Fixing NO_PUBKEY errors from Apt

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July 13, 2011

I’ve been ignoring a problem updating Diodon (a great clipboard manager) whenever Ubuntu’s daily Update Manager tries to alert me of new software updates. I finally opened a shell prompt, ran apt-get update and got this error:

signatures couldn't be verified because the public key is not 
available: NO_PUBKEY 751A20CF523884B2

Here’s how to fix any NO_PUBKEY error in two simple steps:

$ gpg --recv-keys 751A20CF523884B2
gpg: requesting key 523884B2 from hkp server
gpg: /home/id/.gnupg/trustdb.gpg: trustdb created
gpg: key 523884B2: public key "Launchpad PPA for Diodon Team" 
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)

$ gpg --armor --export 751A20CF523884B2 | sudo apt-key add -
<div>Ta-da...&nbsp;<br /></div>
<pre>$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be upgraded:
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 55.4 kB of archives.
After this operation, 115 kB of additional disk space will be used.
Do you want to continue [Y/n]? y

Replace “751A20CF523884B2” with whatever public key value that Apt is complaining about. You can also specify which GPG server to connect to when using the --recv-keys flag, but if you leave it off, I believe it will just connect to their main pool of GPG databases.

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