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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 accord-
ing to mode, which can be either a symbolic representa-
tion of changes to make, or an octal number representing
the bit pattern for the new permissions.
The format of a symbolic mode is `[ugoa...][[+-=][rwxXs-
tugo...]...][,...]'. 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 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.
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 permis-
sions 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 permis-
sions 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@gnu.org>.
COPYRIGHT
Copyright (C) 2004 Free Software Foundation, Inc.
This is free software; see the source for copying condi-
tions. There is NO warranty; not even for MERCHANTABIL-
ITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
The full documentation for chmod is maintained as a Tex-
info manual. If the info and chmod programs are prop-
erly installed at your site, the command
info chmod
should give you access to the complete manual.
chmod 5.3.0 November 2004 CHMOD(1)
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