Server Monitoring with Nagios on Hyper-V: Step-by-Step Setup Guide (2026)

Create the Nagios VM in Hyper-V

Open Hyper-V Manager (Windows + R, type virtmgmt.msc). Right-click your server in the left pane, then New > Virtual Machine.

Recommended specs for a fresh Nagios VM monitoring up to 50 hosts:

• Generation 2 (UEFI, Secure Boot). Required for modern Ubuntu boot.
• 2 vCPU, 4 GB RAM (dynamic, min 2 GB / max 6 GB).
• 30 GB VHDX dynamic disk on a fast volume (Nagios is I/O light but log retention adds up).
• External virtual switch bound to your management LAN (the VM needs to reach probed hosts).
• Set the VM’s MAC address to static if your DHCP uses MAC reservations.

In the VM settings, under Security, set Microsoft UEFI Certificate Authority as the secure boot template (matches Ubuntu’s signed bootloader). Under Integration Services, enable all (especially “Time synchronization” and “Heartbeat”) so the VM stays clock-aligned with the host.

Install Ubuntu 24.04 LTS and harden it

Mount the Ubuntu 24.04 LTS server ISO (download from ubuntu.com). Boot the VM, follow the installer with these choices: minimal install, no LVM, OpenSSH selected, no other snaps. After install, log in and run the standard hardening pass:

sudo apt update
sudo apt upgrade -y
sudo apt install -y ufw fail2ban unattended-upgrades

# Open SSH and (later) Nagios web UI
sudo ufw allow OpenSSH
sudo ufw allow 80/tcp
sudo ufw allow 443/tcp
sudo ufw enable

# Set hostname for clarity
sudo hostnamectl set-hostname nagios-01

If you want the full hardening procedure (SSH key-only, AppArmor enforce, auditd, etc.), follow our Ubuntu 24.04 hardening checklist. A monitoring server is a juicy target — harden it before pointing it at production.

Install Nagios Core 4.5

Ubuntu 24.04 ships Nagios 4.4 in apt; the 4.5.x line has notable bug fixes. The cleanest approach in 2026 is to compile from the official tarball.

# Build dependencies
sudo apt install -y autoconf gcc libc6 make wget unzip apache2 apache2-utils \
  php libapache2-mod-php libgd-dev libssl-dev libmcrypt-dev bc gawk dc build-essential

# Create the nagios user/group
sudo useradd nagios
sudo groupadd nagcmd
sudo usermod -aG nagcmd nagios
sudo usermod -aG nagcmd www-data

# Download and extract Nagios Core 4.5.x
cd /tmp
wget https://github.com/NagiosEnterprises/nagioscore/releases/download/nagios-4.5.9/nagios-4.5.9.tar.gz
tar xzf nagios-4.5.9.tar.gz
cd nagios-4.5.9
./configure --with-command-group=nagcmd
sudo make all
sudo make install
sudo make install-init
sudo make install-config
sudo make install-commandmode
sudo make install-webconf

# Install the standard plugins
cd /tmp
wget https://nagios-plugins.org/download/nagios-plugins-2.4.12.tar.gz
tar xzf nagios-plugins-2.4.12.tar.gz
cd nagios-plugins-2.4.12
./configure --with-nagios-user=nagios --with-nagios-group=nagios
sudo make
sudo make install

Set the web UI password and start the service:

sudo htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
# Enter a strong password when prompted

sudo systemctl enable nagios apache2
sudo systemctl start nagios apache2
sudo a2enmod cgi rewrite
sudo systemctl reload apache2

Open http://nagios-01.local/nagios (or the IP) in your browser. You should see the Nagios login page. Log in with nagiosadmin and the password you just set.

Configure your first host and probes

Nagios reads its config from /usr/local/nagios/etc/objects/. Create a host file per monitored target.

sudo mkdir -p /usr/local/nagios/etc/servers
sudo nano /usr/local/nagios/etc/nagios.cfg
# Add this line:
cfg_dir=/usr/local/nagios/etc/servers

Example host file at /usr/local/nagios/etc/servers/web01.cfg:

define host {
    use             linux-server
    host_name       web01
    alias           Production web server
    address         10.0.0.10
    max_check_attempts 5
    check_period    24x7
    contact_groups  admins
}

define service {
    use                 generic-service
    host_name           web01
    service_description HTTPS
    check_command       check_http!--ssl -H peoplearegeek.com
}

define service {
    use                 generic-service
    host_name           web01
    service_description SSH
    check_command       check_ssh
}

define service {
    use                 generic-service
    host_name           web01
    service_description Disk root partition
    check_command       check_disk!20%!10%!/
}

define service {
    use                 generic-service
    host_name           web01
    service_description MySQL port
    check_command       check_tcp!3306
}

For deeper checks on remote Linux hosts (CPU, memory, disk per partition, specific processes), install NRPE on each target then point Nagios at it:

# On the monitored host
sudo apt install -y nagios-nrpe-server monitoring-plugins
# Add nagios-01 IP to allowed_hosts in /etc/nagios/nrpe.cfg
sudo systemctl restart nagios-nrpe-server

Verify the config and reload Nagios:

sudo /usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg
# Should print "Things look okay - No serious problems were detected"

sudo systemctl reload nagios

Mail alerts (SMTP via msmtp)

Nagios calls /usr/bin/mail when it needs to alert. The easiest sane setup in 2026 is msmtp as a sendmail replacement, configured to relay through an SMTP server (your hosting provider, SendGrid, AWS SES, or your own postfix).

sudo apt install -y msmtp msmtp-mta mailutils

# Edit /etc/msmtprc
sudo nano /etc/msmtprc

defaults
auth           on
tls            on
tls_starttls   on
logfile        /var/log/msmtp.log

account        default
host           smtp.your-provider.com
port           587
from           nagios@yourdomain.com
user           nagios@yourdomain.com
password       your-smtp-app-password

Set permissions and test:

sudo chmod 600 /etc/msmtprc
echo "Test from nagios" | mail -s "Nagios test" you@yourdomain.com
# You should receive the email in less than a minute

By default, Nagios already calls notify-host-by-email and notify-service-by-email commands defined in /usr/local/nagios/etc/objects/commands.cfg. Update the contact email address in /usr/local/nagios/etc/objects/contacts.cfg to your real one, reload Nagios, trigger a test alert (stop a probed service briefly), and confirm the email arrives.

Telegram alerts via bot webhook

Mail is for the record; Telegram is for “you need to look at this now”. Five minutes to wire it up.

Create a bot via @BotFather on Telegram, save the token. Send /start to your new bot from your account, then visit https://api.telegram.org/bot<TOKEN>/getUpdates in a browser to find your chat_id.

Create the notification script /usr/local/nagios/libexec/notify-telegram.sh:

#!/bin/bash
TOKEN="123456:ABC-DEF..."
CHAT_ID="987654321"

MESSAGE="*[$1]* $2: $3
Host: \`$4\`
Service: \`$5\`
State: $6 ($7)
$8"

curl -s -X POST "https://api.telegram.org/bot${TOKEN}/sendMessage" \
    -d "chat_id=${CHAT_ID}" \
    -d "parse_mode=Markdown" \
    -d "text=${MESSAGE}"

sudo chmod +x /usr/local/nagios/libexec/notify-telegram.sh
sudo chown nagios:nagios /usr/local/nagios/libexec/notify-telegram.sh

Register the command and attach to your admin contact:

# /usr/local/nagios/etc/objects/commands.cfg - append:
define command {
    command_name notify-by-telegram
    command_line /usr/local/nagios/libexec/notify-telegram.sh \
      "$NOTIFICATIONTYPE$" "$HOSTSTATE$" "$SERVICESTATE$" \
      "$HOSTNAME$" "$SERVICEDESC$" "$SERVICESTATE$" \
      "$SERVICESTATEID$" "$SERVICEOUTPUT$"
}

# /usr/local/nagios/etc/objects/contacts.cfg - add to the contact block:
service_notification_commands notify-service-by-email,notify-by-telegram
host_notification_commands    notify-host-by-email,notify-by-telegram

Reload Nagios and force a test by stopping a probed service. The Telegram message lands within seconds.

Custom dashboard and views

The default Nagios UI is functional but visually dated. Two community projects modernise it without touching the core:

• Thruk (thruk.org): a Perl-based replacement frontend that consumes the same Nagios config. Better filtering, business-hour reporting, mobile-friendly. sudo apt install thruk.
• NagVis: visual map plugin that overlays host status on a network diagram or a building floor plan. Useful when stakeholders want a “green / red lights” view instead of a status grid.

Both can run side-by-side with the stock Nagios CGI UI; pick whichever your team finds easier on the eyes.

Snapshot and routine maintenance

Take a Hyper-V checkpoint (right-click VM > Checkpoint) now that the install is clean. This is your rollback point if a config change later goes wrong. Repeat after every significant config change.

Routine maintenance cadence:

• Weekly: glance at /var/log/nagios.log for repeated transient warnings (often signal flapping that needs flapping detection thresholds adjusted).
• Monthly: run sudo apt upgrade on the Nagios VM, take a checkpoint before, restart Nagios after.
• Quarterly: audit the host list — every monitored host should still exist, every existing host should be monitored. Drift here is the silent killer of monitoring usefulness.
• Yearly: review and tighten the alert thresholds. New WARNING / CRITICAL levels based on the last 12 months of operating data give better signal than the defaults.