Problems encountered with the su command under unbuntu linux16.04

When using the su command in the terminal, I encountered an error such as: authentication failed.
This is because after Ubuntu is installed, the root user is locked by default, and is not allowed to log in or "su" to root.
You need to change the default password during installation,
enter sudo passwd in the terminal, and then enter the new password twice.
Many blog posts describe the sudo password, however this command is not found in the Mac version of linux 16.04.