Ubuntu 的源存放在在 /etc/apt/ 目录下的 sources.list 文件中，修改前我们先做个备份，在终端中执行以下命令：

sudo cp /etc/apt/sources.list /etc/apt/sources.list.bcakup

然后执行下面的命令打开 sources.list 文件，清空里面的内容，把上面我们编辑好的国内的源复制进去，保存后退出。

sudo vim /etc/apt/sources.list

更换为：或直接新建sources.list文件替换即可

## Note, this file is written by cloud-init on first boot of an instance
## modifications made here will not survive a re-bundle.
## if you wish to make changes you can:
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg
##     or do the same in user-data
## b.) add sources in /etc/apt/sources.list.d
## c.) make changes to template file /etc/cloud/templates/sources.list.tmpl

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal main restricted
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates main restricted
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal universe
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal universe
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates universe
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal multiverse
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal multiverse
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates multiverse
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu/ focal-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu focal partner
# deb-src http://archive.canonical.com/ubuntu focal partner

deb http://mirrors.cloud.aliyuncs.com/ubuntu focal-security main restricted
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu focal-security main restricted
deb http://mirrors.cloud.aliyuncs.com/ubuntu focal-security universe
deb-src http://mirrors.cloud.aliyuncs.com/ubuntu focal-security universe
# deb http://mirrors.cloud.aliyuncs.com/ubuntu focal-security multiverse
# deb-src http://mirrors.cloud.aliyuncs.com/ubuntu focal-security multiverse