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docs/TIME.md
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@ -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.
@ -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.