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.txt, 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/acpi/debug.txt 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.txt 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 whilst 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.txt 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 ca_keys= [KEYS] This parameter identifies a specific key(s) on 465 the system trusted keyring to be used for certificate 466 trust validation. 467 format: { id:<keyid> | builtin } 468 469 cca= [MIPS] Override the kernel pages' cache coherency 470 algorithm. Accepted values range from 0 to 7 471 inclusive. See arch/mips/include/asm/pgtable-bits.h 472 for platform specific values (SB1, Loongson3 and 473 others). 474 475 ccw_timeout_log [S390] 476 See Documentation/s390/CommonIO for details. 477 478 cgroup_disable= [KNL] Disable a particular controller 479 Format: {name of the controller(s) to disable} 480 The effects of cgroup_disable=foo are: 481 - foo isn't auto-mounted if you mount all cgroups in 482 a single hierarchy 483 - foo isn't visible as an individually mountable 484 subsystem 485 {Currently only "memory" controller deal with this and 486 cut the overhead, others just disable the usage. So 487 only cgroup_disable=memory is actually worthy} 488 489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1 490 Format: { controller[,controller...] | "all" } 491 Like cgroup_disable, but only applies to cgroup v1; 492 the blacklisted controllers remain available in cgroup2. 493 494 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 495 Format: <string> 496 nosocket -- Disable socket memory accounting. 497 nokmem -- Disable kernel memory accounting. 498 499 checkreqprot [SELINUX] Set initial checkreqprot flag value. 500 Format: { "0" | "1" } 501 See security/selinux/Kconfig help text. 502 0 -- check protection applied by kernel (includes 503 any implied execute protection). 504 1 -- check protection requested by application. 505 Default value is set via a kernel config option. 506 Value can be changed at runtime via 507 /selinux/checkreqprot. 508 509 cio_ignore= [S390] 510 See Documentation/s390/CommonIO for details. 511 clk_ignore_unused 512 [CLK] 513 Prevents the clock framework from automatically gating 514 clocks that have not been explicitly enabled by a Linux 515 device driver but are enabled in hardware at reset or 516 by the bootloader/firmware. Note that this does not 517 force such clocks to be always-on nor does it reserve 518 those clocks in any way. This parameter is useful for 519 debug and development, but should not be needed on a 520 platform with proper driver support. For more 521 information, see Documentation/driver-api/clk.rst. 522 523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 524 [Deprecated] 525 Forces specified clocksource (if available) to be used 526 when calculating gettimeofday(). If specified 527 clocksource is not available, it defaults to PIT. 528 Format: { pit | tsc | cyclone | pmtmr } 529 530 clocksource= Override the default clocksource 531 Format: <string> 532 Override the default clocksource and use the clocksource 533 with the name specified. 534 Some clocksource names to choose from, depending on 535 the platform: 536 [all] jiffies (this is the base, fallback clocksource) 537 [ACPI] acpi_pm 538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 539 pxa_timer,timer3,32k_counter,timer0_1 540 [X86-32] pit,hpet,tsc; 541 scx200_hrt on Geode; cyclone on IBM x440 542 [MIPS] MIPS 543 [PARISC] cr16 544 [S390] tod 545 [SH] SuperH 546 [SPARC64] tick 547 [X86-64] hpet,tsc 548 549 clocksource.arm_arch_timer.evtstrm= 550 [ARM,ARM64] 551 Format: <bool> 552 Enable/disable the eventstream feature of the ARM 553 architected timer so that code using WFE-based polling 554 loops can be debugged more effectively on production 555 systems. 556 557 clearcpuid=BITNUM [X86] 558 Disable CPUID feature X for the kernel. See 559 arch/x86/include/asm/cpufeatures.h for the valid bit 560 numbers. Note the Linux specific bits are not necessarily 561 stable over kernel options, but the vendor specific 562 ones should be. 563 Also note that user programs calling CPUID directly 564 or using the feature without checking anything 565 will still see it. This just prevents it from 566 being used by the kernel or shown in /proc/cpuinfo. 567 Also note the kernel might malfunction if you disable 568 some critical bits. 569 570 cma=nn[MG]@[start[MG][-end[MG]]] 571 [ARM,X86,KNL] 572 Sets the size of kernel global memory area for 573 contiguous memory allocations and optionally the 574 placement constraint by the physical address range of 575 memory allocations. A value of 0 disables CMA 576 altogether. For more information, see 577 include/linux/dma-contiguous.h 578 579 cmo_free_hint= [PPC] Format: { yes | no } 580 Specify whether pages are marked as being inactive 581 when they are freed. This is used in CMO environments 582 to determine OS memory pressure for page stealing by 583 a hypervisor. 584 Default: yes 585 586 coherent_pool=nn[KMG] [ARM,KNL] 587 Sets the size of memory pool for coherent, atomic dma 588 allocations, by default set to 256K. 589 590 com20020= [HW,NET] ARCnet - COM20020 chipset 591 Format: 592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 593 594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 595 Format: <io>[,<irq>] 596 597 com90xx= [HW,NET] 598 ARCnet - COM90xx chipset (memory-mapped buffers) 599 Format: <io>[,<irq>[,<memstart>]] 600 601 condev= [HW,S390] console device 602 conmode= 603 604 console= [KNL] Output console device and options. 605 606 tty<n> Use the virtual console device <n>. 607 608 ttyS<n>[,options] 609 ttyUSB0[,options] 610 Use the specified serial port. The options are of 611 the form "bbbbpnf", where "bbbb" is the baud rate, 612 "p" is parity ("n", "o", or "e"), "n" is number of 613 bits, and "f" is flow control ("r" for RTS or 614 omit it). Default is "9600n8". 615 616 See Documentation/admin-guide/serial-console.rst for more 617 information. See 618 Documentation/networking/netconsole.txt for an 619 alternative. 620 621 uart[8250],io,<addr>[,options] 622 uart[8250],mmio,<addr>[,options] 623 uart[8250],mmio16,<addr>[,options] 624 uart[8250],mmio32,<addr>[,options] 625 uart[8250],0x<addr>[,options] 626 Start an early, polled-mode console on the 8250/16550 627 UART at the specified I/O port or MMIO address, 628 switching to the matching ttyS device later. 629 MMIO inter-register address stride is either 8-bit 630 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 632 to be equivalent to 'mmio'. 'options' are specified in 633 the same format described for ttyS above; if unspecified, 634 the h/w is not re-initialized. 635 636 hvc<n> Use the hypervisor console device <n>. This is for 637 both Xen and PowerPC hypervisors. 638 639 If the device connected to the port is not a TTY but a braille 640 device, prepend "brl," before the device type, for instance 641 console=brl,ttyS0 642 For now, only VisioBraille is supported. 643 644 console_msg_format= 645 [KNL] Change console messages format 646 default 647 By default we print messages on consoles in 648 "[time stamp] text\n" format (time stamp may not be 649 printed, depending on CONFIG_PRINTK_TIME or 650 `printk_time' param). 651 syslog 652 Switch to syslog format: "<%u>[time stamp] text\n" 653 IOW, each message will have a facility and loglevel 654 prefix. The format is similar to one used by syslog() 655 syscall, or to executing "dmesg -S --raw" or to reading 656 from /proc/kmsg. 657 658 consoleblank= [KNL] The console blank (screen saver) timeout in 659 seconds. A value of 0 disables the blank timer. 660 Defaults to 0. 661 662 coredump_filter= 663 [KNL] Change the default value for 664 /proc/<pid>/coredump_filter. 665 See also Documentation/filesystems/proc.txt. 666 667 coresight_cpu_debug.enable 668 [ARM,ARM64] 669 Format: <bool> 670 Enable/disable the CPU sampling based debugging. 671 0: default value, disable debugging 672 1: enable debugging at boot time 673 674 cpuidle.off=1 [CPU_IDLE] 675 disable the cpuidle sub-system 676 677 cpufreq.off=1 [CPU_FREQ] 678 disable the cpufreq sub-system 679 680 cpu_init_udelay=N 681 [X86] Delay for N microsec between assert and de-assert 682 of APIC INIT to start processors. This delay occurs 683 on every CPU online, such as boot, and resume from suspend. 684 Default: 10000 685 686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 687 Format: 688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 689 690 crashkernel=size[KMG][@offset[KMG]] 691 [KNL] Using kexec, Linux can switch to a 'crash kernel' 692 upon panic. This parameter reserves the physical 693 memory region [offset, offset + size] for that kernel 694 image. If '@offset' is omitted, then a suitable offset 695 is selected automatically. Check 696 Documentation/kdump/kdump.txt for further details. 697 698 crashkernel=range1:size1[,range2:size2,...][@offset] 699 [KNL] Same as above, but depends on the memory 700 in the running system. The syntax of range is 701 start-[end] where start and end are both 702 a memory unit (amount[KMG]). See also 703 Documentation/kdump/kdump.txt for an example. 704 705 crashkernel=size[KMG],high 706 [KNL, x86_64] range could be above 4G. Allow kernel 707 to allocate physical memory region from top, so could 708 be above 4G if system have more than 4G ram installed. 709 Otherwise memory region will be allocated below 4G, if 710 available. 711 It will be ignored if crashkernel=X is specified. 712 crashkernel=size[KMG],low 713 [KNL, x86_64] range under 4G. When crashkernel=X,high 714 is passed, kernel could allocate physical memory region 715 above 4G, that cause second kernel crash on system 716 that require some amount of low memory, e.g. swiotlb 717 requires at least 64M+32K low memory, also enough extra 718 low memory is needed to make sure DMA buffers for 32-bit 719 devices won't run out. Kernel would try to allocate at 720 at least 256M below 4G automatically. 721 This one let user to specify own low range under 4G 722 for second kernel instead. 723 0: to disable low allocation. 724 It will be ignored when crashkernel=X,high is not used 725 or memory reserved is below 4G. 726 727 cryptomgr.notests 728 [KNL] Disable crypto self-tests 729 730 cs89x0_dma= [HW,NET] 731 Format: <dma> 732 733 cs89x0_media= [HW,NET] 734 Format: { rj45 | aui | bnc } 735 736 dasd= [HW,NET] 737 See header of drivers/s390/block/dasd_devmap.c. 738 739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 740 (one device per port) 741 Format: <port#>,<type> 742 See also Documentation/input/devices/joystick-parport.rst 743 744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 745 time. See 746 Documentation/admin-guide/dynamic-debug-howto.rst for 747 details. Deprecated, see dyndbg. 748 749 debug [KNL] Enable kernel debugging (events log level). 750 751 debug_boot_weak_hash 752 [KNL] Enable printing [hashed] pointers early in the 753 boot sequence. If enabled, we use a weak hash instead 754 of siphash to hash pointers. Use this option if you are 755 seeing instances of '(___ptrval___)') and need to see a 756 value (hashed pointer) instead. Cryptographically 757 insecure, please do not use on production kernels. 758 759 debug_locks_verbose= 760 [KNL] verbose self-tests 761 Format=<0|1> 762 Print debugging info while doing the locking API 763 self-tests. 764 We default to 0 (no extra messages), setting it to 765 1 will print _a lot_ more information - normally 766 only useful to kernel developers. 767 768 debug_objects [KNL] Enable object debugging 769 770 no_debug_objects 771 [KNL] Disable object debugging 772 773 debug_guardpage_minorder= 774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 775 parameter allows control of the order of pages that will 776 be intentionally kept free (and hence protected) by the 777 buddy allocator. Bigger value increase the probability 778 of catching random memory corruption, but reduce the 779 amount of memory for normal system use. The maximum 780 possible value is MAX_ORDER/2. Setting this parameter 781 to 1 or 2 should be enough to identify most random 782 memory corruption problems caused by bugs in kernel or 783 driver code when a CPU writes to (or reads from) a 784 random memory location. Note that there exists a class 785 of memory corruptions problems caused by buggy H/W or 786 F/W or by drivers badly programing DMA (basically when 787 memory is written at bus level and the CPU MMU is 788 bypassed) which are not detectable by 789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 790 tracking down these problems. 791 792 debug_pagealloc= 793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 794 parameter enables the feature at boot time. In 795 default, it is disabled. We can avoid allocating huge 796 chunk of memory for debug pagealloc if we don't enable 797 it at boot time and the system will work mostly same 798 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 799 on: enable the feature 800 801 debugpat [X86] Enable PAT debugging 802 803 decnet.addr= [HW,NET] 804 Format: <area>[,<node>] 805 See also Documentation/networking/decnet.txt. 806 807 default_hugepagesz= 808 [same as hugepagesz=] The size of the default 809 HugeTLB page size. This is the size represented by 810 the legacy /proc/ hugepages APIs, used for SHM, and 811 default size when mounting hugetlbfs filesystems. 812 Defaults to the default architecture's huge page size 813 if not specified. 814 815 deferred_probe_timeout= 816 [KNL] Debugging option to set a timeout in seconds for 817 deferred probe to give up waiting on dependencies to 818 probe. Only specific dependencies (subsystems or 819 drivers) that have opted in will be ignored. A timeout of 0 820 will timeout at the end of initcalls. This option will also 821 dump out devices still on the deferred probe list after 822 retrying. 823 824 dhash_entries= [KNL] 825 Set number of hash buckets for dentry cache. 826 827 disable_1tb_segments [PPC] 828 Disables the use of 1TB hash page table segments. This 829 causes the kernel to fall back to 256MB segments which 830 can be useful when debugging issues that require an SLB 831 miss to occur. 832 833 disable= [IPV6] 834 See Documentation/networking/ipv6.txt. 835 836 hardened_usercopy= 837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether 838 hardening is enabled for this boot. Hardened 839 usercopy checking is used to protect the kernel 840 from reading or writing beyond known memory 841 allocation boundaries as a proactive defense 842 against bounds-checking flaws in the kernel's 843 copy_to_user()/copy_from_user() interface. 844 on Perform hardened usercopy checks (default). 845 off Disable hardened usercopy checks. 846 847 disable_radix [PPC] 848 Disable RADIX MMU mode on POWER9 849 850 disable_cpu_apicid= [X86,APIC,SMP] 851 Format: <int> 852 The number of initial APIC ID for the 853 corresponding CPU to be disabled at boot, 854 mostly used for the kdump 2nd kernel to 855 disable BSP to wake up multiple CPUs without 856 causing system reset or hang due to sending 857 INIT from AP to BSP. 858 859 perf_v4_pmi= [X86,INTEL] 860 Format: <bool> 861 Disable Intel PMU counter freezing feature. 862 The feature only exists starting from 863 Arch Perfmon v4 (Skylake and newer). 864 865 disable_ddw [PPC/PSERIES] 866 Disable Dynamic DMA Window support. Use this if 867 to workaround buggy firmware. 868 869 disable_ipv6= [IPV6] 870 See Documentation/networking/ipv6.txt. 871 872 disable_mtrr_cleanup [X86] 873 The kernel tries to adjust MTRR layout from continuous 874 to discrete, to make X server driver able to add WB 875 entry later. This parameter disables that. 876 877 disable_mtrr_trim [X86, Intel and AMD only] 878 By default the kernel will trim any uncacheable 879 memory out of your available memory pool based on 880 MTRR settings. This parameter disables that behavior, 881 possibly causing your machine to run very slowly. 882 883 disable_timer_pin_1 [X86] 884 Disable PIN 1 of APIC timer 885 Can be useful to work around chipset bugs. 886 887 dis_ucode_ldr [X86] Disable the microcode loader. 888 889 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 890 this option disables the debugging code at boot. 891 892 dma_debug_entries=<number> 893 This option allows to tune the number of preallocated 894 entries for DMA-API debugging code. One entry is 895 required per DMA-API allocation. Use this if the 896 DMA-API debugging code disables itself because the 897 architectural default is too low. 898 899 dma_debug_driver=<driver_name> 900 With this option the DMA-API debugging driver 901 filter feature can be enabled at boot time. Just 902 pass the driver to filter for as the parameter. 903 The filter can be disabled or changed to another 904 driver later using sysfs. 905 906 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 907 Broken monitors, graphic adapters, KVMs and EDIDless 908 panels may send no or incorrect EDID data sets. 909 This parameter allows to specify an EDID data sets 910 in the /lib/firmware directory that are used instead. 911 Generic built-in EDID data sets are used, if one of 912 edid/1024x768.bin, edid/1280x1024.bin, 913 edid/1680x1050.bin, or edid/1920x1080.bin is given 914 and no file with the same name exists. Details and 915 instructions how to build your own EDID data are 916 available in Documentation/EDID/HOWTO.txt. An EDID 917 data set will only be used for a particular connector, 918 if its name and a colon are prepended to the EDID 919 name. Each connector may use a unique EDID data 920 set by separating the files with a comma. An EDID 921 data set with no connector name will be used for 922 any connectors not explicitly specified. 923 924 dscc4.setup= [NET] 925 926 dt_cpu_ftrs= [PPC] 927 Format: {"off" | "known"} 928 Control how the dt_cpu_ftrs device-tree binding is 929 used for CPU feature discovery and setup (if it 930 exists). 931 off: Do not use it, fall back to legacy cpu table. 932 known: Do not pass through unknown features to guests 933 or userspace, only those that the kernel is aware of. 934 935 dump_apple_properties [X86] 936 Dump name and content of EFI device properties on 937 x86 Macs. Useful for driver authors to determine 938 what data is available or for reverse-engineering. 939 940 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 941 module.dyndbg[="val"] 942 Enable debug messages at boot time. See 943 Documentation/admin-guide/dynamic-debug-howto.rst 944 for details. 945 946 nompx [X86] Disables Intel Memory Protection Extensions. 947 See Documentation/x86/intel_mpx.txt for more 948 information about the feature. 949 950 nopku [X86] Disable Memory Protection Keys CPU feature found 951 in some Intel CPUs. 952 953 module.async_probe [KNL] 954 Enable asynchronous probe on this module. 955 956 early_ioremap_debug [KNL] 957 Enable debug messages in early_ioremap support. This 958 is useful for tracking down temporary early mappings 959 which are not unmapped. 960 961 earlycon= [KNL] Output early console device and options. 962 963 [ARM64] The early console is determined by the 964 stdout-path property in device tree's chosen node, 965 or determined by the ACPI SPCR table. 966 967 [X86] When used with no options the early console is 968 determined by the ACPI SPCR table. 969 970 cdns,<addr>[,options] 971 Start an early, polled-mode console on a Cadence 972 (xuartps) serial port at the specified address. Only 973 supported option is baud rate. If baud rate is not 974 specified, the serial port must already be setup and 975 configured. 976 977 uart[8250],io,<addr>[,options] 978 uart[8250],mmio,<addr>[,options] 979 uart[8250],mmio32,<addr>[,options] 980 uart[8250],mmio32be,<addr>[,options] 981 uart[8250],0x<addr>[,options] 982 Start an early, polled-mode console on the 8250/16550 983 UART at the specified I/O port or MMIO address. 984 MMIO inter-register address stride is either 8-bit 985 (mmio) or 32-bit (mmio32 or mmio32be). 986 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 987 to be equivalent to 'mmio'. 'options' are specified 988 in the same format described for "console=ttyS<n>"; if 989 unspecified, the h/w is not initialized. 990 991 pl011,<addr> 992 pl011,mmio32,<addr> 993 Start an early, polled-mode console on a pl011 serial 994 port at the specified address. The pl011 serial port 995 must already be setup and configured. Options are not 996 yet supported. If 'mmio32' is specified, then only 997 the driver will use only 32-bit accessors to read/write 998 the device registers. 999 1000 meson,<addr> 1001 Start an early, polled-mode console on a meson serial 1002 port at the specified address. The serial port must 1003 already be setup and configured. Options are not yet 1004 supported. 1005 1006 msm_serial,<addr> 1007 Start an early, polled-mode console on an msm serial 1008 port at the specified address. The serial port 1009 must already be setup and configured. Options are not 1010 yet supported. 1011 1012 msm_serial_dm,<addr> 1013 Start an early, polled-mode console on an msm serial 1014 dm port at the specified address. The serial port 1015 must already be setup and configured. Options are not 1016 yet supported. 1017 1018 owl,<addr> 1019 Start an early, polled-mode console on a serial port 1020 of an Actions Semi SoC, such as S500 or S900, at the 1021 specified address. The serial port must already be 1022 setup and configured. Options are not yet supported. 1023 1024 smh Use ARM semihosting calls for early console. 1025 1026 s3c2410,<addr> 1027 s3c2412,<addr> 1028 s3c2440,<addr> 1029 s3c6400,<addr> 1030 s5pv210,<addr> 1031 exynos4210,<addr> 1032 Use early console provided by serial driver available 1033 on Samsung SoCs, requires selecting proper type and 1034 a correct base address of the selected UART port. The 1035 serial port must already be setup and configured. 1036 Options are not yet supported. 1037 1038 lantiq,<addr> 1039 Start an early, polled-mode console on a lantiq serial 1040 (lqasc) port at the specified address. The serial port 1041 must already be setup and configured. Options are not 1042 yet supported. 1043 1044 lpuart,<addr> 1045 lpuart32,<addr> 1046 Use early console provided by Freescale LP UART driver 1047 found on Freescale Vybrid and QorIQ LS1021A processors. 1048 A valid base address must be provided, and the serial 1049 port must already be setup and configured. 1050 1051 ar3700_uart,<addr> 1052 Start an early, polled-mode console on the 1053 Armada 3700 serial port at the specified 1054 address. The serial port must already be setup 1055 and configured. Options are not yet supported. 1056 1057 qcom_geni,<addr> 1058 Start an early, polled-mode console on a Qualcomm 1059 Generic Interface (GENI) based serial port at the 1060 specified address. The serial port must already be 1061 setup and configured. Options are not yet supported. 1062 1063 earlyprintk= [X86,SH,ARM,M68k,S390] 1064 earlyprintk=vga 1065 earlyprintk=efi 1066 earlyprintk=sclp 1067 earlyprintk=xen 1068 earlyprintk=serial[,ttySn[,baudrate]] 1069 earlyprintk=serial[,0x...[,baudrate]] 1070 earlyprintk=ttySn[,baudrate] 1071 earlyprintk=dbgp[debugController#] 1072 earlyprintk=pciserial[,force],bus:device.function[,baudrate] 1073 earlyprintk=xdbc[xhciController#] 1074 1075 earlyprintk is useful when the kernel crashes before 1076 the normal console is initialized. It is not enabled by 1077 default because it has some cosmetic problems. 1078 1079 Append ",keep" to not disable it when the real console 1080 takes over. 1081 1082 Only one of vga, efi, serial, or usb debug port can 1083 be used at a time. 1084 1085 Currently only ttyS0 and ttyS1 may be specified by 1086 name. Other I/O ports may be explicitly specified 1087 on some architectures (x86 and arm at least) by 1088 replacing ttySn with an I/O port address, like this: 1089 earlyprintk=serial,0x1008,115200 1090 You can find the port for a given device in 1091 /proc/tty/driver/serial: 1092 2: uart:ST16650V2 port:00001008 irq:18 ... 1093 1094 Interaction with the standard serial driver is not 1095 very good. 1096 1097 The VGA and EFI output is eventually overwritten by 1098 the real console. 1099 1100 The xen output can only be used by Xen PV guests. 1101 1102 The sclp output can only be used on s390. 1103 1104 The optional "force" to "pciserial" enables use of a 1105 PCI device even when its classcode is not of the 1106 UART class. 1107 1108 edac_report= [HW,EDAC] Control how to report EDAC event 1109 Format: {"on" | "off" | "force"} 1110 on: enable EDAC to report H/W event. May be overridden 1111 by other higher priority error reporting module. 1112 off: disable H/W event reporting through EDAC. 1113 force: enforce the use of EDAC to report H/W event. 1114 default: on. 1115 1116 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1117 ekgdboc=kbd 1118 1119 This is designed to be used in conjunction with 1120 the boot argument: earlyprintk=vga 1121 1122 edd= [EDD] 1123 Format: {"off" | "on" | "skip[mbr]"} 1124 1125 efi= [EFI] 1126 Format: { "old_map", "nochunk", "noruntime", "debug" } 1127 old_map [X86-64]: switch to the old ioremap-based EFI 1128 runtime services mapping. 32-bit still uses this one by 1129 default. 1130 nochunk: disable reading files in "chunks" in the EFI 1131 boot stub, as chunking can cause problems with some 1132 firmware implementations. 1133 noruntime : disable EFI runtime services support 1134 debug: enable misc debug output 1135 1136 efi_no_storage_paranoia [EFI; X86] 1137 Using this parameter you can use more than 50% of 1138 your efi variable storage. Use this parameter only if 1139 you are really sure that your UEFI does sane gc and 1140 fulfills the spec otherwise your board may brick. 1141 1142 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1143 Add arbitrary attribute to specific memory range by 1144 updating original EFI memory map. 1145 Region of memory which aa attribute is added to is 1146 from ss to ss+nn. 1147 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1148 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1149 attribute is added to range 0x100000000-0x180000000 and 1150 0x10a0000000-0x1120000000. 1151 1152 Using this parameter you can do debugging of EFI memmap 1153 related feature. For example, you can do debugging of 1154 Address Range Mirroring feature even if your box 1155 doesn't support it. 1156 1157 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1158 that is to be dynamically loaded by Linux. If there are 1159 multiple variables with the same name but with different 1160 vendor GUIDs, all of them will be loaded. See 1161 Documentation/acpi/ssdt-overlays.txt for details. 1162 1163 1164 eisa_irq_edge= [PARISC,HW] 1165 See header of drivers/parisc/eisa.c. 1166 1167 elanfreq= [X86-32] 1168 See comment before function elanfreq_setup() in 1169 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1170 1171 elevator= [IOSCHED] 1172 Format: {"cfq" | "deadline" | "noop"} 1173 See Documentation/block/cfq-iosched.txt and 1174 Documentation/block/deadline-iosched.txt for details. 1175 1176 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1177 Specifies physical address of start of kernel core 1178 image elf header and optionally the size. Generally 1179 kexec loader will pass this option to capture kernel. 1180 See Documentation/kdump/kdump.txt for details. 1181 1182 enable_mtrr_cleanup [X86] 1183 The kernel tries to adjust MTRR layout from continuous 1184 to discrete, to make X server driver able to add WB 1185 entry later. This parameter enables that. 1186 1187 enable_timer_pin_1 [X86] 1188 Enable PIN 1 of APIC timer 1189 Can be useful to work around chipset bugs 1190 (in particular on some ATI chipsets). 1191 The kernel tries to set a reasonable default. 1192 1193 enforcing [SELINUX] Set initial enforcing status. 1194 Format: {"0" | "1"} 1195 See security/selinux/Kconfig help text. 1196 0 -- permissive (log only, no denials). 1197 1 -- enforcing (deny and log). 1198 Default value is 0. 1199 Value can be changed at runtime via /selinux/enforce. 1200 1201 erst_disable [ACPI] 1202 Disable Error Record Serialization Table (ERST) 1203 support. 1204 1205 ether= [HW,NET] Ethernet cards parameters 1206 This option is obsoleted by the "netdev=" option, which 1207 has equivalent usage. See its documentation for details. 1208 1209 evm= [EVM] 1210 Format: { "fix" } 1211 Permit 'security.evm' to be updated regardless of 1212 current integrity status. 1213 1214 failslab= 1215 fail_page_alloc= 1216 fail_make_request=[KNL] 1217 General fault injection mechanism. 1218 Format: <interval>,<probability>,<space>,<times> 1219 See also Documentation/fault-injection/. 1220 1221 floppy= [HW] 1222 See Documentation/blockdev/floppy.txt. 1223 1224 force_pal_cache_flush 1225 [IA-64] Avoid check_sal_cache_flush which may hang on 1226 buggy SAL_CACHE_FLUSH implementations. Using this 1227 parameter will force ia64_sal_cache_flush to call 1228 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1229 1230 forcepae [X86-32] 1231 Forcefully enable Physical Address Extension (PAE). 1232 Many Pentium M systems disable PAE but may have a 1233 functionally usable PAE implementation. 1234 Warning: use of this parameter will taint the kernel 1235 and may cause unknown problems. 1236 1237 ftrace=[tracer] 1238 [FTRACE] will set and start the specified tracer 1239 as early as possible in order to facilitate early 1240 boot debugging. 1241 1242 ftrace_dump_on_oops[=orig_cpu] 1243 [FTRACE] will dump the trace buffers on oops. 1244 If no parameter is passed, ftrace will dump 1245 buffers of all CPUs, but if you pass orig_cpu, it will 1246 dump only the buffer of the CPU that triggered the 1247 oops. 1248 1249 ftrace_filter=[function-list] 1250 [FTRACE] Limit the functions traced by the function 1251 tracer at boot up. function-list is a comma separated 1252 list of functions. This list can be changed at run 1253 time by the set_ftrace_filter file in the debugfs 1254 tracing directory. 1255 1256 ftrace_notrace=[function-list] 1257 [FTRACE] Do not trace the functions specified in 1258 function-list. This list can be changed at run time 1259 by the set_ftrace_notrace file in the debugfs 1260 tracing directory. 1261 1262 ftrace_graph_filter=[function-list] 1263 [FTRACE] Limit the top level callers functions traced 1264 by the function graph tracer at boot up. 1265 function-list is a comma separated list of functions 1266 that can be changed at run time by the 1267 set_graph_function file in the debugfs tracing directory. 1268 1269 ftrace_graph_notrace=[function-list] 1270 [FTRACE] Do not trace from the functions specified in 1271 function-list. This list is a comma separated list of 1272 functions that can be changed at run time by the 1273 set_graph_notrace file in the debugfs tracing directory. 1274 1275 ftrace_graph_max_depth=<uint> 1276 [FTRACE] Used with the function graph tracer. This is 1277 the max depth it will trace into a function. This value 1278 can be changed at run time by the max_graph_depth file 1279 in the tracefs tracing directory. default: 0 (no limit) 1280 1281 gamecon.map[2|3]= 1282 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1283 support via parallel port (up to 5 devices per port) 1284 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1285 See also Documentation/input/devices/joystick-parport.rst 1286 1287 gamma= [HW,DRM] 1288 1289 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1290 Format: off | on 1291 default: on 1292 1293 gcov_persist= [GCOV] When non-zero (default), profiling data for 1294 kernel modules is saved and remains accessible via 1295 debugfs, even when the module is unloaded/reloaded. 1296 When zero, profiling data is discarded and associated 1297 debugfs files are removed at module unload time. 1298 1299 goldfish [X86] Enable the goldfish android emulator platform. 1300 Don't use this when you are not running on the 1301 android emulator 1302 1303 gpt [EFI] Forces disk with valid GPT signature but 1304 invalid Protective MBR to be treated as GPT. If the 1305 primary GPT is corrupted, it enables the backup/alternate 1306 GPT to be used instead. 1307 1308 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1309 the "Enable 0" bit of the configuration register. 1310 Format: 0 | 1 1311 Default: 0 1312 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1313 the "Enable 0" bit of the configuration register. 1314 Format: 0 | 1 1315 Default: 0 1316 grcan.select= [HW] Select which physical interface to use. 1317 Format: 0 | 1 1318 Default: 0 1319 grcan.txsize= [HW] Sets the size of the tx buffer. 1320 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1321 Default: 1024 1322 grcan.rxsize= [HW] Sets the size of the rx buffer. 1323 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1324 Default: 1024 1325 1326 gpio-mockup.gpio_mockup_ranges 1327 [HW] Sets the ranges of gpiochip of for this device. 1328 Format: <start1>,<end1>,<start2>,<end2>... 1329 1330 hardlockup_all_cpu_backtrace= 1331 [KNL] Should the hard-lockup detector generate 1332 backtraces on all cpus. 1333 Format: <integer> 1334 1335 hashdist= [KNL,NUMA] Large hashes allocated during boot 1336 are distributed across NUMA nodes. Defaults on 1337 for 64-bit NUMA, off otherwise. 1338 Format: 0 | 1 (for off | on) 1339 1340 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1341 1342 hd= [EIDE] (E)IDE hard drive subsystem geometry 1343 Format: <cyl>,<head>,<sect> 1344 1345 hest_disable [ACPI] 1346 Disable Hardware Error Source Table (HEST) support; 1347 corresponding firmware-first mode error processing 1348 logic will be disabled. 1349 1350 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1351 size of <nn>. This works even on boxes that have no 1352 highmem otherwise. This also works to reduce highmem 1353 size on bigger boxes. 1354 1355 highres= [KNL] Enable/disable high resolution timer mode. 1356 Valid parameters: "on", "off" 1357 Default: "on" 1358 1359 hisax= [HW,ISDN] 1360 See Documentation/isdn/README.HiSax. 1361 1362 hlt [BUGS=ARM,SH] 1363 1364 hpet= [X86-32,HPET] option to control HPET usage 1365 Format: { enable (default) | disable | force | 1366 verbose } 1367 disable: disable HPET and use PIT instead 1368 force: allow force enabled of undocumented chips (ICH4, 1369 VIA, nVidia) 1370 verbose: show contents of HPET registers during setup 1371 1372 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1373 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1374 1375 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1376 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1377 On x86-64 and powerpc, this option can be specified 1378 multiple times interleaved with hugepages= to reserve 1379 huge pages of different sizes. Valid pages sizes on 1380 x86-64 are 2M (when the CPU supports "pse") and 1G 1381 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1382 1383 hung_task_panic= 1384 [KNL] Should the hung task detector generate panics. 1385 Format: <integer> 1386 1387 A nonzero value instructs the kernel to panic when a 1388 hung task is detected. The default value is controlled 1389 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time 1390 option. The value selected by this boot parameter can 1391 be changed later by the kernel.hung_task_panic sysctl. 1392 1393 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1394 terminal devices. Valid values: 0..8 1395 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1396 If specified, z/VM IUCV HVC accepts connections 1397 from listed z/VM user IDs only. 1398 1399 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations 1400 which allow the hypervisor to 'idle' the 1401 guest on lock contention. 1402 1403 keep_bootcon [KNL] 1404 Do not unregister boot console at start. This is only 1405 useful for debugging when something happens in the window 1406 between unregistering the boot console and initializing 1407 the real console. 1408 1409 i2c_bus= [HW] Override the default board specific I2C bus speed 1410 or register an additional I2C bus that is not 1411 registered from board initialization code. 1412 Format: 1413 <bus_id>,<clkrate> 1414 1415 i8042.debug [HW] Toggle i8042 debug mode 1416 i8042.unmask_kbd_data 1417 [HW] Enable printing of interrupt data from the KBD port 1418 (disabled by default, and as a pre-condition 1419 requires that i8042.debug=1 be enabled) 1420 i8042.direct [HW] Put keyboard port into non-translated mode 1421 i8042.dumbkbd [HW] Pretend that controller can only read data from 1422 keyboard and cannot control its state 1423 (Don't attempt to blink the leds) 1424 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1425 i8042.nokbd [HW] Don't check/create keyboard port 1426 i8042.noloop [HW] Disable the AUX Loopback command while probing 1427 for the AUX port 1428 i8042.nomux [HW] Don't check presence of an active multiplexing 1429 controller 1430 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1431 controllers 1432 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1433 i8042.reset [HW] Reset the controller during init, cleanup and 1434 suspend-to-ram transitions, only during s2r 1435 transitions, or never reset 1436 Format: { 1 | Y | y | 0 | N | n } 1437 1, Y, y: always reset controller 1438 0, N, n: don't ever reset controller 1439 Default: only on s2r transitions on x86; most other 1440 architectures force reset to be always executed 1441 i8042.unlock [HW] Unlock (ignore) the keylock 1442 i8042.kbdreset [HW] Reset device connected to KBD port 1443 1444 i810= [HW,DRM] 1445 1446 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1447 indicates that the driver is running on unsupported 1448 hardware. 1449 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1450 does not match list of supported models. 1451 i8k.power_status 1452 [HW] Report power status in /proc/i8k 1453 (disabled by default) 1454 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1455 capability is set. 1456 1457 i915.invert_brightness= 1458 [DRM] Invert the sense of the variable that is used to 1459 set the brightness of the panel backlight. Normally a 1460 brightness value of 0 indicates backlight switched off, 1461 and the maximum of the brightness value sets the backlight 1462 to maximum brightness. If this parameter is set to 0 1463 (default) and the machine requires it, or this parameter 1464 is set to 1, a brightness value of 0 sets the backlight 1465 to maximum brightness, and the maximum of the brightness 1466 value switches the backlight off. 1467 -1 -- never invert brightness 1468 0 -- machine default 1469 1 -- force brightness inversion 1470 1471 icn= [HW,ISDN] 1472 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1473 1474 ide-core.nodma= [HW] (E)IDE subsystem 1475 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1476 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1477 .cdrom .chs .ignore_cable are additional options 1478 See Documentation/ide/ide.txt. 1479 1480 ide-generic.probe-mask= [HW] (E)IDE subsystem 1481 Format: <int> 1482 Probe mask for legacy ISA IDE ports. Depending on 1483 platform up to 6 ports are supported, enabled by 1484 setting corresponding bits in the mask to 1. The 1485 default value is 0x0, which has a special meaning. 1486 On systems that have PCI, it triggers scanning the 1487 PCI bus for the first and the second port, which 1488 are then probed. On systems without PCI the value 1489 of 0x0 enables probing the two first ports as if it 1490 was 0x3. 1491 1492 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1493 Claim all unknown PCI IDE storage controllers. 1494 1495 idle= [X86] 1496 Format: idle=poll, idle=halt, idle=nomwait 1497 Poll forces a polling idle loop that can slightly 1498 improve the performance of waking up a idle CPU, but 1499 will use a lot of power and make the system run hot. 1500 Not recommended. 1501 idle=halt: Halt is forced to be used for CPU idle. 1502 In such case C2/C3 won't be used again. 1503 idle=nomwait: Disable mwait for CPU C-states 1504 1505 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1506 Format: { strict | legacy | 2008 | relaxed } 1507 Default: strict 1508 1509 Choose which programs will be accepted for execution 1510 based on the IEEE 754 NaN encoding(s) supported by 1511 the FPU and the NaN encoding requested with the value 1512 of an ELF file header flag individually set by each 1513 binary. Hardware implementations are permitted to 1514 support either or both of the legacy and the 2008 NaN 1515 encoding mode. 1516 1517 Available settings are as follows: 1518 strict accept binaries that request a NaN encoding 1519 supported by the FPU 1520 legacy only accept legacy-NaN binaries, if supported 1521 by the FPU 1522 2008 only accept 2008-NaN binaries, if supported 1523 by the FPU 1524 relaxed accept any binaries regardless of whether 1525 supported by the FPU 1526 1527 The FPU emulator is always able to support both NaN 1528 encodings, so if no FPU hardware is present or it has 1529 been disabled with 'nofpu', then the settings of 1530 'legacy' and '2008' strap the emulator accordingly, 1531 'relaxed' straps the emulator for both legacy-NaN and 1532 2008-NaN, whereas 'strict' enables legacy-NaN only on 1533 legacy processors and both NaN encodings on MIPS32 or 1534 MIPS64 CPUs. 1535 1536 The setting for ABS.fmt/NEG.fmt instruction execution 1537 mode generally follows that for the NaN encoding, 1538 except where unsupported by hardware. 1539 1540 ignore_loglevel [KNL] 1541 Ignore loglevel setting - this will print /all/ 1542 kernel messages to the console. Useful for debugging. 1543 We also add it as printk module parameter, so users 1544 could change it dynamically, usually by 1545 /sys/module/printk/parameters/ignore_loglevel. 1546 1547 ignore_rlimit_data 1548 Ignore RLIMIT_DATA setting for data mappings, 1549 print warning at first misuse. Can be changed via 1550 /sys/module/kernel/parameters/ignore_rlimit_data. 1551 1552 ihash_entries= [KNL] 1553 Set number of hash buckets for inode cache. 1554 1555 ima_appraise= [IMA] appraise integrity measurements 1556 Format: { "off" | "enforce" | "fix" | "log" } 1557 default: "enforce" 1558 1559 ima_appraise_tcb [IMA] 1560 The builtin appraise policy appraises all files 1561 owned by uid=0. 1562 1563 ima_canonical_fmt [IMA] 1564 Use the canonical format for the binary runtime 1565 measurements, instead of host native format. 1566 1567 ima_hash= [IMA] 1568 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1569 | sha512 | ... } 1570 default: "sha1" 1571 1572 The list of supported hash algorithms is defined 1573 in crypto/hash_info.h. 1574 1575 ima_policy= [IMA] 1576 The builtin policies to load during IMA setup. 1577 Format: "tcb | appraise_tcb | secure_boot | 1578 fail_securely" 1579 1580 The "tcb" policy measures all programs exec'd, files 1581 mmap'd for exec, and all files opened with the read 1582 mode bit set by either the effective uid (euid=0) or 1583 uid=0. 1584 1585 The "appraise_tcb" policy appraises the integrity of 1586 all files owned by root. (This is the equivalent 1587 of ima_appraise_tcb.) 1588 1589 The "secure_boot" policy appraises the integrity 1590 of files (eg. kexec kernel image, kernel modules, 1591 firmware, policy, etc) based on file signatures. 1592 1593 The "fail_securely" policy forces file signature 1594 verification failure also on privileged mounted 1595 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE 1596 flag. 1597 1598 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1599 Load a policy which meets the needs of the Trusted 1600 Computing Base. This means IMA will measure all 1601 programs exec'd, files mmap'd for exec, and all files 1602 opened for read by uid=0. 1603 1604 ima_template= [IMA] 1605 Select one of defined IMA measurements template formats. 1606 Formats: { "ima" | "ima-ng" | "ima-sig" } 1607 Default: "ima-ng" 1608 1609 ima_template_fmt= 1610 [IMA] Define a custom template format. 1611 Format: { "field1|...|fieldN" } 1612 1613 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1614 Format: <min_file_size> 1615 Set the minimal file size for using asynchronous hash. 1616 If left unspecified, ahash usage is disabled. 1617 1618 ahash performance varies for different data sizes on 1619 different crypto accelerators. This option can be used 1620 to achieve the best performance for a particular HW. 1621 1622 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1623 Format: <bufsize> 1624 Set hashing buffer size. Default: 4k. 1625 1626 ahash performance varies for different chunk sizes on 1627 different crypto accelerators. This option can be used 1628 to achieve best performance for particular HW. 1629 1630 init= [KNL] 1631 Format: <full_path> 1632 Run specified binary instead of /sbin/init as init 1633 process. 1634 1635 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1636 for working out where the kernel is dying during 1637 startup. 1638 1639 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1640 initcall functions. Useful for debugging built-in 1641 modules and initcalls. 1642 1643 initrd= [BOOT] Specify the location of the initial ramdisk 1644 1645 init_pkru= [x86] Specify the default memory protection keys rights 1646 register contents for all processes. 0x55555554 by 1647 default (disallow access to all but pkey 0). Can 1648 override in debugfs after boot. 1649 1650 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1651 Format: <irq> 1652 1653 int_pln_enable [x86] Enable power limit notification interrupt 1654 1655 integrity_audit=[IMA] 1656 Format: { "0" | "1" } 1657 0 -- basic integrity auditing messages. (Default) 1658 1 -- additional integrity auditing messages. 1659 1660 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1661 on 1662 Enable intel iommu driver. 1663 off 1664 Disable intel iommu driver. 1665 igfx_off [Default Off] 1666 By default, gfx is mapped as normal device. If a gfx 1667 device has a dedicated DMAR unit, the DMAR unit is 1668 bypassed by not enabling DMAR with this option. In 1669 this case, gfx device will use physical address for 1670 DMA. 1671 forcedac [x86_64] 1672 With this option iommu will not optimize to look 1673 for io virtual address below 32-bit forcing dual 1674 address cycle on pci bus for cards supporting greater 1675 than 32-bit addressing. The default is to look 1676 for translation below 32-bit and if not available 1677 then look in the higher range. 1678 strict [Default Off] 1679 With this option on every unmap_single operation will 1680 result in a hardware IOTLB flush operation as opposed 1681 to batching them for performance. 1682 sp_off [Default Off] 1683 By default, super page will be supported if Intel IOMMU 1684 has the capability. With this option, super page will 1685 not be supported. 1686 ecs_off [Default Off] 1687 By default, extended context tables will be supported if 1688 the hardware advertises that it has support both for the 1689 extended tables themselves, and also PASID support. With 1690 this option set, extended tables will not be used even 1691 on hardware which claims to support them. 1692 tboot_noforce [Default Off] 1693 Do not force the Intel IOMMU enabled under tboot. 1694 By default, tboot will force Intel IOMMU on, which 1695 could harm performance of some high-throughput 1696 devices like 40GBit network cards, even if identity 1697 mapping is enabled. 1698 Note that using this option lowers the security 1699 provided by tboot because it makes the system 1700 vulnerable to DMA attacks. 1701 1702 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1703 0 disables intel_idle and fall back on acpi_idle. 1704 1 to 9 specify maximum depth of C-state. 1705 1706 intel_pstate= [X86] 1707 disable 1708 Do not enable intel_pstate as the default 1709 scaling driver for the supported processors 1710 passive 1711 Use intel_pstate as a scaling driver, but configure it 1712 to work with generic cpufreq governors (instead of 1713 enabling its internal governor). This mode cannot be 1714 used along with the hardware-managed P-states (HWP) 1715 feature. 1716 force 1717 Enable intel_pstate on systems that prohibit it by default 1718 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1719 instead of acpi-cpufreq may disable platform features, such 1720 as thermal controls and power capping, that rely on ACPI 1721 P-States information being indicated to OSPM and therefore 1722 should be used with caution. This option does not work with 1723 processors that aren't supported by the intel_pstate driver 1724 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1725 no_hwp 1726 Do not enable hardware P state control (HWP) 1727 if available. 1728 hwp_only 1729 Only load intel_pstate on systems which support 1730 hardware P state control (HWP) if available. 1731 support_acpi_ppc 1732 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1733 Description Table, specifies preferred power management 1734 profile as "Enterprise Server" or "Performance Server", 1735 then this feature is turned on by default. 1736 per_cpu_perf_limits 1737 Allow per-logical-CPU P-State performance control limits using 1738 cpufreq sysfs interface 1739 1740 intremap= [X86-64, Intel-IOMMU] 1741 on enable Interrupt Remapping (default) 1742 off disable Interrupt Remapping 1743 nosid disable Source ID checking 1744 no_x2apic_optout 1745 BIOS x2APIC opt-out request will be ignored 1746 nopost disable Interrupt Posting 1747 1748 iomem= Disable strict checking of access to MMIO memory 1749 strict regions from userspace. 1750 relaxed 1751 1752 iommu= [x86] 1753 off 1754 force 1755 noforce 1756 biomerge 1757 panic 1758 nopanic 1759 merge 1760 nomerge 1761 soft 1762 pt [x86] 1763 nopt [x86] 1764 nobypass [PPC/POWERNV] 1765 Disable IOMMU bypass, using IOMMU for PCI devices. 1766 1767 iommu.strict= [ARM64] Configure TLB invalidation behaviour 1768 Format: { "0" | "1" } 1769 0 - Lazy mode. 1770 Request that DMA unmap operations use deferred 1771 invalidation of hardware TLBs, for increased 1772 throughput at the cost of reduced device isolation. 1773 Will fall back to strict mode if not supported by 1774 the relevant IOMMU driver. 1775 1 - Strict mode (default). 1776 DMA unmap operations invalidate IOMMU hardware TLBs 1777 synchronously. 1778 1779 iommu.passthrough= 1780 [ARM64] Configure DMA to bypass the IOMMU by default. 1781 Format: { "0" | "1" } 1782 0 - Use IOMMU translation for DMA. 1783 1 - Bypass the IOMMU for DMA. 1784 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH. 1785 1786 io7= [HW] IO7 for Marvel based alpha systems 1787 See comment before marvel_specify_io7 in 1788 arch/alpha/kernel/core_marvel.c. 1789 1790 io_delay= [X86] I/O delay method 1791 0x80 1792 Standard port 0x80 based delay 1793 0xed 1794 Alternate port 0xed based delay (needed on some systems) 1795 udelay 1796 Simple two microseconds delay 1797 none 1798 No delay 1799 1800 ip= [IP_PNP] 1801 See Documentation/filesystems/nfs/nfsroot.txt. 1802 1803 irqaffinity= [SMP] Set the default irq affinity mask 1804 The argument is a cpu list, as described above. 1805 1806 irqchip.gicv2_force_probe= 1807 [ARM, ARM64] 1808 Format: <bool> 1809 Force the kernel to look for the second 4kB page 1810 of a GICv2 controller even if the memory range 1811 exposed by the device tree is too small. 1812 1813 irqchip.gicv3_nolpi= 1814 [ARM, ARM64] 1815 Force the kernel to ignore the availability of 1816 LPIs (and by consequence ITSs). Intended for system 1817 that use the kernel as a bootloader, and thus want 1818 to let secondary kernels in charge of setting up 1819 LPIs. 1820 1821 irqfixup [HW] 1822 When an interrupt is not handled search all handlers 1823 for it. Intended to get systems with badly broken 1824 firmware running. 1825 1826 irqpoll [HW] 1827 When an interrupt is not handled search all handlers 1828 for it. Also check all handlers each timer 1829 interrupt. Intended to get systems with badly broken 1830 firmware running. 1831 1832 isapnp= [ISAPNP] 1833 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1834 1835 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance. 1836 [Deprecated - use cpusets instead] 1837 Format: [flag-list,]<cpu-list> 1838 1839 Specify one or more CPUs to isolate from disturbances 1840 specified in the flag list (default: domain): 1841 1842 nohz 1843 Disable the tick when a single task runs. 1844 1845 A residual 1Hz tick is offloaded to workqueues, which you 1846 need to affine to housekeeping through the global 1847 workqueue's affinity configured via the 1848 /sys/devices/virtual/workqueue/cpumask sysfs file, or 1849 by using the 'domain' flag described below. 1850 1851 NOTE: by default the global workqueue runs on all CPUs, 1852 so to protect individual CPUs the 'cpumask' file has to 1853 be configured manually after bootup. 1854 1855 domain 1856 Isolate from the general SMP balancing and scheduling 1857 algorithms. Note that performing domain isolation this way 1858 is irreversible: it's not possible to bring back a CPU to 1859 the domains once isolated through isolcpus. It's strongly 1860 advised to use cpusets instead to disable scheduler load 1861 balancing through the "cpuset.sched_load_balance" file. 1862 It offers a much more flexible interface where CPUs can 1863 move in and out of an isolated set anytime. 1864 1865 You can move a process onto or off an "isolated" CPU via 1866 the CPU affinity syscalls or cpuset. 1867 <cpu number> begins at 0 and the maximum value is 1868 "number of CPUs in system - 1". 1869 1870 The format of <cpu-list> is described above. 1871 1872 1873 1874 iucv= [HW,NET] 1875 1876 ivrs_ioapic [HW,X86_64] 1877 Provide an override to the IOAPIC-ID<->DEVICE-ID 1878 mapping provided in the IVRS ACPI table. For 1879 example, to map IOAPIC-ID decimal 10 to 1880 PCI device 00:14.0 write the parameter as: 1881 ivrs_ioapic[10]=00:14.0 1882 1883 ivrs_hpet [HW,X86_64] 1884 Provide an override to the HPET-ID<->DEVICE-ID 1885 mapping provided in the IVRS ACPI table. For 1886 example, to map HPET-ID decimal 0 to 1887 PCI device 00:14.0 write the parameter as: 1888 ivrs_hpet[0]=00:14.0 1889 1890 ivrs_acpihid [HW,X86_64] 1891 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1892 mapping provided in the IVRS ACPI table. For 1893 example, to map UART-HID:UID AMD0020:0 to 1894 PCI device 00:14.5 write the parameter as: 1895 ivrs_acpihid[00:14.5]=AMD0020:0 1896 1897 js= [HW,JOY] Analog joystick 1898 See Documentation/input/joydev/joystick.rst. 1899 1900 nokaslr [KNL] 1901 When CONFIG_RANDOMIZE_BASE is set, this disables 1902 kernel and module base offset ASLR (Address Space 1903 Layout Randomization). 1904 1905 kasan_multi_shot 1906 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print 1907 report on every invalid memory access. Without this 1908 parameter KASAN will print report only for the first 1909 invalid access. 1910 1911 keepinitrd [HW,ARM] 1912 1913 kernelcore= [KNL,X86,IA-64,PPC] 1914 Format: nn[KMGTPE] | nn% | "mirror" 1915 This parameter specifies the amount of memory usable by 1916 the kernel for non-movable allocations. The requested 1917 amount is spread evenly throughout all nodes in the 1918 system as ZONE_NORMAL. The remaining memory is used for 1919 movable memory in its own zone, ZONE_MOVABLE. In the 1920 event, a node is too small to have both ZONE_NORMAL and 1921 ZONE_MOVABLE, kernelcore memory will take priority and 1922 other nodes will have a larger ZONE_MOVABLE. 1923 1924 ZONE_MOVABLE is used for the allocation of pages that 1925 may be reclaimed or moved by the page migration 1926 subsystem. Note that allocations like PTEs-from-HighMem 1927 still use the HighMem zone if it exists, and the Normal 1928 zone if it does not. 1929 1930 It is possible to specify the exact amount of memory in 1931 the form of "nn[KMGTPE]", a percentage of total system 1932 memory in the form of "nn%", or "mirror". If "mirror" 1933 option is specified, mirrored (reliable) memory is used 1934 for non-movable allocations and remaining memory is used 1935 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror" 1936 are exclusive, so you cannot specify multiple forms. 1937 1938 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1939 Format: <Controller#>[,poll interval] 1940 The controller # is the number of the ehci usb debug 1941 port as it is probed via PCI. The poll interval is 1942 optional and is the number seconds in between 1943 each poll cycle to the debug port in case you need 1944 the functionality for interrupting the kernel with 1945 gdb or control-c on the dbgp connection. When 1946 not using this parameter you use sysrq-g to break into 1947 the kernel debugger. 1948 1949 kgdboc= [KGDB,HW] kgdb over consoles. 1950 Requires a tty driver that supports console polling, 1951 or a supported polling keyboard driver (non-usb). 1952 Serial only format: <serial_device>[,baud] 1953 keyboard only format: kbd 1954 keyboard and serial format: kbd,<serial_device>[,baud] 1955 Optional Kernel mode setting: 1956 kms, kbd format: kms,kbd 1957 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1958 1959 kgdbwait [KGDB] Stop kernel execution and enter the 1960 kernel debugger at the earliest opportunity. 1961 1962 kmac= [MIPS] korina ethernet MAC address. 1963 Configure the RouterBoard 532 series on-chip 1964 Ethernet adapter MAC address. 1965 1966 kmemleak= [KNL] Boot-time kmemleak enable/disable 1967 Valid arguments: on, off 1968 Default: on 1969 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1970 the default is off. 1971 1972 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1973 Default is 0 (don't ignore, but inject #GP) 1974 1975 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface. 1976 Default is false (don't support). 1977 1978 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1979 KVM MMU at runtime. 1980 Default is 0 (off) 1981 1982 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1983 Default is 1 (enabled) 1984 1985 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1986 for all guests. 1987 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1988 1989 kvm-arm.vgic_v3_group0_trap= 1990 [KVM,ARM] Trap guest accesses to GICv3 group-0 1991 system registers 1992 1993 kvm-arm.vgic_v3_group1_trap= 1994 [KVM,ARM] Trap guest accesses to GICv3 group-1 1995 system registers 1996 1997 kvm-arm.vgic_v3_common_trap= 1998 [KVM,ARM] Trap guest accesses to GICv3 common 1999 system registers 2000 2001 kvm-arm.vgic_v4_enable= 2002 [KVM,ARM] Allow use of GICv4 for direct injection of 2003 LPIs. 2004 2005 kvm-intel.ept= [KVM,Intel] Disable extended page tables 2006 (virtualized MMU) support on capable Intel chips. 2007 Default is 1 (enabled) 2008 2009 kvm-intel.emulate_invalid_guest_state= 2010 [KVM,Intel] Enable emulation of invalid guest states 2011 Default is 0 (disabled) 2012 2013 kvm-intel.flexpriority= 2014 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 2015 Default is 1 (enabled) 2016 2017 kvm-intel.nested= 2018 [KVM,Intel] Enable VMX nesting (nVMX). 2019 Default is 0 (disabled) 2020 2021 kvm-intel.unrestricted_guest= 2022 [KVM,Intel] Disable unrestricted guest feature 2023 (virtualized real and unpaged mode) on capable 2024 Intel chips. Default is 1 (enabled) 2025 2026 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault 2027 CVE-2018-3620. 2028 2029 Valid arguments: never, cond, always 2030 2031 always: L1D cache flush on every VMENTER. 2032 cond: Flush L1D on VMENTER only when the code between 2033 VMEXIT and VMENTER can leak host memory. 2034 never: Disables the mitigation 2035 2036 Default is cond (do L1 cache flush in specific instances) 2037 2038 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 2039 feature (tagged TLBs) on capable Intel chips. 2040 Default is 1 (enabled) 2041 2042 l1tf= [X86] Control mitigation of the L1TF vulnerability on 2043 affected CPUs 2044 2045 The kernel PTE inversion protection is unconditionally 2046 enabled and cannot be disabled. 2047 2048 full 2049 Provides all available mitigations for the 2050 L1TF vulnerability. Disables SMT and 2051 enables all mitigations in the 2052 hypervisors, i.e. unconditional L1D flush. 2053 2054 SMT control and L1D flush control via the 2055 sysfs interface is still possible after 2056 boot. Hypervisors will issue a warning 2057 when the first VM is started in a 2058 potentially insecure configuration, 2059 i.e. SMT enabled or L1D flush disabled. 2060 2061 full,force 2062 Same as 'full', but disables SMT and L1D 2063 flush runtime control. Implies the 2064 'nosmt=force' command line option. 2065 (i.e. sysfs control of SMT is disabled.) 2066 2067 flush 2068 Leaves SMT enabled and enables the default 2069 hypervisor mitigation, i.e. conditional 2070 L1D flush. 2071 2072 SMT control and L1D flush control via the 2073 sysfs interface is still possible after 2074 boot. Hypervisors will issue a warning 2075 when the first VM is started in a 2076 potentially insecure configuration, 2077 i.e. SMT enabled or L1D flush disabled. 2078 2079 flush,nosmt 2080 2081 Disables SMT and enables the default 2082 hypervisor mitigation. 2083 2084 SMT control and L1D flush control via the 2085 sysfs interface is still possible after 2086 boot. Hypervisors will issue a warning 2087 when the first VM is started in a 2088 potentially insecure configuration, 2089 i.e. SMT enabled or L1D flush disabled. 2090 2091 flush,nowarn 2092 Same as 'flush', but hypervisors will not 2093 warn when a VM is started in a potentially 2094 insecure configuration. 2095 2096 off 2097 Disables hypervisor mitigations and doesn't 2098 emit any warnings. 2099 2100 Default is 'flush'. 2101 2102 For details see: Documentation/admin-guide/l1tf.rst 2103 2104 l2cr= [PPC] 2105 2106 l3cr= [PPC] 2107 2108 lapic [X86-32,APIC] Enable the local APIC even if BIOS 2109 disabled it. 2110 2111 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 2112 value for LAPIC timer one-shot implementation. Default 2113 back to the programmable timer unit in the LAPIC. 2114 2115 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 2116 in C2 power state. 2117 2118 libata.dma= [LIBATA] DMA control 2119 libata.dma=0 Disable all PATA and SATA DMA 2120 libata.dma=1 PATA and SATA Disk DMA only 2121 libata.dma=2 ATAPI (CDROM) DMA only 2122 libata.dma=4 Compact Flash DMA only 2123 Combinations also work, so libata.dma=3 enables DMA 2124 for disks and CDROMs, but not CFs. 2125 2126 libata.ignore_hpa= [LIBATA] Ignore HPA limit 2127 libata.ignore_hpa=0 keep BIOS limits (default) 2128 libata.ignore_hpa=1 ignore limits, using full disk 2129 2130 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 2131 when set. 2132 Format: <int> 2133 2134 libata.force= [LIBATA] Force configurations. The format is comma 2135 separated list of "[ID:]VAL" where ID is 2136 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 2137 matching port, link or device. Basically, it matches 2138 the ATA ID string printed on console by libata. If 2139 the whole ID part is omitted, the last PORT and DEVICE 2140 values are used. If ID hasn't been specified yet, the 2141 configuration applies to all ports, links and devices. 2142 2143 If only DEVICE is omitted, the parameter applies to 2144 the port and all links and devices behind it. DEVICE 2145 number of 0 either selects the first device or the 2146 first fan-out link behind PMP device. It does not 2147 select the host link. DEVICE number of 15 selects the 2148 host link and device attached to it. 2149 2150 The VAL specifies the configuration to force. As long 2151 as there's no ambiguity shortcut notation is allowed. 2152 For example, both 1.5 and 1.5G would work for 1.5Gbps. 2153 The following configurations can be forced. 2154 2155 * Cable type: 40c, 80c, short40c, unk, ign or sata. 2156 Any ID with matching PORT is used. 2157 2158 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 2159 2160 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 2161 udma[/][16,25,33,44,66,100,133] notation is also 2162 allowed. 2163 2164 * [no]ncq: Turn on or off NCQ. 2165 2166 * [no]ncqtrim: Turn off queued DSM TRIM. 2167 2168 * nohrst, nosrst, norst: suppress hard, soft 2169 and both resets. 2170 2171 * rstonce: only attempt one reset during 2172 hot-unplug link recovery 2173 2174 * dump_id: dump IDENTIFY data. 2175 2176 * atapi_dmadir: Enable ATAPI DMADIR bridge support 2177 2178 * disable: Disable this device. 2179 2180 If there are multiple matching configurations changing 2181 the same attribute, the last one is used. 2182 2183 memblock=debug [KNL] Enable memblock debug messages. 2184 2185 load_ramdisk= [RAM] List of ramdisks to load from floppy 2186 See Documentation/blockdev/ramdisk.txt. 2187 2188 lockd.nlm_grace_period=P [NFS] Assign grace period. 2189 Format: <integer> 2190 2191 lockd.nlm_tcpport=N [NFS] Assign TCP port. 2192 Format: <integer> 2193 2194 lockd.nlm_timeout=T [NFS] Assign timeout value. 2195 Format: <integer> 2196 2197 lockd.nlm_udpport=M [NFS] Assign UDP port. 2198 Format: <integer> 2199 2200 locktorture.nreaders_stress= [KNL] 2201 Set the number of locking read-acquisition kthreads. 2202 Defaults to being automatically set based on the 2203 number of online CPUs. 2204 2205 locktorture.nwriters_stress= [KNL] 2206 Set the number of locking write-acquisition kthreads. 2207 2208 locktorture.onoff_holdoff= [KNL] 2209 Set time (s) after boot for CPU-hotplug testing. 2210 2211 locktorture.onoff_interval= [KNL] 2212 Set time (s) between CPU-hotplug operations, or 2213 zero to disable CPU-hotplug testing. 2214 2215 locktorture.shuffle_interval= [KNL] 2216 Set task-shuffle interval (jiffies). Shuffling 2217 tasks allows some CPUs to go into dyntick-idle 2218 mode during the locktorture test. 2219 2220 locktorture.shutdown_secs= [KNL] 2221 Set time (s) after boot system shutdown. This 2222 is useful for hands-off automated testing. 2223 2224 locktorture.stat_interval= [KNL] 2225 Time (s) between statistics printk()s. 2226 2227 locktorture.stutter= [KNL] 2228 Time (s) to stutter testing, for example, 2229 specifying five seconds causes the test to run for 2230 five seconds, wait for five seconds, and so on. 2231 This tests the locking primitive's ability to 2232 transition abruptly to and from idle. 2233 2234 locktorture.torture_type= [KNL] 2235 Specify the locking implementation to test. 2236 2237 locktorture.verbose= [KNL] 2238 Enable additional printk() statements. 2239 2240 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 2241 Format: <irq> 2242 2243 loglevel= All Kernel Messages with a loglevel smaller than the 2244 console loglevel will be printed to the console. It can 2245 also be changed with klogd or other programs. The 2246 loglevels are defined as follows: 2247 2248 0 (KERN_EMERG) system is unusable 2249 1 (KERN_ALERT) action must be taken immediately 2250 2 (KERN_CRIT) critical conditions 2251 3 (KERN_ERR) error conditions 2252 4 (KERN_WARNING) warning conditions 2253 5 (KERN_NOTICE) normal but significant condition 2254 6 (KERN_INFO) informational 2255 7 (KERN_DEBUG) debug-level messages 2256 2257 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 2258 in bytes. n must be a power of two and greater 2259 than the minimal size. The minimal size is defined 2260 by LOG_BUF_SHIFT kernel config parameter. There is 2261 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 2262 that allows to increase the default size depending on 2263 the number of CPUs. See init/Kconfig for more details. 2264 2265 logo.nologo [FB] Disables display of the built-in Linux logo. 2266 This may be used to provide more screen space for 2267 kernel log messages and is useful when debugging 2268 kernel boot problems. 2269 2270 lp=0 [LP] Specify parallel ports to use, e.g, 2271 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 2272 lp=reset first parallel port). 'lp=0' disables the 2273 lp=auto printer driver. 'lp=reset' (which can be 2274 specified in addition to the ports) causes 2275 attached printers to be reset. Using 2276 lp=port1,port2,... specifies the parallel ports 2277 to associate lp devices with, starting with 2278 lp0. A port specification may be 'none' to skip 2279 that lp device, or a parport name such as 2280 'parport0'. Specifying 'lp=auto' instead of a 2281 port specification list means that device IDs 2282 from each port should be examined, to see if 2283 an IEEE 1284-compliant printer is attached; if 2284 so, the driver will manage that printer. 2285 See also header of drivers/char/lp.c. 2286 2287 lpj=n [KNL] 2288 Sets loops_per_jiffy to given constant, thus avoiding 2289 time-consuming boot-time autodetection (up to 250 ms per 2290 CPU). 0 enables autodetection (default). To determine 2291 the correct value for your kernel, boot with normal 2292 autodetection and see what value is printed. Note that 2293 on SMP systems the preset will be applied to all CPUs, 2294 which is likely to cause problems if your CPUs need 2295 significantly divergent settings. An incorrect value 2296 will cause delays in the kernel to be wrong, leading to 2297 unpredictable I/O errors and other breakage. Although 2298 unlikely, in the extreme case this might damage your 2299 hardware. 2300 2301 ltpc= [NET] 2302 Format: <io>,<irq>,<dma> 2303 2304 lsm.debug [SECURITY] Enable LSM initialization debugging output. 2305 2306 machvec= [IA-64] Force the use of a particular machine-vector 2307 (machvec) in a generic kernel. 2308 Example: machvec=hpzx1_swiotlb 2309 2310 machtype= [Loongson] Share the same kernel image file between different 2311 yeeloong laptop. 2312 Example: machtype=lemote-yeeloong-2f-7inch 2313 2314 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2315 than or equal to this physical address is ignored. 2316 2317 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2318 will bring up during bootup. maxcpus=n : n >= 0 limits 2319 the kernel to bring up 'n' processors. Surely after 2320 bootup you can bring up the other plugged cpu by executing 2321 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2322 only takes effect during system bootup. 2323 While n=0 is a special case, it is equivalent to "nosmp", 2324 which also disables the IO APIC. 2325 2326 max_loop= [LOOP] The number of loop block devices that get 2327 (loop.max_loop) unconditionally pre-created at init time. The default 2328 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2329 of statically allocating a predefined number, loop 2330 devices can be requested on-demand with the 2331 /dev/loop-control interface. 2332 2333 mce [X86-32] Machine Check Exception 2334 2335 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2336 2337 md= [HW] RAID subsystems devices and level 2338 See Documentation/admin-guide/md.rst. 2339 2340 mdacon= [MDA] 2341 Format: <first>,<last> 2342 Specifies range of consoles to be captured by the MDA. 2343 2344 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2345 Amount of memory to be used when the kernel is not able 2346 to see the whole system memory or for test. 2347 [X86] Work as limiting max address. Use together 2348 with memmap= to avoid physical address space collisions. 2349 Without memmap= PCI devices could be placed at addresses 2350 belonging to unused RAM. 2351 2352 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2353 memory. 2354 2355 memchunk=nn[KMG] 2356 [KNL,SH] Allow user to override the default size for 2357 per-device physically contiguous DMA buffers. 2358 2359 memhp_default_state=online/offline 2360 [KNL] Set the initial state for the memory hotplug 2361 onlining policy. If not specified, the default value is 2362 set according to the 2363 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2364 option. 2365 See Documentation/memory-hotplug.txt. 2366 2367 memmap=exactmap [KNL,X86] Enable setting of an exact 2368 E820 memory map, as specified by the user. 2369 Such memmap=exactmap lines can be constructed based on 2370 BIOS output or other requirements. See the memmap=nn@ss 2371 option description. 2372 2373 memmap=nn[KMG]@ss[KMG] 2374 [KNL] Force usage of a specific region of memory. 2375 Region of memory to be used is from ss to ss+nn. 2376 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG], 2377 which limits max address to nn[KMG]. 2378 Multiple different regions can be specified, 2379 comma delimited. 2380 Example: 2381 memmap=100M@2G,100M#3G,1G!1024G 2382 2383 memmap=nn[KMG]#ss[KMG] 2384 [KNL,ACPI] Mark specific memory as ACPI data. 2385 Region of memory to be marked is from ss to ss+nn. 2386 2387 memmap=nn[KMG]$ss[KMG] 2388 [KNL,ACPI] Mark specific memory as reserved. 2389 Region of memory to be reserved is from ss to ss+nn. 2390 Example: Exclude memory from 0x18690000-0x1869ffff 2391 memmap=64K$0x18690000 2392 or 2393 memmap=0x10000$0x18690000 2394 Some bootloaders may need an escape character before '$', 2395 like Grub2, otherwise '$' and the following number 2396 will be eaten. 2397 2398 memmap=nn[KMG]!ss[KMG] 2399 [KNL,X86] Mark specific memory as protected. 2400 Region of memory to be used, from ss to ss+nn. 2401 The memory region may be marked as e820 type 12 (0xc) 2402 and is NVDIMM or ADR memory. 2403 2404 memmap=<size>%<offset>-<oldtype>+<newtype> 2405 [KNL,ACPI] Convert memory within the specified region 2406 from <oldtype> to <newtype>. If "-<oldtype>" is left 2407 out, the whole region will be marked as <newtype>, 2408 even if previously unavailable. If "+<newtype>" is left 2409 out, matching memory will be removed. Types are 2410 specified as e820 types, e.g., 1 = RAM, 2 = reserved, 2411 3 = ACPI, 12 = PRAM. 2412 2413 memory_corruption_check=0/1 [X86] 2414 Some BIOSes seem to corrupt the first 64k of 2415 memory when doing things like suspend/resume. 2416 Setting this option will scan the memory 2417 looking for corruption. Enabling this will 2418 both detect corruption and prevent the kernel 2419 from using the memory being corrupted. 2420 However, its intended as a diagnostic tool; if 2421 repeatable BIOS-originated corruption always 2422 affects the same memory, you can use memmap= 2423 to prevent the kernel from using that memory. 2424 2425 memory_corruption_check_size=size [X86] 2426 By default it checks for corruption in the low 2427 64k, making this memory unavailable for normal 2428 use. Use this parameter to scan for 2429 corruption in more or less memory. 2430 2431 memory_corruption_check_period=seconds [X86] 2432 By default it checks for corruption every 60 2433 seconds. Use this parameter to check at some 2434 other rate. 0 disables periodic checking. 2435 2436 memtest= [KNL,X86,ARM,PPC] Enable memtest 2437 Format: <integer> 2438 default : 0 <disable> 2439 Specifies the number of memtest passes to be 2440 performed. Each pass selects another test 2441 pattern from a given set of patterns. Memtest 2442 fills the memory with this pattern, validates 2443 memory contents and reserves bad memory 2444 regions that are detected. 2445 2446 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control 2447 Valid arguments: on, off 2448 Default (depends on kernel configuration option): 2449 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) 2450 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n) 2451 mem_encrypt=on: Activate SME 2452 mem_encrypt=off: Do not activate SME 2453 2454 Refer to Documentation/x86/amd-memory-encryption.txt 2455 for details on when memory encryption can be activated. 2456 2457 mem_sleep_default= [SUSPEND] Default system suspend mode: 2458 s2idle - Suspend-To-Idle 2459 shallow - Power-On Suspend or equivalent (if supported) 2460 deep - Suspend-To-RAM or equivalent (if supported) 2461 See Documentation/admin-guide/pm/sleep-states.rst. 2462 2463 meye.*= [HW] Set MotionEye Camera parameters 2464 See Documentation/media/v4l-drivers/meye.rst. 2465 2466 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2467 Multi-Function General Purpose Timers on AMD Geode 2468 platforms. 2469 2470 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2471 the BIOS has incorrectly applied a workaround. TinyBIOS 2472 version 0.98 is known to be affected, 0.99 fixes the 2473 problem by letting the user disable the workaround. 2474 2475 mga= [HW,DRM] 2476 2477 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2478 physical address is ignored. 2479 2480 mini2440= [ARM,HW,KNL] 2481 Format:[0..2][b][c][t] 2482 Default: "0tb" 2483 MINI2440 configuration specification: 2484 0 - The attached screen is the 3.5" TFT 2485 1 - The attached screen is the 7" TFT 2486 2 - The VGA Shield is attached (1024x768) 2487 Leaving out the screen size parameter will not load 2488 the TFT driver, and the framebuffer will be left 2489 unconfigured. 2490 b - Enable backlight. The TFT backlight pin will be 2491 linked to the kernel VESA blanking code and a GPIO 2492 LED. This parameter is not necessary when using the 2493 VGA shield. 2494 c - Enable the s3c camera interface. 2495 t - Reserved for enabling touchscreen support. The 2496 touchscreen support is not enabled in the mainstream 2497 kernel as of 2.6.30, a preliminary port can be found 2498 in the "bleeding edge" mini2440 support kernel at 2499 http://repo.or.cz/w/linux-2.6/mini2440.git 2500 2501 mminit_loglevel= 2502 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2503 parameter allows control of the logging verbosity for 2504 the additional memory initialisation checks. A value 2505 of 0 disables mminit logging and a level of 4 will 2506 log everything. Information is printed at KERN_DEBUG 2507 so loglevel=8 may also need to be specified. 2508 2509 module.sig_enforce 2510 [KNL] When CONFIG_MODULE_SIG is set, this means that 2511 modules without (valid) signatures will fail to load. 2512 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2513 is always true, so this option does nothing. 2514 2515 module_blacklist= [KNL] Do not load a comma-separated list of 2516 modules. Useful for debugging problem modules. 2517 2518 mousedev.tap_time= 2519 [MOUSE] Maximum time between finger touching and 2520 leaving touchpad surface for touch to be considered 2521 a tap and be reported as a left button click (for 2522 touchpads working in absolute mode only). 2523 Format: <msecs> 2524 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2525 reporting absolute coordinates, such as tablets 2526 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2527 reporting absolute coordinates, such as tablets 2528 2529 movablecore= [KNL,X86,IA-64,PPC] 2530 Format: nn[KMGTPE] | nn% 2531 This parameter is the complement to kernelcore=, it 2532 specifies the amount of memory used for migratable 2533 allocations. If both kernelcore and movablecore is 2534 specified, then kernelcore will be at *least* the 2535 specified value but may be more. If movablecore on its 2536 own is specified, the administrator must be careful 2537 that the amount of memory usable for all allocations 2538 is not too small. 2539 2540 movable_node [KNL] Boot-time switch to make hotplugable memory 2541 NUMA nodes to be movable. This means that the memory 2542 of such nodes will be usable only for movable 2543 allocations which rules out almost all kernel 2544 allocations. Use with caution! 2545 2546 MTD_Partition= [MTD] 2547 Format: <name>,<region-number>,<size>,<offset> 2548 2549 MTD_Region= [MTD] Format: 2550 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2551 2552 mtdparts= [MTD] 2553 See drivers/mtd/cmdlinepart.c. 2554 2555 multitce=off [PPC] This parameter disables the use of the pSeries 2556 firmware feature for updating multiple TCE entries 2557 at a time. 2558 2559 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2560 2561 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2562 2563 boundary - index of last SLC block on Flex-OneNAND. 2564 The remaining blocks are configured as MLC blocks. 2565 lock - Configure if Flex-OneNAND boundary should be locked. 2566 Once locked, the boundary cannot be changed. 2567 1 indicates lock status, 0 indicates unlock status. 2568 2569 mtdset= [ARM] 2570 ARM/S3C2412 JIVE boot control 2571 2572 See arch/arm/mach-s3c2412/mach-jive.c 2573 2574 mtouchusb.raw_coordinates= 2575 [HW] Make the MicroTouch USB driver use raw coordinates 2576 ('y', default) or cooked coordinates ('n') 2577 2578 mtrr_chunk_size=nn[KMG] [X86] 2579 used for mtrr cleanup. It is largest continuous chunk 2580 that could hold holes aka. UC entries. 2581 2582 mtrr_gran_size=nn[KMG] [X86] 2583 Used for mtrr cleanup. It is granularity of mtrr block. 2584 Default is 1. 2585 Large value could prevent small alignment from 2586 using up MTRRs. 2587 2588 mtrr_spare_reg_nr=n [X86] 2589 Format: <integer> 2590 Range: 0,7 : spare reg number 2591 Default : 1 2592 Used for mtrr cleanup. It is spare mtrr entries number. 2593 Set to 2 or more if your graphical card needs more. 2594 2595 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2596 2597 netdev= [NET] Network devices parameters 2598 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2599 Note that mem_start is often overloaded to mean 2600 something different and driver-specific. 2601 This usage is only documented in each driver source 2602 file if at all. 2603 2604 nf_conntrack.acct= 2605 [NETFILTER] Enable connection tracking flow accounting 2606 0 to disable accounting 2607 1 to enable accounting 2608 Default value is 0. 2609 2610 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2611 See Documentation/filesystems/nfs/nfsroot.txt. 2612 2613 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2614 See Documentation/filesystems/nfs/nfsroot.txt. 2615 2616 nfsrootdebug [NFS] enable nfsroot debugging messages. 2617 See Documentation/filesystems/nfs/nfsroot.txt. 2618 2619 nfs.callback_nr_threads= 2620 [NFSv4] set the total number of threads that the 2621 NFS client will assign to service NFSv4 callback 2622 requests. 2623 2624 nfs.callback_tcpport= 2625 [NFS] set the TCP port on which the NFSv4 callback 2626 channel should listen. 2627 2628 nfs.cache_getent= 2629 [NFS] sets the pathname to the program which is used 2630 to update the NFS client cache entries. 2631 2632 nfs.cache_getent_timeout= 2633 [NFS] sets the timeout after which an attempt to 2634 update a cache entry is deemed to have failed. 2635 2636 nfs.idmap_cache_timeout= 2637 [NFS] set the maximum lifetime for idmapper cache 2638 entries. 2639 2640 nfs.enable_ino64= 2641 [NFS] enable 64-bit inode numbers. 2642 If zero, the NFS client will fake up a 32-bit inode 2643 number for the readdir() and stat() syscalls instead 2644 of returning the full 64-bit number. 2645 The default is to return 64-bit inode numbers. 2646 2647 nfs.max_session_cb_slots= 2648 [NFSv4.1] Sets the maximum number of session 2649 slots the client will assign to the callback 2650 channel. This determines the maximum number of 2651 callbacks the client will process in parallel for 2652 a particular server. 2653 2654 nfs.max_session_slots= 2655 [NFSv4.1] Sets the maximum number of session slots 2656 the client will attempt to negotiate with the server. 2657 This limits the number of simultaneous RPC requests 2658 that the client can send to the NFSv4.1 server. 2659 Note that there is little point in setting this 2660 value higher than the max_tcp_slot_table_limit. 2661 2662 nfs.nfs4_disable_idmapping= 2663 [NFSv4] When set to the default of '1', this option 2664 ensures that both the RPC level authentication 2665 scheme and the NFS level operations agree to use 2666 numeric uids/gids if the mount is using the 2667 'sec=sys' security flavour. In effect it is 2668 disabling idmapping, which can make migration from 2669 legacy NFSv2/v3 systems to NFSv4 easier. 2670 Servers that do not support this mode of operation 2671 will be autodetected by the client, and it will fall 2672 back to using the idmapper. 2673 To turn off this behaviour, set the value to '0'. 2674 nfs.nfs4_unique_id= 2675 [NFS4] Specify an additional fixed unique ident- 2676 ification string that NFSv4 clients can insert into 2677 their nfs_client_id4 string. This is typically a 2678 UUID that is generated at system install time. 2679 2680 nfs.send_implementation_id = 2681 [NFSv4.1] Send client implementation identification 2682 information in exchange_id requests. 2683 If zero, no implementation identification information 2684 will be sent. 2685 The default is to send the implementation identification 2686 information. 2687 2688 nfs.recover_lost_locks = 2689 [NFSv4] Attempt to recover locks that were lost due 2690 to a lease timeout on the server. Please note that 2691 doing this risks data corruption, since there are 2692 no guarantees that the file will remain unchanged 2693 after the locks are lost. 2694 If you want to enable the kernel legacy behaviour of 2695 attempting to recover these locks, then set this 2696 parameter to '1'. 2697 The default parameter value of '0' causes the kernel 2698 not to attempt recovery of lost locks. 2699 2700 nfs4.layoutstats_timer = 2701 [NFSv4.2] Change the rate at which the kernel sends 2702 layoutstats to the pNFS metadata server. 2703 2704 Setting this to value to 0 causes the kernel to use 2705 whatever value is the default set by the layout 2706 driver. A non-zero value sets the minimum interval 2707 in seconds between layoutstats transmissions. 2708 2709 nfsd.nfs4_disable_idmapping= 2710 [NFSv4] When set to the default of '1', the NFSv4 2711 server will return only numeric uids and gids to 2712 clients using auth_sys, and will accept numeric uids 2713 and gids from such clients. This is intended to ease 2714 migration from NFSv2/v3. 2715 2716 nmi_debug= [KNL,SH] Specify one or more actions to take 2717 when a NMI is triggered. 2718 Format: [state][,regs][,debounce][,die] 2719 2720 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2721 Format: [panic,][nopanic,][num] 2722 Valid num: 0 or 1 2723 0 - turn hardlockup detector in nmi_watchdog off 2724 1 - turn hardlockup detector in nmi_watchdog on 2725 When panic is specified, panic when an NMI watchdog 2726 timeout occurs (or 'nopanic' to override the opposite 2727 default). To disable both hard and soft lockup detectors, 2728 please see 'nowatchdog'. 2729 This is useful when you use a panic=... timeout and 2730 need the box quickly up again. 2731 2732 These settings can be accessed at runtime via 2733 the nmi_watchdog and hardlockup_panic sysctls. 2734 2735 netpoll.carrier_timeout= 2736 [NET] Specifies amount of time (in seconds) that 2737 netpoll should wait for a carrier. By default netpoll 2738 waits 4 seconds. 2739 2740 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2741 emulation library even if a 387 maths coprocessor 2742 is present. 2743 2744 no5lvl [X86-64] Disable 5-level paging mode. Forces 2745 kernel to use 4-level paging instead. 2746 2747 no_console_suspend 2748 [HW] Never suspend the console 2749 Disable suspending of consoles during suspend and 2750 hibernate operations. Once disabled, debugging 2751 messages can reach various consoles while the rest 2752 of the system is being put to sleep (ie, while 2753 debugging driver suspend/resume hooks). This may 2754 not work reliably with all consoles, but is known 2755 to work with serial and VGA consoles. 2756 To facilitate more flexible debugging, we also add 2757 console_suspend, a printk module parameter to control 2758 it. Users could use console_suspend (usually 2759 /sys/module/printk/parameters/console_suspend) to 2760 turn on/off it dynamically. 2761 2762 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2763 caches in the slab allocator. Saves per-node memory, 2764 but will impact performance. 2765 2766 noalign [KNL,ARM] 2767 2768 noaltinstr [S390] Disables alternative instructions patching 2769 (CPU alternatives feature). 2770 2771 noapic [SMP,APIC] Tells the kernel to not make use of any 2772 IOAPICs that may be present in the system. 2773 2774 noautogroup Disable scheduler automatic task group creation. 2775 2776 nobats [PPC] Do not use BATs for mapping kernel lowmem 2777 on "Classic" PPC cores. 2778 2779 nocache [ARM] 2780 2781 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2782 2783 nodelayacct [KNL] Disable per-task delay accounting 2784 2785 nodsp [SH] Disable hardware DSP at boot time. 2786 2787 noefi Disable EFI runtime services support. 2788 2789 noexec [IA-64] 2790 2791 noexec [X86] 2792 On X86-32 available only on PAE configured kernels. 2793 noexec=on: enable non-executable mappings (default) 2794 noexec=off: disable non-executable mappings 2795 2796 nosmap [X86] 2797 Disable SMAP (Supervisor Mode Access Prevention) 2798 even if it is supported by processor. 2799 2800 nosmep [X86] 2801 Disable SMEP (Supervisor Mode Execution Prevention) 2802 even if it is supported by processor. 2803 2804 noexec32 [X86-64] 2805 This affects only 32-bit executables. 2806 noexec32=on: enable non-executable mappings (default) 2807 read doesn't imply executable mappings 2808 noexec32=off: disable non-executable mappings 2809 read implies executable mappings 2810 2811 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2812 2813 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2814 register save and restore. The kernel will only save 2815 legacy floating-point registers on task switch. 2816 2817 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2818 2819 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2820 Equivalent to smt=1. 2821 2822 [KNL,x86] Disable symmetric multithreading (SMT). 2823 nosmt=force: Force disable SMT, cannot be undone 2824 via the sysfs control file. 2825 2826 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds 2827 check bypass). With this option data leaks are possible 2828 in the system. 2829 2830 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2 2831 (indirect branch prediction) vulnerability. System may 2832 allow data leaks with this option, which is equivalent 2833 to spectre_v2=off. 2834 2835 nospec_store_bypass_disable 2836 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability 2837 2838 noxsave [BUGS=X86] Disables x86 extended register state save 2839 and restore using xsave. The kernel will fallback to 2840 enabling legacy floating-point and sse state. 2841 2842 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2843 register states. The kernel will fall back to use 2844 xsave to save the states. By using this parameter, 2845 performance of saving the states is degraded because 2846 xsave doesn't support modified optimization while 2847 xsaveopt supports it on xsaveopt enabled systems. 2848 2849 noxsaves [X86] Disables xsaves and xrstors used in saving and 2850 restoring x86 extended register state in compacted 2851 form of xsave area. The kernel will fall back to use 2852 xsaveopt and xrstor to save and restore the states 2853 in standard form of xsave area. By using this 2854 parameter, xsave area per process might occupy more 2855 memory on xsaves enabled systems. 2856 2857 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2858 wfi(ARM) instruction doesn't work correctly and not to 2859 use it. This is also useful when using JTAG debugger. 2860 2861 no_file_caps Tells the kernel not to honor file capabilities. The 2862 only way then for a file to be executed with privilege 2863 is to be setuid root or executed by root. 2864 2865 nohalt [IA-64] Tells the kernel not to use the power saving 2866 function PAL_HALT_LIGHT when idle. This increases 2867 power-consumption. On the positive side, it reduces 2868 interrupt wake-up latency, which may improve performance 2869 in certain environments such as networked servers or 2870 real-time systems. 2871 2872 nohibernate [HIBERNATION] Disable hibernation and resume. 2873 2874 nohz= [KNL] Boottime enable/disable dynamic ticks 2875 Valid arguments: on, off 2876 Default: on 2877 2878 nohz_full= [KNL,BOOT,SMP,ISOL] 2879 The argument is a cpu list, as described above. 2880 In kernels built with CONFIG_NO_HZ_FULL=y, set 2881 the specified list of CPUs whose tick will be stopped 2882 whenever possible. The boot CPU will be forced outside 2883 the range to maintain the timekeeping. Any CPUs 2884 in this list will have their RCU callbacks offloaded, 2885 just as if they had also been called out in the 2886 rcu_nocbs= boot parameter. 2887 2888 noiotrap [SH] Disables trapped I/O port accesses. 2889 2890 noirqdebug [X86-32] Disables the code which attempts to detect and 2891 disable unhandled interrupt sources. 2892 2893 no_timer_check [X86,APIC] Disables the code which tests for 2894 broken timer IRQ sources. 2895 2896 noisapnp [ISAPNP] Disables ISA PnP code. 2897 2898 noinitrd [RAM] Tells the kernel not to load any configured 2899 initial RAM disk. 2900 2901 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2902 remapping. 2903 [Deprecated - use intremap=off] 2904 2905 nointroute [IA-64] 2906 2907 noinvpcid [X86] Disable the INVPCID cpu feature. 2908 2909 nojitter [IA-64] Disables jitter checking for ITC timers. 2910 2911 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2912 2913 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2914 fault handling. 2915 2916 no-vmw-sched-clock 2917 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2918 clock and use the default one. 2919 2920 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2921 steal time is computed, but won't influence scheduler 2922 behaviour 2923 2924 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2925 2926 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2927 2928 noltlbs [PPC] Do not use large page/tlb entries for kernel 2929 lowmem mapping on PPC40x and PPC8xx 2930 2931 nomca [IA-64] Disable machine check abort handling 2932 2933 nomce [X86-32] Disable Machine Check Exception 2934 2935 nomfgpt [X86-32] Disable Multi-Function General Purpose 2936 Timer usage (for AMD Geode machines). 2937 2938 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2939 shutdown the other cpus. Instead use the REBOOT_VECTOR 2940 irq. 2941 2942 nomodule Disable module load 2943 2944 nopat [X86] Disable PAT (page attribute table extension of 2945 pagetables) support. 2946 2947 nopcid [X86-64] Disable the PCID cpu feature. 2948 2949 norandmaps Don't use address space randomization. Equivalent to 2950 echo 0 > /proc/sys/kernel/randomize_va_space 2951 2952 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2953 with UP alternatives 2954 2955 nordrand [X86] Disable kernel use of the RDRAND and 2956 RDSEED instructions even if they are supported 2957 by the processor. RDRAND and RDSEED are still 2958 available to user space applications. 2959 2960 noresume [SWSUSP] Disables resume and restores original swap 2961 space. 2962 2963 no-scroll [VGA] Disables scrollback. 2964 This is required for the Braillex ib80-piezo Braille 2965 reader made by F.H. Papenmeier (Germany). 2966 2967 nosbagart [IA-64] 2968 2969 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2970 2971 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2972 and disable the IO APIC. legacy for "maxcpus=0". 2973 2974 nosoftlockup [KNL] Disable the soft-lockup detector. 2975 2976 nosync [HW,M68K] Disables sync negotiation for all devices. 2977 2978 nowatchdog [KNL] Disable both lockup detectors, i.e. 2979 soft-lockup and NMI watchdog (hard-lockup). 2980 2981 nowb [ARM] 2982 2983 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2984 2985 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2986 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2987 Some features depend on CPU0. Known dependencies are: 2988 1. Resume from suspend/hibernate depends on CPU0. 2989 Suspend/hibernate will fail if CPU0 is offline and you 2990 need to online CPU0 before suspend/hibernate. 2991 2. PIC interrupts also depend on CPU0. CPU0 can't be 2992 removed if a PIC interrupt is detected. 2993 It's said poweroff/reboot may depend on CPU0 on some 2994 machines although I haven't seen such issues so far 2995 after CPU0 is offline on a few tested machines. 2996 If the dependencies are under your control, you can 2997 turn on cpu0_hotplug. 2998 2999 nps_mtm_hs_ctr= [KNL,ARC] 3000 This parameter sets the maximum duration, in 3001 cycles, each HW thread of the CTOP can run 3002 without interruptions, before HW switches it. 3003 The actual maximum duration is 16 times this 3004 parameter's value. 3005 Format: integer between 1 and 255 3006 Default: 255 3007 3008 nptcg= [IA-64] Override max number of concurrent global TLB 3009 purges which is reported from either PAL_VM_SUMMARY or 3010 SAL PALO. 3011 3012 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 3013 could support. nr_cpus=n : n >= 1 limits the kernel to 3014 support 'n' processors. It could be larger than the 3015 number of already plugged CPU during bootup, later in 3016 runtime you can physically add extra cpu until it reaches 3017 n. So during boot up some boot time memory for per-cpu 3018 variables need be pre-allocated for later physical cpu 3019 hot plugging. 3020 3021 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 3022 3023 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 3024 Allowed values are enable and disable 3025 3026 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 3027 'node', 'default' can be specified 3028 This can be set from sysctl after boot. 3029 See Documentation/sysctl/vm.txt for details. 3030 3031 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 3032 See Documentation/debugging-via-ohci1394.txt for more 3033 info. 3034 3035 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 3036 Rather than timing out after 20 ms if an EC 3037 command is not properly ACKed, override the length 3038 of the timeout. We have interrupts disabled while 3039 waiting for the ACK, so if this is set too high 3040 interrupts *may* be lost! 3041 3042 omap_mux= [OMAP] Override bootloader pin multiplexing. 3043 Format: <mux_mode0.mode_name=value>... 3044 For example, to override I2C bus2: 3045 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 3046 3047 oprofile.timer= [HW] 3048 Use timer interrupt instead of performance counters 3049 3050 oprofile.cpu_type= Force an oprofile cpu type 3051 This might be useful if you have an older oprofile 3052 userland or if you want common events. 3053 Format: { arch_perfmon } 3054 arch_perfmon: [X86] Force use of architectural 3055 perfmon on Intel CPUs instead of the 3056 CPU specific event set. 3057 timer: [X86] Force use of architectural NMI 3058 timer mode (see also oprofile.timer 3059 for generic hr timer mode) 3060 3061 oops=panic Always panic on oopses. Default is to just kill the 3062 process, but there is a small probability of 3063 deadlocking the machine. 3064 This will also cause panics on machine check exceptions. 3065 Useful together with panic=30 to trigger a reboot. 3066 3067 page_owner= [KNL] Boot-time page_owner enabling option. 3068 Storage of the information about who allocated 3069 each page is disabled in default. With this switch, 3070 we can turn it on. 3071 on: enable the feature 3072 3073 page_poison= [KNL] Boot-time parameter changing the state of 3074 poisoning on the buddy allocator, available with 3075 CONFIG_PAGE_POISONING=y. 3076 off: turn off poisoning (default) 3077 on: turn on poisoning 3078 3079 panic= [KNL] Kernel behaviour on panic: delay <timeout> 3080 timeout > 0: seconds before rebooting 3081 timeout = 0: wait forever 3082 timeout < 0: reboot immediately 3083 Format: <timeout> 3084 3085 panic_on_warn panic() instead of WARN(). Useful to cause kdump 3086 on a WARN(). 3087 3088 crash_kexec_post_notifiers 3089 Run kdump after running panic-notifiers and dumping 3090 kmsg. This only for the users who doubt kdump always 3091 succeeds in any situation. 3092 Note that this also increases risks of kdump failure, 3093 because some panic notifiers can make the crashed 3094 kernel more unstable. 3095 3096 parkbd.port= [HW] Parallel port number the keyboard adapter is 3097 connected to, default is 0. 3098 Format: <parport#> 3099 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 3100 0 for XT, 1 for AT (default is AT). 3101 Format: <mode> 3102 3103 parport= [HW,PPT] Specify parallel ports. 0 disables. 3104 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 3105 Use 'auto' to force the driver to use any 3106 IRQ/DMA settings detected (the default is to 3107 ignore detected IRQ/DMA settings because of 3108 possible conflicts). You can specify the base 3109 address, IRQ, and DMA settings; IRQ and DMA 3110 should be numbers, or 'auto' (for using detected 3111 settings on that particular port), or 'nofifo' 3112 (to avoid using a FIFO even if it is detected). 3113 Parallel ports are assigned in the order they 3114 are specified on the command line, starting 3115 with parport0. 3116 3117 parport_init_mode= [HW,PPT] 3118 Configure VIA parallel port to operate in 3119 a specific mode. This is necessary on Pegasos 3120 computer where firmware has no options for setting 3121 up parallel port mode and sets it to spp. 3122 Currently this function knows 686a and 8231 chips. 3123 Format: [spp|ps2|epp|ecp|ecpepp] 3124 3125 pause_on_oops= 3126 Halt all CPUs after the first oops has been printed for 3127 the specified number of seconds. This is to be used if 3128 your oopses keep scrolling off the screen. 3129 3130 pcbit= [HW,ISDN] 3131 3132 pcd. [PARIDE] 3133 See header of drivers/block/paride/pcd.c. 3134 See also Documentation/blockdev/paride.txt. 3135 3136 pci=option[,option...] [PCI] various PCI subsystem options. 3137 3138 Some options herein operate on a specific device 3139 or a set of devices (<pci_dev>). These are 3140 specified in one of the following formats: 3141 3142 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]* 3143 pci:<vendor>:<device>[:<subvendor>:<subdevice>] 3144 3145 Note: the first format specifies a PCI 3146 bus/device/function address which may change 3147 if new hardware is inserted, if motherboard 3148 firmware changes, or due to changes caused 3149 by other kernel parameters. If the 3150 domain is left unspecified, it is 3151 taken to be zero. Optionally, a path 3152 to a device through multiple device/function 3153 addresses can be specified after the base 3154 address (this is more robust against 3155 renumbering issues). The second format 3156 selects devices using IDs from the 3157 configuration space which may match multiple 3158 devices in the system. 3159 3160 earlydump dump PCI config space before the kernel 3161 changes anything 3162 off [X86] don't probe for the PCI bus 3163 bios [X86-32] force use of PCI BIOS, don't access 3164 the hardware directly. Use this if your machine 3165 has a non-standard PCI host bridge. 3166 nobios [X86-32] disallow use of PCI BIOS, only direct 3167 hardware access methods are allowed. Use this 3168 if you experience crashes upon bootup and you 3169 suspect they are caused by the BIOS. 3170 conf1 [X86] Force use of PCI Configuration Access 3171 Mechanism 1 (config address in IO port 0xCF8, 3172 data in IO port 0xCFC, both 32-bit). 3173 conf2 [X86] Force use of PCI Configuration Access 3174 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 3175 the function, IO port 0xCFA, also 8-bit, sets 3176 bus number. The config space is then accessed 3177 through ports 0xC000-0xCFFF). 3178 See http://wiki.osdev.org/PCI for more info 3179 on the configuration access mechanisms. 3180 noaer [PCIE] If the PCIEAER kernel config parameter is 3181 enabled, this kernel boot option can be used to 3182 disable the use of PCIE advanced error reporting. 3183 nodomains [PCI] Disable support for multiple PCI 3184 root domains (aka PCI segments, in ACPI-speak). 3185 nommconf [X86] Disable use of MMCONFIG for PCI 3186 Configuration 3187 check_enable_amd_mmconf [X86] check for and enable 3188 properly configured MMIO access to PCI 3189 config space on AMD family 10h CPU 3190 nomsi [MSI] If the PCI_MSI kernel config parameter is 3191 enabled, this kernel boot option can be used to 3192 disable the use of MSI interrupts system-wide. 3193 noioapicquirk [APIC] Disable all boot interrupt quirks. 3194 Safety option to keep boot IRQs enabled. This 3195 should never be necessary. 3196 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 3197 primary IO-APIC for bridges that cannot disable 3198 boot IRQs. This fixes a source of spurious IRQs 3199 when the system masks IRQs. 3200 noioapicreroute [APIC] Disable workaround that uses the 3201 boot IRQ equivalent of an IRQ that connects to 3202 a chipset where boot IRQs cannot be disabled. 3203 The opposite of ioapicreroute. 3204 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 3205 routing table. These calls are known to be buggy 3206 on several machines and they hang the machine 3207 when used, but on other computers it's the only 3208 way to get the interrupt routing table. Try 3209 this option if the kernel is unable to allocate 3210 IRQs or discover secondary PCI buses on your 3211 motherboard. 3212 rom [X86] Assign address space to expansion ROMs. 3213 Use with caution as certain devices share 3214 address decoders between ROMs and other 3215 resources. 3216 norom [X86] Do not assign address space to 3217 expansion ROMs that do not already have 3218 BIOS assigned address ranges. 3219 nobar [X86] Do not assign address space to the 3220 BARs that weren't assigned by the BIOS. 3221 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 3222 assigned automatically to PCI devices. You can 3223 make the kernel exclude IRQs of your ISA cards 3224 this way. 3225 pirqaddr=0xAAAAA [X86] Specify the physical address 3226 of the PIRQ table (normally generated 3227 by the BIOS) if it is outside the 3228 F0000h-100000h range. 3229 lastbus=N [X86] Scan all buses thru bus #N. Can be 3230 useful if the kernel is unable to find your 3231 secondary buses and you want to tell it 3232 explicitly which ones they are. 3233 assign-busses [X86] Always assign all PCI bus 3234 numbers ourselves, overriding 3235 whatever the firmware may have done. 3236 usepirqmask [X86] Honor the possible IRQ mask stored 3237 in the BIOS $PIR table. This is needed on 3238 some systems with broken BIOSes, notably 3239 some HP Pavilion N5400 and Omnibook XE3 3240 notebooks. This will have no effect if ACPI 3241 IRQ routing is enabled. 3242 noacpi [X86] Do not use ACPI for IRQ routing 3243 or for PCI scanning. 3244 use_crs [X86] Use PCI host bridge window information 3245 from ACPI. On BIOSes from 2008 or later, this 3246 is enabled by default. If you need to use this, 3247 please report a bug. 3248 nocrs [X86] Ignore PCI host bridge windows from ACPI. 3249 If you need to use this, please report a bug. 3250 routeirq Do IRQ routing for all PCI devices. 3251 This is normally done in pci_enable_device(), 3252 so this option is a temporary workaround 3253 for broken drivers that don't call it. 3254 skip_isa_align [X86] do not align io start addr, so can 3255 handle more pci cards 3256 noearly [X86] Don't do any early type 1 scanning. 3257 This might help on some broken boards which 3258 machine check when some devices' config space 3259 is read. But various workarounds are disabled 3260 and some IOMMU drivers will not work. 3261 bfsort Sort PCI devices into breadth-first order. 3262 This sorting is done to get a device 3263 order compatible with older (<= 2.4) kernels. 3264 nobfsort Don't sort PCI devices into breadth-first order. 3265 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 3266 tuning and use the BIOS-configured MPS defaults. 3267 pcie_bus_safe Set every device's MPS to the largest value 3268 supported by all devices below the root complex. 3269 pcie_bus_perf Set device MPS to the largest allowable MPS 3270 based on its parent bus. Also set MRRS (Max 3271 Read Request Size) to the largest supported 3272 value (no larger than the MPS that the device 3273 or bus can support) for best performance. 3274 pcie_bus_peer2peer Set every device's MPS to 128B, which 3275 every device is guaranteed to support. This 3276 configuration allows peer-to-peer DMA between 3277 any pair of devices, possibly at the cost of 3278 reduced performance. This also guarantees 3279 that hot-added devices will work. 3280 cbiosize=nn[KMG] The fixed amount of bus space which is 3281 reserved for the CardBus bridge's IO window. 3282 The default value is 256 bytes. 3283 cbmemsize=nn[KMG] The fixed amount of bus space which is 3284 reserved for the CardBus bridge's memory 3285 window. The default value is 64 megabytes. 3286 resource_alignment= 3287 Format: 3288 [<order of align>@]<pci_dev>[; ...] 3289 Specifies alignment and device to reassign 3290 aligned memory resources. How to 3291 specify the device is described above. 3292 If <order of align> is not specified, 3293 PAGE_SIZE is used as alignment. 3294 PCI-PCI bridge can be specified, if resource 3295 windows need to be expanded. 3296 To specify the alignment for several 3297 instances of a device, the PCI vendor, 3298 device, subvendor, and subdevice may be 3299 specified, e.g., 4096@pci:8086:9c22:103c:198f 3300 ecrc= Enable/disable PCIe ECRC (transaction layer 3301 end-to-end CRC checking). 3302 bios: Use BIOS/firmware settings. This is the 3303 the default. 3304 off: Turn ECRC off 3305 on: Turn ECRC on. 3306 hpiosize=nn[KMG] The fixed amount of bus space which is 3307 reserved for hotplug bridge's IO window. 3308 Default size is 256 bytes. 3309 hpmemsize=nn[KMG] The fixed amount of bus space which is 3310 reserved for hotplug bridge's memory window. 3311 Default size is 2 megabytes. 3312 hpbussize=nn The minimum amount of additional bus numbers 3313 reserved for buses below a hotplug bridge. 3314 Default is 1. 3315 realloc= Enable/disable reallocating PCI bridge resources 3316 if allocations done by BIOS are too small to 3317 accommodate resources required by all child 3318 devices. 3319 off: Turn realloc off 3320 on: Turn realloc on 3321 realloc same as realloc=on 3322 noari do not use PCIe ARI. 3323 noats [PCIE, Intel-IOMMU, AMD-IOMMU] 3324 do not use PCIe ATS (and IOMMU device IOTLB). 3325 pcie_scan_all Scan all possible PCIe devices. Otherwise we 3326 only look for one device below a PCIe downstream 3327 port. 3328 big_root_window Try to add a big 64bit memory window to the PCIe 3329 root complex on AMD CPUs. Some GFX hardware 3330 can resize a BAR to allow access to all VRAM. 3331 Adding the window is slightly risky (it may 3332 conflict with unreported devices), so this 3333 taints the kernel. 3334 disable_acs_redir=<pci_dev>[; ...] 3335 Specify one or more PCI devices (in the format 3336 specified above) separated by semicolons. 3337 Each device specified will have the PCI ACS 3338 redirect capabilities forced off which will 3339 allow P2P traffic between devices through 3340 bridges without forcing it upstream. Note: 3341 this removes isolation between devices and 3342 may put more devices in an IOMMU group. 3343 3344 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 3345 Management. 3346 off Disable ASPM. 3347 force Enable ASPM even on devices that claim not to support it. 3348 WARNING: Forcing ASPM on may cause system lockups. 3349 3350 pcie_ports= [PCIE] PCIe port services handling: 3351 native Use native PCIe services (PME, AER, DPC, PCIe hotplug) 3352 even if the platform doesn't give the OS permission to 3353 use them. This may cause conflicts if the platform 3354 also tries to use these services. 3355 compat Disable native PCIe services (PME, AER, DPC, PCIe 3356 hotplug). 3357 3358 pcie_port_pm= [PCIE] PCIe port power management handling: 3359 off Disable power management of all PCIe ports 3360 force Forcibly enable power management of all PCIe ports 3361 3362 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 3363 nomsi Do not use MSI for native PCIe PME signaling (this makes 3364 all PCIe root ports use INTx for all services). 3365 3366 pcmv= [HW,PCMCIA] BadgePAD 4 3367 3368 pd_ignore_unused 3369 [PM] 3370 Keep all power-domains already enabled by bootloader on, 3371 even if no driver has claimed them. This is useful 3372 for debug and development, but should not be 3373 needed on a platform with proper driver support. 3374 3375 pd. [PARIDE] 3376 See Documentation/blockdev/paride.txt. 3377 3378 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3379 boot time. 3380 Format: { 0 | 1 } 3381 See arch/parisc/kernel/pdc_chassis.c 3382 3383 percpu_alloc= Select which percpu first chunk allocator to use. 3384 Currently supported values are "embed" and "page". 3385 Archs may support subset or none of the selections. 3386 See comments in mm/percpu.c for details on each 3387 allocator. This parameter is primarily for debugging 3388 and performance comparison. 3389 3390 pf. [PARIDE] 3391 See Documentation/blockdev/paride.txt. 3392 3393 pg. [PARIDE] 3394 See Documentation/blockdev/paride.txt. 3395 3396 pirq= [SMP,APIC] Manual mp-table setup 3397 See Documentation/x86/i386/IO-APIC.txt. 3398 3399 plip= [PPT,NET] Parallel port network link 3400 Format: { parport<nr> | timid | 0 } 3401 See also Documentation/admin-guide/parport.rst. 3402 3403 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3404 Override pmtimer IOPort with a hex value. 3405 e.g. pmtmr=0x508 3406 3407 pnp.debug=1 [PNP] 3408 Enable PNP debug messages (depends on the 3409 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3410 via /sys/module/pnp/parameters/debug. We always show 3411 current resource usage; turning this on also shows 3412 possible settings and some assignment information. 3413 3414 pnpacpi= [ACPI] 3415 { off } 3416 3417 pnpbios= [ISAPNP] 3418 { on | off | curr | res | no-curr | no-res } 3419 3420 pnp_reserve_irq= 3421 [ISAPNP] Exclude IRQs for the autoconfiguration 3422 3423 pnp_reserve_dma= 3424 [ISAPNP] Exclude DMAs for the autoconfiguration 3425 3426 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3427 Ranges are in pairs (I/O port base and size). 3428 3429 pnp_reserve_mem= 3430 [ISAPNP] Exclude memory regions for the 3431 autoconfiguration. 3432 Ranges are in pairs (memory base and size). 3433 3434 ports= [IP_VS_FTP] IPVS ftp helper module 3435 Default is 21. 3436 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3437 may be specified. 3438 Format: <port>,<port>.... 3439 3440 powersave=off [PPC] This option disables power saving features. 3441 It specifically disables cpuidle and sets the 3442 platform machine description specific power_save 3443 function to NULL. On Idle the CPU just reduces 3444 execution priority. 3445 3446 ppc_strict_facility_enable 3447 [PPC] This option catches any kernel floating point, 3448 Altivec, VSX and SPE outside of regions specifically 3449 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3450 There is some performance impact when enabling this. 3451 3452 ppc_tm= [PPC] 3453 Format: {"off"} 3454 Disable Hardware Transactional Memory 3455 3456 print-fatal-signals= 3457 [KNL] debug: print fatal signals 3458 3459 If enabled, warn about various signal handling 3460 related application anomalies: too many signals, 3461 too many POSIX.1 timers, fatal signals causing a 3462 coredump - etc. 3463 3464 If you hit the warning due to signal overflow, 3465 you might want to try "ulimit -i unlimited". 3466 3467 default: off. 3468 3469 printk.always_kmsg_dump= 3470 Trigger kmsg_dump for cases other than kernel oops or 3471 panics 3472 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3473 default: disabled 3474 3475 printk.devkmsg={on,off,ratelimit} 3476 Control writing to /dev/kmsg. 3477 on - unlimited logging to /dev/kmsg from userspace 3478 off - logging to /dev/kmsg disabled 3479 ratelimit - ratelimit the logging 3480 Default: ratelimit 3481 3482 printk.time= Show timing data prefixed to each printk message line 3483 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3484 3485 processor.max_cstate= [HW,ACPI] 3486 Limit processor to maximum C-state 3487 max_cstate=9 overrides any DMI blacklist limit. 3488 3489 processor.nocst [HW,ACPI] 3490 Ignore the _CST method to determine C-states, 3491 instead using the legacy FADT method 3492 3493 profile= [KNL] Enable kernel profiling via /proc/profile 3494 Format: [<profiletype>,]<number> 3495 Param: <profiletype>: "schedule", "sleep", or "kvm" 3496 [defaults to kernel profiling] 3497 Param: "schedule" - profile schedule points. 3498 Param: "sleep" - profile D-state sleeping (millisecs). 3499 Requires CONFIG_SCHEDSTATS 3500 Param: "kvm" - profile VM exits. 3501 Param: <number> - step/bucket size as a power of 2 for 3502 statistical time based profiling. 3503 3504 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3505 before loading. 3506 See Documentation/blockdev/ramdisk.txt. 3507 3508 psi= [KNL] Enable or disable pressure stall information 3509 tracking. 3510 Format: <bool> 3511 3512 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3513 probe for; one of (bare|imps|exps|lifebook|any). 3514 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3515 per second. 3516 psmouse.resetafter= [HW,MOUSE] 3517 Try to reset the device after so many bad packets 3518 (0 = never). 3519 psmouse.resolution= 3520 [HW,MOUSE] Set desired mouse resolution, in dpi. 3521 psmouse.smartscroll= 3522 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3523 0 = disabled, 1 = enabled (default). 3524 3525 pstore.backend= Specify the name of the pstore backend to use 3526 3527 pt. [PARIDE] 3528 See Documentation/blockdev/paride.txt. 3529 3530 pti= [X86_64] Control Page Table Isolation of user and 3531 kernel address spaces. Disabling this feature 3532 removes hardening, but improves performance of 3533 system calls and interrupts. 3534 3535 on - unconditionally enable 3536 off - unconditionally disable 3537 auto - kernel detects whether your CPU model is 3538 vulnerable to issues that PTI mitigates 3539 3540 Not specifying this option is equivalent to pti=auto. 3541 3542 nopti [X86_64] 3543 Equivalent to pti=off 3544 3545 pty.legacy_count= 3546 [KNL] Number of legacy pty's. Overwrites compiled-in 3547 default number. 3548 3549 quiet [KNL] Disable most log messages 3550 3551 r128= [HW,DRM] 3552 3553 raid= [HW,RAID] 3554 See Documentation/admin-guide/md.rst. 3555 3556 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3557 See Documentation/blockdev/ramdisk.txt. 3558 3559 random.trust_cpu={on,off} 3560 [KNL] Enable or disable trusting the use of the 3561 CPU's random number generator (if available) to 3562 fully seed the kernel's CRNG. Default is controlled 3563 by CONFIG_RANDOM_TRUST_CPU. 3564 3565 ras=option[,option,...] [KNL] RAS-specific options 3566 3567 cec_disable [X86] 3568 Disable the Correctable Errors Collector, 3569 see CONFIG_RAS_CEC help text. 3570 3571 rcu_nocbs= [KNL] 3572 The argument is a cpu list, as described above. 3573 3574 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3575 the specified list of CPUs to be no-callback CPUs. 3576 Invocation of these CPUs' RCU callbacks will be 3577 offloaded to "rcuox/N" kthreads created for that 3578 purpose, where "x" is "p" for RCU-preempt, and 3579 "s" for RCU-sched, and "N" is the CPU number. 3580 This reduces OS jitter on the offloaded CPUs, 3581 which can be useful for HPC and real-time 3582 workloads. It can also improve energy efficiency 3583 for asymmetric multiprocessors. 3584 3585 rcu_nocb_poll [KNL] 3586 Rather than requiring that offloaded CPUs 3587 (specified by rcu_nocbs= above) explicitly 3588 awaken the corresponding "rcuoN" kthreads, 3589 make these kthreads poll for callbacks. 3590 This improves the real-time response for the 3591 offloaded CPUs by relieving them of the need to 3592 wake up the corresponding kthread, but degrades 3593 energy efficiency by requiring that the kthreads 3594 periodically wake up to do the polling. 3595 3596 rcutree.blimit= [KNL] 3597 Set maximum number of finished RCU callbacks to 3598 process in one batch. 3599 3600 rcutree.dump_tree= [KNL] 3601 Dump the structure of the rcu_node combining tree 3602 out at early boot. This is used for diagnostic 3603 purposes, to verify correct tree setup. 3604 3605 rcutree.gp_cleanup_delay= [KNL] 3606 Set the number of jiffies to delay each step of 3607 RCU grace-period cleanup. 3608 3609 rcutree.gp_init_delay= [KNL] 3610 Set the number of jiffies to delay each step of 3611 RCU grace-period initialization. 3612 3613 rcutree.gp_preinit_delay= [KNL] 3614 Set the number of jiffies to delay each step of 3615 RCU grace-period pre-initialization, that is, 3616 the propagation of recent CPU-hotplug changes up 3617 the rcu_node combining tree. 3618 3619 rcutree.rcu_fanout_exact= [KNL] 3620 Disable autobalancing of the rcu_node combining 3621 tree. This is used by rcutorture, and might 3622 possibly be useful for architectures having high 3623 cache-to-cache transfer latencies. 3624 3625 rcutree.rcu_fanout_leaf= [KNL] 3626 Change the number of CPUs assigned to each 3627 leaf rcu_node structure. Useful for very 3628 large systems, which will choose the value 64, 3629 and for NUMA systems with large remote-access 3630 latencies, which will choose a value aligned 3631 with the appropriate hardware boundaries. 3632 3633 rcutree.jiffies_till_sched_qs= [KNL] 3634 Set required age in jiffies for a 3635 given grace period before RCU starts 3636 soliciting quiescent-state help from 3637 rcu_note_context_switch(). If not specified, the 3638 kernel will calculate a value based on the most 3639 recent settings of rcutree.jiffies_till_first_fqs 3640 and rcutree.jiffies_till_next_fqs. 3641 This calculated value may be viewed in 3642 rcutree.jiffies_to_sched_qs. Any attempt to 3643 set rcutree.jiffies_to_sched_qs will be 3644 cheerfully overwritten. 3645 3646 rcutree.jiffies_till_first_fqs= [KNL] 3647 Set delay from grace-period initialization to 3648 first attempt to force quiescent states. 3649 Units are jiffies, minimum value is zero, 3650 and maximum value is HZ. 3651 3652 rcutree.jiffies_till_next_fqs= [KNL] 3653 Set delay between subsequent attempts to force 3654 quiescent states. Units are jiffies, minimum 3655 value is one, and maximum value is HZ. 3656 3657 rcutree.kthread_prio= [KNL,BOOT] 3658 Set the SCHED_FIFO priority of the RCU per-CPU 3659 kthreads (rcuc/N). This value is also used for 3660 the priority of the RCU boost threads (rcub/N) 3661 and for the RCU grace-period kthreads (rcu_bh, 3662 rcu_preempt, and rcu_sched). If RCU_BOOST is 3663 set, valid values are 1-99 and the default is 1 3664 (the least-favored priority). Otherwise, when 3665 RCU_BOOST is not set, valid values are 0-99 and 3666 the default is zero (non-realtime operation). 3667 3668 rcutree.rcu_nocb_leader_stride= [KNL] 3669 Set the number of NOCB kthread groups, which 3670 defaults to the square root of the number of 3671 CPUs. Larger numbers reduces the wakeup overhead 3672 on the per-CPU grace-period kthreads, but increases 3673 that same overhead on each group's leader. 3674 3675 rcutree.qhimark= [KNL] 3676 Set threshold of queued RCU callbacks beyond which 3677 batch limiting is disabled. 3678 3679 rcutree.qlowmark= [KNL] 3680 Set threshold of queued RCU callbacks below which 3681 batch limiting is re-enabled. 3682 3683 rcutree.rcu_idle_gp_delay= [KNL] 3684 Set wakeup interval for idle CPUs that have 3685 RCU callbacks (RCU_FAST_NO_HZ=y). 3686 3687 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3688 Set wakeup interval for idle CPUs that have 3689 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3690 Lazy RCU callbacks are those which RCU can 3691 prove do nothing more than free memory. 3692 3693 rcutree.rcu_kick_kthreads= [KNL] 3694 Cause the grace-period kthread to get an extra 3695 wake_up() if it sleeps three times longer than 3696 it should at force-quiescent-state time. 3697 This wake_up() will be accompanied by a 3698 WARN_ONCE() splat and an ftrace_dump(). 3699 3700 rcuperf.gp_async= [KNL] 3701 Measure performance of asynchronous 3702 grace-period primitives such as call_rcu(). 3703 3704 rcuperf.gp_async_max= [KNL] 3705 Specify the maximum number of outstanding 3706 callbacks per writer thread. When a writer 3707 thread exceeds this limit, it invokes the 3708 corresponding flavor of rcu_barrier() to allow 3709 previously posted callbacks to drain. 3710 3711 rcuperf.gp_exp= [KNL] 3712 Measure performance of expedited synchronous 3713 grace-period primitives. 3714 3715 rcuperf.holdoff= [KNL] 3716 Set test-start holdoff period. The purpose of 3717 this parameter is to delay the start of the 3718 test until boot completes in order to avoid 3719 interference. 3720 3721 rcuperf.nreaders= [KNL] 3722 Set number of RCU readers. The value -1 selects 3723 N, where N is the number of CPUs. A value 3724 "n" less than -1 selects N-n+1, where N is again 3725 the number of CPUs. For example, -2 selects N 3726 (the number of CPUs), -3 selects N+1, and so on. 3727 A value of "n" less than or equal to -N selects 3728 a single reader. 3729 3730 rcuperf.nwriters= [KNL] 3731 Set number of RCU writers. The values operate 3732 the same as for rcuperf.nreaders. 3733 N, where N is the number of CPUs 3734 3735 rcuperf.perf_type= [KNL] 3736 Specify the RCU implementation to test. 3737 3738 rcuperf.shutdown= [KNL] 3739 Shut the system down after performance tests 3740 complete. This is useful for hands-off automated 3741 testing. 3742 3743 rcuperf.verbose= [KNL] 3744 Enable additional printk() statements. 3745 3746 rcuperf.writer_holdoff= [KNL] 3747 Write-side holdoff between grace periods, 3748 in microseconds. The default of zero says 3749 no holdoff. 3750 3751 rcutorture.cbflood_inter_holdoff= [KNL] 3752 Set holdoff time (jiffies) between successive 3753 callback-flood tests. 3754 3755 rcutorture.cbflood_intra_holdoff= [KNL] 3756 Set holdoff time (jiffies) between successive 3757 bursts of callbacks within a given callback-flood 3758 test. 3759 3760 rcutorture.cbflood_n_burst= [KNL] 3761 Set the number of bursts making up a given 3762 callback-flood test. Set this to zero to 3763 disable callback-flood testing. 3764 3765 rcutorture.cbflood_n_per_burst= [KNL] 3766 Set the number of callbacks to be registered 3767 in a given burst of a callback-flood test. 3768 3769 rcutorture.fqs_duration= [KNL] 3770 Set duration of force_quiescent_state bursts 3771 in microseconds. 3772 3773 rcutorture.fqs_holdoff= [KNL] 3774 Set holdoff time within force_quiescent_state bursts 3775 in microseconds. 3776 3777 rcutorture.fqs_stutter= [KNL] 3778 Set wait time between force_quiescent_state bursts 3779 in seconds. 3780 3781 rcutorture.gp_cond= [KNL] 3782 Use conditional/asynchronous update-side 3783 primitives, if available. 3784 3785 rcutorture.gp_exp= [KNL] 3786 Use expedited update-side primitives, if available. 3787 3788 rcutorture.gp_normal= [KNL] 3789 Use normal (non-expedited) asynchronous 3790 update-side primitives, if available. 3791 3792 rcutorture.gp_sync= [KNL] 3793 Use normal (non-expedited) synchronous 3794 update-side primitives, if available. If all 3795 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3796 rcutorture.gp_normal=, and rcutorture.gp_sync= 3797 are zero, rcutorture acts as if is interpreted 3798 they are all non-zero. 3799 3800 rcutorture.n_barrier_cbs= [KNL] 3801 Set callbacks/threads for rcu_barrier() testing. 3802 3803 rcutorture.nfakewriters= [KNL] 3804 Set number of concurrent RCU writers. These just 3805 stress RCU, they don't participate in the actual 3806 test, hence the "fake". 3807 3808 rcutorture.nreaders= [KNL] 3809 Set number of RCU readers. The value -1 selects 3810 N-1, where N is the number of CPUs. A value 3811 "n" less than -1 selects N-n-2, where N is again 3812 the number of CPUs. For example, -2 selects N 3813 (the number of CPUs), -3 selects N+1, and so on. 3814 3815 rcutorture.object_debug= [KNL] 3816 Enable debug-object double-call_rcu() testing. 3817 3818 rcutorture.onoff_holdoff= [KNL] 3819 Set time (s) after boot for CPU-hotplug testing. 3820 3821 rcutorture.onoff_interval= [KNL] 3822 Set time (jiffies) between CPU-hotplug operations, 3823 or zero to disable CPU-hotplug testing. 3824 3825 rcutorture.shuffle_interval= [KNL] 3826 Set task-shuffle interval (s). Shuffling tasks 3827 allows some CPUs to go into dyntick-idle mode 3828 during the rcutorture test. 3829 3830 rcutorture.shutdown_secs= [KNL] 3831 Set time (s) after boot system shutdown. This 3832 is useful for hands-off automated testing. 3833 3834 rcutorture.stall_cpu= [KNL] 3835 Duration of CPU stall (s) to test RCU CPU stall 3836 warnings, zero to disable. 3837 3838 rcutorture.stall_cpu_holdoff= [KNL] 3839 Time to wait (s) after boot before inducing stall. 3840 3841 rcutorture.stall_cpu_irqsoff= [KNL] 3842 Disable interrupts while stalling if set. 3843 3844 rcutorture.stat_interval= [KNL] 3845 Time (s) between statistics printk()s. 3846 3847 rcutorture.stutter= [KNL] 3848 Time (s) to stutter testing, for example, specifying 3849 five seconds causes the test to run for five seconds, 3850 wait for five seconds, and so on. This tests RCU's 3851 ability to transition abruptly to and from idle. 3852 3853 rcutorture.test_boost= [KNL] 3854 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3855 "Maybe" means test if the RCU implementation 3856 under test support RCU priority boosting. 3857 3858 rcutorture.test_boost_duration= [KNL] 3859 Duration (s) of each individual boost test. 3860 3861 rcutorture.test_boost_interval= [KNL] 3862 Interval (s) between each boost test. 3863 3864 rcutorture.test_no_idle_hz= [KNL] 3865 Test RCU's dyntick-idle handling. See also the 3866 rcutorture.shuffle_interval parameter. 3867 3868 rcutorture.torture_type= [KNL] 3869 Specify the RCU implementation to test. 3870 3871 rcutorture.verbose= [KNL] 3872 Enable additional printk() statements. 3873 3874 rcupdate.rcu_cpu_stall_suppress= [KNL] 3875 Suppress RCU CPU stall warning messages. 3876 3877 rcupdate.rcu_cpu_stall_timeout= [KNL] 3878 Set timeout for RCU CPU stall warning messages. 3879 3880 rcupdate.rcu_expedited= [KNL] 3881 Use expedited grace-period primitives, for 3882 example, synchronize_rcu_expedited() instead 3883 of synchronize_rcu(). This reduces latency, 3884 but can increase CPU utilization, degrade 3885 real-time latency, and degrade energy efficiency. 3886 No effect on CONFIG_TINY_RCU kernels. 3887 3888 rcupdate.rcu_normal= [KNL] 3889 Use only normal grace-period primitives, 3890 for example, synchronize_rcu() instead of 3891 synchronize_rcu_expedited(). This improves 3892 real-time latency, CPU utilization, and 3893 energy efficiency, but can expose users to 3894 increased grace-period latency. This parameter 3895 overrides rcupdate.rcu_expedited. No effect on 3896 CONFIG_TINY_RCU kernels. 3897 3898 rcupdate.rcu_normal_after_boot= [KNL] 3899 Once boot has completed (that is, after 3900 rcu_end_inkernel_boot() has been invoked), use 3901 only normal grace-period primitives. No effect 3902 on CONFIG_TINY_RCU kernels. 3903 3904 rcupdate.rcu_task_stall_timeout= [KNL] 3905 Set timeout in jiffies for RCU task stall warning 3906 messages. Disable with a value less than or equal 3907 to zero. 3908 3909 rcupdate.rcu_self_test= [KNL] 3910 Run the RCU early boot self tests 3911 3912 rdinit= [KNL] 3913 Format: <full_path> 3914 Run specified binary instead of /init from the ramdisk, 3915 used for early userspace startup. See initrd. 3916 3917 rdt= [HW,X86,RDT] 3918 Turn on/off individual RDT features. List is: 3919 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp, 3920 mba. 3921 E.g. to turn on cmt and turn off mba use: 3922 rdt=cmt,!mba 3923 3924 reboot= [KNL] 3925 Format (x86 or x86_64): 3926 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3927 [[,]s[mp]#### \ 3928 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3929 [[,]f[orce] 3930 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3931 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3932 reboot_force is either force or not specified, 3933 reboot_cpu is s[mp]#### with #### being the processor 3934 to be used for rebooting. 3935 3936 relax_domain_level= 3937 [KNL, SMP] Set scheduler's default relax_domain_level. 3938 See Documentation/cgroup-v1/cpusets.txt. 3939 3940 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory 3941 Format: <base1>,<size1>[,<base2>,<size2>,...] 3942 Reserve I/O ports or memory so the kernel won't use 3943 them. If <base> is less than 0x10000, the region 3944 is assumed to be I/O ports; otherwise it is memory. 3945 3946 reservetop= [X86-32] 3947 Format: nn[KMG] 3948 Reserves a hole at the top of the kernel virtual 3949 address space. 3950 3951 reservelow= [X86] 3952 Format: nn[K] 3953 Set the amount of memory to reserve for BIOS at 3954 the bottom of the address space. 3955 3956 reset_devices [KNL] Force drivers to reset the underlying device 3957 during initialization. 3958 3959 resume= [SWSUSP] 3960 Specify the partition device for software suspend 3961 Format: 3962 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3963 3964 resume_offset= [SWSUSP] 3965 Specify the offset from the beginning of the partition 3966 given by "resume=" at which the swap header is located, 3967 in <PAGE_SIZE> units (needed only for swap files). 3968 See Documentation/power/swsusp-and-swap-files.txt 3969 3970 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3971 read the resume files 3972 3973 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3974 Useful for devices that are detected asynchronously 3975 (e.g. USB and MMC devices). 3976 3977 hibernate= [HIBERNATION] 3978 noresume Don't check if there's a hibernation image 3979 present during boot. 3980 nocompress Don't compress/decompress hibernation images. 3981 no Disable hibernation and resume. 3982 protect_image Turn on image protection during restoration 3983 (that will set all pages holding image data 3984 during restoration read-only). 3985 3986 retain_initrd [RAM] Keep initrd memory after extraction 3987 3988 rfkill.default_state= 3989 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3990 etc. communication is blocked by default. 3991 1 Unblocked. 3992 3993 rfkill.master_switch_mode= 3994 0 The "airplane mode" button does nothing. 3995 1 The "airplane mode" button toggles between everything 3996 blocked and the previous configuration. 3997 2 The "airplane mode" button toggles between everything 3998 blocked and everything unblocked. 3999 4000 rhash_entries= [KNL,NET] 4001 Set number of hash buckets for route cache 4002 4003 ring3mwait=disable 4004 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported 4005 CPUs. 4006 4007 ro [KNL] Mount root device read-only on boot 4008 4009 rodata= [KNL] 4010 on Mark read-only kernel memory as read-only (default). 4011 off Leave read-only kernel memory writable for debugging. 4012 4013 rockchip.usb_uart 4014 Enable the uart passthrough on the designated usb port 4015 on Rockchip SoCs. When active, the signals of the 4016 debug-uart get routed to the D+ and D- pins of the usb 4017 port and the regular usb controller gets disabled. 4018 4019 root= [KNL] Root filesystem 4020 See name_to_dev_t comment in init/do_mounts.c. 4021 4022 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 4023 mount the root filesystem 4024 4025 rootflags= [KNL] Set root filesystem mount option string 4026 4027 rootfstype= [KNL] Set root filesystem type 4028 4029 rootwait [KNL] Wait (indefinitely) for root device to show up. 4030 Useful for devices that are detected asynchronously 4031 (e.g. USB and MMC devices). 4032 4033 rproc_mem=nn[KMG][@address] 4034 [KNL,ARM,CMA] Remoteproc physical memory block. 4035 Memory area to be used by remote processor image, 4036 managed by CMA. 4037 4038 rw [KNL] Mount root device read-write on boot 4039 4040 S [KNL] Run init in single mode 4041 4042 s390_iommu= [HW,S390] 4043 Set s390 IOTLB flushing mode 4044 strict 4045 With strict flushing every unmap operation will result in 4046 an IOTLB flush. Default is lazy flushing before reuse, 4047 which is faster. 4048 4049 sa1100ir [NET] 4050 See drivers/net/irda/sa1100_ir.c. 4051 4052 sbni= [NET] Granch SBNI12 leased line adapter 4053 4054 sched_debug [KNL] Enables verbose scheduler debug messages. 4055 4056 schedstats= [KNL,X86] Enable or disable scheduled statistics. 4057 Allowed values are enable and disable. This feature 4058 incurs a small amount of overhead in the scheduler 4059 but is useful for debugging and performance tuning. 4060 4061 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 4062 xtime_lock contention on larger systems, and/or RCU lock 4063 contention on all systems with CONFIG_MAXSMP set. 4064 Format: { "0" | "1" } 4065 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 4066 1 -- enable. 4067 Note: increases power consumption, thus should only be 4068 enabled if running jitter sensitive (HPC/RT) workloads. 4069 4070 security= [SECURITY] Choose a security module to enable at boot. 4071 If this boot parameter is not specified, only the first 4072 security module asking for security registration will be 4073 loaded. An invalid security module name will be treated 4074 as if no module has been chosen. 4075 4076 selinux= [SELINUX] Disable or enable SELinux at boot time. 4077 Format: { "0" | "1" } 4078 See security/selinux/Kconfig help text. 4079 0 -- disable. 4080 1 -- enable. 4081 Default value is set via kernel config option. 4082 If enabled at boot time, /selinux/disable can be used 4083 later to disable prior to initial policy load. 4084 4085 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 4086 Format: { "0" | "1" } 4087 See security/apparmor/Kconfig help text 4088 0 -- disable. 4089 1 -- enable. 4090 Default value is set via kernel config option. 4091 4092 serialnumber [BUGS=X86-32] 4093 4094 shapers= [NET] 4095 Maximal number of shapers. 4096 4097 simeth= [IA-64] 4098 simscsi= 4099 4100 slram= [HW,MTD] 4101 4102 slab_nomerge [MM] 4103 Disable merging of slabs with similar size. May be 4104 necessary if there is some reason to distinguish 4105 allocs to different slabs, especially in hardened 4106 environments where the risk of heap overflows and 4107 layout control by attackers can usually be 4108 frustrated by disabling merging. This will reduce 4109 most of the exposure of a heap attack to a single 4110 cache (risks via metadata attacks are mostly 4111 unchanged). Debug options disable merging on their 4112 own. 4113 For more information see Documentation/vm/slub.rst. 4114 4115 slab_max_order= [MM, SLAB] 4116 Determines the maximum allowed order for slabs. 4117 A high setting may cause OOMs due to memory 4118 fragmentation. Defaults to 1 for systems with 4119 more than 32MB of RAM, 0 otherwise. 4120 4121 slub_debug[=options[,slabs]] [MM, SLUB] 4122 Enabling slub_debug allows one to determine the 4123 culprit if slab objects become corrupted. Enabling 4124 slub_debug can create guard zones around objects and 4125 may poison objects when not in use. Also tracks the 4126 last alloc / free. For more information see 4127 Documentation/vm/slub.rst. 4128 4129 slub_memcg_sysfs= [MM, SLUB] 4130 Determines whether to enable sysfs directories for 4131 memory cgroup sub-caches. 1 to enable, 0 to disable. 4132 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON. 4133 Enabling this can lead to a very high number of debug 4134 directories and files being created under 4135 /sys/kernel/slub. 4136 4137 slub_max_order= [MM, SLUB] 4138 Determines the maximum allowed order for slabs. 4139 A high setting may cause OOMs due to memory 4140 fragmentation. For more information see 4141 Documentation/vm/slub.rst. 4142 4143 slub_min_objects= [MM, SLUB] 4144 The minimum number of objects per slab. SLUB will 4145 increase the slab order up to slub_max_order to 4146 generate a sufficiently large slab able to contain 4147 the number of objects indicated. The higher the number 4148 of objects the smaller the overhead of tracking slabs 4149 and the less frequently locks need to be acquired. 4150 For more information see Documentation/vm/slub.rst. 4151 4152 slub_min_order= [MM, SLUB] 4153 Determines the minimum page order for slabs. Must be 4154 lower than slub_max_order. 4155 For more information see Documentation/vm/slub.rst. 4156 4157 slub_nomerge [MM, SLUB] 4158 Same with slab_nomerge. This is supported for legacy. 4159 See slab_nomerge for more information. 4160 4161 smart2= [HW] 4162 Format: <io1>[,<io2>[,...,<io8>]] 4163 4164 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 4165 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 4166 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 4167 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 4168 smsc-ircc2.ircc_irq= [HW] IRQ line 4169 smsc-ircc2.ircc_dma= [HW] DMA channel 4170 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 4171 0: Toshiba Satellite 1800 (GP data pin select) 4172 1: Fast pin select (default) 4173 2: ATC IRMode 4174 4175 smt [KNL,S390] Set the maximum number of threads (logical 4176 CPUs) to use per physical CPU on systems capable of 4177 symmetric multithreading (SMT). Will be capped to the 4178 actual hardware limit. 4179 Format: <integer> 4180 Default: -1 (no limit) 4181 4182 softlockup_panic= 4183 [KNL] Should the soft-lockup detector generate panics. 4184 Format: <integer> 4185 4186 A nonzero value instructs the soft-lockup detector 4187 to panic the machine when a soft-lockup occurs. This 4188 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC 4189 which is the respective build-time switch to that 4190 functionality. 4191 4192 softlockup_all_cpu_backtrace= 4193 [KNL] Should the soft-lockup detector generate 4194 backtraces on all cpus. 4195 Format: <integer> 4196 4197 sonypi.*= [HW] Sony Programmable I/O Control Device driver 4198 See Documentation/laptops/sonypi.txt 4199 4200 spectre_v2= [X86] Control mitigation of Spectre variant 2 4201 (indirect branch speculation) vulnerability. 4202 The default operation protects the kernel from 4203 user space attacks. 4204 4205 on - unconditionally enable, implies 4206 spectre_v2_user=on 4207 off - unconditionally disable, implies 4208 spectre_v2_user=off 4209 auto - kernel detects whether your CPU model is 4210 vulnerable 4211 4212 Selecting 'on' will, and 'auto' may, choose a 4213 mitigation method at run time according to the 4214 CPU, the available microcode, the setting of the 4215 CONFIG_RETPOLINE configuration option, and the 4216 compiler with which the kernel was built. 4217 4218 Selecting 'on' will also enable the mitigation 4219 against user space to user space task attacks. 4220 4221 Selecting 'off' will disable both the kernel and 4222 the user space protections. 4223 4224 Specific mitigations can also be selected manually: 4225 4226 retpoline - replace indirect branches 4227 retpoline,generic - google's original retpoline 4228 retpoline,amd - AMD-specific minimal thunk 4229 4230 Not specifying this option is equivalent to 4231 spectre_v2=auto. 4232 4233 spectre_v2_user= 4234 [X86] Control mitigation of Spectre variant 2 4235 (indirect branch speculation) vulnerability between 4236 user space tasks 4237 4238 on - Unconditionally enable mitigations. Is 4239 enforced by spectre_v2=on 4240 4241 off - Unconditionally disable mitigations. Is 4242 enforced by spectre_v2=off 4243 4244 prctl - Indirect branch speculation is enabled, 4245 but mitigation can be enabled via prctl 4246 per thread. The mitigation control state 4247 is inherited on fork. 4248 4249 prctl,ibpb 4250 - Like "prctl" above, but only STIBP is 4251 controlled per thread. IBPB is issued 4252 always when switching between different user 4253 space processes. 4254 4255 seccomp 4256 - Same as "prctl" above, but all seccomp 4257 threads will enable the mitigation unless 4258 they explicitly opt out. 4259 4260 seccomp,ibpb 4261 - Like "seccomp" above, but only STIBP is 4262 controlled per thread. IBPB is issued 4263 always when switching between different 4264 user space processes. 4265 4266 auto - Kernel selects the mitigation depending on 4267 the available CPU features and vulnerability. 4268 4269 Default mitigation: 4270 If CONFIG_SECCOMP=y then "seccomp", otherwise "prctl" 4271 4272 Not specifying this option is equivalent to 4273 spectre_v2_user=auto. 4274 4275 spec_store_bypass_disable= 4276 [HW] Control Speculative Store Bypass (SSB) Disable mitigation 4277 (Speculative Store Bypass vulnerability) 4278 4279 Certain CPUs are vulnerable to an exploit against a 4280 a common industry wide performance optimization known 4281 as "Speculative Store Bypass" in which recent stores 4282 to the same memory location may not be observed by 4283 later loads during speculative execution. The idea 4284 is that such stores are unlikely and that they can 4285 be detected prior to instruction retirement at the 4286 end of a particular speculation execution window. 4287 4288 In vulnerable processors, the speculatively forwarded 4289 store can be used in a cache side channel attack, for 4290 example to read memory to which the attacker does not 4291 directly have access (e.g. inside sandboxed code). 4292 4293 This parameter controls whether the Speculative Store 4294 Bypass optimization is used. 4295 4296 On x86 the options are: 4297 4298 on - Unconditionally disable Speculative Store Bypass 4299 off - Unconditionally enable Speculative Store Bypass 4300 auto - Kernel detects whether the CPU model contains an 4301 implementation of Speculative Store Bypass and 4302 picks the most appropriate mitigation. If the 4303 CPU is not vulnerable, "off" is selected. If the 4304 CPU is vulnerable the default mitigation is 4305 architecture and Kconfig dependent. See below. 4306 prctl - Control Speculative Store Bypass per thread 4307 via prctl. Speculative Store Bypass is enabled 4308 for a process by default. The state of the control 4309 is inherited on fork. 4310 seccomp - Same as "prctl" above, but all seccomp threads 4311 will disable SSB unless they explicitly opt out. 4312 4313 Default mitigations: 4314 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl" 4315 4316 On powerpc the options are: 4317 4318 on,auto - On Power8 and Power9 insert a store-forwarding 4319 barrier on kernel entry and exit. On Power7 4320 perform a software flush on kernel entry and 4321 exit. 4322 off - No action. 4323 4324 Not specifying this option is equivalent to 4325 spec_store_bypass_disable=auto. 4326 4327 spia_io_base= [HW,MTD] 4328 spia_fio_base= 4329 spia_pedr= 4330 spia_peddr= 4331 4332 srcutree.counter_wrap_check [KNL] 4333 Specifies how frequently to check for 4334 grace-period sequence counter wrap for the 4335 srcu_data structure's ->srcu_gp_seq_needed field. 4336 The greater the number of bits set in this kernel 4337 parameter, the less frequently counter wrap will 4338 be checked for. Note that the bottom two bits 4339 are ignored. 4340 4341 srcutree.exp_holdoff [KNL] 4342 Specifies how many nanoseconds must elapse 4343 since the end of the last SRCU grace period for 4344 a given srcu_struct until the next normal SRCU 4345 grace period will be considered for automatic 4346 expediting. Set to zero to disable automatic 4347 expediting. 4348 4349 ssbd= [ARM64,HW] 4350 Speculative Store Bypass Disable control 4351 4352 On CPUs that are vulnerable to the Speculative 4353 Store Bypass vulnerability and offer a 4354 firmware based mitigation, this parameter 4355 indicates how the mitigation should be used: 4356 4357 force-on: Unconditionally enable mitigation for 4358 for both kernel and userspace 4359 force-off: Unconditionally disable mitigation for 4360 for both kernel and userspace 4361 kernel: Always enable mitigation in the 4362 kernel, and offer a prctl interface 4363 to allow userspace to register its 4364 interest in being mitigated too. 4365 4366 stack_guard_gap= [MM] 4367 override the default stack gap protection. The value 4368 is in page units and it defines how many pages prior 4369 to (for stacks growing down) resp. after (for stacks 4370 growing up) the main stack are reserved for no other 4371 mapping. Default value is 256 pages. 4372 4373 stacktrace [FTRACE] 4374 Enabled the stack tracer on boot up. 4375 4376 stacktrace_filter=[function-list] 4377 [FTRACE] Limit the functions that the stack tracer 4378 will trace at boot up. function-list is a comma separated 4379 list of functions. This list can be changed at run 4380 time by the stack_trace_filter file in the debugfs 4381 tracing directory. Note, this enables stack tracing 4382 and the stacktrace above is not needed. 4383 4384 sti= [PARISC,HW] 4385 Format: <num> 4386 Set the STI (builtin display/keyboard on the HP-PARISC 4387 machines) console (graphic card) which should be used 4388 as the initial boot-console. 4389 See also comment in drivers/video/console/sticore.c. 4390 4391 sti_font= [HW] 4392 See comment in drivers/video/console/sticore.c. 4393 4394 stifb= [HW] 4395 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 4396 4397 sunrpc.min_resvport= 4398 sunrpc.max_resvport= 4399 [NFS,SUNRPC] 4400 SunRPC servers often require that client requests 4401 originate from a privileged port (i.e. a port in the 4402 range 0 < portnr < 1024). 4403 An administrator who wishes to reserve some of these 4404 ports for other uses may adjust the range that the 4405 kernel's sunrpc client considers to be privileged 4406 using these two parameters to set the minimum and 4407 maximum port values. 4408 4409 sunrpc.svc_rpc_per_connection_limit= 4410 [NFS,SUNRPC] 4411 Limit the number of requests that the server will 4412 process in parallel from a single connection. 4413 The default value is 0 (no limit). 4414 4415 sunrpc.pool_mode= 4416 [NFS] 4417 Control how the NFS server code allocates CPUs to 4418 service thread pools. Depending on how many NICs 4419 you have and where their interrupts are bound, this 4420 option will affect which CPUs will do NFS serving. 4421 Note: this parameter cannot be changed while the 4422 NFS server is running. 4423 4424 auto the server chooses an appropriate mode 4425 automatically using heuristics 4426 global a single global pool contains all CPUs 4427 percpu one pool for each CPU 4428 pernode one pool for each NUMA node (equivalent 4429 to global on non-NUMA machines) 4430 4431 sunrpc.tcp_slot_table_entries= 4432 sunrpc.udp_slot_table_entries= 4433 [NFS,SUNRPC] 4434 Sets the upper limit on the number of simultaneous 4435 RPC calls that can be sent from the client to a 4436 server. Increasing these values may allow you to 4437 improve throughput, but will also increase the 4438 amount of memory reserved for use by the client. 4439 4440 suspend.pm_test_delay= 4441 [SUSPEND] 4442 Sets the number of seconds to remain in a suspend test 4443 mode before resuming the system (see 4444 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 4445 is set. Default value is 5. 4446 4447 swapaccount=[0|1] 4448 [KNL] Enable accounting of swap in memory resource 4449 controller if no parameter or 1 is given or disable 4450 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 4451 4452 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 4453 Format: { <int> | force | noforce } 4454 <int> -- Number of I/O TLB slabs 4455 force -- force using of bounce buffers even if they 4456 wouldn't be automatically used by the kernel 4457 noforce -- Never use bounce buffers (for debugging) 4458 4459 switches= [HW,M68k] 4460 4461 sysfs.deprecated=0|1 [KNL] 4462 Enable/disable old style sysfs layout for old udev 4463 on older distributions. When this option is enabled 4464 very new udev will not work anymore. When this option 4465 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 4466 in older udev will not work anymore. 4467 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 4468 the kernel configuration. 4469 4470 sysrq_always_enabled 4471 [KNL] 4472 Ignore sysrq setting - this boot parameter will 4473 neutralize any effect of /proc/sys/kernel/sysrq. 4474 Useful for debugging. 4475 4476 tcpmhash_entries= [KNL,NET] 4477 Set the number of tcp_metrics_hash slots. 4478 Default value is 8192 or 16384 depending on total 4479 ram pages. This is used to specify the TCP metrics 4480 cache size. See Documentation/networking/ip-sysctl.txt 4481 "tcp_no_metrics_save" section for more details. 4482 4483 tdfx= [HW,DRM] 4484 4485 test_suspend= [SUSPEND][,N] 4486 Specify "mem" (for Suspend-to-RAM) or "standby" (for 4487 standby suspend) or "freeze" (for suspend type freeze) 4488 as the system sleep state during system startup with 4489 the optional capability to repeat N number of times. 4490 The system is woken from this state using a 4491 wakeup-capable RTC alarm. 4492 4493 thash_entries= [KNL,NET] 4494 Set number of hash buckets for TCP connection 4495 4496 thermal.act= [HW,ACPI] 4497 -1: disable all active trip points in all thermal zones 4498 <degrees C>: override all lowest active trip points 4499 4500 thermal.crt= [HW,ACPI] 4501 -1: disable all critical trip points in all thermal zones 4502 <degrees C>: override all critical trip points 4503 4504 thermal.nocrt= [HW,ACPI] 4505 Set to disable actions on ACPI thermal zone 4506 critical and hot trip points. 4507 4508 thermal.off= [HW,ACPI] 4509 1: disable ACPI thermal control 4510 4511 thermal.psv= [HW,ACPI] 4512 -1: disable all passive trip points 4513 <degrees C>: override all passive trip points to this 4514 value 4515 4516 thermal.tzp= [HW,ACPI] 4517 Specify global default ACPI thermal zone polling rate 4518 <deci-seconds>: poll all this frequency 4519 0: no polling (default) 4520 4521 threadirqs [KNL] 4522 Force threading of all interrupt handlers except those 4523 marked explicitly IRQF_NO_THREAD. 4524 4525 tmem [KNL,XEN] 4526 Enable the Transcendent memory driver if built-in. 4527 4528 tmem.cleancache=0|1 [KNL, XEN] 4529 Default is on (1). Disable the usage of the cleancache 4530 API to send anonymous pages to the hypervisor. 4531 4532 tmem.frontswap=0|1 [KNL, XEN] 4533 Default is on (1). Disable the usage of the frontswap 4534 API to send swap pages to the hypervisor. If disabled 4535 the selfballooning and selfshrinking are force disabled. 4536 4537 tmem.selfballooning=0|1 [KNL, XEN] 4538 Default is on (1). Disable the driving of swap pages 4539 to the hypervisor. 4540 4541 tmem.selfshrinking=0|1 [KNL, XEN] 4542 Default is on (1). Partial swapoff that immediately 4543 transfers pages from Xen hypervisor back to the 4544 kernel based on different criteria. 4545 4546 topology= [S390] 4547 Format: {off | on} 4548 Specify if the kernel should make use of the cpu 4549 topology information if the hardware supports this. 4550 The scheduler will make use of this information and 4551 e.g. base its process migration decisions on it. 4552 Default is on. 4553 4554 topology_updates= [KNL, PPC, NUMA] 4555 Format: {off} 4556 Specify if the kernel should ignore (off) 4557 topology updates sent by the hypervisor to this 4558 LPAR. 4559 4560 tp720= [HW,PS2] 4561 4562 tpm_suspend_pcr=[HW,TPM] 4563 Format: integer pcr id 4564 Specify that at suspend time, the tpm driver 4565 should extend the specified pcr with zeros, 4566 as a workaround for some chips which fail to 4567 flush the last written pcr on TPM_SaveState. 4568 This will guarantee that all the other pcrs 4569 are saved. 4570 4571 trace_buf_size=nn[KMG] 4572 [FTRACE] will set tracing buffer size on each cpu. 4573 4574 trace_event=[event-list] 4575 [FTRACE] Set and start specified trace events in order 4576 to facilitate early boot debugging. The event-list is a 4577 comma separated list of trace events to enable. See 4578 also Documentation/trace/events.rst 4579 4580 trace_options=[option-list] 4581 [FTRACE] Enable or disable tracer options at boot. 4582 The option-list is a comma delimited list of options 4583 that can be enabled or disabled just as if you were 4584 to echo the option name into 4585 4586 /sys/kernel/debug/tracing/trace_options 4587 4588 For example, to enable stacktrace option (to dump the 4589 stack trace of each event), add to the command line: 4590 4591 trace_options=stacktrace 4592 4593 See also Documentation/trace/ftrace.rst "trace options" 4594 section. 4595 4596 tp_printk[FTRACE] 4597 Have the tracepoints sent to printk as well as the 4598 tracing ring buffer. This is useful for early boot up 4599 where the system hangs or reboots and does not give the 4600 option for reading the tracing buffer or performing a 4601 ftrace_dump_on_oops. 4602 4603 To turn off having tracepoints sent to printk, 4604 echo 0 > /proc/sys/kernel/tracepoint_printk 4605 Note, echoing 1 into this file without the 4606 tracepoint_printk kernel cmdline option has no effect. 4607 4608 ** CAUTION ** 4609 4610 Having tracepoints sent to printk() and activating high 4611 frequency tracepoints such as irq or sched, can cause 4612 the system to live lock. 4613 4614 traceoff_on_warning 4615 [FTRACE] enable this option to disable tracing when a 4616 warning is hit. This turns off "tracing_on". Tracing can 4617 be enabled again by echoing '1' into the "tracing_on" 4618 file located in /sys/kernel/debug/tracing/ 4619 4620 This option is useful, as it disables the trace before 4621 the WARNING dump is called, which prevents the trace to 4622 be filled with content caused by the warning output. 4623 4624 This option can also be set at run time via the sysctl 4625 option: kernel/traceoff_on_warning 4626 4627 transparent_hugepage= 4628 [KNL] 4629 Format: [always|madvise|never] 4630 Can be used to control the default behavior of the system 4631 with respect to transparent hugepages. 4632 See Documentation/admin-guide/mm/transhuge.rst 4633 for more details. 4634 4635 tsc= Disable clocksource stability checks for TSC. 4636 Format: <string> 4637 [x86] reliable: mark tsc clocksource as reliable, this 4638 disables clocksource verification at runtime, as well 4639 as the stability checks done at bootup. Used to enable 4640 high-resolution timer mode on older hardware, and in 4641 virtualized environment. 4642 [x86] noirqtime: Do not use TSC to do irq accounting. 4643 Used to run time disable IRQ_TIME_ACCOUNTING on any 4644 platforms where RDTSC is slow and this accounting 4645 can add overhead. 4646 [x86] unstable: mark the TSC clocksource as unstable, this 4647 marks the TSC unconditionally unstable at bootup and 4648 avoids any further wobbles once the TSC watchdog notices. 4649 4650 turbografx.map[2|3]= [HW,JOY] 4651 TurboGraFX parallel port interface 4652 Format: 4653 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4654 See also Documentation/input/devices/joystick-parport.rst 4655 4656 udbg-immortal [PPC] When debugging early kernel crashes that 4657 happen after console_init() and before a proper 4658 console driver takes over, this boot options might 4659 help "seeing" what's going on. 4660 4661 uhash_entries= [KNL,NET] 4662 Set number of hash buckets for UDP/UDP-Lite connections 4663 4664 uhci-hcd.ignore_oc= 4665 [USB] Ignore overcurrent events (default N). 4666 Some badly-designed motherboards generate lots of 4667 bogus events, for ports that aren't wired to 4668 anything. Set this parameter to avoid log spamming. 4669 Note that genuine overcurrent events won't be 4670 reported either. 4671 4672 unknown_nmi_panic 4673 [X86] Cause panic on unknown NMI. 4674 4675 usbcore.authorized_default= 4676 [USB] Default USB device authorization: 4677 (default -1 = authorized except for wireless USB, 4678 0 = not authorized, 1 = authorized) 4679 4680 usbcore.autosuspend= 4681 [USB] The autosuspend time delay (in seconds) used 4682 for newly-detected USB devices (default 2). This 4683 is the time required before an idle device will be 4684 autosuspended. Devices for which the delay is set 4685 to a negative value won't be autosuspended at all. 4686 4687 usbcore.usbfs_snoop= 4688 [USB] Set to log all usbfs traffic (default 0 = off). 4689 4690 usbcore.usbfs_snoop_max= 4691 [USB] Maximum number of bytes to snoop in each URB 4692 (default = 65536). 4693 4694 usbcore.blinkenlights= 4695 [USB] Set to cycle leds on hubs (default 0 = off). 4696 4697 usbcore.old_scheme_first= 4698 [USB] Start with the old device initialization 4699 scheme, applies only to low and full-speed devices 4700 (default 0 = off). 4701 4702 usbcore.usbfs_memory_mb= 4703 [USB] Memory limit (in MB) for buffers allocated by 4704 usbfs (default = 16, 0 = max = 2047). 4705 4706 usbcore.use_both_schemes= 4707 [USB] Try the other device initialization scheme 4708 if the first one fails (default 1 = enabled). 4709 4710 usbcore.initial_descriptor_timeout= 4711 [USB] Specifies timeout for the initial 64-byte 4712 USB_REQ_GET_DESCRIPTOR request in milliseconds 4713 (default 5000 = 5.0 seconds). 4714 4715 usbcore.nousb [USB] Disable the USB subsystem 4716 4717 usbcore.quirks= 4718 [USB] A list of quirk entries to augment the built-in 4719 usb core quirk list. List entries are separated by 4720 commas. Each entry has the form 4721 VendorID:ProductID:Flags. The IDs are 4-digit hex 4722 numbers and Flags is a set of letters. Each letter 4723 will change the built-in quirk; setting it if it is 4724 clear and clearing it if it is set. The letters have 4725 the following meanings: 4726 a = USB_QUIRK_STRING_FETCH_255 (string 4727 descriptors must not be fetched using 4728 a 255-byte read); 4729 b = USB_QUIRK_RESET_RESUME (device can't resume 4730 correctly so reset it instead); 4731 c = USB_QUIRK_NO_SET_INTF (device can't handle 4732 Set-Interface requests); 4733 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't 4734 handle its Configuration or Interface 4735 strings); 4736 e = USB_QUIRK_RESET (device can't be reset 4737 (e.g morph devices), don't use reset); 4738 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has 4739 more interface descriptions than the 4740 bNumInterfaces count, and can't handle 4741 talking to these interfaces); 4742 g = USB_QUIRK_DELAY_INIT (device needs a pause 4743 during initialization, after we read 4744 the device descriptor); 4745 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For 4746 high speed and super speed interrupt 4747 endpoints, the USB 2.0 and USB 3.0 spec 4748 require the interval in microframes (1 4749 microframe = 125 microseconds) to be 4750 calculated as interval = 2 ^ 4751 (bInterval-1). 4752 Devices with this quirk report their 4753 bInterval as the result of this 4754 calculation instead of the exponent 4755 variable used in the calculation); 4756 i = USB_QUIRK_DEVICE_QUALIFIER (device can't 4757 handle device_qualifier descriptor 4758 requests); 4759 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device 4760 generates spurious wakeup, ignore 4761 remote wakeup capability); 4762 k = USB_QUIRK_NO_LPM (device can't handle Link 4763 Power Management); 4764 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL 4765 (Device reports its bInterval as linear 4766 frames instead of the USB 2.0 4767 calculation); 4768 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs 4769 to be disconnected before suspend to 4770 prevent spurious wakeup); 4771 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a 4772 pause after every control message); 4773 o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra 4774 delay after resetting its port); 4775 Example: quirks=0781:5580:bk,0a5c:5834:gij 4776 4777 usbhid.mousepoll= 4778 [USBHID] The interval which mice are to be polled at. 4779 4780 usbhid.jspoll= 4781 [USBHID] The interval which joysticks are to be polled at. 4782 4783 usbhid.kbpoll= 4784 [USBHID] The interval which keyboards are to be polled at. 4785 4786 usb-storage.delay_use= 4787 [UMS] The delay in seconds before a new device is 4788 scanned for Logical Units (default 1). 4789 4790 usb-storage.quirks= 4791 [UMS] A list of quirks entries to supplement or 4792 override the built-in unusual_devs list. List 4793 entries are separated by commas. Each entry has 4794 the form VID:PID:Flags where VID and PID are Vendor 4795 and Product ID values (4-digit hex numbers) and 4796 Flags is a set of characters, each corresponding 4797 to a common usb-storage quirk flag as follows: 4798 a = SANE_SENSE (collect more than 18 bytes 4799 of sense data); 4800 b = BAD_SENSE (don't collect more than 18 4801 bytes of sense data); 4802 c = FIX_CAPACITY (decrease the reported 4803 device capacity by one sector); 4804 d = NO_READ_DISC_INFO (don't use 4805 READ_DISC_INFO command); 4806 e = NO_READ_CAPACITY_16 (don't use 4807 READ_CAPACITY_16 command); 4808 f = NO_REPORT_OPCODES (don't use report opcodes 4809 command, uas only); 4810 g = MAX_SECTORS_240 (don't transfer more than 4811 240 sectors at a time, uas only); 4812 h = CAPACITY_HEURISTICS (decrease the 4813 reported device capacity by one 4814 sector if the number is odd); 4815 i = IGNORE_DEVICE (don't bind to this 4816 device); 4817 j = NO_REPORT_LUNS (don't use report luns 4818 command, uas only); 4819 l = NOT_LOCKABLE (don't try to lock and 4820 unlock ejectable media); 4821 m = MAX_SECTORS_64 (don't transfer more 4822 than 64 sectors = 32 KB at a time); 4823 n = INITIAL_READ10 (force a retry of the 4824 initial READ(10) command); 4825 o = CAPACITY_OK (accept the capacity 4826 reported by the device); 4827 p = WRITE_CACHE (the device cache is ON 4828 by default); 4829 r = IGNORE_RESIDUE (the device reports 4830 bogus residue values); 4831 s = SINGLE_LUN (the device has only one 4832 Logical Unit); 4833 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4834 commands, uas only); 4835 u = IGNORE_UAS (don't bind to the uas driver); 4836 w = NO_WP_DETECT (don't test whether the 4837 medium is write-protected). 4838 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4839 even if the device claims no cache) 4840 Example: quirks=0419:aaf5:rl,0421:0433:rc 4841 4842 user_debug= [KNL,ARM] 4843 Format: <int> 4844 See arch/arm/Kconfig.debug help text. 4845 1 - undefined instruction events 4846 2 - system calls 4847 4 - invalid data aborts 4848 8 - SIGSEGV faults 4849 16 - SIGBUS faults 4850 Example: user_debug=31 4851 4852 userpte= 4853 [X86] Flags controlling user PTE allocations. 4854 4855 nohigh = do not allocate PTE pages in 4856 HIGHMEM regardless of setting 4857 of CONFIG_HIGHPTE. 4858 4859 vdso= [X86,SH] 4860 On X86_32, this is an alias for vdso32=. Otherwise: 4861 4862 vdso=1: enable VDSO (the default) 4863 vdso=0: disable VDSO mapping 4864 4865 vdso32= [X86] Control the 32-bit vDSO 4866 vdso32=1: enable 32-bit VDSO 4867 vdso32=0 or vdso32=2: disable 32-bit VDSO 4868 4869 See the help text for CONFIG_COMPAT_VDSO for more 4870 details. If CONFIG_COMPAT_VDSO is set, the default is 4871 vdso32=0; otherwise, the default is vdso32=1. 4872 4873 For compatibility with older kernels, vdso32=2 is an 4874 alias for vdso32=0. 4875 4876 Try vdso32=0 if you encounter an error that says: 4877 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4878 4879 vector= [IA-64,SMP] 4880 vector=percpu: enable percpu vector domain 4881 4882 video= [FB] Frame buffer configuration 4883 See Documentation/fb/modedb.txt. 4884 4885 video.brightness_switch_enabled= [0,1] 4886 If set to 1, on receiving an ACPI notify event 4887 generated by hotkey, video driver will adjust brightness 4888 level and then send out the event to user space through 4889 the allocated input device; If set to 0, video driver 4890 will only send out the event without touching backlight 4891 brightness level. 4892 default: 1 4893 4894 virtio_mmio.device= 4895 [VMMIO] Memory mapped virtio (platform) device. 4896 4897 <size>@<baseaddr>:<irq>[:<id>] 4898 where: 4899 <size> := size (can use standard suffixes 4900 like K, M and G) 4901 <baseaddr> := physical base address 4902 <irq> := interrupt number (as passed to 4903 request_irq()) 4904 <id> := (optional) platform device id 4905 example: 4906 virtio_mmio.device=1K@0x100b0000:48:7 4907 4908 Can be used multiple times for multiple devices. 4909 4910 vga= [BOOT,X86-32] Select a particular video mode 4911 See Documentation/x86/boot.txt and 4912 Documentation/svga.txt. 4913 Use vga=ask for menu. 4914 This is actually a boot loader parameter; the value is 4915 passed to the kernel using a special protocol. 4916 4917 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y. 4918 May slow down system boot speed, especially when 4919 enabled on systems with a large amount of memory. 4920 All options are enabled by default, and this 4921 interface is meant to allow for selectively 4922 enabling or disabling specific virtual memory 4923 debugging features. 4924 4925 Available options are: 4926 P Enable page structure init time poisoning 4927 - Disable all of the above options 4928 4929 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4930 size of <nn>. This can be used to increase the 4931 minimum size (128MB on x86). It can also be used to 4932 decrease the size and leave more room for directly 4933 mapped kernel RAM. 4934 4935 vmcp_cma=nn[MG] [KNL,S390] 4936 Sets the memory size reserved for contiguous memory 4937 allocations for the vmcp device driver. 4938 4939 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4940 Format: <command> 4941 4942 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4943 Format: <command> 4944 4945 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4946 Format: <command> 4947 4948 vsyscall= [X86-64] 4949 Controls the behavior of vsyscalls (i.e. calls to 4950 fixed addresses of 0xffffffffff600x00 from legacy 4951 code). Most statically-linked binaries and older 4952 versions of glibc use these calls. Because these 4953 functions are at fixed addresses, they make nice 4954 targets for exploits that can control RIP. 4955 4956 emulate [default] Vsyscalls turn into traps and are 4957 emulated reasonably safely. 4958 4959 native Vsyscalls are native syscall instructions. 4960 This is a little bit faster than trapping 4961 and makes a few dynamic recompilers work 4962 better than they would in emulation mode. 4963 It also makes exploits much easier to write. 4964 4965 none Vsyscalls don't work at all. This makes 4966 them quite hard to use for exploits but 4967 might break your system. 4968 4969 vt.color= [VT] Default text color. 4970 Format: 0xYX, X = foreground, Y = background. 4971 Default: 0x07 = light gray on black. 4972 4973 vt.cur_default= [VT] Default cursor shape. 4974 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4975 the parameters of the <Esc>[?A;B;Cc escape sequence; 4976 see VGA-softcursor.txt. Default: 2 = underline. 4977 4978 vt.default_blu= [VT] 4979 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4980 Change the default blue palette of the console. 4981 This is a 16-member array composed of values 4982 ranging from 0-255. 4983 4984 vt.default_grn= [VT] 4985 Format: <green0>,<green1>,<green2>,...,<green15> 4986 Change the default green palette of the console. 4987 This is a 16-member array composed of values 4988 ranging from 0-255. 4989 4990 vt.default_red= [VT] 4991 Format: <red0>,<red1>,<red2>,...,<red15> 4992 Change the default red palette of the console. 4993 This is a 16-member array composed of values 4994 ranging from 0-255. 4995 4996 vt.default_utf8= 4997 [VT] 4998 Format=<0|1> 4999 Set system-wide default UTF-8 mode for all tty's. 5000 Default is 1, i.e. UTF-8 mode is enabled for all 5001 newly opened terminals. 5002 5003 vt.global_cursor_default= 5004 [VT] 5005 Format=<-1|0|1> 5006 Set system-wide default for whether a cursor 5007 is shown on new VTs. Default is -1, 5008 i.e. cursors will be created by default unless 5009 overridden by individual drivers. 0 will hide 5010 cursors, 1 will display them. 5011 5012 vt.italic= [VT] Default color for italic text; 0-15. 5013 Default: 2 = green. 5014 5015 vt.underline= [VT] Default color for underlined text; 0-15. 5016 Default: 3 = cyan. 5017 5018 watchdog timers [HW,WDT] For information on watchdog timers, 5019 see Documentation/watchdog/watchdog-parameters.txt 5020 or other driver-specific files in the 5021 Documentation/watchdog/ directory. 5022 5023 workqueue.watchdog_thresh= 5024 If CONFIG_WQ_WATCHDOG is configured, workqueue can 5025 warn stall conditions and dump internal state to 5026 help debugging. 0 disables workqueue stall 5027 detection; otherwise, it's the stall threshold 5028 duration in seconds. The default value is 30 and 5029 it can be updated at runtime by writing to the 5030 corresponding sysfs file. 5031 5032 workqueue.disable_numa 5033 By default, all work items queued to unbound 5034 workqueues are affine to the NUMA nodes they're 5035 issued on, which results in better behavior in 5036 general. If NUMA affinity needs to be disabled for 5037 whatever reason, this option can be used. Note 5038 that this also can be controlled per-workqueue for 5039 workqueues visible under /sys/bus/workqueue/. 5040 5041 workqueue.power_efficient 5042 Per-cpu workqueues are generally preferred because 5043 they show better performance thanks to cache 5044 locality; unfortunately, per-cpu workqueues tend to 5045 be more power hungry than unbound workqueues. 5046 5047 Enabling this makes the per-cpu workqueues which 5048 were observed to contribute significantly to power 5049 consumption unbound, leading to measurably lower 5050 power usage at the cost of small performance 5051 overhead. 5052 5053 The default value of this parameter is determined by 5054 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 5055 5056 workqueue.debug_force_rr_cpu 5057 Workqueue used to implicitly guarantee that work 5058 items queued without explicit CPU specified are put 5059 on the local CPU. This guarantee is no longer true 5060 and while local CPU is still preferred work items 5061 may be put on foreign CPUs. This debug option 5062 forces round-robin CPU selection to flush out 5063 usages which depend on the now broken guarantee. 5064 When enabled, memory and cache locality will be 5065 impacted. 5066 5067 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 5068 default x2apic cluster mode on platforms 5069 supporting x2apic. 5070 5071 x86_intel_mid_timer= [X86-32,APBT] 5072 Choose timer option for x86 Intel MID platform. 5073 Two valid options are apbt timer only and lapic timer 5074 plus one apbt timer for broadcast timer. 5075 x86_intel_mid_timer=apbt_only | lapic_and_apbt 5076 5077 xen_512gb_limit [KNL,X86-64,XEN] 5078 Restricts the kernel running paravirtualized under Xen 5079 to use only up to 512 GB of RAM. The reason to do so is 5080 crash analysis tools and Xen tools for doing domain 5081 save/restore/migration must be enabled to handle larger 5082 domains. 5083 5084 xen_emul_unplug= [HW,X86,XEN] 5085 Unplug Xen emulated devices 5086 Format: [unplug0,][unplug1] 5087 ide-disks -- unplug primary master IDE devices 5088 aux-ide-disks -- unplug non-primary-master IDE devices 5089 nics -- unplug network devices 5090 all -- unplug all emulated devices (NICs and IDE disks) 5091 unnecessary -- unplugging emulated devices is 5092 unnecessary even if the host did not respond to 5093 the unplug protocol 5094 never -- do not unplug even if version check succeeds 5095 5096 xen_nopvspin [X86,XEN] 5097 Disables the ticketlock slowpath using Xen PV 5098 optimizations. 5099 5100 xen_nopv [X86] 5101 Disables the PV optimizations forcing the HVM guest to 5102 run as generic HVM guest with no PV drivers. 5103 5104 xen_scrub_pages= [XEN] 5105 Boolean option to control scrubbing pages before giving them back 5106 to Xen, for use by other domains. Can be also changed at runtime 5107 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. 5108 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. 5109 5110 xirc2ps_cs= [NET,PCMCIA] 5111 Format: 5112 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 5113 5114 xhci-hcd.quirks [USB,KNL] 5115 A hex value specifying bitmask with supplemental xhci 5116 host controller quirks. Meaning of each bit can be 5117 consulted in header drivers/usb/host/xhci.h. 5118