/etc/xen/xl.conf - XL Global/Host Configuration
file allows configuration of hostwide "xl"
For details of per-domain configuration options please see xl.cfg
The config file consists of a series of "KEY=VALUE" pairs.
A value "VALUE" is one of:
- A string, surrounded by either single or double quotes.
- A number, in either decimal, octal (using a 0 prefix) or hexadecimal
(using an "0x" prefix).
- A "NUMBER" interpreted as "False" (0) or
"True" (any other value).
- [ VALUE, VALUE, ... ]
- A list of "VALUES" of the above types. Lists are homogeneous and
are not nested.
The semantics of each "KEY" defines which form of "VALUE" is
- If set to "on" then "xl" will automatically reduce the
amount of memory assigned to domain 0 in order to free memory for new
If set to "off" then "xl" will not automatically reduce
the amount of domain 0 memory.
If set to "auto" then auto-ballooning will be disabled if the
"dom0_mem" option was provided on the Xen command line.
You are strongly recommended to set this to "off" (or
"auto") if you use the "dom0_mem" hypervisor command
line to reduce the amount of memory given to domain 0 by default.
- If disabled hotplug scripts will be called from udev, as it used to be in
the previous releases. With the default option, hotplug scripts will be
launched by xl directly.
- Sets the path to the lock file used by xl to serialise certain operations
(primarily domain creation).
- Configures the default hotplug script used by virtual network devices.
The old vifscript option is deprecated and should not be used.
- Configures the default bridge to set for virtual network devices.
The old defaultbridge option is deprecated and should not be used.
- Configures the default backend to set for virtual network devices.
- Configures the default gateway device to set for virtual network devices.
- Configures the default script used by Remus to setup network buffering.
- Configures the default script used by COLO to setup colo-proxy.
- Configures the default output format used by xl when printing
"machine readable" information. The default is to use the
"JSON" <http://www.json.org/> syntax. However for
compatibility with the previous "xm" toolstack this can be
configured to use the old "SXP" (S-Expression-like) syntax
- Configures the name of the first block device to be used for temporary
block device allocations by the toolstack. The default choice is
- If this option is enabled then when a guest is created there will be an
guarantee that there is memory available for the guest. This is an
particularly acute problem on hosts with memory over-provisioned guests
that use tmem and have self-balloon enabled (which is the default option).
The self-balloon mechanism can deflate/inflate the balloon quickly and the
amount of free memory (which "xl info" can show) is stale the
moment it is printed. When claim is enabled a reservation for the amount
of memory (see 'memory' in xl.conf(5)) is set, which is then
reduced as the domain's memory is populated and eventually reaches zero.
The free memory in "xl info" is the combination of the
hypervisor's free heap memory minus the outstanding claims value.
If the reservation cannot be meet the guest creation fails immediately
instead of taking seconds/minutes (depending on the size of the guest)
while the guest is populated.
Note that to enable tmem type guests, one needs to provide "tmem"
on the Xen hypervisor argument and as well on the Linux kernel command
Note that the claim call is not attempted if "superpages" option
is used in the guest config (see xl.cfg(5)).
- No claim is made. Memory population during guest creation will be
attempted as normal and may fail due to memory exhaustion.
- Normal memory and freeable pool of ephemeral pages (tmem) is used when
calculating whether there is enough memory free to launch a guest. This
guarantees immediate feedback whether the guest can be launched due to
memory exhaustion (which can take a long time to find out if launching
massively huge guests).