FANOTIFY(7)                Linux Programmer's Manual               FANOTIFY(7)

       fanotify - monitoring filesystem events

       The  fanotify  API provides notification and interception of filesystem
       events.  Use cases include virus scanning and hierarchical storage man-
       agement.   Currently,  only  a  limited set of events is supported.  In
       particular, there is no support for create, delete,  and  move  events.
       (See inotify(7) for details of an API that does notify those events.)

       Additional  capabilities  compared  to  the  inotify(7) API include the
       ability to monitor all of the objects  in  a  mounted  filesystem,  the
       ability  to  make  access  permission decisions, and the possibility to
       read or modify files before access by other applications.

       The following system calls are used with  this  API:  fanotify_init(2),
       fanotify_mark(2), read(2), write(2), and close(2).

   fanotify_init(), fanotify_mark(), and notification groups
       The  fanotify_init(2)  system  call creates and initializes an fanotify
       notification group and returns a file descriptor referring to it.

       An fanotify notification group is a kernel-internal object that holds a
       list  of  files,  directories,  filesystems, and mount points for which
       events shall be created.

       For each entry in an fanotify notification group, two bit masks  exist:
       the  mark mask and the ignore mask.  The mark mask defines file activi-
       ties for which an event shall be created.  The ignore mask defines  ac-
       tivities for which no event shall be generated.  Having these two types
       of masks permits a filesystem, mount point, or directory to  be  marked
       for  receiving  events, while at the same time ignoring events for spe-
       cific objects under a mount point or directory.

       The fanotify_mark(2) system call adds a file, directory, filesystem  or
       mount point to a notification group and specifies which events shall be
       reported (or ignored), or removes or modifies such an entry.

       A possible usage of the ignore mask is for a file cache.  Events of in-
       terest  for  a file cache are modification of a file and closing of the
       same.  Hence, the cached directory or mount point is to  be  marked  to
       receive these events.  After receiving the first event informing that a
       file has been modified, the corresponding cache entry will  be  invali-
       dated.   No  further  modification events for this file are of interest
       until the file is closed.  Hence, the modify event can be added to  the
       ignore  mask.   Upon receiving the close event, the modify event can be
       removed from the ignore mask and the file cache entry can be updated.

       The entries in the fanotify notification groups refer to files and  di-
       rectories  via their inode number and to mounts via their mount ID.  If
       files or directories are renamed or moved within the  same  mount,  the
       respective  entries  survive.   If  files or directories are deleted or
       moved to another mount or if filesystems or mounts are  unmounted,  the
       corresponding entries are deleted.

   The event queue
       As  events  occur on the filesystem objects monitored by a notification
       group, the fanotify system generates events that  are  collected  in  a
       queue.   These  events can then be read (using read(2) or similar) from
       the fanotify file descriptor returned by fanotify_init(2).

       Two types of events are generated: notification events  and  permission
       events.   Notification events are merely informative and require no ac-
       tion to be taken by the receiving application with the exception  being
       that  the  file  descriptor  provided  within  a  generic event must be
       closed.  The closing of file descriptors for each event applies only to
       applications  that  have  initialized  fanotify  without  using FAN_RE-
       PORT_FID (see below).  Permission events are requests to the  receiving
       application  to  decide  whether  permission for a file access shall be
       granted.  For these events, the recipient must write a  response  which
       decides whether access is granted or not.

       An  event is removed from the event queue of the fanotify group when it
       has been read.  Permission events that have been read are  kept  in  an
       internal  list of the fanotify group until either a permission decision
       has been taken by writing to the fanotify file descriptor or  the  fan-
       otify file descriptor is closed.

   Reading fanotify events
       Calling  read(2)  for  the file descriptor returned by fanotify_init(2)
       blocks (if the flag FAN_NONBLOCK is not specified in the call  to  fan-
       otify_init(2))  until  either a file event occurs or the call is inter-
       rupted by a signal (see signal(7)).

       The use of the FAN_REPORT_FID flag in fanotify_init(2) influences  what
       data structures are returned to the event listener for each event.  Af-
       ter a successful read(2), the read buffer contains one or more  of  the
       following structures:

           struct fanotify_event_metadata {
               __u32 event_len;
               __u8 vers;
               __u8 reserved;
               __u16 metadata_len;
               __aligned_u64 mask;
               __s32 fd;
               __s32 pid;

       In  the  case  where  FAN_REPORT_FID is supplied as one of the flags to
       fanotify_init(2), you should also expect to receive the  structure  de-
       tailed  below  following  the generic fanotify_event_metadata structure
       within the read buffer:

           struct fanotify_event_info_fid {
               struct fanotify_event_info_header hdr;
               __kernel_fsid_t fsid;
               unsigned char file_handle[0];

       For performance reasons, it is recommended to use a large  buffer  size
       (for  example, 4096 bytes), so that multiple events can be retrieved by
       a single read(2).

       The return value of read(2) is the number of bytes placed in  the  buf-
       fer, or -1 in case of an error (but see BUGS).

       The fields of the fanotify_event_metadata structure are as follows:

              This  is  the  length  of the data for the current event and the
              offset to the next event in the buffer.  Without FAN_REPORT_FID,
              the  value  of event_len is always FAN_EVENT_METADATA_LEN.  With
              FAN_REPORT_FID, event_len also includes the variable length file

       vers   This field holds a version number for the structure.  It must be
              compared to FANOTIFY_METADATA_VERSION to verify that the  struc-
              tures  returned at run time match the structures defined at com-
              pile time.  In case of a mismatch, the application should  aban-
              don trying to use the fanotify file descriptor.

              This field is not used.

              This  is  the length of the structure.  The field was introduced
              to facilitate the implementation of optional headers  per  event
              type.  No such optional headers exist in the current implementa-

       mask   This is a bit mask describing the event (see below).

       fd     This is an open file descriptor for the object  being  accessed,
              or  FAN_NOFD if a queue overflow occurred.  If the fanotify file
              descriptor has been initialized using  FAN_REPORT_FID,  applica-
              tions  should  expect  this value to be set to FAN_NOFD for each
              event that is received.  The file descriptor can be used to  ac-
              cess the contents of the monitored file or directory.  The read-
              ing application is responsible for closing this file descriptor.

              When calling fanotify_init(2), the caller may specify  (via  the
              event_f_flags argument) various file status flags that are to be
              set on the open file description that corresponds to  this  file
              descriptor.   In  addition, the (kernel-internal) FMODE_NONOTIFY
              file status flag is set on the open file description.  This flag
              suppresses  fanotify event generation.  Hence, when the receiver
              of the fanotify event accesses the notified  file  or  directory
              using  this  file  descriptor, no additional events will be cre-

       pid    If flag FAN_REPORT_TID was set in fanotify_init(2), this is  the
              TID  of  the  thread that caused the event.  Otherwise, this the
              PID of the process that caused the event.

       A program listening to fanotify events can compare this PID to the  PID
       returned  by getpid(2), to determine whether the event is caused by the
       listener itself, or is due to a file access by another process.

       The bit mask in mask indicates which events have occurred for a  single
       filesystem object.  Multiple bits may be set in this mask, if more than
       one event occurred for the monitored filesystem object.  In particular,
       consecutive  events for the same filesystem object and originating from
       the same process may be merged into a single event, with the  exception
       that two permission events are never merged into one queue entry.

       The bits that may appear in mask are as follows:

              A file or a directory (but see BUGS) was accessed (read).

              A file or a directory was opened.

              A  file was opened with the intent to be executed.  See NOTES in
              fanotify_mark(2) for additional details.

              A file or directory metadata was changed.

              A child file or directory was created in a watched parent.

              A child file or directory was deleted in a watched parent.

              A watched file or directory was deleted.

              A file or directory has been moved from a watched parent  direc-

              A  file  or  directory has been moved to a watched parent direc-

              A watched file or directory was moved.

              A file was modified.

              A file that was opened for  writing  (O_WRONLY  or  O_RDWR)  was

              A  file  or  directory  that was opened read-only (O_RDONLY) was

              The event queue exceeded the limit of 16384 entries.  This limit
              can  be  overridden  by  specifying the FAN_UNLIMITED_QUEUE flag
              when calling fanotify_init(2).

              An application wants to read a file or  directory,  for  example
              using  read(2)  or readdir(2).  The reader must write a response
              (as described below) that determines whether the  permission  to
              access the filesystem object shall be granted.

              An  application  wants  to open a file or directory.  The reader
              must write a response that determines whether the permission  to
              open the filesystem object shall be granted.

              An  application  wants to open a file for execution.  The reader
              must write a response that determines whether the permission  to
              open  the filesystem object for execution shall be granted.  See
              NOTES in fanotify_mark(2) for additional details.

       To check for any close event, the following bit mask may be used:

              A file was closed.  This is a synonym for:


       To check for any move event, the following bit mask may be used:

              A file or directory was moved.  This is a synonym for:

                  FAN_MOVED_FROM | FAN_MOVED_TO

       The following bits may appear in mask only in  conjunction  with  other
       event type bits:

              The  events  described  in the mask have occurred on a directory
              object.  Reporting events on directories requires  setting  this
              flag  in the mark mask.  See fanotify_mark(2) for additional de-
              tails.  The FAN_ONDIR flag is reported in an event mask only  if
              the  fanotify  group  has been initialized with the flag FAN_RE-

       The fields of the fanotify_event_info_fid structure are as follows:

       hdr    This is a structure of type fanotify_event_info_header.  It is a
              generic  header that contains information used to describe addi-
              tional information attached to the event.  For example, when  an
              fanotify  file  descriptor  is created using FAN_REPORT_FID, the
              info_type    field    of    this    header     is     set     to
              FAN_EVENT_INFO_TYPE_FID.   Event listeners can use this field to
              check that the additional information received for an  event  is
              of     the     correct    type.     Additionally,    the    fan-
              otify_event_info_header also contains a len field.  In the  cur-
              rent  implementation,  the  value  of len is always (event_len -

       fsid   This is a unique identifier of the filesystem containing the ob-
              ject  associated  with  the  event.   It  is a structure of type
              __kernel_fsid_t and contains the same value as f_fsid when call-
              ing statfs(2).

              This  is a variable length structure of type file_handle.  It is
              an opaque handle that corresponds to a  specified  object  on  a
              filesystem  as returned by name_to_handle_at(2).  It can be used
              to uniquely identify a file on a filesystem and can be passed as
              an  argument  to  open_by_handle_at(2).  Note that for directory
              entry events, such as FAN_CREATE, FAN_DELETE, and FAN_MOVE,  the
              file_handle  describes  the  modified directory and not the cre-
              ated/deleted/moved  child  object.    The   events   FAN_ATTRIB,
              FAN_DELETE_SELF,  and  FAN_MOVE_SELF  will carry the file_handle
              information for the child object if the child  object  is  being

       The  following  macros are provided to iterate over a buffer containing
       fanotify event metadata returned by a read(2) from an fanotify file de-

       FAN_EVENT_OK(meta, len)
              This  macro  checks  the remaining length len of the buffer meta
              against the length of the metadata structure and  the  event_len
              field of the first metadata structure in the buffer.

       FAN_EVENT_NEXT(meta, len)
              This  macro  uses the length indicated in the event_len field of
              the metadata structure pointed to by meta to calculate  the  ad-
              dress  of the next metadata structure that follows meta.  len is
              the number of bytes of metadata that  currently  remain  in  the
              buffer.  The macro returns a pointer to the next metadata struc-
              ture that follows meta, and reduces len by the number  of  bytes
              in  the  metadata structure that has been skipped over (i.e., it
              subtracts meta->event_len from len).

       In addition, there is:

              This macro returns the size (in bytes)  of  the  structure  fan-
              otify_event_metadata.   This  is the minimum size (and currently
              the only size) of any event metadata.

   Monitoring an fanotify file descriptor for events
       When an fanotify event occurs, the fanotify file  descriptor  indicates
       as readable when passed to epoll(7), poll(2), or select(2).

   Dealing with permission events
       For permission events, the application must write(2) a structure of the
       following form to the fanotify file descriptor:

           struct fanotify_response {
               __s32 fd;
               __u32 response;

       The fields of this structure are as follows:

       fd     This  is  the  file   descriptor   from   the   structure   fan-

              This  field  indicates  whether  or  not the permission is to be
              granted.  Its value must be either FAN_ALLOW to allow  the  file
              operation or FAN_DENY to deny the file operation.

       If  access  is  denied, the requesting application call will receive an
       EPERM error.

   Closing the fanotify file descriptor
       When all file descriptors referring to the fanotify notification  group
       are  closed, the fanotify group is released and its resources are freed
       for reuse by the kernel.  Upon close(2), outstanding permission  events
       will be set to allowed.

       The  file  /proc/[pid]/fdinfo/[fd]  contains information about fanotify
       marks for file descriptor fd of process pid.  See proc(5) for details.

       In addition to the usual errors for read(2), the following  errors  can
       occur when reading from the fanotify file descriptor:

       EINVAL The buffer is too small to hold the event.

       EMFILE The  per-process  limit  on  the  number  of open files has been
              reached.  See the description of RLIMIT_NOFILE in getrlimit(2).

       ENFILE The system-wide limit on the total number of open files has been
              reached.  See /proc/sys/fs/file-max in proc(5).

              This  error  is  returned  by  read(2) if O_RDWR or O_WRONLY was
              specified  in  the  event_f_flags  argument  when  calling  fan-
              otify_init(2) and an event occurred for a monitored file that is
              currently being executed.

       In addition to the usual errors for write(2), the following errors  can
       occur when writing to the fanotify file descriptor:

       EINVAL Fanotify  access  permissions are not enabled in the kernel con-
              figuration or the value of response in the response structure is
              not valid.

       ENOENT The  file  descriptor fd in the response structure is not valid.
              This may occur when a response for the permission event has  al-
              ready been written.

       The  fanotify  API was introduced in version 2.6.36 of the Linux kernel
       and enabled in version 2.6.37.  Fdinfo support  was  added  in  version

       The fanotify API is Linux-specific.

       The  fanotify  API  is  available only if the kernel was built with the
       CONFIG_FANOTIFY configuration option enabled.   In  addition,  fanotify
       permission  handling  is  available  only  if  the  CONFIG_FANOTIFY_AC-
       CESS_PERMISSIONS configuration option is enabled.

   Limitations and caveats
       Fanotify reports only events that a user-space program triggers through
       the  filesystem API.  As a result, it does not catch remote events that
       occur on network filesystems.

       The fanotify API does not report file accesses and  modifications  that
       may occur because of mmap(2), msync(2), and munmap(2).

       Events  for  directories  are  created  only if the directory itself is
       opened, read, and closed.  Adding, removing, or changing children of  a
       marked directory does not create events for the monitored directory it-

       Fanotify monitoring of directories is not recursive: to monitor  subdi-
       rectories  under  a  directory, additional marks must be created.  (But
       note that the fanotify API provides no way of detecting when  a  subdi-
       rectory  has  been created under a marked directory, which makes recur-
       sive monitoring difficult.)  Monitoring mounts offers the capability to
       monitor  a whole directory tree.  Monitoring filesystems offers the ca-
       pability to monitor changes made from any mount  of  a  filesystem  in-

       The event queue can overflow.  In this case, events are lost.

       Before  Linux  3.19,  fallocate(2)  did  not  generate fanotify events.
       Since Linux 3.19, calls to fallocate(2) generate FAN_MODIFY events.

       As of Linux 3.17, the following bugs exist:

       *  On Linux, a filesystem object may  be  accessible  through  multiple
          paths,  for  example,  a part of a filesystem may be remounted using
          the --bind option of mount(8).  A listener that marked a mount  will
          be  notified only of events that were triggered for a filesystem ob-
          ject using the same mount.  Any other event will pass unnoticed.

       *  When an event is generated, no check is made to see whether the user
          ID  of  the receiving process has authorization to read or write the
          file before passing a file descriptor for that file.  This  poses  a
          security risk, when the CAP_SYS_ADMIN capability is set for programs
          executed by unprivileged users.

       *  If a call to read(2) processes multiple  events  from  the  fanotify
          queue and an error occurs, the return value will be the total length
          of the events successfully copied to the  user-space  buffer  before
          the error occurred.  The return value will not be -1, and errno will
          not be set.  Thus, the reading application has no way to detect  the

       The  two  example  programs below demonstrate the usage of the fanotify

   Example program: fanotify_example.c
       The first program is an example of fanotify being used with  its  event
       object  information  passed in the form of a file descriptor.  The pro-
       gram marks the mount point passed as a command-line argument and  waits
       for  events  of type FAN_OPEN_PERM and FAN_CLOSE_WRITE.  When a permis-
       sion event occurs, a FAN_ALLOW response is given.

       The following shell session shows an example of running  this  program.
       This  session  involved editing the file /home/user/temp/notes.  Before
       the file was opened, a FAN_OPEN_PERM event occurred.   After  the  file
       was closed, a FAN_CLOSE_WRITE event occurred.  Execution of the program
       ends when the user presses the ENTER key.

           # ./fanotify_example /home
           Press enter key to terminate.
           Listening for events.
           FAN_OPEN_PERM: File /home/user/temp/notes
           FAN_CLOSE_WRITE: File /home/user/temp/notes

           Listening for events stopped.

   Program source: fanotify_example.c

       #define _GNU_SOURCE     /* Needed to get O_LARGEFILE definition */
       #include <errno.h>
       #include <fcntl.h>
       #include <limits.h>
       #include <poll.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/fanotify.h>
       #include <unistd.h>

       /* Read all available fanotify events from the file descriptor 'fd' */

       static void
       handle_events(int fd)
           const struct fanotify_event_metadata *metadata;
           struct fanotify_event_metadata buf[200];
           ssize_t len;
           char path[PATH_MAX];
           ssize_t path_len;
           char procfd_path[PATH_MAX];
           struct fanotify_response response;

           /* Loop while events can be read from fanotify file descriptor */

           for (;;) {

               /* Read some events */

               len = read(fd, (void *) &buf, sizeof(buf));
               if (len == -1 && errno != EAGAIN) {

               /* Check if end of available data reached */

               if (len <= 0)

               /* Point to the first event in the buffer */

               metadata = buf;

               /* Loop over all events in the buffer */

               while (FAN_EVENT_OK(metadata, len)) {

                   /* Check that run-time and compile-time structures match */

                   if (metadata->vers != FANOTIFY_METADATA_VERSION) {
                               "Mismatch of fanotify metadata version.\n");

                   /* metadata->fd contains either FAN_NOFD, indicating a
                      queue overflow, or a file descriptor (a nonnegative
                      integer). Here, we simply ignore queue overflow. */

                   if (metadata->fd >= 0) {

                       /* Handle open permission event */

                       if (metadata->mask & FAN_OPEN_PERM) {
                           printf("FAN_OPEN_PERM: ");

                           /* Allow file to be opened */

                           response.fd = metadata->fd;
                           response.response = FAN_ALLOW;
                           write(fd, &response,
                                 sizeof(struct fanotify_response));

                       /* Handle closing of writable file event */

                       if (metadata->mask & FAN_CLOSE_WRITE)
                           printf("FAN_CLOSE_WRITE: ");

                       /* Retrieve and print pathname of the accessed file */

                       snprintf(procfd_path, sizeof(procfd_path),
                                "/proc/self/fd/%d", metadata->fd);
                       path_len = readlink(procfd_path, path,
                                           sizeof(path) - 1);
                       if (path_len == -1) {

                       path[path_len] = '\0';
                       printf("File %s\n", path);

                       /* Close the file descriptor of the event */


                   /* Advance to next event */

                   metadata = FAN_EVENT_NEXT(metadata, len);

       main(int argc, char *argv[])
           char buf;
           int fd, poll_num;
           nfds_t nfds;
           struct pollfd fds[2];

           /* Check mount point is supplied */

           if (argc != 2) {
               fprintf(stderr, "Usage: %s MOUNT\n", argv[0]);

           printf("Press enter key to terminate.\n");

           /* Create the file descriptor for accessing the fanotify API */

           fd = fanotify_init(FAN_CLOEXEC | FAN_CLASS_CONTENT | FAN_NONBLOCK,
                              O_RDONLY | O_LARGEFILE);
           if (fd == -1) {

           /* Mark the mount for:
              - permission events before opening files
              - notification events after closing a write-enabled
                file descriptor */

           if (fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
                             FAN_OPEN_PERM | FAN_CLOSE_WRITE, AT_FDCWD,
                             argv[1]) == -1) {

           /* Prepare for polling */

           nfds = 2;

           /* Console input */

           fds[0].fd = STDIN_FILENO;
           fds[0].events = POLLIN;

           /* Fanotify input */

           fds[1].fd = fd;
           fds[1].events = POLLIN;

           /* This is the loop to wait for incoming events */

           printf("Listening for events.\n");

           while (1) {
               poll_num = poll(fds, nfds, -1);
               if (poll_num == -1) {
                   if (errno == EINTR)     /* Interrupted by a signal */
                       continue;           /* Restart poll() */

                   perror("poll");         /* Unexpected error */

               if (poll_num > 0) {
                   if (fds[0].revents & POLLIN) {

                       /* Console input is available: empty stdin and quit */

                       while (read(STDIN_FILENO, &buf, 1) > 0 && buf != '\n')

                   if (fds[1].revents & POLLIN) {

                       /* Fanotify events are available */


           printf("Listening for events stopped.\n");

   Example program: fanotify_fid.c
       The second program is an example of fanotify being  used  with  FAN_RE-
       PORT_FID  enabled.   The  program  marks  the filesystem object that is
       passed as a command-line argument and waits  until  an  event  of  type
       FAN_CREATE  has  occurred.   The  event  mask  indicates  which type of
       filesystem object--either a file or a directory--was created.  Once all
       events  have  been  read from the buffer and processed accordingly, the
       program simply terminates.

       The following shell sessions show two  different  invocations  of  this
       program, with different actions performed on a watched object.

       The  first  session  shows  a mark being placed on /home/user.  This is
       followed by the creation of a  regular  file,  /home/user/testfile.txt.
       This results in a FAN_CREATE event being generated and reported against
       the file's parent watched directory  object.   Program  execution  ends
       once all events captured within the buffer have been processed.

           # ./fanotify_fid /home/user
           Listening for events.
           FAN_CREATE (file created):
                   Directory /home/user has been modified.
           All events processed successfully. Program exiting.

           $ touch /home/user/testfile.txt              # In another terminal

       The  second  session  shows a mark being placed on /home/user.  This is
       followed by the creation of a directory, /home/user/testdir.  This spe-
       cific  action  results in a FAN_CREATE event being generated and is re-
       ported with the FAN_ONDIR flag set.

           # ./fanotify_fid /home/user
           Listening for events.
           FAN_CREATE | FAN_ONDIR (subdirectory created):
                   Directory /home/user has been modified.
           All events processed successfully. Program exiting.

           $ mkdir -p /home/user/testdir          # In another terminal

   Program source: fanotify_fid.c

       #define _GNU_SOURCE
       #include <errno.h>
       #include <fcntl.h>
       #include <limits.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/types.h>
       #include <sys/stat.h>
       #include <sys/fanotify.h>
       #include <unistd.h>

       #define BUF_SIZE 256

       main(int argc, char **argv)
           int fd, ret, event_fd, mount_fd;
           ssize_t len, path_len;
           char path[PATH_MAX];
           char procfd_path[PATH_MAX];
           char events_buf[BUF_SIZE];
           struct file_handle *file_handle;
           struct fanotify_event_metadata *metadata;
           struct fanotify_event_info_fid *fid;

           if (argc != 2) {
               fprintf(stderr, "Invalid number of command line arguments.\n");

           mount_fd = open(argv[1], O_DIRECTORY | O_RDONLY);
           if (mount_fd == -1) {

           /* Create an fanotify file descriptor with FAN_REPORT_FID as a flag
              so that program can receive fid events. */

           fd = fanotify_init(FAN_CLASS_NOTIF | FAN_REPORT_FID, 0);
           if (fd == -1) {

           /* Place a mark on the filesystem object supplied in argv[1]. */

           ret = fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_ONLYDIR,
                               FAN_CREATE | FAN_ONDIR,
                               AT_FDCWD, argv[1]);
           if (ret == -1) {

           printf("Listening for events.\n");

           /* Read events from the event queue into a buffer */

           len = read(fd, (void *) &events_buf, sizeof(events_buf));
           if (len == -1 && errno != EAGAIN) {

           /* Process all events within the buffer */

           for (metadata = (struct fanotify_event_metadata *) events_buf;
                   FAN_EVENT_OK(metadata, len);
                   metadata = FAN_EVENT_NEXT(metadata, len)) {
               fid = (struct fanotify_event_info_fid *) (metadata + 1);
               file_handle = (struct file_handle *) fid->handle;

               /* Ensure that the event info is of the correct type */

               if (fid->hdr.info_type != FAN_EVENT_INFO_TYPE_FID) {
                   fprintf(stderr, "Received unexpected event info type.\n");

               if (metadata->mask == FAN_CREATE)
                   printf("FAN_CREATE (file created):\n");

               if (metadata->mask == (FAN_CREATE | FAN_ONDIR))
                   printf("FAN_CREATE | FAN_ONDIR (subdirectory created):\n");

               /* metadata->fd is set to FAN_NOFD when FAN_REPORT_FID is
                  enabled.  To obtain a file descriptor for the file object
                  corresponding to an event you can use the struct file_handle
                  that's provided within the fanotify_event_info_fid in
                  conjunction with the open_by_handle_at(2) system call.
                  A check for ESTALE is done to accommodate for the situation
                  where the file handle for the object was deleted prior to
                  this system call. */

               event_fd = open_by_handle_at(mount_fd, file_handle, O_RDONLY);
               if (event_fd == -1) {
                   if (errno == ESTALE) {
                       printf("File handle is no longer valid. "
                               "File has been deleted\n");
                   } else {

               snprintf(procfd_path, sizeof(procfd_path), "/proc/self/fd/%d",

               /* Retrieve and print the path of the modified dentry */

               path_len = readlink(procfd_path, path, sizeof(path) - 1);
               if (path_len == -1) {

               path[path_len] = '\0';
               printf("\tDirectory '%s' has been modified.\n", path);

               /* Close associated file descriptor for this event */


           printf("All events processed successfully. Program exiting.\n");

       fanotify_init(2), fanotify_mark(2), inotify(7)

       This page is part of release 5.07 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2020-06-09                       FANOTIFY(7)

Man(1) output converted with man2html
list of all man pages