Use sudo in the crosh shell: VT-2, Chromebrew, Crostini not needed!

[CroutonIsFun]

EDIT: Closing and leaving for reference...

Here is the short version:

1. Turn on debugging features and assign a root password
2. From the crosh shell, ssh root@localhost
3. As root, assign a chronos password with passwd chronos (do not use chromeos-setdevpasswd)
4. Exit root with Ctrl-D
5. Log into your Chromebook with ssh chronos@localhost

From here on out, sudo will work as before, except you will have to provide the chronos password.

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Behind the scenes: Turning on debugging can only be done the first time you transition from verified mode to developer mode. Even powerwash will not help. If you're already in developer mode, then reboot, and at the verify screen, press the space bar. When your Chromebook boots back up, set it up as your normally would, and reboot again.

When you get back to the login screen, tap Esc Refresh Power to trigger the transition back to developer mode. Press Ctrl-D at the verify screen. When you see "Welcome to your Chromebook", wait 5 or 10 seconds until the 3rd option becomes clickable: Turn on debugging features. Now click it.

Your Chromebook will restart (the screen will go dark for a few seconds), and when it comes back to you, enter and confirm a root password. Set up your computer as you normally would. When you're done, you should be able to press Ctrl Alt T, followed by typing "shell" and pressing Enter.

At this point, you only need to ssh chronos@localhost to continue.