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On 26/04/13 07:57, staticsafe wrote: |
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> On 4/25/2013 19:50, Alan McKinnon wrote: |
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>> On 26/04/2013 01:42, William Kenworthy wrote: |
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>>> Does anyone know a good guide to using time sync in VM's, for both |
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>>> windows and linux (gentoo) guests using libvirt? Especially for guests |
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>>> that are resumed, or the whole virtualisation system is hibernated? (ntp |
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>>> refuses to resync after guest pause/save/restore/resume (known problem), |
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>>> even with "tinker panic 0" |
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>> |
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>> |
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>> That's not a bug, it's by design. |
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>> |
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>> If ntpd detects the clock is out by more than X seconds [1], it will not |
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>> try to correct the difference, concluding that something is wrong and a |
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>> human must decide. It can't easily tell the difference between a resumed |
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>> guest (or even that it was resumed at all) and a severe problem. |
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>> |
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>> We fixed this by taking the easy route of least resistance; |
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>> |
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>> 1. run ntpdate on startup/restart once before ntpd starts |
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>> 2. start ntpd as normal |
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>> 3. a colleague wrote a $MAGIC_HOOK to detect resumed guests that runs |
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>> ntpdate once |
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>> |
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>> True, it's a brutal solution and uses a baseball bat where some finesse |
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>> might be less ugly, but it suits our needs just fine. |
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>> |
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>> [1] I forget what X is and am too lazy to look it up. Is it 30 seconds |
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>> or thereabouts? |
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>> |
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>> |
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> |
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> "When first started, the daemon normally polls the servers listed in the |
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> configuration file at 64-s intervals. In order to allow a sufficient |
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> number of samples for the NTP algorithms to reliably discriminate |
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> between correctly operating servers and possible intruders, at least |
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> four valid messages from the majority of servers and peers listed in the |
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> configuration file is required before the daemon can set the local |
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> clock. However, if the difference between the client time and server |
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> time is greater than the panic threshold, which defaults to 1000 s, the |
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> daemon will send a message to the system log and shut down without |
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> setting the clock." [0] |
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> |
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> [0] - http://doc.ntp.org/4.1.1/debug.htm |
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> |
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Keep reading :) |
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Check out "tinker panic o" I mentioned, or the -g argument to ntpd |
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The docs say its a "once only" adjustment in one place, but I am not |
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sure thats actually the case. |
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BillK |
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