Nagios Core 4 on CentOS 7: Part 1 – Installation

A quick foreword, I am not a native Linux SA. If there are corrections to terminology needed or if I have mislabeled something, please, let me know so I can update this page. It took me quite a while to figure out how to allow things to work properly without having to disable SELinux. Thank you!

Beginning from a fresh installation of CentOS 7.

First, we’ll temporarily enable Root SSH Access by editing /etc/ssh/sshd_config.

vi /etc/ssh/sshd_config

Press the I key to begin editing. Note: for the rest of this document, if edits are required, you will likely need to remember this.

Remove the # from before PermitRootLogin Yes.

#LoginGraceTime 2m
PermitRootLogin yes
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

Next, you’ll write quite. Note: to do this you will need to press the Escape key and then type “:wq!” without the quotes to save and exit. (As above with the I key, you will need to remember this.)

:wq!

Restart SSH.

service sshd restart

Open Putty or your favorite SSH method and connect to the device. If you’re using DHCP, you may need to run the command below to get the IP Address.

ip addr show

Next we’ll install dependencies.

yum install -y wget httpd php gcc glibc glibc-common gd gd-devel make net-snmp mod_ssl unzip

Download or SFTP necessary files, the versions I successfully used are listed below.

monitoring-plugins-2.2.tar.gz
nagios-4.3.4.tar.gz
nagios-plugins-2.2.1.tar.gz
nagios-selinux-4.3.4-2.el7.nuxref.x86_64.rpm
nagios-plugins-selinux-2.2.1-1.el7.nuxref.x86_64.rpm

(Nagios SELinux RPMs can be found using this link.)

Next we’ll create the nagios user and groups. (You will be prompted for a password on the next command.)

useradd nagios && passwd nagios
groupadd nagcmd
usermod -a -G nagcmd nagios
usermod -a -G nagcmd apache

Now that everything’s prepared, we’ll extract and install Nagios Core 4.

tar xvf nagios-4.3.4.tar.gz
cd nagios-4.3.4
./configure -with-command-group=nagcmd
make all
make install
make install-init
make install-commandmode
make install-config
make install-webconf

Now, we’ll copy the Event Handlers and apply proper ownership.

cp -R contrib/eventhandlers/ /usr/local/nagios/libexec/
chown -R nagios:nagios /usr/local/nagios/libexec/eventhandlers

Next, we’ll test the config.

/usr/local/nagios/bin/nagios -v /usr/local/nagios/etc/nagios.cfg

On to creation of the web user for Nagios and prepping the web service. (You will be asked to set a password after the next command.)

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
systemctl restart httpd.service
chkconfig --add nagios && chkconfig --level 35 nagios on
systemctl enable httpd.service

Next, we’re going to add a permanent firewall rule for HTTPS, you can change this to HTTP if you would prefer and then we’re restarting the service.

firewall-cmd --zone=public --permanent --add-service=https
systemctl restart firewalld.service

Return to root user directory and remove installer files for Nagios Core 4.

cd ~
rm -rf nagios-4.3.4*

Install Nagios SELinux packages to allow it to run in Enforcing mode then restart Nagios.

yum install nagios-selinux-4.3.4-2.el7.nuxref.x86_64.rpm –y
rm -rf nagios-selinux-4.3.4-2.el7.nuxref.x86_64.rpm
service nagios restart

Extract and Install Nagios Monitoring Plugins.

tar -xvf nagios-plugins-2.2.1.tar.gz
cd nagios-plugins-2.2.1
./configure --prefix=/usr/local/nagios --with-cgiurl=/nagios/cgi-bin
make
make install
make install-root

Remove Nagios Monitoring Plugins installer files.

cd ~
rm -rf nagios-plugins-2.2.1*

Extract and install the monitoring plugins.

cd ~
tar xvf monitoring-plugins-2.2.tar.gz
cd monitoring-plugins-2.2
./configure -with-nagios-user=nagios -with-nagios-group=nagios --prefix=/usr/local/nagios
make
make install

Remove the monitoring plugins installer files.

cd ~
rm -rf monitoring-plugins-2.2*

Install SELinux policy for Plugins.

yum install nagios-plugins-selinux-2.2.1-1.el7.nuxref.x86_64.rpm –y
rm -rf nagios-plugins-selinux-2.2.1-1.el7.nuxref.x86_64.rpm

Change context of Nagios directories for SELinux.

chcon -R --reference=/var/www/html /usr/local/nagios/share
chcon -R --reference=/var/www/html /usr/local/nagios/var
chcon -R --reference=/var/www/cgi-bin /usr/local/nagios/sbin
chcon -R -t httpd_sys_rw_content_t /usr/local/nagios/var/rw

Restart the Nagios service.

service nagios restart

From here you should be able to navigate to your server and make sure everything is working properly.

https://serverip/nagios/

If everything worked well, you should return and disable root SSH access.

vi /etc/ssh/sshd_config

Add # before PermitRootLogin yes.

#LoginGraceTime 2m
#PermitRootLogin yes
#StrictModes yes
#MaxAuthTries 6
#MaxSessions 10

Save and quit vi.

:wq!

Restart SSH.

service sshd restart

And now you’re ready to start configuring your Nagios server.

This post is only one part of a series of Nagios documentation I am be preparing.

Nagios Core 4 on CentOS 7: Part 1 – Installation

Nagios Core 4 on CentOS 7: Part 2 – Installation and Configuration of PNP4Nagios

Nagios Core 4 on CentOS 7: Part 3 – Installation and Configuration of Grafana over HTTPS

Nagios Core 4 on CentOS 7: Part 4 – Installation of V-Shell 2

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