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journald disk usage: 47.7 MB to 16.0 MB after rotate and vacuum
How do I limit journald disk usage?
After writing 200,000 log lines, journalctl --disk-usage reported 47.7 MB; journalctl --rotate then --vacuum-size=20M reduced it to 16.0 MB. A permanent cap is SystemMaxUse in a journald.conf drop-in.
Results
| after 200k lines | 47.7 MB |
|---|---|
| after rotate + vacuum 20M | 16.0 MB |
How it was measured
systemd-cat flood, then rotate and vacuum.
[Journal]
SystemMaxUse=200M
MaxRetentionSec=14dayWhy
journald enforces caps when rotating.
When this does not apply
Defaults differ by distribution.
Environment
GitHub-hosted Ubuntu 24.04 runner (2 vCPU, ~8 GB RAM), systemd 255. Measured 2026-10-12.
Source: linux-lab/03-journald-cap.sh in my content-engine repository. Treat any single run as a direction; re-run it on your hardware.
By Josué Barros, senior software engineer (full-stack, data and AI).