1 acpi= [HW,ACPI,X86,ARM64]
2 Advanced Configuration and Power Interface
3 Format: { force | on | off | strict | noirq | rsdt |
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"
16 See also Documentation/power/runtime_pm.txt, pci=noacpi
18 acpi_apic_instance= [ACPI, IOAPIC]
20 2: use 2nd APIC table, if available
21 1,0: use 1st APIC table
24 acpi_backlight= [HW,ACPI]
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.
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.
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.
45 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
46 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
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.
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
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.
73 acpi_enforce_resources= [ACPI]
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.
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
94 acpi_irq_balance [HW,ACPI]
95 ACPI will balance active IRQs
98 acpi_irq_nobalance [HW,ACPI]
99 ACPI will not move active IRQs (default)
102 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
103 Format: <irq>,<irq>...
105 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
107 Format: <irq>,<irq>...
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
114 This facility can be used to prevent such uncontrolled
118 acpi_no_auto_serialize [HW,ACPI]
119 Disable auto-serialization of AML methods
120 AML control methods that contain the opcodes to create
121 named objects will be marked as "Serialized" by the
122 auto-serialization feature.
123 This feature is enabled by default.
124 This option allows to turn off the feature.
126 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
129 acpi_no_static_ssdt [HW,ACPI]
130 Disable installation of static SSDTs at early boot time
131 By default, SSDTs contained in the RSDT/XSDT will be
132 installed automatically and they will appear under
133 /sys/firmware/acpi/tables.
134 This option turns off this feature.
135 Note that specifying this option does not affect
136 dynamic table installation which will install SSDT
137 tables to /sys/firmware/acpi/tables/dynamic.
139 acpi_rsdp= [ACPI,EFI,KEXEC]
140 Pass the RSDP address to the kernel, mostly used
141 on machines running EFI runtime service to boot the
142 second kernel for kdump.
144 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
145 Format: To spoof as Windows 98: ="Microsoft Windows"
147 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
148 of 2 which is mandated by ACPI 6) as the supported ACPI
149 specification revision (when using this switch, it may
150 be necessary to carry out a cold reboot _twice_ in a
151 row to make it take effect on the platform firmware).
153 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
154 acpi_osi="string1" # add string1
155 acpi_osi="!string2" # remove string2
156 acpi_osi=!* # remove all strings
157 acpi_osi=! # disable all built-in OS vendor
159 acpi_osi=!! # enable all built-in OS vendor
161 acpi_osi= # disable all strings
163 'acpi_osi=!' can be used in combination with single or
164 multiple 'acpi_osi="string1"' to support specific OS
165 vendor string(s). Note that such command can only
166 affect the default state of the OS vendor strings, thus
167 it cannot affect the default state of the feature group
168 strings and the current state of the OS vendor strings,
169 specifying it multiple times through kernel command line
170 is meaningless. This command is useful when one do not
171 care about the state of the feature group strings which
172 should be controlled by the OSPM.
174 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
175 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
176 can make '_OSI("Windows 2000")' TRUE.
178 'acpi_osi=' cannot be used in combination with other
179 'acpi_osi=' command lines, the _OSI method will not
180 exist in the ACPI namespace. NOTE that such command can
181 only affect the _OSI support state, thus specifying it
182 multiple times through kernel command line is also
185 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
188 'acpi_osi=!*' can be used in combination with single or
189 multiple 'acpi_osi="string1"' to support specific
190 string(s). Note that such command can affect the
191 current state of both the OS vendor strings and the
192 feature group strings, thus specifying it multiple times
193 through kernel command line is meaningful. But it may
194 still not able to affect the final state of a string if
195 there are quirks related to this string. This command
196 is useful when one want to control the state of the
197 feature group strings to debug BIOS issues related to
200 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
201 '_OSI("Module Device")' FALSE.
202 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
203 '_OSI("Module Device")' TRUE.
204 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
206 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
208 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
209 they all will make '_OSI("Windows 2000")' TRUE.
212 Override the pmtimer bug detection: force the kernel
213 to assume that this machine's pmtimer latches its value
214 and always returns good values.
216 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
217 Format: { level | edge | high | low }
219 acpi_skip_timer_override [HW,ACPI]
220 Recognize and ignore IRQ0/pin2 Interrupt Override.
221 For broken nForce2 BIOS resulting in XT-PIC timer.
223 acpi_sleep= [HW,ACPI] Sleep options
224 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
225 old_ordering, nonvs, sci_force_enable, nobl }
226 See Documentation/power/video.txt for information on
228 s3_beep is for debugging; it makes the PC's speaker beep
229 as soon as the kernel's real-mode entry point is called.
230 s4_nohwsig prevents ACPI hardware signature from being
231 used during resume from hibernation.
232 old_ordering causes the ACPI 1.0 ordering of the _PTS
233 control method, with respect to putting devices into
234 low power states, to be enforced (the ACPI 2.0 ordering
235 of _PTS is used by default).
236 nonvs prevents the kernel from saving/restoring the
237 ACPI NVS memory during suspend/hibernation and resume.
238 sci_force_enable causes the kernel to set SCI_EN directly
239 on resume from S1/S3 (which is against the ACPI spec,
240 but some broken systems don't work without it).
241 nobl causes the internal blacklist of systems known to
242 behave incorrectly in some ways with respect to system
243 suspend and resume to be ignored (use wisely).
245 acpi_use_timer_override [HW,ACPI]
246 Use timer override. For some broken Nvidia NF5 boards
247 that require a timer override, but don't have HPET
249 add_efi_memmap [EFI; X86] Include EFI memory map in
250 kernel's map of available physical RAM.
253 { off | try_unsupported }
254 off: disable AGP support
255 try_unsupported: try to drive unsupported chipsets
256 (may crash computer or cause data corruption)
259 See Documentation/sound/alsa-configuration.rst
262 Allow the default userspace alignment fault handler
263 behaviour to be specified. Bit 0 enables warnings,
264 bit 1 enables fixups, and bit 2 sends a segfault.
266 align_va_addr= [X86-64]
267 Align virtual addresses by clearing slice [14:12] when
268 allocating a VMA at process creation time. This option
269 gives you up to 3% performance improvement on AMD F15h
270 machines (where it is enabled by default) for a
271 CPU-intensive style benchmark, and it can vary highly in
272 a microbenchmark depending on workload and compiler.
274 32: only for 32-bit processes
275 64: only for 64-bit processes
276 on: enable for both 32- and 64-bit processes
277 off: disable for both 32- and 64-bit processes
279 alloc_snapshot [FTRACE]
280 Allocate the ftrace snapshot buffer on boot up when the
281 main buffer is allocated. This is handy if debugging
282 and you need to use tracing_snapshot() on boot up, and
283 do not want to use tracing_snapshot_alloc() as it needs
284 to be done where GFP_KERNEL allocations are allowed.
286 amd_iommu= [HW,X86-64]
287 Pass parameters to the AMD IOMMU driver in the system.
289 fullflush - enable flushing of IO/TLB entries when
290 they are unmapped. Otherwise they are
291 flushed before they will be reused, which
293 off - do not initialize any AMD IOMMU found in
295 force_isolation - Force device isolation for all
296 devices. The IOMMU driver is not
297 allowed anymore to lift isolation
298 requirements as needed. This option
299 does not override iommu=pt
301 amd_iommu_dump= [HW,X86-64]
302 Enable AMD IOMMU driver option to dump the ACPI table
303 for AMD IOMMU. With this option enabled, AMD IOMMU
304 driver will print ACPI tables for AMD IOMMU during
305 IOMMU initialization.
307 amd_iommu_intr= [HW,X86-64]
308 Specifies one of the following AMD IOMMU interrupt
310 legacy - Use legacy interrupt remapping mode.
311 vapic - Use virtual APIC mode, which allows IOMMU
312 to inject interrupts directly into guest.
313 This mode requires kvm-amd.avic=1.
314 (Default when IOMMU HW support is present.)
316 amijoy.map= [HW,JOY] Amiga joystick support
317 Map of devices attached to JOY0DAT and JOY1DAT
319 See also Documentation/input/joydev/joystick.rst
321 analog.map= [HW,JOY] Analog joystick and gamepad support
322 Specifies type or capabilities of an analog joystick
323 connected to one of 16 gameports
324 Format: <type1>,<type2>,..<type16>
327 Power management functions (SPARCstation-4/5 + deriv.)
329 Disable APC CPU standby support. SPARCstation-Fox does
330 not play well with APC CPU idle - disable it if you have
331 APC and your system crashes randomly.
333 apic= [APIC,X86] Advanced Programmable Interrupt Controller
334 Change the output verbosity whilst booting
335 Format: { quiet (default) | verbose | debug }
336 Change the amount of debugging information output
337 when initialising the APIC and IO-APIC components.
338 For X86-32, this can also be used to specify an APIC
340 Format: apic=driver_name
341 Examples: apic=bigsmp
343 apic_extnmi= [APIC,X86] External NMI delivery setting
344 Format: { bsp (default) | all | none }
345 bsp: External NMI is delivered only to CPU 0
346 all: External NMIs are broadcast to all CPUs as a
348 none: External NMI is masked for all CPUs. This is
349 useful so that a dump capture kernel won't be
353 See Documentation/networking/ipv6.txt.
355 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
356 Limit apic dumping. The parameter defines the maximal
357 number of local apics being dumped. Also it is possible
358 to set it to "all" by meaning -- no limit here.
359 Format: { 1 (default) | 2 | ... | all }.
360 The parameter valid if only apic=debug or
361 apic=verbose is specified.
362 Example: apic=debug show_lapic=all
364 apm= [APM] Advanced Power Management
365 See header of arch/x86/kernel/apm_32.c.
367 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
368 Format: <io>,<irq>,<nodeID>
372 atarimouse= [HW,MOUSE] Atari Mouse
374 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
375 EzKey and similar keyboards
377 atkbd.reset= [HW] Reset keyboard during initialization
379 atkbd.set= [HW] Select keyboard code set
380 Format: <int> (2 = AT (default), 3 = PS/2)
382 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
385 atkbd.softraw= [HW] Choose between synthetic and real raw mode
386 Format: <bool> (0 = real, 1 = synthetic (default))
388 atkbd.softrepeat= [HW]
389 Use software keyboard repeat
391 audit= [KNL] Enable the audit sub-system
392 Format: { "0" | "1" | "off" | "on" }
393 0 | off - kernel audit is disabled and can not be
394 enabled until the next reboot
395 unset - kernel audit is initialized but disabled and
396 will be fully enabled by the userspace auditd.
397 1 | on - kernel audit is initialized and partially
398 enabled, storing at most audit_backlog_limit
399 messages in RAM until it is fully enabled by the
403 audit_backlog_limit= [KNL] Set the audit queue size limit.
404 Format: <int> (must be >=0)
407 bau= [X86_UV] Enable the BAU on SGI UV. The default
408 behavior is to disable the BAU (i.e. bau=0).
409 Format: { "0" | "1" }
412 unset - Disable the BAU.
414 baycom_epp= [HW,AX25]
417 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
419 See header of drivers/net/hamradio/baycom_par.c.
421 baycom_ser_fdx= [HW,AX25]
422 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
423 Format: <io>,<irq>,<mode>[,<baud>]
424 See header of drivers/net/hamradio/baycom_ser_fdx.c.
426 baycom_ser_hdx= [HW,AX25]
427 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
428 Format: <io>,<irq>,<mode>
429 See header of drivers/net/hamradio/baycom_ser_hdx.c.
431 blkdevparts= Manual partition parsing of block device(s) for
432 embedded devices based on command line input.
433 See Documentation/block/cmdline-partition.txt
435 boot_delay= Milliseconds to delay each printk during boot.
436 Values larger than 10 seconds (10000) are changed to
440 bootmem_debug [KNL] Enable bootmem allocator debug messages.
443 Disable BERT OS support on buggy BIOSes.
445 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
446 bttv.radio= Most important insmod options are available as
448 bttv.pll= See Documentation/media/v4l-drivers/bttv.rst
451 bulk_remove=off [PPC] This parameter disables the use of the pSeries
452 firmware feature for flushing multiple hpte entries
455 c101= [NET] Moxa C101 synchronous serial card
457 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
458 Sometimes CPU hardware bugs make them report the cache
459 size incorrectly. The kernel will attempt work arounds
460 to fix known problems, but for some CPUs it is not
461 possible to determine what the correct size should be.
462 This option provides an override for these situations.
464 ca_keys= [KEYS] This parameter identifies a specific key(s) on
465 the system trusted keyring to be used for certificate
467 format: { id:<keyid> | builtin }
469 cca= [MIPS] Override the kernel pages' cache coherency
470 algorithm. Accepted values range from 0 to 7
471 inclusive. See arch/mips/include/asm/pgtable-bits.h
472 for platform specific values (SB1, Loongson3 and
475 ccw_timeout_log [S390]
476 See Documentation/s390/CommonIO for details.
478 cgroup_disable= [KNL] Disable a particular controller
479 Format: {name of the controller(s) to disable}
480 The effects of cgroup_disable=foo are:
481 - foo isn't auto-mounted if you mount all cgroups in
483 - foo isn't visible as an individually mountable
485 {Currently only "memory" controller deal with this and
486 cut the overhead, others just disable the usage. So
487 only cgroup_disable=memory is actually worthy}
489 cgroup_no_v1= [KNL] Disable one, multiple, all cgroup controllers in v1
490 Format: { controller[,controller...] | "all" }
491 Like cgroup_disable, but only applies to cgroup v1;
492 the blacklisted controllers remain available in cgroup2.
494 cgroup.memory= [KNL] Pass options to the cgroup memory controller.
496 nosocket -- Disable socket memory accounting.
497 nokmem -- Disable kernel memory accounting.
499 checkreqprot [SELINUX] Set initial checkreqprot flag value.
500 Format: { "0" | "1" }
501 See security/selinux/Kconfig help text.
502 0 -- check protection applied by kernel (includes
503 any implied execute protection).
504 1 -- check protection requested by application.
505 Default value is set via a kernel config option.
506 Value can be changed at runtime via
507 /selinux/checkreqprot.
510 See Documentation/s390/CommonIO for details.
513 Prevents the clock framework from automatically gating
514 clocks that have not been explicitly enabled by a Linux
515 device driver but are enabled in hardware at reset or
516 by the bootloader/firmware. Note that this does not
517 force such clocks to be always-on nor does it reserve
518 those clocks in any way. This parameter is useful for
519 debug and development, but should not be needed on a
520 platform with proper driver support. For more
521 information, see Documentation/driver-api/clk.rst.
523 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
525 Forces specified clocksource (if available) to be used
526 when calculating gettimeofday(). If specified
527 clocksource is not available, it defaults to PIT.
528 Format: { pit | tsc | cyclone | pmtmr }
530 clocksource= Override the default clocksource
532 Override the default clocksource and use the clocksource
533 with the name specified.
534 Some clocksource names to choose from, depending on
536 [all] jiffies (this is the base, fallback clocksource)
538 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
539 pxa_timer,timer3,32k_counter,timer0_1
540 [X86-32] pit,hpet,tsc;
541 scx200_hrt on Geode; cyclone on IBM x440
549 clocksource.arm_arch_timer.evtstrm=
552 Enable/disable the eventstream feature of the ARM
553 architected timer so that code using WFE-based polling
554 loops can be debugged more effectively on production
557 clearcpuid=BITNUM [X86]
558 Disable CPUID feature X for the kernel. See
559 arch/x86/include/asm/cpufeatures.h for the valid bit
560 numbers. Note the Linux specific bits are not necessarily
561 stable over kernel options, but the vendor specific
563 Also note that user programs calling CPUID directly
564 or using the feature without checking anything
565 will still see it. This just prevents it from
566 being used by the kernel or shown in /proc/cpuinfo.
567 Also note the kernel might malfunction if you disable
570 cma=nn[MG]@[start[MG][-end[MG]]]
572 Sets the size of kernel global memory area for
573 contiguous memory allocations and optionally the
574 placement constraint by the physical address range of
575 memory allocations. A value of 0 disables CMA
576 altogether. For more information, see
577 include/linux/dma-contiguous.h
579 cmo_free_hint= [PPC] Format: { yes | no }
580 Specify whether pages are marked as being inactive
581 when they are freed. This is used in CMO environments
582 to determine OS memory pressure for page stealing by
586 coherent_pool=nn[KMG] [ARM,KNL]
587 Sets the size of memory pool for coherent, atomic dma
588 allocations, by default set to 256K.
590 com20020= [HW,NET] ARCnet - COM20020 chipset
592 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
594 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
598 ARCnet - COM90xx chipset (memory-mapped buffers)
599 Format: <io>[,<irq>[,<memstart>]]
601 condev= [HW,S390] console device
604 console= [KNL] Output console device and options.
606 tty<n> Use the virtual console device <n>.
610 Use the specified serial port. The options are of
611 the form "bbbbpnf", where "bbbb" is the baud rate,
612 "p" is parity ("n", "o", or "e"), "n" is number of
613 bits, and "f" is flow control ("r" for RTS or
614 omit it). Default is "9600n8".
616 See Documentation/admin-guide/serial-console.rst for more
618 Documentation/networking/netconsole.txt for an
621 uart[8250],io,<addr>[,options]
622 uart[8250],mmio,<addr>[,options]
623 uart[8250],mmio16,<addr>[,options]
624 uart[8250],mmio32,<addr>[,options]
625 uart[8250],0x<addr>[,options]
626 Start an early, polled-mode console on the 8250/16550
627 UART at the specified I/O port or MMIO address,
628 switching to the matching ttyS device later.
629 MMIO inter-register address stride is either 8-bit
630 (mmio), 16-bit (mmio16), or 32-bit (mmio32).
631 If none of [io|mmio|mmio16|mmio32], <addr> is assumed
632 to be equivalent to 'mmio'. 'options' are specified in
633 the same format described for ttyS above; if unspecified,
634 the h/w is not re-initialized.
636 hvc<n> Use the hypervisor console device <n>. This is for
637 both Xen and PowerPC hypervisors.
639 If the device connected to the port is not a TTY but a braille
640 device, prepend "brl," before the device type, for instance
642 For now, only VisioBraille is supported.
645 [KNL] Change console messages format
647 By default we print messages on consoles in
648 "[time stamp] text\n" format (time stamp may not be
649 printed, depending on CONFIG_PRINTK_TIME or
650 `printk_time' param).
652 Switch to syslog format: "<%u>[time stamp] text\n"
653 IOW, each message will have a facility and loglevel
654 prefix. The format is similar to one used by syslog()
655 syscall, or to executing "dmesg -S --raw" or to reading
658 consoleblank= [KNL] The console blank (screen saver) timeout in
659 seconds. A value of 0 disables the blank timer.
663 [KNL] Change the default value for
664 /proc/<pid>/coredump_filter.
665 See also Documentation/filesystems/proc.txt.
667 coresight_cpu_debug.enable
670 Enable/disable the CPU sampling based debugging.
671 0: default value, disable debugging
672 1: enable debugging at boot time
674 cpuidle.off=1 [CPU_IDLE]
675 disable the cpuidle sub-system
677 cpufreq.off=1 [CPU_FREQ]
678 disable the cpufreq sub-system
681 [X86] Delay for N microsec between assert and de-assert
682 of APIC INIT to start processors. This delay occurs
683 on every CPU online, such as boot, and resume from suspend.
686 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
688 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
690 crashkernel=size[KMG][@offset[KMG]]
691 [KNL] Using kexec, Linux can switch to a 'crash kernel'
692 upon panic. This parameter reserves the physical
693 memory region [offset, offset + size] for that kernel
694 image. If '@offset' is omitted, then a suitable offset
695 is selected automatically. Check
696 Documentation/kdump/kdump.txt for further details.
698 crashkernel=range1:size1[,range2:size2,...][@offset]
699 [KNL] Same as above, but depends on the memory
700 in the running system. The syntax of range is
701 start-[end] where start and end are both
702 a memory unit (amount[KMG]). See also
703 Documentation/kdump/kdump.txt for an example.
705 crashkernel=size[KMG],high
706 [KNL, x86_64] range could be above 4G. Allow kernel
707 to allocate physical memory region from top, so could
708 be above 4G if system have more than 4G ram installed.
709 Otherwise memory region will be allocated below 4G, if
711 It will be ignored if crashkernel=X is specified.
712 crashkernel=size[KMG],low
713 [KNL, x86_64] range under 4G. When crashkernel=X,high
714 is passed, kernel could allocate physical memory region
715 above 4G, that cause second kernel crash on system
716 that require some amount of low memory, e.g. swiotlb
717 requires at least 64M+32K low memory, also enough extra
718 low memory is needed to make sure DMA buffers for 32-bit
719 devices won't run out. Kernel would try to allocate at
720 at least 256M below 4G automatically.
721 This one let user to specify own low range under 4G
722 for second kernel instead.
723 0: to disable low allocation.
724 It will be ignored when crashkernel=X,high is not used
725 or memory reserved is below 4G.
728 [KNL] Disable crypto self-tests
733 cs89x0_media= [HW,NET]
734 Format: { rj45 | aui | bnc }
737 See header of drivers/s390/block/dasd_devmap.c.
739 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
740 (one device per port)
741 Format: <port#>,<type>
742 See also Documentation/input/devices/joystick-parport.rst
744 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
746 Documentation/admin-guide/dynamic-debug-howto.rst for
747 details. Deprecated, see dyndbg.
749 debug [KNL] Enable kernel debugging (events log level).
752 [KNL] Enable printing [hashed] pointers early in the
753 boot sequence. If enabled, we use a weak hash instead
754 of siphash to hash pointers. Use this option if you are
755 seeing instances of '(___ptrval___)') and need to see a
756 value (hashed pointer) instead. Cryptographically
757 insecure, please do not use on production kernels.
760 [KNL] verbose self-tests
762 Print debugging info while doing the locking API
764 We default to 0 (no extra messages), setting it to
765 1 will print _a lot_ more information - normally
766 only useful to kernel developers.
768 debug_objects [KNL] Enable object debugging
771 [KNL] Disable object debugging
773 debug_guardpage_minorder=
774 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
775 parameter allows control of the order of pages that will
776 be intentionally kept free (and hence protected) by the
777 buddy allocator. Bigger value increase the probability
778 of catching random memory corruption, but reduce the
779 amount of memory for normal system use. The maximum
780 possible value is MAX_ORDER/2. Setting this parameter
781 to 1 or 2 should be enough to identify most random
782 memory corruption problems caused by bugs in kernel or
783 driver code when a CPU writes to (or reads from) a
784 random memory location. Note that there exists a class
785 of memory corruptions problems caused by buggy H/W or
786 F/W or by drivers badly programing DMA (basically when
787 memory is written at bus level and the CPU MMU is
788 bypassed) which are not detectable by
789 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
790 tracking down these problems.
793 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
794 parameter enables the feature at boot time. In
795 default, it is disabled. We can avoid allocating huge
796 chunk of memory for debug pagealloc if we don't enable
797 it at boot time and the system will work mostly same
798 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
799 on: enable the feature
801 debugpat [X86] Enable PAT debugging
803 decnet.addr= [HW,NET]
804 Format: <area>[,<node>]
805 See also Documentation/networking/decnet.txt.
808 [same as hugepagesz=] The size of the default
809 HugeTLB page size. This is the size represented by
810 the legacy /proc/ hugepages APIs, used for SHM, and
811 default size when mounting hugetlbfs filesystems.
812 Defaults to the default architecture's huge page size
815 deferred_probe_timeout=
816 [KNL] Debugging option to set a timeout in seconds for
817 deferred probe to give up waiting on dependencies to
818 probe. Only specific dependencies (subsystems or
819 drivers) that have opted in will be ignored. A timeout of 0
820 will timeout at the end of initcalls. This option will also
821 dump out devices still on the deferred probe list after
825 Set number of hash buckets for dentry cache.
827 disable_1tb_segments [PPC]
828 Disables the use of 1TB hash page table segments. This
829 causes the kernel to fall back to 256MB segments which
830 can be useful when debugging issues that require an SLB
834 See Documentation/networking/ipv6.txt.
837 [KNL] Under CONFIG_HARDENED_USERCOPY, whether
838 hardening is enabled for this boot. Hardened
839 usercopy checking is used to protect the kernel
840 from reading or writing beyond known memory
841 allocation boundaries as a proactive defense
842 against bounds-checking flaws in the kernel's
843 copy_to_user()/copy_from_user() interface.
844 on Perform hardened usercopy checks (default).
845 off Disable hardened usercopy checks.
848 Disable RADIX MMU mode on POWER9
850 disable_cpu_apicid= [X86,APIC,SMP]
852 The number of initial APIC ID for the
853 corresponding CPU to be disabled at boot,
854 mostly used for the kdump 2nd kernel to
855 disable BSP to wake up multiple CPUs without
856 causing system reset or hang due to sending
859 disable_counter_freezing [HW]
860 Disable Intel PMU counter freezing feature.
861 The feature only exists starting from
862 Arch Perfmon v4 (Skylake and newer).
864 disable_ddw [PPC/PSERIES]
865 Disable Dynamic DMA Window support. Use this if
866 to workaround buggy firmware.
869 See Documentation/networking/ipv6.txt.
871 disable_mtrr_cleanup [X86]
872 The kernel tries to adjust MTRR layout from continuous
873 to discrete, to make X server driver able to add WB
874 entry later. This parameter disables that.
876 disable_mtrr_trim [X86, Intel and AMD only]
877 By default the kernel will trim any uncacheable
878 memory out of your available memory pool based on
879 MTRR settings. This parameter disables that behavior,
880 possibly causing your machine to run very slowly.
882 disable_timer_pin_1 [X86]
883 Disable PIN 1 of APIC timer
884 Can be useful to work around chipset bugs.
886 dis_ucode_ldr [X86] Disable the microcode loader.
888 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
889 this option disables the debugging code at boot.
891 dma_debug_entries=<number>
892 This option allows to tune the number of preallocated
893 entries for DMA-API debugging code. One entry is
894 required per DMA-API allocation. Use this if the
895 DMA-API debugging code disables itself because the
896 architectural default is too low.
898 dma_debug_driver=<driver_name>
899 With this option the DMA-API debugging driver
900 filter feature can be enabled at boot time. Just
901 pass the driver to filter for as the parameter.
902 The filter can be disabled or changed to another
903 driver later using sysfs.
905 drm.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
906 Broken monitors, graphic adapters, KVMs and EDIDless
907 panels may send no or incorrect EDID data sets.
908 This parameter allows to specify an EDID data sets
909 in the /lib/firmware directory that are used instead.
910 Generic built-in EDID data sets are used, if one of
911 edid/1024x768.bin, edid/1280x1024.bin,
912 edid/1680x1050.bin, or edid/1920x1080.bin is given
913 and no file with the same name exists. Details and
914 instructions how to build your own EDID data are
915 available in Documentation/EDID/HOWTO.txt. An EDID
916 data set will only be used for a particular connector,
917 if its name and a colon are prepended to the EDID
918 name. Each connector may use a unique EDID data
919 set by separating the files with a comma. An EDID
920 data set with no connector name will be used for
921 any connectors not explicitly specified.
926 Format: {"off" | "known"}
927 Control how the dt_cpu_ftrs device-tree binding is
928 used for CPU feature discovery and setup (if it
930 off: Do not use it, fall back to legacy cpu table.
931 known: Do not pass through unknown features to guests
932 or userspace, only those that the kernel is aware of.
934 dump_apple_properties [X86]
935 Dump name and content of EFI device properties on
936 x86 Macs. Useful for driver authors to determine
937 what data is available or for reverse-engineering.
939 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
940 module.dyndbg[="val"]
941 Enable debug messages at boot time. See
942 Documentation/admin-guide/dynamic-debug-howto.rst
945 nompx [X86] Disables Intel Memory Protection Extensions.
946 See Documentation/x86/intel_mpx.txt for more
947 information about the feature.
949 nopku [X86] Disable Memory Protection Keys CPU feature found
952 module.async_probe [KNL]
953 Enable asynchronous probe on this module.
955 early_ioremap_debug [KNL]
956 Enable debug messages in early_ioremap support. This
957 is useful for tracking down temporary early mappings
958 which are not unmapped.
960 earlycon= [KNL] Output early console device and options.
962 [ARM64] The early console is determined by the
963 stdout-path property in device tree's chosen node,
964 or determined by the ACPI SPCR table.
966 [X86] When used with no options the early console is
967 determined by the ACPI SPCR table.
969 cdns,<addr>[,options]
970 Start an early, polled-mode console on a Cadence
971 (xuartps) serial port at the specified address. Only
972 supported option is baud rate. If baud rate is not
973 specified, the serial port must already be setup and
976 uart[8250],io,<addr>[,options]
977 uart[8250],mmio,<addr>[,options]
978 uart[8250],mmio32,<addr>[,options]
979 uart[8250],mmio32be,<addr>[,options]
980 uart[8250],0x<addr>[,options]
981 Start an early, polled-mode console on the 8250/16550
982 UART at the specified I/O port or MMIO address.
983 MMIO inter-register address stride is either 8-bit
984 (mmio) or 32-bit (mmio32 or mmio32be).
985 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
986 to be equivalent to 'mmio'. 'options' are specified
987 in the same format described for "console=ttyS<n>"; if
988 unspecified, the h/w is not initialized.
992 Start an early, polled-mode console on a pl011 serial
993 port at the specified address. The pl011 serial port
994 must already be setup and configured. Options are not
995 yet supported. If 'mmio32' is specified, then only
996 the driver will use only 32-bit accessors to read/write
997 the device registers.
1000 Start an early, polled-mode console on a meson serial
1001 port at the specified address. The serial port must
1002 already be setup and configured. Options are not yet
1006 Start an early, polled-mode console on an msm serial
1007 port at the specified address. The serial port
1008 must already be setup and configured. Options are not
1011 msm_serial_dm,<addr>
1012 Start an early, polled-mode console on an msm serial
1013 dm port at the specified address. The serial port
1014 must already be setup and configured. Options are not
1018 Start an early, polled-mode console on a serial port
1019 of an Actions Semi SoC, such as S500 or S900, at the
1020 specified address. The serial port must already be
1021 setup and configured. Options are not yet supported.
1023 smh Use ARM semihosting calls for early console.
1031 Use early console provided by serial driver available
1032 on Samsung SoCs, requires selecting proper type and
1033 a correct base address of the selected UART port. The
1034 serial port must already be setup and configured.
1035 Options are not yet supported.
1038 Start an early, polled-mode console on a lantiq serial
1039 (lqasc) port at the specified address. The serial port
1040 must already be setup and configured. Options are not
1045 Use early console provided by Freescale LP UART driver
1046 found on Freescale Vybrid and QorIQ LS1021A processors.
1047 A valid base address must be provided, and the serial
1048 port must already be setup and configured.
1051 Start an early, polled-mode console on the
1052 Armada 3700 serial port at the specified
1053 address. The serial port must already be setup
1054 and configured. Options are not yet supported.
1057 Start an early, polled-mode console on a Qualcomm
1058 Generic Interface (GENI) based serial port at the
1059 specified address. The serial port must already be
1060 setup and configured. Options are not yet supported.
1062 earlyprintk= [X86,SH,ARM,M68k,S390]
1067 earlyprintk=serial[,ttySn[,baudrate]]
1068 earlyprintk=serial[,0x...[,baudrate]]
1069 earlyprintk=ttySn[,baudrate]
1070 earlyprintk=dbgp[debugController#]
1071 earlyprintk=pciserial[,force],bus:device.function[,baudrate]
1072 earlyprintk=xdbc[xhciController#]
1074 earlyprintk is useful when the kernel crashes before
1075 the normal console is initialized. It is not enabled by
1076 default because it has some cosmetic problems.
1078 Append ",keep" to not disable it when the real console
1081 Only one of vga, efi, serial, or usb debug port can
1084 Currently only ttyS0 and ttyS1 may be specified by
1085 name. Other I/O ports may be explicitly specified
1086 on some architectures (x86 and arm at least) by
1087 replacing ttySn with an I/O port address, like this:
1088 earlyprintk=serial,0x1008,115200
1089 You can find the port for a given device in
1090 /proc/tty/driver/serial:
1091 2: uart:ST16650V2 port:00001008 irq:18 ...
1093 Interaction with the standard serial driver is not
1096 The VGA and EFI output is eventually overwritten by
1099 The xen output can only be used by Xen PV guests.
1101 The sclp output can only be used on s390.
1103 The optional "force" to "pciserial" enables use of a
1104 PCI device even when its classcode is not of the
1107 edac_report= [HW,EDAC] Control how to report EDAC event
1108 Format: {"on" | "off" | "force"}
1109 on: enable EDAC to report H/W event. May be overridden
1110 by other higher priority error reporting module.
1111 off: disable H/W event reporting through EDAC.
1112 force: enforce the use of EDAC to report H/W event.
1115 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1118 This is designed to be used in conjunction with
1119 the boot argument: earlyprintk=vga
1122 Format: {"off" | "on" | "skip[mbr]"}
1125 Format: { "old_map", "nochunk", "noruntime", "debug" }
1126 old_map [X86-64]: switch to the old ioremap-based EFI
1127 runtime services mapping. 32-bit still uses this one by
1129 nochunk: disable reading files in "chunks" in the EFI
1130 boot stub, as chunking can cause problems with some
1131 firmware implementations.
1132 noruntime : disable EFI runtime services support
1133 debug: enable misc debug output
1135 efi_no_storage_paranoia [EFI; X86]
1136 Using this parameter you can use more than 50% of
1137 your efi variable storage. Use this parameter only if
1138 you are really sure that your UEFI does sane gc and
1139 fulfills the spec otherwise your board may brick.
1141 efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
1142 Add arbitrary attribute to specific memory range by
1143 updating original EFI memory map.
1144 Region of memory which aa attribute is added to is
1146 If efi_fake_mem=2G@4G:0x10000,2G@0x10a0000000:0x10000
1147 is specified, EFI_MEMORY_MORE_RELIABLE(0x10000)
1148 attribute is added to range 0x100000000-0x180000000 and
1149 0x10a0000000-0x1120000000.
1151 Using this parameter you can do debugging of EFI memmap
1152 related feature. For example, you can do debugging of
1153 Address Range Mirroring feature even if your box
1156 efivar_ssdt= [EFI; X86] Name of an EFI variable that contains an SSDT
1157 that is to be dynamically loaded by Linux. If there are
1158 multiple variables with the same name but with different
1159 vendor GUIDs, all of them will be loaded. See
1160 Documentation/acpi/ssdt-overlays.txt for details.
1163 eisa_irq_edge= [PARISC,HW]
1164 See header of drivers/parisc/eisa.c.
1167 See comment before function elanfreq_setup() in
1168 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1171 Format: {"cfq" | "deadline" | "noop"}
1172 See Documentation/block/cfq-iosched.txt and
1173 Documentation/block/deadline-iosched.txt for details.
1175 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
1176 Specifies physical address of start of kernel core
1177 image elf header and optionally the size. Generally
1178 kexec loader will pass this option to capture kernel.
1179 See Documentation/kdump/kdump.txt for details.
1181 enable_mtrr_cleanup [X86]
1182 The kernel tries to adjust MTRR layout from continuous
1183 to discrete, to make X server driver able to add WB
1184 entry later. This parameter enables that.
1186 enable_timer_pin_1 [X86]
1187 Enable PIN 1 of APIC timer
1188 Can be useful to work around chipset bugs
1189 (in particular on some ATI chipsets).
1190 The kernel tries to set a reasonable default.
1192 enforcing [SELINUX] Set initial enforcing status.
1194 See security/selinux/Kconfig help text.
1195 0 -- permissive (log only, no denials).
1196 1 -- enforcing (deny and log).
1198 Value can be changed at runtime via /selinux/enforce.
1201 Disable Error Record Serialization Table (ERST)
1204 ether= [HW,NET] Ethernet cards parameters
1205 This option is obsoleted by the "netdev=" option, which
1206 has equivalent usage. See its documentation for details.
1210 Permit 'security.evm' to be updated regardless of
1211 current integrity status.
1215 fail_make_request=[KNL]
1216 General fault injection mechanism.
1217 Format: <interval>,<probability>,<space>,<times>
1218 See also Documentation/fault-injection/.
1221 See Documentation/blockdev/floppy.txt.
1223 force_pal_cache_flush
1224 [IA-64] Avoid check_sal_cache_flush which may hang on
1225 buggy SAL_CACHE_FLUSH implementations. Using this
1226 parameter will force ia64_sal_cache_flush to call
1227 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1230 Forcefully enable Physical Address Extension (PAE).
1231 Many Pentium M systems disable PAE but may have a
1232 functionally usable PAE implementation.
1233 Warning: use of this parameter will taint the kernel
1234 and may cause unknown problems.
1237 [FTRACE] will set and start the specified tracer
1238 as early as possible in order to facilitate early
1241 ftrace_dump_on_oops[=orig_cpu]
1242 [FTRACE] will dump the trace buffers on oops.
1243 If no parameter is passed, ftrace will dump
1244 buffers of all CPUs, but if you pass orig_cpu, it will
1245 dump only the buffer of the CPU that triggered the
1248 ftrace_filter=[function-list]
1249 [FTRACE] Limit the functions traced by the function
1250 tracer at boot up. function-list is a comma separated
1251 list of functions. This list can be changed at run
1252 time by the set_ftrace_filter file in the debugfs
1255 ftrace_notrace=[function-list]
1256 [FTRACE] Do not trace the functions specified in
1257 function-list. This list can be changed at run time
1258 by the set_ftrace_notrace file in the debugfs
1261 ftrace_graph_filter=[function-list]
1262 [FTRACE] Limit the top level callers functions traced
1263 by the function graph tracer at boot up.
1264 function-list is a comma separated list of functions
1265 that can be changed at run time by the
1266 set_graph_function file in the debugfs tracing directory.
1268 ftrace_graph_notrace=[function-list]
1269 [FTRACE] Do not trace from the functions specified in
1270 function-list. This list is a comma separated list of
1271 functions that can be changed at run time by the
1272 set_graph_notrace file in the debugfs tracing directory.
1274 ftrace_graph_max_depth=<uint>
1275 [FTRACE] Used with the function graph tracer. This is
1276 the max depth it will trace into a function. This value
1277 can be changed at run time by the max_graph_depth file
1278 in the tracefs tracing directory. default: 0 (no limit)
1281 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1282 support via parallel port (up to 5 devices per port)
1283 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1284 See also Documentation/input/devices/joystick-parport.rst
1288 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1292 gcov_persist= [GCOV] When non-zero (default), profiling data for
1293 kernel modules is saved and remains accessible via
1294 debugfs, even when the module is unloaded/reloaded.
1295 When zero, profiling data is discarded and associated
1296 debugfs files are removed at module unload time.
1298 goldfish [X86] Enable the goldfish android emulator platform.
1299 Don't use this when you are not running on the
1302 gpt [EFI] Forces disk with valid GPT signature but
1303 invalid Protective MBR to be treated as GPT. If the
1304 primary GPT is corrupted, it enables the backup/alternate
1305 GPT to be used instead.
1307 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1308 the "Enable 0" bit of the configuration register.
1311 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1312 the "Enable 0" bit of the configuration register.
1315 grcan.select= [HW] Select which physical interface to use.
1318 grcan.txsize= [HW] Sets the size of the tx buffer.
1319 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1321 grcan.rxsize= [HW] Sets the size of the rx buffer.
1322 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1325 gpio-mockup.gpio_mockup_ranges
1326 [HW] Sets the ranges of gpiochip of for this device.
1327 Format: <start1>,<end1>,<start2>,<end2>...
1329 hardlockup_all_cpu_backtrace=
1330 [KNL] Should the hard-lockup detector generate
1331 backtraces on all cpus.
1334 hashdist= [KNL,NUMA] Large hashes allocated during boot
1335 are distributed across NUMA nodes. Defaults on
1336 for 64-bit NUMA, off otherwise.
1337 Format: 0 | 1 (for off | on)
1339 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1341 hd= [EIDE] (E)IDE hard drive subsystem geometry
1342 Format: <cyl>,<head>,<sect>
1345 Disable Hardware Error Source Table (HEST) support;
1346 corresponding firmware-first mode error processing
1347 logic will be disabled.
1349 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1350 size of <nn>. This works even on boxes that have no
1351 highmem otherwise. This also works to reduce highmem
1352 size on bigger boxes.
1354 highres= [KNL] Enable/disable high resolution timer mode.
1355 Valid parameters: "on", "off"
1359 See Documentation/isdn/README.HiSax.
1363 hpet= [X86-32,HPET] option to control HPET usage
1364 Format: { enable (default) | disable | force |
1366 disable: disable HPET and use PIT instead
1367 force: allow force enabled of undocumented chips (ICH4,
1369 verbose: show contents of HPET registers during setup
1371 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1372 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1374 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1375 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
1376 On x86-64 and powerpc, this option can be specified
1377 multiple times interleaved with hugepages= to reserve
1378 huge pages of different sizes. Valid pages sizes on
1379 x86-64 are 2M (when the CPU supports "pse") and 1G
1380 (when the CPU supports the "pdpe1gb" cpuinfo flag).
1383 [KNL] Should the hung task detector generate panics.
1386 A nonzero value instructs the kernel to panic when a
1387 hung task is detected. The default value is controlled
1388 by the CONFIG_BOOTPARAM_HUNG_TASK_PANIC build-time
1389 option. The value selected by this boot parameter can
1390 be changed later by the kernel.hung_task_panic sysctl.
1392 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1393 terminal devices. Valid values: 0..8
1394 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1395 If specified, z/VM IUCV HVC accepts connections
1396 from listed z/VM user IDs only.
1398 hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
1399 which allow the hypervisor to 'idle' the
1400 guest on lock contention.
1403 Do not unregister boot console at start. This is only
1404 useful for debugging when something happens in the window
1405 between unregistering the boot console and initializing
1408 i2c_bus= [HW] Override the default board specific I2C bus speed
1409 or register an additional I2C bus that is not
1410 registered from board initialization code.
1414 i8042.debug [HW] Toggle i8042 debug mode
1415 i8042.unmask_kbd_data
1416 [HW] Enable printing of interrupt data from the KBD port
1417 (disabled by default, and as a pre-condition
1418 requires that i8042.debug=1 be enabled)
1419 i8042.direct [HW] Put keyboard port into non-translated mode
1420 i8042.dumbkbd [HW] Pretend that controller can only read data from
1421 keyboard and cannot control its state
1422 (Don't attempt to blink the leds)
1423 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
1424 i8042.nokbd [HW] Don't check/create keyboard port
1425 i8042.noloop [HW] Disable the AUX Loopback command while probing
1427 i8042.nomux [HW] Don't check presence of an active multiplexing
1429 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1431 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1432 i8042.reset [HW] Reset the controller during init, cleanup and
1433 suspend-to-ram transitions, only during s2r
1434 transitions, or never reset
1435 Format: { 1 | Y | y | 0 | N | n }
1436 1, Y, y: always reset controller
1437 0, N, n: don't ever reset controller
1438 Default: only on s2r transitions on x86; most other
1439 architectures force reset to be always executed
1440 i8042.unlock [HW] Unlock (ignore) the keylock
1441 i8042.kbdreset [HW] Reset device connected to KBD port
1445 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1446 indicates that the driver is running on unsupported
1448 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1449 does not match list of supported models.
1451 [HW] Report power status in /proc/i8k
1452 (disabled by default)
1453 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1456 i915.invert_brightness=
1457 [DRM] Invert the sense of the variable that is used to
1458 set the brightness of the panel backlight. Normally a
1459 brightness value of 0 indicates backlight switched off,
1460 and the maximum of the brightness value sets the backlight
1461 to maximum brightness. If this parameter is set to 0
1462 (default) and the machine requires it, or this parameter
1463 is set to 1, a brightness value of 0 sets the backlight
1464 to maximum brightness, and the maximum of the brightness
1465 value switches the backlight off.
1466 -1 -- never invert brightness
1467 0 -- machine default
1468 1 -- force brightness inversion
1471 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1473 ide-core.nodma= [HW] (E)IDE subsystem
1474 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
1475 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1476 .cdrom .chs .ignore_cable are additional options
1477 See Documentation/ide/ide.txt.
1479 ide-generic.probe-mask= [HW] (E)IDE subsystem
1481 Probe mask for legacy ISA IDE ports. Depending on
1482 platform up to 6 ports are supported, enabled by
1483 setting corresponding bits in the mask to 1. The
1484 default value is 0x0, which has a special meaning.
1485 On systems that have PCI, it triggers scanning the
1486 PCI bus for the first and the second port, which
1487 are then probed. On systems without PCI the value
1488 of 0x0 enables probing the two first ports as if it
1491 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1492 Claim all unknown PCI IDE storage controllers.
1495 Format: idle=poll, idle=halt, idle=nomwait
1496 Poll forces a polling idle loop that can slightly
1497 improve the performance of waking up a idle CPU, but
1498 will use a lot of power and make the system run hot.
1500 idle=halt: Halt is forced to be used for CPU idle.
1501 In such case C2/C3 won't be used again.
1502 idle=nomwait: Disable mwait for CPU C-states
1504 ieee754= [MIPS] Select IEEE Std 754 conformance mode
1505 Format: { strict | legacy | 2008 | relaxed }
1508 Choose which programs will be accepted for execution
1509 based on the IEEE 754 NaN encoding(s) supported by
1510 the FPU and the NaN encoding requested with the value
1511 of an ELF file header flag individually set by each
1512 binary. Hardware implementations are permitted to
1513 support either or both of the legacy and the 2008 NaN
1516 Available settings are as follows:
1517 strict accept binaries that request a NaN encoding
1518 supported by the FPU
1519 legacy only accept legacy-NaN binaries, if supported
1521 2008 only accept 2008-NaN binaries, if supported
1523 relaxed accept any binaries regardless of whether
1524 supported by the FPU
1526 The FPU emulator is always able to support both NaN
1527 encodings, so if no FPU hardware is present or it has
1528 been disabled with 'nofpu', then the settings of
1529 'legacy' and '2008' strap the emulator accordingly,
1530 'relaxed' straps the emulator for both legacy-NaN and
1531 2008-NaN, whereas 'strict' enables legacy-NaN only on
1532 legacy processors and both NaN encodings on MIPS32 or
1535 The setting for ABS.fmt/NEG.fmt instruction execution
1536 mode generally follows that for the NaN encoding,
1537 except where unsupported by hardware.
1539 ignore_loglevel [KNL]
1540 Ignore loglevel setting - this will print /all/
1541 kernel messages to the console. Useful for debugging.
1542 We also add it as printk module parameter, so users
1543 could change it dynamically, usually by
1544 /sys/module/printk/parameters/ignore_loglevel.
1547 Ignore RLIMIT_DATA setting for data mappings,
1548 print warning at first misuse. Can be changed via
1549 /sys/module/kernel/parameters/ignore_rlimit_data.
1551 ihash_entries= [KNL]
1552 Set number of hash buckets for inode cache.
1554 ima_appraise= [IMA] appraise integrity measurements
1555 Format: { "off" | "enforce" | "fix" | "log" }
1558 ima_appraise_tcb [IMA]
1559 The builtin appraise policy appraises all files
1562 ima_canonical_fmt [IMA]
1563 Use the canonical format for the binary runtime
1564 measurements, instead of host native format.
1567 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1571 The list of supported hash algorithms is defined
1572 in crypto/hash_info.h.
1575 The builtin policies to load during IMA setup.
1576 Format: "tcb | appraise_tcb | secure_boot |
1579 The "tcb" policy measures all programs exec'd, files
1580 mmap'd for exec, and all files opened with the read
1581 mode bit set by either the effective uid (euid=0) or
1584 The "appraise_tcb" policy appraises the integrity of
1585 all files owned by root. (This is the equivalent
1586 of ima_appraise_tcb.)
1588 The "secure_boot" policy appraises the integrity
1589 of files (eg. kexec kernel image, kernel modules,
1590 firmware, policy, etc) based on file signatures.
1592 The "fail_securely" policy forces file signature
1593 verification failure also on privileged mounted
1594 filesystems with the SB_I_UNVERIFIABLE_SIGNATURE
1597 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
1598 Load a policy which meets the needs of the Trusted
1599 Computing Base. This means IMA will measure all
1600 programs exec'd, files mmap'd for exec, and all files
1601 opened for read by uid=0.
1604 Select one of defined IMA measurements template formats.
1605 Formats: { "ima" | "ima-ng" | "ima-sig" }
1609 [IMA] Define a custom template format.
1610 Format: { "field1|...|fieldN" }
1612 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1613 Format: <min_file_size>
1614 Set the minimal file size for using asynchronous hash.
1615 If left unspecified, ahash usage is disabled.
1617 ahash performance varies for different data sizes on
1618 different crypto accelerators. This option can be used
1619 to achieve the best performance for a particular HW.
1621 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1623 Set hashing buffer size. Default: 4k.
1625 ahash performance varies for different chunk sizes on
1626 different crypto accelerators. This option can be used
1627 to achieve best performance for particular HW.
1631 Run specified binary instead of /sbin/init as init
1634 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1635 for working out where the kernel is dying during
1638 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1639 initcall functions. Useful for debugging built-in
1640 modules and initcalls.
1642 initrd= [BOOT] Specify the location of the initial ramdisk
1644 init_pkru= [x86] Specify the default memory protection keys rights
1645 register contents for all processes. 0x55555554 by
1646 default (disallow access to all but pkey 0). Can
1647 override in debugfs after boot.
1649 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1652 int_pln_enable [x86] Enable power limit notification interrupt
1654 integrity_audit=[IMA]
1655 Format: { "0" | "1" }
1656 0 -- basic integrity auditing messages. (Default)
1657 1 -- additional integrity auditing messages.
1659 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
1661 Enable intel iommu driver.
1663 Disable intel iommu driver.
1664 igfx_off [Default Off]
1665 By default, gfx is mapped as normal device. If a gfx
1666 device has a dedicated DMAR unit, the DMAR unit is
1667 bypassed by not enabling DMAR with this option. In
1668 this case, gfx device will use physical address for
1671 With this option iommu will not optimize to look
1672 for io virtual address below 32-bit forcing dual
1673 address cycle on pci bus for cards supporting greater
1674 than 32-bit addressing. The default is to look
1675 for translation below 32-bit and if not available
1676 then look in the higher range.
1677 strict [Default Off]
1678 With this option on every unmap_single operation will
1679 result in a hardware IOTLB flush operation as opposed
1680 to batching them for performance.
1681 sp_off [Default Off]
1682 By default, super page will be supported if Intel IOMMU
1683 has the capability. With this option, super page will
1685 ecs_off [Default Off]
1686 By default, extended context tables will be supported if
1687 the hardware advertises that it has support both for the
1688 extended tables themselves, and also PASID support. With
1689 this option set, extended tables will not be used even
1690 on hardware which claims to support them.
1691 tboot_noforce [Default Off]
1692 Do not force the Intel IOMMU enabled under tboot.
1693 By default, tboot will force Intel IOMMU on, which
1694 could harm performance of some high-throughput
1695 devices like 40GBit network cards, even if identity
1697 Note that using this option lowers the security
1698 provided by tboot because it makes the system
1699 vulnerable to DMA attacks.
1701 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1702 0 disables intel_idle and fall back on acpi_idle.
1703 1 to 9 specify maximum depth of C-state.
1707 Do not enable intel_pstate as the default
1708 scaling driver for the supported processors
1710 Use intel_pstate as a scaling driver, but configure it
1711 to work with generic cpufreq governors (instead of
1712 enabling its internal governor). This mode cannot be
1713 used along with the hardware-managed P-states (HWP)
1716 Enable intel_pstate on systems that prohibit it by default
1717 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1718 instead of acpi-cpufreq may disable platform features, such
1719 as thermal controls and power capping, that rely on ACPI
1720 P-States information being indicated to OSPM and therefore
1721 should be used with caution. This option does not work with
1722 processors that aren't supported by the intel_pstate driver
1723 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
1725 Do not enable hardware P state control (HWP)
1728 Only load intel_pstate on systems which support
1729 hardware P state control (HWP) if available.
1731 Enforce ACPI _PPC performance limits. If the Fixed ACPI
1732 Description Table, specifies preferred power management
1733 profile as "Enterprise Server" or "Performance Server",
1734 then this feature is turned on by default.
1736 Allow per-logical-CPU P-State performance control limits using
1737 cpufreq sysfs interface
1739 intremap= [X86-64, Intel-IOMMU]
1740 on enable Interrupt Remapping (default)
1741 off disable Interrupt Remapping
1742 nosid disable Source ID checking
1744 BIOS x2APIC opt-out request will be ignored
1745 nopost disable Interrupt Posting
1747 iomem= Disable strict checking of access to MMIO memory
1748 strict regions from userspace.
1763 nobypass [PPC/POWERNV]
1764 Disable IOMMU bypass, using IOMMU for PCI devices.
1766 iommu.strict= [ARM64] Configure TLB invalidation behaviour
1767 Format: { "0" | "1" }
1769 Request that DMA unmap operations use deferred
1770 invalidation of hardware TLBs, for increased
1771 throughput at the cost of reduced device isolation.
1772 Will fall back to strict mode if not supported by
1773 the relevant IOMMU driver.
1774 1 - Strict mode (default).
1775 DMA unmap operations invalidate IOMMU hardware TLBs
1779 [ARM64] Configure DMA to bypass the IOMMU by default.
1780 Format: { "0" | "1" }
1781 0 - Use IOMMU translation for DMA.
1782 1 - Bypass the IOMMU for DMA.
1783 unset - Use value of CONFIG_IOMMU_DEFAULT_PASSTHROUGH.
1785 io7= [HW] IO7 for Marvel based alpha systems
1786 See comment before marvel_specify_io7 in
1787 arch/alpha/kernel/core_marvel.c.
1789 io_delay= [X86] I/O delay method
1791 Standard port 0x80 based delay
1793 Alternate port 0xed based delay (needed on some systems)
1795 Simple two microseconds delay
1800 See Documentation/filesystems/nfs/nfsroot.txt.
1802 irqaffinity= [SMP] Set the default irq affinity mask
1803 The argument is a cpu list, as described above.
1805 irqchip.gicv2_force_probe=
1808 Force the kernel to look for the second 4kB page
1809 of a GICv2 controller even if the memory range
1810 exposed by the device tree is too small.
1812 irqchip.gicv3_nolpi=
1814 Force the kernel to ignore the availability of
1815 LPIs (and by consequence ITSs). Intended for system
1816 that use the kernel as a bootloader, and thus want
1817 to let secondary kernels in charge of setting up
1821 When an interrupt is not handled search all handlers
1822 for it. Intended to get systems with badly broken
1826 When an interrupt is not handled search all handlers
1827 for it. Also check all handlers each timer
1828 interrupt. Intended to get systems with badly broken
1832 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1834 isolcpus= [KNL,SMP,ISOL] Isolate a given set of CPUs from disturbance.
1835 [Deprecated - use cpusets instead]
1836 Format: [flag-list,]<cpu-list>
1838 Specify one or more CPUs to isolate from disturbances
1839 specified in the flag list (default: domain):
1842 Disable the tick when a single task runs.
1844 A residual 1Hz tick is offloaded to workqueues, which you
1845 need to affine to housekeeping through the global
1846 workqueue's affinity configured via the
1847 /sys/devices/virtual/workqueue/cpumask sysfs file, or
1848 by using the 'domain' flag described below.
1850 NOTE: by default the global workqueue runs on all CPUs,
1851 so to protect individual CPUs the 'cpumask' file has to
1852 be configured manually after bootup.
1855 Isolate from the general SMP balancing and scheduling
1856 algorithms. Note that performing domain isolation this way
1857 is irreversible: it's not possible to bring back a CPU to
1858 the domains once isolated through isolcpus. It's strongly
1859 advised to use cpusets instead to disable scheduler load
1860 balancing through the "cpuset.sched_load_balance" file.
1861 It offers a much more flexible interface where CPUs can
1862 move in and out of an isolated set anytime.
1864 You can move a process onto or off an "isolated" CPU via
1865 the CPU affinity syscalls or cpuset.
1866 <cpu number> begins at 0 and the maximum value is
1867 "number of CPUs in system - 1".
1869 The format of <cpu-list> is described above.
1875 ivrs_ioapic [HW,X86_64]
1876 Provide an override to the IOAPIC-ID<->DEVICE-ID
1877 mapping provided in the IVRS ACPI table. For
1878 example, to map IOAPIC-ID decimal 10 to
1879 PCI device 00:14.0 write the parameter as:
1880 ivrs_ioapic[10]=00:14.0
1882 ivrs_hpet [HW,X86_64]
1883 Provide an override to the HPET-ID<->DEVICE-ID
1884 mapping provided in the IVRS ACPI table. For
1885 example, to map HPET-ID decimal 0 to
1886 PCI device 00:14.0 write the parameter as:
1887 ivrs_hpet[0]=00:14.0
1889 ivrs_acpihid [HW,X86_64]
1890 Provide an override to the ACPI-HID:UID<->DEVICE-ID
1891 mapping provided in the IVRS ACPI table. For
1892 example, to map UART-HID:UID AMD0020:0 to
1893 PCI device 00:14.5 write the parameter as:
1894 ivrs_acpihid[00:14.5]=AMD0020:0
1896 js= [HW,JOY] Analog joystick
1897 See Documentation/input/joydev/joystick.rst.
1900 When CONFIG_RANDOMIZE_BASE is set, this disables
1901 kernel and module base offset ASLR (Address Space
1902 Layout Randomization).
1905 [KNL] Enforce KASAN (Kernel Address Sanitizer) to print
1906 report on every invalid memory access. Without this
1907 parameter KASAN will print report only for the first
1912 kernelcore= [KNL,X86,IA-64,PPC]
1913 Format: nn[KMGTPE] | nn% | "mirror"
1914 This parameter specifies the amount of memory usable by
1915 the kernel for non-movable allocations. The requested
1916 amount is spread evenly throughout all nodes in the
1917 system as ZONE_NORMAL. The remaining memory is used for
1918 movable memory in its own zone, ZONE_MOVABLE. In the
1919 event, a node is too small to have both ZONE_NORMAL and
1920 ZONE_MOVABLE, kernelcore memory will take priority and
1921 other nodes will have a larger ZONE_MOVABLE.
1923 ZONE_MOVABLE is used for the allocation of pages that
1924 may be reclaimed or moved by the page migration
1925 subsystem. Note that allocations like PTEs-from-HighMem
1926 still use the HighMem zone if it exists, and the Normal
1927 zone if it does not.
1929 It is possible to specify the exact amount of memory in
1930 the form of "nn[KMGTPE]", a percentage of total system
1931 memory in the form of "nn%", or "mirror". If "mirror"
1932 option is specified, mirrored (reliable) memory is used
1933 for non-movable allocations and remaining memory is used
1934 for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
1935 are exclusive, so you cannot specify multiple forms.
1937 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1938 Format: <Controller#>[,poll interval]
1939 The controller # is the number of the ehci usb debug
1940 port as it is probed via PCI. The poll interval is
1941 optional and is the number seconds in between
1942 each poll cycle to the debug port in case you need
1943 the functionality for interrupting the kernel with
1944 gdb or control-c on the dbgp connection. When
1945 not using this parameter you use sysrq-g to break into
1946 the kernel debugger.
1948 kgdboc= [KGDB,HW] kgdb over consoles.
1949 Requires a tty driver that supports console polling,
1950 or a supported polling keyboard driver (non-usb).
1951 Serial only format: <serial_device>[,baud]
1952 keyboard only format: kbd
1953 keyboard and serial format: kbd,<serial_device>[,baud]
1954 Optional Kernel mode setting:
1955 kms, kbd format: kms,kbd
1956 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
1958 kgdbwait [KGDB] Stop kernel execution and enter the
1959 kernel debugger at the earliest opportunity.
1961 kmac= [MIPS] korina ethernet MAC address.
1962 Configure the RouterBoard 532 series on-chip
1963 Ethernet adapter MAC address.
1965 kmemleak= [KNL] Boot-time kmemleak enable/disable
1966 Valid arguments: on, off
1968 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1971 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1972 Default is 0 (don't ignore, but inject #GP)
1974 kvm.enable_vmware_backdoor=[KVM] Support VMware backdoor PV interface.
1975 Default is false (don't support).
1977 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1981 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
1982 Default is 1 (enabled)
1984 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1986 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
1988 kvm-arm.vgic_v3_group0_trap=
1989 [KVM,ARM] Trap guest accesses to GICv3 group-0
1992 kvm-arm.vgic_v3_group1_trap=
1993 [KVM,ARM] Trap guest accesses to GICv3 group-1
1996 kvm-arm.vgic_v3_common_trap=
1997 [KVM,ARM] Trap guest accesses to GICv3 common
2000 kvm-arm.vgic_v4_enable=
2001 [KVM,ARM] Allow use of GICv4 for direct injection of
2004 kvm-intel.ept= [KVM,Intel] Disable extended page tables
2005 (virtualized MMU) support on capable Intel chips.
2006 Default is 1 (enabled)
2008 kvm-intel.emulate_invalid_guest_state=
2009 [KVM,Intel] Enable emulation of invalid guest states
2010 Default is 0 (disabled)
2012 kvm-intel.flexpriority=
2013 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
2014 Default is 1 (enabled)
2017 [KVM,Intel] Enable VMX nesting (nVMX).
2018 Default is 0 (disabled)
2020 kvm-intel.unrestricted_guest=
2021 [KVM,Intel] Disable unrestricted guest feature
2022 (virtualized real and unpaged mode) on capable
2023 Intel chips. Default is 1 (enabled)
2025 kvm-intel.vmentry_l1d_flush=[KVM,Intel] Mitigation for L1 Terminal Fault
2028 Valid arguments: never, cond, always
2030 always: L1D cache flush on every VMENTER.
2031 cond: Flush L1D on VMENTER only when the code between
2032 VMEXIT and VMENTER can leak host memory.
2033 never: Disables the mitigation
2035 Default is cond (do L1 cache flush in specific instances)
2037 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
2038 feature (tagged TLBs) on capable Intel chips.
2039 Default is 1 (enabled)
2041 l1tf= [X86] Control mitigation of the L1TF vulnerability on
2044 The kernel PTE inversion protection is unconditionally
2045 enabled and cannot be disabled.
2048 Provides all available mitigations for the
2049 L1TF vulnerability. Disables SMT and
2050 enables all mitigations in the
2051 hypervisors, i.e. unconditional L1D flush.
2053 SMT control and L1D flush control via the
2054 sysfs interface is still possible after
2055 boot. Hypervisors will issue a warning
2056 when the first VM is started in a
2057 potentially insecure configuration,
2058 i.e. SMT enabled or L1D flush disabled.
2061 Same as 'full', but disables SMT and L1D
2062 flush runtime control. Implies the
2063 'nosmt=force' command line option.
2064 (i.e. sysfs control of SMT is disabled.)
2067 Leaves SMT enabled and enables the default
2068 hypervisor mitigation, i.e. conditional
2071 SMT control and L1D flush control via the
2072 sysfs interface is still possible after
2073 boot. Hypervisors will issue a warning
2074 when the first VM is started in a
2075 potentially insecure configuration,
2076 i.e. SMT enabled or L1D flush disabled.
2080 Disables SMT and enables the default
2081 hypervisor mitigation.
2083 SMT control and L1D flush control via the
2084 sysfs interface is still possible after
2085 boot. Hypervisors will issue a warning
2086 when the first VM is started in a
2087 potentially insecure configuration,
2088 i.e. SMT enabled or L1D flush disabled.
2091 Same as 'flush', but hypervisors will not
2092 warn when a VM is started in a potentially
2093 insecure configuration.
2096 Disables hypervisor mitigations and doesn't
2101 For details see: Documentation/admin-guide/l1tf.rst
2107 lapic [X86-32,APIC] Enable the local APIC even if BIOS
2110 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
2111 value for LAPIC timer one-shot implementation. Default
2112 back to the programmable timer unit in the LAPIC.
2114 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
2117 libata.dma= [LIBATA] DMA control
2118 libata.dma=0 Disable all PATA and SATA DMA
2119 libata.dma=1 PATA and SATA Disk DMA only
2120 libata.dma=2 ATAPI (CDROM) DMA only
2121 libata.dma=4 Compact Flash DMA only
2122 Combinations also work, so libata.dma=3 enables DMA
2123 for disks and CDROMs, but not CFs.
2125 libata.ignore_hpa= [LIBATA] Ignore HPA limit
2126 libata.ignore_hpa=0 keep BIOS limits (default)
2127 libata.ignore_hpa=1 ignore limits, using full disk
2129 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
2133 libata.force= [LIBATA] Force configurations. The format is comma
2134 separated list of "[ID:]VAL" where ID is
2135 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
2136 matching port, link or device. Basically, it matches
2137 the ATA ID string printed on console by libata. If
2138 the whole ID part is omitted, the last PORT and DEVICE
2139 values are used. If ID hasn't been specified yet, the
2140 configuration applies to all ports, links and devices.
2142 If only DEVICE is omitted, the parameter applies to
2143 the port and all links and devices behind it. DEVICE
2144 number of 0 either selects the first device or the
2145 first fan-out link behind PMP device. It does not
2146 select the host link. DEVICE number of 15 selects the
2147 host link and device attached to it.
2149 The VAL specifies the configuration to force. As long
2150 as there's no ambiguity shortcut notation is allowed.
2151 For example, both 1.5 and 1.5G would work for 1.5Gbps.
2152 The following configurations can be forced.
2154 * Cable type: 40c, 80c, short40c, unk, ign or sata.
2155 Any ID with matching PORT is used.
2157 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
2159 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
2160 udma[/][16,25,33,44,66,100,133] notation is also
2163 * [no]ncq: Turn on or off NCQ.
2165 * [no]ncqtrim: Turn off queued DSM TRIM.
2167 * nohrst, nosrst, norst: suppress hard, soft
2170 * rstonce: only attempt one reset during
2171 hot-unplug link recovery
2173 * dump_id: dump IDENTIFY data.
2175 * atapi_dmadir: Enable ATAPI DMADIR bridge support
2177 * disable: Disable this device.
2179 If there are multiple matching configurations changing
2180 the same attribute, the last one is used.
2182 memblock=debug [KNL] Enable memblock debug messages.
2184 load_ramdisk= [RAM] List of ramdisks to load from floppy
2185 See Documentation/blockdev/ramdisk.txt.
2187 lockd.nlm_grace_period=P [NFS] Assign grace period.
2190 lockd.nlm_tcpport=N [NFS] Assign TCP port.
2193 lockd.nlm_timeout=T [NFS] Assign timeout value.
2196 lockd.nlm_udpport=M [NFS] Assign UDP port.
2199 locktorture.nreaders_stress= [KNL]
2200 Set the number of locking read-acquisition kthreads.
2201 Defaults to being automatically set based on the
2202 number of online CPUs.
2204 locktorture.nwriters_stress= [KNL]
2205 Set the number of locking write-acquisition kthreads.
2207 locktorture.onoff_holdoff= [KNL]
2208 Set time (s) after boot for CPU-hotplug testing.
2210 locktorture.onoff_interval= [KNL]
2211 Set time (s) between CPU-hotplug operations, or
2212 zero to disable CPU-hotplug testing.
2214 locktorture.shuffle_interval= [KNL]
2215 Set task-shuffle interval (jiffies). Shuffling
2216 tasks allows some CPUs to go into dyntick-idle
2217 mode during the locktorture test.
2219 locktorture.shutdown_secs= [KNL]
2220 Set time (s) after boot system shutdown. This
2221 is useful for hands-off automated testing.
2223 locktorture.stat_interval= [KNL]
2224 Time (s) between statistics printk()s.
2226 locktorture.stutter= [KNL]
2227 Time (s) to stutter testing, for example,
2228 specifying five seconds causes the test to run for
2229 five seconds, wait for five seconds, and so on.
2230 This tests the locking primitive's ability to
2231 transition abruptly to and from idle.
2233 locktorture.torture_type= [KNL]
2234 Specify the locking implementation to test.
2236 locktorture.verbose= [KNL]
2237 Enable additional printk() statements.
2239 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
2242 loglevel= All Kernel Messages with a loglevel smaller than the
2243 console loglevel will be printed to the console. It can
2244 also be changed with klogd or other programs. The
2245 loglevels are defined as follows:
2247 0 (KERN_EMERG) system is unusable
2248 1 (KERN_ALERT) action must be taken immediately
2249 2 (KERN_CRIT) critical conditions
2250 3 (KERN_ERR) error conditions
2251 4 (KERN_WARNING) warning conditions
2252 5 (KERN_NOTICE) normal but significant condition
2253 6 (KERN_INFO) informational
2254 7 (KERN_DEBUG) debug-level messages
2256 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
2257 in bytes. n must be a power of two and greater
2258 than the minimal size. The minimal size is defined
2259 by LOG_BUF_SHIFT kernel config parameter. There is
2260 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
2261 that allows to increase the default size depending on
2262 the number of CPUs. See init/Kconfig for more details.
2264 logo.nologo [FB] Disables display of the built-in Linux logo.
2265 This may be used to provide more screen space for
2266 kernel log messages and is useful when debugging
2267 kernel boot problems.
2269 lp=0 [LP] Specify parallel ports to use, e.g,
2270 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
2271 lp=reset first parallel port). 'lp=0' disables the
2272 lp=auto printer driver. 'lp=reset' (which can be
2273 specified in addition to the ports) causes
2274 attached printers to be reset. Using
2275 lp=port1,port2,... specifies the parallel ports
2276 to associate lp devices with, starting with
2277 lp0. A port specification may be 'none' to skip
2278 that lp device, or a parport name such as
2279 'parport0'. Specifying 'lp=auto' instead of a
2280 port specification list means that device IDs
2281 from each port should be examined, to see if
2282 an IEEE 1284-compliant printer is attached; if
2283 so, the driver will manage that printer.
2284 See also header of drivers/char/lp.c.
2287 Sets loops_per_jiffy to given constant, thus avoiding
2288 time-consuming boot-time autodetection (up to 250 ms per
2289 CPU). 0 enables autodetection (default). To determine
2290 the correct value for your kernel, boot with normal
2291 autodetection and see what value is printed. Note that
2292 on SMP systems the preset will be applied to all CPUs,
2293 which is likely to cause problems if your CPUs need
2294 significantly divergent settings. An incorrect value
2295 will cause delays in the kernel to be wrong, leading to
2296 unpredictable I/O errors and other breakage. Although
2297 unlikely, in the extreme case this might damage your
2301 Format: <io>,<irq>,<dma>
2303 lsm.debug [SECURITY] Enable LSM initialization debugging output.
2305 machvec= [IA-64] Force the use of a particular machine-vector
2306 (machvec) in a generic kernel.
2307 Example: machvec=hpzx1_swiotlb
2309 machtype= [Loongson] Share the same kernel image file between different
2311 Example: machtype=lemote-yeeloong-2f-7inch
2313 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
2314 than or equal to this physical address is ignored.
2316 maxcpus= [SMP] Maximum number of processors that an SMP kernel
2317 will bring up during bootup. maxcpus=n : n >= 0 limits
2318 the kernel to bring up 'n' processors. Surely after
2319 bootup you can bring up the other plugged cpu by executing
2320 "echo 1 > /sys/devices/system/cpu/cpuX/online". So maxcpus
2321 only takes effect during system bootup.
2322 While n=0 is a special case, it is equivalent to "nosmp",
2323 which also disables the IO APIC.
2325 max_loop= [LOOP] The number of loop block devices that get
2326 (loop.max_loop) unconditionally pre-created at init time. The default
2327 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
2328 of statically allocating a predefined number, loop
2329 devices can be requested on-demand with the
2330 /dev/loop-control interface.
2332 mce [X86-32] Machine Check Exception
2334 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
2336 md= [HW] RAID subsystems devices and level
2337 See Documentation/admin-guide/md.rst.
2340 Format: <first>,<last>
2341 Specifies range of consoles to be captured by the MDA.
2343 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
2344 Amount of memory to be used when the kernel is not able
2345 to see the whole system memory or for test.
2346 [X86] Work as limiting max address. Use together
2347 with memmap= to avoid physical address space collisions.
2348 Without memmap= PCI devices could be placed at addresses
2349 belonging to unused RAM.
2351 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
2355 [KNL,SH] Allow user to override the default size for
2356 per-device physically contiguous DMA buffers.
2358 memhp_default_state=online/offline
2359 [KNL] Set the initial state for the memory hotplug
2360 onlining policy. If not specified, the default value is
2361 set according to the
2362 CONFIG_MEMORY_HOTPLUG_DEFAULT_ONLINE kernel config
2364 See Documentation/memory-hotplug.txt.
2366 memmap=exactmap [KNL,X86] Enable setting of an exact
2367 E820 memory map, as specified by the user.
2368 Such memmap=exactmap lines can be constructed based on
2369 BIOS output or other requirements. See the memmap=nn@ss
2372 memmap=nn[KMG]@ss[KMG]
2373 [KNL] Force usage of a specific region of memory.
2374 Region of memory to be used is from ss to ss+nn.
2375 If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
2376 which limits max address to nn[KMG].
2377 Multiple different regions can be specified,
2380 memmap=100M@2G,100M#3G,1G!1024G
2382 memmap=nn[KMG]#ss[KMG]
2383 [KNL,ACPI] Mark specific memory as ACPI data.
2384 Region of memory to be marked is from ss to ss+nn.
2386 memmap=nn[KMG]$ss[KMG]
2387 [KNL,ACPI] Mark specific memory as reserved.
2388 Region of memory to be reserved is from ss to ss+nn.
2389 Example: Exclude memory from 0x18690000-0x1869ffff
2390 memmap=64K$0x18690000
2392 memmap=0x10000$0x18690000
2393 Some bootloaders may need an escape character before '$',
2394 like Grub2, otherwise '$' and the following number
2397 memmap=nn[KMG]!ss[KMG]
2398 [KNL,X86] Mark specific memory as protected.
2399 Region of memory to be used, from ss to ss+nn.
2400 The memory region may be marked as e820 type 12 (0xc)
2401 and is NVDIMM or ADR memory.
2403 memmap=<size>%<offset>-<oldtype>+<newtype>
2404 [KNL,ACPI] Convert memory within the specified region
2405 from <oldtype> to <newtype>. If "-<oldtype>" is left
2406 out, the whole region will be marked as <newtype>,
2407 even if previously unavailable. If "+<newtype>" is left
2408 out, matching memory will be removed. Types are
2409 specified as e820 types, e.g., 1 = RAM, 2 = reserved,
2410 3 = ACPI, 12 = PRAM.
2412 memory_corruption_check=0/1 [X86]
2413 Some BIOSes seem to corrupt the first 64k of
2414 memory when doing things like suspend/resume.
2415 Setting this option will scan the memory
2416 looking for corruption. Enabling this will
2417 both detect corruption and prevent the kernel
2418 from using the memory being corrupted.
2419 However, its intended as a diagnostic tool; if
2420 repeatable BIOS-originated corruption always
2421 affects the same memory, you can use memmap=
2422 to prevent the kernel from using that memory.
2424 memory_corruption_check_size=size [X86]
2425 By default it checks for corruption in the low
2426 64k, making this memory unavailable for normal
2427 use. Use this parameter to scan for
2428 corruption in more or less memory.
2430 memory_corruption_check_period=seconds [X86]
2431 By default it checks for corruption every 60
2432 seconds. Use this parameter to check at some
2433 other rate. 0 disables periodic checking.
2435 memtest= [KNL,X86,ARM,PPC] Enable memtest
2437 default : 0 <disable>
2438 Specifies the number of memtest passes to be
2439 performed. Each pass selects another test
2440 pattern from a given set of patterns. Memtest
2441 fills the memory with this pattern, validates
2442 memory contents and reserves bad memory
2443 regions that are detected.
2445 mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
2446 Valid arguments: on, off
2447 Default (depends on kernel configuration option):
2448 on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
2449 off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
2450 mem_encrypt=on: Activate SME
2451 mem_encrypt=off: Do not activate SME
2453 Refer to Documentation/x86/amd-memory-encryption.txt
2454 for details on when memory encryption can be activated.
2456 mem_sleep_default= [SUSPEND] Default system suspend mode:
2457 s2idle - Suspend-To-Idle
2458 shallow - Power-On Suspend or equivalent (if supported)
2459 deep - Suspend-To-RAM or equivalent (if supported)
2460 See Documentation/admin-guide/pm/sleep-states.rst.
2462 meye.*= [HW] Set MotionEye Camera parameters
2463 See Documentation/media/v4l-drivers/meye.rst.
2465 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2466 Multi-Function General Purpose Timers on AMD Geode
2469 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2470 the BIOS has incorrectly applied a workaround. TinyBIOS
2471 version 0.98 is known to be affected, 0.99 fixes the
2472 problem by letting the user disable the workaround.
2476 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2477 physical address is ignored.
2479 mini2440= [ARM,HW,KNL]
2480 Format:[0..2][b][c][t]
2482 MINI2440 configuration specification:
2483 0 - The attached screen is the 3.5" TFT
2484 1 - The attached screen is the 7" TFT
2485 2 - The VGA Shield is attached (1024x768)
2486 Leaving out the screen size parameter will not load
2487 the TFT driver, and the framebuffer will be left
2489 b - Enable backlight. The TFT backlight pin will be
2490 linked to the kernel VESA blanking code and a GPIO
2491 LED. This parameter is not necessary when using the
2493 c - Enable the s3c camera interface.
2494 t - Reserved for enabling touchscreen support. The
2495 touchscreen support is not enabled in the mainstream
2496 kernel as of 2.6.30, a preliminary port can be found
2497 in the "bleeding edge" mini2440 support kernel at
2498 http://repo.or.cz/w/linux-2.6/mini2440.git
2501 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2502 parameter allows control of the logging verbosity for
2503 the additional memory initialisation checks. A value
2504 of 0 disables mminit logging and a level of 4 will
2505 log everything. Information is printed at KERN_DEBUG
2506 so loglevel=8 may also need to be specified.
2509 [KNL] When CONFIG_MODULE_SIG is set, this means that
2510 modules without (valid) signatures will fail to load.
2511 Note that if CONFIG_MODULE_SIG_FORCE is set, that
2512 is always true, so this option does nothing.
2514 module_blacklist= [KNL] Do not load a comma-separated list of
2515 modules. Useful for debugging problem modules.
2518 [MOUSE] Maximum time between finger touching and
2519 leaving touchpad surface for touch to be considered
2520 a tap and be reported as a left button click (for
2521 touchpads working in absolute mode only).
2523 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2524 reporting absolute coordinates, such as tablets
2525 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2526 reporting absolute coordinates, such as tablets
2528 movablecore= [KNL,X86,IA-64,PPC]
2529 Format: nn[KMGTPE] | nn%
2530 This parameter is the complement to kernelcore=, it
2531 specifies the amount of memory used for migratable
2532 allocations. If both kernelcore and movablecore is
2533 specified, then kernelcore will be at *least* the
2534 specified value but may be more. If movablecore on its
2535 own is specified, the administrator must be careful
2536 that the amount of memory usable for all allocations
2539 movable_node [KNL] Boot-time switch to make hotplugable memory
2540 NUMA nodes to be movable. This means that the memory
2541 of such nodes will be usable only for movable
2542 allocations which rules out almost all kernel
2543 allocations. Use with caution!
2545 MTD_Partition= [MTD]
2546 Format: <name>,<region-number>,<size>,<offset>
2548 MTD_Region= [MTD] Format:
2549 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
2552 See drivers/mtd/cmdlinepart.c.
2554 multitce=off [PPC] This parameter disables the use of the pSeries
2555 firmware feature for updating multiple TCE entries
2558 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2560 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2562 boundary - index of last SLC block on Flex-OneNAND.
2563 The remaining blocks are configured as MLC blocks.
2564 lock - Configure if Flex-OneNAND boundary should be locked.
2565 Once locked, the boundary cannot be changed.
2566 1 indicates lock status, 0 indicates unlock status.
2569 ARM/S3C2412 JIVE boot control
2571 See arch/arm/mach-s3c2412/mach-jive.c
2573 mtouchusb.raw_coordinates=
2574 [HW] Make the MicroTouch USB driver use raw coordinates
2575 ('y', default) or cooked coordinates ('n')
2577 mtrr_chunk_size=nn[KMG] [X86]
2578 used for mtrr cleanup. It is largest continuous chunk
2579 that could hold holes aka. UC entries.
2581 mtrr_gran_size=nn[KMG] [X86]
2582 Used for mtrr cleanup. It is granularity of mtrr block.
2584 Large value could prevent small alignment from
2587 mtrr_spare_reg_nr=n [X86]
2589 Range: 0,7 : spare reg number
2591 Used for mtrr cleanup. It is spare mtrr entries number.
2592 Set to 2 or more if your graphical card needs more.
2594 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2596 netdev= [NET] Network devices parameters
2597 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2598 Note that mem_start is often overloaded to mean
2599 something different and driver-specific.
2600 This usage is only documented in each driver source
2604 [NETFILTER] Enable connection tracking flow accounting
2605 0 to disable accounting
2606 1 to enable accounting
2609 nfsaddrs= [NFS] Deprecated. Use ip= instead.
2610 See Documentation/filesystems/nfs/nfsroot.txt.
2612 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
2613 See Documentation/filesystems/nfs/nfsroot.txt.
2615 nfsrootdebug [NFS] enable nfsroot debugging messages.
2616 See Documentation/filesystems/nfs/nfsroot.txt.
2618 nfs.callback_nr_threads=
2619 [NFSv4] set the total number of threads that the
2620 NFS client will assign to service NFSv4 callback
2623 nfs.callback_tcpport=
2624 [NFS] set the TCP port on which the NFSv4 callback
2625 channel should listen.
2628 [NFS] sets the pathname to the program which is used
2629 to update the NFS client cache entries.
2631 nfs.cache_getent_timeout=
2632 [NFS] sets the timeout after which an attempt to
2633 update a cache entry is deemed to have failed.
2635 nfs.idmap_cache_timeout=
2636 [NFS] set the maximum lifetime for idmapper cache
2640 [NFS] enable 64-bit inode numbers.
2641 If zero, the NFS client will fake up a 32-bit inode
2642 number for the readdir() and stat() syscalls instead
2643 of returning the full 64-bit number.
2644 The default is to return 64-bit inode numbers.
2646 nfs.max_session_cb_slots=
2647 [NFSv4.1] Sets the maximum number of session
2648 slots the client will assign to the callback
2649 channel. This determines the maximum number of
2650 callbacks the client will process in parallel for
2651 a particular server.
2653 nfs.max_session_slots=
2654 [NFSv4.1] Sets the maximum number of session slots
2655 the client will attempt to negotiate with the server.
2656 This limits the number of simultaneous RPC requests
2657 that the client can send to the NFSv4.1 server.
2658 Note that there is little point in setting this
2659 value higher than the max_tcp_slot_table_limit.
2661 nfs.nfs4_disable_idmapping=
2662 [NFSv4] When set to the default of '1', this option
2663 ensures that both the RPC level authentication
2664 scheme and the NFS level operations agree to use
2665 numeric uids/gids if the mount is using the
2666 'sec=sys' security flavour. In effect it is
2667 disabling idmapping, which can make migration from
2668 legacy NFSv2/v3 systems to NFSv4 easier.
2669 Servers that do not support this mode of operation
2670 will be autodetected by the client, and it will fall
2671 back to using the idmapper.
2672 To turn off this behaviour, set the value to '0'.
2674 [NFS4] Specify an additional fixed unique ident-
2675 ification string that NFSv4 clients can insert into
2676 their nfs_client_id4 string. This is typically a
2677 UUID that is generated at system install time.
2679 nfs.send_implementation_id =
2680 [NFSv4.1] Send client implementation identification
2681 information in exchange_id requests.
2682 If zero, no implementation identification information
2684 The default is to send the implementation identification
2687 nfs.recover_lost_locks =
2688 [NFSv4] Attempt to recover locks that were lost due
2689 to a lease timeout on the server. Please note that
2690 doing this risks data corruption, since there are
2691 no guarantees that the file will remain unchanged
2692 after the locks are lost.
2693 If you want to enable the kernel legacy behaviour of
2694 attempting to recover these locks, then set this
2696 The default parameter value of '0' causes the kernel
2697 not to attempt recovery of lost locks.
2699 nfs4.layoutstats_timer =
2700 [NFSv4.2] Change the rate at which the kernel sends
2701 layoutstats to the pNFS metadata server.
2703 Setting this to value to 0 causes the kernel to use
2704 whatever value is the default set by the layout
2705 driver. A non-zero value sets the minimum interval
2706 in seconds between layoutstats transmissions.
2708 nfsd.nfs4_disable_idmapping=
2709 [NFSv4] When set to the default of '1', the NFSv4
2710 server will return only numeric uids and gids to
2711 clients using auth_sys, and will accept numeric uids
2712 and gids from such clients. This is intended to ease
2713 migration from NFSv2/v3.
2715 nmi_debug= [KNL,SH] Specify one or more actions to take
2716 when a NMI is triggered.
2717 Format: [state][,regs][,debounce][,die]
2719 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
2720 Format: [panic,][nopanic,][num]
2722 0 - turn hardlockup detector in nmi_watchdog off
2723 1 - turn hardlockup detector in nmi_watchdog on
2724 When panic is specified, panic when an NMI watchdog
2725 timeout occurs (or 'nopanic' to override the opposite
2726 default). To disable both hard and soft lockup detectors,
2727 please see 'nowatchdog'.
2728 This is useful when you use a panic=... timeout and
2729 need the box quickly up again.
2731 These settings can be accessed at runtime via
2732 the nmi_watchdog and hardlockup_panic sysctls.
2734 netpoll.carrier_timeout=
2735 [NET] Specifies amount of time (in seconds) that
2736 netpoll should wait for a carrier. By default netpoll
2739 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
2740 emulation library even if a 387 maths coprocessor
2743 no5lvl [X86-64] Disable 5-level paging mode. Forces
2744 kernel to use 4-level paging instead.
2747 [HW] Never suspend the console
2748 Disable suspending of consoles during suspend and
2749 hibernate operations. Once disabled, debugging
2750 messages can reach various consoles while the rest
2751 of the system is being put to sleep (ie, while
2752 debugging driver suspend/resume hooks). This may
2753 not work reliably with all consoles, but is known
2754 to work with serial and VGA consoles.
2755 To facilitate more flexible debugging, we also add
2756 console_suspend, a printk module parameter to control
2757 it. Users could use console_suspend (usually
2758 /sys/module/printk/parameters/console_suspend) to
2759 turn on/off it dynamically.
2761 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2762 caches in the slab allocator. Saves per-node memory,
2763 but will impact performance.
2767 noaltinstr [S390] Disables alternative instructions patching
2768 (CPU alternatives feature).
2770 noapic [SMP,APIC] Tells the kernel to not make use of any
2771 IOAPICs that may be present in the system.
2773 noautogroup Disable scheduler automatic task group creation.
2775 nobats [PPC] Do not use BATs for mapping kernel lowmem
2776 on "Classic" PPC cores.
2780 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2782 nodelayacct [KNL] Disable per-task delay accounting
2784 nodsp [SH] Disable hardware DSP at boot time.
2786 noefi Disable EFI runtime services support.
2791 On X86-32 available only on PAE configured kernels.
2792 noexec=on: enable non-executable mappings (default)
2793 noexec=off: disable non-executable mappings
2796 Disable SMAP (Supervisor Mode Access Prevention)
2797 even if it is supported by processor.
2800 Disable SMEP (Supervisor Mode Execution Prevention)
2801 even if it is supported by processor.
2804 This affects only 32-bit executables.
2805 noexec32=on: enable non-executable mappings (default)
2806 read doesn't imply executable mappings
2807 noexec32=off: disable non-executable mappings
2808 read implies executable mappings
2810 nofpu [MIPS,SH] Disable hardware FPU at boot time.
2812 nofxsr [BUGS=X86-32] Disables x86 floating point extended
2813 register save and restore. The kernel will only save
2814 legacy floating-point registers on task switch.
2816 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2818 nosmt [KNL,S390] Disable symmetric multithreading (SMT).
2819 Equivalent to smt=1.
2821 [KNL,x86] Disable symmetric multithreading (SMT).
2822 nosmt=force: Force disable SMT, cannot be undone
2823 via the sysfs control file.
2825 nospectre_v1 [PPC] Disable mitigations for Spectre Variant 1 (bounds
2826 check bypass). With this option data leaks are possible
2829 nospectre_v2 [X86] Disable all mitigations for the Spectre variant 2
2830 (indirect branch prediction) vulnerability. System may
2831 allow data leaks with this option, which is equivalent
2834 nospec_store_bypass_disable
2835 [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
2837 noxsave [BUGS=X86] Disables x86 extended register state save
2838 and restore using xsave. The kernel will fallback to
2839 enabling legacy floating-point and sse state.
2841 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2842 register states. The kernel will fall back to use
2843 xsave to save the states. By using this parameter,
2844 performance of saving the states is degraded because
2845 xsave doesn't support modified optimization while
2846 xsaveopt supports it on xsaveopt enabled systems.
2848 noxsaves [X86] Disables xsaves and xrstors used in saving and
2849 restoring x86 extended register state in compacted
2850 form of xsave area. The kernel will fall back to use
2851 xsaveopt and xrstor to save and restore the states
2852 in standard form of xsave area. By using this
2853 parameter, xsave area per process might occupy more
2854 memory on xsaves enabled systems.
2856 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2857 wfi(ARM) instruction doesn't work correctly and not to
2858 use it. This is also useful when using JTAG debugger.
2860 no_file_caps Tells the kernel not to honor file capabilities. The
2861 only way then for a file to be executed with privilege
2862 is to be setuid root or executed by root.
2864 nohalt [IA-64] Tells the kernel not to use the power saving
2865 function PAL_HALT_LIGHT when idle. This increases
2866 power-consumption. On the positive side, it reduces
2867 interrupt wake-up latency, which may improve performance
2868 in certain environments such as networked servers or
2871 nohibernate [HIBERNATION] Disable hibernation and resume.
2873 nohz= [KNL] Boottime enable/disable dynamic ticks
2874 Valid arguments: on, off
2877 nohz_full= [KNL,BOOT,SMP,ISOL]
2878 The argument is a cpu list, as described above.
2879 In kernels built with CONFIG_NO_HZ_FULL=y, set
2880 the specified list of CPUs whose tick will be stopped
2881 whenever possible. The boot CPU will be forced outside
2882 the range to maintain the timekeeping. Any CPUs
2883 in this list will have their RCU callbacks offloaded,
2884 just as if they had also been called out in the
2885 rcu_nocbs= boot parameter.
2887 noiotrap [SH] Disables trapped I/O port accesses.
2889 noirqdebug [X86-32] Disables the code which attempts to detect and
2890 disable unhandled interrupt sources.
2892 no_timer_check [X86,APIC] Disables the code which tests for
2893 broken timer IRQ sources.
2895 noisapnp [ISAPNP] Disables ISA PnP code.
2897 noinitrd [RAM] Tells the kernel not to load any configured
2900 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2902 [Deprecated - use intremap=off]
2906 noinvpcid [X86] Disable the INVPCID cpu feature.
2908 nojitter [IA-64] Disables jitter checking for ITC timers.
2910 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2912 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2916 [X86,PV_OPS] Disable paravirtualized VMware scheduler
2917 clock and use the default one.
2919 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2920 steal time is computed, but won't influence scheduler
2923 nolapic [X86-32,APIC] Do not enable or use the local APIC.
2925 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
2927 noltlbs [PPC] Do not use large page/tlb entries for kernel
2928 lowmem mapping on PPC40x and PPC8xx
2930 nomca [IA-64] Disable machine check abort handling
2932 nomce [X86-32] Disable Machine Check Exception
2934 nomfgpt [X86-32] Disable Multi-Function General Purpose
2935 Timer usage (for AMD Geode machines).
2937 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2938 shutdown the other cpus. Instead use the REBOOT_VECTOR
2941 nomodule Disable module load
2943 nopat [X86] Disable PAT (page attribute table extension of
2944 pagetables) support.
2946 nopcid [X86-64] Disable the PCID cpu feature.
2948 norandmaps Don't use address space randomization. Equivalent to
2949 echo 0 > /proc/sys/kernel/randomize_va_space
2951 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
2952 with UP alternatives
2954 nordrand [X86] Disable kernel use of the RDRAND and
2955 RDSEED instructions even if they are supported
2956 by the processor. RDRAND and RDSEED are still
2957 available to user space applications.
2959 noresume [SWSUSP] Disables resume and restores original swap
2962 no-scroll [VGA] Disables scrollback.
2963 This is required for the Braillex ib80-piezo Braille
2964 reader made by F.H. Papenmeier (Germany).
2968 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
2970 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2971 and disable the IO APIC. legacy for "maxcpus=0".
2973 nosoftlockup [KNL] Disable the soft-lockup detector.
2975 nosync [HW,M68K] Disables sync negotiation for all devices.
2977 nowatchdog [KNL] Disable both lockup detectors, i.e.
2978 soft-lockup and NMI watchdog (hard-lockup).
2982 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2984 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2985 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2986 Some features depend on CPU0. Known dependencies are:
2987 1. Resume from suspend/hibernate depends on CPU0.
2988 Suspend/hibernate will fail if CPU0 is offline and you
2989 need to online CPU0 before suspend/hibernate.
2990 2. PIC interrupts also depend on CPU0. CPU0 can't be
2991 removed if a PIC interrupt is detected.
2992 It's said poweroff/reboot may depend on CPU0 on some
2993 machines although I haven't seen such issues so far
2994 after CPU0 is offline on a few tested machines.
2995 If the dependencies are under your control, you can
2996 turn on cpu0_hotplug.
2998 nps_mtm_hs_ctr= [KNL,ARC]
2999 This parameter sets the maximum duration, in
3000 cycles, each HW thread of the CTOP can run
3001 without interruptions, before HW switches it.
3002 The actual maximum duration is 16 times this
3004 Format: integer between 1 and 255
3007 nptcg= [IA-64] Override max number of concurrent global TLB
3008 purges which is reported from either PAL_VM_SUMMARY or
3011 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
3012 could support. nr_cpus=n : n >= 1 limits the kernel to
3013 support 'n' processors. It could be larger than the
3014 number of already plugged CPU during bootup, later in
3015 runtime you can physically add extra cpu until it reaches
3016 n. So during boot up some boot time memory for per-cpu
3017 variables need be pre-allocated for later physical cpu
3020 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
3022 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
3023 Allowed values are enable and disable
3025 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
3026 'node', 'default' can be specified
3027 This can be set from sysctl after boot.
3028 See Documentation/sysctl/vm.txt for details.
3030 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
3031 See Documentation/debugging-via-ohci1394.txt for more
3034 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
3035 Rather than timing out after 20 ms if an EC
3036 command is not properly ACKed, override the length
3037 of the timeout. We have interrupts disabled while
3038 waiting for the ACK, so if this is set too high
3039 interrupts *may* be lost!
3041 omap_mux= [OMAP] Override bootloader pin multiplexing.
3042 Format: <mux_mode0.mode_name=value>...
3043 For example, to override I2C bus2:
3044 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
3046 oprofile.timer= [HW]
3047 Use timer interrupt instead of performance counters
3049 oprofile.cpu_type= Force an oprofile cpu type
3050 This might be useful if you have an older oprofile
3051 userland or if you want common events.
3052 Format: { arch_perfmon }
3053 arch_perfmon: [X86] Force use of architectural
3054 perfmon on Intel CPUs instead of the
3055 CPU specific event set.
3056 timer: [X86] Force use of architectural NMI
3057 timer mode (see also oprofile.timer
3058 for generic hr timer mode)
3060 oops=panic Always panic on oopses. Default is to just kill the
3061 process, but there is a small probability of
3062 deadlocking the machine.
3063 This will also cause panics on machine check exceptions.
3064 Useful together with panic=30 to trigger a reboot.
3066 page_owner= [KNL] Boot-time page_owner enabling option.
3067 Storage of the information about who allocated
3068 each page is disabled in default. With this switch,
3070 on: enable the feature
3072 page_poison= [KNL] Boot-time parameter changing the state of
3073 poisoning on the buddy allocator, available with
3074 CONFIG_PAGE_POISONING=y.
3075 off: turn off poisoning (default)
3076 on: turn on poisoning
3078 panic= [KNL] Kernel behaviour on panic: delay <timeout>
3079 timeout > 0: seconds before rebooting
3080 timeout = 0: wait forever
3081 timeout < 0: reboot immediately
3084 panic_on_warn panic() instead of WARN(). Useful to cause kdump
3087 crash_kexec_post_notifiers
3088 Run kdump after running panic-notifiers and dumping
3089 kmsg. This only for the users who doubt kdump always
3090 succeeds in any situation.
3091 Note that this also increases risks of kdump failure,
3092 because some panic notifiers can make the crashed
3093 kernel more unstable.
3095 parkbd.port= [HW] Parallel port number the keyboard adapter is
3096 connected to, default is 0.
3098 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
3099 0 for XT, 1 for AT (default is AT).
3102 parport= [HW,PPT] Specify parallel ports. 0 disables.
3103 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
3104 Use 'auto' to force the driver to use any
3105 IRQ/DMA settings detected (the default is to
3106 ignore detected IRQ/DMA settings because of
3107 possible conflicts). You can specify the base
3108 address, IRQ, and DMA settings; IRQ and DMA
3109 should be numbers, or 'auto' (for using detected
3110 settings on that particular port), or 'nofifo'
3111 (to avoid using a FIFO even if it is detected).
3112 Parallel ports are assigned in the order they
3113 are specified on the command line, starting
3116 parport_init_mode= [HW,PPT]
3117 Configure VIA parallel port to operate in
3118 a specific mode. This is necessary on Pegasos
3119 computer where firmware has no options for setting
3120 up parallel port mode and sets it to spp.
3121 Currently this function knows 686a and 8231 chips.
3122 Format: [spp|ps2|epp|ecp|ecpepp]
3125 Halt all CPUs after the first oops has been printed for
3126 the specified number of seconds. This is to be used if
3127 your oopses keep scrolling off the screen.
3132 See header of drivers/block/paride/pcd.c.
3133 See also Documentation/blockdev/paride.txt.
3135 pci=option[,option...] [PCI] various PCI subsystem options.
3137 Some options herein operate on a specific device
3138 or a set of devices (<pci_dev>). These are
3139 specified in one of the following formats:
3141 [<domain>:]<bus>:<dev>.<func>[/<dev>.<func>]*
3142 pci:<vendor>:<device>[:<subvendor>:<subdevice>]
3144 Note: the first format specifies a PCI
3145 bus/device/function address which may change
3146 if new hardware is inserted, if motherboard
3147 firmware changes, or due to changes caused
3148 by other kernel parameters. If the
3149 domain is left unspecified, it is
3150 taken to be zero. Optionally, a path
3151 to a device through multiple device/function
3152 addresses can be specified after the base
3153 address (this is more robust against
3154 renumbering issues). The second format
3155 selects devices using IDs from the
3156 configuration space which may match multiple
3157 devices in the system.
3159 earlydump dump PCI config space before the kernel
3161 off [X86] don't probe for the PCI bus
3162 bios [X86-32] force use of PCI BIOS, don't access
3163 the hardware directly. Use this if your machine
3164 has a non-standard PCI host bridge.
3165 nobios [X86-32] disallow use of PCI BIOS, only direct
3166 hardware access methods are allowed. Use this
3167 if you experience crashes upon bootup and you
3168 suspect they are caused by the BIOS.
3169 conf1 [X86] Force use of PCI Configuration Access
3170 Mechanism 1 (config address in IO port 0xCF8,
3171 data in IO port 0xCFC, both 32-bit).
3172 conf2 [X86] Force use of PCI Configuration Access
3173 Mechanism 2 (IO port 0xCF8 is an 8-bit port for
3174 the function, IO port 0xCFA, also 8-bit, sets
3175 bus number. The config space is then accessed
3176 through ports 0xC000-0xCFFF).
3177 See http://wiki.osdev.org/PCI for more info
3178 on the configuration access mechanisms.
3179 noaer [PCIE] If the PCIEAER kernel config parameter is
3180 enabled, this kernel boot option can be used to
3181 disable the use of PCIE advanced error reporting.
3182 nodomains [PCI] Disable support for multiple PCI
3183 root domains (aka PCI segments, in ACPI-speak).
3184 nommconf [X86] Disable use of MMCONFIG for PCI
3186 check_enable_amd_mmconf [X86] check for and enable
3187 properly configured MMIO access to PCI
3188 config space on AMD family 10h CPU
3189 nomsi [MSI] If the PCI_MSI kernel config parameter is
3190 enabled, this kernel boot option can be used to
3191 disable the use of MSI interrupts system-wide.
3192 noioapicquirk [APIC] Disable all boot interrupt quirks.
3193 Safety option to keep boot IRQs enabled. This
3194 should never be necessary.
3195 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
3196 primary IO-APIC for bridges that cannot disable
3197 boot IRQs. This fixes a source of spurious IRQs
3198 when the system masks IRQs.
3199 noioapicreroute [APIC] Disable workaround that uses the
3200 boot IRQ equivalent of an IRQ that connects to
3201 a chipset where boot IRQs cannot be disabled.
3202 The opposite of ioapicreroute.
3203 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
3204 routing table. These calls are known to be buggy
3205 on several machines and they hang the machine
3206 when used, but on other computers it's the only
3207 way to get the interrupt routing table. Try
3208 this option if the kernel is unable to allocate
3209 IRQs or discover secondary PCI buses on your
3211 rom [X86] Assign address space to expansion ROMs.
3212 Use with caution as certain devices share
3213 address decoders between ROMs and other
3215 norom [X86] Do not assign address space to
3216 expansion ROMs that do not already have
3217 BIOS assigned address ranges.
3218 nobar [X86] Do not assign address space to the
3219 BARs that weren't assigned by the BIOS.
3220 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
3221 assigned automatically to PCI devices. You can
3222 make the kernel exclude IRQs of your ISA cards
3224 pirqaddr=0xAAAAA [X86] Specify the physical address
3225 of the PIRQ table (normally generated
3226 by the BIOS) if it is outside the
3227 F0000h-100000h range.
3228 lastbus=N [X86] Scan all buses thru bus #N. Can be
3229 useful if the kernel is unable to find your
3230 secondary buses and you want to tell it
3231 explicitly which ones they are.
3232 assign-busses [X86] Always assign all PCI bus
3233 numbers ourselves, overriding
3234 whatever the firmware may have done.
3235 usepirqmask [X86] Honor the possible IRQ mask stored
3236 in the BIOS $PIR table. This is needed on
3237 some systems with broken BIOSes, notably
3238 some HP Pavilion N5400 and Omnibook XE3
3239 notebooks. This will have no effect if ACPI
3240 IRQ routing is enabled.
3241 noacpi [X86] Do not use ACPI for IRQ routing
3242 or for PCI scanning.
3243 use_crs [X86] Use PCI host bridge window information
3244 from ACPI. On BIOSes from 2008 or later, this
3245 is enabled by default. If you need to use this,
3246 please report a bug.
3247 nocrs [X86] Ignore PCI host bridge windows from ACPI.
3248 If you need to use this, please report a bug.
3249 routeirq Do IRQ routing for all PCI devices.
3250 This is normally done in pci_enable_device(),
3251 so this option is a temporary workaround
3252 for broken drivers that don't call it.
3253 skip_isa_align [X86] do not align io start addr, so can
3254 handle more pci cards
3255 noearly [X86] Don't do any early type 1 scanning.
3256 This might help on some broken boards which
3257 machine check when some devices' config space
3258 is read. But various workarounds are disabled
3259 and some IOMMU drivers will not work.
3260 bfsort Sort PCI devices into breadth-first order.
3261 This sorting is done to get a device
3262 order compatible with older (<= 2.4) kernels.
3263 nobfsort Don't sort PCI devices into breadth-first order.
3264 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
3265 tuning and use the BIOS-configured MPS defaults.
3266 pcie_bus_safe Set every device's MPS to the largest value
3267 supported by all devices below the root complex.
3268 pcie_bus_perf Set device MPS to the largest allowable MPS
3269 based on its parent bus. Also set MRRS (Max
3270 Read Request Size) to the largest supported
3271 value (no larger than the MPS that the device
3272 or bus can support) for best performance.
3273 pcie_bus_peer2peer Set every device's MPS to 128B, which
3274 every device is guaranteed to support. This
3275 configuration allows peer-to-peer DMA between
3276 any pair of devices, possibly at the cost of
3277 reduced performance. This also guarantees
3278 that hot-added devices will work.
3279 cbiosize=nn[KMG] The fixed amount of bus space which is
3280 reserved for the CardBus bridge's IO window.
3281 The default value is 256 bytes.
3282 cbmemsize=nn[KMG] The fixed amount of bus space which is
3283 reserved for the CardBus bridge's memory
3284 window. The default value is 64 megabytes.
3287 [<order of align>@]<pci_dev>[; ...]
3288 Specifies alignment and device to reassign
3289 aligned memory resources. How to
3290 specify the device is described above.
3291 If <order of align> is not specified,
3292 PAGE_SIZE is used as alignment.
3293 PCI-PCI bridge can be specified, if resource
3294 windows need to be expanded.
3295 To specify the alignment for several
3296 instances of a device, the PCI vendor,
3297 device, subvendor, and subdevice may be
3298 specified, e.g., 4096@pci:8086:9c22:103c:198f
3299 ecrc= Enable/disable PCIe ECRC (transaction layer
3300 end-to-end CRC checking).
3301 bios: Use BIOS/firmware settings. This is the
3305 hpiosize=nn[KMG] The fixed amount of bus space which is
3306 reserved for hotplug bridge's IO window.
3307 Default size is 256 bytes.
3308 hpmemsize=nn[KMG] The fixed amount of bus space which is
3309 reserved for hotplug bridge's memory window.
3310 Default size is 2 megabytes.
3311 hpbussize=nn The minimum amount of additional bus numbers
3312 reserved for buses below a hotplug bridge.
3314 realloc= Enable/disable reallocating PCI bridge resources
3315 if allocations done by BIOS are too small to
3316 accommodate resources required by all child
3318 off: Turn realloc off
3320 realloc same as realloc=on
3321 noari do not use PCIe ARI.
3322 noats [PCIE, Intel-IOMMU, AMD-IOMMU]
3323 do not use PCIe ATS (and IOMMU device IOTLB).
3324 pcie_scan_all Scan all possible PCIe devices. Otherwise we
3325 only look for one device below a PCIe downstream
3327 big_root_window Try to add a big 64bit memory window to the PCIe
3328 root complex on AMD CPUs. Some GFX hardware
3329 can resize a BAR to allow access to all VRAM.
3330 Adding the window is slightly risky (it may
3331 conflict with unreported devices), so this
3333 disable_acs_redir=<pci_dev>[; ...]
3334 Specify one or more PCI devices (in the format
3335 specified above) separated by semicolons.
3336 Each device specified will have the PCI ACS
3337 redirect capabilities forced off which will
3338 allow P2P traffic between devices through
3339 bridges without forcing it upstream. Note:
3340 this removes isolation between devices and
3341 may put more devices in an IOMMU group.
3343 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
3346 force Enable ASPM even on devices that claim not to support it.
3347 WARNING: Forcing ASPM on may cause system lockups.
3349 pcie_ports= [PCIE] PCIe port services handling:
3350 native Use native PCIe services (PME, AER, DPC, PCIe hotplug)
3351 even if the platform doesn't give the OS permission to
3352 use them. This may cause conflicts if the platform
3353 also tries to use these services.
3354 compat Disable native PCIe services (PME, AER, DPC, PCIe
3357 pcie_port_pm= [PCIE] PCIe port power management handling:
3358 off Disable power management of all PCIe ports
3359 force Forcibly enable power management of all PCIe ports
3361 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
3362 nomsi Do not use MSI for native PCIe PME signaling (this makes
3363 all PCIe root ports use INTx for all services).
3365 pcmv= [HW,PCMCIA] BadgePAD 4
3369 Keep all power-domains already enabled by bootloader on,
3370 even if no driver has claimed them. This is useful
3371 for debug and development, but should not be
3372 needed on a platform with proper driver support.
3375 See Documentation/blockdev/paride.txt.
3377 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
3380 See arch/parisc/kernel/pdc_chassis.c
3382 percpu_alloc= Select which percpu first chunk allocator to use.
3383 Currently supported values are "embed" and "page".
3384 Archs may support subset or none of the selections.
3385 See comments in mm/percpu.c for details on each
3386 allocator. This parameter is primarily for debugging
3387 and performance comparison.
3390 See Documentation/blockdev/paride.txt.
3393 See Documentation/blockdev/paride.txt.
3395 pirq= [SMP,APIC] Manual mp-table setup
3396 See Documentation/x86/i386/IO-APIC.txt.
3398 plip= [PPT,NET] Parallel port network link
3399 Format: { parport<nr> | timid | 0 }
3400 See also Documentation/admin-guide/parport.rst.
3402 pmtmr= [X86] Manual setup of pmtmr I/O Port.
3403 Override pmtimer IOPort with a hex value.
3407 Enable PNP debug messages (depends on the
3408 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
3409 via /sys/module/pnp/parameters/debug. We always show
3410 current resource usage; turning this on also shows
3411 possible settings and some assignment information.
3417 { on | off | curr | res | no-curr | no-res }
3420 [ISAPNP] Exclude IRQs for the autoconfiguration
3423 [ISAPNP] Exclude DMAs for the autoconfiguration
3425 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
3426 Ranges are in pairs (I/O port base and size).
3429 [ISAPNP] Exclude memory regions for the
3431 Ranges are in pairs (memory base and size).
3433 ports= [IP_VS_FTP] IPVS ftp helper module
3435 Up to 8 (IP_VS_APP_MAX_PORTS) ports
3437 Format: <port>,<port>....
3439 powersave=off [PPC] This option disables power saving features.
3440 It specifically disables cpuidle and sets the
3441 platform machine description specific power_save
3442 function to NULL. On Idle the CPU just reduces
3445 ppc_strict_facility_enable
3446 [PPC] This option catches any kernel floating point,
3447 Altivec, VSX and SPE outside of regions specifically
3448 allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
3449 There is some performance impact when enabling this.
3453 Disable Hardware Transactional Memory
3455 print-fatal-signals=
3456 [KNL] debug: print fatal signals
3458 If enabled, warn about various signal handling
3459 related application anomalies: too many signals,
3460 too many POSIX.1 timers, fatal signals causing a
3463 If you hit the warning due to signal overflow,
3464 you might want to try "ulimit -i unlimited".
3468 printk.always_kmsg_dump=
3469 Trigger kmsg_dump for cases other than kernel oops or
3471 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3474 printk.devkmsg={on,off,ratelimit}
3475 Control writing to /dev/kmsg.
3476 on - unlimited logging to /dev/kmsg from userspace
3477 off - logging to /dev/kmsg disabled
3478 ratelimit - ratelimit the logging
3481 printk.time= Show timing data prefixed to each printk message line
3482 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
3484 processor.max_cstate= [HW,ACPI]
3485 Limit processor to maximum C-state
3486 max_cstate=9 overrides any DMI blacklist limit.
3488 processor.nocst [HW,ACPI]
3489 Ignore the _CST method to determine C-states,
3490 instead using the legacy FADT method
3492 profile= [KNL] Enable kernel profiling via /proc/profile
3493 Format: [<profiletype>,]<number>
3494 Param: <profiletype>: "schedule", "sleep", or "kvm"
3495 [defaults to kernel profiling]
3496 Param: "schedule" - profile schedule points.
3497 Param: "sleep" - profile D-state sleeping (millisecs).
3498 Requires CONFIG_SCHEDSTATS
3499 Param: "kvm" - profile VM exits.
3500 Param: <number> - step/bucket size as a power of 2 for
3501 statistical time based profiling.
3503 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
3505 See Documentation/blockdev/ramdisk.txt.
3507 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
3508 probe for; one of (bare|imps|exps|lifebook|any).
3509 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
3511 psmouse.resetafter= [HW,MOUSE]
3512 Try to reset the device after so many bad packets
3515 [HW,MOUSE] Set desired mouse resolution, in dpi.
3516 psmouse.smartscroll=
3517 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
3518 0 = disabled, 1 = enabled (default).
3520 pstore.backend= Specify the name of the pstore backend to use
3523 See Documentation/blockdev/paride.txt.
3525 pti= [X86_64] Control Page Table Isolation of user and
3526 kernel address spaces. Disabling this feature
3527 removes hardening, but improves performance of
3528 system calls and interrupts.
3530 on - unconditionally enable
3531 off - unconditionally disable
3532 auto - kernel detects whether your CPU model is
3533 vulnerable to issues that PTI mitigates
3535 Not specifying this option is equivalent to pti=auto.
3538 Equivalent to pti=off
3541 [KNL] Number of legacy pty's. Overwrites compiled-in
3544 quiet [KNL] Disable most log messages
3549 See Documentation/admin-guide/md.rst.
3551 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
3552 See Documentation/blockdev/ramdisk.txt.
3554 random.trust_cpu={on,off}
3555 [KNL] Enable or disable trusting the use of the
3556 CPU's random number generator (if available) to
3557 fully seed the kernel's CRNG. Default is controlled
3558 by CONFIG_RANDOM_TRUST_CPU.
3560 ras=option[,option,...] [KNL] RAS-specific options
3563 Disable the Correctable Errors Collector,
3564 see CONFIG_RAS_CEC help text.
3567 The argument is a cpu list, as described above.
3569 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3570 the specified list of CPUs to be no-callback CPUs.
3571 Invocation of these CPUs' RCU callbacks will be
3572 offloaded to "rcuox/N" kthreads created for that
3573 purpose, where "x" is "p" for RCU-preempt, and
3574 "s" for RCU-sched, and "N" is the CPU number.
3575 This reduces OS jitter on the offloaded CPUs,
3576 which can be useful for HPC and real-time
3577 workloads. It can also improve energy efficiency
3578 for asymmetric multiprocessors.
3581 Rather than requiring that offloaded CPUs
3582 (specified by rcu_nocbs= above) explicitly
3583 awaken the corresponding "rcuoN" kthreads,
3584 make these kthreads poll for callbacks.
3585 This improves the real-time response for the
3586 offloaded CPUs by relieving them of the need to
3587 wake up the corresponding kthread, but degrades
3588 energy efficiency by requiring that the kthreads
3589 periodically wake up to do the polling.
3591 rcutree.blimit= [KNL]
3592 Set maximum number of finished RCU callbacks to
3593 process in one batch.
3595 rcutree.dump_tree= [KNL]
3596 Dump the structure of the rcu_node combining tree
3597 out at early boot. This is used for diagnostic
3598 purposes, to verify correct tree setup.
3600 rcutree.gp_cleanup_delay= [KNL]
3601 Set the number of jiffies to delay each step of
3602 RCU grace-period cleanup.
3604 rcutree.gp_init_delay= [KNL]
3605 Set the number of jiffies to delay each step of
3606 RCU grace-period initialization.
3608 rcutree.gp_preinit_delay= [KNL]
3609 Set the number of jiffies to delay each step of
3610 RCU grace-period pre-initialization, that is,
3611 the propagation of recent CPU-hotplug changes up
3612 the rcu_node combining tree.
3614 rcutree.rcu_fanout_exact= [KNL]
3615 Disable autobalancing of the rcu_node combining
3616 tree. This is used by rcutorture, and might
3617 possibly be useful for architectures having high
3618 cache-to-cache transfer latencies.
3620 rcutree.rcu_fanout_leaf= [KNL]
3621 Change the number of CPUs assigned to each
3622 leaf rcu_node structure. Useful for very
3623 large systems, which will choose the value 64,
3624 and for NUMA systems with large remote-access
3625 latencies, which will choose a value aligned
3626 with the appropriate hardware boundaries.
3628 rcutree.jiffies_till_sched_qs= [KNL]
3629 Set required age in jiffies for a
3630 given grace period before RCU starts
3631 soliciting quiescent-state help from
3632 rcu_note_context_switch(). If not specified, the
3633 kernel will calculate a value based on the most
3634 recent settings of rcutree.jiffies_till_first_fqs
3635 and rcutree.jiffies_till_next_fqs.
3636 This calculated value may be viewed in
3637 rcutree.jiffies_to_sched_qs. Any attempt to
3638 set rcutree.jiffies_to_sched_qs will be
3639 cheerfully overwritten.
3641 rcutree.jiffies_till_first_fqs= [KNL]
3642 Set delay from grace-period initialization to
3643 first attempt to force quiescent states.
3644 Units are jiffies, minimum value is zero,
3645 and maximum value is HZ.
3647 rcutree.jiffies_till_next_fqs= [KNL]
3648 Set delay between subsequent attempts to force
3649 quiescent states. Units are jiffies, minimum
3650 value is one, and maximum value is HZ.
3652 rcutree.kthread_prio= [KNL,BOOT]
3653 Set the SCHED_FIFO priority of the RCU per-CPU
3654 kthreads (rcuc/N). This value is also used for
3655 the priority of the RCU boost threads (rcub/N)
3656 and for the RCU grace-period kthreads (rcu_bh,
3657 rcu_preempt, and rcu_sched). If RCU_BOOST is
3658 set, valid values are 1-99 and the default is 1
3659 (the least-favored priority). Otherwise, when
3660 RCU_BOOST is not set, valid values are 0-99 and
3661 the default is zero (non-realtime operation).
3663 rcutree.rcu_nocb_leader_stride= [KNL]
3664 Set the number of NOCB kthread groups, which
3665 defaults to the square root of the number of
3666 CPUs. Larger numbers reduces the wakeup overhead
3667 on the per-CPU grace-period kthreads, but increases
3668 that same overhead on each group's leader.
3670 rcutree.qhimark= [KNL]
3671 Set threshold of queued RCU callbacks beyond which
3672 batch limiting is disabled.
3674 rcutree.qlowmark= [KNL]
3675 Set threshold of queued RCU callbacks below which
3676 batch limiting is re-enabled.
3678 rcutree.rcu_idle_gp_delay= [KNL]
3679 Set wakeup interval for idle CPUs that have
3680 RCU callbacks (RCU_FAST_NO_HZ=y).
3682 rcutree.rcu_idle_lazy_gp_delay= [KNL]
3683 Set wakeup interval for idle CPUs that have
3684 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3685 Lazy RCU callbacks are those which RCU can
3686 prove do nothing more than free memory.
3688 rcutree.rcu_kick_kthreads= [KNL]
3689 Cause the grace-period kthread to get an extra
3690 wake_up() if it sleeps three times longer than
3691 it should at force-quiescent-state time.
3692 This wake_up() will be accompanied by a
3693 WARN_ONCE() splat and an ftrace_dump().
3695 rcuperf.gp_async= [KNL]
3696 Measure performance of asynchronous
3697 grace-period primitives such as call_rcu().
3699 rcuperf.gp_async_max= [KNL]
3700 Specify the maximum number of outstanding
3701 callbacks per writer thread. When a writer
3702 thread exceeds this limit, it invokes the
3703 corresponding flavor of rcu_barrier() to allow
3704 previously posted callbacks to drain.
3706 rcuperf.gp_exp= [KNL]
3707 Measure performance of expedited synchronous
3708 grace-period primitives.
3710 rcuperf.holdoff= [KNL]
3711 Set test-start holdoff period. The purpose of
3712 this parameter is to delay the start of the
3713 test until boot completes in order to avoid
3716 rcuperf.nreaders= [KNL]
3717 Set number of RCU readers. The value -1 selects
3718 N, where N is the number of CPUs. A value
3719 "n" less than -1 selects N-n+1, where N is again
3720 the number of CPUs. For example, -2 selects N
3721 (the number of CPUs), -3 selects N+1, and so on.
3722 A value of "n" less than or equal to -N selects
3725 rcuperf.nwriters= [KNL]
3726 Set number of RCU writers. The values operate
3727 the same as for rcuperf.nreaders.
3728 N, where N is the number of CPUs
3730 rcuperf.perf_type= [KNL]
3731 Specify the RCU implementation to test.
3733 rcuperf.shutdown= [KNL]
3734 Shut the system down after performance tests
3735 complete. This is useful for hands-off automated
3738 rcuperf.verbose= [KNL]
3739 Enable additional printk() statements.
3741 rcuperf.writer_holdoff= [KNL]
3742 Write-side holdoff between grace periods,
3743 in microseconds. The default of zero says
3746 rcutorture.cbflood_inter_holdoff= [KNL]
3747 Set holdoff time (jiffies) between successive
3748 callback-flood tests.
3750 rcutorture.cbflood_intra_holdoff= [KNL]
3751 Set holdoff time (jiffies) between successive
3752 bursts of callbacks within a given callback-flood
3755 rcutorture.cbflood_n_burst= [KNL]
3756 Set the number of bursts making up a given
3757 callback-flood test. Set this to zero to
3758 disable callback-flood testing.
3760 rcutorture.cbflood_n_per_burst= [KNL]
3761 Set the number of callbacks to be registered
3762 in a given burst of a callback-flood test.
3764 rcutorture.fqs_duration= [KNL]
3765 Set duration of force_quiescent_state bursts
3768 rcutorture.fqs_holdoff= [KNL]
3769 Set holdoff time within force_quiescent_state bursts
3772 rcutorture.fqs_stutter= [KNL]
3773 Set wait time between force_quiescent_state bursts
3776 rcutorture.gp_cond= [KNL]
3777 Use conditional/asynchronous update-side
3778 primitives, if available.
3780 rcutorture.gp_exp= [KNL]
3781 Use expedited update-side primitives, if available.
3783 rcutorture.gp_normal= [KNL]
3784 Use normal (non-expedited) asynchronous
3785 update-side primitives, if available.
3787 rcutorture.gp_sync= [KNL]
3788 Use normal (non-expedited) synchronous
3789 update-side primitives, if available. If all
3790 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3791 rcutorture.gp_normal=, and rcutorture.gp_sync=
3792 are zero, rcutorture acts as if is interpreted
3793 they are all non-zero.
3795 rcutorture.n_barrier_cbs= [KNL]
3796 Set callbacks/threads for rcu_barrier() testing.
3798 rcutorture.nfakewriters= [KNL]
3799 Set number of concurrent RCU writers. These just
3800 stress RCU, they don't participate in the actual
3801 test, hence the "fake".
3803 rcutorture.nreaders= [KNL]
3804 Set number of RCU readers. The value -1 selects
3805 N-1, where N is the number of CPUs. A value
3806 "n" less than -1 selects N-n-2, where N is again
3807 the number of CPUs. For example, -2 selects N
3808 (the number of CPUs), -3 selects N+1, and so on.
3810 rcutorture.object_debug= [KNL]
3811 Enable debug-object double-call_rcu() testing.
3813 rcutorture.onoff_holdoff= [KNL]
3814 Set time (s) after boot for CPU-hotplug testing.
3816 rcutorture.onoff_interval= [KNL]
3817 Set time (jiffies) between CPU-hotplug operations,
3818 or zero to disable CPU-hotplug testing.
3820 rcutorture.shuffle_interval= [KNL]
3821 Set task-shuffle interval (s). Shuffling tasks
3822 allows some CPUs to go into dyntick-idle mode
3823 during the rcutorture test.
3825 rcutorture.shutdown_secs= [KNL]
3826 Set time (s) after boot system shutdown. This
3827 is useful for hands-off automated testing.
3829 rcutorture.stall_cpu= [KNL]
3830 Duration of CPU stall (s) to test RCU CPU stall
3831 warnings, zero to disable.
3833 rcutorture.stall_cpu_holdoff= [KNL]
3834 Time to wait (s) after boot before inducing stall.
3836 rcutorture.stall_cpu_irqsoff= [KNL]
3837 Disable interrupts while stalling if set.
3839 rcutorture.stat_interval= [KNL]
3840 Time (s) between statistics printk()s.
3842 rcutorture.stutter= [KNL]
3843 Time (s) to stutter testing, for example, specifying
3844 five seconds causes the test to run for five seconds,
3845 wait for five seconds, and so on. This tests RCU's
3846 ability to transition abruptly to and from idle.
3848 rcutorture.test_boost= [KNL]
3849 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3850 "Maybe" means test if the RCU implementation
3851 under test support RCU priority boosting.
3853 rcutorture.test_boost_duration= [KNL]
3854 Duration (s) of each individual boost test.
3856 rcutorture.test_boost_interval= [KNL]
3857 Interval (s) between each boost test.
3859 rcutorture.test_no_idle_hz= [KNL]
3860 Test RCU's dyntick-idle handling. See also the
3861 rcutorture.shuffle_interval parameter.
3863 rcutorture.torture_type= [KNL]
3864 Specify the RCU implementation to test.
3866 rcutorture.verbose= [KNL]
3867 Enable additional printk() statements.
3869 rcupdate.rcu_cpu_stall_suppress= [KNL]
3870 Suppress RCU CPU stall warning messages.
3872 rcupdate.rcu_cpu_stall_timeout= [KNL]
3873 Set timeout for RCU CPU stall warning messages.
3875 rcupdate.rcu_expedited= [KNL]
3876 Use expedited grace-period primitives, for
3877 example, synchronize_rcu_expedited() instead
3878 of synchronize_rcu(). This reduces latency,
3879 but can increase CPU utilization, degrade
3880 real-time latency, and degrade energy efficiency.
3881 No effect on CONFIG_TINY_RCU kernels.
3883 rcupdate.rcu_normal= [KNL]
3884 Use only normal grace-period primitives,
3885 for example, synchronize_rcu() instead of
3886 synchronize_rcu_expedited(). This improves
3887 real-time latency, CPU utilization, and
3888 energy efficiency, but can expose users to
3889 increased grace-period latency. This parameter
3890 overrides rcupdate.rcu_expedited. No effect on
3891 CONFIG_TINY_RCU kernels.
3893 rcupdate.rcu_normal_after_boot= [KNL]
3894 Once boot has completed (that is, after
3895 rcu_end_inkernel_boot() has been invoked), use
3896 only normal grace-period primitives. No effect
3897 on CONFIG_TINY_RCU kernels.
3899 rcupdate.rcu_task_stall_timeout= [KNL]
3900 Set timeout in jiffies for RCU task stall warning
3901 messages. Disable with a value less than or equal
3904 rcupdate.rcu_self_test= [KNL]
3905 Run the RCU early boot self tests
3909 Run specified binary instead of /init from the ramdisk,
3910 used for early userspace startup. See initrd.
3913 Turn on/off individual RDT features. List is:
3914 cmt, mbmtotal, mbmlocal, l3cat, l3cdp, l2cat, l2cdp,
3916 E.g. to turn on cmt and turn off mba use:
3920 Format (x86 or x86_64):
3921 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3923 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3925 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3926 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3927 reboot_force is either force or not specified,
3928 reboot_cpu is s[mp]#### with #### being the processor
3929 to be used for rebooting.
3932 [KNL, SMP] Set scheduler's default relax_domain_level.
3933 See Documentation/cgroup-v1/cpusets.txt.
3935 reserve= [KNL,BUGS] Force kernel to ignore I/O ports or memory
3936 Format: <base1>,<size1>[,<base2>,<size2>,...]
3937 Reserve I/O ports or memory so the kernel won't use
3938 them. If <base> is less than 0x10000, the region
3939 is assumed to be I/O ports; otherwise it is memory.
3941 reservetop= [X86-32]
3943 Reserves a hole at the top of the kernel virtual
3948 Set the amount of memory to reserve for BIOS at
3949 the bottom of the address space.
3951 reset_devices [KNL] Force drivers to reset the underlying device
3952 during initialization.
3955 Specify the partition device for software suspend
3957 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
3959 resume_offset= [SWSUSP]
3960 Specify the offset from the beginning of the partition
3961 given by "resume=" at which the swap header is located,
3962 in <PAGE_SIZE> units (needed only for swap files).
3963 See Documentation/power/swsusp-and-swap-files.txt
3965 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3966 read the resume files
3968 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3969 Useful for devices that are detected asynchronously
3970 (e.g. USB and MMC devices).
3972 hibernate= [HIBERNATION]
3973 noresume Don't check if there's a hibernation image
3974 present during boot.
3975 nocompress Don't compress/decompress hibernation images.
3976 no Disable hibernation and resume.
3977 protect_image Turn on image protection during restoration
3978 (that will set all pages holding image data
3979 during restoration read-only).
3981 retain_initrd [RAM] Keep initrd memory after extraction
3983 rfkill.default_state=
3984 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3985 etc. communication is blocked by default.
3988 rfkill.master_switch_mode=
3989 0 The "airplane mode" button does nothing.
3990 1 The "airplane mode" button toggles between everything
3991 blocked and the previous configuration.
3992 2 The "airplane mode" button toggles between everything
3993 blocked and everything unblocked.
3995 rhash_entries= [KNL,NET]
3996 Set number of hash buckets for route cache
3999 [KNL] Disable ring 3 MONITOR/MWAIT feature on supported
4002 ro [KNL] Mount root device read-only on boot
4005 on Mark read-only kernel memory as read-only (default).
4006 off Leave read-only kernel memory writable for debugging.
4009 Enable the uart passthrough on the designated usb port
4010 on Rockchip SoCs. When active, the signals of the
4011 debug-uart get routed to the D+ and D- pins of the usb
4012 port and the regular usb controller gets disabled.
4014 root= [KNL] Root filesystem
4015 See name_to_dev_t comment in init/do_mounts.c.
4017 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
4018 mount the root filesystem
4020 rootflags= [KNL] Set root filesystem mount option string
4022 rootfstype= [KNL] Set root filesystem type
4024 rootwait [KNL] Wait (indefinitely) for root device to show up.
4025 Useful for devices that are detected asynchronously
4026 (e.g. USB and MMC devices).
4028 rproc_mem=nn[KMG][@address]
4029 [KNL,ARM,CMA] Remoteproc physical memory block.
4030 Memory area to be used by remote processor image,
4033 rw [KNL] Mount root device read-write on boot
4035 S [KNL] Run init in single mode
4037 s390_iommu= [HW,S390]
4038 Set s390 IOTLB flushing mode
4040 With strict flushing every unmap operation will result in
4041 an IOTLB flush. Default is lazy flushing before reuse,
4045 See drivers/net/irda/sa1100_ir.c.
4047 sbni= [NET] Granch SBNI12 leased line adapter
4049 sched_debug [KNL] Enables verbose scheduler debug messages.
4051 schedstats= [KNL,X86] Enable or disable scheduled statistics.
4052 Allowed values are enable and disable. This feature
4053 incurs a small amount of overhead in the scheduler
4054 but is useful for debugging and performance tuning.
4056 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
4057 xtime_lock contention on larger systems, and/or RCU lock
4058 contention on all systems with CONFIG_MAXSMP set.
4059 Format: { "0" | "1" }
4060 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
4062 Note: increases power consumption, thus should only be
4063 enabled if running jitter sensitive (HPC/RT) workloads.
4065 security= [SECURITY] Choose a security module to enable at boot.
4066 If this boot parameter is not specified, only the first
4067 security module asking for security registration will be
4068 loaded. An invalid security module name will be treated
4069 as if no module has been chosen.
4071 selinux= [SELINUX] Disable or enable SELinux at boot time.
4072 Format: { "0" | "1" }
4073 See security/selinux/Kconfig help text.
4076 Default value is set via kernel config option.
4077 If enabled at boot time, /selinux/disable can be used
4078 later to disable prior to initial policy load.
4080 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
4081 Format: { "0" | "1" }
4082 See security/apparmor/Kconfig help text
4085 Default value is set via kernel config option.
4087 serialnumber [BUGS=X86-32]
4090 Maximal number of shapers.
4098 Disable merging of slabs with similar size. May be
4099 necessary if there is some reason to distinguish
4100 allocs to different slabs, especially in hardened
4101 environments where the risk of heap overflows and
4102 layout control by attackers can usually be
4103 frustrated by disabling merging. This will reduce
4104 most of the exposure of a heap attack to a single
4105 cache (risks via metadata attacks are mostly
4106 unchanged). Debug options disable merging on their
4108 For more information see Documentation/vm/slub.rst.
4110 slab_max_order= [MM, SLAB]
4111 Determines the maximum allowed order for slabs.
4112 A high setting may cause OOMs due to memory
4113 fragmentation. Defaults to 1 for systems with
4114 more than 32MB of RAM, 0 otherwise.
4116 slub_debug[=options[,slabs]] [MM, SLUB]
4117 Enabling slub_debug allows one to determine the
4118 culprit if slab objects become corrupted. Enabling
4119 slub_debug can create guard zones around objects and
4120 may poison objects when not in use. Also tracks the
4121 last alloc / free. For more information see
4122 Documentation/vm/slub.rst.
4124 slub_memcg_sysfs= [MM, SLUB]
4125 Determines whether to enable sysfs directories for
4126 memory cgroup sub-caches. 1 to enable, 0 to disable.
4127 The default is determined by CONFIG_SLUB_MEMCG_SYSFS_ON.
4128 Enabling this can lead to a very high number of debug
4129 directories and files being created under
4132 slub_max_order= [MM, SLUB]
4133 Determines the maximum allowed order for slabs.
4134 A high setting may cause OOMs due to memory
4135 fragmentation. For more information see
4136 Documentation/vm/slub.rst.
4138 slub_min_objects= [MM, SLUB]
4139 The minimum number of objects per slab. SLUB will
4140 increase the slab order up to slub_max_order to
4141 generate a sufficiently large slab able to contain
4142 the number of objects indicated. The higher the number
4143 of objects the smaller the overhead of tracking slabs
4144 and the less frequently locks need to be acquired.
4145 For more information see Documentation/vm/slub.rst.
4147 slub_min_order= [MM, SLUB]
4148 Determines the minimum page order for slabs. Must be
4149 lower than slub_max_order.
4150 For more information see Documentation/vm/slub.rst.
4152 slub_nomerge [MM, SLUB]
4153 Same with slab_nomerge. This is supported for legacy.
4154 See slab_nomerge for more information.
4157 Format: <io1>[,<io2>[,...,<io8>]]
4159 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
4160 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
4161 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
4162 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
4163 smsc-ircc2.ircc_irq= [HW] IRQ line
4164 smsc-ircc2.ircc_dma= [HW] DMA channel
4165 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
4166 0: Toshiba Satellite 1800 (GP data pin select)
4167 1: Fast pin select (default)
4170 smt [KNL,S390] Set the maximum number of threads (logical
4171 CPUs) to use per physical CPU on systems capable of
4172 symmetric multithreading (SMT). Will be capped to the
4173 actual hardware limit.
4175 Default: -1 (no limit)
4178 [KNL] Should the soft-lockup detector generate panics.
4181 A nonzero value instructs the soft-lockup detector
4182 to panic the machine when a soft-lockup occurs. This
4183 is also controlled by CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC
4184 which is the respective build-time switch to that
4187 softlockup_all_cpu_backtrace=
4188 [KNL] Should the soft-lockup detector generate
4189 backtraces on all cpus.
4192 sonypi.*= [HW] Sony Programmable I/O Control Device driver
4193 See Documentation/laptops/sonypi.txt
4195 spectre_v2= [X86] Control mitigation of Spectre variant 2
4196 (indirect branch speculation) vulnerability.
4198 on - unconditionally enable
4199 off - unconditionally disable
4200 auto - kernel detects whether your CPU model is
4203 Selecting 'on' will, and 'auto' may, choose a
4204 mitigation method at run time according to the
4205 CPU, the available microcode, the setting of the
4206 CONFIG_RETPOLINE configuration option, and the
4207 compiler with which the kernel was built.
4209 Specific mitigations can also be selected manually:
4211 retpoline - replace indirect branches
4212 retpoline,generic - google's original retpoline
4213 retpoline,amd - AMD-specific minimal thunk
4215 Not specifying this option is equivalent to
4218 spec_store_bypass_disable=
4219 [HW] Control Speculative Store Bypass (SSB) Disable mitigation
4220 (Speculative Store Bypass vulnerability)
4222 Certain CPUs are vulnerable to an exploit against a
4223 a common industry wide performance optimization known
4224 as "Speculative Store Bypass" in which recent stores
4225 to the same memory location may not be observed by
4226 later loads during speculative execution. The idea
4227 is that such stores are unlikely and that they can
4228 be detected prior to instruction retirement at the
4229 end of a particular speculation execution window.
4231 In vulnerable processors, the speculatively forwarded
4232 store can be used in a cache side channel attack, for
4233 example to read memory to which the attacker does not
4234 directly have access (e.g. inside sandboxed code).
4236 This parameter controls whether the Speculative Store
4237 Bypass optimization is used.
4239 On x86 the options are:
4241 on - Unconditionally disable Speculative Store Bypass
4242 off - Unconditionally enable Speculative Store Bypass
4243 auto - Kernel detects whether the CPU model contains an
4244 implementation of Speculative Store Bypass and
4245 picks the most appropriate mitigation. If the
4246 CPU is not vulnerable, "off" is selected. If the
4247 CPU is vulnerable the default mitigation is
4248 architecture and Kconfig dependent. See below.
4249 prctl - Control Speculative Store Bypass per thread
4250 via prctl. Speculative Store Bypass is enabled
4251 for a process by default. The state of the control
4252 is inherited on fork.
4253 seccomp - Same as "prctl" above, but all seccomp threads
4254 will disable SSB unless they explicitly opt out.
4256 Default mitigations:
4257 X86: If CONFIG_SECCOMP=y "seccomp", otherwise "prctl"
4259 On powerpc the options are:
4261 on,auto - On Power8 and Power9 insert a store-forwarding
4262 barrier on kernel entry and exit. On Power7
4263 perform a software flush on kernel entry and
4267 Not specifying this option is equivalent to
4268 spec_store_bypass_disable=auto.
4270 spia_io_base= [HW,MTD]
4275 srcutree.counter_wrap_check [KNL]
4276 Specifies how frequently to check for
4277 grace-period sequence counter wrap for the
4278 srcu_data structure's ->srcu_gp_seq_needed field.
4279 The greater the number of bits set in this kernel
4280 parameter, the less frequently counter wrap will
4281 be checked for. Note that the bottom two bits
4284 srcutree.exp_holdoff [KNL]
4285 Specifies how many nanoseconds must elapse
4286 since the end of the last SRCU grace period for
4287 a given srcu_struct until the next normal SRCU
4288 grace period will be considered for automatic
4289 expediting. Set to zero to disable automatic
4293 Speculative Store Bypass Disable control
4295 On CPUs that are vulnerable to the Speculative
4296 Store Bypass vulnerability and offer a
4297 firmware based mitigation, this parameter
4298 indicates how the mitigation should be used:
4300 force-on: Unconditionally enable mitigation for
4301 for both kernel and userspace
4302 force-off: Unconditionally disable mitigation for
4303 for both kernel and userspace
4304 kernel: Always enable mitigation in the
4305 kernel, and offer a prctl interface
4306 to allow userspace to register its
4307 interest in being mitigated too.
4309 stack_guard_gap= [MM]
4310 override the default stack gap protection. The value
4311 is in page units and it defines how many pages prior
4312 to (for stacks growing down) resp. after (for stacks
4313 growing up) the main stack are reserved for no other
4314 mapping. Default value is 256 pages.
4317 Enabled the stack tracer on boot up.
4319 stacktrace_filter=[function-list]
4320 [FTRACE] Limit the functions that the stack tracer
4321 will trace at boot up. function-list is a comma separated
4322 list of functions. This list can be changed at run
4323 time by the stack_trace_filter file in the debugfs
4324 tracing directory. Note, this enables stack tracing
4325 and the stacktrace above is not needed.
4329 Set the STI (builtin display/keyboard on the HP-PARISC
4330 machines) console (graphic card) which should be used
4331 as the initial boot-console.
4332 See also comment in drivers/video/console/sticore.c.
4335 See comment in drivers/video/console/sticore.c.
4338 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
4340 sunrpc.min_resvport=
4341 sunrpc.max_resvport=
4343 SunRPC servers often require that client requests
4344 originate from a privileged port (i.e. a port in the
4345 range 0 < portnr < 1024).
4346 An administrator who wishes to reserve some of these
4347 ports for other uses may adjust the range that the
4348 kernel's sunrpc client considers to be privileged
4349 using these two parameters to set the minimum and
4350 maximum port values.
4352 sunrpc.svc_rpc_per_connection_limit=
4354 Limit the number of requests that the server will
4355 process in parallel from a single connection.
4356 The default value is 0 (no limit).
4360 Control how the NFS server code allocates CPUs to
4361 service thread pools. Depending on how many NICs
4362 you have and where their interrupts are bound, this
4363 option will affect which CPUs will do NFS serving.
4364 Note: this parameter cannot be changed while the
4365 NFS server is running.
4367 auto the server chooses an appropriate mode
4368 automatically using heuristics
4369 global a single global pool contains all CPUs
4370 percpu one pool for each CPU
4371 pernode one pool for each NUMA node (equivalent
4372 to global on non-NUMA machines)
4374 sunrpc.tcp_slot_table_entries=
4375 sunrpc.udp_slot_table_entries=
4377 Sets the upper limit on the number of simultaneous
4378 RPC calls that can be sent from the client to a
4379 server. Increasing these values may allow you to
4380 improve throughput, but will also increase the
4381 amount of memory reserved for use by the client.
4383 suspend.pm_test_delay=
4385 Sets the number of seconds to remain in a suspend test
4386 mode before resuming the system (see
4387 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
4388 is set. Default value is 5.
4391 [KNL] Enable accounting of swap in memory resource
4392 controller if no parameter or 1 is given or disable
4393 it if 0 is given (See Documentation/cgroup-v1/memory.txt)
4395 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
4396 Format: { <int> | force | noforce }
4397 <int> -- Number of I/O TLB slabs
4398 force -- force using of bounce buffers even if they
4399 wouldn't be automatically used by the kernel
4400 noforce -- Never use bounce buffers (for debugging)
4404 sysfs.deprecated=0|1 [KNL]
4405 Enable/disable old style sysfs layout for old udev
4406 on older distributions. When this option is enabled
4407 very new udev will not work anymore. When this option
4408 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
4409 in older udev will not work anymore.
4410 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
4411 the kernel configuration.
4413 sysrq_always_enabled
4415 Ignore sysrq setting - this boot parameter will
4416 neutralize any effect of /proc/sys/kernel/sysrq.
4417 Useful for debugging.
4419 tcpmhash_entries= [KNL,NET]
4420 Set the number of tcp_metrics_hash slots.
4421 Default value is 8192 or 16384 depending on total
4422 ram pages. This is used to specify the TCP metrics
4423 cache size. See Documentation/networking/ip-sysctl.txt
4424 "tcp_no_metrics_save" section for more details.
4428 test_suspend= [SUSPEND][,N]
4429 Specify "mem" (for Suspend-to-RAM) or "standby" (for
4430 standby suspend) or "freeze" (for suspend type freeze)
4431 as the system sleep state during system startup with
4432 the optional capability to repeat N number of times.
4433 The system is woken from this state using a
4434 wakeup-capable RTC alarm.
4436 thash_entries= [KNL,NET]
4437 Set number of hash buckets for TCP connection
4439 thermal.act= [HW,ACPI]
4440 -1: disable all active trip points in all thermal zones
4441 <degrees C>: override all lowest active trip points
4443 thermal.crt= [HW,ACPI]
4444 -1: disable all critical trip points in all thermal zones
4445 <degrees C>: override all critical trip points
4447 thermal.nocrt= [HW,ACPI]
4448 Set to disable actions on ACPI thermal zone
4449 critical and hot trip points.
4451 thermal.off= [HW,ACPI]
4452 1: disable ACPI thermal control
4454 thermal.psv= [HW,ACPI]
4455 -1: disable all passive trip points
4456 <degrees C>: override all passive trip points to this
4459 thermal.tzp= [HW,ACPI]
4460 Specify global default ACPI thermal zone polling rate
4461 <deci-seconds>: poll all this frequency
4462 0: no polling (default)
4465 Force threading of all interrupt handlers except those
4466 marked explicitly IRQF_NO_THREAD.
4469 Enable the Transcendent memory driver if built-in.
4471 tmem.cleancache=0|1 [KNL, XEN]
4472 Default is on (1). Disable the usage of the cleancache
4473 API to send anonymous pages to the hypervisor.
4475 tmem.frontswap=0|1 [KNL, XEN]
4476 Default is on (1). Disable the usage of the frontswap
4477 API to send swap pages to the hypervisor. If disabled
4478 the selfballooning and selfshrinking are force disabled.
4480 tmem.selfballooning=0|1 [KNL, XEN]
4481 Default is on (1). Disable the driving of swap pages
4484 tmem.selfshrinking=0|1 [KNL, XEN]
4485 Default is on (1). Partial swapoff that immediately
4486 transfers pages from Xen hypervisor back to the
4487 kernel based on different criteria.
4491 Specify if the kernel should make use of the cpu
4492 topology information if the hardware supports this.
4493 The scheduler will make use of this information and
4494 e.g. base its process migration decisions on it.
4497 topology_updates= [KNL, PPC, NUMA]
4499 Specify if the kernel should ignore (off)
4500 topology updates sent by the hypervisor to this
4505 tpm_suspend_pcr=[HW,TPM]
4506 Format: integer pcr id
4507 Specify that at suspend time, the tpm driver
4508 should extend the specified pcr with zeros,
4509 as a workaround for some chips which fail to
4510 flush the last written pcr on TPM_SaveState.
4511 This will guarantee that all the other pcrs
4514 trace_buf_size=nn[KMG]
4515 [FTRACE] will set tracing buffer size on each cpu.
4517 trace_event=[event-list]
4518 [FTRACE] Set and start specified trace events in order
4519 to facilitate early boot debugging. The event-list is a
4520 comma separated list of trace events to enable. See
4521 also Documentation/trace/events.rst
4523 trace_options=[option-list]
4524 [FTRACE] Enable or disable tracer options at boot.
4525 The option-list is a comma delimited list of options
4526 that can be enabled or disabled just as if you were
4527 to echo the option name into
4529 /sys/kernel/debug/tracing/trace_options
4531 For example, to enable stacktrace option (to dump the
4532 stack trace of each event), add to the command line:
4534 trace_options=stacktrace
4536 See also Documentation/trace/ftrace.rst "trace options"
4540 Have the tracepoints sent to printk as well as the
4541 tracing ring buffer. This is useful for early boot up
4542 where the system hangs or reboots and does not give the
4543 option for reading the tracing buffer or performing a
4544 ftrace_dump_on_oops.
4546 To turn off having tracepoints sent to printk,
4547 echo 0 > /proc/sys/kernel/tracepoint_printk
4548 Note, echoing 1 into this file without the
4549 tracepoint_printk kernel cmdline option has no effect.
4553 Having tracepoints sent to printk() and activating high
4554 frequency tracepoints such as irq or sched, can cause
4555 the system to live lock.
4558 [FTRACE] enable this option to disable tracing when a
4559 warning is hit. This turns off "tracing_on". Tracing can
4560 be enabled again by echoing '1' into the "tracing_on"
4561 file located in /sys/kernel/debug/tracing/
4563 This option is useful, as it disables the trace before
4564 the WARNING dump is called, which prevents the trace to
4565 be filled with content caused by the warning output.
4567 This option can also be set at run time via the sysctl
4568 option: kernel/traceoff_on_warning
4570 transparent_hugepage=
4572 Format: [always|madvise|never]
4573 Can be used to control the default behavior of the system
4574 with respect to transparent hugepages.
4575 See Documentation/admin-guide/mm/transhuge.rst
4578 tsc= Disable clocksource stability checks for TSC.
4580 [x86] reliable: mark tsc clocksource as reliable, this
4581 disables clocksource verification at runtime, as well
4582 as the stability checks done at bootup. Used to enable
4583 high-resolution timer mode on older hardware, and in
4584 virtualized environment.
4585 [x86] noirqtime: Do not use TSC to do irq accounting.
4586 Used to run time disable IRQ_TIME_ACCOUNTING on any
4587 platforms where RDTSC is slow and this accounting
4589 [x86] unstable: mark the TSC clocksource as unstable, this
4590 marks the TSC unconditionally unstable at bootup and
4591 avoids any further wobbles once the TSC watchdog notices.
4593 turbografx.map[2|3]= [HW,JOY]
4594 TurboGraFX parallel port interface
4596 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
4597 See also Documentation/input/devices/joystick-parport.rst
4599 udbg-immortal [PPC] When debugging early kernel crashes that
4600 happen after console_init() and before a proper
4601 console driver takes over, this boot options might
4602 help "seeing" what's going on.
4604 uhash_entries= [KNL,NET]
4605 Set number of hash buckets for UDP/UDP-Lite connections
4608 [USB] Ignore overcurrent events (default N).
4609 Some badly-designed motherboards generate lots of
4610 bogus events, for ports that aren't wired to
4611 anything. Set this parameter to avoid log spamming.
4612 Note that genuine overcurrent events won't be
4616 [X86] Cause panic on unknown NMI.
4618 usbcore.authorized_default=
4619 [USB] Default USB device authorization:
4620 (default -1 = authorized except for wireless USB,
4621 0 = not authorized, 1 = authorized)
4623 usbcore.autosuspend=
4624 [USB] The autosuspend time delay (in seconds) used
4625 for newly-detected USB devices (default 2). This
4626 is the time required before an idle device will be
4627 autosuspended. Devices for which the delay is set
4628 to a negative value won't be autosuspended at all.
4630 usbcore.usbfs_snoop=
4631 [USB] Set to log all usbfs traffic (default 0 = off).
4633 usbcore.usbfs_snoop_max=
4634 [USB] Maximum number of bytes to snoop in each URB
4637 usbcore.blinkenlights=
4638 [USB] Set to cycle leds on hubs (default 0 = off).
4640 usbcore.old_scheme_first=
4641 [USB] Start with the old device initialization
4642 scheme, applies only to low and full-speed devices
4645 usbcore.usbfs_memory_mb=
4646 [USB] Memory limit (in MB) for buffers allocated by
4647 usbfs (default = 16, 0 = max = 2047).
4649 usbcore.use_both_schemes=
4650 [USB] Try the other device initialization scheme
4651 if the first one fails (default 1 = enabled).
4653 usbcore.initial_descriptor_timeout=
4654 [USB] Specifies timeout for the initial 64-byte
4655 USB_REQ_GET_DESCRIPTOR request in milliseconds
4656 (default 5000 = 5.0 seconds).
4658 usbcore.nousb [USB] Disable the USB subsystem
4661 [USB] A list of quirk entries to augment the built-in
4662 usb core quirk list. List entries are separated by
4663 commas. Each entry has the form
4664 VendorID:ProductID:Flags. The IDs are 4-digit hex
4665 numbers and Flags is a set of letters. Each letter
4666 will change the built-in quirk; setting it if it is
4667 clear and clearing it if it is set. The letters have
4668 the following meanings:
4669 a = USB_QUIRK_STRING_FETCH_255 (string
4670 descriptors must not be fetched using
4672 b = USB_QUIRK_RESET_RESUME (device can't resume
4673 correctly so reset it instead);
4674 c = USB_QUIRK_NO_SET_INTF (device can't handle
4675 Set-Interface requests);
4676 d = USB_QUIRK_CONFIG_INTF_STRINGS (device can't
4677 handle its Configuration or Interface
4679 e = USB_QUIRK_RESET (device can't be reset
4680 (e.g morph devices), don't use reset);
4681 f = USB_QUIRK_HONOR_BNUMINTERFACES (device has
4682 more interface descriptions than the
4683 bNumInterfaces count, and can't handle
4684 talking to these interfaces);
4685 g = USB_QUIRK_DELAY_INIT (device needs a pause
4686 during initialization, after we read
4687 the device descriptor);
4688 h = USB_QUIRK_LINEAR_UFRAME_INTR_BINTERVAL (For
4689 high speed and super speed interrupt
4690 endpoints, the USB 2.0 and USB 3.0 spec
4691 require the interval in microframes (1
4692 microframe = 125 microseconds) to be
4693 calculated as interval = 2 ^
4695 Devices with this quirk report their
4696 bInterval as the result of this
4697 calculation instead of the exponent
4698 variable used in the calculation);
4699 i = USB_QUIRK_DEVICE_QUALIFIER (device can't
4700 handle device_qualifier descriptor
4702 j = USB_QUIRK_IGNORE_REMOTE_WAKEUP (device
4703 generates spurious wakeup, ignore
4704 remote wakeup capability);
4705 k = USB_QUIRK_NO_LPM (device can't handle Link
4707 l = USB_QUIRK_LINEAR_FRAME_INTR_BINTERVAL
4708 (Device reports its bInterval as linear
4709 frames instead of the USB 2.0
4711 m = USB_QUIRK_DISCONNECT_SUSPEND (Device needs
4712 to be disconnected before suspend to
4713 prevent spurious wakeup);
4714 n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
4715 pause after every control message);
4716 Example: quirks=0781:5580:bk,0a5c:5834:gij
4719 [USBHID] The interval which mice are to be polled at.
4722 [USBHID] The interval which joysticks are to be polled at.
4725 [USBHID] The interval which keyboards are to be polled at.
4727 usb-storage.delay_use=
4728 [UMS] The delay in seconds before a new device is
4729 scanned for Logical Units (default 1).
4732 [UMS] A list of quirks entries to supplement or
4733 override the built-in unusual_devs list. List
4734 entries are separated by commas. Each entry has
4735 the form VID:PID:Flags where VID and PID are Vendor
4736 and Product ID values (4-digit hex numbers) and
4737 Flags is a set of characters, each corresponding
4738 to a common usb-storage quirk flag as follows:
4739 a = SANE_SENSE (collect more than 18 bytes
4741 b = BAD_SENSE (don't collect more than 18
4742 bytes of sense data);
4743 c = FIX_CAPACITY (decrease the reported
4744 device capacity by one sector);
4745 d = NO_READ_DISC_INFO (don't use
4746 READ_DISC_INFO command);
4747 e = NO_READ_CAPACITY_16 (don't use
4748 READ_CAPACITY_16 command);
4749 f = NO_REPORT_OPCODES (don't use report opcodes
4751 g = MAX_SECTORS_240 (don't transfer more than
4752 240 sectors at a time, uas only);
4753 h = CAPACITY_HEURISTICS (decrease the
4754 reported device capacity by one
4755 sector if the number is odd);
4756 i = IGNORE_DEVICE (don't bind to this
4758 j = NO_REPORT_LUNS (don't use report luns
4760 l = NOT_LOCKABLE (don't try to lock and
4761 unlock ejectable media);
4762 m = MAX_SECTORS_64 (don't transfer more
4763 than 64 sectors = 32 KB at a time);
4764 n = INITIAL_READ10 (force a retry of the
4765 initial READ(10) command);
4766 o = CAPACITY_OK (accept the capacity
4767 reported by the device);
4768 p = WRITE_CACHE (the device cache is ON
4770 r = IGNORE_RESIDUE (the device reports
4771 bogus residue values);
4772 s = SINGLE_LUN (the device has only one
4774 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
4775 commands, uas only);
4776 u = IGNORE_UAS (don't bind to the uas driver);
4777 w = NO_WP_DETECT (don't test whether the
4778 medium is write-protected).
4779 y = ALWAYS_SYNC (issue a SYNCHRONIZE_CACHE
4780 even if the device claims no cache)
4781 Example: quirks=0419:aaf5:rl,0421:0433:rc
4783 user_debug= [KNL,ARM]
4785 See arch/arm/Kconfig.debug help text.
4786 1 - undefined instruction events
4788 4 - invalid data aborts
4791 Example: user_debug=31
4794 [X86] Flags controlling user PTE allocations.
4796 nohigh = do not allocate PTE pages in
4797 HIGHMEM regardless of setting
4801 On X86_32, this is an alias for vdso32=. Otherwise:
4803 vdso=1: enable VDSO (the default)
4804 vdso=0: disable VDSO mapping
4806 vdso32= [X86] Control the 32-bit vDSO
4807 vdso32=1: enable 32-bit VDSO
4808 vdso32=0 or vdso32=2: disable 32-bit VDSO
4810 See the help text for CONFIG_COMPAT_VDSO for more
4811 details. If CONFIG_COMPAT_VDSO is set, the default is
4812 vdso32=0; otherwise, the default is vdso32=1.
4814 For compatibility with older kernels, vdso32=2 is an
4817 Try vdso32=0 if you encounter an error that says:
4818 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
4821 vector=percpu: enable percpu vector domain
4823 video= [FB] Frame buffer configuration
4824 See Documentation/fb/modedb.txt.
4826 video.brightness_switch_enabled= [0,1]
4827 If set to 1, on receiving an ACPI notify event
4828 generated by hotkey, video driver will adjust brightness
4829 level and then send out the event to user space through
4830 the allocated input device; If set to 0, video driver
4831 will only send out the event without touching backlight
4836 [VMMIO] Memory mapped virtio (platform) device.
4838 <size>@<baseaddr>:<irq>[:<id>]
4840 <size> := size (can use standard suffixes
4842 <baseaddr> := physical base address
4843 <irq> := interrupt number (as passed to
4845 <id> := (optional) platform device id
4847 virtio_mmio.device=1K@0x100b0000:48:7
4849 Can be used multiple times for multiple devices.
4851 vga= [BOOT,X86-32] Select a particular video mode
4852 See Documentation/x86/boot.txt and
4853 Documentation/svga.txt.
4854 Use vga=ask for menu.
4855 This is actually a boot loader parameter; the value is
4856 passed to the kernel using a special protocol.
4858 vm_debug[=options] [KNL] Available with CONFIG_DEBUG_VM=y.
4859 May slow down system boot speed, especially when
4860 enabled on systems with a large amount of memory.
4861 All options are enabled by default, and this
4862 interface is meant to allow for selectively
4863 enabling or disabling specific virtual memory
4866 Available options are:
4867 P Enable page structure init time poisoning
4868 - Disable all of the above options
4870 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
4871 size of <nn>. This can be used to increase the
4872 minimum size (128MB on x86). It can also be used to
4873 decrease the size and leave more room for directly
4876 vmcp_cma=nn[MG] [KNL,S390]
4877 Sets the memory size reserved for contiguous memory
4878 allocations for the vmcp device driver.
4880 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
4883 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
4886 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4890 Controls the behavior of vsyscalls (i.e. calls to
4891 fixed addresses of 0xffffffffff600x00 from legacy
4892 code). Most statically-linked binaries and older
4893 versions of glibc use these calls. Because these
4894 functions are at fixed addresses, they make nice
4895 targets for exploits that can control RIP.
4897 emulate [default] Vsyscalls turn into traps and are
4898 emulated reasonably safely.
4900 native Vsyscalls are native syscall instructions.
4901 This is a little bit faster than trapping
4902 and makes a few dynamic recompilers work
4903 better than they would in emulation mode.
4904 It also makes exploits much easier to write.
4906 none Vsyscalls don't work at all. This makes
4907 them quite hard to use for exploits but
4908 might break your system.
4910 vt.color= [VT] Default text color.
4911 Format: 0xYX, X = foreground, Y = background.
4912 Default: 0x07 = light gray on black.
4914 vt.cur_default= [VT] Default cursor shape.
4915 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4916 the parameters of the <Esc>[?A;B;Cc escape sequence;
4917 see VGA-softcursor.txt. Default: 2 = underline.
4919 vt.default_blu= [VT]
4920 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4921 Change the default blue palette of the console.
4922 This is a 16-member array composed of values
4925 vt.default_grn= [VT]
4926 Format: <green0>,<green1>,<green2>,...,<green15>
4927 Change the default green palette of the console.
4928 This is a 16-member array composed of values
4931 vt.default_red= [VT]
4932 Format: <red0>,<red1>,<red2>,...,<red15>
4933 Change the default red palette of the console.
4934 This is a 16-member array composed of values
4940 Set system-wide default UTF-8 mode for all tty's.
4941 Default is 1, i.e. UTF-8 mode is enabled for all
4942 newly opened terminals.
4944 vt.global_cursor_default=
4947 Set system-wide default for whether a cursor
4948 is shown on new VTs. Default is -1,
4949 i.e. cursors will be created by default unless
4950 overridden by individual drivers. 0 will hide
4951 cursors, 1 will display them.
4953 vt.italic= [VT] Default color for italic text; 0-15.
4956 vt.underline= [VT] Default color for underlined text; 0-15.
4959 watchdog timers [HW,WDT] For information on watchdog timers,
4960 see Documentation/watchdog/watchdog-parameters.txt
4961 or other driver-specific files in the
4962 Documentation/watchdog/ directory.
4964 workqueue.watchdog_thresh=
4965 If CONFIG_WQ_WATCHDOG is configured, workqueue can
4966 warn stall conditions and dump internal state to
4967 help debugging. 0 disables workqueue stall
4968 detection; otherwise, it's the stall threshold
4969 duration in seconds. The default value is 30 and
4970 it can be updated at runtime by writing to the
4971 corresponding sysfs file.
4973 workqueue.disable_numa
4974 By default, all work items queued to unbound
4975 workqueues are affine to the NUMA nodes they're
4976 issued on, which results in better behavior in
4977 general. If NUMA affinity needs to be disabled for
4978 whatever reason, this option can be used. Note
4979 that this also can be controlled per-workqueue for
4980 workqueues visible under /sys/bus/workqueue/.
4982 workqueue.power_efficient
4983 Per-cpu workqueues are generally preferred because
4984 they show better performance thanks to cache
4985 locality; unfortunately, per-cpu workqueues tend to
4986 be more power hungry than unbound workqueues.
4988 Enabling this makes the per-cpu workqueues which
4989 were observed to contribute significantly to power
4990 consumption unbound, leading to measurably lower
4991 power usage at the cost of small performance
4994 The default value of this parameter is determined by
4995 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4997 workqueue.debug_force_rr_cpu
4998 Workqueue used to implicitly guarantee that work
4999 items queued without explicit CPU specified are put
5000 on the local CPU. This guarantee is no longer true
5001 and while local CPU is still preferred work items
5002 may be put on foreign CPUs. This debug option
5003 forces round-robin CPU selection to flush out
5004 usages which depend on the now broken guarantee.
5005 When enabled, memory and cache locality will be
5008 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
5009 default x2apic cluster mode on platforms
5012 x86_intel_mid_timer= [X86-32,APBT]
5013 Choose timer option for x86 Intel MID platform.
5014 Two valid options are apbt timer only and lapic timer
5015 plus one apbt timer for broadcast timer.
5016 x86_intel_mid_timer=apbt_only | lapic_and_apbt
5018 xen_512gb_limit [KNL,X86-64,XEN]
5019 Restricts the kernel running paravirtualized under Xen
5020 to use only up to 512 GB of RAM. The reason to do so is
5021 crash analysis tools and Xen tools for doing domain
5022 save/restore/migration must be enabled to handle larger
5025 xen_emul_unplug= [HW,X86,XEN]
5026 Unplug Xen emulated devices
5027 Format: [unplug0,][unplug1]
5028 ide-disks -- unplug primary master IDE devices
5029 aux-ide-disks -- unplug non-primary-master IDE devices
5030 nics -- unplug network devices
5031 all -- unplug all emulated devices (NICs and IDE disks)
5032 unnecessary -- unplugging emulated devices is
5033 unnecessary even if the host did not respond to
5035 never -- do not unplug even if version check succeeds
5037 xen_nopvspin [X86,XEN]
5038 Disables the ticketlock slowpath using Xen PV
5042 Disables the PV optimizations forcing the HVM guest to
5043 run as generic HVM guest with no PV drivers.
5045 xen_scrub_pages= [XEN]
5046 Boolean option to control scrubbing pages before giving them back
5047 to Xen, for use by other domains. Can be also changed at runtime
5048 with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
5049 Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
5051 xirc2ps_cs= [NET,PCMCIA]
5053 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
5055 xhci-hcd.quirks [USB,KNL]
5056 A hex value specifying bitmask with supplemental xhci
5057 host controller quirks. Meaning of each bit can be
5058 consulted in header drivers/usb/host/xhci.h.
git.samba.org / sfrench / cifs-2.6.git / blob