NAGIOS NRPE MONITORING & EMAIL SETUP

Introduction

NRPE (Nagios Remote Plugin Executor) allows the Nagios Master server to monitor remote Linux Slave servers. This guide explains step-by-step configuration for monitoring and email alert setup.

Part 1: Monitor Slave from Master using NRPE

  1. Configure NRPE Daemon (Slave Server)
    • Open NRPE configuration file: 
      nano /usr/local/nagios/etc/nrpe.cfg
    • Modify allowed_hosts: 
      allowed_hosts=127.0.0.1,192.168.1.10
    • Restart NRPE: 
      sudo systemctl restart nrpe
  2. Verify Connection from Master 
    /usr/local/nagios/plugins/check_nrpe -H <Slave_IP_Address>
  3. Define Slave Host on Master 
    nano /usr/local/nagios/etc/objects/slave.cfg
    define host{
    use                     linux-server
    host_name               Slave-Server-01
    alias                   My Remote Linux Host
    address                 <Slave_IP_Address>
    max_check_attempts      5
    check_period            24x7
    notification_interval   30
    notification_period     24x7
    contact_groups          admins
    register                1
}
  4. Define Services 
    # CPU Load
define service{
    use                     generic-service
    host_name               Slave-Server-01
    service_description     CPU Load
    check_command           check_nrpe!check_load
}

# Current Users
define service{
    use                     generic-service
    host_name               Slave-Server-01
    service_description     Current Users
    check_command           check_nrpe!check_users
}

# Root Disk Space
define service{
    use                     generic-service
    host_name               Slave-Server-01
    service_description     Root Disk Space
    check_command           check_nrpe!check_disk
}
  5. Enable Config & Restart Nagios 
    nano /usr/local/nagios/etc/nagios.cfg
    cfg_file=/usr/local/nagios/etc/objects/slave.cfg
    sudo systemctl restart nagios

Part 2: Configure Email Notifications

  1. Install Mail Service

    Nagios requires an MTA like Postfix.

    echo "Test" | mail -s "Test Email" user@example.com
  2. Define Contact (contacts.cfg) 
    define contact {
    contact_name                shanmugananthan
    use                         generic-contact
    alias                       shan
    email                       shan@example.com
    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
}
  3. Add Contact to Group 
    define contactgroup{
    contactgroup_name admins
    alias             Nagios Administrators
    members           nagiosadmin,shanmugananthan
}
  4. Apply Contact Group to Host 
    define host {
    use             linux-server
    host_name       web-server-01
    alias           Web Server
    address         192.168.1.10
    contact_groups  admins
}
  5. Verify & Restart 
    /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
    sudo systemctl restart nagios

Final Result