Install & configure a Nagios Server

What is Nagios ?

“Nagios is a powerful monitoring system that enables organizations to identify and resolve IT infrastructure problems before they affect critical business processes.” https://www.nagios.org/

In simple words, you can monitor your servers (linux, MSSSQL, etc …) and databases (Oracle, SQL Server, Postgres, MySQL, MariaDB, etc …) with nagios.

We use the free version !!! 😀

VM configuration :

OS     : CentOS Linux 7 
CPU    : Intel(R) Xeon(R) CPU E5-2620 v4 @ 2.10GHz 
Memory : 3GB 
Disk   : 15GB

What we need :

1. We need Nagios Core. This is the brain of our Nagios server. All the configuration will be done in this part (set the contacts, set the notification massages, etc …)
2. We must install Nagios plugins. Plugins are standalone extensions to Nagios Core that make it possible to monitor anything and everything with Core. Plugins process command-line arguments, perform a specific check, and then return the results to Nagios Core
3. The NRPE addon is designed to allow you to execute Nagios plugins on remote Linux/Unix machines. The main reason for doing this is to allow Nagios to monitor “local” resources (like CPU load, memory usage,etc.) on remote machines. Since these public resources are not usually exposed to external machines, an agent like NRPE must be installed on the remote Linux/Unix machines.

Preconditions

All below installation are as root user.

Installation steps

1. Install Nagios Core (I will not explain it. Because their documentation is complete)
   support.nagios.com/kb/article/nagios-core-installing-nagios-core-from-source-96.html#CentOS
2. Install Nagios Plugins

   support.nagios.com/kb/article/nagios-core-installing-nagios-core-from-source-96.html#CentOS

3. Install NRPE
   https://support.nagios.com/kb/article.php?id=515
4. Now you must decide which type of database you want to monitor. Then install the check_health plugin for it (you can install all of them if you want)
   Here we install the Oracle and SQL Server check_health

Install and configure Oracle Check_health

You need Oracle client to communicate with an Oracle instance 

• Download and install check_oracle_health (https://labs.consol.de/nagios/check_oracle_health/index.html)

  wget https://labs.consol.de/assets/downloads/nagios/check_oracle_health-3.2.1.2.tar.gz 
  tar xvfz check_oracle_health-3.2.1.2.tar.gz 
  cd check_oracle_health-3.2.1.2 
  ./configure 
  make 
  make install

• Download and install Oracle Client (here we installed 12c version – https://www.oracle.com/database/technologies/oracle12c-linux-12201-downloads.html)
• Create check_oracle_health_wrapped file in /usr/local/nagios/libexec
• Set parameters+variables needed to start the plugin check_oracle_health

  #!/bin/sh
  ### -------------------------------------------------------------------------------- ###
  ### We set some environment variable before to start the check_oracle_health script.
  ### -------------------------------------------------------------------------------- ###
  ### Set parameters+variables needed to start the plugin check_oracle_health:
  
  export ORACLE_HOME=/u01/app/oracle/product/12.2.0/client_1
  export LD_LIBRARY_PATH=$ORACLE_HOME/lib
  export TNS_ADMIN=/usr/local/nagios/tns
  export PATH=$PATH:$ORACLE_HOME/bin
  
  export ARGS="$*"
  
  ### start the plugin check_oracle_health with the arguments of the Nagios Service:
  
  /usr/local/nagios/libexec/check_oracle_health $ARGS

• Create the tns folder in /usr/local/nagios and then make a tnsnames.ora file and add a tns

  DBTEST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = TCP)(HOST = 172.22.10.2)(PORT = 1521))
      (CONNECT_DATA =
        (SERVER = DEDICATED)
        (SID = DBTEST)
      )
    )

• Test the connection

  [nagios@vmnagios objects]$ check_oracle_health_wrapped --connect DBTEST --mode tnsping

Install and configure MSSQL Check_health

• Download and install the check_mssql_health

  wget https://labs.consol.de/assets/downloads/nagios/check_mssql_health-2.6.4.16.tar.gz
  tar xvfz check_mssql_health-2.6.4.16.tar.gz
  cd check_mssql_health-2.6.4.16
  ./configure 
  make 
  make install

• Download and install freetds  (www.freetds.org/software.html)

  wget ftp://ftp.freetds.org/pub/freetds/stable/freetds-1.1.20.tar.gz
  tar xvfz freetds-1.1.20
  ./configure --prefix=/usr/local/freetds
  make
  make install
  yum install freedts freetds-devel gcc make perl-ExtUtils-CBuilder perl-ExtUtils-MakeMaker

• Download and install DBD-Sybase

  wget http://search.cpan.org/CPAN/authors/id/M/ME/MEWP/DBD-Sybase-1.15.tar.gz
  tar xvfz DBD-Sybase-1.15
  cd DBD-Sybase-1.15
  export SYBASE=/usr/local/freetds
  perl Makefile.PL
  make
  make install

• Add your instance information in : /usr/local/freetds/etc/freetds.conf

Configuration steps

1. Set your domaine name

   [root@vmnagios ~]# cat /etc/resolv.conf
   # Generated by NetworkManager
   search exemple.ads
   nameserver 10.175.222.10

2. Set SMPT and Postfix

   [root@vmnagios ~]# /etc/postfix/main.cf
   ### ----------------- added by dbi-services ---------------- ###
   relayhost = http://smtp.exemple.net
   smtp_generic_maps = hash:/etc/postfix/generic
   sender_canonical_maps = hash:/etc/postfix/canonical
   -------------------------------------------------------- ###

3. Configure Postfix

   [root@vmnagios ~]# cat /etc/postfix/generic
   @localdomain.local [email protected]
   @.exemple.ads [email protected]
   
   [root@vmnagios ~]# cat /etc/postfix/canonical
   root [email protected]
   nagios [email protected]

   After we need to generate the generic.db and canonical.db
   postmap /etc/postfix/generic
   postmap /etc/postfix/canonical

Done ! 🙂

Now you have a new Nagios Server. All you should do is to configure your client and create a config file on your brand new Nagios server.