chmod man page on aLinux

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CHMOD(1)			 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 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	 dele‐
       tion  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

       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 sym‐
       bolic 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 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.

       Change the mode of each FILE to MODE.

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

	      do not treat `/' specially (the default)

	      fail to operate recursively on `/'

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

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

	      use RFILE's mode instead of MODE values

       -R, --recursive
	      change files and directories recursively

       --help display this help and exit

	      output version information and exit

       Each MODE is of the form `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.

       Written by David MacKenzie and Jim Meyering.

       Report bugs to <>.

       Copyright © 2008 Free Software Foundation, Inc.	 License  GPLv3+:  GNU
       GPL version 3 or later <>
       This  is	 free  software:  you  are free to change and redistribute it.
       There is NO WARRANTY, to the extent permitted by law.


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

	      info chmod

       should give you access to the complete manual.

GNU coreutils 2008			      CHMOD(1)

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