Re: [Dovecot] VMware and Time moved backwards
on 5-21-2008 2:39 PM Bjørn T Johansen spake the following: Why not? I have been running ntp inside vmware for many years now, without any problems And I occasionally fail to come to a full stop at a stop sign, and don't get a ticket, but is it the proper thing to do? -- MailScanner is like deodorant... You hope everybody uses it, and you notice quickly if they don't signature.asc Description: OpenPGP digital signature
Re: [Dovecot] VMware and Time moved backwards
the short explanation is that both the VM container and ntp adjust the clock tick, and both think they are the only application that does so. There are longer explanations in many places around the internet. On 2008 May 21 (Wed) at 23:39:17 +0200 (+0200), Bj??rn T Johansen wrote: :Why not? I have been running ntp inside vmware for many years now, without any problems : :BTJ : :On Wed, 21 May 2008 12:30:01 -0700 :Peter Hessler <[EMAIL PROTECTED]> wrote: : :> 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. -- "A power so great, it can only be used for Good or Evil!" -- Firesign Theatre, "The Giant Rat of Sumatra"
Re: [Dovecot] VMware and Time moved backwards
Why not? I have been running ntp inside vmware for many years now, without any problems BTJ On Wed, 21 May 2008 12:30:01 -0700 Peter Hessler <[EMAIL PROTECTED]> wrote: > 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 > : > : >
Re: [Dovecot] VMware and Time moved backwards
Thank you for the prompt answers @Luuk Vosslamber >finding correct values for the following entrys in your vmware(host) >config file might solve some things: >host.cpukHz = 1596000 <== depends on processor speed ;-) >host.noTSC = TRUE >ptsc.noTSC = TRUE >hostinfo.noTSC = TRUE >tools.syntime = TRUE > >Above values go with the presumption that the host CPU is running at a >fixed frequency. The variable frequency seems to be the origin of this >problem.. We tried your parameters already, but they are not an option, unless you have the following a) machine smp disabled (enabled in our case) b) other machines on the host system have really low load c) vmware tools should not be missing on guest @Peter Hessler >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. Thank you very much Peter, this hint opens up a bunch of new possibilities only mentioning "adjtimex" ... BUT: And this brings me back to, why I posted this issue to the dovecot mailinglist and not elsewhere: All these guest based solutions lead to a fixed time movement (we used previously ntpdate -u every 7 minutes, ntp itself synchronizes every 11 minutes with the hardware clock for calculating drifts), which happens about once per week, that the time movement backward is larger than 11 seconds between two dovecot imap operations, which leads to an immediate shutdown of the dovecot process. All other services on these machine can cope with this. So the question is how to get these adjustments smooth or close to realtime. Best regards, Robert Btw.: We are running Dovecot 1.0.13 from Debian etch-backports (which is an important information since debian seems to have its own rules ;) )
Re: [Dovecot] VMware and Time moved backwards
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 : : -- Magpie, n.: A bird whose thievish disposition suggested to someone that it might be taught to talk. -- Ambrose Bierce, "The Devil's Dictionary"
Re: [Dovecot] VMware and Time moved backwards
At 8:27 PM +0200 5/21/08, 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 That page seems to say that running ntpd inside a VMware guest is not a good choice. I would think that you'd be best off doing what your vendor advises on that page, at least as a start, rather than trusting in the consistently brilliant and consistently unified consensus view of the Dovecot admin community on a question which is only very tangentially related to Dovecot. 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? I think that trying to avoid VMware-specific software in a VMware environment is unwise. VMware software is what provides your virtual system with a clock. -- Bill Cole [EMAIL PROTECTED]
[Dovecot] VMware and Time moved backwards
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
