aptitude update 找不到 GPG key 的處理

執行的 aptitude update 以後，出現錯誤訊息：

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 00A6F0A3C300EE8C
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 4F4EA0AAE5267A6C

可以透過下列指令去 import keys：

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com {KEY}

例如上面的錯誤，可以這樣 import key：

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 00A6F0A3C300EE8C
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 4F4EA0AAE5267A6C

reference: How do I fix the GPG error “NO_PUBKEY”?