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 acpi_backlight=vendor 26 acpi_backlight=video 27 If set to vendor, prefer vendor specific driver 28 (e.g. thinkpad_acpi, sony_acpi, etc.) instead 29 of the ACPI video.ko driver. 30 31 acpi_force_32bit_fadt_addr 32 force FADT to use 32 bit addresses rather than the 33 64 bit X_* addresses. Some firmware have broken 64 34 bit addresses for force ACPI ignore these and use 35 the older legacy 32 bit addresses. 36 37 acpica_no_return_repair [HW, ACPI] 38 Disable AML predefined validation mechanism 39 This mechanism can repair the evaluation result to make 40 the return objects more ACPI specification compliant. 41 This option is useful for developers to identify the 42 root cause of an AML interpreter issue when the issue 43 has something to do with the repair mechanism. 44 45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] 46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG] 47 Format: <int> 48 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI 49 debug output. Bits in debug_layer correspond to a 50 _COMPONENT in an ACPI source file, e.g., 51 #define _COMPONENT ACPI_PCI_COMPONENT 52 Bits in debug_level correspond to a level in 53 ACPI_DEBUG_PRINT statements, e.g., 54 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... 55 The debug_level mask defaults to "info". See 56 Documentation/firmware-guide/acpi/debug.rst for more information about 57 debug layers and levels. 58 59 Enable processor driver info messages: 60 acpi.debug_layer=0x20000000 61 Enable PCI/PCI interrupt routing info messages: 62 acpi.debug_layer=0x400000 63 Enable AML "Debug" output, i.e., stores to the Debug 64 object while interpreting AML: 65 acpi.debug_layer=0xffffffff acpi.debug_level=0x2 66 Enable all messages related to ACPI hardware: 67 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff 68 69 Some values produce so much output that the system is 70 unusable. The "log_buf_len" parameter may be useful 71 if you need to capture more output. 72 73 acpi_enforce_resources= [ACPI] 74 { strict | lax | no } 75 Check for resource conflicts between native drivers 76 and ACPI OperationRegions (SystemIO and SystemMemory 77 only). IO ports and memory declared in ACPI might be 78 used by the ACPI subsystem in arbitrary AML code and 79 can interfere with legacy drivers. 80 strict (default): access to resources claimed by ACPI 81 is denied; legacy drivers trying to access reserved 82 resources will fail to bind to device using them. 83 lax: access to resources claimed by ACPI is allowed; 84 legacy drivers trying to access reserved resources 85 will bind successfully but a warning message is logged. 86 no: ACPI OperationRegions are not marked as reserved, 87 no further checks are performed. 88 89 acpi_force_table_verification [HW,ACPI] 90 Enable table checksum verification during early stage. 91 By default, this is disabled due to x86 early mapping 92 size limitation. 93 94 acpi_irq_balance [HW,ACPI] 95 ACPI will balance active IRQs 96 default in APIC mode 97 98 acpi_irq_nobalance [HW,ACPI] 99 ACPI will not move active IRQs (default) 100 default in PIC mode 101 102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA 103 Format: <irq>,<irq>... 104 105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for 106 use by PCI 107 Format: <irq>,<irq>... 108 109 acpi_mask_gpe= [HW,ACPI] 110 Due to the existence of _Lxx/_Exx, some GPEs triggered 111 by unsupported hardware/firmware features can result in 112 GPE floodings that cannot be automatically disabled by 113 the GPE dispatcher. 114 This facility can be used to prevent such uncontrolled 115 GPE floodings. 116 Format: <int> 117 118 acpi_no_auto_serialize [HW,ACPI] 119 Disable auto-serialization of AML methods 120 AML control methods that contain the opcodes to create 121 named objects will be marked as "Serialized" by the 122 auto-serialization feature. 123 This feature is enabled by default. 124 This option allows to turn off the feature. 125 126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 127 kernels. 128 129 acpi_no_static_ssdt [HW,ACPI] 130 Disable installation of static SSDTs at early boot time 131 By default, SSDTs contained in the RSDT/XSDT will be 132 installed automatically and they will appear under 133 /sys/firmware/acpi/tables. 134 This option turns off this feature. 135 Note that specifying this option does not affect 136 dynamic table installation which will install SSDT 137 tables to /sys/firmware/acpi/tables/dynamic. 138 139 acpi_rsdp= [ACPI,EFI,KEXEC] 140 Pass the RSDP address to the kernel, mostly used 141 on machines running EFI runtime service to boot the 142 second kernel for kdump. 143 144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 145 Format: To spoof as Windows 98: ="Microsoft Windows" 146 147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 148 of 2 which is mandated by ACPI 6) as the supported ACPI 149 specification revision (when using this switch, it may 150 be necessary to carry out a cold reboot _twice_ in a 151 row to make it take effect on the platform firmware). 152 153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 154 acpi_osi="string1" # add string1 155 acpi_osi="!string2" # remove string2 156 acpi_osi=!* # remove all strings 157 acpi_osi=! # disable all built-in OS vendor 158 strings 159 acpi_osi=!! # enable all built-in OS vendor 160 strings 161 acpi_osi= # disable all strings 162 163 'acpi_osi=!' can be used in combination with single or 164 multiple 'acpi_osi="string1"' to support specific OS 165 vendor string(s). Note that such command can only 166 affect the default state of the OS vendor strings, thus 167 it cannot affect the default state of the feature group 168 strings and the current state of the OS vendor strings, 169 specifying it multiple times through kernel command line 170 is meaningless. This command is useful when one do not 171 care about the state of the feature group strings which 172 should be controlled by the OSPM. 173 Examples: 174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 176 can make '_OSI("Windows 2000")' TRUE. 177 178 'acpi_osi=' cannot be used in combination with other 179 'acpi_osi=' command lines, the _OSI method will not 180 exist in the ACPI namespace. NOTE that such command can 181 only affect the _OSI support state, thus specifying it 182 multiple times through kernel command line is also 183 meaningless. 184 Examples: 185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 186 FALSE. 187 188 'acpi_osi=!*' can be used in combination with single or 189 multiple 'acpi_osi="string1"' to support specific 190 string(s). Note that such command can affect the 191 current state of both the OS vendor strings and the 192 feature group strings, thus specifying it multiple times 193 through kernel command line is meaningful. But it may 194 still not able to affect the final state of a string if 195 there are quirks related to this string. This command 196 is useful when one want to control the state of the 197 feature group strings to debug BIOS issues related to 198 the OSPM features. 199 Examples: 200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 201 '_OSI("Module Device")' FALSE. 202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 203 '_OSI("Module Device")' TRUE. 204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 205 equivalent to 206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 207 and 208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 209 they all will make '_OSI("Windows 2000")' TRUE. 210 211 acpi_pm_good [X86] 212 Override the pmtimer bug detection: force the kernel 213 to assume that this machine's pmtimer latches its value 214 and always returns good values. 215 216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 217 Format: { level | edge | high | low } 218 219 acpi_skip_timer_override [HW,ACPI] 220 Recognize and ignore IRQ0/pin2 Interrupt Override. 221 For broken nForce2 BIOS resulting in XT-PIC timer. 222 223 acpi_sleep= [HW,ACPI] Sleep options 224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 225 old_ordering, nonvs, sci_force_enable, nobl } 226 See Documentation/power/video.rst for information on 227 s3_bios and s3_mode. 228 s3_beep is for debugging; it makes the PC's speaker beep 229 as soon as the kernel's real-mode entry point is called. 230 s4_nohwsig prevents ACPI hardware signature from being 231 used during resume from hibernation. 232 old_ordering causes the ACPI 1.0 ordering of the _PTS 233 control method, with respect to putting devices into 234 low power states, to be enforced (the ACPI 2.0 ordering 235 of _PTS is used by default). 236 nonvs prevents the kernel from saving/restoring the 237 ACPI NVS memory during suspend/hibernation and resume. 238 sci_force_enable causes the kernel to set SCI_EN directly 239 on resume from S1/S3 (which is against the ACPI spec, 240 but some broken systems don't work without it). 241 nobl causes the internal blacklist of systems known to 242 behave incorrectly in some ways with respect to system 243 suspend and resume to be ignored (use wisely). 244 245 acpi_use_timer_override [HW,ACPI] 246 Use timer override. For some broken Nvidia NF5 boards 247 that require a timer override, but don't have HPET 248 249 add_efi_memmap [EFI; X86] Include EFI memory map in 250 kernel's map of available physical RAM. 251 252 agp= [AGP] 253 { off | try_unsupported } 254 off: disable AGP support 255 try_unsupported: try to drive unsupported chipsets 256 (may crash computer or cause data corruption) 257 258 ALSA [HW,ALSA] 259 See Documentation/sound/alsa-configuration.rst 260 261 alignment= [KNL,ARM] 262 Allow the default userspace alignment fault handler 263 behaviour to be specified. Bit 0 enables warnings, 264 bit 1 enables fixups, and bit 2 sends a segfault. 265 266 align_va_addr= [X86-64] 267 Align virtual addresses by clearing slice [14:12] when 268 allocating a VMA at process creation time. This option 269 gives you up to 3% performance improvement on AMD F15h 270 machines (where it is enabled by default) for a 271 CPU-intensive style benchmark, and it can vary highly in 272 a microbenchmark depending on workload and compiler. 273 274 32: only for 32-bit processes 275 64: only for 64-bit processes 276 on: enable for both 32- and 64-bit processes 277 off: disable for both 32- and 64-bit processes 278 279 alloc_snapshot [FTRACE] 280 Allocate the ftrace snapshot buffer on boot up when the 281 main buffer is allocated. This is handy if debugging 282 and you need to use tracing_snapshot() on boot up, and 283 do not want to use tracing_snapshot_alloc() as it needs 284 to be done where GFP_KERNEL allocations are allowed. 285 286 amd_iommu= [HW,X86-64] 287 Pass parameters to the AMD IOMMU driver in the system. 288 Possible values are: 289 fullflush - enable flushing of IO/TLB entries when 290 they are unmapped. Otherwise they are 291 flushed before they will be reused, which 292 is a lot of faster 293 off - do not initialize any AMD IOMMU found in 294 the system 295 force_isolation - Force device isolation for all 296 devices. The IOMMU driver is not 297 allowed anymore to lift isolation 298 requirements as needed. This option 299 does not override iommu=pt 300 301 amd_iommu_dump= [HW,X86-64] 302 Enable AMD IOMMU driver option to dump the ACPI table 303 for AMD IOMMU. With this option enabled, AMD IOMMU 304 driver will print ACPI tables for AMD IOMMU during 305 IOMMU initialization. 306 307 amd_iommu_intr= [HW,X86-64] 308 Specifies one of the following AMD IOMMU interrupt 309 remapping modes: 310 legacy - Use legacy interrupt remapping mode. 311 vapic - Use virtual APIC mode, which allows IOMMU 312 to inject interrupts directly into guest. 313 This mode requires kvm-amd.avic=1. 314 (Default when IOMMU HW support is present.) 315 316 amijoy.map= [HW,JOY] Amiga joystick support 317 Map of devices attached to JOY0DAT and JOY1DAT 318 Format: <a>,<b> 319 See also Documentation/input/joydev/joystick.rst 320 321 analog.map= [HW,JOY] Analog joystick and gamepad support 322 Specifies type or capabilities of an analog joystick 323 connected to one of 16 gameports 324 Format: <type1>,<type2>,..<type16> 325 326 apc= [HW,SPARC] 327 Power management functions (SPARCstation-4/5 + deriv.) 328 Format: noidle 329 Disable APC CPU standby support. SPARCstation-Fox does 330 not play well with APC CPU idle - disable it if you have 331 APC and your system crashes randomly. 332 333 apic= [APIC,X86] Advanced Programmable Interrupt Controller 334 Change the output verbosity while booting 335 Format: { quiet (default) | verbose | debug } 336 Change the amount of debugging information output 337 when initialising the APIC and IO-APIC components. 338 For X86-32, this can also be used to specify an APIC 339 driver name. 340 Format: apic=driver_name 341 Examples: apic=bigsmp 342 343 apic_extnmi= [APIC,X86] External NMI delivery setting 344 Format: { bsp (default) | all | none } 345 bsp: External NMI is delivered only to CPU 0 346 all: External NMIs are broadcast to all CPUs as a 347 backup of CPU 0 348 none: External NMI is masked for all CPUs. This is 349 useful so that a dump capture kernel won't be 350 shot down by NMI 351 352 autoconf= [IPV6] 353 See Documentation/networking/ipv6.txt. 354 355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 356 Limit apic dumping. The parameter defines the maximal 357 number of local apics being dumped. Also it is possible 358 to set it to "all" by meaning -- no limit here. 359 Format: { 1 (default) | 2 | ... | all }. 360 The parameter valid if only apic=debug or 361 apic=verbose is specified. 362 Example: apic=debug show_lapic=all 363 364 apm= [APM] Advanced Power Management 365 See header of arch/x86/kernel/apm_32.c. 366 367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 368 Format: <io>,<irq>,<nodeID> 369 370 ataflop= [HW,M68k] 371 372 atarimouse= [HW,MOUSE] Atari Mouse 373 374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 375 EzKey and similar keyboards 376 377 atkbd.reset= [HW] Reset keyboard during initialization 378 379 atkbd.set= [HW] Select keyboard code set 380 Format: <int> (2 = AT (default), 3 = PS/2) 381 382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 383 keyboards 384 385 atkbd.softraw= [HW] Choose between synthetic and real raw mode 386 Format: <bool> (0 = real, 1 = synthetic (default)) 387 388 atkbd.softrepeat= [HW] 389 Use software keyboard repeat 390 391 audit= [KNL] Enable the audit sub-system 392 Format: { "0" | "1" | "off" | "on" } 393 0 | off - kernel audit is disabled and can not be 394 enabled until the next reboot 395 unset - kernel audit is initialized but disabled and 396 will be fully enabled by the userspace auditd. 397 1 | on - kernel audit is initialized and partially 398 enabled, storing at most audit_backlog_limit 399 messages in RAM until it is fully enabled by the 400 userspace auditd. 401 Default: unset 402 403 audit_backlog_limit= [KNL] Set the audit queue size limit. 404 Format: <int> (must be >=0) 405 Default: 64 406 407 bau= [X86_UV] Enable the BAU on SGI UV. The default 408 behavior is to disable the BAU (i.e. bau=0). 409 Format: { "0" | "1" } 410 0 - Disable the BAU. 411 1 - Enable the BAU. 412 unset - Disable the BAU. 413 414 baycom_epp= [HW,AX25] 415 Format: <io>,<mode> 416 417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 418 Format: <io>,<mode> 419 See header of drivers/net/hamradio/baycom_par.c. 420 421 baycom_ser_fdx= [HW,AX25] 422 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 423 Format: <io>,<irq>,<mode>[,<baud>] 424 See header of drivers/net/hamradio/baycom_ser_fdx.c. 425 426 baycom_ser_hdx= [HW,AX25] 427 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 428 Format: <io>,<irq>,<mode> 429 See header of drivers/net/hamradio/baycom_ser_hdx.c. 430 431 blkdevparts= Manual partition parsing of block device(s) for 432 embedded devices based on command line input. 433 See Documentation/block/cmdline-partition.rst 434 435 boot_delay= Milliseconds to delay each printk during boot. 436 Values larger than 10 seconds (10000) are changed to 437 no delay (0). 438 Format: integer 439 440 bootmem_debug [KNL] Enable bootmem allocator debug messages. 441 442 bert_disable [ACPI] 443 Disable BERT OS support on buggy BIOSes. 444 445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 446 bttv.radio= Most important insmod options are available as 447 kernel args too. 448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst 449 bttv.tuner= 450 451 bulk_remove=off [PPC] This parameter disables the use of the pSeries 452 firmware feature for flushing multiple hpte entries 453 at a time. 454 455 c101= [NET] Moxa C101 synchronous serial card 456 457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 458 Sometimes CPU hardware bugs make them report the cache 459 size incorrectly. The kernel will attempt work arounds 460 to fix known problems, but for some CPUs it is not 461 possible to determine what the correct size should be. 462 This option provides an override for these situations. 463 464 carrier_timeout= 465 [NET] Specifies amount of time (in seconds) that 466 the kernel should wait for a network carrier. By default 467 it waits 120 seconds. 468 469 ca_keys= [KEYS] This parameter identifies a specific key(s) on 470 the system trusted keyring to be used for certificate 471 trust validation. 472 format: { id:<keyid> | builtin } 473 474 cca= [MIPS] Override the kernel pages' cache coherency 475 algorithm. Accepted values range from 0 to 7 476 inclusive. See arch/mips/include/asm/pgtable-bits.h 477 for platform specific values (SB1, Loongson3 and 478 others). 479 480 ccw_timeout_log [S390] 481 See Documentation/s390/common_io.rst for details. 482 483 cgroup_disable= [KNL] Disable a particular controller 484 Format: {name of the controller(s) to disable} 485 The effects of cgroup_disable=foo are: 486 - foo isn't auto-mounted if you mount all cgroups in 487 a single hierarchy 488 - foo isn't visible as an individually mountable 489 subsystem 490 {Currently only "memory" controller deal with this and 491 cut the overhead, others just disable the usage. So 492 only cgroup_disable=memory is actually worthy} 493 494 cgroup_no_v1= [KNL] Disable cgroup controllers and named hierarchies in v1 495 Format: { { controller | "all" | "named" } 496 [,{ controller | "all" | "named" }...] } 497 Like cgroup_disable, but only applies to cgroup v1; 498 the blacklisted controllers remain available in cgroup2. 499 "all" blacklists all controllers and "named" disables 500 named mounts. Specifying both "all" and "named" disables 501 all v1 hierarchies. 502 503 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 504 Format: <string> 505 nosocket -- Disable socket memory accounting. 506 nokmem -- Disable kernel memory accounting. 507 508 checkreqprot [SELINUX] Set initial checkreqprot flag value. 509 Format: { "0" | "1" } 510 See security/selinux/Kconfig help text. 511 0 -- check protection applied by kernel (includes 512 any implied execute protection). 513 1 -- check protection requested by application. 514 Default value is set via a kernel config option. 515 Value can be changed at runtime via 516 /selinux/checkreqprot. 517 518 cio_ignore= [S390] 519 See Documentation/s390/common_io.rst for details. 520 clk_ignore_unused 521 [CLK] 522 Prevents the clock framework from automatically gating 523 clocks that have not been explicitly enabled by a Linux 524 device driver but are enabled in hardware at reset or 525 by the bootloader/firmware. Note that this does not 526 force such clocks to be always-on nor does it reserve 527 those clocks in any way. This parameter is useful for 528 debug and development, but should not be needed on a 529 platform with proper driver support. For more 530 information, see Documentation/driver-api/clk.rst. 531 532 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 533 [Deprecated] 534 Forces specified clocksource (if available) to be used 535 when calculating gettimeofday(). If specified 536 clocksource is not available, it defaults to PIT. 537 Format: { pit | tsc | cyclone | pmtmr } 538 539 clocksource= Override the default clocksource 540 Format: <string> 541 Override the default clocksource and use the clocksource 542 with the name specified. 543 Some clocksource names to choose from, depending on 544 the platform: 545 [all] jiffies (this is the base, fallback clocksource) 546 [ACPI] acpi_pm 547 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 548 pxa_timer,timer3,32k_counter,timer0_1 549 [X86-32] pit,hpet,tsc; 550 scx200_hrt on Geode; cyclone on IBM x440 551 [MIPS] MIPS 552 [PARISC] cr16 553 [S390] tod 554 [SH] SuperH 555 [SPARC64] tick 556 [X86-64] hpet,tsc 557 558 clocksource.arm_arch_timer.evtstrm= 559 [ARM,ARM64] 560 Format: <bool> 561 Enable/disable the eventstream feature of the ARM 562 architected timer so that code using WFE-based polling 563 loops can be debugged more effectively on production 564 systems. 565 566 clearcpuid=BITNUM [X86] 567 Disable CPUID feature X for the kernel. See 568 arch/x86/include/asm/cpufeatures.h for the valid bit 569 numbers. Note the Linux specific bits are not necessarily 570 stable over kernel options, but the vendor specific 571 ones should be. 572 Also note that user programs calling CPUID directly 573 or using the feature without checking anything 574 will still see it. This just prevents it from 575 being used by the kernel or shown in /proc/cpuinfo. 576 Also note the kernel might malfunction if you disable 577 some critical bits. 578 579 cma=nn[MG]@[start[MG][-end[MG]]] 580 [ARM,X86,KNL] 581 Sets the size of kernel global memory area for 582 contiguous memory allocations and optionally the 583 placement constraint by the physical address range of 584 memory allocations. A value of 0 disables CMA 585 altogether. For more information, see 586 include/linux/dma-contiguous.h 587 588 cmo_free_hint= [PPC] Format: { yes | no } 589 Specify whether pages are marked as being inactive 590 when they are freed. This is used in CMO environments 591 to determine OS memory pressure for page stealing by 592 a hypervisor. 593 Default: yes 594 595 coherent_pool=nn[KMG] [ARM,KNL] 596 Sets the size of memory pool for coherent, atomic dma 597 allocations, by default set to 256K. 598 599 com20020= [HW,NET] ARCnet - COM20020 chipset 600 Format: 601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 602 603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 604 Format: <io>[,<irq>] 605 606 com90xx= [HW,NET] 607 ARCnet - COM90xx chipset (memory-mapped buffers) 608 Format: <io>[,<irq>[,<memstart>]] 609 610 condev= [HW,S390] console device 611 conmode= 612 613 console= [KNL] Output console device and options. 614 615 tty<n> Use the virtual console device <n>. 616 617 ttyS<n>[,options] 618 ttyUSB0[,options] 619 Use the specified serial port. The options are of 620 the form "bbbbpnf", where "bbbb" is the baud rate, 621 "p" is parity ("n", "o", or "e"), "n" is number of 622 bits, and "f" is flow control ("r" for RTS or 623 omit it). Default is "9600n8". 624 625 See Documentation/admin-guide/serial-console.rst for more 626 information. See 627 Documentation/networking/netconsole.txt for an 628 alternative. 629 630 uart[8250],io,<addr>[,options] 631 uart[8250],mmio,<addr>[,options] 632 uart[8250],mmio16,<addr>[,options] 633 uart[8250],mmio32,<addr>[,options] 634 uart[8250],0x<addr>[,options] 635 Start an early, polled-mode console on the 8250/16550 636 UART at the specified I/O port or MMIO address, 637 switching to the matching ttyS device later. 638 MMIO inter-register address stride is either 8-bit 639 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 641 to be equivalent to 'mmio'. 'options' are specified in 642 the same format described for ttyS above; if unspecified, 643 the h/w is not re-initialized. 644 645 hvc<n> Use the hypervisor console device <n>. This is for 646 both Xen and PowerPC hypervisors. 647 648 If the device connected to the port is not a TTY but a braille 649 device, prepend "brl," before the device type, for instance 650 console=brl,ttyS0 651 For now, only VisioBraille is supported. 652 653 console_msg_format= 654 [KNL] Change console messages format 655 default 656 By default we print messages on consoles in 657 "[time stamp] text\n" format (time stamp may not be 658 printed, depending on CONFIG_PRINTK_TIME or 659 `printk_time' param). 660 syslog 661 Switch to syslog format: "<%u>[time stamp] text\n" 662 IOW, each message will have a facility and loglevel 663 prefix. The format is similar to one used by syslog() 664 syscall, or to executing "dmesg -S --raw" or to reading 665 from /proc/kmsg. 666 667 consoleblank= [KNL] The console blank (screen saver) timeout in 668 seconds. A value of 0 disables the blank timer. 669 Defaults to 0. 670 671 coredump_filter= 672 [KNL] Change the default value for 673 /proc/<pid>/coredump_filter. 674 See also Documentation/filesystems/proc.txt. 675 676 coresight_cpu_debug.enable 677 [ARM,ARM64] 678 Format: <bool> 679 Enable/disable the CPU sampling based debugging. 680 0: default value, disable debugging 681 1: enable debugging at boot time 682 683 cpuidle.off=1 [CPU_IDLE] 684 disable the cpuidle sub-system 685 686 cpuidle.governor= 687 [CPU_IDLE] Name of the cpuidle governor to use. 688 689 cpufreq.off=1 [CPU_FREQ] 690 disable the cpufreq sub-system 691 692 cpu_init_udelay=N 693 [X86] Delay for N microsec between assert and de-assert 694 of APIC INIT to start processors. This delay occurs 695 on every CPU online, such as boot, and resume from suspend. 696 Default: 10000 697 698 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 699 Format: 700 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 701 702 crashkernel=size[KMG][@offset[KMG]] 703 [KNL] Using kexec, Linux can switch to a 'crash kernel' 704 upon panic. This parameter reserves the physical 705 memory region [offset, offset + size] for that kernel 706 image. If '@offset' is omitted, then a suitable offset 707 is selected automatically. 708 [KNL, x86_64] select a region under 4G first, and 709 fall back to reserve region above 4G when '@offset' 710 hasn't been specified. 711 See Documentation/admin-guide/kdump/kdump.rst for further details. 712 713 crashkernel=range1:size1[,range2:size2,...][@offset] 714 [KNL] Same as above, but depends on the memory 715 in the running system. The syntax of range is 716 start-[end] where start and end are both 717 a memory unit (amount[KMG]). See also 718 Documentation/admin-guide/kdump/kdump.rst for an example. 719 720 crashkernel=size[KMG],high 721 [KNL, x86_64] range could be above 4G. Allow kernel 722 to allocate physical memory region from top, so could 723 be above 4G if system have more than 4G ram installed. 724 Otherwise memory region will be allocated below 4G, if 725 available. 726 It will be ignored if crashkernel=X is specified. 727 crashkernel=size[KMG],low 728 [KNL, x86_64] range under 4G. When crashkernel=X,high 729 is passed, kernel could allocate physical memory region 730 above 4G, that cause second kernel crash on system 731 that require some amount of low memory, e.g. swiotlb 732 requires at least 64M+32K low memory, also enough extra 733 low memory is needed to make sure DMA buffers for 32-bit 734 devices won't run out. Kernel would try to allocate at 735 at least 256M below 4G automatically. 736 This one let user to specify own low range under 4G 737 for second kernel instead. 738 0: to disable low allocation. 739 It will be ignored when crashkernel=X,high is not used 740 or memory reserved is below 4G. 741 742 cryptomgr.notests 743 [KNL] Disable crypto self-tests 744 745 cs89x0_dma= [HW,NET] 746 Format: <dma> 747 748 cs89x0_media= [HW,NET] 749 Format: { rj45 | aui | bnc } 750 751 dasd= [HW,NET] 752 See header of drivers/s390/block/dasd_devmap.c. 753 754 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 755 (one device per port) 756 Format: <port#>,<type> 757 See also Documentation/input/devices/joystick-parport.rst 758 759 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 760 time. See 761 Documentation/admin-guide/dynamic-debug-howto.rst for 762 details. Deprecated, see dyndbg. 763 764 debug [KNL] Enable kernel debugging (events log level). 765 766 debug_boot_weak_hash 767 [KNL] Enable printing [hashed] pointers early in the 768 boot sequence. If enabled, we use a weak hash instead 769 of siphash to hash pointers. Use this option if you are 770 seeing instances of '(___ptrval___)') and need to see a 771 value (hashed pointer) instead. Cryptographically 772 insecure, please do not use on production kernels. 773 774 debug_locks_verbose= 775 [KNL] verbose self-tests 776 Format=<0|1> 777 Print debugging info while doing the locking API 778 self-tests. 779 We default to 0 (no extra messages), setting it to 780 1 will print _a lot_ more information - normally 781 only useful to kernel developers. 782 783 debug_objects [KNL] Enable object debugging 784 785 no_debug_objects 786 [KNL] Disable object debugging 787 788 debug_guardpage_minorder= 789 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 790 parameter allows control of the order of pages that will 791 be intentionally kept free (and hence protected) by the 792 buddy allocator. Bigger value increase the probability 793 of catching random memory corruption, but reduce the 794 amount of memory for normal system use. The maximum 795 possible value is MAX_ORDER/2. Setting this parameter 796 to 1 or 2 should be enough to identify most random 797 memory corruption problems caused by bugs in kernel or 798 driver code when a CPU writes to (or reads from) a 799 random memory location. Note that there exists a class 800 of memory corruptions problems caused by buggy H/W or 801 F/W or by drivers badly programing DMA (basically when 802 memory is written at bus level and the CPU MMU is 803 bypassed) which are not detectable by 804 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 805 tracking down these problems. 806 807 debug_pagealloc= 808 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter 809 enables the feature at boot time. By default, it is 810 disabled and the system will work mostly the same as a 811 kernel built without CONFIG_DEBUG_PAGEALLOC. 812 on: enable the feature 813 814 debugpat [X86] Enable PAT debugging 815 816 decnet.addr= [HW,NET] 817 Format: <area>[,<node>] 818 See also Documentation/networking/decnet.txt. 819 820 default_hugepagesz= 821 [same as hugepagesz=] The size of the default 822 HugeTLB page size. This is the size represented by 823 the legacy /proc/ hugepages APIs, used for SHM, and 824 default size when mounting hugetlbfs filesystems. 825 Defaults to the default architecture's huge page size 826 if not specified. 827 828 deferred_probe_timeout= 829 [KNL] Debugging option to set a timeout in seconds for 830 deferred probe to give up waiting on dependencies to 831 probe. Only specific dependencies (subsystems or 832 drivers) that have opted in will be ignored. A timeout of 0 833 will timeout at the end of initcalls. This option will also 834 dump out devices still on the deferred probe list after 835 retrying. 836 837 dhash_entries= [KNL] 838 Set number of hash buckets for dentry cache. 839 840 disable_1tb_segments [PPC] 841 Disables the use of 1TB hash page table segments. This 842 causes the kernel to fall back to 256MB segments which 843 can be useful when debugging issues that require an SLB 844 miss to occur. 845 846 disable= [IPV6] 847 See Documentation/networking/ipv6.txt. 848 849 hardened_usercopy= 850 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 851 hardening is enabled for this boot. Hardened 852 usercopy checking is used to protect the kernel 853 from reading or writing beyond known memory 854 allocation boundaries as a proactive defense 855 against bounds-checking flaws in the kernel's 856 copy_to_user()/copy_from_user() interface. 857 on Perform hardened usercopy checks (default). 858 off Disable hardened usercopy checks. 859 860 disable_radix [PPC] 861 Disable RADIX MMU mode on POWER9 862 863 disable_tlbie [PPC] 864 Disable TLBIE instruction. Currently does not work 865 with KVM, with HASH MMU, or with coherent accelerators. 866 867 disable_cpu_apicid= [X86,APIC,SMP] 868 Format: <int> 869 The number of initial APIC ID for the 870 corresponding CPU to be disabled at boot, 871 mostly used for the kdump 2nd kernel to 872 disable BSP to wake up multiple CPUs without 873 causing system reset or hang due to sending 874 INIT from AP to BSP. 875 876 perf_v4_pmi= [X86,INTEL] 877 Format: <bool> 878 Disable Intel PMU counter freezing feature. 879 The feature only exists starting from 880 Arch Perfmon v4 (Skylake and newer). 881 882 disable_ddw [PPC/PSERIES] 883 Disable Dynamic DMA Window support. Use this if 884 to workaround buggy firmware. 885 886 disable_ipv6= [IPV6] 887 See Documentation/networking/ipv6.txt. 888 889 disable_mtrr_cleanup [X86] 890 The kernel tries to adjust MTRR layout from continuous 891 to discrete, to make X server driver able to add WB 892 entry later. This parameter disables that. 893 894 disable_mtrr_trim [X86, Intel and AMD only] 895 By default the kernel will trim any uncacheable 896 memory out of your available memory pool based on 897 MTRR settings. This parameter disables that behavior, 898 possibly causing your machine to run very slowly. 899 900 disable_timer_pin_1 [X86] 901 Disable PIN 1 of APIC timer 902 Can be useful to work around chipset bugs. 903 904 dis_ucode_ldr [X86] Disable the microcode loader. 905 906 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 907 this option disables the debugging code at boot. 908 909 dma_debug_entries=<number> 910 This option allows to tune the number of preallocated 911 entries for DMA-API debugging code. One entry is 912 required per DMA-API allocation. Use this if the 913 DMA-API debugging code disables itself because the 914 architectural default is too low. 915 916 dma_debug_driver=<driver_name> 917 With this option the DMA-API debugging driver 918 filter feature can be enabled at boot time. Just 919 pass the driver to filter for as the parameter. 920 The filter can be disabled or changed to another 921 driver later using sysfs. 922 923 driver_async_probe= [KNL] 924 List of driver names to be probed asynchronously. 925 Format: <driver_name1>,<driver_name2>... 926 927 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 928 Broken monitors, graphic adapters, KVMs and EDIDless 929 panels may send no or incorrect EDID data sets. 930 This parameter allows to specify an EDID data sets 931 in the /lib/firmware directory that are used instead. 932 Generic built-in EDID data sets are used, if one of 933 edid/1024x768.bin, edid/1280x1024.bin, 934 edid/1680x1050.bin, or edid/1920x1080.bin is given 935 and no file with the same name exists. Details and 936 instructions how to build your own EDID data are 937 available in Documentation/driver-api/edid.rst. An EDID 938 data set will only be used for a particular connector, 939 if its name and a colon are prepended to the EDID 940 name. Each connector may use a unique EDID data 941 set by separating the files with a comma. An EDID 942 data set with no connector name will be used for 943 any connectors not explicitly specified. 944 945 dscc4.setup= [NET] 946 947 dt_cpu_ftrs= [PPC] 948 Format: {"off" | "known"} 949 Control how the dt_cpu_ftrs device-tree binding is 950 used for CPU feature discovery and setup (if it 951 exists). 952 off: Do not use it, fall back to legacy cpu table. 953 known: Do not pass through unknown features to guests 954 or userspace, only those that the kernel is aware of. 955 956 dump_apple_properties [X86] 957 Dump name and content of EFI device properties on 958 x86 Macs. Useful for driver authors to determine 959 what data is available or for reverse-engineering. 960 961 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 962 module.dyndbg[="val"] 963 Enable debug messages at boot time. See 964 Documentation/admin-guide/dynamic-debug-howto.rst 965 for details. 966 967 nompx [X86] Disables Intel Memory Protection Extensions. 968 See Documentation/x86/intel_mpx.rst for more 969 information about the feature. 970 971 nopku [X86] Disable Memory Protection Keys CPU feature found 972 in some Intel CPUs. 973 974 module.async_probe [KNL] 975 Enable asynchronous probe on this module. 976 977 early_ioremap_debug [KNL] 978 Enable debug messages in early_ioremap support. This 979 is useful for tracking down temporary early mappings 980 which are not unmapped. 981 982 earlycon= [KNL] Output early console device and options. 983 984 [ARM64] The early console is determined by the 985 stdout-path property in device tree's chosen node, 986 or determined by the ACPI SPCR table. 987 988 [X86] When used with no options the early console is 989 determined by the ACPI SPCR table. 990 991 cdns,<addr>[,options] 992 Start an early, polled-mode console on a Cadence 993 (xuartps) serial port at the specified address. Only 994 supported option is baud rate. If baud rate is not 995 specified, the serial port must already be setup and 996 configured. 997 998 uart[8250],io,<addr>[,options] 999 uart[8250],mmio,<addr>[,options] 1000 uart[8250],mmio32,<addr>[,options] 1001 uart[8250],mmio32be,<addr>[,options] 1002 uart[8250],0x<addr>[,options] 1003 Start an early, polled-mode console on the 8250/16550 1004 UART at the specified I/O port or MMIO address. 1005 MMIO inter-register address stride is either 8-bit 1006 (mmio) or 32-bit (mmio32 or mmio32be). 1007 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 1008 to be equivalent to 'mmio'. 'options' are specified 1009 in the same format described for "console=ttyS<n>"; if 1010 unspecified, the h/w is not initialized. 1011 1012 pl011,<addr> 1013 pl011,mmio32,<addr> 1014 Start an early, polled-mode console on a pl011 serial 1015 port at the specified address. The pl011 serial port 1016 must already be setup and configured. Options are not 1017 yet supported. If 'mmio32' is specified, then only 1018 the driver will use only 32-bit accessors to read/write 1019 the device registers. 1020 1021 meson,<addr> 1022 Start an early, polled-mode console on a meson serial 1023 port at the specified address. The serial port must 1024 already be setup and configured. Options are not yet 1025 supported. 1026 1027 msm_serial,<addr> 1028 Start an early, polled-mode console on an msm serial 1029 port at the specified address. The serial port 1030 must already be setup and configured. Options are not 1031 yet supported. 1032 1033 msm_serial_dm,<addr> 1034 Start an early, polled-mode console on an msm serial 1035 dm port at the specified address. The serial port 1036 must already be setup and configured. Options are not 1037 yet supported. 1038 1039 owl,<addr> 1040 Start an early, polled-mode console on a serial port 1041 of an Actions Semi SoC, such as S500 or S900, at the 1042 specified address. The serial port must already be 1043 setup and configured. Options are not yet supported. 1044 1045 rda,<addr> 1046 Start an early, polled-mode console on a serial port 1047 of an RDA Micro SoC, such as RDA8810PL, at the 1048 specified address. The serial port must already be 1049 setup and configured. Options are not yet supported. 1050 1051 sbi 1052 Use RISC-V SBI (Supervisor Binary Interface) for early 1053 console. 1054 1055 smh Use ARM semihosting calls for early console. 1056 1057 s3c2410,<addr> 1058 s3c2412,<addr> 1059 s3c2440,<addr> 1060 s3c6400,<addr> 1061 s5pv210,<addr> 1062 exynos4210,<addr> 1063 Use early console provided by serial driver available 1064 on Samsung SoCs, requires selecting proper type and 1065 a correct base address of the selected UART port. The 1066 serial port must already be setup and configured. 1067 Options are not yet supported. 1068 1069 lantiq,<addr> 1070 Start an early, polled-mode console on a lantiq serial 1071 (lqasc) port at the specified address. The serial port 1072 must already be setup and configured. Options are not 1073 yet supported. 1074 1075 lpuart,<addr> 1076 lpuart32,<addr> 1077 Use early console provided by Freescale LP UART driver 1078 found on Freescale Vybrid and QorIQ LS1021A processors. 1079 A valid base address must be provided, and the serial 1080 port must already be setup and configured. 1081 1082 ar3700_uart,<addr> 1083 Start an early, polled-mode console on the 1084 Armada 3700 serial port at the specified 1085 address. The serial port must already be setup 1086 and configured. Options are not yet supported. 1087 1088 qcom_geni,<addr> 1089 Start an early, polled-mode console on a Qualcomm 1090 Generic Interface (GENI) based serial port at the 1091 specified address. The serial port must already be 1092 setup and configured. Options are not yet supported. 1093 1094 efifb,[options] 1095 Start an early, unaccelerated console on the EFI 1096 memory mapped framebuffer (if available). On cache 1097 coherent non-x86 systems that use system memory for 1098 the framebuffer, pass the 'ram' option so that it is 1099 mapped with the correct attributes. 1100 1101 linflex,<addr> 1102 Use early console provided by Freescale LinFlex UART 1103 serial driver for NXP S32V234 SoCs. A valid base 1104 address must be provided, and the serial port must 1105 already be setup and configured. 1106 1107 earlyprintk= [X86,SH,ARM,M68k,S390] 1108 earlyprintk=vga 1109 earlyprintk=sclp 1110 earlyprintk=xen 1111 earlyprintk=serial[,ttySn[,baudrate]] 1112 earlyprintk=serial[,0x...[,baudrate]] 1113 earlyprintk=ttySn[,baudrate] 1114 earlyprintk=dbgp[debugController#] 1115 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1116 earlyprintk=xdbc[xhciController#] 1117 1118 earlyprintk is useful when the kernel crashes before 1119 the normal console is initialized. It is not enabled by 1120 default because it has some cosmetic problems. 1121 1122 Append ",keep" to not disable it when the real console 1123 takes over. 1124 1125 Only one of vga, efi, serial, or usb debug port can 1126 be used at a time. 1127 1128 Currently only ttyS0 and ttyS1 may be specified by 1129 name. Other I/O ports may be explicitly specified 1130 on some architectures (x86 and arm at least) by 1131 replacing ttySn with an I/O port address, like this: 1132 earlyprintk=serial,0x1008,115200 1133 You can find the port for a given device in 1134 /proc/tty/driver/serial: 1135 2: uart:ST16650V2 port:00001008 irq:18 ... 1136 1137 Interaction with the standard serial driver is not 1138 very good. 1139 1140 The VGA and EFI output is eventually overwritten by 1141 the real console. 1142 1143 The xen output can only be used by Xen PV guests. 1144 1145 The sclp output can only be used on s390. 1146 1147 The optional "force" to "pciserial" enables use of a 1148 PCI device even when its classcode is not of the 1149 UART class. 1150 1151 edac_report= [HW,EDAC] Control how to report EDAC event 1152 Format: {"on" | "off" | "force"} 1153 on: enable EDAC to report H/W event. May be overridden 1154 by other higher priority error reporting module. 1155 off: disable H/W event reporting through EDAC. 1156 force: enforce the use of EDAC to report H/W event. 1157 default: on. 1158 1159 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1160 ekgdboc=kbd 1161 1162 This is designed to be used in conjunction with 1163 the boot argument: earlyprintk=vga 1164 1165 edd= [EDD] 1166 Format: {"off" | "on" | "skip[mbr]"} 1167 1168 efi= [EFI] 1169 Format: { "old_map", "nochunk", "noruntime", "debug" } 1170 old_map [X86-64]: switch to the old ioremap-based EFI 1171 runtime services mapping. 32-bit still uses this one by 1172 default. 1173 nochunk: disable reading files in "chunks" in the EFI 1174 boot stub, as chunking can cause problems with some 1175 firmware implementations. 1176 noruntime : disable EFI runtime services support 1177 debug: enable misc debug output 1178 1179 efi_no_storage_paranoia [EFI; X86] 1180 Using this parameter you can use more than 50% of 1181 your efi variable storage. Use this parameter only if 1182 you are really sure that your UEFI does sane gc and 1183 fulfills the spec otherwise your board may brick. 1184 1185 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1186 Add arbitrary attribute to specific memory range by 1187 updating original EFI memory map. 1188 Region of memory which aa attribute is added to is 1189 from ss to ss+nn. 1190 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1191 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1192 attribute is added to range 0x100000000-0x180000000 and 1193 0x10a0000000-0x1120000000. 1194 1195 Using this parameter you can do debugging of EFI memmap 1196 related feature. For example, you can do debugging of 1197 Address Range Mirroring feature even if your box 1198 doesn't support it. 1199 1200 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1201 that is to be dynamically loaded by Linux. If there are 1202 multiple variables with the same name but with different 1203 vendor GUIDs, all of them will be loaded. See 1204 Documentation/admin-guide/acpi/ssdt-overlays.rst for details. 1205 1206 1207 eisa_irq_edge= [PARISC,HW] 1208 See header of drivers/parisc/eisa.c. 1209 1210 elanfreq= [X86-32] 1211 See comment before function elanfreq_setup() in 1212 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1213 1214 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1215 Specifies physical address of start of kernel core 1216 image elf header and optionally the size. Generally 1217 kexec loader will pass this option to capture kernel. 1218 See Documentation/admin-guide/kdump/kdump.rst for details. 1219 1220 enable_mtrr_cleanup [X86] 1221 The kernel tries to adjust MTRR layout from continuous 1222 to discrete, to make X server driver able to add WB 1223 entry later. This parameter enables that. 1224 1225 enable_timer_pin_1 [X86] 1226 Enable PIN 1 of APIC timer 1227 Can be useful to work around chipset bugs 1228 (in particular on some ATI chipsets). 1229 The kernel tries to set a reasonable default. 1230 1231 enforcing [SELINUX] Set initial enforcing status. 1232 Format: {"0" | "1"} 1233 See security/selinux/Kconfig help text. 1234 0 -- permissive (log only, no denials). 1235 1 -- enforcing (deny and log). 1236 Default value is 0. 1237 Value can be changed at runtime via /selinux/enforce. 1238 1239 erst_disable [ACPI] 1240 Disable Error Record Serialization Table (ERST) 1241 support. 1242 1243 ether= [HW,NET] Ethernet cards parameters 1244 This option is obsoleted by the "netdev=" option, which 1245 has equivalent usage. See its documentation for details. 1246 1247 evm= [EVM] 1248 Format: { "fix" } 1249 Permit 'security.evm' to be updated regardless of 1250 current integrity status. 1251 1252 failslab= 1253 fail_page_alloc= 1254 fail_make_request=[KNL] 1255 General fault injection mechanism. 1256 Format: <interval>,<probability>,<space>,<times> 1257 See also Documentation/fault-injection/. 1258 1259 floppy= [HW] 1260 See Documentation/admin-guide/blockdev/floppy.rst. 1261 1262 force_pal_cache_flush 1263 [IA-64] Avoid check_sal_cache_flush which may hang on 1264 buggy SAL_CACHE_FLUSH implementations. Using this 1265 parameter will force ia64_sal_cache_flush to call 1266 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1267 1268 forcepae [X86-32] 1269 Forcefully enable Physical Address Extension (PAE). 1270 Many Pentium M systems disable PAE but may have a 1271 functionally usable PAE implementation. 1272 Warning: use of this parameter will taint the kernel 1273 and may cause unknown problems. 1274 1275 ftrace=[tracer] 1276 [FTRACE] will set and start the specified tracer 1277 as early as possible in order to facilitate early 1278 boot debugging. 1279 1280 ftrace_dump_on_oops[=orig_cpu] 1281 [FTRACE] will dump the trace buffers on oops. 1282 If no parameter is passed, ftrace will dump 1283 buffers of all CPUs, but if you pass orig_cpu, it will 1284 dump only the buffer of the CPU that triggered the 1285 oops. 1286 1287 ftrace_filter=[function-list] 1288 [FTRACE] Limit the functions traced by the function 1289 tracer at boot up. function-list is a comma separated 1290 list of functions. This list can be changed at run 1291 time by the set_ftrace_filter file in the debugfs 1292 tracing directory. 1293 1294 ftrace_notrace=[function-list] 1295 [FTRACE] Do not trace the functions specified in 1296 function-list. This list can be changed at run time 1297 by the set_ftrace_notrace file in the debugfs 1298 tracing directory. 1299 1300 ftrace_graph_filter=[function-list] 1301 [FTRACE] Limit the top level callers functions traced 1302 by the function graph tracer at boot up. 1303 function-list is a comma separated list of functions 1304 that can be changed at run time by the 1305 set_graph_function file in the debugfs tracing directory. 1306 1307 ftrace_graph_notrace=[function-list] 1308 [FTRACE] Do not trace from the functions specified in 1309 function-list. This list is a comma separated list of 1310 functions that can be changed at run time by the 1311 set_graph_notrace file in the debugfs tracing directory. 1312 1313 ftrace_graph_max_depth=<uint> 1314 [FTRACE] Used with the function graph tracer. This is 1315 the max depth it will trace into a function. This value 1316 can be changed at run time by the max_graph_depth file 1317 in the tracefs tracing directory. default: 0 (no limit) 1318 1319 gamecon.map[2|3]= 1320 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1321 support via parallel port (up to 5 devices per port) 1322 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1323 See also Documentation/input/devices/joystick-parport.rst 1324 1325 gamma= [HW,DRM] 1326 1327 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1328 Format: off | on 1329 default: on 1330 1331 gcov_persist= [GCOV] When non-zero (default), profiling data for 1332 kernel modules is saved and remains accessible via 1333 debugfs, even when the module is unloaded/reloaded. 1334 When zero, profiling data is discarded and associated 1335 debugfs files are removed at module unload time. 1336 1337 goldfish [X86] Enable the goldfish android emulator platform. 1338 Don't use this when you are not running on the 1339 android emulator 1340 1341 gpt [EFI] Forces disk with valid GPT signature but 1342 invalid Protective MBR to be treated as GPT. If the 1343 primary GPT is corrupted, it enables the backup/alternate 1344 GPT to be used instead. 1345 1346 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1347 the "Enable 0" bit of the configuration register. 1348 Format: 0 | 1 1349 Default: 0 1350 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1351 the "Enable 0" bit of the configuration register. 1352 Format: 0 | 1 1353 Default: 0 1354 grcan.select= [HW] Select which physical interface to use. 1355 Format: 0 | 1 1356 Default: 0 1357 grcan.txsize= [HW] Sets the size of the tx buffer. 1358 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1359 Default: 1024 1360 grcan.rxsize= [HW] Sets the size of the rx buffer. 1361 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1362 Default: 1024 1363 1364 gpio-mockup.gpio_mockup_ranges 1365 [HW] Sets the ranges of gpiochip of for this device. 1366 Format: <start1>,<end1>,<start2>,<end2>... 1367 1368 hardlockup_all_cpu_backtrace= 1369 [KNL] Should the hard-lockup detector generate 1370 backtraces on all cpus. 1371 Format: <integer> 1372 1373 hashdist= [KNL,NUMA] Large hashes allocated during boot 1374 are distributed across NUMA nodes. Defaults on 1375 for 64-bit NUMA, off otherwise. 1376 Format: 0 | 1 (for off | on) 1377 1378 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1379 1380 hd= [EIDE] (E)IDE hard drive subsystem geometry 1381 Format: <cyl>,<head>,<sect> 1382 1383 hest_disable [ACPI] 1384 Disable Hardware Error Source Table (HEST) support; 1385 corresponding firmware-first mode error processing 1386 logic will be disabled. 1387 1388 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1389 size of <nn>. This works even on boxes that have no 1390 highmem otherwise. This also works to reduce highmem 1391 size on bigger boxes. 1392 1393 highres= [KNL] Enable/disable high resolution timer mode. 1394 Valid parameters: "on", "off" 1395 Default: "on" 1396 1397 hlt [BUGS=ARM,SH] 1398 1399 hpet= [X86-32,HPET] option to control HPET usage 1400 Format: { enable (default) | disable | force | 1401 verbose } 1402 disable: disable HPET and use PIT instead 1403 force: allow force enabled of undocumented chips (ICH4, 1404 VIA, nVidia) 1405 verbose: show contents of HPET registers during setup 1406 1407 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1408 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1409 1410 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1411 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1412 On x86-64 and powerpc, this option can be specified 1413 multiple times interleaved with hugepages= to reserve 1414 huge pages of different sizes. Valid pages sizes on 1415 x86-64 are 2M (when the CPU supports "pse") and 1G 1416 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1417 1418 hung_task_panic= 1419 [KNL] Should the hung task detector generate panics. 1420 Format: <integer> 1421 1422 A nonzero value instructs the kernel to panic when a 1423 hung task is detected. The default value is controlled 1424 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1425 option. The value selected by this boot parameter can 1426 be changed later by the kernel.hung_task_panic sysctl. 1427 1428 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1429 terminal devices. Valid values: 0..8 1430 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1431 If specified, z/VM IUCV HVC accepts connections 1432 from listed z/VM user IDs only. 1433 1434 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1435 which allow the hypervisor to 'idle' the 1436 guest on lock contention. 1437 1438 keep_bootcon [KNL] 1439 Do not unregister boot console at start. This is only 1440 useful for debugging when something happens in the window 1441 between unregistering the boot console and initializing 1442 the real console. 1443 1444 i2c_bus= [HW] Override the default board specific I2C bus speed 1445 or register an additional I2C bus that is not 1446 registered from board initialization code. 1447 Format: 1448 <bus_id>,<clkrate> 1449 1450 i8042.debug [HW] Toggle i8042 debug mode 1451 i8042.unmask_kbd_data 1452 [HW] Enable printing of interrupt data from the KBD port 1453 (disabled by default, and as a pre-condition 1454 requires that i8042.debug=1 be enabled) 1455 i8042.direct [HW] Put keyboard port into non-translated mode 1456 i8042.dumbkbd [HW] Pretend that controller can only read data from 1457 keyboard and cannot control its state 1458 (Don't attempt to blink the leds) 1459 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1460 i8042.nokbd [HW] Don't check/create keyboard port 1461 i8042.noloop [HW] Disable the AUX Loopback command while probing 1462 for the AUX port 1463 i8042.nomux [HW] Don't check presence of an active multiplexing 1464 controller 1465 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1466 controllers 1467 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1468 i8042.reset [HW] Reset the controller during init, cleanup and 1469 suspend-to-ram transitions, only during s2r 1470 transitions, or never reset 1471 Format: { 1 | Y | y | 0 | N | n } 1472 1, Y, y: always reset controller 1473 0, N, n: don't ever reset controller 1474 Default: only on s2r transitions on x86; most other 1475 architectures force reset to be always executed 1476 i8042.unlock [HW] Unlock (ignore) the keylock 1477 i8042.kbdreset [HW] Reset device connected to KBD port 1478 1479 i810= [HW,DRM] 1480 1481 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1482 indicates that the driver is running on unsupported 1483 hardware. 1484 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1485 does not match list of supported models. 1486 i8k.power_status 1487 [HW] Report power status in /proc/i8k 1488 (disabled by default) 1489 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1490 capability is set. 1491 1492 i915.invert_brightness= 1493 [DRM] Invert the sense of the variable that is used to 1494 set the brightness of the panel backlight. Normally a 1495 brightness value of 0 indicates backlight switched off, 1496 and the maximum of the brightness value sets the backlight 1497 to maximum brightness. If this parameter is set to 0 1498 (default) and the machine requires it, or this parameter 1499 is set to 1, a brightness value of 0 sets the backlight 1500 to maximum brightness, and the maximum of the brightness 1501 value switches the backlight off. 1502 -1 -- never invert brightness 1503 0 -- machine default 1504 1 -- force brightness inversion 1505 1506 icn= [HW,ISDN] 1507 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1508 1509 ide-core.nodma= [HW] (E)IDE subsystem 1510 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1511 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1512 .cdrom .chs .ignore_cable are additional options 1513 See Documentation/ide/ide.rst. 1514 1515 ide-generic.probe-mask= [HW] (E)IDE subsystem 1516 Format: <int> 1517 Probe mask for legacy ISA IDE ports. Depending on 1518 platform up to 6 ports are supported, enabled by 1519 setting corresponding bits in the mask to 1. The 1520 default value is 0x0, which has a special meaning. 1521 On systems that have PCI, it triggers scanning the 1522 PCI bus for the first and the second port, which 1523 are then probed. On systems without PCI the value 1524 of 0x0 enables probing the two first ports as if it 1525 was 0x3. 1526 1527 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1528 Claim all unknown PCI IDE storage controllers. 1529 1530 idle= [X86] 1531 Format: idle=poll, idle=halt, idle=nomwait 1532 Poll forces a polling idle loop that can slightly 1533 improve the performance of waking up a idle CPU, but 1534 will use a lot of power and make the system run hot. 1535 Not recommended. 1536 idle=halt: Halt is forced to be used for CPU idle. 1537 In such case C2/C3 won't be used again. 1538 idle=nomwait: Disable mwait for CPU C-states 1539 1540 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1541 Format: { strict | legacy | 2008 | relaxed } 1542 Default: strict 1543 1544 Choose which programs will be accepted for execution 1545 based on the IEEE 754 NaN encoding(s) supported by 1546 the FPU and the NaN encoding requested with the value 1547 of an ELF file header flag individually set by each 1548 binary. Hardware implementations are permitted to 1549 support either or both of the legacy and the 2008 NaN 1550 encoding mode. 1551 1552 Available settings are as follows: 1553 strict accept binaries that request a NaN encoding 1554 supported by the FPU 1555 legacy only accept legacy-NaN binaries, if supported 1556 by the FPU 1557 2008 only accept 2008-NaN binaries, if supported 1558 by the FPU 1559 relaxed accept any binaries regardless of whether 1560 supported by the FPU 1561 1562 The FPU emulator is always able to support both NaN 1563 encodings, so if no FPU hardware is present or it has 1564 been disabled with 'nofpu', then the settings of 1565 'legacy' and '2008' strap the emulator accordingly, 1566 'relaxed' straps the emulator for both legacy-NaN and 1567 2008-NaN, whereas 'strict' enables legacy-NaN only on 1568 legacy processors and both NaN encodings on MIPS32 or 1569 MIPS64 CPUs. 1570 1571 The setting for ABS.fmt/NEG.fmt instruction execution 1572 mode generally follows that for the NaN encoding, 1573 except where unsupported by hardware. 1574 1575 ignore_loglevel [KNL] 1576 Ignore loglevel setting - this will print /all/ 1577 kernel messages to the console. Useful for debugging. 1578 We also add it as printk module parameter, so users 1579 could change it dynamically, usually by 1580 /sys/module/printk/parameters/ignore_loglevel. 1581 1582 ignore_rlimit_data 1583 Ignore RLIMIT_DATA setting for data mappings, 1584 print warning at first misuse. Can be changed via 1585 /sys/module/kernel/parameters/ignore_rlimit_data. 1586 1587 ihash_entries= [KNL] 1588 Set number of hash buckets for inode cache. 1589 1590 ima_appraise= [IMA] appraise integrity measurements 1591 Format: { "off" | "enforce" | "fix" | "log" } 1592 default: "enforce" 1593 1594 ima_appraise_tcb [IMA] Deprecated. Use ima_policy= instead. 1595 The builtin appraise policy appraises all files 1596 owned by uid=0. 1597 1598 ima_canonical_fmt [IMA] 1599 Use the canonical format for the binary runtime 1600 measurements, instead of host native format. 1601 1602 ima_hash= [IMA] 1603 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1604 | sha512 | ... } 1605 default: "sha1" 1606 1607 The list of supported hash algorithms is defined 1608 in crypto/hash_info.h. 1609 1610 ima_policy= [IMA] 1611 The builtin policies to load during IMA setup. 1612 Format: "tcb | appraise_tcb | secure_boot | 1613 fail_securely" 1614 1615 The "tcb" policy measures all programs exec'd, files 1616 mmap'd for exec, and all files opened with the read 1617 mode bit set by either the effective uid (euid=0) or 1618 uid=0. 1619 1620 The "appraise_tcb" policy appraises the integrity of 1621 all files owned by root. 1622 1623 The "secure_boot" policy appraises the integrity 1624 of files (eg. kexec kernel image, kernel modules, 1625 firmware, policy, etc) based on file signatures. 1626 1627 The "fail_securely" policy forces file signature 1628 verification failure also on privileged mounted 1629 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1630 flag. 1631 1632 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1633 Load a policy which meets the needs of the Trusted 1634 Computing Base. This means IMA will measure all 1635 programs exec'd, files mmap'd for exec, and all files 1636 opened for read by uid=0. 1637 1638 ima_template= [IMA] 1639 Select one of defined IMA measurements template formats. 1640 Formats: { "ima" | "ima-ng" | "ima-sig" } 1641 Default: "ima-ng" 1642 1643 ima_template_fmt= 1644 [IMA] Define a custom template format. 1645 Format: { "field1|...|fieldN" } 1646 1647 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1648 Format: <min_file_size> 1649 Set the minimal file size for using asynchronous hash. 1650 If left unspecified, ahash usage is disabled. 1651 1652 ahash performance varies for different data sizes on 1653 different crypto accelerators. This option can be used 1654 to achieve the best performance for a particular HW. 1655 1656 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1657 Format: <bufsize> 1658 Set hashing buffer size. Default: 4k. 1659 1660 ahash performance varies for different chunk sizes on 1661 different crypto accelerators. This option can be used 1662 to achieve best performance for particular HW. 1663 1664 init= [KNL] 1665 Format: <full_path> 1666 Run specified binary instead of /sbin/init as init 1667 process. 1668 1669 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1670 for working out where the kernel is dying during 1671 startup. 1672 1673 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1674 initcall functions. Useful for debugging built-in 1675 modules and initcalls. 1676 1677 initrd= [BOOT] Specify the location of the initial ramdisk 1678 1679 init_on_alloc= [MM] Fill newly allocated pages and heap objects with 1680 zeroes. 1681 Format: 0 | 1 1682 Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON. 1683 1684 init_on_free= [MM] Fill freed pages and heap objects with zeroes. 1685 Format: 0 | 1 1686 Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON. 1687 1688 init_pkru= [x86] Specify the default memory protection keys rights 1689 register contents for all processes. 0x55555554 by 1690 default (disallow access to all but pkey 0). Can 1691 override in debugfs after boot. 1692 1693 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1694 Format: <irq> 1695 1696 int_pln_enable [x86] Enable power limit notification interrupt 1697 1698 integrity_audit=[IMA] 1699 Format: { "0" | "1" } 1700 0 -- basic integrity auditing messages. (Default) 1701 1 -- additional integrity auditing messages. 1702 1703 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1704 on 1705 Enable intel iommu driver. 1706 off 1707 Disable intel iommu driver. 1708 igfx_off [Default Off] 1709 By default, gfx is mapped as normal device. If a gfx 1710 device has a dedicated DMAR unit, the DMAR unit is 1711 bypassed by not enabling DMAR with this option. In 1712 this case, gfx device will use physical address for 1713 DMA. 1714 forcedac [x86_64] 1715 With this option iommu will not optimize to look 1716 for io virtual address below 32-bit forcing dual 1717 address cycle on pci bus for cards supporting greater 1718 than 32-bit addressing. The default is to look 1719 for translation below 32-bit and if not available 1720 then look in the higher range. 1721 strict [Default Off] 1722 With this option on every unmap_single operation will 1723 result in a hardware IOTLB flush operation as opposed 1724 to batching them for performance. 1725 sp_off [Default Off] 1726 By default, super page will be supported if Intel IOMMU 1727 has the capability. With this option, super page will 1728 not be supported. 1729 sm_on [Default Off] 1730 By default, scalable mode will be disabled even if the 1731 hardware advertises that it has support for the scalable 1732 mode translation. With this option set, scalable mode 1733 will be used on hardware which claims to support it. 1734 tboot_noforce [Default Off] 1735 Do not force the Intel IOMMU enabled under tboot. 1736 By default, tboot will force Intel IOMMU on, which 1737 could harm performance of some high-throughput 1738 devices like 40GBit network cards, even if identity 1739 mapping is enabled. 1740 Note that using this option lowers the security 1741 provided by tboot because it makes the system 1742 vulnerable to DMA attacks. 1743 nobounce [Default off] 1744 Disable bounce buffer for unstrusted devices such as 1745 the Thunderbolt devices. This will treat the untrusted 1746 devices as the trusted ones, hence might expose security 1747 risks of DMA attacks. 1748 1749 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1750 0 disables intel_idle and fall back on acpi_idle. 1751 1 to 9 specify maximum depth of C-state. 1752 1753 intel_pstate= [X86] 1754 disable 1755 Do not enable intel_pstate as the default 1756 scaling driver for the supported processors 1757 passive 1758 Use intel_pstate as a scaling driver, but configure it 1759 to work with generic cpufreq governors (instead of 1760 enabling its internal governor). This mode cannot be 1761 used along with the hardware-managed P-states (HWP) 1762 feature. 1763 force 1764 Enable intel_pstate on systems that prohibit it by default 1765 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1766 instead of acpi-cpufreq may disable platform features, such 1767 as thermal controls and power capping, that rely on ACPI 1768 P-States information being indicated to OSPM and therefore 1769 should be used with caution. This option does not work with 1770 processors that aren't supported by the intel_pstate driver 1771 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1772 no_hwp 1773 Do not enable hardware P state control (HWP) 1774 if available. 1775 hwp_only 1776 Only load intel_pstate on systems which support 1777 hardware P state control (HWP) if available. 1778 support_acpi_ppc 1779 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1780 Description Table, specifies preferred power management 1781 profile as "Enterprise Server" or "Performance Server", 1782 then this feature is turned on by default. 1783 per_cpu_perf_limits 1784 Allow per-logical-CPU P-State performance control limits using 1785 cpufreq sysfs interface 1786 1787 intremap= [X86-64, Intel-IOMMU] 1788 on enable Interrupt Remapping (default) 1789 off disable Interrupt Remapping 1790 nosid disable Source ID checking 1791 no_x2apic_optout 1792 BIOS x2APIC opt-out request will be ignored 1793 nopost disable Interrupt Posting 1794 1795 iomem= Disable strict checking of access to MMIO memory 1796 strict regions from userspace. 1797 relaxed 1798 1799 iommu= [x86] 1800 off 1801 force 1802 noforce 1803 biomerge 1804 panic 1805 nopanic 1806 merge 1807 nomerge 1808 soft 1809 pt [x86] 1810 nopt [x86] 1811 nobypass [PPC/POWERNV] 1812 Disable IOMMU bypass, using IOMMU for PCI devices. 1813 1814 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1815 Format: { "0" | "1" } 1816 0 - Lazy mode. 1817 Request that DMA unmap operations use deferred 1818 invalidation of hardware TLBs, for increased 1819 throughput at the cost of reduced device isolation. 1820 Will fall back to strict mode if not supported by 1821 the relevant IOMMU driver. 1822 1 - Strict mode (default). 1823 DMA unmap operations invalidate IOMMU hardware TLBs 1824 synchronously. 1825 1826 iommu.passthrough= 1827 [ARM64, X86] Configure DMA to bypass the IOMMU by default. 1828 Format: { "0" | "1" } 1829 0 - Use IOMMU translation for DMA. 1830 1 - Bypass the IOMMU for DMA. 1831 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1832 1833 io7= [HW] IO7 for Marvel based alpha systems 1834 See comment before marvel_specify_io7 in 1835 arch/alpha/kernel/core_marvel.c. 1836 1837 io_delay= [X86] I/O delay method 1838 0x80 1839 Standard port 0x80 based delay 1840 0xed 1841 Alternate port 0xed based delay (needed on some systems) 1842 udelay 1843 Simple two microseconds delay 1844 none 1845 No delay 1846 1847 ip= [IP_PNP] 1848 See Documentation/filesystems/nfs/nfsroot.txt. 1849 1850 ipcmni_extend [KNL] Extend the maximum number of unique System V 1851 IPC identifiers from 32,768 to 16,777,216. 1852 1853 irqaffinity= [SMP] Set the default irq affinity mask 1854 The argument is a cpu list, as described above. 1855 1856 irqchip.gicv2_force_probe= 1857 [ARM, ARM64] 1858 Format: <bool> 1859 Force the kernel to look for the second 4kB page 1860 of a GICv2 controller even if the memory range 1861 exposed by the device tree is too small. 1862 1863 irqchip.gicv3_nolpi= 1864 [ARM, ARM64] 1865 Force the kernel to ignore the availability of 1866 LPIs (and by consequence ITSs). Intended for system 1867 that use the kernel as a bootloader, and thus want 1868 to let secondary kernels in charge of setting up 1869 LPIs. 1870 1871 irqchip.gicv3_pseudo_nmi= [ARM64] 1872 Enables support for pseudo-NMIs in the kernel. This 1873 requires the kernel to be built with 1874 CONFIG_ARM64_PSEUDO_NMI. 1875 1876 irqfixup [HW] 1877 When an interrupt is not handled search all handlers 1878 for it. Intended to get systems with badly broken 1879 firmware running. 1880 1881 irqpoll [HW] 1882 When an interrupt is not handled search all handlers 1883 for it. Also check all handlers each timer 1884 interrupt. Intended to get systems with badly broken 1885 firmware running. 1886 1887 isapnp= [ISAPNP] 1888 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1889 1890 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1891 [Deprecated - use cpusets instead] 1892 Format: [flag-list,]<cpu-list> 1893 1894 Specify one or more CPUs to isolate from disturbances 1895 specified in the flag list (default: domain): 1896 1897 nohz 1898 Disable the tick when a single task runs. 1899 1900 A residual 1Hz tick is offloaded to workqueues, which you 1901 need to affine to housekeeping through the global 1902 workqueue's affinity configured via the 1903 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1904 by using the 'domain' flag described below. 1905 1906 NOTE: by default the global workqueue runs on all CPUs, 1907 so to protect individual CPUs the 'cpumask' file has to 1908 be configured manually after bootup. 1909 1910 domain 1911 Isolate from the general SMP balancing and scheduling 1912 algorithms. Note that performing domain isolation this way 1913 is irreversible: it's not possible to bring back a CPU to 1914 the domains once isolated through isolcpus. It's strongly 1915 advised to use cpusets instead to disable scheduler load 1916 balancing through the "cpuset.sched_load_balance" file. 1917 It offers a much more flexible interface where CPUs can 1918 move in and out of an isolated set anytime. 1919 1920 You can move a process onto or off an "isolated" CPU via 1921 the CPU affinity syscalls or cpuset. 1922 <cpu number> begins at 0 and the maximum value is 1923 "number of CPUs in system - 1". 1924 1925 The format of <cpu-list> is described above. 1926 1927 1928 1929 iucv= [HW,NET] 1930 1931 ivrs_ioapic [HW,X86_64] 1932 Provide an override to the IOAPIC-ID<->DEVICE-ID 1933 mapping provided in the IVRS ACPI table. For 1934 example, to map IOAPIC-ID decimal 10 to 1935 PCI device 00:14.0 write the parameter as: 1936 ivrs_ioapic[10]=00:14.0 1937 1938 ivrs_hpet [HW,X86_64] 1939 Provide an override to the HPET-ID<->DEVICE-ID 1940 mapping provided in the IVRS ACPI table. For 1941 example, to map HPET-ID decimal 0 to 1942 PCI device 00:14.0 write the parameter as: 1943 ivrs_hpet[0]=00:14.0 1944 1945 ivrs_acpihid [HW,X86_64] 1946 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1947 mapping provided in the IVRS ACPI table. For 1948 example, to map UART-HID:UID AMD0020:0 to 1949 PCI device 00:14.5 write the parameter as: 1950 ivrs_acpihid[00:14.5]=AMD0020:0 1951 1952 js= [HW,JOY] Analog joystick 1953 See Documentation/input/joydev/joystick.rst. 1954 1955 nokaslr [KNL] 1956 When CONFIG_RANDOMIZE_BASE is set, this disables 1957 kernel and module base offset ASLR (Address Space 1958 Layout Randomization). 1959 1960 kasan_multi_shot 1961 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1962 report on every invalid memory access. Without this 1963 parameter KASAN will print report only for the first 1964 invalid access. 1965 1966 keepinitrd [HW,ARM] 1967 1968 kernelcore= [KNL,X86,IA-64,PPC] 1969 Format: nn[KMGTPE] | nn% | "mirror" 1970 This parameter specifies the amount of memory usable by 1971 the kernel for non-movable allocations. The requested 1972 amount is spread evenly throughout all nodes in the 1973 system as ZONE_NORMAL. The remaining memory is used for 1974 movable memory in its own zone, ZONE_MOVABLE. In the 1975 event, a node is too small to have both ZONE_NORMAL and 1976 ZONE_MOVABLE, kernelcore memory will take priority and 1977 other nodes will have a larger ZONE_MOVABLE. 1978 1979 ZONE_MOVABLE is used for the allocation of pages that 1980 may be reclaimed or moved by the page migration 1981 subsystem. Note that allocations like PTEs-from-HighMem 1982 still use the HighMem zone if it exists, and the Normal 1983 zone if it does not. 1984 1985 It is possible to specify the exact amount of memory in 1986 the form of "nn[KMGTPE]", a percentage of total system 1987 memory in the form of "nn%", or "mirror". If "mirror" 1988 option is specified, mirrored (reliable) memory is used 1989 for non-movable allocations and remaining memory is used 1990 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1991 are exclusive, so you cannot specify multiple forms. 1992 1993 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1994 Format: <Controller#>[,poll interval] 1995 The controller # is the number of the ehci usb debug 1996 port as it is probed via PCI. The poll interval is 1997 optional and is the number seconds in between 1998 each poll cycle to the debug port in case you need 1999 the functionality for interrupting the kernel with 2000 gdb or control-c on the dbgp connection. When 2001 not using this parameter you use sysrq-g to break into 2002 the kernel debugger. 2003 2004 kgdboc= [KGDB,HW] kgdb over consoles. 2005 Requires a tty driver that supports console polling, 2006 or a supported polling keyboard driver (non-usb). 2007 Serial only format: <serial_device>[,baud] 2008 keyboard only format: kbd 2009 keyboard and serial format: kbd,<serial_device>[,baud] 2010 Optional Kernel mode setting: 2011 kms, kbd format: kms,kbd 2012 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 2013 2014 kgdbwait [KGDB] Stop kernel execution and enter the 2015 kernel debugger at the earliest opportunity. 2016 2017 kmac= [MIPS] korina ethernet MAC address. 2018 Configure the RouterBoard 532 series on-chip 2019 Ethernet adapter MAC address. 2020 2021 kmemleak= [KNL] Boot-time kmemleak enable/disable 2022 Valid arguments: on, off 2023 Default: on 2024 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 2025 the default is off. 2026 2027 kprobe_event=[probe-list] 2028 [FTRACE] Add kprobe events and enable at boot time. 2029 The probe-list is a semicolon delimited list of probe 2030 definitions. Each definition is same as kprobe_events 2031 interface, but the parameters are comma delimited. 2032 For example, to add a kprobe event on vfs_read with 2033 arg1 and arg2, add to the command line; 2034 2035 kprobe_event=p,vfs_read,$arg1,$arg2 2036 2037 See also Documentation/trace/kprobetrace.rst "Kernel 2038 Boot Parameter" section. 2039 2040 kpti= [ARM64] Control page table isolation of user 2041 and kernel address spaces. 2042 Default: enabled on cores which need mitigation. 2043 0: force disabled 2044 1: force enabled 2045 2046 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 2047 Default is 0 (don't ignore, but inject #GP) 2048 2049 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 2050 Default is false (don't support). 2051 2052 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 2053 KVM MMU at runtime. 2054 Default is 0 (off) 2055 2056 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 2057 Default is 1 (enabled) 2058 2059 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 2060 for all guests. 2061 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 2062 2063 kvm-arm.vgic_v3_group0_trap= 2064 [KVM,ARM] Trap guest accesses to GICv3 group-0 2065 system registers 2066 2067 kvm-arm.vgic_v3_group1_trap= 2068 [KVM,ARM] Trap guest accesses to GICv3 group-1 2069 system registers 2070 2071 kvm-arm.vgic_v3_common_trap= 2072 [KVM,ARM] Trap guest accesses to GICv3 common 2073 system registers 2074 2075 kvm-arm.vgic_v4_enable= 2076 [KVM,ARM] Allow use of GICv4 for direct injection of 2077 LPIs. 2078 2079 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2080 (virtualized MMU) support on capable Intel chips. 2081 Default is 1 (enabled) 2082 2083 kvm-intel.emulate_invalid_guest_state= 2084 [KVM,Intel] Enable emulation of invalid guest states 2085 Default is 0 (disabled) 2086 2087 kvm-intel.flexpriority= 2088 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2089 Default is 1 (enabled) 2090 2091 kvm-intel.nested= 2092 [KVM,Intel] Enable VMX nesting (nVMX). 2093 Default is 0 (disabled) 2094 2095 kvm-intel.unrestricted_guest= 2096 [KVM,Intel] Disable unrestricted guest feature 2097 (virtualized real and unpaged mode) on capable 2098 Intel chips. Default is 1 (enabled) 2099 2100 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2101 CVE-2018-3620. 2102 2103 Valid arguments: never, cond, always 2104 2105 always: L1D cache flush on every VMENTER. 2106 cond: Flush L1D on VMENTER only when the code between 2107 VMEXIT and VMENTER can leak host memory. 2108 never: Disables the mitigation 2109 2110 Default is cond (do L1 cache flush in specific instances) 2111 2112 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2113 feature (tagged TLBs) on capable Intel chips. 2114 Default is 1 (enabled) 2115 2116 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2117 affected CPUs 2118 2119 The kernel PTE inversion protection is unconditionally 2120 enabled and cannot be disabled. 2121 2122 full 2123 Provides all available mitigations for the 2124 L1TF vulnerability. Disables SMT and 2125 enables all mitigations in the 2126 hypervisors, i.e. unconditional L1D flush. 2127 2128 SMT control and L1D flush control via the 2129 sysfs interface is still possible after 2130 boot. Hypervisors will issue a warning 2131 when the first VM is started in a 2132 potentially insecure configuration, 2133 i.e. SMT enabled or L1D flush disabled. 2134 2135 full,force 2136 Same as 'full', but disables SMT and L1D 2137 flush runtime control. Implies the 2138 'nosmt=force' command line option. 2139 (i.e. sysfs control of SMT is disabled.) 2140 2141 flush 2142 Leaves SMT enabled and enables the default 2143 hypervisor mitigation, i.e. conditional 2144 L1D flush. 2145 2146 SMT control and L1D flush control via the 2147 sysfs interface is still possible after 2148 boot. Hypervisors will issue a warning 2149 when the first VM is started in a 2150 potentially insecure configuration, 2151 i.e. SMT enabled or L1D flush disabled. 2152 2153 flush,nosmt 2154 2155 Disables SMT and enables the default 2156 hypervisor mitigation. 2157 2158 SMT control and L1D flush control via the 2159 sysfs interface is still possible after 2160 boot. Hypervisors will issue a warning 2161 when the first VM is started in a 2162 potentially insecure configuration, 2163 i.e. SMT enabled or L1D flush disabled. 2164 2165 flush,nowarn 2166 Same as 'flush', but hypervisors will not 2167 warn when a VM is started in a potentially 2168 insecure configuration. 2169 2170 off 2171 Disables hypervisor mitigations and doesn't 2172 emit any warnings. 2173 It also drops the swap size and available 2174 RAM limit restriction on both hypervisor and 2175 bare metal. 2176 2177 Default is 'flush'. 2178 2179 For details see: Documentation/admin-guide/hw-vuln/l1tf.rst 2180 2181 l2cr= [PPC] 2182 2183 l3cr= [PPC] 2184 2185 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2186 disabled it. 2187 2188 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2189 value for LAPIC timer one-shot implementation. Default 2190 back to the programmable timer unit in the LAPIC. 2191 2192 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2193 in C2 power state. 2194 2195 libata.dma= [LIBATA] DMA control 2196 libata.dma=0 Disable all PATA and SATA DMA 2197 libata.dma=1 PATA and SATA Disk DMA only 2198 libata.dma=2 ATAPI (CDROM) DMA only 2199 libata.dma=4 Compact Flash DMA only 2200 Combinations also work, so libata.dma=3 enables DMA 2201 for disks and CDROMs, but not CFs. 2202 2203 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2204 libata.ignore_hpa=0 keep BIOS limits (default) 2205 libata.ignore_hpa=1 ignore limits, using full disk 2206 2207 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2208 when set. 2209 Format: <int> 2210 2211 libata.force= [LIBATA] Force configurations. The format is comma 2212 separated list of "[ID:]VAL" where ID is 2213 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2214 matching port, link or device. Basically, it matches 2215 the ATA ID string printed on console by libata. If 2216 the whole ID part is omitted, the last PORT and DEVICE 2217 values are used. If ID hasn't been specified yet, the 2218 configuration applies to all ports, links and devices. 2219 2220 If only DEVICE is omitted, the parameter applies to 2221 the port and all links and devices behind it. DEVICE 2222 number of 0 either selects the first device or the 2223 first fan-out link behind PMP device. It does not 2224 select the host link. DEVICE number of 15 selects the 2225 host link and device attached to it. 2226 2227 The VAL specifies the configuration to force. As long 2228 as there's no ambiguity shortcut notation is allowed. 2229 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2230 The following configurations can be forced. 2231 2232 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2233 Any ID with matching PORT is used. 2234 2235 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2236 2237 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2238 udma[/][16,25,33,44,66,100,133] notation is also 2239 allowed. 2240 2241 * [no]ncq: Turn on or off NCQ. 2242 2243 * [no]ncqtrim: Turn off queued DSM TRIM. 2244 2245 * nohrst, nosrst, norst: suppress hard, soft 2246 and both resets. 2247 2248 * rstonce: only attempt one reset during 2249 hot-unplug link recovery 2250 2251 * dump_id: dump IDENTIFY data. 2252 2253 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2254 2255 * disable: Disable this device. 2256 2257 If there are multiple matching configurations changing 2258 the same attribute, the last one is used. 2259 2260 memblock=debug [KNL] Enable memblock debug messages. 2261 2262 load_ramdisk= [RAM] List of ramdisks to load from floppy 2263 See Documentation/admin-guide/blockdev/ramdisk.rst. 2264 2265 lockd.nlm_grace_period=P [NFS] Assign grace period. 2266 Format: <integer> 2267 2268 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2269 Format: <integer> 2270 2271 lockd.nlm_timeout=T [NFS] Assign timeout value. 2272 Format: <integer> 2273 2274 lockd.nlm_udpport=M [NFS] Assign UDP port. 2275 Format: <integer> 2276 2277 locktorture.nreaders_stress= [KNL] 2278 Set the number of locking read-acquisition kthreads. 2279 Defaults to being automatically set based on the 2280 number of online CPUs. 2281 2282 locktorture.nwriters_stress= [KNL] 2283 Set the number of locking write-acquisition kthreads. 2284 2285 locktorture.onoff_holdoff= [KNL] 2286 Set time (s) after boot for CPU-hotplug testing. 2287 2288 locktorture.onoff_interval= [KNL] 2289 Set time (s) between CPU-hotplug operations, or 2290 zero to disable CPU-hotplug testing. 2291 2292 locktorture.shuffle_interval= [KNL] 2293 Set task-shuffle interval (jiffies). Shuffling 2294 tasks allows some CPUs to go into dyntick-idle 2295 mode during the locktorture test. 2296 2297 locktorture.shutdown_secs= [KNL] 2298 Set time (s) after boot system shutdown. This 2299 is useful for hands-off automated testing. 2300 2301 locktorture.stat_interval= [KNL] 2302 Time (s) between statistics printk()s. 2303 2304 locktorture.stutter= [KNL] 2305 Time (s) to stutter testing, for example, 2306 specifying five seconds causes the test to run for 2307 five seconds, wait for five seconds, and so on. 2308 This tests the locking primitive's ability to 2309 transition abruptly to and from idle. 2310 2311 locktorture.torture_type= [KNL] 2312 Specify the locking implementation to test. 2313 2314 locktorture.verbose= [KNL] 2315 Enable additional printk() statements. 2316 2317 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2318 Format: <irq> 2319 2320 loglevel= All Kernel Messages with a loglevel smaller than the 2321 console loglevel will be printed to the console. It can 2322 also be changed with klogd or other programs. The 2323 loglevels are defined as follows: 2324 2325 0 (KERN_EMERG) system is unusable 2326 1 (KERN_ALERT) action must be taken immediately 2327 2 (KERN_CRIT) critical conditions 2328 3 (KERN_ERR) error conditions 2329 4 (KERN_WARNING) warning conditions 2330 5 (KERN_NOTICE) normal but significant condition 2331 6 (KERN_INFO) informational 2332 7 (KERN_DEBUG) debug-level messages 2333 2334 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2335 in bytes. n must be a power of two and greater 2336 than the minimal size. The minimal size is defined 2337 by LOG_BUF_SHIFT kernel config parameter. There is 2338 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2339 that allows to increase the default size depending on 2340 the number of CPUs. See init/Kconfig for more details. 2341 2342 logo.nologo [FB] Disables display of the built-in Linux logo. 2343 This may be used to provide more screen space for 2344 kernel log messages and is useful when debugging 2345 kernel boot problems. 2346 2347 lp=0 [LP] Specify parallel ports to use, e.g, 2348 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2349 lp=reset first parallel port). 'lp=0' disables the 2350 lp=auto printer driver. 'lp=reset' (which can be 2351 specified in addition to the ports) causes 2352 attached printers to be reset. Using 2353 lp=port1,port2,... specifies the parallel ports 2354 to associate lp devices with, starting with 2355 lp0. A port specification may be 'none' to skip 2356 that lp device, or a parport name such as 2357 'parport0'. Specifying 'lp=auto' instead of a 2358 port specification list means that device IDs 2359 from each port should be examined, to see if 2360 an IEEE 1284-compliant printer is attached; if 2361 so, the driver will manage that printer. 2362 See also header of drivers/char/lp.c. 2363 2364 lpj=n [KNL] 2365 Sets loops_per_jiffy to given constant, thus avoiding 2366 time-consuming boot-time autodetection (up to 250 ms per 2367 CPU). 0 enables autodetection (default). To determine 2368 the correct value for your kernel, boot with normal 2369 autodetection and see what value is printed. Note that 2370 on SMP systems the preset will be applied to all CPUs, 2371 which is likely to cause problems if your CPUs need 2372 significantly divergent settings. An incorrect value 2373 will cause delays in the kernel to be wrong, leading to 2374 unpredictable I/O errors and other breakage. Although 2375 unlikely, in the extreme case this might damage your 2376 hardware. 2377 2378 ltpc= [NET] 2379 Format: <io>,<irq>,<dma> 2380 2381 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2382 2383 lsm=lsm1,...,lsmN 2384 [SECURITY] Choose order of LSM initialization. This 2385 overrides CONFIG_LSM, and the "security=" parameter. 2386 2387 machvec= [IA-64] Force the use of a particular machine-vector 2388 (machvec) in a generic kernel. 2389 Example: machvec=hpzx1 2390 2391 machtype= [Loongson] Share the same kernel image file between different 2392 yeeloong laptop. 2393 Example: machtype=lemote-yeeloong-2f-7inch 2394 2395 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2396 than or equal to this physical address is ignored. 2397 2398 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2399 will bring up during bootup. maxcpus=n : n >= 0 limits 2400 the kernel to bring up 'n' processors. Surely after 2401 bootup you can bring up the other plugged cpu by executing 2402 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2403 only takes effect during system bootup. 2404 While n=0 is a special case, it is equivalent to "nosmp", 2405 which also disables the IO APIC. 2406 2407 max_loop= [LOOP] The number of loop block devices that get 2408 (loop.max_loop) unconditionally pre-created at init time. The default 2409 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2410 of statically allocating a predefined number, loop 2411 devices can be requested on-demand with the 2412 /dev/loop-control interface. 2413 2414 mce [X86-32] Machine Check Exception 2415 2416 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.rst 2417 2418 md= [HW] RAID subsystems devices and level 2419 See Documentation/admin-guide/md.rst. 2420 2421 mdacon= [MDA] 2422 Format: <first>,<last> 2423 Specifies range of consoles to be captured by the MDA. 2424 2425 mds= [X86,INTEL] 2426 Control mitigation for the Micro-architectural Data 2427 Sampling (MDS) vulnerability. 2428 2429 Certain CPUs are vulnerable to an exploit against CPU 2430 internal buffers which can forward information to a 2431 disclosure gadget under certain conditions. 2432 2433 In vulnerable processors, the speculatively 2434 forwarded data can be used in a cache side channel 2435 attack, to access data to which the attacker does 2436 not have direct access. 2437 2438 This parameter controls the MDS mitigation. The 2439 options are: 2440 2441 full - Enable MDS mitigation on vulnerable CPUs 2442 full,nosmt - Enable MDS mitigation and disable 2443 SMT on vulnerable CPUs 2444 off - Unconditionally disable MDS mitigation 2445 2446 Not specifying this option is equivalent to 2447 mds=full. 2448 2449 For details see: Documentation/admin-guide/hw-vuln/mds.rst 2450 2451 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2452 Amount of memory to be used when the kernel is not able 2453 to see the whole system memory or for test. 2454 [X86] Work as limiting max address. Use together 2455 with memmap= to avoid physical address space collisions. 2456 Without memmap= PCI devices could be placed at addresses 2457 belonging to unused RAM. 2458 2459 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2460 memory. 2461 2462 memchunk=nn[KMG] 2463 [KNL,SH] Allow user to override the default size for 2464 per-device physically contiguous DMA buffers. 2465 2466 memhp_default_state=online/offline 2467 [KNL] Set the initial state for the memory hotplug 2468 onlining policy. If not specified, the default value is 2469 set according to the 2470 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2471 option. 2472 See Documentation/admin-guide/mm/memory-hotplug.rst. 2473 2474 memmap=exactmap [KNL,X86] Enable setting of an exact 2475 E820 memory map, as specified by the user. 2476 Such memmap=exactmap lines can be constructed based on 2477 BIOS output or other requirements. See the memmap=nn@ss 2478 option description. 2479 2480 memmap=nn[KMG]@ss[KMG] 2481 [KNL] Force usage of a specific region of memory. 2482 Region of memory to be used is from ss to ss+nn. 2483 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2484 which limits max address to nn[KMG]. 2485 Multiple different regions can be specified, 2486 comma delimited. 2487 Example: 2488 memmap=100M@2G,100M#3G,1G!1024G 2489 2490 memmap=nn[KMG]#ss[KMG] 2491 [KNL,ACPI] Mark specific memory as ACPI data. 2492 Region of memory to be marked is from ss to ss+nn. 2493 2494 memmap=nn[KMG]$ss[KMG] 2495 [KNL,ACPI] Mark specific memory as reserved. 2496 Region of memory to be reserved is from ss to ss+nn. 2497 Example: Exclude memory from 0x18690000-0x1869ffff 2498 memmap=64K$0x18690000 2499 or 2500 memmap=0x10000$0x18690000 2501 Some bootloaders may need an escape character before '$', 2502 like Grub2, otherwise '$' and the following number 2503 will be eaten. 2504 2505 memmap=nn[KMG]!ss[KMG] 2506 [KNL,X86] Mark specific memory as protected. 2507 Region of memory to be used, from ss to ss+nn. 2508 The memory region may be marked as e820 type 12 (0xc) 2509 and is NVDIMM or ADR memory. 2510 2511 memmap=<size>%<offset>-<oldtype>+<newtype> 2512 [KNL,ACPI] Convert memory within the specified region 2513 from <oldtype> to <newtype>. If "-<oldtype>" is left 2514 out, the whole region will be marked as <newtype>, 2515 even if previously unavailable. If "+<newtype>" is left 2516 out, matching memory will be removed. Types are 2517 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2518 3 = ACPI, 12 = PRAM. 2519 2520 memory_corruption_check=0/1 [X86] 2521 Some BIOSes seem to corrupt the first 64k of 2522 memory when doing things like suspend/resume. 2523 Setting this option will scan the memory 2524 looking for corruption. Enabling this will 2525 both detect corruption and prevent the kernel 2526 from using the memory being corrupted. 2527 However, its intended as a diagnostic tool; if 2528 repeatable BIOS-originated corruption always 2529 affects the same memory, you can use memmap= 2530 to prevent the kernel from using that memory. 2531 2532 memory_corruption_check_size=size [X86] 2533 By default it checks for corruption in the low 2534 64k, making this memory unavailable for normal 2535 use. Use this parameter to scan for 2536 corruption in more or less memory. 2537 2538 memory_corruption_check_period=seconds [X86] 2539 By default it checks for corruption every 60 2540 seconds. Use this parameter to check at some 2541 other rate. 0 disables periodic checking. 2542 2543 memtest= [KNL,X86,ARM,PPC] Enable memtest 2544 Format: <integer> 2545 default : 0 <disable> 2546 Specifies the number of memtest passes to be 2547 performed. Each pass selects another test 2548 pattern from a given set of patterns. Memtest 2549 fills the memory with this pattern, validates 2550 memory contents and reserves bad memory 2551 regions that are detected. 2552 2553 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2554 Valid arguments: on, off 2555 Default (depends on kernel configuration option): 2556 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2557 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2558 mem_encrypt=on: Activate SME 2559 mem_encrypt=off: Do not activate SME 2560 2561 Refer to Documentation/virt/kvm/amd-memory-encryption.rst 2562 for details on when memory encryption can be activated. 2563 2564 mem_sleep_default= [SUSPEND] Default system suspend mode: 2565 s2idle - Suspend-To-Idle 2566 shallow - Power-On Suspend or equivalent (if supported) 2567 deep - Suspend-To-RAM or equivalent (if supported) 2568 See Documentation/admin-guide/pm/sleep-states.rst. 2569 2570 meye.*= [HW] Set MotionEye Camera parameters 2571 See Documentation/media/v4l-drivers/meye.rst. 2572 2573 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2574 Multi-Function General Purpose Timers on AMD Geode 2575 platforms. 2576 2577 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2578 the BIOS has incorrectly applied a workaround. TinyBIOS 2579 version 0.98 is known to be affected, 0.99 fixes the 2580 problem by letting the user disable the workaround. 2581 2582 mga= [HW,DRM] 2583 2584 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2585 physical address is ignored. 2586 2587 mini2440= [ARM,HW,KNL] 2588 Format:[0..2][b][c][t] 2589 Default: "0tb" 2590 MINI2440 configuration specification: 2591 0 - The attached screen is the 3.5" TFT 2592 1 - The attached screen is the 7" TFT 2593 2 - The VGA Shield is attached (1024x768) 2594 Leaving out the screen size parameter will not load 2595 the TFT driver, and the framebuffer will be left 2596 unconfigured. 2597 b - Enable backlight. The TFT backlight pin will be 2598 linked to the kernel VESA blanking code and a GPIO 2599 LED. This parameter is not necessary when using the 2600 VGA shield. 2601 c - Enable the s3c camera interface. 2602 t - Reserved for enabling touchscreen support. The 2603 touchscreen support is not enabled in the mainstream 2604 kernel as of 2.6.30, a preliminary port can be found 2605 in the "bleeding edge" mini2440 support kernel at 2606 http://repo.or.cz/w/linux-2.6/mini2440.git 2607 2608 mitigations= 2609 [X86,PPC,S390,ARM64] Control optional mitigations for 2610 CPU vulnerabilities. This is a set of curated, 2611 arch-independent options, each of which is an 2612 aggregation of existing arch-specific options. 2613 2614 off 2615 Disable all optional CPU mitigations. This 2616 improves system performance, but it may also 2617 expose users to several CPU vulnerabilities. 2618 Equivalent to: nopti [X86,PPC] 2619 kpti=0 [ARM64] 2620 nospectre_v1 [X86,PPC] 2621 nobp=0 [S390] 2622 nospectre_v2 [X86,PPC,S390,ARM64] 2623 spectre_v2_user=off [X86] 2624 spec_store_bypass_disable=off [X86,PPC] 2625 ssbd=force-off [ARM64] 2626 l1tf=off [X86] 2627 mds=off [X86] 2628 2629 auto (default) 2630 Mitigate all CPU vulnerabilities, but leave SMT 2631 enabled, even if it's vulnerable. This is for 2632 users who don't want to be surprised by SMT 2633 getting disabled across kernel upgrades, or who 2634 have other ways of avoiding SMT-based attacks. 2635 Equivalent to: (default behavior) 2636 2637 auto,nosmt 2638 Mitigate all CPU vulnerabilities, disabling SMT 2639 if needed. This is for users who always want to 2640 be fully mitigated, even if it means losing SMT. 2641 Equivalent to: l1tf=flush,nosmt [X86] 2642 mds=full,nosmt [X86] 2643 2644 mminit_loglevel= 2645 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2646 parameter allows control of the logging verbosity for 2647 the additional memory initialisation checks. A value 2648 of 0 disables mminit logging and a level of 4 will 2649 log everything. Information is printed at KERN_DEBUG 2650 so loglevel=8 may also need to be specified. 2651 2652 module.sig_enforce 2653 [KNL] When CONFIG_MODULE_SIG is set, this means that 2654 modules without (valid) signatures will fail to load. 2655 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2656 is always true, so this option does nothing. 2657 2658 module_blacklist= [KNL] Do not load a comma-separated list of 2659 modules. Useful for debugging problem modules. 2660 2661 mousedev.tap_time= 2662 [MOUSE] Maximum time between finger touching and 2663 leaving touchpad surface for touch to be considered 2664 a tap and be reported as a left button click (for 2665 touchpads working in absolute mode only). 2666 Format: <msecs> 2667 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2668 reporting absolute coordinates, such as tablets 2669 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2670 reporting absolute coordinates, such as tablets 2671 2672 movablecore= [KNL,X86,IA-64,PPC] 2673 Format: nn[KMGTPE] | nn% 2674 This parameter is the complement to kernelcore=, it 2675 specifies the amount of memory used for migratable 2676 allocations. If both kernelcore and movablecore is 2677 specified, then kernelcore will be at *least* the 2678 specified value but may be more. If movablecore on its 2679 own is specified, the administrator must be careful 2680 that the amount of memory usable for all allocations 2681 is not too small. 2682 2683 movable_node [KNL] Boot-time switch to make hotplugable memory 2684 NUMA nodes to be movable. This means that the memory 2685 of such nodes will be usable only for movable 2686 allocations which rules out almost all kernel 2687 allocations. Use with caution! 2688 2689 MTD_Partition= [MTD] 2690 Format: <name>,<region-number>,<size>,<offset> 2691 2692 MTD_Region= [MTD] Format: 2693 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2694 2695 mtdparts= [MTD] 2696 See drivers/mtd/cmdlinepart.c. 2697 2698 multitce=off [PPC] This parameter disables the use of the pSeries 2699 firmware feature for updating multiple TCE entries 2700 at a time. 2701 2702 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2703 2704 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2705 2706 boundary - index of last SLC block on Flex-OneNAND. 2707 The remaining blocks are configured as MLC blocks. 2708 lock - Configure if Flex-OneNAND boundary should be locked. 2709 Once locked, the boundary cannot be changed. 2710 1 indicates lock status, 0 indicates unlock status. 2711 2712 mtdset= [ARM] 2713 ARM/S3C2412 JIVE boot control 2714 2715 See arch/arm/mach-s3c2412/mach-jive.c 2716 2717 mtouchusb.raw_coordinates= 2718 [HW] Make the MicroTouch USB driver use raw coordinates 2719 ('y', default) or cooked coordinates ('n') 2720 2721 mtrr_chunk_size=nn[KMG] [X86] 2722 used for mtrr cleanup. It is largest continuous chunk 2723 that could hold holes aka. UC entries. 2724 2725 mtrr_gran_size=nn[KMG] [X86] 2726 Used for mtrr cleanup. It is granularity of mtrr block. 2727 Default is 1. 2728 Large value could prevent small alignment from 2729 using up MTRRs. 2730 2731 mtrr_spare_reg_nr=n [X86] 2732 Format: <integer> 2733 Range: 0,7 : spare reg number 2734 Default : 1 2735 Used for mtrr cleanup. It is spare mtrr entries number. 2736 Set to 2 or more if your graphical card needs more. 2737 2738 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2739 2740 netdev= [NET] Network devices parameters 2741 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2742 Note that mem_start is often overloaded to mean 2743 something different and driver-specific. 2744 This usage is only documented in each driver source 2745 file if at all. 2746 2747 nf_conntrack.acct= 2748 [NETFILTER] Enable connection tracking flow accounting 2749 0 to disable accounting 2750 1 to enable accounting 2751 Default value is 0. 2752 2753 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2754 See Documentation/filesystems/nfs/nfsroot.txt. 2755 2756 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2757 See Documentation/filesystems/nfs/nfsroot.txt. 2758 2759 nfsrootdebug [NFS] enable nfsroot debugging messages. 2760 See Documentation/filesystems/nfs/nfsroot.txt. 2761 2762 nfs.callback_nr_threads= 2763 [NFSv4] set the total number of threads that the 2764 NFS client will assign to service NFSv4 callback 2765 requests. 2766 2767 nfs.callback_tcpport= 2768 [NFS] set the TCP port on which the NFSv4 callback 2769 channel should listen. 2770 2771 nfs.cache_getent= 2772 [NFS] sets the pathname to the program which is used 2773 to update the NFS client cache entries. 2774 2775 nfs.cache_getent_timeout= 2776 [NFS] sets the timeout after which an attempt to 2777 update a cache entry is deemed to have failed. 2778 2779 nfs.idmap_cache_timeout= 2780 [NFS] set the maximum lifetime for idmapper cache 2781 entries. 2782 2783 nfs.enable_ino64= 2784 [NFS] enable 64-bit inode numbers. 2785 If zero, the NFS client will fake up a 32-bit inode 2786 number for the readdir() and stat() syscalls instead 2787 of returning the full 64-bit number. 2788 The default is to return 64-bit inode numbers. 2789 2790 nfs.max_session_cb_slots= 2791 [NFSv4.1] Sets the maximum number of session 2792 slots the client will assign to the callback 2793 channel. This determines the maximum number of 2794 callbacks the client will process in parallel for 2795 a particular server. 2796 2797 nfs.max_session_slots= 2798 [NFSv4.1] Sets the maximum number of session slots 2799 the client will attempt to negotiate with the server. 2800 This limits the number of simultaneous RPC requests 2801 that the client can send to the NFSv4.1 server. 2802 Note that there is little point in setting this 2803 value higher than the max_tcp_slot_table_limit. 2804 2805 nfs.nfs4_disable_idmapping= 2806 [NFSv4] When set to the default of '1', this option 2807 ensures that both the RPC level authentication 2808 scheme and the NFS level operations agree to use 2809 numeric uids/gids if the mount is using the 2810 'sec=sys' security flavour. In effect it is 2811 disabling idmapping, which can make migration from 2812 legacy NFSv2/v3 systems to NFSv4 easier. 2813 Servers that do not support this mode of operation 2814 will be autodetected by the client, and it will fall 2815 back to using the idmapper. 2816 To turn off this behaviour, set the value to '0'. 2817 nfs.nfs4_unique_id= 2818 [NFS4] Specify an additional fixed unique ident- 2819 ification string that NFSv4 clients can insert into 2820 their nfs_client_id4 string. This is typically a 2821 UUID that is generated at system install time. 2822 2823 nfs.send_implementation_id = 2824 [NFSv4.1] Send client implementation identification 2825 information in exchange_id requests. 2826 If zero, no implementation identification information 2827 will be sent. 2828 The default is to send the implementation identification 2829 information. 2830 2831 nfs.recover_lost_locks = 2832 [NFSv4] Attempt to recover locks that were lost due 2833 to a lease timeout on the server. Please note that 2834 doing this risks data corruption, since there are 2835 no guarantees that the file will remain unchanged 2836 after the locks are lost. 2837 If you want to enable the kernel legacy behaviour of 2838 attempting to recover these locks, then set this 2839 parameter to '1'. 2840 The default parameter value of '0' causes the kernel 2841 not to attempt recovery of lost locks. 2842 2843 nfs4.layoutstats_timer = 2844 [NFSv4.2] Change the rate at which the kernel sends 2845 layoutstats to the pNFS metadata server. 2846 2847 Setting this to value to 0 causes the kernel to use 2848 whatever value is the default set by the layout 2849 driver. A non-zero value sets the minimum interval 2850 in seconds between layoutstats transmissions. 2851 2852 nfsd.nfs4_disable_idmapping= 2853 [NFSv4] When set to the default of '1', the NFSv4 2854 server will return only numeric uids and gids to 2855 clients using auth_sys, and will accept numeric uids 2856 and gids from such clients. This is intended to ease 2857 migration from NFSv2/v3. 2858 2859 nmi_debug= [KNL,SH] Specify one or more actions to take 2860 when a NMI is triggered. 2861 Format: [state][,regs][,debounce][,die] 2862 2863 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2864 Format: [panic,][nopanic,][num] 2865 Valid num: 0 or 1 2866 0 - turn hardlockup detector in nmi_watchdog off 2867 1 - turn hardlockup detector in nmi_watchdog on 2868 When panic is specified, panic when an NMI watchdog 2869 timeout occurs (or 'nopanic' to not panic on an NMI 2870 watchdog, if CONFIG_BOOTPARAM_HARDLOCKUP_PANIC is set) 2871 To disable both hard and soft lockup detectors, 2872 please see 'nowatchdog'. 2873 This is useful when you use a panic=... timeout and 2874 need the box quickly up again. 2875 2876 These settings can be accessed at runtime via 2877 the nmi_watchdog and hardlockup_panic sysctls. 2878 2879 netpoll.carrier_timeout= 2880 [NET] Specifies amount of time (in seconds) that 2881 netpoll should wait for a carrier. By default netpoll 2882 waits 4 seconds. 2883 2884 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2885 emulation library even if a 387 maths coprocessor 2886 is present. 2887 2888 no5lvl [X86-64] Disable 5-level paging mode. Forces 2889 kernel to use 4-level paging instead. 2890 2891 no_console_suspend 2892 [HW] Never suspend the console 2893 Disable suspending of consoles during suspend and 2894 hibernate operations. Once disabled, debugging 2895 messages can reach various consoles while the rest 2896 of the system is being put to sleep (ie, while 2897 debugging driver suspend/resume hooks). This may 2898 not work reliably with all consoles, but is known 2899 to work with serial and VGA consoles. 2900 To facilitate more flexible debugging, we also add 2901 console_suspend, a printk module parameter to control 2902 it. Users could use console_suspend (usually 2903 /sys/module/printk/parameters/console_suspend) to 2904 turn on/off it dynamically. 2905 2906 novmcoredd [KNL,KDUMP] 2907 Disable device dump. Device dump allows drivers to 2908 append dump data to vmcore so you can collect driver 2909 specified debug info. Drivers can append the data 2910 without any limit and this data is stored in memory, 2911 so this may cause significant memory stress. Disabling 2912 device dump can help save memory but the driver debug 2913 data will be no longer available. This parameter 2914 is only available when CONFIG_PROC_VMCORE_DEVICE_DUMP 2915 is set. 2916 2917 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2918 caches in the slab allocator. Saves per-node memory, 2919 but will impact performance. 2920 2921 noalign [KNL,ARM] 2922 2923 noaltinstr [S390] Disables alternative instructions patching 2924 (CPU alternatives feature). 2925 2926 noapic [SMP,APIC] Tells the kernel to not make use of any 2927 IOAPICs that may be present in the system. 2928 2929 noautogroup Disable scheduler automatic task group creation. 2930 2931 nobats [PPC] Do not use BATs for mapping kernel lowmem 2932 on "Classic" PPC cores. 2933 2934 nocache [ARM] 2935 2936 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2937 2938 nodelayacct [KNL] Disable per-task delay accounting 2939 2940 nodsp [SH] Disable hardware DSP at boot time. 2941 2942 noefi Disable EFI runtime services support. 2943 2944 noexec [IA-64] 2945 2946 noexec [X86] 2947 On X86-32 available only on PAE configured kernels. 2948 noexec=on: enable non-executable mappings (default) 2949 noexec=off: disable non-executable mappings 2950 2951 nosmap [X86,PPC] 2952 Disable SMAP (Supervisor Mode Access Prevention) 2953 even if it is supported by processor. 2954 2955 nosmep [X86,PPC] 2956 Disable SMEP (Supervisor Mode Execution Prevention) 2957 even if it is supported by processor. 2958 2959 noexec32 [X86-64] 2960 This affects only 32-bit executables. 2961 noexec32=on: enable non-executable mappings (default) 2962 read doesn't imply executable mappings 2963 noexec32=off: disable non-executable mappings 2964 read implies executable mappings 2965 2966 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2967 2968 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2969 register save and restore. The kernel will only save 2970 legacy floating-point registers on task switch. 2971 2972 nohugeiomap [KNL,x86,PPC] Disable kernel huge I/O mappings. 2973 2974 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2975 Equivalent to smt=1. 2976 2977 [KNL,x86] Disable symmetric multithreading (SMT). 2978 nosmt=force: Force disable SMT, cannot be undone 2979 via the sysfs control file. 2980 2981 nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1 2982 (bounds check bypass). With this option data leaks are 2983 possible in the system. 2984 2985 nospectre_v2 [X86,PPC_FSL_BOOK3E,ARM64] Disable all mitigations for 2986 the Spectre variant 2 (indirect branch prediction) 2987 vulnerability. System may allow data leaks with this 2988 option. 2989 2990 nospec_store_bypass_disable 2991 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2992 2993 noxsave [BUGS=X86] Disables x86 extended register state save 2994 and restore using xsave. The kernel will fallback to 2995 enabling legacy floating-point and sse state. 2996 2997 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2998 register states. The kernel will fall back to use 2999 xsave to save the states. By using this parameter, 3000 performance of saving the states is degraded because 3001 xsave doesn't support modified optimization while 3002 xsaveopt supports it on xsaveopt enabled systems. 3003 3004 noxsaves [X86] Disables xsaves and xrstors used in saving and 3005 restoring x86 extended register state in compacted 3006 form of xsave area. The kernel will fall back to use 3007 xsaveopt and xrstor to save and restore the states 3008 in standard form of xsave area. By using this 3009 parameter, xsave area per process might occupy more 3010 memory on xsaves enabled systems. 3011 3012 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 3013 wfi(ARM) instruction doesn't work correctly and not to 3014 use it. This is also useful when using JTAG debugger. 3015 3016 no_file_caps Tells the kernel not to honor file capabilities. The 3017 only way then for a file to be executed with privilege 3018 is to be setuid root or executed by root. 3019 3020 nohalt [IA-64] Tells the kernel not to use the power saving 3021 function PAL_HALT_LIGHT when idle. This increases 3022 power-consumption. On the positive side, it reduces 3023 interrupt wake-up latency, which may improve performance 3024 in certain environments such as networked servers or 3025 real-time systems. 3026 3027 nohibernate [HIBERNATION] Disable hibernation and resume. 3028 3029 nohz= [KNL] Boottime enable/disable dynamic ticks 3030 Valid arguments: on, off 3031 Default: on 3032 3033 nohz_full= [KNL,BOOT,SMP,ISOL] 3034 The argument is a cpu list, as described above. 3035 In kernels built with CONFIG_NO_HZ_FULL=y, set 3036 the specified list of CPUs whose tick will be stopped 3037 whenever possible. The boot CPU will be forced outside 3038 the range to maintain the timekeeping. Any CPUs 3039 in this list will have their RCU callbacks offloaded, 3040 just as if they had also been called out in the 3041 rcu_nocbs= boot parameter. 3042 3043 noiotrap [SH] Disables trapped I/O port accesses. 3044 3045 noirqdebug [X86-32] Disables the code which attempts to detect and 3046 disable unhandled interrupt sources. 3047 3048 no_timer_check [X86,APIC] Disables the code which tests for 3049 broken timer IRQ sources. 3050 3051 noisapnp [ISAPNP] Disables ISA PnP code. 3052 3053 noinitrd [RAM] Tells the kernel not to load any configured 3054 initial RAM disk. 3055 3056 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 3057 remapping. 3058 [Deprecated - use intremap=off] 3059 3060 nointroute [IA-64] 3061 3062 noinvpcid [X86] Disable the INVPCID cpu feature. 3063 3064 nojitter [IA-64] Disables jitter checking for ITC timers. 3065 3066 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 3067 3068 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 3069 fault handling. 3070 3071 no-vmw-sched-clock 3072 [X86,PV_OPS] Disable paravirtualized VMware scheduler 3073 clock and use the default one. 3074 3075 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 3076 steal time is computed, but won't influence scheduler 3077 behaviour 3078 3079 nolapic [X86-32,APIC] Do not enable or use the local APIC. 3080 3081 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 3082 3083 noltlbs [PPC] Do not use large page/tlb entries for kernel 3084 lowmem mapping on PPC40x and PPC8xx 3085 3086 nomca [IA-64] Disable machine check abort handling 3087 3088 nomce [X86-32] Disable Machine Check Exception 3089 3090 nomfgpt [X86-32] Disable Multi-Function General Purpose 3091 Timer usage (for AMD Geode machines). 3092 3093 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 3094 shutdown the other cpus. Instead use the REBOOT_VECTOR 3095 irq. 3096 3097 nomodule Disable module load 3098 3099 nopat [X86] Disable PAT (page attribute table extension of 3100 pagetables) support. 3101 3102 nopcid [X86-64] Disable the PCID cpu feature. 3103 3104 norandmaps Don't use address space randomization. Equivalent to 3105 echo 0 > /proc/sys/kernel/randomize_va_space 3106 3107 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 3108 with UP alternatives 3109 3110 nordrand [X86] Disable kernel use of the RDRAND and 3111 RDSEED instructions even if they are supported 3112 by the processor. RDRAND and RDSEED are still 3113 available to user space applications. 3114 3115 noresume [SWSUSP] Disables resume and restores original swap 3116 space. 3117 3118 no-scroll [VGA] Disables scrollback. 3119 This is required for the Braillex ib80-piezo Braille 3120 reader made by F.H. Papenmeier (Germany). 3121 3122 nosbagart [IA-64] 3123 3124 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 3125 3126 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 3127 and disable the IO APIC. legacy for "maxcpus=0". 3128 3129 nosoftlockup [KNL] Disable the soft-lockup detector. 3130 3131 nosync [HW,M68K] Disables sync negotiation for all devices. 3132 3133 nowatchdog [KNL] Disable both lockup detectors, i.e. 3134 soft-lockup and NMI watchdog (hard-lockup). 3135 3136 nowb [ARM] 3137 3138 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 3139 3140 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 3141 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 3142 Some features depend on CPU0. Known dependencies are: 3143 1. Resume from suspend/hibernate depends on CPU0. 3144 Suspend/hibernate will fail if CPU0 is offline and you 3145 need to online CPU0 before suspend/hibernate. 3146 2. PIC interrupts also depend on CPU0. CPU0 can't be 3147 removed if a PIC interrupt is detected. 3148 It's said poweroff/reboot may depend on CPU0 on some 3149 machines although I haven't seen such issues so far 3150 after CPU0 is offline on a few tested machines. 3151 If the dependencies are under your control, you can 3152 turn on cpu0_hotplug. 3153 3154 nps_mtm_hs_ctr= [KNL,ARC] 3155 This parameter sets the maximum duration, in 3156 cycles, each HW thread of the CTOP can run 3157 without interruptions, before HW switches it. 3158 The actual maximum duration is 16 times this 3159 parameter's value. 3160 Format: integer between 1 and 255 3161 Default: 255 3162 3163 nptcg= [IA-64] Override max number of concurrent global TLB 3164 purges which is reported from either PAL_VM_SUMMARY or 3165 SAL PALO. 3166 3167 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3168 could support. nr_cpus=n : n >= 1 limits the kernel to 3169 support 'n' processors. It could be larger than the 3170 number of already plugged CPU during bootup, later in 3171 runtime you can physically add extra cpu until it reaches 3172 n. So during boot up some boot time memory for per-cpu 3173 variables need be pre-allocated for later physical cpu 3174 hot plugging. 3175 3176 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3177 3178 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3179 Allowed values are enable and disable 3180 3181 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3182 'node', 'default' can be specified 3183 This can be set from sysctl after boot. 3184 See Documentation/admin-guide/sysctl/vm.rst for details. 3185 3186 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3187 See Documentation/debugging-via-ohci1394.txt for more 3188 info. 3189 3190 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3191 Rather than timing out after 20 ms if an EC 3192 command is not properly ACKed, override the length 3193 of the timeout. We have interrupts disabled while 3194 waiting for the ACK, so if this is set too high 3195 interrupts *may* be lost! 3196 3197 omap_mux= [OMAP] Override bootloader pin multiplexing. 3198 Format: <mux_mode0.mode_name=value>... 3199 For example, to override I2C bus2: 3200 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3201 3202 oprofile.timer= [HW] 3203 Use timer interrupt instead of performance counters 3204 3205 oprofile.cpu_type= Force an oprofile cpu type 3206 This might be useful if you have an older oprofile 3207 userland or if you want common events. 3208 Format: { arch_perfmon } 3209 arch_perfmon: [X86] Force use of architectural 3210 perfmon on Intel CPUs instead of the 3211 CPU specific event set. 3212 timer: [X86] Force use of architectural NMI 3213 timer mode (see also oprofile.timer 3214 for generic hr timer mode) 3215 3216 oops=panic Always panic on oopses. Default is to just kill the 3217 process, but there is a small probability of 3218 deadlocking the machine. 3219 This will also cause panics on machine check exceptions. 3220 Useful together with panic=30 to trigger a reboot. 3221 3222 page_alloc.shuffle= 3223 [KNL] Boolean flag to control whether the page allocator 3224 should randomize its free lists. The randomization may 3225 be automatically enabled if the kernel detects it is 3226 running on a platform with a direct-mapped memory-side 3227 cache, and this parameter can be used to 3228 override/disable that behavior. The state of the flag 3229 can be read from sysfs at: 3230 /sys/module/page_alloc/parameters/shuffle. 3231 3232 page_owner= [KNL] Boot-time page_owner enabling option. 3233 Storage of the information about who allocated 3234 each page is disabled in default. With this switch, 3235 we can turn it on. 3236 on: enable the feature 3237 3238 page_poison= [KNL] Boot-time parameter changing the state of 3239 poisoning on the buddy allocator, available with 3240 CONFIG_PAGE_POISONING=y. 3241 off: turn off poisoning (default) 3242 on: turn on poisoning 3243 3244 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3245 timeout > 0: seconds before rebooting 3246 timeout = 0: wait forever 3247 timeout < 0: reboot immediately 3248 Format: <timeout> 3249 3250 panic_print= Bitmask for printing system info when panic happens. 3251 User can chose combination of the following bits: 3252 bit 0: print all tasks info 3253 bit 1: print system memory info 3254 bit 2: print timer info 3255 bit 3: print locks info if CONFIG_LOCKDEP is on 3256 bit 4: print ftrace buffer 3257 bit 5: print all printk messages in buffer 3258 3259 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3260 on a WARN(). 3261 3262 crash_kexec_post_notifiers 3263 Run kdump after running panic-notifiers and dumping 3264 kmsg. This only for the users who doubt kdump always 3265 succeeds in any situation. 3266 Note that this also increases risks of kdump failure, 3267 because some panic notifiers can make the crashed 3268 kernel more unstable. 3269 3270 parkbd.port= [HW] Parallel port number the keyboard adapter is 3271 connected to, default is 0. 3272 Format: <parport#> 3273 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3274 0 for XT, 1 for AT (default is AT). 3275 Format: <mode> 3276 3277 parport= [HW,PPT] Specify parallel ports. 0 disables. 3278 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3279 Use 'auto' to force the driver to use any 3280 IRQ/DMA settings detected (the default is to 3281 ignore detected IRQ/DMA settings because of 3282 possible conflicts). You can specify the base 3283 address, IRQ, and DMA settings; IRQ and DMA 3284 should be numbers, or 'auto' (for using detected 3285 settings on that particular port), or 'nofifo' 3286 (to avoid using a FIFO even if it is detected). 3287 Parallel ports are assigned in the order they 3288 are specified on the command line, starting 3289 with parport0. 3290 3291 parport_init_mode= [HW,PPT] 3292 Configure VIA parallel port to operate in 3293 a specific mode. This is necessary on Pegasos 3294 computer where firmware has no options for setting 3295 up parallel port mode and sets it to spp. 3296 Currently this function knows 686a and 8231 chips. 3297 Format: [spp|ps2|epp|ecp|ecpepp] 3298 3299 pause_on_oops= 3300 Halt all CPUs after the first oops has been printed for 3301 the specified number of seconds. This is to be used if 3302 your oopses keep scrolling off the screen. 3303 3304 pcbit= [HW,ISDN] 3305 3306 pcd. [PARIDE] 3307 See header of drivers/block/paride/pcd.c. 3308 See also Documentation/admin-guide/blockdev/paride.rst. 3309 3310 pci=option[,option...] [PCI] various PCI subsystem options. 3311 3312 Some options herein operate on a specific device 3313 or a set of devices (<pci_dev>). These are 3314 specified in one of the following formats: 3315 3316 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3317 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3318 3319 Note: the first format specifies a PCI 3320 bus/device/function address which may change 3321 if new hardware is inserted, if motherboard 3322 firmware changes, or due to changes caused 3323 by other kernel parameters. If the 3324 domain is left unspecified, it is 3325 taken to be zero. Optionally, a path 3326 to a device through multiple device/function 3327 addresses can be specified after the base 3328 address (this is more robust against 3329 renumbering issues). The second format 3330 selects devices using IDs from the 3331 configuration space which may match multiple 3332 devices in the system. 3333 3334 earlydump dump PCI config space before the kernel 3335 changes anything 3336 off [X86] don't probe for the PCI bus 3337 bios [X86-32] force use of PCI BIOS, don't access 3338 the hardware directly. Use this if your machine 3339 has a non-standard PCI host bridge. 3340 nobios [X86-32] disallow use of PCI BIOS, only direct 3341 hardware access methods are allowed. Use this 3342 if you experience crashes upon bootup and you 3343 suspect they are caused by the BIOS. 3344 conf1 [X86] Force use of PCI Configuration Access 3345 Mechanism 1 (config address in IO port 0xCF8, 3346 data in IO port 0xCFC, both 32-bit). 3347 conf2 [X86] Force use of PCI Configuration Access 3348 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3349 the function, IO port 0xCFA, also 8-bit, sets 3350 bus number. The config space is then accessed 3351 through ports 0xC000-0xCFFF). 3352 See http://wiki.osdev.org/PCI for more info 3353 on the configuration access mechanisms. 3354 noaer [PCIE] If the PCIEAER kernel config parameter is 3355 enabled, this kernel boot option can be used to 3356 disable the use of PCIE advanced error reporting. 3357 nodomains [PCI] Disable support for multiple PCI 3358 root domains (aka PCI segments, in ACPI-speak). 3359 nommconf [X86] Disable use of MMCONFIG for PCI 3360 Configuration 3361 check_enable_amd_mmconf [X86] check for and enable 3362 properly configured MMIO access to PCI 3363 config space on AMD family 10h CPU 3364 nomsi [MSI] If the PCI_MSI kernel config parameter is 3365 enabled, this kernel boot option can be used to 3366 disable the use of MSI interrupts system-wide. 3367 noioapicquirk [APIC] Disable all boot interrupt quirks. 3368 Safety option to keep boot IRQs enabled. This 3369 should never be necessary. 3370 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3371 primary IO-APIC for bridges that cannot disable 3372 boot IRQs. This fixes a source of spurious IRQs 3373 when the system masks IRQs. 3374 noioapicreroute [APIC] Disable workaround that uses the 3375 boot IRQ equivalent of an IRQ that connects to 3376 a chipset where boot IRQs cannot be disabled. 3377 The opposite of ioapicreroute. 3378 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3379 routing table. These calls are known to be buggy 3380 on several machines and they hang the machine 3381 when used, but on other computers it's the only 3382 way to get the interrupt routing table. Try 3383 this option if the kernel is unable to allocate 3384 IRQs or discover secondary PCI buses on your 3385 motherboard. 3386 rom [X86] Assign address space to expansion ROMs. 3387 Use with caution as certain devices share 3388 address decoders between ROMs and other 3389 resources. 3390 norom [X86] Do not assign address space to 3391 expansion ROMs that do not already have 3392 BIOS assigned address ranges. 3393 nobar [X86] Do not assign address space to the 3394 BARs that weren't assigned by the BIOS. 3395 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3396 assigned automatically to PCI devices. You can 3397 make the kernel exclude IRQs of your ISA cards 3398 this way. 3399 pirqaddr=0xAAAAA [X86] Specify the physical address 3400 of the PIRQ table (normally generated 3401 by the BIOS) if it is outside the 3402 F0000h-100000h range. 3403 lastbus=N [X86] Scan all buses thru bus #N. Can be 3404 useful if the kernel is unable to find your 3405 secondary buses and you want to tell it 3406 explicitly which ones they are. 3407 assign-busses [X86] Always assign all PCI bus 3408 numbers ourselves, overriding 3409 whatever the firmware may have done. 3410 usepirqmask [X86] Honor the possible IRQ mask stored 3411 in the BIOS $PIR table. This is needed on 3412 some systems with broken BIOSes, notably 3413 some HP Pavilion N5400 and Omnibook XE3 3414 notebooks. This will have no effect if ACPI 3415 IRQ routing is enabled. 3416 noacpi [X86] Do not use ACPI for IRQ routing 3417 or for PCI scanning. 3418 use_crs [X86] Use PCI host bridge window information 3419 from ACPI. On BIOSes from 2008 or later, this 3420 is enabled by default. If you need to use this, 3421 please report a bug. 3422 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3423 If you need to use this, please report a bug. 3424 routeirq Do IRQ routing for all PCI devices. 3425 This is normally done in pci_enable_device(), 3426 so this option is a temporary workaround 3427 for broken drivers that don't call it. 3428 skip_isa_align [X86] do not align io start addr, so can 3429 handle more pci cards 3430 noearly [X86] Don't do any early type 1 scanning. 3431 This might help on some broken boards which 3432 machine check when some devices' config space 3433 is read. But various workarounds are disabled 3434 and some IOMMU drivers will not work. 3435 bfsort Sort PCI devices into breadth-first order. 3436 This sorting is done to get a device 3437 order compatible with older (<= 2.4) kernels. 3438 nobfsort Don't sort PCI devices into breadth-first order. 3439 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3440 tuning and use the BIOS-configured MPS defaults. 3441 pcie_bus_safe Set every device's MPS to the largest value 3442 supported by all devices below the root complex. 3443 pcie_bus_perf Set device MPS to the largest allowable MPS 3444 based on its parent bus. Also set MRRS (Max 3445 Read Request Size) to the largest supported 3446 value (no larger than the MPS that the device 3447 or bus can support) for best performance. 3448 pcie_bus_peer2peer Set every device's MPS to 128B, which 3449 every device is guaranteed to support. This 3450 configuration allows peer-to-peer DMA between 3451 any pair of devices, possibly at the cost of 3452 reduced performance. This also guarantees 3453 that hot-added devices will work. 3454 cbiosize=nn[KMG] The fixed amount of bus space which is 3455 reserved for the CardBus bridge's IO window. 3456 The default value is 256 bytes. 3457 cbmemsize=nn[KMG] The fixed amount of bus space which is 3458 reserved for the CardBus bridge's memory 3459 window. The default value is 64 megabytes. 3460 resource_alignment= 3461 Format: 3462 [<order of align>@]<pci_dev>[; ...] 3463 Specifies alignment and device to reassign 3464 aligned memory resources. How to 3465 specify the device is described above. 3466 If <order of align> is not specified, 3467 PAGE_SIZE is used as alignment. 3468 PCI-PCI bridge can be specified, if resource 3469 windows need to be expanded. 3470 To specify the alignment for several 3471 instances of a device, the PCI vendor, 3472 device, subvendor, and subdevice may be 3473 specified, e.g., 4096@pci:8086:9c22:103c:198f 3474 ecrc= Enable/disable PCIe ECRC (transaction layer 3475 end-to-end CRC checking). 3476 bios: Use BIOS/firmware settings. This is the 3477 the default. 3478 off: Turn ECRC off 3479 on: Turn ECRC on. 3480 hpiosize=nn[KMG] The fixed amount of bus space which is 3481 reserved for hotplug bridge's IO window. 3482 Default size is 256 bytes. 3483 hpmemsize=nn[KMG] The fixed amount of bus space which is 3484 reserved for hotplug bridge's memory window. 3485 Default size is 2 megabytes. 3486 hpbussize=nn The minimum amount of additional bus numbers 3487 reserved for buses below a hotplug bridge. 3488 Default is 1. 3489 realloc= Enable/disable reallocating PCI bridge resources 3490 if allocations done by BIOS are too small to 3491 accommodate resources required by all child 3492 devices. 3493 off: Turn realloc off 3494 on: Turn realloc on 3495 realloc same as realloc=on 3496 noari do not use PCIe ARI. 3497 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3498 do not use PCIe ATS (and IOMMU device IOTLB). 3499 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3500 only look for one device below a PCIe downstream 3501 port. 3502 big_root_window Try to add a big 64bit memory window to the PCIe 3503 root complex on AMD CPUs. Some GFX hardware 3504 can resize a BAR to allow access to all VRAM. 3505 Adding the window is slightly risky (it may 3506 conflict with unreported devices), so this 3507 taints the kernel. 3508 disable_acs_redir=<pci_dev>[; ...] 3509 Specify one or more PCI devices (in the format 3510 specified above) separated by semicolons. 3511 Each device specified will have the PCI ACS 3512 redirect capabilities forced off which will 3513 allow P2P traffic between devices through 3514 bridges without forcing it upstream. Note: 3515 this removes isolation between devices and 3516 may put more devices in an IOMMU group. 3517 force_floating [S390] Force usage of floating interrupts. 3518 nomio [S390] Do not use MIO instructions. 3519 3520 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3521 Management. 3522 off Disable ASPM. 3523 force Enable ASPM even on devices that claim not to support it. 3524 WARNING: Forcing ASPM on may cause system lockups. 3525 3526 pcie_ports= [PCIE] PCIe port services handling: 3527 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3528 even if the platform doesn't give the OS permission to 3529 use them. This may cause conflicts if the platform 3530 also tries to use these services. 3531 compat Disable native PCIe services (PME, AER, DPC, PCIe 3532 hotplug). 3533 3534 pcie_port_pm= [PCIE] PCIe port power management handling: 3535 off Disable power management of all PCIe ports 3536 force Forcibly enable power management of all PCIe ports 3537 3538 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3539 nomsi Do not use MSI for native PCIe PME signaling (this makes 3540 all PCIe root ports use INTx for all services). 3541 3542 pcmv= [HW,PCMCIA] BadgePAD 4 3543 3544 pd_ignore_unused 3545 [PM] 3546 Keep all power-domains already enabled by bootloader on, 3547 even if no driver has claimed them. This is useful 3548 for debug and development, but should not be 3549 needed on a platform with proper driver support. 3550 3551 pd. [PARIDE] 3552 See Documentation/admin-guide/blockdev/paride.rst. 3553 3554 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3555 boot time. 3556 Format: { 0 | 1 } 3557 See arch/parisc/kernel/pdc_chassis.c 3558 3559 percpu_alloc= Select which percpu first chunk allocator to use. 3560 Currently supported values are "embed" and "page". 3561 Archs may support subset or none of the selections. 3562 See comments in mm/percpu.c for details on each 3563 allocator. This parameter is primarily for debugging 3564 and performance comparison. 3565 3566 pf. [PARIDE] 3567 See Documentation/admin-guide/blockdev/paride.rst. 3568 3569 pg. [PARIDE] 3570 See Documentation/admin-guide/blockdev/paride.rst. 3571 3572 pirq= [SMP,APIC] Manual mp-table setup 3573 See Documentation/x86/i386/IO-APIC.rst. 3574 3575 plip= [PPT,NET] Parallel port network link 3576 Format: { parport<nr> | timid | 0 } 3577 See also Documentation/admin-guide/parport.rst. 3578 3579 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3580 Override pmtimer IOPort with a hex value. 3581 e.g. pmtmr=0x508 3582 3583 pnp.debug=1 [PNP] 3584 Enable PNP debug messages (depends on the 3585 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3586 via /sys/module/pnp/parameters/debug. We always show 3587 current resource usage; turning this on also shows 3588 possible settings and some assignment information. 3589 3590 pnpacpi= [ACPI] 3591 { off } 3592 3593 pnpbios= [ISAPNP] 3594 { on | off | curr | res | no-curr | no-res } 3595 3596 pnp_reserve_irq= 3597 [ISAPNP] Exclude IRQs for the autoconfiguration 3598 3599 pnp_reserve_dma= 3600 [ISAPNP] Exclude DMAs for the autoconfiguration 3601 3602 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3603 Ranges are in pairs (I/O port base and size). 3604 3605 pnp_reserve_mem= 3606 [ISAPNP] Exclude memory regions for the 3607 autoconfiguration. 3608 Ranges are in pairs (memory base and size). 3609 3610 ports= [IP_VS_FTP] IPVS ftp helper module 3611 Default is 21. 3612 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3613 may be specified. 3614 Format: <port>,<port>.... 3615 3616 powersave=off [PPC] This option disables power saving features. 3617 It specifically disables cpuidle and sets the 3618 platform machine description specific power_save 3619 function to NULL. On Idle the CPU just reduces 3620 execution priority. 3621 3622 ppc_strict_facility_enable 3623 [PPC] This option catches any kernel floating point, 3624 Altivec, VSX and SPE outside of regions specifically 3625 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3626 There is some performance impact when enabling this. 3627 3628 ppc_tm= [PPC] 3629 Format: {"off"} 3630 Disable Hardware Transactional Memory 3631 3632 print-fatal-signals= 3633 [KNL] debug: print fatal signals 3634 3635 If enabled, warn about various signal handling 3636 related application anomalies: too many signals, 3637 too many POSIX.1 timers, fatal signals causing a 3638 coredump - etc. 3639 3640 If you hit the warning due to signal overflow, 3641 you might want to try "ulimit -i unlimited". 3642 3643 default: off. 3644 3645 printk.always_kmsg_dump= 3646 Trigger kmsg_dump for cases other than kernel oops or 3647 panics 3648 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3649 default: disabled 3650 3651 printk.devkmsg={on,off,ratelimit} 3652 Control writing to /dev/kmsg. 3653 on - unlimited logging to /dev/kmsg from userspace 3654 off - logging to /dev/kmsg disabled 3655 ratelimit - ratelimit the logging 3656 Default: ratelimit 3657 3658 printk.time= Show timing data prefixed to each printk message line 3659 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3660 3661 processor.max_cstate= [HW,ACPI] 3662 Limit processor to maximum C-state 3663 max_cstate=9 overrides any DMI blacklist limit. 3664 3665 processor.nocst [HW,ACPI] 3666 Ignore the _CST method to determine C-states, 3667 instead using the legacy FADT method 3668 3669 profile= [KNL] Enable kernel profiling via /proc/profile 3670 Format: [<profiletype>,]<number> 3671 Param: <profiletype>: "schedule", "sleep", or "kvm" 3672 [defaults to kernel profiling] 3673 Param: "schedule" - profile schedule points. 3674 Param: "sleep" - profile D-state sleeping (millisecs). 3675 Requires CONFIG_SCHEDSTATS 3676 Param: "kvm" - profile VM exits. 3677 Param: <number> - step/bucket size as a power of 2 for 3678 statistical time based profiling. 3679 3680 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3681 before loading. 3682 See Documentation/admin-guide/blockdev/ramdisk.rst. 3683 3684 psi= [KNL] Enable or disable pressure stall information 3685 tracking. 3686 Format: <bool> 3687 3688 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3689 probe for; one of (bare|imps|exps|lifebook|any). 3690 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3691 per second. 3692 psmouse.resetafter= [HW,MOUSE] 3693 Try to reset the device after so many bad packets 3694 (0 = never). 3695 psmouse.resolution= 3696 [HW,MOUSE] Set desired mouse resolution, in dpi. 3697 psmouse.smartscroll= 3698 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3699 0 = disabled, 1 = enabled (default). 3700 3701 pstore.backend= Specify the name of the pstore backend to use 3702 3703 pt. [PARIDE] 3704 See Documentation/admin-guide/blockdev/paride.rst. 3705 3706 pti= [X86_64] Control Page Table Isolation of user and 3707 kernel address spaces. Disabling this feature 3708 removes hardening, but improves performance of 3709 system calls and interrupts. 3710 3711 on - unconditionally enable 3712 off - unconditionally disable 3713 auto - kernel detects whether your CPU model is 3714 vulnerable to issues that PTI mitigates 3715 3716 Not specifying this option is equivalent to pti=auto. 3717 3718 nopti [X86_64] 3719 Equivalent to pti=off 3720 3721 pty.legacy_count= 3722 [KNL] Number of legacy pty's. Overwrites compiled-in 3723 default number. 3724 3725 quiet [KNL] Disable most log messages 3726 3727 r128= [HW,DRM] 3728 3729 raid= [HW,RAID] 3730 See Documentation/admin-guide/md.rst. 3731 3732 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3733 See Documentation/admin-guide/blockdev/ramdisk.rst. 3734 3735 random.trust_cpu={on,off} 3736 [KNL] Enable or disable trusting the use of the 3737 CPU's random number generator (if available) to 3738 fully seed the kernel's CRNG. Default is controlled 3739 by CONFIG_RANDOM_TRUST_CPU. 3740 3741 ras=option[,option,...] [KNL] RAS-specific options 3742 3743 cec_disable [X86] 3744 Disable the Correctable Errors Collector, 3745 see CONFIG_RAS_CEC help text. 3746 3747 rcu_nocbs= [KNL] 3748 The argument is a cpu list, as described above, 3749 except that the string "all" can be used to 3750 specify every CPU on the system. 3751 3752 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3753 the specified list of CPUs to be no-callback CPUs. 3754 Invocation of these CPUs' RCU callbacks will be 3755 offloaded to "rcuox/N" kthreads created for that 3756 purpose, where "x" is "p" for RCU-preempt, and 3757 "s" for RCU-sched, and "N" is the CPU number. 3758 This reduces OS jitter on the offloaded CPUs, 3759 which can be useful for HPC and real-time 3760 workloads. It can also improve energy efficiency 3761 for asymmetric multiprocessors. 3762 3763 rcu_nocb_poll [KNL] 3764 Rather than requiring that offloaded CPUs 3765 (specified by rcu_nocbs= above) explicitly 3766 awaken the corresponding "rcuoN" kthreads, 3767 make these kthreads poll for callbacks. 3768 This improves the real-time response for the 3769 offloaded CPUs by relieving them of the need to 3770 wake up the corresponding kthread, but degrades 3771 energy efficiency by requiring that the kthreads 3772 periodically wake up to do the polling. 3773 3774 rcutree.blimit= [KNL] 3775 Set maximum number of finished RCU callbacks to 3776 process in one batch. 3777 3778 rcutree.dump_tree= [KNL] 3779 Dump the structure of the rcu_node combining tree 3780 out at early boot. This is used for diagnostic 3781 purposes, to verify correct tree setup. 3782 3783 rcutree.gp_cleanup_delay= [KNL] 3784 Set the number of jiffies to delay each step of 3785 RCU grace-period cleanup. 3786 3787 rcutree.gp_init_delay= [KNL] 3788 Set the number of jiffies to delay each step of 3789 RCU grace-period initialization. 3790 3791 rcutree.gp_preinit_delay= [KNL] 3792 Set the number of jiffies to delay each step of 3793 RCU grace-period pre-initialization, that is, 3794 the propagation of recent CPU-hotplug changes up 3795 the rcu_node combining tree. 3796 3797 rcutree.use_softirq= [KNL] 3798 If set to zero, move all RCU_SOFTIRQ processing to 3799 per-CPU rcuc kthreads. Defaults to a non-zero 3800 value, meaning that RCU_SOFTIRQ is used by default. 3801 Specify rcutree.use_softirq=0 to use rcuc kthreads. 3802 3803 rcutree.rcu_fanout_exact= [KNL] 3804 Disable autobalancing of the rcu_node combining 3805 tree. This is used by rcutorture, and might 3806 possibly be useful for architectures having high 3807 cache-to-cache transfer latencies. 3808 3809 rcutree.rcu_fanout_leaf= [KNL] 3810 Change the number of CPUs assigned to each 3811 leaf rcu_node structure. Useful for very 3812 large systems, which will choose the value 64, 3813 and for NUMA systems with large remote-access 3814 latencies, which will choose a value aligned 3815 with the appropriate hardware boundaries. 3816 3817 rcutree.jiffies_till_first_fqs= [KNL] 3818 Set delay from grace-period initialization to 3819 first attempt to force quiescent states. 3820 Units are jiffies, minimum value is zero, 3821 and maximum value is HZ. 3822 3823 rcutree.jiffies_till_next_fqs= [KNL] 3824 Set delay between subsequent attempts to force 3825 quiescent states. Units are jiffies, minimum 3826 value is one, and maximum value is HZ. 3827 3828 rcutree.jiffies_till_sched_qs= [KNL] 3829 Set required age in jiffies for a 3830 given grace period before RCU starts 3831 soliciting quiescent-state help from 3832 rcu_note_context_switch() and cond_resched(). 3833 If not specified, the kernel will calculate 3834 a value based on the most recent settings 3835 of rcutree.jiffies_till_first_fqs 3836 and rcutree.jiffies_till_next_fqs. 3837 This calculated value may be viewed in 3838 rcutree.jiffies_to_sched_qs. Any attempt to set 3839 rcutree.jiffies_to_sched_qs will be cheerfully 3840 overwritten. 3841 3842 rcutree.kthread_prio= [KNL,BOOT] 3843 Set the SCHED_FIFO priority of the RCU per-CPU 3844 kthreads (rcuc/N). This value is also used for 3845 the priority of the RCU boost threads (rcub/N) 3846 and for the RCU grace-period kthreads (rcu_bh, 3847 rcu_preempt, and rcu_sched). If RCU_BOOST is 3848 set, valid values are 1-99 and the default is 1 3849 (the least-favored priority). Otherwise, when 3850 RCU_BOOST is not set, valid values are 0-99 and 3851 the default is zero (non-realtime operation). 3852 3853 rcutree.rcu_nocb_gp_stride= [KNL] 3854 Set the number of NOCB callback kthreads in 3855 each group, which defaults to the square root 3856 of the number of CPUs. Larger numbers reduce 3857 the wakeup overhead on the global grace-period 3858 kthread, but increases that same overhead on 3859 each group's NOCB grace-period kthread. 3860 3861 rcutree.qhimark= [KNL] 3862 Set threshold of queued RCU callbacks beyond which 3863 batch limiting is disabled. 3864 3865 rcutree.qlowmark= [KNL] 3866 Set threshold of queued RCU callbacks below which 3867 batch limiting is re-enabled. 3868 3869 rcutree.rcu_idle_gp_delay= [KNL] 3870 Set wakeup interval for idle CPUs that have 3871 RCU callbacks (RCU_FAST_NO_HZ=y). 3872 3873 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3874 Set wakeup interval for idle CPUs that have 3875 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3876 Lazy RCU callbacks are those which RCU can 3877 prove do nothing more than free memory. 3878 3879 rcutree.rcu_kick_kthreads= [KNL] 3880 Cause the grace-period kthread to get an extra 3881 wake_up() if it sleeps three times longer than 3882 it should at force-quiescent-state time. 3883 This wake_up() will be accompanied by a 3884 WARN_ONCE() splat and an ftrace_dump(). 3885 3886 rcutree.sysrq_rcu= [KNL] 3887 Commandeer a sysrq key to dump out Tree RCU's 3888 rcu_node tree with an eye towards determining 3889 why a new grace period has not yet started. 3890 3891 rcuperf.gp_async= [KNL] 3892 Measure performance of asynchronous 3893 grace-period primitives such as call_rcu(). 3894 3895 rcuperf.gp_async_max= [KNL] 3896 Specify the maximum number of outstanding 3897 callbacks per writer thread. When a writer 3898 thread exceeds this limit, it invokes the 3899 corresponding flavor of rcu_barrier() to allow 3900 previously posted callbacks to drain. 3901 3902 rcuperf.gp_exp= [KNL] 3903 Measure performance of expedited synchronous 3904 grace-period primitives. 3905 3906 rcuperf.holdoff= [KNL] 3907 Set test-start holdoff period. The purpose of 3908 this parameter is to delay the start of the 3909 test until boot completes in order to avoid 3910 interference. 3911 3912 rcuperf.nreaders= [KNL] 3913 Set number of RCU readers. The value -1 selects 3914 N, where N is the number of CPUs. A value 3915 "n" less than -1 selects N-n+1, where N is again 3916 the number of CPUs. For example, -2 selects N 3917 (the number of CPUs), -3 selects N+1, and so on. 3918 A value of "n" less than or equal to -N selects 3919 a single reader. 3920 3921 rcuperf.nwriters= [KNL] 3922 Set number of RCU writers. The values operate 3923 the same as for rcuperf.nreaders. 3924 N, where N is the number of CPUs 3925 3926 rcuperf.perf_type= [KNL] 3927 Specify the RCU implementation to test. 3928 3929 rcuperf.shutdown= [KNL] 3930 Shut the system down after performance tests 3931 complete. This is useful for hands-off automated 3932 testing. 3933 3934 rcuperf.verbose= [KNL] 3935 Enable additional printk() statements. 3936 3937 rcuperf.writer_holdoff= [KNL] 3938 Write-side holdoff between grace periods, 3939 in microseconds. The default of zero says 3940 no holdoff. 3941 3942 rcutorture.fqs_duration= [KNL] 3943 Set duration of force_quiescent_state bursts 3944 in microseconds. 3945 3946 rcutorture.fqs_holdoff= [KNL] 3947 Set holdoff time within force_quiescent_state bursts 3948 in microseconds. 3949 3950 rcutorture.fqs_stutter= [KNL] 3951 Set wait time between force_quiescent_state bursts 3952 in seconds. 3953 3954 rcutorture.fwd_progress= [KNL] 3955 Enable RCU grace-period forward-progress testing 3956 for the types of RCU supporting this notion. 3957 3958 rcutorture.fwd_progress_div= [KNL] 3959 Specify the fraction of a CPU-stall-warning 3960 period to do tight-loop forward-progress testing. 3961 3962 rcutorture.fwd_progress_holdoff= [KNL] 3963 Number of seconds to wait between successive 3964 forward-progress tests. 3965 3966 rcutorture.fwd_progress_need_resched= [KNL] 3967 Enclose cond_resched() calls within checks for 3968 need_resched() during tight-loop forward-progress 3969 testing. 3970 3971 rcutorture.gp_cond= [KNL] 3972 Use conditional/asynchronous update-side 3973 primitives, if available. 3974 3975 rcutorture.gp_exp= [KNL] 3976 Use expedited update-side primitives, if available. 3977 3978 rcutorture.gp_normal= [KNL] 3979 Use normal (non-expedited) asynchronous 3980 update-side primitives, if available. 3981 3982 rcutorture.gp_sync= [KNL] 3983 Use normal (non-expedited) synchronous 3984 update-side primitives, if available. If all 3985 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3986 rcutorture.gp_normal=, and rcutorture.gp_sync= 3987 are zero, rcutorture acts as if is interpreted 3988 they are all non-zero. 3989 3990 rcutorture.n_barrier_cbs= [KNL] 3991 Set callbacks/threads for rcu_barrier() testing. 3992 3993 rcutorture.nfakewriters= [KNL] 3994 Set number of concurrent RCU writers. These just 3995 stress RCU, they don't participate in the actual 3996 test, hence the "fake". 3997 3998 rcutorture.nreaders= [KNL] 3999 Set number of RCU readers. The value -1 selects 4000 N-1, where N is the number of CPUs. A value 4001 "n" less than -1 selects N-n-2, where N is again 4002 the number of CPUs. For example, -2 selects N 4003 (the number of CPUs), -3 selects N+1, and so on. 4004 4005 rcutorture.object_debug= [KNL] 4006 Enable debug-object double-call_rcu() testing. 4007 4008 rcutorture.onoff_holdoff= [KNL] 4009 Set time (s) after boot for CPU-hotplug testing. 4010 4011 rcutorture.onoff_interval= [KNL] 4012 Set time (jiffies) between CPU-hotplug operations, 4013 or zero to disable CPU-hotplug testing. 4014 4015 rcutorture.shuffle_interval= [KNL] 4016 Set task-shuffle interval (s). Shuffling tasks 4017 allows some CPUs to go into dyntick-idle mode 4018 during the rcutorture test. 4019 4020 rcutorture.shutdown_secs= [KNL] 4021 Set time (s) after boot system shutdown. This 4022 is useful for hands-off automated testing. 4023 4024 rcutorture.stall_cpu= [KNL] 4025 Duration of CPU stall (s) to test RCU CPU stall 4026 warnings, zero to disable. 4027 4028 rcutorture.stall_cpu_holdoff= [KNL] 4029 Time to wait (s) after boot before inducing stall. 4030 4031 rcutorture.stall_cpu_irqsoff= [KNL] 4032 Disable interrupts while stalling if set. 4033 4034 rcutorture.stat_interval= [KNL] 4035 Time (s) between statistics printk()s. 4036 4037 rcutorture.stutter= [KNL] 4038 Time (s) to stutter testing, for example, specifying 4039 five seconds causes the test to run for five seconds, 4040 wait for five seconds, and so on. This tests RCU's 4041 ability to transition abruptly to and from idle. 4042 4043 rcutorture.test_boost= [KNL] 4044 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 4045 "Maybe" means test if the RCU implementation 4046 under test support RCU priority boosting. 4047 4048 rcutorture.test_boost_duration= [KNL] 4049 Duration (s) of each individual boost test. 4050 4051 rcutorture.test_boost_interval= [KNL] 4052 Interval (s) between each boost test. 4053 4054 rcutorture.test_no_idle_hz= [KNL] 4055 Test RCU's dyntick-idle handling. See also the 4056 rcutorture.shuffle_interval parameter. 4057 4058 rcutorture.torture_type= [KNL] 4059 Specify the RCU implementation to test. 4060 4061 rcutorture.verbose= [KNL] 4062 Enable additional printk() statements. 4063 4064 rcupdate.rcu_cpu_stall_ftrace_dump= [KNL] 4065 Dump ftrace buffer after reporting RCU CPU 4066 stall warning. 4067 4068 rcupdate.rcu_cpu_stall_suppress= [KNL] 4069 Suppress RCU CPU stall warning messages. 4070 4071 rcupdate.rcu_cpu_stall_timeout= [KNL] 4072 Set timeout for RCU CPU stall warning messages. 4073 4074 rcupdate.rcu_expedited= [KNL] 4075 Use expedited grace-period primitives, for 4076 example, synchronize_rcu_expedited() instead 4077 of synchronize_rcu(). This reduces latency, 4078 but can increase CPU utilization, degrade 4079 real-time latency, and degrade energy efficiency. 4080 No effect on CONFIG_TINY_RCU kernels. 4081 4082 rcupdate.rcu_normal= [KNL] 4083 Use only normal grace-period primitives, 4084 for example, synchronize_rcu() instead of 4085 synchronize_rcu_expedited(). This improves 4086 real-time latency, CPU utilization, and 4087 energy efficiency, but can expose users to 4088 increased grace-period latency. This parameter 4089 overrides rcupdate.rcu_expedited. No effect on 4090 CONFIG_TINY_RCU kernels. 4091 4092 rcupdate.rcu_normal_after_boot= [KNL] 4093 Once boot has completed (that is, after 4094 rcu_end_inkernel_boot() has been invoked), use 4095 only normal grace-period primitives. No effect 4096 on CONFIG_TINY_RCU kernels. 4097 4098 rcupdate.rcu_task_stall_timeout= [KNL] 4099 Set timeout in jiffies for RCU task stall warning 4100 messages. Disable with a value less than or equal 4101 to zero. 4102 4103 rcupdate.rcu_self_test= [KNL] 4104 Run the RCU early boot self tests 4105 4106 rdinit= [KNL] 4107 Format: <full_path> 4108 Run specified binary instead of /init from the ramdisk, 4109 used for early userspace startup. See initrd. 4110 4111 rdrand= [X86] 4112 force - Override the decision by the kernel to hide the 4113 advertisement of RDRAND support (this affects 4114 certain AMD processors because of buggy BIOS 4115 support, specifically around the suspend/resume 4116 path). 4117 4118 rdt= [HW,X86,RDT] 4119 Turn on/off individual RDT features. List is: 4120 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 4121 mba. 4122 E.g. to turn on cmt and turn off mba use: 4123 rdt=cmt,!mba 4124 4125 reboot= [KNL] 4126 Format (x86 or x86_64): 4127 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 4128 [[,]s[mp]#### \ 4129 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 4130 [[,]f[orce] 4131 Where reboot_mode is one of warm (soft) or cold (hard) or gpio 4132 (prefix with 'panic_' to set mode for panic 4133 reboot only), 4134 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 4135 reboot_force is either force or not specified, 4136 reboot_cpu is s[mp]#### with #### being the processor 4137 to be used for rebooting. 4138 4139 relax_domain_level= 4140 [KNL, SMP] Set scheduler's default relax_domain_level. 4141 See Documentation/admin-guide/cgroup-v1/cpusets.rst. 4142 4143 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 4144 Format: <base1>,<size1>[,<base2>,<size2>,...] 4145 Reserve I/O ports or memory so the kernel won't use 4146 them. If <base> is less than 0x10000, the region 4147 is assumed to be I/O ports; otherwise it is memory. 4148 4149 reservetop= [X86-32] 4150 Format: nn[KMG] 4151 Reserves a hole at the top of the kernel virtual 4152 address space. 4153 4154 reservelow= [X86] 4155 Format: nn[K] 4156 Set the amount of memory to reserve for BIOS at 4157 the bottom of the address space. 4158 4159 reset_devices [KNL] Force drivers to reset the underlying device 4160 during initialization. 4161 4162 resume= [SWSUSP] 4163 Specify the partition device for software suspend 4164 Format: 4165 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 4166 4167 resume_offset= [SWSUSP] 4168 Specify the offset from the beginning of the partition 4169 given by "resume=" at which the swap header is located, 4170 in <PAGE_SIZE> units (needed only for swap files). 4171 See Documentation/power/swsusp-and-swap-files.rst 4172 4173 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 4174 read the resume files 4175 4176 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 4177 Useful for devices that are detected asynchronously 4178 (e.g. USB and MMC devices). 4179 4180 hibernate= [HIBERNATION] 4181 noresume Don't check if there's a hibernation image 4182 present during boot. 4183 nocompress Don't compress/decompress hibernation images. 4184 no Disable hibernation and resume. 4185 protect_image Turn on image protection during restoration 4186 (that will set all pages holding image data 4187 during restoration read-only). 4188 4189 retain_initrd [RAM] Keep initrd memory after extraction 4190 4191 rfkill.default_state= 4192 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 4193 etc. communication is blocked by default. 4194 1 Unblocked. 4195 4196 rfkill.master_switch_mode= 4197 0 The "airplane mode" button does nothing. 4198 1 The "airplane mode" button toggles between everything 4199 blocked and the previous configuration. 4200 2 The "airplane mode" button toggles between everything 4201 blocked and everything unblocked. 4202 4203 rhash_entries= [KNL,NET] 4204 Set number of hash buckets for route cache 4205 4206 ring3mwait=disable 4207 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4208 CPUs. 4209 4210 ro [KNL] Mount root device read-only on boot 4211 4212 rodata= [KNL] 4213 on Mark read-only kernel memory as read-only (default). 4214 off Leave read-only kernel memory writable for debugging. 4215 4216 rockchip.usb_uart 4217 Enable the uart passthrough on the designated usb port 4218 on Rockchip SoCs. When active, the signals of the 4219 debug-uart get routed to the D+ and D- pins of the usb 4220 port and the regular usb controller gets disabled. 4221 4222 root= [KNL] Root filesystem 4223 See name_to_dev_t comment in init/do_mounts.c. 4224 4225 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4226 mount the root filesystem 4227 4228 rootflags= [KNL] Set root filesystem mount option string 4229 4230 rootfstype= [KNL] Set root filesystem type 4231 4232 rootwait [KNL] Wait (indefinitely) for root device to show up. 4233 Useful for devices that are detected asynchronously 4234 (e.g. USB and MMC devices). 4235 4236 rproc_mem=nn[KMG][@address] 4237 [KNL,ARM,CMA] Remoteproc physical memory block. 4238 Memory area to be used by remote processor image, 4239 managed by CMA. 4240 4241 rw [KNL] Mount root device read-write on boot 4242 4243 S [KNL] Run init in single mode 4244 4245 s390_iommu= [HW,S390] 4246 Set s390 IOTLB flushing mode 4247 strict 4248 With strict flushing every unmap operation will result in 4249 an IOTLB flush. Default is lazy flushing before reuse, 4250 which is faster. 4251 4252 sa1100ir [NET] 4253 See drivers/net/irda/sa1100_ir.c. 4254 4255 sbni= [NET] Granch SBNI12 leased line adapter 4256 4257 sched_debug [KNL] Enables verbose scheduler debug messages. 4258 4259 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4260 Allowed values are enable and disable. This feature 4261 incurs a small amount of overhead in the scheduler 4262 but is useful for debugging and performance tuning. 4263 4264 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4265 xtime_lock contention on larger systems, and/or RCU lock 4266 contention on all systems with CONFIG_MAXSMP set. 4267 Format: { "0" | "1" } 4268 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4269 1 -- enable. 4270 Note: increases power consumption, thus should only be 4271 enabled if running jitter sensitive (HPC/RT) workloads. 4272 4273 security= [SECURITY] Choose a legacy "major" security module to 4274 enable at boot. This has been deprecated by the 4275 "lsm=" parameter. 4276 4277 selinux= [SELINUX] Disable or enable SELinux at boot time. 4278 Format: { "0" | "1" } 4279 See security/selinux/Kconfig help text. 4280 0 -- disable. 4281 1 -- enable. 4282 Default value is set via kernel config option. 4283 If enabled at boot time, /selinux/disable can be used 4284 later to disable prior to initial policy load. 4285 4286 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4287 Format: { "0" | "1" } 4288 See security/apparmor/Kconfig help text 4289 0 -- disable. 4290 1 -- enable. 4291 Default value is set via kernel config option. 4292 4293 serialnumber [BUGS=X86-32] 4294 4295 shapers= [NET] 4296 Maximal number of shapers. 4297 4298 simeth= [IA-64] 4299 simscsi= 4300 4301 slram= [HW,MTD] 4302 4303 slab_nomerge [MM] 4304 Disable merging of slabs with similar size. May be 4305 necessary if there is some reason to distinguish 4306 allocs to different slabs, especially in hardened 4307 environments where the risk of heap overflows and 4308 layout control by attackers can usually be 4309 frustrated by disabling merging. This will reduce 4310 most of the exposure of a heap attack to a single 4311 cache (risks via metadata attacks are mostly 4312 unchanged). Debug options disable merging on their 4313 own. 4314 For more information see Documentation/vm/slub.rst. 4315 4316 slab_max_order= [MM, SLAB] 4317 Determines the maximum allowed order for slabs. 4318 A high setting may cause OOMs due to memory 4319 fragmentation. Defaults to 1 for systems with 4320 more than 32MB of RAM, 0 otherwise. 4321 4322 slub_debug[=options[,slabs]] [MM, SLUB] 4323 Enabling slub_debug allows one to determine the 4324 culprit if slab objects become corrupted. Enabling 4325 slub_debug can create guard zones around objects and 4326 may poison objects when not in use. Also tracks the 4327 last alloc / free. For more information see 4328 Documentation/vm/slub.rst. 4329 4330 slub_memcg_sysfs= [MM, SLUB] 4331 Determines whether to enable sysfs directories for 4332 memory cgroup sub-caches. 1 to enable, 0 to disable. 4333 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4334 Enabling this can lead to a very high number of debug 4335 directories and files being created under 4336 /sys/kernel/slub. 4337 4338 slub_max_order= [MM, SLUB] 4339 Determines the maximum allowed order for slabs. 4340 A high setting may cause OOMs due to memory 4341 fragmentation. For more information see 4342 Documentation/vm/slub.rst. 4343 4344 slub_min_objects= [MM, SLUB] 4345 The minimum number of objects per slab. SLUB will 4346 increase the slab order up to slub_max_order to 4347 generate a sufficiently large slab able to contain 4348 the number of objects indicated. The higher the number 4349 of objects the smaller the overhead of tracking slabs 4350 and the less frequently locks need to be acquired. 4351 For more information see Documentation/vm/slub.rst. 4352 4353 slub_min_order= [MM, SLUB] 4354 Determines the minimum page order for slabs. Must be 4355 lower than slub_max_order. 4356 For more information see Documentation/vm/slub.rst. 4357 4358 slub_nomerge [MM, SLUB] 4359 Same with slab_nomerge. This is supported for legacy. 4360 See slab_nomerge for more information. 4361 4362 smart2= [HW] 4363 Format: <io1>[,<io2>[,...,<io8>]] 4364 4365 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4366 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4367 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4368 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4369 smsc-ircc2.ircc_irq= [HW] IRQ line 4370 smsc-ircc2.ircc_dma= [HW] DMA channel 4371 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4372 0: Toshiba Satellite 1800 (GP data pin select) 4373 1: Fast pin select (default) 4374 2: ATC IRMode 4375 4376 smt [KNL,S390] Set the maximum number of threads (logical 4377 CPUs) to use per physical CPU on systems capable of 4378 symmetric multithreading (SMT). Will be capped to the 4379 actual hardware limit. 4380 Format: <integer> 4381 Default: -1 (no limit) 4382 4383 softlockup_panic= 4384 [KNL] Should the soft-lockup detector generate panics. 4385 Format: <integer> 4386 4387 A nonzero value instructs the soft-lockup detector 4388 to panic the machine when a soft-lockup occurs. This 4389 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4390 which is the respective build-time switch to that 4391 functionality. 4392 4393 softlockup_all_cpu_backtrace= 4394 [KNL] Should the soft-lockup detector generate 4395 backtraces on all cpus. 4396 Format: <integer> 4397 4398 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4399 See Documentation/admin-guide/laptops/sonypi.rst 4400 4401 spectre_v2= [X86] Control mitigation of Spectre variant 2 4402 (indirect branch speculation) vulnerability. 4403 The default operation protects the kernel from 4404 user space attacks. 4405 4406 on - unconditionally enable, implies 4407 spectre_v2_user=on 4408 off - unconditionally disable, implies 4409 spectre_v2_user=off 4410 auto - kernel detects whether your CPU model is 4411 vulnerable 4412 4413 Selecting 'on' will, and 'auto' may, choose a 4414 mitigation method at run time according to the 4415 CPU, the available microcode, the setting of the 4416 CONFIG_RETPOLINE configuration option, and the 4417 compiler with which the kernel was built. 4418 4419 Selecting 'on' will also enable the mitigation 4420 against user space to user space task attacks. 4421 4422 Selecting 'off' will disable both the kernel and 4423 the user space protections. 4424 4425 Specific mitigations can also be selected manually: 4426 4427 retpoline - replace indirect branches 4428 retpoline,generic - google's original retpoline 4429 retpoline,amd - AMD-specific minimal thunk 4430 4431 Not specifying this option is equivalent to 4432 spectre_v2=auto. 4433 4434 spectre_v2_user= 4435 [X86] Control mitigation of Spectre variant 2 4436 (indirect branch speculation) vulnerability between 4437 user space tasks 4438 4439 on - Unconditionally enable mitigations. Is 4440 enforced by spectre_v2=on 4441 4442 off - Unconditionally disable mitigations. Is 4443 enforced by spectre_v2=off 4444 4445 prctl - Indirect branch speculation is enabled, 4446 but mitigation can be enabled via prctl 4447 per thread. The mitigation control state 4448 is inherited on fork. 4449 4450 prctl,ibpb 4451 - Like "prctl" above, but only STIBP is 4452 controlled per thread. IBPB is issued 4453 always when switching between different user 4454 space processes. 4455 4456 seccomp 4457 - Same as "prctl" above, but all seccomp 4458 threads will enable the mitigation unless 4459 they explicitly opt out. 4460 4461 seccomp,ibpb 4462 - Like "seccomp" above, but only STIBP is 4463 controlled per thread. IBPB is issued 4464 always when switching between different 4465 user space processes. 4466 4467 auto - Kernel selects the mitigation depending on 4468 the available CPU features and vulnerability. 4469 4470 Default mitigation: 4471 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4472 4473 Not specifying this option is equivalent to 4474 spectre_v2_user=auto. 4475 4476 spec_store_bypass_disable= 4477 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4478 (Speculative Store Bypass vulnerability) 4479 4480 Certain CPUs are vulnerable to an exploit against a 4481 a common industry wide performance optimization known 4482 as "Speculative Store Bypass" in which recent stores 4483 to the same memory location may not be observed by 4484 later loads during speculative execution. The idea 4485 is that such stores are unlikely and that they can 4486 be detected prior to instruction retirement at the 4487 end of a particular speculation execution window. 4488 4489 In vulnerable processors, the speculatively forwarded 4490 store can be used in a cache side channel attack, for 4491 example to read memory to which the attacker does not 4492 directly have access (e.g. inside sandboxed code). 4493 4494 This parameter controls whether the Speculative Store 4495 Bypass optimization is used. 4496 4497 On x86 the options are: 4498 4499 on - Unconditionally disable Speculative Store Bypass 4500 off - Unconditionally enable Speculative Store Bypass 4501 auto - Kernel detects whether the CPU model contains an 4502 implementation of Speculative Store Bypass and 4503 picks the most appropriate mitigation. If the 4504 CPU is not vulnerable, "off" is selected. If the 4505 CPU is vulnerable the default mitigation is 4506 architecture and Kconfig dependent. See below. 4507 prctl - Control Speculative Store Bypass per thread 4508 via prctl. Speculative Store Bypass is enabled 4509 for a process by default. The state of the control 4510 is inherited on fork. 4511 seccomp - Same as "prctl" above, but all seccomp threads 4512 will disable SSB unless they explicitly opt out. 4513 4514 Default mitigations: 4515 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4516 4517 On powerpc the options are: 4518 4519 on,auto - On Power8 and Power9 insert a store-forwarding 4520 barrier on kernel entry and exit. On Power7 4521 perform a software flush on kernel entry and 4522 exit. 4523 off - No action. 4524 4525 Not specifying this option is equivalent to 4526 spec_store_bypass_disable=auto. 4527 4528 spia_io_base= [HW,MTD] 4529 spia_fio_base= 4530 spia_pedr= 4531 spia_peddr= 4532 4533 srcutree.counter_wrap_check [KNL] 4534 Specifies how frequently to check for 4535 grace-period sequence counter wrap for the 4536 srcu_data structure's ->srcu_gp_seq_needed field. 4537 The greater the number of bits set in this kernel 4538 parameter, the less frequently counter wrap will 4539 be checked for. Note that the bottom two bits 4540 are ignored. 4541 4542 srcutree.exp_holdoff [KNL] 4543 Specifies how many nanoseconds must elapse 4544 since the end of the last SRCU grace period for 4545 a given srcu_struct until the next normal SRCU 4546 grace period will be considered for automatic 4547 expediting. Set to zero to disable automatic 4548 expediting. 4549 4550 ssbd= [ARM64,HW] 4551 Speculative Store Bypass Disable control 4552 4553 On CPUs that are vulnerable to the Speculative 4554 Store Bypass vulnerability and offer a 4555 firmware based mitigation, this parameter 4556 indicates how the mitigation should be used: 4557 4558 force-on: Unconditionally enable mitigation for 4559 for both kernel and userspace 4560 force-off: Unconditionally disable mitigation for 4561 for both kernel and userspace 4562 kernel: Always enable mitigation in the 4563 kernel, and offer a prctl interface 4564 to allow userspace to register its 4565 interest in being mitigated too. 4566 4567 stack_guard_gap= [MM] 4568 override the default stack gap protection. The value 4569 is in page units and it defines how many pages prior 4570 to (for stacks growing down) resp. after (for stacks 4571 growing up) the main stack are reserved for no other 4572 mapping. Default value is 256 pages. 4573 4574 stacktrace [FTRACE] 4575 Enabled the stack tracer on boot up. 4576 4577 stacktrace_filter=[function-list] 4578 [FTRACE] Limit the functions that the stack tracer 4579 will trace at boot up. function-list is a comma separated 4580 list of functions. This list can be changed at run 4581 time by the stack_trace_filter file in the debugfs 4582 tracing directory. Note, this enables stack tracing 4583 and the stacktrace above is not needed. 4584 4585 sti= [PARISC,HW] 4586 Format: <num> 4587 Set the STI (builtin display/keyboard on the HP-PARISC 4588 machines) console (graphic card) which should be used 4589 as the initial boot-console. 4590 See also comment in drivers/video/console/sticore.c. 4591 4592 sti_font= [HW] 4593 See comment in drivers/video/console/sticore.c. 4594 4595 stifb= [HW] 4596 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4597 4598 sunrpc.min_resvport= 4599 sunrpc.max_resvport= 4600 [NFS,SUNRPC] 4601 SunRPC servers often require that client requests 4602 originate from a privileged port (i.e. a port in the 4603 range 0 < portnr < 1024). 4604 An administrator who wishes to reserve some of these 4605 ports for other uses may adjust the range that the 4606 kernel's sunrpc client considers to be privileged 4607 using these two parameters to set the minimum and 4608 maximum port values. 4609 4610 sunrpc.svc_rpc_per_connection_limit= 4611 [NFS,SUNRPC] 4612 Limit the number of requests that the server will 4613 process in parallel from a single connection. 4614 The default value is 0 (no limit). 4615 4616 sunrpc.pool_mode= 4617 [NFS] 4618 Control how the NFS server code allocates CPUs to 4619 service thread pools. Depending on how many NICs 4620 you have and where their interrupts are bound, this 4621 option will affect which CPUs will do NFS serving. 4622 Note: this parameter cannot be changed while the 4623 NFS server is running. 4624 4625 auto the server chooses an appropriate mode 4626 automatically using heuristics 4627 global a single global pool contains all CPUs 4628 percpu one pool for each CPU 4629 pernode one pool for each NUMA node (equivalent 4630 to global on non-NUMA machines) 4631 4632 sunrpc.tcp_slot_table_entries= 4633 sunrpc.udp_slot_table_entries= 4634 [NFS,SUNRPC] 4635 Sets the upper limit on the number of simultaneous 4636 RPC calls that can be sent from the client to a 4637 server. Increasing these values may allow you to 4638 improve throughput, but will also increase the 4639 amount of memory reserved for use by the client. 4640 4641 suspend.pm_test_delay= 4642 [SUSPEND] 4643 Sets the number of seconds to remain in a suspend test 4644 mode before resuming the system (see 4645 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4646 is set. Default value is 5. 4647 4648 svm= [PPC] 4649 Format: { on | off | y | n | 1 | 0 } 4650 This parameter controls use of the Protected 4651 Execution Facility on pSeries. 4652 4653 swapaccount=[0|1] 4654 [KNL] Enable accounting of swap in memory resource 4655 controller if no parameter or 1 is given or disable 4656 it if 0 is given (See Documentation/admin-guide/cgroup-v1/memory.rst) 4657 4658 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4659 Format: { <int> | force | noforce } 4660 <int> -- Number of I/O TLB slabs 4661 force -- force using of bounce buffers even if they 4662 wouldn't be automatically used by the kernel 4663 noforce -- Never use bounce buffers (for debugging) 4664 4665 switches= [HW,M68k] 4666 4667 sysfs.deprecated=0|1 [KNL] 4668 Enable/disable old style sysfs layout for old udev 4669 on older distributions. When this option is enabled 4670 very new udev will not work anymore. When this option 4671 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4672 in older udev will not work anymore. 4673 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4674 the kernel configuration. 4675 4676 sysrq_always_enabled 4677 [KNL] 4678 Ignore sysrq setting - this boot parameter will 4679 neutralize any effect of /proc/sys/kernel/sysrq. 4680 Useful for debugging. 4681 4682 tcpmhash_entries= [KNL,NET] 4683 Set the number of tcp_metrics_hash slots. 4684 Default value is 8192 or 16384 depending on total 4685 ram pages. This is used to specify the TCP metrics 4686 cache size. See Documentation/networking/ip-sysctl.txt 4687 "tcp_no_metrics_save" section for more details. 4688 4689 tdfx= [HW,DRM] 4690 4691 test_suspend= [SUSPEND][,N] 4692 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4693 standby suspend) or "freeze" (for suspend type freeze) 4694 as the system sleep state during system startup with 4695 the optional capability to repeat N number of times. 4696 The system is woken from this state using a 4697 wakeup-capable RTC alarm. 4698 4699 thash_entries= [KNL,NET] 4700 Set number of hash buckets for TCP connection 4701 4702 thermal.act= [HW,ACPI] 4703 -1: disable all active trip points in all thermal zones 4704 <degrees C>: override all lowest active trip points 4705 4706 thermal.crt= [HW,ACPI] 4707 -1: disable all critical trip points in all thermal zones 4708 <degrees C>: override all critical trip points 4709 4710 thermal.nocrt= [HW,ACPI] 4711 Set to disable actions on ACPI thermal zone 4712 critical and hot trip points. 4713 4714 thermal.off= [HW,ACPI] 4715 1: disable ACPI thermal control 4716 4717 thermal.psv= [HW,ACPI] 4718 -1: disable all passive trip points 4719 <degrees C>: override all passive trip points to this 4720 value 4721 4722 thermal.tzp= [HW,ACPI] 4723 Specify global default ACPI thermal zone polling rate 4724 <deci-seconds>: poll all this frequency 4725 0: no polling (default) 4726 4727 threadirqs [KNL] 4728 Force threading of all interrupt handlers except those 4729 marked explicitly IRQF_NO_THREAD. 4730 4731 topology= [S390] 4732 Format: {off | on} 4733 Specify if the kernel should make use of the cpu 4734 topology information if the hardware supports this. 4735 The scheduler will make use of this information and 4736 e.g. base its process migration decisions on it. 4737 Default is on. 4738 4739 topology_updates= [KNL, PPC, NUMA] 4740 Format: {off} 4741 Specify if the kernel should ignore (off) 4742 topology updates sent by the hypervisor to this 4743 LPAR. 4744 4745 tp720= [HW,PS2] 4746 4747 tpm_suspend_pcr=[HW,TPM] 4748 Format: integer pcr id 4749 Specify that at suspend time, the tpm driver 4750 should extend the specified pcr with zeros, 4751 as a workaround for some chips which fail to 4752 flush the last written pcr on TPM_SaveState. 4753 This will guarantee that all the other pcrs 4754 are saved. 4755 4756 trace_buf_size=nn[KMG] 4757 [FTRACE] will set tracing buffer size on each cpu. 4758 4759 trace_event=[event-list] 4760 [FTRACE] Set and start specified trace events in order 4761 to facilitate early boot debugging. The event-list is a 4762 comma separated list of trace events to enable. See 4763 also Documentation/trace/events.rst 4764 4765 trace_options=[option-list] 4766 [FTRACE] Enable or disable tracer options at boot. 4767 The option-list is a comma delimited list of options 4768 that can be enabled or disabled just as if you were 4769 to echo the option name into 4770 4771 /sys/kernel/debug/tracing/trace_options 4772 4773 For example, to enable stacktrace option (to dump the 4774 stack trace of each event), add to the command line: 4775 4776 trace_options=stacktrace 4777 4778 See also Documentation/trace/ftrace.rst "trace options" 4779 section. 4780 4781 tp_printk[FTRACE] 4782 Have the tracepoints sent to printk as well as the 4783 tracing ring buffer. This is useful for early boot up 4784 where the system hangs or reboots and does not give the 4785 option for reading the tracing buffer or performing a 4786 ftrace_dump_on_oops. 4787 4788 To turn off having tracepoints sent to printk, 4789 echo 0 > /proc/sys/kernel/tracepoint_printk 4790 Note, echoing 1 into this file without the 4791 tracepoint_printk kernel cmdline option has no effect. 4792 4793 ** CAUTION ** 4794 4795 Having tracepoints sent to printk() and activating high 4796 frequency tracepoints such as irq or sched, can cause 4797 the system to live lock. 4798 4799 traceoff_on_warning 4800 [FTRACE] enable this option to disable tracing when a 4801 warning is hit. This turns off "tracing_on". Tracing can 4802 be enabled again by echoing '1' into the "tracing_on" 4803 file located in /sys/kernel/debug/tracing/ 4804 4805 This option is useful, as it disables the trace before 4806 the WARNING dump is called, which prevents the trace to 4807 be filled with content caused by the warning output. 4808 4809 This option can also be set at run time via the sysctl 4810 option: kernel/traceoff_on_warning 4811 4812 transparent_hugepage= 4813 [KNL] 4814 Format: [always|madvise|never] 4815 Can be used to control the default behavior of the system 4816 with respect to transparent hugepages. 4817 See Documentation/admin-guide/mm/transhuge.rst 4818 for more details. 4819 4820 tsc= Disable clocksource stability checks for TSC. 4821 Format: <string> 4822 [x86] reliable: mark tsc clocksource as reliable, this 4823 disables clocksource verification at runtime, as well 4824 as the stability checks done at bootup. Used to enable 4825 high-resolution timer mode on older hardware, and in 4826 virtualized environment. 4827 [x86] noirqtime: Do not use TSC to do irq accounting. 4828 Used to run time disable IRQ_TIME_ACCOUNTING on any 4829 platforms where RDTSC is slow and this accounting 4830 can add overhead. 4831 [x86] unstable: mark the TSC clocksource as unstable, this 4832 marks the TSC unconditionally unstable at bootup and 4833 avoids any further wobbles once the TSC watchdog notices. 4834 [x86] nowatchdog: disable clocksource watchdog. Used 4835 in situations with strict latency requirements (where 4836 interruptions from clocksource watchdog are not 4837 acceptable). 4838 4839 turbografx.map[2|3]= [HW,JOY] 4840 TurboGraFX parallel port interface 4841 Format: 4842 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4843 See also Documentation/input/devices/joystick-parport.rst 4844 4845 udbg-immortal [PPC] When debugging early kernel crashes that 4846 happen after console_init() and before a proper 4847 console driver takes over, this boot options might 4848 help "seeing" what's going on. 4849 4850 uhash_entries= [KNL,NET] 4851 Set number of hash buckets for UDP/UDP-Lite connections 4852 4853 uhci-hcd.ignore_oc= 4854 [USB] Ignore overcurrent events (default N). 4855 Some badly-designed motherboards generate lots of 4856 bogus events, for ports that aren't wired to 4857 anything. Set this parameter to avoid log spamming. 4858 Note that genuine overcurrent events won't be 4859 reported either. 4860 4861 unknown_nmi_panic 4862 [X86] Cause panic on unknown NMI. 4863 4864 usbcore.authorized_default= 4865 [USB] Default USB device authorization: 4866 (default -1 = authorized except for wireless USB, 4867 0 = not authorized, 1 = authorized, 2 = authorized 4868 if device connected to internal port) 4869 4870 usbcore.autosuspend= 4871 [USB] The autosuspend time delay (in seconds) used 4872 for newly-detected USB devices (default 2). This 4873 is the time required before an idle device will be 4874 autosuspended. Devices for which the delay is set 4875 to a negative value won't be autosuspended at all. 4876 4877 usbcore.usbfs_snoop= 4878 [USB] Set to log all usbfs traffic (default 0 = off). 4879 4880 usbcore.usbfs_snoop_max= 4881 [USB] Maximum number of bytes to snoop in each URB 4882 (default = 65536). 4883 4884 usbcore.blinkenlights= 4885 [USB] Set to cycle leds on hubs (default 0 = off). 4886 4887 usbcore.old_scheme_first= 4888 [USB] Start with the old device initialization 4889 scheme, applies only to low and full-speed devices 4890 (default 0 = off). 4891 4892 usbcore.usbfs_memory_mb= 4893 [USB] Memory limit (in MB) for buffers allocated by 4894 usbfs (default = 16, 0 = max = 2047). 4895 4896 usbcore.use_both_schemes= 4897 [USB] Try the other device initialization scheme 4898 if the first one fails (default 1 = enabled). 4899 4900 usbcore.initial_descriptor_timeout= 4901 [USB] Specifies timeout for the initial 64-byte 4902 USB_REQ_GET_DESCRIPTOR request in milliseconds 4903 (default 5000 = 5.0 seconds). 4904 4905 usbcore.nousb [USB] Disable the USB subsystem 4906 4907 usbcore.quirks= 4908 [USB] A list of quirk entries to augment the built-in 4909 usb core quirk list. List entries are separated by 4910 commas. Each entry has the form 4911 VendorID:ProductID:Flags. The IDs are 4-digit hex 4912 numbers and Flags is a set of letters. Each letter 4913 will change the built-in quirk; setting it if it is 4914 clear and clearing it if it is set. The letters have 4915 the following meanings: 4916 a = USB_QUIRK_STRING_FETCH_255 (string 4917 descriptors must not be fetched using 4918 a 255-byte read); 4919 b = USB_QUIRK_RESET_RESUME (device can't resume 4920 correctly so reset it instead); 4921 c = USB_QUIRK_NO_SET_INTF (device can't handle 4922 Set-Interface requests); 4923 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4924 handle its Configuration or Interface 4925 strings); 4926 e = USB_QUIRK_RESET (device can't be reset 4927 (e.g morph devices), don't use reset); 4928 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4929 more interface descriptions than the 4930 bNumInterfaces count, and can't handle 4931 talking to these interfaces); 4932 g = USB_QUIRK_DELAY_INIT (device needs a pause 4933 during initialization, after we read 4934 the device descriptor); 4935 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4936 high speed and super speed interrupt 4937 endpoints, the USB 2.0 and USB 3.0 spec 4938 require the interval in microframes (1 4939 microframe = 125 microseconds) to be 4940 calculated as interval = 2 ^ 4941 (bInterval-1). 4942 Devices with this quirk report their 4943 bInterval as the result of this 4944 calculation instead of the exponent 4945 variable used in the calculation); 4946 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4947 handle device_qualifier descriptor 4948 requests); 4949 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4950 generates spurious wakeup, ignore 4951 remote wakeup capability); 4952 k = USB_QUIRK_NO_LPM (device can't handle Link 4953 Power Management); 4954 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4955 (Device reports its bInterval as linear 4956 frames instead of the USB 2.0 4957 calculation); 4958 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4959 to be disconnected before suspend to 4960 prevent spurious wakeup); 4961 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4962 pause after every control message); 4963 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4964 delay after resetting its port); 4965 Example: quirks=0781:5580:bk,0a5c:5834:gij 4966 4967 usbhid.mousepoll= 4968 [USBHID] The interval which mice are to be polled at. 4969 4970 usbhid.jspoll= 4971 [USBHID] The interval which joysticks are to be polled at. 4972 4973 usbhid.kbpoll= 4974 [USBHID] The interval which keyboards are to be polled at. 4975 4976 usb-storage.delay_use= 4977 [UMS] The delay in seconds before a new device is 4978 scanned for Logical Units (default 1). 4979 4980 usb-storage.quirks= 4981 [UMS] A list of quirks entries to supplement or 4982 override the built-in unusual_devs list. List 4983 entries are separated by commas. Each entry has 4984 the form VID:PID:Flags where VID and PID are Vendor 4985 and Product ID values (4-digit hex numbers) and 4986 Flags is a set of characters, each corresponding 4987 to a common usb-storage quirk flag as follows: 4988 a = SANE_SENSE (collect more than 18 bytes 4989 of sense data); 4990 b = BAD_SENSE (don't collect more than 18 4991 bytes of sense data); 4992 c = FIX_CAPACITY (decrease the reported 4993 device capacity by one sector); 4994 d = NO_READ_DISC_INFO (don't use 4995 READ_DISC_INFO command); 4996 e = NO_READ_CAPACITY_16 (don't use 4997 READ_CAPACITY_16 command); 4998 f = NO_REPORT_OPCODES (don't use report opcodes 4999 command, uas only); 5000 g = MAX_SECTORS_240 (don't transfer more than 5001 240 sectors at a time, uas only); 5002 h = CAPACITY_HEURISTICS (decrease the 5003 reported device capacity by one 5004 sector if the number is odd); 5005 i = IGNORE_DEVICE (don't bind to this 5006 device); 5007 j = NO_REPORT_LUNS (don't use report luns 5008 command, uas only); 5009 l = NOT_LOCKABLE (don't try to lock and 5010 unlock ejectable media); 5011 m = MAX_SECTORS_64 (don't transfer more 5012 than 64 sectors = 32 KB at a time); 5013 n = INITIAL_READ10 (force a retry of the 5014 initial READ(10) command); 5015 o = CAPACITY_OK (accept the capacity 5016 reported by the device); 5017 p = WRITE_CACHE (the device cache is ON 5018 by default); 5019 r = IGNORE_RESIDUE (the device reports 5020 bogus residue values); 5021 s = SINGLE_LUN (the device has only one 5022 Logical Unit); 5023 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 5024 commands, uas only); 5025 u = IGNORE_UAS (don't bind to the uas driver); 5026 w = NO_WP_DETECT (don't test whether the 5027 medium is write-protected). 5028 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 5029 even if the device claims no cache) 5030 Example: quirks=0419:aaf5:rl,0421:0433:rc 5031 5032 user_debug= [KNL,ARM] 5033 Format: <int> 5034 See arch/arm/Kconfig.debug help text. 5035 1 - undefined instruction events 5036 2 - system calls 5037 4 - invalid data aborts 5038 8 - SIGSEGV faults 5039 16 - SIGBUS faults 5040 Example: user_debug=31 5041 5042 userpte= 5043 [X86] Flags controlling user PTE allocations. 5044 5045 nohigh = do not allocate PTE pages in 5046 HIGHMEM regardless of setting 5047 of CONFIG_HIGHPTE. 5048 5049 vdso= [X86,SH] 5050 On X86_32, this is an alias for vdso32=. Otherwise: 5051 5052 vdso=1: enable VDSO (the default) 5053 vdso=0: disable VDSO mapping 5054 5055 vdso32= [X86] Control the 32-bit vDSO 5056 vdso32=1: enable 32-bit VDSO 5057 vdso32=0 or vdso32=2: disable 32-bit VDSO 5058 5059 See the help text for CONFIG_COMPAT_VDSO for more 5060 details. If CONFIG_COMPAT_VDSO is set, the default is 5061 vdso32=0; otherwise, the default is vdso32=1. 5062 5063 For compatibility with older kernels, vdso32=2 is an 5064 alias for vdso32=0. 5065 5066 Try vdso32=0 if you encounter an error that says: 5067 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 5068 5069 vector= [IA-64,SMP] 5070 vector=percpu: enable percpu vector domain 5071 5072 video= [FB] Frame buffer configuration 5073 See Documentation/fb/modedb.rst. 5074 5075 video.brightness_switch_enabled= [0,1] 5076 If set to 1, on receiving an ACPI notify event 5077 generated by hotkey, video driver will adjust brightness 5078 level and then send out the event to user space through 5079 the allocated input device; If set to 0, video driver 5080 will only send out the event without touching backlight 5081 brightness level. 5082 default: 1 5083 5084 virtio_mmio.device= 5085 [VMMIO] Memory mapped virtio (platform) device. 5086 5087 <size>@<baseaddr>:<irq>[:<id>] 5088 where: 5089 <size> := size (can use standard suffixes 5090 like K, M and G) 5091 <baseaddr> := physical base address 5092 <irq> := interrupt number (as passed to 5093 request_irq()) 5094 <id> := (optional) platform device id 5095 example: 5096 virtio_mmio.device=1K@0x100b0000:48:7 5097 5098 Can be used multiple times for multiple devices. 5099 5100 vga= [BOOT,X86-32] Select a particular video mode 5101 See Documentation/x86/boot.rst and 5102 Documentation/admin-guide/svga.rst. 5103 Use vga=ask for menu. 5104 This is actually a boot loader parameter; the value is 5105 passed to the kernel using a special protocol. 5106 5107 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 5108 May slow down system boot speed, especially when 5109 enabled on systems with a large amount of memory. 5110 All options are enabled by default, and this 5111 interface is meant to allow for selectively 5112 enabling or disabling specific virtual memory 5113 debugging features. 5114 5115 Available options are: 5116 P Enable page structure init time poisoning 5117 - Disable all of the above options 5118 5119 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 5120 size of <nn>. This can be used to increase the 5121 minimum size (128MB on x86). It can also be used to 5122 decrease the size and leave more room for directly 5123 mapped kernel RAM. 5124 5125 vmcp_cma=nn[MG] [KNL,S390] 5126 Sets the memory size reserved for contiguous memory 5127 allocations for the vmcp device driver. 5128 5129 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 5130 Format: <command> 5131 5132 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 5133 Format: <command> 5134 5135 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 5136 Format: <command> 5137 5138 vsyscall= [X86-64] 5139 Controls the behavior of vsyscalls (i.e. calls to 5140 fixed addresses of 0xffffffffff600x00 from legacy 5141 code). Most statically-linked binaries and older 5142 versions of glibc use these calls. Because these 5143 functions are at fixed addresses, they make nice 5144 targets for exploits that can control RIP. 5145 5146 emulate [default] Vsyscalls turn into traps and are 5147 emulated reasonably safely. The vsyscall 5148 page is readable. 5149 5150 xonly Vsyscalls turn into traps and are 5151 emulated reasonably safely. The vsyscall 5152 page is not readable. 5153 5154 none Vsyscalls don't work at all. This makes 5155 them quite hard to use for exploits but 5156 might break your system. 5157 5158 vt.color= [VT] Default text color. 5159 Format: 0xYX, X = foreground, Y = background. 5160 Default: 0x07 = light gray on black. 5161 5162 vt.cur_default= [VT] Default cursor shape. 5163 Format: 0xCCBBAA, where AA, BB, and CC are the same as 5164 the parameters of the <Esc>[?A;B;Cc escape sequence; 5165 see VGA-softcursor.txt. Default: 2 = underline. 5166 5167 vt.default_blu= [VT] 5168 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 5169 Change the default blue palette of the console. 5170 This is a 16-member array composed of values 5171 ranging from 0-255. 5172 5173 vt.default_grn= [VT] 5174 Format: <green0>,<green1>,<green2>,...,<green15> 5175 Change the default green palette of the console. 5176 This is a 16-member array composed of values 5177 ranging from 0-255. 5178 5179 vt.default_red= [VT] 5180 Format: <red0>,<red1>,<red2>,...,<red15> 5181 Change the default red palette of the console. 5182 This is a 16-member array composed of values 5183 ranging from 0-255. 5184 5185 vt.default_utf8= 5186 [VT] 5187 Format=<0|1> 5188 Set system-wide default UTF-8 mode for all tty's. 5189 Default is 1, i.e. UTF-8 mode is enabled for all 5190 newly opened terminals. 5191 5192 vt.global_cursor_default= 5193 [VT] 5194 Format=<-1|0|1> 5195 Set system-wide default for whether a cursor 5196 is shown on new VTs. Default is -1, 5197 i.e. cursors will be created by default unless 5198 overridden by individual drivers. 0 will hide 5199 cursors, 1 will display them. 5200 5201 vt.italic= [VT] Default color for italic text; 0-15. 5202 Default: 2 = green. 5203 5204 vt.underline= [VT] Default color for underlined text; 0-15. 5205 Default: 3 = cyan. 5206 5207 watchdog timers [HW,WDT] For information on watchdog timers, 5208 see Documentation/watchdog/watchdog-parameters.rst 5209 or other driver-specific files in the 5210 Documentation/watchdog/ directory. 5211 5212 watchdog_thresh= 5213 [KNL] 5214 Set the hard lockup detector stall duration 5215 threshold in seconds. The soft lockup detector 5216 threshold is set to twice the value. A value of 0 5217 disables both lockup detectors. Default is 10 5218 seconds. 5219 5220 workqueue.watchdog_thresh= 5221 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5222 warn stall conditions and dump internal state to 5223 help debugging. 0 disables workqueue stall 5224 detection; otherwise, it's the stall threshold 5225 duration in seconds. The default value is 30 and 5226 it can be updated at runtime by writing to the 5227 corresponding sysfs file. 5228 5229 workqueue.disable_numa 5230 By default, all work items queued to unbound 5231 workqueues are affine to the NUMA nodes they're 5232 issued on, which results in better behavior in 5233 general. If NUMA affinity needs to be disabled for 5234 whatever reason, this option can be used. Note 5235 that this also can be controlled per-workqueue for 5236 workqueues visible under /sys/bus/workqueue/. 5237 5238 workqueue.power_efficient 5239 Per-cpu workqueues are generally preferred because 5240 they show better performance thanks to cache 5241 locality; unfortunately, per-cpu workqueues tend to 5242 be more power hungry than unbound workqueues. 5243 5244 Enabling this makes the per-cpu workqueues which 5245 were observed to contribute significantly to power 5246 consumption unbound, leading to measurably lower 5247 power usage at the cost of small performance 5248 overhead. 5249 5250 The default value of this parameter is determined by 5251 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5252 5253 workqueue.debug_force_rr_cpu 5254 Workqueue used to implicitly guarantee that work 5255 items queued without explicit CPU specified are put 5256 on the local CPU. This guarantee is no longer true 5257 and while local CPU is still preferred work items 5258 may be put on foreign CPUs. This debug option 5259 forces round-robin CPU selection to flush out 5260 usages which depend on the now broken guarantee. 5261 When enabled, memory and cache locality will be 5262 impacted. 5263 5264 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5265 default x2apic cluster mode on platforms 5266 supporting x2apic. 5267 5268 x86_intel_mid_timer= [X86-32,APBT] 5269 Choose timer option for x86 Intel MID platform. 5270 Two valid options are apbt timer only and lapic timer 5271 plus one apbt timer for broadcast timer. 5272 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5273 5274 xen_512gb_limit [KNL,X86-64,XEN] 5275 Restricts the kernel running paravirtualized under Xen 5276 to use only up to 512 GB of RAM. The reason to do so is 5277 crash analysis tools and Xen tools for doing domain 5278 save/restore/migration must be enabled to handle larger 5279 domains. 5280 5281 xen_emul_unplug= [HW,X86,XEN] 5282 Unplug Xen emulated devices 5283 Format: [unplug0,][unplug1] 5284 ide-disks -- unplug primary master IDE devices 5285 aux-ide-disks -- unplug non-primary-master IDE devices 5286 nics -- unplug network devices 5287 all -- unplug all emulated devices (NICs and IDE disks) 5288 unnecessary -- unplugging emulated devices is 5289 unnecessary even if the host did not respond to 5290 the unplug protocol 5291 never -- do not unplug even if version check succeeds 5292 5293 xen_nopvspin [X86,XEN] 5294 Disables the ticketlock slowpath using Xen PV 5295 optimizations. 5296 5297 xen_nopv [X86] 5298 Disables the PV optimizations forcing the HVM guest to 5299 run as generic HVM guest with no PV drivers. 5300 This option is obsoleted by the "nopv" option, which 5301 has equivalent effect for XEN platform. 5302 5303 xen_scrub_pages= [XEN] 5304 Boolean option to control scrubbing pages before giving them back 5305 to Xen, for use by other domains. Can be also changed at runtime 5306 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5307 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5308 5309 xen_timer_slop= [X86-64,XEN] 5310 Set the timer slop (in nanoseconds) for the virtual Xen 5311 timers (default is 100000). This adjusts the minimum 5312 delta of virtualized Xen timers, where lower values 5313 improve timer resolution at the expense of processing 5314 more timer interrupts. 5315 5316 nopv= [X86,XEN,KVM,HYPER_V,VMWARE] 5317 Disables the PV optimizations forcing the guest to run 5318 as generic guest with no PV drivers. Currently support 5319 XEN HVM, KVM, HYPER_V and VMWARE guest. 5320 5321 xirc2ps_cs= [NET,PCMCIA] 5322 Format: 5323 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5324 5325 xive= [PPC] 5326 By default on POWER9 and above, the kernel will 5327 natively use the XIVE interrupt controller. This option 5328 allows the fallback firmware mode to be used: 5329 5330 off Fallback to firmware control of XIVE interrupt 5331 controller on both pseries and powernv 5332 platforms. Only useful on POWER9 and above. 5333 5334 xhci-hcd.quirks [USB,KNL] 5335 A hex value specifying bitmask with supplemental xhci 5336 host controller quirks. Meaning of each bit can be 5337 consulted in header drivers/usb/host/xhci.h. 5338 5339 xmon [PPC] 5340 Format: { early | on | rw | ro | off } 5341 Controls if xmon debugger is enabled. Default is off. 5342 Passing only "xmon" is equivalent to "xmon=early". 5343 early Call xmon as early as possible on boot; xmon 5344 debugger is called from setup_arch(). 5345 on xmon debugger hooks will be installed so xmon 5346 is only called on a kernel crash. Default mode, 5347 i.e. either "ro" or "rw" mode, is controlled 5348 with CONFIG_XMON_DEFAULT_RO_MODE. 5349 rw xmon debugger hooks will be installed so xmon 5350 is called only on a kernel crash, mode is write, 5351 meaning SPR registers, memory and, other data 5352 can be written using xmon commands. 5353 ro same as "rw" option above but SPR registers, 5354 memory, and other data can't be written using 5355 xmon commands. 5356 off xmon is disabled. 5357