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Xen 3.0 Virtualization User Guide
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10.3 Xen Boot Options

These options are used to configure Xen's behaviour at runtime. They should be appended to Xen's command line, either manually or by editing grub.conf.

Don't reboot the machine automatically on errors. This is useful to catch debug output if you aren't catching console messages via the serial line.
Disable SMP support. This option is implied by `ignorebiostables'.
Enable NMI watchdog which can report certain failures.
Disable software IRQ balancing and affinity. This can be used on systems such as Dell 1850/2850 that have workarounds in hardware for IRQ-routing issues.
badpage=<page number>,<page number>, ...
Specify a list of pages not to be allocated for use because they contain bad bytes. For example, if your memory tester says that byte 0x12345678 is bad, you would place `badpage=0x12345' on Xen's command line.
com1=<baud>,DPS,<io_base>,<irq> com2=<baud>,DPS,<io_base>,<irq>

Xen supports up to two 16550-compatible serial ports. For example: `com1=9600, 8n1, 0x408, 5' maps COM1 to a 9600-baud port, 8 data bits, no parity, 1 stop bit, I/O port base 0x408, IRQ 5. If some configuration options are standard (e.g., I/O base and IRQ), then only a prefix of the full configuration string need be specified. If the baud rate is pre-configured (e.g., by the bootloader) then you can specify `auto' in place of a numeric baud rate.
console=<specifier list>
Specify the destination for Xen console I/O. This is a comma-separated list of, for example:
Use VGA console and allow keyboard input.
Use serial port com1.
Use serial port com2. Transmitted chars will have the MSB set. Received chars must have MSB set.
Use serial port com2. Transmitted chars will have the MSB cleared. Received chars must have MSB cleared.
The latter two examples allow a single port to be shared by two subsystems (e.g. console and debugger). Sharing is controlled by MSB of each transmitted/received character. [NB. Default for this option is `com1,vga']
Force synchronous console output. This is useful if you system fails unexpectedly before it has sent all available output to the console. In most cases Xen will automatically enter synchronous mode when an exceptional event occurs, but this option provides a manual fallback.
Specify how to switch serial-console input between Xen and DOM0. The required sequence is CTRL-<switch-char> pressed three times. Specifying the backtick character disables switching. The <auto-switch-char> specifies whether Xen should auto-switch input to DOM0 when it boots -- if it is `x' then auto-switching is disabled. Any other value, or omitting the character, enables auto-switching. [NB. Default switch-char is `a'.]
Specify what to do with an NMI parity or I/O error.
`nmi=fatal': Xen prints a diagnostic and then hangs.
`nmi=dom0': Inform DOM0 of the NMI.
`nmi=ignore': Ignore the NMI.
Set the physical RAM address limit. Any RAM appearing beyond this physical address in the memory map will be ignored. This parameter may be specified with a B, K, M or G suffix, representing bytes, kilobytes, megabytes and gigabytes respectively. The default unit, if no suffix is specified, is kilobytes.
Set the amount of memory to be allocated to domain0. In Xen 3.x the parameter may be specified with a B, K, M or G suffix, representing bytes, kilobytes, megabytes and gigabytes respectively; if no suffix is specified, the parameter defaults to kilobytes. In previous versions of Xen, suffixes were not supported and the value is always interpreted as kilobytes.
Set the size of the per-cpu trace buffers, in pages (default 1). Note that the trace buffers are only enabled in debug builds. Most users can ignore this feature completely.
Select the CPU scheduler Xen should use. The current possibilities are `sedf' (default) and `bvt'.
Print more detailed information about local APIC and IOAPIC configuration.
Force use of local APIC even when left disabled by uniprocessor BIOS.
Ignore local APIC in a uniprocessor system, even if enabled by the BIOS.
Specify NUMA platform. This can usually be probed automatically.

In addition, the following options may be specified on the Xen command line. Since domain 0 shares responsibility for booting the platform, Xen will automatically propagate these options to its command line. These options are taken from Linux's command-line syntax with unchanged semantics.

Modify how Xen (and domain 0) parses the BIOS ACPI tables.
Instruct Xen (and domain 0) to ignore timer-interrupt override instructions specified by the BIOS ACPI tables.
Instruct Xen (and domain 0) to ignore any IOAPICs that are present in the system, and instead continue to use the legacy PIC.

Xen 3.0 Virtualization User Guide
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  Published under the terms of the GNU General Public License Design by Interspire