Verifique se você consegue acessar os servidores que hospedam os repositórios do yum. Você pode usar o yum-config-manager
para obter os endereços HTTP da seguinte forma:
$ yum-config-manager |grep "mirrorlist.*http"
mirrorlist = http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=os
mirrorlist = https://mirrors.fedoraproject.org/metalink?repo=epel-6&arch=x86_64
mirrorlist = http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=extras
mirrorlist = http://mirrorlist.centos.org/?release=6&arch=x86_64&repo=updates
Em seguida, execute ping nos servidores para garantir que eles sejam acessíveis ao seu servidor:
$ ping -c 4 mirrorlist.centos.org
PING mirrorlist.centos.org (72.232.223.58) 56(84) bytes of data.
64 bytes from 58.223.232.72.static.reverse.ltdomains.com (72.232.223.58): icmp_seq=1 ttl=52 time=48.5 ms
64 bytes from 58.223.232.72.static.reverse.ltdomains.com (72.232.223.58): icmp_seq=2 ttl=52 time=42.8 ms
64 bytes from 58.223.232.72.static.reverse.ltdomains.com (72.232.223.58): icmp_seq=3 ttl=52 time=47.7 ms
64 bytes from 58.223.232.72.static.reverse.ltdomains.com (72.232.223.58): icmp_seq=4 ttl=52 time=46.9 ms
--- mirrorlist.centos.org ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3053ms
rtt min/avg/max/mdev = 42.855/46.531/48.596/2.202 ms