[franciscohs]

Not sure if this is what you need, it wont generate an iso, just a vob, but that works fine.

First use "lsdvd" to look into the chapters of the DVD.

Then: mplayer dvd://$track -dvd-device "$source" -dumpstream -dumpfile work.vob

where:
$track=number of track to rip
$source=can be an iso of a DVD or can be "/dev/dvd" for your dvd player