Cr-48 Developer Mode

The CR-48 has a switch in the battery compartment which is being called the jail-break switch.  That isn't strictly correct, but you get the idea. The switch is concealed under black tape here:

It's a hard microswitch:

Away from the battery terminals is normal, towards is developer.

The system will erase the volatile partition, so be careful.  You shouldn't have much on there anyway:

When you boot up now, you get a scary error message:

I especially love the sad face.  The computer should be happy!  

Anyway, you'll have to hit Ctrl-D here.  If you don't, you'll get an even scarier error message:

Well, now the computer is just aggravated!  I haven't explored just how this works internally, yet, but just hit Ctrl D at the first prompt and all is well.

Now you'll have to take your picture again, and do the initial login again.  

But you will now be able to run the "shell" command from crosh and get a recognizable linux shell:

A bash shell, to be precise.

Try su sudo - and Bob's your uncle.

Now for fun stuff!!

UPDATES:

The recovery kernel

More on switching to dev mode.