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Nagios : Quick install and configuration guide (Version 1.0)

June 2, 2013 , 11:39 pm


In our last post, we had discussed about network monitoring tools.  There I had mentioned about Nagios, a monitoring tool which can be installed on the server. In this post, I would like to tell about the installation, configuration and using of Nagios.

Abstract

Nagios is an efficient tool for network and system monitoring. However, first install and configuration is pretty intricate since it requires to understand a major part of the official documentation (250pages). This tutorial is for ones who want to quickly build a working configuration so as to monitor simple networks including NFSv4 clients and servers. This guide goes through installation and basicconfiguration of Nagios.

With Nagios you can:

 

  1.  Monitor your entire IT infrastructure
  2.  Spot problems before they occur
  3.  Know immediately when problems arise
  4.  Share availability data with stakeholders
  5.  Detect security breaches
  6.  Plan and budget for IT upgrades
  7.  Reduce downtime and business losses

System Requirements

The only requirement of running Nagios Core is a machine running Linux (or UNIX variant) that has network access and a C compiler installed (if installing from source code).

You are not required to use the CGIs included with Nagios Core. However, if you do decide to use them, you will need to have the following software installed…

  1. A web server (preferrably Apache)
  2. Thomas Boutell’s gd library version 1.6.3 or higher (required by the status map and trends CGIs)

Install

1. Copy distribution and plug in

First, you must get the latest Nagios release (nagios-x.y.tar.gz) and the official Nagios plugins

(nagios-plugins-x.y.z) from http://www.nagios.org/download/. I also advise to get the official

Nagios documentation (http://www.nagios.org/docs/) if you plan to tune the configuration explained here.

Unpack the tarball :

tar xzf nagios-2.0.tar.gz tar xzf nagios-plugins-1.4.2.tar.gz 1.2

2. Create user

First, we need to create the user Nagios will run under :

adduser nagios mkdir /usr/local/nagios

chown nagios.nagios /usr/local/nagios

You will probably want to issue external commands from the web interface. So you need to identify the

user your web-server run as. For Apache, you can get it with :

grep “^User” /etc/httpd/conf/httpd.conf

By default, the user is Apache. See /etc/passwd file or report to you web-server installation if you

are running another web server. Also note that the path to httpd.conf can vary depending on your

system.

We need to create a group whose members include the user your web server is running as and the user

Nagios is running as.

/usr/sbin/groupadd nagcmd

/usr/sbin/usermod -G nagcmd apache

/usr/sbin/usermod -G nagcmd nagios

Recall to replace apache by the user name you obtained at last step.

3. Configuration and compilation

We can now configure and install Nagios. Go to the directory where you untared the distribution and

run :

./configure –prefix=/usr/local/nagios –with-nagios-user=nagios

–with-nagios-group=nagios –with-command-group=nagios

Depending on your system, you should get a configuration like the following :

2Configuration summary for nagios 2.0 02-07-2006 ***:

General Options:

————————-

Nagios executable: nagios

Nagios user/group: nagios,nagios

Command user/group: nagios,nagios

Embedded Perl: no

Event Broker: yes

Install ${prefix}: /usr/local/nagios

Lock file: ${prefix}/var/nagios.lock

Init directory: /etc/rc.d/init.d

Host OS: linux-gnu

Web Interface Options:

————————

HTML URL: http://localhost/nagios/

CGI URL: http://localhost/nagios/cgi-bin/

Traceroute (used by WAP): /bin/traceroute

Now let’s compile and install :

make all

make install

make install-init

make install-config

make install-init allows to run nagios at startup (/etc/rc.d/init.d/nagios). This does

not always work (I had problems on Fedora Core 4) but we see another way to run it at startup later on.

make install-config installs the sample configuration files. This will be useful to setup a basic

configuration.

In order for nagios to be of any use to you, you need to install some plugins. First, install the official

plugins. Go to the directory where you untared nagios-plugin-x.y.z and run :

./configure

make

make install

Configuration

Normally, you should already have some configuration sample files in /usr/local/nagios/etc.

Else, try to run again make install-config. Files should be called xxxx.cfg-sample, so you

need to rename them :

cd /usr/local/nagios/etc

mv bigger.cfg-sample bigger.cfg

The entry point is through nagios.cfg. This file is run first when nagios starts. You may not need a

lot of modifications in this file.

log_file=/usr/local/nagios/var/nagios.log

indicates where the logs will go. Set the appropriate owner of the log file :

chown nagios.nagios /usr/local/nagios/var/nagios.log

Other configuration files are called from nagios.cfg, for instance at lines :

cfg_file=/usr/local/nagios/etc/checkcommands.cfg

cfg_file=/usr/local/nagios/etc/misccommands.cfg

Those files contain commands definition.

And finally, our own configuration will be written in a new file (ma_conf.cfg for instance) so we need

to replace :

cfg_file=/usr/local/nagios/etc/minimal.cfg

By :

cfg_file=/usr/local/nagios/etc/ma_conf.cfg

To create our configuration, we will take minimal.cfg as the basis :

cp minimal.cfg ma_conf.cfg

And now let’s edit it to setup a configuration for a simple network with one monitoring station and one

NFSv4 server.

1. Time periods

Time periods are used to define some monitoring periods. For the time being we can keep 24*7 but you

may need to change it -for instance not to receive alarms if your NFS servers are down during night.

2. Contacts

You will certainly need to add some contacts, which are persons in charge of monitoring the network. By

default they will receive notification in 24*7 by e-mail.

define contact{

contact_name adminNFS

alias Jonathan Lyard

service_notification_period 24×7

host_notification_period 24×7

service_notification_options w,u,c,r

host_notification_options d,r

service_notification_commands notify-by-email

host_notification_commands host-notify-by-email

email adminNFS@localhost

}

Now let’s create a contact group. This one will be used to indicate which contacts should be notified for

each issue. Here is only one group, but feel free to add all groups you need (for instance if the ones in

charge of NFS administration are different from network administrators).

define contactgroup{

contactgroup_name admins

alias Nagios Administrators

members nagios-admin,adminNFS

}

3. Hosts

In addition to localhost, you must specify all hosts your are monitoring. I assume they are all on-link

(in the same LAN as your monitoring station). Else, see Nagios official documentation to get it working

through routers (use parents option).

Here is what is required in order to monitor a machine called nfs2 with IP address 192.168.0.5. Alarms

from this host will be reported to the “admins” group.

define host{

use generic-host ; Name of host template to use

host_name nfs2

alias nfs2

address 192.168.0.5

check_command check-host-alive

max_check_attempts 10

notification_interval 120

notification_period 24×7

notification_options d,r

contact_groups admins

}

4. Hostgroups

In this basic configuration, we will only have one hostgroup. You can define several hostgroups to group

hosts together in Nagios interface.

define hostgroup{

hostgroup_name nfsv4config

alias NFSv4 test configuration

members localhost,nfs2

}

5. Services

Finally, one can find services definition. Services do not necessarily mean real services that run on host

(FTP, POP, HTTP…) but also some other types of metric associated with the host (response to ping,

number of logged-in user, free disk space…).

For instance, to monitor connectivity for localhost and our nfs2 server, we need the following service

definition :

define service{

use generic-service ; Name of service template to use

host_name localhost,nfs2

service_description PING

is_volatile 0

check_period 24×7

max_check_attempts 4

normal_check_interval 5

retry_check_interval 1

contact_groups admins

notification_options w,u,c,r

notification_interval 960

notification_period 24×7

check_command check_ping!100.0,20%!500.0,60%

}

Later on, we will also define a service to monitor NFSv4.

6. Web server configuration

In this step, you will learn how to configure the web-server. I assume you are using Apache, but the

configuration may be similar for other web-servers. Check your own web-server’s documentation to put

it at work.

Add the following lines in httpd.conf (in general /etc/httpd/conf/httpd.conf).

ScriptAlias /nagios/cgi-bin /usr/local/nagios/sbin

Directory /usr/local/nagios/sbin

# SSLRequireSSL

Options ExecCGI

AllowOverride None

Order allow,deny

Allow from all

# Order deny,allow

# Deny from all

# Allow from 127.0.0.1

AuthName Nagios Access

AuthType Basic

AuthUserFile /usr/local/nagios/etc/htpasswd.users

Require valid-user

/Directory

Alias /nagios /usr/local/nagios/share

Directory /usr/local/nagios/share

# SSLRequireSSL

Options None

AllowOverride None

Order allow,deny

Allow from all

# Order deny,allow

# Deny from all

# Allow from 127.0.0.1

AuthName Nagios Access

AuthType Basic

AuthUserFile /usr/local/nagios/etc/htpasswd.users

Require valid-user

/Directory

This configuration enable authentication. The first directory entry is for CGI scripts, the second for html

pages. Of course, you can tune this configuration to fit your requirements.

You can also disable authentication by setting use_authentication=0 in /usr/local/nagios/etc/cgi.cfg

but then, you will not be allowed to run remote commands. Use it only if you have a problem with authentication.

You now need to create one or more users being able to authenticate. For the first one (-c to create the

file htpasswd.users) :

htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin

and for (possible) next users :

htpasswd /usr/local/nagios/etc/htpasswd.users nagiosadmin2

Then, you need to give some rights to the users.

You can do it by editing the file /usr/local/nagios/etc/cgi.cfg.

For instance :

authorized_for_system_information=nagiosadmin,nagiosadmin2

And so on for all line you want to grant privilege to nagiosadmin and nagiosadmin2. I have uncommented

all authorized line and give access to nagiosadmin. I advised to at least do the same if want to be able to

configure everything from the web interface.

For more details on the access rights, read the chapter “Authentication and Authorization in the CGIs” in

Nagios official documentation.

Restart your web browser to take modifications into account :

/usr/sbin/httpd -k restart

You should be able to point http://localhost in your web browser proving that your web server is

up.

You should also be able to point http://localhost/nagios/ and authenticate yourself with one

of the user created previously (htpasswd). At this time, the CGI will not works since Nagios is not

running.

Run Nagios

To run Nagios, you can use the following command to make it start as a foreground process:

/usr/local/nagios/bin/nagios /usr/local/nagios/etc/nagios.cfg &

If make install-init failed to make Nagios run at startup you can add this command to /etc/rc.d/rc.local

(here on FC4 but path and filename can vary depending on distribution).

To check that all configuration files are alright, you can issue :

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

Finally, a useful command to restart Nagios and therefore consider modifications in the configuration

files :

killall -SIGHUP nagios

Enjoy monitoring systems with Nagios!

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