Checking ssh connection

Question

Is it possible to detect the activity of the ssh connection when the connection is broken. I connect to the server via phone (ssh client) and turn off the internet, but the system (w, netstat) says I'm still on the server. Is it possible to immediately determine the activity or wait for a timeout?

Answer 1

For the server see man 5 sshd_config, options ClientAliveInterval and ClientAliveCountMax. If you want the server to detect when a connection breaks then you need to use these options in /etc/ssh/sshd_config on the server machine.

For the client see man 5 ssh_config, options ServerAliveInterval and ServerAliveCountMax. If you want the client to detect when a connection breaks then you need to use these options in /etc/ssh/ssh_config or in ~/.ssh/config on the client machine, or in the command line while starting the connection (ssh -o ServerAliveInterval=… -o ServerAliveCountMax=…).

Read this another answer of mine, it elaborates and gives few interesting links. Note the OP there wants to disconnect an idle user (which is not a job for ClientAlive*/ServerAlive* mechanisms), while you want to detect a broken connection (which is exactly the job of the mechanisms).