How to get PID of process I ve just started within java program

Question

I ve started a process with following code   ProcessBuilder pb   new ProcessBuilder  cmd     c    path     try        Process p   pb start                catch  IOException ex       Now I need to know the process s pid that I ve just started

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the jnr-process project provides this capability   It is part of the java native runtime used by jruby and can be considered a prototype for a future java-FFI

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This page has the HOWTO   http   www golesny de p code javagetpid  On Windows   Runtime exec       Returns an instance of  java lang Win32Process   OR  java lang ProcessImpl   Both have a private field  handle    This is an OS handle for the process  You will have to use this   Win32 API to query PID  That page has details on how to do that

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Since Java 9 class Process has new method long pid    so it is as simple as  ProcessBuilder pb   new ProcessBuilder  cmd     c    path    try       Process p   pb start        long pid   p pid            catch  IOException ex

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In my testing all IMPL classes had the field  pid   This has worked for me   public static int getPid Process process        try           Class lt   gt  cProcessImpl   process getClass            Field fPid   cProcessImpl getDeclaredField  pid            if   fPid isAccessible                  fPid setAccessible true                     return fPid getInt process         catch  Exception e            return -1            Just make sure the returned value is not -1  If it is  then parse the output of ps

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For GNU Linux  amp  MacOS  or generally UNIX like  systems  I ve used below method which works fine   private int tryGetPid Process process        if  process getClass   getName   equals  java lang UNIXProcess                  try                       Field f   process getClass   getDeclaredField  pid                f setAccessible true               return f getInt process                     catch  IllegalAccessException   IllegalArgumentException   NoSuchFieldException   SecurityException e                                 return 0

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If portability is not a concern  and you just want to get the pid on Windows without a lot of hassle while using code that is tested and known to work on all modern versions of Windows  you can use kohsuke s winp library  It is also available on Maven Central for easy consumption   Process process          WinProcess wp   new WinProcess process   int pid   wp getPid

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In Unix System  Linux  amp  Mac    public static synchronized long getPidOfProcess Process p        long pid   -1       try         if  p getClass   getName   equals  java lang UNIXProcess              Field f   p getClass   getDeclaredField  pid            f setAccessible true           pid   f getLong p           f setAccessible false                 catch  Exception e          pid   -1            return pid

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There isn t a simple solution   The way I ve done it in the past is to start another process to run either the ps command on Unix-like systems  or the tasklist command on Windows  and then parse the output of that command for the PID I want   In reality  I ended up putting that code into a separate shell script for each platform which just returned the PID  so that I could keep the Java piece as platform independent as possible   This doesn t work well for short-lived tasks  but that wasn t an issue for me

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Include jna  both  JNA  and  JNA Platform   in your library and use this function   import com sun jna Pointer  import com sun jna platform win32 Kernel32  import com sun jna platform win32 WinNT  import java lang reflect Field   public static long getProcessID Process p                long result   -1          try                         for windows             if  p getClass   getName   equals  java lang Win32Process                         p getClass   getName   equals  java lang ProcessImpl                                   Field f   p getClass   getDeclaredField  handle                    f setAccessible true                                 long handl   f getLong p                   Kernel32 kernel   Kernel32 INSTANCE                  WinNT HANDLE hand   new WinNT HANDLE                    hand setPointer Pointer createConstant handl                    result   kernel GetProcessId hand                   f setAccessible false                               for unix based operating systems             else if  p getClass   getName   equals  java lang UNIXProcess                                   Field f   p getClass   getDeclaredField  pid                    f setAccessible true                   result   f getLong p                   f setAccessible false                                   catch Exception ex                        result   -1                    return result          You can also download JNA from here and JNA Platform from here

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Using JNA  supporting old and new JVM to get process id  public static long getProcessId Process p       long pid   -1      try         pid   p pid          catch  NoSuchMethodError e            try                         for windows             if  p getClass   getName   equals  java lang Win32Process      p getClass   getName   equals  java lang ProcessImpl                      Field f   p getClass   getDeclaredField  handle                    f setAccessible true                                 long handl   f getLong p                   Kernel32 kernel   Kernel32 INSTANCE                  WinNT HANDLE hand   new WinNT HANDLE                    hand setPointer Pointer createConstant handl                    pid   kernel GetProcessId hand                   f setAccessible false                               for unix based operating systems             else if  p getClass   getName   equals  java lang UNIXProcess                                   Field f   p getClass   getDeclaredField  pid                    f setAccessible true                   pid   f getLong p                   f setAccessible false                                   catch Exception ex                        pid   -1                              return pid

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I believe the only portable way to do this  is to run a  child  process through another  parent  Java process  which will inform me the actual PID of the parent process  The child process could be anything   The code of this wrapper is  package com panayotis wrapper   import java io File  import java io IOException  import java lang management ManagementFactory   public class Main       public static void main String   args  throws IOException  InterruptedException           System out println ManagementFactory getRuntimeMXBean   getName   split      0            ProcessBuilder pb   new ProcessBuilder args           pb directory new File System getProperty  user dir              pb redirectInput ProcessBuilder Redirect INHERIT           pb redirectOutput ProcessBuilder Redirect INHERIT           pb redirectError ProcessBuilder Redirect INHERIT           pb start   waitFor              To use it  create a jar file with just this one  and call it with command arguments this   String java   System getProperty  java home     separator    bin    separator    java exe   String jar wrapper    path  of  wrapper jar    String   args   new String   java   -cp   jar wrapper   com panayotis wrapper Main   actual exec args

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This is not a generic answer   However  Some programs  especially services and long-running programs  create  or offer to create  optionally  a  pid file    For instance  LibreOffice offers --pidfile  file   see the docs   I was looking for quite some time for a Java Linux solution but the PID was  in my case  lying at hand

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I used a non-portable approach to retrieve the UNIX PID from the Process object that is very simple to follow   STEP 1  Use some Reflection API calls to identify the Process implementation class on the target server JRE  remember that Process is an abstract class   If your UNIX implementation is like mine  you will see an implementation class that has a property named pid that contains the PID of the process  Here is the logging code that I used         --------------------------------------------------------------------        Jim Tough - 2014-11-04        This temporary Reflection code is used to log the name of the        class that implements the abstract Process class on the target        JRE  all of its  Fields   properties and methods  and the value        of each field                I only care about how this behaves on our UNIX servers  so I ll        deploy a snapshot release of this code to a QA server  run it once         then check the logs                TODO Remove this logging code before building final release      final Class lt   gt  clazz   process getClass        logger info  Concrete implementation of     Process class getName                   is      clazz getName            Array of all fields in this class  regardless of access level     final Field   allFields   clazz getDeclaredFields        for  Field field   allFields            field setAccessible true      allows access to non-public fields         Class lt   gt  fieldClass   field getType            StringBuilder sb   new StringBuilder field getName             sb append     type              sb append fieldClass getName             sb append     value               Object fieldValue   null          try               fieldValue   field get process               sb append fieldValue               sb append                 catch  Exception e                logger error  Unable to get value for                          field getName          e                     logger info sb toString                 --------------------------------------------------------------------   STEP 2  Based on the implementation class and field name that you obtained from the Reflection logging  write some code to pickpocket the Process implementation class and retrieve the PID from it using the Reflection API  The code below works for me on my flavour of UNIX  You may have to adjust the EXPECTED IMPL CLASS NAME and EXPECTED PID FIELD NAME constants to make it work for you          Get the process id  PID  associated with a   code Process      param process   code Process   or null     return Integer containing the PID of the process  null if the     PID could not be retrieved or if a null parameter was supplied     Integer retrievePID final Process process        if  process    null            return null               --------------------------------------------------------------------        Jim Tough - 2014-11-04        NON PORTABLE CODE WARNING         The code in this block works on the company UNIX servers  but may        not work on  any  UNIX server  Definitely will not work on any        Windows Server instances      final String EXPECTED IMPL CLASS NAME    java lang UNIXProcess       final String EXPECTED PID FIELD NAME    pid       final Class lt   extends Process gt  processImplClass   process getClass        if  processImplClass getName   equals EXPECTED IMPL CLASS NAME             try               Field f   processImplClass getDeclaredField                      EXPECTED PID FIELD NAME               f setAccessible true      allows access to non-public fields             int pid   f getInt process               return pid            catch  Exception e                logger warn  Unable to get PID   e                   else           logger warn Process class getName       implementation was not                     EXPECTED IMPL CLASS NAME     - cannot retrieve PID                        actual type was      processImplClass getName                 --------------------------------------------------------------------      return null     If PID was not retrievable  just return null

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There is no public API for this yet  see Sun Bug 4244896  Sun Bug 4250622  As a workaround    Runtime exec        returns an Object of type   java lang Process   The Process class is abstract  and what you get back is some subclass of Process which is designed for your operating system  For example on Macs  it returns java lang UnixProcess which has a private field called pid  Using Reflection you can easily get the value of this field   This is admittedly a hack  but it might help   What do you need the PID for anyway

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There is an open-source library that has such a function  and it has cross-platform implementations  https   github com OpenHFT Java-Thread-Affinity  It may be overkill just to get the PID  but if you want other things like CPU and thread id  and specifically thread affinity  it may be adequate for you   To get the current thread s PID  just call Affinity getAffinityImpl   getProcessId     This is implemented using JNA  see arcsin s answer

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I think I have found out a solution  that looks quite bulletproof while working on most platforms  Here is the idea    Create a JVM-wide mutex that you acquire before spawning new process killing a process Use platform-dependent code to acquire list of child processes   pids of your JVM process Spawn new process Acquire new list of child processes   pids and compare with the previous list  The one that is new is your guy    Since you check only for child processes  you cannot be wronged by some other process in the same machine  JVM-wide mutex than allows you to be sure  that the new process is the correct one   Reading child process list is simpler than getting PID from process objects  because it does not require WIN API calls on windows  and  more importantly  it has been done already in several libs   Below is an implementation of the above idea using JavaSysMon library  It  class UDKSpawner        private int uccPid      private Logger uccLog                  Mutex that forces only one child process to be spawned at a time                       private static final Object spawnProcessMutex   new Object                    Spawns a new UDK process and sets   link  uccPid  to it s PID  To work correctly         the code relies on the fact that no other method in this JVM runs UDK processes and        that no method kills a process unless it acquires lock on spawnProcessMutex          param procBuilder         return              private Process spawnUDK ProcessBuilder procBuilder  throws IOException           synchronized  spawnProcessMutex                           JavaSysMon monitor   new JavaSysMon                DirectUDKChildProcessVisitor beforeVisitor   new DirectUDKChildProcessVisitor                monitor visitProcessTree monitor currentPid    beforeVisitor               Set lt Integer gt  alreadySpawnedProcesses   beforeVisitor getUdkPids                 Process proc   procBuilder start                 DirectUDKChildProcessVisitor afterVisitor   new DirectUDKChildProcessVisitor                monitor visitProcessTree monitor currentPid    afterVisitor               Set lt Integer gt  newProcesses   afterVisitor getUdkPids                 newProcesses removeAll alreadySpawnedProcesses                if newProcesses isEmpty                     uccLog severe  There is no new UKD PID                               else if newProcesses size    gt  1                   uccLog severe  Multiple new candidate UDK PIDs                  else                   uccPid   newProcesses iterator   next                              return proc                           private void killUDKByPID            if uccPid  lt  0               uccLog severe  Cannot kill UCC by PID  PID not set                 return                    synchronized spawnProcessMutex               JavaSysMon monitor   new JavaSysMon                monitor killProcessTree uccPid  false                        private static class DirectUDKChildProcessVisitor implements ProcessVisitor           Set lt Integer gt  udkPids   new HashSet lt Integer gt               Override         public boolean visit OsProcess op  int i                if op processInfo   getName   equals  UDK exe                     udkPids add op processInfo   getPid                               return false                     public Set lt Integer gt  getUdkPids                 return udkPids

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One solution is to use the idiosyncratic tools the platform offers   private static String invokeLinuxPsProcess String filterByCommand        List lt String gt  args   Arrays asList  ps -e -o stat pid unit args   split                Example output         Sl   22245 bpds-api service                 opt libreoffice5 4 program soffice bin --headless        Z    22250 -                                soffice bin   lt defunct gt       try           Process psAux   new ProcessBuilder args  redirectErrorStream true  start            try               Thread sleep 100      TODO  Find some passive way            catch  InterruptedException e               try  BufferedReader reader   new BufferedReader new InputStreamReader psAux getInputStream    StandardCharsets UTF 8                  String line              while   line   reader readLine       null                    if   line contains filterByCommand                       continue                  String   parts   line split    w                     if  parts length  lt  4                      throw new RuntimeException  Unexpected format of the  ps  line  expected at least 4 columns  n t    line                   String pid   parts 1                   return pid                                    catch  IOException ex            log warn String format  Failed executing  s   s   args  ex getMessage     ex             return null      Disclaimer  Not tested  but you get the idea    Call ps to list the processes  Find your one because you know the command you launched it with  If there are multiple processes with the same command  you can    Add another dummy argument to differentiate them Rely on the increasing PID  not really safe  not concurrent  Check the time of process creation  could be too coarse to really differentiate  also not concurrent  Add a specific environment variable and list it with ps too

[java] How to get PID of process I've just started within java program?

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