The Linux Command Line-09.12

8/13/2019 The Linux Command Line-09.12

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The Linux

Command Line

William E. Shotts, Jr.

A LinuxCommand.org Book


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Copyright 2008-2009, William E. Shotts, Jr.

This work is licese! "!er the Creati#e Commos $ttri%"tio-&ocommercial-&o'eri#ati#e Works (.0 )ite! States *icese. To #iew a copy o+ this licese, #isit

httpcreati#ecommos.orgliceses%y-c-!(.0"s or se! a letter to Creati#eCommos, / Seco! Street, S"ite (00, Sa racisco, Cali+oria, 910, )S$.

*i"3 is the registere! tra!emark o+ *i"s Tor#al!s. $ll other tra!emarks %elog totheir respecti#e owers.

This %ook is part o+ the *i"3Comma!.org pro4ect, a site +or *i"3 e!"catio a!a!#ocacy !e#ote! to helpig "sers o+ legacy operatig systems migrate ito the +"t"re.5o" may cotact the *i"3Comma!.org pro4ect at httpli"3comma!.org.

6rite! copies o+ this %ook, i large, easy-to-rea!-+ormat, are a#aila%le +orp"rchase +rom l"l".com. 7r!ers may %e place! at the +ollowig

httpwww.l"l".comcotetpaper%ack-%ookthe-li"3-comma!-lie/9181

Release History

Version Date Description

09.2 'ecem%er 1, 2009 irst E!itio.

09. &o#em%er 9, 2009 o"rth !ra+t with almost all re#iewer +ee!%ackicorporate! a! e!ite! thro"gh chapter (/.

09.0 7cto%er (, 2009 Thir! !ra+t with re#ise! ta%le +ormattig,

partial applicatio o+ re#iewers +ee!%ack a!e!ite! thro"gh chapter 8.

09.08 $"g"st 2, 2009 Seco! !ra+t icorporatig the +irst e!itigpass.

09.0/ J"ly 8, 2009 Complete! +irst !ra+t.
http://creativecommons.org/licenses/by-nc-nd/3.0/us/http://linuxcommand.org/http://linuxcommand.org/http://www.lulu.com/content/paperback-book/the-linux-command-line/7594184http://linuxcommand.org/http://www.lulu.com/content/paperback-book/the-linux-command-line/7594184http://creativecommons.org/licenses/by-nc-nd/3.0/us/


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Table of Contents

Part 1 Introduction.........................................................................1

1 Introduction................................................................................................2

Why Use The Command Line?.......................................................................................2What This Book Is About.................................................................................................3Who Shoud !ead This Book..........................................................................................3What"s In This Book.........................................................................................................#$o% To !ead This Book..................................................................................................&

'rere(uisites...............................................................................................................&Why I )on"t Ca It *+,U-Linux.............................................................................&

A/kno%edgments...........................................................................................................01our eedba/k Is ,eeded..............................................................................................4urther !eading...............................................................................................................4Coo5hon.........................................................................................................................4

Part 2 Learning The Shell..............................................................

2 What Is The Shell?...................................................................................10Termina 6muators........................................................................................................781our irst 9eystrokes....................................................................................................78

Command $istory.....................................................................................................77Cursor :o;ement.....................................................................................................77

A e% Words About :i/e And o/us...................................................................77Try Some Sim5e Commands........................................................................................726nding A Termina Session............................................................................................73

The Consoe Behind The Curtain........................................................................73urther !eading.............................................................................................................73

3 Navigation.................................................................................................1

Understanding The ie System Tree............................................................................7#The Current Working )ire/tory......................................................................................7#Listing The Contents

i


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Im5ortant a/ts About ienames........................................................................7>

!"#loring The S$ste%.............................................................................20

:ore un With s...........................................................................................................28


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%hatis )is5ay A ery Brie= )es/ri5tion


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Com5etion....................................................................................................................>0'rogrammabe Com5etion..................................................................................>>

Using $istory.................................................................................................................>>Sear/hing $istory.....................................................................................................>@$istory 6x5ansion.....................................................................................................@7

s/ri5t....................................................................................................................@7

Summing U5..................................................................................................................@2urther !eading.............................................................................................................@2

10 er%issions............................................................................................3


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:odi=ying The 6n;ironment.........................................................................................73#Whi/h ies Shoud We :odi=y?.............................................................................73#Text 6ditors.............................................................................................................73#Using A Text 6ditor.................................................................................................73&

Why Comments Are Im5ortant..........................................................................73>A/ti;ating

Part ' Common Tas(s #nd $ssential Tools.............................1)

1& ac,age 'anage%ent..........................................................................10

#


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'a/kaging Systems.....................................................................................................748$o% A 'a/kage System Works...................................................................................747

'a/kage ies.........................................................................................................747!e5ositories............................................................................................................747)e5enden/ies.........................................................................................................742$igh And Lo%e;e 'a/kage Toos........................................................................742

Common 'a/kage :anagement Tasks.......................................................................743inding A 'a/kage In A !e5ository........................................................................743Instaing A 'a/kage rom A !e5ository.................................................................743Instaing A 'a/kage rom A 'a/kage ie.............................................................74#!emo;ing A 'a/kage.............................................................................................74#U5dating 'a/kages rom A !e5ository..................................................................74&U5grading A 'a/kage rom A 'a/kage ie...........................................................74&Listing Instaed 'a/kages......................................................................................740)etermining I= A 'a/kage Is Instaed.....................................................................740)is5aying In=o About An Instaed 'a/kage...........................................................744inding Whi/h 'a/kage Instaed A ie.................................................................744

Summing U5................................................................................................................744The Linux So=t%are Instaation :yth.................................................................74>

urther !eading..........................................................................................................74@

1+ Storage 'edia.......................................................................................1-0

:ounting And Unmounting Storage )e;i/es..............................................................7>8ie%ing A List 2

Why Unmounting Is Im5ortant...........................................................................7>&)etermining )e;i/e ,ames....................................................................................7>0

Creating ,e% ie Systems.........................................................................................7>@:ani5uating 'artitions With =disk..........................................................................7>@Creating A ,e% ie System With mk=s..................................................................7@2

Testing And !e5airing ie Systems............................................................................7@3What The =s/k?..................................................................................................7@3

ormatting o55y )isks..............................................................................................7@3:o;ing )ata )ire/ty To-rom )e;i/es.......................................................................7@#Creating C)!


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=t5............................................................................................................................28#=t5 A Better =t5.....................................................................................................280

%get........................................................................................................................280Se/ure Communi/ation With !emote $osts...............................................................280

ssh..........................................................................................................................284Tunneing With SS$..........................................................................................278

s/5 And s=t5............................................................................................................277An SS$ Cient or Windo%s?............................................................................272

urther !eading..........................................................................................................272

1- Searching (or (iles..............................................................................213

o/ate ind ies The 6asy Way...............................................................................273Where )oes The o/ate )atabase Come rom?..............................................27&

=ind ind ies The $ard Way...................................................................................27&Tests.......................................................................................................................270'rede=ined A/tions..................................................................................................227User )e=ined A/tions..............................................................................................223

Im5ro;ing 6==i/ien/y...............................................................................................22#xargs.......................................................................................................................22#)eaing With unny ienames..........................................................................22&

A !eturn To The 'ayground..................................................................................220

urther !eading..........................................................................................................22@

1 )rchiving )nd 6ac,u#.........................................................................230

Com5ressing ies.......................................................................................................238gHi5.........................................................................................................................237bHi52.......................................................................................................................233

)ont Be Com5ressi;e Com5usi;e...................................................................23#Ar/hi;ing ies.............................................................................................................23#

tar............................................................................................................................23#Hi5...........................................................................................................................2#8

Syn/hroniHing ies And )ire/tories............................................................................2#2Using rsyn/


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'Aternation...................................................................................................................2&@Duanti=iers...................................................................................................................208

? :at/h An 6ement Kero


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=mt A Sim5e Text ormatter................................................................................3735r ormat Text or 'rinting..................................................................................3745rint= ormat And 'rint )ata................................................................................37>

)o/ument ormatting Systems...................................................................................327gro==.........................................................................................................................322

Summing U5................................................................................................................32>

urther !eading..........................................................................................................32>

23 rinting..................................................................................................330

A Brie= $istory

$o% To Write A She S/ri5t.........................................................................................3&>S/ri5t ie ormat........................................................................................................3&@6xe/utabe 'ermissions..............................................................................................308S/ri5t ie Lo/ation......................................................................................................308

+ood Lo/ations or S/ri5ts....................................................................................302:ore ormatting Tri/ks................................................................................................302

Long


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Indentation And Line Continuation.........................................................................302Con=iguring ;im or S/ri5t Writing.....................................................................303

Summing U5................................................................................................................30#urther !eading..........................................................................................................30#

2+ Starting ) ro9ect.................................................................................3+&

irst StageQ :inima )o/ument...................................................................................30&Se/ond StageQ Adding A Litte )ata............................................................................304ariabes And Constants.............................................................................................30>

Assigning aues To ariabes And Constants.......................................................347$ere )o/uments.........................................................................................................342Summing U5................................................................................................................34&urther !eading..........................................................................................................34&

2 To#:*o5n *esign.................................................................................3+

She un/tions............................................................................................................344Lo/a ariabes............................................................................................................3>89ee5 S/ri5ts !unning..................................................................................................3>7

She un/tions In 1our .bashr/ ie..................................................................3>#Summing U5................................................................................................................3>#urther !eading..........................................................................................................3>#

2- (lo5 Control; 6ranching With if.........................................................3-&

i=...................................................................................................................................3>&6xit Status...................................................................................................................3>0test...............................................................................................................................3>>

ie 6x5ressions.....................................................................................................3>>String 6x5ressions..................................................................................................3@7Integer 6x5ressions................................................................................................3@2

A :ore :odern ersion

:enus..........................................................................................................................#8@Summing U5................................................................................................................#77

6xtra Credit.............................................................................................................#77urther !eading...........................................................................................................#77

30 (lo5 Control;


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Loo5ing........................................................................................................................#72%hie........................................................................................................................#72

Breaking

31 Troubleshooting...................................................................................1

Synta/ti/ 6rrors...........................................................................................................#7@:issing Duotes.......................................................................................................#28:issing


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3& Strings )nd Nu%bers..........................................................................&

'arameter 6x5ansion..................................................................................................#&4Basi/ 'arameters...................................................................................................#&46x5ansions To :anage 6m5ty ariabes...............................................................#&>6x5ansions That !eturn ariabe ,ames..............................................................#08

String 0

Tra5s............................................................................................................................#>>Tem5orary ies.................................................................................................#@7

Asyn/hronous 6xe/ution.............................................................................................#@2%ait.........................................................................................................................#@2

,amed 'i5es...............................................................................................................#@3Setting U5 A ,amed 'i5e.......................................................................................#@#Using ,amed 'i5es................................................................................................#@#

Summing U5................................................................................................................#@&urther !eading..........................................................................................................#@&

Inde"..............................................................................................................+

3ii


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6art tro!"ctio

'art 7 Introdu/tion


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tro!"ctio

1 Introduction

wat to tell yo" a story.

&o, ot the story o+ how, i 99, *i"s Tor#al!s wrote the +irst #ersio o+ the *i"3kerel. 5o" ca rea! that story i lots o+ *i"3 %ooks. &or am goig to tell yo" thestory o+ how, some years earlier, :ichar! Stallma %ega the ;&) 6ro4ect to create a +ree

)i3-like operatig system. Thatay people speak o+ ?+ree!om@ with regar! to *i"3, %"t !o


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Why )se The Comma! *ie

the comp"ter, he e#er to"ches a mo"se tay other %ooks try to %roa!e their appeal %yicl"!ig other plat+orms s"ch as geeric )i3 a! >ac7S G. !oig so, they ?water!ow@ their cotet to +eat"re oly geeral topics. This %ook, o the other ha!, olyco#ers cotemporary *i"3 !istri%"tios. &iety-+i#e percet o+ the cotet is "se+"l +or"sers o+ other )i3-like systems, %"t this %ook is highly targete! at the mo!er *i"3comma! lie "ser.

+ho Should ead This /oo(

This %ook is +or ew *i"3 "sers who ha#e migrate! +rom other plat+orms. >ost likelyyo" are a ?power "ser@ o+ some #ersio o+ >icroso+t Wi!ows. 6erhaps yo"r %oss hastol! yo" to a!miister a *i"3 ser#er, or may%e yo"


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tro!"ctio

all the sec"rity pro%lems a! wat to gi#e *i"3 a try. That


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What,@isert the li#e C', a! re%oot. )sig a li#e C' is a great way to test a comp"ter+or *i"3 compati%ility prior to istallatio. The !isa!#atage o+ "sig a li#e C'is that it may %e #ery slow compare! to ha#ig *i"3 istalle! o yo"r har! !ri#e.oth )%"t" a! e!ora amog othersF ha#e li#e C' #ersios.

:egar!less o+ how yo" istall *i"3, yo" will ee! to ha#e occasioal s"per"ser i.e.,a!miistrati#eF pri#ileges to carry o"t the lessos i this %ook.

$+ter yo" ha#e a workig istallatio, start rea!ig a! +ollow alog with yo"r owcomp"ter. >ost o+ the material i this %ook is ?ha!s o,@ so sit !ow a! get typigL

+h, I Dont Call It 567-8Linux9 some ="arters, it


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tro!"ctio

people i a #ast, !istri%"te! !e#elopmet e++ort. Techically speakig, *i"3 isthe ame o+ the operatig systemr. '#orak !escri%e! the process o+ writig ?Aell. Write 200 wor!s a !ay a!i a year, yo" ha#e a o#el.@ This a!#ice le! me to write a page a !ay "til ha! a %ook.

'mitri 6opo# wrote a article i ree So+tware >agaDie title!, ?Creatig a %ooktemplate with Writer,@ which ispire! me to "se 7pe7++ice.org Writer +or composig

the te3t. $s it t"re! o"t, it worke! wo!er+"lly.

>ark 6olesky per+orme! a e3traor!iary re#iew a! test o+ the te3t.

Jesse ecker, TomasD ChrDcDoowicD, >ichael *e#i, Spece >ier also teste! a!re#iewe! portios o+ the te3t.

K


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$ckowle!gmets

Mare >. Shotts cotri%"te! a lot o+ ho"rs, polishig my so-calle! Eglish %y e!itig thete3t.

$! lastly, the rea!ers o+ *i"3Comma!.org, who ha#e set me so may ki! emails.

Their eco"ragemet ga#e me the i!ea that was really o to somethigL

:our ;eed0ac( Is 7eededore " With ls

'eskto7 'ocuments +usic ictures ublic Tem7lates ;ideos

6usr:bin games kerberos libexec sbin srcetc include lib local share tm7

We ca also chage the +ormat o+ the o"tp"t to re#eal more !etail

[me@linuxbox ~]$ ls -ltotal ".dr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( 'eskto7dr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( 'ocumentsdr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( +usic

dr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( icturesdr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( ublicdr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( Tem7latesdr9xr9xr-x ! me me %(0. !(()-#(-!. #):!( ;ideos

y a!!ig ?-l@ to the comma!, we chage! the o"tp"t to the log +ormat.

ost comma!s "se optios cosistig o+ a sigle character prece!e! %y a !ash, +ore3ample, ?-l@, %"t may comma!s, icl"!ig those +rom the ;&) 6ro4ect, also s"pportlong options, cosistig o+ a wor! prece!e! %y two !ashes. $lso, may comma!s allowm"ltiple short optios to %e str"g together. this e3ample, the lscomma! is gi#e

two optios, the ?l@ optio to pro!"ce log +ormat o"tp"t, a! the ?t@ optio to sort theres"lt %y the +ile


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1 E3plorig The System

We


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>ore " With ls

-r9-r--r-- # root root ").!0. !(()-(%-( ##:(" &x7erience ubuntu


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file filename

Whe i#oke!, the filecomma! will prit a %rie+ !escriptio o+ the +ile6( a! J6E;, thereare may ki!s that are a little less o%#io"s a! a +ew that are ="ite strage.

Vie4ing ;ile Contents +ith less

The lesscomma! is a program to #iew te3t +iles. Thro"gho"t o"r *i"3 system, there

are may +iles that cotai h"ma-rea!a%le te3t. The less program pro#i!es a

co#eiet way to e3amie them.

+hat Is 5Text9

There are may ways to represet i+ormatio o a comp"ter. $ll metho!si#ol#e !e+iig a relatioship %etwee the i+ormatio a! some "m%ers thatwill %e "se! to represet it. Comp"ters, a+ter all, oly "!ersta! "m%ers a! all!ata is co#erte! to "meric represetatio.

Some o+ these represetatio systems are #ery comple3 s"ch as compresse!#i!eo +ilesF, while others are rather simple. 7e o+ the earliest a! simplest iscalle!)S%** te+t. $SC proo"ce! Q$s-MeyQF is short +or $merica Sta!ar!Co!e +or +ormatio terchage. This is a simple eco!ig scheme that was +irst"se! o Teletype machies to map key%oar! characters to "m%ers.

Te3t is a simple oe-to-oe mappig o+ characters to "m%ers. t is #ery compact.

i+ty characters o+ te3t traslates to +i+ty %ytes o+ !ata. t is importat to"!ersta! that te3t oly cotais a simple mappig o+ characters to "m%ers. tis ot the same as a wor! processor !oc"met s"ch as oe create! %y >icroso+tWor! or 7pe7++ice.org Writer. Those +iles, i cotrast to simple $SC te3t,

21


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Riewig ile Cotets With less

cotai may o-te3t elemets that are "se! to !escri%e its str"ct"re a!+ormattig. 6lai $SC te3t +iles cotai oly the characters themsel#es a! a

+ew r"!imetary cotrol co!es like ta%s, carriage ret"rs a! lie +ee!s.

Thro"gho"t a *i"3 system, may +iles are store! i te3t +ormat a! there aremay *i"3 tools that work with te3t +iles. E#e Wi!ows recogiDes theimportace o+ this +ormat. The well-kow &7TE6$'.EGE program is a e!itor+or plai $SC te3t +iles.

Why wo"l! we wat to e3amie te3t +iles eca"se may o+ the +iles that cotai systemsettigs calle! configuration filesF are store! i this +ormat, a! %eig a%le to rea! themgi#es "s isight a%o"t how the system works. a!!itio, may o+ the act"al programsthat the system "ses calle! scriptsF are store! i this +ormat. later chapters, we will

lear how to e!it te3t +iles i or!er to mo!i+y systems settigs a! write o"r ow scripts,%"t +or ow we will 4"st look at their cotets.

The lesscomma! is "se! like this

less filename

7ce starte!, the lessprogram allows yo" to scroll +orwar! a! %ackwar! thro"gh a

te3t +ile. or e3ample, to e3amie the +ile that !e+ies all the system


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'ow $rrow Scroll !ow oe lie

>o#e to the e! o+ the te3t +ile

#or g >o#e to the %egiig o+ the te3t +ile

6characters Search +orwar! to the e3t occ"rrece o+ characters

n Search +or the e3t occ"rrece o+ the pre#io"s search

h 'isplay help scree

B "it less

Less Is >oreThe lessprogram was !esige! as a impro#e! replacemet o+ a earlier )i3

program calle! more. The ame ?less@ is a play o the phrase ?less is more@Bamotto o+ mo!erist architects a! !esigers.

less+alls ito the class o+ programs calle! ?pagers,@ programs that allow the

easy #iewig o+ log te3t !oc"mets i a page %y page maer. Whereas themoreprogram co"l! oly page +orwar!, the lessprogram allows pagig %oth

+orwar! a! %ackwar! a! has may other +eat"res as well.

# 6uided Tour

The +ile system layo"t o yo"r *i"3 system is m"ch like that +o"! o other )i3-likesystems. The !esig is act"ally speci+ie! i a p"%lishe! sta!ar! calle! the (inu+Filesystem ,ierarchy Standard. &ot all *i"3 !istri%"tios co+orm to the sta!ar!e3actly %"t most come pretty close.

&e3t, we are goig to wa!er aro"! the +ile system o"rsel#es to see what makes o"r*i"3 system tick. This will gi#e yo" a chace to practice yo"r a#igatio skills. 7e o+the thigs we will !isco#er is that may o+ the iterestig +iles are i plai h"ma-rea!a%le te3t. $s we go a%o"t o"r to"r, try the +ollowig

. cdito a gi#e !irectory

2. *ist the !irectory cotets with ls -l

(. + yo" see a iterestig +ile, !etermie its cotets with file

1. + it looks like it might %e te3t, try #iewig it with less

2K


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$ ;"i!e! To"r

Remember the co(y and (aste trick + yo" are "sig a mo"se, yo" ca !o"%leclick o a +ileame to copy it a! mi!!le click to paste it ito comma!s.

$s we wa!er aro"!, !o


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Director, Comments

6home ormal co+ig"ratios, each "ser is gi#e a !irectory i6home. 7r!iary "sers ca oly write +iles i their home

!irectories. This limitatio protects the system +rom errat"ser acti#ity.

6lib Cotais share! li%rary +iles "se! %y the core systemprograms. These are similar to '**s i Wi!ows.

6lost8found Each +ormatte! partitio or !e#ice "sig a *i"3 +ile system,s"ch as e3t(, will ha#e this !irectory. t is "se! i the caseo+ a partial reco#ery +rom a +ile system corr"ptio e#et.)less somethig really %a! has happee! to yo"r system,this !irectory will remai empty.

6media 7 mo!er *i"3 systems the 6media!irectory willcotai the mo"t poits +or remo#a%le me!ia s"ch )S!ri#es, C'-:7>s, etc. that are mo"te! a"tomatically atisertio.

6mnt 7 ol!er *i"3 systems, the 6mnt!irectory cotais mo"t

poits +or remo#a%le !e#ices that ha#e %ee mo"te!ma"ally.

6o7t The 6o7t!irectory is "se! to istall ?optioal@ so+tware.

This is maily "se! to hol! commercial so+tware pro!"ctsthat may %e istalle! o yo"r system.

67roc The 67roc!irectory is special. t


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$ ;"i!e! To"r

Director, Comments

6usr The 6usr!irectory tree is likely the largest oe o a *i"3

system. t cotais all the programs a! s"pport +iles "se!%y reg"lar "sers.

6usr6bin 6usr6bincotais the e3ec"ta%le programs istalle! %y

yo"r *i"3 !istri%"tio. t is ot "commo +or this!irectory to hol! tho"sa!s o+ programs.

6usr6lib The share! li%raries +or the programs i 6usr6bin.

6usr6local The 6usr6localtree is where programs that are ot

icl"!e! with yo"r !istri%"tio %"t are ite!e! +or system-wi!e "se are istalle!. 6rograms compile! +rom so"rce co!eare ormally istalle! i 6usr6local6bin. 7 a ewly

istalle! *i"3 system, this tree e3ists, %"t it will %e empty"til the system a!miistrator p"ts somethig i it.

6usr6sbin Cotais more system a!miistratio programs.

6usr6share 6usr6sharecotais all the share! !ata "se! %y

programs i 6usr6bin. This icl"!es thigs like !e+a"lt

co+ig"ratio +iles, icos, scree %ackgro"!s, so"! +iles,etc.

6usr6share6doc >ost packages istalle! o the system will icl"!e someki! o+ !oc"metatio. 6usr6share6doc, we will

+i! !oc"metatio +iles orgaiDe! %y package.6var With the e3ceptio o+ 6tm7a! 6home, the !irectories we

ha#e looke! at so +ar remai relati#ely static, that is, theircotets !o


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lr9xr9xr9x # root root ## !(()-(/-## ():% libc


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>aip"latig iles $! 'irectories

& 'ani#ulating (iles )nd *irectories

$t this poit, we are rea!y +or some real workL This chapter will itro!"ce the +ollowigcomma!s

c7 Copy +iles a! !irectories

mv >o#ereame +iles a! !irectories

mkdir Create !irectories

rm :emo#e +iles a! !irectories

ln Create har! a! sym%olic liks

These +i#e comma!s are amog the most +re="etly "se! *i"3 comma!s. They are"se! +or maip"latig %oth +iles a! !irectories.

&ow, to %e +rak, some o+ the tasks per+orme! %y these comma!s are more easily !oewith a graphical +ile maager. With a +ile maager, we ca !rag a! !rop a +ile +rom oe!irectory to aother, c"t a! paste +iles, !elete +iles, etc. So why "se these ol! comma!

lie programsThe aswer is power a! +le3i%ility. While it is easy to per+orm simple +ile maip"latioswith a graphical +ile maager, complicate! tasks ca %e easier with the comma! lieprograms. or e3ample, how co"l! we copy all the AT>* +iles +rom oe !irectory toaother, %"t oly copy +iles that !o ot e3ist i the !estiatio !irectory or are ewer thathe #ersios i the !estiatio !irectory 6retty har! with with a +ile maager. 6retty easywith the comma! lie

cp -u *.html destination

+ildcards

e+ore we %egi "sig o"r comma!s, we ee! to talk a%o"t a shell +eat"re that makesthese comma!s so power+"l. Sice the shell "ses +ileames so m"ch, it pro#i!es specialcharacters to help yo" rapi!ly speci+y gro"ps o+ +ileames. These special characters are

(


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calle! wildcards. )sig wil!car!s which is also kow as globbingF allow yo" to select+ileames %ase! o patters o+ characters. The ta%le %elow lists the wil!car!s a! whatthey select

Table .-1: /ildcards

+ildcard >eaning

E >atches ay characters

F >atches ay sigle character

[characters] >atches ay character that is a mem%er o+ the set characters

[Gcharacters] >atches ay character that is ot a mem%er o+ the setcharacters

[[:class:]] >atches ay character that is a mem%er o+ the speci+ie!class

Ta%le -2 lists the most commoly "se! character classes

Table .-': %ommonly 0sed %haracter %lasses

Character Class >eaning

[:alnum:] >atches ay alpha"meric character

[:al7ha:] >atches ay alpha%etic character

[:digit:] >atches ay "meral

[:lo9er:] >atches ay lowercase letter

[:u77er:] >atches ay "ppercase letter

)sig wil!car!s makes it possi%le to costr"ct #ery sophisticate! selectio criteria +or+ileames. Aere are some e3amples o+ patters a! what they match

Table .-3: /ildcard +amples

Pattern >atches

E $ll +iles

gE $y +ile %egiig with ?g@

bE


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>ay i!eas origially +o"! i the comma! lie iter+ace make their way itothe graphical iter+ace, too. t is oe o+ the may thigs that make the *i"3

!esktop so power+"l.

mkdir Create Directories

The mkdircomma! is "se! to create !irectories. t works like this

mkdir directory...

# note on notation5Whe three perio!s +ollow a arg"met i the !escriptio o+ acomma! as a%o#eF, it meas that the arg"met ca %e repeate!, th"s

mkdir dir1

wo"l! create a sigle !irectory ame! ?!ir@, while

mkdir dir1 dir2 dir

wo"l! create three !irectories ame! ?!ir@, ?!ir2@, a! ?!ir(@.

cp Cop, ;iles #nd Directories

The c7comma! copies +iles or !irectories. t ca %e "se! two !i++eret ways

cp item1item2

to copy the sigle +ile or !irectory ?item@ to +ile or !irectory ?item2@ a!

cp item... directory

to copy m"ltiple items either +iles or !irectoriesF ito a !irectory.

(1


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cp Copy iles $! 'irectories

Use=u eaning

-a> --archive Copy the +iles a! !irectories a! all o+ their attri%"tes,icl"!ig owerships a! permissios. &ormally,copies take o the !e+a"lt attri%"tes o+ the "serper+ormig the copy.

-i> --interactive e+ore o#erwritig a e3istig +ile, prompt the "ser +orco+irmatio. )" this o(tion is not s(eci"ied6 cp+ill

silently over+rite "iles.-r> --recursive :ec"rsi#ely copy !irectories a! their cotets. This

optio or the -aoptioF is re="ire! whe copyig

!irectories.

-u> --u7date Whe copyig +iles +rom oe !irectory to aother, olycopy +iles that either !o --verbose 'isplay i+ormati#e messages as the copy isper+orme!.

Table .-.: cp +amples

Command esults

c7 file1file2 Copy file1to file'. )" file2exists6 it is over+ritten+ith the contents o" file1. + file'!oes ot e3ist, itis create!.

c7 -i file1file2 Same as a%o#e, e3cept that i+ file'e3ists, the "ser isprompte! %e+ore it is o#erwritte.

c7 file1file2dir1 Copy file1a! file'ito !irectory dir1. dir1m"stalrea!y e3ist.

c7 dir#6E dir! )sig a wil!car!, all the +iles i dir1are copie!ito dir'. dir'm"st alrea!y e3ist.

(


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c7 -r dir1dir2 Copy the cotets o+ !irectory dir1to !irectorydir'. + !irectory dir'!oes ot e3ist, it is create!a!, a+ter the copy, will cotai the same cotets

as !irectory dir1.+ !irectory dir'!oes e3ist, the !irectory dir1a!its cotetsF will %e copie! ito dir'.

mv >o%e #nd ename ;iles

The mvcomma! per+orms %oth +ile mo#ig a! +ile reamig, !epe!ig o how it is

"se!. either case, the origial +ileame o loger e3ists a+ter the operatio. mvis "se!

i m"ch the same way as c7

mv item1item2

to mo#e or reame +ile or !irectory ?item@ to ?item2@ or

mv item... directory

to mo#e oe or more items +rom oe !irectory to aother.

Use=u eaning

-i> --interactive e+ore o#erwritig a e3istig +ile, prompt the "ser +orco+irmatio. )" this o(tion is not s(eci"ied6 mv+ill

silently over+rite "iles.

-u> --u7date Whe mo#ig +iles +rom oe !irectory to aother, olymo#e +iles that either !o --verbose 'isplay i+ormati#e messages as the mo#e is

(K


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m# >o#e $! :eame iles

per+orme!.

Table .-: mv +amples

Command esults

mv file1file2 >o#e file1to file'. )" file2exists6 it is over+ritten+ith the contents o" file1. + file'!oes ot e3ist, itis create!. )n either case6 file1ceases to exist.

mv -i file1file2 Same as a%o#e, e3cept that i+ file'e3ists, the "ser isprompte! %e+ore it is o#erwritte.

mv file1file2dir1 >o#e file1a! file'ito !irectory dir1. dir1m"stalrea!y e3ist.

mv dir1dir2 + !irectory dir'!oes ot e3ist, create !irectorydir'a! mo#e the cotets o+ !irectory dir1itodir'a! !elete !irectory dir1.+ !irectory dir'!oes e3ist, mo#e !irectory dir1a! its cotetsF ito !irectory dir'.

rm emo%e ;iles #nd Directories

The rmcomma! is "se! to remo#e !eleteF +iles a! !irectories

rm item...

where ?item@ is oe or more +iles or !irectories.

Use=u eaning

-i> --interactive e+ore !eletig a e3istig +ile, prompt the "ser +orco+irmatio. )" this o(tion is not s(eci"ied6 rm+ill

silently delete "iles.

(/


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-r> --recursive :ec"rsi#ely !elete !irectories. This meas that i+ a!irectory %eig !elete! has s"%!irectories, !elete themtoo. To !elete a !irectory, this optio m"st %e

speci+ie!.

-f> --force gore oe3istet +iles a! !o ot prompt. Thiso#erri!es the --interactiveoptio.

-v> --verbose 'isplay i+ormati#e messages as the !eletio isper+orme!.

Table .-5: rm +amples

Command esults

rm file1 'elete file1siletly.rm -i file1 Same as a%o#e, e3cept that the "ser is prompte! +or

co+irmatio %e+ore the !eletio is per+orme!.

rm -r file1dir1 'eletefile1a! dir1a! its cotets.

rm -rf file1dir1 Same as a%o#e, e3cept that i+ either file1or dir1!oot e3ist, rmwill coti"e siletly.

/e Care"ul +ith rmaip"latig iles $! 'irectories

:o;ing And !enaming ies

&ow, the ame ?passw!@ !oes


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*et


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The lscomma! has a way to re#eal this i+ormatio. t is i#oke! with the ?-i@ optio

[me@linuxbox 7la1ground]$ ls -litotal #.#!""0 dr9xr9xr-x ! me me %(0. !((/-(#-#% #.:#) dir##!""%( dr9xr9xr-x ! me me %(0. !((/-(#-#% #.:#) dir!#!""/ -r9-r--r-- % me me #."( !((/-(#-#( #.: fun#!""/ -r9-r--r-- % me me #."( !((/-(#-#( #.: fun-hard

this #ersio o+ the listig, the +irst +iel! is the io!e "m%er a!, as we ca see, %othfun a! fun-hardshare the same io!e "m%er, which co+irms they are the same

+ile.

Creating Symboi/ LinksSym%olic liks were create! to o#ercome the two !isa!#atages o+ har! liks har! likscaot spa physical !e#ices a! har! liks caot re+erece !irectories, oly +iles.Sym%olic liks are a special type o+ +ile that cotais a te3t poiter to the target +ile or!irectory.

Creatig sym%olic liks is similar to creatig har! liks

[me@linuxbox 7la1ground]$ ln -s fun fun-s!m[me@linuxbox 7la1ground]$ ln -s ../fun dir1/fun-s!m[me@linuxbox 7la1ground]$ ln -s ../fun dir2/fun-s!m

The +irst e3ample is pretty straight+orwar!, we simply a!! the ?-s@ optio to create asym%olic lik rather tha a har! lik. "t what a%o"t the e3t two :emem%er, whe wecreate a sym%olic lik, we are creatig a te3t !escriptio o+ where the target +ile isrelati#e to the sym%olic lik. t


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*et


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[me@linuxbox 7la1ground]$ rm -i funrm: remove regular file JfunKF

Eter ?y@ at the prompt a! the +ile is !elete!. "t let


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*etE a! M'E pro#i!e a easy a! a"tomaticmetho! o+ creatig sym%olic liks. With ;&7>E, hol!ig the CtrlVShi+t keyswhile !raggig a +ile will create a lik rather tha copyig or mo#igF the +ile. M'E, a small me" appears whee#er a +ile is !roppe!, o++erig a choice o+copyig, mo#ig, or likig the +ile.

Summing U5We


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K Workig With Comma!s

+ Wor,ing With Co%%ands

)p to this poit, we ha#e see a series o+ mysterio"s comma!s, each with its owmysterio"s optios a! arg"mets. this chapter, we will attempt to remo#e some o+that mystery a! e#e create some o+ o"r ow comma!s. The comma!s itro!"ce! ithis chapter are

t17e !icate how a comma! ame is iterprete! 9hich 'isplay which e3ec"ta%le program will %e e3ec"te!

man 'isplay a comma!


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!eti+yig Comma!s

Identi",ing Commands

t is o+te "se+"l to kow e3actly which o+ the +o"r ki!s o+ comma!s is %eig "se! a!*i"3 pro#i!es a co"ple o+ ways to +i! o"t.

t17e )is5ay A Command"s Ty5e

The t17ecomma! is a shell %"ilti that !isplays the ki! o+ comma! the shell will

e3ec"te, gi#e a partic"lar comma! ame. t works like this

t!pe command

where ?comma!@ is the ame o+ the comma! yo" wat to e3amie. Aere are some

e3amples

[me@linuxbox ~]$ t!pe t!pet17e is a shell builtin[me@linuxbox ~]$ t!pe lsls is aliased to Jls --colorMtt1K[me@linuxbox ~]$ t!pe cpc7 is 6bin6c7

Aere we see the res"lts +or three !i++eret comma!s. &otice that the oe +or lstake

+rom a e!ora systemF a! how the lscomma! is act"ally a alias +or the lscomma!

with the ?-- colortty@ optio a!!e!. &ow we kow why the o"tp"t +rom lsis !isplaye!

i colorL

9hich )is5ay An 6xe/utabe"s Lo/ation

Sometimes there is more tha oe #ersio o+ a e3ec"ta%le program istalle! o asystem. While this is ot #ery commo o !esktop systems, it


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e3ample, cd, we either get o respose or a error message

[me@linuxbox ~]$ which cd6usr6bin69hich: no cd inN6o7t6jre# thenC'4TS is not used< Af the director1 is not found> and the shello7tion JcdableOvarsK is set> then tr1 the 9ord as a variable name then cd to the value of that variableiscellaeo"s

8 System a!miistratio comma!s

Sometimes we ee! to look i a speci+ic sectio o+ the ma"al to +i! what we arelookig +or. This is partic"larly tr"e i+ we are lookig +or a +ile +ormat that is also theame o+ a comma!. Witho"t speci+yig a sectio "m%er, we will always get the +irstistace o+ a match, pro%a%ly i sectio . To speci+y a sectio "m%er, we "se manlike

this

man sectionsearch_term

or e3ample

[me@linuxbox ~]$ man " passwd

2


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;ettig $ Comma!


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o#er eighty pages log a! e3tremely !ese, a! its str"ct"re makes a%sol"tely osese to a ew "ser.

7 the other ha!, it is #ery acc"rate a! cocise, as well as %eig e3tremelycomplete. So check it o"t i+ yo" !are a! look +orwar! to the !ay whe yo" carea! it a! it all makes sese.

info )is5ay A 'rogram"s In=o 6ntry

The ;&) 6ro4ect pro#i!es a alterati#e to ma pages +or their programs, calle! ?i+o.@+o pages are !isplaye! with a rea!er program ame!, appropriately eo"gh, info.

+o pages are hyperlinkedm"ch like we% pages. Aere is a sample

ile: coreutils Lode: ls invocation> Lext: dir invocation>37: 'irector1 listing

#(including directoriesP< 7tions and file arguments can be intermixed

arbitraril1> as usual b1default JlsK lists the contents of directories> not recursivel1> andomitting files 9ith names beginning 9ith J b1 default JlsK lists just the filename< Af no non-o7tionargument is s7ecified> JlsK o7erates on the current director1> actingas if it had been invoked 9ith a single argument of J the out7ut is sorted al7habeticall1> according to the---Anfo: Ncoreutils


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Creating :our ?4n Commands +ith alias

&ow +or o"r #ery +irst e3periece with programmigL We will create a comma! o+ o"row "sig the alias comma!. "t %e+ore we start, we ee! to re#eal a small

comma! lie trick. t


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Creatig 5o"r 7w Comma!s With alias

&otice the str"ct"re o+ this comma!

alias name$%string%

$+ter the comma! ?alias@ we gi#e alias a ame +ollowe! imme!iately o whitespaceallowe!F %y a e="als sig, +ollowe! imme!iately %y a ="ote! strig cotaiig themeaig to %e assige! to the ame. $+ter we !e+ie o"r alias, it ca %e "se! aywherethe shell wo"l! e3pect a comma!. *et


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+ig"re o"t what they all !o

[me@linuxbox ~]$ aliasalias l


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/ :e!irectio

/edirection

this lesso we are goig to "leash what may %e the coolest +eat"re o+ the comma!lie. t


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/ :e!irectio

7 re!irectio allows "s to chage where o"tp"t goes a! where ip"t comes +rom.&ormally, o"tp"t goes to the scree a! ip"t comes +rom the key%oar!, %"t with 7re!irectio, we ca chage that.

edirecting Standard ?utput

7 re!irectio allows "s to re!e+ie where sta!ar! o"tp"t goes. To re!irect sta!ar!o"tp"t to aother +ile %esi!es the scree, we "se the ?X@ re!irectio operator +ollowe! %ythe ame o+ the +ile. Why wo"l! we wat to !o this t


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:e!irectig Sta!ar! 7"tp"t

how to re!irect sta!ar! error i 4"st a mi"te, %"t +irst, let


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/ :e!irectio

sta!ar! error we m"st re+er to its file descriptor. $ program ca pro!"ce o"tp"t o ayo+ se#eral "m%ere! +ile streams. While we ha#e re+erre! to the +irst three o+ these +ilestreams as sta!ar! ip"t, o"tp"t a! error, the shell re+ereces them iterally as +ile

!escriptors Dero, oe a! two, respecti#ely. The shell pro#i!es a otatio +or re!irectig+iles "sig the +ile !escriptor "m%er. Sice sta!ar! error is the same as +ile !escriptor"m%er two, we ca re!irect sta!ar! error with this otatio

[me@linuxbox ~]$ ls -l /bin/usr 2& ls-error.txt

The +ile !escriptor ?2@ is place! imme!iately %e+ore the re!irectio operator to per+ormthe re!irectio o+ sta!ar! error to the +ile ls-error


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:e!irectig Sta!ar! Error

com%ie! re!irectio

[me@linuxbox ~]$ ls -l /bin/usr '& ls-output.txt

this e3ample, we "se the sigle otatio YD to re!irect %oth sta!ar! o"tp"t a!

sta!ar! error to the +ile ls-out7ut


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:e!irectig Sta!ar! p"t

[me@linuxbox ~]$ cat+he ,uick brown fox jumped over the la! dog.The Buick bro9n fox jum7ed over the la1 dogoth@ +ormat. Thisway, the !irectory ames will sort i chroological or!er. We co"l! type o"t a completelist o+ !irectories, %"t that


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8 Seeig The Worl! $s The Shell Sees t

[me@linuxbox ~]$ printenv 0 less

5o" may ha#e otice! that with other types o+ e3pasio, i+ yo" mistype a patter, thee3pasio will ot take place a! the echocomma! will simply !isplay the mistype!

patter. With parameter e3pasio, i+ yo" misspell the ame o+ a #aria%le, the e3pasiowill still take place, %"t will res"lt i a empty strig

[me@linuxbox ~]$ echo 3FEGH

[me@linuxbox ~]$

Command SubstitutionComma! s"%stit"tio allows "s to "se the o"tp"t o+ a comma! as a e3pasio

[me@linuxbox ~]$ echo 34ls6'eskto7 'ocuments ls-out7ut


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E3pasio

6usr6bin6funi7: &= !-bit =*H executable> Antel /(/.>version # N*U*;P> d1namicall1 linked Nuses shared libsP> forL36=inux !


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treate! as or!iary characters. The e3ceptios are ?[@, ?\@ %ackslashF, a! ?]@ %ack-="oteF. This meas that wor!-splittig, pathame e3pasio, til!e e3pasio, a! %racee3pasio are s"ppresse!, %"t parameter e3pasio, arithmetic e3pasio, a! comma!

s"%stit"tio are still carrie! o"t. )sig !o"%le ="otes, we ca cope with +ileamescotaiig em%e!!e! spaces. Say we were the "+ort"ate #ictim o+ a +ile calle!t9o 9ords


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"otig

y !e+a"lt, wor!-splittig looks +or the presece o+ spaces, ta%s, a! ewlies lie+ee!charactersF a! treats them as delimiters %etwee wor!s. This meas that "="ote!spaces, ta%s, a! ewlies are ot cosi!ere! to %e part o+ the te3t. They oly ser#e as

separators. Sice they separate the wor!s ito !i++eret arg"mets, o"r e3amplecomma! lie cotais a comma! +ollowe! %y +o"r !istict arg"mets. + we a!!!o"%le ="otes

[me@linuxbox ~]$ echo Jthis is a testJthis is a test

wor!-splittig is s"ppresse! a! the em%e!!e! spaces are ot treate! as !elimiters, ratherthey %ecome part o+ the arg"met. 7ce the !o"%le ="otes are a!!e!, o"r comma! liecotais a comma! +ollowe! %y a sigle arg"met.

The +act that ewlies are cosi!ere! !elimiters %y the wor!-splittig mechaism ca"sesa iterestig, al%eit s"%tle, e++ect o comma! s"%stit"tio. Cosi!er the +ollowig

[me@linuxbox ~]$ echo 34cal6ebruar1 !((/ *u +o Tu ,e Th r *a # ! % " . ) / 0 #( ## #! # #%#" #. #) #/ #0 !( !# !! ! !% !" !. !) !/ !0[me@linuxbox ~]$ echo J34cal6J ebruar1 !((/*u +o Tu ,e Th r *a # ! % " . ) / 0

#( ## #! # #% #" #.#) #/ #0 !( !# !! !!% !" !. !) !/ !0

the +irst istace, the "="ote! comma! s"%stit"tio res"lte! i a comma! liecotaiig thirty-eight arg"mets. the seco!, a comma! lie with oe arg"met thaticl"!es the em%e!!e! spaces a! ewlies.

Singe Duotes

+ we ee! to s"ppress alle3pasios, we "se single


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[me@linuxbox ~]$ echo Jtext ~/*.txt 9a;b> 34echo foo6 34425266 3EFGHJtext ~6Eb\ foo % me

[me@linuxbox ~]$ echo %text ~/*.txt 9a;b> 34echo foo6 34425266 3EFGH%text ~6Eb\ $Necho fooP $NN!8!PP $3*&R

$s we ca see, with each s"ccee!ig le#el o+ ="otig, more a! more o+ the e3pasiosare s"ppresse!.

6s/a5ing Chara/ters

Sometimes we oly wat to ="ote a sigle character. To !o this, we ca prece!e acharacter with a %ackslash, which i this cote3t is calle! the escape character. 7+tethis is !oe isi!e !o"%le ="otes to selecti#ely pre#et a e3pasio

[me@linuxbox ~]$ echo J+he balance for user 3EFGH is K3".JThe balance for user me is: $"


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"otig

The ta%le a%o#e lists some o+ the commo %ackslash escape se="eces. The i!ea%ehi! this represetatio "sig the %ackslash origiate! i the C programmig

lag"age a! has %ee a!opte! %y may others, icl"!ig the shell.

$!!ig the ?-e@ optio to echowill ea%le iterpretatio o+ escape se="eces.

5o" may also place them isi!e $K K. Aere, "sig the slee7 comma!, a

simple program that 4"st waits +or the speci+ie! "m%er o+ seco!s a! the e3its,we ca create a primiti#e co"t!ow timer

sleep 1# echo -e J+ime%s upKaJ

We co"l! also !o this

sleep 1# echo J+ime%s upJ 3%Ka%

Summing -p

$s we mo#e +orwar! with "sig the shell, we will +i! that e3pasios a! ="otig will%e "se! with icreasig +re="ecy, so it makes sese to get a goo! "!ersta!ig o+ theway they works. +act, it co"l! %e arg"e! that they are the most importat s"%4ects tolear a%o"t the shell. Witho"t a proper "!ersta!ig o+ e3pasio, the shell will always%e a so"rce o+ mystery a! co+"sio, a! m"ch o+ it potetial power waste!.

;urther eading

The bashma page has ma4or sectios o %oth e3pasio a! ="otig whichco#er these topics i a more +ormal maer.

The 8ash 9eference !anualalso cotais chapters o e3pasio a! ="otighttpwww.g".orgso+tware%ashma"al%ashre+.html

8(

$scape SeBuence >eaning

a ell ?$lert@ - ca"ses the comp"ter to %eepF

b ackspace

n &ewlie. 7 )i3-like systems, thispro!"ces a lie+ee!.

r Carriage ret"r

t Ta%
http://www.gnu.org/software/bash/manual/bashref.htmlhttp://www.gnu.org/software/bash/manual/bashref.html


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9 $!#ace! Mey%oar! Tricks

)dvanced e$board Tric,s

o+te ki!!igly !escri%e )i3 as ?the operatig system +or people who like to type.@ 7+co"rse, the +act that it e#e has a comma! lie is a testamet to that. "t comma! lie"sers !o


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Comma! *ie E!itig

Table 5-1: %ursor !ovement %ommands

=e, #ction

Ctrl-a >o#e c"rsor to the %egiig o+ the lie.Ctrl-e >o#e c"rsor to the e! o+ the lie.

Ctrl-f >o#e c"rsor +orwar! oe characterH same as the right arrow key.

Ctrl-b >o#e c"rsor %ackwar! oe characterH same as the le+t arrow key.

4lt-f >o#e c"rsor +orwar! oe wor!.

4lt-b >o#e c"rsor %ackwar! oe wor!.

Ctrl-l Clear the scree a! mo#e the c"rsor to the top le+t corer. Theclearcomma! !oes the same thig.

:odi=ying Text

Ta%le 9-2 lists key%oar! comma!s that are "se! to e!it characters o the comma! lie.

Table 5-': Te+t diting %ommands

=e, #ction

Ctrl-d 'elete the character at the c"rsor locatio

Ctrl-t Traspose e3chageF the character at the c"rsor locatio with the

oe prece!ig it.

4lt-t Traspose the wor! at the c"rsor locatio with the oe prece!ig it.

4lt-l Co#ert the characters +rom the c"rsor locatio to the e! o+ thewor! to lowercase.

4lt-u Co#ert the characters +rom the c"rsor locatio to the e! o+ thewor! to "ppercase.

Cutting And 'asting E9iing And 1ankingF Text

The :ea!lie !oc"metatio "ses the terms killinga!yankingto re+er to what we wo"l!commoly call c"ttig a! pastig. tems that are c"t are store! i a %"++er calle! thekill-ring.

8


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Table 5-3: %ut )nd 6aste %ommands

=e, #ction

Ctrl-k Mill te3t +rom the c"rsor locatio to the e! o+ lie.Ctrl-u Mill te3t +rom the c"rsor locatio to the %egiig o+ the lie.

4lt-d Mill te3t +rom the c"rsor locatio to the e! o+ the c"rret wor!.

4lt-Hacks7ace

Mill te3t +rom the c"rsor locatio to the %egiig o+ the c"rretwor!. + the c"rsor is at the %egiig o+ a wor!, kill the pre#io"swor!.

Ctrl-1 5ak te3t +rom the kill-rig a! isert it at the c"rsor locatio.

The >eta =e,

+ yo" #et"re ito the :ea!lie !oc"metatio, which ca %e +o"! i the:E$'*&E sectio o+ the bashma page, yo" will eco"ter the term ?meta

key.@ 7 mo!er key%oar!s this maps to the 4ltkey %"t it was


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Completio

this works. ;i#e a home !irectory that looks like this

[me@linuxbox ~]$ ls'eskto7 ls-out7ut


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The completio is s"ccess+"l.

While this e3ample shows completio o+ pathames, which is its most commo "se,completio will also work o #aria%les i+ the %egiig o+ the wor! is a ?[@F, "ser ames

i+ the wor! %egis with ?@F, comma!s i+ the wor! is the +irst wor! o the lie.F a!host ames i+ the %egiig o+ the wor! is ?N@F. Aost ame completio oly works +orhost ames liste! i 6etc6hosts.

There are a "m%er o+ cotrol a! meta key se="eces that are associate! withcompletio

Table 5-$: %ompletion %ommands

=e, #ction

4lt-F 'isplay list o+ possi%le completios. &n most systems you can also

do this by pressing the tab key a second time" which is much easier#4lt-E sert all possi%le completios. This is "se+"l whe yo" wat to "se

more tha oe possi%le match.

There ="ite a +ew more that +i! rather o%sc"re. 5o" ca see a list i the bashma

page "!er ?:E$'*&E@.

Programma0le Completion

:ecet #ersios o+ bash ha#e a +acility calle! programmable completion.6rogramma%le completio allows yo" or more likely, yo"r !istri%"tio pro#i!erFto a!! a!!itioal completio r"les. )s"ally this is !oe to a!! s"pport +orspeci+ic applicatios. or e3ample it is possi%le to a!! completios +or the optiolist o+ a comma! or match partic"lar +ile types that a applicatio s"pports.)%"t" has a +airly large set !e+ie! %y !e+a"lt. 6rogramma%le completio isimplemete! %y shell +"ctios, a ki! o+ mii shell script that we will co#er ilater chapters. + yo" are c"rio"s, try

set 0 less

a! see i+ yo" ca +i! them. &ot all !istri%"tios icl"!e them %y !e+a"lt.

-sing 3istor,

$s we !isco#ere! i Chapter 2, bashmaitais a history o+ comma!s that ha#e %ee

etere!. This list o+ comma!s is kept i yo"r home !irectory i a +ile calle!

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[me@linuxbox ~]$

irst type Ctrl-r

Nreverse-i-searchPJK:

The prompt chages to i!icate that we are per+ormig a re#erse icremetal search. t is?re#erse@ %eca"se we are searchig +rom ?ow@ to some time i the past. &e3t, we starttypig o"r search te3t. this e3ample ?"sr%i@

Nreverse-i-searchPJ/usr/binK: ls -l 6usr6bin D ls-out7uto#e to the pre#io"s history etry. Same actio as the "p arrow.

Ctrl-n >o#e to the e3t history etry. Same actio as the !ow arrow.

4lt-X >o#e to the %egiig topF o+ the history list.

4lt-D >o#e to the e! %ottomF o+ the history list, i.e., the c"rretcomma! lie.

Ctrl-r :e#erse icremetal search. Searches icremetally +rom thec"rret comma! lie "p the history list.

4lt-7 :e#erse search, o-icremetal. With this key, type i the searchstrig a! press eter %e+ore the search is per+orme!.

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)sig Aistory

4lt-n orwar! search, o-icremetal.

Ctrl-o E3ec"te the c"rret item i the history list a! a!#ace to the e3t

oe. This is ha!y i+ yo" are tryig to re-e3ec"te a se="ece o+comma!s i the history list.

$istory 6x5ansion

The shell o++ers a specialiDe! type o+ e3pasio +or items i the history list %y "sig the?L@ character. We ha#e alrea!y see how the e3clamatio poit ca %e +ollowe! %y a"m%er to isert a etry +rom the history list. There are a "m%er o+ other e3pasio+eat"res

Table 5-2: ,istory +pansion %ommandsSeBuence #ction

GG :epeat the last comma!. t is pro%a%ly easier to press "p arrowa! eter.

Gnumber :epeat history list item number.

Gstring :epeat last history list item startig with strig.

GFstring :epeat last history list item cotaiig strig.

wo"l! ca"tio agaist "sig the ?Lstrig@ a! ?Lstrig@ +orms "less yo" are a%sol"telys"re o+ the cotets o+ the history list items.

There are may more elemets a#aila%le i the history e3pasio mechaism, %"t thiss"%4ect is alrea!y too arcae a! o"r hea!s may e3plo!e i+ we coti"e. The AST7:5EG6$&S7& sectio o+ the bashma page goes ito all the gory !etails. eel +ree to

e3ploreL

script

a!!itio to the comma! history +eat"re i bash, most *i"3 !istri%"tios

icl"!e a program calle! scri7t that ca %e "se! to recor! a etire shell

sessio a! store it i a +ile. The %asic syta3 o+ the comma! is

scri7t [file]

9


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10 er%issions

7peratig systems i the )i3 tra!itio !i++er +rom those i the >S-'7S tra!itio ithat they are ot oly multitaskingsystems, %"t also multi-usersystems, as well.

What e3actly !oes this mea t meas that more tha oe perso ca %e "sig thecomp"ter at the same time. While a typical comp"ter will likely ha#e oly oe key%oar!

a! moitor, it ca still %e "se! %y more tha oe "ser. or e3ample, i+ a comp"ter isattache! to a etwork or the teret, remote "sers ca log i #ia sshsec"re shellF a!

operate the comp"ter. +act, remote "sers ca e3ec"te graphical applicatios a! ha#ethe graphical o"tp"t appear o a remote !isplay. The G Wi!ow System s"pports this aspart o+ its %asic !esig.

The m"lti-"ser capa%ility o+ *i"3 is ot a recet Qio#atio,Q %"t rather a +eat"re that is!eeply em%e!!e! ito the !esig o+ the operatig system. Cosi!erig the e#irometi which )i3 was create!, this makes per+ect sese. 5ears ago, %e+ore comp"ters wereQpersoal,Q they were large, e3pesi#e, a! cetraliDe!. $ typical "i#ersity comp"tersystem, +or e3ample, cosiste! o+ a large cetral comp"ter locate! i oe %"il!ig a!termials which were locate! thro"gho"t the camp"s, each coecte! to the large cetral

comp"ter. The comp"ter wo"l! s"pport may "sers at the same time.

or!er to make this practical, a metho! ha! to %e !e#ise! to protect the "sers +rom eachother. $+ter all, the actios o+ oe "ser co"l! ot %e allowe! to crash the comp"ter, orco"l! oe "ser iter+ere with the +iles %elogig to aother "ser.

this chapter we are goig to look at this essetial part o+ system sec"rity a! itro!"cethe +ollowig comma!s

id 'isplay "ser i!etity

chmod Chage a +ile


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0 6ermissios

chgr7 Chage a +ile no read 7ermission[me@linuxbox ~]$ less /etc/shadow6etc6shado9: ermission denied

The reaso +or this error message is that, as reg"lar "sers, we !o ot ha#e permissio torea! this +ile.

the )i3 sec"rity mo!el, a "ser may own+iles a! !irectories. Whe a "ser ows a +ileor !irectory, the "ser has cotrol o#er its access. )sers ca, i t"r, %elog to a groupcosistig o+ oe or more "sers who are gi#e access to +iles a! !irectories %y theirowers. a!!itio to gratig access to a gro"p, a ower may also grat some set o+access rights to e#ery%o!y, which i )i3 terms is re+erre! to as the world. To +i! o"ti+ormatio a%o"t yo"r i!etity, "se the idcomma!

[me@linuxbox ~]$ id

uidM"((NmeP gidM"((NmeP grou7sM"((NmeP

*et!0NaudioP>(Ndi7P>%%NvideoP>%.N7lugdevP>#(/Nl7adminP>##%NadminP>#(((NmeP

$s we ca see, the "i! a! gi! "m%ers are !i++eret. This is simply %eca"se e!orastarts its "m%erig o+ reg"lar "ser acco"ts at 00, while )%"t" starts at 000. We ca

91


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7wers, ;ro"p >em%ers, $! E#ery%o!y Else

also see that the )%"t" "ser %elogs to a lot more gro"ps. This has to !o with the way)%"t" maages pri#ileges +or system !e#ices a! ser#ices.

So where !oes this i+ormatio come +rom *ike so may thigs i *i"3, +rom a co"ple

o+ te3t +iles. )ser acco"ts are !e+ie! i the 6etc67ass9d+ile a! gro"ps are !e+ie!i the 6etc6grou7 +ile. Whe "ser acco"ts a! gro"ps are create!, these +iles are

mo!i+ie! alog with 6etc6shado9which hol!s i+ormatio a%o"t the "ser


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0 6ermissios

c $ character special file. This +ile type re+ers to a !e#ice thatha!les !ata as a stream o+ %ytes, s"ch as a termial or mo!em.

b$ block special file. This +ile type re+ers to a !e#ice that ha!les!ata i %locks, s"ch as a har! !ri#e or C'-:7> !ri#e.

The remaiig ie characters o+ the +ile attri%"tes, calle! the file mode"represet therea!, write, a! e3ec"te permissios +or the +ile


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:ea!ig, Writig, $! E3ec"tig

Table 1=-3: 6ermission )ttribute +amples

;ile #ttri0utes >eaning

-r9x------ $ reg"lar +ile that is rea!a%le, writa%le, a! e3ec"ta%le %y the+ile


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0 6ermissios

+hat The 3ec( Is ?ctal

&ctal%ase 8F, a! its co"si, he+adecimal%ase KF are "m%er systems o+te"se! to e3press "m%ers o comp"ters. We h"mas, owig to the +act that we orat least most o+ "sF were %or with te +igers, co"t "sig a %ase 0 "m%ersystem. Comp"ters, o the other the other ha!, were %or with oly oe +igera! th"s !o all all their co"tig i binary %ase 2F. Their "m%er system olyhas two "merals, Dero a! oe. So i %iary, co"tig looks like this

0, , 0, , 00, 0, 0, , 000, 00, 00, 0...

octal, co"tig is !oe with the "merals Dero thro"gh se#e, like so

0, , 2, (, 1, , K, /, 0, , 2, (, 1, , K, /, 20, 2...

Ae3a!ecimal co"tig "ses the "merals Dero thro"gh ie pl"s the letters ?$@thro"gh ?@

0, , 2, (, 1, , K, /, 8, 9, $, , C, ', E, , 0, , 2, (...

While we ca see the sese i %iary sice comp"ters oly ha#e oe +igerF,what are octal a! he3a!ecimal goo! +or The aswer has to !o with h"maco#eiece. >ay times, small portios o+ !ata are represete! o comp"ters asbit patterns. Take +or e3ample a :; color. 7 most comp"ter !isplays, eachpi3el is compose! o+ three color compoets eight %its o+ re!, eight %its o+ gree,a! eight %its o+ %l"e. $ lo#ely me!i"m %l"e wo"l! %e a twety-+o"r !igit"m%er

0000000000Aow wo"l! yo" like to rea! a! write those ki!s o+ "m%ers all !ay !i!


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each !igit i a octal "m%er represets three %iary !igits, this maps icely to thescheme "se! to store the +ile mo!e. This ta%le shows what we mea

?ctal /inar, ;ile >ode

( ((( ---

# ((# --x

! (#( -9-

(## -9x

% #(( r--

" #(# r-x

. ##( r9-

) ### r9xy "sig three octal !igits, we ca set the +ile mo!e +or the ower, gro"p ower, a!worl!

[me@linuxbox ~]$ & foo.txt[me@linuxbox ~]$ ls -l foo.txt-r9-r9-r-- # me me ( !((/-(-(. #%:"! foo


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0 6ermissios

o Short +or ?others,@ %"t meas worl!.

a Short +or ?all.@ The com%iatio o+ ?"@, ?g@, a! ?o@.

+ o character is speci+ie!, ?all@ will %e ass"me!. The operatio may %e a ?V@ i!icatigthat a permissio is to %e a!!e!, a ?-@ i!icatig that a permissio is to %e take away, ora ?@ i!icatig that oly the speci+ie! permissios are to %e applie! a! that all othersare to %e remo#e!.

6ermissios are speci+ie! with the ?r@, ?w@, a! ?3@ characters. Aere are some e3ampleso+ sym%olic otatio

Table 1=-.: chmod Symbolic >otation +amples

7otation >eaning

u8x $!! e3ec"te permissio +or the ower.

u-x :emo#e e3ec"te permissio +rom the ower.

8x $!! e3ec"te permissio +or the ower, gro"p, a! worl!.E="i#alet to a8x.

o-r9 :emo#e the rea! a! write permissio +rom ayoe %esi!es theower a! gro"p ower.

goMr9 Set the gro"p ower a! ayoe %esi!es the ower to ha#e rea! a!write permissio. + either the gro"p ower or worl! pre#io"sly ha!e3ec"te permissios, they are remo#e!.

u8x>goMrx $!! e3ec"te permissio +or the ower a! set the permissios +orthe gro"p a! others to rea! a! e3ec"te. >"ltiple speci+icatiosmay %e separate! %y commas.

Some people pre+er to "se octal otatio, some +olks really like the sym%olic. Sym%olicotatio !oes o++er the a!#atage o+ allowig yo" to set a sigle attri%"te witho"t!ist"r%ig ay o+ the others.

Take a look at the chmodma page +or more !etails a! a list o+ optios. $ wor! o+

ca"tio regar!ig the ?--rec"rsi#e@ optio it acts o %oth +iles a! !irectories, so it


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"!ersta! the permissio !ialogs i the ;). %oth &a"til"s ;&7>EF a!Mo="eror M'EF, right-clickig a +ile or !irectory ico will e3pose a properties !ialog.Aere is a e3ample +rom M'E (.

Aere we ca see the settigs +or the ower, gro"p, a! worl!. M'E, clickig o the?$!#ace! 6ermissios@ %"tto %rigs "p aother !ialog that allows yo" to set each o+the mo!e attri%"tes i!i#i!"ally. $other #ictory +or "!ersta!ig %ro"ght to "s %y thecomma! lieL

umask Set )e=aut 'ermissions

The umaskcomma! cotrols the !e+a"lt permissios gi#e to a +ile whe it is create!.

t "ses octal otatio to e3press a mask o+ %its to %e remo#e! +rom a +ile


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0 6ermissios

[me@linuxbox ~]$ ls -l foo.txt-r9-r9-r-- # me me ( !((/-(-(. #%:" foo


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$gai, where a appears i the %iary #al"e, the correspo!ig attri%"te is "set. 6laywith some #al"es try some se#esF to get "se! to how this works. Whe yo"


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0 6ermissios

)sig this +orm, a sigle comma! lie is passe! to the ew shell +or e3ec"tio. t isimportat to eclose the comma! i ="otes, as we !o ot wat e3pasio to occ"r i o"rshell, %"t rather i the ew shell

[me@linuxbox ~]$ su -c %ls -l /root/*%ass9ord:-r9------- # root root )"% !(()-(/-## (:#0 6root6anaconda-ks


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Chagig !etities

N4==P 4==

-0untu #nd sudo

7e o+ the rec"rret pro%lems +or reg"lar "sers is how to per+orm certai tasksthat re="ire s"per"ser pri#ileges. These tasks icl"!e istallig a! "p!atigso+tware, e!itig system co+ig"ratio +iles, a! accessig !e#ices. theWi!ows worl!, this is o+te !oe %y gi#ig "sers a!miistrati#e pri#ileges. Thisallows "sers to per+orm these tasks. Aowe#er, it also ea%les programs e3ec"te!%y the "ser to ha#e the same a%ilities. This is !esira%le i most cases, %"t it alsopermits malware malicio"s so+twareF s"ch as #ir"ses to ha#e +ree reig o+ thecomp"ter.

the )i3 worl!, there has always %ee a larger !i#isio %etwee reg"lar "sersa! a!miistrators, owig to the m"lti-"ser heritage o+ )i3. The approach takei )i3 is to grat s"per"ser pri#ileges oly whe ee!e!. To !o this, the sua!

sudocomma!s are commoly "se!.

)p "til a co"ple o+ years ago, most *i"3 !istri%"tios relie! o su +or this

p"rpose. su!i!


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0 6ermissios

chown (owner)((group)) file...

cho9nca chage the +ile ower a!or the +ile gro"p ower !epe!ig o the +irstarg"met o+ the comma!. Aere are some e3amples

Table 1=-2: chown )rgument +amples

#rgument esults

bob Chages the owership o+ the +ile +rom its c"rret ower to "serbob.

bob:users Chages the owership o+ the +ile +rom its c"rret ower to "serboba! chages the +ile gro"p ower to gro"p "sers.

:admins Chages the gro"p ower to the gro"p admins. The +ile ower is"chage!.

bob: Chage the +ile ower +rom the c"rret ower to "ser boba!

chages the gro"p ower to the logi gro"p o+ "ser bob.

*et


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Chagig !etities

r"s o"t.

/hgr5 Change +rou5


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0 6ermissios

[bill@linuxbox ~]$ sudo mkdir /usr/local/share/Ousicass9ord:

Sice bill is maip"latig +iles o"tsi!e his home !irectory, s"per"ser pri#ileges are

re="ire!. $+ter the !irectory is create!, it has the +ollowig owerships a! permissios

[bill@linuxbox ~]$ ls -ld /usr/local/share/Ousicdr9xr-xr-x ! root root %(0. !((/-(-!# #/:(" 6usr6local6share6+usic

$s we ca see, the !irectory is owe! %y roota! has / permissios. To make this

!irectory shara%le, billee!s to chage the gro"p owership a! the gro"p permissios

to allow writig

[bill@linuxbox ~]$ sudo chown music /usr/local/share/Ousic[bill@linuxbox ~]$ sudo chmod CC" /usr/local/share/Ousic[bill@linuxbox ~]$ ls -ld /usr/local/share/Ousicdr9xr9xr-x ! root music %(0. !((/-(-!# #/:(" 6usr6local6share6+usic

So what !oes this all mea t meas that we ow ha#e a !irectory,6usr6local6share6+usic that is owe! %y root a! allows rea! a! write

access to gro"p music. ;ro"p musichas mem%ers billa! karen, th"s billa!

karenca create +iles i !irectory 6usr6local6share6+usic. 7ther "sers ca

list the cotets o+ the !irectory %"t caot create +iles there."t we still ha#e a pro%lem. With the c"rret permissios, +iles a! !irectories create!withi the >"sic !irectory will ha#e the ormal permissios o+ the "sers bill a!

karen

[bill@linuxbox ~]$ & /usr/local/share/Ousic/testfile[bill@linuxbox ~]$ ls -l /usr/local/share/Ousic-r9-r--r-- # bill bill ( !((/-(-!% !(:( testOfile

$ct"ally there are two pro%lems. irst, the !e+a"lt umasko this system is 0022 which

pre#ets gro"p mem%ers +rom writig +iles %elogig to other mem%ers o+ the gro"p.This wo"l! ot %e a pro%lem i+ the share! !irectory oly cotaie! +iles, %"t sice this!irectory will store m"sic, a! m"sic is "s"ally orgaiDe! i a hierarchy o+ artists a!al%"ms, mem%ers o+ the gro"p will ee! the a%ility to create +iles a! !irectories isi!e!irectories create! %y other mem%ers. We ee! to chage the umask"se! %y billa!

0


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E3ercisig 7"r 6ri#ileges

karento 0002 istea!.

Seco!, each +ile a! !irectory create! %y oe mem%er will %e set to the primary gro"p o+the "ser rather tha the gro"p music. This ca %e +i3e! %y settig the setgi! %it o the

!irectory

[bill@linuxbox ~]$ sudo chmod g5s /usr/local/share/Ousic[bill@linuxbox ~]$ ls -ld /usr/local/share/Ousicdr9xr9sr-x ! root music %(0. !((/-(-!% !(:( 6usr6local6share6+usic

&ow we test to see i+ the ew permissios +i3 the pro%lem. bill sets his umask to

0002, remo#es the pre#io"s test +ile, creates a ew test +ile a! !irectory

[bill@linuxbox ~]$ umask 2[bill@linuxbox ~]$ rm /usr/local/share/Ousic/testfile[bill@linuxbox ~]$ & /usr/local/share/Ousic/testfile[bill@linuxbox ~]$ mkdir /usr/local/share/Ousic/testdir[bill@linuxbox ~]$ ls -l /usr/local/share/Ousicdr9xr9sr-x ! bill music %(0. !((/-(-!% !(:!% testOdir-r9-r9-r-- # bill music ( !((/-(-!% !(:!! testOfile[bill@linuxbox ~]$

oth +iles a! !irectories are ow create! with the correct permissios to allow allmem%ers o+ the gro"p musicto create +iles a! !irectories isi!e the +usic!irectory.

The oe remaiig iss"e is umask. The ecessary settig oly lasts "til the e! o+sessio a! m"st %e reset. the e3t part o+ the %ook, we


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0 6ermissios

[me@linuxbox ~]$ passwdNcurrentP 3LAV 7ass9ord:Le9 3LAV 7ass9ord:

The 7ass9dcomma! will try to e+orce "se o+ ?strog@ passwor!s. This meas the it

will re+"se to accept passwor!s that are too short, too similar to pre#io"s passwor!s, are!ictioary wor!s, or too easily g"esse!

[me@linuxbox ~]$ passwdNcurrentP 3LAV 7ass9ord:Le9 3LAV 7ass9ord:H4' 4**,R': is too similar to the old oneLe9 3LAV 7ass9ord:H4' 4**,R': it is ,4U too short

Le9 3LAV 7ass9ord:H4' 4**,R': it is based on a dictionar1 9ord

+ yo" ha#e s"per"ser pri#ileges, yo" ca speci+y a "ser ame as a arg"met to the7ass9d comma! to set the passwor! +or aother "ser. There are other optios

a#aila%le to the s"per"ser to allow acco"t lockig, passwor! e3piratio, etc. See the7ass9dma page +or !etails.

;urther eading

Wikipe!ia has a goo! article o malwarehttpe.wikipe!ia.orgwiki>alware

There are "m%er o+ comma! lie programs "se! to create a! maitai "sers a!gro"ps. or more i+ormatio, see the ma pages +or the +ollowig comma!s

adduser

useradd

grou7add

2
http://en.wikipedia.org/wiki/Malwarehttp://en.wikipedia.org/wiki/Malware


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6rocesses

11 rocesses

>o!er operatig systems are "s"ally multitasking, meaig that they create the ill"sioo+ !oig more tha oe thig at oce %y rapi!ly switchig +rom oe e3ec"tig program toaother. The *i"3 kerel maages this thro"gh the "se o+processes. 6rocesses are how*i"3 orgaiDes the !i++eret programs waitig +or their t"r at the C6).

Sometimes a comp"ter will %ecome sl"ggish or a applicatio will stop respo!ig. this chapter, we will look at some o+ the tools a#aila%le at the comma! lie that let "se3amie what programs are !oig, a! how to termiate processes that are mis%eha#ig.

This chapter will itro!"ce the +ollowig comma!s

7s :eport a sapshot o+ c"rret processes

to7 'isplay tasks

jobs *ist acti#e 4o%s

bg 6lace a 4o% i the %ackgro"!

fg 6lace a 4o% i the +oregro"!

kill Se! a sigal to a process

killall Mill processes %y ame

shutdo9n Sh"t!ow or re%oot the system

3o4 # Process +or(s

Whe a system starts "p, the kerel iitiates a +ew o+ its ow acti#ities as processes a!la"ches a program calle! init. init, i t"r, r"s a series o+ shell scripts locate! i

6etcF calle! init scripts, which start all the system ser#ices. >ay o+ these ser#ices are

implemete! as daemon programs, programs that 4"st sit i the %ackgro"! a! !o theirthig witho"t ha#ig ay "ser iter+ace. So e#e i+ we are ot logge! i, the system is atleast a little %"sy per+ormig ro"tie st"++.

The +act that a program ca la"ch other programs is e3presse! i the process scheme asaparent processpro!"cig a child process.

(


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The kerel maitais i+ormatio a%o"t each process to help keep thigs orgaiDe!. ore3ample, each process is assige! a "m%er calle! a process * or 6*. 6's areassige! i asce!ig or!er, with init always gettig 6' . The kerel also keeps

track o+ the memory assige! to each process, as well as the processes< rea!iess tores"me e3ec"tio. *ike +iles, processes also ha#e owers a! "ser 's, e++ecti#e "ser's, etc.

Vie4ing Processes

The most commoly "se! comma! to #iew processes there are se#eralF is 7s. The 7s

program has a lot o+ optios, %"t i it simplest +orm it is "se! like this

[me@linuxbox ~]$ ps A' TTU TA+& C+'

"#0/ 7ts6# ((:((:(( bash#(#!0 7ts6# ((:((:(( 7s

The res"lt i this e3ample lists two processes, process 98 a! process 029, which arebasha! 7s respecti#ely. $s we ca see, %y !e+a"lt, 7s!oes


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Riewig 6rocesses

$!!ig the ?3@ optio ote that there is o lea!ig !ashF tells 7sto show all o+ o"r

processes regar!less o+ what termial i+ ayF they are cotrolle! %y. The presece o+ a?@ i the TTUcol"m i!icates o cotrollig termial. )sig this optio, we see a list

o+ e#ery process that we ow.Sice the system is r"ig a lot o+ processes, 7spro!"ces a log list. t is o+te help+"l

to pipe the o"tp"t +rom 7sito less+or easier #iewig. Some optio com%iatios also

pro!"ce log lies o+ o"tp"t, so ma3imiDig the termial em"lator wi!ow may %e agoo! i!ea, too.

$ ew col"m title! *T4Thas %ee a!!e! to the o"tp"t. *T4Tis short +or ?state@ a!

re#eals the c"rret stat"s o+ the process

Table 11-1: 6rocess States

State >eaning

R :"ig. This meas that the process is r"ig or rea!y to r".

* Sleepig. $ process is ot r"igH rather, it is waitig +or a e#et,s"ch as a keystroke or etwork packet.

' )iterr"pti%le Sleep. 6rocess is waitig +or 7 s"ch as a !isk!ri#e.

T Stoppe!. 6rocess has %ee istr"cte! to stop. >ore o this later.

I $ !e+"ct or ?Dom%ie@ process. This is a chil! process that hastermiate!, %"t has ot %ee cleae! "p %y its paret.

X $ high priority process. t


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[me@linuxbox ~]$ ps aux3*&R A' 5C3 5+&+ ;*I R** TTU *T4T *T4RT TA+& C++4L'root # (


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6rocesses

that are waitig to r", that is, the "m%er o+processes that are i a r"a%le state a! aresharig the C6). Three #al"es are show,

each +or a !i++eret perio! o+ time. The +irst isthe a#erage +or the last K0 seco!s, the e3t thepre#io"s mi"tes, a! +ially the pre#io"s mi"tes. Ral"es "!er .0 i!icate that themachie is ot %"sy.

2 Tasks: This s"mmariDes the "m%er o+ processes a!their #ario"s process states.

( C7uNsP: This row !escri%es the character o+ theacti#ities that the C6) is per+ormig.

(aager i Wi!ows worksF, %"t +i!

that to7is %etter tha the graphical #ersios %eca"se it is +aster a! it cos"mes +ar

+ewer system reso"rces. $+ter all, o"r system moitor program sho"l!


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Cotrollig 6rocesses

e3perimets, we


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program. WeIll !o this %y placig the program i the background. Thik o+ the termialas ha#ig a foregroundwith st"++ #isi%le o the s"r+ace like the shell promptF a! a%ackgro"! with hi!!e st"++ %ehi! the s"r+ace.F To la"ch a program so that it is

imme!iately place! i the %ackgro"!, we +ollow the comma! with a- ?^@ character

[me@linuxbox ~]$ xlogo '[#] !/!.[me@linuxbox ~]$

$+ter eterig the comma!, the xlogowi!ow appeare! a! the shell prompt ret"re!,

%"t some +"y "m%ers were prite! too. This message is part o+ a shell +eat"re calle!Aob control. With this message, the shell is tellig "s that we ha#e starte! 4o% "m%er ?[#]@F a! that it has 6' 282(K. + we r" 7s, we ca see o"r process

[me@linuxbox ~]$ ps A' TTU TA+& C+'#(.( 7ts6# ((:((:(( bash!/!. 7ts6# ((:((:(( xlogo!/!0 7ts6# ((:((:(( 7s

The shell


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Cotrollig 6rocesses

xlogo

The comma! fg+ollowe! %y a percet sig a! the 4o% "m%er calle! aAobspecF !oesthe trick. + we oly ha#e oe %ackgro"! 4o%, the 4o%spec is optioal. To termiatexlogo, type Ctrl-c.

Sto55ing E'ausingF A 'ro/ess

Sometimes weo#ig a process +rom the +oregro"! to the %ackgro"! is ha!y i+ we la"ch agraphical program +rom the comma!, %"t +orget to place it i the %ackgro"! %yappe!ig the trailig ?^@.

Why wo"l! yo" wat to la"ch a graphical program +rom the comma! lie There aretwo reasos. irst, the program yo" wish to r" might ot %e liste! o the wi!ow

maager


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Signals

The killcomma! is "se! to ?kill@ programs. This allows "s to

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The Linux Command Line-09.12

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