CHMOD(1)                                  User Commands                                  CHMOD(1)



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 representing the bit pattern for the new permissions.

       The format of a symbolic mode is '[ugoa...][[+-=][rwxXstugo...]...][,...]'.  Multiple sym-
       bolic operations can be given, separated 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 permis-
       sions 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 permission 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 val-
       ues; 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 symbolic link listed on the command line, chmod changes the
       permissions of the pointed-to file.  In contrast, chmod ignores symbolic links encountered
       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 systems, and the Linux kernel ignores the sticky
       bit on files.  Other kernels 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 one or more of the letters ugoa, one of the symbols +-= and one  or  more  of
       the letters rwxXstugo.

AUTHOR
       Written by David MacKenzie and Jim Meyering.

REPORTING BUGS
       Report bugs to <>.

COPYRIGHT
       Copyright (C) 2004 Free Software Foundation, Inc.
       This  is  free software; see the source for copying conditions.  There is NO warranty; not
       even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

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 coreutils chmod

       should give you access to the complete manual.



chmod (coreutils) 5.2.1                   November 2008                                  CHMOD(1)