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Autore: Didier Kryn
Data:  
To: dng
Oggetto: Re: [DNG] Detailed technical treatise of systemd
Le 10/11/2015 01:01, Hendrik Boom a écrit :
> On Mon, Nov 09, 2015 at 09:57:48PM +0100, Didier Kryn wrote:
>> Le 09/11/2015 20:12, Rainer Weikusat a écrit :
>>> After booting, the discrepancy between the RTC clock and the actual time
>>> is unknown.
>>      I remember having had a problem with two servers when the time
>> discrepency reached 5mn (It was for kerberos authentication). We
>> discovered that one of the two was not synchronized by NTP at all.
>> The problem showed up after 4 years with many reboots and no clock
>> adjustment on the non-synchronized host.

>>
>>      NTP does not adjust the RTC brutally; it seems to adjust slowly
>> the frequency so that synchronization happens without the process
>> being noticeable to other apps - it can take hours. On shutdown it
>> saves the RTC settings in /var/lib/ntp/ntp.drift, and (AFAIU)
>> /var/lib/hwclock/adjtime. After some days of running NTP, your RTC
>> is well trimmed and does not drift much. It does not stop running
>> when you power-off your computer. Therefore, at startup the
>> discrepancy is very small - unless the battery of the RTC is dead or
>> you stopped the computer for a year.

>>
>>      Everything above is non-authoritative; it is the result of my
>> own observations.
> I used chrony as my NTP client.  If the discrepancy between local time
> on the machine and the correct time, it just gave up.  I/m not sure at
> what discrepancy this happened, but it helped a lot to explicitly set
> the time by my watch.  Once the time was properly synced, though,
> chrony worked well to keep it correct.

>
>


     I use the package simply named "ntp" in Debian repo. Time synchro 
is critical for servers using Kerberos authentication, and for diskless 
embedded machines using NFS, for the filesystem time to match the host 
time - imagine what 'make' can do when you edit a source file and it 
gets a modification time in the past.


     This ntp client doesn't give up.


     Didier