=head1 NAME

/etc/xen/xl.conf - XL Global/Host Configuration 

=head1 DESCRIPTION

The F<xl.conf> file allows configuration of hostwide C<xl> toolstack
options.

For details of per-domain configuration options please see
L<xl.cfg(5)>.

=head1 SYNTAX

The config file consists of a series of C<KEY=VALUE> pairs.

A value C<VALUE> is one of:

=over 4

=item B<"STRING">

A string, surrounded by either single or double quotes.

=item B<NUMBER>

A number, in either decimal, octal (using a C<0> prefix) or
hexadecimal (using an C<0x> prefix).

=item B<BOOLEAN>

A C<NUMBER> interpreted as C<False> (C<0>) or C<True> (any other
value).

=item B<[ VALUE, VALUE, ... ]>

A list of C<VALUES> of the above types. Lists are homogeneous and are
not nested.

=back

The semantics of each C<KEY> defines which form of C<VALUE> is required.

=head1 OPTIONS

=over 4

=item B<autoballoon="off"|"on"|"auto">

If set to "on" then C<xl> will automatically reduce the amount of
memory assigned to domain 0 in order to free memory for new domains.

If set to "off" then C<xl> will not automatically reduce the amount of
domain 0 memory.

If set to "auto" then auto-ballooning will be disabled if the
C<dom0_mem> option was provided on the Xen command line.

You are strongly recommended to set this to C<"off"> (or C<"auto">) if
you use the C<dom0_mem> hypervisor command line to reduce the amount
of memory given to domain 0 by default.

Default: C<"auto">

=item B<run_hotplug_scripts=BOOLEAN>

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.

Default: C<1>

=item B<lockfile="PATH">

Sets the path to the lock file used by xl to serialise certain
operations (primarily domain creation).

Default: C</var/lock/xl>

=item B<vif.default.script="PATH">

Configures the default hotplug script used by virtual network devices.

The old B<vifscript> option is deprecated and should not be used.

Default: C</etc/xen/scripts/vif-bridge>

=item B<vif.default.bridge="NAME">

Configures the default bridge to set for virtual network devices.

The old B<defaultbridge> option is deprecated and should not be used.

Default: C<xenbr0>

=item B<vif.default.backend="NAME">

Configures the default backend to set for virtual network devices.

Default: C<0>

=item B<vif.default.gatewaydev="NAME">

Configures the default gateway device to set for virtual network devices.

Default: C<None>

=item B<output_format="json|sxp">

Configures the default output format used by xl when printing "machine
readable" information. The default is to use the C<JSON>
L<http://www.json.org/> syntax. However for compatibility with the
previous C<xm> toolstack this can be configured to use the old C<SXP>
(S-Expression-like) syntax instead.

Default: C<json>

=item B<blkdev_start="NAME">

Configures the name of the first block device to be used for temporary
block device allocations by the toolstack.
The default choice is "xvda".

=item B<claim_mode=BOOLEAN>

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 C<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 C<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 C<tmem> on the
Xen hypervisor argument and as well on the Linux kernel command line.

Note that the claim call is not attempted if C<superpages> option is
used in the guest config (see xl.cfg(5)).

Default: C<1>

=over 4

=item C<0>

No claim is made. Memory population during guest creation will be
attempted as normal and may fail due to memory exhaustion.

=item C<1>

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).

=back

=back

=head1 SEE ALSO

=over 4

=item L<xl(1)>

=item L<xl.cfg(5)>

=item http://www.json.org/

=back