For loop in a Script Shell

Question

My script is:

for i in $(seq $nb_lignes) a list of machines
do
ssh root@$machine -x "java ....." 
sleep 10
done

--> i execute this script from machine C

i have two machines A and B ($nb_lignes=2)

ssh root@$machineA -x "java ....." : create a node with Pastry overlay 
wait 10 secondes
ssh root@$machineB -x "java .....":create another node join the first (that's way i     have use sleep 10 secondes)

i run the script from machine C: i'd like that it display : node 1 is created , wait 10 seconds and display node 2 is created

My problem: it display node 1 is created only

i tape ctrl+c it diplay node 2 is created

PS: the two process java are still runing in machine A and B

Thank you

Your loop is for i in ..., but you refer to $machine in the body of the loop. I guess what you really meant was for machine in .... Please post code that's as close as possible to the code you're actually running, so we don't have to guess which problem are in your original code and which you introduced when you re-typed it. — Keith Thompson
– Keith Thompson, Commented Oct 11, 2012 at 0:04

ghoti · Accepted Answer · 2012-10-10 23:37:40Z

From the way I'm reading this, armani is correct; since your java program does not exit, the second iteration of the loop doesn't get run until you "break" the first one. I would guess that the Java program is ignoring a break signal sent to it by ssh.

Rather than backgrounding each SSH with a &, you're probably better off using the tools provided to you by ssh itself. From the ssh man page:

 -f      Requests ssh to go to background just before command execution.
         This is useful if ssh is going to ask for passwords or
         passphrases, but the user wants it in the background.  This
         implies -n.  The recommended way to start X11 programs at a
         remote site is with something like ssh -f host xterm.

So ... your script would look something like this:

for host in machineA machineB; do
    ssh -x -f root@${host} "java ....." 
    sleep 10
done

armani · Accepted Answer · 2012-10-10 19:34:16Z

1

Try the "&" character after the "ssh" command. That spawns the process separately [background] and continues on with the script.

Otherwise, your script is stuck running ssh.

EDIT: For clarity, this would be your script:

for i in $(seq $nb_lignes) a list of machines
do
ssh root@$machine -x "java ....." &
sleep 10
done

answered Oct 10, 2012 at 19:34

armani

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4 Comments

armani Over a year ago

Further explanation: Being stuck in the first SSH program, when you Ctrl-C you kill THAT process, and THEN you are allowed to move on to creating node 2. See why it would say that after you hit Ctrl-C?

user1735757 Over a year ago

no with ctrl-C the process is not killed, when i tappe ctrl+C it passes au second iteration (the shell does not return with ctrl+c .. it passes au second iteration and it display node 2 is created!!

user1735757 Over a year ago

:i can't access now to the machines, i have already add & but it did'nt execute sleep 10!

user1735757 Over a year ago

Please, i have another question, how can display only the result of command java of node A only , i'd like redirect that of B ? thank you so much

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