Ubuntu 解决：当执行sudo apt-get update或者sudo apt-get install命令是出现的 “apt-get 404 Not Found Package Repository Errors” 问题 和 “E: Some index files failed to download They have been ignored, or old ones used” 问题
当你执行sudo apt-get update命令的时候，如果你遇到下面的问题：
W: The repository 'http://ppa.launchpad.net/ackondro/tibesti/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/ackondro/tibesti/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.
E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable)
E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it?或者
W: The repository 'http://ppa.launchpad.net/ackondro/tibesti/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://ppa.launchpad.net/ackondro/tibesti/ubuntu/dists/xenial/main/binary-amd64/Packages 404 Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.解决方法
首先，我们将现在出问题的 /etc/apt/sources.list 文件备份一份。（只是一个好习惯而已）
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup注：
/etc/apt/sources.list文件 里面存放的是 Linux系统需要的软件源的网站。
接着，我们重新编写一个 /etc/apt/sources.list 文件：
sudo gedit /etc/apt/sources.list将下面的模板内容，复制粘贴到 /etc/apt/sources.list 文件里面后，保存就可以了：（我们使用的Ubuntu 是16.04）
deb http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
##测试版源
deb http://cn.archive.ubuntu.com/ubuntu/ xenial-proposed main restricted universe multiverse
# 源码
deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-security main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted universe multiverse
deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse
##测试版源
deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-proposed main restricted universe multiverse如要用于其他版本，把 xenial 换成版本代号就好：
16.04
xenial（模板详细内容）
15.10
willy（模板详细内容）
14.04
trusty（模板详细内容）
12.04
precise（模板详细内容）
现在，再执行：
sudo apt-get update现在就没有“apt-get 404 Not Found Package Repository Errors” 问题了。
小结：
这个问题，解决方法简单，但是对于初学者来说，却是一个触手的问题。
出现这个问题的原因是： 之前 /etc/apt/sources.list 路径里面的软件源更新网站有的已经过时了，需要更新新的网站。
Unable to connect to cn.archive.ubuntu.com:http: [112.124.140.210 80]如果你出现这样的错误，说明你的网断了，查看网络连接情况。
参考网站：
How to fix Ubuntu/Debian apt-get 404 Not Found Package Repository Errors (Saucy, Raring, Quantal, Oneiric, Natty…)
https://smyl.es/how-to-fix-ubuntudebian-apt-get-404-not-found-package-repository-errors-saucy-raring-quantal-oneiric-natty/
Ubuntu apt-get unable to fetch packages
http://*.com/questions/30316812/ubuntu-apt-get-unable-to-fetch-packages
源列表
http://wiki.ubuntu.org.cn/%E6%BA%90%E5%88%97%E8%A1%A8