Imagine you are logged into a remote system and want to forward a local port to the remote system without logging out and logging in again. This little trick will tell you how to do this.
According to OpenSSH man pages:
Escape Characters
When a pseudo terminal has been requested, ssh supports a number of
functions through the use of an escape character.
....
The supported escapes (assuming the default `~') are:
.....
~C Open command line (only useful for adding port forwardings using
the -L and -R options)
.....
So, to add a local forward after logging into the remote system procede as follows:
ssh user@remote_host
Once logged in…
CR~C
Hit carriage return then ~ and the C and you’ll get a prompt where you could type something like this:
ssh> -L 8022:127.0.0.1:22
Forwarding port