chmod(2)

NAME

chmod, fchmod, lchmod - change mode of file

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/stat.h>
int
chmod(const char *path, modet_mode);
int
fchmod(int fd, modet_mode);
int
lchmod(const char *path, modet_mode);

DESCRIPTION

The file permission bits of the file named specified by path

or referenced by the file descriptor fd are changed to mode. The

chmod() system
call verifies that the process owner (user) either owns the

file specified by path (or fd), or is the super-user. The chmod()

system call follows symbolic links to operate on the target of the link

rather than the
link itself.

The lchmod() system call is similar to chmod() but does not

follow symbolic links.

A mode is created from or'd permission bit masks defined in

#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 execu

tion */
#ifndef BSD_VISIBLE
#define S_ISTXT 0001000 /* sticky bit */
#endif

The FreeBSD VM system totally ignores the sticky bit (ISTXT)

for executables. On UFS-based file systems (FFS, LFS) the sticky bit

may only be
set upon directories.

If mode ISTXT (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 sticky(8).

If mode ISUID (set UID) is set on a directory, and the

MNT_SUIDDIR option
was used in the mount of the file system, then the owner of

any new files
and sub-directories created within this directory are set to

be the same
as the owner of that directory. If this function is en

abled, new directories will inherit the bit from their parents. Execute

bits are removed
from the file, and it will not be given to root. This be

havior does not
change the requirements for the user to be allowed to write

the file, but
only the eventual owner after it has been created. Group

inheritance is
not affected.

This feature is designed for use on fileservers serving PC

users via ftp,
SAMBA, or netatalk. It provides security holes for shell

users and as
such should not be used on shell machines, especially on

home directories. This option requires the SUIDDIR option in the kernel

to work.
Only UFS file systems support this option. For more details

of the suiddir mount option, see mount(8).

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 modi

fied, at the
expense of a degree of compatibility.

RETURN VALUES

The function returns the value 0 if successful; otherwise

the value -1 is
returned and the global variable errno is set to indicate

the error.

ERRORS

The chmod() system call will fail and the file mode will be

unchanged if:

[ENOTDIR] A component of the path prefix is not a

directory.

[ENAMETOOLONG] A component of a pathname exceeded 255

characters, or

an entire path name exceeded 1023 charac

ters.

[ENOENT] The named file does not exist.

[EACCES] Search permission is denied for a compo

nent of the

path prefix.

[ELOOP] Too many symbolic links were encountered

in translat

ing the pathname.

[EPERM] The effective user ID does not match the

owner of the

file and the effective user ID is not the

super-user.

[EROFS] The named file resides on a read-only

file system.

[EFAULT] The path argument points outside the pro

cess's allo

cated address space.

[EIO] An I/O error occurred while reading from

or writing to

the file system.

[EFTYPE] An attempt was made to set the sticky bit

upon an exe

cutable.

The fchmod() system call will fail if:

[EBADF] The descriptor is not valid.

[EINVAL] The fd argument refers to a socket, not

to a file.

[EROFS] The file resides on a read-only file sys

tem.

[EIO] An I/O error occurred while reading from

or writing to

the file system.

SEE ALSO

chmod(1), chown(2), open(2), stat(2), sticky(8)

STANDARDS

The chmod() system call is expected to conform to ISO/IEC

9945-1:1990
(``POSIX.1''), except for the return of EFTYPE and the use

of S_ISTXT.

HISTORY

The chmod() function appeared in Version 7 AT&T UNIX. The

fchmod() system call appeared in 4.2BSD. The lchmod() system call ap

peared in
FreeBSD 3.0.

BSD December 29, 2004

BSD