Binary System:

a)

1 -> active , 0 -> inactive

b) 4 -> r (read)

c) 2 -> w (write)

d) 1 -> x (execute)

Binary			Decimal	Permission
0	0	0	0	no permision
0	0	1	1	0 + 0 +execute
0	1	0	2	0 + write + 0
0	1	1	3	0 + write+execute
1	0	0	4	read + 0 + 0
1	0	1	5	read + 0 +execute
1	1	0	6	read + write
1	1	1	7	read + write+execute

# chmod 777 file_name [to give all permission to everyone ]

# chmod 000 file_name [to give no permission to anyone ]

# chgrp group_name file_name [ to add a file under a group]

Example:

Group name-> iiuc , User name-> cse & eee , File name-> test

user+cse-> all access and

eee and others -> only read

Process:

# groupadd iiuc

# useradd cse

# passwd cse [type and retype the password]

# useradd eee

# passwd eee [type and retype the password]

# usermod -G iiuc cse

# vi /home/test

# chgrp iiuc /home/test

# chmod 774 /home/test