Init

In Unix-like computer operating systems, init (short for initialization) is the first user-space process started during booting of the operating system. Init is a daemon process that continues running until the system is shut down. It is the direct or indirect ancestor of all other processes and automatically adopts all orphaned processes. Init is started by the kernel during the booting process; in most Unix-like systems, a kernel panic will occur if the kernel is unable to start it or if it dies for any reason. Init is typically assigned process identifier 1. In Unix systems such as System III and System V, the design of init diverged from the functionality provided by the init in Research Unix and its BSD derivatives. Up until the early 2010s, most Linux distributions employed a traditional init that was somewhat compatible with System V, while some distributions such as Slackware use BSD-style startup scripts, and other distributions such as Gentoo have their own customized versions. Since then, most Linux distributions have employed a more modern init system, with most employing the init provided by the systemd project. Some distributions have elected to create their own System V-init compatible system, such as Gentoo Linux's OpenRC and Void Linux's runit. These projects typically include features originally not in System V's init, such as multi-threading or interactive init. Most modern init systems are also able to dynamically start, stop and enable services after boot with prompting by the user.