How To Install Nagios and NRPE On CentOS 6

 Install Nagios and NRPE  On CentOS 6 and  Monitoring Windows with Nagios

In this tutorial we will learn How to install and configure nagios server  and install  nrpe on client pc's. We will also do some configuration changes in nagios server so that we could monitor the servers.

In this scenario we will add a server to monitor.

Operating System : CentOS 6.3
Nagios Server : hostname: nagios-server , ip-address: 192.168.18.1

Nagios Client : hostname: linuxw-server-1 , ip-address: 192.168.18.128
Nagios Client : hostname :  windows-server-1, ip-address: 192.168.18.129

First the install the prerequisites for Nagios Server(192.168.18.1)

[root@thelinuxwiki  ~]# yum install -y gd gd-devel httpd php gcc glibc glibc-common

By default nagios is not found in CentOS official repository, so add the EPEL repository to install nagios.

[root@thelinuxwiki  ~]# wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
[root@thelinuxwiki  ~]# rpm -ivh epel-release-6-8.noarch.rpm

Now install nagios in 192.168.18.1 Server

[root@thelinuxwiki ~]# yum install -y nagios*

Configure Nagios

Add the admin mail address in the nagios contact file to receive alerts from nagios server.

[root@thelinuxwiki]# vi /etc/nagios/objects/contacts.cfg

### Line 35 - Edit the mail id ###
email                           admin@thelinuxwiki.in  ; 

[root@thelinuxwiki]# egrep -v '^#|^$' /etc/nagios/objects/contacts.cfg 
define contact{
        contact_name                    nagiosadmin  ; Short name of user
 use    generic-contact  ; Inherit default values from generic-contact template (defined above)
        alias                           Nagios Admin  ; Full name of user
        email                           UREMAILID@gmail.com  ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
        }
define contact{
        contact_name                    naveencontact             ; Short name of user
        use                             generic-contact         ; Inherit default values from generic-contact template (defined above)
        alias                           Nagios Admin            ; Full name of user
        email                           naveen@thelinuxwiki.in   ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ******
        }
define contactgroup{
        contactgroup_name       admins
        alias                   Nagios Administrators
        members                 nagiosadmin,naveencontact
        }

Edit the following lines in nagios config file

[root@thelinuxwiki]#vi /etc/httpd/conf.d/nagios.conf

## Comment Lines 15 & 16 ##
#   Order allow,deny
#   Allow from all

## Uncomment and Change lines 17,18 & 19 as shown below ##
Order deny,allow
Deny from all
Allow from 127.0.0.1 192.168.1.0/24

Set nagiosadmin password

[root@server ~]# htpasswd /etc/nagios/passwd nagiosadmin
New password:
Re-type new password:
Updating password for user nagiosadmin

Start nagios and httpd services and let them to start automatically on every boot.

[root@thelinuxwiki]#/etc/init.d/nagios start
Starting nagios: done.
[root@thelinuxwiki]# /etc/init.d/httpd start
Starting httpd:                                            [  OK  ]
[root@thelinuxwiki]#chkconfig nagios on
[root@thelinuxwiki]#chkconfig httpd on

Open nagios administrator console and enter the nagiosadmin password as created before

http://192.168.18.1/nagios/

Adding clients to Nagios server

Now we should add our hosts that will be monitored by Nagios. For example, we will use linux-server-1 (198.168.18.128) and windows-server-1 (198.168.18.129).
From public ports, we can monitor ping, any open ports such as webserver, e-mail server, etc.
For internal services that are listening on localhost, such as MySQL, memcached, system services, we will need to use NRPE.

 Install NRPE on Clients-192.168.18.128

---

[root@thelinuxwiki  ~] # rpm -Uvh http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
[root@thelinuxwiki  ~] # rpm -Uvh http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
[root@thelinuxwiki  ~] # yum -y install  nagios-plugins-all nrpe openssl
[root@thelinuxwiki  ~] # chkconfig nrpe on

This next step is where you get to specify any manual commands that Monitoring server can send via NRPE to these client hosts.
Make sure to change allowed_hosts to your own values. 

Edit /etc/nagios/nrpe.cfg

log_facility=daemon
pid_file=/var/run/nrpe/nrpe.pid
server_port=5666
nrpe_user=nrpe
nrpe_group=nrpe
allowed_hosts=192.168.18.1 # This is the Nagios Server IP address
dont_blame_nrpe=1
debug=0
command_timeout=60
connection_timeout=300
include_dir=/etc/nrpe.d/
command[check_users]=/usr/lib64/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib64/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_disk]=/usr/lib64/nagios/plugins/check_disk -w 20% -c 10% -p /dev/sda1
command[check_zombie_procs]=/usr/lib64/nagios/plugins/check_procs -w 5 -c 10 -s Z
command[check_total_procs]=/usr/lib64/nagios/plugins/check_procs -w 150 -c 200
command[check_procs]=/usr/lib64/nagios/plugins/check_procs -w $ARG1$ -c $ARG2$ -s $ARG3$

Note:
In above block you can see command are already defined.
for eg. command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
just keep a note of it.The nrpe will use only these commands or plugins in nagios client which are defined in nrpe.cfg file.
If you want to add any other command or plugin you have to edit the nrpe.cfg file in same manner.
for eg.
command[check_pluginName]=/usr/lib/nagios/plugins/check_pluginName -w <value>  -c <value>

In check_disk above, the partition being checked is /dev/sda1 - make sure your droplet has the same partition by running df -h /

You can also modify when to trigger warnings or critical alerts - above configuration sets Warning at 20% free disk space remaining, and Critical alert at 10% free space remaining.

If you want change any arguments you can change as per your requirement, but follow 

the same syntax while editing or creating new rule.

Now you can start NRPE on all of your client hosts:

[root@thelinuxwiki]# service nrpe start

 Install NRPE on Clients-192.168.18.129(Windows-Server-1)

Windows configuration
Install NSClient++ on the Windows host.

Download and install.
Also if you want to check for a newer version. Here’s the full list: http://nsclient.org/nscp/downloads

Here’s a screenshot of one part of the installation.

Those are the features that I chose. Enable at least common check plugins and nsclient server.

Look for these lines and add them if they’re missing:
allowed hosts = 192.168.18.1
password =
port = 12489

Restart the NSClient++ service:
Start > Administrative tools > Services 

Configuration in windows server has been completed 

Now goto Nagios Server and Add the Two Clients(Linux-192.168.18.128 and Windows-192. 168.18.129) in nagios configuration file 

Add Server Configurations on Monitoring Server

---

Back on our Monitoring server, we will have to create config files for each of our client servers: 

[root@thelinuxwiki]# echo "cfg_dir=/etc/nagios/servers" >> /etc/nagios/nagios.cfg
[root@thelinuxwiki]# cd /etc/nagios/servers
[root@thelinuxwiki]# touch linux-server-1.cfg
[root@thelinuxwiki]# touch windows-server-1.cfg

Edit each client's configuration file and define which services you would like monitored.

First We will configure linux-server-1(192.168.18.128)

[root@linux-servers]# vi /etc/nagios/servers/linux-server-1.cfg

[root@thelinuxwiki]# egrep -v '^#|^$' /etc/nagios/servers/linux-server-1.cfg 
define host {
        use                     linux-server
        host_name               linux-server-1
        alias                   server1
        address                 192.168.18.128
 max_check_attempts              5
 check_period                    24x7 
 notification_interval           30
 notification_period             24x7
        }
define service {
        use                             generic-service
        host_name                       server1
        service_description             PING
        check_command                   check_ping!100.0,20%!500.0,60%
        }
define service {
        use                             generic-service
        host_name                       server1
        service_description             SSH
        check_command                   check_ssh
        notifications_enabled           0
        }
define service {
        use                             generic-service
        host_name                       server1
        service_description             CPU Load
        check_command                   check_nrpe!check_load
        }
define service {
        use                             generic-service
        host_name                       server1
        service_description             login users
        check_command                   check_nrpe!check_users
        }
define service {
        use                             generic-service
        host_name                       server1
        service_description             hard disk space
        check_command                   check_nrpe!check_sda3
        }
[root@thelinuxwiki]# 

[root@thelinuxwiki]# vi /etc/nagios/servers/windows-server-1.cfg

[root@thelinuxwiki]# egrep -v '^#|^$' /etc/nagios/servers/windows-server-1.cfg 
define host{
 use  windows-server ; Inherit default values from a template
 host_name windows-server-1 ; The name we're giving to this host
 alias  My Windows Server ; A longer name associated with the host
 address  192.168.18.129 ; IP address of the host
 }
define hostgroup{
 hostgroup_name windows-servers ; The name of the hostgroup
 alias  Windows Servers ; Long name of the group
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description NSClient++ Version
 check_command  check_nt!CLIENTVERSION
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description Uptime
 check_command  check_nt!UPTIME
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description CPU Load
 check_command  check_nt!CPULOAD!-l 5,80,90
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description Memory Usage
 check_command  check_nt!MEMUSE!-w 80 -c 90
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description C:\ Drive Space
 check_command  check_nt!USEDDISKSPACE!-l c -w 85 -c 90
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description W3SVC
 check_command  check_nt!SERVICESTATE!-d SHOWALL -l W3SVC
 }
define service{
 use   generic-service
 host_name  windows-server-1

 service_description Explorer
 check_command  check_nt!PROCSTATE!-d SHOWALL -l Explorer.exe
 }
[root@thelinuxwiki]# 
Finally, after you are done adding all the client configurations, you should set folder permissions correctly and restart Nagios on your Monitoring Server:
chown -R nagios. /etc/nagios
service nagios restart
Let’s see what our nagios web page tells us:

http://192.168.18.1/nagios
Go to the Services on left hand menu and you should see something similiar to this:



Note: You have to add following into commands.cfg of your nagios server
[root@thelinuxwiki.in]# vi /etc/nagios/objects/commands.cfg
# 'check_nt' command definition # This is for Windows Clients
define command{
        command_name    check_nt
        command_line    $USER1$/check_nt -H $HOSTADDRESS$ -p 12489 -v $ARG1$ $ARG2$
        }

# 'check_nrpe' command definition # This is for Linux Clients
define command{
        command_name check_nrpe
        command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$