Package: linuxcnc-uspace Thank you Jeff for suggesting this is an OpenGL issue.
Indeed, I went looking and I cannot run glxgears on my system, so I think it would be fair to say that OpenGL is a dependency beyond the 'package dependencies,' and that without it I can't run the plain vanilla, prettier interface of LinuxCNC. It was particularly helpful for you to mention tklinuxcnc, because I had no idea it was there. I followed the instructions at http://linuxcnc.org/docs/2.7/html/gui/tklinuxcnc.html (one finds the ini files, as of this writing, located at ~/linuxcnc/configs/sim.axis, and modifies/copies one to have a line DISPLAY = tklinuxcnc ) Therefore, by using the tklinuxcnc interface, my problem is solve: I have a working copy of LinuxCNC! This is as Jeff said an unusual attempt to get a Single Board Computer to run LinuxCNC, but it may become a more common problem for folks onceLinuxCNC becomes available in Debian Bookworm. Therefore, a more fulsome message would probably reduce support work downstream, but I'm not sure how to implement that myself. I'm happy to be pointed in the right direction, either on this board or off. Thanks again for everyone's help.