Ubuntu20.04更换国内镜像源（阿里、网易163、清华、中科大）
------------------- 2022年12月11日更新 ----------------------
今天刚安装了 Ubuntu22.04 ，安装时选好地区，开机默认就是中国内地的镜像源服务器，速度很快，体验极佳，已经基本告别更换镜像源的烦恼了。
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------------------------ 以下是原文 -------------------------
更换方法
Ubuntu采用apt作为软件安装工具，其镜像源列表记录在/etc/apt/source.list文件中。
首先将source.list复制为source.list.bak备份，然后将source.list内容改为需要的镜像源列表即可。
修改完成后保存source.list文件，执行：
sudo apt update
等待更新完成即可。
常用国内镜像源
本节均为 Ubuntu 20.04 的镜像源列表。若为其他版本，将所有focal更改为其他版本代号即可。
常用的Ubuntu版本代号如下：
- Ubuntu 22.04：jammy
- Ubuntu 20.04：focal
- Ubuntu 18.04：bionic
- Ubuntu 16.04：xenial
Ubuntu 通常采用“形容词+小动物”作为版本代号（默认的壁纸），在镜像源列表中只有第一个词。
此外，默认注释了代码源以提高速度，注释了预发布软件源（可能不稳定）。如有需要可以取消注释。
建议将所有常用镜像源保存在/etc/apt目录下，并命名为类似source.list.aliyun的形式，需要使用时直接复制替换source.list文件即可。
阿里云
deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
# deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
## Pre-released source, not recommended.
# 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
清华
deb 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 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 main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ focal-security main restricted universe multiverse
## Pre-released source, not recommended.
# 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
deb 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 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 main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
# deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
## Pre-released source, not recommended.
# 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
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-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-backports main restricted universe multiverse
## Pre-released source, not recommended.
# deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
# deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse