Free disk space on linux with systemd

Date: 07 Jun 2025

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Today I had to perform some operations on a linux VM with 100% disk usage. This is not always straight forward, so I needed a way to free up some space, before doing my operations.

Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           392M   36M  357M  10% /run
/dev/vda1        14G   14G     0 100% /
tmpfs           2.0G     0  2.0G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           392M     0  392M   0% /run/user/1000

After I went through the usual like apt autoclean && apt autoremove or removing files from /tmp and /home without freeing any useful space, I turned to systemd.

Logs will always take up some space on a linux server, and using journalctl it’s straightforward to clean those logs.

Rotate + delete and vacuum journals

Verify the storage usage by logs with the --disk-usage parameter.

–disk-usage
Shows the current disk usage of all journal files. This shows the sum of the disk usage of all archived and active journal files.

Added in version 190.

$ sudo journalctl --disk-usage
Archived and active journals take up 136.0M in the file system.

Rotate

When rotating logs, the current logfile gets marked as archived and renamed, while a new blank log file gets created.

–rotate
Asks the journal daemon to rotate journal files. This call does not return until the rotation operation is complete. Journal file rotation has the effect that all currently active journal files are marked as archived and renamed, so that they are never written to in future. New (empty) journal files are then created in their place. This operation may be combined with –vacuum-size=, –vacuum-time= and –vacuum-file= into a single command, see above.

Added in version 227.

$ sudo journalctl --rotate
(No output from this command)

Delete and vacuum

When old log files have been archived, we can delete and vacuum them to free up disk space.

–vacuum-size
removes the oldest archived journal files until the disk space they use falls below the specified size. Accepts the usual “K”, “M”, “G” and “T” suffixes (to the base of 1024).

Note that running –vacuum-size= has only an indirect effect on the output shown by –disk-usage, as the latter includes active journal files, while the vacuuming operation only operates on archived journal files

$ sudo journalctl --vacuum-size=100M
Deleted archived journal /var/log/journal/2..6/system@1..d.journal (8.0M).
Deleted archived journal /var/log/journal/2..6/system@1..f.journal (8.0M).
Vacuuming done, freed 868.5M of archived journals from /var/log/journal/2..6.
Vacuuming done, freed 0B of archived journals from /run/log/journal.

Verify logs

Before calling it a day, use the --verify option to validate the integrity of the leftover logs.

–verify
Check the journal file for internal consistency. If the file has been generated with FSS enabled and the FSS verification key has been specified with –verify-key=, authenticity of the journal file is verified.

Added in version 189

$ sudo journalctl --verify
PASS: /var/log/journal/2..6/user-1000@d..d.journal
PASS: /var/log/journal/2..6/system@2..1.journal
PASS: /var/log/journal/2..6/user-1000@d..1.journal
PASS: /var/log/journal/2..6/system@2..a.journal
PASS: /var/log/journal/2..6/user-1000.journal

Conclusion

I now have enough free space, to not get errors when trying to start/stop services or run commands, with the need for creating temporary files.

Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           392M  1.2M  391M  10% /run
/dev/vda1        14G   13G  144M  99% /
tmpfs           2.0G     0  2.0G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           392M     0  392M   0% /run/user/1000

Journalctl man page quotes from: journalctl(1)

Tags: Linux, Systemd