解决ubuntu更新源apt-get update时提示NO_PUBKEY

例如：

Err:7 http://mirrors.163.com/debian-security jessie/updates InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9D6D8F6BC857C906  NO_PUBKEY 8B48AD6246925553

使用apt-key adv --recv-keys --keyserver keyserver.ubuntu.com yourKEY

这里是：

apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 9D6D8F6BC857C906
apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 8B48AD6246925553

然后再次更新：sudo apt-get update