How to fix VNC Viewer black screen

Introduction

Have you seen your VNC Viewer showing a black screen intermittently ?  We have a fix for it. This issue has been occurring in our lab servers for a few students intermittently since the past few months on Oracle Linux server 6.5 release.

Problem

The VNC Viewer desktop background turns into a full black screen intermittently. It does not happen all the time and one of our students observed that this issue happens consistently when she  hovers her mouse on the VNC Config icon on the top left hand corner. This issue happens even if this icon is minimized. This observation is correct.

Solution

A workaround is to just close the above VNC config icon instead of minimizing it. But the permanent solution is to let the vncconfig deamon run in nowin mode (no window icon). Our vncserver service is owned by oracle operating system account. 

a) Login to the server using a different protocol such as ssh on port 22.

b) cd /home/oracle/.vnc

b) Edit xstartup file and replace vncconfig -iconic & with vncconfig -nowin &

c) Now bounce the vncserver service using the below commands

vncserver -kill :1.0
vncserver
export DISPLAY=:1.0
xhost +

Conclusion

The -nowin parameter will make the vncconfig functionality stay intact, but without the desktop icon. The actual cause of the problem could be due to an issue with the vnc-server RPM itself, specifically tigervnc-server-module 1.1.0-8.el6_5.x86_64.