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Install Nagios Core on CentOS 7.5

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Prepare your system

In this how to, we are going to install all files to /opt/nagios.

If you want to delete Nagios Core, just remove this folder and the systemd config.

All commands needs to run as user root or via sudo.

useradd -r nagios

Install dependencies

yum install epel-release
yum check-update

yum group install "Development Tools"
yum install wget unzip libpng-devel gd-devel

Download and install Nagios Core

Check for new versions

In this how to I use Nagios 4.4.2. Check if there is a new version available! 

cd /tmp/
wget https://github.com/NagiosEnterprises/nagioscore/archive/nagios-4.4.2.tar.gz
tar xfv nagios-4.4.2.tar.gz
cd nagioscore-nagios-4.4.2/

./configure --prefix=/opt/nagios --with-nagios-user=nagios --with-nagios-group=nagios
mkdir /opt/nagios
make all
make install
make install-commandmode
make install-config
make install-devel

Start Nagios Core (through systemd - recommended)

Copy the following to the file /lib/systemd/system/nagios.service using your favorite editor.

Pitfall!

If you want to use Nagios with the Statusengine Broker Module, it is required that the Gearman Job Server is running, BEFORE your Nagios gets started!
So you need to make sure that systemd will start the Gearman Job Server first.
To configure this, replace the AFTER= line in the following systemd configuration with this: 

After=network.target gearmand.service
If not already done, install the Gearman Job Server now! 
yum install gearmand
systemctl enable gearmand
systemctl start gearmand

[Unit]
Description=Nagios Core
Documentation=https://www.nagios.org/documentation
After=network.target local-fs.target

[Service]
Type=forking
ExecStartPre=/opt/nagios/bin/nagios -v /opt/nagios/etc/nagios.cfg
ExecStart=/opt/nagios/bin/nagios -d /opt/nagios/etc/nagios.cfg
ExecStop=/bin/kill -s TERM ${MAINPID}
ExecStopPost=/bin/rm -f /opt/nagios/var/rw/nagios.cmd
ExecReload=/bin/kill -s HUP ${MAINPID}

[Install]
WantedBy=multi-user.target

systemctl daemon-reload
systemctl start nagios

Now you can check if your Nagios Core is running using systemctl status nagios:

[root@centos7 nagioscore-nagios-4.4.2]# systemctl status nagios.service
● nagios.service - Nagios Core
   Loaded: loaded (/usr/lib/systemd/system/nagios.service; disabled; vendor preset: disabled)
   Active: active (running) since Fr 2018-08-31 16:56:28 UTC; 10s ago
     Docs: https://www.nagios.org/documentation
  Process: 25804 ExecStart=/opt/nagios/bin/nagios -d /opt/nagios/etc/nagios.cfg (code=exited, status=0/SUCCESS)
  Process: 25803 ExecStartPre=/opt/nagios/bin/nagios -v /opt/nagios/etc/nagios.cfg (code=exited, status=0/SUCCESS)
 Main PID: 25807 (nagios)
   CGroup: /system.slice/nagios.service
           ├─25807 /opt/nagios/bin/nagios -d /opt/nagios/etc/nagios.cfg
           ├─25809 /opt/nagios/bin/nagios --worker /opt/nagios/var/rw/nagios.qh
           ├─25810 /opt/nagios/bin/nagios --worker /opt/nagios/var/rw/nagios.qh
           ├─25811 /opt/nagios/bin/nagios --worker /opt/nagios/var/rw/nagios.qh
           ├─25812 /opt/nagios/bin/nagios --worker /opt/nagios/var/rw/nagios.qh
           └─25813 /opt/nagios/bin/nagios -d /opt/nagios/etc/nagios.cfg

Aug 31 16:56:28 centos7 nagios[25807]: qh: core query handler registered
Aug 31 16:56:28 centos7 nagios[25807]: qh: echo service query handler registered
Aug 31 16:56:28 centos7 nagios[25807]: qh: help for the query handler registered
Aug 31 16:56:28 centos7 nagios[25807]: wproc: Successfully registered manager as @wproc with query handler
Aug 31 16:56:28 centos7 nagios[25807]: wproc: Registry request: name=Core Worker 25812;pid=25812
Aug 31 16:56:28 centos7 nagios[25807]: wproc: Registry request: name=Core Worker 25809;pid=25809
Aug 31 16:56:28 centos7 nagios[25807]: wproc: Registry request: name=Core Worker 25810;pid=25810
Aug 31 16:56:28 centos7 nagios[25807]: wproc: Registry request: name=Core Worker 25811;pid=25811
Aug 31 16:56:28 centos7 nagios[25807]: Successfully launched command file worker with pid 25813
Aug 31 16:56:28 centos7 nagios[25807]: HOST ALERT: localhost;DOWN;SOFT;1;(No output on stdout) stderr: execvp(/opt/nagios/libexec/check_ping, ...) failed. errno is 2: No such file or directory
[root@centos7 nagioscore-nagios-4.4.2]#

To make sure that you Nagios will start automatically on boot, you need to enable the systemd configuration:

systemctl enable nagios.service

Install Nagios Plugins

By default, Nagios will install a sample config with some basic checks. So you need to install the nagios plugins to get them to work.

yum install nagios-plugins-all
echo '$USER1$=/usr/lib64/nagios/plugins' > /opt/nagios/etc/resource.cfg
systemctl restart nagios


Congrats! You installed Nagios Core!

Load Statusengine Broker Module

Now you are ready to install and load the Statusengine Broker Module.

Start Nagios in foreground (expert or debugging)

For some reasons it can be useful to run Nagios in foreground.

You can do this with this command /opt/nagios/bin/nagios /opt/nagios/etc/nagios.cfg

[root@centos7 nagioscore-nagios-4.4.2]# sudo -u nagios /bin/bash
bash-4.2$ /opt/nagios/bin/nagios /opt/nagios/etc/nagios.cfg

Nagios Core 4.4.2
Copyright (c) 2009-present Nagios Core Development Team and Community Contributors
Copyright (c) 1999-2009 Ethan Galstad
Last Modified: 2018-08-16
License: GPL

Website: https://www.nagios.org
Nagios 4.4.2 starting... (PID=26147)
Local time is Fri Aug 31 16:58:26 UTC 2018
wproc: Successfully registered manager as @wproc with query handler
wproc: Registry request: name=Core Worker 26151;pid=26151
wproc: Registry request: name=Core Worker 26148;pid=26148
wproc: Registry request: name=Core Worker 26149;pid=26149
wproc: Registry request: name=Core Worker 26150;pid=26150
Successfully launched command file worker with pid 26152
^C
bash-4.2$

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