ubuntu20.04更换清华源
最近写毕设，做不出来。安装了多次Ubuntu，写篇傻子式（傻子才需要这么详细）文章压压惊。
Ubuntu安装完之后进行更换为国内源可以让下载更新的的速度快一点。
修改源之前提示大家先查看版本名，ubuntu20.04对应的是“focal”。本篇中的源只适用于20.04，也就是查出来的是“focal”。
“xenial”代表ubuntu16.04，“bionic”代表ubuntu18.04，“disco”代表ubuntu19.04，“eoan”代表ubuntu19.10。
用以下命令查看版本名：
lsb_release -c
1.备份原来的源，将以前的源备份一下，以防以后需要用的。
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
执行这条命令会让你输入密码，就是你安装的时候你自己设的密码，输入之后回车就可以的，输入过程是看不见密码的。
2.打开/etc/apt/sources.list文件，添加源，并保存。
sudo vim /etc/apt/sources.list
如果是刚安装的系统，在这里应该会报“sudo: vim：找不到命令”，
执行一下以下命令安装vim：
sudo apt-get install vim
执行之后系统会询问你是不是要安装，[Y/n]? 输入Y，让它进行安装。
安装结束再执行：
sudo vim /etc/apt/sources.list
3.vim打开文件之后，按“Esc”键进入命令模式，之后狂按"dd"，就是一直按小d，按到文档内容都删除完，再按“i”进入插入模式，把下面的源复制进去。（复制，右键粘贴应该会吧。）
清华源：
#添加清华源
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 multiverse
4.粘贴完之后，按“Esc”进入命令模式，输入“：wq”,回车键退出。是冒号和w和q，不要漏了冒号。
5.执行命令更新
sudo apt-get update
sudo apt-get upgrade
换源就完成了。
下面献上一些其他的源
常用国内源：
阿里云源
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
清华源
# 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
中科大源
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
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
网易163源
deb http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
Ubuntu20.04安装的时候会自动安装了vmware-tools，可以进行和物理机之间的复制粘贴。如果你的不能进行复制粘贴等操作，自己百度先安装VMware-Tools。