Documentation/x86_64/boot-options.txt

   1 AMD64 specific boot options
   2
   3 There are many others (usually documented in driver documentation), but
   4 only the AMD64 specific ones are listed here.
   5
   6 Machine check
   7
   8    mce=off disable machine check
   9    mce=bootlog Enable logging of machine checks left over from booting.
  10                Disabled by default on AMD because some BIOS leave bogus ones.
  11                If your BIOS doesn't do that it's a good idea to enable though
  12                to make sure you log even machine check events that result
  13                in a reboot. On Intel systems it is enabled by default.
  14    mce=nobootlog
  15                 Disable boot machine check logging.
  16    mce=tolerancelevel (number)
  17                 0: always panic, 1: panic if deadlock possible,
  18                 2: try to avoid panic, 3: never panic or exit (for testing)
  19                 default is 1
  20                 Can be also set using sysfs which is preferable.
  21
  22    nomce (for compatibility with i386): same as mce=off
  23
  24    Everything else is in sysfs now.
  25
  26 APICs
  27
  28    apic          Use IO-APIC. Default
  29
  30    noapic        Don't use the IO-APIC.
  31
  32    disableapic   Don't use the local APIC
  33
  34    nolapic       Don't use the local APIC (alias for i386 compatibility)
  35
  36    pirq=...      See Documentation/i386/IO-APIC.txt
  37
  38    noapictimer   Don't set up the APIC timer
  39
  40    no_timer_check Don't check the IO-APIC timer. This can work around
  41                  problems with incorrect timer initialization on some boards.
  42
  43    apicmaintimer Run time keeping from the local APIC timer instead
  44                  of using the PIT/HPET interrupt for this. This is useful
  45                  when the PIT/HPET interrupts are unreliable.
  46
  47    noapicmaintimer  Don't do time keeping using the APIC timer.
  48                  Useful when this option was auto selected, but doesn't work.
  49
  50    apicpmtimer
  51                  Do APIC timer calibration using the pmtimer. Implies
  52                  apicmaintimer. Useful when your PIT timer is totally
  53                  broken.
  54
  55    disable_8254_timer / enable_8254_timer
  56                  Enable interrupt 0 timer routing over the 8254 in addition to over
  57                  the IO-APIC. The kernel tries to set a sensible default.
  58
  59 Early Console
  60
  61    syntax: earlyprintk=vga
  62            earlyprintk=serial[,ttySn[,baudrate]]
  63
  64    The early console is useful when the kernel crashes before the
  65    normal console is initialized. It is not enabled by
  66    default because it has some cosmetic problems.
  67    Append ,keep to not disable it when the real console takes over.
  68    Only vga or serial at a time, not both.
  69    Currently only ttyS0 and ttyS1 are supported.
  70    Interaction with the standard serial driver is not very good.
  71    The VGA output is eventually overwritten by the real console.
  72
  73 Timing
  74
  75   notsc
  76   Don't use the CPU time stamp counter to read the wall time.
  77   This can be used to work around timing problems on multiprocessor systems
  78   with not properly synchronized CPUs.
  79
  80   report_lost_ticks
  81   Report when timer interrupts are lost because some code turned off
  82   interrupts for too long.
  83
  84   nmi_watchdog=NUMBER[,panic]
  85   NUMBER can be:
  86   0 don't use an NMI watchdog
  87   1 use the IO-APIC timer for the NMI watchdog
  88   2 use the local APIC for the NMI watchdog using a performance counter. Note
  89   This will use one performance counter and the local APIC's performance
  90   vector.
  91   When panic is specified panic when an NMI watchdog timeout occurs.
  92   This is useful when you use a panic=... timeout and need the box
  93   quickly up again.
  94
  95   nohpet
  96   Don't use the HPET timer.
  97
  98 Idle loop
  99
 100   idle=poll
 101   Don't do power saving in the idle loop using HLT, but poll for rescheduling
 102   event. This will make the CPUs eat a lot more power, but may be useful
 103   to get slightly better performance in multiprocessor benchmarks. It also
 104   makes some profiling using performance counters more accurate.
 105   Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
 106   CPUs) this option has no performance advantage over the normal idle loop.
 107   It may also interact badly with hyperthreading.
 108
 109 Rebooting
 110
 111    reboot=b[ios] | t[riple] | k[bd] [, [w]arm | [c]old]
 112    bios   Use the CPU reboot vector for warm reset
 113    warm   Don't set the cold reboot flag
 114    cold   Set the cold reboot flag
 115    triple Force a triple fault (init)
 116    kbd    Use the keyboard controller. cold reset (default)
 117
 118    Using warm reset will be much faster especially on big memory
 119    systems because the BIOS will not go through the memory check.
 120    Disadvantage is that not all hardware will be completely reinitialized
 121    on reboot so there may be boot problems on some systems.
 122
 123    reboot=force
 124
 125    Don't stop other CPUs on reboot. This can make reboot more reliable
 126    in some cases.
 127
 128 Non Executable Mappings
 129
 130   noexec=on|off
 131
 132   on      Enable(default)
 133   off     Disable
 134
 135 SMP
 136
 137   nosmp Only use a single CPU
 138
 139   maxcpus=NUMBER only use upto NUMBER CPUs
 140
 141   cpumask=MASK   only use cpus with bits set in mask
 142
 143   additional_cpus=NUM Allow NUM more CPUs for hotplug
 144                  (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
 145
 146 NUMA
 147
 148   numa=off      Only set up a single NUMA node spanning all memory.
 149
 150   numa=noacpi   Don't parse the SRAT table for NUMA setup
 151
 152   numa=fake=X   Fake X nodes and ignore NUMA setup of the actual machine.
 153
 154   numa=hotadd=percent
 155                 Only allow hotadd memory to preallocate page structures upto
 156                 percent of already available memory.
 157                 numa=hotadd=0 will disable hotadd memory.
 158
 159 ACPI
 160
 161   acpi=off      Don't enable ACPI
 162   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 163                 interpreter
 164   acpi=force    Force ACPI on (currently not needed)
 165
 166   acpi=strict   Disable out of spec ACPI workarounds.
 167
 168   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 169
 170   acpi=noirq    Don't route interrupts
 171
 172 PCI
 173
 174   pci=off       Don't use PCI
 175   pci=conf1     Use conf1 access.
 176   pci=conf2     Use conf2 access.
 177   pci=rom       Assign ROMs.
 178   pci=assign-busses    Assign busses
 179   pci=irqmask=MASK             Set PCI interrupt mask to MASK
 180   pci=lastbus=NUMBER           Scan upto NUMBER busses, no matter what the mptable says.
 181   pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 182
 183 IOMMU
 184
 185  iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
 186          [,forcesac][,fullflush][,nomerge][,noaperture]
 187    size  set size of iommu (in bytes)
 188    noagp don't initialize the AGP driver and use full aperture.
 189    off   don't use the IOMMU
 190    leak  turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
 191    memaper[=order] allocate an own aperture over RAM with size 32MB^order.
 192    noforce don't force IOMMU usage. Default.
 193    force  Force IOMMU.
 194    merge  Do SG merging. Implies force (experimental)
 195    nomerge Don't do SG merging.
 196    forcesac For SAC mode for masks <40bits  (experimental)
 197    fullflush Flush IOMMU on each allocation (default)
 198    nofullflush Don't use IOMMU fullflush
 199    allowed  overwrite iommu off workarounds for specific chipsets.
 200    soft  Use software bounce buffering (default for Intel machines)
 201    noaperture Don't touch the aperture for AGP.
 202    allowdac Allow DMA >4GB
 203             When off all DMA over >4GB is forced through an IOMMU or bounce
 204             buffering.
 205    nodac    Forbid DMA >4GB
 206    panic    Always panic when IOMMU overflows
 207
 208   swiotlb=pages[,force]
 209
 210   pages  Prereserve that many 128K pages for the software IO bounce buffering.
 211   force  Force all IO through the software TLB.
 212
 213   calgary=[64k,128k,256k,512k,1M,2M,4M,8M]
 214   calgary=[translate_empty_slots]
 215   calgary=[disable=<PCI bus number>]
 216
 217     64k,...,8M - Set the size of each PCI slot's translation table
 218     when using the Calgary IOMMU. This is the size of the translation
 219     table itself in main memory. The smallest table, 64k, covers an IO
 220     space of 32MB; the largest, 8MB table, can cover an IO space of
 221     4GB. Normally the kernel will make the right choice by itself.
 222
 223     translate_empty_slots - Enable translation even on slots that have
 224     no devices attached to them, in case a device will be hotplugged
 225     in the future.
 226
 227     disable=<PCI bus number> - Disable translation on a given PHB. For
 228     example, the built-in graphics adapter resides on the first bridge
 229     (PCI bus number 0); if translation (isolation) is enabled on this
 230     bridge, X servers that access the hardware directly from user
 231     space might stop working. Use this option if you have devices that
 232     are accessed from userspace directly on some PCI host bridge.
 233
 234 Debugging
 235
 236   oops=panic Always panic on oopses. Default is to just kill the process,
 237              but there is a small probability of deadlocking the machine.
 238              This will also cause panics on machine check exceptions.
 239              Useful together with panic=30 to trigger a reboot.
 240
 241   kstack=N   Print that many words from the kernel stack in oops dumps.
 242
 243   pagefaulttrace Dump all page faults. Only useful for extreme debugging
 244                 and will create a lot of output.
 245
 246   call_trace=[old|both|newfallback|new]
 247                 old: use old inexact backtracer
 248                 new: use new exact dwarf2 unwinder
 249                 both: print entries from both
 250                 newfallback: use new unwinder but fall back to old if it gets
 251                         stuck (default)
 252
 253   call_trace=[old|both|newfallback|new]
 254                 old: use old inexact backtracer
 255                 new: use new exact dwarf2 unwinder
 256                 both: print entries from both
 257                 newfallback: use new unwinder but fall back to old if it gets
 258                         stuck (default)
 259
 260 Misc
 261
 262   noreplacement  Don't replace instructions with more appropriate ones
 263                  for the CPU. This may be useful on asymmetric MP systems
 264                  where some CPU have less capabilities than the others.