[Dovecot] VMware and Time moved backwards
phessler at theapt.org
Wed May 21 22:30:01 EEST 2008
never ever ever run ntp on virtual hardware.
instead, run ntp on the host hardware, and tell the client to always
obey the bios clock. I add "* * * * * /sbin/hwclock --localtime --hctosys"
to my crontab for that.
On 2008 May 21 (Wed) at 20:27:09 +0200 (+0200), Robert Henjes wrote:
:I followed the discussions regarding the "time moved backward" problem
:and the use of ntp in such cases. At our department we are running two
:dovecot servers within an vmware server environment, and unfortunately
:the timedrift (with ntpd active) exceeds sometimes up to 30 minutes
:virtual drift within 10 minutes realtime (mostly into future). This is
:due to some overcorrections within the TSC algorithms of the vmware
:More information and some hints to workaround are documented here:
:Nevertheless we are currently working on evaluating a stable solution by
:doing some system measurements, which would be the best option to cope
:with this problem, since the XEN environment seems to have a similar
:Running "ntpdate -u" as a cronjob is not an option due to two facts:
:a) Time is moving quickly and may cause "major problems" ;)
:b) It is not recommended by the vmware team itself as well
:We are currently considering two options:
:a) Using the "clock=pit" kernel option, which may cause the system to be
:b) using vmware tools and use only the ntp synchronisation of the host
:(we have currently only little experience with this). Also vmware tools
:are somewhat critical in case of updates. So our intention was to
:use as less vmware specific things as possible within the virtual
:machine, so only our host itself depends on vmware specific software.
:The question is, which option would you prefer? Is there another
:solution beside the mentioned ones?
:According to Timo's postings, workarounds within the dovecot itself to
:cope with "time moved backward" problems are not planned yet to be
:So best regards,
A bird whose thievish disposition suggested to someone that it
might be taught to talk.
-- Ambrose Bierce, "The Devil's Dictionary"
More information about the dovecot