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Working With Sytemd

Learn how to start, stop, enable, disable a systemctl and how to list linux services.

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Systemd :

Master of everything and the first process/service ( PID = 1 ) to start after the Linux kernel boot. Hence, our guy systemd will starts up and supervises almost the entire system units : -> Services -> Mounts -> Sockets ->Targets use systemctl -t help to list all units. -) systemd-analyze blame -> in case you want to know what takes time on boot. -) systemd-analyze security -> check the security of a unit.

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Systemd Files :

-) /usr/lib/systemd/system -> default unit files that have been installed from RPM -) /etc/systemd/system -> All costume unit files -) /run/systemd/system -> All units files that have automatically been generated in the run-time.

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Prevent modifying a unit file in /usr/lib/systemd/system unless you know what you are doing.

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Systemd Status :

A unit $status can be : Loaded - Active - Running - Exited - Waiting - Dead - Enabled - Disabled - Static.

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Systemctl :

Used command to manage all the units through systemd. Below, you will find almost all the commands to help you managing units.

  • systemctl --type=services --all -> list all the services (active, inactive)

  • systemctl list-units -> display all the active units that systemd know about.

  • systemctl --failed --type=services

  • systemctl status -l <service_name>

  • systemctl cat <service_name> -> current config of this unit.

  • systemctl show <service_name> -> show available configs

  • systemctl edit --full <service_name> -> to modify the default configs. watch this video : https://www.youtube.com/watch?v=xXGLUY30fuYarrow-up-right

  • systemctl daemon-reload -> To ensure that systemd reload with the new configuration.

  • systemctl enable --now <service_name> -> to make the service starts autmoatically at boot.

  • systemctl reload <service_name> -> reload the config files of a service.

  • systemctl disable <service_name> -> to disable the service from starting automatically at boot

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Practice Time:

1 - Make sure httpd service is automatically started. 2 - Edit its configuration file such that on failure, it will continue after 130s.

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Answer :

First lets edit the unit config file of httpd service, systemctl edit --full httpd [service] Restart = always Restartsec= 130s systemctl daemon-reload killall httpd systemctl restart httpd systemctl enable --now httpd systemctl status httpd systemctl cat httpd.service -> to verify the changes.

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