Index: /trunk/include/VBox/HostServices/GuestControlSvc.h
===================================================================
--- /trunk/include/VBox/HostServices/GuestControlSvc.h	(revision 84547)
+++ /trunk/include/VBox/HostServices/GuestControlSvc.h	(revision 84548)
@@ -211,4 +211,8 @@
      */
     HOST_MSG_PATH_USER_HOME,
+    /**
+     * Issues a shutdown / reboot of the guest OS.
+     */
+    HOST_MSG_SHUTDOWN,
 
     /** Blow the type up to 32-bits. */
@@ -248,4 +252,5 @@
         RT_CASE_RET_STR(HOST_MSG_PATH_USER_DOCUMENTS);
         RT_CASE_RET_STR(HOST_MSG_PATH_USER_HOME);
+        RT_CASE_RET_STR(HOST_MSG_SHUTDOWN);
         RT_CASE_RET_STR(HOST_MSG_32BIT_HACK);
     }
@@ -699,4 +704,6 @@
  *  GUESTPROCESS_DEFAULT_CMD_LEN / GUESTPROCESS_DEFAULT_ARGS_LEN / GUESTPROCESS_DEFAULT_ENV_LEN (bytes, in total). */
 #define VBOX_GUESTCTRL_GF_0_PROCESS_DYNAMIC_SIZES   RT_BIT_64(2)
+/** Supports shutting down / rebooting the guest. */
+#define VBOX_GUESTCTRL_GF_0_SHUTDOWN                RT_BIT_64(3)
 /** Bit that must be set in the 2nd parameter, will be cleared if the host reponds
  * correctly (old hosts might not). */
@@ -873,4 +880,16 @@
     HGCMFunctionParameter context;
 } HGCMMsgPathUserHome;
+
+/**
+ * Shuts down / reboots the guest.
+ */
+typedef struct HGCMMsgShutdown
+{
+    VBGLIOCHGCMCALL hdr;
+    /** UInt32: Context ID. */
+    HGCMFunctionParameter context;
+    /** UInt32: Action flags. */
+    HGCMFunctionParameter action;
+} HGCMMsgShutdown;
 
 /**
Index: /trunk/include/VBox/VBoxGuestLib.h
===================================================================
--- /trunk/include/VBox/VBoxGuestLib.h	(revision 84547)
+++ /trunk/include/VBox/VBoxGuestLib.h	(revision 84548)
@@ -1042,4 +1042,5 @@
 VBGLR3DECL(int) VbglR3GuestCtrlPathGetUserDocuments(PVBGLR3GUESTCTRLCMDCTX pCtx);
 VBGLR3DECL(int) VbglR3GuestCtrlPathGetUserHome(PVBGLR3GUESTCTRLCMDCTX pCtx);
+VBGLR3DECL(int) VbglR3GuestCtrlGetShutdown(PVBGLR3GUESTCTRLCMDCTX pCtx, uint32_t *pfAction);
 /* Guest process execution. */
 VBGLR3DECL(int) VbglR3GuestCtrlProcStartupInfoInit(PVBGLR3GUESTCTRLPROCSTARTUPINFO pStartupInfo);
Index: /trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR3LibGuestCtrl.cpp
===================================================================
--- /trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR3LibGuestCtrl.cpp	(revision 84547)
+++ /trunk/src/VBox/Additions/common/VBoxGuest/lib/VBoxGuestR3LibGuestCtrl.cpp	(revision 84548)
@@ -1027,4 +1027,33 @@
 
 /**
+ * Retrieves a HOST_MSG_SHUTDOWN message.
+ *
+ * @returns VBox status code.
+ * @param   pCtx                Guest control command context to use.
+ * @param   pfAction            Where to store the action flags on success.
+ */
+VBGLR3DECL(int) VbglR3GuestCtrlGetShutdown(PVBGLR3GUESTCTRLCMDCTX pCtx, uint32_t *pfAction)
+{
+    AssertPtrReturn(pCtx, VERR_INVALID_POINTER);
+    AssertReturn(pCtx->uNumParms == 1, VERR_INVALID_PARAMETER);
+
+    int rc;
+    do
+    {
+        HGCMMsgShutdown Msg;
+        VBGL_HGCM_HDR_INIT(&Msg.hdr, pCtx->uClientID, vbglR3GuestCtrlGetMsgFunctionNo(pCtx->uClientID), pCtx->uNumParms);
+        VbglHGCMParmUInt32Set(&Msg.context, HOST_MSG_SHUTDOWN);
+
+        rc = VbglR3HGCMCall(&Msg.hdr, sizeof(Msg));
+        if (RT_SUCCESS(rc))
+        {
+            Msg.context.GetUInt32(&pCtx->uContextID);
+            Msg.action.GetUInt32(pfAction);
+        }
+    } while (rc == VERR_INTERRUPTED && g_fVbglR3GuestCtrlHavePeekGetCancel);
+    return rc;
+}
+
+/**
  * Initializes a process startup info, extended version.
  *
Index: /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControl.cpp
===================================================================
--- /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControl.cpp	(revision 84547)
+++ /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControl.cpp	(revision 84548)
@@ -247,5 +247,6 @@
         const uint64_t fGuestFeatures = VBOX_GUESTCTRL_GF_0_SET_SIZE
                                       | VBOX_GUESTCTRL_GF_0_PROCESS_ARGV0
-                                      | VBOX_GUESTCTRL_GF_0_PROCESS_DYNAMIC_SIZES;
+                                      | VBOX_GUESTCTRL_GF_0_PROCESS_DYNAMIC_SIZES
+                                      | VBOX_GUESTCTRL_GF_0_SHUTDOWN;
 
         rc = VbglR3GuestCtrlReportFeatures(g_idControlSvcClient, fGuestFeatures, &g_fControlHostFeatures0);
Index: /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControlSession.cpp
===================================================================
--- /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControlSession.cpp	(revision 84547)
+++ /trunk/src/VBox/Additions/common/VBoxService/VBoxServiceControlSession.cpp	(revision 84548)
@@ -34,4 +34,5 @@
 #include <iprt/process.h>
 #include <iprt/rand.h>
+#include <iprt/system.h> /* For RTShutdown. */
 
 #include "VBoxServiceInternal.h"
@@ -990,4 +991,50 @@
 
 /**
+ * Handles shutting down / rebooting the guest OS.
+ *
+ * @returns VBox status code.
+ * @param   pSession        Guest session.
+ * @param   pHostCtx        Host context.
+ */
+static int vgsvcGstCtrlSessionHandleShutdown(PVBOXSERVICECTRLSESSION pSession, PVBGLR3GUESTCTRLCMDCTX pHostCtx)
+{
+    AssertPtrReturn(pSession, VERR_INVALID_POINTER);
+    AssertPtrReturn(pHostCtx, VERR_INVALID_POINTER);
+
+    /*
+     * Retrieve the request.
+     */
+    uint32_t fAction;
+    int rc = VbglR3GuestCtrlGetShutdown(pHostCtx, &fAction);
+    if (RT_SUCCESS(rc))
+    {
+        VGSvcVerbose(1, "Host requested to %s system ...\n", (fAction & RTSYSTEM_SHUTDOWN_REBOOT) ? "reboot" : "shutdown");
+
+        /* Reply first to the host, in order to avoid host hangs when issuing the guest shutdown. */
+        rc = VbglR3GuestCtrlMsgReply(pHostCtx, VINF_SUCCESS);
+        if (RT_FAILURE(rc))
+        {
+            VGSvcError("Failed to reply to shutdown / reboot request, rc=%Rrc\n", rc);
+        }
+        else
+        {
+            rc = RTSystemShutdown(0 /*cMsDelay*/,
+                                  fAction | RTSYSTEM_SHUTDOWN_PLANNED,
+                                  "VBoxService");
+            if (RT_FAILURE(rc))
+                VGSvcError("%s system failed with %Rrc\n", (fAction & RTSYSTEM_SHUTDOWN_REBOOT) ? "Rebooting" : "Shuting down");
+        }
+    }
+    else
+    {
+        VGSvcError("Error fetching parameters for shutdown / reboot request: %Rrc\n", rc);
+        VbglR3GuestCtrlMsgSkip(pHostCtx->uClientID, rc, UINT32_MAX);
+    }
+
+    return rc;
+}
+
+
+/**
  * Handles getting the user's home directory.
  *
@@ -1412,4 +1459,8 @@
             if (fImpersonated)
                 rc = vgsvcGstCtrlSessionHandlePathUserHome(pSession, pHostCtx);
+            break;
+
+        case HOST_MSG_SHUTDOWN:
+            rc = vgsvcGstCtrlSessionHandleShutdown(pSession, pHostCtx);
             break;