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/Documentation/x86_64/boot-options.txt

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  1AMD64 specific boot options
  2
  3There are many others (usually documented in driver documentation), but
  4only the AMD64 specific ones are listed here.
  5
  6Machine 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
 14APICs
 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
 28Early 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
 42Timing
 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
 67Idle 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
 75Rebooting
 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
 94Non Executable Mappings
 95
 96  noexec=on|off
 97
 98  on      Enable(default)
 99  off     Disable
100
101SMP
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
109NUMA
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
117ACPI
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
130PCI
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
141IOMMU
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
166Debugging
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
175Misc
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