Checking if a process is runing on linux via Java code

Question

The issue is i want to kill a process only if its running, otherwise i want to do something else.

This is my code right now (sublime as an example):

try {
    Process p = Runtime.getRuntime().exec("pidof sublime_text");

    if (p != null){
        Runtime.getRuntime().exec("pkill -f sublime");
    }
}
catch (Exception e) {
    System.out.println(e.getMessage());
}

Runtime.getRuntime().exec("pidof sublime_text"); ALWAYS returns a process, even if this one doesn't exist, i mean, i can execute: Runtime.getRuntime().exec("pidof nonExistingProcess"); and this will still return a process without error, and then the kill "pkill" command Runtime.getRuntime().exec("pkill -f nonExistingProcess"); doesn't throw an Exception either, what can i do?

Possible duplicate of [How to check is a certain process is running - java on linux](https://stackoverflow.com/questions/31366975/how-to-check-is-a-certain-process-is-running-java-on-linux) — Turamarth, Oct 05 '18 at 12:48

score 1 · Answer 1 · answered Oct 05 '18 at 12:50

You're starting the processes but are not reading their output or return status (or even waiting for them to complete), so your code doesn't actually react in any way to the processes you start.

You might be used to system in PHP or similar systems where that call only returns once the executed command is complete. Runtime.exec() is different in that you start the process but it's up to you to read it's output from the Process that gets returned.

So p doesn't actually represent sublime, but it's the process executing pidof and you must read its output to get to the information you want.

score 0 · Answer 2 · answered Oct 05 '18 at 12:49

Of course there's a process; 'pidof someRandomGarbage' is still an application that runs. The fact that the application, if run, returns 'nope', doesn't magically make the process disappear. You have to use the methods of the Process class to determine what the result of running pidof someRandomGarbage does. p.exitValue() is probably what you're looking for. To determine the actual output you'd have to use p.getInputStream().

Note that using relative paths is a very bad idea; it means you're reliant on the PATH variable and on java parsing it properly. Try /usr/bin/pkill, or something configurable.

Checking if a process is runing on linux via Java code

2 Answers2