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 Support masking of GPEs numbered from 0x00 to 0x7f. 118 119 acpi_no_auto_serialize [HW,ACPI] 120 Disable auto-serialization of AML methods 121 AML control methods that contain the opcodes to create 122 named objects will be marked as "Serialized" by the 123 auto-serialization feature. 124 This feature is enabled by default. 125 This option allows to turn off the feature. 126 127 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump 128 kernels. 129 130 acpi_no_static_ssdt [HW,ACPI] 131 Disable installation of static SSDTs at early boot time 132 By default, SSDTs contained in the RSDT/XSDT will be 133 installed automatically and they will appear under 134 /sys/firmware/acpi/tables. 135 This option turns off this feature. 136 Note that specifying this option does not affect 137 dynamic table installation which will install SSDT 138 tables to /sys/firmware/acpi/tables/dynamic. 139 140 acpi_rsdp= [ACPI,EFI,KEXEC] 141 Pass the RSDP address to the kernel, mostly used 142 on machines running EFI runtime service to boot the 143 second kernel for kdump. 144 145 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS 146 Format: To spoof as Windows 98: ="Microsoft Windows" 147 148 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead 149 of 2 which is mandated by ACPI 6) as the supported ACPI 150 specification revision (when using this switch, it may 151 be necessary to carry out a cold reboot _twice_ in a 152 row to make it take effect on the platform firmware). 153 154 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings 155 acpi_osi="string1" # add string1 156 acpi_osi="!string2" # remove string2 157 acpi_osi=!* # remove all strings 158 acpi_osi=! # disable all built-in OS vendor 159 strings 160 acpi_osi=!! # enable all built-in OS vendor 161 strings 162 acpi_osi= # disable all strings 163 164 'acpi_osi=!' can be used in combination with single or 165 multiple 'acpi_osi="string1"' to support specific OS 166 vendor string(s). Note that such command can only 167 affect the default state of the OS vendor strings, thus 168 it cannot affect the default state of the feature group 169 strings and the current state of the OS vendor strings, 170 specifying it multiple times through kernel command line 171 is meaningless. This command is useful when one do not 172 care about the state of the feature group strings which 173 should be controlled by the OSPM. 174 Examples: 175 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent 176 to 'acpi_osi="Windows 2000" acpi_osi=!', they all 177 can make '_OSI("Windows 2000")' TRUE. 178 179 'acpi_osi=' cannot be used in combination with other 180 'acpi_osi=' command lines, the _OSI method will not 181 exist in the ACPI namespace. NOTE that such command can 182 only affect the _OSI support state, thus specifying it 183 multiple times through kernel command line is also 184 meaningless. 185 Examples: 186 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)' 187 FALSE. 188 189 'acpi_osi=!*' can be used in combination with single or 190 multiple 'acpi_osi="string1"' to support specific 191 string(s). Note that such command can affect the 192 current state of both the OS vendor strings and the 193 feature group strings, thus specifying it multiple times 194 through kernel command line is meaningful. But it may 195 still not able to affect the final state of a string if 196 there are quirks related to this string. This command 197 is useful when one want to control the state of the 198 feature group strings to debug BIOS issues related to 199 the OSPM features. 200 Examples: 201 1. 'acpi_osi="Module Device" acpi_osi=!*' can make 202 '_OSI("Module Device")' FALSE. 203 2. 'acpi_osi=!* acpi_osi="Module Device"' can make 204 '_OSI("Module Device")' TRUE. 205 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is 206 equivalent to 207 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"' 208 and 209 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!', 210 they all will make '_OSI("Windows 2000")' TRUE. 211 212 acpi_pm_good [X86] 213 Override the pmtimer bug detection: force the kernel 214 to assume that this machine's pmtimer latches its value 215 and always returns good values. 216 217 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode 218 Format: { level | edge | high | low } 219 220 acpi_skip_timer_override [HW,ACPI] 221 Recognize and ignore IRQ0/pin2 Interrupt Override. 222 For broken nForce2 BIOS resulting in XT-PIC timer. 223 224 acpi_sleep= [HW,ACPI] Sleep options 225 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, 226 old_ordering, nonvs, sci_force_enable } 227 See Documentation/power/video.txt for information on 228 s3_bios and s3_mode. 229 s3_beep is for debugging; it makes the PC's speaker beep 230 as soon as the kernel's real-mode entry point is called. 231 s4_nohwsig prevents ACPI hardware signature from being 232 used during resume from hibernation. 233 old_ordering causes the ACPI 1.0 ordering of the _PTS 234 control method, with respect to putting devices into 235 low power states, to be enforced (the ACPI 2.0 ordering 236 of _PTS is used by default). 237 nonvs prevents the kernel from saving/restoring the 238 ACPI NVS memory during suspend/hibernation and resume. 239 sci_force_enable causes the kernel to set SCI_EN directly 240 on resume from S1/S3 (which is against the ACPI spec, 241 but some broken systems don't work without it). 242 243 acpi_use_timer_override [HW,ACPI] 244 Use timer override. For some broken Nvidia NF5 boards 245 that require a timer override, but don't have HPET 246 247 add_efi_memmap [EFI; X86] Include EFI memory map in 248 kernel's map of available physical RAM. 249 250 agp= [AGP] 251 { off | try_unsupported } 252 off: disable AGP support 253 try_unsupported: try to drive unsupported chipsets 254 (may crash computer or cause data corruption) 255 256 ALSA [HW,ALSA] 257 See Documentation/sound/alsa/alsa-parameters.txt 258 259 alignment= [KNL,ARM] 260 Allow the default userspace alignment fault handler 261 behaviour to be specified. Bit 0 enables warnings, 262 bit 1 enables fixups, and bit 2 sends a segfault. 263 264 align_va_addr= [X86-64] 265 Align virtual addresses by clearing slice [14:12] when 266 allocating a VMA at process creation time. This option 267 gives you up to 3% performance improvement on AMD F15h 268 machines (where it is enabled by default) for a 269 CPU-intensive style benchmark, and it can vary highly in 270 a microbenchmark depending on workload and compiler. 271 272 32: only for 32-bit processes 273 64: only for 64-bit processes 274 on: enable for both 32- and 64-bit processes 275 off: disable for both 32- and 64-bit processes 276 277 alloc_snapshot [FTRACE] 278 Allocate the ftrace snapshot buffer on boot up when the 279 main buffer is allocated. This is handy if debugging 280 and you need to use tracing_snapshot() on boot up, and 281 do not want to use tracing_snapshot_alloc() as it needs 282 to be done where GFP_KERNEL allocations are allowed. 283 284 amd_iommu= [HW,X86-64] 285 Pass parameters to the AMD IOMMU driver in the system. 286 Possible values are: 287 fullflush - enable flushing of IO/TLB entries when 288 they are unmapped. Otherwise they are 289 flushed before they will be reused, which 290 is a lot of faster 291 off - do not initialize any AMD IOMMU found in 292 the system 293 force_isolation - Force device isolation for all 294 devices. The IOMMU driver is not 295 allowed anymore to lift isolation 296 requirements as needed. This option 297 does not override iommu=pt 298 299 amd_iommu_dump= [HW,X86-64] 300 Enable AMD IOMMU driver option to dump the ACPI table 301 for AMD IOMMU. With this option enabled, AMD IOMMU 302 driver will print ACPI tables for AMD IOMMU during 303 IOMMU initialization. 304 305 amd_iommu_intr= [HW,X86-64] 306 Specifies one of the following AMD IOMMU interrupt 307 remapping modes: 308 legacy - Use legacy interrupt remapping mode. 309 vapic - Use virtual APIC mode, which allows IOMMU 310 to inject interrupts directly into guest. 311 This mode requires kvm-amd.avic=1. 312 (Default when IOMMU HW support is present.) 313 314 amijoy.map= [HW,JOY] Amiga joystick support 315 Map of devices attached to JOY0DAT and JOY1DAT 316 Format: <a>,<b> 317 See also Documentation/input/joystick.txt 318 319 analog.map= [HW,JOY] Analog joystick and gamepad support 320 Specifies type or capabilities of an analog joystick 321 connected to one of 16 gameports 322 Format: <type1>,<type2>,..<type16> 323 324 apc= [HW,SPARC] 325 Power management functions (SPARCstation-4/5 + deriv.) 326 Format: noidle 327 Disable APC CPU standby support. SPARCstation-Fox does 328 not play well with APC CPU idle - disable it if you have 329 APC and your system crashes randomly. 330 331 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller 332 Change the output verbosity whilst booting 333 Format: { quiet (default) | verbose | debug } 334 Change the amount of debugging information output 335 when initialising the APIC and IO-APIC components. 336 337 apic_extnmi= [APIC,X86] External NMI delivery setting 338 Format: { bsp (default) | all | none } 339 bsp: External NMI is delivered only to CPU 0 340 all: External NMIs are broadcast to all CPUs as a 341 backup of CPU 0 342 none: External NMI is masked for all CPUs. This is 343 useful so that a dump capture kernel won't be 344 shot down by NMI 345 346 autoconf= [IPV6] 347 See Documentation/networking/ipv6.txt. 348 349 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller 350 Limit apic dumping. The parameter defines the maximal 351 number of local apics being dumped. Also it is possible 352 to set it to "all" by meaning -- no limit here. 353 Format: { 1 (default) | 2 | ... | all }. 354 The parameter valid if only apic=debug or 355 apic=verbose is specified. 356 Example: apic=debug show_lapic=all 357 358 apm= [APM] Advanced Power Management 359 See header of arch/x86/kernel/apm_32.c. 360 361 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards 362 Format: <io>,<irq>,<nodeID> 363 364 ataflop= [HW,M68k] 365 366 atarimouse= [HW,MOUSE] Atari Mouse 367 368 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, 369 EzKey and similar keyboards 370 371 atkbd.reset= [HW] Reset keyboard during initialization 372 373 atkbd.set= [HW] Select keyboard code set 374 Format: <int> (2 = AT (default), 3 = PS/2) 375 376 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar 377 keyboards 378 379 atkbd.softraw= [HW] Choose between synthetic and real raw mode 380 Format: <bool> (0 = real, 1 = synthetic (default)) 381 382 atkbd.softrepeat= [HW] 383 Use software keyboard repeat 384 385 audit= [KNL] Enable the audit sub-system 386 Format: { "0" | "1" } (0 = disabled, 1 = enabled) 387 0 - kernel audit is disabled and can not be enabled 388 until the next reboot 389 unset - kernel audit is initialized but disabled and 390 will be fully enabled by the userspace auditd. 391 1 - kernel audit is initialized and partially enabled, 392 storing at most audit_backlog_limit messages in 393 RAM until it is fully enabled by the userspace 394 auditd. 395 Default: unset 396 397 audit_backlog_limit= [KNL] Set the audit queue size limit. 398 Format: <int> (must be >=0) 399 Default: 64 400 401 bau= [X86_UV] Enable the BAU on SGI UV. The default 402 behavior is to disable the BAU (i.e. bau=0). 403 Format: { "0" | "1" } 404 0 - Disable the BAU. 405 1 - Enable the BAU. 406 unset - Disable the BAU. 407 408 baycom_epp= [HW,AX25] 409 Format: <io>,<mode> 410 411 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem 412 Format: <io>,<mode> 413 See header of drivers/net/hamradio/baycom_par.c. 414 415 baycom_ser_fdx= [HW,AX25] 416 BayCom Serial Port AX.25 Modem (Full Duplex Mode) 417 Format: <io>,<irq>,<mode>[,<baud>] 418 See header of drivers/net/hamradio/baycom_ser_fdx.c. 419 420 baycom_ser_hdx= [HW,AX25] 421 BayCom Serial Port AX.25 Modem (Half Duplex Mode) 422 Format: <io>,<irq>,<mode> 423 See header of drivers/net/hamradio/baycom_ser_hdx.c. 424 425 blkdevparts= Manual partition parsing of block device(s) for 426 embedded devices based on command line input. 427 See Documentation/block/cmdline-partition.txt 428 429 boot_delay= Milliseconds to delay each printk during boot. 430 Values larger than 10 seconds (10000) are changed to 431 no delay (0). 432 Format: integer 433 434 bootmem_debug [KNL] Enable bootmem allocator debug messages. 435 436 bert_disable [ACPI] 437 Disable BERT OS support on buggy BIOSes. 438 439 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) 440 bttv.radio= Most important insmod options are available as 441 kernel args too. 442 bttv.pll= See Documentation/video4linux/bttv/Insmod-options 443 bttv.tuner= 444 445 bulk_remove=off [PPC] This parameter disables the use of the pSeries 446 firmware feature for flushing multiple hpte entries 447 at a time. 448 449 c101= [NET] Moxa C101 synchronous serial card 450 451 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. 452 Sometimes CPU hardware bugs make them report the cache 453 size incorrectly. The kernel will attempt work arounds 454 to fix known problems, but for some CPUs it is not 455 possible to determine what the correct size should be. 456 This option provides an override for these situations. 457 458 ca_keys= [KEYS] This parameter identifies a specific key(s) on 459 the system trusted keyring to be used for certificate 460 trust validation. 461 format: { id:<keyid> | builtin } 462 463 cca= [MIPS] Override the kernel pages' cache coherency 464 algorithm. Accepted values range from 0 to 7 465 inclusive. See arch/mips/include/asm/pgtable-bits.h 466 for platform specific values (SB1, Loongson3 and 467 others). 468 469 ccw_timeout_log [S390] 470 See Documentation/s390/CommonIO for details. 471 472 cgroup_disable= [KNL] Disable a particular controller 473 Format: {name of the controller(s) to disable} 474 The effects of cgroup_disable=foo are: 475 - foo isn't auto-mounted if you mount all cgroups in 476 a single hierarchy 477 - foo isn't visible as an individually mountable 478 subsystem 479 {Currently only "memory" controller deal with this and 480 cut the overhead, others just disable the usage. So 481 only cgroup_disable=memory is actually worthy} 482 483 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1 484 Format: { controller[,controller...] | "all" } 485 Like cgroup_disable, but only applies to cgroup v1; 486 the blacklisted controllers remain available in cgroup2. 487 488 cgroup.memory= [KNL] Pass options to the cgroup memory controller. 489 Format: <string> 490 nosocket -- Disable socket memory accounting. 491 nokmem -- Disable kernel memory accounting. 492 493 checkreqprot [SELINUX] Set initial checkreqprot flag value. 494 Format: { "0" | "1" } 495 See security/selinux/Kconfig help text. 496 0 -- check protection applied by kernel (includes 497 any implied execute protection). 498 1 -- check protection requested by application. 499 Default value is set via a kernel config option. 500 Value can be changed at runtime via 501 /selinux/checkreqprot. 502 503 cio_ignore= [S390] 504 See Documentation/s390/CommonIO for details. 505 clk_ignore_unused 506 [CLK] 507 Prevents the clock framework from automatically gating 508 clocks that have not been explicitly enabled by a Linux 509 device driver but are enabled in hardware at reset or 510 by the bootloader/firmware. Note that this does not 511 force such clocks to be always-on nor does it reserve 512 those clocks in any way. This parameter is useful for 513 debug and development, but should not be needed on a 514 platform with proper driver support. For more 515 information, see Documentation/clk.txt. 516 517 clock= [BUGS=X86-32, HW] gettimeofday clocksource override. 518 [Deprecated] 519 Forces specified clocksource (if available) to be used 520 when calculating gettimeofday(). If specified 521 clocksource is not available, it defaults to PIT. 522 Format: { pit | tsc | cyclone | pmtmr } 523 524 clocksource= Override the default clocksource 525 Format: <string> 526 Override the default clocksource and use the clocksource 527 with the name specified. 528 Some clocksource names to choose from, depending on 529 the platform: 530 [all] jiffies (this is the base, fallback clocksource) 531 [ACPI] acpi_pm 532 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, 533 pxa_timer,timer3,32k_counter,timer0_1 534 [AVR32] avr32 535 [X86-32] pit,hpet,tsc; 536 scx200_hrt on Geode; cyclone on IBM x440 537 [MIPS] MIPS 538 [PARISC] cr16 539 [S390] tod 540 [SH] SuperH 541 [SPARC64] tick 542 [X86-64] hpet,tsc 543 544 clocksource.arm_arch_timer.evtstrm= 545 [ARM,ARM64] 546 Format: <bool> 547 Enable/disable the eventstream feature of the ARM 548 architected timer so that code using WFE-based polling 549 loops can be debugged more effectively on production 550 systems. 551 552 clocksource.arm_arch_timer.fsl-a008585= 553 [ARM64] 554 Format: <bool> 555 Enable/disable the workaround of Freescale/NXP 556 erratum A-008585. This can be useful for KVM 557 guests, if the guest device tree doesn't show the 558 erratum. If unspecified, the workaround is 559 enabled based on the device tree. 560 561 clearcpuid=BITNUM [X86] 562 Disable CPUID feature X for the kernel. See 563 arch/x86/include/asm/cpufeatures.h for the valid bit 564 numbers. Note the Linux specific bits are not necessarily 565 stable over kernel options, but the vendor specific 566 ones should be. 567 Also note that user programs calling CPUID directly 568 or using the feature without checking anything 569 will still see it. This just prevents it from 570 being used by the kernel or shown in /proc/cpuinfo. 571 Also note the kernel might malfunction if you disable 572 some critical bits. 573 574 cma=nn[MG]@[start[MG][-end[MG]]] 575 [ARM,X86,KNL] 576 Sets the size of kernel global memory area for 577 contiguous memory allocations and optionally the 578 placement constraint by the physical address range of 579 memory allocations. A value of 0 disables CMA 580 altogether. For more information, see 581 include/linux/dma-contiguous.h 582 583 cmo_free_hint= [PPC] Format: { yes | no } 584 Specify whether pages are marked as being inactive 585 when they are freed. This is used in CMO environments 586 to determine OS memory pressure for page stealing by 587 a hypervisor. 588 Default: yes 589 590 coherent_pool=nn[KMG] [ARM,KNL] 591 Sets the size of memory pool for coherent, atomic dma 592 allocations, by default set to 256K. 593 594 code_bytes [X86] How many bytes of object code to print 595 in an oops report. 596 Range: 0 - 8192 597 Default: 64 598 599 com20020= [HW,NET] ARCnet - COM20020 chipset 600 Format: 601 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] 602 603 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) 604 Format: <io>[,<irq>] 605 606 com90xx= [HW,NET] 607 ARCnet - COM90xx chipset (memory-mapped buffers) 608 Format: <io>[,<irq>[,<memstart>]] 609 610 condev= [HW,S390] console device 611 conmode= 612 613 console= [KNL] Output console device and options. 614 615 tty<n> Use the virtual console device <n>. 616 617 ttyS<n>[,options] 618 ttyUSB0[,options] 619 Use the specified serial port. The options are of 620 the form "bbbbpnf", where "bbbb" is the baud rate, 621 "p" is parity ("n", "o", or "e"), "n" is number of 622 bits, and "f" is flow control ("r" for RTS or 623 omit it). Default is "9600n8". 624 625 See Documentation/admin-guide/serial-console.rst for more 626 information. See 627 Documentation/networking/netconsole.txt for an 628 alternative. 629 630 uart[8250],io,<addr>[,options] 631 uart[8250],mmio,<addr>[,options] 632 uart[8250],mmio16,<addr>[,options] 633 uart[8250],mmio32,<addr>[,options] 634 uart[8250],0x<addr>[,options] 635 Start an early, polled-mode console on the 8250/16550 636 UART at the specified I/O port or MMIO address, 637 switching to the matching ttyS device later. 638 MMIO inter-register address stride is either 8-bit 639 (mmio), 16-bit (mmio16), or 32-bit (mmio32). 640 If none of [io|mmio|mmio16|mmio32], <addr> is assumed 641 to be equivalent to 'mmio'. 'options' are specified in 642 the same format described for ttyS above; if unspecified, 643 the h/w is not re-initialized. 644 645 hvc<n> Use the hypervisor console device <n>. This is for 646 both Xen and PowerPC hypervisors. 647 648 If the device connected to the port is not a TTY but a braille 649 device, prepend "brl," before the device type, for instance 650 console=brl,ttyS0 651 For now, only VisioBraille is supported. 652 653 consoleblank= [KNL] The console blank (screen saver) timeout in 654 seconds. Defaults to 10*60 = 10mins. A value of 0 655 disables the blank timer. 656 657 coredump_filter= 658 [KNL] Change the default value for 659 /proc/<pid>/coredump_filter. 660 See also Documentation/filesystems/proc.txt. 661 662 cpuidle.off=1 [CPU_IDLE] 663 disable the cpuidle sub-system 664 665 cpu_init_udelay=N 666 [X86] Delay for N microsec between assert and de-assert 667 of APIC INIT to start processors. This delay occurs 668 on every CPU online, such as boot, and resume from suspend. 669 Default: 10000 670 671 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver 672 Format: 673 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] 674 675 crashkernel=size[KMG][@offset[KMG]] 676 [KNL] Using kexec, Linux can switch to a 'crash kernel' 677 upon panic. This parameter reserves the physical 678 memory region [offset, offset + size] for that kernel 679 image. If '@offset' is omitted, then a suitable offset 680 is selected automatically. Check 681 Documentation/kdump/kdump.txt for further details. 682 683 crashkernel=range1:size1[,range2:size2,...][@offset] 684 [KNL] Same as above, but depends on the memory 685 in the running system. The syntax of range is 686 start-[end] where start and end are both 687 a memory unit (amount[KMG]). See also 688 Documentation/kdump/kdump.txt for an example. 689 690 crashkernel=size[KMG],high 691 [KNL, x86_64] range could be above 4G. Allow kernel 692 to allocate physical memory region from top, so could 693 be above 4G if system have more than 4G ram installed. 694 Otherwise memory region will be allocated below 4G, if 695 available. 696 It will be ignored if crashkernel=X is specified. 697 crashkernel=size[KMG],low 698 [KNL, x86_64] range under 4G. When crashkernel=X,high 699 is passed, kernel could allocate physical memory region 700 above 4G, that cause second kernel crash on system 701 that require some amount of low memory, e.g. swiotlb 702 requires at least 64M+32K low memory, also enough extra 703 low memory is needed to make sure DMA buffers for 32-bit 704 devices won't run out. Kernel would try to allocate at 705 at least 256M below 4G automatically. 706 This one let user to specify own low range under 4G 707 for second kernel instead. 708 0: to disable low allocation. 709 It will be ignored when crashkernel=X,high is not used 710 or memory reserved is below 4G. 711 712 cryptomgr.notests 713 [KNL] Disable crypto self-tests 714 715 cs89x0_dma= [HW,NET] 716 Format: <dma> 717 718 cs89x0_media= [HW,NET] 719 Format: { rj45 | aui | bnc } 720 721 dasd= [HW,NET] 722 See header of drivers/s390/block/dasd_devmap.c. 723 724 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port 725 (one device per port) 726 Format: <port#>,<type> 727 See also Documentation/input/joystick-parport.txt 728 729 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot 730 time. See Documentation/dynamic-debug-howto.txt for 731 details. Deprecated, see dyndbg. 732 733 debug [KNL] Enable kernel debugging (events log level). 734 735 debug_locks_verbose= 736 [KNL] verbose self-tests 737 Format=<0|1> 738 Print debugging info while doing the locking API 739 self-tests. 740 We default to 0 (no extra messages), setting it to 741 1 will print _a lot_ more information - normally 742 only useful to kernel developers. 743 744 debug_objects [KNL] Enable object debugging 745 746 no_debug_objects 747 [KNL] Disable object debugging 748 749 debug_guardpage_minorder= 750 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 751 parameter allows control of the order of pages that will 752 be intentionally kept free (and hence protected) by the 753 buddy allocator. Bigger value increase the probability 754 of catching random memory corruption, but reduce the 755 amount of memory for normal system use. The maximum 756 possible value is MAX_ORDER/2. Setting this parameter 757 to 1 or 2 should be enough to identify most random 758 memory corruption problems caused by bugs in kernel or 759 driver code when a CPU writes to (or reads from) a 760 random memory location. Note that there exists a class 761 of memory corruptions problems caused by buggy H/W or 762 F/W or by drivers badly programing DMA (basically when 763 memory is written at bus level and the CPU MMU is 764 bypassed) which are not detectable by 765 CONFIG_DEBUG_PAGEALLOC, hence this option will not help 766 tracking down these problems. 767 768 debug_pagealloc= 769 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this 770 parameter enables the feature at boot time. In 771 default, it is disabled. We can avoid allocating huge 772 chunk of memory for debug pagealloc if we don't enable 773 it at boot time and the system will work mostly same 774 with the kernel built without CONFIG_DEBUG_PAGEALLOC. 775 on: enable the feature 776 777 debugpat [X86] Enable PAT debugging 778 779 decnet.addr= [HW,NET] 780 Format: <area>[,<node>] 781 See also Documentation/networking/decnet.txt. 782 783 default_hugepagesz= 784 [same as hugepagesz=] The size of the default 785 HugeTLB page size. This is the size represented by 786 the legacy /proc/ hugepages APIs, used for SHM, and 787 default size when mounting hugetlbfs filesystems. 788 Defaults to the default architecture's huge page size 789 if not specified. 790 791 dhash_entries= [KNL] 792 Set number of hash buckets for dentry cache. 793 794 disable_1tb_segments [PPC] 795 Disables the use of 1TB hash page table segments. This 796 causes the kernel to fall back to 256MB segments which 797 can be useful when debugging issues that require an SLB 798 miss to occur. 799 800 disable= [IPV6] 801 See Documentation/networking/ipv6.txt. 802 803 disable_radix [PPC] 804 Disable RADIX MMU mode on POWER9 805 806 disable_cpu_apicid= [X86,APIC,SMP] 807 Format: <int> 808 The number of initial APIC ID for the 809 corresponding CPU to be disabled at boot, 810 mostly used for the kdump 2nd kernel to 811 disable BSP to wake up multiple CPUs without 812 causing system reset or hang due to sending 813 INIT from AP to BSP. 814 815 disable_ddw [PPC/PSERIES] 816 Disable Dynamic DMA Window support. Use this if 817 to workaround buggy firmware. 818 819 disable_ipv6= [IPV6] 820 See Documentation/networking/ipv6.txt. 821 822 disable_mtrr_cleanup [X86] 823 The kernel tries to adjust MTRR layout from continuous 824 to discrete, to make X server driver able to add WB 825 entry later. This parameter disables that. 826 827 disable_mtrr_trim [X86, Intel and AMD only] 828 By default the kernel will trim any uncacheable 829 memory out of your available memory pool based on 830 MTRR settings. This parameter disables that behavior, 831 possibly causing your machine to run very slowly. 832 833 disable_timer_pin_1 [X86] 834 Disable PIN 1 of APIC timer 835 Can be useful to work around chipset bugs. 836 837 dis_ucode_ldr [X86] Disable the microcode loader. 838 839 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, 840 this option disables the debugging code at boot. 841 842 dma_debug_entries=<number> 843 This option allows to tune the number of preallocated 844 entries for DMA-API debugging code. One entry is 845 required per DMA-API allocation. Use this if the 846 DMA-API debugging code disables itself because the 847 architectural default is too low. 848 849 dma_debug_driver=<driver_name> 850 With this option the DMA-API debugging driver 851 filter feature can be enabled at boot time. Just 852 pass the driver to filter for as the parameter. 853 The filter can be disabled or changed to another 854 driver later using sysfs. 855 856 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>] 857 Broken monitors, graphic adapters, KVMs and EDIDless 858 panels may send no or incorrect EDID data sets. 859 This parameter allows to specify an EDID data sets 860 in the /lib/firmware directory that are used instead. 861 Generic built-in EDID data sets are used, if one of 862 edid/1024x768.bin, edid/1280x1024.bin, 863 edid/1680x1050.bin, or edid/1920x1080.bin is given 864 and no file with the same name exists. Details and 865 instructions how to build your own EDID data are 866 available in Documentation/EDID/HOWTO.txt. An EDID 867 data set will only be used for a particular connector, 868 if its name and a colon are prepended to the EDID 869 name. Each connector may use a unique EDID data 870 set by separating the files with a comma. An EDID 871 data set with no connector name will be used for 872 any connectors not explicitly specified. 873 874 dscc4.setup= [NET] 875 876 dump_apple_properties [X86] 877 Dump name and content of EFI device properties on 878 x86 Macs. Useful for driver authors to determine 879 what data is available or for reverse-engineering. 880 881 dyndbg[="val"] [KNL,DYNAMIC_DEBUG] 882 module.dyndbg[="val"] 883 Enable debug messages at boot time. See 884 Documentation/dynamic-debug-howto.txt for details. 885 886 nompx [X86] Disables Intel Memory Protection Extensions. 887 See Documentation/x86/intel_mpx.txt for more 888 information about the feature. 889 890 nopku [X86] Disable Memory Protection Keys CPU feature found 891 in some Intel CPUs. 892 893 module.async_probe [KNL] 894 Enable asynchronous probe on this module. 895 896 early_ioremap_debug [KNL] 897 Enable debug messages in early_ioremap support. This 898 is useful for tracking down temporary early mappings 899 which are not unmapped. 900 901 earlycon= [KNL] Output early console device and options. 902 903 When used with no options, the early console is 904 determined by the stdout-path property in device 905 tree's chosen node. 906 907 cdns,<addr>[,options] 908 Start an early, polled-mode console on a Cadence 909 (xuartps) serial port at the specified address. Only 910 supported option is baud rate. If baud rate is not 911 specified, the serial port must already be setup and 912 configured. 913 914 uart[8250],io,<addr>[,options] 915 uart[8250],mmio,<addr>[,options] 916 uart[8250],mmio32,<addr>[,options] 917 uart[8250],mmio32be,<addr>[,options] 918 uart[8250],0x<addr>[,options] 919 Start an early, polled-mode console on the 8250/16550 920 UART at the specified I/O port or MMIO address. 921 MMIO inter-register address stride is either 8-bit 922 (mmio) or 32-bit (mmio32 or mmio32be). 923 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed 924 to be equivalent to 'mmio'. 'options' are specified 925 in the same format described for "console=ttyS<n>"; if 926 unspecified, the h/w is not initialized. 927 928 pl011,<addr> 929 pl011,mmio32,<addr> 930 Start an early, polled-mode console on a pl011 serial 931 port at the specified address. The pl011 serial port 932 must already be setup and configured. Options are not 933 yet supported. If 'mmio32' is specified, then only 934 the driver will use only 32-bit accessors to read/write 935 the device registers. 936 937 meson,<addr> 938 Start an early, polled-mode console on a meson serial 939 port at the specified address. The serial port must 940 already be setup and configured. Options are not yet 941 supported. 942 943 msm_serial,<addr> 944 Start an early, polled-mode console on an msm serial 945 port at the specified address. The serial port 946 must already be setup and configured. Options are not 947 yet supported. 948 949 msm_serial_dm,<addr> 950 Start an early, polled-mode console on an msm serial 951 dm port at the specified address. The serial port 952 must already be setup and configured. Options are not 953 yet supported. 954 955 smh Use ARM semihosting calls for early console. 956 957 s3c2410,<addr> 958 s3c2412,<addr> 959 s3c2440,<addr> 960 s3c6400,<addr> 961 s5pv210,<addr> 962 exynos4210,<addr> 963 Use early console provided by serial driver available 964 on Samsung SoCs, requires selecting proper type and 965 a correct base address of the selected UART port. The 966 serial port must already be setup and configured. 967 Options are not yet supported. 968 969 lpuart,<addr> 970 lpuart32,<addr> 971 Use early console provided by Freescale LP UART driver 972 found on Freescale Vybrid and QorIQ LS1021A processors. 973 A valid base address must be provided, and the serial 974 port must already be setup and configured. 975 976 armada3700_uart,<addr> 977 Start an early, polled-mode console on the 978 Armada 3700 serial port at the specified 979 address. The serial port must already be setup 980 and configured. Options are not yet supported. 981 982 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k] 983 earlyprintk=vga 984 earlyprintk=efi 985 earlyprintk=xen 986 earlyprintk=serial[,ttySn[,baudrate]] 987 earlyprintk=serial[,0x...[,baudrate]] 988 earlyprintk=ttySn[,baudrate] 989 earlyprintk=dbgp[debugController#] 990 earlyprintk=pciserial,bus:device.function[,baudrate] 991 992 earlyprintk is useful when the kernel crashes before 993 the normal console is initialized. It is not enabled by 994 default because it has some cosmetic problems. 995 996 Append ",keep" to not disable it when the real console 997 takes over. 998 999 Only one of vga, efi, serial, or usb debug port can 1000 be used at a time. 1001 1002 Currently only ttyS0 and ttyS1 may be specified by 1003 name. Other I/O ports may be explicitly specified 1004 on some architectures (x86 and arm at least) by 1005 replacing ttySn with an I/O port address, like this: 1006 earlyprintk=serial,0x1008,115200 1007 You can find the port for a given device in 1008 /proc/tty/driver/serial: 1009 2: uart:ST16650V2 port:00001008 irq:18 ... 1010 1011 Interaction with the standard serial driver is not 1012 very good. 1013 1014 The VGA and EFI output is eventually overwritten by 1015 the real console. 1016 1017 The xen output can only be used by Xen PV guests. 1018 1019 edac_report= [HW,EDAC] Control how to report EDAC event 1020 Format: {"on" | "off" | "force"} 1021 on: enable EDAC to report H/W event. May be overridden 1022 by other higher priority error reporting module. 1023 off: disable H/W event reporting through EDAC. 1024 force: enforce the use of EDAC to report H/W event. 1025 default: on. 1026 1027 ekgdboc= [X86,KGDB] Allow early kernel console debugging 1028 ekgdboc=kbd 1029 1030 This is designed to be used in conjunction with 1031 the boot argument: earlyprintk=vga 1032 1033 edd= [EDD] 1034 Format: {"off" | "on" | "skip[mbr]"} 1035 1036 efi= [EFI] 1037 Format: { "old_map", "nochunk", "noruntime", "debug" } 1038 old_map [X86-64]: switch to the old ioremap-based EFI 1039 runtime services mapping. 32-bit still uses this one by 1040 default. 1041 nochunk: disable reading files in "chunks" in the EFI 1042 boot stub, as chunking can cause problems with some 1043 firmware implementations. 1044 noruntime : disable EFI runtime services support 1045 debug: enable misc debug output 1046 1047 efi_no_storage_paranoia [EFI; X86] 1048 Using this parameter you can use more than 50% of 1049 your efi variable storage. Use this parameter only if 1050 you are really sure that your UEFI does sane gc and 1051 fulfills the spec otherwise your board may brick. 1052 1053 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86] 1054 Add arbitrary attribute to specific memory range by 1055 updating original EFI memory map. 1056 Region of memory which aa attribute is added to is 1057 from ss to ss+nn. 1058 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000 1059 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000) 1060 attribute is added to range 0x100000000-0x180000000 and 1061 0x10a0000000-0x1120000000. 1062 1063 Using this parameter you can do debugging of EFI memmap 1064 related feature. For example, you can do debugging of 1065 Address Range Mirroring feature even if your box 1066 doesn't support it. 1067 1068 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT 1069 that is to be dynamically loaded by Linux. If there are 1070 multiple variables with the same name but with different 1071 vendor GUIDs, all of them will be loaded. See 1072 Documentation/acpi/ssdt-overlays.txt for details. 1073 1074 1075 eisa_irq_edge= [PARISC,HW] 1076 See header of drivers/parisc/eisa.c. 1077 1078 elanfreq= [X86-32] 1079 See comment before function elanfreq_setup() in 1080 arch/x86/kernel/cpu/cpufreq/elanfreq.c. 1081 1082 elevator= [IOSCHED] 1083 Format: {"cfq" | "deadline" | "noop"} 1084 See Documentation/block/cfq-iosched.txt and 1085 Documentation/block/deadline-iosched.txt for details. 1086 1087 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390] 1088 Specifies physical address of start of kernel core 1089 image elf header and optionally the size. Generally 1090 kexec loader will pass this option to capture kernel. 1091 See Documentation/kdump/kdump.txt for details. 1092 1093 enable_mtrr_cleanup [X86] 1094 The kernel tries to adjust MTRR layout from continuous 1095 to discrete, to make X server driver able to add WB 1096 entry later. This parameter enables that. 1097 1098 enable_timer_pin_1 [X86] 1099 Enable PIN 1 of APIC timer 1100 Can be useful to work around chipset bugs 1101 (in particular on some ATI chipsets). 1102 The kernel tries to set a reasonable default. 1103 1104 enforcing [SELINUX] Set initial enforcing status. 1105 Format: {"0" | "1"} 1106 See security/selinux/Kconfig help text. 1107 0 -- permissive (log only, no denials). 1108 1 -- enforcing (deny and log). 1109 Default value is 0. 1110 Value can be changed at runtime via /selinux/enforce. 1111 1112 erst_disable [ACPI] 1113 Disable Error Record Serialization Table (ERST) 1114 support. 1115 1116 ether= [HW,NET] Ethernet cards parameters 1117 This option is obsoleted by the "netdev=" option, which 1118 has equivalent usage. See its documentation for details. 1119 1120 evm= [EVM] 1121 Format: { "fix" } 1122 Permit 'security.evm' to be updated regardless of 1123 current integrity status. 1124 1125 failslab= 1126 fail_page_alloc= 1127 fail_make_request=[KNL] 1128 General fault injection mechanism. 1129 Format: <interval>,<probability>,<space>,<times> 1130 See also Documentation/fault-injection/. 1131 1132 floppy= [HW] 1133 See Documentation/blockdev/floppy.txt. 1134 1135 force_pal_cache_flush 1136 [IA-64] Avoid check_sal_cache_flush which may hang on 1137 buggy SAL_CACHE_FLUSH implementations. Using this 1138 parameter will force ia64_sal_cache_flush to call 1139 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. 1140 1141 forcepae [X86-32] 1142 Forcefully enable Physical Address Extension (PAE). 1143 Many Pentium M systems disable PAE but may have a 1144 functionally usable PAE implementation. 1145 Warning: use of this parameter will taint the kernel 1146 and may cause unknown problems. 1147 1148 ftrace=[tracer] 1149 [FTRACE] will set and start the specified tracer 1150 as early as possible in order to facilitate early 1151 boot debugging. 1152 1153 ftrace_dump_on_oops[=orig_cpu] 1154 [FTRACE] will dump the trace buffers on oops. 1155 If no parameter is passed, ftrace will dump 1156 buffers of all CPUs, but if you pass orig_cpu, it will 1157 dump only the buffer of the CPU that triggered the 1158 oops. 1159 1160 ftrace_filter=[function-list] 1161 [FTRACE] Limit the functions traced by the function 1162 tracer at boot up. function-list is a comma separated 1163 list of functions. This list can be changed at run 1164 time by the set_ftrace_filter file in the debugfs 1165 tracing directory. 1166 1167 ftrace_notrace=[function-list] 1168 [FTRACE] Do not trace the functions specified in 1169 function-list. This list can be changed at run time 1170 by the set_ftrace_notrace file in the debugfs 1171 tracing directory. 1172 1173 ftrace_graph_filter=[function-list] 1174 [FTRACE] Limit the top level callers functions traced 1175 by the function graph tracer at boot up. 1176 function-list is a comma separated list of functions 1177 that can be changed at run time by the 1178 set_graph_function file in the debugfs tracing directory. 1179 1180 ftrace_graph_notrace=[function-list] 1181 [FTRACE] Do not trace from the functions specified in 1182 function-list. This list is a comma separated list of 1183 functions that can be changed at run time by the 1184 set_graph_notrace file in the debugfs tracing directory. 1185 1186 gamecon.map[2|3]= 1187 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad 1188 support via parallel port (up to 5 devices per port) 1189 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> 1190 See also Documentation/input/joystick-parport.txt 1191 1192 gamma= [HW,DRM] 1193 1194 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART 1195 Format: off | on 1196 default: on 1197 1198 gcov_persist= [GCOV] When non-zero (default), profiling data for 1199 kernel modules is saved and remains accessible via 1200 debugfs, even when the module is unloaded/reloaded. 1201 When zero, profiling data is discarded and associated 1202 debugfs files are removed at module unload time. 1203 1204 gpt [EFI] Forces disk with valid GPT signature but 1205 invalid Protective MBR to be treated as GPT. If the 1206 primary GPT is corrupted, it enables the backup/alternate 1207 GPT to be used instead. 1208 1209 grcan.enable0= [HW] Configuration of physical interface 0. Determines 1210 the "Enable 0" bit of the configuration register. 1211 Format: 0 | 1 1212 Default: 0 1213 grcan.enable1= [HW] Configuration of physical interface 1. Determines 1214 the "Enable 0" bit of the configuration register. 1215 Format: 0 | 1 1216 Default: 0 1217 grcan.select= [HW] Select which physical interface to use. 1218 Format: 0 | 1 1219 Default: 0 1220 grcan.txsize= [HW] Sets the size of the tx buffer. 1221 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0. 1222 Default: 1024 1223 grcan.rxsize= [HW] Sets the size of the rx buffer. 1224 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0. 1225 Default: 1024 1226 1227 gpio-mockup.gpio_mockup_ranges 1228 [HW] Sets the ranges of gpiochip of for this device. 1229 Format: <start1>,<end1>,<start2>,<end2>... 1230 1231 hardlockup_all_cpu_backtrace= 1232 [KNL] Should the hard-lockup detector generate 1233 backtraces on all cpus. 1234 Format: <integer> 1235 1236 hashdist= [KNL,NUMA] Large hashes allocated during boot 1237 are distributed across NUMA nodes. Defaults on 1238 for 64-bit NUMA, off otherwise. 1239 Format: 0 | 1 (for off | on) 1240 1241 hcl= [IA-64] SGI's Hardware Graph compatibility layer 1242 1243 hd= [EIDE] (E)IDE hard drive subsystem geometry 1244 Format: <cyl>,<head>,<sect> 1245 1246 hest_disable [ACPI] 1247 Disable Hardware Error Source Table (HEST) support; 1248 corresponding firmware-first mode error processing 1249 logic will be disabled. 1250 1251 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact 1252 size of <nn>. This works even on boxes that have no 1253 highmem otherwise. This also works to reduce highmem 1254 size on bigger boxes. 1255 1256 highres= [KNL] Enable/disable high resolution timer mode. 1257 Valid parameters: "on", "off" 1258 Default: "on" 1259 1260 hisax= [HW,ISDN] 1261 See Documentation/isdn/README.HiSax. 1262 1263 hlt [BUGS=ARM,SH] 1264 1265 hpet= [X86-32,HPET] option to control HPET usage 1266 Format: { enable (default) | disable | force | 1267 verbose } 1268 disable: disable HPET and use PIT instead 1269 force: allow force enabled of undocumented chips (ICH4, 1270 VIA, nVidia) 1271 verbose: show contents of HPET registers during setup 1272 1273 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET 1274 registers. Default set by CONFIG_HPET_MMAP_DEFAULT. 1275 1276 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. 1277 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. 1278 On x86-64 and powerpc, this option can be specified 1279 multiple times interleaved with hugepages= to reserve 1280 huge pages of different sizes. Valid pages sizes on 1281 x86-64 are 2M (when the CPU supports "pse") and 1G 1282 (when the CPU supports the "pdpe1gb" cpuinfo flag). 1283 1284 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) 1285 terminal devices. Valid values: 0..8 1286 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. 1287 If specified, z/VM IUCV HVC accepts connections 1288 from listed z/VM user IDs only. 1289 1290 hwthread_map= [METAG] Comma-separated list of Linux cpu id to 1291 hardware thread id mappings. 1292 Format: <cpu>:<hwthread> 1293 1294 keep_bootcon [KNL] 1295 Do not unregister boot console at start. This is only 1296 useful for debugging when something happens in the window 1297 between unregistering the boot console and initializing 1298 the real console. 1299 1300 i2c_bus= [HW] Override the default board specific I2C bus speed 1301 or register an additional I2C bus that is not 1302 registered from board initialization code. 1303 Format: 1304 <bus_id>,<clkrate> 1305 1306 i8042.debug [HW] Toggle i8042 debug mode 1307 i8042.unmask_kbd_data 1308 [HW] Enable printing of interrupt data from the KBD port 1309 (disabled by default, and as a pre-condition 1310 requires that i8042.debug=1 be enabled) 1311 i8042.direct [HW] Put keyboard port into non-translated mode 1312 i8042.dumbkbd [HW] Pretend that controller can only read data from 1313 keyboard and cannot control its state 1314 (Don't attempt to blink the leds) 1315 i8042.noaux [HW] Don't check for auxiliary (== mouse) port 1316 i8042.nokbd [HW] Don't check/create keyboard port 1317 i8042.noloop [HW] Disable the AUX Loopback command while probing 1318 for the AUX port 1319 i8042.nomux [HW] Don't check presence of an active multiplexing 1320 controller 1321 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX 1322 controllers 1323 i8042.notimeout [HW] Ignore timeout condition signalled by controller 1324 i8042.reset [HW] Reset the controller during init, cleanup and 1325 suspend-to-ram transitions, only during s2r 1326 transitions, or never reset 1327 Format: { 1 | Y | y | 0 | N | n } 1328 1, Y, y: always reset controller 1329 0, N, n: don't ever reset controller 1330 Default: only on s2r transitions on x86; most other 1331 architectures force reset to be always executed 1332 i8042.unlock [HW] Unlock (ignore) the keylock 1333 i8042.kbdreset [HW] Reset device connected to KBD port 1334 1335 i810= [HW,DRM] 1336 1337 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data 1338 indicates that the driver is running on unsupported 1339 hardware. 1340 i8k.force [HW] Activate i8k driver even if SMM BIOS signature 1341 does not match list of supported models. 1342 i8k.power_status 1343 [HW] Report power status in /proc/i8k 1344 (disabled by default) 1345 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN 1346 capability is set. 1347 1348 i915.invert_brightness= 1349 [DRM] Invert the sense of the variable that is used to 1350 set the brightness of the panel backlight. Normally a 1351 brightness value of 0 indicates backlight switched off, 1352 and the maximum of the brightness value sets the backlight 1353 to maximum brightness. If this parameter is set to 0 1354 (default) and the machine requires it, or this parameter 1355 is set to 1, a brightness value of 0 sets the backlight 1356 to maximum brightness, and the maximum of the brightness 1357 value switches the backlight off. 1358 -1 -- never invert brightness 1359 0 -- machine default 1360 1 -- force brightness inversion 1361 1362 icn= [HW,ISDN] 1363 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] 1364 1365 ide-core.nodma= [HW] (E)IDE subsystem 1366 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc 1367 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr 1368 .cdrom .chs .ignore_cable are additional options 1369 See Documentation/ide/ide.txt. 1370 1371 ide-generic.probe-mask= [HW] (E)IDE subsystem 1372 Format: <int> 1373 Probe mask for legacy ISA IDE ports. Depending on 1374 platform up to 6 ports are supported, enabled by 1375 setting corresponding bits in the mask to 1. The 1376 default value is 0x0, which has a special meaning. 1377 On systems that have PCI, it triggers scanning the 1378 PCI bus for the first and the second port, which 1379 are then probed. On systems without PCI the value 1380 of 0x0 enables probing the two first ports as if it 1381 was 0x3. 1382 1383 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem 1384 Claim all unknown PCI IDE storage controllers. 1385 1386 idle= [X86] 1387 Format: idle=poll, idle=halt, idle=nomwait 1388 Poll forces a polling idle loop that can slightly 1389 improve the performance of waking up a idle CPU, but 1390 will use a lot of power and make the system run hot. 1391 Not recommended. 1392 idle=halt: Halt is forced to be used for CPU idle. 1393 In such case C2/C3 won't be used again. 1394 idle=nomwait: Disable mwait for CPU C-states 1395 1396 ieee754= [MIPS] Select IEEE Std 754 conformance mode 1397 Format: { strict | legacy | 2008 | relaxed } 1398 Default: strict 1399 1400 Choose which programs will be accepted for execution 1401 based on the IEEE 754 NaN encoding(s) supported by 1402 the FPU and the NaN encoding requested with the value 1403 of an ELF file header flag individually set by each 1404 binary. Hardware implementations are permitted to 1405 support either or both of the legacy and the 2008 NaN 1406 encoding mode. 1407 1408 Available settings are as follows: 1409 strict accept binaries that request a NaN encoding 1410 supported by the FPU 1411 legacy only accept legacy-NaN binaries, if supported 1412 by the FPU 1413 2008 only accept 2008-NaN binaries, if supported 1414 by the FPU 1415 relaxed accept any binaries regardless of whether 1416 supported by the FPU 1417 1418 The FPU emulator is always able to support both NaN 1419 encodings, so if no FPU hardware is present or it has 1420 been disabled with 'nofpu', then the settings of 1421 'legacy' and '2008' strap the emulator accordingly, 1422 'relaxed' straps the emulator for both legacy-NaN and 1423 2008-NaN, whereas 'strict' enables legacy-NaN only on 1424 legacy processors and both NaN encodings on MIPS32 or 1425 MIPS64 CPUs. 1426 1427 The setting for ABS.fmt/NEG.fmt instruction execution 1428 mode generally follows that for the NaN encoding, 1429 except where unsupported by hardware. 1430 1431 ignore_loglevel [KNL] 1432 Ignore loglevel setting - this will print /all/ 1433 kernel messages to the console. Useful for debugging. 1434 We also add it as printk module parameter, so users 1435 could change it dynamically, usually by 1436 /sys/module/printk/parameters/ignore_loglevel. 1437 1438 ignore_rlimit_data 1439 Ignore RLIMIT_DATA setting for data mappings, 1440 print warning at first misuse. Can be changed via 1441 /sys/module/kernel/parameters/ignore_rlimit_data. 1442 1443 ihash_entries= [KNL] 1444 Set number of hash buckets for inode cache. 1445 1446 ima_appraise= [IMA] appraise integrity measurements 1447 Format: { "off" | "enforce" | "fix" | "log" } 1448 default: "enforce" 1449 1450 ima_appraise_tcb [IMA] 1451 The builtin appraise policy appraises all files 1452 owned by uid=0. 1453 1454 ima_canonical_fmt [IMA] 1455 Use the canonical format for the binary runtime 1456 measurements, instead of host native format. 1457 1458 ima_hash= [IMA] 1459 Format: { md5 | sha1 | rmd160 | sha256 | sha384 1460 | sha512 | ... } 1461 default: "sha1" 1462 1463 The list of supported hash algorithms is defined 1464 in crypto/hash_info.h. 1465 1466 ima_policy= [IMA] 1467 The builtin measurement policy to load during IMA 1468 setup. Specyfing "tcb" as the value, measures all 1469 programs exec'd, files mmap'd for exec, and all files 1470 opened with the read mode bit set by either the 1471 effective uid (euid=0) or uid=0. 1472 Format: "tcb" 1473 1474 ima_tcb [IMA] Deprecated. Use ima_policy= instead. 1475 Load a policy which meets the needs of the Trusted 1476 Computing Base. This means IMA will measure all 1477 programs exec'd, files mmap'd for exec, and all files 1478 opened for read by uid=0. 1479 1480 ima_template= [IMA] 1481 Select one of defined IMA measurements template formats. 1482 Formats: { "ima" | "ima-ng" | "ima-sig" } 1483 Default: "ima-ng" 1484 1485 ima_template_fmt= 1486 [IMA] Define a custom template format. 1487 Format: { "field1|...|fieldN" } 1488 1489 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage 1490 Format: <min_file_size> 1491 Set the minimal file size for using asynchronous hash. 1492 If left unspecified, ahash usage is disabled. 1493 1494 ahash performance varies for different data sizes on 1495 different crypto accelerators. This option can be used 1496 to achieve the best performance for a particular HW. 1497 1498 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size 1499 Format: <bufsize> 1500 Set hashing buffer size. Default: 4k. 1501 1502 ahash performance varies for different chunk sizes on 1503 different crypto accelerators. This option can be used 1504 to achieve best performance for particular HW. 1505 1506 init= [KNL] 1507 Format: <full_path> 1508 Run specified binary instead of /sbin/init as init 1509 process. 1510 1511 initcall_debug [KNL] Trace initcalls as they are executed. Useful 1512 for working out where the kernel is dying during 1513 startup. 1514 1515 initcall_blacklist= [KNL] Do not execute a comma-separated list of 1516 initcall functions. Useful for debugging built-in 1517 modules and initcalls. 1518 1519 initrd= [BOOT] Specify the location of the initial ramdisk 1520 1521 init_pkru= [x86] Specify the default memory protection keys rights 1522 register contents for all processes. 0x55555554 by 1523 default (disallow access to all but pkey 0). Can 1524 override in debugfs after boot. 1525 1526 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver 1527 Format: <irq> 1528 1529 int_pln_enable [x86] Enable power limit notification interrupt 1530 1531 integrity_audit=[IMA] 1532 Format: { "0" | "1" } 1533 0 -- basic integrity auditing messages. (Default) 1534 1 -- additional integrity auditing messages. 1535 1536 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option 1537 on 1538 Enable intel iommu driver. 1539 off 1540 Disable intel iommu driver. 1541 igfx_off [Default Off] 1542 By default, gfx is mapped as normal device. If a gfx 1543 device has a dedicated DMAR unit, the DMAR unit is 1544 bypassed by not enabling DMAR with this option. In 1545 this case, gfx device will use physical address for 1546 DMA. 1547 forcedac [x86_64] 1548 With this option iommu will not optimize to look 1549 for io virtual address below 32-bit forcing dual 1550 address cycle on pci bus for cards supporting greater 1551 than 32-bit addressing. The default is to look 1552 for translation below 32-bit and if not available 1553 then look in the higher range. 1554 strict [Default Off] 1555 With this option on every unmap_single operation will 1556 result in a hardware IOTLB flush operation as opposed 1557 to batching them for performance. 1558 sp_off [Default Off] 1559 By default, super page will be supported if Intel IOMMU 1560 has the capability. With this option, super page will 1561 not be supported. 1562 ecs_off [Default Off] 1563 By default, extended context tables will be supported if 1564 the hardware advertises that it has support both for the 1565 extended tables themselves, and also PASID support. With 1566 this option set, extended tables will not be used even 1567 on hardware which claims to support them. 1568 1569 intel_idle.max_cstate= [KNL,HW,ACPI,X86] 1570 0 disables intel_idle and fall back on acpi_idle. 1571 1 to 9 specify maximum depth of C-state. 1572 1573 intel_pstate= [X86] 1574 disable 1575 Do not enable intel_pstate as the default 1576 scaling driver for the supported processors 1577 passive 1578 Use intel_pstate as a scaling driver, but configure it 1579 to work with generic cpufreq governors (instead of 1580 enabling its internal governor). This mode cannot be 1581 used along with the hardware-managed P-states (HWP) 1582 feature. 1583 force 1584 Enable intel_pstate on systems that prohibit it by default 1585 in favor of acpi-cpufreq. Forcing the intel_pstate driver 1586 instead of acpi-cpufreq may disable platform features, such 1587 as thermal controls and power capping, that rely on ACPI 1588 P-States information being indicated to OSPM and therefore 1589 should be used with caution. This option does not work with 1590 processors that aren't supported by the intel_pstate driver 1591 or on platforms that use pcc-cpufreq instead of acpi-cpufreq. 1592 no_hwp 1593 Do not enable hardware P state control (HWP) 1594 if available. 1595 hwp_only 1596 Only load intel_pstate on systems which support 1597 hardware P state control (HWP) if available. 1598 support_acpi_ppc 1599 Enforce ACPI _PPC performance limits. If the Fixed ACPI 1600 Description Table, specifies preferred power management 1601 profile as "Enterprise Server" or "Performance Server", 1602 then this feature is turned on by default. 1603 per_cpu_perf_limits 1604 Allow per-logical-CPU P-State performance control limits using 1605 cpufreq sysfs interface 1606 1607 intremap= [X86-64, Intel-IOMMU] 1608 on enable Interrupt Remapping (default) 1609 off disable Interrupt Remapping 1610 nosid disable Source ID checking 1611 no_x2apic_optout 1612 BIOS x2APIC opt-out request will be ignored 1613 nopost disable Interrupt Posting 1614 1615 iomem= Disable strict checking of access to MMIO memory 1616 strict regions from userspace. 1617 relaxed 1618 1619 iommu= [x86] 1620 off 1621 force 1622 noforce 1623 biomerge 1624 panic 1625 nopanic 1626 merge 1627 nomerge 1628 forcesac 1629 soft 1630 pt [x86, IA-64] 1631 nobypass [PPC/POWERNV] 1632 Disable IOMMU bypass, using IOMMU for PCI devices. 1633 1634 1635 io7= [HW] IO7 for Marvel based alpha systems 1636 See comment before marvel_specify_io7 in 1637 arch/alpha/kernel/core_marvel.c. 1638 1639 io_delay= [X86] I/O delay method 1640 0x80 1641 Standard port 0x80 based delay 1642 0xed 1643 Alternate port 0xed based delay (needed on some systems) 1644 udelay 1645 Simple two microseconds delay 1646 none 1647 No delay 1648 1649 ip= [IP_PNP] 1650 See Documentation/filesystems/nfs/nfsroot.txt. 1651 1652 irqaffinity= [SMP] Set the default irq affinity mask 1653 The argument is a cpu list, as described above. 1654 1655 irqfixup [HW] 1656 When an interrupt is not handled search all handlers 1657 for it. Intended to get systems with badly broken 1658 firmware running. 1659 1660 irqpoll [HW] 1661 When an interrupt is not handled search all handlers 1662 for it. Also check all handlers each timer 1663 interrupt. Intended to get systems with badly broken 1664 firmware running. 1665 1666 isapnp= [ISAPNP] 1667 Format: <RDP>,<reset>,<pci_scan>,<verbosity> 1668 1669 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. 1670 The argument is a cpu list, as described above. 1671 1672 This option can be used to specify one or more CPUs 1673 to isolate from the general SMP balancing and scheduling 1674 algorithms. You can move a process onto or off an 1675 "isolated" CPU via the CPU affinity syscalls or cpuset. 1676 <cpu number> begins at 0 and the maximum value is 1677 "number of CPUs in system - 1". 1678 1679 This option is the preferred way to isolate CPUs. The 1680 alternative -- manually setting the CPU mask of all 1681 tasks in the system -- can cause problems and 1682 suboptimal load balancer performance. 1683 1684 iucv= [HW,NET] 1685 1686 ivrs_ioapic [HW,X86_64] 1687 Provide an override to the IOAPIC-ID<->DEVICE-ID 1688 mapping provided in the IVRS ACPI table. For 1689 example, to map IOAPIC-ID decimal 10 to 1690 PCI device 00:14.0 write the parameter as: 1691 ivrs_ioapic[10]=00:14.0 1692 1693 ivrs_hpet [HW,X86_64] 1694 Provide an override to the HPET-ID<->DEVICE-ID 1695 mapping provided in the IVRS ACPI table. For 1696 example, to map HPET-ID decimal 0 to 1697 PCI device 00:14.0 write the parameter as: 1698 ivrs_hpet[0]=00:14.0 1699 1700 ivrs_acpihid [HW,X86_64] 1701 Provide an override to the ACPI-HID:UID<->DEVICE-ID 1702 mapping provided in the IVRS ACPI table. For 1703 example, to map UART-HID:UID AMD0020:0 to 1704 PCI device 00:14.5 write the parameter as: 1705 ivrs_acpihid[00:14.5]=AMD0020:0 1706 1707 js= [HW,JOY] Analog joystick 1708 See Documentation/input/joystick.txt. 1709 1710 nokaslr [KNL] 1711 When CONFIG_RANDOMIZE_BASE is set, this disables 1712 kernel and module base offset ASLR (Address Space 1713 Layout Randomization). 1714 1715 keepinitrd [HW,ARM] 1716 1717 kernelcore= [KNL,X86,IA-64,PPC] 1718 Format: nn[KMGTPE] | "mirror" 1719 This parameter 1720 specifies the amount of memory usable by the kernel 1721 for non-movable allocations. The requested amount is 1722 spread evenly throughout all nodes in the system. The 1723 remaining memory in each node is used for Movable 1724 pages. In the event, a node is too small to have both 1725 kernelcore and Movable pages, kernelcore pages will 1726 take priority and other nodes will have a larger number 1727 of Movable pages. The Movable zone is used for the 1728 allocation of pages that may be reclaimed or moved 1729 by the page migration subsystem. This means that 1730 HugeTLB pages may not be allocated from this zone. 1731 Note that allocations like PTEs-from-HighMem still 1732 use the HighMem zone if it exists, and the Normal 1733 zone if it does not. 1734 1735 Instead of specifying the amount of memory (nn[KMGTPE]), 1736 you can specify "mirror" option. In case "mirror" 1737 option is specified, mirrored (reliable) memory is used 1738 for non-movable allocations and remaining memory is used 1739 for Movable pages. nn[KMGTPE] and "mirror" are exclusive, 1740 so you can NOT specify nn[KMGTPE] and "mirror" at the same 1741 time. 1742 1743 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port. 1744 Format: <Controller#>[,poll interval] 1745 The controller # is the number of the ehci usb debug 1746 port as it is probed via PCI. The poll interval is 1747 optional and is the number seconds in between 1748 each poll cycle to the debug port in case you need 1749 the functionality for interrupting the kernel with 1750 gdb or control-c on the dbgp connection. When 1751 not using this parameter you use sysrq-g to break into 1752 the kernel debugger. 1753 1754 kgdboc= [KGDB,HW] kgdb over consoles. 1755 Requires a tty driver that supports console polling, 1756 or a supported polling keyboard driver (non-usb). 1757 Serial only format: <serial_device>[,baud] 1758 keyboard only format: kbd 1759 keyboard and serial format: kbd,<serial_device>[,baud] 1760 Optional Kernel mode setting: 1761 kms, kbd format: kms,kbd 1762 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud] 1763 1764 kgdbwait [KGDB] Stop kernel execution and enter the 1765 kernel debugger at the earliest opportunity. 1766 1767 kmac= [MIPS] korina ethernet MAC address. 1768 Configure the RouterBoard 532 series on-chip 1769 Ethernet adapter MAC address. 1770 1771 kmemleak= [KNL] Boot-time kmemleak enable/disable 1772 Valid arguments: on, off 1773 Default: on 1774 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y, 1775 the default is off. 1776 1777 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode 1778 Valid arguments: 0, 1, 2 1779 kmemcheck=0 (disabled) 1780 kmemcheck=1 (enabled) 1781 kmemcheck=2 (one-shot mode) 1782 Default: 2 (one-shot mode) 1783 1784 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. 1785 Default is 0 (don't ignore, but inject #GP) 1786 1787 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit 1788 KVM MMU at runtime. 1789 Default is 0 (off) 1790 1791 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. 1792 Default is 1 (enabled) 1793 1794 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) 1795 for all guests. 1796 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode. 1797 1798 kvm-intel.ept= [KVM,Intel] Disable extended page tables 1799 (virtualized MMU) support on capable Intel chips. 1800 Default is 1 (enabled) 1801 1802 kvm-intel.emulate_invalid_guest_state= 1803 [KVM,Intel] Enable emulation of invalid guest states 1804 Default is 0 (disabled) 1805 1806 kvm-intel.flexpriority= 1807 [KVM,Intel] Disable FlexPriority feature (TPR shadow). 1808 Default is 1 (enabled) 1809 1810 kvm-intel.nested= 1811 [KVM,Intel] Enable VMX nesting (nVMX). 1812 Default is 0 (disabled) 1813 1814 kvm-intel.unrestricted_guest= 1815 [KVM,Intel] Disable unrestricted guest feature 1816 (virtualized real and unpaged mode) on capable 1817 Intel chips. Default is 1 (enabled) 1818 1819 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification 1820 feature (tagged TLBs) on capable Intel chips. 1821 Default is 1 (enabled) 1822 1823 l2cr= [PPC] 1824 1825 l3cr= [PPC] 1826 1827 lapic [X86-32,APIC] Enable the local APIC even if BIOS 1828 disabled it. 1829 1830 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline 1831 value for LAPIC timer one-shot implementation. Default 1832 back to the programmable timer unit in the LAPIC. 1833 1834 lapic_timer_c2_ok [X86,APIC] trust the local apic timer 1835 in C2 power state. 1836 1837 libata.dma= [LIBATA] DMA control 1838 libata.dma=0 Disable all PATA and SATA DMA 1839 libata.dma=1 PATA and SATA Disk DMA only 1840 libata.dma=2 ATAPI (CDROM) DMA only 1841 libata.dma=4 Compact Flash DMA only 1842 Combinations also work, so libata.dma=3 enables DMA 1843 for disks and CDROMs, but not CFs. 1844 1845 libata.ignore_hpa= [LIBATA] Ignore HPA limit 1846 libata.ignore_hpa=0 keep BIOS limits (default) 1847 libata.ignore_hpa=1 ignore limits, using full disk 1848 1849 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume 1850 when set. 1851 Format: <int> 1852 1853 libata.force= [LIBATA] Force configurations. The format is comma 1854 separated list of "[ID:]VAL" where ID is 1855 PORT[.DEVICE]. PORT and DEVICE are decimal numbers 1856 matching port, link or device. Basically, it matches 1857 the ATA ID string printed on console by libata. If 1858 the whole ID part is omitted, the last PORT and DEVICE 1859 values are used. If ID hasn't been specified yet, the 1860 configuration applies to all ports, links and devices. 1861 1862 If only DEVICE is omitted, the parameter applies to 1863 the port and all links and devices behind it. DEVICE 1864 number of 0 either selects the first device or the 1865 first fan-out link behind PMP device. It does not 1866 select the host link. DEVICE number of 15 selects the 1867 host link and device attached to it. 1868 1869 The VAL specifies the configuration to force. As long 1870 as there's no ambiguity shortcut notation is allowed. 1871 For example, both 1.5 and 1.5G would work for 1.5Gbps. 1872 The following configurations can be forced. 1873 1874 * Cable type: 40c, 80c, short40c, unk, ign or sata. 1875 Any ID with matching PORT is used. 1876 1877 * SATA link speed limit: 1.5Gbps or 3.0Gbps. 1878 1879 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. 1880 udma[/][16,25,33,44,66,100,133] notation is also 1881 allowed. 1882 1883 * [no]ncq: Turn on or off NCQ. 1884 1885 * [no]ncqtrim: Turn off queued DSM TRIM. 1886 1887 * nohrst, nosrst, norst: suppress hard, soft 1888 and both resets. 1889 1890 * rstonce: only attempt one reset during 1891 hot-unplug link recovery 1892 1893 * dump_id: dump IDENTIFY data. 1894 1895 * atapi_dmadir: Enable ATAPI DMADIR bridge support 1896 1897 * disable: Disable this device. 1898 1899 If there are multiple matching configurations changing 1900 the same attribute, the last one is used. 1901 1902 memblock=debug [KNL] Enable memblock debug messages. 1903 1904 load_ramdisk= [RAM] List of ramdisks to load from floppy 1905 See Documentation/blockdev/ramdisk.txt. 1906 1907 lockd.nlm_grace_period=P [NFS] Assign grace period. 1908 Format: <integer> 1909 1910 lockd.nlm_tcpport=N [NFS] Assign TCP port. 1911 Format: <integer> 1912 1913 lockd.nlm_timeout=T [NFS] Assign timeout value. 1914 Format: <integer> 1915 1916 lockd.nlm_udpport=M [NFS] Assign UDP port. 1917 Format: <integer> 1918 1919 locktorture.nreaders_stress= [KNL] 1920 Set the number of locking read-acquisition kthreads. 1921 Defaults to being automatically set based on the 1922 number of online CPUs. 1923 1924 locktorture.nwriters_stress= [KNL] 1925 Set the number of locking write-acquisition kthreads. 1926 1927 locktorture.onoff_holdoff= [KNL] 1928 Set time (s) after boot for CPU-hotplug testing. 1929 1930 locktorture.onoff_interval= [KNL] 1931 Set time (s) between CPU-hotplug operations, or 1932 zero to disable CPU-hotplug testing. 1933 1934 locktorture.shuffle_interval= [KNL] 1935 Set task-shuffle interval (jiffies). Shuffling 1936 tasks allows some CPUs to go into dyntick-idle 1937 mode during the locktorture test. 1938 1939 locktorture.shutdown_secs= [KNL] 1940 Set time (s) after boot system shutdown. This 1941 is useful for hands-off automated testing. 1942 1943 locktorture.stat_interval= [KNL] 1944 Time (s) between statistics printk()s. 1945 1946 locktorture.stutter= [KNL] 1947 Time (s) to stutter testing, for example, 1948 specifying five seconds causes the test to run for 1949 five seconds, wait for five seconds, and so on. 1950 This tests the locking primitive's ability to 1951 transition abruptly to and from idle. 1952 1953 locktorture.torture_runnable= [BOOT] 1954 Start locktorture running at boot time. 1955 1956 locktorture.torture_type= [KNL] 1957 Specify the locking implementation to test. 1958 1959 locktorture.verbose= [KNL] 1960 Enable additional printk() statements. 1961 1962 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver 1963 Format: <irq> 1964 1965 loglevel= All Kernel Messages with a loglevel smaller than the 1966 console loglevel will be printed to the console. It can 1967 also be changed with klogd or other programs. The 1968 loglevels are defined as follows: 1969 1970 0 (KERN_EMERG) system is unusable 1971 1 (KERN_ALERT) action must be taken immediately 1972 2 (KERN_CRIT) critical conditions 1973 3 (KERN_ERR) error conditions 1974 4 (KERN_WARNING) warning conditions 1975 5 (KERN_NOTICE) normal but significant condition 1976 6 (KERN_INFO) informational 1977 7 (KERN_DEBUG) debug-level messages 1978 1979 log_buf_len=n[KMG] Sets the size of the printk ring buffer, 1980 in bytes. n must be a power of two and greater 1981 than the minimal size. The minimal size is defined 1982 by LOG_BUF_SHIFT kernel config parameter. There is 1983 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter 1984 that allows to increase the default size depending on 1985 the number of CPUs. See init/Kconfig for more details. 1986 1987 logo.nologo [FB] Disables display of the built-in Linux logo. 1988 This may be used to provide more screen space for 1989 kernel log messages and is useful when debugging 1990 kernel boot problems. 1991 1992 lp=0 [LP] Specify parallel ports to use, e.g, 1993 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses 1994 lp=reset first parallel port). 'lp=0' disables the 1995 lp=auto printer driver. 'lp=reset' (which can be 1996 specified in addition to the ports) causes 1997 attached printers to be reset. Using 1998 lp=port1,port2,... specifies the parallel ports 1999 to associate lp devices with, starting with 2000 lp0. A port specification may be 'none' to skip 2001 that lp device, or a parport name such as 2002 'parport0'. Specifying 'lp=auto' instead of a 2003 port specification list means that device IDs 2004 from each port should be examined, to see if 2005 an IEEE 1284-compliant printer is attached; if 2006 so, the driver will manage that printer. 2007 See also header of drivers/char/lp.c. 2008 2009 lpj=n [KNL] 2010 Sets loops_per_jiffy to given constant, thus avoiding 2011 time-consuming boot-time autodetection (up to 250 ms per 2012 CPU). 0 enables autodetection (default). To determine 2013 the correct value for your kernel, boot with normal 2014 autodetection and see what value is printed. Note that 2015 on SMP systems the preset will be applied to all CPUs, 2016 which is likely to cause problems if your CPUs need 2017 significantly divergent settings. An incorrect value 2018 will cause delays in the kernel to be wrong, leading to 2019 unpredictable I/O errors and other breakage. Although 2020 unlikely, in the extreme case this might damage your 2021 hardware. 2022 2023 ltpc= [NET] 2024 Format: <io>,<irq>,<dma> 2025 2026 machvec= [IA-64] Force the use of a particular machine-vector 2027 (machvec) in a generic kernel. 2028 Example: machvec=hpzx1_swiotlb 2029 2030 machtype= [Loongson] Share the same kernel image file between different 2031 yeeloong laptop. 2032 Example: machtype=lemote-yeeloong-2f-7inch 2033 2034 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater 2035 than or equal to this physical address is ignored. 2036 2037 maxcpus= [SMP] Maximum number of processors that an SMP kernel 2038 will bring up during bootup. maxcpus=n : n >= 0 limits 2039 the kernel to bring up 'n' processors. Surely after 2040 bootup you can bring up the other plugged cpu by executing 2041 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus 2042 only takes effect during system bootup. 2043 While n=0 is a special case, it is equivalent to "nosmp", 2044 which also disables the IO APIC. 2045 2046 max_loop= [LOOP] The number of loop block devices that get 2047 (loop.max_loop) unconditionally pre-created at init time. The default 2048 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead 2049 of statically allocating a predefined number, loop 2050 devices can be requested on-demand with the 2051 /dev/loop-control interface. 2052 2053 mce [X86-32] Machine Check Exception 2054 2055 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt 2056 2057 md= [HW] RAID subsystems devices and level 2058 See Documentation/admin-guide/md.rst. 2059 2060 mdacon= [MDA] 2061 Format: <first>,<last> 2062 Specifies range of consoles to be captured by the MDA. 2063 2064 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory 2065 Amount of memory to be used when the kernel is not able 2066 to see the whole system memory or for test. 2067 [X86] Work as limiting max address. Use together 2068 with memmap= to avoid physical address space collisions. 2069 Without memmap= PCI devices could be placed at addresses 2070 belonging to unused RAM. 2071 2072 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel 2073 memory. 2074 2075 memchunk=nn[KMG] 2076 [KNL,SH] Allow user to override the default size for 2077 per-device physically contiguous DMA buffers. 2078 2079 memhp_default_state=online/offline 2080 [KNL] Set the initial state for the memory hotplug 2081 onlining policy. If not specified, the default value is 2082 set according to the 2083 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config 2084 option. 2085 See Documentation/memory-hotplug.txt. 2086 2087 memmap=exactmap [KNL,X86] Enable setting of an exact 2088 E820 memory map, as specified by the user. 2089 Such memmap=exactmap lines can be constructed based on 2090 BIOS output or other requirements. See the memmap=nn@ss 2091 option description. 2092 2093 memmap=nn[KMG]@ss[KMG] 2094 [KNL] Force usage of a specific region of memory. 2095 Region of memory to be used is from ss to ss+nn. 2096 2097 memmap=nn[KMG]#ss[KMG] 2098 [KNL,ACPI] Mark specific memory as ACPI data. 2099 Region of memory to be marked is from ss to ss+nn. 2100 2101 memmap=nn[KMG]$ss[KMG] 2102 [KNL,ACPI] Mark specific memory as reserved. 2103 Region of memory to be reserved is from ss to ss+nn. 2104 Example: Exclude memory from 0x18690000-0x1869ffff 2105 memmap=64K$0x18690000 2106 or 2107 memmap=0x10000$0x18690000 2108 2109 memmap=nn[KMG]!ss[KMG] 2110 [KNL,X86] Mark specific memory as protected. 2111 Region of memory to be used, from ss to ss+nn. 2112 The memory region may be marked as e820 type 12 (0xc) 2113 and is NVDIMM or ADR memory. 2114 2115 memory_corruption_check=0/1 [X86] 2116 Some BIOSes seem to corrupt the first 64k of 2117 memory when doing things like suspend/resume. 2118 Setting this option will scan the memory 2119 looking for corruption. Enabling this will 2120 both detect corruption and prevent the kernel 2121 from using the memory being corrupted. 2122 However, its intended as a diagnostic tool; if 2123 repeatable BIOS-originated corruption always 2124 affects the same memory, you can use memmap= 2125 to prevent the kernel from using that memory. 2126 2127 memory_corruption_check_size=size [X86] 2128 By default it checks for corruption in the low 2129 64k, making this memory unavailable for normal 2130 use. Use this parameter to scan for 2131 corruption in more or less memory. 2132 2133 memory_corruption_check_period=seconds [X86] 2134 By default it checks for corruption every 60 2135 seconds. Use this parameter to check at some 2136 other rate. 0 disables periodic checking. 2137 2138 memtest= [KNL,X86,ARM] Enable memtest 2139 Format: <integer> 2140 default : 0 <disable> 2141 Specifies the number of memtest passes to be 2142 performed. Each pass selects another test 2143 pattern from a given set of patterns. Memtest 2144 fills the memory with this pattern, validates 2145 memory contents and reserves bad memory 2146 regions that are detected. 2147 2148 mem_sleep_default= [SUSPEND] Default system suspend mode: 2149 s2idle - Suspend-To-Idle 2150 shallow - Power-On Suspend or equivalent (if supported) 2151 deep - Suspend-To-RAM or equivalent (if supported) 2152 See Documentation/power/states.txt. 2153 2154 meye.*= [HW] Set MotionEye Camera parameters 2155 See Documentation/video4linux/meye.txt. 2156 2157 mfgpt_irq= [IA-32] Specify the IRQ to use for the 2158 Multi-Function General Purpose Timers on AMD Geode 2159 platforms. 2160 2161 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when 2162 the BIOS has incorrectly applied a workaround. TinyBIOS 2163 version 0.98 is known to be affected, 0.99 fixes the 2164 problem by letting the user disable the workaround. 2165 2166 mga= [HW,DRM] 2167 2168 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this 2169 physical address is ignored. 2170 2171 mini2440= [ARM,HW,KNL] 2172 Format:[0..2][b][c][t] 2173 Default: "0tb" 2174 MINI2440 configuration specification: 2175 0 - The attached screen is the 3.5" TFT 2176 1 - The attached screen is the 7" TFT 2177 2 - The VGA Shield is attached (1024x768) 2178 Leaving out the screen size parameter will not load 2179 the TFT driver, and the framebuffer will be left 2180 unconfigured. 2181 b - Enable backlight. The TFT backlight pin will be 2182 linked to the kernel VESA blanking code and a GPIO 2183 LED. This parameter is not necessary when using the 2184 VGA shield. 2185 c - Enable the s3c camera interface. 2186 t - Reserved for enabling touchscreen support. The 2187 touchscreen support is not enabled in the mainstream 2188 kernel as of 2.6.30, a preliminary port can be found 2189 in the "bleeding edge" mini2440 support kernel at 2190 http://repo.or.cz/w/linux-2.6/mini2440.git 2191 2192 mminit_loglevel= 2193 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this 2194 parameter allows control of the logging verbosity for 2195 the additional memory initialisation checks. A value 2196 of 0 disables mminit logging and a level of 4 will 2197 log everything. Information is printed at KERN_DEBUG 2198 so loglevel=8 may also need to be specified. 2199 2200 module.sig_enforce 2201 [KNL] When CONFIG_MODULE_SIG is set, this means that 2202 modules without (valid) signatures will fail to load. 2203 Note that if CONFIG_MODULE_SIG_FORCE is set, that 2204 is always true, so this option does nothing. 2205 2206 module_blacklist= [KNL] Do not load a comma-separated list of 2207 modules. Useful for debugging problem modules. 2208 2209 mousedev.tap_time= 2210 [MOUSE] Maximum time between finger touching and 2211 leaving touchpad surface for touch to be considered 2212 a tap and be reported as a left button click (for 2213 touchpads working in absolute mode only). 2214 Format: <msecs> 2215 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices 2216 reporting absolute coordinates, such as tablets 2217 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices 2218 reporting absolute coordinates, such as tablets 2219 2220 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter 2221 is similar to kernelcore except it specifies the 2222 amount of memory used for migratable allocations. 2223 If both kernelcore and movablecore is specified, 2224 then kernelcore will be at *least* the specified 2225 value but may be more. If movablecore on its own 2226 is specified, the administrator must be careful 2227 that the amount of memory usable for all allocations 2228 is not too small. 2229 2230 movable_node [KNL] Boot-time switch to enable the effects 2231 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details. 2232 2233 MTD_Partition= [MTD] 2234 Format: <name>,<region-number>,<size>,<offset> 2235 2236 MTD_Region= [MTD] Format: 2237 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] 2238 2239 mtdparts= [MTD] 2240 See drivers/mtd/cmdlinepart.c. 2241 2242 multitce=off [PPC] This parameter disables the use of the pSeries 2243 firmware feature for updating multiple TCE entries 2244 at a time. 2245 2246 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration 2247 2248 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] 2249 2250 boundary - index of last SLC block on Flex-OneNAND. 2251 The remaining blocks are configured as MLC blocks. 2252 lock - Configure if Flex-OneNAND boundary should be locked. 2253 Once locked, the boundary cannot be changed. 2254 1 indicates lock status, 0 indicates unlock status. 2255 2256 mtdset= [ARM] 2257 ARM/S3C2412 JIVE boot control 2258 2259 See arch/arm/mach-s3c2412/mach-jive.c 2260 2261 mtouchusb.raw_coordinates= 2262 [HW] Make the MicroTouch USB driver use raw coordinates 2263 ('y', default) or cooked coordinates ('n') 2264 2265 mtrr_chunk_size=nn[KMG] [X86] 2266 used for mtrr cleanup. It is largest continuous chunk 2267 that could hold holes aka. UC entries. 2268 2269 mtrr_gran_size=nn[KMG] [X86] 2270 Used for mtrr cleanup. It is granularity of mtrr block. 2271 Default is 1. 2272 Large value could prevent small alignment from 2273 using up MTRRs. 2274 2275 mtrr_spare_reg_nr=n [X86] 2276 Format: <integer> 2277 Range: 0,7 : spare reg number 2278 Default : 1 2279 Used for mtrr cleanup. It is spare mtrr entries number. 2280 Set to 2 or more if your graphical card needs more. 2281 2282 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card 2283 2284 netdev= [NET] Network devices parameters 2285 Format: <irq>,<io>,<mem_start>,<mem_end>,<name> 2286 Note that mem_start is often overloaded to mean 2287 something different and driver-specific. 2288 This usage is only documented in each driver source 2289 file if at all. 2290 2291 nf_conntrack.acct= 2292 [NETFILTER] Enable connection tracking flow accounting 2293 0 to disable accounting 2294 1 to enable accounting 2295 Default value is 0. 2296 2297 nfsaddrs= [NFS] Deprecated. Use ip= instead. 2298 See Documentation/filesystems/nfs/nfsroot.txt. 2299 2300 nfsroot= [NFS] nfs root filesystem for disk-less boxes. 2301 See Documentation/filesystems/nfs/nfsroot.txt. 2302 2303 nfsrootdebug [NFS] enable nfsroot debugging messages. 2304 See Documentation/filesystems/nfs/nfsroot.txt. 2305 2306 nfs.callback_nr_threads= 2307 [NFSv4] set the total number of threads that the 2308 NFS client will assign to service NFSv4 callback 2309 requests. 2310 2311 nfs.callback_tcpport= 2312 [NFS] set the TCP port on which the NFSv4 callback 2313 channel should listen. 2314 2315 nfs.cache_getent= 2316 [NFS] sets the pathname to the program which is used 2317 to update the NFS client cache entries. 2318 2319 nfs.cache_getent_timeout= 2320 [NFS] sets the timeout after which an attempt to 2321 update a cache entry is deemed to have failed. 2322 2323 nfs.idmap_cache_timeout= 2324 [NFS] set the maximum lifetime for idmapper cache 2325 entries. 2326 2327 nfs.enable_ino64= 2328 [NFS] enable 64-bit inode numbers. 2329 If zero, the NFS client will fake up a 32-bit inode 2330 number for the readdir() and stat() syscalls instead 2331 of returning the full 64-bit number. 2332 The default is to return 64-bit inode numbers. 2333 2334 nfs.max_session_cb_slots= 2335 [NFSv4.1] Sets the maximum number of session 2336 slots the client will assign to the callback 2337 channel. This determines the maximum number of 2338 callbacks the client will process in parallel for 2339 a particular server. 2340 2341 nfs.max_session_slots= 2342 [NFSv4.1] Sets the maximum number of session slots 2343 the client will attempt to negotiate with the server. 2344 This limits the number of simultaneous RPC requests 2345 that the client can send to the NFSv4.1 server. 2346 Note that there is little point in setting this 2347 value higher than the max_tcp_slot_table_limit. 2348 2349 nfs.nfs4_disable_idmapping= 2350 [NFSv4] When set to the default of '1', this option 2351 ensures that both the RPC level authentication 2352 scheme and the NFS level operations agree to use 2353 numeric uids/gids if the mount is using the 2354 'sec=sys' security flavour. In effect it is 2355 disabling idmapping, which can make migration from 2356 legacy NFSv2/v3 systems to NFSv4 easier. 2357 Servers that do not support this mode of operation 2358 will be autodetected by the client, and it will fall 2359 back to using the idmapper. 2360 To turn off this behaviour, set the value to '0'. 2361 nfs.nfs4_unique_id= 2362 [NFS4] Specify an additional fixed unique ident- 2363 ification string that NFSv4 clients can insert into 2364 their nfs_client_id4 string. This is typically a 2365 UUID that is generated at system install time. 2366 2367 nfs.send_implementation_id = 2368 [NFSv4.1] Send client implementation identification 2369 information in exchange_id requests. 2370 If zero, no implementation identification information 2371 will be sent. 2372 The default is to send the implementation identification 2373 information. 2374 2375 nfs.recover_lost_locks = 2376 [NFSv4] Attempt to recover locks that were lost due 2377 to a lease timeout on the server. Please note that 2378 doing this risks data corruption, since there are 2379 no guarantees that the file will remain unchanged 2380 after the locks are lost. 2381 If you want to enable the kernel legacy behaviour of 2382 attempting to recover these locks, then set this 2383 parameter to '1'. 2384 The default parameter value of '0' causes the kernel 2385 not to attempt recovery of lost locks. 2386 2387 nfs4.layoutstats_timer = 2388 [NFSv4.2] Change the rate at which the kernel sends 2389 layoutstats to the pNFS metadata server. 2390 2391 Setting this to value to 0 causes the kernel to use 2392 whatever value is the default set by the layout 2393 driver. A non-zero value sets the minimum interval 2394 in seconds between layoutstats transmissions. 2395 2396 nfsd.nfs4_disable_idmapping= 2397 [NFSv4] When set to the default of '1', the NFSv4 2398 server will return only numeric uids and gids to 2399 clients using auth_sys, and will accept numeric uids 2400 and gids from such clients. This is intended to ease 2401 migration from NFSv2/v3. 2402 2403 objlayoutdriver.osd_login_prog= 2404 [NFS] [OBJLAYOUT] sets the pathname to the program which 2405 is used to automatically discover and login into new 2406 osd-targets. Please see: 2407 Documentation/filesystems/pnfs.txt for more explanations 2408 2409 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take 2410 when a NMI is triggered. 2411 Format: [state][,regs][,debounce][,die] 2412 2413 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels 2414 Format: [panic,][nopanic,][num] 2415 Valid num: 0 or 1 2416 0 - turn hardlockup detector in nmi_watchdog off 2417 1 - turn hardlockup detector in nmi_watchdog on 2418 When panic is specified, panic when an NMI watchdog 2419 timeout occurs (or 'nopanic' to override the opposite 2420 default). To disable both hard and soft lockup detectors, 2421 please see 'nowatchdog'. 2422 This is useful when you use a panic=... timeout and 2423 need the box quickly up again. 2424 2425 netpoll.carrier_timeout= 2426 [NET] Specifies amount of time (in seconds) that 2427 netpoll should wait for a carrier. By default netpoll 2428 waits 4 seconds. 2429 2430 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths 2431 emulation library even if a 387 maths coprocessor 2432 is present. 2433 2434 no_console_suspend 2435 [HW] Never suspend the console 2436 Disable suspending of consoles during suspend and 2437 hibernate operations. Once disabled, debugging 2438 messages can reach various consoles while the rest 2439 of the system is being put to sleep (ie, while 2440 debugging driver suspend/resume hooks). This may 2441 not work reliably with all consoles, but is known 2442 to work with serial and VGA consoles. 2443 To facilitate more flexible debugging, we also add 2444 console_suspend, a printk module parameter to control 2445 it. Users could use console_suspend (usually 2446 /sys/module/printk/parameters/console_suspend) to 2447 turn on/off it dynamically. 2448 2449 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien 2450 caches in the slab allocator. Saves per-node memory, 2451 but will impact performance. 2452 2453 noalign [KNL,ARM] 2454 2455 noapic [SMP,APIC] Tells the kernel to not make use of any 2456 IOAPICs that may be present in the system. 2457 2458 noautogroup Disable scheduler automatic task group creation. 2459 2460 nobats [PPC] Do not use BATs for mapping kernel lowmem 2461 on "Classic" PPC cores. 2462 2463 nocache [ARM] 2464 2465 noclflush [BUGS=X86] Don't use the CLFLUSH instruction 2466 2467 nodelayacct [KNL] Disable per-task delay accounting 2468 2469 nodsp [SH] Disable hardware DSP at boot time. 2470 2471 noefi Disable EFI runtime services support. 2472 2473 noexec [IA-64] 2474 2475 noexec [X86] 2476 On X86-32 available only on PAE configured kernels. 2477 noexec=on: enable non-executable mappings (default) 2478 noexec=off: disable non-executable mappings 2479 2480 nosmap [X86] 2481 Disable SMAP (Supervisor Mode Access Prevention) 2482 even if it is supported by processor. 2483 2484 nosmep [X86] 2485 Disable SMEP (Supervisor Mode Execution Prevention) 2486 even if it is supported by processor. 2487 2488 noexec32 [X86-64] 2489 This affects only 32-bit executables. 2490 noexec32=on: enable non-executable mappings (default) 2491 read doesn't imply executable mappings 2492 noexec32=off: disable non-executable mappings 2493 read implies executable mappings 2494 2495 nofpu [MIPS,SH] Disable hardware FPU at boot time. 2496 2497 nofxsr [BUGS=X86-32] Disables x86 floating point extended 2498 register save and restore. The kernel will only save 2499 legacy floating-point registers on task switch. 2500 2501 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings. 2502 2503 nosmt [KNL,S390] Disable symmetric multithreading (SMT). 2504 Equivalent to smt=1. 2505 2506 noxsave [BUGS=X86] Disables x86 extended register state save 2507 and restore using xsave. The kernel will fallback to 2508 enabling legacy floating-point and sse state. 2509 2510 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended 2511 register states. The kernel will fall back to use 2512 xsave to save the states. By using this parameter, 2513 performance of saving the states is degraded because 2514 xsave doesn't support modified optimization while 2515 xsaveopt supports it on xsaveopt enabled systems. 2516 2517 noxsaves [X86] Disables xsaves and xrstors used in saving and 2518 restoring x86 extended register state in compacted 2519 form of xsave area. The kernel will fall back to use 2520 xsaveopt and xrstor to save and restore the states 2521 in standard form of xsave area. By using this 2522 parameter, xsave area per process might occupy more 2523 memory on xsaves enabled systems. 2524 2525 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or 2526 wfi(ARM) instruction doesn't work correctly and not to 2527 use it. This is also useful when using JTAG debugger. 2528 2529 no_file_caps Tells the kernel not to honor file capabilities. The 2530 only way then for a file to be executed with privilege 2531 is to be setuid root or executed by root. 2532 2533 nohalt [IA-64] Tells the kernel not to use the power saving 2534 function PAL_HALT_LIGHT when idle. This increases 2535 power-consumption. On the positive side, it reduces 2536 interrupt wake-up latency, which may improve performance 2537 in certain environments such as networked servers or 2538 real-time systems. 2539 2540 nohibernate [HIBERNATION] Disable hibernation and resume. 2541 2542 nohz= [KNL] Boottime enable/disable dynamic ticks 2543 Valid arguments: on, off 2544 Default: on 2545 2546 nohz_full= [KNL,BOOT] 2547 The argument is a cpu list, as described above. 2548 In kernels built with CONFIG_NO_HZ_FULL=y, set 2549 the specified list of CPUs whose tick will be stopped 2550 whenever possible. The boot CPU will be forced outside 2551 the range to maintain the timekeeping. 2552 The CPUs in this range must also be included in the 2553 rcu_nocbs= set. 2554 2555 noiotrap [SH] Disables trapped I/O port accesses. 2556 2557 noirqdebug [X86-32] Disables the code which attempts to detect and 2558 disable unhandled interrupt sources. 2559 2560 no_timer_check [X86,APIC] Disables the code which tests for 2561 broken timer IRQ sources. 2562 2563 noisapnp [ISAPNP] Disables ISA PnP code. 2564 2565 noinitrd [RAM] Tells the kernel not to load any configured 2566 initial RAM disk. 2567 2568 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt 2569 remapping. 2570 [Deprecated - use intremap=off] 2571 2572 nointroute [IA-64] 2573 2574 noinvpcid [X86] Disable the INVPCID cpu feature. 2575 2576 nojitter [IA-64] Disables jitter checking for ITC timers. 2577 2578 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver 2579 2580 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page 2581 fault handling. 2582 2583 no-vmw-sched-clock 2584 [X86,PV_OPS] Disable paravirtualized VMware scheduler 2585 clock and use the default one. 2586 2587 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting. 2588 steal time is computed, but won't influence scheduler 2589 behaviour 2590 2591 nolapic [X86-32,APIC] Do not enable or use the local APIC. 2592 2593 nolapic_timer [X86-32,APIC] Do not use the local APIC timer. 2594 2595 noltlbs [PPC] Do not use large page/tlb entries for kernel 2596 lowmem mapping on PPC40x and PPC8xx 2597 2598 nomca [IA-64] Disable machine check abort handling 2599 2600 nomce [X86-32] Disable Machine Check Exception 2601 2602 nomfgpt [X86-32] Disable Multi-Function General Purpose 2603 Timer usage (for AMD Geode machines). 2604 2605 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to 2606 shutdown the other cpus. Instead use the REBOOT_VECTOR 2607 irq. 2608 2609 nomodule Disable module load 2610 2611 nopat [X86] Disable PAT (page attribute table extension of 2612 pagetables) support. 2613 2614 norandmaps Don't use address space randomization. Equivalent to 2615 echo 0 > /proc/sys/kernel/randomize_va_space 2616 2617 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops 2618 2619 noreplace-smp [X86-32,SMP] Don't replace SMP instructions 2620 with UP alternatives 2621 2622 nordrand [X86] Disable kernel use of the RDRAND and 2623 RDSEED instructions even if they are supported 2624 by the processor. RDRAND and RDSEED are still 2625 available to user space applications. 2626 2627 noresume [SWSUSP] Disables resume and restores original swap 2628 space. 2629 2630 no-scroll [VGA] Disables scrollback. 2631 This is required for the Braillex ib80-piezo Braille 2632 reader made by F.H. Papenmeier (Germany). 2633 2634 nosbagart [IA-64] 2635 2636 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. 2637 2638 nosmp [SMP] Tells an SMP kernel to act as a UP kernel, 2639 and disable the IO APIC. legacy for "maxcpus=0". 2640 2641 nosoftlockup [KNL] Disable the soft-lockup detector. 2642 2643 nosync [HW,M68K] Disables sync negotiation for all devices. 2644 2645 notsc [BUGS=X86-32] Disable Time Stamp Counter 2646 2647 nowatchdog [KNL] Disable both lockup detectors, i.e. 2648 soft-lockup and NMI watchdog (hard-lockup). 2649 2650 nowb [ARM] 2651 2652 nox2apic [X86-64,APIC] Do not enable x2APIC mode. 2653 2654 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when 2655 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. 2656 Some features depend on CPU0. Known dependencies are: 2657 1. Resume from suspend/hibernate depends on CPU0. 2658 Suspend/hibernate will fail if CPU0 is offline and you 2659 need to online CPU0 before suspend/hibernate. 2660 2. PIC interrupts also depend on CPU0. CPU0 can't be 2661 removed if a PIC interrupt is detected. 2662 It's said poweroff/reboot may depend on CPU0 on some 2663 machines although I haven't seen such issues so far 2664 after CPU0 is offline on a few tested machines. 2665 If the dependencies are under your control, you can 2666 turn on cpu0_hotplug. 2667 2668 nptcg= [IA-64] Override max number of concurrent global TLB 2669 purges which is reported from either PAL_VM_SUMMARY or 2670 SAL PALO. 2671 2672 nr_cpus= [SMP] Maximum number of processors that an SMP kernel 2673 could support. nr_cpus=n : n >= 1 limits the kernel to 2674 support 'n' processors. It could be larger than the 2675 number of already plugged CPU during bootup, later in 2676 runtime you can physically add extra cpu until it reaches 2677 n. So during boot up some boot time memory for per-cpu 2678 variables need be pre-allocated for later physical cpu 2679 hot plugging. 2680 2681 nr_uarts= [SERIAL] maximum number of UARTs to be registered. 2682 2683 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing. 2684 Allowed values are enable and disable 2685 2686 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. 2687 one of ['zone', 'node', 'default'] can be specified 2688 This can be set from sysctl after boot. 2689 See Documentation/sysctl/vm.txt for details. 2690 2691 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. 2692 See Documentation/debugging-via-ohci1394.txt for more 2693 info. 2694 2695 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands 2696 Rather than timing out after 20 ms if an EC 2697 command is not properly ACKed, override the length 2698 of the timeout. We have interrupts disabled while 2699 waiting for the ACK, so if this is set too high 2700 interrupts *may* be lost! 2701 2702 omap_mux= [OMAP] Override bootloader pin multiplexing. 2703 Format: <mux_mode0.mode_name=value>... 2704 For example, to override I2C bus2: 2705 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100 2706 2707 oprofile.timer= [HW] 2708 Use timer interrupt instead of performance counters 2709 2710 oprofile.cpu_type= Force an oprofile cpu type 2711 This might be useful if you have an older oprofile 2712 userland or if you want common events. 2713 Format: { arch_perfmon } 2714 arch_perfmon: [X86] Force use of architectural 2715 perfmon on Intel CPUs instead of the 2716 CPU specific event set. 2717 timer: [X86] Force use of architectural NMI 2718 timer mode (see also oprofile.timer 2719 for generic hr timer mode) 2720 2721 oops=panic Always panic on oopses. Default is to just kill the 2722 process, but there is a small probability of 2723 deadlocking the machine. 2724 This will also cause panics on machine check exceptions. 2725 Useful together with panic=30 to trigger a reboot. 2726 2727 OSS [HW,OSS] 2728 See Documentation/sound/oss/oss-parameters.txt 2729 2730 page_owner= [KNL] Boot-time page_owner enabling option. 2731 Storage of the information about who allocated 2732 each page is disabled in default. With this switch, 2733 we can turn it on. 2734 on: enable the feature 2735 2736 page_poison= [KNL] Boot-time parameter changing the state of 2737 poisoning on the buddy allocator. 2738 off: turn off poisoning 2739 on: turn on poisoning 2740 2741 panic= [KNL] Kernel behaviour on panic: delay <timeout> 2742 timeout > 0: seconds before rebooting 2743 timeout = 0: wait forever 2744 timeout < 0: reboot immediately 2745 Format: <timeout> 2746 2747 panic_on_warn panic() instead of WARN(). Useful to cause kdump 2748 on a WARN(). 2749 2750 crash_kexec_post_notifiers 2751 Run kdump after running panic-notifiers and dumping 2752 kmsg. This only for the users who doubt kdump always 2753 succeeds in any situation. 2754 Note that this also increases risks of kdump failure, 2755 because some panic notifiers can make the crashed 2756 kernel more unstable. 2757 2758 parkbd.port= [HW] Parallel port number the keyboard adapter is 2759 connected to, default is 0. 2760 Format: <parport#> 2761 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 2762 0 for XT, 1 for AT (default is AT). 2763 Format: <mode> 2764 2765 parport= [HW,PPT] Specify parallel ports. 0 disables. 2766 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } 2767 Use 'auto' to force the driver to use any 2768 IRQ/DMA settings detected (the default is to 2769 ignore detected IRQ/DMA settings because of 2770 possible conflicts). You can specify the base 2771 address, IRQ, and DMA settings; IRQ and DMA 2772 should be numbers, or 'auto' (for using detected 2773 settings on that particular port), or 'nofifo' 2774 (to avoid using a FIFO even if it is detected). 2775 Parallel ports are assigned in the order they 2776 are specified on the command line, starting 2777 with parport0. 2778 2779 parport_init_mode= [HW,PPT] 2780 Configure VIA parallel port to operate in 2781 a specific mode. This is necessary on Pegasos 2782 computer where firmware has no options for setting 2783 up parallel port mode and sets it to spp. 2784 Currently this function knows 686a and 8231 chips. 2785 Format: [spp|ps2|epp|ecp|ecpepp] 2786 2787 pause_on_oops= 2788 Halt all CPUs after the first oops has been printed for 2789 the specified number of seconds. This is to be used if 2790 your oopses keep scrolling off the screen. 2791 2792 pcbit= [HW,ISDN] 2793 2794 pcd. [PARIDE] 2795 See header of drivers/block/paride/pcd.c. 2796 See also Documentation/blockdev/paride.txt. 2797 2798 pci=option[,option...] [PCI] various PCI subsystem options: 2799 earlydump [X86] dump PCI config space before the kernel 2800 changes anything 2801 off [X86] don't probe for the PCI bus 2802 bios [X86-32] force use of PCI BIOS, don't access 2803 the hardware directly. Use this if your machine 2804 has a non-standard PCI host bridge. 2805 nobios [X86-32] disallow use of PCI BIOS, only direct 2806 hardware access methods are allowed. Use this 2807 if you experience crashes upon bootup and you 2808 suspect they are caused by the BIOS. 2809 conf1 [X86] Force use of PCI Configuration Access 2810 Mechanism 1 (config address in IO port 0xCF8, 2811 data in IO port 0xCFC, both 32-bit). 2812 conf2 [X86] Force use of PCI Configuration Access 2813 Mechanism 2 (IO port 0xCF8 is an 8-bit port for 2814 the function, IO port 0xCFA, also 8-bit, sets 2815 bus number. The config space is then accessed 2816 through ports 0xC000-0xCFFF). 2817 See http://wiki.osdev.org/PCI for more info 2818 on the configuration access mechanisms. 2819 noaer [PCIE] If the PCIEAER kernel config parameter is 2820 enabled, this kernel boot option can be used to 2821 disable the use of PCIE advanced error reporting. 2822 nodomains [PCI] Disable support for multiple PCI 2823 root domains (aka PCI segments, in ACPI-speak). 2824 nommconf [X86] Disable use of MMCONFIG for PCI 2825 Configuration 2826 check_enable_amd_mmconf [X86] check for and enable 2827 properly configured MMIO access to PCI 2828 config space on AMD family 10h CPU 2829 nomsi [MSI] If the PCI_MSI kernel config parameter is 2830 enabled, this kernel boot option can be used to 2831 disable the use of MSI interrupts system-wide. 2832 noioapicquirk [APIC] Disable all boot interrupt quirks. 2833 Safety option to keep boot IRQs enabled. This 2834 should never be necessary. 2835 ioapicreroute [APIC] Enable rerouting of boot IRQs to the 2836 primary IO-APIC for bridges that cannot disable 2837 boot IRQs. This fixes a source of spurious IRQs 2838 when the system masks IRQs. 2839 noioapicreroute [APIC] Disable workaround that uses the 2840 boot IRQ equivalent of an IRQ that connects to 2841 a chipset where boot IRQs cannot be disabled. 2842 The opposite of ioapicreroute. 2843 biosirq [X86-32] Use PCI BIOS calls to get the interrupt 2844 routing table. These calls are known to be buggy 2845 on several machines and they hang the machine 2846 when used, but on other computers it's the only 2847 way to get the interrupt routing table. Try 2848 this option if the kernel is unable to allocate 2849 IRQs or discover secondary PCI buses on your 2850 motherboard. 2851 rom [X86] Assign address space to expansion ROMs. 2852 Use with caution as certain devices share 2853 address decoders between ROMs and other 2854 resources. 2855 norom [X86] Do not assign address space to 2856 expansion ROMs that do not already have 2857 BIOS assigned address ranges. 2858 nobar [X86] Do not assign address space to the 2859 BARs that weren't assigned by the BIOS. 2860 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be 2861 assigned automatically to PCI devices. You can 2862 make the kernel exclude IRQs of your ISA cards 2863 this way. 2864 pirqaddr=0xAAAAA [X86] Specify the physical address 2865 of the PIRQ table (normally generated 2866 by the BIOS) if it is outside the 2867 F0000h-100000h range. 2868 lastbus=N [X86] Scan all buses thru bus #N. Can be 2869 useful if the kernel is unable to find your 2870 secondary buses and you want to tell it 2871 explicitly which ones they are. 2872 assign-busses [X86] Always assign all PCI bus 2873 numbers ourselves, overriding 2874 whatever the firmware may have done. 2875 usepirqmask [X86] Honor the possible IRQ mask stored 2876 in the BIOS $PIR table. This is needed on 2877 some systems with broken BIOSes, notably 2878 some HP Pavilion N5400 and Omnibook XE3 2879 notebooks. This will have no effect if ACPI 2880 IRQ routing is enabled. 2881 noacpi [X86] Do not use ACPI for IRQ routing 2882 or for PCI scanning. 2883 use_crs [X86] Use PCI host bridge window information 2884 from ACPI. On BIOSes from 2008 or later, this 2885 is enabled by default. If you need to use this, 2886 please report a bug. 2887 nocrs [X86] Ignore PCI host bridge windows from ACPI. 2888 If you need to use this, please report a bug. 2889 routeirq Do IRQ routing for all PCI devices. 2890 This is normally done in pci_enable_device(), 2891 so this option is a temporary workaround 2892 for broken drivers that don't call it. 2893 skip_isa_align [X86] do not align io start addr, so can 2894 handle more pci cards 2895 noearly [X86] Don't do any early type 1 scanning. 2896 This might help on some broken boards which 2897 machine check when some devices' config space 2898 is read. But various workarounds are disabled 2899 and some IOMMU drivers will not work. 2900 bfsort Sort PCI devices into breadth-first order. 2901 This sorting is done to get a device 2902 order compatible with older (<= 2.4) kernels. 2903 nobfsort Don't sort PCI devices into breadth-first order. 2904 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size) 2905 tuning and use the BIOS-configured MPS defaults. 2906 pcie_bus_safe Set every device's MPS to the largest value 2907 supported by all devices below the root complex. 2908 pcie_bus_perf Set device MPS to the largest allowable MPS 2909 based on its parent bus. Also set MRRS (Max 2910 Read Request Size) to the largest supported 2911 value (no larger than the MPS that the device 2912 or bus can support) for best performance. 2913 pcie_bus_peer2peer Set every device's MPS to 128B, which 2914 every device is guaranteed to support. This 2915 configuration allows peer-to-peer DMA between 2916 any pair of devices, possibly at the cost of 2917 reduced performance. This also guarantees 2918 that hot-added devices will work. 2919 cbiosize=nn[KMG] The fixed amount of bus space which is 2920 reserved for the CardBus bridge's IO window. 2921 The default value is 256 bytes. 2922 cbmemsize=nn[KMG] The fixed amount of bus space which is 2923 reserved for the CardBus bridge's memory 2924 window. The default value is 64 megabytes. 2925 resource_alignment= 2926 Format: 2927 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] 2928 [<order of align>@]pci:<vendor>:<device>\ 2929 [:<subvendor>:<subdevice>][; ...] 2930 Specifies alignment and device to reassign 2931 aligned memory resources. 2932 If <order of align> is not specified, 2933 PAGE_SIZE is used as alignment. 2934 PCI-PCI bridge can be specified, if resource 2935 windows need to be expanded. 2936 To specify the alignment for several 2937 instances of a device, the PCI vendor, 2938 device, subvendor, and subdevice may be 2939 specified, e.g., 4096@pci:8086:9c22:103c:198f 2940 ecrc= Enable/disable PCIe ECRC (transaction layer 2941 end-to-end CRC checking). 2942 bios: Use BIOS/firmware settings. This is the 2943 the default. 2944 off: Turn ECRC off 2945 on: Turn ECRC on. 2946 hpiosize=nn[KMG] The fixed amount of bus space which is 2947 reserved for hotplug bridge's IO window. 2948 Default size is 256 bytes. 2949 hpmemsize=nn[KMG] The fixed amount of bus space which is 2950 reserved for hotplug bridge's memory window. 2951 Default size is 2 megabytes. 2952 hpbussize=nn The minimum amount of additional bus numbers 2953 reserved for buses below a hotplug bridge. 2954 Default is 1. 2955 realloc= Enable/disable reallocating PCI bridge resources 2956 if allocations done by BIOS are too small to 2957 accommodate resources required by all child 2958 devices. 2959 off: Turn realloc off 2960 on: Turn realloc on 2961 realloc same as realloc=on 2962 noari do not use PCIe ARI. 2963 pcie_scan_all Scan all possible PCIe devices. Otherwise we 2964 only look for one device below a PCIe downstream 2965 port. 2966 2967 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power 2968 Management. 2969 off Disable ASPM. 2970 force Enable ASPM even on devices that claim not to support it. 2971 WARNING: Forcing ASPM on may cause system lockups. 2972 2973 pcie_hp= [PCIE] PCI Express Hotplug driver options: 2974 nomsi Do not use MSI for PCI Express Native Hotplug (this 2975 makes all PCIe ports use INTx for hotplug services). 2976 2977 pcie_ports= [PCIE] PCIe ports handling: 2978 auto Ask the BIOS whether or not to use native PCIe services 2979 associated with PCIe ports (PME, hot-plug, AER). Use 2980 them only if that is allowed by the BIOS. 2981 native Use native PCIe services associated with PCIe ports 2982 unconditionally. 2983 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe 2984 ports driver. 2985 2986 pcie_port_pm= [PCIE] PCIe port power management handling: 2987 off Disable power management of all PCIe ports 2988 force Forcibly enable power management of all PCIe ports 2989 2990 pcie_pme= [PCIE,PM] Native PCIe PME signaling options: 2991 nomsi Do not use MSI for native PCIe PME signaling (this makes 2992 all PCIe root ports use INTx for all services). 2993 2994 pcmv= [HW,PCMCIA] BadgePAD 4 2995 2996 pd_ignore_unused 2997 [PM] 2998 Keep all power-domains already enabled by bootloader on, 2999 even if no driver has claimed them. This is useful 3000 for debug and development, but should not be 3001 needed on a platform with proper driver support. 3002 3003 pd. [PARIDE] 3004 See Documentation/blockdev/paride.txt. 3005 3006 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at 3007 boot time. 3008 Format: { 0 | 1 } 3009 See arch/parisc/kernel/pdc_chassis.c 3010 3011 percpu_alloc= Select which percpu first chunk allocator to use. 3012 Currently supported values are "embed" and "page". 3013 Archs may support subset or none of the selections. 3014 See comments in mm/percpu.c for details on each 3015 allocator. This parameter is primarily for debugging 3016 and performance comparison. 3017 3018 pf. [PARIDE] 3019 See Documentation/blockdev/paride.txt. 3020 3021 pg. [PARIDE] 3022 See Documentation/blockdev/paride.txt. 3023 3024 pirq= [SMP,APIC] Manual mp-table setup 3025 See Documentation/x86/i386/IO-APIC.txt. 3026 3027 plip= [PPT,NET] Parallel port network link 3028 Format: { parport<nr> | timid | 0 } 3029 See also Documentation/parport.txt. 3030 3031 pmtmr= [X86] Manual setup of pmtmr I/O Port. 3032 Override pmtimer IOPort with a hex value. 3033 e.g. pmtmr=0x508 3034 3035 pnp.debug=1 [PNP] 3036 Enable PNP debug messages (depends on the 3037 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time 3038 via /sys/module/pnp/parameters/debug. We always show 3039 current resource usage; turning this on also shows 3040 possible settings and some assignment information. 3041 3042 pnpacpi= [ACPI] 3043 { off } 3044 3045 pnpbios= [ISAPNP] 3046 { on | off | curr | res | no-curr | no-res } 3047 3048 pnp_reserve_irq= 3049 [ISAPNP] Exclude IRQs for the autoconfiguration 3050 3051 pnp_reserve_dma= 3052 [ISAPNP] Exclude DMAs for the autoconfiguration 3053 3054 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration 3055 Ranges are in pairs (I/O port base and size). 3056 3057 pnp_reserve_mem= 3058 [ISAPNP] Exclude memory regions for the 3059 autoconfiguration. 3060 Ranges are in pairs (memory base and size). 3061 3062 ports= [IP_VS_FTP] IPVS ftp helper module 3063 Default is 21. 3064 Up to 8 (IP_VS_APP_MAX_PORTS) ports 3065 may be specified. 3066 Format: <port>,<port>.... 3067 3068 powersave=off [PPC] This option disables power saving features. 3069 It specifically disables cpuidle and sets the 3070 platform machine description specific power_save 3071 function to NULL. On Idle the CPU just reduces 3072 execution priority. 3073 3074 ppc_strict_facility_enable 3075 [PPC] This option catches any kernel floating point, 3076 Altivec, VSX and SPE outside of regions specifically 3077 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()). 3078 There is some performance impact when enabling this. 3079 3080 print-fatal-signals= 3081 [KNL] debug: print fatal signals 3082 3083 If enabled, warn about various signal handling 3084 related application anomalies: too many signals, 3085 too many POSIX.1 timers, fatal signals causing a 3086 coredump - etc. 3087 3088 If you hit the warning due to signal overflow, 3089 you might want to try "ulimit -i unlimited". 3090 3091 default: off. 3092 3093 printk.always_kmsg_dump= 3094 Trigger kmsg_dump for cases other than kernel oops or 3095 panics 3096 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3097 default: disabled 3098 3099 printk.devkmsg={on,off,ratelimit} 3100 Control writing to /dev/kmsg. 3101 on - unlimited logging to /dev/kmsg from userspace 3102 off - logging to /dev/kmsg disabled 3103 ratelimit - ratelimit the logging 3104 Default: ratelimit 3105 3106 printk.time= Show timing data prefixed to each printk message line 3107 Format: <bool> (1/Y/y=enable, 0/N/n=disable) 3108 3109 processor.max_cstate= [HW,ACPI] 3110 Limit processor to maximum C-state 3111 max_cstate=9 overrides any DMI blacklist limit. 3112 3113 processor.nocst [HW,ACPI] 3114 Ignore the _CST method to determine C-states, 3115 instead using the legacy FADT method 3116 3117 profile= [KNL] Enable kernel profiling via /proc/profile 3118 Format: [schedule,]<number> 3119 Param: "schedule" - profile schedule points. 3120 Param: <number> - step/bucket size as a power of 2 for 3121 statistical time based profiling. 3122 Param: "sleep" - profile D-state sleeping (millisecs). 3123 Requires CONFIG_SCHEDSTATS 3124 Param: "kvm" - profile VM exits. 3125 3126 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk 3127 before loading. 3128 See Documentation/blockdev/ramdisk.txt. 3129 3130 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to 3131 probe for; one of (bare|imps|exps|lifebook|any). 3132 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports 3133 per second. 3134 psmouse.resetafter= [HW,MOUSE] 3135 Try to reset the device after so many bad packets 3136 (0 = never). 3137 psmouse.resolution= 3138 [HW,MOUSE] Set desired mouse resolution, in dpi. 3139 psmouse.smartscroll= 3140 [HW,MOUSE] Controls Logitech smartscroll autorepeat. 3141 0 = disabled, 1 = enabled (default). 3142 3143 pstore.backend= Specify the name of the pstore backend to use 3144 3145 pt. [PARIDE] 3146 See Documentation/blockdev/paride.txt. 3147 3148 pty.legacy_count= 3149 [KNL] Number of legacy pty's. Overwrites compiled-in 3150 default number. 3151 3152 quiet [KNL] Disable most log messages 3153 3154 r128= [HW,DRM] 3155 3156 raid= [HW,RAID] 3157 See Documentation/admin-guide/md.rst. 3158 3159 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes 3160 See Documentation/blockdev/ramdisk.txt. 3161 3162 rcu_nocbs= [KNL] 3163 The argument is a cpu list, as described above. 3164 3165 In kernels built with CONFIG_RCU_NOCB_CPU=y, set 3166 the specified list of CPUs to be no-callback CPUs. 3167 Invocation of these CPUs' RCU callbacks will 3168 be offloaded to "rcuox/N" kthreads created for 3169 that purpose, where "x" is "b" for RCU-bh, "p" 3170 for RCU-preempt, and "s" for RCU-sched, and "N" 3171 is the CPU number. This reduces OS jitter on the 3172 offloaded CPUs, which can be useful for HPC and 3173 real-time workloads. It can also improve energy 3174 efficiency for asymmetric multiprocessors. 3175 3176 rcu_nocb_poll [KNL] 3177 Rather than requiring that offloaded CPUs 3178 (specified by rcu_nocbs= above) explicitly 3179 awaken the corresponding "rcuoN" kthreads, 3180 make these kthreads poll for callbacks. 3181 This improves the real-time response for the 3182 offloaded CPUs by relieving them of the need to 3183 wake up the corresponding kthread, but degrades 3184 energy efficiency by requiring that the kthreads 3185 periodically wake up to do the polling. 3186 3187 rcutree.blimit= [KNL] 3188 Set maximum number of finished RCU callbacks to 3189 process in one batch. 3190 3191 rcutree.dump_tree= [KNL] 3192 Dump the structure of the rcu_node combining tree 3193 out at early boot. This is used for diagnostic 3194 purposes, to verify correct tree setup. 3195 3196 rcutree.gp_cleanup_delay= [KNL] 3197 Set the number of jiffies to delay each step of 3198 RCU grace-period cleanup. This only has effect 3199 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set. 3200 3201 rcutree.gp_init_delay= [KNL] 3202 Set the number of jiffies to delay each step of 3203 RCU grace-period initialization. This only has 3204 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT 3205 is set. 3206 3207 rcutree.gp_preinit_delay= [KNL] 3208 Set the number of jiffies to delay each step of 3209 RCU grace-period pre-initialization, that is, 3210 the propagation of recent CPU-hotplug changes up 3211 the rcu_node combining tree. This only has effect 3212 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set. 3213 3214 rcutree.rcu_fanout_exact= [KNL] 3215 Disable autobalancing of the rcu_node combining 3216 tree. This is used by rcutorture, and might 3217 possibly be useful for architectures having high 3218 cache-to-cache transfer latencies. 3219 3220 rcutree.rcu_fanout_leaf= [KNL] 3221 Change the number of CPUs assigned to each 3222 leaf rcu_node structure. Useful for very 3223 large systems, which will choose the value 64, 3224 and for NUMA systems with large remote-access 3225 latencies, which will choose a value aligned 3226 with the appropriate hardware boundaries. 3227 3228 rcutree.jiffies_till_sched_qs= [KNL] 3229 Set required age in jiffies for a 3230 given grace period before RCU starts 3231 soliciting quiescent-state help from 3232 rcu_note_context_switch(). 3233 3234 rcutree.jiffies_till_first_fqs= [KNL] 3235 Set delay from grace-period initialization to 3236 first attempt to force quiescent states. 3237 Units are jiffies, minimum value is zero, 3238 and maximum value is HZ. 3239 3240 rcutree.jiffies_till_next_fqs= [KNL] 3241 Set delay between subsequent attempts to force 3242 quiescent states. Units are jiffies, minimum 3243 value is one, and maximum value is HZ. 3244 3245 rcutree.kthread_prio= [KNL,BOOT] 3246 Set the SCHED_FIFO priority of the RCU per-CPU 3247 kthreads (rcuc/N). This value is also used for 3248 the priority of the RCU boost threads (rcub/N) 3249 and for the RCU grace-period kthreads (rcu_bh, 3250 rcu_preempt, and rcu_sched). If RCU_BOOST is 3251 set, valid values are 1-99 and the default is 1 3252 (the least-favored priority). Otherwise, when 3253 RCU_BOOST is not set, valid values are 0-99 and 3254 the default is zero (non-realtime operation). 3255 3256 rcutree.rcu_nocb_leader_stride= [KNL] 3257 Set the number of NOCB kthread groups, which 3258 defaults to the square root of the number of 3259 CPUs. Larger numbers reduces the wakeup overhead 3260 on the per-CPU grace-period kthreads, but increases 3261 that same overhead on each group's leader. 3262 3263 rcutree.qhimark= [KNL] 3264 Set threshold of queued RCU callbacks beyond which 3265 batch limiting is disabled. 3266 3267 rcutree.qlowmark= [KNL] 3268 Set threshold of queued RCU callbacks below which 3269 batch limiting is re-enabled. 3270 3271 rcutree.rcu_idle_gp_delay= [KNL] 3272 Set wakeup interval for idle CPUs that have 3273 RCU callbacks (RCU_FAST_NO_HZ=y). 3274 3275 rcutree.rcu_idle_lazy_gp_delay= [KNL] 3276 Set wakeup interval for idle CPUs that have 3277 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y). 3278 Lazy RCU callbacks are those which RCU can 3279 prove do nothing more than free memory. 3280 3281 rcuperf.gp_exp= [KNL] 3282 Measure performance of expedited synchronous 3283 grace-period primitives. 3284 3285 rcuperf.holdoff= [KNL] 3286 Set test-start holdoff period. The purpose of 3287 this parameter is to delay the start of the 3288 test until boot completes in order to avoid 3289 interference. 3290 3291 rcuperf.nreaders= [KNL] 3292 Set number of RCU readers. The value -1 selects 3293 N, where N is the number of CPUs. A value 3294 "n" less than -1 selects N-n+1, where N is again 3295 the number of CPUs. For example, -2 selects N 3296 (the number of CPUs), -3 selects N+1, and so on. 3297 A value of "n" less than or equal to -N selects 3298 a single reader. 3299 3300 rcuperf.nwriters= [KNL] 3301 Set number of RCU writers. The values operate 3302 the same as for rcuperf.nreaders. 3303 N, where N is the number of CPUs 3304 3305 rcuperf.perf_runnable= [BOOT] 3306 Start rcuperf running at boot time. 3307 3308 rcuperf.shutdown= [KNL] 3309 Shut the system down after performance tests 3310 complete. This is useful for hands-off automated 3311 testing. 3312 3313 rcuperf.perf_type= [KNL] 3314 Specify the RCU implementation to test. 3315 3316 rcuperf.verbose= [KNL] 3317 Enable additional printk() statements. 3318 3319 rcutorture.cbflood_inter_holdoff= [KNL] 3320 Set holdoff time (jiffies) between successive 3321 callback-flood tests. 3322 3323 rcutorture.cbflood_intra_holdoff= [KNL] 3324 Set holdoff time (jiffies) between successive 3325 bursts of callbacks within a given callback-flood 3326 test. 3327 3328 rcutorture.cbflood_n_burst= [KNL] 3329 Set the number of bursts making up a given 3330 callback-flood test. Set this to zero to 3331 disable callback-flood testing. 3332 3333 rcutorture.cbflood_n_per_burst= [KNL] 3334 Set the number of callbacks to be registered 3335 in a given burst of a callback-flood test. 3336 3337 rcutorture.fqs_duration= [KNL] 3338 Set duration of force_quiescent_state bursts 3339 in microseconds. 3340 3341 rcutorture.fqs_holdoff= [KNL] 3342 Set holdoff time within force_quiescent_state bursts 3343 in microseconds. 3344 3345 rcutorture.fqs_stutter= [KNL] 3346 Set wait time between force_quiescent_state bursts 3347 in seconds. 3348 3349 rcutorture.gp_cond= [KNL] 3350 Use conditional/asynchronous update-side 3351 primitives, if available. 3352 3353 rcutorture.gp_exp= [KNL] 3354 Use expedited update-side primitives, if available. 3355 3356 rcutorture.gp_normal= [KNL] 3357 Use normal (non-expedited) asynchronous 3358 update-side primitives, if available. 3359 3360 rcutorture.gp_sync= [KNL] 3361 Use normal (non-expedited) synchronous 3362 update-side primitives, if available. If all 3363 of rcutorture.gp_cond=, rcutorture.gp_exp=, 3364 rcutorture.gp_normal=, and rcutorture.gp_sync= 3365 are zero, rcutorture acts as if is interpreted 3366 they are all non-zero. 3367 3368 rcutorture.n_barrier_cbs= [KNL] 3369 Set callbacks/threads for rcu_barrier() testing. 3370 3371 rcutorture.nfakewriters= [KNL] 3372 Set number of concurrent RCU writers. These just 3373 stress RCU, they don't participate in the actual 3374 test, hence the "fake". 3375 3376 rcutorture.nreaders= [KNL] 3377 Set number of RCU readers. The value -1 selects 3378 N-1, where N is the number of CPUs. A value 3379 "n" less than -1 selects N-n-2, where N is again 3380 the number of CPUs. For example, -2 selects N 3381 (the number of CPUs), -3 selects N+1, and so on. 3382 3383 rcutorture.object_debug= [KNL] 3384 Enable debug-object double-call_rcu() testing. 3385 3386 rcutorture.onoff_holdoff= [KNL] 3387 Set time (s) after boot for CPU-hotplug testing. 3388 3389 rcutorture.onoff_interval= [KNL] 3390 Set time (s) between CPU-hotplug operations, or 3391 zero to disable CPU-hotplug testing. 3392 3393 rcutorture.shuffle_interval= [KNL] 3394 Set task-shuffle interval (s). Shuffling tasks 3395 allows some CPUs to go into dyntick-idle mode 3396 during the rcutorture test. 3397 3398 rcutorture.shutdown_secs= [KNL] 3399 Set time (s) after boot system shutdown. This 3400 is useful for hands-off automated testing. 3401 3402 rcutorture.stall_cpu= [KNL] 3403 Duration of CPU stall (s) to test RCU CPU stall 3404 warnings, zero to disable. 3405 3406 rcutorture.stall_cpu_holdoff= [KNL] 3407 Time to wait (s) after boot before inducing stall. 3408 3409 rcutorture.stat_interval= [KNL] 3410 Time (s) between statistics printk()s. 3411 3412 rcutorture.stutter= [KNL] 3413 Time (s) to stutter testing, for example, specifying 3414 five seconds causes the test to run for five seconds, 3415 wait for five seconds, and so on. This tests RCU's 3416 ability to transition abruptly to and from idle. 3417 3418 rcutorture.test_boost= [KNL] 3419 Test RCU priority boosting? 0=no, 1=maybe, 2=yes. 3420 "Maybe" means test if the RCU implementation 3421 under test support RCU priority boosting. 3422 3423 rcutorture.test_boost_duration= [KNL] 3424 Duration (s) of each individual boost test. 3425 3426 rcutorture.test_boost_interval= [KNL] 3427 Interval (s) between each boost test. 3428 3429 rcutorture.test_no_idle_hz= [KNL] 3430 Test RCU's dyntick-idle handling. See also the 3431 rcutorture.shuffle_interval parameter. 3432 3433 rcutorture.torture_runnable= [BOOT] 3434 Start rcutorture running at boot time. 3435 3436 rcutorture.torture_type= [KNL] 3437 Specify the RCU implementation to test. 3438 3439 rcutorture.verbose= [KNL] 3440 Enable additional printk() statements. 3441 3442 rcupdate.rcu_cpu_stall_suppress= [KNL] 3443 Suppress RCU CPU stall warning messages. 3444 3445 rcupdate.rcu_cpu_stall_timeout= [KNL] 3446 Set timeout for RCU CPU stall warning messages. 3447 3448 rcupdate.rcu_expedited= [KNL] 3449 Use expedited grace-period primitives, for 3450 example, synchronize_rcu_expedited() instead 3451 of synchronize_rcu(). This reduces latency, 3452 but can increase CPU utilization, degrade 3453 real-time latency, and degrade energy efficiency. 3454 No effect on CONFIG_TINY_RCU kernels. 3455 3456 rcupdate.rcu_normal= [KNL] 3457 Use only normal grace-period primitives, 3458 for example, synchronize_rcu() instead of 3459 synchronize_rcu_expedited(). This improves 3460 real-time latency, CPU utilization, and 3461 energy efficiency, but can expose users to 3462 increased grace-period latency. This parameter 3463 overrides rcupdate.rcu_expedited. No effect on 3464 CONFIG_TINY_RCU kernels. 3465 3466 rcupdate.rcu_normal_after_boot= [KNL] 3467 Once boot has completed (that is, after 3468 rcu_end_inkernel_boot() has been invoked), use 3469 only normal grace-period primitives. No effect 3470 on CONFIG_TINY_RCU kernels. 3471 3472 rcupdate.rcu_task_stall_timeout= [KNL] 3473 Set timeout in jiffies for RCU task stall warning 3474 messages. Disable with a value less than or equal 3475 to zero. 3476 3477 rcupdate.rcu_self_test= [KNL] 3478 Run the RCU early boot self tests 3479 3480 rcupdate.rcu_self_test_bh= [KNL] 3481 Run the RCU bh early boot self tests 3482 3483 rcupdate.rcu_self_test_sched= [KNL] 3484 Run the RCU sched early boot self tests 3485 3486 rdinit= [KNL] 3487 Format: <full_path> 3488 Run specified binary instead of /init from the ramdisk, 3489 used for early userspace startup. See initrd. 3490 3491 reboot= [KNL] 3492 Format (x86 or x86_64): 3493 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \ 3494 [[,]s[mp]#### \ 3495 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \ 3496 [[,]f[orce] 3497 Where reboot_mode is one of warm (soft) or cold (hard) or gpio, 3498 reboot_type is one of bios, acpi, kbd, triple, efi, or pci, 3499 reboot_force is either force or not specified, 3500 reboot_cpu is s[mp]#### with #### being the processor 3501 to be used for rebooting. 3502 3503 relax_domain_level= 3504 [KNL, SMP] Set scheduler's default relax_domain_level. 3505 See Documentation/cgroup-v1/cpusets.txt. 3506 3507 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area 3508 3509 reservetop= [X86-32] 3510 Format: nn[KMG] 3511 Reserves a hole at the top of the kernel virtual 3512 address space. 3513 3514 reservelow= [X86] 3515 Format: nn[K] 3516 Set the amount of memory to reserve for BIOS at 3517 the bottom of the address space. 3518 3519 reset_devices [KNL] Force drivers to reset the underlying device 3520 during initialization. 3521 3522 resume= [SWSUSP] 3523 Specify the partition device for software suspend 3524 Format: 3525 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>} 3526 3527 resume_offset= [SWSUSP] 3528 Specify the offset from the beginning of the partition 3529 given by "resume=" at which the swap header is located, 3530 in <PAGE_SIZE> units (needed only for swap files). 3531 See Documentation/power/swsusp-and-swap-files.txt 3532 3533 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to 3534 read the resume files 3535 3536 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up. 3537 Useful for devices that are detected asynchronously 3538 (e.g. USB and MMC devices). 3539 3540 hibernate= [HIBERNATION] 3541 noresume Don't check if there's a hibernation image 3542 present during boot. 3543 nocompress Don't compress/decompress hibernation images. 3544 no Disable hibernation and resume. 3545 protect_image Turn on image protection during restoration 3546 (that will set all pages holding image data 3547 during restoration read-only). 3548 3549 retain_initrd [RAM] Keep initrd memory after extraction 3550 3551 rfkill.default_state= 3552 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm, 3553 etc. communication is blocked by default. 3554 1 Unblocked. 3555 3556 rfkill.master_switch_mode= 3557 0 The "airplane mode" button does nothing. 3558 1 The "airplane mode" button toggles between everything 3559 blocked and the previous configuration. 3560 2 The "airplane mode" button toggles between everything 3561 blocked and everything unblocked. 3562 3563 rhash_entries= [KNL,NET] 3564 Set number of hash buckets for route cache 3565 3566 ro [KNL] Mount root device read-only on boot 3567 3568 rodata= [KNL] 3569 on Mark read-only kernel memory as read-only (default). 3570 off Leave read-only kernel memory writable for debugging. 3571 3572 rockchip.usb_uart 3573 Enable the uart passthrough on the designated usb port 3574 on Rockchip SoCs. When active, the signals of the 3575 debug-uart get routed to the D+ and D- pins of the usb 3576 port and the regular usb controller gets disabled. 3577 3578 root= [KNL] Root filesystem 3579 See name_to_dev_t comment in init/do_mounts.c. 3580 3581 rootdelay= [KNL] Delay (in seconds) to pause before attempting to 3582 mount the root filesystem 3583 3584 rootflags= [KNL] Set root filesystem mount option string 3585 3586 rootfstype= [KNL] Set root filesystem type 3587 3588 rootwait [KNL] Wait (indefinitely) for root device to show up. 3589 Useful for devices that are detected asynchronously 3590 (e.g. USB and MMC devices). 3591 3592 rproc_mem=nn[KMG][@address] 3593 [KNL,ARM,CMA] Remoteproc physical memory block. 3594 Memory area to be used by remote processor image, 3595 managed by CMA. 3596 3597 rw [KNL] Mount root device read-write on boot 3598 3599 S [KNL] Run init in single mode 3600 3601 s390_iommu= [HW,S390] 3602 Set s390 IOTLB flushing mode 3603 strict 3604 With strict flushing every unmap operation will result in 3605 an IOTLB flush. Default is lazy flushing before reuse, 3606 which is faster. 3607 3608 sa1100ir [NET] 3609 See drivers/net/irda/sa1100_ir.c. 3610 3611 sbni= [NET] Granch SBNI12 leased line adapter 3612 3613 sched_debug [KNL] Enables verbose scheduler debug messages. 3614 3615 schedstats= [KNL,X86] Enable or disable scheduled statistics. 3616 Allowed values are enable and disable. This feature 3617 incurs a small amount of overhead in the scheduler 3618 but is useful for debugging and performance tuning. 3619 3620 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate 3621 xtime_lock contention on larger systems, and/or RCU lock 3622 contention on all systems with CONFIG_MAXSMP set. 3623 Format: { "0" | "1" } 3624 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1" 3625 1 -- enable. 3626 Note: increases power consumption, thus should only be 3627 enabled if running jitter sensitive (HPC/RT) workloads. 3628 3629 security= [SECURITY] Choose a security module to enable at boot. 3630 If this boot parameter is not specified, only the first 3631 security module asking for security registration will be 3632 loaded. An invalid security module name will be treated 3633 as if no module has been chosen. 3634 3635 selinux= [SELINUX] Disable or enable SELinux at boot time. 3636 Format: { "0" | "1" } 3637 See security/selinux/Kconfig help text. 3638 0 -- disable. 3639 1 -- enable. 3640 Default value is set via kernel config option. 3641 If enabled at boot time, /selinux/disable can be used 3642 later to disable prior to initial policy load. 3643 3644 apparmor= [APPARMOR] Disable or enable AppArmor at boot time 3645 Format: { "0" | "1" } 3646 See security/apparmor/Kconfig help text 3647 0 -- disable. 3648 1 -- enable. 3649 Default value is set via kernel config option. 3650 3651 serialnumber [BUGS=X86-32] 3652 3653 shapers= [NET] 3654 Maximal number of shapers. 3655 3656 simeth= [IA-64] 3657 simscsi= 3658 3659 slram= [HW,MTD] 3660 3661 slab_nomerge [MM] 3662 Disable merging of slabs with similar size. May be 3663 necessary if there is some reason to distinguish 3664 allocs to different slabs. Debug options disable 3665 merging on their own. 3666 For more information see Documentation/vm/slub.txt. 3667 3668 slab_max_order= [MM, SLAB] 3669 Determines the maximum allowed order for slabs. 3670 A high setting may cause OOMs due to memory 3671 fragmentation. Defaults to 1 for systems with 3672 more than 32MB of RAM, 0 otherwise. 3673 3674 slub_debug[=options[,slabs]] [MM, SLUB] 3675 Enabling slub_debug allows one to determine the 3676 culprit if slab objects become corrupted. Enabling 3677 slub_debug can create guard zones around objects and 3678 may poison objects when not in use. Also tracks the 3679 last alloc / free. For more information see 3680 Documentation/vm/slub.txt. 3681 3682 slub_max_order= [MM, SLUB] 3683 Determines the maximum allowed order for slabs. 3684 A high setting may cause OOMs due to memory 3685 fragmentation. For more information see 3686 Documentation/vm/slub.txt. 3687 3688 slub_min_objects= [MM, SLUB] 3689 The minimum number of objects per slab. SLUB will 3690 increase the slab order up to slub_max_order to 3691 generate a sufficiently large slab able to contain 3692 the number of objects indicated. The higher the number 3693 of objects the smaller the overhead of tracking slabs 3694 and the less frequently locks need to be acquired. 3695 For more information see Documentation/vm/slub.txt. 3696 3697 slub_min_order= [MM, SLUB] 3698 Determines the minimum page order for slabs. Must be 3699 lower than slub_max_order. 3700 For more information see Documentation/vm/slub.txt. 3701 3702 slub_nomerge [MM, SLUB] 3703 Same with slab_nomerge. This is supported for legacy. 3704 See slab_nomerge for more information. 3705 3706 smart2= [HW] 3707 Format: <io1>[,<io2>[,...,<io8>]] 3708 3709 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices 3710 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port 3711 smsc-ircc2.ircc_sir= [HW] SIR base I/O port 3712 smsc-ircc2.ircc_fir= [HW] FIR base I/O port 3713 smsc-ircc2.ircc_irq= [HW] IRQ line 3714 smsc-ircc2.ircc_dma= [HW] DMA channel 3715 smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 3716 0: Toshiba Satellite 1800 (GP data pin select) 3717 1: Fast pin select (default) 3718 2: ATC IRMode 3719 3720 smt [KNL,S390] Set the maximum number of threads (logical 3721 CPUs) to use per physical CPU on systems capable of 3722 symmetric multithreading (SMT). Will be capped to the 3723 actual hardware limit. 3724 Format: <integer> 3725 Default: -1 (no limit) 3726 3727 softlockup_panic= 3728 [KNL] Should the soft-lockup detector generate panics. 3729 Format: <integer> 3730 3731 softlockup_all_cpu_backtrace= 3732 [KNL] Should the soft-lockup detector generate 3733 backtraces on all cpus. 3734 Format: <integer> 3735 3736 sonypi.*= [HW] Sony Programmable I/O Control Device driver 3737 See Documentation/laptops/sonypi.txt 3738 3739 spia_io_base= [HW,MTD] 3740 spia_fio_base= 3741 spia_pedr= 3742 spia_peddr= 3743 3744 stacktrace [FTRACE] 3745 Enabled the stack tracer on boot up. 3746 3747 stacktrace_filter=[function-list] 3748 [FTRACE] Limit the functions that the stack tracer 3749 will trace at boot up. function-list is a comma separated 3750 list of functions. This list can be changed at run 3751 time by the stack_trace_filter file in the debugfs 3752 tracing directory. Note, this enables stack tracing 3753 and the stacktrace above is not needed. 3754 3755 sti= [PARISC,HW] 3756 Format: <num> 3757 Set the STI (builtin display/keyboard on the HP-PARISC 3758 machines) console (graphic card) which should be used 3759 as the initial boot-console. 3760 See also comment in drivers/video/console/sticore.c. 3761 3762 sti_font= [HW] 3763 See comment in drivers/video/console/sticore.c. 3764 3765 stifb= [HW] 3766 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] 3767 3768 sunrpc.min_resvport= 3769 sunrpc.max_resvport= 3770 [NFS,SUNRPC] 3771 SunRPC servers often require that client requests 3772 originate from a privileged port (i.e. a port in the 3773 range 0 < portnr < 1024). 3774 An administrator who wishes to reserve some of these 3775 ports for other uses may adjust the range that the 3776 kernel's sunrpc client considers to be privileged 3777 using these two parameters to set the minimum and 3778 maximum port values. 3779 3780 sunrpc.svc_rpc_per_connection_limit= 3781 [NFS,SUNRPC] 3782 Limit the number of requests that the server will 3783 process in parallel from a single connection. 3784 The default value is 0 (no limit). 3785 3786 sunrpc.pool_mode= 3787 [NFS] 3788 Control how the NFS server code allocates CPUs to 3789 service thread pools. Depending on how many NICs 3790 you have and where their interrupts are bound, this 3791 option will affect which CPUs will do NFS serving. 3792 Note: this parameter cannot be changed while the 3793 NFS server is running. 3794 3795 auto the server chooses an appropriate mode 3796 automatically using heuristics 3797 global a single global pool contains all CPUs 3798 percpu one pool for each CPU 3799 pernode one pool for each NUMA node (equivalent 3800 to global on non-NUMA machines) 3801 3802 sunrpc.tcp_slot_table_entries= 3803 sunrpc.udp_slot_table_entries= 3804 [NFS,SUNRPC] 3805 Sets the upper limit on the number of simultaneous 3806 RPC calls that can be sent from the client to a 3807 server. Increasing these values may allow you to 3808 improve throughput, but will also increase the 3809 amount of memory reserved for use by the client. 3810 3811 suspend.pm_test_delay= 3812 [SUSPEND] 3813 Sets the number of seconds to remain in a suspend test 3814 mode before resuming the system (see 3815 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG 3816 is set. Default value is 5. 3817 3818 swapaccount=[0|1] 3819 [KNL] Enable accounting of swap in memory resource 3820 controller if no parameter or 1 is given or disable 3821 it if 0 is given (See Documentation/cgroup-v1/memory.txt) 3822 3823 swiotlb= [ARM,IA-64,PPC,MIPS,X86] 3824 Format: { <int> | force | noforce } 3825 <int> -- Number of I/O TLB slabs 3826 force -- force using of bounce buffers even if they 3827 wouldn't be automatically used by the kernel 3828 noforce -- Never use bounce buffers (for debugging) 3829 3830 switches= [HW,M68k] 3831 3832 sysfs.deprecated=0|1 [KNL] 3833 Enable/disable old style sysfs layout for old udev 3834 on older distributions. When this option is enabled 3835 very new udev will not work anymore. When this option 3836 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled) 3837 in older udev will not work anymore. 3838 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in 3839 the kernel configuration. 3840 3841 sysrq_always_enabled 3842 [KNL] 3843 Ignore sysrq setting - this boot parameter will 3844 neutralize any effect of /proc/sys/kernel/sysrq. 3845 Useful for debugging. 3846 3847 tcpmhash_entries= [KNL,NET] 3848 Set the number of tcp_metrics_hash slots. 3849 Default value is 8192 or 16384 depending on total 3850 ram pages. This is used to specify the TCP metrics 3851 cache size. See Documentation/networking/ip-sysctl.txt 3852 "tcp_no_metrics_save" section for more details. 3853 3854 tdfx= [HW,DRM] 3855 3856 test_suspend= [SUSPEND][,N] 3857 Specify "mem" (for Suspend-to-RAM) or "standby" (for 3858 standby suspend) or "freeze" (for suspend type freeze) 3859 as the system sleep state during system startup with 3860 the optional capability to repeat N number of times. 3861 The system is woken from this state using a 3862 wakeup-capable RTC alarm. 3863 3864 thash_entries= [KNL,NET] 3865 Set number of hash buckets for TCP connection 3866 3867 thermal.act= [HW,ACPI] 3868 -1: disable all active trip points in all thermal zones 3869 <degrees C>: override all lowest active trip points 3870 3871 thermal.crt= [HW,ACPI] 3872 -1: disable all critical trip points in all thermal zones 3873 <degrees C>: override all critical trip points 3874 3875 thermal.nocrt= [HW,ACPI] 3876 Set to disable actions on ACPI thermal zone 3877 critical and hot trip points. 3878 3879 thermal.off= [HW,ACPI] 3880 1: disable ACPI thermal control 3881 3882 thermal.psv= [HW,ACPI] 3883 -1: disable all passive trip points 3884 <degrees C>: override all passive trip points to this 3885 value 3886 3887 thermal.tzp= [HW,ACPI] 3888 Specify global default ACPI thermal zone polling rate 3889 <deci-seconds>: poll all this frequency 3890 0: no polling (default) 3891 3892 threadirqs [KNL] 3893 Force threading of all interrupt handlers except those 3894 marked explicitly IRQF_NO_THREAD. 3895 3896 tmem [KNL,XEN] 3897 Enable the Transcendent memory driver if built-in. 3898 3899 tmem.cleancache=0|1 [KNL, XEN] 3900 Default is on (1). Disable the usage of the cleancache 3901 API to send anonymous pages to the hypervisor. 3902 3903 tmem.frontswap=0|1 [KNL, XEN] 3904 Default is on (1). Disable the usage of the frontswap 3905 API to send swap pages to the hypervisor. If disabled 3906 the selfballooning and selfshrinking are force disabled. 3907 3908 tmem.selfballooning=0|1 [KNL, XEN] 3909 Default is on (1). Disable the driving of swap pages 3910 to the hypervisor. 3911 3912 tmem.selfshrinking=0|1 [KNL, XEN] 3913 Default is on (1). Partial swapoff that immediately 3914 transfers pages from Xen hypervisor back to the 3915 kernel based on different criteria. 3916 3917 topology= [S390] 3918 Format: {off | on} 3919 Specify if the kernel should make use of the cpu 3920 topology information if the hardware supports this. 3921 The scheduler will make use of this information and 3922 e.g. base its process migration decisions on it. 3923 Default is on. 3924 3925 topology_updates= [KNL, PPC, NUMA] 3926 Format: {off} 3927 Specify if the kernel should ignore (off) 3928 topology updates sent by the hypervisor to this 3929 LPAR. 3930 3931 tp720= [HW,PS2] 3932 3933 tpm_suspend_pcr=[HW,TPM] 3934 Format: integer pcr id 3935 Specify that at suspend time, the tpm driver 3936 should extend the specified pcr with zeros, 3937 as a workaround for some chips which fail to 3938 flush the last written pcr on TPM_SaveState. 3939 This will guarantee that all the other pcrs 3940 are saved. 3941 3942 trace_buf_size=nn[KMG] 3943 [FTRACE] will set tracing buffer size on each cpu. 3944 3945 trace_event=[event-list] 3946 [FTRACE] Set and start specified trace events in order 3947 to facilitate early boot debugging. The event-list is a 3948 comma separated list of trace events to enable. See 3949 also Documentation/trace/events.txt 3950 3951 trace_options=[option-list] 3952 [FTRACE] Enable or disable tracer options at boot. 3953 The option-list is a comma delimited list of options 3954 that can be enabled or disabled just as if you were 3955 to echo the option name into 3956 3957 /sys/kernel/debug/tracing/trace_options 3958 3959 For example, to enable stacktrace option (to dump the 3960 stack trace of each event), add to the command line: 3961 3962 trace_options=stacktrace 3963 3964 See also Documentation/trace/ftrace.txt "trace options" 3965 section. 3966 3967 tp_printk[FTRACE] 3968 Have the tracepoints sent to printk as well as the 3969 tracing ring buffer. This is useful for early boot up 3970 where the system hangs or reboots and does not give the 3971 option for reading the tracing buffer or performing a 3972 ftrace_dump_on_oops. 3973 3974 To turn off having tracepoints sent to printk, 3975 echo 0 > /proc/sys/kernel/tracepoint_printk 3976 Note, echoing 1 into this file without the 3977 tracepoint_printk kernel cmdline option has no effect. 3978 3979 ** CAUTION ** 3980 3981 Having tracepoints sent to printk() and activating high 3982 frequency tracepoints such as irq or sched, can cause 3983 the system to live lock. 3984 3985 traceoff_on_warning 3986 [FTRACE] enable this option to disable tracing when a 3987 warning is hit. This turns off "tracing_on". Tracing can 3988 be enabled again by echoing '1' into the "tracing_on" 3989 file located in /sys/kernel/debug/tracing/ 3990 3991 This option is useful, as it disables the trace before 3992 the WARNING dump is called, which prevents the trace to 3993 be filled with content caused by the warning output. 3994 3995 This option can also be set at run time via the sysctl 3996 option: kernel/traceoff_on_warning 3997 3998 transparent_hugepage= 3999 [KNL] 4000 Format: [always|madvise|never] 4001 Can be used to control the default behavior of the system 4002 with respect to transparent hugepages. 4003 See Documentation/vm/transhuge.txt for more details. 4004 4005 tsc= Disable clocksource stability checks for TSC. 4006 Format: <string> 4007 [x86] reliable: mark tsc clocksource as reliable, this 4008 disables clocksource verification at runtime, as well 4009 as the stability checks done at bootup. Used to enable 4010 high-resolution timer mode on older hardware, and in 4011 virtualized environment. 4012 [x86] noirqtime: Do not use TSC to do irq accounting. 4013 Used to run time disable IRQ_TIME_ACCOUNTING on any 4014 platforms where RDTSC is slow and this accounting 4015 can add overhead. 4016 4017 turbografx.map[2|3]= [HW,JOY] 4018 TurboGraFX parallel port interface 4019 Format: 4020 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> 4021 See also Documentation/input/joystick-parport.txt 4022 4023 udbg-immortal [PPC] When debugging early kernel crashes that 4024 happen after console_init() and before a proper 4025 console driver takes over, this boot options might 4026 help "seeing" what's going on. 4027 4028 uhash_entries= [KNL,NET] 4029 Set number of hash buckets for UDP/UDP-Lite connections 4030 4031 uhci-hcd.ignore_oc= 4032 [USB] Ignore overcurrent events (default N). 4033 Some badly-designed motherboards generate lots of 4034 bogus events, for ports that aren't wired to 4035 anything. Set this parameter to avoid log spamming. 4036 Note that genuine overcurrent events won't be 4037 reported either. 4038 4039 unknown_nmi_panic 4040 [X86] Cause panic on unknown NMI. 4041 4042 usbcore.authorized_default= 4043 [USB] Default USB device authorization: 4044 (default -1 = authorized except for wireless USB, 4045 0 = not authorized, 1 = authorized) 4046 4047 usbcore.autosuspend= 4048 [USB] The autosuspend time delay (in seconds) used 4049 for newly-detected USB devices (default 2). This 4050 is the time required before an idle device will be 4051 autosuspended. Devices for which the delay is set 4052 to a negative value won't be autosuspended at all. 4053 4054 usbcore.usbfs_snoop= 4055 [USB] Set to log all usbfs traffic (default 0 = off). 4056 4057 usbcore.usbfs_snoop_max= 4058 [USB] Maximum number of bytes to snoop in each URB 4059 (default = 65536). 4060 4061 usbcore.blinkenlights= 4062 [USB] Set to cycle leds on hubs (default 0 = off). 4063 4064 usbcore.old_scheme_first= 4065 [USB] Start with the old device initialization 4066 scheme (default 0 = off). 4067 4068 usbcore.usbfs_memory_mb= 4069 [USB] Memory limit (in MB) for buffers allocated by 4070 usbfs (default = 16, 0 = max = 2047). 4071 4072 usbcore.use_both_schemes= 4073 [USB] Try the other device initialization scheme 4074 if the first one fails (default 1 = enabled). 4075 4076 usbcore.initial_descriptor_timeout= 4077 [USB] Specifies timeout for the initial 64-byte 4078 USB_REQ_GET_DESCRIPTOR request in milliseconds 4079 (default 5000 = 5.0 seconds). 4080 4081 usbcore.nousb [USB] Disable the USB subsystem 4082 4083 usbhid.mousepoll= 4084 [USBHID] The interval which mice are to be polled at. 4085 4086 usb-storage.delay_use= 4087 [UMS] The delay in seconds before a new device is 4088 scanned for Logical Units (default 1). 4089 4090 usb-storage.quirks= 4091 [UMS] A list of quirks entries to supplement or 4092 override the built-in unusual_devs list. List 4093 entries are separated by commas. Each entry has 4094 the form VID:PID:Flags where VID and PID are Vendor 4095 and Product ID values (4-digit hex numbers) and 4096 Flags is a set of characters, each corresponding 4097 to a common usb-storage quirk flag as follows: 4098 a = SANE_SENSE (collect more than 18 bytes 4099 of sense data); 4100 b = BAD_SENSE (don't collect more than 18 4101 bytes of sense data); 4102 c = FIX_CAPACITY (decrease the reported 4103 device capacity by one sector); 4104 d = NO_READ_DISC_INFO (don't use 4105 READ_DISC_INFO command); 4106 e = NO_READ_CAPACITY_16 (don't use 4107 READ_CAPACITY_16 command); 4108 f = NO_REPORT_OPCODES (don't use report opcodes 4109 command, uas only); 4110 g = MAX_SECTORS_240 (don't transfer more than 4111 240 sectors at a time, uas only); 4112 h = CAPACITY_HEURISTICS (decrease the 4113 reported device capacity by one 4114 sector if the number is odd); 4115 i = IGNORE_DEVICE (don't bind to this 4116 device); 4117 j = NO_REPORT_LUNS (don't use report luns 4118 command, uas only); 4119 l = NOT_LOCKABLE (don't try to lock and 4120 unlock ejectable media); 4121 m = MAX_SECTORS_64 (don't transfer more 4122 than 64 sectors = 32 KB at a time); 4123 n = INITIAL_READ10 (force a retry of the 4124 initial READ(10) command); 4125 o = CAPACITY_OK (accept the capacity 4126 reported by the device); 4127 p = WRITE_CACHE (the device cache is ON 4128 by default); 4129 r = IGNORE_RESIDUE (the device reports 4130 bogus residue values); 4131 s = SINGLE_LUN (the device has only one 4132 Logical Unit); 4133 t = NO_ATA_1X (don't allow ATA(12) and ATA(16) 4134 commands, uas only); 4135 u = IGNORE_UAS (don't bind to the uas driver); 4136 w = NO_WP_DETECT (don't test whether the 4137 medium is write-protected). 4138 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE 4139 even if the device claims no cache) 4140 Example: quirks=0419:aaf5:rl,0421:0433:rc 4141 4142 user_debug= [KNL,ARM] 4143 Format: <int> 4144 See arch/arm/Kconfig.debug help text. 4145 1 - undefined instruction events 4146 2 - system calls 4147 4 - invalid data aborts 4148 8 - SIGSEGV faults 4149 16 - SIGBUS faults 4150 Example: user_debug=31 4151 4152 userpte= 4153 [X86] Flags controlling user PTE allocations. 4154 4155 nohigh = do not allocate PTE pages in 4156 HIGHMEM regardless of setting 4157 of CONFIG_HIGHPTE. 4158 4159 vdso= [X86,SH] 4160 On X86_32, this is an alias for vdso32=. Otherwise: 4161 4162 vdso=1: enable VDSO (the default) 4163 vdso=0: disable VDSO mapping 4164 4165 vdso32= [X86] Control the 32-bit vDSO 4166 vdso32=1: enable 32-bit VDSO 4167 vdso32=0 or vdso32=2: disable 32-bit VDSO 4168 4169 See the help text for CONFIG_COMPAT_VDSO for more 4170 details. If CONFIG_COMPAT_VDSO is set, the default is 4171 vdso32=0; otherwise, the default is vdso32=1. 4172 4173 For compatibility with older kernels, vdso32=2 is an 4174 alias for vdso32=0. 4175 4176 Try vdso32=0 if you encounter an error that says: 4177 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed! 4178 4179 vector= [IA-64,SMP] 4180 vector=percpu: enable percpu vector domain 4181 4182 video= [FB] Frame buffer configuration 4183 See Documentation/fb/modedb.txt. 4184 4185 video.brightness_switch_enabled= [0,1] 4186 If set to 1, on receiving an ACPI notify event 4187 generated by hotkey, video driver will adjust brightness 4188 level and then send out the event to user space through 4189 the allocated input device; If set to 0, video driver 4190 will only send out the event without touching backlight 4191 brightness level. 4192 default: 1 4193 4194 virtio_mmio.device= 4195 [VMMIO] Memory mapped virtio (platform) device. 4196 4197 <size>@<baseaddr>:<irq>[:<id>] 4198 where: 4199 <size> := size (can use standard suffixes 4200 like K, M and G) 4201 <baseaddr> := physical base address 4202 <irq> := interrupt number (as passed to 4203 request_irq()) 4204 <id> := (optional) platform device id 4205 example: 4206 virtio_mmio.device=1K@0x100b0000:48:7 4207 4208 Can be used multiple times for multiple devices. 4209 4210 vga= [BOOT,X86-32] Select a particular video mode 4211 See Documentation/x86/boot.txt and 4212 Documentation/svga.txt. 4213 Use vga=ask for menu. 4214 This is actually a boot loader parameter; the value is 4215 passed to the kernel using a special protocol. 4216 4217 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact 4218 size of <nn>. This can be used to increase the 4219 minimum size (128MB on x86). It can also be used to 4220 decrease the size and leave more room for directly 4221 mapped kernel RAM. 4222 4223 vmhalt= [KNL,S390] Perform z/VM CP command after system halt. 4224 Format: <command> 4225 4226 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. 4227 Format: <command> 4228 4229 vmpoff= [KNL,S390] Perform z/VM CP command after power off. 4230 Format: <command> 4231 4232 vsyscall= [X86-64] 4233 Controls the behavior of vsyscalls (i.e. calls to 4234 fixed addresses of 0xffffffffff600x00 from legacy 4235 code). Most statically-linked binaries and older 4236 versions of glibc use these calls. Because these 4237 functions are at fixed addresses, they make nice 4238 targets for exploits that can control RIP. 4239 4240 emulate [default] Vsyscalls turn into traps and are 4241 emulated reasonably safely. 4242 4243 native Vsyscalls are native syscall instructions. 4244 This is a little bit faster than trapping 4245 and makes a few dynamic recompilers work 4246 better than they would in emulation mode. 4247 It also makes exploits much easier to write. 4248 4249 none Vsyscalls don't work at all. This makes 4250 them quite hard to use for exploits but 4251 might break your system. 4252 4253 vt.color= [VT] Default text color. 4254 Format: 0xYX, X = foreground, Y = background. 4255 Default: 0x07 = light gray on black. 4256 4257 vt.cur_default= [VT] Default cursor shape. 4258 Format: 0xCCBBAA, where AA, BB, and CC are the same as 4259 the parameters of the <Esc>[?A;B;Cc escape sequence; 4260 see VGA-softcursor.txt. Default: 2 = underline. 4261 4262 vt.default_blu= [VT] 4263 Format: <blue0>,<blue1>,<blue2>,...,<blue15> 4264 Change the default blue palette of the console. 4265 This is a 16-member array composed of values 4266 ranging from 0-255. 4267 4268 vt.default_grn= [VT] 4269 Format: <green0>,<green1>,<green2>,...,<green15> 4270 Change the default green palette of the console. 4271 This is a 16-member array composed of values 4272 ranging from 0-255. 4273 4274 vt.default_red= [VT] 4275 Format: <red0>,<red1>,<red2>,...,<red15> 4276 Change the default red palette of the console. 4277 This is a 16-member array composed of values 4278 ranging from 0-255. 4279 4280 vt.default_utf8= 4281 [VT] 4282 Format=<0|1> 4283 Set system-wide default UTF-8 mode for all tty's. 4284 Default is 1, i.e. UTF-8 mode is enabled for all 4285 newly opened terminals. 4286 4287 vt.global_cursor_default= 4288 [VT] 4289 Format=<-1|0|1> 4290 Set system-wide default for whether a cursor 4291 is shown on new VTs. Default is -1, 4292 i.e. cursors will be created by default unless 4293 overridden by individual drivers. 0 will hide 4294 cursors, 1 will display them. 4295 4296 vt.italic= [VT] Default color for italic text; 0-15. 4297 Default: 2 = green. 4298 4299 vt.underline= [VT] Default color for underlined text; 0-15. 4300 Default: 3 = cyan. 4301 4302 watchdog timers [HW,WDT] For information on watchdog timers, 4303 see Documentation/watchdog/watchdog-parameters.txt 4304 or other driver-specific files in the 4305 Documentation/watchdog/ directory. 4306 4307 workqueue.watchdog_thresh= 4308 If CONFIG_WQ_WATCHDOG is configured, workqueue can 4309 warn stall conditions and dump internal state to 4310 help debugging. 0 disables workqueue stall 4311 detection; otherwise, it's the stall threshold 4312 duration in seconds. The default value is 30 and 4313 it can be updated at runtime by writing to the 4314 corresponding sysfs file. 4315 4316 workqueue.disable_numa 4317 By default, all work items queued to unbound 4318 workqueues are affine to the NUMA nodes they're 4319 issued on, which results in better behavior in 4320 general. If NUMA affinity needs to be disabled for 4321 whatever reason, this option can be used. Note 4322 that this also can be controlled per-workqueue for 4323 workqueues visible under /sys/bus/workqueue/. 4324 4325 workqueue.power_efficient 4326 Per-cpu workqueues are generally preferred because 4327 they show better performance thanks to cache 4328 locality; unfortunately, per-cpu workqueues tend to 4329 be more power hungry than unbound workqueues. 4330 4331 Enabling this makes the per-cpu workqueues which 4332 were observed to contribute significantly to power 4333 consumption unbound, leading to measurably lower 4334 power usage at the cost of small performance 4335 overhead. 4336 4337 The default value of this parameter is determined by 4338 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT. 4339 4340 workqueue.debug_force_rr_cpu 4341 Workqueue used to implicitly guarantee that work 4342 items queued without explicit CPU specified are put 4343 on the local CPU. This guarantee is no longer true 4344 and while local CPU is still preferred work items 4345 may be put on foreign CPUs. This debug option 4346 forces round-robin CPU selection to flush out 4347 usages which depend on the now broken guarantee. 4348 When enabled, memory and cache locality will be 4349 impacted. 4350 4351 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of 4352 default x2apic cluster mode on platforms 4353 supporting x2apic. 4354 4355 x86_intel_mid_timer= [X86-32,APBT] 4356 Choose timer option for x86 Intel MID platform. 4357 Two valid options are apbt timer only and lapic timer 4358 plus one apbt timer for broadcast timer. 4359 x86_intel_mid_timer=apbt_only | lapic_and_apbt 4360 4361 xen_512gb_limit [KNL,X86-64,XEN] 4362 Restricts the kernel running paravirtualized under Xen 4363 to use only up to 512 GB of RAM. The reason to do so is 4364 crash analysis tools and Xen tools for doing domain 4365 save/restore/migration must be enabled to handle larger 4366 domains. 4367 4368 xen_emul_unplug= [HW,X86,XEN] 4369 Unplug Xen emulated devices 4370 Format: [unplug0,][unplug1] 4371 ide-disks -- unplug primary master IDE devices 4372 aux-ide-disks -- unplug non-primary-master IDE devices 4373 nics -- unplug network devices 4374 all -- unplug all emulated devices (NICs and IDE disks) 4375 unnecessary -- unplugging emulated devices is 4376 unnecessary even if the host did not respond to 4377 the unplug protocol 4378 never -- do not unplug even if version check succeeds 4379 4380 xen_nopvspin [X86,XEN] 4381 Disables the ticketlock slowpath using Xen PV 4382 optimizations. 4383 4384 xen_nopv [X86] 4385 Disables the PV optimizations forcing the HVM guest to 4386 run as generic HVM guest with no PV drivers. 4387 4388 xirc2ps_cs= [NET,PCMCIA] 4389 Format: 4390 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] 4391