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INOTIFY(7)		   Linux Programmers 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(2),
       inotify_add_watch(2), inotify_rm_watch(2), read(2), and close(2).

       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(2) either creates a  new	watch  item,  or  modifies  an
       existing watch.	Each watch has a unique "watch descriptor", an integer
       returned by inotify_add_watch(2) 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(2) will block until at  least
       one  event  occurs  (unless  interrupted by a signal, in which case the
       call fails with the error EINTR; see signal(7)).

       Each successful read(2) 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(2).

       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

       The behavior when the buffer given to read(2) is too  small  to	return
       information about the next event depends on the kernel version: in ker
       nels before 2.6.21, read(2) returns 0;  since  kernel  2.6.21,  read(2)
       fails with the error EINVAL.

   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(2) and  may  be
       returned in the mask field returned by read(2):

	   IN_ACCESS	     File was accessed (read) (*).
	   IN_ATTRIB	     Metadata  changed, e.g., permissions, timestamps,
			     extended  attributes,  link  count  (since  Linux
			     2.6.25), UID, GID, 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

	   IN_DONT_FOLLOW (since Linux 2.6.15)
			     Dont  dereference	pathname  if it is a symbolic
	   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 (since Linux 2.6.15)
			     Only watch pathname if it is a directory.

       The following bits may be set in the mask field returned by read(2):

	   IN_IGNORED	     Watch     was     removed	   explicitly	 (ino
			     tify_rm_watch(2))	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

   /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 was merged into the 2.6.13 Linux kernel.  The required  library
       interfaces  were  added	to  glibc  in  version	2.4.  (IN_DONT_FOLLOW,
       IN_MASK_ADD, and IN_ONLYDIR were only added in version 2.5.)

       The inotify API is Linux-specific.

       Inotify file descriptors can be monitored using select(2), poll(2), and
       epoll(7).  When an event is available, the file descriptor indicates as

       Since Linux 2.6.25, signal-driven I/O  notification  is	available  for
       inotify	file  descriptors;  see the discussion of F_SETFL (for setting
       the O_ASYNC flag), F_SETOWN, and F_SETSIG in fcntl(2).	The  siginfo_t
       structure (described in sigaction(2)) that is passed to the signal han
       dler has the following fields set: si_fd is set	to  the  inotify  file
       descriptor number; si_signo is set to the signal number; si_code is set
       to POLL_IN; and POLLIN is set in si_band.

       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(2)	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.

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

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

       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux				  2008-05-15			    INOTIFY(7)

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