I have a reverse ssh tunnel established between a client and a server computer. The client connects on the server on port 22, and creates a reverse ssh tunnel on port 4030.
After the client computer has created the tunnel, it will sent an email confirming the reverse ssh tunnel connection. I just need a command that will output something that proves that the reverse connection has been established, so I can include it in the email.
How can I do this?
You may run an ss command (the modern version of netstat) on the remote system:
ssh me@remote ss -ntp | grep 4030
but better still you should use autossh (it exists on all distros). It checks automatically whether a reverse tunnel is operating and, after some user-defined amount of time without receiving pings has elapsed, automatically restarts the tunnel.
I start it at boot time, and it works perfectly over weeks, if not months.
-p flag: it will tell you which process is using the port, solving the above problem.
netstat -antep |grep 4030will show whether port 4030 is being listened