file permission linux

chmod 400

chmod -> this is used to change the file permission

400 is the rule where this 400 is divided into 3 groups

--------------------------

file permission on linux are *read, write and execute*

number accocated to the permissions are

read -> 4
write -> 2
excute -> 1


so the most we can give permisssion to any file is *777*

7									7				7
(4+2+1)								.				.
user								group			others
user can read write, excute file	group -*-		others -*-

here we have 400

4       0        	0
user	group 		others

means

the owner of the file can read only /- no other permission to group or others.