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Updated: July 2014

chmod (1g)


chmod - change file mode bits


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


User Commands                                            CHMOD(1)

     chmod - change file mode bits

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

     This  manual page documents the GNU version of chmod.  chmod
     changes the file mode bits 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 mode bits.

     The      format      of      a      symbolic     mode     is
     [ugoa...][[+-=][perms...]...], where perms is either zero or
     more  letters  from  the set rwxXst, or a single letter from
     the set ugo.  Multiple symbolic modes 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 selected  file  mode  bits  to  be
     added  to the existing file mode bits of each file; - causes
     them to be removed; and = causes them to be added and causes
     unmentioned  bits  to  be  removed except that a directory's
     unmentioned set user and group ID bits are not affected.

     The letters rwxXst select file mode bits  for  the  affected
     users:  read (r), write (w), execute (or search for directo-
     ries) (x), execute/search only if the file is a directory or
     already  has  execute permission for some user (X), set user
     or group ID on execution (s), restricted  deletion  flag  or
     sticky  bit  (t).   Instead of one or more of these letters,
     you can specify exactly one of the letters ugo: the  permis-
     sions granted to the user who owns the file (u), the permis-
     sions 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.
     Omitted digits are assumed to be leading zeros.   The  first
     digit  selects  the set user ID (4) and set group ID (2) and
     restricted deletion or sticky (1)  attributes.   The  second
     digit  selects  permissions  for the user who owns the file:

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User Commands                                            CHMOD(1)

     read (4), write (2), and execute (1); the third selects per-
     missions  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 symbolic 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.

     chmod  clears  the set-group-ID bit of a regular file if the
     file's group ID does not match the user's effective group ID
     or  one  of  the  user's supplementary group IDs, unless the
     user has appropriate  privileges.   Additional  restrictions
     may  cause  the set-user-ID and set-group-ID bits of MODE or
     RFILE to be ignored.  This behavior depends  on  the  policy
     and functionality of the underlying chmod system call.  When
     in doubt, check the underlying system behavior.

     chmod preserves a directory's set-user-ID  and  set-group-ID
     bits  unless  you explicitly specify otherwise.  You can set
     or clear the bits with symbolic modes like u+s and g-s,  and
     you can set (but not clear) the bits with a numeric mode.

     The  restricted deletion flag or sticky bit is a single bit,
     whose interpretation depends on the file type.  For directo-
     ries, it prevents unprivileged users from removing or renam-
     ing a file in the directory unless they own the file or  the
     directory;  this  is called the restricted deletion flag for
     the directory,  and  is  commonly  found  on  world-writable
     directories like /tmp.  For regular files on some older sys-
     tems, the bit saves the program's text  image  on  the  swap
     device so it will load more quickly when run; this is called
     the sticky bit.

     Change the mode of each FILE  to  MODE.   With  --reference,
     change the mode of each FILE to that of RFILE.

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

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

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

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User Commands                                            CHMOD(1)

          do not treat '/' specially (the default)

          fail to operate recursively on '/'

          use RFILE's mode instead of MODE values

     -R, --recursive
          change files and directories recursively

          display this help and exit

          output version information and exit

     Each         MODE        is        of        the        form

     Written by David MacKenzie and Jim Meyering.

     Report chmod bugs to
     GNU coreutils home page:  <
     General  help  using GNU software: <
     Report chmod  translation  bugs  to  <http://translationpro->

     Copyright  (C)  2012 Free Software Foundation, Inc.  License
     GPLv3+:     GNU     GPL     version     3      or      later
     This  is  free  software:  you are free to change and redis-
     tribute it.  There is NO WARRANTY, to the  extent  permitted
     by law.

     See   attributes(5)   for   descriptions  of  the  following

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User Commands                                            CHMOD(1)

     |Availability   | file/gnu-coreutils |
     |Stability      | Uncommitted        |

     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 invocation'

     should give you access to the complete manual.

     This  software  was   built   from   source   available   at    The  original
     community       source       was       downloaded       from

     Further  information about this software can be found on the
     open source community  website  at

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