Elaborate HostClockNotSynchronising alert

[laurivosandi]

I spent couple minutes trying to understand what this alert means? I ended up looking node exporter source, yet I am not still sure this is about NTP or not?

In any case alert description should elaborate more on the issue and provide solutions. A'la are you sure NTP is working on the host?

[paulfantom]

That alert is not really about NTP as such (the alert is based on kernel timex), but about the lack of successful time synchronization on the server. Potential causes maybe are as follows:

• ntp daemon (ntpd, chronyd, ...) is not running on host
• too large clock skew for automatic correction (for example ntpd does allow skew larger than few minutes)

Side note: The original alert was created by me in https://github.com/prometheus/node_exporter/pull/1480 :) Original source lives in https://github.com/prometheus/node_exporter/blob/master/docs/node-mixin/alerts/alerts.libsonnet#L237-L252 and it has a bit better description, although not much better.

[samber]

Took the description for node_exporter repo => #265