FANOTIFY_INIT(2)	   Linux Programmer's Manual	      FANOTIFY_INIT(2)



NAME
       fanotify_init - create and initialize fanotify group

SYNOPSIS
       #include <fcntl.h>
       #include <sys/fanotify.h>

       int fanotify_init(unsigned int flags, unsigned int event_f_flags);

DESCRIPTION
       For an overview of the fanotify API, see fanotify(7).

       fanotify_init()	initializes  a	new  fanotify group and returns a file
       descriptor for the event queue associated with the group.

       The file descriptor is used in calls to fanotify_mark(2) to specify the
       files,  directories, and mounts for which fanotify events shall be cre-
       ated.  These events are received by reading from the  file  descriptor.
       Some  events  are  only	informative,  indicating  that a file has been
       accessed.  Other events can be used to determine whether another appli-
       cation  is  permitted  to  access  a  file or directory.	 Permission to
       access filesystem objects is granted by writing to the file descriptor.

       Multiple programs may be using the fanotify interface at the same  time
       to monitor the same files.

       In  the	current implementation, the number of fanotify groups per user
       is limited to 128.  This limit cannot be overridden.

       Calling fanotify_init() requires the  CAP_SYS_ADMIN  capability.	  This
       constraint  might be relaxed in future versions of the API.  Therefore,
       certain additional capability checks have been implemented as indicated
       below.

       The flags argument contains a multi-bit field defining the notification
       class of the listening application and further single bit fields speci-
       fying the behavior of the file descriptor.

       If  multiple  listeners	for  permission events exist, the notification
       class is used to establish the sequence in which the listeners  receive
       the events.

       Only  one  of  the  following  notification classes may be specified in
       flags:

       FAN_CLASS_PRE_CONTENT
	      This value allows the receipt of events notifying	 that  a  file
	      has  been accessed and events for permission decisions if a file
	      may be accessed.	It is intended for event listeners  that  need
	      to  access  files	 before	 they  contain their final data.  This
	      notification class might be used by  hierarchical	 storage  man-
	      agers, for example.

       FAN_CLASS_CONTENT
	      This  value  allows  the receipt of events notifying that a file
	      has been accessed and events for permission decisions if a  file
	      may  be  accessed.  It is intended for event listeners that need
	      to access files when they already contain their  final  content.
	      This  notification class might be used by malware detection pro-
	      grams, for example.

       FAN_CLASS_NOTIF
	      This is the default value.  It does not need  to	be  specified.
	      This  value  only	 allows the receipt of events notifying that a
	      file has been accessed.  Permission decisions before the file is
	      accessed are not possible.

       Listeners  with	different  notification classes will receive events in
       the order  FAN_CLASS_PRE_CONTENT,  FAN_CLASS_CONTENT,  FAN_CLASS_NOTIF.
       The  order of notification for listeners in the same notification class
       is undefined.

       The following bits can additionally be set in flags:

       FAN_CLOEXEC
	      Set the close-on-exec flag (FD_CLOEXEC) on the new file descrip-
	      tor.  See the description of the O_CLOEXEC flag in open(2).

       FAN_NONBLOCK
	      Enable  the  nonblocking flag (O_NONBLOCK) for the file descrip-
	      tor.  Reading from the file descriptor will not block.  Instead,
	      if  no  data  is	available,  read(2)  will  fail with the error
	      EAGAIN.

       FAN_UNLIMITED_QUEUE
	      Remove the limit of 16384 events for the event  queue.   Use  of
	      this flag requires the CAP_SYS_ADMIN capability.

       FAN_UNLIMITED_MARKS
	      Remove  the  limit of 8192 marks.	 Use of this flag requires the
	      CAP_SYS_ADMIN capability.

       The event_f_flags argument defines the file status flags that  will  be
       set on the open file descriptions that are created for fanotify events.
       For details of these flags, see the description of the flags values  in
       open(2).	 event_f_flags includes a multi-bit field for the access mode.
       This field can take the following values:

       O_RDONLY
	      This value allows only read access.

       O_WRONLY
	      This value allows only write access.

       O_RDWR This value allows read and write access.

       Additional bits can be set in event_f_flags.  The  most	useful	values
       are:

       O_LARGEFILE
	      Enable  support  for  files exceeding 2 GB.  Failing to set this
	      flag will result in an EOVERFLOW error when  trying  to  open  a
	      large  file  which is monitored by an fanotify group on a 32-bit
	      system.

       O_CLOEXEC (since Linux 3.18)
	      Enable the close-on-exec flag for the file descriptor.  See  the
	      description  of  the  O_CLOEXEC  flag in open(2) for reasons why
	      this may be useful.

       The following are also allowable: O_APPEND, O_DSYNC, O_NOATIME,	O_NON-
       BLOCK,  and  O_SYNC.  Specifying any other flag in event_f_flags yields
       the error EINVAL (but see BUGS).

RETURN VALUE
       On success, fanotify_init() returns a new file descriptor.   On	error,
       -1 is returned, and errno is set to indicate the error.

ERRORS
       EINVAL An   invalid   value  was	 passed	 in  flags  or	event_f_flags.
	      FAN_ALL_INIT_FLAGS defines all allowable bits for flags.

       EMFILE The number of fanotify groups for this user exceeds 128.

       The per-process limit on the number of open file descriptors  has  been
       reached.

       ENOMEM The allocation of memory for the notification group failed.

       ENOSYS This  kernel  does  not implement fanotify_init().  The fanotify
	      API is available only if the kernel  was	configured  with  CON-
	      FIG_FANOTIFY.

       EPERM  The  operation  is  not  permitted  because the caller lacks the
	      CAP_SYS_ADMIN capability.

VERSIONS
       fanotify_init() was introduced in version 2.6.36 of  the	 Linux	kernel
       and enabled in version 2.6.37.

CONFORMING TO
       This system call is Linux-specific.

BUGS
       The following bug was present in Linux kernels before version 3.18:

       *  The O_CLOEXEC is ignored when passed in event_f_flags.

       The following bug was present in Linux kernels before version 3.14:

       *  The  event_f_flags argument is not checked for invalid flags.	 Flags
	  that are intended only for internal use, such as FMODE_EXEC, can  be
	  set,	and will consequently be set for the file descriptors returned
	  when reading from the fanotify file descriptor.

SEE ALSO
       fanotify_mark(2), fanotify(7)

COLOPHON
       This page is part of release 4.10 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
       https://www.kernel.org/doc/man-pages/.



Linux				  2016-10-08		      FANOTIFY_INIT(2)