fluxbox inside rc.local startup script sometimes does not spawn process and start

Question

This issue is driving me crazy. I have no clue why it sometimes happens. Its totally feeling intermittent.

I have a /etc/rc.local shell script that fires off on startup. I am using Ubuntu x64 19.10... For what its worth, I run this off a cloud droplet via Digital Ocean.

Long story short...

My script has at the beginning something like this...

echo "Starting virtual display session..."
export DISPLAY=:0
Xvfb :0 -screen 0 640x360x16 & 
DISPLAY=:0.0 fluxbox &
sleep 1
x11vnc -display :0.0 -usepw -forever -bg

All of this works most of the time....

However the fluxbox sometimes just will not load. I will end up with a X display session but no window manager. When I run ps aux | grep fluxbox I see nada.

The issue is that it only happens sometimes. I can reboot the system and most of the time it will load, but on occasion it just totally does not start process.

UPDATE: I can see the following error happen when this seems to occur:

Error: Couldn't connect to XServer:0.0

Why is this happening if I am setting the export of the display and also setting the display when I start the fluxbox process?

Does anyone have any idea?

Note: I only have the virtual frame buffer via xvfb and it always runs on DISPLAY=:0

Thank you! 🙏

Answer 1

Xvfb :0 -screen 0 640x360x16 & 
DISPLAY=:0.0 fluxbox &

This is simple enough. You've forked off two processes to run in parallel. The Xvfb program hasn't finished initializing by the time that the fluxbox program gets to the point of trying to connect to an X server. You have a multitasking operating system, no doubt a multiprocessor machine, and a non-deterministic load at bootstrap. Race conditions like this exist unless you take steps to avoid/prevent them.

Further reading

• Jonathan de Boyne Pollard (2018). /etc/rc.local is a thing of the past.. Frequently Given Answers.