[ntp:questions] no ntp synchronisation: 2s to 6s time shift !

Unruh unruh-spam at physics.ubc.ca
Tue Feb 12 17:25:05 UTC 2008

Any place where these different clock models is described?
And defined (what is tsc?)

Martin Burnicki <martin.burnicki at meinberg.de> writes:


>Thierry MARTIN wrote:
>> Hello,
>> Can anyone tell me if a time shift greater than 2s per day is ""normal""
>> on a linux system that has no "external" synchronisation (ntp)?
>> I tryied "adjtimex -a" which gives unreliable results: it worked fine on
>>    one machine (less than 1s shift / day) and badly on another one
>> (several seconds shift / day)
>> Any info about this subject would help me.

>Which kernel version are you running? Starting with ~2.6.22 a new clock
>model has made its way into the Linux kernel. There are different modules
>which can use different hardware timers for timekeeping, and there seem to
>be some problems with certain modules on certain hardware (i.e. chipsets on
>the motherboard).

>To list available clock sources under kernel ~2.6.22 or newer:

># cat /sys/devices/system/clocksource/clocksource0/available_clocksource
>hpet acpi_pm pit jiffies tsc

>Check which clocksource is currently being used:

># cat /sys/devices/system/clocksource/clocksource0/current_clocksource

>Change the clock source:

># echo tsc > \

>For a test it is also possible to override the default clock source using a
>boot parameter, e.g.:


>You may want to try if some other of the available modules does a better job
>in timekeeping. If the active module doesn't work correctly then the
>frequency drift often exceeds the maximum drift ntpd can handle.

>Martin Burnicki

>Meinberg Funkuhren
>Bad Pyrmont

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