Linux – Screen sessions getting killed but processes still live on and run

centosgnu-screenlinuxprocessvpn

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:

I detached from the session
performed screen -ls to check the PID
ps -ef | grep screen
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. =)

Best Answer

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.

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