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systemd

A system and service manager for Linux.

systemd boots a Linux system in parallel using socket and D-Bus activation, supervises long-running services, manages logging through the journal, schedules timers (replacing cron for many use cases), handles network configuration through systemd- networkd, manages resolution through systemd-resolved, and provides a unified set of tools for many other tasks that were historically handled by separate daemons (inetd, syslog, fsck, mount, init, and others).

The unified approach has been controversial. The "systemd does too much" critique is a defining argument in modern Linux politics, and several distributions (Devuan, Artix, Void) exist specifically to provide a systemd-free alternative. Despite the controversy, most major distributions have shipped systemd as the default init system since around 2015, and its tooling (systemctl, journalctl, timedatectl, networkctl, resolvectl) has become a common vocabulary across the Linux ecosystem.

Lennart Poettering and Kay Sievers started systemd at Red Hat in 2010. Poettering moved to Microsoft in 2022 but continues to contribute. The licence is LGPL-2.1+ for most of the codebase. For better or worse, systemd is now part of the default Linux landscape and is unlikely to be displaced from that position soon.

systemd is the default init on most Linux distributions and is
preinstalled. To check the version on your system:
  systemctl --version