Nagios: System and Network Monitoring potx

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Nagios
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Wolfgang Barth
Nagios
System andNetwork Monitoring
Munich SanFrancisco
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NAGIOS. Copyright
c
 2006 OpenSource PressGmbH
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LibraryofCongressCataloging-in-Publication Data
Barth, Wolfgang
Nagios :system and network monitoring /Wolfgang Barth 1st ed.
p. cm.
Includes index.
ISBN 1-59327-070-4
1. Computer networks Management Automation. I. Title. TK5105.5.B374 2005
004.6 dc22
2005026745
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Contents
Introduction 15
From Source Code to aRunning Installation 23
1Installation 25
1.1Compilingthe Source Code 26
1.2Installingand TestingPlugins 30
1.2.1Installation 30
1.2.2Plugintest 32
1.3Configuration of theWeb Interface 33
1.3.1SettingUpApache 33

1.3.2UserAuthentication 34
2Nagios Configuration 37
2.1The Main Configuration File nagios.cfg 38
2.2Objects—an Overview 41
2.3Defining theMachines to Be Monitored,with host 44
2.4GroupingComputersTogether with hostgroup 46
2.5Defining Services to Be Monitored with service 47
2.6GroupingServices Together with servicegroup 50
2.7Defining Addressees for ErrorMessages: contact 50
2.8The Message Recipient: contactgroup 52
2.9WhenNagios NeedstoDoSomething: the command Object 53
2.10 DefiningaTime Period with timeperiod 54
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2.11 Templates 54
2.12 Configuration Aids for ThoseToo Lazy to Type 56
2.12.1Defining servicesfor severalcomputers. 56
2.12.2One host groupfor allcomputers 57
2.12.3Other configuration aids 57
2.13 CGIConfiguration in cgi.cfg 57
2.14 TheResources File resource.cfg 59
3Startup61
3.1Checking theConfiguration 61
3.2GettingMonitoringStarted 63
3.2.1Manualstart 63
3.2.2Automatic start. 64
3.2.3Making configuration changescomeintoeffect 64
3.3Overviewofthe WebInterface 64
In More Detail 69

4Nagios Basics 71
4.1Taking into Account theNetworkTopology 72
4.2ForcedHostChecks vs.PeriodicReachabilityTests 75
4.3States of Hostsand Services 75
5Service Checksand HowTheyAre Performed79
5.1Testing Network Services Directly 81
5.2Running Pluginsvia Secure Shellonthe Remote Computer 82
5.3The Nagios Remote Plugin Executor 82
5.4Monitoringvia SNMP 83
5.5The Nagios ServiceCheck Acceptor 84
6Pluginsfor NetworkServices 85
6.1StandardOptions 87
6.2ReachabilityTestwithPing 88
6.2.1 check_icmp as aservicecheck 90
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6.2.2 check_icmp as ahostcheck 91
6.3MonitoringMailServers 92
6.3.1MonitoringSMTPwith check_smtp 92
6.3.2POP andIMAP 95
6.4MonitoringFTP andWeb Servers 97
6.4.1FTP services 97
6.4.2Web servercontrol via HTTP 98
6.4.3MonitoringWeb proxies 101
6.5DomainNameServerunder Control 105
6.5.1DNS check with nslookup 106
6.5.2Monitoringthe name serverwith dig 107
6.6Queryingthe Secure ShellServer 108
6.7Generic Network Plugins 110

6.7.1Testing TCPports 110
6.7.2MonitoringUDP ports 112
6.8MonitoringDatabases 114
6.8.1PostgreSQL 115
6.8.2MySQL 119
6.9MonitoringLDAP DirectoryServices 121
6.10 Checking aDHCPServer. 124
6.11 MonitoringUPS withthe Network UPS Tools 126
7Testing LocalResources 133
7.1FreeHardDrive Capacity 134
7.2Utilizationofthe SwapSpace. 136
7.3Testing theSystem Load 137
7.4MonitoringProcesses 138
7.5Checking LogFiles 141
7.5.1The standardplugin check_log 142
7.5.2The modern variation: check_logs.pl 143
7.6KeepingTabsonthe Number of Logged-in Users 144
7.7Checking theSystem Time 145
7.7.1Checking thesystem time via NTP. 145
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7.7.2Checking system time withthe time protocol 146
7.8Regularly Checking theStatusofthe Mail Queue 147
7.9KeepinganEye on theModification Date of aFile 148
7.10 MonitoringUPSswith apcupsd 149
7.11 Nagios MonitorsItself 150
7.11.1Running thepluginmanually withascript 151
7.11.2 check_nagios as atool for CGIprograms. 152
7.12 Hardware Checks withLMSensors 152

7.13 TheDummy Plugin for Tests 154
8Manipulating Plugin Output155
8.1NegatingPluginResults 155
8.2Inserting Hyperlinks with urlize 156
9Executing Pluginsvia SSH 157
9.1The check_by_ssh Plugin 158
9.2Configuring SSH 160
9.2.1GeneratingSSH keypairs on theNagios server. 160
9.2.2Settingupthe user nagios on thetargethost 161
9.2.3Checking theSSH connectionand check_by_ssh 161
9.3Nagios Configuration 162
10 TheNagios RemotePlugin Executor(NRPE)165
10.1Installation 166
10.1.1Distribution-specificpackages. 166
10.1.2Installation from thesourcecode 167
10.2Startingvia theinetDaemon 168
10.2.1 xinetd configuration 168
10.2.2 inetd configuration 169
10.3NRPEConfiguration on theComputer to Be Monitored 170
10.3.1Passing parametersontolocal plugins 171
10.4Nagios Configuration 172
10.4.1NRPEwithout passing parameterson 172
10.4.2Passing parametersoninNRPE 173
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10.4.3Optimizingthe configuration 173
10.5IndirectChecks 174
11 Collecting Information Relevantfor Monitoring with SNMP 177
11.1IntroductiontoSNMP 178

11.1.1The Management Information Base. 179
11.1.2SNMPprotocolversions 183
11.2NET-SNMP 184
11.2.1Toolsfor SNMP requests 184
11.2.2The NET-SNMP daemon 187
11.3Nagios’s OwnSNMPPlugins 196
11.3.1The genericSNMPplugin check_snmp 196
11.3.2Checking severalinterfaces simultaneously. 201
11.3.3Testing theoperating status of individualinterfaces 203
11.4Other SNMP-basedPlugins 205
11.4.1Monitoringharddrive space andprocesseswith nagios-
snmp-plugins 205
11.4.2Observingthe load on networkinterfaces with check-
iftraffic 207
11.4.3The manubulon.com pluginsfor specialapplicationpur-
poses 209
12 TheNagios Notification System 215
12.1Who Should be InformedofWhat, When?. 216
12.2WhenDoesaMessage Occur? 217
12.3The Message Filter 217
12.3.1Switchingmessagesonand off systemwide 218
12.3.2Enablingand suppressing computer andservice-related
messages 219
12.3.3Person-related filter options 221
12.3.4Caseexamples 222
12.4ExternalNotification Programs 224
12.4.1Notification via e-mail 225
12.4.2Notification via SMS 227
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12.5EscalationManagement 231
12.6Dependences betweenHosts andServices as aFilter Criterion 234
12.6.1The standardcase: service dependencies 234
12.6.2Onlyinexceptional cases:hostdependencies 238
13 PassiveTests with theExternalCommandFile 239
13.1The Interfacefor ExternalCommands 240
13.2Passive ServiceChecks 241
13.3Passive Host Checks 242
13.4ReactingtoOut-of-Date Information of Passive Checks 243
14 TheNagios ServiceCheck Acceptor(NSCA) 247
14.1Installation 248
14.2Configuring theNagios Server 249
14.2.1The configuration file nsca.cfg 249
14.2.2Configurung theinetdaemon 251
14.3Client-sideConfiguration 252
14.4Sending Test Resultstothe Server 253
14.5ApplicationExample I: Integrating syslog andNagios 254
14.5.1Preparing syslog-ng for usewithNagios 255
14.5.2Nagios configuration:volatile services 257
14.5.3Resettingerror states manually 258
14.6ApplicationExample II: Processing SNMP Traps 260
14.6.1Receivingtraps with snmptrapd 260
14.6.2Passing on traps to NSCA 261
14.6.3The matching service definition 263
15 DistributedMonitoring 265
15.1SwitchingOnthe OCSP/OCHPMechanism 266
15.2Defining OCSP/OCHPCommands 267
15.3Practical Scenarios. 269
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15.3.1Avoidingredundancy in configuration files 269
15.3.2Defining templates 270
16 TheWeb Interface273
16.1Recognizingand Acting On Problems 275
16.1.1Commentsonproblematichosts 276
16.1.2Taking responsibilityfor problems:acknowledgements 278
16.2AnOverviewofthe IndividualCGI Programs. 279
16.2.1Variationsinstatusdisplay: status.cgi 279
16.2.2Additional information andcontrol center: extinfo.cgi 284
16.2.3Interfacefor externalcommands: cmd.cgi 288
16.2.4The most important things at aglance: tac.cgi 290
16.2.5Networkplan: thetopological mapofthe network(sta-
tusmap.cgi). 291
16.2.6Navigationin3D: statuswrl.cgi 293
16.2.7Queryingthe status withacell phone: statuswml.cgi 295
16.2.8Analyzingdisrupted partialnetworks: outages.cgi 295
16.2.9Queryingthe object definitionwith config.cgi 295
16.2.10 Availabilitystatistics: avail.cgi 296
16.2.11 What events occur, howoften? histogram.cgi 298
16.2.12 Filteringlog entriesafter specificstates: history.cgi 299
16.2.13 Whowas told what,when? notifications.cgi 300
16.2.14 Showingall logfileentries: showlog.cgi 301
16.2.15 Evaluating whatever youwant: summary.cgi 301
16.2.16 Followingstates graphically over time: trends.cgi 303
16.3Planning Downtimes 304
16.3.1Maintenance periods for hosts 305
16.3.2Downtimefor services 306
16.4Additional Information on Hostsand Services 307

16.4.1Extendedhostinformation 307
16.4.2Extendedserviceinformation 310
16.5Configuration Changesthrough theWeb Interfaces:the Restart
Problem 311
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17 Graphic DisplayofPerformance Data 313
17.1Processing Plugin PerformanceDatawithNagios 314
17.1.1The template mechanism 314
17.1.2Using externalcommandstoprocess performancedata. .317
17.2Graphsfor theWeb withNagiosgraph 317
17.2.1Basic installation 318
17.2.2Configuration 319
17.3Preparing PerformanceDatafor Evaluation withPerf2rrd 325
17.3.1Installation 326
17.3.2Nagios configuration 326
17.3.3Perf2rrd in practice 327
17.4The GraphicsSpecialist drraw 330
17.4.1Installation 330
17.4.2Configuration 331
17.4.3Practical application 332
17.5Automated to aLarge Extent: NagiosGrapher 336
17.5.1Installation 336
17.5.2Configuration 338
17.6Other toolsand thelimitsofgraphic evaluation 349
SpecialApplications 351
18 Monitoring WindowsServers 353
18.1NSClient andNC
Net 354

18.1.1Installation 354
18.1.2The check_nt plugin 355
18.1.3Commandswhich can be runwithNSClient andNC Net .356
18.1.4AdvancedfunctionsofNC Net 363
18.2NRPEfor Windows: NRPE NT 371
18.2.1Installation andconfiguration 372
18.2.2Function test 373
18.2.3The Cygwin plugins. 373
18.2.4Perlplugins in Windows 374
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19 Monitoring Room Temperatureand Humidity 377
19.1Sensors andSoftware 378
19.1.1The PCMeasure software for Linux 378
19.1.2The queryprotocol 379
19.2The Nagios Plugin check_pcmeasure 379
20 Monitoring SAPSystems 383
20.1Checking without aLogin: sapinfo 384
20.1.1Installation 384
20.1.2First test. 384
20.1.3The plugin check_sap.sh 386
20.2MonitoringwithSAP’s OwnMonitoringSystem (CCMS) 388
20.2.1CCMS—a shortoverview 388
20.2.2Obtaining thenecessary SAPusage permissionsfor Nagios 390
20.2.3Monitorsand templates 392
20.2.4The CCMS plugins 394
20.2.5Performanceoptimization 398
Appendixes 399
ARapidlyAlternating States:Flapping 401

A.1FlapDetection withServices 402
A.1.1Nagios configuration 403
A.1.2The historymemoryand thechronological progression of
thechanges in state 404
A.1.3Representationinthe Webinterface 404
A.2FlapDetection for Hosts. 406
BEvent Handlers 409
B.1Execution Timesfor theEvent Handler 410
B.2Defining theEvent Handlerinthe ServiceDefinition 411
B.3The HandlerScript 411
B.4ThingstoNoteWhenUsing EventHandlers 413
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CWriting Your OwnPlugins: Monitoring Oracle with the
InstantClient 415
C.1Installingthe OracleInstant Client 416
C.2Establishing aConnectiontothe OracleDatabase. 417
C.3AWrapper Plugin for sqlplus 417
C.3.1How thewrapperworks 418
C.3.2The Perl plugin in detail 419
DAnOverviewofthe Nagios Configuration Parameters 423
D.1The Main Configuration File nagios.cfg 424
D.2CGI Configuration in cgi.cfg 443
D.2.1Authenticationparameters 443
D.2.2Other Parameters. 444
Index447
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Introduction

It’s ten o’clockonMonday morning. Thebossofthe branch officeisinarage.
He’s been waitingfor hoursfor an important e-mail, anditstill hasn’t arrived. It
can only be thefault of themailserver; it’s probably hung yetagain. Butaquick
checkofthe computer showsthatnomails have got stuckinthe queuethere,and
there’snomention either in thelog filethatamail from thesenderinquestionhas
arrived. So where’sthe problem?
Thecentral mail serverofthe companydoesn’t respondtoaping.That’sprobably
theroot of theproblem. Butthe IT departmentatthe companyheadoffice abso-
lutelyinsists that it is nottoblame.Italsocannotpingthe mail node of thebranch
office, butitmaintains that thenetworkatthe head officeisrunning smoothly,
so theproblemmustlie withthe networkatthe branch office. Thesearchfor the
errorcontinues.
Thehumiliating result:the VPNconnectiontoheadoffice wasdown, andalthough
theISDNbackup connectionwas working, no routetothe head office(andthus
to thecentral mail server) wasdefinedinthe backuprouter.Aglobally operating
IT service provider wasresponsible for thenetworkconnections (VPN andISDN)
betweenbranchand head office, for whom somethinglikethis“just doesn’t hap-
pen”.The endresult: many hoursspent searchingfor theerror,anirritated boss
(the meeting for whichthe e-mail wasurgentlyrequiredhas long sincefinished),
andasweating admin.
With aproperlyconfiguredNagios system,the adminstratorwould already have
noticedthe problemateight in themorning andbeen able to isolateits cause
withinafewminutes.Insteadoflosingvaluable time,the IT service provider would
have been informeddirectly. Thetimethenrequiredtoeliminatethe error(in this
case, half an hour)would have been sufficienttodeliverthe e-mail in time.
Asecondexample:somewhere in Germany, theharddrive on whichthe central
Oracledatabasefor ahospitalstoresits logfilesreaches full capacity.Although
this doesnot cause the“lightstogoout”inthe operating room,the database
stops workingand thereisconsiderable disruptiontoworkprocedures: patients
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Introduction
cannotbeadmitted,examination resultscannotbesaved,and reports cannotbe
documented until theproblemhas been fixed.
If thecritical hard drive hadbeen monitoredwithNagios,the IT departmentwould
have been warned at an earlystage.The problemwould notevenhaveoccurred.
With personnelresources becoming more andmorescarce,noITdepartmentcan
really afford to regularlycheck allsystems manually.Networks that aregrowing
more andmorecomplex especially demand theneed to be informedearly on of
disruptions that have occurred or of problems that areabout to happen. Nagios,
theOpenSourcetool for system andnetworkmonitoring, helpsthe administrator
to detectproblems beforethe phonerings off thehook.
Theaim of thesoftware is to informadministratorsquicklyabout questionable
(WARNING)orcritical conditions (CRITICAL).Whatisregardedas“questionable”or
“critical”isdefinedbythe administrator in theconfiguration.AWebpage sum-
mary then informs theadministrator of normally workingsystems andservices,
whichNagios displays in green,ofquestionable conditions (yellow),and of criti-
cal situations (red). Thereisalsothe possibilityofinforming theadministratorsin
charge—depending on specificservices or systems—selectively by e-mail butalso
by paging servicessuchasSMS.
By concentratingontrafficlight states (green,yellow, red),Nagios is distinct from
networktoolsthatdisplay elapsed time graphically (for exampleinthe load of a
WANinterfaceoraCPU throughout an entire day)orthatrecordand measure
networktraffic(howhighwas theproportion of HTTPonaparticular interface?).
Nagios is involvedplainly andsimplywiththe issueofwhether everything is on
agreen light.The software doesanexcellent jobinlookingafter this,not just in
terms of thecurrent status butalsooverlongperiods of time.
Thetests
When checking critical hostsand services, Nagios distinguishesbetween host and
service checks.Ahost check tests acomputer,called host in Nagios slang, for

reachability—as arule, asimple ping is used.Aservice check selectively tests indi-
vidualnetworkservices such as HTTP, SMTP,DNS,etc., butalsorunning processes,
CPU load, or logfiles. Host checks areperformedbyNagios irregularlyand only
whererequired, for exampleifnoneofthe servicestobemonitored can be reached
on thehostbeing monitored. As long as oneservicecan be addressedthere,then
this is basically valid for theentirecomputer,sothatthistestcan be dropped.
Thesimplesttestfor networkservices consists of lookingtosee whether therele-
vant target portisopen, andwhether aserviceislisteningthere.But this doesnot
necessarily mean that,for example, theSSH daemonreally is running on TCPport
22. Nagios thereforeusestests for many servicesthatgoseveral stepsfurther.For
SMTP,for example, thesoftware tests whether themailserveralsoannounces itself
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Introduction
witha“220” output,the so-called SMTP greeting;and for aPostgreSQLdatabase,
it checks whether this will acceptanSQL query.
Nagios becomesespecially interesting throughthe factthatittakesintoaccount
dependencies in thenetworktopology (ifitisconfiguredtodoso).Ifthe target
system can only be reached throughaparticular router that hasjustgonedown,
then Nagios reports that thetargetsystem is “unreachable”, anddoesnot bother to
bombarditwithfurther host andservicechecks.The software puts administrators
in apositionwhere they can more quicklydetect theactualcause andrectify the
situation.
Thesuppliersofinformation
Thegreat strength of Nagios—evenincomparisonwithother networkmonitoring
tools—liesinits modularstructure:the Nagios core doesnot containone single
test. Insteaditusesexternalprogramsfor service andhostchecks,which areknown
as plugins.The basicequipment already containsanumber of standardplugins for
themostimportant applicationcases.Special requests that go beyond theseare
answered—provided that youhavebasic programming knowledge—by pluginsthat

youcan writeyourself. Beforeyou invest time developing these, however, it is
first worthtaking alook in theInternetand browsing throughthe relevant mailing
lists,
1
as thereislively activityinthisarea. Ready-to-useplugins areavailable,
especially in theNagios exchange platform, .
Apluginisasimple program—often just ashell script (Bash, Perl etc.)—that gives
outone of thefourpossible conditions OK,WARNING, CRITICAL, or (withoperating
errors, for example) UNKNOWN.
This meansthatinprinciple Nagios can testeverythingthatcan be measured
or counted electronically: thetemperature andhumidity in theserverroom,the
amount of rainfall, thepresenceofpersons in acertain room at atimewhenno-
body should enter it.There arenolimitstothis, provided that youcan findaway
of providingmeasurement dataoreventsasinformation that can be evaluated by
computer (for example, withatemperatureand humidity sensor,aninfraredsen-
sor, etc.). Apartfromthe standardplugins,thisbook accordinglyintroducesfurther
freelyavailable plugins, such as theuse of aplugintoquery atemperature and
humidity sensor in Chapter 19 from page 377.
Keepingadminsup-to-date
Nagios possessesasophisticatednotification system.Onthe sender side (thatis,
withthe host or service check) youcan configure when whichgroup of persons—
theso-called contactgroups —are informedabout whichconditionsorevents(fail-
1
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Introduction
ure, recovery,warningsetc.).Onthe receiversideyou can also defineonmultiple
levels what is to be donewithacorresponding message—for examplewhether the
system should forward it,depending on thetimeofday,ordiscardthe message.
If aspecific service is to be monitoredseven daysaweek round theclock, for exam-

ple, this doesnot mean that theadministrator in charge willnever be able to take
abreak: instead, youcan instruct Nagiostonotifythe person only from Mondays
to Fridaysbetween 8am and5pm,every twohours at themost. If theadminis-
trator in charge is notable to solve theproblemwithinaspecified period of time,
eighthours for example, then theheadofdepartmentresponsible should receive
amessage.Thisisalsoknown as escalation management.The corresponding
configuration is explainedinChapter 12.5frompage 231.
Nagios can also make useoffreelyconfigurable,externalprogramsfor notifica-
tions, so that youcan integrate anysystem youlike: from e-mail to SMStoavoice
serverthatthe administrator calls up andreceivesavoicemessage concerning the
error.
With itsWeb interface(Chapter 16 from page 273, Nagios provides theadminis-
trator withawiderange of information,clearly arranged according to theissues
involved. Whether theadmin needsasummary of theoverall situation, adisplay
of problematicservices andhosts andthe causesofnetworkoutages, or thesta-
tusofentiregroupsofhosts or services, Nagios provides an individually structured
information page for nearly everypurpose.
Throughthe Webfront end, an administrator can informcolleagues upon accepting
aparticularproblemsothattheycan concentrate on otherthingsthathavenot yet
been seen to.Information already obtained can be stored as commentsonhosts
andservices,justlikescheduled downtimes:Nagios prevents false alarms going off
in theseperiods.
By reviewingpastevents, theWeb interfacecan reveal what problems occurred in
aselected time interval, whowas informed, what thesituation wasconcerningthe
availabilityofahost and/or servicesduringaparticular time period—allthisalso
taking account of downtimes,ofcourse.
Taking in information from outside
Fortests,notifications, etc.,Nagios makesuse of externalprograms, butthe reverse
is also possible:through aseparateinterface(see13.1frompage 240),independent
programscan send status information andcommandstoNagios.The Webinterface

makeswidespreaduse of this possibility, whichallows theadministrator to send
interactive commandstoNagios.But abackup program unknown to Nagios can
also transmit asuccess or failure to Nagios,aswellasasyslog daemon—thereisno
limit to thepossibilitieshere.
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Introduction
Thanks to this interface, Nagios allows distributed monitoring.Thisinvolvesseveral
decentralized Nagios installationssending theirtestresults to acentral instance,
whichthenhelps to maintain an overviewofthe situationfromacentrallocation.
Othertoolsfor network monitoring
Nagios is notthe only tool for monitoring systemsand networks.The most well-
known“competitor,”perhaps on an equalfooting, is BigBrother (BB).Despite a
number of differences,its Webinterfacealsoservesthe same purposeasthatof
Nagios:displayingtothe administrator what is in the“green area”and what is not.
Thereasonwhy theauthorusesNagios insteadofBig Brotherliesinthe license for
BigBrother,onthe BB homepage
2
called BetterThanFreeLicense:the product
continuestobecommercially developedand distributed.Ifyou useBBand earn
moneywithit, youmustbuy thesoftware.The factthatthe software,including the
source code,may notbepassedonormodifiedexceptwiththe explicit permission
of thevendor meansthatitcannotbereconciledwiththe criteria for Open Source
licenses. This meansthatLinux distributors have theirhands tied.
Forthe graphical displayofcertain measured values over aperiodoftime, such
as theload on anetworkinterface, CPU load, or thenumber of mails perminute,
thereare othertoolsthatperformthistaskbetter than Nagios.The original tool is
certainlythe Multi RouterTrafficGrapher MRTG,
3
which, despitegrowingcom-

petition,still enjoys greatpopularity.The relatively young,but very powerfulal-
ternative is calledCacti
4
:thishas alargerrange of applications,can be configured
via Webinterface, andavoidsthe restrictions in MRTG,which can only displaytwo
measured values at thesametimeand cannotdisplay anynegative values.
Nagios itself can also displayperformancedatagraphically,using extensions(Chap-
ter 17 from page 313).Inmanycases this is sufficient, butfor very dedicatedre-
quirements,the useofNagios in tandem withagraphic representation tool such
as MRTG or Cacti is recommended.
AboutThisBook
This book is directed at networkadministratorswho want to findout aboutthe
conditionoftheir systemsand networks usinganOpenSourcetool.Itdescribes
Nagios version2.0,which is somewhat differentfromits predecessors in itsconfig-
uration. Theplugins,onthe otherhand, lead theirown lives, aretoagreatextent
independentofNagios,and arethereforenot restricted to aparticularversion.
2
/>3
/>4
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Introduction
Even though this book is basedonLinux as theoperating system for theNagios
computer,thisisnot arequirement.Mostdescriptionsalsoapplytoother Unix
systems,
5
only system-specificdetails such as startscripts need to be adjusted
accordingly.Nagios currentlydoesnot work under Windows, however.
Thefirstpartofthisbook dealswithgettingNagios up andrunning withasimple
configuration,but onethatissufficient for many uses,asquicklyaspossible.This

is whyChapters1through3do nothavedetaileddescriptionsand treatments of
alloptions andfeatures. Theseare examined in thesecondpartofthe book.
Chapter 4looksatthe details of service andhostchecks,and in particular intro-
ducestheir dependency on networktopologies.
Theoptions available to Nagios for implementing service checks andobtaining their
resultsisdescribedinChapter 5.
This is followedbythe presentation of individualstandardplugins andanumber
of additional,freelyobtainable plugins: Chapter 6takesalook at theplugins that
inspectthe servicesofanetworkprotocoldirectlyfromthe Nagios host,while
Chapter 7summarizesplugins that need to be installedonthe machinethatis
beingmonitored,and for whichNagios needsadditional utilitiestoget them run-
ning.Several auxiliary plugins, whichdonot performany tests themselves, but
manipulate already establishedresults,are introducedinChapter 8.
TwoutilitiesthatNagios requires to runlocal pluginsonremotehosts areintro-
ducedinthe twosubsequentchapters: in Chapter 9the SSH is described, while
Chapter 10 introducesadaemondevelopedspecifically for Nagios.
Wherever networks arebeing monitored, SNMP also needstobeimplemented.
Chapter 11 notonlydescribesSNMP-capable pluginsbut also examines thepro-
tocoland theSNMPworld itself in detail, providingthe background knowledge
needed for this.
TheNagios notificationsystem is introducedChapter 12, whichalsodeals with
notificationusing SMS, escalation management,and taking account of dependen-
cies.
Theinterfacefor externalcommandsisdiscussedinChapter 13; this forms thebasis
of otherNagios mechanisms,suchasthe Nagios ServiceCheck Acceptor (NSCA),
aclient-server mechanismfor transmitting passive testresults,covered in Chapter
14. Theuse of this is shownintwo concrete examples—integrating syslog-ng and
processing SNMP traps.NSCAisalsoarequirementfor distributed monitoring,
discussedinChapter 15.
Even though youmay have already used theWeb interface, youmight still be

wonderingabout allthe detailedoptions that this offers. Chapter 16 triestoanswer
this question as completelyaspossible,supported by very helpfulscreenshots. It
5
Forexample,*BSD, HP-UX, AIX, andSolaris;the author doesnot know of anyNagiosversions
running under MacOSX.
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Introduction
also describesaseries of parameterswhich until nowhavenot been documented
anywhere, except in thesourcecode.
Althoughinits operation,Nagios concentrates primarily on trafficlight signals
(red-yellow-green), thereare ways of evaluating andrepresentingthe performance
dataprovided by plugins, whichare describedindetail in Chapter 17.
Networksare rarely homogeneous, that is,equippedonlywithLinux andother
Unix-based operating systems. ForthisreasonChapter 18 demonstrates what util-
itiescan be used to integrate andmonitor Windowssystems.
Chapter 19 uses theexample of alow-costhardwaresensortoshowhow room
temperatureand humidity can be monitoredsimplyyet effectively.
Nagios can also monitorproprietary commercialsoftware,aslongasmechanisms
areavailable whichcan querystates of thesystem integrated into aplugin. In
Chapter 20, this is describedusing an SAP-R/3system.
Theappendix Nagios Configuration introducesall theparametersofthe twocen-
tral configuration files nagios.cfg and cgi.cfg,while Rapidly Changing States:
Flapping and EventHandler aredevoted to some useful butsomewhatexoticfea-
tures.
Furthernotes on thebook
At thetimeofgoing to press, Nagios 2.0isclose to completion.Whenthisbook is
on themarket, therecould well be some modifications. Relevant notes,aswellas
corrections, in casesomeerrorshaveslippedintothe book,can be found at
.

Note of Thanks
Many peoplehavecontributed to thesuccess of this book.Mythanksgofirstof
alltoDr. Markus Wirtz, whoinitiated this book withhis comment,“Whydon’t you
writeaNagios book,then?!”,whenherefused to acceptmyNagios activitiesas
an excuse for delays in writinganother book.Iwouldalsoliketothank thetwo
technical editors, SteffenWaitz andJ
¨
orgLinge,for theirsupport. Averyspecial
thanks goes to Patricia Jung,who,asthe technical editor for theGermanlanguage
version, overhauled themanuscriptand pestered me withthousands of questions—
whichwas agood thingfor thecompletenessofthe book,and whichhas ultimately
made it easier for thereadertounderstand.
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From Source Code to aRunning
Installation
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