One of the most common Linux command that we use in our day-to-day life to execute or give permission to a file in Linux system. One way to give permission to a file is through Octal Mode. One of the easiest way set permission on a file. So in this article we are going to learn how to use octal mode.

Octal mode

The word itself says that it use Octal Number System which consist of eight number i.e. 0 to 7 to set permission on file.

Where..

• First digit specify the permission for Owner.
• Second digit specify the permission for Group.
• Third digit specify the permission for Others.

Here is the table of what every number represent in the system :

Octal Value	File Permissions Set	Permissions Description
0	- - -	No permissions
1	- - x	Execute permission only
2	- w -	Write permission only
3	- w x	Write and execute permissions
4	r - -	Read permission only
5	r - x	Read and execute permissions
6	r w -	Read and write permissions
7	r w x	Read, write, and execute permissions

Or we can use binary to octal representation. To do so we have to consider r w x value as a switch which have 0 and 1 value.

So if we have to set only read permission i.e. r - - if we convert it into binary where r w x are 1 and - is 0.

So r - - = 1 0 0

Now converting this binary to octal, which is 1 0 0 = 4 and if we see in table i.e. 4 value is equal to Read permission only.

Let’s solve some example to have better understanding of octal mode :

1. Read permission to only Owner i.e. r-- --- ---

   	File Permission	Binary	Octal
   Owner	r - -	1 0 0	4
   Group	- - -	0 0 0	0
   Other	- - -	0 0 0	0

   chmod 400 file.txt will have read only permission to Owner

2. Read and write permission to Owner and Group i.e. rw- rw- ---

   	File Permission	Binary	Octal
   Owner	r w -	1 1 0	6
   Group	r w -	1 1 0	6
   Other	- - -	0 0 0	0

   chmod 660 file.txt will have read and write permission to Owner and Group only.

3. Read, write and execute permission to everyone i.e. rwx rwx rwx

   	File Permission	Binary	Octal
   Owner	r w x	1 1 1	7
   Group	r w x	1 1 1	7
   Other	r w x	1 1 1	7

   chmod 777 file.txt will have access to every one.

This is how we use Octal mode in Linux to setup a file permission in Linux file system. It seems difficult for the first time but if we understand the concept, it is very easy to implement it on Linux file system.