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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 represen-
       tation  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, 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 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 permis-
       sions 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.  Omitted digits are assumed to be leading zeros.  The
       first digit selects the set user ID (4) and set group ID (2) and  restricted  dele-
       tion  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  permis-
       sions 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 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 underlying system behavior.

       chmod  preserves a directory's set-user-ID and set-group-ID bits unless you explic-
       itly 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 direc-
       tory; this is called the restricted deletion flag for the directory,  and  is  com-
       monly  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-coreutils AT gnu.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 permitted by law.

SEE ALSO
       chmod(2)

       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.



GNU coreutils 8.4                 March 2017                          CHMOD(1)

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