Screen sessions getting killed but processes still live on and run

Question

This is a weird situation I've run into. We have a test server off site (or off site from where I work). To access the server, I need to VPN into its network.

I ran screen to execute a long running process. After I started the process, I did the following to check screen's viability:

1. I detached from the session
2. performed screen -ls to check the PID
3. ps -ef | grep screen
4. screen -r PID

I could see there was a screen session after running these commands and re-attaching/detaching to the session.

Here's the weird part. I come back the next day and there is no screen sessions. I ran those cmds above to check but there's nothing. However, my process is still running. I didn't use nohup to run my process but for some lucky reason, my process didn't die with the session.

Does anyone know what might have happened? Why did I lose my screen session and why did I luck out and have my process keep running?

Thanks for any enlightenment. =)

Solution

You might want to grep for SCREEN instead to verify that your screen really isn't running.

Some systems have tmp cleaners that delete files in /tmp, /var/tmp, /var/run, or similar. This can result in screen not being able to find its socket files. If you can identify the PID of your session, you can do kill -CHLD <PID> to tell screen to rewrite its socket file. screen -r should then work again.

If this is what's happening, you should probably configure screen to use another directory for its sockets.

Comments

[Classified]

Thx for replying. 2 weeks ago when I grepped for screen, it wasn't there. However, this week, for some strange reason, my screen sessions are present when I do a screen -ls, even after waiting overnight. Go figure. I'm guessing it's what you said, that something was cleaning these screen files such that when I went to connect back, it didn't know the PID. It did say something about not finding some file at some location (didn't grab that msg from 2 wks ago). It still doesn't explain why my process luckily didn't die but that doesn't matter. Thanks.