I periodically have problems using Australian Debian mirrors, specifically the testing, unstable and experimental distros (stable appears fine at the moment). When it occurs (it is not uncommon), aptitude update does not report any problems, but moves all the packages from installed to obsolete/local in the curses interface, and cannot install any new packages (no installation candidates). It does at least return a non-zero exit code. apt-get does display the errors, its output
looks like this after deleting everything in /var/lib/apt/lists/partial/ :
Hit
http://ftp.au.debian.org testing InRelease
Hit http://ftp.au.debian.org unstable InRelease
Hit http://ftp.au.debian.org experimental InRelease
Get:1 http://ftp.au.debian.org testing/main Sources [4,787 kB]
Get:5 http://ftp.au.debian.org testing/contrib Sources [43.7 kB]
Get:6 http://ftp.au.debian.org testing/non-free Sources [81.7 kB]
Get:7 http://ftp.au.debian.org testing/main i386 Packages [6,821 kB]
Get:8 http://ftp.au.debian.org testing/contrib i386 Packages [58.6 kB]
Get:9 http://ftp.au.debian.org testing/non-free i386 Packages [108 kB]
Ign http://ftp.au.debian.org testing/contrib TranslationIndex
Hit http://ftp.au.debian.org testing/main TranslationIndex
Ign
http://ftp.au.debian.org testing/non-free TranslationIndex
Get:10 http://ftp.au.debian.org unstable/main Sources [5,203 kB]
Hit http://ftp.au.debian.org unstable/contrib Sources/DiffIndex
Get:11 http://ftp.au.debian.org unstable/non-free Sources [98.4 kB]
Get:12 http://ftp.au.debian.org unstable/main i386 Packages [7,097 kB]
Hit http://ftp.au.debian.org unstable/contrib i386 Packages/DiffIndex
Hit http://ftp.au.debian.org unstable/non-free i386 Packages/DiffIndex
Ign http://ftp.au.debian.org unstable/contrib TranslationIndex
Hit http://ftp.au.debian.org unstable/main TranslationIndex
Ign http://ftp.au.debian.org unstable/non-free TranslationIndex
Get:13 http://ftp.au.debian.org experimental/main Sources [285 kB]
Hit
http://ftp.au.debian.org experimental/contrib Sources/DiffIndex
Get:14 http://ftp.au.debian.org experimental/non-free Sources [5,608 B]
Get:15 http://ftp.au.debian.org experimental/main i386 Packages [468 kB]
Hit http://ftp.au.debian.org experimental/contrib i386
Packages/DiffIndex
Get:16 http://ftp.au.debian.org experimental/non-free i386 Packages [13.0 kB]
Ign http://ftp.au.debian.org experimental/contrib TranslationIndex
Ign http://ftp.au.debian.org experimental/main TranslationIndex
Ign http://ftp.au.debian.org experimental/non-free TranslationIndex
Get:17 http://ftp.au.debian.org experimental/contrib i386 Packages [3,805 B]
Ign http://ftp.au.debian.org testing/contrib Translation-en_AU
Ign http://ftp.au.debian.org testing/contrib Translation-en
Ign http://ftp.au.debian.org testing/non-free Translation-en_AU
Ign http://ftp.au.debian.org testing/non-free Translation-en
Ign http://ftp.au.debian.org unstable/contrib Translation-en_AU
Ign http://ftp.au.debian.org unstable/contrib
Translation-en
Ign http://ftp.au.debian.org unstable/non-free Translation-en_AU
Ign http://ftp.au.debian.org unstable/non-free Translation-en
Ign http://ftp.au.debian.org experimental/contrib Translation-en_AU
Ign http://ftp.au.debian.org experimental/contrib Translation-en
Ign http://ftp.au.debian.org experimental/main Translation-en_AU
Ign http://ftp.au.debian.org
experimental/main Translation-en
Ign http://ftp.au.debian.org experimental/non-free Translation-en_AU
Ign http://ftp.au.debian.org experimental/non-free Translation-en
Fetched 25.1 MB in 49s (511 kB/s)
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_main_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_contrib_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_non-free_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_main_binary-i386_Packages Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_contrib_binary-i386_Packages Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_testing_non-free_binary-i386_Packages Hash Sum mismatch
W: Failed to fetch
bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_unstable_main_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_unstable_non-free_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_unstable_main_binary-i386_Packages Hash Sum mismatch
W: Failed to fetch
bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_experimental_main_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_experimental_non-free_source_Sources Hash Sum mismatch
W: Failed to fetch bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_experimental_main_binary-i386_Packages Hash Sum mismatch
W: Failed to fetch
bzip2:/var/lib/apt/lists/partial/ftp.au.debian.org_debian_dists_experimental_non-free_binary-i386_Packages Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.