when I try using a command with
sudo everything works fine, however, if I want to log in as the superuser using
su it doesn't let me. Why?
What is happening?
To change (switch) users using
su command, you should provide the password of target user, that's how it works. However with
sudo you can use your own password.
For example if you use the
su - command to switch into
root user, you have to use root's password which by default it does not have any password and also its account is disabled.
What is the different?
su we are giving away a single password to all users who needs to switch into the target user, what
sudo does is to overcome this problem.
We setup a file named
sudoers and within it we will define who can do what, so everybody using
sudo and his own password can prove that it's really him and run some specific commands.
What can I do?
You can use:
sudo -i to switch into root with its default shell as a login shell, or for a no-login shell
sudo -s or even old school
sudo su - (login shell again).
You can also use
sudo -l to see what privileges you have, for example do you have the rights to switch into root or user bob or run a specific command using john at a specific machine?
To clarify about root account:
in a Ubuntu machine, by default root account does not have any password and at the same time the account is disabled. When you disable an account an exclamation mark "!", will be added in front of its password hash, so no one can login into that account, whether it has a password or not.
$ sudo grep root /etc/shadow root:!:2020:0:99999:2:::
Which means root does not have any password (second section (delimited by ':') is empty, it only contains an exclamation mark) and at the same time it's disabled: pay attention to