Debian - apt-get update GPG error

I have been running a Debian server here at work for a several years now mostly as a web server, but also as a way for me to have quick access to some of the old cli tools like whois, dig, etc.  While running updates I ran across this error:

Fetched 199 B in 1s (122 B/s)
Reading package lists... Done
W: GPG error: http://debian.opennms.org stable Release: The following signatures couldn't be 
verified because the public key is not available: NO_PUBKEY 57801F6F5B9EFD43

 

You can fix this by simply re-add the key by running the follow command at the command line:

wget -O - http://debian.opennms.org/OPENNMS-GPG-KEY | sudo apt-key add -

 

Enjoy!