doc/cephadm: document the default 'admin' label

Signed-off-by: Sage Weil <sage@newdream.net>

doc/cephadm/host-management.rst

@@ -37,7 +37,7 @@ To add each new host to the cluster, perform two steps:
 
    .. prompt:: bash #
 
-     ceph orch host add *newhost*
+     ceph orch host add *newhost* [*<label1> ...*]
 
    For example:
 
@@ -45,7 +45,16 @@ To add each new host to the cluster, perform two steps:
 
      ceph orch host add host2
      ceph orch host add host3
-     
+
+   One or more labels can also be included to immediately label the
+   new host.  For example, by default the ``_admin`` label will make
+   cephadm maintain a copy of the ``ceph.conf`` file and a
+   ``client.admin`` keyring file in ``/etc/ceph``:
+
+   .. prompt:: bash #
+
+       ceph orch host add host4 _admin
+
 .. _cephadm-removing-hosts:
 
 Removing Hosts

doc/cephadm/install.rst

@@ -148,11 +148,14 @@ This command will:
   host.
 * Generate a new SSH key for the Ceph cluster and add it to the root
   user's ``/root/.ssh/authorized_keys`` file.
+* Write a copy of the public key to ``/etc/ceph/ceph.pub``.
 * Write a minimal configuration file to ``/etc/ceph/ceph.conf``. This
   file is needed to communicate with the new cluster.
 * Write a copy of the ``client.admin`` administrative (privileged!)
   secret key to ``/etc/ceph/ceph.client.admin.keyring``.
-* Write a copy of the public key to ``/etc/ceph/ceph.pub``.
+* Add the ``_admin`` label to the bootstrap host.  By default, any host
+  with this label will (also) get a copy of ``/etc/ceph/ceph.conf`` and
+  ``/etc/ceph/ceph.client.admin.keyring``.
 
 Further information about cephadm bootstrap 
 -------------------------------------------
@@ -272,6 +275,16 @@ Adding Hosts
 
 Next, add all hosts to the cluster by following :ref:`cephadm-adding-hosts`.
 
+By default, a ``ceph.conf`` file and a copy of the ``client.admin`` keyring
+are maintained in ``/etc/ceph`` on all hosts with the ``_admin`` label, which is initially
+applied only to the bootstrap host. We usually recommend that one or more other hosts be
+given the ``_admin`` label so that the Ceph CLI (e.g., via ``cephadm shell``) is easily
+accessible on multiple hosts.  To add the ``_admin`` label to additional host(s),
+
+  .. prompt:: bash #
+
+    ceph orch host label add *<host>* _admin
+
 Adding additional MONs
 ======================
 

doc/cephadm/operations.rst

@@ -306,7 +306,7 @@ Cephadm can distribute copies of the ``ceph.conf`` and client keyring
 files to hosts.  For example, it is usually a good idea to store a
 copy of the config and ``client.admin`` keyring on any hosts that will
 be used to administer the cluster via the CLI.  By default, cephadm will do
-this for any nodes with the ``admin`` label (which normally includes the bootstrap
+this for any nodes with the ``_admin`` label (which normally includes the bootstrap
 host).
 
 When a client keyring is placed under management, cephadm will:
@@ -330,7 +330,7 @@ To place a keyring under management::
 
 - By default, the *path* will be ``/etc/ceph/client.{entity}.keyring``, which is where
   Ceph looks by default.  Be careful specifying alternate locations as existing files
-  maybe overwritten.
+  may be overwritten.
 - A placement of ``*`` (all hosts) is common.
 - The mode defaults to ``0600`` and ownership to ``0:0`` (user root, group root).