查看系统版本命令：
lsb_release -a
换源：
sudo cp /etc/apt/source.list /etc/apt/source.list.bak
sudo vim /etc/apt/source.list
内容选一即可：
# aliyun
deb http://mirrors.aliyun.com/ubuntu/ lunar main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ lunar main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ lunar-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ lunar-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ lunar-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ lunar-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ lunar-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ lunar-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ lunar-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ lunar-backports main restricted universe multiverse
# tsinghua
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-updates main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-updates main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-backports main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-backports main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-security main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-security main restricted universe multiverse
deb https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-proposed main restricted universe multiverse
deb-src https://mirrors.tuna.tsinghua.edu.cn/ubuntu/ lunar-proposed main restricted universe multiverse
# 中科大
deb https://mirrors.ustc.edu.cn/ubuntu/ lunar main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ lunar main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ lunar-updates main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ lunar-updates main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ lunar-backports main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ lunar-backports main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ lunar-security main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ lunar-security main restricted universe multiverse
deb https://mirrors.ustc.edu.cn/ubuntu/ lunar-proposed main restricted universe multiverse
deb-src https://mirrors.ustc.edu.cn/ubuntu/ lunar-proposed main restricted universe multiverse
# 163
deb http://mirrors.163.com/ubuntu/ lunar main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lunar-security main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lunar-updates main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lunar-proposed main restricted universe multiverse
deb http://mirrors.163.com/ubuntu/ lunar-backports main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lunar main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lunar-security main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lunar-updates main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lunar-proposed main restricted universe multiverse
deb-src http://mirrors.163.com/ubuntu/ lunar-backports main restricted universe multiverse