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CHMOD(2)		    BSD	System Calls Manual		      CHMOD(2)

     chmod, fchmod, lchmod, fchmodat --	change mode of file

     Standard C	Library	(libc, -lc)

     #include <sys/stat.h>

     chmod(const char *path, mode_t mode);

     fchmod(int	fd, mode_t mode);

     lchmod(const char *path, mode_t mode);

     fchmodat(int fd, const char *path,	mode_t mode, int flag);

     The file permission bits of the file named	specified by path or refer-
     enced by the file descriptor fd are changed to mode.  The chmod() system
     call verifies that	the process owner (user) either	owns the file speci-
     fied by path (or fd), or is the super-user.  The chmod() system call fol-
     lows 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	sym-
     bolic links.

     The fchmodat() is equivalent to either chmod() or lchmod()	depending on
     the flag except in	the case where path specifies a	relative path.	In
     this case the file	to be changed is determined relative to	the directory
     associated	with the file descriptor fd instead of the current working di-
     rectory.  The values for the flag are constructed by a bitwise-inclusive
     OR	of flags from the following list, defined in <fcntl.h>:

	     If	path names a symbolic link, then the mode of the symbolic link
	     is	changed.

     If	fchmodat() is passed the special value AT_FDCWD	in the fd parameter,
     the current working directory is used.  If	also flag is zero, the behav-
     ior is identical to a call	to chmod().

     A mode is created from or'd permission bit	masks defined in <sys/stat.h>:

	   #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 */
	   #ifndef __BSD_VISIBLE
	   #define S_ISTXT 0001000    /* sticky	bit */

     The FreeBSD VM system totally ignores the sticky bit (ISTXT) for executa-
     bles.  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(7).

     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 enabled, new direc-
     tories will inherit the bit from their parents.  Execute bits are removed
     from the file, and	it will	not be given to	root.  This behavior 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 directo-
     ries.  This option	requires the SUIDDIR option in the kernel to work.
     Only UFS file systems support this	option.	 For more details of the suid-
     dir 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 sys-
     tem 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.

     Upon successful completion, the value 0 is	returned; otherwise the
     value -1 is returned and the global variable errno	is set to indicate the

     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 characters.

     [ENOENT]		The named file does not	exist.

     [EACCES]		Search permission is denied for	a component 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.

     [EPERM]		The effective user ID is not the super-user, the ef-
			fective	user ID	do match the owner of the file,	but
			the group ID of	the file does not match	the effective
			group ID nor one of the	supplementary group IDs.

     [EPERM]		The named file has its immutable or append-only	flag
			set, see the chflags(2)	manual page for	more informa-

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

     [EFAULT]		The path argument points outside the process's allo-
			cated address space.

     [EIO]		An I/O error occurred while reading from or writing to
			the file system.

     [EFTYPE]		The effective user ID is not the super-user, the mode
			includes the sticky bit	(S_ISVTX), and path does not
			refer to a directory.

     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 system.

     [EIO]		An I/O error occurred while reading from or writing to
			the file system.

     In	addition to the	chmod()	errors,	fchmodat() fails if:

     [EBADF]		The path argument does not specify an absolute path
			and the	fd argument is neither AT_FDCWD	nor a valid
			file descriptor	open for searching.

     [EINVAL]		The value of the flag argument is not valid.

     [ENOTDIR]		The path argument is not an absolute path and fd is
			neither	AT_FDCWD nor a file descriptor associated with
			a directory.

     chmod(1), chflags(2), chown(2), open(2), stat(2), sticky(7)

     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.  The
     fchmodat()	system call follows The	Open Group Extended API	Set 2 specifi-

     The chmod() function appeared in Version 7	AT&T UNIX.  The	fchmod() sys-
     tem call appeared in 4.2BSD.  The lchmod()	system call appeared in
     FreeBSD 3.0.  The fchmodat() system call appeared in FreeBSD 8.0.

BSD				April 10, 2008				   BSD


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