some boot time memory for per-cpu 3364 variables need be pre-allocated for later physical cpu 3365 hot plugging. 3366 3367 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3368 3369 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3370 Allowed values are enable and disable 3371 3372 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3373 'node', 'default' can be specified 3374 This can be set from sysctl after boot. 3375 See Documentation/admin-guide/sysctl/vm.rst for details. 3376 3377 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3378 See Documentation/core-api/debugging-via-ohci1394.rst for more 3379 info. 3380 3381 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3382 Rather than timing out after 20 ms if an EC 3383 command is not properly ACKed, override the length 3384 of the timeout. We have interrupts disabled while 3385 waiting for the ACK, so if this is set too high 3386 interrupts *may* be lost! 3387 3388 omap_mux= [OMAP] Override bootloader pin multiplexing. 3389 Format: <mux_mode0.mode_name=value>... 3390 For example, to override I2C bus2: 3391 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3392 3393 oprofile.timer= [HW] 3394 Use timer interrupt instead of performance counters 3395 3396 oprofile.cpu_type= Force an oprofile cpu type 3397 This might be useful if you have an older oprofile 3398 userland or if you want common events. 3399 Format: { arch_perfmon } 3400 arch_perfmon: [X86] Force use of architectural 3401 perfmon on Intel CPUs instead of the 3402 CPU specific event set. 3403 timer: [X86] Force use of architectural NMI 3404 timer mode (see also oprofile.timer 3405 for generic hr timer mode) 3406 3407 oops=panic Always panic on oopses. Default is to just kill the 3408 process, but there is a small probability of 3409 deadlocking the machine. 3410 This will also cause panics on machine check exceptions. 3411 Useful together with panic=30 to trigger a reboot. 3412 3413 page_alloc.shuffle= 3414 [KNL] Boolean flag to control whether the page allocator 3415 should randomize its free lists. The randomization may 3416 be automatically enabled if the kernel detects it is 3417 running on a platform with a direct-mapped memory-side 3418 cache, and this parameter can be used to 3419 override/disable that behavior. The state of the flag 3420 can be read from sysfs at: 3421 /sys/module/page_alloc/parameters/shuffle. 3422 3423 page_owner= [KNL] Boot-time page_owner enabling option. 3424 Storage of the information about who allocated 3425 each page is disabled in default. With this switch, 3426 we can turn it on. 3427 on: enable the feature 3428 3429 page_poison= [KNL] Boot-time parameter changing the state of 3430 poisoning on the buddy allocator, available with 3431 CONFIG_PAGE_POISONING=y. 3432 off: turn off poisoning (default) 3433 on: turn on poisoning 3434 3435 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3436 timeout > 0: seconds before rebooting 3437 timeout = 0: wait forever 3438 timeout < 0: reboot immediately 3439 Format: <timeout> 3440 3441 panic_print= Bitmask for printing system info when panic happens. 3442 User can chose combination of the following bits: 3443 bit 0: print all tasks info 3444 bit 1: print system memory info 3445 bit 2: print timer info 3446 bit 3: print locks info if CONFIG_LOCKDEP is on 3447 bit 4: print ftrace buffer 3448 bit 5: print all printk messages in buffer 3449 3450 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3451 Format: <hex>[,nousertaint] 3452 Hexadecimal bitmask representing the set of TAINT flags 3453 that will cause the kernel to panic when add_taint() is 3454 called with any of the flags in this set. 3455 The optional switch "nousertaint" can be utilized to 3456 prevent userspace forced crashes by writing to sysctl 3457 /proc/sys/kernel/tainted any flagset matching with the 3458 bitmask set on panic_on_taint. 3459 See Documentation/admin-guide/tainted-kernels.rst for 3460 extra details on the taint flags that users can pick 3461 to compose the bitmask to assign to panic_on_taint. 3462 3463 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3464 on a WARN(). 3465 3466 crash_kexec_post_notifiers 3467 Run kdump after running panic-notifiers and dumping 3468 kmsg. This only for the users who doubt kdump always 3469 succeeds in any situation. 3470 Note that this also increases risks of kdump failure, 3471 because some panic notifiers can make the crashed 3472 kernel more unstable. 3473 3474 parkbd.port= [HW] Parallel port number the keyboard adapter is 3475 connected to, default is 0. 3476 Format: <parport#> 3477 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3478 0 for XT, 1 for AT (default is AT). 3479 Format: <mode> 3480 3481 parport= [HW,PPT] Specify parallel ports. 0 disables. 3482 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3483 Use 'auto' to force the driver to use any 3484 IRQ/DMA settings detected (the default is to 3485 ignore detected IRQ/DMA settings because of 3486 possible conflicts). You can specify the base 3487 address, IRQ, and DMA settings; IRQ and DMA 3488 should be numbers, or 'auto' (for using detected 3489 settings on that particular port), or 'nofifo' 3490 (to avoid using a FIFO even if it is detected). 3491 Parallel ports are assigned in the order they 3492 are specified on the command line, starting 3493 with parport0. 3494 3495 parport_init_mode= [HW,PPT] 3496 Configure VIA parallel port to operate in 3497 a specific mode. This is necessary on Pegasos 3498 computer where firmware has no options for setting 3499 up parallel port mode and sets it to spp. 3500 Currently this function knows 686a and 8231 chips. 3501 Format: [spp|ps2|epp|ecp|ecpepp] 3502 3503 pause_on_oops= 3504 Halt all CPUs after the first oops has been printed for 3505 the specified number of seconds. This is to be used if 3506 your oopses keep scrolling off the screen. 3507 3508 pcbit= [HW,ISDN] 3509 3510 pcd. [PARIDE] 3511 See header of drivers/block/paride/pcd.c. 3512 See also Documentation/admin-guide/blockdev/paride.rst. 3513 3514 pci=option[,option...] [PCI] various PCI subsystem options. 3515 3516 Some options herein operate on a specific device 3517 or a set of devices (<pci_dev>). These are 3518 specified in one of the following formats: 3519 3520 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3521 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3522 3523 Note: the first format specifies a PCI 3524 bus/device/function address which may change 3525 if new hardware is inserted, if motherboard 3526 firmware changes, or due to changes caused 3527 by other kernel parameters. If the 3528 domain is left unspecified, it is 3529 taken to be zero. Optionally, a path 3530 to a device through multiple device/function 3531 addresses can be specified after the base 3532 address (this is more robust against 3533 renumbering issues). The second format 3534 selects devices using IDs from the 3535 configuration space which may match multiple 3536 devices in the system. 3537 3538 earlydump dump PCI config space before the kernel 3539 changes anything 3540 off [X86] don't probe for the PCI bus 3541 bios [X86-32] force use of PCI BIOS, don't access 3542 the hardware directly. Use this if your machine 3543 has a non-standard PCI host bridge. 3544 nobios [X86-32] disallow use of PCI BIOS, only direct 3545 hardware access methods are allowed. Use this 3546 if you experience crashes upon bootup and you 3547 suspect they are caused by the BIOS. 3548 conf1 [X86] Force use of PCI Configuration Access 3549 Mechanism 1 (config address in IO port 0xCF8, 3550 data in IO port 0xCFC, both 32-bit). 3551 conf2 [X86] Force use of PCI Configuration Access 3552 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3553 the function, IO port 0xCFA, also 8-bit, sets 3554 bus number. The config space is then accessed 3555 through ports 0xC000-0xCFFF). 3556 See http://wiki.osdev.org/PCI for more info 3557 on the configuration access mechanisms. 3558 noaer [PCIE] If the PCIEAER kernel config parameter is 3559 enabled, this kernel boot option can be used to 3560 disable the use of PCIE advanced error reporting. 3561 nodomains [PCI] Disable support for multiple PCI 3562 root domains (aka PCI segments, in ACPI-speak). 3563 nommconf [X86] Disable use of MMCONFIG for PCI 3564 Configuration 3565 check_enable_amd_mmconf [X86] check for and enable 3566 properly configured MMIO access to PCI 3567 config space on AMD family 10h CPU 3568 nomsi [MSI] If the PCI_MSI kernel config parameter is 3569 enabled, this kernel boot option can be used to 3570 disable the use of MSI interrupts system-wide. 3571 noioapicquirk [APIC] Disable all boot interrupt quirks. 3572 Safety option to keep boot IRQs enabled. This 3573 should never be necessary. 3574 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3575 primary IO-APIC for bridges that cannot disable 3576 boot IRQs. This fixes a source of spurious IRQs 3577 when the system masks IRQs. 3578 noioapicreroute [APIC] Disable workaround that uses the 3579 boot IRQ equivalent of an IRQ that connects to 3580 a chipset where boot IRQs cannot be disabled. 3581 The opposite of ioapicreroute. 3582 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3583 routing table. These calls are known to be buggy 3584 on several machines and they hang the machine 3585 when used, but on other computers it's the only 3586 way to get the interrupt routing table. Try 3587 this option if the kernel is unable to allocate 3588 IRQs or discover secondary PCI buses on your 3589 motherboard. 3590 rom [X86] Assign address space to expansion ROMs. 3591 Use with caution as certain devices share 3592 address decoders between ROMs and other 3593 resources. 3594 norom [X86] Do not assign address space to 3595 expansion ROMs that do not already have 3596 BIOS assigned address ranges. 3597 nobar [X86] Do not assign address space to the 3598 BARs that weren't assigned by the BIOS. 3599 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3600 assigned automatically to PCI devices. You can 3601 make the kernel exclude IRQs of your ISA cards 3602 this way. 3603 pirqaddr=0xAAAAA [X86] Specify the physical address 3604 of the PIRQ table (normally generated 3605 by the BIOS) if it is outside the 3606 F0000h-100000h range. 3607 lastbus=N [X86] Scan all buses thru bus #N. Can be 3608 useful if the kernel is unable to find your 3609 secondary buses and you want to tell it 3610 explicitly which ones they are. 3611 assign-busses [X86] Always assign all PCI bus 3612 numbers ourselves, overriding 3613 whatever the firmware may have done. 3614 usepirqmask [X86] Honor the possible IRQ mask stored 3615 in the BIOS $PIR table. This is needed on 3616 some systems with broken BIOSes, notably 3617 some HP Pavilion N5400 and Omnibook XE3 3618 notebooks. This will have no effect if ACPI 3619 IRQ routing is enabled. 3620 noacpi [X86] Do not use ACPI for IRQ routing 3621 or for PCI scanning. 3622 use_crs [X86] Use PCI host bridge window information 3623 from ACPI. On BIOSes from 2008 or later, this 3624 is enabled by default. If you need to use this, 3625 please report a bug. 3626 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3627 If you need to use this, please report a bug. 3628 routeirq Do IRQ routing for all PCI devices. 3629 This is normally done in pci_enable_device(), 3630 so this option is a temporary workaround 3631 for broken drivers that don't call it. 3632 skip_isa_align [X86] do not align io start addr, so can 3633 handle more pci cards 3634 noearly [X86] Don't do any early type 1 scanning. 3635 This might help on some broken boards which 3636 machine check when some devices' config space 3637 is read. But various workarounds are disabled 3638 and some IOMMU drivers will not work. 3639 bfsort Sort PCI devices into breadth-first order. 3640 This sorting is done to get a device 3641 order compatible with older (<= 2.4) kernels. 3642 nobfsort Don't sort PCI devices into breadth-first order. 3643 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3644 tuning and use the BIOS-configured MPS defaults. 3645 pcie_bus_safe Set every device's MPS to the largest value 3646 supported by all devices below the root complex. 3647 pcie_bus_perf Set device MPS to the largest allowable MPS 3648 based on its parent bus. Also set MRRS (Max 3649 Read Request Size) to the largest supported 3650 value (no larger than the MPS that the device 3651 or bus can support) for best performance. 3652 pcie_bus_peer2peer Set every device's MPS to 128B, which 3653 every device is guaranteed to support. This 3654 configuration allows peer-to-peer DMA between 3655 any pair of devices, possibly at the cost of 3656 reduced performance. This also guarantees 3657 that hot-added devices will work. 3658 cbiosize=nn[KMG] The fixed amount of bus space which is 3659 reserved for the CardBus bridge's IO window. 3660 The default value is 256 bytes. 3661 cbmemsize=nn[KMG] The fixed amount of bus space which is 3662 reserved for the CardBus bridge's memory 3663 window. The default value is 64 megabytes. 3664 resource_alignment= 3665 Format: 3666 [<order of align>@]<pci_dev>[; ...] 3667 Specifies alignment and device to reassign 3668 aligned memory resources. How to 3669 specify the device is described above. 3670 If <order of align> is not specified, 3671 PAGE_SIZE is used as alignment. 3672 A PCI-PCI bridge can be specified if resource 3673 windows need to be expanded. 3674 To specify the alignment for several 3675 instances of a device, the PCI vendor, 3676 device, subvendor, and subdevice may be 3677 specified, e.g., 12@pci:8086:9c22:103c:198f 3678 for 4096-byte alignment. 3679 ecrc= Enable/disable PCIe ECRC (transaction layer 3680 end-to-end CRC checking). 3681 bios: Use BIOS/firmware settings. This is the 3682 the default. 3683 off: Turn ECRC off 3684 on: Turn ECRC on. 3685 hpiosize=nn[KMG] The fixed amount of bus space which is 3686 reserved for hotplug bridge's IO window. 3687 Default size is 256 bytes. 3688 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3689 reserved for hotplug bridge's MMIO window. 3690 Default size is 2 megabytes. 3691 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3692 reserved for hotplug bridge's MMIO_PREF window. 3693 Default size is 2 megabytes. 3694 hpmemsize=nn[KMG] The fixed amount of bus space which is 3695 reserved for hotplug bridge's MMIO and 3696 MMIO_PREF window. 3697 Default size is 2 megabytes. 3698 hpbussize=nn The minimum amount of additional bus numbers 3699 reserved for buses below a hotplug bridge. 3700 Default is 1. 3701 realloc= Enable/disable reallocating PCI bridge resources 3702 if allocations done by BIOS are too small to 3703 accommodate resources required by all child 3704 devices. 3705 off: Turn realloc off 3706 on: Turn realloc on 3707 realloc same as realloc=on 3708 noari do not use PCIe ARI. 3709 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3710 do not use PCIe ATS (and IOMMU device IOTLB). 3711 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3712 only look for one device below a PCIe downstream 3713 port. 3714 big_root_window Try to add a big 64bit memory window to the PCIe 3715 root complex on AMD CPUs. Some GFX hardware 3716 can resize a BAR to allow access to all VRAM. 3717 Adding the window is slightly risky (it may 3718 conflict with unreported devices), so this 3719 taints the kernel. 3720 disable_acs_redir=<pci_dev>[; ...] 3721 Specify one or more PCI devices (in the format 3722 specified above) separated by semicolons. 3723 Each device specified will have the PCI ACS 3724 redirect capabilities forced off which will 3725 allow P2P traffic between devices through 3726 bridges without forcing it upstream. Note: 3727 this removes isolation between devices and 3728 may put more devices in an IOMMU group. 3729 force_floating [S390] Force usage of floating interrupts. 3730 nomio [S390] Do not use MIO instructions. 3731 norid [S390] ignore the RID field and force use of 3732 one PCI domain per PCI function 3733 3734 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3735 Management. 3736 off Disable ASPM. 3737 force Enable ASPM even on devices that claim not to support it. 3738 WARNING: Forcing ASPM on may cause system lockups. 3739 3740 pcie_ports= [PCIE] PCIe port services handling: 3741 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3742 even if the platform doesn't give the OS permission to 3743 use them. This may cause conflicts if the platform 3744 also tries to use these services. 3745 dpc-native Use native PCIe service for DPC only. May 3746 cause conflicts if firmware uses AER or DPC. 3747 compat Disable native PCIe services (PME, AER, DPC, PCIe 3748 hotplug). 3749 3750 pcie_port_pm= [PCIE] PCIe port power management handling: 3751 off Disable power management of all PCIe ports 3752 force Forcibly enable power management of all PCIe ports 3753 3754 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3755 nomsi Do not use MSI for native PCIe PME signaling (this makes 3756 all PCIe root ports use INTx for all services). 3757 3758 pcmv= [HW,PCMCIA] BadgePAD 4 3759 3760 pd_ignore_unused 3761 [PM] 3762 Keep all power-domains already enabled by bootloader on, 3763 even if no driver has claimed them. This is useful 3764 for debug and development, but should not be 3765 needed on a platform with proper driver support. 3766 3767 pd. [PARIDE] 3768 See Documentation/admin-guide/blockdev/paride.rst. 3769 3770 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3771 boot time. 3772 Format: { 0 | 1 } 3773 See arch/parisc/kernel/pdc_chassis.c 3774 3775 percpu_alloc= Select which percpu first chunk allocator to use. 3776 Currently supported values are "embed" and "page". 3777 Archs may support subset or none of the selections. 3778 See comments in mm/percpu.c for details on each 3779 allocator. This parameter is primarily for debugging 3780 and performance comparison. 3781 3782 pf. [PARIDE] 3783 See Documentation/admin-guide/blockdev/paride.rst. 3784 3785 pg. [PARIDE] 3786 See Documentation/admin-guide/blockdev/paride.rst. 3787 3788 pirq= [SMP,APIC] Manual mp-table setup 3789 See Documentation/x86/i386/IO-APIC.rst. 3790 3791 plip= [PPT,NET] Parallel port network link 3792 Format: { parport<nr> | timid | 0 } 3793 See also Documentation/admin-guide/parport.rst. 3794 3795 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3796 Override pmtimer IOPort with a hex value. 3797 e.g. pmtmr=0x508 3798 3799 pm_debug_messages [SUSPEND,KNL] 3800 Enable suspend/resume debug messages during boot up. 3801 3802 pnp.debug=1 [PNP] 3803 Enable PNP debug messages (depends on the 3804 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3805 via /sys/module/pnp/parameters/debug. We always show 3806 current resource usage; turning this on also shows 3807 possible settings and some assignment information. 3808 3809 pnpacpi= [ACPI] 3810 { off } 3811 3812 pnpbios= [ISAPNP] 3813 { on | off | curr | res | no-curr | no-res } 3814 3815 pnp_reserve_irq= 3816 [ISAPNP] Exclude IRQs for the autoconfiguration 3817 3818 pnp_reserve_dma= 3819 [ISAPNP] Exclude DMAs for the autoconfiguration 3820 3821 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3822 Ranges are in pairs (I/O port base and size). 3823 3824 pnp_reserve_mem= 3825 [ISAPNP] Exclude memory regions for the 3826 autoconfiguration. 3827 Ranges are in pairs (memory base and size). 3828 3829 ports= [IP_VS_FTP] IPVS ftp helper module 3830 Default is 21. 3831 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3832 may be specified. 3833 Format: <port>,<port>.... 3834 3835 powersave=off [PPC] This option disables power saving features. 3836 It specifically disables cpuidle and sets the 3837 platform machine description specific power_save 3838 function to NULL. On Idle the CPU just reduces 3839 execution priority. 3840 3841 ppc_strict_facility_enable 3842 [PPC] This option catches any kernel floating point, 3843 Altivec, VSX and SPE outside of regions specifically 3844 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3845 There is some performance impact when enabling this. 3846 3847 ppc_tm= [PPC] 3848 Format: {"off"} 3849 Disable Hardware Transactional Memory 3850 3851 print-fatal-signals= 3852 [KNL] debug: print fatal signals 3853 3854 If enabled, warn about various signal handling 3855 related application anomalies: too many signals, 3856 too many POSIX.1 timers, fatal signals causing a 3857 coredump - etc. 3858 3859 If you hit the warning due to signal overflow, 3860 you might want to try "ulimit -i unlimited". 3861 3862 default: off. 3863 3864 printk.always_kmsg_dump= 3865 Trigger kmsg_dump for cases other than kernel oops or 3866 panics 3867 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3868 default: disabled 3869 3870 printk.devkmsg={on,off,ratelimit} 3871 Control writing to /dev/kmsg. 3872 on - unlimited logging to /dev/kmsg from userspace 3873 off - logging to /dev/kmsg disabled 3874 ratelimit - ratelimit the logging 3875 Default: ratelimit 3876 3877 printk.time= Show timing data prefixed to each printk message line 3878 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3879 3880 processor.max_cstate= [HW,ACPI] 3881 Limit processor to maximum C-state 3882 max_cstate=9 overrides any DMI blacklist limit. 3883 3884 processor.nocst [HW,ACPI] 3885 Ignore the _CST method to determine C-states, 3886 instead using the legacy FADT method 3887 3888 profile= [KNL] Enable kernel profiling via /proc/profile 3889 Format: [<profiletype>,]<number> 3890 Param: <profiletype>: "schedule", "sleep", or "kvm" 3891 [defaults to kernel profiling] 3892 Param: "schedule" - profile schedule points. 3893 Param: "sleep" - profile D-state sleeping (millisecs). 3894 Requires CONFIG_SCHEDSTATS 3895 Param: "kvm" - profile VM exits. 3896 Param: <number> - step/bucket size as a power of 2 for 3897 statistical time based profiling. 3898 3899 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3900 before loading. 3901 See Documentation/admin-guide/blockdev/ramdisk.rst. 3902 3903 prot_virt= [S390] enable hosting protected virtual machines 3904 isolated from the hypervisor (if hardware supports 3905 that). 3906 Format: <bool> 3907 3908 psi= [KNL] Enable or disable pressure stall information 3909 tracking. 3910 Format: <bool> 3911 3912 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3913 probe for; one of (bare|imps|exps|lifebook|any). 3914 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3915 per second. 3916 psmouse.resetafter= [HW,MOUSE] 3917 Try to reset the device after so many bad packets 3918 (0 = never). 3919 psmouse.resolution= 3920 [HW,MOUSE] Set desired mouse resolution, in dpi. 3921 psmouse.smartscroll= 3922 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3923 0 = disabled, 1 = enabled (default). 3924 3925 pstore.backend= Specify the name of the pstore backend to use 3926 3927 pt. [PARIDE] 3928 See Documentation/admin-guide/blockdev/paride.rst. 3929 3930 pti= [X86_64] Control Page Table Isolation of user and 3931 kernel address spaces. Disabling this feature 3932 removes hardening, but improves performance of 3933 system calls and interrupts. 3934 3935 on - unconditionally enable 3936 off - unconditionally disable 3937 auto - kernel detects whether your CPU model is 3938 vulnerable to issues that PTI mitigates 3939 3940 Not specifying this option is equivalent to pti=auto. 3941 3942 nopti [X86_64] 3943 Equivalent to pti=off 3944 3945 pty.legacy_count= 3946 [KNL] Number of legacy pty's. Overwrites compiled-in 3947 default number. 3948 3949 quiet [KNL] Disable most log messages 3950 3951 r128= [HW,DRM] 3952 3953 raid= [HW,RAID] 3954 See Documentation/admin-guide/md.rst. 3955 3956 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3957 See Documentation/admin-guide/blockdev/ramdisk.rst. 3958 3959 random.trust_cpu={on,off} 3960 [KNL] Enable or disable trusting the use of the 3961 CPU's random number generator (if available) to 3962 fully seed the kernel's CRNG. Default is controlled 3963 by CONFIG_RANDOM_TRUST_CPU. 3964 3965 ras=option[,option,...] [KNL] RAS-specific options 3966 3967 cec_disable [X86] 3968 Disable the Correctable Errors Collector, 3969 see CONFIG_RAS_CEC help text. 3970 3971 rcu_nocbs= [KNL] 3972 The argument is a cpu list, as described above, 3973 except that the string "all" can be used to 3974 specify every CPU on the system. 3975 3976 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3977 the specified list of CPUs to be no-callback CPUs. 3978 Invocation of these CPUs' RCU callbacks will be 3979 offloaded to "rcuox/N" kthreads created for that 3980 purpose, where "x" is "p" for RCU-preempt, and 3981 "s" for RCU-sched, and "N" is the CPU number. 3982 This reduces OS jitter on the offloaded CPUs, 3983 which can be useful for HPC and real-time 3984 workloads. It can also improve energy efficiency 3985 for asymmetric multiprocessors. 3986 3987 rcu_nocb_poll [KNL] 3988 Rather than requiring that offloaded CPUs 3989 (specified by rcu_nocbs= above) explicitly 3990 awaken the corresponding "rcuoN" kthreads, 3991 make these kthreads poll for callbacks. 3992 This improves the real-time response for the 3993 offloaded CPUs by relieving them of the need to 3994 wake up the corresponding kthread, but degrades 3995 energy efficiency by requiring that the kthreads 3996 periodically wake up to do the polling. 3997 3998 rcutree.blimit= [KNL] 3999 Set maximum number of finished RCU callbacks to 4000 process in one batch. 4001 4002 rcutree.dump_tree= [KNL] 4003 Dump the structure of the rcu_node combining tree 4004 out at early boot. This is used for diagnostic 4005 purposes, to verify correct tree setup. 4006 4007 rcutree.gp_cleanup_delay= [KNL] 4008 Set the number of jiffies to delay each step of 4009 RCU grace-period cleanup. 4010 4011 rcutree.gp_init_delay= [KNL] 4012 Set the number of jiffies to delay each step of 4013 RCU grace-period initialization. 4014 4015 rcutree.gp_preinit_delay= [KNL] 4016 Set the number of jiffies to delay each step of 4017 RCU grace-period pre-initialization, that is, 4018 the propagation of recent CPU-hotplug changes up 4019 the rcu_node combining tree. 4020 4021 rcutree.use_softirq= [KNL] 4022 If set to zero, move all RCU_SOFTIRQ processing to 4023 per-CPU rcuc kthreads. Defaults to a non-zero 4024 value, meaning that RCU_SOFTIRQ is used by default. 4025 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4026 4027 rcutree.rcu_fanout_exact= [KNL] 4028 Disable autobalancing of the rcu_node combining 4029 tree. This is used by rcutorture, and might 4030 possibly be useful for architectures having high 4031 cache-to-cache transfer latencies. 4032 4033 rcutree.rcu_fanout_leaf= [KNL] 4034 Change the number of CPUs assigned to each 4035 leaf rcu_node structure. Useful for very 4036 large systems, which will choose the value 64, 4037 and for NUMA systems with large remote-access 4038 latencies, which will choose a value aligned 4039 with the appropriate hardware boundaries. 4040 4041 rcutree.jiffies_till_first_fqs= [KNL] 4042 Set delay from grace-period initialization to 4043 first attempt to force quiescent states. 4044 Units are jiffies, minimum value is zero, 4045 and maximum value is HZ. 4046 4047 rcutree.jiffies_till_next_fqs= [KNL] 4048 Set delay between subsequent attempts to force 4049 quiescent states. Units are jiffies, minimum 4050 value is one, and maximum value is HZ. 4051 4052 rcutree.jiffies_till_sched_qs= [KNL] 4053 Set required age in jiffies for a 4054 given grace period before RCU starts 4055 soliciting quiescent-state help from 4056 rcu_note_context_switch() and cond_resched(). 4057 If not specified, the kernel will calculate 4058 a value based on the most recent settings 4059 of rcutree.jiffies_till_first_fqs 4060 and rcutree.jiffies_till_next_fqs. 4061 This calculated value may be viewed in 4062 rcutree.jiffies_to_sched_qs. Any attempt to set 4063 rcutree.jiffies_to_sched_qs will be cheerfully 4064 overwritten. 4065 4066 rcutree.kthread_prio= [KNL,BOOT] 4067 Set the SCHED_FIFO priority of the RCU per-CPU 4068 kthreads (rcuc/N). This value is also used for 4069 the priority of the RCU boost threads (rcub/N) 4070 and for the RCU grace-period kthreads (rcu_bh, 4071 rcu_preempt, and rcu_sched). If RCU_BOOST is 4072 set, valid values are 1-99 and the default is 1 4073 (the least-favored priority). Otherwise, when 4074 RCU_BOOST is not set, valid values are 0-99 and 4075 the default is zero (non-realtime operation). 4076 4077 rcutree.rcu_nocb_gp_stride= [KNL] 4078 Set the number of NOCB callback kthreads in 4079 each group, which defaults to the square root 4080 of the number of CPUs. Larger numbers reduce 4081 the wakeup overhead on the global grace-period 4082 kthread, but increases that same overhead on 4083 each group's NOCB grace-period kthread. 4084 4085 rcutree.qhimark= [KNL] 4086 Set threshold of queued RCU callbacks beyond which 4087 batch limiting is disabled. 4088 4089 rcutree.qlowmark= [KNL] 4090 Set threshold of queued RCU callbacks below which 4091 batch limiting is re-enabled. 4092 4093 rcutree.qovld= [KNL] 4094 Set threshold of queued RCU callbacks beyond which 4095 RCU's force-quiescent-state scan will aggressively 4096 enlist help from cond_resched() and sched IPIs to 4097 help CPUs more quickly reach quiescent states. 4098 Set to less than zero to make this be set based 4099 on rcutree.qhimark at boot time and to zero to 4100 disable more aggressive help enlistment. 4101 4102 rcutree.rcu_idle_gp_delay= [KNL] 4103 Set wakeup interval for idle CPUs that have 4104 RCU callbacks (RCU_FAST_NO_HZ=y). 4105 4106 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4107 Set wakeup interval for idle CPUs that have 4108 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4109 Lazy RCU callbacks are those which RCU can 4110 prove do nothing more than free memory. 4111 4112 rcutree.rcu_kick_kthreads= [KNL] 4113 Cause the grace-period kthread to get an extra 4114 wake_up() if it sleeps three times longer than 4115 it should at force-quiescent-state time. 4116 This wake_up() will be accompanied by a 4117 WARN_ONCE() splat and an ftrace_dump(). 4118 4119 rcutree.sysrq_rcu= [KNL] 4120 Commandeer a sysrq key to dump out Tree RCU's 4121 rcu_node tree with an eye towards determining 4122 why a new grace period has not yet started. 4123 4124 rcuperf.gp_async= [KNL] 4125 Measure performance of asynchronous 4126 grace-period primitives such as call_rcu(). 4127 4128 rcuperf.gp_async_max= [KNL] 4129 Specify the maximum number of outstanding 4130 callbacks per writer thread. When a writer 4131 thread exceeds this limit, it invokes the 4132 corresponding flavor of rcu_barrier() to allow 4133 previously posted callbacks to drain. 4134 4135 rcuperf.gp_exp= [KNL] 4136 Measure performance of expedited synchronous 4137 grace-period primitives. 4138 4139 rcuperf.holdoff= [KNL] 4140 Set test-start holdoff period. The purpose of 4141 this parameter is to delay the start of the 4142 test until boot completes in order to avoid 4143 interference. 4144 4145 rcuperf.kfree_rcu_test= [KNL] 4146 Set to measure performance of kfree_rcu() flooding. 4147 4148 rcuperf.kfree_nthreads= [KNL] 4149 The number of threads running loops of kfree_rcu(). 4150 4151 rcuperf.kfree_alloc_num= [KNL] 4152 Number of allocations and frees done in an iteration. 4153 4154 rcuperf.kfree_loops= [KNL] 4155 Number of loops doing rcuperf.kfree_alloc_num number 4156 of allocations and frees. 4157 4158 rcuperf.nreaders= [KNL] 4159 Set number of RCU readers. The value -1 selects 4160 N, where N is the number of CPUs. A value 4161 "n" less than -1 selects N-n+1, where N is again 4162 the number of CPUs. For example, -2 selects N 4163 (the number of CPUs), -3 selects N+1, and so on. 4164 A value of "n" less than or equal to -N selects 4165 a single reader. 4166 4167 rcuperf.nwriters= [KNL] 4168 Set number of RCU writers. The values operate 4169 the same as for rcuperf.nreaders. 4170 N, where N is the number of CPUs 4171 4172 rcuperf.perf_type= [KNL] 4173 Specify the RCU implementation to test. 4174 4175 rcuperf.shutdown= [KNL] 4176 Shut the system down after performance tests 4177 complete. This is useful for hands-off automated 4178 testing. 4179 4180 rcuperf.verbose= [KNL] 4181 Enable additional printk() statements. 4182 4183 rcuperf.writer_holdoff= [KNL] 4184 Write-side holdoff between grace periods, 4185 in microseconds. The default of zero says 4186 no holdoff. 4187 4188 rcutorture.fqs_duration= [KNL] 4189 Set duration of force_quiescent_state bursts 4190 in microseconds. 4191 4192 rcutorture.fqs_holdoff= [KNL] 4193 Set holdoff time within force_quiescent_state bursts 4194 in microseconds. 4195 4196 rcutorture.fqs_stutter= [KNL] 4197 Set wait time between force_quiescent_state bursts 4198 in seconds. 4199 4200 rcutorture.fwd_progress= [KNL] 4201 Enable RCU grace-period forward-progress testing 4202 for the types of RCU supporting this notion. 4203 4204 rcutorture.fwd_progress_div= [KNL] 4205 Specify the fraction of a CPU-stall-warning 4206 period to do tight-loop forward-progress testing. 4207 4208 rcutorture.fwd_progress_holdoff= [KNL] 4209 Number of seconds to wait between successive 4210 forward-progress tests. 4211 4212 rcutorture.fwd_progress_need_resched= [KNL] 4213 Enclose cond_resched() calls within checks for 4214 need_resched() during tight-loop forward-progress 4215 testing. 4216 4217 rcutorture.gp_cond= [KNL] 4218 Use conditional/asynchronous update-side 4219 primitives, if available. 4220 4221 rcutorture.gp_exp= [KNL] 4222 Use expedited update-side primitives, if available. 4223 4224 rcutorture.gp_normal= [KNL] 4225 Use normal (non-expedited) asynchronous 4226 update-side primitives, if available. 4227 4228 rcutorture.gp_sync= [KNL] 4229 Use normal (non-expedited) synchronous 4230 update-side primitives, if available. If all 4231 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4232 rcutorture.gp_normal=, and rcutorture.gp_sync= 4233 are zero, rcutorture acts as if is interpreted 4234 they are all non-zero. 4235 4236 rcutorture.n_barrier_cbs= [KNL] 4237 Set callbacks/threads for rcu_barrier() testing. 4238 4239 rcutorture.nfakewriters= [KNL] 4240 Set number of concurrent RCU writers. These just 4241 stress RCU, they don't participate in the actual 4242 test, hence the "fake". 4243 4244 rcutorture.nreaders= [KNL] 4245 Set number of RCU readers. The value -1 selects 4246 N-1, where N is the number of CPUs. A value 4247 "n" less than -1 selects N-n-2, where N is again 4248 the number of CPUs. For example, -2 selects N 4249 (the number of CPUs), -3 selects N+1, and so on. 4250 4251 rcutorture.object_debug= [KNL] 4252 Enable debug-object double-call_rcu() testing. 4253 4254 rcutorture.onoff_holdoff= [KNL] 4255 Set time (s) after boot for CPU-hotplug testing. 4256 4257 rcutorture.onoff_interval= [KNL] 4258 Set time (jiffies) between CPU-hotplug operations, 4259 or zero to disable CPU-hotplug testing. 4260 4261 rcutorture.shuffle_interval= [KNL] 4262 Set task-shuffle interval (s). Shuffling tasks 4263 allows some CPUs to go into dyntick-idle mode 4264 during the rcutorture test. 4265 4266 rcutorture.shutdown_secs= [KNL] 4267 Set time (s) after boot system shutdown. This 4268 is useful for hands-off automated testing. 4269 4270 rcutorture.stall_cpu= [KNL] 4271 Duration of CPU stall (s) to test RCU CPU stall 4272 warnings, zero to disable. 4273 4274 rcutorture.stall_cpu_block= [KNL] 4275 Sleep while stalling if set. This will result 4276 in warnings from preemptible RCU in addition 4277 to any other stall-related activity. 4278 4279 rcutorture.stall_cpu_holdoff= [KNL] 4280 Time to wait (s) after boot before inducing stall. 4281 4282 rcutorture.stall_cpu_irqsoff= [KNL] 4283 Disable interrupts while stalling if set. 4284 4285 rcutorture.stall_gp_kthread= [KNL] 4286 Duration (s) of forced sleep within RCU 4287 grace-period kthread to test RCU CPU stall 4288 warnings, zero to disable. If both stall_cpu 4289 and stall_gp_kthread are specified, the 4290 kthread is starved first, then the CPU. 4291 4292 rcutorture.stat_interval= [KNL] 4293 Time (s) between statistics printk()s. 4294 4295 rcutorture.stutter= [KNL] 4296 Time (s) to stutter testing, for example, specifying 4297 five seconds causes the test to run for five seconds, 4298 wait for five seconds, and so on. This tests RCU's 4299 ability to transition abruptly to and from idle. 4300 4301 rcutorture.test_boost= [KNL] 4302 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4303 "Maybe" means test if the RCU implementation 4304 under test support RCU priority boosting. 4305 4306 rcutorture.test_boost_duration= [KNL] 4307 Duration (s) of each individual boost test. 4308 4309 rcutorture.test_boost_interval= [KNL] 4310 Interval (s) between each boost test. 4311 4312 rcutorture.test_no_idle_hz= [KNL] 4313 Test RCU's dyntick-idle handling. See also the 4314 rcutorture.shuffle_interval parameter. 4315 4316 rcutorture.torture_type= [KNL] 4317 Specify the RCU implementation to test. 4318 4319 rcutorture.verbose= [KNL] 4320 Enable additional printk() statements. 4321 4322 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4323 Dump ftrace buffer after reporting RCU CPU 4324 stall warning. 4325 4326 rcupdate.rcu_cpu_stall_suppress= [KNL] 4327 Suppress RCU CPU stall warning messages. 4328 4329 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4330 Suppress RCU CPU stall warning messages and 4331 rcutorture writer stall warnings that occur 4332 during early boot, that is, during the time 4333 before the init task is spawned. 4334 4335 rcupdate.rcu_cpu_stall_timeout= [KNL] 4336 Set timeout for RCU CPU stall warning messages. 4337 4338 rcupdate.rcu_expedited= [KNL] 4339 Use expedited grace-period primitives, for 4340 example, synchronize_rcu_expedited() instead 4341 of synchronize_rcu(). This reduces latency, 4342 but can increase CPU utilization, degrade 4343 real-time latency, and degrade energy efficiency. 4344 No effect on CONFIG_TINY_RCU kernels. 4345 4346 rcupdate.rcu_normal= [KNL] 4347 Use only normal grace-period primitives, 4348 for example, synchronize_rcu() instead of 4349 synchronize_rcu_expedited(). This improves 4350 real-time latency, CPU utilization, and 4351 energy efficiency, but can expose users to 4352 increased grace-period latency. This parameter 4353 overrides rcupdate.rcu_expedited. No effect on 4354 CONFIG_TINY_RCU kernels. 4355 4356 rcupdate.rcu_normal_after_boot= [KNL] 4357 Once boot has completed (that is, after 4358 rcu_end_inkernel_boot() has been invoked), use 4359 only normal grace-period primitives. No effect 4360 on CONFIG_TINY_RCU kernels. 4361 4362 rcupdate.rcu_task_ipi_delay= [KNL] 4363 Set time in jiffies during which RCU tasks will 4364 avoid sending IPIs, starting with the beginning 4365 of a given grace period. Setting a large 4366 number avoids disturbing real-time workloads, 4367 but lengthens grace periods. 4368 4369 rcupdate.rcu_task_stall_timeout= [KNL] 4370 Set timeout in jiffies for RCU task stall warning 4371 messages. Disable with a value less than or equal 4372 to zero. 4373 4374 rcupdate.rcu_self_test= [KNL] 4375 Run the RCU early boot self tests 4376 4377 rdinit= [KNL] 4378 Format: <full_path> 4379 Run specified binary instead of /init from the ramdisk, 4380 used for early userspace startup. See initrd. 4381 4382 rdrand= [X86] 4383 force - Override the decision by the kernel to hide the 4384 advertisement of RDRAND support (this affects 4385 certain AMD processors because of buggy BIOS 4386 support, specifically around the suspend/resume 4387 path). 4388 4389 rdt= [HW,X86,RDT] 4390 Turn on/off individual RDT features. List is: 4391 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4392 mba. 4393 E.g. to turn on cmt and turn off mba use: 4394 rdt=cmt,!mba 4395 4396 reboot= [KNL] 4397 Format (x86 or x86_64): 4398 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4399 [[,]s[mp]#### \ 4400 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4401 [[,]f[orce] 4402 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4403 (prefix with 'panic_' to set mode for panic 4404 reboot only), 4405 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4406 reboot_force is either force or not specified, 4407 reboot_cpu is s[mp]#### with #### being the processor 4408 to be used for rebooting. 4409 4410 relax_domain_level= 4411 [KNL, SMP] Set scheduler's default relax_domain_level. 4412 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4413 4414 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4415 Format: <base1>,<size1>[,<base2>,<size2>,...] 4416 Reserve I/O ports or memory so the kernel won't use 4417 them. If <base> is less than 0x10000, the region 4418 is assumed to be I/O ports; otherwise it is memory. 4419 4420 reservetop= [X86-32] 4421 Format: nn[KMG] 4422 Reserves a hole at the top of the kernel virtual 4423 address space. 4424 4425 reservelow= [X86] 4426 Format: nn[K] 4427 Set the amount of memory to reserve for BIOS at 4428 the bottom of the address space. 4429 4430 reset_devices [KNL] Force drivers to reset the underlying device 4431 during initialization. 4432 4433 resume= [SWSUSP] 4434 Specify the partition device for software suspend 4435 Format: 4436 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4437 4438 resume_offset= [SWSUSP] 4439 Specify the offset from the beginning of the partition 4440 given by "resume=" at which the swap header is located, 4441 in <PAGE_SIZE> units (needed only for swap files). 4442 See Documentation/power/swsusp-and-swap-files.rst 4443 4444 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4445 read the resume files 4446 4447 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4448 Useful for devices that are detected asynchronously 4449 (e.g. USB and MMC devices). 4450 4451 hibernate= [HIBERNATION] 4452 noresume Don't check if there's a hibernation image 4453 present during boot. 4454 nocompress Don't compress/decompress hibernation images. 4455 no Disable hibernation and resume. 4456 protect_image Turn on image protection during restoration 4457 (that will set all pages holding image data 4458 during restoration read-only). 4459 4460 retain_initrd [RAM] Keep initrd memory after extraction 4461 4462 rfkill.default_state= 4463 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4464 etc. communication is blocked by default. 4465 1 Unblocked. 4466 4467 rfkill.master_switch_mode= 4468 0 The "airplane mode" button does nothing. 4469 1 The "airplane mode" button toggles between everything 4470 blocked and the previous configuration. 4471 2 The "airplane mode" button toggles between everything 4472 blocked and everything unblocked. 4473 4474 rhash_entries= [KNL,NET] 4475 Set number of hash buckets for route cache 4476 4477 ring3mwait=disable 4478 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4479 CPUs. 4480 4481 ro [KNL] Mount root device read-only on boot 4482 4483 rodata= [KNL] 4484 on Mark read-only kernel memory as read-only (default). 4485 off Leave read-only kernel memory writable for debugging. 4486 4487 rockchip.usb_uart 4488 Enable the uart passthrough on the designated usb port 4489 on Rockchip SoCs. When active, the signals of the 4490 debug-uart get routed to the D+ and D- pins of the usb 4491 port and the regular usb controller gets disabled. 4492 4493 root= [KNL] Root filesystem 4494 See name_to_dev_t comment in init/do_mounts.c. 4495 4496 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4497 mount the root filesystem 4498 4499 rootflags= [KNL] Set root filesystem mount option string 4500 4501 rootfstype= [KNL] Set root filesystem type 4502 4503 rootwait [KNL] Wait (indefinitely) for root device to show up. 4504 Useful for devices that are detected asynchronously 4505 (e.g. USB and MMC devices). 4506 4507 rproc_mem=nn[KMG][@address] 4508 [KNL,ARM,CMA] Remoteproc physical memory block. 4509 Memory area to be used by remote processor image, 4510 managed by CMA. 4511 4512 rw [KNL] Mount root device read-write on boot 4513 4514 S [KNL] Run init in single mode 4515 4516 s390_iommu= [HW,S390] 4517 Set s390 IOTLB flushing mode 4518 strict 4519 With strict flushing every unmap operation will result in 4520 an IOTLB flush. Default is lazy flushing before reuse, 4521 which is faster. 4522 4523 sa1100ir [NET] 4524 See drivers/net/irda/sa1100_ir.c. 4525 4526 sbni= [NET] Granch SBNI12 leased line adapter 4527 4528 sched_debug [KNL] Enables verbose scheduler debug messages. 4529 4530 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4531 Allowed values are enable and disable. This feature 4532 incurs a small amount of overhead in the scheduler 4533 but is useful for debugging and performance tuning. 4534 4535 sched_thermal_decay_shift= 4536 [KNL, SMP] Set a decay shift for scheduler thermal 4537 pressure signal. Thermal pressure signal follows the 4538 default decay period of other scheduler pelt 4539 signals(usually 32 ms but configurable). Setting 4540 sched_thermal_decay_shift will left shift the decay 4541 period for the thermal pressure signal by the shift 4542 value. 4543 i.e. with the default pelt decay period of 32 ms 4544 sched_thermal_decay_shift thermal pressure decay pr 4545 1 64 ms 4546 2 128 ms 4547 and so on. 4548 Format: integer between 0 and 10 4549 Default is 0. 4550 4551 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4552 xtime_lock contention on larger systems, and/or RCU lock 4553 contention on all systems with CONFIG_MAXSMP set. 4554 Format: { "0" | "1" } 4555 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4556 1 -- enable. 4557 Note: increases power consumption, thus should only be 4558 enabled if running jitter sensitive (HPC/RT) workloads. 4559 4560 security= [SECURITY] Choose a legacy "major" security module to 4561 enable at boot. This has been deprecated by the 4562 "lsm=" parameter. 4563 4564 selinux= [SELINUX] Disable or enable SELinux at boot time. 4565 Format: { "0" | "1" } 4566 See security/selinux/Kconfig help text. 4567 0 -- disable. 4568 1 -- enable. 4569 Default value is 1. 4570 4571 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4572 Format: { "0" | "1" } 4573 See security/apparmor/Kconfig help text 4574 0 -- disable. 4575 1 -- enable. 4576 Default value is set via kernel config option. 4577 4578 serialnumber [BUGS=X86-32] 4579 4580 shapers= [NET] 4581 Maximal number of shapers. 4582 4583 simeth= [IA-64] 4584 simscsi= 4585 4586 slram= [HW,MTD] 4587 4588 slab_nomerge [MM] 4589 Disable merging of slabs with similar size. May be 4590 necessary if there is some reason to distinguish 4591 allocs to different slabs, especially in hardened 4592 environments where the risk of heap overflows and 4593 layout control by attackers can usually be 4594 frustrated by disabling merging. This will reduce 4595 most of the exposure of a heap attack to a single 4596 cache (risks via metadata attacks are mostly 4597 unchanged). Debug options disable merging on their 4598 own. 4599 For more information see Documentation/vm/slub.rst. 4600 4601 slab_max_order= [MM, SLAB] 4602 Determines the maximum allowed order for slabs. 4603 A high setting may cause OOMs due to memory 4604 fragmentation. Defaults to 1 for systems with 4605 more than 32MB of RAM, 0 otherwise. 4606 4607 slub_debug[=options[,slabs]] [MM, SLUB] 4608 Enabling slub_debug allows one to determine the 4609 culprit if slab objects become corrupted. Enabling 4610 slub_debug can create guard zones around objects and 4611 may poison objects when not in use. Also tracks the 4612 last alloc / free. For more information see 4613 Documentation/vm/slub.rst. 4614 4615 slub_memcg_sysfs= [MM, SLUB] 4616 Determines whether to enable sysfs directories for 4617 memory cgroup sub-caches. 1 to enable, 0 to disable. 4618 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4619 Enabling this can lead to a very high number of debug 4620 directories and files being created under 4621 /sys/kernel/slub. 4622 4623 slub_max_order= [MM, SLUB] 4624 Determines the maximum allowed order for slabs. 4625 A high setting may cause OOMs due to memory 4626 fragmentation. For more information see 4627 Documentation/vm/slub.rst. 4628 4629 slub_min_objects= [MM, SLUB] 4630 The minimum number of objects per slab. SLUB will 4631 increase the slab order up to slub_max_order to 4632 generate a sufficiently large slab able to contain 4633 the number of objects indicated. The higher the number 4634 of objects the smaller the overhead of tracking slabs 4635 and the less frequently locks need to be acquired. 4636 For more information see Documentation/vm/slub.rst. 4637 4638 slub_min_order= [MM, SLUB] 4639 Determines the minimum page order for slabs. Must be 4640 lower than slub_max_order. 4641 For more information see Documentation/vm/slub.rst. 4642 4643 slub_nomerge [MM, SLUB] 4644 Same with slab_nomerge. This is supported for legacy. 4645 See slab_nomerge for more information. 4646 4647 smart2= [HW] 4648 Format: <io1>[,<io2>[,...,<io8>]] 4649 4650 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4651 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4652 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4653 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4654 smsc-ircc2.ircc_irq= [HW] IRQ line 4655 smsc-ircc2.ircc_dma= [HW] DMA channel 4656 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4657 0: Toshiba Satellite 1800 (GP data pin select) 4658 1: Fast pin select (default) 4659 2: ATC IRMode 4660 4661 smt [KNL,S390] Set the maximum number of threads (logical 4662 CPUs) to use per physical CPU on systems capable of 4663 symmetric multithreading (SMT). Will be capped to the 4664 actual hardware limit. 4665 Format: <integer> 4666 Default: -1 (no limit) 4667 4668 softlockup_panic= 4669 [KNL] Should the soft-lockup detector generate panics. 4670 Format: 0 | 1 4671 4672 A value of 1 instructs the soft-lockup detector 4673 to panic the machine when a soft-lockup occurs. It is 4674 also controlled by the kernel.softlockup_panic sysctl 4675 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4676 respective build-time switch to that functionality. 4677 4678 softlockup_all_cpu_backtrace= 4679 [KNL] Should the soft-lockup detector generate 4680 backtraces on all cpus. 4681 Format: 0 | 1 4682 4683 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4684 See Documentation/admin-guide/laptops/sonypi.rst 4685 4686 spectre_v2= [X86] Control mitigation of Spectre variant 2 4687 (indirect branch speculation) vulnerability. 4688 The default operation protects the kernel from 4689 user space attacks. 4690 4691 on - unconditionally enable, implies 4692 spectre_v2_user=on 4693 off - unconditionally disable, implies 4694 spectre_v2_user=off 4695 auto - kernel detects whether your CPU model is 4696 vulnerable 4697 4698 Selecting 'on' will, and 'auto' may, choose a 4699 mitigation method at run time according to the 4700 CPU, the available microcode, the setting of the 4701 CONFIG_RETPOLINE configuration option, and the 4702 compiler with which the kernel was built. 4703 4704 Selecting 'on' will also enable the mitigation 4705 against user space to user space task attacks. 4706 4707 Selecting 'off' will disable both the kernel and 4708 the user space protections. 4709 4710 Specific mitigations can also be selected manually: 4711 4712 retpoline - replace indirect branches 4713 retpoline,generic - google's original retpoline 4714 retpoline,amd - AMD-specific minimal thunk 4715 4716 Not specifying this option is equivalent to 4717 spectre_v2=auto. 4718 4719 spectre_v2_user= 4720 [X86] Control mitigation of Spectre variant 2 4721 (indirect branch speculation) vulnerability between 4722 user space tasks 4723 4724 on - Unconditionally enable mitigations. Is 4725 enforced by spectre_v2=on 4726 4727 off - Unconditionally disable mitigations. Is 4728 enforced by spectre_v2=off 4729 4730 prctl - Indirect branch speculation is enabled, 4731 but mitigation can be enabled via prctl 4732 per thread. The mitigation control state 4733 is inherited on fork. 4734 4735 prctl,ibpb 4736 - Like "prctl" above, but only STIBP is 4737 controlled per thread. IBPB is issued 4738 always when switching between different user 4739 space processes. 4740 4741 seccomp 4742 - Same as "prctl" above, but all seccomp 4743 threads will enable the mitigation unless 4744 they explicitly opt out. 4745 4746 seccomp,ibpb 4747 - Like "seccomp" above, but only STIBP is 4748 controlled per thread. IBPB is issued 4749 always when switching between different 4750 user space processes. 4751 4752 auto - Kernel selects the mitigation depending on 4753 the available CPU features and vulnerability. 4754 4755 Default mitigation: 4756 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4757 4758 Not specifying this option is equivalent to 4759 spectre_v2_user=auto. 4760 4761 spec_store_bypass_disable= 4762 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4763 (Speculative Store Bypass vulnerability) 4764 4765 Certain CPUs are vulnerable to an exploit against a 4766 a common industry wide performance optimization known 4767 as "Speculative Store Bypass" in which recent stores 4768 to the same memory location may not be observed by 4769 later loads during speculative execution. The idea 4770 is that such stores are unlikely and that they can 4771 be detected prior to instruction retirement at the 4772 end of a particular speculation execution window. 4773 4774 In vulnerable processors, the speculatively forwarded 4775 store can be used in a cache side channel attack, for 4776 example to read memory to which the attacker does not 4777 directly have access (e.g. inside sandboxed code). 4778 4779 This parameter controls whether the Speculative Store 4780 Bypass optimization is used. 4781 4782 On x86 the options are: 4783 4784 on - Unconditionally disable Speculative Store Bypass 4785 off - Unconditionally enable Speculative Store Bypass 4786 auto - Kernel detects whether the CPU model contains an 4787 implementation of Speculative Store Bypass and 4788 picks the most appropriate mitigation. If the 4789 CPU is not vulnerable, "off" is selected. If the 4790 CPU is vulnerable the default mitigation is 4791 architecture and Kconfig dependent. See below. 4792 prctl - Control Speculative Store Bypass per thread 4793 via prctl. Speculative Store Bypass is enabled 4794 for a process by default. The state of the control 4795 is inherited on fork. 4796 seccomp - Same as "prctl" above, but all seccomp threads 4797 will disable SSB unless they explicitly opt out. 4798 4799 Default mitigations: 4800 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4801 4802 On powerpc the options are: 4803 4804 on,auto - On Power8 and Power9 insert a store-forwarding 4805 barrier on kernel entry and exit. On Power7 4806 perform a software flush on kernel entry and 4807 exit. 4808 off - No action. 4809 4810 Not specifying this option is equivalent to 4811 spec_store_bypass_disable=auto. 4812 4813 spia_io_base= [HW,MTD] 4814 spia_fio_base= 4815 spia_pedr= 4816 spia_peddr= 4817 4818 split_lock_detect= 4819 [X86] Enable split lock detection 4820 4821 When enabled (and if hardware support is present), atomic 4822 instructions that access data across cache line 4823 boundaries will result in an alignment check exception. 4824 4825 off - not enabled 4826 4827 warn - the kernel will emit rate limited warnings 4828 about applications triggering the #AC 4829 exception. This mode is the default on CPUs 4830 that supports split lock detection. 4831 4832 fatal - the kernel will send SIGBUS to applications 4833 that trigger the #AC exception. 4834 4835 If an #AC exception is hit in the kernel or in 4836 firmware (i.e. not while executing in user mode) 4837 the kernel will oops in either "warn" or "fatal" 4838 mode. 4839 4840 srbds= [X86,INTEL] 4841 Control the Special Register Buffer Data Sampling 4842 (SRBDS) mitigation. 4843 4844 Certain CPUs are vulnerable to an MDS-like 4845 exploit which can leak bits from the random 4846 number generator. 4847 4848 By default, this issue is mitigated by 4849 microcode. However, the microcode fix can cause 4850 the RDRAND and RDSEED instructions to become 4851 much slower. Among other effects, this will 4852 result in reduced throughput from /dev/urandom. 4853 4854 The microcode mitigation can be disabled with 4855 the following option: 4856 4857 off: Disable mitigation and remove 4858 performance impact to RDRAND and RDSEED 4859 4860 srcutree.counter_wrap_check [KNL] 4861 Specifies how frequently to check for 4862 grace-period sequence counter wrap for the 4863 srcu_data structure's ->srcu_gp_seq_needed field. 4864 The greater the number of bits set in this kernel 4865 parameter, the less frequently counter wrap will 4866 be checked for. Note that the bottom two bits 4867 are ignored. 4868 4869 srcutree.exp_holdoff [KNL] 4870 Specifies how many nanoseconds must elapse 4871 since the end of the last SRCU grace period for 4872 a given srcu_struct until the next normal SRCU 4873 grace period will be considered for automatic 4874 expediting. Set to zero to disable automatic 4875 expediting. 4876 4877 ssbd= [ARM64,HW] 4878 Speculative Store Bypass Disable control 4879 4880 On CPUs that are vulnerable to the Speculative 4881 Store Bypass vulnerability and offer a 4882 firmware based mitigation, this parameter 4883 indicates how the mitigation should be used: 4884 4885 force-on: Unconditionally enable mitigation for 4886 for both kernel and userspace 4887 force-off: Unconditionally disable mitigation for 4888 for both kernel and userspace 4889 kernel: Always enable mitigation in the 4890 kernel, and offer a prctl interface 4891 to allow userspace to register its 4892 interest in being mitigated too. 4893 4894 stack_guard_gap= [MM] 4895 override the default stack gap protection. The value 4896 is in page units and it defines how many pages prior 4897 to (for stacks growing down) resp. after (for stacks 4898 growing up) the main stack are reserved for no other 4899 mapping. Default value is 256 pages. 4900 4901 stacktrace [FTRACE] 4902 Enabled the stack tracer on boot up. 4903 4904 stacktrace_filter=[function-list] 4905 [FTRACE] Limit the functions that the stack tracer 4906 will trace at boot up. function-list is a comma separated 4907 list of functions. This list can be changed at run 4908 time by the stack_trace_filter file in the debugfs 4909 tracing directory. Note, this enables stack tracing 4910 and the stacktrace above is not needed. 4911 4912 sti= [PARISC,HW] 4913 Format: <num> 4914 Set the STI (builtin display/keyboard on the HP-PARISC 4915 machines) console (graphic card) which should be used 4916 as the initial boot-console. 4917 See also comment in drivers/video/console/sticore.c. 4918 4919 sti_font= [HW] 4920 See comment in drivers/video/console/sticore.c. 4921 4922 stifb= [HW] 4923 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4924 4925 sunrpc.min_resvport= 4926 sunrpc.max_resvport= 4927 [NFS,SUNRPC] 4928 SunRPC servers often require that client requests 4929 originate from a privileged port (i.e. a port in the 4930 range 0 < portnr < 1024). 4931 An administrator who wishes to reserve some of these 4932 ports for other uses may adjust the range that the 4933 kernel's sunrpc client considers to be privileged 4934 using these two parameters to set the minimum and 4935 maximum port values. 4936 4937 sunrpc.svc_rpc_per_connection_limit= 4938 [NFS,SUNRPC] 4939 Limit the number of requests that the server will 4940 process in parallel from a single connection. 4941 The default value is 0 (no limit). 4942 4943 sunrpc.pool_mode= 4944 [NFS] 4945 Control how the NFS server code allocates CPUs to 4946 service thread pools. Depending on how many NICs 4947 you have and where their interrupts are bound, this 4948 option will affect which CPUs will do NFS serving. 4949 Note: this parameter cannot be changed while the 4950 NFS server is running. 4951 4952 auto the server chooses an appropriate mode 4953 automatically using heuristics 4954 global a single global pool contains all CPUs 4955 percpu one pool for each CPU 4956 pernode one pool for each NUMA node (equivalent 4957 to global on non-NUMA machines) 4958 4959 sunrpc.tcp_slot_table_entries= 4960 sunrpc.udp_slot_table_entries= 4961 [NFS,SUNRPC] 4962 Sets the upper limit on the number of simultaneous 4963 RPC calls that can be sent from the client to a 4964 server. Increasing these values may allow you to 4965 improve throughput, but will also increase the 4966 amount of memory reserved for use by the client. 4967 4968 suspend.pm_test_delay= 4969 [SUSPEND] 4970 Sets the number of seconds to remain in a suspend test 4971 mode before resuming the system (see 4972 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4973 is set. Default value is 5. 4974 4975 svm= [PPC] 4976 Format: { on | off | y | n | 1 | 0 } 4977 This parameter controls use of the Protected 4978 Execution Facility on pSeries. 4979 4980 swapaccount=[0|1] 4981 [KNL] Enable accounting of swap in memory resource 4982 controller if no parameter or 1 is given or disable 4983 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4984 4985 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4986 Format: { <int> | force | noforce } 4987 <int> -- Number of I/O TLB slabs 4988 force -- force using of bounce buffers even if they 4989 wouldn't be automatically used by the kernel 4990 noforce -- Never use bounce buffers (for debugging) 4991 4992 switches= [HW,M68k] 4993 4994 sysctl.*= [KNL] 4995 Set a sysctl parameter, right before loading the init 4996 process, as if the value was written to the respective 4997 /proc/sys/... file. Both '.' and '/' are recognized as 4998 separators. Unrecognized parameters and invalid values 4999 are reported in the kernel log. Sysctls registered 5000 later by a loaded module cannot be set this way. 5001 Example: sysctl.vm.swappiness=40 5002 5003 sysfs.deprecated=0|1 [KNL] 5004 Enable/disable old style sysfs layout for old udev 5005 on older distributions. When this option is enabled 5006 very new udev will not work anymore. When this option 5007 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5008 in older udev will not work anymore. 5009 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5010 the kernel configuration. 5011 5012 sysrq_always_enabled 5013 [KNL] 5014 Ignore sysrq setting - this boot parameter will 5015 neutralize any effect of /proc/sys/kernel/sysrq. 5016 Useful for debugging. 5017 5018 tcpmhash_entries= [KNL,NET] 5019 Set the number of tcp_metrics_hash slots. 5020 Default value is 8192 or 16384 depending on total 5021 ram pages. This is used to specify the TCP metrics 5022 cache size. See Documentation/networking/ip-sysctl.rst 5023 "tcp_no_metrics_save" section for more details. 5024 5025 tdfx= [HW,DRM] 5026 5027 test_suspend= [SUSPEND][,N] 5028 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5029 standby suspend) or "freeze" (for suspend type freeze) 5030 as the system sleep state during system startup with 5031 the optional capability to repeat N number of times. 5032 The system is woken from this state using a 5033 wakeup-capable RTC alarm. 5034 5035 thash_entries= [KNL,NET] 5036 Set number of hash buckets for TCP connection 5037 5038 thermal.act= [HW,ACPI] 5039 -1: disable all active trip points in all thermal zones 5040 <degrees C>: override all lowest active trip points 5041 5042 thermal.crt= [HW,ACPI] 5043 -1: disable all critical trip points in all thermal zones 5044 <degrees C>: override all critical trip points 5045 5046 thermal.nocrt= [HW,ACPI] 5047 Set to disable actions on ACPI thermal zone 5048 critical and hot trip points. 5049 5050 thermal.off= [HW,ACPI] 5051 1: disable ACPI thermal control 5052 5053 thermal.psv= [HW,ACPI] 5054 -1: disable all passive trip points 5055 <degrees C>: override all passive trip points to this 5056 value 5057 5058 thermal.tzp= [HW,ACPI] 5059 Specify global default ACPI thermal zone polling rate 5060 <deci-seconds>: poll all this frequency 5061 0: no polling (default) 5062 5063 threadirqs [KNL] 5064 Force threading of all interrupt handlers except those 5065 marked explicitly IRQF_NO_THREAD. 5066 5067 topology= [S390] 5068 Format: {off | on} 5069 Specify if the kernel should make use of the cpu 5070 topology information if the hardware supports this. 5071 The scheduler will make use of this information and 5072 e.g. base its process migration decisions on it. 5073 Default is on. 5074 5075 topology_updates= [KNL, PPC, NUMA] 5076 Format: {off} 5077 Specify if the kernel should ignore (off) 5078 topology updates sent by the hypervisor to this 5079 LPAR. 5080 5081 torture.disable_onoff_at_boot= [KNL] 5082 Prevent the CPU-hotplug component of torturing 5083 until after init has spawned. 5084 5085 tp720= [HW,PS2] 5086 5087 tpm_suspend_pcr=[HW,TPM] 5088 Format: integer pcr id 5089 Specify that at suspend time, the tpm driver 5090 should extend the specified pcr with zeros, 5091 as a workaround for some chips which fail to 5092 flush the last written pcr on TPM_SaveState. 5093 This will guarantee that all the other pcrs 5094 are saved. 5095 5096 trace_buf_size=nn[KMG] 5097 [FTRACE] will set tracing buffer size on each cpu. 5098 5099 trace_event=[event-list] 5100 [FTRACE] Set and start specified trace events in order 5101 to facilitate early boot debugging. The event-list is a 5102 comma separated list of trace events to enable. See 5103 also Documentation/trace/events.rst 5104 5105 trace_options=[option-list] 5106 [FTRACE] Enable or disable tracer options at boot. 5107 The option-list is a comma delimited list of options 5108 that can be enabled or disabled just as if you were 5109 to echo the option name into 5110 5111 /sys/kernel/debug/tracing/trace_options 5112 5113 For example, to enable stacktrace option (to dump the 5114 stack trace of each event), add to the command line: 5115 5116 trace_options=stacktrace 5117 5118 See also Documentation/trace/ftrace.rst "trace options" 5119 section. 5120 5121 tp_printk[FTRACE] 5122 Have the tracepoints sent to printk as well as the 5123 tracing ring buffer. This is useful for early boot up 5124 where the system hangs or reboots and does not give the 5125 option for reading the tracing buffer or performing a 5126 ftrace_dump_on_oops. 5127 5128 To turn off having tracepoints sent to printk, 5129 echo 0 > /proc/sys/kernel/tracepoint_printk 5130 Note, echoing 1 into this file without the 5131 tracepoint_printk kernel cmdline option has no effect. 5132 5133 ** CAUTION ** 5134 5135 Having tracepoints sent to printk() and activating high 5136 frequency tracepoints such as irq or sched, can cause 5137 the system to live lock. 5138 5139 traceoff_on_warning 5140 [FTRACE] enable this option to disable tracing when a 5141 warning is hit. This turns off "tracing_on". Tracing can 5142 be enabled again by echoing '1' into the "tracing_on" 5143 file located in /sys/kernel/debug/tracing/ 5144 5145 This option is useful, as it disables the trace before 5146 the WARNING dump is called, which prevents the trace to 5147 be filled with content caused by the warning output. 5148 5149 This option can also be set at run time via the sysctl 5150 option: kernel/traceoff_on_warning 5151 5152 transparent_hugepage= 5153 [KNL] 5154 Format: [always|madvise|never] 5155 Can be used to control the default behavior of the system 5156 with respect to transparent hugepages. 5157 See Documentation/admin-guide/mm/transhuge.rst 5158 for more details. 5159 5160 tsc= Disable clocksource stability checks for TSC. 5161 Format: <string> 5162 [x86] reliable: mark tsc clocksource as reliable, this 5163 disables clocksource verification at runtime, as well 5164 as the stability checks done at bootup. Used to enable 5165 high-resolution timer mode on older hardware, and in 5166 virtualized environment. 5167 [x86] noirqtime: Do not use TSC to do irq accounting. 5168 Used to run time disable IRQ_TIME_ACCOUNTING on any 5169 platforms where RDTSC is slow and this accounting 5170 can add overhead. 5171 [x86] unstable: mark the TSC clocksource as unstable, this 5172 marks the TSC unconditionally unstable at bootup and 5173 avoids any further wobbles once the TSC watchdog notices. 5174 [x86] nowatchdog: disable clocksource watchdog. Used 5175 in situations with strict latency requirements (where 5176 interruptions from clocksource watchdog are not 5177 acceptable). 5178 5179 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5180 value instead. Useful when the early TSC frequency discovery 5181 procedure is not reliable, such as on overclocked systems 5182 with CPUID.16h support and partial CPUID.15h support. 5183 Format: <unsigned int> 5184 5185 tsx= [X86] Control Transactional Synchronization 5186 Extensions (TSX) feature in Intel processors that 5187 support TSX control. 5188 5189 This parameter controls the TSX feature. The options are: 5190 5191 on - Enable TSX on the system. Although there are 5192 mitigations for all known security vulnerabilities, 5193 TSX has been known to be an accelerator for 5194 several previous speculation-related CVEs, and 5195 so there may be unknown security risks associated 5196 with leaving it enabled. 5197 5198 off - Disable TSX on the system. (Note that this 5199 option takes effect only on newer CPUs which are 5200 not vulnerable to MDS, i.e., have 5201 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5202 the new IA32_TSX_CTRL MSR through a microcode 5203 update. This new MSR allows for the reliable 5204 deactivation of the TSX functionality.) 5205 5206 auto - Disable TSX if X86_BUG_TAA is present, 5207 otherwise enable TSX on the system. 5208 5209 Not specifying this option is equivalent to tsx=off. 5210 5211 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5212 for more details. 5213 5214 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5215 Abort (TAA) vulnerability. 5216 5217 Similar to Micro-architectural Data Sampling (MDS) 5218 certain CPUs that support Transactional 5219 Synchronization Extensions (TSX) are vulnerable to an 5220 exploit against CPU internal buffers which can forward 5221 information to a disclosure gadget under certain 5222 conditions. 5223 5224 In vulnerable processors, the speculatively forwarded 5225 data can be used in a cache side channel attack, to 5226 access data to which the attacker does not have direct 5227 access. 5228 5229 This parameter controls the TAA mitigation. The 5230 options are: 5231 5232 full - Enable TAA mitigation on vulnerable CPUs 5233 if TSX is enabled. 5234 5235 full,nosmt - Enable TAA mitigation and disable SMT on 5236 vulnerable CPUs. If TSX is disabled, SMT 5237 is not disabled because CPU is not 5238 vulnerable to cross-thread TAA attacks. 5239 off - Unconditionally disable TAA mitigation 5240 5241 On MDS-affected machines, tsx_async_abort=off can be 5242 prevented by an active MDS mitigation as both vulnerabilities 5243 are mitigated with the same mechanism so in order to disable 5244 this mitigation, you need to specify mds=off too. 5245 5246 Not specifying this option is equivalent to 5247 tsx_async_abort=full. On CPUs which are MDS affected 5248 and deploy MDS mitigation, TAA mitigation is not 5249 required and doesn't provide any additional 5250 mitigation. 5251 5252 For details see: 5253 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5254 5255 turbografx.map[2|3]= [HW,JOY] 5256 TurboGraFX parallel port interface 5257 Format: 5258 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5259 See also Documentation/input/devices/joystick-parport.rst 5260 5261 udbg-immortal [PPC] When debugging early kernel crashes that 5262 happen after console_init() and before a proper 5263 console driver takes over, this boot options might 5264 help "seeing" what's going on. 5265 5266 uhash_entries= [KNL,NET] 5267 Set number of hash buckets for UDP/UDP-Lite connections 5268 5269 uhci-hcd.ignore_oc= 5270 [USB] Ignore overcurrent events (default N). 5271 Some badly-designed motherboards generate lots of 5272 bogus events, for ports that aren't wired to 5273 anything. Set this parameter to avoid log spamming. 5274 Note that genuine overcurrent events won't be 5275 reported either. 5276 5277 unknown_nmi_panic 5278 [X86] Cause panic on unknown NMI. 5279 5280 usbcore.authorized_default= 5281 [USB] Default USB device authorization: 5282 (default -1 = authorized except for wireless USB, 5283 0 = not authorized, 1 = authorized, 2 = authorized 5284 if device connected to internal port) 5285 5286 usbcore.autosuspend= 5287 [USB] The autosuspend time delay (in seconds) used 5288 for newly-detected USB devices (default 2). This 5289 is the time required before an idle device will be 5290 autosuspended. Devices for which the delay is set 5291 to a negative value won't be autosuspended at all. 5292 5293 usbcore.usbfs_snoop= 5294 [USB] Set to log all usbfs traffic (default 0 = off). 5295 5296 usbcore.usbfs_snoop_max= 5297 [USB] Maximum number of bytes to snoop in each URB 5298 (default = 65536). 5299 5300 usbcore.blinkenlights= 5301 [USB] Set to cycle leds on hubs (default 0 = off). 5302 5303 usbcore.old_scheme_first= 5304 [USB] Start with the old device initialization 5305 scheme (default 0 = off). 5306 5307 usbcore.usbfs_memory_mb= 5308 [USB] Memory limit (in MB) for buffers allocated by 5309 usbfs (default = 16, 0 = max = 2047). 5310 5311 usbcore.use_both_schemes= 5312 [USB] Try the other device initialization scheme 5313 if the first one fails (default 1 = enabled). 5314 5315 usbcore.initial_descriptor_timeout= 5316 [USB] Specifies timeout for the initial 64-byte 5317 USB_REQ_GET_DESCRIPTOR request in milliseconds 5318 (default 5000 = 5.0 seconds). 5319 5320 usbcore.nousb [USB] Disable the USB subsystem 5321 5322 usbcore.quirks= 5323 [USB] A list of quirk entries to augment the built-in 5324 usb core quirk list. List entries are separated by 5325 commas. Each entry has the form 5326 VendorID:ProductID:Flags. The IDs are 4-digit hex 5327 numbers and Flags is a set of letters. Each letter 5328 will change the built-in quirk; setting it if it is 5329 clear and clearing it if it is set. The letters have 5330 the following meanings: 5331 a = USB_QUIRK_STRING_FETCH_255 (string 5332 descriptors must not be fetched using 5333 a 255-byte read); 5334 b = USB_QUIRK_RESET_RESUME (device can't resume 5335 correctly so reset it instead); 5336 c = USB_QUIRK_NO_SET_INTF (device can't handle 5337 Set-Interface requests); 5338 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5339 handle its Configuration or Interface 5340 strings); 5341 e = USB_QUIRK_RESET (device can't be reset 5342 (e.g morph devices), don't use reset); 5343 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5344 more interface descriptions than the 5345 bNumInterfaces count, and can't handle 5346 talking to these interfaces); 5347 g = USB_QUIRK_DELAY_INIT (device needs a pause 5348 during initialization, after we read 5349 the device descriptor); 5350 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5351 high speed and super speed interrupt 5352 endpoints, the USB 2.0 and USB 3.0 spec 5353 require the interval in microframes (1 5354 microframe = 125 microseconds) to be 5355 calculated as interval = 2 ^ 5356 (bInterval-1). 5357 Devices with this quirk report their 5358 bInterval as the result of this 5359 calculation instead of the exponent 5360 variable used in the calculation); 5361 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5362 handle device_qualifier descriptor 5363 requests); 5364 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5365 generates spurious wakeup, ignore 5366 remote wakeup capability); 5367 k = USB_QUIRK_NO_LPM (device can't handle Link 5368 Power Management); 5369 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5370 (Device reports its bInterval as linear 5371 frames instead of the USB 2.0 5372 calculation); 5373 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5374 to be disconnected before suspend to 5375 prevent spurious wakeup); 5376 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5377 pause after every control message); 5378 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5379 delay after resetting its port); 5380 Example: quirks=0781:5580:bk,0a5c:5834:gij 5381 5382 usbhid.mousepoll= 5383 [USBHID] The interval which mice are to be polled at. 5384 5385 usbhid.jspoll= 5386 [USBHID] The interval which joysticks are to be polled at. 5387 5388 usbhid.kbpoll= 5389 [USBHID] The interval which keyboards are to be polled at. 5390 5391 usb-storage.delay_use= 5392 [UMS] The delay in seconds before a new device is 5393 scanned for Logical Units (default 1). 5394 5395 usb-storage.quirks= 5396 [UMS] A list of quirks entries to supplement or 5397 override the built-in unusual_devs list. List 5398 entries are separated by commas. Each entry has 5399 the form VID:PID:Flags where VID and PID are Vendor 5400 and Product ID values (4-digit hex numbers) and 5401 Flags is a set of characters, each corresponding 5402 to a common usb-storage quirk flag as follows: 5403 a = SANE_SENSE (collect more than 18 bytes 5404 of sense data, not on uas); 5405 b = BAD_SENSE (don't collect more than 18 5406 bytes of sense data, not on uas); 5407 c = FIX_CAPACITY (decrease the reported 5408 device capacity by one sector); 5409 d = NO_READ_DISC_INFO (don't use 5410 READ_DISC_INFO command, not on uas); 5411 e = NO_READ_CAPACITY_16 (don't use 5412 READ_CAPACITY_16 command); 5413 f = NO_REPORT_OPCODES (don't use report opcodes 5414 command, uas only); 5415 g = MAX_SECTORS_240 (don't transfer more than 5416 240 sectors at a time, uas only); 5417 h = CAPACITY_HEURISTICS (decrease the 5418 reported device capacity by one 5419 sector if the number is odd); 5420 i = IGNORE_DEVICE (don't bind to this 5421 device); 5422 j = NO_REPORT_LUNS (don't use report luns 5423 command, uas only); 5424 l = NOT_LOCKABLE (don't try to lock and 5425 unlock ejectable media, not on uas); 5426 m = MAX_SECTORS_64 (don't transfer more 5427 than 64 sectors = 32 KB at a time, 5428 not on uas); 5429 n = INITIAL_READ10 (force a retry of the 5430 initial READ(10) command, not on uas); 5431 o = CAPACITY_OK (accept the capacity 5432 reported by the device, not on uas); 5433 p = WRITE_CACHE (the device cache is ON 5434 by default, not on uas); 5435 r = IGNORE_RESIDUE (the device reports 5436 bogus residue values, not on uas); 5437 s = SINGLE_LUN (the device has only one 5438 Logical Unit); 5439 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5440 commands, uas only); 5441 u = IGNORE_UAS (don't bind to the uas driver); 5442 w = NO_WP_DETECT (don't test whether the 5443 medium is write-protected). 5444 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5445 even if the device claims no cache, 5446 not on uas) 5447 Example: quirks=0419:aaf5:rl,0421:0433:rc 5448 5449 user_debug= [KNL,ARM] 5450 Format: <int> 5451 See arch/arm/Kconfig.debug help text. 5452 1 - undefined instruction events 5453 2 - system calls 5454 4 - invalid data aborts 5455 8 - SIGSEGV faults 5456 16 - SIGBUS faults 5457 Example: user_debug=31 5458 5459 userpte= 5460 [X86] Flags controlling user PTE allocations. 5461 5462 nohigh = do not allocate PTE pages in 5463 HIGHMEM regardless of setting 5464 of CONFIG_HIGHPTE. 5465 5466 vdso= [X86,SH] 5467 On X86_32, this is an alias for vdso32=. Otherwise: 5468 5469 vdso=1: enable VDSO (the default) 5470 vdso=0: disable VDSO mapping 5471 5472 vdso32= [X86] Control the 32-bit vDSO 5473 vdso32=1: enable 32-bit VDSO 5474 vdso32=0 or vdso32=2: disable 32-bit VDSO 5475 5476 See the help text for CONFIG_COMPAT_VDSO for more 5477 details. If CONFIG_COMPAT_VDSO is set, the default is 5478 vdso32=0; otherwise, the default is vdso32=1. 5479 5480 For compatibility with older kernels, vdso32=2 is an 5481 alias for vdso32=0. 5482 5483 Try vdso32=0 if you encounter an error that says: 5484 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5485 5486 vector= [IA-64,SMP] 5487 vector=percpu: enable percpu vector domain 5488 5489 video= [FB] Frame buffer configuration 5490 See Documentation/fb/modedb.rst. 5491 5492 video.brightness_switch_enabled= [0,1] 5493 If set to 1, on receiving an ACPI notify event 5494 generated by hotkey, video driver will adjust brightness 5495 level and then send out the event to user space through 5496 the allocated input device; If set to 0, video driver 5497 will only send out the event without touching backlight 5498 brightness level. 5499 default: 1 5500 5501 virtio_mmio.device= 5502 [VMMIO] Memory mapped virtio (platform) device. 5503 5504 <size>@<baseaddr>:<irq>[:<id>] 5505 where: 5506 <size> := size (can use standard suffixes 5507 like K, M and G) 5508 <baseaddr> := physical base address 5509 <irq> := interrupt number (as passed to 5510 request_irq()) 5511 <id> := (optional) platform device id 5512 example: 5513 virtio_mmio.device=1K@0x100b0000:48:7 5514 5515 Can be used multiple times for multiple devices. 5516 5517 vga= [BOOT,X86-32] Select a particular video mode 5518 See Documentation/x86/boot.rst and 5519 Documentation/admin-guide/svga.rst. 5520 Use vga=ask for menu. 5521 This is actually a boot loader parameter; the value is 5522 passed to the kernel using a special protocol. 5523 5524 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5525 May slow down system boot speed, especially when 5526 enabled on systems with a large amount of memory. 5527 All options are enabled by default, and this 5528 interface is meant to allow for selectively 5529 enabling or disabling specific virtual memory 5530 debugging features. 5531 5532 Available options are: 5533 P Enable page structure init time poisoning 5534 - Disable all of the above options 5535 5536 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5537 size of <nn>. This can be used to increase the 5538 minimum size (128MB on x86). It can also be used to 5539 decrease the size and leave more room for directly 5540 mapped kernel RAM. 5541 5542 vmcp_cma=nn[MG] [KNL,S390] 5543 Sets the memory size reserved for contiguous memory 5544 allocations for the vmcp device driver. 5545 5546 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5547 Format: <command> 5548 5549 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5550 Format: <command> 5551 5552 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5553 Format: <command> 5554 5555 vsyscall= [X86-64] 5556 Controls the behavior of vsyscalls (i.e. calls to 5557 fixed addresses of 0xffffffffff600x00 from legacy 5558 code). Most statically-linked binaries and older 5559 versions of glibc use these calls. Because these 5560 functions are at fixed addresses, they make nice 5561 targets for exploits that can control RIP. 5562 5563 emulate [default] Vsyscalls turn into traps and are 5564 emulated reasonably safely. The vsyscall 5565 page is readable. 5566 5567 xonly Vsyscalls turn into traps and are 5568 emulated reasonably safely. The vsyscall 5569 page is not readable. 5570 5571 none Vsyscalls don't work at all. This makes 5572 them quite hard to use for exploits but 5573 might break your system. 5574 5575 vt.color= [VT] Default text color. 5576 Format: 0xYX, X = foreground, Y = background. 5577 Default: 0x07 = light gray on black. 5578 5579 vt.cur_default= [VT] Default cursor shape. 5580 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5581 the parameters of the <Esc>[?A;B;Cc escape sequence; 5582 see VGA-softcursor.txt. Default: 2 = underline. 5583 5584 vt.default_blu= [VT] 5585 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5586 Change the default blue palette of the console. 5587 This is a 16-member array composed of values 5588 ranging from 0-255. 5589 5590 vt.default_grn= [VT] 5591 Format: <green0>,<green1>,<green2>,...,<green15> 5592 Change the default green palette of the console. 5593 This is a 16-member array composed of values 5594 ranging from 0-255. 5595 5596 vt.default_red= [VT] 5597 Format: <red0>,<red1>,<red2>,...,<red15> 5598 Change the default red palette of the console. 5599 This is a 16-member array composed of values 5600 ranging from 0-255. 5601 5602 vt.default_utf8= 5603 [VT] 5604 Format=<0|1> 5605 Set system-wide default UTF-8 mode for all tty's. 5606 Default is 1, i.e. UTF-8 mode is enabled for all 5607 newly opened terminals. 5608 5609 vt.global_cursor_default= 5610 [VT] 5611 Format=<-1|0|1> 5612 Set system-wide default for whether a cursor 5613 is shown on new VTs. Default is -1, 5614 i.e. cursors will be created by default unless 5615 overridden by individual drivers. 0 will hide 5616 cursors, 1 will display them. 5617 5618 vt.italic= [VT] Default color for italic text; 0-15. 5619 Default: 2 = green. 5620 5621 vt.underline= [VT] Default color for underlined text; 0-15. 5622 Default: 3 = cyan. 5623 5624 watchdog timers [HW,WDT] For information on watchdog timers, 5625 see Documentation/watchdog/watchdog-parameters.rst 5626 or other driver-specific files in the 5627 Documentation/watchdog/ directory. 5628 5629 watchdog_thresh= 5630 [KNL] 5631 Set the hard lockup detector stall duration 5632 threshold in seconds. The soft lockup detector 5633 threshold is set to twice the value. A value of 0 5634 disables both lockup detectors. Default is 10 5635 seconds. 5636 5637 workqueue.watchdog_thresh= 5638 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5639 warn stall conditions and dump internal state to 5640 help debugging. 0 disables workqueue stall 5641 detection; otherwise, it's the stall threshold 5642 duration in seconds. The default value is 30 and 5643 it can be updated at runtime by writing to the 5644 corresponding sysfs file. 5645 5646 workqueue.disable_numa 5647 By default, all work items queued to unbound 5648 workqueues are affine to the NUMA nodes they're 5649 issued on, which results in better behavior in 5650 general. If NUMA affinity needs to be disabled for 5651 whatever reason, this option can be used. Note 5652 that this also can be controlled per-workqueue for 5653 workqueues visible under /sys/bus/workqueue/. 5654 5655 workqueue.power_efficient 5656 Per-cpu workqueues are generally preferred because 5657 they show better performance thanks to cache 5658 locality; unfortunately, per-cpu workqueues tend to 5659 be more power hungry than unbound workqueues. 5660 5661 Enabling this makes the per-cpu workqueues which 5662 were observed to contribute significantly to power 5663 consumption unbound, leading to measurably lower 5664 power usage at the cost of small performance 5665 overhead. 5666 5667 The default value of this parameter is determined by 5668 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5669 5670 workqueue.debug_force_rr_cpu 5671 Workqueue used to implicitly guarantee that work 5672 items queued without explicit CPU specified are put 5673 on the local CPU. This guarantee is no longer true 5674 and while local CPU is still preferred work items 5675 may be put on foreign CPUs. This debug option 5676 forces round-robin CPU selection to flush out 5677 usages which depend on the now broken guarantee. 5678 When enabled, memory and cache locality will be 5679 impacted. 5680 5681 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5682 default x2apic cluster mode on platforms 5683 supporting x2apic. 5684 5685 x86_intel_mid_timer= [X86-32,APBT] 5686 Choose timer option for x86 Intel MID platform. 5687 Two valid options are apbt timer only and lapic timer 5688 plus one apbt timer for broadcast timer. 5689 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5690 5691 xen_512gb_limit [KNL,X86-64,XEN] 5692 Restricts the kernel running paravirtualized under Xen 5693 to use only up to 512 GB of RAM. The reason to do so is 5694 crash analysis tools and Xen tools for doing domain 5695 save/restore/migration must be enabled to handle larger 5696 domains. 5697 5698 xen_emul_unplug= [HW,X86,XEN] 5699 Unplug Xen emulated devices 5700 Format: [unplug0,][unplug1] 5701 ide-disks -- unplug primary master IDE devices 5702 aux-ide-disks -- unplug non-primary-master IDE devices 5703 nics -- unplug network devices 5704 all -- unplug all emulated devices (NICs and IDE disks) 5705 unnecessary -- unplugging emulated devices is 5706 unnecessary even if the host did not respond to 5707 the unplug protocol 5708 never -- do not unplug even if version check succeeds 5709 5710 xen_legacy_crash [X86,XEN] 5711 Crash from Xen panic notifier, without executing late 5712 panic() code such as dumping handler. 5713 5714 xen_nopvspin [X86,XEN] 5715 Disables the ticketlock slowpath using Xen PV 5716 optimizations. 5717 5718 xen_nopv [X86] 5719 Disables the PV optimizations forcing the HVM guest to 5720 run as generic HVM guest with no PV drivers. 5721 This option is obsoleted by the "nopv" option, which 5722 has equivalent effect for XEN platform. 5723 5724 xen_scrub_pages= [XEN] 5725 Boolean option to control scrubbing pages before giving them back 5726 to Xen, for use by other domains. Can be also changed at runtime 5727 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5728 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5729 5730 xen_timer_slop= [X86-64,XEN] 5731 Set the timer slop (in nanoseconds) for the virtual Xen 5732 timers (default is 100000). This adjusts the minimum 5733 delta of virtualized Xen timers, where lower values 5734 improve timer resolution at the expense of processing 5735 more timer interrupts. 5736 5737 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5738 Disables the PV optimizations forcing the guest to run 5739 as generic guest with no PV drivers. Currently support 5740 XEN HVM, KVM, HYPER_V and VMWARE guest. 5741 5742 xirc2ps_cs= [NET,PCMCIA] 5743 Format: 5744 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5745 5746 xive= [PPC] 5747 By default on POWER9 and above, the kernel will 5748 natively use the XIVE interrupt controller. This option 5749 allows the fallback firmware mode to be used: 5750 5751 off Fallback to firmware control of XIVE interrupt 5752 controller on both pseries and powernv 5753 platforms. Only useful on POWER9 and above. 5754 5755 xhci-hcd.quirks [USB,KNL] 5756 A hex value specifying bitmask with supplemental xhci 5757 host controller quirks. Meaning of each bit can be 5758 consulted in header drivers/usb/host/xhci.h. 5759 5760 xmon [PPC] 5761 Format: { early | on | rw | ro | off } 5762 Controls if xmon debugger is enabled. Default is off. 5763 Passing only "xmon" is equivalent to "xmon=early". 5764 early Call xmon as early as possible on boot; xmon 5765 debugger is called from setup_arch(). 5766 on xmon debugger hooks will be installed so xmon 5767 is only called on a kernel crash. Default mode, 5768 i.e. either "ro" or "rw" mode, is controlled 5769 with CONFIG_XMON_DEFAULT_RO_MODE. 5770 rw xmon debugger hooks will be installed so xmon 5771 is called only on a kernel crash, mode is write, 5772 meaning SPR registers, memory and, other data 5773 can be written using xmon commands. 5774 ro same as "rw" option above but SPR registers, 5775 memory, and other data can't be written using 5776 xmon commands. 5777 off xmon is disabled. 5778