OReilly BSD hacks may 2004 ISBN 0596006799

•
•
•
•
•
•


TableofContents
Index
Reviews
ReaderReviews
Errata
Academic

BSDHacks
ByDruLavigne

Publisher :O'Reilly
PubDate :May2004
ISBN :0-596-00679-9
Pages :300


Lookingforauniquesetofpracticaltips,
tricks,andtoolsforadministratorsandpower
usersofBSDsystems?Fromhacksto
customizetheuserenvironmentto
networking,securingthesystem,and
optimization,BSDHackstakesacreative

approachtosavingtimeandaccomplishing
morewithfewerresources.Ifyouwantmore
thantheaverageBSDuser--toexploreand


experiment,unearthshortcuts,createuseful
tools--thisbookisamust-have.



•
•
•
•
•
•


TableofContents
Index
Reviews
ReaderReviews
Errata
Academic

BSDHacks
ByDruLavigne

Publisher :O'Reilly
PubDate :May2004

ISBN :0-596-00679-9
Pages :300



Credits
AbouttheAuthor

Contributors



Acknowledgments


Preface
WhyBSDHacks?

HowtoUsethisBook




HowThisBookIsOrganized




UsingCodeExamples

ConventionsUsedinThisBook
We'dLiketoHearfromYou


Chapter1.CustomizingtheUserEnvironment
Section0.Introduction

Section1.GettheMostOutoftheDefaultShell





Section2.UsefultcshShellConfigurationFileOptions




Section3.CreateShellBindings




Section5.UsetheMouseataTerminal




Section7.LocktheScreen

Section9.CustomizeUserConfigurations




Section11.UseanInteractiveShell

Section4.UseTerminalandXBindings
Section6.GetYourDailyDoseofTrivia
Section8.CreateaTrashDirectory
Section10.MaintainYourEnvironmentonMultipleSystems
Section12.UseMultipleScreensonOneTerminal


Chapter2.DealingwithFilesandFilesystems
Section12.Introduction

Section13.FindThings




Section14.GettheMostOutofgrep

Section16.FormatTextattheCommandLine




Section18.DOSFloppyManipulation




Section20.DealwithDiskHogs




Section22.RecreateaDirectoryStructureUsingmtree

Section15.ManipulateFileswithsed
Section17.DelimiterDilemma
Section19.AccessWindowsSharesWithoutaServer
Section21.ManageTemporaryFilesandSwapSpace
Section23.GhostingSystems


Chapter3.TheBootandLoginEnvironments
Introduction

Section24.CustomizetheDefaultBootMenu

Section25.ProtecttheBootProcess




Section27.LogaHeadlessServerRemotely




Section29.ProtectingPasswordsWithBlowfishHashes




Section31.CreateanEffective,ReusablePasswordPolicy




Section33.UseOneTimePasswords

Section26.RunaHeadlessSystem
Section28.RemovetheTerminalLoginBanner
Section30.MonitorPasswordPolicyCompliance
Section32.AutomateMemorablePasswordGeneration
Section34.RestrictLogins

Chapter4.BackingUp
Introduction






Section35.BackUpFreeBSDwithSMBFS




Section37.InteractiveCopy




Section39.AutomateRemoteBackups



Section41.PerformClient-ServerCross-PlatformBackupswithBacula

Section36.CreatePortablePOSIXArchives
Section38.SecureBackupsOveraNetwork
Section40.AutomateDataDumpsforPostgreSQLDatabases

Chapter5.NetworkingHacks
Introduction

Section42.SeeConsoleMessagesOveraRemoteLogin




Section43.SpoofaMACAddress




Section45.SurviveCatastrophicInternetLoss




Section47.UnderstandDNSRecordsandTools




Section49.WhyDoINeedsendmail?




Section51.GettheMostOutofFTP

Section53.InteractiveRemoteAdministration

Section44.UseMultipleWirelessNICConfigurations
Section46.HumanizetcpdumpOutput
Section48.SendandReceiveEmailWithoutaMailClient
Section50.HoldEmailforLaterDelivery
Section52.DistributedCommandExecution


Chapter6.SecuringtheSystem
Introduction

Section54.StriptheKernel




Section55.FreeBSDAccessControlLists




Section57.TightenSecuritywithMandatoryAccessControl




Section59.IntrusionDetectionwithSnort,ACID,MySQL,andFreeBSD

Section61.SudoGotchas




Section63.RestrictanSSHserver




Section65.SecureaWirelessNetworkUsingPF




Section67.AutomateSecurityPatches



Section56.ProtectFileswithFlags
Section58.UsemtreeasaBuilt-inTripwire
Section60.EncryptYourHardDisk
Section62.sudoscript
Section64.ScriptIPFilterRulesets
Section66.AutomaticallyGenerateFirewallRules
Section68.ScanaNetworkofWindowsComputersforViruses

Chapter7.GoingBeyondtheBasics





Introduction




Section70.TrafficShapingonFreeBSD




Section72.UsetheFreeBSDRecoveryProcess




Section74.ConsolidateWebServerLogs



Section76.CreateaTradeShowDemo

Section69.TuneFreeBSDforDifferentApplications
Section71.CreateanEmergencyRepairKit
Section73.UsetheGNUDebuggertoAnalyzeaBufferOverflow

Section75.ScriptUserInteraction


Chapter8.KeepingUp-to-Date
Introduction

Section77.AutomatedInstall




Section78.FreeBSDfromScratch




Section80.AutomateUpdates




Section82.BuildaPortWithoutthePortsTree




Section84.NavigatethePortsSystem

Section86.CreateYourOwnStartupScripts



Section88.EasilyInstallUnixApplicationsonMacOSX

Section79.SafelyMergeChangesto/etc
Section81.CreateaPackageRepository
Section83.KeepPortsUp-to-DatewithCTM
Section85.DowngradeaPort
Section87.AutomateNetBSDPackageBuilds


Chapter9.GrokkingBSD
Introduction

Section89.How'dHeKnowThat?




Section90.CreateYourOwnManpages




Section92.Apply,Understand,andCreatePatches

Section94.DetermineWhoIsontheSystem




Section96.LeaveonTime




Section98.RotateYourSignature



Section9.13.FunwithX



Section91.GettheMostOutofManpages
Section93.DisplayHardwareInformation
Section95.SpellingBee
Section97.RunNativeJavaApplications
Section99.UsefulOne-Liners

Index


Credits

AbouttheAuthor
Contributors
Acknowledgments


AbouttheAuthor
DruLavigneistheauthorofONLamp.com'sFreeBSDBasics
columnandhasbeenanavidBSDusersinceFreeBSD2.2.1.As
anITinstructor,shespecializesinnetworking,routing,and
security.SheisalsoresponsibleforISECOM'sProtocol
Database,whichcanbefoundat.


Contributors
Thefollowingpeoplecontributedtheirhacks,writing,and
inspirationtothisbook:
JohnRichard,knownlocallyasJR,isasystemadministrator
inKingston,Ontario,Canada.Histrademarkinthefieldis
hisinsistenceonaFreeBSDboxastheprimaryfirewallona
network.Hehasenjoyedworkingwiththeauthorinthe
pastataprivatecollegeinKingston.Inhissparetime,he
experimentswithFreeBSDandrideshisHarley-Davidson.
[Hack#64]
JoeWarnerisaTechnicalAnalystforSiemensMedical
SolutionsHealthServicesCorporationandhasbeenusing
FreeBSDasaserveranddesktopsinceOctoberof2000.
JoehaslivedinSaltLakeCity,Utahformostofhislifeand
enjoys*BSD,computing,history,andTheMatrix.
[Hacks#35and#59]
DanLangille(runsaconsulting

groupinOttawa,Canada.Hehasfondmemoriesofhis
yearsinNewZealand,wheretheclimateismuchmore
conducivetoyear-roundmountainbiking.Helivesina
houseruledbyfelines.
[Hack#41]
RobertBernier'sprofessionalcareerhasincluded
engineering,accidentinvestigation,andOlympictrials.In
the1980s,hisinterestreturnedtoITwhenherealizedhe
wouldn'thavetouseapunchcardanymore.Eventuallyhe
discoveredLinuxandbythemid-1990shaddevelopeda


passionforallthingsopensource.Today,Robertteachesat
thelocalcommunitycollegeandwritesforanumberofIT
publicationsbasedinNorthAmericaandEurope.
[Hack#12]
KirkRussell()isakerneltesteratQNX
SoftwareSystems( />[Hack#36]
KarlVogelisasystemadministratorfortheC-17Program
Office.He'sworkedatWright-PattersonAirForceBasefor
22yearsandhasaBSinMechanical&Aerospace
EngineeringfromCornellUniversity.
[Hack#32]
HowardOwendiscoveredcomputersbyreadingabout
Conway's"Life"inLifemagazine.Ittookmanyyearsfrom
thatdiscoverytothetimehecouldactuallymakealiving
withthegodforsakenthings.Oncethathappened,however,
Howardturnedintoa"majorgeek."Hehasworkedasa
sysadmin,systemsengineer,andsystemsarchitect.Heis
currentlyemployedbyIBMinSiliconValleysupporting

Linux,buthestillrunsFreeBSDandOpenBSDathome.
[Hacks#61and#62]
DanielHarrisisastudentandoccasionalconsultantinWest
Virginia.Heisinterestedincomputernetworking,
documentation,andsecurity;healsoenjoyswriting,
armchairpolitics,andamateurradio.
[Hack#55]
AndrewGould,CPA,performsfinancialandclinicaldata


analysisforahospitalinTexas.Hisprimarytoolfordata
integrationisaPostgreSQLdatabaseserverrunningon
FreeBSD.AndrewhasbeenusingFreeBSDatbothworkand
homeforfouryears.AndrewhasaBSinEducationanda
BBAinAccountingfromtheUniversityofTexasatAustin.
[Hacks#172.6,#40,#44,and#68]
JimMockisaFreeBSDadminanddeveloperturnedMacOS
Xuseranddeveloper.He'saFreeBSDcommitter,aswellas
anOpenDarwincommitter,andhecurrentlymaintains50+
DarwinPorts.JimisalsoamemberoftheDarwinPortsPort
Managerteam.Hecanbereachedator
throughhispersonalsiteat />[Hack#88]
AvleenVigisasystemsadministratoratEarthLink
(wherehemaintainsthe
company'sweb,mail,news,andotherInternetservicesfor
over8millionusers.Hespendshissparetimewithhis
newbornson,contributingtothevariousInternetandUnix
communities,andenjoyinglife.Afterseizingthedayin
2001andmovingtoLAfromLondon,he'swaitingtosee
wherelifewilltakehimnext.

[Hack#69]
AlexandruPopaisaCCNAstudyingforaCCNP,andis
activelyinvolvedintheFreeBSDcommunityinhisspare
time.Atthetimeofthiswriting,hewasstudyingComputer
ScienceatthePolitechnicaUniversityofBucharest.Healso
maintainscvsup.ro.freebsd.orgoutofabasementina
desertedbuilding,usingalargehamsterarrayforpower.He
canbecontactedat
[Hack#70]


JensSchweikhardtisaGermansoftwareengineerand
Internetwizardwhoisconstantlylookingforinteresting
thingstodo.Asaseven-timeIOCCCwinner,heiswellknownfortakingCcompilerstotheirlimits.Hecontributes
toUnixstandardizationand,ofcourse,toGod'sOwn
OperatingSystem.Whennothacking,Jenshasbeencaught
writingromanticpoetryandridinghisItalianMotoGuzzi
aroundtheSwabianhillsandvalleys.Ifheweregivenone
modestwish,itwouldbeclearskieswhenhegoes
stargazingwithhistelescope.
[Hack#78]
MatthewSeamanis38yearsoldandaformerscientistand
academic(OxfordUniversitypostgraduate).Heisnowa
specialistincomputersystemadministration,network
architecture,andinfrastructuredesign.
[Hacks#49,#50,and#97]
NathanRosenquistfirsttriedFreeBSDin1996,andhas
beenusingUnixeversince.Duringtheday,hecanbefound
developingPerl-basedwebapplicationsandbusiness
automationsoftware.HelivesinShadowHills,California

withhisgirlfriendCarrieandtheirdogNutmeg.
[Hack#39]
AdrianMayo(hasworkedwith
computersfor20years,specializinginthedesignofsafety
andmission-criticalsoftwarefortheaerospaceandmedical
industries.HehasgainedexposuretoBSDUnixthrough
Apple'sMacOSXoperatingsystem.HeisEditorforthe
newsandsupportsite,writingmost
ofthetechnicalcontent,includingtheUnixtutorialsand
DailyUnixtips.


[Hacks#14,#15,and#16]
SebastianStark()worksasasystem
administratorattheMaxPlanckInstituteforBiological
CyberneticsinGermany.Hemanagesabunchof
workstations,aswellasacomputerclusterthatisusedfor
machine-learningresearch.
[Hack#52]
MarlonBerlin()studieslinguistics,
comparativeliterature,andmathematicsinBerlin.Heworks
forDNS:NET,aGermanISP,asasystemsdeveloper.
[Hack#52]
DavidMaxwell()isaNetBSDDeveloper
andmemberoftheNetBSDSecurity-Officerteam.He
attendedUnixUnanimousinTorontosincethefirstmeeting
intheearly`80s,andstillvisitswhenhecan.Hewasan
avidAmigauser,andrelishesagood(orbad)punwhenhe
canmusterone.DavidcurrentlyworksatIntegratedDevice
Technology,Inc.(IDT).

[Hacks#10,#53,#73,#75,and#76]
JulioMerinoVidalisstudyingInformaticsEngineeringatthe
UPCUniversityofBarcelona,Spain.HehasbeenaNetBSD
developersinceNovember2002,workingontheNetBSD
PackagesCollection(and
translatingthewebsitetoSpanish.Healsomaintainshis
ownfreesoftwareprojects,includingBuildtool
(Youcancontacthimat

[Hacks#27and#87]


JanL.Peterson()isaprofessional
systemadministratorwith16yearsofexperienceworking
withmultipleUnixversions(andtheoccasionalWindows
machine).Laidofffromhislastjobwhenthecompanywas
acquiredbyadirectcompetitor,hehasspentthelastcouple
ofyearsasaconsultant.MoreaboutJancanbefoundat
/>[Hack#74]
MichaelVincewasbornin1977.Hisinitialinterestin
computerswasvideogames,buthesoonventuredinto
manyotherareas,suchasprogramming,Unix,theWeb,
andnetworks.HavingcompletedaDiplomainComputer
SystemsandaCCNA,heisanITadministratorforsoftware
companiesandhasbeeninvolvedinlargesoftwareprojects
thatputhisdevelopmentskillstogooduse.Atechnews
junkie,heisalwaysinterestedinthefutureofcomputing.
Healsoenjoysstayinguplatesolvingdifficultproblemsthat
requirecomplexregularexpressionsinPerl,goingtothe
gym,andhangingoutincafes.Heiscurrentlyworkingona

softwareproductcalledEzmin.
[Hack#64]
DanielCarosonehasbeeninvolvedwithNetBSDasauser,
advocate,anddeveloperforover10years.Heisamember
oftheNetBSDSecurityOfficerteam,whichprovides
leadershipforsecuritymatterswithintheprojectand
coordinatesresponsestopublicincidentsand
vulnerabilities.HeisChiefTechnologistfore-Secure,
specializinginsecurityconsultingandmanagementservices
tofinancial,government,andtelecommunications
organizations.Hepromotessecurityawarenessthrough
conferencepresentationsanduniversitylectures.Helivesin
Melbourne,Australia,andwhennotworkingtoohardenjoys
hiking,driving,andastronomy.


[Hack#60]
AaronCrandall,BSEE,hasusedOpenBSDsince2.7.He
currentlyworksfortheOregonGraduateInstituterunning
computersasapart-timeMaster'sstudent.He'sbuiltand
givenawaymoreOpenBSDfirewallsthanhecancount.
Contacthimat
[Hack#45]
chromaticistheTechnicalEditoroftheO'ReillyNetwork.In
practice,thatmeansheeditsONLamp.com(opensource
administrationanddevelopment)and,occasionally,books
likethisone.Outsideofwork,heenjoyscookingand
somehowproducesawholeslewofweirdsoftwarehacks
likeSDLParrot,tinymailtools,andthatPerl6thing.Wade
throughthedisarrayofhiswebsiteat

/>[Hack#92]
BrettWarden,BSEE,specializesinPerlprogrammingand
embeddedsystems.HelivesintheNorthwestwithhiswife,
son,andtwoantisocialcats.He'scurrentlykeepinganeye
outforcontractingandpermanentpositions.Youcanfinda
collectionofoddprojectsat />[Hack#65]


Acknowledgments
IwouldliketothankthemanyBSDandopensourceuserswho
sowillinglysharedtheirexperiences,ideas,andsupport.You
serveasaconstantreminderthatBSDismorethanan
operatingsystemitisacommunity.
Iwouldalsoliketothankallofmystudentsandthereadersof
theFreeBSDBasicscolumn.Yourquestionsandfeedbackfuel
mycuriosity;maythisbookreturnthatfavor.
ThankstoDavidLentsandRobFlickengerforreviewsand
advice.SpecialthankstoJacekArtymiakforhisinvaluableinput
fromtheOpenBSDandNetBSDperspectives.Andfinally,
specialthankstochromatic.Awritercouldn'thaveaskedfora
bettereditor.


Preface
"WhatwasitaboutUNIXthatwonmyheart?...UNIXis
mysteriouswhenyoufirstapproach.Alittleintimidating,
too.Butdespiteanunadornedandoftenplain
presentation,thediscerningsuitorcantellthere'slot
goingonunderthesurface."
ThomasScoville,

/>Whentheabove-mentionedarticlewasfirstpublished,Iwas
stillverymuchaBSDnewbie.Mysparehourswerespent
strugglingwithkernelrecompiles,PPPconnectivity(orlack
thereof),rmandchmoddisasters,andreadingandrereading
everybitofthethenavailabledocumentation.Yet,thatarticle
gavevoicetomyexperience,for,likethequotedauthor,Ihad
stumbleduponoperatingsystemlove.Inotherwords,Iwas
discoveringhowtohackonBSD.
Sincethen,I'velearnedthatthereisanunspokencommonality
betweenthenoviceUnixuserandtheseasonedguru.Itdoesn't
matterwhetheryou'vejustsurvivedyourfirstsuccessful
installationoryou'vejustexecutedacomplexscriptthatwill
saveyourcompanytimeandmoney,thefeelingisthesame.
It'stheexcitementofventuringintounknownterritoryand
discoveringsomethingnewandwonderful.It'sthatsenseof
accomplishmentthatcomeswithfiguringsomethingoutfor
yourself,withfindingyourownsolutiontotheproblemathand.
Thisbookcontains100hackswrittenbyuserswholovehacking
withBSD.You'llfindhackssuitedtoboththenoviceuserand
theseasonedveteran,aswellaseveryoneinbetween.Read
theminanyorderthatsuitsyourpurpose,butkeepthe"onion
principle"inmind.Whileeachhackdoespresentatleastone


practicalsolutiontoaproblem,that'sjusttheouterlayer.Use
yourimaginationtopeelawaydeeperlayers,exposingnew
solutionsasyoudoso.


WhyBSDHacks?

Thetermhackinghasanunfortunatereputationinthepopular
press,whereitoftenreferstosomeonewhobreaksinto
systemsorwreakshavocwithcomputers.Amongenthusiasts,
ontheotherhand,thetermhackreferstoa"quick-n-dirty"
solutiontoaproblemoracleverwaytodosomething.The
termhackerisverymuchacompliment,praisingsomeonefor
beingcreativeandhavingthetechnicalchopstogetthings
done.O'Reilly'sHacksseriesisanattempttoreclaimtheword,
documentthewayspeoplearehacking(inagoodway),and
passthehackerethicofcreativeparticipationontoanew
generationofhackers.Seeinghowothersapproachsystems
andproblemsisoftenthequickestwaytolearnaboutanew
technology.
BSDHacksisallaboutmakingthemostofyourBSDsystem.
TheBSDsoftodayhaveaproudlineage,tracingbacktosome
oftheoriginalhackerspeoplewhobuiltUnixandtheInternetas
weknowittoday.Asyou'dexpect,theyfacedmanyproblems
andsolvedproblemsbothquicklyandelegantly.We'vecollected
someofthatwisdom,bothclassicandmodern,aboutusingthe
commandline,securingsystems,keepingtrackofyourfiles,
makingbackups,and,mostimportantly,howtobecomeyour
ownBSDgurualongtheway.


HowtoUsethisBook
OneofthebeautiesofUnixisthatyoucanbeveryproductive
withsurprisinglylittleknowledge.Evenbetter,eachnewtrick
youlearncanshaveminutesoffofyourday.We'vearranged
thechaptersinthisbookbysubjectarea,notbyanysuggested
orderoflearning.Skiparoundtowhatinterestsyoumostor

solvesyourcurrentproblem.Ifthecurrenthackdependson
informationinanotherhack,we'llincludealinkforyouto
follow.
Furthermore,the"SeeAlso"sectionsattheendofindividual
hacksoftenincludereferencessuchasmanfortune.These
refertothemanualpagesinstalledonyourmachine.Ifyou're
notfamiliarwiththesemanpages,startwith[Hack#89].


HowThisBookIsOrganized
TomasterBSD,you'llhavetounderstandseveraltopics.We've
arrangedthehackslooselyintochapters.Theyare:

Chapter1CustomizingtheUserEnvironment
ThoughmodernBSDshavemyriadgraphicalapplications
andutilities,thecombinedwisdomof35yearsof
command-lineprogramsisjustashellaway.Thischapter
demonstrateshowtomakethemostofthecommandline,
customizingittoyourneedsandpreferences.

Chapter2DealingwithFilesandFilesystems
WhatgoodisknowingUnixcommandsifyouhavenofiles?
Youhavetoslice,dice,andstoredatasomewhere.This
chapterexplainstechniquesforfindingandprocessing
information,whetherit'sonyourmachineoronaserver
elsewhere.

Chapter3TheBootandLoginEnvironments
Thebest-laidsecurityplansofadministratorsoftengoout
thewindowwhenusersenterthepicture.Keepingthebad

guysoffofsensitivemachinesrequiresatwo-pronged
approach:protectingnormaluseraccountsthroughgood
passwordpoliciesandprotectingtheboxesphysically.This
chapterexploresseveraloptionsforcustomizingand
securingthebootandloginprocesses.


Chapter4BackingUp
Afteryoustartcreatingfiles,you'reboundtorunacross
datayoucan'taffordtolose.That'swherebackupscomein.
Thischapteroffersseveralideasforvariousmethodsof
ensuringthatyourpreciousdatawillpersistinthefaceof
tragedy.

Chapter5NetworkingHacks
Unlessyou'readie-hardindividualist,you'relikely
connectedtoanetwork.Thatfactpresentsseveralnew
opportunitiesforcleverhacksaswellasmystifyingfailures.
Thischapterilluminateswaystotakeadvantageofyour
networkconnection.

Chapter6SecuringtheSystem
Securityisasmuchamindsetasitisaprocess.Knowing
thetoolsatyourdisposalwillhelp.Thischapterdelvesinto
multipletoolsandideasforincreasingthesecurityofyour
systems,whetherkeepingoutthebadguysorstayingon
topofupdates.

Chapter7GoingBeyondtheBasics
Withyearsandyearsofrefinement,theBSDsprovide

powerfulandmaintainableenvironments.Areyoutaking
fulladvantageofeverythingyoursystemhastooffer?This
chapterpushestheenvelopeofwhatyoucanaccomplish.


Chapter8KeepingUp-to-Date
NobraggingaboutBSDiscompletewithoutmentioningthe
portsorpackagessystemthatkeepsthousandsof
applicationsrightatyourfingertips.Keepingup-to-date
couldneverbeeasier,couldit?Thischaptertacklesthe
subjectofinstallingandupdatingsoftware,includingthe
coresystem.

Chapter9GrokkingBSD
YoucannotbeatrueBSDmasteruntilyougroktheUnix
mindset.Howdidthegurusbecomegurus?Isthetruepath
stillopen?Thischapterrevealssomesecretsofthemasters
andhasalittlefunalongtheway.


ConventionsUsedinThisBook
Thisbookusesthefollowingtypographicalconventions:

Italic
Indicatesnewterms,URLs,emailaddresses,filenames,
pathnames,anddirectories.

Constantwidth
Indicatescommands,options,switches,variables,
attributes,functions,userandgroupnames,thecontentsof

files,andtheoutputfromcommands.

Constantwidthbold
Incodeexamples,showscommandsorothertextthat
shouldbetypedliterallybytheuser.

Constantwidthitalic
Showstextthatshouldbereplacedwithuser-supplied
values.

Color
Thesecondcolorisusedtoindicateacross-referencewithin


thetext.

Thisiconsignifiesatip,suggestion,orgeneralnote.

Thisiconindicatesawarningorcaution.

Thethermometericons,foundnexttoeachhack,indicatethe
relativecomplexityofthehack:

beginner

moderate

expert