inotify_add_watch 失败，没有这样的文件或目录

Question

I am trying to watch for the creation of file in my c/c++ program. I am trying to use inotify for this purpose. However, I am getting a no such file or directory when I make the inotify_add_watch() call in my code. I am running my program on an Ubuntu 16.04 machine. The machine is running in the EC2 cloud. Can someone tell me the possible reasons for receiving a no such file or directory error ?

According to the man page for inotify_add_watch , that's not even one of the possible error codes. I've made to sure I have proper read permissions for the file I am trying to monitor etc.

Here's my test program:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/inotify.h>
#include <limits.h>

#define MAX_EVENTS  1024
#define LEN_NAME    16
#define EVENT_SIZE  (sizeof (struct inotify_event))
#define BUF_LEN     (MAX_EVENTS * (EVENT_SIZE + LEN_NAME))

int
main(int argc, char **argv)
{
  int length, i = 0, wd;
  int fd;
  char buffer[BUF_LEN];

  /* Initialize Inotify*/
  fd = inotify_init();
  if (fd < 0) {
    perror("Couldn't initialize inotify");
  }

  /* add watch to starting directory */
  wd = inotify_add_watch(fd, argv[1], IN_CREATE | IN_MODIFY | IN_DELETE);

  if (wd == -1) {
      printf("Couldn't add watch to %s. errno=%d\n", argv[1], errno);
      return -1;
  } else {
      printf("Watching:: %s\n",argv[1]);
  }

  /* do it forever*/
  while (1) {
    i = 0;
    length = read(fd, buffer, BUF_LEN);

    if (length < 0) {
      perror("read");
    }

    while (i < length) {
      struct inotify_event *event = (struct inotify_event *) &buffer[i];
      if (event->len) {
        if (event->mask & IN_CREATE) {
          printf("Create event. file=%s, wf=%d\n", event->name, event->wd);
        }

        if (event->mask & IN_MODIFY) {
          printf("Modify event. file=%s, wf=%d\n", event->name, event->wd);
        }

        if (event->mask & IN_DELETE) {
          printf("Delete event. file=%s, wf=%d\n", event->name, event->wd);
        }

        i += EVENT_SIZE + event->len;
      }
    }
  }

  /* Clean up*/
  inotify_rm_watch(fd, wd);
  close(fd);

  return 0;
}

Answer 1

If you want to monitor the creation of file/directory, you should watch the parent directory since the new file/directory does not exist when you calls inotify_add_watch() . Then when any file/directory is created in your watching directory, you will get a event, and the new file/direcotry name will be in event->name.