I was tired of my system's name so i decided to change it.
I gksudo gedit /etc/hostname and changed my first and never touched computer name to a new one.
Then now when i sudo something like sudo gedit my terminal prompts ~: unable to resolve host <my_new host_name_i_gksudo>.

When i sudo cat /etc/hosts it gives me:

sudo: unable to resolve host <not_of_your_business!>

127.0.0.1   localhost

127.0.1.1   leviathan



# The following lines are desirable for IPv6 capable hosts

::1     ip6-localhost ip6-loopback

fe00::0 ip6-localnet

ff00::0 ip6-mcastprefix

ff02::1 ip6-allnodes

ff02::2 ip6-allrouters

How could i get rid of this problem?
Thanks in advance.