This is procexec/multi_wait.c (Listing 26-1, page 543), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.


Download procexec/multi_wait.c

  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* multi_wait.c

   Demonstrate the use of wait(2): create multiple children and then wait
   for them all.

   Usage: multi_wait sleep-time...

   One child process is created for each command-line argument. Each child
   sleeps for the number of seconds specified in the corresponding command-line
   argument before exiting. After all children have been created, the parent
   loops, waiting for terminated children, and displaying their PIDs.
#include <sys/wait.h>
#include <time.h>
#include "curr_time.h"              /* Declaration of currTime() */
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    int numDead;       /* Number of children so far waited for */
    pid_t childPid;    /* PID of waited for child */
    int j;

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s sleep-time...\n", argv[0]);

    setbuf(stdout, NULL);           /* Disable buffering of stdout */

    for (j = 1; j < argc; j++) {    /* Create one child for each argument */
        switch (fork()) {
        case -1:

        case 0:                     /* Child sleeps for a while then exits */
            printf("[%s] child %d started with PID %ld, sleeping %s "
                    "seconds\n", currTime("%T"), j, (long) getpid(),
            sleep(getInt(argv[j], GN_NONNEG, "sleep-time"));

        default:                    /* Parent just continues around loop */

    numDead = 0;
    for (;;) {                      /* Parent waits for each child to exit */
        childPid = wait(NULL);
        if (childPid == -1) {
            if (errno == ECHILD) {
                printf("No more children - bye!\n");
            } else {                /* Some other (unexpected) error */

        printf("[%s] wait() returned child PID %ld (numDead=%d)\n",
                currTime("%T"), (long) childPid, numDead);


Download procexec/multi_wait.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

Valid XHTML 1.1