Today Nautilus decided it just didn’t like my mounted USB devices.  At first it was a brand new 64 GB FAT32 drive, and so I figured I would just reformat it.  This didn’t change anything; Nautilus (the file browser in Ubuntu 14.04) was insisting that I had read-only permissions on the drive and would not allow me to write to it.

Apparently there is a bug (not necessarily in Nautilus because I am told this will work with other file browsers) that is pretty easily fixed.

Open your terminal and run these two commands:

mv ~/.config/nautilus ~/.config/nautilus-bak
sudo killall nautilus

The first one moves the configuration file for Nautilus (modify if you are using a different file browser) to a backup copy.  The second kills (stops, terminates) the running Nautilus session.  You will need to launch a file browser window to get Nautilus (or other) running again, but that should return your USB drives to writable.