Going hiking here in Japan, you can hardly pass anyone without either saying お疲れさまです, おはようございます (I go hiking in the morning) or こんにちは.
Some people (young males in particular) greet you with either チュワッ or オッス. A great idea, since everybody's out of breath. I gather that チュワッ is a contraction of こんにちは, but オッス could be either お疲れさまです or おはようございます. Does the person greeting you with オッス actually have one of the two possible greetings in mind, or is it just used more like a universal sound, which can be used in any situation?