debian版本
执行以下命令，查看当前debian版本号：
cat /etc/issue
结果如下：
root@l:~# cat /etc/issue
Debian GNU/Linux 10 \n \l
更新源
备份sources.list文件：
mv /etc/apt/sources.list /etc/apt/sources.list.bak
修改sources.list文件内容，删除默认的内容，改成国内源：
deb http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
deb http://mirrors.aliyun.com/debian-security/ buster/updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-updates main non-free contrib
deb-src http://mirrors.aliyun.com/debian/ buster-backports main non-free contrib
deb-src http://mirrors.aliyun.com/debian-security/ buster/updates main non-free contrib
然后执行更新命令：
apt-get update
apt-get upgrade