Source order affects package dependencies

[0]

It's common for Ubuntu packages to be present in multiple repositories. For example, updates to a package in xenial might go to xenial-security and xenial-updates at different times. In the absence of priorities, apt deals with this by installing the latest version from any repository.

This works fine with bcfg2 so long as the dependencies are the same across repositories. If they differ, then bcfg2 arbitrarily selects the dependencies from the first repository that has the package (ref).

I've found this to be problematic with kernel packages. For example, linux-headers-generic currently depends on linux-headers-4.4.0-75-generic in xenial-security and on linux-headers-4.4.0-77-generic in xenial-updates. If I have xenial-security listed first, then bcfg2 wants to see version 75, but apt installs 77.

My workaround for this is to rearrange the sources as necessary, but that won't work in every case.

[AlexanderS]

I have a local patch, that adds priorities to the sources. It should be possible to select the package with the highest version, if multiple sources have the same priority. (Even if it could be really hard to compare debian version numbers.)

[solj]

@AlexanderS that could be useful but I guess we achieve the same effect by sorting? What case is covered by having a priority that wouldn't be covered by sorting sources?

[AlexanderS]

A priority attribute would allow us to define two or more sources with equal priorities.

[xschlef]

To add to this:
bcfg2 could also generate the /etc/apt/preferences to reflect the new source ordering on the clients.

This would limit the choices for the priority values to apt preference settings, but would reflect the source ordering to clients that run with packages version: any