E 'for some' time that I have an annoying problem with my ubuntu pc. Apparently it is released to the battery that powers the CMOS on the motherboard, because when I turn off the computer and take off my food, I always find when you restart the system clock late.
Short of changing the battery (and perhaps should change the computer ;-)) can be remedied with a command run at startup that uses the NTP protocol to synchronize time and date through the network: sudo ntpdate This command, of course, is not well indicated in the case of desktop computers, but it is interesting in the case of servers, as it allows to maintain consistent system logs.
Links:
The NTP protocol