how to make SSH command execution to timeout

Question

I have a program like this:

ssh -q harigm@8.19.71.238 exit
echo \"output value  -->$?\"

In the above code, I am trying to SSH to the remote

Answer 1

You could wrap the call to ssh using the timeout command. The timeout command exits with code 124 if a timeout occurs.

timeout 10s ssh -q harigm@8.19.71.238 exit
if [ $? -eq 124 ]; then
    echo "Timeout out"
fi

Or, as Vorsprung has commented on your question (as I was looking up the man page!):

ssh -oPasswordAuthentication=no -q harigm@8.19.71.238 exit

which will disallow interactive password authentication. You'd then have to check the exit code.

Answer 2

It sounds like the question is asking about 'batch mode' processing against a number of hosts at once (e.g., in a loop). The following ssh command will simply fail if PKA is not configured for a given host (public key authentication -- the "password-less" login mentioned the original question), so it is good for scripts that you just want to continue running regardless of problems connecting to one or two hosts. It also won't bother with all the queries about "are you sure you want to continue connecting" to previously unknown hosts (or you can just add StrictHostKeyChecking no to your ~/.ssh/config for that). For example,

for host in host1 host2 host3  # etc
do
  ssh -o BatchMode=yes -o StrictHostKeyChecking=no -o ConnectTimeout=5 \
      user@$host  'uptime' || echo "problem: host=$host"
done

You'll have to check your (client) ssh man page to see if these options (BatchMode, ConnectTimeout) are supported, though.