Su to root:
$su -
type:
# screen
Now type your commands:
# tshark -i xxxxxxxx
Now hold down the following keys at the same time:
#
This detaches the screen and allows you to exit the terminal window.
To access the detached terminal do the following:
From local:
$ su -
# screen -R
This gets you back into the terminal you were working on.
From remote:
ssh to the server
$ su -
#screen -R
You will she your command still running.
Thanks to scm for showing me this.