After the Linux kernel boots, the first Linux process begins the first process. This process is known as an init process. In modern Linux systems, this process is systemd. Have a look at the following screenshot, which shows the running process in a tree format:

Figure 5.31: A view of the running processes in a tree format

systemd is responsible for starting all processes in parallel during the boot process, except the processes that are created by the kernel. After that, it activates services, among other things, on demand. It also tracks and manages mount points, and it manages system-wide settings such as the hostname.

systemd is an event-driven system. It communicates with the kernel and will react to an event such as a point in time or a user who introduces a new device or who presses Ctrl + Alt + Del.

Working with Units

systemd works with units, which are entities that are managed by systemd and encapsulate information about every...