Usually, people tend to use the mininet prompt ( “mininet>” ) to do small tests, but when doing more “elegant” tests, people tend to open xterminal (xterm) to all or some virtualized nodes. Then, all the Linux command can be used freely. However, xterm may look little expressive for most. I mean, you cannot customize font sizes and colors easyly. Sometimes we can face a moment that we need to give a close to our terminal by resizing fonts (eg. maybe in demo section).
Fortunately, Mininet gives us the chance to use gnome-terminal which is more good-looking. To use it from Mininet, intead of calling xterm, call gterm as in the example bellow.
mininet> gterm h1 h2
This should work. If not, make sure that you have installed gnome-terminal. If not yet, you can install it easyly (eg. on Debian-based distros)
$ sudo apt-get install gnome-terminal