:: how to change date and time on xen vm
+ enable independent_wallclock on xen vm

# echo 1 > /proc/sys/xen/independent_wallclock

+ set the date and time, example on 12 May 2011 07:12:00

# date -s "12 May 2011 07:12:00"
# date
Thu May 12 07:12:01 WIT 2011

+ if you want this setting to persist through a reboot of the virtual machine

# vi /etc/sysctl.conf
### add this line
xen/independent_wallclock = 1 

:: links
+ google
+ citrix
+ cyberciti