Linux - Init systems
Init systems
Init systems in Linux are the first processes started by the kernel after booting, responsible for initializing the system and managing services. They are assigned process ID (PID) 1 and act as the parent for all other processes.
The choice of init system can impact system boot time, service management capabilities, and overall system architecture. While systemd is the default in most contemporary Linux distributions, other init systems offer alternatives for users seeking different approaches to system initialization and service management.
Key functions of an init system include:
System Initialization
Mounting file systems, setting up networking, and preparing the environment for user interaction.
Service Management
Starting, stopping, restarting, and monitoring system services (daemons) like web servers, databases, or SSH servers.
Process Management
Adopting orphaned processes (those whose parent processes have terminated) and ensuring proper system shutdown.
Prominent init systems in Linux
SysVinit
The traditional init system, based on System V Unix. It uses runlevels to define different system states and relies on shell scripts for service management.
systemd
A modern and widely adopted init system that aims to provide a comprehensive system and service manager. It uses units to define services, targets to group units, and offers features like parallel service startup, cgroup management, and journaling.
OpenRC
A dependency-based init system known for its simplicity and flexibility, often found in distributions like Gentoo.
Runit
A lightweight and fast init system focused on simplicity and reliability.
Upstart
An event-driven init system developed by Canonical, previously used in Ubuntu.