How tos nagios - centos wiki

HowTos/Nagios - CentOS Wiki http://wiki.centos.org/HowTos/Nagios

Installing Nagios on CentOS 4.x/5.x

Note added 28 Jul 2010: This piece seems to be abandoned, is unmaintained, and refers to
only one of the nagios versions in circulation. Supplemented: 11 Oct 2012 It needs a re-write out
of the conversational style

Contents

1. Installing Nagios on CentOS 4.x/5.x
1. System:
2. References:
3. Packages:
4. General Upgrades
1. Upgrading from 2.4
2. Upgrading from 2.5
5. Set up Apache
6. Installation/Configuration
1. Configure the Nagios Apache file
2. Set up the password file
3. Set up the CGI file
4. Setting up nagios.cfg
7. Object configuration files
1. Timeperiods
2. Contacts/Contacts groups
3. Host and host groups
4. Services
8. Starting Nagios
9. Escalations
10. Extended information
11. Dependencies
12. SELinux
13. That's all, folks!

This document will breeze through installing and configuring everything necessary to get Nagios up and
running. This will not touch in detail on the actual configuration directives Nagios uses. For that,
documentation is readily available from the Nagios website, or available locally after Nagios is
installed. I'll be explaining installation through RPMs and yum from Dag's repo (RPMforge), but source
is available if you prefer to build your own. Again, documentation for this is readily available. Please
see the third-party Repositories section of the CentOS wiki in you don't already know how to enable
repos. This also assumes you already have a working e-mail server in your existing network as well.
That's how notifications will get sent, and that's beyond the scope of this.

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System:
CentOS 4.x/5x (Should work for any RHEL/Fedora flavor.)
Nagios: 2.9

References:

Nagios: http://www.nagios.org/
Official Docs: http://nagios.org/docs/
Community Docs: Repositories
Monitoring Exchange: http://www.monitoringexchange.org/
Web Interfaces: http://www.nagios.org/faqs/viewfaq.php?faq_id=183
Visualization additions: http://www.nagvis.org/

Packages:
nagios-2.9-1.el4.rf
nagios-devel-2.9-1.el4.rf
nagios-plugins-nrpe-2.5.2-1.el4.rf
nagios-plugins-1.4.8-2.el4.rf

Other:

Apache 2.0

General Upgrades
A quick note about upgrading. Generally, upgrading is as simple as typing yum update package_name.
Just to be on the cautious side, backup your configuration files in /etc before upgrading. Secondly,
always read the release notes to make sure configuration files and directives haven't change.

Upgrading from 2.4

A quick note about upgrading. If you're upgrading from version 2.4 (and previous 2.x version), and
you've installed following this guide then a simple yum upgrade will work just fine. As always, it's best
to backup any previous configurations before upgrading just in case something goes awry. Also, from
release 2.4 to 2.5 the only packages that Dag has re-spun are nagios and nagios-devel.

[me@mymachine ~] yum update nagios nagios-plugins nagios-devel nagios-
plugins-nrpe

Upgrading from 2.5

2 of 16 18-Oct-12 8:15 AM


If you're upgrading from version 2.5 to 2.6, Dag's RPMs had a few quirks. Make sure you backup
/etc/nagios before continuing.

[me@mymachine ~] service nagios stop
[me@mymachine ~] cp -ar /etc/nagios /wherever/nagios_2.5_backup
[me@mymachine ~] yum update nagios nagios-plugins nagios-devel nagios-
plugins-nrpe

If cgi.cfg, misccommands.cfg, or checkcommands.cfg are missing or saved as .rpmsave or .rpmnew,
then just copy them back from your backup that you just created. Otherwise, ignore the error just
mentioned because the RPMs have been repaired. Thanks Dag! Also, there is a mistake int he
check_linux_raid.pl script in the contributed plugins. This is easily fixed. Again, if you don't have any
problems running this plugin, then it was fixed as well. This was brought to my attention from the
Nagios mailing list. A user had spooted this and reported things to the packager, so this is probably
resolved by now. Anyways, to correct the check_linux_raid.pl:

[me@mymachine ~] vim /usr/lib/nagios/plugins/contrib/check_linux_raid.pl
Comment out line 26:
use strict;
#use lib utils.pm
use utils qw(%ERRORS);

[me@mymachine ~] nagios -v /etc/nagios/nagios.cfg
[me@mymachine ~] service nagios start

Set up Apache
Make sure you have Apache installed, then you'll need to quickly configure it if not. Chances are you
probably already have some web service running on your machine, but if not, get it running quickly this
way.

[me@mymachine ~] yum install httpd
[me@mymachine ~] vim /etc/httpd/conf/httpd.conf

At least edit the server name directive to your IP address within /etc/httpd/conf/httpd.conf. Then turn on
Apache, and make sure it's set to start.

[me@mymachine ~] chkconfig httpd on
[me@mymachine ~] service httpd start

Now open up a browser and see if your web server is running: http://localhost (or your IP). You
should see the Apache 2 test page. If so, move along.

If you require further assistance with getting Apache going, especially if you have a need to secure the
server, then please follow the documentation at http://www.apache.org. This will get your web server
up and running quickly, but provides no means of security what-so-ever, I just want to warn you. If
you're running completely internal, then it shouldn't be a big deal. Ok, after you get that running, let's
install Nagios and start working on setting it up. By default, the RPMs you are going to install
automatically create a nagios.conf file for Apache to use. This file is in /etc/httpd/conf.d/nagios.conf.

Installation/Configuration

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Nagios requires several different packages be installed so that it may perform the magic it does so
well. The core is the Nagios package itself. Without the plugins package, though, Nagios won't be able
to actually process any checks on your system. The development package obviously contains all the
libraries, headers, and document files for developing Nagios. The other optional packages are the
NRPE package, and the NSCA (Nagios Service Check Acceptor) which I don't use. You may have use
for it, so check out the main site for details. Also, Nagios must run under both the user and group
"nagios." The RPM install takes care of this step for you, so there's no need to create the user and
group.

[me@mymachine ~] yum install nagios nagios-plugins nagios-plugins-nrpe
nagios-devel

It'll go ahead and pull down a few other packages for dependencies as well. That's it for installation.
Let's move back over to Apache's side for a bit.

Configure the Nagios Apache file

Unless you want other options such as SSL configurations or allowing access to the CGI from only
certain hosts, then the default nagios.conf file will suit your needs. Here's what it looks like:

ScriptAlias /nagios/cgi-bin "/usr/lib/nagios/cgi"
<Directory "/usr/lib/nagios/cgi">
# 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 /etc/nagios/htpasswd.users
Require valid-user
Alias /nagios "/usr/share/nagios"
<Directory "/usr/share/nagios">
# 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 /etc/nagios/htpasswd.users
Require valid-user
</Directory>

Unless you want other options configured, that's it for now. Let's set up authentication now.

Set up the password file

If you don't want to use the name "nagiosadmin" simply substitute your name. Remember later on
you'll need to use the same name in some CGI configuration settings.

[me@mymachine ~] htpasswd -c /etc/nagios/htpasswd.users nagiosadmin

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New password: type_your_password
Re-type new password: re-type_your_password
Adding password for user nagiosadmin

It's also up to you if you'd like to create a "guest" account. The guest account would allow viewers to
see various things you specify within Nagios, but it won't give them total access to the CGI interface.
For example, viewers could see host status information, but can't schedule downtime for hosts...things
like this. If you want a guest account, add the account.

[me@mymachine ~] htpasswd /etc/nagios/htpasswd.users guest
New password: type_your_password
Re-type new password: re-type_your_password
Adding password for user guest

NOTE: Notice I took away the "-c" option. This is the create option. Since you already created the file,
make sure any other accounts you add are not with the create option. You'll wipe the file out if you do.

Set up the CGI file

The next step is to set up the users you just created in the main CGI configuration file. I'm going to
assume that you are not using a guest account, and that you have only created one admin
"nagiosadmin" account. Also, ensure you have it set up to use authentication. 1 means on, 0 means off.

[me@mymachine ~] cd /etc/nagios
[me@mymachine nagios] vim cgi.cfg

# AUTHENTICATION USAGE
use_authentication=1

# SYSTEM/PROCESS INFORMATION ACCESS
authorized_for_system_information=nagiosadmin

# CONFIGURATION INFORMATION ACCESS
authorized_for_configuration_information=nagiosadmin

# SYSTEM/PROCESS COMMAND ACCESS
authorized_for_system_commands=nagiosadmin

# GLOBAL HOST/SERVICE VIEW ACCESS
authorized_for_all_services=nagiosadmin
authorized_for_all_hosts=nagiosadmin

# GLOBAL HOST/SERVICE COMMAND ACCESS
authorized_for_all_service_commands=nagiosadmin
authorized_for_all_host_commands=nagiosadmin

Save this file when you are finished editing it. There are a lot of other optional parameters to change or
play with, so have fun customizing the web interface to your liking. Let's test out what you've done so
far. Restart Apache and browse to http://localhost/nagios/. You should see your pretty little web
interface to Nagios now, after you supply the credentials that you just created. You can browse through
the links to the left, but the majority of them won't work because nothing is configured yet.

Setting up nagios.cfg

Once you start checking around in /etc/nagios, you'll see there are few example configuration files to
take a peek at. One being "localhost.cfg." This file uses an all in one approach to configuring the object
files later on. I find this confusing, especially if you eventually have a very large network to monitor.

5 of 16 18-Oct-12 8:15 AM


Instead, you'll split out the configurations into separate files, which will keep you sane later on. Go
ahead and move this file. Previously, the sample files were named "bigger.cfg" and "minimal.cfg" but
with Nagios 2.9 it's now just the one file.

[me@mymachine ~] cd /etc/nagios
[me@mymachine nagios] mv localhost.cfg localhost.cfg_org

Now we're going to open up the main Nagios configuration file. This file is basically self-explanatory
with the comments inside of it. The short version is as follows. Nagios allows you to specify every
configuration from one single file, "localhost.cfg," if so desired. When you have only a few hosts and
services to monitor this idea is rational, but when you have tons of items to monitor this is a bad idea.
It's going to take you a long time to get used to setting up Nagios to begin with, so do yourself a favor
and split out all your files into the categories as mentioned below. Meaning, use a separate file for
hosts and hostgroups, a separate file for services and servicegroups, and a separate file for everything
else you decide to configure. You'll thank me later. Let's start with the basics needed. The external
command options I turn on in order to allow commands to be executed from the CGI web interface.

[me@mymachine nagios] vim nagios.cfg

# OBJECT CONFIGURATION FILE(S)
cfg_file=/etc/nagios/contactgroups.cfg
cfg_file=/etc/nagios/contacts.cfg
cfg_file=/etc/nagios/hostgroups.cfg
cfg_file=/etc/nagios/hosts.cfg
cfg_file=/etc/nagios/services.cfg
cfg_file=/etc/nagios/timeperiods.cfg

# EXTERNAL COMMAND OPTION
check_external_commands=1

# EXTERNAL COMMAND CHECK INTERVAL
command_check_interval=1

Go ahead and save the file. Now, for each file you you specified above you'll need to create the file
because it doesn't exist within /etc/nagios.

[me@mymachine nagios] touch contactgroups.cfg contacts.cfg
hostgroups.cfg hosts.cfg services.cfg timeperiods.cfg
[me@mymachine nagios] chown nagios.nagios contactgroups.cfg
contacts.cfg hostgroups.cfg hosts.cfg services.cfg timeperiods.cfg

One last note about this section. If you are planning on using the external commands on the CGI
interface (check_external_commands), you might run into a few permissions issues. Please check out
the Nagios FAQ interface if you get any errors when you try to run a command on the web interface.
The FAQ is located here: http://nagios.sourceforge.net/docs/2_0/commandfile.html

Object configuration files
As mentioned, when the configuration files are split up, Nagios reads the data from these files in order
for it to process host and service checks across the network. Before I begin, detailed documentation of
all of the options for the template based objects are located at the website. This will help get you
started though, so let's begin with the timeperiods file. Obviously, you can substitute your options if
you want different values.

6 of 16 18-Oct-12 8:15 AM


Timeperiods

[me@mymachine nagios] vim timeperiods.cfg

# '24x7' timeperiod definition
define timeperiod{
timeperiod_name 24x7
alias 24 Hours A Day, 7 Days A Week
sunday 00:00-24:00
monday 00:00-24:00
tuesday 00:00-24:00
wednesday 00:00-24:00
thursday 00:00-24:00
friday 00:00-24:00
saturday 00:00-24:00
}

# 'workhours' timeperiod definition
define timeperiod{
timeperiod_name workhours
alias "Normal" Working Hours
monday 08:00-17:00
tuesday 08:00-17:00
wednesday 08:00-17:00
thursday 08:00-17:00
friday 08:00-17:00
}

# 'nonworkhours' timeperiod definition
define timeperiod{
timeperiod_name nonworkhours
alias Non-Work Hours
sunday 00:00-24:00
monday 00:00-09:00,17:00-24:00
tuesday 00:00-09:00,17:00-24:00
wednesday 00:00-09:00,17:00-24:00
thursday 00:00-09:00,17:00-24:00
friday 00:00-09:00,17:00-24:00
saturday 00:00-24:00
}

# 'none' timeperiod definition
define timeperiod{
timeperiod_name none
alias No Time Is A Good Time
}

You can specify as many of these as you want. For instance, say you have a need to contact folks only
on the weekends. You can create a template "weekends" and use only Friday, Saturday, Sunday with
the appropriate times as you see fit.

Contacts/Contacts groups

Contacts are split into two different files. One holds the actual contact options, and the other holds
contacts together in groups. The groups are whom you specify Nagios to contact later on.

[me@mymachine nagios] vim contacts.cfg

# service_notification_options are w,u,c,r,f,n
# w=warning u=unknown c=critical r=recovery f=flapping n=none

7 of 16 18-Oct-12 8:15 AM


# host_notification_options d,u,r,f,n
# d=down u=unreachable r=recovery f=flapping n=none

define contact{
contact_name me
alias me
service_notification_period 24x7
host_notification_period 24x7
service_notification_options c,r
host_notification_options d,r
service_notification_commands notify-by-email
host_notification_commands host-notify-by-email
email me@myemailaddress.whatever
}

define contact{
contact_name you
alias you
service_notification_period workhours
host_notification_period workhours
service_notification_options c,r
host_notification_options d,r
service_notification_commands notify-by-email
host_notification_commands host-notify-by-email
email you@youremailaddress.whatever
}

You can choose to do as you wish, but for my purposes I only set contacts up to be notified on critical
and recovery alerts. I really have no interest in most things I'm monitoring alerting me when there may
be a temporary glitch, or when something is in a warning state, especially at 4:00 a.m. The reason I
don't is because a) I frequently check the Nagios CGI interface throughout the day, and b) all of my
alerts get forwarded to a ticketing system. With that said, I don't want unnecessary tickets being
generated simply because a plugin failed to execute this time around. If I was very inspired, I could set
up a separate contact and group to receive only the warning and unknowns, and then pipe these through
a different e-mail address. Again, completely adaptive to your needs. Also, I'm using e-mail only. My
e-mail system takes care of processing where the alerts are going. However, you could set up nagios to
pipe messages straight to pagers. Again, check the object configuration options for timeperiods.cfg on
the docs. If you want to see the commands being prosecuted for alerts, check out /etc/nagios
/misccommands.cfg. On to the contact groups.

[me@mymachine nagios] vim contactgroups.cfg

# 'einsteins' contact group definitions
define contactgroup{
contactgroup_name einsteins
alias einsteins
members me,you
}

This is a simple example of contacts and contact groups. You can nest as many possibilities as you
really want to. You can create as many contacts you need as well. It's rather straightforward.

Host and host groups

Host and host group information is stored in the two files hosts.cfg and hostgroups.cfg. Just as you can
mix and match contacts in various contact groups, you can do the same thing with host names in host
groups. I prefer to create template configurations that I can leech off of later on in my configuration file.
It saves you an incredible amount of time typing down the road.

8 of 16 18-Oct-12 8:15 AM


[me@mymachine nagios] vim hosts.cfg

# Generic host definitions
define host{
name generic-host ; Generic
template name
notifications_enabled 1 ; Host
notifications are enabled
event_handler_enabled 1 ; Host event
handler is enabled
flap_detection_enabled 1 ; Flap
detection is enabled
process_perf_data 1 ; Process
performance data
retain_status_information 1 ; Retain status
information across program restarts
retain_nonstatus_information 1 ; Retain
non-status information across program restarts
register 0 ; DONT REGISTER
THIS DEFINITION - ITS NOT A REAL HOST, JUST A TEMPLATE!
}

# This creates a generic template that any host can use.
# Notifies never, checks 15 times before showing critical on CGI
interface,

define host{
name basic-host
use generic-host
check_command check-host-alive
max_check_attempts 15
notification_interval 0
notification_period none
notification_options n
register 0
}

# This creates a generic host that your routers can use
# monitors host(s) 24x7, notifies on down and recovery, checks 15 times
before going critical,
# notifies the contact_group every 30 minutes

define host{
name your-routers-host
use generic-host
check_command check-host-alive
notification_period 24x7
notification_options d,r
register 0
}

define host{
use basic-host
host_name mymachine1
alias mymachine1
address 192.168.100.101
contact_groups einsteins
# notification_options d,r #overrides the basic-host option
}

define host{
use your-routers-host

9 of 16 18-Oct-12 8:15 AM


host_name router1
alias router1
address 192.168.100.100
}

You can begin to see how much time predefined templates can save you down the road when adding
hosts. I'm monitoring around 100 hosts and over 200 services, so doing things the template way can
really be productive in the long haul. It can get a little confusing, but stick to the docs and you'll learn
pretty quickly. When it comes to all of the template object options each file can contain, look for this
http://localhost(or your IP)/nagios/docs/configobject.html. This will help you tremendously, because
there are so many options Nagios allows you to choose from. I split things up because I want
notifications on your-routers-host, but I don't want notification on the basic-host container. If you want
to override the basic-host notification container, then just specify it within the host definition itself.
Starting to understand why you use templates?

Some people have commented that my logic here is confusing, but it will save you a ton of typing. If
you only have a few hosts to be checking on then it probably is overkill. Ok, now on to host groups.

[me@mymachine nagios] vim hostgroups.cfg

define hostgroup{
hostgroup_name basic-clients
alias basic clients
members mymachine1
}

define hostgroup{
hostgroup_name your-routers
alias routers
members router1
}

That's about as simple as this can get. You specify your clients from hosts.cfg into host groups in this
file. You can split them into multiple groups. For instance, mymachine1 can live within both the basic-
clients and your-routers group if you so desired. Pretty simple...

Services

To start, you're going to need at least one service to monitor. This would be a simple check-host-alive,
or ping. Again, you can split things into templates to make it easier down the road just as demonstrated
above.

[me@mymachine nagios] vim services.cfg

# Generic service definition template
define service{
name generic-service ; Generic
service name
active_checks_enabled 1 ; Active
service checks are enabled
passive_checks_enabled 1 ; Passive
service checks are enabled/accepted
parallelize_check 1 ; Active
service checks should be parallelized (Don't disable)
obsess_over_service 1 ; We should
obsess over this service (if necessary)
check_freshness 0 ; Default is to

10 of 16 18-Oct-12 8:15 AM


NOT check service 'freshness'
notifications_enabled 1 ; Service
notifications are enabled
event_handler_enabled 1 ; Service event
handler is enabled
flap_detection_enabled 1 ; Flap
detection is enabled
process_perf_data 1 ; Process
performance data
retain_status_information 1 ; Retain status
information across program restarts
retain_nonstatus_information 1 ; Retain
non-status information across program restarts
register 0 ; DONT REGISTER
THIS DEFINITION - NOT A REAL SERVICE, JUST A TEMPLATE!
}

# Generic for all services
define service{
use generic-service
name basic-service
is_volatile 0
check_period 24x7
normal_check_interval 10
retry_check_interval 2
notification_period none
register 0
}

define service{
use basic-service
name ping-service
notification_options n
check_command check_ping!1000.0,20%!2000.0,60%
register 0
}

define service{
use ping-service
service_description PING
hostgroup_name basic-clients,your-routers
# host_name one_client
}

This is the example of how to nest templates. You can use hostgroup_name or host_name individually.
I've declared a general template to use called "basic-service" which leeches off of the "generic-service"
definitions above that. Then ping-service is used to define it down even lower. The reason I split this
out is because say you want to create another host group called "your-switches," but you want
notifications to go out on this service to a different contact group. Then you just define another service
definition and add this host group to that definition, and apply a different contact group. Ultimately, the
last definitions override all other containers above it. Last man standing type deal. The last option
Nagios sees, is the one it goes by. For example below. The ping-service is still the same, but I want it
to go to a different contact group. Same logic as was explained in the hosts.cfg and hostgroups.cfg file.

define service{
use ping-service
contact_groups group2
hostgroup_name your-switches

11 of 16 18-Oct-12 8:15 AM


}

The services.cfg file can get pretty cumbersome because of all the different checks you can configure.
For instance, you can set it up to check smtp service through check_smtp, http services through
check_http, dhcp, dns, and all sorts of items through SNMP plugins. I'll give you an example of an smtp
service check.

# SMTP - ensure SMTP services are available.
define service{
use basic-service
name smtp-service
service_description SMTP
notification_options c,r
notification_period 24x7
check_command check_smtp
register 0
}

define service{
use smtp-service
hostgroup_name smtp-servers
}

Again, obviously this leeches off the template above it, then defines the actual host groups to check.
The host group smtp-servers would have to exist in hostgroups.cfg, and there would have to be hosts
defined in hosts.cfg.

Before I continue, let me explain a bit as to what actually occurs with these files. Nagios reads the
configuration options from all of these text files. When it's time to process the smtp-service you have
defined, it looks to see what check_command it's supposed to execute. It then looks in the
checkcommands.cfg file to look up what check_smtp is supposed to actually do. This would be:

# 'check_smtp' command definition
define command{
command_name check_smtp
command_line $USER1$/check_smtp -H $HOSTADDRESS$
}

Great it says, I've found it! Nagios now knows to go to /usr/lib/nagios/plugins/ (default path for the
RPM install) and execute the check_smtp plugin it finds there. It substitutes the $HOSTADDRESS$
with the hosts located in the host groups, goes out and checks the server to see if SMTP is running. It
then returns back with a yay or nay, Nagios processes this information according to the options you
have laid out in the configuration files, and displays the information on the CGI interface.

This in essence is how to start setting up Nagios. I've simplified this quite a bit, but you should now
have a good understand of where to at least begin with configuring hosts and services. Look in /usr/lib
/nagios/plugins to see everything you can check out of the box. The list is very large with various
things. Also, check out http://www.monitoringexchange.org to view all sorts of third-party plugins
written by many community members. I do a lot of checks across SNMP, so be sure to check that out.
Also, you can easily write your own plugins to use. There are many extra things you can do within
Nagios itself, such as define escalations and extended service/host information. I'll explain that after
you get Nagios fired up so you can see what it's about.

12 of 16 18-Oct-12 8:15 AM


Starting Nagios
At this point, you should have a working configuration with a host or two for monitoring. Since we
haven't done so yet, let's start the Nagios daemon, configure it to start at boot, and check the
configurations file for errors.

[me@mymachine nagios] chkconfig nagios on
[me@mymachine nagios] nagios -v nagios.cfg

Nagios 2.4
Copyright (c) 1999-2006 Ethan Galstad (http://www.nagios.org)
Last Modified: 05-31-2006
License: GPL

Reading configuration data...

Running pre-flight check on configuration data...

Total Warnings: 85
Total Errors: 0

Things look okay - No serious problems were detected during the
pre-flight check

[me@mymachine nagios] service nagios start

Starting network monitor: nagios

You'll notice my instance has 85 warnings displayed. This is because I have 85 services being checked
that have no contact group(s) associated with the service. Warnings are usually ok to let go. As long as
the check (nagios -v) says "Things look okay" then you're usually fine. To avoid the warnings, simply
do what the warning says and fix the issue it's spewing.

Escalations
Escalations are pretty cool in that they allow you to specify where second, third, fourth, and so on,
notifications can go. For instance, you have the SMTP service set up to notify a contact group every 30
minutes indefinitely until someone resolves the problem. With an escalation set up, you can tell
notifications 2,3,4 to go to this e-mail address, or this pager, and then you can tell notifications 5,6,7 to
go to yet another address or pager, and so on. I use this extensively because I have the first notification
go to ticketing software, I then set all subsequent notifications to go to simply a pager. I don't want
multiple tickets being created by the same incident, but I want Nagios to page the hell out of me until I
respond to the event. Let's take a peek. This assumes you've added this in the nagios.cfg file as well as
created the file in /etc/nagios.

[me@mymachine nagios] vim escalations.cfg
define serviceescalation{
host_name mymachine1
service_description SMTP
first_notification 1
last_notification 0
contact_groups mypager
}

13 of 16 18-Oct-12 8:15 AM


I define host escalations and service escalations all in the same file as above. You can split these two
out just like anything else. Just specify it in the nagios.cfg file to tell the program where the file
resides. I don't split these because I don't have too many escalations to really be concerned with. Your
mileage may vary.

Extended information
Extended information is a bonus feature and is used mainly for just aesthetic reasons on the web
interface. It can be split up into host extended information and service extended information. The things
you can do with this are put pretty little icons beside host names, specify URL's to links outside of
Nagios, and make things look "pretty" on the map systems. I use the service extended information to
point to links outside of nagios hosting MRTG graphs. I'll show you how you can do this. Remember to
specify this file exists in nagios.cfg and create the file.

[me@mymachine nagios] vim serviceextinfo.cfg
# yum's definitions
define serviceextinfo{
host_name yum
notes_url http://mynagiosbox/mrtg/myfile.html
icon_image graph.gif
icon_image_alt View graphs
}

This puts a pretty little icon beside the PING service on the web interface. When you click on this icon,
it takes you directly to the MRTG graph I have running on the same machine. In my case, I have an
internal yum server rsyncing every night to the mirrors. All of the ethernet traffic is graphed through
MRTG, then Nagios points a link to this so it's easy to navigate to. This proves to create a good history
of bandwith usage, and other things. Use some creativity and you can log, graph, and link to just about
anything you want. For example, processes and users logged into a system.

Dependencies
Another interesting file I use is the host and service dependencies options. What this does is set up a
tier of checks before something alarms out. For example, I check a login service of a server that's not a
Linux box. I have about 15 other services being checked on this host, but they are dependent on being
able to login to the machine before processing these checks. When a login is unsuccessful, I don't want
15 services to start freaking out and paging me, so I set up a dependency tree. If login fails, only the
login alarms out...I get one notification for this, not a zillion for all the other checks. You can use this
feature for hosts as well. Again, specify it in the nagios.cfg file and create the files.

define servicedependency{
host_name your_host
service_description LOGIN
dependent_host_name your_host
dependent_service_description another_service
execution_failure_criteria w,u,c
notification_failure_criteria w,u,c
}

The execution failure criteria tells Nagios what it's supposed to do if the "LOGIN" service is down.
Meaning "another_service" won't even bother to check the service if login is on a warning, unknown, or

14 of 16 18-Oct-12 8:15 AM


critical state. The notification failure criteria determines when notifications should not be sent out. If
the login check is in a warning, unknown, or critical status, then no messages will be sent out on
another_service.

Just make sure when you are done adding, editing, or creating new configuration files, that you run the
nagios -v nagios.cfg option. This processes your configuration files and does a check on them prior to
actually refreshing the service.

SELinux
A word about SELinux. I don't use it currently, because in 4.x, it messed with some things, and I haven't
taken the time to learn it. I know in 5, it's supposed to be much more mature, so try it out. I turned it off
when I verified this worked on CentOS 5, so if you run into any strange things, keep SELinux in mind.
A security feature of CentOS 5.2 SELinux prevents the access from the apache httpd server to the
needed /var/nagios files. A CentOS 5.2 workaround is to execute the command:

chcon -R httpd_sys_content_t /var/nagios

Note: It is also reported that. for CentOS 6, the form:

chcon -R --type=httpd_sys_content_t /var/nagios

works, in this later CentOS version.

That's all, folks!
Basically, this is Nagios summed up. I'm simplifying almost everything. I hope I've explained things in a
simple fashion anyways. Documentation for the utility is wonderful, but there's so much documentation
that it's hard to learn where to get started sometimes. If you have a network to maintain, I advocate
getting Nagios (unless you like other utilities) running to big brother your hosts and devices. It's saved
my IT departments' skin on more than one occasion. Like I mentioned before, it'll take you a long time
to get good at it, and it's not easy to figure out at first, but once you get a grip on Nagios, you'll wonder
how you got along without it before. I'm checking everything from simple pings to check host alive
status, to disk usage stats, memory stats, DHCP, DNS, HTTP, temperature in machines rooms, yum
updates, cpu loads, SNMP information from hosts, to anything you can imagine. I'm leaving a lot of
things out, but you get the idea. Virtually anything you can think of keeping an eye on, you can do so
across Nagios. You can write your own plugins, or visit the Monitoring Exchange site I mentioned
earlier to find just about anything.

One more thing I would like to mention is the ability to configure and maintain Nagios solely through
the web interface. Nagios doesn't come with pre-packaged add-ons for doing so, but you can find
information for three different packages here: http://www.nagios.org/faqs/viewfaq.php?faq_id=183. I
personally have not used any of them, but I guess for the command line challenged it could prove
useful.

If you have anything to add or if you notice something wrong, please let me know so I can correct it.
The original is written in HTML, and I have to adapt my formatting to use on this wiki, so there might
be some typos. Enjoy.

15 of 16 18-Oct-12 8:15 AM


As MaxHetrick has apparently departed the CentOS Wiki, this page is now presumably fair game for
those with edit privileges. This page has been recommended as a "clearer" howto.

HowTos/Nagios (last edited 2012-10-11 15:34:46 by RussHerrold)

16 of 16 18-Oct-12 8:15 AM

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