It turns out this is not a Tethys problem. Current Docker only supports 64-bit OS.
I ran into this issue because I accidentally installed a 32-bit Ubuntu. Installation of Tethys was going well until this step "tethys docker ip ", showing:
PostGIS/Database: Not Running.
GeoServer: Not Running.
52 North WPS: Not Running.
I re-issued command "tethys docker start" several times but containers could not get started.
If you have a similar problem like this, be sure to check you have installed a 64-bit OS.
Drew