Initjärjestelmää

Initjärjestelmää refers to the init system used in Linux and other Unix-like operating systems. It is the first process started by the kernel during the boot process, hence its name "init" (short for initialization). Its primary role is to manage all other processes on the system, acting as a parent to them.

Historically, the most common init system was System V init, which used a series of runlevels to determine which services should be started or stopped. These runlevels represented different operating states, such as single-user mode or multi-user mode with networking. Scripts located in specific directories (`/etc/rc.d/init.d` and `/etc/rc?.d/`) controlled the startup and shutdown of services.

In recent years, systemd has emerged as the dominant init system in many Linux distributions. Systemd introduces a more modern approach, utilizing a dependency-based system with "units" for managing services, devices, mount points, and more. It aims to improve boot speed, system management, and logging capabilities through features like parallel service startup and a centralized logging daemon.

Other init systems exist, such as Upstart, which was developed by Canonical for Ubuntu, and OpenRC, which is used in distributions like Gentoo. The choice of init system can impact how services are managed, how the system boots, and the overall user experience. Regardless of the specific implementation, the core function of an init system remains to orchestrate the startup, management, and shutdown of system processes.