doc: document "ceph config get <who> <option>"

... and note the confusing asymmetry with "ceph config set <who>
<option> <value>".

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

diff --git a/doc/rados/configuration/ceph-conf.rst b/doc/rados/configuration/ceph-conf.rst
index 3e11bcc19ab05b3f8cb9ba1f312a8d5effde6e70..a4a7df17ce1d8650069b485c1e4c14422f051de3 100644 (file)
--- a/doc/rados/configuration/ceph-conf.rst
+++ b/doc/rados/configuration/ceph-conf.rst
@@ -457,12 +457,17 @@ Commands
 
 The following CLI commands are used to configure the cluster:
 
-* ``ceph config dump`` will dump the entire configuration database for
-  the cluster.
+* ``ceph config dump`` will dump the entire monitors' configuration
+  database for the cluster.
 
-* ``ceph config get <who>`` will dump the configuration for a specific
-  daemon or client (e.g., ``mds.a``), as stored in the monitors'
-  configuration database.
+* ``ceph config get <who>`` will dump configuration options stored in
+  the monitors' configuration database for a specific daemon or client
+  (e.g., ``mds.a``).
+
+* ``ceph config get <who> <option>`` will show a configuration value
+  stored in the monitors' configuration database for a specific daemon
+  or client (e.g., ``mds.a``), or, if not present in the monitors'
+  configuration database, the compiled-in default value.
 
 * ``ceph config set <who> <option> <value>`` will set a configuration
   option in the monitors' configuration database.
@@ -482,6 +487,11 @@ The following CLI commands are used to configure the cluster:
   *output file*.  This command is useful for transitioning from legacy
   configuration files to centralized monitor-based configuration.
 
+Note that ``ceph config set <who> <option> <value>`` and ``ceph config get
+<who> <option>`` aren't symmetric because the latter also shows compiled-in
+default values.  In order to determine whether a configuration option is
+present in the monitors' configuration database, use ``ceph config dump``.
+
 
 Help
 ====