在用 sudo apt-get update 时出现这样的报错：
W: GPG error: http://archive.ubuntukylin.com:10006/ubuntukylin xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8D5A09DC9B929006
解决方案:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <PUBKEY>
这里 <PUBKEY> 为8D5A09DC9B929006
然后再
sudo apt-get update