Ubuntu系统中，软件源文件地址为：/etc/apt/sources.list
1.备份原来的源，将以前的源备份一下，以防以后可以用的。
$ sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2.打开/etc/apt/sources.list文件，在前面添加如下条目，并保存。
$ sudo vim /etc/apt/sources.list（可将vim更换为自己熟悉的编辑器）
#腾讯源
deb http://mirrors.cloud.tencent.com/ubuntu/ focal main restricted universe
multiverse
deb http://mirrors.cloud.tencent.com/ubuntu/ focal-security main restricted
universe multiverse
deb http://mirrors.cloud.tencent.com/ubuntu/ focal-updates main restricted
universe multiverse
#deb http://mirrors.cloud.tencent.com/ubuntu/ focal-proposed main restricted
universe multiverse
#deb http://mirrors.cloud.tencent.com/ubuntu/ focal-backports main restricted
universe multiverse
# deb-src http://mirrors.cloud.tencent.com/ubuntu/ focal main restricted universe
multiverse
# deb-src http://mirrors.cloud.tencent.com/ubuntu/ focal-security main restricted
universe multiverse
# deb-src http://mirrors.cloud.tencent.com/ubuntu/ focal-updates main restricted
universe multiverse
#deb-src http://mirrors.cloud.tencent.com/ubuntu/ focal-proposed main restricted
universe multiverse
#deb-src http://mirrors.cloud.tencent.com/ubuntu/ focal-backports main restricted
universe multiverse
#中科大源
# 默认注释了源码仓库，如有需要可自行取消注释
deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe
multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe
multiverse
