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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Modified by Michael Haardt (michael@moria.de)
.\" Modified Wed Jul 21 20:18:11 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified Sun Jan 12 14:31:17 MET 1997 by Michael Haardt
.\" (michael@cantor.informatik.rwth-aachen.de): NFS details
.\"
.TH CHMOD 2 "10 December 1997" "Linux 2.0.32" "Linux Programmer's Manual"
.SH NAME
chmod, fchmod \- change permissions of a file
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <sys/stat.h>
.sp
.BI "int chmod(const char *" path ", mode_t " mode );
.br
.BI "int fchmod(int " fildes ", mode_t " mode );
.SH DESCRIPTION
The mode of the file given by
.I path
or referenced by
.I fildes
is changed.
Modes are specified by
.IR or'ing
the following:
.RS
.sp
.TP 1.0i
S_ISUID
04000 set user ID on execution
.TP
S_ISGID
02000 set group ID on execution
.TP
S_ISVTX
01000 sticky bit
.TP
S_IRUSR (S_IREAD)
00400 read by owner
.TP
S_IWUSR (S_IWRITE)
00200 write by owner
.TP
S_IXUSR (S_IEXEC)
00100 execute/search by owner
.TP
S_IRGRP
00040 read by group
.TP
S_IWGRP
00020 write by group
.TP
S_IXGRP
00010 execute/search by group
.TP
S_IROTH
00004 read by others
.TP
S_IWOTH
00002 write by others
.TP
S_IXOTH
00001 execute/search by others
.sp
.RE
The effective UID of the process must be zero or must match the owner of
the file.
If the effective UID of the process is not zero and the group of the file
does not match the effective group ID of the process or one of its
supplementary group IDs, the S_ISGID bit will be turned off,
but this will not cause an error to be returned.
Depending on the file system, set user ID and set group ID execution bits
may be turned off if a file is written. On some file systems, only the
super-user can set the sticky bit, which may have a special meaning (e.g.,
for directories, a file can only be deleted by the owner or the super-user).
On NFS file systems, restricting the permissions will immediately influence
already open files, because the access control is done on the server, but
open files are maintained by the client. Widening the permissions may be
delayed for other clients if attribute caching is enabled on them.
.SH "RETURN VALUE"
On success, zero is returned. On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
Depending on the file system, other errors can be returned. The more
general errors for
.B chmod
are listed below:
.TP
.B EPERM
The effective UID does not match the owner of the file, and is not zero.
.TP
.B EROFS
The named file resides on a read-only file system.
.TP
.B EFAULT
.I path
points outside your accessible address space.
.TP
.B ENAMETOOLONG
.I path
is too long.
.TP
.B ENOENT
The file does not exist.
.TP
.B ENOMEM
Insufficient kernel memory was available.
.TP
.B ENOTDIR
A component of the path prefix is not a directory.
.TP
.B EACCES
Search permission is denied on a component of the path prefix.
.TP
.B ELOOP
Too many symbolic links were encountered in resolving
.IR path .
.TP
.B EIO
An I/O error occurred.
.PP
The general errors for
.B fchmod
are listed below:
.TP
.B EBADF
The file descriptor
.I fildes
is not valid.
.TP
.B EROFS
See above.
.TP
.B EPERM
See above.
.TP
.B EIO
See above.
.SH "CONFORMING TO"
The
.B chmod
call conforms to SVr4, SVID, POSIX, X/OPEN, 4.4BSD.
SVr4 documents EINTR, ENOLINK and EMULTIHOP returns, but no
ENOMEM. POSIX.1 does not document EFAULT, ENOMEM, ELOOP or EIO error
conditions, or the macros \fBS_IREAD\fP, \fBS_IWRITE\fP and \fBS_IEXEC\fP.
.PP
The
.B fchmod
call conforms to 4.4BSD and SVr4.
SVr4 documents additional EINTR and ENOLINK error conditions.
POSIX requires the
.B fchmod
function if at least one of
.B _POSIX_MAPPED_FILES
and
.B _POSIX_SHARED_MEMORY_OBJECTS
is defined, and documents additional ENOSYS and EINVAL error
conditions, but does not document EIO.
.PP
POSIX and X/OPEN do not document the sticky bit.
.SH "SEE ALSO"
.BR open (2),
.BR chown (2),
.BR execve (2),
.BR stat (2)
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