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I see. In that case, why not just put the exercises online?

To get used to the kernel way of sending patches: email.

Gamification ... you need to "level up" to get new challenges.

Actually, it's processed by a script (a bot if you like), however, if something fails a person replies to you. This is the problem with many of the challengers. When everything is ok they proceed, when something fails[1] it might take weeks to get a reply.

[1]: failure might be because of a corner case or an implementation not working on a specific configuration.

The author _says_ that it's done by shell scripts, but in reality he's checking them by hand (i.e. in the coding tasks you get actual code review).