This document is for a development version of Ceph.

Converting an existing cluster to cephadm

It is possible to convert some existing clusters so that they can be managed with cephadm. This statement applies to some clusters that were deployed with ceph-deploy, ceph-ansible, or DeepSea.

This section of the documentation explains how to determine whether your clusters can be converted to a state in which they can be managed by cephadm and how to perform those conversions.


  • Cephadm works only with BlueStore OSDs.


  1. Make sure that the cephadm command line tool is available on each host in the existing cluster. See Install cephadm to learn how.

  2. Prepare each host for use by cephadm by running this command on that host:

    cephadm prepare-host
  3. Choose a version of Ceph to use for the conversion. This procedure will work with any release of Ceph that is Octopus (15.2.z) or later. The latest stable release of Ceph is the default. You might be upgrading from an earlier Ceph release at the same time that you’re performing this conversion. If you are upgrading from an earlier release, make sure to follow any upgrade-related instructions for that release.

    Pass the Ceph container image to cephadm with the following command:

    cephadm --image $IMAGE <rest of command goes here>

    The conversion begins.

  4. Confirm that the conversion is underway by running cephadm ls and making sure that the style of the daemons is changed:

    cephadm ls

    Before starting the conversion process, cephadm ls reports all existing daemons with the style legacy. As the adoption process progresses, adopted daemons will appear with the style cephadm:v1.

Adoption process

  1. Make sure that the ceph configuration has been migrated to use the cluster’s central config database. If /etc/ceph/ceph.conf is identical on all hosts, then the following command can be run on one host and will take effect for all hosts:

    ceph config assimilate-conf -i /etc/ceph/ceph.conf

    If there are configuration variations between hosts, you will need to repeat this command on each host, taking care that if there are conflicting option settings across hosts, the values from the last host will be used. During this adoption process, view the cluster’s central configuration to confirm that it is complete by running the following command:

    ceph config dump
  2. Adopt each Monitor:

    cephadm adopt --style legacy --name mon.<hostname>

    Each legacy Monitor will stop, quickly restart as a cephadm container, and rejoin the quorum.

  3. Adopt each Manager:

    cephadm adopt --style legacy --name mgr.<hostname>
  4. Enable cephadm orchestration:

    ceph mgr module enable cephadm
    ceph orch set backend cephadm
  5. Generate an SSH key for cephadm:

    ceph cephadm generate-key
    ceph cephadm get-pub-key > ~/
  6. Install the cephadm SSH key on each host in the cluster:

    ssh-copy-id -f -i ~/ root@<host>


    It is also possible to import an existing SSH key. See SSH errors in the troubleshooting document for instructions that describe how to import existing SSH keys.


    It is also possible to arrange for cephadm to use a non-root user to SSH into cluster hosts. This user needs to have passwordless sudo access. Use ceph cephadm set-user <user> and copy the SSH key to that user’s home directory on each host. See Configuring a different SSH user

  7. Tell cephadm which hosts to manage:

    ceph orch host add <hostname> [ip-address]

    This will run cephadm check-host on each host before adding it. This check ensures that the host is functioning properly. The IP address argument is recommended. If the address is not provided, then the host name will be resolved via DNS.

  8. Verify that the adopted monitor and manager daemons are visible:

    ceph orch ps
  9. Adopt all OSDs in the cluster:

    cephadm adopt --style legacy --name <name>

    For example:

    cephadm adopt --style legacy --name osd.1
    cephadm adopt --style legacy --name osd.2
  10. Redeploy CephFS MDS daemons (if deployed) by telling cephadm how many daemons to run for each file system. List CephFS file systems by name with the command ceph fs ls. Run the following command on the master nodes to redeploy the MDS daemons:

    ceph orch apply mds <fs-name> [--placement=<placement>]

    For example, in a cluster with a single file system called foo:

    ceph fs ls
    name: foo, metadata pool: foo_metadata, data pools: [foo_data ]
    ceph orch apply mds foo 2

    Confirm that the new MDS daemons have started:

    ceph orch ps --daemon-type mds

    Finally, stop and remove the legacy MDS daemons:

    systemctl stop
    rm -rf /var/lib/ceph/mds/ceph-*
  11. Redeploy Ceph Object Gateway RGW daemons if deployed. Cephadm manages RGW daemons by zone. For each zone, deploy new RGW daemons with cephadm:

    ceph orch apply rgw <svc_id> [--realm=<realm>] [--zone=<zone>] [--port=<port>] [--ssl] [--placement=<placement>]

    where <placement> can be a simple daemon count, or a list of specific hosts (see Daemon Placement). The zone and realm arguments are needed only for a multisite setup.

    After the daemons have started and you have confirmed that they are functioning, stop and remove the legacy daemons:

    systemctl stop
    rm -rf /var/lib/ceph/radosgw/ceph-*
  12. Check the output of the command ceph health detail for cephadm warnings about stray cluster daemons or hosts that are not yet managed by cephadm.

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