How to run a shell script from Java and have it co

Question

I'm writing a plugin in order to restart a server application on Linux (though I'm testing on OSX). The way I'm doing this is using a shell script which commands the application to stop, and then oversees the death of the process, safely starting a new one when the time comes.

My script works when I execute it manually from the command line. However, when I execute it from within the application, the shell process is killed along with the application.

I've tried two different methods of running the process from Java:

String scriptArgs[] = {"sh", "restart.sh", "&"};

    try {
        Runtime.getRuntime().exec(scriptArgs);
    } catch (IOException e) {
        e.printStackTrace();
    }

and

ProcessBuilder processBuilder = new ProcessBuilder("sh", "restart.sh");
    try {
        processBuilder.directory(new File(System.getProperty("user.dir")));
        processBuilder.redirectErrorStream(false);
        processBuilder.start();
    } catch (IOException e) {
        e.printStackTrace();
    }

Both of these methods gave the same result: the script was called, it successfully shut down the application, and then it died before it could continue. Is there any method to start a completely independent process from Java?

Answer 1

When you run a process from java you are creating a shell instance which then runs the process. The shell will only exit once this process has finished even if it is being run in the background &

To run a process in headless mode you need to use the nohup command. For details, see here.

A usage could look like this:

ProcessBuilder processBuilder = new ProcessBuilder("nohup", "sh", "restart.sh");
try {
    processBuilder.directory(new File(System.getProperty("user.dir")));
    processBuilder.redirectErrorStream(false);
    processBuilder.start();
} catch (IOException e) {
    e.printStackTrace();
}