command lineusb
I would like to list ONLY devices connected via usb.
The problem is that Ubuntu seems to see all thumb drives as removable (in /sys/block/*/removable), but it does not see external hard drives the same way.
This is a bit more specific than How to detect an USB device?
Use Disks utility, select the partition you want to automount and click this 
button, then Edit mount options, turn off auto options then check the Mount on startup box and edit mount point as you like.
Well, I spent a second whole day on it and now I've cracked it.
I sincerely hope some other poor soul gets some value out of this.
Here's a recipe that works (at least, on my iMac with Ubuntu 14.04):
/boot/)/dev/disk3, /dev/disk3s1)Install rEFInd on your USB's EFI partition. From the refind directory:
./refind-install -–usedefault /dev/disk3s1
(you can drag the file into command prompt to get full path)
Then when you reboot, you can "EFI Boot" to rEFInd, and there should be an option to boot GRUB/linux.
I have documented this in more detail here: http://coljac.net/2014/stuff/installing-ubuntu-onto-a-bootable-usb-stick-or-other-device-on-a-mac/
Best Answer
If you are looking for the mounted disks, a simple
will list them along with all your other disks along with some useful info.