I needed to Monitor My CentOS 6.4 Box, many monitoring software like Nagios, cacti and zabbix need SNMP enabled on system to be monitored.

so here you are

yum install net-snmp-utils

Once you have installed the SNMP you need to configure the public query access to box.

Configure SMNP
first backup the snmp.conf

mv /etc/snmp/snmpd.conf /etc/snmp/snmpd.conf.back
nano /etc/snmp/snmpd.conf

past following in the file

rocommunity  public
syslocation  "PDC, Peters DataCenter"
syscontact  some@email_address.ext

save the file and restart the snmpd and add snmpd to start automatically

/etc/init.d/snmpd start
chkconfig snmpd on

You are done. now SNMP based monitoring software will be able to query your centos box.