Ubuntu20.04更换国内源

备份源文件

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

执行chmod命令更改文件权限

sudo chmod 777 /etc/apt/sources.list

通过gedit命令编辑软件源

sudo gedit /etc/apt/sources.list

执行上面命令后如果报sudo: gedit: command not found的错误，执行下面命令

sudo apt install vim 
vim /etc/apt/sources.list

阿里云国内源

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

换完源之后执行以下命令

sudo apt update
sudo apt upgrade