ubuntu系统，关于源（source）的配置

1. 现象：（出现的错误）

执行 sudo apt-get update, 报错：apt-get 404 Not Found Package Repository Errors

执行 sudo apt-get install, 报错：Some index files failed to download They have been ignored, or old ones used

2. 解决方法：

（1）sudo cp  /etc/apt/sources.list    /etc/apt/sources.list_backup

（2）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

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。

参考文献：https://blog.csdn.net/github_35160620/article/details/52115542