linux-modules-nvidia-510-server fails to install

[Ian May]

$ sudo apt install linux-modules-nvidia-510-server-$(uname -r)
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 linux-modules-nvidia-510-server-5.4.0-135-generic : Depends: linux-signatures-nvidia-5.4.0-135-generic (= 5.4.0-135.152) but 5.4.0-135.152+1 is to be installed
                                                     Depends: nvidia-kernel-common-510-server (<= 510.85.02-1) but it is not going to be installed
                                                     Depends: nvidia-kernel-common-510-server (>= 510.85.02) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

$ lsb_release -rd
Description: Ubuntu 20.04.5 LTS
Release: 20.04

[dann frazier (dannf)]

What happened here is that we dropped the 510 driver in lrm 5.4.0-135.152+1, transitioning it to the 515 driver. It therefore did not produce a 5.4.0-135.152+1 version of linux-modules-nvidia-510-server-5.4.0-135-generic. Ubuntu always keeps the latest version of a binary package in the archive, even if the source that produced it has been superseded. Because of that, the 5.4.0-135.152 version of linux-modules-nvidia-510-server-5.4.0-135-generic is sticking around. 5.4.0-135.152 correctly had a strict versioned dep on a matching linux-signatures package, and that linux-signatures package was superseded by a new one. Superseded packages *are* dropped from the archive, so that dependency can no longer be met.

TLDR; this is all normal (though not ideal) behavior, and this one is particularly confusing because we dropped (and transitioned) the 510 driver during a refresh of the drivers for a kernel that previously had a 510 driver.

Lesson: Installing modules for anything other than the latest kernel update is not supported, even if those modules appear to still be available in the archive.