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So, I noticed there's about a 10 minute drift on my VM hosting server from what time it's supposed to be. In traditional environments, I would just restart the system (and change the BIOS time if necassary).

The hosting server is Ubuntu 12.04. Undertsanding that some process could be time sensitive (NTP?), I was wondering how this might affect the relation between the host and hosted system (currently hosting 4: 3 Ubuntu 12.04 servers with one being a web server, and 1 Windows Server 2008 file server). I am using Virtual Box 4 with it's headless option.

Ultimately, I am trying to avoid from shutting down the host (which ultimately mean shutthing down the other hosted systems). Is this safe?

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1 Answer 1

up vote 4 down vote accepted

Just do the right thing and configure it with multiple NTP sources.

The 'hwclock' command is how you talk to the system clock, so there's no need for BIOS changes.

For the VM hosts (perhaps it's not necessary anymore), but I like to run hwclock --systohc every day or two to update the BIOS clock.

I don't have any KVM virtualization hosts anymore, but if you're getting drift you should probably also adjust your ticket granularity about 10x larger so that the host doesn't drift. I ended up using the 'divider' kernel option, but it may not be appropriate for your equipment and kernel. I'd this this link: http://s19n.net/articles/2011/kvm_clock.html

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I'm not seeing any drift in KVM guests on current versions of KVM; they have a nice new paravirtualized RTC that works very well. –  Michael Hampton Sep 14 '12 at 21:42
    
@MichaelHampton Quite likely to be true. They were working pretty hard on that problem when I started moving over to VMWare. When I started mucking around with KVM, the drift was bad enough that NTP couldn't correct it either. –  Magellan Sep 14 '12 at 21:44

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