Linux-Basics-Complete-Course-With-Notes-Slides

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.bob-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