sd_event_add_inotify(3) — Linux manual page


SD_EVENT_ADD_INOTIFY(3)   sd_event_add_inotify   SD_EVENT_ADD_INOTIFY(3)

NAME         top

       sd_event_add_inotify, sd_event_add_inotify_fd,
       sd_event_source_get_inotify_mask, sd_event_inotify_handler_t -
       Add an "inotify" file system inode event source to an event loop

SYNOPSIS         top

       #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 *mask);

DESCRIPTION         top

       sd_event_add_inotify() adds a new inotify(7) file system inode
       event source to an event loop. The event loop object is specified
       in the event parameter, the event source object is returned in
       the source parameter. The path parameter specifies the path of
       the file system inode to watch. The mask parameter specifies
       which types of inode events to watch specifically. It must
       contain an OR-ed combination of IN_ACCESS, IN_ATTRIB,
       IN_CLOSE_WRITE, ... flags. See inotify(7) for further

       The handler must reference a function to call when the inode
       changes or NULL. The handler function will be passed the userdata
       pointer, which may be chosen freely by the caller. The handler
       also receives a pointer to a struct inotify_event structure
       containing information 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. 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

       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_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.

RETURN VALUE         top

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

       Returned errors may indicate the following problems:

           Not enough memory to allocate an object.

           An invalid argument has been passed. This includes specifying
           a mask with IN_MASK_ADD set.

           The event loop is already terminated.

           The event loop has been created in a different process,
           library or module instance.

           The passed event source is not an inotify process event

           The passed file descriptor is not valid.

           Added in version 250.

           sd_event_add_inotify_fd() was called without /proc/ mounted.

           Added in version 250.

EXAMPLES         top

       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_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);


             return 0;

NOTES         top

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

       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

HISTORY         top

       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.

SEE ALSO         top

       systemd(1), sd-event(3), sd_event_new(3), sd_event_now(3),
       sd_event_add_io(3), sd_event_add_time(3), sd_event_add_signal(3),
       sd_event_add_defer(3), sd_event_add_child(3),
       sd_event_source_set_enabled(3), sd_event_source_set_priority(3),
       sd_event_source_set_floating(3), waitid(2)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

systemd 255                                      SD_EVENT_ADD_INOTIFY(3)

Pages that refer to this page: sd-event(3)sd_event_add_child(3)sd_event_add_defer(3)sd_event_add_io(3)sd_event_add_memory_pressure(3)sd_event_add_signal(3)sd_event_add_time(3)sd_event_exit(3)sd_event_new(3)sd_event_run(3)sd_event_set_watchdog(3)sd_event_source_get_event(3)sd_event_source_get_pending(3)sd_event_source_set_description(3)sd_event_source_set_destroy_callback(3)sd_event_source_set_enabled(3)sd_event_source_set_exit_on_failure(3)sd_event_source_set_floating(3)sd_event_source_set_prepare(3)sd_event_source_set_priority(3)sd_event_source_set_ratelimit(3)sd_event_source_set_userdata(3)sd_event_source_unref(3)sd_event_wait(3)systemd.directives(7)systemd.index(7)