[FIXED JENKINS-11742] don't change PID when a daemon is restarting

changelog.html

@@ -55,6 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
+  <li class=bug>
+    If running as a daemon, don't daemonize one more time during restart.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-11742">issue 11742</a>)
   <li class=bug>
     Fixed NPE in Subversion polling of Maven jobs.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-11592">issue 11592</a>)

core/src/main/java/hudson/lifecycle/UnixLifecycle.java

@@ -52,6 +52,9 @@ public class UnixLifecycle extends Lifecycle {
     public UnixLifecycle() throws IOException {
         try {
             args = JavaVMArguments.current();
+
+            // if we are running as daemon, don't fork into background one more time during restart
+            args.remove("--daemon");
         } catch (UnsupportedOperationException e) {
             // can't restart
             failedToObtainArgs = e;