1, the original file backup
sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
2, edit the source file list
sudo vim /etc/apt/sources.list
3, delete the original list, add the following (USTC mirror source)
:%d
Empty original
deb http://mirrors.ustc.edu.cn/ubuntu/ great main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ great-security main restricted universe multiverse
deb http: //mirrors.ustc .edu.cn / ubuntu / great-updates main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu/ great-proposed main restricted universe multiverse
deb http://mirrors.ustc.edu.cn/ubuntu / great-backports main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ great main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ great-security main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ great-updates main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ great-proposed main restricted universe multiverse
deb-src http://mirrors.ustc.edu.cn/ubuntu/ great-backports main restricted universe multiverse
ctrl+ins
Copied to virtual machine
:wq
Quit after writing
4, update
sudo apt-get update