diff --git a/usr.sbin/cron/cron/cron.c b/usr.sbin/cron/cron/cron.c
index 48f431d9368c..460dd58dbd0d 100644
--- a/usr.sbin/cron/cron/cron.c
+++ b/usr.sbin/cron/cron/cron.c
@@ -46,7 +46,9 @@ static	void	usage(void),
 		parse_args(int c, char *v[]);
 
 static int	run_at_secres(cron_db *);
+static void	find_interval_entry(pid_t);
 
+static cron_db	database;
 static time_t	last_time = 0;
 static int	dst_enabled = 0;
 static int	dont_daemonize = 0;
@@ -100,7 +102,6 @@ main(argc, argv)
 	int	argc;
 	char	*argv[];
 {
-	cron_db	database;
 	int runnum;
 	int secres1, secres2;
 	struct tm *tm;
@@ -154,8 +155,8 @@ main(argc, argv)
 	database.mtime = (time_t) 0;
 	load_database(&database);
 	secres1 = secres2 = run_at_secres(&database);
-	run_reboot_jobs(&database);
 	cron_sync(secres1);
+	run_reboot_jobs(&database);
 	runnum = 0;
 	while (TRUE) {
 # if DEBUGGING
@@ -210,6 +211,9 @@ run_reboot_jobs(db)
 			if (e->flags & WHEN_REBOOT) {
 				job_add(e, u);
 			}
+			if (e->flags & INTERVAL) {
+				e->lastexit = TargetTime;
+			}
 		}
 	}
 	(void) job_runqueue();
@@ -313,6 +317,13 @@ cron_tick(cron_db *db, int secres)
 					  env_get("LOGNAME", e->envp),
 					  e->uid, e->gid, e->cmd))
 
+			if (e->flags & INTERVAL) {
+				if (e->lastexit > 0 &&
+				    TargetTime >= e->lastexit + e->interval)
+					job_add(e, u);
+				continue;
+			}
+
 			if ( diff != 0 && (e->flags & (RUN_AT|NOT_UNTIL)) ) {
 				if (bit_test(e->second, otzsecond)
 				 && bit_test(e->minute, otzminute)
@@ -489,6 +500,7 @@ sigchld_handler(int x)
 				("[%d] sigchld...no dead kids\n", getpid()))
 			return;
 		default:
+			find_interval_entry(pid);
 			Debug(DPROC,
 				("[%d] sigchld...pid #%d died, stat=%d\n",
 				getpid(), pid, WEXITSTATUS(waiter)))
@@ -557,9 +569,26 @@ run_at_secres(cron_db *db)
 
 	for (u = db->head;  u != NULL;  u = u->next) {
 		for (e = u->crontab;  e != NULL;  e = e->next) {
-			if ((e->flags & SEC_RES) != 0)
+			if ((e->flags & (SEC_RES | INTERVAL)) != 0)
 				return 1;
 		}
 	}
 	return 0;
 }
+
+static void
+find_interval_entry(pid_t pid)
+{
+	user *u;
+	entry *e;
+
+	for (u = database.head;  u != NULL;  u = u->next) {
+		for (e = u->crontab;  e != NULL;  e = e->next) {
+			if ((e->flags & INTERVAL) && e->child == pid) {
+				e->lastexit = time(NULL);
+				e->child = 0;
+				break;
+			}
+		}
+	}
+}
diff --git a/usr.sbin/cron/cron/cron.h b/usr.sbin/cron/cron/cron.h
index a6810be84005..bb4f5287daea 100644
--- a/usr.sbin/cron/cron/cron.h
+++ b/usr.sbin/cron/cron/cron.h
@@ -168,19 +168,29 @@ typedef	struct _entry {
 #endif
 	char		**envp;
 	char		*cmd;
-	bitstr_t	bit_decl(second, SECOND_COUNT);
-	bitstr_t	bit_decl(minute, MINUTE_COUNT);
-	bitstr_t	bit_decl(hour,   HOUR_COUNT);
-	bitstr_t	bit_decl(dom,    DOM_COUNT);
-	bitstr_t	bit_decl(month,  MONTH_COUNT);
-	bitstr_t	bit_decl(dow,    DOW_COUNT);
+	union {
+		struct {
+			bitstr_t	bit_decl(second, SECOND_COUNT);
+			bitstr_t	bit_decl(minute, MINUTE_COUNT);
+			bitstr_t	bit_decl(hour,   HOUR_COUNT);
+			bitstr_t	bit_decl(dom,    DOM_COUNT);
+			bitstr_t	bit_decl(month,  MONTH_COUNT);
+			bitstr_t	bit_decl(dow,    DOW_COUNT);
+		};
+		struct {
+			time_t	lastexit;
+			time_t	interval;
+			pid_t	child;
+		};
+	};
 	int		flags;
 #define	DOM_STAR	0x01
 #define	DOW_STAR	0x02
 #define	WHEN_REBOOT	0x04
-#define	RUN_AT	0x08
+#define	RUN_AT		0x08
 #define	NOT_UNTIL	0x10
 #define	SEC_RES		0x20
+#define	INTERVAL	0x40
 	time_t	lastrun;
 } entry;
 
diff --git a/usr.sbin/cron/cron/do_command.c b/usr.sbin/cron/cron/do_command.c
index 4d7c1f439d0e..f62303a5df29 100644
--- a/usr.sbin/cron/cron/do_command.c
+++ b/usr.sbin/cron/cron/do_command.c
@@ -47,6 +47,8 @@ do_command(e, u)
 	entry	*e;
 	user	*u;
 {
+	pid_t pid;
+
 	Debug(DPROC, ("[%d] do_command(%s, (%s,%d,%d))\n",
 		getpid(), e->cmd, u->name, e->uid, e->gid))
 
@@ -57,9 +59,11 @@ do_command(e, u)
 	 * vfork() is unsuitable, since we have much to do, and the parent
 	 * needs to be able to run off and fork other processes.
 	 */
-	switch (fork()) {
+	switch ((pid = fork())) {
 	case -1:
 		log_it("CRON",getpid(),"error","can't fork");
+		if (e->flags & INTERVAL)
+			e->lastexit = time(NULL);
 		break;
 	case 0:
 		/* child process */
@@ -70,6 +74,12 @@ do_command(e, u)
 		break;
 	default:
 		/* parent process */
+		Debug(DPROC, ("[%d] main process forked child #%d, "
+		    "returning to work\n", getpid(), pid))
+		if (e->flags & INTERVAL) {
+			e->lastexit = 0;
+			e->child = pid;
+		}
 		break;
 	}
 	Debug(DPROC, ("[%d] main process returning to work\n", getpid()))
diff --git a/usr.sbin/cron/crontab/crontab.5 b/usr.sbin/cron/crontab/crontab.5
index acd6cb5381a6..697242b4d0fc 100644
--- a/usr.sbin/cron/crontab/crontab.5
+++ b/usr.sbin/cron/crontab/crontab.5
@@ -17,7 +17,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 5, 2016
+.Dd June 6, 2018
 .Dt CRONTAB 5
 .Os
 .Sh NAME
@@ -220,7 +220,10 @@ would cause a command to be run at 4:30 am on the 1st and 15th of each
 month, plus every Friday.
 .Pp
 Instead of the first five fields,
-one of eight special strings may appear:
+a line may start with
+.Sq @
+symbol followed either by one of eight special strings or by a numeric value.
+The recognized special strings are:
 .Bd -literal -offset indent
 string		meaning
 ------		-------
@@ -235,6 +238,16 @@ string		meaning
 @every_minute	Run once a minute, "*/1 * * * *".
 @every_second	Run once a second.
 .Ed
+.Pp
+The
+.Sq @
+symbol followed by a numeric value has a special notion of running
+a job that much seconds after completion of previous invocation of
+the job.
+Unlike regular syntax, it guarantees not to overlap two or more
+invocations of the same job.
+The first run is scheduled specified amount of seconds after cron
+has started.
 .Sh EXAMPLE CRON FILE
 .Bd -literal
 
@@ -251,6 +264,8 @@ MAILTO=paul
 0 22 * * 1-5	mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
 23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
 5 4 * * sun     echo "run at 5 after 4 every sunday"
+# run at 5 minutes intervals, no matter how long it takes
+@300		svnlite up /usr/src
 .Ed
 .Sh SEE ALSO
 .Xr crontab 1 ,
@@ -292,7 +307,7 @@ either).
 .Pp
 All of the
 .Sq @
-commands that can appear in place of the first five fields
+directives that can appear in place of the first five fields
 are extensions.
 .Sh AUTHORS
 .An Paul Vixie Aq Mt paul@vix.com
diff --git a/usr.sbin/cron/lib/entry.c b/usr.sbin/cron/lib/entry.c
index 57f72554d344..a8ec3ae8b568 100644
--- a/usr.sbin/cron/lib/entry.c
+++ b/usr.sbin/cron/lib/entry.c
@@ -132,6 +132,9 @@ load_entry(file, error_func, pw, envp)
 	}
 
 	if (ch == '@') {
+		long interval;
+		char *endptr;
+
 		/* all of these should be flagged and load-limited; i.e.,
 		 * instead of @hourly meaning "0 * * * *" it should mean
 		 * "close to the front of every hour but not 'til the
@@ -209,6 +212,13 @@ load_entry(file, error_func, pw, envp)
 			bit_nset(e->dom, 0, (LAST_DOM-FIRST_DOM+1));
 			bit_nset(e->month, 0, (LAST_MONTH-FIRST_MONTH+1));
 			bit_nset(e->dow, 0, (LAST_DOW-FIRST_DOW+1));
+		} else if (*cmd != '\0' &&
+		    (interval = strtol(cmd, &endptr, 10)) > 0 &&
+		    *endptr == '\0') {
+			Debug(DPARS, ("load_entry()... %ld seconds "
+			    "since last run\n", interval))
+			e->interval = interval;
+			e->flags = INTERVAL;
 		} else {
 			ecode = e_timespec;
 			goto eof;