Important Info Regarding Rpi4/5 Images.

Following on form this thread.
forum.linuxcnc.org/9-installing-linuxcnc...build-boot-initrd-gz

Please do not run dist-upgrade or attempt to upgrade the kernel, unless you know exactly you are doing and are using the RPi kernel sources from the github page, and be aware some branches do not build or install the device tree files. The kernel was chosen carefully when the image was being built.

The kernel sources are specific to the RPi platform, from memory a Debian Arm kernel didn't allow for device tree overlays, which becomes an issue for enabling I2C and SPI to begin with.

If you find yourself in this position, back up you configs and reburn the image to the SD card, and copy across your configs. If you find a way to fix it by any other means great, but this is not a subject I wish to get involved in nor support.

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On a normal daily driver or even server kernel upgrades are fine.
The issue in this instance is that the kernel used in the image is particular to the RPi and is custom built.
From playing around with various Arm devices the boards aren't as "generic" as the PC platform. Each Arm processor or SOC has it's own quirks as such. The device tree is a way to let the Linux kernel know which devices are available, device tree overlays are used to further customise the setup.
Then there are custom patches that are used to further "tune" a particular board.
I have 3 main machines at home running Linux, one desktop and laptop running Mint and a server running Ubuntu, kernel upgrades are not an issue on any of these 3.
Obviously I have an RPi5 & 4 for testing Linuxcnc images, so these don't see kernel upgrades unless testing new images.
The Orangepi PC that running my hacked together reflow oven doesn't get upgrades, it works and is left alone, but it does have a custom device tree has I needed some status LEDs and an off button on the front panel from the GPIO header. Now if I was to upgrade this kernel I would also have to rebuild the device tree file to suit.
Whilst the Arm platform is good, it's come along way in 20 years, it's not as generic as the PC platform, it's kinda like pre PC days.......but without the OS software issues.

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It was dist-upgrade being the issue, upgrade is fine as the kernel is pinned anyways.

As usual your comments add nothing to the discussion.

I have no idea how Ubuntu got in the conversation, these images are based on Debian with the Rpi kernel.

The kernel version used is ahead of the standard Debian versions so things break on a dist-upgrade.

Is dist-upgrade ever a good idea?

For the Linuxcnc Raspberry Pi images just don't do dist-upgrade, it will break things, this has been proven.

You get get away without doing any kind of upgrade.

If you are worried about security, updates are only a small part of the picture. The first step should always be physical security, which should be the number one priority with a computer running a cnc machine.I'd take data loss over damage to a cnc machine any day of the week, you can't back up a cnc machine.