chmod

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A Unix/Linux shell command to change file permissions.

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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 representing the bit pattern for the new permissions.

The format of a symbolic mode is `[ugoa...][[+-=][rwxXstugo...]...][,...]'. Multiple symbolic operations 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 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 permission 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 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.  

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 systems, and the Linux kernel ignores the sticky bit on files. Other kernels 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.

 

Index

NAME
SYNOPSIS
DESCRIPTION
STICKY FILES
STICKY DIRECTORIES
OPTIONS
AUTHOR
REPORTING BUGS
COPYRIGHT
SEE ALSO
Updated Time:: 05:48:33 GMT, August 30, 2008 
Chmod

Chmod ugoa =+- rwx filename

	WHO		
	U= user		
	G= group
	O= owner
	A= all

Or Chmod xxx filename

	R = 4		Read
	W = 2		Write
      	X = 1		Execute


Ie Chmod 744 file.ksh

	User can 	Read 		4
			Write 		+2
			Execute	        +1
					=7

	Group can 	Read		4

	Everyone can	Read		4


Wenn 4 Zahlen benutzt werden können noch weitere Sonderrecht vergeben werden.

Auch hier wird 1+2+4 addiert. 1 für "Rest der Welt", 2 für "Gruppe" und 4 für "Besitzer".


Substitute UserID Bit (SUID) "Wert": 4 - Besitzer

Dieses Recht gilt ausschließlich für ausführbare Dateien. Hat eine ausführbare Datei dieses Recht gesetzt, so erscheint in der Darstellung durch das ls -l Kommando statt dem x beim Eigentümerrecht ein s. Jeder User, der dieses Programm ausführt, tut dies unter der effektiven UserID des Users, dem die Datei geh?rt. 

$ chmod 4755 test
$ ls -lha test
-rwsr-xr-x  1 took took 0 Mär 15 23:20 test*


Substitute GroupID Bit (SGID) "Wert": 2 - Gruppe

Dieses Recht gilt einerseits für ausführbare Dateien und andererseits für Verzeichnisse. Hat ein ausführbares Programm dieses Recht gesetzt, so gilt der gleiche Mechanismus, wie beim Substitute UserID Bit, nur diesmal eben die Gruppenmitgliedschaft betreffend. Ein User, der dieses Programm ausführt, tut dies als Gruppenmitglied der Gruppe, der das Programm gehört, statt seiner eigentlichen Gruppenkennung. Er hat also die Rechte eines Gruppenmitglieds dieser Gruppe. 

$ ls -lha test
-rwxr-sr-x  1 took took 0 Mär 15 23:20 test*

Hat ein Verzeichnis dieses Recht gesetzt, dann liegt der Fall etwas anders. Legt ein User, der Schreibrecht auf ein Verzeichnis hat, in diesem Verzeichnis eine Datei an, so erh?lt diese Datei normalerweise die Gruppenmitgliedschaft der prim?ren Gruppe des Users, der sie eben angelegt hat. Das f?hrt schnell zum Chaos, wenn z.B. mehrere User zusammen an einem Projekt arbeiten. Alle diese User sind Gruppenmitglieder einer bestimmten Gruppe, aber sie haben diese...?!?! hundfred: pls continue


T "Wert": 1 -rest der Welt

da steht dann t bzw T.. wat dat bedeutet... wissema noch nich 

$ chmod 1755 test
$ ls -lha test
-rwxr-xr-t  1 took took 0 Mär 15 23:20 test*
$ chmod 1754 test
$ ls -lha test
-rwxr-xr-T  1 took took 0 Mär 15 23:20 test*


Absolute modes are octal numbers specifying the complete list of attributes for the files; you specify attributes by OR'ing together these bits. 

    01000000  temporary file
    02000000  compressed file
    04000000  sparse file
    4000      Hidden file (setuid bit)
    2000      System file (setgid bit)
    1000      Archive bit (sticky bit)
    0400      Individual read
    0200      Individual write
    0100      Individual execute (or list directory)
    0040      Group read
    0020      Group write
    0010      Group execute
    0004      Other read
    0002      Other write
    0001      Other execute

See also: POSIX_ACL

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