| Re: [chrony-users] System Clock is updated before the TAI-UTC offset is applied for PHC source in chrony 6.4.1 |
[ Thread Index |
Date Index
| More chrony.tuxfamily.org/chrony-users Archives
]
- To: Simon Plackett <plackettsj1@xxxxxxxxx>
- Subject: Re: [chrony-users] System Clock is updated before the TAI-UTC offset is applied for PHC source in chrony 6.4.1
- From: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
- Date: Mon, 19 Jan 2026 10:50:56 +0100
- Cc: chrony-users@xxxxxxxxxxxxxxxxxxxx
- Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1768816260; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lq9Yshi1TC8ziMpZ+I61CqQZCGvECpxcRHPwplwm+xA=; b=QqIaU1q4CSzhJOVwDXONLyqhuIqHb7kHQNDPn5GsyLDs75Ry6rtV46oqGNxxGPI5qVx70d fcJOg2LCxHUcaT93t3U4w1BRjdrv/gcF65aZLaVYY78xG5nkmiVDN9QGLxi/Evaqc2K/35 nok+uO4g2cGx1xETyZmgYdNpOCrQjdw=
On Fri, Jan 16, 2026 at 06:28:35AM +0000, Simon Plackett wrote:
> The issue is that on startup the system clock is set by the PHC source
> before the TAI-UTC adjustment has been applied which means it jumps
> 36+ seconds one way and then back again during the startup. This
> obviously trashes the PHC as a source, and it didn't happen
> previously.
I don't see that happening in my tests with 4.6.1 and 4.8.
Is the PHC already synchronized when chronyd is started? Please check
the ptp4l and chronyd logs and see if chronyd is not started too soon.
Some NIC drivers initilize the PHC to the system time when the driver
is loaded, but not applying any UTC-TAI offset, so you could see a 37
jump back and forth if the PHC was corrected after chronyd was
started.
That's one of the reasons it's better to use the chrony SOCK/SHM
refclock fed by phc2sys using the ntpshm or refclock_sock servo. With
the timemaster program that should be easy to configure.
--
Miroslav Lichvar
--
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "help" in the subject.
Trouble? Email listmaster@xxxxxxxxxxxxxxxxxxxx.