Errata for "The Linux Programming Interface"

In the second paragraph, change:

which was subsequently adopted in 1990 as an International Standards Organization (ISO) standard

to:

which was subsequently adopted in 1990 as an International Organization for Standardization (ISO) standard

Explanation:

Although often referred to as the International Standards Organization, the correct title is International Organization for Standardization.

2011-08-04

In the last sentence of the first paragraph in Section 2.12, change:

However, each thread has it own stack…

to:

However, each thread has its own stack…

Reported by Jaewook Yu.

2011-04-09

Near the end of Listing 4-2, change:

    fd = open("w.log", O_WRONLY | O_CREAT | O_TRUNC | O_APPEND,
                       S_IRUSR | S_IWUSR);

to:

    fd = open("w.log", O_WRONLY | O_CREAT | O_APPEND,
                       S_IRUSR | S_IWUSR);

Explanation:

The code as originally given was technically correct, but the presence of O_TRUNC was superfluous for the purpose of the example, and its semantics were not explained in the accompanying comment.

Reported by Jessica T McKellar.

2011-05-26

In Table 4-3, move two rows to a different part of the table:

Flag	Purpose	SUS?
O_RDONLY	Open for reading only	v3
O_WRONLY	Open for writing only	v3
O_RDWR	Open for reading and writing	v3
O_CLOEXEC	Set the close-on-exec flag (since Linux 2.6.23)	v4
O_CREAT	Create file if it doesn't already exist	v3
O_DIRECT	File I/O bypasses buffer cache
O_DIRECTORY	Fail if pathname is not a directory	v4
O_EXCL	With O_CREAT: create file exclusively	v3
O_LARGEFILE	Used on 32-bit systems to open large files
O_NOATIME	Don't update file last access time on read() (since Linux 2.6.8)
O_NOCTTY	Don't let pathname become the controlling terminal	v3
O_NOFOLLOW	Don't dereference symbolic links	v4
O_TRUNC	Truncate existing file to zero length	v3
O_APPEND	Writes are always appended to end of file	v3
O_ASYNC	Generate a signal when I/O is possible
O_DSYNC	Provide synchronized I/O data integrity (since Linux 2.6.33)	v3
O_NONBLOCK	Open in nonblocking mode	v3
O_SYNC	Make file writes synchronous	v3

to give the following:

Flag	Purpose	SUS?
O_RDONLY	Open for reading only	v3
O_WRONLY	Open for writing only	v3
O_RDWR	Open for reading and writing	v3
O_CLOEXEC	Set the close-on-exec flag (since Linux 2.6.23)	v4
O_CREAT	Create file if it doesn't already exist	v3
O_DIRECTORY	Fail if pathname is not a directory	v4
O_EXCL	With O_CREAT: create file exclusively	v3
O_LARGEFILE	Used on 32-bit systems to open large files
O_NOCTTY	Don't let pathname become the controlling terminal	v3
O_NOFOLLOW	Don't dereference symbolic links	v4
O_TRUNC	Truncate existing file to zero length	v3
O_APPEND	Writes are always appended to end of file	v3
O_ASYNC	Generate a signal when I/O is possible
O_DIRECT	File I/O bypasses buffer cache
O_DSYNC	Provide synchronized I/O data integrity (since Linux 2.6.33)	v3
O_NOATIME	Don't update file last access time on read() (since Linux 2.6.8)
O_NONBLOCK	Open in nonblocking mode	v3
O_SYNC	Make file writes synchronous	v3

Explanation:

As noted on page 93, O_DIRECT and O_NOATIME are open file status flags that can be retrieved and modified using fcntl(). These flags were accidentally misplaced in the file creation flags section of Table 4-3.

Reported by Madhavan Kasthurirangan.

2011-09-04

In the prototype box for fcntl() at the top of the page, change:

Return on success depends on cmd, or –1 on error

to:

Return value on success depends on cmd; returns –1 on error

Explanation:

A minor wording improvement.

2011-06-16

About one third of the way down the page (in the paragraph starting "Assuming the normal situation"), change:

dup() will create the duplicate of descriptor 1 using file 3.

to:

dup() will create the duplicate of descriptor 1 using descriptor 3.

Reported by Simon Durrant.

2011-08-07

At the end of the paragraph second from the bottom of the page, add a sentence:

The preadv() and pwritev() system calls perform the same task as readv() and writev(), but perform the I/O at the file location specified by offset (like pread() and pwrite()). These system calls don't change the file offset.

Explanation:

The reader may have been able to draw this implication from the text (since it is explained that these system calls are like readv() and writev()), but it's better to make the point explicit.

Reported by Sun Jian.

2011-06-15

In the small-font at the top of the page, change:

The main difference was that a nonblocking write() on System V returned 0 if a write() could not be completed or if no input was available to satisfy a read().

to:

The main difference was that a nonblocking write() on System V returned 0 if a write() could not be completed and a nonblocking read() returned 0 if no input was available.

Reported by Sun Jian.

2011-06-15

In the first line of the small-font note toward the bottom of the page, change:

(e.g., Alpha, IA-64)

to:

(e.g., x86-64, Alpha, and IA-64)

Explanation:

It was an oversight to omit the most common 64-bit architecture here.

2011-12-11

In the first line of Exercise 5-1, change:

Modify the program in Listing 5-3

to:

If you have access to a 32-bit Linux system, modify the program in Listing 5-3

Explanation:

From Section 5.10, the reader can deduce that this exercise applies only to 32-bit systems. However, it is of course better to make that assumption explicit.

Reported by Sandipan Razzaque.

2011-12-11

In the last paragraph on this page, change:

When we compile the program in Listing 6-6 normally, we see the expected output:

to:

When we compile the program in Listing 6-6 without optimization, we see the expected output:

Explanation:

By default (i.e., "normally"), gcc compiles without optimization. This change makes that point more explicit.

Reported by Bill McConnaughey.

2011-06-28

In the paragraph below the prototype box for malloc(), change:

aligned on a byte boundary suitable for any type of C data structure.

to:

aligned on a byte boundary suitable for efficient access to any type of C data structure.

Explanation:

This change makes the intended idea behind the explanation clearer.

Reported by Sun Jian.

2011-04-07

Add a line at the top of Listing 7-1 (memalloc/free_and_sbrk.c):

#define _BSD_SOURCE
#include "tlpi_hdr.h"

#define MAX_ALLOCS 1000000

Explanation:

As noted on page 140, a feature test macro definition is needed for sbrk(). Without it, gcc complains ("implicit declaration of function 'sbrk'") when invoked with (for example) -std=c99.

I missed this problem because of the combination of two reasons: (1) the feature test macro requirements for sbrk() changed in the version of glibc (2.12) that was released not long before the book went to press (see the man page for details), and (2) there was a breakage in my main Makefile (now fixed in the latest version of the source code tarball).

Reported by Lei Yang.

2011-07-05

In the first line of the example code near the top of this page, change:

    struct { /* Some field definitions */ } myStruct;

to:

    struct myStruct { /* Some field definitions */ };

Reported by Sangman Lee.

2011-04-13

In the second bullet point, change:

In this case, the password field in /etc/passwd conventionally contains the letter x (although any nonempty character string may appear), and the encrypted password is instead stored in the shadow password file (Section 8.2).

to:

In this case, the password field in /etc/passwd contains the letter x, and the encrypted password is instead stored in the shadow password file (Section 8.2).

2012-02-08

In Exercise 8-1, completely replace the text:

8-1. When we execute the following code, we find that it displays the same number twice, even though the two users have different IDs in the password file. Why is this?

    printf("%ld %ld\n", (long) (getpwnam("avr")->pw_uid),
                        (long) (getpwnam("tsr")->pw_uid));

with the following text:

8-1. When we execute the following code, which attempts to display the usernames for two different user IDs, we find that it displays the same username twice. Why is this?

    printf("%s %s\n", getpwuid(uid1)->pw_name,
                      getpwuid(uid2)->pw_name);

Explanation:

The exercise was intended to demonstrate the nonreentrant nature of getpwnam() (and related functions, such as getpwuid()), but the experiment I proposed to do so was wrong. (And unfortunately it looks as though I didn't test this exact example.) As René Thomsen pointed out, the code of the original exercise wouldn't yield the results described in the text "since after each argument a copy of the value in the passwd structure for pw_uid is passed, and since this a direct value (not a reference) there should be no trouble [with] the next call overwriting this value, since it still has the copy."

The revised exercise correctly shows the point I wanted to make. A complete program that can be used to demonstrate the point is shown below.

#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <pwd.h>

int
main(int argc, char *argv[])
{
    if (argc != 3 || strcmp(argv[1], "--help") == 0) {
        fprintf(stderr, "Usage: %s uid1 uid2\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    printf("%s %s\n", getpwuid(atoi(argv[1]))->pw_name,
                      getpwuid(atoi(argv[2]))->pw_name);

    exit(EXIT_SUCCESS);
}

Reported by René Thomsen.

2011-07-14

About two thirds of the way down the page, change:

Alternatively, an application can make a call to getgroups() specifying gidtsetsize as 0.

to:

Alternatively, an application can make a call to getgroups() specifying gidsetsize as 0.

Reported by Simon Durrant.

2011-08-12

In the fifth line from the top of the page, change:

IDs by scanning /etc/groups

to:

IDs by scanning /etc/group

Reported by Yang Yang.

2011-11-30

At the end of the last paragraph on this page, add a sentence:

This argument is now obsolete and should always be specified as NULL. (SUSv4 marks gettimeofday() obsolete, presumably in favor of the POSIX clocks API described in Section 23.5.)

Explanation:

The fact that SUSv4 marks gettimeofday() obsolescent was noted in page 16, but it should also be mentioned here.

2011-08-12

At the end of the page, add a small-font note as follows:

SUSv4 marks ctime() and asctime() obsolete, because they do not return localized strings (and they are nonreentrant).

Explanation:

This point was noted on page 16, but it bears repeating here, where these functions are described in detail.

2011-08-12

Starting in the sixth line of the small-font note about one third of the way down the page, change:

which is the per-user limit on the number of processes that may created by this process

to:

which is the per-user limit on the number of processes that may be created by this process

Reported by Yongzhi Pan.

2011-09-20

In the fifth line from the top of the page, change:

synchronized I/O data completion

to:

synchronized I/O data integrity completion

Reported by Junjiro Okajima.

2012-01-16

Two changes in the third paragraph.

In the fourth line, change:

synchronized I/O data integrity (i.e., prior to performing the read…

to:

synchronized I/O data integrity completion (i.e., prior to performing the read…

In the seventh and eighth lines, change:

synchronized I/O file integrity (i.e., prior to performing the read…

to:

synchronized I/O file integrity completion (i.e., prior to performing the read…

Reported by Junjiro Okajima.

2012-01-16

In the last sentence of the paragraph explaining POSIX_FADV_SEQUENTIAL, change:

to the twice the default size

to:

to twice the default size

Reported by Simon Durrant.

2011-08-23

In the second bullet point half-way down the page, change:

Examples of block devices include disks and tape drives.

to:

Disks are a common example of block devices.

Explanation:

Tapes are normally character devices.

Reported by Junjiro Okajima.

2012-01-16

In the "Key" box in the upper right hand corner of Figure 14-2, change:

2IPB = Double IBP

to:

2IPB = Double IPB

Reported by Yongzhi Pan.

2011-09-20

In the paragraph near the top of the page describing MS_BIND, change:

If this flag is specified, then the fstype, mountflags, and data arguments are ignored.

to:

If this flag is specified, then the fstype and data arguments are ignored, as are flags in mountflags other than MS_REC (described below).

2011-04-02

In the paragraph in the middle of the page describing MS_MOVE, change the last sentence:

When this flag is specified, the fstype, mountflags, and data arguments are ignored.

to:

When this flag is specified, the fstype and data arguments are ignored, as are the remaining flags in mountflags.

Reported by Sangman Lee.

2011-04-02

In the sentence immediately preceding Section 14.9.5, change:

we can simply create bind mounts for these directories (possibly mounted read-only) within the jail

to:

we can simply create bind mounts for these directories within the jail

Explanation:

It isn't possible to make read-only bind mounts to read-write directories. As noted on page 265, mountflags other than MS_REC are ignored when MS_BIND is specified.

Reported by Junjiro Okajima.

2012-01-16

In the third line from the bottom of the page, change:

(x000001, x000001, x0000002, and so on)

to:

(x000000, x000001, x0000002, and so on)

Reported by Junjiro Okajima.

2012-01-16

In the third line of the small-font note at the bottom of the page, change:

None of other fields

to:

None of the other fields

Reported by Simon Durrant.

2011-08-23

At the end of the small-font note at the bottom of the page (after the sentence beginning "On Linux, lstat() returns…"), add the following sentence:

SUSv4 tightens the requirements on an implementation, requiring lstat() to return valid information in all fields of the stat structure except the permission bits of st_mode.

2011-09-30

In Table 15-2, in the entry for truncate(), change:

Same for ftruncate(); timestamps change only if file size changes

to:

Same for ftruncate()

Explanation:

The original text did not completely match Linux behavior, but the story here is complicated. On Linux, ftruncate() always changes the file timestamps, even if the file size is not changed. However, Linux truncate() only changes the timestamps if the file size changes. This more or less mirrors the specifications in SUSv3. SUSv3 makes no mention of file size changes when specifying that ftruncate() changes the file timestamps. By contrast, SUSv3 says for truncate() that if the file size is changed, the file timestamps are updated, implying that if the file size is unchanged, the timestamps should not be changed. A planned fix to SUSv4 would require that truncate() behave like ftruncate().

2012-02-14

In the sentence immediately preceding heading 15.2.1, change:

can be accessed using field names such st_atim.tv_nsec

to:

can be accessed using field names such as st_atim.tv_nsec

Reported by Yongzhi Pan.

2011-09-20

In the prototype box for futimens() at the bottom of the page change:

#include _GNU_SOURCE

to:

#define _GNU_SOURCE

Reported by Junjiro Okajima.

2012-01-16

Add some words to the last sentence in the small-font note at the top of the page:

To ensure that we are using an unadulterated ls, we can specify the full pathname of the command (/bin/ls) or precede the ls command with a backslash to prevent alias substitution.

Reported by Junjiro Okajima.

2012-01-16

In the first line on the page, change:

The various FL_* flags and their meanings are as follows:

to:

The various FS_* flags and their meanings are as follows:

Reported by Douglas Luu.

2011-11-12

In the first sentence of the paragraph that precedes the bulleted list in Section 16.2, change:

It is only possible to place user EAs on files and directories.

to:

It is only possible to place user EAs on regular files and directories.

Explanation:

From the bulleted list, the reader can deduce that this sentence is referring to regular files, but it's better to make that explicit.

Reported by Junjiro Okajima.

2012-01-16

In the second paragraph under the heading Retrieving entries from an in-memory ACL, change the last sentence:

Thus, we can loop through all of the entries in an ACL by specifying type as ACL_FIRST_ENTRY in the first call to acl_get_entry() and specifying type as ACL_NEXT_ENTRY in subsequent calls.

to:

Thus, we can loop through all of the entries in an ACL by specifying entry_id as ACL_FIRST_ENTRY in the first call to acl_get_entry() and specifying entry_id as ACL_NEXT_ENTRY in subsequent calls.

Reported by Yongzhi Pan.

2011-09-20

In the first sentence of the small-font note near the top of the page, change:

The acl_check() and acl_error() functions (the latter is a Linux extension)

to:

The acl_check() and acl_error() functions (both are Linux extensions)

Reported by Junjiro Okajima.

2012-01-16

About one third of the way down the page, change:

        /* Retrieve and display optional tag qualifier */

        if (tag == ACL_USER) {
            uidp = acl_get_qualifier(entry);
            if (uidp == NULL)
                errExit("acl_get_qualifier");

            name = groupNameFromId(*uidp);

to:

        /* Retrieve and display optional tag qualifier */

        if (tag == ACL_USER) {
            uidp = acl_get_qualifier(entry);
            if (uidp == NULL)
                errExit("acl_get_qualifier");

            name = userNameFromId(*uidp);

Reported by René Thomsen.

2011-08-11

In the third line of the paragraph near the top of the page that starts "The cookie field…", change:

and then an IN_MOVED_TO is

to:

and then an IN_MOVED_TO event is

2011-12-08

Add a sentence at the end of the paragraph near the top of the page that starts "The cookie field…":

These two events will have the same unique value in their cookie field, thus allowing the application to associate them. For all other types of event, the cookie field is set to 0.

Explanation:

This point was made implicitly in the program in Listing 19-1 (where the displayInotifyEvent() function contains the check if (i->cookie > 0)), but should of course have been made explicit in the text.

Reported by Yang Yang.

2011-12-06

In the third paragraph from the bottom of the page (starting "Using a larger buffer size"), change:

A read() from an inotify file descriptor returns the minimum of the number of events that are available and the number of events that will fit in the supplied buffer.

to:

A read() from an inotify file descriptor reads the minimum of the number of events that are available and the number of events that will fit in the supplied buffer.

Explanation:

This change is made to prevent the possible misinterpretation that the return value of read() is the number of items read. As shown in Figure 19-2, a read() from an inotify file descriptor returns the number of bytes read (as with a read() from other types of file descriptors).

Reported by Junjiro Okajima.

2012-01-16

In the third line of the paragraph describing SIGLOST, change:

if the NSF client fails

to:

if the NFS client fails

Reported by Suse Shi.

2011-04-22

In the paragraph just above the heading for Section 20-7, change:

This program takes two command-line arguments, a signal number and a process ID,

to:

This program takes two command-line arguments, a process ID and a signal number,

Explanation:

This makes the order of the arguments given in the text match the order of the arguments for Listing 20-3.

2011-05-18

In Listing 20-3 (signals/t_kill.c), change:

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s sig-num pid\n", argv[0]);

to:

    if (argc != 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s pid sig-num\n", argv[0]);

Explanation:

See also the erratum on page 404.

Reported by Madhavan Kasthurirangan.

2011-05-18

In the first sentence below the prototype box for sigemptyset() and sigfillset(), change:

One of sigemptyset() or sigaddset() must be used to initialize a signal set.

to:

One of sigemptyset() or sigfillset() must be used to initialize a signal set.

Reported by Bill McConnaughey.

2011-07-18

In the last line of the prototype box at the top of the page, change:

Returns 1 if sig is empty, otherwise 0

to:

Returns 1 if set is empty, otherwise 0

Reported by Junjiro Okajima.

2012-01-16

In the first paragraph of Section 21.1.3, in the third line from end of the paragraph, change:

using the volatile attribute

to:

using the volatile keyword

Explanation:

Tightening up the terminology, so as to avoid possible confusion with the gcc attribute feature.

Reported by Yang Yang.

2011-12-09

In the second line of the last paragraph on this page, change:

that may be queued to a process

to:

that may be queued by a process

2011-12-12

Replace the first two paragraphs on this page:

On Linux, this call returns –1. The reason for this is that Linux employs a different model for limiting the number of realtime signals that may be queued to a process. In Linux versions up to and including 2.6.7, the kernel enforces a system-wide limit on the total number of realtime signals that may be queued to all processes. This limit can be viewed and (with privilege) changed via the Linux-specific /proc/sys/kernel/rtsig-max file. The default value in this file is 1024. The number of currently queued realtime signals can be found in the Linux-specific /proc/sys/kernel/rtsig-nr file.

Starting with Linux 2.6.8, this model was changed, and the aforementioned /proc interfaces were removed. Under the new model, the RLIMIT_SIGPENDING soft resource limit defines a limit on the number of signals that can be queued to all processes owned by a particular real user ID. We describe this limit further in Section 36.3.

with:

In systems with glibc versions before 2.4, this call returns –1. Since glibc 2.4, the return value depends on the kernel version. Before Linux 2.6.8, the call returns the value in the Linux-specific /proc/sys/kernel/rtsig-max file. This file defines a system-wide limit on the number of realtime signals that may be queued to all processes. The default value is 1024, but a privileged process can change it. The Linux-specific /proc/sys/kernel/rtsig-nr file shows the number of currently queued realtime signals.

Starting with Linux 2.6.8, these /proc files disappear. In their place, the RLIMIT_SIGPENDING resource limit (Section 36.3) limits the number of signals that can be queued to all processes owned by a particular real user ID. Since glibc 2.10, the sysconf() call returns the RLIMIT_SIGPENDING limit. (The SigQ field of the Linux-specific /proc/PID/status file displays the number of realtime signals pending for a process.)

Explanation:

Once upon a time, sysconf(_SC_SIGQUEUE_MAX) always returned –1. Although the other points in the text relating to the /proc files and the RLIMIT_SIGPENDING limit were all correct, I missed the fact that the glibc behavior changed, and to best capture the implications of that fact required reworking the entire text.

Reported by Yang Yang.

2011-12-12

In the second paragraph from the top of the page, change the second sentence:

This program takes up to four arguments, of which the first three are mandatory: a signal number, a target process ID, and an integer value to accompany the realtime signal.

to:

This program takes up to four arguments, of which the first three are mandatory: a target process ID, a signal number, and an integer value to accompany the realtime signal.

Explanation:

This change makes the order of the text match the order of the arguments in the program in Listing 22-2.

Reported by Sangman Lee.

2011-04-02

At the end of Listing 22-3 (signals/catch_rtsigs.c), change:

    while (!allDone)                    /* Wait for incoming signals */
        pause();
}

to:

    while (!allDone)                    /* Wait for incoming signals */
        pause();

    printf("Caught %d signals\n", sigCnt);
    exit(EXIT_SUCCESS);
}

Explanation:

These lines were accidentally deleted from the published version of the program. Without them, the line of output "Caught 6 signals" will not appear in the shell session shown on page 462.

Reported by Yang Yang.

2011-12-12

At the top of the page, insert a small-font note as follows:

According to SUSv3, calling sigwaitinfo() without blocking the signals in set results in undefined behavior.

2011-12-08

In the definition of the struct signalfd_siginfo structure, change:

    int32_t ssi_fd;        /* File descriptor (SIGPOLL/SIGIO) */
    uint32_t ssi_tid;      /* Kernel timer ID (POSIX timers) */
    uint32_t ssi_band;     /* Band event (SIGPOLL/SIGIO) */
    uint32_t ssi_tid;      /* (Kernel-internal) timer ID (POSIX timers) */
    uint32_t ssi_overrun;  /* Overrun count (POSIX timers) */

to:

    int32_t ssi_fd;        /* File descriptor (SIGPOLL/SIGIO) */
    uint32_t ssi_tid;      /* (Kernel-internal) timer ID (POSIX timers) */
    uint32_t ssi_band;     /* Band event (SIGPOLL/SIGIO) */
    uint32_t ssi_overrun;  /* Overrun count (POSIX timers) */

Explanation:

The definition of the ssi_tid field was accidentally duplicated, with two different accompanying comments. The fix removes the duplicate while retaining the slightly more detailed comment.

Reported by Sangman Lee.

2011-05-12

In the prototype box at the bottom of the page, change:

int sigmask(sig);

to:

int sigmask(int sig);

Reported by Junjiro Okajima.

2012-01-16

In the third paragraph, change:

When the timer reaches 0, the corresponding signal is sent to the process, and then, if the interval (it_interval) is nonzero, the timer value (it_value) is reloaded, and counting down toward 0 recommences.

to:

When the timer reaches 0, the corresponding signal is sent to the process, and then, if the interval (it_interval) is nonzero, the timer value (it_value) is reloaded with the interval value, and counting down toward 0 recommences.

Explanation:

This change helps avoid reader misunderstanding by reiterating a point already made (in different words) at the foot of page 480.

Reported by Sangman Lee.

2011-04-02

In the fourth line from the top of the page, change:

non-async-signal-functions

to:

non-async-signal-safe functions

Reported by Kiju Kim.

2012-02-15

About two thirds of the way down the page, in the paragraph beginning "The time value", change the last sentence in the paragraph:

The clock_getres() system call returns a pointer to a timespec structure containing the resolution of the clock specified in clockid.

to:

The clock_getres() system call returns, via the argument res, a pointer to a timespec structure containing the resolution of the clock specified in clockid.

Explanation:

The reader could probably deduce this information from the declaration in the preceding prototype box, but this change removes any ambiguity about whether the information is returned as the function result or via the argument res.

Reported by Bill McConnaughey.

2011-08-12

In the definition of the sigevent structure in the middle of the page, change:

        pid_t      _tid;      /* ID of thread to be signaled /

to:

        pid_t      _tid;      /* ID of thread to be signaled */

Reported by Junjiro Okajima.

2012-01-16

Add a sentence under the description of SIGEV_THREAD_ID; change:

(With SIGEV_SIGNAL notification, a signal is queued to the process as a whole, and, if there are multiple threads in the process, the signal will be delivered to an arbitrarily selected thread in the process.)

to:

(With SIGEV_SIGNAL notification, a signal is queued to the process as a whole, and, if there are multiple threads in the process, the signal will be delivered to an arbitrarily selected thread in the process. See Section 33.2 for a discussion of the interaction of threads and signals.)

2011-07-19

In the second paragraph from the bottom of the page, change:

that it inherits during the during the fork().

to:

that it inherits during the fork().

Reported by Bill McConnaughey.

2011-07-18

In the last line of the first bullet point at the top of the page, change:

virtual memory page frames

to:

physical memory page frames

Reported by Madhavan Kasthurirangan.

2011-09-04

In Exercise 24-3, change:

at a given moment in time

to:

at a given point in the program

Explanation:

The revised wording is more precise.

Reported by Bill McConnaughey.

2011-07-18

In the first normal-size paragraph at the top of the page, change:

2,147,482,647

to:

2,147,483,647

Reported by Junjiro Okajima.

2012-01-16

In Listing 26-4 (procexec/make_zombie.c), change:

    default:    /* Parent */
        sleep(3);               /* Give child a chance to start and exit */
        snprintf(cmd, CMD_SIZE, "ps | grep %s", basename(argv[0]));
        cmd[CMD_SIZE - 1] = '\0';       /* Ensure string is null-terminated */
        system(cmd);            /* View zombie child */

to:

    default:    /* Parent */
        sleep(3);               /* Give child a chance to start and exit */
        snprintf(cmd, CMD_SIZE, "ps | grep %s", basename(argv[0]));
        system(cmd);            /* View zombie child */

Explanation:

While writing a few code examples, it looks like I forgot that snprintf() always terminates its argument, even when it completely fills the buffer. (This was probably me confusing with the behavior of strncpy(). See page 793 of the book.)

Reported by Madhavan Kasthurirangan.

2011-09-02

In the explanation of ETXTBSY, change:

The file referred to by pathname is open for writing by another process

to:

The file referred to by pathname is open for writing by one or more processes

Explanation:

The ETXTBSY error could of course occur if the caller of execve() has itself opened pathname for writing.

Reported by Junjiro Okajima.

2012-01-16

In the fifth line of the first paragraph of the small-font note on this page, change:

(which is given as an argument to the script,

to:

(which is given as an argument to the interpreter,

Reported by Junjiro Okajima.

2012-01-16

In the fourth line of the second paragraph of the small-font note on this page, change:

(and these are passed as separate words to the script)

to:

(and these are passed as separate words to the interpreter)

Reported by Junjiro Okajima.

2012-01-16

In the third of the bullet points at the top of the page, change:

If all system calls succeed, then system() returns the termination status of the child shell used to execute command. (The termination status of a shell is the termination status of the last command it executes.)

to:

If all system calls succeed, then system() returns the termination status of the child shell used to execute command. The termination status of a shell is the exit status of the last command it executes; if that command is killed by a signal, most shells exit with the value 128+n, where n is the signal number. (If the child shell is itself killed by a signal, the termination status is as described in Section 26.1.3.)

Explanation:

There are two clarifications here. The first of these reiterates a point made in a small-font note near the top of page 532: when a command is terminated by a signal, the shell indicates that fact with a status of 128 plus the signal number.

The second, more significant fix (regarding what happens if the child shell is killed by a signal) results from Yang Yang's report. Yang Yang noted that on his Ubuntu system, the output in the last few lines of the shell session is different from that shown in the book. In the book, the following output is shown near the end of the shell session:

    $ fg
    ./t_system
    system() returned: status=0x000f (0,15)
    child killed by signal 15 (Terminated)

By contrast, Yang Yang obtained output of the form:

    $ fg
    ./t_system
    system() returned: status=0x8f00 (143,0)
    child exited, status=143

The differing output is a consequence of differences in the shells executed by system() on the two systems. A small-font note at the bottom of page 583 notes that some shells, when executing a simple command with sh -c, directly execute the command, rather than forking a new child shell to execute the command. On shells that perform this optimization, when system() is asked to execute the sleep 100 command, only a single process is created as a consequence of the call:

    system()    [process calls system("sleep 100")]
        |
    fork()
      :  \
      :   exec("sh")                  [Child process execs a shell]
      :     |
      :   exec("sleep")               [Child shell directly execs "sleep"]
      :     |
      :   [killed by SIGTERM]
      :  /
     waitpid(..., &status, ...)       [Sees "Killed by signal 15"]

By contrast, some shells don't perform this optimization, and the call to system() creates two processes, yielding the scenario shown in Figure 27-2 on page 584:

    system()    [process calls system("sleep 100")]
        |
    fork()
      :  \
      :   exec("sh")                  [Child process execs a shell]
      :     |
      :   fork()                      [Shell creates a new child]
      :     : \
      :     :  exec("sleep")          [New child execs "sleep"]
      :     :    |
      :     :  [killed by SIGTERM]
      :     : /
      :   waitpid(..., &status, ...)  [Sees "Killed by signal 15"]
      :     |
      :   exit(128+15)
      :  /
    waitpid(..., &status, ...)        [Sees "Exited normally, with status 143"]

The output in the book corresponds to the first of the scenarios described above. The shell executed by system() is bash, which does perform the optimization. In this case, the process running sleep is the child shell created by system(), and when that process is killed the status reported back by system() is as for a process killed by a signal.

The output for Yang Yang's case corresponds to the second scenario. The shell executed by system() is one that does not perform the optimization (dash, the default shell used to execute scripts on Ubuntu since version 6.10). In this case, the process running sleep is a child of the child shell created by system(). When that process is killed by a signal, the child shell observes the termination, and itself terminates with a status of the form 128+signum, which is in turn returned to the caller of system().

Reported by Yang Yang.

2011-12-23

In the second bullet point on this page, at the end of the first sentence ("If CHILD_SIG is nonzero…"), add a circled "5" as a reference to the corresponding line in Listing 28-3.

Reported by Junjiro Okajima.

2012-01-16

Inside the prototype box for pthread_exit(), change:

include <pthread.h>

to:

#include <pthread.h>

Reported by Fabien Galand.

2011-07-13

Inside the prototype boxes for pthread_self() and pthread_equal() (i.e., two changes!), change:

include <pthread.h>

to:

#include <pthread.h>

Reported by Fabien Galand.

2011-07-13

Inside the prototype box for pthread_join(), change:

include <pthread.h>

to:

#include <pthread.h>

Reported by Fabien Galand.

2011-07-13

Near the top of Listing 30-1 (threads/thread_incr.c), change:

static int glob = 0;

static void *                   /* Loop 'arg' times incrementing 'glob' */
threadFunc(void *arg)

to:

static volatile int glob = 0;   /* "volatile" prevents compiler optimizations
                                   of arithmetic operations on 'glob' */
static void *                   /* Loop 'arg' times incrementing 'glob' */
threadFunc(void *arg)

Explanation:

Making glob volatile means that the program more easily produces the "incorrect" output described on pages 633 and 634, even in the face of compiler optimization. Yang Yang's email report summarized the issue well, so I will just reproduce a lightly edited version of his comments:

I think failing to declare "glob" as volatile makes the program less "incorrect", because in this case, the output is determined by both the kernel's CPU scheduling decisions (as described on page 634) and the compiler's optimization decisions.

I've compiled Listing 30-1 with –O[0123] (GCC 4.5.2):

1. –O2 and –O3 results in the same assembly code, which ably simplifies the entire loop to a single addition "glob += n". It's very hard to observe an incorrect output even with a huge n (overflow doesn't count), although the race condition does exist.
2. –O1 uses a register to save the intermediate sum in each iteration, and writes the result into "glob" only once when the loop ends. Thus the output will be either n (more likely with a big n) or 2*n (more likely with a small n, as the first output on page 633).
3. –O0 faithfully executes the load-increment-store routine (as if volatile were added), and its behavior matches both outputs on page 633.

With volatile, of course, the program's behavior will always be the same "incorrect" as in the text.

Because it is a common misunderstanding, it's perhaps worth pointing out that it is not generally necessary to employ the volatile qualifier on global variables in multithreaded programs. For further information on this point, see, for example, various Stack Overflow questions: When to use volatile with multi threading?, Should ALL global variables be volatile-qualified?, and Is 'volatile' needed in this multi-threaded C++ code?.

Reported by Yang Yang.

2011-12-25

In the sentence that immediately precedes Section 30.1.1, change:

In order to safely handle shared variables, all threads must cooperate in their use of a mutex, abiding by the locking rules it enforces.

to:

In order to safely handle shared variables, all threads must cooperate in their use of a mutex, abiding by its locking rules.

Explanation:

The use of the word "enforces" in the original text was a little confusing, suggesting a meaning that runs counter to the point that mutex locking is advisory.

Reported by Bill McConnaughey.

2011-07-18

In the second-to-last line on the page, remove the extra space between the words "early" and "futex".

Reported by Fabien Galand.

2011-11-26

In the seventh line of the second paragraph, change:

threads are designed to perform the exactly same task

to:

threads are designed to perform exactly the same task

Reported by Simon Durrant.

2011-09-26

This erratum makes changes on pages 649 and 650 to fix a single problem in Listing 30-4 (threads/thread_multijoin.c).

On page 649, in the second line from the bottom of the page, change:

    int idx = *((int *) arg);

to:

    int idx = (int) arg;

On page 650, about two thirds of the way down the page, change:

        s = pthread_create(&thread[idx].tid, NULL, threadFunc, &idx);

to:

        s = pthread_create(&thread[idx].tid, NULL, threadFunc, (void *) idx);

Explanation:

There was a race condition in the program. In the main program, the value &idx was passed as the final argument of the call to pthread_create(), which is located within a for loop indexed on idx. In the new thread, the passed pointer value was dereferenced to obtain the value for the local variable idx used within the thread. However, this will only succeed if the new thread dereferences the pointer before the main thread increments idx inside the for loop.

The changes given in the erratum correct the problem, and should generally work on any platform, but, as noted toward the bottom of page 622, casting an int back and forth to a pointer type is not strictly standards-conformant. A standards-conformant solution would be to apply a patch to the original program something like the following:

@@ -16,19 +16,22 @@
     TS_JOINED                   /* Thread terminated, and joined */
 };

-static struct {                 /* Info about each thread */
+struct tinfo {                  /* Info about each thread */
     pthread_t tid;              /* ID of this thread */
     enum tstate state;          /* Thread state (TS_* constants above) */
     int sleepTime;              /* Number seconds to live before terminating */
-} *thread;
+};
+
+static struct tinfo *thread;

 static void *                   /* Start function for thread */
 threadFunc(void *arg)
 {
-    int idx = *((int *) arg);
+    struct tinfo *tptr = arg;
+    int idx = tptr - thread;    /* Obtain index in 'thread' array */
     int s;

-    sleep(thread[idx].sleepTime);       /* Simulate doing some work */
+    sleep(tptr->sleepTime);     /* Simulate doing some work */
     printf("Thread %d terminating\n", idx);

     s = pthread_mutex_lock(&threadMutex);
@@ -36,7 +39,7 @@
         errExitEN(s, "pthread_mutex_lock");

     numUnjoined++;
-    thread[idx].state = TS_TERMINATED;
+    tptr->state = TS_TERMINATED;

     s = pthread_mutex_unlock(&threadMutex);
     if (s != 0)
@@ -65,7 +68,7 @@
     for (idx = 0; idx < argc - 1; idx++) {
         thread[idx].sleepTime = getInt(argv[idx + 1], GN_NONNEG, NULL);
         thread[idx].state = TS_ALIVE;
-        s = pthread_create(&thread[idx].tid, NULL, threadFunc, &idx);
+        s = pthread_create(&thread[idx].tid, NULL, threadFunc, &thread[idx]);
         if (s != 0)
             errExitEN(s, "pthread_create");
     }

2012-10-15 follow-up: Ideally, instead of using int in the modified code, it would have been preferable to use uintptr_t:

    uintptr_t idx = (uintptr_t) arg;

The problem with using int is that the cast generates a compiler warning ("cast from pointer to integer of different size") when compiling on 64-bit systems. However, using uintptr_t would have required more substantial changes to the code: an adjustment to the format specifier used in the printf() call in threadFunc(), and a corresponding change to the declaration of idx in main(). But, there's not much point in trying to make a perfect solution here, since the correct fix is really something like the longer patch above.

Reported by Jacob Mandelson.

2011-04-02

In the second paragraph from the top of the page, change:

lock that mutex when the function is called, and unlock it when the mutex returns

to:

lock that mutex when the function is called, and unlock it when the function returns

Reported by Sun Jian.

2011-09-05

In the shell session toward the bottom of the page, change:

    $ ./t_pthread_cancel

to:

    $ ./thread_cancel

Reported by Yang Yang.

2011-12-28

In the last line of the prototype box for getsid() at the bottom of the page, change:

or (pid_t) –1 on error

to:

or –1 on error

Explanation:

Such a cast is not needed when the standards require the type to be a signed integer. SUSv3 and SUSv4 incorrectly documented a cast as being needed for getsid() and a few other functions. For some more details, see this Austin bug report.

2012-01-16

In the last line of the prototype box for setsid() at the top of the page, change:

or (pid_t) –1 on error

to:

or –1 on error

Explanation:

See the erratum for the getsid() prototype box on page 704.

2012-01-16

Change the last sentence on the page:

As a result, processes with low nice values receive less CPU than before, and processes with high nice values obtain a greater proportion of the CPU.

to:

As a result, processes with low priorities receive less CPU than before, and processes with high priorities obtain a greater proportion of the CPU.

Explanation:

This wording change is intended to prevent reader confusion over whether "low nice value" means a process that has a low priority (actually a high nice value) or processes whose nice value is a low number (meaning a high priority).

Reported by Bill McConnaughey.

2011-07-18

Change the third paragraph:

In Linux kernels before 2.6.12, an unprivileged process may use setpriority() only to (irreversibly) lower its own or another process's nice value. A privileged (CAP_SYS_NICE) process can use setpriority() to raise nice values.

to:

In Linux kernels before 2.6.12, an unprivileged process may use setpriority() only to (irreversibly) lower its own or another process's priority. A privileged (CAP_SYS_NICE) process can use setpriority() to raise priorities.

Explanation:

By rewording in terms of priorities, this wording change is intended to prevent reader confusion over whether lowering (raising) the nice value means adding a positive or negative number to the nice value. See also the erratum for page 734.

Reported by Junjiro Okajima.

2012-01-16

Change the initial sentences of the fourth paragraph:

Since kernel 2.6.12, Linux provides the RLIMIT_NICE resource limit, which permits unprivileged processes to increase nice values. An unprivileged process can raise its own nice value to the maximum specified by the formula 20 – rlim_cur, where rlim_cur is the current RLIMIT_NICE soft resource limit. As an example, if a process's RLIMIT_NICE soft limit is 25, then its nice value can be raised to –5.

to:

Since kernel 2.6.12, Linux provides the RLIMIT_NICE resource limit, which permits unprivileged processes to raise priorities. An unprivileged process can set its own nice value to the maximum specified by the formula 20 – rlim_cur, where rlim_cur is the current RLIMIT_NICE soft resource limit. As an example, if a process's RLIMIT_NICE soft limit is 25, then its nice value can be set to –5.

Explanation:

This wording change is intended to prevent reader confusion over whether lowering (raising) the nice value means adding a positive or negative number to the nice value. See also the erratum for page 734.

Reported by Junjiro Okajima.

2012-01-16

Change the last sentence of the second paragraph:

Thus, the lowest SCHED_RR priority would be specified as sched_get_priority_min(SCHED_FIFO), the next higher priority as sched_get_priority_min(SCHED_FIFO) + 1, and so on.

to:

Thus, the lowest SCHED_RR priority would be specified as sched_get_priority_min(SCHED_RR), the next higher priority as sched_get_priority_min(SCHED_RR) + 1, and so on.

Reported by Junjiro Okajima.

2012-01-16

In the code snippet near the top of the page, change:

    sched_setaffinity(pid, CPU_SETSIZE, &set);

to:

    sched_setaffinity(pid, sizeof(cpu_set_t), &set);

Explanation:

The setting of the second argument to sched_setaffinity() was correctly explained at the foot of page 749, and demonstrated in the example program, procpri/t_sched_setaffinity.c, provided in the source code distribution for the book, but unfortunately was shown incorrectly in this example. The fix above corrects the error. An alternative would have been to use the value CPU_SETSIZE / 8 as the second argument of the call.

Reported by Emmanuel Gras.

2011-10-14

In Listing 37-3 (daemons/daemon_SIGHUP.c), change:

static volatile sig_atomic_t hupReceived = 0;
                                    /* Set nonzero on receipt of SIGHUP */
 from
static void
sighupHandler(int sig)
{

to:

static volatile sig_atomic_t hupReceived = 0;
                                    /* Set nonzero on receipt of SIGHUP */

static void
sighupHandler(int sig)
{

Explanation:

This was a random piece of text that crept into the text during production; the problem didn't occur in the actual source code of the example program.

Reported by Simon Durrant.

2011-10-04

This change spans the code at the bottom of page 774 and top of page 775.

Change the lines:

        if (hupReceived) {              /* If we got SIGHUP... */
            logClose();
            logOpen(LOG_FILE);
            readConfigFile(CONFIG_FILE);
            hupReceived = 0;            /* Get ready for next SIGHUP */
        }

to:

        if (hupReceived) {              /* If we got SIGHUP... */
            hupReceived = 0;            /* Get ready for next SIGHUP */
            logClose();
            logOpen(LOG_FILE);
            readConfigFile(CONFIG_FILE);
        }

Explanation:

This fixes a race condition that occurs if two SIGHUP signals arrive in quick succession (i.e., there were two closely spaced attempts to reinitialize the daemon).

In the original ordering of the code, if the second SIGHUP signal was received just after (say) the call to readConfigFile(), then, because hupReceived is immediately reset to zero, the daemon would not be reinitialized a second time.

Reported by Yacine Belkadi.

2011-04-19

At the bottom of the page, after the small-font note beginning "Although syslog(2) and syslog(3) share the same name", add a further small-font paragraph:

Some modern implementations of syslogd, such as rsyslog and syslog-ng, dispense with the need for a separate klogd daemon by instead themselves reading directly from /proc/kmsg.

Reported by Przemysław Pawełczyk.

2011-06-12

In the second bullet point in Section 39.10, change:

Since Linux 2.6.24, file capabilities can be disabled if the kernel is built without the CONFIG_SECURITY_FILE_CAPABILITIES option.

to:

In Linux kernel versions 2.6.24 through to 2.6.32, file capabilities can be disabled if the kernel is built without the CONFIG_SECURITY_FILE_CAPABILITIES option.

2011-09-17

In the prototype box at the top of the page, change:

void updwtmpx(char *wtmpx_file, struct utmpx *ut);

to:

void updwtmpx(const char *wtmpx_file, const struct utmpx *ut);

Reported by Yang Yang.

2012-01-23

Change the first sentence under the heading Further information:

Various information related to static and shared libraries can be found in the ar(1), gcc(1), ld(1), ldconfig(8), ld.so(8), dlopen(3), and objdump(1) manual pages and in the info documentation for ld and readelf.

to:

Various information related to static and shared libraries can be found in the ar(1), gcc(1), ld(1), ldconfig(8), ld.so(8), dlopen(3), readelf(1), and objdump(1) manual pages and in the info documentation for ld.

Explanation:

The readelf documentation is available via info, but it's actually a manual page, and so is best listed as such here.

Reported by Yang Yang.

2012-01-27

In the fourth line from the bottom of the page, change:

The data exchanged via pipes, FIFOs, and datagram sockets

to:

The data exchanged via pipes, FIFOs, and stream sockets

Reported by Yang Yang.

2012-01-28

In the first bullet point at the top of the page, change:

The System V IPC facilities are connectionless. These facilities provide no notion of a handle (like a file descriptor) referring to an open IPC object. In later chapters, we'll sometimes talk of "opening" a System V IPC object, but this is really just shorthand to describe the process of obtaining a handle to refer to the object.

to:

The System V IPC facilities are connectionless. These facilities provide no notion of a handle (like a file descriptor) referring to an open IPC object. In later chapters, we'll sometimes talk of "opening" a System V IPC object, but this is really just shorthand to describe the process of obtaining an identifier that refers to the object.

Explanation:

The original text is a little confusing, since it talks of "obtaining a handle to refer to the object", whereas the preceding sentence says that there is "no notion … of a handle referring to an open IPC object". The reader can probably deduce the intended sense (that there is no notion of something like an open file handle) from the rest of the chapter, and the point is made quite clear in Section 45.1, but the wording here could be better.

Reported by Yang Yang.

2012-01-28

In Listing 44-5 (pipes/popen_glob.c), at the bottom of the page, change:

        /* Build and execute command to glob 'pat' */

        snprintf(popenCmd, PCMD_BUF_SIZE, POPEN_FMT, pat);
        popenCmd[PCMD_BUF_SIZE - 1] = '\0';     /* Ensure string is
                                                   null-terminated */
        fp = popen(popenCmd, "r");

to:

        /* Build and execute command to glob 'pat' */

        snprintf(popenCmd, PCMD_BUF_SIZE, POPEN_FMT, pat);

        fp = popen(popenCmd, "r");

Explanation:

See the erratum for page 555.

2011-09-02

About one third of the way down the page (three lines above the mkfifo() prototype box), change:

and ls –F appends an the pipe symbol (|) to the FIFO pathname.

to:

and ls –F appends a pipe symbol (|) to the FIFO pathname.

Reported by Fabien Galand.

2011-11-26

In the first line of the second bullet point at the top of the page, change:

If the FIFO is being opened FIFO for writing,

to:

If the FIFO is being opened for writing,

Reported by Yang Yang.

2012-02-02

In the shell session output at the top of the page, change:

$ ./svshm_create -p 102400
9633796
$ ./svshm_create -p 3276800
9666565
$ ./svshm_create -p 102400
1015817
$ ./svshm_create -p 3276800
1048586

to:

$ ./svshm_create -p 102400
9633796
$ ./svshm_create -p 3276800
9666565

Explanation:

By accident, two superfluous invocations of the svshm_create program were included in the shell session output. These superfluous invocations do no harm (the remainder of the shell session output is still correct), but they are unnecessary and thus confusing.

Reported by Fabien Galand.

2011-11-26

In the second paragraph of Section 49.10 (i.e., nearly two thirds of the way down the page), change:

when explaining why it usually preferable to specify

to:

when explaining why it is usually preferable to specify

Reported by Fabien Galand.

2011-11-26

In the code snippet about half way down the page, change:

remap_file_pages(addr, ps, 0, 2, 0);
                         /* Maps page 0 of file into page 2 of region */
remap_file_pages(addr + 2 * ps, ps, 0, 0, 0);
                         /* Maps page 2 of file into page 0 of region */

to:

remap_file_pages(addr, ps, 0, 2, 0);
                         /* Maps page 2 of file into page 0 of region */
remap_file_pages(addr + 2 * ps, ps, 0, 0, 0);
                         /* Maps page 0 of file into page 2 of region */

Reported by Madhavan Kasthurirangan.

2011-09-18

In the third line of the second-to-last paragraph (beginning "The munlock() system call…"), change:

in the same way as for munlock().

to:

in the same way as for mlock().

Reported by Simon Durrant.

2011-12-13

In the last line of the paragraph describing, SIGEV_NONE, change:

when a new messages arrives on an empty queue.

to:

when a new message arrives on an empty queue.

Reported by Bill McConnaughey.

2011-07-18

A bit more than half way down the page, change:

    $ ls -li /dev/sda7 | awk '$6 == "3," && $7 == 10'

to:

    $ ls -li /dev | awk '$6 == "3," && $7 == 7'

Explanation:

Initial report by Corentin Chary (2011-08-23). My initial errata improved after a note from Gerald Demitre (2012-01-14).

Reported by Corentin Chary and Gerald Demitre

2012-01-14

At the start of the third paragraph, change:

The src_addr and addrlen arguments

to:

The remaining arguments

Reported by Simon Durrant.

2011-12-13

In the second paragraph on this page, change:

The range of IANA registered ports is 1024 to 41951.

to:

The range of IANA registered ports is 1024 to 49151.

Explanation:

A typo…

Reported by Yang Firo.

2011-05-04

In the right-hand "TCP endpoint" box in Figure 58-8, the boxes labeled "send buffer" and "receive buffer" should be reversed, so that "receive buffer" is at the top and "send buffer" is at the bottom.

Reported by Yongzhi Pan.

2012-01-15

In the first line of the first paragraph, change:

The sin_family field is set to AF_INET6.

to:

The sin6_family field is set to AF_INET6.

Reported by Simon Durrant.

2012-01-02

At the end of the ninth line from the bottom of the page, change:

The in_addr field

to:

The ai_addr field

Reported by Simon Durrant.

2012-01-02

In Listing 59-9 (sockets/inet_sockets.c), near the end of the listing, change:

    if (getnameinfo(addr, addrlen, host, NI_MAXHOST,
                    service, NI_MAXSERV, NI_NUMERICSERV) == 0)
        snprintf(addrStr, addrStrLen, "(%s, %s)", host, service);
    else
        snprintf(addrStr, addrStrLen, "(?UNKNOWN?)");

    addrStr[addrStrLen - 1] = '\0';     /* Ensure result is null-terminated */
    return addrStr;

to:

    if (getnameinfo(addr, addrlen, host, NI_MAXHOST,
                    service, NI_MAXSERV, NI_NUMERICSERV) == 0)
        snprintf(addrStr, addrStrLen, "(%s, %s)", host, service);
    else
        snprintf(addrStr, addrStrLen, "(?UNKNOWN?)");

    return addrStr;

Explanation:

See the erratum for page 555.

2011-09-02

In the last line of the first paragraph in Section 59.14, change:

In the case,

to:

In this case,

Reported by Simon Durrant.

2012-01-02

In the small-font note near the bottom of the page, change:

Performance benefits could also be obtained if sendfile() could be used to transfer bytes between two regular files. On Linux 2.4 and earlier, out_fd could refer to a regular file. Some reworking of the underlying implementation meant that this possibility disappeared in the 2.6 kernel. However, this feature may be reinstated in a future kernel version

to:

Performance benefits could also be obtained if sendfile() could be used to transfer bytes between two regular files. On Linux 2.4 and earlier, out_fd could refer to a regular file. Some reworking of the underlying implementation meant that this possibility disappeared in the 2.6 kernel. Some later changes restored this feature in Linux 2.6.33.

2011-09-11

In the first sentence after the poll() prototype box, change:

The fds argument and the pollfd array (nfds) specify the file descriptors that poll() is to monitor.

to:

The pollfd array (fds) and the nfds argument specify the file descriptors that poll() is to monitor.

Reported by Simon Durrant.

2012-01-02

Just over half way down the page, change:

        if (gotSigio) {                 /* Is input available? */

            /* Read all available input until error (probably EAGAIN)
               or EOF (not actually possible in cbreak mode) or a
               hash (#) character is read */

            while (read(STDIN_FILENO, &ch, 1) > 0 && !done) {
                printf("cnt=%d; read %c\n", cnt, ch);
                done = ch == '#';
            }
 
            gotSigio = 0;
        }

to:

        if (gotSigio) {                 /* Is input available? */
            gotSigio = 0;

            /* Read all available input until error (probably EAGAIN)
               or EOF (not actually possible in cbreak mode) or a
               hash (#) character is read */

            while (read(STDIN_FILENO, &ch, 1) > 0 && !done) {
                printf("cnt=%d; read %c\n", cnt, ch);
                done = ch == '#';
            }
        }

Explanation:

This fixes a race condition that occurs if two SIGIO signals arrive in quick succession.

The race condition in the original code is as follows. Suppose that some input has been supplied to the program, a SIGIO signal has been generated, and we have just returned from the signal handler and have entered the block of code shown in the erratum. If further input arrived and a second SIGIO signal was received just after the while loop terminated, then, because gotSigio is immediately reset to zero, the program would not read the new input (until the delivery of a further SIGIO signal).

Reported by Yacine Belkadi.

2011-04-19

In the fourth line from the top of the page, change:

The F_GETOWN_EX operation is the converse of the F_GETOWN_EX operation.

to:

The F_GETOWN_EX operation is the converse of the F_SETOWN_EX operation.

Reported by Bill McConnaughey.

2011-07-18

In the shell session in the middle of this page, change:

$ fg
./epoll_input p q
About to epoll_wait()
Ready: 2
  fd=4; events: EPOLLIN
    read 4 bytes: ppp

  fd=5; events: EPOLLIN EPOLLHUP
    read 4 bytes: qqq

    closing fd 5
About to epoll_wait()

to:

$ fg
./epoll_input p q
About to epoll_wait()
Ready: 2
  fd=4; events: EPOLLIN
    read 4 bytes: ppp

  fd=5; events: EPOLLIN EPOLLHUP
    read 4 bytes: qqq

About to epoll_wait()
Ready: 1
  fd=5; events: EPOLLHUP
    closing fd 5
About to epoll_wait()

Explanation:

The shell output originally shown was produced by an earlier version of the program that contained a small bug. The bug was fixed, but I overlooked to refresh the shell session demonstrating the use of the program.

Reported by Pedro Dominguez.

2011-04-28

Change the second-to-last paragraph on the page:

The two blank lines in the above output are the newlines that were read by the instances of cat, written to the FIFOs, and then read and echoed by our monitoring program.

to:

The two blank lines in the above output are the newlines that were read by the instances of cat, written to the FIFOs, and then read and echoed by our program.

Explanation:

This isn't an error fix at all. The change (which shortens the paragraph by one line) was made solely to create enough vertical space on the page to accommodate the previous change (which added three lines to the page).

2011-04-28

In the code snippet a bit more than half way down the page, change:

    if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd, ev) == -1)

to:

    if (epoll_ctl(epfd, EPOLL_CTL_ADD, fd, &ev) == -1)

Reported by tjuer.

2011-12-16

At the end of the last paragraph on this page, add a sentence:

This file can be viewed using zcat(1) and searched using zgrep(1). The /proc/config.gz file is itself only available if the kernel was configured with the CONFIG_IKCONFIG and CONFIG_IKCONFIG_PROC configuration options enabled.

Explanation:

In print run 7, a fix was made to remedy a minor error that occurred when applying this erratum: /proc/config.z was changed to /proc/config.gz.

Reported by Bill McConnaughey.

2011-07-18

In the solution for Exercise 8-1, change:

8-1. The two getpwnam() calls are executed before the printf() output string is constructed, and—since getpwnam() returns its result in a statically allocated buffer—the second call overwrites the result returned by the first call.

to:

8-1. The two getpwuid() calls are executed before the printf() output string is constructed, and—since getpwuid() returns its pw_name result in a statically allocated buffer—the second call overwrites the result returned by the first call.

Explanation:

See the erratum for Exercise 8-1 on page 166.

Reported by René Thomsen.

2011-07-14

Under the bibliography entry for "Gont, F. 2008", change the URL:

http://www.cpni.gov.uk/Docs/InternetProtocol.pdf

to:

http://www.gont.com.ar/papers/InternetProtocol.pdf

Reported by Kiju Kim.

2012-01-20

Under the bibliography entry for "Gont, F. 2009 (a)", change the URL:

http://www.cpni.gov.uk/Docs/tn-03-09-security-assessment-TCP.pdf

to:

http://www.gont.com.ar/papers/tn-03-09-security-assessment-TCP.pdf

Reported by Kiju Kim.

2012-01-20

Under the bibliography entry for "Hallyn, S. 2007", change the URL:

http://www.ibm.com/developerworks/library/l-posixcap.html

to:

http://www.ibm.com/developerworks/library/l-posixcap/index.html

Reported by Kiju Kim.

2012-01-20

In the small-font note under the bibliography entry for "Josey, A. (ed.). 2004", change:

A newer version of this guide (published in 2010) for version 4 of the specification can be ordered online at http://www.opengroup.org/bookstore/catalog/.

to:

A newer version of this guide (published in 2010) for version 4 of the specification can be found at http://www.unix.org/version4/theguide.html.

Reported by Kiju Kim.

2012-01-20

Under the bibliography entry for "Kent, A., and Mogul, J.C. 1987", change the URL:

http://www.acm.org/sigcomm/ccr/archive/1995/jan95/ccr-9501-mogulf1.pdf

to:

http://ccr.sigcomm.org/archive/1995/jan95/ccr-9501-mogulf1.html

Reported by Kiju Kim.

2012-01-20

Under the bibliography entry for "Lu, H.J. 1995" replace the URL:

http://www.trunix.org/programlama/os/elf-hl/Documentation/elf/elf.html

to:

This paper can be found online at a variety of locations.

Explanation:

There is currently a version at https://www.linux.co.cr/free-unix-os/review/acrobat/950517.pdf, but I'm not sure how stable that location is.

Reported by Kiju Kim.

2012-01-20

Under the bibliography entry for "Stone, J., and Partridge, C. 2000", change the URL:

http://www.acm.org/sigcomm/sigcomm2000/conf/abstract/9-1.htm

to:

http://dl.acm.org/citation.cfm?doid=347059.347561

Reported by Kiju Kim.

2012-01-20

Change the index entry:

International Standards Organization (ISO), 11

to:

International Organization for Standardization (ISO), 11

Explanation:

See the erratum for page 11.

2011-08-04

Change the index entry:

ISO (International Standards Organization), 11

to:

ISO (International Organization for Standardization), 11

Explanation:

See the erratum for page 11.

2011-08-04