Re: emergency or init=/bin/sh mode and terminal signals

[Willy Tarreau <w@1wt.eu>]

On Sun, Jun 18, 2006 at 11:23:03PM +0200, Samuel Thibault wrote:
> Hi,
> 
> There's a long-standing issue in init=/bin/sh mode: pressing control-C
> doesn't send a SIGINT to programs running on the console. The incurred
> typical pitfall is if one runs ping without a -c option... no way to
> stop it!
> 
> This is because no session is set up by the kernel, and shells don't
> start sessions on their own, so that no session (hence no controlling
> tty) is set up.
> 
> The attached patch sets such session and controlling tty up, which fixes
> the issue. The unfortunate effect is that init might be killed if one
> presses control-C very fast after its start.

This downside is a little problematic. Wouldn't it be possible to disable
the interrupt signal on the terminal, and let the user re-enable it when
needed using "stty intr ^C" ?

I too am used to starting with init=/bin/sh, but I'm also used to launch
ping in the background. However, if getting Ctrl-C working implies a risk
of killing init, then I'd rather keep it the old way.

> Samuel

Regards,
Willy

> --- linux-2.6.17-orig/init/main.c	2006-06-18 19:22:40.000000000 +0200
> +++ linux-2.6.17-perso/init/main.c	2006-06-18 23:00:00.000000000 +0200
> @@ -703,9 +703,13 @@
>  	system_state = SYSTEM_RUNNING;
>  	numa_default_policy();
>  
> +	sys_setsid();
> +
>  	if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
>  		printk(KERN_WARNING "Warning: unable to open an initial console.\n");
>  
> +	sys_ioctl(0, TIOCSCTTY, 1);
> +
>  	(void) sys_dup(0);
>  	(void) sys_dup(0);
>