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
# dnf -y install gcc glibc glibc-common gd gd-devel make net-snmp openssl-devel unzip wget gettext autoconf net-snmp-utils automake perl-Net-SNMP
2. Installing Nagios Core
①Download and Extract
# wget https://go.nagios.org/get-core/4-5-12
# tar zxvf 4-5-12
# cd nagios-4.5.12
# ./configure
# make all
➁Create Nagios Users and Groups
# make install-groups-users
groupadd -r nagios
useradd -g nagios nagios
➂Add Apache User to Nagios Group
# usermod -aG nagios apache
④Install Nagios Core
# make install
⑤Install external command files and permissions
# 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 ***
⑥Install Nagios Configuration Files
# 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.
⑦Install Apache configuration files for Nagios
# make install-webconf
/usr/bin/install -c -m 644 sample-config/httpd.conf /etc/apache2/sites-available/nagios.conf
if [ 1 -eq 1 ]; then \
ln -s /etc/apache2/sites-available/nagios.conf /etc/apache2/sites-enabled/nagios.conf; \
fi
*** Nagios/Apache conf file installed ***
# systemctl restart httpd
⑧Create a Systemd service file (install a Systemd unit file)
# make install-daemoninit
/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
Created symlink '/etc/systemd/system/multi-user.target.wants/nagios.service' → '/usr/lib/systemd/system/nagios.service'.
*** Init script installed ***
3. Install Nagios Plugin
①Install the prerequisites for the Nagios plugin
# 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
➁Download the latest code from the Nagios Plugins page
# cd
# wget https://nagios-plugins.org/download/nagios-plugins-2.5.tar.gz
➂Install
# tar -xvf 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:
# ls /usr/local/nagios/libexec
check_apt check_dummy check_ifstatus check_mrtgtraf check_overcr check_snmp check_uptime
check_breeze check_file_age check_imap check_nagios check_pgsql check_spop check_users
check_by_ssh check_flexlm check_ircd check_nntp check_ping check_ssh check_wave
check_clamd check_fping check_jabber check_nntps check_pop check_ssl_validity negate
check_cluster check_ftp check_ldap check_nt check_procs check_ssmtp remove_perfdata
check_dhcp check_hpjd check_ldaps check_ntp check_real check_swap urlize
check_dig check_http check_load check_ntp_peer check_rpc check_tcp utils.pm
check_disk check_icmp check_log check_ntp_time check_sensors check_time utils.sh
check_disk_smb check_ide_smart check_mailq check_nwstat check_simap check_udp
check_dns check_ifoperstatus check_mrtg check_oracle check_smtp check_ups
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.
# 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
# chown apache:apache /usr/local/nagios/etc/htpasswd.users
# chmod 640 /usr/local/nagios/etc/htpasswd.users
5. Starting Nagios
Restart Apache
# systemctl restart httpd
Start and enable the Nagios service
# systemctl enable nagios --now
# systemctl start nagios
Check if the service is running
# systemctl status nagios
● nagios.service - Nagios Core 4.5.12
Loaded: loaded (/usr/lib/systemd/system/nagios.service; enabled; preset: disabled)
Active: active (running) since Thu 2026-06-04 14:20:50 JST; 27s ago
Invocation: fb46e7bbbaf642819737e8e3e238e4d3
Docs: https://www.nagios.org/documentation
Process: 44911 ExecStartPre=/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg (code=exited, status=0>
Process: 44913 ExecStart=/usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg (code=exited, status=0/SU>
Main PID: 44914 (nagios)
Tasks: 6 (limit: 22808)
Memory: 6.9M (peak: 8.4M)
CPU: 210ms
CGroup: /system.slice/nagios.service
├─44914 /usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg
├─44916 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh
├─44917 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh
├─44918 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh
├─44919 /usr/local/nagios/bin/nagios --worker /usr/local/nagios/var/rw/nagios.qh
└─44927 /usr/local/nagios/bin/nagios -d /usr/local/nagios/etc/nagios.cfg
Jun 04 14:20:50 Lepard nagios[44914]: qh: Socket '/usr/local/nagios/var/rw/nagios.qh' successfully initialized
Jun 04 14:20:50 Lepard nagios[44914]: qh: core query handler registered
Jun 04 14:20:50 Lepard nagios[44914]: qh: echo service query handler registered
Jun 04 14:20:50 Lepard nagios[44914]: qh: help for the query handler registered
Jun 04 14:20:50 Lepard nagios[44914]: wproc: Successfully registered manager as @wproc with query handler
Jun 04 14:20:50 Lepard nagios[44914]: wproc: Registry request: name=Core Worker 44916;pid=44916
Jun 04 14:20:50 Lepard nagios[44914]: wproc: Registry request: name=Core Worker 44917;pid=44917
Jun 04 14:20:50 Lepard nagios[44914]: wproc: Registry request: name=Core Worker 44919;pid=44919
Jun 04 14:20:50 Lepard nagios[44914]: wproc: Registry request: name=Core Worker 44918;pid=44918
Jun 04 14:20:51 Lepard nagios[44914]: Successfully launched command file worker with pid 44927
6. Access the Nagios Web Interface
Access http://[IP_Address]/nagios/ with any browser
Username : nagoisadmin
Password : Password specified when the user was created above
After successful login, the following dashboard will appear
Show host availability
Click on [Hosts] in the left menu
Currently, only the Nagios Server is displayed.
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.
7. Nagios Agent Configuration
To monitor the agent. Install the following
・NRPE Agent to run plugins
① Installing Nagios NRPE Agent
# cd
# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.3/nrpe-4.1.3.tar.gz
# tar zxvf nrpe-4.1.3.tar.gz
# cd nrpe-4.1.3
# ./configure
# make check_nrpe
# make install-plugin
➁Open the NRPE port in the firewall
By default, NRPE uses TCP port 5666.
If a firewall is in use, open this port to allow external checks from the Nagios monitoring server.
# firewall-cmd --add-port=5666/tcp
# firewall-cmd --reload
8. Adding a monitored host
Add the following server to the host and configure it as a target for simple ping death/activity monitoring
OS : RockyLinux10.1
IP address : 192.168.11.85
①Configuration File Editing
# vi /usr/local/nagios/etc/nagios.cfg
Line 51 : Uncomment
cfg_dir=/usr/local/nagios/etc/servers
➁ Directory Create
# mkdir /usr/local/nagios/etc/servers
# chgrp nagios /usr/local/nagios/etc/servers
# chmod 750 /usr/local/nagios/etc/servers
➂ Create new definition file
The name "korodes.cfg" can be arbitrary.
# 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%
}
④ Restart Nagios server
# systemctl restart nagios.service
Log in to the Nagios server (http://[server IP address]/nagios) and look at Hosts, and the host is added.
9. Adding Monitoring Services
Add monitoring services to the hosts added above.
OS : RockyLinux10.1
IPアドレス : 192.168.11.85
You need to install the NRPE daemon and the Nagios plugin.
9.1 Configuration on the server to be monitored
①Install the Nagios plugin
# 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
# cd
# wget https://nagios-plugins.org/download/nagios-plugins-2.5.tar.gz
# tar -xvf nagios-plugins-2.5.tar.gz
# cd nagios-plugins-2.5
# ./configure
# make
# make install
➁ Install the NRPE agent on the host to be monitored
# dnf install -y gcc glibc glibc-common openssl openssl-devel perl wget
# cd
# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.3/nrpe-4.1.3.tar.gz
# tar zxvf nrpe-4.1.3.tar.gz
# cd nrpe-4.1.3
# ./configure --enable-command-args
# make all
Create Users and Groups
# make install-groups-users
groupadd -r nagios
useradd -r -g nagios nagios
Install the NRPE binary, the NRPE daemon, and the check_npre plugin
# make install
Install the configuration file
# make install-config
Update the service file
# sh -c "echo >> /etc/services"
# sh -c "echo '# Nagios services' >> /etc/services"
# sh -c "echo 'nrpe 5666/tcp' >> /etc/services"
Install the NPRE service daemon
# make install-init
# systemctl enable nrpe
➂Open the NRPE port in the firewall
# firewall-cmd --add-port=5666/tcp
# firewall-cmd --add-port=5666/udp
# firewall-cmd --reload
④ Configuration File Editing
# vi /usr/local/nagios/etc/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 $ARG1$
⑤ nrpe server activation and startup
# systemctl start nrpe
※To verify that NRPE is running, execute the following command on the Nagios server. If the output looks like this, everything is OK.
# /usr/local/nagios/libexec/check_nrpe -H 192.168.11.85
NRPE v4.1.3
9.2 Nagios Server Side Configuration
① nrpe plugin installation
# dnf install -y gcc glibc glibc-common openssl openssl-devel perl wget
# cd
# wget https://github.com/NagiosEnterprises/nrpe/releases/download/nrpe-4.1.3/nrpe-4.1.3.tar.gz
# tar zxvf nrpe-4.1.3.tar.gz
# cd nrpe-4.1.3
# ./configure --enable-command-args
# make all
➁Install the NRPE binary, the NRPE daemon, and the check_npre plugin
# make install
➂Install the configuration file
# make install-config
④Update the service file
# sh -c "echo >> /etc/services"
# sh -c "echo '# Nagios services' >> /etc/services"
# sh -c "echo 'nrpe 5666/tcp' >> /etc/services"
⑤Install the NPRE service daemon
# make install-init
# systemctl enable nrpe
⑥ commands.cfg edit
# 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 $ARG1$
}
⑦Edit and add korodes.cfg created when you added the host earlier
I'll add HTTP,SSH,FTP this time.
# 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 Restart Nagios
# systemctl restart nagios.service
⑨ Access http://[Nagios Server IP Address]/nagios
Newly added monitoring services are added as shown in the figure below.
