Ubuntu 26.04 LTS – root filesystem fills due to systemd journal growth – Fix & Prevention

📖 ~1 min read

Table of contents

1. Symptom & Impact
2. Environment & Reproduction
3. Root Cause Analysis
4. Quick Triage
5. Step-by-Step Diagnosis
6. Solution – Primary Fix
7. Solution – Alternative Approaches
8. Verification & Acceptance Criteria
9. Rollback Plan
10. Prevention & Hardening
11. Related Errors & Cross-Refs
12. References & Further Reading

Symptom & Impact

Disk usage spikes and services fail due to no space left on device.

Environment & Reproduction

Persistent high log volume or debug mode floods systemd journal storage.

df -h
sudo du -sh /var/log/journal
journalctl --disk-usage
systemctl status systemd-journald --no-pager

Root Cause Analysis

Journal retention settings are too permissive for available root volume capacity.

Quick Triage

Estimate growth rate and identify top noisy services.

journalctl -p err --since '1 day ago' | wc -l
journalctl -u SERVICE --since '1 day ago' | tail -n 100
ls -lh /var/log/journal/*/*.journal

Step-by-Step Diagnosis

Inspect journald config and active unit log rates before pruning.

grep -v '^#' /etc/systemd/journald.conf
systemd-analyze cat-config systemd/journald.conf
journalctl --since '6 hours ago' | tail -n 200

Solution – Primary Fix

Vacuum old logs and enforce bounded journal size settings.

sudo journalctl --vacuum-time=7d
sudo journalctl --vacuum-size=500M
sudo sed -i 's/^#*SystemMaxUse=.*/SystemMaxUse=500M/' /etc/systemd/journald.conf
sudo systemctl restart systemd-journald

Solution – Alternative Approaches

Forward logs centrally and reduce local retention for constrained nodes.

sudo apt install rsyslog -y
sudo systemctl enable --now rsyslog
sudo journalctl --flush

Verification & Acceptance Criteria

Accepted when free space stabilizes and journal usage remains under defined cap.

df -h /
journalctl --disk-usage
systemctl is-active systemd-journald

Rollback Plan

Restore previous journald settings if reduced retention impacts incident investigations.

sudo cp -a /etc/systemd/journald.conf.bak /etc/systemd/journald.conf
sudo systemctl restart systemd-journald

Prevention & Hardening

Set baseline log budget and alert on sudden journal growth trends.

journalctl --disk-usage
crontab -l
sudo du -sh /var/log/*

Related Errors & Cross-Refs

Related errors include ENOSPC, failed to write entry, and repeated service restarts due to full filesystem.

Related tutorial: View the step-by-step tutorial for Ubuntu 26.04 LTS.

View all Ubuntu 26.04 LTS tutorials on the Tutorials Hub →

Browse all common problems & solutions on the Tutorials Hub.

References & Further Reading

systemd-journald documentation, Ubuntu logging guidance, and disk pressure response runbooks.