This error appears when attempting to use the yum command.

[john.doe@server1 ~]# yum install example
. . .

One of the configured repositories failed (Unknown)
. . .

PING

This error will appear if you are unable to communicate with computers in other networks. If you are unable to ping computers in other networks, this implies some issue with your IP configuration or default gateway.

[john.doe@server1 ~]# ping -cf www.google.com
. . .
4 packets transmitted, 0 received, 100% packet loss, time 2999ms

DNS

If you are able to communicate with computers in other networks, there may be some problem with the DNS servers you are using. Ensure the name servers in your /etc/resolv.conf file are able to resolve a hostname to an IP address.

[root@server1 ~]# cat /etc/resolv.conf
nameserver 8.8.8.8
nameserver 8.8.4.4

DHCP

If your system is using DHCP to lease IP configuration information from a DHCP server, use the dhclient command to renew your IP configuraiton information.

[john.doe@client1 ~]# sudo dhclient eth0

Base URL

The base URL is found in the The content of the file /etc/yum.repos.d/CentOS-Base.repo file. Ensure the mirrorlist site is accessible.

[root@localhost ~]# cat /etc/yum.repos.d/CentOS-Base.repo
. . .
[base]
name=CentOS-$releasever - Base
mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=os&infra=$infra
. . .