Hi, my knowledge of booting from an initramfs is limited right now, so keep that in mind. However, I will attempt to answer some of your questions.
On Fri, Aug 05, 2011 at 10:06:48PM +0200, Sven Vermeulen wrote:
> I'm all in favor of documenting what an initramfs does (or at least what it
> is supposed to do), how it works, how to create one, how to debug issues
> while booting with one, etc.
>
> That said, I'm a bit hesitant to describing that we "recommend" it
> regardless of the situation. What is wrong with describing when? At least
> inform our users that the udev rules have evolved to more than just "detect
> and mknod" scripts and that they are now relying on files and binaries
> available in other locations, like /usr and /var.
It looks like the situation where we will have to have one is if /usr
and /var are not on the same file system as /, because of how udev has
evolved.
> How does the tool that creates an initramfs know which files to copy from
> /usr and /var anyhow?
My understanding is that nothing gets copied from /usr and /var, and it
doesn't have to.
Here is my basic understanding of how the boot sequence works:
1) rootfs is mounted on /. Rootfs contains the contents of the
initramfs.
2) the init program inside the initramfs is run.
3) This init program will mount the real /usr and /var.
4) This init program will then mount the real root on top of rootfs.
(there is a call that does this, but I'll need to look that up again). I
vaguely remember reading that you don't mount the real root on /newroot
then pivet_root as mentioned earlier in this thread; I think that is
part of the old initrd method.
5) This init program will now run /sbin/init or which ever init program
the user wants to run.
> Also, how well does this play with all our profiles (so not only the popular
> architectures)? What about SELinux and/or grSecurity's RBAC model? Are these
> supported throughout the initramfs?
This one I can't answer.
Regards,
William
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