mirror of
https://github.com/prometheus/node_exporter.git
synced 2024-12-20 15:36:07 +01:00
80 lines
3.5 KiB
Markdown
80 lines
3.5 KiB
Markdown
# Monitoring time sync with node_exporter
|
||
|
||
## `ntp` collector
|
||
|
||
This collector is intended for usage with local NTPD like [ntp.org](http://ntp.org/), [chrony](https://chrony.tuxfamily.org/comparison.html) or [OpenNTPD](http://www.openntpd.org/).
|
||
|
||
Note, some chrony packages have `local stratum 10` configuration value making chrony a valid server when it it is unsynchronised. This configuration makes one of `node_ntp_sanity` heuristics unreliable.
|
||
|
||
Note, OpenNTPD does not listen for SNTP queries by default, you should add `listen on 127.0.0.1` configuration line to use this collector with OpenNTPD.
|
||
|
||
### `node_ntp_stratum`
|
||
|
||
This metric shows [stratum](https://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_strata) of local NTPD.
|
||
|
||
Stratum `16` means that clock are unsynchronised. See also aforementioned note about default local stratum in chrony.
|
||
|
||
### `node_ntp_leap`
|
||
|
||
Raw leap flag value. 0 – OK, 1 – add leap second at UTC midnight, 2 – delete leap second at UTC midnight, 3 – unsynchronised.
|
||
|
||
OpenNTPD ignores leap seconds and never sets leap flag to `1` or `2`.
|
||
|
||
### `node_ntp_rtt`
|
||
|
||
RTT (round-trip time) from node_exporter collector to local NTPD. This value is
|
||
used in sanity check as part of causality violation estimate.
|
||
|
||
### `node_ntp_offset`
|
||
|
||
[Clock offset](https://en.wikipedia.org/wiki/Network_Time_Protocol#Clock_synchronization_algorithm) between local time and NTPD time.
|
||
|
||
ntp.org always sets NTPD time to local clock instead of relaying remote NTP
|
||
time, so this offset is irrelevant for this NTPD.
|
||
|
||
This value is used in sanity check as part of causality violation estimate.
|
||
|
||
### `node_ntp_reference_timestamp_seconds`
|
||
|
||
Reference Time. This field show time when the last adjustment was made, but
|
||
implementation details vary from "**local** wall-clock time" to "Reference Time
|
||
field in incoming SNTP packet".
|
||
|
||
`time() - node_ntp_reference_timestamp_seconds` and
|
||
`node_time_seconds - node_ntp_reference_timestamp_seconds` represent some estimate of
|
||
"freshness" of synchronization.
|
||
|
||
### `node_ntp_root_delay` and `node_ntp_root_dispersion`
|
||
|
||
These values are used to calculate synchronization distance that is limited by
|
||
`collector.ntp.max-distance`.
|
||
|
||
ntp.org adds known local offset to announced root dispersion and linearly
|
||
increases dispersion in case of NTP connectivity problems, OpenNTPD does not
|
||
account dispersion at all and always reports `0`.
|
||
|
||
### `node_ntp_sanity`
|
||
|
||
Aggregate NTPD health including stratum, leap flag, sane freshness, root
|
||
distance being less than `collector.ntp.max-distance` and causality violation
|
||
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.
|