Skip in-container sshd setup for single-node container runs

cvs/core/orchestrators/container.py

@@ -446,15 +446,27 @@ def setup_sshd(self):
         - Starts sshd on port 2224
         - Validates SSH daemon started successfully
 
+        The in-container sshd exists solely so MPI (mpirun's ``plm_rsh_args -p
+        2224``) can reach peer ranks on other nodes. A single-node run never
+        distributes over MPI -- it execs directly via ``docker exec`` -- so sshd
+        is dead weight there. On a single-host cluster this is a no-op, which
+        also lets minimal images that ship no ``/usr/sbin/sshd`` run single-node
+        without tripping the start/validate steps below.
+
         Returns:
-            bool: True if SSH setup succeeded on all nodes, False otherwise
+            bool: True if SSH setup succeeded on all nodes (or was skipped as
+            unnecessary for a single-node run), False otherwise
 
         Raises:
             RuntimeError: If no containers are currently running
         """
         if not self.container_id:
             raise RuntimeError("No containers running. Call setup_containers() first.")
 
+        if len(self.hosts) <= 1:
+            self.log.info("Single-node run: skipping in-container sshd setup (no inter-node MPI/SSH needed)")
+            return True
+
         self.log.info(f"Setting up SSH daemon in containers: {self.container_id}")
 
         # Execute SSH setup commands

cvs/core/orchestrators/unittests/test_container.py

@@ -222,6 +222,43 @@ def test_partition_by_status_missing_host_is_probe_failed(self):
         self.assertEqual(absent, [])
         self.assertEqual(probe_failed, ["h_gone"])
 
+    # ------------------------------------------------------------------
+    # setup_sshd single-node guard
+    # ------------------------------------------------------------------
+
+    def test_setup_sshd_single_node_skips_and_returns_true(self):
+        # The in-container sshd is only needed for multinode MPI. On a single-host
+        # cluster setup_sshd must short-circuit: no exec into the container, no
+        # dependency on the image shipping /usr/sbin/sshd.
+        orch, runtime = self._make(lifetime="per_run")
+        orch.hosts = ["10.0.0.1"]
+        orch.container_id = "cvs_iter_test"
+        self.assertTrue(orch.setup_sshd())
+        runtime.exec.assert_not_called()
+
+    def test_setup_sshd_requires_container_even_single_node(self):
+        # The container_id precondition is checked BEFORE the single-node guard,
+        # so a single-node orch with no running container still raises rather than
+        # silently returning True.
+        orch, _ = self._make(lifetime="per_run")
+        orch.hosts = ["10.0.0.1"]
+        self.assertIsNone(orch.container_id)
+        with self.assertRaises(RuntimeError):
+            orch.setup_sshd()
+
+    @patch("time.sleep", lambda *_a, **_k: None)
+    def test_setup_sshd_multinode_attempts_setup(self):
+        # The guard must NOT skip a genuine multinode run: every setup command and
+        # the final validation probe are exec'd into the container.
+        orch, runtime = self._make(lifetime="per_run")
+        orch.container_id = "cvs_iter_test"
+        runtime.exec.return_value = {
+            "10.0.0.1": {"exit_code": 0},
+            "10.0.0.2": {"exit_code": 0},
+        }
+        self.assertTrue(orch.setup_sshd())
+        self.assertTrue(runtime.exec.called)
+
     # ------------------------------------------------------------------
     # teardown_containers lifetime branching
     # ------------------------------------------------------------------