File access categories and permissions:

The three file access categories, owner, group, and other, has a set of three access permissions associated with it.The access permissions are read, write, and execute.

File permissions are represented by positions two through ten of the ls –l display. The nine character positions consist of three groups of three characters. Each three character group indicates read (r), write (w), and execute (x) permissions.

The three groups indicate permissions for the owner, group, and other users respectively.

In the example above, both the owner and the group have read (r) and write (w) permissions for the file, while other users have only read (r) permission.

The alphabetic permission indicators are commonly assigned numeric values according to the scheme shown in the table below:

if the owner has read, write, and execute permissions, the owner’s permissions can be represented by the single digit 7 (4+2+1). If the group has read and execute permissions, that can be represented by the single digit 5 (4+0+1). If other users have no permissions, that can be represented by the single digit 0 (0+0+0). These three numbers would then be listed in the order of owner, group, other, in this case 750 as a way to definitively describe the permissions on this file.

Enjoy:-)