Pass command to running java process?

Question

I have a Java process that I run. If I start the process via SSH and pass commands to it works fine, but if I then terminate the SSH session I lose "control" of the process. How can I regain "control" of that process? It's still running.

I know the process ID. Is this possible or must I restart the process?

Answer 1

You probably want to start a screen.

Try typing screen at the prompt. (Install the program if you don't have it.)

Example run:

$ ssh yourserver
Password:
$ screen # start the screen
$ java -jar YourApp.jar
output...
more output...
<Ctrl-A D> # detach process for later reattach
$ exit # exit your ssh session

next day

$ ssh yourserver
Password:
$ screen -x # reattach process
$ java -jar YourApp.jar
output...
more output... # back to where we were yesterday.

Type man screen for more information.

• sam: I've been using screen, maybe you can help with the problem. I am trying to send a command to a detatched process, the manual says to use the -X operator but it doesn't seem to be working. If my screen process ID is 123 and I want to send the command "reboot" to my process what would be the syntax? screen -S 123 -X "reboot" doesn't work.
• aioobe: Have a look at mail-archive.com/[email protected]/…
• sam: Aha! That works, thanks. I do have one more issue though. if I want to "emulate" me typing something in using -X how could I do that? This program responds to me typing "hello" but "hello" is an unrecognised command. is there a special character I use to emulate typing?

Answer 2

Use GNU screen program.

Answer 3

There is no way to reconnect the standard input / output of a process that has become disconnected like that. This is not specific to Java apps.

To avoid getting into this situation, run your application using the screen utility or something similar.