update 2022.04.23:
Ubuntu 22.04 的稳定版已经于 2022 年 4 月 21 日发布，Ubuntu 22.04 稳定版下载地址：https://ubuntu.com/download/desktop
Ubuntu 22.04 的稳定版计划于 2022 年 4 月 21 日发布。开发工作已经在紧锣密鼓地进行，它将遵循如下发布时间表：
- 2022 年 2 月 24 日：功能冻结
- 2022 年 3 月 17 日：用户界面冻结
- 2022 年 3 月 31 日：测试版发布
- 2022 年 4 月 14 日：候选版本
- 2022 年 4 月 21 日：最终稳定版本
Linux 5.15 LTS是Ubuntu 22.04的默认内核，GCC 11.2是默认的系统编译器，Mesa 22.0提供开源图形驱动支持。Canonical一直在为Ubuntu开发新的桌面安装程序，但是随着22.04 LTS的发布，现有的Ubiquity仍然是默认使用的。
如果你想在备用机器或虚拟机上测试它，你可以从 Ubuntu 的网站下载Ubuntu 22.04 每日构建版。
下载 Ubuntu 22.04 每日构建（不稳定）https://cdimage.ubuntu.com/daily-live/current/
国内有很多Ubuntu的镜像源，包括阿里的、网易的，还有很多教育网的源，比如：清华源、中科大源。
我们这里以清华源为例讲解如何修改Ubuntu 22.04里面默认的源。
编辑/etc/apt/sources.list文件, 在文件最前面添加以下条目(操作前请做好相应备份)：
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/ jammy main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
# 预发布软件源，不建议启用
# deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-proposed main restricted universe multiverse
# deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ jammy-proposed main restricted universe multiverse
然后执行命令：
sudo apt-get update
sudo apt-get upgrade
其他几份国内源如下：
阿里源
deb http://mirrors.aliyun.com/ubuntu/ jammy main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ jammy-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ jammy-backports main restricted universe multiverse
中科大源
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ jammy-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ jammy-proposed main restricted universe multiverse
网易163源
deb http://mirrors.163.com/ubuntu/ jammy main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jammy-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jammy-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ jammy-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jammy main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jammy-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jammy-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jammy-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ jammy-backports main restricted universe multiverse
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