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參考文章：https://www.jianshu.com/p/97c35d569aa3
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因為Ubuntu自帶的源服務器在國外，下載和更新軟件的時候速度很慢，不穩定，所以需要將源更新為國內的源。國內的源比較多，常用的就是阿里的源。
1.備份原有源文件，方便在替換出問題時回滾
sudo cp /etc/apt/sources.list /etc/apt/source.list.bk
2.更改sources.list文件
vim /etc/apt/sources.list
替換里面的內容為
# 阿里源 deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
這里需要注意的是不同的ubuntu發行版本對應的源也是不一樣的，主要的區別在版本號
Ubuntu 12.04 (LTS)代號為precise。
Ubuntu 14.04 (LTS)代號為trusty。
Ubuntu 15.04 代號為vivid。
Ubuntu 15.10 代號為wily。
Ubuntu 16.04 (LTS)代號為xenial。
Ubuntu 18.04 (LTS)代號為bionic。
Ubuntu 19.10 代號為eoan。
目前我的版本是18.04所以里面的版本號是bionic，如果是其他版本號直接替換里面的版本編號即可。
查看自己ubuntu的版本號：
lsb_release -c
3.更新源
sudo apt update
附錄：
中科大鏡像源：
deb http://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse deb http://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse deb-src http://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
清華鏡像源
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed 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 main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
附：
剛安裝Ubuntu時，系統只自帶了vi,而沒有vim
安裝vim
apt install vim
vim全選刪除
按esc進入視圖模式，ggVG進行全選，d刪除