Re: [gentoo-user] Server system date synchronizaion

[staticsafe <me@staticsafe.ca>]

On 4/25/2013 19:50, Alan McKinnon wrote:
> On 26/04/2013 01:42, William Kenworthy wrote:
>> Does anyone know a good guide to using time sync in VM's, for both
>> windows and linux (gentoo) guests using libvirt?  Especially for guests
>> that are resumed, or the whole virtualisation system is hibernated? (ntp
>> refuses to resync after guest pause/save/restore/resume (known problem),
>> even with "tinker panic 0"
> 
> 
> That's not a bug, it's by design.
> 
> If ntpd detects the clock is out by more than X seconds [1], it will not
> try to correct the difference, concluding that something is wrong and a
> human must decide. It can't easily tell the difference between a resumed
> guest (or even that it was resumed at all) and a severe problem.
> 
> We fixed this by taking the easy route of least resistance;
> 
> 1. run ntpdate on startup/restart once before ntpd starts
> 2. start ntpd as normal
> 3. a colleague wrote a $MAGIC_HOOK to detect resumed guests that runs
> ntpdate once
> 
> True, it's a brutal solution and uses a baseball bat where some finesse
> might be less ugly, but it suits our needs just fine.
> 
> [1] I forget what X is and am too lazy to look it up. Is it 30 seconds
> or thereabouts?
> 
> 

"When first started, the daemon normally polls the servers listed in the
configuration file at 64-s intervals. In order to allow a sufficient
number of samples for the NTP algorithms to reliably discriminate
between correctly operating servers and possible intruders, at least
four valid messages from the majority of servers and peers listed in the
configuration file is required before the daemon can set the local
clock. However, if the difference between the client time and server
time is greater than the panic threshold, which defaults to 1000 s, the
daemon will send a message to the system log and shut down without
setting the clock." [0]

[0] - http://doc.ntp.org/4.1.1/debug.htm
-- 
staticsafe
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