GNU Screen Problems

Question

I am trying to run screen in a special way (I am making an unusual script), and it is not working correctly.

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My script:

#!/bin/bash
#startserver


set -m

cd /home/USER/SERVER_FOLDER/

screen -Dm -S SERVER java -Xmx768M -Xms768M -jar ./JARFILE.jar $@ &

PID=$!
echo $PID > ./.mc.pid
(sleep 0.5; sudo /usr/bin/oom-priority $PID) &

(wait $PID; startserver_after) &

screen -r $PID.SERVER

/usr/bin/oom-priority is a coommand I made that sets the priority of the pid to -16.

startserver_after is a command I want to run after java exits.

This isn't working because I cannot resume the screen. Looking at the screen manpage:

-D -m   This also starts screen in "detached" mode, but doesn't fork a new process. The command exits if the session terminates.

That should mean:

1. The pid of screen should be the same as that of java, however that works.
2. It is still screen, so I should be able to get to it by screen -r SERVER (but I can't).

When I run the line without the ampersand putting it in the background, it just does nothing until java exits. There is no output.

Answer 1

If you run screen with -Dm, it will not return to you command line prompt (the "no fork" idea; that's why it doesn't do anything until your java exits if you have no ampersand). If you run it with the -dm, it returns to your command line prompt immediately.

By putting the -Dm in the background, you have caused it to fork and set $! with the PID of your screen process. So that's good.

You are setting the oom-priority of your screen (I doubt you want to do that; I think you were aiming at Java). You can get the pid of your child, like this:

pidchild=$(pgrep -P $PID)

Do you really want to startserver_after after the screen exits? Maybe you want to wait on the child, as well.

Regarding the screen -r at the end: It should work, unless you don't have a tty as stdin of your script, or the java has already exited. Try a ps -p $pidchild immediately after the screen -r and see if the child is still alive. Also run tty as the last command of your script, and make sure it does not return Not a tty.