Initjärjestelmien

Initjärjestelmien, often referred to as init systems, are the first process launched by the kernel during the boot process of Unix-like operating systems. Its primary role is to bring the system up to a usable state by initializing and managing other processes and services. The init system is responsible for transitioning the system through different runlevels or target states, each corresponding to a specific set of services that should be active.

Historically, the most common init system was System V init. This system used a series of runlevels, numbered 0 through 6, each defined by scripts located in directories like /etc/rc.d/ or /etc/rcN.d/. Scripts in these directories would be executed sequentially to start or stop services as the system changed runlevels. However, System V init was often criticized for its sequential nature, leading to slower boot times.

More modern init systems like systemd and Upstart have emerged to address these limitations. Systemd, which has become the de facto standard on many Linux distributions, utilizes a dependency-based model and parallel execution of services, significantly improving boot performance. It also offers advanced features for service management, logging, and device management. Upstart, developed by Canonical, was another influential init system that introduced event-based starting and stopping of services, offering a more dynamic approach than System V init. The choice of init system impacts how services are managed and how quickly a system can become operational.