etcinittab

Etcinittab refers to the /etc/inittab file, the initialization table used by traditional System V–style init processes on Unix-like systems. It governs how the system starts up, which processes are started at different runlevels, and how those processes should be managed. While many modern Linux distributions rely on systemd, inittab remains relevant for SysV-compatible or legacy environments and is a useful reference for understanding historical init behavior.

The file is composed of lines representing entries. Each non-comment line uses four fields separated by colons: id, runlevels, action, and process. The id is a unique identifier for the entry. The runlevels field lists the runlevels in which the entry is active (for example 2345 or s). The action indicates what init should do (such as initdefault, sysinit, respawn, wait, once, boot, bootwait, or ctrlaltdel). The process field specifies the command or program to execute; for some actions, the process field may be empty (as in the initdefault entry).

Common examples include:

- A line that sets the default runlevel, such as: id:3:initdefault:

- A system initialization line, such as: si:sysinit:/etc/rc.d/rc.sysinit

- A getty entry to spawn a login prompt on a console, such as: tty1:2345:respawn:/sbin/getty 38400 tty1

- A Ctrl-Alt-Del handler, such as: ca:ctrlaltdel:ctrlaltdel:/sbin/shutdown -t1 -r now

Editing etcinittab requires caution. Incorrect syntax or ill-considered entries can prevent a system from booting or logging in. Always back up the file before changes and validate syntax against the hosting system’s init implementation. In modern distributions, inittab may be unused or only provide compatibility, with systemd or other init systems handling initialization instead.