对于错误
GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY B70731143DD9F856
可以通过以下方式解决
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
