Sync time?

You can't synchronize exactly, there will always be a small margin of error. A better question is why you need the time synchronized, and how accurate you need it to be?

For example Kerberos requires time synchronization and allows ~10 minute margin of error. This is due to timing of tickets.

You may want to look at NTP this can roughly synchronize the clocks, but its best to be sure that you actually need to.

i want to do a game with server-side damage, so i need clocks syncronized to know the time when a player shoots :)

You have made a very common assumption, take a look at the FAQ question number 25.