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By default, XenVMs have their clocks synchronized to the XenServer Host that hosts them and will ignore requests to adjust the time made by an ntp daemon if one is running. If you want a XenVM to have an independent clock, log on to its Text Console and issue the command

then run an NTP daemon.

To revert to the default, issue the command

For more setting up an NTP on the XenServer please refer to the below kb article. Refer to the below kb article for “How to set up an NTP Server for a XenServer network”

• http://support.citrix.com/article/CTX121278
• http://support.citrix.com/article/CTX116307

You can check which hosts are talking to your time server by using the monlist command of ntpdc, e.g. ntpdc -c monlist Please note that a maximum of 600 entries is supported with current versions of ntpdc. The protocol (or better: the contents of the return packets) used by ntpdc is not standardized, therefore it is recommended to only use ntpdc with a matching ntpd, i.e. both should have the same version number.

To get by this 600 entry limitation, many server operators run client statistics scripts, such as Wayne Schlitt’s ntp_clients and ntp_clients_stats scripts, which can be found at http://www.schlitt.net/scripts/ntp/index.html . They work very well, but can use quite a bit of system resources if your client counts are in the high thousands. Examples of these scripts in action can be found at:

• http://www.schlitt.net/ntpstats/ntp_stats.txt
• http://saturn.dennishilberg.com/ntpstats/ntp_clients_stats.php (slightly modified)

ntpq -p

The character in the left margin indicates the fate of this peer in the clock selection process. The codes mean: