[Dovecot] ntp revisited (so what to do ?)

[Stan Hoeppner]

On 5/8/2011 7:36 AM, Jose Celestino wrote:
> On Dom, 2011-05-08 at 11:07 +0100, Spyros Tsiolis wrote:
>> OK,
>>
>> So what you people say is :
>>
>> 1. Run "ntpdate" during startup only once
>> 2. After that, keep time with ntpd
>>
>> Right ?
>>
>
> Right, that ensures that time is correct (ntpdate run at startup) and
> that it is kept correct without the clock going back (ntp running as
> daemon).

This is not correct.  You're assuming that ntpd doesn't perform sanity 
checks on the system time when the daemon starts, which is not the case.

Again, use ntpd or ntpdate, not both.  Preferably, today, in 2011, and 
for many years now, only use ntpd, except in guests sitting atop a 
hypervisor.  In the virtual environment case you run ntpd in the 
hypervisor and configure the guest kernels appropriately.

There is a plethora of platform specific documentation out there 
covering the VM time keeping case so I won't attempt to repeat it all 
here, except to say that with Linux the first/best step is running a 
tickless kernel, which is now the default on many distros, as it helps 
both laptops/netbooks when in sleep mode and VM guests when they get 
time sliced into what is in essence a sleep state as far as the kernel 
sees system clock ticks.

-- 
Stan