因为linux系统自带的镜像源都在国外，国内用户下载或更新软件会比较慢，有时是非常慢，所以国内某些机构，如大学，研究院所，就在国内建了linux的镜像源服务器供国内linux用户使用，而我们要使用这些源，就要更改自己linux系统的更新源配置文件，下面是更新源操作步骤。
不同版本的Ubuntu更新源和更新源配置文件会不一样，一样要根据自己使用的Ubuntu版本来使用对应的更新源（百度都能找到）
1.备份系统自带更新源配置文件
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2.修改配置文件sources.list内容
输入命令 sudo vi /etc/apt/sources.list 进入该文件键盘输入i进入输入模式删除里面所有内容，再将国内更新源粘贴进去，保存退出（键盘点击Esc,然后输入 :wq）。
一些国内的更新源
阿里云源
deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
清华大学
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
还有很多其他的更新源，可以自行百度。
3.更新源
输入命令：sudo apt-get update
由于网速的问题耗费时间各不相同，耐心等待即可。
