NAME

       F_NOTIFY - file and directory change notification

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #define _GNU_SOURCE
       #include <fcntl.h>

       int fcntl(int fd, F_NOTIFY, int arg);

DESCRIPTION

       Provide  notification  when  the  directory  referred  to  by  fd or any of the files that it contains is
       changed.  The events to be notified are specified in arg, which is a bit mask specified by ORing together
       zero or more of the following bits:

       DN_ACCESS
              A file was accessed (read(2), pread(2), readv(2), and similar)

       DN_MODIFY
              A file was modified (write(2), pwrite(2), writev(2), truncate(2), ftruncate(2), and similar).

       DN_CREATE
              A file was created (open(2), creat(2), mknod(2), mkdir(2),  link(2),  symlink(2),  rename(2)  into
              this directory).

       DN_DELETE
              A file was unlinked (unlink(2), rename(2) to another directory, rmdir(2)).

       DN_RENAME
              A file was renamed within this directory (rename(2)).

       DN_ATTRIB
              The attributes of a file were changed (chown(2), chmod(2), utime(2), utimensat(2), and similar).

       (In  order  to  obtain  these  definitions,  the  _GNU_SOURCE  feature  test macro must be defined before
       including any header files.)

       Directory notifications are normally "one-shot", and the application must reregister to  receive  further
       notifications.   Alternatively,  if  DN_MULTISHOT  is  included  in arg, then notification will remain in
       effect until explicitly removed.

       A series of F_NOTIFY requests is cumulative, with the events in  arg  being  added  to  the  set  already
       monitored.  To disable notification of all events, make an F_NOTIFY call specifying arg as 0.

       Notification occurs via delivery of a signal.  The default signal is SIGIO, but this can be changed using
       the F_SETSIG operation to fcntl().  (Note that SIGIO is one of the nonqueuing standard signals; switching
       to the use of a real-time signal means that multiple notifications can be queued to the process.)  In the
       latter case, the signal handler receives a siginfo_t structure as its second argument (if the handler was
       established  using  SA_SIGINFO)  and the si_fd field of this structure contains the file descriptor which
       generated the notification (useful when establishing notification on multiple directories).

       Especially when using DN_MULTISHOT, a real time signal should be used for notification, so that  multiple
       notifications can be queued.

       NOTE:  New applications should use the inotify interface (available since Linux 2.6.13), which provides a
       much superior interface for obtaining notifications of filesystem events.  See inotify(7).

RETURN VALUE

       Zero.

       On error, -1 is returned, and errno is set to indicate the error.

ERRORS

       See fcntl(2).

       ENOTDIR
              fd does not refer to a directory.

STANDARDS

       Linux.

HISTORY

       Linux 2.4.

SEE ALSO

       fcntl(2)

Linux man-pages 6.16                               2025-07-20                                   F_NOTIFY(2const)