NO PUBKEY solved

PPAs are great. But, if you try to add third-party sources to your Ubuntu system, you're probably going to get an error about the key used to digitally sign the packages in that PPA. For whatever reason, the keys which are required to sign the software (for verification) are not also automatically nor easily installed by sofware management applications like apt-get or synaptic. They'll probably improve this soon, but in the meantime, this is what you need to know.

It is relatively easy to install these keys (fixing the error message) if you know the right commands. There is a a PPA to your Ubuntu repositories| HOWTO on the Launchpad site, but I think it's often missed.

I am comfortable with the command-line and it's the quickest solution. Assuming you add the Gwibber microblogging client (where the key id is 5afadbd4aa1c92b0), this is the command sequence:

gpg --keyserver keyserver.ubuntu.com --recv 5afadbd4aa1c92b0
gpg --export --armor 5afadbd4aa1c92b0 | sudo apt-key add -

Alternatively this does it in one line:

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 5afadbd4aa1c92b0

Note

Note that if you visit the PPA overview page, then maybe you'll see the instructions for adding the key, but many times you'll find some blog entry that skips right over these details

If you are more comfortable with graphical tools, then see the help.launchpad.net site where it walks you through those steps.