Gfilui

I used my super user hoping that I will be able to do everything with it, but to access one directory, I still had to do sudo su command to switch to root because I was getting access denied. Then how come super user is super user and still can’t access directory? And if I was switching to root, why sudo su didn't ask for password for root user and it worked without or with super user password which wasn't allowed to execute dir?

Superuser and root are synonyms. Your user is probably a sudoer, not a superuser.

In Ubuntu, you can perform a single command as root using the sudo command. Or you can open a root’s shell using sudo su, sudo -s or sudo -i. (I won’t discuss the differences here. Also, plain su could be used – if you knew the root’s password.)

sudo cd makes no sense since it would change the directory and then drop to your shell which might not be able to open the directory. Therefore Ubuntu disallows it completely:

$ sudo cd /root
sudo: cd: command not found

However, we can issue:

$ sudo ls -l /root
total 0

So how can we cd to the directory? We have to use a root shell:

$ sudo su
root@my-ubuntu:/home/mirek# cd /root
root@my-ubuntu:~# ls -l
total 0

You asked why you haven’t to input password in this case. It’s because you have used sudo recently. To force it to need the password again, you can issue sudo -k. Otherwise, it starts to require the password after a few minutes again.

You can't run the cd command with sudo or else you will get errors. You must run:

sudo su

or

sudo -s

to get into a root shell before using cd as root.