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I am trying to boot Linux (Ubuntu 12.10) without an initrd image. There are various sources online, but I'm not able to find anything that is detailed. There are many pointers as to how to achieve this. So I tried to do this myself, and obviously ran into problems.

The general idea is:

  • Configure and re-build the kernel, to disable initramfs and RAM disk support (I did this to optimize for size, maybe optional)
    • Also make sure to make all drivers available
  • Configure GRUB to not load an initrd image
  • The root filesystem should be sufficiently modified to be able to boot easily (which I have no clue how)

Theoretically, initrd is used to solve the chicke-egg problem. There are drivers necessarily be loaded to load the kernel.

I have done the following on my system.

Kernel configure

RAM filesystem and RAM disk support

I disabled this, which can be found in General Support in the make menuconfig option menu ![RAM filesystem and RAM disk support][1]

RAM block device

I disabled the RAM block device support ![RAM block device support][2]

GRUB configure

In the GRUB boot screen, I hit e and and edited the command line, and removed the line

initrd      /boot/initrd.img-3.12.4

The result

The final result was a kernel that hung during:

Loading initial ramdisk...

Although, I removed ramdisk support from the kernel I built, the kernel doesn't seem to load. I'm obviously missing something. Do I need to modify init scripts in the kernel I built, to make the bootloader not load the initrd image. This would mean I use the busybox init scripts.

GRUB modifications?

I analyzed the grub script that loads the kernel, It does a few module insertions, like

insmod part_dos
insmod ext2

Will it be possible for me to insert a few kernel modules that is required to boot the kernel and boot the kernel with noinitrd option?

And further the boot time that is reduced when initrd isn't used, should be great. So do systems with single digit boot-time have initrd images.

PS: To anyone wondering why I want to disable initrd in the first place, I am
doing this as a good learning experience. Thank you.
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