libvirt users - Oct 2014 - Re: wrong time in guest logs

Hi,

i have several vm's running on KVM hosts. Recently i found out that the time
in the log-files of the guests (/var/log/libvirt/qemu/xxx.log) is wrong. The
time on the guest itself is right, just the time in the log-files is one hour
back. Windows and linux vm's are affected. Also on another host the same.
Changing the clock offset does not have any influence, still the wrong time in
the log file.
Any ideas ?


Bernd

--
Bernd Lentes

Systemadministration
Institut für Entwicklungsgenetik
Gebäude 35.34 - Raum 208
HelmholtzZentrum münchen
bernd.lentes@helmholtz-muenchen.de
phone: +49 89 3187 1241
fax:   +49 89 3187 2294
http://www.helmholtz-muenchen.de/idg

Die Freiheit wird nicht durch weniger Freiheit verteidigt


Helmholtz Zentrum München
Deutsches Forschungszentrum für Gesundheit und Umwelt (GmbH)
Ingolstädter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: MinDir´in Bärbel Brumme-Bothe
Geschäftsführer: Prof. Dr. Günther Wess, Dr. Nikolaus Blum, Dr. Alfons Enhsen
Registergericht: Amtsgericht München HRB 6466
USt-IdNr: DE 129521671

On Tue, Oct 28, 2014 at 05:08:45PM +0100, Lentes, Bernd
wrote:
> Hi,
> 
> i have several vm's running on KVM hosts. Recently i found out that the
> time in the log-files of the guests (/var/log/libvirt/qemu/xxx.log) is
> wrong. The time on the guest itself is right, just the time in the
log-files
> is one hour back. Windows and linux vm's are affected. Also on another
host
> the same. Changing the clock offset does not have any influence, still the
> wrong time in the log file.
> Any ideas ?
The timestamps in libvirt log files should always be in UTC, never local
timezone. We had to roll our own code for generating timestamps since the
standard glibc formatting turned out to not be re-entrant safe, and as a
results we unfortunately cannot do localtime conversion.


Regards,
Daniel
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On 10/28/2014 10:08 AM, Lentes, Bernd wrote:
> Hi,
[can you convince your mailer to wrap long lines?]
> 
> i have several vm's running on KVM hosts. Recently i found out that the
time in the log-files of the guests (/var/log/libvirt/qemu/xxx.log) is wrong.
The time on the guest itself is right, just the time in the log-files is one
hour back. Windows and linux vm's are affected. Also on another host the
same. Changing the clock offset does not have any influence, still the wrong
time in the log file.
The time in libvirt logs is ALWAYS tied to UTC, precisely because that
is unambiguous (any log that outputs timestamps in local time risks
being misinterpreted if the log is read from a different timezone,
especially if the timezone name is not included as part of the
timestamp).  Based on you email address, it looks like your problem is
that Germany is coincident with UTC in the summer, but one hour off in
the winter, and that your "problem" (which is not a bug) was made
manifest because Germany left daylight savings this week.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

Eric wrote:

> -----Ursprüngliche Nachricht-----
> Von: Eric Blake [mailto:eblake@redhat.com]
> Gesendet: Dienstag, 28. Oktober 2014 17:18
> An: Lentes, Bernd; libvirt-ML (libvirt-users@redhat.com)
> Betreff: Re: [libvirt-users] wrong time in guest logs
>
> On 10/28/2014 10:08 AM, Lentes, Bernd wrote:
> > Hi,
>
> [can you convince your mailer to wrap long lines?]
>
> >
> > i have several vm's running on KVM hosts. Recently i found out
that the
> time in the log-files of the guests (/var/log/libvirt/qemu/xxx.log) is
wrong.
> The time on the guest itself is right, just the time in the log-files is
one hour
> back. Windows and linux vm's are affected. Also on another host the
same.
> Changing the clock offset does not have any influence, still the wrong time
in
> the log file.
>
> The time in libvirt logs is ALWAYS tied to UTC, precisely because that is
> unambiguous (any log that outputs timestamps in local time risks being
> misinterpreted if the log is read from a different timezone, especially if
the
> timezone name is not included as part of the timestamp).  Based on you
> email address, it looks like your problem is that Germany is coincident
with
> UTC in the summer, but one hour off in the winter, and that your
"problem"
> (which is not a bug) was made manifest because Germany left daylight
> savings this week.
>
Nearly. In summer we have in germany UTC+2, in winter UTC+1.


Bernd

Helmholtz Zentrum München
Deutsches Forschungszentrum für Gesundheit und Umwelt (GmbH)
Ingolstädter Landstr. 1
85764 Neuherberg
www.helmholtz-muenchen.de
Aufsichtsratsvorsitzende: MinDir´in Bärbel Brumme-Bothe
Geschäftsführer: Prof. Dr. Günther Wess, Dr. Nikolaus Blum, Dr. Alfons Enhsen
Registergericht: Amtsgericht München HRB 6466
USt-IdNr: DE 129521671