diff -r 4c8295f2f849 -r e48d93811ed7 src/Pure/Admin/isabelle_cronjob.scala
--- a/src/Pure/Admin/isabelle_cronjob.scala	Sat Oct 03 23:01:40 2020 +0100
+++ b/src/Pure/Admin/isabelle_cronjob.scala	Mon Oct 05 21:15:58 2020 +0200
@@ -476,7 +476,7 @@
 
     val log_dir: Path = main_dir + Build_Log.log_subdir(start_date)
 
-    Isabelle_System.mkdirs(log_dir)
+    Isabelle_System.make_directory(log_dir)
     log(start_date, "started")
   }