CentOS 6
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Update System
[1] After installing CentOS, Update it to the latest system like follows. For yum-plugin-fastestmirror, it is installed for dependency of yum, but if it's not installed, it had better install it.
[root@dlp ~]#
yum -y install yum-plugin-fastestmirror

Setting up Install Process
Resolving Dependencies
--> Running transaction check
----> Package yum-plugin-fastestmirror.noarch 0:1.1.26-11.el6 set to be updated
---> Finished Dependency Resolution

Dependencies Resolved

 Package                       Arch        Version              Repository     Size
 yum-plugin-fastestmirror      noarch      1.1.26-11.el6        base       17 k

Transaction Summary
Install       1 Package(s)
Upgrade       0 Package(s)

Total download size: 17 k
Installed size: 33 k
Downloading Packages:
yum-plugin-fastestmirror-1.1.26-11.el6.noarch.rpm        |  17 kB     00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing     : yum-plugin-fastestmirror-1.1.26-11.el6.noarch            1/1

  yum-plugin-fastestmirror.noarch 0:1.1.26-11.el6

[root@dlp ~]#
yum -y update