From owner-freebsd-hackers@FreeBSD.ORG  Sat Feb 14 23:49:46 2015
Return-Path: <owner-freebsd-hackers@FreeBSD.ORG>
Delivered-To: freebsd-hackers@freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115])
 (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits))
 (No client certificate requested)
 by hub.freebsd.org (Postfix) with ESMTPS id 50DB1720
 for <freebsd-hackers@freebsd.org>; Sat, 14 Feb 2015 23:49:46 +0000 (UTC)
Received: from mx1.stack.nl (relay04.stack.nl [IPv6:2001:610:1108:5010::107])
 (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits))
 (Client CN "mailhost.stack.nl",
 Issuer "CA Cert Signing Authority" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id 151117A9
 for <freebsd-hackers@freebsd.org>; Sat, 14 Feb 2015 23:49:46 +0000 (UTC)
Received: from snail.stack.nl (snail.stack.nl [IPv6:2001:610:1108:5010::131])
 by mx1.stack.nl (Postfix) with ESMTP id 687E5B8056;
 Sun, 15 Feb 2015 00:49:43 +0100 (CET)
Received: by snail.stack.nl (Postfix, from userid 1677)
 id 533B228494; Sun, 15 Feb 2015 00:49:43 +0100 (CET)
Date: Sun, 15 Feb 2015 00:49:43 +0100
From: Jilles Tjoelker <jilles@stack.nl>
To: Perry Hutchison <perryh@pluto.rain.com>
Subject: Re: RFC: make init(8) aware of /rescue/sh
Message-ID: <20150214234943.GB1360@stack.nl>
References: <54db2f2f.gIXyruGSeJuY3FbJ%perryh@pluto.rain.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <54db2f2f.gIXyruGSeJuY3FbJ%perryh@pluto.rain.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Cc: freebsd-hackers@freebsd.org
X-BeenThere: freebsd-hackers@freebsd.org
X-Mailman-Version: 2.1.18-1
Precedence: list
List-Id: Technical Discussions relating to FreeBSD
 <freebsd-hackers.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/options/freebsd-hackers>, 
 <mailto:freebsd-hackers-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-hackers/>
List-Post: <mailto:freebsd-hackers@freebsd.org>
List-Help: <mailto:freebsd-hackers-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-hackers>,
 <mailto:freebsd-hackers-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 14 Feb 2015 23:49:46 -0000

On Wed, Feb 11, 2015 at 02:30:07AM -0800, Perry Hutchison wrote:
> Seems to me it might be desirable for init(8) to fall back
> to /rescue/sh for single-user mode if neither the default
> (kenv:init_shell) nor /bin/sh is usable.  Thoughts?

> (Patch generated against stable/8, but will likely apply to
> HEAD also -- not much has changed in init.)

> --- init.c-orig
> +++ init.c
> @@ -79,6 +79,9 @@
>  #include <login_cap.h>
>  #endif
>  
> +/* Ideally this value should come from the RESCUE side of paths.h */
> +#define	_PATH_R_BSHELL	"/rescue/sh"
> +
>  #include "pathnames.h"
>  
>  /*
> @@ -706,7 +709,8 @@
>  
>  		/*
>  		 * Fire off a shell.
> -		 * If the default one doesn't work, try the Bourne shell.
> +		 * If the default one doesn't work, try the Bourne shell;
> +		 * if that doesn't work either, try the rescue shell.
>  		 */
>  
>  		char name[] = "-sh";
> @@ -717,6 +721,8 @@
>  		emergency("can't exec %s for single user: %m", shell);
>  		execv(_PATH_BSHELL, argv);
>  		emergency("can't exec %s for single user: %m", _PATH_BSHELL);
> +		execv(_PATH_R_BSHELL, argv);
> +		emergency("can't exec %s for single user: %m", _PATH_R_BSHELL);
>  		sleep(STALL_TIMEOUT);
>  		_exit(1);
>  	}

It is already possible to type "/rescue/sh" at the prompt (the Makefile
always compiles with -DDEBUGSHELL). This must be done manually but also
covers the case where /bin/sh exists but rtld or shared libraries are
missing or broken.

I'm not really sure this is worth the extra code.

-- 
Jilles Tjoelker