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Move timex docs to the top of the file #3351

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31 changes: 16 additions & 15 deletions docs/TIME.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,21 @@
# Monitoring time sync with node_exporter

## `timex` collector

This collector exports state of kernel time synchronization flag that should be
maintained by time-keeping daemon and is eventually raised by Linux kernel if
time-keeping daemon does not update it regularly.

Unfortunately some daemons do not handle this flag properly, e.g. chrony-1.30
from Debian/jessie clears `STA_UNSYNC` flag during daemon initialisation and
does not indicate clock synchronization status using this flag. Modern chrony
versions should work better. All chrony versions require `rtcsync` option to
maintain this flag. OpenNTPD does not touch this flag at all till
OpenNTPD-5.9p1.

On the other hand combination of `sync_status` and `offset` exported by `timex`
module is the way to monitor if systemd-timesyncd does its job.

## `ntp` collector

NOTE: This collector is deprecated and will be removed in the next major version release.
Expand Down Expand Up @@ -64,18 +80,3 @@ being less than `collector.ntp.local-offset-tolerance`.
Causality violation is lower bound estimate of clock error done using SNTP,
it's calculated as positive portion of `abs(node_ntp_offset) - node_ntp_rtt / 2`.

## `timex` collector

This collector exports state of kernel time synchronization flag that should be
maintained by time-keeping daemon and is eventually raised by Linux kernel if
time-keeping daemon does not update it regularly.

Unfortunately some daemons do not handle this flag properly, e.g. chrony-1.30
from Debian/jessie clears `STA_UNSYNC` flag during daemon initialisation and
does not indicate clock synchronization status using this flag. Modern chrony
versions should work better. All chrony versions require `rtcsync` option to
maintain this flag. OpenNTPD does not touch this flag at all till
OpenNTPD-5.9p1.

On the other hand combination of `sync_status` and `offset` exported by `timex`
module is the way to monitor if systemd-timesyncd does its job.