NodeClockNotSynced: what to do when it fires

Alert rule

alert: NodeClockNotSynced
expr: node_timex_sync_status == 0
for: 15m
severity: warning

Alert message: Time is not synchronized ({{ $labels.instance }})

What it means

The kernel reports that the clock is not synchronised (node_timex_sync_status == 0) for more than 15 minutes. The alert can also appear with a small offset, before NodeClockSkew fires.

Common causes

The same as for NodeClockSkew; also the time service has only just been started and has not yet reached synchronisation, or is not installed at all.

Diagnostics

timedatectl status          # the "System clock synchronized" line
chronyc tracking
journalctl -u chronyd -u systemd-timesyncd --since "1 hour ago" --no-pager

How to fix

Install and enable an NTP client, open outbound UDP 123 or specify reachable servers in the configuration (/etc/chrony.conf or /etc/systemd/timesyncd.conf).

When it is OK to silence

For machines deliberately running without synchronisation (lab setups).

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