You may be trying to perform administrative tasks from the macOS Mojave terminal, for instance, if you are developing locally (on a Mac, of course).

You may encounter permissions issues using your local administrative user.

You may attempt to use the following command:

sudo

But unfortunately, this is unlikely to work, as the root user is disabled by default in macOS.

You may also try to get around this by prefixing the popular 'su' command to your command, only to be greeted by an irritating 'Sorry!'

Don't worry, you can get around this quite easily.

Here's the solution:

sudo su

When the password prompt appears, simply enter the login password for your macOS account.

From now on, you can perform root-user-level tasks without having to use 'su'.

And you won't have to re-enter that pesky password.