Ubuntu – How to run a Java program in background

background-processbashjavascriptsssh

I try to make a init.d script which should start this java command:

java -cp ./:/opt/glassfish/domains/domain1/lib/*:/opt/glassfish/lib/* com.name.it.svcimpl.OrderRequestDispatcher &

With & it starts as background process and this is fine. The problems are starting when you are trying to get it to the foreground:

[1] 10119
user@server:$ fg 10119
-bash: fg: 10119: no such job

After you are pressing enter this happens:

[1]+  Stopped                 java -cp ./:/opt/glassfish/domains/domain1/lib/*:/opt/glassfish/lib/* name.alcar.it.svcimpl.OrderRequestDispatcher

As you see there was no process like 10119 so why does it stop?
But the things getting much more difficult when the command is in a init.d bash script:

#!/bin/bash
(cd /opt/glassfish/domains/domain1/applications/AS/WEB-INF/classes; java -cp ./:/opt/glassfish/domains/domain1/lib/*:/opt/glassfish/lib/* com.name.it.svcimpl.OrderRequestDispatcher &)

(Need to started under the path /opt/glassfish/domains/domain1/applications/AS/WEB-INF/classes)

Now my question as not java programmer is:

Is it possible to run a java program in background with the option to foreground it from any terminal session?

As you can read it is really important to run it in background. Any user that are logged in should be able to put it to the foreground. The users are connecting with SSH to the terminal.

Best Answer

You can't foreground a process from a different sesion. The functionality you want is probably possible with the screen command.

As for the java app failing to run in init.d; you are not changing to the /opt/glassfish/domains/domain1/applications/AS/WEB-INF/classes folder. You have '.' in your classpath so it matters where you run from.

Ideally, I think you should keep the bash script and run that from init.d. However, you could also add the full path to your init.d classpath explicitly. Though I suspect you will need to use screen because of the inability to foreground the app.

For screen, this is an example of what you are looking for

$ screen -S myScreen -d -m ./dostuff.sh
$ screen -r myScreen

Related Solutions

Ubuntu – How to wake a sleeping bash script

When a Bash script is running a sleep, here's what the pstree might look like:

bash(10102)───sleep(8506)

Both have process IDs (PIDs), even when running as a script. If we wanted to interrupt the sleep, we'd send kill 8506 and the Bash session would resume... The problem is in a scripted environment we don't know the PID of the sleep command and there isn't a human to look at the process tree.

We can get the PID of the Bash session through the $$ magic variable. If we can store that somewhere, we can then target instances of sleep that are running underneath that PID. Here's what I'd put in the script:

# write the current session's PID to file
echo $$ >> myscript.pid

# go to sleep for a long time
sleep 1000

And then we can tell pkill to nuke sleep instances running underneath that PID:

pkill -P $(<myscript.pid) sleep

Again, this is limiting itself to only sleep processes running directly under that one Bash session. As long as the PID was logged correctly, this makes it a lot safer than killall sleep or pkill sleep, which could nuke any sleep process on the system (permissions allowing).

We can prove that theory with the following example where we have three separate bash sessions, two running sleep. Only because we're specifying the PID of the top-left bash session, only its sleep is killed.

enter image description here

An alternative approach is to push sleep into the background, store its PID and then return it to the foreground. In the script:

sleep 1000 &
echo $! > myscript.sleep.pid
fg

And to kill it:

kill $(<myscript.sleep.pid)

Best Answer

Related Solutions

Ubuntu – How to wake a sleeping bash script

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