How to add linux host to Nagios monitoring server
In our previous article we discussed about installation and configuration of nagios server. Here we will discuss about adding remote host to nagios server using nrpe.
NRPE plugin: Nagios Remote Plugin Executor(nrpe) plugin allows you to monitor applications and services running on remote Linux / windows hosts. This NRPE Add-on helps Nagios to monitor local resources like memory,disk,ping,swap,CPU etc of remote host.
Note: The NRPE addon requires that Nagios Plugins must be installed on the remote Linux machine. Without these, the NRPE daemon will not work and will not monitor anything.
Installation of nrpe plugin on remote host
Remote host ip: 192.168.0.10
Nagios server ip: 192.168.0.192
First we need to install few dependency packages like below
[root@lampblogs ~]# yum install -y gcc glibc glibc-common gd gd-devel make net-snmp openssl-develcreate nagios user and set password
[root@lampblogs ~]# useradd nagios
[root@lampblogs ~]# passwd nagiosInstall nagios plugins
Create one directory for installation and download plugins into that directory.
[root@lampblogs ~]# mkdir nagios
[root@lampblogs ~]# cd nagios
[root@lampblogs nagios]# wget https://nagios-plugins.org/download/nagios-plugins-2.2.1.tar.gz
[root@lampblogs nagios]# tar -xvzf nagios-plugins-2.2.1.tar.gzonce you have downloaded and extracted nagios plugins, Now you need to compile them as shown below.
Compile and install plugins
Run below command to compile
[root@lampblogs nagios]# cd nagios-plugins-2.2.1/
[root@lampblogs nagios-plugins-2.2.1]# ./configure
[root@lampblogs nagios-plugins-2.2.1]# make
[root@lampblogs nagios-plugins-2.2.1]# make install
set permissions on plugin directory
[root@lampblogs nagios-plugins-2.2.1]# chown nagios.nagios /usr/local/nagios
[root@lampblogs nagios-plugins-2.2.1]# chown -R nagios.nagios /usr/local/nagios/libexecInstall NRPE
download and install nrpe plugins
[root@lampblogs nagios-plugins-2.2.1]# cd /root/nagios
[root@lampblogs nagios]# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.1/nrpe-3.2.1.tar.gz
[root@lampblogs nagios]# tar -xvzf nrpe-3.2.1.tar.gzcompile and install nrpe as shown below
[root@lampblogs nagios]# cd nrpe-3.2.1
[root@lampblogs nrpe-3.2.1]# ./configure
[root@lampblogs nrpe-3.2.1]# make all
##### Install binaries #####
[root@lampblogs nrpe-3.2.1]# make install
####### Install Configuration Files ########
[root@lampblogs nrpe-3.2.1]# make install-config
update services file
The /etc/services file is used by applications to translate human readable service names into port numbers when connecting to a machine across a network.
[root@lampblogs ~]# echo >> /etc/services
[root@lampblogs ~]# echo '# Nagios services' >> /etc/services
[root@lampblogs ~]# echo 'nrpe 5666/tcp' >> /etc/servicesInstall service /daemon files
[root@lampblogs nrpe-3.2.1]# make install-initupdate nrpe config file
Add nagios server ip allowed hosts in nrpe.cfg
[root@lampblogs ~]# vi /usr/local/nagios/etc/nrpe.cfgchange allowed_hosts as below (add nagios server ip) and save it.
allowed_hosts=127.0.0.1,192.168.0.192Now start nrpe service and also enable in startup as below
[root@lampblogs ~]# systemctl start nrpe
[root@lampblogs ~]# systemctl enable nrpeverify nrpe daemon with netstat command
[root@lampblogs ~]# netstat -antp | grep nrpe
tcp 0 0 0.0.0.0:5666 0.0.0.0:* LISTEN 11285/nrpe
tcp6 0 0 :::5666 :::* LISTEN 11285/nrpe Next, verify the NRPE daemon is functioning properly. Run the “check_nrpe” command that was installed earlier for testing purposes.
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1
sample output
NRPE v3.2.1configure firewall
Make sure that firewall on the local machine will allow the NRPE daemon to be accessed from remote servers.To do this run following command
[root@lampblogs ~]# firewall-cmd --permanent --zone=public --add-port=5666/tcpcustomize nrpe commands
The default NRPE configuration file that got installed has several command definitions that will be used to monitor this machine.sample file is located at below path.
[root@lampblogs ~]# vi /usr/local/nagios/etc/nrpe.cfgThe following are the default command definitions that are located at the bottom of the configuration file. You can check them by using the following commands.
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_load
CRITICAL - load average: 0.50, 1.16, 1.19|load1=0.500;0.150;0.300;0; load5=1.160;0.100;0.250;0; load15=1.190;0.050;0.200;0;
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_users
USERS OK - 2 users currently logged in |users=2;5;10;0
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_sda1
DISK OK - free space: /boot 815 MB (80.47% inode=100%);| /boot=198MB;811;912;0;1014
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_total_procs
PROCS WARNING: 179 processes | procs=179;150;200;0;
[root@lampblogs ~]# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 -c check_zombie_procs
PROCS OK: 0 processes with STATE = Z | procs=0;5;10;0;
If you want to check like ssh,swap usage and http service etc then add below to nrpe.cfg file and check these also like above.
command[check_ssh]=/usr/local/nagios/libexec/check_ssh -p $ARG1$ -H $HOSTADDRESS$
command[check_swap]=/usr/local/nagios/libexec/check_swap -w 20% -c 10%
command[check_http]=/usr/local/nagios/libexec/check_http -I 192.168.0.192
You can edit and add new command definitions by editing the NRPE config file. Finally, we have successfully installed and configured NRPE agent on Remote host.Now we will configure Nrpe and few services on Nagios server.
Install nrpe plugin in nagios server like below
[root@centos ~]# mkdir nagios
[root@centos ~]# cd nagios
[root@centos nagios]# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.1/nrpe-3.2.1.tar.gz
[root@centos nagios]# tar xzf nrpe-3.2.1.tar.gz
[root@centos nagios]# cd nrpe-3.2.1
[root@centos nrpe-3.2.1]# ./configure
[root@centos nrpe-3.2.1]# make all
[root@centos nrpe-3.2.1]# make install
[root@centos nrpe-3.2.1]# make install-config
[root@centos nrpe-3.2.1]# make install-init
############ Add service like below ################
[root@centos ~]# echo >> /etc/services
[root@centos ~]# echo '# Nagios services' >> /etc/services
[root@centos ~]# echo 'nrpe 5666/tcp' >> /etc/services
now start and enable nrpe service like below
[root@centos ~]# systemctl start nrpe
[root@centos ~]# systemctl enable nrpeVerify nrpe daemon remotely
Make sure that the check_nrpe plugin can communicate with the NRPE daemon on the remote host.you need to add ip address of remote host
[root@centos ~]# /usr/local/nagios/libexec/check_nrpe -H 192.168.0.10
NRPE v3.2.1
Allow nrpe port in firewall if firewall is running on your server and also make sure firewall not blocking between remote host and nagios server.
Add remote Linux host to Nagios server
To add remote host you need to create two new files hosts.cfg and services.cfg
[root@centos ~]# cd /usr/local/nagios/etc/
[root@centos etc]# touch hosts.cfg
[root@centos etc]# touch services.cfgNow add these two files to main Nagios configuration file.
[root@centos ~]# vi /usr/local/nagios/etc/nagios.cfgadd below lines to config file
# You can specify individual object config files
cfg_file=/usr/local/nagios/etc/hosts.cfg
cfg_file=/usr/local/nagios/etc/services.cfgNow open hosts.cfg file and add the default host template name and define remote hosts as shown below. Make sure to replace host_name, alias and address with your remote host server details.
[root@centos ~]# vi /usr/local/nagios/etc/hosts.cfg## Default Linux Host Template ##
define host{
name linux-box ; Name of this template
use generic-host ; Inherit default values
check_period 24x7
check_interval 5
retry_interval 1
max_check_attempts 10
check_command check-host-alive
notification_period 24x7
notification_interval 30
notification_options d,r
contact_groups admins
register 0 ; DONT REGISTER THIS - ITS A TEMPLATE
}
## Default
define host{
use linux-box ; Inherit default values from a template
host_name lampblogs.com ; The name we're giving to this server
alias CentOS 7 ; A longer name for the server
address 192.168.0.10 ; IP address of Remote Linux host
}
save the file. Next open services.cfg file and add the following services to be monitored.
[root@centos ~]# vi /usr/local/nagios/etc/services.cfgdefine service{
use generic-service
host_name lampblogs.com
service_description PING
check_command check_ping!100.0,20%!500.0,60%
}
define service{
use generic-service
host_name lampblogs.com
service_description SSH
check_command check_ssh
notifications_enabled 0
}
define service{
use generic-service
host_name lampblogs.com
service_description CPU Load
check_command check_nrpe!check_load
}
define service{
use generic-service
host_name lampblogs.com
service_description Total Processes
check_command check_nrpe!check_total_procs
}
define service{
use generic-service
host_name lampblogs.com
service_description Current Users
check_command check_nrpe!check_users
}
define service{
use generic-service
host_name lampblogs.com
service_description HTTP
check_command check_nrpe!check_http
}
define service{
use generic-service
host_name lampblogs.com
service_description Swap Usage
check_command check_nrpe!check_swap
}
Now NRPE command definition needs to be created in commands.cfg file.
[root@centos ~]# vi /usr/local/nagios/etc/objects/commands.cfgAdd below content at the end of the file.
###############################################################################
# NRPE CHECK COMMAND
#
# Command to use NRPE to check remote host systems
###############################################################################
define command{
command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}Now, verify Nagios Configuration files for any errors.
[root@centos ~]# /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfgsample output
Total Warnings: 0
Total Errors: 0
Things look okay - No serious problems were detected during the pre-flight check
Finally restart nagios service with below command
[root@centos ~]# systemctl restart nagios
[root@centos ~]# systemctl status nagios
That's it. Now goto nagios web interface in your browser with http://ip_address/nagios with username nagiosadmin and password.check whether remote linux is added and is being monitored.
click on services and check all are running perfect.
