Clock occasionally jumps backwards on 11.1-RELEASE

[Alan Somers]

On Tue, Jan 23, 2018 at 3:48 AM, Mike Pumford <michaelp at bsquare.com> wrote:

> On 22/01/2018 17:07, Alan Somers wrote:
>
>> Since upgrading my jail server to 11.1-RELEASE, the clock occasionally
>> jumps backwards by 5-35 minutes for no apparent reason.  Has anybody seen
>> something like this?
>>
>> Details
>> =====
>>
>> * Happens about once a day on my jail server, and has happened at least
>> once on a separate bhyve server.
>>
>> * The jumps almost always happen between 1 and 3 AM, but I've also seen
>> them happen at 06:30 and 20:15.
>>
>> That's the window when the period scripts are run which if you have a
> default configuration and a lot of jails will put the system under a lot of
> stress.
>

That did not fail to escape my notice.  However, none of the jails'
periodic jobs involve the clock in any way.  And I wouldn't think that a
high CPU load could cause clock drift, could it?  This isn't Windows XP,
after all.


> * I'm using the default ntp.conf file.
>>
>> Are you running ntpd inside the jail or on the jail host? On my jail
> systems (which are 10.3 and 11.1) I run ntpd out the jail host (outside all
> jails) and not inside the jails and the jails then get the accurate time as
> the underlying host has accurate time.
>

Only on the host.

New info: there is a possibility that my NFS server is hanging for awhile.
That would explain my problem's timing.  However, ntpd shouldn't be
accessing any NFS shares, and I wouldn't think that a hung NFS server
should be able to pause the clock.  I'm doing a new experiment that should
be more informative.  But I'll have to wait until the problem recurs to
learn anything.

-Alan