.\" Copyright (C) 2005 Robert Love
.\" and Copyright, 2006 Michael Kerrisk
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.\" 2005-07-19 Robert Love <rlove@rlove.org> - initial version
.\" 2006-02-07 mtk, various changes
.\"
.TH inotify_add_watch 2 2023-03-30 "Linux man-pages 6.04"
.SH NAME
inotify_add_watch \- add a watch to an initialized inotify instance
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/inotify.h>
.PP
.BI "int inotify_add_watch(int " fd ", const char *" pathname ", uint32_t " mask );
.fi
.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 .
.PP
A successful call to
.BR inotify_add_watch ()
returns a unique watch descriptor for this inotify instance,
for the filesystem object (inode) 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.
.PP
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 watch descriptor (a nonnegative integer).
On error, \-1 is returned and
.I errno
is set to indicate the error.
.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 EEXIST
.I mask
contains
.B IN_MASK_CREATE
and
.I pathname
refers to a file already being watched by the same
.IR fd .
.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 mask
contains both
.B IN_MASK_ADD
and
.BR IN_MASK_CREATE ;
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.
.TP
.B ENOTDIR
.I mask
contains
.B IN_ONLYDIR
and
.I pathname
is not a directory.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.6.13.
.SH EXAMPLES
See
.BR inotify (7).
.SH SEE ALSO
.BR inotify_init (2),
.BR inotify_rm_watch (2),
.BR inotify (7)