Upon computer boot-up, and after the Kernel process is started, it traditionally launched the '''init'''process (usually Process ID #: 1). This important process manages (launches) other common services. In many ways, the The init process is also has the ability to manage process (for example, respawing or "ancestor processrestarting" and any process that is currently running on the Unix/Linux system is either directly or indirectly related to the init processprocesses if they are terminated for some reason).

TraditionallyIn many ways, the init program would run default processes that were defined in process is the "shell scriptsancestor process" contained in appropriate run-level directoryand any process that is currently running on the Unix/Linux system is either directly or indirectly related to the init process.

Traditionally, the init program would run default processes that were defined in "shell scripts" contained in appropriate '''run-level''' directory. The run level is a defined state that the Unix/Linux system is currently in (for example, graphical-mode, text-based mode with networking, text-based mode without networking, etc).== The Newer Way: Why Switch to systemd ? ==  Why switch to systemd when the concept of init and run levels seemed to work for 40 years! If it isn't broke, why try to fix it?  Yes, the concept is very easy to understand. On the other hand, with modern operating systems, there is pressure to "evolve" into more efficent running operating systems.