Connect the beaglebone to a monitor and keyboard. Boot up.
In the earlier versions of the kernel, the system booted into X (the gui), and you were logged in as the debian user. You would type ctrl-alt-F5 to get to a terminal login (this is quicker).
In later versions of debian, the X system is not installed by default. You should see a full screen with a login prompt. Use debian:temppwd to login.
Type uname -a to determine your OS version. When you look for beaglebone tips on the internet, be aware that there are huge differences based on kernel. This blog is based on 4.14.71-ti-r80 (stable version) kernel.
Set the root password with sudo su (use temppwd as the password). Type passwd and enter the desired root password twice.
Switch directories to /etc/ssh, and edit sshd_config with nano. Change the line “PermitRootLogin prohibit-password” to “PermitRootLogin yes” and restart sshd with “service ssh restart.” This will allow you to ssh into the box as root using the new root password.