Add refresh-client -q to query terminal size, useful for terminals which

do not respond to SIGWINCH (such as serial). GitHub issue 5766 from
Charlie Stanley.

cmd-refresh-client.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-refresh-client.c,v 1.56 2026/10/09 13:12:14 nicm Exp $ */
+/* $OpenBSD: cmd-refresh-client.c,v 1.57 2026/10/26 10:14:59 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -35,8 +35,8 @@ const struct cmd_entry cmd_refresh_client_entry = {
 	.description = "Refresh or resize a client.",
 	.alias = "refresh",
 
-	.args = { "A:B:cC:Df:r:F:lLRSt:U", 0, 1, NULL },
-	.usage = "[-cDlLRSU] [-A pane:state] [-B name:what:format] "
+	.args = { "A:B:cC:Df:r:F:lLqRSt:U", 0, 1, NULL },
+	.usage = "[-cDlLqRSU] [-A pane:state] [-B name:what:format] "
 		 "[-C XxY] [-f flags] [-r pane:report] " CMD_TARGET_CLIENT_USAGE
 		 " [adjustment]",
 
@@ -240,6 +240,11 @@ cmd_refresh_client_exec(struct cmd *self, struct cmdq_item *item)
 		return (CMD_RETURN_NORMAL);
 	}
 
+	if (args_has(args, 'q')) {
+		tty_size_query(&tc->tty);
+		return (CMD_RETURN_NORMAL);
+	}
+
 	if (args_has(args, 'F')) /* -F is an alias for -f */
 		server_client_set_flags(tc, args_get(args, 'F'));
 	if (args_has(args, 'f'))

server-client.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: server-client.c,v 1.527 2026/10/23 06:45:15 nicm Exp $ */
+/* $OpenBSD: server-client.c,v 1.528 2026/10/26 10:14:59 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -338,6 +338,36 @@ server_client_fire_resized(struct client *c, u_int old_sx, u_int old_sy)
 	events_fire("client-resized", ep);
 }
 
+/* Recalculate sizes and notify a resized client. */
+static void
+server_client_apply_resize(struct client *c, u_int old_sx, u_int old_sy)
+{
+	if (c->session != NULL) {
+		recalculate_sizes();
+		server_redraw_client(c);
+		server_client_fire_resized(c, old_sx, old_sy);
+	}
+}
+
+/* Apply a new reported size. */
+void
+server_client_size_changed(struct client *c, u_int sx, u_int sy)
+{
+	u_int	old_sx = c->tty.sx, old_sy = c->tty.sy;
+
+	if (c->flags & CLIENT_CONTROL)
+		return;
+	if (sx == 0 || sy == 0 || (sx == old_sx && sy == old_sy))
+		return;
+
+	log_debug("%s: reported size %ux%u (was %ux%u)", c->name, sx, sy,
+	    old_sx, old_sy);
+	server_client_update_latest(c);
+	tty_set_size(&c->tty, sx, sy, c->tty.xpixel, c->tty.ypixel);
+	tty_invalidate(&c->tty);
+	server_client_apply_resize(c, old_sx, old_sy);
+}
+
 /* Set client session. */
 void
 server_client_set_session(struct client *c, struct session *s)
@@ -2699,10 +2729,7 @@ server_client_dispatch(struct imsg *imsg, void *arg)
 		old_sy = c->tty.sy;
 		tty_resize(&c->tty);
 		tty_repeat_requests(&c->tty, 0);
-		recalculate_sizes();
-		server_redraw_client(c);
-		if (c->session != NULL)
-			server_client_fire_resized(c, old_sx, old_sy);
+		server_client_apply_resize(c, old_sx, old_sy);
 		break;
 	case MSG_EXITING:
 		if (datalen != 0)

tmux.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1191 2026/10/20 06:45:56 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1192 2026/10/26 10:14:59 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -14,7 +14,7 @@
 .\" IN 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: October 20 2026 $
+.Dd $Mdocdate: October 26 2026 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -1448,7 +1448,7 @@ and sets an environment variable for the newly created session; it may be
 specified multiple times.
 .Tg refresh
 .It Xo Ic refresh\-client
-.Op Fl cDlLRSU
+.Op Fl cDlLqRSU
 .Op Fl A Ar pane:state
 .Op Fl B Ar name:what:format
 .Op Fl C Ar size
@@ -1575,6 +1575,9 @@ requests the clipboard from the client using the
 .Xr xterm 1
 escape sequence and stores it in a new paste buffer.
 .Pp
+.Fl q
+queries the client terminal for its size.
+.Pp
 .Fl L ,
 .Fl R ,
 .Fl U

tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1470 2026/10/23 06:45:15 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1471 2026/10/26 10:14:59 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1759,6 +1759,9 @@ struct tty_style_ctx {
 	struct hyperlinks	*hyperlinks;
 };
 
+/* Maximum reported terminal size. */
+#define CLIENT_MAX_TERM_SIZE 10000
+
 /* Client terminal. */
 struct tty {
 	struct client	*client;
@@ -1824,6 +1827,8 @@ struct tty {
 #define TTY_BRACKETPASTE 0x8000
 #define TTY_HAVESYNC 0x10000
 #define TTY_HAVEKITTYGRAPHICS 0x20000
+#define TTY_WINSZPIXELS 0x40000
+#define TTY_WINSZAPPLY 0x80000
 #define TTY_ALL_REQUEST_FLAGS \
 	(TTY_HAVEDA|TTY_HAVEDA2|TTY_HAVEXDA|TTY_HAVESYNC|TTY_HAVEKITTYGRAPHICS)
 	int		 flags;
@@ -2957,6 +2962,7 @@ void	tty_cell(struct tty *, const struct grid_cell *,
 int	tty_init(struct tty *, struct client *);
 void	tty_resize(struct tty *);
 int	tty_set_size(struct tty *, u_int, u_int, u_int, u_int);
+void	tty_size_query(struct tty *);
 void	tty_invalidate(struct tty *);
 void	tty_start_tty(struct tty *);
 void	tty_send_requests(struct tty *);
@@ -3337,6 +3343,7 @@ void	 server_client_exec(struct client *, const char *);
 void	 server_client_loop(void);
 const char *server_client_get_cwd(struct client *, struct session *);
 void	 server_client_set_flags(struct client *, const char *);
+void	 server_client_size_changed(struct client *, u_int, u_int);
 const char *server_client_get_flags(struct client *);
 void	 server_client_remove_pane(struct window_pane *);
 void	 server_client_print(struct client *, int, struct evbuffer *);

tty-keys.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty-keys.c,v 1.221 2026/10/22 07:16:40 nicm Exp $ */
+/* $OpenBSD: tty-keys.c,v 1.222 2026/10/26 10:14:59 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -937,8 +937,8 @@ partial_key:
 		if (delay < 500)
 			delay = 500;
 	}
-	if (tty->flags & (TTY_WAITFG|TTY_WAITBG) ||
-	    tty->flags & (TTY_OSC52QUERY|TTY_WINSZQUERY) ||
+	if (tty->flags & (TTY_WAITFG|TTY_WAITBG|TTY_OSC52QUERY) ||
+	    tty->flags & (TTY_WINSZQUERY|TTY_WINSZPIXELS) ||
 	    (tty->flags & TTY_ALL_REQUEST_FLAGS) != TTY_ALL_REQUEST_FLAGS ||
 	    !TAILQ_EMPTY(&c->input_requests)) {
 		log_debug("%s: increasing delay (active query)", c->name);
@@ -1875,11 +1875,12 @@ tty_keys_winsz(struct tty *tty, const char *buf, size_t len, size_t *size,
 	size_t		 end;
 	char		 tmp[64];
 	u_int		 sx, sy, xpixel, ypixel, char_x, char_y;
+	int		 resize;
 
 	*size = 0;
 
 	/* If we did not request this, ignore it. */
-	if (!(tty->flags & TTY_WINSZQUERY))
+	if (!(tty->flags & (TTY_WINSZQUERY|TTY_WINSZPIXELS)))
 		return (-1);
 
 	/* First two bytes are always \033[. */
@@ -1892,10 +1893,7 @@ tty_keys_winsz(struct tty *tty, const char *buf, size_t len, size_t *size,
 	if (len == 2)
 		return (1);
 
-	/*
-	 * Stop at either 't' or anything that isn't a
-	 * number or ';'.
-	 */
+	/* Stop at either 't' or anything that isn't a number or ';'. */
 	for (end = 2; end < len && end != sizeof tmp; end++) {
 		if (buf[end] == 't')
 			break;
@@ -1913,28 +1911,42 @@ tty_keys_winsz(struct tty *tty, const char *buf, size_t len, size_t *size,
 
 	/* Try to parse the window size sequence. */
 	if (sscanf(tmp, "8;%u;%u", &sy, &sx) == 2) {
+		if (!(tty->flags & TTY_WINSZQUERY))
+			return (-1);
 		*size = end + 1;
 		if (!apply)
 			return (0);
 
-		/* Window size in characters. */
-		if (tty_set_size(tty, sx, sy, tty->xpixel, tty->ypixel))
+		resize = (tty->flags & TTY_WINSZAPPLY);
+		tty->flags &= ~(TTY_WINSZQUERY|TTY_WINSZAPPLY);
+
+		if (sx == 0 ||
+		    sy == 0 ||
+		    sx > CLIENT_MAX_TERM_SIZE ||
+		    sy > CLIENT_MAX_TERM_SIZE) {
+			log_debug("%s: ignoring reported size %ux%u",
+			    c->name, sx, sy);
+			return (0);
+		}
+		if (resize)
+			server_client_size_changed(c, sx, sy);
+		else if (tty_set_size(tty, sx, sy, tty->xpixel, tty->ypixel))
 			server_redraw_client(c);
 		return (0);
 	} else if (sscanf(tmp, "4;%u;%u", &ypixel, &xpixel) == 2) {
+		if (!(tty->flags & TTY_WINSZPIXELS))
+			return (-1);
 		*size = end + 1;
 		if (!apply)
 			return (0);
+		tty->flags &= ~TTY_WINSZPIXELS;
 
-		/* Window size in pixels. */
 		char_x = (xpixel && tty->sx) ? xpixel / tty->sx : 0;
 		char_y = (ypixel && tty->sy) ? ypixel / tty->sy : 0;
 		if (tty_set_size(tty, tty->sx, tty->sy, char_x, char_y))
 			server_redraw_client(c);
 		tty_invalidate(tty);
 		recalculate_sizes();
-
-		tty->flags &= ~TTY_WINSZQUERY;
 		return (0);
 	}
 

tty.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty.c,v 1.496 2026/10/22 07:16:40 nicm Exp $ */
+/* $OpenBSD: tty.c,v 1.497 2026/10/26 10:14:59 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -38,6 +38,7 @@ static int	tty_log_fd = -1;
 static void	tty_start_timer_callback(int, short, void *);
 static void	tty_start_start_timer(struct tty *);
 static void	tty_clipboard_query_callback(int, short, void *);
+static void	tty_send_size_query(struct tty *, int);
 static void	tty_set_italics(struct tty *);
 static int	tty_try_colour(struct tty *, int, const char *);
 static void	tty_force_cursor_colour(struct tty *, int);
@@ -116,6 +117,16 @@ tty_init(struct tty *tty, struct client *c)
 	return (0);
 }
 
+static void
+tty_send_size_query(struct tty *tty, int apply)
+{
+	tty_puts(tty, "\033[18t\033[14t");
+	tty->flags |= (TTY_WINSZQUERY|TTY_WINSZPIXELS);
+	if (apply)
+		tty->flags |= TTY_WINSZAPPLY;
+	tty_start_start_timer(tty);
+}
+
 void
 tty_resize(struct tty *tty)
 {
@@ -139,12 +150,9 @@ tty_resize(struct tty *tty)
 
 		if ((xpixel == 0 || ypixel == 0) &&
 		    (tty->flags & TTY_STARTED) &&
-		    !(tty->flags & TTY_WINSZQUERY) &&
-		    (tty->term->flags & TERM_VT100LIKE)) {
-			tty_puts(tty, "\033[18t\033[14t");
-			tty->flags |= TTY_WINSZQUERY;
-			tty_start_start_timer(tty);
-		}
+		    !(tty->flags & (TTY_WINSZQUERY|TTY_WINSZPIXELS)) &&
+		    (tty->term->flags & TERM_VT100LIKE))
+			tty_send_size_query(tty, 0);
 	} else {
 		sx = 80;
 		sy = 24;
@@ -322,7 +330,11 @@ tty_start_timer_callback(__unused int fd, __unused short events, void *data)
 		tty_update_features(tty);
 	tty->flags |= TTY_ALL_REQUEST_FLAGS;
 
-	tty->flags &= ~(TTY_WAITBG|TTY_WAITFG|TTY_WINSZQUERY);
+	if (tty->flags & TTY_WINSZQUERY)
+		log_debug("%s: size query timed out", c->name);
+
+	tty->flags &= ~(TTY_WAITBG|TTY_WAITFG);
+	tty->flags &= ~(TTY_WINSZQUERY|TTY_WINSZPIXELS|TTY_WINSZAPPLY);
 }
 
 static void
@@ -470,7 +482,7 @@ tty_stop_tty(struct tty *tty)
 
 	evtimer_del(&tty->start_timer);
 	evtimer_del(&tty->clipboard_timer);
-	tty->flags &= ~TTY_WINSZQUERY;
+	tty->flags &= ~(TTY_WINSZQUERY|TTY_WINSZPIXELS|TTY_WINSZAPPLY);
 
 	event_del(&tty->timer);
 	tty->flags &= ~TTY_BLOCK;
@@ -2990,6 +3002,19 @@ tty_clipboard_query(struct tty *tty)
 	}
 }
 
+void
+tty_size_query(struct tty *tty)
+{
+	if (!(tty->flags & TTY_STARTED) ||
+	    tty->out == NULL ||
+	    tty->client->flags & CLIENT_CONTROL ||
+	    !(tty->term->flags & TERM_VT100LIKE) ||
+	    tty->flags & (TTY_WINSZQUERY|TTY_WINSZPIXELS))
+		return;
+	log_debug("%s: querying terminal size", tty->client->name);
+	tty_send_size_query(tty, 1);
+}
+
 void
 tty_set_progress_bar(struct tty *tty, struct progress_bar *pb)
 {