diff --git a/run/O2HitMerger.h b/run/O2HitMerger.h
index d32f6370ca2db..30ddd57ba91da 100644
--- a/run/O2HitMerger.h
+++ b/run/O2HitMerger.h
@@ -88,6 +88,29 @@ namespace o2
 namespace devices
 {
 
+// Function communicating to primary particle server that it is now safe to shutdown.
+// From the perspective of o2-sim, this is the case when all configs have been propagated and the system
+// is running ok: For instance after the HitMerger is initialized and got it's first data from Geant workers.
+bool primaryServer_sendShutdownPermission(fair::mq::Channel& channel)
+{
+  std::unique_ptr<fair::mq::Message> request(channel.NewSimpleMessage((int)o2::O2PrimaryServerInfoRequest::AllowShutdown));
+  std::unique_ptr<fair::mq::Message> reply(channel.NewMessage());
+
+  int timeoutinMS = 100;
+  if (channel.Send(request, timeoutinMS) > 0) {
+    LOG(info) << "Sending Shutdown permission to particle server";
+    if (channel.Receive(reply, timeoutinMS) > 0) {
+      // the answer is a simple ack with a status code
+      LOG(info) << "Shutdown permission was acknowledged";
+    } else {
+      LOG(error) << "No answer received within " << timeoutinMS << "ms\n";
+      return false;
+    }
+    return true;
+  }
+  return false;
+}
+
 class O2HitMerger : public fair::mq::Device
 {
 
@@ -129,6 +152,9 @@ class O2HitMerger : public fair::mq::Device
     if (o2::devices::O2SimDevice::querySimConfig(GetChannels().at("o2sim-primserv-info").at(0))) {
       outfilename = o2::base::NameConf::getMCKinematicsFileName(o2::conf::SimConfig::Instance().getOutPrefix().c_str());
       mNExpectedEvents = o2::conf::SimConfig::Instance().getNEvents();
+    } else {
+      // we didn't manage to get a configuration --> better to fail
+      LOG(fatal) << "No configuration received. Aborting";
     }
     mAsService = o2::conf::SimConfig::Instance().asService();
     mForwardKine = o2::conf::SimConfig::Instance().forwardKine();
@@ -354,6 +380,13 @@ class O2HitMerger : public fair::mq::Device
       // for the next batch
       return waitForControlInput();
     }
+
+    static bool initAcknowledged = false;
+    if (!initAcknowledged) {
+      primaryServer_sendShutdownPermission(GetChannels().at("o2sim-primserv-info").at(0));
+      initAcknowledged = true;
+    }
+
     return more;
   }
 
@@ -413,10 +446,6 @@ class O2HitMerger : public fair::mq::Device
         };
       }
     }
-    if (!expectmore) {
-      // somehow FairMQ has difficulties shutting down; helping manually
-      // raise(SIGINT);
-    }
     return expectmore;
   }
 
diff --git a/run/O2PrimaryServerDevice.h b/run/O2PrimaryServerDevice.h
index 0c09c2105f403..b8703ffcddb28 100644
--- a/run/O2PrimaryServerDevice.h
+++ b/run/O2PrimaryServerDevice.h
@@ -247,11 +247,10 @@ class O2PrimaryServerDevice final : public fair::mq::Device
     }
   }
 
-  // launches a thread that listens for status requests from outside asynchronously
+  // launches a thread that listens for status/config/shutdown requests from outside asynchronously
   void launchInfoThread()
   {
     static std::vector<std::thread> threads;
-
     auto sendErrorReply = [](fair::mq::Channel& channel) {
       LOG(error) << "UNKNOWN REQUEST";
       std::unique_ptr<fair::mq::Message> reply(channel.NewSimpleMessage((int)(404)));
@@ -260,7 +259,9 @@ class O2PrimaryServerDevice final : public fair::mq::Device
 
     LOG(info) << "LAUNCHING STATUS THREAD";
     auto lambda = [this, sendErrorReply]() {
-      while (mState != O2PrimaryServerState::Stopped) {
+      bool canShutdown{false};
+      // Exit only when both: serving stopped and allowed from outside.
+      while (!(mState == O2PrimaryServerState::Stopped && canShutdown)) {
         auto& channel = GetChannels().at("o2sim-primserv-info").at(0);
         if (!channel.IsValid()) {
           LOG(error) << "channel primserv-info not valid";
@@ -285,6 +286,11 @@ class O2PrimaryServerDevice final : public fair::mq::Device
             }
           } else if (request_payload == (int)O2PrimaryServerInfoRequest::Config) {
             HandleConfigRequest(channel);
+          } else if (request_payload == (int)O2PrimaryServerInfoRequest::AllowShutdown) {
+            LOG(info) << "Got info that we may shutdown";
+            std::unique_ptr<fair::mq::Message> ack(channel.NewSimpleMessage(200));
+            channel.Send(ack);
+            canShutdown = true;
           } else {
             sendErrorReply(channel);
           }
@@ -518,10 +524,13 @@ class O2PrimaryServerDevice final : public fair::mq::Device
 
   void PostRun() override
   {
+    // We shouldn't shut down immediately when all events have been served
+    // Instead we also need to wait until the info thread running some communication server
+    // with other processes is finished.
     while (!mInfoThreadStopped) {
       LOG(info) << "Waiting info thread";
       using namespace std::chrono_literals;
-      std::this_thread::sleep_for(100ms);
+      std::this_thread::sleep_for(1000ms);
     }
   }
 
@@ -534,7 +543,7 @@ class O2PrimaryServerDevice final : public fair::mq::Device
     if (mEventCounter >= mMaxEvents && mNeedNewEvent) {
       workavailable = false;
     }
-    if (!(mState == O2PrimaryServerState::ReadyToServe || mState == O2PrimaryServerState::WaitingEvent)) {
+    if (!(mState.load() == O2PrimaryServerState::ReadyToServe || mState.load() == O2PrimaryServerState::WaitingEvent)) {
       // send a zero answer
       workavailable = false;
     }
diff --git a/run/O2SimDevice.h b/run/O2SimDevice.h
index 35a0c31986702..9256734cce487 100644
--- a/run/O2SimDevice.h
+++ b/run/O2SimDevice.h
@@ -95,9 +95,6 @@ class O2SimDevice final : public fair::mq::Device
   // returns true if successful / false if not
   static bool querySimConfig(fair::mq::Channel& channel)
   {
-    // auto text = new std::string("configrequest");
-    // std::unique_ptr<fair::mq::Message> request(channel.NewMessage(const_cast<char*>(text->c_str()),
-    //                                                           text->length(), CustomCleanup, text));
     std::unique_ptr<fair::mq::Message> request(channel.NewSimpleMessage((int)O2PrimaryServerInfoRequest::Config));
     std::unique_ptr<fair::mq::Message> reply(channel.NewMessage());
 
diff --git a/run/PrimaryServerState.h b/run/PrimaryServerState.h
index 5a15cca12b9b1..4bae1d566dc60 100644
--- a/run/PrimaryServerState.h
+++ b/run/PrimaryServerState.h
@@ -25,10 +25,11 @@ enum class O2PrimaryServerState {
 };
 static const char* PrimStateToString[5] = {"INIT", "SERVING", "WAITEVENT", "IDLE", "STOPPED"};
 
-/// enum class for type of info request
+/// enum class for request to o2sim-primserv-info channel of the O2PrimaryServerDevice
 enum class O2PrimaryServerInfoRequest {
-  Status = 1,
-  Config = 2
+  Status = 1,       // asks to retrieve current status of O2PrimaryServerDevice --> will send O2PrimaryServerState
+  Config = 2,       // asks for o2-sim config reply
+  AllowShutdown = 3 // can be used to let particle server know that shutdown is now safe (once all components initialized)
 };
 
 /// Struct to be used as payload when making a request