Parse the systemd journal with QJournalctl

Going Remote

If you wondered at the beginning why QJournalctl needs the libssh library, the explanation is that QJournalctl can also display logs from remote computers via SSH. The Remote menu item offers commands for opening connections via SSH, as well as saving the access credentials for cases in which you query the same computers frequently. QJournalctl supports password-based access, as well as the use of a key file (Figure 3).

Figure 3: Easy access to remote machines via SSH is a special treat. You can save the credentials of remote machines and quickly connect later.

Under the bar with the three tabs, the main window offers options named Follow the journal in realtime and Reverse output (latest message on top). The box to the left of Follow the journal in realtime always stays gray. If you are looking at the log of the currently active boot process, the live function is automatically added, which is also indicated by the additional (realtime following enabled) message at the end of the top line. If you are looking at the log of an older boot process, the live function doesn't make much sense, of course. But you can still check the Reverse output box to display the journal output in reverse order.

What's Missing?

QJournalctl deliberately does not provide functions for performing many of the administrative tasks that journalctl handles in the terminal. Systemd takes the total size of the journal, as well as the individual files, from the /etc/systemd/journald.conf configuration file. Optionally, you can truncate the journal on the fly; for example, the command from the first line of Listing 4 truncates it to 100MB.

Listing 4

Manual Work

01 $ sudo journalctl --vacuum-size=100M
02 $ sudo journalctl --vacuum-time=1month
03 $ systemctl status systemd-journald

You can also drop all messages more than, say, one month old (Line 2). The only status query QJournalctl allows in this context relates to the total size of the journal. You still need to query the general health of the service in the terminal (Line 3); use journalctl --verify to check the integrity of individual journals.


QJournalctl is a handy tool for anyone who doesn't use the journal regularly and thus does not have all the necessary commands for the terminal at their fingertips. In particular, QJournalctl facilitates searching within date and time constraints. The ability to display log files on remote computers and select them from a saved list is quite useful.

The QJournalctl project is maintained on GitHub. The developer told us that a major update is coming which will include a new colorized output feature that will help you highlight and organize log data [3].

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