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- In this video, we are going
to explore the use of su.

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Su is for switch user.

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It allows you to open a
shell as any specific user.

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For instance, if you use su Lisa,

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then it'll prompt for a password

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and open a shell as user Lisa.

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Notice that it will only
prompt for a password.

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If you are doing this as an ordinary user,

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user root can open a shell as any user

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without entering a password.

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If you just use su, then it'll
prompt for the root password

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and open a root shell.

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You use su without any further
arguments to open a subshell.

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Subshell means that not all environments

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are set as the target user.

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If you use su -, you open a login shell.

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In a login shell, environment variables

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are set as the target user.

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The result is that su -
is the better solution

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because it guarantees

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that you are in the
appropriate environment.

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The user root can use su
to become any other user

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without entering a password.

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And a regular users can use su as well,

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but they need to enter
the target user password.

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Let's go check this out.

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So as you can see, I'm in
a shell, su is a student.

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And in the shell su
student, I can type su -

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and it'll prompt for a password.

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And right now, I'm in a root shell.

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You can recognize the root shell

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because I have a root@centos with a hash

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and that is showing that
I'm in a root shell.

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So if I type whoami, for instance,

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then I can see that I'm root.

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This is one way to open
a temporary root shell.

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Disadvantages that in order to use su -,

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you need to know the root password.

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Now as a root, I can use su Linda

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to open a shell as user Linda.

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As you can see, I'm not prompted

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for any password whatsoever.

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To exit from the shell you type exit.

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I just did, and that brings
me back to the root shell.

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And if I type exit again, then
I'm back in my student shell.

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Now I want to show you what is happening

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if I use su - linda.

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Again, I would advise
you always to use su -

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because really you want
to set the environment

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the right way.

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So su - linda doing what,

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it's prompting for the password Linda.

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And you know what?

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Linda doesn't have a password

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so I can try whatever I want.

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This is not going to work.

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Now, let's also do this on Ubuntu.

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So here we go.

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I am user student right now,

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and what is happening if I use su -,

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well it's prompting for the root password.

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And what is the root password?

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Well, that is exactly the problem.

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The root user on Ubuntu
does not have a password.

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Su and su - straight like this on Ubuntu

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is not a good option.

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On Ubuntu, you go for sudo.

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And that is what is going to
be discussed in the next video.