I have installed wireshark to my Ubuntu server but when running from the command line using this simple example:

 wireshark -k -a duration:120 -w wireshark_results

I get a display error:

 ** (wireshark:32689): WARNING **: Could not open X display

 (wireshark:32689): Gtk-WARNING **: cannot open display: :0.0

This was after running:
DISPLAY=:0.0; export DISPLAY

What do I need to do to setup Wireshark on Ubuntu on DigitalOcean to capture packet data to file?

Thanks,

Luke