when you’re running commands with sudo at beginning. It outputs “sudo:unable to resolve host Lily-desktop”(here assume current host-name is Lily-desktop), however the commands work as well as before.

This always happens after host-name changed.After change host-name by edit /etc/hostname, we also need to do a change in /etc/hosts file.

Edit /etc/hosts:

gksudo gedit /etc/hosts

make it looks like (change boldfaced words to current host-name):	localhost	Lily-desktop

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts