File and folder Permissions

Permissions are set using a command called CHMOD. CHMOD stands for CHange MODe. You are giving the host computer new instructions about this file or directory.

CHMOD comes as a set of 3 numbers. Each of these 3 numbers is a sum total of 3 other numbers. So you have to add 3 numbers to get the first CHMOD number, add 3 numbers to get the second CHMOD number and add 3 numbers to get the third CHMOD number.

Understanding the numbers...

Each digit is a number value from 0 to 7. The value specifies what capabilities are available (or not). These numbers correspond to 3 command types. Read, write and execute.

Read (r) has a value of 4. It allows listing files in the directory.
Write (w) has a value of 2. It allows the addition of new files to the directory.
Execute (x) has a value of 1. It allows access to the files in the directory.

Here are the possible combinations available using these command types :

Digit	rwx	Result
0	---	no access
1	--x	execute
2	-w-	Write
3	-wx	Write and execute
4	r--	Read
5	r-x	read and execute
6	rw-	read and write
7	rwx	read write execute