Unable to getting a working vnc block to work "BadAccess (attempt to access private resource denied)"

ropelletier87 · February 3, 2024, 7:43pm

I am actually trying to use this project (GitHub - nucleardreamer/xserver-web-vnc: Run a web VNC client to interact with and view your local xserver) as an example, but all other attempts have been met with the same issue. vnc fails to start with the following error:

xserver-web-vnc  X11 MIT Shared Memory Attach failed:
 xserver-web-vnc    Is your DISPLAY=:0 on a remote machine?
 xserver-web-vnc    Suggestion, use: x11vnc -display :0 ... for local display :0
 xserver-web-vnc  
 xserver-web-vnc  caught X11 error:
 xserver-web-vnc  21/08/2021 02:46:26 deleted 60 tile_row polling images.
 xserver-web-vnc  X Error of failed request:  BadAccess (attempt to access private resource denied)
 xserver-web-vnc    Major opcode of failed request:  130 (MIT-SHM)
 xserver-web-vnc    Minor opcode of failed request:  1 (X_ShmAttach)
 xserver-web-vnc    Serial number of failed request:  56

This project is using the exact type of xerver implementation I am so if we can fix this one, then we can fix mine. I am hesitating to post mine right now because it is still in dev and a bit more messy and complicate. I will happily post more information as needed, but just wanted to get the ball rolling in case maybe someone knows the obvious reason why this does not work. Appreciate nay thoughts.

ropelletier87 · February 4, 2024, 2:05am

While doing a bunch of googling trying to resolve this issue I ran across this:

github.com/jessfraz/dockerfiles

MIT-SHM error solutions

opened 09:36AM - 21 Mar 18 UTC

mviereck

bug enhancement

Running dockered GUI applications on host display `:0` can lead to MIT-SHM error…s and rendering issues. Sample setup: ``` xhost + # security issue, you know docker run -it \ -v /tmp/.X11-unix:/tmp/.X11-unix \ -e DISPLAY=unix$DISPLAY \ jess/gimp ``` Sample error message: ``` X Error of failed request: BadValue (integer parameter out of range for operation) Major opcode of failed request: 130 (MIT-SHM) Minor opcode of failed request: 3 (X_ShmPutImage) [...] ``` I got this `MIT-SHM` error quite often if I share host display `:0`. Though, normally it does not crash the application, but leads to rendering issues and artefacts after some time. (Some applications regard `unix` in `unix$DISPLAY` and don't use `MIT-SHM`. But that is not reliable.) To avoid this error it is possible to disable IPC namespacing, thus allowing shared memory: ``` --ipc=host ``` I don't like the solution to disable IPC namespacing with `--ipc=host` because of isolation loss. Instead I prefer to run additional X servers with extension `MIT-SHM` disabled. Simpified example: ``` Displaynumber=50 Xephyr :$Displaynumber -retro -extension MIT-SHM & # '-extension' disables, '+extension' enables sleep 1 # give Xephyr time to get ready env DISPLAY=:$Displaynumber xfwm4 & # window manager docker run -it \ -v /tmp/.X11-unix/X$Displaynumber:/tmp/.X11-unix/X$Displaynumber \ -e DISPLAY=:$Displaynumber \ jess/gimp ``` I gave a more [extended example on stack overflow](https://stackoverflow.com/questions/16296753/can-you-run-gui-apps-in-a-docker-container/39681017#39681017). ------------- @jessfraz Hello jess! I want to thank you for your work at docker and for your investigations to run GUI applications, too. Inspired by your examples I developed a tool to run GUI applications and desktops in docker containers that also adresses X security issues and additionally provides features like sound and hardware acceleration. I often thought about how to tell you about this without looking like someone who wants to advertise his project. Well, I take this opportunity, and I hope you like it. The project is hosted on github: [x11docker](https://github.com/mviereck/x11docker) Examples: ``` # LXDE desktop x11docker --desktop x11docker/lxde ``` ``` # GIMP x11docker jess/gimp ```

Still trying to wrap my head around it, but this may be relevant.

mpous · February 5, 2024, 12:13pm

Hello @ropelletier87

could you please confirm what device type are you using? what balenaOS version do you have?

Let us know if you could fix this!

ropelletier87 · February 6, 2024, 11:35am

@mopus. Yes that would indeed be helpful information, I am sure. Ha. I am using an RPi 4B with 5.1.20 installed.

I have “fixed” this. I had to install vnc in the xserver block (Dockerfile) itself then running it from entry.sh. Really do not like this solution, as running vnc in its own block is far more elegant, but can’t find a solution to the problem above and been at it for hoooouuurs.