Ghost User
--- a/src/knot/server/zones.c
+++ b/src/knot/server/zones.c
+		return KNOT_ERROR;
+	}
+
+	return data->conf->serial_policy;
+}
+
+static uint32_t zones_next_serial(int64_t old_sn, int serial_policy)
+{
+	if (old_sn < 0) {
+		return KNOT_EINVAL;
+	}
+
+	switch (serial_policy) {
+	case CONF_SERIAL_INCREMENT:
+		return (uint32_t)old_sn + 1;
+		break;
--- a/src/knot/server/zones.c
+++ b/src/knot/server/zones.c
 		log_zone_info("%s Signing zone...\n", msgpref);
 	}

+	uint32_t old_serial = knot_zone_serial(knot_zone_contents(zone));
--- a/src/libknot/dnssec/zone-events.c
+++ b/src/libknot/dnssec/zone-events.c
 }

 static int zone_sign(knot_zone_t *zone, knot_changeset_t *out_ch, bool force,
-                    knot_update_serial_t soa_up, uint32_t *expires_at)
+                    knot_update_serial_t soa_up, uint32_t *expires_at,
+                    uint32_t new_serial)
--- a/src/libknot/dnssec/zone-events.c
+++ b/src/libknot/dnssec/zone-events.c
 	                                          KNOT_RRTYPE_SOA);
 	assert(soa);
 	result = knot_zone_sign_update_soa(soa, &zone_keys, &policy,
--- a/doc/reference.texi
+++ b/doc/reference.texi
+@subsubsection serial-policy
+@vindex serial-policy
+
+Specifies how the zone serial is updated after DDNS (dynamic update) and
+automatic DNSSEC signing. If the serial is changed by the dynamic update, no
+change is made.
+
+increment - After update or signing, the serial is automatically incremented
+(according to serial number arithmetic).
+
+unixtime - After update or signing, serial is set to the current unix time.
+
+@strong{Warning:} If your serial was in other than unix time format, be careful with
+transition to unix time. It may happen that the new serial will be 'lower' than
+the old one. If this is the case, the transition should be done by hand (consult:
+http://www.zytrax.com/books/dns/ch9/serial.html).
--- a/src/knot/conf/conf.h
+++ b/src/knot/conf/conf.h
 } conf_zone_t;

 /*!
+* \brief Serial policy options.
+*/
+typedef enum conf_serial_policy_t {
+	CONF_SERIAL_INCREMENT	= 1 << 0,
+	CONF_SERIAL_UNIXTIME	= 1 << 1
+} conf_serial_policy_t;