.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
+.\" and Copyright (C) 2006, 2014 Michael Kerrisk
.\"
.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" <michael@cantor.informatik.rwth-aachen.de>: NFS details
.\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
-.TH CHMOD 2 2010-09-26 "Linux" "Linux Programmer's Manual"
+.TH CHMOD 2 2014-08-19 "Linux" "Linux Programmer's Manual"
.SH NAME
-chmod, fchmod \- change permissions of a file
+chmod, fchmod, fchmodat \- change permissions of a file
.SH SYNOPSIS
+.nf
.B #include <sys/stat.h>
.sp
-.BI "int chmod(const char *" path ", mode_t " mode );
+.BI "int chmod(const char *" pathname ", mode_t " mode );
.br
.BI "int fchmod(int " fd ", mode_t " mode );
.sp
+.BR "#include <fcntl.h>" " /* Definition of AT_* constants */"
+.B #include <sys/stat.h>
+.sp
+.BI "int fchmodat(int " dirfd ", const char *" pathname ", mode_t " \
+mode ", int " flags );
+.fi
+.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE\ >=\ 200809L
.RE
.PD
+.sp
+.BR fchmodat ():
+.PD 0
+.ad l
+.RS 4
+.TP 4
+Since glibc 2.10:
+_XOPEN_SOURCE\ >=\ 700 || _POSIX_C_SOURCE\ >=\ 200809L
+.TP
+Before glibc 2.10:
+_ATFILE_SOURCE
+.RE
+.ad
+.PD
.ad
.SH DESCRIPTION
-These system calls change the permissions of a file.
+The
+.BR chmod ()
+and
+.BR fchmod ()
+system calls change the permissions of a file.
They differ only in how the file is specified:
.IP * 2
.BR chmod ()
changes the permissions of the file specified whose pathname is given in
-.IR path ,
+.IR pathname ,
which is dereferenced if it is a symbolic link.
.IP *
.BR fchmod ()
open files are maintained by the client.
Widening the permissions may be
delayed for other clients if attribute caching is enabled on them.
+.\"
+.\"
+.SS fchmodat()
+The
+.BR fchmodat ()
+system call operates in exactly the same way as
+.BR chmod (),
+except for the differences described here.
+
+If the pathname given in
+.I pathname
+is relative, then it is interpreted relative to the directory
+referred to by the file descriptor
+.I dirfd
+(rather than relative to the current working directory of
+the calling process, as is done by
+.BR chmod ()
+for a relative pathname).
+
+If
+.I pathname
+is relative and
+.I dirfd
+is the special value
+.BR AT_FDCWD ,
+then
+.I pathname
+is interpreted relative to the current working
+directory of the calling process (like
+.BR chmod ()).
+
+If
+.I pathname
+is absolute, then
+.I dirfd
+is ignored.
+
+.I flags
+can either be 0, or include the following flag:
+.TP
+.B AT_SYMLINK_NOFOLLOW
+If
+.I pathname
+is a symbolic link, do not dereference it:
+instead operate on the link itself.
+This flag is not currently implemented.
+.PP
+See
+.BR openat (2)
+for an explanation of the need for
+.BR fchmodat ().
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
-Depending on the filesystem, other errors can be returned.
+Depending on the filesystem,
+errors other than those listed below can be returned.
+
The more general errors for
.BR chmod ()
are listed below:
.BR path_resolution (7).)
.TP
.B EFAULT
-.I path
+.I pathname
points outside your accessible address space.
.TP
.B EIO
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
-.IR path .
+.IR pathname .
.TP
.B ENAMETOOLONG
-.I path
+.I pathname
is too long.
.TP
.B ENOENT
.TP
.B EROFS
See above.
+.PP
+The same errors that occur for
+.BR chmod ()
+can also occur for
+.BR fchmodat ().
+The following additional errors can occur for
+.BR fchmodat ():
+.TP
+.B EBADF
+.I dirfd
+is not a valid file descriptor.
+.TP
+.B EINVAL
+Invalid flag specified in
+.IR flags .
+.TP
+.B ENOTDIR
+.I pathname
+is relative and
+.I dirfd
+is a file descriptor referring to a file other than a directory.
+.TP
+.B ENOTSUP
+.I flags
+specified
+.BR AT_SYMLINK_NOFOLLOW ,
+which is not supported.
+.SH VERSIONS
+.BR fchmodat ()
+was added to Linux in kernel 2.6.16;
+library support was added to glibc in version 2.4.
.SH CONFORMING TO
-4.4BSD, SVr4, POSIX.1-2001.
+.BR chmod (),
+.BR fchmod ():
+4.4BSD, SVr4, POSIX.1-2001i, POSIX.1-2008.
+
+.BR fchmodat ():
+POSIX.1-2008.
+.SH NOTES
+.SS C library/kernel ABI differences
+The GNU C library
+.BR fchmodat ()
+wrapper function implements the POSIX-specified
+interface described in this page.
+This interface differs from the underlying Linux system call, which does
+.I not
+have a
+.I flags
+argument.
+.SS Glibc notes
+On older kernels where
+.BR fchmodat ()
+is unavailable, the glibc wrapper function falls back to the use of
+.BR chmod ().
+When
+.I pathname
+is a relative pathname,
+glibc constructs a pathname based on the symbolic link in
+.IR /proc/self/fd
+that corresponds to the
+.IR dirfd
+argument.
.SH SEE ALSO
.BR chown (2),
.BR execve (2),
-.BR fchmodat (2),
.BR open (2),
.BR stat (2),
-.BR path_resolution (7)
+.BR path_resolution (7),
+.BR symlink (7)
+.SH COLOPHON
+This page is part of release 3.79 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/.
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