我第一次得到这个
Failed to download package files. Check internet connection
错误并尝试解决方案对于大多数遇到同样问题的人来说，这似乎很有效……更改下载位置。我尝试了几个不同的服务器，但都没有效果。我还尝试了上面链接中的第二种解决方案（让 apt 创建一个新源列表文件）。
最近，错误变成了“安装需要从未经认证的来源进行安装”。这个帖子与上面第一个链接中的第二个解决方案相同，对我的情况没有影响。在我开始添加公钥或任何其他解决方案之前，我认为最好是具体发布我的输出，看看社区怎么说。
这是我的输出为了apt-get update。
这是我的输出为了apt-get upgrade。
我的声誉不够高，无法发布超过两个链接，因此这里直接输出/etc/apt/sources.list：
~$ 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
根据输出底部的第 6 个错误apt-get update，似乎至少有一个问题是无法验证来自 Nvidia 的某些包（可能是我刚才安装的 cuda 存储库——我这样做是不是太愚蠢了？）。
不确定下一步该做什么，希望得到任何指导！提前致谢。
答案1
不确定你为什么要将 lucid 存储库添加到 trusty，但无论如何应该已经知道你在做什么。Lucid 已到使用寿命结束，其存储库已移至http://old-releases.ubuntu.com/因此将这些行更改为：
deb http://old-releases.ubuntu.com/ubuntu lucid-security main deb http://old-releases.ubuntu.com/ubuntu lucid main对于有关 cuda 包身份验证的第二个错误，您的系统缺少 nvidia 存储库 GPG 公钥，请使用以下方式添加它
wget -q http://developer.download.nvidia.com/compute/cuda/repos/ubuntu1404/x86_64/7fa2af80.pub -O- | sudo apt-key add -