Deploying a new Ceph cluster

Cephadm creates a new Ceph cluster by bootstrapping 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 the legacy ntpd)

  • 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


In Quincy, cephadm is not distributed as an executable compiled from source code. That feature was introduced in the Reef release.

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 search release-ceph
dnf install --assumeyes centos-release-ceph-quincy
dnf install --assumeyes cephadm

In Fedora:

dnf -y install cephadm


zypper install -y cephadm

curl-based installation

  • First, determine what version of Ceph you wish to install. You can use the releases page to find the latest active releases. For example, we might find that 18.2.1 is the latest active release.

  • Use curl to fetch a build of cephadm for that release.

    CEPH_RELEASE=18.2.0 # replace this with the active release
    curl --silent --remote-name --location${CEPH_RELEASE}/el9/noarch/cephadm

    Ensure the cephadm file is executable:

    chmod +x cephadm

    This file can be run directly from the current directory:

    ./cephadm <arguments...>
  • If you encounter any issues with running cephadm due to errors including the message bad interpreter, then you may not have Python or the correct version of Python installed. The cephadm tool requires Python 3.6 or later. You can manually run cephadm with a particular version of Python by prefixing the command with your installed Python version. For example:

    python3.8 ./cephadm <arguments...>
  • Although the standalone cephadm is sufficient to bootstrap a cluster, it is best 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 quincy
    ./cephadm install

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

    which cephadm

    A successful which cephadm command will return this:


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. 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.


ssh must be installed and running in order for the bootstrapping procedure to succeed.


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


When installing the Quincy release of Ceph, you might see the following error message:

Deploying ceph-exporter service with default
placement...  Non-zero exit code 22

If you see this error message, add the --skip-monitoring-stack flag to your cephadm bootstrap command. To do this, run a command of the following form:

cephadm bootstrap --mon-ip {monitor IP address} --skip-monitoring-stack

This command should result in a successfully-deployed cluster. Expand the successfully deployed cluster by deploying the monitoring stack without ceph-exporter by running the following commands:

ceph orch apply prometheus
ceph orch apply grafana
ceph orch apply node-exporter
ceph orch apply alertmanager

This error occurs because some Quincy releases contain a faulty ceph-exporter. After this fault was discovered, ceph-exporter was removed from Quincy. If your binary of cephadm is from the release with the fault, you will hit this error.

Running the bootstrap command

Run the ceph bootstrap command:

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

This command will:

  • Create a Monitor and a 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 Ceph daemons.

  • 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 process 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 best 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 be a subnet in CIDR notation (for example or fe80::/64).

  • cephadm bootstrap writes to /etc/ceph 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 designate 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 image from a 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 container 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 quincy
    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

Add all hosts to the cluster by following the instructions in Adding Hosts.

By default, a ceph.conf file and a copy of the client.admin keyring are maintained in /etc/ceph on all hosts that have the _admin label. This label is initially applied only to the bootstrap host. We recommend that one or more other hosts be given the _admin label so that the Ceph CLI (for example, via cephadm shell) is easily accessible on multiple hosts. To add the _admin label to additional host(s), run a command of the following form:

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. Most clusters do not benefit from seven or more Monitors.

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 (converged infrastructure), reduce the memory consumption of Ceph like so:

# converged 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 deploy a Ceph cluster running on a single host, use the --single-host-defaults flag when bootstrapping. For use cases, see One Node Cluster. Such clusters are generally not suitable for production.

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 (an “isolated” or “airgapped” environment). This requires the use of a custom container registry. 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>*

Deployment with custom SSH keys

Bootstrap allows users to create their own private/public SSH key pair rather than having cephadm generate them automatically.

To use custom SSH keys, pass the --ssh-private-key and --ssh-public-key fields to bootstrap. Both parameters require a path to the file where the keys are stored:

cephadm bootstrap --mon-ip <ip-addr> --ssh-private-key <private-key-filepath> --ssh-public-key <public-key-filepath>

This setup allows users to use a key that has already been distributed to hosts the user wants in the cluster before bootstrap.


In order for cephadm to connect to other hosts you’d like to add to the cluster, make sure the public key of the key pair provided is set up as an authorized key for the ssh user being used, typically root. If you’d like more info on using a non-root user as the ssh user, see Further information about cephadm bootstrap

Deployment with CA signed SSH keys

As an alternative to standard public key authentication, cephadm also supports deployment using CA signed keys. Before bootstrapping it’s recommended to set up the CA public key as a trusted CA key on hosts you’d like to eventually add to the cluster. For example:

# we will act as our own CA, therefore we'll need to make a CA key
[root@host1 ~]# ssh-keygen -t rsa -f ca-key -N ""

# make the ca key trusted on the host we've generated it on
# this requires adding in a line in our /etc/sshd_config
# to mark this key as trusted
[root@host1 ~]# cp /etc/ssh
[root@host1 ~]# vi /etc/ssh/sshd_config
[root@host1 ~]# cat /etc/ssh/sshd_config | grep ca-key
TrustedUserCAKeys /etc/ssh/
# now restart sshd so it picks up the config change
[root@host1 ~]# systemctl restart sshd

# now, on all other hosts we want in the cluster, also install the CA key
[root@host1 ~]# scp /etc/ssh/ host2:/etc/ssh/

# on other hosts, make the same changes to the sshd_config
[root@host2 ~]# vi /etc/ssh/sshd_config
[root@host2 ~]# cat /etc/ssh/sshd_config | grep ca-key
TrustedUserCAKeys /etc/ssh/
# and restart sshd so it picks up the config change
[root@host2 ~]# systemctl restart sshd

Once the CA key has been installed and marked as a trusted key, you are ready to use a private key/CA signed cert combination for SSH. Continuing with our current example, we will create a new key-pair for for host access and then sign it with our CA key

# make a new key pair
[root@host1 ~]# ssh-keygen -t rsa -f cephadm-ssh-key -N ""
# sign the private key. This will create a new
# note here we're using user "root". If you'd like to use a non-root
# user the arguments to the -I and -n params would need to be adjusted
# Additionally, note the -V param indicates how long until the cert
# this creates will expire
[root@host1 ~]# ssh-keygen -s ca-key -I user_root -n root -V +52w cephadm-ssh-key
[root@host1 ~]# ls
ca-key  cephadm-ssh-key

# verify our signed key is working. To do this, make sure the generated private
# key ("cephadm-ssh-key" in our example) and the newly signed cert are stored
# in the same directory. Then try to ssh using the private key
[root@host1 ~]# ssh -i cephadm-ssh-key host2

Once you have your private key and corresponding CA signed cert and have tested SSH authentication using that key works, you can pass those keys to bootstrap in order to have cephadm use them for SSHing between cluster hosts

[root@host1 ~]# cephadm bootstrap --mon-ip <ip-addr> --ssh-private-key cephadm-ssh-key --ssh-signed-cert

Note that this setup does not require installing the corresponding public key from the private key passed to bootstrap on other nodes. In fact, cephadm will reject the --ssh-public-key argument when passed along with --ssh-signed-cert. This is not because having the public key breaks anything, but rather because it is not at all needed and helps the bootstrap command differentiate if the user wants the CA signed keys setup or standard pubkey encryption. What this means is that SSH key rotation would simply be a matter of getting another key signed by the same CA and providing cephadm with the new private key and signed cert. No additional distribution of keys to cluster nodes is needed after the initial setup of the CA key as a trusted key, no matter how many new private key/signed cert pairs are rotated in.