Provide the -n switch like in the other imsg daemons for testing

the configuration file.
"yes please, ok" henning@

src/usr.sbin/ntpd/ntpd.8

@@ -1,4 +1,4 @@
-.\" $OpenBSD: ntpd.8,v 1.19 2007/08/22 21:04:30 ckuethe Exp $
+.\" $OpenBSD: ntpd.8,v 1.20 2007/09/13 14:34:36 pyr Exp $
 .\"
 .\" Copyright (c) 2003, 2004, 2006 Henning Brauer <henning@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
 .\" OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: August 22 2007 $
+.Dd $Mdocdate: September 13 2007 $
 .Dt NTPD 8
 .Os
 .Sh NAME
@@ -23,7 +23,7 @@
 .Sh SYNOPSIS
 .Nm ntpd
 .Bk -words
-.Op Fl dSsv
+.Op Fl dnSsv
 .Op Fl f Ar file
 .Ek
 .Sh DESCRIPTION
@@ -89,6 +89,9 @@ Use
 as the configuration file,
 instead of the default
 .Pa /etc/ntpd.conf .
+.It Fl n
+Configtest mode.
+Only check the configuration file for validity.
 .It Fl S
 Do not set the time immediately at startup.
 This is the default.

src/usr.sbin/ntpd/ntpd.c

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.c,v 1.50 2007/08/22 21:04:30 ckuethe Exp $ */
+/*	$OpenBSD: ntpd.c,v 1.51 2007/09/13 14:34:36 pyr Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -96,7 +96,7 @@ main(int argc, char *argv[])
 	log_init(1);		/* log to stderr until daemonized */
 	res_init();		/* XXX */
 
-	while ((ch = getopt(argc, argv, "df:sSv")) != -1) {
+	while ((ch = getopt(argc, argv, "df:nsSv")) != -1) {
 		switch (ch) {
 		case 'd':
 			lconf.debug = 1;
@@ -104,6 +104,9 @@ main(int argc, char *argv[])
 		case 'f':
 			conffile = optarg;
 			break;
+		case 'n':
+			lconf.noaction = 1;
+			break;
 		case 's':
 			lconf.settime = 1;
 			break;
@@ -122,6 +125,11 @@ main(int argc, char *argv[])
 	if (parse_config(conffile, &lconf))
 		exit(1);
 
+	if (lconf.noaction) {
+		fprintf(stderr, "configuration OK\n");
+		exit(0);
+	}
+
 	if (geteuid()) {
 		fprintf(stderr, "ntpd: need root privileges\n");
 		exit(1);

src/usr.sbin/ntpd/ntpd.h

@@ -1,4 +1,4 @@
-/*	$OpenBSD: ntpd.h,v 1.86 2007/09/12 21:08:46 ckuethe Exp $ */
+/*	$OpenBSD: ntpd.h,v 1.87 2007/09/13 14:34:36 pyr Exp $ */
 
 /*
  * Copyright (c) 2003, 2004 Henning Brauer <henning@openbsd.org>
@@ -172,6 +172,7 @@ struct ntpd_conf {
 	u_int8_t					settime;
 	u_int8_t					debug;
 	u_int32_t					scale;
+	u_int8_t					noaction;
 };
 
 struct buf {