Ubuntu Release Upgrade 官方源似乎挂了？

最近在折腾发行版升级（ precise -> trusty ），今早升完几台机器，继续操作其他机器时发现 do-release-upgrade 一直报 404 Not Found 错误。

~# do-release-upgrad
Checking for a new Ubuntu release
Err Upgrade tool signature
404 Not Found [IP: 23.251.96.133 80]
Err Upgrade tool
404 Not Found [IP: 23.251.96.133 80]
Fetched 0 B in 0s (0 B/s)
WARNING:root:file 'trusty.tar.gz.gpg' missing
Failed to fetch
Fetching the upgrade failed. There may be a n etwork problem.

然后我找到 /var/lib/update-manager/meta-release-lts 这个文件查了内容，发现里面的 URL 用浏览器直接访问或者 wget 也是 404 ，这个文件的内容在今早成功升级的机器，和现在没法升级的机器上，都是一致的。

Dist: trusty
Name: Trusty Tahr
Version: 14.04.5 LTS
Date: Thu, 17 Apr 2014 14:04:00 UTC
Supported: 1
Description: This is the 14.04.5 LTS release
Release-File: http://archive.ubuntu.com/ubuntu/dists/trusty/Release
ReleaseNotes: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/dist-upgrader-all/current/ReleaseAnnouncement
ReleaseNotesHtml: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/dist-upgrader-all/current/ReleaseAnnouncement.html
UpgradeTool: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/dist-upgrader-all/current/trusty.tar.gz
UpgradeToolSignature: http://archive.ubuntu.com/ubuntu/dists/trusty-updates/main/dist-upgrader-all/current/trusty.tar.gz.gpg

公司内的镜像源因为每天同步几次官方源，在去查相应路径时发现对应的目录也已经是空的了。
这是药丸啊…