Frequently Asked Question

What is systemd?

systemd is the program that runs as PID 1 on almost every modern Linux distribution. Its job is to bring the system from a freshly booted kernel up to a working multi-user (or graphical) state, supervise the services that make that state useful, and tear everything down again on shutdown. It was started in 2010 by Lennart Poettering and Kay Sievers at Red Hat as a replacement for the older sysvinit and Upstart, and by around 2015 it had been adopted as the default on Debian, Ubuntu, Fedora, RHEL, openSUSE, Arch, and most other mainstream distributions.

Strictly speaking, "systemd" is not just an init system. It is a suite of around 70 binaries that handle service management, logging (journald), DNS (resolved), network configuration (networkd), login session tracking (logind), time synchronisation (timesyncd), device hot-plug, scheduled tasks, and more. That breadth is part of why systemd was controversial when it landed, and it is also why learning it well repays the effort: once you understand the unit model and systemctl, you have a single mental framework for most of what used to be a dozen unrelated subsystems.