Micro_Mart_-_January_7_2016_

thecursorispromptingyoutotypea command.Commands
inLinuxare sometimesreferredtoasbinaries,whichsimply
meansthatthey’re pre-compiledcode.Theyrunina terminal
session,butsomecandetachfromthesessionandruninthe
background,waitingforaneventtotriggerthem.Thistypeof
commandissaidtoberunningasa daemon.
Scriptsare essentiallytextfilesthatcanberunasan
executableprogram.Theyconsistofa seriesofcommands
combinedusingtheshell’s commandsyntaxtocarryoutmore
complextasks.
OneimportantdifferencebetweenLinuxandtheWindows
DOSshellisthatLinuxiscasesensitive.Commandsare almost
alwayslower-caseonly, butfilesordirectoriesmaynotbe,
so/home/Picturesisdifferentto/home/pictures,forexample.
Thisiseasytoforgetatfirstandcan§leadto‘commandnot
found’or‘nosuchfileordirectory’errors.

Anothercommonproblemis‘permissiondenied’when
tryingtousea command.Thisisusuallyeitherbecauseyou
donothavepermissiontoexecutethecommandoryou
donothaveaccesstofilesyouare tryingtomodify. Many
commandsrequire rootaccess.Aswellasbeingthebaseof
thedirectorytree,rootistheallpowerfulsuperuser, whocan
accessallareas(ofwhichmore later).

FindingYourWayAround
Navigatinga filesystemwithouta GUIcanbeconfusingatfirst.
Thefilesystemisconsideredtobeshapedlikea tree.The
baseofthesystemistheroot,andthisbranchesinto...er,
directories.Directoriescancontainfilesandotherdirectories.
Thetreeanalogyisthentotallylost,asa directorycontaining
otherdirectoriesisknownastheparent,andthedirectories
itcontainsare calledchilddirectories.Theforwardslashis
usedtodenotea steponthepathtoa particularfile.The
rootdirectoryisdesignatedbya singleforwardslash( / ) and
shouldonlycontaindirectories.Eachstepdeeperintothe
directorytreeismarkedwitha furtherforwardslashthus:/
var/log/test/test.log.
Bydefault,whenyoulauncha shellsession,youwillbe
inyourownhomedirectory, whichwillbe/home/<youruser
name>(e.g./home/fred).
Thelsandcdcommandscanbeusedtofindyourway
aroundthefilesystem,andI suggestyoutrytheseoutto
familiariseyourselfwithyournewdomain.
ls(list)isusedtoviewthecontentsofthecurrentdirectory,
showingallfilesandsubdirectories.Itcanalsobeusedto
displaythecontentsofa differentdirectory(e.g.ls/etcwill
listthecontentsofthe/etcdirectory).
Someshellsindicatethetypeoffilesina directoryby
colours.Forexample,inmyshell,executablesare green,text
filesare white,anddirectoriesare blue.
cd(changedirectory)isthecommandusedtomovearound
thefilesystem.Itcanbeusedtomoveupanddownthe
filesystemtreeortojumptoanotherlocationwithinit.Typing

cdonitsownwillreturnyoutoyourhomedirectory. cd/ will

takeyoudirecttothe/ (root)directory, andtypinga pathwill

takeyoudirectlytothedirectoryattheendofit(e.g.cd/var/

logwilltakeyoutothelogdirectoryinside/var).

There are severalabbreviationsthatare useful:

..representstheparentdirectory, socd..willmoveyouup

onestep.

• representsthepreviousdirectory, socd- jumpsbackto
  where youjustcamefrom.
  ./representsthecurrentdirectoryandisusedforexecuting
  commandswithinthecurrentworkingdirectory(e.g../
  installscriptorsudo./installscriptwillrunthecommand
  installscriptwithinyourcurrentworkingdirectory).
  ~representsthehomedirectoryofthecurrentlylogged-in
  user, socd~/PictureswilltakeyoutothePicturesdirectoryin
  yourownhomefolder.

Whenyougetlost,a usefulcommandispwd(print

workingdirectory),whichwilldisplaythefullpathofthe

directorythatyouare currentlyworkingin(e.g./var/log/

www).

CommandUsage

ThoseofyouwhohaveusedDOSwillseesomesimilaritiesin

theLinuxshell.Bothofthemare basedhistoricallyontheUnix

commandline.

Whenyoutypea command,theshellwillsearcha seriesof

directoriesinturnandexecutethefirstmatchingcommand

thatitfinds.This meansoncea commandisinstalled,just

typingitsnameatthecommandpromptwillrunit.

iVariousstylesofdirectorylisting:ls,ls -l andls -a

Navigating a files ystem

without a GUI can be

confusing at first

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