--- loncom/loncron	2011/04/23 16:18:49	1.88
+++ loncom/loncron	2011/05/14 16:12:53	1.89
@@ -2,7 +2,7 @@
 
 # Housekeeping program, started by cron, loncontrol and loncron.pl
 #
-# $Id: loncron,v 1.88 2011/04/23 16:18:49 raeburn Exp $
+# $Id: loncron,v 1.89 2011/05/14 16:12:53 raeburn Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -32,6 +32,7 @@ use strict;
 
 use lib '/home/httpd/lib/perl/';
 use LONCAPA::Configuration;
+use LONCAPA;
 use Apache::lonnet;
 use Apache::loncommon;
 
@@ -821,8 +822,11 @@ sub main () {
                 print $fh "$key\n";
             }
             close($fh);
-            my $execpath = $perlvar{'lonDaemons'}.'/lciptables';
-            system("$execpath $tmpfile");
+            if (&LONCAPA::try_to_lock('/tmp/lock_lciptables')) {
+                my $execpath = $perlvar{'lonDaemons'}.'/lciptables';
+                system("$execpath $tmpfile");
+                unlink('/tmp/lock_lciptables');  # Remove the lock file. 
+            }
             unlink($tmpfile);
         }
     }