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>]
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.
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:
Install the cluster’s public SSH key in the new host’s root user’s
ssh-copy-id -f -i /etc/ceph/ceph.pub root@*<new-host>*
ssh-copy-id -f -i /etc/ceph/ceph.pub root@host2 ssh-copy-id -f -i /etc/ceph/ceph.pub root@host3
Tell Ceph that the new node is part of the cluster:
ceph orch host add *<newhost>* [*<ip>*] [*<label1> ...*]
ceph orch host add host2 10.10.0.102 ceph orch host add host3 10.10.0.103
It is best to explicitly provide the host IP address. If an IP is not provided, then the host name will be immediately resolved via DNS and that IP will be used.
One or more labels can also be included to immediately label the new host. For example, by default the
_adminlabel will make cephadm maintain a copy of the
ceph.conffile and a
client.adminkeyring file in
ceph orch host add host4 10.10.0.104 --labels _admin
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>*
_no_schedule label will be applied to the host. See
Special host labels.
All OSDs on the host will be scheduled to be removed. You can check the 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.
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
Even 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.
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
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_autotune_memory: Do not autotune memory on this host.
This label will prevent daemon memory from being tuned even when the
osd_memory_target_autotuneor 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
_adminlabel is applied to the first host in the cluster (where bootstrap was originally run), and the
client.adminkey 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
Place a host in and out of maintenance mode (stops all Ceph daemons on host):
ceph orch host maintenance enter <hostname> [--force] ceph orch host maintenance exit <hostname>
Where the force flag when entering maintenance allows the user to bypass warnings (but not alerts)
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 host rescan. A rescan is typically non-disruptive, and can be performed with the following CLI command:
ceph orch host rescan <hostname> [--with-summary]
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 addr: 192.168.0.10 labels: - example1 - example2 --- service_type: host hostname: node-01 addr: 192.168.0.11 labels: - grafana --- service_type: host hostname: node-02 addr: 192.168.0.12
This can be combined with service specifications (below) 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 addr: 192.168.0.10 location: rack: rack1
location attribute will be only affect the initial CRUSH location. Subsequent
changes of the
location property will be ignored. Also, removing a host will no remove
any CRUSH buckets.
See also Types and Buckets.
OS Tuning Profiles
Cephadm can be used to manage operating-system-tuning profiles that apply sets of sysctl settings to sets of hosts.
Create a YAML spec file in the following format:
profile_name: 23-mon-host-profile placement: hosts: - mon-host-01 - mon-host-02 settings: 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
/etc/sysctl.d/ on each host that matches the
hosts specified in the placement block of the yaml, and
sysctl --system is
run on the host.
The exact filename that the profile is written to within
profile_name setting that you specify in the YAML spec. Because
sysctl settings are applied in lexicographical order (sorted by the filename
in which the setting is specified), you may want to set the
in your spec so that it is applied before or after other conf files.
These settings are applied only at the host level, and are not specific to any particular daemon or container.
Applying tuned 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.
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.
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
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
--no-overwrite flag is passed.
Cephadm uses SSH to connect to remote hosts. SSH uses a key to authenticate with those hosts in a secure way.
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:
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
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 either need to 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).
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:
Using the bare host name. In this case:
hostnamereturns the bare host name.
hostname -freturns the FQDN.
Using the fully qualified domain name as the host name. In this case:
hostnamereturns the FQDN
hostname -sreturn the bare host name
man hostname recommends
hostname to return the bare
The FQDN (Fully Qualified Domain Name) of the system is the name that the resolver(3) returns for the host name, such as, ursula.example.com. It is usually the hostname followed by the DNS domain name (the part after the first dot). You can check the FQDN using
hostname --fqdnor 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 127.0.1.1 ursula.example.com ursula
man hostname recommends
hostname to return the bare
host name. This in turn means that Ceph will return the bare host names
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>.