sudo cannot resolve the local hostname

If you get:

sudo cannot resolve the local hostname

Just go to terminal and type:

sudo nano /etc/host

Ensure that the following lines exist

127.0.0.1       localhost
127.0.1.1       replace this with your laptop/computer name

Hopefully this will remove your problem.

source:
 https://bugs.launchpad.net/ubuntu/+source/sudo/+bug/32906