su doesn't work from regular or sudoers

Question

I'm trying to use su command to change my identity on ubuntu 18.04
But from neither regular user to sudoer user or sudoer to regular user it doesnt work!
I get

su: Authentication failure

The sudo works and i can login to my users using ssh (ssh user@127.0.0.1) but cannot use su

What is the problem?

---

my cammand is simply this:

from user bob:

su alice

Answer 1

You could try:

• sudo passwd alice to renew password

Or, as a workaround:

• sudo su - alice
• sudo -i then su alice

When switching from root password isn't asked.