Get:1 http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease [36.5 kB]
Hit:2 http://us.archive.ubuntu.com/ubuntu yakkety InRelease                    
Err:1 http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease      
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7FCC7D46ACCC4CF8
Hit:3 http://us.archive.ubuntu.com/ubuntu yakkety-updates InRelease     
Hit:4 http://security.ubuntu.com/ubuntu yakkety-security InRelease      
Hit:5 http://us.archive.ubuntu.com/ubuntu yakkety-backports InRelease
Reading package lists... Done                      
W: GPG error: http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7FCC7D46ACCC4CF8
E: The repository 'http://apt.postgresql.org/pub/repos/apt xenial-pgdg InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.