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

["linux-os \(Dick Johnson\)" <linux-os@analogic.com>]

On Mon, 19 Jun 2006, Samuel Thibault wrote:

> linux-os (Dick Johnson), le Mon 19 Jun 2006 07:37:02 -0400, a écrit :
>> You can't allow some terminal input to affect init. It has been the
>> de facto standard in Unix, that the only time one should have a
>> controlling terminal is after somebody logs in and owns something to
>> control.
>
> Ok. The following still makes sense, doesn't it? (i.e. set a session for
> the emergency shell)
>
> --- linux-2.6.17-orig/init/main.c	2006-06-18 19:22:40.000000000 +0200
> +++ linux-2.6.17-perso/init/main.c	2006-06-20 00:07:07.000000000 +0200
> @@ -729,6 +729,11 @@
> 	run_init_process("/sbin/init");
> 	run_init_process("/etc/init");
> 	run_init_process("/bin/init");
> +
> +	/* Set a session for the shell.  */
> +	sys_setsid();
> +	sys_ioctl(0, TIOCSCTTY, 1);
> +
> 	run_init_process("/bin/sh");
>
> 	panic("No init found.  Try passing init= option to kernel.");
>

Well this makes 'sense' however, you should not modify the kernel
for this, you should do (trivialized and not tested):

int main(int count, char *argv[], char *env[])
{
    setsid();
    strcpy(argv[0], "/bin/bash");
    ioctl(0, TIOCSCTTY, 1);
    execve(argv[0], argv, env);
}

That gets you a shell with ^C capability. You could also
set up some signal handlers to minimize the potential of
killing your 'init' even though bash will set up its own.


Cheers,
Dick Johnson
Penguin : Linux version 2.6.16.4 on an i686 machine (5592.72 BogoMips).
New book: http://www.AbominableFirebug.com/
_


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