Index: head/include/resolv.h
===================================================================
--- head/include/resolv.h
+++ head/include/resolv.h
@@ -176,7 +176,8 @@
 	int	res_h_errno;		/*%< last one set for this context */
 	int	_vcsock;		/*%< PRIVATE: for res_send VC i/o */
 	u_int	_flags;			/*%< PRIVATE: see below */
-	u_int	_pad;			/*%< make _u 64 bit aligned */
+	u_short	reload_period;		/*%< seconds between stat(resolv.conf)*/
+	u_short	_pad;			/*%< make _u 64 bit aligned */
 	union {
 		/* On an 32-bit arch this means 512b total. */
 		char	pad[72 - 4*sizeof (int) - 3*sizeof (void *)];
@@ -188,6 +189,8 @@
 		} _ext;
 	} _u;
 	u_char	*_rnd;			/*%< PRIVATE: random state */
+	struct timespec	conf_mtim;	/*%< mod time of loaded resolv.conf */
+	time_t		conf_stat;	/*%< time of last stat(resolv.conf) */
 };
 
 typedef struct __res_state *res_state;
Index: head/lib/libc/resolv/res_init.c
===================================================================
--- head/lib/libc/resolv/res_init.c
+++ head/lib/libc/resolv/res_init.c
@@ -78,6 +78,7 @@
 #include <sys/types.h>
 #include <sys/param.h>
 #include <sys/socket.h>
+#include <sys/stat.h>
 #include <sys/time.h>
 
 #include <netinet/in.h>
@@ -227,6 +228,7 @@
 	statp->pfcode = 0;
 	statp->_vcsock = -1;
 	statp->_flags = 0;
+	statp->reload_period = 2;
 	statp->qhook = NULL;
 	statp->rhook = NULL;
 	statp->_u._ext.nscount = 0;
@@ -321,6 +323,22 @@
 
 	nserv = 0;
 	if ((fp = fopen(_PATH_RESCONF, "re")) != NULL) {
+	    struct stat sb;
+	    struct timespec now;
+
+	    if (_fstat(fileno(fp), &sb) == 0) {
+		statp->conf_mtim = sb.st_mtim;
+		if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) == 0) {
+		    statp->conf_stat = now.tv_sec;
+		} else {
+		    statp->conf_stat = 0;
+		}
+	    } else {
+		statp->conf_mtim.tv_sec = 0;
+		statp->conf_mtim.tv_nsec = 0;
+		statp->conf_stat = 0;
+	    }
+
 	    /* read the config file */
 	    while (fgets(buf, sizeof(buf), fp) != NULL) {
 		/* skip comments */
@@ -666,6 +684,10 @@
 		} else if (!strncmp(cp, "no-check-names",
 				    sizeof("no-check-names") - 1)) {
 			statp->options |= RES_NOCHECKNAME;
+		} else if (!strncmp(cp, "reload-period:",
+				    sizeof("reload-period:") - 1)) {
+			statp->reload_period = (u_short)
+				atoi(cp + sizeof("reload-period:") - 1);
 		}
 #ifdef RES_USE_EDNS0
 		else if (!strncmp(cp, "edns0", sizeof("edns0") - 1)) {
Index: head/lib/libc/resolv/res_state.c
===================================================================
--- head/lib/libc/resolv/res_state.c
+++ head/lib/libc/resolv/res_state.c
@@ -26,6 +26,8 @@
  */
 
 #include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/time.h>
 #include <netinet/in.h>
 #include <arpa/nameser.h>
 #include <resolv.h>
@@ -59,13 +61,38 @@
 	res_thr_keycreated = thr_keycreate(&res_key, free_res) == 0;
 }
 
+static res_state
+res_check_reload(res_state statp)
+{
+	struct timespec now;
+	struct stat sb;
+
+	if ((statp->options & RES_INIT) == 0 || statp->reload_period == 0) {
+		return (statp);
+	}
+
+	if (clock_gettime(CLOCK_MONOTONIC_FAST, &now) != 0 ||
+	    (now.tv_sec - statp->conf_stat) < statp->reload_period) {
+		return (statp);
+	}
+
+	statp->conf_stat = now.tv_sec;
+	if (stat(_PATH_RESCONF, &sb) == 0 &&
+	    (sb.st_mtim.tv_sec  != statp->conf_mtim.tv_sec ||
+	     sb.st_mtim.tv_nsec != statp->conf_mtim.tv_nsec)) {
+		statp->options &= ~RES_INIT;
+	}
+
+	return (statp);
+}
+
 res_state
 __res_state(void)
 {
 	res_state statp;
 
 	if (thr_main() != 0)
-		return (&_res);
+		return res_check_reload(&_res);
 
 	if (thr_once(&res_init_once, res_keycreate) != 0 ||
 	    !res_thr_keycreated)
@@ -73,7 +100,7 @@
 
 	statp = thr_getspecific(res_key);
 	if (statp != NULL)
-		return (statp);
+		return res_check_reload(statp);
 	statp = calloc(1, sizeof(*statp));
 	if (statp == NULL)
 		return (&_res);
Index: head/share/man/man5/resolver.5
===================================================================
--- head/share/man/man5/resolver.5
+++ head/share/man/man5/resolver.5
@@ -28,7 +28,7 @@
 .\"     @(#)resolver.5	8.1 (Berkeley) 6/5/93
 .\" $FreeBSD$
 .\"
-.Dd December 25, 2013
+.Dd October 12, 2015
 .Dt RESOLVER 5
 .Os
 .Sh NAME
@@ -175,6 +175,19 @@
 and
 .Sy search
 rules with the given name.
+.It Sy reload-period: Ns Ar n
+The resolver checks the modification time of
+.Pa /etc/resolv.conf
+every
+.Ar n
+seconds.
+If
+.Pa /etc/resolv.conf
+has changed, it is automatically reloaded.
+The default for
+.Ar n
+is two seconds.
+Setting it to zero disables the file check.
 .El
 .Pp
 Options may also be specified as a space or tab separated list using the
@@ -191,8 +204,7 @@
 the last instance will override.
 .Pp
 The keyword and value must appear on a single line, and the keyword
-(e.g.\&
-.Sy nameserver )
+.Pq for example, Sy nameserver
 must start the line.
 The value follows the keyword, separated by white space.
 .Sh FILES