Get the UNIX process ID of the java program

[Anonymous]

Hi there,
I need to start a java program, and the program
will use its UNIX process ID to do some processing.
How can I find the UNIX PID inside the java program?
Thanks,
Mike.

[George Brown]

That's an interesting problem.
But is it appropriate for a Java program to get the UNIX PID? You would be looking for the PID of the JVM, and since Java is meant to be OS-independent, if it is possible it would make your java code thoroughly non-portable. For that reason, I would imagine that Sun has made no provision for it in their Standard Edition.
My solution would be to rewrite the program in C or C++ and to use getpid().

[Vlad Patryshev]

This is an interesting answer.
How then can I find a way to tell one runnin ginstance of the same java program from another, be it on Unix or on Windows or on Mac or on my cellphone?

[William Barnes]

I just wrote some code that did that. I was trying to make a unique ID with the pid of the JVM as one of the attributes. You need to write a small c/c++ program that does "getpid()" and than use JNI to call it.

[Michael Schloh von Bennew]

Originally posted by christopher foran:
I just wrote some code that did that. I was trying to make a unique ID with the pid of the JVM as one of the attributes. You need to write a small c/c++ program that does "getpid()" and than use JNI to call it.

Can you please post your code? Especially interesteing is how you called the c++ portion from within java (JNI?)

[Michael Ernest]

The easiest way to get the PID is through the shell environment variable $$. Use a System.exec() call to "echo $$"
I don't agree that this is inappropriate for a Java program -- it just has the unhappy side effect of making the program non-portable across OS platforms. If you don't care about platform-agnostic code -- and I don't see how you can if you care about PIDs -- Java is still *way* easier to use than C.
------------------
Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide
[This message has been edited by Michael Ernest (edited October 12, 2001).]

[George Brown]

Originally posted by Michael Ernest:
The easiest way to get the PID is through the shell environment variable $$. Use a System.exec() call to "echo $$"

I guess you mean a Runtime.exec() call ?
I thought those were always run in a separate (spawned) process, and if you use "echo $$" you get the PID of that process rather than the running java process. On the other hand, if you're using the Korn shell (or equivalent) I guess you could use "echo $PPID" to get the PID of the shell's parent (ie. the java process).
But I still don't think that java is ideal for grabbing PIDs even though it can be easier than some other programming languages.

[Michael Ernest]

oops -- good point on PPID.

[Jim Lang]

So I tried a practical example, and used the following lines:

import java.io.* ;
   
public class C
{
        public C()
        {
                String cmd = new String( "echo $PPID" ) ;
                System.out.println( "client command: '" + cmd + "'" ) ;
                try
                {
                        Process myProcess = Runtime.getRuntime().exec( cmd ) ;
                        BufferedReader stdout = new BufferedReader( new InputStreamReader( myProcess.getInputStream() ) ) ;
                        String line = stdout.readLine() ;
                        while ( line != null )
                        {
                                System.out.println( line ) ;
                                line = stdout.readLine() ;
                        }
                        int exitVal = myProcess.waitFor() ;
                        System.out.println( "exit value: " + exitVal ) ;
                }
        }
        
        public static void main( String[] args )
        {
                C myC = new C() ;
        }
}

However, that only gives me a way to output the input stream to the subprocess. How can I capture the output stream of the executed subprocess? Is this possible?
[This message has been edited by Jim Lang (edited October 13, 2001).]

[Michael Ernest]

Process supports both getInputStream() and getOutputStream().
------------------
Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide

[Roseanne Zhang]

Did any body tried, I admit that I tried and could not make it work. The output is $PPID instead of the number. If any of you made it work, please tell me how. Thanks a lot!!!
If I directly call "echo $$" or "echo $PPID" or "sh -c 'echo $PPID'" from prompt, they all works, but put them in the code, none works.
Here is my modified code from above

import java.io.*;
public class CC
{
    public CC()
    {                
        //String cmd = new String("echo Hello world");
        String cmd = new String("echo $PPID") ; 
        try 
        {                        
            Process myProcess = Runtime.getRuntime().exec(cmd);
                        
            BufferedReader stdout = new BufferedReader(new InputStreamReader(myProcess.getInputStream()));
            String line = stdout.readLine();
            while ( line != null )
            {           
                System.out.println( line );
                line = stdout.readLine();
            }
            int exitVal = myProcess.waitFor();
            System.out.println( "exit value: " + exitVal );
        }
        catch (IOException ioe)
        {
            ioe.printStackTrace();
        }
        catch (InterruptedException ie)
        {
            ie.printStackTrace();
        }
    }                
    public static void main( String[] args )
    {
        CC myC = new CC();
    }
}

[Roseanne Zhang]

It compiles, runs, and has output, but no process IDs.
Help!

[Michael Ernest]

Ok, figured it out. I thought of this problem before but got lazy and didn't test. Actually, I didn't write anything to test. But hey, just another example of free help achieving its true worth.
Runtime.exec() generates a Unix system call execve(), which you can see by trussing the JVM process. On Solaris I did this with
$ truss -af java CC 2>errorlog
That way all the process results go to the console while the truss output goes to errorlog (and there's a mess o' truss output).

I naively assumed that Runtime.exec() would spawn a shell, which it does not. You need a shell to get environment variables like $PPID. So I wrote a script called rtn and invoked that from Runtime.exec(). Here's Roseanne's code slightly modified:

import java.io.*;
public class CC
{
   BufferedReader stdout;
   Process myProcess;
   InputStream is;
   InputStreamReader isr;
   public CC() throws IOException, InterruptedException 
   {
      String cmd = "rtn";
      try {
         myProcess = Runtime.getRuntime.exec(cmd);
         is = myProcess.getInputStream();
         stdout = new BufferedReader(new InputStreamReader(is));
         String line = stdout.readLine();
      
         while (line != null) {
            System.out.println(line);
            line = stdout.readLine();
         }
         int exitVal = myProcess.waitFor();
         System.out.println("exit value: " + exitVal);
      }
   }
   public static void main(String args[]) {
      CC run = new CC();
   }
}

and here is the script rtn:

#!/bin/ksh
echo $PPID

This does the trick. Make sure the execute bits are on for the file rtn.
------------------
Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide
[This message has been edited by Michael Ernest (edited October 18, 2001).]

[Roseanne Zhang]

Michael
Thank you so much for the help!!!
I still did not get it to work.
The code above is not compilable, 3 compile errors. After I fixed them, I got either a shell error message or runtime exception, it depends I put "rtn" or ". rtn" as my command.
If I directly run the shell script by ". rtn", it works fine.
I'll look into it more. If you have some idea what mistake i've made, please let me know. Thanks again.
What a busy day!!!
Roseanne

[George Brown]

Roseanne,
Michael's code definitely works (with the minor fixes - I think he was in a hurry).
Nice one Michael, but I'd venture that it still feels a bit Heath Robinson to me when you could use getpid(), getppid(), etc. C isn't that tricky, especially when the system calls are all laid out for you...
Just my opinion perhaps.
[This message has been edited by George Brown (edited October 19, 2001).]

[Michael Ernest]

Hey George
I don't know the Heath Robinson reference but I get what you're saying. I can think of a few related tradeoffs:
- What Ive demonstrated is skeletal, I presume what the original enquirer wants to do is far more involved, and possibly wants to keep overhead to a minimum; and
- $PPID is known by the shell, so you don't need to make a system call. The cost of a system call is negligible in this example, of course, but if you were looking to save the trap into kernel execution, this would do it. But even if you're trying to dash something off;
- You don't need a compiler handy to do it this way. Living off Solaris and often changing machines as I do, that's meaningful to me. YMMV.
------------------
Michael Ernest, co-author of: The Complete Java 2 Certification Study Guide

[George Brown]

Originally posted by Michael Ernest:
I don't know the Heath Robinson reference but I get what you're saying.

This url should make my comment clearer (a real gem of a cartoonist)... http://www.bbc.co.uk/history/discovery/bypeople/robinson_01.shtml

[Janardhan Babu Chinta]

import java.io.*;
public class CC{
public CC(){
BufferedReader stdout;
Process process;
try {
process = Runtime.getRuntime().exec("ppid");
stdout = new BufferedReader(new InputStreamReader(process.getInputStream()));
int exitVal = process.waitFor();
String line;
while ((line=stdout.readLine())!= null) System.out.println(line);
// uncomment the below line and make the java process not die
// the pid of java vm is printed on the console
// u can check pid using the 'ps -ef | grep CC' command
// while(true) Thread.currentThread().sleep(1000);
}catch(Exception ex){
ex.printStackTrace();
}
}
public static void main(String args[]) {
CC run = new CC();
}
}

// to compile use
// gcc -o ppid ppid.c
int main(){
printf("%d\n",getppid());
return 0;
}

[Marcond Marchi]

Hi there. If You don't have access to a C compiler, the shell macros can be used to get the pid:

static int getPid ()
{
Random r = new Random ();

// Let's create a hand-made pid for default
int pid = r.nextInt () & 0x7fffffff;

// Cmd to obtain the pid using macro ($PPID becomes the pid number)
String cmd = "/bin/sh -c @$PPID@";

try
{
Process myProcess = Runtime.getRuntime ().exec (cmd);
// Yes, the cmd above hopefully leads to an error msg - with the pid number we need
InputStream is = myProcess.getErrorStream();
BufferedReader stdout = new BufferedReader(new InputStreamReader(is));

String line = stdout.readLine();

StringTokenizer st = new StringTokenizer (line, "@");

if (st.hasMoreTokens ())
{
st.nextToken ();

int ppid = Integer.parseInt (st.nextToken ());

if (ppid > 0)
{
pid = ppid;

System.out.println ("JVM real Pid: " + pid);
}
}
}
catch (Exception e)
{
// Problem obtaining pid, lets keep the hand-made pid.
System.out.println ("JVM hand-made Pid: " + pid);
}

return (pid);
}

It's just a clue, because I have tested this method of getting the PPID and it looks to me that before spawnning the exec (on Linux) the Java forks a new Java process, that is the parent pid, that dies when the spawned command terminates. The result is that multiple calls to getPid() returns increasing numbers. I haven't tested this somewhere else (Solaris, AIX), so Your milleage may vary.

[Stefan Wagner]

Let's hope, Mike L. was patient enough the last 5 years, to wait for this solution.

btw.: can you edit your post and decorate the code by using code-tags, to make indentation work properly?

[Kaido Lepisto]

FWIW, here's my humble solution to the same problem. I needed the PID too , so I did some poking and discovered the script is unnecessary and it also works with bash.

/**
   * Gets a string representing the pid of this program - Java VM
   */
  public static String getPid() throws IOException,InterruptedException {
    
    Vector<String> commands=new Vector<String>();
    commands.add("/bin/bash");
    commands.add("-c");
    commands.add("echo $PPID");
    ProcessBuilder pb=new ProcessBuilder(commands);
    
    Process pr=pb.start();
    pr.waitFor();
    if (pr.exitValue()==0) {
      BufferedReader outReader=new BufferedReader(new InputStreamReader(pr.getInputStream()));
      return outReader.readLine().trim();
    } else {
      System.out.println("Error while getting PID");
      return "";
    }
  }

[Mr. C Lamont Gilbert]

You can create a small shell script to start your java program and record the PID into a text file. Some linux programs do this so they are able to shut themselves down with a similar script call.

[Raghavan Muthu]

Scott Arrowood wrote:Joe, While I agree about waking zombies, All seven years of info is beneficial to those of us who happen to be looking for it the first time. Thanks for the help guys.

Yes of course. I just remember the recent discussion on the same topic yesterday with Paul Wheaton here.

My Google search took me here and it was good to get/see the updated/added information upon the older replies! (whether the link *really* helps the individual or not to solve his issue).

As Eric mentioned in the linked URL, the second point ("People saying I have a similar problem [Start a new thread, do not hijack, add a link back]") still holds good. Right?

Of course, the opinion differs!

[Steve Betnér]

This method can extract the UNIX PID from the Process. It might not work on every platform and implementation but it seems to work fine on GNU/Linux and Oracle JRE 1.6.

    int getUnixPID(Process process) throws IllegalArgumentException, IllegalAccessException, NoSuchFieldException {
        if (process.getClass().getName().equals("java.lang.UNIXProcess")) {
            Class proc = process.getClass();
            Field field = proc.getDeclaredField("pid");
            field.setAccessible(true);
            Object pid = field.get(process);
            return (Integer) pid;
        } else {
            throw new IllegalArgumentException("Not a UNIXProcess");
        }
    }

[Emilia con]

If I get a process object in Java through Runtime.getRuntime().exec(...), or ProcessBuilder.start(), I can wait for it through Process.waitFor(), which is like Thread.join(), or I could kill it with Process.destroy(), which is like the deprecated Thread.stop(). BUT: How do I find the pid of the Process Object? I don't see a method for doing that in The Official Documentation. Can I do this in Java? If so, how?

[Duc Quoc]

Emilia con wrote:If I get a process object in Java through Runtime.getRuntime().exec(...), or ProcessBuilder.start(), I can wait for it through Process.waitFor(), which is like Thread.join(), or I could kill it with Process.destroy(), which is like the deprecated Thread.stop(). BUT: How do I find the pid of the Process Object? I don't see a method for doing that in The Official Documentation. Can I do this in Java? If so, how?

Did you try the above suggestions?

I would try to invoke the "jps" (assumed Sun's JDK) with the Runtime.exec(...) , if I were you

--Duc

[Ken Tanaka]

For Groovy and Java 1.6:

import java.lang.management.*;
 
final String name = ManagementFactory.getRuntimeMXBean().getName();
final Integer pid = Integer.parseInt(name[0..name.indexOf("@")-1]);

Taken from http://snipplr.com/view/20787/
The name should be something like "[e-mail]" (This is not guaranteed, and can vary by Java implementation)

Alternatively, if you are using Groovy on a linux/unix platform, here is how the PID can be retreived from a shell execution:

ProcessBuilder pb = new ProcessBuilder( ['/bin/sh', '-c', 'echo $PPID'] )
println 'PID via ProcessBuilder: ' + pb.start().text

[Campbell Ritchie]

welcome to the Ranch