Arch Linux

Summary and Info:

Partial upgrade of the system and/or installation of a new package on old installation can make some other packages broken.

Problem description:

So, you should have working installation with old packages. Then say pacman -Sy, and upgrade one, or install a new one package.

For example (I will write about specific packages just below), you have an old package A with version 1.0, which depends on old library libB. At that, in the description of the package A version on the needed library is not specified.

You want to install new/upgrade old package C to the version 1.1. This package needs libB version 1.1. Ok, pacman will upgrade/install C version 1.1, and will automatically upgrade existing libB.
At that, it is very possible, that the package A became unworking, because it has a binary, for example /usr/bin/A, which is linked with the /usr/lib/libB-1.0.so.0 .

There are a lot of examples, but, it seems to me that the best one is mplayer. Here are a few commands output from my system:

# LANG=C pacman -Qi mplayer | grep -A 3 Depends
Depends On : libxxf86dga libxv libmad giflib cdparanoia gtk2 sdl
lame libtheora xvidcore zlib libmng libxss libgl
smbclient aalib jack-audio-connection-kit x264>=20090108
faac lirc-utils ttf-dejavu fribidi

# ldd /usr/bin/mplayer | grep libjpeg
libjpeg.so.62 => not found
libjpeg.so.62 => not found


So, libjpeg library binary is not found, because I have upgraded ghostscript which needs libjpeg>=7. As the result, pacman thinks that all right, but mplayer does not work.

So, I think there are two ways to solve this problem:

1) While upgrading any package, pacman should check, that all packages that depend on the upgraded package can be dynamically linked with a new version of the upgraded package. I.e., when pacman decides to upgrade libjpeg, for example, it should check (with ldd, or, for example, readelf) all binary of all packages that depends on the libjpeg to be sure, that they can be dynamically linked with that version. I case of some of them can not work with new version, pacman should show error and exit, or suggest to upgrade that packages too, in my case it will be mplayer.

Advantage: This method should work in any system just after this functionality will be implemented in the pacman utility. All existing "bad" packages will be checked.

Disadvantage: This method can be very slow, at that this check will be run at any computer with any upgrade or new package install.

2) Modify package build script to make such check at a build time:
Makepkg should build package (in our case -- mplayer), then should collate depends=() from the PKGBUILD and ldd mplayer.
In case of PKGBUILD has words like "libjpeg>=6", or "libjpeg", but ldd (readelf) says that the /usr/bin/mplayer depends on libjpeg.so.62, it is clear that when pacman will upgrade libjpeg to the version 7-1, mplayer will not work, while all its dependencies officially satisfied.

Unfortunately it is not clear to me what to do after this potential problem will be detected. May be makepkg should show warning, or it should write needed libjpeg version to the dependencies of the binary package like Debian build system can do this (this is better but harder to implement).

Advantage: Check is performed only once at the build time.
Disadvantage: This fix will work only when all existing packages with not quite correct dependencies will be replaced by the packages whose dependencies specified precisely. This can take a lot of time, especially on systems that upgraded seldom.