1 acpi= [HW,ACPI,X86,ARM64] 2 Advanced Configuration and Power Interface 3 Format: { force | on | off | strict | noirq | rsdt | 4 copy_dsdt } 5 force -- enable ACPI if default was off 6 on -- enable ACPI but allow fallback to DT [arm64] 7 off -- disable ACPI if default was on 8 noirq -- do not use ACPI for IRQ routing 9 strict -- Be less tolerant of platforms that are not 10 strictly ACPI specification compliant. 11 rsdt -- prefer RSDT over (default) XSDT 12 copy_dsdt -- copy DSDT to memory 13 For ARM64, ONLY "acpi=off", "acpi=on" or "acpi=force" 14 are available 15 16 See also Documentation/power/runtime_pm.rst, pci=noacpi 17 18 acpi_apic_instance= [ACPI, IOAPIC] 19 Format: <int> 20 2: use 2nd APIC table, if available 21 1,0: use 1st APIC table 22 default: 0 23 24 acpi_backlight= [HW,ACPI] 25 { vendor | video | native | none } 26 If set to vendor, prefer vendor-specific driver 27 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 28 of the ACPI video.ko driver. 29 If set to video, use the ACPI video.ko driver. 30 If set to native, use the device's native backlight mode. 31 If set to none, disable the ACPI backlight interface. 32 33 acpi_force_32bit_fadt_addr 34 force FADT to use 32 bit addresses rather than the 35 64 bit X_* addresses. Some firmware have broken 64 36 bit addresses for force ACPI ignore these and use 37 the older legacy 32 bit addresses. 38 39 acpica_no_return_repair [HW, ACPI] 40 Disable AML predefined validation mechanism 41 This mechanism can repair the evaluation result to make 42 the return objects more ACPI specification compliant. 43 This option is useful for developers to identify the 44 root cause of an AML interpreter issue when the issue 45 has something to do with the repair mechanism. 46 47 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 48 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 49 Format: <int> 50 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 51 debug output. Bits in debug_layer correspond to a 52 _COMPONENT in an ACPI source file, e.g., 53 #define _COMPONENT ACPI_PCI_COMPONENT 54 Bits in debug_level correspond to a level in 55 ACPI_DEBUG_PRINT statements, e.g., 56 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 57 The debug_level mask defaults to "info". See 58 Documentation/firmware-guide/acpi/debug.rst for more information about 59 debug layers and levels. 60 61 Enable processor driver info messages: 62 acpi.debug_layer=0x20000000 63 Enable PCI/PCI interrupt routing info messages: 64 acpi.debug_layer=0x400000 65 Enable AML "Debug" output, i.e., stores to the Debug 66 object while interpreting AML: 67 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 68 Enable all messages related to ACPI hardware: 69 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 70 71 Some values produce so much output that the system is 72 unusable. The "log_buf_len" parameter may be useful 73 if you need to capture more output. 74 75 acpi_enforce_resources= [ACPI] 76 { strict | lax | no } 77 Check for resource conflicts between native drivers 78 and ACPI OperationRegions (SystemIO and SystemMemory 79 only). IO ports and memory declared in ACPI might be 80 used by the ACPI subsystem in arbitrary AML code and 81 can interfere with legacy drivers. 82 strict (default): access to resources claimed by ACPI 83 is denied; legacy drivers trying to access reserved 84 resources will fail to bind to device using them. 85 lax: access to resources claimed by ACPI is allowed; 86 legacy drivers trying to access reserved resources 87 will bind successfully but a warning message is logged. 88 no: ACPI OperationRegions are not marked as reserved, 89 no further checks are performed. 90 91 acpi_force_table_verification [HW,ACPI] 92 Enable table checksum verification during early stage. 93 By default, this is disabled due to x86 early mapping 94 size limitation. 95 96 acpi_irq_balance [HW,ACPI] 97 ACPI will balance active IRQs 98 default in APIC mode 99 100 acpi_irq_nobalance [HW,ACPI] 101 ACPI will not move active IRQs (default) 102 default in PIC mode 103 104 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 105 Format: <irq>,<irq>... 106 107 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 108 use by PCI 109 Format: <irq>,<irq>... 110 111 acpi_mask_gpe= [HW,ACPI] 112 Due to the existence of _Lxx/_Exx, some GPEs triggered 113 by unsupported hardware/firmware features can result in 114 GPE floodings that cannot be automatically disabled by 115 the GPE dispatcher. 116 This facility can be used to prevent such uncontrolled 117 GPE floodings. 118 Format: <byte> 119 120 acpi_no_auto_serialize [HW,ACPI] 121 Disable auto-serialization of AML methods 122 AML control methods that contain the opcodes to create 123 named objects will be marked as "Serialized" by the 124 auto-serialization feature. 125 This feature is enabled by default. 126 This option allows to turn off the feature. 127 128 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 129 kernels. 130 131 acpi_no_static_ssdt [HW,ACPI] 132 Disable installation of static SSDTs at early boot time 133 By default, SSDTs contained in the RSDT/XSDT will be 134 installed automatically and they will appear under 135 /sys/firmware/acpi/tables. 136 This option turns off this feature. 137 Note that specifying this option does not affect 138 dynamic table installation which will install SSDT 139 tables to /sys/firmware/acpi/tables/dynamic. 140 141 acpi_no_watchdog [HW,ACPI,WDT] 142 Ignore the ACPI-based watchdog interface (WDAT) and let 143 a native driver control the watchdog device instead. 144 145 acpi_rsdp= [ACPI,EFI,KEXEC] 146 Pass the RSDP address to the kernel, mostly used 147 on machines running EFI runtime service to boot the 148 second kernel for kdump. 149 150 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 151 Format: To spoof as Windows 98: ="Microsoft Windows" 152 153 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 154 of 2 which is mandated by ACPI 6) as the supported ACPI 155 specification revision (when using this switch, it may 156 be necessary to carry out a cold reboot _twice_ in a 157 row to make it take effect on the platform firmware). 158 159 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 160 acpi_osi="string1" # add string1 161 acpi_osi="!string2" # remove string2 162 acpi_osi=!* # remove all strings 163 acpi_osi=! # disable all built-in OS vendor 164 strings 165 acpi_osi=!! # enable all built-in OS vendor 166 strings 167 acpi_osi= # disable all strings 168 169 'acpi_osi=!' can be used in combination with single or 170 multiple 'acpi_osi="string1"' to support specific OS 171 vendor string(s). Note that such command can only 172 affect the default state of the OS vendor strings, thus 173 it cannot affect the default state of the feature group 174 strings and the current state of the OS vendor strings, 175 specifying it multiple times through kernel command line 176 is meaningless. This command is useful when one do not 177 care about the state of the feature group strings which 178 should be controlled by the OSPM. 179 Examples: 180 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 181 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 182 can make '_OSI("Windows 2000")' TRUE. 183 184 'acpi_osi=' cannot be used in combination with other 185 'acpi_osi=' command lines, the _OSI method will not 186 exist in the ACPI namespace. NOTE that such command can 187 only affect the _OSI support state, thus specifying it 188 multiple times through kernel command line is also 189 meaningless. 190 Examples: 191 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 192 FALSE. 193 194 'acpi_osi=!*' can be used in combination with single or 195 multiple 'acpi_osi="string1"' to support specific 196 string(s). Note that such command can affect the 197 current state of both the OS vendor strings and the 198 feature group strings, thus specifying it multiple times 199 through kernel command line is meaningful. But it may 200 still not able to affect the final state of a string if 201 there are quirks related to this string. This command 202 is useful when one want to control the state of the 203 feature group strings to debug BIOS issues related to 204 the OSPM features. 205 Examples: 206 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 207 '_OSI("Module Device")' FALSE. 208 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 209 '_OSI("Module Device")' TRUE. 210 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 211 equivalent to 212 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 213 and 214 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 215 they all will make '_OSI("Windows 2000")' TRUE. 216 217 acpi_pm_good [X86] 218 Override the pmtimer bug detection: force the kernel 219 to assume that this machine's pmtimer latches its value 220 and always returns good values. 221 222 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 223 Format: { level | edge | high | low } 224 225 acpi_skip_timer_override [HW,ACPI] 226 Recognize and ignore IRQ0/pin2 Interrupt Override. 227 For broken nForce2 BIOS resulting in XT-PIC timer. 228 229 acpi_sleep= [HW,ACPI] Sleep options 230 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 231 old_ordering, nonvs, sci_force_enable, nobl } 232 See Documentation/power/video.rst for information on 233 s3_bios and s3_mode. 234 s3_beep is for debugging; it makes the PC's speaker beep 235 as soon as the kernel's real-mode entry point is called. 236 s4_nohwsig prevents ACPI hardware signature from being 237 used during resume from hibernation. 238 old_ordering causes the ACPI 1.0 ordering of the _PTS 239 control method, with respect to putting devices into 240 low power states, to be enforced (the ACPI 2.0 ordering 241 of _PTS is used by default). 242 nonvs prevents the kernel from saving/restoring the 243 ACPI NVS memory during suspend/hibernation and resume. 244 sci_force_enable causes the kernel to set SCI_EN directly 245 on resume from S1/S3 (which is against the ACPI spec, 246 but some broken systems don't work without it). 247 nobl causes the internal blacklist of systems known to 248 behave incorrectly in some ways with respect to system 249 suspend and resume to be ignored (use wisely). 250 251 acpi_use_timer_override [HW,ACPI] 252 Use timer override. For some broken Nvidia NF5 boards 253 that require a timer override, but don't have HPET 254 255 add_efi_memmap [EFI; X86] Include EFI memory map in 256 kernel's map of available physical RAM. 257 258 agp= [AGP] 259 { off | try_unsupported } 260 off: disable AGP support 261 try_unsupported: try to drive unsupported chipsets 262 (may crash computer or cause data corruption) 263 264 ALSA [HW,ALSA] 265 See Documentation/sound/alsa-configuration.rst 266 267 alignment= [KNL,ARM] 268 Allow the default userspace alignment fault handler 269 behaviour to be specified. Bit 0 enables warnings, 270 bit 1 enables fixups, and bit 2 sends a segfault. 271 272 align_va_addr= [X86-64] 273 Align virtual addresses by clearing slice [14:12] when 274 allocating a VMA at process creation time. This option 275 gives you up to 3% performance improvement on AMD F15h 276 machines (where it is enabled by default) for a 277 CPU-intensive style benchmark, and it can vary highly in 278 a microbenchmark depending on workload and compiler. 279 280 32: only for 32-bit processes 281 64: only for 64-bit processes 282 on: enable for both 32- and 64-bit processes 283 off: disable for both 32- and 64-bit processes 284 285 alloc_snapshot [FTRACE] 286 Allocate the ftrace snapshot buffer on boot up when the 287 main buffer is allocated. This is handy if debugging 288 and you need to use tracing_snapshot() on boot up, and 289 do not want to use tracing_snapshot_alloc() as it needs 290 to be done where GFP_KERNEL allocations are allowed. 291 292 amd_iommu= [HW,X86-64] 293 Pass parameters to the AMD IOMMU driver in the system. 294 Possible values are: 295 fullflush - enable flushing of IO/TLB entries when 296 they are unmapped. Otherwise they are 297 flushed before they will be reused, which 298 is a lot of faster 299 off - do not initialize any AMD IOMMU found in 300 the system 301 force_isolation - Force device isolation for all 302 devices. The IOMMU driver is not 303 allowed anymore to lift isolation 304 requirements as needed. This option 305 does not override iommu=pt 306 307 amd_iommu_dump= [HW,X86-64] 308 Enable AMD IOMMU driver option to dump the ACPI table 309 for AMD IOMMU. With this option enabled, AMD IOMMU 310 driver will print ACPI tables for AMD IOMMU during 311 IOMMU initialization. 312 313 amd_iommu_intr= [HW,X86-64] 314 Specifies one of the following AMD IOMMU interrupt 315 remapping modes: 316 legacy - Use legacy interrupt remapping mode. 317 vapic - Use virtual APIC mode, which allows IOMMU 318 to inject interrupts directly into guest. 319 This mode requires kvm-amd.avic=1. 320 (Default when IOMMU HW support is present.) 321 322 amijoy.map= [HW,JOY] Amiga joystick support 323 Map of devices attached to JOY0DAT and JOY1DAT 324 Format: <a>,<b> 325 See also Documentation/input/joydev/joystick.rst 326 327 analog.map= [HW,JOY] Analog joystick and gamepad support 328 Specifies type or capabilities of an analog joystick 329 connected to one of 16 gameports 330 Format: <type1>,<type2>,..<type16> 331 332 apc= [HW,SPARC] 333 Power management functions (SPARCstation-4/5 + deriv.) 334 Format: noidle 335 Disable APC CPU standby support. SPARCstation-Fox does 336 not play well with APC CPU idle - disable it if you have 337 APC and your system crashes randomly. 338 339 apic= [APIC,X86] Advanced Programmable Interrupt Controller 340 Change the output verbosity while booting 341 Format: { quiet (default) | verbose | debug } 342 Change the amount of debugging information output 343 when initialising the APIC and IO-APIC components. 344 For X86-32, this can also be used to specify an APIC 345 driver name. 346 Format: apic=driver_name 347 Examples: apic=bigsmp 348 349 apic_extnmi= [APIC,X86] External NMI delivery setting 350 Format: { bsp (default) | all | none } 351 bsp: External NMI is delivered only to CPU 0 352 all: External NMIs are broadcast to all CPUs as a 353 backup of CPU 0 354 none: External NMI is masked for all CPUs. This is 355 useful so that a dump capture kernel won't be 356 shot down by NMI 357 358 autoconf= [IPV6] 359 See Documentation/networking/ipv6.rst. 360 361 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 362 Limit apic dumping. The parameter defines the maximal 363 number of local apics being dumped. Also it is possible 364 to set it to "all" by meaning -- no limit here. 365 Format: { 1 (default) | 2 | ... | all }. 366 The parameter valid if only apic=debug or 367 apic=verbose is specified. 368 Example: apic=debug show_lapic=all 369 370 apm= [APM] Advanced Power Management 371 See header of arch/x86/kernel/apm_32.c. 372 373 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 374 Format: <io>,<irq>,<nodeID> 375 376 ataflop= [HW,M68k] 377 378 atarimouse= [HW,MOUSE] Atari Mouse 379 380 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 381 EzKey and similar keyboards 382 383 atkbd.reset= [HW] Reset keyboard during initialization 384 385 atkbd.set= [HW] Select keyboard code set 386 Format: <int> (2 = AT (default), 3 = PS/2) 387 388 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 389 keyboards 390 391 atkbd.softraw= [HW] Choose between synthetic and real raw mode 392 Format: <bool> (0 = real, 1 = synthetic (default)) 393 394 atkbd.softrepeat= [HW] 395 Use software keyboard repeat 396 397 audit= [KNL] Enable the audit sub-system 398 Format: { "0" | "1" | "off" | "on" } 399 0 | off - kernel audit is disabled and can not be 400 enabled until the next reboot 401 unset - kernel audit is initialized but disabled and 402 will be fully enabled by the userspace auditd. 403 1 | on - kernel audit is initialized and partially 404 enabled, storing at most audit_backlog_limit 405 messages in RAM until it is fully enabled by the 406 userspace auditd. 407 Default: unset 408 409 audit_backlog_limit= [KNL] Set the audit queue size limit. 410 Format: <int> (must be >=0) 411 Default: 64 412 413 bau= [X86_UV] Enable the BAU on SGI UV. The default 414 behavior is to disable the BAU (i.e. bau=0). 415 Format: { "0" | "1" } 416 0 - Disable the BAU. 417 1 - Enable the BAU. 418 unset - Disable the BAU. 419 420 baycom_epp= [HW,AX25] 421 Format: <io>,<mode> 422 423 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 424 Format: <io>,<mode> 425 See header of drivers/net/hamradio/baycom_par.c. 426 427 baycom_ser_fdx= [HW,AX25] 428 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 429 Format: <io>,<irq>,<mode>[,<baud>] 430 See header of drivers/net/hamradio/baycom_ser_fdx.c. 431 432 baycom_ser_hdx= [HW,AX25] 433 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 434 Format: <io>,<irq>,<mode> 435 See header of drivers/net/hamradio/baycom_ser_hdx.c. 436 437 blkdevparts= Manual partition parsing of block device(s) for 438 embedded devices based on command line input. 439 See Documentation/block/cmdline-partition.rst 440 441 boot_delay= Milliseconds to delay each printk during boot. 442 Values larger than 10 seconds (10000) are changed to 443 no delay (0). 444 Format: integer 445 446 bootconfig [KNL] 447 Extended command line options can be added to an initrd 448 and this will cause the kernel to look for it. 449 450 See Documentation/admin-guide/bootconfig.rst 451 452 bert_disable [ACPI] 453 Disable BERT OS support on buggy BIOSes. 454 455 bgrt_disable [ACPI][X86] 456 Disable BGRT to avoid flickering OEM logo. 457 458 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 459 bttv.radio= Most important insmod options are available as 460 kernel args too. 461 bttv.pll= See Documentation/admin-guide/media/bttv.rst 462 bttv.tuner= 463 464 bulk_remove=off [PPC] This parameter disables the use of the pSeries 465 firmware feature for flushing multiple hpte entries 466 at a time. 467 468 c101= [NET] Moxa C101 synchronous serial card 469 470 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 471 Sometimes CPU hardware bugs make them report the cache 472 size incorrectly. The kernel will attempt work arounds 473 to fix known problems, but for some CPUs it is not 474 possible to determine what the correct size should be. 475 This option provides an override for these situations. 476 477 carrier_timeout= 478 [NET] Specifies amount of time (in seconds) that 479 the kernel should wait for a network carrier. By default 480 it waits 120 seconds. 481 482 ca_keys= [KEYS] This parameter identifies a specific key(s) on 483 the system trusted keyring to be used for certificate 484 trust validation. 485 format: { id:<keyid> | builtin } 486 487 cca= [MIPS] Override the kernel pages' cache coherency 488 algorithm. Accepted values range from 0 to 7 489 inclusive. See arch/mips/include/asm/pgtable-bits.h 490 for platform specific values (SB1, Loongson3 and 491 others). 492 493 ccw_timeout_log [S390] 494 See Documentation/s390/common_io.rst for details. 495 496 cgroup_disable= [KNL] Disable a particular controller 497 Format: {name of the controller(s) to disable} 498 The effects of cgroup_disable=foo are: 499 - foo isn't auto-mounted if you mount all cgroups in 500 a single hierarchy 501 - foo isn't visible as an individually mountable 502 subsystem 503 {Currently only "memory" controller deal with this and 504 cut the overhead, others just disable the usage. So 505 only cgroup_disable=memory is actually worthy} 506 507 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 508 Format: { { controller | "all" | "named" } 509 [,{ controller | "all" | "named" }...] } 510 Like cgroup_disable, but only applies to cgroup v1; 511 the blacklisted controllers remain available in cgroup2. 512 "all" blacklists all controllers and "named" disables 513 named mounts. Specifying both "all" and "named" disables 514 all v1 hierarchies. 515 516 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 517 Format: <string> 518 nosocket -- Disable socket memory accounting. 519 nokmem -- Disable kernel memory accounting. 520 521 checkreqprot [SELINUX] Set initial checkreqprot flag value. 522 Format: { "0" | "1" } 523 See security/selinux/Kconfig help text. 524 0 -- check protection applied by kernel (includes 525 any implied execute protection). 526 1 -- check protection requested by application. 527 Default value is set via a kernel config option. 528 Value can be changed at runtime via 529 /sys/fs/selinux/checkreqprot. 530 Setting checkreqprot to 1 is deprecated. 531 532 cio_ignore= [S390] 533 See Documentation/s390/common_io.rst for details. 534 clk_ignore_unused 535 [CLK] 536 Prevents the clock framework from automatically gating 537 clocks that have not been explicitly enabled by a Linux 538 device driver but are enabled in hardware at reset or 539 by the bootloader/firmware. Note that this does not 540 force such clocks to be always-on nor does it reserve 541 those clocks in any way. This parameter is useful for 542 debug and development, but should not be needed on a 543 platform with proper driver support. For more 544 information, see Documentation/driver-api/clk.rst. 545 546 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 547 [Deprecated] 548 Forces specified clocksource (if available) to be used 549 when calculating gettimeofday(). If specified 550 clocksource is not available, it defaults to PIT. 551 Format: { pit | tsc | cyclone | pmtmr } 552 553 clocksource= Override the default clocksource 554 Format: <string> 555 Override the default clocksource and use the clocksource 556 with the name specified. 557 Some clocksource names to choose from, depending on 558 the platform: 559 [all] jiffies (this is the base, fallback clocksource) 560 [ACPI] acpi_pm 561 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 562 pxa_timer,timer3,32k_counter,timer0_1 563 [X86-32] pit,hpet,tsc; 564 scx200_hrt on Geode; cyclone on IBM x440 565 [MIPS] MIPS 566 [PARISC] cr16 567 [S390] tod 568 [SH] SuperH 569 [SPARC64] tick 570 [X86-64] hpet,tsc 571 572 clocksource.arm_arch_timer.evtstrm= 573 [ARM,ARM64] 574 Format: <bool> 575 Enable/disable the eventstream feature of the ARM 576 architected timer so that code using WFE-based polling 577 loops can be debugged more effectively on production 578 systems. 579 580 clearcpuid=BITNUM[,BITNUM...] [X86] 581 Disable CPUID feature X for the kernel. See 582 arch/x86/include/asm/cpufeatures.h for the valid bit 583 numbers. Note the Linux specific bits are not necessarily 584 stable over kernel options, but the vendor specific 585 ones should be. 586 Also note that user programs calling CPUID directly 587 or using the feature without checking anything 588 will still see it. This just prevents it from 589 being used by the kernel or shown in /proc/cpuinfo. 590 Also note the kernel might malfunction if you disable 591 some critical bits. 592 593 cma=nn[MG]@[start[MG][-end[MG]]] 594 [KNL,CMA] 595 Sets the size of kernel global memory area for 596 contiguous memory allocations and optionally the 597 placement constraint by the physical address range of 598 memory allocations. A value of 0 disables CMA 599 altogether. For more information, see 600 kernel/dma/contiguous.c 601 602 cma_pernuma=nn[MG] 603 [ARM64,KNL] 604 Sets the size of kernel per-numa memory area for 605 contiguous memory allocations. A value of 0 disables 606 per-numa CMA altogether. And If this option is not 607 specificed, the default value is 0. 608 With per-numa CMA enabled, DMA users on node nid will 609 first try to allocate buffer from the pernuma area 610 which is located in node nid, if the allocation fails, 611 they will fallback to the global default memory area. 612 613 cmo_free_hint= [PPC] Format: { yes | no } 614 Specify whether pages are marked as being inactive 615 when they are freed. This is used in CMO environments 616 to determine OS memory pressure for page stealing by 617 a hypervisor. 618 Default: yes 619 620 coherent_pool=nn[KMG] [ARM,KNL] 621 Sets the size of memory pool for coherent, atomic dma 622 allocations, by default set to 256K. 623 624 com20020= [HW,NET] ARCnet - COM20020 chipset 625 Format: 626 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 627 628 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 629 Format: <io>[,<irq>] 630 631 com90xx= [HW,NET] 632 ARCnet - COM90xx chipset (memory-mapped buffers) 633 Format: <io>[,<irq>[,<memstart>]] 634 635 condev= [HW,S390] console device 636 conmode= 637 638 console= [KNL] Output console device and options. 639 640 tty<n> Use the virtual console device <n>. 641 642 ttyS<n>[,options] 643 ttyUSB0[,options] 644 Use the specified serial port. The options are of 645 the form "bbbbpnf", where "bbbb" is the baud rate, 646 "p" is parity ("n", "o", or "e"), "n" is number of 647 bits, and "f" is flow control ("r" for RTS or 648 omit it). Default is "9600n8". 649 650 See Documentation/admin-guide/serial-console.rst for more 651 information. See 652 Documentation/networking/netconsole.rst for an 653 alternative. 654 655 uart[8250],io,<addr>[,options] 656 uart[8250],mmio,<addr>[,options] 657 uart[8250],mmio16,<addr>[,options] 658 uart[8250],mmio32,<addr>[,options] 659 uart[8250],0x<addr>[,options] 660 Start an early, polled-mode console on the 8250/16550 661 UART at the specified I/O port or MMIO address, 662 switching to the matching ttyS device later. 663 MMIO inter-register address stride is either 8-bit 664 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 665 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 666 to be equivalent to 'mmio'. 'options' are specified in 667 the same format described for ttyS above; if unspecified, 668 the h/w is not re-initialized. 669 670 hvc<n> Use the hypervisor console device <n>. This is for 671 both Xen and PowerPC hypervisors. 672 673 If the device connected to the port is not a TTY but a braille 674 device, prepend "brl," before the device type, for instance 675 console=brl,ttyS0 676 For now, only VisioBraille is supported. 677 678 console_msg_format= 679 [KNL] Change console messages format 680 default 681 By default we print messages on consoles in 682 "[time stamp] text\n" format (time stamp may not be 683 printed, depending on CONFIG_PRINTK_TIME or 684 `printk_time' param). 685 syslog 686 Switch to syslog format: "<%u>[time stamp] text\n" 687 IOW, each message will have a facility and loglevel 688 prefix. The format is similar to one used by syslog() 689 syscall, or to executing "dmesg -S --raw" or to reading 690 from /proc/kmsg. 691 692 consoleblank= [KNL] The console blank (screen saver) timeout in 693 seconds. A value of 0 disables the blank timer. 694 Defaults to 0. 695 696 coredump_filter= 697 [KNL] Change the default value for 698 /proc/<pid>/coredump_filter. 699 See also Documentation/filesystems/proc.rst. 700 701 coresight_cpu_debug.enable 702 [ARM,ARM64] 703 Format: <bool> 704 Enable/disable the CPU sampling based debugging. 705 0: default value, disable debugging 706 1: enable debugging at boot time 707 708 cpuidle.off=1 [CPU_IDLE] 709 disable the cpuidle sub-system 710 711 cpuidle.governor= 712 [CPU_IDLE] Name of the cpuidle governor to use. 713 714 cpufreq.off=1 [CPU_FREQ] 715 disable the cpufreq sub-system 716 717 cpufreq.default_governor= 718 [CPU_FREQ] Name of the default cpufreq governor or 719 policy to use. This governor must be registered in the 720 kernel before the cpufreq driver probes. 721 722 cpu_init_udelay=N 723 [X86] Delay for N microsec between assert and de-assert 724 of APIC INIT to start processors. This delay occurs 725 on every CPU online, such as boot, and resume from suspend. 726 Default: 10000 727 728 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 729 Format: 730 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 731 732 crashkernel=size[KMG][@offset[KMG]] 733 [KNL] Using kexec, Linux can switch to a 'crash kernel' 734 upon panic. This parameter reserves the physical 735 memory region [offset, offset + size] for that kernel 736 image. If '@offset' is omitted, then a suitable offset 737 is selected automatically. 738 [KNL, X86-64] Select a region under 4G first, and 739 fall back to reserve region above 4G when '@offset' 740 hasn't been specified. 741 See Documentation/admin-guide/kdump/kdump.rst for further details. 742 743 crashkernel=range1:size1[,range2:size2,...][@offset] 744 [KNL] Same as above, but depends on the memory 745 in the running system. The syntax of range is 746 start-[end] where start and end are both 747 a memory unit (amount[KMG]). See also 748 Documentation/admin-guide/kdump/kdump.rst for an example. 749 750 crashkernel=size[KMG],high 751 [KNL, X86-64] range could be above 4G. Allow kernel 752 to allocate physical memory region from top, so could 753 be above 4G if system have more than 4G ram installed. 754 Otherwise memory region will be allocated below 4G, if 755 available. 756 It will be ignored if crashkernel=X is specified. 757 crashkernel=size[KMG],low 758 [KNL, X86-64] range under 4G. When crashkernel=X,high 759 is passed, kernel could allocate physical memory region 760 above 4G, that cause second kernel crash on system 761 that require some amount of low memory, e.g. swiotlb 762 requires at least 64M+32K low memory, also enough extra 763 low memory is needed to make sure DMA buffers for 32-bit 764 devices won't run out. Kernel would try to allocate at 765 at least 256M below 4G automatically. 766 This one let user to specify own low range under 4G 767 for second kernel instead. 768 0: to disable low allocation. 769 It will be ignored when crashkernel=X,high is not used 770 or memory reserved is below 4G. 771 772 cryptomgr.notests 773 [KNL] Disable crypto self-tests 774 775 cs89x0_dma= [HW,NET] 776 Format: <dma> 777 778 cs89x0_media= [HW,NET] 779 Format: { rj45 | aui | bnc } 780 781 dasd= [HW,NET] 782 See header of drivers/s390/block/dasd_devmap.c. 783 784 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 785 (one device per port) 786 Format: <port#>,<type> 787 See also Documentation/input/devices/joystick-parport.rst 788 789 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 790 time. See 791 Documentation/admin-guide/dynamic-debug-howto.rst for 792 details. Deprecated, see dyndbg. 793 794 debug [KNL] Enable kernel debugging (events log level). 795 796 debug_boot_weak_hash 797 [KNL] Enable printing [hashed] pointers early in the 798 boot sequence. If enabled, we use a weak hash instead 799 of siphash to hash pointers. Use this option if you are 800 seeing instances of '(___ptrval___)') and need to see a 801 value (hashed pointer) instead. Cryptographically 802 insecure, please do not use on production kernels. 803 804 debug_locks_verbose= 805 [KNL] verbose self-tests 806 Format=<0|1> 807 Print debugging info while doing the locking API 808 self-tests. 809 We default to 0 (no extra messages), setting it to 810 1 will print _a lot_ more information - normally 811 only useful to kernel developers. 812 813 debug_objects [KNL] Enable object debugging 814 815 no_debug_objects 816 [KNL] Disable object debugging 817 818 debug_guardpage_minorder= 819 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 820 parameter allows control of the order of pages that will 821 be intentionally kept free (and hence protected) by the 822 buddy allocator. Bigger value increase the probability 823 of catching random memory corruption, but reduce the 824 amount of memory for normal system use. The maximum 825 possible value is MAX_ORDER/2. Setting this parameter 826 to 1 or 2 should be enough to identify most random 827 memory corruption problems caused by bugs in kernel or 828 driver code when a CPU writes to (or reads from) a 829 random memory location. Note that there exists a class 830 of memory corruptions problems caused by buggy H/W or 831 F/W or by drivers badly programing DMA (basically when 832 memory is written at bus level and the CPU MMU is 833 bypassed) which are not detectable by 834 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 835 tracking down these problems. 836 837 debug_pagealloc= 838 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 839 enables the feature at boot time. By default, it is 840 disabled and the system will work mostly the same as a 841 kernel built without CONFIG_DEBUG_PAGEALLOC. 842 Note: to get most of debug_pagealloc error reports, it's 843 useful to also enable the page_owner functionality. 844 on: enable the feature 845 846 debugfs= [KNL] This parameter enables what is exposed to userspace 847 and debugfs internal clients. 848 Format: { on, no-mount, off } 849 on: All functions are enabled. 850 no-mount: 851 Filesystem is not registered but kernel clients can 852 access APIs and a crashkernel can be used to read 853 its content. There is nothing to mount. 854 off: Filesystem is not registered and clients 855 get a -EPERM as result when trying to register files 856 or directories within debugfs. 857 This is equivalent of the runtime functionality if 858 debugfs was not enabled in the kernel at all. 859 Default value is set in build-time with a kernel configuration. 860 861 debugpat [X86] Enable PAT debugging 862 863 decnet.addr= [HW,NET] 864 Format: <area>[,<node>] 865 See also Documentation/networking/decnet.rst. 866 867 default_hugepagesz= 868 [HW] The size of the default HugeTLB page. This is 869 the size represented by the legacy /proc/ hugepages 870 APIs. In addition, this is the default hugetlb size 871 used for shmget(), mmap() and mounting hugetlbfs 872 filesystems. If not specified, defaults to the 873 architecture's default huge page size. Huge page 874 sizes are architecture dependent. See also 875 Documentation/admin-guide/mm/hugetlbpage.rst. 876 Format: size[KMG] 877 878 deferred_probe_timeout= 879 [KNL] Debugging option to set a timeout in seconds for 880 deferred probe to give up waiting on dependencies to 881 probe. Only specific dependencies (subsystems or 882 drivers) that have opted in will be ignored. A timeout of 0 883 will timeout at the end of initcalls. This option will also 884 dump out devices still on the deferred probe list after 885 retrying. 886 887 dfltcc= [HW,S390] 888 Format: { on | off | def_only | inf_only | always } 889 on: s390 zlib hardware support for compression on 890 level 1 and decompression (default) 891 off: No s390 zlib hardware support 892 def_only: s390 zlib hardware support for deflate 893 only (compression on level 1) 894 inf_only: s390 zlib hardware support for inflate 895 only (decompression) 896 always: Same as 'on' but ignores the selected compression 897 level always using hardware support (used for debugging) 898 899 dhash_entries= [KNL] 900 Set number of hash buckets for dentry cache. 901 902 disable_1tb_segments [PPC] 903 Disables the use of 1TB hash page table segments. This 904 causes the kernel to fall back to 256MB segments which 905 can be useful when debugging issues that require an SLB 906 miss to occur. 907 908 stress_slb [PPC] 909 Limits the number of kernel SLB entries, and flushes 910 them frequently to increase the rate of SLB faults 911 on kernel addresses. 912 913 disable= [IPV6] 914 See Documentation/networking/ipv6.rst. 915 916 hardened_usercopy= 917 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 918 hardening is enabled for this boot. Hardened 919 usercopy checking is used to protect the kernel 920 from reading or writing beyond known memory 921 allocation boundaries as a proactive defense 922 against bounds-checking flaws in the kernel's 923 copy_to_user()/copy_from_user() interface. 924 on Perform hardened usercopy checks (default). 925 off Disable hardened usercopy checks. 926 927 disable_radix [PPC] 928 Disable RADIX MMU mode on POWER9 929 930 radix_hcall_invalidate=on [PPC/PSERIES] 931 Disable RADIX GTSE feature and use hcall for TLB 932 invalidate. 933 934 disable_tlbie [PPC] 935 Disable TLBIE instruction. Currently does not work 936 with KVM, with HASH MMU, or with coherent accelerators. 937 938 disable_cpu_apicid= [X86,APIC,SMP] 939 Format: <int> 940 The number of initial APIC ID for the 941 corresponding CPU to be disabled at boot, 942 mostly used for the kdump 2nd kernel to 943 disable BSP to wake up multiple CPUs without 944 causing system reset or hang due to sending 945 INIT from AP to BSP. 946 947 perf_v4_pmi= [X86,INTEL] 948 Format: <bool> 949 Disable Intel PMU counter freezing feature. 950 The feature only exists starting from 951 Arch Perfmon v4 (Skylake and newer). 952 953 disable_ddw [PPC/PSERIES] 954 Disable Dynamic DMA Window support. Use this 955 to workaround buggy firmware. 956 957 disable_ipv6= [IPV6] 958 See Documentation/networking/ipv6.rst. 959 960 disable_mtrr_cleanup [X86] 961 The kernel tries to adjust MTRR layout from continuous 962 to discrete, to make X server driver able to add WB 963 entry later. This parameter disables that. 964 965 disable_mtrr_trim [X86, Intel and AMD only] 966 By default the kernel will trim any uncacheable 967 memory out of your available memory pool based on 968 MTRR settings. This parameter disables that behavior, 969 possibly causing your machine to run very slowly. 970 971 disable_timer_pin_1 [X86] 972 Disable PIN 1 of APIC timer 973 Can be useful to work around chipset bugs. 974 975 dis_ucode_ldr [X86] Disable the microcode loader. 976 977 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 978 this option disables the debugging code at boot. 979 980 dma_debug_entries=<number> 981 This option allows to tune the number of preallocated 982 entries for DMA-API debugging code. One entry is 983 required per DMA-API allocation. Use this if the 984 DMA-API debugging code disables itself because the 985 architectural default is too low. 986 987 dma_debug_driver=<driver_name> 988 With this option the DMA-API debugging driver 989 filter feature can be enabled at boot time. Just 990 pass the driver to filter for as the parameter. 991 The filter can be disabled or changed to another 992 driver later using sysfs. 993 994 driver_async_probe= [KNL] 995 List of driver names to be probed asynchronously. 996 Format: <driver_name1>,<driver_name2>... 997 998 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 999 Broken monitors, graphic adapters, KVMs and EDIDless 1000 panels may send no or incorrect EDID data sets. 1001 This parameter allows to specify an EDID data sets 1002 in the /lib/firmware directory that are used instead. 1003 Generic built-in EDID data sets are used, if one of 1004 edid/1024x768.bin, edid/1280x1024.bin, 1005 edid/1680x1050.bin, or edid/1920x1080.bin is given 1006 and no file with the same name exists. Details and 1007 instructions how to build your own EDID data are 1008 available in Documentation/admin-guide/edid.rst. An EDID 1009 data set will only be used for a particular connector, 1010 if its name and a colon are prepended to the EDID 1011 name. Each connector may use a unique EDID data 1012 set by separating the files with a comma. An EDID 1013 data set with no connector name will be used for 1014 any connectors not explicitly specified. 1015 1016 dscc4.setup= [NET] 1017 1018 dt_cpu_ftrs= [PPC] 1019 Format: {"off" | "known"} 1020 Control how the dt_cpu_ftrs device-tree binding is 1021 used for CPU feature discovery and setup (if it 1022 exists). 1023 off: Do not use it, fall back to legacy cpu table. 1024 known: Do not pass through unknown features to guests 1025 or userspace, only those that the kernel is aware of. 1026 1027 dump_apple_properties [X86] 1028 Dump name and content of EFI device properties on 1029 x86 Macs. Useful for driver authors to determine 1030 what data is available or for reverse-engineering. 1031 1032 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 1033 <module>.dyndbg[="val"] 1034 Enable debug messages at boot time. See 1035 Documentation/admin-guide/dynamic-debug-howto.rst 1036 for details. 1037 1038 nopku [X86] Disable Memory Protection Keys CPU feature found 1039 in some Intel CPUs. 1040 1041 <module>.async_probe [KNL] 1042 Enable asynchronous probe on this module. 1043 1044 early_ioremap_debug [KNL] 1045 Enable debug messages in early_ioremap support. This 1046 is useful for tracking down temporary early mappings 1047 which are not unmapped. 1048 1049 earlycon= [KNL] Output early console device and options. 1050 1051 When used with no options, the early console is 1052 determined by stdout-path property in device tree's 1053 chosen node or the ACPI SPCR table if supported by 1054 the platform. 1055 1056 cdns,<addr>[,options] 1057 Start an early, polled-mode console on a Cadence 1058 (xuartps) serial port at the specified address. Only 1059 supported option is baud rate. If baud rate is not 1060 specified, the serial port must already be setup and 1061 configured. 1062 1063 uart[8250],io,<addr>[,options] 1064 uart[8250],mmio,<addr>[,options] 1065 uart[8250],mmio32,<addr>[,options] 1066 uart[8250],mmio32be,<addr>[,options] 1067 uart[8250],0x<addr>[,options] 1068 Start an early, polled-mode console on the 8250/16550 1069 UART at the specified I/O port or MMIO address. 1070 MMIO inter-register address stride is either 8-bit 1071 (mmio) or 32-bit (mmio32 or mmio32be). 1072 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1073 to be equivalent to 'mmio'. 'options' are specified 1074 in the same format described for "console=ttyS<n>"; if 1075 unspecified, the h/w is not initialized. 1076 1077 pl011,<addr> 1078 pl011,mmio32,<addr> 1079 Start an early, polled-mode console on a pl011 serial 1080 port at the specified address. The pl011 serial port 1081 must already be setup and configured. Options are not 1082 yet supported. If 'mmio32' is specified, then only 1083 the driver will use only 32-bit accessors to read/write 1084 the device registers. 1085 1086 meson,<addr> 1087 Start an early, polled-mode console on a meson serial 1088 port at the specified address. The serial port must 1089 already be setup and configured. Options are not yet 1090 supported. 1091 1092 msm_serial,<addr> 1093 Start an early, polled-mode console on an msm serial 1094 port at the specified address. The serial port 1095 must already be setup and configured. Options are not 1096 yet supported. 1097 1098 msm_serial_dm,<addr> 1099 Start an early, polled-mode console on an msm serial 1100 dm port at the specified address. The serial port 1101 must already be setup and configured. Options are not 1102 yet supported. 1103 1104 owl,<addr> 1105 Start an early, polled-mode console on a serial port 1106 of an Actions Semi SoC, such as S500 or S900, at the 1107 specified address. The serial port must already be 1108 setup and configured. Options are not yet supported. 1109 1110 rda,<addr> 1111 Start an early, polled-mode console on a serial port 1112 of an RDA Micro SoC, such as RDA8810PL, at the 1113 specified address. The serial port must already be 1114 setup and configured. Options are not yet supported. 1115 1116 sbi 1117 Use RISC-V SBI (Supervisor Binary Interface) for early 1118 console. 1119 1120 smh Use ARM semihosting calls for early console. 1121 1122 s3c2410,<addr> 1123 s3c2412,<addr> 1124 s3c2440,<addr> 1125 s3c6400,<addr> 1126 s5pv210,<addr> 1127 exynos4210,<addr> 1128 Use early console provided by serial driver available 1129 on Samsung SoCs, requires selecting proper type and 1130 a correct base address of the selected UART port. The 1131 serial port must already be setup and configured. 1132 Options are not yet supported. 1133 1134 lantiq,<addr> 1135 Start an early, polled-mode console on a lantiq serial 1136 (lqasc) port at the specified address. The serial port 1137 must already be setup and configured. Options are not 1138 yet supported. 1139 1140 lpuart,<addr> 1141 lpuart32,<addr> 1142 Use early console provided by Freescale LP UART driver 1143 found on Freescale Vybrid and QorIQ LS1021A processors. 1144 A valid base address must be provided, and the serial 1145 port must already be setup and configured. 1146 1147 ec_imx21,<addr> 1148 ec_imx6q,<addr> 1149 Start an early, polled-mode, output-only console on the 1150 Freescale i.MX UART at the specified address. The UART 1151 must already be setup and configured. 1152 1153 ar3700_uart,<addr> 1154 Start an early, polled-mode console on the 1155 Armada 3700 serial port at the specified 1156 address. The serial port must already be setup 1157 and configured. Options are not yet supported. 1158 1159 qcom_geni,<addr> 1160 Start an early, polled-mode console on a Qualcomm 1161 Generic Interface (GENI) based serial port at the 1162 specified address. The serial port must already be 1163 setup and configured. Options are not yet supported. 1164 1165 efifb,[options] 1166 Start an early, unaccelerated console on the EFI 1167 memory mapped framebuffer (if available). On cache 1168 coherent non-x86 systems that use system memory for 1169 the framebuffer, pass the 'ram' option so that it is 1170 mapped with the correct attributes. 1171 1172 linflex,<addr> 1173 Use early console provided by Freescale LINFlexD UART 1174 serial driver for NXP S32V234 SoCs. A valid base 1175 address must be provided, and the serial port must 1176 already be setup and configured. 1177 1178 earlyprintk= [X86,SH,ARM,M68k,S390] 1179 earlyprintk=vga 1180 earlyprintk=sclp 1181 earlyprintk=xen 1182 earlyprintk=serial[,ttySn[,baudrate]] 1183 earlyprintk=serial[,0x...[,baudrate]] 1184 earlyprintk=ttySn[,baudrate] 1185 earlyprintk=dbgp[debugController#] 1186 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1187 earlyprintk=xdbc[xhciController#] 1188 1189 earlyprintk is useful when the kernel crashes before 1190 the normal console is initialized. It is not enabled by 1191 default because it has some cosmetic problems. 1192 1193 Append ",keep" to not disable it when the real console 1194 takes over. 1195 1196 Only one of vga, efi, serial, or usb debug port can 1197 be used at a time. 1198 1199 Currently only ttyS0 and ttyS1 may be specified by 1200 name. Other I/O ports may be explicitly specified 1201 on some architectures (x86 and arm at least) by 1202 replacing ttySn with an I/O port address, like this: 1203 earlyprintk=serial,0x1008,115200 1204 You can find the port for a given device in 1205 /proc/tty/driver/serial: 1206 2: uart:ST16650V2 port:00001008 irq:18 ... 1207 1208 Interaction with the standard serial driver is not 1209 very good. 1210 1211 The VGA and EFI output is eventually overwritten by 1212 the real console. 1213 1214 The xen output can only be used by Xen PV guests. 1215 1216 The sclp output can only be used on s390. 1217 1218 The optional "force" to "pciserial" enables use of a 1219 PCI device even when its classcode is not of the 1220 UART class. 1221 1222 edac_report= [HW,EDAC] Control how to report EDAC event 1223 Format: {"on" | "off" | "force"} 1224 on: enable EDAC to report H/W event. May be overridden 1225 by other higher priority error reporting module. 1226 off: disable H/W event reporting through EDAC. 1227 force: enforce the use of EDAC to report H/W event. 1228 default: on. 1229 1230 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1231 ekgdboc=kbd 1232 1233 This is designed to be used in conjunction with 1234 the boot argument: earlyprintk=vga 1235 1236 This parameter works in place of the kgdboc parameter 1237 but can only be used if the backing tty is available 1238 very early in the boot process. For early debugging 1239 via a serial port see kgdboc_earlycon instead. 1240 1241 edd= [EDD] 1242 Format: {"off" | "on" | "skip[mbr]"} 1243 1244 efi= [EFI] 1245 Format: { "debug", "disable_early_pci_dma", 1246 "nochunk", "noruntime", "nosoftreserve", 1247 "novamap", "no_disable_early_pci_dma" } 1248 debug: enable misc debug output. 1249 disable_early_pci_dma: disable the busmaster bit on all 1250 PCI bridges while in the EFI boot stub. 1251 nochunk: disable reading files in "chunks" in the EFI 1252 boot stub, as chunking can cause problems with some 1253 firmware implementations. 1254 noruntime : disable EFI runtime services support 1255 nosoftreserve: The EFI_MEMORY_SP (Specific Purpose) 1256 attribute may cause the kernel to reserve the 1257 memory range for a memory mapping driver to 1258 claim. Specify efi=nosoftreserve to disable this 1259 reservation and treat the memory by its base type 1260 (i.e. EFI_CONVENTIONAL_MEMORY / "System RAM"). 1261 novamap: do not call SetVirtualAddressMap(). 1262 no_disable_early_pci_dma: Leave the busmaster bit set 1263 on all PCI bridges while in the EFI boot stub 1264 1265 efi_no_storage_paranoia [EFI; X86] 1266 Using this parameter you can use more than 50% of 1267 your efi variable storage. Use this parameter only if 1268 you are really sure that your UEFI does sane gc and 1269 fulfills the spec otherwise your board may brick. 1270 1271 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1272 Add arbitrary attribute to specific memory range by 1273 updating original EFI memory map. 1274 Region of memory which aa attribute is added to is 1275 from ss to ss+nn. 1276 1277 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1278 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1279 attribute is added to range 0x100000000-0x180000000 and 1280 0x10a0000000-0x1120000000. 1281 1282 If efi_fake_mem=8G@9G:0x40000 is specified, the 1283 EFI_MEMORY_SP(0x40000) attribute is added to 1284 range 0x240000000-0x43fffffff. 1285 1286 Using this parameter you can do debugging of EFI memmap 1287 related features. For example, you can do debugging of 1288 Address Range Mirroring feature even if your box 1289 doesn't support it, or mark specific memory as 1290 "soft reserved". 1291 1292 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1293 that is to be dynamically loaded by Linux. If there are 1294 multiple variables with the same name but with different 1295 vendor GUIDs, all of them will be loaded. See 1296 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1297 1298 1299 eisa_irq_edge= [PARISC,HW] 1300 See header of drivers/parisc/eisa.c. 1301 1302 elanfreq= [X86-32] 1303 See comment before function elanfreq_setup() in 1304 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1305 1306 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1307 Specifies physical address of start of kernel core 1308 image elf header and optionally the size. Generally 1309 kexec loader will pass this option to capture kernel. 1310 See Documentation/admin-guide/kdump/kdump.rst for details. 1311 1312 enable_mtrr_cleanup [X86] 1313 The kernel tries to adjust MTRR layout from continuous 1314 to discrete, to make X server driver able to add WB 1315 entry later. This parameter enables that. 1316 1317 enable_timer_pin_1 [X86] 1318 Enable PIN 1 of APIC timer 1319 Can be useful to work around chipset bugs 1320 (in particular on some ATI chipsets). 1321 The kernel tries to set a reasonable default. 1322 1323 enforcing [SELINUX] Set initial enforcing status. 1324 Format: {"0" | "1"} 1325 See security/selinux/Kconfig help text. 1326 0 -- permissive (log only, no denials). 1327 1 -- enforcing (deny and log). 1328 Default value is 0. 1329 Value can be changed at runtime via 1330 /sys/fs/selinux/enforce. 1331 1332 erst_disable [ACPI] 1333 Disable Error Record Serialization Table (ERST) 1334 support. 1335 1336 ether= [HW,NET] Ethernet cards parameters 1337 This option is obsoleted by the "netdev=" option, which 1338 has equivalent usage. See its documentation for details. 1339 1340 evm= [EVM] 1341 Format: { "fix" } 1342 Permit 'security.evm' to be updated regardless of 1343 current integrity status. 1344 1345 failslab= 1346 fail_usercopy= 1347 fail_page_alloc= 1348 fail_make_request=[KNL] 1349 General fault injection mechanism. 1350 Format: <interval>,<probability>,<space>,<times> 1351 See also Documentation/fault-injection/. 1352 1353 fb_tunnels= [NET] 1354 Format: { initns | none } 1355 See Documentation/admin-guide/sysctl/net.rst for 1356 fb_tunnels_only_for_init_ns 1357 1358 floppy= [HW] 1359 See Documentation/admin-guide/blockdev/floppy.rst. 1360 1361 force_pal_cache_flush 1362 [IA-64] Avoid check_sal_cache_flush which may hang on 1363 buggy SAL_CACHE_FLUSH implementations. Using this 1364 parameter will force ia64_sal_cache_flush to call 1365 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1366 1367 forcepae [X86-32] 1368 Forcefully enable Physical Address Extension (PAE). 1369 Many Pentium M systems disable PAE but may have a 1370 functionally usable PAE implementation. 1371 Warning: use of this parameter will taint the kernel 1372 and may cause unknown problems. 1373 1374 ftrace=[tracer] 1375 [FTRACE] will set and start the specified tracer 1376 as early as possible in order to facilitate early 1377 boot debugging. 1378 1379 ftrace_dump_on_oops[=orig_cpu] 1380 [FTRACE] will dump the trace buffers on oops. 1381 If no parameter is passed, ftrace will dump 1382 buffers of all CPUs, but if you pass orig_cpu, it will 1383 dump only the buffer of the CPU that triggered the 1384 oops. 1385 1386 ftrace_filter=[function-list] 1387 [FTRACE] Limit the functions traced by the function 1388 tracer at boot up. function-list is a comma separated 1389 list of functions. This list can be changed at run 1390 time by the set_ftrace_filter file in the debugfs 1391 tracing directory. 1392 1393 ftrace_notrace=[function-list] 1394 [FTRACE] Do not trace the functions specified in 1395 function-list. This list can be changed at run time 1396 by the set_ftrace_notrace file in the debugfs 1397 tracing directory. 1398 1399 ftrace_graph_filter=[function-list] 1400 [FTRACE] Limit the top level callers functions traced 1401 by the function graph tracer at boot up. 1402 function-list is a comma separated list of functions 1403 that can be changed at run time by the 1404 set_graph_function file in the debugfs tracing directory. 1405 1406 ftrace_graph_notrace=[function-list] 1407 [FTRACE] Do not trace from the functions specified in 1408 function-list. This list is a comma separated list of 1409 functions that can be changed at run time by the 1410 set_graph_notrace file in the debugfs tracing directory. 1411 1412 ftrace_graph_max_depth=<uint> 1413 [FTRACE] Used with the function graph tracer. This is 1414 the max depth it will trace into a function. This value 1415 can be changed at run time by the max_graph_depth file 1416 in the tracefs tracing directory. default: 0 (no limit) 1417 1418 fw_devlink= [KNL] Create device links between consumer and supplier 1419 devices by scanning the firmware to infer the 1420 consumer/supplier relationships. This feature is 1421 especially useful when drivers are loaded as modules as 1422 it ensures proper ordering of tasks like device probing 1423 (suppliers first, then consumers), supplier boot state 1424 clean up (only after all consumers have probed), 1425 suspend/resume & runtime PM (consumers first, then 1426 suppliers). 1427 Format: { off | permissive | on | rpm } 1428 off -- Don't create device links from firmware info. 1429 permissive -- Create device links from firmware info 1430 but use it only for ordering boot state clean 1431 up (sync_state() calls). 1432 on -- Create device links from firmware info and use it 1433 to enforce probe and suspend/resume ordering. 1434 rpm -- Like "on", but also use to order runtime PM. 1435 1436 gamecon.map[2|3]= 1437 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1438 support via parallel port (up to 5 devices per port) 1439 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1440 See also Documentation/input/devices/joystick-parport.rst 1441 1442 gamma= [HW,DRM] 1443 1444 gart_fix_e820= [X86-64] disable the fix e820 for K8 GART 1445 Format: off | on 1446 default: on 1447 1448 gcov_persist= [GCOV] When non-zero (default), profiling data for 1449 kernel modules is saved and remains accessible via 1450 debugfs, even when the module is unloaded/reloaded. 1451 When zero, profiling data is discarded and associated 1452 debugfs files are removed at module unload time. 1453 1454 goldfish [X86] Enable the goldfish android emulator platform. 1455 Don't use this when you are not running on the 1456 android emulator 1457 1458 gpt [EFI] Forces disk with valid GPT signature but 1459 invalid Protective MBR to be treated as GPT. If the 1460 primary GPT is corrupted, it enables the backup/alternate 1461 GPT to be used instead. 1462 1463 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1464 the "Enable 0" bit of the configuration register. 1465 Format: 0 | 1 1466 Default: 0 1467 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1468 the "Enable 0" bit of the configuration register. 1469 Format: 0 | 1 1470 Default: 0 1471 grcan.select= [HW] Select which physical interface to use. 1472 Format: 0 | 1 1473 Default: 0 1474 grcan.txsize= [HW] Sets the size of the tx buffer. 1475 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1476 Default: 1024 1477 grcan.rxsize= [HW] Sets the size of the rx buffer. 1478 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1479 Default: 1024 1480 1481 gpio-mockup.gpio_mockup_ranges 1482 [HW] Sets the ranges of gpiochip of for this device. 1483 Format: <start1>,<end1>,<start2>,<end2>... 1484 1485 hardlockup_all_cpu_backtrace= 1486 [KNL] Should the hard-lockup detector generate 1487 backtraces on all cpus. 1488 Format: 0 | 1 1489 1490 hashdist= [KNL,NUMA] Large hashes allocated during boot 1491 are distributed across NUMA nodes. Defaults on 1492 for 64-bit NUMA, off otherwise. 1493 Format: 0 | 1 (for off | on) 1494 1495 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1496 1497 hd= [EIDE] (E)IDE hard drive subsystem geometry 1498 Format: <cyl>,<head>,<sect> 1499 1500 hest_disable [ACPI] 1501 Disable Hardware Error Source Table (HEST) support; 1502 corresponding firmware-first mode error processing 1503 logic will be disabled. 1504 1505 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1506 size of <nn>. This works even on boxes that have no 1507 highmem otherwise. This also works to reduce highmem 1508 size on bigger boxes. 1509 1510 highres= [KNL] Enable/disable high resolution timer mode. 1511 Valid parameters: "on", "off" 1512 Default: "on" 1513 1514 hlt [BUGS=ARM,SH] 1515 1516 hpet= [X86-32,HPET] option to control HPET usage 1517 Format: { enable (default) | disable | force | 1518 verbose } 1519 disable: disable HPET and use PIT instead 1520 force: allow force enabled of undocumented chips (ICH4, 1521 VIA, nVidia) 1522 verbose: show contents of HPET registers during setup 1523 1524 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1525 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1526 1527 hugetlb_cma= [HW] The size of a cma area used for allocation 1528 of gigantic hugepages. 1529 Format: nn[KMGTPE] 1530 1531 Reserve a cma area of given size and allocate gigantic 1532 hugepages using the cma allocator. If enabled, the 1533 boot-time allocation of gigantic hugepages is skipped. 1534 1535 hugepages= [HW] Number of HugeTLB pages to allocate at boot. 1536 If this follows hugepagesz (below), it specifies 1537 the number of pages of hugepagesz to be allocated. 1538 If this is the first HugeTLB parameter on the command 1539 line, it specifies the number of pages to allocate for 1540 the default huge page size. See also 1541 Documentation/admin-guide/mm/hugetlbpage.rst. 1542 Format: <integer> 1543 1544 hugepagesz= 1545 [HW] The size of the HugeTLB pages. This is used in 1546 conjunction with hugepages (above) to allocate huge 1547 pages of a specific size at boot. The pair 1548 hugepagesz=X hugepages=Y can be specified once for 1549 each supported huge page size. Huge page sizes are 1550 architecture dependent. See also 1551 Documentation/admin-guide/mm/hugetlbpage.rst. 1552 Format: size[KMG] 1553 1554 hung_task_panic= 1555 [KNL] Should the hung task detector generate panics. 1556 Format: 0 | 1 1557 1558 A value of 1 instructs the kernel to panic when a 1559 hung task is detected. The default value is controlled 1560 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1561 option. The value selected by this boot parameter can 1562 be changed later by the kernel.hung_task_panic sysctl. 1563 1564 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1565 terminal devices. Valid values: 0..8 1566 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1567 If specified, z/VM IUCV HVC accepts connections 1568 from listed z/VM user IDs only. 1569 1570 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1571 which allow the hypervisor to 'idle' the 1572 guest on lock contention. 1573 1574 keep_bootcon [KNL] 1575 Do not unregister boot console at start. This is only 1576 useful for debugging when something happens in the window 1577 between unregistering the boot console and initializing 1578 the real console. 1579 1580 i2c_bus= [HW] Override the default board specific I2C bus speed 1581 or register an additional I2C bus that is not 1582 registered from board initialization code. 1583 Format: 1584 <bus_id>,<clkrate> 1585 1586 i8042.debug [HW] Toggle i8042 debug mode 1587 i8042.unmask_kbd_data 1588 [HW] Enable printing of interrupt data from the KBD port 1589 (disabled by default, and as a pre-condition 1590 requires that i8042.debug=1 be enabled) 1591 i8042.direct [HW] Put keyboard port into non-translated mode 1592 i8042.dumbkbd [HW] Pretend that controller can only read data from 1593 keyboard and cannot control its state 1594 (Don't attempt to blink the leds) 1595 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1596 i8042.nokbd [HW] Don't check/create keyboard port 1597 i8042.noloop [HW] Disable the AUX Loopback command while probing 1598 for the AUX port 1599 i8042.nomux [HW] Don't check presence of an active multiplexing 1600 controller 1601 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1602 controllers 1603 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1604 i8042.reset [HW] Reset the controller during init, cleanup and 1605 suspend-to-ram transitions, only during s2r 1606 transitions, or never reset 1607 Format: { 1 | Y | y | 0 | N | n } 1608 1, Y, y: always reset controller 1609 0, N, n: don't ever reset controller 1610 Default: only on s2r transitions on x86; most other 1611 architectures force reset to be always executed 1612 i8042.unlock [HW] Unlock (ignore) the keylock 1613 i8042.kbdreset [HW] Reset device connected to KBD port 1614 1615 i810= [HW,DRM] 1616 1617 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1618 indicates that the driver is running on unsupported 1619 hardware. 1620 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1621 does not match list of supported models. 1622 i8k.power_status 1623 [HW] Report power status in /proc/i8k 1624 (disabled by default) 1625 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1626 capability is set. 1627 1628 i915.invert_brightness= 1629 [DRM] Invert the sense of the variable that is used to 1630 set the brightness of the panel backlight. Normally a 1631 brightness value of 0 indicates backlight switched off, 1632 and the maximum of the brightness value sets the backlight 1633 to maximum brightness. If this parameter is set to 0 1634 (default) and the machine requires it, or this parameter 1635 is set to 1, a brightness value of 0 sets the backlight 1636 to maximum brightness, and the maximum of the brightness 1637 value switches the backlight off. 1638 -1 -- never invert brightness 1639 0 -- machine default 1640 1 -- force brightness inversion 1641 1642 icn= [HW,ISDN] 1643 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1644 1645 ide-core.nodma= [HW] (E)IDE subsystem 1646 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1647 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1648 .cdrom .chs .ignore_cable are additional options 1649 See Documentation/ide/ide.rst. 1650 1651 ide-generic.probe-mask= [HW] (E)IDE subsystem 1652 Format: <int> 1653 Probe mask for legacy ISA IDE ports. Depending on 1654 platform up to 6 ports are supported, enabled by 1655 setting corresponding bits in the mask to 1. The 1656 default value is 0x0, which has a special meaning. 1657 On systems that have PCI, it triggers scanning the 1658 PCI bus for the first and the second port, which 1659 are then probed. On systems without PCI the value 1660 of 0x0 enables probing the two first ports as if it 1661 was 0x3. 1662 1663 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1664 Claim all unknown PCI IDE storage controllers. 1665 1666 idle= [X86] 1667 Format: idle=poll, idle=halt, idle=nomwait 1668 Poll forces a polling idle loop that can slightly 1669 improve the performance of waking up a idle CPU, but 1670 will use a lot of power and make the system run hot. 1671 Not recommended. 1672 idle=halt: Halt is forced to be used for CPU idle. 1673 In such case C2/C3 won't be used again. 1674 idle=nomwait: Disable mwait for CPU C-states 1675 1676 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1677 Format: { strict | legacy | 2008 | relaxed } 1678 Default: strict 1679 1680 Choose which programs will be accepted for execution 1681 based on the IEEE 754 NaN encoding(s) supported by 1682 the FPU and the NaN encoding requested with the value 1683 of an ELF file header flag individually set by each 1684 binary. Hardware implementations are permitted to 1685 support either or both of the legacy and the 2008 NaN 1686 encoding mode. 1687 1688 Available settings are as follows: 1689 strict accept binaries that request a NaN encoding 1690 supported by the FPU 1691 legacy only accept legacy-NaN binaries, if supported 1692 by the FPU 1693 2008 only accept 2008-NaN binaries, if supported 1694 by the FPU 1695 relaxed accept any binaries regardless of whether 1696 supported by the FPU 1697 1698 The FPU emulator is always able to support both NaN 1699 encodings, so if no FPU hardware is present or it has 1700 been disabled with 'nofpu', then the settings of 1701 'legacy' and '2008' strap the emulator accordingly, 1702 'relaxed' straps the emulator for both legacy-NaN and 1703 2008-NaN, whereas 'strict' enables legacy-NaN only on 1704 legacy processors and both NaN encodings on MIPS32 or 1705 MIPS64 CPUs. 1706 1707 The setting for ABS.fmt/NEG.fmt instruction execution 1708 mode generally follows that for the NaN encoding, 1709 except where unsupported by hardware. 1710 1711 ignore_loglevel [KNL] 1712 Ignore loglevel setting - this will print /all/ 1713 kernel messages to the console. Useful for debugging. 1714 We also add it as printk module parameter, so users 1715 could change it dynamically, usually by 1716 /sys/module/printk/parameters/ignore_loglevel. 1717 1718 ignore_rlimit_data 1719 Ignore RLIMIT_DATA setting for data mappings, 1720 print warning at first misuse. Can be changed via 1721 /sys/module/kernel/parameters/ignore_rlimit_data. 1722 1723 ihash_entries= [KNL] 1724 Set number of hash buckets for inode cache. 1725 1726 ima_appraise= [IMA] appraise integrity measurements 1727 Format: { "off" | "enforce" | "fix" | "log" } 1728 default: "enforce" 1729 1730 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1731 The builtin appraise policy appraises all files 1732 owned by uid=0. 1733 1734 ima_canonical_fmt [IMA] 1735 Use the canonical format for the binary runtime 1736 measurements, instead of host native format. 1737 1738 ima_hash= [IMA] 1739 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1740 | sha512 | ... } 1741 default: "sha1" 1742 1743 The list of supported hash algorithms is defined 1744 in crypto/hash_info.h. 1745 1746 ima_policy= [IMA] 1747 The builtin policies to load during IMA setup. 1748 Format: "tcb | appraise_tcb | secure_boot | 1749 fail_securely" 1750 1751 The "tcb" policy measures all programs exec'd, files 1752 mmap'd for exec, and all files opened with the read 1753 mode bit set by either the effective uid (euid=0) or 1754 uid=0. 1755 1756 The "appraise_tcb" policy appraises the integrity of 1757 all files owned by root. 1758 1759 The "secure_boot" policy appraises the integrity 1760 of files (eg. kexec kernel image, kernel modules, 1761 firmware, policy, etc) based on file signatures. 1762 1763 The "fail_securely" policy forces file signature 1764 verification failure also on privileged mounted 1765 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1766 flag. 1767 1768 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1769 Load a policy which meets the needs of the Trusted 1770 Computing Base. This means IMA will measure all 1771 programs exec'd, files mmap'd for exec, and all files 1772 opened for read by uid=0. 1773 1774 ima_template= [IMA] 1775 Select one of defined IMA measurements template formats. 1776 Formats: { "ima" | "ima-ng" | "ima-sig" } 1777 Default: "ima-ng" 1778 1779 ima_template_fmt= 1780 [IMA] Define a custom template format. 1781 Format: { "field1|...|fieldN" } 1782 1783 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1784 Format: <min_file_size> 1785 Set the minimal file size for using asynchronous hash. 1786 If left unspecified, ahash usage is disabled. 1787 1788 ahash performance varies for different data sizes on 1789 different crypto accelerators. This option can be used 1790 to achieve the best performance for a particular HW. 1791 1792 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1793 Format: <bufsize> 1794 Set hashing buffer size. Default: 4k. 1795 1796 ahash performance varies for different chunk sizes on 1797 different crypto accelerators. This option can be used 1798 to achieve best performance for particular HW. 1799 1800 init= [KNL] 1801 Format: <full_path> 1802 Run specified binary instead of /sbin/init as init 1803 process. 1804 1805 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1806 for working out where the kernel is dying during 1807 startup. 1808 1809 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1810 initcall functions. Useful for debugging built-in 1811 modules and initcalls. 1812 1813 initrd= [BOOT] Specify the location of the initial ramdisk 1814 1815 initrdmem= [KNL] Specify a physical address and size from which to 1816 load the initrd. If an initrd is compiled in or 1817 specified in the bootparams, it takes priority over this 1818 setting. 1819 Format: ss[KMG],nn[KMG] 1820 Default is 0, 0 1821 1822 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1823 zeroes. 1824 Format: 0 | 1 1825 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1826 1827 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1828 Format: 0 | 1 1829 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1830 1831 init_pkru= [X86] Specify the default memory protection keys rights 1832 register contents for all processes. 0x55555554 by 1833 default (disallow access to all but pkey 0). Can 1834 override in debugfs after boot. 1835 1836 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1837 Format: <irq> 1838 1839 int_pln_enable [X86] Enable power limit notification interrupt 1840 1841 integrity_audit=[IMA] 1842 Format: { "0" | "1" } 1843 0 -- basic integrity auditing messages. (Default) 1844 1 -- additional integrity auditing messages. 1845 1846 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1847 on 1848 Enable intel iommu driver. 1849 off 1850 Disable intel iommu driver. 1851 igfx_off [Default Off] 1852 By default, gfx is mapped as normal device. If a gfx 1853 device has a dedicated DMAR unit, the DMAR unit is 1854 bypassed by not enabling DMAR with this option. In 1855 this case, gfx device will use physical address for 1856 DMA. 1857 forcedac [X86-64] 1858 With this option iommu will not optimize to look 1859 for io virtual address below 32-bit forcing dual 1860 address cycle on pci bus for cards supporting greater 1861 than 32-bit addressing. The default is to look 1862 for translation below 32-bit and if not available 1863 then look in the higher range. 1864 strict [Default Off] 1865 With this option on every unmap_single operation will 1866 result in a hardware IOTLB flush operation as opposed 1867 to batching them for performance. 1868 sp_off [Default Off] 1869 By default, super page will be supported if Intel IOMMU 1870 has the capability. With this option, super page will 1871 not be supported. 1872 sm_on [Default Off] 1873 By default, scalable mode will be disabled even if the 1874 hardware advertises that it has support for the scalable 1875 mode translation. With this option set, scalable mode 1876 will be used on hardware which claims to support it. 1877 tboot_noforce [Default Off] 1878 Do not force the Intel IOMMU enabled under tboot. 1879 By default, tboot will force Intel IOMMU on, which 1880 could harm performance of some high-throughput 1881 devices like 40GBit network cards, even if identity 1882 mapping is enabled. 1883 Note that using this option lowers the security 1884 provided by tboot because it makes the system 1885 vulnerable to DMA attacks. 1886 1887 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1888 0 disables intel_idle and fall back on acpi_idle. 1889 1 to 9 specify maximum depth of C-state. 1890 1891 intel_pstate= [X86] 1892 disable 1893 Do not enable intel_pstate as the default 1894 scaling driver for the supported processors 1895 passive 1896 Use intel_pstate as a scaling driver, but configure it 1897 to work with generic cpufreq governors (instead of 1898 enabling its internal governor). This mode cannot be 1899 used along with the hardware-managed P-states (HWP) 1900 feature. 1901 force 1902 Enable intel_pstate on systems that prohibit it by default 1903 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1904 instead of acpi-cpufreq may disable platform features, such 1905 as thermal controls and power capping, that rely on ACPI 1906 P-States information being indicated to OSPM and therefore 1907 should be used with caution. This option does not work with 1908 processors that aren't supported by the intel_pstate driver 1909 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1910 no_hwp 1911 Do not enable hardware P state control (HWP) 1912 if available. 1913 hwp_only 1914 Only load intel_pstate on systems which support 1915 hardware P state control (HWP) if available. 1916 support_acpi_ppc 1917 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1918 Description Table, specifies preferred power management 1919 profile as "Enterprise Server" or "Performance Server", 1920 then this feature is turned on by default. 1921 per_cpu_perf_limits 1922 Allow per-logical-CPU P-State performance control limits using 1923 cpufreq sysfs interface 1924 1925 intremap= [X86-64, Intel-IOMMU] 1926 on enable Interrupt Remapping (default) 1927 off disable Interrupt Remapping 1928 nosid disable Source ID checking 1929 no_x2apic_optout 1930 BIOS x2APIC opt-out request will be ignored 1931 nopost disable Interrupt Posting 1932 1933 iomem= Disable strict checking of access to MMIO memory 1934 strict regions from userspace. 1935 relaxed 1936 1937 iommu= [X86] 1938 off 1939 force 1940 noforce 1941 biomerge 1942 panic 1943 nopanic 1944 merge 1945 nomerge 1946 soft 1947 pt [X86] 1948 nopt [X86] 1949 nobypass [PPC/POWERNV] 1950 Disable IOMMU bypass, using IOMMU for PCI devices. 1951 1952 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1953 Format: { "0" | "1" } 1954 0 - Lazy mode. 1955 Request that DMA unmap operations use deferred 1956 invalidation of hardware TLBs, for increased 1957 throughput at the cost of reduced device isolation. 1958 Will fall back to strict mode if not supported by 1959 the relevant IOMMU driver. 1960 1 - Strict mode (default). 1961 DMA unmap operations invalidate IOMMU hardware TLBs 1962 synchronously. 1963 1964 iommu.passthrough= 1965 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1966 Format: { "0" | "1" } 1967 0 - Use IOMMU translation for DMA. 1968 1 - Bypass the IOMMU for DMA. 1969 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1970 1971 io7= [HW] IO7 for Marvel-based Alpha systems 1972 See comment before marvel_specify_io7 in 1973 arch/alpha/kernel/core_marvel.c. 1974 1975 io_delay= [X86] I/O delay method 1976 0x80 1977 Standard port 0x80 based delay 1978 0xed 1979 Alternate port 0xed based delay (needed on some systems) 1980 udelay 1981 Simple two microseconds delay 1982 none 1983 No delay 1984 1985 ip= [IP_PNP] 1986 See Documentation/admin-guide/nfs/nfsroot.rst. 1987 1988 ipcmni_extend [KNL] Extend the maximum number of unique System V 1989 IPC identifiers from 32,768 to 16,777,216. 1990 1991 irqaffinity= [SMP] Set the default irq affinity mask 1992 The argument is a cpu list, as described above. 1993 1994 irqchip.gicv2_force_probe= 1995 [ARM, ARM64] 1996 Format: <bool> 1997 Force the kernel to look for the second 4kB page 1998 of a GICv2 controller even if the memory range 1999 exposed by the device tree is too small. 2000 2001 irqchip.gicv3_nolpi= 2002 [ARM, ARM64] 2003 Force the kernel to ignore the availability of 2004 LPIs (and by consequence ITSs). Intended for system 2005 that use the kernel as a bootloader, and thus want 2006 to let secondary kernels in charge of setting up 2007 LPIs. 2008 2009 irqchip.gicv3_pseudo_nmi= [ARM64] 2010 Enables support for pseudo-NMIs in the kernel. This 2011 requires the kernel to be built with 2012 CONFIG_ARM64_PSEUDO_NMI. 2013 2014 irqfixup [HW] 2015 When an interrupt is not handled search all handlers 2016 for it. Intended to get systems with badly broken 2017 firmware running. 2018 2019 irqpoll [HW] 2020 When an interrupt is not handled search all handlers 2021 for it. Also check all handlers each timer 2022 interrupt. Intended to get systems with badly broken 2023 firmware running. 2024 2025 isapnp= [ISAPNP] 2026 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2027 2028 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2029 [Deprecated - use cpusets instead] 2030 Format: [flag-list,]<cpu-list> 2031 2032 Specify one or more CPUs to isolate from disturbances 2033 specified in the flag list (default: domain): 2034 2035 nohz 2036 Disable the tick when a single task runs. 2037 2038 A residual 1Hz tick is offloaded to workqueues, which you 2039 need to affine to housekeeping through the global 2040 workqueue's affinity configured via the 2041 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2042 by using the 'domain' flag described below. 2043 2044 NOTE: by default the global workqueue runs on all CPUs, 2045 so to protect individual CPUs the 'cpumask' file has to 2046 be configured manually after bootup. 2047 2048 domain 2049 Isolate from the general SMP balancing and scheduling 2050 algorithms. Note that performing domain isolation this way 2051 is irreversible: it's not possible to bring back a CPU to 2052 the domains once isolated through isolcpus. It's strongly 2053 advised to use cpusets instead to disable scheduler load 2054 balancing through the "cpuset.sched_load_balance" file. 2055 It offers a much more flexible interface where CPUs can 2056 move in and out of an isolated set anytime. 2057 2058 You can move a process onto or off an "isolated" CPU via 2059 the CPU affinity syscalls or cpuset. 2060 <cpu number> begins at 0 and the maximum value is 2061 "number of CPUs in system - 1". 2062 2063 managed_irq 2064 2065 Isolate from being targeted by managed interrupts 2066 which have an interrupt mask containing isolated 2067 CPUs. The affinity of managed interrupts is 2068 handled by the kernel and cannot be changed via 2069 the /proc/irq/* interfaces. 2070 2071 This isolation is best effort and only effective 2072 if the automatically assigned interrupt mask of a 2073 device queue contains isolated and housekeeping 2074 CPUs. If housekeeping CPUs are online then such 2075 interrupts are directed to the housekeeping CPU 2076 so that IO submitted on the housekeeping CPU 2077 cannot disturb the isolated CPU. 2078 2079 If a queue's affinity mask contains only isolated 2080 CPUs then this parameter has no effect on the 2081 interrupt routing decision, though interrupts are 2082 only delivered when tasks running on those 2083 isolated CPUs submit IO. IO submitted on 2084 housekeeping CPUs has no influence on those 2085 queues. 2086 2087 The format of <cpu-list> is described above. 2088 2089 iucv= [HW,NET] 2090 2091 ivrs_ioapic [HW,X86-64] 2092 Provide an override to the IOAPIC-ID<->DEVICE-ID 2093 mapping provided in the IVRS ACPI table. For 2094 example, to map IOAPIC-ID decimal 10 to 2095 PCI device 00:14.0 write the parameter as: 2096 ivrs_ioapic[10]=00:14.0 2097 2098 ivrs_hpet [HW,X86-64] 2099 Provide an override to the HPET-ID<->DEVICE-ID 2100 mapping provided in the IVRS ACPI table. For 2101 example, to map HPET-ID decimal 0 to 2102 PCI device 00:14.0 write the parameter as: 2103 ivrs_hpet[0]=00:14.0 2104 2105 ivrs_acpihid [HW,X86-64] 2106 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2107 mapping provided in the IVRS ACPI table. For 2108 example, to map UART-HID:UID AMD0020:0 to 2109 PCI device 00:14.5 write the parameter as: 2110 ivrs_acpihid[00:14.5]=AMD0020:0 2111 2112 js= [HW,JOY] Analog joystick 2113 See Documentation/input/joydev/joystick.rst. 2114 2115 nokaslr [KNL] 2116 When CONFIG_RANDOMIZE_BASE is set, this disables 2117 kernel and module base offset ASLR (Address Space 2118 Layout Randomization). 2119 2120 kasan_multi_shot 2121 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2122 report on every invalid memory access. Without this 2123 parameter KASAN will print report only for the first 2124 invalid access. 2125 2126 keepinitrd [HW,ARM] 2127 2128 kernelcore= [KNL,X86,IA-64,PPC] 2129 Format: nn[KMGTPE] | nn% | "mirror" 2130 This parameter specifies the amount of memory usable by 2131 the kernel for non-movable allocations. The requested 2132 amount is spread evenly throughout all nodes in the 2133 system as ZONE_NORMAL. The remaining memory is used for 2134 movable memory in its own zone, ZONE_MOVABLE. In the 2135 event, a node is too small to have both ZONE_NORMAL and 2136 ZONE_MOVABLE, kernelcore memory will take priority and 2137 other nodes will have a larger ZONE_MOVABLE. 2138 2139 ZONE_MOVABLE is used for the allocation of pages that 2140 may be reclaimed or moved by the page migration 2141 subsystem. Note that allocations like PTEs-from-HighMem 2142 still use the HighMem zone if it exists, and the Normal 2143 zone if it does not. 2144 2145 It is possible to specify the exact amount of memory in 2146 the form of "nn[KMGTPE]", a percentage of total system 2147 memory in the form of "nn%", or "mirror". If "mirror" 2148 option is specified, mirrored (reliable) memory is used 2149 for non-movable allocations and remaining memory is used 2150 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2151 are exclusive, so you cannot specify multiple forms. 2152 2153 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2154 Format: <Controller#>[,poll interval] 2155 The controller # is the number of the ehci usb debug 2156 port as it is probed via PCI. The poll interval is 2157 optional and is the number seconds in between 2158 each poll cycle to the debug port in case you need 2159 the functionality for interrupting the kernel with 2160 gdb or control-c on the dbgp connection. When 2161 not using this parameter you use sysrq-g to break into 2162 the kernel debugger. 2163 2164 kgdboc= [KGDB,HW] kgdb over consoles. 2165 Requires a tty driver that supports console polling, 2166 or a supported polling keyboard driver (non-usb). 2167 Serial only format: <serial_device>[,baud] 2168 keyboard only format: kbd 2169 keyboard and serial format: kbd,<serial_device>[,baud] 2170 Optional Kernel mode setting: 2171 kms, kbd format: kms,kbd 2172 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2173 2174 kgdboc_earlycon= [KGDB,HW] 2175 If the boot console provides the ability to read 2176 characters and can work in polling mode, you can use 2177 this parameter to tell kgdb to use it as a backend 2178 until the normal console is registered. Intended to 2179 be used together with the kgdboc parameter which 2180 specifies the normal console to transition to. 2181 2182 The name of the early console should be specified 2183 as the value of this parameter. Note that the name of 2184 the early console might be different than the tty 2185 name passed to kgdboc. It's OK to leave the value 2186 blank and the first boot console that implements 2187 read() will be picked. 2188 2189 kgdbwait [KGDB] Stop kernel execution and enter the 2190 kernel debugger at the earliest opportunity. 2191 2192 kmac= [MIPS] Korina ethernet MAC address. 2193 Configure the RouterBoard 532 series on-chip 2194 Ethernet adapter MAC address. 2195 2196 kmemleak= [KNL] Boot-time kmemleak enable/disable 2197 Valid arguments: on, off 2198 Default: on 2199 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2200 the default is off. 2201 2202 kprobe_event=[probe-list] 2203 [FTRACE] Add kprobe events and enable at boot time. 2204 The probe-list is a semicolon delimited list of probe 2205 definitions. Each definition is same as kprobe_events 2206 interface, but the parameters are comma delimited. 2207 For example, to add a kprobe event on vfs_read with 2208 arg1 and arg2, add to the command line; 2209 2210 kprobe_event=p,vfs_read,$arg1,$arg2 2211 2212 See also Documentation/trace/kprobetrace.rst "Kernel 2213 Boot Parameter" section. 2214 2215 kpti= [ARM64] Control page table isolation of user 2216 and kernel address spaces. 2217 Default: enabled on cores which need mitigation. 2218 0: force disabled 2219 1: force enabled 2220 2221 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2222 Default is 0 (don't ignore, but inject #GP) 2223 2224 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2225 Default is false (don't support). 2226 2227 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2228 KVM MMU at runtime. 2229 Default is 0 (off) 2230 2231 kvm.nx_huge_pages= 2232 [KVM] Controls the software workaround for the 2233 X86_BUG_ITLB_MULTIHIT bug. 2234 force : Always deploy workaround. 2235 off : Never deploy workaround. 2236 auto : Deploy workaround based on the presence of 2237 X86_BUG_ITLB_MULTIHIT. 2238 2239 Default is 'auto'. 2240 2241 If the software workaround is enabled for the host, 2242 guests do need not to enable it for nested guests. 2243 2244 kvm.nx_huge_pages_recovery_ratio= 2245 [KVM] Controls how many 4KiB pages are periodically zapped 2246 back to huge pages. 0 disables the recovery, otherwise if 2247 the value is N KVM will zap 1/Nth of the 4KiB pages every 2248 minute. The default is 60. 2249 2250 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2251 Default is 1 (enabled) 2252 2253 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2254 for all guests. 2255 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2256 2257 kvm-arm.vgic_v3_group0_trap= 2258 [KVM,ARM] Trap guest accesses to GICv3 group-0 2259 system registers 2260 2261 kvm-arm.vgic_v3_group1_trap= 2262 [KVM,ARM] Trap guest accesses to GICv3 group-1 2263 system registers 2264 2265 kvm-arm.vgic_v3_common_trap= 2266 [KVM,ARM] Trap guest accesses to GICv3 common 2267 system registers 2268 2269 kvm-arm.vgic_v4_enable= 2270 [KVM,ARM] Allow use of GICv4 for direct injection of 2271 LPIs. 2272 2273 kvm_cma_resv_ratio=n [PPC] 2274 Reserves given percentage from system memory area for 2275 contiguous memory allocation for KVM hash pagetable 2276 allocation. 2277 By default it reserves 5% of total system memory. 2278 Format: <integer> 2279 Default: 5 2280 2281 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2282 (virtualized MMU) support on capable Intel chips. 2283 Default is 1 (enabled) 2284 2285 kvm-intel.emulate_invalid_guest_state= 2286 [KVM,Intel] Enable emulation of invalid guest states 2287 Default is 0 (disabled) 2288 2289 kvm-intel.flexpriority= 2290 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2291 Default is 1 (enabled) 2292 2293 kvm-intel.nested= 2294 [KVM,Intel] Enable VMX nesting (nVMX). 2295 Default is 0 (disabled) 2296 2297 kvm-intel.unrestricted_guest= 2298 [KVM,Intel] Disable unrestricted guest feature 2299 (virtualized real and unpaged mode) on capable 2300 Intel chips. Default is 1 (enabled) 2301 2302 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2303 CVE-2018-3620. 2304 2305 Valid arguments: never, cond, always 2306 2307 always: L1D cache flush on every VMENTER. 2308 cond: Flush L1D on VMENTER only when the code between 2309 VMEXIT and VMENTER can leak host memory. 2310 never: Disables the mitigation 2311 2312 Default is cond (do L1 cache flush in specific instances) 2313 2314 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2315 feature (tagged TLBs) on capable Intel chips. 2316 Default is 1 (enabled) 2317 2318 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2319 affected CPUs 2320 2321 The kernel PTE inversion protection is unconditionally 2322 enabled and cannot be disabled. 2323 2324 full 2325 Provides all available mitigations for the 2326 L1TF vulnerability. Disables SMT and 2327 enables all mitigations in the 2328 hypervisors, i.e. unconditional L1D flush. 2329 2330 SMT control and L1D flush control via the 2331 sysfs interface is still possible after 2332 boot. Hypervisors will issue a warning 2333 when the first VM is started in a 2334 potentially insecure configuration, 2335 i.e. SMT enabled or L1D flush disabled. 2336 2337 full,force 2338 Same as 'full', but disables SMT and L1D 2339 flush runtime control. Implies the 2340 'nosmt=force' command line option. 2341 (i.e. sysfs control of SMT is disabled.) 2342 2343 flush 2344 Leaves SMT enabled and enables the default 2345 hypervisor mitigation, i.e. conditional 2346 L1D flush. 2347 2348 SMT control and L1D flush control via the 2349 sysfs interface is still possible after 2350 boot. Hypervisors will issue a warning 2351 when the first VM is started in a 2352 potentially insecure configuration, 2353 i.e. SMT enabled or L1D flush disabled. 2354 2355 flush,nosmt 2356 2357 Disables SMT and enables the default 2358 hypervisor mitigation. 2359 2360 SMT control and L1D flush control via the 2361 sysfs interface is still possible after 2362 boot. Hypervisors will issue a warning 2363 when the first VM is started in a 2364 potentially insecure configuration, 2365 i.e. SMT enabled or L1D flush disabled. 2366 2367 flush,nowarn 2368 Same as 'flush', but hypervisors will not 2369 warn when a VM is started in a potentially 2370 insecure configuration. 2371 2372 off 2373 Disables hypervisor mitigations and doesn't 2374 emit any warnings. 2375 It also drops the swap size and available 2376 RAM limit restriction on both hypervisor and 2377 bare metal. 2378 2379 Default is 'flush'. 2380 2381 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2382 2383 l2cr= [PPC] 2384 2385 l3cr= [PPC] 2386 2387 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2388 disabled it. 2389 2390 lapic= [X86,APIC] Do not use TSC deadline 2391 value for LAPIC timer one-shot implementation. Default 2392 back to the programmable timer unit in the LAPIC. 2393 Format: notscdeadline 2394 2395 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2396 in C2 power state. 2397 2398 libata.dma= [LIBATA] DMA control 2399 libata.dma=0 Disable all PATA and SATA DMA 2400 libata.dma=1 PATA and SATA Disk DMA only 2401 libata.dma=2 ATAPI (CDROM) DMA only 2402 libata.dma=4 Compact Flash DMA only 2403 Combinations also work, so libata.dma=3 enables DMA 2404 for disks and CDROMs, but not CFs. 2405 2406 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2407 libata.ignore_hpa=0 keep BIOS limits (default) 2408 libata.ignore_hpa=1 ignore limits, using full disk 2409 2410 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2411 when set. 2412 Format: <int> 2413 2414 libata.force= [LIBATA] Force configurations. The format is comma 2415 separated list of "[ID:]VAL" where ID is 2416 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2417 matching port, link or device. Basically, it matches 2418 the ATA ID string printed on console by libata. If 2419 the whole ID part is omitted, the last PORT and DEVICE 2420 values are used. If ID hasn't been specified yet, the 2421 configuration applies to all ports, links and devices. 2422 2423 If only DEVICE is omitted, the parameter applies to 2424 the port and all links and devices behind it. DEVICE 2425 number of 0 either selects the first device or the 2426 first fan-out link behind PMP device. It does not 2427 select the host link. DEVICE number of 15 selects the 2428 host link and device attached to it. 2429 2430 The VAL specifies the configuration to force. As long 2431 as there's no ambiguity shortcut notation is allowed. 2432 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2433 The following configurations can be forced. 2434 2435 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2436 Any ID with matching PORT is used. 2437 2438 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2439 2440 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2441 udma[/][16,25,33,44,66,100,133] notation is also 2442 allowed. 2443 2444 * [no]ncq: Turn on or off NCQ. 2445 2446 * [no]ncqtrim: Turn off queued DSM TRIM. 2447 2448 * nohrst, nosrst, norst: suppress hard, soft 2449 and both resets. 2450 2451 * rstonce: only attempt one reset during 2452 hot-unplug link recovery 2453 2454 * dump_id: dump IDENTIFY data. 2455 2456 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2457 2458 * disable: Disable this device. 2459 2460 If there are multiple matching configurations changing 2461 the same attribute, the last one is used. 2462 2463 memblock=debug [KNL] Enable memblock debug messages. 2464 2465 load_ramdisk= [RAM] [Deprecated] 2466 2467 lockd.nlm_grace_period=P [NFS] Assign grace period. 2468 Format: <integer> 2469 2470 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2471 Format: <integer> 2472 2473 lockd.nlm_timeout=T [NFS] Assign timeout value. 2474 Format: <integer> 2475 2476 lockd.nlm_udpport=M [NFS] Assign UDP port. 2477 Format: <integer> 2478 2479 lockdown= [SECURITY] 2480 { integrity | confidentiality } 2481 Enable the kernel lockdown feature. If set to 2482 integrity, kernel features that allow userland to 2483 modify the running kernel are disabled. If set to 2484 confidentiality, kernel features that allow userland 2485 to extract confidential information from the kernel 2486 are also disabled. 2487 2488 locktorture.nreaders_stress= [KNL] 2489 Set the number of locking read-acquisition kthreads. 2490 Defaults to being automatically set based on the 2491 number of online CPUs. 2492 2493 locktorture.nwriters_stress= [KNL] 2494 Set the number of locking write-acquisition kthreads. 2495 2496 locktorture.onoff_holdoff= [KNL] 2497 Set time (s) after boot for CPU-hotplug testing. 2498 2499 locktorture.onoff_interval= [KNL] 2500 Set time (s) between CPU-hotplug operations, or 2501 zero to disable CPU-hotplug testing. 2502 2503 locktorture.shuffle_interval= [KNL] 2504 Set task-shuffle interval (jiffies). Shuffling 2505 tasks allows some CPUs to go into dyntick-idle 2506 mode during the locktorture test. 2507 2508 locktorture.shutdown_secs= [KNL] 2509 Set time (s) after boot system shutdown. This 2510 is useful for hands-off automated testing. 2511 2512 locktorture.stat_interval= [KNL] 2513 Time (s) between statistics printk()s. 2514 2515 locktorture.stutter= [KNL] 2516 Time (s) to stutter testing, for example, 2517 specifying five seconds causes the test to run for 2518 five seconds, wait for five seconds, and so on. 2519 This tests the locking primitive's ability to 2520 transition abruptly to and from idle. 2521 2522 locktorture.torture_type= [KNL] 2523 Specify the locking implementation to test. 2524 2525 locktorture.verbose= [KNL] 2526 Enable additional printk() statements. 2527 2528 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2529 Format: <irq> 2530 2531 loglevel= All Kernel Messages with a loglevel smaller than the 2532 console loglevel will be printed to the console. It can 2533 also be changed with klogd or other programs. The 2534 loglevels are defined as follows: 2535 2536 0 (KERN_EMERG) system is unusable 2537 1 (KERN_ALERT) action must be taken immediately 2538 2 (KERN_CRIT) critical conditions 2539 3 (KERN_ERR) error conditions 2540 4 (KERN_WARNING) warning conditions 2541 5 (KERN_NOTICE) normal but significant condition 2542 6 (KERN_INFO) informational 2543 7 (KERN_DEBUG) debug-level messages 2544 2545 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2546 in bytes. n must be a power of two and greater 2547 than the minimal size. The minimal size is defined 2548 by LOG_BUF_SHIFT kernel config parameter. There is 2549 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2550 that allows to increase the default size depending on 2551 the number of CPUs. See init/Kconfig for more details. 2552 2553 logo.nologo [FB] Disables display of the built-in Linux logo. 2554 This may be used to provide more screen space for 2555 kernel log messages and is useful when debugging 2556 kernel boot problems. 2557 2558 lp=0 [LP] Specify parallel ports to use, e.g, 2559 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2560 lp=reset first parallel port). 'lp=0' disables the 2561 lp=auto printer driver. 'lp=reset' (which can be 2562 specified in addition to the ports) causes 2563 attached printers to be reset. Using 2564 lp=port1,port2,... specifies the parallel ports 2565 to associate lp devices with, starting with 2566 lp0. A port specification may be 'none' to skip 2567 that lp device, or a parport name such as 2568 'parport0'. Specifying 'lp=auto' instead of a 2569 port specification list means that device IDs 2570 from each port should be examined, to see if 2571 an IEEE 1284-compliant printer is attached; if 2572 so, the driver will manage that printer. 2573 See also header of drivers/char/lp.c. 2574 2575 lpj=n [KNL] 2576 Sets loops_per_jiffy to given constant, thus avoiding 2577 time-consuming boot-time autodetection (up to 250 ms per 2578 CPU). 0 enables autodetection (default). To determine 2579 the correct value for your kernel, boot with normal 2580 autodetection and see what value is printed. Note that 2581 on SMP systems the preset will be applied to all CPUs, 2582 which is likely to cause problems if your CPUs need 2583 significantly divergent settings. An incorrect value 2584 will cause delays in the kernel to be wrong, leading to 2585 unpredictable I/O errors and other breakage. Although 2586 unlikely, in the extreme case this might damage your 2587 hardware. 2588 2589 ltpc= [NET] 2590 Format: <io>,<irq>,<dma> 2591 2592 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2593 2594 lsm=lsm1,...,lsmN 2595 [SECURITY] Choose order of LSM initialization. This 2596 overrides CONFIG_LSM, and the "security=" parameter. 2597 2598 machvec= [IA-64] Force the use of a particular machine-vector 2599 (machvec) in a generic kernel. 2600 Example: machvec=hpzx1 2601 2602 machtype= [Loongson] Share the same kernel image file between 2603 different yeeloong laptops. 2604 Example: machtype=lemote-yeeloong-2f-7inch 2605 2606 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2607 than or equal to this physical address is ignored. 2608 2609 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2610 will bring up during bootup. maxcpus=n : n >= 0 limits 2611 the kernel to bring up 'n' processors. Surely after 2612 bootup you can bring up the other plugged cpu by executing 2613 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2614 only takes effect during system bootup. 2615 While n=0 is a special case, it is equivalent to "nosmp", 2616 which also disables the IO APIC. 2617 2618 max_loop= [LOOP] The number of loop block devices that get 2619 (loop.max_loop) unconditionally pre-created at init time. The default 2620 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2621 of statically allocating a predefined number, loop 2622 devices can be requested on-demand with the 2623 /dev/loop-control interface. 2624 2625 mce [X86-32] Machine Check Exception 2626 2627 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2628 2629 md= [HW] RAID subsystems devices and level 2630 See Documentation/admin-guide/md.rst. 2631 2632 mdacon= [MDA] 2633 Format: <first>,<last> 2634 Specifies range of consoles to be captured by the MDA. 2635 2636 mds= [X86,INTEL] 2637 Control mitigation for the Micro-architectural Data 2638 Sampling (MDS) vulnerability. 2639 2640 Certain CPUs are vulnerable to an exploit against CPU 2641 internal buffers which can forward information to a 2642 disclosure gadget under certain conditions. 2643 2644 In vulnerable processors, the speculatively 2645 forwarded data can be used in a cache side channel 2646 attack, to access data to which the attacker does 2647 not have direct access. 2648 2649 This parameter controls the MDS mitigation. The 2650 options are: 2651 2652 full - Enable MDS mitigation on vulnerable CPUs 2653 full,nosmt - Enable MDS mitigation and disable 2654 SMT on vulnerable CPUs 2655 off - Unconditionally disable MDS mitigation 2656 2657 On TAA-affected machines, mds=off can be prevented by 2658 an active TAA mitigation as both vulnerabilities are 2659 mitigated with the same mechanism so in order to disable 2660 this mitigation, you need to specify tsx_async_abort=off 2661 too. 2662 2663 Not specifying this option is equivalent to 2664 mds=full. 2665 2666 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2667 2668 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2669 Amount of memory to be used in cases as follows: 2670 2671 1 for test; 2672 2 when the kernel is not able to see the whole system memory; 2673 3 memory that lies after 'mem=' boundary is excluded from 2674 the hypervisor, then assigned to KVM guests. 2675 2676 [X86] Work as limiting max address. Use together 2677 with memmap= to avoid physical address space collisions. 2678 Without memmap= PCI devices could be placed at addresses 2679 belonging to unused RAM. 2680 2681 Note that this only takes effects during boot time since 2682 in above case 3, memory may need be hot added after boot 2683 if system memory of hypervisor is not sufficient. 2684 2685 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2686 memory. 2687 2688 memchunk=nn[KMG] 2689 [KNL,SH] Allow user to override the default size for 2690 per-device physically contiguous DMA buffers. 2691 2692 memhp_default_state=online/offline 2693 [KNL] Set the initial state for the memory hotplug 2694 onlining policy. If not specified, the default value is 2695 set according to the 2696 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2697 option. 2698 See Documentation/admin-guide/mm/memory-hotplug.rst. 2699 2700 memmap=exactmap [KNL,X86] Enable setting of an exact 2701 E820 memory map, as specified by the user. 2702 Such memmap=exactmap lines can be constructed based on 2703 BIOS output or other requirements. See the memmap=nn@ss 2704 option description. 2705 2706 memmap=nn[KMG]@ss[KMG] 2707 [KNL, X86, MIPS, XTENSA] Force usage of a specific region of memory. 2708 Region of memory to be used is from ss to ss+nn. 2709 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2710 which limits max address to nn[KMG]. 2711 Multiple different regions can be specified, 2712 comma delimited. 2713 Example: 2714 memmap=100M@2G,100M#3G,1G!1024G 2715 2716 memmap=nn[KMG]#ss[KMG] 2717 [KNL,ACPI] Mark specific memory as ACPI data. 2718 Region of memory to be marked is from ss to ss+nn. 2719 2720 memmap=nn[KMG]$ss[KMG] 2721 [KNL,ACPI] Mark specific memory as reserved. 2722 Region of memory to be reserved is from ss to ss+nn. 2723 Example: Exclude memory from 0x18690000-0x1869ffff 2724 memmap=64K$0x18690000 2725 or 2726 memmap=0x10000$0x18690000 2727 Some bootloaders may need an escape character before '$', 2728 like Grub2, otherwise '$' and the following number 2729 will be eaten. 2730 2731 memmap=nn[KMG]!ss[KMG] 2732 [KNL,X86] Mark specific memory as protected. 2733 Region of memory to be used, from ss to ss+nn. 2734 The memory region may be marked as e820 type 12 (0xc) 2735 and is NVDIMM or ADR memory. 2736 2737 memmap=<size>%<offset>-<oldtype>+<newtype> 2738 [KNL,ACPI] Convert memory within the specified region 2739 from <oldtype> to <newtype>. If "-<oldtype>" is left 2740 out, the whole region will be marked as <newtype>, 2741 even if previously unavailable. If "+<newtype>" is left 2742 out, matching memory will be removed. Types are 2743 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2744 3 = ACPI, 12 = PRAM. 2745 2746 memory_corruption_check=0/1 [X86] 2747 Some BIOSes seem to corrupt the first 64k of 2748 memory when doing things like suspend/resume. 2749 Setting this option will scan the memory 2750 looking for corruption. Enabling this will 2751 both detect corruption and prevent the kernel 2752 from using the memory being corrupted. 2753 However, its intended as a diagnostic tool; if 2754 repeatable BIOS-originated corruption always 2755 affects the same memory, you can use memmap= 2756 to prevent the kernel from using that memory. 2757 2758 memory_corruption_check_size=size [X86] 2759 By default it checks for corruption in the low 2760 64k, making this memory unavailable for normal 2761 use. Use this parameter to scan for 2762 corruption in more or less memory. 2763 2764 memory_corruption_check_period=seconds [X86] 2765 By default it checks for corruption every 60 2766 seconds. Use this parameter to check at some 2767 other rate. 0 disables periodic checking. 2768 2769 memtest= [KNL,X86,ARM,PPC] Enable memtest 2770 Format: <integer> 2771 default : 0 <disable> 2772 Specifies the number of memtest passes to be 2773 performed. Each pass selects another test 2774 pattern from a given set of patterns. Memtest 2775 fills the memory with this pattern, validates 2776 memory contents and reserves bad memory 2777 regions that are detected. 2778 2779 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2780 Valid arguments: on, off 2781 Default (depends on kernel configuration option): 2782 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2783 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2784 mem_encrypt=on: Activate SME 2785 mem_encrypt=off: Do not activate SME 2786 2787 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2788 for details on when memory encryption can be activated. 2789 2790 mem_sleep_default= [SUSPEND] Default system suspend mode: 2791 s2idle - Suspend-To-Idle 2792 shallow - Power-On Suspend or equivalent (if supported) 2793 deep - Suspend-To-RAM or equivalent (if supported) 2794 See Documentation/admin-guide/pm/sleep-states.rst. 2795 2796 meye.*= [HW] Set MotionEye Camera parameters 2797 See Documentation/admin-guide/media/meye.rst. 2798 2799 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2800 Multi-Function General Purpose Timers on AMD Geode 2801 platforms. 2802 2803 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2804 the BIOS has incorrectly applied a workaround. TinyBIOS 2805 version 0.98 is known to be affected, 0.99 fixes the 2806 problem by letting the user disable the workaround. 2807 2808 mga= [HW,DRM] 2809 2810 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2811 physical address is ignored. 2812 2813 mini2440= [ARM,HW,KNL] 2814 Format:[0..2][b][c][t] 2815 Default: "0tb" 2816 MINI2440 configuration specification: 2817 0 - The attached screen is the 3.5" TFT 2818 1 - The attached screen is the 7" TFT 2819 2 - The VGA Shield is attached (1024x768) 2820 Leaving out the screen size parameter will not load 2821 the TFT driver, and the framebuffer will be left 2822 unconfigured. 2823 b - Enable backlight. The TFT backlight pin will be 2824 linked to the kernel VESA blanking code and a GPIO 2825 LED. This parameter is not necessary when using the 2826 VGA shield. 2827 c - Enable the s3c camera interface. 2828 t - Reserved for enabling touchscreen support. The 2829 touchscreen support is not enabled in the mainstream 2830 kernel as of 2.6.30, a preliminary port can be found 2831 in the "bleeding edge" mini2440 support kernel at 2832 https://repo.or.cz/w/linux-2.6/mini2440.git 2833 2834 mitigations= 2835 [X86,PPC,S390,ARM64] Control optional mitigations for 2836 CPU vulnerabilities. This is a set of curated, 2837 arch-independent options, each of which is an 2838 aggregation of existing arch-specific options. 2839 2840 off 2841 Disable all optional CPU mitigations. This 2842 improves system performance, but it may also 2843 expose users to several CPU vulnerabilities. 2844 Equivalent to: nopti [X86,PPC] 2845 kpti=0 [ARM64] 2846 nospectre_v1 [X86,PPC] 2847 nobp=0 [S390] 2848 nospectre_v2 [X86,PPC,S390,ARM64] 2849 spectre_v2_user=off [X86] 2850 spec_store_bypass_disable=off [X86,PPC] 2851 ssbd=force-off [ARM64] 2852 l1tf=off [X86] 2853 mds=off [X86] 2854 tsx_async_abort=off [X86] 2855 kvm.nx_huge_pages=off [X86] 2856 no_entry_flush [PPC] 2857 no_uaccess_flush [PPC] 2858 2859 Exceptions: 2860 This does not have any effect on 2861 kvm.nx_huge_pages when 2862 kvm.nx_huge_pages=force. 2863 2864 auto (default) 2865 Mitigate all CPU vulnerabilities, but leave SMT 2866 enabled, even if it's vulnerable. This is for 2867 users who don't want to be surprised by SMT 2868 getting disabled across kernel upgrades, or who 2869 have other ways of avoiding SMT-based attacks. 2870 Equivalent to: (default behavior) 2871 2872 auto,nosmt 2873 Mitigate all CPU vulnerabilities, disabling SMT 2874 if needed. This is for users who always want to 2875 be fully mitigated, even if it means losing SMT. 2876 Equivalent to: l1tf=flush,nosmt [X86] 2877 mds=full,nosmt [X86] 2878 tsx_async_abort=full,nosmt [X86] 2879 2880 mminit_loglevel= 2881 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2882 parameter allows control of the logging verbosity for 2883 the additional memory initialisation checks. A value 2884 of 0 disables mminit logging and a level of 4 will 2885 log everything. Information is printed at KERN_DEBUG 2886 so loglevel=8 may also need to be specified. 2887 2888 module.sig_enforce 2889 [KNL] When CONFIG_MODULE_SIG is set, this means that 2890 modules without (valid) signatures will fail to load. 2891 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2892 is always true, so this option does nothing. 2893 2894 module_blacklist= [KNL] Do not load a comma-separated list of 2895 modules. Useful for debugging problem modules. 2896 2897 mousedev.tap_time= 2898 [MOUSE] Maximum time between finger touching and 2899 leaving touchpad surface for touch to be considered 2900 a tap and be reported as a left button click (for 2901 touchpads working in absolute mode only). 2902 Format: <msecs> 2903 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2904 reporting absolute coordinates, such as tablets 2905 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2906 reporting absolute coordinates, such as tablets 2907 2908 movablecore= [KNL,X86,IA-64,PPC] 2909 Format: nn[KMGTPE] | nn% 2910 This parameter is the complement to kernelcore=, it 2911 specifies the amount of memory used for migratable 2912 allocations. If both kernelcore and movablecore is 2913 specified, then kernelcore will be at *least* the 2914 specified value but may be more. If movablecore on its 2915 own is specified, the administrator must be careful 2916 that the amount of memory usable for all allocations 2917 is not too small. 2918 2919 movable_node [KNL] Boot-time switch to make hotplugable memory 2920 NUMA nodes to be movable. This means that the memory 2921 of such nodes will be usable only for movable 2922 allocations which rules out almost all kernel 2923 allocations. Use with caution! 2924 2925 MTD_Partition= [MTD] 2926 Format: <name>,<region-number>,<size>,<offset> 2927 2928 MTD_Region= [MTD] Format: 2929 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2930 2931 mtdparts= [MTD] 2932 See drivers/mtd/parsers/cmdlinepart.c 2933 2934 multitce=off [PPC] This parameter disables the use of the pSeries 2935 firmware feature for updating multiple TCE entries 2936 at a time. 2937 2938 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2939 2940 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2941 2942 boundary - index of last SLC block on Flex-OneNAND. 2943 The remaining blocks are configured as MLC blocks. 2944 lock - Configure if Flex-OneNAND boundary should be locked. 2945 Once locked, the boundary cannot be changed. 2946 1 indicates lock status, 0 indicates unlock status. 2947 2948 mtdset= [ARM] 2949 ARM/S3C2412 JIVE boot control 2950 2951 See arch/arm/mach-s3c/mach-jive.c 2952 2953 mtouchusb.raw_coordinates= 2954 [HW] Make the MicroTouch USB driver use raw coordinates 2955 ('y', default) or cooked coordinates ('n') 2956 2957 mtrr_chunk_size=nn[KMG] [X86] 2958 used for mtrr cleanup. It is largest continuous chunk 2959 that could hold holes aka. UC entries. 2960 2961 mtrr_gran_size=nn[KMG] [X86] 2962 Used for mtrr cleanup. It is granularity of mtrr block. 2963 Default is 1. 2964 Large value could prevent small alignment from 2965 using up MTRRs. 2966 2967 mtrr_spare_reg_nr=n [X86] 2968 Format: <integer> 2969 Range: 0,7 : spare reg number 2970 Default : 1 2971 Used for mtrr cleanup. It is spare mtrr entries number. 2972 Set to 2 or more if your graphical card needs more. 2973 2974 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2975 2976 netdev= [NET] Network devices parameters 2977 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2978 Note that mem_start is often overloaded to mean 2979 something different and driver-specific. 2980 This usage is only documented in each driver source 2981 file if at all. 2982 2983 nf_conntrack.acct= 2984 [NETFILTER] Enable connection tracking flow accounting 2985 0 to disable accounting 2986 1 to enable accounting 2987 Default value is 0. 2988 2989 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2990 See Documentation/admin-guide/nfs/nfsroot.rst. 2991 2992 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2993 See Documentation/admin-guide/nfs/nfsroot.rst. 2994 2995 nfsrootdebug [NFS] enable nfsroot debugging messages. 2996 See Documentation/admin-guide/nfs/nfsroot.rst. 2997 2998 nfs.callback_nr_threads= 2999 [NFSv4] set the total number of threads that the 3000 NFS client will assign to service NFSv4 callback 3001 requests. 3002 3003 nfs.callback_tcpport= 3004 [NFS] set the TCP port on which the NFSv4 callback 3005 channel should listen. 3006 3007 nfs.cache_getent= 3008 [NFS] sets the pathname to the program which is used 3009 to update the NFS client cache entries. 3010 3011 nfs.cache_getent_timeout= 3012 [NFS] sets the timeout after which an attempt to 3013 update a cache entry is deemed to have failed. 3014 3015 nfs.idmap_cache_timeout= 3016 [NFS] set the maximum lifetime for idmapper cache 3017 entries. 3018 3019 nfs.enable_ino64= 3020 [NFS] enable 64-bit inode numbers. 3021 If zero, the NFS client will fake up a 32-bit inode 3022 number for the readdir() and stat() syscalls instead 3023 of returning the full 64-bit number. 3024 The default is to return 64-bit inode numbers. 3025 3026 nfs.max_session_cb_slots= 3027 [NFSv4.1] Sets the maximum number of session 3028 slots the client will assign to the callback 3029 channel. This determines the maximum number of 3030 callbacks the client will process in parallel for 3031 a particular server. 3032 3033 nfs.max_session_slots= 3034 [NFSv4.1] Sets the maximum number of session slots 3035 the client will attempt to negotiate with the server. 3036 This limits the number of simultaneous RPC requests 3037 that the client can send to the NFSv4.1 server. 3038 Note that there is little point in setting this 3039 value higher than the max_tcp_slot_table_limit. 3040 3041 nfs.nfs4_disable_idmapping= 3042 [NFSv4] When set to the default of '1', this option 3043 ensures that both the RPC level authentication 3044 scheme and the NFS level operations agree to use 3045 numeric uids/gids if the mount is using the 3046 'sec=sys' security flavour. In effect it is 3047 disabling idmapping, which can make migration from 3048 legacy NFSv2/v3 systems to NFSv4 easier. 3049 Servers that do not support this mode of operation 3050 will be autodetected by the client, and it will fall 3051 back to using the idmapper. 3052 To turn off this behaviour, set the value to '0'. 3053 nfs.nfs4_unique_id= 3054 [NFS4] Specify an additional fixed unique ident- 3055 ification string that NFSv4 clients can insert into 3056 their nfs_client_id4 string. This is typically a 3057 UUID that is generated at system install time. 3058 3059 nfs.send_implementation_id = 3060 [NFSv4.1] Send client implementation identification 3061 information in exchange_id requests. 3062 If zero, no implementation identification information 3063 will be sent. 3064 The default is to send the implementation identification 3065 information. 3066 3067 nfs.recover_lost_locks = 3068 [NFSv4] Attempt to recover locks that were lost due 3069 to a lease timeout on the server. Please note that 3070 doing this risks data corruption, since there are 3071 no guarantees that the file will remain unchanged 3072 after the locks are lost. 3073 If you want to enable the kernel legacy behaviour of 3074 attempting to recover these locks, then set this 3075 parameter to '1'. 3076 The default parameter value of '0' causes the kernel 3077 not to attempt recovery of lost locks. 3078 3079 nfs4.layoutstats_timer = 3080 [NFSv4.2] Change the rate at which the kernel sends 3081 layoutstats to the pNFS metadata server. 3082 3083 Setting this to value to 0 causes the kernel to use 3084 whatever value is the default set by the layout 3085 driver. A non-zero value sets the minimum interval 3086 in seconds between layoutstats transmissions. 3087 3088 nfsd.nfs4_disable_idmapping= 3089 [NFSv4] When set to the default of '1', the NFSv4 3090 server will return only numeric uids and gids to 3091 clients using auth_sys, and will accept numeric uids 3092 and gids from such clients. This is intended to ease 3093 migration from NFSv2/v3. 3094 3095 nmi_backtrace.backtrace_idle [KNL] 3096 Dump stacks even of idle CPUs in response to an 3097 NMI stack-backtrace request. 3098 3099 nmi_debug= [KNL,SH] Specify one or more actions to take 3100 when a NMI is triggered. 3101 Format: [state][,regs][,debounce][,die] 3102 3103 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3104 Format: [panic,][nopanic,][num] 3105 Valid num: 0 or 1 3106 0 - turn hardlockup detector in nmi_watchdog off 3107 1 - turn hardlockup detector in nmi_watchdog on 3108 When panic is specified, panic when an NMI watchdog 3109 timeout occurs (or 'nopanic' to not panic on an NMI 3110 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3111 To disable both hard and soft lockup detectors, 3112 please see 'nowatchdog'. 3113 This is useful when you use a panic=... timeout and 3114 need the box quickly up again. 3115 3116 These settings can be accessed at runtime via 3117 the nmi_watchdog and hardlockup_panic sysctls. 3118 3119 netpoll.carrier_timeout= 3120 [NET] Specifies amount of time (in seconds) that 3121 netpoll should wait for a carrier. By default netpoll 3122 waits 4 seconds. 3123 3124 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3125 emulation library even if a 387 maths coprocessor 3126 is present. 3127 3128 no5lvl [X86-64] Disable 5-level paging mode. Forces 3129 kernel to use 4-level paging instead. 3130 3131 nofsgsbase [X86] Disables FSGSBASE instructions. 3132 3133 no_console_suspend 3134 [HW] Never suspend the console 3135 Disable suspending of consoles during suspend and 3136 hibernate operations. Once disabled, debugging 3137 messages can reach various consoles while the rest 3138 of the system is being put to sleep (ie, while 3139 debugging driver suspend/resume hooks). This may 3140 not work reliably with all consoles, but is known 3141 to work with serial and VGA consoles. 3142 To facilitate more flexible debugging, we also add 3143 console_suspend, a printk module parameter to control 3144 it. Users could use console_suspend (usually 3145 /sys/module/printk/parameters/console_suspend) to 3146 turn on/off it dynamically. 3147 3148 novmcoredd [KNL,KDUMP] 3149 Disable device dump. Device dump allows drivers to 3150 append dump data to vmcore so you can collect driver 3151 specified debug info. Drivers can append the data 3152 without any limit and this data is stored in memory, 3153 so this may cause significant memory stress. Disabling 3154 device dump can help save memory but the driver debug 3155 data will be no longer available. This parameter 3156 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3157 is set. 3158 3159 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3160 caches in the slab allocator. Saves per-node memory, 3161 but will impact performance. 3162 3163 noalign [KNL,ARM] 3164 3165 noaltinstr [S390] Disables alternative instructions patching 3166 (CPU alternatives feature). 3167 3168 noapic [SMP,APIC] Tells the kernel to not make use of any 3169 IOAPICs that may be present in the system. 3170 3171 noautogroup Disable scheduler automatic task group creation. 3172 3173 nobats [PPC] Do not use BATs for mapping kernel lowmem 3174 on "Classic" PPC cores. 3175 3176 nocache [ARM] 3177 3178 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3179 3180 nodelayacct [KNL] Disable per-task delay accounting 3181 3182 nodsp [SH] Disable hardware DSP at boot time. 3183 3184 noefi Disable EFI runtime services support. 3185 3186 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3187 3188 noexec [IA-64] 3189 3190 noexec [X86] 3191 On X86-32 available only on PAE configured kernels. 3192 noexec=on: enable non-executable mappings (default) 3193 noexec=off: disable non-executable mappings 3194 3195 nosmap [X86,PPC] 3196 Disable SMAP (Supervisor Mode Access Prevention) 3197 even if it is supported by processor. 3198 3199 nosmep [X86,PPC] 3200 Disable SMEP (Supervisor Mode Execution Prevention) 3201 even if it is supported by processor. 3202 3203 noexec32 [X86-64] 3204 This affects only 32-bit executables. 3205 noexec32=on: enable non-executable mappings (default) 3206 read doesn't imply executable mappings 3207 noexec32=off: disable non-executable mappings 3208 read implies executable mappings 3209 3210 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3211 3212 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3213 register save and restore. The kernel will only save 3214 legacy floating-point registers on task switch. 3215 3216 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3217 3218 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3219 Equivalent to smt=1. 3220 3221 [KNL,X86] Disable symmetric multithreading (SMT). 3222 nosmt=force: Force disable SMT, cannot be undone 3223 via the sysfs control file. 3224 3225 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3226 (bounds check bypass). With this option data leaks are 3227 possible in the system. 3228 3229 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3230 the Spectre variant 2 (indirect branch prediction) 3231 vulnerability. System may allow data leaks with this 3232 option. 3233 3234 nospec_store_bypass_disable 3235 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3236 3237 no_uaccess_flush 3238 [PPC] Don't flush the L1-D cache after accessing user data. 3239 3240 noxsave [BUGS=X86] Disables x86 extended register state save 3241 and restore using xsave. The kernel will fallback to 3242 enabling legacy floating-point and sse state. 3243 3244 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3245 register states. The kernel will fall back to use 3246 xsave to save the states. By using this parameter, 3247 performance of saving the states is degraded because 3248 xsave doesn't support modified optimization while 3249 xsaveopt supports it on xsaveopt enabled systems. 3250 3251 noxsaves [X86] Disables xsaves and xrstors used in saving and 3252 restoring x86 extended register state in compacted 3253 form of xsave area. The kernel will fall back to use 3254 xsaveopt and xrstor to save and restore the states 3255 in standard form of xsave area. By using this 3256 parameter, xsave area per process might occupy more 3257 memory on xsaves enabled systems. 3258 3259 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3260 wfi(ARM) instruction doesn't work correctly and not to 3261 use it. This is also useful when using JTAG debugger. 3262 3263 no_file_caps Tells the kernel not to honor file capabilities. The 3264 only way then for a file to be executed with privilege 3265 is to be setuid root or executed by root. 3266 3267 nohalt [IA-64] Tells the kernel not to use the power saving 3268 function PAL_HALT_LIGHT when idle. This increases 3269 power-consumption. On the positive side, it reduces 3270 interrupt wake-up latency, which may improve performance 3271 in certain environments such as networked servers or 3272 real-time systems. 3273 3274 nohibernate [HIBERNATION] Disable hibernation and resume. 3275 3276 nohz= [KNL] Boottime enable/disable dynamic ticks 3277 Valid arguments: on, off 3278 Default: on 3279 3280 nohz_full= [KNL,BOOT,SMP,ISOL] 3281 The argument is a cpu list, as described above. 3282 In kernels built with CONFIG_NO_HZ_FULL=y, set 3283 the specified list of CPUs whose tick will be stopped 3284 whenever possible. The boot CPU will be forced outside 3285 the range to maintain the timekeeping. Any CPUs 3286 in this list will have their RCU callbacks offloaded, 3287 just as if they had also been called out in the 3288 rcu_nocbs= boot parameter. 3289 3290 noiotrap [SH] Disables trapped I/O port accesses. 3291 3292 noirqdebug [X86-32] Disables the code which attempts to detect and 3293 disable unhandled interrupt sources. 3294 3295 no_timer_check [X86,APIC] Disables the code which tests for 3296 broken timer IRQ sources. 3297 3298 noisapnp [ISAPNP] Disables ISA PnP code. 3299 3300 noinitrd [RAM] Tells the kernel not to load any configured 3301 initial RAM disk. 3302 3303 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3304 remapping. 3305 [Deprecated - use intremap=off] 3306 3307 nointroute [IA-64] 3308 3309 noinvpcid [X86] Disable the INVPCID cpu feature. 3310 3311 nojitter [IA-64] Disables jitter checking for ITC timers. 3312 3313 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3314 3315 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3316 fault handling. 3317 3318 no-vmw-sched-clock 3319 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3320 clock and use the default one. 3321 3322 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3323 accounting. steal time is computed, but won't 3324 influence scheduler behaviour 3325 3326 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3327 3328 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3329 3330 noltlbs [PPC] Do not use large page/tlb entries for kernel 3331 lowmem mapping on PPC40x and PPC8xx 3332 3333 nomca [IA-64] Disable machine check abort handling 3334 3335 nomce [X86-32] Disable Machine Check Exception 3336 3337 nomfgpt [X86-32] Disable Multi-Function General Purpose 3338 Timer usage (for AMD Geode machines). 3339 3340 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3341 shutdown the other cpus. Instead use the REBOOT_VECTOR 3342 irq. 3343 3344 nomodule Disable module load 3345 3346 nopat [X86] Disable PAT (page attribute table extension of 3347 pagetables) support. 3348 3349 nopcid [X86-64] Disable the PCID cpu feature. 3350 3351 norandmaps Don't use address space randomization. Equivalent to 3352 echo 0 > /proc/sys/kernel/randomize_va_space 3353 3354 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3355 with UP alternatives 3356 3357 nordrand [X86] Disable kernel use of the RDRAND and 3358 RDSEED instructions even if they are supported 3359 by the processor. RDRAND and RDSEED are still 3360 available to user space applications. 3361 3362 noresume [SWSUSP] Disables resume and restores original swap 3363 space. 3364 3365 no-scroll [VGA] Disables scrollback. 3366 This is required for the Braillex ib80-piezo Braille 3367 reader made by F.H. Papenmeier (Germany). 3368 3369 nosbagart [IA-64] 3370 3371 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3372 3373 nosgx [X86-64,SGX] Disables Intel SGX kernel support. 3374 3375 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3376 and disable the IO APIC. legacy for "maxcpus=0". 3377 3378 nosoftlockup [KNL] Disable the soft-lockup detector. 3379 3380 nosync [HW,M68K] Disables sync negotiation for all devices. 3381 3382 nowatchdog [KNL] Disable both lockup detectors, i.e. 3383 soft-lockup and NMI watchdog (hard-lockup). 3384 3385 nowb [ARM] 3386 3387 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3388 3389 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3390 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3391 Some features depend on CPU0. Known dependencies are: 3392 1. Resume from suspend/hibernate depends on CPU0. 3393 Suspend/hibernate will fail if CPU0 is offline and you 3394 need to online CPU0 before suspend/hibernate. 3395 2. PIC interrupts also depend on CPU0. CPU0 can't be 3396 removed if a PIC interrupt is detected. 3397 It's said poweroff/reboot may depend on CPU0 on some 3398 machines although I haven't seen such issues so far 3399 after CPU0 is offline on a few tested machines. 3400 If the dependencies are under your control, you can 3401 turn on cpu0_hotplug. 3402 3403 nps_mtm_hs_ctr= [KNL,ARC] 3404 This parameter sets the maximum duration, in 3405 cycles, each HW thread of the CTOP can run 3406 without interruptions, before HW switches it. 3407 The actual maximum duration is 16 times this 3408 parameter's value. 3409 Format: integer between 1 and 255 3410 Default: 255 3411 3412 nptcg= [IA-64] Override max number of concurrent global TLB 3413 purges which is reported from either PAL_VM_SUMMARY or 3414 SAL PALO. 3415 3416 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3417 could support. nr_cpus=n : n >= 1 limits the kernel to 3418 support 'n' processors. It could be larger than the 3419 number of already plugged CPU during bootup, later in 3420 runtime you can physically add extra cpu until it reaches 3421 n. So during boot up some boot time memory for per-cpu 3422 variables need be pre-allocated for later physical cpu 3423 hot plugging. 3424 3425 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3426 3427 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3428 Allowed values are enable and disable 3429 3430 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3431 'node', 'default' can be specified 3432 This can be set from sysctl after boot. 3433 See Documentation/admin-guide/sysctl/vm.rst for details. 3434 3435 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3436 See Documentation/core-api/debugging-via-ohci1394.rst for more 3437 info. 3438 3439 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3440 Rather than timing out after 20 ms if an EC 3441 command is not properly ACKed, override the length 3442 of the timeout. We have interrupts disabled while 3443 waiting for the ACK, so if this is set too high 3444 interrupts *may* be lost! 3445 3446 omap_mux= [OMAP] Override bootloader pin multiplexing. 3447 Format: <mux_mode0.mode_name=value>... 3448 For example, to override I2C bus2: 3449 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3450 3451 oprofile.timer= [HW] 3452 Use timer interrupt instead of performance counters 3453 3454 oprofile.cpu_type= Force an oprofile cpu type 3455 This might be useful if you have an older oprofile 3456 userland or if you want common events. 3457 Format: { arch_perfmon } 3458 arch_perfmon: [X86] Force use of architectural 3459 perfmon on Intel CPUs instead of the 3460 CPU specific event set. 3461 timer: [X86] Force use of architectural NMI 3462 timer mode (see also oprofile.timer 3463 for generic hr timer mode) 3464 3465 oops=panic Always panic on oopses. Default is to just kill the 3466 process, but there is a small probability of 3467 deadlocking the machine. 3468 This will also cause panics on machine check exceptions. 3469 Useful together with panic=30 to trigger a reboot. 3470 3471 page_alloc.shuffle= 3472 [KNL] Boolean flag to control whether the page allocator 3473 should randomize its free lists. The randomization may 3474 be automatically enabled if the kernel detects it is 3475 running on a platform with a direct-mapped memory-side 3476 cache, and this parameter can be used to 3477 override/disable that behavior. The state of the flag 3478 can be read from sysfs at: 3479 /sys/module/page_alloc/parameters/shuffle. 3480 3481 page_owner= [KNL] Boot-time page_owner enabling option. 3482 Storage of the information about who allocated 3483 each page is disabled in default. With this switch, 3484 we can turn it on. 3485 on: enable the feature 3486 3487 page_poison= [KNL] Boot-time parameter changing the state of 3488 poisoning on the buddy allocator, available with 3489 CONFIG_PAGE_POISONING=y. 3490 off: turn off poisoning (default) 3491 on: turn on poisoning 3492 3493 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3494 timeout > 0: seconds before rebooting 3495 timeout = 0: wait forever 3496 timeout < 0: reboot immediately 3497 Format: <timeout> 3498 3499 panic_print= Bitmask for printing system info when panic happens. 3500 User can chose combination of the following bits: 3501 bit 0: print all tasks info 3502 bit 1: print system memory info 3503 bit 2: print timer info 3504 bit 3: print locks info if CONFIG_LOCKDEP is on 3505 bit 4: print ftrace buffer 3506 bit 5: print all printk messages in buffer 3507 3508 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3509 Format: <hex>[,nousertaint] 3510 Hexadecimal bitmask representing the set of TAINT flags 3511 that will cause the kernel to panic when add_taint() is 3512 called with any of the flags in this set. 3513 The optional switch "nousertaint" can be utilized to 3514 prevent userspace forced crashes by writing to sysctl 3515 /proc/sys/kernel/tainted any flagset matching with the 3516 bitmask set on panic_on_taint. 3517 See Documentation/admin-guide/tainted-kernels.rst for 3518 extra details on the taint flags that users can pick 3519 to compose the bitmask to assign to panic_on_taint. 3520 3521 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3522 on a WARN(). 3523 3524 crash_kexec_post_notifiers 3525 Run kdump after running panic-notifiers and dumping 3526 kmsg. This only for the users who doubt kdump always 3527 succeeds in any situation. 3528 Note that this also increases risks of kdump failure, 3529 because some panic notifiers can make the crashed 3530 kernel more unstable. 3531 3532 parkbd.port= [HW] Parallel port number the keyboard adapter is 3533 connected to, default is 0. 3534 Format: <parport#> 3535 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3536 0 for XT, 1 for AT (default is AT). 3537 Format: <mode> 3538 3539 parport= [HW,PPT] Specify parallel ports. 0 disables. 3540 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3541 Use 'auto' to force the driver to use any 3542 IRQ/DMA settings detected (the default is to 3543 ignore detected IRQ/DMA settings because of 3544 possible conflicts). You can specify the base 3545 address, IRQ, and DMA settings; IRQ and DMA 3546 should be numbers, or 'auto' (for using detected 3547 settings on that particular port), or 'nofifo' 3548 (to avoid using a FIFO even if it is detected). 3549 Parallel ports are assigned in the order they 3550 are specified on the command line, starting 3551 with parport0. 3552 3553 parport_init_mode= [HW,PPT] 3554 Configure VIA parallel port to operate in 3555 a specific mode. This is necessary on Pegasos 3556 computer where firmware has no options for setting 3557 up parallel port mode and sets it to spp. 3558 Currently this function knows 686a and 8231 chips. 3559 Format: [spp|ps2|epp|ecp|ecpepp] 3560 3561 pause_on_oops= 3562 Halt all CPUs after the first oops has been printed for 3563 the specified number of seconds. This is to be used if 3564 your oopses keep scrolling off the screen. 3565 3566 pcbit= [HW,ISDN] 3567 3568 pcd. [PARIDE] 3569 See header of drivers/block/paride/pcd.c. 3570 See also Documentation/admin-guide/blockdev/paride.rst. 3571 3572 pci=option[,option...] [PCI] various PCI subsystem options. 3573 3574 Some options herein operate on a specific device 3575 or a set of devices (<pci_dev>). These are 3576 specified in one of the following formats: 3577 3578 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3579 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3580 3581 Note: the first format specifies a PCI 3582 bus/device/function address which may change 3583 if new hardware is inserted, if motherboard 3584 firmware changes, or due to changes caused 3585 by other kernel parameters. If the 3586 domain is left unspecified, it is 3587 taken to be zero. Optionally, a path 3588 to a device through multiple device/function 3589 addresses can be specified after the base 3590 address (this is more robust against 3591 renumbering issues). The second format 3592 selects devices using IDs from the 3593 configuration space which may match multiple 3594 devices in the system. 3595 3596 earlydump dump PCI config space before the kernel 3597 changes anything 3598 off [X86] don't probe for the PCI bus 3599 bios [X86-32] force use of PCI BIOS, don't access 3600 the hardware directly. Use this if your machine 3601 has a non-standard PCI host bridge. 3602 nobios [X86-32] disallow use of PCI BIOS, only direct 3603 hardware access methods are allowed. Use this 3604 if you experience crashes upon bootup and you 3605 suspect they are caused by the BIOS. 3606 conf1 [X86] Force use of PCI Configuration Access 3607 Mechanism 1 (config address in IO port 0xCF8, 3608 data in IO port 0xCFC, both 32-bit). 3609 conf2 [X86] Force use of PCI Configuration Access 3610 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3611 the function, IO port 0xCFA, also 8-bit, sets 3612 bus number. The config space is then accessed 3613 through ports 0xC000-0xCFFF). 3614 See http://wiki.osdev.org/PCI for more info 3615 on the configuration access mechanisms. 3616 noaer [PCIE] If the PCIEAER kernel config parameter is 3617 enabled, this kernel boot option can be used to 3618 disable the use of PCIE advanced error reporting. 3619 nodomains [PCI] Disable support for multiple PCI 3620 root domains (aka PCI segments, in ACPI-speak). 3621 nommconf [X86] Disable use of MMCONFIG for PCI 3622 Configuration 3623 check_enable_amd_mmconf [X86] check for and enable 3624 properly configured MMIO access to PCI 3625 config space on AMD family 10h CPU 3626 nomsi [MSI] If the PCI_MSI kernel config parameter is 3627 enabled, this kernel boot option can be used to 3628 disable the use of MSI interrupts system-wide. 3629 noioapicquirk [APIC] Disable all boot interrupt quirks. 3630 Safety option to keep boot IRQs enabled. This 3631 should never be necessary. 3632 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3633 primary IO-APIC for bridges that cannot disable 3634 boot IRQs. This fixes a source of spurious IRQs 3635 when the system masks IRQs. 3636 noioapicreroute [APIC] Disable workaround that uses the 3637 boot IRQ equivalent of an IRQ that connects to 3638 a chipset where boot IRQs cannot be disabled. 3639 The opposite of ioapicreroute. 3640 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3641 routing table. These calls are known to be buggy 3642 on several machines and they hang the machine 3643 when used, but on other computers it's the only 3644 way to get the interrupt routing table. Try 3645 this option if the kernel is unable to allocate 3646 IRQs or discover secondary PCI buses on your 3647 motherboard. 3648 rom [X86] Assign address space to expansion ROMs. 3649 Use with caution as certain devices share 3650 address decoders between ROMs and other 3651 resources. 3652 norom [X86] Do not assign address space to 3653 expansion ROMs that do not already have 3654 BIOS assigned address ranges. 3655 nobar [X86] Do not assign address space to the 3656 BARs that weren't assigned by the BIOS. 3657 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3658 assigned automatically to PCI devices. You can 3659 make the kernel exclude IRQs of your ISA cards 3660 this way. 3661 pirqaddr=0xAAAAA [X86] Specify the physical address 3662 of the PIRQ table (normally generated 3663 by the BIOS) if it is outside the 3664 F0000h-100000h range. 3665 lastbus=N [X86] Scan all buses thru bus #N. Can be 3666 useful if the kernel is unable to find your 3667 secondary buses and you want to tell it 3668 explicitly which ones they are. 3669 assign-busses [X86] Always assign all PCI bus 3670 numbers ourselves, overriding 3671 whatever the firmware may have done. 3672 usepirqmask [X86] Honor the possible IRQ mask stored 3673 in the BIOS $PIR table. This is needed on 3674 some systems with broken BIOSes, notably 3675 some HP Pavilion N5400 and Omnibook XE3 3676 notebooks. This will have no effect if ACPI 3677 IRQ routing is enabled. 3678 noacpi [X86] Do not use ACPI for IRQ routing 3679 or for PCI scanning. 3680 use_crs [X86] Use PCI host bridge window information 3681 from ACPI. On BIOSes from 2008 or later, this 3682 is enabled by default. If you need to use this, 3683 please report a bug. 3684 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3685 If you need to use this, please report a bug. 3686 routeirq Do IRQ routing for all PCI devices. 3687 This is normally done in pci_enable_device(), 3688 so this option is a temporary workaround 3689 for broken drivers that don't call it. 3690 skip_isa_align [X86] do not align io start addr, so can 3691 handle more pci cards 3692 noearly [X86] Don't do any early type 1 scanning. 3693 This might help on some broken boards which 3694 machine check when some devices' config space 3695 is read. But various workarounds are disabled 3696 and some IOMMU drivers will not work. 3697 bfsort Sort PCI devices into breadth-first order. 3698 This sorting is done to get a device 3699 order compatible with older (<= 2.4) kernels. 3700 nobfsort Don't sort PCI devices into breadth-first order. 3701 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3702 tuning and use the BIOS-configured MPS defaults. 3703 pcie_bus_safe Set every device's MPS to the largest value 3704 supported by all devices below the root complex. 3705 pcie_bus_perf Set device MPS to the largest allowable MPS 3706 based on its parent bus. Also set MRRS (Max 3707 Read Request Size) to the largest supported 3708 value (no larger than the MPS that the device 3709 or bus can support) for best performance. 3710 pcie_bus_peer2peer Set every device's MPS to 128B, which 3711 every device is guaranteed to support. This 3712 configuration allows peer-to-peer DMA between 3713 any pair of devices, possibly at the cost of 3714 reduced performance. This also guarantees 3715 that hot-added devices will work. 3716 cbiosize=nn[KMG] The fixed amount of bus space which is 3717 reserved for the CardBus bridge's IO window. 3718 The default value is 256 bytes. 3719 cbmemsize=nn[KMG] The fixed amount of bus space which is 3720 reserved for the CardBus bridge's memory 3721 window. The default value is 64 megabytes. 3722 resource_alignment= 3723 Format: 3724 [<order of align>@]<pci_dev>[; ...] 3725 Specifies alignment and device to reassign 3726 aligned memory resources. How to 3727 specify the device is described above. 3728 If <order of align> is not specified, 3729 PAGE_SIZE is used as alignment. 3730 A PCI-PCI bridge can be specified if resource 3731 windows need to be expanded. 3732 To specify the alignment for several 3733 instances of a device, the PCI vendor, 3734 device, subvendor, and subdevice may be 3735 specified, e.g., 12@pci:8086:9c22:103c:198f 3736 for 4096-byte alignment. 3737 ecrc= Enable/disable PCIe ECRC (transaction layer 3738 end-to-end CRC checking). 3739 bios: Use BIOS/firmware settings. This is the 3740 the default. 3741 off: Turn ECRC off 3742 on: Turn ECRC on. 3743 hpiosize=nn[KMG] The fixed amount of bus space which is 3744 reserved for hotplug bridge's IO window. 3745 Default size is 256 bytes. 3746 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3747 reserved for hotplug bridge's MMIO window. 3748 Default size is 2 megabytes. 3749 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3750 reserved for hotplug bridge's MMIO_PREF window. 3751 Default size is 2 megabytes. 3752 hpmemsize=nn[KMG] The fixed amount of bus space which is 3753 reserved for hotplug bridge's MMIO and 3754 MMIO_PREF window. 3755 Default size is 2 megabytes. 3756 hpbussize=nn The minimum amount of additional bus numbers 3757 reserved for buses below a hotplug bridge. 3758 Default is 1. 3759 realloc= Enable/disable reallocating PCI bridge resources 3760 if allocations done by BIOS are too small to 3761 accommodate resources required by all child 3762 devices. 3763 off: Turn realloc off 3764 on: Turn realloc on 3765 realloc same as realloc=on 3766 noari do not use PCIe ARI. 3767 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3768 do not use PCIe ATS (and IOMMU device IOTLB). 3769 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3770 only look for one device below a PCIe downstream 3771 port. 3772 big_root_window Try to add a big 64bit memory window to the PCIe 3773 root complex on AMD CPUs. Some GFX hardware 3774 can resize a BAR to allow access to all VRAM. 3775 Adding the window is slightly risky (it may 3776 conflict with unreported devices), so this 3777 taints the kernel. 3778 disable_acs_redir=<pci_dev>[; ...] 3779 Specify one or more PCI devices (in the format 3780 specified above) separated by semicolons. 3781 Each device specified will have the PCI ACS 3782 redirect capabilities forced off which will 3783 allow P2P traffic between devices through 3784 bridges without forcing it upstream. Note: 3785 this removes isolation between devices and 3786 may put more devices in an IOMMU group. 3787 force_floating [S390] Force usage of floating interrupts. 3788 nomio [S390] Do not use MIO instructions. 3789 norid [S390] ignore the RID field and force use of 3790 one PCI domain per PCI function 3791 3792 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3793 Management. 3794 off Disable ASPM. 3795 force Enable ASPM even on devices that claim not to support it. 3796 WARNING: Forcing ASPM on may cause system lockups. 3797 3798 pcie_ports= [PCIE] PCIe port services handling: 3799 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3800 even if the platform doesn't give the OS permission to 3801 use them. This may cause conflicts if the platform 3802 also tries to use these services. 3803 dpc-native Use native PCIe service for DPC only. May 3804 cause conflicts if firmware uses AER or DPC. 3805 compat Disable native PCIe services (PME, AER, DPC, PCIe 3806 hotplug). 3807 3808 pcie_port_pm= [PCIE] PCIe port power management handling: 3809 off Disable power management of all PCIe ports 3810 force Forcibly enable power management of all PCIe ports 3811 3812 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3813 nomsi Do not use MSI for native PCIe PME signaling (this makes 3814 all PCIe root ports use INTx for all services). 3815 3816 pcmv= [HW,PCMCIA] BadgePAD 4 3817 3818 pd_ignore_unused 3819 [PM] 3820 Keep all power-domains already enabled by bootloader on, 3821 even if no driver has claimed them. This is useful 3822 for debug and development, but should not be 3823 needed on a platform with proper driver support. 3824 3825 pd. [PARIDE] 3826 See Documentation/admin-guide/blockdev/paride.rst. 3827 3828 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3829 boot time. 3830 Format: { 0 | 1 } 3831 See arch/parisc/kernel/pdc_chassis.c 3832 3833 percpu_alloc= Select which percpu first chunk allocator to use. 3834 Currently supported values are "embed" and "page". 3835 Archs may support subset or none of the selections. 3836 See comments in mm/percpu.c for details on each 3837 allocator. This parameter is primarily for debugging 3838 and performance comparison. 3839 3840 pf. [PARIDE] 3841 See Documentation/admin-guide/blockdev/paride.rst. 3842 3843 pg. [PARIDE] 3844 See Documentation/admin-guide/blockdev/paride.rst. 3845 3846 pirq= [SMP,APIC] Manual mp-table setup 3847 See Documentation/x86/i386/IO-APIC.rst. 3848 3849 plip= [PPT,NET] Parallel port network link 3850 Format: { parport<nr> | timid | 0 } 3851 See also Documentation/admin-guide/parport.rst. 3852 3853 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3854 Override pmtimer IOPort with a hex value. 3855 e.g. pmtmr=0x508 3856 3857 pm_debug_messages [SUSPEND,KNL] 3858 Enable suspend/resume debug messages during boot up. 3859 3860 pnp.debug=1 [PNP] 3861 Enable PNP debug messages (depends on the 3862 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3863 via /sys/module/pnp/parameters/debug. We always show 3864 current resource usage; turning this on also shows 3865 possible settings and some assignment information. 3866 3867 pnpacpi= [ACPI] 3868 { off } 3869 3870 pnpbios= [ISAPNP] 3871 { on | off | curr | res | no-curr | no-res } 3872 3873 pnp_reserve_irq= 3874 [ISAPNP] Exclude IRQs for the autoconfiguration 3875 3876 pnp_reserve_dma= 3877 [ISAPNP] Exclude DMAs for the autoconfiguration 3878 3879 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3880 Ranges are in pairs (I/O port base and size). 3881 3882 pnp_reserve_mem= 3883 [ISAPNP] Exclude memory regions for the 3884 autoconfiguration. 3885 Ranges are in pairs (memory base and size). 3886 3887 ports= [IP_VS_FTP] IPVS ftp helper module 3888 Default is 21. 3889 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3890 may be specified. 3891 Format: <port>,<port>.... 3892 3893 powersave=off [PPC] This option disables power saving features. 3894 It specifically disables cpuidle and sets the 3895 platform machine description specific power_save 3896 function to NULL. On Idle the CPU just reduces 3897 execution priority. 3898 3899 ppc_strict_facility_enable 3900 [PPC] This option catches any kernel floating point, 3901 Altivec, VSX and SPE outside of regions specifically 3902 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3903 There is some performance impact when enabling this. 3904 3905 ppc_tm= [PPC] 3906 Format: {"off"} 3907 Disable Hardware Transactional Memory 3908 3909 print-fatal-signals= 3910 [KNL] debug: print fatal signals 3911 3912 If enabled, warn about various signal handling 3913 related application anomalies: too many signals, 3914 too many POSIX.1 timers, fatal signals causing a 3915 coredump - etc. 3916 3917 If you hit the warning due to signal overflow, 3918 you might want to try "ulimit -i unlimited". 3919 3920 default: off. 3921 3922 printk.always_kmsg_dump= 3923 Trigger kmsg_dump for cases other than kernel oops or 3924 panics 3925 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3926 default: disabled 3927 3928 printk.devkmsg={on,off,ratelimit} 3929 Control writing to /dev/kmsg. 3930 on - unlimited logging to /dev/kmsg from userspace 3931 off - logging to /dev/kmsg disabled 3932 ratelimit - ratelimit the logging 3933 Default: ratelimit 3934 3935 printk.time= Show timing data prefixed to each printk message line 3936 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3937 3938 processor.max_cstate= [HW,ACPI] 3939 Limit processor to maximum C-state 3940 max_cstate=9 overrides any DMI blacklist limit. 3941 3942 processor.nocst [HW,ACPI] 3943 Ignore the _CST method to determine C-states, 3944 instead using the legacy FADT method 3945 3946 profile= [KNL] Enable kernel profiling via /proc/profile 3947 Format: [<profiletype>,]<number> 3948 Param: <profiletype>: "schedule", "sleep", or "kvm" 3949 [defaults to kernel profiling] 3950 Param: "schedule" - profile schedule points. 3951 Param: "sleep" - profile D-state sleeping (millisecs). 3952 Requires CONFIG_SCHEDSTATS 3953 Param: "kvm" - profile VM exits. 3954 Param: <number> - step/bucket size as a power of 2 for 3955 statistical time based profiling. 3956 3957 prompt_ramdisk= [RAM] [Deprecated] 3958 3959 prot_virt= [S390] enable hosting protected virtual machines 3960 isolated from the hypervisor (if hardware supports 3961 that). 3962 Format: <bool> 3963 3964 psi= [KNL] Enable or disable pressure stall information 3965 tracking. 3966 Format: <bool> 3967 3968 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3969 probe for; one of (bare|imps|exps|lifebook|any). 3970 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3971 per second. 3972 psmouse.resetafter= [HW,MOUSE] 3973 Try to reset the device after so many bad packets 3974 (0 = never). 3975 psmouse.resolution= 3976 [HW,MOUSE] Set desired mouse resolution, in dpi. 3977 psmouse.smartscroll= 3978 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3979 0 = disabled, 1 = enabled (default). 3980 3981 pstore.backend= Specify the name of the pstore backend to use 3982 3983 pt. [PARIDE] 3984 See Documentation/admin-guide/blockdev/paride.rst. 3985 3986 pti= [X86-64] Control Page Table Isolation of user and 3987 kernel address spaces. Disabling this feature 3988 removes hardening, but improves performance of 3989 system calls and interrupts. 3990 3991 on - unconditionally enable 3992 off - unconditionally disable 3993 auto - kernel detects whether your CPU model is 3994 vulnerable to issues that PTI mitigates 3995 3996 Not specifying this option is equivalent to pti=auto. 3997 3998 nopti [X86-64] 3999 Equivalent to pti=off 4000 4001 pty.legacy_count= 4002 [KNL] Number of legacy pty's. Overwrites compiled-in 4003 default number. 4004 4005 quiet [KNL] Disable most log messages 4006 4007 r128= [HW,DRM] 4008 4009 raid= [HW,RAID] 4010 See Documentation/admin-guide/md.rst. 4011 4012 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4013 See Documentation/admin-guide/blockdev/ramdisk.rst. 4014 4015 ramdisk_start= [RAM] RAM disk image start address 4016 4017 random.trust_cpu={on,off} 4018 [KNL] Enable or disable trusting the use of the 4019 CPU's random number generator (if available) to 4020 fully seed the kernel's CRNG. Default is controlled 4021 by CONFIG_RANDOM_TRUST_CPU. 4022 4023 ras=option[,option,...] [KNL] RAS-specific options 4024 4025 cec_disable [X86] 4026 Disable the Correctable Errors Collector, 4027 see CONFIG_RAS_CEC help text. 4028 4029 rcu_nocbs= [KNL] 4030 The argument is a cpu list, as described above, 4031 except that the string "all" can be used to 4032 specify every CPU on the system. 4033 4034 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4035 the specified list of CPUs to be no-callback CPUs. 4036 Invocation of these CPUs' RCU callbacks will be 4037 offloaded to "rcuox/N" kthreads created for that 4038 purpose, where "x" is "p" for RCU-preempt, and 4039 "s" for RCU-sched, and "N" is the CPU number. 4040 This reduces OS jitter on the offloaded CPUs, 4041 which can be useful for HPC and real-time 4042 workloads. It can also improve energy efficiency 4043 for asymmetric multiprocessors. 4044 4045 rcu_nocb_poll [KNL] 4046 Rather than requiring that offloaded CPUs 4047 (specified by rcu_nocbs= above) explicitly 4048 awaken the corresponding "rcuoN" kthreads, 4049 make these kthreads poll for callbacks. 4050 This improves the real-time response for the 4051 offloaded CPUs by relieving them of the need to 4052 wake up the corresponding kthread, but degrades 4053 energy efficiency by requiring that the kthreads 4054 periodically wake up to do the polling. 4055 4056 rcutree.blimit= [KNL] 4057 Set maximum number of finished RCU callbacks to 4058 process in one batch. 4059 4060 rcutree.dump_tree= [KNL] 4061 Dump the structure of the rcu_node combining tree 4062 out at early boot. This is used for diagnostic 4063 purposes, to verify correct tree setup. 4064 4065 rcutree.gp_cleanup_delay= [KNL] 4066 Set the number of jiffies to delay each step of 4067 RCU grace-period cleanup. 4068 4069 rcutree.gp_init_delay= [KNL] 4070 Set the number of jiffies to delay each step of 4071 RCU grace-period initialization. 4072 4073 rcutree.gp_preinit_delay= [KNL] 4074 Set the number of jiffies to delay each step of 4075 RCU grace-period pre-initialization, that is, 4076 the propagation of recent CPU-hotplug changes up 4077 the rcu_node combining tree. 4078 4079 rcutree.use_softirq= [KNL] 4080 If set to zero, move all RCU_SOFTIRQ processing to 4081 per-CPU rcuc kthreads. Defaults to a non-zero 4082 value, meaning that RCU_SOFTIRQ is used by default. 4083 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4084 4085 rcutree.rcu_fanout_exact= [KNL] 4086 Disable autobalancing of the rcu_node combining 4087 tree. This is used by rcutorture, and might 4088 possibly be useful for architectures having high 4089 cache-to-cache transfer latencies. 4090 4091 rcutree.rcu_fanout_leaf= [KNL] 4092 Change the number of CPUs assigned to each 4093 leaf rcu_node structure. Useful for very 4094 large systems, which will choose the value 64, 4095 and for NUMA systems with large remote-access 4096 latencies, which will choose a value aligned 4097 with the appropriate hardware boundaries. 4098 4099 rcutree.rcu_min_cached_objs= [KNL] 4100 Minimum number of objects which are cached and 4101 maintained per one CPU. Object size is equal 4102 to PAGE_SIZE. The cache allows to reduce the 4103 pressure to page allocator, also it makes the 4104 whole algorithm to behave better in low memory 4105 condition. 4106 4107 rcutree.jiffies_till_first_fqs= [KNL] 4108 Set delay from grace-period initialization to 4109 first attempt to force quiescent states. 4110 Units are jiffies, minimum value is zero, 4111 and maximum value is HZ. 4112 4113 rcutree.jiffies_till_next_fqs= [KNL] 4114 Set delay between subsequent attempts to force 4115 quiescent states. Units are jiffies, minimum 4116 value is one, and maximum value is HZ. 4117 4118 rcutree.jiffies_till_sched_qs= [KNL] 4119 Set required age in jiffies for a 4120 given grace period before RCU starts 4121 soliciting quiescent-state help from 4122 rcu_note_context_switch() and cond_resched(). 4123 If not specified, the kernel will calculate 4124 a value based on the most recent settings 4125 of rcutree.jiffies_till_first_fqs 4126 and rcutree.jiffies_till_next_fqs. 4127 This calculated value may be viewed in 4128 rcutree.jiffies_to_sched_qs. Any attempt to set 4129 rcutree.jiffies_to_sched_qs will be cheerfully 4130 overwritten. 4131 4132 rcutree.kthread_prio= [KNL,BOOT] 4133 Set the SCHED_FIFO priority of the RCU per-CPU 4134 kthreads (rcuc/N). This value is also used for 4135 the priority of the RCU boost threads (rcub/N) 4136 and for the RCU grace-period kthreads (rcu_bh, 4137 rcu_preempt, and rcu_sched). If RCU_BOOST is 4138 set, valid values are 1-99 and the default is 1 4139 (the least-favored priority). Otherwise, when 4140 RCU_BOOST is not set, valid values are 0-99 and 4141 the default is zero (non-realtime operation). 4142 4143 rcutree.rcu_nocb_gp_stride= [KNL] 4144 Set the number of NOCB callback kthreads in 4145 each group, which defaults to the square root 4146 of the number of CPUs. Larger numbers reduce 4147 the wakeup overhead on the global grace-period 4148 kthread, but increases that same overhead on 4149 each group's NOCB grace-period kthread. 4150 4151 rcutree.qhimark= [KNL] 4152 Set threshold of queued RCU callbacks beyond which 4153 batch limiting is disabled. 4154 4155 rcutree.qlowmark= [KNL] 4156 Set threshold of queued RCU callbacks below which 4157 batch limiting is re-enabled. 4158 4159 rcutree.qovld= [KNL] 4160 Set threshold of queued RCU callbacks beyond which 4161 RCU's force-quiescent-state scan will aggressively 4162 enlist help from cond_resched() and sched IPIs to 4163 help CPUs more quickly reach quiescent states. 4164 Set to less than zero to make this be set based 4165 on rcutree.qhimark at boot time and to zero to 4166 disable more aggressive help enlistment. 4167 4168 rcutree.rcu_idle_gp_delay= [KNL] 4169 Set wakeup interval for idle CPUs that have 4170 RCU callbacks (RCU_FAST_NO_HZ=y). 4171 4172 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4173 Set wakeup interval for idle CPUs that have 4174 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4175 Lazy RCU callbacks are those which RCU can 4176 prove do nothing more than free memory. 4177 4178 rcutree.rcu_kick_kthreads= [KNL] 4179 Cause the grace-period kthread to get an extra 4180 wake_up() if it sleeps three times longer than 4181 it should at force-quiescent-state time. 4182 This wake_up() will be accompanied by a 4183 WARN_ONCE() splat and an ftrace_dump(). 4184 4185 rcutree.rcu_unlock_delay= [KNL] 4186 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4187 this specifies an rcu_read_unlock()-time delay 4188 in microseconds. This defaults to zero. 4189 Larger delays increase the probability of 4190 catching RCU pointer leaks, that is, buggy use 4191 of RCU-protected pointers after the relevant 4192 rcu_read_unlock() has completed. 4193 4194 rcutree.sysrq_rcu= [KNL] 4195 Commandeer a sysrq key to dump out Tree RCU's 4196 rcu_node tree with an eye towards determining 4197 why a new grace period has not yet started. 4198 4199 rcuscale.gp_async= [KNL] 4200 Measure performance of asynchronous 4201 grace-period primitives such as call_rcu(). 4202 4203 rcuscale.gp_async_max= [KNL] 4204 Specify the maximum number of outstanding 4205 callbacks per writer thread. When a writer 4206 thread exceeds this limit, it invokes the 4207 corresponding flavor of rcu_barrier() to allow 4208 previously posted callbacks to drain. 4209 4210 rcuscale.gp_exp= [KNL] 4211 Measure performance of expedited synchronous 4212 grace-period primitives. 4213 4214 rcuscale.holdoff= [KNL] 4215 Set test-start holdoff period. The purpose of 4216 this parameter is to delay the start of the 4217 test until boot completes in order to avoid 4218 interference. 4219 4220 rcuscale.kfree_rcu_test= [KNL] 4221 Set to measure performance of kfree_rcu() flooding. 4222 4223 rcuscale.kfree_nthreads= [KNL] 4224 The number of threads running loops of kfree_rcu(). 4225 4226 rcuscale.kfree_alloc_num= [KNL] 4227 Number of allocations and frees done in an iteration. 4228 4229 rcuscale.kfree_loops= [KNL] 4230 Number of loops doing rcuscale.kfree_alloc_num number 4231 of allocations and frees. 4232 4233 rcuscale.nreaders= [KNL] 4234 Set number of RCU readers. The value -1 selects 4235 N, where N is the number of CPUs. A value 4236 "n" less than -1 selects N-n+1, where N is again 4237 the number of CPUs. For example, -2 selects N 4238 (the number of CPUs), -3 selects N+1, and so on. 4239 A value of "n" less than or equal to -N selects 4240 a single reader. 4241 4242 rcuscale.nwriters= [KNL] 4243 Set number of RCU writers. The values operate 4244 the same as for rcuscale.nreaders. 4245 N, where N is the number of CPUs 4246 4247 rcuscale.perf_type= [KNL] 4248 Specify the RCU implementation to test. 4249 4250 rcuscale.shutdown= [KNL] 4251 Shut the system down after performance tests 4252 complete. This is useful for hands-off automated 4253 testing. 4254 4255 rcuscale.verbose= [KNL] 4256 Enable additional printk() statements. 4257 4258 rcuscale.writer_holdoff= [KNL] 4259 Write-side holdoff between grace periods, 4260 in microseconds. The default of zero says 4261 no holdoff. 4262 4263 rcutorture.fqs_duration= [KNL] 4264 Set duration of force_quiescent_state bursts 4265 in microseconds. 4266 4267 rcutorture.fqs_holdoff= [KNL] 4268 Set holdoff time within force_quiescent_state bursts 4269 in microseconds. 4270 4271 rcutorture.fqs_stutter= [KNL] 4272 Set wait time between force_quiescent_state bursts 4273 in seconds. 4274 4275 rcutorture.fwd_progress= [KNL] 4276 Enable RCU grace-period forward-progress testing 4277 for the types of RCU supporting this notion. 4278 4279 rcutorture.fwd_progress_div= [KNL] 4280 Specify the fraction of a CPU-stall-warning 4281 period to do tight-loop forward-progress testing. 4282 4283 rcutorture.fwd_progress_holdoff= [KNL] 4284 Number of seconds to wait between successive 4285 forward-progress tests. 4286 4287 rcutorture.fwd_progress_need_resched= [KNL] 4288 Enclose cond_resched() calls within checks for 4289 need_resched() during tight-loop forward-progress 4290 testing. 4291 4292 rcutorture.gp_cond= [KNL] 4293 Use conditional/asynchronous update-side 4294 primitives, if available. 4295 4296 rcutorture.gp_exp= [KNL] 4297 Use expedited update-side primitives, if available. 4298 4299 rcutorture.gp_normal= [KNL] 4300 Use normal (non-expedited) asynchronous 4301 update-side primitives, if available. 4302 4303 rcutorture.gp_sync= [KNL] 4304 Use normal (non-expedited) synchronous 4305 update-side primitives, if available. If all 4306 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4307 rcutorture.gp_normal=, and rcutorture.gp_sync= 4308 are zero, rcutorture acts as if is interpreted 4309 they are all non-zero. 4310 4311 rcutorture.irqreader= [KNL] 4312 Run RCU readers from irq handlers, or, more 4313 accurately, from a timer handler. Not all RCU 4314 flavors take kindly to this sort of thing. 4315 4316 rcutorture.leakpointer= [KNL] 4317 Leak an RCU-protected pointer out of the reader. 4318 This can of course result in splats, and is 4319 intended to test the ability of things like 4320 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4321 such leaks. 4322 4323 rcutorture.n_barrier_cbs= [KNL] 4324 Set callbacks/threads for rcu_barrier() testing. 4325 4326 rcutorture.nfakewriters= [KNL] 4327 Set number of concurrent RCU writers. These just 4328 stress RCU, they don't participate in the actual 4329 test, hence the "fake". 4330 4331 rcutorture.nreaders= [KNL] 4332 Set number of RCU readers. The value -1 selects 4333 N-1, where N is the number of CPUs. A value 4334 "n" less than -1 selects N-n-2, where N is again 4335 the number of CPUs. For example, -2 selects N 4336 (the number of CPUs), -3 selects N+1, and so on. 4337 4338 rcutorture.object_debug= [KNL] 4339 Enable debug-object double-call_rcu() testing. 4340 4341 rcutorture.onoff_holdoff= [KNL] 4342 Set time (s) after boot for CPU-hotplug testing. 4343 4344 rcutorture.onoff_interval= [KNL] 4345 Set time (jiffies) between CPU-hotplug operations, 4346 or zero to disable CPU-hotplug testing. 4347 4348 rcutorture.read_exit= [KNL] 4349 Set the number of read-then-exit kthreads used 4350 to test the interaction of RCU updaters and 4351 task-exit processing. 4352 4353 rcutorture.read_exit_burst= [KNL] 4354 The number of times in a given read-then-exit 4355 episode that a set of read-then-exit kthreads 4356 is spawned. 4357 4358 rcutorture.read_exit_delay= [KNL] 4359 The delay, in seconds, between successive 4360 read-then-exit testing episodes. 4361 4362 rcutorture.shuffle_interval= [KNL] 4363 Set task-shuffle interval (s). Shuffling tasks 4364 allows some CPUs to go into dyntick-idle mode 4365 during the rcutorture test. 4366 4367 rcutorture.shutdown_secs= [KNL] 4368 Set time (s) after boot system shutdown. This 4369 is useful for hands-off automated testing. 4370 4371 rcutorture.stall_cpu= [KNL] 4372 Duration of CPU stall (s) to test RCU CPU stall 4373 warnings, zero to disable. 4374 4375 rcutorture.stall_cpu_block= [KNL] 4376 Sleep while stalling if set. This will result 4377 in warnings from preemptible RCU in addition 4378 to any other stall-related activity. 4379 4380 rcutorture.stall_cpu_holdoff= [KNL] 4381 Time to wait (s) after boot before inducing stall. 4382 4383 rcutorture.stall_cpu_irqsoff= [KNL] 4384 Disable interrupts while stalling if set. 4385 4386 rcutorture.stall_gp_kthread= [KNL] 4387 Duration (s) of forced sleep within RCU 4388 grace-period kthread to test RCU CPU stall 4389 warnings, zero to disable. If both stall_cpu 4390 and stall_gp_kthread are specified, the 4391 kthread is starved first, then the CPU. 4392 4393 rcutorture.stat_interval= [KNL] 4394 Time (s) between statistics printk()s. 4395 4396 rcutorture.stutter= [KNL] 4397 Time (s) to stutter testing, for example, specifying 4398 five seconds causes the test to run for five seconds, 4399 wait for five seconds, and so on. This tests RCU's 4400 ability to transition abruptly to and from idle. 4401 4402 rcutorture.test_boost= [KNL] 4403 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4404 "Maybe" means test if the RCU implementation 4405 under test support RCU priority boosting. 4406 4407 rcutorture.test_boost_duration= [KNL] 4408 Duration (s) of each individual boost test. 4409 4410 rcutorture.test_boost_interval= [KNL] 4411 Interval (s) between each boost test. 4412 4413 rcutorture.test_no_idle_hz= [KNL] 4414 Test RCU's dyntick-idle handling. See also the 4415 rcutorture.shuffle_interval parameter. 4416 4417 rcutorture.torture_type= [KNL] 4418 Specify the RCU implementation to test. 4419 4420 rcutorture.verbose= [KNL] 4421 Enable additional printk() statements. 4422 4423 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4424 Dump ftrace buffer after reporting RCU CPU 4425 stall warning. 4426 4427 rcupdate.rcu_cpu_stall_suppress= [KNL] 4428 Suppress RCU CPU stall warning messages. 4429 4430 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4431 Suppress RCU CPU stall warning messages and 4432 rcutorture writer stall warnings that occur 4433 during early boot, that is, during the time 4434 before the init task is spawned. 4435 4436 rcupdate.rcu_cpu_stall_timeout= [KNL] 4437 Set timeout for RCU CPU stall warning messages. 4438 4439 rcupdate.rcu_expedited= [KNL] 4440 Use expedited grace-period primitives, for 4441 example, synchronize_rcu_expedited() instead 4442 of synchronize_rcu(). This reduces latency, 4443 but can increase CPU utilization, degrade 4444 real-time latency, and degrade energy efficiency. 4445 No effect on CONFIG_TINY_RCU kernels. 4446 4447 rcupdate.rcu_normal= [KNL] 4448 Use only normal grace-period primitives, 4449 for example, synchronize_rcu() instead of 4450 synchronize_rcu_expedited(). This improves 4451 real-time latency, CPU utilization, and 4452 energy efficiency, but can expose users to 4453 increased grace-period latency. This parameter 4454 overrides rcupdate.rcu_expedited. No effect on 4455 CONFIG_TINY_RCU kernels. 4456 4457 rcupdate.rcu_normal_after_boot= [KNL] 4458 Once boot has completed (that is, after 4459 rcu_end_inkernel_boot() has been invoked), use 4460 only normal grace-period primitives. No effect 4461 on CONFIG_TINY_RCU kernels. 4462 4463 rcupdate.rcu_task_ipi_delay= [KNL] 4464 Set time in jiffies during which RCU tasks will 4465 avoid sending IPIs, starting with the beginning 4466 of a given grace period. Setting a large 4467 number avoids disturbing real-time workloads, 4468 but lengthens grace periods. 4469 4470 rcupdate.rcu_task_stall_timeout= [KNL] 4471 Set timeout in jiffies for RCU task stall warning 4472 messages. Disable with a value less than or equal 4473 to zero. 4474 4475 rcupdate.rcu_self_test= [KNL] 4476 Run the RCU early boot self tests 4477 4478 rdinit= [KNL] 4479 Format: <full_path> 4480 Run specified binary instead of /init from the ramdisk, 4481 used for early userspace startup. See initrd. 4482 4483 rdrand= [X86] 4484 force - Override the decision by the kernel to hide the 4485 advertisement of RDRAND support (this affects 4486 certain AMD processors because of buggy BIOS 4487 support, specifically around the suspend/resume 4488 path). 4489 4490 rdt= [HW,X86,RDT] 4491 Turn on/off individual RDT features. List is: 4492 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4493 mba. 4494 E.g. to turn on cmt and turn off mba use: 4495 rdt=cmt,!mba 4496 4497 reboot= [KNL] 4498 Format (x86 or x86_64): 4499 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4500 [[,]s[mp]#### \ 4501 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4502 [[,]f[orce] 4503 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4504 (prefix with 'panic_' to set mode for panic 4505 reboot only), 4506 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4507 reboot_force is either force or not specified, 4508 reboot_cpu is s[mp]#### with #### being the processor 4509 to be used for rebooting. 4510 4511 refscale.holdoff= [KNL] 4512 Set test-start holdoff period. The purpose of 4513 this parameter is to delay the start of the 4514 test until boot completes in order to avoid 4515 interference. 4516 4517 refscale.loops= [KNL] 4518 Set the number of loops over the synchronization 4519 primitive under test. Increasing this number 4520 reduces noise due to loop start/end overhead, 4521 but the default has already reduced the per-pass 4522 noise to a handful of picoseconds on ca. 2020 4523 x86 laptops. 4524 4525 refscale.nreaders= [KNL] 4526 Set number of readers. The default value of -1 4527 selects N, where N is roughly 75% of the number 4528 of CPUs. A value of zero is an interesting choice. 4529 4530 refscale.nruns= [KNL] 4531 Set number of runs, each of which is dumped onto 4532 the console log. 4533 4534 refscale.readdelay= [KNL] 4535 Set the read-side critical-section duration, 4536 measured in microseconds. 4537 4538 refscale.scale_type= [KNL] 4539 Specify the read-protection implementation to test. 4540 4541 refscale.shutdown= [KNL] 4542 Shut down the system at the end of the performance 4543 test. This defaults to 1 (shut it down) when 4544 refscale is built into the kernel and to 0 (leave 4545 it running) when refscale is built as a module. 4546 4547 refscale.verbose= [KNL] 4548 Enable additional printk() statements. 4549 4550 relax_domain_level= 4551 [KNL, SMP] Set scheduler's default relax_domain_level. 4552 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4553 4554 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4555 Format: <base1>,<size1>[,<base2>,<size2>,...] 4556 Reserve I/O ports or memory so the kernel won't use 4557 them. If <base> is less than 0x10000, the region 4558 is assumed to be I/O ports; otherwise it is memory. 4559 4560 reservetop= [X86-32] 4561 Format: nn[KMG] 4562 Reserves a hole at the top of the kernel virtual 4563 address space. 4564 4565 reservelow= [X86] 4566 Format: nn[K] 4567 Set the amount of memory to reserve for BIOS at 4568 the bottom of the address space. 4569 4570 reset_devices [KNL] Force drivers to reset the underlying device 4571 during initialization. 4572 4573 resume= [SWSUSP] 4574 Specify the partition device for software suspend 4575 Format: 4576 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4577 4578 resume_offset= [SWSUSP] 4579 Specify the offset from the beginning of the partition 4580 given by "resume=" at which the swap header is located, 4581 in <PAGE_SIZE> units (needed only for swap files). 4582 See Documentation/power/swsusp-and-swap-files.rst 4583 4584 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4585 read the resume files 4586 4587 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4588 Useful for devices that are detected asynchronously 4589 (e.g. USB and MMC devices). 4590 4591 hibernate= [HIBERNATION] 4592 noresume Don't check if there's a hibernation image 4593 present during boot. 4594 nocompress Don't compress/decompress hibernation images. 4595 no Disable hibernation and resume. 4596 protect_image Turn on image protection during restoration 4597 (that will set all pages holding image data 4598 during restoration read-only). 4599 4600 retain_initrd [RAM] Keep initrd memory after extraction 4601 4602 rfkill.default_state= 4603 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4604 etc. communication is blocked by default. 4605 1 Unblocked. 4606 4607 rfkill.master_switch_mode= 4608 0 The "airplane mode" button does nothing. 4609 1 The "airplane mode" button toggles between everything 4610 blocked and the previous configuration. 4611 2 The "airplane mode" button toggles between everything 4612 blocked and everything unblocked. 4613 4614 rhash_entries= [KNL,NET] 4615 Set number of hash buckets for route cache 4616 4617 ring3mwait=disable 4618 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4619 CPUs. 4620 4621 ro [KNL] Mount root device read-only on boot 4622 4623 rodata= [KNL] 4624 on Mark read-only kernel memory as read-only (default). 4625 off Leave read-only kernel memory writable for debugging. 4626 4627 rockchip.usb_uart 4628 Enable the uart passthrough on the designated usb port 4629 on Rockchip SoCs. When active, the signals of the 4630 debug-uart get routed to the D+ and D- pins of the usb 4631 port and the regular usb controller gets disabled. 4632 4633 root= [KNL] Root filesystem 4634 See name_to_dev_t comment in init/do_mounts.c. 4635 4636 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4637 mount the root filesystem 4638 4639 rootflags= [KNL] Set root filesystem mount option string 4640 4641 rootfstype= [KNL] Set root filesystem type 4642 4643 rootwait [KNL] Wait (indefinitely) for root device to show up. 4644 Useful for devices that are detected asynchronously 4645 (e.g. USB and MMC devices). 4646 4647 rproc_mem=nn[KMG][@address] 4648 [KNL,ARM,CMA] Remoteproc physical memory block. 4649 Memory area to be used by remote processor image, 4650 managed by CMA. 4651 4652 rw [KNL] Mount root device read-write on boot 4653 4654 S [KNL] Run init in single mode 4655 4656 s390_iommu= [HW,S390] 4657 Set s390 IOTLB flushing mode 4658 strict 4659 With strict flushing every unmap operation will result in 4660 an IOTLB flush. Default is lazy flushing before reuse, 4661 which is faster. 4662 4663 sa1100ir [NET] 4664 See drivers/net/irda/sa1100_ir.c. 4665 4666 sbni= [NET] Granch SBNI12 leased line adapter 4667 4668 sched_debug [KNL] Enables verbose scheduler debug messages. 4669 4670 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4671 Allowed values are enable and disable. This feature 4672 incurs a small amount of overhead in the scheduler 4673 but is useful for debugging and performance tuning. 4674 4675 sched_thermal_decay_shift= 4676 [KNL, SMP] Set a decay shift for scheduler thermal 4677 pressure signal. Thermal pressure signal follows the 4678 default decay period of other scheduler pelt 4679 signals(usually 32 ms but configurable). Setting 4680 sched_thermal_decay_shift will left shift the decay 4681 period for the thermal pressure signal by the shift 4682 value. 4683 i.e. with the default pelt decay period of 32 ms 4684 sched_thermal_decay_shift thermal pressure decay pr 4685 1 64 ms 4686 2 128 ms 4687 and so on. 4688 Format: integer between 0 and 10 4689 Default is 0. 4690 4691 scftorture.holdoff= [KNL] 4692 Number of seconds to hold off before starting 4693 test. Defaults to zero for module insertion and 4694 to 10 seconds for built-in smp_call_function() 4695 tests. 4696 4697 scftorture.longwait= [KNL] 4698 Request ridiculously long waits randomly selected 4699 up to the chosen limit in seconds. Zero (the 4700 default) disables this feature. Please note 4701 that requesting even small non-zero numbers of 4702 seconds can result in RCU CPU stall warnings, 4703 softlockup complaints, and so on. 4704 4705 scftorture.nthreads= [KNL] 4706 Number of kthreads to spawn to invoke the 4707 smp_call_function() family of functions. 4708 The default of -1 specifies a number of kthreads 4709 equal to the number of CPUs. 4710 4711 scftorture.onoff_holdoff= [KNL] 4712 Number seconds to wait after the start of the 4713 test before initiating CPU-hotplug operations. 4714 4715 scftorture.onoff_interval= [KNL] 4716 Number seconds to wait between successive 4717 CPU-hotplug operations. Specifying zero (which 4718 is the default) disables CPU-hotplug operations. 4719 4720 scftorture.shutdown_secs= [KNL] 4721 The number of seconds following the start of the 4722 test after which to shut down the system. The 4723 default of zero avoids shutting down the system. 4724 Non-zero values are useful for automated tests. 4725 4726 scftorture.stat_interval= [KNL] 4727 The number of seconds between outputting the 4728 current test statistics to the console. A value 4729 of zero disables statistics output. 4730 4731 scftorture.stutter_cpus= [KNL] 4732 The number of jiffies to wait between each change 4733 to the set of CPUs under test. 4734 4735 scftorture.use_cpus_read_lock= [KNL] 4736 Use use_cpus_read_lock() instead of the default 4737 preempt_disable() to disable CPU hotplug 4738 while invoking one of the smp_call_function*() 4739 functions. 4740 4741 scftorture.verbose= [KNL] 4742 Enable additional printk() statements. 4743 4744 scftorture.weight_single= [KNL] 4745 The probability weighting to use for the 4746 smp_call_function_single() function with a zero 4747 "wait" parameter. A value of -1 selects the 4748 default if all other weights are -1. However, 4749 if at least one weight has some other value, a 4750 value of -1 will instead select a weight of zero. 4751 4752 scftorture.weight_single_wait= [KNL] 4753 The probability weighting to use for the 4754 smp_call_function_single() function with a 4755 non-zero "wait" parameter. See weight_single. 4756 4757 scftorture.weight_many= [KNL] 4758 The probability weighting to use for the 4759 smp_call_function_many() function with a zero 4760 "wait" parameter. See weight_single. 4761 Note well that setting a high probability for 4762 this weighting can place serious IPI load 4763 on the system. 4764 4765 scftorture.weight_many_wait= [KNL] 4766 The probability weighting to use for the 4767 smp_call_function_many() function with a 4768 non-zero "wait" parameter. See weight_single 4769 and weight_many. 4770 4771 scftorture.weight_all= [KNL] 4772 The probability weighting to use for the 4773 smp_call_function_all() function with a zero 4774 "wait" parameter. See weight_single and 4775 weight_many. 4776 4777 scftorture.weight_all_wait= [KNL] 4778 The probability weighting to use for the 4779 smp_call_function_all() function with a 4780 non-zero "wait" parameter. See weight_single 4781 and weight_many. 4782 4783 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4784 xtime_lock contention on larger systems, and/or RCU lock 4785 contention on all systems with CONFIG_MAXSMP set. 4786 Format: { "0" | "1" } 4787 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4788 1 -- enable. 4789 Note: increases power consumption, thus should only be 4790 enabled if running jitter sensitive (HPC/RT) workloads. 4791 4792 security= [SECURITY] Choose a legacy "major" security module to 4793 enable at boot. This has been deprecated by the 4794 "lsm=" parameter. 4795 4796 selinux= [SELINUX] Disable or enable SELinux at boot time. 4797 Format: { "0" | "1" } 4798 See security/selinux/Kconfig help text. 4799 0 -- disable. 4800 1 -- enable. 4801 Default value is 1. 4802 4803 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4804 Format: { "0" | "1" } 4805 See security/apparmor/Kconfig help text 4806 0 -- disable. 4807 1 -- enable. 4808 Default value is set via kernel config option. 4809 4810 serialnumber [BUGS=X86-32] 4811 4812 shapers= [NET] 4813 Maximal number of shapers. 4814 4815 simeth= [IA-64] 4816 simscsi= 4817 4818 slram= [HW,MTD] 4819 4820 slab_nomerge [MM] 4821 Disable merging of slabs with similar size. May be 4822 necessary if there is some reason to distinguish 4823 allocs to different slabs, especially in hardened 4824 environments where the risk of heap overflows and 4825 layout control by attackers can usually be 4826 frustrated by disabling merging. This will reduce 4827 most of the exposure of a heap attack to a single 4828 cache (risks via metadata attacks are mostly 4829 unchanged). Debug options disable merging on their 4830 own. 4831 For more information see Documentation/vm/slub.rst. 4832 4833 slab_max_order= [MM, SLAB] 4834 Determines the maximum allowed order for slabs. 4835 A high setting may cause OOMs due to memory 4836 fragmentation. Defaults to 1 for systems with 4837 more than 32MB of RAM, 0 otherwise. 4838 4839 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4840 Enabling slub_debug allows one to determine the 4841 culprit if slab objects become corrupted. Enabling 4842 slub_debug can create guard zones around objects and 4843 may poison objects when not in use. Also tracks the 4844 last alloc / free. For more information see 4845 Documentation/vm/slub.rst. 4846 4847 slub_memcg_sysfs= [MM, SLUB] 4848 Determines whether to enable sysfs directories for 4849 memory cgroup sub-caches. 1 to enable, 0 to disable. 4850 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4851 Enabling this can lead to a very high number of debug 4852 directories and files being created under 4853 /sys/kernel/slub. 4854 4855 slub_max_order= [MM, SLUB] 4856 Determines the maximum allowed order for slabs. 4857 A high setting may cause OOMs due to memory 4858 fragmentation. For more information see 4859 Documentation/vm/slub.rst. 4860 4861 slub_min_objects= [MM, SLUB] 4862 The minimum number of objects per slab. SLUB will 4863 increase the slab order up to slub_max_order to 4864 generate a sufficiently large slab able to contain 4865 the number of objects indicated. The higher the number 4866 of objects the smaller the overhead of tracking slabs 4867 and the less frequently locks need to be acquired. 4868 For more information see Documentation/vm/slub.rst. 4869 4870 slub_min_order= [MM, SLUB] 4871 Determines the minimum page order for slabs. Must be 4872 lower than slub_max_order. 4873 For more information see Documentation/vm/slub.rst. 4874 4875 slub_nomerge [MM, SLUB] 4876 Same with slab_nomerge. This is supported for legacy. 4877 See slab_nomerge for more information. 4878 4879 smart2= [HW] 4880 Format: <io1>[,<io2>[,...,<io8>]] 4881 4882 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4883 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4884 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4885 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4886 smsc-ircc2.ircc_irq= [HW] IRQ line 4887 smsc-ircc2.ircc_dma= [HW] DMA channel 4888 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4889 0: Toshiba Satellite 1800 (GP data pin select) 4890 1: Fast pin select (default) 4891 2: ATC IRMode 4892 4893 smt [KNL,S390] Set the maximum number of threads (logical 4894 CPUs) to use per physical CPU on systems capable of 4895 symmetric multithreading (SMT). Will be capped to the 4896 actual hardware limit. 4897 Format: <integer> 4898 Default: -1 (no limit) 4899 4900 softlockup_panic= 4901 [KNL] Should the soft-lockup detector generate panics. 4902 Format: 0 | 1 4903 4904 A value of 1 instructs the soft-lockup detector 4905 to panic the machine when a soft-lockup occurs. It is 4906 also controlled by the kernel.softlockup_panic sysctl 4907 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4908 respective build-time switch to that functionality. 4909 4910 softlockup_all_cpu_backtrace= 4911 [KNL] Should the soft-lockup detector generate 4912 backtraces on all cpus. 4913 Format: 0 | 1 4914 4915 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4916 See Documentation/admin-guide/laptops/sonypi.rst 4917 4918 spectre_v2= [X86] Control mitigation of Spectre variant 2 4919 (indirect branch speculation) vulnerability. 4920 The default operation protects the kernel from 4921 user space attacks. 4922 4923 on - unconditionally enable, implies 4924 spectre_v2_user=on 4925 off - unconditionally disable, implies 4926 spectre_v2_user=off 4927 auto - kernel detects whether your CPU model is 4928 vulnerable 4929 4930 Selecting 'on' will, and 'auto' may, choose a 4931 mitigation method at run time according to the 4932 CPU, the available microcode, the setting of the 4933 CONFIG_RETPOLINE configuration option, and the 4934 compiler with which the kernel was built. 4935 4936 Selecting 'on' will also enable the mitigation 4937 against user space to user space task attacks. 4938 4939 Selecting 'off' will disable both the kernel and 4940 the user space protections. 4941 4942 Specific mitigations can also be selected manually: 4943 4944 retpoline - replace indirect branches 4945 retpoline,generic - google's original retpoline 4946 retpoline,amd - AMD-specific minimal thunk 4947 4948 Not specifying this option is equivalent to 4949 spectre_v2=auto. 4950 4951 spectre_v2_user= 4952 [X86] Control mitigation of Spectre variant 2 4953 (indirect branch speculation) vulnerability between 4954 user space tasks 4955 4956 on - Unconditionally enable mitigations. Is 4957 enforced by spectre_v2=on 4958 4959 off - Unconditionally disable mitigations. Is 4960 enforced by spectre_v2=off 4961 4962 prctl - Indirect branch speculation is enabled, 4963 but mitigation can be enabled via prctl 4964 per thread. The mitigation control state 4965 is inherited on fork. 4966 4967 prctl,ibpb 4968 - Like "prctl" above, but only STIBP is 4969 controlled per thread. IBPB is issued 4970 always when switching between different user 4971 space processes. 4972 4973 seccomp 4974 - Same as "prctl" above, but all seccomp 4975 threads will enable the mitigation unless 4976 they explicitly opt out. 4977 4978 seccomp,ibpb 4979 - Like "seccomp" above, but only STIBP is 4980 controlled per thread. IBPB is issued 4981 always when switching between different 4982 user space processes. 4983 4984 auto - Kernel selects the mitigation depending on 4985 the available CPU features and vulnerability. 4986 4987 Default mitigation: 4988 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4989 4990 Not specifying this option is equivalent to 4991 spectre_v2_user=auto. 4992 4993 spec_store_bypass_disable= 4994 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4995 (Speculative Store Bypass vulnerability) 4996 4997 Certain CPUs are vulnerable to an exploit against a 4998 a common industry wide performance optimization known 4999 as "Speculative Store Bypass" in which recent stores 5000 to the same memory location may not be observed by 5001 later loads during speculative execution. The idea 5002 is that such stores are unlikely and that they can 5003 be detected prior to instruction retirement at the 5004 end of a particular speculation execution window. 5005 5006 In vulnerable processors, the speculatively forwarded 5007 store can be used in a cache side channel attack, for 5008 example to read memory to which the attacker does not 5009 directly have access (e.g. inside sandboxed code). 5010 5011 This parameter controls whether the Speculative Store 5012 Bypass optimization is used. 5013 5014 On x86 the options are: 5015 5016 on - Unconditionally disable Speculative Store Bypass 5017 off - Unconditionally enable Speculative Store Bypass 5018 auto - Kernel detects whether the CPU model contains an 5019 implementation of Speculative Store Bypass and 5020 picks the most appropriate mitigation. If the 5021 CPU is not vulnerable, "off" is selected. If the 5022 CPU is vulnerable the default mitigation is 5023 architecture and Kconfig dependent. See below. 5024 prctl - Control Speculative Store Bypass per thread 5025 via prctl. Speculative Store Bypass is enabled 5026 for a process by default. The state of the control 5027 is inherited on fork. 5028 seccomp - Same as "prctl" above, but all seccomp threads 5029 will disable SSB unless they explicitly opt out. 5030 5031 Default mitigations: 5032 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5033 5034 On powerpc the options are: 5035 5036 on,auto - On Power8 and Power9 insert a store-forwarding 5037 barrier on kernel entry and exit. On Power7 5038 perform a software flush on kernel entry and 5039 exit. 5040 off - No action. 5041 5042 Not specifying this option is equivalent to 5043 spec_store_bypass_disable=auto. 5044 5045 spia_io_base= [HW,MTD] 5046 spia_fio_base= 5047 spia_pedr= 5048 spia_peddr= 5049 5050 split_lock_detect= 5051 [X86] Enable split lock detection 5052 5053 When enabled (and if hardware support is present), atomic 5054 instructions that access data across cache line 5055 boundaries will result in an alignment check exception. 5056 5057 off - not enabled 5058 5059 warn - the kernel will emit rate limited warnings 5060 about applications triggering the #AC 5061 exception. This mode is the default on CPUs 5062 that supports split lock detection. 5063 5064 fatal - the kernel will send SIGBUS to applications 5065 that trigger the #AC exception. 5066 5067 If an #AC exception is hit in the kernel or in 5068 firmware (i.e. not while executing in user mode) 5069 the kernel will oops in either "warn" or "fatal" 5070 mode. 5071 5072 srbds= [X86,INTEL] 5073 Control the Special Register Buffer Data Sampling 5074 (SRBDS) mitigation. 5075 5076 Certain CPUs are vulnerable to an MDS-like 5077 exploit which can leak bits from the random 5078 number generator. 5079 5080 By default, this issue is mitigated by 5081 microcode. However, the microcode fix can cause 5082 the RDRAND and RDSEED instructions to become 5083 much slower. Among other effects, this will 5084 result in reduced throughput from /dev/urandom. 5085 5086 The microcode mitigation can be disabled with 5087 the following option: 5088 5089 off: Disable mitigation and remove 5090 performance impact to RDRAND and RDSEED 5091 5092 srcutree.counter_wrap_check [KNL] 5093 Specifies how frequently to check for 5094 grace-period sequence counter wrap for the 5095 srcu_data structure's ->srcu_gp_seq_needed field. 5096 The greater the number of bits set in this kernel 5097 parameter, the less frequently counter wrap will 5098 be checked for. Note that the bottom two bits 5099 are ignored. 5100 5101 srcutree.exp_holdoff [KNL] 5102 Specifies how many nanoseconds must elapse 5103 since the end of the last SRCU grace period for 5104 a given srcu_struct until the next normal SRCU 5105 grace period will be considered for automatic 5106 expediting. Set to zero to disable automatic 5107 expediting. 5108 5109 ssbd= [ARM64,HW] 5110 Speculative Store Bypass Disable control 5111 5112 On CPUs that are vulnerable to the Speculative 5113 Store Bypass vulnerability and offer a 5114 firmware based mitigation, this parameter 5115 indicates how the mitigation should be used: 5116 5117 force-on: Unconditionally enable mitigation for 5118 for both kernel and userspace 5119 force-off: Unconditionally disable mitigation for 5120 for both kernel and userspace 5121 kernel: Always enable mitigation in the 5122 kernel, and offer a prctl interface 5123 to allow userspace to register its 5124 interest in being mitigated too. 5125 5126 stack_guard_gap= [MM] 5127 override the default stack gap protection. The value 5128 is in page units and it defines how many pages prior 5129 to (for stacks growing down) resp. after (for stacks 5130 growing up) the main stack are reserved for no other 5131 mapping. Default value is 256 pages. 5132 5133 stacktrace [FTRACE] 5134 Enabled the stack tracer on boot up. 5135 5136 stacktrace_filter=[function-list] 5137 [FTRACE] Limit the functions that the stack tracer 5138 will trace at boot up. function-list is a comma separated 5139 list of functions. This list can be changed at run 5140 time by the stack_trace_filter file in the debugfs 5141 tracing directory. Note, this enables stack tracing 5142 and the stacktrace above is not needed. 5143 5144 sti= [PARISC,HW] 5145 Format: <num> 5146 Set the STI (builtin display/keyboard on the HP-PARISC 5147 machines) console (graphic card) which should be used 5148 as the initial boot-console. 5149 See also comment in drivers/video/console/sticore.c. 5150 5151 sti_font= [HW] 5152 See comment in drivers/video/console/sticore.c. 5153 5154 stifb= [HW] 5155 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5156 5157 sunrpc.min_resvport= 5158 sunrpc.max_resvport= 5159 [NFS,SUNRPC] 5160 SunRPC servers often require that client requests 5161 originate from a privileged port (i.e. a port in the 5162 range 0 < portnr < 1024). 5163 An administrator who wishes to reserve some of these 5164 ports for other uses may adjust the range that the 5165 kernel's sunrpc client considers to be privileged 5166 using these two parameters to set the minimum and 5167 maximum port values. 5168 5169 sunrpc.svc_rpc_per_connection_limit= 5170 [NFS,SUNRPC] 5171 Limit the number of requests that the server will 5172 process in parallel from a single connection. 5173 The default value is 0 (no limit). 5174 5175 sunrpc.pool_mode= 5176 [NFS] 5177 Control how the NFS server code allocates CPUs to 5178 service thread pools. Depending on how many NICs 5179 you have and where their interrupts are bound, this 5180 option will affect which CPUs will do NFS serving. 5181 Note: this parameter cannot be changed while the 5182 NFS server is running. 5183 5184 auto the server chooses an appropriate mode 5185 automatically using heuristics 5186 global a single global pool contains all CPUs 5187 percpu one pool for each CPU 5188 pernode one pool for each NUMA node (equivalent 5189 to global on non-NUMA machines) 5190 5191 sunrpc.tcp_slot_table_entries= 5192 sunrpc.udp_slot_table_entries= 5193 [NFS,SUNRPC] 5194 Sets the upper limit on the number of simultaneous 5195 RPC calls that can be sent from the client to a 5196 server. Increasing these values may allow you to 5197 improve throughput, but will also increase the 5198 amount of memory reserved for use by the client. 5199 5200 suspend.pm_test_delay= 5201 [SUSPEND] 5202 Sets the number of seconds to remain in a suspend test 5203 mode before resuming the system (see 5204 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5205 is set. Default value is 5. 5206 5207 svm= [PPC] 5208 Format: { on | off | y | n | 1 | 0 } 5209 This parameter controls use of the Protected 5210 Execution Facility on pSeries. 5211 5212 swapaccount=[0|1] 5213 [KNL] Enable accounting of swap in memory resource 5214 controller if no parameter or 1 is given or disable 5215 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5216 5217 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5218 Format: { <int> | force | noforce } 5219 <int> -- Number of I/O TLB slabs 5220 force -- force using of bounce buffers even if they 5221 wouldn't be automatically used by the kernel 5222 noforce -- Never use bounce buffers (for debugging) 5223 5224 switches= [HW,M68k] 5225 5226 sysctl.*= [KNL] 5227 Set a sysctl parameter, right before loading the init 5228 process, as if the value was written to the respective 5229 /proc/sys/... file. Both '.' and '/' are recognized as 5230 separators. Unrecognized parameters and invalid values 5231 are reported in the kernel log. Sysctls registered 5232 later by a loaded module cannot be set this way. 5233 Example: sysctl.vm.swappiness=40 5234 5235 sysfs.deprecated=0|1 [KNL] 5236 Enable/disable old style sysfs layout for old udev 5237 on older distributions. When this option is enabled 5238 very new udev will not work anymore. When this option 5239 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5240 in older udev will not work anymore. 5241 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5242 the kernel configuration. 5243 5244 sysrq_always_enabled 5245 [KNL] 5246 Ignore sysrq setting - this boot parameter will 5247 neutralize any effect of /proc/sys/kernel/sysrq. 5248 Useful for debugging. 5249 5250 tcpmhash_entries= [KNL,NET] 5251 Set the number of tcp_metrics_hash slots. 5252 Default value is 8192 or 16384 depending on total 5253 ram pages. This is used to specify the TCP metrics 5254 cache size. See Documentation/networking/ip-sysctl.rst 5255 "tcp_no_metrics_save" section for more details. 5256 5257 tdfx= [HW,DRM] 5258 5259 test_suspend= [SUSPEND][,N] 5260 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5261 standby suspend) or "freeze" (for suspend type freeze) 5262 as the system sleep state during system startup with 5263 the optional capability to repeat N number of times. 5264 The system is woken from this state using a 5265 wakeup-capable RTC alarm. 5266 5267 thash_entries= [KNL,NET] 5268 Set number of hash buckets for TCP connection 5269 5270 thermal.act= [HW,ACPI] 5271 -1: disable all active trip points in all thermal zones 5272 <degrees C>: override all lowest active trip points 5273 5274 thermal.crt= [HW,ACPI] 5275 -1: disable all critical trip points in all thermal zones 5276 <degrees C>: override all critical trip points 5277 5278 thermal.nocrt= [HW,ACPI] 5279 Set to disable actions on ACPI thermal zone 5280 critical and hot trip points. 5281 5282 thermal.off= [HW,ACPI] 5283 1: disable ACPI thermal control 5284 5285 thermal.psv= [HW,ACPI] 5286 -1: disable all passive trip points 5287 <degrees C>: override all passive trip points to this 5288 value 5289 5290 thermal.tzp= [HW,ACPI] 5291 Specify global default ACPI thermal zone polling rate 5292 <deci-seconds>: poll all this frequency 5293 0: no polling (default) 5294 5295 threadirqs [KNL] 5296 Force threading of all interrupt handlers except those 5297 marked explicitly IRQF_NO_THREAD. 5298 5299 topology= [S390] 5300 Format: {off | on} 5301 Specify if the kernel should make use of the cpu 5302 topology information if the hardware supports this. 5303 The scheduler will make use of this information and 5304 e.g. base its process migration decisions on it. 5305 Default is on. 5306 5307 topology_updates= [KNL, PPC, NUMA] 5308 Format: {off} 5309 Specify if the kernel should ignore (off) 5310 topology updates sent by the hypervisor to this 5311 LPAR. 5312 5313 torture.disable_onoff_at_boot= [KNL] 5314 Prevent the CPU-hotplug component of torturing 5315 until after init has spawned. 5316 5317 torture.ftrace_dump_at_shutdown= [KNL] 5318 Dump the ftrace buffer at torture-test shutdown, 5319 even if there were no errors. This can be a 5320 very costly operation when many torture tests 5321 are running concurrently, especially on systems 5322 with rotating-rust storage. 5323 5324 tp720= [HW,PS2] 5325 5326 tpm_suspend_pcr=[HW,TPM] 5327 Format: integer pcr id 5328 Specify that at suspend time, the tpm driver 5329 should extend the specified pcr with zeros, 5330 as a workaround for some chips which fail to 5331 flush the last written pcr on TPM_SaveState. 5332 This will guarantee that all the other pcrs 5333 are saved. 5334 5335 trace_buf_size=nn[KMG] 5336 [FTRACE] will set tracing buffer size on each cpu. 5337 5338 trace_event=[event-list] 5339 [FTRACE] Set and start specified trace events in order 5340 to facilitate early boot debugging. The event-list is a 5341 comma separated list of trace events to enable. See 5342 also Documentation/trace/events.rst 5343 5344 trace_options=[option-list] 5345 [FTRACE] Enable or disable tracer options at boot. 5346 The option-list is a comma delimited list of options 5347 that can be enabled or disabled just as if you were 5348 to echo the option name into 5349 5350 /sys/kernel/debug/tracing/trace_options 5351 5352 For example, to enable stacktrace option (to dump the 5353 stack trace of each event), add to the command line: 5354 5355 trace_options=stacktrace 5356 5357 See also Documentation/trace/ftrace.rst "trace options" 5358 section. 5359 5360 tp_printk[FTRACE] 5361 Have the tracepoints sent to printk as well as the 5362 tracing ring buffer. This is useful for early boot up 5363 where the system hangs or reboots and does not give the 5364 option for reading the tracing buffer or performing a 5365 ftrace_dump_on_oops. 5366 5367 To turn off having tracepoints sent to printk, 5368 echo 0 > /proc/sys/kernel/tracepoint_printk 5369 Note, echoing 1 into this file without the 5370 tracepoint_printk kernel cmdline option has no effect. 5371 5372 ** CAUTION ** 5373 5374 Having tracepoints sent to printk() and activating high 5375 frequency tracepoints such as irq or sched, can cause 5376 the system to live lock. 5377 5378 traceoff_on_warning 5379 [FTRACE] enable this option to disable tracing when a 5380 warning is hit. This turns off "tracing_on". Tracing can 5381 be enabled again by echoing '1' into the "tracing_on" 5382 file located in /sys/kernel/debug/tracing/ 5383 5384 This option is useful, as it disables the trace before 5385 the WARNING dump is called, which prevents the trace to 5386 be filled with content caused by the warning output. 5387 5388 This option can also be set at run time via the sysctl 5389 option: kernel/traceoff_on_warning 5390 5391 transparent_hugepage= 5392 [KNL] 5393 Format: [always|madvise|never] 5394 Can be used to control the default behavior of the system 5395 with respect to transparent hugepages. 5396 See Documentation/admin-guide/mm/transhuge.rst 5397 for more details. 5398 5399 tsc= Disable clocksource stability checks for TSC. 5400 Format: <string> 5401 [x86] reliable: mark tsc clocksource as reliable, this 5402 disables clocksource verification at runtime, as well 5403 as the stability checks done at bootup. Used to enable 5404 high-resolution timer mode on older hardware, and in 5405 virtualized environment. 5406 [x86] noirqtime: Do not use TSC to do irq accounting. 5407 Used to run time disable IRQ_TIME_ACCOUNTING on any 5408 platforms where RDTSC is slow and this accounting 5409 can add overhead. 5410 [x86] unstable: mark the TSC clocksource as unstable, this 5411 marks the TSC unconditionally unstable at bootup and 5412 avoids any further wobbles once the TSC watchdog notices. 5413 [x86] nowatchdog: disable clocksource watchdog. Used 5414 in situations with strict latency requirements (where 5415 interruptions from clocksource watchdog are not 5416 acceptable). 5417 5418 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5419 value instead. Useful when the early TSC frequency discovery 5420 procedure is not reliable, such as on overclocked systems 5421 with CPUID.16h support and partial CPUID.15h support. 5422 Format: <unsigned int> 5423 5424 tsx= [X86] Control Transactional Synchronization 5425 Extensions (TSX) feature in Intel processors that 5426 support TSX control. 5427 5428 This parameter controls the TSX feature. The options are: 5429 5430 on - Enable TSX on the system. Although there are 5431 mitigations for all known security vulnerabilities, 5432 TSX has been known to be an accelerator for 5433 several previous speculation-related CVEs, and 5434 so there may be unknown security risks associated 5435 with leaving it enabled. 5436 5437 off - Disable TSX on the system. (Note that this 5438 option takes effect only on newer CPUs which are 5439 not vulnerable to MDS, i.e., have 5440 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5441 the new IA32_TSX_CTRL MSR through a microcode 5442 update. This new MSR allows for the reliable 5443 deactivation of the TSX functionality.) 5444 5445 auto - Disable TSX if X86_BUG_TAA is present, 5446 otherwise enable TSX on the system. 5447 5448 Not specifying this option is equivalent to tsx=off. 5449 5450 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5451 for more details. 5452 5453 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5454 Abort (TAA) vulnerability. 5455 5456 Similar to Micro-architectural Data Sampling (MDS) 5457 certain CPUs that support Transactional 5458 Synchronization Extensions (TSX) are vulnerable to an 5459 exploit against CPU internal buffers which can forward 5460 information to a disclosure gadget under certain 5461 conditions. 5462 5463 In vulnerable processors, the speculatively forwarded 5464 data can be used in a cache side channel attack, to 5465 access data to which the attacker does not have direct 5466 access. 5467 5468 This parameter controls the TAA mitigation. The 5469 options are: 5470 5471 full - Enable TAA mitigation on vulnerable CPUs 5472 if TSX is enabled. 5473 5474 full,nosmt - Enable TAA mitigation and disable SMT on 5475 vulnerable CPUs. If TSX is disabled, SMT 5476 is not disabled because CPU is not 5477 vulnerable to cross-thread TAA attacks. 5478 off - Unconditionally disable TAA mitigation 5479 5480 On MDS-affected machines, tsx_async_abort=off can be 5481 prevented by an active MDS mitigation as both vulnerabilities 5482 are mitigated with the same mechanism so in order to disable 5483 this mitigation, you need to specify mds=off too. 5484 5485 Not specifying this option is equivalent to 5486 tsx_async_abort=full. On CPUs which are MDS affected 5487 and deploy MDS mitigation, TAA mitigation is not 5488 required and doesn't provide any additional 5489 mitigation. 5490 5491 For details see: 5492 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5493 5494 turbografx.map[2|3]= [HW,JOY] 5495 TurboGraFX parallel port interface 5496 Format: 5497 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5498 See also Documentation/input/devices/joystick-parport.rst 5499 5500 udbg-immortal [PPC] When debugging early kernel crashes that 5501 happen after console_init() and before a proper 5502 console driver takes over, this boot options might 5503 help "seeing" what's going on. 5504 5505 uhash_entries= [KNL,NET] 5506 Set number of hash buckets for UDP/UDP-Lite connections 5507 5508 uhci-hcd.ignore_oc= 5509 [USB] Ignore overcurrent events (default N). 5510 Some badly-designed motherboards generate lots of 5511 bogus events, for ports that aren't wired to 5512 anything. Set this parameter to avoid log spamming. 5513 Note that genuine overcurrent events won't be 5514 reported either. 5515 5516 unknown_nmi_panic 5517 [X86] Cause panic on unknown NMI. 5518 5519 usbcore.authorized_default= 5520 [USB] Default USB device authorization: 5521 (default -1 = authorized except for wireless USB, 5522 0 = not authorized, 1 = authorized, 2 = authorized 5523 if device connected to internal port) 5524 5525 usbcore.autosuspend= 5526 [USB] The autosuspend time delay (in seconds) used 5527 for newly-detected USB devices (default 2). This 5528 is the time required before an idle device will be 5529 autosuspended. Devices for which the delay is set 5530 to a negative value won't be autosuspended at all. 5531 5532 usbcore.usbfs_snoop= 5533 [USB] Set to log all usbfs traffic (default 0 = off). 5534 5535 usbcore.usbfs_snoop_max= 5536 [USB] Maximum number of bytes to snoop in each URB 5537 (default = 65536). 5538 5539 usbcore.blinkenlights= 5540 [USB] Set to cycle leds on hubs (default 0 = off). 5541 5542 usbcore.old_scheme_first= 5543 [USB] Start with the old device initialization 5544 scheme (default 0 = off). 5545 5546 usbcore.usbfs_memory_mb= 5547 [USB] Memory limit (in MB) for buffers allocated by 5548 usbfs (default = 16, 0 = max = 2047). 5549 5550 usbcore.use_both_schemes= 5551 [USB] Try the other device initialization scheme 5552 if the first one fails (default 1 = enabled). 5553 5554 usbcore.initial_descriptor_timeout= 5555 [USB] Specifies timeout for the initial 64-byte 5556 USB_REQ_GET_DESCRIPTOR request in milliseconds 5557 (default 5000 = 5.0 seconds). 5558 5559 usbcore.nousb [USB] Disable the USB subsystem 5560 5561 usbcore.quirks= 5562 [USB] A list of quirk entries to augment the built-in 5563 usb core quirk list. List entries are separated by 5564 commas. Each entry has the form 5565 VendorID:ProductID:Flags. The IDs are 4-digit hex 5566 numbers and Flags is a set of letters. Each letter 5567 will change the built-in quirk; setting it if it is 5568 clear and clearing it if it is set. The letters have 5569 the following meanings: 5570 a = USB_QUIRK_STRING_FETCH_255 (string 5571 descriptors must not be fetched using 5572 a 255-byte read); 5573 b = USB_QUIRK_RESET_RESUME (device can't resume 5574 correctly so reset it instead); 5575 c = USB_QUIRK_NO_SET_INTF (device can't handle 5576 Set-Interface requests); 5577 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5578 handle its Configuration or Interface 5579 strings); 5580 e = USB_QUIRK_RESET (device can't be reset 5581 (e.g morph devices), don't use reset); 5582 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5583 more interface descriptions than the 5584 bNumInterfaces count, and can't handle 5585 talking to these interfaces); 5586 g = USB_QUIRK_DELAY_INIT (device needs a pause 5587 during initialization, after we read 5588 the device descriptor); 5589 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5590 high speed and super speed interrupt 5591 endpoints, the USB 2.0 and USB 3.0 spec 5592 require the interval in microframes (1 5593 microframe = 125 microseconds) to be 5594 calculated as interval = 2 ^ 5595 (bInterval-1). 5596 Devices with this quirk report their 5597 bInterval as the result of this 5598 calculation instead of the exponent 5599 variable used in the calculation); 5600 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5601 handle device_qualifier descriptor 5602 requests); 5603 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5604 generates spurious wakeup, ignore 5605 remote wakeup capability); 5606 k = USB_QUIRK_NO_LPM (device can't handle Link 5607 Power Management); 5608 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5609 (Device reports its bInterval as linear 5610 frames instead of the USB 2.0 5611 calculation); 5612 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5613 to be disconnected before suspend to 5614 prevent spurious wakeup); 5615 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5616 pause after every control message); 5617 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5618 delay after resetting its port); 5619 Example: quirks=0781:5580:bk,0a5c:5834:gij 5620 5621 usbhid.mousepoll= 5622 [USBHID] The interval which mice are to be polled at. 5623 5624 usbhid.jspoll= 5625 [USBHID] The interval which joysticks are to be polled at. 5626 5627 usbhid.kbpoll= 5628 [USBHID] The interval which keyboards are to be polled at. 5629 5630 usb-storage.delay_use= 5631 [UMS] The delay in seconds before a new device is 5632 scanned for Logical Units (default 1). 5633 5634 usb-storage.quirks= 5635 [UMS] A list of quirks entries to supplement or 5636 override the built-in unusual_devs list. List 5637 entries are separated by commas. Each entry has 5638 the form VID:PID:Flags where VID and PID are Vendor 5639 and Product ID values (4-digit hex numbers) and 5640 Flags is a set of characters, each corresponding 5641 to a common usb-storage quirk flag as follows: 5642 a = SANE_SENSE (collect more than 18 bytes 5643 of sense data, not on uas); 5644 b = BAD_SENSE (don't collect more than 18 5645 bytes of sense data, not on uas); 5646 c = FIX_CAPACITY (decrease the reported 5647 device capacity by one sector); 5648 d = NO_READ_DISC_INFO (don't use 5649 READ_DISC_INFO command, not on uas); 5650 e = NO_READ_CAPACITY_16 (don't use 5651 READ_CAPACITY_16 command); 5652 f = NO_REPORT_OPCODES (don't use report opcodes 5653 command, uas only); 5654 g = MAX_SECTORS_240 (don't transfer more than 5655 240 sectors at a time, uas only); 5656 h = CAPACITY_HEURISTICS (decrease the 5657 reported device capacity by one 5658 sector if the number is odd); 5659 i = IGNORE_DEVICE (don't bind to this 5660 device); 5661 j = NO_REPORT_LUNS (don't use report luns 5662 command, uas only); 5663 k = NO_SAME (do not use WRITE_SAME, uas only) 5664 l = NOT_LOCKABLE (don't try to lock and 5665 unlock ejectable media, not on uas); 5666 m = MAX_SECTORS_64 (don't transfer more 5667 than 64 sectors = 32 KB at a time, 5668 not on uas); 5669 n = INITIAL_READ10 (force a retry of the 5670 initial READ(10) command, not on uas); 5671 o = CAPACITY_OK (accept the capacity 5672 reported by the device, not on uas); 5673 p = WRITE_CACHE (the device cache is ON 5674 by default, not on uas); 5675 r = IGNORE_RESIDUE (the device reports 5676 bogus residue values, not on uas); 5677 s = SINGLE_LUN (the device has only one 5678 Logical Unit); 5679 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5680 commands, uas only); 5681 u = IGNORE_UAS (don't bind to the uas driver); 5682 w = NO_WP_DETECT (don't test whether the 5683 medium is write-protected). 5684 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5685 even if the device claims no cache, 5686 not on uas) 5687 Example: quirks=0419:aaf5:rl,0421:0433:rc 5688 5689 user_debug= [KNL,ARM] 5690 Format: <int> 5691 See arch/arm/Kconfig.debug help text. 5692 1 - undefined instruction events 5693 2 - system calls 5694 4 - invalid data aborts 5695 8 - SIGSEGV faults 5696 16 - SIGBUS faults 5697 Example: user_debug=31 5698 5699 userpte= 5700 [X86] Flags controlling user PTE allocations. 5701 5702 nohigh = do not allocate PTE pages in 5703 HIGHMEM regardless of setting 5704 of CONFIG_HIGHPTE. 5705 5706 vdso= [X86,SH] 5707 On X86_32, this is an alias for vdso32=. Otherwise: 5708 5709 vdso=1: enable VDSO (the default) 5710 vdso=0: disable VDSO mapping 5711 5712 vdso32= [X86] Control the 32-bit vDSO 5713 vdso32=1: enable 32-bit VDSO 5714 vdso32=0 or vdso32=2: disable 32-bit VDSO 5715 5716 See the help text for CONFIG_COMPAT_VDSO for more 5717 details. If CONFIG_COMPAT_VDSO is set, the default is 5718 vdso32=0; otherwise, the default is vdso32=1. 5719 5720 For compatibility with older kernels, vdso32=2 is an 5721 alias for vdso32=0. 5722 5723 Try vdso32=0 if you encounter an error that says: 5724 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5725 5726 vector= [IA-64,SMP] 5727 vector=percpu: enable percpu vector domain 5728 5729 video= [FB] Frame buffer configuration 5730 See Documentation/fb/modedb.rst. 5731 5732 video.brightness_switch_enabled= [0,1] 5733 If set to 1, on receiving an ACPI notify event 5734 generated by hotkey, video driver will adjust brightness 5735 level and then send out the event to user space through 5736 the allocated input device; If set to 0, video driver 5737 will only send out the event without touching backlight 5738 brightness level. 5739 default: 1 5740 5741 virtio_mmio.device= 5742 [VMMIO] Memory mapped virtio (platform) device. 5743 5744 <size>@<baseaddr>:<irq>[:<id>] 5745 where: 5746 <size> := size (can use standard suffixes 5747 like K, M and G) 5748 <baseaddr> := physical base address 5749 <irq> := interrupt number (as passed to 5750 request_irq()) 5751 <id> := (optional) platform device id 5752 example: 5753 virtio_mmio.device=1K@0x100b0000:48:7 5754 5755 Can be used multiple times for multiple devices. 5756 5757 vga= [BOOT,X86-32] Select a particular video mode 5758 See Documentation/x86/boot.rst and 5759 Documentation/admin-guide/svga.rst. 5760 Use vga=ask for menu. 5761 This is actually a boot loader parameter; the value is 5762 passed to the kernel using a special protocol. 5763 5764 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5765 May slow down system boot speed, especially when 5766 enabled on systems with a large amount of memory. 5767 All options are enabled by default, and this 5768 interface is meant to allow for selectively 5769 enabling or disabling specific virtual memory 5770 debugging features. 5771 5772 Available options are: 5773 P Enable page structure init time poisoning 5774 - Disable all of the above options 5775 5776 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5777 size of <nn>. This can be used to increase the 5778 minimum size (128MB on x86). It can also be used to 5779 decrease the size and leave more room for directly 5780 mapped kernel RAM. 5781 5782 vmcp_cma=nn[MG] [KNL,S390] 5783 Sets the memory size reserved for contiguous memory 5784 allocations for the vmcp device driver. 5785 5786 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5787 Format: <command> 5788 5789 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5790 Format: <command> 5791 5792 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5793 Format: <command> 5794 5795 vsyscall= [X86-64] 5796 Controls the behavior of vsyscalls (i.e. calls to 5797 fixed addresses of 0xffffffffff600x00 from legacy 5798 code). Most statically-linked binaries and older 5799 versions of glibc use these calls. Because these 5800 functions are at fixed addresses, they make nice 5801 targets for exploits that can control RIP. 5802 5803 emulate [default] Vsyscalls turn into traps and are 5804 emulated reasonably safely. The vsyscall 5805 page is readable. 5806 5807 xonly Vsyscalls turn into traps and are 5808 emulated reasonably safely. The vsyscall 5809 page is not readable. 5810 5811 none Vsyscalls don't work at all. This makes 5812 them quite hard to use for exploits but 5813 might break your system. 5814 5815 vt.color= [VT] Default text color. 5816 Format: 0xYX, X = foreground, Y = background. 5817 Default: 0x07 = light gray on black. 5818 5819 vt.cur_default= [VT] Default cursor shape. 5820 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5821 the parameters of the <Esc>[?A;B;Cc escape sequence; 5822 see VGA-softcursor.txt. Default: 2 = underline. 5823 5824 vt.default_blu= [VT] 5825 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5826 Change the default blue palette of the console. 5827 This is a 16-member array composed of values 5828 ranging from 0-255. 5829 5830 vt.default_grn= [VT] 5831 Format: <green0>,<green1>,<green2>,...,<green15> 5832 Change the default green palette of the console. 5833 This is a 16-member array composed of values 5834 ranging from 0-255. 5835 5836 vt.default_red= [VT] 5837 Format: <red0>,<red1>,<red2>,...,<red15> 5838 Change the default red palette of the console. 5839 This is a 16-member array composed of values 5840 ranging from 0-255. 5841 5842 vt.default_utf8= 5843 [VT] 5844 Format=<0|1> 5845 Set system-wide default UTF-8 mode for all tty's. 5846 Default is 1, i.e. UTF-8 mode is enabled for all 5847 newly opened terminals. 5848 5849 vt.global_cursor_default= 5850 [VT] 5851 Format=<-1|0|1> 5852 Set system-wide default for whether a cursor 5853 is shown on new VTs. Default is -1, 5854 i.e. cursors will be created by default unless 5855 overridden by individual drivers. 0 will hide 5856 cursors, 1 will display them. 5857 5858 vt.italic= [VT] Default color for italic text; 0-15. 5859 Default: 2 = green. 5860 5861 vt.underline= [VT] Default color for underlined text; 0-15. 5862 Default: 3 = cyan. 5863 5864 watchdog timers [HW,WDT] For information on watchdog timers, 5865 see Documentation/watchdog/watchdog-parameters.rst 5866 or other driver-specific files in the 5867 Documentation/watchdog/ directory. 5868 5869 watchdog_thresh= 5870 [KNL] 5871 Set the hard lockup detector stall duration 5872 threshold in seconds. The soft lockup detector 5873 threshold is set to twice the value. A value of 0 5874 disables both lockup detectors. Default is 10 5875 seconds. 5876 5877 workqueue.watchdog_thresh= 5878 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5879 warn stall conditions and dump internal state to 5880 help debugging. 0 disables workqueue stall 5881 detection; otherwise, it's the stall threshold 5882 duration in seconds. The default value is 30 and 5883 it can be updated at runtime by writing to the 5884 corresponding sysfs file. 5885 5886 workqueue.disable_numa 5887 By default, all work items queued to unbound 5888 workqueues are affine to the NUMA nodes they're 5889 issued on, which results in better behavior in 5890 general. If NUMA affinity needs to be disabled for 5891 whatever reason, this option can be used. Note 5892 that this also can be controlled per-workqueue for 5893 workqueues visible under /sys/bus/workqueue/. 5894 5895 workqueue.power_efficient 5896 Per-cpu workqueues are generally preferred because 5897 they show better performance thanks to cache 5898 locality; unfortunately, per-cpu workqueues tend to 5899 be more power hungry than unbound workqueues. 5900 5901 Enabling this makes the per-cpu workqueues which 5902 were observed to contribute significantly to power 5903 consumption unbound, leading to measurably lower 5904 power usage at the cost of small performance 5905 overhead. 5906 5907 The default value of this parameter is determined by 5908 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5909 5910 workqueue.debug_force_rr_cpu 5911 Workqueue used to implicitly guarantee that work 5912 items queued without explicit CPU specified are put 5913 on the local CPU. This guarantee is no longer true 5914 and while local CPU is still preferred work items 5915 may be put on foreign CPUs. This debug option 5916 forces round-robin CPU selection to flush out 5917 usages which depend on the now broken guarantee. 5918 When enabled, memory and cache locality will be 5919 impacted. 5920 5921 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5922 default x2apic cluster mode on platforms 5923 supporting x2apic. 5924 5925 x86_intel_mid_timer= [X86-32,APBT] 5926 Choose timer option for x86 Intel MID platform. 5927 Two valid options are apbt timer only and lapic timer 5928 plus one apbt timer for broadcast timer. 5929 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5930 5931 xen_512gb_limit [KNL,X86-64,XEN] 5932 Restricts the kernel running paravirtualized under Xen 5933 to use only up to 512 GB of RAM. The reason to do so is 5934 crash analysis tools and Xen tools for doing domain 5935 save/restore/migration must be enabled to handle larger 5936 domains. 5937 5938 xen_emul_unplug= [HW,X86,XEN] 5939 Unplug Xen emulated devices 5940 Format: [unplug0,][unplug1] 5941 ide-disks -- unplug primary master IDE devices 5942 aux-ide-disks -- unplug non-primary-master IDE devices 5943 nics -- unplug network devices 5944 all -- unplug all emulated devices (NICs and IDE disks) 5945 unnecessary -- unplugging emulated devices is 5946 unnecessary even if the host did not respond to 5947 the unplug protocol 5948 never -- do not unplug even if version check succeeds 5949 5950 xen_legacy_crash [X86,XEN] 5951 Crash from Xen panic notifier, without executing late 5952 panic() code such as dumping handler. 5953 5954 xen_nopvspin [X86,XEN] 5955 Disables the qspinlock slowpath using Xen PV optimizations. 5956 This parameter is obsoleted by "nopvspin" parameter, which 5957 has equivalent effect for XEN platform. 5958 5959 xen_nopv [X86] 5960 Disables the PV optimizations forcing the HVM guest to 5961 run as generic HVM guest with no PV drivers. 5962 This option is obsoleted by the "nopv" option, which 5963 has equivalent effect for XEN platform. 5964 5965 xen_scrub_pages= [XEN] 5966 Boolean option to control scrubbing pages before giving them back 5967 to Xen, for use by other domains. Can be also changed at runtime 5968 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5969 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5970 5971 xen_timer_slop= [X86-64,XEN] 5972 Set the timer slop (in nanoseconds) for the virtual Xen 5973 timers (default is 100000). This adjusts the minimum 5974 delta of virtualized Xen timers, where lower values 5975 improve timer resolution at the expense of processing 5976 more timer interrupts. 5977 5978 xen.event_eoi_delay= [XEN] 5979 How long to delay EOI handling in case of event 5980 storms (jiffies). Default is 10. 5981 5982 xen.event_loop_timeout= [XEN] 5983 After which time (jiffies) the event handling loop 5984 should start to delay EOI handling. Default is 2. 5985 5986 xen.fifo_events= [XEN] 5987 Boolean parameter to disable using fifo event handling 5988 even if available. Normally fifo event handling is 5989 preferred over the 2-level event handling, as it is 5990 fairer and the number of possible event channels is 5991 much higher. Default is on (use fifo events). 5992 5993 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5994 Disables the PV optimizations forcing the guest to run 5995 as generic guest with no PV drivers. Currently support 5996 XEN HVM, KVM, HYPER_V and VMWARE guest. 5997 5998 nopvspin [X86,XEN,KVM] 5999 Disables the qspinlock slow path using PV optimizations 6000 which allow the hypervisor to 'idle' the guest on lock 6001 contention. 6002 6003 xirc2ps_cs= [NET,PCMCIA] 6004 Format: 6005 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6006 6007 xive= [PPC] 6008 By default on POWER9 and above, the kernel will 6009 natively use the XIVE interrupt controller. This option 6010 allows the fallback firmware mode to be used: 6011 6012 off Fallback to firmware control of XIVE interrupt 6013 controller on both pseries and powernv 6014 platforms. Only useful on POWER9 and above. 6015 6016 xhci-hcd.quirks [USB,KNL] 6017 A hex value specifying bitmask with supplemental xhci 6018 host controller quirks. Meaning of each bit can be 6019 consulted in header drivers/usb/host/xhci.h. 6020 6021 xmon [PPC] 6022 Format: { early | on | rw | ro | off } 6023 Controls if xmon debugger is enabled. Default is off. 6024 Passing only "xmon" is equivalent to "xmon=early". 6025 early Call xmon as early as possible on boot; xmon 6026 debugger is called from setup_arch(). 6027 on xmon debugger hooks will be installed so xmon 6028 is only called on a kernel crash. Default mode, 6029 i.e. either "ro" or "rw" mode, is controlled 6030 with CONFIG_XMON_DEFAULT_RO_MODE. 6031 rw xmon debugger hooks will be installed so xmon 6032 is called only on a kernel crash, mode is write, 6033 meaning SPR registers, memory and, other data 6034 can be written using xmon commands. 6035 ro same as "rw" option above but SPR registers, 6036 memory, and other data can't be written using 6037 xmon commands. 6038 off xmon is disabled. 6039