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03-SYSTEMD-Tools.md

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SYSTEMD Tools to Manage SYSTEMD service

In this lecture we will explore two major SYSTEMD tools:

  • SYSTEMCTL
  • JOURNALCTL

SYSTEMCTL

  • Systemctl is the main command used to manage services on a SYSTEMD managed server.

  • It can be used to manage services such as START/STOP/RESTART/RELOAD as well as ENABLE/DISABLE services during the system boot.

  • It is also used to LIST AND MANAGE UNITS and LIST AND UPDATE TARGETS

    Systemctl

Systemctl Commands

  • To start a service use the start command, for example to start a docker service use systemctl start docker

    [~]$ systemctl start docker

  • To stop a service use the stop command, for example to stop a docker service use systemctl stop docker

    [~]$ systemctl stop docker

  • To restart a service use the restart command, for example to restart a docker service use systemctl restart docker this will stop and start again.

    [~]$ systemctl restart docker

  • To reload a service use the reload command, for example to reload a docker service use systemctl reload docker, this will reload all the configuration without interrupting the normal functionaltiy of the service

    [~]$ systemctl reload docker

  • To enable a service and make it persistent accross reboots use the enable command, for example to enable a docker service use systemctl enable docker

    [~]$ systemctl enable docker

  • To disable a service at boot use the disable command, for example to disable a docker service use systemctl disable docker command.

    [~]$ systemctl disable docker

  • To know the status of the service use systemctl status docker command. This command provided the state of the service. If running properly is should show active (running) state as shown in screenshot below.

    [~]$ systemctl status docker

  • Besides active (running) state there are few other state that you should be aware off.

    Other

  • Running systemctl daemon reload command after making changes to service unit file reloads the system manager configuration and makes the systemd aware of the changes.

  • To edit the service file use command systemctl edit project-mercury.service --full this will open a text editor, you can make the changes and re-write the settings as needed, making changing this way applied immediately without running the systemctl daemon reload command

    [~]$ systemctl daemon-reload
[~]$ systemctl edit project-mercury.service --full

  • To see the current runlevel use systemctl get-default

    [~]$ systemctl get default

  • To change the runleve to a different target use systemctl set-default multi-user.target

    [~]$ systemctl set-default multi-user.target

  • To list all the units that systemd has loaded use systemctl list-units --all, this lists all the unit which are active, inactive or anyother state.

    [~]$ systemctl list-units --all

  • To list only active units use systemctl list-units command

    [~]$ systemctl list-units

  • To view, and also locate a unit file use systemctl cat command. A comment line containing the path to the unit file is printed as the first line of output.

    [~]$ systemctl cat project-mercury.service

JOURNALCTL

  • Journalctl is a command for quering/viewing logs collected by systemd.

  • The systemd-journald service is responsible for systemd’s log collection, and it retrieves messages from the kernel systemd services, and other sources.

  • Very useful when you are troubleshooting issues with systemd services.

    Journalctl

  • Using journalctl commands print all the log entries from oldest to the newest.

    [~]$ journalctl

  • Using journalctl -b command print all the logs from the current boot.

    [~]$ journalctl -b

  • Using journalctl -u docker.service command print all the logs specific to the unit specified, for example docker in this case.

    [~]$ journalctl -u docker.service

  • Using journalctl -u docker.service --since command print all the logs specific to the unit specified since the given time, for example docker in this case.

    [~]$ journalctl -u docker.service --since "2022-01-01 13:45:00"