This article was first written in November 2005 for the BeezNest technical website (http://glasnost.beeznest.org/articles/304).
If you notice warning messages like these when doing an APT update, read this to fix it:
W: GPG error: ftp://ftp.tux.org unstable Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY BB5E459A529B8BDA
To fix it, take the last 8 characters of the PUBKEY here above and issue the following commands:
testmachine$ gpg --keyserver pgp.mit.edu --recv-keys 529B8BDA gpg: requesting key 529B8BDA from hkp server pgp.mit.edu gpg: key 529B8BDA: public key "Blackdown Java-Linux Package Signing Key <firstname.lastname@example.org>" imported gpg: no ultimately trusted keys found gpg: Total number processed: 1 gpg: imported: 1 testmachine:~$ gpg --armor --export 529B8BDA | sudo apt-key add - gpg: no ultimately trusted keys found OK
I copied the output for you to see how it should work. Then, if you issue, for example the following command, the warning will be gone:
testmachine:~$ sudo apt-get update
Hope this helps!