There will be a warning on the top bar saying that 'the update information is outdated... '
If 'sudo apt-get update', get the following errors:
W: A error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://archive.canonical.com raring Release: The following signatures were invalid: BADSIG 40976EAF437D05B5 Ubuntu Archive Automatic Signing Key <firstname.lastname@example.org>
W: Failed to fetch http://archive.canonical.com/ubuntu/...raring/Release
W: Some index files failed to download. They have been ignored, or old ones used instead.
How can I deal with it? Thanks!