If I plug in a usb thumb drive, it shows up in the unity panel and in Nautilus. However, there is no response from my usb external hard drive. I know it is recognized, and I can manually mount it.
fdisk -l shows the drive as "Hidden". I suspect this may be important.
I tried the following instructions found here:
sudo mkdir /media/USERNAME
sudo chown USERNAME.USERNAME /media/USERNAME
with no success
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