NO_PUBKEY? During apt-get update

This happens to me pretty frequently, as I jump over different repositories to get ubuntu packages:

W: GPG error: http://ppa.launchpad.net jaunty Release: The following 
signatures couldn't be verified because the public key is not 
available: NO_PUBKEY 2836CB0A8AC93F7A
W: You may want to run apt-get update to correct these problems

Note this happens during apt-get update, so running it is not the solution!

Assuming this is a repository you trust on, let us just add this key to your ubuntu so you can download updates from there:

1. $ gpg --keyserver keyserver.ubuntu.com --recv 2836CB0A8AC93F7A
   gpg: requesting key 8AC93F7A from hkp server keyserver.ubuntu.com
   gpg: key 8AC93F7A: public key "Launchpad Kubuntu Updates" imported
   gpg: Total number processed: 1
   gpg:               imported: 1  (RSA: 1)
   

   (The number 2836CB0A8AC93F7A is the key listed as missing in the error message)
   



2. $ gpg --export --armor 2836CB0A8AC93F7A | sudo apt-key add -
   OK
   

   (Again, replace that value by your key)
   

Voila. Run apt-get update again and you should be able to receive that repositories' packages.

Update: palo points out you can do the same with just this line:

sudo apt-key adv --recv-key --keyserver keyserver.ubuntu.com 2836CB0A8AC93F7A

And that's even shorter -- thanks!