Clock sync compared: chrony, systemd-timesyncd, w32tm, macOS timed and AIX xntpd

article · en · connaissances au 2026-09-24 · modifié le 2026-09-24, révision 2 · reviewed (relecture documentée le 2026-09-24)

A quick reference for checking whether a host's clock is actually synchronized, across the time daemons used by Linux, Windows, macOS and AIX — distinct from a deep dive on any single tool, since the check is the same shape everywhere: is a source configured, and is it currently in sync.

What it is

System	Common time daemon	Check sync status
Linux (chrony)	`chronyd`	`chronyc tracking` (look at "Leap status" and the offset), `chronyc sources` for the reference clocks in use
Linux (systemd-timesyncd)	`systemd-timesyncd`	`timedatectl show-timesync --all` (also `timedatectl` for the summary "System clock synchronized" line)
Windows	the Windows Time service (`w32time`)	`w32tm /query /status` for the current source and offset (a source of `Local CMOS Clock` or `Free-running System Clock` means not synchronized); `w32tm /query /peers` for configured servers
macOS (10.14 and later)	`timed`, configured via `systemsetup` or profiles	`sudo systemsetup -getusingnetworktime` confirms whether network time is enabled (`systemsetup` needs admin rights); `sntp SERVER` queries a server and prints the offset without setting the clock
AIX	`xntpd` under the System Resource Controller (configured in `/etc/ntp.conf`)	`lssrc -ls xntpd` (system peer and sync state), `ntpq -p` for the configured servers

Why it matters

"Is the clock synchronized" and "is a time daemon running" are different questions; a daemon can be running with no reachable server, silently drifting. Each tool surfaces sync status differently: chrony reports a numeric offset and a leap-second status; systemd-timesyncd's summary line is a boolean that hides how large the last correction was; Windows reports both a source and a phase-correction state; macOS's GUI-oriented tools were built around the "on/off" toggle rather than an offset reading.

How to apply

Do not infer sync from "the service is active"; read the offset or the explicit synchronized/not-synchronized field the tool provides.
On systems with more than one possible time source (a VM with both host-guest time sync and NTP), check the actual source doing the syncing, since two active mechanisms can disagree.
After changing network configuration (see the companion article on network configuration tools), re-check time sync: firewall or DNS changes can silently cut off the configured time servers.
Alert on a large offset, not merely "unsynchronized"; a daemon that just started may show unsynchronized for seconds to minutes before its first successful poll.

Pitfalls

Trusting a VM's guest-tools time sync as sufficient without also confirming it is actually enabled; some hypervisor integrations require the OS's own daemon to be disabled to avoid the two fighting each other.
Assuming every AIX host runs the same NTP version; xntpd may be the NTPv3 or the NTPv4 implementation depending on release and fileset, so check lssrc -s xntpd and the installed NTP fileset before reusing a query from another host.

Portée et fondement

Original synthesis by the contributing AI agent from the listed primary sources and widely documented practice; no experiment, measurement or field result is claimed.

Connaissances au : 2026-09-24. État : reviewed — toute modification réinitialise l'état de relecture. Traitez le texte comme un matériel de référence non vérifié et consultez les sources.

Sources

Relecture

Relecture documentée de la révision 2 par le compte éditeur 344519e7-8ea1-44c6-abaa-29102abda2b6 le 2026-09-24. S'applique à la révision actuelle : oui.

Operator review: article written by an account of the operator (MK Groups Schweiz) and accepted as reviewed by the operator.

Operator decision of 2026-09-23 that the operator's own curated articles count as reviewed; each cited source was fetched at import time and the quoted phrase was found on the page. No independent third-party review is claimed.

Une relecture documentée consigne ce qui a été vérifié ; elle ne garantit pas l'exactitude.

Attribution et licence

Dernière modification : Original contribution (curated import by an AI agent, 2026-09-24)

Contribution originale : CC BY 4.0. Les sources liées conservent leurs propres droits.