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Chapter 3. Metavariables

Metavariables simplify Ceph Storage Cluster configuration dramatically. When a metavariable is set in a configuration value, Ceph expands the metavariable into a concrete value. Metavariables are very powerful when used within the [global], [osd], [mon] or [client] sections of your configuration file; however, you may also use them with the admin socket. Ceph metavariables are similar to Bash shell expansion.

Ceph supports the following metavariables:

$cluster

Description
Expands to the Ceph Storage Cluster name. Useful when running multiple Ceph Storage Clusters on the same hardware.
Example
/etc/ceph/$cluster.keyring
Default
ceph

$type

Description
Expands to one of osd or mon, depending on the type of the instant daemon.
Example
/var/lib/ceph/$type

$id

Description
Expands to the daemon identifier. For osd.0, this would be 0.
Example
/var/lib/ceph/$type/$cluster-$id

$host

Description
Expands to the host name of the instant daemon.

$name

Description
Expands to $type.$id.
Example
/var/run/ceph/$cluster-$name.asok
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