Hello,


What is difference between "

1. Hardware set to local time

2. Hardware clock set to UTC


And what does the following mean.

3. NTP server - automatic time synchronization (using NPT )


Thanks

Varun

Your PC BIOS has a clock.

If you set your BIOS clock to local time (normal time when you look at your watch) then it's (1).

If you set your BIOS clock to UTC (which is kindof like GMT but does not change with daylight savings time) then you will have to create offsets to your local time.

If you live in England you use UTC+0 (or +1 for DST) if you live in Kiev you use UTC+2, etc.

If you boot a few OS on one box you should use UTC or you will get confused with all the settings.

You can use NTPD (Network Time Protocol Daemon) which will send queries to NTP servers to set the time on your OS from atomic clocks around the world. Linux normally gets its time from your BIOS clock but BIOS clocks are usually not very accurate. After a day they will get worse and worse. If you set up NTPD properly it will apply corrections until your PC time is exactly correct. You can also use certain apps to set your PC BIOS clock from your Linux clock.

Obviously you can find lots of information on the subject by just googling. You will find that time can be very complex.

In a nutshell the clock in your computer is not very accurate over a long period of time and will drift. A NTP server is a computer that is connected to a very accurate time standard clock. The ntp deamon automatically sets your system clock to the time standard, compensates for network delays and clock drift. The main difference between running ntp and just manually changing your clock time is that you can not compensate for drift.

The only time it really matters if your clock it set to UTC versus local time is if you are dual booting. Windows expects the clock to be set to local time.