Hello there,

I am carrying out some wireless testbed experiments and my testbed consists of 6 laptops. One of the conditions of the experiments is that I need to initiate the applications and protocols at the same time in each laptop. To suit this requirement, I am wondering as to how I can write a simple script to specify that the follwing applications need to begin exactly at (say) 13:15.

run application1 and application2 at 13:15

Thanks in advance for taking your invaluable time to answer my question.

Best Regards,

Siva

First of all you have to syncronize all the laptops against a NTP server to be sure that the system time is the same for all. Second you can run an application at a specified time by means of cron. This implies:
1) the crond (cron daemon) must be running on all the laptops
2) you have to allow the execution of cron jobs on a user basis
3) you have to write a proper crontab, e.g.
See man cron & man -S5 crontab for details. If the applications are to be run only once, you may consider the at command as well (this can also be launched from a shell script)

Hello Colucix,

Thanks for your quick response. Given that my applications need to be run exactly at once, I thought of using "at" and tried the follwing:

at -V -f <runMyApplication-script> -mv 5.52

runMyApplication is a script that calls all my applications. When I tried to use the above, nothing seemed to happen. I wasn't sure whether the jobs were running in the back-ground ??? Do you have an idea as to why I couldn't see anything on the console when I tried to use the above "at" utility ???

Thanks and Regards,

Siva

Of course there is a little syntax error on the command line you have posted, or better there is no indication about the time at which execute the application. A correct way to use at is, e.g.
You see you have to type a TIME specification (now + 3 hours) and then the command(s) to execute. This is an interactive usage of at, in the sense you have to type commands at the at> prompt and terminate input by typing Ctrl-D.
The alternative is the one you have just seen, that is option -f to execute command written in a file:
See man at for a correct form of the TIME specification. Just an hint: the option -V simply output the version of the at software, the -v simply print the TIME specification on the terminal in the date command format. They are quite unuseful in your experiment.

Hello Colucix,

I tried in the way you suggested and it works fine. But the problem is that the processes run in the background. Given that I need to monitor the console for the output of my running applications, the use of "at" would not be any use, unless I find a mechanism to redirect the output to a file and read it using "watch". The other option is to write my own script that does the work for me without using "at". Do you have an idea as to how I can write a simple script that can be a substitute to "at"

Thanks in advance.

Regards

Siva

Your idea is good, you can redirect the standard output together with the standard error in a file. During the execution you can see the progression of the file using
pressing Ctrl-C to interrupt the tail command.
Sincerely I have no idea, at and cron are the only ways to run a program at a specified (delayed) time. Writing such a script could result in writing the source code of the at command! By the way a dirty way to do this in a bash script, could be
Please note the reversed single quotes around the date command. The code above query the output of the date command, waiting for a specific hour and minute (11:33 in my example) with a timestep of 5 seconds (sleep 5) between each query. When the hour and minute is reached the while loop is terminated and you can put the commands to execute after and outside the loop itself.

Hello Colucix,

Thanks for your time !, your script works for me.

Cheers

Siva

You are welcome!