Linux 101 : Systemd Overview

Units replace i a way scripts for launching programs and targets are the equivalents of runlevels.

A unit describes a service on the system. The unit has the following components:

Below are some of the unit types in Linux:

device : device managed by systemd
mount : mountpoint managed by systemd
target : refers to different states of the OS depending on the programs launched.
service : defines how applications are managed by systemd

The systemd uses the following naming convention, name.type for example sshd.service.

You use the systemctl command to list the units currently loaded in your Linux system:

Configuring Units:

Units use a configuration files that tell systemd which programs to start and how to start them.

The configuration files live in the /lib/systemd/system directory.

Below is the ssh service unit configuration file - sshd.service -:

Below is a simple description of same of the parameters that we have seen above:

Description : a short description of the service.
ExecStart : command that runs when the service is launched.
After : describes the program that need to run before sshd
Wantedby : describes the target level of the system that we need to be on to start sshd.
Restart : describes when to start the service.

Target units:

Target units use configuration to tell systemd which service units it needs to start.

For example for the graphical target - starts a system with a graphical interface -:

Systemctl is the tool we use to manage services/targets.

Below are some parameters that we could use with the systemctl command:

Example:

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