Index: source/Commands/CommandObjectThread.cpp
===================================================================
--- source/Commands/CommandObjectThread.cpp
+++ source/Commands/CommandObjectThread.cpp
@@ -94,7 +94,7 @@
     bool all_threads = false;
     if (command.GetArgumentCount() == 0) {
       Thread *thread = m_exe_ctx.GetThreadPtr();
-      if (!HandleOneThread(thread->GetID(), result))
+      if (!thread || !HandleOneThread(thread->GetID(), result))
         return false;
       return result.Succeeded();
     } else if (command.GetArgumentCount() == 1) {
@@ -775,6 +775,12 @@
       else
         error = process->Resume();
 
+      if (!error.Success()) {
+        result.AppendMessage(error.AsCString());
+        result.SetStatus(eReturnStatusFailed);
+        return false;
+      }
+
       // There is a race condition where this thread will return up the call
       // stack to the main command handler
       // and show an (lldb) prompt before HandlePrivateEvent (from
Index: source/Plugins/Process/elf-core/ProcessElfCore.h
===================================================================
--- source/Plugins/Process/elf-core/ProcessElfCore.h
+++ source/Plugins/Process/elf-core/ProcessElfCore.h
@@ -89,6 +89,8 @@
   //------------------------------------------------------------------
   bool IsAlive() override;
 
+  bool WarnBeforeDetach() const override { return false; }
+
   //------------------------------------------------------------------
   // Process Memory
   //------------------------------------------------------------------
Index: source/Target/Process.cpp
===================================================================
--- source/Target/Process.cpp
+++ source/Target/Process.cpp
@@ -1621,7 +1621,12 @@
       log->Printf("Process::Resume: -- TrySetRunning failed, not resuming.");
     return error;
   }
-  return PrivateResume();
+  Status error = PrivateResume();
+  if (!error.Success()) {
+    // Undo running state change
+    m_public_run_lock.SetStopped();
+  }
+  return error;
 }
 
 Status Process::ResumeSynchronous(Stream *stream) {
@@ -1650,6 +1655,9 @@
       error.SetErrorStringWithFormat(
           "process not in stopped state after synchronous resume: %s",
           StateAsCString(state));
+  } else {
+    // Undo running state change
+    m_public_run_lock.SetStopped();
   }
 
   // Undo the hijacking of process events...