1.12 Xen Boot Parameters

You can pass the following parameters to the Xen hypervisor. They can be appended to Xen’s command line by using the Boot Loader program in YaST. For more information, see Section 1.8, The Boot Loader Program.

NOTE:All parameters must be entered on a single line and be separated by a single space between each parameter.

Table 1-3 Xen Boot Parameters

Parameter

Description

noreboot

Do not automatically reboot the host when an error occurs. This parameter is useful to catch debug output if console messages via the serial line are not being caught.

nosmp

Disable SMP support. This parameter is implied by ignorebiostables.

watchdog

Enable NMI watchdog support, which can report certain types of failures.

noirqbalance

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=<pagenum>,[pagenum],...

Specify a list of pages not to be allocated because they contain bad bytes. For example, if byte 0x12345678 is bad, use the parameter badpage=0x12345.

com1=<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.

Standard configuration options, such as I/O base and IRQ, only require a prefix of the full configuration string. If the baud rate is already configured, for example, by the boot loader, then auto can be specified in place of a numeric baud rate.

console=<item>,[item] ...

Specify the destination for Xen console I/O. The default option is com1,vga.

  • vga - Use a VGA console and allow keyboard input.

  • com1 - User COM1 serial port.

  • com2H - Use COM2 serial port. Transmitted characters have the MSB set. Received characters must also have the MSB set.

  • com2L - Use COM2 serial port. Transmitted characters have the MSB cleared. Received characters must also have the MSB cleared.

The last two examples allow a single port to be shared by two subsystems, such as a console and debugger. Sharing is controlled by the MSB of each transmitted/received character.

sync_console

Force synchronous console output. This parameter is useful if the system fails unexpectedly before all available output is sent to the console. In most cases, Xen automatically enters synchronous mode when an exceptional event occurs, but this parameter provides an additional manual fallback.

conswitch=<switch-char><auto-switch-char>

Specify how to switch serial-console input between Xen and domain 0.

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 domain 0 when it boots . If it is set to x, auto-switching is disabled. If any other character is entered or if the character is omitted, auto-switching is enabled.

The default switch-char is a.

nmi=<action>

Specify what action to perform when an NMI parity or I/O error occurs.

  • fatal - Xen prints a diagnostic and then hangs.

  • dom0 - Inform domain 0 of the NMI.

  • ignore - Ignore the NMI.

mem=<kilobytes>

Set the physical RAM address limit. Any RAM appearing beyond this address in the memory map is ignored.

A suffix, such as B, K, M, or G can be appended to specify bytes, kilobytes, megabytes, or gigabytes.

dom0_mem=<kilobytes>

Set the amount of RAM to be allocated to domain 0.

A suffix, such as B, K, M, or G can be appended to specify bytes, kilobytes, megabytes, or gigabytes.

tbuf_size=<size>

Set the size of the per-CPU trace buffers in pages. The trace buffers are only enabled in debug builds, so most users can ignore this parameter.

sched=<scheduler>

Select which CPU scheduler Xen uses. Current schedulers include sedf, bvt, and credit scheduler (default).

apic_verbosity=debug,verbose

Print more detailed information about local APIC and IOAPIC configurations.

lapic

Force the use of local APIC even when it is disabled by a uniprocessor BIOS.

nolapic

Ignore the local APIC in a uniprocessor system, even if it is enabled by the BIOS.

apic=bigsmp,default,es7000,summit

Specify the NUMA platform. This information can usually be probed automatically.

apic=off,force,strict,ht,noirq,...

Modify how Xen and domain 0 parse the BIOS ACPI tables.

This parameter is automatically passed to the Linux kernel running on domain 0.

apci_skip_timer_override

Instruct Xen and domain 0 to ignore timer-interrupt overide instructions specified by the BIOS ACPI tables.

This parameter is automatically passed to the Linux kernel running on domain 0.

noapic

Instruct Xen and domain 0 to use the legacy PIC and ignore any IOAPICs that are present in the system.

This parameter is automatically passed to the Linux kernel running on domain 0.