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I'm trying to learn (refresh, actually) stuff about X and vt* etc.

I was fooling around, and somehow screwed up, hit a black screen, and even the usual Ctrl-Alt-F1/F2/...F7 to get to a Console didn't work anymore at all (no reaction).

First of all, is my understanding correct that Ctrl-Alt-F1/F2/...F7 is a "kernel" functionality? As in, which code traps Ctrl-Alt-F1/F2/...F7 and.. does something about it?

If Ctrl-Alt-F1/F2/...F7 don't work anymore, has the kernel panic'd and you really have to reboot? Or would ssh in from another machine still have worked (I hadn't tried - and don't know how to screw it up again..) Is there another way to get a terminal to kill.. something to re-establish Ctrl-Alt-F1/F2/...F7 (what) ?

This is just for learning - no actual real life problem. Thanks!

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  1. is my understanding correct that Ctrl-Alt-F1/F2/...F7 is a "kernel" functionality ?
    yes.

There's an inherent race condition when switching vt's in an X window envinronment, which would hang the whole system.

It's an ongoing effort to get rid of the archaic vt from kernel, specifically CONFIG_VT.
See David Herrmann impressive work for more details.

References:
1. How VT-switching works
2. Sane Session-Switching

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To the first question the answer is yes. When you press Ctrl+Alt+F? you are invoking a particular virtual console. In a text console you only need to press Alt+F?, but to be consistent with the X session it will yield the same behaviour with the Ctrl+Alt+F? combination.

When these key combinations stop working usually it means something when very wrong. It can be a kernel panic but also hardware failure or an hardware induced lock. The later releases of kernel 2 used to lock on Sandy Bridge architectures.

In essence, if you reach a state where you can't switch virtual consoles a reboot is most likely your only way out.

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