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 cpufreq.default_governor= 707 [CPU_FREQ] Name of the default cpufreq governor or 708 policy to use. This governor must be registered in the 709 kernel before the cpufreq driver probes. 710 711 cpu_init_udelay=N 712 [X86] Delay for N microsec between assert and de-assert 713 of APIC INIT to start processors. This delay occurs 714 on every CPU online, such as boot, and resume from suspend. 715 Default: 10000 716 717 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 718 Format: 719 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 720 721 crashkernel=size[KMG][@offset[KMG]] 722 [KNL] Using kexec, Linux can switch to a 'crash kernel' 723 upon panic. This parameter reserves the physical 724 memory region [offset, offset + size] for that kernel 725 image. If '@offset' is omitted, then a suitable offset 726 is selected automatically. 727 [KNL, x86_64] select a region under 4G first, and 728 fall back to reserve region above 4G when '@offset' 729 hasn't been specified. 730 See Documentation/admin-guide/kdump/kdump.rst for further details. 731 732 crashkernel=range1:size1[,range2:size2,...][@offset] 733 [KNL] Same as above, but depends on the memory 734 in the running system. The syntax of range is 735 start-[end] where start and end are both 736 a memory unit (amount[KMG]). See also 737 Documentation/admin-guide/kdump/kdump.rst for an example. 738 739 crashkernel=size[KMG],high 740 [KNL, x86_64] range could be above 4G. Allow kernel 741 to allocate physical memory region from top, so could 742 be above 4G if system have more than 4G ram installed. 743 Otherwise memory region will be allocated below 4G, if 744 available. 745 It will be ignored if crashkernel=X is specified. 746 crashkernel=size[KMG],low 747 [KNL, x86_64] range under 4G. When crashkernel=X,high 748 is passed, kernel could allocate physical memory region 749 above 4G, that cause second kernel crash on system 750 that require some amount of low memory, e.g. swiotlb 751 requires at least 64M+32K low memory, also enough extra 752 low memory is needed to make sure DMA buffers for 32-bit 753 devices won't run out. Kernel would try to allocate at 754 at least 256M below 4G automatically. 755 This one let user to specify own low range under 4G 756 for second kernel instead. 757 0: to disable low allocation. 758 It will be ignored when crashkernel=X,high is not used 759 or memory reserved is below 4G. 760 761 cryptomgr.notests 762 [KNL] Disable crypto self-tests 763 764 cs89x0_dma= [HW,NET] 765 Format: <dma> 766 767 cs89x0_media= [HW,NET] 768 Format: { rj45 | aui | bnc } 769 770 dasd= [HW,NET] 771 See header of drivers/s390/block/dasd_devmap.c. 772 773 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 774 (one device per port) 775 Format: <port#>,<type> 776 See also Documentation/input/devices/joystick-parport.rst 777 778 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 779 time. See 780 Documentation/admin-guide/dynamic-debug-howto.rst for 781 details. Deprecated, see dyndbg. 782 783 debug [KNL] Enable kernel debugging (events log level). 784 785 debug_boot_weak_hash 786 [KNL] Enable printing [hashed] pointers early in the 787 boot sequence. If enabled, we use a weak hash instead 788 of siphash to hash pointers. Use this option if you are 789 seeing instances of '(___ptrval___)') and need to see a 790 value (hashed pointer) instead. Cryptographically 791 insecure, please do not use on production kernels. 792 793 debug_locks_verbose= 794 [KNL] verbose self-tests 795 Format=<0|1> 796 Print debugging info while doing the locking API 797 self-tests. 798 We default to 0 (no extra messages), setting it to 799 1 will print _a lot_ more information - normally 800 only useful to kernel developers. 801 802 debug_objects [KNL] Enable object debugging 803 804 no_debug_objects 805 [KNL] Disable object debugging 806 807 debug_guardpage_minorder= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 809 parameter allows control of the order of pages that will 810 be intentionally kept free (and hence protected) by the 811 buddy allocator. Bigger value increase the probability 812 of catching random memory corruption, but reduce the 813 amount of memory for normal system use. The maximum 814 possible value is MAX_ORDER/2. Setting this parameter 815 to 1 or 2 should be enough to identify most random 816 memory corruption problems caused by bugs in kernel or 817 driver code when a CPU writes to (or reads from) a 818 random memory location. Note that there exists a class 819 of memory corruptions problems caused by buggy H/W or 820 F/W or by drivers badly programing DMA (basically when 821 memory is written at bus level and the CPU MMU is 822 bypassed) which are not detectable by 823 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 824 tracking down these problems. 825 826 debug_pagealloc= 827 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 828 enables the feature at boot time. By default, it is 829 disabled and the system will work mostly the same as a 830 kernel built without CONFIG_DEBUG_PAGEALLOC. 831 Note: to get most of debug_pagealloc error reports, it's 832 useful to also enable the page_owner functionality. 833 on: enable the feature 834 835 debugfs= [KNL] This parameter enables what is exposed to userspace 836 and debugfs internal clients. 837 Format: { on, no-mount, off } 838 on: All functions are enabled. 839 no-mount: 840 Filesystem is not registered but kernel clients can 841 access APIs and a crashkernel can be used to read 842 its content. There is nothing to mount. 843 off: Filesystem is not registered and clients 844 get a -EPERM as result when trying to register files 845 or directories within debugfs. 846 This is equivalent of the runtime functionality if 847 debugfs was not enabled in the kernel at all. 848 Default value is set in build-time with a kernel configuration. 849 850 debugpat [X86] Enable PAT debugging 851 852 decnet.addr= [HW,NET] 853 Format: <area>[,<node>] 854 See also Documentation/networking/decnet.rst. 855 856 default_hugepagesz= 857 [HW] The size of the default HugeTLB page. This is 858 the size represented by the legacy /proc/ hugepages 859 APIs. In addition, this is the default hugetlb size 860 used for shmget(), mmap() and mounting hugetlbfs 861 filesystems. If not specified, defaults to the 862 architecture's default huge page size. Huge page 863 sizes are architecture dependent. See also 864 Documentation/admin-guide/mm/hugetlbpage.rst. 865 Format: size[KMG] 866 867 deferred_probe_timeout= 868 [KNL] Debugging option to set a timeout in seconds for 869 deferred probe to give up waiting on dependencies to 870 probe. Only specific dependencies (subsystems or 871 drivers) that have opted in will be ignored. A timeout of 0 872 will timeout at the end of initcalls. This option will also 873 dump out devices still on the deferred probe list after 874 retrying. 875 876 dfltcc= [HW,S390] 877 Format: { on | off | def_only | inf_only | always } 878 on: s390 zlib hardware support for compression on 879 level 1 and decompression (default) 880 off: No s390 zlib hardware support 881 def_only: s390 zlib hardware support for deflate 882 only (compression on level 1) 883 inf_only: s390 zlib hardware support for inflate 884 only (decompression) 885 always: Same as 'on' but ignores the selected compression 886 level always using hardware support (used for debugging) 887 888 dhash_entries= [KNL] 889 Set number of hash buckets for dentry cache. 890 891 disable_1tb_segments [PPC] 892 Disables the use of 1TB hash page table segments. This 893 causes the kernel to fall back to 256MB segments which 894 can be useful when debugging issues that require an SLB 895 miss to occur. 896 897 stress_slb [PPC] 898 Limits the number of kernel SLB entries, and flushes 899 them frequently to increase the rate of SLB faults 900 on kernel addresses. 901 902 disable= [IPV6] 903 See Documentation/networking/ipv6.rst. 904 905 hardened_usercopy= 906 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 907 hardening is enabled for this boot. Hardened 908 usercopy checking is used to protect the kernel 909 from reading or writing beyond known memory 910 allocation boundaries as a proactive defense 911 against bounds-checking flaws in the kernel's 912 copy_to_user()/copy_from_user() interface. 913 on Perform hardened usercopy checks (default). 914 off Disable hardened usercopy checks. 915 916 disable_radix [PPC] 917 Disable RADIX MMU mode on POWER9 918 919 disable_tlbie [PPC] 920 Disable TLBIE instruction. Currently does not work 921 with KVM, with HASH MMU, or with coherent accelerators. 922 923 disable_cpu_apicid= [X86,APIC,SMP] 924 Format: <int> 925 The number of initial APIC ID for the 926 corresponding CPU to be disabled at boot, 927 mostly used for the kdump 2nd kernel to 928 disable BSP to wake up multiple CPUs without 929 causing system reset or hang due to sending 930 INIT from AP to BSP. 931 932 perf_v4_pmi= [X86,INTEL] 933 Format: <bool> 934 Disable Intel PMU counter freezing feature. 935 The feature only exists starting from 936 Arch Perfmon v4 (Skylake and newer). 937 938 disable_ddw [PPC/PSERIES] 939 Disable Dynamic DMA Window support. Use this if 940 to workaround buggy firmware. 941 942 disable_ipv6= [IPV6] 943 See Documentation/networking/ipv6.rst. 944 945 disable_mtrr_cleanup [X86] 946 The kernel tries to adjust MTRR layout from continuous 947 to discrete, to make X server driver able to add WB 948 entry later. This parameter disables that. 949 950 disable_mtrr_trim [X86, Intel and AMD only] 951 By default the kernel will trim any uncacheable 952 memory out of your available memory pool based on 953 MTRR settings. This parameter disables that behavior, 954 possibly causing your machine to run very slowly. 955 956 disable_timer_pin_1 [X86] 957 Disable PIN 1 of APIC timer 958 Can be useful to work around chipset bugs. 959 960 dis_ucode_ldr [X86] Disable the microcode loader. 961 962 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 963 this option disables the debugging code at boot. 964 965 dma_debug_entries=<number> 966 This option allows to tune the number of preallocated 967 entries for DMA-API debugging code. One entry is 968 required per DMA-API allocation. Use this if the 969 DMA-API debugging code disables itself because the 970 architectural default is too low. 971 972 dma_debug_driver=<driver_name> 973 With this option the DMA-API debugging driver 974 filter feature can be enabled at boot time. Just 975 pass the driver to filter for as the parameter. 976 The filter can be disabled or changed to another 977 driver later using sysfs. 978 979 driver_async_probe= [KNL] 980 List of driver names to be probed asynchronously. 981 Format: <driver_name1>,<driver_name2>... 982 983 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 984 Broken monitors, graphic adapters, KVMs and EDIDless 985 panels may send no or incorrect EDID data sets. 986 This parameter allows to specify an EDID data sets 987 in the /lib/firmware directory that are used instead. 988 Generic built-in EDID data sets are used, if one of 989 edid/1024x768.bin, edid/1280x1024.bin, 990 edid/1680x1050.bin, or edid/1920x1080.bin is given 991 and no file with the same name exists. Details and 992 instructions how to build your own EDID data are 993 available in Documentation/admin-guide/edid.rst. An EDID 994 data set will only be used for a particular connector, 995 if its name and a colon are prepended to the EDID 996 name. Each connector may use a unique EDID data 997 set by separating the files with a comma. An EDID 998 data set with no connector name will be used for 999 any connectors not explicitly specified. 1000 1001 dscc4.setup= [NET] 1002 1003 dt_cpu_ftrs= [PPC] 1004 Format: {"off" | "known"} 1005 Control how the dt_cpu_ftrs device-tree binding is 1006 used for CPU feature discovery and setup (if it 1007 exists). 1008 off: Do not use it, fall back to legacy cpu table. 1009 known: Do not pass through unknown features to guests 1010 or userspace, only those that the kernel is aware of. 1011 1012 dump_apple_properties [X86] 1013 Dump name and content of EFI device properties on 1014 x86 Macs. Useful for driver authors to determine 1015 what data is available or for reverse-engineering. 1016 1017 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1018 module.dyndbg[="val"] 1019 Enable debug messages at boot time. See 1020 Documentation/admin-guide/dynamic-debug-howto.rst 1021 for details. 1022 1023 nopku [X86] Disable Memory Protection Keys CPU feature found 1024 in some Intel CPUs. 1025 1026 module.async_probe [KNL] 1027 Enable asynchronous probe on this module. 1028 1029 early_ioremap_debug [KNL] 1030 Enable debug messages in early_ioremap support. This 1031 is useful for tracking down temporary early mappings 1032 which are not unmapped. 1033 1034 earlycon= [KNL] Output early console device and options. 1035 1036 When used with no options, the early console is 1037 determined by stdout-path property in device tree's 1038 chosen node or the ACPI SPCR table if supported by 1039 the platform. 1040 1041 cdns,<addr>[,options] 1042 Start an early, polled-mode console on a Cadence 1043 (xuartps) serial port at the specified address. Only 1044 supported option is baud rate. If baud rate is not 1045 specified, the serial port must already be setup and 1046 configured. 1047 1048 uart[8250],io,<addr>[,options] 1049 uart[8250],mmio,<addr>[,options] 1050 uart[8250],mmio32,<addr>[,options] 1051 uart[8250],mmio32be,<addr>[,options] 1052 uart[8250],0x<addr>[,options] 1053 Start an early, polled-mode console on the 8250/16550 1054 UART at the specified I/O port or MMIO address. 1055 MMIO inter-register address stride is either 8-bit 1056 (mmio) or 32-bit (mmio32 or mmio32be). 1057 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1058 to be equivalent to 'mmio'. 'options' are specified 1059 in the same format described for "console=ttyS<n>"; if 1060 unspecified, the h/w is not initialized. 1061 1062 pl011,<addr> 1063 pl011,mmio32,<addr> 1064 Start an early, polled-mode console on a pl011 serial 1065 port at the specified address. The pl011 serial port 1066 must already be setup and configured. Options are not 1067 yet supported. If 'mmio32' is specified, then only 1068 the driver will use only 32-bit accessors to read/write 1069 the device registers. 1070 1071 meson,<addr> 1072 Start an early, polled-mode console on a meson serial 1073 port at the specified address. The serial port must 1074 already be setup and configured. Options are not yet 1075 supported. 1076 1077 msm_serial,<addr> 1078 Start an early, polled-mode console on an msm serial 1079 port at the specified address. The serial port 1080 must already be setup and configured. Options are not 1081 yet supported. 1082 1083 msm_serial_dm,<addr> 1084 Start an early, polled-mode console on an msm serial 1085 dm port at the specified address. The serial port 1086 must already be setup and configured. Options are not 1087 yet supported. 1088 1089 owl,<addr> 1090 Start an early, polled-mode console on a serial port 1091 of an Actions Semi SoC, such as S500 or S900, at the 1092 specified address. The serial port must already be 1093 setup and configured. Options are not yet supported. 1094 1095 rda,<addr> 1096 Start an early, polled-mode console on a serial port 1097 of an RDA Micro SoC, such as RDA8810PL, at the 1098 specified address. The serial port must already be 1099 setup and configured. Options are not yet supported. 1100 1101 sbi 1102 Use RISC-V SBI (Supervisor Binary Interface) for early 1103 console. 1104 1105 smh Use ARM semihosting calls for early console. 1106 1107 s3c2410,<addr> 1108 s3c2412,<addr> 1109 s3c2440,<addr> 1110 s3c6400,<addr> 1111 s5pv210,<addr> 1112 exynos4210,<addr> 1113 Use early console provided by serial driver available 1114 on Samsung SoCs, requires selecting proper type and 1115 a correct base address of the selected UART port. The 1116 serial port must already be setup and configured. 1117 Options are not yet supported. 1118 1119 lantiq,<addr> 1120 Start an early, polled-mode console on a lantiq serial 1121 (lqasc) port at the specified address. The serial port 1122 must already be setup and configured. Options are not 1123 yet supported. 1124 1125 lpuart,<addr> 1126 lpuart32,<addr> 1127 Use early console provided by Freescale LP UART driver 1128 found on Freescale Vybrid and QorIQ LS1021A processors. 1129 A valid base address must be provided, and the serial 1130 port must already be setup and configured. 1131 1132 ec_imx21,<addr> 1133 ec_imx6q,<addr> 1134 Start an early, polled-mode, output-only console on the 1135 Freescale i.MX UART at the specified address. The UART 1136 must already be setup and configured. 1137 1138 ar3700_uart,<addr> 1139 Start an early, polled-mode console on the 1140 Armada 3700 serial port at the specified 1141 address. The serial port must already be setup 1142 and configured. Options are not yet supported. 1143 1144 qcom_geni,<addr> 1145 Start an early, polled-mode console on a Qualcomm 1146 Generic Interface (GENI) based serial port at the 1147 specified address. The serial port must already be 1148 setup and configured. Options are not yet supported. 1149 1150 efifb,[options] 1151 Start an early, unaccelerated console on the EFI 1152 memory mapped framebuffer (if available). On cache 1153 coherent non-x86 systems that use system memory for 1154 the framebuffer, pass the 'ram' option so that it is 1155 mapped with the correct attributes. 1156 1157 linflex,<addr> 1158 Use early console provided by Freescale LINFlexD UART 1159 serial driver for NXP S32V234 SoCs. A valid base 1160 address must be provided, and the serial port must 1161 already be setup and configured. 1162 1163 earlyprintk= [X86,SH,ARM,M68k,S390] 1164 earlyprintk=vga 1165 earlyprintk=sclp 1166 earlyprintk=xen 1167 earlyprintk=serial[,ttySn[,baudrate]] 1168 earlyprintk=serial[,0x...[,baudrate]] 1169 earlyprintk=ttySn[,baudrate] 1170 earlyprintk=dbgp[debugController#] 1171 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1172 earlyprintk=xdbc[xhciController#] 1173 1174 earlyprintk is useful when the kernel crashes before 1175 the normal console is initialized. It is not enabled by 1176 default because it has some cosmetic problems. 1177 1178 Append ",keep" to not disable it when the real console 1179 takes over. 1180 1181 Only one of vga, efi, serial, or usb debug port can 1182 be used at a time. 1183 1184 Currently only ttyS0 and ttyS1 may be specified by 1185 name. Other I/O ports may be explicitly specified 1186 on some architectures (x86 and arm at least) by 1187 replacing ttySn with an I/O port address, like this: 1188 earlyprintk=serial,0x1008,115200 1189 You can find the port for a given device in 1190 /proc/tty/driver/serial: 1191 2: uart:ST16650V2 port:00001008 irq:18 ... 1192 1193 Interaction with the standard serial driver is not 1194 very good. 1195 1196 The VGA and EFI output is eventually overwritten by 1197 the real console. 1198 1199 The xen output can only be used by Xen PV guests. 1200 1201 The sclp output can only be used on s390. 1202 1203 The optional "force" to "pciserial" enables use of a 1204 PCI device even when its classcode is not of the 1205 UART class. 1206 1207 edac_report= [HW,EDAC] Control how to report EDAC event 1208 Format: {"on" | "off" | "force"} 1209 on: enable EDAC to report H/W event. May be overridden 1210 by other higher priority error reporting module. 1211 off: disable H/W event reporting through EDAC. 1212 force: enforce the use of EDAC to report H/W event. 1213 default: on. 1214 1215 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1216 ekgdboc=kbd 1217 1218 This is designed to be used in conjunction with 1219 the boot argument: earlyprintk=vga 1220 1221 This parameter works in place of the kgdboc parameter 1222 but can only be used if the backing tty is available 1223 very early in the boot process. For early debugging 1224 via a serial port see kgdboc_earlycon instead. 1225 1226 edd= [EDD] 1227 Format: {"off" | "on" | "skip[mbr]"} 1228 1229 efi= [EFI] 1230 Format: { "debug", "disable_early_pci_dma", 1231 "nochunk", "noruntime", "nosoftreserve", 1232 "novamap", "no_disable_early_pci_dma", 1233 "old_map" } 1234 debug: enable misc debug output. 1235 disable_early_pci_dma: disable the busmaster bit on all 1236 PCI bridges while in the EFI boot stub. 1237 nochunk: disable reading files in "chunks" in the EFI 1238 boot stub, as chunking can cause problems with some 1239 firmware implementations. 1240 noruntime : disable EFI runtime services support 1241 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1242 attribute may cause the kernel to reserve the 1243 memory range for a memory mapping driver to 1244 claim. Specify efi=nosoftreserve to disable this 1245 reservation and treat the memory by its base type 1246 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1247 novamap: do not call SetVirtualAddressMap(). 1248 no_disable_early_pci_dma: Leave the busmaster bit set 1249 on all PCI bridges while in the EFI boot stub 1250 old_map [X86-64]: switch to the old ioremap-based EFI 1251 runtime services mapping. [Needs CONFIG_X86_UV=y] 1252 1253 efi_no_storage_paranoia [EFI; X86] 1254 Using this parameter you can use more than 50% of 1255 your efi variable storage. Use this parameter only if 1256 you are really sure that your UEFI does sane gc and 1257 fulfills the spec otherwise your board may brick. 1258 1259 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1260 Add arbitrary attribute to specific memory range by 1261 updating original EFI memory map. 1262 Region of memory which aa attribute is added to is 1263 from ss to ss+nn. 1264 1265 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1266 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1267 attribute is added to range 0x100000000-0x180000000 and 1268 0x10a0000000-0x1120000000. 1269 1270 If efi_fake_mem=8G@9G:0x40000 is specified, the 1271 EFI_MEMORY_SP(0x40000) attribute is added to 1272 range 0x240000000-0x43fffffff. 1273 1274 Using this parameter you can do debugging of EFI memmap 1275 related features. For example, you can do debugging of 1276 Address Range Mirroring feature even if your box 1277 doesn't support it, or mark specific memory as 1278 "soft reserved". 1279 1280 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1281 that is to be dynamically loaded by Linux. If there are 1282 multiple variables with the same name but with different 1283 vendor GUIDs, all of them will be loaded. See 1284 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1285 1286 1287 eisa_irq_edge= [PARISC,HW] 1288 See header of drivers/parisc/eisa.c. 1289 1290 elanfreq= [X86-32] 1291 See comment before function elanfreq_setup() in 1292 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1293 1294 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1295 Specifies physical address of start of kernel core 1296 image elf header and optionally the size. Generally 1297 kexec loader will pass this option to capture kernel. 1298 See Documentation/admin-guide/kdump/kdump.rst for details. 1299 1300 enable_mtrr_cleanup [X86] 1301 The kernel tries to adjust MTRR layout from continuous 1302 to discrete, to make X server driver able to add WB 1303 entry later. This parameter enables that. 1304 1305 enable_timer_pin_1 [X86] 1306 Enable PIN 1 of APIC timer 1307 Can be useful to work around chipset bugs 1308 (in particular on some ATI chipsets). 1309 The kernel tries to set a reasonable default. 1310 1311 enforcing [SELINUX] Set initial enforcing status. 1312 Format: {"0" | "1"} 1313 See security/selinux/Kconfig help text. 1314 0 -- permissive (log only, no denials). 1315 1 -- enforcing (deny and log). 1316 Default value is 0. 1317 Value can be changed at runtime via 1318 /sys/fs/selinux/enforce. 1319 1320 erst_disable [ACPI] 1321 Disable Error Record Serialization Table (ERST) 1322 support. 1323 1324 ether= [HW,NET] Ethernet cards parameters 1325 This option is obsoleted by the "netdev=" option, which 1326 has equivalent usage. See its documentation for details. 1327 1328 evm= [EVM] 1329 Format: { "fix" } 1330 Permit 'security.evm' to be updated regardless of 1331 current integrity status. 1332 1333 failslab= 1334 fail_page_alloc= 1335 fail_make_request=[KNL] 1336 General fault injection mechanism. 1337 Format: <interval>,<probability>,<space>,<times> 1338 See also Documentation/fault-injection/. 1339 1340 floppy= [HW] 1341 See Documentation/admin-guide/blockdev/floppy.rst. 1342 1343 force_pal_cache_flush 1344 [IA-64] Avoid check_sal_cache_flush which may hang on 1345 buggy SAL_CACHE_FLUSH implementations. Using this 1346 parameter will force ia64_sal_cache_flush to call 1347 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1348 1349 forcepae [X86-32] 1350 Forcefully enable Physical Address Extension (PAE). 1351 Many Pentium M systems disable PAE but may have a 1352 functionally usable PAE implementation. 1353 Warning: use of this parameter will taint the kernel 1354 and may cause unknown problems. 1355 1356 ftrace=[tracer] 1357 [FTRACE] will set and start the specified tracer 1358 as early as possible in order to facilitate early 1359 boot debugging. 1360 1361 ftrace_dump_on_oops[=orig_cpu] 1362 [FTRACE] will dump the trace buffers on oops. 1363 If no parameter is passed, ftrace will dump 1364 buffers of all CPUs, but if you pass orig_cpu, it will 1365 dump only the buffer of the CPU that triggered the 1366 oops. 1367 1368 ftrace_filter=[function-list] 1369 [FTRACE] Limit the functions traced by the function 1370 tracer at boot up. function-list is a comma separated 1371 list of functions. This list can be changed at run 1372 time by the set_ftrace_filter file in the debugfs 1373 tracing directory. 1374 1375 ftrace_notrace=[function-list] 1376 [FTRACE] Do not trace the functions specified in 1377 function-list. This list can be changed at run time 1378 by the set_ftrace_notrace file in the debugfs 1379 tracing directory. 1380 1381 ftrace_graph_filter=[function-list] 1382 [FTRACE] Limit the top level callers functions traced 1383 by the function graph tracer at boot up. 1384 function-list is a comma separated list of functions 1385 that can be changed at run time by the 1386 set_graph_function file in the debugfs tracing directory. 1387 1388 ftrace_graph_notrace=[function-list] 1389 [FTRACE] Do not trace from the functions specified in 1390 function-list. This list is a comma separated list of 1391 functions that can be changed at run time by the 1392 set_graph_notrace file in the debugfs tracing directory. 1393 1394 ftrace_graph_max_depth=<uint> 1395 [FTRACE] Used with the function graph tracer. This is 1396 the max depth it will trace into a function. This value 1397 can be changed at run time by the max_graph_depth file 1398 in the tracefs tracing directory. default: 0 (no limit) 1399 1400 fw_devlink= [KNL] Create device links between consumer and supplier 1401 devices by scanning the firmware to infer the 1402 consumer/supplier relationships. This feature is 1403 especially useful when drivers are loaded as modules as 1404 it ensures proper ordering of tasks like device probing 1405 (suppliers first, then consumers), supplier boot state 1406 clean up (only after all consumers have probed), 1407 suspend/resume & runtime PM (consumers first, then 1408 suppliers). 1409 Format: { off | permissive | on | rpm } 1410 off -- Don't create device links from firmware info. 1411 permissive -- Create device links from firmware info 1412 but use it only for ordering boot state clean 1413 up (sync_state() calls). 1414 on -- Create device links from firmware info and use it 1415 to enforce probe and suspend/resume ordering. 1416 rpm -- Like "on", but also use to order runtime PM. 1417 1418 gamecon.map[2|3]= 1419 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1420 support via parallel port (up to 5 devices per port) 1421 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1422 See also Documentation/input/devices/joystick-parport.rst 1423 1424 gamma= [HW,DRM] 1425 1426 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1427 Format: off | on 1428 default: on 1429 1430 gcov_persist= [GCOV] When non-zero (default), profiling data for 1431 kernel modules is saved and remains accessible via 1432 debugfs, even when the module is unloaded/reloaded. 1433 When zero, profiling data is discarded and associated 1434 debugfs files are removed at module unload time. 1435 1436 goldfish [X86] Enable the goldfish android emulator platform. 1437 Don't use this when you are not running on the 1438 android emulator 1439 1440 gpt [EFI] Forces disk with valid GPT signature but 1441 invalid Protective MBR to be treated as GPT. If the 1442 primary GPT is corrupted, it enables the backup/alternate 1443 GPT to be used instead. 1444 1445 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1446 the "Enable 0" bit of the configuration register. 1447 Format: 0 | 1 1448 Default: 0 1449 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1450 the "Enable 0" bit of the configuration register. 1451 Format: 0 | 1 1452 Default: 0 1453 grcan.select= [HW] Select which physical interface to use. 1454 Format: 0 | 1 1455 Default: 0 1456 grcan.txsize= [HW] Sets the size of the tx buffer. 1457 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1458 Default: 1024 1459 grcan.rxsize= [HW] Sets the size of the rx buffer. 1460 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1461 Default: 1024 1462 1463 gpio-mockup.gpio_mockup_ranges 1464 [HW] Sets the ranges of gpiochip of for this device. 1465 Format: <start1>,<end1>,<start2>,<end2>... 1466 1467 hardlockup_all_cpu_backtrace= 1468 [KNL] Should the hard-lockup detector generate 1469 backtraces on all cpus. 1470 Format: 0 | 1 1471 1472 hashdist= [KNL,NUMA] Large hashes allocated during boot 1473 are distributed across NUMA nodes. Defaults on 1474 for 64-bit NUMA, off otherwise. 1475 Format: 0 | 1 (for off | on) 1476 1477 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1478 1479 hd= [EIDE] (E)IDE hard drive subsystem geometry 1480 Format: <cyl>,<head>,<sect> 1481 1482 hest_disable [ACPI] 1483 Disable Hardware Error Source Table (HEST) support; 1484 corresponding firmware-first mode error processing 1485 logic will be disabled. 1486 1487 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1488 size of <nn>. This works even on boxes that have no 1489 highmem otherwise. This also works to reduce highmem 1490 size on bigger boxes. 1491 1492 highres= [KNL] Enable/disable high resolution timer mode. 1493 Valid parameters: "on", "off" 1494 Default: "on" 1495 1496 hlt [BUGS=ARM,SH] 1497 1498 hpet= [X86-32,HPET] option to control HPET usage 1499 Format: { enable (default) | disable | force | 1500 verbose } 1501 disable: disable HPET and use PIT instead 1502 force: allow force enabled of undocumented chips (ICH4, 1503 VIA, nVidia) 1504 verbose: show contents of HPET registers during setup 1505 1506 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1507 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1508 1509 hugetlb_cma= [HW] The size of a cma area used for allocation 1510 of gigantic hugepages. 1511 Format: nn[KMGTPE] 1512 1513 Reserve a cma area of given size and allocate gigantic 1514 hugepages using the cma allocator. If enabled, the 1515 boot-time allocation of gigantic hugepages is skipped. 1516 1517 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1518 If this follows hugepagesz (below), it specifies 1519 the number of pages of hugepagesz to be allocated. 1520 If this is the first HugeTLB parameter on the command 1521 line, it specifies the number of pages to allocate for 1522 the default huge page size. See also 1523 Documentation/admin-guide/mm/hugetlbpage.rst. 1524 Format: <integer> 1525 1526 hugepagesz= 1527 [HW] The size of the HugeTLB pages. This is used in 1528 conjunction with hugepages (above) to allocate huge 1529 pages of a specific size at boot. The pair 1530 hugepagesz=X hugepages=Y can be specified once for 1531 each supported huge page size. Huge page sizes are 1532 architecture dependent. See also 1533 Documentation/admin-guide/mm/hugetlbpage.rst. 1534 Format: size[KMG] 1535 1536 hung_task_panic= 1537 [KNL] Should the hung task detector generate panics. 1538 Format: 0 | 1 1539 1540 A value of 1 instructs the kernel to panic when a 1541 hung task is detected. The default value is controlled 1542 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1543 option. The value selected by this boot parameter can 1544 be changed later by the kernel.hung_task_panic sysctl. 1545 1546 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1547 terminal devices. Valid values: 0..8 1548 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1549 If specified, z/VM IUCV HVC accepts connections 1550 from listed z/VM user IDs only. 1551 1552 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1553 which allow the hypervisor to 'idle' the 1554 guest on lock contention. 1555 1556 keep_bootcon [KNL] 1557 Do not unregister boot console at start. This is only 1558 useful for debugging when something happens in the window 1559 between unregistering the boot console and initializing 1560 the real console. 1561 1562 i2c_bus= [HW] Override the default board specific I2C bus speed 1563 or register an additional I2C bus that is not 1564 registered from board initialization code. 1565 Format: 1566 <bus_id>,<clkrate> 1567 1568 i8042.debug [HW] Toggle i8042 debug mode 1569 i8042.unmask_kbd_data 1570 [HW] Enable printing of interrupt data from the KBD port 1571 (disabled by default, and as a pre-condition 1572 requires that i8042.debug=1 be enabled) 1573 i8042.direct [HW] Put keyboard port into non-translated mode 1574 i8042.dumbkbd [HW] Pretend that controller can only read data from 1575 keyboard and cannot control its state 1576 (Don't attempt to blink the leds) 1577 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1578 i8042.nokbd [HW] Don't check/create keyboard port 1579 i8042.noloop [HW] Disable the AUX Loopback command while probing 1580 for the AUX port 1581 i8042.nomux [HW] Don't check presence of an active multiplexing 1582 controller 1583 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1584 controllers 1585 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1586 i8042.reset [HW] Reset the controller during init, cleanup and 1587 suspend-to-ram transitions, only during s2r 1588 transitions, or never reset 1589 Format: { 1 | Y | y | 0 | N | n } 1590 1, Y, y: always reset controller 1591 0, N, n: don't ever reset controller 1592 Default: only on s2r transitions on x86; most other 1593 architectures force reset to be always executed 1594 i8042.unlock [HW] Unlock (ignore) the keylock 1595 i8042.kbdreset [HW] Reset device connected to KBD port 1596 1597 i810= [HW,DRM] 1598 1599 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1600 indicates that the driver is running on unsupported 1601 hardware. 1602 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1603 does not match list of supported models. 1604 i8k.power_status 1605 [HW] Report power status in /proc/i8k 1606 (disabled by default) 1607 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1608 capability is set. 1609 1610 i915.invert_brightness= 1611 [DRM] Invert the sense of the variable that is used to 1612 set the brightness of the panel backlight. Normally a 1613 brightness value of 0 indicates backlight switched off, 1614 and the maximum of the brightness value sets the backlight 1615 to maximum brightness. If this parameter is set to 0 1616 (default) and the machine requires it, or this parameter 1617 is set to 1, a brightness value of 0 sets the backlight 1618 to maximum brightness, and the maximum of the brightness 1619 value switches the backlight off. 1620 -1 -- never invert brightness 1621 0 -- machine default 1622 1 -- force brightness inversion 1623 1624 icn= [HW,ISDN] 1625 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1626 1627 ide-core.nodma= [HW] (E)IDE subsystem 1628 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1629 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1630 .cdrom .chs .ignore_cable are additional options 1631 See Documentation/ide/ide.rst. 1632 1633 ide-generic.probe-mask= [HW] (E)IDE subsystem 1634 Format: <int> 1635 Probe mask for legacy ISA IDE ports. Depending on 1636 platform up to 6 ports are supported, enabled by 1637 setting corresponding bits in the mask to 1. The 1638 default value is 0x0, which has a special meaning. 1639 On systems that have PCI, it triggers scanning the 1640 PCI bus for the first and the second port, which 1641 are then probed. On systems without PCI the value 1642 of 0x0 enables probing the two first ports as if it 1643 was 0x3. 1644 1645 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1646 Claim all unknown PCI IDE storage controllers. 1647 1648 idle= [X86] 1649 Format: idle=poll, idle=halt, idle=nomwait 1650 Poll forces a polling idle loop that can slightly 1651 improve the performance of waking up a idle CPU, but 1652 will use a lot of power and make the system run hot. 1653 Not recommended. 1654 idle=halt: Halt is forced to be used for CPU idle. 1655 In such case C2/C3 won't be used again. 1656 idle=nomwait: Disable mwait for CPU C-states 1657 1658 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1659 Format: { strict | legacy | 2008 | relaxed } 1660 Default: strict 1661 1662 Choose which programs will be accepted for execution 1663 based on the IEEE 754 NaN encoding(s) supported by 1664 the FPU and the NaN encoding requested with the value 1665 of an ELF file header flag individually set by each 1666 binary. Hardware implementations are permitted to 1667 support either or both of the legacy and the 2008 NaN 1668 encoding mode. 1669 1670 Available settings are as follows: 1671 strict accept binaries that request a NaN encoding 1672 supported by the FPU 1673 legacy only accept legacy-NaN binaries, if supported 1674 by the FPU 1675 2008 only accept 2008-NaN binaries, if supported 1676 by the FPU 1677 relaxed accept any binaries regardless of whether 1678 supported by the FPU 1679 1680 The FPU emulator is always able to support both NaN 1681 encodings, so if no FPU hardware is present or it has 1682 been disabled with 'nofpu', then the settings of 1683 'legacy' and '2008' strap the emulator accordingly, 1684 'relaxed' straps the emulator for both legacy-NaN and 1685 2008-NaN, whereas 'strict' enables legacy-NaN only on 1686 legacy processors and both NaN encodings on MIPS32 or 1687 MIPS64 CPUs. 1688 1689 The setting for ABS.fmt/NEG.fmt instruction execution 1690 mode generally follows that for the NaN encoding, 1691 except where unsupported by hardware. 1692 1693 ignore_loglevel [KNL] 1694 Ignore loglevel setting - this will print /all/ 1695 kernel messages to the console. Useful for debugging. 1696 We also add it as printk module parameter, so users 1697 could change it dynamically, usually by 1698 /sys/module/printk/parameters/ignore_loglevel. 1699 1700 ignore_rlimit_data 1701 Ignore RLIMIT_DATA setting for data mappings, 1702 print warning at first misuse. Can be changed via 1703 /sys/module/kernel/parameters/ignore_rlimit_data. 1704 1705 ihash_entries= [KNL] 1706 Set number of hash buckets for inode cache. 1707 1708 ima_appraise= [IMA] appraise integrity measurements 1709 Format: { "off" | "enforce" | "fix" | "log" } 1710 default: "enforce" 1711 1712 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1713 The builtin appraise policy appraises all files 1714 owned by uid=0. 1715 1716 ima_canonical_fmt [IMA] 1717 Use the canonical format for the binary runtime 1718 measurements, instead of host native format. 1719 1720 ima_hash= [IMA] 1721 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1722 | sha512 | ... } 1723 default: "sha1" 1724 1725 The list of supported hash algorithms is defined 1726 in crypto/hash_info.h. 1727 1728 ima_policy= [IMA] 1729 The builtin policies to load during IMA setup. 1730 Format: "tcb | appraise_tcb | secure_boot | 1731 fail_securely" 1732 1733 The "tcb" policy measures all programs exec'd, files 1734 mmap'd for exec, and all files opened with the read 1735 mode bit set by either the effective uid (euid=0) or 1736 uid=0. 1737 1738 The "appraise_tcb" policy appraises the integrity of 1739 all files owned by root. 1740 1741 The "secure_boot" policy appraises the integrity 1742 of files (eg. kexec kernel image, kernel modules, 1743 firmware, policy, etc) based on file signatures. 1744 1745 The "fail_securely" policy forces file signature 1746 verification failure also on privileged mounted 1747 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1748 flag. 1749 1750 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1751 Load a policy which meets the needs of the Trusted 1752 Computing Base. This means IMA will measure all 1753 programs exec'd, files mmap'd for exec, and all files 1754 opened for read by uid=0. 1755 1756 ima_template= [IMA] 1757 Select one of defined IMA measurements template formats. 1758 Formats: { "ima" | "ima-ng" | "ima-sig" } 1759 Default: "ima-ng" 1760 1761 ima_template_fmt= 1762 [IMA] Define a custom template format. 1763 Format: { "field1|...|fieldN" } 1764 1765 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1766 Format: <min_file_size> 1767 Set the minimal file size for using asynchronous hash. 1768 If left unspecified, ahash usage is disabled. 1769 1770 ahash performance varies for different data sizes on 1771 different crypto accelerators. This option can be used 1772 to achieve the best performance for a particular HW. 1773 1774 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1775 Format: <bufsize> 1776 Set hashing buffer size. Default: 4k. 1777 1778 ahash performance varies for different chunk sizes on 1779 different crypto accelerators. This option can be used 1780 to achieve best performance for particular HW. 1781 1782 init= [KNL] 1783 Format: <full_path> 1784 Run specified binary instead of /sbin/init as init 1785 process. 1786 1787 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1788 for working out where the kernel is dying during 1789 startup. 1790 1791 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1792 initcall functions. Useful for debugging built-in 1793 modules and initcalls. 1794 1795 initrd= [BOOT] Specify the location of the initial ramdisk 1796 1797 initrdmem= [KNL] Specify a physical address and size from which to 1798 load the initrd. If an initrd is compiled in or 1799 specified in the bootparams, it takes priority over this 1800 setting. 1801 Format: ss[KMG],nn[KMG] 1802 Default is 0, 0 1803 1804 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1805 zeroes. 1806 Format: 0 | 1 1807 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1808 1809 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1810 Format: 0 | 1 1811 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1812 1813 init_pkru= [x86] Specify the default memory protection keys rights 1814 register contents for all processes. 0x55555554 by 1815 default (disallow access to all but pkey 0). Can 1816 override in debugfs after boot. 1817 1818 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1819 Format: <irq> 1820 1821 int_pln_enable [x86] Enable power limit notification interrupt 1822 1823 integrity_audit=[IMA] 1824 Format: { "0" | "1" } 1825 0 -- basic integrity auditing messages. (Default) 1826 1 -- additional integrity auditing messages. 1827 1828 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1829 on 1830 Enable intel iommu driver. 1831 off 1832 Disable intel iommu driver. 1833 igfx_off [Default Off] 1834 By default, gfx is mapped as normal device. If a gfx 1835 device has a dedicated DMAR unit, the DMAR unit is 1836 bypassed by not enabling DMAR with this option. In 1837 this case, gfx device will use physical address for 1838 DMA. 1839 forcedac [x86_64] 1840 With this option iommu will not optimize to look 1841 for io virtual address below 32-bit forcing dual 1842 address cycle on pci bus for cards supporting greater 1843 than 32-bit addressing. The default is to look 1844 for translation below 32-bit and if not available 1845 then look in the higher range. 1846 strict [Default Off] 1847 With this option on every unmap_single operation will 1848 result in a hardware IOTLB flush operation as opposed 1849 to batching them for performance. 1850 sp_off [Default Off] 1851 By default, super page will be supported if Intel IOMMU 1852 has the capability. With this option, super page will 1853 not be supported. 1854 sm_on [Default Off] 1855 By default, scalable mode will be disabled even if the 1856 hardware advertises that it has support for the scalable 1857 mode translation. With this option set, scalable mode 1858 will be used on hardware which claims to support it. 1859 tboot_noforce [Default Off] 1860 Do not force the Intel IOMMU enabled under tboot. 1861 By default, tboot will force Intel IOMMU on, which 1862 could harm performance of some high-throughput 1863 devices like 40GBit network cards, even if identity 1864 mapping is enabled. 1865 Note that using this option lowers the security 1866 provided by tboot because it makes the system 1867 vulnerable to DMA attacks. 1868 nobounce [Default off] 1869 Disable bounce buffer for untrusted devices such as 1870 the Thunderbolt devices. This will treat the untrusted 1871 devices as the trusted ones, hence might expose security 1872 risks of DMA attacks. 1873 1874 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1875 0 disables intel_idle and fall back on acpi_idle. 1876 1 to 9 specify maximum depth of C-state. 1877 1878 intel_pstate= [X86] 1879 disable 1880 Do not enable intel_pstate as the default 1881 scaling driver for the supported processors 1882 passive 1883 Use intel_pstate as a scaling driver, but configure it 1884 to work with generic cpufreq governors (instead of 1885 enabling its internal governor). This mode cannot be 1886 used along with the hardware-managed P-states (HWP) 1887 feature. 1888 force 1889 Enable intel_pstate on systems that prohibit it by default 1890 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1891 instead of acpi-cpufreq may disable platform features, such 1892 as thermal controls and power capping, that rely on ACPI 1893 P-States information being indicated to OSPM and therefore 1894 should be used with caution. This option does not work with 1895 processors that aren't supported by the intel_pstate driver 1896 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1897 no_hwp 1898 Do not enable hardware P state control (HWP) 1899 if available. 1900 hwp_only 1901 Only load intel_pstate on systems which support 1902 hardware P state control (HWP) if available. 1903 support_acpi_ppc 1904 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1905 Description Table, specifies preferred power management 1906 profile as "Enterprise Server" or "Performance Server", 1907 then this feature is turned on by default. 1908 per_cpu_perf_limits 1909 Allow per-logical-CPU P-State performance control limits using 1910 cpufreq sysfs interface 1911 1912 intremap= [X86-64, Intel-IOMMU] 1913 on enable Interrupt Remapping (default) 1914 off disable Interrupt Remapping 1915 nosid disable Source ID checking 1916 no_x2apic_optout 1917 BIOS x2APIC opt-out request will be ignored 1918 nopost disable Interrupt Posting 1919 1920 iomem= Disable strict checking of access to MMIO memory 1921 strict regions from userspace. 1922 relaxed 1923 1924 iommu= [x86] 1925 off 1926 force 1927 noforce 1928 biomerge 1929 panic 1930 nopanic 1931 merge 1932 nomerge 1933 soft 1934 pt [x86] 1935 nopt [x86] 1936 nobypass [PPC/POWERNV] 1937 Disable IOMMU bypass, using IOMMU for PCI devices. 1938 1939 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1940 Format: { "0" | "1" } 1941 0 - Lazy mode. 1942 Request that DMA unmap operations use deferred 1943 invalidation of hardware TLBs, for increased 1944 throughput at the cost of reduced device isolation. 1945 Will fall back to strict mode if not supported by 1946 the relevant IOMMU driver. 1947 1 - Strict mode (default). 1948 DMA unmap operations invalidate IOMMU hardware TLBs 1949 synchronously. 1950 1951 iommu.passthrough= 1952 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1953 Format: { "0" | "1" } 1954 0 - Use IOMMU translation for DMA. 1955 1 - Bypass the IOMMU for DMA. 1956 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1957 1958 io7= [HW] IO7 for Marvel based alpha systems 1959 See comment before marvel_specify_io7 in 1960 arch/alpha/kernel/core_marvel.c. 1961 1962 io_delay= [X86] I/O delay method 1963 0x80 1964 Standard port 0x80 based delay 1965 0xed 1966 Alternate port 0xed based delay (needed on some systems) 1967 udelay 1968 Simple two microseconds delay 1969 none 1970 No delay 1971 1972 ip= [IP_PNP] 1973 See Documentation/admin-guide/nfs/nfsroot.rst. 1974 1975 ipcmni_extend [KNL] Extend the maximum number of unique System V 1976 IPC identifiers from 32,768 to 16,777,216. 1977 1978 irqaffinity= [SMP] Set the default irq affinity mask 1979 The argument is a cpu list, as described above. 1980 1981 irqchip.gicv2_force_probe= 1982 [ARM, ARM64] 1983 Format: <bool> 1984 Force the kernel to look for the second 4kB page 1985 of a GICv2 controller even if the memory range 1986 exposed by the device tree is too small. 1987 1988 irqchip.gicv3_nolpi= 1989 [ARM, ARM64] 1990 Force the kernel to ignore the availability of 1991 LPIs (and by consequence ITSs). Intended for system 1992 that use the kernel as a bootloader, and thus want 1993 to let secondary kernels in charge of setting up 1994 LPIs. 1995 1996 irqchip.gicv3_pseudo_nmi= [ARM64] 1997 Enables support for pseudo-NMIs in the kernel. This 1998 requires the kernel to be built with 1999 CONFIG_ARM64_PSEUDO_NMI. 2000 2001 irqfixup [HW] 2002 When an interrupt is not handled search all handlers 2003 for it. Intended to get systems with badly broken 2004 firmware running. 2005 2006 irqpoll [HW] 2007 When an interrupt is not handled search all handlers 2008 for it. Also check all handlers each timer 2009 interrupt. Intended to get systems with badly broken 2010 firmware running. 2011 2012 isapnp= [ISAPNP] 2013 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2014 2015 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2016 [Deprecated - use cpusets instead] 2017 Format: [flag-list,]<cpu-list> 2018 2019 Specify one or more CPUs to isolate from disturbances 2020 specified in the flag list (default: domain): 2021 2022 nohz 2023 Disable the tick when a single task runs. 2024 2025 A residual 1Hz tick is offloaded to workqueues, which you 2026 need to affine to housekeeping through the global 2027 workqueue's affinity configured via the 2028 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2029 by using the 'domain' flag described below. 2030 2031 NOTE: by default the global workqueue runs on all CPUs, 2032 so to protect individual CPUs the 'cpumask' file has to 2033 be configured manually after bootup. 2034 2035 domain 2036 Isolate from the general SMP balancing and scheduling 2037 algorithms. Note that performing domain isolation this way 2038 is irreversible: it's not possible to bring back a CPU to 2039 the domains once isolated through isolcpus. It's strongly 2040 advised to use cpusets instead to disable scheduler load 2041 balancing through the "cpuset.sched_load_balance" file. 2042 It offers a much more flexible interface where CPUs can 2043 move in and out of an isolated set anytime. 2044 2045 You can move a process onto or off an "isolated" CPU via 2046 the CPU affinity syscalls or cpuset. 2047 <cpu number> begins at 0 and the maximum value is 2048 "number of CPUs in system - 1". 2049 2050 managed_irq 2051 2052 Isolate from being targeted by managed interrupts 2053 which have an interrupt mask containing isolated 2054 CPUs. The affinity of managed interrupts is 2055 handled by the kernel and cannot be changed via 2056 the /proc/irq/* interfaces. 2057 2058 This isolation is best effort and only effective 2059 if the automatically assigned interrupt mask of a 2060 device queue contains isolated and housekeeping 2061 CPUs. If housekeeping CPUs are online then such 2062 interrupts are directed to the housekeeping CPU 2063 so that IO submitted on the housekeeping CPU 2064 cannot disturb the isolated CPU. 2065 2066 If a queue's affinity mask contains only isolated 2067 CPUs then this parameter has no effect on the 2068 interrupt routing decision, though interrupts are 2069 only delivered when tasks running on those 2070 isolated CPUs submit IO. IO submitted on 2071 housekeeping CPUs has no influence on those 2072 queues. 2073 2074 The format of <cpu-list> is described above. 2075 2076 iucv= [HW,NET] 2077 2078 ivrs_ioapic [HW,X86_64] 2079 Provide an override to the IOAPIC-ID<->DEVICE-ID 2080 mapping provided in the IVRS ACPI table. For 2081 example, to map IOAPIC-ID decimal 10 to 2082 PCI device 00:14.0 write the parameter as: 2083 ivrs_ioapic[10]=00:14.0 2084 2085 ivrs_hpet [HW,X86_64] 2086 Provide an override to the HPET-ID<->DEVICE-ID 2087 mapping provided in the IVRS ACPI table. For 2088 example, to map HPET-ID decimal 0 to 2089 PCI device 00:14.0 write the parameter as: 2090 ivrs_hpet[0]=00:14.0 2091 2092 ivrs_acpihid [HW,X86_64] 2093 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2094 mapping provided in the IVRS ACPI table. For 2095 example, to map UART-HID:UID AMD0020:0 to 2096 PCI device 00:14.5 write the parameter as: 2097 ivrs_acpihid[00:14.5]=AMD0020:0 2098 2099 js= [HW,JOY] Analog joystick 2100 See Documentation/input/joydev/joystick.rst. 2101 2102 nokaslr [KNL] 2103 When CONFIG_RANDOMIZE_BASE is set, this disables 2104 kernel and module base offset ASLR (Address Space 2105 Layout Randomization). 2106 2107 kasan_multi_shot 2108 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2109 report on every invalid memory access. Without this 2110 parameter KASAN will print report only for the first 2111 invalid access. 2112 2113 keepinitrd [HW,ARM] 2114 2115 kernelcore= [KNL,X86,IA-64,PPC] 2116 Format: nn[KMGTPE] | nn% | "mirror" 2117 This parameter specifies the amount of memory usable by 2118 the kernel for non-movable allocations. The requested 2119 amount is spread evenly throughout all nodes in the 2120 system as ZONE_NORMAL. The remaining memory is used for 2121 movable memory in its own zone, ZONE_MOVABLE. In the 2122 event, a node is too small to have both ZONE_NORMAL and 2123 ZONE_MOVABLE, kernelcore memory will take priority and 2124 other nodes will have a larger ZONE_MOVABLE. 2125 2126 ZONE_MOVABLE is used for the allocation of pages that 2127 may be reclaimed or moved by the page migration 2128 subsystem. Note that allocations like PTEs-from-HighMem 2129 still use the HighMem zone if it exists, and the Normal 2130 zone if it does not. 2131 2132 It is possible to specify the exact amount of memory in 2133 the form of "nn[KMGTPE]", a percentage of total system 2134 memory in the form of "nn%", or "mirror". If "mirror" 2135 option is specified, mirrored (reliable) memory is used 2136 for non-movable allocations and remaining memory is used 2137 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2138 are exclusive, so you cannot specify multiple forms. 2139 2140 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2141 Format: <Controller#>[,poll interval] 2142 The controller # is the number of the ehci usb debug 2143 port as it is probed via PCI. The poll interval is 2144 optional and is the number seconds in between 2145 each poll cycle to the debug port in case you need 2146 the functionality for interrupting the kernel with 2147 gdb or control-c on the dbgp connection. When 2148 not using this parameter you use sysrq-g to break into 2149 the kernel debugger. 2150 2151 kgdboc= [KGDB,HW] kgdb over consoles. 2152 Requires a tty driver that supports console polling, 2153 or a supported polling keyboard driver (non-usb). 2154 Serial only format: <serial_device>[,baud] 2155 keyboard only format: kbd 2156 keyboard and serial format: kbd,<serial_device>[,baud] 2157 Optional Kernel mode setting: 2158 kms, kbd format: kms,kbd 2159 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2160 2161 kgdboc_earlycon= [KGDB,HW] 2162 If the boot console provides the ability to read 2163 characters and can work in polling mode, you can use 2164 this parameter to tell kgdb to use it as a backend 2165 until the normal console is registered. Intended to 2166 be used together with the kgdboc parameter which 2167 specifies the normal console to transition to. 2168 2169 The name of the early console should be specified 2170 as the value of this parameter. Note that the name of 2171 the early console might be different than the tty 2172 name passed to kgdboc. It's OK to leave the value 2173 blank and the first boot console that implements 2174 read() will be picked. 2175 2176 kgdbwait [KGDB] Stop kernel execution and enter the 2177 kernel debugger at the earliest opportunity. 2178 2179 kmac= [MIPS] korina ethernet MAC address. 2180 Configure the RouterBoard 532 series on-chip 2181 Ethernet adapter MAC address. 2182 2183 kmemleak= [KNL] Boot-time kmemleak enable/disable 2184 Valid arguments: on, off 2185 Default: on 2186 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2187 the default is off. 2188 2189 kprobe_event=[probe-list] 2190 [FTRACE] Add kprobe events and enable at boot time. 2191 The probe-list is a semicolon delimited list of probe 2192 definitions. Each definition is same as kprobe_events 2193 interface, but the parameters are comma delimited. 2194 For example, to add a kprobe event on vfs_read with 2195 arg1 and arg2, add to the command line; 2196 2197 kprobe_event=p,vfs_read,$arg1,$arg2 2198 2199 See also Documentation/trace/kprobetrace.rst "Kernel 2200 Boot Parameter" section. 2201 2202 kpti= [ARM64] Control page table isolation of user 2203 and kernel address spaces. 2204 Default: enabled on cores which need mitigation. 2205 0: force disabled 2206 1: force enabled 2207 2208 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2209 Default is 0 (don't ignore, but inject #GP) 2210 2211 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2212 Default is false (don't support). 2213 2214 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2215 KVM MMU at runtime. 2216 Default is 0 (off) 2217 2218 kvm.nx_huge_pages= 2219 [KVM] Controls the software workaround for the 2220 X86_BUG_ITLB_MULTIHIT bug. 2221 force : Always deploy workaround. 2222 off : Never deploy workaround. 2223 auto : Deploy workaround based on the presence of 2224 X86_BUG_ITLB_MULTIHIT. 2225 2226 Default is 'auto'. 2227 2228 If the software workaround is enabled for the host, 2229 guests do need not to enable it for nested guests. 2230 2231 kvm.nx_huge_pages_recovery_ratio= 2232 [KVM] Controls how many 4KiB pages are periodically zapped 2233 back to huge pages. 0 disables the recovery, otherwise if 2234 the value is N KVM will zap 1/Nth of the 4KiB pages every 2235 minute. The default is 60. 2236 2237 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2238 Default is 1 (enabled) 2239 2240 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2241 for all guests. 2242 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2243 2244 kvm-arm.vgic_v3_group0_trap= 2245 [KVM,ARM] Trap guest accesses to GICv3 group-0 2246 system registers 2247 2248 kvm-arm.vgic_v3_group1_trap= 2249 [KVM,ARM] Trap guest accesses to GICv3 group-1 2250 system registers 2251 2252 kvm-arm.vgic_v3_common_trap= 2253 [KVM,ARM] Trap guest accesses to GICv3 common 2254 system registers 2255 2256 kvm-arm.vgic_v4_enable= 2257 [KVM,ARM] Allow use of GICv4 for direct injection of 2258 LPIs. 2259 2260 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2261 (virtualized MMU) support on capable Intel chips. 2262 Default is 1 (enabled) 2263 2264 kvm-intel.emulate_invalid_guest_state= 2265 [KVM,Intel] Enable emulation of invalid guest states 2266 Default is 0 (disabled) 2267 2268 kvm-intel.flexpriority= 2269 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2270 Default is 1 (enabled) 2271 2272 kvm-intel.nested= 2273 [KVM,Intel] Enable VMX nesting (nVMX). 2274 Default is 0 (disabled) 2275 2276 kvm-intel.unrestricted_guest= 2277 [KVM,Intel] Disable unrestricted guest feature 2278 (virtualized real and unpaged mode) on capable 2279 Intel chips. Default is 1 (enabled) 2280 2281 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2282 CVE-2018-3620. 2283 2284 Valid arguments: never, cond, always 2285 2286 always: L1D cache flush on every VMENTER. 2287 cond: Flush L1D on VMENTER only when the code between 2288 VMEXIT and VMENTER can leak host memory. 2289 never: Disables the mitigation 2290 2291 Default is cond (do L1 cache flush in specific instances) 2292 2293 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2294 feature (tagged TLBs) on capable Intel chips. 2295 Default is 1 (enabled) 2296 2297 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2298 affected CPUs 2299 2300 The kernel PTE inversion protection is unconditionally 2301 enabled and cannot be disabled. 2302 2303 full 2304 Provides all available mitigations for the 2305 L1TF vulnerability. Disables SMT and 2306 enables all mitigations in the 2307 hypervisors, i.e. unconditional L1D flush. 2308 2309 SMT control and L1D flush control via the 2310 sysfs interface is still possible after 2311 boot. Hypervisors will issue a warning 2312 when the first VM is started in a 2313 potentially insecure configuration, 2314 i.e. SMT enabled or L1D flush disabled. 2315 2316 full,force 2317 Same as 'full', but disables SMT and L1D 2318 flush runtime control. Implies the 2319 'nosmt=force' command line option. 2320 (i.e. sysfs control of SMT is disabled.) 2321 2322 flush 2323 Leaves SMT enabled and enables the default 2324 hypervisor mitigation, i.e. conditional 2325 L1D flush. 2326 2327 SMT control and L1D flush control via the 2328 sysfs interface is still possible after 2329 boot. Hypervisors will issue a warning 2330 when the first VM is started in a 2331 potentially insecure configuration, 2332 i.e. SMT enabled or L1D flush disabled. 2333 2334 flush,nosmt 2335 2336 Disables SMT and enables the default 2337 hypervisor mitigation. 2338 2339 SMT control and L1D flush control via the 2340 sysfs interface is still possible after 2341 boot. Hypervisors will issue a warning 2342 when the first VM is started in a 2343 potentially insecure configuration, 2344 i.e. SMT enabled or L1D flush disabled. 2345 2346 flush,nowarn 2347 Same as 'flush', but hypervisors will not 2348 warn when a VM is started in a potentially 2349 insecure configuration. 2350 2351 off 2352 Disables hypervisor mitigations and doesn't 2353 emit any warnings. 2354 It also drops the swap size and available 2355 RAM limit restriction on both hypervisor and 2356 bare metal. 2357 2358 Default is 'flush'. 2359 2360 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2361 2362 l2cr= [PPC] 2363 2364 l3cr= [PPC] 2365 2366 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2367 disabled it. 2368 2369 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2370 value for LAPIC timer one-shot implementation. Default 2371 back to the programmable timer unit in the LAPIC. 2372 2373 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2374 in C2 power state. 2375 2376 libata.dma= [LIBATA] DMA control 2377 libata.dma=0 Disable all PATA and SATA DMA 2378 libata.dma=1 PATA and SATA Disk DMA only 2379 libata.dma=2 ATAPI (CDROM) DMA only 2380 libata.dma=4 Compact Flash DMA only 2381 Combinations also work, so libata.dma=3 enables DMA 2382 for disks and CDROMs, but not CFs. 2383 2384 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2385 libata.ignore_hpa=0 keep BIOS limits (default) 2386 libata.ignore_hpa=1 ignore limits, using full disk 2387 2388 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2389 when set. 2390 Format: <int> 2391 2392 libata.force= [LIBATA] Force configurations. The format is comma 2393 separated list of "[ID:]VAL" where ID is 2394 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2395 matching port, link or device. Basically, it matches 2396 the ATA ID string printed on console by libata. If 2397 the whole ID part is omitted, the last PORT and DEVICE 2398 values are used. If ID hasn't been specified yet, the 2399 configuration applies to all ports, links and devices. 2400 2401 If only DEVICE is omitted, the parameter applies to 2402 the port and all links and devices behind it. DEVICE 2403 number of 0 either selects the first device or the 2404 first fan-out link behind PMP device. It does not 2405 select the host link. DEVICE number of 15 selects the 2406 host link and device attached to it. 2407 2408 The VAL specifies the configuration to force. As long 2409 as there's no ambiguity shortcut notation is allowed. 2410 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2411 The following configurations can be forced. 2412 2413 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2414 Any ID with matching PORT is used. 2415 2416 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2417 2418 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2419 udma[/][16,25,33,44,66,100,133] notation is also 2420 allowed. 2421 2422 * [no]ncq: Turn on or off NCQ. 2423 2424 * [no]ncqtrim: Turn off queued DSM TRIM. 2425 2426 * nohrst, nosrst, norst: suppress hard, soft 2427 and both resets. 2428 2429 * rstonce: only attempt one reset during 2430 hot-unplug link recovery 2431 2432 * dump_id: dump IDENTIFY data. 2433 2434 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2435 2436 * disable: Disable this device. 2437 2438 If there are multiple matching configurations changing 2439 the same attribute, the last one is used. 2440 2441 memblock=debug [KNL] Enable memblock debug messages. 2442 2443 load_ramdisk= [RAM] List of ramdisks to load from floppy 2444 See Documentation/admin-guide/blockdev/ramdisk.rst. 2445 2446 lockd.nlm_grace_period=P [NFS] Assign grace period. 2447 Format: <integer> 2448 2449 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2450 Format: <integer> 2451 2452 lockd.nlm_timeout=T [NFS] Assign timeout value. 2453 Format: <integer> 2454 2455 lockd.nlm_udpport=M [NFS] Assign UDP port. 2456 Format: <integer> 2457 2458 lockdown= [SECURITY] 2459 { integrity | confidentiality } 2460 Enable the kernel lockdown feature. If set to 2461 integrity, kernel features that allow userland to 2462 modify the running kernel are disabled. If set to 2463 confidentiality, kernel features that allow userland 2464 to extract confidential information from the kernel 2465 are also disabled. 2466 2467 locktorture.nreaders_stress= [KNL] 2468 Set the number of locking read-acquisition kthreads. 2469 Defaults to being automatically set based on the 2470 number of online CPUs. 2471 2472 locktorture.nwriters_stress= [KNL] 2473 Set the number of locking write-acquisition kthreads. 2474 2475 locktorture.onoff_holdoff= [KNL] 2476 Set time (s) after boot for CPU-hotplug testing. 2477 2478 locktorture.onoff_interval= [KNL] 2479 Set time (s) between CPU-hotplug operations, or 2480 zero to disable CPU-hotplug testing. 2481 2482 locktorture.shuffle_interval= [KNL] 2483 Set task-shuffle interval (jiffies). Shuffling 2484 tasks allows some CPUs to go into dyntick-idle 2485 mode during the locktorture test. 2486 2487 locktorture.shutdown_secs= [KNL] 2488 Set time (s) after boot system shutdown. This 2489 is useful for hands-off automated testing. 2490 2491 locktorture.stat_interval= [KNL] 2492 Time (s) between statistics printk()s. 2493 2494 locktorture.stutter= [KNL] 2495 Time (s) to stutter testing, for example, 2496 specifying five seconds causes the test to run for 2497 five seconds, wait for five seconds, and so on. 2498 This tests the locking primitive's ability to 2499 transition abruptly to and from idle. 2500 2501 locktorture.torture_type= [KNL] 2502 Specify the locking implementation to test. 2503 2504 locktorture.verbose= [KNL] 2505 Enable additional printk() statements. 2506 2507 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2508 Format: <irq> 2509 2510 loglevel= All Kernel Messages with a loglevel smaller than the 2511 console loglevel will be printed to the console. It can 2512 also be changed with klogd or other programs. The 2513 loglevels are defined as follows: 2514 2515 0 (KERN_EMERG) system is unusable 2516 1 (KERN_ALERT) action must be taken immediately 2517 2 (KERN_CRIT) critical conditions 2518 3 (KERN_ERR) error conditions 2519 4 (KERN_WARNING) warning conditions 2520 5 (KERN_NOTICE) normal but significant condition 2521 6 (KERN_INFO) informational 2522 7 (KERN_DEBUG) debug-level messages 2523 2524 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2525 in bytes. n must be a power of two and greater 2526 than the minimal size. The minimal size is defined 2527 by LOG_BUF_SHIFT kernel config parameter. There is 2528 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2529 that allows to increase the default size depending on 2530 the number of CPUs. See init/Kconfig for more details. 2531 2532 logo.nologo [FB] Disables display of the built-in Linux logo. 2533 This may be used to provide more screen space for 2534 kernel log messages and is useful when debugging 2535 kernel boot problems. 2536 2537 lp=0 [LP] Specify parallel ports to use, e.g, 2538 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2539 lp=reset first parallel port). 'lp=0' disables the 2540 lp=auto printer driver. 'lp=reset' (which can be 2541 specified in addition to the ports) causes 2542 attached printers to be reset. Using 2543 lp=port1,port2,... specifies the parallel ports 2544 to associate lp devices with, starting with 2545 lp0. A port specification may be 'none' to skip 2546 that lp device, or a parport name such as 2547 'parport0'. Specifying 'lp=auto' instead of a 2548 port specification list means that device IDs 2549 from each port should be examined, to see if 2550 an IEEE 1284-compliant printer is attached; if 2551 so, the driver will manage that printer. 2552 See also header of drivers/char/lp.c. 2553 2554 lpj=n [KNL] 2555 Sets loops_per_jiffy to given constant, thus avoiding 2556 time-consuming boot-time autodetection (up to 250 ms per 2557 CPU). 0 enables autodetection (default). To determine 2558 the correct value for your kernel, boot with normal 2559 autodetection and see what value is printed. Note that 2560 on SMP systems the preset will be applied to all CPUs, 2561 which is likely to cause problems if your CPUs need 2562 significantly divergent settings. An incorrect value 2563 will cause delays in the kernel to be wrong, leading to 2564 unpredictable I/O errors and other breakage. Although 2565 unlikely, in the extreme case this might damage your 2566 hardware. 2567 2568 ltpc= [NET] 2569 Format: <io>,<irq>,<dma> 2570 2571 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2572 2573 lsm=lsm1,...,lsmN 2574 [SECURITY] Choose order of LSM initialization. This 2575 overrides CONFIG_LSM, and the "security=" parameter. 2576 2577 machvec= [IA-64] Force the use of a particular machine-vector 2578 (machvec) in a generic kernel. 2579 Example: machvec=hpzx1 2580 2581 machtype= [Loongson] Share the same kernel image file between different 2582 yeeloong laptop. 2583 Example: machtype=lemote-yeeloong-2f-7inch 2584 2585 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2586 than or equal to this physical address is ignored. 2587 2588 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2589 will bring up during bootup. maxcpus=n : n >= 0 limits 2590 the kernel to bring up 'n' processors. Surely after 2591 bootup you can bring up the other plugged cpu by executing 2592 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2593 only takes effect during system bootup. 2594 While n=0 is a special case, it is equivalent to "nosmp", 2595 which also disables the IO APIC. 2596 2597 max_loop= [LOOP] The number of loop block devices that get 2598 (loop.max_loop) unconditionally pre-created at init time. The default 2599 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2600 of statically allocating a predefined number, loop 2601 devices can be requested on-demand with the 2602 /dev/loop-control interface. 2603 2604 mce [X86-32] Machine Check Exception 2605 2606 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2607 2608 md= [HW] RAID subsystems devices and level 2609 See Documentation/admin-guide/md.rst. 2610 2611 mdacon= [MDA] 2612 Format: <first>,<last> 2613 Specifies range of consoles to be captured by the MDA. 2614 2615 mds= [X86,INTEL] 2616 Control mitigation for the Micro-architectural Data 2617 Sampling (MDS) vulnerability. 2618 2619 Certain CPUs are vulnerable to an exploit against CPU 2620 internal buffers which can forward information to a 2621 disclosure gadget under certain conditions. 2622 2623 In vulnerable processors, the speculatively 2624 forwarded data can be used in a cache side channel 2625 attack, to access data to which the attacker does 2626 not have direct access. 2627 2628 This parameter controls the MDS mitigation. The 2629 options are: 2630 2631 full - Enable MDS mitigation on vulnerable CPUs 2632 full,nosmt - Enable MDS mitigation and disable 2633 SMT on vulnerable CPUs 2634 off - Unconditionally disable MDS mitigation 2635 2636 On TAA-affected machines, mds=off can be prevented by 2637 an active TAA mitigation as both vulnerabilities are 2638 mitigated with the same mechanism so in order to disable 2639 this mitigation, you need to specify tsx_async_abort=off 2640 too. 2641 2642 Not specifying this option is equivalent to 2643 mds=full. 2644 2645 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2646 2647 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2648 Amount of memory to be used in cases as follows: 2649 2650 1 for test; 2651 2 when the kernel is not able to see the whole system memory; 2652 3 memory that lies after 'mem=' boundary is excluded from 2653 the hypervisor, then assigned to KVM guests. 2654 2655 [X86] Work as limiting max address. Use together 2656 with memmap= to avoid physical address space collisions. 2657 Without memmap= PCI devices could be placed at addresses 2658 belonging to unused RAM. 2659 2660 Note that this only takes effects during boot time since 2661 in above case 3, memory may need be hot added after boot 2662 if system memory of hypervisor is not sufficient. 2663 2664 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2665 memory. 2666 2667 memchunk=nn[KMG] 2668 [KNL,SH] Allow user to override the default size for 2669 per-device physically contiguous DMA buffers. 2670 2671 memhp_default_state=online/offline 2672 [KNL] Set the initial state for the memory hotplug 2673 onlining policy. If not specified, the default value is 2674 set according to the 2675 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2676 option. 2677 See Documentation/admin-guide/mm/memory-hotplug.rst. 2678 2679 memmap=exactmap [KNL,X86] Enable setting of an exact 2680 E820 memory map, as specified by the user. 2681 Such memmap=exactmap lines can be constructed based on 2682 BIOS output or other requirements. See the memmap=nn@ss 2683 option description. 2684 2685 memmap=nn[KMG]@ss[KMG] 2686 [KNL] Force usage of a specific region of memory. 2687 Region of memory to be used is from ss to ss+nn. 2688 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2689 which limits max address to nn[KMG]. 2690 Multiple different regions can be specified, 2691 comma delimited. 2692 Example: 2693 memmap=100M@2G,100M#3G,1G!1024G 2694 2695 memmap=nn[KMG]#ss[KMG] 2696 [KNL,ACPI] Mark specific memory as ACPI data. 2697 Region of memory to be marked is from ss to ss+nn. 2698 2699 memmap=nn[KMG]$ss[KMG] 2700 [KNL,ACPI] Mark specific memory as reserved. 2701 Region of memory to be reserved is from ss to ss+nn. 2702 Example: Exclude memory from 0x18690000-0x1869ffff 2703 memmap=64K$0x18690000 2704 or 2705 memmap=0x10000$0x18690000 2706 Some bootloaders may need an escape character before '$', 2707 like Grub2, otherwise '$' and the following number 2708 will be eaten. 2709 2710 memmap=nn[KMG]!ss[KMG] 2711 [KNL,X86] Mark specific memory as protected. 2712 Region of memory to be used, from ss to ss+nn. 2713 The memory region may be marked as e820 type 12 (0xc) 2714 and is NVDIMM or ADR memory. 2715 2716 memmap=<size>%<offset>-<oldtype>+<newtype> 2717 [KNL,ACPI] Convert memory within the specified region 2718 from <oldtype> to <newtype>. If "-<oldtype>" is left 2719 out, the whole region will be marked as <newtype>, 2720 even if previously unavailable. If "+<newtype>" is left 2721 out, matching memory will be removed. Types are 2722 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2723 3 = ACPI, 12 = PRAM. 2724 2725 memory_corruption_check=0/1 [X86] 2726 Some BIOSes seem to corrupt the first 64k of 2727 memory when doing things like suspend/resume. 2728 Setting this option will scan the memory 2729 looking for corruption. Enabling this will 2730 both detect corruption and prevent the kernel 2731 from using the memory being corrupted. 2732 However, its intended as a diagnostic tool; if 2733 repeatable BIOS-originated corruption always 2734 affects the same memory, you can use memmap= 2735 to prevent the kernel from using that memory. 2736 2737 memory_corruption_check_size=size [X86] 2738 By default it checks for corruption in the low 2739 64k, making this memory unavailable for normal 2740 use. Use this parameter to scan for 2741 corruption in more or less memory. 2742 2743 memory_corruption_check_period=seconds [X86] 2744 By default it checks for corruption every 60 2745 seconds. Use this parameter to check at some 2746 other rate. 0 disables periodic checking. 2747 2748 memtest= [KNL,X86,ARM,PPC] Enable memtest 2749 Format: <integer> 2750 default : 0 <disable> 2751 Specifies the number of memtest passes to be 2752 performed. Each pass selects another test 2753 pattern from a given set of patterns. Memtest 2754 fills the memory with this pattern, validates 2755 memory contents and reserves bad memory 2756 regions that are detected. 2757 2758 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2759 Valid arguments: on, off 2760 Default (depends on kernel configuration option): 2761 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2762 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2763 mem_encrypt=on: Activate SME 2764 mem_encrypt=off: Do not activate SME 2765 2766 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2767 for details on when memory encryption can be activated. 2768 2769 mem_sleep_default= [SUSPEND] Default system suspend mode: 2770 s2idle - Suspend-To-Idle 2771 shallow - Power-On Suspend or equivalent (if supported) 2772 deep - Suspend-To-RAM or equivalent (if supported) 2773 See Documentation/admin-guide/pm/sleep-states.rst. 2774 2775 meye.*= [HW] Set MotionEye Camera parameters 2776 See Documentation/admin-guide/media/meye.rst. 2777 2778 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2779 Multi-Function General Purpose Timers on AMD Geode 2780 platforms. 2781 2782 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2783 the BIOS has incorrectly applied a workaround. TinyBIOS 2784 version 0.98 is known to be affected, 0.99 fixes the 2785 problem by letting the user disable the workaround. 2786 2787 mga= [HW,DRM] 2788 2789 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2790 physical address is ignored. 2791 2792 mini2440= [ARM,HW,KNL] 2793 Format:[0..2][b][c][t] 2794 Default: "0tb" 2795 MINI2440 configuration specification: 2796 0 - The attached screen is the 3.5" TFT 2797 1 - The attached screen is the 7" TFT 2798 2 - The VGA Shield is attached (1024x768) 2799 Leaving out the screen size parameter will not load 2800 the TFT driver, and the framebuffer will be left 2801 unconfigured. 2802 b - Enable backlight. The TFT backlight pin will be 2803 linked to the kernel VESA blanking code and a GPIO 2804 LED. This parameter is not necessary when using the 2805 VGA shield. 2806 c - Enable the s3c camera interface. 2807 t - Reserved for enabling touchscreen support. The 2808 touchscreen support is not enabled in the mainstream 2809 kernel as of 2.6.30, a preliminary port can be found 2810 in the "bleeding edge" mini2440 support kernel at 2811 https://repo.or.cz/w/linux-2.6/mini2440.git 2812 2813 mitigations= 2814 [X86,PPC,S390,ARM64] Control optional mitigations for 2815 CPU vulnerabilities. This is a set of curated, 2816 arch-independent options, each of which is an 2817 aggregation of existing arch-specific options. 2818 2819 off 2820 Disable all optional CPU mitigations. This 2821 improves system performance, but it may also 2822 expose users to several CPU vulnerabilities. 2823 Equivalent to: nopti [X86,PPC] 2824 kpti=0 [ARM64] 2825 nospectre_v1 [X86,PPC] 2826 nobp=0 [S390] 2827 nospectre_v2 [X86,PPC,S390,ARM64] 2828 spectre_v2_user=off [X86] 2829 spec_store_bypass_disable=off [X86,PPC] 2830 ssbd=force-off [ARM64] 2831 l1tf=off [X86] 2832 mds=off [X86] 2833 tsx_async_abort=off [X86] 2834 kvm.nx_huge_pages=off [X86] 2835 2836 Exceptions: 2837 This does not have any effect on 2838 kvm.nx_huge_pages when 2839 kvm.nx_huge_pages=force. 2840 2841 auto (default) 2842 Mitigate all CPU vulnerabilities, but leave SMT 2843 enabled, even if it's vulnerable. This is for 2844 users who don't want to be surprised by SMT 2845 getting disabled across kernel upgrades, or who 2846 have other ways of avoiding SMT-based attacks. 2847 Equivalent to: (default behavior) 2848 2849 auto,nosmt 2850 Mitigate all CPU vulnerabilities, disabling SMT 2851 if needed. This is for users who always want to 2852 be fully mitigated, even if it means losing SMT. 2853 Equivalent to: l1tf=flush,nosmt [X86] 2854 mds=full,nosmt [X86] 2855 tsx_async_abort=full,nosmt [X86] 2856 2857 mminit_loglevel= 2858 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2859 parameter allows control of the logging verbosity for 2860 the additional memory initialisation checks. A value 2861 of 0 disables mminit logging and a level of 4 will 2862 log everything. Information is printed at KERN_DEBUG 2863 so loglevel=8 may also need to be specified. 2864 2865 module.sig_enforce 2866 [KNL] When CONFIG_MODULE_SIG is set, this means that 2867 modules without (valid) signatures will fail to load. 2868 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2869 is always true, so this option does nothing. 2870 2871 module_blacklist= [KNL] Do not load a comma-separated list of 2872 modules. Useful for debugging problem modules. 2873 2874 mousedev.tap_time= 2875 [MOUSE] Maximum time between finger touching and 2876 leaving touchpad surface for touch to be considered 2877 a tap and be reported as a left button click (for 2878 touchpads working in absolute mode only). 2879 Format: <msecs> 2880 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2881 reporting absolute coordinates, such as tablets 2882 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2883 reporting absolute coordinates, such as tablets 2884 2885 movablecore= [KNL,X86,IA-64,PPC] 2886 Format: nn[KMGTPE] | nn% 2887 This parameter is the complement to kernelcore=, it 2888 specifies the amount of memory used for migratable 2889 allocations. If both kernelcore and movablecore is 2890 specified, then kernelcore will be at *least* the 2891 specified value but may be more. If movablecore on its 2892 own is specified, the administrator must be careful 2893 that the amount of memory usable for all allocations 2894 is not too small. 2895 2896 movable_node [KNL] Boot-time switch to make hotplugable memory 2897 NUMA nodes to be movable. This means that the memory 2898 of such nodes will be usable only for movable 2899 allocations which rules out almost all kernel 2900 allocations. Use with caution! 2901 2902 MTD_Partition= [MTD] 2903 Format: <name>,<region-number>,<size>,<offset> 2904 2905 MTD_Region= [MTD] Format: 2906 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2907 2908 mtdparts= [MTD] 2909 See drivers/mtd/parsers/cmdlinepart.c 2910 2911 multitce=off [PPC] This parameter disables the use of the pSeries 2912 firmware feature for updating multiple TCE entries 2913 at a time. 2914 2915 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2916 2917 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2918 2919 boundary - index of last SLC block on Flex-OneNAND. 2920 The remaining blocks are configured as MLC blocks. 2921 lock - Configure if Flex-OneNAND boundary should be locked. 2922 Once locked, the boundary cannot be changed. 2923 1 indicates lock status, 0 indicates unlock status. 2924 2925 mtdset= [ARM] 2926 ARM/S3C2412 JIVE boot control 2927 2928 See arch/arm/mach-s3c2412/mach-jive.c 2929 2930 mtouchusb.raw_coordinates= 2931 [HW] Make the MicroTouch USB driver use raw coordinates 2932 ('y', default) or cooked coordinates ('n') 2933 2934 mtrr_chunk_size=nn[KMG] [X86] 2935 used for mtrr cleanup. It is largest continuous chunk 2936 that could hold holes aka. UC entries. 2937 2938 mtrr_gran_size=nn[KMG] [X86] 2939 Used for mtrr cleanup. It is granularity of mtrr block. 2940 Default is 1. 2941 Large value could prevent small alignment from 2942 using up MTRRs. 2943 2944 mtrr_spare_reg_nr=n [X86] 2945 Format: <integer> 2946 Range: 0,7 : spare reg number 2947 Default : 1 2948 Used for mtrr cleanup. It is spare mtrr entries number. 2949 Set to 2 or more if your graphical card needs more. 2950 2951 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2952 2953 netdev= [NET] Network devices parameters 2954 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2955 Note that mem_start is often overloaded to mean 2956 something different and driver-specific. 2957 This usage is only documented in each driver source 2958 file if at all. 2959 2960 nf_conntrack.acct= 2961 [NETFILTER] Enable connection tracking flow accounting 2962 0 to disable accounting 2963 1 to enable accounting 2964 Default value is 0. 2965 2966 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2967 See Documentation/admin-guide/nfs/nfsroot.rst. 2968 2969 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2970 See Documentation/admin-guide/nfs/nfsroot.rst. 2971 2972 nfsrootdebug [NFS] enable nfsroot debugging messages. 2973 See Documentation/admin-guide/nfs/nfsroot.rst. 2974 2975 nfs.callback_nr_threads= 2976 [NFSv4] set the total number of threads that the 2977 NFS client will assign to service NFSv4 callback 2978 requests. 2979 2980 nfs.callback_tcpport= 2981 [NFS] set the TCP port on which the NFSv4 callback 2982 channel should listen. 2983 2984 nfs.cache_getent= 2985 [NFS] sets the pathname to the program which is used 2986 to update the NFS client cache entries. 2987 2988 nfs.cache_getent_timeout= 2989 [NFS] sets the timeout after which an attempt to 2990 update a cache entry is deemed to have failed. 2991 2992 nfs.idmap_cache_timeout= 2993 [NFS] set the maximum lifetime for idmapper cache 2994 entries. 2995 2996 nfs.enable_ino64= 2997 [NFS] enable 64-bit inode numbers. 2998 If zero, the NFS client will fake up a 32-bit inode 2999 number for the readdir() and stat() syscalls instead 3000 of returning the full 64-bit number. 3001 The default is to return 64-bit inode numbers. 3002 3003 nfs.max_session_cb_slots= 3004 [NFSv4.1] Sets the maximum number of session 3005 slots the client will assign to the callback 3006 channel. This determines the maximum number of 3007 callbacks the client will process in parallel for 3008 a particular server. 3009 3010 nfs.max_session_slots= 3011 [NFSv4.1] Sets the maximum number of session slots 3012 the client will attempt to negotiate with the server. 3013 This limits the number of simultaneous RPC requests 3014 that the client can send to the NFSv4.1 server. 3015 Note that there is little point in setting this 3016 value higher than the max_tcp_slot_table_limit. 3017 3018 nfs.nfs4_disable_idmapping= 3019 [NFSv4] When set to the default of '1', this option 3020 ensures that both the RPC level authentication 3021 scheme and the NFS level operations agree to use 3022 numeric uids/gids if the mount is using the 3023 'sec=sys' security flavour. In effect it is 3024 disabling idmapping, which can make migration from 3025 legacy NFSv2/v3 systems to NFSv4 easier. 3026 Servers that do not support this mode of operation 3027 will be autodetected by the client, and it will fall 3028 back to using the idmapper. 3029 To turn off this behaviour, set the value to '0'. 3030 nfs.nfs4_unique_id= 3031 [NFS4] Specify an additional fixed unique ident- 3032 ification string that NFSv4 clients can insert into 3033 their nfs_client_id4 string. This is typically a 3034 UUID that is generated at system install time. 3035 3036 nfs.send_implementation_id = 3037 [NFSv4.1] Send client implementation identification 3038 information in exchange_id requests. 3039 If zero, no implementation identification information 3040 will be sent. 3041 The default is to send the implementation identification 3042 information. 3043 3044 nfs.recover_lost_locks = 3045 [NFSv4] Attempt to recover locks that were lost due 3046 to a lease timeout on the server. Please note that 3047 doing this risks data corruption, since there are 3048 no guarantees that the file will remain unchanged 3049 after the locks are lost. 3050 If you want to enable the kernel legacy behaviour of 3051 attempting to recover these locks, then set this 3052 parameter to '1'. 3053 The default parameter value of '0' causes the kernel 3054 not to attempt recovery of lost locks. 3055 3056 nfs4.layoutstats_timer = 3057 [NFSv4.2] Change the rate at which the kernel sends 3058 layoutstats to the pNFS metadata server. 3059 3060 Setting this to value to 0 causes the kernel to use 3061 whatever value is the default set by the layout 3062 driver. A non-zero value sets the minimum interval 3063 in seconds between layoutstats transmissions. 3064 3065 nfsd.nfs4_disable_idmapping= 3066 [NFSv4] When set to the default of '1', the NFSv4 3067 server will return only numeric uids and gids to 3068 clients using auth_sys, and will accept numeric uids 3069 and gids from such clients. This is intended to ease 3070 migration from NFSv2/v3. 3071 3072 nmi_debug= [KNL,SH] Specify one or more actions to take 3073 when a NMI is triggered. 3074 Format: [state][,regs][,debounce][,die] 3075 3076 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3077 Format: [panic,][nopanic,][num] 3078 Valid num: 0 or 1 3079 0 - turn hardlockup detector in nmi_watchdog off 3080 1 - turn hardlockup detector in nmi_watchdog on 3081 When panic is specified, panic when an NMI watchdog 3082 timeout occurs (or 'nopanic' to not panic on an NMI 3083 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3084 To disable both hard and soft lockup detectors, 3085 please see 'nowatchdog'. 3086 This is useful when you use a panic=... timeout and 3087 need the box quickly up again. 3088 3089 These settings can be accessed at runtime via 3090 the nmi_watchdog and hardlockup_panic sysctls. 3091 3092 netpoll.carrier_timeout= 3093 [NET] Specifies amount of time (in seconds) that 3094 netpoll should wait for a carrier. By default netpoll 3095 waits 4 seconds. 3096 3097 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3098 emulation library even if a 387 maths coprocessor 3099 is present. 3100 3101 no5lvl [X86-64] Disable 5-level paging mode. Forces 3102 kernel to use 4-level paging instead. 3103 3104 nofsgsbase [X86] Disables FSGSBASE instructions. 3105 3106 no_console_suspend 3107 [HW] Never suspend the console 3108 Disable suspending of consoles during suspend and 3109 hibernate operations. Once disabled, debugging 3110 messages can reach various consoles while the rest 3111 of the system is being put to sleep (ie, while 3112 debugging driver suspend/resume hooks). This may 3113 not work reliably with all consoles, but is known 3114 to work with serial and VGA consoles. 3115 To facilitate more flexible debugging, we also add 3116 console_suspend, a printk module parameter to control 3117 it. Users could use console_suspend (usually 3118 /sys/module/printk/parameters/console_suspend) to 3119 turn on/off it dynamically. 3120 3121 novmcoredd [KNL,KDUMP] 3122 Disable device dump. Device dump allows drivers to 3123 append dump data to vmcore so you can collect driver 3124 specified debug info. Drivers can append the data 3125 without any limit and this data is stored in memory, 3126 so this may cause significant memory stress. Disabling 3127 device dump can help save memory but the driver debug 3128 data will be no longer available. This parameter 3129 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3130 is set. 3131 3132 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3133 caches in the slab allocator. Saves per-node memory, 3134 but will impact performance. 3135 3136 noalign [KNL,ARM] 3137 3138 noaltinstr [S390] Disables alternative instructions patching 3139 (CPU alternatives feature). 3140 3141 noapic [SMP,APIC] Tells the kernel to not make use of any 3142 IOAPICs that may be present in the system. 3143 3144 noautogroup Disable scheduler automatic task group creation. 3145 3146 nobats [PPC] Do not use BATs for mapping kernel lowmem 3147 on "Classic" PPC cores. 3148 3149 nocache [ARM] 3150 3151 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3152 3153 nodelayacct [KNL] Disable per-task delay accounting 3154 3155 nodsp [SH] Disable hardware DSP at boot time. 3156 3157 noefi Disable EFI runtime services support. 3158 3159 noexec [IA-64] 3160 3161 noexec [X86] 3162 On X86-32 available only on PAE configured kernels. 3163 noexec=on: enable non-executable mappings (default) 3164 noexec=off: disable non-executable mappings 3165 3166 nosmap [X86,PPC] 3167 Disable SMAP (Supervisor Mode Access Prevention) 3168 even if it is supported by processor. 3169 3170 nosmep [X86,PPC] 3171 Disable SMEP (Supervisor Mode Execution Prevention) 3172 even if it is supported by processor. 3173 3174 noexec32 [X86-64] 3175 This affects only 32-bit executables. 3176 noexec32=on: enable non-executable mappings (default) 3177 read doesn't imply executable mappings 3178 noexec32=off: disable non-executable mappings 3179 read implies executable mappings 3180 3181 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3182 3183 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3184 register save and restore. The kernel will only save 3185 legacy floating-point registers on task switch. 3186 3187 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 3188 3189 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3190 Equivalent to smt=1. 3191 3192 [KNL,x86] Disable symmetric multithreading (SMT). 3193 nosmt=force: Force disable SMT, cannot be undone 3194 via the sysfs control file. 3195 3196 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3197 (bounds check bypass). With this option data leaks are 3198 possible in the system. 3199 3200 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3201 the Spectre variant 2 (indirect branch prediction) 3202 vulnerability. System may allow data leaks with this 3203 option. 3204 3205 nospec_store_bypass_disable 3206 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3207 3208 noxsave [BUGS=X86] Disables x86 extended register state save 3209 and restore using xsave. The kernel will fallback to 3210 enabling legacy floating-point and sse state. 3211 3212 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3213 register states. The kernel will fall back to use 3214 xsave to save the states. By using this parameter, 3215 performance of saving the states is degraded because 3216 xsave doesn't support modified optimization while 3217 xsaveopt supports it on xsaveopt enabled systems. 3218 3219 noxsaves [X86] Disables xsaves and xrstors used in saving and 3220 restoring x86 extended register state in compacted 3221 form of xsave area. The kernel will fall back to use 3222 xsaveopt and xrstor to save and restore the states 3223 in standard form of xsave area. By using this 3224 parameter, xsave area per process might occupy more 3225 memory on xsaves enabled systems. 3226 3227 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3228 wfi(ARM) instruction doesn't work correctly and not to 3229 use it. This is also useful when using JTAG debugger. 3230 3231 no_file_caps Tells the kernel not to honor file capabilities. The 3232 only way then for a file to be executed with privilege 3233 is to be setuid root or executed by root. 3234 3235 nohalt [IA-64] Tells the kernel not to use the power saving 3236 function PAL_HALT_LIGHT when idle. This increases 3237 power-consumption. On the positive side, it reduces 3238 interrupt wake-up latency, which may improve performance 3239 in certain environments such as networked servers or 3240 real-time systems. 3241 3242 nohibernate [HIBERNATION] Disable hibernation and resume. 3243 3244 nohz= [KNL] Boottime enable/disable dynamic ticks 3245 Valid arguments: on, off 3246 Default: on 3247 3248 nohz_full= [KNL,BOOT,SMP,ISOL] 3249 The argument is a cpu list, as described above. 3250 In kernels built with CONFIG_NO_HZ_FULL=y, set 3251 the specified list of CPUs whose tick will be stopped 3252 whenever possible. The boot CPU will be forced outside 3253 the range to maintain the timekeeping. Any CPUs 3254 in this list will have their RCU callbacks offloaded, 3255 just as if they had also been called out in the 3256 rcu_nocbs= boot parameter. 3257 3258 noiotrap [SH] Disables trapped I/O port accesses. 3259 3260 noirqdebug [X86-32] Disables the code which attempts to detect and 3261 disable unhandled interrupt sources. 3262 3263 no_timer_check [X86,APIC] Disables the code which tests for 3264 broken timer IRQ sources. 3265 3266 noisapnp [ISAPNP] Disables ISA PnP code. 3267 3268 noinitrd [RAM] Tells the kernel not to load any configured 3269 initial RAM disk. 3270 3271 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3272 remapping. 3273 [Deprecated - use intremap=off] 3274 3275 nointroute [IA-64] 3276 3277 noinvpcid [X86] Disable the INVPCID cpu feature. 3278 3279 nojitter [IA-64] Disables jitter checking for ITC timers. 3280 3281 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3282 3283 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3284 fault handling. 3285 3286 no-vmw-sched-clock 3287 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3288 clock and use the default one. 3289 3290 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3291 accounting. steal time is computed, but won't 3292 influence scheduler behaviour 3293 3294 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3295 3296 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3297 3298 noltlbs [PPC] Do not use large page/tlb entries for kernel 3299 lowmem mapping on PPC40x and PPC8xx 3300 3301 nomca [IA-64] Disable machine check abort handling 3302 3303 nomce [X86-32] Disable Machine Check Exception 3304 3305 nomfgpt [X86-32] Disable Multi-Function General Purpose 3306 Timer usage (for AMD Geode machines). 3307 3308 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3309 shutdown the other cpus. Instead use the REBOOT_VECTOR 3310 irq. 3311 3312 nomodule Disable module load 3313 3314 nopat [X86] Disable PAT (page attribute table extension of 3315 pagetables) support. 3316 3317 nopcid [X86-64] Disable the PCID cpu feature. 3318 3319 norandmaps Don't use address space randomization. Equivalent to 3320 echo 0 > /proc/sys/kernel/randomize_va_space 3321 3322 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3323 with UP alternatives 3324 3325 nordrand [X86] Disable kernel use of the RDRAND and 3326 RDSEED instructions even if they are supported 3327 by the processor. RDRAND and RDSEED are still 3328 available to user space applications. 3329 3330 noresume [SWSUSP] Disables resume and restores original swap 3331 space. 3332 3333 no-scroll [VGA] Disables scrollback. 3334 This is required for the Braillex ib80-piezo Braille 3335 reader made by F.H. Papenmeier (Germany). 3336 3337 nosbagart [IA-64] 3338 3339 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3340 3341 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3342 and disable the IO APIC. legacy for "maxcpus=0". 3343 3344 nosoftlockup [KNL] Disable the soft-lockup detector. 3345 3346 nosync [HW,M68K] Disables sync negotiation for all devices. 3347 3348 nowatchdog [KNL] Disable both lockup detectors, i.e. 3349 soft-lockup and NMI watchdog (hard-lockup). 3350 3351 nowb [ARM] 3352 3353 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3354 3355 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3356 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3357 Some features depend on CPU0. Known dependencies are: 3358 1. Resume from suspend/hibernate depends on CPU0. 3359 Suspend/hibernate will fail if CPU0 is offline and you 3360 need to online CPU0 before suspend/hibernate. 3361 2. PIC interrupts also depend on CPU0. CPU0 can't be 3362 removed if a PIC interrupt is detected. 3363 It's said poweroff/reboot may depend on CPU0 on some 3364 machines although I haven't seen such issues so far 3365 after CPU0 is offline on a few tested machines. 3366 If the dependencies are under your control, you can 3367 turn on cpu0_hotplug. 3368 3369 nps_mtm_hs_ctr= [KNL,ARC] 3370 This parameter sets the maximum duration, in 3371 cycles, each HW thread of the CTOP can run 3372 without interruptions, before HW switches it. 3373 The actual maximum duration is 16 times this 3374 parameter's value. 3375 Format: integer between 1 and 255 3376 Default: 255 3377 3378 nptcg= [IA-64] Override max number of concurrent global TLB 3379 purges which is reported from either PAL_VM_SUMMARY or 3380 SAL PALO. 3381 3382 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3383 could support. nr_cpus=n : n >= 1 limits the kernel to 3384 support 'n' processors. It could be larger than the 3385 number of already plugged CPU during bootup, later in 3386 runtime you can physically add extra cpu until it reaches 3387 n. So during boot up some boot time memory for per-cpu 3388 variables need be pre-allocated for later physical cpu 3389 hot plugging. 3390 3391 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3392 3393 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3394 Allowed values are enable and disable 3395 3396 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3397 'node', 'default' can be specified 3398 This can be set from sysctl after boot. 3399 See Documentation/admin-guide/sysctl/vm.rst for details. 3400 3401 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3402 See Documentation/core-api/debugging-via-ohci1394.rst for more 3403 info. 3404 3405 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3406 Rather than timing out after 20 ms if an EC 3407 command is not properly ACKed, override the length 3408 of the timeout. We have interrupts disabled while 3409 waiting for the ACK, so if this is set too high 3410 interrupts *may* be lost! 3411 3412 omap_mux= [OMAP] Override bootloader pin multiplexing. 3413 Format: <mux_mode0.mode_name=value>... 3414 For example, to override I2C bus2: 3415 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3416 3417 oprofile.timer= [HW] 3418 Use timer interrupt instead of performance counters 3419 3420 oprofile.cpu_type= Force an oprofile cpu type 3421 This might be useful if you have an older oprofile 3422 userland or if you want common events. 3423 Format: { arch_perfmon } 3424 arch_perfmon: [X86] Force use of architectural 3425 perfmon on Intel CPUs instead of the 3426 CPU specific event set. 3427 timer: [X86] Force use of architectural NMI 3428 timer mode (see also oprofile.timer 3429 for generic hr timer mode) 3430 3431 oops=panic Always panic on oopses. Default is to just kill the 3432 process, but there is a small probability of 3433 deadlocking the machine. 3434 This will also cause panics on machine check exceptions. 3435 Useful together with panic=30 to trigger a reboot. 3436 3437 page_alloc.shuffle= 3438 [KNL] Boolean flag to control whether the page allocator 3439 should randomize its free lists. The randomization may 3440 be automatically enabled if the kernel detects it is 3441 running on a platform with a direct-mapped memory-side 3442 cache, and this parameter can be used to 3443 override/disable that behavior. The state of the flag 3444 can be read from sysfs at: 3445 /sys/module/page_alloc/parameters/shuffle. 3446 3447 page_owner= [KNL] Boot-time page_owner enabling option. 3448 Storage of the information about who allocated 3449 each page is disabled in default. With this switch, 3450 we can turn it on. 3451 on: enable the feature 3452 3453 page_poison= [KNL] Boot-time parameter changing the state of 3454 poisoning on the buddy allocator, available with 3455 CONFIG_PAGE_POISONING=y. 3456 off: turn off poisoning (default) 3457 on: turn on poisoning 3458 3459 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3460 timeout > 0: seconds before rebooting 3461 timeout = 0: wait forever 3462 timeout < 0: reboot immediately 3463 Format: <timeout> 3464 3465 panic_print= Bitmask for printing system info when panic happens. 3466 User can chose combination of the following bits: 3467 bit 0: print all tasks info 3468 bit 1: print system memory info 3469 bit 2: print timer info 3470 bit 3: print locks info if CONFIG_LOCKDEP is on 3471 bit 4: print ftrace buffer 3472 bit 5: print all printk messages in buffer 3473 3474 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3475 Format: <hex>[,nousertaint] 3476 Hexadecimal bitmask representing the set of TAINT flags 3477 that will cause the kernel to panic when add_taint() is 3478 called with any of the flags in this set. 3479 The optional switch "nousertaint" can be utilized to 3480 prevent userspace forced crashes by writing to sysctl 3481 /proc/sys/kernel/tainted any flagset matching with the 3482 bitmask set on panic_on_taint. 3483 See Documentation/admin-guide/tainted-kernels.rst for 3484 extra details on the taint flags that users can pick 3485 to compose the bitmask to assign to panic_on_taint. 3486 3487 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3488 on a WARN(). 3489 3490 crash_kexec_post_notifiers 3491 Run kdump after running panic-notifiers and dumping 3492 kmsg. This only for the users who doubt kdump always 3493 succeeds in any situation. 3494 Note that this also increases risks of kdump failure, 3495 because some panic notifiers can make the crashed 3496 kernel more unstable. 3497 3498 parkbd.port= [HW] Parallel port number the keyboard adapter is 3499 connected to, default is 0. 3500 Format: <parport#> 3501 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3502 0 for XT, 1 for AT (default is AT). 3503 Format: <mode> 3504 3505 parport= [HW,PPT] Specify parallel ports. 0 disables. 3506 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3507 Use 'auto' to force the driver to use any 3508 IRQ/DMA settings detected (the default is to 3509 ignore detected IRQ/DMA settings because of 3510 possible conflicts). You can specify the base 3511 address, IRQ, and DMA settings; IRQ and DMA 3512 should be numbers, or 'auto' (for using detected 3513 settings on that particular port), or 'nofifo' 3514 (to avoid using a FIFO even if it is detected). 3515 Parallel ports are assigned in the order they 3516 are specified on the command line, starting 3517 with parport0. 3518 3519 parport_init_mode= [HW,PPT] 3520 Configure VIA parallel port to operate in 3521 a specific mode. This is necessary on Pegasos 3522 computer where firmware has no options for setting 3523 up parallel port mode and sets it to spp. 3524 Currently this function knows 686a and 8231 chips. 3525 Format: [spp|ps2|epp|ecp|ecpepp] 3526 3527 pause_on_oops= 3528 Halt all CPUs after the first oops has been printed for 3529 the specified number of seconds. This is to be used if 3530 your oopses keep scrolling off the screen. 3531 3532 pcbit= [HW,ISDN] 3533 3534 pcd. [PARIDE] 3535 See header of drivers/block/paride/pcd.c. 3536 See also Documentation/admin-guide/blockdev/paride.rst. 3537 3538 pci=option[,option...] [PCI] various PCI subsystem options. 3539 3540 Some options herein operate on a specific device 3541 or a set of devices (<pci_dev>). These are 3542 specified in one of the following formats: 3543 3544 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3545 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3546 3547 Note: the first format specifies a PCI 3548 bus/device/function address which may change 3549 if new hardware is inserted, if motherboard 3550 firmware changes, or due to changes caused 3551 by other kernel parameters. If the 3552 domain is left unspecified, it is 3553 taken to be zero. Optionally, a path 3554 to a device through multiple device/function 3555 addresses can be specified after the base 3556 address (this is more robust against 3557 renumbering issues). The second format 3558 selects devices using IDs from the 3559 configuration space which may match multiple 3560 devices in the system. 3561 3562 earlydump dump PCI config space before the kernel 3563 changes anything 3564 off [X86] don't probe for the PCI bus 3565 bios [X86-32] force use of PCI BIOS, don't access 3566 the hardware directly. Use this if your machine 3567 has a non-standard PCI host bridge. 3568 nobios [X86-32] disallow use of PCI BIOS, only direct 3569 hardware access methods are allowed. Use this 3570 if you experience crashes upon bootup and you 3571 suspect they are caused by the BIOS. 3572 conf1 [X86] Force use of PCI Configuration Access 3573 Mechanism 1 (config address in IO port 0xCF8, 3574 data in IO port 0xCFC, both 32-bit). 3575 conf2 [X86] Force use of PCI Configuration Access 3576 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3577 the function, IO port 0xCFA, also 8-bit, sets 3578 bus number. The config space is then accessed 3579 through ports 0xC000-0xCFFF). 3580 See http://wiki.osdev.org/PCI for more info 3581 on the configuration access mechanisms. 3582 noaer [PCIE] If the PCIEAER kernel config parameter is 3583 enabled, this kernel boot option can be used to 3584 disable the use of PCIE advanced error reporting. 3585 nodomains [PCI] Disable support for multiple PCI 3586 root domains (aka PCI segments, in ACPI-speak). 3587 nommconf [X86] Disable use of MMCONFIG for PCI 3588 Configuration 3589 check_enable_amd_mmconf [X86] check for and enable 3590 properly configured MMIO access to PCI 3591 config space on AMD family 10h CPU 3592 nomsi [MSI] If the PCI_MSI kernel config parameter is 3593 enabled, this kernel boot option can be used to 3594 disable the use of MSI interrupts system-wide. 3595 noioapicquirk [APIC] Disable all boot interrupt quirks. 3596 Safety option to keep boot IRQs enabled. This 3597 should never be necessary. 3598 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3599 primary IO-APIC for bridges that cannot disable 3600 boot IRQs. This fixes a source of spurious IRQs 3601 when the system masks IRQs. 3602 noioapicreroute [APIC] Disable workaround that uses the 3603 boot IRQ equivalent of an IRQ that connects to 3604 a chipset where boot IRQs cannot be disabled. 3605 The opposite of ioapicreroute. 3606 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3607 routing table. These calls are known to be buggy 3608 on several machines and they hang the machine 3609 when used, but on other computers it's the only 3610 way to get the interrupt routing table. Try 3611 this option if the kernel is unable to allocate 3612 IRQs or discover secondary PCI buses on your 3613 motherboard. 3614 rom [X86] Assign address space to expansion ROMs. 3615 Use with caution as certain devices share 3616 address decoders between ROMs and other 3617 resources. 3618 norom [X86] Do not assign address space to 3619 expansion ROMs that do not already have 3620 BIOS assigned address ranges. 3621 nobar [X86] Do not assign address space to the 3622 BARs that weren't assigned by the BIOS. 3623 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3624 assigned automatically to PCI devices. You can 3625 make the kernel exclude IRQs of your ISA cards 3626 this way. 3627 pirqaddr=0xAAAAA [X86] Specify the physical address 3628 of the PIRQ table (normally generated 3629 by the BIOS) if it is outside the 3630 F0000h-100000h range. 3631 lastbus=N [X86] Scan all buses thru bus #N. Can be 3632 useful if the kernel is unable to find your 3633 secondary buses and you want to tell it 3634 explicitly which ones they are. 3635 assign-busses [X86] Always assign all PCI bus 3636 numbers ourselves, overriding 3637 whatever the firmware may have done. 3638 usepirqmask [X86] Honor the possible IRQ mask stored 3639 in the BIOS $PIR table. This is needed on 3640 some systems with broken BIOSes, notably 3641 some HP Pavilion N5400 and Omnibook XE3 3642 notebooks. This will have no effect if ACPI 3643 IRQ routing is enabled. 3644 noacpi [X86] Do not use ACPI for IRQ routing 3645 or for PCI scanning. 3646 use_crs [X86] Use PCI host bridge window information 3647 from ACPI. On BIOSes from 2008 or later, this 3648 is enabled by default. If you need to use this, 3649 please report a bug. 3650 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3651 If you need to use this, please report a bug. 3652 routeirq Do IRQ routing for all PCI devices. 3653 This is normally done in pci_enable_device(), 3654 so this option is a temporary workaround 3655 for broken drivers that don't call it. 3656 skip_isa_align [X86] do not align io start addr, so can 3657 handle more pci cards 3658 noearly [X86] Don't do any early type 1 scanning. 3659 This might help on some broken boards which 3660 machine check when some devices' config space 3661 is read. But various workarounds are disabled 3662 and some IOMMU drivers will not work. 3663 bfsort Sort PCI devices into breadth-first order. 3664 This sorting is done to get a device 3665 order compatible with older (<= 2.4) kernels. 3666 nobfsort Don't sort PCI devices into breadth-first order. 3667 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3668 tuning and use the BIOS-configured MPS defaults. 3669 pcie_bus_safe Set every device's MPS to the largest value 3670 supported by all devices below the root complex. 3671 pcie_bus_perf Set device MPS to the largest allowable MPS 3672 based on its parent bus. Also set MRRS (Max 3673 Read Request Size) to the largest supported 3674 value (no larger than the MPS that the device 3675 or bus can support) for best performance. 3676 pcie_bus_peer2peer Set every device's MPS to 128B, which 3677 every device is guaranteed to support. This 3678 configuration allows peer-to-peer DMA between 3679 any pair of devices, possibly at the cost of 3680 reduced performance. This also guarantees 3681 that hot-added devices will work. 3682 cbiosize=nn[KMG] The fixed amount of bus space which is 3683 reserved for the CardBus bridge's IO window. 3684 The default value is 256 bytes. 3685 cbmemsize=nn[KMG] The fixed amount of bus space which is 3686 reserved for the CardBus bridge's memory 3687 window. The default value is 64 megabytes. 3688 resource_alignment= 3689 Format: 3690 [<order of align>@]<pci_dev>[; ...] 3691 Specifies alignment and device to reassign 3692 aligned memory resources. How to 3693 specify the device is described above. 3694 If <order of align> is not specified, 3695 PAGE_SIZE is used as alignment. 3696 A PCI-PCI bridge can be specified if resource 3697 windows need to be expanded. 3698 To specify the alignment for several 3699 instances of a device, the PCI vendor, 3700 device, subvendor, and subdevice may be 3701 specified, e.g., 12@pci:8086:9c22:103c:198f 3702 for 4096-byte alignment. 3703 ecrc= Enable/disable PCIe ECRC (transaction layer 3704 end-to-end CRC checking). 3705 bios: Use BIOS/firmware settings. This is the 3706 the default. 3707 off: Turn ECRC off 3708 on: Turn ECRC on. 3709 hpiosize=nn[KMG] The fixed amount of bus space which is 3710 reserved for hotplug bridge's IO window. 3711 Default size is 256 bytes. 3712 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3713 reserved for hotplug bridge's MMIO window. 3714 Default size is 2 megabytes. 3715 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3716 reserved for hotplug bridge's MMIO_PREF window. 3717 Default size is 2 megabytes. 3718 hpmemsize=nn[KMG] The fixed amount of bus space which is 3719 reserved for hotplug bridge's MMIO and 3720 MMIO_PREF window. 3721 Default size is 2 megabytes. 3722 hpbussize=nn The minimum amount of additional bus numbers 3723 reserved for buses below a hotplug bridge. 3724 Default is 1. 3725 realloc= Enable/disable reallocating PCI bridge resources 3726 if allocations done by BIOS are too small to 3727 accommodate resources required by all child 3728 devices. 3729 off: Turn realloc off 3730 on: Turn realloc on 3731 realloc same as realloc=on 3732 noari do not use PCIe ARI. 3733 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3734 do not use PCIe ATS (and IOMMU device IOTLB). 3735 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3736 only look for one device below a PCIe downstream 3737 port. 3738 big_root_window Try to add a big 64bit memory window to the PCIe 3739 root complex on AMD CPUs. Some GFX hardware 3740 can resize a BAR to allow access to all VRAM. 3741 Adding the window is slightly risky (it may 3742 conflict with unreported devices), so this 3743 taints the kernel. 3744 disable_acs_redir=<pci_dev>[; ...] 3745 Specify one or more PCI devices (in the format 3746 specified above) separated by semicolons. 3747 Each device specified will have the PCI ACS 3748 redirect capabilities forced off which will 3749 allow P2P traffic between devices through 3750 bridges without forcing it upstream. Note: 3751 this removes isolation between devices and 3752 may put more devices in an IOMMU group. 3753 force_floating [S390] Force usage of floating interrupts. 3754 nomio [S390] Do not use MIO instructions. 3755 norid [S390] ignore the RID field and force use of 3756 one PCI domain per PCI function 3757 3758 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3759 Management. 3760 off Disable ASPM. 3761 force Enable ASPM even on devices that claim not to support it. 3762 WARNING: Forcing ASPM on may cause system lockups. 3763 3764 pcie_ports= [PCIE] PCIe port services handling: 3765 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3766 even if the platform doesn't give the OS permission to 3767 use them. This may cause conflicts if the platform 3768 also tries to use these services. 3769 dpc-native Use native PCIe service for DPC only. May 3770 cause conflicts if firmware uses AER or DPC. 3771 compat Disable native PCIe services (PME, AER, DPC, PCIe 3772 hotplug). 3773 3774 pcie_port_pm= [PCIE] PCIe port power management handling: 3775 off Disable power management of all PCIe ports 3776 force Forcibly enable power management of all PCIe ports 3777 3778 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3779 nomsi Do not use MSI for native PCIe PME signaling (this makes 3780 all PCIe root ports use INTx for all services). 3781 3782 pcmv= [HW,PCMCIA] BadgePAD 4 3783 3784 pd_ignore_unused 3785 [PM] 3786 Keep all power-domains already enabled by bootloader on, 3787 even if no driver has claimed them. This is useful 3788 for debug and development, but should not be 3789 needed on a platform with proper driver support. 3790 3791 pd. [PARIDE] 3792 See Documentation/admin-guide/blockdev/paride.rst. 3793 3794 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3795 boot time. 3796 Format: { 0 | 1 } 3797 See arch/parisc/kernel/pdc_chassis.c 3798 3799 percpu_alloc= Select which percpu first chunk allocator to use. 3800 Currently supported values are "embed" and "page". 3801 Archs may support subset or none of the selections. 3802 See comments in mm/percpu.c for details on each 3803 allocator. This parameter is primarily for debugging 3804 and performance comparison. 3805 3806 pf. [PARIDE] 3807 See Documentation/admin-guide/blockdev/paride.rst. 3808 3809 pg. [PARIDE] 3810 See Documentation/admin-guide/blockdev/paride.rst. 3811 3812 pirq= [SMP,APIC] Manual mp-table setup 3813 See Documentation/x86/i386/IO-APIC.rst. 3814 3815 plip= [PPT,NET] Parallel port network link 3816 Format: { parport<nr> | timid | 0 } 3817 See also Documentation/admin-guide/parport.rst. 3818 3819 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3820 Override pmtimer IOPort with a hex value. 3821 e.g. pmtmr=0x508 3822 3823 pm_debug_messages [SUSPEND,KNL] 3824 Enable suspend/resume debug messages during boot up. 3825 3826 pnp.debug=1 [PNP] 3827 Enable PNP debug messages (depends on the 3828 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3829 via /sys/module/pnp/parameters/debug. We always show 3830 current resource usage; turning this on also shows 3831 possible settings and some assignment information. 3832 3833 pnpacpi= [ACPI] 3834 { off } 3835 3836 pnpbios= [ISAPNP] 3837 { on | off | curr | res | no-curr | no-res } 3838 3839 pnp_reserve_irq= 3840 [ISAPNP] Exclude IRQs for the autoconfiguration 3841 3842 pnp_reserve_dma= 3843 [ISAPNP] Exclude DMAs for the autoconfiguration 3844 3845 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3846 Ranges are in pairs (I/O port base and size). 3847 3848 pnp_reserve_mem= 3849 [ISAPNP] Exclude memory regions for the 3850 autoconfiguration. 3851 Ranges are in pairs (memory base and size). 3852 3853 ports= [IP_VS_FTP] IPVS ftp helper module 3854 Default is 21. 3855 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3856 may be specified. 3857 Format: <port>,<port>.... 3858 3859 powersave=off [PPC] This option disables power saving features. 3860 It specifically disables cpuidle and sets the 3861 platform machine description specific power_save 3862 function to NULL. On Idle the CPU just reduces 3863 execution priority. 3864 3865 ppc_strict_facility_enable 3866 [PPC] This option catches any kernel floating point, 3867 Altivec, VSX and SPE outside of regions specifically 3868 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3869 There is some performance impact when enabling this. 3870 3871 ppc_tm= [PPC] 3872 Format: {"off"} 3873 Disable Hardware Transactional Memory 3874 3875 print-fatal-signals= 3876 [KNL] debug: print fatal signals 3877 3878 If enabled, warn about various signal handling 3879 related application anomalies: too many signals, 3880 too many POSIX.1 timers, fatal signals causing a 3881 coredump - etc. 3882 3883 If you hit the warning due to signal overflow, 3884 you might want to try "ulimit -i unlimited". 3885 3886 default: off. 3887 3888 printk.always_kmsg_dump= 3889 Trigger kmsg_dump for cases other than kernel oops or 3890 panics 3891 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3892 default: disabled 3893 3894 printk.devkmsg={on,off,ratelimit} 3895 Control writing to /dev/kmsg. 3896 on - unlimited logging to /dev/kmsg from userspace 3897 off - logging to /dev/kmsg disabled 3898 ratelimit - ratelimit the logging 3899 Default: ratelimit 3900 3901 printk.time= Show timing data prefixed to each printk message line 3902 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3903 3904 processor.max_cstate= [HW,ACPI] 3905 Limit processor to maximum C-state 3906 max_cstate=9 overrides any DMI blacklist limit. 3907 3908 processor.nocst [HW,ACPI] 3909 Ignore the _CST method to determine C-states, 3910 instead using the legacy FADT method 3911 3912 profile= [KNL] Enable kernel profiling via /proc/profile 3913 Format: [<profiletype>,]<number> 3914 Param: <profiletype>: "schedule", "sleep", or "kvm" 3915 [defaults to kernel profiling] 3916 Param: "schedule" - profile schedule points. 3917 Param: "sleep" - profile D-state sleeping (millisecs). 3918 Requires CONFIG_SCHEDSTATS 3919 Param: "kvm" - profile VM exits. 3920 Param: <number> - step/bucket size as a power of 2 for 3921 statistical time based profiling. 3922 3923 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3924 before loading. 3925 See Documentation/admin-guide/blockdev/ramdisk.rst. 3926 3927 prot_virt= [S390] enable hosting protected virtual machines 3928 isolated from the hypervisor (if hardware supports 3929 that). 3930 Format: <bool> 3931 3932 psi= [KNL] Enable or disable pressure stall information 3933 tracking. 3934 Format: <bool> 3935 3936 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3937 probe for; one of (bare|imps|exps|lifebook|any). 3938 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3939 per second. 3940 psmouse.resetafter= [HW,MOUSE] 3941 Try to reset the device after so many bad packets 3942 (0 = never). 3943 psmouse.resolution= 3944 [HW,MOUSE] Set desired mouse resolution, in dpi. 3945 psmouse.smartscroll= 3946 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3947 0 = disabled, 1 = enabled (default). 3948 3949 pstore.backend= Specify the name of the pstore backend to use 3950 3951 pt. [PARIDE] 3952 See Documentation/admin-guide/blockdev/paride.rst. 3953 3954 pti= [X86_64] Control Page Table Isolation of user and 3955 kernel address spaces. Disabling this feature 3956 removes hardening, but improves performance of 3957 system calls and interrupts. 3958 3959 on - unconditionally enable 3960 off - unconditionally disable 3961 auto - kernel detects whether your CPU model is 3962 vulnerable to issues that PTI mitigates 3963 3964 Not specifying this option is equivalent to pti=auto. 3965 3966 nopti [X86_64] 3967 Equivalent to pti=off 3968 3969 pty.legacy_count= 3970 [KNL] Number of legacy pty's. Overwrites compiled-in 3971 default number. 3972 3973 quiet [KNL] Disable most log messages 3974 3975 r128= [HW,DRM] 3976 3977 raid= [HW,RAID] 3978 See Documentation/admin-guide/md.rst. 3979 3980 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3981 See Documentation/admin-guide/blockdev/ramdisk.rst. 3982 3983 random.trust_cpu={on,off} 3984 [KNL] Enable or disable trusting the use of the 3985 CPU's random number generator (if available) to 3986 fully seed the kernel's CRNG. Default is controlled 3987 by CONFIG_RANDOM_TRUST_CPU. 3988 3989 ras=option[,option,...] [KNL] RAS-specific options 3990 3991 cec_disable [X86] 3992 Disable the Correctable Errors Collector, 3993 see CONFIG_RAS_CEC help text. 3994 3995 rcu_nocbs= [KNL] 3996 The argument is a cpu list, as described above, 3997 except that the string "all" can be used to 3998 specify every CPU on the system. 3999 4000 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4001 the specified list of CPUs to be no-callback CPUs. 4002 Invocation of these CPUs' RCU callbacks will be 4003 offloaded to "rcuox/N" kthreads created for that 4004 purpose, where "x" is "p" for RCU-preempt, and 4005 "s" for RCU-sched, and "N" is the CPU number. 4006 This reduces OS jitter on the offloaded CPUs, 4007 which can be useful for HPC and real-time 4008 workloads. It can also improve energy efficiency 4009 for asymmetric multiprocessors. 4010 4011 rcu_nocb_poll [KNL] 4012 Rather than requiring that offloaded CPUs 4013 (specified by rcu_nocbs= above) explicitly 4014 awaken the corresponding "rcuoN" kthreads, 4015 make these kthreads poll for callbacks. 4016 This improves the real-time response for the 4017 offloaded CPUs by relieving them of the need to 4018 wake up the corresponding kthread, but degrades 4019 energy efficiency by requiring that the kthreads 4020 periodically wake up to do the polling. 4021 4022 rcutree.blimit= [KNL] 4023 Set maximum number of finished RCU callbacks to 4024 process in one batch. 4025 4026 rcutree.dump_tree= [KNL] 4027 Dump the structure of the rcu_node combining tree 4028 out at early boot. This is used for diagnostic 4029 purposes, to verify correct tree setup. 4030 4031 rcutree.gp_cleanup_delay= [KNL] 4032 Set the number of jiffies to delay each step of 4033 RCU grace-period cleanup. 4034 4035 rcutree.gp_init_delay= [KNL] 4036 Set the number of jiffies to delay each step of 4037 RCU grace-period initialization. 4038 4039 rcutree.gp_preinit_delay= [KNL] 4040 Set the number of jiffies to delay each step of 4041 RCU grace-period pre-initialization, that is, 4042 the propagation of recent CPU-hotplug changes up 4043 the rcu_node combining tree. 4044 4045 rcutree.use_softirq= [KNL] 4046 If set to zero, move all RCU_SOFTIRQ processing to 4047 per-CPU rcuc kthreads. Defaults to a non-zero 4048 value, meaning that RCU_SOFTIRQ is used by default. 4049 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4050 4051 rcutree.rcu_fanout_exact= [KNL] 4052 Disable autobalancing of the rcu_node combining 4053 tree. This is used by rcutorture, and might 4054 possibly be useful for architectures having high 4055 cache-to-cache transfer latencies. 4056 4057 rcutree.rcu_fanout_leaf= [KNL] 4058 Change the number of CPUs assigned to each 4059 leaf rcu_node structure. Useful for very 4060 large systems, which will choose the value 64, 4061 and for NUMA systems with large remote-access 4062 latencies, which will choose a value aligned 4063 with the appropriate hardware boundaries. 4064 4065 rcutree.rcu_min_cached_objs= [KNL] 4066 Minimum number of objects which are cached and 4067 maintained per one CPU. Object size is equal 4068 to PAGE_SIZE. The cache allows to reduce the 4069 pressure to page allocator, also it makes the 4070 whole algorithm to behave better in low memory 4071 condition. 4072 4073 rcutree.jiffies_till_first_fqs= [KNL] 4074 Set delay from grace-period initialization to 4075 first attempt to force quiescent states. 4076 Units are jiffies, minimum value is zero, 4077 and maximum value is HZ. 4078 4079 rcutree.jiffies_till_next_fqs= [KNL] 4080 Set delay between subsequent attempts to force 4081 quiescent states. Units are jiffies, minimum 4082 value is one, and maximum value is HZ. 4083 4084 rcutree.jiffies_till_sched_qs= [KNL] 4085 Set required age in jiffies for a 4086 given grace period before RCU starts 4087 soliciting quiescent-state help from 4088 rcu_note_context_switch() and cond_resched(). 4089 If not specified, the kernel will calculate 4090 a value based on the most recent settings 4091 of rcutree.jiffies_till_first_fqs 4092 and rcutree.jiffies_till_next_fqs. 4093 This calculated value may be viewed in 4094 rcutree.jiffies_to_sched_qs. Any attempt to set 4095 rcutree.jiffies_to_sched_qs will be cheerfully 4096 overwritten. 4097 4098 rcutree.kthread_prio= [KNL,BOOT] 4099 Set the SCHED_FIFO priority of the RCU per-CPU 4100 kthreads (rcuc/N). This value is also used for 4101 the priority of the RCU boost threads (rcub/N) 4102 and for the RCU grace-period kthreads (rcu_bh, 4103 rcu_preempt, and rcu_sched). If RCU_BOOST is 4104 set, valid values are 1-99 and the default is 1 4105 (the least-favored priority). Otherwise, when 4106 RCU_BOOST is not set, valid values are 0-99 and 4107 the default is zero (non-realtime operation). 4108 4109 rcutree.rcu_nocb_gp_stride= [KNL] 4110 Set the number of NOCB callback kthreads in 4111 each group, which defaults to the square root 4112 of the number of CPUs. Larger numbers reduce 4113 the wakeup overhead on the global grace-period 4114 kthread, but increases that same overhead on 4115 each group's NOCB grace-period kthread. 4116 4117 rcutree.qhimark= [KNL] 4118 Set threshold of queued RCU callbacks beyond which 4119 batch limiting is disabled. 4120 4121 rcutree.qlowmark= [KNL] 4122 Set threshold of queued RCU callbacks below which 4123 batch limiting is re-enabled. 4124 4125 rcutree.qovld= [KNL] 4126 Set threshold of queued RCU callbacks beyond which 4127 RCU's force-quiescent-state scan will aggressively 4128 enlist help from cond_resched() and sched IPIs to 4129 help CPUs more quickly reach quiescent states. 4130 Set to less than zero to make this be set based 4131 on rcutree.qhimark at boot time and to zero to 4132 disable more aggressive help enlistment. 4133 4134 rcutree.rcu_idle_gp_delay= [KNL] 4135 Set wakeup interval for idle CPUs that have 4136 RCU callbacks (RCU_FAST_NO_HZ=y). 4137 4138 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4139 Set wakeup interval for idle CPUs that have 4140 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4141 Lazy RCU callbacks are those which RCU can 4142 prove do nothing more than free memory. 4143 4144 rcutree.rcu_kick_kthreads= [KNL] 4145 Cause the grace-period kthread to get an extra 4146 wake_up() if it sleeps three times longer than 4147 it should at force-quiescent-state time. 4148 This wake_up() will be accompanied by a 4149 WARN_ONCE() splat and an ftrace_dump(). 4150 4151 rcutree.sysrq_rcu= [KNL] 4152 Commandeer a sysrq key to dump out Tree RCU's 4153 rcu_node tree with an eye towards determining 4154 why a new grace period has not yet started. 4155 4156 rcuperf.gp_async= [KNL] 4157 Measure performance of asynchronous 4158 grace-period primitives such as call_rcu(). 4159 4160 rcuperf.gp_async_max= [KNL] 4161 Specify the maximum number of outstanding 4162 callbacks per writer thread. When a writer 4163 thread exceeds this limit, it invokes the 4164 corresponding flavor of rcu_barrier() to allow 4165 previously posted callbacks to drain. 4166 4167 rcuperf.gp_exp= [KNL] 4168 Measure performance of expedited synchronous 4169 grace-period primitives. 4170 4171 rcuperf.holdoff= [KNL] 4172 Set test-start holdoff period. The purpose of 4173 this parameter is to delay the start of the 4174 test until boot completes in order to avoid 4175 interference. 4176 4177 rcuperf.kfree_rcu_test= [KNL] 4178 Set to measure performance of kfree_rcu() flooding. 4179 4180 rcuperf.kfree_nthreads= [KNL] 4181 The number of threads running loops of kfree_rcu(). 4182 4183 rcuperf.kfree_alloc_num= [KNL] 4184 Number of allocations and frees done in an iteration. 4185 4186 rcuperf.kfree_loops= [KNL] 4187 Number of loops doing rcuperf.kfree_alloc_num number 4188 of allocations and frees. 4189 4190 rcuperf.nreaders= [KNL] 4191 Set number of RCU readers. The value -1 selects 4192 N, where N is the number of CPUs. A value 4193 "n" less than -1 selects N-n+1, where N is again 4194 the number of CPUs. For example, -2 selects N 4195 (the number of CPUs), -3 selects N+1, and so on. 4196 A value of "n" less than or equal to -N selects 4197 a single reader. 4198 4199 rcuperf.nwriters= [KNL] 4200 Set number of RCU writers. The values operate 4201 the same as for rcuperf.nreaders. 4202 N, where N is the number of CPUs 4203 4204 rcuperf.perf_type= [KNL] 4205 Specify the RCU implementation to test. 4206 4207 rcuperf.shutdown= [KNL] 4208 Shut the system down after performance tests 4209 complete. This is useful for hands-off automated 4210 testing. 4211 4212 rcuperf.verbose= [KNL] 4213 Enable additional printk() statements. 4214 4215 rcuperf.writer_holdoff= [KNL] 4216 Write-side holdoff between grace periods, 4217 in microseconds. The default of zero says 4218 no holdoff. 4219 4220 rcutorture.fqs_duration= [KNL] 4221 Set duration of force_quiescent_state bursts 4222 in microseconds. 4223 4224 rcutorture.fqs_holdoff= [KNL] 4225 Set holdoff time within force_quiescent_state bursts 4226 in microseconds. 4227 4228 rcutorture.fqs_stutter= [KNL] 4229 Set wait time between force_quiescent_state bursts 4230 in seconds. 4231 4232 rcutorture.fwd_progress= [KNL] 4233 Enable RCU grace-period forward-progress testing 4234 for the types of RCU supporting this notion. 4235 4236 rcutorture.fwd_progress_div= [KNL] 4237 Specify the fraction of a CPU-stall-warning 4238 period to do tight-loop forward-progress testing. 4239 4240 rcutorture.fwd_progress_holdoff= [KNL] 4241 Number of seconds to wait between successive 4242 forward-progress tests. 4243 4244 rcutorture.fwd_progress_need_resched= [KNL] 4245 Enclose cond_resched() calls within checks for 4246 need_resched() during tight-loop forward-progress 4247 testing. 4248 4249 rcutorture.gp_cond= [KNL] 4250 Use conditional/asynchronous update-side 4251 primitives, if available. 4252 4253 rcutorture.gp_exp= [KNL] 4254 Use expedited update-side primitives, if available. 4255 4256 rcutorture.gp_normal= [KNL] 4257 Use normal (non-expedited) asynchronous 4258 update-side primitives, if available. 4259 4260 rcutorture.gp_sync= [KNL] 4261 Use normal (non-expedited) synchronous 4262 update-side primitives, if available. If all 4263 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4264 rcutorture.gp_normal=, and rcutorture.gp_sync= 4265 are zero, rcutorture acts as if is interpreted 4266 they are all non-zero. 4267 4268 rcutorture.n_barrier_cbs= [KNL] 4269 Set callbacks/threads for rcu_barrier() testing. 4270 4271 rcutorture.nfakewriters= [KNL] 4272 Set number of concurrent RCU writers. These just 4273 stress RCU, they don't participate in the actual 4274 test, hence the "fake". 4275 4276 rcutorture.nreaders= [KNL] 4277 Set number of RCU readers. The value -1 selects 4278 N-1, where N is the number of CPUs. A value 4279 "n" less than -1 selects N-n-2, where N is again 4280 the number of CPUs. For example, -2 selects N 4281 (the number of CPUs), -3 selects N+1, and so on. 4282 4283 rcutorture.object_debug= [KNL] 4284 Enable debug-object double-call_rcu() testing. 4285 4286 rcutorture.onoff_holdoff= [KNL] 4287 Set time (s) after boot for CPU-hotplug testing. 4288 4289 rcutorture.onoff_interval= [KNL] 4290 Set time (jiffies) between CPU-hotplug operations, 4291 or zero to disable CPU-hotplug testing. 4292 4293 rcutorture.read_exit= [KNL] 4294 Set the number of read-then-exit kthreads used 4295 to test the interaction of RCU updaters and 4296 task-exit processing. 4297 4298 rcutorture.read_exit_burst= [KNL] 4299 The number of times in a given read-then-exit 4300 episode that a set of read-then-exit kthreads 4301 is spawned. 4302 4303 rcutorture.read_exit_delay= [KNL] 4304 The delay, in seconds, between successive 4305 read-then-exit testing episodes. 4306 4307 rcutorture.shuffle_interval= [KNL] 4308 Set task-shuffle interval (s). Shuffling tasks 4309 allows some CPUs to go into dyntick-idle mode 4310 during the rcutorture test. 4311 4312 rcutorture.shutdown_secs= [KNL] 4313 Set time (s) after boot system shutdown. This 4314 is useful for hands-off automated testing. 4315 4316 rcutorture.stall_cpu= [KNL] 4317 Duration of CPU stall (s) to test RCU CPU stall 4318 warnings, zero to disable. 4319 4320 rcutorture.stall_cpu_block= [KNL] 4321 Sleep while stalling if set. This will result 4322 in warnings from preemptible RCU in addition 4323 to any other stall-related activity. 4324 4325 rcutorture.stall_cpu_holdoff= [KNL] 4326 Time to wait (s) after boot before inducing stall. 4327 4328 rcutorture.stall_cpu_irqsoff= [KNL] 4329 Disable interrupts while stalling if set. 4330 4331 rcutorture.stall_gp_kthread= [KNL] 4332 Duration (s) of forced sleep within RCU 4333 grace-period kthread to test RCU CPU stall 4334 warnings, zero to disable. If both stall_cpu 4335 and stall_gp_kthread are specified, the 4336 kthread is starved first, then the CPU. 4337 4338 rcutorture.stat_interval= [KNL] 4339 Time (s) between statistics printk()s. 4340 4341 rcutorture.stutter= [KNL] 4342 Time (s) to stutter testing, for example, specifying 4343 five seconds causes the test to run for five seconds, 4344 wait for five seconds, and so on. This tests RCU's 4345 ability to transition abruptly to and from idle. 4346 4347 rcutorture.test_boost= [KNL] 4348 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4349 "Maybe" means test if the RCU implementation 4350 under test support RCU priority boosting. 4351 4352 rcutorture.test_boost_duration= [KNL] 4353 Duration (s) of each individual boost test. 4354 4355 rcutorture.test_boost_interval= [KNL] 4356 Interval (s) between each boost test. 4357 4358 rcutorture.test_no_idle_hz= [KNL] 4359 Test RCU's dyntick-idle handling. See also the 4360 rcutorture.shuffle_interval parameter. 4361 4362 rcutorture.torture_type= [KNL] 4363 Specify the RCU implementation to test. 4364 4365 rcutorture.verbose= [KNL] 4366 Enable additional printk() statements. 4367 4368 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4369 Dump ftrace buffer after reporting RCU CPU 4370 stall warning. 4371 4372 rcupdate.rcu_cpu_stall_suppress= [KNL] 4373 Suppress RCU CPU stall warning messages. 4374 4375 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4376 Suppress RCU CPU stall warning messages and 4377 rcutorture writer stall warnings that occur 4378 during early boot, that is, during the time 4379 before the init task is spawned. 4380 4381 rcupdate.rcu_cpu_stall_timeout= [KNL] 4382 Set timeout for RCU CPU stall warning messages. 4383 4384 rcupdate.rcu_expedited= [KNL] 4385 Use expedited grace-period primitives, for 4386 example, synchronize_rcu_expedited() instead 4387 of synchronize_rcu(). This reduces latency, 4388 but can increase CPU utilization, degrade 4389 real-time latency, and degrade energy efficiency. 4390 No effect on CONFIG_TINY_RCU kernels. 4391 4392 rcupdate.rcu_normal= [KNL] 4393 Use only normal grace-period primitives, 4394 for example, synchronize_rcu() instead of 4395 synchronize_rcu_expedited(). This improves 4396 real-time latency, CPU utilization, and 4397 energy efficiency, but can expose users to 4398 increased grace-period latency. This parameter 4399 overrides rcupdate.rcu_expedited. No effect on 4400 CONFIG_TINY_RCU kernels. 4401 4402 rcupdate.rcu_normal_after_boot= [KNL] 4403 Once boot has completed (that is, after 4404 rcu_end_inkernel_boot() has been invoked), use 4405 only normal grace-period primitives. No effect 4406 on CONFIG_TINY_RCU kernels. 4407 4408 rcupdate.rcu_task_ipi_delay= [KNL] 4409 Set time in jiffies during which RCU tasks will 4410 avoid sending IPIs, starting with the beginning 4411 of a given grace period. Setting a large 4412 number avoids disturbing real-time workloads, 4413 but lengthens grace periods. 4414 4415 rcupdate.rcu_task_stall_timeout= [KNL] 4416 Set timeout in jiffies for RCU task stall warning 4417 messages. Disable with a value less than or equal 4418 to zero. 4419 4420 rcupdate.rcu_self_test= [KNL] 4421 Run the RCU early boot self tests 4422 4423 rdinit= [KNL] 4424 Format: <full_path> 4425 Run specified binary instead of /init from the ramdisk, 4426 used for early userspace startup. See initrd. 4427 4428 rdrand= [X86] 4429 force - Override the decision by the kernel to hide the 4430 advertisement of RDRAND support (this affects 4431 certain AMD processors because of buggy BIOS 4432 support, specifically around the suspend/resume 4433 path). 4434 4435 rdt= [HW,X86,RDT] 4436 Turn on/off individual RDT features. List is: 4437 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4438 mba. 4439 E.g. to turn on cmt and turn off mba use: 4440 rdt=cmt,!mba 4441 4442 reboot= [KNL] 4443 Format (x86 or x86_64): 4444 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4445 [[,]s[mp]#### \ 4446 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4447 [[,]f[orce] 4448 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4449 (prefix with 'panic_' to set mode for panic 4450 reboot only), 4451 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4452 reboot_force is either force or not specified, 4453 reboot_cpu is s[mp]#### with #### being the processor 4454 to be used for rebooting. 4455 4456 refscale.holdoff= [KNL] 4457 Set test-start holdoff period. The purpose of 4458 this parameter is to delay the start of the 4459 test until boot completes in order to avoid 4460 interference. 4461 4462 refscale.loops= [KNL] 4463 Set the number of loops over the synchronization 4464 primitive under test. Increasing this number 4465 reduces noise due to loop start/end overhead, 4466 but the default has already reduced the per-pass 4467 noise to a handful of picoseconds on ca. 2020 4468 x86 laptops. 4469 4470 refscale.nreaders= [KNL] 4471 Set number of readers. The default value of -1 4472 selects N, where N is roughly 75% of the number 4473 of CPUs. A value of zero is an interesting choice. 4474 4475 refscale.nruns= [KNL] 4476 Set number of runs, each of which is dumped onto 4477 the console log. 4478 4479 refscale.readdelay= [KNL] 4480 Set the read-side critical-section duration, 4481 measured in microseconds. 4482 4483 refscale.scale_type= [KNL] 4484 Specify the read-protection implementation to test. 4485 4486 refscale.shutdown= [KNL] 4487 Shut down the system at the end of the performance 4488 test. This defaults to 1 (shut it down) when 4489 rcuperf is built into the kernel and to 0 (leave 4490 it running) when rcuperf is built as a module. 4491 4492 refscale.verbose= [KNL] 4493 Enable additional printk() statements. 4494 4495 relax_domain_level= 4496 [KNL, SMP] Set scheduler's default relax_domain_level. 4497 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4498 4499 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4500 Format: <base1>,<size1>[,<base2>,<size2>,...] 4501 Reserve I/O ports or memory so the kernel won't use 4502 them. If <base> is less than 0x10000, the region 4503 is assumed to be I/O ports; otherwise it is memory. 4504 4505 reservetop= [X86-32] 4506 Format: nn[KMG] 4507 Reserves a hole at the top of the kernel virtual 4508 address space. 4509 4510 reservelow= [X86] 4511 Format: nn[K] 4512 Set the amount of memory to reserve for BIOS at 4513 the bottom of the address space. 4514 4515 reset_devices [KNL] Force drivers to reset the underlying device 4516 during initialization. 4517 4518 resume= [SWSUSP] 4519 Specify the partition device for software suspend 4520 Format: 4521 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4522 4523 resume_offset= [SWSUSP] 4524 Specify the offset from the beginning of the partition 4525 given by "resume=" at which the swap header is located, 4526 in <PAGE_SIZE> units (needed only for swap files). 4527 See Documentation/power/swsusp-and-swap-files.rst 4528 4529 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4530 read the resume files 4531 4532 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4533 Useful for devices that are detected asynchronously 4534 (e.g. USB and MMC devices). 4535 4536 hibernate= [HIBERNATION] 4537 noresume Don't check if there's a hibernation image 4538 present during boot. 4539 nocompress Don't compress/decompress hibernation images. 4540 no Disable hibernation and resume. 4541 protect_image Turn on image protection during restoration 4542 (that will set all pages holding image data 4543 during restoration read-only). 4544 4545 retain_initrd [RAM] Keep initrd memory after extraction 4546 4547 rfkill.default_state= 4548 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4549 etc. communication is blocked by default. 4550 1 Unblocked. 4551 4552 rfkill.master_switch_mode= 4553 0 The "airplane mode" button does nothing. 4554 1 The "airplane mode" button toggles between everything 4555 blocked and the previous configuration. 4556 2 The "airplane mode" button toggles between everything 4557 blocked and everything unblocked. 4558 4559 rhash_entries= [KNL,NET] 4560 Set number of hash buckets for route cache 4561 4562 ring3mwait=disable 4563 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4564 CPUs. 4565 4566 ro [KNL] Mount root device read-only on boot 4567 4568 rodata= [KNL] 4569 on Mark read-only kernel memory as read-only (default). 4570 off Leave read-only kernel memory writable for debugging. 4571 4572 rockchip.usb_uart 4573 Enable the uart passthrough on the designated usb port 4574 on Rockchip SoCs. When active, the signals of the 4575 debug-uart get routed to the D+ and D- pins of the usb 4576 port and the regular usb controller gets disabled. 4577 4578 root= [KNL] Root filesystem 4579 See name_to_dev_t comment in init/do_mounts.c. 4580 4581 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4582 mount the root filesystem 4583 4584 rootflags= [KNL] Set root filesystem mount option string 4585 4586 rootfstype= [KNL] Set root filesystem type 4587 4588 rootwait [KNL] Wait (indefinitely) for root device to show up. 4589 Useful for devices that are detected asynchronously 4590 (e.g. USB and MMC devices). 4591 4592 rproc_mem=nn[KMG][@address] 4593 [KNL,ARM,CMA] Remoteproc physical memory block. 4594 Memory area to be used by remote processor image, 4595 managed by CMA. 4596 4597 rw [KNL] Mount root device read-write on boot 4598 4599 S [KNL] Run init in single mode 4600 4601 s390_iommu= [HW,S390] 4602 Set s390 IOTLB flushing mode 4603 strict 4604 With strict flushing every unmap operation will result in 4605 an IOTLB flush. Default is lazy flushing before reuse, 4606 which is faster. 4607 4608 sa1100ir [NET] 4609 See drivers/net/irda/sa1100_ir.c. 4610 4611 sbni= [NET] Granch SBNI12 leased line adapter 4612 4613 sched_debug [KNL] Enables verbose scheduler debug messages. 4614 4615 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4616 Allowed values are enable and disable. This feature 4617 incurs a small amount of overhead in the scheduler 4618 but is useful for debugging and performance tuning. 4619 4620 sched_thermal_decay_shift= 4621 [KNL, SMP] Set a decay shift for scheduler thermal 4622 pressure signal. Thermal pressure signal follows the 4623 default decay period of other scheduler pelt 4624 signals(usually 32 ms but configurable). Setting 4625 sched_thermal_decay_shift will left shift the decay 4626 period for the thermal pressure signal by the shift 4627 value. 4628 i.e. with the default pelt decay period of 32 ms 4629 sched_thermal_decay_shift thermal pressure decay pr 4630 1 64 ms 4631 2 128 ms 4632 and so on. 4633 Format: integer between 0 and 10 4634 Default is 0. 4635 4636 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4637 xtime_lock contention on larger systems, and/or RCU lock 4638 contention on all systems with CONFIG_MAXSMP set. 4639 Format: { "0" | "1" } 4640 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4641 1 -- enable. 4642 Note: increases power consumption, thus should only be 4643 enabled if running jitter sensitive (HPC/RT) workloads. 4644 4645 security= [SECURITY] Choose a legacy "major" security module to 4646 enable at boot. This has been deprecated by the 4647 "lsm=" parameter. 4648 4649 selinux= [SELINUX] Disable or enable SELinux at boot time. 4650 Format: { "0" | "1" } 4651 See security/selinux/Kconfig help text. 4652 0 -- disable. 4653 1 -- enable. 4654 Default value is 1. 4655 4656 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4657 Format: { "0" | "1" } 4658 See security/apparmor/Kconfig help text 4659 0 -- disable. 4660 1 -- enable. 4661 Default value is set via kernel config option. 4662 4663 serialnumber [BUGS=X86-32] 4664 4665 shapers= [NET] 4666 Maximal number of shapers. 4667 4668 simeth= [IA-64] 4669 simscsi= 4670 4671 slram= [HW,MTD] 4672 4673 slab_nomerge [MM] 4674 Disable merging of slabs with similar size. May be 4675 necessary if there is some reason to distinguish 4676 allocs to different slabs, especially in hardened 4677 environments where the risk of heap overflows and 4678 layout control by attackers can usually be 4679 frustrated by disabling merging. This will reduce 4680 most of the exposure of a heap attack to a single 4681 cache (risks via metadata attacks are mostly 4682 unchanged). Debug options disable merging on their 4683 own. 4684 For more information see Documentation/vm/slub.rst. 4685 4686 slab_max_order= [MM, SLAB] 4687 Determines the maximum allowed order for slabs. 4688 A high setting may cause OOMs due to memory 4689 fragmentation. Defaults to 1 for systems with 4690 more than 32MB of RAM, 0 otherwise. 4691 4692 slub_debug[=options[,slabs]] [MM, SLUB] 4693 Enabling slub_debug allows one to determine the 4694 culprit if slab objects become corrupted. Enabling 4695 slub_debug can create guard zones around objects and 4696 may poison objects when not in use. Also tracks the 4697 last alloc / free. For more information see 4698 Documentation/vm/slub.rst. 4699 4700 slub_memcg_sysfs= [MM, SLUB] 4701 Determines whether to enable sysfs directories for 4702 memory cgroup sub-caches. 1 to enable, 0 to disable. 4703 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4704 Enabling this can lead to a very high number of debug 4705 directories and files being created under 4706 /sys/kernel/slub. 4707 4708 slub_max_order= [MM, SLUB] 4709 Determines the maximum allowed order for slabs. 4710 A high setting may cause OOMs due to memory 4711 fragmentation. For more information see 4712 Documentation/vm/slub.rst. 4713 4714 slub_min_objects= [MM, SLUB] 4715 The minimum number of objects per slab. SLUB will 4716 increase the slab order up to slub_max_order to 4717 generate a sufficiently large slab able to contain 4718 the number of objects indicated. The higher the number 4719 of objects the smaller the overhead of tracking slabs 4720 and the less frequently locks need to be acquired. 4721 For more information see Documentation/vm/slub.rst. 4722 4723 slub_min_order= [MM, SLUB] 4724 Determines the minimum page order for slabs. Must be 4725 lower than slub_max_order. 4726 For more information see Documentation/vm/slub.rst. 4727 4728 slub_nomerge [MM, SLUB] 4729 Same with slab_nomerge. This is supported for legacy. 4730 See slab_nomerge for more information. 4731 4732 smart2= [HW] 4733 Format: <io1>[,<io2>[,...,<io8>]] 4734 4735 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4736 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4737 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4738 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4739 smsc-ircc2.ircc_irq= [HW] IRQ line 4740 smsc-ircc2.ircc_dma= [HW] DMA channel 4741 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4742 0: Toshiba Satellite 1800 (GP data pin select) 4743 1: Fast pin select (default) 4744 2: ATC IRMode 4745 4746 smt [KNL,S390] Set the maximum number of threads (logical 4747 CPUs) to use per physical CPU on systems capable of 4748 symmetric multithreading (SMT). Will be capped to the 4749 actual hardware limit. 4750 Format: <integer> 4751 Default: -1 (no limit) 4752 4753 softlockup_panic= 4754 [KNL] Should the soft-lockup detector generate panics. 4755 Format: 0 | 1 4756 4757 A value of 1 instructs the soft-lockup detector 4758 to panic the machine when a soft-lockup occurs. It is 4759 also controlled by the kernel.softlockup_panic sysctl 4760 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4761 respective build-time switch to that functionality. 4762 4763 softlockup_all_cpu_backtrace= 4764 [KNL] Should the soft-lockup detector generate 4765 backtraces on all cpus. 4766 Format: 0 | 1 4767 4768 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4769 See Documentation/admin-guide/laptops/sonypi.rst 4770 4771 spectre_v2= [X86] Control mitigation of Spectre variant 2 4772 (indirect branch speculation) vulnerability. 4773 The default operation protects the kernel from 4774 user space attacks. 4775 4776 on - unconditionally enable, implies 4777 spectre_v2_user=on 4778 off - unconditionally disable, implies 4779 spectre_v2_user=off 4780 auto - kernel detects whether your CPU model is 4781 vulnerable 4782 4783 Selecting 'on' will, and 'auto' may, choose a 4784 mitigation method at run time according to the 4785 CPU, the available microcode, the setting of the 4786 CONFIG_RETPOLINE configuration option, and the 4787 compiler with which the kernel was built. 4788 4789 Selecting 'on' will also enable the mitigation 4790 against user space to user space task attacks. 4791 4792 Selecting 'off' will disable both the kernel and 4793 the user space protections. 4794 4795 Specific mitigations can also be selected manually: 4796 4797 retpoline - replace indirect branches 4798 retpoline,generic - google's original retpoline 4799 retpoline,amd - AMD-specific minimal thunk 4800 4801 Not specifying this option is equivalent to 4802 spectre_v2=auto. 4803 4804 spectre_v2_user= 4805 [X86] Control mitigation of Spectre variant 2 4806 (indirect branch speculation) vulnerability between 4807 user space tasks 4808 4809 on - Unconditionally enable mitigations. Is 4810 enforced by spectre_v2=on 4811 4812 off - Unconditionally disable mitigations. Is 4813 enforced by spectre_v2=off 4814 4815 prctl - Indirect branch speculation is enabled, 4816 but mitigation can be enabled via prctl 4817 per thread. The mitigation control state 4818 is inherited on fork. 4819 4820 prctl,ibpb 4821 - Like "prctl" above, but only STIBP is 4822 controlled per thread. IBPB is issued 4823 always when switching between different user 4824 space processes. 4825 4826 seccomp 4827 - Same as "prctl" above, but all seccomp 4828 threads will enable the mitigation unless 4829 they explicitly opt out. 4830 4831 seccomp,ibpb 4832 - Like "seccomp" above, but only STIBP is 4833 controlled per thread. IBPB is issued 4834 always when switching between different 4835 user space processes. 4836 4837 auto - Kernel selects the mitigation depending on 4838 the available CPU features and vulnerability. 4839 4840 Default mitigation: 4841 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4842 4843 Not specifying this option is equivalent to 4844 spectre_v2_user=auto. 4845 4846 spec_store_bypass_disable= 4847 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4848 (Speculative Store Bypass vulnerability) 4849 4850 Certain CPUs are vulnerable to an exploit against a 4851 a common industry wide performance optimization known 4852 as "Speculative Store Bypass" in which recent stores 4853 to the same memory location may not be observed by 4854 later loads during speculative execution. The idea 4855 is that such stores are unlikely and that they can 4856 be detected prior to instruction retirement at the 4857 end of a particular speculation execution window. 4858 4859 In vulnerable processors, the speculatively forwarded 4860 store can be used in a cache side channel attack, for 4861 example to read memory to which the attacker does not 4862 directly have access (e.g. inside sandboxed code). 4863 4864 This parameter controls whether the Speculative Store 4865 Bypass optimization is used. 4866 4867 On x86 the options are: 4868 4869 on - Unconditionally disable Speculative Store Bypass 4870 off - Unconditionally enable Speculative Store Bypass 4871 auto - Kernel detects whether the CPU model contains an 4872 implementation of Speculative Store Bypass and 4873 picks the most appropriate mitigation. If the 4874 CPU is not vulnerable, "off" is selected. If the 4875 CPU is vulnerable the default mitigation is 4876 architecture and Kconfig dependent. See below. 4877 prctl - Control Speculative Store Bypass per thread 4878 via prctl. Speculative Store Bypass is enabled 4879 for a process by default. The state of the control 4880 is inherited on fork. 4881 seccomp - Same as "prctl" above, but all seccomp threads 4882 will disable SSB unless they explicitly opt out. 4883 4884 Default mitigations: 4885 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4886 4887 On powerpc the options are: 4888 4889 on,auto - On Power8 and Power9 insert a store-forwarding 4890 barrier on kernel entry and exit. On Power7 4891 perform a software flush on kernel entry and 4892 exit. 4893 off - No action. 4894 4895 Not specifying this option is equivalent to 4896 spec_store_bypass_disable=auto. 4897 4898 spia_io_base= [HW,MTD] 4899 spia_fio_base= 4900 spia_pedr= 4901 spia_peddr= 4902 4903 split_lock_detect= 4904 [X86] Enable split lock detection 4905 4906 When enabled (and if hardware support is present), atomic 4907 instructions that access data across cache line 4908 boundaries will result in an alignment check exception. 4909 4910 off - not enabled 4911 4912 warn - the kernel will emit rate limited warnings 4913 about applications triggering the #AC 4914 exception. This mode is the default on CPUs 4915 that supports split lock detection. 4916 4917 fatal - the kernel will send SIGBUS to applications 4918 that trigger the #AC exception. 4919 4920 If an #AC exception is hit in the kernel or in 4921 firmware (i.e. not while executing in user mode) 4922 the kernel will oops in either "warn" or "fatal" 4923 mode. 4924 4925 srbds= [X86,INTEL] 4926 Control the Special Register Buffer Data Sampling 4927 (SRBDS) mitigation. 4928 4929 Certain CPUs are vulnerable to an MDS-like 4930 exploit which can leak bits from the random 4931 number generator. 4932 4933 By default, this issue is mitigated by 4934 microcode. However, the microcode fix can cause 4935 the RDRAND and RDSEED instructions to become 4936 much slower. Among other effects, this will 4937 result in reduced throughput from /dev/urandom. 4938 4939 The microcode mitigation can be disabled with 4940 the following option: 4941 4942 off: Disable mitigation and remove 4943 performance impact to RDRAND and RDSEED 4944 4945 srcutree.counter_wrap_check [KNL] 4946 Specifies how frequently to check for 4947 grace-period sequence counter wrap for the 4948 srcu_data structure's ->srcu_gp_seq_needed field. 4949 The greater the number of bits set in this kernel 4950 parameter, the less frequently counter wrap will 4951 be checked for. Note that the bottom two bits 4952 are ignored. 4953 4954 srcutree.exp_holdoff [KNL] 4955 Specifies how many nanoseconds must elapse 4956 since the end of the last SRCU grace period for 4957 a given srcu_struct until the next normal SRCU 4958 grace period will be considered for automatic 4959 expediting. Set to zero to disable automatic 4960 expediting. 4961 4962 ssbd= [ARM64,HW] 4963 Speculative Store Bypass Disable control 4964 4965 On CPUs that are vulnerable to the Speculative 4966 Store Bypass vulnerability and offer a 4967 firmware based mitigation, this parameter 4968 indicates how the mitigation should be used: 4969 4970 force-on: Unconditionally enable mitigation for 4971 for both kernel and userspace 4972 force-off: Unconditionally disable mitigation for 4973 for both kernel and userspace 4974 kernel: Always enable mitigation in the 4975 kernel, and offer a prctl interface 4976 to allow userspace to register its 4977 interest in being mitigated too. 4978 4979 stack_guard_gap= [MM] 4980 override the default stack gap protection. The value 4981 is in page units and it defines how many pages prior 4982 to (for stacks growing down) resp. after (for stacks 4983 growing up) the main stack are reserved for no other 4984 mapping. Default value is 256 pages. 4985 4986 stacktrace [FTRACE] 4987 Enabled the stack tracer on boot up. 4988 4989 stacktrace_filter=[function-list] 4990 [FTRACE] Limit the functions that the stack tracer 4991 will trace at boot up. function-list is a comma separated 4992 list of functions. This list can be changed at run 4993 time by the stack_trace_filter file in the debugfs 4994 tracing directory. Note, this enables stack tracing 4995 and the stacktrace above is not needed. 4996 4997 sti= [PARISC,HW] 4998 Format: <num> 4999 Set the STI (builtin display/keyboard on the HP-PARISC 5000 machines) console (graphic card) which should be used 5001 as the initial boot-console. 5002 See also comment in drivers/video/console/sticore.c. 5003 5004 sti_font= [HW] 5005 See comment in drivers/video/console/sticore.c. 5006 5007 stifb= [HW] 5008 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5009 5010 sunrpc.min_resvport= 5011 sunrpc.max_resvport= 5012 [NFS,SUNRPC] 5013 SunRPC servers often require that client requests 5014 originate from a privileged port (i.e. a port in the 5015 range 0 < portnr < 1024). 5016 An administrator who wishes to reserve some of these 5017 ports for other uses may adjust the range that the 5018 kernel's sunrpc client considers to be privileged 5019 using these two parameters to set the minimum and 5020 maximum port values. 5021 5022 sunrpc.svc_rpc_per_connection_limit= 5023 [NFS,SUNRPC] 5024 Limit the number of requests that the server will 5025 process in parallel from a single connection. 5026 The default value is 0 (no limit). 5027 5028 sunrpc.pool_mode= 5029 [NFS] 5030 Control how the NFS server code allocates CPUs to 5031 service thread pools. Depending on how many NICs 5032 you have and where their interrupts are bound, this 5033 option will affect which CPUs will do NFS serving. 5034 Note: this parameter cannot be changed while the 5035 NFS server is running. 5036 5037 auto the server chooses an appropriate mode 5038 automatically using heuristics 5039 global a single global pool contains all CPUs 5040 percpu one pool for each CPU 5041 pernode one pool for each NUMA node (equivalent 5042 to global on non-NUMA machines) 5043 5044 sunrpc.tcp_slot_table_entries= 5045 sunrpc.udp_slot_table_entries= 5046 [NFS,SUNRPC] 5047 Sets the upper limit on the number of simultaneous 5048 RPC calls that can be sent from the client to a 5049 server. Increasing these values may allow you to 5050 improve throughput, but will also increase the 5051 amount of memory reserved for use by the client. 5052 5053 suspend.pm_test_delay= 5054 [SUSPEND] 5055 Sets the number of seconds to remain in a suspend test 5056 mode before resuming the system (see 5057 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5058 is set. Default value is 5. 5059 5060 svm= [PPC] 5061 Format: { on | off | y | n | 1 | 0 } 5062 This parameter controls use of the Protected 5063 Execution Facility on pSeries. 5064 5065 swapaccount=[0|1] 5066 [KNL] Enable accounting of swap in memory resource 5067 controller if no parameter or 1 is given or disable 5068 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5069 5070 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5071 Format: { <int> | force | noforce } 5072 <int> -- Number of I/O TLB slabs 5073 force -- force using of bounce buffers even if they 5074 wouldn't be automatically used by the kernel 5075 noforce -- Never use bounce buffers (for debugging) 5076 5077 switches= [HW,M68k] 5078 5079 sysctl.*= [KNL] 5080 Set a sysctl parameter, right before loading the init 5081 process, as if the value was written to the respective 5082 /proc/sys/... file. Both '.' and '/' are recognized as 5083 separators. Unrecognized parameters and invalid values 5084 are reported in the kernel log. Sysctls registered 5085 later by a loaded module cannot be set this way. 5086 Example: sysctl.vm.swappiness=40 5087 5088 sysfs.deprecated=0|1 [KNL] 5089 Enable/disable old style sysfs layout for old udev 5090 on older distributions. When this option is enabled 5091 very new udev will not work anymore. When this option 5092 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5093 in older udev will not work anymore. 5094 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5095 the kernel configuration. 5096 5097 sysrq_always_enabled 5098 [KNL] 5099 Ignore sysrq setting - this boot parameter will 5100 neutralize any effect of /proc/sys/kernel/sysrq. 5101 Useful for debugging. 5102 5103 tcpmhash_entries= [KNL,NET] 5104 Set the number of tcp_metrics_hash slots. 5105 Default value is 8192 or 16384 depending on total 5106 ram pages. This is used to specify the TCP metrics 5107 cache size. See Documentation/networking/ip-sysctl.rst 5108 "tcp_no_metrics_save" section for more details. 5109 5110 tdfx= [HW,DRM] 5111 5112 test_suspend= [SUSPEND][,N] 5113 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5114 standby suspend) or "freeze" (for suspend type freeze) 5115 as the system sleep state during system startup with 5116 the optional capability to repeat N number of times. 5117 The system is woken from this state using a 5118 wakeup-capable RTC alarm. 5119 5120 thash_entries= [KNL,NET] 5121 Set number of hash buckets for TCP connection 5122 5123 thermal.act= [HW,ACPI] 5124 -1: disable all active trip points in all thermal zones 5125 <degrees C>: override all lowest active trip points 5126 5127 thermal.crt= [HW,ACPI] 5128 -1: disable all critical trip points in all thermal zones 5129 <degrees C>: override all critical trip points 5130 5131 thermal.nocrt= [HW,ACPI] 5132 Set to disable actions on ACPI thermal zone 5133 critical and hot trip points. 5134 5135 thermal.off= [HW,ACPI] 5136 1: disable ACPI thermal control 5137 5138 thermal.psv= [HW,ACPI] 5139 -1: disable all passive trip points 5140 <degrees C>: override all passive trip points to this 5141 value 5142 5143 thermal.tzp= [HW,ACPI] 5144 Specify global default ACPI thermal zone polling rate 5145 <deci-seconds>: poll all this frequency 5146 0: no polling (default) 5147 5148 threadirqs [KNL] 5149 Force threading of all interrupt handlers except those 5150 marked explicitly IRQF_NO_THREAD. 5151 5152 topology= [S390] 5153 Format: {off | on} 5154 Specify if the kernel should make use of the cpu 5155 topology information if the hardware supports this. 5156 The scheduler will make use of this information and 5157 e.g. base its process migration decisions on it. 5158 Default is on. 5159 5160 topology_updates= [KNL, PPC, NUMA] 5161 Format: {off} 5162 Specify if the kernel should ignore (off) 5163 topology updates sent by the hypervisor to this 5164 LPAR. 5165 5166 torture.disable_onoff_at_boot= [KNL] 5167 Prevent the CPU-hotplug component of torturing 5168 until after init has spawned. 5169 5170 torture.ftrace_dump_at_shutdown= [KNL] 5171 Dump the ftrace buffer at torture-test shutdown, 5172 even if there were no errors. This can be a 5173 very costly operation when many torture tests 5174 are running concurrently, especially on systems 5175 with rotating-rust storage. 5176 5177 tp720= [HW,PS2] 5178 5179 tpm_suspend_pcr=[HW,TPM] 5180 Format: integer pcr id 5181 Specify that at suspend time, the tpm driver 5182 should extend the specified pcr with zeros, 5183 as a workaround for some chips which fail to 5184 flush the last written pcr on TPM_SaveState. 5185 This will guarantee that all the other pcrs 5186 are saved. 5187 5188 trace_buf_size=nn[KMG] 5189 [FTRACE] will set tracing buffer size on each cpu. 5190 5191 trace_event=[event-list] 5192 [FTRACE] Set and start specified trace events in order 5193 to facilitate early boot debugging. The event-list is a 5194 comma separated list of trace events to enable. See 5195 also Documentation/trace/events.rst 5196 5197 trace_options=[option-list] 5198 [FTRACE] Enable or disable tracer options at boot. 5199 The option-list is a comma delimited list of options 5200 that can be enabled or disabled just as if you were 5201 to echo the option name into 5202 5203 /sys/kernel/debug/tracing/trace_options 5204 5205 For example, to enable stacktrace option (to dump the 5206 stack trace of each event), add to the command line: 5207 5208 trace_options=stacktrace 5209 5210 See also Documentation/trace/ftrace.rst "trace options" 5211 section. 5212 5213 tp_printk[FTRACE] 5214 Have the tracepoints sent to printk as well as the 5215 tracing ring buffer. This is useful for early boot up 5216 where the system hangs or reboots and does not give the 5217 option for reading the tracing buffer or performing a 5218 ftrace_dump_on_oops. 5219 5220 To turn off having tracepoints sent to printk, 5221 echo 0 > /proc/sys/kernel/tracepoint_printk 5222 Note, echoing 1 into this file without the 5223 tracepoint_printk kernel cmdline option has no effect. 5224 5225 ** CAUTION ** 5226 5227 Having tracepoints sent to printk() and activating high 5228 frequency tracepoints such as irq or sched, can cause 5229 the system to live lock. 5230 5231 traceoff_on_warning 5232 [FTRACE] enable this option to disable tracing when a 5233 warning is hit. This turns off "tracing_on". Tracing can 5234 be enabled again by echoing '1' into the "tracing_on" 5235 file located in /sys/kernel/debug/tracing/ 5236 5237 This option is useful, as it disables the trace before 5238 the WARNING dump is called, which prevents the trace to 5239 be filled with content caused by the warning output. 5240 5241 This option can also be set at run time via the sysctl 5242 option: kernel/traceoff_on_warning 5243 5244 transparent_hugepage= 5245 [KNL] 5246 Format: [always|madvise|never] 5247 Can be used to control the default behavior of the system 5248 with respect to transparent hugepages. 5249 See Documentation/admin-guide/mm/transhuge.rst 5250 for more details. 5251 5252 tsc= Disable clocksource stability checks for TSC. 5253 Format: <string> 5254 [x86] reliable: mark tsc clocksource as reliable, this 5255 disables clocksource verification at runtime, as well 5256 as the stability checks done at bootup. Used to enable 5257 high-resolution timer mode on older hardware, and in 5258 virtualized environment. 5259 [x86] noirqtime: Do not use TSC to do irq accounting. 5260 Used to run time disable IRQ_TIME_ACCOUNTING on any 5261 platforms where RDTSC is slow and this accounting 5262 can add overhead. 5263 [x86] unstable: mark the TSC clocksource as unstable, this 5264 marks the TSC unconditionally unstable at bootup and 5265 avoids any further wobbles once the TSC watchdog notices. 5266 [x86] nowatchdog: disable clocksource watchdog. Used 5267 in situations with strict latency requirements (where 5268 interruptions from clocksource watchdog are not 5269 acceptable). 5270 5271 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5272 value instead. Useful when the early TSC frequency discovery 5273 procedure is not reliable, such as on overclocked systems 5274 with CPUID.16h support and partial CPUID.15h support. 5275 Format: <unsigned int> 5276 5277 tsx= [X86] Control Transactional Synchronization 5278 Extensions (TSX) feature in Intel processors that 5279 support TSX control. 5280 5281 This parameter controls the TSX feature. The options are: 5282 5283 on - Enable TSX on the system. Although there are 5284 mitigations for all known security vulnerabilities, 5285 TSX has been known to be an accelerator for 5286 several previous speculation-related CVEs, and 5287 so there may be unknown security risks associated 5288 with leaving it enabled. 5289 5290 off - Disable TSX on the system. (Note that this 5291 option takes effect only on newer CPUs which are 5292 not vulnerable to MDS, i.e., have 5293 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5294 the new IA32_TSX_CTRL MSR through a microcode 5295 update. This new MSR allows for the reliable 5296 deactivation of the TSX functionality.) 5297 5298 auto - Disable TSX if X86_BUG_TAA is present, 5299 otherwise enable TSX on the system. 5300 5301 Not specifying this option is equivalent to tsx=off. 5302 5303 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5304 for more details. 5305 5306 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5307 Abort (TAA) vulnerability. 5308 5309 Similar to Micro-architectural Data Sampling (MDS) 5310 certain CPUs that support Transactional 5311 Synchronization Extensions (TSX) are vulnerable to an 5312 exploit against CPU internal buffers which can forward 5313 information to a disclosure gadget under certain 5314 conditions. 5315 5316 In vulnerable processors, the speculatively forwarded 5317 data can be used in a cache side channel attack, to 5318 access data to which the attacker does not have direct 5319 access. 5320 5321 This parameter controls the TAA mitigation. The 5322 options are: 5323 5324 full - Enable TAA mitigation on vulnerable CPUs 5325 if TSX is enabled. 5326 5327 full,nosmt - Enable TAA mitigation and disable SMT on 5328 vulnerable CPUs. If TSX is disabled, SMT 5329 is not disabled because CPU is not 5330 vulnerable to cross-thread TAA attacks. 5331 off - Unconditionally disable TAA mitigation 5332 5333 On MDS-affected machines, tsx_async_abort=off can be 5334 prevented by an active MDS mitigation as both vulnerabilities 5335 are mitigated with the same mechanism so in order to disable 5336 this mitigation, you need to specify mds=off too. 5337 5338 Not specifying this option is equivalent to 5339 tsx_async_abort=full. On CPUs which are MDS affected 5340 and deploy MDS mitigation, TAA mitigation is not 5341 required and doesn't provide any additional 5342 mitigation. 5343 5344 For details see: 5345 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5346 5347 turbografx.map[2|3]= [HW,JOY] 5348 TurboGraFX parallel port interface 5349 Format: 5350 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5351 See also Documentation/input/devices/joystick-parport.rst 5352 5353 udbg-immortal [PPC] When debugging early kernel crashes that 5354 happen after console_init() and before a proper 5355 console driver takes over, this boot options might 5356 help "seeing" what's going on. 5357 5358 uhash_entries= [KNL,NET] 5359 Set number of hash buckets for UDP/UDP-Lite connections 5360 5361 uhci-hcd.ignore_oc= 5362 [USB] Ignore overcurrent events (default N). 5363 Some badly-designed motherboards generate lots of 5364 bogus events, for ports that aren't wired to 5365 anything. Set this parameter to avoid log spamming. 5366 Note that genuine overcurrent events won't be 5367 reported either. 5368 5369 unknown_nmi_panic 5370 [X86] Cause panic on unknown NMI. 5371 5372 usbcore.authorized_default= 5373 [USB] Default USB device authorization: 5374 (default -1 = authorized except for wireless USB, 5375 0 = not authorized, 1 = authorized, 2 = authorized 5376 if device connected to internal port) 5377 5378 usbcore.autosuspend= 5379 [USB] The autosuspend time delay (in seconds) used 5380 for newly-detected USB devices (default 2). This 5381 is the time required before an idle device will be 5382 autosuspended. Devices for which the delay is set 5383 to a negative value won't be autosuspended at all. 5384 5385 usbcore.usbfs_snoop= 5386 [USB] Set to log all usbfs traffic (default 0 = off). 5387 5388 usbcore.usbfs_snoop_max= 5389 [USB] Maximum number of bytes to snoop in each URB 5390 (default = 65536). 5391 5392 usbcore.blinkenlights= 5393 [USB] Set to cycle leds on hubs (default 0 = off). 5394 5395 usbcore.old_scheme_first= 5396 [USB] Start with the old device initialization 5397 scheme (default 0 = off). 5398 5399 usbcore.usbfs_memory_mb= 5400 [USB] Memory limit (in MB) for buffers allocated by 5401 usbfs (default = 16, 0 = max = 2047). 5402 5403 usbcore.use_both_schemes= 5404 [USB] Try the other device initialization scheme 5405 if the first one fails (default 1 = enabled). 5406 5407 usbcore.initial_descriptor_timeout= 5408 [USB] Specifies timeout for the initial 64-byte 5409 USB_REQ_GET_DESCRIPTOR request in milliseconds 5410 (default 5000 = 5.0 seconds). 5411 5412 usbcore.nousb [USB] Disable the USB subsystem 5413 5414 usbcore.quirks= 5415 [USB] A list of quirk entries to augment the built-in 5416 usb core quirk list. List entries are separated by 5417 commas. Each entry has the form 5418 VendorID:ProductID:Flags. The IDs are 4-digit hex 5419 numbers and Flags is a set of letters. Each letter 5420 will change the built-in quirk; setting it if it is 5421 clear and clearing it if it is set. The letters have 5422 the following meanings: 5423 a = USB_QUIRK_STRING_FETCH_255 (string 5424 descriptors must not be fetched using 5425 a 255-byte read); 5426 b = USB_QUIRK_RESET_RESUME (device can't resume 5427 correctly so reset it instead); 5428 c = USB_QUIRK_NO_SET_INTF (device can't handle 5429 Set-Interface requests); 5430 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5431 handle its Configuration or Interface 5432 strings); 5433 e = USB_QUIRK_RESET (device can't be reset 5434 (e.g morph devices), don't use reset); 5435 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5436 more interface descriptions than the 5437 bNumInterfaces count, and can't handle 5438 talking to these interfaces); 5439 g = USB_QUIRK_DELAY_INIT (device needs a pause 5440 during initialization, after we read 5441 the device descriptor); 5442 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5443 high speed and super speed interrupt 5444 endpoints, the USB 2.0 and USB 3.0 spec 5445 require the interval in microframes (1 5446 microframe = 125 microseconds) to be 5447 calculated as interval = 2 ^ 5448 (bInterval-1). 5449 Devices with this quirk report their 5450 bInterval as the result of this 5451 calculation instead of the exponent 5452 variable used in the calculation); 5453 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5454 handle device_qualifier descriptor 5455 requests); 5456 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5457 generates spurious wakeup, ignore 5458 remote wakeup capability); 5459 k = USB_QUIRK_NO_LPM (device can't handle Link 5460 Power Management); 5461 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5462 (Device reports its bInterval as linear 5463 frames instead of the USB 2.0 5464 calculation); 5465 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5466 to be disconnected before suspend to 5467 prevent spurious wakeup); 5468 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5469 pause after every control message); 5470 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5471 delay after resetting its port); 5472 Example: quirks=0781:5580:bk,0a5c:5834:gij 5473 5474 usbhid.mousepoll= 5475 [USBHID] The interval which mice are to be polled at. 5476 5477 usbhid.jspoll= 5478 [USBHID] The interval which joysticks are to be polled at. 5479 5480 usbhid.kbpoll= 5481 [USBHID] The interval which keyboards are to be polled at. 5482 5483 usb-storage.delay_use= 5484 [UMS] The delay in seconds before a new device is 5485 scanned for Logical Units (default 1). 5486 5487 usb-storage.quirks= 5488 [UMS] A list of quirks entries to supplement or 5489 override the built-in unusual_devs list. List 5490 entries are separated by commas. Each entry has 5491 the form VID:PID:Flags where VID and PID are Vendor 5492 and Product ID values (4-digit hex numbers) and 5493 Flags is a set of characters, each corresponding 5494 to a common usb-storage quirk flag as follows: 5495 a = SANE_SENSE (collect more than 18 bytes 5496 of sense data, not on uas); 5497 b = BAD_SENSE (don't collect more than 18 5498 bytes of sense data, not on uas); 5499 c = FIX_CAPACITY (decrease the reported 5500 device capacity by one sector); 5501 d = NO_READ_DISC_INFO (don't use 5502 READ_DISC_INFO command, not on uas); 5503 e = NO_READ_CAPACITY_16 (don't use 5504 READ_CAPACITY_16 command); 5505 f = NO_REPORT_OPCODES (don't use report opcodes 5506 command, uas only); 5507 g = MAX_SECTORS_240 (don't transfer more than 5508 240 sectors at a time, uas only); 5509 h = CAPACITY_HEURISTICS (decrease the 5510 reported device capacity by one 5511 sector if the number is odd); 5512 i = IGNORE_DEVICE (don't bind to this 5513 device); 5514 j = NO_REPORT_LUNS (don't use report luns 5515 command, uas only); 5516 l = NOT_LOCKABLE (don't try to lock and 5517 unlock ejectable media, not on uas); 5518 m = MAX_SECTORS_64 (don't transfer more 5519 than 64 sectors = 32 KB at a time, 5520 not on uas); 5521 n = INITIAL_READ10 (force a retry of the 5522 initial READ(10) command, not on uas); 5523 o = CAPACITY_OK (accept the capacity 5524 reported by the device, not on uas); 5525 p = WRITE_CACHE (the device cache is ON 5526 by default, not on uas); 5527 r = IGNORE_RESIDUE (the device reports 5528 bogus residue values, not on uas); 5529 s = SINGLE_LUN (the device has only one 5530 Logical Unit); 5531 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5532 commands, uas only); 5533 u = IGNORE_UAS (don't bind to the uas driver); 5534 w = NO_WP_DETECT (don't test whether the 5535 medium is write-protected). 5536 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5537 even if the device claims no cache, 5538 not on uas) 5539 Example: quirks=0419:aaf5:rl,0421:0433:rc 5540 5541 user_debug= [KNL,ARM] 5542 Format: <int> 5543 See arch/arm/Kconfig.debug help text. 5544 1 - undefined instruction events 5545 2 - system calls 5546 4 - invalid data aborts 5547 8 - SIGSEGV faults 5548 16 - SIGBUS faults 5549 Example: user_debug=31 5550 5551 userpte= 5552 [X86] Flags controlling user PTE allocations. 5553 5554 nohigh = do not allocate PTE pages in 5555 HIGHMEM regardless of setting 5556 of CONFIG_HIGHPTE. 5557 5558 vdso= [X86,SH] 5559 On X86_32, this is an alias for vdso32=. Otherwise: 5560 5561 vdso=1: enable VDSO (the default) 5562 vdso=0: disable VDSO mapping 5563 5564 vdso32= [X86] Control the 32-bit vDSO 5565 vdso32=1: enable 32-bit VDSO 5566 vdso32=0 or vdso32=2: disable 32-bit VDSO 5567 5568 See the help text for CONFIG_COMPAT_VDSO for more 5569 details. If CONFIG_COMPAT_VDSO is set, the default is 5570 vdso32=0; otherwise, the default is vdso32=1. 5571 5572 For compatibility with older kernels, vdso32=2 is an 5573 alias for vdso32=0. 5574 5575 Try vdso32=0 if you encounter an error that says: 5576 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5577 5578 vector= [IA-64,SMP] 5579 vector=percpu: enable percpu vector domain 5580 5581 video= [FB] Frame buffer configuration 5582 See Documentation/fb/modedb.rst. 5583 5584 video.brightness_switch_enabled= [0,1] 5585 If set to 1, on receiving an ACPI notify event 5586 generated by hotkey, video driver will adjust brightness 5587 level and then send out the event to user space through 5588 the allocated input device; If set to 0, video driver 5589 will only send out the event without touching backlight 5590 brightness level. 5591 default: 1 5592 5593 virtio_mmio.device= 5594 [VMMIO] Memory mapped virtio (platform) device. 5595 5596 <size>@<baseaddr>:<irq>[:<id>] 5597 where: 5598 <size> := size (can use standard suffixes 5599 like K, M and G) 5600 <baseaddr> := physical base address 5601 <irq> := interrupt number (as passed to 5602 request_irq()) 5603 <id> := (optional) platform device id 5604 example: 5605 virtio_mmio.device=1K@0x100b0000:48:7 5606 5607 Can be used multiple times for multiple devices. 5608 5609 vga= [BOOT,X86-32] Select a particular video mode 5610 See Documentation/x86/boot.rst and 5611 Documentation/admin-guide/svga.rst. 5612 Use vga=ask for menu. 5613 This is actually a boot loader parameter; the value is 5614 passed to the kernel using a special protocol. 5615 5616 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5617 May slow down system boot speed, especially when 5618 enabled on systems with a large amount of memory. 5619 All options are enabled by default, and this 5620 interface is meant to allow for selectively 5621 enabling or disabling specific virtual memory 5622 debugging features. 5623 5624 Available options are: 5625 P Enable page structure init time poisoning 5626 - Disable all of the above options 5627 5628 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5629 size of <nn>. This can be used to increase the 5630 minimum size (128MB on x86). It can also be used to 5631 decrease the size and leave more room for directly 5632 mapped kernel RAM. 5633 5634 vmcp_cma=nn[MG] [KNL,S390] 5635 Sets the memory size reserved for contiguous memory 5636 allocations for the vmcp device driver. 5637 5638 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5639 Format: <command> 5640 5641 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5642 Format: <command> 5643 5644 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5645 Format: <command> 5646 5647 vsyscall= [X86-64] 5648 Controls the behavior of vsyscalls (i.e. calls to 5649 fixed addresses of 0xffffffffff600x00 from legacy 5650 code). Most statically-linked binaries and older 5651 versions of glibc use these calls. Because these 5652 functions are at fixed addresses, they make nice 5653 targets for exploits that can control RIP. 5654 5655 emulate [default] Vsyscalls turn into traps and are 5656 emulated reasonably safely. The vsyscall 5657 page is readable. 5658 5659 xonly Vsyscalls turn into traps and are 5660 emulated reasonably safely. The vsyscall 5661 page is not readable. 5662 5663 none Vsyscalls don't work at all. This makes 5664 them quite hard to use for exploits but 5665 might break your system. 5666 5667 vt.color= [VT] Default text color. 5668 Format: 0xYX, X = foreground, Y = background. 5669 Default: 0x07 = light gray on black. 5670 5671 vt.cur_default= [VT] Default cursor shape. 5672 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5673 the parameters of the <Esc>[?A;B;Cc escape sequence; 5674 see VGA-softcursor.txt. Default: 2 = underline. 5675 5676 vt.default_blu= [VT] 5677 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5678 Change the default blue palette of the console. 5679 This is a 16-member array composed of values 5680 ranging from 0-255. 5681 5682 vt.default_grn= [VT] 5683 Format: <green0>,<green1>,<green2>,...,<green15> 5684 Change the default green palette of the console. 5685 This is a 16-member array composed of values 5686 ranging from 0-255. 5687 5688 vt.default_red= [VT] 5689 Format: <red0>,<red1>,<red2>,...,<red15> 5690 Change the default red palette of the console. 5691 This is a 16-member array composed of values 5692 ranging from 0-255. 5693 5694 vt.default_utf8= 5695 [VT] 5696 Format=<0|1> 5697 Set system-wide default UTF-8 mode for all tty's. 5698 Default is 1, i.e. UTF-8 mode is enabled for all 5699 newly opened terminals. 5700 5701 vt.global_cursor_default= 5702 [VT] 5703 Format=<-1|0|1> 5704 Set system-wide default for whether a cursor 5705 is shown on new VTs. Default is -1, 5706 i.e. cursors will be created by default unless 5707 overridden by individual drivers. 0 will hide 5708 cursors, 1 will display them. 5709 5710 vt.italic= [VT] Default color for italic text; 0-15. 5711 Default: 2 = green. 5712 5713 vt.underline= [VT] Default color for underlined text; 0-15. 5714 Default: 3 = cyan. 5715 5716 watchdog timers [HW,WDT] For information on watchdog timers, 5717 see Documentation/watchdog/watchdog-parameters.rst 5718 or other driver-specific files in the 5719 Documentation/watchdog/ directory. 5720 5721 watchdog_thresh= 5722 [KNL] 5723 Set the hard lockup detector stall duration 5724 threshold in seconds. The soft lockup detector 5725 threshold is set to twice the value. A value of 0 5726 disables both lockup detectors. Default is 10 5727 seconds. 5728 5729 workqueue.watchdog_thresh= 5730 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5731 warn stall conditions and dump internal state to 5732 help debugging. 0 disables workqueue stall 5733 detection; otherwise, it's the stall threshold 5734 duration in seconds. The default value is 30 and 5735 it can be updated at runtime by writing to the 5736 corresponding sysfs file. 5737 5738 workqueue.disable_numa 5739 By default, all work items queued to unbound 5740 workqueues are affine to the NUMA nodes they're 5741 issued on, which results in better behavior in 5742 general. If NUMA affinity needs to be disabled for 5743 whatever reason, this option can be used. Note 5744 that this also can be controlled per-workqueue for 5745 workqueues visible under /sys/bus/workqueue/. 5746 5747 workqueue.power_efficient 5748 Per-cpu workqueues are generally preferred because 5749 they show better performance thanks to cache 5750 locality; unfortunately, per-cpu workqueues tend to 5751 be more power hungry than unbound workqueues. 5752 5753 Enabling this makes the per-cpu workqueues which 5754 were observed to contribute significantly to power 5755 consumption unbound, leading to measurably lower 5756 power usage at the cost of small performance 5757 overhead. 5758 5759 The default value of this parameter is determined by 5760 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5761 5762 workqueue.debug_force_rr_cpu 5763 Workqueue used to implicitly guarantee that work 5764 items queued without explicit CPU specified are put 5765 on the local CPU. This guarantee is no longer true 5766 and while local CPU is still preferred work items 5767 may be put on foreign CPUs. This debug option 5768 forces round-robin CPU selection to flush out 5769 usages which depend on the now broken guarantee. 5770 When enabled, memory and cache locality will be 5771 impacted. 5772 5773 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5774 default x2apic cluster mode on platforms 5775 supporting x2apic. 5776 5777 x86_intel_mid_timer= [X86-32,APBT] 5778 Choose timer option for x86 Intel MID platform. 5779 Two valid options are apbt timer only and lapic timer 5780 plus one apbt timer for broadcast timer. 5781 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5782 5783 xen_512gb_limit [KNL,X86-64,XEN] 5784 Restricts the kernel running paravirtualized under Xen 5785 to use only up to 512 GB of RAM. The reason to do so is 5786 crash analysis tools and Xen tools for doing domain 5787 save/restore/migration must be enabled to handle larger 5788 domains. 5789 5790 xen_emul_unplug= [HW,X86,XEN] 5791 Unplug Xen emulated devices 5792 Format: [unplug0,][unplug1] 5793 ide-disks -- unplug primary master IDE devices 5794 aux-ide-disks -- unplug non-primary-master IDE devices 5795 nics -- unplug network devices 5796 all -- unplug all emulated devices (NICs and IDE disks) 5797 unnecessary -- unplugging emulated devices is 5798 unnecessary even if the host did not respond to 5799 the unplug protocol 5800 never -- do not unplug even if version check succeeds 5801 5802 xen_legacy_crash [X86,XEN] 5803 Crash from Xen panic notifier, without executing late 5804 panic() code such as dumping handler. 5805 5806 xen_nopvspin [X86,XEN] 5807 Disables the ticketlock slowpath using Xen PV 5808 optimizations. 5809 5810 xen_nopv [X86] 5811 Disables the PV optimizations forcing the HVM guest to 5812 run as generic HVM guest with no PV drivers. 5813 This option is obsoleted by the "nopv" option, which 5814 has equivalent effect for XEN platform. 5815 5816 xen_scrub_pages= [XEN] 5817 Boolean option to control scrubbing pages before giving them back 5818 to Xen, for use by other domains. Can be also changed at runtime 5819 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5820 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5821 5822 xen_timer_slop= [X86-64,XEN] 5823 Set the timer slop (in nanoseconds) for the virtual Xen 5824 timers (default is 100000). This adjusts the minimum 5825 delta of virtualized Xen timers, where lower values 5826 improve timer resolution at the expense of processing 5827 more timer interrupts. 5828 5829 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5830 Disables the PV optimizations forcing the guest to run 5831 as generic guest with no PV drivers. Currently support 5832 XEN HVM, KVM, HYPER_V and VMWARE guest. 5833 5834 xirc2ps_cs= [NET,PCMCIA] 5835 Format: 5836 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5837 5838 xive= [PPC] 5839 By default on POWER9 and above, the kernel will 5840 natively use the XIVE interrupt controller. This option 5841 allows the fallback firmware mode to be used: 5842 5843 off Fallback to firmware control of XIVE interrupt 5844 controller on both pseries and powernv 5845 platforms. Only useful on POWER9 and above. 5846 5847 xhci-hcd.quirks [USB,KNL] 5848 A hex value specifying bitmask with supplemental xhci 5849 host controller quirks. Meaning of each bit can be 5850 consulted in header drivers/usb/host/xhci.h. 5851 5852 xmon [PPC] 5853 Format: { early | on | rw | ro | off } 5854 Controls if xmon debugger is enabled. Default is off. 5855 Passing only "xmon" is equivalent to "xmon=early". 5856 early Call xmon as early as possible on boot; xmon 5857 debugger is called from setup_arch(). 5858 on xmon debugger hooks will be installed so xmon 5859 is only called on a kernel crash. Default mode, 5860 i.e. either "ro" or "rw" mode, is controlled 5861 with CONFIG_XMON_DEFAULT_RO_MODE. 5862 rw xmon debugger hooks will be installed so xmon 5863 is called only on a kernel crash, mode is write, 5864 meaning SPR registers, memory and, other data 5865 can be written using xmon commands. 5866 ro same as "rw" option above but SPR registers, 5867 memory, and other data can't be written using 5868 xmon commands. 5869 off xmon is disabled. 5870