Let’s find out what is the permission in Linux,

d rwx rwx rwx

1st rwx owner

2nd rwx group

3rd rwx everybody else

r : Permission to read, w : Permission to write, x : Permission to executable,

There are some possible permission combinations we can change. Each combination has three digit of binary number. That three digit make an decimal number. Those numbers are 0 to 7.

---   000   0

--x   001   1

-w-   010   2

-wx   011   3

r--   100   4

r-x   101   5

rw-   110   6

rwx   111   7

We want to memorise only three combinations and decimal numbers of those combinations. They are,

--x   001   1

-w-   010   2

r--   100   4

Then we can calculate others.

r--   +   -w-  +    --x = rwx
 4    +    2   +     1  =  7

r--   +   -w-   =   rw-
 4    +    2    =    6

r--   +   --x   =   r-x
 4    +    1    =    5 

-w-   +   --x   =   -wx
 2    +    1    =    3

Only owner can change the ownership

sudo

In Linux, the administrative user is called root. The root user owns the system. Some programs need root user permission. In that time we need to do sudo command.

root is the super user. That sudo command meaning is “do as super user.”

When you run sudo command it will ask for your password. After you giving your password it can be use fifteen minutes.

morty@c137:~$ sudo ls /root
[sudo] password for morty:
morty  rick