wiki/notebook/linux.systemd.services.org

systemd services

• Service management basics
• Service configuration

One of the functions of the system suite is service management. Like most of the components, it can be used at user-level with their set locations, managing the service daemon, and all.

Service management basics

Just plop down a service unit file at one of the search paths and you can start managing right away. For more information, see the manual page (i.e., systemd.service.5). A summarized version can be found at /foodogsquared/wiki/src/branch/master/notebook/Service%20configuration.

Here's an example of a user service resided as $HOME/.config/systemd/user/drive-backup.service.

[Unit]
Description=Periodic safety backup for my external drive
Documentation=man:borg(1) https://www.borgbackup.org/ https://torsion.org/borgmatic/

[Service]
Type=oneshot
ExecStart=%h/.nix-profile/bin/borgmatic --config %h/dotfiles/borgmatic/personal-drive.yaml --verbosity 2 create
ExecStart=%h/.nix-profile/bin/borgmatic --config %h/dotfiles/borgmatic/personal-drive.yaml --verbosity 2 prune
ExecStart=%h/.nix-profile/bin/borgmatic --config %h/dotfiles/borgmatic/personal-drive.yaml --verbosity 2 check

[Install]
WantedBy=default.target

You can then start the service with:

systemctl --user start drive-backup.service

You can also stop it with the stop subcommand (e.g., systemctl --user stop drive-backup.service) and restart it with restart (e.g., systemctl --user restart drive-backup.service).

If you want to enable it at startup, you can go with enable subcommand. (To disable it, use the disable subcommand.)

systemctl --user enable drive-backup.service

systemd will use the configuration file as-is by the time it is started/enabled. Which means if the config file has been modified after activation, it will not take effect until you restarted it. For this, you can reload the daemon with daemon-reload subcommand. But for simpler cases, you can use the reload subcommand without fully restarting the daemon.

systemctl --user reload drive-backup.service

# You could also use...
#   systemctl --user daemon-reload
# ...if you need a stronger option.

Service configuration

There are different types of services.

• The most common type of service is simple which considers the unit active after the main process is forked (e.g., Service.ExecStart). This is the recommended type for long-running processes.
• oneshot marks the service resolved after the main process exits. Due to the behavior, it will directly go from activating to deactivating instead of active.
• exec considers the service active after the binary has been executed.

Aside from types, each service may have one or more commands although the behavior is set depending on the type.

• ExecStart which is usually the main command and most services will throw an error if it's missing. All services, unless specified as a oneshot service, only have one of these values.
• ExecStop only executes after the main command successfully starts.
• ExecStartPre and ExecStartPost gives you additional commands that will be executed before and after the main command, respectively.
• ExecStopPre and ExecStopPost is similar to the pre- and post-start commands except for the stop command.
• Reload sets whether the service restarts on fail. Values accepted are no, on-failure, and on-success.