[SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

Cbhihe · 2019-04-01 06:52:06

Hi, first time I see this ...

[...]
:: Starting full system upgrade...
resolving dependencies...
looking for conflicting packages...
warning: dependency cycle detected:
warning: x264 will be installed before its ffmpeg dependency
[...]
:: Proceed with installation? [Y/n]

.. and after both reading an Arch sticky on upgrading and consulting news and announcements, I am left wondering what is the appropriate way to deal with this ?
On some third party forums, reached via search engine, responses to queries from users encountering "dependency cyles" range from "don't do the update" to "go ahead and see what error messages will punctuate your update process.", the which many times, oddly ends up being ca-certificate upgrade issues. So in my case I said "Y" in response to ":: Proceed with installation? [Y/n]". The install proceeded uneventfully.

I'm sort of "quietly" confused about this. How does pacman go about resolving circular dependencies ? Flip of a coin ? Heuristic ? ...
Just would like to understand. Cheers.

Last edited by Cbhihe (2019-04-01 13:18:21)

jasonwryan · 2019-04-01 07:23:58

There is an explicit recommendation [Y/n]. You should always follow pacman's advice.

Cbhihe · 2019-04-01 07:38:36

Sure. So I did, but I could not find any documentation on the why's and how's... Even it means looking at code...

Lone_Wolf · 2019-04-01 10:53:18

Check the dependencies for x264 and ffmpeg .

You'll find x264 depeends on ffmpeg , while ffmpeg depends on libx64.so .
That's the dependency cycle.

Dependency cycles require special treatment during building, but normally not at install time.
pacman has no logic to solve a dependency cycle, so warns about it.

Over time the number of dependency cycles has gone down a lot, but a few are still there.

Last edited by Lone_Wolf (2019-04-01 10:53:41)

WorMzy · 2019-04-01 12:26:05

With the advent of alpm hooks, the risk of cyclic dependencies has been greatly diminished. Previously, there was a risk that package_a would run a post_install scriptlet which called a binary from package_b, and package_b would do the same with a binary from package_a. So no matter which package was installed first, the former would fail it's post install procedure.

Nowadays both package_a and package_b get installed, and then post-install hooks execute both binaries with no issues. It's still possible for the above scenario to be encountered in this day and age, so pacman still prints a warning, but package maintainers are able to overcome the limitation. AFAIK, there are no cyclic dependency issues on Arch, so you can safely ignore the warning.

Cbhihe · 2019-04-01 13:20:39

Thanks @Lone_Wolf and @WorMzy for filling me in.
[CLOSED]

Arch Linux

#1 2019-04-01 06:52:06

[SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

#2 2019-04-01 07:23:58

Re: [SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

#3 2019-04-01 07:38:36

Re: [SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

#4 2019-04-01 10:53:18

Re: [SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

#5 2019-04-01 12:26:05

Re: [SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

#6 2019-04-01 13:20:39

Re: [SOLVED] Dependency cycle during regular system upgrade `pacman -Syu`

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