PART Ⅰ Files and Users 1
Chapter 1 Introduction 3
1.1 The Linux/Unix File Model 4
1.1.1 Files and Permissions 4
1.1.2 Directories and Filenames 6
1.1.3 Executable Files 7
1.1.4 Devices 9
1.2 The Linux/Unix Process Model 10
1.2.1 Pipes：Hooking Processes Together 12
1.3 Standard C vs.Original C 12
1.4 Why GNU Programs Are Better 14
1.4.1 Program Design 15
1.4.2 Program Behavior 16
1.4.3 C Code Programming 16
1.4.4 Things That Make a GNU Program Better 17
1.4.5 Parting Thoughts about the"GNU Coding Standards" 19
1.5 Portability Revisited 19
1.6 Suggested Reading 20
1.7 Summary 21
Exercises 22
Chapter 2 Arguments,Options,and the Environment 23
2.1 Option and Argument Conventions 24
2.1.1 POSIX Conventions 25
2.1.2 GNU Long Options 27
2.2 Basic Command-Line Processing 28
2.2.1 The V7 echo Program 29
2.3 Option Parsing：getopt()and getopt_long() 30
2.3.1 Single-Letter Options 30
2.3.2 GNU getopt()and Option Ordering 33
2.3.3 Long Options 34
2.3.3.1 Long Options Table 34
2.3.3.2 Long Options,POSIX Style 37
2.3.3.3 getopt_long()Return Value Summary 37
2.3.3.4 GNU getopt()or getopt_long()in User Programs 39
2.4 The Environment 40
2.4.1 Environment Management Functions 41
2.4.2 The Entire Environment：environ 43
2.4.3 GNU env 44
2.5 Summary 49
Exercises 50
Chapter 3 User-Level Memory Management 51
3.1 Linux/Unix Address Space 52
3.2 Memory Allocation 56
3.2.1 Library Calls：malloc(),calloc(),realloc(),free() 56
3.2.1.1 Examining C Language Details 57
3.2.1.2 Initially Allocating Memory：malloc() 58
3.2.1.3 Releasing Memory：free() 60
3.2.1.4 Changing Size：realloc() 62
3.2.1.5 Allocating and Zero-filling：calloc() 65
3.2.1.6 Summarizing from the GNU Coding Standards 66
3.2.1.7 Using Private Allocators 67
3.2.1.8 Example：Reading Arbitrarily Long Lines 67
3.2.1.9 GLIBC Only：Reading Entire Lines：getline()and getdelim() 73
3.2.2 String Copying：strdup() 74
3.2.3 System Calls：brk()and sbrk() 75
3.2.4 Lazy Programmer Calls：alloca() 76
3.2.5 Address Space Examination 78
3.3 Summary 80
Exercises 81
Chapter 4 Files and File I/O 83
4.1 Introducing the Linux/Unix I/O Model 84
4.2 Presenting a Basic Program Structure 84
4.3 Determining What Went Wrong 86
4.3.1 Values for errno 87
4.3.2 Error Message Style 90
4.4 Doing Input and Output 91
4.4.1 Understanding File Descriptors 92
4.4.2 Opening and Closing Files 93
4.4.2.1 Mapping FILE Variables to File Descriptors 95
4.4.2.2 Closing All Open Files 96
4.4.3 Reading and Writing 96
4.4.4 Example：Unix cat 99
4.5 Random Access：Moving Around within a File 102
4.6 Creating Files 106
4.6.1 Specifying Initial File Permissions 106
4.6.2 Creating Files with creat() 109
4.6.3 Revisiting open() 110
4.7 Forcing Data to Disk 113
4.8 Setting File Length 114
4.9 Summary 115
Exercises 115
Chapter 5 Directories and File Metadata 117
5.1 Considering Directory Contents 118
5.1.1 Definitions 118
5.1.2 Directory Contents 120
5.1.3 Hard Links 122
5.1.3.1 The GNU link Program 123
5.1.3.2 Dot and Dot-Dot 125
5.1.4 File Renaming 125
5.1.5 File Removal 126
5.1.5.1 Removing Open Files 127
5.1.5.2 Using ISO C：remove() 127
5.1.6 Symbolic Links 128
5.2 Creating and Removing Directories 130
5.3 Reading Directories 132
5.3.1 Basic Directory Reading 133
5.3.1.1 Portability Considerations 136
5.3.1.2 Linux and BSD Directory Entries 137
5.3.2 BSD Directory Positioning Functions 138
5.4 Obtaining Information about Files 139
5.4.1 Linux File Types 139
5.4.2 Retrieving File Information 141
5.4.3 Linux Only：Specifying Higher-Precision File Times 143
5.4.4 Determining File Type 144
5.4.4.1 Device Information 147
5.4.4.2 The V7 cat Revisited 150
5.4.5 Working with Symbolic Links 151
5.5 Changing Ownership,Permission,and Modification Times 155
5.5.1 Changing File Ownership：chown(),fchown(),and lchown() 155
5.5.2 Changing Permissions：chmod()and fchmod() 156
5.5.3 Changing Timestamps：utime() 157
5.5.3.1 Faking utime(file,NULL) 159
5.5.4 Using fchown()and fchmod()for Security 161
5.6 Summary 162
Exercises 163
Chapter 6 General Library Interfaces—Part 1 165
6.1 Times and Dates 166
6.1.1 Retrieving the Current Time：time()and difftime() 167
6.1.2 Breaking Down Times：gmtime()and localtime() 168
6.1.3 Formatting Dates and Times 170
6.1.3.1 Simple Time Formatting：asctime()and ctime() 170
6.1.3.2 Complex Time Formatting：strftime() 171
6.1.4 Converting a Broken-Down Time to a time_t 176
6.1.5 Getting Time-Zone Information 178
6.1.5.1 BSD Systems Gotcha：timezone(),Not timezone 179
6.2 Sorting and Searching Functions 181
6.2.1 Sorting：qsort() 181
6.2.1.1 Example：Sorting Employees 183
6.2.1.2 Example：Sorting Directory Contents 188
6.2.2 Binary Searching：bsearch() 191
6.3 User and Group Names 195
6.3.1 User Database 196
6.3.2 Group Database 199
6.4 Terminals：isatty() 202
6.5 Suggested Reading 203
6.6 Summary 203
Exercises 205
Chapter 7 Putting It All Together：ls 207
7.1 V7 ls Options 208
7.2 V7 ls Code 209
7.3 Summary 225
Exercises 226
Chapter 8 Filesystems and Directory Walks 227
8.1 Mounting and Unmounting Filesystems 228
8.1.1 Reviewing the Background 228
8.1.2 Looking at Different Filesystem Types 232
8.1.3 Mounting Filesystems：mount 236
8.1.4 Unmounting Filesystems：umount 237
8.2 Files for Filesystem Administration 238
8.2.1 Using Mount Options 239
8.2.2 Working with Mounted Filesystems：getmntent() 241
8.3 Retrieving Per-Filesystem Information 244
8.3.1 POSIX Style：statvfs()and fstatvfs() 244
8.3.2 Linux Style：statfs()and fstatfs() 252
8.4 Moving Around in the File Hierarchy 256
8.4.1 Changing Directory：chdir()and fchdir() 256
8.4.2 Getting the Current Directory：getcwd() 258
8.4.3 Walking a Hierarchy：nftw() 260
8.4.3.1 The nftw()Interface 261
8.4.3.2 The nftw()Callback Function 263
8.5 Walking a File Tree：GNU du 269
8.6 Changing the Root Directory：chroot() 276
8.7 Summary 277
Exercises 278
PART Ⅱ Processes,IPC,and Internationalization 281
Chapter 9 Process Management and Pipes 283
9.1 Process Creation and Management 284
9.1.1 Creating a Process：fork() 284
9.1.1.1 After the fork()：Shared and Distinct Attributes 285
9.1.1.2 File Descriptor Sharing 286
9.1.1.3 File Descriptor Sharing and close() 288
9.1.2 Identifying a Process：getpid()and getppid() 289
9.1.3 Setting Process Priority：nice() 291
9.1.3.1 POSIX vs.Reality 293
9.1.4 Starting New Programs：The exec()Family 293
9.1.4.1 The execve()System Call 294
9.1.4.2 Wrapper Functions：execl()et al 295
9.1.4.3 Program Names and argv[0] 297
9.1.4.4 Attributes Inherited across exec() 298
9.1.5 Terminating a Process 300
9.1.5.1 Defining Process Exit Status 300
9.1.5.2 Returning from main() 301
9.1.5.3 Exiting Functions 302
9.1.6 Recovering a Child's Exit Status 305
9.1.6.1 Using POSOX Functions：wait()and waitpid() 306
9.1.6.2 Using BSD Functions：wait3()and wait4() 310
9.2 Process Groups 312
9.2.1 Job Control Overview 312
9.2.2 Process Group Identification：getpgrp()and getpgid() 314
9.2.3 Process Group Setting：setpgid()and setpgrp() 314
9.3 Basic Interprocess Communication：Pipes and FIFOs 315
9.3.1 Pipes 315
9.3.1.1 Creating Pipes 316
9.3.1.2 Pipe Buffering 318
9.3.2 FIFOs 319
9.4 File Descriptor Management 320
9.4.1 Duplicating Open Files：dup()and dup2() 321
9.4.2 Creating Nonlinear Pipelines：/dev/fd/XX 326
9.4.3 Managing File Attributes：fcntl() 328
9.4.3.1 The Close-on-exec Flag 329
9.4.3.2 File Descriptor Duplication 331
9.4.3.3 Manipulation of File Status Flags and Access Modes 332
9.4.3.4 Nonblocking I/O for Pipes and FIFOs 333
9.4.3.5 fcntl()Summary 336
9.5 Example：Two-Way Pipes in gawk 337
9.6 Suggested Reading 341
9.7 Summary 342
Exercises 344
Chapter 10 Signals 347
10.1 Introduction 348
10.2 Signal Actions 348
10.3 Standard C Signals：signal()and raise() 349
10.3.1 The signal()Function 349
10.3.2 Sending Signals Programmatically：raise() 353
10.4 Signal Handlers in Action 353
10.4.1 Traditional Systems 353
10.4.2 BSD and GNU/Linux 356
10.4.3 Ignoring Signals 356
10.4.4 Restartable System Calls 357
10.4.4.1 Example：GNU Coreutils safe_read()and safe_write() 359
10.4.4.2 GLIBC Only：TEMP_FAILURE_RETRY() 360
10.4.5 Race Conditions and sig_atomic_t(ISO C) 361
10.4.6 Additional Caveats 363
10.4.7 Our Story So Far,Episode I 363
10.5 The System V Release 3 Signal APIs：sigset()et al 365
10.6 POSIX Signals 367
10.6.1 Uncovering the Problem 367
10.6.2 Signal Sets：sigset_t and Related Functions 368
10.6.3 Managing the Signal Mask：sigprocmask()et al 369
10.6.4 Catching Signals：sigaction() 370
10.6.5 Retrieving Pending Signals：sigpending() 375
10.6.6 Making Functions Interruptible：siginterrupt() 376
10.6.7 Sending Signals：kill()and killpg() 376
10.6.8 Our Story So Far.Episode Ⅱ 378
10.7 Signals for Interprocess Communication 379
10.8 Important Special-Purpose Signals 382
10.8.1 Alarm Clocks：sleep(),alarm(),and SIGALRM 382
10.8.1.1 Harder but with More Control：alarm()and SIGALRM 382
10.8.1.2 Simple and Easy：sleep() 383
10.8.2 Job Control Signals 383
10.8.3 Parental Supervision：Three Different Strategies 385
10.8.3.1 Poor Parenting：Ignoring Children Completely 385
10.8.3.2 Permissive Parenting：Supervising Minimally 386
10.8.3.3 Strict Parental Control 393
10.9 Signals Across fork()and exec() 398
10.10 Summary 399
Exercises 401
Chapter 11 Permissions and User and Group ID Numbers 403
11.1 Checking Permissions 404
11.1.1 Real and Effective IDs 405
11.1.2 Setuid and Setgid Bits 406
11.2 Retrieving User and Group IDs 407
11.3 Checking As the Real User：access() 410
11.4 Checking as the Effective User：euidaccess()(GLIBC) 412
11.5 Setting Extra Permission Bits for Directories 412
11.5.1 Default Group for New Files and Directories 412
11.5.2 Directories and the Sticky Bit 414
11.6 Setting Real and Effective IDs 415
11.6.1 Changing the Group Set 416
11.6.2 Changing the Real and Effective IDs 416
11.6.3 Using the Setuid and Setgid Bits 419
11.7 Working with All Three IDs：getresuid()and setresuid()(Linux) 421
11.8 Crossing a Security Minefield：Setuid root 422
11.9 Suggested Reading 423
11.10 Summary 424
Exercises 426
Chapter 12 General Library Interfaces—Part 2 427
12.1 Assertion Statements：assert() 428
12.2 Low-Level Memory：The memXXX()Functions 432
12.2.1 Setting Memory：memset() 432
12.2.2 Copying Memory：memcpy(),memmove(),and memccpy() 433
12.2.3 Comparing Memory Blocks：memcmp() 434
12.2.4 Searching for a Byte Value：memchr() 435
12.3 Temporary Files 436
12.3.1 Generating Temporary Filenames(Bad) 437
12.3.2 Creating and Opening Temporary Files(Good) 441
12.3.3 Using the TMPDIR Environment Variable 443
12.4 Committing Suicide：abort() 445
12.5 Nonlocal Gotos 446
12.5.1 Using Standard Functions：setjmp()and longjmp() 447
12.5.2 Handling Signal Masks：sigsetjmp()and siglongjmp() 449
12.5.3 Observing Important Caveats 450
12.6 Pseudorandom Numbers 454
12.6.1 Standard C：rand()and srand() 455
12.6.2 POSIX Functions：random()and srandom() 457
12.6.3 The/dev/random and/dev/urandom Special Files 460
12.7 Metacharacter Expansions 461
12.7.1 Simple Pattern Matching：fnmatch() 462
12.7.2 Filename Expansion：glob()and globfree() 464
12.7.3 Shell Word Expansion：wordexp()and wordfree() 470
12.8 Regular Expressions 471
12.9 Suggested Reading 480
12.10 Summary 481
Exercises 482
Chapter 13 Internationalization and Localization 485
13.1 Introduction 486
13.2 Locales and the C Library 487
13.2.1 Locale Categories and Environment Variables 487
13.2.2 Setting the Locale：setlocale() 489
13.2.3 String Collation：strcoll()and strxfrm() 490
13.2.4 Low-Level Numeric and Monetary Formatting：localeconv() 494
13.2.5 High-Level Numeric and Monetary Formatting：strfmon()and printf() 498
13.2.6 Example：Formatting Numeric Values in gawk 501
13.2.7 Formatting Date and Time Values：ctime()and strftime() 503
13.2.8 Other Locale Information：nl_langinfo() 504
13.3 Dynamic Translation of Program Messages 507
13.3.1 Setting the Text Domain：textdomain() 507
13.3.2 Translating Messages：gettext() 508
13.3.3 Working with Plurals：ngettext() 509
13.3.4 Making gettext()Easy to Use 510
13.3.4.1 Portable Programs："gettext.h: 511
13.3.4.2 GLIBC Only：＜libintl.h＞ 513
13.3.5 Rearranging Word Order with printf() 514
13.3.6 Testing Translations in a Private Directory 515
13.3.7 Preparing Internationalized Programs 516
13.3.8 Creating Translations 517
13.4 Can You Spell That for Me,Please? 521
13.4.1 Wide Characters 523
13.4.2 Multibyte Character Encodings 523
13.4.3 Languages 524
13.4.4 Conclusion 525
13.5 Suggested Reading 526
13.6 Summary 526
Exercises 527
Chapter 14 Extended Interfaces 529
14.1 Allocating Aligned Memory：posix_memalign()and memalign() 530
14.2 Locking Files 531
14.2.1 File Locking Concepts 531
14.2.2 POSIX Locking：fcntl()and lockf() 533
14.2.2.1 Describing a Lock 533
14.2.2.2 Obtaining and Releasing Locks 536
14.2.2.3 Observing Locking Caveats 538
14.2.3 BSD Locking：flock() 539
14.2.4 Mandatory Locking 540
14.3 More Precise Times 543
14.3.1 Microsecond Times：gettimeofday() 544
14.3.2 Microsecond File Times：utimes() 545
14.3.3 Interval Timers：setitimer()and getitimer() 546
14.3.4 More Exact Pauses：nanosleep() 550
14.4 Advanced Searching with Binary Trees 551
14.4.1 Introduction to Binary Trees 551
14.4.2 Tree Management Functions 554
14.4.3 Tree Insertion：tsearch() 554
14.4.4 Tree Lookup and Use of A Returned Pointer：tfind()and tsearch() 555
14.4.5 Tree Traversal：twalk() 557
14.4.6 Tree Node Removal and Tree Deletion：tdelete()and tdestroy() 561
14.5 Summary 562
Exercises 563
PART Ⅲ Debugging and Final project 565
Chapter 15 Debugging 567
15.1 First Things First 568
15.2 Compilation for Debugging 569
15.3 GDB Basics 570
15.3.1 Running GDB 571
15.3.2 Setting Breakpoints,Single-Stepping,and Setting Watchpoints 574
15.4 Programming for Debugging 577
15.4.1 Compile-Time Debugging Code 577
15.4.1.1 Use Debugging Macros 577
15.4.1.2 Avoid Expression Macros If Possible 580
15.4.1.3 Reorder Code If Necessary 582
15.4.1.4 Use Debugging Helper Functions 584
15.4.1.5 Avoid Unions When Possible 591
15.4.2 Runtime Debugging Code 595
15.4.2.1 Add Debugging Options and Variables 595
15.4.2.2 Use Special Environment Variables 597
15.4.2.3 Add Logging Code 601
15.4.2.4 Runtime Debugging Files 602
15.4.2.5 Add Special Hooks for Breakpoints 603
15.5 Debugging Tools 605
15.5.1 The dbug Library—A Sophisticated printf() 606
15.5.2 Memory Allocation Debuggers 612
15.5.2.1 GNU/Linux mtrace 613
15.5.2.2 Electric Fence 614
15.5.2.3 Debugging Malloc：dmalloc 619
15.5.2.4 Valgrind：A Versatile Tool 623
15.5.2.5 Other Malloc Debuggers 629
15.5.3 A Modern lint 631
15.6 Software Testing 632
15.7 Debugging Rules 633
15.8 Suggested Reading 637
15.9 Summary 638
Exercises 639
Chapter 16 A Project That Ties Everything Together 641
16.1 Project Description 642
16.2 Suggested Reading 644
PART Ⅳ Appendixes 647
Appendix A Teach Yourself Programming in Ten Years 649
Appendix B Caldera Ancient UNIX License 655
Appendix C GNU General Public License 657
Index 667