chmod(2)

NAME

       chmod - change file access permissions

SYNOPSIS

       chmod [OPTION]... MODE[,MODE]... FILE...
       chmod [OPTION]... OCTAL-MODE FILE...
       chmod [OPTION]... --reference=RFILE FILE...

DESCRIPTION

       This manual page documents the GNU version of chmod.  chmod changes the
       permissions of each given file according to mode, which can be either a
       symbolic  representation  of changes to make, or an octal number repre-
       senting the bit pattern for the new permissions.

       The   format   of   a   symbolic   mode   is    `[ugoa...][[+-=][rwxXs-
       tugo...]...][,...]'.   Multiple symbolic operations can be given, sepa-
       rated by commas.

       A combination of the letters `ugoa' controls which users' access to the
       file  will  be  changed:  the  user who owns it (u), other users in the
       file's group (g), other users not in the file's group (o), or all users
       (a).   If  none of these are given, the effect is as if `a' were given,
       but bits that are set in the umask are not affected.

       The operator `+' causes the permissions selected to  be  added  to  the
       existing  permissions  of each file; `-' causes them to be removed; and
       `=' causes them to be the only permissions that the file has.

       The letters `rwxXstugo' select the new  permissions  for  the  affected
       users:  read  (r),  write (w), execute (or access for directories) (x),
       execute only if the file is a directory or already has execute  permis-
       sion  for  some user (X), set user or group ID on execution (s), sticky
       (t), the permissions granted to the user who owns  the  file  (u),  the
       permissions  granted to other users who are members of the file's group
       (g), and the permissions granted to users that are in  neither  of  the
       two preceding categories (o).

       A  numeric  mode  is  from  one  to four octal digits (0-7), derived by
       adding up the bits with values 4, 2, and 1.   Any  omitted  digits  are
       assumed  to  be leading zeros.  The first digit selects the set user ID
       (4) and set group ID (2) and sticky (1) attributes.  The  second  digit
       selects  permissions  for  the  user who owns the file: read (4), write
       (2), and execute (1); the third selects permissions for other users  in
       the  file's group, with the same values; and the fourth for other users
       not in the file's group, with the same values.

       chmod never changes the permissions of symbolic links; the chmod system
       call  cannot change their permissions.  This is not a problem since the
       permissions of symbolic links are never used.  However, for  each  sym-
       bolic link listed on the command line, chmod changes the permissions of
       the pointed-to file.  In contrast, chmod ignores symbolic links encoun-
       tered during recursive directory traversals.

STICKY FILES

       On  older  Unix  systems,  the sticky bit caused executable files to be
       hoarded in swap space.  This feature is not useful on  modern  VM  sys-
       tems, and the Linux kernel ignores the sticky bit on files.  Other ker-
       nels may use the sticky bit on files for system-defined  purposes.   On
       some systems, only the superuser can set the sticky bit on files.

STICKY DIRECTORIES

       When  the sticky bit is set on a directory, files in that directory may
       be unlinked or renamed only by root or their owner.  Without the sticky
       bit,  anyone able to write to the directory can delete or rename files.
       The sticky bit is commonly found on directories, such as /tmp, that are
       world-writable.

OPTIONS

       Change the mode of each FILE to MODE.

       -c, --changes
              like verbose but report only when a change is made

       --no-preserve-root
              do not treat `/' specially (the default)

       --preserve-root
              fail to operate recursively on `/'

       -f, --silent, --quiet
              suppress most error messages

       -v, --verbose
              output a diagnostic for every file processed

       --reference=RFILE
              use RFILE's mode instead of MODE values

       -R, --recursive
              change files and directories recursively

       --help display this help and exit

       --version
              output version information and exit

       Each MODE is of the form `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.

AUTHOR

       Written by David MacKenzie and Jim Meyering.

REPORTING BUGS

       Report bugs to <bug-coreutils@gnu.org>.

COPYRIGHT

       Copyright (C) 2005 Free Software Foundation, Inc.
       This  is  free  software.   You may redistribute copies of it under the
       terms      of      the      GNU      General       Public       License
       <http://www.gnu.org/licenses/gpl.html>.   There  is NO WARRANTY, to the
       extent permitted by law.

SEE ALSO

       The full documentation for chmod is maintained as a Texinfo manual.  If
       the  info  and  chmod programs are properly installed at your site, the
       command

              info chmod

       should give you access to the complete manual.

chmod 5.93                       November 2005                        CHMOD(1)