how to send different commands to multiple hosts to run programs in Linux - linux

Question

I am an R user. I always run programs on multiple computers of campus. For example, I need to run 10 different programs. I need to open PuTTY 10 times to log into the 10 different computers. And submit each of programs to each of 10 computers (their OS is Linux). Is there a way to log in 10 different computers and send them command at same time? I use following command to submit program
nohup Rscript L_1_cc.R > L_1_sh.txt
nohup Rscript L_2_cc.R > L_2_sh.txt
nohup Rscript L_3_cc.R > L_3_sh.txt

Answer 1

First set up ssh so that you can login without entering a password (google for that if you don't know how). Then write a script to ssh to each remote host to run the command. Below is an example.
#!/bin/bash
host_list="host1 host2 host3 host4 host5 host6 host7 host8 host9 host10"
for h in $host_list
do
case $h in
host1)
ssh $h nohup Rscript L_1_cc.R > L_1_sh.txt
;;
host2)
ssh $h nohup Rscript L_2_cc.R > L_2_sh.txt
;;
esac
done
This is a very simplistic example. You can do much better than this (for example, you can put the ".R" and the ".txt" file names into a variable and use that rather than explicitly listing every option in the case).

Answer 2

Based on your topic tags I am assuming you are using ssh to log into the remote machines. Hopefully the machine you are using is *nix based so you can use the following script. If you are on Windows consider cygwin.
First, read this article to set up public key authentication on each remote target: http://www.cyberciti.biz/tips/ssh-public-key-based-authentication-how-to.html
This will prevent ssh from prompting you to input a password each time you log into every target. You can then script the command execution on each target with something like the following:
#!/bin/bash
#kill script if we throw an error code during execution
set -e
#define hosts
hosts=( 127.0.0.1 127.0.0.1 127.0.0.1)
#define associated user names for each host
users=( joe bob steve )
#counter to track iteration for correct user name
j=0
#iterate through each host and ssh into each with user#host combo
for i in ${hosts[*]}
do
#modify ssh command string as necessary to get your script to execute properly
#you could even add commands to transfer the file into which you seem to be dumping your results
ssh ${users[$j]}#$i 'nohup Rscript L_1_cc.R > L_1_sh.txt'
let "j=j+1"
done
#exit no error
exit 0
If you set up the public key authentication, you should just have to execute your script to make every remote host do their thing. You could even look into loading the users/hosts data from file to avoid having to hard code that information into the arrays.