From: Andrew Richards (andrew_at_tic.ch)
Date: Mon Feb 03 1997 - 07:40:53 EST
Hi,
Here's some general info for those of you who may be interested. It's the method I
used to get Linux to run on my Thinkpad 701CS without using any HD space - i.e.
a partial boot from floppy to the point that my PCMCIA SCSI card is recognised
(New Media Bus Toaster). It is a somewhat unsatisfactory solution, since at the
times that the Jaz is not mounted, the system is trying to do things to the 'Wrong'
root partition (i.e. a dummy root partition during startup, and once the PCMCIA
drivers get unloaded, well, erm, there is no root partition). Still, it works.
Also note that I read in a message to a Linux mailing list that the PCMCIA drivers
in a future release will be such that they can be compiled into the kernel.
Note that this method allows you to create a very portable Linux boot disk: I've
tried it in another notebook and it worked first time (i.e. the notebook had the Jaz
drive connected with the same Linux medium in)
cheers,
Andrew.
SETTING UP LINUX TO BOOT FROM SCSI DISK ATTACHED VIA PCMCIA
(c) Andrew Richards, January 1997 (andrew_at_tic.ch).
Introduction
I have a laptop that is very tight on space on the hard disk, so
I decided to install Linux on my Jaz drive, attached via a PCMCIA
SCSI card (New Media Bus Toaster). The problem with Linux and
PCMCIA in this scenario is that PCMCIA support normally only
gets loaded _after_ the root filesystem has been mounted. PCMCIA
support cannot be compiled into the kernel.
By using LILO (or LOADLIN with a similar method) it is possible
to setup a boot floppy or a program you can fire from DOS,
which contains the kernel and a skeleton root filesystem with
enough information and drivers to load the PCMCIA drivers for
the SCSI card. Once these drivers are loaded it is possible to
mount the real root filesystem.
The kernel offers a facility called initrd which makes this chain
of events possible. Once the real root filesystem is loaded, the
skeleton root filesystem is moved to a subdirectory where it is
still mounted. This can then be unmounted if desired.
Here are some notes on what I did to get this working on _my_
setup - yours could well be different, so take care to adjust e.g.
device names to match your system when reading this document. I
assume technical competence and some willpower - this procedure
isn't easy! I hope this document helps someone out there...
Distributing this document
Feel free to distribute this document; on the same terms as the
GNU license.
Starting point
You need to run a basic Linux somehow to generate the boot floppy
or hard-disk setup. Talk nicely to a friend or do as I did:
The distribution of Linux that I'm using makes it possible to
run Linux from the CD-ROM - which contains a 'Live filesystem',
with the exception of about 30Mbyte of files which have to be
on a read/writeable device, i.e. a directory on the hard disk.
Note that this setup is unsatisfactory for normal Linux use
because it is botched together, slow (because of the CD-ROM)
and inflexible if I want to add bits to it. But to get our boot
floppy it's great.
Also note that you need a reasonably recent version of Linux -
I guess anything from 1996 onwards. Anything with a version 2.x
kernel is fine.
The Jaz drive
I used this for three things when setting up the root floppy -
a place to store my skeleton root filesystem, a place to compile
a kernel for my floppy, and for the real root filesystem. I did
this by having three partitions of the Jaz disk - generated by
using cfdisk. The skeleton root filesystem must fit into a
partition of 5 Megabytes - any bigger and there's no chance it'll
compress onto a single floppy disk.
The Kernel
I decided to build my own kernel to minimise space. This is
actually not strictly necessary - you could easily use one of
the precompiled kernels from the distribution. To do this I
copied /usr/src/linux and subdirectories to a writeable device
(in fact a small partition on the Jaz drive), then executed
these commands from the ....src/linux directory,
make menuconfig
make dep
make clean
make zImage
This creates (after a long compilation - about an hour for me)
the file zImage in ....src/linux/arch/i386/boot. Make sure that
you include RAM disk support and SCSI support (but no specific
low-level SCSI drivers are required - the PCMCIA module doesn't
need these).
You now have a compressed kernel image that will be used later...
The skeleton root filesystem
I setup a 5Mbyte partition on the Jaz drive, i.e /dev/sda2
(/dev/sda1 is where the real Linux root filesystem is, /dev/sda3
is the partition I used to generate the kernel). Before
creating a filesystem on it, 'Zero' it so that it compresses well:
dd if=/dev/zero of=/dev/sda2 bs=1k count=5120
then create a filesystem on it,
mke2fs -b 1024 -m 0 /dev/sda2 5120
mount it,
mount /dev/sda2 /mnt
and put the necessary files in it (see my directory structure
below - the options d, p, and R for the cp command are very useful
for this step). You will need to create a special file /linuxrc
which is run for the skeleton root filesystem. Mine looks like
this,
#!/bin/bash
/etc/rd.d/pcmcia start
fsck /dev/sda1
- alternatively, make /linuxrc a symbolic link to a shell, so
that you can then type in commands manually,
cd /mnt
ln -s bin/bash linuxrc
Note that if you choose this second option, when you boot your
system with the new boot floppy, you will have a shell prompt.
Typically type the comands above (pcmcia start, fsck) before
typing 'exit' - once the shell terminates (i.e. the program
linuxrc), the real root filesystem is mounted.
Now unmount the filesystem,
umount /mnt
Compress it to a file,
dd if=/dev/sda2 bs=1k count=5120 | gzip -9 > /skeleton.gz
This file will be used later...
The floppy
Take an old unwanted floppy that's been formatted at least once
in it's lifetime (i.e. under DOS). Create a filesystem on it,
mke2fs /dev/fd0 -m 0
mount it,
mount /dev/fd0 /mnt
and remove the lost+found directory for extra space,
rm -r /mnt/lost+found
Copy the 'Loader' to the floppy (see LILO documentation),
cp /boot/boot.b /mnt
Copy the kernel image that you wish to use to the floppy,
cp ....zImage /mnt
Copy the compressed skeleton root filesystem to the floppy,
cp /skeleton.gz /mnt
Note that if skeleton.gz doesn't fit on this floppy, that's not
a problem - see the next section - but before you do that, tell
LILO to put the finishing touches to the disk:
Create a file /etc/lilo.conf with contents e.g.,
boot = /dev/fd0
compact
install=/mnt/boot.b
map=/mnt/map
image=/mnt/zImage
label=linux
root=/dev/sda1
initrd=/mnt/skeleton.gz
- in this example the real root filesystem is on /dev/sda1. If
you had to put skeleton.gz on a separate disk, add the indented
line (under image...),
append="prompt_ramdisk=1"
Run LILO to process the lilo.conf file, updating your floppy,
lilo
tidy up by unmounting the floppy
umount /mnt
- you've now created your boot floppy, but don't reboot just yet....
Creating a separate root floppy if necessary (see previous section)
Again using an old unwanted formatted floppy,
dd if=/skeleton.gz of=/dev/fd0
The real root filesystem
Set this up from the Linux install disks if you haven't already,
and add the empty directory /initrd to it. The skeleton filesystem
will get moved to this directory when the real root filesystem
gets mounted.
Does it work?
Cross your fingers. Now reboot the system with your boot floppy
in the drive.
Using LOADLIN instead of a boot floppy
Using LOADLIN it's possible to fire Linux from DOS using files
found on the hard disk (formatted for DOS). It needs most of
the steps above - in particular a kernel and a compressed
skeleton root filesystem. Then proceed as follows:
*THIS SECTION STILL TO BE WRITTEN*
Still to be added to this document
Altering the startup and shutdown files to not dismount the
root filesystem until the latest possible moment, and not to
unload PCMCIA support while the root filesystem needs to be
accessed (my current thoughts are to put a couple of syncs
in the /etc/pcmcia/scsi file).
Sources
I used lots of Linux documents to sort this out. Personal
contributions from Dave Ahn, Chris Bednar and Huber Mantel
and the documents, Kernel HOWTO, Module HOWTO, Installation
HOWTO, PCMCIA HOWTO, BOOTDISK HOWTO, LILO documentation and
man pages, and in particular the initrd.txt and ramdisk.txt
documents (for me in /usr/src/linux/Documentation).
The skeleton root file system
Here is a listing of the skeleton root file system:
total 11
drwxr-xr-x bin
drwxr-xr-x dev
drwxr-xr-x etc
drwxr-xr-x lib
-rwxr-xr-x linuxrc
drwxr-xr-x mnt
drwxr-xr-x modules
drwxr-xr-x proc
lrwxrwxrwx rmmod -> bin/insmod
lrwxrwxrwx sbin -> bin
drwxr-xr-x tmp
drwxr-xr-x usr
drwxr-xr-x var
bin:
total 753
drwxr-xr-x init.d
lrwxrwxrwx sh -> bash
and ordinary files:
agetty, bash, cardmgr, cat, echo, fgrep, fsck, fsck.ext2, init, insmod,
kill, loadkeys, ls, mingetty, mknod, mount, ps, pwd, rm, scsi_info, sleep,
umount, uname
bin/init.d:
total 7
-rwxr-xr-x boot
-rwxr-xr-x pcmcia
-rwxr-xr-x rc
dev:
total 1
lrwxrwxrwx core -> /proc/kcore
lrwxrwxrwx fd -> /proc/self/fd
drwxr-xr-x inet
lrwxrwxrwx ram -> ram0
lrwxrwxrwx ramdisk -> ram0
lrwxrwxrwx stderr -> fd/2
lrwxrwxrwx stdin -> fd/0
lrwxrwxrwx stdout -> fd/1
and the following devices (from standard dev directory)
console, fd0, fd1, full, hda, hda1, hda2, hda3, hda4, hda5, hda6,
hdb, hdb1, hdb2, hdc, hdc1, hdc2, initrd, kmem, mem, nst0, null, port,
ram0, ram1, random, scd0, scd1, sda, sda1, sda2, sda3, sda4, sda5,
sda6, sda7, sda8, sda9, sdb, sdb1, sdb2, sdb3, sdb4, sdb5, sdb6, sdb7, sdc,
sdc1, sdc2, sr0, sr1, st0, tty, tty0, tty1, tty2, tty3, tty4, urandom, zero
dev/inet:
total 0
etc:
total 26
-rw-r--r-- fstab
-rw-r--r-- ld.so.cache
drwxr-xr-x pcmcia
-rw-r--r-- rc.config
lrwxrwxrwx rc.d -> ../sbin/init.d
etc/pcmcia:
total 48
-r-xr-xr-x cdrom
-r--r--r-- cdrom.opts
-rw-r--r-- config
-r--r--r-- config.opts
-r-xr-xr-x fixed
-r--r--r-- fixed.opts
-r-xr-xr-x ftl
-r--r--r-- ftl.opts
-r-xr-xr-x memory
-r--r--r-- memory.opts
-r-xr-xr-x network
-r--r--r-- network.opts
-r-xr-xr-x pcmem
-r--r--r-- pcmem.opts
-r-xr-xr-x rc.pcmcia
-r-xr-xr-x scsi
-r--r--r-- scsi.opts
-r-xr-xr-x serial
-r--r--r-- serial.opts
lib:
total 1208
-rwxr-xr-x ld-linux.so.1
lrwxrwxrwx ld-linux.so.1. -> ld-linux.so.1
lrwxrwxrwx libc.so.5 -> libc.so.5.2.18
-rwxr-xr-x libc.so.5.2.18
-rwxr-xr-x libncurses.so.1.9.9g
lrwxrwxrwx libncurses.so.3.0 -> libncurses.so.1.9.9g
drwxr-xr-x modules
lib/modules:
total 1
drwxr-xr-x 2.0.25
lib/modules/2.0.25:
total 14
drwxr-xr-x block
drwxr-xr-x cdrom
drwxr-xr-x fs
drwxr-xr-x ipv4
drwxr-xr-x misc
-rw-r--r-- modules.dep
drwxr-xr-x net
drwxr-xr-x pcmcia
drwxr-xr-x scsi
lib/modules/2.0.25/block:
total 0
lib/modules/2.0.25/cdrom:
total 0
lib/modules/2.0.25/fs:
total 12
-rw-r--r-- binfmt_elf.o
lib/modules/2.0.25/ipv4:
total 0
lib/modules/2.0.25/misc:
total 11
-rw-r--r-- vtx.o
lib/modules/2.0.25/net:
total 0
lib/modules/2.0.25/pcmcia:
total 120
-rw-r--r-- aha152x_cs.o
-rw-r--r-- ds.o
-rw-r--r-- fixed_cs.o
-rw-r--r-- ftl_cs.o
-rw-r--r-- i82365.o
-rw-r--r-- pcmcia_core.o
-rw-r--r-- tcic.o
lib/modules/2.0.25/scsi:
total 104
-rw-r--r-- scsi_mod.o
-rw-r--r-- scsi_syms.o
-rw-r--r-- sd_mod.o
-rw-r--r-- sg.o
-rw-r--r-- sr_mod.o
mnt:
total 0
modules:
total 123
-rw-r--r-- aha152x.o
-rw-r--r-- aha152x_cs.o
-rw-r--r-- cdrom.o
-rw-r--r-- i82365.o
-rw-r--r-- pcmcia_core.o
proc:
total 1
-r--r--r-- devices
tmp:
total 0
usr:
total 2
drwxr-xr-x adm
drwxr-xr-x lib
usr/adm:
total 0
usr/lib:
total 0
var:
total 1
drwxr-xr-x run
var/run:
total 0
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