I was trying to install SAP Hana Data provisioning agent for which SAP Note said that we need a non-root user who should have read/write access to /usr/sap folder and display access. So I started vncserver for that non-root user and I was able to download agent and closed that session. Now for installing agent I logged into same session however it said you dont have GUI access since I had exported display for that single session only. Now I added display variable in /etc/environment file logged in as root and started vncserver again. Now I was able to open GUI/xclock using root user only. if I type xclock on terminal after logging in using any user other than root, I get stuck on that command prompt.
I also tried setting export DISPLAY=:0.0 in each user specific .bashrc file.