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
   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'

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