Ubuntu20.04 LTS更换清华源

安装好ubuntu20.04LTS系统后，默认的软件更新源是国外的，需要更换成国内的源，这样才能高速安装和更新软件。
首先你需要备份原始源文件sources.list

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

然后修改源文件sources.list

#首先赋编辑权限
sudo chmod 777 /etc/apt/sources.list
#打开文件
sudo gedit /etc/apt/sources.list 

删除原来的文件内容，复制下面清华源20.044LTS内容到其中并保存

# 默认注释了源码镜像以提高 apt update 速度，如有需要可自行取消注释
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse

# 预发布软件源，不建议启用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse

更新软件列表，

sudo apt update