There are two main clocks in a Linux system:The Hardware Clock: This is a clock that runs independently of any control program running in the CPU and even when the machine is powered off. The System Time: This is the time kept by a clock inside the Linux kernel and driven by a timer interrupt. It has meaning only while Linux is running on the machine. Often-times, it happens that when you reboot, your clock does not reflect the correct date and time. You may be forgetting to sync the hardware clock with the current system time. Here is how: First check and set the current system date and time.
# date # date -s 'Wed May 28 11:35:00 EST 2003'
Then sync your hardware clock with the system time.
# hwclock --show # hwclock --systohc
man date and hwclock for more info...