Linux Survival Basics

Check systemd Journal Disk Usage

Disk alerts often lead people to delete the wrong files without checking whether the systemd journal is the real consumer.

Command

journalctl --disk-usage

What changed

Nothing changes. journalctl reports the total disk used by archived and active journal files.

Danger

safe

When to use it

Use during disk-space triage before deciding whether journal retention needs adjustment.

When not to use it

Do not use it to find application log directories outside journald.

Undo or recovery

No undo needed because the command is read-only.

Expected output

Archived and active journals take up a measured amount of disk.

demo script

Disposable terminal steps

journalctl --disk-usage
free -h

Terminal transcript Demo JSON

simulated output

What it looks like

disposable vessel

::fixture-ready::
$ journalctl --disk-usage
Archived and active journals take up 412.8M in the file system.
::exit-code::0
$ free -h
               total        used        free      shared  buff/cache   available
Mem:           1.9Gi       1.3Gi       120Mi        12Mi       420Mi       390Mi
Swap:          2.0Gi       128Mi       1.9Gi
::exit-code::0

YouTube Short

Is journald eating your disk?

Do not delete random log files during a disk alert. First check how much space the systemd journal actually uses.

experiments

A/B tests to run

Metric: completion_rate

A: Do not delete random logs.

B: Check journald usage first.