Birmingham mumbai

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With this style, there are only a few possibilities for numbers you can achieve when 
combining these octal values (each can only be used once). Therefore, we can get 
0
, 
1
, 
2
, 
3
, 
4
, 
5
, 
6
, and 
7
 by adding (or not adding) these numbers in different combinations. 
Some of them you'll almost never see, such as an object having write access but not 
read. For the most part, you'll see 
0
, 
4
, 
5
, 
6
, and 
7
 used with 
chmod
 most often. For 
example, if we add 
Read
 and 
Write
, we get 
6
. If we add 
Read
 and 
Execute
, we get 
5
. 
If we add all three, we get 
7
. If we add no permissions, we get 
0
. We repeat this for 
each column (
User
, 
Group
, and 
Other
) to come up with a string of three numbers. 
Here are some examples:
• 
600
: User has read and write (4+2). No other permissions are set.
This is the same as 
-rw-------
.
• 
740
: User has read, write, and execute. Group has read. Other has nothing.
This is the same as 
-rwxr-----
.
• 
770
: Both user and group have full access (read, write, execute). Other has 
nothing.
This is the same as 
-rwxrwx---
.
• 
777
: Everyone has everything.
This is the same as 
-rwxrwxrwx
.
Going back to 
chmod
, we can use this numbering system in practice:
• 
chmod 600 filename.txt
• 
chmod 740 filename.txt
• 
chmod 770 filename.txt
Hopefully you get the idea. If you wanted to change the permissions of a directory, 
the 
-R
 option may be helpful to you. This makes the changes recursive, meaning 
that you'll not only make the changes to the directory but all files and directories 
underneath it in one shot:
chmod 770 -R mydir

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Chapter 2