Only in openntpd-3.9p1.old: configure
diff -ur --unidirectional-new-file openntpd-3.9p1.old/configure.ac openntpd-3.9p1/configure.ac
--- openntpd-3.9p1.old/configure.ac	2006-05-14 07:29:23.000000000 +0200
+++ openntpd-3.9p1/configure.ac	2008-02-07 13:13:18.066366142 +0100
@@ -583,6 +583,11 @@
 	[ builtin_arc4random=$withval ]
 )

+AC_ARG_WITH(adjtimex,
+	    	[  --with-adjtimex         Use adjtimex to adjust kernel skew],
+	    	[ AC_DEFINE(USE_ADJTIMEX, [], [Use adjust skew with adjtimex (experimental)]) ]
+	    )
+
 AC_ARG_WITH(mantype,
 	[  --with-mantype=man|cat|doc  Set man page type],
 	[
diff -ur --unidirectional-new-file openntpd-3.9p1.old/defines.h openntpd-3.9p1/defines.h
--- openntpd-3.9p1.old/defines.h	2006-05-14 07:29:21.000000000 +0200
+++ openntpd-3.9p1/defines.h	2008-02-07 13:14:34.488711868 +0100
@@ -20,6 +20,10 @@
 # define setproctitle(x)
 #endif

+#ifdef USE_ADJTIMEX
+# define adjtime(a,b)	(_compat_adjtime((a),(b)))
+#endif
+
 #if !defined(SA_LEN)
 # if defined(HAVE_STRUCT_SOCKADDR_SA_LEN)
 #  define SA_LEN(x)	((x)->sa_len)
Only in openntpd-3.9p1.old: ntpd.0
Only in openntpd-3.9p1.old: ntpd.conf.0
diff -ur --unidirectional-new-file openntpd-3.9p1.old/openbsd-compat/Makefile.in openntpd-3.9p1/openbsd-compat/Makefile.in
--- openntpd-3.9p1.old/openbsd-compat/Makefile.in	2006-05-14 07:29:19.000000000 +0200
+++ openntpd-3.9p1/openbsd-compat/Makefile.in	2008-02-07 13:31:39.499728930 +0100
@@ -9,7 +9,7 @@
 COMPAT=		atomicio.o bsd-arc4random.o bsd-misc.o bsd-poll.o \
 		bsd-snprintf.o bsd-getifaddrs.o bsd-setresuid.o \
 		bsd-setresgid.o fake-rfc2553.o
-PORT=		port-qnx.o
+PORT=		port-linux.o port-qnx.o

 VPATH=@srcdir@
 CC=@CC@
diff -ur --unidirectional-new-file openntpd-3.9p1.old/openbsd-compat/openbsd-compat.h openntpd-3.9p1/openbsd-compat/openbsd-compat.h
--- openntpd-3.9p1.old/openbsd-compat/openbsd-compat.h	2006-05-14 07:29:19.000000000 +0200
+++ openntpd-3.9p1/openbsd-compat/openbsd-compat.h	2008-02-07 13:17:00.272366764 +0100
@@ -46,6 +46,11 @@
                 __attribute__((__format__ (printf, 2, 3)));
 #endif

+#ifdef USE_ADJTIMEX
+# include <sys/time.h>
+int _compat_adjtime(const struct timeval *, struct timeval *);
+#endif
+
 #ifndef HAVE_INET_PTON
 int inet_pton(int, const char *, void *);
 #endif
diff -ur --unidirectional-new-file openntpd-3.9p1.old/openbsd-compat/port-linux.c openntpd-3.9p1/openbsd-compat/port-linux.c
--- openntpd-3.9p1.old/openbsd-compat/port-linux.c	1970-01-01 01:00:00.000000000 +0100
+++ openntpd-3.9p1/openbsd-compat/port-linux.c	2008-02-07 13:24:43.800366563 +0100
@@ -0,0 +1,105 @@
+
+
+/*
+ * Copyright (c) 2004 Darren Tucker <dtucker at zip com au>
+ *
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include "includes.h"
+
+#ifdef USE_ADJTIMEX
+#include <sys/timex.h>
+#include <errno.h>
+#ifdef adjtime
+# undef adjtime
+#endif
+
+#include "ntpd.h"
+
+/* scale factor used by adjtimex freq param.  1 ppm = 65536 */
+#define ADJTIMEX_FREQ_SCALE 65536
+
+/* maximum change to skew per adjustment, in PPM */
+#define MAX_SKEW_DELTA 5.0
+
+int
+_compat_adjtime(const struct timeval *delta, struct timeval *olddelta)
+{
+	static struct timeval tlast = {0,0};
+	static double tskew = 0;
+	static int synced = -1;
+	struct timeval tnow, tdelta;
+	double skew = 0, newskew, deltaskew, adjust, interval = 0;
+	struct timex tmx;
+	int result, saved_errno;
+
+	gettimeofday(&tnow, NULL);
+	adjust = (double)delta->tv_sec;
+	adjust += (double)delta->tv_usec / 1000000;
+
+	/* Even if the caller doesn't care about the olddelta, we do */
+	if (olddelta == NULL)
+		olddelta = &tdelta;
+
+	result = adjtime(delta, olddelta);
+	saved_errno = errno;
+
+	if (olddelta->tv_sec == 0 && olddelta->tv_usec == 0 &&
+	    synced != INT_MAX)
+		synced++;
+	 else
+		synced = 0;
+
+	/*
+	 * do skew calculations if we have synced
+	 */
+	if (synced == 0 ) {
+		tmx.modes = 0;
+		if (adjtimex(&tmx) == -1)
+			log_warn("adjtimex get failed");
+		else
+			tskew = (double)tmx.freq / ADJTIMEX_FREQ_SCALE;
+	} else if (synced >= 1) {
+		interval = (double)(tnow.tv_sec - tlast.tv_sec);
+		interval += (double)(tnow.tv_usec - tlast.tv_usec) / 1000000;
+
+		skew = (adjust * 1000000) / interval;
+		newskew = ((tskew * synced) + skew) / synced;
+		deltaskew = newskew - tskew;
+
+		if (deltaskew > MAX_SKEW_DELTA) {
+			log_info("skew change %0.3lf exceeds limit", deltaskew);
+			tskew += MAX_SKEW_DELTA;
+		} else if (deltaskew < -MAX_SKEW_DELTA) {
+			log_info("skew change %0.3lf exceeds limit", deltaskew);
+			tskew -= MAX_SKEW_DELTA;
+		} else {
+			tskew = newskew;
+		}
+
+		/* Adjust the kernel skew.  */
+		tmx.freq = (long)(tskew * ADJTIMEX_FREQ_SCALE);
+		tmx.modes = ADJ_FREQUENCY;
+		if (adjtimex(&tmx) == -1)
+			log_warn("adjtimex set freq failed");
+	}
+
+	log_debug("interval %0.3lf skew %0.3lf total skew %0.3lf", interval,
+	    skew, tskew);
+
+	tlast = tnow;
+	errno = saved_errno;
+	return result;
+}
+#endif