UnitDateien

UnitDateien are configuration files used by systemd, the init and service manager for Linux. They describe units, which are resources or services that systemd manages, and determine how and when these units start, stop, and interact with each other.

A unit file is a plain text file with an INI-like structure. It is divided into sections such as [Unit], [Service], and [Install], each containing key=value pairs. Common directives include Description and Documentation in [Unit], ExecStart, ExecStop, User, Group, Restart, Environment, and WorkingDirectory in [Service], and WantedBy and Also in [Install]. These settings define metadata, dependencies, startup behavior, and installation targets.

Unit types describe the kind of resource. Typical types include service (daemons), socket (socket-activated services), timer (time-based triggers), path, mount, automount, swap, target (unit groups), slice (resource management), device, and scope. Templates use the @ notation to create multiple instances of a unit, such as [email protected].

Locations and overrides: unit files reside in system-wide locations such as /lib/systemd/system, /usr/lib/systemd/system, or /etc/systemd/system. Administrators commonly place custom units or overrides in /etc/systemd/system. Drop-in snippets in /etc/systemd/system/FOO.service.d/*.conf can override or extend settings without modifying the main unit file.

Management: after creating or editing unit files, systemd must be reloaded with systemctl daemon-reload. Units can be enabled to start at boot, started or stopped manually, and queried for status. Enabling creates startup symlinks under targets like multi-user.target.wants. Templates and dependencies allow flexible and scalable service orchestration.