How to create a bash script to check the SSH connection?

bash ssh connection
chutsu picture chutsu · Sep 10, 2009 · Viewed 163.7k times · Source

I am in the process of creating a bash script that would log into the remote machines and create private and public keys.

My problem is that the remote machines are not very reliable, and they are not always up. I need a bash script that would check if the SSH connection is up. Before actually creating the keys for future use.

Answer

user156676 picture user156676 · Sep 10, 2009

You can check this with the return-value ssh gives you:

$ ssh -q user@downhost exit
$ echo $?
255

$ ssh -q user@uphost exit
$ echo $?
0

EDIT: Another approach would be to use nmap (you won't need to have keys or login-stuff):

$ a=`nmap uphost -PN -p ssh | grep open`
$ b=`nmap downhost -PN -p ssh | grep open`

$ echo $a
22/tcp open ssh
$ echo $b
(empty string)

But you'll have to grep the message (nmap does not use the return-value to show if a port was filtered, closed or open).

EDIT2:

If you're interested in the actual state of the ssh-port, you can substitute grep open with egrep 'open|closed|filtered':

$ nmap host -PN -p ssh | egrep 'open|closed|filtered'

Just to be complete.

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