diff -r 89a12af9c330 -r 8be4030394b8 src/Pure/System/numa.scala
--- a/src/Pure/System/numa.scala	Sat Sep 08 22:09:52 2018 +0200
+++ b/src/Pure/System/numa.scala	Sat Sep 08 22:21:19 2018 +0200
@@ -39,7 +39,7 @@
   def policy(node: Int): String =
     if (numactl_available) "numactl -m" + node + " -N" + node else ""
 
-  def policy_options(options: Options, numa_node: Option[Int]): Options =
+  def policy_options(options: Options, numa_node: Option[Int] = Some(0)): Options =
     numa_node match {
       case None => options
       case Some(n) => options.string("ML_process_policy") = policy(n)
@@ -48,6 +48,10 @@
 
   /* shuffling of CPU nodes */
 
+  def enabled: Boolean =
+    try { nodes().length >= 2 && numactl_available }
+    catch { case ERROR(_) => false }
+
   def enabled_warning(progress: Progress, enabled: Boolean): Boolean =
   {
     def warning =