inotify_add_watch manpage

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

       inotify_add_watch - add a watch to an initialized inotify instance

       #include <sys/inotify.h>

       int inotify_add_watch(int fd, const char *pathname, uint32_t mask);

       inotify_add_watch()  adds  a  new watch, or modifies an existing watch,
       for the file whose location is specified in pathname; the  caller  must
       have read permission for this file.  The fd argument is a file descrip-
       tor referring to the inotify instance whose watch list is to  be	 modi-
       fied.   The  events  to	be monitored for pathname are specified in the
       mask bit-mask argument.	See inotify(7) for a description of  the  bits
       that can be set in mask.

       A  successful  call  to	inotify_add_watch()  returns  a	 unique	 watch
       descriptor for this inotify instance, for the filesystem object (inode)
       that  corresponds to pathname.  If the filesystem object was not previ-
       ously being watched by this inotify instance, then the watch descriptor
       is newly allocated.  If the filesystem object was already being watched
       (perhaps via a different link to the same object), then the  descriptor
       for the existing watch is returned.

       The  watch  descriptor  is  returned by later read(2)s from the inotify
       file descriptor.	 These reads fetch inotify_event structures (see  ino-
       tify(7)) indicating filesystem events; the watch descriptor inside this
       structure identifies the object for which the event occurred.

       On success, inotify_add_watch() returns a nonnegative watch descriptor.
       On error, -1 is returned and errno is set appropriately.

       EACCES Read access to the given file is not permitted.

       EBADF  The given file descriptor is not valid.

       EFAULT pathname	points	outside	 of  the  process's accessible address

       EINVAL The given event mask contains no valid events; or fd is  not  an
	      inotify file descriptor.

	      pathname is too long.

       ENOENT A	 directory  component  in pathname does not exist or is a dan-
	      gling symbolic link.

       ENOMEM Insufficient kernel memory was available.

       ENOSPC The user limit on	 the  total  number  of	 inotify  watches  was
	      reached or the kernel failed to allocate a needed resource.

       Inotify was merged into the 2.6.13 Linux kernel.

       This system call is Linux-specific.

       inotify_init(2), inotify_rm_watch(2), inotify(7)

       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

Linux				  2017-03-13		  INOTIFY_ADD_WATCH(2)