当我尝试在 Debian 上使用apt-get update命令时，我发现自己陷入了一种错误循环，并出现以下两个错误：NO_PUBKEY 和 KEYEXPIRED
W: There is no public key available for the following key IDs:
4D270D06F42584E6
W: GPG error: http://archive.debian.org lenny/updates Release: The following signatures were invalid: KEYEXPIRED 1356982504
W: GPG error: http://archive.debian.org lenny/volatile Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DFD993306D849617
W: Failed to fetch http://archive.debian.org/debian-securty/dists/lenny/updates/main/source/Sources 404 Not Found [IP: 130.89.148.13 80]
首先我得到 KEYEXPIRED 错误（使用 NO_PUBKEY 但这不是现在的重点）然后我尝试了这个解决方案：
http://community.aegirproject.org/node/757/revisions/2077/view
（但我不确定我是否正确地完成了所有操作）
W: There is no public key available …