Every component of Ceph, whether it's MON, OSD, MDS, or RGW, runs as a service on top of an underlying operating system. As a Ceph storage administrator, you should know about the Ceph services and how to operate them. As per Red Hat based distributions, Ceph daemons are managed as a traditional systemd manager service. Each time you start, restart, and stop Ceph daemons (or your entire cluster), you must specify at least one option and one command. You may also specify a daemon type or a daemon instance. The general syntax for this is as follows:

systemctl [options...] command [service name...]

The systemctl options include:

• --help or -h: Prints a short help text
• --all or -a: When listing units, show all loaded units, regardless of their state
• --signal or -s: When used will kill, choose which signal to send to the selected process
• --force or -f: When used with enable, overwrites any existing conflicting symlinks
• --host or -h: Execute an operation on a remote host

The systemctl commands include the following:

• status: Shows status of the daemon
• start: Starts the daemon
• stop: Stops the daemon
• restart: Stops and then starts the daemon
• kill: Kills the specified daemon
• reload: Reloads the config file without interrupting pending operations
• list-units: Lists known units managed by systemd
• condrestart: Restarts if the service is already running
• enable: Turns the service on for the next boot or other triggering event
• disable: Turns the service off for the next boot or other triggering event
• is-enabled: Used to check whether a service is configured to start or not in the current environment

systemctl can target the following Ceph service types:

• ceph-mon
• ceph-osd
• ceph-mds
• ceph-radosgw