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
  10    nomce (for compatibility with i386): same as mce=off
  11
  12    Everything else is in sysfs now.
  13
  14 APICs
  15
  16    apic          Use IO-APIC. Default
  17
  18    noapic        Don't use the IO-APIC.
  19
  20    disableapic   Don't use the local APIC
  21
  22    nolapic       Don't use the local APIC (alias for i386 compatibility)
  23
  24    pirq=...      See Documentation/i386/IO-APIC.txt
  25
  26    noapictimer   Don't set up the APIC timer
  27
  28 Early Console
  29
  30    syntax: earlyprintk=vga
  31            earlyprintk=serial[,ttySn[,baudrate]]
  32
  33    The early console is useful when the kernel crashes before the
  34    normal console is initialized. It is not enabled by
  35    default because it has some cosmetic problems.
  36    Append ,keep to not disable it when the real console takes over.
  37    Only vga or serial at a time, not both.
  38    Currently only ttyS0 and ttyS1 are supported.
  39    Interaction with the standard serial driver is not very good.
  40    The VGA output is eventually overwritten by the real console.
  41
  42 Timing
  43
  44   notsc
  45   Don't use the CPU time stamp counter to read the wall time.
  46   This can be used to work around timing problems on multiprocessor systems
  47   with not properly synchronized CPUs. Only useful with a SMP kernel
  48
  49   report_lost_ticks
  50   Report when timer interrupts are lost because some code turned off
  51   interrupts for too long.
  52
  53   nmi_watchdog=NUMBER[,panic]
  54   NUMBER can be:
  55   0 don't use an NMI watchdog
  56   1 use the IO-APIC timer for the NMI watchdog
  57   2 use the local APIC for the NMI watchdog using a performance counter. Note
  58   This will use one performance counter and the local APIC's performance
  59   vector.
  60   When panic is specified panic when an NMI watchdog timeout occurs.
  61   This is useful when you use a panic=... timeout and need the box
  62   quickly up again.
  63
  64   nohpet
  65   Don't use the HPET timer.
  66
  67 Idle loop
  68
  69   idle=poll
  70   Don't do power saving in the idle loop using HLT, but poll for rescheduling
  71   event. This will make the CPUs eat a lot more power, but may be useful
  72   to get slightly better performance in multiprocessor benchmarks. It also
  73   makes some profiling using performance counters more accurate.
  74
  75 Rebooting
  76
  77    reboot=b[ios] | t[riple] | k[bd] [, [w]arm | [c]old]
  78    bios   Use the CPU reboto vector for warm reset
  79    warm   Don't set the cold reboot flag
  80    cold   Set the cold reboot flag
  81    triple Force a triple fault (init)
  82    kbd    Use the keyboard controller. cold reset (default)
  83
  84    Using warm reset will be much faster especially on big memory
  85    systems because the BIOS will not go through the memory check.
  86    Disadvantage is that not all hardware will be completely reinitialized
  87    on reboot so there may be boot problems on some systems.
  88
  89    reboot=force
  90
  91    Don't stop other CPUs on reboot. This can make reboot more reliable
  92    in some cases.
  93
  94 Non Executable Mappings
  95
  96   noexec=on|off
  97
  98   on      Enable(default)
  99   off     Disable
 100
 101 SMP
 102
 103   nosmp Only use a single CPU
 104
 105   maxcpus=NUMBER only use upto NUMBER CPUs
 106
 107   cpumask=MASK   only use cpus with bits set in mask
 108
 109 NUMA
 110
 111   numa=off      Only set up a single NUMA node spanning all memory.
 112
 113   numa=noacpi   Don't parse the SRAT table for NUMA setup
 114
 115   numa=fake=X   Fake X nodes and ignore NUMA setup of the actual machine.
 116
 117 ACPI
 118
 119   acpi=off      Don't enable ACPI
 120   acpi=ht       Use ACPI boot table parsing, but don't enable ACPI
 121                 interpreter
 122   acpi=force    Force ACPI on (currently not needed)
 123
 124   acpi=strict   Disable out of spec ACPI workarounds.
 125
 126   acpi_sci={edge,level,high,low}  Set up ACPI SCI interrupt.
 127
 128   acpi=noirq    Don't route interrupts
 129
 130 PCI
 131
 132   pci=off       Don't use PCI
 133   pci=conf1     Use conf1 access.
 134   pci=conf2     Use conf2 access.
 135   pci=rom       Assign ROMs.
 136   pci=assign-busses    Assign busses
 137   pci=irqmask=MASK             Set PCI interrupt mask to MASK
 138   pci=lastbus=NUMBER           Scan upto NUMBER busses, no matter what the mptable says.
 139   pci=noacpi            Don't use ACPI to set up PCI interrupt routing.
 140
 141 IOMMU
 142
 143  iommu=[size][,noagp][,off][,force][,noforce][,leak][,memaper[=order]][,merge]
 144          [,forcesac][,fullflush][,nomerge][,noaperture]
 145    size  set size of iommu (in bytes)
 146    noagp don't initialize the AGP driver and use full aperture.
 147    off   don't use the IOMMU
 148    leak  turn on simple iommu leak tracing (only when CONFIG_IOMMU_LEAK is on)
 149    memaper[=order] allocate an own aperture over RAM with size 32MB^order.
 150    noforce don't force IOMMU usage. Default.
 151    force  Force IOMMU.
 152    merge  Do SG merging. Implies force (experimental)
 153    nomerge Don't do SG merging.
 154    forcesac For SAC mode for masks <40bits  (experimental)
 155    fullflush Flush IOMMU on each allocation (default)
 156    nofullflush Don't use IOMMU fullflush
 157    allowed  overwrite iommu off workarounds for specific chipsets.
 158    soft  Use software bounce buffering (default for Intel machines)
 159    noaperture Don't touch the aperture for AGP.
 160
 161   swiotlb=pages[,force]
 162
 163   pages  Prereserve that many 128K pages for the software IO bounce buffering.
 164   force  Force all IO through the software TLB.
 165
 166 Debugging
 167
 168   oops=panic Always panic on oopses. Default is to just kill the process,
 169              but there is a small probability of deadlocking the machine.
 170              This will also cause panics on machine check exceptions.
 171              Useful together with panic=30 to trigger a reboot.
 172
 173   kstack=N   Print that many words from the kernel stack in oops dumps.
 174
 175 Misc
 176
 177   noreplacement  Don't replace instructions with more appropiate ones
 178                                  for the CPU. This may be useful on asymmetric MP systems
 179                                  where some CPU have less capabilities than the others.
 180