PERMISSION

CHMOD is used to change permissions of a file.

        PERMISSION      COMMAND   

         U   G   W
        rwx rwx rwx     chmod 777 filename      
        rwx rwx r-x     chmod 775 filename
        rwx r-x r-x     chmod 755 filename
        rw- rw- r--     chmod 664 filename
        rw- r-- r--     chmod 644 filename

        U = User 
        G = Group 
        W = World

        r = Readable
        w = writable
        x = executable 
        - = no permission

Here is another way of looking at it: 



Permissions:

400     read by owner
040     read by group
004     read by anybody (other)
200     write by owner
020     write by group
002     write by anybody
100     execute by owner
010     execute by group
001     execute by anybody

To get a combination, just add them up. For example, to get read, write, execute by owner, read, execute, by group, and execute by anybody, you would add 400+200+100+040+010+001 to give 751.