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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 representing the bit pattern for the new
permissions.
The format of a symbolic mode is ‘[ugoa...][[+-=][rwxXstugo...]...][,...]’. Multi-
ple 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 per-
missions 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 pre-
ceding 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 one or more of the letters ugoa, one of the symbols +-= and one or
more of the letters rwxXstugo.
AUTHOR
Written by David MacKenzie and Jim Meyering.
REPORTING BUGS
Report bugs to <bug-coreutils AT gnu.org>.
COPYRIGHT
Copyright © 2004 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO war-
ranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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 coreutils chmod
should give you access to the complete manual.
chmod (coreutils) 5.2.1 July 2005 CHMOD(1)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2009-01-08 06:45 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)