How to quickly add DNS settings in Linux (CentOS)?

Summary: 

This note will show you how to quickly fix DNS settings on linux. Am using centOS

[root@localhost ~]# cat /etc/*release* CentOS release 6.3 (Final) CentOS release 6.3 (Final) CentOS release 6.3 (Final) cpe:/o:centos:linux:6:GA

Problem or Goal:

Pinging a domain name like "yahoo.com" returns error

[root@localhost ~]# ping yahoo.com ping: unknown host yahoo.com [root@localhost ~]#

Cause:

Checking the ifcfg files, there is no DNS settings defined!!

[root@localhost ~]# cd /etc/sysconfig/network-scripts/ [root@localhost network-scripts]# more ifcfg-eth0 DEVICE="eth0" BOOTPROTO="static" BROADCAST="172.17.6.255" GATEWAY="172.17.6.3" HWADDR="14:FE:B5:DF:B9:A9" IPADDR="172.17.6.44" NETMASK="255.255.255.0" NM_CONTROLLED="yes" ONBOOT="yes" TYPE="Ethernet"

Solution:

Check and make sure you have proper internet connection, i tested by pinging a public DNS 8.8.8.8

[root@localhost network-scripts]# ping 172.29.1.111 PING 172.29.1.111 (172.29.1.111) 56(84) bytes of data. 64 bytes from 172.29.1.111: icmp_seq=1 ttl=125 time=0.943 ms 64 bytes from 172.29.1.111: icmp_seq=2 ttl=125 time=0.675 ms ^C --- 172.29.1.111 ping statistics --- 2 packets transmitted, 2 received, 0% packet loss, time 1712ms rtt min/avg/max/mdev = 0.675/0.809/0.943/0.134 ms [root@localhost network-scripts]#

Now add the DNS settings in the ifcfg-eth0 file, make sure you know your network DNS IPs to use, or you can use the public DNS, 8.8.8.8 if it's allowed on your network.

[root@localhost network-scripts]# vi ifcfg-eth0 DEVICE="eth0" BOOTPROTO="static" BROADCAST="172.17.6.255" GATEWAY="172.17.6.3" HWADDR="14:FE:B5:DF:B9:A9" IPADDR="172.17.6.44" NETMASK="255.255.255.0" DNS1="172.29.1.111" DNS2="8.8.8.8" NM_CONTROLLED="yes" ONBOOT="yes" TYPE="Ethernet"

Restart the network services

[root@localhost etc]# /etc/init.d/network restart Shutting down interface eth0:                              [  OK  ] Shutting down loopback interface:                          [  OK  ] Bringing up loopback interface:                            [  OK  ] Bringing up interface eth0:                                [  OK  ] [root@localhost etc]#

Problem Solved?

Test by ping a domain name, for example "yahoo.com"

[root@localhost ~]# ping www.yahoo.com PING atsv2-fp.wg1.b.yahoo.com (46.228.47.115) 56(84) bytes of data. 64 bytes from ir1.fp.vip.ir2.yahoo.com (46.228.47.115): icmp_seq=1 ttl=53 time=202 ms 64 bytes from ir1.fp.vip.ir2.yahoo.com (46.228.47.115): icmp_seq=2 ttl=53 time=202 ms 64 bytes from ir1.fp.vip.ir2.yahoo.com (46.228.47.115): icmp_seq=3 ttl=53 time=202 ms 64 bytes from ir1.fp.vip.ir2.yahoo.com (46.228.47.115): icmp_seq=4 ttl=53 time=202 ms 64 bytes from ir1.fp.vip.ir2.yahoo.com (46.228.47.115): icmp_seq=5 ttl=53 time=203 ms ^C --- atsv2-fp.wg1.b.yahoo.com ping statistics --- 6 packets transmitted, 5 received, 16% packet loss, time 5035ms rtt min/avg/max/mdev = 202.167/202.646/203.652/0.772 ms [root@localhost ~]#