初学者注意！Ubuntu20.04 LTS系统默认源source.list的源文件！

由于在使用中需要修改系统默认源source.list文件里面的内容，但是我并不是很了解里面代码所表达的意思，因此为了避免修改里面的内容而导致系统出现其他的问题，在这里做一个备份。

首先是打开该文件的指令。

sudo gedit /etc/apt/sources.list

ubuntu20.04系统默认源source.list文件的具体内容如下：

# 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://mirrors.huaweicloud.com/repository/ubuntu/ focal main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://mirrors.huaweicloud.com/repository/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.huaweicloud.com/repository/ubuntu/ focal universe
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal universe
deb http://mirrors.huaweicloud.com/repository/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://mirrors.huaweicloud.com/repository/ubuntu/ focal multiverse
# deb-src http://cn.archive.ubuntu.com/ubuntu/ focal multiverse
deb http://mirrors.huaweicloud.com/repository/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.

## 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.huaweicloud.com/repository/ubuntu/ focal-security main restricted
deb http://mirrors.huaweicloud.com/repository/ubuntu/ focal-security universe
# deb-src http://security.ubuntu.com/ubuntu focal-security universe
deb http://mirrors.huaweicloud.com/repository/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.