I have a hostlist and there are several hosts. I want to use ssh to connect to them. I want to see whether the host is available or not by the time length of ssh takes. If it take long than 5s (which means it is not available). Then stop it, and ssh to next host. Once a host is available, then output the name of host. I previously use nmap, but the IT security told it is not allowed to install it on the desktop on campus.
The above script is all I can do.

Just need to point out that you only REALLY need to check if port 22 is accepting connections at that address. For that your could use nc (netcat) or even telnet. There is also a bash trick that uses a virtual device file for shell network activity. Most likely the telnet thing is easiest. I seem to remember solving a problem somewhat like that in perl once, which may apply here.

There are undoubtedly other and arguably better ways. The optimal choice for you may depend upon the software set that is acceptable in your environment. I cannot determine that from your initial post.

The important point is: do not limit yourself to using ssh. Find another tool, one that is readily available to you, that will help you solve that problem.

Instead of making a session with ssh, why not use "ssh $line echo 'Ok'". That way you will get back an "Ok" message if things are working (and exit status 0) --- and if your timeout occurs, things are NOT working (exit status 124).

I see you marked the thread solved. Can you mention what you used in your solution?