LinuxCNC on Raspberry Pi 4

I installed it, and it seems to work, but I need to install the linux headers. When attempting that for this image with:
sudo apt-get install linux-headers-$(uname -r)
the install fails, it cannot locate the package.
Any idea what this can be?

In fact I have not installed this file... 

The files are here:
github.com/kdoren/linux/releases
and the installation procedure is as follows:

OK I'm seeing the problem with the "64bit version based on Bullseye with LinuxCNC 2.9.0pre" screen going "no signal" was not what I thought.

That, and this linuxcnc_2.8.4_buster_arm64_rt.zip, on another monitor shows up, but the sync is all wrong, the screen is diagonally skewed.

So neither of these monitors like the RPI4 HDMI in whatever video mode it tries to switch to.

Is there a way to remedy other than randomly buying monitors until one works?

I would suggest you check the operation of the HDMI cable in addition to the monitor.
Try using a cable that is not very long.

Instead, to quickly check the operation of LinuxCNC using another computer, there are at least 2 ways.

The first is to use a remote desktop like VNCViewer
( www.realvnc.com/en/connect/download/viewer/ )

The other is to use an SSH terminal emulator with X-Windows like MobaXterm
( mobaxterm.mobatek.net/ )

In any case, using the raspi-config terminal command you can select the most appropriate resolution for your monitors.

Thanks, that got me one step further in my etherlabmaster installation. Now im stuck in with the following:

pi@raspberrypi:~/etherlabmaster $ make dkms_build

make[1]: Entering directory '/home/pi/etherlabmaster/etherlabmaster-code'
/usr/sbin/dkms build -m etherlabmaster -v 1.5.2

Kernel preparation unnecessary for this kernel. Skipping...

Building module:
cleaning build area...
make -j1 KERNELRELEASE=5.15.65-rt49-v8+ -C /lib/modules/5.15.65-rt49-v8+/build M=/var/lib/dkms/etherlabmaster/1.5.2/build modules....(bad exit status: 2)
Error! Bad return status for module build on kernel: 5.15.65-rt49-v8+ (aarch64)
Consult /var/lib/dkms/etherlabmaster/1.5.2/build/make.log for more information.
make[1]: *** [etherlabmaster.Makefile:62: dkms_build] Error 10
make[1]: Leaving directory '/home/pi/etherlabmaster/etherlabmaster-code'
make: *** [/home/pi/etherlabmaster/configure/E3/RULES_ETHERLAB:96: dkms_build] Error 2


the contents of make.log:

DKMS make.log for etherlabmaster-1.5.2 for kernel 5.15.65-rt49-v8+ (aarch64)
Sat 14 Jan 17:29:56 GMT 2023
make[2]: Entering directory '/usr/src/linux-headers-5.15.65-rt49-v8+'
warning: the compiler differs from the one used to build the kernel
  The kernel was built by: aarch64-linux-gnu-gcc (GCC) 8.4.0
  You are using:           gcc (Debian 8.3.0-6) 8.3.0
  CC [M]  /var/lib/dkms/etherlabmaster/1.5.2/build/examples/mini/mini.o
Assembler messages:
Error: unknown architecture `armv8.5-a'

Error: unrecognized option -march=armv8.5-a
make[5]: *** [scripts/Makefile.build:289: /var/lib/dkms/etherlabmaster/1.5.2/build/examples/mini/mini.o] Error 1
make[4]: *** [scripts/Makefile.build:552: /var/lib/dkms/etherlabmaster/1.5.2/build/examples/mini] Error 2
make[3]: *** [scripts/Makefile.build:552: /var/lib/dkms/etherlabmaster/1.5.2/build/examples] Error 2
make[2]: *** [Makefile:1896: /var/lib/dkms/etherlabmaster/1.5.2/build] Error 2
make[2]: Leaving directory '/usr/src/linux-headers-5.15.65-rt49-v8+'

Any clue how to resolve this?

Look in the makefile for -march=armv8.5-a and try to figure out where it came from?
Possibly a confused autoconfigure?

Maybe try arm64?