Deploying a new Ceph cluster

Cephadm creates a new Ceph cluster by “bootstrapping” on a single host, expanding the cluster to encompass any additional hosts, and then deploying the needed services.


  • Python 3

  • Systemd

  • Podman or Docker for running containers

  • Time synchronization (such as chrony or NTP)

  • LVM2 for provisioning storage devices

Any modern Linux distribution should be sufficient. Dependencies are installed automatically by the bootstrap process below.

See the section Compatibility With Podman Versions for a table of Ceph versions that are compatible with Podman. Not every version of Podman is compatible with Ceph.

Install cephadm

There are two ways to install cephadm:

  1. a curl-based installation method

  2. distribution-specific installation methods

curl-based installation

  • Use curl to fetch the most recent version of the standalone script.

    curl --silent --remote-name --location

    Make the cephadm script executable:

    chmod +x cephadm

    This script can be run directly from the current directory:

    ./cephadm <arguments...>
  • Although the standalone script is sufficient to get a cluster started, it is convenient to have the cephadm command installed on the host. To install the packages that provide the cephadm command, run the following commands:

    ./cephadm add-repo --release pacific
    ./cephadm install

    Confirm that cephadm is now in your PATH by running which:

    which cephadm

    A successful which cephadm command will return this:


distribution-specific installations


The methods of installing cephadm in this section are distinct from the curl-based method above. Use either the curl-based method above or one of the methods in this section, but not both the curl-based method and one of these.

Some Linux distributions may already include up-to-date Ceph packages. In that case, you can install cephadm directly. For example:

In Ubuntu:

apt install -y cephadm

In CentOS Stream:

dnf install --assumeyes centos-release-ceph-pacific.noarch
dnf install --assumeyes cephadm

In Fedora:

dnf -y install cephadm


zypper install -y cephadm

Bootstrap a new cluster

What to know before you bootstrap

The first step in creating a new Ceph cluster is running the cephadm bootstrap command on the Ceph cluster’s first host. The act of running the cephadm bootstrap command on the Ceph cluster’s first host creates the Ceph cluster’s first “monitor daemon”, and that monitor daemon needs an IP address. You must pass the IP address of the Ceph cluster’s first host to the ceph bootstrap command, so you’ll need to know the IP address of that host.


If there are multiple networks and interfaces, be sure to choose one that will be accessible by any host accessing the Ceph cluster.

Running the bootstrap command

Run the ceph bootstrap command:

cephadm bootstrap --mon-ip *<mon-ip>*

This command will:

  • Create a monitor and manager daemon for the new cluster on the local 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/

  • 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.

  • 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

The default bootstrap behavior will work for most users. But if you’d like immediately to know more about cephadm bootstrap, read the list below.

Also, you can run cephadm bootstrap -h to see all of cephadm’s available options.

  • By default, Ceph daemons send their log output to stdout/stderr, which is picked up by the container runtime (docker or podman) and (on most systems) sent to journald. If you want Ceph to write traditional log files to /var/log/ceph/$fsid, use the --log-to-file option during bootstrap.

  • Larger Ceph clusters perform better when (external to the Ceph cluster) public network traffic is separated from (internal to the Ceph cluster) cluster traffic. The internal cluster traffic handles replication, recovery, and heartbeats between OSD daemons. You can define the cluster network by supplying the --cluster-network option to the bootstrap subcommand. This parameter must define a subnet in CIDR notation (for example or fe80::/64).

  • cephadm bootstrap writes to /etc/ceph the files needed to access the new cluster. This central location makes it possible for Ceph packages installed on the host (e.g., packages that give access to the cephadm command line interface) to find these files.

    Daemon containers deployed with cephadm, however, do not need /etc/ceph at all. Use the --output-dir *<directory>* option to put them in a different directory (for example, .). This may help avoid conflicts with an existing Ceph configuration (cephadm or otherwise) on the same host.

  • You can pass any initial Ceph configuration options to the new cluster by putting them in a standard ini-style configuration file and using the --config *<config-file>* option. For example:

    $ cat <<EOF > initial-ceph.conf
    osd crush chooseleaf type = 0
    $ ./cephadm bootstrap --config initial-ceph.conf ...
  • The --ssh-user *<user>* option makes it possible to choose which SSH user cephadm will use to connect to hosts. The associated SSH key will be added to /home/*<user>*/.ssh/authorized_keys. The user that you designate with this option must have passwordless sudo access.

  • If you are using a container on an authenticated registry that requires login, you may add the argument:

    • --registry-json <path to json file>

    example contents of JSON file with login info:

    {"url":"REGISTRY_URL", "username":"REGISTRY_USERNAME", "password":"REGISTRY_PASSWORD"}

    Cephadm will attempt to log in to this registry so it can pull your container and then store the login info in its config database. Other hosts added to the cluster will then also be able to make use of the authenticated registry.

  • See Different deployment scenarios for additional examples for using cephadm bootstrap.

Enable Ceph CLI

Cephadm does not require any Ceph packages to be installed on the host. However, we recommend enabling easy access to the ceph command. There are several ways to do this:

  • The cephadm shell command launches a bash shell in a container with all of the Ceph packages installed. By default, if configuration and keyring files are found in /etc/ceph on the host, they are passed into the container environment so that the shell is fully functional. Note that when executed on a MON host, cephadm shell will infer the config from the MON container instead of using the default configuration. If --mount <path> is given, then the host <path> (file or directory) will appear under /mnt inside the container:

    cephadm shell
  • To execute ceph commands, you can also run commands like this:

    cephadm shell -- ceph -s
  • You can install the ceph-common package, which contains all of the ceph commands, including ceph, rbd, mount.ceph (for mounting CephFS file systems), etc.:

    cephadm add-repo --release pacific
    cephadm install ceph-common

Confirm that the ceph command is accessible with:

ceph -v

Confirm that the ceph command can connect to the cluster and also its status with:

ceph status

Adding Hosts

Next, add all hosts to the cluster by following 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):

ceph orch host label add *<host>* _admin

Adding additional MONs

A typical Ceph cluster has three or five monitor daemons spread across different hosts. We recommend deploying five monitors if there are five or more nodes in your cluster.

Please follow Deploying additional monitors to deploy additional MONs.

Adding Storage

To add storage to the cluster, you can tell Ceph to consume any available and unused device(s):

ceph orch apply osd --all-available-devices

See Deploy OSDs for more detailed instructions.

Enabling OSD memory autotuning


By default, cephadm enables osd_memory_target_autotune on bootstrap, with mgr/cephadm/autotune_memory_target_ratio set to .7 of total host memory.

See Automatically tuning OSD memory.

To deploy hyperconverged Ceph with TripleO, please refer to the TripleO documentation: Scenario: Deploy Hyperconverged Ceph

In other cases where the cluster hardware is not exclusively used by Ceph (hyperconverged), reduce the memory consumption of Ceph like so:

# hyperconverged only:
ceph config set mgr mgr/cephadm/autotune_memory_target_ratio 0.2

Then enable memory autotuning:

ceph config set osd osd_memory_target_autotune true

Using Ceph

To use the Ceph Filesystem, follow Deploy CephFS.

To use the Ceph Object Gateway, follow Deploy RGWs.

To use NFS, follow NFS Service

To use iSCSI, follow Deploying iSCSI

Different deployment scenarios

Single host

To configure a Ceph cluster to run on a single host, use the --single-host-defaults flag when bootstrapping. For use cases of this, see One Node Cluster.

The --single-host-defaults flag sets the following configuration options:

global/osd_crush_chooseleaf_type = 0
global/osd_pool_default_size = 2
mgr/mgr_standby_modules = False

For more information on these options, see One Node Cluster and mgr_standby_modules in ceph-mgr administrator’s guide.

Deployment in an isolated environment

You might need to install cephadm in an environment that is not connected directly to the internet (such an environment is also called an “isolated environment”). This can be done if a custom container registry is used. Either of two kinds of custom container registry can be used in this scenario: (1) a Podman-based or Docker-based insecure registry, or (2) a secure registry.

The practice of installing software on systems that are not connected directly to the internet is called “airgapping” and registries that are not connected directly to the internet are referred to as “airgapped”.

Make sure that your container image is inside the registry. Make sure that you have access to all hosts that you plan to add to the cluster.

  1. Run a local container registry:

    podman run --privileged -d --name registry -p 5000:5000 -v /var/lib/registry:/var/lib/registry --restart=always registry:2
  2. If you are using an insecure registry, configure Podman or Docker with the hostname and port where the registry is running.


    You must repeat this step for every host that accesses the local insecure registry.

  3. Push your container image to your local registry. Here are some acceptable kinds of container images:

    • Ceph container image. See Ceph Container Images.

    • Prometheus container image

    • Node exporter container image

    • Grafana container image

    • Alertmanager container image

  4. Create a temporary configuration file to store the names of the monitoring images. (See Using custom images):

    cat <<EOF > initial-ceph.conf
    mgr/cephadm/container_image_prometheus *<hostname>*:5000/prometheus
    mgr/cephadm/container_image_node_exporter *<hostname>*:5000/node_exporter
    mgr/cephadm/container_image_grafana *<hostname>*:5000/grafana
    mgr/cephadm/container_image_alertmanager *<hostname>*:5000/alertmanger
  5. Run bootstrap using the --image flag and pass the name of your container image as the argument of the image flag. For example:

    cephadm --image *<hostname>*:5000/ceph/ceph bootstrap --mon-ip *<mon-ip>*