问题描述
我之前已经问了这个问题，但它已作为”duplicate.”关闭了我可以向你保证我的方案是原创的，因为它没有提到第三方PPA。我有系统更新的GPG问题。它说没有可用的公钥，我也被警告我的更新信息已经过时。这是终端文字：
W: A error occurred during the signature verification.
The repository is not updated and the previous index files will be used. GPG error:http://extras.ubuntu.com quantal Release:
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 16126D3A3E5C1192
W: GPG error: http:// archive.canonical.com quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http:// us.archive.ubuntu.com quantal Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http:// us.archive.ubuntu.com quantal-updates Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http:// us.archive.ubuntu.com quantal-backports Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: GPG error: http:// us.archive.ubuntu.com quantal-security Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 40976EAF437D05B5 NO_PUBKEY 3B4FE6ACC0B21F32
W: Failed to fetch http:// extras.ubuntu.com/ubuntu/dists/quantal/Release
W: Some index files failed to download. They have been ignored, or old ones used instead.
我在网址中放置了空格，因为每个问题不允许新用户超过两个超链接。
请不要将其作为副本关闭。它不是指第三方PPA，它指的是Canonical发布的标准更新包。
最佳解决方案
在终端中运行以下命令：
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 40976EAF437D05B5
sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com 3B4FE6ACC0B21F32
这将从Ubuntu GPG密钥服务器下载丢失的GPG密钥(如原始错误消息中所述)。