Problem

no more mirrors to try

Solution

yum clean all
yum --disablerepo=\* --enablerepo=base,extras,updates update
rm -rf /var/cache/yum

Problem

unable to resolve host

Solution

https://www.centos.org/forums/viewtopic.php?t=7633

Problem

Nginx not running

Solution

$ lsof -i :80
$ yum remove httpd