CHMOD(1)		  BSD General Commands Manual		      CHMOD(1)

NAME
     chmod — change file modes

SYNOPSIS
     chmod [-fhv] [-R [-H | -L | -P]] mode file ...

DESCRIPTION
     The chmod utility modifies the file mode bits of the listed files as
     specified by the mode operand.

     The options are as follows:

     -f	     Do not display a diagnostic message if chmod could not modify the
	     mode for file, nor modify the exit status to reflect such fail‐
	     ures.

     -H	     If the -R option is specified, symbolic links on the command line
	     are followed.  (Symbolic links encountered in the tree traversal
	     are not followed by default.)

     -h	     If the file is a symbolic link, change the mode of the link
	     itself rather than the file that the link points to.

     -L	     If the -R option is specified, all symbolic links are followed.

     -P	     If the -R option is specified, no symbolic links are followed.
	     This is the default.

     -R	     Change the modes of the file hierarchies rooted in the files
	     instead of just the files themselves.

     -v	     Cause chmod to be verbose, showing filenames as the mode is modi‐
	     fied.  If the -v flag is specified more than once, the old and
	     new modes of the file will also be printed, in both octal and
	     symbolic notation.

     The -H, -L and -P options are ignored unless the -R option is specified.
     In addition, these options override each other and the command's actions
     are determined by the last one specified.

     Only the owner of a file or the super-user is permitted to change the
     mode of a file.

EXIT STATUS
     The chmod utility exits 0 on success, and >0 if an error occurs.

MODES
     Modes may be absolute or symbolic.	 An absolute mode is an octal number
     constructed from the sum of one or more of the following values:

	   4000	   (the setuid bit).  Executable files with this bit set will
		   run with effective uid set to the uid of the file owner.
		   Directories with this bit set will force all files and sub-
		   directories created in them to be owned by the directory
		   owner and not by the uid of the creating process, if the
		   underlying file system supports this feature: see chmod(2)
		   and the suiddir option to mount(8).
	   2000	   (the setgid bit).  Executable files with this bit set will
		   run with effective gid set to the gid of the file owner.
	   1000	   (the sticky bit).  See chmod(2) and sticky(8).
	   0400	   Allow read by owner.
	   0200	   Allow write by owner.
	   0100	   For files, allow execution by owner.	 For directories,
		   allow the owner to search in the directory.
	   0040	   Allow read by group members.
	   0020	   Allow write by group members.
	   0010	   For files, allow execution by group members.	 For directo‐
		   ries, allow group members to search in the directory.
	   0004	   Allow read by others.
	   0002	   Allow write by others.
	   0001	   For files, allow execution by others.  For directories
		   allow others to search in the directory.

     For example, the absolute mode that permits read, write and execute by
     the owner, read and execute by group members, read and execute by others,
     and no set-uid or set-gid behaviour is 755 (400+200+100+040+010+004+001).

     The symbolic mode is described by the following grammar:

	   mode		::= clause [, clause ...]
	   clause	::= [who ...] [action ...] action
	   action	::= op [perm ...]
	   who		::= a | u | g | o
	   op		::= + | - | =
	   perm		::= r | s | t | w | x | X | u | g | o

     The who symbols ``u'', ``g'', and ``o'' specify the user, group, and
     other parts of the mode bits, respectively.  The who symbol ``a'' is
     equivalent to ``ugo''.

     The perm symbols represent the portions of the mode bits as follows:

	   r	   The read bits.
	   s	   The set-user-ID-on-execution and set-group-ID-on-execution
		   bits.
	   t	   The sticky bit.
	   w	   The write bits.
	   x	   The execute/search bits.
	   X	   The execute/search bits if the file is a directory or any
		   of the execute/search bits are set in the original (unmodi‐
		   fied) mode.	Operations with the perm symbol ``X'' are only
		   meaningful in conjunction with the op symbol ``+'', and are
		   ignored in all other cases.
	   u	   The user permission bits in the original mode of the file.
	   g	   The group permission bits in the original mode of the file.
	   o	   The other permission bits in the original mode of the file.

     The op symbols represent the operation performed, as follows:

     +	   If no value is supplied for perm, the ``+'' operation has no
	   effect.  If no value is supplied for who, each permission bit spec‐
	   ified in perm, for which the corresponding bit in the file mode
	   creation mask (see umask(2)) is clear, is set.  Otherwise, the mode
	   bits represented by the specified who and perm values are set.

     -	   If no value is supplied for perm, the ``-'' operation has no
	   effect.  If no value is supplied for who, each permission bit spec‐
	   ified in perm, for which the corresponding bit in the file mode
	   creation mask is clear, is cleared.	Otherwise, the mode bits rep‐
	   resented by the specified who and perm values are cleared.

     =	   The mode bits specified by the who value are cleared, or, if no who
	   value is specified, the owner, group and other mode bits are
	   cleared.  Then, if no value is supplied for who, each permission
	   bit specified in perm, for which the corresponding bit in the file
	   mode creation mask is clear, is set.	 Otherwise, the mode bits rep‐
	   resented by the specified who and perm values are set.

     Each clause specifies one or more operations to be performed on the mode
     bits, and each operation is applied to the mode bits in the order speci‐
     fied.

     Operations upon the other permissions only (specified by the symbol ``o''
     by itself), in combination with the perm symbols ``s'' or ``t'', are
     ignored.

     The ``w'' permission on directories will permit file creation, reloca‐
     tion, and copy into that directory.  Files created within the directory
     itself will inherit its group ID.

EXAMPLES
     644	   make a file readable by anyone and writable by the owner
		   only.

     go-w	   deny write permission to group and others.

     =rw,+X	   set the read and write permissions to the usual defaults,
		   but retain any execute permissions that are currently set.

     +X		   make a directory or file searchable/executable by everyone
		   if it is already searchable/executable by anyone.

     755
     u=rwx,go=rx
     u=rwx,go=u-w  make a file readable/executable by everyone and writable by
		   the owner only.

     go=	   clear all mode bits for group and others.

     g=u-w	   set the group bits equal to the user bits, but clear the
		   group write bit.

COMPATIBILITY
     The -v option is non-standard and its use in scripts is not recommended.

SEE ALSO
     chflags(1), install(1), setfacl(1), chmod(2), stat(2), umask(2), fts(3),
     setmode(3), symlink(7), chown(8), mount(8), sticky(8)

STANDARDS
     The chmod utility is expected to be IEEE Std 1003.2 (“POSIX.2”) compati‐
     ble with the exception of the perm symbol “t” which is not included in
     that standard.

HISTORY
     A chmod command appeared in Version 1 AT&T UNIX.

BUGS
     There is no perm option for the naughty bits of a horse.

BSD			       January 26, 2009				   BSD

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