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02-Creating-a-SYSTEMD-Service.md

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Creating your own SYSTEMD Service

In this lecture we will learn how to create a SYSTEMD Service.

  • All the major distributions, such as Rhel, CentOS, Fedora, Ubuntu, Debian and Archlinux, adopted systemd as their init system.
  • Systemd is a Linux initialization system and service manager that includes features like on-demand starting of daemons, mount and automount point maintenance etc.
  • Systemd also provides a logging daemon and other tools and utilities to help with common system administration tasks.

What is a service unit?

  • A file with the .service suffix contains information about a process which is managed by systemd. It is composed by three main sections:

    1.Unit

    • The Unit section of a .service file contains the description of the unit itself, and information about its behavior and its dependencies: (to work correctly a service can depend on another one). Here we discuss some of the most relevant options which can be used in this section

    • First of all we have the Description option. By using this option we can provide a description of the unit. The description will then appear, for example, when calling the systemctl command, which returns an overview of the status of systemd.

    • Secondly, we have Documentation option. By using this option we can get the details of the service and documentation related to it.

    • By using the After option, we can state that our unit should be started after the units we provide in the form of a space-separated list.

      [~]$ cat /etc/systemd/system/project-mercury.service
[Unit]
Description=Python Django for Project Mercury
Documentation=http://wiki.caleston-dev.ca/mercury
After=postgresql.service

    2.Service

    • In the Service section of a service unit, we can specify things as the command to be executed when the service is started, or the type of the service itself.

      [Service]
ExecStart=/usr/bin/project-mercury.sh
User=project_mercury
Restart=on-failure
RestartSec=10

    3.Install

    • This Install section contains information about the installation of the unit

      [Install]
WantedBy=graphical.target

How to Start the Service now ?

  • The system to detect the changes you have done in the file, we need to reload the daemon and start the service.

    [~]$ systemctl daemon-reload

[~]$ systemctl start project-mercury.service