How to diagnose crashing LinuxCNC

I just followed linuxcnc.org/docs/stable/html/getting-st...th_preempt_rt_kernel and installed Raspbian bookworm Lite on a Raspberry 3B, and installed the Preempt-RT Kernel, and then installed LinuxCNC using the install script.

I have no desktop environment and want to run only the LinuxCNC application using the X11 server, without any other bloat.

Now, after installing xorg, i can successfully run LinuxCNC using


Now, the terminal of the rpi turns into a black window, that renders LinuxCNC fullscreen, without a desktop environment. (Screenshot in Attachments)

However, when I select any config (e.g. sim->axis->axis) and click ok, the window closes and the normal EMC2 splash screen appears for a few seconds, like it should, and then it just closes without any message and the X11 server stops.

Following is the command line output:


And here is the same command with a script that just echos "hi":


X.Org X Server 1.21.1.7
X Protocol Version 11, Revision 0
Current Operating System: Linux cnc 6.6.31+rpt-rpi-v8 #1 SMP PREEMPT Debian 1:6.6.31-1+rpt1 (2024-05-29) aarch64
Kernel command line: coherent_pool=1M 8250.nr_uarts=0 snd_bcm2835.enable_headphones=0 snd_bcm2835.enable_headphones=1 snd_bcm2835.enable_hdmi=1 snd_bcm2835.enable_hdmi=0  vc_mem.mem_base=0x3ec00000 vc_mem.mem_size=0x40000000  console=ttyS0,115200 console=tty1 root=PARTUUID=6396eb0b-02 rootfstype=ext4 fsck.repair=yes rootwait cfg80211.ieee80211_regdom=GB
xorg-server 2:21.1.7-3+rpt2+deb12u7 (www.debian.org/support)
Current version of pixman: 0.42.2
        Before reporting problems, check wiki.x.org
        to make sure that you have the latest version.
Markers: (--) probed, (**) from config file, (==) default setting,
        (++) from command line, (!!) notice, (II) informational,
        (WW) warning, (EE) error, (NI) not implemented, (??) unknown.
(==) Log file: "/var/log/Xorg.0.log", Time: Mon Jul  8 21:44:26 2024
(==) Using config directory: "/etc/X11/xorg.conf.d"
(==) Using system config directory "/usr/share/X11/xorg.conf.d"
hi
xinit: connection to X server lost

waiting for X server to shut down (II) Server terminated successfully (0). Closing log file.
[/code]

So, as you can see, command line output is printed directly and LinuxCNC does not produce any.

How can I diagnose this issue? If LinuxCNC stops without any command line output, can I find a log file somewhere? Or can I enable some debug features?

Thank you for any answers!

Alright, I found the solution already.

Firstly:
I was able to get debug information out of LinuxCNC by having xinit instead loading a script, that calls LinuxCNC and redirects its output to a file.

Secondly:
It turned out LinuxCNC cannot run as root, however xinit must run as root, which means the script needed to use "sudo -u cnc linuxcnc" to run it as a normal user even though xinit runs it as root.

And thirdly:
There was also an issue where it did not load forever and apparently it was waiting for user input in the console, which was not visible.
In the end it turned out it's a lot easier to run "sudo xinit" in one terminal, to run the xorg server, and in another terminal run linuxcnc manually, thereby not having an issue with root and you can also do user input.

I cannot attach a Screenshot here but it works now and I have LinuxCNC running fullscreen on a Raspberry PI, without a desktop environment.