If you are used to pulling the mssql-server images from the microsoft repository, e.g.,
docker pull microsoft/mssql-server
that won’t work for the 2019 CTP.
I was able to repull (aka update) using the former repository, but that wasn’t working for the CTP whose tag is vNext-CTP2.0-ubuntu.
I finally noticed the new docker pull command on the docker hub page for the image
It says: docker pull mcr.microsoft.com/mssql/server
So the command for pulling the CTP using it’s tag is as follows:
docker pull mcr.microsoft.com/mssql/server:vNext-CTP2.0-ubuntu