安装utuntu20.04后修改 sources.list

在默认安装的ubuntu 上更新或安装软件时，会报很多莫名其妙的错误，通过以下修正，可以解决大部分系统原因的报错

`#deb cdrom:[Ubuntu 20.04 LTS _Focal Fossa_ - Release amd64 (20200423)]/ focal main restricted`

`# See [http://help.ubuntu.com/community/UpgradeNotes](http://help.ubuntu.com/community/UpgradeNotes) for how to upgrade to`

`# newer versions of the distribution.`

`deb [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal main restricted`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](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/](http://cn.archive.ubuntu.com/ubuntu/) focal-updates main restricted`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](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/](http://cn.archive.ubuntu.com/ubuntu/) focal universe`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal universe`

`deb [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal-updates universe`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](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/](http://cn.archive.ubuntu.com/ubuntu/) focal multiverse`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal multiverse`

`deb [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal-updates multiverse`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](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 [http://cn.archive.ubuntu.com/ubuntu/](http://cn.archive.ubuntu.com/ubuntu/) focal-backports main restricted universe multiverse`

`# deb-src [http://cn.archive.ubuntu.com/ubuntu/](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](http://archive.canonical.com/ubuntu) focal partner`

`# deb-src [http://archive.canonical.com/ubuntu](http://archive.canonical.com/ubuntu) focal partner`

`deb [http://security.ubuntu.com/ubuntu](http://security.ubuntu.com/ubuntu) focal-security main restricted`

`# deb-src [http://security.ubuntu.com/ubuntu](http://security.ubuntu.com/ubuntu) focal-security main restricted`

`deb [http://security.ubuntu.com/ubuntu](http://security.ubuntu.com/ubuntu) focal-security universe`

`# deb-src [http://security.ubuntu.com/ubuntu](http://security.ubuntu.com/ubuntu) focal-security universe`

`deb [http://security.ubuntu.com/ubuntu](http://security.ubuntu.com/ubuntu) focal-security multiverse`

`# deb-src [http://security.ubuntu.com/ubuntu](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.`