ubuntu18.4版本的更新源

Ubuntu 18.04 的更新源可以通过以下步骤进行更改：

1. 打开终端（Ctrl+Alt+T）。
2. 输入以下命令备份原来的源列表文件（sources.list）：

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

3. 打开源列表文件：

   sudo nano /etc/apt/sources.list

4. 在文件中找到以下行：

   deb http://archive.ubuntu.com/ubuntu/ bionic main restricted
   deb http://archive.ubuntu.com/ubuntu/ bionic-updates main restricted
   deb http://archive.ubuntu.com/ubuntu/ bionic universe
   deb http://archive.ubuntu.com/ubuntu/ bionic-updates universe
   deb http://archive.ubuntu.com/ubuntu/ bionic multiverse
   deb http://archive.ubuntu.com/ubuntu/ bionic-updates multiverse
   deb http://archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
   deb http://security.ubuntu.com/ubuntu/ bionic-security main restricted
   deb http://security.ubuntu.com/ubuntu/ bionic-security universe
   deb http://security.ubuntu.com/ubuntu/ bionic-security multiverse

5. 将以上行改为以下行：

   deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted
   deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted
   deb http://mirrors.aliyun.com/ubuntu/ bionic universe
   deb http://mirrors.aliyun.com/ubuntu/ bionic-updates universe
   deb http://mirrors.aliyun.com/ubuntu/ bionic multiverse
   deb http://mirrors.aliyun.com/ubuntu/ bionic-updates multiverse
   deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
   deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted
   deb http://mirrors.aliyun.com/ubuntu/ bionic-security universe
   deb http://mirrors.aliyun.com/ubuntu/ bionic-security multiverse

6. 保存文件并退出（Ctrl+X，Y，Enter）。
7. 更新源列表：

   sudo apt update

现在，您的 Ubuntu 18.04 系统将使用阿里云的软件源来更新和安装软件包。