System V IPC is the label used to refer to three different mechanisms for interprocess communication: message queues, semaphores, and shared memory.
Although these three forms of IPC are quite diverse in function, there are good reasons for discussing them together. One reason is that these mechanisms were developed together, and originally made their way into mainstream Unix by appearing in System V--hence the appellation System V IPC. A more significant reason for discussing the System V IPC mechanisms together is that their programming interfaces share a number of common characteristics, so that many of the same concepts apply to all of these mechanisms.
This chapter provides an overview of the System V IPC mechanisms and details those features that are common to all three mechanisms. The three mechanisms are then discussed individually in the following chapters.
45 Introduction to System V IPC
45.1 API Overview
45.2 IPC Keys
45.3 Associated Data Structure and Object Permissions
45.4 IPC Identifiers and Client-server Applications
45.5 Algorithm Employed by System V IPC get Calls
45.6 The ipcs and ipcrm Commands
45.7 Obtaining a List of All IPC Objects
45.8 IPC Limits
45.9 Summary
45.10 Exercises
2009-10-08
Chapter 44: Pipes and FIFOs
This chapter describes pipes and FIFOs. Pipes are the oldest method of IPC on the Unix system, having appeared in Third Edition Unix in the early 1970s. Pipes provide an elegant solution to a frequent requirement: Having created two processes to run different programs (commands), how can the shell allow the output produced by one process to be used as the input to the other process? Pipes can be used to pass data between related processes. FIFOs are a variation on the pipe concept. The important difference is that FIFOs can be used for communication between any processes.
44 Pipes and FIFOs
44.1 Overview
44.2 Creating and Using Pipes
44.3 Pipes As a Method of Process Synchronization
44.4 Using Pipes to Connect Filters
44.5 Talking to a Shell Command via a Pipe: popen() and pclose()
44.6 Pipes and stdio Buffering
44.7 FIFOs
44.8 A Client-server Application Using FIFOs
44.9 Nonblocking I/O
44.10 Semantics of read() and write() on Pipes and FIFOs
44.11 Summary
44.12 Exercises
44 Pipes and FIFOs
44.1 Overview
44.2 Creating and Using Pipes
44.3 Pipes As a Method of Process Synchronization
44.4 Using Pipes to Connect Filters
44.5 Talking to a Shell Command via a Pipe: popen() and pclose()
44.6 Pipes and stdio Buffering
44.7 FIFOs
44.8 A Client-server Application Using FIFOs
44.9 Nonblocking I/O
44.10 Semantics of read() and write() on Pipes and FIFOs
44.11 Summary
44.12 Exercises
2009-10-07
Chapter 43: Interprocess Communication Overview
This chapter presents a brief overview of the facilities that processes and threads can use to communicate with one another and to synchronize their actions. The following chapters provide more details about these facilities.
43 Interprocess Communication Overview
43.1 A Taxonomy of IPC Facilities
43.2 Communication Facilities
43.3 Synchronization Facilities
43.4 Comparing IPC Facilities
43.5 Summary
43.6 Exercises
43 Interprocess Communication Overview
43.1 A Taxonomy of IPC Facilities
43.2 Communication Facilities
43.3 Synchronization Facilities
43.4 Comparing IPC Facilities
43.5 Summary
43.6 Exercises
2009-10-02
We have a book title!
A few weeks ago, I posted some candidate titles for my book, and asked for feedback from readers about what title(s) they thought worked. I also pinged many of my technical reviewers to ask them for their thoughts on the titles in the blog post.
The candidate titles were:
1. Linux System and Network Programming
This was my original working title, conceived in a time when I planned to write a smaller book in which the network programming component would be a substantial portion of the book.
This title got almost no votes, and a number of negative responses from my tech reviewers. Those responses were generally along the lines: "networking is an important part of the book, but just a small part of a book that covers many APIs". This was exactly the reason why I had already decided that I didn't much like this title, and the feedback was enough to confirm to me that this was not the right title.
2. Linux/UNIX System and Network Programming
This scored only negative votes, which was no surprise to me (I only included it for the purposes of shoehorning "UNIX" into the previous title, to see if that got any positive response).
Two down.
3. Linux and UNIX System Programming
This title got several solid votes from a few people, including a few of my key reviewers, and no one had strong reservations.
The virtue of this title is its simplicity, and that it captures key points: Linux, UNIX (and thus portability), and system programming.
Some people agreed with me that this title is solid.
And some agreed that it's a little bland; the title lacks distinction. As Bill O. Gallmeister wrote:
The conservative in me said: solid is good; bland is not fatal. However, when I factored in the crowded namespace, I was left with the feeling that while I could live with this title, I was not really convinced by it.
Two down, one left standing (just).
4. The Craft of Linux Programming
Titles 4 and 5 got the most votes. Among other things, this said to me that many people are interested primarily in Linux, and don't need to see UNIX in the title.
I concluded that one reason why people like title 4 is that it is distinctive. (This was one reason that title 4 was for a long time my favorite.) Title 4 also got several responses along the lines that the title was "soft" and "vague" ("I'm not quite sure from this title what your book is about"). I take their point. This is a significant weakness of the title. And in the end, I decided the weakness was fatal.
Three down, one left standing (just).
5. Advanced Programming in the Linux Environment
This title kept surprising me with its level of positive response. It got about as many positive votes as title 4.
I take the strong positive vote for this title as meaning this:
6. Something else?
This is the virtue of the FOSS approach: use other people's good ideas.
In among several lengthy mails I got, there was one from a friend and former colleague, Alejandro Forero Cuervo. Alejo offered some short and incisive criticisms of my five candidate titles, and then did a nice analysis to come up with an alternative:
But, there seemed to be some downsides to this title:
There is for me a positive aspect in focusing on just Linux in the title: it is because of Linux (a free UNIX) that I am writing this book, and indeed it may even be because of Linux that I'm still in computing. And then, Linux is becoming by a margin the most popular UNIX. Focusing on Linux in the title is an acknowledgement of these facts.
On the other hand, UNIX is what got us here (and where I started learning), and I do like history and acknowledging origins. And of course, my book devotes quite a lot of space to portability across contemporary UNIX implementations.
I decided that UNIX must be kept somehow, but the way to do this was is in a subtitle.
The lack of the word System in the title also bothered me, since the term System Programming is commonly applied to programming with the interfaces that this book is about. So, I leaned toward an alternative title: The Linux System Programming Interface. I reasoned that this was nearly as short and elegant as the other title, was still somewhat distinctive, and was a helpful indicator for those people who might not be sure which interface was being referred to.
I asked a few people who had sent more detailed responses on the other titles for their thoughts about these two new titles. The response was generally very positive, but there was no clear winner between the two versions.
As I reflected on this further, I began to wonder whether adding System to the title did indeed detract too much from its simplicity and elegance. (Alejo was quite certain that the word System was not needed.) And so I began to lean back towards Alejo's initial proposal, and consider whether we could preserve the words System Programming in the subtitle. What finally confirmed things for me was the belief of my publisher, Bill Pollock, that the shorter title is better.
So there we have it: The Linux Programming Interface, with a subtitle that will include the terms UNIX and System Programming.
Updated, 2009-10-08: fixed an incorrect hyperlink
The candidate titles were:
1. Linux System and Network ProgrammingThis is what happened.
2. Linux/UNIX System and Network Programming
3. Linux and UNIX System Programming
4. The Craft of Linux Programming
5. Advanced Programming in the Linux Environment
6. Something else?
1. Linux System and Network Programming
This was my original working title, conceived in a time when I planned to write a smaller book in which the network programming component would be a substantial portion of the book.
This title got almost no votes, and a number of negative responses from my tech reviewers. Those responses were generally along the lines: "networking is an important part of the book, but just a small part of a book that covers many APIs". This was exactly the reason why I had already decided that I didn't much like this title, and the feedback was enough to confirm to me that this was not the right title.
2. Linux/UNIX System and Network Programming
This scored only negative votes, which was no surprise to me (I only included it for the purposes of shoehorning "UNIX" into the previous title, to see if that got any positive response).
Two down.
3. Linux and UNIX System Programming
This title got several solid votes from a few people, including a few of my key reviewers, and no one had strong reservations.
The virtue of this title is its simplicity, and that it captures key points: Linux, UNIX (and thus portability), and system programming.
Some people agreed with me that this title is solid.
And some agreed that it's a little bland; the title lacks distinction. As Bill O. Gallmeister wrote:
And you could substitute the word "UNIX" for "Linux" in the above paragraph, and the argument would also hold. (There already exist several books that use "UNIX System Programming" in their titles.)The problem with many of the Linux programming book titles, in my opinion, is they run together. I guess that's just because there are a lot of them. Some combination of the words Linux, System, Programming, Network, Kernel, Advanced...
The conservative in me said: solid is good; bland is not fatal. However, when I factored in the crowded namespace, I was left with the feeling that while I could live with this title, I was not really convinced by it.
Two down, one left standing (just).
4. The Craft of Linux Programming
Titles 4 and 5 got the most votes. Among other things, this said to me that many people are interested primarily in Linux, and don't need to see UNIX in the title.
I concluded that one reason why people like title 4 is that it is distinctive. (This was one reason that title 4 was for a long time my favorite.) Title 4 also got several responses along the lines that the title was "soft" and "vague" ("I'm not quite sure from this title what your book is about"). I take their point. This is a significant weakness of the title. And in the end, I decided the weakness was fatal.
Three down, one left standing (just).
5. Advanced Programming in the Linux Environment
This title kept surprising me with its level of positive response. It got about as many positive votes as title 4.
I take the strong positive vote for this title as meaning this:
- From my tech reviewers: a strong vote of confidence in the quality of what they have read.
- From others (and perhaps some technical reviewers as well): a desire to see a book that is near the quality of Advanced Programming in the UNIX Environment (a quality sustained by Steve Rago in the second edition), but focused on Linux.
- The titles APLE and APUE would just be too close. Some people will get confused by the closeness. (One person noted that this might be to my benefit!)
- The title suggests my book is a clone of APUE, which isn't accurate. I cover many subjects that aren't in APUE and give special focus to a particular UNIX implementation.
- While I like the notion of acknowledging the brilliance of Rich Stevens book(s) with a play on his title, in the end, the closeness of the titles was just too great for me to feel comfortable.
6. Something else?
This is the virtue of the FOSS approach: use other people's good ideas.
In among several lengthy mails I got, there was one from a friend and former colleague, Alejandro Forero Cuervo. Alejo offered some short and incisive criticisms of my five candidate titles, and then did a nice analysis to come up with an alternative:
It took me a day or so of reflection, but then I decided that I really liked The Linux Programming Interface as a title:You want to convey very briefly what your book is about. In a few words I would say the book is about the abstractions provided in Linux, and to some extent other UNIX systems, that one needs to know to effectively develop applications (daemons, command line tools, networking clients, etc.). I think the word "Programming" very appropriately conveys part of that (rather than things like "Software development" or such). Also, something remarkable about your book is, I think, that it provides very complete coverage of the topics it touches on. That is, your book isn't just a short leaflet on where to look for what, but rather provides *everything* one should need to know.
Programming in Linux. Is this title taken? I quite like it. It emphasizes the scope of your book: you're publishing the best book for how to program in Linux so far. The title has the beauty of being simple and acknowledges that your book will be, probably for a long time (if not ever) the best book about how to program in Linux. A variation of this could be Linux Programming.
The Linux Programming Interface. This very precisely matches the topic of the book, right? I think it very briefly conveys entirely what the book is about. Of all the titles, this would probably be the one I'd choose.
- It's short and elegant.
- It's distinctive.
- As Alejo noted, it succinctly captures the essence of the book.
But, there seemed to be some downsides to this title:
- It doesn't mention UNIX.
- It doesn't mention System Programming, which is a term some people might search on.
There is for me a positive aspect in focusing on just Linux in the title: it is because of Linux (a free UNIX) that I am writing this book, and indeed it may even be because of Linux that I'm still in computing. And then, Linux is becoming by a margin the most popular UNIX. Focusing on Linux in the title is an acknowledgement of these facts.
On the other hand, UNIX is what got us here (and where I started learning), and I do like history and acknowledging origins. And of course, my book devotes quite a lot of space to portability across contemporary UNIX implementations.
I decided that UNIX must be kept somehow, but the way to do this was is in a subtitle.
The lack of the word System in the title also bothered me, since the term System Programming is commonly applied to programming with the interfaces that this book is about. So, I leaned toward an alternative title: The Linux System Programming Interface. I reasoned that this was nearly as short and elegant as the other title, was still somewhat distinctive, and was a helpful indicator for those people who might not be sure which interface was being referred to.
I asked a few people who had sent more detailed responses on the other titles for their thoughts about these two new titles. The response was generally very positive, but there was no clear winner between the two versions.
As I reflected on this further, I began to wonder whether adding System to the title did indeed detract too much from its simplicity and elegance. (Alejo was quite certain that the word System was not needed.) And so I began to lean back towards Alejo's initial proposal, and consider whether we could preserve the words System Programming in the subtitle. What finally confirmed things for me was the belief of my publisher, Bill Pollock, that the shorter title is better.
So there we have it: The Linux Programming Interface, with a subtitle that will include the terms UNIX and System Programming.
Updated, 2009-10-08: fixed an incorrect hyperlink
2009-10-01
Chapters 49 and 50 are in copyedit
Chapters 45 to 48 already went to the copyeditor, and came back. Now, chapters 49 and 50 are in copyedit.
2009-09-30
Chapters 1 to 42
Copyediting is now completed through to chapter 42, and thus is complete for five of the eight logical parts of my book (see this earlier post). So, here's an updated version of the detailed table of contents so far.
1 History and Standards [~20 pages]
1.1 A Brief History of Unix and C
1.2 A Brief History of Linux
1.2.1 The GNU Project
1.2.2 The Linux Kernel
1.3 Standardization
1.3.1 The C Programming Language
1.3.2 The First POSIX Standards
1.3.3 X/Open Company and The Open Group
1.3.4 SUSv3 and POSIX.1-2001
1.3.5 SUSv4 and POSIX.1-2008
1.3.6 Unix Standards Timeline
1.3.7 Implementation Standards
1.3.8 Linux, Standards, and the Linux Standard Base
1.4 Summary
2 Fundamental Concepts [~20 pages]
2.1 The Core Operating System: The Kernel
2.2 The Shell
2.3 Users and Groups
2.4 Single Directory Hierarchy, Directories, Links, and Files
2.5 File I/O Model
2.6 Programs
2.7 Processes
2.8 Memory Mappings
2.9 Static and Shared Libraries
2.10 Interprocess Communication and Synchronization
2.11 Signals
2.12 Threads
2.13 Process Groups and Shell Job Control
2.14 Sessions, Controlling Terminals, and Controlling Processes
2.15 Pseudoterminals
2.16 Date and Time
2.17 Client-server Architecture
2.18 Realtime
2.19 The /proc File System
2.20 Summary
3 System Programming Concepts [~25 pages]
3.1 System Calls
3.2 Library Functions
3.3 The Standard C Library; The GNU C Library (glibc)
3.4 Handling Errors from System Calls and Library Functions
3.5 Notes on the Example Programs in This Book
3.5.1 Command-line Options and Arguments
3.5.2 Common Functions and Header Files
3.6 Portability Issues
3.6.1 Feature Test Macros
3.6.2 System Data Types
3.6.3 Miscellaneous Portability Issues
3.7 Summary
3.8 Exercises
4 File I/O: The Universal I/O Model [~20 pages]
4.1 Overview
4.2 Universality of I/O
4.3 Opening a File: open()
4.4 Reading from a File: read()
4.5 Writing to a File: write()
4.6 Closing a File: close()
4.7 Changing the Current File Offset: lseek()
4.8 Operations Outside the Universal I/O Model: ioctl()
4.9 Summary
4.10 Exercises
5 File I/O: Further Details [~25 pages]
5.1 Atomicity and Race Conditions
5.2 File Control Operations: fcntl()
5.3 Open File Status Flags
5.4 Relationship Between File Descriptors and Open Files
5.5 Duplicating File Descriptors
5.6 File I/O at a Specified Offset: pread() and pwrite()
5.7 Scatter-gather I/O: readv() and writev()
5.8 Truncating a File: truncate() and ftruncate()
5.9 Nonblocking I/O
5.10 I/O on Large Files
5.11 The /dev/fd Directory
5.12 Creating Temporary Files
5.13 Summary
5.14 Exercises
6 Processes [~25 pages]
6.1 Processes and Programs
6.2 Process ID and Parent Process ID
6.3 Memory Layout of a Process
6.4 Virtual Memory Management
6.5 The Stack and Stack Frames
6.6 Command-line Arguments (argc, argv)
6.7 Environment List
6.8 Performing a Nonlocal Goto: setjmp() and longjmp()
6.9 Summary
6.10 Exercises
7 Memory Allocation [~15 pages]
7.1 Allocating Memory on the Heap
7.1.1 Adjusting the Program Break: brk() and sbrk()
7.1.2 Allocating Memory on the Heap: malloc() and free()
7.1.3 Implementation of malloc() and free()
7.1.4 Other Methods of Allocating Memory on the Heap
7.2 Allocating Memory on the Stack: alloca()
7.3 Summary
7.4 Exercises
8 Users and Groups [~15 pages]
8.1 The Password File: /etc/passwd
8.2 The Shadow Password File: /etc/shadow
8.3 The Group File: /etc/group
8.4 Retrieving User and Group Information
8.5 Password Encryption and User Authentication
8.6 Summary
8.7 Exercises
9 Process Credentials [~20 pages]
9.1 Real User ID and Real Group ID
9.2 Effective User ID and Effective Group ID
9.3 Set-user-ID and Set-group-ID Programs
9.4 Saved Set-user-ID and Saved Set-group-ID
9.5 File System User ID and File System Group ID
9.6 Supplementary Group IDs
9.7 Retrieving and Modifying Process Credentials
9.7.1 Retrieving and Modifying Real, Effective, and Saved Set IDs
9.7.2 Retrieving and Modifying File System IDs
9.7.3 Retrieving and Modifying Supplementary Group IDs
9.7.4 Summary of Calls for Modifying Process Credentials
9.7.5 Example: Displaying Process Credentials
9.8 Summary
9.9 Exercises
10 Times and Dates [~25 pages]
10.1 Calendar Time
10.2 Time-Conversion Functions
10.2.1 Converting time_t to Printable Form
10.2.2 Converting Between time_t and Broken-down Time
10.2.3 Converting Between Broken-down Time and Printable Form
10.3 Timezones
10.4 Locales
10.5 Updating the System Clock
10.6 The Software Clock (Jiffies)
10.7 Process Time
10.8 Summary
10.9 Exercises
11 System Limits and Options [~10 pages]
11.1 System Limits
11.2 Retrieving System Limits (and Options) at Run Time
11.3 Retrieving File-related Limits (and Options) at Run Time
11.4 Indeterminate Limits
11.5 System Options
11.6 Summary
11.7 Exercises
12 System and Process Information [~10 pages]
12.1 The /proc File System
12.1.1 Obtaining Information about a Process: /proc/PID
12.1.2 System Information under /proc
12.1.3 Accessing /proc Files
12.2 System Identification: uname()
12.3 Summary
12.4 Exercises
13 File I/O Buffering [~20 pages]
13.1 Kernel Buffering of File I/O: The Buffer Cache
13.2 Buffering in the stdio Library
13.3 Controlling Kernel Buffering of File I/O
13.4 Summary of I/O Buffering
13.5 Giving the Kernel Hints about I/O Patterns: posix_fadvise()
13.6 Bypassing the Buffer Cache: Direct I/O
13.7 Mixing Library Functions and System Calls for File I/O
13.8 Summary
13.9 Exercises
14 File Systems [~30 pages]
14.1 Device Special Files (Devices)
14.2 Disks and Partitions
14.3 File Systems
14.4 I-nodes
14.5 The Virtual File System (VFS)
14.6 Journaling File Systems
14.7 Single Directory Hierarchy and Mount Points
14.8 Mounting and Unmounting File Systems
14.8.1 Mounting a File System: mount()
14.8.2 Unmounting a File System: umount() and umount2()
14.9 Advanced Mount Features
14.9.1 Mounting a File System at Multiple Mount Points
14.9.2 Stacking Multiple Mounts on the Same Mount Point
14.9.3 Mount Flags That Are Per-mount Options
14.9.4 Bind Mounts
14.9.5 Recursive Bind Mounts
14.10 A Virtual Memory File System: tmpfs
14.11 Obtaining Information about a File System: statvfs()
14.12 Summary
14.13 Exercises
15 File Attributes [~30 pages]
15.1 Retrieving File Information: stat()
15.2 File Timestamps
15.2.1 Changing File Timestamps with utime() and utimes()
15.2.2 Changing File Timestamps with utimensat() and futimens()
15.3 File Ownership
15.3.1 Ownership of New Files
15.3.2 Changing File Ownership: chown(), fchown(), and lchown()
15.4 File Permissions
15.4.1 Permissions on Regular Files
15.4.2 Permissions on Directories
15.4.3 Permission Checking Algorithm
15.4.4 Checking File Accessibility: access()
15.4.5 Set-user-ID, Set-group-ID, and Sticky Bits
15.4.6 The Process File Mode Creation Mask: umask()
15.4.7 Changing File Permissions: chmod() and fchmod()
15.5 I-node Flags (ext2 Extended File Attributes)
15.6 Summary
15.7 Exercises
16 Extended Attributes [~8 pages]
16.1 Overview
16.2 Extended Attribute Implementation Details
16.3 System Calls for Manipulating Extended Attributes
16.4 Summary
16.5 Exercises
17 Access Control Lists [~20 pages]
17.1 Overview
17.2 ACL Permission-Checking Algorithm
17.3 Long and Short Text Forms for ACLs
17.4 The ACL_MASK Entry and the ACL Group Class
17.5 The getfacl and setfacl Commands
17.6 Default ACLs and File Creation
17.7 ACL Implementation Limits
17.8 The ACL API
17.9 Summary
17.10 Exercises
18 Directories and Links [~35 pages]
18.1 Directories and (Hard) Links
18.2 Symbolic (Soft) Links
18.3 Creating and Removing (Hard) Links: link() and unlink()
18.4 Changing the Name of a File: rename()
18.5 Working with Symbolic Links: symlink() and readlink()
18.6 Creating and Removing Directories: mkdir() and rmdir()
18.7 Removing a File or Directory: remove()
18.8 Reading Directories: opendir() and readdir()
18.9 File Tree Walking: nftw()
18.10 The Current Working Directory of a Process
18.11 Operating Relative to a Directory File Descriptor
18.12 Changing the Root Directory of a Process: chroot()
18.13 Resolving a Pathname: realpath()
18.14 Parsing Pathname Strings: dirname() and basename()
18.15 Summary
18.16 Exercises
19 Monitoring File Events [~12 pages]
19.1 Overview
19.2 The inotify API
19.3 inotify Events
19.4 Reading inotify Events
19.5 Queue Limits and /proc Files
19.6 An Older System for Monitoring File Events: dnotify
19.7 Summary
19.8 Exercises
20 Signals: Fundamental Concepts [~30 pages]
20.1 Concepts and Overview
20.2 Signal Types and Default Actions
20.3 Changing Signal Dispositions: signal()
20.4 Introduction to Signal Handlers
20.5 Sending Signals: kill()
20.6 Checking for the Existence of a Process
20.7 Other Ways of Sending Signals: raise() and killpg()
20.8 Displaying Signal Descriptions
20.9 Signal Sets
20.10 The Signal Mask (Blocking Signal Delivery)
20.11 Pending Signals
20.12 Signals Are Not Queued
20.13 Changing Signal Dispositions: sigaction()
20.14 Waiting for a Signal: pause()
20.15 Summary
20.16 Exercises
21 Signals: Signal Handlers [~25 pages]
21.1 Designing Signal Handlers
21.1.1 Signals Are Not Queued (Revisited)
21.1.2 Reentrant and Async-signal-safe Functions
21.1.3 Global Variables and the sig_atomic_t Data Type
21.2 Other Methods of Terminating a Signal Handler
21.2.1 Performing a Nonlocal Goto from a Signal Handler
21.2.2 Terminating a Process Abnormally: abort()
21.3 Handling a Signal on an Alternate Stack: sigaltstack()
21.4 The SA_SIGINFO Flag
21.5 Interruption and Restarting of System Calls
21.6 Summary
21.7 Exercises
22 Signals: Advanced Features [~30 pages]
22.1 Core Dump Files
22.2 Special Cases for Signal Delivery, Disposition, and Handling
22.3 Interruptible and Uninterruptible Process Sleep States
22.4 Hardware-generated Signals
22.5 Synchronous and Asynchronous Signal Generation
22.6 Timing and Order of Signal Delivery
22.7 Implementation and Portability of signal()
22.8 Realtime Signals
22.8.1 Sending Realtime Signals
22.8.2 Handling Realtime Signals
22.9 Waiting for a Signal Using a Mask: sigsuspend()
22.10 Synchronously Waiting for a Signal
22.11 Fetching Signals via a File Descriptor
22.12 Interprocess Communication with Signals
22.13 Earlier Signal APIs (System V and BSD)
22.14 Summary
22.15 Exercises
23 Timers and Sleeping [~30 pages]
23.1 Interval Timers
23.2 Scheduling and Accuracy of Timers
23.3 Setting Timeouts on Blocking Operations
23.4 Suspending Execution for a Fixed Interval (Sleeping)
23.4.1 Low-resolution Sleeping: sleep()
23.4.2 High-resolution Sleeping: nanosleep()
23.5 POSIX Clocks
23.5.1 Retrieving the Value of a Clock: timer_gettime()
23.5.2 Updating the Value of a Clock: timer_gettime()
23.5.3 Obtaining the Clock ID of a Specific Process or Thread
23.5.4 Improved High-resolution Sleeping: clock_nanosleep()
23.6 POSIX Interval Timers
23.6.1 Creating a Timer: timer_create()
23.6.2 Arming and Disarming a Timer: timer_settime()
23.6.3 Retrieving the Current Value of a Timer: timer_gettime()
23.6.4 Deleting a Timer: timer_delete()
23.6.5 Notification via a Signal (SIGEV_SIGNAL)
23.6.6 Timer Overruns
23.6.7 Notification via a Thread (SIGEV_THREAD)
23.7 Timers That Notify via File Descriptors: the timerfd API
23.8 Summary
23.9 Exercises
24 Process Creation [~20 pages]
24.1 Overview of fork(), exit(), wait(), and execve()
24.2 Creating a New Process: fork()
24.2.1 File Sharing Between Parent and Child
24.2.2 Memory Semantics of fork()
24.3 The vfork() System Call
24.4 Race Conditions after fork()
24.5 Avoiding Race Conditions by Synchronizing with Signals
24.6 Summary
25 Process Termination [~10 pages]
25.1 Terminating a Process: _exit() and exit()
25.2 Details of Process Termination
25.3 Exit Handlers
25.4 Interactions Between fork(), stdio Buffers, and _exit()
25.5 Summary
25.6 Exercises
26 Monitoring Child Processes [~20 pages]
26.1 Waiting on a Child Process
26.1.1 The wait() System Call
26.1.2 The waitpid() System Call
26.1.3 The Wait Status Value
26.1.4 Process Termination from a Signal Handler
26.1.5 The waitid() System Call
26.1.6 The wait3() and wait4() System Calls
26.2 Orphans and Zombies
26.3 The SIGCHLD Signal
26.3.1 Establishing a Handler for SIGCHLD
26.3.2 Delivery of SIGCHLD for Stopped Children
26.3.3 Ignoring Dead Child Processes
26.4 Summary
26.5 Exercises
27 Program Execution [~20 pages]
27.1 Executing a New Program: execve()
27.2 The exec() Library Functions
27.2.1 The PATH Environment Variable
27.2.2 Specifying Program Arguments As a List
27.2.3 Passing the Caller's Environment to the New Program
27.2.4 Executing a File Referred to by a Descriptor: fexecve()
27.3 Interpreter Scripts
27.4 File Descriptors and exec()
27.5 Signals and exec()
27.6 Executing a Shell Command: system()
27.7 Implementing system()
27.8 Summary
27.9 Exercises
28 Process Creation and Program Execution in More Detail [~25 pages]
28.1 Process Accounting
28.2 The clone() System Call
28.2.1 The clone() flags Argument
28.2.2 Extensions to waitpid() for Cloned Children
28.3 Speed of Process Creation
28.4 Effect of exec() and fork() on Process Attributes
28.5 Summary
28.6 Exercises
29 Threads: Introduction [~15 pages]
29.1 Overview
29.2 Background Details of the Pthreads API
29.3 Thread Creation
29.4 Thread Termination
29.5 Thread IDs
29.6 Joining with a Terminated Thread: pthread_join()
29.7 Detaching a Thread: pthread_detach()
29.8 Thread Attributes
29.9 Threads Versus Processes
29.10 Summary
29.11 Exercises
30 Threads: Thread Synchronization [~25 pages]
30.1 Protecting Accesses to Shared Variables: Mutexes
30.1.1 Statically Allocated Mutexes
30.1.2 Locking and Unlocking a Mutex
30.1.3 Performance of Mutexes
30.1.4 Mutex Deadlocks
30.1.5 Dynamically Initializing a Mutex
30.1.6 Mutex Attributes
30.1.7 Mutex Types
30.2 Signaling Changes of State: Condition Variables
30.2.1 Statically Allocated Condition Variables
30.2.2 Signaling and Waiting on Condition Variables
30.2.3 Testing a Condition Variable’s Predicate
30.2.4 Example Program: Joining Any Terminated Thread
30.2.5 Dynamically Allocated Condition Variables
30.3 Summary
30.4 Exercises
31 Threads: Thread Safety and Per-thread Storage [~15 pages]
31.1 Thread Safety (and Reentrancy Revisited)
31.2 One-time Initialization
31.3 Thread-specific Data
31.3.1 Thread-specific Data from the Library Function’s Perspective
31.3.2 Overview of the Thread-specific Data API
31.3.3 Details of the Thread-specific Data API
31.3.4 Employing the Thread-specific Data API
31.3.5 Thread-specific Data Implementation Limits
31.4 Thread-local Storage
31.5 Summary
31.6 Exercises
32 Threads: Thread Cancellation [~10 pages]
32.1 Canceling a Thread
32.2 Cancellation State and Type
32.3 Cancellation Points
32.4 Testing for Thread Cancellation
32.5 Cleanup Handlers
32.6 Asynchronous Cancelability
32.7 Summary
32.8 Exercises
33 Threads: Further Details [~15 pages]
33.1 Thread Stacks
33.2 Threads and Signals
33.2.1 How the Unix Signal Model Maps to Threads
33.2.2 Manipulating the Thread Signal Mask
33.2.3 Sending a Signal to a Thread
33.2.4 Dealing with Asynchronous Signals Sanely
33.3 Threads and Process Control
33.4 Thread Implementation Models
33.5 Linux Implementations of POSIX Threads
33.5.1 LinuxThreads
33.5.2 NPTL
33.5.3 Which Threading Implementation?
33.6 Advanced Features of the Pthreads API
33.7 Summary
33.8 Exercises
34 Process Groups, Sessions, and Job Control [~35 pages]
34.1 Overview
34.2 Process Groups
34.3 Sessions
34.4 Controlling Terminals and Controlling Processes
34.5 Foreground and Background Process Groups
34.6 The SIGHUP Signal
34.6.1 Handling of SIGHUP by the Shell
34.6.2 SIGHUP and Termination of the Controlling Process
34.7 Job Control
34.7.1 Using Job Control within the Shell
34.7.2 Implementing Job Control
34.7.3 Handling Job-control Signals
34.7.4 Orphaned Process Groups (and SIGHUP Revisited)
34.8 Summary
34.9 Exercises
35 Process Priorities and Scheduling [~20 pages]
35.1 Process Priorities (Nice Values)
35.2 Overview of Realtime Process Scheduling
35.2.1 The SCHED_RR Policy
35.2.2 The SCHED_FIFO Policy
35.2.3 The SCHED_BATCH and SCHED_IDLE Policies
35.3 Realtime Process Scheduling API
35.3.1 Realtime Priority Ranges
35.3.2 Modifying and Retrieving Policies and Priorities
35.3.3 Relinquishing the CPU
35.3.4 The SCHED_RR Time Slice
35.4 CPU Affinity
35.5 Summary
35.6 Exercises
36 Process Resources [~15 pages]
36.1 Process Resource Usage: getrusage()
36.2 Process Resource Limits: getrlimit() and setrlimit()
36.3 Details of Specific Resource Limits
36.4 Summary
36.5 Exercises
37 Daemons [~15 pages]
37.1 Overview
37.2 Creating a Daemon
37.3 Guidelines for Writing Daemons
37.4 Using SIGHUP to Reinitialize a Daemon
37.5 Logging Messages and Errors Using syslog
37.5.1 Overview
37.5.2 The syslog API
37.5.3 The /etc/syslog.conf File
37.6 Summary
37.7 Exercises
38 Writing Secure Privileged Programs [~15 pages]
38.1 A Checklist for Secure Programming
38.2 Summary
38.3 Exercises
39 Capabilities [~20 pages]
39.1 Rationale for Capabilities
39.2 The Linux Capabilities
39.3 Process and File Capabilities
39.3.1 Process Capabilities
39.3.2 File Capabilities
39.3.3 Purpose of the Process Permitted and Effective Capability Sets
39.3.4 Purpose of the File Permitted and Effective Capability Sets
39.3.5 Purpose of the Process and File Inheritable Sets
39.3.6 Assigning and Viewing File Capabilities from the Shell
39.4 The Modern Capabilities Implementation
39.5 Transformation of Process Capabilities during exec()
39.5.1 Capability Bounding Set
39.5.2 Preserving root Semantics
39.6 Effect on Process Capabilities of Changing User IDs
39.7 Changing Process Capabilities Programmatically
39.8 Creating Capabilities-only Environments
39.9 Discovering the Capabilities Required by a Program
39.10 Older Kernels and Systems without File Capabilities
39.11 Summary
39.12 Exercises
40 Login Accounting [~15 pages]
40.1 Overview of the utmp and wtmp Files
40.2 The utmpx API
40.3 The utmpx Structure
40.4 Retrieving Information from the utmp and wtmp Files
40.5 Retrieving the Login Name: getlogin()
40.6 Updating the utmp and wtmp Files for a Login Session
40.7 The lastlog File
40.8 Summary
40.9 Exercises
41 Fundamentals of Shared Libraries [~25 pages]
41.1 Object Libraries
41.2 Static Libraries
41.3 Overview of Shared Libraries
41.4 Creating and Using Shared Libraries--A First Pass
41.4.1 Creating a Shared Library
41.4.2 Position-independent Code
41.4.3 Using a Shared Library
41.4.4 The Shared Library Soname
41.5 Useful Tools for Working with Shared Libraries
41.6 Shared Library Versions and Naming Conventions
41.7 Installing Shared Libraries
41.8 Compatible Versus Incompatible Libraries
41.9 Upgrading Shared Libraries
41.10 Specifying Library Search Directories in an Object File
41.11 Finding Shared Libraries at Run Time
41.12 Run-time Symbol Resolution
41.13 Using a Static Library Instead of a Shared Library
41.14 Summary
41.15 Exercises
42 Advanced Features of Shared Libraries [~20 pages]
42.1 Dynamically Loaded Libraries
42.1.1 Opening a Shared Library
42.1.2 Diagnosing Errors from the dlopen API
42.1.3 Obtaining the Address of a Symbol: dlsym()
42.1.4 Closing a Shared Library: dlclose()
42.1.5 Obtaining Information about Loaded Symbols: dladdr()
42.1.6 Accessing Symbols in the Main Program
42.2 Controlling Symbol Visibility
42.3 Linker Version Scripts
42.3.1 Controlling Symbol Visibility with Version Scripts
42.3.2 Symbol Versioning
42.4 Initialization and Finalization Functions
42.5 Preloading Shared Libraries
42.6 Monitoring the Dynamic Linker: LD_DEBUG
42.7 Summary
42.8 Exercises
1 History and Standards [~20 pages]
1.1 A Brief History of Unix and C
1.2 A Brief History of Linux
1.2.1 The GNU Project
1.2.2 The Linux Kernel
1.3 Standardization
1.3.1 The C Programming Language
1.3.2 The First POSIX Standards
1.3.3 X/Open Company and The Open Group
1.3.4 SUSv3 and POSIX.1-2001
1.3.5 SUSv4 and POSIX.1-2008
1.3.6 Unix Standards Timeline
1.3.7 Implementation Standards
1.3.8 Linux, Standards, and the Linux Standard Base
1.4 Summary
2 Fundamental Concepts [~20 pages]
2.1 The Core Operating System: The Kernel
2.2 The Shell
2.3 Users and Groups
2.4 Single Directory Hierarchy, Directories, Links, and Files
2.5 File I/O Model
2.6 Programs
2.7 Processes
2.8 Memory Mappings
2.9 Static and Shared Libraries
2.10 Interprocess Communication and Synchronization
2.11 Signals
2.12 Threads
2.13 Process Groups and Shell Job Control
2.14 Sessions, Controlling Terminals, and Controlling Processes
2.15 Pseudoterminals
2.16 Date and Time
2.17 Client-server Architecture
2.18 Realtime
2.19 The /proc File System
2.20 Summary
3 System Programming Concepts [~25 pages]
3.1 System Calls
3.2 Library Functions
3.3 The Standard C Library; The GNU C Library (glibc)
3.4 Handling Errors from System Calls and Library Functions
3.5 Notes on the Example Programs in This Book
3.5.1 Command-line Options and Arguments
3.5.2 Common Functions and Header Files
3.6 Portability Issues
3.6.1 Feature Test Macros
3.6.2 System Data Types
3.6.3 Miscellaneous Portability Issues
3.7 Summary
3.8 Exercises
4 File I/O: The Universal I/O Model [~20 pages]
4.1 Overview
4.2 Universality of I/O
4.3 Opening a File: open()
4.4 Reading from a File: read()
4.5 Writing to a File: write()
4.6 Closing a File: close()
4.7 Changing the Current File Offset: lseek()
4.8 Operations Outside the Universal I/O Model: ioctl()
4.9 Summary
4.10 Exercises
5 File I/O: Further Details [~25 pages]
5.1 Atomicity and Race Conditions
5.2 File Control Operations: fcntl()
5.3 Open File Status Flags
5.4 Relationship Between File Descriptors and Open Files
5.5 Duplicating File Descriptors
5.6 File I/O at a Specified Offset: pread() and pwrite()
5.7 Scatter-gather I/O: readv() and writev()
5.8 Truncating a File: truncate() and ftruncate()
5.9 Nonblocking I/O
5.10 I/O on Large Files
5.11 The /dev/fd Directory
5.12 Creating Temporary Files
5.13 Summary
5.14 Exercises
6 Processes [~25 pages]
6.1 Processes and Programs
6.2 Process ID and Parent Process ID
6.3 Memory Layout of a Process
6.4 Virtual Memory Management
6.5 The Stack and Stack Frames
6.6 Command-line Arguments (argc, argv)
6.7 Environment List
6.8 Performing a Nonlocal Goto: setjmp() and longjmp()
6.9 Summary
6.10 Exercises
7 Memory Allocation [~15 pages]
7.1 Allocating Memory on the Heap
7.1.1 Adjusting the Program Break: brk() and sbrk()
7.1.2 Allocating Memory on the Heap: malloc() and free()
7.1.3 Implementation of malloc() and free()
7.1.4 Other Methods of Allocating Memory on the Heap
7.2 Allocating Memory on the Stack: alloca()
7.3 Summary
7.4 Exercises
8 Users and Groups [~15 pages]
8.1 The Password File: /etc/passwd
8.2 The Shadow Password File: /etc/shadow
8.3 The Group File: /etc/group
8.4 Retrieving User and Group Information
8.5 Password Encryption and User Authentication
8.6 Summary
8.7 Exercises
9 Process Credentials [~20 pages]
9.1 Real User ID and Real Group ID
9.2 Effective User ID and Effective Group ID
9.3 Set-user-ID and Set-group-ID Programs
9.4 Saved Set-user-ID and Saved Set-group-ID
9.5 File System User ID and File System Group ID
9.6 Supplementary Group IDs
9.7 Retrieving and Modifying Process Credentials
9.7.1 Retrieving and Modifying Real, Effective, and Saved Set IDs
9.7.2 Retrieving and Modifying File System IDs
9.7.3 Retrieving and Modifying Supplementary Group IDs
9.7.4 Summary of Calls for Modifying Process Credentials
9.7.5 Example: Displaying Process Credentials
9.8 Summary
9.9 Exercises
10 Times and Dates [~25 pages]
10.1 Calendar Time
10.2 Time-Conversion Functions
10.2.1 Converting time_t to Printable Form
10.2.2 Converting Between time_t and Broken-down Time
10.2.3 Converting Between Broken-down Time and Printable Form
10.3 Timezones
10.4 Locales
10.5 Updating the System Clock
10.6 The Software Clock (Jiffies)
10.7 Process Time
10.8 Summary
10.9 Exercises
11 System Limits and Options [~10 pages]
11.1 System Limits
11.2 Retrieving System Limits (and Options) at Run Time
11.3 Retrieving File-related Limits (and Options) at Run Time
11.4 Indeterminate Limits
11.5 System Options
11.6 Summary
11.7 Exercises
12 System and Process Information [~10 pages]
12.1 The /proc File System
12.1.1 Obtaining Information about a Process: /proc/PID
12.1.2 System Information under /proc
12.1.3 Accessing /proc Files
12.2 System Identification: uname()
12.3 Summary
12.4 Exercises
13 File I/O Buffering [~20 pages]
13.1 Kernel Buffering of File I/O: The Buffer Cache
13.2 Buffering in the stdio Library
13.3 Controlling Kernel Buffering of File I/O
13.4 Summary of I/O Buffering
13.5 Giving the Kernel Hints about I/O Patterns: posix_fadvise()
13.6 Bypassing the Buffer Cache: Direct I/O
13.7 Mixing Library Functions and System Calls for File I/O
13.8 Summary
13.9 Exercises
14 File Systems [~30 pages]
14.1 Device Special Files (Devices)
14.2 Disks and Partitions
14.3 File Systems
14.4 I-nodes
14.5 The Virtual File System (VFS)
14.6 Journaling File Systems
14.7 Single Directory Hierarchy and Mount Points
14.8 Mounting and Unmounting File Systems
14.8.1 Mounting a File System: mount()
14.8.2 Unmounting a File System: umount() and umount2()
14.9 Advanced Mount Features
14.9.1 Mounting a File System at Multiple Mount Points
14.9.2 Stacking Multiple Mounts on the Same Mount Point
14.9.3 Mount Flags That Are Per-mount Options
14.9.4 Bind Mounts
14.9.5 Recursive Bind Mounts
14.10 A Virtual Memory File System: tmpfs
14.11 Obtaining Information about a File System: statvfs()
14.12 Summary
14.13 Exercises
15 File Attributes [~30 pages]
15.1 Retrieving File Information: stat()
15.2 File Timestamps
15.2.1 Changing File Timestamps with utime() and utimes()
15.2.2 Changing File Timestamps with utimensat() and futimens()
15.3 File Ownership
15.3.1 Ownership of New Files
15.3.2 Changing File Ownership: chown(), fchown(), and lchown()
15.4 File Permissions
15.4.1 Permissions on Regular Files
15.4.2 Permissions on Directories
15.4.3 Permission Checking Algorithm
15.4.4 Checking File Accessibility: access()
15.4.5 Set-user-ID, Set-group-ID, and Sticky Bits
15.4.6 The Process File Mode Creation Mask: umask()
15.4.7 Changing File Permissions: chmod() and fchmod()
15.5 I-node Flags (ext2 Extended File Attributes)
15.6 Summary
15.7 Exercises
16 Extended Attributes [~8 pages]
16.1 Overview
16.2 Extended Attribute Implementation Details
16.3 System Calls for Manipulating Extended Attributes
16.4 Summary
16.5 Exercises
17 Access Control Lists [~20 pages]
17.1 Overview
17.2 ACL Permission-Checking Algorithm
17.3 Long and Short Text Forms for ACLs
17.4 The ACL_MASK Entry and the ACL Group Class
17.5 The getfacl and setfacl Commands
17.6 Default ACLs and File Creation
17.7 ACL Implementation Limits
17.8 The ACL API
17.9 Summary
17.10 Exercises
18 Directories and Links [~35 pages]
18.1 Directories and (Hard) Links
18.2 Symbolic (Soft) Links
18.3 Creating and Removing (Hard) Links: link() and unlink()
18.4 Changing the Name of a File: rename()
18.5 Working with Symbolic Links: symlink() and readlink()
18.6 Creating and Removing Directories: mkdir() and rmdir()
18.7 Removing a File or Directory: remove()
18.8 Reading Directories: opendir() and readdir()
18.9 File Tree Walking: nftw()
18.10 The Current Working Directory of a Process
18.11 Operating Relative to a Directory File Descriptor
18.12 Changing the Root Directory of a Process: chroot()
18.13 Resolving a Pathname: realpath()
18.14 Parsing Pathname Strings: dirname() and basename()
18.15 Summary
18.16 Exercises
19 Monitoring File Events [~12 pages]
19.1 Overview
19.2 The inotify API
19.3 inotify Events
19.4 Reading inotify Events
19.5 Queue Limits and /proc Files
19.6 An Older System for Monitoring File Events: dnotify
19.7 Summary
19.8 Exercises
20 Signals: Fundamental Concepts [~30 pages]
20.1 Concepts and Overview
20.2 Signal Types and Default Actions
20.3 Changing Signal Dispositions: signal()
20.4 Introduction to Signal Handlers
20.5 Sending Signals: kill()
20.6 Checking for the Existence of a Process
20.7 Other Ways of Sending Signals: raise() and killpg()
20.8 Displaying Signal Descriptions
20.9 Signal Sets
20.10 The Signal Mask (Blocking Signal Delivery)
20.11 Pending Signals
20.12 Signals Are Not Queued
20.13 Changing Signal Dispositions: sigaction()
20.14 Waiting for a Signal: pause()
20.15 Summary
20.16 Exercises
21 Signals: Signal Handlers [~25 pages]
21.1 Designing Signal Handlers
21.1.1 Signals Are Not Queued (Revisited)
21.1.2 Reentrant and Async-signal-safe Functions
21.1.3 Global Variables and the sig_atomic_t Data Type
21.2 Other Methods of Terminating a Signal Handler
21.2.1 Performing a Nonlocal Goto from a Signal Handler
21.2.2 Terminating a Process Abnormally: abort()
21.3 Handling a Signal on an Alternate Stack: sigaltstack()
21.4 The SA_SIGINFO Flag
21.5 Interruption and Restarting of System Calls
21.6 Summary
21.7 Exercises
22 Signals: Advanced Features [~30 pages]
22.1 Core Dump Files
22.2 Special Cases for Signal Delivery, Disposition, and Handling
22.3 Interruptible and Uninterruptible Process Sleep States
22.4 Hardware-generated Signals
22.5 Synchronous and Asynchronous Signal Generation
22.6 Timing and Order of Signal Delivery
22.7 Implementation and Portability of signal()
22.8 Realtime Signals
22.8.1 Sending Realtime Signals
22.8.2 Handling Realtime Signals
22.9 Waiting for a Signal Using a Mask: sigsuspend()
22.10 Synchronously Waiting for a Signal
22.11 Fetching Signals via a File Descriptor
22.12 Interprocess Communication with Signals
22.13 Earlier Signal APIs (System V and BSD)
22.14 Summary
22.15 Exercises
23 Timers and Sleeping [~30 pages]
23.1 Interval Timers
23.2 Scheduling and Accuracy of Timers
23.3 Setting Timeouts on Blocking Operations
23.4 Suspending Execution for a Fixed Interval (Sleeping)
23.4.1 Low-resolution Sleeping: sleep()
23.4.2 High-resolution Sleeping: nanosleep()
23.5 POSIX Clocks
23.5.1 Retrieving the Value of a Clock: timer_gettime()
23.5.2 Updating the Value of a Clock: timer_gettime()
23.5.3 Obtaining the Clock ID of a Specific Process or Thread
23.5.4 Improved High-resolution Sleeping: clock_nanosleep()
23.6 POSIX Interval Timers
23.6.1 Creating a Timer: timer_create()
23.6.2 Arming and Disarming a Timer: timer_settime()
23.6.3 Retrieving the Current Value of a Timer: timer_gettime()
23.6.4 Deleting a Timer: timer_delete()
23.6.5 Notification via a Signal (SIGEV_SIGNAL)
23.6.6 Timer Overruns
23.6.7 Notification via a Thread (SIGEV_THREAD)
23.7 Timers That Notify via File Descriptors: the timerfd API
23.8 Summary
23.9 Exercises
24 Process Creation [~20 pages]
24.1 Overview of fork(), exit(), wait(), and execve()
24.2 Creating a New Process: fork()
24.2.1 File Sharing Between Parent and Child
24.2.2 Memory Semantics of fork()
24.3 The vfork() System Call
24.4 Race Conditions after fork()
24.5 Avoiding Race Conditions by Synchronizing with Signals
24.6 Summary
25 Process Termination [~10 pages]
25.1 Terminating a Process: _exit() and exit()
25.2 Details of Process Termination
25.3 Exit Handlers
25.4 Interactions Between fork(), stdio Buffers, and _exit()
25.5 Summary
25.6 Exercises
26 Monitoring Child Processes [~20 pages]
26.1 Waiting on a Child Process
26.1.1 The wait() System Call
26.1.2 The waitpid() System Call
26.1.3 The Wait Status Value
26.1.4 Process Termination from a Signal Handler
26.1.5 The waitid() System Call
26.1.6 The wait3() and wait4() System Calls
26.2 Orphans and Zombies
26.3 The SIGCHLD Signal
26.3.1 Establishing a Handler for SIGCHLD
26.3.2 Delivery of SIGCHLD for Stopped Children
26.3.3 Ignoring Dead Child Processes
26.4 Summary
26.5 Exercises
27 Program Execution [~20 pages]
27.1 Executing a New Program: execve()
27.2 The exec() Library Functions
27.2.1 The PATH Environment Variable
27.2.2 Specifying Program Arguments As a List
27.2.3 Passing the Caller's Environment to the New Program
27.2.4 Executing a File Referred to by a Descriptor: fexecve()
27.3 Interpreter Scripts
27.4 File Descriptors and exec()
27.5 Signals and exec()
27.6 Executing a Shell Command: system()
27.7 Implementing system()
27.8 Summary
27.9 Exercises
28 Process Creation and Program Execution in More Detail [~25 pages]
28.1 Process Accounting
28.2 The clone() System Call
28.2.1 The clone() flags Argument
28.2.2 Extensions to waitpid() for Cloned Children
28.3 Speed of Process Creation
28.4 Effect of exec() and fork() on Process Attributes
28.5 Summary
28.6 Exercises
29 Threads: Introduction [~15 pages]
29.1 Overview
29.2 Background Details of the Pthreads API
29.3 Thread Creation
29.4 Thread Termination
29.5 Thread IDs
29.6 Joining with a Terminated Thread: pthread_join()
29.7 Detaching a Thread: pthread_detach()
29.8 Thread Attributes
29.9 Threads Versus Processes
29.10 Summary
29.11 Exercises
30 Threads: Thread Synchronization [~25 pages]
30.1 Protecting Accesses to Shared Variables: Mutexes
30.1.1 Statically Allocated Mutexes
30.1.2 Locking and Unlocking a Mutex
30.1.3 Performance of Mutexes
30.1.4 Mutex Deadlocks
30.1.5 Dynamically Initializing a Mutex
30.1.6 Mutex Attributes
30.1.7 Mutex Types
30.2 Signaling Changes of State: Condition Variables
30.2.1 Statically Allocated Condition Variables
30.2.2 Signaling and Waiting on Condition Variables
30.2.3 Testing a Condition Variable’s Predicate
30.2.4 Example Program: Joining Any Terminated Thread
30.2.5 Dynamically Allocated Condition Variables
30.3 Summary
30.4 Exercises
31 Threads: Thread Safety and Per-thread Storage [~15 pages]
31.1 Thread Safety (and Reentrancy Revisited)
31.2 One-time Initialization
31.3 Thread-specific Data
31.3.1 Thread-specific Data from the Library Function’s Perspective
31.3.2 Overview of the Thread-specific Data API
31.3.3 Details of the Thread-specific Data API
31.3.4 Employing the Thread-specific Data API
31.3.5 Thread-specific Data Implementation Limits
31.4 Thread-local Storage
31.5 Summary
31.6 Exercises
32 Threads: Thread Cancellation [~10 pages]
32.1 Canceling a Thread
32.2 Cancellation State and Type
32.3 Cancellation Points
32.4 Testing for Thread Cancellation
32.5 Cleanup Handlers
32.6 Asynchronous Cancelability
32.7 Summary
32.8 Exercises
33 Threads: Further Details [~15 pages]
33.1 Thread Stacks
33.2 Threads and Signals
33.2.1 How the Unix Signal Model Maps to Threads
33.2.2 Manipulating the Thread Signal Mask
33.2.3 Sending a Signal to a Thread
33.2.4 Dealing with Asynchronous Signals Sanely
33.3 Threads and Process Control
33.4 Thread Implementation Models
33.5 Linux Implementations of POSIX Threads
33.5.1 LinuxThreads
33.5.2 NPTL
33.5.3 Which Threading Implementation?
33.6 Advanced Features of the Pthreads API
33.7 Summary
33.8 Exercises
34 Process Groups, Sessions, and Job Control [~35 pages]
34.1 Overview
34.2 Process Groups
34.3 Sessions
34.4 Controlling Terminals and Controlling Processes
34.5 Foreground and Background Process Groups
34.6 The SIGHUP Signal
34.6.1 Handling of SIGHUP by the Shell
34.6.2 SIGHUP and Termination of the Controlling Process
34.7 Job Control
34.7.1 Using Job Control within the Shell
34.7.2 Implementing Job Control
34.7.3 Handling Job-control Signals
34.7.4 Orphaned Process Groups (and SIGHUP Revisited)
34.8 Summary
34.9 Exercises
35 Process Priorities and Scheduling [~20 pages]
35.1 Process Priorities (Nice Values)
35.2 Overview of Realtime Process Scheduling
35.2.1 The SCHED_RR Policy
35.2.2 The SCHED_FIFO Policy
35.2.3 The SCHED_BATCH and SCHED_IDLE Policies
35.3 Realtime Process Scheduling API
35.3.1 Realtime Priority Ranges
35.3.2 Modifying and Retrieving Policies and Priorities
35.3.3 Relinquishing the CPU
35.3.4 The SCHED_RR Time Slice
35.4 CPU Affinity
35.5 Summary
35.6 Exercises
36 Process Resources [~15 pages]
36.1 Process Resource Usage: getrusage()
36.2 Process Resource Limits: getrlimit() and setrlimit()
36.3 Details of Specific Resource Limits
36.4 Summary
36.5 Exercises
37 Daemons [~15 pages]
37.1 Overview
37.2 Creating a Daemon
37.3 Guidelines for Writing Daemons
37.4 Using SIGHUP to Reinitialize a Daemon
37.5 Logging Messages and Errors Using syslog
37.5.1 Overview
37.5.2 The syslog API
37.5.3 The /etc/syslog.conf File
37.6 Summary
37.7 Exercises
38 Writing Secure Privileged Programs [~15 pages]
38.1 A Checklist for Secure Programming
38.2 Summary
38.3 Exercises
39 Capabilities [~20 pages]
39.1 Rationale for Capabilities
39.2 The Linux Capabilities
39.3 Process and File Capabilities
39.3.1 Process Capabilities
39.3.2 File Capabilities
39.3.3 Purpose of the Process Permitted and Effective Capability Sets
39.3.4 Purpose of the File Permitted and Effective Capability Sets
39.3.5 Purpose of the Process and File Inheritable Sets
39.3.6 Assigning and Viewing File Capabilities from the Shell
39.4 The Modern Capabilities Implementation
39.5 Transformation of Process Capabilities during exec()
39.5.1 Capability Bounding Set
39.5.2 Preserving root Semantics
39.6 Effect on Process Capabilities of Changing User IDs
39.7 Changing Process Capabilities Programmatically
39.8 Creating Capabilities-only Environments
39.9 Discovering the Capabilities Required by a Program
39.10 Older Kernels and Systems without File Capabilities
39.11 Summary
39.12 Exercises
40 Login Accounting [~15 pages]
40.1 Overview of the utmp and wtmp Files
40.2 The utmpx API
40.3 The utmpx Structure
40.4 Retrieving Information from the utmp and wtmp Files
40.5 Retrieving the Login Name: getlogin()
40.6 Updating the utmp and wtmp Files for a Login Session
40.7 The lastlog File
40.8 Summary
40.9 Exercises
41 Fundamentals of Shared Libraries [~25 pages]
41.1 Object Libraries
41.2 Static Libraries
41.3 Overview of Shared Libraries
41.4 Creating and Using Shared Libraries--A First Pass
41.4.1 Creating a Shared Library
41.4.2 Position-independent Code
41.4.3 Using a Shared Library
41.4.4 The Shared Library Soname
41.5 Useful Tools for Working with Shared Libraries
41.6 Shared Library Versions and Naming Conventions
41.7 Installing Shared Libraries
41.8 Compatible Versus Incompatible Libraries
41.9 Upgrading Shared Libraries
41.10 Specifying Library Search Directories in an Object File
41.11 Finding Shared Libraries at Run Time
41.12 Run-time Symbol Resolution
41.13 Using a Static Library Instead of a Shared Library
41.14 Summary
41.15 Exercises
42 Advanced Features of Shared Libraries [~20 pages]
42.1 Dynamically Loaded Libraries
42.1.1 Opening a Shared Library
42.1.2 Diagnosing Errors from the dlopen API
42.1.3 Obtaining the Address of a Symbol: dlsym()
42.1.4 Closing a Shared Library: dlclose()
42.1.5 Obtaining Information about Loaded Symbols: dladdr()
42.1.6 Accessing Symbols in the Main Program
42.2 Controlling Symbol Visibility
42.3 Linker Version Scripts
42.3.1 Controlling Symbol Visibility with Version Scripts
42.3.2 Symbol Versioning
42.4 Initialization and Finalization Functions
42.5 Preloading Shared Libraries
42.6 Monitoring the Dynamic Linker: LD_DEBUG
42.7 Summary
42.8 Exercises
2009-09-29
Chapter 42: Advanced Features of Shared Libraries
The previous chapter covered the fundamentals of shared libraries. This chapter describes a number of advanced features of shared libraries, including the following:
42.1 Dynamically Loaded Libraries
42.1.1 Opening a Shared Library
42.1.2 Diagnosing Errors from the dlopen API
42.1.3 Obtaining the Address of a Symbol: dlsym()
42.1.4 Closing a Shared Library: dlclose()
42.1.5 Obtaining Information about Loaded Symbols: dladdr()
42.1.6 Accessing Symbols in the Main Program
42.2 Controlling Symbol Visibility
42.3 Linker Version Scripts
42.3.1 Controlling Symbol Visibility with Version Scripts
42.3.2 Symbol Versioning
42.4 Initialization and Finalization Functions
42.5 Preloading Shared Libraries
42.6 Monitoring the Dynamic Linker: LD_DEBUG
42.7 Summary
42.8 Exercises
- dynamically loading shared libraries;
- controlling the visibility of symbols defined by a shared library;
- using linker scripts to create versioned symbols;
- using initialization and finalization functions to automatically execute code when a library is loaded and unloaded;
- shared library preloading; and
- using LD_DEBUG to monitor the operation of the dynamic linker.
42.1 Dynamically Loaded Libraries
42.1.1 Opening a Shared Library
42.1.2 Diagnosing Errors from the dlopen API
42.1.3 Obtaining the Address of a Symbol: dlsym()
42.1.4 Closing a Shared Library: dlclose()
42.1.5 Obtaining Information about Loaded Symbols: dladdr()
42.1.6 Accessing Symbols in the Main Program
42.2 Controlling Symbol Visibility
42.3 Linker Version Scripts
42.3.1 Controlling Symbol Visibility with Version Scripts
42.3.2 Symbol Versioning
42.4 Initialization and Finalization Functions
42.5 Preloading Shared Libraries
42.6 Monitoring the Dynamic Linker: LD_DEBUG
42.7 Summary
42.8 Exercises
2009-09-28
See you at LCA 2010!
One of my proposals got accepted for LCA 2010, in Wellington, New Zealand! As usual, there look to be lots of interesting papers at LCA. I'm presenting a tutorial on writing secure privileged programs, which will draw heavily on Chapter 38 of my book.
2009-09-24
Capter 41: Fundamentals of Shared Libraries
Shared libraries are a technique for placing library functions into a single unit that can be shared by multiple processes at run time. This technique can save both disk space and RAM. This chapter covers the fundamentals of shared libraries. The next chapter covers a number of advanced features of shared libraries.
41 Fundamentals of Shared Libraries
41.1 Object Libraries
41.2 Static Libraries
41.3 Overview of Shared Libraries
41.4 Creating and Using Shared Libraries--A First Pass
41.4.1 Creating a Shared Library
41.4.2 Position-independent Code
41.4.3 Using a Shared Library
41.4.4 The Shared Library Soname
41.5 Useful Tools for Working with Shared Libraries
41.6 Shared Library Versions and Naming Conventions
41.7 Installing Shared Libraries
41.8 Compatible Versus Incompatible Libraries
41.9 Upgrading Shared Libraries
41.10 Specifying Library Search Directories in an Object File
41.11 Finding Shared Libraries at Run Time
41.12 Run-time Symbol Resolution
41.13 Using a Static Library Instead of a Shared Library
41.14 Summary
41.15 Exercises
41 Fundamentals of Shared Libraries
41.1 Object Libraries
41.2 Static Libraries
41.3 Overview of Shared Libraries
41.4 Creating and Using Shared Libraries--A First Pass
41.4.1 Creating a Shared Library
41.4.2 Position-independent Code
41.4.3 Using a Shared Library
41.4.4 The Shared Library Soname
41.5 Useful Tools for Working with Shared Libraries
41.6 Shared Library Versions and Naming Conventions
41.7 Installing Shared Libraries
41.8 Compatible Versus Incompatible Libraries
41.9 Upgrading Shared Libraries
41.10 Specifying Library Search Directories in an Object File
41.11 Finding Shared Libraries at Run Time
41.12 Run-time Symbol Resolution
41.13 Using a Static Library Instead of a Shared Library
41.14 Summary
41.15 Exercises
2009-09-22
Chapter 40: Login Accounting
Login accounting is concerned with recording which users are currently logged in to the system, and recording past logins and logouts. This chapter looks at the login accounting files and the library functions used to retrieve and update the information they contain. We also describe the steps that an application providing a login service should perform in order to update these files when a user logs in and out.
40 Login Accounting
40.1 Overview of the utmp and wtmp Files
40.2 The utmpx API
40.3 The utmpx Structure
40.4 Retrieving Information from the utmp and wtmp Files
40.5 Retrieving the Login Name: getlogin()
40.6 Updating the utmp and wtmp Files for a Login Session
40.7 The lastlog File
40.8 Summary
40.9 Exercises
40 Login Accounting
40.1 Overview of the utmp and wtmp Files
40.2 The utmpx API
40.3 The utmpx Structure
40.4 Retrieving Information from the utmp and wtmp Files
40.5 Retrieving the Login Name: getlogin()
40.6 Updating the utmp and wtmp Files for a Login Session
40.7 The lastlog File
40.8 Summary
40.9 Exercises
2009-09-21
Chapter 39: Capabilities
This chapter describes the Linux capabilities scheme, which divides the traditional all-or-nothing Unix privilege scheme into individual capabilities that can be independently enabled or disabled. Using capabilities allows a program to perform some privileged operations, while preventing it from performing others.
39 Capabilities
39.1 Rationale for Capabilities
39.2 The Linux Capabilities
39.3 Process and File Capabilities
39.3.1 Process Capabilities
39.3.2 File Capabilities
39.3.3 Purpose of the Process Permitted and Effective Capability Sets
39.3.4 Purpose of the File Permitted and Effective Capability Sets
39.3.5 Purpose of the Process and File Inheritable Sets
39.3.6 Assigning and Viewing File Capabilities from the Shell
39.4 The Modern Capabilities Implementation
39.5 Transformation of Process Capabilities during exec()
39.5.1 Capability Bounding Set
39.5.2 Preserving root Semantics
39.6 Effect on Process Capabilities of Changing User IDs
39.7 Changing Process Capabilities Programmatically
39.8 Creating Capabilities-only Environments
39.9 Discovering the Capabilities Required by a Program
39.10 Older Kernels and Systems without File Capabilities
39.11 Summary
39.12 Exercises
39 Capabilities
39.1 Rationale for Capabilities
39.2 The Linux Capabilities
39.3 Process and File Capabilities
39.3.1 Process Capabilities
39.3.2 File Capabilities
39.3.3 Purpose of the Process Permitted and Effective Capability Sets
39.3.4 Purpose of the File Permitted and Effective Capability Sets
39.3.5 Purpose of the Process and File Inheritable Sets
39.3.6 Assigning and Viewing File Capabilities from the Shell
39.4 The Modern Capabilities Implementation
39.5 Transformation of Process Capabilities during exec()
39.5.1 Capability Bounding Set
39.5.2 Preserving root Semantics
39.6 Effect on Process Capabilities of Changing User IDs
39.7 Changing Process Capabilities Programmatically
39.8 Creating Capabilities-only Environments
39.9 Discovering the Capabilities Required by a Program
39.10 Older Kernels and Systems without File Capabilities
39.11 Summary
39.12 Exercises
2009-09-19
Chapters 43 to 44 are in copyedit
Chapters 41 and 42 already went to copyedit a while back, and by now chapters 37 to 42 came back from copyedit. Chapters 43 and 44 are now in copyedit.
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