In this tutorial, we will assume that the hostname you want is “pluto”.

For Ubuntu 12.04 (Precise Pangolin)

1. On your SSH Terminal, type: hostname pluto
2. Using nano, you can then type: nano /etc/hostname
3. Type in pluto, then press Ctrl + X, then Y, then Enter.
4. Now, again using nano, type nano /etc/hosts to edit the hosts file.
5. Add another line on top, it should read: 127.0.0.1 pluto
6. Confirm your changes by typing hostname.

For Ubuntu 14.04 (Trusty Tahr) / 14.10 (Utopic Unicorn)

1. Newer Ubuntu versions make it even easier, you can just type: hostnamectl set-hostname pluto
2. Confirm your changes by typing hostname.