我以前问过这个问题，但它被关闭为“重复”。我可以向您保证，我的方案是原创的，因为它不涉及第三方 PPA。我有系统更新的 GPG 问题。它说没有可用的公钥，并且我也被警告说我的更新信息已过时。这是终端文本：
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 …