一、前言
如果你按照了其他博客换源的操作，应该都有一个备份的默认源：
其他博客中备份的指令：
cp /etc/apt/sources.list /etc/apt/sources.list.backup
二、步骤
1、查看备份文件
我们需要走到源的文件夹下，查看备份是否存在：
cd /etc/apt
ls
这里显示：sources.list.backup，说明我当时保存了。
2、恢复方法
方法1：
（1）复制文件
方法描述：如果有备份，直接拷贝恢复source.list。
还记得第一步吗，直接反向操作就行：
sudo cp /etc/apt/sources.list.backup /etc/apt/sources.list
（2）查看文件
再查看一下：
gedit sources.list
没问题就是备份完了。
方法2：
①直接打开备份文件：
gedit sources.list.backup
②手动复制
然后，我们接下来就是要把里面的内容复制到sources.list里面
先Ctrl+C拷贝上面的内容，然后以sudo形式打开source.list
sudo gedit sources.list
打开文件复制进去保存即可，如果不加sudo就是只读模式，记得要加。
方法3：
参考：
anaconda换源和恢复默认源
Ubuntu系统镜像备份及恢复
三、Ubuntu 22.04 LTS
这里提供一份ubuntu22.04的：
#deb cdrom:[Ubuntu 22.04.1 LTS _Jammy Jellyfish_ - Release amd64 (20220809.1)]/ jammy main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ jammy main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ jammy-updates main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy-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://cn.archive.ubuntu.com/ubuntu/ jammy universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy universe
deb http://cn.archive.ubuntu.com/ubuntu/ jammy-updates universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy-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://cn.archive.ubuntu.com/ubuntu/ jammy multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ jammy-updates multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy-updates multiverse
## 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://cn.archive.ubuntu.com/ubuntu/ jammy-backports main restricted universe multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ jammy-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu jammy-security main restricted
# deb-src http://security.ubuntu.com/ubuntu jammy-security main restricted
deb http://security.ubuntu.com/ubuntu jammy-security universe
# deb-src http://security.ubuntu.com/ubuntu jammy-security universe
deb http://security.ubuntu.com/ubuntu jammy-security multiverse
# deb-src http://security.ubuntu.com/ubuntu jammy-security multiverse
# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.
四、Ubutnu20.04.5 LTS
再提供一个20.04.5的
# deb cdrom:[Ubuntu 20.04.5 LTS _Focal Fossa_ - Release amd64 (20220831)]/ focal main restricted
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ focal main restricted
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://cn.archive.ubuntu.com/ubuntu/ focal-updates restricted main
# deb-src http://cn.archive.ubuntu.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://cn.archive.ubuntu.com/ubuntu/ focal universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal universe
deb http://cn.archive.ubuntu.com/ubuntu/ focal-updates universe
# deb-src http://cn.archive.ubuntu.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://cn.archive.ubuntu.com/ubuntu/ focal multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://cn.archive.ubuntu.com/ubuntu/ focal-updates multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal-updates multiverse
## 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-src http://cn.archive.ubuntu.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://security.ubuntu.com/ubuntu focal-security restricted main
# deb-src http://security.ubuntu.com/ubuntu focal-security main restricted
deb http://security.ubuntu.com/ubuntu focal-security universe
# deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://security.ubuntu.com/ubuntu focal-security multiverse
# deb-src http://security.ubuntu.com/ubuntu focal-security multiverse
# This system was installed using small removable media
# (e.g. netinst, live or single CD). The matching "deb cdrom"
# entries were disabled at the end of the installation process.
# For information about how to configure apt package sources,
# see the sources.list(5) manual.