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_EVENTS 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 AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <byte> or <bitmap-list> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_no_watchdog [HW,ACPI,WDT] 140 Ignore the ACPI-based watchdog interface (WDAT) and let 141 a native driver control the watchdog device instead. 142 143 acpi_rsdp= [ACPI,EFI,KEXEC] 144 Pass the RSDP address to the kernel, mostly used 145 on machines running EFI runtime service to boot the 146 second kernel for kdump. 147 148 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 149 Format: To spoof as Windows 98: ="Microsoft Windows" 150 151 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 152 of 2 which is mandated by ACPI 6) as the supported ACPI 153 specification revision (when using this switch, it may 154 be necessary to carry out a cold reboot _twice_ in a 155 row to make it take effect on the platform firmware). 156 157 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 158 acpi_osi="string1" # add string1 159 acpi_osi="!string2" # remove string2 160 acpi_osi=!* # remove all strings 161 acpi_osi=! # disable all built-in OS vendor 162 strings 163 acpi_osi=!! # enable all built-in OS vendor 164 strings 165 acpi_osi= # disable all strings 166 167 'acpi_osi=!' can be used in combination with single or 168 multiple 'acpi_osi="string1"' to support specific OS 169 vendor string(s). Note that such command can only 170 affect the default state of the OS vendor strings, thus 171 it cannot affect the default state of the feature group 172 strings and the current state of the OS vendor strings, 173 specifying it multiple times through kernel command line 174 is meaningless. This command is useful when one do not 175 care about the state of the feature group strings which 176 should be controlled by the OSPM. 177 Examples: 178 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 179 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 180 can make '_OSI("Windows 2000")' TRUE. 181 182 'acpi_osi=' cannot be used in combination with other 183 'acpi_osi=' command lines, the _OSI method will not 184 exist in the ACPI namespace. NOTE that such command can 185 only affect the _OSI support state, thus specifying it 186 multiple times through kernel command line is also 187 meaningless. 188 Examples: 189 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 190 FALSE. 191 192 'acpi_osi=!*' can be used in combination with single or 193 multiple 'acpi_osi="string1"' to support specific 194 string(s). Note that such command can affect the 195 current state of both the OS vendor strings and the 196 feature group strings, thus specifying it multiple times 197 through kernel command line is meaningful. But it may 198 still not able to affect the final state of a string if 199 there are quirks related to this string. This command 200 is useful when one want to control the state of the 201 feature group strings to debug BIOS issues related to 202 the OSPM features. 203 Examples: 204 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 205 '_OSI("Module Device")' FALSE. 206 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 207 '_OSI("Module Device")' TRUE. 208 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 209 equivalent to 210 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 211 and 212 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 213 they all will make '_OSI("Windows 2000")' TRUE. 214 215 acpi_pm_good [X86] 216 Override the pmtimer bug detection: force the kernel 217 to assume that this machine's pmtimer latches its value 218 and always returns good values. 219 220 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 221 Format: { level | edge | high | low } 222 223 acpi_skip_timer_override [HW,ACPI] 224 Recognize and ignore IRQ0/pin2 Interrupt Override. 225 For broken nForce2 BIOS resulting in XT-PIC timer. 226 227 acpi_sleep= [HW,ACPI] Sleep options 228 Format: { s3_bios, s3_mode, s3_beep, s4_hwsig, 229 s4_nohwsig, old_ordering, nonvs, 230 sci_force_enable, nobl } 231 See Documentation/power/video.rst for information on 232 s3_bios and s3_mode. 233 s3_beep is for debugging; it makes the PC's speaker beep 234 as soon as the kernel's real-mode entry point is called. 235 s4_hwsig causes the kernel to check the ACPI hardware 236 signature during resume from hibernation, and gracefully 237 refuse to resume if it has changed. This complies with 238 the ACPI specification but not with reality, since 239 Windows does not do this and many laptops do change it 240 on docking. So the default behaviour is to allow resume 241 and simply warn when the signature changes, unless the 242 s4_hwsig option is enabled. 243 s4_nohwsig prevents ACPI hardware signature from being 244 used (or even warned about) during resume. 245 old_ordering causes the ACPI 1.0 ordering of the _PTS 246 control method, with respect to putting devices into 247 low power states, to be enforced (the ACPI 2.0 ordering 248 of _PTS is used by default). 249 nonvs prevents the kernel from saving/restoring the 250 ACPI NVS memory during suspend/hibernation and resume. 251 sci_force_enable causes the kernel to set SCI_EN directly 252 on resume from S1/S3 (which is against the ACPI spec, 253 but some broken systems don't work without it). 254 nobl causes the internal blacklist of systems known to 255 behave incorrectly in some ways with respect to system 256 suspend and resume to be ignored (use wisely). 257 258 acpi_use_timer_override [HW,ACPI] 259 Use timer override. For some broken Nvidia NF5 boards 260 that require a timer override, but don't have HPET 261 262 add_efi_memmap [EFI; X86] Include EFI memory map in 263 kernel's map of available physical RAM. 264 265 agp= [AGP] 266 { off | try_unsupported } 267 off: disable AGP support 268 try_unsupported: try to drive unsupported chipsets 269 (may crash computer or cause data corruption) 270 271 ALSA [HW,ALSA] 272 See Documentation/sound/alsa-configuration.rst 273 274 alignment= [KNL,ARM] 275 Allow the default userspace alignment fault handler 276 behaviour to be specified. Bit 0 enables warnings, 277 bit 1 enables fixups, and bit 2 sends a segfault. 278 279 align_va_addr= [X86-64] 280 Align virtual addresses by clearing slice [14:12] when 281 allocating a VMA at process creation time. This option 282 gives you up to 3% performance improvement on AMD F15h 283 machines (where it is enabled by default) for a 284 CPU-intensive style benchmark, and it can vary highly in 285 a microbenchmark depending on workload and compiler. 286 287 32: only for 32-bit processes 288 64: only for 64-bit processes 289 on: enable for both 32- and 64-bit processes 290 off: disable for both 32- and 64-bit processes 291 292 alloc_snapshot [FTRACE] 293 Allocate the ftrace snapshot buffer on boot up when the 294 main buffer is allocated. This is handy if debugging 295 and you need to use tracing_snapshot() on boot up, and 296 do not want to use tracing_snapshot_alloc() as it needs 297 to be done where GFP_KERNEL allocations are allowed. 298 299 allow_mismatched_32bit_el0 [ARM64] 300 Allow execve() of 32-bit applications and setting of the 301 PER_LINUX32 personality on systems where only a strict 302 subset of the CPUs support 32-bit EL0. When this 303 parameter is present, the set of CPUs supporting 32-bit 304 EL0 is indicated by /sys/devices/system/cpu/aarch32_el0 305 and hot-unplug operations may be restricted. 306 307 See Documentation/arm64/asymmetric-32bit.rst for more 308 information. 309 310 amd_iommu= [HW,X86-64] 311 Pass parameters to the AMD IOMMU driver in the system. 312 Possible values are: 313 fullflush - Deprecated, equivalent to iommu.strict=1 314 off - do not initialize any AMD IOMMU found in 315 the system 316 force_isolation - Force device isolation for all 317 devices. The IOMMU driver is not 318 allowed anymore to lift isolation 319 requirements as needed. This option 320 does not override iommu=pt 321 force_enable - Force enable the IOMMU on platforms known 322 to be buggy with IOMMU enabled. Use this 323 option with care. 324 325 amd_iommu_dump= [HW,X86-64] 326 Enable AMD IOMMU driver option to dump the ACPI table 327 for AMD IOMMU. With this option enabled, AMD IOMMU 328 driver will print ACPI tables for AMD IOMMU during 329 IOMMU initialization. 330 331 amd_iommu_intr= [HW,X86-64] 332 Specifies one of the following AMD IOMMU interrupt 333 remapping modes: 334 legacy - Use legacy interrupt remapping mode. 335 vapic - Use virtual APIC mode, which allows IOMMU 336 to inject interrupts directly into guest. 337 This mode requires kvm-amd.avic=1. 338 (Default when IOMMU HW support is present.) 339 340 amijoy.map= [HW,JOY] Amiga joystick support 341 Map of devices attached to JOY0DAT and JOY1DAT 342 Format: <a>,<b> 343 See also Documentation/input/joydev/joystick.rst 344 345 analog.map= [HW,JOY] Analog joystick and gamepad support 346 Specifies type or capabilities of an analog joystick 347 connected to one of 16 gameports 348 Format: <type1>,<type2>,..<type16> 349 350 apc= [HW,SPARC] 351 Power management functions (SPARCstation-4/5 + deriv.) 352 Format: noidle 353 Disable APC CPU standby support. SPARCstation-Fox does 354 not play well with APC CPU idle - disable it if you have 355 APC and your system crashes randomly. 356 357 apic= [APIC,X86] Advanced Programmable Interrupt Controller 358 Change the output verbosity while booting 359 Format: { quiet (default) | verbose | debug } 360 Change the amount of debugging information output 361 when initialising the APIC and IO-APIC components. 362 For X86-32, this can also be used to specify an APIC 363 driver name. 364 Format: apic=driver_name 365 Examples: apic=bigsmp 366 367 apic_extnmi= [APIC,X86] External NMI delivery setting 368 Format: { bsp (default) | all | none } 369 bsp: External NMI is delivered only to CPU 0 370 all: External NMIs are broadcast to all CPUs as a 371 backup of CPU 0 372 none: External NMI is masked for all CPUs. This is 373 useful so that a dump capture kernel won't be 374 shot down by NMI 375 376 autoconf= [IPV6] 377 See Documentation/networking/ipv6.rst. 378 379 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 380 Limit apic dumping. The parameter defines the maximal 381 number of local apics being dumped. Also it is possible 382 to set it to "all" by meaning -- no limit here. 383 Format: { 1 (default) | 2 | ... | all }. 384 The parameter valid if only apic=debug or 385 apic=verbose is specified. 386 Example: apic=debug show_lapic=all 387 388 apm= [APM] Advanced Power Management 389 See header of arch/x86/kernel/apm_32.c. 390 391 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 392 Format: <io>,<irq>,<nodeID> 393 394 arm64.nobti [ARM64] Unconditionally disable Branch Target 395 Identification support 396 397 arm64.nopauth [ARM64] Unconditionally disable Pointer Authentication 398 support 399 400 arm64.nomte [ARM64] Unconditionally disable Memory Tagging Extension 401 support 402 403 ataflop= [HW,M68k] 404 405 atarimouse= [HW,MOUSE] Atari Mouse 406 407 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 408 EzKey and similar keyboards 409 410 atkbd.reset= [HW] Reset keyboard during initialization 411 412 atkbd.set= [HW] Select keyboard code set 413 Format: <int> (2 = AT (default), 3 = PS/2) 414 415 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 416 keyboards 417 418 atkbd.softraw= [HW] Choose between synthetic and real raw mode 419 Format: <bool> (0 = real, 1 = synthetic (default)) 420 421 atkbd.softrepeat= [HW] 422 Use software keyboard repeat 423 424 audit= [KNL] Enable the audit sub-system 425 Format: { "0" | "1" | "off" | "on" } 426 0 | off - kernel audit is disabled and can not be 427 enabled until the next reboot 428 unset - kernel audit is initialized but disabled and 429 will be fully enabled by the userspace auditd. 430 1 | on - kernel audit is initialized and partially 431 enabled, storing at most audit_backlog_limit 432 messages in RAM until it is fully enabled by the 433 userspace auditd. 434 Default: unset 435 436 audit_backlog_limit= [KNL] Set the audit queue size limit. 437 Format: <int> (must be >=0) 438 Default: 64 439 440 bau= [X86_UV] Enable the BAU on SGI UV. The default 441 behavior is to disable the BAU (i.e. bau=0). 442 Format: { "0" | "1" } 443 0 - Disable the BAU. 444 1 - Enable the BAU. 445 unset - Disable the BAU. 446 447 baycom_epp= [HW,AX25] 448 Format: <io>,<mode> 449 450 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 451 Format: <io>,<mode> 452 See header of drivers/net/hamradio/baycom_par.c. 453 454 baycom_ser_fdx= [HW,AX25] 455 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 456 Format: <io>,<irq>,<mode>[,<baud>] 457 See header of drivers/net/hamradio/baycom_ser_fdx.c. 458 459 baycom_ser_hdx= [HW,AX25] 460 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 461 Format: <io>,<irq>,<mode> 462 See header of drivers/net/hamradio/baycom_ser_hdx.c. 463 464 bert_disable [ACPI] 465 Disable BERT OS support on buggy BIOSes. 466 467 bgrt_disable [ACPI][X86] 468 Disable BGRT to avoid flickering OEM logo. 469 470 blkdevparts= Manual partition parsing of block device(s) for 471 embedded devices based on command line input. 472 See Documentation/block/cmdline-partition.rst 473 474 boot_delay= Milliseconds to delay each printk during boot. 475 Values larger than 10 seconds (10000) are changed to 476 no delay (0). 477 Format: integer 478 479 bootconfig [KNL] 480 Extended command line options can be added to an initrd 481 and this will cause the kernel to look for it. 482 483 See Documentation/admin-guide/bootconfig.rst 484 485 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 486 bttv.radio= Most important insmod options are available as 487 kernel args too. 488 bttv.pll= See Documentation/admin-guide/media/bttv.rst 489 bttv.tuner= 490 491 bulk_remove=off [PPC] This parameter disables the use of the pSeries 492 firmware feature for flushing multiple hpte entries 493 at a time. 494 495 c101= [NET] Moxa C101 synchronous serial card 496 497 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 498 Sometimes CPU hardware bugs make them report the cache 499 size incorrectly. The kernel will attempt work arounds 500 to fix known problems, but for some CPUs it is not 501 possible to determine what the correct size should be. 502 This option provides an override for these situations. 503 504 carrier_timeout= 505 [NET] Specifies amount of time (in seconds) that 506 the kernel should wait for a network carrier. By default 507 it waits 120 seconds. 508 509 ca_keys= [KEYS] This parameter identifies a specific key(s) on 510 the system trusted keyring to be used for certificate 511 trust validation. 512 format: { id:<keyid> | builtin } 513 514 cca= [MIPS] Override the kernel pages' cache coherency 515 algorithm. Accepted values range from 0 to 7 516 inclusive. See arch/mips/include/asm/pgtable-bits.h 517 for platform specific values (SB1, Loongson3 and 518 others). 519 520 ccw_timeout_log [S390] 521 See Documentation/s390/common_io.rst for details. 522 523 cgroup_disable= [KNL] Disable a particular controller or optional feature 524 Format: {name of the controller(s) or feature(s) to disable} 525 The effects of cgroup_disable=foo are: 526 - foo isn't auto-mounted if you mount all cgroups in 527 a single hierarchy 528 - foo isn't visible as an individually mountable 529 subsystem 530 - if foo is an optional feature then the feature is 531 disabled and corresponding cgroup files are not 532 created 533 {Currently only "memory" controller deal with this and 534 cut the overhead, others just disable the usage. So 535 only cgroup_disable=memory is actually worthy} 536 Specifying "pressure" disables per-cgroup pressure 537 stall information accounting feature 538 539 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 540 Format: { { controller | "all" | "named" } 541 [,{ controller | "all" | "named" }...] } 542 Like cgroup_disable, but only applies to cgroup v1; 543 the blacklisted controllers remain available in cgroup2. 544 "all" blacklists all controllers and "named" disables 545 named mounts. Specifying both "all" and "named" disables 546 all v1 hierarchies. 547 548 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 549 Format: <string> 550 nosocket -- Disable socket memory accounting. 551 nokmem -- Disable kernel memory accounting. 552 553 checkreqprot [SELINUX] Set initial checkreqprot flag value. 554 Format: { "0" | "1" } 555 See security/selinux/Kconfig help text. 556 0 -- check protection applied by kernel (includes 557 any implied execute protection). 558 1 -- check protection requested by application. 559 Default value is set via a kernel config option. 560 Value can be changed at runtime via 561 /sys/fs/selinux/checkreqprot. 562 Setting checkreqprot to 1 is deprecated. 563 564 cio_ignore= [S390] 565 See Documentation/s390/common_io.rst for details. 566 567 clearcpuid=X[,X...] [X86] 568 Disable CPUID feature X for the kernel. See 569 arch/x86/include/asm/cpufeatures.h for the valid bit 570 numbers X. Note the Linux-specific bits are not necessarily 571 stable over kernel options, but the vendor-specific 572 ones should be. 573 X can also be a string as appearing in the flags: line 574 in /proc/cpuinfo which does not have the above 575 instability issue. However, not all features have names 576 in /proc/cpuinfo. 577 Note that using this option will taint your kernel. 578 Also note that user programs calling CPUID directly 579 or using the feature without checking anything 580 will still see it. This just prevents it from 581 being used by the kernel or shown in /proc/cpuinfo. 582 Also note the kernel might malfunction if you disable 583 some critical bits. 584 585 clk_ignore_unused 586 [CLK] 587 Prevents the clock framework from automatically gating 588 clocks that have not been explicitly enabled by a Linux 589 device driver but are enabled in hardware at reset or 590 by the bootloader/firmware. Note that this does not 591 force such clocks to be always-on nor does it reserve 592 those clocks in any way. This parameter is useful for 593 debug and development, but should not be needed on a 594 platform with proper driver support. For more 595 information, see Documentation/driver-api/clk.rst. 596 597 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 598 [Deprecated] 599 Forces specified clocksource (if available) to be used 600 when calculating gettimeofday(). If specified 601 clocksource is not available, it defaults to PIT. 602 Format: { pit | tsc | cyclone | pmtmr } 603 604 clocksource= Override the default clocksource 605 Format: <string> 606 Override the default clocksource and use the clocksource 607 with the name specified. 608 Some clocksource names to choose from, depending on 609 the platform: 610 [all] jiffies (this is the base, fallback clocksource) 611 [ACPI] acpi_pm 612 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 613 pxa_timer,timer3,32k_counter,timer0_1 614 [X86-32] pit,hpet,tsc; 615 scx200_hrt on Geode; cyclone on IBM x440 616 [MIPS] MIPS 617 [PARISC] cr16 618 [S390] tod 619 [SH] SuperH 620 [SPARC64] tick 621 [X86-64] hpet,tsc 622 623 clocksource.arm_arch_timer.evtstrm= 624 [ARM,ARM64] 625 Format: <bool> 626 Enable/disable the eventstream feature of the ARM 627 architected timer so that code using WFE-based polling 628 loops can be debugged more effectively on production 629 systems. 630 631 clocksource.max_cswd_read_retries= [KNL] 632 Number of clocksource_watchdog() retries due to 633 external delays before the clock will be marked 634 unstable. Defaults to two retries, that is, 635 three attempts to read the clock under test. 636 637 clocksource.verify_n_cpus= [KNL] 638 Limit the number of CPUs checked for clocksources 639 marked with CLOCK_SOURCE_VERIFY_PERCPU that 640 are marked unstable due to excessive skew. 641 A negative value says to check all CPUs, while 642 zero says not to check any. Values larger than 643 nr_cpu_ids are silently truncated to nr_cpu_ids. 644 The actual CPUs are chosen randomly, with 645 no replacement if the same CPU is chosen twice. 646 647 clocksource-wdtest.holdoff= [KNL] 648 Set the time in seconds that the clocksource 649 watchdog test waits before commencing its tests. 650 Defaults to zero when built as a module and to 651 10 seconds when built into the kernel. 652 653 cma=nn[MG]@[start[MG][-end[MG]]] 654 [KNL,CMA] 655 Sets the size of kernel global memory area for 656 contiguous memory allocations and optionally the 657 placement constraint by the physical address range of 658 memory allocations. A value of 0 disables CMA 659 altogether. For more information, see 660 kernel/dma/contiguous.c 661 662 cma_pernuma=nn[MG] 663 [ARM64,KNL,CMA] 664 Sets the size of kernel per-numa memory area for 665 contiguous memory allocations. A value of 0 disables 666 per-numa CMA altogether. And If this option is not 667 specificed, the default value is 0. 668 With per-numa CMA enabled, DMA users on node nid will 669 first try to allocate buffer from the pernuma area 670 which is located in node nid, if the allocation fails, 671 they will fallback to the global default memory area. 672 673 cmo_free_hint= [PPC] Format: { yes | no } 674 Specify whether pages are marked as being inactive 675 when they are freed. This is used in CMO environments 676 to determine OS memory pressure for page stealing by 677 a hypervisor. 678 Default: yes 679 680 coherent_pool=nn[KMG] [ARM,KNL] 681 Sets the size of memory pool for coherent, atomic dma 682 allocations, by default set to 256K. 683 684 com20020= [HW,NET] ARCnet - COM20020 chipset 685 Format: 686 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 687 688 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 689 Format: <io>[,<irq>] 690 691 com90xx= [HW,NET] 692 ARCnet - COM90xx chipset (memory-mapped buffers) 693 Format: <io>[,<irq>[,<memstart>]] 694 695 condev= [HW,S390] console device 696 conmode= 697 698 console= [KNL] Output console device and options. 699 700 tty<n> Use the virtual console device <n>. 701 702 ttyS<n>[,options] 703 ttyUSB0[,options] 704 Use the specified serial port. The options are of 705 the form "bbbbpnf", where "bbbb" is the baud rate, 706 "p" is parity ("n", "o", or "e"), "n" is number of 707 bits, and "f" is flow control ("r" for RTS or 708 omit it). Default is "9600n8". 709 710 See Documentation/admin-guide/serial-console.rst for more 711 information. See 712 Documentation/networking/netconsole.rst for an 713 alternative. 714 715 uart[8250],io,<addr>[,options] 716 uart[8250],mmio,<addr>[,options] 717 uart[8250],mmio16,<addr>[,options] 718 uart[8250],mmio32,<addr>[,options] 719 uart[8250],0x<addr>[,options] 720 Start an early, polled-mode console on the 8250/16550 721 UART at the specified I/O port or MMIO address, 722 switching to the matching ttyS device later. 723 MMIO inter-register address stride is either 8-bit 724 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 725 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 726 to be equivalent to 'mmio'. 'options' are specified in 727 the same format described for ttyS above; if unspecified, 728 the h/w is not re-initialized. 729 730 hvc<n> Use the hypervisor console device <n>. This is for 731 both Xen and PowerPC hypervisors. 732 733 { null | "" } 734 Use to disable console output, i.e., to have kernel 735 console messages discarded. 736 This must be the only console= parameter used on the 737 kernel command line. 738 739 If the device connected to the port is not a TTY but a braille 740 device, prepend "brl," before the device type, for instance 741 console=brl,ttyS0 742 For now, only VisioBraille is supported. 743 744 console_msg_format= 745 [KNL] Change console messages format 746 default 747 By default we print messages on consoles in 748 "[time stamp] text\n" format (time stamp may not be 749 printed, depending on CONFIG_PRINTK_TIME or 750 `printk_time' param). 751 syslog 752 Switch to syslog format: "<%u>[time stamp] text\n" 753 IOW, each message will have a facility and loglevel 754 prefix. The format is similar to one used by syslog() 755 syscall, or to executing "dmesg -S --raw" or to reading 756 from /proc/kmsg. 757 758 consoleblank= [KNL] The console blank (screen saver) timeout in 759 seconds. A value of 0 disables the blank timer. 760 Defaults to 0. 761 762 coredump_filter= 763 [KNL] Change the default value for 764 /proc/<pid>/coredump_filter. 765 See also Documentation/filesystems/proc.rst. 766 767 coresight_cpu_debug.enable 768 [ARM,ARM64] 769 Format: <bool> 770 Enable/disable the CPU sampling based debugging. 771 0: default value, disable debugging 772 1: enable debugging at boot time 773 774 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 775 Format: 776 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 777 778 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 779 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 780 Some features depend on CPU0. Known dependencies are: 781 1. Resume from suspend/hibernate depends on CPU0. 782 Suspend/hibernate will fail if CPU0 is offline and you 783 need to online CPU0 before suspend/hibernate. 784 2. PIC interrupts also depend on CPU0. CPU0 can't be 785 removed if a PIC interrupt is detected. 786 It's said poweroff/reboot may depend on CPU0 on some 787 machines although I haven't seen such issues so far 788 after CPU0 is offline on a few tested machines. 789 If the dependencies are under your control, you can 790 turn on cpu0_hotplug. 791 792 cpuidle.off=1 [CPU_IDLE] 793 disable the cpuidle sub-system 794 795 cpuidle.governor= 796 [CPU_IDLE] Name of the cpuidle governor to use. 797 798 cpufreq.off=1 [CPU_FREQ] 799 disable the cpufreq sub-system 800 801 cpufreq.default_governor= 802 [CPU_FREQ] Name of the default cpufreq governor or 803 policy to use. This governor must be registered in the 804 kernel before the cpufreq driver probes. 805 806 cpu_init_udelay=N 807 [X86] Delay for N microsec between assert and de-assert 808 of APIC INIT to start processors. This delay occurs 809 on every CPU online, such as boot, and resume from suspend. 810 Default: 10000 811 812 crash_kexec_post_notifiers 813 Run kdump after running panic-notifiers and dumping 814 kmsg. This only for the users who doubt kdump always 815 succeeds in any situation. 816 Note that this also increases risks of kdump failure, 817 because some panic notifiers can make the crashed 818 kernel more unstable. 819 820 crashkernel=size[KMG][@offset[KMG]] 821 [KNL] Using kexec, Linux can switch to a 'crash kernel' 822 upon panic. This parameter reserves the physical 823 memory region [offset, offset + size] for that kernel 824 image. If '@offset' is omitted, then a suitable offset 825 is selected automatically. 826 [KNL, X86-64] Select a region under 4G first, and 827 fall back to reserve region above 4G when '@offset' 828 hasn't been specified. 829 See Documentation/admin-guide/kdump/kdump.rst for further details. 830 831 crashkernel=range1:size1[,range2:size2,...][@offset] 832 [KNL] Same as above, but depends on the memory 833 in the running system. The syntax of range is 834 start-[end] where start and end are both 835 a memory unit (amount[KMG]). See also 836 Documentation/admin-guide/kdump/kdump.rst for an example. 837 838 crashkernel=size[KMG],high 839 [KNL, X86-64, ARM64] range could be above 4G. Allow kernel 840 to allocate physical memory region from top, so could 841 be above 4G if system have more than 4G ram installed. 842 Otherwise memory region will be allocated below 4G, if 843 available. 844 It will be ignored if crashkernel=X is specified. 845 crashkernel=size[KMG],low 846 [KNL, X86-64] range under 4G. When crashkernel=X,high 847 is passed, kernel could allocate physical memory region 848 above 4G, that cause second kernel crash on system 849 that require some amount of low memory, e.g. swiotlb 850 requires at least 64M+32K low memory, also enough extra 851 low memory is needed to make sure DMA buffers for 32-bit 852 devices won't run out. Kernel would try to allocate 853 at least 256M below 4G automatically. 854 This one lets the user specify own low range under 4G 855 for second kernel instead. 856 0: to disable low allocation. 857 It will be ignored when crashkernel=X,high is not used 858 or memory reserved is below 4G. 859 860 [KNL, ARM64] range in low memory. 861 This one lets the user specify a low range in the 862 DMA zone for the crash dump kernel. 863 It will be ignored when crashkernel=X,high is not used 864 or memory reserved is located in the DMA zones. 865 866 cryptomgr.notests 867 [KNL] Disable crypto self-tests 868 869 cs89x0_dma= [HW,NET] 870 Format: <dma> 871 872 cs89x0_media= [HW,NET] 873 Format: { rj45 | aui | bnc } 874 875 csdlock_debug= [KNL] Enable debug add-ons of cross-CPU function call 876 handling. When switched on, additional debug data is 877 printed to the console in case a hanging CPU is 878 detected, and that CPU is pinged again in order to try 879 to resolve the hang situation. 880 0: disable csdlock debugging (default) 881 1: enable basic csdlock debugging (minor impact) 882 ext: enable extended csdlock debugging (more impact, 883 but more data) 884 885 dasd= [HW,NET] 886 See header of drivers/s390/block/dasd_devmap.c. 887 888 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 889 (one device per port) 890 Format: <port#>,<type> 891 See also Documentation/input/devices/joystick-parport.rst 892 893 debug [KNL] Enable kernel debugging (events log level). 894 895 debug_boot_weak_hash 896 [KNL] Enable printing [hashed] pointers early in the 897 boot sequence. If enabled, we use a weak hash instead 898 of siphash to hash pointers. Use this option if you are 899 seeing instances of '(___ptrval___)') and need to see a 900 value (hashed pointer) instead. Cryptographically 901 insecure, please do not use on production kernels. 902 903 debug_locks_verbose= 904 [KNL] verbose locking self-tests 905 Format: <int> 906 Print debugging info while doing the locking API 907 self-tests. 908 Bitmask for the various LOCKTYPE_ tests. Defaults to 0 909 (no extra messages), setting it to -1 (all bits set) 910 will print _a_lot_ more information - normally only 911 useful to lockdep developers. 912 913 debug_objects [KNL] Enable object debugging 914 915 no_debug_objects 916 [KNL] Disable object debugging 917 918 debug_guardpage_minorder= 919 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 920 parameter allows control of the order of pages that will 921 be intentionally kept free (and hence protected) by the 922 buddy allocator. Bigger value increase the probability 923 of catching random memory corruption, but reduce the 924 amount of memory for normal system use. The maximum 925 possible value is MAX_ORDER/2. Setting this parameter 926 to 1 or 2 should be enough to identify most random 927 memory corruption problems caused by bugs in kernel or 928 driver code when a CPU writes to (or reads from) a 929 random memory location. Note that there exists a class 930 of memory corruptions problems caused by buggy H/W or 931 F/W or by drivers badly programing DMA (basically when 932 memory is written at bus level and the CPU MMU is 933 bypassed) which are not detectable by 934 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 935 tracking down these problems. 936 937 debug_pagealloc= 938 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 939 enables the feature at boot time. By default, it is 940 disabled and the system will work mostly the same as a 941 kernel built without CONFIG_DEBUG_PAGEALLOC. 942 Note: to get most of debug_pagealloc error reports, it's 943 useful to also enable the page_owner functionality. 944 on: enable the feature 945 946 debugfs= [KNL] This parameter enables what is exposed to userspace 947 and debugfs internal clients. 948 Format: { on, no-mount, off } 949 on: All functions are enabled. 950 no-mount: 951 Filesystem is not registered but kernel clients can 952 access APIs and a crashkernel can be used to read 953 its content. There is nothing to mount. 954 off: Filesystem is not registered and clients 955 get a -EPERM as result when trying to register files 956 or directories within debugfs. 957 This is equivalent of the runtime functionality if 958 debugfs was not enabled in the kernel at all. 959 Default value is set in build-time with a kernel configuration. 960 961 debugpat [X86] Enable PAT debugging 962 963 decnet.addr= [HW,NET] 964 Format: <area>[,<node>] 965 See also Documentation/networking/decnet.rst. 966 967 default_hugepagesz= 968 [HW] The size of the default HugeTLB page. This is 969 the size represented by the legacy /proc/ hugepages 970 APIs. In addition, this is the default hugetlb size 971 used for shmget(), mmap() and mounting hugetlbfs 972 filesystems. If not specified, defaults to the 973 architecture's default huge page size. Huge page 974 sizes are architecture dependent. See also 975 Documentation/admin-guide/mm/hugetlbpage.rst. 976 Format: size[KMG] 977 978 deferred_probe_timeout= 979 [KNL] Debugging option to set a timeout in seconds for 980 deferred probe to give up waiting on dependencies to 981 probe. Only specific dependencies (subsystems or 982 drivers) that have opted in will be ignored. A timeout of 0 983 will timeout at the end of initcalls. This option will also 984 dump out devices still on the deferred probe list after 985 retrying. 986 987 delayacct [KNL] Enable per-task delay accounting 988 989 dell_smm_hwmon.ignore_dmi= 990 [HW] Continue probing hardware even if DMI data 991 indicates that the driver is running on unsupported 992 hardware. 993 994 dell_smm_hwmon.force= 995 [HW] Activate driver even if SMM BIOS signature does 996 not match list of supported models and enable otherwise 997 blacklisted features. 998 999 dell_smm_hwmon.power_status= 1000 [HW] Report power status in /proc/i8k 1001 (disabled by default). 1002 1003 dell_smm_hwmon.restricted= 1004 [HW] Allow controlling fans only if SYS_ADMIN 1005 capability is set. 1006 1007 dell_smm_hwmon.fan_mult= 1008 [HW] Factor to multiply fan speed with. 1009 1010 dell_smm_hwmon.fan_max= 1011 [HW] Maximum configurable fan speed. 1012 1013 dfltcc= [HW,S390] 1014 Format: { on | off | def_only | inf_only | always } 1015 on: s390 zlib hardware support for compression on 1016 level 1 and decompression (default) 1017 off: No s390 zlib hardware support 1018 def_only: s390 zlib hardware support for deflate 1019 only (compression on level 1) 1020 inf_only: s390 zlib hardware support for inflate 1021 only (decompression) 1022 always: Same as 'on' but ignores the selected compression 1023 level always using hardware support (used for debugging) 1024 1025 dhash_entries= [KNL] 1026 Set number of hash buckets for dentry cache. 1027 1028 disable_1tb_segments [PPC] 1029 Disables the use of 1TB hash page table segments. This 1030 causes the kernel to fall back to 256MB segments which 1031 can be useful when debugging issues that require an SLB 1032 miss to occur. 1033 1034 stress_slb [PPC] 1035 Limits the number of kernel SLB entries, and flushes 1036 them frequently to increase the rate of SLB faults 1037 on kernel addresses. 1038 1039 disable= [IPV6] 1040 See Documentation/networking/ipv6.rst. 1041 1042 disable_radix [PPC] 1043 Disable RADIX MMU mode on POWER9 1044 1045 radix_hcall_invalidate=on [PPC/PSERIES] 1046 Disable RADIX GTSE feature and use hcall for TLB 1047 invalidate. 1048 1049 disable_tlbie [PPC] 1050 Disable TLBIE instruction. Currently does not work 1051 with KVM, with HASH MMU, or with coherent accelerators. 1052 1053 disable_cpu_apicid= [X86,APIC,SMP] 1054 Format: <int> 1055 The number of initial APIC ID for the 1056 corresponding CPU to be disabled at boot, 1057 mostly used for the kdump 2nd kernel to 1058 disable BSP to wake up multiple CPUs without 1059 causing system reset or hang due to sending 1060 INIT from AP to BSP. 1061 1062 disable_ddw [PPC/PSERIES] 1063 Disable Dynamic DMA Window support. Use this 1064 to workaround buggy firmware. 1065 1066 disable_ipv6= [IPV6] 1067 See Documentation/networking/ipv6.rst. 1068 1069 disable_mtrr_cleanup [X86] 1070 The kernel tries to adjust MTRR layout from continuous 1071 to discrete, to make X server driver able to add WB 1072 entry later. This parameter disables that. 1073 1074 disable_mtrr_trim [X86, Intel and AMD only] 1075 By default the kernel will trim any uncacheable 1076 memory out of your available memory pool based on 1077 MTRR settings. This parameter disables that behavior, 1078 possibly causing your machine to run very slowly. 1079 1080 disable_timer_pin_1 [X86] 1081 Disable PIN 1 of APIC timer 1082 Can be useful to work around chipset bugs. 1083 1084 dis_ucode_ldr [X86] Disable the microcode loader. 1085 1086 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 1087 this option disables the debugging code at boot. 1088 1089 dma_debug_entries=<number> 1090 This option allows to tune the number of preallocated 1091 entries for DMA-API debugging code. One entry is 1092 required per DMA-API allocation. Use this if the 1093 DMA-API debugging code disables itself because the 1094 architectural default is too low. 1095 1096 dma_debug_driver=<driver_name> 1097 With this option the DMA-API debugging driver 1098 filter feature can be enabled at boot time. Just 1099 pass the driver to filter for as the parameter. 1100 The filter can be disabled or changed to another 1101 driver later using sysfs. 1102 1103 driver_async_probe= [KNL] 1104 List of driver names to be probed asynchronously. 1105 Format: <driver_name1>,<driver_name2>... 1106 1107 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 1108 Broken monitors, graphic adapters, KVMs and EDIDless 1109 panels may send no or incorrect EDID data sets. 1110 This parameter allows to specify an EDID data sets 1111 in the /lib/firmware directory that are used instead. 1112 Generic built-in EDID data sets are used, if one of 1113 edid/1024x768.bin, edid/1280x1024.bin, 1114 edid/1680x1050.bin, or edid/1920x1080.bin is given 1115 and no file with the same name exists. Details and 1116 instructions how to build your own EDID data are 1117 available in Documentation/admin-guide/edid.rst. An EDID 1118 data set will only be used for a particular connector, 1119 if its name and a colon are prepended to the EDID 1120 name. Each connector may use a unique EDID data 1121 set by separating the files with a comma. An EDID 1122 data set with no connector name will be used for 1123 any connectors not explicitly specified. 1124 1125 dscc4.setup= [NET] 1126 1127 dt_cpu_ftrs= [PPC] 1128 Format: {"off" | "known"} 1129 Control how the dt_cpu_ftrs device-tree binding is 1130 used for CPU feature discovery and setup (if it 1131 exists). 1132 off: Do not use it, fall back to legacy cpu table. 1133 known: Do not pass through unknown features to guests 1134 or userspace, only those that the kernel is aware of. 1135 1136 dump_apple_properties [X86] 1137 Dump name and content of EFI device properties on 1138 x86 Macs. Useful for driver authors to determine 1139 what data is available or for reverse-engineering. 1140 1141 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1142 <module>.dyndbg[="val"] 1143 Enable debug messages at boot time. See 1144 Documentation/admin-guide/dynamic-debug-howto.rst 1145 for details. 1146 1147 nopku [X86] Disable Memory Protection Keys CPU feature found 1148 in some Intel CPUs. 1149 1150 <module>.async_probe [KNL] 1151 Enable asynchronous probe on this module. 1152 1153 early_ioremap_debug [KNL] 1154 Enable debug messages in early_ioremap support. This 1155 is useful for tracking down temporary early mappings 1156 which are not unmapped. 1157 1158 earlycon= [KNL] Output early console device and options. 1159 1160 When used with no options, the early console is 1161 determined by stdout-path property in device tree's 1162 chosen node or the ACPI SPCR table if supported by 1163 the platform. 1164 1165 cdns,<addr>[,options] 1166 Start an early, polled-mode console on a Cadence 1167 (xuartps) serial port at the specified address. Only 1168 supported option is baud rate. If baud rate is not 1169 specified, the serial port must already be setup and 1170 configured. 1171 1172 uart[8250],io,<addr>[,options] 1173 uart[8250],mmio,<addr>[,options] 1174 uart[8250],mmio32,<addr>[,options] 1175 uart[8250],mmio32be,<addr>[,options] 1176 uart[8250],0x<addr>[,options] 1177 Start an early, polled-mode console on the 8250/16550 1178 UART at the specified I/O port or MMIO address. 1179 MMIO inter-register address stride is either 8-bit 1180 (mmio) or 32-bit (mmio32 or mmio32be). 1181 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1182 to be equivalent to 'mmio'. 'options' are specified 1183 in the same format described for "console=ttyS<n>"; if 1184 unspecified, the h/w is not initialized. 1185 1186 pl011,<addr> 1187 pl011,mmio32,<addr> 1188 Start an early, polled-mode console on a pl011 serial 1189 port at the specified address. The pl011 serial port 1190 must already be setup and configured. Options are not 1191 yet supported. If 'mmio32' is specified, then only 1192 the driver will use only 32-bit accessors to read/write 1193 the device registers. 1194 1195 liteuart,<addr> 1196 Start an early console on a litex serial port at the 1197 specified address. The serial port must already be 1198 setup and configured. Options are not yet supported. 1199 1200 meson,<addr> 1201 Start an early, polled-mode console on a meson serial 1202 port at the specified address. The serial port must 1203 already be setup and configured. Options are not yet 1204 supported. 1205 1206 msm_serial,<addr> 1207 Start an early, polled-mode console on an msm serial 1208 port at the specified address. The serial port 1209 must already be setup and configured. Options are not 1210 yet supported. 1211 1212 msm_serial_dm,<addr> 1213 Start an early, polled-mode console on an msm serial 1214 dm port at the specified address. The serial port 1215 must already be setup and configured. Options are not 1216 yet supported. 1217 1218 owl,<addr> 1219 Start an early, polled-mode console on a serial port 1220 of an Actions Semi SoC, such as S500 or S900, at the 1221 specified address. The serial port must already be 1222 setup and configured. Options are not yet supported. 1223 1224 rda,<addr> 1225 Start an early, polled-mode console on a serial port 1226 of an RDA Micro SoC, such as RDA8810PL, at the 1227 specified address. The serial port must already be 1228 setup and configured. Options are not yet supported. 1229 1230 sbi 1231 Use RISC-V SBI (Supervisor Binary Interface) for early 1232 console. 1233 1234 smh Use ARM semihosting calls for early console. 1235 1236 s3c2410,<addr> 1237 s3c2412,<addr> 1238 s3c2440,<addr> 1239 s3c6400,<addr> 1240 s5pv210,<addr> 1241 exynos4210,<addr> 1242 Use early console provided by serial driver available 1243 on Samsung SoCs, requires selecting proper type and 1244 a correct base address of the selected UART port. The 1245 serial port must already be setup and configured. 1246 Options are not yet supported. 1247 1248 lantiq,<addr> 1249 Start an early, polled-mode console on a lantiq serial 1250 (lqasc) port at the specified address. The serial port 1251 must already be setup and configured. Options are not 1252 yet supported. 1253 1254 lpuart,<addr> 1255 lpuart32,<addr> 1256 Use early console provided by Freescale LP UART driver 1257 found on Freescale Vybrid and QorIQ LS1021A processors. 1258 A valid base address must be provided, and the serial 1259 port must already be setup and configured. 1260 1261 ec_imx21,<addr> 1262 ec_imx6q,<addr> 1263 Start an early, polled-mode, output-only console on the 1264 Freescale i.MX UART at the specified address. The UART 1265 must already be setup and configured. 1266 1267 ar3700_uart,<addr> 1268 Start an early, polled-mode console on the 1269 Armada 3700 serial port at the specified 1270 address. The serial port must already be setup 1271 and configured. Options are not yet supported. 1272 1273 qcom_geni,<addr> 1274 Start an early, polled-mode console on a Qualcomm 1275 Generic Interface (GENI) based serial port at the 1276 specified address. The serial port must already be 1277 setup and configured. Options are not yet supported. 1278 1279 efifb,[options] 1280 Start an early, unaccelerated console on the EFI 1281 memory mapped framebuffer (if available). On cache 1282 coherent non-x86 systems that use system memory for 1283 the framebuffer, pass the 'ram' option so that it is 1284 mapped with the correct attributes. 1285 1286 linflex,<addr> 1287 Use early console provided by Freescale LINFlexD UART 1288 serial driver for NXP S32V234 SoCs. A valid base 1289 address must be provided, and the serial port must 1290 already be setup and configured. 1291 1292 earlyprintk= [X86,SH,ARM,M68k,S390] 1293 earlyprintk=vga 1294 earlyprintk=sclp 1295 earlyprintk=xen 1296 earlyprintk=serial[,ttySn[,baudrate]] 1297 earlyprintk=serial[,0x...[,baudrate]] 1298 earlyprintk=ttySn[,baudrate] 1299 earlyprintk=dbgp[debugController#] 1300 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1301 earlyprintk=xdbc[xhciController#] 1302 1303 earlyprintk is useful when the kernel crashes before 1304 the normal console is initialized. It is not enabled by 1305 default because it has some cosmetic problems. 1306 1307 Append ",keep" to not disable it when the real console 1308 takes over. 1309 1310 Only one of vga, serial, or usb debug port can 1311 be used at a time. 1312 1313 Currently only ttyS0 and ttyS1 may be specified by 1314 name. Other I/O ports may be explicitly specified 1315 on some architectures (x86 and arm at least) by 1316 replacing ttySn with an I/O port address, like this: 1317 earlyprintk=serial,0x1008,115200 1318 You can find the port for a given device in 1319 /proc/tty/driver/serial: 1320 2: uart:ST16650V2 port:00001008 irq:18 ... 1321 1322 Interaction with the standard serial driver is not 1323 very good. 1324 1325 The VGA output is eventually overwritten by 1326 the real console. 1327 1328 The xen option can only be used in Xen domains. 1329 1330 The sclp output can only be used on s390. 1331 1332 The optional "force" to "pciserial" enables use of a 1333 PCI device even when its classcode is not of the 1334 UART class. 1335 1336 edac_report= [HW,EDAC] Control how to report EDAC event 1337 Format: {"on" | "off" | "force"} 1338 on: enable EDAC to report H/W event. May be overridden 1339 by other higher priority error reporting module. 1340 off: disable H/W event reporting through EDAC. 1341 force: enforce the use of EDAC to report H/W event. 1342 default: on. 1343 1344 edd= [EDD] 1345 Format: {"off" | "on" | "skip[mbr]"} 1346 1347 efi= [EFI] 1348 Format: { "debug", "disable_early_pci_dma", 1349 "nochunk", "noruntime", "nosoftreserve", 1350 "novamap", "no_disable_early_pci_dma" } 1351 debug: enable misc debug output. 1352 disable_early_pci_dma: disable the busmaster bit on all 1353 PCI bridges while in the EFI boot stub. 1354 nochunk: disable reading files in "chunks" in the EFI 1355 boot stub, as chunking can cause problems with some 1356 firmware implementations. 1357 noruntime : disable EFI runtime services support 1358 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1359 attribute may cause the kernel to reserve the 1360 memory range for a memory mapping driver to 1361 claim. Specify efi=nosoftreserve to disable this 1362 reservation and treat the memory by its base type 1363 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1364 novamap: do not call SetVirtualAddressMap(). 1365 no_disable_early_pci_dma: Leave the busmaster bit set 1366 on all PCI bridges while in the EFI boot stub 1367 1368 efi_no_storage_paranoia [EFI; X86] 1369 Using this parameter you can use more than 50% of 1370 your efi variable storage. Use this parameter only if 1371 you are really sure that your UEFI does sane gc and 1372 fulfills the spec otherwise your board may brick. 1373 1374 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1375 Add arbitrary attribute to specific memory range by 1376 updating original EFI memory map. 1377 Region of memory which aa attribute is added to is 1378 from ss to ss+nn. 1379 1380 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1381 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1382 attribute is added to range 0x100000000-0x180000000 and 1383 0x10a0000000-0x1120000000. 1384 1385 If efi_fake_mem=8G@9G:0x40000 is specified, the 1386 EFI_MEMORY_SP(0x40000) attribute is added to 1387 range 0x240000000-0x43fffffff. 1388 1389 Using this parameter you can do debugging of EFI memmap 1390 related features. For example, you can do debugging of 1391 Address Range Mirroring feature even if your box 1392 doesn't support it, or mark specific memory as 1393 "soft reserved". 1394 1395 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1396 that is to be dynamically loaded by Linux. If there are 1397 multiple variables with the same name but with different 1398 vendor GUIDs, all of them will be loaded. See 1399 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1400 1401 1402 eisa_irq_edge= [PARISC,HW] 1403 See header of drivers/parisc/eisa.c. 1404 1405 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1406 Format: ekgdboc=kbd 1407 1408 This is designed to be used in conjunction with 1409 the boot argument: earlyprintk=vga 1410 1411 This parameter works in place of the kgdboc parameter 1412 but can only be used if the backing tty is available 1413 very early in the boot process. For early debugging 1414 via a serial port see kgdboc_earlycon instead. 1415 1416 elanfreq= [X86-32] 1417 See comment before function elanfreq_setup() in 1418 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1419 1420 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1421 Specifies physical address of start of kernel core 1422 image elf header and optionally the size. Generally 1423 kexec loader will pass this option to capture kernel. 1424 See Documentation/admin-guide/kdump/kdump.rst for details. 1425 1426 enable_mtrr_cleanup [X86] 1427 The kernel tries to adjust MTRR layout from continuous 1428 to discrete, to make X server driver able to add WB 1429 entry later. This parameter enables that. 1430 1431 enable_timer_pin_1 [X86] 1432 Enable PIN 1 of APIC timer 1433 Can be useful to work around chipset bugs 1434 (in particular on some ATI chipsets). 1435 The kernel tries to set a reasonable default. 1436 1437 enforcing [SELINUX] Set initial enforcing status. 1438 Format: {"0" | "1"} 1439 See security/selinux/Kconfig help text. 1440 0 -- permissive (log only, no denials). 1441 1 -- enforcing (deny and log). 1442 Default value is 0. 1443 Value can be changed at runtime via 1444 /sys/fs/selinux/enforce. 1445 1446 erst_disable [ACPI] 1447 Disable Error Record Serialization Table (ERST) 1448 support. 1449 1450 ether= [HW,NET] Ethernet cards parameters 1451 This option is obsoleted by the "netdev=" option, which 1452 has equivalent usage. See its documentation for details. 1453 1454 evm= [EVM] 1455 Format: { "fix" } 1456 Permit 'security.evm' to be updated regardless of 1457 current integrity status. 1458 1459 failslab= 1460 fail_usercopy= 1461 fail_page_alloc= 1462 fail_make_request=[KNL] 1463 General fault injection mechanism. 1464 Format: <interval>,<probability>,<space>,<times> 1465 See also Documentation/fault-injection/. 1466 1467 fb_tunnels= [NET] 1468 Format: { initns | none } 1469 See Documentation/admin-guide/sysctl/net.rst for 1470 fb_tunnels_only_for_init_ns 1471 1472 floppy= [HW] 1473 See Documentation/admin-guide/blockdev/floppy.rst. 1474 1475 force_pal_cache_flush 1476 [IA-64] Avoid check_sal_cache_flush which may hang on 1477 buggy SAL_CACHE_FLUSH implementations. Using this 1478 parameter will force ia64_sal_cache_flush to call 1479 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1480 1481 forcepae [X86-32] 1482 Forcefully enable Physical Address Extension (PAE). 1483 Many Pentium M systems disable PAE but may have a 1484 functionally usable PAE implementation. 1485 Warning: use of this parameter will taint the kernel 1486 and may cause unknown problems. 1487 1488 ftrace=[tracer] 1489 [FTRACE] will set and start the specified tracer 1490 as early as possible in order to facilitate early 1491 boot debugging. 1492 1493 ftrace_boot_snapshot 1494 [FTRACE] On boot up, a snapshot will be taken of the 1495 ftrace ring buffer that can be read at: 1496 /sys/kernel/tracing/snapshot. 1497 This is useful if you need tracing information from kernel 1498 boot up that is likely to be overridden by user space 1499 start up functionality. 1500 1501 ftrace_dump_on_oops[=orig_cpu] 1502 [FTRACE] will dump the trace buffers on oops. 1503 If no parameter is passed, ftrace will dump 1504 buffers of all CPUs, but if you pass orig_cpu, it will 1505 dump only the buffer of the CPU that triggered the 1506 oops. 1507 1508 ftrace_filter=[function-list] 1509 [FTRACE] Limit the functions traced by the function 1510 tracer at boot up. function-list is a comma-separated 1511 list of functions. This list can be changed at run 1512 time by the set_ftrace_filter file in the debugfs 1513 tracing directory. 1514 1515 ftrace_notrace=[function-list] 1516 [FTRACE] Do not trace the functions specified in 1517 function-list. This list can be changed at run time 1518 by the set_ftrace_notrace file in the debugfs 1519 tracing directory. 1520 1521 ftrace_graph_filter=[function-list] 1522 [FTRACE] Limit the top level callers functions traced 1523 by the function graph tracer at boot up. 1524 function-list is a comma-separated list of functions 1525 that can be changed at run time by the 1526 set_graph_function file in the debugfs tracing directory. 1527 1528 ftrace_graph_notrace=[function-list] 1529 [FTRACE] Do not trace from the functions specified in 1530 function-list. This list is a comma-separated list of 1531 functions that can be changed at run time by the 1532 set_graph_notrace file in the debugfs tracing directory. 1533 1534 ftrace_graph_max_depth=<uint> 1535 [FTRACE] Used with the function graph tracer. This is 1536 the max depth it will trace into a function. This value 1537 can be changed at run time by the max_graph_depth file 1538 in the tracefs tracing directory. default: 0 (no limit) 1539 1540 fw_devlink= [KNL] Create device links between consumer and supplier 1541 devices by scanning the firmware to infer the 1542 consumer/supplier relationships. This feature is 1543 especially useful when drivers are loaded as modules as 1544 it ensures proper ordering of tasks like device probing 1545 (suppliers first, then consumers), supplier boot state 1546 clean up (only after all consumers have probed), 1547 suspend/resume & runtime PM (consumers first, then 1548 suppliers). 1549 Format: { off | permissive | on | rpm } 1550 off -- Don't create device links from firmware info. 1551 permissive -- Create device links from firmware info 1552 but use it only for ordering boot state clean 1553 up (sync_state() calls). 1554 on -- Create device links from firmware info and use it 1555 to enforce probe and suspend/resume ordering. 1556 rpm -- Like "on", but also use to order runtime PM. 1557 1558 fw_devlink.strict=<bool> 1559 [KNL] Treat all inferred dependencies as mandatory 1560 dependencies. This only applies for fw_devlink=on|rpm. 1561 Format: <bool> 1562 1563 gamecon.map[2|3]= 1564 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1565 support via parallel port (up to 5 devices per port) 1566 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1567 See also Documentation/input/devices/joystick-parport.rst 1568 1569 gamma= [HW,DRM] 1570 1571 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1572 Format: off | on 1573 default: on 1574 1575 gcov_persist= [GCOV] When non-zero (default), profiling data for 1576 kernel modules is saved and remains accessible via 1577 debugfs, even when the module is unloaded/reloaded. 1578 When zero, profiling data is discarded and associated 1579 debugfs files are removed at module unload time. 1580 1581 goldfish [X86] Enable the goldfish android emulator platform. 1582 Don't use this when you are not running on the 1583 android emulator 1584 1585 gpio-mockup.gpio_mockup_ranges 1586 [HW] Sets the ranges of gpiochip of for this device. 1587 Format: <start1>,<end1>,<start2>,<end2>... 1588 gpio-mockup.gpio_mockup_named_lines 1589 [HW] Let the driver know GPIO lines should be named. 1590 1591 gpt [EFI] Forces disk with valid GPT signature but 1592 invalid Protective MBR to be treated as GPT. If the 1593 primary GPT is corrupted, it enables the backup/alternate 1594 GPT to be used instead. 1595 1596 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1597 the "Enable 0" bit of the configuration register. 1598 Format: 0 | 1 1599 Default: 0 1600 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1601 the "Enable 0" bit of the configuration register. 1602 Format: 0 | 1 1603 Default: 0 1604 grcan.select= [HW] Select which physical interface to use. 1605 Format: 0 | 1 1606 Default: 0 1607 grcan.txsize= [HW] Sets the size of the tx buffer. 1608 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1609 Default: 1024 1610 grcan.rxsize= [HW] Sets the size of the rx buffer. 1611 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1612 Default: 1024 1613 1614 hardened_usercopy= 1615 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 1616 hardening is enabled for this boot. Hardened 1617 usercopy checking is used to protect the kernel 1618 from reading or writing beyond known memory 1619 allocation boundaries as a proactive defense 1620 against bounds-checking flaws in the kernel's 1621 copy_to_user()/copy_from_user() interface. 1622 on Perform hardened usercopy checks (default). 1623 off Disable hardened usercopy checks. 1624 1625 hardlockup_all_cpu_backtrace= 1626 [KNL] Should the hard-lockup detector generate 1627 backtraces on all cpus. 1628 Format: 0 | 1 1629 1630 hashdist= [KNL,NUMA] Large hashes allocated during boot 1631 are distributed across NUMA nodes. Defaults on 1632 for 64-bit NUMA, off otherwise. 1633 Format: 0 | 1 (for off | on) 1634 1635 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1636 1637 hd= [EIDE] (E)IDE hard drive subsystem geometry 1638 Format: <cyl>,<head>,<sect> 1639 1640 hest_disable [ACPI] 1641 Disable Hardware Error Source Table (HEST) support; 1642 corresponding firmware-first mode error processing 1643 logic will be disabled. 1644 1645 hibernate= [HIBERNATION] 1646 noresume Don't check if there's a hibernation image 1647 present during boot. 1648 nocompress Don't compress/decompress hibernation images. 1649 no Disable hibernation and resume. 1650 protect_image Turn on image protection during restoration 1651 (that will set all pages holding image data 1652 during restoration read-only). 1653 1654 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1655 size of <nn>. This works even on boxes that have no 1656 highmem otherwise. This also works to reduce highmem 1657 size on bigger boxes. 1658 1659 highres= [KNL] Enable/disable high resolution timer mode. 1660 Valid parameters: "on", "off" 1661 Default: "on" 1662 1663 hlt [BUGS=ARM,SH] 1664 1665 hpet= [X86-32,HPET] option to control HPET usage 1666 Format: { enable (default) | disable | force | 1667 verbose } 1668 disable: disable HPET and use PIT instead 1669 force: allow force enabled of undocumented chips (ICH4, 1670 VIA, nVidia) 1671 verbose: show contents of HPET registers during setup 1672 1673 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1674 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1675 1676 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1677 If this follows hugepagesz (below), it specifies 1678 the number of pages of hugepagesz to be allocated. 1679 If this is the first HugeTLB parameter on the command 1680 line, it specifies the number of pages to allocate for 1681 the default huge page size. If using node format, the 1682 number of pages to allocate per-node can be specified. 1683 See also Documentation/admin-guide/mm/hugetlbpage.rst. 1684 Format: <integer> or (node format) 1685 <node>:<integer>[,<node>:<integer>] 1686 1687 hugepagesz= 1688 [HW] The size of the HugeTLB pages. This is used in 1689 conjunction with hugepages (above) to allocate huge 1690 pages of a specific size at boot. The pair 1691 hugepagesz=X hugepages=Y can be specified once for 1692 each supported huge page size. Huge page sizes are 1693 architecture dependent. See also 1694 Documentation/admin-guide/mm/hugetlbpage.rst. 1695 Format: size[KMG] 1696 1697 hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation 1698 of gigantic hugepages. Or using node format, the size 1699 of a CMA area per node can be specified. 1700 Format: nn[KMGTPE] or (node format) 1701 <node>:nn[KMGTPE][,<node>:nn[KMGTPE]] 1702 1703 Reserve a CMA area of given size and allocate gigantic 1704 hugepages using the CMA allocator. If enabled, the 1705 boot-time allocation of gigantic hugepages is skipped. 1706 1707 hugetlb_free_vmemmap= 1708 [KNL] Reguires CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP 1709 enabled. 1710 Allows heavy hugetlb users to free up some more 1711 memory (7 * PAGE_SIZE for each 2MB hugetlb page). 1712 Format: { [oO][Nn]/Y/y/1 | [oO][Ff]/N/n/0 (default) } 1713 1714 [oO][Nn]/Y/y/1: enable the feature 1715 [oO][Ff]/N/n/0: disable the feature 1716 1717 Built with CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON=y, 1718 the default is on. 1719 1720 This is not compatible with memory_hotplug.memmap_on_memory. 1721 If both parameters are enabled, hugetlb_free_vmemmap takes 1722 precedence over memory_hotplug.memmap_on_memory. 1723 1724 hung_task_panic= 1725 [KNL] Should the hung task detector generate panics. 1726 Format: 0 | 1 1727 1728 A value of 1 instructs the kernel to panic when a 1729 hung task is detected. The default value is controlled 1730 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1731 option. The value selected by this boot parameter can 1732 be changed later by the kernel.hung_task_panic sysctl. 1733 1734 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1735 terminal devices. Valid values: 0..8 1736 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1737 If specified, z/VM IUCV HVC accepts connections 1738 from listed z/VM user IDs only. 1739 1740 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1741 which allow the hypervisor to 'idle' the 1742 guest on lock contention. 1743 1744 keep_bootcon [KNL] 1745 Do not unregister boot console at start. This is only 1746 useful for debugging when something happens in the window 1747 between unregistering the boot console and initializing 1748 the real console. 1749 1750 i2c_bus= [HW] Override the default board specific I2C bus speed 1751 or register an additional I2C bus that is not 1752 registered from board initialization code. 1753 Format: 1754 <bus_id>,<clkrate> 1755 1756 i8042.debug [HW] Toggle i8042 debug mode 1757 i8042.unmask_kbd_data 1758 [HW] Enable printing of interrupt data from the KBD port 1759 (disabled by default, and as a pre-condition 1760 requires that i8042.debug=1 be enabled) 1761 i8042.direct [HW] Put keyboard port into non-translated mode 1762 i8042.dumbkbd [HW] Pretend that controller can only read data from 1763 keyboard and cannot control its state 1764 (Don't attempt to blink the leds) 1765 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1766 i8042.nokbd [HW] Don't check/create keyboard port 1767 i8042.noloop [HW] Disable the AUX Loopback command while probing 1768 for the AUX port 1769 i8042.nomux [HW] Don't check presence of an active multiplexing 1770 controller 1771 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1772 controllers 1773 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1774 i8042.reset [HW] Reset the controller during init, cleanup and 1775 suspend-to-ram transitions, only during s2r 1776 transitions, or never reset 1777 Format: { 1 | Y | y | 0 | N | n } 1778 1, Y, y: always reset controller 1779 0, N, n: don't ever reset controller 1780 Default: only on s2r transitions on x86; most other 1781 architectures force reset to be always executed 1782 i8042.unlock [HW] Unlock (ignore) the keylock 1783 i8042.kbdreset [HW] Reset device connected to KBD port 1784 i8042.probe_defer 1785 [HW] Allow deferred probing upon i8042 probe errors 1786 1787 i810= [HW,DRM] 1788 1789 i915.invert_brightness= 1790 [DRM] Invert the sense of the variable that is used to 1791 set the brightness of the panel backlight. Normally a 1792 brightness value of 0 indicates backlight switched off, 1793 and the maximum of the brightness value sets the backlight 1794 to maximum brightness. If this parameter is set to 0 1795 (default) and the machine requires it, or this parameter 1796 is set to 1, a brightness value of 0 sets the backlight 1797 to maximum brightness, and the maximum of the brightness 1798 value switches the backlight off. 1799 -1 -- never invert brightness 1800 0 -- machine default 1801 1 -- force brightness inversion 1802 1803 icn= [HW,ISDN] 1804 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1805 1806 1807 idle= [X86] 1808 Format: idle=poll, idle=halt, idle=nomwait 1809 Poll forces a polling idle loop that can slightly 1810 improve the performance of waking up a idle CPU, but 1811 will use a lot of power and make the system run hot. 1812 Not recommended. 1813 idle=halt: Halt is forced to be used for CPU idle. 1814 In such case C2/C3 won't be used again. 1815 idle=nomwait: Disable mwait for CPU C-states 1816 1817 idxd.sva= [HW] 1818 Format: <bool> 1819 Allow force disabling of Shared Virtual Memory (SVA) 1820 support for the idxd driver. By default it is set to 1821 true (1). 1822 1823 idxd.tc_override= [HW] 1824 Format: <bool> 1825 Allow override of default traffic class configuration 1826 for the device. By default it is set to false (0). 1827 1828 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1829 Format: { strict | legacy | 2008 | relaxed } 1830 Default: strict 1831 1832 Choose which programs will be accepted for execution 1833 based on the IEEE 754 NaN encoding(s) supported by 1834 the FPU and the NaN encoding requested with the value 1835 of an ELF file header flag individually set by each 1836 binary. Hardware implementations are permitted to 1837 support either or both of the legacy and the 2008 NaN 1838 encoding mode. 1839 1840 Available settings are as follows: 1841 strict accept binaries that request a NaN encoding 1842 supported by the FPU 1843 legacy only accept legacy-NaN binaries, if supported 1844 by the FPU 1845 2008 only accept 2008-NaN binaries, if supported 1846 by the FPU 1847 relaxed accept any binaries regardless of whether 1848 supported by the FPU 1849 1850 The FPU emulator is always able to support both NaN 1851 encodings, so if no FPU hardware is present or it has 1852 been disabled with 'nofpu', then the settings of 1853 'legacy' and '2008' strap the emulator accordingly, 1854 'relaxed' straps the emulator for both legacy-NaN and 1855 2008-NaN, whereas 'strict' enables legacy-NaN only on 1856 legacy processors and both NaN encodings on MIPS32 or 1857 MIPS64 CPUs. 1858 1859 The setting for ABS.fmt/NEG.fmt instruction execution 1860 mode generally follows that for the NaN encoding, 1861 except where unsupported by hardware. 1862 1863 ignore_loglevel [KNL] 1864 Ignore loglevel setting - this will print /all/ 1865 kernel messages to the console. Useful for debugging. 1866 We also add it as printk module parameter, so users 1867 could change it dynamically, usually by 1868 /sys/module/printk/parameters/ignore_loglevel. 1869 1870 ignore_rlimit_data 1871 Ignore RLIMIT_DATA setting for data mappings, 1872 print warning at first misuse. Can be changed via 1873 /sys/module/kernel/parameters/ignore_rlimit_data. 1874 1875 ihash_entries= [KNL] 1876 Set number of hash buckets for inode cache. 1877 1878 ima_appraise= [IMA] appraise integrity measurements 1879 Format: { "off" | "enforce" | "fix" | "log" } 1880 default: "enforce" 1881 1882 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1883 The builtin appraise policy appraises all files 1884 owned by uid=0. 1885 1886 ima_canonical_fmt [IMA] 1887 Use the canonical format for the binary runtime 1888 measurements, instead of host native format. 1889 1890 ima_hash= [IMA] 1891 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1892 | sha512 | ... } 1893 default: "sha1" 1894 1895 The list of supported hash algorithms is defined 1896 in crypto/hash_info.h. 1897 1898 ima_policy= [IMA] 1899 The builtin policies to load during IMA setup. 1900 Format: "tcb | appraise_tcb | secure_boot | 1901 fail_securely | critical_data" 1902 1903 The "tcb" policy measures all programs exec'd, files 1904 mmap'd for exec, and all files opened with the read 1905 mode bit set by either the effective uid (euid=0) or 1906 uid=0. 1907 1908 The "appraise_tcb" policy appraises the integrity of 1909 all files owned by root. 1910 1911 The "secure_boot" policy appraises the integrity 1912 of files (eg. kexec kernel image, kernel modules, 1913 firmware, policy, etc) based on file signatures. 1914 1915 The "fail_securely" policy forces file signature 1916 verification failure also on privileged mounted 1917 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1918 flag. 1919 1920 The "critical_data" policy measures kernel integrity 1921 critical data. 1922 1923 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1924 Load a policy which meets the needs of the Trusted 1925 Computing Base. This means IMA will measure all 1926 programs exec'd, files mmap'd for exec, and all files 1927 opened for read by uid=0. 1928 1929 ima_template= [IMA] 1930 Select one of defined IMA measurements template formats. 1931 Formats: { "ima" | "ima-ng" | "ima-ngv2" | "ima-sig" | 1932 "ima-sigv2" } 1933 Default: "ima-ng" 1934 1935 ima_template_fmt= 1936 [IMA] Define a custom template format. 1937 Format: { "field1|...|fieldN" } 1938 1939 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1940 Format: <min_file_size> 1941 Set the minimal file size for using asynchronous hash. 1942 If left unspecified, ahash usage is disabled. 1943 1944 ahash performance varies for different data sizes on 1945 different crypto accelerators. This option can be used 1946 to achieve the best performance for a particular HW. 1947 1948 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1949 Format: <bufsize> 1950 Set hashing buffer size. Default: 4k. 1951 1952 ahash performance varies for different chunk sizes on 1953 different crypto accelerators. This option can be used 1954 to achieve best performance for particular HW. 1955 1956 init= [KNL] 1957 Format: <full_path> 1958 Run specified binary instead of /sbin/init as init 1959 process. 1960 1961 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1962 for working out where the kernel is dying during 1963 startup. 1964 1965 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1966 initcall functions. Useful for debugging built-in 1967 modules and initcalls. 1968 1969 initramfs_async= [KNL] 1970 Format: <bool> 1971 Default: 1 1972 This parameter controls whether the initramfs 1973 image is unpacked asynchronously, concurrently 1974 with devices being probed and 1975 initialized. This should normally just work, 1976 but as a debugging aid, one can get the 1977 historical behaviour of the initramfs 1978 unpacking being completed before device_ and 1979 late_ initcalls. 1980 1981 initrd= [BOOT] Specify the location of the initial ramdisk 1982 1983 initrdmem= [KNL] Specify a physical address and size from which to 1984 load the initrd. If an initrd is compiled in or 1985 specified in the bootparams, it takes priority over this 1986 setting. 1987 Format: ss[KMG],nn[KMG] 1988 Default is 0, 0 1989 1990 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1991 zeroes. 1992 Format: 0 | 1 1993 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1994 1995 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1996 Format: 0 | 1 1997 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1998 1999 init_pkru= [X86] Specify the default memory protection keys rights 2000 register contents for all processes. 0x55555554 by 2001 default (disallow access to all but pkey 0). Can 2002 override in debugfs after boot. 2003 2004 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 2005 Format: <irq> 2006 2007 int_pln_enable [X86] Enable power limit notification interrupt 2008 2009 integrity_audit=[IMA] 2010 Format: { "0" | "1" } 2011 0 -- basic integrity auditing messages. (Default) 2012 1 -- additional integrity auditing messages. 2013 2014 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 2015 on 2016 Enable intel iommu driver. 2017 off 2018 Disable intel iommu driver. 2019 igfx_off [Default Off] 2020 By default, gfx is mapped as normal device. If a gfx 2021 device has a dedicated DMAR unit, the DMAR unit is 2022 bypassed by not enabling DMAR with this option. In 2023 this case, gfx device will use physical address for 2024 DMA. 2025 strict [Default Off] 2026 Deprecated, equivalent to iommu.strict=1. 2027 sp_off [Default Off] 2028 By default, super page will be supported if Intel IOMMU 2029 has the capability. With this option, super page will 2030 not be supported. 2031 sm_on 2032 Enable the Intel IOMMU scalable mode if the hardware 2033 advertises that it has support for the scalable mode 2034 translation. 2035 sm_off 2036 Disallow use of the Intel IOMMU scalable mode. 2037 tboot_noforce [Default Off] 2038 Do not force the Intel IOMMU enabled under tboot. 2039 By default, tboot will force Intel IOMMU on, which 2040 could harm performance of some high-throughput 2041 devices like 40GBit network cards, even if identity 2042 mapping is enabled. 2043 Note that using this option lowers the security 2044 provided by tboot because it makes the system 2045 vulnerable to DMA attacks. 2046 2047 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 2048 0 disables intel_idle and fall back on acpi_idle. 2049 1 to 9 specify maximum depth of C-state. 2050 2051 intel_pstate= [X86] 2052 disable 2053 Do not enable intel_pstate as the default 2054 scaling driver for the supported processors 2055 passive 2056 Use intel_pstate as a scaling driver, but configure it 2057 to work with generic cpufreq governors (instead of 2058 enabling its internal governor). This mode cannot be 2059 used along with the hardware-managed P-states (HWP) 2060 feature. 2061 force 2062 Enable intel_pstate on systems that prohibit it by default 2063 in favor of acpi-cpufreq. Forcing the intel_pstate driver 2064 instead of acpi-cpufreq may disable platform features, such 2065 as thermal controls and power capping, that rely on ACPI 2066 P-States information being indicated to OSPM and therefore 2067 should be used with caution. This option does not work with 2068 processors that aren't supported by the intel_pstate driver 2069 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 2070 no_hwp 2071 Do not enable hardware P state control (HWP) 2072 if available. 2073 hwp_only 2074 Only load intel_pstate on systems which support 2075 hardware P state control (HWP) if available. 2076 support_acpi_ppc 2077 Enforce ACPI _PPC performance limits. If the Fixed ACPI 2078 Description Table, specifies preferred power management 2079 profile as "Enterprise Server" or "Performance Server", 2080 then this feature is turned on by default. 2081 per_cpu_perf_limits 2082 Allow per-logical-CPU P-State performance control limits using 2083 cpufreq sysfs interface 2084 2085 intremap= [X86-64, Intel-IOMMU] 2086 on enable Interrupt Remapping (default) 2087 off disable Interrupt Remapping 2088 nosid disable Source ID checking 2089 no_x2apic_optout 2090 BIOS x2APIC opt-out request will be ignored 2091 nopost disable Interrupt Posting 2092 2093 iomem= Disable strict checking of access to MMIO memory 2094 strict regions from userspace. 2095 relaxed 2096 2097 iommu= [X86] 2098 off 2099 force 2100 noforce 2101 biomerge 2102 panic 2103 nopanic 2104 merge 2105 nomerge 2106 soft 2107 pt [X86] 2108 nopt [X86] 2109 nobypass [PPC/POWERNV] 2110 Disable IOMMU bypass, using IOMMU for PCI devices. 2111 2112 iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices. 2113 Format: { "0" | "1" } 2114 0 - Try to allocate a 32-bit DMA address first, before 2115 falling back to the full range if needed. 2116 1 - Allocate directly from the full usable range, 2117 forcing Dual Address Cycle for PCI cards supporting 2118 greater than 32-bit addressing. 2119 2120 iommu.strict= [ARM64, X86] Configure TLB invalidation behaviour 2121 Format: { "0" | "1" } 2122 0 - Lazy mode. 2123 Request that DMA unmap operations use deferred 2124 invalidation of hardware TLBs, for increased 2125 throughput at the cost of reduced device isolation. 2126 Will fall back to strict mode if not supported by 2127 the relevant IOMMU driver. 2128 1 - Strict mode. 2129 DMA unmap operations invalidate IOMMU hardware TLBs 2130 synchronously. 2131 unset - Use value of CONFIG_IOMMU_DEFAULT_DMA_{LAZY,STRICT}. 2132 Note: on x86, strict mode specified via one of the 2133 legacy driver-specific options takes precedence. 2134 2135 iommu.passthrough= 2136 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 2137 Format: { "0" | "1" } 2138 0 - Use IOMMU translation for DMA. 2139 1 - Bypass the IOMMU for DMA. 2140 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 2141 2142 io7= [HW] IO7 for Marvel-based Alpha systems 2143 See comment before marvel_specify_io7 in 2144 arch/alpha/kernel/core_marvel.c. 2145 2146 io_delay= [X86] I/O delay method 2147 0x80 2148 Standard port 0x80 based delay 2149 0xed 2150 Alternate port 0xed based delay (needed on some systems) 2151 udelay 2152 Simple two microseconds delay 2153 none 2154 No delay 2155 2156 ip= [IP_PNP] 2157 See Documentation/admin-guide/nfs/nfsroot.rst. 2158 2159 ipcmni_extend [KNL] Extend the maximum number of unique System V 2160 IPC identifiers from 32,768 to 16,777,216. 2161 2162 irqaffinity= [SMP] Set the default irq affinity mask 2163 The argument is a cpu list, as described above. 2164 2165 irqchip.gicv2_force_probe= 2166 [ARM, ARM64] 2167 Format: <bool> 2168 Force the kernel to look for the second 4kB page 2169 of a GICv2 controller even if the memory range 2170 exposed by the device tree is too small. 2171 2172 irqchip.gicv3_nolpi= 2173 [ARM, ARM64] 2174 Force the kernel to ignore the availability of 2175 LPIs (and by consequence ITSs). Intended for system 2176 that use the kernel as a bootloader, and thus want 2177 to let secondary kernels in charge of setting up 2178 LPIs. 2179 2180 irqchip.gicv3_pseudo_nmi= [ARM64] 2181 Enables support for pseudo-NMIs in the kernel. This 2182 requires the kernel to be built with 2183 CONFIG_ARM64_PSEUDO_NMI. 2184 2185 irqfixup [HW] 2186 When an interrupt is not handled search all handlers 2187 for it. Intended to get systems with badly broken 2188 firmware running. 2189 2190 irqpoll [HW] 2191 When an interrupt is not handled search all handlers 2192 for it. Also check all handlers each timer 2193 interrupt. Intended to get systems with badly broken 2194 firmware running. 2195 2196 isapnp= [ISAPNP] 2197 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2198 2199 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2200 [Deprecated - use cpusets instead] 2201 Format: [flag-list,]<cpu-list> 2202 2203 Specify one or more CPUs to isolate from disturbances 2204 specified in the flag list (default: domain): 2205 2206 nohz 2207 Disable the tick when a single task runs. 2208 2209 A residual 1Hz tick is offloaded to workqueues, which you 2210 need to affine to housekeeping through the global 2211 workqueue's affinity configured via the 2212 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2213 by using the 'domain' flag described below. 2214 2215 NOTE: by default the global workqueue runs on all CPUs, 2216 so to protect individual CPUs the 'cpumask' file has to 2217 be configured manually after bootup. 2218 2219 domain 2220 Isolate from the general SMP balancing and scheduling 2221 algorithms. Note that performing domain isolation this way 2222 is irreversible: it's not possible to bring back a CPU to 2223 the domains once isolated through isolcpus. It's strongly 2224 advised to use cpusets instead to disable scheduler load 2225 balancing through the "cpuset.sched_load_balance" file. 2226 It offers a much more flexible interface where CPUs can 2227 move in and out of an isolated set anytime. 2228 2229 You can move a process onto or off an "isolated" CPU via 2230 the CPU affinity syscalls or cpuset. 2231 <cpu number> begins at 0 and the maximum value is 2232 "number of CPUs in system - 1". 2233 2234 managed_irq 2235 2236 Isolate from being targeted by managed interrupts 2237 which have an interrupt mask containing isolated 2238 CPUs. The affinity of managed interrupts is 2239 handled by the kernel and cannot be changed via 2240 the /proc/irq/* interfaces. 2241 2242 This isolation is best effort and only effective 2243 if the automatically assigned interrupt mask of a 2244 device queue contains isolated and housekeeping 2245 CPUs. If housekeeping CPUs are online then such 2246 interrupts are directed to the housekeeping CPU 2247 so that IO submitted on the housekeeping CPU 2248 cannot disturb the isolated CPU. 2249 2250 If a queue's affinity mask contains only isolated 2251 CPUs then this parameter has no effect on the 2252 interrupt routing decision, though interrupts are 2253 only delivered when tasks running on those 2254 isolated CPUs submit IO. IO submitted on 2255 housekeeping CPUs has no influence on those 2256 queues. 2257 2258 The format of <cpu-list> is described above. 2259 2260 iucv= [HW,NET] 2261 2262 ivrs_ioapic [HW,X86-64] 2263 Provide an override to the IOAPIC-ID<->DEVICE-ID 2264 mapping provided in the IVRS ACPI table. For 2265 example, to map IOAPIC-ID decimal 10 to 2266 PCI device 00:14.0 write the parameter as: 2267 ivrs_ioapic[10]=00:14.0 2268 2269 ivrs_hpet [HW,X86-64] 2270 Provide an override to the HPET-ID<->DEVICE-ID 2271 mapping provided in the IVRS ACPI table. For 2272 example, to map HPET-ID decimal 0 to 2273 PCI device 00:14.0 write the parameter as: 2274 ivrs_hpet[0]=00:14.0 2275 2276 ivrs_acpihid [HW,X86-64] 2277 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2278 mapping provided in the IVRS ACPI table. For 2279 example, to map UART-HID:UID AMD0020:0 to 2280 PCI device 00:14.5 write the parameter as: 2281 ivrs_acpihid[00:14.5]=AMD0020:0 2282 2283 js= [HW,JOY] Analog joystick 2284 See Documentation/input/joydev/joystick.rst. 2285 2286 nokaslr [KNL] 2287 When CONFIG_RANDOMIZE_BASE is set, this disables 2288 kernel and module base offset ASLR (Address Space 2289 Layout Randomization). 2290 2291 kasan_multi_shot 2292 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2293 report on every invalid memory access. Without this 2294 parameter KASAN will print report only for the first 2295 invalid access. 2296 2297 keepinitrd [HW,ARM] 2298 2299 kernelcore= [KNL,X86,IA-64,PPC] 2300 Format: nn[KMGTPE] | nn% | "mirror" 2301 This parameter specifies the amount of memory usable by 2302 the kernel for non-movable allocations. The requested 2303 amount is spread evenly throughout all nodes in the 2304 system as ZONE_NORMAL. The remaining memory is used for 2305 movable memory in its own zone, ZONE_MOVABLE. In the 2306 event, a node is too small to have both ZONE_NORMAL and 2307 ZONE_MOVABLE, kernelcore memory will take priority and 2308 other nodes will have a larger ZONE_MOVABLE. 2309 2310 ZONE_MOVABLE is used for the allocation of pages that 2311 may be reclaimed or moved by the page migration 2312 subsystem. Note that allocations like PTEs-from-HighMem 2313 still use the HighMem zone if it exists, and the Normal 2314 zone if it does not. 2315 2316 It is possible to specify the exact amount of memory in 2317 the form of "nn[KMGTPE]", a percentage of total system 2318 memory in the form of "nn%", or "mirror". If "mirror" 2319 option is specified, mirrored (reliable) memory is used 2320 for non-movable allocations and remaining memory is used 2321 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2322 are exclusive, so you cannot specify multiple forms. 2323 2324 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2325 Format: <Controller#>[,poll interval] 2326 The controller # is the number of the ehci usb debug 2327 port as it is probed via PCI. The poll interval is 2328 optional and is the number seconds in between 2329 each poll cycle to the debug port in case you need 2330 the functionality for interrupting the kernel with 2331 gdb or control-c on the dbgp connection. When 2332 not using this parameter you use sysrq-g to break into 2333 the kernel debugger. 2334 2335 kgdboc= [KGDB,HW] kgdb over consoles. 2336 Requires a tty driver that supports console polling, 2337 or a supported polling keyboard driver (non-usb). 2338 Serial only format: <serial_device>[,baud] 2339 keyboard only format: kbd 2340 keyboard and serial format: kbd,<serial_device>[,baud] 2341 Optional Kernel mode setting: 2342 kms, kbd format: kms,kbd 2343 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2344 2345 kgdboc_earlycon= [KGDB,HW] 2346 If the boot console provides the ability to read 2347 characters and can work in polling mode, you can use 2348 this parameter to tell kgdb to use it as a backend 2349 until the normal console is registered. Intended to 2350 be used together with the kgdboc parameter which 2351 specifies the normal console to transition to. 2352 2353 The name of the early console should be specified 2354 as the value of this parameter. Note that the name of 2355 the early console might be different than the tty 2356 name passed to kgdboc. It's OK to leave the value 2357 blank and the first boot console that implements 2358 read() will be picked. 2359 2360 kgdbwait [KGDB] Stop kernel execution and enter the 2361 kernel debugger at the earliest opportunity. 2362 2363 kmac= [MIPS] Korina ethernet MAC address. 2364 Configure the RouterBoard 532 series on-chip 2365 Ethernet adapter MAC address. 2366 2367 kmemleak= [KNL] Boot-time kmemleak enable/disable 2368 Valid arguments: on, off 2369 Default: on 2370 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2371 the default is off. 2372 2373 kprobe_event=[probe-list] 2374 [FTRACE] Add kprobe events and enable at boot time. 2375 The probe-list is a semicolon delimited list of probe 2376 definitions. Each definition is same as kprobe_events 2377 interface, but the parameters are comma delimited. 2378 For example, to add a kprobe event on vfs_read with 2379 arg1 and arg2, add to the command line; 2380 2381 kprobe_event=p,vfs_read,$arg1,$arg2 2382 2383 See also Documentation/trace/kprobetrace.rst "Kernel 2384 Boot Parameter" section. 2385 2386 kpti= [ARM64] Control page table isolation of user 2387 and kernel address spaces. 2388 Default: enabled on cores which need mitigation. 2389 0: force disabled 2390 1: force enabled 2391 2392 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2393 Default is 0 (don't ignore, but inject #GP) 2394 2395 kvm.eager_page_split= 2396 [KVM,X86] Controls whether or not KVM will try to 2397 proactively split all huge pages during dirty logging. 2398 Eager page splitting reduces interruptions to vCPU 2399 execution by eliminating the write-protection faults 2400 and MMU lock contention that would otherwise be 2401 required to split huge pages lazily. 2402 2403 VM workloads that rarely perform writes or that write 2404 only to a small region of VM memory may benefit from 2405 disabling eager page splitting to allow huge pages to 2406 still be used for reads. 2407 2408 The behavior of eager page splitting depends on whether 2409 KVM_DIRTY_LOG_INITIALLY_SET is enabled or disabled. If 2410 disabled, all huge pages in a memslot will be eagerly 2411 split when dirty logging is enabled on that memslot. If 2412 enabled, eager page splitting will be performed during 2413 the KVM_CLEAR_DIRTY ioctl, and only for the pages being 2414 cleared. 2415 2416 Eager page splitting currently only supports splitting 2417 huge pages mapped by the TDP MMU. 2418 2419 Default is Y (on). 2420 2421 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2422 Default is false (don't support). 2423 2424 kvm.nx_huge_pages= 2425 [KVM] Controls the software workaround for the 2426 X86_BUG_ITLB_MULTIHIT bug. 2427 force : Always deploy workaround. 2428 off : Never deploy workaround. 2429 auto : Deploy workaround based on the presence of 2430 X86_BUG_ITLB_MULTIHIT. 2431 2432 Default is 'auto'. 2433 2434 If the software workaround is enabled for the host, 2435 guests do need not to enable it for nested guests. 2436 2437 kvm.nx_huge_pages_recovery_ratio= 2438 [KVM] Controls how many 4KiB pages are periodically zapped 2439 back to huge pages. 0 disables the recovery, otherwise if 2440 the value is N KVM will zap 1/Nth of the 4KiB pages every 2441 period (see below). The default is 60. 2442 2443 kvm.nx_huge_pages_recovery_period_ms= 2444 [KVM] Controls the time period at which KVM zaps 4KiB pages 2445 back to huge pages. If the value is a non-zero N, KVM will 2446 zap a portion (see ratio above) of the pages every N msecs. 2447 If the value is 0 (the default), KVM will pick a period based 2448 on the ratio, such that a page is zapped after 1 hour on average. 2449 2450 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2451 Default is 1 (enabled) 2452 2453 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2454 for all guests. 2455 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2456 2457 kvm-arm.mode= 2458 [KVM,ARM] Select one of KVM/arm64's modes of operation. 2459 2460 none: Forcefully disable KVM. 2461 2462 nvhe: Standard nVHE-based mode, without support for 2463 protected guests. 2464 2465 protected: nVHE-based mode with support for guests whose 2466 state is kept private from the host. 2467 Not valid if the kernel is running in EL2. 2468 2469 Defaults to VHE/nVHE based on hardware support. Setting 2470 mode to "protected" will disable kexec and hibernation 2471 for the host. 2472 2473 kvm-arm.vgic_v3_group0_trap= 2474 [KVM,ARM] Trap guest accesses to GICv3 group-0 2475 system registers 2476 2477 kvm-arm.vgic_v3_group1_trap= 2478 [KVM,ARM] Trap guest accesses to GICv3 group-1 2479 system registers 2480 2481 kvm-arm.vgic_v3_common_trap= 2482 [KVM,ARM] Trap guest accesses to GICv3 common 2483 system registers 2484 2485 kvm-arm.vgic_v4_enable= 2486 [KVM,ARM] Allow use of GICv4 for direct injection of 2487 LPIs. 2488 2489 kvm_cma_resv_ratio=n [PPC] 2490 Reserves given percentage from system memory area for 2491 contiguous memory allocation for KVM hash pagetable 2492 allocation. 2493 By default it reserves 5% of total system memory. 2494 Format: <integer> 2495 Default: 5 2496 2497 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2498 (virtualized MMU) support on capable Intel chips. 2499 Default is 1 (enabled) 2500 2501 kvm-intel.emulate_invalid_guest_state= 2502 [KVM,Intel] Disable emulation of invalid guest state. 2503 Ignored if kvm-intel.enable_unrestricted_guest=1, as 2504 guest state is never invalid for unrestricted guests. 2505 This param doesn't apply to nested guests (L2), as KVM 2506 never emulates invalid L2 guest state. 2507 Default is 1 (enabled) 2508 2509 kvm-intel.flexpriority= 2510 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2511 Default is 1 (enabled) 2512 2513 kvm-intel.nested= 2514 [KVM,Intel] Enable VMX nesting (nVMX). 2515 Default is 0 (disabled) 2516 2517 kvm-intel.unrestricted_guest= 2518 [KVM,Intel] Disable unrestricted guest feature 2519 (virtualized real and unpaged mode) on capable 2520 Intel chips. Default is 1 (enabled) 2521 2522 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2523 CVE-2018-3620. 2524 2525 Valid arguments: never, cond, always 2526 2527 always: L1D cache flush on every VMENTER. 2528 cond: Flush L1D on VMENTER only when the code between 2529 VMEXIT and VMENTER can leak host memory. 2530 never: Disables the mitigation 2531 2532 Default is cond (do L1 cache flush in specific instances) 2533 2534 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2535 feature (tagged TLBs) on capable Intel chips. 2536 Default is 1 (enabled) 2537 2538 l1d_flush= [X86,INTEL] 2539 Control mitigation for L1D based snooping vulnerability. 2540 2541 Certain CPUs are vulnerable to an exploit against CPU 2542 internal buffers which can forward information to a 2543 disclosure gadget under certain conditions. 2544 2545 In vulnerable processors, the speculatively 2546 forwarded data can be used in a cache side channel 2547 attack, to access data to which the attacker does 2548 not have direct access. 2549 2550 This parameter controls the mitigation. The 2551 options are: 2552 2553 on - enable the interface for the mitigation 2554 2555 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2556 affected CPUs 2557 2558 The kernel PTE inversion protection is unconditionally 2559 enabled and cannot be disabled. 2560 2561 full 2562 Provides all available mitigations for the 2563 L1TF vulnerability. Disables SMT and 2564 enables all mitigations in the 2565 hypervisors, i.e. unconditional L1D flush. 2566 2567 SMT control and L1D flush control via the 2568 sysfs interface is still possible after 2569 boot. Hypervisors will issue a warning 2570 when the first VM is started in a 2571 potentially insecure configuration, 2572 i.e. SMT enabled or L1D flush disabled. 2573 2574 full,force 2575 Same as 'full', but disables SMT and L1D 2576 flush runtime control. Implies the 2577 'nosmt=force' command line option. 2578 (i.e. sysfs control of SMT is disabled.) 2579 2580 flush 2581 Leaves SMT enabled and enables the default 2582 hypervisor mitigation, i.e. conditional 2583 L1D flush. 2584 2585 SMT control and L1D flush control via the 2586 sysfs interface is still possible after 2587 boot. Hypervisors will issue a warning 2588 when the first VM is started in a 2589 potentially insecure configuration, 2590 i.e. SMT enabled or L1D flush disabled. 2591 2592 flush,nosmt 2593 2594 Disables SMT and enables the default 2595 hypervisor mitigation. 2596 2597 SMT control and L1D flush control via the 2598 sysfs interface is still possible after 2599 boot. Hypervisors will issue a warning 2600 when the first VM is started in a 2601 potentially insecure configuration, 2602 i.e. SMT enabled or L1D flush disabled. 2603 2604 flush,nowarn 2605 Same as 'flush', but hypervisors will not 2606 warn when a VM is started in a potentially 2607 insecure configuration. 2608 2609 off 2610 Disables hypervisor mitigations and doesn't 2611 emit any warnings. 2612 It also drops the swap size and available 2613 RAM limit restriction on both hypervisor and 2614 bare metal. 2615 2616 Default is 'flush'. 2617 2618 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2619 2620 l2cr= [PPC] 2621 2622 l3cr= [PPC] 2623 2624 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2625 disabled it. 2626 2627 lapic= [X86,APIC] Do not use TSC deadline 2628 value for LAPIC timer one-shot implementation. Default 2629 back to the programmable timer unit in the LAPIC. 2630 Format: notscdeadline 2631 2632 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2633 in C2 power state. 2634 2635 libata.dma= [LIBATA] DMA control 2636 libata.dma=0 Disable all PATA and SATA DMA 2637 libata.dma=1 PATA and SATA Disk DMA only 2638 libata.dma=2 ATAPI (CDROM) DMA only 2639 libata.dma=4 Compact Flash DMA only 2640 Combinations also work, so libata.dma=3 enables DMA 2641 for disks and CDROMs, but not CFs. 2642 2643 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2644 libata.ignore_hpa=0 keep BIOS limits (default) 2645 libata.ignore_hpa=1 ignore limits, using full disk 2646 2647 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2648 when set. 2649 Format: <int> 2650 2651 libata.force= [LIBATA] Force configurations. The format is a comma- 2652 separated list of "[ID:]VAL" where ID is PORT[.DEVICE]. 2653 PORT and DEVICE are decimal numbers matching port, link 2654 or device. Basically, it matches the ATA ID string 2655 printed on console by libata. If the whole ID part is 2656 omitted, the last PORT and DEVICE values are used. If 2657 ID hasn't been specified yet, the configuration applies 2658 to all ports, links and devices. 2659 2660 If only DEVICE is omitted, the parameter applies to 2661 the port and all links and devices behind it. DEVICE 2662 number of 0 either selects the first device or the 2663 first fan-out link behind PMP device. It does not 2664 select the host link. DEVICE number of 15 selects the 2665 host link and device attached to it. 2666 2667 The VAL specifies the configuration to force. As long 2668 as there is no ambiguity, shortcut notation is allowed. 2669 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2670 The following configurations can be forced. 2671 2672 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2673 Any ID with matching PORT is used. 2674 2675 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2676 2677 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2678 udma[/][16,25,33,44,66,100,133] notation is also 2679 allowed. 2680 2681 * nohrst, nosrst, norst: suppress hard, soft and both 2682 resets. 2683 2684 * rstonce: only attempt one reset during hot-unplug 2685 link recovery. 2686 2687 * [no]dbdelay: Enable or disable the extra 200ms delay 2688 before debouncing a link PHY and device presence 2689 detection. 2690 2691 * [no]ncq: Turn on or off NCQ. 2692 2693 * [no]ncqtrim: Enable or disable queued DSM TRIM. 2694 2695 * [no]ncqati: Enable or disable NCQ trim on ATI chipset. 2696 2697 * [no]trim: Enable or disable (unqueued) TRIM. 2698 2699 * trim_zero: Indicate that TRIM command zeroes data. 2700 2701 * max_trim_128m: Set 128M maximum trim size limit. 2702 2703 * [no]dma: Turn on or off DMA transfers. 2704 2705 * atapi_dmadir: Enable ATAPI DMADIR bridge support. 2706 2707 * atapi_mod16_dma: Enable the use of ATAPI DMA for 2708 commands that are not a multiple of 16 bytes. 2709 2710 * [no]dmalog: Enable or disable the use of the 2711 READ LOG DMA EXT command to access logs. 2712 2713 * [no]iddevlog: Enable or disable access to the 2714 identify device data log. 2715 2716 * [no]logdir: Enable or disable access to the general 2717 purpose log directory. 2718 2719 * max_sec_128: Set transfer size limit to 128 sectors. 2720 2721 * max_sec_1024: Set or clear transfer size limit to 2722 1024 sectors. 2723 2724 * max_sec_lba48: Set or clear transfer size limit to 2725 65535 sectors. 2726 2727 * [no]lpm: Enable or disable link power management. 2728 2729 * [no]setxfer: Indicate if transfer speed mode setting 2730 should be skipped. 2731 2732 * dump_id: Dump IDENTIFY data. 2733 2734 * disable: Disable this device. 2735 2736 If there are multiple matching configurations changing 2737 the same attribute, the last one is used. 2738 2739 load_ramdisk= [RAM] [Deprecated] 2740 2741 lockd.nlm_grace_period=P [NFS] Assign grace period. 2742 Format: <integer> 2743 2744 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2745 Format: <integer> 2746 2747 lockd.nlm_timeout=T [NFS] Assign timeout value. 2748 Format: <integer> 2749 2750 lockd.nlm_udpport=M [NFS] Assign UDP port. 2751 Format: <integer> 2752 2753 lockdown= [SECURITY] 2754 { integrity | confidentiality } 2755 Enable the kernel lockdown feature. If set to 2756 integrity, kernel features that allow userland to 2757 modify the running kernel are disabled. If set to 2758 confidentiality, kernel features that allow userland 2759 to extract confidential information from the kernel 2760 are also disabled. 2761 2762 locktorture.nreaders_stress= [KNL] 2763 Set the number of locking read-acquisition kthreads. 2764 Defaults to being automatically set based on the 2765 number of online CPUs. 2766 2767 locktorture.nwriters_stress= [KNL] 2768 Set the number of locking write-acquisition kthreads. 2769 2770 locktorture.onoff_holdoff= [KNL] 2771 Set time (s) after boot for CPU-hotplug testing. 2772 2773 locktorture.onoff_interval= [KNL] 2774 Set time (s) between CPU-hotplug operations, or 2775 zero to disable CPU-hotplug testing. 2776 2777 locktorture.shuffle_interval= [KNL] 2778 Set task-shuffle interval (jiffies). Shuffling 2779 tasks allows some CPUs to go into dyntick-idle 2780 mode during the locktorture test. 2781 2782 locktorture.shutdown_secs= [KNL] 2783 Set time (s) after boot system shutdown. This 2784 is useful for hands-off automated testing. 2785 2786 locktorture.stat_interval= [KNL] 2787 Time (s) between statistics printk()s. 2788 2789 locktorture.stutter= [KNL] 2790 Time (s) to stutter testing, for example, 2791 specifying five seconds causes the test to run for 2792 five seconds, wait for five seconds, and so on. 2793 This tests the locking primitive's ability to 2794 transition abruptly to and from idle. 2795 2796 locktorture.torture_type= [KNL] 2797 Specify the locking implementation to test. 2798 2799 locktorture.verbose= [KNL] 2800 Enable additional printk() statements. 2801 2802 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2803 Format: <irq> 2804 2805 loglevel= All Kernel Messages with a loglevel smaller than the 2806 console loglevel will be printed to the console. It can 2807 also be changed with klogd or other programs. The 2808 loglevels are defined as follows: 2809 2810 0 (KERN_EMERG) system is unusable 2811 1 (KERN_ALERT) action must be taken immediately 2812 2 (KERN_CRIT) critical conditions 2813 3 (KERN_ERR) error conditions 2814 4 (KERN_WARNING) warning conditions 2815 5 (KERN_NOTICE) normal but significant condition 2816 6 (KERN_INFO) informational 2817 7 (KERN_DEBUG) debug-level messages 2818 2819 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2820 in bytes. n must be a power of two and greater 2821 than the minimal size. The minimal size is defined 2822 by LOG_BUF_SHIFT kernel config parameter. There is 2823 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2824 that allows to increase the default size depending on 2825 the number of CPUs. See init/Kconfig for more details. 2826 2827 logo.nologo [FB] Disables display of the built-in Linux logo. 2828 This may be used to provide more screen space for 2829 kernel log messages and is useful when debugging 2830 kernel boot problems. 2831 2832 lp=0 [LP] Specify parallel ports to use, e.g, 2833 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2834 lp=reset first parallel port). 'lp=0' disables the 2835 lp=auto printer driver. 'lp=reset' (which can be 2836 specified in addition to the ports) causes 2837 attached printers to be reset. Using 2838 lp=port1,port2,... specifies the parallel ports 2839 to associate lp devices with, starting with 2840 lp0. A port specification may be 'none' to skip 2841 that lp device, or a parport name such as 2842 'parport0'. Specifying 'lp=auto' instead of a 2843 port specification list means that device IDs 2844 from each port should be examined, to see if 2845 an IEEE 1284-compliant printer is attached; if 2846 so, the driver will manage that printer. 2847 See also header of drivers/char/lp.c. 2848 2849 lpj=n [KNL] 2850 Sets loops_per_jiffy to given constant, thus avoiding 2851 time-consuming boot-time autodetection (up to 250 ms per 2852 CPU). 0 enables autodetection (default). To determine 2853 the correct value for your kernel, boot with normal 2854 autodetection and see what value is printed. Note that 2855 on SMP systems the preset will be applied to all CPUs, 2856 which is likely to cause problems if your CPUs need 2857 significantly divergent settings. An incorrect value 2858 will cause delays in the kernel to be wrong, leading to 2859 unpredictable I/O errors and other breakage. Although 2860 unlikely, in the extreme case this might damage your 2861 hardware. 2862 2863 ltpc= [NET] 2864 Format: <io>,<irq>,<dma> 2865 2866 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2867 2868 lsm=lsm1,...,lsmN 2869 [SECURITY] Choose order of LSM initialization. This 2870 overrides CONFIG_LSM, and the "security=" parameter. 2871 2872 machvec= [IA-64] Force the use of a particular machine-vector 2873 (machvec) in a generic kernel. 2874 Example: machvec=hpzx1 2875 2876 machtype= [Loongson] Share the same kernel image file between 2877 different yeeloong laptops. 2878 Example: machtype=lemote-yeeloong-2f-7inch 2879 2880 max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater 2881 than or equal to this physical address is ignored. 2882 2883 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2884 will bring up during bootup. maxcpus=n : n >= 0 limits 2885 the kernel to bring up 'n' processors. Surely after 2886 bootup you can bring up the other plugged cpu by executing 2887 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2888 only takes effect during system bootup. 2889 While n=0 is a special case, it is equivalent to "nosmp", 2890 which also disables the IO APIC. 2891 2892 max_loop= [LOOP] The number of loop block devices that get 2893 (loop.max_loop) unconditionally pre-created at init time. The default 2894 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2895 of statically allocating a predefined number, loop 2896 devices can be requested on-demand with the 2897 /dev/loop-control interface. 2898 2899 mce [X86-32] Machine Check Exception 2900 2901 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2902 2903 md= [HW] RAID subsystems devices and level 2904 See Documentation/admin-guide/md.rst. 2905 2906 mdacon= [MDA] 2907 Format: <first>,<last> 2908 Specifies range of consoles to be captured by the MDA. 2909 2910 mds= [X86,INTEL] 2911 Control mitigation for the Micro-architectural Data 2912 Sampling (MDS) vulnerability. 2913 2914 Certain CPUs are vulnerable to an exploit against CPU 2915 internal buffers which can forward information to a 2916 disclosure gadget under certain conditions. 2917 2918 In vulnerable processors, the speculatively 2919 forwarded data can be used in a cache side channel 2920 attack, to access data to which the attacker does 2921 not have direct access. 2922 2923 This parameter controls the MDS mitigation. The 2924 options are: 2925 2926 full - Enable MDS mitigation on vulnerable CPUs 2927 full,nosmt - Enable MDS mitigation and disable 2928 SMT on vulnerable CPUs 2929 off - Unconditionally disable MDS mitigation 2930 2931 On TAA-affected machines, mds=off can be prevented by 2932 an active TAA mitigation as both vulnerabilities are 2933 mitigated with the same mechanism so in order to disable 2934 this mitigation, you need to specify tsx_async_abort=off 2935 too. 2936 2937 Not specifying this option is equivalent to 2938 mds=full. 2939 2940 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2941 2942 mem=nn[KMG] [HEXAGON] Set the memory size. 2943 Must be specified, otherwise memory size will be 0. 2944 2945 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2946 Amount of memory to be used in cases as follows: 2947 2948 1 for test; 2949 2 when the kernel is not able to see the whole system memory; 2950 3 memory that lies after 'mem=' boundary is excluded from 2951 the hypervisor, then assigned to KVM guests. 2952 4 to limit the memory available for kdump kernel. 2953 2954 [ARC,MICROBLAZE] - the limit applies only to low memory, 2955 high memory is not affected. 2956 2957 [ARM64] - only limits memory covered by the linear 2958 mapping. The NOMAP regions are not affected. 2959 2960 [X86] Work as limiting max address. Use together 2961 with memmap= to avoid physical address space collisions. 2962 Without memmap= PCI devices could be placed at addresses 2963 belonging to unused RAM. 2964 2965 Note that this only takes effects during boot time since 2966 in above case 3, memory may need be hot added after boot 2967 if system memory of hypervisor is not sufficient. 2968 2969 mem=nn[KMG]@ss[KMG] 2970 [ARM,MIPS] - override the memory layout reported by 2971 firmware. 2972 Define a memory region of size nn[KMG] starting at 2973 ss[KMG]. 2974 Multiple different regions can be specified with 2975 multiple mem= parameters on the command line. 2976 2977 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2978 memory. 2979 2980 memblock=debug [KNL] Enable memblock debug messages. 2981 2982 memchunk=nn[KMG] 2983 [KNL,SH] Allow user to override the default size for 2984 per-device physically contiguous DMA buffers. 2985 2986 memhp_default_state=online/offline 2987 [KNL] Set the initial state for the memory hotplug 2988 onlining policy. If not specified, the default value is 2989 set according to the 2990 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2991 option. 2992 See Documentation/admin-guide/mm/memory-hotplug.rst. 2993 2994 memmap=exactmap [KNL,X86] Enable setting of an exact 2995 E820 memory map, as specified by the user. 2996 Such memmap=exactmap lines can be constructed based on 2997 BIOS output or other requirements. See the memmap=nn@ss 2998 option description. 2999 3000 memmap=nn[KMG]@ss[KMG] 3001 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 3002 Region of memory to be used is from ss to ss+nn. 3003 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 3004 which limits max address to nn[KMG]. 3005 Multiple different regions can be specified, 3006 comma delimited. 3007 Example: 3008 memmap=100M@2G,100M#3G,1G!1024G 3009 3010 memmap=nn[KMG]#ss[KMG] 3011 [KNL,ACPI] Mark specific memory as ACPI data. 3012 Region of memory to be marked is from ss to ss+nn. 3013 3014 memmap=nn[KMG]$ss[KMG] 3015 [KNL,ACPI] Mark specific memory as reserved. 3016 Region of memory to be reserved is from ss to ss+nn. 3017 Example: Exclude memory from 0x18690000-0x1869ffff 3018 memmap=64K$0x18690000 3019 or 3020 memmap=0x10000$0x18690000 3021 Some bootloaders may need an escape character before '$', 3022 like Grub2, otherwise '$' and the following number 3023 will be eaten. 3024 3025 memmap=nn[KMG]!ss[KMG] 3026 [KNL,X86] Mark specific memory as protected. 3027 Region of memory to be used, from ss to ss+nn. 3028 The memory region may be marked as e820 type 12 (0xc) 3029 and is NVDIMM or ADR memory. 3030 3031 memmap=<size>%<offset>-<oldtype>+<newtype> 3032 [KNL,ACPI] Convert memory within the specified region 3033 from <oldtype> to <newtype>. If "-<oldtype>" is left 3034 out, the whole region will be marked as <newtype>, 3035 even if previously unavailable. If "+<newtype>" is left 3036 out, matching memory will be removed. Types are 3037 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 3038 3 = ACPI, 12 = PRAM. 3039 3040 memory_corruption_check=0/1 [X86] 3041 Some BIOSes seem to corrupt the first 64k of 3042 memory when doing things like suspend/resume. 3043 Setting this option will scan the memory 3044 looking for corruption. Enabling this will 3045 both detect corruption and prevent the kernel 3046 from using the memory being corrupted. 3047 However, its intended as a diagnostic tool; if 3048 repeatable BIOS-originated corruption always 3049 affects the same memory, you can use memmap= 3050 to prevent the kernel from using that memory. 3051 3052 memory_corruption_check_size=size [X86] 3053 By default it checks for corruption in the low 3054 64k, making this memory unavailable for normal 3055 use. Use this parameter to scan for 3056 corruption in more or less memory. 3057 3058 memory_corruption_check_period=seconds [X86] 3059 By default it checks for corruption every 60 3060 seconds. Use this parameter to check at some 3061 other rate. 0 disables periodic checking. 3062 3063 memory_hotplug.memmap_on_memory 3064 [KNL,X86,ARM] Boolean flag to enable this feature. 3065 Format: {on | off (default)} 3066 When enabled, runtime hotplugged memory will 3067 allocate its internal metadata (struct pages) 3068 from the hotadded memory which will allow to 3069 hotadd a lot of memory without requiring 3070 additional memory to do so. 3071 This feature is disabled by default because it 3072 has some implication on large (e.g. GB) 3073 allocations in some configurations (e.g. small 3074 memory blocks). 3075 The state of the flag can be read in 3076 /sys/module/memory_hotplug/parameters/memmap_on_memory. 3077 Note that even when enabled, there are a few cases where 3078 the feature is not effective. 3079 3080 This is not compatible with hugetlb_free_vmemmap. If 3081 both parameters are enabled, hugetlb_free_vmemmap takes 3082 precedence over memory_hotplug.memmap_on_memory. 3083 3084 memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest 3085 Format: <integer> 3086 default : 0 <disable> 3087 Specifies the number of memtest passes to be 3088 performed. Each pass selects another test 3089 pattern from a given set of patterns. Memtest 3090 fills the memory with this pattern, validates 3091 memory contents and reserves bad memory 3092 regions that are detected. 3093 3094 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 3095 Valid arguments: on, off 3096 Default (depends on kernel configuration option): 3097 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 3098 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 3099 mem_encrypt=on: Activate SME 3100 mem_encrypt=off: Do not activate SME 3101 3102 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 3103 for details on when memory encryption can be activated. 3104 3105 mem_sleep_default= [SUSPEND] Default system suspend mode: 3106 s2idle - Suspend-To-Idle 3107 shallow - Power-On Suspend or equivalent (if supported) 3108 deep - Suspend-To-RAM or equivalent (if supported) 3109 See Documentation/admin-guide/pm/sleep-states.rst. 3110 3111 meye.*= [HW] Set MotionEye Camera parameters 3112 See Documentation/admin-guide/media/meye.rst. 3113 3114 mfgpt_irq= [IA-32] Specify the IRQ to use for the 3115 Multi-Function General Purpose Timers on AMD Geode 3116 platforms. 3117 3118 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 3119 the BIOS has incorrectly applied a workaround. TinyBIOS 3120 version 0.98 is known to be affected, 0.99 fixes the 3121 problem by letting the user disable the workaround. 3122 3123 mga= [HW,DRM] 3124 3125 min_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory below this 3126 physical address is ignored. 3127 3128 mini2440= [ARM,HW,KNL] 3129 Format:[0..2][b][c][t] 3130 Default: "0tb" 3131 MINI2440 configuration specification: 3132 0 - The attached screen is the 3.5" TFT 3133 1 - The attached screen is the 7" TFT 3134 2 - The VGA Shield is attached (1024x768) 3135 Leaving out the screen size parameter will not load 3136 the TFT driver, and the framebuffer will be left 3137 unconfigured. 3138 b - Enable backlight. The TFT backlight pin will be 3139 linked to the kernel VESA blanking code and a GPIO 3140 LED. This parameter is not necessary when using the 3141 VGA shield. 3142 c - Enable the s3c camera interface. 3143 t - Reserved for enabling touchscreen support. The 3144 touchscreen support is not enabled in the mainstream 3145 kernel as of 2.6.30, a preliminary port can be found 3146 in the "bleeding edge" mini2440 support kernel at 3147 https://repo.or.cz/w/linux-2.6/mini2440.git 3148 3149 mitigations= 3150 [X86,PPC,S390,ARM64] Control optional mitigations for 3151 CPU vulnerabilities. This is a set of curated, 3152 arch-independent options, each of which is an 3153 aggregation of existing arch-specific options. 3154 3155 off 3156 Disable all optional CPU mitigations. This 3157 improves system performance, but it may also 3158 expose users to several CPU vulnerabilities. 3159 Equivalent to: nopti [X86,PPC] 3160 kpti=0 [ARM64] 3161 nospectre_v1 [X86,PPC] 3162 nobp=0 [S390] 3163 nospectre_v2 [X86,PPC,S390,ARM64] 3164 spectre_v2_user=off [X86] 3165 spec_store_bypass_disable=off [X86,PPC] 3166 ssbd=force-off [ARM64] 3167 l1tf=off [X86] 3168 mds=off [X86] 3169 tsx_async_abort=off [X86] 3170 kvm.nx_huge_pages=off [X86] 3171 srbds=off [X86,INTEL] 3172 no_entry_flush [PPC] 3173 no_uaccess_flush [PPC] 3174 3175 Exceptions: 3176 This does not have any effect on 3177 kvm.nx_huge_pages when 3178 kvm.nx_huge_pages=force. 3179 3180 auto (default) 3181 Mitigate all CPU vulnerabilities, but leave SMT 3182 enabled, even if it's vulnerable. This is for 3183 users who don't want to be surprised by SMT 3184 getting disabled across kernel upgrades, or who 3185 have other ways of avoiding SMT-based attacks. 3186 Equivalent to: (default behavior) 3187 3188 auto,nosmt 3189 Mitigate all CPU vulnerabilities, disabling SMT 3190 if needed. This is for users who always want to 3191 be fully mitigated, even if it means losing SMT. 3192 Equivalent to: l1tf=flush,nosmt [X86] 3193 mds=full,nosmt [X86] 3194 tsx_async_abort=full,nosmt [X86] 3195 3196 mminit_loglevel= 3197 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 3198 parameter allows control of the logging verbosity for 3199 the additional memory initialisation checks. A value 3200 of 0 disables mminit logging and a level of 4 will 3201 log everything. Information is printed at KERN_DEBUG 3202 so loglevel=8 may also need to be specified. 3203 3204 module.sig_enforce 3205 [KNL] When CONFIG_MODULE_SIG is set, this means that 3206 modules without (valid) signatures will fail to load. 3207 Note that if CONFIG_MODULE_SIG_FORCE is set, that 3208 is always true, so this option does nothing. 3209 3210 module_blacklist= [KNL] Do not load a comma-separated list of 3211 modules. Useful for debugging problem modules. 3212 3213 mousedev.tap_time= 3214 [MOUSE] Maximum time between finger touching and 3215 leaving touchpad surface for touch to be considered 3216 a tap and be reported as a left button click (for 3217 touchpads working in absolute mode only). 3218 Format: <msecs> 3219 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 3220 reporting absolute coordinates, such as tablets 3221 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 3222 reporting absolute coordinates, such as tablets 3223 3224 movablecore= [KNL,X86,IA-64,PPC] 3225 Format: nn[KMGTPE] | nn% 3226 This parameter is the complement to kernelcore=, it 3227 specifies the amount of memory used for migratable 3228 allocations. If both kernelcore and movablecore is 3229 specified, then kernelcore will be at *least* the 3230 specified value but may be more. If movablecore on its 3231 own is specified, the administrator must be careful 3232 that the amount of memory usable for all allocations 3233 is not too small. 3234 3235 movable_node [KNL] Boot-time switch to make hotplugable memory 3236 NUMA nodes to be movable. This means that the memory 3237 of such nodes will be usable only for movable 3238 allocations which rules out almost all kernel 3239 allocations. Use with caution! 3240 3241 MTD_Partition= [MTD] 3242 Format: <name>,<region-number>,<size>,<offset> 3243 3244 MTD_Region= [MTD] Format: 3245 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 3246 3247 mtdparts= [MTD] 3248 See drivers/mtd/parsers/cmdlinepart.c 3249 3250 mtdset= [ARM] 3251 ARM/S3C2412 JIVE boot control 3252 3253 See arch/arm/mach-s3c/mach-jive.c 3254 3255 mtouchusb.raw_coordinates= 3256 [HW] Make the MicroTouch USB driver use raw coordinates 3257 ('y', default) or cooked coordinates ('n') 3258 3259 mtrr_chunk_size=nn[KMG] [X86] 3260 used for mtrr cleanup. It is largest continuous chunk 3261 that could hold holes aka. UC entries. 3262 3263 mtrr_gran_size=nn[KMG] [X86] 3264 Used for mtrr cleanup. It is granularity of mtrr block. 3265 Default is 1. 3266 Large value could prevent small alignment from 3267 using up MTRRs. 3268 3269 mtrr_spare_reg_nr=n [X86] 3270 Format: <integer> 3271 Range: 0,7 : spare reg number 3272 Default : 1 3273 Used for mtrr cleanup. It is spare mtrr entries number. 3274 Set to 2 or more if your graphical card needs more. 3275 3276 multitce=off [PPC] This parameter disables the use of the pSeries 3277 firmware feature for updating multiple TCE entries 3278 at a time. 3279 3280 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 3281 3282 netdev= [NET] Network devices parameters 3283 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 3284 Note that mem_start is often overloaded to mean 3285 something different and driver-specific. 3286 This usage is only documented in each driver source 3287 file if at all. 3288 3289 netpoll.carrier_timeout= 3290 [NET] Specifies amount of time (in seconds) that 3291 netpoll should wait for a carrier. By default netpoll 3292 waits 4 seconds. 3293 3294 nf_conntrack.acct= 3295 [NETFILTER] Enable connection tracking flow accounting 3296 0 to disable accounting 3297 1 to enable accounting 3298 Default value is 0. 3299 3300 nfsaddrs= [NFS] Deprecated. Use ip= instead. 3301 See Documentation/admin-guide/nfs/nfsroot.rst. 3302 3303 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 3304 See Documentation/admin-guide/nfs/nfsroot.rst. 3305 3306 nfsrootdebug [NFS] enable nfsroot debugging messages. 3307 See Documentation/admin-guide/nfs/nfsroot.rst. 3308 3309 nfs.callback_nr_threads= 3310 [NFSv4] set the total number of threads that the 3311 NFS client will assign to service NFSv4 callback 3312 requests. 3313 3314 nfs.callback_tcpport= 3315 [NFS] set the TCP port on which the NFSv4 callback 3316 channel should listen. 3317 3318 nfs.cache_getent= 3319 [NFS] sets the pathname to the program which is used 3320 to update the NFS client cache entries. 3321 3322 nfs.cache_getent_timeout= 3323 [NFS] sets the timeout after which an attempt to 3324 update a cache entry is deemed to have failed. 3325 3326 nfs.idmap_cache_timeout= 3327 [NFS] set the maximum lifetime for idmapper cache 3328 entries. 3329 3330 nfs.enable_ino64= 3331 [NFS] enable 64-bit inode numbers. 3332 If zero, the NFS client will fake up a 32-bit inode 3333 number for the readdir() and stat() syscalls instead 3334 of returning the full 64-bit number. 3335 The default is to return 64-bit inode numbers. 3336 3337 nfs.max_session_cb_slots= 3338 [NFSv4.1] Sets the maximum number of session 3339 slots the client will assign to the callback 3340 channel. This determines the maximum number of 3341 callbacks the client will process in parallel for 3342 a particular server. 3343 3344 nfs.max_session_slots= 3345 [NFSv4.1] Sets the maximum number of session slots 3346 the client will attempt to negotiate with the server. 3347 This limits the number of simultaneous RPC requests 3348 that the client can send to the NFSv4.1 server. 3349 Note that there is little point in setting this 3350 value higher than the max_tcp_slot_table_limit. 3351 3352 nfs.nfs4_disable_idmapping= 3353 [NFSv4] When set to the default of '1', this option 3354 ensures that both the RPC level authentication 3355 scheme and the NFS level operations agree to use 3356 numeric uids/gids if the mount is using the 3357 'sec=sys' security flavour. In effect it is 3358 disabling idmapping, which can make migration from 3359 legacy NFSv2/v3 systems to NFSv4 easier. 3360 Servers that do not support this mode of operation 3361 will be autodetected by the client, and it will fall 3362 back to using the idmapper. 3363 To turn off this behaviour, set the value to '0'. 3364 nfs.nfs4_unique_id= 3365 [NFS4] Specify an additional fixed unique ident- 3366 ification string that NFSv4 clients can insert into 3367 their nfs_client_id4 string. This is typically a 3368 UUID that is generated at system install time. 3369 3370 nfs.send_implementation_id = 3371 [NFSv4.1] Send client implementation identification 3372 information in exchange_id requests. 3373 If zero, no implementation identification information 3374 will be sent. 3375 The default is to send the implementation identification 3376 information. 3377 3378 nfs.recover_lost_locks = 3379 [NFSv4] Attempt to recover locks that were lost due 3380 to a lease timeout on the server. Please note that 3381 doing this risks data corruption, since there are 3382 no guarantees that the file will remain unchanged 3383 after the locks are lost. 3384 If you want to enable the kernel legacy behaviour of 3385 attempting to recover these locks, then set this 3386 parameter to '1'. 3387 The default parameter value of '0' causes the kernel 3388 not to attempt recovery of lost locks. 3389 3390 nfs4.layoutstats_timer = 3391 [NFSv4.2] Change the rate at which the kernel sends 3392 layoutstats to the pNFS metadata server. 3393 3394 Setting this to value to 0 causes the kernel to use 3395 whatever value is the default set by the layout 3396 driver. A non-zero value sets the minimum interval 3397 in seconds between layoutstats transmissions. 3398 3399 nfsd.inter_copy_offload_enable = 3400 [NFSv4.2] When set to 1, the server will support 3401 server-to-server copies for which this server is 3402 the destination of the copy. 3403 3404 nfsd.nfsd4_ssc_umount_timeout = 3405 [NFSv4.2] When used as the destination of a 3406 server-to-server copy, knfsd temporarily mounts 3407 the source server. It caches the mount in case 3408 it will be needed again, and discards it if not 3409 used for the number of milliseconds specified by 3410 this parameter. 3411 3412 nfsd.nfs4_disable_idmapping= 3413 [NFSv4] When set to the default of '1', the NFSv4 3414 server will return only numeric uids and gids to 3415 clients using auth_sys, and will accept numeric uids 3416 and gids from such clients. This is intended to ease 3417 migration from NFSv2/v3. 3418 3419 3420 nmi_backtrace.backtrace_idle [KNL] 3421 Dump stacks even of idle CPUs in response to an 3422 NMI stack-backtrace request. 3423 3424 nmi_debug= [KNL,SH] Specify one or more actions to take 3425 when a NMI is triggered. 3426 Format: [state][,regs][,debounce][,die] 3427 3428 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3429 Format: [panic,][nopanic,][num] 3430 Valid num: 0 or 1 3431 0 - turn hardlockup detector in nmi_watchdog off 3432 1 - turn hardlockup detector in nmi_watchdog on 3433 When panic is specified, panic when an NMI watchdog 3434 timeout occurs (or 'nopanic' to not panic on an NMI 3435 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3436 To disable both hard and soft lockup detectors, 3437 please see 'nowatchdog'. 3438 This is useful when you use a panic=... timeout and 3439 need the box quickly up again. 3440 3441 These settings can be accessed at runtime via 3442 the nmi_watchdog and hardlockup_panic sysctls. 3443 3444 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3445 emulation library even if a 387 maths coprocessor 3446 is present. 3447 3448 no5lvl [X86-64] Disable 5-level paging mode. Forces 3449 kernel to use 4-level paging instead. 3450 3451 nofsgsbase [X86] Disables FSGSBASE instructions. 3452 3453 no_console_suspend 3454 [HW] Never suspend the console 3455 Disable suspending of consoles during suspend and 3456 hibernate operations. Once disabled, debugging 3457 messages can reach various consoles while the rest 3458 of the system is being put to sleep (ie, while 3459 debugging driver suspend/resume hooks). This may 3460 not work reliably with all consoles, but is known 3461 to work with serial and VGA consoles. 3462 To facilitate more flexible debugging, we also add 3463 console_suspend, a printk module parameter to control 3464 it. Users could use console_suspend (usually 3465 /sys/module/printk/parameters/console_suspend) to 3466 turn on/off it dynamically. 3467 3468 novmcoredd [KNL,KDUMP] 3469 Disable device dump. Device dump allows drivers to 3470 append dump data to vmcore so you can collect driver 3471 specified debug info. Drivers can append the data 3472 without any limit and this data is stored in memory, 3473 so this may cause significant memory stress. Disabling 3474 device dump can help save memory but the driver debug 3475 data will be no longer available. This parameter 3476 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3477 is set. 3478 3479 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3480 caches in the slab allocator. Saves per-node memory, 3481 but will impact performance. 3482 3483 noalign [KNL,ARM] 3484 3485 noaltinstr [S390] Disables alternative instructions patching 3486 (CPU alternatives feature). 3487 3488 noapic [SMP,APIC] Tells the kernel to not make use of any 3489 IOAPICs that may be present in the system. 3490 3491 noautogroup Disable scheduler automatic task group creation. 3492 3493 nobats [PPC] Do not use BATs for mapping kernel lowmem 3494 on "Classic" PPC cores. 3495 3496 nocache [ARM] 3497 3498 nodsp [SH] Disable hardware DSP at boot time. 3499 3500 noefi Disable EFI runtime services support. 3501 3502 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3503 3504 noexec [IA-64] 3505 3506 nosmap [PPC] 3507 Disable SMAP (Supervisor Mode Access Prevention) 3508 even if it is supported by processor. 3509 3510 nosmep [PPC64s] 3511 Disable SMEP (Supervisor Mode Execution Prevention) 3512 even if it is supported by processor. 3513 3514 noexec32 [X86-64] 3515 This affects only 32-bit executables. 3516 noexec32=on: enable non-executable mappings (default) 3517 read doesn't imply executable mappings 3518 noexec32=off: disable non-executable mappings 3519 read implies executable mappings 3520 3521 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3522 3523 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3524 register save and restore. The kernel will only save 3525 legacy floating-point registers on task switch. 3526 3527 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3528 3529 nohugevmalloc [PPC] Disable kernel huge vmalloc mappings. 3530 3531 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3532 Equivalent to smt=1. 3533 3534 [KNL,X86] Disable symmetric multithreading (SMT). 3535 nosmt=force: Force disable SMT, cannot be undone 3536 via the sysfs control file. 3537 3538 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3539 (bounds check bypass). With this option data leaks are 3540 possible in the system. 3541 3542 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3543 the Spectre variant 2 (indirect branch prediction) 3544 vulnerability. System may allow data leaks with this 3545 option. 3546 3547 nospec_store_bypass_disable 3548 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3549 3550 no_uaccess_flush 3551 [PPC] Don't flush the L1-D cache after accessing user data. 3552 3553 noxsave [BUGS=X86] Disables x86 extended register state save 3554 and restore using xsave. The kernel will fallback to 3555 enabling legacy floating-point and sse state. 3556 3557 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3558 register states. The kernel will fall back to use 3559 xsave to save the states. By using this parameter, 3560 performance of saving the states is degraded because 3561 xsave doesn't support modified optimization while 3562 xsaveopt supports it on xsaveopt enabled systems. 3563 3564 noxsaves [X86] Disables xsaves and xrstors used in saving and 3565 restoring x86 extended register state in compacted 3566 form of xsave area. The kernel will fall back to use 3567 xsaveopt and xrstor to save and restore the states 3568 in standard form of xsave area. By using this 3569 parameter, xsave area per process might occupy more 3570 memory on xsaves enabled systems. 3571 3572 nohlt [ARM,ARM64,MICROBLAZE,SH] Forces the kernel to busy wait 3573 in do_idle() and not use the arch_cpu_idle() 3574 implementation; requires CONFIG_GENERIC_IDLE_POLL_SETUP 3575 to be effective. This is useful on platforms where the 3576 sleep(SH) or wfi(ARM,ARM64) instructions do not work 3577 correctly or when doing power measurements to evalute 3578 the impact of the sleep instructions. This is also 3579 useful when using JTAG debugger. 3580 3581 no_file_caps Tells the kernel not to honor file capabilities. The 3582 only way then for a file to be executed with privilege 3583 is to be setuid root or executed by root. 3584 3585 nohalt [IA-64] Tells the kernel not to use the power saving 3586 function PAL_HALT_LIGHT when idle. This increases 3587 power-consumption. On the positive side, it reduces 3588 interrupt wake-up latency, which may improve performance 3589 in certain environments such as networked servers or 3590 real-time systems. 3591 3592 no_hash_pointers 3593 Force pointers printed to the console or buffers to be 3594 unhashed. By default, when a pointer is printed via %p 3595 format string, that pointer is "hashed", i.e. obscured 3596 by hashing the pointer value. This is a security feature 3597 that hides actual kernel addresses from unprivileged 3598 users, but it also makes debugging the kernel more 3599 difficult since unequal pointers can no longer be 3600 compared. However, if this command-line option is 3601 specified, then all normal pointers will have their true 3602 value printed. This option should only be specified when 3603 debugging the kernel. Please do not use on production 3604 kernels. 3605 3606 nohibernate [HIBERNATION] Disable hibernation and resume. 3607 3608 nohz= [KNL] Boottime enable/disable dynamic ticks 3609 Valid arguments: on, off 3610 Default: on 3611 3612 nohz_full= [KNL,BOOT,SMP,ISOL] 3613 The argument is a cpu list, as described above. 3614 In kernels built with CONFIG_NO_HZ_FULL=y, set 3615 the specified list of CPUs whose tick will be stopped 3616 whenever possible. The boot CPU will be forced outside 3617 the range to maintain the timekeeping. Any CPUs 3618 in this list will have their RCU callbacks offloaded, 3619 just as if they had also been called out in the 3620 rcu_nocbs= boot parameter. 3621 3622 noiotrap [SH] Disables trapped I/O port accesses. 3623 3624 noirqdebug [X86-32] Disables the code which attempts to detect and 3625 disable unhandled interrupt sources. 3626 3627 no_timer_check [X86,APIC] Disables the code which tests for 3628 broken timer IRQ sources. 3629 3630 noisapnp [ISAPNP] Disables ISA PnP code. 3631 3632 noinitrd [RAM] Tells the kernel not to load any configured 3633 initial RAM disk. 3634 3635 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3636 remapping. 3637 [Deprecated - use intremap=off] 3638 3639 nointroute [IA-64] 3640 3641 noinvpcid [X86] Disable the INVPCID cpu feature. 3642 3643 nojitter [IA-64] Disables jitter checking for ITC timers. 3644 3645 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3646 3647 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3648 fault handling. 3649 3650 no-vmw-sched-clock 3651 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3652 clock and use the default one. 3653 3654 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3655 accounting. steal time is computed, but won't 3656 influence scheduler behaviour 3657 3658 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3659 3660 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3661 3662 noltlbs [PPC] Do not use large page/tlb entries for kernel 3663 lowmem mapping on PPC40x and PPC8xx 3664 3665 nomca [IA-64] Disable machine check abort handling 3666 3667 nomce [X86-32] Disable Machine Check Exception 3668 3669 nomfgpt [X86-32] Disable Multi-Function General Purpose 3670 Timer usage (for AMD Geode machines). 3671 3672 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3673 shutdown the other cpus. Instead use the REBOOT_VECTOR 3674 irq. 3675 3676 nomodeset Disable kernel modesetting. DRM drivers will not perform 3677 display-mode changes or accelerated rendering. Only the 3678 system framebuffer will be available for use if this was 3679 set-up by the firmware or boot loader. 3680 3681 Useful as fallback, or for testing and debugging. 3682 3683 nomodule Disable module load 3684 3685 nopat [X86] Disable PAT (page attribute table extension of 3686 pagetables) support. 3687 3688 nopcid [X86-64] Disable the PCID cpu feature. 3689 3690 norandmaps Don't use address space randomization. Equivalent to 3691 echo 0 > /proc/sys/kernel/randomize_va_space 3692 3693 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3694 with UP alternatives 3695 3696 nordrand [X86] Disable kernel use of the RDRAND and 3697 RDSEED instructions even if they are supported 3698 by the processor. RDRAND and RDSEED are still 3699 available to user space applications. 3700 3701 noresume [SWSUSP] Disables resume and restores original swap 3702 space. 3703 3704 no-scroll [VGA] Disables scrollback. 3705 This is required for the Braillex ib80-piezo Braille 3706 reader made by F.H. Papenmeier (Germany). 3707 3708 nosbagart [IA-64] 3709 3710 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3711 3712 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3713 and disable the IO APIC. legacy for "maxcpus=0". 3714 3715 nosoftlockup [KNL] Disable the soft-lockup detector. 3716 3717 nosync [HW,M68K] Disables sync negotiation for all devices. 3718 3719 nowatchdog [KNL] Disable both lockup detectors, i.e. 3720 soft-lockup and NMI watchdog (hard-lockup). 3721 3722 nowb [ARM] 3723 3724 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3725 3726 nps_mtm_hs_ctr= [KNL,ARC] 3727 This parameter sets the maximum duration, in 3728 cycles, each HW thread of the CTOP can run 3729 without interruptions, before HW switches it. 3730 The actual maximum duration is 16 times this 3731 parameter's value. 3732 Format: integer between 1 and 255 3733 Default: 255 3734 3735 nptcg= [IA-64] Override max number of concurrent global TLB 3736 purges which is reported from either PAL_VM_SUMMARY or 3737 SAL PALO. 3738 3739 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3740 could support. nr_cpus=n : n >= 1 limits the kernel to 3741 support 'n' processors. It could be larger than the 3742 number of already plugged CPU during bootup, later in 3743 runtime you can physically add extra cpu until it reaches 3744 n. So during boot up some boot time memory for per-cpu 3745 variables need be pre-allocated for later physical cpu 3746 hot plugging. 3747 3748 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3749 3750 numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only 3751 set up a single NUMA node spanning all memory. 3752 3753 numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic 3754 NUMA balancing. 3755 Allowed values are enable and disable 3756 3757 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3758 'node', 'default' can be specified 3759 This can be set from sysctl after boot. 3760 See Documentation/admin-guide/sysctl/vm.rst for details. 3761 3762 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3763 See Documentation/core-api/debugging-via-ohci1394.rst for more 3764 info. 3765 3766 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3767 Rather than timing out after 20 ms if an EC 3768 command is not properly ACKed, override the length 3769 of the timeout. We have interrupts disabled while 3770 waiting for the ACK, so if this is set too high 3771 interrupts *may* be lost! 3772 3773 omap_mux= [OMAP] Override bootloader pin multiplexing. 3774 Format: <mux_mode0.mode_name=value>... 3775 For example, to override I2C bus2: 3776 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3777 3778 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 3779 3780 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 3781 3782 boundary - index of last SLC block on Flex-OneNAND. 3783 The remaining blocks are configured as MLC blocks. 3784 lock - Configure if Flex-OneNAND boundary should be locked. 3785 Once locked, the boundary cannot be changed. 3786 1 indicates lock status, 0 indicates unlock status. 3787 3788 oops=panic Always panic on oopses. Default is to just kill the 3789 process, but there is a small probability of 3790 deadlocking the machine. 3791 This will also cause panics on machine check exceptions. 3792 Useful together with panic=30 to trigger a reboot. 3793 3794 page_alloc.shuffle= 3795 [KNL] Boolean flag to control whether the page allocator 3796 should randomize its free lists. The randomization may 3797 be automatically enabled if the kernel detects it is 3798 running on a platform with a direct-mapped memory-side 3799 cache, and this parameter can be used to 3800 override/disable that behavior. The state of the flag 3801 can be read from sysfs at: 3802 /sys/module/page_alloc/parameters/shuffle. 3803 3804 page_owner= [KNL] Boot-time page_owner enabling option. 3805 Storage of the information about who allocated 3806 each page is disabled in default. With this switch, 3807 we can turn it on. 3808 on: enable the feature 3809 3810 page_poison= [KNL] Boot-time parameter changing the state of 3811 poisoning on the buddy allocator, available with 3812 CONFIG_PAGE_POISONING=y. 3813 off: turn off poisoning (default) 3814 on: turn on poisoning 3815 3816 page_reporting.page_reporting_order= 3817 [KNL] Minimal page reporting order 3818 Format: <integer> 3819 Adjust the minimal page reporting order. The page 3820 reporting is disabled when it exceeds (MAX_ORDER-1). 3821 3822 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3823 timeout > 0: seconds before rebooting 3824 timeout = 0: wait forever 3825 timeout < 0: reboot immediately 3826 Format: <timeout> 3827 3828 panic_print= Bitmask for printing system info when panic happens. 3829 User can chose combination of the following bits: 3830 bit 0: print all tasks info 3831 bit 1: print system memory info 3832 bit 2: print timer info 3833 bit 3: print locks info if CONFIG_LOCKDEP is on 3834 bit 4: print ftrace buffer 3835 bit 5: print all printk messages in buffer 3836 bit 6: print all CPUs backtrace (if available in the arch) 3837 *Be aware* that this option may print a _lot_ of lines, 3838 so there are risks of losing older messages in the log. 3839 Use this option carefully, maybe worth to setup a 3840 bigger log buffer with "log_buf_len" along with this. 3841 3842 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3843 Format: <hex>[,nousertaint] 3844 Hexadecimal bitmask representing the set of TAINT flags 3845 that will cause the kernel to panic when add_taint() is 3846 called with any of the flags in this set. 3847 The optional switch "nousertaint" can be utilized to 3848 prevent userspace forced crashes by writing to sysctl 3849 /proc/sys/kernel/tainted any flagset matching with the 3850 bitmask set on panic_on_taint. 3851 See Documentation/admin-guide/tainted-kernels.rst for 3852 extra details on the taint flags that users can pick 3853 to compose the bitmask to assign to panic_on_taint. 3854 3855 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3856 on a WARN(). 3857 3858 parkbd.port= [HW] Parallel port number the keyboard adapter is 3859 connected to, default is 0. 3860 Format: <parport#> 3861 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3862 0 for XT, 1 for AT (default is AT). 3863 Format: <mode> 3864 3865 parport= [HW,PPT] Specify parallel ports. 0 disables. 3866 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3867 Use 'auto' to force the driver to use any 3868 IRQ/DMA settings detected (the default is to 3869 ignore detected IRQ/DMA settings because of 3870 possible conflicts). You can specify the base 3871 address, IRQ, and DMA settings; IRQ and DMA 3872 should be numbers, or 'auto' (for using detected 3873 settings on that particular port), or 'nofifo' 3874 (to avoid using a FIFO even if it is detected). 3875 Parallel ports are assigned in the order they 3876 are specified on the command line, starting 3877 with parport0. 3878 3879 parport_init_mode= [HW,PPT] 3880 Configure VIA parallel port to operate in 3881 a specific mode. This is necessary on Pegasos 3882 computer where firmware has no options for setting 3883 up parallel port mode and sets it to spp. 3884 Currently this function knows 686a and 8231 chips. 3885 Format: [spp|ps2|epp|ecp|ecpepp] 3886 3887 pata_legacy.all= [HW,LIBATA] 3888 Format: <int> 3889 Set to non-zero to probe primary and secondary ISA 3890 port ranges on PCI systems where no PCI PATA device 3891 has been found at either range. Disabled by default. 3892 3893 pata_legacy.autospeed= [HW,LIBATA] 3894 Format: <int> 3895 Set to non-zero if a chip is present that snoops speed 3896 changes. Disabled by default. 3897 3898 pata_legacy.ht6560a= [HW,LIBATA] 3899 Format: <int> 3900 Set to 1, 2, or 3 for HT 6560A on the primary channel, 3901 the secondary channel, or both channels respectively. 3902 Disabled by default. 3903 3904 pata_legacy.ht6560b= [HW,LIBATA] 3905 Format: <int> 3906 Set to 1, 2, or 3 for HT 6560B on the primary channel, 3907 the secondary channel, or both channels respectively. 3908 Disabled by default. 3909 3910 pata_legacy.iordy_mask= [HW,LIBATA] 3911 Format: <int> 3912 IORDY enable mask. Set individual bits to allow IORDY 3913 for the respective channel. Bit 0 is for the first 3914 legacy channel handled by this driver, bit 1 is for 3915 the second channel, and so on. The sequence will often 3916 correspond to the primary legacy channel, the secondary 3917 legacy channel, and so on, but the handling of a PCI 3918 bus and the use of other driver options may interfere 3919 with the sequence. By default IORDY is allowed across 3920 all channels. 3921 3922 pata_legacy.opti82c46x= [HW,LIBATA] 3923 Format: <int> 3924 Set to 1, 2, or 3 for Opti 82c611A on the primary 3925 channel, the secondary channel, or both channels 3926 respectively. Disabled by default. 3927 3928 pata_legacy.opti82c611a= [HW,LIBATA] 3929 Format: <int> 3930 Set to 1, 2, or 3 for Opti 82c465MV on the primary 3931 channel, the secondary channel, or both channels 3932 respectively. Disabled by default. 3933 3934 pata_legacy.pio_mask= [HW,LIBATA] 3935 Format: <int> 3936 PIO mode mask for autospeed devices. Set individual 3937 bits to allow the use of the respective PIO modes. 3938 Bit 0 is for mode 0, bit 1 is for mode 1, and so on. 3939 All modes allowed by default. 3940 3941 pata_legacy.probe_all= [HW,LIBATA] 3942 Format: <int> 3943 Set to non-zero to probe tertiary and further ISA 3944 port ranges on PCI systems. Disabled by default. 3945 3946 pata_legacy.probe_mask= [HW,LIBATA] 3947 Format: <int> 3948 Probe mask for legacy ISA PATA ports. Depending on 3949 platform configuration and the use of other driver 3950 options up to 6 legacy ports are supported: 0x1f0, 3951 0x170, 0x1e8, 0x168, 0x1e0, 0x160, however probing 3952 of individual ports can be disabled by setting the 3953 corresponding bits in the mask to 1. Bit 0 is for 3954 the first port in the list above (0x1f0), and so on. 3955 By default all supported ports are probed. 3956 3957 pata_legacy.qdi= [HW,LIBATA] 3958 Format: <int> 3959 Set to non-zero to probe QDI controllers. By default 3960 set to 1 if CONFIG_PATA_QDI_MODULE, 0 otherwise. 3961 3962 pata_legacy.winbond= [HW,LIBATA] 3963 Format: <int> 3964 Set to non-zero to probe Winbond controllers. Use 3965 the standard I/O port (0x130) if 1, otherwise the 3966 value given is the I/O port to use (typically 0x1b0). 3967 By default set to 1 if CONFIG_PATA_WINBOND_VLB_MODULE, 3968 0 otherwise. 3969 3970 pata_platform.pio_mask= [HW,LIBATA] 3971 Format: <int> 3972 Supported PIO mode mask. Set individual bits to allow 3973 the use of the respective PIO modes. Bit 0 is for 3974 mode 0, bit 1 is for mode 1, and so on. Mode 0 only 3975 allowed by default. 3976 3977 pause_on_oops= 3978 Halt all CPUs after the first oops has been printed for 3979 the specified number of seconds. This is to be used if 3980 your oopses keep scrolling off the screen. 3981 3982 pcbit= [HW,ISDN] 3983 3984 pcd. [PARIDE] 3985 See header of drivers/block/paride/pcd.c. 3986 See also Documentation/admin-guide/blockdev/paride.rst. 3987 3988 pci=option[,option...] [PCI] various PCI subsystem options. 3989 3990 Some options herein operate on a specific device 3991 or a set of devices (<pci_dev>). These are 3992 specified in one of the following formats: 3993 3994 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3995 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3996 3997 Note: the first format specifies a PCI 3998 bus/device/function address which may change 3999 if new hardware is inserted, if motherboard 4000 firmware changes, or due to changes caused 4001 by other kernel parameters. If the 4002 domain is left unspecified, it is 4003 taken to be zero. Optionally, a path 4004 to a device through multiple device/function 4005 addresses can be specified after the base 4006 address (this is more robust against 4007 renumbering issues). The second format 4008 selects devices using IDs from the 4009 configuration space which may match multiple 4010 devices in the system. 4011 4012 earlydump dump PCI config space before the kernel 4013 changes anything 4014 off [X86] don't probe for the PCI bus 4015 bios [X86-32] force use of PCI BIOS, don't access 4016 the hardware directly. Use this if your machine 4017 has a non-standard PCI host bridge. 4018 nobios [X86-32] disallow use of PCI BIOS, only direct 4019 hardware access methods are allowed. Use this 4020 if you experience crashes upon bootup and you 4021 suspect they are caused by the BIOS. 4022 conf1 [X86] Force use of PCI Configuration Access 4023 Mechanism 1 (config address in IO port 0xCF8, 4024 data in IO port 0xCFC, both 32-bit). 4025 conf2 [X86] Force use of PCI Configuration Access 4026 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 4027 the function, IO port 0xCFA, also 8-bit, sets 4028 bus number. The config space is then accessed 4029 through ports 0xC000-0xCFFF). 4030 See http://wiki.osdev.org/PCI for more info 4031 on the configuration access mechanisms. 4032 noaer [PCIE] If the PCIEAER kernel config parameter is 4033 enabled, this kernel boot option can be used to 4034 disable the use of PCIE advanced error reporting. 4035 nodomains [PCI] Disable support for multiple PCI 4036 root domains (aka PCI segments, in ACPI-speak). 4037 nommconf [X86] Disable use of MMCONFIG for PCI 4038 Configuration 4039 check_enable_amd_mmconf [X86] check for and enable 4040 properly configured MMIO access to PCI 4041 config space on AMD family 10h CPU 4042 nomsi [MSI] If the PCI_MSI kernel config parameter is 4043 enabled, this kernel boot option can be used to 4044 disable the use of MSI interrupts system-wide. 4045 noioapicquirk [APIC] Disable all boot interrupt quirks. 4046 Safety option to keep boot IRQs enabled. This 4047 should never be necessary. 4048 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 4049 primary IO-APIC for bridges that cannot disable 4050 boot IRQs. This fixes a source of spurious IRQs 4051 when the system masks IRQs. 4052 noioapicreroute [APIC] Disable workaround that uses the 4053 boot IRQ equivalent of an IRQ that connects to 4054 a chipset where boot IRQs cannot be disabled. 4055 The opposite of ioapicreroute. 4056 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 4057 routing table. These calls are known to be buggy 4058 on several machines and they hang the machine 4059 when used, but on other computers it's the only 4060 way to get the interrupt routing table. Try 4061 this option if the kernel is unable to allocate 4062 IRQs or discover secondary PCI buses on your 4063 motherboard. 4064 rom [X86] Assign address space to expansion ROMs. 4065 Use with caution as certain devices share 4066 address decoders between ROMs and other 4067 resources. 4068 norom [X86] Do not assign address space to 4069 expansion ROMs that do not already have 4070 BIOS assigned address ranges. 4071 nobar [X86] Do not assign address space to the 4072 BARs that weren't assigned by the BIOS. 4073 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 4074 assigned automatically to PCI devices. You can 4075 make the kernel exclude IRQs of your ISA cards 4076 this way. 4077 pirqaddr=0xAAAAA [X86] Specify the physical address 4078 of the PIRQ table (normally generated 4079 by the BIOS) if it is outside the 4080 F0000h-100000h range. 4081 lastbus=N [X86] Scan all buses thru bus #N. Can be 4082 useful if the kernel is unable to find your 4083 secondary buses and you want to tell it 4084 explicitly which ones they are. 4085 assign-busses [X86] Always assign all PCI bus 4086 numbers ourselves, overriding 4087 whatever the firmware may have done. 4088 usepirqmask [X86] Honor the possible IRQ mask stored 4089 in the BIOS $PIR table. This is needed on 4090 some systems with broken BIOSes, notably 4091 some HP Pavilion N5400 and Omnibook XE3 4092 notebooks. This will have no effect if ACPI 4093 IRQ routing is enabled. 4094 noacpi [X86] Do not use ACPI for IRQ routing 4095 or for PCI scanning. 4096 use_crs [X86] Use PCI host bridge window information 4097 from ACPI. On BIOSes from 2008 or later, this 4098 is enabled by default. If you need to use this, 4099 please report a bug. 4100 nocrs [X86] Ignore PCI host bridge windows from ACPI. 4101 If you need to use this, please report a bug. 4102 use_e820 [X86] Use E820 reservations to exclude parts of 4103 PCI host bridge windows. This is a workaround 4104 for BIOS defects in host bridge _CRS methods. 4105 If you need to use this, please report a bug to 4106 <linux-pci@vger.kernel.org>. 4107 no_e820 [X86] Ignore E820 reservations for PCI host 4108 bridge windows. This is the default on modern 4109 hardware. If you need to use this, please report 4110 a bug to <linux-pci@vger.kernel.org>. 4111 routeirq Do IRQ routing for all PCI devices. 4112 This is normally done in pci_enable_device(), 4113 so this option is a temporary workaround 4114 for broken drivers that don't call it. 4115 skip_isa_align [X86] do not align io start addr, so can 4116 handle more pci cards 4117 noearly [X86] Don't do any early type 1 scanning. 4118 This might help on some broken boards which 4119 machine check when some devices' config space 4120 is read. But various workarounds are disabled 4121 and some IOMMU drivers will not work. 4122 bfsort Sort PCI devices into breadth-first order. 4123 This sorting is done to get a device 4124 order compatible with older (<= 2.4) kernels. 4125 nobfsort Don't sort PCI devices into breadth-first order. 4126 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 4127 tuning and use the BIOS-configured MPS defaults. 4128 pcie_bus_safe Set every device's MPS to the largest value 4129 supported by all devices below the root complex. 4130 pcie_bus_perf Set device MPS to the largest allowable MPS 4131 based on its parent bus. Also set MRRS (Max 4132 Read Request Size) to the largest supported 4133 value (no larger than the MPS that the device 4134 or bus can support) for best performance. 4135 pcie_bus_peer2peer Set every device's MPS to 128B, which 4136 every device is guaranteed to support. This 4137 configuration allows peer-to-peer DMA between 4138 any pair of devices, possibly at the cost of 4139 reduced performance. This also guarantees 4140 that hot-added devices will work. 4141 cbiosize=nn[KMG] The fixed amount of bus space which is 4142 reserved for the CardBus bridge's IO window. 4143 The default value is 256 bytes. 4144 cbmemsize=nn[KMG] The fixed amount of bus space which is 4145 reserved for the CardBus bridge's memory 4146 window. The default value is 64 megabytes. 4147 resource_alignment= 4148 Format: 4149 [<order of align>@]<pci_dev>[; ...] 4150 Specifies alignment and device to reassign 4151 aligned memory resources. How to 4152 specify the device is described above. 4153 If <order of align> is not specified, 4154 PAGE_SIZE is used as alignment. 4155 A PCI-PCI bridge can be specified if resource 4156 windows need to be expanded. 4157 To specify the alignment for several 4158 instances of a device, the PCI vendor, 4159 device, subvendor, and subdevice may be 4160 specified, e.g., 12@pci:8086:9c22:103c:198f 4161 for 4096-byte alignment. 4162 ecrc= Enable/disable PCIe ECRC (transaction layer 4163 end-to-end CRC checking). 4164 bios: Use BIOS/firmware settings. This is the 4165 the default. 4166 off: Turn ECRC off 4167 on: Turn ECRC on. 4168 hpiosize=nn[KMG] The fixed amount of bus space which is 4169 reserved for hotplug bridge's IO window. 4170 Default size is 256 bytes. 4171 hpmmiosize=nn[KMG] The fixed amount of bus space which is 4172 reserved for hotplug bridge's MMIO window. 4173 Default size is 2 megabytes. 4174 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 4175 reserved for hotplug bridge's MMIO_PREF window. 4176 Default size is 2 megabytes. 4177 hpmemsize=nn[KMG] The fixed amount of bus space which is 4178 reserved for hotplug bridge's MMIO and 4179 MMIO_PREF window. 4180 Default size is 2 megabytes. 4181 hpbussize=nn The minimum amount of additional bus numbers 4182 reserved for buses below a hotplug bridge. 4183 Default is 1. 4184 realloc= Enable/disable reallocating PCI bridge resources 4185 if allocations done by BIOS are too small to 4186 accommodate resources required by all child 4187 devices. 4188 off: Turn realloc off 4189 on: Turn realloc on 4190 realloc same as realloc=on 4191 noari do not use PCIe ARI. 4192 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 4193 do not use PCIe ATS (and IOMMU device IOTLB). 4194 pcie_scan_all Scan all possible PCIe devices. Otherwise we 4195 only look for one device below a PCIe downstream 4196 port. 4197 big_root_window Try to add a big 64bit memory window to the PCIe 4198 root complex on AMD CPUs. Some GFX hardware 4199 can resize a BAR to allow access to all VRAM. 4200 Adding the window is slightly risky (it may 4201 conflict with unreported devices), so this 4202 taints the kernel. 4203 disable_acs_redir=<pci_dev>[; ...] 4204 Specify one or more PCI devices (in the format 4205 specified above) separated by semicolons. 4206 Each device specified will have the PCI ACS 4207 redirect capabilities forced off which will 4208 allow P2P traffic between devices through 4209 bridges without forcing it upstream. Note: 4210 this removes isolation between devices and 4211 may put more devices in an IOMMU group. 4212 force_floating [S390] Force usage of floating interrupts. 4213 nomio [S390] Do not use MIO instructions. 4214 norid [S390] ignore the RID field and force use of 4215 one PCI domain per PCI function 4216 4217 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 4218 Management. 4219 off Disable ASPM. 4220 force Enable ASPM even on devices that claim not to support it. 4221 WARNING: Forcing ASPM on may cause system lockups. 4222 4223 pcie_ports= [PCIE] PCIe port services handling: 4224 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 4225 even if the platform doesn't give the OS permission to 4226 use them. This may cause conflicts if the platform 4227 also tries to use these services. 4228 dpc-native Use native PCIe service for DPC only. May 4229 cause conflicts if firmware uses AER or DPC. 4230 compat Disable native PCIe services (PME, AER, DPC, PCIe 4231 hotplug). 4232 4233 pcie_port_pm= [PCIE] PCIe port power management handling: 4234 off Disable power management of all PCIe ports 4235 force Forcibly enable power management of all PCIe ports 4236 4237 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 4238 nomsi Do not use MSI for native PCIe PME signaling (this makes 4239 all PCIe root ports use INTx for all services). 4240 4241 pcmv= [HW,PCMCIA] BadgePAD 4 4242 4243 pd_ignore_unused 4244 [PM] 4245 Keep all power-domains already enabled by bootloader on, 4246 even if no driver has claimed them. This is useful 4247 for debug and development, but should not be 4248 needed on a platform with proper driver support. 4249 4250 pd. [PARIDE] 4251 See Documentation/admin-guide/blockdev/paride.rst. 4252 4253 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 4254 boot time. 4255 Format: { 0 | 1 } 4256 See arch/parisc/kernel/pdc_chassis.c 4257 4258 percpu_alloc= Select which percpu first chunk allocator to use. 4259 Currently supported values are "embed" and "page". 4260 Archs may support subset or none of the selections. 4261 See comments in mm/percpu.c for details on each 4262 allocator. This parameter is primarily for debugging 4263 and performance comparison. 4264 4265 pf. [PARIDE] 4266 See Documentation/admin-guide/blockdev/paride.rst. 4267 4268 pg. [PARIDE] 4269 See Documentation/admin-guide/blockdev/paride.rst. 4270 4271 pirq= [SMP,APIC] Manual mp-table setup 4272 See Documentation/x86/i386/IO-APIC.rst. 4273 4274 plip= [PPT,NET] Parallel port network link 4275 Format: { parport<nr> | timid | 0 } 4276 See also Documentation/admin-guide/parport.rst. 4277 4278 pmtmr= [X86] Manual setup of pmtmr I/O Port. 4279 Override pmtimer IOPort with a hex value. 4280 e.g. pmtmr=0x508 4281 4282 pmu_override= [PPC] Override the PMU. 4283 This option takes over the PMU facility, so it is no 4284 longer usable by perf. Setting this option starts the 4285 PMU counters by setting MMCR0 to 0 (the FC bit is 4286 cleared). If a number is given, then MMCR1 is set to 4287 that number, otherwise (e.g., 'pmu_override=on'), MMCR1 4288 remains 0. 4289 4290 pm_debug_messages [SUSPEND,KNL] 4291 Enable suspend/resume debug messages during boot up. 4292 4293 pnp.debug=1 [PNP] 4294 Enable PNP debug messages (depends on the 4295 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 4296 via /sys/module/pnp/parameters/debug. We always show 4297 current resource usage; turning this on also shows 4298 possible settings and some assignment information. 4299 4300 pnpacpi= [ACPI] 4301 { off } 4302 4303 pnpbios= [ISAPNP] 4304 { on | off | curr | res | no-curr | no-res } 4305 4306 pnp_reserve_irq= 4307 [ISAPNP] Exclude IRQs for the autoconfiguration 4308 4309 pnp_reserve_dma= 4310 [ISAPNP] Exclude DMAs for the autoconfiguration 4311 4312 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 4313 Ranges are in pairs (I/O port base and size). 4314 4315 pnp_reserve_mem= 4316 [ISAPNP] Exclude memory regions for the 4317 autoconfiguration. 4318 Ranges are in pairs (memory base and size). 4319 4320 ports= [IP_VS_FTP] IPVS ftp helper module 4321 Default is 21. 4322 Up to 8 (IP_VS_APP_MAX_PORTS) ports 4323 may be specified. 4324 Format: <port>,<port>.... 4325 4326 powersave=off [PPC] This option disables power saving features. 4327 It specifically disables cpuidle and sets the 4328 platform machine description specific power_save 4329 function to NULL. On Idle the CPU just reduces 4330 execution priority. 4331 4332 ppc_strict_facility_enable 4333 [PPC] This option catches any kernel floating point, 4334 Altivec, VSX and SPE outside of regions specifically 4335 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 4336 There is some performance impact when enabling this. 4337 4338 ppc_tm= [PPC] 4339 Format: {"off"} 4340 Disable Hardware Transactional Memory 4341 4342 preempt= [KNL] 4343 Select preemption mode if you have CONFIG_PREEMPT_DYNAMIC 4344 none - Limited to cond_resched() calls 4345 voluntary - Limited to cond_resched() and might_sleep() calls 4346 full - Any section that isn't explicitly preempt disabled 4347 can be preempted anytime. 4348 4349 print-fatal-signals= 4350 [KNL] debug: print fatal signals 4351 4352 If enabled, warn about various signal handling 4353 related application anomalies: too many signals, 4354 too many POSIX.1 timers, fatal signals causing a 4355 coredump - etc. 4356 4357 If you hit the warning due to signal overflow, 4358 you might want to try "ulimit -i unlimited". 4359 4360 default: off. 4361 4362 printk.always_kmsg_dump= 4363 Trigger kmsg_dump for cases other than kernel oops or 4364 panics 4365 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4366 default: disabled 4367 4368 printk.console_no_auto_verbose= 4369 Disable console loglevel raise on oops, panic 4370 or lockdep-detected issues (only if lock debug is on). 4371 With an exception to setups with low baudrate on 4372 serial console, keeping this 0 is a good choice 4373 in order to provide more debug information. 4374 Format: <bool> 4375 default: 0 (auto_verbose is enabled) 4376 4377 printk.devkmsg={on,off,ratelimit} 4378 Control writing to /dev/kmsg. 4379 on - unlimited logging to /dev/kmsg from userspace 4380 off - logging to /dev/kmsg disabled 4381 ratelimit - ratelimit the logging 4382 Default: ratelimit 4383 4384 printk.time= Show timing data prefixed to each printk message line 4385 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4386 4387 processor.max_cstate= [HW,ACPI] 4388 Limit processor to maximum C-state 4389 max_cstate=9 overrides any DMI blacklist limit. 4390 4391 processor.nocst [HW,ACPI] 4392 Ignore the _CST method to determine C-states, 4393 instead using the legacy FADT method 4394 4395 profile= [KNL] Enable kernel profiling via /proc/profile 4396 Format: [<profiletype>,]<number> 4397 Param: <profiletype>: "schedule", "sleep", or "kvm" 4398 [defaults to kernel profiling] 4399 Param: "schedule" - profile schedule points. 4400 Param: "sleep" - profile D-state sleeping (millisecs). 4401 Requires CONFIG_SCHEDSTATS 4402 Param: "kvm" - profile VM exits. 4403 Param: <number> - step/bucket size as a power of 2 for 4404 statistical time based profiling. 4405 4406 prompt_ramdisk= [RAM] [Deprecated] 4407 4408 prot_virt= [S390] enable hosting protected virtual machines 4409 isolated from the hypervisor (if hardware supports 4410 that). 4411 Format: <bool> 4412 4413 psi= [KNL] Enable or disable pressure stall information 4414 tracking. 4415 Format: <bool> 4416 4417 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 4418 probe for; one of (bare|imps|exps|lifebook|any). 4419 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 4420 per second. 4421 psmouse.resetafter= [HW,MOUSE] 4422 Try to reset the device after so many bad packets 4423 (0 = never). 4424 psmouse.resolution= 4425 [HW,MOUSE] Set desired mouse resolution, in dpi. 4426 psmouse.smartscroll= 4427 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 4428 0 = disabled, 1 = enabled (default). 4429 4430 pstore.backend= Specify the name of the pstore backend to use 4431 4432 pt. [PARIDE] 4433 See Documentation/admin-guide/blockdev/paride.rst. 4434 4435 pti= [X86-64] Control Page Table Isolation of user and 4436 kernel address spaces. Disabling this feature 4437 removes hardening, but improves performance of 4438 system calls and interrupts. 4439 4440 on - unconditionally enable 4441 off - unconditionally disable 4442 auto - kernel detects whether your CPU model is 4443 vulnerable to issues that PTI mitigates 4444 4445 Not specifying this option is equivalent to pti=auto. 4446 4447 nopti [X86-64] 4448 Equivalent to pti=off 4449 4450 pty.legacy_count= 4451 [KNL] Number of legacy pty's. Overwrites compiled-in 4452 default number. 4453 4454 quiet [KNL] Disable most log messages 4455 4456 r128= [HW,DRM] 4457 4458 raid= [HW,RAID] 4459 See Documentation/admin-guide/md.rst. 4460 4461 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4462 See Documentation/admin-guide/blockdev/ramdisk.rst. 4463 4464 ramdisk_start= [RAM] RAM disk image start address 4465 4466 random.trust_cpu={on,off} 4467 [KNL] Enable or disable trusting the use of the 4468 CPU's random number generator (if available) to 4469 fully seed the kernel's CRNG. Default is controlled 4470 by CONFIG_RANDOM_TRUST_CPU. 4471 4472 random.trust_bootloader={on,off} 4473 [KNL] Enable or disable trusting the use of a 4474 seed passed by the bootloader (if available) to 4475 fully seed the kernel's CRNG. Default is controlled 4476 by CONFIG_RANDOM_TRUST_BOOTLOADER. 4477 4478 randomize_kstack_offset= 4479 [KNL] Enable or disable kernel stack offset 4480 randomization, which provides roughly 5 bits of 4481 entropy, frustrating memory corruption attacks 4482 that depend on stack address determinism or 4483 cross-syscall address exposures. This is only 4484 available on architectures that have defined 4485 CONFIG_HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET. 4486 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 4487 Default is CONFIG_RANDOMIZE_KSTACK_OFFSET_DEFAULT. 4488 4489 ras=option[,option,...] [KNL] RAS-specific options 4490 4491 cec_disable [X86] 4492 Disable the Correctable Errors Collector, 4493 see CONFIG_RAS_CEC help text. 4494 4495 rcu_nocbs[=cpu-list] 4496 [KNL] The optional argument is a cpu list, 4497 as described above. 4498 4499 In kernels built with CONFIG_RCU_NOCB_CPU=y, 4500 enable the no-callback CPU mode, which prevents 4501 such CPUs' callbacks from being invoked in 4502 softirq context. Invocation of such CPUs' RCU 4503 callbacks will instead be offloaded to "rcuox/N" 4504 kthreads created for that purpose, where "x" is 4505 "p" for RCU-preempt, "s" for RCU-sched, and "g" 4506 for the kthreads that mediate grace periods; and 4507 "N" is the CPU number. This reduces OS jitter on 4508 the offloaded CPUs, which can be useful for HPC 4509 and real-time workloads. It can also improve 4510 energy efficiency for asymmetric multiprocessors. 4511 4512 If a cpulist is passed as an argument, the specified 4513 list of CPUs is set to no-callback mode from boot. 4514 4515 Otherwise, if the '=' sign and the cpulist 4516 arguments are omitted, no CPU will be set to 4517 no-callback mode from boot but the mode may be 4518 toggled at runtime via cpusets. 4519 4520 rcu_nocb_poll [KNL] 4521 Rather than requiring that offloaded CPUs 4522 (specified by rcu_nocbs= above) explicitly 4523 awaken the corresponding "rcuoN" kthreads, 4524 make these kthreads poll for callbacks. 4525 This improves the real-time response for the 4526 offloaded CPUs by relieving them of the need to 4527 wake up the corresponding kthread, but degrades 4528 energy efficiency by requiring that the kthreads 4529 periodically wake up to do the polling. 4530 4531 rcutree.blimit= [KNL] 4532 Set maximum number of finished RCU callbacks to 4533 process in one batch. 4534 4535 rcutree.dump_tree= [KNL] 4536 Dump the structure of the rcu_node combining tree 4537 out at early boot. This is used for diagnostic 4538 purposes, to verify correct tree setup. 4539 4540 rcutree.gp_cleanup_delay= [KNL] 4541 Set the number of jiffies to delay each step of 4542 RCU grace-period cleanup. 4543 4544 rcutree.gp_init_delay= [KNL] 4545 Set the number of jiffies to delay each step of 4546 RCU grace-period initialization. 4547 4548 rcutree.gp_preinit_delay= [KNL] 4549 Set the number of jiffies to delay each step of 4550 RCU grace-period pre-initialization, that is, 4551 the propagation of recent CPU-hotplug changes up 4552 the rcu_node combining tree. 4553 4554 rcutree.use_softirq= [KNL] 4555 If set to zero, move all RCU_SOFTIRQ processing to 4556 per-CPU rcuc kthreads. Defaults to a non-zero 4557 value, meaning that RCU_SOFTIRQ is used by default. 4558 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4559 4560 But note that CONFIG_PREEMPT_RT=y kernels disable 4561 this kernel boot parameter, forcibly setting it 4562 to zero. 4563 4564 rcutree.rcu_fanout_exact= [KNL] 4565 Disable autobalancing of the rcu_node combining 4566 tree. This is used by rcutorture, and might 4567 possibly be useful for architectures having high 4568 cache-to-cache transfer latencies. 4569 4570 rcutree.rcu_fanout_leaf= [KNL] 4571 Change the number of CPUs assigned to each 4572 leaf rcu_node structure. Useful for very 4573 large systems, which will choose the value 64, 4574 and for NUMA systems with large remote-access 4575 latencies, which will choose a value aligned 4576 with the appropriate hardware boundaries. 4577 4578 rcutree.rcu_min_cached_objs= [KNL] 4579 Minimum number of objects which are cached and 4580 maintained per one CPU. Object size is equal 4581 to PAGE_SIZE. The cache allows to reduce the 4582 pressure to page allocator, also it makes the 4583 whole algorithm to behave better in low memory 4584 condition. 4585 4586 rcutree.rcu_delay_page_cache_fill_msec= [KNL] 4587 Set the page-cache refill delay (in milliseconds) 4588 in response to low-memory conditions. The range 4589 of permitted values is in the range 0:100000. 4590 4591 rcutree.jiffies_till_first_fqs= [KNL] 4592 Set delay from grace-period initialization to 4593 first attempt to force quiescent states. 4594 Units are jiffies, minimum value is zero, 4595 and maximum value is HZ. 4596 4597 rcutree.jiffies_till_next_fqs= [KNL] 4598 Set delay between subsequent attempts to force 4599 quiescent states. Units are jiffies, minimum 4600 value is one, and maximum value is HZ. 4601 4602 rcutree.jiffies_till_sched_qs= [KNL] 4603 Set required age in jiffies for a 4604 given grace period before RCU starts 4605 soliciting quiescent-state help from 4606 rcu_note_context_switch() and cond_resched(). 4607 If not specified, the kernel will calculate 4608 a value based on the most recent settings 4609 of rcutree.jiffies_till_first_fqs 4610 and rcutree.jiffies_till_next_fqs. 4611 This calculated value may be viewed in 4612 rcutree.jiffies_to_sched_qs. Any attempt to set 4613 rcutree.jiffies_to_sched_qs will be cheerfully 4614 overwritten. 4615 4616 rcutree.kthread_prio= [KNL,BOOT] 4617 Set the SCHED_FIFO priority of the RCU per-CPU 4618 kthreads (rcuc/N). This value is also used for 4619 the priority of the RCU boost threads (rcub/N) 4620 and for the RCU grace-period kthreads (rcu_bh, 4621 rcu_preempt, and rcu_sched). If RCU_BOOST is 4622 set, valid values are 1-99 and the default is 1 4623 (the least-favored priority). Otherwise, when 4624 RCU_BOOST is not set, valid values are 0-99 and 4625 the default is zero (non-realtime operation). 4626 When RCU_NOCB_CPU is set, also adjust the 4627 priority of NOCB callback kthreads. 4628 4629 rcutree.rcu_nocb_gp_stride= [KNL] 4630 Set the number of NOCB callback kthreads in 4631 each group, which defaults to the square root 4632 of the number of CPUs. Larger numbers reduce 4633 the wakeup overhead on the global grace-period 4634 kthread, but increases that same overhead on 4635 each group's NOCB grace-period kthread. 4636 4637 rcutree.qhimark= [KNL] 4638 Set threshold of queued RCU callbacks beyond which 4639 batch limiting is disabled. 4640 4641 rcutree.qlowmark= [KNL] 4642 Set threshold of queued RCU callbacks below which 4643 batch limiting is re-enabled. 4644 4645 rcutree.qovld= [KNL] 4646 Set threshold of queued RCU callbacks beyond which 4647 RCU's force-quiescent-state scan will aggressively 4648 enlist help from cond_resched() and sched IPIs to 4649 help CPUs more quickly reach quiescent states. 4650 Set to less than zero to make this be set based 4651 on rcutree.qhimark at boot time and to zero to 4652 disable more aggressive help enlistment. 4653 4654 rcutree.rcu_kick_kthreads= [KNL] 4655 Cause the grace-period kthread to get an extra 4656 wake_up() if it sleeps three times longer than 4657 it should at force-quiescent-state time. 4658 This wake_up() will be accompanied by a 4659 WARN_ONCE() splat and an ftrace_dump(). 4660 4661 rcutree.rcu_unlock_delay= [KNL] 4662 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4663 this specifies an rcu_read_unlock()-time delay 4664 in microseconds. This defaults to zero. 4665 Larger delays increase the probability of 4666 catching RCU pointer leaks, that is, buggy use 4667 of RCU-protected pointers after the relevant 4668 rcu_read_unlock() has completed. 4669 4670 rcutree.sysrq_rcu= [KNL] 4671 Commandeer a sysrq key to dump out Tree RCU's 4672 rcu_node tree with an eye towards determining 4673 why a new grace period has not yet started. 4674 4675 rcuscale.gp_async= [KNL] 4676 Measure performance of asynchronous 4677 grace-period primitives such as call_rcu(). 4678 4679 rcuscale.gp_async_max= [KNL] 4680 Specify the maximum number of outstanding 4681 callbacks per writer thread. When a writer 4682 thread exceeds this limit, it invokes the 4683 corresponding flavor of rcu_barrier() to allow 4684 previously posted callbacks to drain. 4685 4686 rcuscale.gp_exp= [KNL] 4687 Measure performance of expedited synchronous 4688 grace-period primitives. 4689 4690 rcuscale.holdoff= [KNL] 4691 Set test-start holdoff period. The purpose of 4692 this parameter is to delay the start of the 4693 test until boot completes in order to avoid 4694 interference. 4695 4696 rcuscale.kfree_rcu_test= [KNL] 4697 Set to measure performance of kfree_rcu() flooding. 4698 4699 rcuscale.kfree_rcu_test_double= [KNL] 4700 Test the double-argument variant of kfree_rcu(). 4701 If this parameter has the same value as 4702 rcuscale.kfree_rcu_test_single, both the single- 4703 and double-argument variants are tested. 4704 4705 rcuscale.kfree_rcu_test_single= [KNL] 4706 Test the single-argument variant of kfree_rcu(). 4707 If this parameter has the same value as 4708 rcuscale.kfree_rcu_test_double, both the single- 4709 and double-argument variants are tested. 4710 4711 rcuscale.kfree_nthreads= [KNL] 4712 The number of threads running loops of kfree_rcu(). 4713 4714 rcuscale.kfree_alloc_num= [KNL] 4715 Number of allocations and frees done in an iteration. 4716 4717 rcuscale.kfree_loops= [KNL] 4718 Number of loops doing rcuscale.kfree_alloc_num number 4719 of allocations and frees. 4720 4721 rcuscale.nreaders= [KNL] 4722 Set number of RCU readers. The value -1 selects 4723 N, where N is the number of CPUs. A value 4724 "n" less than -1 selects N-n+1, where N is again 4725 the number of CPUs. For example, -2 selects N 4726 (the number of CPUs), -3 selects N+1, and so on. 4727 A value of "n" less than or equal to -N selects 4728 a single reader. 4729 4730 rcuscale.nwriters= [KNL] 4731 Set number of RCU writers. The values operate 4732 the same as for rcuscale.nreaders. 4733 N, where N is the number of CPUs 4734 4735 rcuscale.perf_type= [KNL] 4736 Specify the RCU implementation to test. 4737 4738 rcuscale.shutdown= [KNL] 4739 Shut the system down after performance tests 4740 complete. This is useful for hands-off automated 4741 testing. 4742 4743 rcuscale.verbose= [KNL] 4744 Enable additional printk() statements. 4745 4746 rcuscale.writer_holdoff= [KNL] 4747 Write-side holdoff between grace periods, 4748 in microseconds. The default of zero says 4749 no holdoff. 4750 4751 rcutorture.fqs_duration= [KNL] 4752 Set duration of force_quiescent_state bursts 4753 in microseconds. 4754 4755 rcutorture.fqs_holdoff= [KNL] 4756 Set holdoff time within force_quiescent_state bursts 4757 in microseconds. 4758 4759 rcutorture.fqs_stutter= [KNL] 4760 Set wait time between force_quiescent_state bursts 4761 in seconds. 4762 4763 rcutorture.fwd_progress= [KNL] 4764 Specifies the number of kthreads to be used 4765 for RCU grace-period forward-progress testing 4766 for the types of RCU supporting this notion. 4767 Defaults to 1 kthread, values less than zero or 4768 greater than the number of CPUs cause the number 4769 of CPUs to be used. 4770 4771 rcutorture.fwd_progress_div= [KNL] 4772 Specify the fraction of a CPU-stall-warning 4773 period to do tight-loop forward-progress testing. 4774 4775 rcutorture.fwd_progress_holdoff= [KNL] 4776 Number of seconds to wait between successive 4777 forward-progress tests. 4778 4779 rcutorture.fwd_progress_need_resched= [KNL] 4780 Enclose cond_resched() calls within checks for 4781 need_resched() during tight-loop forward-progress 4782 testing. 4783 4784 rcutorture.gp_cond= [KNL] 4785 Use conditional/asynchronous update-side 4786 primitives, if available. 4787 4788 rcutorture.gp_exp= [KNL] 4789 Use expedited update-side primitives, if available. 4790 4791 rcutorture.gp_normal= [KNL] 4792 Use normal (non-expedited) asynchronous 4793 update-side primitives, if available. 4794 4795 rcutorture.gp_sync= [KNL] 4796 Use normal (non-expedited) synchronous 4797 update-side primitives, if available. If all 4798 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4799 rcutorture.gp_normal=, and rcutorture.gp_sync= 4800 are zero, rcutorture acts as if is interpreted 4801 they are all non-zero. 4802 4803 rcutorture.irqreader= [KNL] 4804 Run RCU readers from irq handlers, or, more 4805 accurately, from a timer handler. Not all RCU 4806 flavors take kindly to this sort of thing. 4807 4808 rcutorture.leakpointer= [KNL] 4809 Leak an RCU-protected pointer out of the reader. 4810 This can of course result in splats, and is 4811 intended to test the ability of things like 4812 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4813 such leaks. 4814 4815 rcutorture.n_barrier_cbs= [KNL] 4816 Set callbacks/threads for rcu_barrier() testing. 4817 4818 rcutorture.nfakewriters= [KNL] 4819 Set number of concurrent RCU writers. These just 4820 stress RCU, they don't participate in the actual 4821 test, hence the "fake". 4822 4823 rcutorture.nocbs_nthreads= [KNL] 4824 Set number of RCU callback-offload togglers. 4825 Zero (the default) disables toggling. 4826 4827 rcutorture.nocbs_toggle= [KNL] 4828 Set the delay in milliseconds between successive 4829 callback-offload toggling attempts. 4830 4831 rcutorture.nreaders= [KNL] 4832 Set number of RCU readers. The value -1 selects 4833 N-1, where N is the number of CPUs. A value 4834 "n" less than -1 selects N-n-2, where N is again 4835 the number of CPUs. For example, -2 selects N 4836 (the number of CPUs), -3 selects N+1, and so on. 4837 4838 rcutorture.object_debug= [KNL] 4839 Enable debug-object double-call_rcu() testing. 4840 4841 rcutorture.onoff_holdoff= [KNL] 4842 Set time (s) after boot for CPU-hotplug testing. 4843 4844 rcutorture.onoff_interval= [KNL] 4845 Set time (jiffies) between CPU-hotplug operations, 4846 or zero to disable CPU-hotplug testing. 4847 4848 rcutorture.read_exit= [KNL] 4849 Set the number of read-then-exit kthreads used 4850 to test the interaction of RCU updaters and 4851 task-exit processing. 4852 4853 rcutorture.read_exit_burst= [KNL] 4854 The number of times in a given read-then-exit 4855 episode that a set of read-then-exit kthreads 4856 is spawned. 4857 4858 rcutorture.read_exit_delay= [KNL] 4859 The delay, in seconds, between successive 4860 read-then-exit testing episodes. 4861 4862 rcutorture.shuffle_interval= [KNL] 4863 Set task-shuffle interval (s). Shuffling tasks 4864 allows some CPUs to go into dyntick-idle mode 4865 during the rcutorture test. 4866 4867 rcutorture.shutdown_secs= [KNL] 4868 Set time (s) after boot system shutdown. This 4869 is useful for hands-off automated testing. 4870 4871 rcutorture.stall_cpu= [KNL] 4872 Duration of CPU stall (s) to test RCU CPU stall 4873 warnings, zero to disable. 4874 4875 rcutorture.stall_cpu_block= [KNL] 4876 Sleep while stalling if set. This will result 4877 in warnings from preemptible RCU in addition 4878 to any other stall-related activity. 4879 4880 rcutorture.stall_cpu_holdoff= [KNL] 4881 Time to wait (s) after boot before inducing stall. 4882 4883 rcutorture.stall_cpu_irqsoff= [KNL] 4884 Disable interrupts while stalling if set. 4885 4886 rcutorture.stall_gp_kthread= [KNL] 4887 Duration (s) of forced sleep within RCU 4888 grace-period kthread to test RCU CPU stall 4889 warnings, zero to disable. If both stall_cpu 4890 and stall_gp_kthread are specified, the 4891 kthread is starved first, then the CPU. 4892 4893 rcutorture.stat_interval= [KNL] 4894 Time (s) between statistics printk()s. 4895 4896 rcutorture.stutter= [KNL] 4897 Time (s) to stutter testing, for example, specifying 4898 five seconds causes the test to run for five seconds, 4899 wait for five seconds, and so on. This tests RCU's 4900 ability to transition abruptly to and from idle. 4901 4902 rcutorture.test_boost= [KNL] 4903 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4904 "Maybe" means test if the RCU implementation 4905 under test support RCU priority boosting. 4906 4907 rcutorture.test_boost_duration= [KNL] 4908 Duration (s) of each individual boost test. 4909 4910 rcutorture.test_boost_interval= [KNL] 4911 Interval (s) between each boost test. 4912 4913 rcutorture.test_no_idle_hz= [KNL] 4914 Test RCU's dyntick-idle handling. See also the 4915 rcutorture.shuffle_interval parameter. 4916 4917 rcutorture.torture_type= [KNL] 4918 Specify the RCU implementation to test. 4919 4920 rcutorture.verbose= [KNL] 4921 Enable additional printk() statements. 4922 4923 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4924 Dump ftrace buffer after reporting RCU CPU 4925 stall warning. 4926 4927 rcupdate.rcu_cpu_stall_suppress= [KNL] 4928 Suppress RCU CPU stall warning messages. 4929 4930 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4931 Suppress RCU CPU stall warning messages and 4932 rcutorture writer stall warnings that occur 4933 during early boot, that is, during the time 4934 before the init task is spawned. 4935 4936 rcupdate.rcu_cpu_stall_timeout= [KNL] 4937 Set timeout for RCU CPU stall warning messages. 4938 The value is in seconds and the maximum allowed 4939 value is 300 seconds. 4940 4941 rcupdate.rcu_exp_cpu_stall_timeout= [KNL] 4942 Set timeout for expedited RCU CPU stall warning 4943 messages. The value is in milliseconds 4944 and the maximum allowed value is 21000 4945 milliseconds. Please note that this value is 4946 adjusted to an arch timer tick resolution. 4947 Setting this to zero causes the value from 4948 rcupdate.rcu_cpu_stall_timeout to be used (after 4949 conversion from seconds to milliseconds). 4950 4951 rcupdate.rcu_expedited= [KNL] 4952 Use expedited grace-period primitives, for 4953 example, synchronize_rcu_expedited() instead 4954 of synchronize_rcu(). This reduces latency, 4955 but can increase CPU utilization, degrade 4956 real-time latency, and degrade energy efficiency. 4957 No effect on CONFIG_TINY_RCU kernels. 4958 4959 rcupdate.rcu_normal= [KNL] 4960 Use only normal grace-period primitives, 4961 for example, synchronize_rcu() instead of 4962 synchronize_rcu_expedited(). This improves 4963 real-time latency, CPU utilization, and 4964 energy efficiency, but can expose users to 4965 increased grace-period latency. This parameter 4966 overrides rcupdate.rcu_expedited. No effect on 4967 CONFIG_TINY_RCU kernels. 4968 4969 rcupdate.rcu_normal_after_boot= [KNL] 4970 Once boot has completed (that is, after 4971 rcu_end_inkernel_boot() has been invoked), use 4972 only normal grace-period primitives. No effect 4973 on CONFIG_TINY_RCU kernels. 4974 4975 But note that CONFIG_PREEMPT_RT=y kernels enables 4976 this kernel boot parameter, forcibly setting 4977 it to the value one, that is, converting any 4978 post-boot attempt at an expedited RCU grace 4979 period to instead use normal non-expedited 4980 grace-period processing. 4981 4982 rcupdate.rcu_task_collapse_lim= [KNL] 4983 Set the maximum number of callbacks present 4984 at the beginning of a grace period that allows 4985 the RCU Tasks flavors to collapse back to using 4986 a single callback queue. This switching only 4987 occurs when rcupdate.rcu_task_enqueue_lim is 4988 set to the default value of -1. 4989 4990 rcupdate.rcu_task_contend_lim= [KNL] 4991 Set the minimum number of callback-queuing-time 4992 lock-contention events per jiffy required to 4993 cause the RCU Tasks flavors to switch to per-CPU 4994 callback queuing. This switching only occurs 4995 when rcupdate.rcu_task_enqueue_lim is set to 4996 the default value of -1. 4997 4998 rcupdate.rcu_task_enqueue_lim= [KNL] 4999 Set the number of callback queues to use for the 5000 RCU Tasks family of RCU flavors. The default 5001 of -1 allows this to be automatically (and 5002 dynamically) adjusted. This parameter is intended 5003 for use in testing. 5004 5005 rcupdate.rcu_task_ipi_delay= [KNL] 5006 Set time in jiffies during which RCU tasks will 5007 avoid sending IPIs, starting with the beginning 5008 of a given grace period. Setting a large 5009 number avoids disturbing real-time workloads, 5010 but lengthens grace periods. 5011 5012 rcupdate.rcu_task_stall_info= [KNL] 5013 Set initial timeout in jiffies for RCU task stall 5014 informational messages, which give some indication 5015 of the problem for those not patient enough to 5016 wait for ten minutes. Informational messages are 5017 only printed prior to the stall-warning message 5018 for a given grace period. Disable with a value 5019 less than or equal to zero. Defaults to ten 5020 seconds. A change in value does not take effect 5021 until the beginning of the next grace period. 5022 5023 rcupdate.rcu_task_stall_info_mult= [KNL] 5024 Multiplier for time interval between successive 5025 RCU task stall informational messages for a given 5026 RCU tasks grace period. This value is clamped 5027 to one through ten, inclusive. It defaults to 5028 the value three, so that the first informational 5029 message is printed 10 seconds into the grace 5030 period, the second at 40 seconds, the third at 5031 160 seconds, and then the stall warning at 600 5032 seconds would prevent a fourth at 640 seconds. 5033 5034 rcupdate.rcu_task_stall_timeout= [KNL] 5035 Set timeout in jiffies for RCU task stall 5036 warning messages. Disable with a value less 5037 than or equal to zero. Defaults to ten minutes. 5038 A change in value does not take effect until 5039 the beginning of the next grace period. 5040 5041 rcupdate.rcu_self_test= [KNL] 5042 Run the RCU early boot self tests 5043 5044 rdinit= [KNL] 5045 Format: <full_path> 5046 Run specified binary instead of /init from the ramdisk, 5047 used for early userspace startup. See initrd. 5048 5049 rdrand= [X86] 5050 force - Override the decision by the kernel to hide the 5051 advertisement of RDRAND support (this affects 5052 certain AMD processors because of buggy BIOS 5053 support, specifically around the suspend/resume 5054 path). 5055 5056 rdt= [HW,X86,RDT] 5057 Turn on/off individual RDT features. List is: 5058 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 5059 mba. 5060 E.g. to turn on cmt and turn off mba use: 5061 rdt=cmt,!mba 5062 5063 reboot= [KNL] 5064 Format (x86 or x86_64): 5065 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] | d[efault] \ 5066 [[,]s[mp]#### \ 5067 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 5068 [[,]f[orce] 5069 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 5070 (prefix with 'panic_' to set mode for panic 5071 reboot only), 5072 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 5073 reboot_force is either force or not specified, 5074 reboot_cpu is s[mp]#### with #### being the processor 5075 to be used for rebooting. 5076 5077 refscale.holdoff= [KNL] 5078 Set test-start holdoff period. The purpose of 5079 this parameter is to delay the start of the 5080 test until boot completes in order to avoid 5081 interference. 5082 5083 refscale.loops= [KNL] 5084 Set the number of loops over the synchronization 5085 primitive under test. Increasing this number 5086 reduces noise due to loop start/end overhead, 5087 but the default has already reduced the per-pass 5088 noise to a handful of picoseconds on ca. 2020 5089 x86 laptops. 5090 5091 refscale.nreaders= [KNL] 5092 Set number of readers. The default value of -1 5093 selects N, where N is roughly 75% of the number 5094 of CPUs. A value of zero is an interesting choice. 5095 5096 refscale.nruns= [KNL] 5097 Set number of runs, each of which is dumped onto 5098 the console log. 5099 5100 refscale.readdelay= [KNL] 5101 Set the read-side critical-section duration, 5102 measured in microseconds. 5103 5104 refscale.scale_type= [KNL] 5105 Specify the read-protection implementation to test. 5106 5107 refscale.shutdown= [KNL] 5108 Shut down the system at the end of the performance 5109 test. This defaults to 1 (shut it down) when 5110 refscale is built into the kernel and to 0 (leave 5111 it running) when refscale is built as a module. 5112 5113 refscale.verbose= [KNL] 5114 Enable additional printk() statements. 5115 5116 refscale.verbose_batched= [KNL] 5117 Batch the additional printk() statements. If zero 5118 (the default) or negative, print everything. Otherwise, 5119 print every Nth verbose statement, where N is the value 5120 specified. 5121 5122 relax_domain_level= 5123 [KNL, SMP] Set scheduler's default relax_domain_level. 5124 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 5125 5126 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 5127 Format: <base1>,<size1>[,<base2>,<size2>,...] 5128 Reserve I/O ports or memory so the kernel won't use 5129 them. If <base> is less than 0x10000, the region 5130 is assumed to be I/O ports; otherwise it is memory. 5131 5132 reservetop= [X86-32] 5133 Format: nn[KMG] 5134 Reserves a hole at the top of the kernel virtual 5135 address space. 5136 5137 reset_devices [KNL] Force drivers to reset the underlying device 5138 during initialization. 5139 5140 resume= [SWSUSP] 5141 Specify the partition device for software suspend 5142 Format: 5143 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 5144 5145 resume_offset= [SWSUSP] 5146 Specify the offset from the beginning of the partition 5147 given by "resume=" at which the swap header is located, 5148 in <PAGE_SIZE> units (needed only for swap files). 5149 See Documentation/power/swsusp-and-swap-files.rst 5150 5151 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 5152 read the resume files 5153 5154 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 5155 Useful for devices that are detected asynchronously 5156 (e.g. USB and MMC devices). 5157 5158 retain_initrd [RAM] Keep initrd memory after extraction 5159 5160 rfkill.default_state= 5161 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 5162 etc. communication is blocked by default. 5163 1 Unblocked. 5164 5165 rfkill.master_switch_mode= 5166 0 The "airplane mode" button does nothing. 5167 1 The "airplane mode" button toggles between everything 5168 blocked and the previous configuration. 5169 2 The "airplane mode" button toggles between everything 5170 blocked and everything unblocked. 5171 5172 rhash_entries= [KNL,NET] 5173 Set number of hash buckets for route cache 5174 5175 ring3mwait=disable 5176 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 5177 CPUs. 5178 5179 ro [KNL] Mount root device read-only on boot 5180 5181 rodata= [KNL] 5182 on Mark read-only kernel memory as read-only (default). 5183 off Leave read-only kernel memory writable for debugging. 5184 5185 rockchip.usb_uart 5186 Enable the uart passthrough on the designated usb port 5187 on Rockchip SoCs. When active, the signals of the 5188 debug-uart get routed to the D+ and D- pins of the usb 5189 port and the regular usb controller gets disabled. 5190 5191 root= [KNL] Root filesystem 5192 See name_to_dev_t comment in init/do_mounts.c. 5193 5194 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 5195 mount the root filesystem 5196 5197 rootflags= [KNL] Set root filesystem mount option string 5198 5199 rootfstype= [KNL] Set root filesystem type 5200 5201 rootwait [KNL] Wait (indefinitely) for root device to show up. 5202 Useful for devices that are detected asynchronously 5203 (e.g. USB and MMC devices). 5204 5205 rproc_mem=nn[KMG][@address] 5206 [KNL,ARM,CMA] Remoteproc physical memory block. 5207 Memory area to be used by remote processor image, 5208 managed by CMA. 5209 5210 rw [KNL] Mount root device read-write on boot 5211 5212 S [KNL] Run init in single mode 5213 5214 s390_iommu= [HW,S390] 5215 Set s390 IOTLB flushing mode 5216 strict 5217 With strict flushing every unmap operation will result in 5218 an IOTLB flush. Default is lazy flushing before reuse, 5219 which is faster. 5220 5221 s390_iommu_aperture= [KNL,S390] 5222 Specifies the size of the per device DMA address space 5223 accessible through the DMA and IOMMU APIs as a decimal 5224 factor of the size of main memory. 5225 The default is 1 meaning that one can concurrently use 5226 as many DMA addresses as physical memory is installed, 5227 if supported by hardware, and thus map all of memory 5228 once. With a value of 2 one can map all of memory twice 5229 and so on. As a special case a factor of 0 imposes no 5230 restrictions other than those given by hardware at the 5231 cost of significant additional memory use for tables. 5232 5233 sa1100ir [NET] 5234 See drivers/net/irda/sa1100_ir.c. 5235 5236 sched_verbose [KNL] Enables verbose scheduler debug messages. 5237 5238 schedstats= [KNL,X86] Enable or disable scheduled statistics. 5239 Allowed values are enable and disable. This feature 5240 incurs a small amount of overhead in the scheduler 5241 but is useful for debugging and performance tuning. 5242 5243 sched_thermal_decay_shift= 5244 [KNL, SMP] Set a decay shift for scheduler thermal 5245 pressure signal. Thermal pressure signal follows the 5246 default decay period of other scheduler pelt 5247 signals(usually 32 ms but configurable). Setting 5248 sched_thermal_decay_shift will left shift the decay 5249 period for the thermal pressure signal by the shift 5250 value. 5251 i.e. with the default pelt decay period of 32 ms 5252 sched_thermal_decay_shift thermal pressure decay pr 5253 1 64 ms 5254 2 128 ms 5255 and so on. 5256 Format: integer between 0 and 10 5257 Default is 0. 5258 5259 scftorture.holdoff= [KNL] 5260 Number of seconds to hold off before starting 5261 test. Defaults to zero for module insertion and 5262 to 10 seconds for built-in smp_call_function() 5263 tests. 5264 5265 scftorture.longwait= [KNL] 5266 Request ridiculously long waits randomly selected 5267 up to the chosen limit in seconds. Zero (the 5268 default) disables this feature. Please note 5269 that requesting even small non-zero numbers of 5270 seconds can result in RCU CPU stall warnings, 5271 softlockup complaints, and so on. 5272 5273 scftorture.nthreads= [KNL] 5274 Number of kthreads to spawn to invoke the 5275 smp_call_function() family of functions. 5276 The default of -1 specifies a number of kthreads 5277 equal to the number of CPUs. 5278 5279 scftorture.onoff_holdoff= [KNL] 5280 Number seconds to wait after the start of the 5281 test before initiating CPU-hotplug operations. 5282 5283 scftorture.onoff_interval= [KNL] 5284 Number seconds to wait between successive 5285 CPU-hotplug operations. Specifying zero (which 5286 is the default) disables CPU-hotplug operations. 5287 5288 scftorture.shutdown_secs= [KNL] 5289 The number of seconds following the start of the 5290 test after which to shut down the system. The 5291 default of zero avoids shutting down the system. 5292 Non-zero values are useful for automated tests. 5293 5294 scftorture.stat_interval= [KNL] 5295 The number of seconds between outputting the 5296 current test statistics to the console. A value 5297 of zero disables statistics output. 5298 5299 scftorture.stutter_cpus= [KNL] 5300 The number of jiffies to wait between each change 5301 to the set of CPUs under test. 5302 5303 scftorture.use_cpus_read_lock= [KNL] 5304 Use use_cpus_read_lock() instead of the default 5305 preempt_disable() to disable CPU hotplug 5306 while invoking one of the smp_call_function*() 5307 functions. 5308 5309 scftorture.verbose= [KNL] 5310 Enable additional printk() statements. 5311 5312 scftorture.weight_single= [KNL] 5313 The probability weighting to use for the 5314 smp_call_function_single() function with a zero 5315 "wait" parameter. A value of -1 selects the 5316 default if all other weights are -1. However, 5317 if at least one weight has some other value, a 5318 value of -1 will instead select a weight of zero. 5319 5320 scftorture.weight_single_wait= [KNL] 5321 The probability weighting to use for the 5322 smp_call_function_single() function with a 5323 non-zero "wait" parameter. See weight_single. 5324 5325 scftorture.weight_many= [KNL] 5326 The probability weighting to use for the 5327 smp_call_function_many() function with a zero 5328 "wait" parameter. See weight_single. 5329 Note well that setting a high probability for 5330 this weighting can place serious IPI load 5331 on the system. 5332 5333 scftorture.weight_many_wait= [KNL] 5334 The probability weighting to use for the 5335 smp_call_function_many() function with a 5336 non-zero "wait" parameter. See weight_single 5337 and weight_many. 5338 5339 scftorture.weight_all= [KNL] 5340 The probability weighting to use for the 5341 smp_call_function_all() function with a zero 5342 "wait" parameter. See weight_single and 5343 weight_many. 5344 5345 scftorture.weight_all_wait= [KNL] 5346 The probability weighting to use for the 5347 smp_call_function_all() function with a 5348 non-zero "wait" parameter. See weight_single 5349 and weight_many. 5350 5351 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 5352 xtime_lock contention on larger systems, and/or RCU lock 5353 contention on all systems with CONFIG_MAXSMP set. 5354 Format: { "0" | "1" } 5355 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 5356 1 -- enable. 5357 Note: increases power consumption, thus should only be 5358 enabled if running jitter sensitive (HPC/RT) workloads. 5359 5360 security= [SECURITY] Choose a legacy "major" security module to 5361 enable at boot. This has been deprecated by the 5362 "lsm=" parameter. 5363 5364 selinux= [SELINUX] Disable or enable SELinux at boot time. 5365 Format: { "0" | "1" } 5366 See security/selinux/Kconfig help text. 5367 0 -- disable. 5368 1 -- enable. 5369 Default value is 1. 5370 5371 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 5372 Format: { "0" | "1" } 5373 See security/apparmor/Kconfig help text 5374 0 -- disable. 5375 1 -- enable. 5376 Default value is set via kernel config option. 5377 5378 serialnumber [BUGS=X86-32] 5379 5380 sev=option[,option...] [X86-64] See Documentation/x86/x86_64/boot-options.rst 5381 5382 shapers= [NET] 5383 Maximal number of shapers. 5384 5385 simeth= [IA-64] 5386 simscsi= 5387 5388 slram= [HW,MTD] 5389 5390 slab_merge [MM] 5391 Enable merging of slabs with similar size when the 5392 kernel is built without CONFIG_SLAB_MERGE_DEFAULT. 5393 5394 slab_nomerge [MM] 5395 Disable merging of slabs with similar size. May be 5396 necessary if there is some reason to distinguish 5397 allocs to different slabs, especially in hardened 5398 environments where the risk of heap overflows and 5399 layout control by attackers can usually be 5400 frustrated by disabling merging. This will reduce 5401 most of the exposure of a heap attack to a single 5402 cache (risks via metadata attacks are mostly 5403 unchanged). Debug options disable merging on their 5404 own. 5405 For more information see Documentation/vm/slub.rst. 5406 5407 slab_max_order= [MM, SLAB] 5408 Determines the maximum allowed order for slabs. 5409 A high setting may cause OOMs due to memory 5410 fragmentation. Defaults to 1 for systems with 5411 more than 32MB of RAM, 0 otherwise. 5412 5413 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 5414 Enabling slub_debug allows one to determine the 5415 culprit if slab objects become corrupted. Enabling 5416 slub_debug can create guard zones around objects and 5417 may poison objects when not in use. Also tracks the 5418 last alloc / free. For more information see 5419 Documentation/vm/slub.rst. 5420 5421 slub_max_order= [MM, SLUB] 5422 Determines the maximum allowed order for slabs. 5423 A high setting may cause OOMs due to memory 5424 fragmentation. For more information see 5425 Documentation/vm/slub.rst. 5426 5427 slub_min_objects= [MM, SLUB] 5428 The minimum number of objects per slab. SLUB will 5429 increase the slab order up to slub_max_order to 5430 generate a sufficiently large slab able to contain 5431 the number of objects indicated. The higher the number 5432 of objects the smaller the overhead of tracking slabs 5433 and the less frequently locks need to be acquired. 5434 For more information see Documentation/vm/slub.rst. 5435 5436 slub_min_order= [MM, SLUB] 5437 Determines the minimum page order for slabs. Must be 5438 lower than slub_max_order. 5439 For more information see Documentation/vm/slub.rst. 5440 5441 slub_merge [MM, SLUB] 5442 Same with slab_merge. 5443 5444 slub_nomerge [MM, SLUB] 5445 Same with slab_nomerge. This is supported for legacy. 5446 See slab_nomerge for more information. 5447 5448 smart2= [HW] 5449 Format: <io1>[,<io2>[,...,<io8>]] 5450 5451 smp.csd_lock_timeout= [KNL] 5452 Specify the period of time in milliseconds 5453 that smp_call_function() and friends will wait 5454 for a CPU to release the CSD lock. This is 5455 useful when diagnosing bugs involving CPUs 5456 disabling interrupts for extended periods 5457 of time. Defaults to 5,000 milliseconds, and 5458 setting a value of zero disables this feature. 5459 This feature may be more efficiently disabled 5460 using the csdlock_debug- kernel parameter. 5461 5462 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 5463 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 5464 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 5465 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 5466 smsc-ircc2.ircc_irq= [HW] IRQ line 5467 smsc-ircc2.ircc_dma= [HW] DMA channel 5468 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 5469 0: Toshiba Satellite 1800 (GP data pin select) 5470 1: Fast pin select (default) 5471 2: ATC IRMode 5472 5473 smt= [KNL,S390] Set the maximum number of threads (logical 5474 CPUs) to use per physical CPU on systems capable of 5475 symmetric multithreading (SMT). Will be capped to the 5476 actual hardware limit. 5477 Format: <integer> 5478 Default: -1 (no limit) 5479 5480 softlockup_panic= 5481 [KNL] Should the soft-lockup detector generate panics. 5482 Format: 0 | 1 5483 5484 A value of 1 instructs the soft-lockup detector 5485 to panic the machine when a soft-lockup occurs. It is 5486 also controlled by the kernel.softlockup_panic sysctl 5487 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 5488 respective build-time switch to that functionality. 5489 5490 softlockup_all_cpu_backtrace= 5491 [KNL] Should the soft-lockup detector generate 5492 backtraces on all cpus. 5493 Format: 0 | 1 5494 5495 sonypi.*= [HW] Sony Programmable I/O Control Device driver 5496 See Documentation/admin-guide/laptops/sonypi.rst 5497 5498 spectre_v2= [X86] Control mitigation of Spectre variant 2 5499 (indirect branch speculation) vulnerability. 5500 The default operation protects the kernel from 5501 user space attacks. 5502 5503 on - unconditionally enable, implies 5504 spectre_v2_user=on 5505 off - unconditionally disable, implies 5506 spectre_v2_user=off 5507 auto - kernel detects whether your CPU model is 5508 vulnerable 5509 5510 Selecting 'on' will, and 'auto' may, choose a 5511 mitigation method at run time according to the 5512 CPU, the available microcode, the setting of the 5513 CONFIG_RETPOLINE configuration option, and the 5514 compiler with which the kernel was built. 5515 5516 Selecting 'on' will also enable the mitigation 5517 against user space to user space task attacks. 5518 5519 Selecting 'off' will disable both the kernel and 5520 the user space protections. 5521 5522 Specific mitigations can also be selected manually: 5523 5524 retpoline - replace indirect branches 5525 retpoline,generic - Retpolines 5526 retpoline,lfence - LFENCE; indirect branch 5527 retpoline,amd - alias for retpoline,lfence 5528 eibrs - enhanced IBRS 5529 eibrs,retpoline - enhanced IBRS + Retpolines 5530 eibrs,lfence - enhanced IBRS + LFENCE 5531 5532 Not specifying this option is equivalent to 5533 spectre_v2=auto. 5534 5535 spectre_v2_user= 5536 [X86] Control mitigation of Spectre variant 2 5537 (indirect branch speculation) vulnerability between 5538 user space tasks 5539 5540 on - Unconditionally enable mitigations. Is 5541 enforced by spectre_v2=on 5542 5543 off - Unconditionally disable mitigations. Is 5544 enforced by spectre_v2=off 5545 5546 prctl - Indirect branch speculation is enabled, 5547 but mitigation can be enabled via prctl 5548 per thread. The mitigation control state 5549 is inherited on fork. 5550 5551 prctl,ibpb 5552 - Like "prctl" above, but only STIBP is 5553 controlled per thread. IBPB is issued 5554 always when switching between different user 5555 space processes. 5556 5557 seccomp 5558 - Same as "prctl" above, but all seccomp 5559 threads will enable the mitigation unless 5560 they explicitly opt out. 5561 5562 seccomp,ibpb 5563 - Like "seccomp" above, but only STIBP is 5564 controlled per thread. IBPB is issued 5565 always when switching between different 5566 user space processes. 5567 5568 auto - Kernel selects the mitigation depending on 5569 the available CPU features and vulnerability. 5570 5571 Default mitigation: "prctl" 5572 5573 Not specifying this option is equivalent to 5574 spectre_v2_user=auto. 5575 5576 spec_store_bypass_disable= 5577 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 5578 (Speculative Store Bypass vulnerability) 5579 5580 Certain CPUs are vulnerable to an exploit against a 5581 a common industry wide performance optimization known 5582 as "Speculative Store Bypass" in which recent stores 5583 to the same memory location may not be observed by 5584 later loads during speculative execution. The idea 5585 is that such stores are unlikely and that they can 5586 be detected prior to instruction retirement at the 5587 end of a particular speculation execution window. 5588 5589 In vulnerable processors, the speculatively forwarded 5590 store can be used in a cache side channel attack, for 5591 example to read memory to which the attacker does not 5592 directly have access (e.g. inside sandboxed code). 5593 5594 This parameter controls whether the Speculative Store 5595 Bypass optimization is used. 5596 5597 On x86 the options are: 5598 5599 on - Unconditionally disable Speculative Store Bypass 5600 off - Unconditionally enable Speculative Store Bypass 5601 auto - Kernel detects whether the CPU model contains an 5602 implementation of Speculative Store Bypass and 5603 picks the most appropriate mitigation. If the 5604 CPU is not vulnerable, "off" is selected. If the 5605 CPU is vulnerable the default mitigation is 5606 architecture and Kconfig dependent. See below. 5607 prctl - Control Speculative Store Bypass per thread 5608 via prctl. Speculative Store Bypass is enabled 5609 for a process by default. The state of the control 5610 is inherited on fork. 5611 seccomp - Same as "prctl" above, but all seccomp threads 5612 will disable SSB unless they explicitly opt out. 5613 5614 Default mitigations: 5615 X86: "prctl" 5616 5617 On powerpc the options are: 5618 5619 on,auto - On Power8 and Power9 insert a store-forwarding 5620 barrier on kernel entry and exit. On Power7 5621 perform a software flush on kernel entry and 5622 exit. 5623 off - No action. 5624 5625 Not specifying this option is equivalent to 5626 spec_store_bypass_disable=auto. 5627 5628 spia_io_base= [HW,MTD] 5629 spia_fio_base= 5630 spia_pedr= 5631 spia_peddr= 5632 5633 split_lock_detect= 5634 [X86] Enable split lock detection or bus lock detection 5635 5636 When enabled (and if hardware support is present), atomic 5637 instructions that access data across cache line 5638 boundaries will result in an alignment check exception 5639 for split lock detection or a debug exception for 5640 bus lock detection. 5641 5642 off - not enabled 5643 5644 warn - the kernel will emit rate-limited warnings 5645 about applications triggering the #AC 5646 exception or the #DB exception. This mode is 5647 the default on CPUs that support split lock 5648 detection or bus lock detection. Default 5649 behavior is by #AC if both features are 5650 enabled in hardware. 5651 5652 fatal - the kernel will send SIGBUS to applications 5653 that trigger the #AC exception or the #DB 5654 exception. Default behavior is by #AC if 5655 both features are enabled in hardware. 5656 5657 ratelimit:N - 5658 Set system wide rate limit to N bus locks 5659 per second for bus lock detection. 5660 0 < N <= 1000. 5661 5662 N/A for split lock detection. 5663 5664 5665 If an #AC exception is hit in the kernel or in 5666 firmware (i.e. not while executing in user mode) 5667 the kernel will oops in either "warn" or "fatal" 5668 mode. 5669 5670 #DB exception for bus lock is triggered only when 5671 CPL > 0. 5672 5673 srbds= [X86,INTEL] 5674 Control the Special Register Buffer Data Sampling 5675 (SRBDS) mitigation. 5676 5677 Certain CPUs are vulnerable to an MDS-like 5678 exploit which can leak bits from the random 5679 number generator. 5680 5681 By default, this issue is mitigated by 5682 microcode. However, the microcode fix can cause 5683 the RDRAND and RDSEED instructions to become 5684 much slower. Among other effects, this will 5685 result in reduced throughput from /dev/urandom. 5686 5687 The microcode mitigation can be disabled with 5688 the following option: 5689 5690 off: Disable mitigation and remove 5691 performance impact to RDRAND and RDSEED 5692 5693 srcutree.big_cpu_lim [KNL] 5694 Specifies the number of CPUs constituting a 5695 large system, such that srcu_struct structures 5696 should immediately allocate an srcu_node array. 5697 This kernel-boot parameter defaults to 128, 5698 but takes effect only when the low-order four 5699 bits of srcutree.convert_to_big is equal to 3 5700 (decide at boot). 5701 5702 srcutree.convert_to_big [KNL] 5703 Specifies under what conditions an SRCU tree 5704 srcu_struct structure will be converted to big 5705 form, that is, with an rcu_node tree: 5706 5707 0: Never. 5708 1: At init_srcu_struct() time. 5709 2: When rcutorture decides to. 5710 3: Decide at boot time (default). 5711 0x1X: Above plus if high contention. 5712 5713 Either way, the srcu_node tree will be sized based 5714 on the actual runtime number of CPUs (nr_cpu_ids) 5715 instead of the compile-time CONFIG_NR_CPUS. 5716 5717 srcutree.counter_wrap_check [KNL] 5718 Specifies how frequently to check for 5719 grace-period sequence counter wrap for the 5720 srcu_data structure's ->srcu_gp_seq_needed field. 5721 The greater the number of bits set in this kernel 5722 parameter, the less frequently counter wrap will 5723 be checked for. Note that the bottom two bits 5724 are ignored. 5725 5726 srcutree.exp_holdoff [KNL] 5727 Specifies how many nanoseconds must elapse 5728 since the end of the last SRCU grace period for 5729 a given srcu_struct until the next normal SRCU 5730 grace period will be considered for automatic 5731 expediting. Set to zero to disable automatic 5732 expediting. 5733 5734 srcutree.small_contention_lim [KNL] 5735 Specifies the number of update-side contention 5736 events per jiffy will be tolerated before 5737 initiating a conversion of an srcu_struct 5738 structure to big form. Note that the value of 5739 srcutree.convert_to_big must have the 0x10 bit 5740 set for contention-based conversions to occur. 5741 5742 ssbd= [ARM64,HW] 5743 Speculative Store Bypass Disable control 5744 5745 On CPUs that are vulnerable to the Speculative 5746 Store Bypass vulnerability and offer a 5747 firmware based mitigation, this parameter 5748 indicates how the mitigation should be used: 5749 5750 force-on: Unconditionally enable mitigation for 5751 for both kernel and userspace 5752 force-off: Unconditionally disable mitigation for 5753 for both kernel and userspace 5754 kernel: Always enable mitigation in the 5755 kernel, and offer a prctl interface 5756 to allow userspace to register its 5757 interest in being mitigated too. 5758 5759 stack_guard_gap= [MM] 5760 override the default stack gap protection. The value 5761 is in page units and it defines how many pages prior 5762 to (for stacks growing down) resp. after (for stacks 5763 growing up) the main stack are reserved for no other 5764 mapping. Default value is 256 pages. 5765 5766 stack_depot_disable= [KNL] 5767 Setting this to true through kernel command line will 5768 disable the stack depot thereby saving the static memory 5769 consumed by the stack hash table. By default this is set 5770 to false. 5771 5772 stacktrace [FTRACE] 5773 Enabled the stack tracer on boot up. 5774 5775 stacktrace_filter=[function-list] 5776 [FTRACE] Limit the functions that the stack tracer 5777 will trace at boot up. function-list is a comma-separated 5778 list of functions. This list can be changed at run 5779 time by the stack_trace_filter file in the debugfs 5780 tracing directory. Note, this enables stack tracing 5781 and the stacktrace above is not needed. 5782 5783 sti= [PARISC,HW] 5784 Format: <num> 5785 Set the STI (builtin display/keyboard on the HP-PARISC 5786 machines) console (graphic card) which should be used 5787 as the initial boot-console. 5788 See also comment in drivers/video/console/sticore.c. 5789 5790 sti_font= [HW] 5791 See comment in drivers/video/console/sticore.c. 5792 5793 stifb= [HW] 5794 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5795 5796 strict_sas_size= 5797 [X86] 5798 Format: <bool> 5799 Enable or disable strict sigaltstack size checks 5800 against the required signal frame size which 5801 depends on the supported FPU features. This can 5802 be used to filter out binaries which have 5803 not yet been made aware of AT_MINSIGSTKSZ. 5804 5805 sunrpc.min_resvport= 5806 sunrpc.max_resvport= 5807 [NFS,SUNRPC] 5808 SunRPC servers often require that client requests 5809 originate from a privileged port (i.e. a port in the 5810 range 0 < portnr < 1024). 5811 An administrator who wishes to reserve some of these 5812 ports for other uses may adjust the range that the 5813 kernel's sunrpc client considers to be privileged 5814 using these two parameters to set the minimum and 5815 maximum port values. 5816 5817 sunrpc.svc_rpc_per_connection_limit= 5818 [NFS,SUNRPC] 5819 Limit the number of requests that the server will 5820 process in parallel from a single connection. 5821 The default value is 0 (no limit). 5822 5823 sunrpc.pool_mode= 5824 [NFS] 5825 Control how the NFS server code allocates CPUs to 5826 service thread pools. Depending on how many NICs 5827 you have and where their interrupts are bound, this 5828 option will affect which CPUs will do NFS serving. 5829 Note: this parameter cannot be changed while the 5830 NFS server is running. 5831 5832 auto the server chooses an appropriate mode 5833 automatically using heuristics 5834 global a single global pool contains all CPUs 5835 percpu one pool for each CPU 5836 pernode one pool for each NUMA node (equivalent 5837 to global on non-NUMA machines) 5838 5839 sunrpc.tcp_slot_table_entries= 5840 sunrpc.udp_slot_table_entries= 5841 [NFS,SUNRPC] 5842 Sets the upper limit on the number of simultaneous 5843 RPC calls that can be sent from the client to a 5844 server. Increasing these values may allow you to 5845 improve throughput, but will also increase the 5846 amount of memory reserved for use by the client. 5847 5848 suspend.pm_test_delay= 5849 [SUSPEND] 5850 Sets the number of seconds to remain in a suspend test 5851 mode before resuming the system (see 5852 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5853 is set. Default value is 5. 5854 5855 svm= [PPC] 5856 Format: { on | off | y | n | 1 | 0 } 5857 This parameter controls use of the Protected 5858 Execution Facility on pSeries. 5859 5860 swapaccount= [KNL] 5861 Format: [0|1] 5862 Enable accounting of swap in memory resource 5863 controller if no parameter or 1 is given or disable 5864 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5865 5866 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5867 Format: { <int> | force | noforce } 5868 <int> -- Number of I/O TLB slabs 5869 force -- force using of bounce buffers even if they 5870 wouldn't be automatically used by the kernel 5871 noforce -- Never use bounce buffers (for debugging) 5872 5873 switches= [HW,M68k] 5874 5875 sysctl.*= [KNL] 5876 Set a sysctl parameter, right before loading the init 5877 process, as if the value was written to the respective 5878 /proc/sys/... file. Both '.' and '/' are recognized as 5879 separators. Unrecognized parameters and invalid values 5880 are reported in the kernel log. Sysctls registered 5881 later by a loaded module cannot be set this way. 5882 Example: sysctl.vm.swappiness=40 5883 5884 sysfs.deprecated=0|1 [KNL] 5885 Enable/disable old style sysfs layout for old udev 5886 on older distributions. When this option is enabled 5887 very new udev will not work anymore. When this option 5888 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5889 in older udev will not work anymore. 5890 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5891 the kernel configuration. 5892 5893 sysrq_always_enabled 5894 [KNL] 5895 Ignore sysrq setting - this boot parameter will 5896 neutralize any effect of /proc/sys/kernel/sysrq. 5897 Useful for debugging. 5898 5899 tcpmhash_entries= [KNL,NET] 5900 Set the number of tcp_metrics_hash slots. 5901 Default value is 8192 or 16384 depending on total 5902 ram pages. This is used to specify the TCP metrics 5903 cache size. See Documentation/networking/ip-sysctl.rst 5904 "tcp_no_metrics_save" section for more details. 5905 5906 tdfx= [HW,DRM] 5907 5908 test_suspend= [SUSPEND] 5909 Format: { "mem" | "standby" | "freeze" }[,N] 5910 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5911 standby suspend) or "freeze" (for suspend type freeze) 5912 as the system sleep state during system startup with 5913 the optional capability to repeat N number of times. 5914 The system is woken from this state using a 5915 wakeup-capable RTC alarm. 5916 5917 thash_entries= [KNL,NET] 5918 Set number of hash buckets for TCP connection 5919 5920 thermal.act= [HW,ACPI] 5921 -1: disable all active trip points in all thermal zones 5922 <degrees C>: override all lowest active trip points 5923 5924 thermal.crt= [HW,ACPI] 5925 -1: disable all critical trip points in all thermal zones 5926 <degrees C>: override all critical trip points 5927 5928 thermal.nocrt= [HW,ACPI] 5929 Set to disable actions on ACPI thermal zone 5930 critical and hot trip points. 5931 5932 thermal.off= [HW,ACPI] 5933 1: disable ACPI thermal control 5934 5935 thermal.psv= [HW,ACPI] 5936 -1: disable all passive trip points 5937 <degrees C>: override all passive trip points to this 5938 value 5939 5940 thermal.tzp= [HW,ACPI] 5941 Specify global default ACPI thermal zone polling rate 5942 <deci-seconds>: poll all this frequency 5943 0: no polling (default) 5944 5945 threadirqs [KNL] 5946 Force threading of all interrupt handlers except those 5947 marked explicitly IRQF_NO_THREAD. 5948 5949 topology= [S390] 5950 Format: {off | on} 5951 Specify if the kernel should make use of the cpu 5952 topology information if the hardware supports this. 5953 The scheduler will make use of this information and 5954 e.g. base its process migration decisions on it. 5955 Default is on. 5956 5957 topology_updates= [KNL, PPC, NUMA] 5958 Format: {off} 5959 Specify if the kernel should ignore (off) 5960 topology updates sent by the hypervisor to this 5961 LPAR. 5962 5963 torture.disable_onoff_at_boot= [KNL] 5964 Prevent the CPU-hotplug component of torturing 5965 until after init has spawned. 5966 5967 torture.ftrace_dump_at_shutdown= [KNL] 5968 Dump the ftrace buffer at torture-test shutdown, 5969 even if there were no errors. This can be a 5970 very costly operation when many torture tests 5971 are running concurrently, especially on systems 5972 with rotating-rust storage. 5973 5974 torture.verbose_sleep_frequency= [KNL] 5975 Specifies how many verbose printk()s should be 5976 emitted between each sleep. The default of zero 5977 disables verbose-printk() sleeping. 5978 5979 torture.verbose_sleep_duration= [KNL] 5980 Duration of each verbose-printk() sleep in jiffies. 5981 5982 tp720= [HW,PS2] 5983 5984 tpm_suspend_pcr=[HW,TPM] 5985 Format: integer pcr id 5986 Specify that at suspend time, the tpm driver 5987 should extend the specified pcr with zeros, 5988 as a workaround for some chips which fail to 5989 flush the last written pcr on TPM_SaveState. 5990 This will guarantee that all the other pcrs 5991 are saved. 5992 5993 tp_printk [FTRACE] 5994 Have the tracepoints sent to printk as well as the 5995 tracing ring buffer. This is useful for early boot up 5996 where the system hangs or reboots and does not give the 5997 option for reading the tracing buffer or performing a 5998 ftrace_dump_on_oops. 5999 6000 To turn off having tracepoints sent to printk, 6001 echo 0 > /proc/sys/kernel/tracepoint_printk 6002 Note, echoing 1 into this file without the 6003 tracepoint_printk kernel cmdline option has no effect. 6004 6005 The tp_printk_stop_on_boot (see below) can also be used 6006 to stop the printing of events to console at 6007 late_initcall_sync. 6008 6009 ** CAUTION ** 6010 6011 Having tracepoints sent to printk() and activating high 6012 frequency tracepoints such as irq or sched, can cause 6013 the system to live lock. 6014 6015 tp_printk_stop_on_boot [FTRACE] 6016 When tp_printk (above) is set, it can cause a lot of noise 6017 on the console. It may be useful to only include the 6018 printing of events during boot up, as user space may 6019 make the system inoperable. 6020 6021 This command line option will stop the printing of events 6022 to console at the late_initcall_sync() time frame. 6023 6024 trace_buf_size=nn[KMG] 6025 [FTRACE] will set tracing buffer size on each cpu. 6026 6027 trace_clock= [FTRACE] Set the clock used for tracing events 6028 at boot up. 6029 local - Use the per CPU time stamp counter 6030 (converted into nanoseconds). Fast, but 6031 depending on the architecture, may not be 6032 in sync between CPUs. 6033 global - Event time stamps are synchronize across 6034 CPUs. May be slower than the local clock, 6035 but better for some race conditions. 6036 counter - Simple counting of events (1, 2, ..) 6037 note, some counts may be skipped due to the 6038 infrastructure grabbing the clock more than 6039 once per event. 6040 uptime - Use jiffies as the time stamp. 6041 perf - Use the same clock that perf uses. 6042 mono - Use ktime_get_mono_fast_ns() for time stamps. 6043 mono_raw - Use ktime_get_raw_fast_ns() for time 6044 stamps. 6045 boot - Use ktime_get_boot_fast_ns() for time stamps. 6046 Architectures may add more clocks. See 6047 Documentation/trace/ftrace.rst for more details. 6048 6049 trace_event=[event-list] 6050 [FTRACE] Set and start specified trace events in order 6051 to facilitate early boot debugging. The event-list is a 6052 comma-separated list of trace events to enable. See 6053 also Documentation/trace/events.rst 6054 6055 trace_options=[option-list] 6056 [FTRACE] Enable or disable tracer options at boot. 6057 The option-list is a comma delimited list of options 6058 that can be enabled or disabled just as if you were 6059 to echo the option name into 6060 6061 /sys/kernel/debug/tracing/trace_options 6062 6063 For example, to enable stacktrace option (to dump the 6064 stack trace of each event), add to the command line: 6065 6066 trace_options=stacktrace 6067 6068 See also Documentation/trace/ftrace.rst "trace options" 6069 section. 6070 6071 traceoff_on_warning 6072 [FTRACE] enable this option to disable tracing when a 6073 warning is hit. This turns off "tracing_on". Tracing can 6074 be enabled again by echoing '1' into the "tracing_on" 6075 file located in /sys/kernel/debug/tracing/ 6076 6077 This option is useful, as it disables the trace before 6078 the WARNING dump is called, which prevents the trace to 6079 be filled with content caused by the warning output. 6080 6081 This option can also be set at run time via the sysctl 6082 option: kernel/traceoff_on_warning 6083 6084 transparent_hugepage= 6085 [KNL] 6086 Format: [always|madvise|never] 6087 Can be used to control the default behavior of the system 6088 with respect to transparent hugepages. 6089 See Documentation/admin-guide/mm/transhuge.rst 6090 for more details. 6091 6092 trusted.source= [KEYS] 6093 Format: <string> 6094 This parameter identifies the trust source as a backend 6095 for trusted keys implementation. Supported trust 6096 sources: 6097 - "tpm" 6098 - "tee" 6099 - "caam" 6100 If not specified then it defaults to iterating through 6101 the trust source list starting with TPM and assigns the 6102 first trust source as a backend which is initialized 6103 successfully during iteration. 6104 6105 trusted.rng= [KEYS] 6106 Format: <string> 6107 The RNG used to generate key material for trusted keys. 6108 Can be one of: 6109 - "kernel" 6110 - the same value as trusted.source: "tpm" or "tee" 6111 - "default" 6112 If not specified, "default" is used. In this case, 6113 the RNG's choice is left to each individual trust source. 6114 6115 tsc= Disable clocksource stability checks for TSC. 6116 Format: <string> 6117 [x86] reliable: mark tsc clocksource as reliable, this 6118 disables clocksource verification at runtime, as well 6119 as the stability checks done at bootup. Used to enable 6120 high-resolution timer mode on older hardware, and in 6121 virtualized environment. 6122 [x86] noirqtime: Do not use TSC to do irq accounting. 6123 Used to run time disable IRQ_TIME_ACCOUNTING on any 6124 platforms where RDTSC is slow and this accounting 6125 can add overhead. 6126 [x86] unstable: mark the TSC clocksource as unstable, this 6127 marks the TSC unconditionally unstable at bootup and 6128 avoids any further wobbles once the TSC watchdog notices. 6129 [x86] nowatchdog: disable clocksource watchdog. Used 6130 in situations with strict latency requirements (where 6131 interruptions from clocksource watchdog are not 6132 acceptable). 6133 6134 tsc_early_khz= [X86] Skip early TSC calibration and use the given 6135 value instead. Useful when the early TSC frequency discovery 6136 procedure is not reliable, such as on overclocked systems 6137 with CPUID.16h support and partial CPUID.15h support. 6138 Format: <unsigned int> 6139 6140 tsx= [X86] Control Transactional Synchronization 6141 Extensions (TSX) feature in Intel processors that 6142 support TSX control. 6143 6144 This parameter controls the TSX feature. The options are: 6145 6146 on - Enable TSX on the system. Although there are 6147 mitigations for all known security vulnerabilities, 6148 TSX has been known to be an accelerator for 6149 several previous speculation-related CVEs, and 6150 so there may be unknown security risks associated 6151 with leaving it enabled. 6152 6153 off - Disable TSX on the system. (Note that this 6154 option takes effect only on newer CPUs which are 6155 not vulnerable to MDS, i.e., have 6156 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 6157 the new IA32_TSX_CTRL MSR through a microcode 6158 update. This new MSR allows for the reliable 6159 deactivation of the TSX functionality.) 6160 6161 auto - Disable TSX if X86_BUG_TAA is present, 6162 otherwise enable TSX on the system. 6163 6164 Not specifying this option is equivalent to tsx=off. 6165 6166 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6167 for more details. 6168 6169 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 6170 Abort (TAA) vulnerability. 6171 6172 Similar to Micro-architectural Data Sampling (MDS) 6173 certain CPUs that support Transactional 6174 Synchronization Extensions (TSX) are vulnerable to an 6175 exploit against CPU internal buffers which can forward 6176 information to a disclosure gadget under certain 6177 conditions. 6178 6179 In vulnerable processors, the speculatively forwarded 6180 data can be used in a cache side channel attack, to 6181 access data to which the attacker does not have direct 6182 access. 6183 6184 This parameter controls the TAA mitigation. The 6185 options are: 6186 6187 full - Enable TAA mitigation on vulnerable CPUs 6188 if TSX is enabled. 6189 6190 full,nosmt - Enable TAA mitigation and disable SMT on 6191 vulnerable CPUs. If TSX is disabled, SMT 6192 is not disabled because CPU is not 6193 vulnerable to cross-thread TAA attacks. 6194 off - Unconditionally disable TAA mitigation 6195 6196 On MDS-affected machines, tsx_async_abort=off can be 6197 prevented by an active MDS mitigation as both vulnerabilities 6198 are mitigated with the same mechanism so in order to disable 6199 this mitigation, you need to specify mds=off too. 6200 6201 Not specifying this option is equivalent to 6202 tsx_async_abort=full. On CPUs which are MDS affected 6203 and deploy MDS mitigation, TAA mitigation is not 6204 required and doesn't provide any additional 6205 mitigation. 6206 6207 For details see: 6208 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 6209 6210 turbografx.map[2|3]= [HW,JOY] 6211 TurboGraFX parallel port interface 6212 Format: 6213 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 6214 See also Documentation/input/devices/joystick-parport.rst 6215 6216 udbg-immortal [PPC] When debugging early kernel crashes that 6217 happen after console_init() and before a proper 6218 console driver takes over, this boot options might 6219 help "seeing" what's going on. 6220 6221 uhash_entries= [KNL,NET] 6222 Set number of hash buckets for UDP/UDP-Lite connections 6223 6224 uhci-hcd.ignore_oc= 6225 [USB] Ignore overcurrent events (default N). 6226 Some badly-designed motherboards generate lots of 6227 bogus events, for ports that aren't wired to 6228 anything. Set this parameter to avoid log spamming. 6229 Note that genuine overcurrent events won't be 6230 reported either. 6231 6232 unknown_nmi_panic 6233 [X86] Cause panic on unknown NMI. 6234 6235 usbcore.authorized_default= 6236 [USB] Default USB device authorization: 6237 (default -1 = authorized except for wireless USB, 6238 0 = not authorized, 1 = authorized, 2 = authorized 6239 if device connected to internal port) 6240 6241 usbcore.autosuspend= 6242 [USB] The autosuspend time delay (in seconds) used 6243 for newly-detected USB devices (default 2). This 6244 is the time required before an idle device will be 6245 autosuspended. Devices for which the delay is set 6246 to a negative value won't be autosuspended at all. 6247 6248 usbcore.usbfs_snoop= 6249 [USB] Set to log all usbfs traffic (default 0 = off). 6250 6251 usbcore.usbfs_snoop_max= 6252 [USB] Maximum number of bytes to snoop in each URB 6253 (default = 65536). 6254 6255 usbcore.blinkenlights= 6256 [USB] Set to cycle leds on hubs (default 0 = off). 6257 6258 usbcore.old_scheme_first= 6259 [USB] Start with the old device initialization 6260 scheme (default 0 = off). 6261 6262 usbcore.usbfs_memory_mb= 6263 [USB] Memory limit (in MB) for buffers allocated by 6264 usbfs (default = 16, 0 = max = 2047). 6265 6266 usbcore.use_both_schemes= 6267 [USB] Try the other device initialization scheme 6268 if the first one fails (default 1 = enabled). 6269 6270 usbcore.initial_descriptor_timeout= 6271 [USB] Specifies timeout for the initial 64-byte 6272 USB_REQ_GET_DESCRIPTOR request in milliseconds 6273 (default 5000 = 5.0 seconds). 6274 6275 usbcore.nousb [USB] Disable the USB subsystem 6276 6277 usbcore.quirks= 6278 [USB] A list of quirk entries to augment the built-in 6279 usb core quirk list. List entries are separated by 6280 commas. Each entry has the form 6281 VendorID:ProductID:Flags. The IDs are 4-digit hex 6282 numbers and Flags is a set of letters. Each letter 6283 will change the built-in quirk; setting it if it is 6284 clear and clearing it if it is set. The letters have 6285 the following meanings: 6286 a = USB_QUIRK_STRING_FETCH_255 (string 6287 descriptors must not be fetched using 6288 a 255-byte read); 6289 b = USB_QUIRK_RESET_RESUME (device can't resume 6290 correctly so reset it instead); 6291 c = USB_QUIRK_NO_SET_INTF (device can't handle 6292 Set-Interface requests); 6293 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 6294 handle its Configuration or Interface 6295 strings); 6296 e = USB_QUIRK_RESET (device can't be reset 6297 (e.g morph devices), don't use reset); 6298 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 6299 more interface descriptions than the 6300 bNumInterfaces count, and can't handle 6301 talking to these interfaces); 6302 g = USB_QUIRK_DELAY_INIT (device needs a pause 6303 during initialization, after we read 6304 the device descriptor); 6305 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 6306 high speed and super speed interrupt 6307 endpoints, the USB 2.0 and USB 3.0 spec 6308 require the interval in microframes (1 6309 microframe = 125 microseconds) to be 6310 calculated as interval = 2 ^ 6311 (bInterval-1). 6312 Devices with this quirk report their 6313 bInterval as the result of this 6314 calculation instead of the exponent 6315 variable used in the calculation); 6316 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 6317 handle device_qualifier descriptor 6318 requests); 6319 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 6320 generates spurious wakeup, ignore 6321 remote wakeup capability); 6322 k = USB_QUIRK_NO_LPM (device can't handle Link 6323 Power Management); 6324 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 6325 (Device reports its bInterval as linear 6326 frames instead of the USB 2.0 6327 calculation); 6328 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 6329 to be disconnected before suspend to 6330 prevent spurious wakeup); 6331 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 6332 pause after every control message); 6333 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 6334 delay after resetting its port); 6335 Example: quirks=0781:5580:bk,0a5c:5834:gij 6336 6337 usbhid.mousepoll= 6338 [USBHID] The interval which mice are to be polled at. 6339 6340 usbhid.jspoll= 6341 [USBHID] The interval which joysticks are to be polled at. 6342 6343 usbhid.kbpoll= 6344 [USBHID] The interval which keyboards are to be polled at. 6345 6346 usb-storage.delay_use= 6347 [UMS] The delay in seconds before a new device is 6348 scanned for Logical Units (default 1). 6349 6350 usb-storage.quirks= 6351 [UMS] A list of quirks entries to supplement or 6352 override the built-in unusual_devs list. List 6353 entries are separated by commas. Each entry has 6354 the form VID:PID:Flags where VID and PID are Vendor 6355 and Product ID values (4-digit hex numbers) and 6356 Flags is a set of characters, each corresponding 6357 to a common usb-storage quirk flag as follows: 6358 a = SANE_SENSE (collect more than 18 bytes 6359 of sense data, not on uas); 6360 b = BAD_SENSE (don't collect more than 18 6361 bytes of sense data, not on uas); 6362 c = FIX_CAPACITY (decrease the reported 6363 device capacity by one sector); 6364 d = NO_READ_DISC_INFO (don't use 6365 READ_DISC_INFO command, not on uas); 6366 e = NO_READ_CAPACITY_16 (don't use 6367 READ_CAPACITY_16 command); 6368 f = NO_REPORT_OPCODES (don't use report opcodes 6369 command, uas only); 6370 g = MAX_SECTORS_240 (don't transfer more than 6371 240 sectors at a time, uas only); 6372 h = CAPACITY_HEURISTICS (decrease the 6373 reported device capacity by one 6374 sector if the number is odd); 6375 i = IGNORE_DEVICE (don't bind to this 6376 device); 6377 j = NO_REPORT_LUNS (don't use report luns 6378 command, uas only); 6379 k = NO_SAME (do not use WRITE_SAME, uas only) 6380 l = NOT_LOCKABLE (don't try to lock and 6381 unlock ejectable media, not on uas); 6382 m = MAX_SECTORS_64 (don't transfer more 6383 than 64 sectors = 32 KB at a time, 6384 not on uas); 6385 n = INITIAL_READ10 (force a retry of the 6386 initial READ(10) command, not on uas); 6387 o = CAPACITY_OK (accept the capacity 6388 reported by the device, not on uas); 6389 p = WRITE_CACHE (the device cache is ON 6390 by default, not on uas); 6391 r = IGNORE_RESIDUE (the device reports 6392 bogus residue values, not on uas); 6393 s = SINGLE_LUN (the device has only one 6394 Logical Unit); 6395 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 6396 commands, uas only); 6397 u = IGNORE_UAS (don't bind to the uas driver); 6398 w = NO_WP_DETECT (don't test whether the 6399 medium is write-protected). 6400 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 6401 even if the device claims no cache, 6402 not on uas) 6403 Example: quirks=0419:aaf5:rl,0421:0433:rc 6404 6405 user_debug= [KNL,ARM] 6406 Format: <int> 6407 See arch/arm/Kconfig.debug help text. 6408 1 - undefined instruction events 6409 2 - system calls 6410 4 - invalid data aborts 6411 8 - SIGSEGV faults 6412 16 - SIGBUS faults 6413 Example: user_debug=31 6414 6415 userpte= 6416 [X86] Flags controlling user PTE allocations. 6417 6418 nohigh = do not allocate PTE pages in 6419 HIGHMEM regardless of setting 6420 of CONFIG_HIGHPTE. 6421 6422 vdso= [X86,SH,SPARC] 6423 On X86_32, this is an alias for vdso32=. Otherwise: 6424 6425 vdso=1: enable VDSO (the default) 6426 vdso=0: disable VDSO mapping 6427 6428 vdso32= [X86] Control the 32-bit vDSO 6429 vdso32=1: enable 32-bit VDSO 6430 vdso32=0 or vdso32=2: disable 32-bit VDSO 6431 6432 See the help text for CONFIG_COMPAT_VDSO for more 6433 details. If CONFIG_COMPAT_VDSO is set, the default is 6434 vdso32=0; otherwise, the default is vdso32=1. 6435 6436 For compatibility with older kernels, vdso32=2 is an 6437 alias for vdso32=0. 6438 6439 Try vdso32=0 if you encounter an error that says: 6440 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 6441 6442 vector= [IA-64,SMP] 6443 vector=percpu: enable percpu vector domain 6444 6445 video= [FB] Frame buffer configuration 6446 See Documentation/fb/modedb.rst. 6447 6448 video.brightness_switch_enabled= [ACPI] 6449 Format: [0|1] 6450 If set to 1, on receiving an ACPI notify event 6451 generated by hotkey, video driver will adjust brightness 6452 level and then send out the event to user space through 6453 the allocated input device. If set to 0, video driver 6454 will only send out the event without touching backlight 6455 brightness level. 6456 default: 1 6457 6458 virtio_mmio.device= 6459 [VMMIO] Memory mapped virtio (platform) device. 6460 6461 <size>@<baseaddr>:<irq>[:<id>] 6462 where: 6463 <size> := size (can use standard suffixes 6464 like K, M and G) 6465 <baseaddr> := physical base address 6466 <irq> := interrupt number (as passed to 6467 request_irq()) 6468 <id> := (optional) platform device id 6469 example: 6470 virtio_mmio.device=1K@0x100b0000:48:7 6471 6472 Can be used multiple times for multiple devices. 6473 6474 vga= [BOOT,X86-32] Select a particular video mode 6475 See Documentation/x86/boot.rst and 6476 Documentation/admin-guide/svga.rst. 6477 Use vga=ask for menu. 6478 This is actually a boot loader parameter; the value is 6479 passed to the kernel using a special protocol. 6480 6481 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 6482 May slow down system boot speed, especially when 6483 enabled on systems with a large amount of memory. 6484 All options are enabled by default, and this 6485 interface is meant to allow for selectively 6486 enabling or disabling specific virtual memory 6487 debugging features. 6488 6489 Available options are: 6490 P Enable page structure init time poisoning 6491 - Disable all of the above options 6492 6493 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 6494 size of <nn>. This can be used to increase the 6495 minimum size (128MB on x86). It can also be used to 6496 decrease the size and leave more room for directly 6497 mapped kernel RAM. 6498 6499 vmcp_cma=nn[MG] [KNL,S390] 6500 Sets the memory size reserved for contiguous memory 6501 allocations for the vmcp device driver. 6502 6503 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 6504 Format: <command> 6505 6506 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 6507 Format: <command> 6508 6509 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 6510 Format: <command> 6511 6512 vsyscall= [X86-64] 6513 Controls the behavior of vsyscalls (i.e. calls to 6514 fixed addresses of 0xffffffffff600x00 from legacy 6515 code). Most statically-linked binaries and older 6516 versions of glibc use these calls. Because these 6517 functions are at fixed addresses, they make nice 6518 targets for exploits that can control RIP. 6519 6520 emulate [default] Vsyscalls turn into traps and are 6521 emulated reasonably safely. The vsyscall 6522 page is readable. 6523 6524 xonly Vsyscalls turn into traps and are 6525 emulated reasonably safely. The vsyscall 6526 page is not readable. 6527 6528 none Vsyscalls don't work at all. This makes 6529 them quite hard to use for exploits but 6530 might break your system. 6531 6532 vt.color= [VT] Default text color. 6533 Format: 0xYX, X = foreground, Y = background. 6534 Default: 0x07 = light gray on black. 6535 6536 vt.cur_default= [VT] Default cursor shape. 6537 Format: 0xCCBBAA, where AA, BB, and CC are the same as 6538 the parameters of the <Esc>[?A;B;Cc escape sequence; 6539 see VGA-softcursor.txt. Default: 2 = underline. 6540 6541 vt.default_blu= [VT] 6542 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 6543 Change the default blue palette of the console. 6544 This is a 16-member array composed of values 6545 ranging from 0-255. 6546 6547 vt.default_grn= [VT] 6548 Format: <green0>,<green1>,<green2>,...,<green15> 6549 Change the default green palette of the console. 6550 This is a 16-member array composed of values 6551 ranging from 0-255. 6552 6553 vt.default_red= [VT] 6554 Format: <red0>,<red1>,<red2>,...,<red15> 6555 Change the default red palette of the console. 6556 This is a 16-member array composed of values 6557 ranging from 0-255. 6558 6559 vt.default_utf8= 6560 [VT] 6561 Format=<0|1> 6562 Set system-wide default UTF-8 mode for all tty's. 6563 Default is 1, i.e. UTF-8 mode is enabled for all 6564 newly opened terminals. 6565 6566 vt.global_cursor_default= 6567 [VT] 6568 Format=<-1|0|1> 6569 Set system-wide default for whether a cursor 6570 is shown on new VTs. Default is -1, 6571 i.e. cursors will be created by default unless 6572 overridden by individual drivers. 0 will hide 6573 cursors, 1 will display them. 6574 6575 vt.italic= [VT] Default color for italic text; 0-15. 6576 Default: 2 = green. 6577 6578 vt.underline= [VT] Default color for underlined text; 0-15. 6579 Default: 3 = cyan. 6580 6581 watchdog timers [HW,WDT] For information on watchdog timers, 6582 see Documentation/watchdog/watchdog-parameters.rst 6583 or other driver-specific files in the 6584 Documentation/watchdog/ directory. 6585 6586 watchdog_thresh= 6587 [KNL] 6588 Set the hard lockup detector stall duration 6589 threshold in seconds. The soft lockup detector 6590 threshold is set to twice the value. A value of 0 6591 disables both lockup detectors. Default is 10 6592 seconds. 6593 6594 workqueue.watchdog_thresh= 6595 If CONFIG_WQ_WATCHDOG is configured, workqueue can 6596 warn stall conditions and dump internal state to 6597 help debugging. 0 disables workqueue stall 6598 detection; otherwise, it's the stall threshold 6599 duration in seconds. The default value is 30 and 6600 it can be updated at runtime by writing to the 6601 corresponding sysfs file. 6602 6603 workqueue.disable_numa 6604 By default, all work items queued to unbound 6605 workqueues are affine to the NUMA nodes they're 6606 issued on, which results in better behavior in 6607 general. If NUMA affinity needs to be disabled for 6608 whatever reason, this option can be used. Note 6609 that this also can be controlled per-workqueue for 6610 workqueues visible under /sys/bus/workqueue/. 6611 6612 workqueue.power_efficient 6613 Per-cpu workqueues are generally preferred because 6614 they show better performance thanks to cache 6615 locality; unfortunately, per-cpu workqueues tend to 6616 be more power hungry than unbound workqueues. 6617 6618 Enabling this makes the per-cpu workqueues which 6619 were observed to contribute significantly to power 6620 consumption unbound, leading to measurably lower 6621 power usage at the cost of small performance 6622 overhead. 6623 6624 The default value of this parameter is determined by 6625 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 6626 6627 workqueue.debug_force_rr_cpu 6628 Workqueue used to implicitly guarantee that work 6629 items queued without explicit CPU specified are put 6630 on the local CPU. This guarantee is no longer true 6631 and while local CPU is still preferred work items 6632 may be put on foreign CPUs. This debug option 6633 forces round-robin CPU selection to flush out 6634 usages which depend on the now broken guarantee. 6635 When enabled, memory and cache locality will be 6636 impacted. 6637 6638 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 6639 default x2apic cluster mode on platforms 6640 supporting x2apic. 6641 6642 xen_512gb_limit [KNL,X86-64,XEN] 6643 Restricts the kernel running paravirtualized under Xen 6644 to use only up to 512 GB of RAM. The reason to do so is 6645 crash analysis tools and Xen tools for doing domain 6646 save/restore/migration must be enabled to handle larger 6647 domains. 6648 6649 xen_emul_unplug= [HW,X86,XEN] 6650 Unplug Xen emulated devices 6651 Format: [unplug0,][unplug1] 6652 ide-disks -- unplug primary master IDE devices 6653 aux-ide-disks -- unplug non-primary-master IDE devices 6654 nics -- unplug network devices 6655 all -- unplug all emulated devices (NICs and IDE disks) 6656 unnecessary -- unplugging emulated devices is 6657 unnecessary even if the host did not respond to 6658 the unplug protocol 6659 never -- do not unplug even if version check succeeds 6660 6661 xen_legacy_crash [X86,XEN] 6662 Crash from Xen panic notifier, without executing late 6663 panic() code such as dumping handler. 6664 6665 xen_nopvspin [X86,XEN] 6666 Disables the qspinlock slowpath using Xen PV optimizations. 6667 This parameter is obsoleted by "nopvspin" parameter, which 6668 has equivalent effect for XEN platform. 6669 6670 xen_nopv [X86] 6671 Disables the PV optimizations forcing the HVM guest to 6672 run as generic HVM guest with no PV drivers. 6673 This option is obsoleted by the "nopv" option, which 6674 has equivalent effect for XEN platform. 6675 6676 xen_no_vector_callback 6677 [KNL,X86,XEN] Disable the vector callback for Xen 6678 event channel interrupts. 6679 6680 xen_scrub_pages= [XEN] 6681 Boolean option to control scrubbing pages before giving them back 6682 to Xen, for use by other domains. Can be also changed at runtime 6683 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 6684 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 6685 6686 xen_timer_slop= [X86-64,XEN] 6687 Set the timer slop (in nanoseconds) for the virtual Xen 6688 timers (default is 100000). This adjusts the minimum 6689 delta of virtualized Xen timers, where lower values 6690 improve timer resolution at the expense of processing 6691 more timer interrupts. 6692 6693 xen.balloon_boot_timeout= [XEN] 6694 The time (in seconds) to wait before giving up to boot 6695 in case initial ballooning fails to free enough memory. 6696 Applies only when running as HVM or PVH guest and 6697 started with less memory configured than allowed at 6698 max. Default is 180. 6699 6700 xen.event_eoi_delay= [XEN] 6701 How long to delay EOI handling in case of event 6702 storms (jiffies). Default is 10. 6703 6704 xen.event_loop_timeout= [XEN] 6705 After which time (jiffies) the event handling loop 6706 should start to delay EOI handling. Default is 2. 6707 6708 xen.fifo_events= [XEN] 6709 Boolean parameter to disable using fifo event handling 6710 even if available. Normally fifo event handling is 6711 preferred over the 2-level event handling, as it is 6712 fairer and the number of possible event channels is 6713 much higher. Default is on (use fifo events). 6714 6715 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 6716 Disables the PV optimizations forcing the guest to run 6717 as generic guest with no PV drivers. Currently support 6718 XEN HVM, KVM, HYPER_V and VMWARE guest. 6719 6720 nopvspin [X86,XEN,KVM] 6721 Disables the qspinlock slow path using PV optimizations 6722 which allow the hypervisor to 'idle' the guest on lock 6723 contention. 6724 6725 xirc2ps_cs= [NET,PCMCIA] 6726 Format: 6727 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6728 6729 xive= [PPC] 6730 By default on POWER9 and above, the kernel will 6731 natively use the XIVE interrupt controller. This option 6732 allows the fallback firmware mode to be used: 6733 6734 off Fallback to firmware control of XIVE interrupt 6735 controller on both pseries and powernv 6736 platforms. Only useful on POWER9 and above. 6737 6738 xive.store-eoi=off [PPC] 6739 By default on POWER10 and above, the kernel will use 6740 stores for EOI handling when the XIVE interrupt mode 6741 is active. This option allows the XIVE driver to use 6742 loads instead, as on POWER9. 6743 6744 xhci-hcd.quirks [USB,KNL] 6745 A hex value specifying bitmask with supplemental xhci 6746 host controller quirks. Meaning of each bit can be 6747 consulted in header drivers/usb/host/xhci.h. 6748 6749 xmon [PPC] 6750 Format: { early | on | rw | ro | off } 6751 Controls if xmon debugger is enabled. Default is off. 6752 Passing only "xmon" is equivalent to "xmon=early". 6753 early Call xmon as early as possible on boot; xmon 6754 debugger is called from setup_arch(). 6755 on xmon debugger hooks will be installed so xmon 6756 is only called on a kernel crash. Default mode, 6757 i.e. either "ro" or "rw" mode, is controlled 6758 with CONFIG_XMON_DEFAULT_RO_MODE. 6759 rw xmon debugger hooks will be installed so xmon 6760 is called only on a kernel crash, mode is write, 6761 meaning SPR registers, memory and, other data 6762 can be written using xmon commands. 6763 ro same as "rw" option above but SPR registers, 6764 memory, and other data can't be written using 6765 xmon commands. 6766 off xmon is disabled. 6767