screen -r で attach できないときの対処 ref: http://qiita.com/libitte/items/e048a0e52aa6266dcfdb

file0.txt

$ screen -ls
There are screens on:
        11119.pts-8.ip-10-10-10-10        (Attached)
        11520.pts-1.ip-10-10-10-20        (Detached)
2 Sockets in /var/run/screen/S-foobar-user.

$ screen -r 11119.pts-8.ip-10-10-10-10
There is a screen on:
    11119.pts-8.ip-10-10-10-10  (Attached)
There is no screen to be resumed matching 11119.pts-1.ip-10-10-10-10.

file1.txt

$ ps aux|grep pts|grep sshd
foobar-user 12393  0.0  0.0 111576  1992 ?        S    15:53   0:00 sshd: ec2-user@pts/8
foobar-user 12685  0.0  0.0 111576  1992 ?        S    16:10   0:00 sshd: ec2-user@pts/0
foobar-user 12788  0.0  0.0 114500   896 pts/0    S+   16:12   0:00 grep sshd

file2.txt

$ kill 12393

file3.txt

# Attach したいセッションが(Detached) になっていることを確認
$ screen -ls

# attachする
$ screen -r 11119.pts-8.ip-10-10-10-10