Re: boot-time messages, /init touch not found

[songbird <songbird@anthive.com>]

The Wanderer wrote:
> Henrique de Moraes Holschuh wrote:
>> songbird wrote:
>>
>>> # cpio -i -v < /boot/initrd.img-3.18.0-trunk-686-pae
>>> kernel
>>> kernel/x86
>>> kernel/x86/microcode
>>> kernel/x86/microcode/GenuineIntel.bin
>>> 22 blocks
>>=20
>> Yeah, well, you have a multi-segment initramfs. There's an
>> uncompressed cpio archive first with the "early initramfs" (used for
>> platform firmware such as processor microcode updates and ACPI table
>> overrides). It is followed by a compressed cpio archive with the rest
>> of the initramfs contents.

  ah, good to know the name of it, now with google 
i can still find no way to take it apart to examine
the parts.


>> The Linux kernel definition of an initramfs image is: "one or more
>> cpio archives, compressed or uncompressed, one after the other. Any
>> of these cpio archives can be zero-padded to any lenght, as long as
>> it is a multiple of 4". It only supports a very specific subset of
>> the possible cpio archive formats, too.

  sure, makes sense.


>> The kernel doesn't really care if you change compression type, or
>> alternate compressed and uncompressed while loading the regular
>> initramfs, but the early initramfs MUST be the first segment, and it
>> MUST be uncompressed.
>
> Hm. That's informative, thanks.
>
> So how does one manually expand such a multi-segment archive, to examine
> and possibly manipulate its contents?

  lsinitramfs will list them, lsinitramfs does work for such
archives.

  https://wiki.debian.org/InitramfsDebug mentions them, but only to
say that they exist and that described methods don't work on them.


> The only method I can think of which seems likely to be effective is to
> scan through the file for a gzip-or-suchlike header within the file,
> then 'cat' the remainder of the file out to where gunzip can find it,
> and proceed from there - but I don't know of any way to do that using
> standard tools; if I wanted to try it, I'd have to write code for the
> purpose myself.
>
> Presumably appropriate tools do exist, if only within the kernel tree...

  is it the kernel or the init script that initramfs-tools
is using that is doing the work?

  i think the lsinitramfs source code may provide some 
interesting ideas too, but this is beyond me at the 
moment to look into.


  songbird