how to check if sshd runs on a remote machine [closed]

Question

ssh -q -o "BatchMode=yes" user@host "echo 2>&1" && echo "OK" || echo "NOK"

this method is suitable but it returns true when the pub.key is copied to host. I need to see if an ssh is connectiable between two devices without keys.

Simply wants to check if the sshd is running remotely.

Answer 1

If you just want to check if you can connect to a host via ssh, you could simply check if port 22 is open. There are various ways to to this.

Using nmap (replace localhost with your target host):

$ nmap -p22 localhost

Starting Nmap 5.21 ( http://nmap.org ) at 2012-08-15 13:18 BST
Nmap scan report for localhost (127.0.0.1)
Host is up (0.000044s latency).
PORT   STATE SERVICE
22/tcp open  ssh

Nmap done: 1 IP address (1 host up) scanned in 0.04 seconds

To use this in a script:

if nmap -p22 localhost -oG - | grep -q 22/open; then 
    echo "OK"
else 
    echo "NOK"
fi

You can also use netcat:

$ nc -zv localhost 22
Connection to localhost 22 port [tcp/ssh] succeeded!

To use this in a script:

if nc -zv localhost 80 2>&1 | grep -q succeeded; then 
    echo "OK"
else 
    echo "NOK"
fi

---

This is a quick check which is sufficient in most situations, however it is not fool-proof. There is no guarantee that the service listening on the remote port is actually an SSH server.

You could attempt a dummy connection and inspect the returned header, e.g:

$ echo "dummy" | nc localhost 22
SSH-2.0-OpenSSH_5.9p1 Debian-5ubuntu1
Protocol mismatch.

however such an approach is undesirable for various reasons. The only guaranteed way would be to establish an actual connection as you've shown in your question.