在使用docker容器时，有时候里边没有安装vim，敲vim命令时提示说：vim: command not found，这个时候就需要安装vim，可是当你敲apt-get install vim命令时，提示：

Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package vim

凉凉，找不到vim编辑器，这时候就需要敲：apt-get update

这个命令的作用是：同步 /etc/apt/sources.list 和 /etc/apt/sources.list.d 中列出的源的索引，这样才能获取到最新的软件包。等更新完毕以后再敲命令：apt-get install vim安装vim即可。

但是你会发现国内机器在更新源的索引时异常的慢，这是由于下载地址是海外地址，下载速度异常慢而且可能中断更新流程，这时候我们不得不考虑换源，相关替换命令如下：

# 备份源文件
mv /etc/apt/sources.list /etc/apt/sources.list.bak

# 清华源
echo "deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free" >> /etc/apt/sources.list
echo "deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster main contrib non-free" >> /etc/apt/sources.list
echo "deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free" >> /etc/apt/sources.list
echo "deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-updates main contrib non-free" >> /etc/apt/sources.list
echo "deb https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free" >> /etc/apt/sources.list
echo "deb-src https://mirrors.tuna.tsinghua.edu.cn/debian/ buster-backports main contrib non-free" >> /etc/apt/sources.list
echo "deb https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free" >> /etc/apt/sources.list
echo "deb-src https://mirrors.tuna.tsinghua.edu.cn/debian-security buster/updates main contrib non-free" >> /etc/apt/sources.list

# 更新索引
apt-get update

然后就可以使用命令apt-get install vim安装vim编辑器了