.\" Copyright (C) 2005 Robert Love
.\" and Copyright, 2006 Michael Kerrisk
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, see
.\" <http://www.gnu.org/licenses/>.
.\" %%%LICENSE_END
.\"
.\" 2005-07-19 Robert Love <rlove@rlove.org> - initial version
.\" 2006-02-07 mtk, various changes
.\"
.TH INOTIFY_ADD_WATCH 2 2014-07-08 "Linux" "Linux Programmer's Manual"
.SH NAME
inotify_add_watch \- add a watch to an initialized inotify instance
.SH SYNOPSIS
.B #include <sys/inotify.h>
.sp
.BI "int inotify_add_watch(int " fd ", const char *" pathname ", uint32_t " mask );
.SH DESCRIPTION
.BR inotify_add_watch ()
adds a new watch, or modifies an existing watch,
for the file whose location is specified in
.IR pathname ;
the caller must have read permission for this file.
The
.I fd
argument is a file descriptor referring to the
inotify instance whose watch list is to be modified.
The events to be monitored for
.I pathname
are specified in the
.I mask
bit-mask argument.
See
.BR inotify (7)
for a description of the bits that can be set in
.IR mask .

A successful call to
.BR inotify_add_watch ()
returns a unique watch descriptor for this inotify instance,
for the filesystem object that corresponds to
.IR pathname .
If the filesystem object
was not previously 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
.BR read (2)s
from the inotify file descriptor.
These reads fetch
.I inotify_event
structures (see
.BR inotify (7))
indicating filesystem events;
the watch descriptor inside this structure identifies
the object for which the event occurred.
.SH RETURN VALUE
On success,
.BR inotify_add_watch ()
returns a nonnegative watch descriptor.
On error, \-1 is returned and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EACCES
Read access to the given file is not permitted.
.TP
.B EBADF
The given file descriptor is not valid.
.TP
.B EFAULT
.I pathname
points outside of the process's accessible address space.
.TP
.B EINVAL
The given event mask contains no valid events; or
.I fd
is not an inotify file descriptor.
.TP
.B ENAMETOOLONG
.I pathname
is too long.
.TP
.B ENOENT
A directory component in
.I pathname
does not exist or is a dangling symbolic link.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOSPC
The user limit on the total number of inotify watches was reached or the
kernel failed to allocate a needed resource.
.SH VERSIONS
Inotify was merged into the 2.6.13 Linux kernel.
.SH CONFORMING TO
This system call is Linux-specific.
.SH SEE ALSO
.BR inotify_init (2),
.BR inotify_rm_watch (2),
.BR inotify (7)
.SH COLOPHON
This page is part of release 3.74 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%http://www.kernel.org/doc/man\-pages/.