Host Management

Listing Hosts

Run a command of this form to list hosts associated with the cluster:

ceph orch host ls [--format yaml] [--host-pattern <name>] [--label <label>] [--host-status <status>] [--detail]

In commands of this form, the arguments “host-pattern”, “label”, and “host-status” are optional and are used for filtering.

  • “host-pattern” is a regex that matches against hostnames and returns only matching hosts.

  • “label” returns only hosts with the specified label.

  • “host-status” returns only hosts with the specified status (currently “offline” or “maintenance”).

  • Any combination of these filtering flags is valid. It is possible to filter against name, label and status simultaneously, or to filter against any proper subset of name, label and status.

The “detail” parameter provides more host related information for cephadm based clusters. For example:

# ceph orch host ls --detail
HOSTNAME     ADDRESS         LABELS  STATUS  VENDOR/MODEL                           CPU    HDD      SSD  NIC
ceph-master  _admin          QEMU (Standard PC (Q35 + ICH9, 2009))  4C/4T  4/1.6TB  -    1
1 hosts in cluster

Adding Hosts

Hosts must have these Requirements installed. Hosts without all the necessary requirements will fail to be added to the cluster.

To add each new host to the cluster, perform two steps:

  1. Install the cluster’s public SSH key in the new host’s root user’s authorized_keys file:

    ssh-copy-id -f -i /etc/ceph/ root@*<new-host>*

    For example:

    ssh-copy-id -f -i /etc/ceph/ root@host2
    ssh-copy-id -f -i /etc/ceph/ root@host3
  2. Tell Ceph that the new node is part of the cluster:

    ceph orch host add *<newhost>* [*<ip>*] [*<label1> ...*]

    For example:

    ceph orch host add host2
    ceph orch host add host3

    It is best to explicitly provide the host IP address. If an address is not provided, then the host name will be immediately resolved via DNS and the result will be used.

    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:

    ceph orch host add host4 --labels _admin

Removing Hosts

A host can safely be removed from the cluster after all daemons are removed from it.

To drain all daemons from a host, run a command of the following form:

ceph orch host drain *<host>*

The _no_schedule and _no_conf_keyring labels will be applied to the host. See Special host labels.

If you only want to drain daemons but leave managed ceph conf and keyring files on the host, you may pass the --keep-conf-keyring flag to the drain command.

ceph orch host drain *<host>* --keep-conf-keyring

This will apply the _no_schedule label to the host but not the _no_conf_keyring label.

If you want to drain daemons but leave managed ceph.conf and keyring files on the host, you may pass the --keep-conf-keyring flag to the drain command.

ceph orch host drain *<host>* --keep-conf-keyring

This will apply the _no_schedule label to the host but not the _no_conf_keyring label.

All OSDs on the host will be scheduled to be removed. You can check progress of the OSD removal operation with the following command:

ceph orch osd rm status

See Remove an OSD for more details about OSD removal.

The orch host drain command also supports a --zap-osd-devices flag. Setting this flag while draining a host will cause cephadm to zap the devices of the OSDs it is removing as part of the drain process

ceph orch host drain *<host>* --zap-osd-devices

Use the following command to determine whether any daemons are still on the host:

ceph orch ps <host>

After all daemons have been removed from the host, remove the host from the cluster by running the following command:

ceph orch host rm <host>

Offline host removal

If a host is offline and can not be recovered, it can be removed from the cluster by running a command of the following form:

ceph orch host rm <host> --offline --force


This can potentially cause data loss. This command forcefully purges OSDs from the cluster by calling osd purge-actual for each OSD. Any service specs that still contain this host should be manually updated.

Host labels

The orchestrator supports assigning labels to hosts. Labels are free form and have no particular meaning by itself and each host can have multiple labels. They can be used to specify placement of daemons. See Placement by labels

Labels can be added when adding a host with the --labels flag:

ceph orch host add my_hostname --labels=my_label1
ceph orch host add my_hostname --labels=my_label1,my_label2

To add a label a existing host, run:

ceph orch host label add my_hostname my_label

To remove a label, run:

ceph orch host label rm my_hostname my_label

Special host labels

The following host labels have a special meaning to cephadm. All start with _.

  • _no_schedule: Do not schedule or deploy daemons on this host.

    This label prevents cephadm from deploying daemons on this host. If it is added to an existing host that already contains Ceph daemons, it will cause cephadm to move those daemons elsewhere (except OSDs, which are not removed automatically).

  • _no_conf_keyring: Do not deploy config files or keyrings on this host.

    This label is effectively the same as _no_schedule but instead of working for daemons it works for client keyrings and ceph conf files that are being managed by cephadm

  • _no_autotune_memory: Do not autotune memory on this host.

    This label will prevent daemon memory from being tuned even when the osd_memory_target_autotune or similar option is enabled for one or more daemons on that host.

  • _admin: Distribute client.admin and ceph.conf to this host.

    By default, an _admin label is applied to the first host in the cluster (where bootstrap was originally run), and the client.admin key is set to be distributed to that host via the ceph orch client-keyring ... function. Adding this label to additional hosts will normally cause cephadm to deploy config and keyring files in /etc/ceph. Starting from versions 16.2.10 (Pacific) and 17.2.1 (Quincy) in addition to the default location /etc/ceph/ cephadm also stores config and keyring files in the /var/lib/ceph/<fsid>/config directory.

Maintenance Mode

Place a host in and out of maintenance mode (stops all Ceph daemons on host):

ceph orch host maintenance enter <hostname> [--force] [--yes-i-really-mean-it]
ceph orch host maintenance exit <hostname>

The --force flag allows the user to bypass warnings (but not alerts). The --yes-i-really-mean-it flag bypasses all safety checks and will attempt to force the host into maintenance mode no matter what.


Using the –yes-i-really-mean-it flag to force the host to enter maintenance mode can potentially cause loss of data availability, the mon quorum to break down due to too few running monitors, mgr module commands (such as ceph orch . . . commands) to be become unresponsive, and a number of other possible issues. Please only use this flag if you’re absolutely certain you know what you’re doing.

See also Fully qualified domain names vs bare host names

Rescanning Host Devices

Some servers and external enclosures may not register device removal or insertion with the kernel. In these scenarios, you’ll need to perform a device rescan on the appropriate host. A rescan is typically non-disruptive, and can be performed with the following CLI command:

ceph orch host rescan <hostname> [--with-summary]

The with-summary flag provides a breakdown of the number of HBAs found and scanned, together with any that failed:

ceph orch host rescan rh9-ceph1 --with-summary
Ok. 2 adapters detected: 2 rescanned, 0 skipped, 0 failed (0.32s)

Creating many hosts at once

Many hosts can be added at once using ceph orch apply -i by submitting a multi-document YAML file:

service_type: host
hostname: node-00
- example1
- example2
service_type: host
hostname: node-01
- grafana
service_type: host
hostname: node-02

This can be combined with service specifications to create a cluster spec file to deploy a whole cluster in one command. see cephadm bootstrap --apply-spec also to do this during bootstrap. Cluster SSH Keys must be copied to hosts prior to adding them.

Setting the initial CRUSH location of host

Hosts can contain a location identifier which will instruct cephadm to create a new CRUSH host located in the specified hierarchy.

service_type: host
hostname: node-00
  rack: rack1


The location attribute will be only affect the initial CRUSH location. Subsequent changes of the location property will be ignored. Also, removing a host will not remove an associated CRUSH bucket unless the --rm-crush-entry flag is provided to the orch host rm command

See also Types and Buckets.

Removing a host from the CRUSH map

The ceph orch host rm command has support for removing the associated host bucket from the CRUSH map. This is done by providing the --rm-crush-entry flag.

ceph orch host rm host1 --rm-crush-entry

When this flag is specified, cephadm will attempt to remove the host bucket from the CRUSH map as part of the host removal process. Note that if it fails to do so, cephadm will report the failure and the host will remain under cephadm control.


Removal from the CRUSH map will fail if there are OSDs deployed on the host. If you would like to remove all the host’s OSDs as well, please start by using the ceph orch host drain command to do so. Once the OSDs have been removed, then you may direct cephadm remove the CRUSH bucket along with the host using the --rm-crush-entry flag.

OS Tuning Profiles

Cephadm can be used to manage operating system tuning profiles that apply sysctl settings to sets of hosts.

To do so, create a YAML spec file in the following format:

profile_name: 23-mon-host-profile
    - mon-host-01
    - mon-host-02
  fs.file-max: 1000000
  vm.swappiness: '13'

Apply the tuning profile with the following command:

ceph orch tuned-profile apply -i <tuned-profile-file-name>

This profile is written to a file under /etc/sysctl.d/ on each host specified in the placement block, then sysctl --system is run on the host.


The exact filename that the profile is written to within /etc/sysctl.d/ is <profile-name>-cephadm-tuned-profile.conf, where <profile-name> is the profile_name setting that you specify in the YAML spec. We suggest naming these profiles following the usual sysctl.d NN-xxxxx convention. Because sysctl settings are applied in lexicographical order (sorted by the filename in which the setting is specified), you may want to carefully choose the profile_name in your spec so that it is applied before or after other conf files. Careful selection ensures that values supplied here override or do not override those in other sysctl.d files as desired.


These settings are applied only at the host level, and are not specific to any particular daemon or container.


Applying tuning profiles is idempotent when the --no-overwrite option is passed. Moreover, if the --no-overwrite option is passed, existing profiles with the same name are not overwritten.

Viewing Profiles

Run the following command to view all the profiles that cephadm currently manages:

ceph orch tuned-profile ls


To make modifications and re-apply a profile, pass --format yaml to the tuned-profile ls command. The tuned-profile ls --format yaml command presents the profiles in a format that is easy to copy and re-apply.

Removing Profiles

To remove a previously applied profile, run this command:

ceph orch tuned-profile rm <profile-name>

When a profile is removed, cephadm cleans up the file previously written to /etc/sysctl.d.

Modifying Profiles

Profiles can be modified by re-applying a YAML spec with the same name as the profile that you want to modify, but settings within existing profiles can be adjusted with the following commands.

To add or modify a setting in an existing profile:

ceph orch tuned-profile add-setting <profile-name> <setting-name> <value>

To remove a setting from an existing profile:

ceph orch tuned-profile rm-setting <profile-name> <setting-name>


Modifying the placement requires re-applying a profile with the same name. Remember that profiles are tracked by their names, so when a profile with the same name as an existing profile is applied, it overwrites the old profile unless the --no-overwrite flag is passed.

SSH Configuration

Cephadm uses SSH to connect to remote hosts. SSH uses a key to authenticate with those hosts in a secure way.

Default behavior

Cephadm stores an SSH key in the monitor that is used to connect to remote hosts. When the cluster is bootstrapped, this SSH key is generated automatically and no additional configuration is necessary.

A new SSH key can be generated with:

ceph cephadm generate-key

The public portion of the SSH key can be retrieved with:

ceph cephadm get-pub-key

The currently stored SSH key can be deleted with:

ceph cephadm clear-key

You can make use of an existing key by directly importing it with:

ceph config-key set mgr/cephadm/ssh_identity_key -i <key>
ceph config-key set mgr/cephadm/ssh_identity_pub -i <pub>

You will then need to restart the mgr daemon to reload the configuration with:

ceph mgr fail

Configuring a different SSH user

Cephadm must be able to log into all the Ceph cluster nodes as an user that has enough privileges to download container images, start containers and execute commands without prompting for a password. If you do not want to use the “root” user (default option in cephadm), you must provide cephadm the name of the user that is going to be used to perform all the cephadm operations. Use the command:

ceph cephadm set-user <user>

Prior to running this the cluster SSH key needs to be added to this users authorized_keys file and non-root users must have passwordless sudo access.

Customizing the SSH configuration

Cephadm generates an appropriate ssh_config file that is used for connecting to remote hosts. This configuration looks something like this:

Host *
User root
StrictHostKeyChecking no
UserKnownHostsFile /dev/null

There are two ways to customize this configuration for your environment:

  1. Import a customized configuration file that will be stored by the monitor with:

    ceph cephadm set-ssh-config -i <ssh_config_file>

    To remove a customized SSH config and revert back to the default behavior:

    ceph cephadm clear-ssh-config
  2. You can configure a file location for the SSH configuration file with:

    ceph config set mgr mgr/cephadm/ssh_config_file <path>

    We do not recommend this approach. The path name must be visible to any mgr daemon, and cephadm runs all daemons as containers. That means that the file must either be placed inside a customized container image for your deployment, or manually distributed to the mgr data directory (/var/lib/ceph/<cluster-fsid>/mgr.<id> on the host, visible at /var/lib/ceph/mgr/ceph-<id> from inside the container).

Setting up CA signed keys for the cluster

Cephadm also supports using CA signed keys for SSH authentication across cluster nodes. In this setup, instead of needing a private key and public key, we instead need a private key and certificate created by signing that private key with a CA key. For more info on setting up nodes for authentication using a CA signed key, see Deployment with CA signed SSH keys. Once you have your private key and signed cert, they can be set up for cephadm to use by running:

ceph config-key set mgr/cephadm/ssh_identity_key -i <private-key-file>
ceph config-key set mgr/cephadm/ssh_identity_cert -i <signed-cert-file>

Fully qualified domain names vs bare host names


cephadm demands that the name of the host given via ceph orch host add equals the output of hostname on remote hosts.

Otherwise cephadm can’t be sure that names returned by ceph * metadata match the hosts known to cephadm. This might result in a CEPHADM_STRAY_HOST warning.

When configuring new hosts, there are two valid ways to set the hostname of a host:

  1. Using the bare host name. In this case:

  • hostname returns the bare host name.

  • hostname -f returns the FQDN.

  1. Using the fully qualified domain name as the host name. In this case:

  • hostname returns the FQDN

  • hostname -s return the bare host name

Note that man hostname recommends hostname to return the bare host name:

The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver(3) returns for the host name, for example It is usually the short hostname followed by the DNS domain name (the part after the first dot). You can check the FQDN using hostname --fqdn or the domain name using dnsdomainname.

You cannot change the FQDN with hostname or dnsdomainname.

The recommended method of setting the FQDN is to make the hostname
be an alias for the fully qualified name using /etc/hosts, DNS, or
NIS. For example, if the hostname was "ursula", one might have
a line in /etc/hosts which reads ursula

Which means, man hostname recommends hostname to return the bare host name. This in turn means that Ceph will return the bare host names when executing ceph * metadata. This in turn means cephadm also requires the bare host name when adding a host to the cluster: ceph orch host add <bare-name>.