ubuntu20.04 LTS系统默认源sources.list文件的修改

sudo gedit /etc/apt/sources.list

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

# 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 http://cn.archive.ubuntu.com/ubuntu/ focal-backports main restricted universe multiverse

# 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 main restricted

# 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.

sudo apt update