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: : :Hi, : :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 :virtual machine. : :More information and some hints to workaround are documented here: :http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1420 : :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 :issue. : :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 :to slow :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 :impelented. : :So best regards, :Robert : :
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