How to Install and Configure Nagios on Rocky Linux 9
Nagios is a popular and one of the most powerful open-source monitoring systems. It monitors your IT infrastructure and keeps your networks, servers, applications and processes running smoothly. With a monitoring system, you can detect problems before they occur and fix them quickly to save costs and downtime.
This tutorial teaches you how to install and configure Nagios on a Rocky Linux 9 server. We will also do some basic configuration and install the Nagios Remote Plugin Executor (NPRE), which allows us to monitor remote hosts.
Prerequisites
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A server running Rocky Linux 9.
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A non-sudo user with root privileges.
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SELinux is disabled. For this tutorial, even if you keep SELinux enabled, it would work without any issues. But depending on the Nagios monitors you use, you will either need to configure SELinux or would be better off keeping it disabled.
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Another server running Rocky Linux 9 that you want to monitor.
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Ensure that everything is updated.
$ sudo dnf update
Step 1 - Configure Firewall
The first step is to configure the firewall. Rocky Linux server comes with the Firewalld firewall.
Check if the firewall is running.
$ sudo firewall-cmd --state
You should get the following output.
running
Check the current allowed services/ports.
$ sudo firewall-cmd --permanent --list-services
It should show the following output.
dhcpv6-client mdns ssh
Allow HTTP and HTTPS ports.
$ sudo firewall-cmd --permanent --add-service=http $ sudo firewall-cmd --permanent --add-service=https
Recheck the status of the firewall.
$ sudo firewall-cmd --permanent --list-services
You should see a similar output.
dhcpv6-client http https mdns ssh
Reload the Firewall.
$ sudo firewall-cmd --reload
Step 2 - Install Apache and PHP
To run Nagios, you will need Apache along with PHP installed.
Install and enable Apache service.
$ sudo dnf install httpd $ sudo systemctl enable httpd
To install PHP, we will use the Remi Repository. Install Remi Repo and enable PHP 8.1.
$ sudo dnf install dnf-utils http://rpms.remirepo.net/enterprise/remi-release-9.rpm $ sudo dnf module reset php -y $ sudo dnf module enable php:remi-8.1 -y
Install PHP and several common PHP modules.
$ sudo dnf install -y php php-gd php-curl
Verify the PHP installation.
$ php --version
PHP 8.1.16 (cli) (built: Feb 14 2023 18:59:41) (NTS gcc x86_64)
Copyright (c) The PHP Group
Zend Engine v4.1.16, Copyright (c) Zend Technologies
with Zend OPcache v8.1.16, Copyright (c), by Zend Technologies
Enable PHP and start the service.
$ sudo systemctl enable --now php-fpm
Restart the Apache service for the change to take effect.
$ sudo systemctl restart httpd
You can check the installation of Apache and PHP by creating a file info.php in the /var/www/html directory which was created by the Apache installer.
$ sudo nano /var/www/html/info.php
Paste the following code in the editor.
<?php phpinfo();
Save the file by pressing Ctrl + X and entering Y when prompted.
Open the URL http://<yourserverip>/info.php in your browser and you should be greeted by the following page.
Step 3 - Install Nagios
Most of this tutorial will require you to install and work on your main server.
Install Dependencies
This tutorial will require Nagios and its plugins to be built from the source. Therefore, you need to install a few development libraries first. We need the EPEL repository as well but it was automatically installed with the Remi repo in the previous step so we can skip it here.
$ sudo dnf install gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel unzip wget gettext autoconf net-snmp-utils postfix automake perl-Net-SNMP
Download Nagios
Download the latest version from the Nagios' GitHub releases page. At the time of the tutorial, 4.4.10 is the latest version available. Modify the command in case you want a different version.
$ cd ~ $ sudo wget -O nagios.tar.gz https://github.com/NagiosEnterprises/nagioscore/releases/download/nagios-4.4.10/nagios-4.4.10.tar.gz
Extract the tar file.
$ sudo tar zxf nagios.tar.gz
Move the extracted directory to the /usr/src directory.
sudo mv nagios-4.4.10 /usr/src/nagios
Switch to the /usr/src/nagios directory.
$ cd /usr/src/nagios
Compile Nagios
The next step is to compile Nagios from its source files. Run the configure script to perform checks to make sure all dependencies are present.
$ sudo ./configure
You should get a similar output after the successful completion of the script.
*** Configuration summary for nagios 4.4.10 2023-01-17 ***:
General Options:
-------------------------
Nagios executable: nagios
Nagios user/group: nagios,nagios
Command user/group: nagios,nagios
Event Broker: yes
Install ${prefix}: /usr/local/nagios
Install ${includedir}: /usr/local/nagios/include/nagios
Lock file: /run/nagios.lock
Check result directory: /usr/local/nagios/var/spool/checkresults
Init directory: /lib/systemd/system
Apache conf.d directory: /etc/httpd/conf.d
Mail program: /usr/sbin/sendmail
Host OS: linux-gnu
IOBroker Method: epoll
Web Interface Options:
------------------------
HTML URL: http://localhost/nagios/
CGI URL: http://localhost/nagios/cgi-bin/
Traceroute (used by WAP):
Review the options above for accuracy. If they look okay,
type 'make all' to compile the main program and CGIs.
Start the compilation.
$ sudo make all
Create Nagios User and Group
Create a new user and group that will run the Nagios process.
$ sudo make install-groups-users
You should see the following output.
groupadd -r nagios useradd -g nagios nagios
Add the apache user to the nagios group.
$ sudo usermod -a -G nagios apache
Install Nagios Binaries
Run the following command to install Nagios binaries, CGIs, and HTML files.
$ sudo make install
Create External Command Directory
Nagios can process commands from external applications and for it, it needs a directory to be set up.
$ sudo make install-commandmode /bin/install -c -m 775 -o nagios -g nagios -d /usr/local/nagios/var/rw chmod g+s /usr/local/nagios/var/rw *** External command directory configured ***
Install Nagios Configuration Files
Install the sample configuration files.
$ sudo make install-config
Install Apache Configuration Files
Run the following command to install the Apache configuration files.
$ sudo make install-webconf
Restart the webserver to activate the configuration.
$ sudo systemctl restart httpd
Create a Systemd Service File
Run the following command to install a systemd unit file.
$ sudo make install-daemoninit
Enable HTTP Authentication
You can lock the Nagios web interface via HTTP authentication. Run the following command to use htpasswd to create the user. You will be prompted for a password.
$ sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin New password: Re-type new password: Adding password for user nagiosadmin
The default name for the user is nagiosadmin. You can use another username by replacing all the instances of nagiosadmin in the /usr/local/nagios/etc/cgi.cfg file by the preferred username. Or you can add the username by using a comma like the following.
authorized_for_system_information=nagiosadmin, username1 authorized_for_configuration_information=nagiosadmin, username1 authorized_for_system_commands=nagiosadmin, username1 authorized_for_all_services=nagiosadmin, username1 authorized_for_all_hosts=nagiosadmin, username1 authorized_for_all_service_commands=nagiosadmin, username1 authorized_for_all_host_commands=nagiosadmin, username1
You can add users with read-only access by enabling the following configuration in the file by removing the hash (#) in front of it. Then, run the htpasswd with the username.
authorized_for_read_only=username2
Restart the server for the configuration to take effect.
$ sudo systemctl restart httpd
Step 4 - Install Nagios Plugins
Install the prerequisites required for the Nagios plugins.
$ sudo dnf install epel-release $ sudo dnf install -y gcc glibc glibc-common make gettext automake autoconf wget openssl-devel net-snmp net-snmp-utils postgresql-devel openldap-devel bind-utils samba-client fping openssh-clients lm_sensors perl-Net-SNMP
Download the latest version from Nagios plugins' GitHub page. At the time of the tutorial, 2.4.3 is the latest version available. Modify the command in case you want a different version.
$ cd ~ $ sudo wget -O nagios-plugins.tar.gz https://github.com/nagios-plugins/nagios-plugins/releases/download/release-2.4.3/nagios-plugins-2.4.3.tar.gz
Extract the tar file.
$ sudo tar zxf nagios-plugins.tar.gz
Move the extracted directory to the /usr/src directory.
$ sudo mv nagios-plugins-2.4.3 /usr/src/nagios-plugins
Switch back to the /usr/src/nagios-plugins directory.
$ cd /usr/src/nagios-plugins
Run the following commands to compile and install the plugins.
$ sudo ./configure $ sudo make $ sudo make install
Step 5 - Install check_nrpe Plugin
Download the latest version from NRPE GitHub releases page. At the time of writing this tutorial, the latest version available is 4.1.0. Modify the following command in case you want a different version.
$ cd ~ $ wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.0/nrpe-4.1.0.tar.gz
Extract the archive.
$ tar zxf nrpe-*.tar.gz
Move the extracted directory to the /usr/src directory.
$ sudo mv nrpe-4.1.0 /usr/src/nrpe
Switch to the /usr/src/nrpe directory.
$ cd /usr/src/nrpe
Configure and Install the plugin.
$ sudo ./configure $ sudo make check_nrpe $ sudo make install-plugin
This will place the check_nrpe plugin in the /usr/local/nagios/libexec/ directory.
Step 6 - Start Nagios
With Nagios and the plugins installed, it is time to start the Nagios service.
$ sudo systemctl start nagios
Check the status of the service to see if it is running properly.
$ sudo systemctl status nagios
Nagios Web Interface
Open the URL http://<domain_or_ip_address>/nagios in your browser. You should see a login prompt.
Enter the credentials you created during the HTTP authentication method and you should be greeted with the following screen.
Step 7 - Monitoring Hosts
To monitor a host, you need to install NRPE Daemon and Nagios plugins on the host. We will monitor a Rocky Linux 9 server from our Nagios server.
Log in to your host.
$ ssh user@monitored_server_ip
Install Nagios Plugins
Install the Nagios plugins by repeating step 4 from before.
Install NRPE
Install the prerequisites required for the NRPE daemon.
$ sudo dnf install -y gcc glibc glibc-common openssl openssl-devel perl wget
Download NRPE.
$ cd ~ $ wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.0/nrpe-4.1.0.tar.gz
Extract the archive.
$ tar zxf nrpe-*.tar.gz
Move the extracted directory to the /usr/src directory.
$ sudo mv nrpe-4.1.0 /usr/src/nrpe
Change to the NRPE directory.
$ cd /usr/src/nrpe
Configure and install NRPE.
$ sudo ./configure --enable-command-args $ sudo make all
Create the User and group.
$ sudo make install-groups-users
Install the NRPE Binaries, NRPE daemon and the check_npre plugin.
$ sudo make install
Install the configuration files.
$ sudo make install-config
Update the services file. The /etc/services file is used to translate service names to port numbers.
$ sudo sh -c "echo >> /etc/services" $ sudo sh -c "sudo echo '# Nagios services' >> /etc/services" $ sudo sh -c "sudo echo 'nrpe 5666/tcp' >> /etc/services"
Install the NPRE service daemon.
$ sudo make install-init $ sudo systemctl enable nrpe
You need to update the NPRE configuration file located at /usr/local/nagios/etc/nrpe.cfg.
Open the file for editing.
$ sudo nano /usr/local/nagios/etc/nrpe.cfg
By default, NPRE listens to requests only from the Localhost (127.0.0.1). You need to add the IP address of your Nagios server to the file.
allowed_hosts=127.0.0.1,10.25.5.2
The following option determines whether or not the NPRE daemon will allow clients to specify command arguments. Allow the option by entering the value as 1 which enables advanced NPRE configurations.
dont_blame_nrpe=1
Next, as you scroll down, you will come across a list of NRPE commands with their definitions. All of them are commented out. You need to uncomment them so Nagios can use them.
Each command can be passed arguments. Some of the commands have arguments hardcoded in front of them while some can accept arguments from the user. Each command can have the following notification options.
- W stands for Warning service states
- C stands for Critical service states
- R stands for notify on service recovering (OK states)
Thus, you can specify at what level which type of notification a command can send. We won't be diving into the detailed description and function of each of the commands since they are beyond the scope of this tutorial.
# The following examples use hardcoded command arguments... # This is by far the most secure method of using NRPE command[check_users]=/usr/local/nagios/libexec/check_users -w 5 -c 10 command[check_load]=/usr/local/nagios/libexec/check_load -r -w .15,.10,.05 -c .30,.25,.20 command[check_hda1]=/usr/local/nagios/libexec/check_disk -w 20% -c 10% -p /dev/hda1 command[check_zombie_procs]=/usr/local/nagios/libexec/check_procs -w 5 -c 10 -s Z command[check_total_procs]=/usr/local/nagios/libexec/check_procs -w 150 -c 200 # The following examples allow user-supplied arguments and can # only be used if the NRPE daemon was compiled with support for # command arguments *AND* the dont_blame_nrpe directive in this # config file is set to '1'. This poses a potential security risk, so # make sure you read the SECURITY file before doing this. ### MISC SYSTEM METRICS ### command[check_users]=/usr/local/nagios/libexec/check_users $ARG1$ command[check_load]=/usr/local/nagios/libexec/check_load $ARG1$ command[check_disk]=/usr/local/nagios/libexec/check_disk $ARG1$ command[check_swap]=/usr/local/nagios/libexec/check_swap $ARG1$ command[check_cpu_stats]=/usr/local/nagios/libexec/check_cpu_stats.sh $ARG1$ command[check_mem]=/usr/local/nagios/libexec/custom_check_mem -n $ARG1$ ### GENERIC SERVICES ### command[check_init_service]=sudo /usr/local/nagios/libexec/check_init_service $ARG1$ command[check_services]=/usr/local/nagios/libexec/check_services -p $ARG1$ ### SYSTEM UPDATES ### command[check_yum]=/usr/local/nagios/libexec/check_yum #command[check_apt]=/usr/local/nagios/libexec/check_apt ### PROCESSES ### command[check_all_procs]=/usr/local/nagios/libexec/custom_check_procs command[check_procs]=/usr/local/nagios/libexec/check_procs $ARG1$ ### OPEN FILES ### command[check_open_files]=/usr/local/nagios/libexec/check_open_files.pl $ARG1$ ### NETWORK CONNECTIONS ### command[check_netstat]=/usr/local/nagios/libexec/check_netstat.pl -p $ARG1$ $ARG2$
Uncomment the above commands by removing the # symbol in front of them. You can uncomment as many commands as you require.
Add the following command to check the root disk space.
