Java - how to check whether another (non-Java) process is running on Linux

Question

I'm having some weird problems with this.

We are using Xvfb virtual desktop manager and want to make sure it's running before I continue. Using pure shell, I could do this easily:

    ps -ef | grep Xvfb | grep -v grep

And that gives me exactly what I need, a single line containing information about the Xvfb proc. Next, I want to incorporate this into my Java program and parse the results and store the PID of the running Xvfb process. So I am trying this:

    String line;
    try {
      Process p = Runtime.getRuntime().exec("ps -ef | grep Xvfb | grep -v grep");
      BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
      while ((line = input.readLine()) != null)
      {
        System.out.println(line);
      }
    } catch (Exception err) {
      System.out.println(err);
    }

The bizarre thing is that if I use "ps -ef", I get a huge list of processes dumped to my console when I run my app. But if I use | grep to narrow the list of processes returned, I get zero results. input.readLine() gets null every time.

I have also tried:

    ps -ef | grep Xvfb | grep -v grep | awk {'print $2'}

To just grab the process id. Also, no luck.

Has anyone else experienced this or know what I'm doing wrong?

Answer 1

You're trying to use the "|" which is a pipe function that is particular to the shell, therefore you cannot do it in the java process. You could just try getting the process ID by using pidof Xvfb.

Answer 2

Maybe Runtime.getRuntime().exec() tries to execute the program as it is in the argument. That is, it runs the program ps with arguments -ef, |, grep, etc. And so, the program fails because it does not understand what's going on.

If you need to run piped commands, you should call the shell explicitly:

Runtime.getRuntime().exec(new String[] {"sh", "-c", "ps -ef | grep Xvfb | grep -v grep"});