Get subprocess id in Java

Question

I'm creating subprocesses in this way:

String command = new String("some_program");

Process p = Runtime.getRuntime().exec(command);

How I can get that subprocess id?

P.S. I'm working on Linux.

Answer 1

There is still no public API for this (see http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4244896) but there are workarounds.

A first workaround would be to use an external program like ps and to call it using Runtime.exec() to get the pid :)

Another one is based on the fact that the java.lang.Process class is abstract and that you actually get a concrete subclass depending on your platform. On Linux, you'll get a java.lang.UnixProcess which has a private field int pid. Using reflection, you can easily get the value of this field:

Field f = p.getClass().getDeclaredField("pid");
f.setAccessible(true);
System.out.println( f.get( p ) );

Answer 2

I tried (and failed) to do this a while back. I ended up wrapping my command in a shell script that dumped the pid to a file. Not the best solution but it got me past this hurdle.