With the growing number of servers, monitoring often becomes harder day by day. There are various solutions for this. Two very popular I have seen around are Zenoss and Nagios.
Well, here comes the very common question. Which one to use? The best answer would be, the one with less learning and more features
Most often the combination isn’t so easy to achieve.
There are so many comparisons around monitoring tools. I have found these two relevant to this post, one from Linux.com and another from Zenoss.org Help yourself with the links, I am not going to make any comparison between these two.
At Eucalyptus, we have customers who run a lot of servers and monitoring tool is not another fancy product for them, rather it’s a necessity.
But deploying a quick Nagios monitoring system on CentOS is only few steps away. It should not be any different on other distros as well.
Install Nagios packages,
yum install -y nagios nagios-plugins nagios-plugins-nrpe nagios-plugins-all
Set password for Nagios admin,
htpasswd /etc/nagios/passwd nagiosadmin
Start the services and update runlevel for each of them,
chkconfig nagios on chkconfig httpd on service nagios start service httpd start
Define host and services
vim /etc/nagios/objects/host1.cfg
# Define a host
define host{
use linux-server
host_name host1
address 10.104.3.128
}
# Define a service
define service{
use generic-service
host_name host1
service_description PING
check_command check_ping!100.0,20%!500.0,60%
}
Add the following line to nagios.cfg,
cfg_file=/etc/nagios/objects/host1.cfg
Reload Nagios service,
service nagios reload
Check Nagios admin panel at http://<ip_address>/nagios
Tada!!
And of course, it is released under the GPL license.

Do anyone know how to install and configure the check_snmp in nagios??
Hello Sunil.
I came across this blog post today, hope this will help you in this case, http://blog.redbranch.net/2011/01/10/snmp-with-nagios/