What's an initrd.img?

hotel-lima · 06-11-2004, 04:23 PM

Hi,

while doing some kernel-compiling I saw that some kernels need an initrd.img while booting and some kernels do not.
For instance my Debian system uses an initrd with kernel 2.4.18-k7.
Some kernel-compiling instructions do not mention an initrd.
So, what exactly is an initrd and when do I need this?

Can I compile and use a new kernel without it?

How do I create an initrd after compiling a new kernel?

Hope, somebody can explain this to me.

Thanks in advance!

Greetings
hotel-lima

ranger_nemo · 06-11-2004, 05:39 PM

From man mkinitrd...

Code:

DESCRIPTION
       mkinitrd creates filesystem images which are suitable  for
       use  as Linux initial ramdisk (initrd) images. Such images
       are often used for preloading  the  block  device  modules
       (such as SCSI or RAID) which are needed to access the root
       filesystem.    mkinitrd    automatically     loads     all
       scsi_hostadapter entries in /etc/conf.modules, which makes
       it simple to build and  use  kernels  using  moduler  SCSI
       devices.

       Any  module  options  specified  in  /etc/conf.modules are
       passed to the modules as they are loaded  by  the  initial
       ramdisk.

The most common need for an initrd is when you have your / on a filesystem type that you don't have compiled into your kernel. If your / is on EXT3 or Reiser, and you have them as modules in your kernel, then the kernel can't read / at boot, because it doesn't have the modules loaded yet.

hotel-lima · 06-11-2004, 05:50 PM

Hi,

thanks for answering.

That means that initrd is not necessary for me, because my / is ext3 and this support is compiled into my kernel.

Ok then I think it's clear.

Thank you.

Greetings,
hotel-lima