What is an init process?

The init process (or init process) is the very first process that starts in Unix/Linux operating systems after the kernel loads. It has PID 1 and is the parent of all other processes in the system. Its main functions:

• System initialization: Starting necessary services, daemons, and setting up the environment.
• Managing the lifecycle of processes: Starting, stopping, and restarting other processes according to configured runlevels or targets.
• Collecting orphaned processes: Reassigning processes whose parent has finished to its care to prevent them from becoming zombie processes.
• Signal handling: Responding to system signals such as SIGINT, SIGTERM, SIGKILL for proper termination.

Modern Linux distributions often use systemd as the init system, which also performs init process functions but with a broader range of capabilities, including service dependency management, logging, and device management. In older or specialized distributions, the following may be used:

• SysVinit: A classic init system based on scripts in /etc/rc.d/ or /etc/init.d/ directories.
• Upstart: Developed by Ubuntu, based on events.