问题描述
我昨天尝试安装VLC Player，并且遇到了Requires installation of untrusted packages错误。为了解决这个问题，我搜索了几个小时，终于找到了一个建议，说改变服务器下载更新。我这样做了，当我点击Update Manager中的”Check”时，它给了我一个404错误。我尝试将服务器切换回主服务器(之后还有其他几个服务器)，但我现在仍然遇到404错误：
下载或更新时出现的其他错误：
编辑：cat /etc/apt/sources.list的输出：
deb-src http://us.archive.ubuntu.com/ubuntu/ precise main restricted #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/ precise main restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise multiverse universe #Added by software-properties
## Major bug fix updates produced after the final release of the
## distribution.
deb http://us.archive.ubuntu.com/ubuntu/ precise-updates main restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-updates restricted main multiverse universe #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/ precise universe
deb http://us.archive.ubuntu.com/ubuntu/ precise-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/ precise-backports main restricted universe multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-backports main restricted universe multiverse #Added by software-properties
deb http://us.archive.ubuntu.com/ubuntu/ precise-security main restricted multiverse
deb-src http://us.archive.ubuntu.com/ubuntu/ precise-security restricted main multiverse universe #Added by software-properties
deb http://us.archive.ubuntu.com/ubuntu/ precise-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 precise partner
deb-src http://archive.canonical.com/ubuntu precise partner
## This software is not part of Ubuntu, but is offered by third-party
## developers who want to ship their latest software.
最佳解决方案
根据您在我以前的答案的评论部分中粘贴的错误，我有另一种可能的解决方案：
sudo apt-get clean
cd /var/lib/apt
sudo mv lists lists.old
sudo mkdir -p lists/partial
sudo apt-get clean
sudo apt-get update
这将重建缓存。礼貌：http://ubuntuforums.org/showthread.php?t=1983220#8
次佳解决方案
This link may help。它解决了一个非常类似的问题。
基本上，你打开一个终端并键入sudo apt-get update && sudo apt-get upgrade。那为我做了。
第三种解决方案
我接受的答案对我来说并没有帮助(Ubuntu 13.10)，但是我可以通过命令行而不是通过Software Updater更新问题(以防其他人遇到此问题)。
sudo aptitude upgrade
向我介绍了来自不受信任来源(Google的音乐经理)的特定软件包，并询问我是否愿意接受并升级。
第四种方案
尝试更新系统指示灯时，我遇到了完全相同的错误。
在我的情况下，这是因为缺少GPG密钥。这里有一个答案，将指示您安装PPA管理器，它可以尝试导入所有丢失的密钥。我这样做，它没有给我任何确认遗漏的键被导入，但我后来运行更新，它安装正常。
这是一个可怕的(non-useful)错误信息，在这种情况下我必须说。
https://askubuntu.com/a/386003/11929