permissions

SYNOPSIS
chmod -fR file...
chmod -fR file...

DESCRIPTION
chmod changes or assigns the mode of a file. The mode of a file specifies its permissions and other attributes. The mode may be absolute or symbolic.
Absolute mode
An absolute mode is specified using octal numbers:
chmod nnnn file ...
where:
n
a number from 0 to 7. An absolute mode is constructed from the OR of any of the following modes:
4000
Set user ID on execution.
20#0
Set group ID on execution if # is 7, 5, 3, or 1. Enable mandatory locking if # is 6, 4, 2, or 0. For directories, files are created with BSD semantics for propagation of the group ID. With this option, files and subdirectories created in the directory inherit the group ID of the directory, rather than of the current process. It may be cleared only by using symbolic mode.
1000
Turn on sticky bit. See chmod(2).
0400
Allow read by owner.
0200
Allow write by owner.
0100
Allow execute (search in directory) by owner.
0700
Allow read, write, and execute (search) by owner.
0040
Allow read by group.
0020
Allow write by group.
0010
Allow execute (search in directory) by group.
0070
Allow read, write, and execute (search) by group.
0004
Allow read by others.
0002
Allow write by others.
0001
Allow execute (search in directory) by others.
0007
Allow read, write, and execute (search) by others.
Note that the setgid bit cannot be set (or cleared) in absolute mode; it must be set (or cleared) in symbolic mode using g+s (or g-s).
Symbolic mode
A symbolic mode specification has the following format:
chmod file...
where: is a comma-separated list (with no intervening whitespace) of symbolic mode expressions of the form:
who operator permissions
Operations are performed in the order given. Multiple permissions letters following a single operator cause the corresponding operations to be performed simultaneously.
who
zero or more of the characters u, g, o, and a specifying whose permissions are to be changed or assigned:
u
user's permissions
g
group's permissions
o
others' permissions
a
all permissions (user, group, and other)
If who is omitted, it defaults to a, but the setting of the file mode creation mask (see umask in sh(1) or csh(1) for more information) is taken into account. When who is omitted, chmod will not override the restrictions of your user mask.
operator either +, -, or =, signifying how permissions are to be changed:
+
Add permissions.
If permissions is omitted, nothing is added.
If who is omitted, add the file mode bits represented by permissions, except for the those with corresponding bits in the file mode creation mask.
If who is present, add the file mode bits represented by the permissions.
-
Take away permissions.
If permissions is omitted, do nothing.
If who is omitted, clear the file mode bits represented by permissions, except for those with corresponding bits in the file mode creation mask.
If who is present, clear the file mode bits represented by permissions.
=
Assign permissions absolutely.
If who is omitted, clear all file mode bits; if who is present, clear the file mode bits represented by who. If permissions is omitted, do nothing else.
If who is omitted, add the file mode bits represented by permissions, except for the those with corresponding bits in the file mode creation mask.
If who is present, add the file mode bits represented by permissions.
Unlike other symbolic operations, = has an absolute effect in that it resets all other bits represented by who. Omitting permissions is useful only with = to take away all permissions.
permission
any compatible combination of the following letters:
r
read permission
w
write permission
x
execute permission
l
mandatory locking
s
user or group set-ID
t
sticky bit
u,g,o
indicate that permission is to be taken from the current user, group or other mode respectively.
Permissions to a file may vary depending on your user identification number (UID) or group identification number (GID). Permissions are described in three sequences each having three characters:
User Group Other rwx rwx rwx
This example (user, group, and others all have permission to read, write, and execute a given file) demonstrates two categories for granting permissions: the access class and the permissions themselves.
The letter s is only meaningful with u or g, and t only works with u.
Mandatory file and record locking (l) refers to a file's ability to have its reading or writing permissions locked while a program is accessing that file.
In a directory which has the set-group-ID bit set (reflected as either -----s--- or ----l--- in the output of `ls -ld'), files and subdirectories are created with the group-ID of the parent directory-not that of current process.
It is not possible to permit group execution and enable a file to be locked on execution at the same time. In addition, it is not possible to turn on the set-group-ID bit and enable a file to be locked on execution at the same time. The following examples, therefore, are invalid and elicit error messages:
chmod g+x,+l file
chmod g+s,+l file
Only the owner of a file or directory (or the super-user) may change that file's or directory's mode. Only the super-user may set the sticky bit on a non-directory file. If you are not super-user, chmod will mask the sticky-bit but will not return an error. In order to turn on a file's set-group-ID bit, your own group ID must correspond to the file's and group execution must be set.

OPTIONS
The following options are supported:
-f
Force. chmod will not complain if it fails to change the mode of a file.
-R
Recursively descend through directory arguments, setting the mode for each file as described above. When symbolic links are encountered, the mode of the target file is changed, but no recursion takes place.

This information was used from a man page listing at.
Princeton University Campus CGI
http://campuscgi.princeton.edu/man?chmod