无法更新软件包-“无法下载软件包文件。正在检查Internet ...”或“需要从未经身份验证的来源进行安装”

我首先得到这个

Failed to download package files. Check internet connection

错误，并尝试了对大多数遇到相同问题的其他人似乎有效的解决方案...更改下载位置。我尝试了几种不同的服务器，但没有任何效果。我还在上面的链接中尝试了第二种解决方案（已制作了一个新的源列表文件）。

最近，错误改为“安装需要从未经身份验证的来源进行安装”。在第一个解决方案这篇文章是一样的，从上面的第一个链接的第二个解决方案，使我的情况没有什么区别。在开始添加公共密钥或任何其他解决方案之前，我认为最好是专门发布我的输出并查看社区的意见。

这里是我的输出为apt-get update。

这里是我的输出为apt-get upgrade。

我的信誉不高，无法发布两个以上的链接，因此以下是/etc/apt/sources.list直接的输出：

~$ cat /etc/apt/sources.list
# deb cdrom:[Ubuntu 14.04.3 LTS _Trusty Tahr_ - Beta amd64 (20150805)]/ trusty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty 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/ trusty main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty universe multiverse #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
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-updates universe main multiverse restricted #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.
deb http://us.archive.ubuntu.com/ubuntu/ trusty multiverse
deb http://us.archive.ubuntu.com/ubuntu/ trusty-updates multiverse

## 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://us.archive.ubuntu.com/ubuntu/ trusty-security main restricted
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-security universe main multiverse restricted #Added by software-properties
deb http://us.archive.ubuntu.com/ubuntu/ trusty-security universe
deb http://us.archive.ubuntu.com/ubuntu/ trusty-security multiverse

## 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

## added myself -- http://stackoverflow.com/questions/29630434/graphviz-installation-ubuntu-14-04
deb http://security.ubuntu.com/ubuntu lucid-security main
deb http://cz.archive.ubuntu.com/ubuntu lucid main
deb http://repository.spotify.com stable non-free
# deb-src http://repository.spotify.com stable non-free
# deb-src http://repository.spotify.com stable non-free
deb http://us.archive.ubuntu.com/ubuntu/ trusty-proposed multiverse restricted universe main
deb-src http://us.archive.ubuntu.com/ubuntu/ trusty-proposed multiverse restricted universe main #Added by software-properties

根据for的输出底部的第6个错误apt-get update，看来至少有一个问题是无法对Nvidia的某些程序包进行身份验证（可能是我刚才安装的cuda存储库–是我的愚蠢之举）。做？）。

不知道下一步该怎么做，将不胜感激任何指导！提前致谢。