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 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 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.   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 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 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.  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

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

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

       --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]))+|[-+=][0-7]+'.

AUTHOR

       Written by David MacKenzie and Jim Meyering.

REPORTING BUGS

       GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
       Report chmod translation bugs to <http://translationproject.org/team/>

COPYRIGHT

       Copyright © 2016 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)

       Full documentation at: <http://www.gnu.org/software/coreutils/chmod>
       or available locally via: info '(coreutils) chmod invocation'