diff --git a/src/cosd.cc b/src/cosd.cc
index fc455f16ca1..9c01046fac3 100644
--- a/src/cosd.cc
+++ b/src/cosd.cc
@@ -145,11 +145,9 @@ int main(int argc, const char **argv)
 
   g_timer.shutdown();
   messenger->register_entity(entity_name_t::OSD(whoami));
-  assert_warn(messenger);
   if (!messenger)
     return 1;
   messenger_hb->register_entity(entity_name_t::OSD(whoami));
-  assert_warn(messenger_hb);
   if (!messenger_hb)
     return 1;
 
@@ -157,13 +155,22 @@ int main(int argc, const char **argv)
   messenger->set_policy(entity_name_t::TYPE_MON, SimpleMessenger::Policy::client());
   messenger->set_policy(entity_name_t::TYPE_OSD, SimpleMessenger::Policy::lossless_peer());
 
+
+  OSD *osd = new OSD(whoami, messenger, messenger_hb, &mc, g_conf.osd_data, g_conf.osd_journal, mkjournal);
+
+  int err = osd->pre_init();
+  if (err < 0) {
+    char buf[80];
+    cerr << "error initializing osd: " << strerror_r(-err, buf, sizeof(buf)) << std::endl;
+    return 1;
+  }
+
   messenger->start();
   messenger_hb->start(true);  // only need to daemon() once
 
   // start osd
-  OSD *osd = new OSD(whoami, messenger, messenger_hb, &mc, g_conf.osd_data, g_conf.osd_journal, mkjournal);
   if (osd->init() < 0) {
-    cout << "error initializing osd" << std::endl;
+    cout << "error starting osd" << std::endl;
     return 1;
   }
 
diff --git a/src/os/FileStore.cc b/src/os/FileStore.cc
index 7ca992c596f..1c60267273b 100644
--- a/src/os/FileStore.cc
+++ b/src/os/FileStore.cc
@@ -351,12 +351,29 @@ int FileStore::lock_fsid()
   int r = ::fcntl(fsid_fd, F_SETLK, &l);
   if (r < 0) {
     char buf[80];
-    derr(0) << "mount failed to lock " << basedir << "/fsid, is another cosd still running? " << strerror_r(errno, buf, sizeof(buf)) << dendl;
+    derr(0) << "lock_fsid failed to lock " << basedir << "/fsid, is another cosd still running? " << strerror_r(errno, buf, sizeof(buf)) << dendl;
     return -errno;
   }
   return 0;
 }
 
+bool FileStore::test_mount_in_use()
+{
+  dout(5) << "test_mount basedir " << basedir << " journal " << journalpath << dendl;
+  char fn[PATH_MAX];
+  snprintf(fn, sizeof(fn), "%s/fsid", basedir.c_str());
+
+  // verify fs isn't in use
+
+  fsid_fd = ::open(fn, O_RDWR, 0644);
+  if (fsid_fd < 0)
+    return 0;   // no fsid, ok.
+  bool inuse = lock_fsid() < 0;
+  ::close(fsid_fd);
+  fsid_fd = -1;
+  return inuse;
+}
+
 int FileStore::mount() 
 {
   char buf[80];
diff --git a/src/os/FileStore.h b/src/os/FileStore.h
index fc1d43e6642..6cceed96b9a 100644
--- a/src/os/FileStore.h
+++ b/src/os/FileStore.h
@@ -106,6 +106,7 @@ class FileStore : public JournalingObjectStore {
     lock("FileStore::lock"),
     sync_epoch(0), stop(false), sync_thread(this), flusher_queue_len(0), flusher_thread(this) { }
 
+  bool test_mount_in_use();
   int mount();
   int umount();
   int mkfs();
diff --git a/src/os/ObjectStore.h b/src/os/ObjectStore.h
index 8423457dd59..527313d631d 100644
--- a/src/os/ObjectStore.h
+++ b/src/os/ObjectStore.h
@@ -430,6 +430,7 @@ public:
   virtual ~ObjectStore() {}
 
   // mgmt
+  virtual bool test_mount_in_use() = 0;
   virtual int mount() = 0;
   virtual int umount() = 0;
   virtual int mkfs() = 0;  // wipe
diff --git a/src/osd/OSD.cc b/src/osd/OSD.cc
index ff7f4a86176..18164a6635c 100644
--- a/src/osd/OSD.cc
+++ b/src/osd/OSD.cc
@@ -389,17 +389,33 @@ void handle_signal(int signal)
 
 void cls_initialize(OSD *_osd);
 
+
+int OSD::pre_init()
+{
+  Mutex::Locker lock(osd_lock);
+  
+  assert(!store);
+  store = create_object_store(dev_path, journal_path);
+  if (!store) {
+    dout(0) << " unable to create object store" << dendl;
+    return -ENODEV;
+  }
+
+  if (store->test_mount_in_use()) {
+    dout(0) << "object store " << dev_path << " is currently in use" << dendl;
+    cout << "object store " << dev_path << " is currently in use (cosd already running?)" << std::endl;
+    return -EBUSY;
+  }
+  return 0;
+}
+
 int OSD::init()
 {
   Mutex::Locker lock(osd_lock);
 
   // mount.
   dout(2) << "mounting " << dev_path << " " << (journal_path ? journal_path : "(no journal)") << dendl;
-  store = create_object_store(dev_path, journal_path);
-  if (!store) {
-    dout(0) << " unable to create object store" << dendl;
-    return -ENODEV;
-  }
+  assert(store);  // call pre_init() first!
 
   if (mknewjournal) {
     int r = store->mkjournal();
diff --git a/src/osd/OSD.h b/src/osd/OSD.h
index ece5afcdc23..e378fd6e69e 100644
--- a/src/osd/OSD.h
+++ b/src/osd/OSD.h
@@ -865,6 +865,7 @@ public:
   
 
   // startup/shutdown
+  int pre_init();
   int init();
   int shutdown();