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How do I change permissions on a file?
This page will cover the following:
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Introduction to permissions
There are three basic modes to files and directories:
- (r)eadable - Value: 4
- (w)ritable - Value: 2
- e(x)ecutable - Value: 1
Additionally, each of these modes can be applied to the
The user means you, the person who owns the file.
The group refers to a determined group to which you belong. Most
students will belong to a group called "sasugrad". To find out what
groups you belong to type groups at the unix prompt.
If you want to create your own special group of users, consult the man
page for chgrp
The other means everyone else or world.
How to determine current file permissions
You can determine the permissions on files by executing the ls -l command. The leftmost field for each file will
contain the permissions of the files.
The first space is reserved to show whether or not it is a file or a
directory. The next three spaces are the permissions for the user.
The next three are for the group and the last three is for
other.
As an example:
help@sas(/gla/help)% ls -l
|
-rw-r--r-- |
1 user |
group |
273 |
Mar 24 |
11:28 |
file1 |
|
-rwxrwxrwx |
1 user |
group |
1449 |
Jan 29 |
14:01 |
file2 |
|
-rwx------ |
1 user |
group |
4119 |
Jan 26 |
13:22 |
file3 |
File 1 is readable and writable to the user, and readable to everyone.
File 2 is readable, writable, and executable by everyone.
File 3 is readable, writable, and executable only to the user.
Changing permissions of everything in your html directory
To change the permissions of every file and directory in your html
directory so that they are readable to all:
- At the MAIN MENU prompt, type:
unix and press the enter/return key.
- At the unix prompt, type:
permissions and press the enter/return
key.
Changing permissions using letters
In unix, to change the permissions of a file, use chmod, with
the following syntax:
% chmod [who][op][permissions] filename
[who] refers to the users that have a particular permission: the user
("u"), the group ("g"), or other users ("o", also known as "world").
[op]
determines whether to add ("+"), remove ("-") or explicitly set ("=") the
particular permissions.
[permissions] are whether the file should be readable ("r"), writable
("w"), or executable ("x").
As an example:
% chmod u+x file1
will add executable permission for the user to file1.
% chmod o-w file2
will remove write permission for others for file2.
% chmod ugo=rx file3
will explicitly make file3 readable and executable to everyone. Note that
you can combine the [who] and [permissions] fields to allow multiple
values.
Changing permissions using numbers
As mentioned in the Introduction, the modes readable,
writable, and executable have numerical values. These values can be used
to change permissions easily by adding these numbers.
The modes follow a hierarchy of user, group, and then others. Using this
we can assign three numerical values.
For example: to make a file readable to all, executable to the group
and writable to the user, just add the permission values.
user = readable + writable = 4 + 2 = 6
group = readable + executable = 4 + 1 = 5
other = readable = 4
So to change the permission, type:
% chmod 654 filename
For more information on changing permissions, type man chmod
at the unix prompt.
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Last modified: Tuesday, 28-May-2002 10:03:37 EDT
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