"cannot open display: :0" error when using sudo with any GTK app

Question

I want to run gmsartcontrol (UI tool for smartctl) which needs to be run as root in order to access the drives and read their SMART status.

However doing this:

sudo gmsartcontrol

I get this error:

No protocol specified
[gtk] cannot open display: :0

Answer 1

For graphical applications use gksu:

gksu gsmartcontrol

If it is not installed on your system you can get it via:

apt-get install gksu

Answer 2

As your login user, do

xhost +


xhost root 

root being added to access control list

vim /etc/sudoers
Defaults env_keep="XAUTHORIZATION XAUTHORITY TZ PS2 PS1 PATH LS_COLORS 
KRB5CCNAME HOSTNAME HOME DISPLAY COLORS"

Optional

1952  adduser $USER wireshark
1953  chgrp wireshark /usr/bin/dumpcap
1954  setcap cap_net_raw,cap_net_admin=eip /usr/bin/dumpcap
1955  getcap /usr/bin/dumpcap