Q:

Can't get detached screen to resume

I use putty and have an unreliable wireless connection, so I use screen to keep my work going. Often I'll get disconnected, and then I can't reattach my screen. I'll run screen -D -RR and it will just sit there indefinitely. I've tried ctrl+z to get my console back, followed by ps aux | grep screen and then kill -9 for all results, and then screen -D -RR again but I get the same results. I try any combination of d's and r's you care to mention, but still it just sits there. My screen is there, it just won't do anything, least of all resume.
Anybody have any tips or tricks or ideas for how to get my screen session to resume?

A:

I've seen this when I drop a connection to an active screen then reconnect.  Bug #27462 ("Reconnect stalls when original session is lost") describes the problem as I see it.  What appears to happen is that screen is trying to notify the tty that holds it that it is about to leave, but since the tty is hung due to a dropped connection it has to wait for the timeout to happen (which is upwards of five minutes in some cases).
To fix it, I do this:

figure out which tty is holding on to the screen session ps -ef | grep screen | grep pty
find the login bash that is associated with that tty ps -ef | grep bash | grep $PTY
kill that bash kill -KILL $PID

This causes screen to complete its disconnect correctly, and lets you reconnect normally.
See here for an example script automating this somewhat.

