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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
6cececfc 168 acpi= [HW,ACPI,X86]
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
1da177e4 178
395cf969 179 See also Documentation/power/runtime_pm.txt, pci=noacpi
1da177e4 180
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181 acpi_rsdp= [ACPI,EFI,KEXEC]
182 Pass the RSDP address to the kernel, mostly used
183 on machines running EFI runtime service to boot the
184 second kernel for kdump.
185
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186 acpi_apic_instance= [ACPI, IOAPIC]
187 Format: <int>
188 2: use 2nd APIC table, if available
189 1,0: use 1st APIC table
4e381a4f 190 default: 0
a1fdcc0d 191
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192 acpi_backlight= [HW,ACPI]
193 acpi_backlight=vendor
194 acpi_backlight=video
195 If set to vendor, prefer vendor specific driver
196 (e.g. thinkpad_acpi, sony_acpi, etc.) instead
197 of the ACPI video.ko driver.
198
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199 acpi.debug_layer= [HW,ACPI,ACPI_DEBUG]
200 acpi.debug_level= [HW,ACPI,ACPI_DEBUG]
1da177e4 201 Format: <int>
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202 CONFIG_ACPI_DEBUG must be enabled to produce any ACPI
203 debug output. Bits in debug_layer correspond to a
204 _COMPONENT in an ACPI source file, e.g.,
205 #define _COMPONENT ACPI_PCI_COMPONENT
206 Bits in debug_level correspond to a level in
207 ACPI_DEBUG_PRINT statements, e.g.,
208 ACPI_DEBUG_PRINT((ACPI_DB_INFO, ...
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209 The debug_level mask defaults to "info". See
210 Documentation/acpi/debug.txt for more information about
211 debug layers and levels.
a0d84a92 212
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213 Enable processor driver info messages:
214 acpi.debug_layer=0x20000000
215 Enable PCI/PCI interrupt routing info messages:
216 acpi.debug_layer=0x400000
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217 Enable AML "Debug" output, i.e., stores to the Debug
218 object while interpreting AML:
219 acpi.debug_layer=0xffffffff acpi.debug_level=0x2
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220 Enable all messages related to ACPI hardware:
221 acpi.debug_layer=0x2 acpi.debug_level=0xffffffff
222
223 Some values produce so much output that the system is
224 unusable. The "log_buf_len" parameter may be useful
225 if you need to capture more output.
f989106c 226
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227 acpi_force_table_verification [HW,ACPI]
228 Enable table checksum verification during early stage.
229 By default, this is disabled due to x86 early mapping
230 size limitation.
231
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232 acpi_irq_balance [HW,ACPI]
233 ACPI will balance active IRQs
234 default in APIC mode
235
236 acpi_irq_nobalance [HW,ACPI]
237 ACPI will not move active IRQs (default)
238 default in PIC mode
239
240 acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA
241 Format: <irq>,<irq>...
242
243 acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for
244 use by PCI
245 Format: <irq>,<irq>...
246
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247 acpi_no_auto_serialize [HW,ACPI]
248 Disable auto-serialization of AML methods
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249 AML control methods that contain the opcodes to create
250 named objects will be marked as "Serialized" by the
251 auto-serialization feature.
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252 This feature is enabled by default.
253 This option allows to turn off the feature.
22b5afce 254
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255 acpi_no_static_ssdt [HW,ACPI]
256 Disable installation of static SSDTs at early boot time
257 By default, SSDTs contained in the RSDT/XSDT will be
258 installed automatically and they will appear under
259 /sys/firmware/acpi/tables.
260 This option turns off this feature.
261 Note that specifying this option does not affect
262 dynamic table installation which will install SSDT
263 tables to /sys/firmware/acpi/tables/dynamic.
0cb55ad2 264
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265 acpica_no_return_repair [HW, ACPI]
266 Disable AML predefined validation mechanism
267 This mechanism can repair the evaluation result to make
268 the return objects more ACPI specification compliant.
269 This option is useful for developers to identify the
270 root cause of an AML interpreter issue when the issue
271 has something to do with the repair mechanism.
272
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273 acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS
274 Format: To spoof as Windows 98: ="Microsoft Windows"
275
276 acpi_osi= [HW,ACPI] Modify list of supported OS interface strings
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277 acpi_osi="string1" # add string1
278 acpi_osi="!string2" # remove string2
741d8128 279 acpi_osi=!* # remove all strings
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280 acpi_osi=! # disable all built-in OS vendor
281 strings
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282 acpi_osi= # disable all strings
283
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284 'acpi_osi=!' can be used in combination with single or
285 multiple 'acpi_osi="string1"' to support specific OS
286 vendor string(s). Note that such command can only
287 affect the default state of the OS vendor strings, thus
288 it cannot affect the default state of the feature group
289 strings and the current state of the OS vendor strings,
290 specifying it multiple times through kernel command line
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291 is meaningless. This command is useful when one do not
292 care about the state of the feature group strings which
293 should be controlled by the OSPM.
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294 Examples:
295 1. 'acpi_osi=! acpi_osi="Windows 2000"' is equivalent
296 to 'acpi_osi="Windows 2000" acpi_osi=!', they all
297 can make '_OSI("Windows 2000")' TRUE.
298
299 'acpi_osi=' cannot be used in combination with other
300 'acpi_osi=' command lines, the _OSI method will not
301 exist in the ACPI namespace. NOTE that such command can
302 only affect the _OSI support state, thus specifying it
303 multiple times through kernel command line is also
304 meaningless.
305 Examples:
306 1. 'acpi_osi=' can make 'CondRefOf(_OSI, Local1)'
307 FALSE.
308
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309 'acpi_osi=!*' can be used in combination with single or
310 multiple 'acpi_osi="string1"' to support specific
311 string(s). Note that such command can affect the
312 current state of both the OS vendor strings and the
313 feature group strings, thus specifying it multiple times
314 through kernel command line is meaningful. But it may
315 still not able to affect the final state of a string if
316 there are quirks related to this string. This command
317 is useful when one want to control the state of the
318 feature group strings to debug BIOS issues related to
319 the OSPM features.
320 Examples:
321 1. 'acpi_osi="Module Device" acpi_osi=!*' can make
322 '_OSI("Module Device")' FALSE.
323 2. 'acpi_osi=!* acpi_osi="Module Device"' can make
324 '_OSI("Module Device")' TRUE.
325 3. 'acpi_osi=! acpi_osi=!* acpi_osi="Windows 2000"' is
326 equivalent to
327 'acpi_osi=!* acpi_osi=! acpi_osi="Windows 2000"'
328 and
329 'acpi_osi=!* acpi_osi="Windows 2000" acpi_osi=!',
330 they all will make '_OSI("Windows 2000")' TRUE.
331
6cececfc 332 acpi_pm_good [X86]
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333 Override the pmtimer bug detection: force the kernel
334 to assume that this machine's pmtimer latches its value
335 and always returns good values.
336
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337 acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode
338 Format: { level | edge | high | low }
339
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340 acpi_skip_timer_override [HW,ACPI]
341 Recognize and ignore IRQ0/pin2 Interrupt Override.
342 For broken nForce2 BIOS resulting in XT-PIC timer.
343
344 acpi_sleep= [HW,ACPI] Sleep options
345 Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig,
c3b0795c 346 old_ordering, nonvs, sci_force_enable }
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347 See Documentation/power/video.txt for information on
348 s3_bios and s3_mode.
349 s3_beep is for debugging; it makes the PC's speaker beep
350 as soon as the kernel's real-mode entry point is called.
351 s4_nohwsig prevents ACPI hardware signature from being
352 used during resume from hibernation.
353 old_ordering causes the ACPI 1.0 ordering of the _PTS
354 control method, with respect to putting devices into
355 low power states, to be enforced (the ACPI 2.0 ordering
356 of _PTS is used by default).
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357 nonvs prevents the kernel from saving/restoring the
358 ACPI NVS memory during suspend/hibernation and resume.
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359 sci_force_enable causes the kernel to set SCI_EN directly
360 on resume from S1/S3 (which is against the ACPI spec,
361 but some broken systems don't work without it).
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362
363 acpi_use_timer_override [HW,ACPI]
364 Use timer override. For some broken Nvidia NF5 boards
365 that require a timer override, but don't have HPET
366
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367 acpi_enforce_resources= [ACPI]
368 { strict | lax | no }
369 Check for resource conflicts between native drivers
370 and ACPI OperationRegions (SystemIO and SystemMemory
371 only). IO ports and memory declared in ACPI might be
372 used by the ACPI subsystem in arbitrary AML code and
373 can interfere with legacy drivers.
374 strict (default): access to resources claimed by ACPI
375 is denied; legacy drivers trying to access reserved
376 resources will fail to bind to device using them.
377 lax: access to resources claimed by ACPI is allowed;
378 legacy drivers trying to access reserved resources
379 will bind successfully but a warning message is logged.
380 no: ACPI OperationRegions are not marked as reserved,
381 no further checks are performed.
382
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383 acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
384 kernels.
385
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386 add_efi_memmap [EFI; X86] Include EFI memory map in
387 kernel's map of available physical RAM.
388
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389 agp= [AGP]
390 { off | try_unsupported }
391 off: disable AGP support
392 try_unsupported: try to drive unsupported chipsets
393 (may crash computer or cause data corruption)
394
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395 ALSA [HW,ALSA]
396 See Documentation/sound/alsa/alsa-parameters.txt
397
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398 alignment= [KNL,ARM]
399 Allow the default userspace alignment fault handler
400 behaviour to be specified. Bit 0 enables warnings,
401 bit 1 enables fixups, and bit 2 sends a segfault.
402
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403 align_va_addr= [X86-64]
404 Align virtual addresses by clearing slice [14:12] when
405 allocating a VMA at process creation time. This option
406 gives you up to 3% performance improvement on AMD F15h
407 machines (where it is enabled by default) for a
408 CPU-intensive style benchmark, and it can vary highly in
409 a microbenchmark depending on workload and compiler.
410
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411 32: only for 32-bit processes
412 64: only for 64-bit processes
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413 on: enable for both 32- and 64-bit processes
414 off: disable for both 32- and 64-bit processes
415
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416 alloc_snapshot [FTRACE]
417 Allocate the ftrace snapshot buffer on boot up when the
418 main buffer is allocated. This is handy if debugging
419 and you need to use tracing_snapshot() on boot up, and
420 do not want to use tracing_snapshot_alloc() as it needs
421 to be done where GFP_KERNEL allocations are allowed.
422
89e0b9a3 423 amd_iommu= [HW,X86-64]
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424 Pass parameters to the AMD IOMMU driver in the system.
425 Possible values are:
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426 fullflush - enable flushing of IO/TLB entries when
427 they are unmapped. Otherwise they are
428 flushed before they will be reused, which
429 is a lot of faster
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430 off - do not initialize any AMD IOMMU found in
431 the system
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432 force_isolation - Force device isolation for all
433 devices. The IOMMU driver is not
434 allowed anymore to lift isolation
435 requirements as needed. This option
436 does not override iommu=pt
afa9fdc2 437
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438 amd_iommu_dump= [HW,X86-64]
439 Enable AMD IOMMU driver option to dump the ACPI table
440 for AMD IOMMU. With this option enabled, AMD IOMMU
441 driver will print ACPI tables for AMD IOMMU during
442 IOMMU initialization.
443
1da177e4
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444 amijoy.map= [HW,JOY] Amiga joystick support
445 Map of devices attached to JOY0DAT and JOY1DAT
446 Format: <a>,<b>
395cf969 447 See also Documentation/input/joystick.txt
1da177e4
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448
449 analog.map= [HW,JOY] Analog joystick and gamepad support
450 Specifies type or capabilities of an analog joystick
451 connected to one of 16 gameports
452 Format: <type1>,<type2>,..<type16>
453
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454 apc= [HW,SPARC]
455 Power management functions (SPARCstation-4/5 + deriv.)
1da177e4
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456 Format: noidle
457 Disable APC CPU standby support. SPARCstation-Fox does
458 not play well with APC CPU idle - disable it if you have
459 APC and your system crashes randomly.
460
ca1eda2d 461 apic= [APIC,X86-32] Advanced Programmable Interrupt Controller
c8facbb6 462 Change the output verbosity whilst booting
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LT
463 Format: { quiet (default) | verbose | debug }
464 Change the amount of debugging information output
465 when initialising the APIC and IO-APIC components.
a9913044 466
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467 autoconf= [IPV6]
468 See Documentation/networking/ipv6.txt.
469
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470 show_lapic= [APIC,X86] Advanced Programmable Interrupt Controller
471 Limit apic dumping. The parameter defines the maximal
472 number of local apics being dumped. Also it is possible
473 to set it to "all" by meaning -- no limit here.
474 Format: { 1 (default) | 2 | ... | all }.
475 The parameter valid if only apic=debug or
476 apic=verbose is specified.
477 Example: apic=debug show_lapic=all
478
1da177e4 479 apm= [APM] Advanced Power Management
71f77055 480 See header of arch/x86/kernel/apm_32.c.
1da177e4 481
1da177e4
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482 arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards
483 Format: <io>,<irq>,<nodeID>
484
485 ataflop= [HW,M68k]
486
487 atarimouse= [HW,MOUSE] Atari Mouse
488
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489 atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess,
490 EzKey and similar keyboards
491
492 atkbd.reset= [HW] Reset keyboard during initialization
493
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494 atkbd.set= [HW] Select keyboard code set
495 Format: <int> (2 = AT (default), 3 = PS/2)
1da177e4
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496
497 atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar
498 keyboards
499
500 atkbd.softraw= [HW] Choose between synthetic and real raw mode
501 Format: <bool> (0 = real, 1 = synthetic (default))
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502
503 atkbd.softrepeat= [HW]
504 Use software keyboard repeat
1da177e4 505
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506 audit= [KNL] Enable the audit sub-system
507 Format: { "0" | "1" } (0 = disabled, 1 = enabled)
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508 0 - kernel audit is disabled and can not be enabled
509 until the next reboot
510 unset - kernel audit is initialized but disabled and
511 will be fully enabled by the userspace auditd.
512 1 - kernel audit is initialized and partially enabled,
513 storing at most audit_backlog_limit messages in
514 RAM until it is fully enabled by the userspace
515 auditd.
a106fb0c 516 Default: unset
f3411cb2 517
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518 audit_backlog_limit= [KNL] Set the audit queue size limit.
519 Format: <int> (must be >=0)
520 Default: 64
521
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522 baycom_epp= [HW,AX25]
523 Format: <io>,<mode>
a9913044 524
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525 baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem
526 Format: <io>,<mode>
527 See header of drivers/net/hamradio/baycom_par.c.
528
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529 baycom_ser_fdx= [HW,AX25]
530 BayCom Serial Port AX.25 Modem (Full Duplex Mode)
1da177e4
LT
531 Format: <io>,<irq>,<mode>[,<baud>]
532 See header of drivers/net/hamradio/baycom_ser_fdx.c.
533
a9913044
RD
534 baycom_ser_hdx= [HW,AX25]
535 BayCom Serial Port AX.25 Modem (Half Duplex Mode)
1da177e4
LT
536 Format: <io>,<irq>,<mode>
537 See header of drivers/net/hamradio/baycom_ser_hdx.c.
538
080506ad
PG
539 blkdevparts= Manual partition parsing of block device(s) for
540 embedded devices based on command line input.
541 See Documentation/block/cmdline-partition.txt
542
bfe8df3d
RD
543 boot_delay= Milliseconds to delay each printk during boot.
544 Values larger than 10 seconds (10000) are changed to
545 no delay (0).
546 Format: integer
547
35fc908d
AH
548 bootmem_debug [KNL] Enable bootmem allocator debug messages.
549
1da177e4 550 bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards)
a9913044
RD
551 bttv.radio= Most important insmod options are available as
552 kernel args too.
1da177e4 553 bttv.pll= See Documentation/video4linux/bttv/Insmod-options
395cf969 554 bttv.tuner=
1da177e4 555
4e89a2d8
WS
556 bulk_remove=off [PPC] This parameter disables the use of the pSeries
557 firmware feature for flushing multiple hpte entries
558 at a time.
559
1da177e4
LT
560 c101= [NET] Moxa C101 synchronous serial card
561
cd4f0ef7 562 cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection.
1da177e4
LT
563 Sometimes CPU hardware bugs make them report the cache
564 size incorrectly. The kernel will attempt work arounds
565 to fix known problems, but for some CPUs it is not
566 possible to determine what the correct size should be.
567 This option provides an override for these situations.
568
14ff56bb
SO
569 ccw_timeout_log [S390]
570 See Documentation/s390/CommonIO for details.
1da177e4 571
8bab8dde
PM
572 cgroup_disable= [KNL] Disable a particular controller
573 Format: {name of the controller(s) to disable}
ca0bdbb5
QH
574 The effects of cgroup_disable=foo are:
575 - foo isn't auto-mounted if you mount all cgroups in
576 a single hierarchy
577 - foo isn't visible as an individually mountable
578 subsystem
579 {Currently only "memory" controller deal with this and
580 cut the overhead, others just disable the usage. So
581 only cgroup_disable=memory is actually worthy}
8bab8dde 582
1da177e4
LT
583 checkreqprot [SELINUX] Set initial checkreqprot flag value.
584 Format: { "0" | "1" }
585 See security/selinux/Kconfig help text.
a9913044
RD
586 0 -- check protection applied by kernel (includes
587 any implied execute protection).
1da177e4
LT
588 1 -- check protection requested by application.
589 Default value is set via a kernel config option.
a9913044
RD
590 Value can be changed at runtime via
591 /selinux/checkreqprot.
592
661ca0da
SO
593 cio_ignore= [S390]
594 See Documentation/s390/CommonIO for details.
1e435256
OJ
595 clk_ignore_unused
596 [CLK]
597 Keep all clocks already enabled by bootloader on,
598 even if no driver has claimed them. This is useful
599 for debug and development, but should not be
600 needed on a platform with proper driver support.
601 For more information, see Documentation/clk.txt.
661ca0da 602
cd4f0ef7 603 clock= [BUGS=X86-32, HW] gettimeofday clocksource override.
734efb46 604 [Deprecated]
3f6dee9b 605 Forces specified clocksource (if available) to be used
734efb46 606 when calculating gettimeofday(). If specified
3f6dee9b 607 clocksource is not available, it defaults to PIT.
1da177e4
LT
608 Format: { pit | tsc | cyclone | pmtmr }
609
592913ec 610 clocksource= Override the default clocksource
3d6ac984
RD
611 Format: <string>
612 Override the default clocksource and use the clocksource
613 with the name specified.
614 Some clocksource names to choose from, depending on
615 the platform:
616 [all] jiffies (this is the base, fallback clocksource)
617 [ACPI] acpi_pm
618 [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2,
619 pxa_timer,timer3,32k_counter,timer0_1
620 [AVR32] avr32
9863c90f 621 [X86-32] pit,hpet,tsc;
3d6ac984
RD
622 scx200_hrt on Geode; cyclone on IBM x440
623 [MIPS] MIPS
624 [PARISC] cr16
625 [S390] tod
626 [SH] SuperH
627 [SPARC64] tick
628 [X86-64] hpet,tsc
629
ac72e788
AK
630 clearcpuid=BITNUM [X86]
631 Disable CPUID feature X for the kernel. See
07983f0e
RD
632 arch/x86/include/asm/cpufeature.h for the valid bit
633 numbers. Note the Linux specific bits are not necessarily
ac72e788
AK
634 stable over kernel options, but the vendor specific
635 ones should be.
636 Also note that user programs calling CPUID directly
637 or using the feature without checking anything
638 will still see it. This just prevents it from
639 being used by the kernel or shown in /proc/cpuinfo.
640 Also note the kernel might malfunction if you disable
641 some critical bits.
642
5ea3b1b2
AM
643 cma=nn[MG]@[start[MG][-end[MG]]]
644 [ARM,X86,KNL]
645 Sets the size of kernel global memory area for
646 contiguous memory allocations and optionally the
647 placement constraint by the physical address range of
c64be2bb
MS
648 memory allocations. For more information, see
649 include/linux/dma-contiguous.h
650
14f966e7
RJ
651 cmo_free_hint= [PPC] Format: { yes | no }
652 Specify whether pages are marked as being inactive
653 when they are freed. This is used in CMO environments
654 to determine OS memory pressure for page stealing by
655 a hypervisor.
656 Default: yes
657
c7909509
MS
658 coherent_pool=nn[KMG] [ARM,KNL]
659 Sets the size of memory pool for coherent, atomic dma
e9da6e99 660 allocations, by default set to 256K.
c7909509 661
6cececfc 662 code_bytes [X86] How many bytes of object code to print
a25bd949 663 in an oops report.
86c41837
CE
664 Range: 0 - 8192
665 Default: 64
666
1da177e4 667 com20020= [HW,NET] ARCnet - COM20020 chipset
a9913044
RD
668 Format:
669 <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]]
1da177e4
LT
670
671 com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers)
672 Format: <io>[,<irq>]
673
a9913044
RD
674 com90xx= [HW,NET]
675 ARCnet - COM90xx chipset (memory-mapped buffers)
1da177e4
LT
676 Format: <io>[,<irq>[,<memstart>]]
677
678 condev= [HW,S390] console device
679 conmode=
a9913044 680
1da177e4
LT
681 console= [KNL] Output console device and options.
682
683 tty<n> Use the virtual console device <n>.
684
685 ttyS<n>[,options]
f1a1c2dc 686 ttyUSB0[,options]
1da177e4 687 Use the specified serial port. The options are of
f1a1c2dc
RD
688 the form "bbbbpnf", where "bbbb" is the baud rate,
689 "p" is parity ("n", "o", or "e"), "n" is number of
690 bits, and "f" is flow control ("r" for RTS or
691 omit it). Default is "9600n8".
692
693 See Documentation/serial-console.txt for more
694 information. See
695 Documentation/networking/netconsole.txt for an
696 alternative.
1da177e4 697
18a8bd94
YL
698 uart[8250],io,<addr>[,options]
699 uart[8250],mmio,<addr>[,options]
1da177e4
LT
700 Start an early, polled-mode console on the 8250/16550
701 UART at the specified I/O port or MMIO address,
702 switching to the matching ttyS device later. The
703 options are the same as for ttyS, above.
a2fd6419
KRW
704 hvc<n> Use the hypervisor console device <n>. This is for
705 both Xen and PowerPC hypervisors.
1da177e4 706
f7511d5f
ST
707 If the device connected to the port is not a TTY but a braille
708 device, prepend "brl," before the device type, for instance
709 console=brl,ttyS0
710 For now, only VisioBraille is supported.
711
f324edc8
DM
712 consoleblank= [KNL] The console blank (screen saver) timeout in
713 seconds. Defaults to 10*60 = 10mins. A value of 0
714 disables the blank timer.
715
4cb0e11b
HK
716 coredump_filter=
717 [KNL] Change the default value for
718 /proc/<pid>/coredump_filter.
719 See also Documentation/filesystems/proc.txt.
720
62027aea
LB
721 cpuidle.off=1 [CPU_IDLE]
722 disable the cpuidle sub-system
723
1da177e4 724 cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver
a9913044
RD
725 Format:
726 <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>]
1da177e4 727
6f21e646
AD
728 crashkernel=size[KMG][@offset[KMG]]
729 [KNL] Using kexec, Linux can switch to a 'crash kernel'
730 upon panic. This parameter reserves the physical
731 memory region [offset, offset + size] for that kernel
732 image. If '@offset' is omitted, then a suitable offset
733 is selected automatically. Check
734 Documentation/kdump/kdump.txt for further details.
dc009d92 735
fb391599
BW
736 crashkernel=range1:size1[,range2:size2,...][@offset]
737 [KNL] Same as above, but depends on the memory
738 in the running system. The syntax of range is
739 start-[end] where start and end are both
740 a memory unit (amount[KMG]). See also
6f21e646 741 Documentation/kdump/kdump.txt for an example.
fb391599 742
adbc742b 743 crashkernel=size[KMG],high
55a20ee7
YL
744 [KNL, x86_64] range could be above 4G. Allow kernel
745 to allocate physical memory region from top, so could
746 be above 4G if system have more than 4G ram installed.
747 Otherwise memory region will be allocated below 4G, if
748 available.
749 It will be ignored if crashkernel=X is specified.
adbc742b
YL
750 crashkernel=size[KMG],low
751 [KNL, x86_64] range under 4G. When crashkernel=X,high
752 is passed, kernel could allocate physical memory region
c729de8f
YL
753 above 4G, that cause second kernel crash on system
754 that require some amount of low memory, e.g. swiotlb
755 requires at least 64M+32K low memory. Kernel would
756 try to allocate 72M below 4G automatically.
757 This one let user to specify own low range under 4G
758 for second kernel instead.
759 0: to disable low allocation.
adbc742b 760 It will be ignored when crashkernel=X,high is not used
55a20ee7 761 or memory reserved is below 4G.
c729de8f 762
1da177e4
LT
763 cs89x0_dma= [HW,NET]
764 Format: <dma>
765
766 cs89x0_media= [HW,NET]
767 Format: { rj45 | aui | bnc }
a9913044 768
a9913044 769 dasd= [HW,NET]
1da177e4
LT
770 See header of drivers/s390/block/dasd_devmap.c.
771
772 db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port
773 (one device per port)
774 Format: <port#>,<type>
775 See also Documentation/input/joystick-parport.txt
776
a648ec05
TR
777 ddebug_query= [KNL,DYNAMIC_DEBUG] Enable debug messages at early boot
778 time. See Documentation/dynamic-debug-howto.txt for
29e36c9f 779 details. Deprecated, see dyndbg.
a648ec05 780
1da177e4
LT
781 debug [KNL] Enable kernel debugging (events log level).
782
cae2ed9a
IM
783 debug_locks_verbose=
784 [KNL] verbose self-tests
785 Format=<0|1>
786 Print debugging info while doing the locking API
787 self-tests.
788 We default to 0 (no extra messages), setting it to
789 1 will print _a lot_ more information - normally
790 only useful to kernel developers.
791
3ac7fe5a
TG
792 debug_objects [KNL] Enable object debugging
793
3e8ebb5c
KM
794 no_debug_objects
795 [KNL] Disable object debugging
796
c0a32fc5
SG
797 debug_guardpage_minorder=
798 [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
799 parameter allows control of the order of pages that will
800 be intentionally kept free (and hence protected) by the
801 buddy allocator. Bigger value increase the probability
802 of catching random memory corruption, but reduce the
803 amount of memory for normal system use. The maximum
804 possible value is MAX_ORDER/2. Setting this parameter
805 to 1 or 2 should be enough to identify most random
806 memory corruption problems caused by bugs in kernel or
807 driver code when a CPU writes to (or reads from) a
808 random memory location. Note that there exists a class
809 of memory corruptions problems caused by buggy H/W or
810 F/W or by drivers badly programing DMA (basically when
811 memory is written at bus level and the CPU MMU is
812 bypassed) which are not detectable by
813 CONFIG_DEBUG_PAGEALLOC, hence this option will not help
814 tracking down these problems.
815
d3af01f1
TG
816 debugpat [X86] Enable PAT debugging
817
2d27a966 818 decnet.addr= [HW,NET]
1da177e4
LT
819 Format: <area>[,<node>]
820 See also Documentation/networking/decnet.txt.
821
0cb55ad2
RD
822 default_hugepagesz=
823 [same as hugepagesz=] The size of the default
824 HugeTLB page size. This is the size represented by
825 the legacy /proc/ hugepages APIs, used for SHM, and
826 default size when mounting hugetlbfs filesystems.
827 Defaults to the default architecture's huge page size
828 if not specified.
55ff9780 829
1da177e4
LT
830 dhash_entries= [KNL]
831 Set number of hash buckets for dentry cache.
a9913044 832
b0f83b28
BH
833 disable= [IPV6]
834 See Documentation/networking/ipv6.txt.
835
151e0c7d
HD
836 disable_cpu_apicid= [X86,APIC,SMP]
837 Format: <int>
838 The number of initial APIC ID for the
839 corresponding CPU to be disabled at boot,
840 mostly used for the kdump 2nd kernel to
841 disable BSP to wake up multiple CPUs without
842 causing system reset or hang due to sending
843 INIT from AP to BSP.
844
4e8b0cf4
NA
845 disable_ddw [PPC/PSERIES]
846 Disable Dynamic DMA Window support. Use this if
847 to workaround buggy firmware.
848
b0f83b28
BH
849 disable_ipv6= [IPV6]
850 See Documentation/networking/ipv6.txt.
851
95ffa243 852 disable_mtrr_cleanup [X86]
95ffa243
YL
853 The kernel tries to adjust MTRR layout from continuous
854 to discrete, to make X server driver able to add WB
0cb55ad2 855 entry later. This parameter disables that.
95ffa243 856
093af8d7 857 disable_mtrr_trim [X86, Intel and AMD only]
99fc8d42
JB
858 By default the kernel will trim any uncacheable
859 memory out of your available memory pool based on
860 MTRR settings. This parameter disables that behavior,
861 possibly causing your machine to run very slowly.
862
6cececfc 863 disable_timer_pin_1 [X86]
0cb55ad2
RD
864 Disable PIN 1 of APIC timer
865 Can be useful to work around chipset bugs.
866
0cb55ad2
RD
867 dma_debug=off If the kernel is compiled with DMA_API_DEBUG support,
868 this option disables the debugging code at boot.
869
870 dma_debug_entries=<number>
871 This option allows to tune the number of preallocated
872 entries for DMA-API debugging code. One entry is
873 required per DMA-API allocation. Use this if the
874 DMA-API debugging code disables itself because the
875 architectural default is too low.
876
1745de5e
JR
877 dma_debug_driver=<driver_name>
878 With this option the DMA-API debugging driver
879 filter feature can be enabled at boot time. Just
880 pass the driver to filter for as the parameter.
881 The filter can be disabled or changed to another
882 driver later using sysfs.
883
da0df92b
CE
884 drm_kms_helper.edid_firmware=[<connector>:]<file>
885 Broken monitors, graphic adapters and KVMs may
886 send no or incorrect EDID data sets. This parameter
887 allows to specify an EDID data set in the
888 /lib/firmware directory that is used instead.
889 Generic built-in EDID data sets are used, if one of
890 edid/1024x768.bin, edid/1280x1024.bin,
891 edid/1680x1050.bin, or edid/1920x1080.bin is given
892 and no file with the same name exists. Details and
893 instructions how to build your own EDID data are
894 available in Documentation/EDID/HOWTO.txt. An EDID
895 data set will only be used for a particular connector,
896 if its name and a colon are prepended to the EDID
897 name.
898
1da177e4
LT
899 dscc4.setup= [NET]
900
29e36c9f
JC
901 dyndbg[="val"] [KNL,DYNAMIC_DEBUG]
902 module.dyndbg[="val"]
903 Enable debug messages at boot time. See
904 Documentation/dynamic-debug-howto.txt for details.
905
56aeeba8
MS
906 early_ioremap_debug [KNL]
907 Enable debug messages in early_ioremap support. This
908 is useful for tracking down temporary early mappings
909 which are not unmapped.
910
0cb55ad2 911 earlycon= [KNL] Output early console device and options.
0d3c673e 912
0cb55ad2
RD
913 uart[8250],io,<addr>[,options]
914 uart[8250],mmio,<addr>[,options]
1917ac76 915 uart[8250],mmio32,<addr>[,options]
0cb55ad2
RD
916 Start an early, polled-mode console on the 8250/16550
917 UART at the specified I/O port or MMIO address.
16290246
RD
918 MMIO inter-register address stride is either 8-bit
919 (mmio) or 32-bit (mmio32).
0cb55ad2
RD
920 The options are the same as for ttyS, above.
921
0d3c673e
RH
922 pl011,<addr>
923 Start an early, polled-mode console on a pl011 serial
924 port at the specified address. The pl011 serial port
925 must already be setup and configured. Options are not
926 yet supported.
927
d50d7269
RH
928 smh Use ARM semihosting calls for early console.
929
7913ad1a 930 earlyprintk= [X86,SH,BLACKFIN,ARM,M68k]
1da177e4 931 earlyprintk=vga
72548e83 932 earlyprintk=efi
2482a92e 933 earlyprintk=xen
1da177e4 934 earlyprintk=serial[,ttySn[,baudrate]]
147ea091 935 earlyprintk=serial[,0x...[,baudrate]]
ea3acb19 936 earlyprintk=ttySn[,baudrate]
9780bc41 937 earlyprintk=dbgp[debugController#]
1da177e4 938
147ea091
DH
939 earlyprintk is useful when the kernel crashes before
940 the normal console is initialized. It is not enabled by
941 default because it has some cosmetic problems.
942
a9913044 943 Append ",keep" to not disable it when the real console
1da177e4
LT
944 takes over.
945
72548e83
MF
946 Only one of vga, efi, serial, or usb debug port can
947 be used at a time.
1da177e4 948
147ea091
DH
949 Currently only ttyS0 and ttyS1 may be specified by
950 name. Other I/O ports may be explicitly specified
951 on some architectures (x86 and arm at least) by
952 replacing ttySn with an I/O port address, like this:
953 earlyprintk=serial,0x1008,115200
954 You can find the port for a given device in
955 /proc/tty/driver/serial:
956 2: uart:ST16650V2 port:00001008 irq:18 ...
1da177e4
LT
957
958 Interaction with the standard serial driver is not
959 very good.
960
72548e83
MF
961 The VGA and EFI output is eventually overwritten by
962 the real console.
1da177e4 963
2482a92e
KRW
964 The xen output can only be used by Xen PV guests.
965
c700f013
CG
966 edac_report= [HW,EDAC] Control how to report EDAC event
967 Format: {"on" | "off" | "force"}
968 on: enable EDAC to report H/W event. May be overridden
969 by other higher priority error reporting module.
970 off: disable H/W event reporting through EDAC.
971 force: enforce the use of EDAC to report H/W event.
972 default: on.
973
9731191f
JW
974 ekgdboc= [X86,KGDB] Allow early kernel console debugging
975 ekgdboc=kbd
976
25985edc 977 This is designed to be used in conjunction with
9731191f
JW
978 the boot argument: earlyprintk=vga
979
1da177e4 980 edd= [EDD]
8c4dd606 981 Format: {"off" | "on" | "skip[mbr]"}
1da177e4 982
d2f7cbe7
BP
983 efi= [EFI]
984 Format: { "old_map" }
985 old_map [X86-64]: switch to the old ioremap-based EFI
986 runtime services mapping. 32-bit still uses this one by
987 default.
988
8c58bf3e
RW
989 efi_no_storage_paranoia [EFI; X86]
990 Using this parameter you can use more than 50% of
991 your efi variable storage. Use this parameter only if
992 you are really sure that your UEFI does sane gc and
993 fulfills the spec otherwise your board may brick.
994
1da177e4
LT
995 eisa_irq_edge= [PARISC,HW]
996 See header of drivers/parisc/eisa.c.
997
cd4f0ef7 998 elanfreq= [X86-32]
1da177e4 999 See comment before function elanfreq_setup() in
71f77055 1000 arch/x86/kernel/cpu/cpufreq/elanfreq.c.
1da177e4
LT
1001
1002 elevator= [IOSCHED]
17a9e7bb 1003 Format: {"cfq" | "deadline" | "noop"}
395cf969 1004 See Documentation/block/cfq-iosched.txt and
a9913044
RD
1005 Documentation/block/deadline-iosched.txt for details.
1006
d3bf3795 1007 elfcorehdr=[size[KMG]@]offset[KMG] [IA64,PPC,SH,X86,S390]
a9913044 1008 Specifies physical address of start of kernel core
d3bf3795
MH
1009 image elf header and optionally the size. Generally
1010 kexec loader will pass this option to capture kernel.
aac04b32 1011 See Documentation/kdump/kdump.txt for details.
1da177e4 1012
0cb55ad2
RD
1013 enable_mtrr_cleanup [X86]
1014 The kernel tries to adjust MTRR layout from continuous
1015 to discrete, to make X server driver able to add WB
1016 entry later. This parameter enables that.
1017
ca1eda2d 1018 enable_timer_pin_1 [X86]
0cb55ad2
RD
1019 Enable PIN 1 of APIC timer
1020 Can be useful to work around chipset bugs
1021 (in particular on some ATI chipsets).
1022 The kernel tries to set a reasonable default.
1023
1da177e4
LT
1024 enforcing [SELINUX] Set initial enforcing status.
1025 Format: {"0" | "1"}
1026 See security/selinux/Kconfig help text.
1027 0 -- permissive (log only, no denials).
1028 1 -- enforcing (deny and log).
1029 Default value is 0.
1030 Value can be changed at runtime via /selinux/enforce.
1031
a08f82d0
HY
1032 erst_disable [ACPI]
1033 Disable Error Record Serialization Table (ERST)
1034 support.
1035
1da177e4
LT
1036 ether= [HW,NET] Ethernet cards parameters
1037 This option is obsoleted by the "netdev=" option, which
1038 has equivalent usage. See its documentation for details.
1039
7102ebcd
MZ
1040 evm= [EVM]
1041 Format: { "fix" }
1042 Permit 'security.evm' to be updated regardless of
1043 current integrity status.
1044
de1ba09b
AM
1045 failslab=
1046 fail_page_alloc=
1047 fail_make_request=[KNL]
1048 General fault injection mechanism.
1049 Format: <interval>,<probability>,<space>,<times>
395cf969 1050 See also Documentation/fault-injection/.
de1ba09b 1051
1da177e4 1052 floppy= [HW]
31c00fc1 1053 See Documentation/blockdev/floppy.txt.
1da177e4 1054
f13ae30e
AC
1055 force_pal_cache_flush
1056 [IA-64] Avoid check_sal_cache_flush which may hang on
1057 buggy SAL_CACHE_FLUSH implementations. Using this
1058 parameter will force ia64_sal_cache_flush to call
1059 ia64_pal_cache_flush instead of SAL_CACHE_FLUSH.
1060
69f2366c
CB
1061 forcepae [X86-32]
1062 Forcefully enable Physical Address Extension (PAE).
1063 Many Pentium M systems disable PAE but may have a
1064 functionally usable PAE implementation.
1065 Warning: use of this parameter will taint the kernel
1066 and may cause unknown problems.
1067
d9e54076 1068 ftrace=[tracer]
2af15d6a 1069 [FTRACE] will set and start the specified tracer
d9e54076
PZ
1070 as early as possible in order to facilitate early
1071 boot debugging.
1072
cecbca96 1073 ftrace_dump_on_oops[=orig_cpu]
2af15d6a 1074 [FTRACE] will dump the trace buffers on oops.
cecbca96
FW
1075 If no parameter is passed, ftrace will dump
1076 buffers of all CPUs, but if you pass orig_cpu, it will
1077 dump only the buffer of the CPU that triggered the
1078 oops.
2af15d6a
SR
1079
1080 ftrace_filter=[function-list]
1081 [FTRACE] Limit the functions traced by the function
1082 tracer at boot up. function-list is a comma separated
1083 list of functions. This list can be changed at run
1084 time by the set_ftrace_filter file in the debugfs
16290246 1085 tracing directory.
2af15d6a
SR
1086
1087 ftrace_notrace=[function-list]
1088 [FTRACE] Do not trace the functions specified in
1089 function-list. This list can be changed at run time
1090 by the set_ftrace_notrace file in the debugfs
1091 tracing directory.
d9e54076 1092
369bc18f
SA
1093 ftrace_graph_filter=[function-list]
1094 [FTRACE] Limit the top level callers functions traced
1095 by the function graph tracer at boot up.
1096 function-list is a comma separated list of functions
1097 that can be changed at run time by the
1098 set_graph_function file in the debugfs tracing directory.
1099
1da177e4
LT
1100 gamecon.map[2|3]=
1101 [HW,JOY] Multisystem joystick and NES/SNES/PSX pad
1102 support via parallel port (up to 5 devices per port)
1103 Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5>
1104 See also Documentation/input/joystick-parport.txt
1105
1106 gamma= [HW,DRM]
1107
aaf23042
YL
1108 gart_fix_e820= [X86_64] disable the fix e820 for K8 GART
1109 Format: off | on
1110 default: on
1111
2521f2c2
PO
1112 gcov_persist= [GCOV] When non-zero (default), profiling data for
1113 kernel modules is saved and remains accessible via
1114 debugfs, even when the module is unloaded/reloaded.
1115 When zero, profiling data is discarded and associated
1116 debugfs files are removed at module unload time.
1117
1da177e4 1118 gpt [EFI] Forces disk with valid GPT signature but
6c5de79b
DB
1119 invalid Protective MBR to be treated as GPT. If the
1120 primary GPT is corrupted, it enables the backup/alternate
1121 GPT to be used instead.
1da177e4 1122
6cec9b07
AL
1123 grcan.enable0= [HW] Configuration of physical interface 0. Determines
1124 the "Enable 0" bit of the configuration register.
1125 Format: 0 | 1
1126 Default: 0
1127 grcan.enable1= [HW] Configuration of physical interface 1. Determines
1128 the "Enable 0" bit of the configuration register.
1129 Format: 0 | 1
1130 Default: 0
1131 grcan.select= [HW] Select which physical interface to use.
1132 Format: 0 | 1
1133 Default: 0
1134 grcan.txsize= [HW] Sets the size of the tx buffer.
1135 Format: <unsigned int> such that (txsize & ~0x1fffc0) == 0.
1136 Default: 1024
1137 grcan.rxsize= [HW] Sets the size of the rx buffer.
1138 Format: <unsigned int> such that (rxsize & ~0x1fffc0) == 0.
1139 Default: 1024
1140
1da177e4
LT
1141 hashdist= [KNL,NUMA] Large hashes allocated during boot
1142 are distributed across NUMA nodes. Defaults on
16290246 1143 for 64-bit NUMA, off otherwise.
a9913044 1144 Format: 0 | 1 (for off | on)
1da177e4
LT
1145
1146 hcl= [IA-64] SGI's Hardware Graph compatibility layer
1147
1148 hd= [EIDE] (E)IDE hard drive subsystem geometry
1149 Format: <cyl>,<head>,<sect>
1150
ea8c071c
HY
1151 hest_disable [ACPI]
1152 Disable Hardware Error Source Table (HEST) support;
1153 corresponding firmware-first mode error processing
1154 logic will be disabled.
1155
1da177e4
LT
1156 highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
1157 size of <nn>. This works even on boxes that have no
1158 highmem otherwise. This also works to reduce highmem
1159 size on bigger boxes.
1160
54cdfdb4
TG
1161 highres= [KNL] Enable/disable high resolution timer mode.
1162 Valid parameters: "on", "off"
1163 Default: "on"
1164
1da177e4
LT
1165 hisax= [HW,ISDN]
1166 See Documentation/isdn/README.HiSax.
1167
0cb55ad2
RD
1168 hlt [BUGS=ARM,SH]
1169
1170 hpet= [X86-32,HPET] option to control HPET usage
1171 Format: { enable (default) | disable | force |
1172 verbose }
1173 disable: disable HPET and use PIT instead
1174 force: allow force enabled of undocumented chips (ICH4,
1175 VIA, nVidia)
1176 verbose: show contents of HPET registers during setup
1177
3d035f58
PB
1178 hpet_mmap= [X86, HPET_MMAP] Allow userspace to mmap HPET
1179 registers. Default set by CONFIG_HPET_MMAP_DEFAULT.
1180
b4718e62
AK
1181 hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
1182 hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
0d9ea754
JT
1183 On x86-64 and powerpc, this option can be specified
1184 multiple times interleaved with hugepages= to reserve
1185 huge pages of different sizes. Valid pages sizes on
1186 x86-64 are 2M (when the CPU supports "pse") and 1G
1187 (when the CPU supports the "pdpe1gb" cpuinfo flag)
b4718e62
AK
1188 Note that 1GB pages can only be allocated at boot time
1189 using hugepages= and not freed afterwards.
6902aa84 1190
555d61d6
HB
1191 hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC)
1192 terminal devices. Valid values: 0..8
431429ff
HB
1193 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs.
1194 If specified, z/VM IUCV HVC accepts connections
1195 from listed z/VM user IDs only.
cef7125d 1196
fdabf525
JH
1197 hwthread_map= [METAG] Comma-separated list of Linux cpu id to
1198 hardware thread id mappings.
1199 Format: <cpu>:<hwthread>
1200
7bf69395
FDN
1201 keep_bootcon [KNL]
1202 Do not unregister boot console at start. This is only
1203 useful for debugging when something happens in the window
1204 between unregistering the boot console and initializing
1205 the real console.
1206
3a853fb9 1207 i2c_bus= [HW] Override the default board specific I2C bus speed
7954763b
JN
1208 or register an additional I2C bus that is not
1209 registered from board initialization code.
3a853fb9
JN
1210 Format:
1211 <bus_id>,<clkrate>
1212
36d95739 1213 i8042.debug [HW] Toggle i8042 debug mode
1da177e4 1214 i8042.direct [HW] Put keyboard port into non-translated mode
84eb8d06
ML
1215 i8042.dumbkbd [HW] Pretend that controller can only read data from
1216 keyboard and cannot control its state
1da177e4
LT
1217 (Don't attempt to blink the leds)
1218 i8042.noaux [HW] Don't check for auxiliary (== mouse) port
945ef0d4 1219 i8042.nokbd [HW] Don't check/create keyboard port
75d08c78
JK
1220 i8042.noloop [HW] Disable the AUX Loopback command while probing
1221 for the AUX port
1da177e4
LT
1222 i8042.nomux [HW] Don't check presence of an active multiplexing
1223 controller
1224 i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX
1225 controllers
24775d65 1226 i8042.notimeout [HW] Ignore timeout condition signalled by controller
1da177e4
LT
1227 i8042.reset [HW] Reset the controller during init and cleanup
1228 i8042.unlock [HW] Unlock (ignore) the keylock
1229
1230 i810= [HW,DRM]
1231
e70c9d5e
DT
1232 i8k.ignore_dmi [HW] Continue probing hardware even if DMI data
1233 indicates that the driver is running on unsupported
1234 hardware.
1da177e4
LT
1235 i8k.force [HW] Activate i8k driver even if SMM BIOS signature
1236 does not match list of supported models.
1237 i8k.power_status
1238 [HW] Report power status in /proc/i8k
1239 (disabled by default)
1240 i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN
1241 capability is set.
1242
4dca20ef 1243 i915.invert_brightness=
7bd90909
CE
1244 [DRM] Invert the sense of the variable that is used to
1245 set the brightness of the panel backlight. Normally a
4dca20ef
CE
1246 brightness value of 0 indicates backlight switched off,
1247 and the maximum of the brightness value sets the backlight
1248 to maximum brightness. If this parameter is set to 0
1249 (default) and the machine requires it, or this parameter
1250 is set to 1, a brightness value of 0 sets the backlight
1251 to maximum brightness, and the maximum of the brightness
1252 value switches the backlight off.
1253 -1 -- never invert brightness
1254 0 -- machine default
1255 1 -- force brightness inversion
7bd90909 1256
1da177e4
LT
1257 icn= [HW,ISDN]
1258 Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
1259
0af80c04
DF
1260 ide-core.nodma= [HW] (E)IDE subsystem
1261 Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc
075affcb
BZ
1262 .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr
1263 .cdrom .chs .ignore_cable are additional options
1c10e938 1264 See Documentation/ide/ide.txt.
1da177e4 1265
0cb55ad2
RD
1266 ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem
1267 Claim all unknown PCI IDE storage controllers.
1268
f039b754 1269 idle= [X86]
69fb3676 1270 Format: idle=poll, idle=halt, idle=nomwait
ada9cfdd
RD
1271 Poll forces a polling idle loop that can slightly
1272 improve the performance of waking up a idle CPU, but
1273 will use a lot of power and make the system run hot.
1274 Not recommended.
ada9cfdd 1275 idle=halt: Halt is forced to be used for CPU idle.
c1e3b377 1276 In such case C2/C3 won't be used again.
ada9cfdd 1277 idle=nomwait: Disable mwait for CPU C-states
a9913044 1278
79290822
IM
1279 ignore_loglevel [KNL]
1280 Ignore loglevel setting - this will print /all/
1281 kernel messages to the console. Useful for debugging.
0eca6b7c
YZ
1282 We also add it as printk module parameter, so users
1283 could change it dynamically, usually by
1284 /sys/module/printk/parameters/ignore_loglevel.
79290822 1285
1da177e4
LT
1286 ihash_entries= [KNL]
1287 Set number of hash buckets for inode cache.
1288
2fe5d6de
MZ
1289 ima_appraise= [IMA] appraise integrity measurements
1290 Format: { "off" | "enforce" | "fix" }
1291 default: "enforce"
1292
07f6a794
MZ
1293 ima_appraise_tcb [IMA]
1294 The builtin appraise policy appraises all files
1295 owned by uid=0.
1296
3323eec9 1297 ima_hash= [IMA]
e7a2ad7e
MZ
1298 Format: { md5 | sha1 | rmd160 | sha256 | sha384
1299 | sha512 | ... }
3323eec9
MZ
1300 default: "sha1"
1301
e7a2ad7e
MZ
1302 The list of supported hash algorithms is defined
1303 in crypto/hash_info.h.
1304
5789ba3b
EP
1305 ima_tcb [IMA]
1306 Load a policy which meets the needs of the Trusted
1307 Computing Base. This means IMA will measure all
1308 programs exec'd, files mmap'd for exec, and all files
1309 opened for read by uid=0.
1310
9b9d4ce5
RS
1311 ima_template= [IMA]
1312 Select one of defined IMA measurements template formats.
1313 Formats: { "ima" | "ima-ng" }
1314 Default: "ima-ng"
1315
3bcced39
DK
1316 ima.ahash_minsize= [IMA] Minimum file size for asynchronous hash usage
1317 Format: <min_file_size>
1318 Set the minimal file size for using asynchronous hash.
1319 If left unspecified, ahash usage is disabled.
1320
1321 ahash performance varies for different data sizes on
1322 different crypto accelerators. This option can be used
1323 to achieve the best performance for a particular HW.
1324
6edf7a89
DK
1325 ima.ahash_bufsize= [IMA] Asynchronous hash buffer size
1326 Format: <bufsize>
1327 Set hashing buffer size. Default: 4k.
1328
1329 ahash performance varies for different chunk sizes on
1330 different crypto accelerators. This option can be used
1331 to achieve best performance for particular HW.
1332
1da177e4
LT
1333 init= [KNL]
1334 Format: <full_path>
1335 Run specified binary instead of /sbin/init as init
1336 process.
1337
1338 initcall_debug [KNL] Trace initcalls as they are executed. Useful
1339 for working out where the kernel is dying during
1340 startup.
1341
7b0b73d7
PB
1342 initcall_blacklist= [KNL] Do not execute a comma-separated list of
1343 initcall functions. Useful for debugging built-in
1344 modules and initcalls.
1345
1da177e4
LT
1346 initrd= [BOOT] Specify the location of the initial ramdisk
1347
1348 inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver
1349 Format: <irq>
1350
6bb2ff84
FY
1351 int_pln_enable [x86] Enable power limit notification interrupt
1352
d726d8d7
MZ
1353 integrity_audit=[IMA]
1354 Format: { "0" | "1" }
1355 0 -- basic integrity auditing messages. (Default)
1356 1 -- additional integrity auditing messages.
1357
ba395927 1358 intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option
0cd5c3c8
KM
1359 on
1360 Enable intel iommu driver.
ba395927
KA
1361 off
1362 Disable intel iommu driver.
1363 igfx_off [Default Off]
1364 By default, gfx is mapped as normal device. If a gfx
1365 device has a dedicated DMAR unit, the DMAR unit is
1366 bypassed by not enabling DMAR with this option. In
1367 this case, gfx device will use physical address for
1368 DMA.
7d3b03ce
KA
1369 forcedac [x86_64]
1370 With this option iommu will not optimize to look
16290246 1371 for io virtual address below 32-bit forcing dual
7d3b03ce 1372 address cycle on pci bus for cards supporting greater
16290246
RD
1373 than 32-bit addressing. The default is to look
1374 for translation below 32-bit and if not available
7d3b03ce 1375 then look in the higher range.
5e0d2a6f 1376 strict [Default Off]
1377 With this option on every unmap_single operation will
1378 result in a hardware IOTLB flush operation as opposed
1379 to batching them for performance.
6dd9a7c7
YS
1380 sp_off [Default Off]
1381 By default, super page will be supported if Intel IOMMU
1382 has the capability. With this option, super page will
1383 not be supported.
2e92c7ad
MI
1384
1385 intel_idle.max_cstate= [KNL,HW,ACPI,X86]
1386 0 disables intel_idle and fall back on acpi_idle.
1387 1 to 6 specify maximum depth of C-state.
1388
6be26498
DB
1389 intel_pstate= [X86]
1390 disable
1391 Do not enable intel_pstate as the default
1392 scaling driver for the supported processors
1393
d1423d56 1394 intremap= [X86-64, Intel-IOMMU]
d1423d56
CW
1395 on enable Interrupt Remapping (default)
1396 off disable Interrupt Remapping
1397 nosid disable Source ID checking
41750d31
SS
1398 no_x2apic_optout
1399 BIOS x2APIC opt-out request will be ignored
d1423d56 1400
0cb55ad2
RD
1401 iomem= Disable strict checking of access to MMIO memory
1402 strict regions from userspace.
1403 relaxed
1404
1405 iommu= [x86]
1406 off
1407 force
1408 noforce
1409 biomerge
1410 panic
1411 nopanic
1412 merge
1413 nomerge
1414 forcesac
1415 soft
bcb71abe 1416 pt [x86, IA-64]
bcb71abe 1417
0cb55ad2
RD
1418
1419 io7= [HW] IO7 for Marvel based alpha systems
1420 See comment before marvel_specify_io7 in
1421 arch/alpha/kernel/core_marvel.c.
1422
6cececfc 1423 io_delay= [X86] I/O delay method
6e7c4025
IM
1424 0x80
1425 Standard port 0x80 based delay
1426 0xed
1427 Alternate port 0xed based delay (needed on some systems)
b02aae9c 1428 udelay
6e7c4025
IM
1429 Simple two microseconds delay
1430 none
1431 No delay
b02aae9c 1432
1da177e4 1433 ip= [IP_PNP]
dc7a0816 1434 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
1435
1436 ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards
c8facbb6
RD
1437 See comment before ip2_setup() in
1438 drivers/char/ip2/ip2base.c.
1da177e4 1439
200803df
AC
1440 irqfixup [HW]
1441 When an interrupt is not handled search all handlers
1442 for it. Intended to get systems with badly broken
1443 firmware running.
1444
1445 irqpoll [HW]
1446 When an interrupt is not handled search all handlers
1447 for it. Also check all handlers each timer
1448 interrupt. Intended to get systems with badly broken
1449 firmware running.
1450
1da177e4 1451 isapnp= [ISAPNP]
a9913044 1452 Format: <RDP>,<reset>,<pci_scan>,<verbosity>
1da177e4
LT
1453
1454 isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler.
22f2e280
DF
1455 Format:
1456 <cpu number>,...,<cpu number>
1457 or
b225d44e
LZ
1458 <cpu number>-<cpu number>
1459 (must be a positive range in ascending order)
22f2e280
DF
1460 or a mixture
1461 <cpu number>,...,<cpu number>-<cpu number>
b225d44e 1462
1da177e4
LT
1463 This option can be used to specify one or more CPUs
1464 to isolate from the general SMP balancing and scheduling
b225d44e
LZ
1465 algorithms. You can move a process onto or off an
1466 "isolated" CPU via the CPU affinity syscalls or cpuset.
1da177e4
LT
1467 <cpu number> begins at 0 and the maximum value is
1468 "number of CPUs in system - 1".
1469
1470 This option is the preferred way to isolate CPUs. The
a9913044
RD
1471 alternative -- manually setting the CPU mask of all
1472 tasks in the system -- can cause problems and
1473 suboptimal load balancer performance.
1da177e4 1474
a9913044 1475 iucv= [HW,NET]
1da177e4 1476
7d8bfa26
JR
1477 ivrs_ioapic [HW,X86_64]
1478 Provide an override to the IOAPIC-ID<->DEVICE-ID
1479 mapping provided in the IVRS ACPI table. For
1480 example, to map IOAPIC-ID decimal 10 to
1481 PCI device 00:14.0 write the parameter as:
1482 ivrs_ioapic[10]=00:14.0
1483
1484 ivrs_hpet [HW,X86_64]
1485 Provide an override to the HPET-ID<->DEVICE-ID
1486 mapping provided in the IVRS ACPI table. For
1487 example, to map HPET-ID decimal 0 to
1488 PCI device 00:14.0 write the parameter as:
1489 ivrs_hpet[0]=00:14.0
1490
1da177e4
LT
1491 js= [HW,JOY] Analog joystick
1492 See Documentation/input/joystick.txt.
1493
24f2e027
KC
1494 kaslr/nokaslr [X86]
1495 Enable/disable kernel and module base offset ASLR
1496 (Address Space Layout Randomization) if built into
1497 the kernel. When CONFIG_HIBERNATION is selected,
1498 kASLR is disabled by default. When kASLR is enabled,
1499 hibernation will be disabled.
1500
0cb55ad2
RD
1501 keepinitrd [HW,ARM]
1502
6cececfc 1503 kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
ed7ed365
MG
1504 specifies the amount of memory usable by the kernel
1505 for non-movable allocations. The requested amount is
1506 spread evenly throughout all nodes in the system. The
1507 remaining memory in each node is used for Movable
1508 pages. In the event, a node is too small to have both
1509 kernelcore and Movable pages, kernelcore pages will
1510 take priority and other nodes will have a larger number
675217fd 1511 of Movable pages. The Movable zone is used for the
ed7ed365
MG
1512 allocation of pages that may be reclaimed or moved
1513 by the page migration subsystem. This means that
1514 HugeTLB pages may not be allocated from this zone.
1515 Note that allocations like PTEs-from-HighMem still
1516 use the HighMem zone if it exists, and the Normal
1517 zone if it does not.
1518
4fe1da4e
JW
1519 kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
1520 Format: <Controller#>[,poll interval]
1521 The controller # is the number of the ehci usb debug
1522 port as it is probed via PCI. The poll interval is
1523 optional and is the number seconds in between
1524 each poll cycle to the debug port in case you need
1525 the functionality for interrupting the kernel with
1526 gdb or control-c on the dbgp connection. When
1527 not using this parameter you use sysrq-g to break into
1528 the kernel debugger.
1529
84c08fd6 1530 kgdboc= [KGDB,HW] kgdb over consoles.
ada64e4c
JW
1531 Requires a tty driver that supports console polling,
1532 or a supported polling keyboard driver (non-usb).
65b5ac14
JW
1533 Serial only format: <serial_device>[,baud]
1534 keyboard only format: kbd
1535 keyboard and serial format: kbd,<serial_device>[,baud]
1536 Optional Kernel mode setting:
1537 kms, kbd format: kms,kbd
1538 kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
6cdf6e06 1539
84c08fd6
JW
1540 kgdbwait [KGDB] Stop kernel execution and enter the
1541 kernel debugger at the earliest opportunity.
1542
9bed90c6
FF
1543 kmac= [MIPS] korina ethernet MAC address.
1544 Configure the RouterBoard 532 series on-chip
1545 Ethernet adapter MAC address.
1546
04f70336
CM
1547 kmemleak= [KNL] Boot-time kmemleak enable/disable
1548 Valid arguments: on, off
1549 Default: on
1550
c3ac14b2
XQ
1551 kmemcheck= [X86] Boot-time kmemcheck enable/disable/one-shot mode
1552 Valid arguments: 0, 1, 2
1553 kmemcheck=0 (disabled)
1554 kmemcheck=1 (enabled)
1555 kmemcheck=2 (one-shot mode)
1556 Default: 2 (one-shot mode)
1557
6cececfc 1558 kstack=N [X86] Print N words from the kernel stack
0cb55ad2
RD
1559 in oops dumps.
1560
fef07aae
AP
1561 kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs.
1562 Default is 0 (don't ignore, but inject #GP)
1563
a182d873
XG
1564 kvm.mmu_audit= [KVM] This is a R/W parameter which allows audit
1565 KVM MMU at runtime.
fef07aae
AP
1566 Default is 0 (off)
1567
fef07aae 1568 kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM.
8475f94a 1569 Default is 1 (enabled)
fef07aae
AP
1570
1571 kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU)
1572 for all guests.
16290246 1573 Default is 1 (enabled) if in 64-bit or 32-bit PAE mode.
fef07aae 1574
fef07aae
AP
1575 kvm-intel.ept= [KVM,Intel] Disable extended page tables
1576 (virtualized MMU) support on capable Intel chips.
1577 Default is 1 (enabled)
1578
1579 kvm-intel.emulate_invalid_guest_state=
1580 [KVM,Intel] Enable emulation of invalid guest states
1581 Default is 0 (disabled)
1582
1583 kvm-intel.flexpriority=
1584 [KVM,Intel] Disable FlexPriority feature (TPR shadow).
1585 Default is 1 (enabled)
1586
e1a72ae2
SL
1587 kvm-intel.nested=
1588 [KVM,Intel] Enable VMX nesting (nVMX).
1589 Default is 0 (disabled)
1590
fef07aae
AP
1591 kvm-intel.unrestricted_guest=
1592 [KVM,Intel] Disable unrestricted guest feature
1593 (virtualized real and unpaged mode) on capable
1594 Intel chips. Default is 1 (enabled)
1595
1596 kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification
1597 feature (tagged TLBs) on capable Intel chips.
1598 Default is 1 (enabled)
1599
1da177e4
LT
1600 l2cr= [PPC]
1601
a78bfbfc
RB
1602 l3cr= [PPC]
1603
cd4f0ef7 1604 lapic [X86-32,APIC] Enable the local APIC even if BIOS
a9913044 1605 disabled it.
1da177e4 1606
279f1461
SS
1607 lapic= [x86,APIC] "notscdeadline" Do not use TSC deadline
1608 value for LAPIC timer one-shot implementation. Default
1609 back to the programmable timer unit in the LAPIC.
1610
6cececfc 1611 lapic_timer_c2_ok [X86,APIC] trust the local apic timer
ada9cfdd 1612 in C2 power state.
e585bef8 1613
fcb71f6f
FC
1614 libata.dma= [LIBATA] DMA control
1615 libata.dma=0 Disable all PATA and SATA DMA
1616 libata.dma=1 PATA and SATA Disk DMA only
1617 libata.dma=2 ATAPI (CDROM) DMA only
16290246 1618 libata.dma=4 Compact Flash DMA only
fcb71f6f
FC
1619 Combinations also work, so libata.dma=3 enables DMA
1620 for disks and CDROMs, but not CFs.
16290246 1621
20308871
MP
1622 libata.ignore_hpa= [LIBATA] Ignore HPA limit
1623 libata.ignore_hpa=0 keep BIOS limits (default)
1624 libata.ignore_hpa=1 ignore limits, using full disk
fcb71f6f 1625
78e70c23
DJ
1626 libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume
1627 when set.
1628 Format: <int>
1629
33267325
TH
1630 libata.force= [LIBATA] Force configurations. The format is comma
1631 separated list of "[ID:]VAL" where ID is
4c44f309 1632 PORT[.DEVICE]. PORT and DEVICE are decimal numbers
33267325
TH
1633 matching port, link or device. Basically, it matches
1634 the ATA ID string printed on console by libata. If
1635 the whole ID part is omitted, the last PORT and DEVICE
1636 values are used. If ID hasn't been specified yet, the
1637 configuration applies to all ports, links and devices.
1638
1639 If only DEVICE is omitted, the parameter applies to
1640 the port and all links and devices behind it. DEVICE
1641 number of 0 either selects the first device or the
1642 first fan-out link behind PMP device. It does not
1643 select the host link. DEVICE number of 15 selects the
1644 host link and device attached to it.
1645
1646 The VAL specifies the configuration to force. As long
1647 as there's no ambiguity shortcut notation is allowed.
1648 For example, both 1.5 and 1.5G would work for 1.5Gbps.
1649 The following configurations can be forced.
1650
1651 * Cable type: 40c, 80c, short40c, unk, ign or sata.
1652 Any ID with matching PORT is used.
1653
1654 * SATA link speed limit: 1.5Gbps or 3.0Gbps.
1655
1656 * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7].
1657 udma[/][16,25,33,44,66,100,133] notation is also
1658 allowed.
1659
1660 * [no]ncq: Turn on or off NCQ.
1661
05944bdf
TH
1662 * nohrst, nosrst, norst: suppress hard, soft
1663 and both resets.
1664
ca6d43b0
DW
1665 * rstonce: only attempt one reset during
1666 hot-unplug link recovery
1667
43c9c591
TH
1668 * dump_id: dump IDENTIFY data.
1669
966fbe19
VP
1670 * atapi_dmadir: Enable ATAPI DMADIR bridge support
1671
b8bd6dc3
RJ
1672 * disable: Disable this device.
1673
33267325
TH
1674 If there are multiple matching configurations changing
1675 the same attribute, the last one is used.
1676
95f72d1e 1677 memblock=debug [KNL] Enable memblock debug messages.
7c4be253 1678
1da177e4 1679 load_ramdisk= [RAM] List of ramdisks to load from floppy
31c00fc1 1680 See Documentation/blockdev/ramdisk.txt.
1da177e4 1681
a6b25b67
RD
1682 lockd.nlm_grace_period=P [NFS] Assign grace period.
1683 Format: <integer>
1da177e4 1684
a6b25b67
RD
1685 lockd.nlm_tcpport=N [NFS] Assign TCP port.
1686 Format: <integer>
1687
1688 lockd.nlm_timeout=T [NFS] Assign timeout value.
1689 Format: <integer>
1690
1691 lockd.nlm_udpport=M [NFS] Assign UDP port.
1692 Format: <integer>
1da177e4
LT
1693
1694 logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
1695 Format: <irq>
1696
1697 loglevel= All Kernel Messages with a loglevel smaller than the
1698 console loglevel will be printed to the console. It can
1699 also be changed with klogd or other programs. The
1700 loglevels are defined as follows:
1701
1702 0 (KERN_EMERG) system is unusable
1703 1 (KERN_ALERT) action must be taken immediately
1704 2 (KERN_CRIT) critical conditions
1705 3 (KERN_ERR) error conditions
1706 4 (KERN_WARNING) warning conditions
1707 5 (KERN_NOTICE) normal but significant condition
1708 6 (KERN_INFO) informational
1709 7 (KERN_DEBUG) debug-level messages
1710
c756d08a
RD
1711 log_buf_len=n[KMG] Sets the size of the printk ring buffer,
1712 in bytes. n must be a power of two. The default
1713 size is set in the kernel config file.
1da177e4 1714
accaa24c
RD
1715 logo.nologo [FB] Disables display of the built-in Linux logo.
1716 This may be used to provide more screen space for
1717 kernel log messages and is useful when debugging
1718 kernel boot problems.
1719
1da177e4
LT
1720 lp=0 [LP] Specify parallel ports to use, e.g,
1721 lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses
1722 lp=reset first parallel port). 'lp=0' disables the
1723 lp=auto printer driver. 'lp=reset' (which can be
1724 specified in addition to the ports) causes
1725 attached printers to be reset. Using
1726 lp=port1,port2,... specifies the parallel ports
1727 to associate lp devices with, starting with
1728 lp0. A port specification may be 'none' to skip
1729 that lp device, or a parport name such as
1730 'parport0'. Specifying 'lp=auto' instead of a
1731 port specification list means that device IDs
1732 from each port should be examined, to see if
1733 an IEEE 1284-compliant printer is attached; if
1734 so, the driver will manage that printer.
1735 See also header of drivers/char/lp.c.
1736
1737 lpj=n [KNL]
1738 Sets loops_per_jiffy to given constant, thus avoiding
1739 time-consuming boot-time autodetection (up to 250 ms per
1740 CPU). 0 enables autodetection (default). To determine
1741 the correct value for your kernel, boot with normal
1742 autodetection and see what value is printed. Note that
1743 on SMP systems the preset will be applied to all CPUs,
1744 which is likely to cause problems if your CPUs need
1745 significantly divergent settings. An incorrect value
1746 will cause delays in the kernel to be wrong, leading to
1747 unpredictable I/O errors and other breakage. Although
1748 unlikely, in the extreme case this might damage your
1749 hardware.
1750
1751 ltpc= [NET]
1752 Format: <io>,<irq>,<dma>
1753
16290246 1754 machvec= [IA-64] Force the use of a particular machine-vector
a9913044
RD
1755 (machvec) in a generic kernel.
1756 Example: machvec=hpzx1_swiotlb
1da177e4 1757
3209e70e
WZ
1758 machtype= [Loongson] Share the same kernel image file between different
1759 yeeloong laptop.
1760 Example: machtype=lemote-yeeloong-2f-7inch
1761
0cb55ad2
RD
1762 max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater
1763 than or equal to this physical address is ignored.
1da177e4
LT
1764
1765 maxcpus= [SMP] Maximum number of processors that an SMP kernel
61ec7567
LB
1766 should make use of. maxcpus=n : n >= 0 limits the
1767 kernel to using 'n' processors. n=0 is a special case,
1768 it is equivalent to "nosmp", which also disables
1769 the IO APIC.
1da177e4 1770
d134b00b
KS
1771 max_loop= [LOOP] The number of loop block devices that get
1772 (loop.max_loop) unconditionally pre-created at init time. The default
1773 number is configured by BLK_DEV_LOOP_MIN_COUNT. Instead
1774 of statically allocating a predefined number, loop
1775 devices can be requested on-demand with the
1776 /dev/loop-control interface.
2b2c3750 1777
cd4f0ef7 1778 mce [X86-32] Machine Check Exception
1da177e4 1779
71cced6e 1780 mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt
909dd324 1781
1da177e4
LT
1782 md= [HW] RAID subsystems devices and level
1783 See Documentation/md.txt.
a9913044 1784
1da177e4
LT
1785 mdacon= [MDA]
1786 Format: <first>,<last>
1787 Specifies range of consoles to be captured by the MDA.
a9913044 1788
1da177e4
LT
1789 mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
1790 Amount of memory to be used when the kernel is not able
1791 to see the whole system memory or for test.
fbb97d87
WC
1792 [X86] Work as limiting max address. Use together
1793 with memmap= to avoid physical address space collisions.
1794 Without memmap= PCI devices could be placed at addresses
1795 belonging to unused RAM.
1da177e4 1796
cd4f0ef7 1797 mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
1da177e4
LT
1798 memory.
1799
6902aa84
PM
1800 memchunk=nn[KMG]
1801 [KNL,SH] Allow user to override the default size for
1802 per-device physically contiguous DMA buffers.
1803
6cececfc 1804 memmap=exactmap [KNL,X86] Enable setting of an exact
1da177e4
LT
1805 E820 memory map, as specified by the user.
1806 Such memmap=exactmap lines can be constructed based on
1807 BIOS output or other requirements. See the memmap=nn@ss
1808 option description.
1809
1810 memmap=nn[KMG]@ss[KMG]
277cba1d
RD
1811 [KNL] Force usage of a specific region of memory.
1812 Region of memory to be used is from ss to ss+nn.
1da177e4
LT
1813
1814 memmap=nn[KMG]#ss[KMG]
1815 [KNL,ACPI] Mark specific memory as ACPI data.
277cba1d 1816 Region of memory to be marked is from ss to ss+nn.
1da177e4
LT
1817
1818 memmap=nn[KMG]$ss[KMG]
1819 [KNL,ACPI] Mark specific memory as reserved.
277cba1d 1820 Region of memory to be reserved is from ss to ss+nn.
1312848e
PM
1821 Example: Exclude memory from 0x18690000-0x1869ffff
1822 memmap=64K$0x18690000
1823 or
1824 memmap=0x10000$0x18690000
1da177e4 1825
9f077871
JF
1826 memory_corruption_check=0/1 [X86]
1827 Some BIOSes seem to corrupt the first 64k of
1828 memory when doing things like suspend/resume.
1829 Setting this option will scan the memory
1830 looking for corruption. Enabling this will
1831 both detect corruption and prevent the kernel
1832 from using the memory being corrupted.
1833 However, its intended as a diagnostic tool; if
1834 repeatable BIOS-originated corruption always
1835 affects the same memory, you can use memmap=
1836 to prevent the kernel from using that memory.
1837
1838 memory_corruption_check_size=size [X86]
1839 By default it checks for corruption in the low
1840 64k, making this memory unavailable for normal
1841 use. Use this parameter to scan for
1842 corruption in more or less memory.
1843
1844 memory_corruption_check_period=seconds [X86]
1845 By default it checks for corruption every 60
1846 seconds. Use this parameter to check at some
1847 other rate. 0 disables periodic checking.
1848
caadbdce 1849 memtest= [KNL,X86] Enable memtest
c64df707 1850 Format: <integer>
c64df707 1851 default : 0 <disable>
9e5f6cf5
AH
1852 Specifies the number of memtest passes to be
1853 performed. Each pass selects another test
1854 pattern from a given set of patterns. Memtest
1855 fills the memory with this pattern, validates
1856 memory contents and reserves bad memory
1857 regions that are detected.
c64df707 1858
1da177e4
LT
1859 meye.*= [HW] Set MotionEye Camera parameters
1860 See Documentation/video4linux/meye.txt.
1861
8f36881b
AS
1862 mfgpt_irq= [IA-32] Specify the IRQ to use for the
1863 Multi-Function General Purpose Timers on AMD Geode
1864 platforms.
1865
e6c4dc6c
WT
1866 mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when
1867 the BIOS has incorrectly applied a workaround. TinyBIOS
1868 version 0.98 is known to be affected, 0.99 fixes the
1869 problem by letting the user disable the workaround.
1870
1da177e4
LT
1871 mga= [HW,DRM]
1872
1c207f95
RD
1873 min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this
1874 physical address is ignored.
1875
39f45d7b
MP
1876 mini2440= [ARM,HW,KNL]
1877 Format:[0..2][b][c][t]
1878 Default: "0tb"
1879 MINI2440 configuration specification:
1880 0 - The attached screen is the 3.5" TFT
1881 1 - The attached screen is the 7" TFT
1882 2 - The VGA Shield is attached (1024x768)
1883 Leaving out the screen size parameter will not load
1884 the TFT driver, and the framebuffer will be left
1885 unconfigured.
1886 b - Enable backlight. The TFT backlight pin will be
1887 linked to the kernel VESA blanking code and a GPIO
1888 LED. This parameter is not necessary when using the
1889 VGA shield.
1890 c - Enable the s3c camera interface.
1891 t - Reserved for enabling touchscreen support. The
1892 touchscreen support is not enabled in the mainstream
1893 kernel as of 2.6.30, a preliminary port can be found
1894 in the "bleeding edge" mini2440 support kernel at
1895 http://repo.or.cz/w/linux-2.6/mini2440.git
1896
6b74ab97
MG
1897 mminit_loglevel=
1898 [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
1899 parameter allows control of the logging verbosity for
1900 the additional memory initialisation checks. A value
1901 of 0 disables mminit logging and a level of 4 will
1902 log everything. Information is printed at KERN_DEBUG
1903 so loglevel=8 may also need to be specified.
1904
106a4ee2
RR
1905 module.sig_enforce
1906 [KNL] When CONFIG_MODULE_SIG is set, this means that
1907 modules without (valid) signatures will fail to load.
2a039be7 1908 Note that if CONFIG_MODULE_SIG_FORCE is set, that
106a4ee2
RR
1909 is always true, so this option does nothing.
1910
1da177e4
LT
1911 mousedev.tap_time=
1912 [MOUSE] Maximum time between finger touching and
1913 leaving touchpad surface for touch to be considered
1914 a tap and be reported as a left button click (for
1915 touchpads working in absolute mode only).
1916 Format: <msecs>
1917 mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices
1918 reporting absolute coordinates, such as tablets
1919 mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
1920 reporting absolute coordinates, such as tablets
1921
6cececfc 1922 movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter
0cb55ad2
RD
1923 is similar to kernelcore except it specifies the
1924 amount of memory used for migratable allocations.
1925 If both kernelcore and movablecore is specified,
1926 then kernelcore will be at *least* the specified
1927 value but may be more. If movablecore on its own
1928 is specified, the administrator must be careful
1929 that the amount of memory usable for all allocations
1930 is not too small.
1931
c5320926
TC
1932 movable_node [KNL,X86] Boot-time switch to enable the effects
1933 of CONFIG_MOVABLE_NODE=y. See mm/Kconfig for details.
1934
1da177e4
LT
1935 MTD_Partition= [MTD]
1936 Format: <name>,<region-number>,<size>,<offset>
1937
a9913044
RD
1938 MTD_Region= [MTD] Format:
1939 <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>]
1da177e4
LT
1940
1941 mtdparts= [MTD]
c8facbb6 1942 See drivers/mtd/cmdlinepart.c.
1da177e4 1943
4e89a2d8
WS
1944 multitce=off [PPC] This parameter disables the use of the pSeries
1945 firmware feature for updating multiple TCE entries
1946 at a time.
1947
5988af23
RH
1948 onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration
1949
1950 Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock]
1951
1952 boundary - index of last SLC block on Flex-OneNAND.
1953 The remaining blocks are configured as MLC blocks.
1954 lock - Configure if Flex-OneNAND boundary should be locked.
1955 Once locked, the boundary cannot be changed.
1956 1 indicates lock status, 0 indicates unlock status.
1957
9db829f4
BD
1958 mtdset= [ARM]
1959 ARM/S3C2412 JIVE boot control
1960
1961 See arch/arm/mach-s3c2412/mach-jive.c
1962
1da177e4 1963 mtouchusb.raw_coordinates=
a9913044
RD
1964 [HW] Make the MicroTouch USB driver use raw coordinates
1965 ('y', default) or cooked coordinates ('n')
1da177e4 1966
0cb55ad2 1967 mtrr_chunk_size=nn[KMG] [X86]
19f59460 1968 used for mtrr cleanup. It is largest continuous chunk
0cb55ad2
RD
1969 that could hold holes aka. UC entries.
1970
1971 mtrr_gran_size=nn[KMG] [X86]
1972 Used for mtrr cleanup. It is granularity of mtrr block.
1973 Default is 1.
1974 Large value could prevent small alignment from
1975 using up MTRRs.
1976
1977 mtrr_spare_reg_nr=n [X86]
1978 Format: <integer>
1979 Range: 0,7 : spare reg number
1980 Default : 1
1981 Used for mtrr cleanup. It is spare mtrr entries number.
1982 Set to 2 or more if your graphical card needs more.
1983
1da177e4
LT
1984 n2= [NET] SDL Inc. RISCom/N2 synchronous serial card
1985
1da177e4
LT
1986 netdev= [NET] Network devices parameters
1987 Format: <irq>,<io>,<mem_start>,<mem_end>,<name>
1988 Note that mem_start is often overloaded to mean
1989 something different and driver-specific.
a9913044
RD
1990 This usage is only documented in each driver source
1991 file if at all.
1992
58401572
KPO
1993 nf_conntrack.acct=
1994 [NETFILTER] Enable connection tracking flow accounting
1995 0 to disable accounting
1996 1 to enable accounting
d70a011d 1997 Default value is 0.
58401572 1998
306a0753 1999 nfsaddrs= [NFS] Deprecated. Use ip= instead.
dc7a0816 2000 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4
LT
2001
2002 nfsroot= [NFS] nfs root filesystem for disk-less boxes.
dc7a0816 2003 See Documentation/filesystems/nfs/nfsroot.txt.
1da177e4 2004
306a0753
CL
2005 nfsrootdebug [NFS] enable nfsroot debugging messages.
2006 See Documentation/filesystems/nfs/nfsroot.txt.
2007
a72b4422
TM
2008 nfs.callback_tcpport=
2009 [NFS] set the TCP port on which the NFSv4 callback
2010 channel should listen.
2011
e571cbf1
TM
2012 nfs.cache_getent=
2013 [NFS] sets the pathname to the program which is used
2014 to update the NFS client cache entries.
2015
2016 nfs.cache_getent_timeout=
2017 [NFS] sets the timeout after which an attempt to
2018 update a cache entry is deemed to have failed.
2019
58df095b
TM
2020 nfs.idmap_cache_timeout=
2021 [NFS] set the maximum lifetime for idmapper cache
2022 entries.
2023
f43bf0be
TM
2024 nfs.enable_ino64=
2025 [NFS] enable 64-bit inode numbers.
2026 If zero, the NFS client will fake up a 32-bit inode
2027 number for the readdir() and stat() syscalls instead
2028 of returning the full 64-bit number.
2029 The default is to return 64-bit inode numbers.
2030
ef159e91
TM
2031 nfs.max_session_slots=
2032 [NFSv4.1] Sets the maximum number of session slots
2033 the client will attempt to negotiate with the server.
2034 This limits the number of simultaneous RPC requests
2035 that the client can send to the NFSv4.1 server.
2036 Note that there is little point in setting this
2037 value higher than the max_tcp_slot_table_limit.
2038
b064eca2 2039 nfs.nfs4_disable_idmapping=
074b1d12
TM
2040 [NFSv4] When set to the default of '1', this option
2041 ensures that both the RPC level authentication
2042 scheme and the NFS level operations agree to use
2043 numeric uids/gids if the mount is using the
2044 'sec=sys' security flavour. In effect it is
2045 disabling idmapping, which can make migration from
2046 legacy NFSv2/v3 systems to NFSv4 easier.
2047 Servers that do not support this mode of operation
2048 will be autodetected by the client, and it will fall
2049 back to using the idmapper.
2050 To turn off this behaviour, set the value to '0'.
6f2ea7f2
CL
2051 nfs.nfs4_unique_id=
2052 [NFS4] Specify an additional fixed unique ident-
2053 ification string that NFSv4 clients can insert into
2054 their nfs_client_id4 string. This is typically a
2055 UUID that is generated at system install time.
b064eca2 2056
db8ac8ba
WAA
2057 nfs.send_implementation_id =
2058 [NFSv4.1] Send client implementation identification
2059 information in exchange_id requests.
2060 If zero, no implementation identification information
2061 will be sent.
2062 The default is to send the implementation identification
2063 information.
f6de7a39
TM
2064
2065 nfs.recover_lost_locks =
2066 [NFSv4] Attempt to recover locks that were lost due
2067 to a lease timeout on the server. Please note that
2068 doing this risks data corruption, since there are
2069 no guarantees that the file will remain unchanged
2070 after the locks are lost.
2071 If you want to enable the kernel legacy behaviour of
2072 attempting to recover these locks, then set this
2073 parameter to '1'.
2074 The default parameter value of '0' causes the kernel
2075 not to attempt recovery of lost locks.
db8ac8ba 2076
e9541ce8
BF
2077 nfsd.nfs4_disable_idmapping=
2078 [NFSv4] When set to the default of '1', the NFSv4
2079 server will return only numeric uids and gids to
2080 clients using auth_sys, and will accept numeric uids
2081 and gids from such clients. This is intended to ease
2082 migration from NFSv2/v3.
db8ac8ba 2083
18d98f6c
SB
2084 objlayoutdriver.osd_login_prog=
2085 [NFS] [OBJLAYOUT] sets the pathname to the program which
2086 is used to automatically discover and login into new
2087 osd-targets. Please see:
2088 Documentation/filesystems/pnfs.txt for more explanations
2089
1e1030dc 2090 nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take
e7ba176b
HS
2091 when a NMI is triggered.
2092 Format: [state][,regs][,debounce][,die]
2093
6cececfc 2094 nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels
fef2c9bc 2095 Format: [panic,][nopanic,][num]
5dc30558 2096 Valid num: 0
5b9a0e14 2097 0 - turn nmi_watchdog off
0cb55ad2 2098 When panic is specified, panic when an NMI watchdog
fef2c9bc
DZ
2099 timeout occurs (or 'nopanic' to override the opposite
2100 default).
0cb55ad2
RD
2101 This is useful when you use a panic=... timeout and
2102 need the box quickly up again.
1da177e4 2103
bff38771
AV
2104 netpoll.carrier_timeout=
2105 [NET] Specifies amount of time (in seconds) that
2106 netpoll should wait for a carrier. By default netpoll
2107 waits 4 seconds.
2108
cd4f0ef7 2109 no387 [BUGS=X86-32] Tells the kernel to use the 387 maths
1da177e4
LT
2110 emulation library even if a 387 maths coprocessor
2111 is present.
2112
0cb55ad2
RD
2113 no_console_suspend
2114 [HW] Never suspend the console
2115 Disable suspending of consoles during suspend and
2116 hibernate operations. Once disabled, debugging
2117 messages can reach various consoles while the rest
2118 of the system is being put to sleep (ie, while
2119 debugging driver suspend/resume hooks). This may
2120 not work reliably with all consoles, but is known
2121 to work with serial and VGA consoles.
134620f7
YZ
2122 To facilitate more flexible debugging, we also add
2123 console_suspend, a printk module parameter to control
2124 it. Users could use console_suspend (usually
2125 /sys/module/printk/parameters/console_suspend) to
2126 turn on/off it dynamically.
0cb55ad2 2127
c1aee215
CL
2128 noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
2129 caches in the slab allocator. Saves per-node memory,
2130 but will impact performance.
3395ee05 2131
a9913044
RD
2132 noalign [KNL,ARM]
2133
1da177e4
LT
2134 noapic [SMP,APIC] Tells the kernel to not make use of any
2135 IOAPICs that may be present in the system.
2136
5091faa4
MG
2137 noautogroup Disable scheduler automatic task group creation.
2138
1da177e4
LT
2139 nobats [PPC] Do not use BATs for mapping kernel lowmem
2140 on "Classic" PPC cores.
2141
2142 nocache [ARM]
a9913044 2143
0cb55ad2
RD
2144 noclflush [BUGS=X86] Don't use the CLFLUSH instruction
2145
163ecdff
SN
2146 nodelayacct [KNL] Disable per-task delay accounting
2147
1da177e4
LT
2148 nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects.
2149
6902aa84
PM
2150 nodsp [SH] Disable hardware DSP at boot time.
2151
6cececfc 2152 noefi [X86] Disable EFI runtime services support.
8b2cb7a8 2153
1da177e4
LT
2154 noexec [IA-64]
2155
6cececfc 2156 noexec [X86]
f5a1b191 2157 On X86-32 available only on PAE configured kernels.
1da177e4 2158 noexec=on: enable non-executable mappings (default)
f5a1b191
JS
2159 noexec=off: disable non-executable mappings
2160
52b6179a
PA
2161 nosmap [X86]
2162 Disable SMAP (Supervisor Mode Access Prevention)
2163 even if it is supported by processor.
2164
de5397ad 2165 nosmep [X86]
52b6179a 2166 Disable SMEP (Supervisor Mode Execution Prevention)
de5397ad
FY
2167 even if it is supported by processor.
2168
f5a1b191
JS
2169 noexec32 [X86-64]
2170 This affects only 32-bit executables.
2171 noexec32=on: enable non-executable mappings (default)
2172 read doesn't imply executable mappings
2173 noexec32=off: disable non-executable mappings
2174 read implies executable mappings
1da177e4 2175
6902aa84
PM
2176 nofpu [SH] Disable hardware FPU at boot time.
2177
cd4f0ef7 2178 nofxsr [BUGS=X86-32] Disables x86 floating point extended
4f886511
CE
2179 register save and restore. The kernel will only save
2180 legacy floating-point registers on task switch.
1da177e4 2181
0c752a93
SS
2182 noxsave [BUGS=X86] Disables x86 extended register state save
2183 and restore using xsave. The kernel will fallback to
2184 enabling legacy floating-point and sse state.
2185
5d2bd700 2186 eagerfpu= [X86]
e0022981 2187 on enable eager fpu restore
5d2bd700 2188 off disable eager fpu restore
e0022981
SS
2189 auto selects the default scheme, which automatically
2190 enables eagerfpu restore for xsaveopt.
5d2bd700 2191
01a24d2b
PZ
2192 nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or
2193 wfi(ARM) instruction doesn't work correctly and not to
2194 use it. This is also useful when using JTAG debugger.
a9913044 2195
1f29fae2
SH
2196 no_file_caps Tells the kernel not to honor file capabilities. The
2197 only way then for a file to be executed with privilege
2198 is to be setuid root or executed by root.
2199
1da177e4
LT
2200 nohalt [IA-64] Tells the kernel not to use the power saving
2201 function PAL_HALT_LIGHT when idle. This increases
2202 power-consumption. On the positive side, it reduces
2203 interrupt wake-up latency, which may improve performance
2204 in certain environments such as networked servers or
2205 real-time systems.
2206
a6e15a39
KC
2207 nohibernate [HIBERNATION] Disable hibernation and resume.
2208
79bf2bb3
TG
2209 nohz= [KNL] Boottime enable/disable dynamic ticks
2210 Valid arguments: on, off
2211 Default: on
2212
c5bfece2
FW
2213 nohz_full= [KNL,BOOT]
2214 In kernels built with CONFIG_NO_HZ_FULL=y, set
a831881b 2215 the specified list of CPUs whose tick will be stopped
0453b435
FW
2216 whenever possible. The boot CPU will be forced outside
2217 the range to maintain the timekeeping.
d1e43fa5
FW
2218 The CPUs in this range must also be included in the
2219 rcu_nocbs= set.
a831881b 2220
eeee7853
PM
2221 noiotrap [SH] Disables trapped I/O port accesses.
2222
cd4f0ef7 2223 noirqdebug [X86-32] Disables the code which attempts to detect and
1da177e4
LT
2224 disable unhandled interrupt sources.
2225
6cececfc 2226 no_timer_check [X86,APIC] Disables the code which tests for
8542b200
ZA
2227 broken timer IRQ sources.
2228
1da177e4
LT
2229 noisapnp [ISAPNP] Disables ISA PnP code.
2230
2231 noinitrd [RAM] Tells the kernel not to load any configured
2232 initial RAM disk.
2233
03ea8155
WH
2234 nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
2235 remapping.
d1423d56 2236 [Deprecated - use intremap=off]
03ea8155 2237
1da177e4
LT
2238 nointroute [IA-64]
2239
16290246 2240 nojitter [IA-64] Disables jitter checking for ITC timers.
0aa366f3 2241
9cf4c4fc
JK
2242 no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
2243
fd10cde9
GN
2244 no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
2245 fault handling.
2246
d910f5c1
GC
2247 no-steal-acc [X86,KVM] Disable paravirtualized steal time accounting.
2248 steal time is computed, but won't influence scheduler
2249 behaviour
2250
cd4f0ef7 2251 nolapic [X86-32,APIC] Do not enable or use the local APIC.
1da177e4 2252
cd4f0ef7 2253 nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
ad62ca2b 2254
1da177e4
LT
2255 noltlbs [PPC] Do not use large page/tlb entries for kernel
2256 lowmem mapping on PPC40x.
2257
312f1f01
H
2258 nomca [IA-64] Disable machine check abort handling
2259
cd4f0ef7 2260 nomce [X86-32] Machine Check Exception
abe37e5a 2261
83d7384f
AS
2262 nomfgpt [X86-32] Disable Multi-Function General Purpose
2263 Timer usage (for AMD Geode machines).
2264
bda62633
DZ
2265 nonmi_ipi [X86] Disable using NMI IPIs during panic/reboot to
2266 shutdown the other cpus. Instead use the REBOOT_VECTOR
2267 irq.
2268
02608bef
DY
2269 nomodule Disable module load
2270
016ddd9b
JK
2271 nopat [X86] Disable PAT (page attribute table extension of
2272 pagetables) support.
2273
0cb55ad2
RD
2274 norandmaps Don't use address space randomization. Equivalent to
2275 echo 0 > /proc/sys/kernel/randomize_va_space
2276
bbff2168 2277 noreplace-paravirt [X86,IA-64,PV_OPS] Don't patch paravirt_ops
959b4fdf 2278
cd4f0ef7 2279 noreplace-smp [X86-32,SMP] Don't replace SMP instructions
b7fb4af0
JF
2280 with UP alternatives
2281
7a5091d5
PA
2282 nordrand [X86] Disable kernel use of the RDRAND and
2283 RDSEED instructions even if they are supported
2284 by the processor. RDRAND and RDSEED are still
2285 available to user space applications.
49d859d7 2286
a9913044
RD
2287 noresume [SWSUSP] Disables resume and restores original swap
2288 space.
2289
1da177e4
LT
2290 no-scroll [VGA] Disables scrollback.
2291 This is required for the Braillex ib80-piezo Braille
2292 reader made by F.H. Papenmeier (Germany).
2293
2294 nosbagart [IA-64]
2295
cd4f0ef7 2296 nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support.
4f886511 2297
61ec7567
LB
2298 nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
2299 and disable the IO APIC. legacy for "maxcpus=0".
1da177e4 2300
97842216
DJ
2301 nosoftlockup [KNL] Disable the soft-lockup detector.
2302
1da177e4
LT
2303 nosync [HW,M68K] Disables sync negotiation for all devices.
2304
cd4f0ef7 2305 notsc [BUGS=X86-32] Disable Time Stamp Counter
1da177e4
LT
2306
2307 nousb [USB] Disable the USB subsystem
2308
55142374 2309 nowatchdog [KNL] Disable the lockup detector (NMI watchdog).
58687acb 2310
1da177e4 2311 nowb [ARM]
a9913044 2312
2b2fd87a
WH
2313 nox2apic [X86-64,APIC] Do not enable x2APIC mode.
2314
f78cff48
FY
2315 cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
2316 CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
2317 Some features depend on CPU0. Known dependencies are:
2318 1. Resume from suspend/hibernate depends on CPU0.
2319 Suspend/hibernate will fail if CPU0 is offline and you
2320 need to online CPU0 before suspend/hibernate.
2321 2. PIC interrupts also depend on CPU0. CPU0 can't be
2322 removed if a PIC interrupt is detected.
2323 It's said poweroff/reboot may depend on CPU0 on some
2324 machines although I haven't seen such issues so far
2325 after CPU0 is offline on a few tested machines.
2326 If the dependencies are under your control, you can
2327 turn on cpu0_hotplug.
2328
16290246 2329 nptcg= [IA-64] Override max number of concurrent global TLB
a6c75b86
FY
2330 purges which is reported from either PAL_VM_SUMMARY or
2331 SAL PALO.
2332
2b633e3f
YL
2333 nr_cpus= [SMP] Maximum number of processors that an SMP kernel
2334 could support. nr_cpus=n : n >= 1 limits the kernel to
2335 supporting 'n' processors. Later in runtime you can not
2336 use hotplug cpu feature to put more cpu back to online.
2337 just like you compile the kernel NR_CPUS=n
2338
0cb55ad2
RD
2339 nr_uarts= [SERIAL] maximum number of UARTs to be registered.
2340
1a687c2e
MG
2341 numa_balancing= [KNL,X86] Enable or disable automatic NUMA balancing.
2342 Allowed values are enable and disable
2343
f0c0b2b8
KH
2344 numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
2345 one of ['zone', 'node', 'default'] can be specified
2346 This can be set from sysctl after boot.
2347 See Documentation/sysctl/vm.txt for details.
2348
7c4be253
RD
2349 ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
2350 See Documentation/debugging-via-ohci1394.txt for more
2351 info.
2352
3ef0e1f8
AS
2353 olpc_ec_timeout= [OLPC] ms delay when issuing EC commands
2354 Rather than timing out after 20 ms if an EC
2355 command is not properly ACKed, override the length
2356 of the timeout. We have interrupts disabled while
2357 waiting for the ACK, so if this is set too high
2358 interrupts *may* be lost!
2359
15ac7afe
TL
2360 omap_mux= [OMAP] Override bootloader pin multiplexing.
2361 Format: <mux_mode0.mode_name=value>...
2362 For example, to override I2C bus2:
2363 omap_mux=i2c2_scl.i2c2_scl=0x100,i2c2_sda.i2c2_sda=0x100
2364
1da177e4
LT
2365 oprofile.timer= [HW]
2366 Use timer interrupt instead of performance counters
2367
7e4e0bd5
RR
2368 oprofile.cpu_type= Force an oprofile cpu type
2369 This might be useful if you have an older oprofile
2370 userland or if you want common events.
8d7ff4f2
RR
2371 Format: { arch_perfmon }
2372 arch_perfmon: [X86] Force use of architectural
7e4e0bd5
RR
2373 perfmon on Intel CPUs instead of the
2374 CPU specific event set.
159a80b2
RR
2375 timer: [X86] Force use of architectural NMI
2376 timer mode (see also oprofile.timer
2377 for generic hr timer mode)
dd3c4670
AK
2378 [s390] Force legacy basic mode sampling
2379 (report cpu_type "timer")
1dcdb5a9 2380
44a4dcf7
RD
2381 oops=panic Always panic on oopses. Default is to just kill the
2382 process, but there is a small probability of
2383 deadlocking the machine.
d404ab0a
OH
2384 This will also cause panics on machine check exceptions.
2385 Useful together with panic=30 to trigger a reboot.
2386
bcfde334
RD
2387 OSS [HW,OSS]
2388 See Documentation/sound/oss/oss-parameters.txt
2389
44a4dcf7 2390 panic= [KNL] Kernel behaviour on panic: delay <timeout>
4302fbc8
HD
2391 timeout > 0: seconds before rebooting
2392 timeout = 0: wait forever
2393 timeout < 0: reboot immediately
1da177e4
LT
2394 Format: <timeout>
2395
f06e5153
MH
2396 crash_kexec_post_notifiers
2397 Run kdump after running panic-notifiers and dumping
2398 kmsg. This only for the users who doubt kdump always
2399 succeeds in any situation.
2400 Note that this also increases risks of kdump failure,
2401 because some panic notifiers can make the crashed
2402 kernel more unstable.
2403
1da177e4
LT
2404 parkbd.port= [HW] Parallel port number the keyboard adapter is
2405 connected to, default is 0.
2406 Format: <parport#>
2407 parkbd.mode= [HW] Parallel port keyboard adapter mode of operation,
2408 0 for XT, 1 for AT (default is AT).
a9913044
RD
2409 Format: <mode>
2410
2411 parport= [HW,PPT] Specify parallel ports. 0 disables.
2412 Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] }
2413 Use 'auto' to force the driver to use any
2414 IRQ/DMA settings detected (the default is to
2415 ignore detected IRQ/DMA settings because of
2416 possible conflicts). You can specify the base
2417 address, IRQ, and DMA settings; IRQ and DMA
2418 should be numbers, or 'auto' (for using detected
2419 settings on that particular port), or 'nofifo'
2420 (to avoid using a FIFO even if it is detected).
2421 Parallel ports are assigned in the order they
2422 are specified on the command line, starting
2423 with parport0.
2424
2425 parport_init_mode= [HW,PPT]
2426 Configure VIA parallel port to operate in
2427 a specific mode. This is necessary on Pegasos
2428 computer where firmware has no options for setting
2429 up parallel port mode and sets it to spp.
2430 Currently this function knows 686a and 8231 chips.
1da177e4
LT
2431 Format: [spp|ps2|epp|ecp|ecpepp]
2432
dd287796
AM
2433 pause_on_oops=
2434 Halt all CPUs after the first oops has been printed for
2435 the specified number of seconds. This is to be used if
2436 your oopses keep scrolling off the screen.
2437
1da177e4
LT
2438 pcbit= [HW,ISDN]
2439
2440 pcd. [PARIDE]
2441 See header of drivers/block/paride/pcd.c.
31c00fc1 2442 See also Documentation/blockdev/paride.txt.
1da177e4 2443
a9913044 2444 pci=option[,option...] [PCI] various PCI subsystem options:
1cc0ca26
BH
2445 earlydump [X86] dump PCI config space before the kernel
2446 changes anything
c0115606 2447 off [X86] don't probe for the PCI bus
cd4f0ef7 2448 bios [X86-32] force use of PCI BIOS, don't access
a9913044
RD
2449 the hardware directly. Use this if your machine
2450 has a non-standard PCI host bridge.
cd4f0ef7 2451 nobios [X86-32] disallow use of PCI BIOS, only direct
a9913044
RD
2452 hardware access methods are allowed. Use this
2453 if you experience crashes upon bootup and you
2454 suspect they are caused by the BIOS.
c0115606 2455 conf1 [X86] Force use of PCI Configuration
a9913044 2456 Mechanism 1.
c0115606 2457 conf2 [X86] Force use of PCI Configuration
a9913044 2458 Mechanism 2.
7f785763
RD
2459 noaer [PCIE] If the PCIEAER kernel config parameter is
2460 enabled, this kernel boot option can be used to
2461 disable the use of PCIE advanced error reporting.
32a2eea7
JG
2462 nodomains [PCI] Disable support for multiple PCI
2463 root domains (aka PCI segments, in ACPI-speak).
6cececfc 2464 nommconf [X86] Disable use of MMCONFIG for PCI
61be6d66 2465 Configuration
12983077
AH
2466 check_enable_amd_mmconf [X86] check for and enable
2467 properly configured MMIO access to PCI
2468 config space on AMD family 10h CPU
309e57df
MW
2469 nomsi [MSI] If the PCI_MSI kernel config parameter is
2470 enabled, this kernel boot option can be used to
2471 disable the use of MSI interrupts system-wide.
a9322f64
SA
2472 noioapicquirk [APIC] Disable all boot interrupt quirks.
2473 Safety option to keep boot IRQs enabled. This
2474 should never be necessary.
9197979b
SA
2475 ioapicreroute [APIC] Enable rerouting of boot IRQs to the
2476 primary IO-APIC for bridges that cannot disable
2477 boot IRQs. This fixes a source of spurious IRQs
2478 when the system masks IRQs.
41b9eb26
SA
2479 noioapicreroute [APIC] Disable workaround that uses the
2480 boot IRQ equivalent of an IRQ that connects to
2481 a chipset where boot IRQs cannot be disabled.
2482 The opposite of ioapicreroute.
cd4f0ef7 2483 biosirq [X86-32] Use PCI BIOS calls to get the interrupt
a9913044
RD
2484 routing table. These calls are known to be buggy
2485 on several machines and they hang the machine
2486 when used, but on other computers it's the only
2487 way to get the interrupt routing table. Try
2488 this option if the kernel is unable to allocate
2489 IRQs or discover secondary PCI buses on your
2490 motherboard.
c0115606 2491 rom [X86] Assign address space to expansion ROMs.
a9913044
RD
2492 Use with caution as certain devices share
2493 address decoders between ROMs and other
2494 resources.
c0115606 2495 norom [X86] Do not assign address space to
bb71ad88
GH
2496 expansion ROMs that do not already have
2497 BIOS assigned address ranges.
7bd1c365
MH
2498 nobar [X86] Do not assign address space to the
2499 BARs that weren't assigned by the BIOS.
c0115606 2500 irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be
a9913044
RD
2501 assigned automatically to PCI devices. You can
2502 make the kernel exclude IRQs of your ISA cards
2503 this way.
c0115606 2504 pirqaddr=0xAAAAA [X86] Specify the physical address
a9913044
RD
2505 of the PIRQ table (normally generated
2506 by the BIOS) if it is outside the
2507 F0000h-100000h range.
c0115606 2508 lastbus=N [X86] Scan all buses thru bus #N. Can be
a9913044
RD
2509 useful if the kernel is unable to find your
2510 secondary buses and you want to tell it
2511 explicitly which ones they are.
c0115606 2512 assign-busses [X86] Always assign all PCI bus
a9913044
RD
2513 numbers ourselves, overriding
2514 whatever the firmware may have done.
c0115606 2515 usepirqmask [X86] Honor the possible IRQ mask stored
a9913044
RD
2516 in the BIOS $PIR table. This is needed on
2517 some systems with broken BIOSes, notably
2518 some HP Pavilion N5400 and Omnibook XE3
2519 notebooks. This will have no effect if ACPI
2520 IRQ routing is enabled.
c0115606 2521 noacpi [X86] Do not use ACPI for IRQ routing
a9913044 2522 or for PCI scanning.
7bc5e3f2
BH
2523 use_crs [X86] Use PCI host bridge window information
2524 from ACPI. On BIOSes from 2008 or later, this
2525 is enabled by default. If you need to use this,
2526 please report a bug.
2527 nocrs [X86] Ignore PCI host bridge windows from ACPI.
2528 If you need to use this, please report a bug.
a9913044
RD
2529 routeirq Do IRQ routing for all PCI devices.
2530 This is normally done in pci_enable_device(),
2531 so this option is a temporary workaround
2532 for broken drivers that don't call it.
13a6ddb0
YL
2533 skip_isa_align [X86] do not align io start addr, so can
2534 handle more pci cards
a9913044
RD
2535 firmware [ARM] Do not re-enumerate the bus but instead
2536 just use the configuration from the
2537 bootloader. This is currently used on
2538 IXP2000 systems where the bus has to be
2539 configured a certain way for adjunct CPUs.
0637a70a
AK
2540 noearly [X86] Don't do any early type 1 scanning.
2541 This might help on some broken boards which
2542 machine check when some devices' config space
2543 is read. But various workarounds are disabled
2544 and some IOMMU drivers will not work.
6b4b78fe
MD
2545 bfsort Sort PCI devices into breadth-first order.
2546 This sorting is done to get a device
2547 order compatible with older (<= 2.4) kernels.
2548 nobfsort Don't sort PCI devices into breadth-first order.
fa238712
YW
2549 pcie_bus_tune_off Disable PCIe MPS (Max Payload Size)
2550 tuning and use the BIOS-configured MPS defaults.
2551 pcie_bus_safe Set every device's MPS to the largest value
2552 supported by all devices below the root complex.
2553 pcie_bus_perf Set device MPS to the largest allowable MPS
2554 based on its parent bus. Also set MRRS (Max
2555 Read Request Size) to the largest supported
2556 value (no larger than the MPS that the device
2557 or bus can support) for best performance.
2558 pcie_bus_peer2peer Set every device's MPS to 128B, which
2559 every device is guaranteed to support. This
2560 configuration allows peer-to-peer DMA between
2561 any pair of devices, possibly at the cost of
2562 reduced performance. This also guarantees
2563 that hot-added devices will work.
4516a618
AN
2564 cbiosize=nn[KMG] The fixed amount of bus space which is
2565 reserved for the CardBus bridge's IO window.
2566 The default value is 256 bytes.
2567 cbmemsize=nn[KMG] The fixed amount of bus space which is
2568 reserved for the CardBus bridge's memory
2569 window. The default value is 64 megabytes.
32a9a682
YS
2570 resource_alignment=
2571 Format:
2572 [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...]
2573 Specifies alignment and device to reassign
2574 aligned memory resources.
2575 If <order of align> is not specified,
2576 PAGE_SIZE is used as alignment.
2577 PCI-PCI bridge can be specified, if resource
2578 windows need to be expanded.
43c16408
AP
2579 ecrc= Enable/disable PCIe ECRC (transaction layer
2580 end-to-end CRC checking).
2581 bios: Use BIOS/firmware settings. This is the
2582 the default.
2583 off: Turn ECRC off
2584 on: Turn ECRC on.
8c8803c5
YW
2585 hpiosize=nn[KMG] The fixed amount of bus space which is
2586 reserved for hotplug bridge's IO window.
2587 Default size is 256 bytes.
2588 hpmemsize=nn[KMG] The fixed amount of bus space which is
2589 reserved for hotplug bridge's memory window.
2590 Default size is 2 megabytes.
b55438fd
YL
2591 realloc= Enable/disable reallocating PCI bridge resources
2592 if allocations done by BIOS are too small to
2593 accommodate resources required by all child
2594 devices.
2595 off: Turn realloc off
2596 on: Turn realloc on
2597 realloc same as realloc=on
6748dcc2 2598 noari do not use PCIe ARI.
284f5f9d
BH
2599 pcie_scan_all Scan all possible PCIe devices. Otherwise we
2600 only look for one device below a PCIe downstream
2601 port.
6b4b78fe 2602
e5665a45
CE
2603 pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power
2604 Management.
2605 off Disable ASPM.
2606 force Enable ASPM even on devices that claim not to support it.
2607 WARNING: Forcing ASPM on may cause system lockups.
2608
7570a333
MT
2609 pcie_hp= [PCIE] PCI Express Hotplug driver options:
2610 nomsi Do not use MSI for PCI Express Native Hotplug (this
2611 makes all PCIe ports use INTx for hotplug services).
2612
79dd9182 2613 pcie_ports= [PCIE] PCIe ports handling:
28eb5f27
RW
2614 auto Ask the BIOS whether or not to use native PCIe services
2615 associated with PCIe ports (PME, hot-plug, AER). Use
2616 them only if that is allowed by the BIOS.
2617 native Use native PCIe services associated with PCIe ports
2618 unconditionally.
79dd9182
RW
2619 compat Treat PCIe ports as PCI-to-PCI bridges, disable the PCIe
2620 ports driver.
2621
c7f48656 2622 pcie_pme= [PCIE,PM] Native PCIe PME signaling options:
c39fae14 2623 nomsi Do not use MSI for native PCIe PME signaling (this makes
28eb5f27 2624 all PCIe root ports use INTx for all services).
c7f48656 2625
1da177e4
LT
2626 pcmv= [HW,PCMCIA] BadgePAD 4
2627
39ac5ba5
TB
2628 pd_ignore_unused
2629 [PM]
2630 Keep all power-domains already enabled by bootloader on,
2631 even if no driver has claimed them. This is useful
2632 for debug and development, but should not be
2633 needed on a platform with proper driver support.
2634
1da177e4 2635 pd. [PARIDE]
31c00fc1 2636 See Documentation/blockdev/paride.txt.
1da177e4
LT
2637
2638 pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at
2639 boot time.
2640 Format: { 0 | 1 }
2641 See arch/parisc/kernel/pdc_chassis.c
2642
f58dc01b 2643 percpu_alloc= Select which percpu first chunk allocator to use.
e933a73f
TH
2644 Currently supported values are "embed" and "page".
2645 Archs may support subset or none of the selections.
2646 See comments in mm/percpu.c for details on each
2647 allocator. This parameter is primarily for debugging
2648 and performance comparison.
fa8a7094 2649
1da177e4 2650 pf. [PARIDE]
31c00fc1 2651 See Documentation/blockdev/paride.txt.
1da177e4
LT
2652
2653 pg. [PARIDE]
31c00fc1 2654 See Documentation/blockdev/paride.txt.
1da177e4
LT
2655
2656 pirq= [SMP,APIC] Manual mp-table setup
71cced6e 2657 See Documentation/x86/i386/IO-APIC.txt.
1da177e4
LT
2658
2659 plip= [PPT,NET] Parallel port network link
2660 Format: { parport<nr> | timid | 0 }
2661 See also Documentation/parport.txt.
2662
16290246 2663 pmtmr= [X86] Manual setup of pmtmr I/O Port.
de32a243
TG
2664 Override pmtimer IOPort with a hex value.
2665 e.g. pmtmr=0x508
2666
96242116
BH
2667 pnp.debug=1 [PNP]
2668 Enable PNP debug messages (depends on the
2669 CONFIG_PNP_DEBUG_MESSAGES option). Change at run-time
2670 via /sys/module/pnp/parameters/debug. We always show
2671 current resource usage; turning this on also shows
2672 possible settings and some assignment information.
97ef062b 2673
1da177e4
LT
2674 pnpacpi= [ACPI]
2675 { off }
2676
2677 pnpbios= [ISAPNP]
2678 { on | off | curr | res | no-curr | no-res }
2679
2680 pnp_reserve_irq=
2681 [ISAPNP] Exclude IRQs for the autoconfiguration
2682
2683 pnp_reserve_dma=
2684 [ISAPNP] Exclude DMAs for the autoconfiguration
2685
2686 pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration
a9913044 2687 Ranges are in pairs (I/O port base and size).
1da177e4
LT
2688
2689 pnp_reserve_mem=
a9913044
RD
2690 [ISAPNP] Exclude memory regions for the
2691 autoconfiguration.
1da177e4
LT
2692 Ranges are in pairs (memory base and size).
2693
4af94f39
RD
2694 ports= [IP_VS_FTP] IPVS ftp helper module
2695 Default is 21.
2696 Up to 8 (IP_VS_APP_MAX_PORTS) ports
2697 may be specified.
2698 Format: <port>,<port>....
2699
45807a1d
IM
2700 print-fatal-signals=
2701 [KNL] debug: print fatal signals
f84d49b2
NO
2702
2703 If enabled, warn about various signal handling
2704 related application anomalies: too many signals,
2705 too many POSIX.1 timers, fatal signals causing a
2706 coredump - etc.
2707
2708 If you hit the warning due to signal overflow,
2709 you might want to try "ulimit -i unlimited".
2710
45807a1d
IM
2711 default: off.
2712
c22ab332
MG
2713 printk.always_kmsg_dump=
2714 Trigger kmsg_dump for cases other than kernel oops or
2715 panics
2716 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2717 default: disabled
2718
e84845c4
RD
2719 printk.time= Show timing data prefixed to each printk message line
2720 Format: <bool> (1/Y/y=enable, 0/N/n=disable)
2721
0cb55ad2
RD
2722 processor.max_cstate= [HW,ACPI]
2723 Limit processor to maximum C-state
2724 max_cstate=9 overrides any DMI blacklist limit.
2725
2726 processor.nocst [HW,ACPI]
2727 Ignore the _CST method to determine C-states,
2728 instead using the legacy FADT method
2729
1da177e4 2730 profile= [KNL] Enable kernel profiling via /proc/profile
a9913044
RD
2731 Format: [schedule,]<number>
2732 Param: "schedule" - profile schedule points.
2733 Param: <number> - step/bucket size as a power of 2 for
2734 statistical time based profiling.
b3da2a73
MG
2735 Param: "sleep" - profile D-state sleeping (millisecs).
2736 Requires CONFIG_SCHEDSTATS
c0fe2e69 2737 Param: "kvm" - profile VM exits.
1da177e4 2738
1da177e4
LT
2739 prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk
2740 before loading.
31c00fc1 2741 See Documentation/blockdev/ramdisk.txt.
1da177e4 2742
a9913044
RD
2743 psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to
2744 probe for; one of (bare|imps|exps|lifebook|any).
1da177e4
LT
2745 psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports
2746 per second.
a9913044
RD
2747 psmouse.resetafter= [HW,MOUSE]
2748 Try to reset the device after so many bad packets
1da177e4
LT
2749 (0 = never).
2750 psmouse.resolution=
2751 [HW,MOUSE] Set desired mouse resolution, in dpi.
2752 psmouse.smartscroll=
a9913044 2753 [HW,MOUSE] Controls Logitech smartscroll autorepeat.
1da177e4
LT
2754 0 = disabled, 1 = enabled (default).
2755
dee28e72
MG
2756 pstore.backend= Specify the name of the pstore backend to use
2757
1da177e4 2758 pt. [PARIDE]
31c00fc1 2759 See Documentation/blockdev/paride.txt.
1da177e4 2760
dc8c8587
KS
2761 pty.legacy_count=
2762 [KNL] Number of legacy pty's. Overwrites compiled-in
2763 default number.
2764
7d2c502f 2765 quiet [KNL] Disable most log messages
a9913044 2766
1da177e4
LT
2767 r128= [HW,DRM]
2768
2769 raid= [HW,RAID]
2770 See Documentation/md.txt.
2771
a9913044 2772 ramdisk_blocksize= [RAM]
31c00fc1 2773 See Documentation/blockdev/ramdisk.txt.
a9913044 2774
1da177e4 2775 ramdisk_size= [RAM] Sizes of RAM disks in kilobytes
31c00fc1 2776 See Documentation/blockdev/ramdisk.txt.
1da177e4 2777
4102adab 2778 rcu_nocbs= [KNL]
3fbfbf7a
PM
2779 In kernels built with CONFIG_RCU_NOCB_CPU=y, set
2780 the specified list of CPUs to be no-callback CPUs.
2781 Invocation of these CPUs' RCU callbacks will
a4889858
PM
2782 be offloaded to "rcuox/N" kthreads created for
2783 that purpose, where "x" is "b" for RCU-bh, "p"
2784 for RCU-preempt, and "s" for RCU-sched, and "N"
2785 is the CPU number. This reduces OS jitter on the
3fbfbf7a
PM
2786 offloaded CPUs, which can be useful for HPC and
2787 real-time workloads. It can also improve energy
2788 efficiency for asymmetric multiprocessors.
2789
4102adab 2790 rcu_nocb_poll [KNL]
3fbfbf7a
PM
2791 Rather than requiring that offloaded CPUs
2792 (specified by rcu_nocbs= above) explicitly
2793 awaken the corresponding "rcuoN" kthreads,
2794 make these kthreads poll for callbacks.
2795 This improves the real-time response for the
2796 offloaded CPUs by relieving them of the need to
2797 wake up the corresponding kthread, but degrades
2798 energy efficiency by requiring that the kthreads
2799 periodically wake up to do the polling.
2800
4102adab 2801 rcutree.blimit= [KNL]
97e63f0c
PM
2802 Set maximum number of finished RCU callbacks to
2803 process in one batch.
21a1ea9e 2804
4102adab 2805 rcutree.rcu_fanout_leaf= [KNL]
f885b7f2
PM
2806 Increase the number of CPUs assigned to each
2807 leaf rcu_node structure. Useful for very large
2808 systems.
2809
4102adab 2810 rcutree.jiffies_till_first_fqs= [KNL]
c0f4dfd4
PM
2811 Set delay from grace-period initialization to
2812 first attempt to force quiescent states.
2813 Units are jiffies, minimum value is zero,
2814 and maximum value is HZ.
2815
4102adab 2816 rcutree.jiffies_till_next_fqs= [KNL]
c0f4dfd4
PM
2817 Set delay between subsequent attempts to force
2818 quiescent states. Units are jiffies, minimum
2819 value is one, and maximum value is HZ.
2820
4102adab 2821 rcutree.qhimark= [KNL]
97e63f0c
PM
2822 Set threshold of queued RCU callbacks beyond which
2823 batch limiting is disabled.
21a1ea9e 2824
4102adab 2825 rcutree.qlowmark= [KNL]
24aaef8d
RD
2826 Set threshold of queued RCU callbacks below which
2827 batch limiting is re-enabled.
21a1ea9e 2828
4102adab 2829 rcutree.rcu_idle_gp_delay= [KNL]
c0f4dfd4
PM
2830 Set wakeup interval for idle CPUs that have
2831 RCU callbacks (RCU_FAST_NO_HZ=y).
d40011f6 2832
4102adab 2833 rcutree.rcu_idle_lazy_gp_delay= [KNL]
c0f4dfd4
PM
2834 Set wakeup interval for idle CPUs that have
2835 only "lazy" RCU callbacks (RCU_FAST_NO_HZ=y).
2836 Lazy RCU callbacks are those which RCU can
2837 prove do nothing more than free memory.
d40011f6 2838
4102adab 2839 rcutorture.fqs_duration= [KNL]
dabb8aa9
PM
2840 Set duration of force_quiescent_state bursts.
2841
4102adab 2842 rcutorture.fqs_holdoff= [KNL]
dabb8aa9
PM
2843 Set holdoff time within force_quiescent_state bursts.
2844
4102adab 2845 rcutorture.fqs_stutter= [KNL]
dabb8aa9
PM
2846 Set wait time between force_quiescent_state bursts.
2847
4102adab
PM
2848 rcutorture.gp_exp= [KNL]
2849 Use expedited update-side primitives.
2850
2851 rcutorture.gp_normal= [KNL]
2852 Use normal (non-expedited) update-side primitives.
2853 If both gp_exp and gp_normal are set, do both.
2854 If neither gp_exp nor gp_normal are set, still
2855 do both.
dabb8aa9 2856
4102adab 2857 rcutorture.n_barrier_cbs= [KNL]
dabb8aa9
PM
2858 Set callbacks/threads for rcu_barrier() testing.
2859
4102adab 2860 rcutorture.nfakewriters= [KNL]
dabb8aa9
PM
2861 Set number of concurrent RCU writers. These just
2862 stress RCU, they don't participate in the actual
2863 test, hence the "fake".
2864
4102adab 2865 rcutorture.nreaders= [KNL]
dabb8aa9
PM
2866 Set number of RCU readers.
2867
4102adab
PM
2868 rcutorture.object_debug= [KNL]
2869 Enable debug-object double-call_rcu() testing.
2870
2871 rcutorture.onoff_holdoff= [KNL]
dabb8aa9
PM
2872 Set time (s) after boot for CPU-hotplug testing.
2873
4102adab 2874 rcutorture.onoff_interval= [KNL]
dabb8aa9
PM
2875 Set time (s) between CPU-hotplug operations, or
2876 zero to disable CPU-hotplug testing.
2877
4102adab
PM
2878 rcutorture.rcutorture_runnable= [BOOT]
2879 Start rcutorture running at boot time.
2880
2881 rcutorture.shuffle_interval= [KNL]
dabb8aa9
PM
2882 Set task-shuffle interval (s). Shuffling tasks
2883 allows some CPUs to go into dyntick-idle mode
2884 during the rcutorture test.
2885
4102adab 2886 rcutorture.shutdown_secs= [KNL]
dabb8aa9
PM
2887 Set time (s) after boot system shutdown. This
2888 is useful for hands-off automated testing.
2889
4102adab 2890 rcutorture.stall_cpu= [KNL]
dabb8aa9
PM
2891 Duration of CPU stall (s) to test RCU CPU stall
2892 warnings, zero to disable.
2893
4102adab 2894 rcutorture.stall_cpu_holdoff= [KNL]
dabb8aa9
PM
2895 Time to wait (s) after boot before inducing stall.
2896
4102adab 2897 rcutorture.stat_interval= [KNL]
dabb8aa9
PM
2898 Time (s) between statistics printk()s.
2899
4102adab 2900 rcutorture.stutter= [KNL]
dabb8aa9
PM
2901 Time (s) to stutter testing, for example, specifying
2902 five seconds causes the test to run for five seconds,
2903 wait for five seconds, and so on. This tests RCU's
2904 ability to transition abruptly to and from idle.
2905
4102adab 2906 rcutorture.test_boost= [KNL]
dabb8aa9
PM
2907 Test RCU priority boosting? 0=no, 1=maybe, 2=yes.
2908 "Maybe" means test if the RCU implementation
2909 under test support RCU priority boosting.
2910
4102adab 2911 rcutorture.test_boost_duration= [KNL]
dabb8aa9
PM
2912 Duration (s) of each individual boost test.
2913
4102adab 2914 rcutorture.test_boost_interval= [KNL]
dabb8aa9
PM
2915 Interval (s) between each boost test.
2916
4102adab 2917 rcutorture.test_no_idle_hz= [KNL]
dabb8aa9
PM
2918 Test RCU's dyntick-idle handling. See also the
2919 rcutorture.shuffle_interval parameter.
2920
4102adab 2921 rcutorture.torture_type= [KNL]
dabb8aa9
PM
2922 Specify the RCU implementation to test.
2923
4102adab 2924 rcutorture.verbose= [KNL]
dabb8aa9
PM
2925 Enable additional printk() statements.
2926
4102adab
PM
2927 rcupdate.rcu_expedited= [KNL]
2928 Use expedited grace-period primitives, for
2929 example, synchronize_rcu_expedited() instead
2930 of synchronize_rcu(). This reduces latency,
2931 but can increase CPU utilization, degrade
2932 real-time latency, and degrade energy efficiency.
2933
2934 rcupdate.rcu_cpu_stall_suppress= [KNL]
2935 Suppress RCU CPU stall warning messages.
2936
2937 rcupdate.rcu_cpu_stall_timeout= [KNL]
2938 Set timeout for RCU CPU stall warning messages.
2939
ffdfc409
OJ
2940 rdinit= [KNL]
2941 Format: <full_path>
2942 Run specified binary instead of /init from the ramdisk,
2943 used for early userspace startup. See initrd.
2944
1b3a5d02
RH
2945 reboot= [KNL]
2946 Format (x86 or x86_64):
2947 [w[arm] | c[old] | h[ard] | s[oft] | g[pio]] \
2948 [[,]s[mp]#### \
2949 [[,]b[ios] | a[cpi] | k[bd] | t[riple] | e[fi] | p[ci]] \
2950 [[,]f[orce]
2951 Where reboot_mode is one of warm (soft) or cold (hard) or gpio,
2952 reboot_type is one of bios, acpi, kbd, triple, efi, or pci,
2953 reboot_force is either force or not specified,
2954 reboot_cpu is s[mp]#### with #### being the processor
2955 to be used for rebooting.
1da177e4 2956
46b6d94e
PJ
2957 relax_domain_level=
2958 [KNL, SMP] Set scheduler's default relax_domain_level.
21acb9ca 2959 See Documentation/cgroups/cpusets.txt.
46b6d94e 2960
0399d4db
RW
2961 relative_sleep_states=
2962 [SUSPEND] Use sleep state labeling where the deepest
2963 state available other than hibernation is always "mem".
2964 Format: { "0" | "1" }
2965 0 -- Traditional sleep state labels.
2966 1 -- Relative sleep state labels.
2967
1da177e4
LT
2968 reserve= [KNL,BUGS] Force the kernel to ignore some iomem area
2969
cd4f0ef7 2970 reservetop= [X86-32]
461a9aff
ZA
2971 Format: nn[KMG]
2972 Reserves a hole at the top of the kernel virtual
2973 address space.
2974
9ea77bdb
PA
2975 reservelow= [X86]
2976 Format: nn[K]
2977 Set the amount of memory to reserve for BIOS at
2978 the bottom of the address space.
2979
7e96287d
VG
2980 reset_devices [KNL] Force drivers to reset the underlying device
2981 during initialization.
2982
a9913044
RD
2983 resume= [SWSUSP]
2984 Specify the partition device for software suspend
2df83fa4
MB
2985 Format:
2986 {/dev/<dev> | PARTUUID=<uuid> | <int>:<int> | <hex>}
1da177e4 2987
ecbd0da1
RW
2988 resume_offset= [SWSUSP]
2989 Specify the offset from the beginning of the partition
2990 given by "resume=" at which the swap header is located,
2991 in <PAGE_SIZE> units (needed only for swap files).
2992 See Documentation/power/swsusp-and-swap-files.txt
2993
f126f733
BS
2994 resumedelay= [HIBERNATION] Delay (in seconds) to pause before attempting to
2995 read the resume files
2996
6f8d7022
BS
2997 resumewait [HIBERNATION] Wait (indefinitely) for resume device to show up.
2998 Useful for devices that are detected asynchronously
2999 (e.g. USB and MMC devices).
3000
f996fc96
BS
3001 hibernate= [HIBERNATION]
3002 noresume Don't check if there's a hibernation image
3003 present during boot.
3004 nocompress Don't compress/decompress hibernation images.
a6e15a39 3005 no Disable hibernation and resume.
f996fc96 3006
0a7b35cb
MN
3007 retain_initrd [RAM] Keep initrd memory after extraction
3008
1da177e4
LT
3009 rhash_entries= [KNL,NET]
3010 Set number of hash buckets for route cache
3011
1da177e4
LT
3012 ro [KNL] Mount root device read-only on boot
3013
3014 root= [KNL] Root filesystem
f2d34fd9 3015 See name_to_dev_t comment in init/do_mounts.c.
1da177e4
LT
3016
3017 rootdelay= [KNL] Delay (in seconds) to pause before attempting to
3018 mount the root filesystem
3019
3020 rootflags= [KNL] Set root filesystem mount option string
3021
3022 rootfstype= [KNL] Set root filesystem type
3023
cc1ed754
PO
3024 rootwait [KNL] Wait (indefinitely) for root device to show up.
3025 Useful for devices that are detected asynchronously
3026 (e.g. USB and MMC devices).
3027
5c71d618
RT
3028 rproc_mem=nn[KMG][@address]
3029 [KNL,ARM,CMA] Remoteproc physical memory block.
3030 Memory area to be used by remote processor image,
3031 managed by CMA.
3032
1da177e4
LT
3033 rw [KNL] Mount root device read-write on boot
3034
3035 S [KNL] Run init in single mode
3036
3037 sa1100ir [NET]
3038 See drivers/net/irda/sa1100_ir.c.
3039
1da177e4 3040 sbni= [NET] Granch SBNI12 leased line adapter
a9913044 3041
f6630114
MT
3042 sched_debug [KNL] Enables verbose scheduler debug messages.
3043
5307c955
MG
3044 skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
3045 xtime_lock contention on larger systems, and/or RCU lock
3046 contention on all systems with CONFIG_MAXSMP set.
3047 Format: { "0" | "1" }
3048 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
3049 1 -- enable.
3050 Note: increases power consumption, thus should only be
3051 enabled if running jitter sensitive (HPC/RT) workloads.
3052
0cb55ad2
RD
3053 security= [SECURITY] Choose a security module to enable at boot.
3054 If this boot parameter is not specified, only the first
3055 security module asking for security registration will be
3056 loaded. An invalid security module name will be treated
3057 as if no module has been chosen.
3058
3059 selinux= [SELINUX] Disable or enable SELinux at boot time.
1da177e4
LT
3060 Format: { "0" | "1" }
3061 See security/selinux/Kconfig help text.
3062 0 -- disable.
3063 1 -- enable.
3064 Default value is set via kernel config option.
3065 If enabled at boot time, /selinux/disable can be used
3066 later to disable prior to initial policy load.
3067
c1c124e9
JJ
3068 apparmor= [APPARMOR] Disable or enable AppArmor at boot time
3069 Format: { "0" | "1" }
3070 See security/apparmor/Kconfig help text
3071 0 -- disable.
3072 1 -- enable.
3073 Default value is set via kernel config option.
3074
cd4f0ef7 3075 serialnumber [BUGS=X86-32]
1da177e4 3076
1da177e4
LT
3077 shapers= [NET]
3078 Maximal number of shapers.
a9913044 3079
b05f78f5
YL
3080 show_msr= [x86] show boot-time MSR settings
3081 Format: { <integer> }
3082 Show boot-time (BIOS-initialized) MSR settings.
3083 The parameter means the number of CPUs to show,
3084 for example 1 means boot CPU only.
3085
1da177e4
LT
3086 simeth= [IA-64]
3087 simscsi=
a9913044 3088
1da177e4
LT
3089 slram= [HW,MTD]
3090
3df1cccd
DR
3091 slab_max_order= [MM, SLAB]
3092 Determines the maximum allowed order for slabs.
3093 A high setting may cause OOMs due to memory
3094 fragmentation. Defaults to 1 for systems with
3095 more than 32MB of RAM, 0 otherwise.
3096
f0630fff
CL
3097 slub_debug[=options[,slabs]] [MM, SLUB]
3098 Enabling slub_debug allows one to determine the
3099 culprit if slab objects become corrupted. Enabling
3100 slub_debug can create guard zones around objects and
3101 may poison objects when not in use. Also tracks the
3102 last alloc / free. For more information see
3103 Documentation/vm/slub.txt.
c1aee215
CL
3104
3105 slub_max_order= [MM, SLUB]
f0630fff
CL
3106 Determines the maximum allowed order for slabs.
3107 A high setting may cause OOMs due to memory
3108 fragmentation. For more information see
3109 Documentation/vm/slub.txt.
c1aee215
CL
3110
3111 slub_min_objects= [MM, SLUB]
f0630fff
CL
3112 The minimum number of objects per slab. SLUB will
3113 increase the slab order up to slub_max_order to
3114 generate a sufficiently large slab able to contain
3115 the number of objects indicated. The higher the number
3116 of objects the smaller the overhead of tracking slabs
3117 and the less frequently locks need to be acquired.
c1aee215
CL
3118 For more information see Documentation/vm/slub.txt.
3119
3120 slub_min_order= [MM, SLUB]
24775d65 3121 Determines the minimum page order for slabs. Must be
f0630fff 3122 lower than slub_max_order.
c1aee215
CL
3123 For more information see Documentation/vm/slub.txt.
3124
3125 slub_nomerge [MM, SLUB]
f0630fff 3126 Disable merging of slabs with similar size. May be
c1aee215 3127 necessary if there is some reason to distinguish
f0630fff
CL
3128 allocs to different slabs. Debug options disable
3129 merging on their own.
c1aee215
CL
3130 For more information see Documentation/vm/slub.txt.
3131
1da177e4
LT
3132 smart2= [HW]
3133 Format: <io1>[,<io2>[,...,<io8>]]
3134
d0d4f69b
BH
3135 smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices
3136 smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port
3137 smsc-ircc2.ircc_sir= [HW] SIR base I/O port
3138 smsc-ircc2.ircc_fir= [HW] FIR base I/O port
3139 smsc-ircc2.ircc_irq= [HW] IRQ line
3140 smsc-ircc2.ircc_dma= [HW] DMA channel
3141 smsc-ircc2.ircc_transceiver= [HW] Transceiver type:
3142 0: Toshiba Satellite 1800 (GP data pin select)
3143 1: Fast pin select (default)
3144 2: ATC IRMode
3145
9c44bc03
IM
3146 softlockup_panic=
3147 [KNL] Should the soft-lockup detector generate panics.
44a4dcf7 3148 Format: <integer>
9c44bc03 3149
ed235875
AT
3150 softlockup_all_cpu_backtrace=
3151 [KNL] Should the soft-lockup detector generate
3152 backtraces on all cpus.
3153 Format: <integer>
3154
1da177e4 3155 sonypi.*= [HW] Sony Programmable I/O Control Device driver
395cf969 3156 See Documentation/laptops/sonypi.txt
1da177e4 3157
1da177e4
LT
3158 spia_io_base= [HW,MTD]
3159 spia_fio_base=
3160 spia_pedr=
3161 spia_peddr=
3162
f38f1d2a
SR
3163 stacktrace [FTRACE]
3164 Enabled the stack tracer on boot up.
3165
762e1207
SR
3166 stacktrace_filter=[function-list]
3167 [FTRACE] Limit the functions that the stack tracer
3168 will trace at boot up. function-list is a comma separated
3169 list of functions. This list can be changed at run
3170 time by the stack_trace_filter file in the debugfs
3171 tracing directory. Note, this enables stack tracing
3172 and the stacktrace above is not needed.
3173
1da177e4
LT
3174 sti= [PARISC,HW]
3175 Format: <num>
3176 Set the STI (builtin display/keyboard on the HP-PARISC
3177 machines) console (graphic card) which should be used
3178 as the initial boot-console.
3179 See also comment in drivers/video/console/sticore.c.
3180
3181 sti_font= [HW]
3182 See comment in drivers/video/console/sticore.c.
3183
3184 stifb= [HW]
3185 Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]]
3186
cbf11071
TM
3187 sunrpc.min_resvport=
3188 sunrpc.max_resvport=
3189 [NFS,SUNRPC]
3190 SunRPC servers often require that client requests
3191 originate from a privileged port (i.e. a port in the
3192 range 0 < portnr < 1024).
3193 An administrator who wishes to reserve some of these
3194 ports for other uses may adjust the range that the
3195 kernel's sunrpc client considers to be privileged
3196 using these two parameters to set the minimum and
3197 maximum port values.
3198
42a7fc4a
GB
3199 sunrpc.pool_mode=
3200 [NFS]
3201 Control how the NFS server code allocates CPUs to
3202 service thread pools. Depending on how many NICs
3203 you have and where their interrupts are bound, this
3204 option will affect which CPUs will do NFS serving.
3205 Note: this parameter cannot be changed while the
3206 NFS server is running.
3207
3208 auto the server chooses an appropriate mode
3209 automatically using heuristics
3210 global a single global pool contains all CPUs
3211 percpu one pool for each CPU
3212 pernode one pool for each NUMA node (equivalent
3213 to global on non-NUMA machines)
3214
cbf11071
TM
3215 sunrpc.tcp_slot_table_entries=
3216 sunrpc.udp_slot_table_entries=
3217 [NFS,SUNRPC]
3218 Sets the upper limit on the number of simultaneous
3219 RPC calls that can be sent from the client to a
3220 server. Increasing these values may allow you to
3221 improve throughput, but will also increase the
3222 amount of memory reserved for use by the client.
3223
07555ac1 3224 swapaccount=[0|1]
a42c390c
MH
3225 [KNL] Enable accounting of swap in memory resource
3226 controller if no parameter or 1 is given or disable
3227 it if 0 is given (See Documentation/cgroups/memory.txt)
3228
91fec0f5
JK
3229 swiotlb= [ARM,IA-64,PPC,MIPS,X86]
3230 Format: { <int> | force }
3231 <int> -- Number of I/O TLB slabs
3232 force -- force using of bounce buffers even if they
3233 wouldn't be automatically used by the kernel
a9913044 3234
1da177e4
LT
3235 switches= [HW,M68k]
3236
e52eec13
AK
3237 sysfs.deprecated=0|1 [KNL]
3238 Enable/disable old style sysfs layout for old udev
3239 on older distributions. When this option is enabled
3240 very new udev will not work anymore. When this option
3241 is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
3242 in older udev will not work anymore.
3243 Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
3244 the kernel configuration.
3245
5d6f647f
IM
3246 sysrq_always_enabled
3247 [KNL]
3248 Ignore sysrq setting - this boot parameter will
3249 neutralize any effect of /proc/sys/kernel/sysrq.
3250 Useful for debugging.
3251
1da177e4
LT
3252 tdfx= [HW,DRM]
3253
77437fd4
DB
3254 test_suspend= [SUSPEND]
3255 Specify "mem" (for Suspend-to-RAM) or "standby" (for
3256 standby suspend) as the system sleep state to briefly
3257 enter during system startup. The system is woken from
3258 this state using a wakeup-capable RTC alarm.
3259
1da177e4
LT
3260 thash_entries= [KNL,NET]
3261 Set number of hash buckets for TCP connection
3262
f8707ec9
LB
3263 thermal.act= [HW,ACPI]
3264 -1: disable all active trip points in all thermal zones
3265 <degrees C>: override all lowest active trip points
3266
c52a7419
LB
3267 thermal.crt= [HW,ACPI]
3268 -1: disable all critical trip points in all thermal zones
22a94d79 3269 <degrees C>: override all critical trip points
c52a7419 3270
f5487145
LB
3271 thermal.nocrt= [HW,ACPI]
3272 Set to disable actions on ACPI thermal zone
3273 critical and hot trip points.
3274
72b33ef8
LB
3275 thermal.off= [HW,ACPI]
3276 1: disable ACPI thermal control
3277
a70cdc52
LB
3278 thermal.psv= [HW,ACPI]
3279 -1: disable all passive trip points
ada9cfdd
RD
3280 <degrees C>: override all passive trip points to this
3281 value
a70cdc52 3282
730ff34d
LB
3283 thermal.tzp= [HW,ACPI]
3284 Specify global default ACPI thermal zone polling rate
3285 <deci-seconds>: poll all this frequency
3286 0: no polling (default)
3287
8d32a307
TG
3288 threadirqs [KNL]
3289 Force threading of all interrupt handlers except those
24775d65 3290 marked explicitly IRQF_NO_THREAD.
8d32a307 3291
2ca62b04
KRW
3292 tmem [KNL,XEN]
3293 Enable the Transcendent memory driver if built-in.
3294
3295 tmem.cleancache=0|1 [KNL, XEN]
3296 Default is on (1). Disable the usage of the cleancache
3297 API to send anonymous pages to the hypervisor.
3298
3299 tmem.frontswap=0|1 [KNL, XEN]
3300 Default is on (1). Disable the usage of the frontswap
37d46e15
KRW
3301 API to send swap pages to the hypervisor. If disabled
3302 the selfballooning and selfshrinking are force disabled.
2ca62b04
KRW
3303
3304 tmem.selfballooning=0|1 [KNL, XEN]
3305 Default is on (1). Disable the driving of swap pages
3306 to the hypervisor.
3307
3308 tmem.selfshrinking=0|1 [KNL, XEN]
3309 Default is on (1). Partial swapoff that immediately
3310 transfers pages from Xen hypervisor back to the
3311 kernel based on different criteria.
3312
2b1a61f0
HC
3313 topology= [S390]
3314 Format: {off | on}
3315 Specify if the kernel should make use of the cpu
f65e51d7
SL
3316 topology information if the hardware supports this.
3317 The scheduler will make use of this information and
2b1a61f0 3318 e.g. base its process migration decisions on it.
c9af3fa9 3319 Default is on.
2b1a61f0 3320
1da177e4
LT
3321 tp720= [HW,PS2]
3322
225a9be2
RA
3323 tpm_suspend_pcr=[HW,TPM]
3324 Format: integer pcr id
3325 Specify that at suspend time, the tpm driver
3326 should extend the specified pcr with zeros,
3327 as a workaround for some chips which fail to
3328 flush the last written pcr on TPM_SaveState.
3329 This will guarantee that all the other pcrs
3330 are saved.
3331
9d612bef
LZ
3332 trace_buf_size=nn[KMG]
3333 [FTRACE] will set tracing buffer size.
631595fb 3334
020e5f85
LZ
3335 trace_event=[event-list]
3336 [FTRACE] Set and start specified trace events in order
3337 to facilitate early boot debugging.
3338 See also Documentation/trace/events.txt
3339
7bcfaf54
SR
3340 trace_options=[option-list]
3341 [FTRACE] Enable or disable tracer options at boot.
3342 The option-list is a comma delimited list of options
3343 that can be enabled or disabled just as if you were
3344 to echo the option name into
3345
3346 /sys/kernel/debug/tracing/trace_options
3347
3348 For example, to enable stacktrace option (to dump the
3349 stack trace of each event), add to the command line:
3350
3351 trace_options=stacktrace
3352
3353 See also Documentation/trace/ftrace.txt "trace options"
3354 section.
3355
de7edd31
SRRH
3356 traceoff_on_warning
3357 [FTRACE] enable this option to disable tracing when a
3358 warning is hit. This turns off "tracing_on". Tracing can
3359 be enabled again by echoing '1' into the "tracing_on"
3360 file located in /sys/kernel/debug/tracing/
3361
3362 This option is useful, as it disables the trace before
3363 the WARNING dump is called, which prevents the trace to
3364 be filled with content caused by the warning output.
3365
3366 This option can also be set at run time via the sysctl
3367 option: kernel/traceoff_on_warning
3368
fcf4d821
JK
3369 transparent_hugepage=
3370 [KNL]
3371 Format: [always|madvise|never]
3372 Can be used to control the default behavior of the system
3373 with respect to transparent hugepages.
3374 See Documentation/vm/transhuge.txt for more details.
3375
d3b8f889 3376 tsc= Disable clocksource stability checks for TSC.
395628ef
AK
3377 Format: <string>
3378 [x86] reliable: mark tsc clocksource as reliable, this
d3b8f889
JS
3379 disables clocksource verification at runtime, as well
3380 as the stability checks done at bootup. Used to enable
3381 high-resolution timer mode on older hardware, and in
3382 virtualized environment.
e82b8e4e
VP
3383 [x86] noirqtime: Do not use TSC to do irq accounting.
3384 Used to run time disable IRQ_TIME_ACCOUNTING on any
3385 platforms where RDTSC is slow and this accounting
3386 can add overhead.
395628ef 3387
a9913044
RD
3388 turbografx.map[2|3]= [HW,JOY]
3389 TurboGraFX parallel port interface
3390 Format:
3391 <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7>
1da177e4
LT
3392 See also Documentation/input/joystick-parport.txt
3393
b6935f8c
CK
3394 udbg-immortal [PPC] When debugging early kernel crashes that
3395 happen after console_init() and before a proper
3396 console driver takes over, this boot options might
3397 help "seeing" what's going on.
3398
f86dcc5a
ED
3399 uhash_entries= [KNL,NET]
3400 Set number of hash buckets for UDP/UDP-Lite connections
3401
5f8364b7
AS
3402 uhci-hcd.ignore_oc=
3403 [USB] Ignore overcurrent events (default N).
3404 Some badly-designed motherboards generate lots of
3405 bogus events, for ports that aren't wired to
3406 anything. Set this parameter to avoid log spamming.
3407 Note that genuine overcurrent events won't be
3408 reported either.
3409
e3a61b0a 3410 unknown_nmi_panic
44a4dcf7 3411 [X86] Cause panic on unknown NMI.
e3a61b0a 3412
c4fc2342
CDH
3413 usbcore.authorized_default=
3414 [USB] Default USB device authorization:
3415 (default -1 = authorized except for wireless USB,
3416 0 = not authorized, 1 = authorized)
3417
b5e795f8
AS
3418 usbcore.autosuspend=
3419 [USB] The autosuspend time delay (in seconds) used
3420 for newly-detected USB devices (default 2). This
3421 is the time required before an idle device will be
3422 autosuspended. Devices for which the delay is set
eaafbc3a 3423 to a negative value won't be autosuspended at all.
b5e795f8 3424
fd7c519d
JK
3425 usbcore.usbfs_snoop=
3426 [USB] Set to log all usbfs traffic (default 0 = off).
3427
3428 usbcore.blinkenlights=
3429 [USB] Set to cycle leds on hubs (default 0 = off).
3430
3431 usbcore.old_scheme_first=
3432 [USB] Start with the old device initialization
3433 scheme (default 0 = off).
3434
3f5eb8d5
AS
3435 usbcore.usbfs_memory_mb=
3436 [USB] Memory limit (in MB) for buffers allocated by
3437 usbfs (default = 16, 0 = max = 2047).
3438
fd7c519d
JK
3439 usbcore.use_both_schemes=
3440 [USB] Try the other device initialization scheme
3441 if the first one fails (default 1 = enabled).
3442
3443 usbcore.initial_descriptor_timeout=
3444 [USB] Specifies timeout for the initial 64-byte
3445 USB_REQ_GET_DESCRIPTOR request in milliseconds
3446 (default 5000 = 5.0 seconds).
3447
1da177e4
LT
3448 usbhid.mousepoll=
3449 [USBHID] The interval which mice are to be polled at.
a9913044 3450
d4f373e5
AS
3451 usb-storage.delay_use=
3452 [UMS] The delay in seconds before a new device is
3453 scanned for Logical Units (default 5).
3454
3455 usb-storage.quirks=
3456 [UMS] A list of quirks entries to supplement or
3457 override the built-in unusual_devs list. List
3458 entries are separated by commas. Each entry has
3459 the form VID:PID:Flags where VID and PID are Vendor
3460 and Product ID values (4-digit hex numbers) and
3461 Flags is a set of characters, each corresponding
3462 to a common usb-storage quirk flag as follows:
c838ea46
AS
3463 a = SANE_SENSE (collect more than 18 bytes
3464 of sense data);
a0bb1081
AS
3465 b = BAD_SENSE (don't collect more than 18
3466 bytes of sense data);
d4f373e5
AS
3467 c = FIX_CAPACITY (decrease the reported
3468 device capacity by one sector);
5116901d
KR
3469 d = NO_READ_DISC_INFO (don't use
3470 READ_DISC_INFO command);
3471 e = NO_READ_CAPACITY_16 (don't use
3472 READ_CAPACITY_16 command);
c838ea46
AS
3473 h = CAPACITY_HEURISTICS (decrease the
3474 reported device capacity by one
3475 sector if the number is odd);
d4f373e5
AS
3476 i = IGNORE_DEVICE (don't bind to this
3477 device);
3478 l = NOT_LOCKABLE (don't try to lock and
3479 unlock ejectable media);
3480 m = MAX_SECTORS_64 (don't transfer more
3481 than 64 sectors = 32 KB at a time);
21c13a4f
AS
3482 n = INITIAL_READ10 (force a retry of the
3483 initial READ(10) command);
c838ea46
AS
3484 o = CAPACITY_OK (accept the capacity
3485 reported by the device);
eaa05dfc
NJ
3486 p = WRITE_CACHE (the device cache is ON
3487 by default);
d4f373e5
AS
3488 r = IGNORE_RESIDUE (the device reports
3489 bogus residue values);
3490 s = SINGLE_LUN (the device has only one
3491 Logical Unit);
3492 w = NO_WP_DETECT (don't test whether the
3493 medium is write-protected).
3494 Example: quirks=0419:aaf5:rl,0421:0433:rc
3495
ac1667db
SB
3496 user_debug= [KNL,ARM]
3497 Format: <int>
3498 See arch/arm/Kconfig.debug help text.
3499 1 - undefined instruction events
3500 2 - system calls
3501 4 - invalid data aborts
3502 8 - SIGSEGV faults
3503 16 - SIGBUS faults
3504 Example: user_debug=31
3505
14315592
IC
3506 userpte=
3507 [X86] Flags controlling user PTE allocations.
3508
3509 nohigh = do not allocate PTE pages in
3510 HIGHMEM regardless of setting
3511 of CONFIG_HIGHPTE.
3512
6cececfc 3513 vdso= [X86,SH]
b0b49f26
AL
3514 On X86_32, this is an alias for vdso32=. Otherwise:
3515
3516 vdso=1: enable VDSO (the default)
e6e5494c
IM
3517 vdso=0: disable VDSO mapping
3518
b0b49f26
AL
3519 vdso32= [X86] Control the 32-bit vDSO
3520 vdso32=1: enable 32-bit VDSO
3521 vdso32=0 or vdso32=2: disable 32-bit VDSO
3522
3523 See the help text for CONFIG_COMPAT_VDSO for more
3524 details. If CONFIG_COMPAT_VDSO is set, the default is
3525 vdso32=0; otherwise, the default is vdso32=1.
3526
3527 For compatibility with older kernels, vdso32=2 is an
3528 alias for vdso32=0.
3529
3530 Try vdso32=0 if you encounter an error that says:
3531 dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!
af65d648 3532
d080d397
YI
3533 vector= [IA-64,SMP]
3534 vector=percpu: enable percpu vector domain
3535
1da177e4
LT
3536 video= [FB] Frame buffer configuration
3537 See Documentation/fb/modedb.txt.
3538
3afe6dab
AL
3539 video.brightness_switch_enabled= [0,1]
3540 If set to 1, on receiving an ACPI notify event
3541 generated by hotkey, video driver will adjust brightness
3542 level and then send out the event to user space through
3543 the allocated input device; If set to 0, video driver
3544 will only send out the event without touching backlight
3545 brightness level.
886129a8 3546 default: 0
3afe6dab 3547
81a054ce
PM
3548 virtio_mmio.device=
3549 [VMMIO] Memory mapped virtio (platform) device.
3550
3551 <size>@<baseaddr>:<irq>[:<id>]
3552 where:
3553 <size> := size (can use standard suffixes
3554 like K, M and G)
3555 <baseaddr> := physical base address
3556 <irq> := interrupt number (as passed to
3557 request_irq())
3558 <id> := (optional) platform device id
3559 example:
3560 virtio_mmio.device=1K@0x100b0000:48:7
3561
3562 Can be used multiple times for multiple devices.
3563
cd4f0ef7 3564 vga= [BOOT,X86-32] Select a particular video mode
954a8b81 3565 See Documentation/x86/boot.txt and
a9913044 3566 Documentation/svga.txt.
1da177e4
LT
3567 Use vga=ask for menu.
3568 This is actually a boot loader parameter; the value is
3569 passed to the kernel using a special protocol.
3570
a9913044 3571 vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact
1da177e4
LT
3572 size of <nn>. This can be used to increase the
3573 minimum size (128MB on x86). It can also be used to
3574 decrease the size and leave more room for directly
3575 mapped kernel RAM.
3576
585c3047
PO
3577 vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
3578 Format: <command>
1da177e4 3579
585c3047
PO
3580 vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic.
3581 Format: <command>
3582
3583 vmpoff= [KNL,S390] Perform z/VM CP command after power off.
3584 Format: <command>
a9913044 3585
3ae36655
AL
3586 vsyscall= [X86-64]
3587 Controls the behavior of vsyscalls (i.e. calls to
3588 fixed addresses of 0xffffffffff600x00 from legacy
3589 code). Most statically-linked binaries and older
3590 versions of glibc use these calls. Because these
3591 functions are at fixed addresses, they make nice
3592 targets for exploits that can control RIP.
3593
2e57ae05
AL
3594 emulate [default] Vsyscalls turn into traps and are
3595 emulated reasonably safely.
3ae36655 3596
2e57ae05 3597 native Vsyscalls are native syscall instructions.
3ae36655
AL
3598 This is a little bit faster than trapping
3599 and makes a few dynamic recompilers work
3600 better than they would in emulation mode.
3601 It also makes exploits much easier to write.
3602
3603 none Vsyscalls don't work at all. This makes
3604 them quite hard to use for exploits but
3605 might break your system.
3606
3855ae1c
CL
3607 vt.color= [VT] Default text color.
3608 Format: 0xYX, X = foreground, Y = background.
3609 Default: 0x07 = light gray on black.
3610
9ea9a886
CL
3611 vt.cur_default= [VT] Default cursor shape.
3612 Format: 0xCCBBAA, where AA, BB, and CC are the same as
3613 the parameters of the <Esc>[?A;B;Cc escape sequence;
3614 see VGA-softcursor.txt. Default: 2 = underline.
3615
0cb55ad2
RD
3616 vt.default_blu= [VT]
3617 Format: <blue0>,<blue1>,<blue2>,...,<blue15>
3618 Change the default blue palette of the console.
3619 This is a 16-member array composed of values
3620 ranging from 0-255.
3621
3622 vt.default_grn= [VT]
3623 Format: <green0>,<green1>,<green2>,...,<green15>
3624 Change the default green palette of the console.
3625 This is a 16-member array composed of values
3626 ranging from 0-255.
3627
3628 vt.default_red= [VT]
3629 Format: <red0>,<red1>,<red2>,...,<red15>
3630 Change the default red palette of the console.
3631 This is a 16-member array composed of values
3632 ranging from 0-255.
3633
3634 vt.default_utf8=
3635 [VT]
3636 Format=<0|1>
3637 Set system-wide default UTF-8 mode for all tty's.
3638 Default is 1, i.e. UTF-8 mode is enabled for all
3639 newly opened terminals.
3640
f6c06b68
MG
3641 vt.global_cursor_default=
3642 [VT]
3643 Format=<-1|0|1>
3644 Set system-wide default for whether a cursor
3645 is shown on new VTs. Default is -1,
3646 i.e. cursors will be created by default unless
3647 overridden by individual drivers. 0 will hide
3648 cursors, 1 will display them.
3649
3855ae1c
CL
3650 vt.italic= [VT] Default color for italic text; 0-15.
3651 Default: 2 = green.
3652
3653 vt.underline= [VT] Default color for underlined text; 0-15.
3654 Default: 3 = cyan.
3655
4724ba57
RD
3656 watchdog timers [HW,WDT] For information on watchdog timers,
3657 see Documentation/watchdog/watchdog-parameters.txt
3658 or other driver-specific files in the
3659 Documentation/watchdog/ directory.
1da177e4 3660
d55262c4
TH
3661 workqueue.disable_numa
3662 By default, all work items queued to unbound
3663 workqueues are affine to the NUMA nodes they're
3664 issued on, which results in better behavior in
3665 general. If NUMA affinity needs to be disabled for
3666 whatever reason, this option can be used. Note
3667 that this also can be controlled per-workqueue for
3668 workqueues visible under /sys/bus/workqueue/.
3669
cee22a15
VK
3670 workqueue.power_efficient
3671 Per-cpu workqueues are generally preferred because
3672 they show better performance thanks to cache
3673 locality; unfortunately, per-cpu workqueues tend to
3674 be more power hungry than unbound workqueues.
3675
3676 Enabling this makes the per-cpu workqueues which
3677 were observed to contribute significantly to power
3678 consumption unbound, leading to measurably lower
3679 power usage at the cost of small performance
3680 overhead.
3681
3682 The default value of this parameter is determined by
3683 the config option CONFIG_WQ_POWER_EFFICIENT_DEFAULT.
3684
0cb55ad2
RD
3685 x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
3686 default x2apic cluster mode on platforms
3687 supporting x2apic.
3688
712b6aa8
KS
3689 x86_intel_mid_timer= [X86-32,APBT]
3690 Choose timer option for x86 Intel MID platform.
bb24c471
JP
3691 Two valid options are apbt timer only and lapic timer
3692 plus one apbt timer for broadcast timer.
712b6aa8 3693 x86_intel_mid_timer=apbt_only | lapic_and_apbt
bb24c471 3694
c1c5413a
SS
3695 xen_emul_unplug= [HW,X86,XEN]
3696 Unplug Xen emulated devices
3697 Format: [unplug0,][unplug1]
3698 ide-disks -- unplug primary master IDE devices
3699 aux-ide-disks -- unplug non-primary-master IDE devices
3700 nics -- unplug network devices
3701 all -- unplug all emulated devices (NICs and IDE disks)
1dc7ce99
IC
3702 unnecessary -- unplugging emulated devices is
3703 unnecessary even if the host did not respond to
3704 the unplug protocol
c93a4dfb 3705 never -- do not unplug even if version check succeeds
c1c5413a 3706
15a3eac0
KRW
3707 xen_nopvspin [X86,XEN]
3708 Disables the ticketlock slowpath using Xen PV
3709 optimizations.
3710
1da177e4 3711 xirc2ps_cs= [NET,PCMCIA]
a9913044
RD
3712 Format:
3713 <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
1da177e4 3714
a9913044 3715______________________________________________________________________
1da177e4
LT
3716
3717TODO:
3718
1da177e4 3719 Add more DRM drivers.