On Wed, Sep 7, 2016 at 2:25 PM, gevisz <[email protected]> wrote: > > What you have just said implies that I had not had a problem > booting the system after adding a new drive had I used initramfs > correctly. Well, I do agree that, after loading the initramfs, the system > may find the kernel to load with the help of initramfs that understands > UUID. However, how the GRUB could find the initramfs in the first place, > if it could not find the kerner allocated in the same directory as the > initramfs itself?
grub-mkconfig simply searches for a configurable list of filename specifications which your initramfs didn't match. Since /boot could contain all sorts of files, with all sorts of naming conventions, it obviously would be very difficult to accomodate any possible naming convention. We apparently do have it set up to search the filenames generated by the initramfs tools we actually use, so as long as you don't go renaming them you're probably fine. At boot time grub doesn't search for anything. It simply reads the config file and does what it tells it. > > Moreover, in the GRUB menu entry provided above, the initramfs loads > already after the kernel. So, using the initramfs should be irrelevant to > the question of finding the kernel to load by GRUB. > Grub is loading the kernel in your case. The kernel just isn't mounting the root filesystem since there is no initramfs to tell it how to do that. Grub has nothing to do with mounting root at boot time. Grub also loads the initramfs before it ever executes the kernel. The kernel doesn't know how to load an initramfs from disk. It expects it to be in RAM when it runs. The initramfs loaded by grub is just a cpio image that is copied into RAM, and I believe the address gets passed as a kernel command line argument (one you don't even see in grub, it appends it at runtime). The kernel creates a ramfs, extracts the cpio image into the ramfs, and executes init inside of it. At that point the kernel is essentially done with booting the system, the initramfs can mount and pivot to a new root, or the whole system could just run off of an initramfs until it shuts down. This is why the kernel developers have shunned kernel mounting logic/etc in favor of the initramfs; it moves more of the logic into userspace where it is easier to change/maintain/etc, and doesn't have to necessarily run with kernel privs either. Heck, your initramfs could go out on the network, pull in another kernel image and initramfs, and kexec that (which I think is basically the design of coreboot which is a linux-based bootloader). -- Rich
