1:sudo gedit /etc/apt/sources.list
输入下面命令,保存后退出
2:
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted
deb http://mirrors.aliyun.com/ubuntu/ focal universe
deb http://mirrors.aliyun.com/ubuntu/ focal-updates universe
deb http://mirrors.aliyun.com/ubuntu/ focal multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted
deb http://mirrors.aliyun.com/ubuntu/ focal-security universe
deb http://mirrors.aliyun.com/ubuntu/ focal-security multiverse
3:sudo apt-get update //执行这个命令之后会访问源列表里的每个网址,并读取软件列表,更新软件源
4:sudo apt-get upgrade //将本地已安装的软件与刚更新的软件列表里对应软件惊醒对比,如果发现已安装的软件版本太低就会提示更新