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 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.
  14    mce=tolerancelevel (number)
  15                 0: always panic, 1: panic if deadlock possible,
  16                 2: try to avoid panic, 3: never panic or exit (for testing)
  17                 default is 1
  18                 Can be also set using sysfs which is preferable.
  19
  20    nomce (for compatibility with i386): same as mce=off
  21
  22    Everything else is in sysfs now.
  23
  24 APICs
  25
  26    apic          Use IO-APIC. Default
  27
  28    noapic        Don't use the IO-APIC.
  29
  30    disableapic   Don't use the local APIC
  31
  32    nolapic       Don't use the local APIC (alias for i386 compatibility)
  33
  34    pirq=...      See Documentation/i386/IO-APIC.txt
  35
  36    noapictimer   Don't set up the APIC timer
  37
  38    no_timer_check Don't check the IO-APIC timer. This can work around
  39                  problems with incorrect timer initialization on some boards.
  40
  41 Early Console
  42
  43    syntax: earlyprintk=vga
  44            earlyprintk=serial[,ttySn[,baudrate]]
  45
  46    The early console is useful when the kernel crashes before the
  47    normal console is initialized. It is not enabled by
  48    default because it has some cosmetic problems.
  49    Append ,keep to not disable it when the real console takes over.
  50    Only vga or serial at a time, not both.
  51    Currently only ttyS0 and ttyS1 are supported.
  52    Interaction with the standard serial driver is not very good.
  53    The VGA output is eventually overwritten by the real console.
  54
  55 Timing
  56
  57   notsc
  58   Don't use the CPU time stamp counter to read the wall time.
  59   This can be used to work around timing problems on multiprocessor systems
  60   with not properly synchronized CPUs.
  61
  62   report_lost_ticks
  63   Report when timer interrupts are lost because some code turned off
  64   interrupts for too long.
  65
  66   nmi_watchdog=NUMBER[,panic]
  67   NUMBER can be:
  68   0 don't use an NMI watchdog
  69   1 use the IO-APIC timer for the NMI watchdog
  70   2 use the local APIC for the NMI watchdog using a performance counter. Note
  71   This will use one performance counter and the local APIC's performance
  72   vector.
  73   When panic is specified panic when an NMI watchdog timeout occurs.
  74   This is useful when you use a panic=... timeout and need the box
  75   quickly up again.
  76
  77   nohpet
  78   Don't use the HPET timer.
  79
  80 Idle loop
  81
  82   idle=poll
  83   Don't do power saving in the idle loop using HLT, but poll for rescheduling
  84   event. This will make the CPUs eat a lot more power, but may be useful
  85   to get slightly better performance in multiprocessor benchmarks. It also
  86   makes some profiling using performance counters more accurate.
  87   Please note that on systems with MONITOR/MWAIT support (like Intel EM64T
  88   CPUs) this option has no performance advantage over the normal idle loop.
  89   It may also interact badly with hyperthreading.
  90
  91 Rebooting
  92
  93    reboot=b[ios] | t[riple] | k[bd] [, [w]arm | [c]old]
  94    bios   Use the CPU reboto vector for warm reset
  95    warm   Don't set the cold reboot flag
  96    cold   Set the cold reboot flag
  97    triple Force a triple fault (init)
  98    kbd    Use the keyboard controller. cold reset (default)
  99
 100    Using warm reset will be much faster especially on big memory
 101    systems because the BIOS will not go through the memory check.
 102    Disadvantage is that not all hardware will be completely reinitialized
 103    on reboot so there may be boot problems on some systems.
 104
 105    reboot=force
 106
 107    Don't stop other CPUs on reboot. This can make reboot more reliable
 108    in some cases.
 109
 110 Non Executable Mappings
 111
 112   noexec=on|off
 113
 114   on      Enable(default)
 115   off     Disable
 116
 117 SMP
 118
 119   nosmp Only use a single CPU
 120
 121   maxcpus=NUMBER only use upto NUMBER CPUs
 122
 123   cpumask=MASK   only use cpus with bits set in mask
 124
 125   additional_cpus=NUM Allow NUM more CPUs for hotplug
 126                  (defaults are specified by the BIOS or half the available CPUs)
 127
 128 NUMA
 129
 130   numa=off      Only set up a single NUMA node spanning all memory.
 131
 132   numa=noacpi   Don't parse the SRAT table for NUMA setup
 133
 134   numa=fake=X   Fake X nodes and ignore NUMA setup of the actual machine.
 135
 136 ACPI
 137
 138   acpi=off      Don't enable ACPI
 139   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 140                 interpreter
 141   acpi=force    Force ACPI on (currently not needed)
 142
 143   acpi=strict   Disable out of spec ACPI workarounds.
 144
 145   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 146
 147   acpi=noirq    Don't route interrupts
 148
 149 PCI
 150
 151   pci=off       Don't use PCI
 152   pci=conf1     Use conf1 access.
 153   pci=conf2     Use conf2 access.
 154   pci=rom       Assign ROMs.
 155   pci=assign-busses    Assign busses
 156   pci=irqmask=MASK             Set PCI interrupt mask to MASK
 157   pci=lastbus=NUMBER           Scan upto NUMBER busses, no matter what the mptable says.
 158   pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 159
 160 IOMMU
 161
 162  iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
 163          [,forcesac][,fullflush][,nomerge][,noaperture]
 164    size  set size of iommu (in bytes)
 165    noagp don't initialize the AGP driver and use full aperture.
 166    off   don't use the IOMMU
 167    leak  turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
 168    memaper[=order] allocate an own aperture over RAM with size 32MB^order.
 169    noforce don't force IOMMU usage. Default.
 170    force  Force IOMMU.
 171    merge  Do SG merging. Implies force (experimental)
 172    nomerge Don't do SG merging.
 173    forcesac For SAC mode for masks <40bits  (experimental)
 174    fullflush Flush IOMMU on each allocation (default)
 175    nofullflush Don't use IOMMU fullflush
 176    allowed  overwrite iommu off workarounds for specific chipsets.
 177    soft  Use software bounce buffering (default for Intel machines)
 178    noaperture Don't touch the aperture for AGP.
 179
 180   swiotlb=pages[,force]
 181
 182   pages  Prereserve that many 128K pages for the software IO bounce buffering.
 183   force  Force all IO through the software TLB.
 184
 185 Debugging
 186
 187   oops=panic Always panic on oopses. Default is to just kill the process,
 188              but there is a small probability of deadlocking the machine.
 189              This will also cause panics on machine check exceptions.
 190              Useful together with panic=30 to trigger a reboot.
 191
 192   kstack=N   Print that many words from the kernel stack in oops dumps.
 193
 194 Misc
 195
 196   noreplacement  Don't replace instructions with more appropiate ones
 197                  for the CPU. This may be useful on asymmetric MP systems
 198                  where some CPU have less capabilities than the others.