Only change the sysctl variable if it presently points to /kernel.

sys/conf/Makefile.i386

@@ -1,6 +1,6 @@
 # Copyright 1990 W. Jolitz
 #	from: @(#)Makefile.i386	7.1 5/10/91
-#	$Id: Makefile.i386,v 1.72 1995/12/26 13:57:55 bde Exp $
+#	$Id: Makefile.i386,v 1.73 1996/01/05 18:30:10 wollman Exp $
 #
 # Makefile for FreeBSD
 #
@@ -155,7 +155,9 @@ tags:
 install:
 	chflags noschg /kernel
 	mv /kernel /kernel.old
-	sysctl -w kern.bootfile=/kernel.old
+	if [ `sysctl -n kern.bootfile` = "/kernel" ] ; then \
+		sysctl -w kern.bootfile=/kernel.old ; \
+	fi
 	install -c -m 555 -o root -g wheel -fschg kernel /
 
 ioconf.o: ioconf.c $S/sys/param.h machine/pte.h $S/sys/buf.h \

sys/conf/Makefile.powerpc

@@ -1,6 +1,6 @@
 # Copyright 1990 W. Jolitz
 #	from: @(#)Makefile.i386	7.1 5/10/91
-#	$Id: Makefile.i386,v 1.72 1995/12/26 13:57:55 bde Exp $
+#	$Id: Makefile.i386,v 1.73 1996/01/05 18:30:10 wollman Exp $
 #
 # Makefile for FreeBSD
 #
@@ -155,7 +155,9 @@ tags:
 install:
 	chflags noschg /kernel
 	mv /kernel /kernel.old
-	sysctl -w kern.bootfile=/kernel.old
+	if [ `sysctl -n kern.bootfile` = "/kernel" ] ; then \
+		sysctl -w kern.bootfile=/kernel.old ; \
+	fi
 	install -c -m 555 -o root -g wheel -fschg kernel /
 
 ioconf.o: ioconf.c $S/sys/param.h machine/pte.h $S/sys/buf.h \

sys/i386/conf/Makefile.i386

@@ -1,6 +1,6 @@
 # Copyright 1990 W. Jolitz
 #	from: @(#)Makefile.i386	7.1 5/10/91
-#	$Id: Makefile.i386,v 1.72 1995/12/26 13:57:55 bde Exp $
+#	$Id: Makefile.i386,v 1.73 1996/01/05 18:30:10 wollman Exp $
 #
 # Makefile for FreeBSD
 #
@@ -155,7 +155,9 @@ tags:
 install:
 	chflags noschg /kernel
 	mv /kernel /kernel.old
-	sysctl -w kern.bootfile=/kernel.old
+	if [ `sysctl -n kern.bootfile` = "/kernel" ] ; then \
+		sysctl -w kern.bootfile=/kernel.old ; \
+	fi
 	install -c -m 555 -o root -g wheel -fschg kernel /
 
 ioconf.o: ioconf.c $S/sys/param.h machine/pte.h $S/sys/buf.h \