是否需要安装不受信任的软件包？

我昨天尝试安装VLC Player，但Requires installation of untrusted packages出现错误。我花了几个小时寻找解决此问题的方法，最后想到了一个建议，说要更改服务器以从中下载更新。我这样做了，当我在更新管理器中单击“检查”时，它给了我404错误。我尝试将服务器切换回主服务器（之后又切换到其他服务器），但现在仍然出现404错误：

还有我在下载或更新时遇到的另一个错误：

编辑：输出cat /etc/apt/sources.list：

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.

根据您在上一个答案的评论部分粘贴的错误，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

此链接可能会有所帮助。它解决了一个非常类似的问题。

基本上，您打开一个终端并输入sudo apt-get update && sudo apt-get upgrade。对我来说就做到了。

在我的情况下（Ubuntu 13.10），可接受的答案对我没有帮助，但是我能够解决通过命令行而不是通过Software Updater进行更新的问题（以防其他人遇到此问题）。

sudo aptitude upgrade

向我展示了来自不受信任来源（Google的音乐管理器）的特定软件包，并询问我是否要接受并升级。

尝试更新系统指示器时，我遇到了完全相同的错误。

就我而言，这是因为缺少GPG密钥。这里有一个答案，它将指导您安装PPA管理器，并且它可以尝试导入所有丢失的密钥。我这样做了，但并没有给我任何确认，因为我导入了丢失的密钥，但事后我运行了更新，并且安装得很好。

在这种情况下，我必须说这是一条可怕的（无用）错误消息。

https://askubuntu.com/a/386003/11929