# Xen Hypervisor Command Line Options

This document covers the command line options which the Xen
Hypervisor.

## Types of parameter

Most parameters take the form `option=value`.  Different options on
the command line should be space delimited.  All options are case
sensitive, as are all values unless explicitly noted.

### Boolean (`<boolean>`)

All boolean option may be explicitly enabled using a `value` of
> `yes`, `on`, `true`, `enable` or `1`

They may be explicitly disabled using a `value` of
> `no`, `off`, `false`, `disable` or `0`

In addition, a boolean option may be enabled by simply stating its
name, and may be disabled by prefixing its name with `no-`.

####Examples

Enable noreboot mode
> `noreboot=true`

Disable x2apic support (if present)
> `x2apic=off`

Enable synchronous console mode
> `sync_console`

Explicitly specifying any value other than those listed above is
undefined, as is stacking a `no-` prefix with an explicit value.

### Integer (`<integer>`)

An integer parameter will default to decimal and may be prefixed with
a `-` for negative numbers.  Alternatively, a hexadecimal number may be
used by prefixing the number with `0x`, or an octal number may be used
if a leading `0` is present.

Providing a string which does not validly convert to an integer is
undefined.

### Size (`<size>`)

A size parameter may be any integer, with a size suffix

* `G` or `g`: GiB (2^30)
* `M` or `m`: MiB (2^20)
* `K` or `k`: KiB (2^10)
* `B` or `b`: Bytes

Without a size suffix, the default will be kilo.  Providing a suffix
other than those listed above is undefined.

### String

Many parameters are more complicated and require more intricate
configuration.  The detailed description of each individual parameter
specify which values are valid.

### List

Some options take a comma separated list of values.

### Combination

Some parameters act as combinations of the above, most commonly a mix
of Boolean and String.  These are noted in the relevant sections.

## Parameter details

### acpi
> `= force | ht | noirq | <boolean>`

**String**, or **Boolean** to disable.

The **acpi** option is used to control a set of four related boolean
flags; `acpi_force`, `acpi_ht`, `acpi_noirq` and `acpi_disabled`.

By default, Xen will scan the DMI data and blacklist certain systems
which are known to have broken ACPI setups.  Providing `acpi=force`
will cause Xen to ignore the blacklist and attempt to use all ACPI
features.

Using `acpi=ht` causes Xen to parse the ACPI tables enough to
enumerate all CPUs, but will not use other ACPI features.  This is not
common, and only has an effect if your system is blacklisted.

The `acpi=noirq` option causes Xen to not parse the ACPI MADT table
looking for IO-APIC entries.  This is also not common, and any system
which requires this option to function should be blacklisted.
Additionally, this will not prevent Xen from finding IO-APIC entries
from the MP tables.

Finally, any of the boolean false options can be used to disable ACPI
usage entirely.

Because responsibility for ACPI processing is shared between Xen and
the domain 0 kernel this option is automatically propagated to the
domain 0 command line

### acpi\_apic\_instance
> `= <integer>`

Specify which ACPI MADT table to parse for APIC information, if more
than one is present.

### acpi\_pstate\_strict
> `= <integer>`

### acpi\_skip\_timer\_override
> `= <boolean>`

Instruct Xen to ignore timer-interrupt override.

Because responsibility for ACPI processing is shared between Xen and
the domain 0 kernel this option is automatically propagated to the
domain 0 command line

### acpi\_sleep
> `= s3_bios | s3_mode`

### allowsuperpage
> `= <boolean>`

> Default: `true`

Permit Xen to use superpages when performing memory management.

### apic
> `= summit | bigsmp | default`

Override Xen's logic for choosing the APIC driver.  By default, if
there are more than 8 CPUs, Xen will switch to `bigsmp` over
`default`.

### allow\_unsafe
> `= <boolean>`

> Default: `false`

Force boot on potentially unsafe systems. By default Xen will refuse
to boot on systems with the following errata:

* AMD Erratum 121. Processors with this erratum are subject to a guest
  triggerable Denial of Service. Override only if you trust all of
  your PV guests.

### apic\_verbosity
> `= verbose | debug`

Increase the verbosity of the APIC code from the default value.

### ats
> `= <boolean>`

> Default: `true`

Permits Xen to set up and use PCI Address Translation Services, which
is required for PCI Passthrough.

### availmem
> `= <size>`

> Default: `0` (no limit)

Specify a maximum amount of available memory, to which Xen will clamp
the e820 table.

### badpage
> `= List of [ <integer> | <integer>-<integer> ]`

Specify that certain pages, or certain ranges of pages contain bad
bytes and should not be used.  For example, if your memory tester says
that byte `0x12345678` is bad, you would place `badpage=0x12345` on
Xen's command line.

### bootscrub
> `= <boolean>`

> Default: `true`

Scrub free RAM during boot.  This is a safety feature to prevent
accidentally leaking sensitive VM data into other VMs if Xen crashes
and reboots.

### cachesize
> `= <size>`

If set, override Xen's calculation of the level 2 cache line size.

### clocksource
> `= pit | hpet | cyclone | acpi`

If set, override Xen's default choice for the platform timer.

### com1,com2
> `= <baud>[/<clock_hz>][,[DPS][,[<io-base>|pci|amt][,[<irq>][,[<port-bdf>][,[<bridge-bdf>]]]]]]`

Both option `com1` and `com2` follow the same format.

* `<baud>` may be either an integer baud rate, or the string `auto` if
  the bootloader or other earlier firmware has already set it up.
* Optionally, a clock speed measured in hz can be specified.
* `DPS` represents the number of data bits, the parity, and the number
  of stop bits.

  `D` is an integer between 5 and 8 for the number of data bits.

  `P` is a single character representing the type of parity:

   * `n` No
   * `o` Odd
   * `e` Even
   * `m` Mark
   * `s` Space

  `S` is an integer 1 or 2 for the number of stop bits.

* `<io-base>` is an integer which specifies the IO base port for UART
  registers.
* `<irq>` is the IRQ number to use, or `0` to use the UART in poll
  mode only.
* `<port-bdf>` is the PCI location of the UART, in
  `<bus>:<device>.<function>` notation.
* `<bridge-bdf>` is the PCI bridge behind which is the UART, in
  `<bus>:<device>.<function>` notation.
* `pci` indicates that Xen should scan the PCI bus for the UART,
  avoiding Intel AMT devices.
* `amt` indicated that Xen should scan the PCI bus for the UART,
  including Intel AMT devices if present.

A typical setup for most situations might be `com1=115200,8n1`

### conring\_size
> `= <size>`

> Default: `conring_size=16k`

Specify the size of the console ring buffer.

### console
> `= List of [ vga | com1[H,L] | com2[H,L] | dbgp | none ]`

> Default: `console=com1,vga`

Specify which console(s) Xen should use.

`vga` indicates that Xen should try and use the vga graphics adapter.

`com1` and `com2` indicates that Xen should use serial ports 1 and 2
respectively.  Optionally, these arguments may be followed by an `H` or
`L`.  `H` indicates that transmitted characters will have their MSB
set, while received characters must have their MSB set.  `L` indicates
the converse; transmitted and received characters will have their MSB