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.TH FCHMODAT 2 2012-05-22 "Linux" "Linux Programmer's Manual"
.SH NAME
fchmodat \- change permissions of a file relative to a directory \
file descriptor
.SH SYNOPSIS
.nf
.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)):
.in
.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
.SH DESCRIPTION
The
.BR fchmodat ()
system call operates in exactly the same way as
.BR chmod (2),
except for the differences described in this manual page.

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 (2)
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 (2)).

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.
.SH RETURN VALUE
On success,
.BR fchmodat ()
returns 0.
On error, \-1 is returned and
.I errno
is set to indicate the error.
.SH ERRORS
The same errors that occur for
.BR chmod (2)
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
POSIX.1-2008.
.SH NOTES
See
.BR openat (2)
for an explanation of the need for
.BR fchmodat ().

The GNU C library 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.
.SH SEE ALSO
.BR chmod (2),
.BR openat (2),