Automatically run commands over SSH on many servers

There are several tools out there that allow you to log in to and execute series of commands on multiple machines at the same time. Here are a couple:

• pssh
• pdsh
• clusterssh
• clusterit
• mussh

If you're into Python scripting more than bash scripting, then Fabric might be the tool for you.

From the Fabric home page:

Fabric is a Python (2.5 or higher) library and command-line tool for streamlining the use of SSH for application deployment or systems administration tasks.

It provides a basic suite of operations for executing local or remote shell commands (normally or via sudo) and uploading/downloading files, as well as auxiliary functionality such as prompting the running user for input, or aborting execution.

Typical use involves creating a Python module containing one or more functions, then executing them via the fab command-line tool.

Assuming that you are not able to get pssh or others installed, you could do something similar to:

tmpdir=${TMPDIR:-/tmp}/pssh.$$
mkdir -p $tmpdir
count=0
while IFS= read -r userhost; do
    ssh -n -o BatchMode=yes ${userhost} 'uname -a' > ${tmpdir}/${userhost} 2>&1 &
    count=`expr $count + 1`
done < userhost.lst
while [ $count -gt 0 ]; do
    wait $pids
    count=`expr $count - 1`
done
echo "Output for hosts are in $tmpdir"