if i follow the instructions on http://software.jessies.org/salma-hayek/ to install the jessies.org packages: sudo bash <> /etc/apt/sources.list EOF wget -O - http://software.jessies.org/downloads/debian/software.jessies.org.gpg | sudo apt-key add - sudo aptitude update sudo aptitude install ~norg.jessies. then pretty much every day, something's changed and there's a new update to install. as long as i install every version, it works fine. but if i ever miss one, it seems, then until i manually run "apt-get update", i get this error. like i say, the worst part is that "apt-get upgrade" would have told me what to do: Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be upgraded: org.jessies.evergreen org.jessies.scm org.jessies.terminator 3 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 3074kB of archives. After unpacking 12.3kB of additional disk space will be used. Do you want to continue [Y/n]? y Get:1 http://software.jessies.org ./ org.jessies.evergreen 4.37.1970 [1332kB] Get:2 http://software.jessies.org ./ org.jessies.scm 1.243.1970 [767kB] Get:3 http://software.jessies.org ./ org.jessies.terminator 4.158.1970 [975kB] Fetched 3B in 0s (3B/s) Failed to fetch http://software.jessies.org/debian/./org.jessies.evergreen_4.37.1970_i386.deb Size mismatch Failed to fetch http://software.jessies.org/debian/./org.jessies.scm_1.243.1970_i386.deb Size mismatch Failed to fetch http://software.jessies.org/debian/./org.jessies.terminator_4.158.1970_i386.deb Size mismatch E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing? but "Software Updates", by trying to be clever, actually makes things worse. ideally, i think, it would run "apt-get update" for me. apt-get could be improved too; "Size mismatch" doesn't tell me (a) what size it expected, (b) why it expected that size , or (c) what size it got. and looking at the whole sequence i'll include at the bottom of this comment, i'm really not sure my claim above about what causes this problem is right. i mean, the version numbers from the failed attempt are the same as the version numbers in the successful attempt. so what exact file did apt-get have the cached size of? is it actually caching the size of the last-seen file corresponding to a package, but storing just the package name rather than the specific file name? in which case, apt-get could avoid this whole situation by remembering what file size it's cached. but why does it even cache file sizes? to save an "apt-get update"? in that case, couldn't it use the modification date to infer that its cache is out of date and *know* that it needs to "apt-get update"? anyway, here's a whole sequence on the command line, after seeing the "Size mismatch" errors in "Software Update": helium:~$ sudo apt-get upgrade Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be upgraded: org.jessies.evergreen org.jessies.scm org.jessies.terminator 3 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 3074kB of archives. After unpacking 12.3kB of additional disk space will be used. Do you want to continue [Y/n]? y Get:1 http://software.jessies.org ./ org.jessies.evergreen 4.37.1970 [1332kB] Get:2 http://software.jessies.org ./ org.jessies.scm 1.243.1970 [767kB] Get:3 http://software.jessies.org ./ org.jessies.terminator 4.158.1970 [975kB] Fetched 3B in 0s (3B/s) Failed to fetch http://software.jessies.org/debian/./org.jessies.evergreen_4.37.1970_i386.deb Size mismatch Failed to fetch http://software.jessies.org/debian/./org.jessies.scm_1.243.1970_i386.deb Size mismatch Failed to fetch http://software.jessies.org/debian/./org.jessies.terminator_4.158.1970_i386.deb Size mismatch E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing? helium:~$ sudo apt-get update Get:1 http://us.archive.ubuntu.com edgy Release.gpg [191B] Ign http://us.archive.ubuntu.com edgy/main Translation-en_US Get:2 http://security.ubuntu.com edgy-security Release.gpg [191B] Ign http://security.ubuntu.com edgy-security/main Translation-en_US Get:3 http://software.jessies.org ./ Release.gpg [189B] Ign http://software.jessies.org ./ Translation-en_US Ign http://us.archive.ubuntu.com edgy/restricted Translation-en_US Ign http://us.archive.ubuntu.com edgy/multiverse Translation-en_US Ign http://us.archive.ubuntu.com edgy/universe Translation-en_US Get:4 http://us.archive.ubuntu.com edgy-updates Release.gpg [191B] Ign http://us.archive.ubuntu.com edgy-updates/main Translation-en_US Ign http://us.archive.ubuntu.com edgy-updates/restricted Translation-en_US Ign http://security.ubuntu.com edgy-security/restricted Translation-en_US Ign http://security.ubuntu.com edgy-security/multiverse Translation-en_US Ign http://security.ubuntu.com edgy-security/universe Translation-en_US Get:5 http://security.ubuntu.com edgy-security Release [50.9kB] Get:6 http://software.jessies.org ./ Release [438B] Ign http://us.archive.ubuntu.com edgy-updates/multiverse Translation-en_US Ign http://us.archive.ubuntu.com edgy-updates/universe Translation-en_US Hit http://us.archive.ubuntu.com edgy Release Hit http://us.archive.ubuntu.com edgy-updates Release Ign http://software.jessies.org ./ Packages Hit http://us.archive.ubuntu.com edgy/main Packages Get:7 http://software.jessies.org ./ Packages [873B] Hit http://us.archive.ubuntu.com edgy/restricted Packages Hit http://us.archive.ubuntu.com edgy/main Sources Hit http://us.archive.ubuntu.com edgy/restricted Sources Hit http://us.archive.ubuntu.com edgy/multiverse Packages Hit http://us.archive.ubuntu.com edgy/universe Packages Hit http://us.archive.ubuntu.com edgy-updates/main Packages Hit http://us.archive.ubuntu.com edgy-updates/restricted Packages Hit http://us.archive.ubuntu.com edgy-updates/main Sources Hit http://us.archive.ubuntu.com edgy-updates/restricted Sources Hit http://us.archive.ubuntu.com edgy-updates/multiverse Packages Hit http://us.archive.ubuntu.com edgy-updates/universe Packages Get:8 http://security.ubuntu.com edgy-security/main Packages [52.6kB] Get:9 http://security.ubuntu.com edgy-security/restricted Packages [3529B] Get:10 http://security.ubuntu.com edgy-security/main Sources [10.9kB] Get:11 http://security.ubuntu.com edgy-security/restricted Sources [940B] Get:12 http://security.ubuntu.com edgy-security/multiverse Packages [3572B] Get:13 http://security.ubuntu.com edgy-security/universe Packages [31.7kB] Fetched 156kB in 2s (63.5kB/s) Reading package lists... Done helium:~$ sudo apt-get upgrade Reading package lists... Done Building dependency tree Reading state information... Done The following packages will be upgraded: libgtk2.0-0 libgtk2.0-bin libgtk2.0-common org.jessies.evergreen org.jessies.scm org.jessies.terminator 6 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 10.0MB of archives. After unpacking 12.3kB of additional disk space will be used. Do you want to continue [Y/n]? y Get:1 http://security.ubuntu.com edgy-security/main libgtk2.0-common 2.10.6-0ubuntu3.1 [4454kB] Get:2 http://software.jessies.org ./ org.jessies.evergreen 4.37.1970 [1332kB] Get:3 http://software.jessies.org ./ org.jessies.scm 1.243.1970 [767kB] Get:4 http://software.jessies.org ./ org.jessies.terminator 4.158.1970 [975kB] Get:5 http://security.ubuntu.com edgy-security/main libgtk2.0-bin 2.10.6-0ubuntu3.1 [22.4kB] Get:6 http://security.ubuntu.com edgy-security/main libgtk2.0-0 2.10.6-0ubuntu3.1 [2479kB] Fetched 6955kB in 19s (354kB/s) (Reading database ... 102278 files and directories currently installed.) Preparing to replace libgtk2.0-common 2.10.6-0ubuntu3 (using .../libgtk2.0-common_2.10.6-0ubuntu3.1_all.deb) ... Unpacking replacement libgtk2.0-common ... Preparing to replace libgtk2.0-bin 2.10.6-0ubuntu3 (using .../libgtk2.0-bin_2.10.6-0ubuntu3.1_i386.deb) ... Unpacking replacement libgtk2.0-bin ... Preparing to replace libgtk2.0-0 2.10.6-0ubuntu3 (using .../libgtk2.0-0_2.10.6-0ubuntu3.1_i386.deb) ... Unpacking replacement libgtk2.0-0 ... Preparing to replace org.jessies.evergreen 4.34.1955 (using .../org.jessies.evergreen_4.37.1970_i386.deb) ... Unpacking replacement org.jessies.evergreen ... Preparing to replace org.jessies.scm 1.242.1955 (using .../org.jessies.scm_1.243.1970_i386.deb) ... Unpacking replacement org.jessies.scm ... Preparing to replace org.jessies.terminator 4.157.1955 (using .../org.jessies.terminator_4.158.1970_i386.deb) ... Unpacking replacement org.jessies.terminator ... Setting up org.jessies.evergreen (4.37.1970) ... Setting up org.jessies.scm (1.243.1970) ... Setting up org.jessies.terminator (4.158.1970) ... Setting up libgtk2.0-common (2.10.6-0ubuntu3.1) ... Setting up libgtk2.0-bin (2.10.6-0ubuntu3.1) ... Updating the IM modules list for GTK+-2.10.0...done. Updating the gdk-pixbuf loaders list for GTK+-2.10.0...done. Setting up libgtk2.0-0 (2.10.6-0ubuntu3.1) ... helium:~$