⒈備份官方默認更新源文件

cp /etc/apt/sources.list /etc/apt/sources.list.bak        備份官方更新源文件

⒉編輯

　　1.打開　　

vi /etc/apt/sources.list

　　2.清空內容

　　ESC後進入命令模式輸入

:.,$d

　　3.復制為以下內容（清華大學鏡像站）https://mirrors.tuna.tsinghua.edu.cn/help/ubuntu/

# 默認註釋了源碼鏡像以提高 apt update 速度，如有需要可自行取消註釋
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse

# 預發布軟件源，不建議啟用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse

　　4.保存

　　ESC後進入命令模式輸入　　　

:wq

⒊更新源

apt update

Ubuntu18.04更換官方默認更新源sources.list