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1.配置镜像源位置

配置镜像源就在sources.list文件

2.进入终端，切换到/home/user/etc/apt/

cd /etc/apt/

3.默认这个文件是只读的，我们修改一下权限

sudo chmod 777 sources.list

解决对应的问题：-bash: /etc/apt/sources.list: 权限不够

4.修改之前，我们先备份一下系统原来配置的源

sudo cp /etc/apt/sources.list /etc/apt/sources.list.back

5.开始修改，打开/etc/apt/sources.list文件，将原来的内容删除，然后将上述复制的内容，粘贴上，保存。这里用的是 vi 编辑器的操作，桌面版的系统也可以直接右键去编辑

sudo vi /etc/apt/sources.list

6.将下面的镜像源添加到sources.list文件中

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse

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

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

# deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse

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

7.更新源

sudo apt-get update