Misleading error message when package files are not found

[Tony Houghton]

Occasionally update-manager reports, "Some packages failed to download. Check your Internet connection." I'm pretty sure these errors are not usually caused by connectivity issues, and from using apt-get on the command line I think the actual cause is file not found errors. This happens when it's been too long between the check for updates and actually downloading them, so some packages have been updated again in the meantime, replacing the version that update-manager has in its records of what's available.

update-manager should be able to detect that these are file not found errors, and redo the equivalent of apt-get update and/or redo the update before the upgrade if a certain amount of time has elapsed since the update.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: update-manager 1:15.04.7
ProcVersionSignature: Ubuntu 3.19.0-26.28-generic 3.19.8-ckt4
Uname: Linux 3.19.0-26-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.17.2-0ubuntu1.3
Architecture: amd64
CurrentDesktop: Unity
Date: Tue Nov 17 15:16:24 2015
GsettingsChanges:
 b'com.ubuntu.update-manager' b'first-run' b'false'
 b'com.ubuntu.update-manager' b'launch-time' b'1447772734'
InstallationDate: Installed on 2015-08-11 (98 days ago)
InstallationMedia: Ubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: No upgrade log present (probably fresh install)