Xlib: no protocol specified; Can't open display

ron7000 · 11-04-2014, 08:58 AM

i'm trying to run a graphical program,
I use tightvnc to remote into my system as my user account,
if i type 'nedit' then the window pops up and it works fine.
but if i do an 'su' or 'su -' and become root to use nedit, or su to any other account, then for nedit or any other graphical problem i get the following error:

Xlib: connection to "127.0.0.1:4.0" refused by server
Xlib: No protocol specified
NEdit: Can't open display

what causes this and how can i fix it?
I've verified with echo $DISPLAY that before i do an su the contents of DISPLAY are the exact same.

The system this is happening on is running SLES 10.4 and is itanium.
This problem does not happen on my systems that run SLES 11.x which are x86-64. Not sure if it's a security setting that i can change or mistakenly set, or if it's a bug or oversight in SLES 10 that was fixed in SLES 11.
thanks.

smallpond · 11-05-2014, 06:48 AM

With vnc you are connecting to a desktop on the server which is a a program run and owned by the login user. That's why other users can't access it. You can give other users access using xauth.

You should not use vnc over public Wi-Fi or insecure networks since it is sending your password in clear text. I don't use it unless going through a VPN. I log in with ssh and forward X to a server on my laptop. This is also better performance over slow networks.

ron7000 · 11-05-2014, 09:54 AM

http://www.tightvnc.com/faq.php#howsecure

Quote:

How secure is TightVNC?

Although TightVNC encrypts VNC passwords sent over the net, the rest of the traffic is sent as is, unencrypted (for password encryption, VNC uses a DES-encrypted challenge-response scheme, where the password is limited by 8 characters, and the effective DES key length is 56 bits). So using TightVNC over the Internet can be a security risk. To solve this problem, we have plans to implement built-in encryption in future versions of TightVNC.

In the mean time, if you need real security, we recommend installing an SSH server, and using SSH tunneling for all TightVNC connections from untrusted networks.