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David Jones and Bruce Jamieson (15/10/98) Page 2

ForwardThis text is the third of a series of books which have been written for the CQU

subject 85321, Systems Administration. This is the first version which CQU

has printed and distributed to students and also is the first version which hasconcentrated solely on Linux. More information about the unit 85321 is

available on the unit Web site, http://infocom.cqu.edu.au/85321/

The following is a bit of personal blurb from each of the authors of this text.

David Jones

Writing a book, even one as rough around the edges as this one, is a difficult,

frustrating, complex and lengthy task. During the creation of this book a

number of people helped me keep my sanity while others contributed to the

book itself. The people who kept me sane are too many to mention. Thecontributors include Bruce Jamieson, who wrote a number of the chapters and

offered useful and thoughtfull insights, and Elizabeth Tansley and Kylie Jones

who helped proof the book. As you should be able to tell by now neither

Elizabeth or Kylie proofed this forward.

One thing to come out of writing this text is a reinforcement of my hatred of

Microsoft software, in particular Word for Windows.

Bruce Jamieson

It is traditional for the forward to contain thank-yous and pearls of wisdom. It

is because of this that people don't read forwards. However, in keeping with

tradition, I will do both.

Thanks to Tabby, my cat, who has been consistently neurotic since I started

working on this project, mainly due to my weekend absences disrupting her

feeding times. Thanks also to the guppies whose lives were lost supplementing

the aforementioned cat's diet over this period.

I'd like to make one serious comment: when I began working with UNIX, I

hated it. The reason why I hated it was that I didn't understand it. Its obscure

complexities and (for the want of a better word) "different ness" initially made ithard to learn and understand. It is for the same reasons that I now love

working with UNIX systems - I hope this material will inspire you to feel the

same way.


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85321, Systems Administration Table of Contents


Table of Contents

FORWARD.......................................................................................................................................2

DAVID JONES ..................................................................................................................................2

BRUCE JAMIESON ............................................................................................................................2

TABLE OF CONTENTS .................................................................................................................3

CHAPTER 1 THE WHAT, WHY AND HOW OF SYS ADMIN................................................16

INTRODUCTION .............................................................................................................................16

WHAT SYSTEMS ADMINISTRATORS DO...........................................................................................16

USERS ..........................................................................................................................................17

HARDWARE/SOFTWARE .................................................................................................................18

SUPPORT.......................................................................................................................................18

WHAT SYSTEMS ADMINISTRATORS NEED TO KNOW ........................................................................19

WHY UNIX? ................................................................................................................................ 20

UNIX PAST, PRESENT AND FUTURE ................................................................................................20LINUX ..........................................................................................................................................21

SOME MORE SYS ADMIN THEORY ...................................................................................................21

DAILY OPERATIONS .......................................................................................................................21

AUTOMATE, AUTOMATE AND AUTOMATE .......................................................................................22

SYSTEM MONITORING....................................................................................................................22

HARDWARE AND SOFTWARE ..........................................................................................................23

EVALUATION ................................................................................................................................24

PURCHASE ....................................................................................................................................24

INSTALLATION..............................................................................................................................24

HARDWARE ..................................................................................................................................24

ADMINISTRATION AND PLANNING ..................................................................................................25

DOCUMENTATION .........................................................................................................................26

POLICY.........................................................................................................................................28

PENALTIES....................................................................................................................................28

TYPES OF POLICY ..........................................................................................................................29

CREATING POLICY.........................................................................................................................29

CODE OF ETHICS............................................................................................................................29

SAGE-AU CODE OF ETHICS...........................................................................................................29

SAGE-AU CODE OF ETHICS...........................................................................................................30

PEOPLE SKILLS ..............................................................................................................................31

COMMUNICATING WITH USERS ......................................................................................................31

HOW NOT TO COMMUNICATE WITH USERS.......................................................................................34

CONCLUSIONS...............................................................................................................................35

CHAPTER 2 INFORMATION SOURCES.................................................................................. 36INTRODUCTION .............................................................................................................................36

PROFESSIONAL ORGANISATIONS.....................................................................................................36

OTHER ORGANISATIONS ................................................................................................................37

THE SAGE GROUPS ......................................................................................................................37

THE ACS......................................................................................................................................37

UNIX USER GROUPS .....................................................................................................................37

USEFUL BOOKS AND MAGAZINES ....................................................................................................38

BIBLIOGRAPHIES...........................................................................................................................38

MAGAZINES ..................................................................................................................................39

INTERNET RESOURCES ...................................................................................................................39

HOW TO USE THE INTERNET ...........................................................................................................39

SOFTWARE ON THE INTERNET ........................................................................................................39DISCUSSION FORUMS .....................................................................................................................40

USENET NEWS ...............................................................................................................................40


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USEFUL NEWSGROUPS....................................................................................................................40

MAILING LISTS..............................................................................................................................41

OTHER DISCUSSION FORUMS .........................................................................................................41

INFORMATION...............................................................................................................................41

WORLD-WIDE WEB ......................................................................................................................41

ANONYMOUS FTP.........................................................................................................................42

INTERNET BASED LINUX RESOURCES ..............................................................................................42THE LINUX DOCUMENTATION PROJECT..........................................................................................42

REDHAT .......................................................................................................................................42

CONCLUSIONS...............................................................................................................................43

REVIEW QUESTIONS ......................................................................................................................43

CHAPTER 3 USING UNIX............................................................................................................44

INTRODUCTION .............................................................................................................................44

INTRODUCTORY UNIX..................................................................................................................44

UNIX COMMANDS ARE PROGRAMS ................................................................................................45

VI ................................................................................................................................................45

AN INTRODUCTION TO VI ..............................................................................................................45

UNIX COMMANDS ........................................................................................................................46PHILOSOPHY OF UNIX COMMANDS................................................................................................46

UNIX COMMAND FORMAT.............................................................................................................46

A COMMAND FOR EVERYTHING ......................................................................................................47

ONLINE HELP ................................................................................................................................48

USING THE MANUAL PAGES ............................................................................................................48

IS THERE A MAN PAGE FOR... ..........................................................................................................48

MAN PAGE FORMAT........................................................................................................................49

SOME UNIX COMMANDS...............................................................................................................49

IDENTIFICATION COMMANDS .........................................................................................................50

SIMPLE COMMANDS.......................................................................................................................51

FILTERS........................................................................................................................................51

UNIQ .............................................................................................................................................53

TR ................................................................................................................................................53

CUT...............................................................................................................................................54

PASTE ...........................................................................................................................................54

GREP .............................................................................................................................................55

WC ................................................................................................................................................55

GETTING MORE OUT OF FILTERS .....................................................................................................56

CONCLUSIONS...............................................................................................................................56

CHAPTER 4 THE FILE HIERARCHY.......................................................................................57

INTRODUCTION .............................................................................................................................57

WHY?...........................................................................................................................................57

THE IMPORTANT SECTIONS ............................................................................................................58

THE ROOT OF THE PROBLEM...........................................................................................................58

HOMES FOR USERS.........................................................................................................................59

EVERY USER NEEDS A HOME...........................................................................................................59

OTHER HOMES?.............................................................................................................................60

/USR AND/VAR.............................................................................................................................60

AND THE DIFFERENCE IS... .............................................................................................................60

/USR/LOCAL .................................................................................................................................61

LIB, INCLUDE AND SRC...................................................................................................................62

/VAR/SPOOL .................................................................................................................................62

X WINDOWS.................................................................................................................................63

BINS.............................................................................................................................................63

WHICH BIN?..................................................................................................................................63

/BIN ............................................................................................................................................64/SBIN...........................................................................................................................................64


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/USR/BIN.....................................................................................................................................65

/USR/LOCAL/BIN .........................................................................................................................65

CONFIGURATION FILES, LOGS AND OTHER BITS!..............................................................................65

ETC ETC ETC. ................................................................................................................................65

LOGS............................................................................................................................................66

/PROC...........................................................................................................................................66

/DEV ............................................................................................................................................66CONCLUSION ................................................................................................................................66

FUTURE STANDARDS .....................................................................................................................66


4.1 ...............................................................................................................................................67

4.2 ...............................................................................................................................................67

4.3 ...............................................................................................................................................67

CHAPTER 5 PROCESSES AND FILES.......................................................................................68

INTRODUCTION .............................................................................................................................68

MULTIPLE USERS...........................................................................................................................68

IDENTIFYING USERS.......................................................................................................................68

USERS AND GROUPS.......................................................................................................................69NAMES AND NUMBERS ...................................................................................................................69

ID ................................................................................................................................................69

COMMANDS AND PROCESSES..........................................................................................................70

WHERE ARE THE COMMANDS?........................................................................................................70

WHICH ...........................................................................................................................................70

WHEN IS A COMMAND NOT A COMMAND? .......................................................................................70

CONTROLLING PROCESSES .............................................................................................................71

PROCESS ATTRIBUTES....................................................................................................................71

PARENT PROCESSES .......................................................................................................................71

PROCESS UID AND GID ................................................................................................................72

REAL UID AND GID......................................................................................................................72

EFFECTIVE UID AND GID..............................................................................................................72FILES............................................................................................................................................73

FILE TYPES ...................................................................................................................................73

TYPES OF NORMAL FILES................................................................................................................73

FILE ATTRIBUTES ..........................................................................................................................74

VIEWING FILE ATTRIBUTES ............................................................................................................74

FILE PROTECTION..........................................................................................................................76

FILE OPERATIONS ..........................................................................................................................76

USERS, GROUPS AND OTHERS .........................................................................................................77

THREE SETS OF FILE PERMISSIONS...................................................................................................77

SPECIAL PERMISSIONS....................................................................................................................78

CHANGING PASSWORDS .................................................................................................................79

NUMERIC PERMISSIONS..................................................................................................................80

SYMBOLIC TO NUMERIC .................................................................................................................81EXERCISES....................................................................................................................................81

CHANGING FILE PERMISSIONS ........................................................................................................82

CHANGING PERMISSIONS ...............................................................................................................82

CHANGING OWNERS ......................................................................................................................83

CHANGING GROUPS .......................................................................................................................83

THE COMMANDS ...........................................................................................................................84

DEFAULT PERMISSIONS ..................................................................................................................85

FILE PERMISSIONS AND DIRECTORIES..............................................................................................86

FOR EXAMPLE ...............................................................................................................................86

WHAT HAPPENS IF? .......................................................................................................................88

LINKS ...........................................................................................................................................88

SEARCHING THE FILE HIERARCHY...................................................................................................89THE FIND COMMAND .....................................................................................................................89


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EXERCISES....................................................................................................................................93

PERFORMING COMMANDS ON MANY FILES.......................................................................................94

FIND AND-EXEC ...........................................................................................................................94

FIND AND BACK QUOTES ................................................................................................................95

FIND AND XARGS ............................................................................................................................95

CONCLUSION ................................................................................................................................96


CHAPTER 6 THE SHELL ...........................................................................................................99

INTRODUCTION .............................................................................................................................99

EXECUTING COMMANDS................................................................................................................99

DIFFERENT SHELLS......................................................................................................................100

STARTING A SHELL ......................................................................................................................100

PARSING THE COMMAND LINE ......................................................................................................101

THE COMMAND LINE...................................................................................................................102

ARGUMENTS ...............................................................................................................................102

ONE COMMAND TO A LINE............................................................................................................103

COMMANDS IN THE BACKGROUND................................................................................................104

FILENAME SUBSTITUTION ............................................................................................................104EXERCISES..................................................................................................................................106

REMOVING SPECIAL MEANING ......................................................................................................106

INPUT/OUTPUT REDIRECTION .......................................................................................................108

HOW IT WORKS ...........................................................................................................................108

FILE DESCRIPTORS.......................................................................................................................109

STANDARD FILE DESCRIPTORS......................................................................................................109

CHANGING DIRECTION.................................................................................................................109

USING STANDARD I/O..................................................................................................................110

FILTERS......................................................................................................................................110

I/O REDIRECTION EXAMPLES........................................................................................................111

REDIRECTING STANDARD ERROR..................................................................................................111

EVALUATING FROM LEFT TO RIGHT ..............................................................................................112

EVERYTHING IS A FILE .................................................................................................................113

TTY.............................................................................................................................................113

DEVICE FILES ..............................................................................................................................114

REDIRECTING I/O TO DEVICE FILES ..............................................................................................114

SHELL VARIABLES .......................................................................................................................115

ENVIRONMENT CONTROL.............................................................................................................115

THE SET COMMAND .....................................................................................................................116

USING SHELL VARIABLES .............................................................................................................116

ASSIGNING A VALUE ....................................................................................................................116

ACCESSING A VARIABLE'S VALUE .................................................................................................116

UNINITIALISED VARIABLES ..........................................................................................................117

RESETTING A VARIABLE...............................................................................................................117

THE READONLY COMMAND ............................................................................................................117THE UNSET COMMAND .................................................................................................................117

ARITHMETIC ...............................................................................................................................118

THE EXPR COMMAND ...................................................................................................................118

VALID VARIABLE NAMES..............................................................................................................119

{} ..............................................................................................................................................119

ENVIRONMENT CONTROL.............................................................................................................119

PS1ANDPS2.............................................................................................................................120

BASH EXTENSIONS........................................................................................................................120

VARIABLES AND SUB-SHELLS .......................................................................................................120

FOR EXAMPLE .............................................................................................................................121

EXPORT .......................................................................................................................................121

LOCAL VARIABLES ......................................................................................................................121ADVANCED VARIABLE SUBSTITUTION ...........................................................................................122


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EVALUATION ORDER ...................................................................................................................123

WHY ORDER IS IMPORTANT..........................................................................................................123

THE ORDER.................................................................................................................................123

THE EVAL COMMAND ...................................................................................................................124

DOING IT TWICE ..........................................................................................................................124

CONCLUSION ..............................................................................................................................124

REVIEW QUESTIONS ....................................................................................................................125

CHAPTER 7 TEXT MANIPULATION ..................................................................................... 127

INTRODUCTION ...........................................................................................................................127

REGULAR EXPRESSIONS ...............................................................................................................127

RES VERSUS FILENAME SUBSTITUTION..........................................................................................128

HOW THEY WORK........................................................................................................................129

EXTENSIONS TO REGULAR EXPRESSIONS .......................................................................................129

EXAMPLES ..................................................................................................................................130

EXERCISES..................................................................................................................................130

TAGGING ....................................................................................................................................131

FOR EXAMPLE .............................................................................................................................131

EXERCISES..................................................................................................................................132EX, ED, SED AND VI ...................................................................................................................132

SO???.........................................................................................................................................132

WHY USE ED?..............................................................................................................................132

ED COMMANDS ............................................................................................................................133

FOR EXAMPLE .............................................................................................................................135

THE SED COMMAND .....................................................................................................................136

SED COMMAND FORMAT ...............................................................................................................136

CONCLUSIONS.............................................................................................................................137


CHAPTER 8 SHELL PROGRAMMING....................................................................................140

INTRODUCTION ...........................................................................................................................140SHELL PROGRAMMING - WHY?................................................................................................... 140

SHELL PROGRAMMING - WHAT?................................................................................................. 140

SHELL PROGRAMMING - HOW?................................................................................................... 141

THE BASICS ................................................................................................................................141

A BASIC PROGRAM .....................................................................................................................141

AN EXPLANATION OF THE PROGRAM ............................................................................................143

ALL YOU EVER WANTED TO KNOW ABOUT VARIABLES................................................................144

WHY?.........................................................................................................................................145

PREDEFINED VARIABLES .............................................................................................................145

PARAMETERS - SPECIAL SHELL VARIABLES ..................................................................................146

ONLY NINE PARAMETERS? .......................................................................................................... 148

EXERCISE ...................................................................................................................................148

THE DIFFERENCE BETWEEN $* AND$@........................................................................................149THE BASICS OF INPUT/OUTPUT (IO) ..............................................................................................149

AND NOW FOR THE HARD BITS .....................................................................................................151

SCENARIO...................................................................................................................................151

IF ... THEN ... MAYBE?..................................................................................................................152

TESTING TESTING... .................................................................................................................... 154

EXPRESSIONS, EXPRESSIONS!.......................................................................................................155

EXERCISE ...................................................................................................................................156

ALL ABOUT CASE.........................................................................................................................156

LOOPS AND REPEATED ACTION COMMANDS .................................................................................157

WHILE .........................................................................................................................................158

FOR.............................................................................................................................................159

UNTIL .........................................................................................................................................160BREAKAND CONTINUE...................................................................................................................161


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REDIRECTION..............................................................................................................................162

NOW FOR THE REALLY HARD BITS ................................................................................................162

FUNCTIONAL FUNCTIONS.............................................................................................................162

LOCAL .........................................................................................................................................163

THE RETURN TRIP.........................................................................................................................164

RECURSION: (SEE "RECURSION")..................................................................................................164

WAIT'ING AND TRAP'ING ...............................................................................................................165BUGS AND DEBUGGING ...............................................................................................................169

METHOD 1 - SET .........................................................................................................................169

METHOD 2 - ECHO .......................................................................................................................170

VERY COMMON MISTAKES ..........................................................................................................170

AND NOW FOR THE REALLY REALLY HARD BITS.............................................................................170

WRITING GOOD SHELL PROGRAMS................................................................................................170

EVAL THE WONDERFUL! ...............................................................................................................172

STEP-BY-STEP.............................................................................................................................174

THE PROBLEM .............................................................................................................................174

SOLVING THE PROBLEM ...............................................................................................................176

THE FINAL PROGRAM - A LISTING .................................................................................................184

FINAL NOTES ..............................................................................................................................186REVIEW QUESTIONS ....................................................................................................................187

SOURCE OF SCANIT......................................................................................................................188

CHAPTER 9 USERS.................................................................................................................... 191

INTRODUCTION ...........................................................................................................................191

WHAT IS A UNIX ACCOUNT?.......................................................................................................191

LOGIN NAMES .............................................................................................................................191

PASSWORDS................................................................................................................................193

THE UID .................................................................................................................................... 194

HOME DIRECTORIES.....................................................................................................................194

LOGIN SHELL ..............................................................................................................................195

DOT FILES...................................................................................................................................195SKELETON DIRECTORIES ..............................................................................................................196

THE MAIL FILE ............................................................................................................................196

MAIL ALIASES .............................................................................................................................197

ACCOUNT CONFIGURATION FILES .................................................................................................198

/ETC/PASSWD .............................................................................................................................199

EVERYONE CAN READ /ETC/PASSWD ............................................................................................199

THIS IS A PROBLEM ......................................................................................................................199

PASSWORD MATCHING.................................................................................................................200

THE SOLUTION ............................................................................................................................200

SHADOW FILE FORMAT ................................................................................................................200

GROUPS......................................................................................................................................201

/ETC/GROUP ...............................................................................................................................201

SPECIAL ACCOUNTS.....................................................................................................................202

ROOT ...........................................................................................................................................202

RESTRICTED ACTIONS..................................................................................................................202

BE CAREFUL................................................................................................................................203

THE MECHANICS .........................................................................................................................203

OTHER CONSIDERATIONS.............................................................................................................203

PRE-REQUISITE INFORMATION .....................................................................................................203

ADDING AN /ETC/PASSWD ENTRY ................................................................................................204

THE INITIAL PASSWORD ...............................................................................................................204

/ETC/GROUP ENTRY ....................................................................................................................204

THE HOME DIRECTORY ................................................................................................................205

THE STARTUP FILES .....................................................................................................................205

SETTING UP MAIL ........................................................................................................................205TESTING AN ACCOUNT .................................................................................................................206


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INFORM THE USER .......................................................................................................................207

REMOVING AN ACCOUNT .............................................................................................................208

DISABLING AN ACCOUNT .............................................................................................................208

THE GOALS OF ACCOUNT CREATION............................................................................................209

MAKING IT SIMPLE ......................................................................................................................209

USERADD .....................................................................................................................................209

USERDEL AND USERMOD.................................................................................................................210GRAPHICAL TOOLS......................................................................................................................210

AUTOMATION .............................................................................................................................211

GATHERING THE INFORMATION....................................................................................................212

POLICY.......................................................................................................................................212

CREATING THE ACCOUNTS ...........................................................................................................212

ADDITIONAL STEPS .....................................................................................................................213

CHANGING PASSWORDS WITHOUT INTERACTION ...........................................................................213

DELEGATION ..............................................................................................................................213

ALLOCATING ROOT PRIVILEGE.....................................................................................................214

SUDO ...........................................................................................................................................214

SUDO ADVANTAGES......................................................................................................................215

EXERCISES..................................................................................................................................215CONCLUSIONS.............................................................................................................................216


CHAPTER 10 MANAGING FILE SYSTEMS............................................................................218

INTRODUCTION ...........................................................................................................................218

WHAT?.......................................................................................................................................218

WHY?.........................................................................................................................................218

A SCENARIO ...............................................................................................................................219

DEVICES - GATEWAYS TO THE KERNEL .........................................................................................219

A DEVICE IS... ............................................................................................................................. 219

DEVICE FILES ARE... ....................................................................................................................219

DEVICE DRIVERS ARE...................................................................................................................219

/DEV ..........................................................................................................................................220

PHYSICAL CHARACTERISTICS OF DEVICE FILES ..............................................................................222

MAJOR AND MINOR DEVICE NUMBERS ARE... ................................................................................. 222

WHY USE DEVICE FILES?..............................................................................................................223

CREATING DEVICE FILES ..............................................................................................................223

THE USE AND ABUSE OF DEVICE FILES ...........................................................................................224

DEVICES, PARTITIONS AND FILE SYSTEMS ....................................................................................226

DEVICE FILES AND PARTITIONS.....................................................................................................226

PARTITIONS AND FILE SYSTEMS....................................................................................................227

PARTITIONS AND BLOCKS ............................................................................................................228

USING THE PARTITIONS................................................................................................................228

THE VIRTUAL FILE SYSTEM.........................................................................................................229

DIVIDING UP THE FILE HIERARCHY - WHY?....................................................................................230SCENARIO UPDATE......................................................................................................................231

THE LINUX NATIVE FILE SYSTEM - EXT2......................................................................................231

OVERVIEW..................................................................................................................................231

I-NODES .....................................................................................................................................231

PHYSICAL STRUCTURE AND FEATURES .........................................................................................233

CREATING FILE SYSTEMS .............................................................................................................234

MKFS ..........................................................................................................................................234

SCENARIO UPDATE......................................................................................................................234

MOUNTING AND UN-MOUNTING PARTITIONS AND DEVICES ..........................................................235

MOUNT ......................................................................................................................................235

MOUNTING WITH THE /ETC/FSTAB FILE .......................................................................................236

SCENARIO UPDATE......................................................................................................................237FILE OPERATIONS .......................................................................................................................238


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CREATING A FILE.........................................................................................................................238

LINKING FILES.............................................................................................................................238

LN ..............................................................................................................................................239

CHECKING THE FILE SYSTEM ........................................................................................................240

WHY ME?...................................................................................................................................240

WHAT TO DO ..............................................................................................................................240

FSCK...........................................................................................................................................241USING FSCK................................................................................................................................241

WHAT CAUSED THE PROBLEM?.....................................................................................................241

CONCLUSION ..............................................................................................................................242

REVIEW QUESTIONS.....................................................................................................................242

CHAPTER 11 BACKUPS........................................................................................................... 244

INTRODUCTION ...........................................................................................................................244

IT ISN'T JUST USERS WHO ACCIDENTALLY DELETE FILES .................................................................244

CHARACTERISTICS OF A GOOD BACKUP STRATEGY ........................................................................244

EASE OF USE ...............................................................................................................................245

TIME EFFICIENCY ........................................................................................................................245

EASE OF RESTORING FILES ...........................................................................................................245ABILITY TO VERIFY BACKUPS .......................................................................................................246

TOLERANCE OF FAULTY MEDIA ....................................................................................................246

PORTABILTY TO A RANGE OF PLATFORMS .....................................................................................247

CONSIDERATIONS FOR A BACKUP STRATEGY .................................................................................247

THE COMPONENTS OF BACKUPS....................................................................................................247

SCHEDULER ................................................................................................................................248

TRANSPORT ................................................................................................................................248

MEDIA........................................................................................................................................249

COMMANDS ................................................................................................................................249

DUMP AND RESTORE ......................................................................................................................250

USING DUMP AND RESTORE WITHOUT A TAPE ..................................................................................252

OUR PRACTICE FILE SYSTEM.........................................................................................................252DOING A LEVEL 0 DUMP...............................................................................................................253

RESTORING THE BACKUP .............................................................................................................253

ALTERNATIVE.............................................................................................................................254

THE TAR COMMAND .....................................................................................................................254

THE DD COMMAND.......................................................................................................................256

THE MT COMMAND.......................................................................................................................257

COMPRESSION PROGRAMS............................................................................................................258

GZIP ...........................................................................................................................................259

CONCLUSIONS.............................................................................................................................259

REVIEW QUESTIONS.....................................................................................................................259

CHAPTER 12 STARTUP AND SHUTDOWN........................................................................... 261

INTRODUCTION ...........................................................................................................................261

A BOOTING OVERVIEW ................................................................................................................261

FINDING THE KERNEL..................................................................................................................262

ROM..........................................................................................................................................262

THE BOOTSTRAP PROGRAM ..........................................................................................................262

BOOTING ON A PC.......................................................................................................................263

ON THE FLOPPY...........................................................................................................................263

MAKING A BOOT DISK..................................................................................................................263

USING A BOOT LOADER ................................................................................................................264

STARTING THE KERNEL................................................................................................................264

KERNEL BOOT MESSAGES.............................................................................................................265

STARTING THE PROCESSES ...........................................................................................................266

RUN LEVELS................................................................................................................................266/ETC/INITTAB ...........................................................................................................................267


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SYSTEM CONFIGURATION ............................................................................................................270

TERMINAL LOGINS ......................................................................................................................271

STARTUP SCRIPTS........................................................................................................................271

THE LINUX PROCESS ...................................................................................................................272

WHY WON'T IT BOOT? ................................................................................................................. 274

SOLUTIONS.................................................................................................................................274

BOOT AND ROOT DISKS................................................................................................................274MAKING A BOOT AND ROOT DISK..................................................................................................275

USING BOOT AND ROOT ...............................................................................................................276

SOLUTIONS TO HARDWARE PROBLEMS..........................................................................................277

DAMAGED FILE SYSTEMS .............................................................................................................277

IMPROPERLY CONFIGURED KERNELS.............................................................................................277

SHUTTING DOWN ........................................................................................................................278

REASONS SHUTTING DOWN..........................................................................................................278

BEING NICE TO THE USERS ...........................................................................................................279

COMMANDS TO SHUTDOWN .........................................................................................................279

SHUTDOWN....................................................................................................................................280

WHAT HAPPENS............................................................................................................................280

THE OTHER COMMANDS...............................................................................................................281CONCLUSIONS.............................................................................................................................281


CHAPTER 13 KERNEL ............................................................................................................. 282

THE BIT OF THE NUT THAT YOU EAT?............................................................................................282

WHY?.........................................................................................................................................282

HOW?.........................................................................................................................................283

THE LIFELESS IMAGE ...................................................................................................................283

KERNEL GIZZARDS ......................................................................................................................284

THE FIRST INCISION .....................................................................................................................285

MAKING THE HEART BEAT... ........................................................................................................286

MODULES ...................................................................................................................................287

THE /PROC FILE SYSTEM ..............................................................................................................288

REALLY, WHY BOTHER? .............................................................................................................. 289

CONCLUSIONS.............................................................................................................................302


CHAPTER 14 OBSERVATION, AUTOMATION AND LOGGING .......................................303

INTRODUCTION ...........................................................................................................................303

AUTOMATION AND CRON ..............................................................................................................303

COMPONENTS OF CRON.................................................................................................................303

CRONTAB FORMAT ........................................................................................................................304

CREATING CRONTAB FILES ............................................................................................................305

WHAT'S GOING ON ......................................................................................................................306

DF ..............................................................................................................................................306

DU ..............................................................................................................................................307

SYSTEM STATUS .........................................................................................................................307

WHAT'S HAPPENED?....................................................................................................................311

LOGGING AND ACCOUNTING ........................................................................................................311

MANAGING LOG AND ACCOUNTING FILES......................................................................................311

CENTRALISE ...............................................................................................................................311

LOGGING ....................................................................................................................................312

SYSLOG .......................................................................................................................................312

ACCOUNTING..............................................................................................................................316

LOGIN ACCOUNTING....................................................................................................................316

LAST ...........................................................................................................................................316

AC ..............................................................................................................................................316PROCESS ACCOUNTING ................................................................................................................317


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SO WHAT? ..................................................................................................................................318

CONCLUSIONS.............................................................................................................................318


CHAPTER 15 NETWORKS: THE CONNECTION .................................................................321

INTRODUCTION ...........................................................................................................................321

RELATED MATERIAL ...................................................................................................................322NETWORK HARDWARE ................................................................................................................322

NETWORK DEVICES .....................................................................................................................323

ETHERNET ..................................................................................................................................325

CONVERTING HARDWARE ADDRESSES TO INTERNET ADDRESSES ....................................................325

SLIP, PPP AND POINT TO POINT...................................................................................................327

KERNEL SUPPORT FOR NETWORKING ............................................................................................327

TCP/IP BASICS...........................................................................................................................329

HOSTNAMES ...............................................................................................................................329

HOSTNAME....................................................................................................................................330

QUALIFIED NAMES.......................................................................................................................331

IP/INTERNET ADDRESSES ............................................................................................................331

THE INTERNET IS A NETWORK OF NETWORKS ................................................................................333EXERCISES..................................................................................................................................336

NAME RESOLUTION .....................................................................................................................337

ROUTING ....................................................................................................................................340

EXERCISES..................................................................................................................................341

MAKING THE CONNECTION ..........................................................................................................341

CONFIGURING THE DEVICE/INTERFACE .........................................................................................341

CONFIGURING THE NAME RESOLVER.............................................................................................342

CONFIGURING ROUTING...............................................................................................................344

STARTUP FILES............................................................................................................................347

NETWORK MANAGEMENT TOOLS ..............................................................................................347

REDHAT GUI NETWORKING TOOLS.............................................................................................348

NSLOOKUP....................................................................................................................................348

NETSTAT .....................................................................................................................................349

TRACEROUTE ................................................................................................................................349

CONCLUSIONS.............................................................................................................................351


CHAPTER 16 NETWORK APPLICATIONS ...........................................................................354

INTRODUCTION ...........................................................................................................................354

HOW IT ALL WORKS .....................................................................................................................354

PORTS ........................................................................................................................................355

RESERVED PORTS ........................................................................................................................355

LOOK AT PORTS, NETSTAT ............................................................................................................356

NETWORK SERVERS.....................................................................................................................357

HOW NETWORK SERVERS START...................................................................................................357/ETC/INETD.CONF .....................................................................................................................358

HOW IT WORKS ...........................................................................................................................358

EXERCISES..................................................................................................................................359

NETWORK CLIENTS .....................................................................................................................359

THE TELNET CLIENT.....................................................................................................................359

NETWORK PROTOCOLS ................................................................................................................360

REQUEST FOR COMMENT (RFCS)..................................................................................................360

TEXT BASED PROTOCOLS .............................................................................................................360

HOW IT WORKS ...........................................................................................................................361

EXERCISES..................................................................................................................................362

SECURITY ...................................................................................................................................362

TCPWRAPPERS/TCPD ..................................................................................................................362THE DIFFERENCE .........................................................................................................................363


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WHAT'S AN INTRANET? ............................................................................................................... 365SERVICES ON AN INTRANET .........................................................................................................365FILE AND PRINT SHARING.............................................................................................................365SAMBA .......................................................................................................................................366EXERCISES..................................................................................................................................368EMAIL ........................................................................................................................................368

EMAIL COMPONENTS ...................................................................................................................368EMAIL PROTOCOLS .....................................................................................................................369EXERCISES..................................................................................................................................371WORLD-WIDE WEB ....................................................................................................................371CONCLUSIONS.............................................................................................................................371REVIEW QUESTIONS ....................................................................................................................372


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CHAPTER 17 SECURITY..........................................................................................................374

INTRODUCTION ...........................................................................................................................374WHY HAVE SECURITY? ................................................................................................................ 375BEFORE YOU START .....................................................................................................................376SECURITY VERSUS CONVENIENCE .................................................................................................376

A SECURITY POLICY ....................................................................................................................376AUSCERT POLICY DEVELOPMENT .............................................................................................377EVALUATING SECURITY ..............................................................................................................377TYPES OF SECURITY THREATS ......................................................................................................377PHYSICAL THREATS.....................................................................................................................377LOGICAL THREATS ......................................................................................................................378HOW TO BREAK IN .......................................................................................................................378SOCIAL ENGINEERING..................................................................................................................379BREAKING INTO A SYSTEM ...........................................................................................................379INFORMATION ABOUT CRACKING..................................................................................................380PROBLEMS..................................................................................................................................380PASSWORDS................................................................................................................................380PROBLEMS WITH /ETC/PASSWD....................................................................................................381

SEARCH PATHS............................................................................................................................382FULL PATH NAMES.......................................................................................................................383THE FILE SYSTEM ........................................................................................................................384NETWORKS.................................................................................................................................385TOOLS TO EVALUATE SECURITY ..................................................................................................386PROBLEMS WITH THE TOOLS?.......................................................................................................386COPS.........................................................................................................................................386CRACK .......................................................................................................................................387SATAN........................................................................................................................................387REMEDY AND IMPLEMENT ...........................................................................................................388IMPROVING PASSWORD SECURITY.................................................................................................388USER EDUCATION........................................................................................................................388

SHADOW PASSWORDS ..................................................................................................................389PROACTIVE PASSWD .....................................................................................................................389

PASSWORD GENERATORS .............................................................................................................389PASSWORD AGING .......................................................................................................................390PASSWORD CRACKING .................................................................................................................390ONE-TIME PASSWORDS ................................................................................................................390HOW TO REMEMBER THEM ...........................................................................................................391SOLUTIONS TO PACKET SNIFFING..................................................................................................391FILE PERMISSIONS .......................................................................................................................392PROGRAMS TO CHECK..................................................................................................................393TRIPWIRE ...................................................................................................................................393DISK QUOTAS................................................

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