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Date:	Mon, 9 Nov 2009 21:45:06 +0100
From:	Andreas Mohr <andi@...as.de>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Andreas Mohr <andi@...as.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Michael A. Griffith" <grif@....org>, linux-kernel@...r.kernel.org
Subject: [PATCH] provide crucial explanations for the dreaded "No init
	found." boot failure.

On Sun, Nov 08, 2009 at 11:11:53PM +0800, Américo Wang wrote:
> On Sun, Nov 08, 2009 at 03:45:50PM +0100, Andreas Mohr wrote:
> >Hi,
> >
> >On Sun, Nov 08, 2009 at 10:25:06PM +0800, Américo Wang wrote:
> >> On Sun, Nov 08, 2009 at 01:00:08PM +0100, Andreas Mohr wrote:
> >So, where to put it?
> >Documentation/initrd.txt is related, however I'd create something
> >like Documentation/initialization/...
> >Or perhaps Documentation/bootup/init.txt ?
> 
> Personally, I prefer Documentation/init.txt, but adding it to
> initrd.txt also makes sense for me. :)

Yup, chose Documentation/init.txt.

Patch against 2.6.32-rc6 attached, UNTESTED (checkpatch.pl is fine).

Please get something like this committed, half a million $$ in prior damage
ought to be enough for everybody.

Thanks,

Signed-off-by: Andreas Mohr <andi@...as.de>


--- linux-2.6.32-rc6/init/main.c.orig	2009-11-08 11:09:51.000000000 +0100
+++ linux-2.6.32-rc6/init/main.c	2009-11-09 21:34:24.000000000 +0100
@@ -846,7 +846,8 @@
 	run_init_process("/bin/init");
 	run_init_process("/bin/sh");
 
-	panic("No init found.  Try passing init= option to kernel.");
+	panic("No init found.  Try passing init= option to kernel. "
+	      "See Linux Documentation/init.txt for guidance.");
 }
 
 static int __init kernel_init(void * unused)
--- /dev/null	2009-10-09 14:49:35.924999847 +0200
+++ linux-2.6.32-rc6/Documentation/init.txt	2009-11-09 21:27:39.000000000 +0100
@@ -0,0 +1,42 @@
+Explaining the dreaded "No init found." boot hang message
+=========================================================
+
+OK, so you've got this pretty unintuitive message (currently located
+in init/main.c) and are wondering what the H*** went wrong.
+Some high-level reasons for failure (listed roughly in order of execution)
+to load the init binary are:
+A) Unable to mount root FS
+B) init binary doesn't exist on rootfs
+C) other requirements not met
+D) binary exists but dependencies not available
+E) binary cannot be loaded
+
+Detailed explanations:
+A) Please make sure you have the correct root FS type
+(and root= in bootloader or CONFIG_CMDLINE points to the correct partition),
+required drivers such as storage hardware (such as SCSI or USB!)
+and filesystem (ext3, jffs2 etc.) are builtin (alternatively as modules by
+using initrd)
+C) Possibly a conflict in console= setup --> initial console unavailable.
+E.g. some serial consoles are unreliable due to serial IRQ issues (e.g. missing
+interrupt-based configuration).
+Try using a different console= device or e.g. netconsole=.
+D) e.g. crucial library dependencies of the init binary such as
+/lib/ld-linux.so.2 missing or broken. Use readelf -d <INIT>|grep NEEDED
+to find out which libraries are required.
+E) make sure the binary's architecture matches your hardware.
+E.g. i386 vs. x86_64 mismatch, or trying to load x86 on ARM hardware.
+Or did you try loading a non-binary file here!?! (shell script?)
+To find out more, add code patch to display kernel_execve()s return values.
+
+Please extend this explanation whenever you find new failure causes
+(after all loading the init binary is a CRITICAL and hard transition step
+which needs to be made as painless as possible), then submit patch to LKML.
+Further TODOs:
+- Implement the various run_init_process() invocations via a struct array
+  which can then store the kernel_execve() result value and on failure
+  log it all by iterating over _all_ results (very important usability fix).
+- try to make the implementation itself more helpful in general,
+  e.g. by providing additional error messages at affected places.
+
+Andreas Mohr <andi at lisas period de>
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