Linux chmod command man page

This page shows the contents of the Linux chmod comamnd man page. This chmod command output was created on a CentOS Linux system.

You can see this same chmod command man page output by entering this command on your own Linux system:

man chmod

Linux chmod command man page

CHMOD(1)			 User Commands			      CHMOD(1)



NAME
       chmod - change file access permissions

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
       permissions of each given file according to mode, which can be either a
       symbolic	 representation	 of changes to make, or an octal number repre-
       senting the bit pattern for the new permissions.

       The   format   of   a   symbolic	  mode	 is    ‘[ugoa...][[+-=][rwxXs-
       tugo...]...][,...]’.   Multiple symbolic operations 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 permissions selected to  be	added  to  the
       existing	 permissions  of each file; ‘-’ causes them to be removed; and
       ‘=’ causes them to be the only permissions that the file has.

       The letters ‘rwxXstugo’ select the new  permissions  for	 the  affected
       users:  read  (r),  write (w), execute (or access for directories) (x),
       execute only if the file is a directory or already has execute  permis-
       sion  for  some user (X), set user or group ID on execution (s), sticky
       (t), 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.   Any  omitted  digits  are
       assumed	to  be leading zeros.  The first digit selects the set user ID
       (4) and set group ID (2) and 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.

STICKY FILES
       On  older  Unix	systems,  the sticky bit caused executable files to be
       hoarded in swap space.  This feature is not useful on  modern  VM  sys-
       tems, and the Linux kernel ignores the sticky bit on files.  Other ker-
       nels may use the sticky bit on files for system-defined	purposes.   On
       some systems, only the superuser can set the sticky bit on files.

STICKY DIRECTORIES
       When  the sticky bit is set on a directory, files in that directory may
       be unlinked or renamed only by root or their owner.  Without the sticky
       bit,  anyone able to write to the directory can delete or rename files.
       The sticky bit is commonly found on directories, such as /tmp, that are
       world-writable.

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 bugs to <bug-coreutils@gnu.org>.

COPYRIGHT
       Copyright 2006 Free Software Foundation, Inc.
       This  is	 free  software.   You may redistribute copies of it under the
       terms	  of	  the	   GNU	    General	  Public       License
       <http://www.gnu.org/licenses/gpl.html>.	 There	is NO WARRANTY, to the
       extent permitted by law.

SEE ALSO
       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 chmod

       should give you access to the complete manual.


chmod 5.97			 January 2009			      CHMOD(1)

This chmod command man page is included here so we can reference it directly from other chmod command tutorials.