Ubuntu原来的源下载更新很慢 所以我们对源进行更改，换成国内常用的源
源所在的目录是在/var/apt目录下 我们可以先进入这个目录
找到source.list对此文件进行更改，如果需要备份，将此文件进行备份，如果不需要的话可以直接操作，此处更换成阿里源
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
此处我使用nano命令进行修改，其他方式也可以修改，可以自行选择
修改完之后进行更新 sudo apt-get update
此时下载或者更新速度会变得快多了
