While re-opening my Ubuntu 12.04 machine after a 2 weeks vacations, and successfully using the Update Manager to update my applications I see that
The package information was last updated 17 days ago.
Press the Check button below to check for new software updates
After an update the package information should have been updated minutes ago. How do I force the update of the package information ? I already had the problem and I know there is a file to remove or rename in the file system /var (?) something however I don't remember which one.
Thanks @ Eliah Kagan, running
$ sudo apt-get update
did turn up one error related to a missing public key from an update of QGIS [qgis.org] e.g.
W: GPG error: http://qgis.org precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BBA6491F47765B75
The solution was to run
$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys BBA6491F47765B75
Then the cmd. line returned no error and the Update Manager displayed
The package information was just updated.
The question is solved. Thanks.
sudo apt-get updatetries to update this info, but Software Center should've done the equivalent. It'll likely fail... giving error messages illuminating the cause of the problem! (E.g. here it was a 404 with a PPA; there, a BADSIG.) So please run that command, paste its output in your question, select it and Ctrl+K to format it. (Or use http://paste.ubuntu.com and edit your question with a link.) – Eliah Kagan Aug 27 '14 at 18:47