What init system is now used by most Linux distributions?

What init system is now used by most Linux distributions? systemd is the answer. Its primary component starts user space as process ID 1, launches services, supervises them, and coordinates shutdown.

systemd was developed at Red Hat by Lennart Poettering and Kay Sievers, with its project beginning in 2010. It was designed to replace traditional SysVinit startup scripts with dependency-aware service units and greater parallelism during boot. Fedora became the first major distribution to enable it by default in 2011, and adoption spread to distributions including Debian, Ubuntu, Arch Linux, openSUSE, and Red Hat Enterprise Linux.

The wording “most” matters: systemd is widespread but not universal. Gentoo commonly uses OpenRC, Void Linux uses runit, and Devuan provides a systemd-free Debian-based alternative. Another common mix-up is confusing the init system with the kernel; the Linux kernel starts the first userspace process, while systemd manages the services that follow.