1.首先备份原来的源
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup
2.编辑/etc/apt/sources.list文件，将源更换为阿里云的源:
sudo gedit /etc/apt/sources.list
3.在打开的文件前面添加源
#阿里云源
deb http://mirrors.aliyun.com/ubuntu/ disco main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ disco main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ disco-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ disco-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ disco-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ disco-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ disco-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ disco-backports main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ disco-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ disco-proposed main restricted universe multiverse
#中科大源
deb https://mirrors.ustc.edu.cn/ubuntu/ disco main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ disco main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ disco-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ disco-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ disco-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ disco-proposed main restricted universe multiverse
#163源
deb http://mirrors.163.com/ubuntu/ disco main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ disco-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ disco-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ disco-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ disco-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ disco main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ disco-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ disco-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ disco-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ disco-backports main restricted universe multiverse
#清华源
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ disco-proposed main restricted universe multiverse
4.让更新源生效
sudo apt-get update
