WantedBy

WantedBy is a directive used in the Install section of a systemd unit file. It lists units, typically targets, that should cause this unit to be started when they are reached. In practice, WantedBy guides systemd to create installation-time links so that enabling the unit ties it to the specified targets.

How it works: when you enable a unit with systemctl enable, systemd creates symbolic links in the target’s want directory (for example, /etc/systemd/system/multi-user.target.wants/). Each link points to the unit file. When a target is started, systemd starts all units that are listed in their Wants, Requires, or Propagates relationships, including those that appear in a unit’s WantedBy. If a unit has multiple WantedBy entries, enabling it will produce links in multiple targets’ wants directories, making the unit start when any of those targets are activated.

Relationship to other concepts: WantedBy represents a weak, install-time relationship. It is distinct from a unit’s runtime dependencies and from RequiredBy, which is a stronger, demand-based relationship. WantedBy allows administrators to designate common startup runlevels or environments, such as multi-user.target or graphical.target, without hard-coding mandatory dependencies.

Example: a service might include

[Install]

WantedBy=multi-user.target

systemctl enable myservice.service

This creates a link in /etc/systemd/system/multi-user.target.wants/ pointing to the service. Disabling removes the link. The unit can be started immediately with systemctl start and can be activated on boot by enabling.