This is inotify/demo_inotify.c (Listing 19-1, page 382), 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.

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/* demo_inotify.c

   Demonstrate the use of the inotify API.

   Usage: demo_inotify pathname...

   The program monitors each of the files specified on the command line for all
   possible file events.

   This program is Linux-specific. The inotify API is available in Linux 2.6.13
   and later.
#include <sys/inotify.h>
#include <limits.h>
#include "tlpi_hdr.h"
static void             /* Display information from inotify_event structure */
displayInotifyEvent(struct inotify_event *i)
    printf("    wd =%2d; ", i->wd);
    if (i->cookie > 0)
        printf("cookie =%4d; ", i->cookie);

    printf("mask = ");
    if (i->mask & IN_ACCESS)        printf("IN_ACCESS ");
    if (i->mask & IN_ATTRIB)        printf("IN_ATTRIB ");
    if (i->mask & IN_CLOSE_NOWRITE) printf("IN_CLOSE_NOWRITE ");
    if (i->mask & IN_CLOSE_WRITE)   printf("IN_CLOSE_WRITE ");
    if (i->mask & IN_CREATE)        printf("IN_CREATE ");
    if (i->mask & IN_DELETE)        printf("IN_DELETE ");
    if (i->mask & IN_DELETE_SELF)   printf("IN_DELETE_SELF ");
    if (i->mask & IN_IGNORED)       printf("IN_IGNORED ");
    if (i->mask & IN_ISDIR)         printf("IN_ISDIR ");
    if (i->mask & IN_MODIFY)        printf("IN_MODIFY ");
    if (i->mask & IN_MOVE_SELF)     printf("IN_MOVE_SELF ");
    if (i->mask & IN_MOVED_FROM)    printf("IN_MOVED_FROM ");
    if (i->mask & IN_MOVED_TO)      printf("IN_MOVED_TO ");
    if (i->mask & IN_OPEN)          printf("IN_OPEN ");
    if (i->mask & IN_Q_OVERFLOW)    printf("IN_Q_OVERFLOW ");
    if (i->mask & IN_UNMOUNT)       printf("IN_UNMOUNT ");

    if (i->len > 0)
        printf("        name = %s\n", i->name);

#define BUF_LEN (10 * (sizeof(struct inotify_event) + NAME_MAX + 1))
main(int argc, char *argv[])
    int inotifyFd, wd, j;
    char buf[BUF_LEN] __attribute__ ((aligned(8)));
    ssize_t numRead;
    char *p;
    struct inotify_event *event;

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

    inotifyFd = inotify_init();                 /* Create inotify instance */
    if (inotifyFd == -1)

    /* For each command-line argument, add a watch for all events */

    for (j = 1; j < argc; j++) {
        wd = inotify_add_watch(inotifyFd, argv[j], IN_ALL_EVENTS);
        if (wd == -1)

        printf("Watching %s using wd %d\n", argv[j], wd);

    for (;;) {                                  /* Read events forever */
        numRead = read(inotifyFd, buf, BUF_LEN);
        if (numRead == 0)
            fatal("read() from inotify fd returned 0!");

        if (numRead == -1)

        printf("Read %ld bytes from inotify fd\n", (long) numRead);

        /* Process all of the events in buffer returned by read() */

        for (p = buf; p < buf + numRead; ) {
            event = (struct inotify_event *) p;

            p += sizeof(struct inotify_event) + event->len;



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