Index: usr.sbin/newsyslog/extern.h
===================================================================
--- usr.sbin/newsyslog/extern.h
+++ usr.sbin/newsyslog/extern.h
@@ -60,6 +60,9 @@
 int		 ptime_relparse(struct ptime_data *_ptime, int _parseopts,
 		    time_t _basetime, const char *_str);
 const char	*ptimeget_ctime(const struct ptime_data *_ptime);
+char		*ptimeget_ctime_rfc5424(const struct ptime_data *_ptime,
+		    char *timebuf,
+		    size_t bufsize);
 double		 ptimeget_diff(const struct ptime_data *_minuend,
 		    const struct ptime_data *_subtrahend);
 time_t		 ptimeget_secs(const struct ptime_data *_ptime);
Index: usr.sbin/newsyslog/newsyslog.8
===================================================================
--- usr.sbin/newsyslog/newsyslog.8
+++ usr.sbin/newsyslog/newsyslog.8
@@ -17,7 +17,7 @@
 .\" the suitability of this software for any purpose.  It is
 .\" provided "as is" without express or implied warranty.
 .\"
-.Dd April 15, 2017
+.Dd May 19, 2017
 .Dt NEWSYSLOG 8
 .Os
 .Sh NAME
@@ -125,7 +125,8 @@
 Cause
 .Nm
 not to trim the logs, but to print out what it would do if this option
-were not specified. This option implies the
+were not specified.
+This option implies the
 .Fl r
 option.
 .It Fl r
Index: usr.sbin/newsyslog/newsyslog.c
===================================================================
--- usr.sbin/newsyslog/newsyslog.c
+++ usr.sbin/newsyslog/newsyslog.c
@@ -79,6 +79,7 @@
 #include <libgen.h>
 #include <stdlib.h>
 #include <string.h>
+#include <syslog.h>
 #include <time.h>
 #include <unistd.h>
 
@@ -132,6 +133,8 @@
 #define	CE_NODUMP	0x0200	/* Set 'nodump' on newly created log file. */
 #define	CE_PID2CMD	0x0400	/* Replace PID file with a shell command.*/
 
+#define	CE_RFC5424	0x0800	/* Use RFC5424 format rotation message */
+
 #define	MIN_PID         5	/* Don't touch pids lower than this */
 #define	MAX_PID		99999	/* was lower, see /usr/include/sys/proc.h */
 
@@ -247,6 +250,15 @@
 #define	DAYTIME_LEN	16
 static char daytime[DAYTIME_LEN];/* The current time in human readable form,
 				  * used for rotation-tracking messages. */
+
+/* Another buffer to hold the current time in RFC5424 format. Fractional
+ * seconds are allowed by the RFC, but are not included in the
+ * rotation-tracking messages written by newsyslog and so are not accounted for
+ * in the length below.
+ */
+#define	DAYTIME_RFC5424_LEN	sizeof("YYYY-MM-DDTHH:MM:SS+00:00")
+static char daytime_rfc5424[DAYTIME_RFC5424_LEN];
+
 static char hostname[MAXHOSTNAMELEN]; /* hostname */
 
 static const char *path_syslogpid = _PATH_SYSLOGPID;
@@ -630,6 +642,7 @@
 	timenow = ptime_init(NULL);
 	ptimeset_time(timenow, time(NULL));
 	strlcpy(daytime, ptimeget_ctime(timenow) + 4, DAYTIME_LEN);
+	ptimeget_ctime_rfc5424(timenow, daytime_rfc5424, DAYTIME_RFC5424_LEN);
 
 	/* Let's get our hostname */
 	(void)gethostname(hostname, sizeof(hostname));
@@ -1296,11 +1309,14 @@
 			case 'r':
 				working->flags |= CE_PID2CMD;
 				break;
+			case 't':
+				working->flags |= CE_RFC5424;
+				break;
 			case 'u':
 				working->flags |= CE_SIGNALGROUP;
 				break;
 			case 'w':
-				/* Depreciated flag - keep for compatibility purposes */
+				/* Deprecated flag - keep for compatibility purposes */
 				break;
 			case 'x':
 				working->compress = COMPRESS_XZ;
@@ -2101,7 +2117,7 @@
 
 	tmpsiz = sizeof(struct sigwork_entry) + strlen(ent->pid_cmd_file) + 1;
 	stmp = malloc(tmpsiz);
-	
+
 	stmp->sw_runcmd = 0;
 	/* If this is a command to run we just set the flag and run command */
 	if (ent->flags & CE_PID2CMD) {
@@ -2257,15 +2273,34 @@
 	xtra = "";
 	if (log_ent->def_cfg)
 		xtra = " using <default> rule";
-	if (log_ent->firstcreate)
-		fprintf(f, "%s %s newsyslog[%d]: logfile first created%s\n",
-		    daytime, hostname, (int) getpid(), xtra);
-	else if (log_ent->r_reason != NULL)
-		fprintf(f, "%s %s newsyslog[%d]: logfile turned over%s%s\n",
-		    daytime, hostname, (int) getpid(), log_ent->r_reason, xtra);
-	else
-		fprintf(f, "%s %s newsyslog[%d]: logfile turned over%s\n",
-		    daytime, hostname, (int) getpid(), xtra);
+	if (log_ent->flags & CE_RFC5424) {
+		if (log_ent->firstcreate) {
+			fprintf(f, "<%d>1 %s %s newsyslog %d - - %s%s\n",
+			    LOG_MAKEPRI(LOG_USER, LOG_INFO),
+			    daytime_rfc5424, hostname, (int) getpid(),
+			    "logfile first created", xtra);
+		} else if (log_ent->r_reason != NULL) {
+			fprintf(f, "<%d>1 %s %s newsyslog %d - - %s%s%s\n",
+			    LOG_MAKEPRI(LOG_USER, LOG_INFO),
+			    daytime_rfc5424, hostname, (int) getpid(),
+			    "logfile turned over", log_ent->r_reason, xtra);
+		} else {
+			fprintf(f, "<%d>1 %s %s newsyslog %d - - %s%s\n",
+			    LOG_MAKEPRI(LOG_USER, LOG_INFO),
+			    daytime_rfc5424, hostname, (int) getpid(),
+			    "logfile turned over", xtra);
+		}
+	} else {
+		if (log_ent->firstcreate)
+			fprintf(f, "%s %s newsyslog[%d]: logfile first created%s\n",
+			    daytime, hostname, (int) getpid(), xtra);
+		else if (log_ent->r_reason != NULL)
+			fprintf(f, "%s %s newsyslog[%d]: logfile turned over%s%s\n",
+			    daytime, hostname, (int) getpid(), log_ent->r_reason, xtra);
+		else
+			fprintf(f, "%s %s newsyslog[%d]: logfile turned over%s\n",
+			    daytime, hostname, (int) getpid(), xtra);
+	}
 	if (fclose(f) == EOF)
 		err(1, "log_trim: fclose");
 	return (0);
Index: usr.sbin/newsyslog/newsyslog.conf.5
===================================================================
--- usr.sbin/newsyslog/newsyslog.conf.5
+++ usr.sbin/newsyslog/newsyslog.conf.5
@@ -21,7 +21,7 @@
 .\" the suitability of this software for any purpose.  It is
 .\" provided "as is" without express or implied warranty.
 .\"
-.Dd April 15, 2017
+.Dd May 19, 2017
 .Dt NEWSYSLOG.CONF 5
 .Os
 .Sh NAME
@@ -242,7 +242,7 @@
 (i.e., the start of the day; same as
 .Li @01T00 )
 .It Li $M5D6
-rotate on every 5th day of month at 6:00
+rotate on every fifth day of month at 6:00
 (same as
 .Li @05T06 )
 .El
@@ -319,6 +319,11 @@
 .Ar path_to_pid_cmd_file
 after rotation instead of trying to send signal to a process id
 stored in the file.
+.It Cm T
+if this flag is set the informational rotation message written to
+the log file will be in the format specified by RFC5424.
+Normally, the rotation message is written in the traditional (RFC3164)
+syslog format.
 .It Cm U
 indicates that the file specified by
 .Ar path_to_pid_cmd_file
@@ -395,6 +400,17 @@
 .Xr chown 8 ,
 .Xr newsyslog 8 ,
 .Xr syslogd 8
+.Pp
+.Rs
+.%A C. Lonvick
+.%T The BSD syslog Protocol
+.%O RFC3164
+.Re
+.Rs
+.%A R. Gerhards
+.%T The Syslog Protocol
+.%O RFC5424
+.Re
 .Sh HISTORY
 This manual page first appeared in
 .Fx 4.10 .
Index: usr.sbin/newsyslog/ptimes.c
===================================================================
--- usr.sbin/newsyslog/ptimes.c
+++ usr.sbin/newsyslog/ptimes.c
@@ -478,6 +478,74 @@
 	return (ctime(&ptime->tsecs));
 }
 
+/*
+ * Generate a time of day string in an RFC5424 compatible format. Return a
+ * pointer to the buffer with the timestamp string or NULL if an error. If the
+ * time is not supplied, cannot be converted to local time, or the resulting
+ * string would overflow the buffer, the returned string will be the RFC5424
+ * NILVALUE.
+ */
+char *
+ptimeget_ctime_rfc5424(const struct ptime_data *ptime,
+    char *timebuf,
+    size_t bufsize)
+{
+	static const char nilvalue[] = {"-"};	/* RFC5424 specified NILVALUE */
+	int chars;
+	struct tm tm;
+	int tz_hours;
+	int tz_mins;
+	long tz_offset;
+	char tz_sign;
+
+	if (timebuf == NULL)
+		return (NULL);
+
+	if (bufsize < sizeof(nilvalue))
+		return (NULL);
+
+	/*
+	 * Convert to localtime. RFC5424 mandates the use of the NILVALUE if
+	 * the time cannot be obtained, so use that if there is an error in the
+	 * conversion.
+	 */
+	if (ptime == NULL || localtime_r(&(ptime->tsecs), &tm) == NULL) {
+		strlcpy(timebuf, nilvalue, bufsize);
+		return (timebuf);
+	}
+
+	/*
+	 * Convert the time to a string in RFC5424 format. The conversion
+	 * cannot be done with strftime() because it cannot produce the correct
+	 * timezone offset format.
+	 */
+	if (tm.tm_gmtoff < 0) {
+		tz_sign = '-';
+		tz_offset = -tm.tm_gmtoff;
+	} else {
+		tz_sign = '+';
+		tz_offset = tm.tm_gmtoff;
+	}
+
+	tz_hours = tz_offset / 3600;
+	tz_mins	 = (tz_offset % 3600) / 60;
+
+	chars = snprintf(timebuf, bufsize,
+	    "%04d-%02d-%02d"	/* date */
+	    "T%02d:%02d:%02d"	/* time */
+	    "%c%02d:%02d",	/* time zone offset */
+	    tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday,
+	    tm.tm_hour, tm.tm_min, tm.tm_sec,
+	    tz_sign, tz_hours, tz_mins);
+
+	/* If the timestamp is too big for timebuf, return the NILVALUE. */
+	if (chars >= (int)bufsize) {
+		strlcpy(timebuf, nilvalue, bufsize);
+	}
+
+	return (timebuf);
+}
+
 double
 ptimeget_diff(const struct ptime_data *minuend, const struct
     ptime_data *subtrahend)
Index: usr.sbin/newsyslog/tests/legacy_test.sh
===================================================================
--- usr.sbin/newsyslog/tests/legacy_test.sh
+++ usr.sbin/newsyslog/tests/legacy_test.sh
@@ -2,6 +2,15 @@
 
 # $FreeBSD$
 
+# A regular expression matching the format of an RFC-5424 log line header,
+# including the timestamp up through the seconds indicator; it does not include
+# the (optional) timezone offset.
+RFC5424_FMT='^<[0-9][0-9]*>1 [0-9]{4}-[0-9]{2}-[0-9]{2}T[0-9]{2}:[0-9]{2}:[0-9]{2}'
+
+# A regular expression matching the format of an RFC-3164 (traditional syslog)
+# log line header, including the timestamp.
+RFC3164_FMT='^[A-Z][a-z]{2} [ 0-9][0-9] [0-9]{2}:[0-9]{2}:[0-9]{2}'
+
 COUNT=0
 TMPDIR=$(pwd)/work
 if [ $? -ne 0 ]; then
@@ -98,6 +107,32 @@
 	fi
 }
 
+# Verify that the specified file has RFC-5424 rotation messages.
+ckrfc5424()
+{
+	local lc=$(wc -l $1 | cut -w -f2)
+	local rc=$(grep -E "${RFC5424_FMT}" $1 | wc -l | cut -w -f2)
+	if [ "$lc" -eq 0 -o "$rc" -eq 0 -o "$lc" -ne "$rc" ]
+	then
+		notok
+	else
+		ok
+	fi
+}
+
+
+# Verify that the specified file has RFC-3164 rotation messages.
+ckrfc3164()
+{
+	local lc=$(wc -l $1 | cut -w -f2)
+	local rc=$(grep -E "${RFC3164_FMT}" $1 | wc -l | cut -w -f2)
+	if [ "$lc" -eq 0 -o "$rc" -eq 0 -o "$lc" -ne "$rc" ]
+	then
+		notok
+	else
+		ok
+	fi
+}
 
 
 # A part of a test succeeds
@@ -381,6 +416,45 @@
 	tmpdir_clean
 }
 
+tests_rfc5424() {
+	ext="$1"
+	dir="$2"
+
+	if [ -n "$dir" ]; then
+		newsyslog_args=" -a ${dir}"
+		name_postfix="${ext} archive dir"
+	else
+		newsyslog_args=""
+		name_postfix="${ext}"
+	fi
+
+	tmpdir_create
+
+	begin "RFC-5424 - create file ${name_postfix}" -newdir
+	run_newsyslog -C
+	ckfe $LOGFNAME
+	cknt ${dir}${LOGFNAME}.0${ext}
+	ckfe $LOGFNAME5424
+	cknt ${dir}${LOGFNAME5424}.0${ext}
+        ckrfc3164 ${LOGFNAME}
+        ckrfc5424 ${LOGFNAME5424}
+	end
+
+	begin "RFC-5424 - rotate normal 1 ${name_postfix}"
+	run_newsyslog $newsyslog_args
+	ckfe ${LOGFNAME}
+	ckfe ${dir}${LOGFNAME}.0${ext}
+	ckfe $LOGFNAME5424
+	ckfe ${dir}${LOGFNAME5424}.0${ext}
+        ckrfc3164 ${LOGFNAME}
+        ckrfc3164 ${dir}${LOGFNAME}.0${ext}
+        ckrfc5424 ${LOGFNAME5424}
+        ckrfc5424 ${dir}${LOGFNAME5424}.0${ext}
+	end
+
+	tmpdir_clean
+}
+
 echo 1..126
 mkdir -p ${TMPDIR}
 cd ${TMPDIR}
@@ -388,6 +462,10 @@
 LOGFNAME=foo.log
 LOGFPATH=${TMPDIR}/log/${LOGFNAME}
 
+# Log file for RFC-5424 testing
+LOGFNAME5424=foo5424.log
+LOGFPATH5424=${TMPDIR}/log/${LOGFNAME5424}
+
 # Normal, no archive dir, keep X files
 echo "$LOGFPATH	640  0	   *	@T00  NC" > newsyslog.conf
 tests_normal_rotate_keepn 0
@@ -454,4 +532,9 @@
 echo "$LOGFPATH	640  3	   *	@T00  NCJ" > newsyslog.conf
 tests_time_rotate "bz2" "${TMPDIR}/alog/"
 
+# RFC-5424; Normal, no archive dir
+echo "$LOGFPATH5424	640  3	   *	@T00  NCT" > newsyslog.conf
+echo "$LOGFPATH	640  3	   *	@T00  NC" >> newsyslog.conf
+tests_rfc5424
+
 rm -rf "${TMPDIR}"