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fchmod(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, mode_t mode);

     int
     fchmod(int fd, mode_t mode);

     int
     lchmod(const char *path, mode_t mode);

DESCRIPTION

     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.

     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 */
	   #endif

     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
     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.

RETURN VALUES

     Upon successful completion, the value 0 is returned; 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 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.

     [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]		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.

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() sys-
     tem call appeared in 4.2BSD.  The lchmod() system call appeared in
     FreeBSD 3.0.

FreeBSD 5.4		       December 29, 2004		   FreeBSD 5.4

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