You can avoid this file 'initrd.img' and eliminate the need of
'initrd.img', if you build your scsi drivers right into the kernel,
instead of into modules. (Many persons recommend this).
13.3. Linuxman Book
A cut from
"http://www.linuxman.com.cy/rute/node1.html"
chapter 31.7.
SCSI Installation Complications and initrd
Some of the following descriptions may be difficult to understand
without knowledge of kernel modules explained in Chapter 42. You may
want to come back to it later.
Consider a system with zero IDE disks and one SCSI disk containing a
LINUX installation. There are BIOS interrupts to read the SCSI disk,
just as there were for the IDE, so LILO can happily access a kernel
image somewhere inside the SCSI partition. However, the kernel is
going to be lost without a kernel module [lsqb ]See Chapter 42. The
kernel doesn't support every possible kind of hardware out there all
by itself. It is actually divided into a main part (the kernel image
discussed in this chapter) and hundreds of modules (loadable parts
that reside in /lib/modules/) that support the many type of SCSI,
network, sound etc., peripheral devices.] that understands the
particular SCSI driver. So although the kernel can load and execute,
it won't be able to mount its root file system without loading a SCSI
module first. But the module itself resides in the root file system in
/lib/modules/. This is a tricky situation to solve and is done in one
of two ways: either (a) using a kernel with preenabled SCSI support or
(b) using what is known as an initrd preliminary root file system
image.
The first method is what I recommend. It's a straightforward (though
time-consuming) procedure to create a kernel with SCSI support for
your SCSI card built-in (and not in a separate module). Built-in SCSI
and network drivers will also autodetect cards most of the time,
allowing immediate access to the device--they will work without being
given any options [lsqb ]Discussed in Chapter 42.] and, most
importantly, without your having to read up on how to configure them.
This setup is known as compiled-in support for a hardware driver (as
opposed to module support for the driver). The resulting kernel image
will be larger by an amount equal to the size of module. Chapter 42
discusses such kernel compiles.
The second method is faster but trickier. LINUX supports what is known
as an initrd image ( initial rAM disk image). This is a small, +1.5
megabyte file system that is loaded by LILO and mounted by the kernel
instead of the real file system. The kernel mounts this file system as
a RAM disk, executes the file /linuxrc, and then only mounts the real
file system.
31.6 Creating an initrd Image
Start by creating a small file system. Make a directory [nbsp ]/initrd
and copy the following files into it.
drwxr-xr-x 7 root root 1024 Sep 14 20:12 initrd/
drwxr-xr-x 2 root root 1024 Sep 14 20:12 initrd/bin/
-rwxr-xr-x 1 root root 436328 Sep 14 20:12 initrd/bin/insmod
-rwxr-xr-x 1 root root 424680 Sep 14 20:12 initrd/bin/sash
drwxr-xr-x 2 root root 1024 Sep 14 20:12 initrd/dev/
crw-r--r-- 1 root root 5, 1 Sep 14 20:12 initrd/dev/console
crw-r--r-- 1 root root 1, 3 Sep 14 20:12 initrd/dev/null
brw-r--r-- 1 root root 1, 1 Sep 14 20:12 initrd/dev/ram
crw-r--r-- 1 root root 4, 0 Sep 14 20:12 initrd/dev/systty
crw-r--r-- 1 root root 4, 1 Sep 14 20:12 initrd/dev/tty1
crw-r--r-- 1 root root 4, 1 Sep 14 20:12 initrd/dev/tty2
crw-r--r-- 1 root root 4, 1 Sep 14 20:12 initrd/dev/tty3
crw-r--r-- 1 root root 4, 1 Sep 14 20:12 initrd/dev/tty4
drwxr-xr-x 2 root root 1024 Sep 14 20:12 initrd/etc/
drwxr-xr-x 2 root root 1024 Sep 14 20:12 initrd/lib/
-rwxr-xr-x 1 root root 76 Sep 14 20:12 initrd/linuxrc
drwxr-xr-x 2 root root 1024 Sep 14 20:12 initrd/loopfs/
|
On my system, the file initrd/bin/insmod is the statically linked
[lsqb ]meaning it does not require shared libraries.] version copied
from /sbin/insmod.static--a member of the modutils-2.3.13 package.
initrd/bin/sash is a statically linked shell from the sash-3.4
package. You can recompile insmod from source if you don't have a
statically linked version. Alternatively, copy the needed DLLs from
/lib/ to initrd/lib/. (You can get the list of required DLLs by
running ldd /sbin/insmod. Don't forget to also copy symlinks and run
strip -s [lcub ]lib[rcub ] to reduce the size of the DLLs.)
Now copy into the initrd/lib/ directory the SCSI modules you require.
For example, if we have an Adaptec AIC-7850 SCSI adapter, we would
require the aic7xxx.o module from /lib/modules/[lcub ]version[rcub
]/scsi/aic7xxx.o. Then, place it in the initrd/lib/ directory.
-rw-r--r-- 1 root root 129448 Sep 27 1999 initrd/lib/aic7xxx.o
|
The file initrd/linuxrc should contain a script to load all the
modules needed for the kernel to access the SCSI partition. In this
case, just the aic7xxx module [lsqb ] insmod can take options such as
the IRQ and IO-port for the device. See Chapter 42.]:
#!/bin/sash
aliasall
echo "Loading aic7xxx module"
insmod /lib/aic7xxx.o
|
Now double-check all your permissions and then chroot to the file
system for testing.
chroot ~/initrd /bin/sash
/linuxrc
|
Now, create a file system image similar to that in Section 19.9:
dd if=/dev/zero of=~/file-inird count=2500 bs=1024
losetup /dev/loop0 ~/file-inird
mke2fs /dev/loop0
mkdir ~/mnt
mount /dev/loop0 ~/mnt
cp -a initrd/* ~/mnt/
umount ~/mnt
losetup -d /dev/loop0
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Finally, gzip the file system to an appropriately named file:
gzip -c ~/file-inird > initrd-<kernel-version>
|
31.7 Modifying lilo.conf for initrd
Your lilo.conf file can be changed slightly to force use of an initrd
file system. Simply add the initrd option. For example:
boot=/dev/sda
prompt
timeout = 50
compact
vga = extended
linear
image = /boot/vmlinuz-2.2.17
initrd = /boot/initrd-2.2.17
label = linux
root = /dev/sda1
read-only
|
Notice the use of the linear option. This is a BIOS trick that you can
read about in lilo(5). It is often necessary but can make SCSI disks
nonportable to different BIOSs (meaning that you will have to rerun
lilo if you move the disk to a different computer).
