Nagios Server
Nagios is an open source monitoring solution running on Linux.
Nagios is designed to periodically check critical network, application, or server parameters.
These parameters include microprocessor load, number of running processes, log files, disk and memory usage, as well as many other services such as SMTP (Simple Mail Transfer Protocol), HTTP (Hypertext Transfer Protocol), POP3 (Post Office Protocol 3), etc. can be checked.
These parameters require a microprocessor load, a database such as PHP or MySQL to run Nagois, and a web server such as Apache or Nginx. We will proceed under the assumption that all of these have already been configured.
1. Install necessary packages
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# dnf install -y gcc glibc glibc-common # dnf install -y gd gd-devel |
2. Installing Nagios Core
①Create a Nagios user and set a password.
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# /usr/sbin/useradd -m nagios # passwd nagios |
➁To enable the sending of external commands via the web interface, create a new group named "nagcmd". Add both the nagios user and the apache user to that group.
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# /usr/sbin/groupadd nagcmd # /usr/sbin/usermod -a -G nagcmd nagios # /usr/sbin/usermod -a -G nagcmd apache |
➂Nagios Download
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# wget https://sourceforge.net/projects/nagios/files/nagios-4.x/nagios-4.5.12/nagios-4.5.12.tar.gz |
④Install
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# tar zxvf nagios-4.5.12.tar.gz # cd nagios-4.5.12 # ./configure --with-command-group=nagcmd |
It appears as follows
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*** Configuration summary for nagios 4.5.12 2026-03-25 ***: General Options: ------------------------- Nagios executable: nagios Nagios user/group: nagios,nagios Command user/group: nagios,nagcmd 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/mail 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): /usr/sbin/traceroute Review the options above for accuracy. If they look okay, type 'make all' to compile the main program and CGIs. |
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# make all |
It appears as follows
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*** Support Notes ******************************************* If you have questions about configuring or running Nagios, please make sure that you: - Look at the sample config files - Read the documentation on the Nagios Library at: https://library.nagios.com before you post a question to one of the mailing lists. Also make sure to include pertinent information that could help others help you. This might include: - What version of Nagios you are using - What version of the plugins you are using - Relevant snippets from your config files - Relevant error messages from the Nagios log file For more information on obtaining support for Nagios, visit: https://support.nagios.com ************************************************************* Enjoy. |
Install Nagios Core
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# make install |
Install the Nagios init script
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# make install-init /usr/bin/install -c -m 755 -d -o root -g root /lib/systemd/system /usr/bin/install -c -m 755 -o root -g root startup/default-service /lib/systemd/system/nagios.service |
Install external command files and permissions
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# make install-commandmode /usr/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 the Nagios configuration files
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# make install-config *** Config files installed *** Remember, these are *SAMPLE* config files. You'll need to read the documentation for more information on how to actually define services, hosts, etc. to fit your particular needs. |
Edit the /usr/local/nagios/etc/objects/contacts.cfg configuration file and change the email address associated with the nagiosadmin contact definition to the address used for receiving alerts.
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# vi /usr/local/nagios/etc/objects/contacts.cfg Line 32 : Change to your own email address email nagios@localhost ; <<***** CHANGE THIS TO YOUR EMAIL ADDRESS ****** |
Install the Apache configuration file for Nagios
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# make install-webconf /usr/bin/install -c -m 644 sample-config/httpd.conf /etc/httpd/conf.d/nagios.conf if [ 0 -eq 1 ]; then \ ln -s /etc/httpd/conf.d/nagios.conf /etc/apache2/sites-enabled/nagios.conf; \ fi *** Nagios/Apache conf file installed *** |
3. Install the Nagios plugin
①Download the latest code from the Nagios Plugins page
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# wget https://nagios-plugins.org/download/nagios-plugins-2.5.tar.gz |
②Install
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# tar zxvf nagios-plugins-2.5.tar.gz # cd nagios-plugins-2.5 # ./configure --with-nagios-user=nagios --with-nagios-group=nagios # make # make install |
The following nagios-plugins are available
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# ls /usr/local/nagios/libexec check_apt check_disk check_http check_jabber check_nntp check_oracle check_breeze check_disk_smb check_icmp check_load check_nntps check_overcr check_by_ssh check_dns check_ide_smart check_log check_nt check_ping check_clamd check_dummy check_ifoperstatus check_mailq check_ntp check_pop check_cluster check_file_age check_ifstatus check_mrtg check_ntp_peer check_procs check_dhcp check_flexlm check_imap check_mrtgtraf check_ntp_time check_real check_dig check_ftp check_ircd check_nagios check_nwstat check_rpc [root@Lepard nagios-plugins-2.5]# ls /usr/local/nagios/libexec check_apt check_file_age check_load check_ntp_time check_smtp check_users check_breeze check_flexlm check_log check_nwstat check_spop check_wave check_by_ssh check_ftp check_mailq check_oracle check_ssh negate check_clamd check_http check_mrtg check_overcr check_ssl_validity remove_perfdata check_cluster check_icmp check_mrtgtraf check_ping check_ssmtp urlize check_dhcp check_ide_smart check_nagios check_pop check_swap utils.pm check_dig check_ifoperstatus check_nntp check_procs check_tcp utils.sh check_disk check_ifstatus check_nntps check_real check_time check_disk_smb check_imap check_nt check_rpc check_udp check_dns check_ircd check_ntp check_sensors check_ups check_dummy check_jabber check_ntp_peer check_simap check_uptime |
③Create necessary directories
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# mkdir -p /usr/local/nagios/var/spool/checkresults # chown -R nagios:nagios /usr/local/nagios/var/spool/checkresults |
4. Creating a Nagios Web User
Create a user account to access the Nagios Web Dashboard. This user account is used for authentication.
The default name of the user is nagiosadmin, which is defined as the preferred user name in the /usr/local/nagios/etc/cgi.cfg file.
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# htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin New password: [password] Re-type new password: [again password] Adding password for user nagiosadmin |
Set ownership and permissions
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# chown apache:apache /usr/local/nagios/etc/htpasswd.users # chmod 640 /usr/local/nagios/etc/htpasswd.users |
Restart Apache
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# systemctl restart httpd |
Allow HTTP service port in firewall
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# firewall-cmd --add-service=http --permanent # firewall-cmd --reload |
Start and Enable Nagios Services
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# systemctl enable nagios --now Created symlink /etc/systemd/system/multi-user.target.wants/nagios.service → /lib/systemd/system/nagios.service. |
Reboot system
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# shutdown -r now |
Confirmation of service execution
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# systemctl status nagios ● nagios.service - Nagios Core 4.5.12 Loaded: loaded (/usr/lib/systemd/system/nagios.service; enabled; preset: disabled) Drop-In: /usr/lib/systemd/system/service.d └─10-timeout-abort.conf Active: active (running) since Fri 2026-05-01 15:52:12 JST; 1min 8s ago Invocation: 29b6d17a31fe4a98b7d35417272a1eeb Docs: https://www.nagios.org/documentation Process: 1266 ExecStartPre=/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg (code=exited, status=0/SUCCESS) Process: 1288 ExecStart=/usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg (code=exited, status=0/SUCCESS) Main PID: 1292 (nagios) Tasks: 8 (limit: 3436) Memory: 8.1M (peak: 9.4M) CPU: 211ms CGroup: /system.slice/nagios.service ├─1292 /usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg ├─1295 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh ├─1296 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh ├─1297 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh ├─1299 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh ├─1300 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh ├─1301 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh └─1305 /usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg May 01 15:52:12 Lepard nagios[1292]: qh: echo service query handler registered May 01 15:52:12 Lepard nagios[1292]: qh: help for the query handler registered May 01 15:52:12 Lepard nagios[1292]: wproc: Successfully registered manager as @wproc with query handler May 01 15:52:12 Lepard nagios[1292]: wproc: Registry request: name=Core Worker 1295;pid=1295 May 01 15:52:12 Lepard nagios[1292]: wproc: Registry request: name=Core Worker 1300;pid=1300 May 01 15:52:12 Lepard nagios[1292]: wproc: Registry request: name=Core Worker 1296;pid=1296 |
5. Access the Nagios Web Interface
Access http://[FQDN]/nagios or http://[IP address]/nagios in any browser.
Username : nagoisadmin
Password : Password specified when the user was created above
[Sign in]
After successful login, the following dashboard will appear
Show host availability
Click on [Hosts] in the left menu
Click [Tactical Overview] on the left menu to view the monitoring data
Click [Current Status] [Services] on the left menu : The current monitoring service details are displayed.
6. Configuring the NRPE Plugin
To monitor the agent, install the following:
6.1 Install the nrpe plugin
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# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.1/nrpe-4.1.1.tar.gz # tar zxvf nrpe-4.1.1.tar.gz # cd nrpe-4.1.1 |
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# ./configure # make all |
If an SSL error occurs when running "make all"
Use the ./configure --disable-ssl flag to disable SSL in the NRPE configuration
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# ./configure --disable-ssl # make all |
Install the NRPE plugin daemon and sample configuration files
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# make install-plugin # make install-daemon # make install-config |
Install the NRPE daemon as a service
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# make install-init |
Open the /usr/local/nagios/etc/nrpe.cfg file and add the IP addresses of the local host and the Nagios monitoring server
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# vi /usr/local/nagios/etc/nrpe.cfg Line 106 : Add allowed_hosts=127.0.0.1,::1,192.168.11.83 |
Check Version
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# /usr/local/nagios/bin/nrpe -V NRPE - Nagios Remote Plugin Executor Version: 4.1.1 |
Start the service and enable it
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# systemctl enable nrpe Created symlink '/etc/systemd/system/multi-user.target.wants/nrpe.service' → '/usr/lib/systemd/system/nrpe.service'. # systemctl restart nrpe |
Open the NRPE port in the firewall
NRPE uses TCP port 5666 by default. If you have a firewall in place, open this port to allow external checks from the Nagios monitoring server.
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# firewall-cmd --add-port=5666/tcp --permanent # firewall-cmd --reload |
Check if port 5666/tcp is listening
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# netstat -na | grep "5666" tcp 0 0 0.0.0.0:5666 0.0.0.0:* LISTEN |
Run the "check_nrpe" command to verify that the NRPE daemon is running properly
The version of NRPE currently installed is displayed
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# /usr/local/nagios/libexec/check_nrpe -H 127.0.0.1 NRPE v4.1.1 |
7. Adding a monitored host
Add the following server to the host and configure it as a target for simple ping death/activity monitoring
OS : Fedora43
IP address : 192.168.11.85
7.1 Configuration File Editing
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# vi /usr/local/nagios/etc/nagios.cfg Line 51 : Uncomment cfg_dir=/usr/local/nagios/etc/servers |
7.2 Directory Create
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# mkdir /usr/local/nagios/etc/servers # chgrp nagios /usr/local/nagios/etc/servers # chmod 750 /usr/local/nagios/etc/servers |
7.3 Create new definition file
The name "korodes.cfg" can be arbitrary.
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# vi /usr/local/nagios/etc/servers/korodes.cfg define host { use linux-server host_name korodes alias korodes address 192.168.11.85 } define service { use generic-service host_name korodes service_description PING check_command check_ping!100.0,20%!500.0,60% } |
7.4 Restart Nagios server
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# systemctl restart nagios.service |
Log in to the Nagios server (http://[server IP address]/nagios) and look at Hosts, and the host is added.
8. Adding Monitoring Services
Add monitoring services to the hosts added above.
OS : Fedora43
IPアドレス : 192.168.11.85
8.1Configuration on the server to be monitored
8.1.1 Agent installed on monitored hosts
Install NRPE and common service plugins
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# dnf -y install nagios-nrpe nagios-plugins-all |
8.1.2 Configuration File Editing
# vi /etc/nagios/nrpe.cfg
Line 106 : Add a host to allow connections (specify Nagios server)
allowed_hosts=127.0.0.1,::1,192.168.11.83
Line 122 : Allow command arguments
dont_blame_nrpe=1
Line 300-304 : Comment and add
# command[check_users]=/usr/lib/nagios/plugins/check_users -w 5 -c 10
# command[check_load]=/usr/lib/nagios/plugins/check_load -r -w .15,.10,.05 -c .30,.25,.20
# command[check_hda1]=/usr/lib/nagios/plugins/check_disk -w 20% -c 10% -p /dev/hda1
# command[check_zombie_procs]=/usr/lib/nagios/plugins/check_procs -w 5 -c 10 -s Z
# command[check_total_procs]=/usr/lib/nagios/plugins/check_procs -w 150 -c 200
Add part of the plugin
command[check_by_ssh]=/usr/lib/nagios/plugins/check_by_ssh $ARG1$
command[check_dhcp]=/usr/lib/nagios/plugins/check_dhcp $ARG1$
command[check_disk]=/usr/lib/nagios/plugins/check_disk $ARG1$
command[check_file_age]=/usr/lib/nagios/plugins/check_file_age $ARG1$
command[check_ftp]=/usr/lib/nagios/plugins/check_ftp $ARG1$
command[check_http]=/usr/lib/nagios/plugins/check_http $ARG1$
command[check_imap]=/usr/lib/nagios/plugins/check_imap $ARG1$
command[check_load]=/usr/lib/nagios/plugins/check_load $ARG1$
command[check_log]=/usr/lib/nagios/plugins/check_log $ARG1$
command[check_mysql]=/usr/lib/nagios/plugins/check_mysql $ARG1$
command[check_ntp]=/usr/lib/nagios/plugins/check_ntp $ARG1$
command[check_ntp_peer]=/usr/lib/nagios/plugins/check_ntp_peer $ARG1$
command[check_ntp_time]=/usr/lib/nagios/plugins/check_ntp_time $ARG1$
command[check_ping]=/usr/lib/nagios/plugins/check_ping $ARG1$
command[check_pop]=/usr/lib/nagios/plugins/check_pop $ARG1$
command[check_spop]=/usr/lib/nagios/plugins/check_spop $ARG1$
command[check_procs]=/usr/lib/nagios/plugins/check_procs $ARG1$
command[check_smtp]=/usr/lib/nagios/plugins/check_smtp $ARG1$
command[check_ssmtp]=/usr/lib/nagios/plugins/check_ssmtp $ARG1$
command[check_ssh]=/usr/lib/nagios/plugins/check_ssh $ARG1$
command[check_swap]=/usr/lib/nagios/plugins/check_swap $ARG1$
command[check_tcp]=/usr/lib/nagios/plugins/check_tcp $ARG1$
command[check_udp]=/usr/lib/nagios/plugins/check_udp $ARG1$
command[check_ups]=/usr/lib/nagios/plugins/check_ups $ARG1$
command[check_users]=/usr/lib/nagios/plugins/check_users $ARG1$
8.1.3 nrpe server activation and startup
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# systemctl enable --now nrpe Created symlink '/etc/systemd/system/multi-user.target.wants/nrpe.service' → '/usr/lib/systemd/system/nrpe.service'. # systemctl start nrpe # systemctl status nrpe ● nrpe.service - Nagios Remote Plugin Executor Loaded: loaded (/usr/lib/systemd/system/nrpe.service; enabled; preset: disabled) Drop-In: /usr/lib/systemd/system/service.d mq10-timeout-abort.conf Active: active (running) since Fri 2026-05-01 16:08:01 JST; 30s ago Invocation: 68c9d5f90c454704a03432d01cadb816 Docs: http://www.nagios.org/documentation Main PID: 5918 (nrpe) Tasks: 1 (limit: 3435) Memory: 1.5M (peak: 1.7M) CPU: 16ms CGroup: /system.slice/nrpe.service mq5918 /usr/bin/nrpe -c /etc/nagios/nrpe.cfg -f May 01 16:08:01 Lion systemd[1]: Started nrpe.service - Nagios Remote Plugin Executor. May 01 16:08:01 Lion nrpe[5918]: Starting up daemon May 01 16:08:01 Lion nrpe[5918]: Server listening on 0.0.0.0 port 5666. May 01 16:08:01 Lion nrpe[5918]: Server listening on :: port 5666. May 01 16:08:01 Lion nrpe[5918]: Warning: Daemon is configured to accept command arguments from clients! May 01 16:08:01 Lion nrpe[5918]: Listening for connections on port 5666 May 01 16:08:01 Lion nrpe[5918]: Allowing connections from: 127.0.0.1,::1,192.168.11.83 |
8.1.4 Open NRPE ports 5666/tcp and 5666/udp on firewall
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# firewall-cmd --permanent --add-port=5666/tcp # firewall-cmd --permanent --add-port=5666/udp # firewall-cmd --reload |
8.2 Nagios Server Side Configuration
8.2.1 commands.cfg edit
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# vi /usr/local/nagios/etc/objects/commands.cfg # Add to the last line define command { command_name check_nrpe command_line $USER1$/check_nrpe -H $HOSTADDRESS$ -c $ARG1$ } |
8.2.2 Edit and add korodes.cfg created when you added the host earlier
I'll add HTTP,SSH,FTP this time.
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# vi /usr/local/nagios/etc/servers/korodes.cfg # Add the following: # 'HTTP' command definition define service{ use local-service host_name korodes service_description HTTP check_command check_http } # 'SSH' command definition define service{ use local-service host_name korodes service_description SSH check_command check_ssh } # 'FTP' command definition define service{ use local-service host_name korodes service_description FTP check_command check_ftp } |
8.2.5 Restart Nagios
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# systemctl restart nagios.service |
8.2.6 Accsess http://[Nagios Server IP Address]/nagios
Newly added monitoring services are added as shown in the figure below.
