systemd

systemd [OPTIONS...] COMMAND [NAME...]

--version
    Show package version.

--help
    Show help message and exit.

--system
    Connect to the system manager.

--user
    Connect to the user manager.

--machine=MACHINE
    Connect to a specific machine.

--unit=UNIT
    Operate on the specified unit.

Systemd is a suite of system management daemons, libraries, and utilities designed to replace the traditional System V init system. It manages the system during boot, handles process lifecycle management, and controls services and their dependencies. Systemd uses units, which are configuration files that describe services, mount points, devices, sockets, and other system components. It provides features like parallel startup, socket activation, dependency-based service control, journald for centralized logging, and cgroup-based resource management.

Systemd simplifies system administration and improves boot times, making it the standard init system on most modern Linux distributions.

Direct manipulation of systemd files without understanding dependencies can lead to system instability.

Many commands can be passed, systemctl is the most used command to control systemd.

Systemd was first announced in 2010 and rapidly gained adoption in major Linux distributions like Fedora, Debian, and Ubuntu. It replaced System V init, aiming to provide a more efficient and feature-rich system initialization and management framework. Its development has been driven by the need for faster boot times, improved service management, and enhanced system monitoring capabilities.

Its adoption wasn't without controversy, with concerns raised about its complexity and potential for increased attack surface. Despite these concerns, systemd has become the dominant init system in the Linux ecosystem.

systemctl(1), journalctl(1), systemd.unit(5)