'Software Sources' allows changing 3rd party repos lines to duplicate official repos URLs, and parses the user-input URL with higher priority in 'apt-get update'.

[Jonathan Yip]

If, by mistake or otherwise, a user edits a 3rd party repos line in Software Sources and point the URL towards an official repos, e.g. <http://gb.archive.ubuntu.com/ubuntu>, Software Sources will accept the input, recognise the new repos line as part of the official repos, and fail to allow the user to revert the changes via the Software Sources GUI.

The problem here is that most 3rd party repos use <free> and <non-free> tags under their <dist> directories, whereas the official repos use the <main> <universe> <multiverse> <restricted> division. Software Sources can only handle these four tags in its 'Ubuntu Software' tab. When changing a 3rd party line's URL into an official repos URL any reloading of the apt repository list will result in, if previously the 3rd party repos line included the <free> or <non-free> or whatever tags, a 'Meta-index file (malformed Release file?)' error, thus:

W: Failed to fetch http://gb.archive.ubuntu.com/ubuntu/dists/karmic/Release Unable to find expected entry free/binary-i386/Packages in Meta-index file (malformed Release file?)

Note that such manually added lines of repository lists overrides the default official repos lines. And Software Sources allows this.

Note that the problem is that Software Sources accepts such modifications to 3rd party repos lines listed in its 'Other Software' tab. And the only method of reverting such mistake is digging into the </etc/apt/sources.list.d> directory manually, since Software Sources is unable to handle tags other than <main> <universe> <multiverse> <restricted> if a repos line points towards an official repository.

ProblemType: Bug
Architecture: i386
CheckboxSubmission: 6ed8556323e06e5764e11f773197b1d3
CheckboxSystem: d00f84de8a555815fa1c4660280da308
Date: Mon Apr 19 13:26:14 2010
DistroRelease: Ubuntu 9.10
InstallationMedia: Ubuntu 9.10 "Karmic Koala" - Release i386 (20091028.5)
NonfreeKernelModules: nvidia
Package: software-properties-gtk 0.75.4
PackageArchitecture: all
ProcEnviron:
 LANGUAGE=en_GB.UTF-8
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-20.58~ppa3-generic-pae-tuxonice
SourcePackage: software-properties
Uname: Linux 2.6.31-20-generic-pae-tuxonice i686