permissions

[Raul A. Gallegos]

Reading the man page on chmod will help but below is a quick guide on
permissions, at least basic ones.

the ls -l will show you a direct listing in long format of any directory
where you issue the command.  the output will be something like:
-rw-r--r--	1	root	root	112212	Jun 18	17:48	test_file

The first part tells you the permissions set on the file called test_file.
This is the only part I'm going to address here.  Take the -rw-r--r-- and
break it up into 4 parts like this: - rw- r-- r--  The first part tells
you if this is a file or a directory.  if it is a - then it's a file and
if it is a d it's a directory.  The next 3 parts are the permissions for
owner, group, and world.  Each of these 3 parts has 3 flags which can be
on or off.  If they are on you will see a letter and if it is off you will
see just a -.  The permissions are r for read w for write and x for
execute.  So if you have a file which like the example -rw-r--r-- it means
that the owner of the file has read/write access to the file while the
group and the world has only read access to it.  If you look at a binary
file such as /usr/bin/vacation you will see something like -rwxr-xr-x or
-rwx--x--x.  This means that the owner root has read/write/execute
permissions while everyone else either has read/execute or just execute
permissions.

Now to setting the permissions accordingly you use the command chmod.
There are more than one ways to set this but I will demonstrate my
prefered way.  Some may like it some may not, but it is easy
none-the-less.

Let's take the file test-file for example.  to create it just touch
test_file and bang, you  got a file called test file.  Let's clear all the
permissions by typing chmod 000 test_file  This will set the
owner/group/world permissions to ---.  Below is a chart of the
corrisponding number flags when you use chmod.  they range from 0 through
7.  and when you issue them you do it in sets of 3 digits.  first digit is
for owner permission, 2nd is for group permission and 3rd is for world
permission.

0 ---
1 --x
2 -w-
3 -wx
4 r--
5 r-x
6 rw-
7 rwx

So by looking at the chart above 0 means there are no flags set, no
read/write/execute.  1 means execute only, good for binaries.  4 is read
only good for making files that everyone can read from but not write to.
5 is good for scripts, must be readable and executable but not writable.
7 has all the flags set read/write/execute.

Now, if you want to make this file read/write/execute by owner, but only
read/execute by group and read only by world the command would be chmod
754 test_file.  If you want to make this file read/write by owner, and
readonly by group and nothing for world it would be chmod 640 test_file.

As I stated this is a quick guide so you should definately read the man
page but maybe this will help you understand permissions a little.

--- Raul A. Gallegos mailto:raul at asmodean.net http://www.asmodean.net
For millions of years, mankind lived just like the animals..  Then
something happened, which unleashed the power of our imagination...
We learned to talk...

On Sat, 6 Oct 2001, Michael wrote:

>
> High all:
>
> Now that I can hear and get a Linux box up and running as soon as I get
> Slackware 8.0 ,
> I would like to extend a  sincere thanks to those who took the time to lend
> a helping hand.
> I need to prevail on you guys and gals once again.
> Where can I find a good document on permissions and there configurations?
> I'll be sticking with my Redhat 5.2  on leashed for my command reference.
> I don't think the basic commands has changed much sense the mid nineties.
> How ever, I could be mistaken! <grin> '
>
> Chow:
> Michael
>
>
>
>
>
>
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