ubuntu1804 更换国内源

你可以按照以下步骤更换 Ubuntu 18.04 的国内软件源：

1. 打开终端（Ctrl + Alt + T）。

2. 备份原有的源列表文件：

   sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup

3. 编辑源列表文件：

   sudo gedit /etc/apt/sources.list

4. 在文本编辑器中，将原有的内容全部删除，并将以下内容粘贴进去：

对于阿里云源：

   # 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
   deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
   # deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
   
   deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
   # deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
   
   deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
   # deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
   
   deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
   # deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
   
   ## Not recommended
   # deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
   # deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse

对于清华大学源：

   # 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
   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
   
   ## Not recommended
   # 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

5. 保存并关闭文本编辑器。

6. 更新软件包列表：

   sudo apt update

现在，你的 Ubuntu 18.04 将使用国内源进行软件包更新和安装。