How to log into a fresh MariaDB install?

I am usually using Postgres, now I have had to install MySQL/MariaDB to help a friend with some issues.

The problem is just – I am not able to log into the freshly installed database on Debian 9.

When searching for default user name, I am told to use “root” with a blank password. But no matter what I have tried, I am just greeted with Access denied.

mysql -u root
mysql -u root -p

and then repeat with root@localhost and [email protected]. I have tried to use the description in the accepted answer of https://superuser.com/questions/603026/mysql-how-to-fix-access-denied-for-user-rootlocalhost but to no avail.

Where am I messing up? Are there any command line utilities similar to Postgres’ createuser to create a new user?

mysqld 10.1.26-MariaDB-0+deb9u1 on debian stretch (9.3)