Ubuntu 26.04 LTS – chrony and systemd-timesyncd run together causing time flapping

📖 ~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

Administrators observe: Ubuntu 26.04 LTS – chrony and systemd-timesyncd run together causing time flapping. Time-sensitive services become unstable.

Environment & Reproduction

Issue appears after migration from one NTP stack to another without disabling the old service.

# Baseline context
lsb_release -a
timedatectl status
systemctl status chrony systemd-timesyncd --no-pager
chronyc tracking || true
sudo journalctl -p warning -n 120 --no-pager

Root Cause Analysis

Competing NTP daemons can repeatedly step or slew time in opposing patterns.

Quick Triage

Confirm dual-daemon state and choose a single authoritative service.

# Quick triage
systemctl is-active chrony
systemctl is-active systemd-timesyncd
ss -lunp | grep ':123' || true

Step-by-Step Diagnosis

Inspect tracking data and logs for frequent clock source changes.

# Detailed diagnosis
chronyc sources -v || true
chronyc tracking || true
sudo journalctl -u chrony -u systemd-timesyncd --since '2 hours ago' --no-pager

Solution – Primary Fix

Run only chrony for server workloads and disable timesyncd.

# Primary fix
sudo systemctl disable --now systemd-timesyncd
sudo apt-get install -y chrony
sudo systemctl enable --now chrony
timedatectl set-ntp false

Solution – Alternative Approaches

If lightweight setup is preferred, remove chrony and keep timesyncd only.

# Alternative
sudo apt-get purge -y chrony
sudo systemctl enable --now systemd-timesyncd
timedatectl set-ntp true

Verification & Acceptance Criteria

Single time daemon is active and offset remains stable.

# Verify
systemctl is-active chrony
systemctl is-active systemd-timesyncd
chronyc tracking || true
timedatectl status

Rollback Plan

Restore prior daemon choice if policy requires different synchronization stack.

# Rollback
sudo systemctl disable --now chrony || true
sudo systemctl enable --now systemd-timesyncd
timedatectl set-ntp true

Prevention & Hardening

Enforce one NTP daemon in baseline templates and configuration management.

# Hardening
dpkg -l | grep -E '^iis+(chrony|systemd-timesyncd)'
systemctl list-unit-files | grep -E 'chrony|timesyncd'

Related Errors & Cross-Refs

Related patterns include frequent clock jumps and authentication token expiry anomalies.

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

chrony documentation and Ubuntu time service administration guidelines.