Merge tag 'topic/drm-misc-2015-09-25' of git://anongit.freedesktop.org/drm-intel...
[linux-2.6-block.git] / Documentation / kernel-parameters.txt
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1 Kernel Parameters
2 ~~~~~~~~~~~~~~~~~
1da177e4 3
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4The following is a consolidated list of the kernel parameters as
5implemented by the __setup(), core_param() and module_param() macros
6and sorted into English Dictionary order (defined as ignoring all
7punctuation and sorting digits before letters in a case insensitive
8manner), and with descriptions where known.
9
10The kernel parses parameters from the kernel command line up to "--";
11if it doesn't recognize a parameter and it doesn't contain a '.', the
12parameter gets passed to init: parameters with '=' go into init's
13environment, others are passed as command line arguments to init.
14Everything after "--" is passed as an argument to init.
15
16Module parameters can be specified in two ways: via the kernel command
17line with a module name prefix, or via modprobe, e.g.:
18
19 (kernel command line) usbcore.blinkenlights=1
20 (modprobe command line) modprobe usbcore blinkenlights=1
21
22Parameters for modules which are built into the kernel need to be
23specified on the kernel command line. modprobe looks through the
24kernel command line (/proc/cmdline) and collects module parameters
25when it loads a module, so the kernel command line can be used for
26loadable modules too.
1da177e4 27
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28Hyphens (dashes) and underscores are equivalent in parameter names, so
29 log_buf_len=1M print-fatal-signals=1
30can also be entered as
31 log-buf-len=1M print_fatal_signals=1
32
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33Double-quotes can be used to protect spaces in values, e.g.:
34 param="spaces in here"
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36This document may not be entirely up to date and comprehensive. The command
37"modinfo -p ${modulename}" shows a current list of all parameters of a loadable
38module. Loadable modules, after being loaded into the running kernel, also
39reveal their parameters in /sys/module/${modulename}/parameters/. Some of these
40parameters may be changed at runtime by the command
41"echo -n ${value} > /sys/module/${modulename}/parameters/${parm}".
42
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43The parameters listed below are only valid if certain kernel build options were
44enabled and if respective hardware is present. The text in square brackets at
45the beginning of each description states the restrictions within which a
46parameter is applicable:
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47
48 ACPI ACPI support is enabled.
c99c108a 49 AGP AGP (Accelerated Graphics Port) is enabled.
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50 ALSA ALSA sound support is enabled.
51 APIC APIC support is enabled.
52 APM Advanced Power Management support is enabled.
16290246 53 ARM ARM architecture is enabled.
e7ba176b 54 AVR32 AVR32 architecture is enabled.
1da177e4 55 AX25 Appropriate AX.25 support is enabled.
0ae53640 56 BLACKFIN Blackfin architecture is enabled.
1e435256 57 CLK Common clock infrastructure is enabled.
5c71d618 58 CMA Contiguous Memory Area support is enabled.
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59 DRM Direct Rendering Management support is enabled.
60 DYNAMIC_DEBUG Build in debug messages and enable them at runtime
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61 EDD BIOS Enhanced Disk Drive Services (EDD) is enabled
62 EFI EFI Partitioning (GPT) is enabled
63 EIDE EIDE/ATAPI support is enabled.
7102ebcd 64 EVM Extended Verification Module
1da177e4 65 FB The frame buffer device is enabled.
16290246 66 FTRACE Function tracing enabled.
2521f2c2 67 GCOV GCOV profiling is enabled.
1da177e4 68 HW Appropriate hardware is enabled.
1da177e4 69 IA-64 IA-64 architecture is enabled.
6146f0d5 70 IMA Integrity measurement architecture is enabled.
1da177e4 71 IOSCHED More than one I/O scheduler is enabled.
41e2e8be 72 IP_PNP IP DHCP, BOOTP, or RARP is enabled.
b0f83b28 73 IPV6 IPv6 support is enabled.
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74 ISAPNP ISA PnP code is enabled.
75 ISDN Appropriate ISDN support is enabled.
76 JOY Appropriate joystick support is enabled.
84c08fd6 77 KGDB Kernel debugger support is enabled.
fef07aae 78 KVM Kernel Virtual Machine support is enabled.
11ef697b 79 LIBATA Libata driver is enabled
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80 LP Printer support is enabled.
81 LOOP Loopback device support is enabled.
82 M68k M68k architecture is enabled.
83 These options have more detailed description inside of
84 Documentation/m68k/kernel-options.txt.
1da177e4 85 MDA MDA console support is enabled.
16290246 86 MIPS MIPS architecture is enabled.
1da177e4 87 MOUSE Appropriate mouse support is enabled.
309e57df 88 MSI Message Signaled Interrupts (PCI).
c8facbb6 89 MTD MTD (Memory Technology Device) support is enabled.
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90 NET Appropriate network support is enabled.
91 NUMA NUMA support is enabled.
92 NFS Appropriate NFS support is enabled.
93 OSS OSS sound support is enabled.
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94 PV_OPS A paravirtualized kernel is enabled.
95 PARIDE The ParIDE (parallel port IDE) subsystem is enabled.
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96 PARISC The PA-RISC architecture is enabled.
97 PCI PCI bus support is enabled.
7f785763 98 PCIE PCI Express support is enabled.
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99 PCMCIA The PCMCIA subsystem is enabled.
100 PNP Plug & Play support is enabled.
101 PPC PowerPC architecture is enabled.
102 PPT Parallel port support is enabled.
103 PS2 Appropriate PS/2 support is enabled.
104 RAM RAM disk support is enabled.
105 S390 S390 architecture is enabled.
106 SCSI Appropriate SCSI support is enabled.
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107 A lot of drivers have their options described inside
108 the Documentation/scsi/ sub-directory.
20510f2f 109 SECURITY Different security models are enabled.
1da177e4 110 SELINUX SELinux support is enabled.
c1c124e9 111 APPARMOR AppArmor support is enabled.
1da177e4 112 SERIAL Serial support is enabled.
e523d93c 113 SH SuperH architecture is enabled.
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114 SMP The kernel is an SMP kernel.
115 SPARC Sparc architecture is enabled.
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116 SWSUSP Software suspend (hibernation) is enabled.
117 SUSPEND System suspend states are enabled.
225a9be2 118 TPM TPM drivers are enabled.
1da177e4 119 TS Appropriate touchscreen support is enabled.
d4f373e5 120 UMS USB Mass Storage support is enabled.
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121 USB USB support is enabled.
122 USBHID USB Human Interface Device support is enabled.
123 V4L Video For Linux support is enabled.
81a054ce 124 VMMIO Driver for memory mapped virtio devices is enabled.
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125 VGA The VGA console has been enabled.
126 VT Virtual terminal support is enabled.
127 WDT Watchdog support is enabled.
128 XT IBM PC/XT MFM hard disk support is enabled.
cd4f0ef7 129 X86-32 X86-32, aka i386 architecture is enabled.
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130 X86-64 X86-64 architecture is enabled.
131 More X86-64 boot options can be found in
71cced6e 132 Documentation/x86/x86_64/boot-options.txt .
16290246 133 X86 Either 32-bit or 64-bit x86 (same as X86-32+X86-64)
c1c5413a 134 XEN Xen support is enabled
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135
136In addition, the following text indicates that the option:
137
138 BUGS= Relates to possible processor bugs on the said processor.
139 KNL Is a kernel start-up parameter.
140 BOOT Is a boot loader parameter.
141
142Parameters denoted with BOOT are actually interpreted by the boot
143loader, and have no meaning to the kernel directly.
144Do not modify the syntax of boot loader parameters without extreme
954a8b81 145need or coordination with <Documentation/x86/boot.txt>.
1da177e4 146
5558870b 147There are also arch-specific kernel-parameters not documented here.
71cced6e 148See for example <Documentation/x86/x86_64/boot-options.txt>.
5558870b 149
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150Note that ALL kernel parameters listed below are CASE SENSITIVE, and that
151a trailing = on the name of any parameter states that that parameter will
152be entered as an environment variable, whereas its absence indicates that
153it will appear as a kernel argument readable via /proc/cmdline by programs
154running once the system is up.
155
9c4751fd 156The number of kernel parameters is not limited, but the length of the
157complete command line (parameters including spaces etc.) is limited to
158a fixed number of characters. This limit depends on the architecture
159and is between 256 and 4096 characters. It is defined in the file
160./include/asm/setup.h as COMMAND_LINE_SIZE.
161
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162Finally, the [KMG] suffix is commonly described after a number of kernel
163parameter values. These 'K', 'M', and 'G' letters represent the _binary_
164multipliers 'Kilo', 'Mega', and 'Giga', equalling 2^10, 2^20, and 2^30
165bytes respectively. Such letter suffixes can also be entirely omitted.
166
9c4751fd 167
b10d79f7 168 acpi= [HW,ACPI,X86,ARM64]
03d926f8 169 Advanced Configuration and Power Interface
68ca4069 170 Format: { force | off | strict | noirq | rsdt }
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171 force -- enable ACPI if default was off
172 off -- disable ACPI if default was on
173 noirq -- do not use ACPI for IRQ routing
a9913044 174 strict -- Be less tolerant of platforms that are not
1da177e4 175 strictly ACPI specification compliant.
237889bf 176 rsdt -- prefer RSDT over (default) XSDT
aa2110cb 177 copy_dsdt -- copy DSDT to memory
b10d79f7 178 For ARM64, ONLY "acpi=off" or "acpi=force" are available
1da177e4 179
395cf969 180 See also Documentation/power/runtime_pm.txt, pci=noacpi
1da177e4 181
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182 acpi_apic_instance= [ACPI, IOAPIC]
183 Format: <int>
184 2: use 2nd APIC table, if available
185 1,0: use 1st APIC table
4e381a4f 186 default: 0
a1fdcc0d 187
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188 acpi_backlight= [HW,ACPI]
189 acpi_backlight=vendor
190 acpi_backlight=video
191 If set to vendor, prefer vendor specific driver
192 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
193 of the ACPI video.ko driver.
194
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195 acpica_no_return_repair [HW, ACPI]
196 Disable AML predefined validation mechanism
197 This mechanism can repair the evaluation result to make
198 the return objects more ACPI specification compliant.
199 This option is useful for developers to identify the
200 root cause of an AML interpreter issue when the issue
201 has something to do with the repair mechanism.
202
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203 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
204 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
1da177e4 205 Format: <int>
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206 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
207 debug output. Bits in debug_layer correspond to a
208 _COMPONENT in an ACPI source file, e.g.,
209 #define _COMPONENT ACPI_PCI_COMPONENT
210 Bits in debug_level correspond to a level in
211 ACPI_DEBUG_PRINT statements, e.g.,
212 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
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213 The debug_level mask defaults to "info". See
214 Documentation/acpi/debug.txt for more information about
215 debug layers and levels.
a0d84a92 216
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217 Enable processor driver info messages:
218 acpi.debug_layer=0x20000000
219 Enable PCI/PCI interrupt routing info messages:
220 acpi.debug_layer=0x400000
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221 Enable AML "Debug" output, i.e., stores to the Debug
222 object while interpreting AML:
223 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
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224 Enable all messages related to ACPI hardware:
225 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
226
227 Some values produce so much output that the system is
228 unusable. The "log_buf_len" parameter may be useful
229 if you need to capture more output.
f989106c 230
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231 acpi_enforce_resources= [ACPI]
232 { strict | lax | no }
233 Check for resource conflicts between native drivers
234 and ACPI OperationRegions (SystemIO and SystemMemory
235 only). IO ports and memory declared in ACPI might be
236 used by the ACPI subsystem in arbitrary AML code and
237 can interfere with legacy drivers.
238 strict (default): access to resources claimed by ACPI
239 is denied; legacy drivers trying to access reserved
240 resources will fail to bind to device using them.
241 lax: access to resources claimed by ACPI is allowed;
242 legacy drivers trying to access reserved resources
243 will bind successfully but a warning message is logged.
244 no: ACPI OperationRegions are not marked as reserved,
245 no further checks are performed.
246
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247 acpi_force_table_verification [HW,ACPI]
248 Enable table checksum verification during early stage.
249 By default, this is disabled due to x86 early mapping
250 size limitation.
251
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252 acpi_irq_balance [HW,ACPI]
253 ACPI will balance active IRQs
254 default in APIC mode
255
256 acpi_irq_nobalance [HW,ACPI]
257 ACPI will not move active IRQs (default)
258 default in PIC mode
259
260 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
261 Format: <irq>,<irq>...
262
263 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
264 use by PCI
265 Format: <irq>,<irq>...
266
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267 acpi_no_auto_serialize [HW,ACPI]
268 Disable auto-serialization of AML methods
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269 AML control methods that contain the opcodes to create
270 named objects will be marked as "Serialized" by the
271 auto-serialization feature.
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272 This feature is enabled by default.
273 This option allows to turn off the feature.
22b5afce 274
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275 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
276 kernels.
277
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278 acpi_no_static_ssdt [HW,ACPI]
279 Disable installation of static SSDTs at early boot time
280 By default, SSDTs contained in the RSDT/XSDT will be
281 installed automatically and they will appear under
282 /sys/firmware/acpi/tables.
283 This option turns off this feature.
284 Note that specifying this option does not affect
285 dynamic table installation which will install SSDT
286 tables to /sys/firmware/acpi/tables/dynamic.
0cb55ad2 287
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288 acpi_rsdp= [ACPI,EFI,KEXEC]
289 Pass the RSDP address to the kernel, mostly used
290 on machines running EFI runtime service to boot the
291 second kernel for kdump.
4dde507f 292
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293 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
294 Format: To spoof as Windows 98: ="Microsoft Windows"
295
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296 acpi_rev_override [ACPI] Override the _REV object to return 5 (instead
297 of 2 which is mandated by ACPI 6) as the supported ACPI
298 specification revision (when using this switch, it may
299 be necessary to carry out a cold reboot _twice_ in a
300 row to make it take effect on the platform firmware).
301
0cb55ad2 302 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
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303 acpi_osi="string1" # add string1
304 acpi_osi="!string2" # remove string2
741d8128 305 acpi_osi=!* # remove all strings
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306 acpi_osi=! # disable all built-in OS vendor
307 strings
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308 acpi_osi= # disable all strings
309
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310 'acpi_osi=!' can be used in combination with single or
311 multiple 'acpi_osi="string1"' to support specific OS
312 vendor string(s). Note that such command can only
313 affect the default state of the OS vendor strings, thus
314 it cannot affect the default state of the feature group
315 strings and the current state of the OS vendor strings,
316 specifying it multiple times through kernel command line
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317 is meaningless. This command is useful when one do not
318 care about the state of the feature group strings which
319 should be controlled by the OSPM.
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320 Examples:
321 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
322 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
323 can make '_OSI("Windows 2000")' TRUE.
324
325 'acpi_osi=' cannot be used in combination with other
326 'acpi_osi=' command lines, the _OSI method will not
327 exist in the ACPI namespace. NOTE that such command can
328 only affect the _OSI support state, thus specifying it
329 multiple times through kernel command line is also
330 meaningless.
331 Examples:
332 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
333 FALSE.
334
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335 'acpi_osi=!*' can be used in combination with single or
336 multiple 'acpi_osi="string1"' to support specific
337 string(s). Note that such command can affect the
338 current state of both the OS vendor strings and the
339 feature group strings, thus specifying it multiple times
340 through kernel command line is meaningful. But it may
341 still not able to affect the final state of a string if
342 there are quirks related to this string. This command
343 is useful when one want to control the state of the
344 feature group strings to debug BIOS issues related to
345 the OSPM features.
346 Examples:
347 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
348 '_OSI("Module Device")' FALSE.
349 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
350 '_OSI("Module Device")' TRUE.
351 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
352 equivalent to
353 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
354 and
355 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
356 they all will make '_OSI("Windows 2000")' TRUE.
357
6cececfc 358 acpi_pm_good [X86]
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359 Override the pmtimer bug detection: force the kernel
360 to assume that this machine's pmtimer latches its value
361 and always returns good values.
362
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363 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
364 Format: { level | edge | high | low }
365
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366 acpi_skip_timer_override [HW,ACPI]
367 Recognize and ignore IRQ0/pin2 Interrupt Override.
368 For broken nForce2 BIOS resulting in XT-PIC timer.
369
370 acpi_sleep= [HW,ACPI] Sleep options
371 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
c3b0795c 372 old_ordering, nonvs, sci_force_enable }
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373 See Documentation/power/video.txt for information on
374 s3_bios and s3_mode.
375 s3_beep is for debugging; it makes the PC's speaker beep
376 as soon as the kernel's real-mode entry point is called.
377 s4_nohwsig prevents ACPI hardware signature from being
378 used during resume from hibernation.
379 old_ordering causes the ACPI 1.0 ordering of the _PTS
380 control method, with respect to putting devices into
381 low power states, to be enforced (the ACPI 2.0 ordering
382 of _PTS is used by default).
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383 nonvs prevents the kernel from saving/restoring the
384 ACPI NVS memory during suspend/hibernation and resume.
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385 sci_force_enable causes the kernel to set SCI_EN directly
386 on resume from S1/S3 (which is against the ACPI spec,
387 but some broken systems don't work without it).
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388
389 acpi_use_timer_override [HW,ACPI]
390 Use timer override. For some broken Nvidia NF5 boards
391 that require a timer override, but don't have HPET
392
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393 add_efi_memmap [EFI; X86] Include EFI memory map in
394 kernel's map of available physical RAM.
395
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396 agp= [AGP]
397 { off | try_unsupported }
398 off: disable AGP support
399 try_unsupported: try to drive unsupported chipsets
400 (may crash computer or cause data corruption)
401
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402 ALSA [HW,ALSA]
403 See Documentation/sound/alsa/alsa-parameters.txt
404
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405 alignment= [KNL,ARM]
406 Allow the default userspace alignment fault handler
407 behaviour to be specified. Bit 0 enables warnings,
408 bit 1 enables fixups, and bit 2 sends a segfault.
409
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410 align_va_addr= [X86-64]
411 Align virtual addresses by clearing slice [14:12] when
412 allocating a VMA at process creation time. This option
413 gives you up to 3% performance improvement on AMD F15h
414 machines (where it is enabled by default) for a
415 CPU-intensive style benchmark, and it can vary highly in
416 a microbenchmark depending on workload and compiler.
417
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418 32: only for 32-bit processes
419 64: only for 64-bit processes
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420 on: enable for both 32- and 64-bit processes
421 off: disable for both 32- and 64-bit processes
422
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423 alloc_snapshot [FTRACE]
424 Allocate the ftrace snapshot buffer on boot up when the
425 main buffer is allocated. This is handy if debugging
426 and you need to use tracing_snapshot() on boot up, and
427 do not want to use tracing_snapshot_alloc() as it needs
428 to be done where GFP_KERNEL allocations are allowed.
429
89e0b9a3 430 amd_iommu= [HW,X86-64]
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431 Pass parameters to the AMD IOMMU driver in the system.
432 Possible values are:
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433 fullflush - enable flushing of IO/TLB entries when
434 they are unmapped. Otherwise they are
435 flushed before they will be reused, which
436 is a lot of faster
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437 off - do not initialize any AMD IOMMU found in
438 the system
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439 force_isolation - Force device isolation for all
440 devices. The IOMMU driver is not
441 allowed anymore to lift isolation
442 requirements as needed. This option
443 does not override iommu=pt
afa9fdc2 444
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445 amd_iommu_dump= [HW,X86-64]
446 Enable AMD IOMMU driver option to dump the ACPI table
447 for AMD IOMMU. With this option enabled, AMD IOMMU
448 driver will print ACPI tables for AMD IOMMU during
449 IOMMU initialization.
450
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451 amijoy.map= [HW,JOY] Amiga joystick support
452 Map of devices attached to JOY0DAT and JOY1DAT
453 Format: <a>,<b>
395cf969 454 See also Documentation/input/joystick.txt
1da177e4
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455
456 analog.map= [HW,JOY] Analog joystick and gamepad support
457 Specifies type or capabilities of an analog joystick
458 connected to one of 16 gameports
459 Format: <type1>,<type2>,..<type16>
460
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461 apc= [HW,SPARC]
462 Power management functions (SPARCstation-4/5 + deriv.)
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463 Format: noidle
464 Disable APC CPU standby support. SPARCstation-Fox does
465 not play well with APC CPU idle - disable it if you have
466 APC and your system crashes randomly.
467
ca1eda2d 468 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
c8facbb6 469 Change the output verbosity whilst booting
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470 Format: { quiet (default) | verbose | debug }
471 Change the amount of debugging information output
472 when initialising the APIC and IO-APIC components.
a9913044 473
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474 autoconf= [IPV6]
475 See Documentation/networking/ipv6.txt.
476
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477 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
478 Limit apic dumping. The parameter defines the maximal
479 number of local apics being dumped. Also it is possible
480 to set it to "all" by meaning -- no limit here.
481 Format: { 1 (default) | 2 | ... | all }.
482 The parameter valid if only apic=debug or
483 apic=verbose is specified.
484 Example: apic=debug show_lapic=all
485
1da177e4 486 apm= [APM] Advanced Power Management
71f77055 487 See header of arch/x86/kernel/apm_32.c.
1da177e4 488
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489 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
490 Format: <io>,<irq>,<nodeID>
491
492 ataflop= [HW,M68k]
493
494 atarimouse= [HW,MOUSE] Atari Mouse
495
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496 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
497 EzKey and similar keyboards
498
499 atkbd.reset= [HW] Reset keyboard during initialization
500
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501 atkbd.set= [HW] Select keyboard code set
502 Format: <int> (2 = AT (default), 3 = PS/2)
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503
504 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
505 keyboards
506
507 atkbd.softraw= [HW] Choose between synthetic and real raw mode
508 Format: <bool> (0 = real, 1 = synthetic (default))
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509
510 atkbd.softrepeat= [HW]
511 Use software keyboard repeat
1da177e4 512
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513 audit= [KNL] Enable the audit sub-system
514 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
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515 0 - kernel audit is disabled and can not be enabled
516 until the next reboot
517 unset - kernel audit is initialized but disabled and
518 will be fully enabled by the userspace auditd.
519 1 - kernel audit is initialized and partially enabled,
520 storing at most audit_backlog_limit messages in
521 RAM until it is fully enabled by the userspace
522 auditd.
a106fb0c 523 Default: unset
f3411cb2 524
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525 audit_backlog_limit= [KNL] Set the audit queue size limit.
526 Format: <int> (must be >=0)
527 Default: 64
528
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529 baycom_epp= [HW,AX25]
530 Format: <io>,<mode>
a9913044 531
1da177e4
LT
532 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
533 Format: <io>,<mode>
534 See header of drivers/net/hamradio/baycom_par.c.
535
a9913044
RD
536 baycom_ser_fdx= [HW,AX25]
537 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
1da177e4
LT
538 Format: <io>,<irq>,<mode>[,<baud>]
539 See header of drivers/net/hamradio/baycom_ser_fdx.c.
540
a9913044
RD
541 baycom_ser_hdx= [HW,AX25]
542 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
1da177e4
LT
543 Format: <io>,<irq>,<mode>
544 See header of drivers/net/hamradio/baycom_ser_hdx.c.
545
080506ad
PG
546 blkdevparts= Manual partition parsing of block device(s) for
547 embedded devices based on command line input.
548 See Documentation/block/cmdline-partition.txt
549
bfe8df3d
RD
550 boot_delay= Milliseconds to delay each printk during boot.
551 Values larger than 10 seconds (10000) are changed to
552 no delay (0).
553 Format: integer
554
35fc908d
AH
555 bootmem_debug [KNL] Enable bootmem allocator debug messages.
556
1da177e4 557 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
a9913044
RD
558 bttv.radio= Most important insmod options are available as
559 kernel args too.
1da177e4 560 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
395cf969 561 bttv.tuner=
1da177e4 562
4e89a2d8
WS
563 bulk_remove=off [PPC] This parameter disables the use of the pSeries
564 firmware feature for flushing multiple hpte entries
565 at a time.
566
1da177e4
LT
567 c101= [NET] Moxa C101 synchronous serial card
568
cd4f0ef7 569 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
1da177e4
LT
570 Sometimes CPU hardware bugs make them report the cache
571 size incorrectly. The kernel will attempt work arounds
572 to fix known problems, but for some CPUs it is not
573 possible to determine what the correct size should be.
574 This option provides an override for these situations.
575
ffb70f61
DK
576 ca_keys= [KEYS] This parameter identifies a specific key(s) on
577 the system trusted keyring to be used for certificate
578 trust validation.
32c4741c 579 format: { id:<keyid> | builtin }
ffb70f61 580
fd1bb4c9
FF
581 cca= [MIPS] Override the kernel pages' cache coherency
582 algorithm. Accepted values range from 0 to 7
583 inclusive. See arch/mips/include/asm/pgtable-bits.h
584 for platform specific values (SB1, Loongson3 and
585 others).
586
14ff56bb
SO
587 ccw_timeout_log [S390]
588 See Documentation/s390/CommonIO for details.
1da177e4 589
8bab8dde
PM
590 cgroup_disable= [KNL] Disable a particular controller
591 Format: {name of the controller(s) to disable}
ca0bdbb5
QH
592 The effects of cgroup_disable=foo are:
593 - foo isn't auto-mounted if you mount all cgroups in
594 a single hierarchy
595 - foo isn't visible as an individually mountable
596 subsystem
597 {Currently only "memory" controller deal with this and
598 cut the overhead, others just disable the usage. So
599 only cgroup_disable=memory is actually worthy}
8bab8dde 600
1da177e4
LT
601 checkreqprot [SELINUX] Set initial checkreqprot flag value.
602 Format: { "0" | "1" }
603 See security/selinux/Kconfig help text.
a9913044
RD
604 0 -- check protection applied by kernel (includes
605 any implied execute protection).
1da177e4
LT
606 1 -- check protection requested by application.
607 Default value is set via a kernel config option.
a9913044
RD
608 Value can be changed at runtime via
609 /selinux/checkreqprot.
610
661ca0da
SO
611 cio_ignore= [S390]
612 See Documentation/s390/CommonIO for details.
1e435256
OJ
613 clk_ignore_unused
614 [CLK]
e156ee56
MT
615 Prevents the clock framework from automatically gating
616 clocks that have not been explicitly enabled by a Linux
617 device driver but are enabled in hardware at reset or
618 by the bootloader/firmware. Note that this does not
619 force such clocks to be always-on nor does it reserve
620 those clocks in any way. This parameter is useful for
621 debug and development, but should not be needed on a
622 platform with proper driver support. For more
623 information, see Documentation/clk.txt.
661ca0da 624
cd4f0ef7 625 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
734efb46 626 [Deprecated]
3f6dee9b 627 Forces specified clocksource (if available) to be used
734efb46 628 when calculating gettimeofday(). If specified
3f6dee9b 629 clocksource is not available, it defaults to PIT.
1da177e4
LT
630 Format: { pit | tsc | cyclone | pmtmr }
631
592913ec 632 clocksource= Override the default clocksource
3d6ac984
RD
633 Format: <string>
634 Override the default clocksource and use the clocksource
635 with the name specified.
636 Some clocksource names to choose from, depending on
637 the platform:
638 [all] jiffies (this is the base, fallback clocksource)
639 [ACPI] acpi_pm
640 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
641 pxa_timer,timer3,32k_counter,timer0_1
642 [AVR32] avr32
9863c90f 643 [X86-32] pit,hpet,tsc;
3d6ac984
RD
644 scx200_hrt on Geode; cyclone on IBM x440
645 [MIPS] MIPS
646 [PARISC] cr16
647 [S390] tod
648 [SH] SuperH
649 [SPARC64] tick
650 [X86-64] hpet,tsc
651
ac72e788
AK
652 clearcpuid=BITNUM [X86]
653 Disable CPUID feature X for the kernel. See
07983f0e
RD
654 arch/x86/include/asm/cpufeature.h for the valid bit
655 numbers. Note the Linux specific bits are not necessarily
ac72e788
AK
656 stable over kernel options, but the vendor specific
657 ones should be.
658 Also note that user programs calling CPUID directly
659 or using the feature without checking anything
660 will still see it. This just prevents it from
661 being used by the kernel or shown in /proc/cpuinfo.
662 Also note the kernel might malfunction if you disable
663 some critical bits.
664
5ea3b1b2
AM
665 cma=nn[MG]@[start[MG][-end[MG]]]
666 [ARM,X86,KNL]
667 Sets the size of kernel global memory area for
668 contiguous memory allocations and optionally the
669 placement constraint by the physical address range of
f0d6d1f6
JD
670 memory allocations. A value of 0 disables CMA
671 altogether. For more information, see
c64be2bb
MS
672 include/linux/dma-contiguous.h
673
14f966e7
RJ
674 cmo_free_hint= [PPC] Format: { yes | no }
675 Specify whether pages are marked as being inactive
676 when they are freed. This is used in CMO environments
677 to determine OS memory pressure for page stealing by
678 a hypervisor.
679 Default: yes
680
c7909509
MS
681 coherent_pool=nn[KMG] [ARM,KNL]
682 Sets the size of memory pool for coherent, atomic dma
e9da6e99 683 allocations, by default set to 256K.
c7909509 684
6cececfc 685 code_bytes [X86] How many bytes of object code to print
a25bd949 686 in an oops report.
86c41837
CE
687 Range: 0 - 8192
688 Default: 64
689
1da177e4 690 com20020= [HW,NET] ARCnet - COM20020 chipset
a9913044
RD
691 Format:
692 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
1da177e4
LT
693
694 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
695 Format: <io>[,<irq>]
696
a9913044
RD
697 com90xx= [HW,NET]
698 ARCnet - COM90xx chipset (memory-mapped buffers)
1da177e4
LT
699 Format: <io>[,<irq>[,<memstart>]]
700
701 condev= [HW,S390] console device
702 conmode=
a9913044 703
1da177e4
LT
704 console= [KNL] Output console device and options.
705
706 tty<n> Use the virtual console device <n>.
707
708 ttyS<n>[,options]
f1a1c2dc 709 ttyUSB0[,options]
1da177e4 710 Use the specified serial port. The options are of
f1a1c2dc
RD
711 the form "bbbbpnf", where "bbbb" is the baud rate,
712 "p" is parity ("n", "o", or "e"), "n" is number of
713 bits, and "f" is flow control ("r" for RTS or
714 omit it). Default is "9600n8".
715
716 See Documentation/serial-console.txt for more
717 information. See
718 Documentation/networking/netconsole.txt for an
719 alternative.
1da177e4 720
18a8bd94
YL
721 uart[8250],io,<addr>[,options]
722 uart[8250],mmio,<addr>[,options]
ca782f16
PH
723 uart[8250],mmio32,<addr>[,options]
724 uart[8250],0x<addr>[,options]
1da177e4
LT
725 Start an early, polled-mode console on the 8250/16550
726 UART at the specified I/O port or MMIO address,
ca782f16
PH
727 switching to the matching ttyS device later.
728 MMIO inter-register address stride is either 8-bit
729 (mmio) or 32-bit (mmio32).
730 If none of [io|mmio|mmio32], <addr> is assumed to be
731 equivalent to 'mmio'. 'options' are specified in the
732 same format described for ttyS above; if unspecified,
733 the h/w is not re-initialized.
734
a2fd6419
KRW
735 hvc<n> Use the hypervisor console device <n>. This is for
736 both Xen and PowerPC hypervisors.
1da177e4 737
f7511d5f
ST
738 If the device connected to the port is not a TTY but a braille
739 device, prepend "brl," before the device type, for instance
740 console=brl,ttyS0
741 For now, only VisioBraille is supported.
742
f324edc8
DM
743 consoleblank= [KNL] The console blank (screen saver) timeout in
744 seconds. Defaults to 10*60 = 10mins. A value of 0
745 disables the blank timer.
746
4cb0e11b
HK
747 coredump_filter=
748 [KNL] Change the default value for
749 /proc/<pid>/coredump_filter.
750 See also Documentation/filesystems/proc.txt.
751
62027aea
LB
752 cpuidle.off=1 [CPU_IDLE]
753 disable the cpuidle sub-system
754
d68921f9
LB
755 cpu_init_udelay=N
756 [X86] Delay for N microsec between assert and de-assert
757 of APIC INIT to start processors. This delay occurs
758 on every CPU online, such as boot, and resume from suspend.
759 Default: 10000
760
1da177e4 761 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
a9913044
RD
762 Format:
763 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1da177e4 764
6f21e646
AD
765 crashkernel=size[KMG][@offset[KMG]]
766 [KNL] Using kexec, Linux can switch to a 'crash kernel'
767 upon panic. This parameter reserves the physical
768 memory region [offset, offset + size] for that kernel
769 image. If '@offset' is omitted, then a suitable offset
770 is selected automatically. Check
771 Documentation/kdump/kdump.txt for further details.
dc009d92 772
fb391599
BW
773 crashkernel=range1:size1[,range2:size2,...][@offset]
774 [KNL] Same as above, but depends on the memory
775 in the running system. The syntax of range is
776 start-[end] where start and end are both
777 a memory unit (amount[KMG]). See also
6f21e646 778 Documentation/kdump/kdump.txt for an example.
fb391599 779
adbc742b 780 crashkernel=size[KMG],high
55a20ee7
YL
781 [KNL, x86_64] range could be above 4G. Allow kernel
782 to allocate physical memory region from top, so could
783 be above 4G if system have more than 4G ram installed.
784 Otherwise memory region will be allocated below 4G, if
785 available.
786 It will be ignored if crashkernel=X is specified.
adbc742b
YL
787 crashkernel=size[KMG],low
788 [KNL, x86_64] range under 4G. When crashkernel=X,high
789 is passed, kernel could allocate physical memory region
c729de8f
YL
790 above 4G, that cause second kernel crash on system
791 that require some amount of low memory, e.g. swiotlb
792 requires at least 64M+32K low memory. Kernel would
793 try to allocate 72M below 4G automatically.
794 This one let user to specify own low range under 4G
795 for second kernel instead.
796 0: to disable low allocation.
adbc742b 797 It will be ignored when crashkernel=X,high is not used
55a20ee7 798 or memory reserved is below 4G.
c729de8f 799
1da177e4
LT
800 cs89x0_dma= [HW,NET]
801 Format: <dma>
802
803 cs89x0_media= [HW,NET]
804 Format: { rj45 | aui | bnc }
a9913044 805
a9913044 806 dasd= [HW,NET]
1da177e4
LT
807 See header of drivers/s390/block/dasd_devmap.c.
808
809 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
810 (one device per port)
811 Format: <port#>,<type>
812 See also Documentation/input/joystick-parport.txt
813
a648ec05
TR
814 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
815 time. See Documentation/dynamic-debug-howto.txt for
29e36c9f 816 details. Deprecated, see dyndbg.
a648ec05 817
1da177e4
LT
818 debug [KNL] Enable kernel debugging (events log level).
819
cae2ed9a
IM
820 debug_locks_verbose=
821 [KNL] verbose self-tests
822 Format=<0|1>
823 Print debugging info while doing the locking API
824 self-tests.
825 We default to 0 (no extra messages), setting it to
826 1 will print _a lot_ more information - normally
827 only useful to kernel developers.
828
3ac7fe5a
TG
829 debug_objects [KNL] Enable object debugging
830
3e8ebb5c
KM
831 no_debug_objects
832 [KNL] Disable object debugging
833
c0a32fc5
SG
834 debug_guardpage_minorder=
835 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
836 parameter allows control of the order of pages that will
837 be intentionally kept free (and hence protected) by the
838 buddy allocator. Bigger value increase the probability
839 of catching random memory corruption, but reduce the
840 amount of memory for normal system use. The maximum
841 possible value is MAX_ORDER/2. Setting this parameter
842 to 1 or 2 should be enough to identify most random
843 memory corruption problems caused by bugs in kernel or
844 driver code when a CPU writes to (or reads from) a
845 random memory location. Note that there exists a class
846 of memory corruptions problems caused by buggy H/W or
847 F/W or by drivers badly programing DMA (basically when
848 memory is written at bus level and the CPU MMU is
849 bypassed) which are not detectable by
850 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
851 tracking down these problems.
852
031bc574
JK
853 debug_pagealloc=
854 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
855 parameter enables the feature at boot time. In
856 default, it is disabled. We can avoid allocating huge
857 chunk of memory for debug pagealloc if we don't enable
858 it at boot time and the system will work mostly same
859 with the kernel built without CONFIG_DEBUG_PAGEALLOC.
860 on: enable the feature
861
d3af01f1
TG
862 debugpat [X86] Enable PAT debugging
863
2d27a966 864 decnet.addr= [HW,NET]
1da177e4
LT
865 Format: <area>[,<node>]
866 See also Documentation/networking/decnet.txt.
867
0cb55ad2
RD
868 default_hugepagesz=
869 [same as hugepagesz=] The size of the default
870 HugeTLB page size. This is the size represented by
871 the legacy /proc/ hugepages APIs, used for SHM, and
872 default size when mounting hugetlbfs filesystems.
873 Defaults to the default architecture's huge page size
874 if not specified.
55ff9780 875
1da177e4
LT
876 dhash_entries= [KNL]
877 Set number of hash buckets for dentry cache.
a9913044 878
b0f83b28
BH
879 disable= [IPV6]
880 See Documentation/networking/ipv6.txt.
881
151e0c7d
HD
882 disable_cpu_apicid= [X86,APIC,SMP]
883 Format: <int>
884 The number of initial APIC ID for the
885 corresponding CPU to be disabled at boot,
886 mostly used for the kdump 2nd kernel to
887 disable BSP to wake up multiple CPUs without
888 causing system reset or hang due to sending
889 INIT from AP to BSP.
890
4e8b0cf4
NA
891 disable_ddw [PPC/PSERIES]
892 Disable Dynamic DMA Window support. Use this if
893 to workaround buggy firmware.
894
b0f83b28
BH
895 disable_ipv6= [IPV6]
896 See Documentation/networking/ipv6.txt.
897
95ffa243 898 disable_mtrr_cleanup [X86]
95ffa243
YL
899 The kernel tries to adjust MTRR layout from continuous
900 to discrete, to make X server driver able to add WB
0cb55ad2 901 entry later. This parameter disables that.
95ffa243 902
093af8d7 903 disable_mtrr_trim [X86, Intel and AMD only]
99fc8d42
JB
904 By default the kernel will trim any uncacheable
905 memory out of your available memory pool based on
906 MTRR settings. This parameter disables that behavior,
907 possibly causing your machine to run very slowly.
908
6cececfc 909 disable_timer_pin_1 [X86]
0cb55ad2
RD
910 Disable PIN 1 of APIC timer
911 Can be useful to work around chipset bugs.
912
ce14c583
PB
913 dis_ucode_ldr [X86] Disable the microcode loader.
914
0cb55ad2
RD
915 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
916 this option disables the debugging code at boot.
917
918 dma_debug_entries=<number>
919 This option allows to tune the number of preallocated
920 entries for DMA-API debugging code. One entry is
921 required per DMA-API allocation. Use this if the
922 DMA-API debugging code disables itself because the
923 architectural default is too low.
924
1745de5e
JR
925 dma_debug_driver=<driver_name>
926 With this option the DMA-API debugging driver
927 filter feature can be enabled at boot time. Just
928 pass the driver to filter for as the parameter.
929 The filter can be disabled or changed to another
930 driver later using sysfs.
931
96206e29
BP
932 drm_kms_helper.edid_firmware=[<connector>:]<file>[,[<connector>:]<file>]
933 Broken monitors, graphic adapters, KVMs and EDIDless
934 panels may send no or incorrect EDID data sets.
935 This parameter allows to specify an EDID data sets
936 in the /lib/firmware directory that are used instead.
da0df92b
CE
937 Generic built-in EDID data sets are used, if one of
938 edid/1024x768.bin, edid/1280x1024.bin,
939 edid/1680x1050.bin, or edid/1920x1080.bin is given
940 and no file with the same name exists. Details and
941 instructions how to build your own EDID data are
942 available in Documentation/EDID/HOWTO.txt. An EDID
943 data set will only be used for a particular connector,
944 if its name and a colon are prepended to the EDID
96206e29
BP
945 name. Each connector may use a unique EDID data
946 set by separating the files with a comma. An EDID
947 data set with no connector name will be used for
948 any connectors not explicitly specified.
da0df92b 949
1da177e4
LT
950 dscc4.setup= [NET]
951
29e36c9f
JC
952 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
953 module.dyndbg[="val"]
954 Enable debug messages at boot time. See
955 Documentation/dynamic-debug-howto.txt for details.
956
8c3641e9
DH
957 nompx [X86] Disables Intel Memory Protection Extensions.
958 See Documentation/x86/intel_mpx.txt for more
959 information about the feature.
960
f29ba61d
BP
961 eagerfpu= [X86]
962 on enable eager fpu restore
963 off disable eager fpu restore
964 auto selects the default scheme, which automatically
965 enables eagerfpu restore for xsaveopt.
966
f2411da7
LR
967 module.async_probe [KNL]
968 Enable asynchronous probe on this module.
969
56aeeba8
MS
970 early_ioremap_debug [KNL]
971 Enable debug messages in early_ioremap support. This
972 is useful for tracking down temporary early mappings
973 which are not unmapped.
974
0cb55ad2 975 earlycon= [KNL] Output early console device and options.
0d3c673e 976
6fa62fc4
MS
977 cdns,<addr>
978 Start an early, polled-mode console on a cadence serial
979 port at the specified address. The cadence serial port
980 must already be setup and configured. Options are not
981 yet supported.
982
0cb55ad2
RD
983 uart[8250],io,<addr>[,options]
984 uart[8250],mmio,<addr>[,options]
1917ac76 985 uart[8250],mmio32,<addr>[,options]
6e63be3f 986 uart[8250],mmio32be,<addr>[,options]
ca782f16 987 uart[8250],0x<addr>[,options]
0cb55ad2
RD
988 Start an early, polled-mode console on the 8250/16550
989 UART at the specified I/O port or MMIO address.
16290246 990 MMIO inter-register address stride is either 8-bit
6e63be3f
NC
991 (mmio) or 32-bit (mmio32 or mmio32be).
992 If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
993 to be equivalent to 'mmio'. 'options' are specified
994 in the same format described for "console=ttyS<n>"; if
ca782f16 995 unspecified, the h/w is not initialized.
0cb55ad2 996
0d3c673e
RH
997 pl011,<addr>
998 Start an early, polled-mode console on a pl011 serial
999 port at the specified address. The pl011 serial port
1000 must already be setup and configured. Options are not
1001 yet supported.
1002
0efe7296
SB
1003 msm_serial,<addr>
1004 Start an early, polled-mode console on an msm serial
1005 port at the specified address. The serial port
1006 must already be setup and configured. Options are not
1007 yet supported.
1008
1009 msm_serial_dm,<addr>
1010 Start an early, polled-mode console on an msm serial
1011 dm port at the specified address. The serial port
1012 must already be setup and configured. Options are not
1013 yet supported.
1014
d50d7269
RH
1015 smh Use ARM semihosting calls for early console.
1016
b94ba032
TF
1017 s3c2410,<addr>
1018 s3c2412,<addr>
1019 s3c2440,<addr>
1020 s3c6400,<addr>
1021 s5pv210,<addr>
1022 exynos4210,<addr>
1023 Use early console provided by serial driver available
1024 on Samsung SoCs, requires selecting proper type and
1025 a correct base address of the selected UART port. The
1026 serial port must already be setup and configured.
1027 Options are not yet supported.
1028
7913ad1a 1029 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1da177e4 1030 earlyprintk=vga
72548e83 1031 earlyprintk=efi
2482a92e 1032 earlyprintk=xen
1da177e4 1033 earlyprintk=serial[,ttySn[,baudrate]]
147ea091 1034 earlyprintk=serial[,0x...[,baudrate]]
ea3acb19 1035 earlyprintk=ttySn[,baudrate]
9780bc41 1036 earlyprintk=dbgp[debugController#]
c43088e3 1037 earlyprintk=pciserial,bus:device.function[,baudrate]
1da177e4 1038
147ea091
DH
1039 earlyprintk is useful when the kernel crashes before
1040 the normal console is initialized. It is not enabled by
1041 default because it has some cosmetic problems.
1042
a9913044 1043 Append ",keep" to not disable it when the real console
1da177e4
LT
1044 takes over.
1045
72548e83
MF
1046 Only one of vga, efi, serial, or usb debug port can
1047 be used at a time.
1da177e4 1048
147ea091
DH
1049 Currently only ttyS0 and ttyS1 may be specified by
1050 name. Other I/O ports may be explicitly specified
1051 on some architectures (x86 and arm at least) by
1052 replacing ttySn with an I/O port address, like this:
1053 earlyprintk=serial,0x1008,115200
1054 You can find the port for a given device in
1055 /proc/tty/driver/serial:
1056 2: uart:ST16650V2 port:00001008 irq:18 ...
1da177e4
LT
1057
1058 Interaction with the standard serial driver is not
1059 very good.
1060
72548e83
MF
1061 The VGA and EFI output is eventually overwritten by
1062 the real console.
1da177e4 1063
2482a92e
KRW
1064 The xen output can only be used by Xen PV guests.
1065
c700f013
CG
1066 edac_report= [HW,EDAC] Control how to report EDAC event
1067 Format: {"on" | "off" | "force"}
1068 on: enable EDAC to report H/W event. May be overridden
1069 by other higher priority error reporting module.
1070 off: disable H/W event reporting through EDAC.
1071 force: enforce the use of EDAC to report H/W event.
1072 default: on.
1073
9731191f
JW
1074 ekgdboc= [X86,KGDB] Allow early kernel console debugging
1075 ekgdboc=kbd
1076
25985edc 1077 This is designed to be used in conjunction with
9731191f
JW
1078 the boot argument: earlyprintk=vga
1079
1da177e4 1080 edd= [EDD]
8c4dd606 1081 Format: {"off" | "on" | "skip[mbr]"}
1da177e4 1082
d2f7cbe7 1083 efi= [EFI]
fed6cefe 1084 Format: { "old_map", "nochunk", "noruntime", "debug" }
d2f7cbe7
BP
1085 old_map [X86-64]: switch to the old ioremap-based EFI
1086 runtime services mapping. 32-bit still uses this one by
1087 default.
5a17dae4
MF
1088 nochunk: disable reading files in "chunks" in the EFI
1089 boot stub, as chunking can cause problems with some
1090 firmware implementations.
5ae3683c 1091 noruntime : disable EFI runtime services support
fed6cefe 1092 debug: enable misc debug output
d2f7cbe7 1093
8c58bf3e
RW
1094 efi_no_storage_paranoia [EFI; X86]
1095 Using this parameter you can use more than 50% of
1096 your efi variable storage. Use this parameter only if
1097 you are really sure that your UEFI does sane gc and
1098 fulfills the spec otherwise your board may brick.
1099
1da177e4
LT
1100 eisa_irq_edge= [PARISC,HW]
1101 See header of drivers/parisc/eisa.c.
1102
cd4f0ef7 1103 elanfreq= [X86-32]
1da177e4 1104 See comment before function elanfreq_setup() in
71f77055 1105 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1da177e4
LT
1106
1107 elevator= [IOSCHED]
17a9e7bb 1108 Format: {"cfq" | "deadline" | "noop"}
395cf969 1109 See Documentation/block/cfq-iosched.txt and
a9913044
RD
1110 Documentation/block/deadline-iosched.txt for details.
1111
d3bf3795 1112 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
a9913044 1113 Specifies physical address of start of kernel core
d3bf3795
MH
1114 image elf header and optionally the size. Generally
1115 kexec loader will pass this option to capture kernel.
aac04b32 1116 See Documentation/kdump/kdump.txt for details.
1da177e4 1117
0cb55ad2
RD
1118 enable_mtrr_cleanup [X86]
1119 The kernel tries to adjust MTRR layout from continuous
1120 to discrete, to make X server driver able to add WB
1121 entry later. This parameter enables that.
1122
ca1eda2d 1123 enable_timer_pin_1 [X86]
0cb55ad2
RD
1124 Enable PIN 1 of APIC timer
1125 Can be useful to work around chipset bugs
1126 (in particular on some ATI chipsets).
1127 The kernel tries to set a reasonable default.
1128
1da177e4
LT
1129 enforcing [SELINUX] Set initial enforcing status.
1130 Format: {"0" | "1"}
1131 See security/selinux/Kconfig help text.
1132 0 -- permissive (log only, no denials).
1133 1 -- enforcing (deny and log).
1134 Default value is 0.
1135 Value can be changed at runtime via /selinux/enforce.
1136
a08f82d0
HY
1137 erst_disable [ACPI]
1138 Disable Error Record Serialization Table (ERST)
1139 support.
1140
1da177e4
LT
1141 ether= [HW,NET] Ethernet cards parameters
1142 This option is obsoleted by the "netdev=" option, which
1143 has equivalent usage. See its documentation for details.
1144
7102ebcd
MZ
1145 evm= [EVM]
1146 Format: { "fix" }
1147 Permit 'security.evm' to be updated regardless of
1148 current integrity status.
1149
de1ba09b
AM
1150 failslab=
1151 fail_page_alloc=
1152 fail_make_request=[KNL]
1153 General fault injection mechanism.
1154 Format: <interval>,<probability>,<space>,<times>
395cf969 1155 See also Documentation/fault-injection/.
de1ba09b 1156
1da177e4 1157 floppy= [HW]
31c00fc1 1158 See Documentation/blockdev/floppy.txt.
1da177e4 1159
f13ae30e
AC
1160 force_pal_cache_flush
1161 [IA-64] Avoid check_sal_cache_flush which may hang on
1162 buggy SAL_CACHE_FLUSH implementations. Using this
1163 parameter will force ia64_sal_cache_flush to call
1164 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1165
69f2366c
CB
1166 forcepae [X86-32]
1167 Forcefully enable Physical Address Extension (PAE).
1168 Many Pentium M systems disable PAE but may have a
1169 functionally usable PAE implementation.
1170 Warning: use of this parameter will taint the kernel
1171 and may cause unknown problems.
1172
d9e54076 1173 ftrace=[tracer]
2af15d6a 1174 [FTRACE] will set and start the specified tracer
d9e54076
PZ
1175 as early as possible in order to facilitate early
1176 boot debugging.
1177
cecbca96 1178 ftrace_dump_on_oops[=orig_cpu]
2af15d6a 1179 [FTRACE] will dump the trace buffers on oops.
cecbca96
FW
1180 If no parameter is passed, ftrace will dump
1181 buffers of all CPUs, but if you pass orig_cpu, it will
1182 dump only the buffer of the CPU that triggered the
1183 oops.
2af15d6a
SR
1184
1185 ftrace_filter=[function-list]
1186 [FTRACE] Limit the functions traced by the function
1187 tracer at boot up. function-list is a comma separated
1188 list of functions. This list can be changed at run
1189 time by the set_ftrace_filter file in the debugfs
16290246 1190 tracing directory.
2af15d6a
SR
1191
1192 ftrace_notrace=[function-list]
1193 [FTRACE] Do not trace the functions specified in
1194 function-list. This list can be changed at run time
1195 by the set_ftrace_notrace file in the debugfs
1196 tracing directory.
d9e54076 1197
369bc18f
SA
1198 ftrace_graph_filter=[function-list]
1199 [FTRACE] Limit the top level callers functions traced
1200 by the function graph tracer at boot up.
1201 function-list is a comma separated list of functions
1202 that can be changed at run time by the
1203 set_graph_function file in the debugfs tracing directory.
1204
0d7d9a16
NK
1205 ftrace_graph_notrace=[function-list]
1206 [FTRACE] Do not trace from the functions specified in
1207 function-list. This list is a comma separated list of
1208 functions that can be changed at run time by the
1209 set_graph_notrace file in the debugfs tracing directory.
1210
1da177e4
LT
1211 gamecon.map[2|3]=
1212 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1213 support via parallel port (up to 5 devices per port)
1214 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1215 See also Documentation/input/joystick-parport.txt
1216
1217 gamma= [HW,DRM]
1218
aaf23042
YL
1219 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1220 Format: off | on
1221 default: on
1222
2521f2c2
PO
1223 gcov_persist= [GCOV] When non-zero (default), profiling data for
1224 kernel modules is saved and remains accessible via
1225 debugfs, even when the module is unloaded/reloaded.
1226 When zero, profiling data is discarded and associated
1227 debugfs files are removed at module unload time.
1228
1da177e4 1229 gpt [EFI] Forces disk with valid GPT signature but
6c5de79b
DB
1230 invalid Protective MBR to be treated as GPT. If the
1231 primary GPT is corrupted, it enables the backup/alternate
1232 GPT to be used instead.
1da177e4 1233
6cec9b07
AL
1234 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1235 the "Enable 0" bit of the configuration register.
1236 Format: 0 | 1
1237 Default: 0
1238 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1239 the "Enable 0" bit of the configuration register.
1240 Format: 0 | 1
1241 Default: 0
1242 grcan.select= [HW] Select which physical interface to use.
1243 Format: 0 | 1
1244 Default: 0
1245 grcan.txsize= [HW] Sets the size of the tx buffer.
1246 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1247 Default: 1024
1248 grcan.rxsize= [HW] Sets the size of the rx buffer.
1249 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1250 Default: 1024
1251
1da177e4
LT
1252 hashdist= [KNL,NUMA] Large hashes allocated during boot
1253 are distributed across NUMA nodes. Defaults on
16290246 1254 for 64-bit NUMA, off otherwise.
a9913044 1255 Format: 0 | 1 (for off | on)
1da177e4
LT
1256
1257 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1258
1259 hd= [EIDE] (E)IDE hard drive subsystem geometry
1260 Format: <cyl>,<head>,<sect>
1261
ea8c071c
HY
1262 hest_disable [ACPI]
1263 Disable Hardware Error Source Table (HEST) support;
1264 corresponding firmware-first mode error processing
1265 logic will be disabled.
1266
1da177e4
LT
1267 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1268 size of <nn>. This works even on boxes that have no
1269 highmem otherwise. This also works to reduce highmem
1270 size on bigger boxes.
1271
54cdfdb4
TG
1272 highres= [KNL] Enable/disable high resolution timer mode.
1273 Valid parameters: "on", "off"
1274 Default: "on"
1275
1da177e4
LT
1276 hisax= [HW,ISDN]
1277 See Documentation/isdn/README.HiSax.
1278
0cb55ad2
RD
1279 hlt [BUGS=ARM,SH]
1280
1281 hpet= [X86-32,HPET] option to control HPET usage
1282 Format: { enable (default) | disable | force |
1283 verbose }
1284 disable: disable HPET and use PIT instead
1285 force: allow force enabled of undocumented chips (ICH4,
1286 VIA, nVidia)
1287 verbose: show contents of HPET registers during setup
1288
3d035f58
PB
1289 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1290 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1291
b4718e62
AK
1292 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1293 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
0d9ea754
JT
1294 On x86-64 and powerpc, this option can be specified
1295 multiple times interleaved with hugepages= to reserve
1296 huge pages of different sizes. Valid pages sizes on
1297 x86-64 are 2M (when the CPU supports "pse") and 1G
27ec26ec 1298 (when the CPU supports the "pdpe1gb" cpuinfo flag).
6902aa84 1299
555d61d6
HB
1300 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1301 terminal devices. Valid values: 0..8
431429ff
HB
1302 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1303 If specified, z/VM IUCV HVC accepts connections
1304 from listed z/VM user IDs only.
cef7125d 1305
fdabf525
JH
1306 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1307 hardware thread id mappings.
1308 Format: <cpu>:<hwthread>
1309
7bf69395
FDN
1310 keep_bootcon [KNL]
1311 Do not unregister boot console at start. This is only
1312 useful for debugging when something happens in the window
1313 between unregistering the boot console and initializing
1314 the real console.
1315
3a853fb9 1316 i2c_bus= [HW] Override the default board specific I2C bus speed
7954763b
JN
1317 or register an additional I2C bus that is not
1318 registered from board initialization code.
3a853fb9
JN
1319 Format:
1320 <bus_id>,<clkrate>
1321
36d95739 1322 i8042.debug [HW] Toggle i8042 debug mode
e1443d28
SCP
1323 i8042.unmask_kbd_data
1324 [HW] Enable printing of interrupt data from the KBD port
1325 (disabled by default, and as a pre-condition
1326 requires that i8042.debug=1 be enabled)
1da177e4 1327 i8042.direct [HW] Put keyboard port into non-translated mode
84eb8d06
ML
1328 i8042.dumbkbd [HW] Pretend that controller can only read data from
1329 keyboard and cannot control its state
1da177e4
LT
1330 (Don't attempt to blink the leds)
1331 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
945ef0d4 1332 i8042.nokbd [HW] Don't check/create keyboard port
75d08c78
JK
1333 i8042.noloop [HW] Disable the AUX Loopback command while probing
1334 for the AUX port
1da177e4 1335 i8042.nomux [HW] Don't check presence of an active multiplexing
e55a3366 1336 controller
1da177e4
LT
1337 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1338 controllers
24775d65 1339 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1da177e4
LT
1340 i8042.reset [HW] Reset the controller during init and cleanup
1341 i8042.unlock [HW] Unlock (ignore) the keylock
148e9a71 1342 i8042.kbdreset [HW] Reset device connected to KBD port
1da177e4
LT
1343
1344 i810= [HW,DRM]
1345
e70c9d5e
DT
1346 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1347 indicates that the driver is running on unsupported
1348 hardware.
1da177e4
LT
1349 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1350 does not match list of supported models.
1351 i8k.power_status
1352 [HW] Report power status in /proc/i8k
1353 (disabled by default)
1354 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1355 capability is set.
1356
4dca20ef 1357 i915.invert_brightness=
7bd90909
CE
1358 [DRM] Invert the sense of the variable that is used to
1359 set the brightness of the panel backlight. Normally a
4dca20ef
CE
1360 brightness value of 0 indicates backlight switched off,
1361 and the maximum of the brightness value sets the backlight
1362 to maximum brightness. If this parameter is set to 0
1363 (default) and the machine requires it, or this parameter
1364 is set to 1, a brightness value of 0 sets the backlight
1365 to maximum brightness, and the maximum of the brightness
1366 value switches the backlight off.
1367 -1 -- never invert brightness
1368 0 -- machine default
1369 1 -- force brightness inversion
7bd90909 1370
1da177e4
LT
1371 icn= [HW,ISDN]
1372 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1373
0af80c04
DF
1374 ide-core.nodma= [HW] (E)IDE subsystem
1375 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
075affcb
BZ
1376 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1377 .cdrom .chs .ignore_cable are additional options
1c10e938 1378 See Documentation/ide/ide.txt.
1da177e4 1379
0f8b7f5d
MR
1380 ide-generic.probe-mask= [HW] (E)IDE subsystem
1381 Format: <int>
1382 Probe mask for legacy ISA IDE ports. Depending on
1383 platform up to 6 ports are supported, enabled by
1384 setting corresponding bits in the mask to 1. The
1385 default value is 0x0, which has a special meaning.
1386 On systems that have PCI, it triggers scanning the
1387 PCI bus for the first and the second port, which
1388 are then probed. On systems without PCI the value
1389 of 0x0 enables probing the two first ports as if it
1390 was 0x3.
1391
0cb55ad2
RD
1392 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1393 Claim all unknown PCI IDE storage controllers.
1394
f039b754 1395 idle= [X86]
69fb3676 1396 Format: idle=poll, idle=halt, idle=nomwait
ada9cfdd
RD
1397 Poll forces a polling idle loop that can slightly
1398 improve the performance of waking up a idle CPU, but
1399 will use a lot of power and make the system run hot.
1400 Not recommended.
ada9cfdd 1401 idle=halt: Halt is forced to be used for CPU idle.
c1e3b377 1402 In such case C2/C3 won't be used again.
ada9cfdd 1403 idle=nomwait: Disable mwait for CPU C-states
a9913044 1404
79290822
IM
1405 ignore_loglevel [KNL]
1406 Ignore loglevel setting - this will print /all/
1407 kernel messages to the console. Useful for debugging.
0eca6b7c
YZ
1408 We also add it as printk module parameter, so users
1409 could change it dynamically, usually by
1410 /sys/module/printk/parameters/ignore_loglevel.
79290822 1411
1da177e4
LT
1412 ihash_entries= [KNL]
1413 Set number of hash buckets for inode cache.
1414
2fe5d6de 1415 ima_appraise= [IMA] appraise integrity measurements
2faa6ef3 1416 Format: { "off" | "enforce" | "fix" | "log" }
2fe5d6de
MZ
1417 default: "enforce"
1418
07f6a794
MZ
1419 ima_appraise_tcb [IMA]
1420 The builtin appraise policy appraises all files
1421 owned by uid=0.
1422
3323eec9 1423 ima_hash= [IMA]
e7a2ad7e
MZ
1424 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1425 | sha512 | ... }
3323eec9
MZ
1426 default: "sha1"
1427
e7a2ad7e
MZ
1428 The list of supported hash algorithms is defined
1429 in crypto/hash_info.h.
1430
24fd03c8
MZ
1431 ima_policy= [IMA]
1432 The builtin measurement policy to load during IMA
1433 setup. Specyfing "tcb" as the value, measures all
1434 programs exec'd, files mmap'd for exec, and all files
1435 opened with the read mode bit set by either the
1436 effective uid (euid=0) or uid=0.
1437 Format: "tcb"
1438
1439 ima_tcb [IMA] Deprecated. Use ima_policy= instead.
5789ba3b
EP
1440 Load a policy which meets the needs of the Trusted
1441 Computing Base. This means IMA will measure all
1442 programs exec'd, files mmap'd for exec, and all files
1443 opened for read by uid=0.
1444
9b9d4ce5
RS
1445 ima_template= [IMA]
1446 Select one of defined IMA measurements template formats.
8265a2f8 1447 Formats: { "ima" | "ima-ng" | "ima-sig" }
9b9d4ce5
RS
1448 Default: "ima-ng"
1449
c2426d2a
RS
1450 ima_template_fmt=
1451 [IMA] Define a custom template format.
1452 Format: { "field1|...|fieldN" }
1453
3bcced39
DK
1454 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1455 Format: <min_file_size>
1456 Set the minimal file size for using asynchronous hash.
1457 If left unspecified, ahash usage is disabled.
1458
1459 ahash performance varies for different data sizes on
1460 different crypto accelerators. This option can be used
1461 to achieve the best performance for a particular HW.
1462
6edf7a89
DK
1463 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1464 Format: <bufsize>
1465 Set hashing buffer size. Default: 4k.
1466
1467 ahash performance varies for different chunk sizes on
1468 different crypto accelerators. This option can be used
1469 to achieve best performance for particular HW.
1470
1da177e4
LT
1471 init= [KNL]
1472 Format: <full_path>
1473 Run specified binary instead of /sbin/init as init
1474 process.
1475
1476 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1477 for working out where the kernel is dying during
1478 startup.
1479
7b0b73d7
PB
1480 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1481 initcall functions. Useful for debugging built-in
1482 modules and initcalls.
1483
1da177e4
LT
1484 initrd= [BOOT] Specify the location of the initial ramdisk
1485
1486 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1487 Format: <irq>
1488
6bb2ff84
FY
1489 int_pln_enable [x86] Enable power limit notification interrupt
1490
d726d8d7
MZ
1491 integrity_audit=[IMA]
1492 Format: { "0" | "1" }
1493 0 -- basic integrity auditing messages. (Default)
1494 1 -- additional integrity auditing messages.
1495
ba395927 1496 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
0cd5c3c8
KM
1497 on
1498 Enable intel iommu driver.
ba395927
KA
1499 off
1500 Disable intel iommu driver.
1501 igfx_off [Default Off]
1502 By default, gfx is mapped as normal device. If a gfx
1503 device has a dedicated DMAR unit, the DMAR unit is
1504 bypassed by not enabling DMAR with this option. In
1505 this case, gfx device will use physical address for
1506 DMA.
7d3b03ce
KA
1507 forcedac [x86_64]
1508 With this option iommu will not optimize to look
16290246 1509 for io virtual address below 32-bit forcing dual
7d3b03ce 1510 address cycle on pci bus for cards supporting greater
16290246
RD
1511 than 32-bit addressing. The default is to look
1512 for translation below 32-bit and if not available
7d3b03ce 1513 then look in the higher range.
5e0d2a6f 1514 strict [Default Off]
1515 With this option on every unmap_single operation will
1516 result in a hardware IOTLB flush operation as opposed
1517 to batching them for performance.
6dd9a7c7
YS
1518 sp_off [Default Off]
1519 By default, super page will be supported if Intel IOMMU
1520 has the capability. With this option, super page will
1521 not be supported.
c83b2f20
DW
1522 ecs_off [Default Off]
1523 By default, extended context tables will be supported if
1524 the hardware advertises that it has support both for the
1525 extended tables themselves, and also PASID support. With
1526 this option set, extended tables will not be used even
1527 on hardware which claims to support them.
2e92c7ad
MI
1528
1529 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1530 0 disables intel_idle and fall back on acpi_idle.
1531 1 to 6 specify maximum depth of C-state.
1532
6be26498
DB
1533 intel_pstate= [X86]
1534 disable
1535 Do not enable intel_pstate as the default
1536 scaling driver for the supported processors
aa4ea34d
EZ
1537 force
1538 Enable intel_pstate on systems that prohibit it by default
1539 in favor of acpi-cpufreq. Forcing the intel_pstate driver
1540 instead of acpi-cpufreq may disable platform features, such
1541 as thermal controls and power capping, that rely on ACPI
1542 P-States information being indicated to OSPM and therefore
1543 should be used with caution. This option does not work with
1544 processors that aren't supported by the intel_pstate driver
1545 or on platforms that use pcc-cpufreq instead of acpi-cpufreq.
2f86dc4c
DB
1546 no_hwp
1547 Do not enable hardware P state control (HWP)
1548 if available.
d64c3b0b
KCA
1549 hwp_only
1550 Only load intel_pstate on systems which support
1551 hardware P state control (HWP) if available.
6be26498 1552
d1423d56 1553 intremap= [X86-64, Intel-IOMMU]
d1423d56
CW
1554 on enable Interrupt Remapping (default)
1555 off disable Interrupt Remapping
1556 nosid disable Source ID checking
41750d31
SS
1557 no_x2apic_optout
1558 BIOS x2APIC opt-out request will be ignored
d1423d56 1559
0cb55ad2
RD
1560 iomem= Disable strict checking of access to MMIO memory
1561 strict regions from userspace.
1562 relaxed
1563
1564 iommu= [x86]
1565 off
1566 force
1567 noforce
1568 biomerge
1569 panic
1570 nopanic
1571 merge
1572 nomerge
1573 forcesac
1574 soft
bcb71abe 1575 pt [x86, IA-64]
4e287840
TLSC
1576 nobypass [PPC/POWERNV]
1577 Disable IOMMU bypass, using IOMMU for PCI devices.
bcb71abe 1578
0cb55ad2
RD
1579
1580 io7= [HW] IO7 for Marvel based alpha systems
1581 See comment before marvel_specify_io7 in
1582 arch/alpha/kernel/core_marvel.c.
1583
6cececfc 1584 io_delay= [X86] I/O delay method
6e7c4025
IM
1585 0x80
1586 Standard port 0x80 based delay
1587 0xed
1588 Alternate port 0xed based delay (needed on some systems)
b02aae9c 1589 udelay
6e7c4025
IM
1590 Simple two microseconds delay
1591 none
1592 No delay
b02aae9c 1593
1da177e4 1594 ip= [IP_PNP]
dc7a0816 1595 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 1596
200803df
AC
1597 irqfixup [HW]
1598 When an interrupt is not handled search all handlers
1599 for it. Intended to get systems with badly broken
1600 firmware running.
1601
1602 irqpoll [HW]
1603 When an interrupt is not handled search all handlers
1604 for it. Also check all handlers each timer
1605 interrupt. Intended to get systems with badly broken
1606 firmware running.
1607
1da177e4 1608 isapnp= [ISAPNP]
a9913044 1609 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1da177e4
LT
1610
1611 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
22f2e280
DF
1612 Format:
1613 <cpu number>,...,<cpu number>
1614 or
b225d44e
LZ
1615 <cpu number>-<cpu number>
1616 (must be a positive range in ascending order)
22f2e280
DF
1617 or a mixture
1618 <cpu number>,...,<cpu number>-<cpu number>
b225d44e 1619
1da177e4
LT
1620 This option can be used to specify one or more CPUs
1621 to isolate from the general SMP balancing and scheduling
b225d44e
LZ
1622 algorithms. You can move a process onto or off an
1623 "isolated" CPU via the CPU affinity syscalls or cpuset.
1da177e4
LT
1624 <cpu number> begins at 0 and the maximum value is
1625 "number of CPUs in system - 1".
1626
1627 This option is the preferred way to isolate CPUs. The
a9913044
RD
1628 alternative -- manually setting the CPU mask of all
1629 tasks in the system -- can cause problems and
1630 suboptimal load balancer performance.
1da177e4 1631
a9913044 1632 iucv= [HW,NET]
1da177e4 1633
7d8bfa26
JR
1634 ivrs_ioapic [HW,X86_64]
1635 Provide an override to the IOAPIC-ID<->DEVICE-ID
1636 mapping provided in the IVRS ACPI table. For
1637 example, to map IOAPIC-ID decimal 10 to
1638 PCI device 00:14.0 write the parameter as:
1639 ivrs_ioapic[10]=00:14.0
1640
1641 ivrs_hpet [HW,X86_64]
1642 Provide an override to the HPET-ID<->DEVICE-ID
1643 mapping provided in the IVRS ACPI table. For
1644 example, to map HPET-ID decimal 0 to
1645 PCI device 00:14.0 write the parameter as:
1646 ivrs_hpet[0]=00:14.0
1647
1da177e4
LT
1648 js= [HW,JOY] Analog joystick
1649 See Documentation/input/joystick.txt.
1650
24f2e027
KC
1651 kaslr/nokaslr [X86]
1652 Enable/disable kernel and module base offset ASLR
1653 (Address Space Layout Randomization) if built into
1654 the kernel. When CONFIG_HIBERNATION is selected,
1655 kASLR is disabled by default. When kASLR is enabled,
1656 hibernation will be disabled.
1657
0cb55ad2
RD
1658 keepinitrd [HW,ARM]
1659
6cececfc 1660 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
ed7ed365
MG
1661 specifies the amount of memory usable by the kernel
1662 for non-movable allocations. The requested amount is
1663 spread evenly throughout all nodes in the system. The
1664 remaining memory in each node is used for Movable
1665 pages. In the event, a node is too small to have both
1666 kernelcore and Movable pages, kernelcore pages will
1667 take priority and other nodes will have a larger number
675217fd 1668 of Movable pages. The Movable zone is used for the
ed7ed365
MG
1669 allocation of pages that may be reclaimed or moved
1670 by the page migration subsystem. This means that
1671 HugeTLB pages may not be allocated from this zone.
1672 Note that allocations like PTEs-from-HighMem still
1673 use the HighMem zone if it exists, and the Normal
1674 zone if it does not.
1675
4fe1da4e
JW
1676 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1677 Format: <Controller#>[,poll interval]
1678 The controller # is the number of the ehci usb debug
1679 port as it is probed via PCI. The poll interval is
1680 optional and is the number seconds in between
1681 each poll cycle to the debug port in case you need
1682 the functionality for interrupting the kernel with
1683 gdb or control-c on the dbgp connection. When
1684 not using this parameter you use sysrq-g to break into
1685 the kernel debugger.
1686
84c08fd6 1687 kgdboc= [KGDB,HW] kgdb over consoles.
ada64e4c
JW
1688 Requires a tty driver that supports console polling,
1689 or a supported polling keyboard driver (non-usb).
65b5ac14
JW
1690 Serial only format: <serial_device>[,baud]
1691 keyboard only format: kbd
1692 keyboard and serial format: kbd,<serial_device>[,baud]
1693 Optional Kernel mode setting:
1694 kms, kbd format: kms,kbd
1695 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
6cdf6e06 1696
84c08fd6
JW
1697 kgdbwait [KGDB] Stop kernel execution and enter the
1698 kernel debugger at the earliest opportunity.
1699
9bed90c6
FF
1700 kmac= [MIPS] korina ethernet MAC address.
1701 Configure the RouterBoard 532 series on-chip
1702 Ethernet adapter MAC address.
1703
04f70336
CM
1704 kmemleak= [KNL] Boot-time kmemleak enable/disable
1705 Valid arguments: on, off
1706 Default: on
47aeeddc
MI
1707 Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
1708 the default is off.
04f70336 1709
c3ac14b2
XQ
1710 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1711 Valid arguments: 0, 1, 2
1712 kmemcheck=0 (disabled)
1713 kmemcheck=1 (enabled)
1714 kmemcheck=2 (one-shot mode)
1715 Default: 2 (one-shot mode)
1716
6cececfc 1717 kstack=N [X86] Print N words from the kernel stack
0cb55ad2
RD
1718 in oops dumps.
1719
fef07aae
AP
1720 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1721 Default is 0 (don't ignore, but inject #GP)
1722
a182d873
XG
1723 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1724 KVM MMU at runtime.
fef07aae
AP
1725 Default is 0 (off)
1726
fef07aae 1727 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
8475f94a 1728 Default is 1 (enabled)
fef07aae
AP
1729
1730 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1731 for all guests.
16290246 1732 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
fef07aae 1733
fef07aae
AP
1734 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1735 (virtualized MMU) support on capable Intel chips.
1736 Default is 1 (enabled)
1737
1738 kvm-intel.emulate_invalid_guest_state=
1739 [KVM,Intel] Enable emulation of invalid guest states
1740 Default is 0 (disabled)
1741
1742 kvm-intel.flexpriority=
1743 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1744 Default is 1 (enabled)
1745
e1a72ae2
SL
1746 kvm-intel.nested=
1747 [KVM,Intel] Enable VMX nesting (nVMX).
1748 Default is 0 (disabled)
1749
fef07aae
AP
1750 kvm-intel.unrestricted_guest=
1751 [KVM,Intel] Disable unrestricted guest feature
1752 (virtualized real and unpaged mode) on capable
1753 Intel chips. Default is 1 (enabled)
1754
1755 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1756 feature (tagged TLBs) on capable Intel chips.
1757 Default is 1 (enabled)
1758
1da177e4
LT
1759 l2cr= [PPC]
1760
a78bfbfc
RB
1761 l3cr= [PPC]
1762
cd4f0ef7 1763 lapic [X86-32,APIC] Enable the local APIC even if BIOS
a9913044 1764 disabled it.
1da177e4 1765
279f1461
SS
1766 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1767 value for LAPIC timer one-shot implementation. Default
1768 back to the programmable timer unit in the LAPIC.
1769
6cececfc 1770 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
ada9cfdd 1771 in C2 power state.
e585bef8 1772
fcb71f6f
FC
1773 libata.dma= [LIBATA] DMA control
1774 libata.dma=0 Disable all PATA and SATA DMA
1775 libata.dma=1 PATA and SATA Disk DMA only
1776 libata.dma=2 ATAPI (CDROM) DMA only
16290246 1777 libata.dma=4 Compact Flash DMA only
fcb71f6f
FC
1778 Combinations also work, so libata.dma=3 enables DMA
1779 for disks and CDROMs, but not CFs.
16290246 1780
20308871
MP
1781 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1782 libata.ignore_hpa=0 keep BIOS limits (default)
1783 libata.ignore_hpa=1 ignore limits, using full disk
fcb71f6f 1784
78e70c23
DJ
1785 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1786 when set.
1787 Format: <int>
1788
33267325
TH
1789 libata.force= [LIBATA] Force configurations. The format is comma
1790 separated list of "[ID:]VAL" where ID is
4c44f309 1791 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
33267325
TH
1792 matching port, link or device. Basically, it matches
1793 the ATA ID string printed on console by libata. If
1794 the whole ID part is omitted, the last PORT and DEVICE
1795 values are used. If ID hasn't been specified yet, the
1796 configuration applies to all ports, links and devices.
1797
1798 If only DEVICE is omitted, the parameter applies to
1799 the port and all links and devices behind it. DEVICE
1800 number of 0 either selects the first device or the
1801 first fan-out link behind PMP device. It does not
1802 select the host link. DEVICE number of 15 selects the
1803 host link and device attached to it.
1804
1805 The VAL specifies the configuration to force. As long
1806 as there's no ambiguity shortcut notation is allowed.
1807 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1808 The following configurations can be forced.
1809
1810 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1811 Any ID with matching PORT is used.
1812
1813 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1814
1815 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1816 udma[/][16,25,33,44,66,100,133] notation is also
1817 allowed.
1818
1819 * [no]ncq: Turn on or off NCQ.
1820
d7b16e4f
MP
1821 * [no]ncqtrim: Turn off queued DSM TRIM.
1822
05944bdf
TH
1823 * nohrst, nosrst, norst: suppress hard, soft
1824 and both resets.
1825
ca6d43b0
DW
1826 * rstonce: only attempt one reset during
1827 hot-unplug link recovery
1828
43c9c591
TH
1829 * dump_id: dump IDENTIFY data.
1830
966fbe19
VP
1831 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1832
b8bd6dc3
RJ
1833 * disable: Disable this device.
1834
33267325
TH
1835 If there are multiple matching configurations changing
1836 the same attribute, the last one is used.
1837
95f72d1e 1838 memblock=debug [KNL] Enable memblock debug messages.
7c4be253 1839
1da177e4 1840 load_ramdisk= [RAM] List of ramdisks to load from floppy
31c00fc1 1841 See Documentation/blockdev/ramdisk.txt.
1da177e4 1842
a6b25b67
RD
1843 lockd.nlm_grace_period=P [NFS] Assign grace period.
1844 Format: <integer>
1da177e4 1845
a6b25b67
RD
1846 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1847 Format: <integer>
1848
1849 lockd.nlm_timeout=T [NFS] Assign timeout value.
1850 Format: <integer>
1851
1852 lockd.nlm_udpport=M [NFS] Assign UDP port.
1853 Format: <integer>
1da177e4 1854
ec4518aa
PM
1855 locktorture.nreaders_stress= [KNL]
1856 Set the number of locking read-acquisition kthreads.
1857 Defaults to being automatically set based on the
1858 number of online CPUs.
1859
1860 locktorture.nwriters_stress= [KNL]
1861 Set the number of locking write-acquisition kthreads.
1862
1863 locktorture.onoff_holdoff= [KNL]
1864 Set time (s) after boot for CPU-hotplug testing.
1865
1866 locktorture.onoff_interval= [KNL]
1867 Set time (s) between CPU-hotplug operations, or
1868 zero to disable CPU-hotplug testing.
1869
1870 locktorture.shuffle_interval= [KNL]
1871 Set task-shuffle interval (jiffies). Shuffling
1872 tasks allows some CPUs to go into dyntick-idle
1873 mode during the locktorture test.
1874
1875 locktorture.shutdown_secs= [KNL]
1876 Set time (s) after boot system shutdown. This
1877 is useful for hands-off automated testing.
1878
1879 locktorture.stat_interval= [KNL]
1880 Time (s) between statistics printk()s.
1881
1882 locktorture.stutter= [KNL]
1883 Time (s) to stutter testing, for example,
1884 specifying five seconds causes the test to run for
1885 five seconds, wait for five seconds, and so on.
1886 This tests the locking primitive's ability to
1887 transition abruptly to and from idle.
1888
1889 locktorture.torture_runnable= [BOOT]
1890 Start locktorture running at boot time.
1891
1892 locktorture.torture_type= [KNL]
1893 Specify the locking implementation to test.
1894
1895 locktorture.verbose= [KNL]
1896 Enable additional printk() statements.
1897
1da177e4
LT
1898 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1899 Format: <irq>
1900
1901 loglevel= All Kernel Messages with a loglevel smaller than the
1902 console loglevel will be printed to the console. It can
1903 also be changed with klogd or other programs. The
1904 loglevels are defined as follows:
1905
1906 0 (KERN_EMERG) system is unusable
1907 1 (KERN_ALERT) action must be taken immediately
1908 2 (KERN_CRIT) critical conditions
1909 3 (KERN_ERR) error conditions
1910 4 (KERN_WARNING) warning conditions
1911 5 (KERN_NOTICE) normal but significant condition
1912 6 (KERN_INFO) informational
1913 7 (KERN_DEBUG) debug-level messages
1914
c756d08a 1915 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
23b2899f
LR
1916 in bytes. n must be a power of two and greater
1917 than the minimal size. The minimal size is defined
1918 by LOG_BUF_SHIFT kernel config parameter. There is
1919 also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
1920 that allows to increase the default size depending on
1921 the number of CPUs. See init/Kconfig for more details.
1da177e4 1922
accaa24c
RD
1923 logo.nologo [FB] Disables display of the built-in Linux logo.
1924 This may be used to provide more screen space for
1925 kernel log messages and is useful when debugging
1926 kernel boot problems.
1927
1da177e4
LT
1928 lp=0 [LP] Specify parallel ports to use, e.g,
1929 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1930 lp=reset first parallel port). 'lp=0' disables the
1931 lp=auto printer driver. 'lp=reset' (which can be
1932 specified in addition to the ports) causes
1933 attached printers to be reset. Using
1934 lp=port1,port2,... specifies the parallel ports
1935 to associate lp devices with, starting with
1936 lp0. A port specification may be 'none' to skip
1937 that lp device, or a parport name such as
1938 'parport0'. Specifying 'lp=auto' instead of a
1939 port specification list means that device IDs
1940 from each port should be examined, to see if
1941 an IEEE 1284-compliant printer is attached; if
1942 so, the driver will manage that printer.
1943 See also header of drivers/char/lp.c.
1944
1945 lpj=n [KNL]
1946 Sets loops_per_jiffy to given constant, thus avoiding
1947 time-consuming boot-time autodetection (up to 250 ms per
1948 CPU). 0 enables autodetection (default). To determine
1949 the correct value for your kernel, boot with normal
1950 autodetection and see what value is printed. Note that
1951 on SMP systems the preset will be applied to all CPUs,
1952 which is likely to cause problems if your CPUs need
1953 significantly divergent settings. An incorrect value
1954 will cause delays in the kernel to be wrong, leading to
1955 unpredictable I/O errors and other breakage. Although
1956 unlikely, in the extreme case this might damage your
1957 hardware.
1958
1959 ltpc= [NET]
1960 Format: <io>,<irq>,<dma>
1961
16290246 1962 machvec= [IA-64] Force the use of a particular machine-vector
a9913044
RD
1963 (machvec) in a generic kernel.
1964 Example: machvec=hpzx1_swiotlb
1da177e4 1965
3209e70e
WZ
1966 machtype= [Loongson] Share the same kernel image file between different
1967 yeeloong laptop.
1968 Example: machtype=lemote-yeeloong-2f-7inch
1969
0cb55ad2
RD
1970 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1971 than or equal to this physical address is ignored.
1da177e4
LT
1972
1973 maxcpus= [SMP] Maximum number of processors that an SMP kernel
61ec7567
LB
1974 should make use of. maxcpus=n : n >= 0 limits the
1975 kernel to using 'n' processors. n=0 is a special case,
1976 it is equivalent to "nosmp", which also disables
1977 the IO APIC.
1da177e4 1978
d134b00b
KS
1979 max_loop= [LOOP] The number of loop block devices that get
1980 (loop.max_loop) unconditionally pre-created at init time. The default
1981 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1982 of statically allocating a predefined number, loop
1983 devices can be requested on-demand with the
1984 /dev/loop-control interface.
2b2c3750 1985
cd4f0ef7 1986 mce [X86-32] Machine Check Exception
1da177e4 1987
71cced6e 1988 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
909dd324 1989
1da177e4
LT
1990 md= [HW] RAID subsystems devices and level
1991 See Documentation/md.txt.
a9913044 1992
1da177e4
LT
1993 mdacon= [MDA]
1994 Format: <first>,<last>
1995 Specifies range of consoles to be captured by the MDA.
a9913044 1996
1da177e4
LT
1997 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1998 Amount of memory to be used when the kernel is not able
1999 to see the whole system memory or for test.
fbb97d87
WC
2000 [X86] Work as limiting max address. Use together
2001 with memmap= to avoid physical address space collisions.
2002 Without memmap= PCI devices could be placed at addresses
2003 belonging to unused RAM.
1da177e4 2004
cd4f0ef7 2005 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1da177e4
LT
2006 memory.
2007
6902aa84
PM
2008 memchunk=nn[KMG]
2009 [KNL,SH] Allow user to override the default size for
2010 per-device physically contiguous DMA buffers.
2011
6cececfc 2012 memmap=exactmap [KNL,X86] Enable setting of an exact
1da177e4
LT
2013 E820 memory map, as specified by the user.
2014 Such memmap=exactmap lines can be constructed based on
2015 BIOS output or other requirements. See the memmap=nn@ss
2016 option description.
2017
2018 memmap=nn[KMG]@ss[KMG]
277cba1d
RD
2019 [KNL] Force usage of a specific region of memory.
2020 Region of memory to be used is from ss to ss+nn.
1da177e4
LT
2021
2022 memmap=nn[KMG]#ss[KMG]
2023 [KNL,ACPI] Mark specific memory as ACPI data.
277cba1d 2024 Region of memory to be marked is from ss to ss+nn.
1da177e4
LT
2025
2026 memmap=nn[KMG]$ss[KMG]
2027 [KNL,ACPI] Mark specific memory as reserved.
277cba1d 2028 Region of memory to be reserved is from ss to ss+nn.
1312848e
PM
2029 Example: Exclude memory from 0x18690000-0x1869ffff
2030 memmap=64K$0x18690000
2031 or
2032 memmap=0x10000$0x18690000
1da177e4 2033
ec776ef6
CH
2034 memmap=nn[KMG]!ss[KMG]
2035 [KNL,X86] Mark specific memory as protected.
2036 Region of memory to be used, from ss to ss+nn.
2037 The memory region may be marked as e820 type 12 (0xc)
2038 and is NVDIMM or ADR memory.
2039
9f077871
JF
2040 memory_corruption_check=0/1 [X86]
2041 Some BIOSes seem to corrupt the first 64k of
2042 memory when doing things like suspend/resume.
2043 Setting this option will scan the memory
2044 looking for corruption. Enabling this will
2045 both detect corruption and prevent the kernel
2046 from using the memory being corrupted.
2047 However, its intended as a diagnostic tool; if
2048 repeatable BIOS-originated corruption always
2049 affects the same memory, you can use memmap=
2050 to prevent the kernel from using that memory.
2051
2052 memory_corruption_check_size=size [X86]
2053 By default it checks for corruption in the low
2054 64k, making this memory unavailable for normal
2055 use. Use this parameter to scan for
2056 corruption in more or less memory.
2057
2058 memory_corruption_check_period=seconds [X86]
2059 By default it checks for corruption every 60
2060 seconds. Use this parameter to check at some
2061 other rate. 0 disables periodic checking.
2062
e4b0db72 2063 memtest= [KNL,X86,ARM] Enable memtest
c64df707 2064 Format: <integer>
c64df707 2065 default : 0 <disable>
9e5f6cf5
AH
2066 Specifies the number of memtest passes to be
2067 performed. Each pass selects another test
2068 pattern from a given set of patterns. Memtest
2069 fills the memory with this pattern, validates
2070 memory contents and reserves bad memory
2071 regions that are detected.
c64df707 2072
1da177e4
LT
2073 meye.*= [HW] Set MotionEye Camera parameters
2074 See Documentation/video4linux/meye.txt.
2075
8f36881b
AS
2076 mfgpt_irq= [IA-32] Specify the IRQ to use for the
2077 Multi-Function General Purpose Timers on AMD Geode
2078 platforms.
2079
e6c4dc6c
WT
2080 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
2081 the BIOS has incorrectly applied a workaround. TinyBIOS
2082 version 0.98 is known to be affected, 0.99 fixes the
2083 problem by letting the user disable the workaround.
2084
1da177e4
LT
2085 mga= [HW,DRM]
2086
1c207f95
RD
2087 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
2088 physical address is ignored.
2089
39f45d7b
MP
2090 mini2440= [ARM,HW,KNL]
2091 Format:[0..2][b][c][t]
2092 Default: "0tb"
2093 MINI2440 configuration specification:
2094 0 - The attached screen is the 3.5" TFT
2095 1 - The attached screen is the 7" TFT
2096 2 - The VGA Shield is attached (1024x768)
2097 Leaving out the screen size parameter will not load
2098 the TFT driver, and the framebuffer will be left
2099 unconfigured.
2100 b - Enable backlight. The TFT backlight pin will be
2101 linked to the kernel VESA blanking code and a GPIO
2102 LED. This parameter is not necessary when using the
2103 VGA shield.
2104 c - Enable the s3c camera interface.
2105 t - Reserved for enabling touchscreen support. The
2106 touchscreen support is not enabled in the mainstream
2107 kernel as of 2.6.30, a preliminary port can be found
2108 in the "bleeding edge" mini2440 support kernel at
2109 http://repo.or.cz/w/linux-2.6/mini2440.git
2110
6b74ab97
MG
2111 mminit_loglevel=
2112 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
2113 parameter allows control of the logging verbosity for
2114 the additional memory initialisation checks. A value
2115 of 0 disables mminit logging and a level of 4 will
2116 log everything. Information is printed at KERN_DEBUG
2117 so loglevel=8 may also need to be specified.
2118
106a4ee2
RR
2119 module.sig_enforce
2120 [KNL] When CONFIG_MODULE_SIG is set, this means that
2121 modules without (valid) signatures will fail to load.
2a039be7 2122 Note that if CONFIG_MODULE_SIG_FORCE is set, that
106a4ee2
RR
2123 is always true, so this option does nothing.
2124
1da177e4
LT
2125 mousedev.tap_time=
2126 [MOUSE] Maximum time between finger touching and
2127 leaving touchpad surface for touch to be considered
2128 a tap and be reported as a left button click (for
2129 touchpads working in absolute mode only).
2130 Format: <msecs>
2131 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
2132 reporting absolute coordinates, such as tablets
2133 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
2134 reporting absolute coordinates, such as tablets
2135
6cececfc 2136 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
0cb55ad2
RD
2137 is similar to kernelcore except it specifies the
2138 amount of memory used for migratable allocations.
2139 If both kernelcore and movablecore is specified,
2140 then kernelcore will be at *least* the specified
2141 value but may be more. If movablecore on its own
2142 is specified, the administrator must be careful
2143 that the amount of memory usable for all allocations
2144 is not too small.
2145
c5320926
TC
2146 movable_node [KNL,X86] Boot-time switch to enable the effects
2147 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
2148
1da177e4
LT
2149 MTD_Partition= [MTD]
2150 Format: <name>,<region-number>,<size>,<offset>
2151
a9913044
RD
2152 MTD_Region= [MTD] Format:
2153 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1da177e4
LT
2154
2155 mtdparts= [MTD]
c8facbb6 2156 See drivers/mtd/cmdlinepart.c.
1da177e4 2157
4e89a2d8
WS
2158 multitce=off [PPC] This parameter disables the use of the pSeries
2159 firmware feature for updating multiple TCE entries
2160 at a time.
2161
5988af23
RH
2162 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
2163
2164 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
2165
2166 boundary - index of last SLC block on Flex-OneNAND.
2167 The remaining blocks are configured as MLC blocks.
2168 lock - Configure if Flex-OneNAND boundary should be locked.
2169 Once locked, the boundary cannot be changed.
2170 1 indicates lock status, 0 indicates unlock status.
2171
9db829f4
BD
2172 mtdset= [ARM]
2173 ARM/S3C2412 JIVE boot control
2174
2175 See arch/arm/mach-s3c2412/mach-jive.c
2176
1da177e4 2177 mtouchusb.raw_coordinates=
a9913044
RD
2178 [HW] Make the MicroTouch USB driver use raw coordinates
2179 ('y', default) or cooked coordinates ('n')
1da177e4 2180
0cb55ad2 2181 mtrr_chunk_size=nn[KMG] [X86]
19f59460 2182 used for mtrr cleanup. It is largest continuous chunk
0cb55ad2
RD
2183 that could hold holes aka. UC entries.
2184
2185 mtrr_gran_size=nn[KMG] [X86]
2186 Used for mtrr cleanup. It is granularity of mtrr block.
2187 Default is 1.
2188 Large value could prevent small alignment from
2189 using up MTRRs.
2190
2191 mtrr_spare_reg_nr=n [X86]
2192 Format: <integer>
2193 Range: 0,7 : spare reg number
2194 Default : 1
2195 Used for mtrr cleanup. It is spare mtrr entries number.
2196 Set to 2 or more if your graphical card needs more.
2197
1da177e4
LT
2198 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
2199
1da177e4
LT
2200 netdev= [NET] Network devices parameters
2201 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
2202 Note that mem_start is often overloaded to mean
2203 something different and driver-specific.
a9913044
RD
2204 This usage is only documented in each driver source
2205 file if at all.
2206
58401572
KPO
2207 nf_conntrack.acct=
2208 [NETFILTER] Enable connection tracking flow accounting
2209 0 to disable accounting
2210 1 to enable accounting
d70a011d 2211 Default value is 0.
58401572 2212
306a0753 2213 nfsaddrs= [NFS] Deprecated. Use ip= instead.
dc7a0816 2214 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
2215
2216 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
dc7a0816 2217 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 2218
306a0753
CL
2219 nfsrootdebug [NFS] enable nfsroot debugging messages.
2220 See Documentation/filesystems/nfs/nfsroot.txt.
2221
a72b4422
TM
2222 nfs.callback_tcpport=
2223 [NFS] set the TCP port on which the NFSv4 callback
2224 channel should listen.
2225
e571cbf1
TM
2226 nfs.cache_getent=
2227 [NFS] sets the pathname to the program which is used
2228 to update the NFS client cache entries.
2229
2230 nfs.cache_getent_timeout=
2231 [NFS] sets the timeout after which an attempt to
2232 update a cache entry is deemed to have failed.
2233
58df095b
TM
2234 nfs.idmap_cache_timeout=
2235 [NFS] set the maximum lifetime for idmapper cache
2236 entries.
2237
f43bf0be
TM
2238 nfs.enable_ino64=
2239 [NFS] enable 64-bit inode numbers.
2240 If zero, the NFS client will fake up a 32-bit inode
2241 number for the readdir() and stat() syscalls instead
2242 of returning the full 64-bit number.
2243 The default is to return 64-bit inode numbers.
2244
ef159e91
TM
2245 nfs.max_session_slots=
2246 [NFSv4.1] Sets the maximum number of session slots
2247 the client will attempt to negotiate with the server.
2248 This limits the number of simultaneous RPC requests
2249 that the client can send to the NFSv4.1 server.
2250 Note that there is little point in setting this
2251 value higher than the max_tcp_slot_table_limit.
2252
b064eca2 2253 nfs.nfs4_disable_idmapping=
074b1d12
TM
2254 [NFSv4] When set to the default of '1', this option
2255 ensures that both the RPC level authentication
2256 scheme and the NFS level operations agree to use
2257 numeric uids/gids if the mount is using the
2258 'sec=sys' security flavour. In effect it is
2259 disabling idmapping, which can make migration from
2260 legacy NFSv2/v3 systems to NFSv4 easier.
2261 Servers that do not support this mode of operation
2262 will be autodetected by the client, and it will fall
2263 back to using the idmapper.
2264 To turn off this behaviour, set the value to '0'.
6f2ea7f2
CL
2265 nfs.nfs4_unique_id=
2266 [NFS4] Specify an additional fixed unique ident-
2267 ification string that NFSv4 clients can insert into
2268 their nfs_client_id4 string. This is typically a
2269 UUID that is generated at system install time.
b064eca2 2270
db8ac8ba
WAA
2271 nfs.send_implementation_id =
2272 [NFSv4.1] Send client implementation identification
2273 information in exchange_id requests.
2274 If zero, no implementation identification information
2275 will be sent.
2276 The default is to send the implementation identification
2277 information.
f6de7a39
TM
2278
2279 nfs.recover_lost_locks =
2280 [NFSv4] Attempt to recover locks that were lost due
2281 to a lease timeout on the server. Please note that
2282 doing this risks data corruption, since there are
2283 no guarantees that the file will remain unchanged
2284 after the locks are lost.
2285 If you want to enable the kernel legacy behaviour of
2286 attempting to recover these locks, then set this
2287 parameter to '1'.
2288 The default parameter value of '0' causes the kernel
2289 not to attempt recovery of lost locks.
db8ac8ba 2290
bbf58bf3
TM
2291 nfs4.layoutstats_timer =
2292 [NFSv4.2] Change the rate at which the kernel sends
2293 layoutstats to the pNFS metadata server.
2294
2295 Setting this to value to 0 causes the kernel to use
2296 whatever value is the default set by the layout
2297 driver. A non-zero value sets the minimum interval
2298 in seconds between layoutstats transmissions.
2299
e9541ce8
BF
2300 nfsd.nfs4_disable_idmapping=
2301 [NFSv4] When set to the default of '1', the NFSv4
2302 server will return only numeric uids and gids to
2303 clients using auth_sys, and will accept numeric uids
2304 and gids from such clients. This is intended to ease
2305 migration from NFSv2/v3.
db8ac8ba 2306
18d98f6c
SB
2307 objlayoutdriver.osd_login_prog=
2308 [NFS] [OBJLAYOUT] sets the pathname to the program which
2309 is used to automatically discover and login into new
2310 osd-targets. Please see:
2311 Documentation/filesystems/pnfs.txt for more explanations
2312
1e1030dc 2313 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
e7ba176b
HS
2314 when a NMI is triggered.
2315 Format: [state][,regs][,debounce][,die]
2316
6cececfc 2317 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
fef2c9bc 2318 Format: [panic,][nopanic,][num]
195daf66 2319 Valid num: 0 or 1
5b9a0e14 2320 0 - turn nmi_watchdog off
195daf66 2321 1 - turn nmi_watchdog on
0cb55ad2 2322 When panic is specified, panic when an NMI watchdog
fef2c9bc
DZ
2323 timeout occurs (or 'nopanic' to override the opposite
2324 default).
0cb55ad2
RD
2325 This is useful when you use a panic=... timeout and
2326 need the box quickly up again.
1da177e4 2327
bff38771
AV
2328 netpoll.carrier_timeout=
2329 [NET] Specifies amount of time (in seconds) that
2330 netpoll should wait for a carrier. By default netpoll
2331 waits 4 seconds.
2332
cd4f0ef7 2333 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1da177e4
LT
2334 emulation library even if a 387 maths coprocessor
2335 is present.
2336
0cb55ad2
RD
2337 no_console_suspend
2338 [HW] Never suspend the console
2339 Disable suspending of consoles during suspend and
2340 hibernate operations. Once disabled, debugging
2341 messages can reach various consoles while the rest
2342 of the system is being put to sleep (ie, while
2343 debugging driver suspend/resume hooks). This may
2344 not work reliably with all consoles, but is known
2345 to work with serial and VGA consoles.
134620f7
YZ
2346 To facilitate more flexible debugging, we also add
2347 console_suspend, a printk module parameter to control
2348 it. Users could use console_suspend (usually
2349 /sys/module/printk/parameters/console_suspend) to
2350 turn on/off it dynamically.
0cb55ad2 2351
c1aee215
CL
2352 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2353 caches in the slab allocator. Saves per-node memory,
2354 but will impact performance.
3395ee05 2355
a9913044
RD
2356 noalign [KNL,ARM]
2357
1da177e4
LT
2358 noapic [SMP,APIC] Tells the kernel to not make use of any
2359 IOAPICs that may be present in the system.
2360
5091faa4
MG
2361 noautogroup Disable scheduler automatic task group creation.
2362
1da177e4
LT
2363 nobats [PPC] Do not use BATs for mapping kernel lowmem
2364 on "Classic" PPC cores.
2365
2366 nocache [ARM]
a9913044 2367
0cb55ad2
RD
2368 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2369
163ecdff
SN
2370 nodelayacct [KNL] Disable per-task delay accounting
2371
1da177e4
LT
2372 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2373
6902aa84
PM
2374 nodsp [SH] Disable hardware DSP at boot time.
2375
b2e0a54a 2376 noefi Disable EFI runtime services support.
8b2cb7a8 2377
1da177e4
LT
2378 noexec [IA-64]
2379
6cececfc 2380 noexec [X86]
f5a1b191 2381 On X86-32 available only on PAE configured kernels.
1da177e4 2382 noexec=on: enable non-executable mappings (default)
f5a1b191
JS
2383 noexec=off: disable non-executable mappings
2384
52b6179a
PA
2385 nosmap [X86]
2386 Disable SMAP (Supervisor Mode Access Prevention)
2387 even if it is supported by processor.
2388
de5397ad 2389 nosmep [X86]
52b6179a 2390 Disable SMEP (Supervisor Mode Execution Prevention)
de5397ad
FY
2391 even if it is supported by processor.
2392
f5a1b191
JS
2393 noexec32 [X86-64]
2394 This affects only 32-bit executables.
2395 noexec32=on: enable non-executable mappings (default)
2396 read doesn't imply executable mappings
2397 noexec32=off: disable non-executable mappings
2398 read implies executable mappings
1da177e4 2399
fab43ef4 2400 nofpu [MIPS,SH] Disable hardware FPU at boot time.
6902aa84 2401
cd4f0ef7 2402 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4f886511
CE
2403 register save and restore. The kernel will only save
2404 legacy floating-point registers on task switch.
1da177e4 2405
0ddab1d2
TK
2406 nohugeiomap [KNL,x86] Disable kernel huge I/O mappings.
2407
0c752a93
SS
2408 noxsave [BUGS=X86] Disables x86 extended register state save
2409 and restore using xsave. The kernel will fallback to
2410 enabling legacy floating-point and sse state.
2411
b6f42a4a
FY
2412 noxsaveopt [X86] Disables xsaveopt used in saving x86 extended
2413 register states. The kernel will fall back to use
2414 xsave to save the states. By using this parameter,
2415 performance of saving the states is degraded because
2416 xsave doesn't support modified optimization while
2417 xsaveopt supports it on xsaveopt enabled systems.
2418
2419 noxsaves [X86] Disables xsaves and xrstors used in saving and
2420 restoring x86 extended register state in compacted
2421 form of xsave area. The kernel will fall back to use
2422 xsaveopt and xrstor to save and restore the states
2423 in standard form of xsave area. By using this
2424 parameter, xsave area per process might occupy more
2425 memory on xsaves enabled systems.
2426
01a24d2b
PZ
2427 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2428 wfi(ARM) instruction doesn't work correctly and not to
2429 use it. This is also useful when using JTAG debugger.
a9913044 2430
1f29fae2
SH
2431 no_file_caps Tells the kernel not to honor file capabilities. The
2432 only way then for a file to be executed with privilege
2433 is to be setuid root or executed by root.
2434
1da177e4
LT
2435 nohalt [IA-64] Tells the kernel not to use the power saving
2436 function PAL_HALT_LIGHT when idle. This increases
2437 power-consumption. On the positive side, it reduces
2438 interrupt wake-up latency, which may improve performance
2439 in certain environments such as networked servers or
2440 real-time systems.
2441
a6e15a39
KC
2442 nohibernate [HIBERNATION] Disable hibernation and resume.
2443
79bf2bb3
TG
2444 nohz= [KNL] Boottime enable/disable dynamic ticks
2445 Valid arguments: on, off
2446 Default: on
2447
c5bfece2
FW
2448 nohz_full= [KNL,BOOT]
2449 In kernels built with CONFIG_NO_HZ_FULL=y, set
a831881b 2450 the specified list of CPUs whose tick will be stopped
0453b435
FW
2451 whenever possible. The boot CPU will be forced outside
2452 the range to maintain the timekeeping.
d1e43fa5
FW
2453 The CPUs in this range must also be included in the
2454 rcu_nocbs= set.
a831881b 2455
eeee7853
PM
2456 noiotrap [SH] Disables trapped I/O port accesses.
2457
cd4f0ef7 2458 noirqdebug [X86-32] Disables the code which attempts to detect and
1da177e4
LT
2459 disable unhandled interrupt sources.
2460
6cececfc 2461 no_timer_check [X86,APIC] Disables the code which tests for
8542b200
ZA
2462 broken timer IRQ sources.
2463
1da177e4
LT
2464 noisapnp [ISAPNP] Disables ISA PnP code.
2465
2466 noinitrd [RAM] Tells the kernel not to load any configured
2467 initial RAM disk.
2468
03ea8155
WH
2469 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2470 remapping.
d1423d56 2471 [Deprecated - use intremap=off]
03ea8155 2472
1da177e4
LT
2473 nointroute [IA-64]
2474
16290246 2475 nojitter [IA-64] Disables jitter checking for ITC timers.
0aa366f3 2476
9cf4c4fc
JK
2477 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2478
fd10cde9
GN
2479 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2480 fault handling.
2481
d910f5c1
GC
2482 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2483 steal time is computed, but won't influence scheduler
2484 behaviour
2485
cd4f0ef7 2486 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1da177e4 2487
cd4f0ef7 2488 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
ad62ca2b 2489
1da177e4
LT
2490 noltlbs [PPC] Do not use large page/tlb entries for kernel
2491 lowmem mapping on PPC40x.
2492
312f1f01
H
2493 nomca [IA-64] Disable machine check abort handling
2494
13696e0a 2495 nomce [X86-32] Disable Machine Check Exception
abe37e5a 2496
83d7384f
AS
2497 nomfgpt [X86-32] Disable Multi-Function General Purpose
2498 Timer usage (for AMD Geode machines).
2499
bda62633
DZ
2500 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2501 shutdown the other cpus. Instead use the REBOOT_VECTOR
2502 irq.
2503
02608bef
DY
2504 nomodule Disable module load
2505
016ddd9b
JK
2506 nopat [X86] Disable PAT (page attribute table extension of
2507 pagetables) support.
2508
0cb55ad2
RD
2509 norandmaps Don't use address space randomization. Equivalent to
2510 echo 0 > /proc/sys/kernel/randomize_va_space
2511
bbff2168 2512 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
959b4fdf 2513
cd4f0ef7 2514 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
b7fb4af0
JF
2515 with UP alternatives
2516
7a5091d5
PA
2517 nordrand [X86] Disable kernel use of the RDRAND and
2518 RDSEED instructions even if they are supported
2519 by the processor. RDRAND and RDSEED are still
2520 available to user space applications.
49d859d7 2521
a9913044
RD
2522 noresume [SWSUSP] Disables resume and restores original swap
2523 space.
2524
1da177e4
LT
2525 no-scroll [VGA] Disables scrollback.
2526 This is required for the Braillex ib80-piezo Braille
2527 reader made by F.H. Papenmeier (Germany).
2528
2529 nosbagart [IA-64]
2530
cd4f0ef7 2531 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
4f886511 2532
61ec7567
LB
2533 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2534 and disable the IO APIC. legacy for "maxcpus=0".
1da177e4 2535
97842216
DJ
2536 nosoftlockup [KNL] Disable the soft-lockup detector.
2537
1da177e4
LT
2538 nosync [HW,M68K] Disables sync negotiation for all devices.
2539
cd4f0ef7 2540 notsc [BUGS=X86-32] Disable Time Stamp Counter
1da177e4
LT
2541
2542 nousb [USB] Disable the USB subsystem
2543
195daf66
UO
2544 nowatchdog [KNL] Disable both lockup detectors, i.e.
2545 soft-lockup and NMI watchdog (hard-lockup).
58687acb 2546
1da177e4 2547 nowb [ARM]
a9913044 2548
2b2fd87a
WH
2549 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2550
f78cff48
FY
2551 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2552 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2553 Some features depend on CPU0. Known dependencies are:
2554 1. Resume from suspend/hibernate depends on CPU0.
2555 Suspend/hibernate will fail if CPU0 is offline and you
2556 need to online CPU0 before suspend/hibernate.
2557 2. PIC interrupts also depend on CPU0. CPU0 can't be
2558 removed if a PIC interrupt is detected.
2559 It's said poweroff/reboot may depend on CPU0 on some
2560 machines although I haven't seen such issues so far
2561 after CPU0 is offline on a few tested machines.
2562 If the dependencies are under your control, you can
2563 turn on cpu0_hotplug.
2564
16290246 2565 nptcg= [IA-64] Override max number of concurrent global TLB
a6c75b86
FY
2566 purges which is reported from either PAL_VM_SUMMARY or
2567 SAL PALO.
2568
2b633e3f
YL
2569 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2570 could support. nr_cpus=n : n >= 1 limits the kernel to
2571 supporting 'n' processors. Later in runtime you can not
2572 use hotplug cpu feature to put more cpu back to online.
2573 just like you compile the kernel NR_CPUS=n
2574
0cb55ad2
RD
2575 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2576
1a687c2e
MG
2577 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2578 Allowed values are enable and disable
2579
f0c0b2b8
KH
2580 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2581 one of ['zone', 'node', 'default'] can be specified
2582 This can be set from sysctl after boot.
2583 See Documentation/sysctl/vm.txt for details.
2584
7c4be253
RD
2585 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2586 See Documentation/debugging-via-ohci1394.txt for more
2587 info.
2588
3ef0e1f8
AS
2589 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2590 Rather than timing out after 20 ms if an EC
2591 command is not properly ACKed, override the length
2592 of the timeout. We have interrupts disabled while
2593 waiting for the ACK, so if this is set too high
2594 interrupts *may* be lost!
2595
15ac7afe
TL
2596 omap_mux= [OMAP] Override bootloader pin multiplexing.
2597 Format: <mux_mode0.mode_name=value>...
2598 For example, to override I2C bus2:
2599 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2600
1da177e4
LT
2601 oprofile.timer= [HW]
2602 Use timer interrupt instead of performance counters
2603
7e4e0bd5
RR
2604 oprofile.cpu_type= Force an oprofile cpu type
2605 This might be useful if you have an older oprofile
2606 userland or if you want common events.
8d7ff4f2
RR
2607 Format: { arch_perfmon }
2608 arch_perfmon: [X86] Force use of architectural
7e4e0bd5
RR
2609 perfmon on Intel CPUs instead of the
2610 CPU specific event set.
159a80b2
RR
2611 timer: [X86] Force use of architectural NMI
2612 timer mode (see also oprofile.timer
2613 for generic hr timer mode)
dd3c4670
AK
2614 [s390] Force legacy basic mode sampling
2615 (report cpu_type "timer")
1dcdb5a9 2616
44a4dcf7
RD
2617 oops=panic Always panic on oopses. Default is to just kill the
2618 process, but there is a small probability of
2619 deadlocking the machine.
d404ab0a
OH
2620 This will also cause panics on machine check exceptions.
2621 Useful together with panic=30 to trigger a reboot.
2622
bcfde334
RD
2623 OSS [HW,OSS]
2624 See Documentation/sound/oss/oss-parameters.txt
2625
48c96a36
JK
2626 page_owner= [KNL] Boot-time page_owner enabling option.
2627 Storage of the information about who allocated
2628 each page is disabled in default. With this switch,
2629 we can turn it on.
2630 on: enable the feature
2631
44a4dcf7 2632 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4302fbc8
HD
2633 timeout > 0: seconds before rebooting
2634 timeout = 0: wait forever
2635 timeout < 0: reboot immediately
1da177e4
LT
2636 Format: <timeout>
2637
9e3961a0
PB
2638 panic_on_warn panic() instead of WARN(). Useful to cause kdump
2639 on a WARN().
2640
f06e5153
MH
2641 crash_kexec_post_notifiers
2642 Run kdump after running panic-notifiers and dumping
2643 kmsg. This only for the users who doubt kdump always
2644 succeeds in any situation.
2645 Note that this also increases risks of kdump failure,
2646 because some panic notifiers can make the crashed
2647 kernel more unstable.
2648
1da177e4
LT
2649 parkbd.port= [HW] Parallel port number the keyboard adapter is
2650 connected to, default is 0.
2651 Format: <parport#>
2652 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2653 0 for XT, 1 for AT (default is AT).
a9913044
RD
2654 Format: <mode>
2655
2656 parport= [HW,PPT] Specify parallel ports. 0 disables.
2657 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2658 Use 'auto' to force the driver to use any
2659 IRQ/DMA settings detected (the default is to
2660 ignore detected IRQ/DMA settings because of
2661 possible conflicts). You can specify the base
2662 address, IRQ, and DMA settings; IRQ and DMA
2663 should be numbers, or 'auto' (for using detected
2664 settings on that particular port), or 'nofifo'
2665 (to avoid using a FIFO even if it is detected).
2666 Parallel ports are assigned in the order they
2667 are specified on the command line, starting
2668 with parport0.
2669
2670 parport_init_mode= [HW,PPT]
2671 Configure VIA parallel port to operate in
2672 a specific mode. This is necessary on Pegasos
2673 computer where firmware has no options for setting
2674 up parallel port mode and sets it to spp.
2675 Currently this function knows 686a and 8231 chips.
1da177e4
LT
2676 Format: [spp|ps2|epp|ecp|ecpepp]
2677
dd287796
AM
2678 pause_on_oops=
2679 Halt all CPUs after the first oops has been printed for
2680 the specified number of seconds. This is to be used if
2681 your oopses keep scrolling off the screen.
2682
1da177e4
LT
2683 pcbit= [HW,ISDN]
2684
2685 pcd. [PARIDE]
2686 See header of drivers/block/paride/pcd.c.
31c00fc1 2687 See also Documentation/blockdev/paride.txt.
1da177e4 2688
a9913044 2689 pci=option[,option...] [PCI] various PCI subsystem options:
1cc0ca26
BH
2690 earlydump [X86] dump PCI config space before the kernel
2691 changes anything
c0115606 2692 off [X86] don't probe for the PCI bus
cd4f0ef7 2693 bios [X86-32] force use of PCI BIOS, don't access
a9913044
RD
2694 the hardware directly. Use this if your machine
2695 has a non-standard PCI host bridge.
cd4f0ef7 2696 nobios [X86-32] disallow use of PCI BIOS, only direct
a9913044
RD
2697 hardware access methods are allowed. Use this
2698 if you experience crashes upon bootup and you
2699 suspect they are caused by the BIOS.
c0115606 2700 conf1 [X86] Force use of PCI Configuration
a9913044 2701 Mechanism 1.
c0115606 2702 conf2 [X86] Force use of PCI Configuration
a9913044 2703 Mechanism 2.
7f785763
RD
2704 noaer [PCIE] If the PCIEAER kernel config parameter is
2705 enabled, this kernel boot option can be used to
2706 disable the use of PCIE advanced error reporting.
32a2eea7
JG
2707 nodomains [PCI] Disable support for multiple PCI
2708 root domains (aka PCI segments, in ACPI-speak).
6cececfc 2709 nommconf [X86] Disable use of MMCONFIG for PCI
61be6d66 2710 Configuration
12983077
AH
2711 check_enable_amd_mmconf [X86] check for and enable
2712 properly configured MMIO access to PCI
2713 config space on AMD family 10h CPU
309e57df
MW
2714 nomsi [MSI] If the PCI_MSI kernel config parameter is
2715 enabled, this kernel boot option can be used to
2716 disable the use of MSI interrupts system-wide.
a9322f64
SA
2717 noioapicquirk [APIC] Disable all boot interrupt quirks.
2718 Safety option to keep boot IRQs enabled. This
2719 should never be necessary.
9197979b
SA
2720 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2721 primary IO-APIC for bridges that cannot disable
2722 boot IRQs. This fixes a source of spurious IRQs
2723 when the system masks IRQs.
41b9eb26
SA
2724 noioapicreroute [APIC] Disable workaround that uses the
2725 boot IRQ equivalent of an IRQ that connects to
2726 a chipset where boot IRQs cannot be disabled.
2727 The opposite of ioapicreroute.
cd4f0ef7 2728 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
a9913044
RD
2729 routing table. These calls are known to be buggy
2730 on several machines and they hang the machine
2731 when used, but on other computers it's the only
2732 way to get the interrupt routing table. Try
2733 this option if the kernel is unable to allocate
2734 IRQs or discover secondary PCI buses on your
2735 motherboard.
c0115606 2736 rom [X86] Assign address space to expansion ROMs.
a9913044
RD
2737 Use with caution as certain devices share
2738 address decoders between ROMs and other
2739 resources.
c0115606 2740 norom [X86] Do not assign address space to
bb71ad88
GH
2741 expansion ROMs that do not already have
2742 BIOS assigned address ranges.
7bd1c365
MH
2743 nobar [X86] Do not assign address space to the
2744 BARs that weren't assigned by the BIOS.
c0115606 2745 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
a9913044
RD
2746 assigned automatically to PCI devices. You can
2747 make the kernel exclude IRQs of your ISA cards
2748 this way.
c0115606 2749 pirqaddr=0xAAAAA [X86] Specify the physical address
a9913044
RD
2750 of the PIRQ table (normally generated
2751 by the BIOS) if it is outside the
2752 F0000h-100000h range.
c0115606 2753 lastbus=N [X86] Scan all buses thru bus #N. Can be
a9913044
RD
2754 useful if the kernel is unable to find your
2755 secondary buses and you want to tell it
2756 explicitly which ones they are.
c0115606 2757 assign-busses [X86] Always assign all PCI bus
a9913044
RD
2758 numbers ourselves, overriding
2759 whatever the firmware may have done.
c0115606 2760 usepirqmask [X86] Honor the possible IRQ mask stored
a9913044
RD
2761 in the BIOS $PIR table. This is needed on
2762 some systems with broken BIOSes, notably
2763 some HP Pavilion N5400 and Omnibook XE3
2764 notebooks. This will have no effect if ACPI
2765 IRQ routing is enabled.
c0115606 2766 noacpi [X86] Do not use ACPI for IRQ routing
a9913044 2767 or for PCI scanning.
7bc5e3f2
BH
2768 use_crs [X86] Use PCI host bridge window information
2769 from ACPI. On BIOSes from 2008 or later, this
2770 is enabled by default. If you need to use this,
2771 please report a bug.
2772 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2773 If you need to use this, please report a bug.
a9913044
RD
2774 routeirq Do IRQ routing for all PCI devices.
2775 This is normally done in pci_enable_device(),
2776 so this option is a temporary workaround
2777 for broken drivers that don't call it.
13a6ddb0
YL
2778 skip_isa_align [X86] do not align io start addr, so can
2779 handle more pci cards
a9913044
RD
2780 firmware [ARM] Do not re-enumerate the bus but instead
2781 just use the configuration from the
2782 bootloader. This is currently used on
2783 IXP2000 systems where the bus has to be
2784 configured a certain way for adjunct CPUs.
0637a70a
AK
2785 noearly [X86] Don't do any early type 1 scanning.
2786 This might help on some broken boards which
2787 machine check when some devices' config space
2788 is read. But various workarounds are disabled
2789 and some IOMMU drivers will not work.
6b4b78fe
MD
2790 bfsort Sort PCI devices into breadth-first order.
2791 This sorting is done to get a device
2792 order compatible with older (<= 2.4) kernels.
2793 nobfsort Don't sort PCI devices into breadth-first order.
fa238712
YW
2794 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2795 tuning and use the BIOS-configured MPS defaults.
2796 pcie_bus_safe Set every device's MPS to the largest value
2797 supported by all devices below the root complex.
2798 pcie_bus_perf Set device MPS to the largest allowable MPS
2799 based on its parent bus. Also set MRRS (Max
2800 Read Request Size) to the largest supported
2801 value (no larger than the MPS that the device
2802 or bus can support) for best performance.
2803 pcie_bus_peer2peer Set every device's MPS to 128B, which
2804 every device is guaranteed to support. This
2805 configuration allows peer-to-peer DMA between
2806 any pair of devices, possibly at the cost of
2807 reduced performance. This also guarantees
2808 that hot-added devices will work.
4516a618
AN
2809 cbiosize=nn[KMG] The fixed amount of bus space which is
2810 reserved for the CardBus bridge's IO window.
2811 The default value is 256 bytes.
2812 cbmemsize=nn[KMG] The fixed amount of bus space which is
2813 reserved for the CardBus bridge's memory
2814 window. The default value is 64 megabytes.
32a9a682
YS
2815 resource_alignment=
2816 Format:
2817 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2818 Specifies alignment and device to reassign
2819 aligned memory resources.
2820 If <order of align> is not specified,
2821 PAGE_SIZE is used as alignment.
2822 PCI-PCI bridge can be specified, if resource
2823 windows need to be expanded.
43c16408
AP
2824 ecrc= Enable/disable PCIe ECRC (transaction layer
2825 end-to-end CRC checking).
2826 bios: Use BIOS/firmware settings. This is the
2827 the default.
2828 off: Turn ECRC off
2829 on: Turn ECRC on.
8c8803c5
YW
2830 hpiosize=nn[KMG] The fixed amount of bus space which is
2831 reserved for hotplug bridge's IO window.
2832 Default size is 256 bytes.
2833 hpmemsize=nn[KMG] The fixed amount of bus space which is
2834 reserved for hotplug bridge's memory window.
2835 Default size is 2 megabytes.
b55438fd
YL
2836 realloc= Enable/disable reallocating PCI bridge resources
2837 if allocations done by BIOS are too small to
2838 accommodate resources required by all child
2839 devices.
2840 off: Turn realloc off
2841 on: Turn realloc on
2842 realloc same as realloc=on
6748dcc2 2843 noari do not use PCIe ARI.
284f5f9d
BH
2844 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2845 only look for one device below a PCIe downstream
2846 port.
6b4b78fe 2847
e5665a45
CE
2848 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2849 Management.
2850 off Disable ASPM.
2851 force Enable ASPM even on devices that claim not to support it.
2852 WARNING: Forcing ASPM on may cause system lockups.
2853
7570a333
MT
2854 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2855 nomsi Do not use MSI for PCI Express Native Hotplug (this
2856 makes all PCIe ports use INTx for hotplug services).
2857
79dd9182 2858 pcie_ports= [PCIE] PCIe ports handling:
28eb5f27
RW
2859 auto Ask the BIOS whether or not to use native PCIe services
2860 associated with PCIe ports (PME, hot-plug, AER). Use
2861 them only if that is allowed by the BIOS.
2862 native Use native PCIe services associated with PCIe ports
2863 unconditionally.
79dd9182
RW
2864 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2865 ports driver.
2866
c7f48656 2867 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
c39fae14 2868 nomsi Do not use MSI for native PCIe PME signaling (this makes
28eb5f27 2869 all PCIe root ports use INTx for all services).
c7f48656 2870
1da177e4
LT
2871 pcmv= [HW,PCMCIA] BadgePAD 4
2872
39ac5ba5
TB
2873 pd_ignore_unused
2874 [PM]
2875 Keep all power-domains already enabled by bootloader on,
2876 even if no driver has claimed them. This is useful
2877 for debug and development, but should not be
2878 needed on a platform with proper driver support.
2879
1da177e4 2880 pd. [PARIDE]
31c00fc1 2881 See Documentation/blockdev/paride.txt.
1da177e4
LT
2882
2883 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2884 boot time.
2885 Format: { 0 | 1 }
2886 See arch/parisc/kernel/pdc_chassis.c
2887
f58dc01b 2888 percpu_alloc= Select which percpu first chunk allocator to use.
e933a73f
TH
2889 Currently supported values are "embed" and "page".
2890 Archs may support subset or none of the selections.
2891 See comments in mm/percpu.c for details on each
2892 allocator. This parameter is primarily for debugging
2893 and performance comparison.
fa8a7094 2894
1da177e4 2895 pf. [PARIDE]
31c00fc1 2896 See Documentation/blockdev/paride.txt.
1da177e4
LT
2897
2898 pg. [PARIDE]
31c00fc1 2899 See Documentation/blockdev/paride.txt.
1da177e4
LT
2900
2901 pirq= [SMP,APIC] Manual mp-table setup
71cced6e 2902 See Documentation/x86/i386/IO-APIC.txt.
1da177e4
LT
2903
2904 plip= [PPT,NET] Parallel port network link
2905 Format: { parport<nr> | timid | 0 }
2906 See also Documentation/parport.txt.
2907
16290246 2908 pmtmr= [X86] Manual setup of pmtmr I/O Port.
de32a243
TG
2909 Override pmtimer IOPort with a hex value.
2910 e.g. pmtmr=0x508
2911
96242116
BH
2912 pnp.debug=1 [PNP]
2913 Enable PNP debug messages (depends on the
2914 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2915 via /sys/module/pnp/parameters/debug. We always show
2916 current resource usage; turning this on also shows
2917 possible settings and some assignment information.
97ef062b 2918
1da177e4
LT
2919 pnpacpi= [ACPI]
2920 { off }
2921
2922 pnpbios= [ISAPNP]
2923 { on | off | curr | res | no-curr | no-res }
2924
2925 pnp_reserve_irq=
2926 [ISAPNP] Exclude IRQs for the autoconfiguration
2927
2928 pnp_reserve_dma=
2929 [ISAPNP] Exclude DMAs for the autoconfiguration
2930
2931 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
a9913044 2932 Ranges are in pairs (I/O port base and size).
1da177e4
LT
2933
2934 pnp_reserve_mem=
a9913044
RD
2935 [ISAPNP] Exclude memory regions for the
2936 autoconfiguration.
1da177e4
LT
2937 Ranges are in pairs (memory base and size).
2938
4af94f39
RD
2939 ports= [IP_VS_FTP] IPVS ftp helper module
2940 Default is 21.
2941 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2942 may be specified.
2943 Format: <port>,<port>....
2944
45807a1d
IM
2945 print-fatal-signals=
2946 [KNL] debug: print fatal signals
f84d49b2
NO
2947
2948 If enabled, warn about various signal handling
2949 related application anomalies: too many signals,
2950 too many POSIX.1 timers, fatal signals causing a
2951 coredump - etc.
2952
2953 If you hit the warning due to signal overflow,
2954 you might want to try "ulimit -i unlimited".
2955
45807a1d
IM
2956 default: off.
2957
c22ab332
MG
2958 printk.always_kmsg_dump=
2959 Trigger kmsg_dump for cases other than kernel oops or
2960 panics
2961 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2962 default: disabled
2963
e84845c4
RD
2964 printk.time= Show timing data prefixed to each printk message line
2965 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2966
0cb55ad2
RD
2967 processor.max_cstate= [HW,ACPI]
2968 Limit processor to maximum C-state
2969 max_cstate=9 overrides any DMI blacklist limit.
2970
2971 processor.nocst [HW,ACPI]
2972 Ignore the _CST method to determine C-states,
2973 instead using the legacy FADT method
2974
1da177e4 2975 profile= [KNL] Enable kernel profiling via /proc/profile
a9913044
RD
2976 Format: [schedule,]<number>
2977 Param: "schedule" - profile schedule points.
2978 Param: <number> - step/bucket size as a power of 2 for
2979 statistical time based profiling.
b3da2a73
MG
2980 Param: "sleep" - profile D-state sleeping (millisecs).
2981 Requires CONFIG_SCHEDSTATS
c0fe2e69 2982 Param: "kvm" - profile VM exits.
1da177e4 2983
1da177e4
LT
2984 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2985 before loading.
31c00fc1 2986 See Documentation/blockdev/ramdisk.txt.
1da177e4 2987
a9913044
RD
2988 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2989 probe for; one of (bare|imps|exps|lifebook|any).
1da177e4
LT
2990 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2991 per second.
a9913044
RD
2992 psmouse.resetafter= [HW,MOUSE]
2993 Try to reset the device after so many bad packets
1da177e4
LT
2994 (0 = never).
2995 psmouse.resolution=
2996 [HW,MOUSE] Set desired mouse resolution, in dpi.
2997 psmouse.smartscroll=
a9913044 2998 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1da177e4
LT
2999 0 = disabled, 1 = enabled (default).
3000
dee28e72
MG
3001 pstore.backend= Specify the name of the pstore backend to use
3002
1da177e4 3003 pt. [PARIDE]
31c00fc1 3004 See Documentation/blockdev/paride.txt.
1da177e4 3005
dc8c8587
KS
3006 pty.legacy_count=
3007 [KNL] Number of legacy pty's. Overwrites compiled-in
3008 default number.
3009
7d2c502f 3010 quiet [KNL] Disable most log messages
a9913044 3011
1da177e4
LT
3012 r128= [HW,DRM]
3013
3014 raid= [HW,RAID]
3015 See Documentation/md.txt.
3016
a9913044 3017 ramdisk_blocksize= [RAM]
31c00fc1 3018 See Documentation/blockdev/ramdisk.txt.
a9913044 3019
1da177e4 3020 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
31c00fc1 3021 See Documentation/blockdev/ramdisk.txt.
1da177e4 3022
4102adab 3023 rcu_nocbs= [KNL]
3fbfbf7a
PM
3024 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
3025 the specified list of CPUs to be no-callback CPUs.
3026 Invocation of these CPUs' RCU callbacks will
a4889858
PM
3027 be offloaded to "rcuox/N" kthreads created for
3028 that purpose, where "x" is "b" for RCU-bh, "p"
3029 for RCU-preempt, and "s" for RCU-sched, and "N"
3030 is the CPU number. This reduces OS jitter on the
3fbfbf7a
PM
3031 offloaded CPUs, which can be useful for HPC and
3032 real-time workloads. It can also improve energy
3033 efficiency for asymmetric multiprocessors.
3034
4102adab 3035 rcu_nocb_poll [KNL]
3fbfbf7a
PM
3036 Rather than requiring that offloaded CPUs
3037 (specified by rcu_nocbs= above) explicitly
3038 awaken the corresponding "rcuoN" kthreads,
3039 make these kthreads poll for callbacks.
3040 This improves the real-time response for the
3041 offloaded CPUs by relieving them of the need to
3042 wake up the corresponding kthread, but degrades
3043 energy efficiency by requiring that the kthreads
3044 periodically wake up to do the polling.
3045
4102adab 3046 rcutree.blimit= [KNL]
97e63f0c
PM
3047 Set maximum number of finished RCU callbacks to
3048 process in one batch.
21a1ea9e 3049
a3dc2948
PM
3050 rcutree.dump_tree= [KNL]
3051 Dump the structure of the rcu_node combining tree
3052 out at early boot. This is used for diagnostic
3053 purposes, to verify correct tree setup.
3054
0f41c0dd
PM
3055 rcutree.gp_cleanup_delay= [KNL]
3056 Set the number of jiffies to delay each step of
3057 RCU grace-period cleanup. This only has effect
3058 when CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP is set.
3059
37745d28
PM
3060 rcutree.gp_init_delay= [KNL]
3061 Set the number of jiffies to delay each step of
3062 RCU grace-period initialization. This only has
0f41c0dd
PM
3063 effect when CONFIG_RCU_TORTURE_TEST_SLOW_INIT
3064 is set.
3065
3066 rcutree.gp_preinit_delay= [KNL]
3067 Set the number of jiffies to delay each step of
3068 RCU grace-period pre-initialization, that is,
3069 the propagation of recent CPU-hotplug changes up
3070 the rcu_node combining tree. This only has effect
3071 when CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT is set.
37745d28 3072
7fa27001
PM
3073 rcutree.rcu_fanout_exact= [KNL]
3074 Disable autobalancing of the rcu_node combining
3075 tree. This is used by rcutorture, and might
3076 possibly be useful for architectures having high
3077 cache-to-cache transfer latencies.
37745d28 3078
4102adab 3079 rcutree.rcu_fanout_leaf= [KNL]
f885b7f2
PM
3080 Increase the number of CPUs assigned to each
3081 leaf rcu_node structure. Useful for very large
3082 systems.
3083
4a81e832
PM
3084 rcutree.jiffies_till_sched_qs= [KNL]
3085 Set required age in jiffies for a
3086 given grace period before RCU starts
3087 soliciting quiescent-state help from
3088 rcu_note_context_switch().
3089
4102adab 3090 rcutree.jiffies_till_first_fqs= [KNL]
c0f4dfd4
PM
3091 Set delay from grace-period initialization to
3092 first attempt to force quiescent states.
3093 Units are jiffies, minimum value is zero,
3094 and maximum value is HZ.
3095
4102adab 3096 rcutree.jiffies_till_next_fqs= [KNL]
c0f4dfd4
PM
3097 Set delay between subsequent attempts to force
3098 quiescent states. Units are jiffies, minimum
3099 value is one, and maximum value is HZ.
3100
21871d7e 3101 rcutree.kthread_prio= [KNL,BOOT]
d2af1ad7
PM
3102 Set the SCHED_FIFO priority of the RCU per-CPU
3103 kthreads (rcuc/N). This value is also used for
3104 the priority of the RCU boost threads (rcub/N)
3105 and for the RCU grace-period kthreads (rcu_bh,
3106 rcu_preempt, and rcu_sched). If RCU_BOOST is
3107 set, valid values are 1-99 and the default is 1
3108 (the least-favored priority). Otherwise, when
3109 RCU_BOOST is not set, valid values are 0-99 and
3110 the default is zero (non-realtime operation).
21871d7e 3111
fbce7497
PM
3112 rcutree.rcu_nocb_leader_stride= [KNL]
3113 Set the number of NOCB kthread groups, which
3114 defaults to the square root of the number of
3115 CPUs. Larger numbers reduces the wakeup overhead
3116 on the per-CPU grace-period kthreads, but increases
3117 that same overhead on each group's leader.
3118
4102adab 3119 rcutree.qhimark= [KNL]
97e63f0c
PM
3120 Set threshold of queued RCU callbacks beyond which
3121 batch limiting is disabled.
21a1ea9e 3122
4102adab 3123 rcutree.qlowmark= [KNL]
24aaef8d
RD
3124 Set threshold of queued RCU callbacks below which
3125 batch limiting is re-enabled.
21a1ea9e 3126
4102adab 3127 rcutree.rcu_idle_gp_delay= [KNL]
c0f4dfd4
PM
3128 Set wakeup interval for idle CPUs that have
3129 RCU callbacks (RCU_FAST_NO_HZ=y).
d40011f6 3130
4102adab 3131 rcutree.rcu_idle_lazy_gp_delay= [KNL]
c0f4dfd4
PM
3132 Set wakeup interval for idle CPUs that have
3133 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
3134 Lazy RCU callbacks are those which RCU can
3135 prove do nothing more than free memory.
d40011f6 3136
38706bc5
PM
3137 rcutorture.cbflood_inter_holdoff= [KNL]
3138 Set holdoff time (jiffies) between successive
3139 callback-flood tests.
3140
3141 rcutorture.cbflood_intra_holdoff= [KNL]
3142 Set holdoff time (jiffies) between successive
3143 bursts of callbacks within a given callback-flood
3144 test.
3145
3146 rcutorture.cbflood_n_burst= [KNL]
3147 Set the number of bursts making up a given
3148 callback-flood test. Set this to zero to
3149 disable callback-flood testing.
3150
3151 rcutorture.cbflood_n_per_burst= [KNL]
3152 Set the number of callbacks to be registered
3153 in a given burst of a callback-flood test.
3154
4102adab 3155 rcutorture.fqs_duration= [KNL]
21b05de4
PM
3156 Set duration of force_quiescent_state bursts
3157 in microseconds.
dabb8aa9 3158
4102adab 3159 rcutorture.fqs_holdoff= [KNL]
21b05de4
PM
3160 Set holdoff time within force_quiescent_state bursts
3161 in microseconds.
dabb8aa9 3162
4102adab 3163 rcutorture.fqs_stutter= [KNL]
21b05de4
PM
3164 Set wait time between force_quiescent_state bursts
3165 in seconds.
3166
3167 rcutorture.gp_cond= [KNL]
3168 Use conditional/asynchronous update-side
3169 primitives, if available.
dabb8aa9 3170
4102adab 3171 rcutorture.gp_exp= [KNL]
21b05de4 3172 Use expedited update-side primitives, if available.
4102adab
PM
3173
3174 rcutorture.gp_normal= [KNL]
21b05de4
PM
3175 Use normal (non-expedited) asynchronous
3176 update-side primitives, if available.
3177
3178 rcutorture.gp_sync= [KNL]
3179 Use normal (non-expedited) synchronous
3180 update-side primitives, if available. If all
3181 of rcutorture.gp_cond=, rcutorture.gp_exp=,
3182 rcutorture.gp_normal=, and rcutorture.gp_sync=
3183 are zero, rcutorture acts as if is interpreted
3184 they are all non-zero.
dabb8aa9 3185
4102adab 3186 rcutorture.n_barrier_cbs= [KNL]
dabb8aa9
PM
3187 Set callbacks/threads for rcu_barrier() testing.
3188
4102adab 3189 rcutorture.nfakewriters= [KNL]
dabb8aa9
PM
3190 Set number of concurrent RCU writers. These just
3191 stress RCU, they don't participate in the actual
3192 test, hence the "fake".
3193
4102adab 3194 rcutorture.nreaders= [KNL]
3838cc18
PM
3195 Set number of RCU readers. The value -1 selects
3196 N-1, where N is the number of CPUs. A value
3197 "n" less than -1 selects N-n-2, where N is again
3198 the number of CPUs. For example, -2 selects N
3199 (the number of CPUs), -3 selects N+1, and so on.
dabb8aa9 3200
4102adab
PM
3201 rcutorture.object_debug= [KNL]
3202 Enable debug-object double-call_rcu() testing.
3203
3204 rcutorture.onoff_holdoff= [KNL]
dabb8aa9
PM
3205 Set time (s) after boot for CPU-hotplug testing.
3206
4102adab 3207 rcutorture.onoff_interval= [KNL]
dabb8aa9
PM
3208 Set time (s) between CPU-hotplug operations, or
3209 zero to disable CPU-hotplug testing.
3210
4102adab 3211 rcutorture.shuffle_interval= [KNL]
dabb8aa9
PM
3212 Set task-shuffle interval (s). Shuffling tasks
3213 allows some CPUs to go into dyntick-idle mode
3214 during the rcutorture test.
3215
4102adab 3216 rcutorture.shutdown_secs= [KNL]
dabb8aa9
PM
3217 Set time (s) after boot system shutdown. This
3218 is useful for hands-off automated testing.
3219
4102adab 3220 rcutorture.stall_cpu= [KNL]
dabb8aa9
PM
3221 Duration of CPU stall (s) to test RCU CPU stall
3222 warnings, zero to disable.
3223
4102adab 3224 rcutorture.stall_cpu_holdoff= [KNL]
dabb8aa9
PM
3225 Time to wait (s) after boot before inducing stall.
3226
4102adab 3227 rcutorture.stat_interval= [KNL]
dabb8aa9
PM
3228 Time (s) between statistics printk()s.
3229
4102adab 3230 rcutorture.stutter= [KNL]
dabb8aa9
PM
3231 Time (s) to stutter testing, for example, specifying
3232 five seconds causes the test to run for five seconds,
3233 wait for five seconds, and so on. This tests RCU's
3234 ability to transition abruptly to and from idle.
3235
4102adab 3236 rcutorture.test_boost= [KNL]
dabb8aa9
PM
3237 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
3238 "Maybe" means test if the RCU implementation
3239 under test support RCU priority boosting.
3240
4102adab 3241 rcutorture.test_boost_duration= [KNL]
dabb8aa9
PM
3242 Duration (s) of each individual boost test.
3243
4102adab 3244 rcutorture.test_boost_interval= [KNL]
dabb8aa9
PM
3245 Interval (s) between each boost test.
3246
4102adab 3247 rcutorture.test_no_idle_hz= [KNL]
dabb8aa9
PM
3248 Test RCU's dyntick-idle handling. See also the
3249 rcutorture.shuffle_interval parameter.
3250
21b05de4
PM
3251 rcutorture.torture_runnable= [BOOT]
3252 Start rcutorture running at boot time.
3253
4102adab 3254 rcutorture.torture_type= [KNL]
dabb8aa9
PM
3255 Specify the RCU implementation to test.
3256
4102adab 3257 rcutorture.verbose= [KNL]
dabb8aa9
PM
3258 Enable additional printk() statements.
3259
4102adab
PM
3260 rcupdate.rcu_expedited= [KNL]
3261 Use expedited grace-period primitives, for
3262 example, synchronize_rcu_expedited() instead
3263 of synchronize_rcu(). This reduces latency,
3264 but can increase CPU utilization, degrade
3265 real-time latency, and degrade energy efficiency.
3266
3267 rcupdate.rcu_cpu_stall_suppress= [KNL]
3268 Suppress RCU CPU stall warning messages.
3269
3270 rcupdate.rcu_cpu_stall_timeout= [KNL]
3271 Set timeout for RCU CPU stall warning messages.
3272
52db30ab
PM
3273 rcupdate.rcu_task_stall_timeout= [KNL]
3274 Set timeout in jiffies for RCU task stall warning
3275 messages. Disable with a value less than or equal
3276 to zero.
3277
74860fee
PK
3278 rcupdate.rcu_self_test= [KNL]
3279 Run the RCU early boot self tests
3280
3281 rcupdate.rcu_self_test_bh= [KNL]
3282 Run the RCU bh early boot self tests
3283
3284 rcupdate.rcu_self_test_sched= [KNL]
3285 Run the RCU sched early boot self tests
3286
ffdfc409
OJ
3287 rdinit= [KNL]
3288 Format: <full_path>
3289 Run specified binary instead of /init from the ramdisk,
3290 used for early userspace startup. See initrd.
3291
1b3a5d02
RH
3292 reboot= [KNL]
3293 Format (x86 or x86_64):
3294 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
3295 [[,]s[mp]#### \
3296 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
3297 [[,]f[orce]
3298 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
3299 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
3300 reboot_force is either force or not specified,
3301 reboot_cpu is s[mp]#### with #### being the processor
3302 to be used for rebooting.
1da177e4 3303
46b6d94e
PJ
3304 relax_domain_level=
3305 [KNL, SMP] Set scheduler's default relax_domain_level.
21acb9ca 3306 See Documentation/cgroups/cpusets.txt.
46b6d94e 3307
0399d4db
RW
3308 relative_sleep_states=
3309 [SUSPEND] Use sleep state labeling where the deepest
3310 state available other than hibernation is always "mem".
3311 Format: { "0" | "1" }
3312 0 -- Traditional sleep state labels.
3313 1 -- Relative sleep state labels.
3314
1da177e4
LT
3315 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
3316
cd4f0ef7 3317 reservetop= [X86-32]
461a9aff
ZA
3318 Format: nn[KMG]
3319 Reserves a hole at the top of the kernel virtual
3320 address space.
3321
9ea77bdb
PA
3322 reservelow= [X86]
3323 Format: nn[K]
3324 Set the amount of memory to reserve for BIOS at
3325 the bottom of the address space.
3326
7e96287d
VG
3327 reset_devices [KNL] Force drivers to reset the underlying device
3328 during initialization.
3329
a9913044
RD
3330 resume= [SWSUSP]
3331 Specify the partition device for software suspend
2df83fa4
MB
3332 Format:
3333 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
1da177e4 3334
ecbd0da1
RW
3335 resume_offset= [SWSUSP]
3336 Specify the offset from the beginning of the partition
3337 given by "resume=" at which the swap header is located,
3338 in <PAGE_SIZE> units (needed only for swap files).
3339 See Documentation/power/swsusp-and-swap-files.txt
3340
f126f733
BS
3341 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
3342 read the resume files
3343
6f8d7022
BS
3344 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
3345 Useful for devices that are detected asynchronously
3346 (e.g. USB and MMC devices).
3347
f996fc96
BS
3348 hibernate= [HIBERNATION]
3349 noresume Don't check if there's a hibernation image
3350 present during boot.
3351 nocompress Don't compress/decompress hibernation images.
a6e15a39 3352 no Disable hibernation and resume.
f996fc96 3353
0a7b35cb
MN
3354 retain_initrd [RAM] Keep initrd memory after extraction
3355
0efbb786
AC
3356 rfkill.default_state=
3357 0 "airplane mode". All wifi, bluetooth, wimax, gps, fm,
3358 etc. communication is blocked by default.
3359 1 Unblocked.
3360
3361 rfkill.master_switch_mode=
3362 0 The "airplane mode" button does nothing.
3363 1 The "airplane mode" button toggles between everything
3364 blocked and the previous configuration.
3365 2 The "airplane mode" button toggles between everything
3366 blocked and everything unblocked.
3367
1da177e4
LT
3368 rhash_entries= [KNL,NET]
3369 Set number of hash buckets for route cache
3370
1da177e4
LT
3371 ro [KNL] Mount root device read-only on boot
3372
3373 root= [KNL] Root filesystem
f2d34fd9 3374 See name_to_dev_t comment in init/do_mounts.c.
1da177e4
LT
3375
3376 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3377 mount the root filesystem
3378
3379 rootflags= [KNL] Set root filesystem mount option string
3380
3381 rootfstype= [KNL] Set root filesystem type
3382
cc1ed754
PO
3383 rootwait [KNL] Wait (indefinitely) for root device to show up.
3384 Useful for devices that are detected asynchronously
3385 (e.g. USB and MMC devices).
3386
5c71d618
RT
3387 rproc_mem=nn[KMG][@address]
3388 [KNL,ARM,CMA] Remoteproc physical memory block.
3389 Memory area to be used by remote processor image,
3390 managed by CMA.
3391
1da177e4
LT
3392 rw [KNL] Mount root device read-write on boot
3393
3394 S [KNL] Run init in single mode
3395
c60d1ae4
GS
3396 s390_iommu= [HW,S390]
3397 Set s390 IOTLB flushing mode
3398 strict
3399 With strict flushing every unmap operation will result in
3400 an IOTLB flush. Default is lazy flushing before reuse,
3401 which is faster.
3402
1da177e4
LT
3403 sa1100ir [NET]
3404 See drivers/net/irda/sa1100_ir.c.
3405
1da177e4 3406 sbni= [NET] Granch SBNI12 leased line adapter
a9913044 3407
f6630114
MT
3408 sched_debug [KNL] Enables verbose scheduler debug messages.
3409
5307c955
MG
3410 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3411 xtime_lock contention on larger systems, and/or RCU lock
3412 contention on all systems with CONFIG_MAXSMP set.
3413 Format: { "0" | "1" }
3414 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3415 1 -- enable.
3416 Note: increases power consumption, thus should only be
3417 enabled if running jitter sensitive (HPC/RT) workloads.
3418
0cb55ad2
RD
3419 security= [SECURITY] Choose a security module to enable at boot.
3420 If this boot parameter is not specified, only the first
3421 security module asking for security registration will be
3422 loaded. An invalid security module name will be treated
3423 as if no module has been chosen.
3424
3425 selinux= [SELINUX] Disable or enable SELinux at boot time.
1da177e4
LT
3426 Format: { "0" | "1" }
3427 See security/selinux/Kconfig help text.
3428 0 -- disable.
3429 1 -- enable.
3430 Default value is set via kernel config option.
3431 If enabled at boot time, /selinux/disable can be used
3432 later to disable prior to initial policy load.
3433
c1c124e9
JJ
3434 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3435 Format: { "0" | "1" }
3436 See security/apparmor/Kconfig help text
3437 0 -- disable.
3438 1 -- enable.
3439 Default value is set via kernel config option.
3440
cd4f0ef7 3441 serialnumber [BUGS=X86-32]
1da177e4 3442
1da177e4
LT
3443 shapers= [NET]
3444 Maximal number of shapers.
a9913044 3445
b05f78f5
YL
3446 show_msr= [x86] show boot-time MSR settings
3447 Format: { <integer> }
3448 Show boot-time (BIOS-initialized) MSR settings.
3449 The parameter means the number of CPUs to show,
3450 for example 1 means boot CPU only.
3451
1da177e4
LT
3452 simeth= [IA-64]
3453 simscsi=
a9913044 3454
1da177e4
LT
3455 slram= [HW,MTD]
3456
423c929c
JK
3457 slab_nomerge [MM]
3458 Disable merging of slabs with similar size. May be
3459 necessary if there is some reason to distinguish
3460 allocs to different slabs. Debug options disable
3461 merging on their own.
3462 For more information see Documentation/vm/slub.txt.
3463
3df1cccd
DR
3464 slab_max_order= [MM, SLAB]
3465 Determines the maximum allowed order for slabs.
3466 A high setting may cause OOMs due to memory
3467 fragmentation. Defaults to 1 for systems with
3468 more than 32MB of RAM, 0 otherwise.
3469
f0630fff
CL
3470 slub_debug[=options[,slabs]] [MM, SLUB]
3471 Enabling slub_debug allows one to determine the
3472 culprit if slab objects become corrupted. Enabling
3473 slub_debug can create guard zones around objects and
3474 may poison objects when not in use. Also tracks the
3475 last alloc / free. For more information see
3476 Documentation/vm/slub.txt.
c1aee215
CL
3477
3478 slub_max_order= [MM, SLUB]
f0630fff
CL
3479 Determines the maximum allowed order for slabs.
3480 A high setting may cause OOMs due to memory
3481 fragmentation. For more information see
3482 Documentation/vm/slub.txt.
c1aee215
CL
3483
3484 slub_min_objects= [MM, SLUB]
f0630fff
CL
3485 The minimum number of objects per slab. SLUB will
3486 increase the slab order up to slub_max_order to
3487 generate a sufficiently large slab able to contain
3488 the number of objects indicated. The higher the number
3489 of objects the smaller the overhead of tracking slabs
3490 and the less frequently locks need to be acquired.
c1aee215
CL
3491 For more information see Documentation/vm/slub.txt.
3492
3493 slub_min_order= [MM, SLUB]
24775d65 3494 Determines the minimum page order for slabs. Must be
f0630fff 3495 lower than slub_max_order.
c1aee215
CL
3496 For more information see Documentation/vm/slub.txt.
3497
3498 slub_nomerge [MM, SLUB]
423c929c
JK
3499 Same with slab_nomerge. This is supported for legacy.
3500 See slab_nomerge for more information.
c1aee215 3501
1da177e4
LT
3502 smart2= [HW]
3503 Format: <io1>[,<io2>[,...,<io8>]]
3504
d0d4f69b
BH
3505 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3506 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3507 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3508 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3509 smsc-ircc2.ircc_irq= [HW] IRQ line
3510 smsc-ircc2.ircc_dma= [HW] DMA channel
3511 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3512 0: Toshiba Satellite 1800 (GP data pin select)
3513 1: Fast pin select (default)
3514 2: ATC IRMode
3515
9c44bc03
IM
3516 softlockup_panic=
3517 [KNL] Should the soft-lockup detector generate panics.
44a4dcf7 3518 Format: <integer>
9c44bc03 3519
ed235875
AT
3520 softlockup_all_cpu_backtrace=
3521 [KNL] Should the soft-lockup detector generate
3522 backtraces on all cpus.
3523 Format: <integer>
3524
1da177e4 3525 sonypi.*= [HW] Sony Programmable I/O Control Device driver
395cf969 3526 See Documentation/laptops/sonypi.txt
1da177e4 3527
1da177e4
LT
3528 spia_io_base= [HW,MTD]
3529 spia_fio_base=
3530 spia_pedr=
3531 spia_peddr=
3532
f38f1d2a
SR
3533 stacktrace [FTRACE]
3534 Enabled the stack tracer on boot up.
3535
762e1207
SR
3536 stacktrace_filter=[function-list]
3537 [FTRACE] Limit the functions that the stack tracer
3538 will trace at boot up. function-list is a comma separated
3539 list of functions. This list can be changed at run
3540 time by the stack_trace_filter file in the debugfs
3541 tracing directory. Note, this enables stack tracing
3542 and the stacktrace above is not needed.
3543
1da177e4
LT
3544 sti= [PARISC,HW]
3545 Format: <num>
3546 Set the STI (builtin display/keyboard on the HP-PARISC
3547 machines) console (graphic card) which should be used
3548 as the initial boot-console.
3549 See also comment in drivers/video/console/sticore.c.
3550
3551 sti_font= [HW]
3552 See comment in drivers/video/console/sticore.c.
3553
3554 stifb= [HW]
3555 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3556
cbf11071
TM
3557 sunrpc.min_resvport=
3558 sunrpc.max_resvport=
3559 [NFS,SUNRPC]
3560 SunRPC servers often require that client requests
3561 originate from a privileged port (i.e. a port in the
3562 range 0 < portnr < 1024).
3563 An administrator who wishes to reserve some of these
3564 ports for other uses may adjust the range that the
3565 kernel's sunrpc client considers to be privileged
3566 using these two parameters to set the minimum and
3567 maximum port values.
3568
42a7fc4a
GB
3569 sunrpc.pool_mode=
3570 [NFS]
3571 Control how the NFS server code allocates CPUs to
3572 service thread pools. Depending on how many NICs
3573 you have and where their interrupts are bound, this
3574 option will affect which CPUs will do NFS serving.
3575 Note: this parameter cannot be changed while the
3576 NFS server is running.
3577
3578 auto the server chooses an appropriate mode
3579 automatically using heuristics
3580 global a single global pool contains all CPUs
3581 percpu one pool for each CPU
3582 pernode one pool for each NUMA node (equivalent
3583 to global on non-NUMA machines)
3584
cbf11071
TM
3585 sunrpc.tcp_slot_table_entries=
3586 sunrpc.udp_slot_table_entries=
3587 [NFS,SUNRPC]
3588 Sets the upper limit on the number of simultaneous
3589 RPC calls that can be sent from the client to a
3590 server. Increasing these values may allow you to
3591 improve throughput, but will also increase the
3592 amount of memory reserved for use by the client.
3593
1d4a9c17
BN
3594 suspend.pm_test_delay=
3595 [SUSPEND]
3596 Sets the number of seconds to remain in a suspend test
3597 mode before resuming the system (see
3598 /sys/power/pm_test). Only available when CONFIG_PM_DEBUG
3599 is set. Default value is 5.
3600
07555ac1 3601 swapaccount=[0|1]
a42c390c
MH
3602 [KNL] Enable accounting of swap in memory resource
3603 controller if no parameter or 1 is given or disable
3604 it if 0 is given (See Documentation/cgroups/memory.txt)
3605
91fec0f5
JK
3606 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3607 Format: { <int> | force }
3608 <int> -- Number of I/O TLB slabs
3609 force -- force using of bounce buffers even if they
3610 wouldn't be automatically used by the kernel
a9913044 3611
1da177e4
LT
3612 switches= [HW,M68k]
3613
e52eec13
AK
3614 sysfs.deprecated=0|1 [KNL]
3615 Enable/disable old style sysfs layout for old udev
3616 on older distributions. When this option is enabled
3617 very new udev will not work anymore. When this option
3618 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3619 in older udev will not work anymore.
3620 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3621 the kernel configuration.
3622
5d6f647f
IM
3623 sysrq_always_enabled
3624 [KNL]
3625 Ignore sysrq setting - this boot parameter will
3626 neutralize any effect of /proc/sys/kernel/sysrq.
3627 Useful for debugging.
3628
747029a5
FF
3629 tcpmhash_entries= [KNL,NET]
3630 Set the number of tcp_metrics_hash slots.
3631 Default value is 8192 or 16384 depending on total
3632 ram pages. This is used to specify the TCP metrics
3633 cache size. See Documentation/networking/ip-sysctl.txt
3634 "tcp_no_metrics_save" section for more details.
3635
1da177e4
LT
3636 tdfx= [HW,DRM]
3637
acc82342 3638 test_suspend= [SUSPEND][,N]
77437fd4 3639 Specify "mem" (for Suspend-to-RAM) or "standby" (for
acc82342
SP
3640 standby suspend) or "freeze" (for suspend type freeze)
3641 as the system sleep state during system startup with
3642 the optional capability to repeat N number of times.
3643 The system is woken from this state using a
3644 wakeup-capable RTC alarm.
77437fd4 3645
1da177e4
LT
3646 thash_entries= [KNL,NET]
3647 Set number of hash buckets for TCP connection
3648
f8707ec9
LB
3649 thermal.act= [HW,ACPI]
3650 -1: disable all active trip points in all thermal zones
3651 <degrees C>: override all lowest active trip points
3652
c52a7419
LB
3653 thermal.crt= [HW,ACPI]
3654 -1: disable all critical trip points in all thermal zones
22a94d79 3655 <degrees C>: override all critical trip points
c52a7419 3656
f5487145
LB
3657 thermal.nocrt= [HW,ACPI]
3658 Set to disable actions on ACPI thermal zone
3659 critical and hot trip points.
3660
72b33ef8
LB
3661 thermal.off= [HW,ACPI]
3662 1: disable ACPI thermal control
3663
a70cdc52
LB
3664 thermal.psv= [HW,ACPI]
3665 -1: disable all passive trip points
ada9cfdd
RD
3666 <degrees C>: override all passive trip points to this
3667 value
a70cdc52 3668
730ff34d
LB
3669 thermal.tzp= [HW,ACPI]
3670 Specify global default ACPI thermal zone polling rate
3671 <deci-seconds>: poll all this frequency
3672 0: no polling (default)
3673
8d32a307
TG
3674 threadirqs [KNL]
3675 Force threading of all interrupt handlers except those
24775d65 3676 marked explicitly IRQF_NO_THREAD.
8d32a307 3677
2ca62b04
KRW
3678 tmem [KNL,XEN]
3679 Enable the Transcendent memory driver if built-in.
3680
3681 tmem.cleancache=0|1 [KNL, XEN]
3682 Default is on (1). Disable the usage of the cleancache
3683 API to send anonymous pages to the hypervisor.
3684
3685 tmem.frontswap=0|1 [KNL, XEN]
3686 Default is on (1). Disable the usage of the frontswap
37d46e15
KRW
3687 API to send swap pages to the hypervisor. If disabled
3688 the selfballooning and selfshrinking are force disabled.
2ca62b04
KRW
3689
3690 tmem.selfballooning=0|1 [KNL, XEN]
3691 Default is on (1). Disable the driving of swap pages
3692 to the hypervisor.
3693
3694 tmem.selfshrinking=0|1 [KNL, XEN]
3695 Default is on (1). Partial swapoff that immediately
3696 transfers pages from Xen hypervisor back to the
3697 kernel based on different criteria.
3698
2b1a61f0
HC
3699 topology= [S390]
3700 Format: {off | on}
3701 Specify if the kernel should make use of the cpu
f65e51d7
SL
3702 topology information if the hardware supports this.
3703 The scheduler will make use of this information and
2b1a61f0 3704 e.g. base its process migration decisions on it.
c9af3fa9 3705 Default is on.
2b1a61f0 3706
2d73bae1
NA
3707 topology_updates= [KNL, PPC, NUMA]
3708 Format: {off}
3709 Specify if the kernel should ignore (off)
3710 topology updates sent by the hypervisor to this
3711 LPAR.
3712
1da177e4
LT
3713 tp720= [HW,PS2]
3714
225a9be2
RA
3715 tpm_suspend_pcr=[HW,TPM]
3716 Format: integer pcr id
3717 Specify that at suspend time, the tpm driver
3718 should extend the specified pcr with zeros,
3719 as a workaround for some chips which fail to
3720 flush the last written pcr on TPM_SaveState.
3721 This will guarantee that all the other pcrs
3722 are saved.
3723
9d612bef 3724 trace_buf_size=nn[KMG]
3e6fb8e9 3725 [FTRACE] will set tracing buffer size on each cpu.
631595fb 3726
020e5f85
LZ
3727 trace_event=[event-list]
3728 [FTRACE] Set and start specified trace events in order
3729 to facilitate early boot debugging.
3730 See also Documentation/trace/events.txt
3731
7bcfaf54
SR
3732 trace_options=[option-list]
3733 [FTRACE] Enable or disable tracer options at boot.
3734 The option-list is a comma delimited list of options
3735 that can be enabled or disabled just as if you were
3736 to echo the option name into
3737
3738 /sys/kernel/debug/tracing/trace_options
3739
3740 For example, to enable stacktrace option (to dump the
3741 stack trace of each event), add to the command line:
3742
3743 trace_options=stacktrace
3744
3745 See also Documentation/trace/ftrace.txt "trace options"
3746 section.
3747
0daa2302
SRRH
3748 tp_printk[FTRACE]
3749 Have the tracepoints sent to printk as well as the
3750 tracing ring buffer. This is useful for early boot up
3751 where the system hangs or reboots and does not give the
3752 option for reading the tracing buffer or performing a
3753 ftrace_dump_on_oops.
3754
3755 To turn off having tracepoints sent to printk,
3756 echo 0 > /proc/sys/kernel/tracepoint_printk
3757 Note, echoing 1 into this file without the
3758 tracepoint_printk kernel cmdline option has no effect.
3759
3760 ** CAUTION **
3761
3762 Having tracepoints sent to printk() and activating high
3763 frequency tracepoints such as irq or sched, can cause
3764 the system to live lock.
3765
de7edd31
SRRH
3766 traceoff_on_warning
3767 [FTRACE] enable this option to disable tracing when a
3768 warning is hit. This turns off "tracing_on". Tracing can
3769 be enabled again by echoing '1' into the "tracing_on"
3770 file located in /sys/kernel/debug/tracing/
3771
3772 This option is useful, as it disables the trace before
3773 the WARNING dump is called, which prevents the trace to
3774 be filled with content caused by the warning output.
3775
3776 This option can also be set at run time via the sysctl
3777 option: kernel/traceoff_on_warning
3778
fcf4d821
JK
3779 transparent_hugepage=
3780 [KNL]
3781 Format: [always|madvise|never]
3782 Can be used to control the default behavior of the system
3783 with respect to transparent hugepages.
3784 See Documentation/vm/transhuge.txt for more details.
3785
d3b8f889 3786 tsc= Disable clocksource stability checks for TSC.
395628ef
AK
3787 Format: <string>
3788 [x86] reliable: mark tsc clocksource as reliable, this
d3b8f889 3789 disables clocksource verification at runtime, as well
3790 as the stability checks done at bootup. Used to enable
3791 high-resolution timer mode on older hardware, and in
3792 virtualized environment.
e82b8e4e
VP
3793 [x86] noirqtime: Do not use TSC to do irq accounting.
3794 Used to run time disable IRQ_TIME_ACCOUNTING on any
3795 platforms where RDTSC is slow and this accounting
3796 can add overhead.
395628ef 3797
a9913044
RD
3798 turbografx.map[2|3]= [HW,JOY]
3799 TurboGraFX parallel port interface
3800 Format:
3801 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
1da177e4
LT
3802 See also Documentation/input/joystick-parport.txt
3803
b6935f8c
CK
3804 udbg-immortal [PPC] When debugging early kernel crashes that
3805 happen after console_init() and before a proper
3806 console driver takes over, this boot options might
3807 help "seeing" what's going on.
3808
f86dcc5a
ED
3809 uhash_entries= [KNL,NET]
3810 Set number of hash buckets for UDP/UDP-Lite connections
3811
5f8364b7
AS
3812 uhci-hcd.ignore_oc=
3813 [USB] Ignore overcurrent events (default N).
3814 Some badly-designed motherboards generate lots of
3815 bogus events, for ports that aren't wired to
3816 anything. Set this parameter to avoid log spamming.
3817 Note that genuine overcurrent events won't be
3818 reported either.
3819
e3a61b0a 3820 unknown_nmi_panic
44a4dcf7 3821 [X86] Cause panic on unknown NMI.
e3a61b0a 3822
c4fc2342
CDH
3823 usbcore.authorized_default=
3824 [USB] Default USB device authorization:
3825 (default -1 = authorized except for wireless USB,
3826 0 = not authorized, 1 = authorized)
3827
b5e795f8
AS
3828 usbcore.autosuspend=
3829 [USB] The autosuspend time delay (in seconds) used
3830 for newly-detected USB devices (default 2). This
3831 is the time required before an idle device will be
3832 autosuspended. Devices for which the delay is set
eaafbc3a 3833 to a negative value won't be autosuspended at all.
b5e795f8 3834
fd7c519d
JK
3835 usbcore.usbfs_snoop=
3836 [USB] Set to log all usbfs traffic (default 0 = off).
3837
3838 usbcore.blinkenlights=
3839 [USB] Set to cycle leds on hubs (default 0 = off).
3840
3841 usbcore.old_scheme_first=
3842 [USB] Start with the old device initialization
3843 scheme (default 0 = off).
3844
3f5eb8d5
AS
3845 usbcore.usbfs_memory_mb=
3846 [USB] Memory limit (in MB) for buffers allocated by
3847 usbfs (default = 16, 0 = max = 2047).
3848
fd7c519d
JK
3849 usbcore.use_both_schemes=
3850 [USB] Try the other device initialization scheme
3851 if the first one fails (default 1 = enabled).
3852
3853 usbcore.initial_descriptor_timeout=
3854 [USB] Specifies timeout for the initial 64-byte
3855 USB_REQ_GET_DESCRIPTOR request in milliseconds
3856 (default 5000 = 5.0 seconds).
3857
1da177e4
LT
3858 usbhid.mousepoll=
3859 [USBHID] The interval which mice are to be polled at.
a9913044 3860
d4f373e5
AS
3861 usb-storage.delay_use=
3862 [UMS] The delay in seconds before a new device is
19101954 3863 scanned for Logical Units (default 1).
d4f373e5
AS
3864
3865 usb-storage.quirks=
3866 [UMS] A list of quirks entries to supplement or
3867 override the built-in unusual_devs list. List
3868 entries are separated by commas. Each entry has
3869 the form VID:PID:Flags where VID and PID are Vendor
3870 and Product ID values (4-digit hex numbers) and
3871 Flags is a set of characters, each corresponding
3872 to a common usb-storage quirk flag as follows:
c838ea46
AS
3873 a = SANE_SENSE (collect more than 18 bytes
3874 of sense data);
a0bb1081
AS
3875 b = BAD_SENSE (don't collect more than 18
3876 bytes of sense data);
d4f373e5
AS
3877 c = FIX_CAPACITY (decrease the reported
3878 device capacity by one sector);
5116901d
KR
3879 d = NO_READ_DISC_INFO (don't use
3880 READ_DISC_INFO command);
3881 e = NO_READ_CAPACITY_16 (don't use
3882 READ_CAPACITY_16 command);
734016b0
HG
3883 f = NO_REPORT_OPCODES (don't use report opcodes
3884 command, uas only);
ee136af4
HG
3885 g = MAX_SECTORS_240 (don't transfer more than
3886 240 sectors at a time, uas only);
c838ea46
AS
3887 h = CAPACITY_HEURISTICS (decrease the
3888 reported device capacity by one
3889 sector if the number is odd);
d4f373e5
AS
3890 i = IGNORE_DEVICE (don't bind to this
3891 device);
3892 l = NOT_LOCKABLE (don't try to lock and
3893 unlock ejectable media);
3894 m = MAX_SECTORS_64 (don't transfer more
3895 than 64 sectors = 32 KB at a time);
21c13a4f
AS
3896 n = INITIAL_READ10 (force a retry of the
3897 initial READ(10) command);
c838ea46
AS
3898 o = CAPACITY_OK (accept the capacity
3899 reported by the device);
eaa05dfc
NJ
3900 p = WRITE_CACHE (the device cache is ON
3901 by default);
d4f373e5
AS
3902 r = IGNORE_RESIDUE (the device reports
3903 bogus residue values);
3904 s = SINGLE_LUN (the device has only one
3905 Logical Unit);
59307852
HG
3906 t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
3907 commands, uas only);
b6089f19 3908 u = IGNORE_UAS (don't bind to the uas driver);
d4f373e5
AS
3909 w = NO_WP_DETECT (don't test whether the
3910 medium is write-protected).
3911 Example: quirks=0419:aaf5:rl,0421:0433:rc
3912
ac1667db
SB
3913 user_debug= [KNL,ARM]
3914 Format: <int>
3915 See arch/arm/Kconfig.debug help text.
3916 1 - undefined instruction events
3917 2 - system calls
3918 4 - invalid data aborts
3919 8 - SIGSEGV faults
3920 16 - SIGBUS faults
3921 Example: user_debug=31
3922
14315592
IC
3923 userpte=
3924 [X86] Flags controlling user PTE allocations.
3925
3926 nohigh = do not allocate PTE pages in
3927 HIGHMEM regardless of setting
3928 of CONFIG_HIGHPTE.
3929
6cececfc 3930 vdso= [X86,SH]
b0b49f26
AL
3931 On X86_32, this is an alias for vdso32=. Otherwise:
3932
3933 vdso=1: enable VDSO (the default)
e6e5494c
IM
3934 vdso=0: disable VDSO mapping
3935
b0b49f26
AL
3936 vdso32= [X86] Control the 32-bit vDSO
3937 vdso32=1: enable 32-bit VDSO
3938 vdso32=0 or vdso32=2: disable 32-bit VDSO
3939
3940 See the help text for CONFIG_COMPAT_VDSO for more
3941 details. If CONFIG_COMPAT_VDSO is set, the default is
3942 vdso32=0; otherwise, the default is vdso32=1.
3943
3944 For compatibility with older kernels, vdso32=2 is an
3945 alias for vdso32=0.
3946
3947 Try vdso32=0 if you encounter an error that says:
3948 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
af65d648 3949
d080d397
YI
3950 vector= [IA-64,SMP]
3951 vector=percpu: enable percpu vector domain
3952
1da177e4
LT
3953 video= [FB] Frame buffer configuration
3954 See Documentation/fb/modedb.txt.
3955
3afe6dab
AL
3956 video.brightness_switch_enabled= [0,1]
3957 If set to 1, on receiving an ACPI notify event
3958 generated by hotkey, video driver will adjust brightness
3959 level and then send out the event to user space through
3960 the allocated input device; If set to 0, video driver
3961 will only send out the event without touching backlight
3962 brightness level.
2843768b 3963 default: 1
3afe6dab 3964
81a054ce
PM
3965 virtio_mmio.device=
3966 [VMMIO] Memory mapped virtio (platform) device.
3967
3968 <size>@<baseaddr>:<irq>[:<id>]
3969 where:
3970 <size> := size (can use standard suffixes
3971 like K, M and G)
3972 <baseaddr> := physical base address
3973 <irq> := interrupt number (as passed to
3974 request_irq())
3975 <id> := (optional) platform device id
3976 example:
3977 virtio_mmio.device=1K@0x100b0000:48:7
3978
3979 Can be used multiple times for multiple devices.
3980
cd4f0ef7 3981 vga= [BOOT,X86-32] Select a particular video mode
954a8b81 3982 See Documentation/x86/boot.txt and
a9913044 3983 Documentation/svga.txt.
1da177e4
LT
3984 Use vga=ask for menu.
3985 This is actually a boot loader parameter; the value is
3986 passed to the kernel using a special protocol.
3987
a9913044 3988 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
1da177e4
LT
3989 size of <nn>. This can be used to increase the
3990 minimum size (128MB on x86). It can also be used to
3991 decrease the size and leave more room for directly
3992 mapped kernel RAM.
3993
585c3047
PO
3994 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3995 Format: <command>
1da177e4 3996
585c3047
PO
3997 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3998 Format: <command>
3999
4000 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
4001 Format: <command>
a9913044 4002
3ae36655
AL
4003 vsyscall= [X86-64]
4004 Controls the behavior of vsyscalls (i.e. calls to
4005 fixed addresses of 0xffffffffff600x00 from legacy
4006 code). Most statically-linked binaries and older
4007 versions of glibc use these calls. Because these
4008 functions are at fixed addresses, they make nice
4009 targets for exploits that can control RIP.
4010
2e57ae05
AL
4011 emulate [default] Vsyscalls turn into traps and are
4012 emulated reasonably safely.
3ae36655 4013
2e57ae05 4014 native Vsyscalls are native syscall instructions.
3ae36655
AL
4015 This is a little bit faster than trapping
4016 and makes a few dynamic recompilers work
4017 better than they would in emulation mode.
4018 It also makes exploits much easier to write.
4019
4020 none Vsyscalls don't work at all. This makes
4021 them quite hard to use for exploits but
4022 might break your system.
4023
3855ae1c
CL
4024 vt.color= [VT] Default text color.
4025 Format: 0xYX, X = foreground, Y = background.
4026 Default: 0x07 = light gray on black.
4027
9ea9a886
CL
4028 vt.cur_default= [VT] Default cursor shape.
4029 Format: 0xCCBBAA, where AA, BB, and CC are the same as
4030 the parameters of the <Esc>[?A;B;Cc escape sequence;
4031 see VGA-softcursor.txt. Default: 2 = underline.
4032
0cb55ad2
RD
4033 vt.default_blu= [VT]
4034 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
4035 Change the default blue palette of the console.
4036 This is a 16-member array composed of values
4037 ranging from 0-255.
4038
4039 vt.default_grn= [VT]
4040 Format: <green0>,<green1>,<green2>,...,<green15>
4041 Change the default green palette of the console.
4042 This is a 16-member array composed of values
4043 ranging from 0-255.
4044
4045 vt.default_red= [VT]
4046 Format: <red0>,<red1>,<red2>,...,<red15>
4047 Change the default red palette of the console.
4048 This is a 16-member array composed of values
4049 ranging from 0-255.
4050
4051 vt.default_utf8=
4052 [VT]
4053 Format=<0|1>
4054 Set system-wide default UTF-8 mode for all tty's.
4055 Default is 1, i.e. UTF-8 mode is enabled for all
4056 newly opened terminals.
4057
f6c06b68
MG
4058 vt.global_cursor_default=
4059 [VT]
4060 Format=<-1|0|1>
4061 Set system-wide default for whether a cursor
4062 is shown on new VTs. Default is -1,
4063 i.e. cursors will be created by default unless
4064 overridden by individual drivers. 0 will hide
4065 cursors, 1 will display them.
4066
3855ae1c
CL
4067 vt.italic= [VT] Default color for italic text; 0-15.
4068 Default: 2 = green.
4069
4070 vt.underline= [VT] Default color for underlined text; 0-15.
4071 Default: 3 = cyan.
4072
4724ba57
RD
4073 watchdog timers [HW,WDT] For information on watchdog timers,
4074 see Documentation/watchdog/watchdog-parameters.txt
4075 or other driver-specific files in the
4076 Documentation/watchdog/ directory.
1da177e4 4077
d55262c4
TH
4078 workqueue.disable_numa
4079 By default, all work items queued to unbound
4080 workqueues are affine to the NUMA nodes they're
4081 issued on, which results in better behavior in
4082 general. If NUMA affinity needs to be disabled for
4083 whatever reason, this option can be used. Note
4084 that this also can be controlled per-workqueue for
4085 workqueues visible under /sys/bus/workqueue/.
4086
cee22a15
VK
4087 workqueue.power_efficient
4088 Per-cpu workqueues are generally preferred because
4089 they show better performance thanks to cache
4090 locality; unfortunately, per-cpu workqueues tend to
4091 be more power hungry than unbound workqueues.
4092
4093 Enabling this makes the per-cpu workqueues which
4094 were observed to contribute significantly to power
4095 consumption unbound, leading to measurably lower
4096 power usage at the cost of small performance
4097 overhead.
4098
4099 The default value of this parameter is determined by
4100 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
4101
0cb55ad2
RD
4102 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
4103 default x2apic cluster mode on platforms
4104 supporting x2apic.
4105
712b6aa8
KS
4106 x86_intel_mid_timer= [X86-32,APBT]
4107 Choose timer option for x86 Intel MID platform.
bb24c471
JP
4108 Two valid options are apbt timer only and lapic timer
4109 plus one apbt timer for broadcast timer.
712b6aa8 4110 x86_intel_mid_timer=apbt_only | lapic_and_apbt
bb24c471 4111
c70727a5
JG
4112 xen_512gb_limit [KNL,X86-64,XEN]
4113 Restricts the kernel running paravirtualized under Xen
4114 to use only up to 512 GB of RAM. The reason to do so is
4115 crash analysis tools and Xen tools for doing domain
4116 save/restore/migration must be enabled to handle larger
4117 domains.
4118
c1c5413a
SS
4119 xen_emul_unplug= [HW,X86,XEN]
4120 Unplug Xen emulated devices
4121 Format: [unplug0,][unplug1]
4122 ide-disks -- unplug primary master IDE devices
4123 aux-ide-disks -- unplug non-primary-master IDE devices
4124 nics -- unplug network devices
4125 all -- unplug all emulated devices (NICs and IDE disks)
1dc7ce99
IC
4126 unnecessary -- unplugging emulated devices is
4127 unnecessary even if the host did not respond to
4128 the unplug protocol
c93a4dfb 4129 never -- do not unplug even if version check succeeds
c1c5413a 4130
15a3eac0
KRW
4131 xen_nopvspin [X86,XEN]
4132 Disables the ticketlock slowpath using Xen PV
4133 optimizations.
4134
8d693b91
KRW
4135 xen_nopv [X86]
4136 Disables the PV optimizations forcing the HVM guest to
4137 run as generic HVM guest with no PV drivers.
4138
1da177e4 4139 xirc2ps_cs= [NET,PCMCIA]
a9913044
RD
4140 Format:
4141 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1da177e4 4142
a9913044 4143______________________________________________________________________
1da177e4
LT
4144
4145TODO:
4146
1da177e4 4147 Add more DRM drivers.