apt-get failed：The following signatures were invalid: BADSIG

参考如下链接：

https://askubuntu.com/questions/131601/gpg-error-release-the-following-signatures-were-invalid-badsig/158750

sudo apt-get clean
sudo mv /var/lib/apt/lists /tmp
sudo mkdir -p /var/lib/apt/lists/partial
sudo apt-get clean
sudo apt-get update