SD_EVENT_ADD_INOTIFY(3)

📦

version 261.3 · 12 versions

okay bestie, welcome to the SD_EVENT_ADD_INOTIFY(3) manual page — manual name folded in at the top like a little name tag, exactly as requested. This is the systemd page for adding an "inotify" file system inode event source to an event loop, and we are keeping every single fact because the vibes are cute but the details are sacred. 💖✨

🌸 NAME 🌸

sd_event_add_inotify, sd_event_add_inotify_fd, sd_event_source_get_inotify_mask, sd_event_source_get_inotify_path, sd_event_inotify_handler_t — add an "inotify" file system inode event source to an event loop. That's the whole assignment, bestie. 🎀

✨ SYNOPSIS ✨

#include <systemd/sd-event.h>

typedef struct sd_event_source sd_event_source;

typedef int (*sd_event_inotify_handler_t)(sd_event_source *s,
                                          const struct inotify_event *event,
                                          void *userdata);

int sd_event_add_inotify(sd_event *event, sd_event_source **source,
                         const char *path, uint32_t mask,
                         sd_event_inotify_handler_t handler,
                         void *userdata);

int sd_event_add_inotify_fd(sd_event *event, sd_event_source **source,
                            int fd, uint32_t mask,
                            sd_event_inotify_handler_t handler,
                            void *userdata);

int sd_event_source_get_inotify_mask(sd_event_source *source,
                                     uint32_t *ret);

int sd_event_source_get_inotify_path(sd_event_source *source,
                                     const char **ret);

🦋 DESCRIPTION 🦋

sd_event_add_inotify() adds a brand-new inotify(7) file system inode event source to an event loop. The event loop object goes in the event parameter, and the event source object comes back out through source. The path parameter is the path of the file system inode you want to watch. The mask parameter says which types of inode events you actually care about — it must contain an OR-ed combination of IN_ACCESS, IN_ATTRIB, IN_CLOSE_WRITE, ... flags. For the full tea, go read inotify(7). 🔍💅

The handler must reference a function to call when the inode changes, or it can be NULL. That handler function gets the userdata pointer, which the caller may choose freely. It also receives a pointer to a struct inotify_event structure containing the deets about the inode event. The handler may return negative to signal an error (see below); other return values are ignored. If handler is NULL, a default handler that calls sd_event_exit(3) will be used. 🚪✨

sd_event_add_inotify_fd() is identical to sd_event_add_inotify(), except that it takes a file descriptor to an inode (possibly an O_PATH one, but any other will do too) instead of a path in the file system. 🦋

If multiple event sources are installed for the same inode, the backing inotify watch descriptor is automatically shared — besties sharing a watch, iconic. The mask parameter may contain any flag defined by the inotify API, with the exception of IN_MASK_ADD. 🚫

The handler is enabled continuously (SD_EVENT_ON), but this may be changed with sd_event_source_set_enabled(3). Alternatively, the IN_ONESHOT mask flag may be used to request SD_EVENT_ONESHOT mode. If the handler function returns a negative error code, it will be disabled after the invocation, even if the SD_EVENT_ON mode was requested before. 😭

As a special limitation, the priority of inotify event sources may only be altered (see sd_event_source_set_priority(3)) in the time between creation of the event source object with sd_event_add_inotify() and the beginning of the next event loop iteration. Attempts of changing the priority any later will be refused. Consider freeing and allocating a new inotify event source to change the priority at that point. 💀

To destroy an event source object, use sd_event_source_unref(3), but note that the event source is only removed from the event loop when all references to the event source are dropped. To make sure an event source does not fire anymore, even when there's still a reference to it kept, consider disabling it with sd_event_source_set_enabled(3). 🫶

If the second parameter of sd_event_add_inotify() is passed as NULL, no reference to the event source object is returned. In this case, the event source is considered "floating", and will be destroyed implicitly when the event loop itself is destroyed. 🎈

If the handler parameter to sd_event_add_inotify() is NULL, and the event source fires, this will be considered a request to exit the event loop. In this case, the userdata parameter, cast to an integer, is passed as the exit code parameter to sd_event_exit(3). 🚪

sd_event_source_get_inotify_mask() retrieves the configured inotify watch mask of an event source created previously with sd_event_add_inotify(). It takes the event source object as the source parameter and a pointer to a uint32_t variable to return the mask in. 🔍

sd_event_source_get_inotify_path() retrieves the target path of the configured inotify watch of an event source created previously with sd_event_add_inotify(). It takes the event source object as the source parameter and a pointer to a const char ** variable to return the path in. The caller must not free the returned path. 🙅✨

💖 RETURN VALUE 💖

On success, these functions return 0 or a positive integer. On failure, they return a negative errno-style error code. ✅

🫶 Errors 🫶

Returned errors may indicate the following problems:

-ENOMEM — Not enough memory to allocate an object. 😭
-EINVAL — An invalid argument has been passed. This includes specifying a mask with IN_MASK_ADD set. 🚫
-ESTALE — Returned by sd_event_source_add_inotify() or sd_event_source_add_inotify_fd() when the event loop is already terminated. Returned by sd_event_source_get_inotify_path() when no active inode data is assigned to the event source, e.g. when the event source is disabled. 💀
-ECHILD — The event loop has been created in a different process, library or module instance. 👀
-EDOM — The passed event source is not an inotify process event source. 🙈
-EBADF — The passed file descriptor is not valid. 🚫
-ENOSYS — sd_event_add_inotify_fd() or sd_event_source_get_inotify_path() was called without /proc/ mounted. 😵

🌈 EXAMPLES 🌈

🧚 Example 1. A simple program that uses inotify to monitor one or two directories

/* SPDX-License-Identifier: MIT-0 */

#include <stdio.h>
#include <string.h>
#include <sys/inotify.h>

#include <systemd/sd-event.h>

#define _cleanup_(f) __attribute__((cleanup(f)))

static int inotify_handler(sd_event_source *source,
                           const struct inotify_event *event,
                           void *userdata) {

  const char *desc = NULL;

  sd_event_source_get_description(source, &desc);

  if (event->mask & IN_Q_OVERFLOW)
    printf("inotify-handler <%s>: overflow\n", desc);
  else if (event->mask & IN_CREATE)
    printf("inotify-handler <%s>: create on %s\n", desc, event->name);
  else if (event->mask & IN_DELETE)
    printf("inotify-handler <%s>: delete on %s\n", desc, event->name);
  else if (event->mask & IN_MOVED_TO)
    printf("inotify-handler <%s>: moved-to on %s\n", desc, event->name);

  /* Terminate the program if an "exit" file appears */
  if ((event->mask & (IN_CREATE|IN_MOVED_TO)) &&
      strcmp(event->name, "exit") == 0)
    sd_event_exit(sd_event_source_get_event(source), 0);

  return 1;
}

int main(int argc, char **argv) {
  _cleanup_(sd_event_unrefp) sd_event *event = NULL;
  _cleanup_(sd_event_source_unrefp) sd_event_source *source1 = NULL, *source2 = NULL;

  const char *path1 = argc > 1 ? argv[1] : "/tmp";
  const char *path2 = argc > 2 ? argv[2] : NULL;

  /* Note: failure handling is omitted for brevity */

  sd_event_default(&event);

  sd_event_add_inotify(event, &source1, path1,
                       IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
                       inotify_handler, NULL);
  if (path2)
    sd_event_add_inotify(event, &source2, path2,
                         IN_CREATE | IN_DELETE | IN_MODIFY | IN_MOVED_TO,
                         inotify_handler, NULL);

  sd_event_loop(event);

  return 0;
}

🧚 NOTES 🧚

Functions described here are available as a shared library, which can be compiled against and linked to with the libsystemd pkg-config(1) file. 🎀

All functions listed here are thread-agnostic and only a single thread may operate on a given object at any given time. Different threads may access the same object at different times. Multiple independent objects may be used from different threads in parallel. 🧵

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started. ⚠️

🎀 HISTORY 🎀

sd_event_inotify_handler_t(), sd_event_add_inotify(), and sd_event_source_get_inotify_mask() were added in version 239. 💖
sd_event_add_inotify_fd() was added in version 250. 💖
sd_event_source_get_inotify_path() was added in version 256. 💖

that's the whole page, bestie — from systemd 261.3, and the footer's date is not listed, so we're not inventing one. no cap. 💖🔥💅

📦 where this page comes from

ubuntu stonking: libsystemd-dev 261.3-0ubuntu3 · LGPL-2.1-or-later
💖 girlified by deepseek-ai/DeepSeek-V4.1-Flash-1017 on 2026-11-06: a language model's rewrite of the original, under its terms