[ntp:questions] Wrong time after changing hardware

rtxo gnu at localhost.wraith.sf.ca.us
Fri Jul 20 18:51:01 UTC 2007

Marc Muehlfeld wrote:
> Hello,

> I'm running a NTP server on one of my Linux servers that distribute time 
> in our local network. But since I changed Mainboard/CPU/RAM on that 
> machine, the machine is allways having a time in future.

> When I restart the NTP service, the time is sycronized again. But 
> allready after 12h there is a drift difference of about +6 seconds. 
> Meanwhile I reinstalled the service, but that didn't made any changes. 
> Before switching to the new hardware, it run fine for about 1.5 years.

> Any idea?

> The server is running Suse 10.0 with xntp 4.2.0a.

Hi Marc--

If you change the motherboard, you have changed the room temperature
crystal oscillator (RTXO) that NTP previously had calculated a value
for, and stored in the ntp.drift file. If you have changed the motherboard,
you should delete the value in the ntp.drift file (leaving it empty).
This will force NTP to recalculate a value for the new motherboard's
RTXO and store it in the ntp.drift file.

When you reboot, the OS must obtain the current time of day in some
fashion, usually by reading the RTC/TOY (real time clock/time of year)
hardware. There is a utility available for linux, "hwclock" that can
take the time that NTP has calculated and write this to the RTC so
that it agrees with the current date. The time in the RTC is stored
as UTC with unix systems such as linux. The OS converts from UTC to
current time using tables often found in /usr/share/zoneinfo.

You can use this to copy the NTP time to the RTC:

# hwclock --systohc

More information about NTP server using PC GNU/Linux and freebsd is at:



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