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 nobounce [Default off] 1887 Disable bounce buffer for untrusted devices such as 1888 the Thunderbolt devices. This will treat the untrusted 1889 devices as the trusted ones, hence might expose security 1890 risks of DMA attacks. 1891 1892 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1893 0 disables intel_idle and fall back on acpi_idle. 1894 1 to 9 specify maximum depth of C-state. 1895 1896 intel_pstate= [X86] 1897 disable 1898 Do not enable intel_pstate as the default 1899 scaling driver for the supported processors 1900 passive 1901 Use intel_pstate as a scaling driver, but configure it 1902 to work with generic cpufreq governors (instead of 1903 enabling its internal governor). This mode cannot be 1904 used along with the hardware-managed P-states (HWP) 1905 feature. 1906 force 1907 Enable intel_pstate on systems that prohibit it by default 1908 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1909 instead of acpi-cpufreq may disable platform features, such 1910 as thermal controls and power capping, that rely on ACPI 1911 P-States information being indicated to OSPM and therefore 1912 should be used with caution. This option does not work with 1913 processors that aren't supported by the intel_pstate driver 1914 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1915 no_hwp 1916 Do not enable hardware P state control (HWP) 1917 if available. 1918 hwp_only 1919 Only load intel_pstate on systems which support 1920 hardware P state control (HWP) if available. 1921 support_acpi_ppc 1922 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1923 Description Table, specifies preferred power management 1924 profile as "Enterprise Server" or "Performance Server", 1925 then this feature is turned on by default. 1926 per_cpu_perf_limits 1927 Allow per-logical-CPU P-State performance control limits using 1928 cpufreq sysfs interface 1929 1930 intremap= [X86-64, Intel-IOMMU] 1931 on enable Interrupt Remapping (default) 1932 off disable Interrupt Remapping 1933 nosid disable Source ID checking 1934 no_x2apic_optout 1935 BIOS x2APIC opt-out request will be ignored 1936 nopost disable Interrupt Posting 1937 1938 iomem= Disable strict checking of access to MMIO memory 1939 strict regions from userspace. 1940 relaxed 1941 1942 iommu= [X86] 1943 off 1944 force 1945 noforce 1946 biomerge 1947 panic 1948 nopanic 1949 merge 1950 nomerge 1951 soft 1952 pt [X86] 1953 nopt [X86] 1954 nobypass [PPC/POWERNV] 1955 Disable IOMMU bypass, using IOMMU for PCI devices. 1956 1957 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1958 Format: { "0" | "1" } 1959 0 - Lazy mode. 1960 Request that DMA unmap operations use deferred 1961 invalidation of hardware TLBs, for increased 1962 throughput at the cost of reduced device isolation. 1963 Will fall back to strict mode if not supported by 1964 the relevant IOMMU driver. 1965 1 - Strict mode (default). 1966 DMA unmap operations invalidate IOMMU hardware TLBs 1967 synchronously. 1968 1969 iommu.passthrough= 1970 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1971 Format: { "0" | "1" } 1972 0 - Use IOMMU translation for DMA. 1973 1 - Bypass the IOMMU for DMA. 1974 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1975 1976 io7= [HW] IO7 for Marvel-based Alpha systems 1977 See comment before marvel_specify_io7 in 1978 arch/alpha/kernel/core_marvel.c. 1979 1980 io_delay= [X86] I/O delay method 1981 0x80 1982 Standard port 0x80 based delay 1983 0xed 1984 Alternate port 0xed based delay (needed on some systems) 1985 udelay 1986 Simple two microseconds delay 1987 none 1988 No delay 1989 1990 ip= [IP_PNP] 1991 See Documentation/admin-guide/nfs/nfsroot.rst. 1992 1993 ipcmni_extend [KNL] Extend the maximum number of unique System V 1994 IPC identifiers from 32,768 to 16,777,216. 1995 1996 irqaffinity= [SMP] Set the default irq affinity mask 1997 The argument is a cpu list, as described above. 1998 1999 irqchip.gicv2_force_probe= 2000 [ARM, ARM64] 2001 Format: <bool> 2002 Force the kernel to look for the second 4kB page 2003 of a GICv2 controller even if the memory range 2004 exposed by the device tree is too small. 2005 2006 irqchip.gicv3_nolpi= 2007 [ARM, ARM64] 2008 Force the kernel to ignore the availability of 2009 LPIs (and by consequence ITSs). Intended for system 2010 that use the kernel as a bootloader, and thus want 2011 to let secondary kernels in charge of setting up 2012 LPIs. 2013 2014 irqchip.gicv3_pseudo_nmi= [ARM64] 2015 Enables support for pseudo-NMIs in the kernel. This 2016 requires the kernel to be built with 2017 CONFIG_ARM64_PSEUDO_NMI. 2018 2019 irqfixup [HW] 2020 When an interrupt is not handled search all handlers 2021 for it. Intended to get systems with badly broken 2022 firmware running. 2023 2024 irqpoll [HW] 2025 When an interrupt is not handled search all handlers 2026 for it. Also check all handlers each timer 2027 interrupt. Intended to get systems with badly broken 2028 firmware running. 2029 2030 isapnp= [ISAPNP] 2031 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 2032 2033 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 2034 [Deprecated - use cpusets instead] 2035 Format: [flag-list,]<cpu-list> 2036 2037 Specify one or more CPUs to isolate from disturbances 2038 specified in the flag list (default: domain): 2039 2040 nohz 2041 Disable the tick when a single task runs. 2042 2043 A residual 1Hz tick is offloaded to workqueues, which you 2044 need to affine to housekeeping through the global 2045 workqueue's affinity configured via the 2046 /sys/devices/virtual/workqueue/cpumask sysfs file, or 2047 by using the 'domain' flag described below. 2048 2049 NOTE: by default the global workqueue runs on all CPUs, 2050 so to protect individual CPUs the 'cpumask' file has to 2051 be configured manually after bootup. 2052 2053 domain 2054 Isolate from the general SMP balancing and scheduling 2055 algorithms. Note that performing domain isolation this way 2056 is irreversible: it's not possible to bring back a CPU to 2057 the domains once isolated through isolcpus. It's strongly 2058 advised to use cpusets instead to disable scheduler load 2059 balancing through the "cpuset.sched_load_balance" file. 2060 It offers a much more flexible interface where CPUs can 2061 move in and out of an isolated set anytime. 2062 2063 You can move a process onto or off an "isolated" CPU via 2064 the CPU affinity syscalls or cpuset. 2065 <cpu number> begins at 0 and the maximum value is 2066 "number of CPUs in system - 1". 2067 2068 managed_irq 2069 2070 Isolate from being targeted by managed interrupts 2071 which have an interrupt mask containing isolated 2072 CPUs. The affinity of managed interrupts is 2073 handled by the kernel and cannot be changed via 2074 the /proc/irq/* interfaces. 2075 2076 This isolation is best effort and only effective 2077 if the automatically assigned interrupt mask of a 2078 device queue contains isolated and housekeeping 2079 CPUs. If housekeeping CPUs are online then such 2080 interrupts are directed to the housekeeping CPU 2081 so that IO submitted on the housekeeping CPU 2082 cannot disturb the isolated CPU. 2083 2084 If a queue's affinity mask contains only isolated 2085 CPUs then this parameter has no effect on the 2086 interrupt routing decision, though interrupts are 2087 only delivered when tasks running on those 2088 isolated CPUs submit IO. IO submitted on 2089 housekeeping CPUs has no influence on those 2090 queues. 2091 2092 The format of <cpu-list> is described above. 2093 2094 iucv= [HW,NET] 2095 2096 ivrs_ioapic [HW,X86-64] 2097 Provide an override to the IOAPIC-ID<->DEVICE-ID 2098 mapping provided in the IVRS ACPI table. For 2099 example, to map IOAPIC-ID decimal 10 to 2100 PCI device 00:14.0 write the parameter as: 2101 ivrs_ioapic[10]=00:14.0 2102 2103 ivrs_hpet [HW,X86-64] 2104 Provide an override to the HPET-ID<->DEVICE-ID 2105 mapping provided in the IVRS ACPI table. For 2106 example, to map HPET-ID decimal 0 to 2107 PCI device 00:14.0 write the parameter as: 2108 ivrs_hpet[0]=00:14.0 2109 2110 ivrs_acpihid [HW,X86-64] 2111 Provide an override to the ACPI-HID:UID<->DEVICE-ID 2112 mapping provided in the IVRS ACPI table. For 2113 example, to map UART-HID:UID AMD0020:0 to 2114 PCI device 00:14.5 write the parameter as: 2115 ivrs_acpihid[00:14.5]=AMD0020:0 2116 2117 js= [HW,JOY] Analog joystick 2118 See Documentation/input/joydev/joystick.rst. 2119 2120 nokaslr [KNL] 2121 When CONFIG_RANDOMIZE_BASE is set, this disables 2122 kernel and module base offset ASLR (Address Space 2123 Layout Randomization). 2124 2125 kasan_multi_shot 2126 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 2127 report on every invalid memory access. Without this 2128 parameter KASAN will print report only for the first 2129 invalid access. 2130 2131 keepinitrd [HW,ARM] 2132 2133 kernelcore= [KNL,X86,IA-64,PPC] 2134 Format: nn[KMGTPE] | nn% | "mirror" 2135 This parameter specifies the amount of memory usable by 2136 the kernel for non-movable allocations. The requested 2137 amount is spread evenly throughout all nodes in the 2138 system as ZONE_NORMAL. The remaining memory is used for 2139 movable memory in its own zone, ZONE_MOVABLE. In the 2140 event, a node is too small to have both ZONE_NORMAL and 2141 ZONE_MOVABLE, kernelcore memory will take priority and 2142 other nodes will have a larger ZONE_MOVABLE. 2143 2144 ZONE_MOVABLE is used for the allocation of pages that 2145 may be reclaimed or moved by the page migration 2146 subsystem. Note that allocations like PTEs-from-HighMem 2147 still use the HighMem zone if it exists, and the Normal 2148 zone if it does not. 2149 2150 It is possible to specify the exact amount of memory in 2151 the form of "nn[KMGTPE]", a percentage of total system 2152 memory in the form of "nn%", or "mirror". If "mirror" 2153 option is specified, mirrored (reliable) memory is used 2154 for non-movable allocations and remaining memory is used 2155 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 2156 are exclusive, so you cannot specify multiple forms. 2157 2158 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 2159 Format: <Controller#>[,poll interval] 2160 The controller # is the number of the ehci usb debug 2161 port as it is probed via PCI. The poll interval is 2162 optional and is the number seconds in between 2163 each poll cycle to the debug port in case you need 2164 the functionality for interrupting the kernel with 2165 gdb or control-c on the dbgp connection. When 2166 not using this parameter you use sysrq-g to break into 2167 the kernel debugger. 2168 2169 kgdboc= [KGDB,HW] kgdb over consoles. 2170 Requires a tty driver that supports console polling, 2171 or a supported polling keyboard driver (non-usb). 2172 Serial only format: <serial_device>[,baud] 2173 keyboard only format: kbd 2174 keyboard and serial format: kbd,<serial_device>[,baud] 2175 Optional Kernel mode setting: 2176 kms, kbd format: kms,kbd 2177 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2178 2179 kgdboc_earlycon= [KGDB,HW] 2180 If the boot console provides the ability to read 2181 characters and can work in polling mode, you can use 2182 this parameter to tell kgdb to use it as a backend 2183 until the normal console is registered. Intended to 2184 be used together with the kgdboc parameter which 2185 specifies the normal console to transition to. 2186 2187 The name of the early console should be specified 2188 as the value of this parameter. Note that the name of 2189 the early console might be different than the tty 2190 name passed to kgdboc. It's OK to leave the value 2191 blank and the first boot console that implements 2192 read() will be picked. 2193 2194 kgdbwait [KGDB] Stop kernel execution and enter the 2195 kernel debugger at the earliest opportunity. 2196 2197 kmac= [MIPS] Korina ethernet MAC address. 2198 Configure the RouterBoard 532 series on-chip 2199 Ethernet adapter MAC address. 2200 2201 kmemleak= [KNL] Boot-time kmemleak enable/disable 2202 Valid arguments: on, off 2203 Default: on 2204 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2205 the default is off. 2206 2207 kprobe_event=[probe-list] 2208 [FTRACE] Add kprobe events and enable at boot time. 2209 The probe-list is a semicolon delimited list of probe 2210 definitions. Each definition is same as kprobe_events 2211 interface, but the parameters are comma delimited. 2212 For example, to add a kprobe event on vfs_read with 2213 arg1 and arg2, add to the command line; 2214 2215 kprobe_event=p,vfs_read,$arg1,$arg2 2216 2217 See also Documentation/trace/kprobetrace.rst "Kernel 2218 Boot Parameter" section. 2219 2220 kpti= [ARM64] Control page table isolation of user 2221 and kernel address spaces. 2222 Default: enabled on cores which need mitigation. 2223 0: force disabled 2224 1: force enabled 2225 2226 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2227 Default is 0 (don't ignore, but inject #GP) 2228 2229 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2230 Default is false (don't support). 2231 2232 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2233 KVM MMU at runtime. 2234 Default is 0 (off) 2235 2236 kvm.nx_huge_pages= 2237 [KVM] Controls the software workaround for the 2238 X86_BUG_ITLB_MULTIHIT bug. 2239 force : Always deploy workaround. 2240 off : Never deploy workaround. 2241 auto : Deploy workaround based on the presence of 2242 X86_BUG_ITLB_MULTIHIT. 2243 2244 Default is 'auto'. 2245 2246 If the software workaround is enabled for the host, 2247 guests do need not to enable it for nested guests. 2248 2249 kvm.nx_huge_pages_recovery_ratio= 2250 [KVM] Controls how many 4KiB pages are periodically zapped 2251 back to huge pages. 0 disables the recovery, otherwise if 2252 the value is N KVM will zap 1/Nth of the 4KiB pages every 2253 minute. The default is 60. 2254 2255 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2256 Default is 1 (enabled) 2257 2258 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2259 for all guests. 2260 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2261 2262 kvm-arm.vgic_v3_group0_trap= 2263 [KVM,ARM] Trap guest accesses to GICv3 group-0 2264 system registers 2265 2266 kvm-arm.vgic_v3_group1_trap= 2267 [KVM,ARM] Trap guest accesses to GICv3 group-1 2268 system registers 2269 2270 kvm-arm.vgic_v3_common_trap= 2271 [KVM,ARM] Trap guest accesses to GICv3 common 2272 system registers 2273 2274 kvm-arm.vgic_v4_enable= 2275 [KVM,ARM] Allow use of GICv4 for direct injection of 2276 LPIs. 2277 2278 kvm_cma_resv_ratio=n [PPC] 2279 Reserves given percentage from system memory area for 2280 contiguous memory allocation for KVM hash pagetable 2281 allocation. 2282 By default it reserves 5% of total system memory. 2283 Format: <integer> 2284 Default: 5 2285 2286 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2287 (virtualized MMU) support on capable Intel chips. 2288 Default is 1 (enabled) 2289 2290 kvm-intel.emulate_invalid_guest_state= 2291 [KVM,Intel] Enable emulation of invalid guest states 2292 Default is 0 (disabled) 2293 2294 kvm-intel.flexpriority= 2295 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2296 Default is 1 (enabled) 2297 2298 kvm-intel.nested= 2299 [KVM,Intel] Enable VMX nesting (nVMX). 2300 Default is 0 (disabled) 2301 2302 kvm-intel.unrestricted_guest= 2303 [KVM,Intel] Disable unrestricted guest feature 2304 (virtualized real and unpaged mode) on capable 2305 Intel chips. Default is 1 (enabled) 2306 2307 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2308 CVE-2018-3620. 2309 2310 Valid arguments: never, cond, always 2311 2312 always: L1D cache flush on every VMENTER. 2313 cond: Flush L1D on VMENTER only when the code between 2314 VMEXIT and VMENTER can leak host memory. 2315 never: Disables the mitigation 2316 2317 Default is cond (do L1 cache flush in specific instances) 2318 2319 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2320 feature (tagged TLBs) on capable Intel chips. 2321 Default is 1 (enabled) 2322 2323 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2324 affected CPUs 2325 2326 The kernel PTE inversion protection is unconditionally 2327 enabled and cannot be disabled. 2328 2329 full 2330 Provides all available mitigations for the 2331 L1TF vulnerability. Disables SMT and 2332 enables all mitigations in the 2333 hypervisors, i.e. unconditional L1D flush. 2334 2335 SMT control and L1D flush control via the 2336 sysfs interface is still possible after 2337 boot. Hypervisors will issue a warning 2338 when the first VM is started in a 2339 potentially insecure configuration, 2340 i.e. SMT enabled or L1D flush disabled. 2341 2342 full,force 2343 Same as 'full', but disables SMT and L1D 2344 flush runtime control. Implies the 2345 'nosmt=force' command line option. 2346 (i.e. sysfs control of SMT is disabled.) 2347 2348 flush 2349 Leaves SMT enabled and enables the default 2350 hypervisor mitigation, i.e. conditional 2351 L1D flush. 2352 2353 SMT control and L1D flush control via the 2354 sysfs interface is still possible after 2355 boot. Hypervisors will issue a warning 2356 when the first VM is started in a 2357 potentially insecure configuration, 2358 i.e. SMT enabled or L1D flush disabled. 2359 2360 flush,nosmt 2361 2362 Disables SMT and enables the default 2363 hypervisor mitigation. 2364 2365 SMT control and L1D flush control via the 2366 sysfs interface is still possible after 2367 boot. Hypervisors will issue a warning 2368 when the first VM is started in a 2369 potentially insecure configuration, 2370 i.e. SMT enabled or L1D flush disabled. 2371 2372 flush,nowarn 2373 Same as 'flush', but hypervisors will not 2374 warn when a VM is started in a potentially 2375 insecure configuration. 2376 2377 off 2378 Disables hypervisor mitigations and doesn't 2379 emit any warnings. 2380 It also drops the swap size and available 2381 RAM limit restriction on both hypervisor and 2382 bare metal. 2383 2384 Default is 'flush'. 2385 2386 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2387 2388 l2cr= [PPC] 2389 2390 l3cr= [PPC] 2391 2392 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2393 disabled it. 2394 2395 lapic= [X86,APIC] Do not use TSC deadline 2396 value for LAPIC timer one-shot implementation. Default 2397 back to the programmable timer unit in the LAPIC. 2398 Format: notscdeadline 2399 2400 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2401 in C2 power state. 2402 2403 libata.dma= [LIBATA] DMA control 2404 libata.dma=0 Disable all PATA and SATA DMA 2405 libata.dma=1 PATA and SATA Disk DMA only 2406 libata.dma=2 ATAPI (CDROM) DMA only 2407 libata.dma=4 Compact Flash DMA only 2408 Combinations also work, so libata.dma=3 enables DMA 2409 for disks and CDROMs, but not CFs. 2410 2411 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2412 libata.ignore_hpa=0 keep BIOS limits (default) 2413 libata.ignore_hpa=1 ignore limits, using full disk 2414 2415 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2416 when set. 2417 Format: <int> 2418 2419 libata.force= [LIBATA] Force configurations. The format is comma 2420 separated list of "[ID:]VAL" where ID is 2421 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2422 matching port, link or device. Basically, it matches 2423 the ATA ID string printed on console by libata. If 2424 the whole ID part is omitted, the last PORT and DEVICE 2425 values are used. If ID hasn't been specified yet, the 2426 configuration applies to all ports, links and devices. 2427 2428 If only DEVICE is omitted, the parameter applies to 2429 the port and all links and devices behind it. DEVICE 2430 number of 0 either selects the first device or the 2431 first fan-out link behind PMP device. It does not 2432 select the host link. DEVICE number of 15 selects the 2433 host link and device attached to it. 2434 2435 The VAL specifies the configuration to force. As long 2436 as there's no ambiguity shortcut notation is allowed. 2437 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2438 The following configurations can be forced. 2439 2440 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2441 Any ID with matching PORT is used. 2442 2443 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2444 2445 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2446 udma[/][16,25,33,44,66,100,133] notation is also 2447 allowed. 2448 2449 * [no]ncq: Turn on or off NCQ. 2450 2451 * [no]ncqtrim: Turn off queued DSM TRIM. 2452 2453 * nohrst, nosrst, norst: suppress hard, soft 2454 and both resets. 2455 2456 * rstonce: only attempt one reset during 2457 hot-unplug link recovery 2458 2459 * dump_id: dump IDENTIFY data. 2460 2461 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2462 2463 * disable: Disable this device. 2464 2465 If there are multiple matching configurations changing 2466 the same attribute, the last one is used. 2467 2468 memblock=debug [KNL] Enable memblock debug messages. 2469 2470 load_ramdisk= [RAM] [Deprecated] 2471 2472 lockd.nlm_grace_period=P [NFS] Assign grace period. 2473 Format: <integer> 2474 2475 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2476 Format: <integer> 2477 2478 lockd.nlm_timeout=T [NFS] Assign timeout value. 2479 Format: <integer> 2480 2481 lockd.nlm_udpport=M [NFS] Assign UDP port. 2482 Format: <integer> 2483 2484 lockdown= [SECURITY] 2485 { integrity | confidentiality } 2486 Enable the kernel lockdown feature. If set to 2487 integrity, kernel features that allow userland to 2488 modify the running kernel are disabled. If set to 2489 confidentiality, kernel features that allow userland 2490 to extract confidential information from the kernel 2491 are also disabled. 2492 2493 locktorture.nreaders_stress= [KNL] 2494 Set the number of locking read-acquisition kthreads. 2495 Defaults to being automatically set based on the 2496 number of online CPUs. 2497 2498 locktorture.nwriters_stress= [KNL] 2499 Set the number of locking write-acquisition kthreads. 2500 2501 locktorture.onoff_holdoff= [KNL] 2502 Set time (s) after boot for CPU-hotplug testing. 2503 2504 locktorture.onoff_interval= [KNL] 2505 Set time (s) between CPU-hotplug operations, or 2506 zero to disable CPU-hotplug testing. 2507 2508 locktorture.shuffle_interval= [KNL] 2509 Set task-shuffle interval (jiffies). Shuffling 2510 tasks allows some CPUs to go into dyntick-idle 2511 mode during the locktorture test. 2512 2513 locktorture.shutdown_secs= [KNL] 2514 Set time (s) after boot system shutdown. This 2515 is useful for hands-off automated testing. 2516 2517 locktorture.stat_interval= [KNL] 2518 Time (s) between statistics printk()s. 2519 2520 locktorture.stutter= [KNL] 2521 Time (s) to stutter testing, for example, 2522 specifying five seconds causes the test to run for 2523 five seconds, wait for five seconds, and so on. 2524 This tests the locking primitive's ability to 2525 transition abruptly to and from idle. 2526 2527 locktorture.torture_type= [KNL] 2528 Specify the locking implementation to test. 2529 2530 locktorture.verbose= [KNL] 2531 Enable additional printk() statements. 2532 2533 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2534 Format: <irq> 2535 2536 loglevel= All Kernel Messages with a loglevel smaller than the 2537 console loglevel will be printed to the console. It can 2538 also be changed with klogd or other programs. The 2539 loglevels are defined as follows: 2540 2541 0 (KERN_EMERG) system is unusable 2542 1 (KERN_ALERT) action must be taken immediately 2543 2 (KERN_CRIT) critical conditions 2544 3 (KERN_ERR) error conditions 2545 4 (KERN_WARNING) warning conditions 2546 5 (KERN_NOTICE) normal but significant condition 2547 6 (KERN_INFO) informational 2548 7 (KERN_DEBUG) debug-level messages 2549 2550 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2551 in bytes. n must be a power of two and greater 2552 than the minimal size. The minimal size is defined 2553 by LOG_BUF_SHIFT kernel config parameter. There is 2554 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2555 that allows to increase the default size depending on 2556 the number of CPUs. See init/Kconfig for more details. 2557 2558 logo.nologo [FB] Disables display of the built-in Linux logo. 2559 This may be used to provide more screen space for 2560 kernel log messages and is useful when debugging 2561 kernel boot problems. 2562 2563 lp=0 [LP] Specify parallel ports to use, e.g, 2564 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2565 lp=reset first parallel port). 'lp=0' disables the 2566 lp=auto printer driver. 'lp=reset' (which can be 2567 specified in addition to the ports) causes 2568 attached printers to be reset. Using 2569 lp=port1,port2,... specifies the parallel ports 2570 to associate lp devices with, starting with 2571 lp0. A port specification may be 'none' to skip 2572 that lp device, or a parport name such as 2573 'parport0'. Specifying 'lp=auto' instead of a 2574 port specification list means that device IDs 2575 from each port should be examined, to see if 2576 an IEEE 1284-compliant printer is attached; if 2577 so, the driver will manage that printer. 2578 See also header of drivers/char/lp.c. 2579 2580 lpj=n [KNL] 2581 Sets loops_per_jiffy to given constant, thus avoiding 2582 time-consuming boot-time autodetection (up to 250 ms per 2583 CPU). 0 enables autodetection (default). To determine 2584 the correct value for your kernel, boot with normal 2585 autodetection and see what value is printed. Note that 2586 on SMP systems the preset will be applied to all CPUs, 2587 which is likely to cause problems if your CPUs need 2588 significantly divergent settings. An incorrect value 2589 will cause delays in the kernel to be wrong, leading to 2590 unpredictable I/O errors and other breakage. Although 2591 unlikely, in the extreme case this might damage your 2592 hardware. 2593 2594 ltpc= [NET] 2595 Format: <io>,<irq>,<dma> 2596 2597 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2598 2599 lsm=lsm1,...,lsmN 2600 [SECURITY] Choose order of LSM initialization. This 2601 overrides CONFIG_LSM, and the "security=" parameter. 2602 2603 machvec= [IA-64] Force the use of a particular machine-vector 2604 (machvec) in a generic kernel. 2605 Example: machvec=hpzx1 2606 2607 machtype= [Loongson] Share the same kernel image file between 2608 different yeeloong laptops. 2609 Example: machtype=lemote-yeeloong-2f-7inch 2610 2611 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2612 than or equal to this physical address is ignored. 2613 2614 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2615 will bring up during bootup. maxcpus=n : n >= 0 limits 2616 the kernel to bring up 'n' processors. Surely after 2617 bootup you can bring up the other plugged cpu by executing 2618 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2619 only takes effect during system bootup. 2620 While n=0 is a special case, it is equivalent to "nosmp", 2621 which also disables the IO APIC. 2622 2623 max_loop= [LOOP] The number of loop block devices that get 2624 (loop.max_loop) unconditionally pre-created at init time. The default 2625 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2626 of statically allocating a predefined number, loop 2627 devices can be requested on-demand with the 2628 /dev/loop-control interface. 2629 2630 mce [X86-32] Machine Check Exception 2631 2632 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2633 2634 md= [HW] RAID subsystems devices and level 2635 See Documentation/admin-guide/md.rst. 2636 2637 mdacon= [MDA] 2638 Format: <first>,<last> 2639 Specifies range of consoles to be captured by the MDA. 2640 2641 mds= [X86,INTEL] 2642 Control mitigation for the Micro-architectural Data 2643 Sampling (MDS) vulnerability. 2644 2645 Certain CPUs are vulnerable to an exploit against CPU 2646 internal buffers which can forward information to a 2647 disclosure gadget under certain conditions. 2648 2649 In vulnerable processors, the speculatively 2650 forwarded data can be used in a cache side channel 2651 attack, to access data to which the attacker does 2652 not have direct access. 2653 2654 This parameter controls the MDS mitigation. The 2655 options are: 2656 2657 full - Enable MDS mitigation on vulnerable CPUs 2658 full,nosmt - Enable MDS mitigation and disable 2659 SMT on vulnerable CPUs 2660 off - Unconditionally disable MDS mitigation 2661 2662 On TAA-affected machines, mds=off can be prevented by 2663 an active TAA mitigation as both vulnerabilities are 2664 mitigated with the same mechanism so in order to disable 2665 this mitigation, you need to specify tsx_async_abort=off 2666 too. 2667 2668 Not specifying this option is equivalent to 2669 mds=full. 2670 2671 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2672 2673 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2674 Amount of memory to be used in cases as follows: 2675 2676 1 for test; 2677 2 when the kernel is not able to see the whole system memory; 2678 3 memory that lies after 'mem=' boundary is excluded from 2679 the hypervisor, then assigned to KVM guests. 2680 2681 [X86] Work as limiting max address. Use together 2682 with memmap= to avoid physical address space collisions. 2683 Without memmap= PCI devices could be placed at addresses 2684 belonging to unused RAM. 2685 2686 Note that this only takes effects during boot time since 2687 in above case 3, memory may need be hot added after boot 2688 if system memory of hypervisor is not sufficient. 2689 2690 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2691 memory. 2692 2693 memchunk=nn[KMG] 2694 [KNL,SH] Allow user to override the default size for 2695 per-device physically contiguous DMA buffers. 2696 2697 memhp_default_state=online/offline 2698 [KNL] Set the initial state for the memory hotplug 2699 onlining policy. If not specified, the default value is 2700 set according to the 2701 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2702 option. 2703 See Documentation/admin-guide/mm/memory-hotplug.rst. 2704 2705 memmap=exactmap [KNL,X86] Enable setting of an exact 2706 E820 memory map, as specified by the user. 2707 Such memmap=exactmap lines can be constructed based on 2708 BIOS output or other requirements. See the memmap=nn@ss 2709 option description. 2710 2711 memmap=nn[KMG]@ss[KMG] 2712 [KNL] Force usage of a specific region of memory. 2713 Region of memory to be used is from ss to ss+nn. 2714 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2715 which limits max address to nn[KMG]. 2716 Multiple different regions can be specified, 2717 comma delimited. 2718 Example: 2719 memmap=100M@2G,100M#3G,1G!1024G 2720 2721 memmap=nn[KMG]#ss[KMG] 2722 [KNL,ACPI] Mark specific memory as ACPI data. 2723 Region of memory to be marked is from ss to ss+nn. 2724 2725 memmap=nn[KMG]$ss[KMG] 2726 [KNL,ACPI] Mark specific memory as reserved. 2727 Region of memory to be reserved is from ss to ss+nn. 2728 Example: Exclude memory from 0x18690000-0x1869ffff 2729 memmap=64K$0x18690000 2730 or 2731 memmap=0x10000$0x18690000 2732 Some bootloaders may need an escape character before '$', 2733 like Grub2, otherwise '$' and the following number 2734 will be eaten. 2735 2736 memmap=nn[KMG]!ss[KMG] 2737 [KNL,X86] Mark specific memory as protected. 2738 Region of memory to be used, from ss to ss+nn. 2739 The memory region may be marked as e820 type 12 (0xc) 2740 and is NVDIMM or ADR memory. 2741 2742 memmap=<size>%<offset>-<oldtype>+<newtype> 2743 [KNL,ACPI] Convert memory within the specified region 2744 from <oldtype> to <newtype>. If "-<oldtype>" is left 2745 out, the whole region will be marked as <newtype>, 2746 even if previously unavailable. If "+<newtype>" is left 2747 out, matching memory will be removed. Types are 2748 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2749 3 = ACPI, 12 = PRAM. 2750 2751 memory_corruption_check=0/1 [X86] 2752 Some BIOSes seem to corrupt the first 64k of 2753 memory when doing things like suspend/resume. 2754 Setting this option will scan the memory 2755 looking for corruption. Enabling this will 2756 both detect corruption and prevent the kernel 2757 from using the memory being corrupted. 2758 However, its intended as a diagnostic tool; if 2759 repeatable BIOS-originated corruption always 2760 affects the same memory, you can use memmap= 2761 to prevent the kernel from using that memory. 2762 2763 memory_corruption_check_size=size [X86] 2764 By default it checks for corruption in the low 2765 64k, making this memory unavailable for normal 2766 use. Use this parameter to scan for 2767 corruption in more or less memory. 2768 2769 memory_corruption_check_period=seconds [X86] 2770 By default it checks for corruption every 60 2771 seconds. Use this parameter to check at some 2772 other rate. 0 disables periodic checking. 2773 2774 memtest= [KNL,X86,ARM,PPC] Enable memtest 2775 Format: <integer> 2776 default : 0 <disable> 2777 Specifies the number of memtest passes to be 2778 performed. Each pass selects another test 2779 pattern from a given set of patterns. Memtest 2780 fills the memory with this pattern, validates 2781 memory contents and reserves bad memory 2782 regions that are detected. 2783 2784 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2785 Valid arguments: on, off 2786 Default (depends on kernel configuration option): 2787 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2788 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2789 mem_encrypt=on: Activate SME 2790 mem_encrypt=off: Do not activate SME 2791 2792 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2793 for details on when memory encryption can be activated. 2794 2795 mem_sleep_default= [SUSPEND] Default system suspend mode: 2796 s2idle - Suspend-To-Idle 2797 shallow - Power-On Suspend or equivalent (if supported) 2798 deep - Suspend-To-RAM or equivalent (if supported) 2799 See Documentation/admin-guide/pm/sleep-states.rst. 2800 2801 meye.*= [HW] Set MotionEye Camera parameters 2802 See Documentation/admin-guide/media/meye.rst. 2803 2804 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2805 Multi-Function General Purpose Timers on AMD Geode 2806 platforms. 2807 2808 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2809 the BIOS has incorrectly applied a workaround. TinyBIOS 2810 version 0.98 is known to be affected, 0.99 fixes the 2811 problem by letting the user disable the workaround. 2812 2813 mga= [HW,DRM] 2814 2815 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2816 physical address is ignored. 2817 2818 mini2440= [ARM,HW,KNL] 2819 Format:[0..2][b][c][t] 2820 Default: "0tb" 2821 MINI2440 configuration specification: 2822 0 - The attached screen is the 3.5" TFT 2823 1 - The attached screen is the 7" TFT 2824 2 - The VGA Shield is attached (1024x768) 2825 Leaving out the screen size parameter will not load 2826 the TFT driver, and the framebuffer will be left 2827 unconfigured. 2828 b - Enable backlight. The TFT backlight pin will be 2829 linked to the kernel VESA blanking code and a GPIO 2830 LED. This parameter is not necessary when using the 2831 VGA shield. 2832 c - Enable the s3c camera interface. 2833 t - Reserved for enabling touchscreen support. The 2834 touchscreen support is not enabled in the mainstream 2835 kernel as of 2.6.30, a preliminary port can be found 2836 in the "bleeding edge" mini2440 support kernel at 2837 https://repo.or.cz/w/linux-2.6/mini2440.git 2838 2839 mitigations= 2840 [X86,PPC,S390,ARM64] Control optional mitigations for 2841 CPU vulnerabilities. This is a set of curated, 2842 arch-independent options, each of which is an 2843 aggregation of existing arch-specific options. 2844 2845 off 2846 Disable all optional CPU mitigations. This 2847 improves system performance, but it may also 2848 expose users to several CPU vulnerabilities. 2849 Equivalent to: nopti [X86,PPC] 2850 kpti=0 [ARM64] 2851 nospectre_v1 [X86,PPC] 2852 nobp=0 [S390] 2853 nospectre_v2 [X86,PPC,S390,ARM64] 2854 spectre_v2_user=off [X86] 2855 spec_store_bypass_disable=off [X86,PPC] 2856 ssbd=force-off [ARM64] 2857 l1tf=off [X86] 2858 mds=off [X86] 2859 tsx_async_abort=off [X86] 2860 kvm.nx_huge_pages=off [X86] 2861 no_entry_flush [PPC] 2862 no_uaccess_flush [PPC] 2863 2864 Exceptions: 2865 This does not have any effect on 2866 kvm.nx_huge_pages when 2867 kvm.nx_huge_pages=force. 2868 2869 auto (default) 2870 Mitigate all CPU vulnerabilities, but leave SMT 2871 enabled, even if it's vulnerable. This is for 2872 users who don't want to be surprised by SMT 2873 getting disabled across kernel upgrades, or who 2874 have other ways of avoiding SMT-based attacks. 2875 Equivalent to: (default behavior) 2876 2877 auto,nosmt 2878 Mitigate all CPU vulnerabilities, disabling SMT 2879 if needed. This is for users who always want to 2880 be fully mitigated, even if it means losing SMT. 2881 Equivalent to: l1tf=flush,nosmt [X86] 2882 mds=full,nosmt [X86] 2883 tsx_async_abort=full,nosmt [X86] 2884 2885 mminit_loglevel= 2886 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2887 parameter allows control of the logging verbosity for 2888 the additional memory initialisation checks. A value 2889 of 0 disables mminit logging and a level of 4 will 2890 log everything. Information is printed at KERN_DEBUG 2891 so loglevel=8 may also need to be specified. 2892 2893 module.sig_enforce 2894 [KNL] When CONFIG_MODULE_SIG is set, this means that 2895 modules without (valid) signatures will fail to load. 2896 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2897 is always true, so this option does nothing. 2898 2899 module_blacklist= [KNL] Do not load a comma-separated list of 2900 modules. Useful for debugging problem modules. 2901 2902 mousedev.tap_time= 2903 [MOUSE] Maximum time between finger touching and 2904 leaving touchpad surface for touch to be considered 2905 a tap and be reported as a left button click (for 2906 touchpads working in absolute mode only). 2907 Format: <msecs> 2908 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2909 reporting absolute coordinates, such as tablets 2910 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2911 reporting absolute coordinates, such as tablets 2912 2913 movablecore= [KNL,X86,IA-64,PPC] 2914 Format: nn[KMGTPE] | nn% 2915 This parameter is the complement to kernelcore=, it 2916 specifies the amount of memory used for migratable 2917 allocations. If both kernelcore and movablecore is 2918 specified, then kernelcore will be at *least* the 2919 specified value but may be more. If movablecore on its 2920 own is specified, the administrator must be careful 2921 that the amount of memory usable for all allocations 2922 is not too small. 2923 2924 movable_node [KNL] Boot-time switch to make hotplugable memory 2925 NUMA nodes to be movable. This means that the memory 2926 of such nodes will be usable only for movable 2927 allocations which rules out almost all kernel 2928 allocations. Use with caution! 2929 2930 MTD_Partition= [MTD] 2931 Format: <name>,<region-number>,<size>,<offset> 2932 2933 MTD_Region= [MTD] Format: 2934 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2935 2936 mtdparts= [MTD] 2937 See drivers/mtd/parsers/cmdlinepart.c 2938 2939 multitce=off [PPC] This parameter disables the use of the pSeries 2940 firmware feature for updating multiple TCE entries 2941 at a time. 2942 2943 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2944 2945 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2946 2947 boundary - index of last SLC block on Flex-OneNAND. 2948 The remaining blocks are configured as MLC blocks. 2949 lock - Configure if Flex-OneNAND boundary should be locked. 2950 Once locked, the boundary cannot be changed. 2951 1 indicates lock status, 0 indicates unlock status. 2952 2953 mtdset= [ARM] 2954 ARM/S3C2412 JIVE boot control 2955 2956 See arch/arm/mach-s3c2412/mach-jive.c 2957 2958 mtouchusb.raw_coordinates= 2959 [HW] Make the MicroTouch USB driver use raw coordinates 2960 ('y', default) or cooked coordinates ('n') 2961 2962 mtrr_chunk_size=nn[KMG] [X86] 2963 used for mtrr cleanup. It is largest continuous chunk 2964 that could hold holes aka. UC entries. 2965 2966 mtrr_gran_size=nn[KMG] [X86] 2967 Used for mtrr cleanup. It is granularity of mtrr block. 2968 Default is 1. 2969 Large value could prevent small alignment from 2970 using up MTRRs. 2971 2972 mtrr_spare_reg_nr=n [X86] 2973 Format: <integer> 2974 Range: 0,7 : spare reg number 2975 Default : 1 2976 Used for mtrr cleanup. It is spare mtrr entries number. 2977 Set to 2 or more if your graphical card needs more. 2978 2979 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2980 2981 netdev= [NET] Network devices parameters 2982 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2983 Note that mem_start is often overloaded to mean 2984 something different and driver-specific. 2985 This usage is only documented in each driver source 2986 file if at all. 2987 2988 nf_conntrack.acct= 2989 [NETFILTER] Enable connection tracking flow accounting 2990 0 to disable accounting 2991 1 to enable accounting 2992 Default value is 0. 2993 2994 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2995 See Documentation/admin-guide/nfs/nfsroot.rst. 2996 2997 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2998 See Documentation/admin-guide/nfs/nfsroot.rst. 2999 3000 nfsrootdebug [NFS] enable nfsroot debugging messages. 3001 See Documentation/admin-guide/nfs/nfsroot.rst. 3002 3003 nfs.callback_nr_threads= 3004 [NFSv4] set the total number of threads that the 3005 NFS client will assign to service NFSv4 callback 3006 requests. 3007 3008 nfs.callback_tcpport= 3009 [NFS] set the TCP port on which the NFSv4 callback 3010 channel should listen. 3011 3012 nfs.cache_getent= 3013 [NFS] sets the pathname to the program which is used 3014 to update the NFS client cache entries. 3015 3016 nfs.cache_getent_timeout= 3017 [NFS] sets the timeout after which an attempt to 3018 update a cache entry is deemed to have failed. 3019 3020 nfs.idmap_cache_timeout= 3021 [NFS] set the maximum lifetime for idmapper cache 3022 entries. 3023 3024 nfs.enable_ino64= 3025 [NFS] enable 64-bit inode numbers. 3026 If zero, the NFS client will fake up a 32-bit inode 3027 number for the readdir() and stat() syscalls instead 3028 of returning the full 64-bit number. 3029 The default is to return 64-bit inode numbers. 3030 3031 nfs.max_session_cb_slots= 3032 [NFSv4.1] Sets the maximum number of session 3033 slots the client will assign to the callback 3034 channel. This determines the maximum number of 3035 callbacks the client will process in parallel for 3036 a particular server. 3037 3038 nfs.max_session_slots= 3039 [NFSv4.1] Sets the maximum number of session slots 3040 the client will attempt to negotiate with the server. 3041 This limits the number of simultaneous RPC requests 3042 that the client can send to the NFSv4.1 server. 3043 Note that there is little point in setting this 3044 value higher than the max_tcp_slot_table_limit. 3045 3046 nfs.nfs4_disable_idmapping= 3047 [NFSv4] When set to the default of '1', this option 3048 ensures that both the RPC level authentication 3049 scheme and the NFS level operations agree to use 3050 numeric uids/gids if the mount is using the 3051 'sec=sys' security flavour. In effect it is 3052 disabling idmapping, which can make migration from 3053 legacy NFSv2/v3 systems to NFSv4 easier. 3054 Servers that do not support this mode of operation 3055 will be autodetected by the client, and it will fall 3056 back to using the idmapper. 3057 To turn off this behaviour, set the value to '0'. 3058 nfs.nfs4_unique_id= 3059 [NFS4] Specify an additional fixed unique ident- 3060 ification string that NFSv4 clients can insert into 3061 their nfs_client_id4 string. This is typically a 3062 UUID that is generated at system install time. 3063 3064 nfs.send_implementation_id = 3065 [NFSv4.1] Send client implementation identification 3066 information in exchange_id requests. 3067 If zero, no implementation identification information 3068 will be sent. 3069 The default is to send the implementation identification 3070 information. 3071 3072 nfs.recover_lost_locks = 3073 [NFSv4] Attempt to recover locks that were lost due 3074 to a lease timeout on the server. Please note that 3075 doing this risks data corruption, since there are 3076 no guarantees that the file will remain unchanged 3077 after the locks are lost. 3078 If you want to enable the kernel legacy behaviour of 3079 attempting to recover these locks, then set this 3080 parameter to '1'. 3081 The default parameter value of '0' causes the kernel 3082 not to attempt recovery of lost locks. 3083 3084 nfs4.layoutstats_timer = 3085 [NFSv4.2] Change the rate at which the kernel sends 3086 layoutstats to the pNFS metadata server. 3087 3088 Setting this to value to 0 causes the kernel to use 3089 whatever value is the default set by the layout 3090 driver. A non-zero value sets the minimum interval 3091 in seconds between layoutstats transmissions. 3092 3093 nfsd.nfs4_disable_idmapping= 3094 [NFSv4] When set to the default of '1', the NFSv4 3095 server will return only numeric uids and gids to 3096 clients using auth_sys, and will accept numeric uids 3097 and gids from such clients. This is intended to ease 3098 migration from NFSv2/v3. 3099 3100 nmi_backtrace.backtrace_idle [KNL] 3101 Dump stacks even of idle CPUs in response to an 3102 NMI stack-backtrace request. 3103 3104 nmi_debug= [KNL,SH] Specify one or more actions to take 3105 when a NMI is triggered. 3106 Format: [state][,regs][,debounce][,die] 3107 3108 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 3109 Format: [panic,][nopanic,][num] 3110 Valid num: 0 or 1 3111 0 - turn hardlockup detector in nmi_watchdog off 3112 1 - turn hardlockup detector in nmi_watchdog on 3113 When panic is specified, panic when an NMI watchdog 3114 timeout occurs (or 'nopanic' to not panic on an NMI 3115 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 3116 To disable both hard and soft lockup detectors, 3117 please see 'nowatchdog'. 3118 This is useful when you use a panic=... timeout and 3119 need the box quickly up again. 3120 3121 These settings can be accessed at runtime via 3122 the nmi_watchdog and hardlockup_panic sysctls. 3123 3124 netpoll.carrier_timeout= 3125 [NET] Specifies amount of time (in seconds) that 3126 netpoll should wait for a carrier. By default netpoll 3127 waits 4 seconds. 3128 3129 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 3130 emulation library even if a 387 maths coprocessor 3131 is present. 3132 3133 no5lvl [X86-64] Disable 5-level paging mode. Forces 3134 kernel to use 4-level paging instead. 3135 3136 nofsgsbase [X86] Disables FSGSBASE instructions. 3137 3138 no_console_suspend 3139 [HW] Never suspend the console 3140 Disable suspending of consoles during suspend and 3141 hibernate operations. Once disabled, debugging 3142 messages can reach various consoles while the rest 3143 of the system is being put to sleep (ie, while 3144 debugging driver suspend/resume hooks). This may 3145 not work reliably with all consoles, but is known 3146 to work with serial and VGA consoles. 3147 To facilitate more flexible debugging, we also add 3148 console_suspend, a printk module parameter to control 3149 it. Users could use console_suspend (usually 3150 /sys/module/printk/parameters/console_suspend) to 3151 turn on/off it dynamically. 3152 3153 novmcoredd [KNL,KDUMP] 3154 Disable device dump. Device dump allows drivers to 3155 append dump data to vmcore so you can collect driver 3156 specified debug info. Drivers can append the data 3157 without any limit and this data is stored in memory, 3158 so this may cause significant memory stress. Disabling 3159 device dump can help save memory but the driver debug 3160 data will be no longer available. This parameter 3161 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 3162 is set. 3163 3164 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 3165 caches in the slab allocator. Saves per-node memory, 3166 but will impact performance. 3167 3168 noalign [KNL,ARM] 3169 3170 noaltinstr [S390] Disables alternative instructions patching 3171 (CPU alternatives feature). 3172 3173 noapic [SMP,APIC] Tells the kernel to not make use of any 3174 IOAPICs that may be present in the system. 3175 3176 noautogroup Disable scheduler automatic task group creation. 3177 3178 nobats [PPC] Do not use BATs for mapping kernel lowmem 3179 on "Classic" PPC cores. 3180 3181 nocache [ARM] 3182 3183 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 3184 3185 nodelayacct [KNL] Disable per-task delay accounting 3186 3187 nodsp [SH] Disable hardware DSP at boot time. 3188 3189 noefi Disable EFI runtime services support. 3190 3191 no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel. 3192 3193 noexec [IA-64] 3194 3195 noexec [X86] 3196 On X86-32 available only on PAE configured kernels. 3197 noexec=on: enable non-executable mappings (default) 3198 noexec=off: disable non-executable mappings 3199 3200 nosmap [X86,PPC] 3201 Disable SMAP (Supervisor Mode Access Prevention) 3202 even if it is supported by processor. 3203 3204 nosmep [X86,PPC] 3205 Disable SMEP (Supervisor Mode Execution Prevention) 3206 even if it is supported by processor. 3207 3208 noexec32 [X86-64] 3209 This affects only 32-bit executables. 3210 noexec32=on: enable non-executable mappings (default) 3211 read doesn't imply executable mappings 3212 noexec32=off: disable non-executable mappings 3213 read implies executable mappings 3214 3215 nofpu [MIPS,SH] Disable hardware FPU at boot time. 3216 3217 nofxsr [BUGS=X86-32] Disables x86 floating point extended 3218 register save and restore. The kernel will only save 3219 legacy floating-point registers on task switch. 3220 3221 nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings. 3222 3223 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 3224 Equivalent to smt=1. 3225 3226 [KNL,X86] Disable symmetric multithreading (SMT). 3227 nosmt=force: Force disable SMT, cannot be undone 3228 via the sysfs control file. 3229 3230 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 3231 (bounds check bypass). With this option data leaks are 3232 possible in the system. 3233 3234 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 3235 the Spectre variant 2 (indirect branch prediction) 3236 vulnerability. System may allow data leaks with this 3237 option. 3238 3239 nospec_store_bypass_disable 3240 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 3241 3242 no_uaccess_flush 3243 [PPC] Don't flush the L1-D cache after accessing user data. 3244 3245 noxsave [BUGS=X86] Disables x86 extended register state save 3246 and restore using xsave. The kernel will fallback to 3247 enabling legacy floating-point and sse state. 3248 3249 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 3250 register states. The kernel will fall back to use 3251 xsave to save the states. By using this parameter, 3252 performance of saving the states is degraded because 3253 xsave doesn't support modified optimization while 3254 xsaveopt supports it on xsaveopt enabled systems. 3255 3256 noxsaves [X86] Disables xsaves and xrstors used in saving and 3257 restoring x86 extended register state in compacted 3258 form of xsave area. The kernel will fall back to use 3259 xsaveopt and xrstor to save and restore the states 3260 in standard form of xsave area. By using this 3261 parameter, xsave area per process might occupy more 3262 memory on xsaves enabled systems. 3263 3264 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3265 wfi(ARM) instruction doesn't work correctly and not to 3266 use it. This is also useful when using JTAG debugger. 3267 3268 no_file_caps Tells the kernel not to honor file capabilities. The 3269 only way then for a file to be executed with privilege 3270 is to be setuid root or executed by root. 3271 3272 nohalt [IA-64] Tells the kernel not to use the power saving 3273 function PAL_HALT_LIGHT when idle. This increases 3274 power-consumption. On the positive side, it reduces 3275 interrupt wake-up latency, which may improve performance 3276 in certain environments such as networked servers or 3277 real-time systems. 3278 3279 nohibernate [HIBERNATION] Disable hibernation and resume. 3280 3281 nohz= [KNL] Boottime enable/disable dynamic ticks 3282 Valid arguments: on, off 3283 Default: on 3284 3285 nohz_full= [KNL,BOOT,SMP,ISOL] 3286 The argument is a cpu list, as described above. 3287 In kernels built with CONFIG_NO_HZ_FULL=y, set 3288 the specified list of CPUs whose tick will be stopped 3289 whenever possible. The boot CPU will be forced outside 3290 the range to maintain the timekeeping. Any CPUs 3291 in this list will have their RCU callbacks offloaded, 3292 just as if they had also been called out in the 3293 rcu_nocbs= boot parameter. 3294 3295 noiotrap [SH] Disables trapped I/O port accesses. 3296 3297 noirqdebug [X86-32] Disables the code which attempts to detect and 3298 disable unhandled interrupt sources. 3299 3300 no_timer_check [X86,APIC] Disables the code which tests for 3301 broken timer IRQ sources. 3302 3303 noisapnp [ISAPNP] Disables ISA PnP code. 3304 3305 noinitrd [RAM] Tells the kernel not to load any configured 3306 initial RAM disk. 3307 3308 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3309 remapping. 3310 [Deprecated - use intremap=off] 3311 3312 nointroute [IA-64] 3313 3314 noinvpcid [X86] Disable the INVPCID cpu feature. 3315 3316 nojitter [IA-64] Disables jitter checking for ITC timers. 3317 3318 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3319 3320 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3321 fault handling. 3322 3323 no-vmw-sched-clock 3324 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3325 clock and use the default one. 3326 3327 no-steal-acc [X86,PV_OPS,ARM64] Disable paravirtualized steal time 3328 accounting. steal time is computed, but won't 3329 influence scheduler behaviour 3330 3331 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3332 3333 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3334 3335 noltlbs [PPC] Do not use large page/tlb entries for kernel 3336 lowmem mapping on PPC40x and PPC8xx 3337 3338 nomca [IA-64] Disable machine check abort handling 3339 3340 nomce [X86-32] Disable Machine Check Exception 3341 3342 nomfgpt [X86-32] Disable Multi-Function General Purpose 3343 Timer usage (for AMD Geode machines). 3344 3345 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3346 shutdown the other cpus. Instead use the REBOOT_VECTOR 3347 irq. 3348 3349 nomodule Disable module load 3350 3351 nopat [X86] Disable PAT (page attribute table extension of 3352 pagetables) support. 3353 3354 nopcid [X86-64] Disable the PCID cpu feature. 3355 3356 norandmaps Don't use address space randomization. Equivalent to 3357 echo 0 > /proc/sys/kernel/randomize_va_space 3358 3359 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3360 with UP alternatives 3361 3362 nordrand [X86] Disable kernel use of the RDRAND and 3363 RDSEED instructions even if they are supported 3364 by the processor. RDRAND and RDSEED are still 3365 available to user space applications. 3366 3367 noresume [SWSUSP] Disables resume and restores original swap 3368 space. 3369 3370 no-scroll [VGA] Disables scrollback. 3371 This is required for the Braillex ib80-piezo Braille 3372 reader made by F.H. Papenmeier (Germany). 3373 3374 nosbagart [IA-64] 3375 3376 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3377 3378 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3379 and disable the IO APIC. legacy for "maxcpus=0". 3380 3381 nosoftlockup [KNL] Disable the soft-lockup detector. 3382 3383 nosync [HW,M68K] Disables sync negotiation for all devices. 3384 3385 nowatchdog [KNL] Disable both lockup detectors, i.e. 3386 soft-lockup and NMI watchdog (hard-lockup). 3387 3388 nowb [ARM] 3389 3390 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3391 3392 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3393 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3394 Some features depend on CPU0. Known dependencies are: 3395 1. Resume from suspend/hibernate depends on CPU0. 3396 Suspend/hibernate will fail if CPU0 is offline and you 3397 need to online CPU0 before suspend/hibernate. 3398 2. PIC interrupts also depend on CPU0. CPU0 can't be 3399 removed if a PIC interrupt is detected. 3400 It's said poweroff/reboot may depend on CPU0 on some 3401 machines although I haven't seen such issues so far 3402 after CPU0 is offline on a few tested machines. 3403 If the dependencies are under your control, you can 3404 turn on cpu0_hotplug. 3405 3406 nps_mtm_hs_ctr= [KNL,ARC] 3407 This parameter sets the maximum duration, in 3408 cycles, each HW thread of the CTOP can run 3409 without interruptions, before HW switches it. 3410 The actual maximum duration is 16 times this 3411 parameter's value. 3412 Format: integer between 1 and 255 3413 Default: 255 3414 3415 nptcg= [IA-64] Override max number of concurrent global TLB 3416 purges which is reported from either PAL_VM_SUMMARY or 3417 SAL PALO. 3418 3419 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3420 could support. nr_cpus=n : n >= 1 limits the kernel to 3421 support 'n' processors. It could be larger than the 3422 number of already plugged CPU during bootup, later in 3423 runtime you can physically add extra cpu until it reaches 3424 n. So during boot up some boot time memory for per-cpu 3425 variables need be pre-allocated for later physical cpu 3426 hot plugging. 3427 3428 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3429 3430 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3431 Allowed values are enable and disable 3432 3433 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3434 'node', 'default' can be specified 3435 This can be set from sysctl after boot. 3436 See Documentation/admin-guide/sysctl/vm.rst for details. 3437 3438 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3439 See Documentation/core-api/debugging-via-ohci1394.rst for more 3440 info. 3441 3442 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3443 Rather than timing out after 20 ms if an EC 3444 command is not properly ACKed, override the length 3445 of the timeout. We have interrupts disabled while 3446 waiting for the ACK, so if this is set too high 3447 interrupts *may* be lost! 3448 3449 omap_mux= [OMAP] Override bootloader pin multiplexing. 3450 Format: <mux_mode0.mode_name=value>... 3451 For example, to override I2C bus2: 3452 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3453 3454 oprofile.timer= [HW] 3455 Use timer interrupt instead of performance counters 3456 3457 oprofile.cpu_type= Force an oprofile cpu type 3458 This might be useful if you have an older oprofile 3459 userland or if you want common events. 3460 Format: { arch_perfmon } 3461 arch_perfmon: [X86] Force use of architectural 3462 perfmon on Intel CPUs instead of the 3463 CPU specific event set. 3464 timer: [X86] Force use of architectural NMI 3465 timer mode (see also oprofile.timer 3466 for generic hr timer mode) 3467 3468 oops=panic Always panic on oopses. Default is to just kill the 3469 process, but there is a small probability of 3470 deadlocking the machine. 3471 This will also cause panics on machine check exceptions. 3472 Useful together with panic=30 to trigger a reboot. 3473 3474 page_alloc.shuffle= 3475 [KNL] Boolean flag to control whether the page allocator 3476 should randomize its free lists. The randomization may 3477 be automatically enabled if the kernel detects it is 3478 running on a platform with a direct-mapped memory-side 3479 cache, and this parameter can be used to 3480 override/disable that behavior. The state of the flag 3481 can be read from sysfs at: 3482 /sys/module/page_alloc/parameters/shuffle. 3483 3484 page_owner= [KNL] Boot-time page_owner enabling option. 3485 Storage of the information about who allocated 3486 each page is disabled in default. With this switch, 3487 we can turn it on. 3488 on: enable the feature 3489 3490 page_poison= [KNL] Boot-time parameter changing the state of 3491 poisoning on the buddy allocator, available with 3492 CONFIG_PAGE_POISONING=y. 3493 off: turn off poisoning (default) 3494 on: turn on poisoning 3495 3496 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3497 timeout > 0: seconds before rebooting 3498 timeout = 0: wait forever 3499 timeout < 0: reboot immediately 3500 Format: <timeout> 3501 3502 panic_print= Bitmask for printing system info when panic happens. 3503 User can chose combination of the following bits: 3504 bit 0: print all tasks info 3505 bit 1: print system memory info 3506 bit 2: print timer info 3507 bit 3: print locks info if CONFIG_LOCKDEP is on 3508 bit 4: print ftrace buffer 3509 bit 5: print all printk messages in buffer 3510 3511 panic_on_taint= Bitmask for conditionally calling panic() in add_taint() 3512 Format: <hex>[,nousertaint] 3513 Hexadecimal bitmask representing the set of TAINT flags 3514 that will cause the kernel to panic when add_taint() is 3515 called with any of the flags in this set. 3516 The optional switch "nousertaint" can be utilized to 3517 prevent userspace forced crashes by writing to sysctl 3518 /proc/sys/kernel/tainted any flagset matching with the 3519 bitmask set on panic_on_taint. 3520 See Documentation/admin-guide/tainted-kernels.rst for 3521 extra details on the taint flags that users can pick 3522 to compose the bitmask to assign to panic_on_taint. 3523 3524 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3525 on a WARN(). 3526 3527 crash_kexec_post_notifiers 3528 Run kdump after running panic-notifiers and dumping 3529 kmsg. This only for the users who doubt kdump always 3530 succeeds in any situation. 3531 Note that this also increases risks of kdump failure, 3532 because some panic notifiers can make the crashed 3533 kernel more unstable. 3534 3535 parkbd.port= [HW] Parallel port number the keyboard adapter is 3536 connected to, default is 0. 3537 Format: <parport#> 3538 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3539 0 for XT, 1 for AT (default is AT). 3540 Format: <mode> 3541 3542 parport= [HW,PPT] Specify parallel ports. 0 disables. 3543 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3544 Use 'auto' to force the driver to use any 3545 IRQ/DMA settings detected (the default is to 3546 ignore detected IRQ/DMA settings because of 3547 possible conflicts). You can specify the base 3548 address, IRQ, and DMA settings; IRQ and DMA 3549 should be numbers, or 'auto' (for using detected 3550 settings on that particular port), or 'nofifo' 3551 (to avoid using a FIFO even if it is detected). 3552 Parallel ports are assigned in the order they 3553 are specified on the command line, starting 3554 with parport0. 3555 3556 parport_init_mode= [HW,PPT] 3557 Configure VIA parallel port to operate in 3558 a specific mode. This is necessary on Pegasos 3559 computer where firmware has no options for setting 3560 up parallel port mode and sets it to spp. 3561 Currently this function knows 686a and 8231 chips. 3562 Format: [spp|ps2|epp|ecp|ecpepp] 3563 3564 pause_on_oops= 3565 Halt all CPUs after the first oops has been printed for 3566 the specified number of seconds. This is to be used if 3567 your oopses keep scrolling off the screen. 3568 3569 pcbit= [HW,ISDN] 3570 3571 pcd. [PARIDE] 3572 See header of drivers/block/paride/pcd.c. 3573 See also Documentation/admin-guide/blockdev/paride.rst. 3574 3575 pci=option[,option...] [PCI] various PCI subsystem options. 3576 3577 Some options herein operate on a specific device 3578 or a set of devices (<pci_dev>). These are 3579 specified in one of the following formats: 3580 3581 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3582 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3583 3584 Note: the first format specifies a PCI 3585 bus/device/function address which may change 3586 if new hardware is inserted, if motherboard 3587 firmware changes, or due to changes caused 3588 by other kernel parameters. If the 3589 domain is left unspecified, it is 3590 taken to be zero. Optionally, a path 3591 to a device through multiple device/function 3592 addresses can be specified after the base 3593 address (this is more robust against 3594 renumbering issues). The second format 3595 selects devices using IDs from the 3596 configuration space which may match multiple 3597 devices in the system. 3598 3599 earlydump dump PCI config space before the kernel 3600 changes anything 3601 off [X86] don't probe for the PCI bus 3602 bios [X86-32] force use of PCI BIOS, don't access 3603 the hardware directly. Use this if your machine 3604 has a non-standard PCI host bridge. 3605 nobios [X86-32] disallow use of PCI BIOS, only direct 3606 hardware access methods are allowed. Use this 3607 if you experience crashes upon bootup and you 3608 suspect they are caused by the BIOS. 3609 conf1 [X86] Force use of PCI Configuration Access 3610 Mechanism 1 (config address in IO port 0xCF8, 3611 data in IO port 0xCFC, both 32-bit). 3612 conf2 [X86] Force use of PCI Configuration Access 3613 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3614 the function, IO port 0xCFA, also 8-bit, sets 3615 bus number. The config space is then accessed 3616 through ports 0xC000-0xCFFF). 3617 See http://wiki.osdev.org/PCI for more info 3618 on the configuration access mechanisms. 3619 noaer [PCIE] If the PCIEAER kernel config parameter is 3620 enabled, this kernel boot option can be used to 3621 disable the use of PCIE advanced error reporting. 3622 nodomains [PCI] Disable support for multiple PCI 3623 root domains (aka PCI segments, in ACPI-speak). 3624 nommconf [X86] Disable use of MMCONFIG for PCI 3625 Configuration 3626 check_enable_amd_mmconf [X86] check for and enable 3627 properly configured MMIO access to PCI 3628 config space on AMD family 10h CPU 3629 nomsi [MSI] If the PCI_MSI kernel config parameter is 3630 enabled, this kernel boot option can be used to 3631 disable the use of MSI interrupts system-wide. 3632 noioapicquirk [APIC] Disable all boot interrupt quirks. 3633 Safety option to keep boot IRQs enabled. This 3634 should never be necessary. 3635 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3636 primary IO-APIC for bridges that cannot disable 3637 boot IRQs. This fixes a source of spurious IRQs 3638 when the system masks IRQs. 3639 noioapicreroute [APIC] Disable workaround that uses the 3640 boot IRQ equivalent of an IRQ that connects to 3641 a chipset where boot IRQs cannot be disabled. 3642 The opposite of ioapicreroute. 3643 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3644 routing table. These calls are known to be buggy 3645 on several machines and they hang the machine 3646 when used, but on other computers it's the only 3647 way to get the interrupt routing table. Try 3648 this option if the kernel is unable to allocate 3649 IRQs or discover secondary PCI buses on your 3650 motherboard. 3651 rom [X86] Assign address space to expansion ROMs. 3652 Use with caution as certain devices share 3653 address decoders between ROMs and other 3654 resources. 3655 norom [X86] Do not assign address space to 3656 expansion ROMs that do not already have 3657 BIOS assigned address ranges. 3658 nobar [X86] Do not assign address space to the 3659 BARs that weren't assigned by the BIOS. 3660 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3661 assigned automatically to PCI devices. You can 3662 make the kernel exclude IRQs of your ISA cards 3663 this way. 3664 pirqaddr=0xAAAAA [X86] Specify the physical address 3665 of the PIRQ table (normally generated 3666 by the BIOS) if it is outside the 3667 F0000h-100000h range. 3668 lastbus=N [X86] Scan all buses thru bus #N. Can be 3669 useful if the kernel is unable to find your 3670 secondary buses and you want to tell it 3671 explicitly which ones they are. 3672 assign-busses [X86] Always assign all PCI bus 3673 numbers ourselves, overriding 3674 whatever the firmware may have done. 3675 usepirqmask [X86] Honor the possible IRQ mask stored 3676 in the BIOS $PIR table. This is needed on 3677 some systems with broken BIOSes, notably 3678 some HP Pavilion N5400 and Omnibook XE3 3679 notebooks. This will have no effect if ACPI 3680 IRQ routing is enabled. 3681 noacpi [X86] Do not use ACPI for IRQ routing 3682 or for PCI scanning. 3683 use_crs [X86] Use PCI host bridge window information 3684 from ACPI. On BIOSes from 2008 or later, this 3685 is enabled by default. If you need to use this, 3686 please report a bug. 3687 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3688 If you need to use this, please report a bug. 3689 routeirq Do IRQ routing for all PCI devices. 3690 This is normally done in pci_enable_device(), 3691 so this option is a temporary workaround 3692 for broken drivers that don't call it. 3693 skip_isa_align [X86] do not align io start addr, so can 3694 handle more pci cards 3695 noearly [X86] Don't do any early type 1 scanning. 3696 This might help on some broken boards which 3697 machine check when some devices' config space 3698 is read. But various workarounds are disabled 3699 and some IOMMU drivers will not work. 3700 bfsort Sort PCI devices into breadth-first order. 3701 This sorting is done to get a device 3702 order compatible with older (<= 2.4) kernels. 3703 nobfsort Don't sort PCI devices into breadth-first order. 3704 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3705 tuning and use the BIOS-configured MPS defaults. 3706 pcie_bus_safe Set every device's MPS to the largest value 3707 supported by all devices below the root complex. 3708 pcie_bus_perf Set device MPS to the largest allowable MPS 3709 based on its parent bus. Also set MRRS (Max 3710 Read Request Size) to the largest supported 3711 value (no larger than the MPS that the device 3712 or bus can support) for best performance. 3713 pcie_bus_peer2peer Set every device's MPS to 128B, which 3714 every device is guaranteed to support. This 3715 configuration allows peer-to-peer DMA between 3716 any pair of devices, possibly at the cost of 3717 reduced performance. This also guarantees 3718 that hot-added devices will work. 3719 cbiosize=nn[KMG] The fixed amount of bus space which is 3720 reserved for the CardBus bridge's IO window. 3721 The default value is 256 bytes. 3722 cbmemsize=nn[KMG] The fixed amount of bus space which is 3723 reserved for the CardBus bridge's memory 3724 window. The default value is 64 megabytes. 3725 resource_alignment= 3726 Format: 3727 [<order of align>@]<pci_dev>[; ...] 3728 Specifies alignment and device to reassign 3729 aligned memory resources. How to 3730 specify the device is described above. 3731 If <order of align> is not specified, 3732 PAGE_SIZE is used as alignment. 3733 A PCI-PCI bridge can be specified if resource 3734 windows need to be expanded. 3735 To specify the alignment for several 3736 instances of a device, the PCI vendor, 3737 device, subvendor, and subdevice may be 3738 specified, e.g., 12@pci:8086:9c22:103c:198f 3739 for 4096-byte alignment. 3740 ecrc= Enable/disable PCIe ECRC (transaction layer 3741 end-to-end CRC checking). 3742 bios: Use BIOS/firmware settings. This is the 3743 the default. 3744 off: Turn ECRC off 3745 on: Turn ECRC on. 3746 hpiosize=nn[KMG] The fixed amount of bus space which is 3747 reserved for hotplug bridge's IO window. 3748 Default size is 256 bytes. 3749 hpmmiosize=nn[KMG] The fixed amount of bus space which is 3750 reserved for hotplug bridge's MMIO window. 3751 Default size is 2 megabytes. 3752 hpmmioprefsize=nn[KMG] The fixed amount of bus space which is 3753 reserved for hotplug bridge's MMIO_PREF window. 3754 Default size is 2 megabytes. 3755 hpmemsize=nn[KMG] The fixed amount of bus space which is 3756 reserved for hotplug bridge's MMIO and 3757 MMIO_PREF window. 3758 Default size is 2 megabytes. 3759 hpbussize=nn The minimum amount of additional bus numbers 3760 reserved for buses below a hotplug bridge. 3761 Default is 1. 3762 realloc= Enable/disable reallocating PCI bridge resources 3763 if allocations done by BIOS are too small to 3764 accommodate resources required by all child 3765 devices. 3766 off: Turn realloc off 3767 on: Turn realloc on 3768 realloc same as realloc=on 3769 noari do not use PCIe ARI. 3770 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3771 do not use PCIe ATS (and IOMMU device IOTLB). 3772 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3773 only look for one device below a PCIe downstream 3774 port. 3775 big_root_window Try to add a big 64bit memory window to the PCIe 3776 root complex on AMD CPUs. Some GFX hardware 3777 can resize a BAR to allow access to all VRAM. 3778 Adding the window is slightly risky (it may 3779 conflict with unreported devices), so this 3780 taints the kernel. 3781 disable_acs_redir=<pci_dev>[; ...] 3782 Specify one or more PCI devices (in the format 3783 specified above) separated by semicolons. 3784 Each device specified will have the PCI ACS 3785 redirect capabilities forced off which will 3786 allow P2P traffic between devices through 3787 bridges without forcing it upstream. Note: 3788 this removes isolation between devices and 3789 may put more devices in an IOMMU group. 3790 force_floating [S390] Force usage of floating interrupts. 3791 nomio [S390] Do not use MIO instructions. 3792 norid [S390] ignore the RID field and force use of 3793 one PCI domain per PCI function 3794 3795 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3796 Management. 3797 off Disable ASPM. 3798 force Enable ASPM even on devices that claim not to support it. 3799 WARNING: Forcing ASPM on may cause system lockups. 3800 3801 pcie_ports= [PCIE] PCIe port services handling: 3802 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3803 even if the platform doesn't give the OS permission to 3804 use them. This may cause conflicts if the platform 3805 also tries to use these services. 3806 dpc-native Use native PCIe service for DPC only. May 3807 cause conflicts if firmware uses AER or DPC. 3808 compat Disable native PCIe services (PME, AER, DPC, PCIe 3809 hotplug). 3810 3811 pcie_port_pm= [PCIE] PCIe port power management handling: 3812 off Disable power management of all PCIe ports 3813 force Forcibly enable power management of all PCIe ports 3814 3815 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3816 nomsi Do not use MSI for native PCIe PME signaling (this makes 3817 all PCIe root ports use INTx for all services). 3818 3819 pcmv= [HW,PCMCIA] BadgePAD 4 3820 3821 pd_ignore_unused 3822 [PM] 3823 Keep all power-domains already enabled by bootloader on, 3824 even if no driver has claimed them. This is useful 3825 for debug and development, but should not be 3826 needed on a platform with proper driver support. 3827 3828 pd. [PARIDE] 3829 See Documentation/admin-guide/blockdev/paride.rst. 3830 3831 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3832 boot time. 3833 Format: { 0 | 1 } 3834 See arch/parisc/kernel/pdc_chassis.c 3835 3836 percpu_alloc= Select which percpu first chunk allocator to use. 3837 Currently supported values are "embed" and "page". 3838 Archs may support subset or none of the selections. 3839 See comments in mm/percpu.c for details on each 3840 allocator. This parameter is primarily for debugging 3841 and performance comparison. 3842 3843 pf. [PARIDE] 3844 See Documentation/admin-guide/blockdev/paride.rst. 3845 3846 pg. [PARIDE] 3847 See Documentation/admin-guide/blockdev/paride.rst. 3848 3849 pirq= [SMP,APIC] Manual mp-table setup 3850 See Documentation/x86/i386/IO-APIC.rst. 3851 3852 plip= [PPT,NET] Parallel port network link 3853 Format: { parport<nr> | timid | 0 } 3854 See also Documentation/admin-guide/parport.rst. 3855 3856 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3857 Override pmtimer IOPort with a hex value. 3858 e.g. pmtmr=0x508 3859 3860 pm_debug_messages [SUSPEND,KNL] 3861 Enable suspend/resume debug messages during boot up. 3862 3863 pnp.debug=1 [PNP] 3864 Enable PNP debug messages (depends on the 3865 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3866 via /sys/module/pnp/parameters/debug. We always show 3867 current resource usage; turning this on also shows 3868 possible settings and some assignment information. 3869 3870 pnpacpi= [ACPI] 3871 { off } 3872 3873 pnpbios= [ISAPNP] 3874 { on | off | curr | res | no-curr | no-res } 3875 3876 pnp_reserve_irq= 3877 [ISAPNP] Exclude IRQs for the autoconfiguration 3878 3879 pnp_reserve_dma= 3880 [ISAPNP] Exclude DMAs for the autoconfiguration 3881 3882 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3883 Ranges are in pairs (I/O port base and size). 3884 3885 pnp_reserve_mem= 3886 [ISAPNP] Exclude memory regions for the 3887 autoconfiguration. 3888 Ranges are in pairs (memory base and size). 3889 3890 ports= [IP_VS_FTP] IPVS ftp helper module 3891 Default is 21. 3892 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3893 may be specified. 3894 Format: <port>,<port>.... 3895 3896 powersave=off [PPC] This option disables power saving features. 3897 It specifically disables cpuidle and sets the 3898 platform machine description specific power_save 3899 function to NULL. On Idle the CPU just reduces 3900 execution priority. 3901 3902 ppc_strict_facility_enable 3903 [PPC] This option catches any kernel floating point, 3904 Altivec, VSX and SPE outside of regions specifically 3905 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3906 There is some performance impact when enabling this. 3907 3908 ppc_tm= [PPC] 3909 Format: {"off"} 3910 Disable Hardware Transactional Memory 3911 3912 print-fatal-signals= 3913 [KNL] debug: print fatal signals 3914 3915 If enabled, warn about various signal handling 3916 related application anomalies: too many signals, 3917 too many POSIX.1 timers, fatal signals causing a 3918 coredump - etc. 3919 3920 If you hit the warning due to signal overflow, 3921 you might want to try "ulimit -i unlimited". 3922 3923 default: off. 3924 3925 printk.always_kmsg_dump= 3926 Trigger kmsg_dump for cases other than kernel oops or 3927 panics 3928 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3929 default: disabled 3930 3931 printk.devkmsg={on,off,ratelimit} 3932 Control writing to /dev/kmsg. 3933 on - unlimited logging to /dev/kmsg from userspace 3934 off - logging to /dev/kmsg disabled 3935 ratelimit - ratelimit the logging 3936 Default: ratelimit 3937 3938 printk.time= Show timing data prefixed to each printk message line 3939 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3940 3941 processor.max_cstate= [HW,ACPI] 3942 Limit processor to maximum C-state 3943 max_cstate=9 overrides any DMI blacklist limit. 3944 3945 processor.nocst [HW,ACPI] 3946 Ignore the _CST method to determine C-states, 3947 instead using the legacy FADT method 3948 3949 profile= [KNL] Enable kernel profiling via /proc/profile 3950 Format: [<profiletype>,]<number> 3951 Param: <profiletype>: "schedule", "sleep", or "kvm" 3952 [defaults to kernel profiling] 3953 Param: "schedule" - profile schedule points. 3954 Param: "sleep" - profile D-state sleeping (millisecs). 3955 Requires CONFIG_SCHEDSTATS 3956 Param: "kvm" - profile VM exits. 3957 Param: <number> - step/bucket size as a power of 2 for 3958 statistical time based profiling. 3959 3960 prompt_ramdisk= [RAM] [Deprecated] 3961 3962 prot_virt= [S390] enable hosting protected virtual machines 3963 isolated from the hypervisor (if hardware supports 3964 that). 3965 Format: <bool> 3966 3967 psi= [KNL] Enable or disable pressure stall information 3968 tracking. 3969 Format: <bool> 3970 3971 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3972 probe for; one of (bare|imps|exps|lifebook|any). 3973 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3974 per second. 3975 psmouse.resetafter= [HW,MOUSE] 3976 Try to reset the device after so many bad packets 3977 (0 = never). 3978 psmouse.resolution= 3979 [HW,MOUSE] Set desired mouse resolution, in dpi. 3980 psmouse.smartscroll= 3981 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3982 0 = disabled, 1 = enabled (default). 3983 3984 pstore.backend= Specify the name of the pstore backend to use 3985 3986 pt. [PARIDE] 3987 See Documentation/admin-guide/blockdev/paride.rst. 3988 3989 pti= [X86-64] Control Page Table Isolation of user and 3990 kernel address spaces. Disabling this feature 3991 removes hardening, but improves performance of 3992 system calls and interrupts. 3993 3994 on - unconditionally enable 3995 off - unconditionally disable 3996 auto - kernel detects whether your CPU model is 3997 vulnerable to issues that PTI mitigates 3998 3999 Not specifying this option is equivalent to pti=auto. 4000 4001 nopti [X86-64] 4002 Equivalent to pti=off 4003 4004 pty.legacy_count= 4005 [KNL] Number of legacy pty's. Overwrites compiled-in 4006 default number. 4007 4008 quiet [KNL] Disable most log messages 4009 4010 r128= [HW,DRM] 4011 4012 raid= [HW,RAID] 4013 See Documentation/admin-guide/md.rst. 4014 4015 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 4016 See Documentation/admin-guide/blockdev/ramdisk.rst. 4017 4018 ramdisk_start= [RAM] RAM disk image start address 4019 4020 random.trust_cpu={on,off} 4021 [KNL] Enable or disable trusting the use of the 4022 CPU's random number generator (if available) to 4023 fully seed the kernel's CRNG. Default is controlled 4024 by CONFIG_RANDOM_TRUST_CPU. 4025 4026 ras=option[,option,...] [KNL] RAS-specific options 4027 4028 cec_disable [X86] 4029 Disable the Correctable Errors Collector, 4030 see CONFIG_RAS_CEC help text. 4031 4032 rcu_nocbs= [KNL] 4033 The argument is a cpu list, as described above, 4034 except that the string "all" can be used to 4035 specify every CPU on the system. 4036 4037 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 4038 the specified list of CPUs to be no-callback CPUs. 4039 Invocation of these CPUs' RCU callbacks will be 4040 offloaded to "rcuox/N" kthreads created for that 4041 purpose, where "x" is "p" for RCU-preempt, and 4042 "s" for RCU-sched, and "N" is the CPU number. 4043 This reduces OS jitter on the offloaded CPUs, 4044 which can be useful for HPC and real-time 4045 workloads. It can also improve energy efficiency 4046 for asymmetric multiprocessors. 4047 4048 rcu_nocb_poll [KNL] 4049 Rather than requiring that offloaded CPUs 4050 (specified by rcu_nocbs= above) explicitly 4051 awaken the corresponding "rcuoN" kthreads, 4052 make these kthreads poll for callbacks. 4053 This improves the real-time response for the 4054 offloaded CPUs by relieving them of the need to 4055 wake up the corresponding kthread, but degrades 4056 energy efficiency by requiring that the kthreads 4057 periodically wake up to do the polling. 4058 4059 rcutree.blimit= [KNL] 4060 Set maximum number of finished RCU callbacks to 4061 process in one batch. 4062 4063 rcutree.dump_tree= [KNL] 4064 Dump the structure of the rcu_node combining tree 4065 out at early boot. This is used for diagnostic 4066 purposes, to verify correct tree setup. 4067 4068 rcutree.gp_cleanup_delay= [KNL] 4069 Set the number of jiffies to delay each step of 4070 RCU grace-period cleanup. 4071 4072 rcutree.gp_init_delay= [KNL] 4073 Set the number of jiffies to delay each step of 4074 RCU grace-period initialization. 4075 4076 rcutree.gp_preinit_delay= [KNL] 4077 Set the number of jiffies to delay each step of 4078 RCU grace-period pre-initialization, that is, 4079 the propagation of recent CPU-hotplug changes up 4080 the rcu_node combining tree. 4081 4082 rcutree.use_softirq= [KNL] 4083 If set to zero, move all RCU_SOFTIRQ processing to 4084 per-CPU rcuc kthreads. Defaults to a non-zero 4085 value, meaning that RCU_SOFTIRQ is used by default. 4086 Specify rcutree.use_softirq=0 to use rcuc kthreads. 4087 4088 rcutree.rcu_fanout_exact= [KNL] 4089 Disable autobalancing of the rcu_node combining 4090 tree. This is used by rcutorture, and might 4091 possibly be useful for architectures having high 4092 cache-to-cache transfer latencies. 4093 4094 rcutree.rcu_fanout_leaf= [KNL] 4095 Change the number of CPUs assigned to each 4096 leaf rcu_node structure. Useful for very 4097 large systems, which will choose the value 64, 4098 and for NUMA systems with large remote-access 4099 latencies, which will choose a value aligned 4100 with the appropriate hardware boundaries. 4101 4102 rcutree.rcu_min_cached_objs= [KNL] 4103 Minimum number of objects which are cached and 4104 maintained per one CPU. Object size is equal 4105 to PAGE_SIZE. The cache allows to reduce the 4106 pressure to page allocator, also it makes the 4107 whole algorithm to behave better in low memory 4108 condition. 4109 4110 rcutree.jiffies_till_first_fqs= [KNL] 4111 Set delay from grace-period initialization to 4112 first attempt to force quiescent states. 4113 Units are jiffies, minimum value is zero, 4114 and maximum value is HZ. 4115 4116 rcutree.jiffies_till_next_fqs= [KNL] 4117 Set delay between subsequent attempts to force 4118 quiescent states. Units are jiffies, minimum 4119 value is one, and maximum value is HZ. 4120 4121 rcutree.jiffies_till_sched_qs= [KNL] 4122 Set required age in jiffies for a 4123 given grace period before RCU starts 4124 soliciting quiescent-state help from 4125 rcu_note_context_switch() and cond_resched(). 4126 If not specified, the kernel will calculate 4127 a value based on the most recent settings 4128 of rcutree.jiffies_till_first_fqs 4129 and rcutree.jiffies_till_next_fqs. 4130 This calculated value may be viewed in 4131 rcutree.jiffies_to_sched_qs. Any attempt to set 4132 rcutree.jiffies_to_sched_qs will be cheerfully 4133 overwritten. 4134 4135 rcutree.kthread_prio= [KNL,BOOT] 4136 Set the SCHED_FIFO priority of the RCU per-CPU 4137 kthreads (rcuc/N). This value is also used for 4138 the priority of the RCU boost threads (rcub/N) 4139 and for the RCU grace-period kthreads (rcu_bh, 4140 rcu_preempt, and rcu_sched). If RCU_BOOST is 4141 set, valid values are 1-99 and the default is 1 4142 (the least-favored priority). Otherwise, when 4143 RCU_BOOST is not set, valid values are 0-99 and 4144 the default is zero (non-realtime operation). 4145 4146 rcutree.rcu_nocb_gp_stride= [KNL] 4147 Set the number of NOCB callback kthreads in 4148 each group, which defaults to the square root 4149 of the number of CPUs. Larger numbers reduce 4150 the wakeup overhead on the global grace-period 4151 kthread, but increases that same overhead on 4152 each group's NOCB grace-period kthread. 4153 4154 rcutree.qhimark= [KNL] 4155 Set threshold of queued RCU callbacks beyond which 4156 batch limiting is disabled. 4157 4158 rcutree.qlowmark= [KNL] 4159 Set threshold of queued RCU callbacks below which 4160 batch limiting is re-enabled. 4161 4162 rcutree.qovld= [KNL] 4163 Set threshold of queued RCU callbacks beyond which 4164 RCU's force-quiescent-state scan will aggressively 4165 enlist help from cond_resched() and sched IPIs to 4166 help CPUs more quickly reach quiescent states. 4167 Set to less than zero to make this be set based 4168 on rcutree.qhimark at boot time and to zero to 4169 disable more aggressive help enlistment. 4170 4171 rcutree.rcu_idle_gp_delay= [KNL] 4172 Set wakeup interval for idle CPUs that have 4173 RCU callbacks (RCU_FAST_NO_HZ=y). 4174 4175 rcutree.rcu_idle_lazy_gp_delay= [KNL] 4176 Set wakeup interval for idle CPUs that have 4177 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 4178 Lazy RCU callbacks are those which RCU can 4179 prove do nothing more than free memory. 4180 4181 rcutree.rcu_kick_kthreads= [KNL] 4182 Cause the grace-period kthread to get an extra 4183 wake_up() if it sleeps three times longer than 4184 it should at force-quiescent-state time. 4185 This wake_up() will be accompanied by a 4186 WARN_ONCE() splat and an ftrace_dump(). 4187 4188 rcutree.rcu_unlock_delay= [KNL] 4189 In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, 4190 this specifies an rcu_read_unlock()-time delay 4191 in microseconds. This defaults to zero. 4192 Larger delays increase the probability of 4193 catching RCU pointer leaks, that is, buggy use 4194 of RCU-protected pointers after the relevant 4195 rcu_read_unlock() has completed. 4196 4197 rcutree.sysrq_rcu= [KNL] 4198 Commandeer a sysrq key to dump out Tree RCU's 4199 rcu_node tree with an eye towards determining 4200 why a new grace period has not yet started. 4201 4202 rcuscale.gp_async= [KNL] 4203 Measure performance of asynchronous 4204 grace-period primitives such as call_rcu(). 4205 4206 rcuscale.gp_async_max= [KNL] 4207 Specify the maximum number of outstanding 4208 callbacks per writer thread. When a writer 4209 thread exceeds this limit, it invokes the 4210 corresponding flavor of rcu_barrier() to allow 4211 previously posted callbacks to drain. 4212 4213 rcuscale.gp_exp= [KNL] 4214 Measure performance of expedited synchronous 4215 grace-period primitives. 4216 4217 rcuscale.holdoff= [KNL] 4218 Set test-start holdoff period. The purpose of 4219 this parameter is to delay the start of the 4220 test until boot completes in order to avoid 4221 interference. 4222 4223 rcuscale.kfree_rcu_test= [KNL] 4224 Set to measure performance of kfree_rcu() flooding. 4225 4226 rcuscale.kfree_nthreads= [KNL] 4227 The number of threads running loops of kfree_rcu(). 4228 4229 rcuscale.kfree_alloc_num= [KNL] 4230 Number of allocations and frees done in an iteration. 4231 4232 rcuscale.kfree_loops= [KNL] 4233 Number of loops doing rcuscale.kfree_alloc_num number 4234 of allocations and frees. 4235 4236 rcuscale.nreaders= [KNL] 4237 Set number of RCU readers. The value -1 selects 4238 N, where N is the number of CPUs. A value 4239 "n" less than -1 selects N-n+1, where N is again 4240 the number of CPUs. For example, -2 selects N 4241 (the number of CPUs), -3 selects N+1, and so on. 4242 A value of "n" less than or equal to -N selects 4243 a single reader. 4244 4245 rcuscale.nwriters= [KNL] 4246 Set number of RCU writers. The values operate 4247 the same as for rcuscale.nreaders. 4248 N, where N is the number of CPUs 4249 4250 rcuscale.perf_type= [KNL] 4251 Specify the RCU implementation to test. 4252 4253 rcuscale.shutdown= [KNL] 4254 Shut the system down after performance tests 4255 complete. This is useful for hands-off automated 4256 testing. 4257 4258 rcuscale.verbose= [KNL] 4259 Enable additional printk() statements. 4260 4261 rcuscale.writer_holdoff= [KNL] 4262 Write-side holdoff between grace periods, 4263 in microseconds. The default of zero says 4264 no holdoff. 4265 4266 rcutorture.fqs_duration= [KNL] 4267 Set duration of force_quiescent_state bursts 4268 in microseconds. 4269 4270 rcutorture.fqs_holdoff= [KNL] 4271 Set holdoff time within force_quiescent_state bursts 4272 in microseconds. 4273 4274 rcutorture.fqs_stutter= [KNL] 4275 Set wait time between force_quiescent_state bursts 4276 in seconds. 4277 4278 rcutorture.fwd_progress= [KNL] 4279 Enable RCU grace-period forward-progress testing 4280 for the types of RCU supporting this notion. 4281 4282 rcutorture.fwd_progress_div= [KNL] 4283 Specify the fraction of a CPU-stall-warning 4284 period to do tight-loop forward-progress testing. 4285 4286 rcutorture.fwd_progress_holdoff= [KNL] 4287 Number of seconds to wait between successive 4288 forward-progress tests. 4289 4290 rcutorture.fwd_progress_need_resched= [KNL] 4291 Enclose cond_resched() calls within checks for 4292 need_resched() during tight-loop forward-progress 4293 testing. 4294 4295 rcutorture.gp_cond= [KNL] 4296 Use conditional/asynchronous update-side 4297 primitives, if available. 4298 4299 rcutorture.gp_exp= [KNL] 4300 Use expedited update-side primitives, if available. 4301 4302 rcutorture.gp_normal= [KNL] 4303 Use normal (non-expedited) asynchronous 4304 update-side primitives, if available. 4305 4306 rcutorture.gp_sync= [KNL] 4307 Use normal (non-expedited) synchronous 4308 update-side primitives, if available. If all 4309 of rcutorture.gp_cond=, rcutorture.gp_exp=, 4310 rcutorture.gp_normal=, and rcutorture.gp_sync= 4311 are zero, rcutorture acts as if is interpreted 4312 they are all non-zero. 4313 4314 rcutorture.irqreader= [KNL] 4315 Run RCU readers from irq handlers, or, more 4316 accurately, from a timer handler. Not all RCU 4317 flavors take kindly to this sort of thing. 4318 4319 rcutorture.leakpointer= [KNL] 4320 Leak an RCU-protected pointer out of the reader. 4321 This can of course result in splats, and is 4322 intended to test the ability of things like 4323 CONFIG_RCU_STRICT_GRACE_PERIOD=y to detect 4324 such leaks. 4325 4326 rcutorture.n_barrier_cbs= [KNL] 4327 Set callbacks/threads for rcu_barrier() testing. 4328 4329 rcutorture.nfakewriters= [KNL] 4330 Set number of concurrent RCU writers. These just 4331 stress RCU, they don't participate in the actual 4332 test, hence the "fake". 4333 4334 rcutorture.nreaders= [KNL] 4335 Set number of RCU readers. The value -1 selects 4336 N-1, where N is the number of CPUs. A value 4337 "n" less than -1 selects N-n-2, where N is again 4338 the number of CPUs. For example, -2 selects N 4339 (the number of CPUs), -3 selects N+1, and so on. 4340 4341 rcutorture.object_debug= [KNL] 4342 Enable debug-object double-call_rcu() testing. 4343 4344 rcutorture.onoff_holdoff= [KNL] 4345 Set time (s) after boot for CPU-hotplug testing. 4346 4347 rcutorture.onoff_interval= [KNL] 4348 Set time (jiffies) between CPU-hotplug operations, 4349 or zero to disable CPU-hotplug testing. 4350 4351 rcutorture.read_exit= [KNL] 4352 Set the number of read-then-exit kthreads used 4353 to test the interaction of RCU updaters and 4354 task-exit processing. 4355 4356 rcutorture.read_exit_burst= [KNL] 4357 The number of times in a given read-then-exit 4358 episode that a set of read-then-exit kthreads 4359 is spawned. 4360 4361 rcutorture.read_exit_delay= [KNL] 4362 The delay, in seconds, between successive 4363 read-then-exit testing episodes. 4364 4365 rcutorture.shuffle_interval= [KNL] 4366 Set task-shuffle interval (s). Shuffling tasks 4367 allows some CPUs to go into dyntick-idle mode 4368 during the rcutorture test. 4369 4370 rcutorture.shutdown_secs= [KNL] 4371 Set time (s) after boot system shutdown. This 4372 is useful for hands-off automated testing. 4373 4374 rcutorture.stall_cpu= [KNL] 4375 Duration of CPU stall (s) to test RCU CPU stall 4376 warnings, zero to disable. 4377 4378 rcutorture.stall_cpu_block= [KNL] 4379 Sleep while stalling if set. This will result 4380 in warnings from preemptible RCU in addition 4381 to any other stall-related activity. 4382 4383 rcutorture.stall_cpu_holdoff= [KNL] 4384 Time to wait (s) after boot before inducing stall. 4385 4386 rcutorture.stall_cpu_irqsoff= [KNL] 4387 Disable interrupts while stalling if set. 4388 4389 rcutorture.stall_gp_kthread= [KNL] 4390 Duration (s) of forced sleep within RCU 4391 grace-period kthread to test RCU CPU stall 4392 warnings, zero to disable. If both stall_cpu 4393 and stall_gp_kthread are specified, the 4394 kthread is starved first, then the CPU. 4395 4396 rcutorture.stat_interval= [KNL] 4397 Time (s) between statistics printk()s. 4398 4399 rcutorture.stutter= [KNL] 4400 Time (s) to stutter testing, for example, specifying 4401 five seconds causes the test to run for five seconds, 4402 wait for five seconds, and so on. This tests RCU's 4403 ability to transition abruptly to and from idle. 4404 4405 rcutorture.test_boost= [KNL] 4406 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4407 "Maybe" means test if the RCU implementation 4408 under test support RCU priority boosting. 4409 4410 rcutorture.test_boost_duration= [KNL] 4411 Duration (s) of each individual boost test. 4412 4413 rcutorture.test_boost_interval= [KNL] 4414 Interval (s) between each boost test. 4415 4416 rcutorture.test_no_idle_hz= [KNL] 4417 Test RCU's dyntick-idle handling. See also the 4418 rcutorture.shuffle_interval parameter. 4419 4420 rcutorture.torture_type= [KNL] 4421 Specify the RCU implementation to test. 4422 4423 rcutorture.verbose= [KNL] 4424 Enable additional printk() statements. 4425 4426 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4427 Dump ftrace buffer after reporting RCU CPU 4428 stall warning. 4429 4430 rcupdate.rcu_cpu_stall_suppress= [KNL] 4431 Suppress RCU CPU stall warning messages. 4432 4433 rcupdate.rcu_cpu_stall_suppress_at_boot= [KNL] 4434 Suppress RCU CPU stall warning messages and 4435 rcutorture writer stall warnings that occur 4436 during early boot, that is, during the time 4437 before the init task is spawned. 4438 4439 rcupdate.rcu_cpu_stall_timeout= [KNL] 4440 Set timeout for RCU CPU stall warning messages. 4441 4442 rcupdate.rcu_expedited= [KNL] 4443 Use expedited grace-period primitives, for 4444 example, synchronize_rcu_expedited() instead 4445 of synchronize_rcu(). This reduces latency, 4446 but can increase CPU utilization, degrade 4447 real-time latency, and degrade energy efficiency. 4448 No effect on CONFIG_TINY_RCU kernels. 4449 4450 rcupdate.rcu_normal= [KNL] 4451 Use only normal grace-period primitives, 4452 for example, synchronize_rcu() instead of 4453 synchronize_rcu_expedited(). This improves 4454 real-time latency, CPU utilization, and 4455 energy efficiency, but can expose users to 4456 increased grace-period latency. This parameter 4457 overrides rcupdate.rcu_expedited. No effect on 4458 CONFIG_TINY_RCU kernels. 4459 4460 rcupdate.rcu_normal_after_boot= [KNL] 4461 Once boot has completed (that is, after 4462 rcu_end_inkernel_boot() has been invoked), use 4463 only normal grace-period primitives. No effect 4464 on CONFIG_TINY_RCU kernels. 4465 4466 rcupdate.rcu_task_ipi_delay= [KNL] 4467 Set time in jiffies during which RCU tasks will 4468 avoid sending IPIs, starting with the beginning 4469 of a given grace period. Setting a large 4470 number avoids disturbing real-time workloads, 4471 but lengthens grace periods. 4472 4473 rcupdate.rcu_task_stall_timeout= [KNL] 4474 Set timeout in jiffies for RCU task stall warning 4475 messages. Disable with a value less than or equal 4476 to zero. 4477 4478 rcupdate.rcu_self_test= [KNL] 4479 Run the RCU early boot self tests 4480 4481 rdinit= [KNL] 4482 Format: <full_path> 4483 Run specified binary instead of /init from the ramdisk, 4484 used for early userspace startup. See initrd. 4485 4486 rdrand= [X86] 4487 force - Override the decision by the kernel to hide the 4488 advertisement of RDRAND support (this affects 4489 certain AMD processors because of buggy BIOS 4490 support, specifically around the suspend/resume 4491 path). 4492 4493 rdt= [HW,X86,RDT] 4494 Turn on/off individual RDT features. List is: 4495 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4496 mba. 4497 E.g. to turn on cmt and turn off mba use: 4498 rdt=cmt,!mba 4499 4500 reboot= [KNL] 4501 Format (x86 or x86_64): 4502 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4503 [[,]s[mp]#### \ 4504 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4505 [[,]f[orce] 4506 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4507 (prefix with 'panic_' to set mode for panic 4508 reboot only), 4509 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4510 reboot_force is either force or not specified, 4511 reboot_cpu is s[mp]#### with #### being the processor 4512 to be used for rebooting. 4513 4514 refscale.holdoff= [KNL] 4515 Set test-start holdoff period. The purpose of 4516 this parameter is to delay the start of the 4517 test until boot completes in order to avoid 4518 interference. 4519 4520 refscale.loops= [KNL] 4521 Set the number of loops over the synchronization 4522 primitive under test. Increasing this number 4523 reduces noise due to loop start/end overhead, 4524 but the default has already reduced the per-pass 4525 noise to a handful of picoseconds on ca. 2020 4526 x86 laptops. 4527 4528 refscale.nreaders= [KNL] 4529 Set number of readers. The default value of -1 4530 selects N, where N is roughly 75% of the number 4531 of CPUs. A value of zero is an interesting choice. 4532 4533 refscale.nruns= [KNL] 4534 Set number of runs, each of which is dumped onto 4535 the console log. 4536 4537 refscale.readdelay= [KNL] 4538 Set the read-side critical-section duration, 4539 measured in microseconds. 4540 4541 refscale.scale_type= [KNL] 4542 Specify the read-protection implementation to test. 4543 4544 refscale.shutdown= [KNL] 4545 Shut down the system at the end of the performance 4546 test. This defaults to 1 (shut it down) when 4547 refscale is built into the kernel and to 0 (leave 4548 it running) when refscale is built as a module. 4549 4550 refscale.verbose= [KNL] 4551 Enable additional printk() statements. 4552 4553 relax_domain_level= 4554 [KNL, SMP] Set scheduler's default relax_domain_level. 4555 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4556 4557 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4558 Format: <base1>,<size1>[,<base2>,<size2>,...] 4559 Reserve I/O ports or memory so the kernel won't use 4560 them. If <base> is less than 0x10000, the region 4561 is assumed to be I/O ports; otherwise it is memory. 4562 4563 reservetop= [X86-32] 4564 Format: nn[KMG] 4565 Reserves a hole at the top of the kernel virtual 4566 address space. 4567 4568 reservelow= [X86] 4569 Format: nn[K] 4570 Set the amount of memory to reserve for BIOS at 4571 the bottom of the address space. 4572 4573 reset_devices [KNL] Force drivers to reset the underlying device 4574 during initialization. 4575 4576 resume= [SWSUSP] 4577 Specify the partition device for software suspend 4578 Format: 4579 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4580 4581 resume_offset= [SWSUSP] 4582 Specify the offset from the beginning of the partition 4583 given by "resume=" at which the swap header is located, 4584 in <PAGE_SIZE> units (needed only for swap files). 4585 See Documentation/power/swsusp-and-swap-files.rst 4586 4587 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4588 read the resume files 4589 4590 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4591 Useful for devices that are detected asynchronously 4592 (e.g. USB and MMC devices). 4593 4594 hibernate= [HIBERNATION] 4595 noresume Don't check if there's a hibernation image 4596 present during boot. 4597 nocompress Don't compress/decompress hibernation images. 4598 no Disable hibernation and resume. 4599 protect_image Turn on image protection during restoration 4600 (that will set all pages holding image data 4601 during restoration read-only). 4602 4603 retain_initrd [RAM] Keep initrd memory after extraction 4604 4605 rfkill.default_state= 4606 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4607 etc. communication is blocked by default. 4608 1 Unblocked. 4609 4610 rfkill.master_switch_mode= 4611 0 The "airplane mode" button does nothing. 4612 1 The "airplane mode" button toggles between everything 4613 blocked and the previous configuration. 4614 2 The "airplane mode" button toggles between everything 4615 blocked and everything unblocked. 4616 4617 rhash_entries= [KNL,NET] 4618 Set number of hash buckets for route cache 4619 4620 ring3mwait=disable 4621 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4622 CPUs. 4623 4624 ro [KNL] Mount root device read-only on boot 4625 4626 rodata= [KNL] 4627 on Mark read-only kernel memory as read-only (default). 4628 off Leave read-only kernel memory writable for debugging. 4629 4630 rockchip.usb_uart 4631 Enable the uart passthrough on the designated usb port 4632 on Rockchip SoCs. When active, the signals of the 4633 debug-uart get routed to the D+ and D- pins of the usb 4634 port and the regular usb controller gets disabled. 4635 4636 root= [KNL] Root filesystem 4637 See name_to_dev_t comment in init/do_mounts.c. 4638 4639 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4640 mount the root filesystem 4641 4642 rootflags= [KNL] Set root filesystem mount option string 4643 4644 rootfstype= [KNL] Set root filesystem type 4645 4646 rootwait [KNL] Wait (indefinitely) for root device to show up. 4647 Useful for devices that are detected asynchronously 4648 (e.g. USB and MMC devices). 4649 4650 rproc_mem=nn[KMG][@address] 4651 [KNL,ARM,CMA] Remoteproc physical memory block. 4652 Memory area to be used by remote processor image, 4653 managed by CMA. 4654 4655 rw [KNL] Mount root device read-write on boot 4656 4657 S [KNL] Run init in single mode 4658 4659 s390_iommu= [HW,S390] 4660 Set s390 IOTLB flushing mode 4661 strict 4662 With strict flushing every unmap operation will result in 4663 an IOTLB flush. Default is lazy flushing before reuse, 4664 which is faster. 4665 4666 sa1100ir [NET] 4667 See drivers/net/irda/sa1100_ir.c. 4668 4669 sbni= [NET] Granch SBNI12 leased line adapter 4670 4671 sched_debug [KNL] Enables verbose scheduler debug messages. 4672 4673 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4674 Allowed values are enable and disable. This feature 4675 incurs a small amount of overhead in the scheduler 4676 but is useful for debugging and performance tuning. 4677 4678 sched_thermal_decay_shift= 4679 [KNL, SMP] Set a decay shift for scheduler thermal 4680 pressure signal. Thermal pressure signal follows the 4681 default decay period of other scheduler pelt 4682 signals(usually 32 ms but configurable). Setting 4683 sched_thermal_decay_shift will left shift the decay 4684 period for the thermal pressure signal by the shift 4685 value. 4686 i.e. with the default pelt decay period of 32 ms 4687 sched_thermal_decay_shift thermal pressure decay pr 4688 1 64 ms 4689 2 128 ms 4690 and so on. 4691 Format: integer between 0 and 10 4692 Default is 0. 4693 4694 scftorture.holdoff= [KNL] 4695 Number of seconds to hold off before starting 4696 test. Defaults to zero for module insertion and 4697 to 10 seconds for built-in smp_call_function() 4698 tests. 4699 4700 scftorture.longwait= [KNL] 4701 Request ridiculously long waits randomly selected 4702 up to the chosen limit in seconds. Zero (the 4703 default) disables this feature. Please note 4704 that requesting even small non-zero numbers of 4705 seconds can result in RCU CPU stall warnings, 4706 softlockup complaints, and so on. 4707 4708 scftorture.nthreads= [KNL] 4709 Number of kthreads to spawn to invoke the 4710 smp_call_function() family of functions. 4711 The default of -1 specifies a number of kthreads 4712 equal to the number of CPUs. 4713 4714 scftorture.onoff_holdoff= [KNL] 4715 Number seconds to wait after the start of the 4716 test before initiating CPU-hotplug operations. 4717 4718 scftorture.onoff_interval= [KNL] 4719 Number seconds to wait between successive 4720 CPU-hotplug operations. Specifying zero (which 4721 is the default) disables CPU-hotplug operations. 4722 4723 scftorture.shutdown_secs= [KNL] 4724 The number of seconds following the start of the 4725 test after which to shut down the system. The 4726 default of zero avoids shutting down the system. 4727 Non-zero values are useful for automated tests. 4728 4729 scftorture.stat_interval= [KNL] 4730 The number of seconds between outputting the 4731 current test statistics to the console. A value 4732 of zero disables statistics output. 4733 4734 scftorture.stutter_cpus= [KNL] 4735 The number of jiffies to wait between each change 4736 to the set of CPUs under test. 4737 4738 scftorture.use_cpus_read_lock= [KNL] 4739 Use use_cpus_read_lock() instead of the default 4740 preempt_disable() to disable CPU hotplug 4741 while invoking one of the smp_call_function*() 4742 functions. 4743 4744 scftorture.verbose= [KNL] 4745 Enable additional printk() statements. 4746 4747 scftorture.weight_single= [KNL] 4748 The probability weighting to use for the 4749 smp_call_function_single() function with a zero 4750 "wait" parameter. A value of -1 selects the 4751 default if all other weights are -1. However, 4752 if at least one weight has some other value, a 4753 value of -1 will instead select a weight of zero. 4754 4755 scftorture.weight_single_wait= [KNL] 4756 The probability weighting to use for the 4757 smp_call_function_single() function with a 4758 non-zero "wait" parameter. See weight_single. 4759 4760 scftorture.weight_many= [KNL] 4761 The probability weighting to use for the 4762 smp_call_function_many() function with a zero 4763 "wait" parameter. See weight_single. 4764 Note well that setting a high probability for 4765 this weighting can place serious IPI load 4766 on the system. 4767 4768 scftorture.weight_many_wait= [KNL] 4769 The probability weighting to use for the 4770 smp_call_function_many() function with a 4771 non-zero "wait" parameter. See weight_single 4772 and weight_many. 4773 4774 scftorture.weight_all= [KNL] 4775 The probability weighting to use for the 4776 smp_call_function_all() function with a zero 4777 "wait" parameter. See weight_single and 4778 weight_many. 4779 4780 scftorture.weight_all_wait= [KNL] 4781 The probability weighting to use for the 4782 smp_call_function_all() function with a 4783 non-zero "wait" parameter. See weight_single 4784 and weight_many. 4785 4786 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4787 xtime_lock contention on larger systems, and/or RCU lock 4788 contention on all systems with CONFIG_MAXSMP set. 4789 Format: { "0" | "1" } 4790 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4791 1 -- enable. 4792 Note: increases power consumption, thus should only be 4793 enabled if running jitter sensitive (HPC/RT) workloads. 4794 4795 security= [SECURITY] Choose a legacy "major" security module to 4796 enable at boot. This has been deprecated by the 4797 "lsm=" parameter. 4798 4799 selinux= [SELINUX] Disable or enable SELinux at boot time. 4800 Format: { "0" | "1" } 4801 See security/selinux/Kconfig help text. 4802 0 -- disable. 4803 1 -- enable. 4804 Default value is 1. 4805 4806 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4807 Format: { "0" | "1" } 4808 See security/apparmor/Kconfig help text 4809 0 -- disable. 4810 1 -- enable. 4811 Default value is set via kernel config option. 4812 4813 serialnumber [BUGS=X86-32] 4814 4815 shapers= [NET] 4816 Maximal number of shapers. 4817 4818 simeth= [IA-64] 4819 simscsi= 4820 4821 slram= [HW,MTD] 4822 4823 slab_nomerge [MM] 4824 Disable merging of slabs with similar size. May be 4825 necessary if there is some reason to distinguish 4826 allocs to different slabs, especially in hardened 4827 environments where the risk of heap overflows and 4828 layout control by attackers can usually be 4829 frustrated by disabling merging. This will reduce 4830 most of the exposure of a heap attack to a single 4831 cache (risks via metadata attacks are mostly 4832 unchanged). Debug options disable merging on their 4833 own. 4834 For more information see Documentation/vm/slub.rst. 4835 4836 slab_max_order= [MM, SLAB] 4837 Determines the maximum allowed order for slabs. 4838 A high setting may cause OOMs due to memory 4839 fragmentation. Defaults to 1 for systems with 4840 more than 32MB of RAM, 0 otherwise. 4841 4842 slub_debug[=options[,slabs][;[options[,slabs]]...] [MM, SLUB] 4843 Enabling slub_debug allows one to determine the 4844 culprit if slab objects become corrupted. Enabling 4845 slub_debug can create guard zones around objects and 4846 may poison objects when not in use. Also tracks the 4847 last alloc / free. For more information see 4848 Documentation/vm/slub.rst. 4849 4850 slub_memcg_sysfs= [MM, SLUB] 4851 Determines whether to enable sysfs directories for 4852 memory cgroup sub-caches. 1 to enable, 0 to disable. 4853 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4854 Enabling this can lead to a very high number of debug 4855 directories and files being created under 4856 /sys/kernel/slub. 4857 4858 slub_max_order= [MM, SLUB] 4859 Determines the maximum allowed order for slabs. 4860 A high setting may cause OOMs due to memory 4861 fragmentation. For more information see 4862 Documentation/vm/slub.rst. 4863 4864 slub_min_objects= [MM, SLUB] 4865 The minimum number of objects per slab. SLUB will 4866 increase the slab order up to slub_max_order to 4867 generate a sufficiently large slab able to contain 4868 the number of objects indicated. The higher the number 4869 of objects the smaller the overhead of tracking slabs 4870 and the less frequently locks need to be acquired. 4871 For more information see Documentation/vm/slub.rst. 4872 4873 slub_min_order= [MM, SLUB] 4874 Determines the minimum page order for slabs. Must be 4875 lower than slub_max_order. 4876 For more information see Documentation/vm/slub.rst. 4877 4878 slub_nomerge [MM, SLUB] 4879 Same with slab_nomerge. This is supported for legacy. 4880 See slab_nomerge for more information. 4881 4882 smart2= [HW] 4883 Format: <io1>[,<io2>[,...,<io8>]] 4884 4885 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4886 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4887 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4888 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4889 smsc-ircc2.ircc_irq= [HW] IRQ line 4890 smsc-ircc2.ircc_dma= [HW] DMA channel 4891 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4892 0: Toshiba Satellite 1800 (GP data pin select) 4893 1: Fast pin select (default) 4894 2: ATC IRMode 4895 4896 smt [KNL,S390] Set the maximum number of threads (logical 4897 CPUs) to use per physical CPU on systems capable of 4898 symmetric multithreading (SMT). Will be capped to the 4899 actual hardware limit. 4900 Format: <integer> 4901 Default: -1 (no limit) 4902 4903 softlockup_panic= 4904 [KNL] Should the soft-lockup detector generate panics. 4905 Format: 0 | 1 4906 4907 A value of 1 instructs the soft-lockup detector 4908 to panic the machine when a soft-lockup occurs. It is 4909 also controlled by the kernel.softlockup_panic sysctl 4910 and CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC, which is the 4911 respective build-time switch to that functionality. 4912 4913 softlockup_all_cpu_backtrace= 4914 [KNL] Should the soft-lockup detector generate 4915 backtraces on all cpus. 4916 Format: 0 | 1 4917 4918 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4919 See Documentation/admin-guide/laptops/sonypi.rst 4920 4921 spectre_v2= [X86] Control mitigation of Spectre variant 2 4922 (indirect branch speculation) vulnerability. 4923 The default operation protects the kernel from 4924 user space attacks. 4925 4926 on - unconditionally enable, implies 4927 spectre_v2_user=on 4928 off - unconditionally disable, implies 4929 spectre_v2_user=off 4930 auto - kernel detects whether your CPU model is 4931 vulnerable 4932 4933 Selecting 'on' will, and 'auto' may, choose a 4934 mitigation method at run time according to the 4935 CPU, the available microcode, the setting of the 4936 CONFIG_RETPOLINE configuration option, and the 4937 compiler with which the kernel was built. 4938 4939 Selecting 'on' will also enable the mitigation 4940 against user space to user space task attacks. 4941 4942 Selecting 'off' will disable both the kernel and 4943 the user space protections. 4944 4945 Specific mitigations can also be selected manually: 4946 4947 retpoline - replace indirect branches 4948 retpoline,generic - google's original retpoline 4949 retpoline,amd - AMD-specific minimal thunk 4950 4951 Not specifying this option is equivalent to 4952 spectre_v2=auto. 4953 4954 spectre_v2_user= 4955 [X86] Control mitigation of Spectre variant 2 4956 (indirect branch speculation) vulnerability between 4957 user space tasks 4958 4959 on - Unconditionally enable mitigations. Is 4960 enforced by spectre_v2=on 4961 4962 off - Unconditionally disable mitigations. Is 4963 enforced by spectre_v2=off 4964 4965 prctl - Indirect branch speculation is enabled, 4966 but mitigation can be enabled via prctl 4967 per thread. The mitigation control state 4968 is inherited on fork. 4969 4970 prctl,ibpb 4971 - Like "prctl" above, but only STIBP is 4972 controlled per thread. IBPB is issued 4973 always when switching between different user 4974 space processes. 4975 4976 seccomp 4977 - Same as "prctl" above, but all seccomp 4978 threads will enable the mitigation unless 4979 they explicitly opt out. 4980 4981 seccomp,ibpb 4982 - Like "seccomp" above, but only STIBP is 4983 controlled per thread. IBPB is issued 4984 always when switching between different 4985 user space processes. 4986 4987 auto - Kernel selects the mitigation depending on 4988 the available CPU features and vulnerability. 4989 4990 Default mitigation: 4991 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4992 4993 Not specifying this option is equivalent to 4994 spectre_v2_user=auto. 4995 4996 spec_store_bypass_disable= 4997 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4998 (Speculative Store Bypass vulnerability) 4999 5000 Certain CPUs are vulnerable to an exploit against a 5001 a common industry wide performance optimization known 5002 as "Speculative Store Bypass" in which recent stores 5003 to the same memory location may not be observed by 5004 later loads during speculative execution. The idea 5005 is that such stores are unlikely and that they can 5006 be detected prior to instruction retirement at the 5007 end of a particular speculation execution window. 5008 5009 In vulnerable processors, the speculatively forwarded 5010 store can be used in a cache side channel attack, for 5011 example to read memory to which the attacker does not 5012 directly have access (e.g. inside sandboxed code). 5013 5014 This parameter controls whether the Speculative Store 5015 Bypass optimization is used. 5016 5017 On x86 the options are: 5018 5019 on - Unconditionally disable Speculative Store Bypass 5020 off - Unconditionally enable Speculative Store Bypass 5021 auto - Kernel detects whether the CPU model contains an 5022 implementation of Speculative Store Bypass and 5023 picks the most appropriate mitigation. If the 5024 CPU is not vulnerable, "off" is selected. If the 5025 CPU is vulnerable the default mitigation is 5026 architecture and Kconfig dependent. See below. 5027 prctl - Control Speculative Store Bypass per thread 5028 via prctl. Speculative Store Bypass is enabled 5029 for a process by default. The state of the control 5030 is inherited on fork. 5031 seccomp - Same as "prctl" above, but all seccomp threads 5032 will disable SSB unless they explicitly opt out. 5033 5034 Default mitigations: 5035 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 5036 5037 On powerpc the options are: 5038 5039 on,auto - On Power8 and Power9 insert a store-forwarding 5040 barrier on kernel entry and exit. On Power7 5041 perform a software flush on kernel entry and 5042 exit. 5043 off - No action. 5044 5045 Not specifying this option is equivalent to 5046 spec_store_bypass_disable=auto. 5047 5048 spia_io_base= [HW,MTD] 5049 spia_fio_base= 5050 spia_pedr= 5051 spia_peddr= 5052 5053 split_lock_detect= 5054 [X86] Enable split lock detection 5055 5056 When enabled (and if hardware support is present), atomic 5057 instructions that access data across cache line 5058 boundaries will result in an alignment check exception. 5059 5060 off - not enabled 5061 5062 warn - the kernel will emit rate limited warnings 5063 about applications triggering the #AC 5064 exception. This mode is the default on CPUs 5065 that supports split lock detection. 5066 5067 fatal - the kernel will send SIGBUS to applications 5068 that trigger the #AC exception. 5069 5070 If an #AC exception is hit in the kernel or in 5071 firmware (i.e. not while executing in user mode) 5072 the kernel will oops in either "warn" or "fatal" 5073 mode. 5074 5075 srbds= [X86,INTEL] 5076 Control the Special Register Buffer Data Sampling 5077 (SRBDS) mitigation. 5078 5079 Certain CPUs are vulnerable to an MDS-like 5080 exploit which can leak bits from the random 5081 number generator. 5082 5083 By default, this issue is mitigated by 5084 microcode. However, the microcode fix can cause 5085 the RDRAND and RDSEED instructions to become 5086 much slower. Among other effects, this will 5087 result in reduced throughput from /dev/urandom. 5088 5089 The microcode mitigation can be disabled with 5090 the following option: 5091 5092 off: Disable mitigation and remove 5093 performance impact to RDRAND and RDSEED 5094 5095 srcutree.counter_wrap_check [KNL] 5096 Specifies how frequently to check for 5097 grace-period sequence counter wrap for the 5098 srcu_data structure's ->srcu_gp_seq_needed field. 5099 The greater the number of bits set in this kernel 5100 parameter, the less frequently counter wrap will 5101 be checked for. Note that the bottom two bits 5102 are ignored. 5103 5104 srcutree.exp_holdoff [KNL] 5105 Specifies how many nanoseconds must elapse 5106 since the end of the last SRCU grace period for 5107 a given srcu_struct until the next normal SRCU 5108 grace period will be considered for automatic 5109 expediting. Set to zero to disable automatic 5110 expediting. 5111 5112 ssbd= [ARM64,HW] 5113 Speculative Store Bypass Disable control 5114 5115 On CPUs that are vulnerable to the Speculative 5116 Store Bypass vulnerability and offer a 5117 firmware based mitigation, this parameter 5118 indicates how the mitigation should be used: 5119 5120 force-on: Unconditionally enable mitigation for 5121 for both kernel and userspace 5122 force-off: Unconditionally disable mitigation for 5123 for both kernel and userspace 5124 kernel: Always enable mitigation in the 5125 kernel, and offer a prctl interface 5126 to allow userspace to register its 5127 interest in being mitigated too. 5128 5129 stack_guard_gap= [MM] 5130 override the default stack gap protection. The value 5131 is in page units and it defines how many pages prior 5132 to (for stacks growing down) resp. after (for stacks 5133 growing up) the main stack are reserved for no other 5134 mapping. Default value is 256 pages. 5135 5136 stacktrace [FTRACE] 5137 Enabled the stack tracer on boot up. 5138 5139 stacktrace_filter=[function-list] 5140 [FTRACE] Limit the functions that the stack tracer 5141 will trace at boot up. function-list is a comma separated 5142 list of functions. This list can be changed at run 5143 time by the stack_trace_filter file in the debugfs 5144 tracing directory. Note, this enables stack tracing 5145 and the stacktrace above is not needed. 5146 5147 sti= [PARISC,HW] 5148 Format: <num> 5149 Set the STI (builtin display/keyboard on the HP-PARISC 5150 machines) console (graphic card) which should be used 5151 as the initial boot-console. 5152 See also comment in drivers/video/console/sticore.c. 5153 5154 sti_font= [HW] 5155 See comment in drivers/video/console/sticore.c. 5156 5157 stifb= [HW] 5158 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 5159 5160 sunrpc.min_resvport= 5161 sunrpc.max_resvport= 5162 [NFS,SUNRPC] 5163 SunRPC servers often require that client requests 5164 originate from a privileged port (i.e. a port in the 5165 range 0 < portnr < 1024). 5166 An administrator who wishes to reserve some of these 5167 ports for other uses may adjust the range that the 5168 kernel's sunrpc client considers to be privileged 5169 using these two parameters to set the minimum and 5170 maximum port values. 5171 5172 sunrpc.svc_rpc_per_connection_limit= 5173 [NFS,SUNRPC] 5174 Limit the number of requests that the server will 5175 process in parallel from a single connection. 5176 The default value is 0 (no limit). 5177 5178 sunrpc.pool_mode= 5179 [NFS] 5180 Control how the NFS server code allocates CPUs to 5181 service thread pools. Depending on how many NICs 5182 you have and where their interrupts are bound, this 5183 option will affect which CPUs will do NFS serving. 5184 Note: this parameter cannot be changed while the 5185 NFS server is running. 5186 5187 auto the server chooses an appropriate mode 5188 automatically using heuristics 5189 global a single global pool contains all CPUs 5190 percpu one pool for each CPU 5191 pernode one pool for each NUMA node (equivalent 5192 to global on non-NUMA machines) 5193 5194 sunrpc.tcp_slot_table_entries= 5195 sunrpc.udp_slot_table_entries= 5196 [NFS,SUNRPC] 5197 Sets the upper limit on the number of simultaneous 5198 RPC calls that can be sent from the client to a 5199 server. Increasing these values may allow you to 5200 improve throughput, but will also increase the 5201 amount of memory reserved for use by the client. 5202 5203 suspend.pm_test_delay= 5204 [SUSPEND] 5205 Sets the number of seconds to remain in a suspend test 5206 mode before resuming the system (see 5207 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 5208 is set. Default value is 5. 5209 5210 svm= [PPC] 5211 Format: { on | off | y | n | 1 | 0 } 5212 This parameter controls use of the Protected 5213 Execution Facility on pSeries. 5214 5215 swapaccount=[0|1] 5216 [KNL] Enable accounting of swap in memory resource 5217 controller if no parameter or 1 is given or disable 5218 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 5219 5220 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 5221 Format: { <int> | force | noforce } 5222 <int> -- Number of I/O TLB slabs 5223 force -- force using of bounce buffers even if they 5224 wouldn't be automatically used by the kernel 5225 noforce -- Never use bounce buffers (for debugging) 5226 5227 switches= [HW,M68k] 5228 5229 sysctl.*= [KNL] 5230 Set a sysctl parameter, right before loading the init 5231 process, as if the value was written to the respective 5232 /proc/sys/... file. Both '.' and '/' are recognized as 5233 separators. Unrecognized parameters and invalid values 5234 are reported in the kernel log. Sysctls registered 5235 later by a loaded module cannot be set this way. 5236 Example: sysctl.vm.swappiness=40 5237 5238 sysfs.deprecated=0|1 [KNL] 5239 Enable/disable old style sysfs layout for old udev 5240 on older distributions. When this option is enabled 5241 very new udev will not work anymore. When this option 5242 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 5243 in older udev will not work anymore. 5244 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 5245 the kernel configuration. 5246 5247 sysrq_always_enabled 5248 [KNL] 5249 Ignore sysrq setting - this boot parameter will 5250 neutralize any effect of /proc/sys/kernel/sysrq. 5251 Useful for debugging. 5252 5253 tcpmhash_entries= [KNL,NET] 5254 Set the number of tcp_metrics_hash slots. 5255 Default value is 8192 or 16384 depending on total 5256 ram pages. This is used to specify the TCP metrics 5257 cache size. See Documentation/networking/ip-sysctl.rst 5258 "tcp_no_metrics_save" section for more details. 5259 5260 tdfx= [HW,DRM] 5261 5262 test_suspend= [SUSPEND][,N] 5263 Specify "mem" (for Suspend-to-RAM) or "standby" (for 5264 standby suspend) or "freeze" (for suspend type freeze) 5265 as the system sleep state during system startup with 5266 the optional capability to repeat N number of times. 5267 The system is woken from this state using a 5268 wakeup-capable RTC alarm. 5269 5270 thash_entries= [KNL,NET] 5271 Set number of hash buckets for TCP connection 5272 5273 thermal.act= [HW,ACPI] 5274 -1: disable all active trip points in all thermal zones 5275 <degrees C>: override all lowest active trip points 5276 5277 thermal.crt= [HW,ACPI] 5278 -1: disable all critical trip points in all thermal zones 5279 <degrees C>: override all critical trip points 5280 5281 thermal.nocrt= [HW,ACPI] 5282 Set to disable actions on ACPI thermal zone 5283 critical and hot trip points. 5284 5285 thermal.off= [HW,ACPI] 5286 1: disable ACPI thermal control 5287 5288 thermal.psv= [HW,ACPI] 5289 -1: disable all passive trip points 5290 <degrees C>: override all passive trip points to this 5291 value 5292 5293 thermal.tzp= [HW,ACPI] 5294 Specify global default ACPI thermal zone polling rate 5295 <deci-seconds>: poll all this frequency 5296 0: no polling (default) 5297 5298 threadirqs [KNL] 5299 Force threading of all interrupt handlers except those 5300 marked explicitly IRQF_NO_THREAD. 5301 5302 topology= [S390] 5303 Format: {off | on} 5304 Specify if the kernel should make use of the cpu 5305 topology information if the hardware supports this. 5306 The scheduler will make use of this information and 5307 e.g. base its process migration decisions on it. 5308 Default is on. 5309 5310 topology_updates= [KNL, PPC, NUMA] 5311 Format: {off} 5312 Specify if the kernel should ignore (off) 5313 topology updates sent by the hypervisor to this 5314 LPAR. 5315 5316 torture.disable_onoff_at_boot= [KNL] 5317 Prevent the CPU-hotplug component of torturing 5318 until after init has spawned. 5319 5320 torture.ftrace_dump_at_shutdown= [KNL] 5321 Dump the ftrace buffer at torture-test shutdown, 5322 even if there were no errors. This can be a 5323 very costly operation when many torture tests 5324 are running concurrently, especially on systems 5325 with rotating-rust storage. 5326 5327 tp720= [HW,PS2] 5328 5329 tpm_suspend_pcr=[HW,TPM] 5330 Format: integer pcr id 5331 Specify that at suspend time, the tpm driver 5332 should extend the specified pcr with zeros, 5333 as a workaround for some chips which fail to 5334 flush the last written pcr on TPM_SaveState. 5335 This will guarantee that all the other pcrs 5336 are saved. 5337 5338 trace_buf_size=nn[KMG] 5339 [FTRACE] will set tracing buffer size on each cpu. 5340 5341 trace_event=[event-list] 5342 [FTRACE] Set and start specified trace events in order 5343 to facilitate early boot debugging. The event-list is a 5344 comma separated list of trace events to enable. See 5345 also Documentation/trace/events.rst 5346 5347 trace_options=[option-list] 5348 [FTRACE] Enable or disable tracer options at boot. 5349 The option-list is a comma delimited list of options 5350 that can be enabled or disabled just as if you were 5351 to echo the option name into 5352 5353 /sys/kernel/debug/tracing/trace_options 5354 5355 For example, to enable stacktrace option (to dump the 5356 stack trace of each event), add to the command line: 5357 5358 trace_options=stacktrace 5359 5360 See also Documentation/trace/ftrace.rst "trace options" 5361 section. 5362 5363 tp_printk[FTRACE] 5364 Have the tracepoints sent to printk as well as the 5365 tracing ring buffer. This is useful for early boot up 5366 where the system hangs or reboots and does not give the 5367 option for reading the tracing buffer or performing a 5368 ftrace_dump_on_oops. 5369 5370 To turn off having tracepoints sent to printk, 5371 echo 0 > /proc/sys/kernel/tracepoint_printk 5372 Note, echoing 1 into this file without the 5373 tracepoint_printk kernel cmdline option has no effect. 5374 5375 ** CAUTION ** 5376 5377 Having tracepoints sent to printk() and activating high 5378 frequency tracepoints such as irq or sched, can cause 5379 the system to live lock. 5380 5381 traceoff_on_warning 5382 [FTRACE] enable this option to disable tracing when a 5383 warning is hit. This turns off "tracing_on". Tracing can 5384 be enabled again by echoing '1' into the "tracing_on" 5385 file located in /sys/kernel/debug/tracing/ 5386 5387 This option is useful, as it disables the trace before 5388 the WARNING dump is called, which prevents the trace to 5389 be filled with content caused by the warning output. 5390 5391 This option can also be set at run time via the sysctl 5392 option: kernel/traceoff_on_warning 5393 5394 transparent_hugepage= 5395 [KNL] 5396 Format: [always|madvise|never] 5397 Can be used to control the default behavior of the system 5398 with respect to transparent hugepages. 5399 See Documentation/admin-guide/mm/transhuge.rst 5400 for more details. 5401 5402 tsc= Disable clocksource stability checks for TSC. 5403 Format: <string> 5404 [x86] reliable: mark tsc clocksource as reliable, this 5405 disables clocksource verification at runtime, as well 5406 as the stability checks done at bootup. Used to enable 5407 high-resolution timer mode on older hardware, and in 5408 virtualized environment. 5409 [x86] noirqtime: Do not use TSC to do irq accounting. 5410 Used to run time disable IRQ_TIME_ACCOUNTING on any 5411 platforms where RDTSC is slow and this accounting 5412 can add overhead. 5413 [x86] unstable: mark the TSC clocksource as unstable, this 5414 marks the TSC unconditionally unstable at bootup and 5415 avoids any further wobbles once the TSC watchdog notices. 5416 [x86] nowatchdog: disable clocksource watchdog. Used 5417 in situations with strict latency requirements (where 5418 interruptions from clocksource watchdog are not 5419 acceptable). 5420 5421 tsc_early_khz= [X86] Skip early TSC calibration and use the given 5422 value instead. Useful when the early TSC frequency discovery 5423 procedure is not reliable, such as on overclocked systems 5424 with CPUID.16h support and partial CPUID.15h support. 5425 Format: <unsigned int> 5426 5427 tsx= [X86] Control Transactional Synchronization 5428 Extensions (TSX) feature in Intel processors that 5429 support TSX control. 5430 5431 This parameter controls the TSX feature. The options are: 5432 5433 on - Enable TSX on the system. Although there are 5434 mitigations for all known security vulnerabilities, 5435 TSX has been known to be an accelerator for 5436 several previous speculation-related CVEs, and 5437 so there may be unknown security risks associated 5438 with leaving it enabled. 5439 5440 off - Disable TSX on the system. (Note that this 5441 option takes effect only on newer CPUs which are 5442 not vulnerable to MDS, i.e., have 5443 MSR_IA32_ARCH_CAPABILITIES.MDS_NO=1 and which get 5444 the new IA32_TSX_CTRL MSR through a microcode 5445 update. This new MSR allows for the reliable 5446 deactivation of the TSX functionality.) 5447 5448 auto - Disable TSX if X86_BUG_TAA is present, 5449 otherwise enable TSX on the system. 5450 5451 Not specifying this option is equivalent to tsx=off. 5452 5453 See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5454 for more details. 5455 5456 tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async 5457 Abort (TAA) vulnerability. 5458 5459 Similar to Micro-architectural Data Sampling (MDS) 5460 certain CPUs that support Transactional 5461 Synchronization Extensions (TSX) are vulnerable to an 5462 exploit against CPU internal buffers which can forward 5463 information to a disclosure gadget under certain 5464 conditions. 5465 5466 In vulnerable processors, the speculatively forwarded 5467 data can be used in a cache side channel attack, to 5468 access data to which the attacker does not have direct 5469 access. 5470 5471 This parameter controls the TAA mitigation. The 5472 options are: 5473 5474 full - Enable TAA mitigation on vulnerable CPUs 5475 if TSX is enabled. 5476 5477 full,nosmt - Enable TAA mitigation and disable SMT on 5478 vulnerable CPUs. If TSX is disabled, SMT 5479 is not disabled because CPU is not 5480 vulnerable to cross-thread TAA attacks. 5481 off - Unconditionally disable TAA mitigation 5482 5483 On MDS-affected machines, tsx_async_abort=off can be 5484 prevented by an active MDS mitigation as both vulnerabilities 5485 are mitigated with the same mechanism so in order to disable 5486 this mitigation, you need to specify mds=off too. 5487 5488 Not specifying this option is equivalent to 5489 tsx_async_abort=full. On CPUs which are MDS affected 5490 and deploy MDS mitigation, TAA mitigation is not 5491 required and doesn't provide any additional 5492 mitigation. 5493 5494 For details see: 5495 Documentation/admin-guide/hw-vuln/tsx_async_abort.rst 5496 5497 turbografx.map[2|3]= [HW,JOY] 5498 TurboGraFX parallel port interface 5499 Format: 5500 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 5501 See also Documentation/input/devices/joystick-parport.rst 5502 5503 udbg-immortal [PPC] When debugging early kernel crashes that 5504 happen after console_init() and before a proper 5505 console driver takes over, this boot options might 5506 help "seeing" what's going on. 5507 5508 uhash_entries= [KNL,NET] 5509 Set number of hash buckets for UDP/UDP-Lite connections 5510 5511 uhci-hcd.ignore_oc= 5512 [USB] Ignore overcurrent events (default N). 5513 Some badly-designed motherboards generate lots of 5514 bogus events, for ports that aren't wired to 5515 anything. Set this parameter to avoid log spamming. 5516 Note that genuine overcurrent events won't be 5517 reported either. 5518 5519 unknown_nmi_panic 5520 [X86] Cause panic on unknown NMI. 5521 5522 usbcore.authorized_default= 5523 [USB] Default USB device authorization: 5524 (default -1 = authorized except for wireless USB, 5525 0 = not authorized, 1 = authorized, 2 = authorized 5526 if device connected to internal port) 5527 5528 usbcore.autosuspend= 5529 [USB] The autosuspend time delay (in seconds) used 5530 for newly-detected USB devices (default 2). This 5531 is the time required before an idle device will be 5532 autosuspended. Devices for which the delay is set 5533 to a negative value won't be autosuspended at all. 5534 5535 usbcore.usbfs_snoop= 5536 [USB] Set to log all usbfs traffic (default 0 = off). 5537 5538 usbcore.usbfs_snoop_max= 5539 [USB] Maximum number of bytes to snoop in each URB 5540 (default = 65536). 5541 5542 usbcore.blinkenlights= 5543 [USB] Set to cycle leds on hubs (default 0 = off). 5544 5545 usbcore.old_scheme_first= 5546 [USB] Start with the old device initialization 5547 scheme (default 0 = off). 5548 5549 usbcore.usbfs_memory_mb= 5550 [USB] Memory limit (in MB) for buffers allocated by 5551 usbfs (default = 16, 0 = max = 2047). 5552 5553 usbcore.use_both_schemes= 5554 [USB] Try the other device initialization scheme 5555 if the first one fails (default 1 = enabled). 5556 5557 usbcore.initial_descriptor_timeout= 5558 [USB] Specifies timeout for the initial 64-byte 5559 USB_REQ_GET_DESCRIPTOR request in milliseconds 5560 (default 5000 = 5.0 seconds). 5561 5562 usbcore.nousb [USB] Disable the USB subsystem 5563 5564 usbcore.quirks= 5565 [USB] A list of quirk entries to augment the built-in 5566 usb core quirk list. List entries are separated by 5567 commas. Each entry has the form 5568 VendorID:ProductID:Flags. The IDs are 4-digit hex 5569 numbers and Flags is a set of letters. Each letter 5570 will change the built-in quirk; setting it if it is 5571 clear and clearing it if it is set. The letters have 5572 the following meanings: 5573 a = USB_QUIRK_STRING_FETCH_255 (string 5574 descriptors must not be fetched using 5575 a 255-byte read); 5576 b = USB_QUIRK_RESET_RESUME (device can't resume 5577 correctly so reset it instead); 5578 c = USB_QUIRK_NO_SET_INTF (device can't handle 5579 Set-Interface requests); 5580 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 5581 handle its Configuration or Interface 5582 strings); 5583 e = USB_QUIRK_RESET (device can't be reset 5584 (e.g morph devices), don't use reset); 5585 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 5586 more interface descriptions than the 5587 bNumInterfaces count, and can't handle 5588 talking to these interfaces); 5589 g = USB_QUIRK_DELAY_INIT (device needs a pause 5590 during initialization, after we read 5591 the device descriptor); 5592 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 5593 high speed and super speed interrupt 5594 endpoints, the USB 2.0 and USB 3.0 spec 5595 require the interval in microframes (1 5596 microframe = 125 microseconds) to be 5597 calculated as interval = 2 ^ 5598 (bInterval-1). 5599 Devices with this quirk report their 5600 bInterval as the result of this 5601 calculation instead of the exponent 5602 variable used in the calculation); 5603 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 5604 handle device_qualifier descriptor 5605 requests); 5606 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 5607 generates spurious wakeup, ignore 5608 remote wakeup capability); 5609 k = USB_QUIRK_NO_LPM (device can't handle Link 5610 Power Management); 5611 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 5612 (Device reports its bInterval as linear 5613 frames instead of the USB 2.0 5614 calculation); 5615 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 5616 to be disconnected before suspend to 5617 prevent spurious wakeup); 5618 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 5619 pause after every control message); 5620 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 5621 delay after resetting its port); 5622 Example: quirks=0781:5580:bk,0a5c:5834:gij 5623 5624 usbhid.mousepoll= 5625 [USBHID] The interval which mice are to be polled at. 5626 5627 usbhid.jspoll= 5628 [USBHID] The interval which joysticks are to be polled at. 5629 5630 usbhid.kbpoll= 5631 [USBHID] The interval which keyboards are to be polled at. 5632 5633 usb-storage.delay_use= 5634 [UMS] The delay in seconds before a new device is 5635 scanned for Logical Units (default 1). 5636 5637 usb-storage.quirks= 5638 [UMS] A list of quirks entries to supplement or 5639 override the built-in unusual_devs list. List 5640 entries are separated by commas. Each entry has 5641 the form VID:PID:Flags where VID and PID are Vendor 5642 and Product ID values (4-digit hex numbers) and 5643 Flags is a set of characters, each corresponding 5644 to a common usb-storage quirk flag as follows: 5645 a = SANE_SENSE (collect more than 18 bytes 5646 of sense data, not on uas); 5647 b = BAD_SENSE (don't collect more than 18 5648 bytes of sense data, not on uas); 5649 c = FIX_CAPACITY (decrease the reported 5650 device capacity by one sector); 5651 d = NO_READ_DISC_INFO (don't use 5652 READ_DISC_INFO command, not on uas); 5653 e = NO_READ_CAPACITY_16 (don't use 5654 READ_CAPACITY_16 command); 5655 f = NO_REPORT_OPCODES (don't use report opcodes 5656 command, uas only); 5657 g = MAX_SECTORS_240 (don't transfer more than 5658 240 sectors at a time, uas only); 5659 h = CAPACITY_HEURISTICS (decrease the 5660 reported device capacity by one 5661 sector if the number is odd); 5662 i = IGNORE_DEVICE (don't bind to this 5663 device); 5664 j = NO_REPORT_LUNS (don't use report luns 5665 command, uas only); 5666 l = NOT_LOCKABLE (don't try to lock and 5667 unlock ejectable media, not on uas); 5668 m = MAX_SECTORS_64 (don't transfer more 5669 than 64 sectors = 32 KB at a time, 5670 not on uas); 5671 n = INITIAL_READ10 (force a retry of the 5672 initial READ(10) command, not on uas); 5673 o = CAPACITY_OK (accept the capacity 5674 reported by the device, not on uas); 5675 p = WRITE_CACHE (the device cache is ON 5676 by default, not on uas); 5677 r = IGNORE_RESIDUE (the device reports 5678 bogus residue values, not on uas); 5679 s = SINGLE_LUN (the device has only one 5680 Logical Unit); 5681 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5682 commands, uas only); 5683 u = IGNORE_UAS (don't bind to the uas driver); 5684 w = NO_WP_DETECT (don't test whether the 5685 medium is write-protected). 5686 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5687 even if the device claims no cache, 5688 not on uas) 5689 Example: quirks=0419:aaf5:rl,0421:0433:rc 5690 5691 user_debug= [KNL,ARM] 5692 Format: <int> 5693 See arch/arm/Kconfig.debug help text. 5694 1 - undefined instruction events 5695 2 - system calls 5696 4 - invalid data aborts 5697 8 - SIGSEGV faults 5698 16 - SIGBUS faults 5699 Example: user_debug=31 5700 5701 userpte= 5702 [X86] Flags controlling user PTE allocations. 5703 5704 nohigh = do not allocate PTE pages in 5705 HIGHMEM regardless of setting 5706 of CONFIG_HIGHPTE. 5707 5708 vdso= [X86,SH] 5709 On X86_32, this is an alias for vdso32=. Otherwise: 5710 5711 vdso=1: enable VDSO (the default) 5712 vdso=0: disable VDSO mapping 5713 5714 vdso32= [X86] Control the 32-bit vDSO 5715 vdso32=1: enable 32-bit VDSO 5716 vdso32=0 or vdso32=2: disable 32-bit VDSO 5717 5718 See the help text for CONFIG_COMPAT_VDSO for more 5719 details. If CONFIG_COMPAT_VDSO is set, the default is 5720 vdso32=0; otherwise, the default is vdso32=1. 5721 5722 For compatibility with older kernels, vdso32=2 is an 5723 alias for vdso32=0. 5724 5725 Try vdso32=0 if you encounter an error that says: 5726 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5727 5728 vector= [IA-64,SMP] 5729 vector=percpu: enable percpu vector domain 5730 5731 video= [FB] Frame buffer configuration 5732 See Documentation/fb/modedb.rst. 5733 5734 video.brightness_switch_enabled= [0,1] 5735 If set to 1, on receiving an ACPI notify event 5736 generated by hotkey, video driver will adjust brightness 5737 level and then send out the event to user space through 5738 the allocated input device; If set to 0, video driver 5739 will only send out the event without touching backlight 5740 brightness level. 5741 default: 1 5742 5743 virtio_mmio.device= 5744 [VMMIO] Memory mapped virtio (platform) device. 5745 5746 <size>@<baseaddr>:<irq>[:<id>] 5747 where: 5748 <size> := size (can use standard suffixes 5749 like K, M and G) 5750 <baseaddr> := physical base address 5751 <irq> := interrupt number (as passed to 5752 request_irq()) 5753 <id> := (optional) platform device id 5754 example: 5755 virtio_mmio.device=1K@0x100b0000:48:7 5756 5757 Can be used multiple times for multiple devices. 5758 5759 vga= [BOOT,X86-32] Select a particular video mode 5760 See Documentation/x86/boot.rst and 5761 Documentation/admin-guide/svga.rst. 5762 Use vga=ask for menu. 5763 This is actually a boot loader parameter; the value is 5764 passed to the kernel using a special protocol. 5765 5766 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5767 May slow down system boot speed, especially when 5768 enabled on systems with a large amount of memory. 5769 All options are enabled by default, and this 5770 interface is meant to allow for selectively 5771 enabling or disabling specific virtual memory 5772 debugging features. 5773 5774 Available options are: 5775 P Enable page structure init time poisoning 5776 - Disable all of the above options 5777 5778 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5779 size of <nn>. This can be used to increase the 5780 minimum size (128MB on x86). It can also be used to 5781 decrease the size and leave more room for directly 5782 mapped kernel RAM. 5783 5784 vmcp_cma=nn[MG] [KNL,S390] 5785 Sets the memory size reserved for contiguous memory 5786 allocations for the vmcp device driver. 5787 5788 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5789 Format: <command> 5790 5791 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5792 Format: <command> 5793 5794 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5795 Format: <command> 5796 5797 vsyscall= [X86-64] 5798 Controls the behavior of vsyscalls (i.e. calls to 5799 fixed addresses of 0xffffffffff600x00 from legacy 5800 code). Most statically-linked binaries and older 5801 versions of glibc use these calls. Because these 5802 functions are at fixed addresses, they make nice 5803 targets for exploits that can control RIP. 5804 5805 emulate [default] Vsyscalls turn into traps and are 5806 emulated reasonably safely. The vsyscall 5807 page is readable. 5808 5809 xonly Vsyscalls turn into traps and are 5810 emulated reasonably safely. The vsyscall 5811 page is not readable. 5812 5813 none Vsyscalls don't work at all. This makes 5814 them quite hard to use for exploits but 5815 might break your system. 5816 5817 vt.color= [VT] Default text color. 5818 Format: 0xYX, X = foreground, Y = background. 5819 Default: 0x07 = light gray on black. 5820 5821 vt.cur_default= [VT] Default cursor shape. 5822 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5823 the parameters of the <Esc>[?A;B;Cc escape sequence; 5824 see VGA-softcursor.txt. Default: 2 = underline. 5825 5826 vt.default_blu= [VT] 5827 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5828 Change the default blue palette of the console. 5829 This is a 16-member array composed of values 5830 ranging from 0-255. 5831 5832 vt.default_grn= [VT] 5833 Format: <green0>,<green1>,<green2>,...,<green15> 5834 Change the default green palette of the console. 5835 This is a 16-member array composed of values 5836 ranging from 0-255. 5837 5838 vt.default_red= [VT] 5839 Format: <red0>,<red1>,<red2>,...,<red15> 5840 Change the default red palette of the console. 5841 This is a 16-member array composed of values 5842 ranging from 0-255. 5843 5844 vt.default_utf8= 5845 [VT] 5846 Format=<0|1> 5847 Set system-wide default UTF-8 mode for all tty's. 5848 Default is 1, i.e. UTF-8 mode is enabled for all 5849 newly opened terminals. 5850 5851 vt.global_cursor_default= 5852 [VT] 5853 Format=<-1|0|1> 5854 Set system-wide default for whether a cursor 5855 is shown on new VTs. Default is -1, 5856 i.e. cursors will be created by default unless 5857 overridden by individual drivers. 0 will hide 5858 cursors, 1 will display them. 5859 5860 vt.italic= [VT] Default color for italic text; 0-15. 5861 Default: 2 = green. 5862 5863 vt.underline= [VT] Default color for underlined text; 0-15. 5864 Default: 3 = cyan. 5865 5866 watchdog timers [HW,WDT] For information on watchdog timers, 5867 see Documentation/watchdog/watchdog-parameters.rst 5868 or other driver-specific files in the 5869 Documentation/watchdog/ directory. 5870 5871 watchdog_thresh= 5872 [KNL] 5873 Set the hard lockup detector stall duration 5874 threshold in seconds. The soft lockup detector 5875 threshold is set to twice the value. A value of 0 5876 disables both lockup detectors. Default is 10 5877 seconds. 5878 5879 workqueue.watchdog_thresh= 5880 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5881 warn stall conditions and dump internal state to 5882 help debugging. 0 disables workqueue stall 5883 detection; otherwise, it's the stall threshold 5884 duration in seconds. The default value is 30 and 5885 it can be updated at runtime by writing to the 5886 corresponding sysfs file. 5887 5888 workqueue.disable_numa 5889 By default, all work items queued to unbound 5890 workqueues are affine to the NUMA nodes they're 5891 issued on, which results in better behavior in 5892 general. If NUMA affinity needs to be disabled for 5893 whatever reason, this option can be used. Note 5894 that this also can be controlled per-workqueue for 5895 workqueues visible under /sys/bus/workqueue/. 5896 5897 workqueue.power_efficient 5898 Per-cpu workqueues are generally preferred because 5899 they show better performance thanks to cache 5900 locality; unfortunately, per-cpu workqueues tend to 5901 be more power hungry than unbound workqueues. 5902 5903 Enabling this makes the per-cpu workqueues which 5904 were observed to contribute significantly to power 5905 consumption unbound, leading to measurably lower 5906 power usage at the cost of small performance 5907 overhead. 5908 5909 The default value of this parameter is determined by 5910 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5911 5912 workqueue.debug_force_rr_cpu 5913 Workqueue used to implicitly guarantee that work 5914 items queued without explicit CPU specified are put 5915 on the local CPU. This guarantee is no longer true 5916 and while local CPU is still preferred work items 5917 may be put on foreign CPUs. This debug option 5918 forces round-robin CPU selection to flush out 5919 usages which depend on the now broken guarantee. 5920 When enabled, memory and cache locality will be 5921 impacted. 5922 5923 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5924 default x2apic cluster mode on platforms 5925 supporting x2apic. 5926 5927 x86_intel_mid_timer= [X86-32,APBT] 5928 Choose timer option for x86 Intel MID platform. 5929 Two valid options are apbt timer only and lapic timer 5930 plus one apbt timer for broadcast timer. 5931 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5932 5933 xen_512gb_limit [KNL,X86-64,XEN] 5934 Restricts the kernel running paravirtualized under Xen 5935 to use only up to 512 GB of RAM. The reason to do so is 5936 crash analysis tools and Xen tools for doing domain 5937 save/restore/migration must be enabled to handle larger 5938 domains. 5939 5940 xen_emul_unplug= [HW,X86,XEN] 5941 Unplug Xen emulated devices 5942 Format: [unplug0,][unplug1] 5943 ide-disks -- unplug primary master IDE devices 5944 aux-ide-disks -- unplug non-primary-master IDE devices 5945 nics -- unplug network devices 5946 all -- unplug all emulated devices (NICs and IDE disks) 5947 unnecessary -- unplugging emulated devices is 5948 unnecessary even if the host did not respond to 5949 the unplug protocol 5950 never -- do not unplug even if version check succeeds 5951 5952 xen_legacy_crash [X86,XEN] 5953 Crash from Xen panic notifier, without executing late 5954 panic() code such as dumping handler. 5955 5956 xen_nopvspin [X86,XEN] 5957 Disables the qspinlock slowpath using Xen PV optimizations. 5958 This parameter is obsoleted by "nopvspin" parameter, which 5959 has equivalent effect for XEN platform. 5960 5961 xen_nopv [X86] 5962 Disables the PV optimizations forcing the HVM guest to 5963 run as generic HVM guest with no PV drivers. 5964 This option is obsoleted by the "nopv" option, which 5965 has equivalent effect for XEN platform. 5966 5967 xen_scrub_pages= [XEN] 5968 Boolean option to control scrubbing pages before giving them back 5969 to Xen, for use by other domains. Can be also changed at runtime 5970 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5971 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5972 5973 xen_timer_slop= [X86-64,XEN] 5974 Set the timer slop (in nanoseconds) for the virtual Xen 5975 timers (default is 100000). This adjusts the minimum 5976 delta of virtualized Xen timers, where lower values 5977 improve timer resolution at the expense of processing 5978 more timer interrupts. 5979 5980 xen.event_eoi_delay= [XEN] 5981 How long to delay EOI handling in case of event 5982 storms (jiffies). Default is 10. 5983 5984 xen.event_loop_timeout= [XEN] 5985 After which time (jiffies) the event handling loop 5986 should start to delay EOI handling. Default is 2. 5987 5988 xen.fifo_events= [XEN] 5989 Boolean parameter to disable using fifo event handling 5990 even if available. Normally fifo event handling is 5991 preferred over the 2-level event handling, as it is 5992 fairer and the number of possible event channels is 5993 much higher. Default is on (use fifo events). 5994 5995 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5996 Disables the PV optimizations forcing the guest to run 5997 as generic guest with no PV drivers. Currently support 5998 XEN HVM, KVM, HYPER_V and VMWARE guest. 5999 6000 nopvspin [X86,XEN,KVM] 6001 Disables the qspinlock slow path using PV optimizations 6002 which allow the hypervisor to 'idle' the guest on lock 6003 contention. 6004 6005 xirc2ps_cs= [NET,PCMCIA] 6006 Format: 6007 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 6008 6009 xive= [PPC] 6010 By default on POWER9 and above, the kernel will 6011 natively use the XIVE interrupt controller. This option 6012 allows the fallback firmware mode to be used: 6013 6014 off Fallback to firmware control of XIVE interrupt 6015 controller on both pseries and powernv 6016 platforms. Only useful on POWER9 and above. 6017 6018 xhci-hcd.quirks [USB,KNL] 6019 A hex value specifying bitmask with supplemental xhci 6020 host controller quirks. Meaning of each bit can be 6021 consulted in header drivers/usb/host/xhci.h. 6022 6023 xmon [PPC] 6024 Format: { early | on | rw | ro | off } 6025 Controls if xmon debugger is enabled. Default is off. 6026 Passing only "xmon" is equivalent to "xmon=early". 6027 early Call xmon as early as possible on boot; xmon 6028 debugger is called from setup_arch(). 6029 on xmon debugger hooks will be installed so xmon 6030 is only called on a kernel crash. Default mode, 6031 i.e. either "ro" or "rw" mode, is controlled 6032 with CONFIG_XMON_DEFAULT_RO_MODE. 6033 rw xmon debugger hooks will be installed so xmon 6034 is called only on a kernel crash, mode is write, 6035 meaning SPR registers, memory and, other data 6036 can be written using xmon commands. 6037 ro same as "rw" option above but SPR registers, 6038 memory, and other data can't be written using 6039 xmon commands. 6040 off xmon is disabled. 6041