* W: GPG error: http://ppa.launchpad.net trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8BAF9A6F
Execute the following commands in terminal:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <PUBKEY>
where <PUBKEY> is your missing public key for repository, e.g. 8BAF9A6F.
Then update
sudo apt-get update标签：do,sudo,NO,fix,GPG,key,error,PUBKEY From： https://www.cnblogs.com/hansjorn/p/16857840.html