8.3 Advanced Usage
The following sections cover advanced topics for system administrators. For even more
advanced systemd documentation, please refer Lennart Pöttering's series about
systemd for administrators at http://0pointer.de/blog/projects.
8.3.1 System Log
Section 8.1.2, “Debugging Services” (page 136) explains how to view log messages for
given service. However, displaying log messages is not restricted to service logs. You
can also access and query the complete log written by systemd—the so-called
“Journal”. Use the command systemd-journalctl to display the complete log
starting with the oldest entries. Refer to man 1 systemd-journalctl for options
such as applying lters or changing the output format.
8.3.2 Snapshots
You can save the current state of systemd to a named snapshot and later revert to it
with the isolate subcommand. This is useful when testing services or custom targets,
because it allows you to return to a dened state at any time. A snapshot is only available
in the current session and will automatically be deleted on reboot. A snapshot name
must end in .snapshot.
Create a Snapshot
systemctl snapshot <my_snapshot>.snapshot
Delete a Snapshot
systemctl delete <my_snapshot>.snapshot
View a Snapshot
systemctl show <my_snapshot>.snapshot
Activate a Snapshot
systemctl isolate <my_snapshot>.snapshot
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