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.TH FCHMODAT 2 2006-05-05 "Linux 2.6.16" "Linux Programmer's Manual"
.SH NAME
fchmodat \- change permissions of a file relative to a directory \
file descriptor
.SH SYNOPSIS
.nf
.B #include <sys/stat.h>
.sp
.BI "int fchmodat(int " dirfd ", const char *" path ", mode_t " \
mode ", int " flags );
.fi
.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 path
is relative, then it is interpreted relative to the directory
referred to by the file descriptor
.IR 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 the pathname given in 
.I path
is relative and 
.I dirfd
is the special value
.BR AT_FDCWD ,
then
.I path
is interpreted relative to the current working 
directory of the calling process (like
.BR chmod (2)).

If the pathname given in
.IR path
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 path 
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 path
is a relative path and
.I dirfd
is a file descriptor referring to a file other than a directory.
.TP
.B ENOTSUP
.IR flags 
specified
.BR AT_SYMLINK_NOFOLLOW ,
which is not supported.
.SH NOTES
See
.BR openat (2)
for an explanation of the need for
.BR fchmodat ().
.SH "CONFORMING TO"
This system call is non-standard but is proposed
for inclusion in a future revision of POSIX.1.
.SH VERSIONS
.BR fchmodat ()
was added to Linux in kernel 2.6.16.
.SH "SEE ALSO"
.BR chmod (2),
.BR openat (2),
.BR path_resolution (2)