Question

I am trying to run an application on multiple (~20) Unix servers. Rather than SSH’ing into each one individually, I would like to log in to one and use a script to start them all up.

The application does not require any direct user interaction, so I essentially just need to run ‘./app arg1 arg2’ on each machine.

Answer 1

One improvement on straight SSH is to start SSH session in the background and then wait for all of them to finish. This way you can execute command on remote servers simultaneously.

We use this technique in our production scripts.

function start_server ( )
{
  ssh $1 '/path/to/start_service_script'
}

echo "Starting servers"
for serv_name in $( cat /path/to/server-list )
do
    # I usually declare a function, because if SSH command
    # gets more elaborate ( especially if it has ampersands
    # as part of the command, the shell has trouble parsing 
    # the background push (& at the end of the command)
    #
    # In this particular case it would be no trouble to
    # inline ssh here
    start_server ${serv_name} &
done

echo
# Very important to wait till all the spawned processes finish
wait

One thing to note, because all spawned processes are running simultaneously and using the same console, you may see some interleaved output on your screen.