CHMOD(1)                     BSD Reference Manual                     CHMOD(1)

NAME
     chmod - change file modes

SYNOPSIS
     chmod [-R] 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:

     -R      Traverse a file hierarchy.  For each file that is of type direc-
             tory, chmod changes the mode of all files in the file hierarchy
             below it followed by the mode of the directory itself.

     Symbolic links are not indirected through, nor are their modes altered.

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

     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 by or'ing the following values:

           4000    set-user-ID-on-execution
           2000    set-group-ID-on-execution
           1000    sticky bit, see chmod(2)
           0400    read by owner
           0200    write by owner
           0100    execute (or search for directories) by owner
           0070    read, write, execute/search by group
           0007    read, write, execute/search by others

     The read, write, and execute/search values for group and others are en-
     coded as described for owner.

     The symbolic mode is described by the following grammar:

           mode         ::= clause [, clause ...]
           clause       ::= [who ...] [action ...] last_action
           action       ::= op [perm ...]
           last_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 oth-
     er parts of the mode bits, respectively.  The who symbol ``a'' is equiva-
     lent 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 it
                   is ignored in all other cases.

     The op symbols represent the operation performed, as follows:

     +     If no value is supplied for perm, the ``+'' operation has no ef-
           fect.  If no value is supplied for who, each permission bit speci-
           fied in perm, for which the corresponding bit in the file mode cre-
           ation mask 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 ef-
           fect.  If no value is supplied for who, the mode bits represented
           by perm are cleared for the owner, group and other permissions.
           Otherwise, the mode bits represented 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 ig-
     nored.

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 writeable
                   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.

BUGS
     There's no perm option for the naughty bits.

SEE ALSO
     install(1),  chmod(2),  stat(2),  umask(2),  fts(3),  setmode(3),
     chown(8)

STANDARDS
     The chmod utility is expected to be IEEE Std1003.2 (``POSIX'') compatible
     with the exception of the perm symbols ``t'' and ``X'' which are not in-
     cluded in that standard.