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CHMOD(1)                         User Commands                        CHMOD(1)



NAME
       chmod - change file mode bits

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 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  repre-
       senting 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, separated  by  com-
       mas.

       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
       directories)  (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 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 per-
       missions 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: 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 val-
       ues.

       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.

SETUID AND SETGID BITS
       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 underly-
       ing 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.

RESTRICTED DELETION FLAG OR STICKY BIT
       The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type.  For
       directories, it prevents unprivileged users from removing or renaming 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 systems, 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.

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 chmod bugs to bug-coreutilsATgnu.org
       GNU coreutils home page: <http://www.gnu.org/software/coreutils/>;
       General help using GNU software: <http://www.gnu.org/gethelp/>;
       Report chmod translation bugs to <http://translationproject.org/team/>;

COPYRIGHT
       Copyright   (C)   2010   Free   Software   Foundation,   Inc.   License  GPLv3+:  GNU  GPL  version  3  or  later
       <http://gnu.org/licenses/gpl.html>;.
       This is free software: you are free to change and redistribute it.  There is NO WARRANTY, to the extent permit-
       ted by law.

SEE ALSO
       chmod(2)

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

              info coreutils 'chmod invocation'

       should give you access to the complete manual.



GNU coreutils 8.4                 March 2017                          CHMOD(1)