Tag Archives: ntp

Notes on XenServer and NTP

  • XenServer syncs with the NTP server anytime between once every one minute and once every 15-20 minutes, depending on the amount of “drift” your hardware clock exhibits (ref)
  • XenServer syncs the hardware clock with the system clock automatically – I think when ntp starts (ref: /etc/rc.d/init.d/ntpd – on XenServer 5.6 SP 2)
  • VMs (both with and without XenServer Tools) have their hardware clocks synced with XenServers system clock when they start up – if you try and use a command like “hwclock -r” and get the message that the hardware clock cannot be accessed; do not worry, it still works



Ubuntu server time not calculating DST

For some reason, one of the servers I look after was displaying the time as an hour earlier than it should have been. The hardware clock was showing the correct UTC time, the Ubuntu settings specified that the hardware clock was on UTC and not local time, and the timezone said Europe/London, as it should have done.

I tried syncing the server to a time using NTP but that made no difference.

What did work, in the end, was simply resetting the timezone to Europe/London.  Not sure why!

Some useful things I used during this process:

Check that the hardware clock is displaying UTC: hwclock –check

Check that your ubuntu settings describe the hardware clock as UTC rather than localtime, check this file: /etc/default/rcS
The option should be: UTC=yes

Reset the timezone:
dpkg-reconfigure tzdata

Update the time from the internet with NTP:
ntpdate uk.pool.ntp.org