UNIX for Dummies Questions & Answers

Hi!

I need to start a program at several hosts in the network at the same time. Starting time difference should be no more than several milliseconds. What is the best way to do that?


Thanks!

Set up NTP to make sure all your system clocks are synchronized.

OK, but how do I make sure they start simultaneously if the clock is synchronized?

As far as I know precision of cron is of the order of seconds, isn't it?

Thanks

I don't know the precision of cron, but even if it is to to miliseconds you have no guarantee, since you never know when exactly your processes are granted processor time. A lot will depend on other activities on the system.

Isn't it better then to write a C program, that listens on the certain port and starts a program when a sequence of bytes arrives there?

Will it be more precise or there are any better ways of time synchronization then cron?

Thanks.

I have no experience with something like this.

But it seems to me that even if you have some kind of process listening on a specific port you cannot guarantee they start performing their tasks at the exact same time.

Hard to make sure the "trigger code" arrives at the exact same time on each system, because of the number of hops, distance, sending the code simultaniously to a lot of systems etc.

Furthermore, again the load on each system will influence when your process gets processor time.

But maybe, the real c programmers know whether it is possible or not.

Maybe some low level approach (using time stamps of packets), which can calculate when the code was send, the time it took for the code to get there (similar like NTP operates) could do the trick. If that could be done, you could let all processes start e.g. 1 minute after the code was send. You might be able to use some kind of broadcast like packet to make sure all systems get the same information.