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.\"     @(#)chmod.2	8.1 (Berkeley) 6/4/93
.\"
.TH CHMOD 2 "22 February 1996" GNO "System Calls"
.SH NAME
.BR chmod ,
.BR fchmod
\- change mode of file
.SH SYNOPSIS
#include <sys/stat.h>
.sp 1
int
\fBchmod\fR (const char *\fIpath\fR, mode_t \fImode\fR);
.br
int
\fBfchmod\fR (int \fIfd\fR, mode_t \fImode\fR);
.SH DESCRIPTION
The function
.BR chmod 
sets the file permission bits
of the file
specified by the pathname
.I path
to
.IR mode .
.BR fchmod 
sets the permission bits of the specified
file descriptor
.IR fd .
.BR chmod 
verifies that the process owner (user) either owns
the file specified by
.I path
(or
.IR fd )
or
is the super-user.
A mode is created from
.IR or'd  
permission bit masks
defined in <sys/stat.h>:
.nf

#define S_IRWXU 0000700    /* RWX mask for owner */
#define S_IRUSR 0000400    /* R for owner */
#define S_IWUSR 0000200    /* W for owner */
#define S_IXUSR 0000100    /* X for owner */

#define S_IRWXG 0000070    /* RWX mask for group */
#define S_IRGRP 0000040    /* R for group */
#define S_IWGRP 0000020    /* W for group */
#define S_IXGRP 0000010    /* X for group */

#define S_IRWXO 0000007    /* RWX mask for other */
#define S_IROTH 0000004    /* R for other */
#define S_IWOTH 0000002    /* W for other */
#define S_IXOTH 0000001    /* X for other */

#define S_ISUID 0004000    /* set user id on execution */
#define S_ISGID 0002000    /* set group id on execution */
#define S_ISVTX 0001000    /* save swapped text even after use */
.fi
.LP
The
.BR ISVTX
(the
.IR sticky
bit )
indicates to the system which executable files are shareable (the
default) and the system maintains the program text of the files
in the swap area. The sticky bit may only be set by the super user
on shareable executable files.
.LP
If mode
.BR ISVTX
(the `sticky bit') is set on a directory,
an unprivileged user may not delete or rename
files of other users in that directory. The sticky bit may be
set by any user on a directory which the user owns or has appropriate
permissions.
For more details of the properties of the sticky bit, see
.BR sticky (8).
.LP
Writing or changing the owner of a file
turns off the set-user-id and set-group-id bits
unless the user is the super-user.
This makes the system somewhat more secure
by protecting set-user-id (set-group-id) files
from remaining set-user-id (set-group-id) if they are modified,
at the expense of a degree of compatibility.
.SH COMPATIBILITY
The ORCA/C implementation of 
.BR chmod
interprets
.IR mode
as GS/OS access bits.  In order to get this behavior with the GNO 
implementation, mode mapping must be turned off (see
.BR mapMode (3)).
.LP
Under GNO, if UNIX mode mapping is in effect, and the file type 
is either TXT or SRC, and the 
.BR S_IXUSR
bit in
.IR mode
is set, then the file is changed into a shell script by setting the
file type to SRC and the auxilliary file type to EXEC.
.SH RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and
.IR errno
is set to indicate the error.
.SH BUGS
Verification of the ownership of the target file is not currently checked
under GNO.  (This would matter only for Appleshare volumes.)
.LP
Due to GNO's underlying filesystems, the sticky bit is not implemented.
.SH SEE ALSO
.BR chmod (1),
.BR open (2),
.BR chown (2),
.BR stat (2),
.BR sticky (8)
.SH STANDARDS
.BR chmod 
is expected to conform to IEEE Std 1003.1-1988 (POSIX).
.SH HISTORY
The
.BR fchmod 
function call
appeared in 4.2BSD.