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 Early Console
  44
  45    syntax: earlyprintk=vga
  46            earlyprintk=serial[,ttySn[,baudrate]]
  47
  48    The early console is useful when the kernel crashes before the
  49    normal console is initialized. It is not enabled by
  50    default because it has some cosmetic problems.
  51    Append ,keep to not disable it when the real console takes over.
  52    Only vga or serial at a time, not both.
  53    Currently only ttyS0 and ttyS1 are supported.
  54    Interaction with the standard serial driver is not very good.
  55    The VGA output is eventually overwritten by the real console.
  56
  57 Timing
  58
  59   notsc
  60   Don't use the CPU time stamp counter to read the wall time.
  61   This can be used to work around timing problems on multiprocessor systems
  62   with not properly synchronized CPUs.
  63
  64   report_lost_ticks
  65   Report when timer interrupts are lost because some code turned off
  66   interrupts for too long.
  67
  68   nmi_watchdog=NUMBER[,panic]
  69   NUMBER can be:
  70   0 don't use an NMI watchdog
  71   1 use the IO-APIC timer for the NMI watchdog
  72   2 use the local APIC for the NMI watchdog using a performance counter. Note
  73   This will use one performance counter and the local APIC's performance
  74   vector.
  75   When panic is specified panic when an NMI watchdog timeout occurs.
  76   This is useful when you use a panic=... timeout and need the box
  77   quickly up again.
  78
  79   nohpet
  80   Don't use the HPET timer.
  81
  82 Idle loop
  83
  84   idle=poll
  85   Don't do power saving in the idle loop using HLT, but poll for rescheduling
  86   event. This will make the CPUs eat a lot more power, but may be useful
  87   to get slightly better performance in multiprocessor benchmarks. It also
  88   makes some profiling using performance counters more accurate.
  89   Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
  90   CPUs) this option has no performance advantage over the normal idle loop.
  91   It may also interact badly with hyperthreading.
  92
  93 Rebooting
  94
  95    reboot=b[ios] | t[riple] | k[bd] [, [w]arm | [c]old]
  96    bios   Use the CPU reboto vector for warm reset
  97    warm   Don't set the cold reboot flag
  98    cold   Set the cold reboot flag
  99    triple Force a triple fault (init)
 100    kbd    Use the keyboard controller. cold reset (default)
 101
 102    Using warm reset will be much faster especially on big memory
 103    systems because the BIOS will not go through the memory check.
 104    Disadvantage is that not all hardware will be completely reinitialized
 105    on reboot so there may be boot problems on some systems.
 106
 107    reboot=force
 108
 109    Don't stop other CPUs on reboot. This can make reboot more reliable
 110    in some cases.
 111
 112 Non Executable Mappings
 113
 114   noexec=on|off
 115
 116   on      Enable(default)
 117   off     Disable
 118
 119 SMP
 120
 121   nosmp Only use a single CPU
 122
 123   maxcpus=NUMBER only use upto NUMBER CPUs
 124
 125   cpumask=MASK   only use cpus with bits set in mask
 126
 127   additional_cpus=NUM Allow NUM more CPUs for hotplug
 128                  (defaults are specified by the BIOS, see Documentation/x86_64/cpu-hotplug-spec)
 129
 130 NUMA
 131
 132   numa=off      Only set up a single NUMA node spanning all memory.
 133
 134   numa=noacpi   Don't parse the SRAT table for NUMA setup
 135
 136   numa=fake=X   Fake X nodes and ignore NUMA setup of the actual machine.
 137
 138 ACPI
 139
 140   acpi=off      Don't enable ACPI
 141   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 142                 interpreter
 143   acpi=force    Force ACPI on (currently not needed)
 144
 145   acpi=strict   Disable out of spec ACPI workarounds.
 146
 147   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 148
 149   acpi=noirq    Don't route interrupts
 150
 151 PCI
 152
 153   pci=off       Don't use PCI
 154   pci=conf1     Use conf1 access.
 155   pci=conf2     Use conf2 access.
 156   pci=rom       Assign ROMs.
 157   pci=assign-busses    Assign busses
 158   pci=irqmask=MASK             Set PCI interrupt mask to MASK
 159   pci=lastbus=NUMBER           Scan upto NUMBER busses, no matter what the mptable says.
 160   pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 161
 162 IOMMU
 163
 164  iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
 165          [,forcesac][,fullflush][,nomerge][,noaperture]
 166    size  set size of iommu (in bytes)
 167    noagp don't initialize the AGP driver and use full aperture.
 168    off   don't use the IOMMU
 169    leak  turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
 170    memaper[=order] allocate an own aperture over RAM with size 32MB^order.
 171    noforce don't force IOMMU usage. Default.
 172    force  Force IOMMU.
 173    merge  Do SG merging. Implies force (experimental)
 174    nomerge Don't do SG merging.
 175    forcesac For SAC mode for masks <40bits  (experimental)
 176    fullflush Flush IOMMU on each allocation (default)
 177    nofullflush Don't use IOMMU fullflush
 178    allowed  overwrite iommu off workarounds for specific chipsets.
 179    soft  Use software bounce buffering (default for Intel machines)
 180    noaperture Don't touch the aperture for AGP.
 181
 182   swiotlb=pages[,force]
 183
 184   pages  Prereserve that many 128K pages for the software IO bounce buffering.
 185   force  Force all IO through the software TLB.
 186
 187 Debugging
 188
 189   oops=panic Always panic on oopses. Default is to just kill the process,
 190              but there is a small probability of deadlocking the machine.
 191              This will also cause panics on machine check exceptions.
 192              Useful together with panic=30 to trigger a reboot.
 193
 194   kstack=N   Print that many words from the kernel stack in oops dumps.
 195
 196   pagefaulttrace Dump all page faults. Only useful for extreme debugging
 197                 and will create a lot of output.
 198
 199 Misc
 200
 201   noreplacement  Don't replace instructions with more appropriate ones
 202                  for the CPU. This may be useful on asymmetric MP systems
 203                  where some CPU have less capabilities than the others.