- Nagios Installtion
- Installing the check_nrpe Plugin
- Installing NPRE on a Host
- Add a Linux host to Nagios server
- Install Postfix
- Nagios is in Mail Setup
- Create Custom plugin to Nagios
Create a nagios user and nagcmd group. You’ll use these to run the Nagios process.
useradd nagios
groupadd nagcmd
Then add the user to the group:
usermod -a -G nagcmd nagios
Update your package and install the required packages:
apt-get update
apt-get install build-essential libssl-dev unzip
Download Nagios using curl command and extract:
cd ~
apt install curl && curl -L -O https://assets.nagios.com/downloads/nagioscore/releases/nagios-4.4.4.tar.gz
tar zxf nagios-*.tar.gz
cd nagios-4.4.4
Run the configure script to specify the user and group you want Nagios to use. Use the nagios user and nagcmd group you created:
./configure --with-nagios-group=nagios --with-command-group=nagcmd
If you want Nagios to send emails using Postfix, you must install Postfix and configure Nagios to use it by adding "--with-mail=/usr/sbin/sendmail" to the configure command. We won’t cover Postfix in this tutorial, but if you choose to use Postfix and Nagios later, you’ll need to reconfigure and reinstall Nagios to use Postfix support.
Now compile Nagios with this command and configure:
make all
make install
make install-commandmode
make install-init
make install-config
You’ll use Apache to serve Nagios’ web interface, so copy the sample Apache configuration file to the /etc/apache2/sites-available folder:
/usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
usermod -G nagcmd www-data
Nagios is now installed. Let’s install a plugin which will allow Nagios to collect data from various hosts.
cd ~
curl -L -O https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-3.2.1/nrpe-3.2.1.tar.gz
tar zxf nrpe-3.2.1.tar.gz
cd nrpe-3.2.1
./configure
make check_nrpe
make install-plugin
Open the main Nagios configuration file in your text editor:
sudo nano /usr/local/nagios/etc/nagios.cfg
Find this line in the file:
....
#cfg_dir=/usr/local/nagios/etc/servers
....
Uncomment this line by deleting the # character from the front of the line:
cfg_dir=/usr/local/nagios/etc/servers
Save the file and exit the editor.
Now create the directory that will store the configuration file for each server that you will monitor:
sudo mkdir /usr/local/nagios/etc/servers
Open the Nagios contacts configuration in your text editor:
sudo nano /usr/local/nagios/etc/objects/contacts.cfg
Find the email directive and replace its value with your own email address.
Next, add a new command to your Nagios configuration that lets you use the check_nrpe command in Nagios service definitions.
sudo nano /usr/local/nagios/etc/objects/commands.cfg
Add the following to the end of the file to define a new command called check_nrpe:
…
define command{
command_name check_nrpe
command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$
}
Save and exit the editor.
Now configure Apache to serve the Nagios user interface. Enable the Apache rewrite and cgi modules with the a2enmod command:
sudo a2enmod rewrite
sudo a2enmod cgi
Use the htpasswd command to create an admin user called nagiosadmin that can access the Nagios web interface:
sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Enter a password at the prompt. Remember this password, as you will need it to access the Nagios web interface.
Note: If you create a user with a name other than nagiosadmin, you will need to edit /usr/local/nagios/etc/cgi.cfg and change all the nagiosadmin references to the user you created.
Now create a symbolic link for nagios.conf to the sites-enabled directory. This enables the Nagios virtual host.
sudo ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/
Next, open the Apache configuration file for Nagios.
vi /etc/apache2/sites-available/nagios.conf
If you’ve configured Apache to serve pages over HTTPS, locate both occurrences of this line:
# SSLRequireSSL
Uncomment both occurrances by removing the # symbol.
If you want to restrict the IP addresses that can access the Nagios web interface so that only certain IP addresses can access the interface, find the following two lines:
Order allow,deny
Allow from all
Comment them out by adding # symbols in front of them:
# Order allow,deny
# Allow from all
Then find the following lines:
# Order deny,allow
# Deny from all
# Allow from 127.0.0.1
Uncomment them by deleting the # symbols, and add the IP addresses or ranges (space delimited) that you want to allow to in the Allow from line:
Order deny,allow
Deny from all
Allow from 127.0.0.1 your_ip_address
These lines appear twice in the configuration file, so ensure you change both occurrences. Then save and exit the editor.
Restart Apache to load the new Apache configuration:
sudo service nagios restart
sudo nano /etc/systemd/system/nagios.service
Enter the following definition into the file
[Unit]
Description=Nagios
BindTo=network.target
[Install]
WantedBy=multi-user.target
[Service]
Type=simple
User=nagios
Group=nagios
ExecStart=/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg
Save the file and exit your editor.
Then start Nagios and enable it to start when the server boots:
sudo systemctl enable /etc/systemd/system/nagios.service
sudo systemctl start nagios
Nagios is now running, so let’s log in to its web interface.
Note: If not working all Nagios plugin. run following command:
apt-get install nagios-plugins
Copy plugin according your requirement:
cp /usr/lib/nagios/plugins/plugin_name /usr/local/nagios/libexec/
Log in to the second server, which we’ll call the monitored server.
apt update
apt install -y nagios-nrpe-server nagios-plugins
Modify the NRPE configuration file to accept the connection from the Nagios server, Edit the /etc/nagios/nrpe.cfg file.
vi /etc/nagios/nrpe.cfg
Add the Nagios servers IP address, separated by comma like below.
allowed_hosts=192.168.1.10
The /etc/nagios/nrpe.cfg file contains the basic commands to check the attributes (CPU, Memory, Disk, etc.architecure) and services (HTTP, FTP, etc.) on remote hosts. Below command lines let you monitor attributes with the help of Nagios plugins.
command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
command[check_load]=/usr/lib/nagios/plugins/check_load -w 15,10,5 -c 30,25,20
command[check_root]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/mapper/server--vg-root
command[check_swap]=/usr/lib/nagios/plugins/check_swap -w 20% -c 10%
command[check_total_procs]=/usr/lib/nagios/plugins/check_procs -w 150 -c 200
In the above command definition -w stands for warning and -c stands for critical.
Create a client configuration file /usr/local/nagios/etc/servers/host.local.cfg to define the host and service definitions of remote Linux host.
vi /usr/local/nagios/etc/servers/host.local.cfg
Copy the below content to the above file.
You can also use the following template and modify it according to your requirement. The following template is for monitoring logged in users, system load, disk usage (/ – partitions), swap, and total process.
define host{
use linux-server
host_name client.itzgeek.local
alias client.itzgeek.local
address 192.168.1.20
}
define hostgroup{
hostgroup_name linux-server
alias Linux Servers
members client.itzgeek.local
}
define service{
use local-service
host_name client.itzgeek.local
service_description SWAP Uasge
check_command check_nrpe!check_swap
}
define service{
use local-service
host_name client.itzgeek.local
service_description Root / Partition
check_command check_nrpe!check_root
}
define service{
use local-service
host_name client.itzgeek.local
service_description Current Users
check_command check_nrpe!check_users
}
define service{
use local-service
host_name client.itzgeek.local
service_description Total Processes
check_command check_nrpe!check_total_procs
}
define service{
use local-service
host_name client.itzgeek.local
service_description Current Load
check_command check_nrpe!check_load
}
Verify Nagios for any errors.
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
Restart the Nagios server.
systemctl restart nagios
Check NRPE:
/usr/local/nagios/libexec/check_nrpe -H localhost
sudo apt-get install postfix mailutils libsasl2-2 ca-certificates libsasl2-modules
while installing Postfix will ask about some settings:
- choose
Internet Site - choose domain name for unqualified mail addresses allow networks should be kept at 127.0.0.1 if you want local relay or you can specify list of IPs or networks from which to allow relay
After installation is over go to Postfix’s config:
sudo nano /etc/postfix/main.cf
and add this to the end:
relayhost = [smtp.gmail.com]:587
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_use_tls = yes
Now we need to define username and password for gmail, edit this file:
sudo nano /etc/postfix/sasl/sasl_passwd
And add the following line:
smtp.gmail.com USERNAME@gmail.com:PASSWORD
Once you have entered your username / password run postmap to create postfix lookup table:
postmap /etc/postfix/sasl/sasl_passwd
This will create sasl_passd.db lookup table in same directory.
Next make sure that sasl_passwd and sasl_passd.db files have the right permissions:
chown -R root:postfix /etc/postfix/sasl
chmod 750 /etc/postfix/sasl
chmod 640 /etc/postfix/sasl/sasl_passwd*
Restart postfix
sudo service postfix restart
And test if email relays are working:
echo "Tested" | mail -s "Testing Gmail Relay" user@example.net
First define contacts that you wish to notify and their email addresses in:
sudo nano /usr/local/nagios/etc/objects/contacts.cfg
In order to change sendmail to mailx or mail for example we need to edit
sudo nano /usr/local/nagios/etc/objects/commands.cfg
and change notify-host-by-email and notify-service-by-email commands:
# 'notify-host-by-email' command definition
define command{
command_name notify-host-by-email
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\nHost: $HOSTNAME$\nState: $HOSTSTATE$\nAddress: $HOSTADDRESS$\nInfo: $HOSTOUTPUT$\n\nDate/Time: $LONGDATETIME$\n" | /usr/bin/mailx -s "** $NOTIFICATIONTYPE$ Host Alert: $HOSTNAME$ is $HOSTSTATE$ **" $CONTACTEMAIL$
}
# 'notify-service-by-email' command definition
define command{
command_name notify-service-by-email
command_line /usr/bin/printf "%b" "***** Nagios *****\n\nNotification Type: $NOTIFICATIONTYPE$\n\nService: $SERVICEDESC$\nHost: $HOSTALIAS$\nAddress: $HOSTADDRESS$\nState: $SERVICESTATE$\n\nDate/Time: $LONGDATETIME$\n\nAdditional Info:\n\n$SERVICEOUTPUT$\n" | /usr/bin/mailx -s "** $NOTIFICATIONTYPE$ Service Alert: $HOSTALIAS$/$SERVICEDESC$ is $SERVICESTATE$ **" $CONTACTEMAIL$
}
First create two contact template:
vi templates.cfg
Configure contact and add following line:
Note: one contact add and another is default
define contact {
name generic-contact
service_notification_period 24x7
host_notification_period 24x7
service_notification_options w,u,c,r,f,s
host_notification_options d,u,r,f,s
service_notification_commands notify-service-by-email
host_notification_commands notify-host-by-email
register 0
}
define contact {
name critical-contact
service_notification_period 24x7
host_notification_period 24x7
service_notification_options u,c,r,f,s
host_notification_options d,u,r,f,s
service_notification_commands notify-service-by-email
host_notification_commands notify-host-by-email
register 0
}
Configure contact to contacts.cfg file:
vi contacts.cfg
Note: one contact add and another is default
define contact {
contact_name nagiosadmin
use generic-contact
alias Nagios Admin ; Full name of user
email sample@gmail.com ; <<**** CHANGE THIS TO YOUR EMAIL ADDRESS
}
define contact {
contact_name test
use critical-contact
alias Linux Admin
email sample@study24x7.com ; <<**** CHANGE THIS TO YOUR EMAIL ADDRESS
}
define contactgroup {
contactgroup_name admins
alias Nagios Administrators
members nagiosadmin,test
}
cd /usr/local/nagios/libexec
Create bash file like:
vi check_mongodb.sh
Add following line for mongodb:
#!/bin/bash
status=$(systemctl status mongod.service | grep Active | awk '{print $2}')
UPTIME=$(systemctl status mongod.service | grep Active| awk '{$1=$2=$3=""; print $0}')
if [ "$status" = "active" ]
then
echo "Uptime - $UPTIME"
exit 0
else
echo "DIST Testing MongoDB service is not working , Please check.."
exit 2
fi
After that configure remote server or local server rules:
cd /usr/local/nagios/etc/objects
If configure rule local server edit to localhost.cfg and if configure rules remote server, So edit remote host file
vi localhost.cfg
OR
vi ../servers/Remote_Host_Name.cfg
Add following line and add according your configuration:
define service {
use local-service ; service template to use
host_name LOCAL_SERVER
service_description DIST Testing MongoDB
check_command check_mongodb
}
Configuration commands.cfg file
vi commands.cfg
Add following line according your configration:
define command{
command_name check_mongodb
command_line /usr/local/nagios/libexec/check_mongodb.sh
}
Check all syntex is done:
/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
Restart Nagios Server
systemctl restart nagios.service
Reference for some links:
https://assets.nagios.com/downloads/nagioscore/docs/nagioscore/3/en/objectdefinitions.html
https://www.itzgeek.com/how-tos/linux/centos-how-tos/monitor-remote-linux-system-with-nagios-3.html