Yum update is not working properly in centos

Question

Yum update is not working.I am not able to ping the external networks too

   yum update
   Loaded plugins: fastestmirror, refresh-packagekit, security
   Loading mirror speeds from cached hostfile
   Could not retrieve mirrorlist http://mirrorlist.centos.org/?   release=6&arch=x86_64&repo=os error was
  14: PYCURL ERROR 6 - "Couldn't resolve host 'mirrorlist.centos.org'"
   Error: Cannot find a valid baseurl for repo: base


      ping mirrorlist.centos.org
      ping: unknown host mirrorlist.centos.org

Answer 1

You need to make sure that your DNS settings are correctly configured. This can be done in two ways:

Method 1

1. Edit the interface configuration, using vi /etc/sysconfig/network-scripts/ifcfg-eth0

2. Change the settings to those of your network interface, thus change the DNS to suit your DNS.

   DEVICE=eth0
   BOOTPROTO=manual
   ONBOOT=yes
   IPADDR=10.0.1.27
   NETWORK=10.0.1.0
   NETMASK=255.255.255.0
   DNS=8.8.8.8
   

Method 2:

1. Use vi /etc/sysconfig/network-scripts/ifcfg-eth0.
   Add a new property PEERDNS=no as shown below:

   DEVICE=eth0
   BOOTPROTO=manual
   ONBOOT=yes
   IPADDR=10.0.1.27
   NETWORK=10.0.1.0
   NETMASK=255.255.255.0
   PEERDNS=no
   

2. Then vi /etc/resolv.conf

   Add DNS server (also referred to as nameserver) to /etc/resolv.conf:

   nameserver 8.8.8.8
   

   Finally, save the changes using :wq.

   Restart the service by typing service network restart.

Also, you might have to run tests to determine whether you are now able to connect to the internet; this can be done by performing ping tests:

1. Ping the gateway (tests IP and mask settings)
2. Ping google (tests DNS and default gateway settings)

Answer 2

The error message Couldn't resolve host 'mirrorlist.centos.org' points to an issue with name resolution.

Try the command host mirrorlist.centos.org: if it fails, then that is the first problem to solve (check your DNS settings, and whether the machine is able to connect to the internet at all).