使用方法 ： https://my.oschina.net/liuyuantao/blog/756133
From <https://serverfault.com/questions/874471/centos-7-4-can-not-install-dnffrom-epel>
WARNING: EPEL 7 DNF is very old and has issues to include security flaws. This appears to be the reason it was removed. That said here is the work around to get it working on Centos 7.
wget http://springdale.math.ias.edu/data/puias/unsupported/7/x86_64/dnf-conf-0.6.4-2.sdl7.noarch.rpm
wget http://springdale.math.ias.edu/data/puias/unsupported/7/x86_64//dnf-0.6.4-2.sdl7.noarch.rpm
wget http://springdale.math.ias.edu/data/puias/unsupported/7/x86_64/python-dnf-0.6.4-2.sdl7.noarch.rpm
yum install python-dnf-0.6.4-2.sdl7.noarch.rpm dnf-0.6.4-2.sdl7.noarch.rpm dnf-conf-0.6.4-2.sdl7.noarch.rpm