“Hey, Pal! How are you? Remember that little project I had on the CubieTruck? I resumed hacking on it. But it’s a pity, I lost my root password… I have to start all over again. Any chance you remember what silly password we choose together?”
If only it was the user’s account password, it would be easy: log as root, change the password on behalf of the user, done. That time, who is going to save the root account? Is there any rootroot account, by any chance? No. But don’t worry, we’re going to hack into the root account nonetheless. But how? It’s Linux, it’s super secure, it’s the root account, I choose a 50-bits-of-entropy-random-super-secure password… Maybe. But almost any security will fail, once the hacker has access to the hardware. And today, we’re the hacker!