diff -r 840f0cadeba8 -r 94f6ca69d983 src/Pure/Admin/build_jdk.scala
--- a/src/Pure/Admin/build_jdk.scala	Sat Dec 08 14:28:14 2018 +0100
+++ b/src/Pure/Admin/build_jdk.scala	Sat Dec 08 14:58:56 2018 +0100
@@ -102,8 +102,7 @@
           "unzip -x " + File.bash_path(archive.absolute), cwd = tmp_dir.file).check
       }
       else {
-        Isabelle_System.gnutar(
-          "-C " + File.bash_path(tmp_dir) + " -xzf " + File.bash_path(archive)).check
+        Isabelle_System.gnutar("-xzf " + File.bash_path(archive), dir = tmp_dir).check
       }
 
       val dir_entry =
@@ -204,8 +203,9 @@
         }
 
         progress.echo("Archiving ...")
-        Isabelle_System.gnutar("--owner=root --group=root -C " + File.bash_path(dir) +
-          " -czf " + File.bash_path(target_dir + jdk_path.ext("tar.gz")) + " " + jdk_name).check
+        Isabelle_System.gnutar(
+          "-czf " + File.bash_path(target_dir + jdk_path.ext("tar.gz")) + " " + jdk_name,
+          dir = dir).check
       })
   }