安装好ubuntu18.04或ubuntu20.04后，软件更新默认使用国外源，在国内更新时速度很慢，所以需要更换成国内源，这样软件的更新和安装才能快速、正常。

一、ubuntu18.04换源

1.备份原始源文件source.list

打开终端，输入：sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak

2.修改源文件

1.继续输入：sudo gedit /etc/apt/sources.list；
2.输入上面命令后会打开一个TXT文本文档，对此文件进行编辑；
3.删除文档里原来内容，复制下面任意一个源，保存；
4.修改源后，更新软件列表和软件。

sudo apt update
sudo apt upgrade
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5.国内源

注意版本codename，检查版本codename：lsb_release -a。
18.04是bionic

阿里源：

deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
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中科大源：

deb https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
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163源：

deb http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ bionic-backports main restricted universe multiverse
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二、ubuntu20.04换源

前面步骤跟18.04的一样，不同的地方在20.04版本codename。
20.04版本codename是focal

阿里源：

deb http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ focal-backports main restricted universe multiverse
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中科大源：

deb https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ focal-proposed main restricted universe multiverse
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163源：

deb http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ focal-backports main restricted universe multiverse
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三、其他换源方法

1.打开设置，在设置选项右侧下拉找到“关于”，点击 Software Updates。

2.在软件和更新界面里可以看到“下载自…”，我们可以在这里进行修改。

3.推荐选择 mirros.aliyun.com ，你也可以点击选择最佳服务器，测试连接最快的软件源。

4.最后，退出界面时，会提示更新软件列表信息，点击重新载入即可。