Step1. 备份 list 文件
进入对应文件夹，用管理员权限，执行复制操作：
cd /etc/apt/
sudo cp sources.list sources.list.bakStep2. 修改 list 文件
通过管理员权限，使用 vim 进行修改：
sudo vim sources.list将下列代码替换 sources.list文件内容
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
Step3. 更新软件列表
使用管理员权限，执行命令：
sudo apt-get update
sudo apt-get upgrade注意：要更新源的前提是ubuntu能够联网。
如果出现以下情况就说明没有联网忙，所以要先解决无法联网的问题，再进行换源
错误:1 https://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic InRelease
无法解析域名“mirrors.tuna.tsinghua.edu.cn”
错误:2 https://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-updates InRelease
无法解析域名“mirrors.tuna.tsinghua.edu.cn”
错误:3 https://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-backports InRelease
无法解析域名“mirrors.tuna.tsinghua.edu.cn”
错误:4 https://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-security InRelease
无法解析域名“mirrors.tuna.tsinghua.edu.cn”
错误:5 https://mirrors.tuna.tsinghua.edu.cn/ubuntu bionic-proposed InRelease
无法解析域名“mirrors.tuna.tsinghua.edu.cn”
正在读取软件包列表... 完成
正在分析软件包的依赖关系树
正在读取状态信息... 完成
所有软件包均为最新。
W: 无法下载 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/bionic/InRelease 无法解析域名“mirrors.tuna.tsinghua.edu.cn”
W: 无法下载 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/bionic-updates/InRelease 无法解析域名“mirrors.tuna.tsinghua.edu.cn”
W: 无法下载 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/bionic-backports/InRelease 无法解析域名“mirrors.tuna.tsinghua.edu.cn”
W: 无法下载 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/bionic-security/InRelease 无法解析域名“mirrors.tuna.tsinghua.edu.cn”
W: 无法下载 https://mirrors.tuna.tsinghua.edu.cn/ubuntu/dists/bionic-proposed/InRelease 无法解析域名“mirrors.tuna.tsinghua.edu.cn”
W: 部分索引文件下载失败。如果忽略它们，那将转而使用旧的索引文件。在主机为无线上网，虚拟机设定的时候最好用“桥接模式”方法如下：
- 关闭正在运行的虚拟机ubuntu，将其联网方式设定为“桥接模式”。
2. 启动ubuntu虚拟机即可
附：国内常见源
阿里云：
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
中科大：
deb https://mirrors.ustc.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src 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-src 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-src 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-src 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-proposed main restricted universe multiverse
网易：
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
清华：
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ bionic-proposed main restricted universe multiverse
