Inasmuch as I was losing mine, I needed theirs to get back to having a functioning Linux Mint desktop.
The saga began when I restarted my machine and got the message:
cinnamon just crashed you are currently running in Fallback Mode
The mode had fallen so far backwards that I couldn’t reliably resume a guest virtual machine because the display capabilities had degraded. It also didn’t provide any way to restart the machine, and provided no easy way to logout (though there are brute strength ways to do both).
I tried various voodoo solutions found from web searching for the error message but, to cut a long story short, none of them worked. I use the NVIDIA video driver because the Linux nouveau video driver doesn’t (yet) support my video card, but updating the driver in the blind hope of fixing the problem had failed to uninstall the old driver and I hadn’t wanted to force the issue. However, on reading the nvidia-installer manpage for a solution to that problem, I noticed there is a --sanity option to “Perform basic sanity checks on an existing NVIDIA driver installation.” Since I was losing mine, I thought I’d try some of theirs.
nvidia-installer --sanity reported changes in some configuration files, which wasn’t too surprising, but it also reported:
ERROR: File ‘/usr/lib/xorg/modules/extensions/libglx.so’ is not a symbolic link.
and similarly for another library. About halfway through the 45 days since I’d last rebooted, some software update had replaced symbolic links to NVIDIA-installed libraries with other libraries or links to other libraries. Once I restored the links to the NVIDIA libraries, which were still in the various directories, I was able to restart for the umpteenth time and, this time, get back to having a fully functioning desktop.