我是 Ubuntu 新手。我在 VMware 中使用 Ubuntu 14.04.02 LTS。由于我位于网络防火墙后面，因此我编辑了 apt.conf 文件，以便 apt-get 可以在代理服务器后面工作，这很好。但是，当我这样做时
sudo apt-get 更新
我得到以下信息：
Ign http://security.ubuntu.com trusty-security InRelease
Ign http://us.archive.ubuntu.com trusty InRelease
Ign http://extras.ubuntu.com trusty InRelease
Ign http://files.ettus.com trusty InRelease
Ign http://security.ubuntu.com trusty-security Release.gpg
Ign http://us.archive.ubuntu.com trusty-updates InRelease
Ign http://archive.ubuntu.com trusty InRelease
Ign http://extras.ubuntu.com trusty Release.gpg
Ign http://files.ettus.com trusty Release.gpg
Ign http://us.archive.ubuntu.com trusty-backports InRelease
Ign http://security.ubuntu.com trusty-security Release
Ign http://us.archive.ubuntu.com trusty Release.gpg
Ign http://extras.ubuntu.com trusty Release
Ign http://files.ettus.com trusty Release
Ign http://us.archive.ubuntu.com trusty-updates Release.gpg
Ign http://us.archive.ubuntu.com trusty-backports Release.gpg
Ign http://archive.ubuntu.com trusty Release.gpg
Ign http://us.archive.ubuntu.com trusty Release
Ign http://us.archive.ubuntu.com trusty-updates Release
Ign http://archive.ubuntu.com trusty Release
Ign http://us.archive.ubuntu.com trusty-backports Release
Err http://archive.ubuntu.com trusty/main Sources
404 Not Found
Err http://archive.ubuntu.com trusty/restricted Sources
404 Not Found
Err http://archive.ubuntu.com trusty/multiverse Sources
404 Not Found
Err http://files.ettus.com trusty/main amd64 Packages
404 Not Found
Err http://files.ettus.com trusty/main i386 Packages
404 Not Found
Err http://extras.ubuntu.com trusty/main Sources
404 Not Found
Ign http://files.ettus.com trusty/main Translation-en_US
Ign http://files.ettus.com trusty/main Translation-en
Err http://extras.ubuntu.com trusty/main amd64 Packages
404 Not Found
Err http://extras.ubuntu.com trusty/main i386 Packages
404 Not Found
... 这里还有更多...
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/universe/source/Sources 404 Not Found
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/main/source/Sources 404 Not Found
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/restricted/source/Sources 404 Not Found
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/multiverse/source/Sources 404 Not Found
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/main/binary-amd64/Packages 404 Not Found
W: Failed to fetch http://security.ubuntu.com/ubuntu/dists/trusty-security/restricted/binary-amd64/Packages 404 Not Found
...还有更多...
我在网上搜索了一下，发现有些路径末尾缺少文件扩展名。这是问题的一部分吗？就像我说的，我对 Ubuntu 完全陌生，仍在摸索。我该如何解决这个问题？
我执行了 etc/apt/sources.list 并得到以下内容：
# deb cdrom:[Ubuntu 14.04.2 LTS _Trusty Tahr_ - Release amd64 (20150218.1)]/ trusty main restricted
deb-src http://archive.ubuntu.com/ubuntu trusty main restricted multiverse #Added by software-properties
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://us.archive.ubuntu.com/ubuntu/ trusty main restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty universe main restricted #Added by software-properties
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates main restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe main restricted multiverse #Added by software-properties
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ trusty universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-backports main restricted universe multiverse #Added by software-properties
deb http://security.ubuntu.com/ubuntu trusty-security main restricted multiverse
deb-src http://security.ubuntu.com/ubuntu trusty-security universe main restricted multiverse #Added by software-properties
deb http://security.ubuntu.com/ubuntu trusty-security universe
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu trusty partner
# deb-src http://archive.canonical.com/ubuntu trusty partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
deb http://extras.ubuntu.com/ubuntu trusty main
deb-src http://extras.ubuntu.com/ubuntu trusty main
我发现这答案，但我的 sources.list 文件甚至不包含需要删除的行，所以这没有帮助。我也看了这里但这并没有解决我的问题。我被这个问题难住了。有什么建议吗？这是我没有找到的重复问题吗？谢谢你的帮助。
问候，马歇尔
答案1
好吧，在同事的帮助下，我成功了。我们主要做了两件事：
(1) 我们在环境文件中设置代理设置，而不是在 apt.conf 中（因此代理设置将针对每个应用程序进行设置）。此外，我们确实发现我的代理设置有误（感谢 steeldriver 要求我仔细检查）。
http_proxy=<correct proxy setting>
https_proxy=<correct proxy setting>
no_proxy=<internal work website url>
no_proxy 设置适用于我自己的工作内部网站，因为我们不使用代理来访问它，所以如果没有 no_proxy 环境变量，我就无法访问该网站。
(2) 我进入了 /etc/sudoers 文件，并在 Defaults env_reset 之后为每个环境变量添加了 Defaults（因此我添加了 3 行）。结果发现这有问题；相反，我们只是在 Defaults env_reset 和 env_keep 的同一行上添加了 3 个环境变量，如下所示：
Defaults env_reset, env_keep+=no_proxy, env_keep+=http_proxy, env_keep+=https_proxy
这样，每次使用 sudo 时这些环境变量就不会消失。现在我可以正常运行了。