INOTIFY(7)                 Linux Programmer's Manual                INOTIFY(7)
       inotify - monitoring file system events

       The inotify API provides a mechanism for monitoring file system events.
       Inotify can be used to monitor individual files, or to monitor directo-
       ries.   When  a  directory is monitored, inotify will return events for
       the directory itself, and for files inside the directory.

       The following system calls are used with this API: inotify_init(), ino-
       tify_add_watch(), inotify_rm_watch(), read(), and close().

       inotify_init(2) creates an inotify instance and returns a file descrip-
       tor referring to the inotify instance.

       inotify_add_watch(2) manipulates the "watch list"  associated  with  an
       inotify  instance.  Each item ("watch") in the watch list specifies the
       pathname of a file or directory, along with some set of events that the
       kernel  should monitor for the file referred to by that pathname.  ino-
       tify_add_watch() either creates a new watch item, or modifies an exist-
       ing  watch.   Each  watch  has  a unique "watch descriptor", an integer
       returned by inotify_add_watch() when the watch is created.

       inotify_rm_watch(2) removes an item from an inotify watch list.

       When all file descriptors referring to an inotify  instance  have  been
       closed, the underlying object and its resources are freed for re-use by
       the kernel; all associated watches are automatically freed.

       To determine what events have occurred, an  application  read(2)s  from
       the  inotify file descriptor.  If no events have so far occurred, then,
       assuming a blocking file descriptor, read() will block until  at  least
       one event occurs.

       Each  successful  read() returns a buffer containing one or more of the
       following structures:

         struct inotify_event {
             int      wd;       /* Watch descriptor */
             uint32_t mask;     /* Mask of events */
             uint32_t cookie;   /* Unique cookie associating related
                                   events (for rename(2)) */
             uint32_t len;      /* Size of 'name' field */
             char     name[];   /* Optional null-terminated name */

       wd identifies the watch for which this event occurs.  It is one of  the
       watch descriptors returned by a previous call to inotify_add_watch().

       mask contains bits that describe the event that occurred (see below).

       cookie  is  a  unique  integer that connects related events.  Currently
       this is only used for rename events, and allows the resulting  pair  of
       IN_MOVE_FROM  and IN_MOVE_TO events to be connected by the application.

       The name field is only present when an event is  returned  for  a  file
       inside a watched directory; it identifies the file pathname relative to
       the watched directory.   This  pathname  is  null-terminated,  and  may
       include  further  null  bytes  to  align subsequent reads to a suitable
       address boundary.

       The len field counts all of the  bytes  in  name,  including  the  null
       bytes;  the  length of each inotify_event structure is thus sizeof(ino-

   inotify events
       The inotify_add_watch(2) mask argument and the mask field of  the  ino-
       tify_event  structure returned when read(2)ing an inotify file descrip-
       tor are both bit masks identifying inotify events.  The following  bits
       can  be  specified  in mask when calling inotify_add_watch() and may be
       returned in the mask field returned by read():

         Bit                Description
         IN_ACCESS          File was accessed (read) (*)
         IN_ATTRIB          Metadata changed (permissions, timestamps,
                            extended attributes, etc.) (*)
         IN_CLOSE_WRITE     File opened for writing was closed (*)
         IN_CLOSE_NOWRITE   File not opened for writing was closed (*)
         IN_CREATE          File/directory created in watched directory (*)
         IN_DELETE          File/directory deleted from watched directory (*)
         IN_DELETE_SELF     Watched file/directory was itself deleted
         IN_MODIFY          File was modified (*)
         IN_MOVE_SELF       Watched file/directory was itself moved
         IN_MOVED_FROM      File moved out of watched directory (*)
         IN_MOVED_TO        File moved into watched directory (*)
         IN_OPEN            File was opened (*)

       When monitoring a directory, the events marked  with  an  asterisk  (*)
       above  can  occur  for  files  in the directory, in which case the name
       field in the returned inotify_event structure identifies  the  name  of
       the file within the directory.

       The  IN_ALL_EVENTS  macro  is defined as a bit mask of all of the above
       events.  This macro can be used as the mask argument when calling  ino-

       Two  additional  convenience  macros  are  IN_MOVE,  which  equates  to
       IN_MOVED_FROM|IN_MOVED_TO,    and    IN_CLOSE    which    equates    to

       The  following  further bits can be specified in mask when calling ino-

         Bit              Description
         IN_DONT_FOLLOW   Don't dereference pathname if it is a symbolic link
         IN_MASK_ADD      Add (OR) events to watch mask for this pathname if
                          it already exists (instead of replacing mask)
         IN_ONESHOT       Monitor pathname for one event, then remove from
                          watch list
         IN_ONLYDIR       Only watch pathname if it is a directory

       The following bits may be set in the mask field returned by read():

         Bit             Description
         IN_IGNORED      Watch was removed explicitly (inotify_rm_watch())
                         or automatically (file was deleted, or
                         file system was unmounted)
         IN_ISDIR        Subject of this event is a directory
         IN_Q_OVERFLOW   Event queue overflowed (wd is -1 for this event)
         IN_UNMOUNT      File system containing watched object was unmounted

   /proc interfaces
       The following interfaces can be used to limit the amount of kernel mem-
       ory consumed by inotify:

              The  value  in  this file is used when an application calls ino-
              tify_init(2) to set an upper limit on the number of events  that
              can  be queued to the corresponding inotify instance.  Events in
              excess of this limit are dropped, but an IN_Q_OVERFLOW event  is
              always generated.

              This specifies an upper limit on the number of inotify instances
              that can be created per real user ID.

              This specifies a limit on the number  of  watches  that  can  be
              associated with each inotify instance.

       Inotify file descriptors can be monitored using select(2), poll(2), and

       If successive output  inotify  events  produced  on  the  inotify  file
       descriptor  are  identical  (same wd, mask, cookie, and name) then they
       are coalesced into a single event.

       The events returned by reading from an inotify file descriptor form  an
       ordered  queue.  Thus, for example, it is guaranteed that when renaming
       from one directory to another, events will be produced in  the  correct
       order on the inotify file descriptor.

       The FIONREAD ioctl() returns the number of bytes available to read from
       an inotify file descriptor.

       Inotify monitoring of directories is not recursive: to  monitor  subdi-
       rectories under a directory, additional watches must be created.

       Inotify  was merged into the 2.6.13 Linux kernel.  The required library
       interfaces were added to glibc in version 2.4.

       In kernels before 2.6.16, the IN_ONESHOT mask flag does not work.

       As at glibc 2.4, the definitions for IN_DONT_FOLLOW,  IN_MASK_ADD,  and
       IN_ONLYDIR are missing from <sys/inotify.h>.

       The inotify API is Linux specific.

       inotify_add_watch(2),  inotify_init(2),  inotify_rm_watch(2),  read(2),
       stat(2), Documentation/filesystems/inotify.txt.

Linux 2.6.15                      2006-02-07                        INOTIFY(7)