Add a -D flag to ask tmux not to daemonize, useful both for running a debugger

(lldb does not have follow-fork-mode) and for running with a managed supervisor
init system. GitHub issue 2190.

proc.c

@@ -35,6 +35,7 @@ struct tmuxproc {
 
 	void		(*signalcb)(int);
 
+	struct event	  ev_sigint;
 	struct event	  ev_sighup;
 	struct event	  ev_sigchld;
 	struct event	  ev_sigcont;
@@ -219,10 +220,13 @@ proc_set_signals(struct tmuxproc *tp, void (*signalcb)(int))
 	sa.sa_flags = SA_RESTART;
 	sa.sa_handler = SIG_IGN;
 
-	sigaction(SIGINT, &sa, NULL);
 	sigaction(SIGPIPE, &sa, NULL);
 	sigaction(SIGTSTP, &sa, NULL);
+	sigaction(SIGTTIN, &sa, NULL);
+	sigaction(SIGTTOU, &sa, NULL);
 
+	signal_set(&tp->ev_sigint, SIGINT, proc_signal_cb, tp);
+	signal_add(&tp->ev_sigint, NULL);
 	signal_set(&tp->ev_sighup, SIGHUP, proc_signal_cb, tp);
 	signal_add(&tp->ev_sighup, NULL);
 	signal_set(&tp->ev_sigchld, SIGCHLD, proc_signal_cb, tp);
@@ -249,10 +253,10 @@ proc_clear_signals(struct tmuxproc *tp, int defaults)
 	sa.sa_flags = SA_RESTART;
 	sa.sa_handler = SIG_DFL;
 
-	sigaction(SIGINT, &sa, NULL);
 	sigaction(SIGPIPE, &sa, NULL);
 	sigaction(SIGTSTP, &sa, NULL);
 
+	signal_del(&tp->ev_sigint);
 	signal_del(&tp->ev_sighup);
 	signal_del(&tp->ev_sigchld);
 	signal_del(&tp->ev_sigcont);
@@ -262,6 +266,7 @@ proc_clear_signals(struct tmuxproc *tp, int defaults)
 	signal_del(&tp->ev_sigwinch);
 
 	if (defaults) {
+		sigaction(SIGINT, &sa, NULL);
 		sigaction(SIGHUP, &sa, NULL);
 		sigaction(SIGCHLD, &sa, NULL);
 		sigaction(SIGCONT, &sa, NULL);

server-client.c

@@ -236,11 +236,22 @@ server_client_create(int fd)
 int
 server_client_open(struct client *c, char **cause)
 {
+	const char	*ttynam = _PATH_TTY;
+
 	if (c->flags & CLIENT_CONTROL)
 		return (0);
 
-	if (strcmp(c->ttyname, "/dev/tty") == 0) {
+	if (strcmp(c->ttyname, ttynam) ||
-		*cause = xstrdup("can't use /dev/tty");
+	    ((isatty(STDIN_FILENO) &&
+	    (ttynam = ttyname(STDIN_FILENO)) != NULL &&
+	    strcmp(c->ttyname, ttynam) == 0) ||
+	    (isatty(STDOUT_FILENO) &&
+	    (ttynam = ttyname(STDOUT_FILENO)) != NULL &&
+	    strcmp(c->ttyname, ttynam) == 0) ||
+	    (isatty(STDERR_FILENO) &&
+	    (ttynam = ttyname(STDERR_FILENO)) != NULL &&
+	    strcmp(c->ttyname, ttynam) == 0))) {
+		xasprintf(cause, "can't use %s", c->ttyname);
 		return (-1);
 	}
 

server.c

@@ -160,29 +160,35 @@ server_start(struct tmuxproc *client, int flags, struct event_base *base,
 	struct client	*c;
 	char		*cause = NULL;
 
-	if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
-		fatal("socketpair failed");
-	server_client_flags = flags;
-
 	sigfillset(&set);
 	sigprocmask(SIG_BLOCK, &set, &oldset);
-	switch (fork()) {
+
-	case -1:
+	if (~flags & CLIENT_NOFORK) {
-		fatal("fork failed");
+		if (socketpair(AF_UNIX, SOCK_STREAM, PF_UNSPEC, pair) != 0)
-	case 0:
+			fatal("socketpair failed");
-		break;
+
-	default:
+		switch (fork()) {
-		sigprocmask(SIG_SETMASK, &oldset, NULL);
+		case -1:
-		close(pair[1]);
+			fatal("fork failed");
-		return (pair[0]);
+		case 0:
+			break;
+		default:
+			sigprocmask(SIG_SETMASK, &oldset, NULL);
+			close(pair[1]);
+			return (pair[0]);
+		}
+		close(pair[0]);
+		if (daemon(1, 0) != 0)
+			fatal("daemon failed");
 	}
-	close(pair[0]);
+
-	if (daemon(1, 0) != 0)
+	server_client_flags = flags;
-		fatal("daemon failed");
 	proc_clear_signals(client, 0);
+
 	if (event_reinit(base) != 0)
 		fatalx("event_reinit failed");
 	server_proc = proc_start("server");
+
 	proc_set_signals(server_proc, server_signal);
 	sigprocmask(SIG_SETMASK, &oldset, NULL);
 
@@ -204,7 +210,10 @@ server_start(struct tmuxproc *client, int flags, struct event_base *base,
 	server_fd = server_create_socket(flags, &cause);
 	if (server_fd != -1)
 		server_update_socket();
-	c = server_client_create(pair[1]);
+	if (~flags & CLIENT_NOFORK)
+		c = server_client_create(pair[1]);
+	else
+		options_set_number(global_options, "exit-empty", 0);
 
 	if (lockfd >= 0) {
 		unlink(lockfile);
@@ -395,6 +404,7 @@ server_signal(int sig)
 
 	log_debug("%s: %s", __func__, strsignal(sig));
 	switch (sig) {
+	case SIGINT:
 	case SIGTERM:
 		server_exit = 1;
 		server_send_exit();

tmux.1

@@ -23,7 +23,7 @@
 .Sh SYNOPSIS
 .Nm tmux
 .Bk -words
-.Op Fl 2CluvV
+.Op Fl 2CDluvV
 .Op Fl c Ar shell-command
 .Op Fl f Ar file
 .Op Fl L Ar socket-name
@@ -122,6 +122,17 @@ This option is for compatibility with
 when
 .Nm
 is used as a login shell.
+.It Fl D
+Do not start the
+.Nm
+server as a daemon.
+This also turns the
+.Ic exit-empty
+option off.
+With
+.Fl D ,
+.Ar command
+may not be specified.
 .It Fl f Ar file
 Specify an alternative configuration file.
 By default,

tmux.c

@@ -54,7 +54,7 @@ static __dead void
 usage(void)
 {
 	fprintf(stderr,
-	    "usage: %s [-2CluvV] [-c shell-command] [-f file] [-L socket-name]\n"
+	    "usage: %s [-2CDluvV] [-c shell-command] [-f file] [-L socket-name]\n"
 	    "            [-S socket-path] [-T features] [command [flags]]\n",
 	    getprogname());
 	exit(1);
@@ -327,7 +327,7 @@ main(int argc, char **argv)
 	if (**argv == '-')
 		flags = CLIENT_LOGIN;
 
-	while ((opt = getopt(argc, argv, "2c:Cdf:lL:qS:T:uUvV")) != -1) {
+	while ((opt = getopt(argc, argv, "2c:CDdf:lL:qS:T:uUvV")) != -1) {
 		switch (opt) {
 		case '2':
 			tty_add_features(&feat, "256", ":,");
@@ -335,6 +335,9 @@ main(int argc, char **argv)
 		case 'c':
 			shell_command = optarg;
 			break;
+		case 'D':
+			flags |= CLIENT_NOFORK;
+			break;
 		case 'C':
 			if (flags & CLIENT_CONTROL)
 				flags |= CLIENT_CONTROLCONTROL;
@@ -378,6 +381,8 @@ main(int argc, char **argv)
 
 	if (shell_command != NULL && argc != 0)
 		usage();
+	if ((flags & CLIENT_NOFORK) && argc != 0)
+		usage();
 
 	if ((ptm_fd = getptmfd()) == -1)
 		err(1, "getptmfd");

tmux.h

@@ -1586,6 +1586,7 @@ struct client {
 #define CLIENT_DEFAULTSOCKET 0x8000000
 #define CLIENT_STARTSERVER 0x10000000
 #define CLIENT_REDRAWPANES 0x20000000
+#define CLIENT_NOFORK 0x40000000
 #define CLIENT_ALLREDRAWFLAGS		\
 	(CLIENT_REDRAWWINDOW|		\
 	 CLIENT_REDRAWSTATUS|		\

tty.c

@@ -154,16 +154,21 @@ tty_read_callback(__unused int fd, __unused short events, void *data)
 {
 	struct tty	*tty = data;
 	struct client	*c = tty->client;
+	const char	*name = c->name;
 	size_t		 size = EVBUFFER_LENGTH(tty->in);
 	int		 nread;
 
 	nread = evbuffer_read(tty->in, tty->fd, -1);
 	if (nread == 0 || nread == -1) {
+		if (nread == 0)
+			log_debug("%s: read closed", name);
+		else
+			log_debug("%s: read error: %s", name, strerror(errno));
 		event_del(&tty->event_in);
 		server_client_lost(tty->client);
 		return;
 	}
-	log_debug("%s: read %d bytes (already %zu)", c->name, nread, size);
+	log_debug("%s: read %d bytes (already %zu)", name, nread, size);
 
 	while (tty_keys_next(tty))
 		;