How to re-download unauthenticated packages
12054
How do I deal with "unauthenticated sources" errors in the Software Center?
145917
Removing broken packages on distro update (13.04 to 13.10)
124576
Unable to download from an authenticated webserver
53588
How do remove the CD / DVD install as a source for apt-get packages when installing new features?
147458
How can I duplicate my existing software packages on a new system?
55857
How do I get a list of obsolete packages?
109677
How do I to resolve unmet dependencies to uninstall and reinstall package
32200
How do I downgrade a package?
23273
How to delete broken packages in ubuntu
138747
How to list installed packages in apt that are not backed by a repository?
98807
How can I download a distribution?
134563
How do I remove a broken software source?
4450
How can I reproduce the error "package... needs to be reinstalled, but I can't find an archive for it" for testing?
114246
apt-get update, unlinking
109539
How can I perform an offline upgrade using Ubiquity on the installation disc?
45526
How can I install packages without starting their associated services?
19565
Restore default apt repositories in sources.list from command line