init

The parent of all Linux processes.

Description

The init command is the process initialization tool for Linux. The init process is the parent of all Linux processes and always has a Process ID (PID) of 1. It is an essential part of the Linux operating system, started by the kernel during the boot process as the very first process.

Syntax

init [options] [runlevel]

Options

-b : Boot directly into single-user mode without running scripts.
-s : Switch to single-user mode.

Parameters

Runlevel: Specify the target runlevel for the system to switch to.

Examples

Commonly used commands:

• View system processes: ps -ef | head
• View the init configuration: more /etc/inittab
• View the current runlevel: runlevel

Runlevels

A runlevel is a state of the operating system. Runlevels range from 0 to 6, each with different functions:

# 0  Halt (do NOT set initdefault to 0)
# 1  Single-user mode
# 2  Multi-user, without NFS (similar to level 3 but stops some services)
# 3  Full multi-user mode
# 4  Unused
# 5  X11 (Graphical user interface)
# 6  Reboot (do NOT set initdefault to 6)