'\" et
.TH FCHMOD "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
fchmod
\(em change mode of a file
.SH SYNOPSIS
.LP
.nf
#include <sys/stat.h>
.P
int fchmod(int \fIfildes\fP, mode_t \fImode\fP);
.fi
.SH DESCRIPTION
The
\fIfchmod\fR()
function shall be equivalent to
\fIchmod\fR()
except that the file whose permissions are changed is specified
by the file descriptor
.IR fildes .
.P
If
.IR fildes
references a shared memory object, the
\fIfchmod\fR()
function need only affect the S_IRUSR, S_IWUSR, S_IRGRP, S_IWGRP,
S_IROTH, and S_IWOTH file permission bits.
.P
If
.IR fildes
references a typed memory object, the behavior of
\fIfchmod\fR()
is unspecified.
.P
If
.IR fildes
refers to a socket, the behavior of
\fIfchmod\fR()
is unspecified.
.P
If
.IR fildes
refers to a STREAM (which is
\fIfattach\fR()-ed
into the file system name space) the call returns successfully, doing
nothing.
.SH "RETURN VALUE"
Upon successful completion,
\fIfchmod\fR()
shall return 0. Otherwise, it shall return \-1 and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIfchmod\fR()
function shall fail if:
.TP
.BR EBADF
The
.IR fildes
argument is not an open file descriptor.
.TP
.BR EPERM
The effective user ID does not match the owner of the file and the
process does not have appropriate privileges.
.TP
.BR EROFS
The file referred to by
.IR fildes
resides on a read-only file system.
.P
The
\fIfchmod\fR()
function may fail if:
.TP
.BR EINTR
The
\fIfchmod\fR()
function was interrupted by a signal.
.TP
.BR EINVAL
The value of the
.IR mode
argument is invalid.
.TP
.BR EINVAL
The
.IR fildes
argument refers to a pipe and the implementation disallows execution of
\fIfchmod\fR()
on a pipe.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
.SS "Changing the Current Permissions for a File"
.P
The following example shows how to change the permissions for a
file named
.BR /home/cnd/mod1
so that the owner and group have read/write/execute permissions, but
the world only has read/write permissions.
.sp
.RS 4
.nf

#include <sys/stat.h>
#include <fcntl.h>
.P
mode_t mode;
int    fildes;
\&...
fildes = open("/home/cnd/mod1", O_RDWR);
fchmod(fildes, S_IRWXU | S_IRWXG | S_IROTH | S_IWOTH);
.fi
.P
.RE
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIchmod\fR\^(\|)",
.IR "\fIchown\fR\^(\|)",
.IR "\fIcreat\fR\^(\|)",
.IR "\fIfcntl\fR\^(\|)",
.IR "\fIfstatat\fR\^(\|)",
.IR "\fIfstatvfs\fR\^(\|)",
.IR "\fImknod\fR\^(\|)",
.IR "\fIopen\fR\^(\|)",
.IR "\fIread\fR\^(\|)",
.IR "\fIwrite\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<sys_stat.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .