.service File — Systemd Service Unit

SERVICE files are systemd unit files that define how system services (daemons) are started, stopped, and managed on modern Linux distributions. Systemd is the init system and service manager for most major Linux distributions including Ubuntu, Fedora, Debian, Arch Linux, and RHEL. Service unit files use an INI-like format with sections: [Unit] for dependencies and descriptions, [Service] for execution parameters (ExecStart, ExecStop, Restart policy, User, WorkingDirectory, Environment), and [Install] for boot-time enablement (WantedBy=multi-user.target). Service files define the lifecycle of background processes including web servers, databases, application servers, and custom daemons. Key features include automatic restart on failure, resource limits (CPU, memory, file descriptors), security sandboxing (ProtectSystem, PrivateTmp, NoNewPrivileges), socket activation, and dependency ordering. Service files are placed in /etc/systemd/system/ (admin) or /usr/lib/systemd/system/ (package). The systemctl command manages services (start, stop, enable, disable, status, restart). Systemd's journal (journalctl) provides centralized logging for all service output. Understanding service unit files is essential for Linux system administration and application deployment.