diff --git a/cmd-attach-session.c b/cmd-attach-session.c
index 8c30c767..38d9c024 100644
--- a/cmd-attach-session.c
+++ b/cmd-attach-session.c
@@ -37,8 +37,9 @@ const struct cmd_entry cmd_attach_session_entry = {
 	.name = "attach-session",
 	.alias = "attach",
 
-	.args = { "c:dErt:x", 0, 0 },
-	.usage = "[-dErx] [-c working-directory] " CMD_TARGET_SESSION_USAGE,
+	.args = { "c:dEf:rt:x", 0, 0 },
+	.usage = "[-dErx] [-c working-directory] [-f flags] "
+	         CMD_TARGET_SESSION_USAGE,
 
 	/* -t is special */
 
@@ -48,7 +49,7 @@ const struct cmd_entry cmd_attach_session_entry = {
 
 enum cmd_retval
 cmd_attach_session(struct cmdq_item *item, const char *tflag, int dflag,
-    int xflag, int rflag, const char *cflag, int Eflag)
+    int xflag, int rflag, const char *cflag, int Eflag, const char *fflag)
 {
 	struct cmd_find_state	*current = cmdq_get_current(item);
 	struct cmd_find_state	 target;
@@ -101,6 +102,10 @@ cmd_attach_session(struct cmdq_item *item, const char *tflag, int dflag,
 		free((void *)s->cwd);
 		s->cwd = format_single(item, cflag, c, s, wl, wp);
 	}
+	if (fflag)
+		server_client_set_flags(c, fflag);
+	if (rflag)
+		c->flags |= (CLIENT_READONLY|CLIENT_IGNORESIZE);
 
 	c->last_session = c->session;
 	if (c->session != NULL) {
@@ -135,8 +140,6 @@ cmd_attach_session(struct cmdq_item *item, const char *tflag, int dflag,
 			free(cause);
 			return (CMD_RETURN_ERROR);
 		}
-		if (rflag)
-			c->flags |= CLIENT_READONLY;
 
 		if (dflag || xflag) {
 			if (xflag)
@@ -182,5 +185,5 @@ cmd_attach_session_exec(struct cmd *self, struct cmdq_item *item)
 
 	return (cmd_attach_session(item, args_get(args, 't'),
 	    args_has(args, 'd'), args_has(args, 'x'), args_has(args, 'r'),
-	    args_get(args, 'c'), args_has(args, 'E')));
+	    args_get(args, 'c'), args_has(args, 'E'), args_get(args, 'f')));
 }
diff --git a/cmd-list-clients.c b/cmd-list-clients.c
index 75118c8e..d450f017 100644
--- a/cmd-list-clients.c
+++ b/cmd-list-clients.c
@@ -28,10 +28,10 @@
  * List all clients.
  */
 
-#define LIST_CLIENTS_TEMPLATE					\
-	"#{client_name}: #{session_name} "			\
-	"[#{client_width}x#{client_height} #{client_termname}]"	\
-	"#{?client_utf8, (utf8),} #{?client_readonly, (ro),}"
+#define LIST_CLIENTS_TEMPLATE						\
+	"#{client_name}: #{session_name} "				\
+	"[#{client_width}x#{client_height} #{client_termname}] "	\
+	"#{?client_flags,(,}#{client_flags}#{?client_flags,),}"
 
 static enum cmd_retval	cmd_list_clients_exec(struct cmd *, struct cmdq_item *);
 
diff --git a/cmd-new-session.c b/cmd-new-session.c
index 9815e1e1..a9a0376b 100644
--- a/cmd-new-session.c
+++ b/cmd-new-session.c
@@ -39,9 +39,9 @@ const struct cmd_entry cmd_new_session_entry = {
 	.name = "new-session",
 	.alias = "new",
 
-	.args = { "Ac:dDe:EF:n:Ps:t:x:Xy:", 0, -1 },
+	.args = { "Ac:dDe:EF:f:n:Ps:t:x:Xy:", 0, -1 },
 	.usage = "[-AdDEPX] [-c start-directory] [-e environment] [-F format] "
-		 "[-n window-name] [-s session-name] "
+		 "[-f flags] [-n window-name] [-s session-name] "
 		 CMD_TARGET_SESSION_USAGE " [-x width] [-y height] [command]",
 
 	.target = { 't', CMD_FIND_SESSION, CMD_FIND_CANFAIL },
@@ -112,7 +112,7 @@ cmd_new_session_exec(struct cmd *self, struct cmdq_item *item)
 		if (as != NULL) {
 			retval = cmd_attach_session(item, as->name,
 			    args_has(args, 'D'), args_has(args, 'X'), 0, NULL,
-			    args_has(args, 'E'));
+			    args_has(args, 'E'), args_get(args, 'f'));
 			free(newname);
 			return (retval);
 		}
@@ -306,6 +306,8 @@ cmd_new_session_exec(struct cmd *self, struct cmdq_item *item)
 	 * taking this session and needs to get MSG_READY and stay around.
 	 */
 	if (!detached) {
+		if (args_has(args, 'f'))
+			server_client_set_flags(c, args_get(args, 'f'));
 		if (!already_attached) {
 			if (~c->flags & CLIENT_CONTROL)
 				proc_send(c->peer, MSG_READY, -1, NULL, 0);
diff --git a/cmd-refresh-client.c b/cmd-refresh-client.c
index 5514ff73..c53a6a78 100644
--- a/cmd-refresh-client.c
+++ b/cmd-refresh-client.c
@@ -34,8 +34,8 @@ const struct cmd_entry cmd_refresh_client_entry = {
 	.name = "refresh-client",
 	.alias = "refresh",
 
-	.args = { "cC:DF:lLRSt:U", 0, 1 },
-	.usage = "[-cDlLRSU] [-C XxY] [-F flags] " CMD_TARGET_CLIENT_USAGE
+	.args = { "cC:Df:F:lLRSt:U", 0, 1 },
+	.usage = "[-cDlLRSU] [-C XxY] [-f flags] " CMD_TARGET_CLIENT_USAGE
 		" [adjustment]",
 
 	.flags = CMD_AFTERHOOK|CMD_CLIENT_TFLAG,
@@ -50,7 +50,6 @@ cmd_refresh_client_exec(struct cmd *self, struct cmdq_item *item)
 	struct tty	*tty = &tc->tty;
 	struct window	*w;
 	const char	*size, *errstr;
-	char		*copy, *next, *s;
 	u_int		 x, y, adjust;
 
 	if (args_has(args, 'c') ||
@@ -108,7 +107,12 @@ cmd_refresh_client_exec(struct cmd *self, struct cmdq_item *item)
 		return (CMD_RETURN_NORMAL);
 	}
 
-	if (args_has(args, 'C') || args_has(args, 'F')) {
+	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_set_flags(tc, args_get(args, 'f'));
+
+	if (args_has(args, 'C')) {
 		if (args_has(args, 'C')) {
 			if (!(tc->flags & CLIENT_CONTROL)) {
 				cmdq_error(item, "not a control client");
@@ -129,19 +133,6 @@ cmd_refresh_client_exec(struct cmd *self, struct cmdq_item *item)
 			tc->flags |= CLIENT_SIZECHANGED;
 			recalculate_sizes();
 		}
-		if (args_has(args, 'F')) {
-			if (!(tc->flags & CLIENT_CONTROL)) {
-				cmdq_error(item, "not a control client");
-				return (CMD_RETURN_ERROR);
-			}
-			s = copy = xstrdup(args_get(args, 'F'));
-			while ((next = strsep(&s, ",")) != NULL) {
-				/* Unknown flags are ignored. */
-				if (strcmp(next, "no-output") == 0)
-					tc->flags |= CLIENT_CONTROL_NOOUTPUT;
-			}
-			free(copy);
-		}
 		return (CMD_RETURN_NORMAL);
 	}
 
diff --git a/cmd-switch-client.c b/cmd-switch-client.c
index 82510ce6..d062b946 100644
--- a/cmd-switch-client.c
+++ b/cmd-switch-client.c
@@ -34,7 +34,7 @@ const struct cmd_entry cmd_switch_client_entry = {
 	.name = "switch-client",
 	.alias = "switchc",
 
-	.args = { "lc:Enpt:rT:Z", 0, 0 },
+	.args = { "lc:EFnpt:rT:Z", 0, 0 },
 	.usage = "[-ElnprZ] [-c target-client] [-t target-session] "
 		 "[-T key-table]",
 
@@ -74,8 +74,12 @@ cmd_switch_client_exec(struct cmd *self, struct cmdq_item *item)
 	wl = target.wl;
 	wp = target.wp;
 
-	if (args_has(args, 'r'))
-		tc->flags ^= CLIENT_READONLY;
+	if (args_has(args, 'r')) {
+		if (tc->flags & CLIENT_READONLY)
+			tc->flags &= ~(CLIENT_READONLY|CLIENT_IGNORESIZE);
+		else
+			tc->flags |= (CLIENT_READONLY|CLIENT_IGNORESIZE);
+	}
 
 	tablename = args_get(args, 'T');
 	if (tablename != NULL) {
diff --git a/format.c b/format.c
index a2b2822f..3b9af626 100644
--- a/format.c
+++ b/format.c
@@ -2678,11 +2678,11 @@ format_defaults_client(struct format_tree *ft, struct client *c)
 		format_add(ft, "client_utf8", "%d", 1);
 	else
 		format_add(ft, "client_utf8", "%d", 0);
-
 	if (c->flags & CLIENT_READONLY)
 		format_add(ft, "client_readonly", "%d", 1);
 	else
 		format_add(ft, "client_readonly", "%d", 0);
+	format_add(ft, "client_flags", "%s", server_client_get_flags(c));
 
 	s = c->session;
 	if (s != NULL)
diff --git a/resize.c b/resize.c
index 96d733f0..15d146d8 100644
--- a/resize.c
+++ b/resize.c
@@ -72,17 +72,17 @@ ignore_client_size(struct client *c)
 		return (1);
 	if (c->flags & CLIENT_NOSIZEFLAGS)
 		return (1);
-	if (c->flags & CLIENT_READONLY) {
+	if (c->flags & CLIENT_IGNORESIZE) {
 		/*
-		 * Ignore readonly clients if there are any attached clients
-		 * that aren't readonly.
+		 * Ignore flagged clients if there are any attached clients
+		 * that aren't flagged.
 		 */
 		TAILQ_FOREACH (loop, &clients, entry) {
 			if (loop->session == NULL)
 				continue;
 			if (loop->flags & CLIENT_NOSIZEFLAGS)
 				continue;
-			if (~loop->flags & CLIENT_READONLY)
+			if (~loop->flags & CLIENT_IGNORESIZE)
 				return (1);
 		}
 	}
diff --git a/server-client.c b/server-client.c
index a45e9812..86b7a1b8 100644
--- a/server-client.c
+++ b/server-client.c
@@ -2253,3 +2253,61 @@ server_client_get_cwd(struct client *c, struct session *s)
 		return (home);
 	return ("/");
 }
+
+/* Set client flags. */
+void
+server_client_set_flags(struct client *c, const char *flags)
+{
+	char	*s, *copy, *next;
+	int	 flag, not;
+
+	s = copy = xstrdup (flags);
+	while ((next = strsep(&s, ",")) != NULL) {
+		not = (*next == '!');
+		if (not)
+			next++;
+
+		if (strcmp(next, "no-output") == 0)
+			flag = CLIENT_CONTROL_NOOUTPUT;
+		else if (strcmp(next, "read-only") == 0)
+			flag = CLIENT_READONLY;
+		else if (strcmp(next, "ignore-size") == 0)
+			flag = CLIENT_IGNORESIZE;
+		else
+			continue;
+
+		log_debug("client %s set flag %s", c->name, next);
+		if (not)
+			c->flags &= ~flag;
+		else
+			c->flags |= flag;
+	}
+	free(copy);
+
+}
+
+/*Get client flags. This is only flags useful to show to users. */
+const char *
+server_client_get_flags(struct client *c)
+{
+	static char s[256];
+
+	*s = '\0';
+	if (c->flags & CLIENT_ATTACHED)
+		strlcat(s, "attached,", sizeof s);
+	if (c->flags & CLIENT_CONTROL)
+		strlcat(s, "control-mode,", sizeof s);
+	if (c->flags & CLIENT_IGNORESIZE)
+		strlcat(s, "ignore-size,", sizeof s);
+	if (c->flags & CLIENT_CONTROL_NOOUTPUT)
+		strlcat(s, "no-output,", sizeof s);
+	if (c->flags & CLIENT_READONLY)
+		strlcat(s, "read-only,", sizeof s);
+	if (c->flags & CLIENT_SUSPENDED)
+		strlcat(s, "suspended,", sizeof s);
+	if (c->flags & CLIENT_UTF8)
+		strlcat(s, "UTF-8,", sizeof s);
+	if (*s != '\0')
+		s[strlen(s) - 1] = '\0';
+	return (s);
+}
diff --git a/tmux.1 b/tmux.1
index eafa3751..97d57d5b 100644
--- a/tmux.1
+++ b/tmux.1
@@ -947,6 +947,7 @@ The following commands are available to manage clients and sessions:
 .It Xo Ic attach-session
 .Op Fl dErx
 .Op Fl c Ar working-directory
+.Op Fl f Ar flags
 .Op Fl t Ar target-session
 .Xc
 .D1 (alias: Ic attach )
@@ -964,12 +965,30 @@ is given, send
 .Dv SIGHUP
 to the parent process of the client as well as
 detaching the client, typically causing it to exit.
+.Fl f
+sets a comma-separated list of client flags.
+The flags are:
+.Bl -tag -width Ds
+.It read-only
+the client is read-only
+.It ignore-size
+the client does not affect the size of other clients
+.It no-output
+the client does not receive pane output in control mode
+.El
+.Pp
+A leading
+.Ql !
+turns a flag off if the client is already attached.
 .Fl r
-signifies the client is read-only (only keys bound to the
+is an alias for
+.Fl f
+.Ar read-only,ignore-size .
+When a client is read-only, only keys bound to the
 .Ic detach-client
 or
 .Ic switch-client
-commands have any effect)
+commands have any effect.
 .Pp
 If no server is started,
 .Ic attach-session
@@ -1095,6 +1114,7 @@ Lock all clients attached to
 .Op Fl AdDEPX
 .Op Fl c Ar start-directory
 .Op Fl e Ar environment
+.Op Fl f Ar flags
 .Op Fl F Ar format
 .Op Fl n Ar window-name
 .Op Fl s Ar session-name
@@ -1132,6 +1152,9 @@ or
 is given, the
 .Ic default-size
 option is set for the session.
+.Fl f
+sets a comma-separated list of client flags (see
+.Ic attach-session ) .
 .Pp
 If run from a terminal, any
 .Xr termios 4
@@ -1209,7 +1232,7 @@ specified multiple times.
 .It Xo Ic refresh-client
 .Op Fl cDlLRSU
 .Op Fl C Ar XxY
-.Op Fl F Ar flags
+.Op Fl f Ar flags
 .Op Fl t Ar target-client
 .Op Ar adjustment
 .Xc
@@ -1252,12 +1275,10 @@ window, changing the current window in the attached session will reset
 it.
 .Pp
 .Fl C
-sets the width and height of a control client and
-.Fl F
-sets a comma-separated list of flags.
-Currently the only flag available is
-.Ql no-output
-to disable receiving pane output.
+sets the width and height of a control client.
+.Fl f
+sets a comma-separated list of client flags, see
+.Ic attach-session .
 .Pp
 .Fl l
 requests the clipboard from the client using the
@@ -1377,7 +1398,11 @@ or
 is used, the client is moved to the last, next or previous session
 respectively.
 .Fl r
-toggles whether a client is read-only (see the
+toggles the client
+.Ic read-only
+and
+.Ic ignore-size
+flags (see the
 .Ic attach-session
 command).
 .Pp
@@ -4480,6 +4505,7 @@ The following variables are available, where appropriate:
 .It Li "client_control_mode" Ta "" Ta "1 if client is in control mode"
 .It Li "client_created" Ta "" Ta "Time client created"
 .It Li "client_discarded" Ta "" Ta "Bytes discarded when client behind"
+.It Li "client_flags" Ta "" Ta "List of client flags"
 .It Li "client_height" Ta "" Ta "Height of client"
 .It Li "client_key_table" Ta "" Ta "Current key table"
 .It Li "client_last_session" Ta "" Ta "Name of the client's last session"
diff --git a/tmux.h b/tmux.h
index 811b5fb6..7a687c09 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1568,7 +1568,7 @@ struct client {
 #define CLIENT_CONTROLCONTROL 0x4000
 #define CLIENT_FOCUSED 0x8000
 #define CLIENT_UTF8 0x10000
-/* 0x20000 unused */
+#define CLIENT_IGNORESIZE 0x20000
 #define CLIENT_IDENTIFIED 0x40000
 #define CLIENT_STATUSFORCE 0x80000
 #define CLIENT_DOUBLECLICK 0x100000
@@ -2163,7 +2163,7 @@ char		*cmd_template_replace(const char *, const char *, int);
 
 /* cmd-attach-session.c */
 enum cmd_retval	 cmd_attach_session(struct cmdq_item *, const char *, int, int,
-		     int, const char *, int);
+		     int, const char *, int, const char *);
 
 /* cmd-parse.c */
 void		 cmd_parse_empty(struct cmd_parse_input *);
@@ -2302,6 +2302,8 @@ void	 server_client_push_stderr(struct client *);
 void printflike(2, 3) server_client_add_message(struct client *, const char *,
 	     ...);
 const char *server_client_get_cwd(struct client *, struct session *);
+void	 server_client_set_flags(struct client *, const char *);
+const char *server_client_get_flags(struct client *);
 
 /* server-fn.c */
 void	 server_redraw_client(struct client *);