Background SSH

SSH usually operates in the foreground where it provides an interactive login or displays the output of a remote command (see remote commands). Although using the forwarding services (see port forwarding and agent forwarding) requires successful authentication, it does not have to result in a shell.

Therefore, SSH may be pushed into the background with the -f parameter just before the command is executed: ssh -f HOST COMMAND

The only requirement is using a remote command (see remote commands). This is especially useful if running a remote X client for which the SSH tunnel will remain active until the command terminates.

There is also a way of restricting such a forwarding to an interval of time: ssh -f HOST sleep N

Independent of the actual usage, the instance of SSH will terminate after N seconds.

Most of the time you will probably want a forwarding to be available for an unlimited amount of time: ssh -fN HOST

(The -N parameter prevents the execution of a remote command.)