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 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  preced‐
       ing 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 dig‐
       its 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 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  functional‐
       ity 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  directo‐
       ries,  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  directo‐
       ries  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@gnu.org
       GNU coreutils home page: 
       General help using GNU software: 
       Report chmod translation bugs to 

COPYRIGHT
       Copyright   ©   2011   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.

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 8.12.197-032bb				  September 2011						  CHMOD(1)