After trying everything that I can think of for hours, I've finally given up. I just can't seem to mount a dmg image under ubuntu 12.04. I've updated all packages, I have the latest kernel available through ubuntu's update system. This is an 64 bit installation.

I have a dmg image. I've converted it to img via dmg2img. I do modprobe hfsplus then try to mount it and I always and always get the following:

mount: wrong fs type, bad option, bad superblock on /dev/loop0,
missing codepage or helper program, or other error
In some cases useful info is found in syslog - try
dmesg | tail or so

dmesg | tail says:

hfs: unable to find HFS+ superblock

This is really driving me mad. Nothing else worked, I've tried

sudo mount -t hfsplus javafx.img.iso jfxgui
sudo mount -t hfsplus -o loop javafx.img.iso jfxgui
sudo mount -t hfsplus -o loop javafx.dmg jfxgui
sudo mount -o loop javafx.dmg jfxgui (gives me: you need to specify filesystem type etc)

you name it.

What am I missing here?