book

Linux® Programming by Example

Name: Linux® Programming by Example
Author: Arnold Robbins
ISBN: 0131429647

by Arnold Robbins

April 2004

Beginner

720 pages

15h 47m

English

Pearson

Read now

Unlock full access

Copyright
Dedication
Preface
AudienceWhat You Will LearnSmall Is Beautiful: Unix ProgramsStandardsFeatures and Power: GNU ProgramsSummary of ChaptersTypographical ConventionsWhere to Get Unix and GNU Source CodeUnix CodeGNU CodeWhere to Get the Example Programs Used in This BookAbout the CoverAcknowledgments
I. Files and Users
1. Introduction
1.1. The Linux/Unix File Model1.1.1. Files and Permissions1.1.2. Directories and Filenames1.1.3. Executable Files1.1.4. Devices1.2. The Linux/Unix Process Model1.2.1. Pipes: Hooking Processes Together1.3. Standard C vs. Original C1.4. Why GNU Programs Are Better1.4.1. Program Design1.4.2. Program Behavior1.4.3. C Code Programming1.4.4. Things That Make a GNU Program Better1.4.5. Parting Thoughts about the “GNU Coding Standards”1.5. Portability Revisited1.6. Suggested Reading1.7. SummaryExercises
2. Arguments, Options, and the Environment
2.1. Option and Argument Conventions2.1.1. POSIX Conventions2.1.2. GNU Long Options2.2. Basic Command-Line Processing2.2.1. The V7 echo Program2.3. Option Parsing: getopt() and getopt_long()2.3.1. Single-Letter Options2.3.2. GNU getopt() and Option Ordering2.3.3. Long Options2.3.3.1. Long Options Table2.3.3.2. Long Options, POSIX Style2.3.3.3. getopt_long() Return Value Summary2.3.3.4. GNU getopt() or getopt_long() in User Programs2.4. The Environment2.4.1. Environment Management Functions2.4.2. The Entire Environment: environ2.4.3. GNU env2.5. SummaryExercises
3. User-Level Memory Management
3.1. Linux/Unix Address Space3.2. Memory Allocation3.2.1. Library Calls: malloc(), calloc(), realloc(), free()3.2.1.1. Examining C Language Details3.2.1.2. Initially Allocating Memory: malloc()3.2.1.3. Releasing Memory: free()3.2.1.4. Changing Size: realloc()3.2.1.5. Allocating and Zero-filling: calloc()3.2.1.6. Summarizing from the GNU Coding Standards3.2.1.7. Using Private Allocators3.2.1.8. Example: Reading Arbitrarily Long Lines3.2.1.9. GLIBC Only: Reading Entire Lines: getline() and getdelim()3.2.2. String Copying: strdup()3.2.3. System Calls: brk() and sbrk()3.2.4. Lazy Programmer Calls: alloca()3.2.5. Address Space Examination3.3. SummaryExercises
4. Files and File I/O
4.1. Introducing the Linux/Unix I/O Model4.2. Presenting a Basic Program Structure4.3. Determining What Went Wrong4.3.1. Values for errno4.3.2. Error Message Style4.4. Doing Input and Output4.4.1. Understanding File Descriptors4.4.2. Opening and Closing Files4.4.2.1. Mapping FILE * Variables to File Descriptors4.4.2.2. Closing All Open Files4.4.3. Reading and Writing4.4.4. Example: Unix cat4.5. Random Access: Moving Around within a File4.6. Creating Files4.6.1. Specifying Initial File Permissions4.6.2. Creating Files with creat()4.6.3. Revisiting open()4.7. Forcing Data to Disk4.8. Setting File Length4.9. SummaryExercises
5. Directories and File Metadata
5.1. Considering Directory Contents5.1.1. Definitions5.1.2. Directory Contents5.1.3. Hard Links5.1.3.1. The GNU link Program5.1.3.2. Dot and Dot-Dot5.1.4. File Renaming5.1.5. File Removal5.1.5.1. Removing Open Files5.1.5.2. Using ISO C: remove()5.1.6. Symbolic Links5.2. Creating and Removing Directories5.3. Reading Directories5.3.1. Basic Directory Reading5.3.1.1. Portability Considerations5.3.1.2. Linux and BSD Directory Entries5.3.2. BSD Directory Positioning Functions5.4. Obtaining Information about Files5.4.1. Linux File Types5.4.2. Retrieving File Information5.4.3. Linux Only: Specifying Higher-Precision File Times5.4.4. Determining File Type5.4.4.1. Device Information5.4.4.2. The V7 cat Revisited5.4.5. Working with Symbolic Links5.5. Changing Ownership, Permission, and Modification Times5.5.1. Changing File Ownership: chown(), fchown(), and lchown()5.5.2. Changing Permissions: chmod() and fchmod()5.5.3. Changing Timestamps: utime()5.5.3.1. Faking utime(file, NULL)5.5.4. Using fchown() and fchmod() for Security5.6. SummaryExercises
6. General Library Interfaces — Part 1
6.1. Times and Dates6.1.1. Retrieving the Current Time: time() and difftime()6.1.2. Breaking Down Times: gmtime() and localtime()6.1.3. Formatting Dates and Times6.1.3.1. Simple Time Formatting: asctime() and ctime()6.1.3.2. Complex Time Formatting: strftime()6.1.4. Converting a Broken-Down Time to a time_t6.1.5. Getting Time-Zone Information6.1.5.1. BSD Systems Gotcha: timezone(), Not timezone6.2. Sorting and Searching Functions6.2.1. Sorting: qsort()6.2.1.1. Example: Sorting Employees6.2.1.2. Example: Sorting Directory Contents6.2.2. Binary Searching: bsearch()6.3. User and Group Names6.3.1. User Database6.3.2. Group Database6.4. Terminals: isatty()6.5. Suggested Reading6.6. SummaryExercises
7. Putting It All Together: ls
7.1. V7 ls Options7.2. V7 ls Code7.3. SummaryExercises

8. Filesystems and Directory Walks
8.1. Mounting and Unmounting Filesystems8.1.1. Reviewing the Background8.1.2. Looking at Different Filesystem Types8.1.3. Mounting Filesystems: mount8.1.4. Unmounting Filesystems: umount8.2. Files for Filesystem Administration8.2.1. Using Mount Options8.2.2. Working with Mounted Filesystems: getmntent()8.3. Retrieving Per-Filesystem Information8.3.1. POSIX Style: statvfs() and fstatvfs()8.3.2. Linux Style: statfs() and fstatfs()8.4. Moving Around in the File Hierarchy8.4.1. Changing Directory: chdir() and fchdir()8.4.2. Getting the Current Directory: getcwd()8.4.3. Walking a Hierarchy: nftw()8.4.3.1. The nftw() Interface8.4.3.2. The nftw() Callback Function8.5. Walking a File Tree: GNU du8.6. Changing the Root Directory: chroot()8.7. SummaryExercises
II. Processes, IPC, and Internationalization
9. Process Management and Pipes
9.1. Process Creation and Management9.1.1. Creating a Process: fork()9.1.1.1. After the fork(): Shared and Distinct Attributes9.1.1.2. File Descriptor Sharing9.1.1.3. File Descriptor Sharing and Close()9.1.2. Identifying a Process: getpid() and getppid()9.1.3. Setting Process Priority: nice()9.1.3.1. POSIX vs. Reality9.1.4. Starting New Programs: The exec() Family9.1.4.1. The execve() System Call9.1.4.2. Wrapper Functions: excel() et al.9.1.4.3. Program Names and argv[0]9.1.4.4. Attributes Inherited across exec()9.1.5. Terminating a Process9.1.5.1. Defining Process Exit Status9.1.5.2. Returning from main()9.1.5.3. Exiting Functions9.1.6. Recovering a Child’s Exit Status9.1.6.1. Using POSIX Functions: wait() and waitpid()9.1.6.2. Using BSD Functions: wait3() and wait4()9.2. Process Groups9.2.1. Job Control Overview9.2.2. Process Group Identification: getpgrp() and getpgid()9.2.3. Process Group Setting: setpgid() and setpgrp()9.3. Basic Interprocess Communication: Pipes and FIFOs9.3.1. Pipes9.3.1.1. Creating Pipes9.3.1.2. Pipe Buffering9.3.2. FIFOs9.4. File Descriptor Management9.4.1. Duplicating Open Files: dup() and dup2()9.4.2. Creating Nonlinear Pipelines: /dev/fd/XX9.4.3. Managing File Attributes: fcntl()9.4.3.1. The Close-on-exec Flag9.4.3.2. File Descriptor Duplication9.4.3.3. Manipulation of File Status Flags and Access Modes9.4.3.4. Nonblocking I/O for Pipes and FIFOs9.4.3.5. fcntl() Summary9.5. Example: Two-Way Pipes in gawk9.6. Suggested Reading9.7. SummaryExercises
10. Signals
10.1. Introduction10.2. Signal Actions10.3. Standard C Signals: signal() and raise()10.3.1. The signal() Function10.3.2. Sending Signals Programmatically: raise()10.4. Signal Handlers in Action10.4.1. Traditional Systems10.4.2. BSD and GNU/Linux10.4.3. Ignoring Signals10.4.4. Restartable System Calls10.4.4.1. Example: GNU Coreutils safe_read() and safe_write()10.4.4.2. GLIBC Only: TEMP_FAILURE_RETRY()10.4.5. Race Conditions and sig_atomic_t (ISO C)10.4.6. Additional Caveats10.4.7. Our Story So Far, Episode I10.5. The System V Release 3 Signal APIs: sigset() et al.10.6. POSIX Signals10.6.1. Uncovering the Problem10.6.2. Signal Sets: Sigset_t and Related Functions10.6.3. Managing the Signal Mask: sigprocmask() et al.10.6.4. Catching Signals: sigaction()10.6.5. Retrieving Pending Signals: sigpending()10.6.6. Making Functions Interruptible: siginterrupt()10.6.7. Sending Signals: kill() and killpg()10.6.8. Our Story So Far, Episode II10.7. Signals for Interprocess Communication10.8. Important Special-Purpose Signals10.8.1. Alarm Clocks: sleep(), alarm(), and SIGALRM10.8.1.1. Harder but with More Control: alarm() and SIGALRM10.8.1.2. Simple and Easy: sleep()10.8.2. Job Control Signals10.8.3. Parental Supervision: Three Different Strategies10.8.3.1. Poor Parenting: Ignoring Children Completely10.8.3.2. Permissive Parenting: Supervising Minimally10.8.3.3. Strict Parental Control10.9. Signals Across fork() and exec()10.10. SummaryExercises
11. Permissions and User and Group ID Numbers
11.1. Checking Permissions11.1.1. Real and Effective IDs11.1.2. Setuid and Setgid Bits11.2. Retrieving User and Group IDs11.3. Checking as the Real User: access()11.4. Checking as the Effective User: euidaccess() (GLIBC)11.5. Setting Extra Permission Bits for Directories11.5.1. Default Group for New Files and Directories11.5.2. Directories and the Sticky Bit11.6. Setting Real and Effective IDs11.6.1. Changing the Group Set11.6.2. Changing the Real and Effective IDs11.6.3. Using the Setuid and Setgid Bits11.7. Working with All Three IDs: getresuid() and setresuid() (Linux)11.8. Crossing a Security Minefield: Setuid root11.9. Suggested Reading11.10. SummaryExercises
12. General Library Interfaces — Part 2
12.1. Assertion Statements: assert()12.2. Low-Level Memory: The memXXX() Functions12.2.1. Setting Memory: memset()12.2.2. Copying Memory: memcpy(),memmove(), and memccpy()12.2.3. Comparing Memory Blocks: memcmp()12.2.4. Searching for a Byte Value: memchr()12.3. Temporary Files12.3.1. Generating Temporary Filenames (Bad)12.3.2. Creating and Opening Temporary Files (Good)12.3.3. Using the TMPDIR Environment Variable12.4. Committing Suicide: abort()12.5. Nonlocal Gotos12.5.1. Using Standard Functions: setjmp() and longjmp()12.5.2. Handling Signal Masks: sigsetjmp() and siglongjmp()12.5.3. Observing Important Caveats12.6. Pseudorandom Numbers12.6.1. Standard C: rand() and srand()12.6.2. POSIX Functions: random() and srandom()12.6.3. The /dev/random and /dev/urandom Special Files12.7. Metacharacter Expansions12.7.1. Simple Pattern Matching: fnmatch()12.7.2. Filename Expansion: glob() and globfree()12.7.3. Shell Word Expansion: wordexp() and wordfree()12.8. Regular Expressions12.9. Suggested Reading12.10. SummaryExercises
13. Internationalization and Localization
13.1. Introduction13.2. Locales and the C Library13.2.1. Locale Categories and Environment Variables13.2.2. Setting the Locale: setlocale()13.2.3. String Collation: strcoll() and strxfrm()13.2.4. Low-Level Numeric and Monetary Formatting: localeconv()13.2.5. High-Level Numeric and Monetary Formatting: strfmon() and printf()13.2.6. Example: Formatting Numeric Values in gawk13.2.7. Formatting Date and Time Values: ctime() and strftime()13.2.8. Other Locale Information: nl_langinfo()13.3. Dynamic Translation of Program Messages13.3.1. Setting the Text Domain: textdomain()13.3.2. Translating Messages: gettext()13.3.3. Working with Plurals: ngettext()13.3.4. Making gettext() Easy to Use13.3.4.1. Portable Programs: "gettext.h"13.3.4.2. GLIBC Only: <libintl.h>13.3.5. Rearranging Word Order with printf()13.3.6. Testing Translations in a Private Directory13.3.7. Preparing Internationalized Programs13.3.8. Creating Translations13.4. Can You Spell That for Me, Please?13.4.1. Wide Characters13.4.2. Multibyte Character Encodings13.4.3. Languages13.4.4. Conclusion13.5. Suggested Reading13.6. SummaryExercises
14. Extended Interfaces
14.1. Allocating Aligned Memory: posix_memalign() and memalign()14.2. Locking Files14.2.1. File Locking Concepts14.2.2. POSIX Locking: fcntl() and lockf()14.2.2.1. Describing a Lock14.2.2.2. Obtaining and Releasing Locks14.2.2.3. Observing Locking Caveats14.2.3. BSD Locking: flock()14.2.4. Mandatory Locking14.3. More Precise Times14.3.1. Microsecond Times: gettimeofday()14.3.2. Microsecond File Times: utimes()14.3.3. Interval Timers: setitimer() and getitimer()14.3.4. More Exact Pauses: nanosleep()14.4. Advanced Searching with Binary Trees14.4.1. Introduction to Binary Trees14.4.2. Tree Management Functions14.4.3. Tree Insertion: tsearch()14.4.4. Tree Lookup and Use of A Returned Pointer: tfind() and tsearch()14.4.5. Tree Traversal: twalk()14.4.6. Tree Node Removal and Tree Deletion: tdelete() and tdestroy()14.5. SummaryExercises
III. Debugging and Final Project
15. Debugging
15.1. First Things First15.2. Compilation for Debugging15.3. GDB Basics15.3.1. Running GDB15.3.2. Setting Breakpoints, Single-Stepping, and Setting Watchpoints15.4. Programming for Debugging15.4.1. Compile-Time Debugging Code15.4.1.1. Use Debugging Macros15.4.1.2. Avoid Expression Macros If Possible15.4.1.3. Reorder Code If Necessary15.4.1.4. Use Debugging Helper Functions15.4.1.5. Avoid Unions When Possible15.4.2. Runtime Debugging Code15.4.2.1. Add Debugging Options and Variables15.4.2.2. Use Special Environment Variables15.4.2.3. Add Logging Code15.4.2.4. Runtime Debugging Files15.4.2.5. Add Special Hooks for Breakpoints15.5. Debugging Tools15.5.1. The dbug Library — A Sophisticated printf()15.5.2. Memory Allocation Debuggers15.5.2.1. GNU/Linux mtrace15.5.2.2. Electric Fence15.5.2.3. Debugging Malloc: dmalloc15.5.2.4. Valgrind: A Versatile Tool15.5.2.5. Other Malloc Debuggers15.5.3. A Modern lint15.6. Software Testing15.7. Debugging Rules15.8. Suggested Reading15.9. SummaryExercises
16. A Project that Ties Everything Together
16.1. Project Description16.2. Suggested Reading
IV. Appendixes
A. Teach Yourself Programming in Ten Years
Why Is Everyone in Such a Rush?Teach Yourself Programming in Ten YearsReferencesAnswersFootnotes
B. Caldera Ancient UNIX License
C. GNU General Public License
PreambleTerms and Conditions for Copying, Distribution and ModificationHow to Apply These Terms to Your New ProgramsExample Use

Content preview from Linux® Programming by Example

Chapter 11. Permissions and User and Group ID Numbers

In this chapter

11.1 Checking Permissions page 404
11.2 Retrieving User and Group IDs page 407
11.3 Checking as the Real User: access() page 410
11.4 Checking as the Effective User: euidaccess() (GLIBC) page 412
11.5 Setting Extra Permission Bits for Directories page 412
11.6 Setting Real and Effective IDs page 415
11.7 Working with All Three IDs: getresuid() and setresuid() (Linux) page 421
11.8 Crossing a Security Minefield: Setuid root page 422
11.9 Suggested Reading page 423
11.10 Summary page 424
Exercises page 426

Linux, following Unix, is a multiuser system. Unlike most operating systems for personal computers,^[1] in which there is only one user and whoever is physically in front of the computer ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.

Read now

Unlock full access

More than 5,000 organizations count on O’Reilly

O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.

Julian F.

Head of Cybersecurity

I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.

Addison B.

Field Engineer

I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.

Amir M.

Data Platform Tech Lead

I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.

Mark W.

Embedded Software Engineer

Publisher Resources

ISBN: 0131429647Purchase book

Cloud Computing

Data Engineering

Data Science

AI & ML

Programming Languages

Software Architecture

IT/Ops

Security

Design

Business

Soft Skills

Linux® Programming by Example

by Arnold Robbins

Chapter 11. Permissions and User and Group ID Numbers

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.