Name
chmod, fchmod — change permissions of a file
Synopsis
int
chmod( |
const char * |
path, |
| |
mode_t |
mode); |
int
fchmod( |
int |
fildes, |
| |
mode_t |
mode); |
DESCRIPTION
The mode of the file given by path or referenced by
fildes is
changed.
Modes are specified by or'ing the following:
S_ISUID-
04000 set user ID on execution
S_ISGID-
02000 set group ID on execution
S_ISVTX-
01000 sticky bit
S_IRUSR-
00400 read by owner
S_IWUSR-
00200 write by owner
S_IXUSR-
00100 execute/search by owner
S_IRGRP-
00040 read by group
S_IWGRP-
00020 write by group
S_IXGRP-
00010 execute/search by group
S_IROTH-
00004 read by others
S_IWOTH-
00002 write by others
S_IXOTH-
00001 execute/search by others
The effective UID of the calling process must match the
owner of the file, or the process must be privileged (Linux:
it must have the CAP_FOWNER
capability).
If the calling process is not privileged (Linux: does not
have the CAP_FSETID
capability), 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.
As a security measure, depending on the file system, the
set-user-ID and set-group-ID execution bits may be turned off
if a file is written. (On Linux this occurs if the writing
process does not have the CAP_FSETID capability.) On some file
systems, only the superuser can set the sticky bit, which may
have a special meaning. For the sticky bit, and for
set-user-ID and set-group-ID bits on directories, see
stat(2).
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.
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
ERRORS
Depending on the file system, other errors can be
returned. The more general errors for chmod() are listed below:
- EACCES
-
Search permission is denied on a component of the
path prefix. (See also path_resolution(7).)
- EFAULT
-
path points
outside your accessible address space.
- EIO
-
An I/O error occurred.
- ELOOP
-
Too many symbolic links were encountered in
resolving path.
- ENAMETOOLONG
-
path is too
long.
- ENOENT
-
The file does not exist.
- ENOMEM
-
Insufficient kernel memory was available.
- ENOTDIR
-
A component of the path prefix is not a
directory.
- EPERM
-
The effective UID does not match the owner of the
file, and the process is not privileged (Linux: it does
not have the CAP_FOWNER
capability).
- EROFS
-
The named file resides on a read-only file
system.
The general errors for fchmod() are listed below:
- EBADF
-
The file descriptor fildes is not valid.
- EIO
-
See above.
- EPERM
-
See above.
- EROFS
-
See above.
CONFORMING TO
4.4BSD, SVr4, POSIX.1-2001.
SEE ALSO
chown(2), execve(2), fchmodat(2), open(2), stat(2), path_resolution(7)
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 1993-07-21 by Rik Faith <faith@cs.unc.edu>
Modified 1997-01-12 by Michael Haardt
<michael@cantor.informatik.rwth-aachen.de>: NFS details
Modified 2004-06-23 by Michael Kerrisk <mtk-manpages@gmx.net>
|
