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A PROJECT REPORT
ON
RHEL 5Submittedto
HCLCDC Patna.
RED HAT NETWORD SERVICES AND SECURITY ADMINISTRATION
Submittedby
Mr. Ravi Narain
COMBO BATCH(Pat Com 002)
Reg No:-800119695
Under theguidance
Mr. Prashant kumar chaudhary.
HCLCDC PATNA.
8th
Commercial Building NorthS.K.Puri
Near Children Park Boring Road Patna.
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ACKNOWLEDGEMENTS
Before I getintothink ofthethings w ould liketo addheartfelt
words for the people
who where partofthis PROJECTREPORT innumerous ways
People whogaveunending support.
We arehighlyindebtedto Mr. Amit Kumar Center Manager ofHCLCDC
Patna, for his
encouragement andfor providing all thenecessaryfacilities.
Itis withgreat pleasurethat we acknowledgetheconsolation and
assistanceof
Mr. Prashant kumar chaudhary projectguide. Tohimowemorethan
wecanmention.. mostly
for teachingus to seethe silver liningineverydark cloud.
Andfinallymyheartfelt appreciationtomycolleagues. no word are
sufficientto
express mygratitudetomyfriend and seniors for their
kindcooperation.
Mr. Ravi Narain
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CERTIFICATE
This is tocertifiedthatthe project reportonRHEL 5
submittedby Mr. Ravi Narain
as a
partial fulfillmentfor requirementofHCLCDC Patna for the
academic session 2007 is the
original work carriedoutbyhimunder the supervision
andguidanceofMr.Prashant kumar
chaudharytrainer ofHCLCDC PATNA.
HCLCDC Patna Center Manager
Place: Patna Guide
Date: 22/11/2008
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CONTENTS
Case Studies
01. Whatis Linux
02. Differentflavors ofLinux & Architecturedifferentfrom
Windows.
03. Comparetheuser/ group managementin Linux & Windows.
04. FileSystemSupportedby Linuxincludingfile systems
nativetoother OS.
05. Not all ofthenetwork driver are supportedby Linux, so
searchthe Web and
getthedrivers in Rpms / binaries andmakethem work.
06. Configure Mail Server Sendmail.
Project
Add Physical memorytothe system andmodifythe swap
partitiontomake
it active.
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LINUX
Linuxhas longbeen a contender inthecorporate worldto Windows .
In addition,
consumer interestis onthe risefor this free, open source
alternativeto Windows or the
Macintosh OS.
Inthedays beforethegraphical user interface (GUI), which was
firstmade popular
byApple (Nasdaq: AAPL) andthenclonedby Microsoft., thecomputing
world was ruledbythe
command-line structure. Whether theoperating system was Unixor
DOS, graphics and audio
capabilities were limited. Computer users typedcommands at a
promptto run programs.
Pointingdevices didnotexist andmenus were rudimentary,
text-basedoptions lists.
Linuxdeveloped along similar lines as Windows interms ofGUI and
performance
capabilities withonemajor distinction--upgradingfromone Windows
versionto another was
fairly seamless. Not so with Linux.
"Linuxdominates the server market andis makingbiginroads
intotheembedded
market (TiVo, cell phones, PDAs and routers)," Patrick Davila,
co-hostof"The Linux Link Tech
Show", told LinuxInsider. "The last area for ittoconquer is
onthedesktop."
All things considered, Davila sees Linux as a suitable
replacementfor Windows.
"Linuxis readyfor thedesktop for themajorityofdesktop home
andbusiness users. It's safer
becauseitis not vulnerableto viruses and spyware, is more stable
andis cheaper than running
Windows."
Case Studies - 01
Different Flavors
Linuxis notjust a singleoperating system. Itexists in several
dozen versions called
distributions. Unlike Windows, noonecompanyhas
guidedthedevelopmentofLinux. Today,
the Linux OShas manyfaces andis the
productofmuchfamilycross-breeding.
Its open-sourcenaturecontinues
tocontributetodifferentdevelopment paths. Each
oneis controlledby a uniquecommunityofcode writers,
voluntarytechnical helpers andusers.
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The look andfeel ofthe Linuxdesktop is
controlledbythetypeofshell built around
the Linuxcore. Thetwomost predominant shell architectures are
known as Gnome andKDE .
Theybothhave similarities to Windows.
Some Linuxdistributions aredevelopedonuser-friendly standards,
butnot all ofthem
areeasytouse. Even withthedesktop shell, configuringthe policies
for program access canoftenbeconfusing anduninviting.
The samecanbe saidofthe process ofinstallingthird-party
software. Linux-
capable softwareis distributedin packages, mostlybydownload.
Dependingonthe Linux
version, some (or a lotof) manual interventionmaybeneededfor
software additions notfound
inthe pre-installed software library.
"Linux, bynatureofthedifferentusers that
supporteachofthedistributions, lends
itselfwell tousers with specific requirements," said Nate Melby,
aninstructor at Kaplan
University's School ofInformationSystems and Technology.
The real task is finding a distributionthat suits a potential
user's needs. Live CDs thatcan
runthenewest Linux versions andharddrive partitions
runningdual-boot software let
consumers usetheir hardwarefor multiple purposes, he
suggested.
Thefollowing listincludes distributions that areideal for
novices andothers that arefor
more advancedusers whohave access to IT support:
y Debian GNU/Linuxis a freeoperating system withmorethan 15,490
pre-compiledinstallation packages. Debian runs on almost all PCs,
includingmanyolder models.
y Knoppix Linuxis a freedistributionbasedon Debian GNU/Linux.
Knoppixcomes withrecent Linux software anddesktop environments
thatinclude OpenOffice.org, Abiword,
Gimp, Konqueror, Firefox, Apache, PHP, MySQL andhundreds ofother
open-source
programs.
y Mandriva Linuxusedtobecalled Mandrake Linux andis famous for
its easeofuseforboth servers andhomeofficeuses. The Mandriva Linux
PowerPack contains morethan
2,300 high-quality applications including a completeoffice
suite. This freedistribution
comes with several pre-configured levels ofsecurity. Commercial
supportis available.
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y Red Hat (NYSE: RHT) Enterprise Linuxis the leadingcommercial
platformfor open-sourcecomputing andis soldby subscription. Itis
not a goodchoicefor homeusers and
Linuxnewcomers.
y SuSE Linuxis a leading, professional-class OSthatis popular
bothfor enterprise andhomecomputinguse;SuSE Linux Professional
includes morethan 1,000 leadingopen-
source applications andis availableinenterprise anddesktop
versions. The purchase
price varies withthe version andthenumber ofinstallations.
y Ubuntuis a free Linuxdistributionfor desktop or server use,
whichincludes Live CD,regular releases, applications
installedbydefault, andfastdownloads ofother software
packages. Professional technical supportis available.
y Xandros Desktop Home Edition (US$39.99) and Home Edition
Premium ($79.99)arebuiltonthe Debian Linux platform
andincludetheXandros SecuritySuite withtheXandros
Firewall, Anti-Virus, Xandros Networks Updates, and a
rootkitchecker (anti-spyware).
Linuxis not a free versionofWindows. Thetwo systems differ
notonly visually,
inthegraphical user interfacetheuser sees, but alsofunctionally,
as is frequentlydiscussed,and legallytoboot, whichis
constantlyemphasizedbythe Free softwarecommunity. The
differences betweenthem are sofundamental thatdrawing a
comparisonbetweenthemis
nearlyimpossible. There are somanymoot points
thattheycouldmakeup a very long list.
This partofmy articleconcerns the architectures ofWindows
systems. The systems
themselves arebafflingones, to putitmildly, butto know themis
morethan a necessity. (And a
forced necessity sometimes ) When I say Windows, I meanthe
wholefamilyofoperating
systems - NT/2k/XP/Vista -butmainlyXP Professional. Many a time
Iv e read anti-Microsoft
rants, wherethe authors complained about lack ofcommand
linefunctionality (poor in
Windows and very advancedin Linux), or installation processes,
whichcreate some problemsanderratic applicationupgrades (just atthe
pointthecomparisons to Linux programs like apt-
get, emerge and rpm show up). A lotofgrumbles pertainingto
wrongly set-up defaultuser and
root accounts couldbefoundthere. And soon.
Theseinconveniences aregrievous ones inmyopinion, more, they
shouldbe
branded as top-level ones. Butthefact remains that
somethingcanbedone withthem-more
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or less. For example, any Windows system I mtalking abouthere
allows tocreate a user
account after all. Linux as well makes it possibletounlock root
accountto work with. No
problem. I mustemphasizeonething it can be done. Regardless
whether someone will doit
or not. I can tcontradict as well the sentencethat Windows
defaultconfigurationis p olitically
incorrect
. Butthis verytextconcerns architectural solutions
whichcannotbechangedone
iota, mainlydueto projects derailed
design philosophy.
I admitto a certain simplifications incomments, evendrasticones,
with
premeditation. I wantthe articletobeunderstoodbyeveryone whohas
a basic knowledgeof
operating systems, so I ask those who know the subject well to
remember this anddonot show
the signs ofthe ROTFL syndrome
This is a collectionofrandomthoughts rather than a scientific
article about
Windows architecture so keep this inmind when reading
andcommenting.
As we all know, operating systems makeuseofa user notion. Wecan
logintothe
user account andthen run amok withinthe computer space
the accountis definedby. With
theexceptionofa group ofsystemfunctions which are restrictedfor
a uniqueuser calledthe
s ystem administrator . This factis common knowledge. Itcanbe a
Unixs r oot
, a NetWares
s upervisor , or another a dmin
. Thedistinctivefeatureofthis peculiarityis thefactthatthe
user is a real Master ofhis system as Zeus was for the ancient
Greeks.
Providedthat wedonottalk about Microsoft Windows systems,
otherwisethe
matter wouldbecomemorecomplex. Namely, the Microsofts flagship
producthas at leasttwo
distinct administrators, as someofyou know (and some of you
dont). Oneofthemis called
ADMINISTRATOR user, theother is namedSYSTEM user. The
standardSYSTEM accountis likean a gent
fromthe Wachowskibrothers Ma trixtrilogy. Ifwe look atthe
process listinTask
Managerwell s eethatmostofthembelongtoSYSTEM user. Itis
alsotheowner ofthe
technical files liketheSystem Volume Information (SVI) directory
andits files. Our electronic
friend, theSYSTEM user, is the onlydefaultowner ofthefile,
soifwe wanttocheck the spaceit
takes we will haveto addthe ADMINISTRATOR user tothe
listofpermissibleusers. (Other users
canbe addedtoo, but I donot recommendthis option.)
I will trytoexplaininthenextchapters why I think that T
houghthis bemadness,
yetthereis methodinit
, andthattheSYSTEM user is indispensablefor the Windows
systems
functionality. Butnow, a short afterthoughtonits existencetaken
as a whole. Itis commonknowledgethatevery probleminthe IT
worldcanbe resolvedinmany ways. Are all ofthem
equally simple? Decidedlyno. Butthe Kiss, K eep ItSimple,
Stupid
, rulehas provedto work in
real life. As I have written above, all operating systems
haveonlyone administrator in principle,
andthats a s imple solution. Thats for sure,
thattheexistenceofanother administrator would
automaticallycreatecertaincomplications, to putitmildly. A
trivial example:nearly all common
Windows users donot know how togetintoSVI directory (sotheydon
tneedthe a dvanced
users at all).
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IfI wantedto write a dirtytrick whichgathers a Windows users
passw ords,
projects andeveryday agenda, I d putthedatajustthere.
Firstofall, theSVI directoryis not
visited at all. Whats more, mostoftheusers donot know aboutits
existence. Secondly, the
directoryevinces a magicfeatureofchanging sizeinflushes byup to
several hundreds ofMB -
bothup anddown. (Failover informationis storedthere). Theideal
place. Whatis important, a
computer virus is moreefficientifitis
abletoinfectexecutablefiles withthehighestpermissions. Oncemore,
theSYSTEM user is thebestfor thesetypes oftasks. For sure, the
SYSTEM user will notmake a hue andcry, as itisn t Artificially
Intelligent.
Making an analysis ofa Windows architecture, itmight appear
thatthe
implementationofthe a gent
was vitaltothe system R eally? Ill a nswer in a while.
Lets v ote, which system- Windows or Linux- starts faster. Most
IT users would
votefor the Windows systems. Itis a solid prooffor a thesis
thatone shoulddeal with a
democracy withutmostcare. I suggestto run a test. Lets
measurethe startingtimes ofthetwo
systems withthehelp ofa stopwatch. Lets s tart with Windows
first. We switchonthecomputer, weobserve POST messages or a
BIOSmanufacturers l ogo, and at last weface a boot
manager (GRUB, LILO, etc.) or we see a systems l oading process.
Here weturnonthe
stopwatch. Boringmoments pass. Boredomfillingour limbs T he
systemcrunches andminces
somedata, but we are still lazilyyawning O nemoretime andthe
login window appears. Most
oftheusers would stop the stopwatchnow. Unrecoverableerror! The
system loadingis still
goingon! Wetypein a password and we seehow thegraphical
environmentemerges. Begyour
pardon. Thegraphical environmentandthe system. Windows
systemfinishes loading-
dependingonconfiguration- after several dozens ofseconds after
user actually logs in!
Toexaminethe reasons thatthe systembooting process was solvedin
a particular
way, wemust startfromthegroundup, or seetothenotionofthe systems
kernel. Its funny-buteveryoneuses OperatingSystems names, butonly a
few know whatit reallyis. Ifa precise
definitioncannotbedelivered, itis advisabletocreate a
listoffeatures which will describethe
idea. However, eventheoperating systems sp ecialistcannot
agreehow todefineoperating
systems. Nearly all features arethe same, butthereis always a
small but
. Eventheoperating
systems bible-Silberschatzs book (A. Silberschatz, P. Galvin
Operating System Concepts )
names twodefinitions. Generally, itis consideredthattheoperating
systemis a program, which
runs incessantlyinthecomputer fromthebeginning (whentheoperating
systemhas been
started, notthecomputer!) until thecomputer is turnedoff(or
restarted). All other programs
arecalled appl ications .
Anoperating system resembles a government. It provides means to
proper usage
ofcomputer resources. And similar tothegovernmentitdoesn
tmakeuseofanyuseful
functions. It simplycreates anenvironmentin whichother programs
mightfacilitatetheuseful
functions.
Inthis view theoperating systems definitionis tantamountto a
kerneldefinition. In
other words, onecould place anequality signbetweenthe word k
ernel andthetechnical
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conceptofanoperating system. Generally, the phrase operating
system
is usedtodenote all
those programs which are providedby a manufacturer to
satisfythedemandfor such a working
environment. Thats w hythe Linuxnameis oftenusedtodefinethe
whole system, althoughthe
namedenotes the kernel only. Lets ass umethat when I write about
kernel I will use a full name
-operating system. However, I say s ystem
when I wanttodescribe all the programs as a
whole, together withthe kernel.
Now, thedifficulties appear. The kernel tasks aredefined very
loosely. Noone
knows ifmanagement refers toblocking access to system resources
or to allowingthemtobe
accessible (e.g. a network card), or ithas todeliver a handler
(evenifa partial one). In practice,
the solutionis not a simpleone, as tomaster the resources, their
specifications mustbe known.
Inother words, the problemboils downtoonequestion: whether the
kernel shouldbe a
programcontainingcomplete solutions, however basic, or the
program shouldbefocusedon
only onething- administration, leaving all the works todoto
external (to kernel)
applications?
Withthefirstexample weget a reallybig programcalled a monolithic
kernel. The
secondexampledefines a small andfastmicrokernel, which looks
like an underdeveloped
versionoffullyfledged kernel. Monolithic kernels areusedby Linux
systems (sometimes called
Linuxdistros). Microkernels, for examplethe Machmicrokernel,
arefoundations to Mac OSX
operating systems (attachedto Applecomputers) and
GNU/Hurdoperating system whichis still
inits infancy (whichis thecasefor almosttwodecades).
And another importantmatter. Anoperating system, or
everyoperating system, is
build like a cake (or gteau). As we know thebottom partconsists
ofa layer ofbiscuit, thenits
covered with sweetfudge, then another biscuitdisk, letitbe a
coffee-flavoredone, andonce
more a fudge layer covered withjelly. As far as programmingis
concerned, such a layeredstructureis alsousedbutits called
abstraction layers. And so as wehavethefirstbiscuit level
(layer) in a cake which l ies on a hardware
(on a table), so wehave a kernel inoperating
systems whichmanagethehardware (all operations dependonthe
layer). Next levels arethen
buildontop ofthe kernel. For example-first wehaveX Window
System, thenontop ofit a
graphical environment (e.g. KDE), then window manager (e.g.
kWin), andonlythen, ontop of
all the la yers , a Firefox webbrowser. Itdoes matter thatevery
layer sends messages onlyto
its directneighbors. When ajellydribbles downonto a tableitis
hightimeto layoffthecook.
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Operating System Architecture
Keepinginmindthe layeredmodel we will comeback to Windows
systems
booting. Firstofall wehavetoemphasizethatthe Windows systems k
ernel is similar to a
microkernel. (To be more precise, the kernel is called a hybrid
kernel - it can be placed between
monolithic and microkernels. None the less, it needs many
helpers ).
After startingthecomputer, thefirstthing whichis loadedis a
kernel indeed
(ntoskrnl.exe). Nextcomes its best friend
, namelyHALmodule-H
ardware Abstraction Layerwhichmanages drivers neededfor system
loading. Whentheenvironmentis ready, a Session
Manager is putintomotion (smss.exe - Session Manager Subsystem)
which starts identification
and authentication programs -or using simpleterms - which shows
the login screen. A user
satisfiedthathis Windows is ready
touse, mayenter a password, whichmakes the system
load system permissiondata (Group Policy) andthenhaveup and
runningthetasks definedin
Runonce andRun keys placedin Windows Registry (e.g.
HKLM\SOFTWARE\Microsoft\CurrentVersion\Runonce). Attheend,
Autostart (fromStart Menu)
applications are loaded.
Linux systems present a different approachtowards this problem.
After the
monolithic kernel has been loaded, theinitprocess is started,
whichinturninvokes otherprocesses (I suggesttoissue
apstreecommandin a console whilethis happens). Practically, all
thenecessary system processes are startedduringthe system start.
So when a user sees login
window (or screen) theonlything lefttodois to attendtothe KDE or
GNOME graphical
environments. Anythingbeyondthatis readytouse. (Ubuntuteam works
at presentto replace
theinitscript with anupstartscript. Butitdoesn t affectour
reasoning.)
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Thequestion- which solutionis better -mustbe left without an
answer. However, a
shortdigressionmustbe addedtotheend. Microsoftuses thetrick
notoriously. As psychology
teaches, themostfrustratingis a mans inabilityto act andhis lack
ofinfluenceon any
processes, somovingthe login phaseintothemiddleofstarting
sequenceofevents, will give
theuser psychological comfort andit will be receivedbetter.
Andeventhoughthemonitor has
displayedthefamous task bar andicons, noone will be ableto load
an advanced spreadsheetapplicationor a game. Mostoftheusers are
awaretheymust wait a whileyet. Such solutionis
a better onethan previous ones interms
ofmarketingbutitbacklashes in lesser stabilityor the
systems sa fety and leads sometimes
tothefrustrationofinexperiencedusers.
Takingintoconsiderationthewhole start sequence- Linuxdoesn t
load slower than
Windows systems. Thefoundationofoperating systems, thatis, all
whatis hiddenbehindthe
nameis knownfor years. Theres no wizardryinthis world.
Operating System
Whytheopinionthat Linux systems are safer thanthe Windows
systems is so
prevalent? Perhaps duetothefactthatitis true. But why? Lets
goback tothe previous point.
As I wrote, anoperating system resembles a cake. Youll findits
kernel atthebottom, andits
applications placedontop. Accordingtothecake, picturethe kernel
together with associated
programs creating a socalled kernel layer. The restofthe
runningtasks makeup a user layer. Inother words -the kernel layer
creates anenvironmentin whichtheuser layer is ran. The system
is dividedintotwo-upper and lower parts.
Wecan simplifythematter ifwe areto write aboutthe Linux, Mach
(Mac OS X
kernel), Solaris or BSD systems. Safetytasks are run withinthe
kernel layer. Basically, inthe
kernel alone. The Machmicrokernel has additional safetymodules
which runinthe kernel layer
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as auxiliary programs. Protectionin Unix systems is always on,
moreover, itis simpleinterms of
design andduetothat statisticallytougher tocrack.
The samecannotbe said about Windows systems. The protection
subsystems are
morecomplex andthey run withintheuser layer. The logic
lyingbehindis screwedup. The
operating systemis deafandblind. Itcreates anenvironment. The
programs whichcan talk totheenvironment are startedintheuser layer,
sothe protection which works onthe same level
shouldbeefficient. Readfrom a paper, itis true, but lifeis not
so rosy. Firstofall, any program
runningintheuser layer (protectionis implemented as another
program) is more vulnerableor
proneto disarmament
than protectionimplementedinthe kernel layer. For second,
oneof
themost popular computer protection systems, not playing
withdetails, is a firewall. As it
works intheuser layer, itmustbedesignedin such a waythatit
shouldn tfinditselfnot
startinginthe systems l oading process. At last, itis a program,
andcontrarytothe kernel itself,
itdoesn thaveto work.
A small digression. I have writtenearlier aboutthe SYSTEM user .
This SYSTEM isneededbythe Windows systems to start programs
intheuser layer, amongothers. After all, we
mustn t waitto launch a firewall until JohnSmithis logged-in
(after several hours in whichhis
computer has beenup and running). SotheSYSTEM user is used.
Butit suffices, likeinthe
Machexample, to placethe protection subsystemin lower layer
andhavethe problemoffofa
head.
Lets ass ume something likethis. I have loggedinto a Windows
system as a
commonuser. Lets check whatdisks havebeen attachedtomy systemor
speaking precisely-
whatdisks havebeenmappedtomy system. I havefound, as a normal
user, a few network
disks fromtwo servers. Mycomputer runs several programs. Youll
find amongthem local ones,
onefromthefirst server, and another onefromthe second server.
All the applications makeuseofseveral dozenfiles atonce, someofthem
placedonthetwo servers.
Lets ass umenow that atonetime I havedecidedto readthedata from
a fileowned
by a server administrator (and it has just happened to be me).
Oh, Lord! How I didyearnto
work with any Unix systemin suchconditions! Any attemptto attach
admin resources will end
up withthemessage: Multiple links to server or to shared
resources by the same user, making
use of the users name more than once, is not allowed. Disconnect
all previous server
connections and try to reconnect. Marvelous!
IfI was workingunder Linuxor OSX
I dbe abletomounttheneededdevice andtomakeuseofa file, using a
nice and simple programcalledsmbmount. The programtreats every
connection as a uniqueone and pa ys no attention
to suchconditions where another copyof
itselfhasjustmade a connectiontothe samedeviceunder
thenameofanother user. This is
thedirect resultofconceptuallycomplexdesignoftheuser layer,
which I describedearlier in
this article. Itcanbecommentedonlyone way: another prooffor
superiorityofsimplicityover
complexity.
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Itis notthe authors intentionto rekindle another flame war
between Windows
and Linuxusers. The author asks both sides interestedinthis
topicto refrainfromdarting
names ontoeachother. Ifonefeels necessitytocommentthe article,
please write itis bador
not
, or point whereit shouldbe rewrittenin a broader perspective-
whatdoesn tmeanit
should show superiorityofoneofthe systems over theother. Such a
statement wouldbehighly
subjective. And whenI reckon Windows ar chitectureinferior to
Linuxone, itdoesn tmeanitisinferior. Theydiffer. Writingoperating
systemis a complexmatter andtoomanytimes the
chosen solutionis socalled a s olutionoflesser evil . Oneis
ableto write a similar l ist
of
architectural items pertainingto Linux systems, butit
wouldhavenothingtodo with Photoshop
runningor notoneveryofthetwo systems.
Case Studies - 02
Users and Groups Management in Linux
Control ofusers andgroupsis a coreelementofRed Hat Linux
system
administration.
Userscanbeeither people, meaning accounts tiedto physical users,
or accounts which
existfor specific applications touse.
Groups are logical expressions oforganization, tyingusers
together for a common
purpose. Users withinthe samegroup can read, write, or
executefiles ownedbythegroup.
Eachuser andgroup have a uniquenumerical identificationnumber
called a userid
(UID) and a groupid(GID) respectively.
When a fileis created, itis assigned a user andgroup owner. Itis
also assigned
separate read, write, andexecute permissions for theowner,
thegroup, andeveryoneelse. The
user andthegroup to which a filebelongs, as well as the access
permissions onthefile, canbe
changedbythe rootuser or, inmostcases, bythecreator
ofthefile.
Proper managementofusers andgroups,
andeffectivemanagementoffile
permissions are amongthemostimportanttasks a system
administrator undertakes. For a
detailed look at strategies for managingusers andgroups, refer
tothechapter titledManaging
Accounts and GroupintheRed Hat Linux System Administration
Primer.
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User and Group Management in Windows
Thegroup is is one area where win.mit.edu, or WIN, diverges from
a typical Windows
Domain. WIN users andgroups aredefined andmaintainedinthe MIT
systemofrecord, Moira.
There are a varietyoftools availableto add anexistinguser to
anexistinggroup.
Theseincludethe Moira listmanagement webinterface, moira
commands likeblanche, andthe
WIN machine Moira MMC snap-in.
On a WIN machineyoumay runmoira or blanchefromthecommand lineor
the run
menu. Youmay also startthe Moira MMC snap-infromthemenuitem
"Start-> Programs->
Administrative Tools-> Moira Account Management."
Moira MMC Procedure
To add a user to a group usingthe Moira MMC:
1. SelectList Managementfromthe left panel and rightclick onthe
selection.2. SelectFind Lists.3. Click onName, enter the listname
andhitSearch.4. Selectthe listname andhitDisplay.5. Rightclick
onthe listname and selectProperties.6. Click ontheMemberstab.7.
Ifyouhavethe permission, theAddbutton will be sensitized, soclick
onit.8. Choosethetypeofobjectyou wishto add andenter its name.9.
Click OK.
Case Studies - 03
File System
It keep thedata inorganized. It allocates the spacetothe
anddirectories andit assign
attributes tothefiledirectories.
Linuxusedext2 & ext3
It arrange all thefile anddirectories inhighrical way
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/ This is toplabledirectoryinthehighrical whichis called root.
Itis thetop ofthefile
system structure . All thedirectory aremountedunder it.
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This is a layoutfrom a RedHat system. Dependingonthe system
admin, the
operating system andthemissionofthe UNIXmachine, the
structuremay vary, anddirectories
maybe leftoutor added at will. Thenames arenoteven required;they
areonly a convention.
Thetreeofthefile system starts atthetrunk or slash, indicatedby
a forward slash
(/). This directory, containing all underlyingdirectories
andfiles, is alsocalledtheroot directoryor "the root" ofthefile
system.
Directories that areonlyone level below the rootdirectory
areoften precededby a
slash, toindicatetheir position and preventconfusion withother
directories thatcouldhave
the samename. When starting with a new system, itis always a
goodidea totake a look inthe
rootdirectory. Let's see whatyoucould runinto:
Directory Content
/bin Common programs, sharedbythe system, the system
administrator andtheusers.
/boot
The startup files andthe kernel, vmlinuz. In some
recentdistributions alsogrubdata.
Grubis the GRand Unified Boot loader andis an attempttoget
ridofthemany
differentboot-loaders we know today.
/devContains references to all the CPU peripheral hardware,
which are represented as files
with special properties.
/etcMostimportant systemconfigurationfiles arein /etc, this
directorycontains data
similar tothoseinthe Control Panel in Windows
/home Homedirectories ofthecommonusers.
/initrd (on somedistributions) Informationfor booting. Donot
remove!
/libLibraryfiles, includes files for all kinds ofprograms
neededbythe system andthe
users.
/lost+foundEvery partitionhas a lost+foundinits upper directory.
Files that were savedduring
failures arehere.
/misc For miscellaneous purposes.
/mnt Standardmount pointfor external file systems, e.g. a CD-ROM
or a digital camera.
/net Standardmount pointfor entire remotefile systems
/opt Typicallycontains extra andthird party software.
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Directory Content
/proc
A virtual file systemcontaininginformation about system
resources. Moreinformation
aboutthemeaningofthefiles in procis
obtainedbyenteringthecommandmanproc
in a terminal window. Thefile proc.txtdiscusses the virtual file
systemindetail.
/rootThe administrativeuser's homedirectory.
Mindthedifferencebetween /, the root
directory and /root, thehomedirectoryoftherootuser.
/sbin Programs for usebythe system andthe system
administrator.
/tmpTemporary spacefor usebythe system, cleanedupon reboot,
sodon'tusethis for
saving any work!
/usr Programs, libraries, documentationetc. for all user-related
programs.
/var
Storagefor all variablefiles andtemporaryfiles createdbyusers,
such as logfiles, the
mail queue, the print spooler area, spacefor temporary
storageoffiles downloaded
fromthe Internet, or to keep animageofa CD beforeburningit.
Case Studies - 04
Software project site Oftenindividual software project will
offer their own setof
RPM packages for their own project. This is particularlyuseful
for projectunder continuous
development. Ifthe projectdoesn toffer RPMs, they will
typicallyoffer codein whatis called a
tarball. Thetarball mayincludebinarycodeor moreoften,
sourcecodeyoucanbuildfor your
environment.
Mostfedora repositories are lightondescriptions ofthe packages
theyoffer. The
following list summarizes someother Web sites
thatyoucanbrowsetofinddetailed
information about softwarethat runs in Linux. Thenyoucan search
Fedora repositories for
Fedora-or RHEL-specific versions ofthose packages
*Freshment(www.freshmeat.net) this sitemaintains a massive
indexof
LinuxSoftware. Youcando keyword searches for software projects
or browsefor softwareby
category.
*SourceForge (www.sourceforge.net) This sitehosts thousands
ofopen
source software projects. Youcandownload software
anddocumentationfromthose projects
throughtheSourceForge site.
*Rpmfind (www.rpmfingd.net) This sitehosts thousands ofopen
source
softwarethatis packageinthe RPM Package Management(RPM) format
across a varietyof
repositories. Youcando a keyword searchfromthis Website.
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Wecanjustdownload a single software packagetogetthe
softwareinthat packageto word. Many packagedepends onother
packages. For example
software packagefor playing audio & videotypically
relyonother software packages for
decodingdifferent kinds ofcontent.
Case Studiesb - 05
Sendmail shouldbe installedbydefault whenyou install Red Hat
Linux. If it is not
thenyouneedtoinstall theSendmail RPM's withthe Red
Hatdistribution.
Download the Sendmail RPM's from the RedHat website, from a
mirroror from
your Red Hatinstallation CD.
These RPM's are required:
sendmail-{ver}.i386.rpm
sendmail-cf-{ver}.i386.rpm
sendmail-devel-{ver}.i386.rpm
Configuring Sendmail
1). Editfile "/etc/mail/sendmail.mc" - Look for the line:
DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')
Changethis lineto:
dnl DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')
Savethefile.
2). Makethe sendmail configurationfile:
$>m4 /etc/mail/sendmail.mc> /etc/sendmail.cf
3).RestartSendmail:
$> /etc/rc.d/init.d/sendmail restart
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PROJECT ON RHEL 5
All about Linux swap space
Whenyour computer needs to run programs that arebigger thanyour
available
physical memory, mostmodernoperating systems use a
techniquecalled swapping, in which
chunks ofmemory aretemporarily storedontheharddisk whileother
data is movedinto
physical memory space. Here are sometechniques thatmayhelp
youbetter manage swapping
on Linux systems andgetthebest performancefromthe Linux swapping
subsystem.
Linuxdivides its physical RAM (random access memory) intochucks
ofmemory
called pages. Swappingis the process whereby a pageofmemoryis
copiedtothe preconfigured
spaceontheharddisk, called swap space, tofreeup that
pageofmemory. Thecombined sizes
ofthe physical memory andthe swap spaceis the amountofvirtual
memory available.
Swappingis necessaryfor twoimportant reasons. First, whenthe
system requires
morememorythanis physically available, the kernel swaps out less
used pages andgives
memorytothecurrent application (process) thatneeds
thememoryimmediately. Second, a
significantnumber ofthe pages usedby an applicationduringits
startup phasemayonlybe
usedfor initialization andthennever used again. The systemcan
swap outthose pages andfree
thememoryfor other applications or evenfor thedisk cache.
However, swappingdoes have a downside. Comparedtomemory, disks
are veryslow. Memory speeds canbemeasuredinnanoseconds, whiledisks
aremeasuredin
milliseconds, so accessingthedisk canbetens ofthousands times
slower than accessing
physical memory. Themore swappingthatoccurs, the slower your
system will be. Sometimes
excessive swappingor thrashingoccurs where a pageis swappedout
andthen very soon
swappedin andthen swappedout again and soon. In such situations
the systemis strugglingto
findfreememory and keep applications running atthe sametime.
Inthis caseonly addingmore
RAM will help.
Linuxhas twoforms ofswap space:the swap partition andthe swap
file. The swap
partitionis anindependent sectionoftheharddisk used solelyfor
swapping;noother files can
residethere. The swap fileis a special fileinthefilesystemthat
resides amongstyour system
anddata files.
To see what swap spaceyouhave, usethecommandswapon-s. Theoutput
will look
something likethis:
Filename Type Size Used Priority
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/dev/sda5 partition 859436 0 -1
Each line lists a separate swap spacebeingusedbythe system.
Here, the'Type'field
indicates thatthis swap spaceis a partition rather than a file,
andfrom'Filename' we seethatit
is onthedisk sda5. The'Size'is listedin kilobytes,
andthe'Used'fieldtells us how many
kilobytes ofswap spacehas beenused (inthis casenone).
'Priority'tells Linux which swap spacetousefirst. Onegreatthing
aboutthe Linux swapping subsystemis thatifyoumounttwo (or
more) swap spaces (preferablyontwodifferentdevices) withthe same
priority, Linux will
interleaveits swapping activitybetweenthem,
whichcangreatlyincrease swapping
performance.
To add anextra swap partitiontoyour system, youfirstneedto
prepareit. Step one
is toensurethatthe partitionis marked as a swap partition and
step twois tomakethe swap
filesystem. Tocheck thatthe partitionis markedfor swap, run as
root:
fdisk -l /dev/hdb
Replace /dev/hdb withthedeviceoftheharddisk onyour system
withthe swap
partitiononit. You should seeoutputthat looks likethis:
Device Boot Start End Blocks Id System
/dev/hdb1 2328 2434 859446 82 Linux swap / Solaris
Ifthe partitionisn'tmarked as swap you will needto alter itby
runningfdisk and
usingthe't'menuoption. Becareful when working with partitions
--youdon't wanttodelete
important partitions bymistakeor changetheidofyour system
partitionto swap bymistake.
All data on a swap partition will be lost, sodouble-check
everychangeyoumake. Alsonotethat
Solaris uses the same ID as Linux swap spacefor its partitions,
sobecareful notto kill your
Solaris partitions bymistake.
Once a partitionis marked as swap, youneedto
prepareitusingthemkswap (make
swap) command as root:
mkswap /dev/hdb1
Ifyou seenoerrors, your swap spaceis readytouse. To
activateitimmediately, type:
swapon /dev/hdb1
Youcan verifythatitis beingusedby runningswapon-s. Tomountthe
swap space
automatically atboottime, youmust add anentrytothe
/etc/fstabfile, whichcontains a listof
filesystems and swap spaces thatneedtobemounted atbootup.
Theformatofeach lineis:
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Since swap spaceis a special typeoffilesystem, manyofthese
parameters aren't applicable.
For swap space, add:
/dev/hdb1 none swap sw 0 0
where /dev/hdb1 is the swap partition. Itdoesn'thave a
specificmount point,hencenone. Itis oftypeswap withoptions ofsw,
andthe lasttwo parameters aren'tused so
they areentered as 0.
Tocheck thatyour swap spaceis being automaticallymounted
withouthaving
to reboot, youcan runtheswapoff-acommand (whichturns offall swap
spaces) andthenswapon
-a (whichmounts all swap spaces listedinthe /etc/fstabfile)
andthencheck it withswapon-s.
Swap file
As well as the swap partition, Linux also supports a swap
filethatyoucancreate,prepare, andmountin a fashion similar
tothatofa swap partition. The advantageofswap files
is thatyoudon'tneedtofind anempty partitionor repartition a disk
to add additional swap
space.
Tocreate a swap file, usetheddcommandtocreate anemptyfile.
Tocreate a 1GB file, type:
ddif=/dev/zeroof=/swapfilebs=1024 count=1048576
/swapfileis thenameofthe swap file, andthecountof1048576 is the
sizein kilobytes
(i.e. 1GB).
Preparethe swap fileusingmkswapjust as you would a partition,
butthis timeusethe
nameofthe swap file:
mkswap /swapfile
And similarly, mountitusingthe swaponcommand:swapon
/swapfile.
The /etc/fstabentryfor a swap file would look likethis:
/swapfile none swap sw 0 0
How big should my swap space be?
Itis possibleto run a Linux system without a swap space, andthe
system will run well
ifyouhave a large amountofmemory--butifyou runoutofphysical
memorythenthe system
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will crash, as ithas nothingelseitcando, soitis advisabletohave
a swap space, especially
sincedisk spaceis relativelycheap.
The keyquestionis how much? Older versions ofUnix-typeoperating
systems (such
as Sun OS and Ultrix) demanded a swap spaceoftwotothreetimes
thatofphysical memory.
Modernimplementations (such as Linux) don't requirethatmuch,
buttheycanuseitifyouconfigureit. A ruleofthumbis as follows: 1) for
a desktop system, use a swap spaceofdouble
systemmemory, as it will allow youto run a largenumber
ofapplications (manyofwhichmay
will beidle andeasily swapped), makingmore RAM availablefor the
active applications; 2) for a
server, have a smaller amountofswap available (sayhalfofphysical
memory) sothatyouhave
someflexibilityfor swapping whenneeded, butmonitor the
amountofswap spaceused and
upgradeyour RAM ifnecessary; 3) for older desktop machines (with
sayonly 128MB), use as
much swap space as youcan spare, evenup to 1GB.
The Linux 2.6 kernel added a new kernel parameter
calledswappinessto let
administrators tweak the way Linux swaps. Itis a number from 0
to 100. Inessence, highervalues leadtomore pages being swapped, and
lower values leadtomore applications being
keptinmemory, evenifthey areidle. Kernel maintainer Andrew
Mortonhas saidthathe runs
his desktop machines with a swappiness of100, statingthat "My
pointis thatdecreasingthe
tendencyofthe kernel to swap stuffoutis wrong. You reallydon't
wanthundreds ofmegabytes
ofBloatyApp's untouchedmemoryfloating aboutinthemachine.
Getitoutonthedisk, usethe
memoryfor somethinguseful."
Onedownsideto Morton's idea is thatifmemoryis
swappedouttooquicklythen
application responsetimedrops, because whenthe application's
window is clickedthe system
has to swap the applicationback intomemory, which will
makeitfeel slow.
Thedefault valuefor swappiness is 60. Youcan alter ittemporarily
(until younext
reboot) bytyping as root:
echo 50 > /proc/sys/vm/swappiness
Ifyou wantto alter it
permanentlythenyouneedtochangethevm.swappiness
parameter inthe /etc/sysctl.conffile.
Conclusion
Managing swap spaceis anessential aspectofsystem administration.
Withgood
planning and proper use swappingcan providemanybenefits. Don'tbe
afraidtoexperiment,
and always monitor your systemtoensureyou aregettingthe results
youneed.