Screen Basics - Commands

List screen sessions:
$ screen -ls
There is a screen on:
        9020.ttyp0.thinkpad     (Attached)
        17938.foo       (Detached)
        29945.ttyp9.thinkpad    (Detached)
3 Sockets in /tmp/uscreens/S-mike.

Reattach to an existing session:
$ screen -r 29945 (reconnect to detached session with pid 29945)
$ screen -r foo   (reconnect to detached session named "foo")
$ screen -dr 9020 (reconnect to attached session with pid 9020)