[PATCH] vt: Add boot param for setting default vt console

[PATCH] vt: Add boot param for setting default vt console

[Adam Saponara]

Presently the default console is hard-coded to vt1.

The param allows for setting a different default. The param defaults to 0
(vt1), preserving the current behavior. It is clamped by the constants
`(MIN|MAX)_NR_CONSOLES`. If set `>= MIN`, `con_init` will initialize that
vt as well (a couple extra kilobytes heap for the `vc_data` and
`vc_screenbuf` structs).

Without this feature, users achieve the same effect with an init
script[0][1][2][3]. This works but requires an extra `chvt(1)` which can
race with user interaction and flicker the screen at login.

[0]: https://bbs.archlinux.org/viewtopic.php?id=232058
[1]: https://unix.stackexchange.com/questions/399986
[2]: https://github.com/systemd/systemd/issues/7247
[3]: https://www.linuxquestions.org/questions/linux-general-1/x-4175722418

Signed-off-by: Adam Saponara <as@php.net>
---
 .../admin-guide/kernel-parameters.txt         |  5 +++
 drivers/tty/vt/vt.c                           | 44 +++++++++++++------
 2 files changed, 36 insertions(+), 13 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb850e5290c2..6694b2edcfd6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -8429,6 +8429,11 @@ Kernel parameters
 			overridden by individual drivers. 0 will hide
 			cursors, 1 will display them.
 
+	vt.default_console=
+			[VT]
+			Set default console; 0-62.
+			Default: 0 (vt1)
+
 	vt.italic=	[VT] Default color for italic text; 0-15.
 			Default: 2 = green.
 
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index c1f152d8b03b..e566942c380f 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -140,6 +140,7 @@ EXPORT_SYMBOL(vc_cons);
 static const struct consw *con_driver_map[MAX_NR_CONSOLES];
 
 static int con_open(struct tty_struct *, struct file *);
+static void con_init_vc(int console_idx);
 static void vc_init(struct vc_data *vc, int do_clear);
 static void gotoxy(struct vc_data *vc, int new_x, int new_y);
 static void restore_cur(struct vc_data *vc);
@@ -159,10 +160,14 @@ static void unblank_screen(void);
 
 int default_utf8 = true;
 module_param(default_utf8, int, S_IRUGO | S_IWUSR);
+
 int global_cursor_default = -1;
 module_param(global_cursor_default, int, S_IRUGO | S_IWUSR);
 EXPORT_SYMBOL(global_cursor_default);
 
+int default_console;
+module_param(default_console, int, S_IRUGO | S_IWUSR);
+
 static int cur_default = CUR_UNDERLINE;
 module_param(cur_default, int, S_IRUGO | S_IWUSR);
 
@@ -3742,7 +3747,7 @@ static int __init con_init(void)
 {
 	const char *display_desc = NULL;
 	struct vc_data *vc;
-	unsigned int currcons = 0, i;
+	unsigned int i, di;
 
 	console_lock();
 
@@ -3776,18 +3781,18 @@ static int __init con_init(void)
 		mod_timer(&console_timer, jiffies + (blankinterval * HZ));
 	}
 
-	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
-		vc_cons[currcons].d = vc = kzalloc_obj(struct vc_data,
-						       GFP_NOWAIT);
-		INIT_WORK(&vc_cons[currcons].SAK_work, vc_SAK);
-		tty_port_init(&vc->port);
-		visual_init(vc, currcons, true);
-		/* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
-		vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
-		vc_init(vc, currcons || !vc->vc_sw->con_save_screen);
-	}
-	currcons = fg_console = 0;
-	master_display_fg = vc = vc_cons[currcons].d;
+	for (i = 0; i < MIN_NR_CONSOLES; i++)
+		con_init_vc(i);
+
+	/* Init default_console if we didn't already do that above */
+	di = clamp(default_console, 0, MAX_NR_CONSOLES - 1);
+	if (di >= MIN_NR_CONSOLES)
+		con_init_vc(di);
+
+	fg_console = di;
+
+	vc = vc_cons[fg_console].d;
+	master_display_fg = vc;
 	set_origin(vc);
 	save_screen(vc);
 	gotoxy(vc, vc->state.x, vc->state.y);
@@ -3806,6 +3811,19 @@ static int __init con_init(void)
 }
 console_initcall(con_init);
 
+static void con_init_vc(int console_idx)
+{
+	struct vc_data *vc = kzalloc_obj(struct vc_data, GFP_NOWAIT);
+
+	vc_cons[console_idx].d = vc;
+	INIT_WORK(&vc_cons[console_idx].SAK_work, vc_SAK);
+	tty_port_init(&vc->port);
+	visual_init(vc, console_idx, true);
+	/* Assuming vc->vc_{cols,rows,screenbuf_size} are sane here. */
+	vc->vc_screenbuf = kzalloc(vc->vc_screenbuf_size, GFP_NOWAIT);
+	vc_init(vc, console_idx || !vc->vc_sw->con_save_screen);
+}
+
 static const struct tty_operations con_ops = {
 	.install = con_install,
 	.open = con_open,
-- 
2.51.0

Re: [PATCH] vt: Add boot param for setting default vt console

[Greg Kroah-Hartman]

On Sun, Mar 01, 2026 at 04:48:04PM -0500, Adam Saponara wrote:
> Presently the default console is hard-coded to vt1.
> 
> The param allows for setting a different default. The param defaults to 0
> (vt1), preserving the current behavior. It is clamped by the constants
> `(MIN|MAX)_NR_CONSOLES`. If set `>= MIN`, `con_init` will initialize that
> vt as well (a couple extra kilobytes heap for the `vc_data` and
> `vc_screenbuf` structs).
> 
> Without this feature, users achieve the same effect with an init
> script[0][1][2][3]. This works but requires an extra `chvt(1)` which can
> race with user interaction and flicker the screen at login.

What user interaction races?  I'm loath to change this as I've not seen
any bug reports for this.  What changed to cause this issue?

And this is for the "odd" systems that want a graphical login, BUT still
want to default to the console?  That's a very odd configuration, and I
think that we should just stick with the fix that we have for those that
want to do this as adding more boot parameters that we need to support
for forever feels like a bad idea.

sorry,

greg k-h