Honolulu city camping permits are now available online...

I didn't reserve anything but the process seems pretty easy

For some reason it cost 37$ to get a permit but I remember being free or like 5$.

I believe for the state parks they also have a online permit system..makes it alot easier to secure a campsite if your traveling here.

http://camping.honolulu.gov/#&slider1=2

state site
http://www.hawaiistateparks.org/camping/