ubuntu 升级过程中丢失session

Do a

sudo screen -list
There is a screen on:
2953.ubuntu-release-upgrade-screen-window   (09/13/2012 04:48:02 AM)    (Detached)
1 Socket in /var/run/screen/S-root.

Then to reattach do:

sudo screen -d -r root/2953.ubuntu-release-upgrade-screen-window

Using the previously listed screen after 

root/

You should be back to where you lost connection.