The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 3B4

ubuntu apt-get update报错：

The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32

解决方案：

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 40976EAF437D05B5

参考文档：

Fix apt-get update “the following signatures couldn’t be verified because the public key is not available”