How to create a Linux "Hidden OS"

There has never been a publicly shared method to run Linux with forensic deniability on the level of VeraCrypt's (formerly TrueCrypt's) "Hidden Operating System" feature. If you wanted such a level of computing privacy, until now you've been forced to use Windows.

Moreover, the security of VeraCrypt's "Hidden OS" feature was defeated by researchers in 2017. That particular feature can no longer be relied upon for forensically private computing.

Now with HiddenVM, it is possible to run almost any Linux operating system with this level of privacy. Whatever runs on VirtualBox works with HiddenVM.

Here's a working guide for how to create a Linux "Hidden OS" using HiddenVM, with the Tails operating system as the host and Ubuntu as the example hidden guest.

[To be finished later.]