问题
我在Ubuntu上使用apt安装软件时总是报一些错误，不是版本不对，就是依赖关系不对。尝试了各种方法，突然想到是不是软件源有问题。
查看/etc/apt/sources.list文件，发现使用了阿里云的软件源：
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
看到上面的bionic代号，我就知道果然是软件源的问题。
代号bionic、xeninal 和focal
不同版本的Ubuntu的软件源及软件包依赖关系是不同的，Ubuntu就是靠版本信息中的Codename代号来区分的。不光是对 Ubuntu 适用，对deepin、uos等debain系列的操作系统都适用。
使用lsb_release -a查看版本信息：
可见我的Ubuntu版本是20.04，代号是focal。
更改软件源
sudo vi /etc/apt/sources.list
将软件源修改为：
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiversedeb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
更新：
sudo apt-get update
sudo apt-get upgrade
