su in terminal does not accept password

I am using Linux Mint 19 and a HP desktop computer, dual booting with Windows 10. I did not create an encryption of my drive, a simple password only. I log in with it, and permitted a software download with it from software manager. All good, but when I tried opening a terminal and using su, it did not accept the password. There is only one password, right?

Is there a fix?

What are you really trying to do?

In Linux Mint you have an admin user which can elevate privileges using sudo.

sudo -i

See "man sudo" and, especially, "man sudoers"

However, that is a misuse of sudo and you should really spend some time configuring it properly. The idea is to give specific privileges, not all-or-nothing.

See also Michael W Lucas' talk:

• sudo: you're doing it wrong (slides)
• sudo: you're doing it wrong (video)

Mint just like Ubuntu does not enable root by default. While you can use sudo to run commands as root you can not become root. It is possible to enable root if so desired.

https://help.ubuntu.com/community/RootSudo