Turn off multi-node launch if only 1 node (#322)

* turn off multi-node launch if only 1 node

deepspeed/pt/deepspeed_run.py

@@ -247,9 +247,6 @@ def main(args=None):
                                                  args.include,
                                                  args.exclude)
 
-    if multi_node_exec and not shutil.which('pdsh'):
-        raise RuntimeError("pdsh is not installed, unable to proceed")
-
     env = os.environ.copy()
 
     if not args.master_addr:
@@ -278,6 +275,11 @@ def main(args=None):
     # encode world info as base64 to make it easier to pass via command line
     world_info_base64 = encode_world_info(active_resources)
 
+    multi_node_exec = len(active_resources) > 1
+
+    if multi_node_exec and not shutil.which('pdsh'):
+        raise RuntimeError("pdsh is not installed, unable to proceed")
+
     if not multi_node_exec:
         deepspeed_launch = [
             sys.executable,