[Devil-linux-develop] [Devil-Linux-discuss] Hack to install onto harddisk instead of memory (low memory solution)

[Heiko Z. <hz...@pr...>]

----- Forwarded by Heiko Zuerker/ITS/Propack Data Corporation on 05/15/=
2002
09:58 AM -----
|---------+----------------------------------------------->
|         |           "Walter Haidinger"                  |
|         |           <wal...@gm...>           |
|         |           Sent by:                            |
|         |           dev...@li...|
|         |           ceforge.net                         |
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|         |                                               |
|         |           05/15/2002 06:24 AM                 |
|         |                                               |
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  |        To:      <dev...@li...>        =
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  |        Subject: [Devil-Linux-discuss] Hack to install onto harddisk=
 instead of memory (low memory solution)                               =
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Hi!

I've successfully installed Devil-Linux this weekend on an old machine
(486/66) with just 24 MB of RAM. I think that even 16 MB would be
sufficient.
However, in order to do that I had to make Devil-Linux boot onto a
harddisk partition instead of a ramdisk. I was forced to do this
because _both_ of my 32MB SIMMs turned out to be defective... :-(
Well, here's what I did. Perhaps it helps somebody who has a similar
problem. How about adding a docs section like "installing Devil-Linux
on machines with less than 64 MB RAM" ?
This may have been done already but I didn't search the mailing-list
archives when I did it because I had no internet access at that time.

Anyways, here goes:

With my setup, I used three partitions (on an old 200+ MB IDE drive):
* /dev/hda1 - DOS (C:), about 50 MB
  Required because that old machine could not boot from CD-Rom and if
  I have to use a harddisk anyways we can as well use it for booting to=
o.
  Please note that the floppy containing the config is still required
  any may have to configure the BIOS to boot from HD first.
* /dev/hda2 - Linux SWAP, 64 MB
  I have free disk space so why not extend the already limited physical=

  memory and set up a swap partition?
* /dev/hda3 - Linux ext2, about 100 MB
  Used as subsitute for the ramdisk. I've hacked the initrd to use
  this partition instead of /dev/shm (see below).

After setting up a DOS partition to boot from (C:), I copied the
boot directory from the CD (to C:\boot). Next, I had to modify to
linuxrc  script of initrd.gz.
To do this, follow these steps (under Linux):
1. Copy the initrd.gz from the CD-Rom somewhere, e.g.
   > cp /cdrom/boot/initrd.gz /tmp
2. Unpack it
   > gunzip /tmp/initrd.gz
3. Mount the file using the loopback-device:
   > mount /tmp/initrd -o rw,loop=3D/dev/loop0 /mnt
4. Modify /mnt/linuxrc with your favourite editor according to the
   next section below.
   > your-editor /mnt/linuxrc
5. Copy your /sbin/swapon and /sbin/mkswap files to /mnt/sbin
   Make sure that the binaries run on your Devil-Linux Version.
   For me, binaries from SuSE-Linux 7.3 run on Devil-Linux 0.5.
6. Unmount again
   > umount /mnt
7. Pack the modified image
   > gzip initrd
8. Copy the new initrd.gz to the boot directory of the DOS partition
   (C:\boot)

Now for the fun part: Howto modify linuxrc
(I've modifed linuxrc v1.7 from the 0.5rc1 distribution)

Here are the diffs in detail:

28a29,32
> SWAP_PART=3D/dev/hda2
> echo "Adding swapspace on $SWAP_PART"
> /sbin/swapon $SWAP_PART && print_status success || print_status failu=
re
>

Add the swap partition. You might add a /sbin/mkswap $SWAP_PART right
before swapon but I doubt that this is necessary. Well, of course you
need to create the swap-space _once_ !
31a36,43
> DATA_PART=3D/dev/hda3
> echo "Using $DATA_PART as ramdisk substitute:"
> test -d /hd || mkdir /hd
> echo -n "Creating ext2 filesystem on $DATA_PART"
> /sbin/mke2fs -q $DATA_PART print_status success || print_status failu=
re
> echo -n "Mounting $DATA_PART"
> mount -t ext2 -o rw $DATA_PART /hd && print_status success ||
> print_status failure>

Use partition set by DATA_PART as the ramdisk substitute.
First create a mountpoint, then create the filesystem and mount it.
*** WARNING:
The partition is created _without_ question! Any previously stored
data is lost! Actually, that is a good thing as it really simulates
ramdisk behaviour and is therefore a security benefit.
Also, you can simply turn off the machine without shutting down which
is good if you have users power on/off the router without further
knowledge.However, it can be *very* disastrous if you edit your partiti=
on
table
and forget to assign the correct partition in DATA_PART.
33,35c45,49
< test -d /dev/shm || mkdir /dev/shm
< echo -n "Mounting SHM FS on /dev/shm"
< mount -t shm -o size=3D40g shmfs /dev/shm && print_status success ||
print_status failure---
> #test -d /dev/shm || mkdir /dev/shm
> #echo -n "Mounting SHM FS on /dev/shm"
> #mount -t shm -o size=3D40g shmfs /dev/shm && print_status success ||=

> print_status failure> rm -rf /dev/shm > /dev/null 2>&1
> ln -s /hd /dev/shm
39c53,54
< ln -s /dev/shm /ram
---
> #ln -s /dev/shm /ram
> ln -s /hd /ram

Remove (comment) the shared memory stuff and replace it by symlinks.
This allows transparent usage of the partition instead of /dev/shm,
i.e. not subsequent scripts need to be modified.

That are all changes made to linuxrc.
I've attached a context diff with the changes.
To apply it, run (replacing step 4 above) in /mnt after saving the
attachment (to, say, /tmp):
   patch < ../tmp/linuxrc.diff

*** Security warning:
If you store the boot files (kernel, initrd, ...) on the harddisk
(i.e. if you do _not_ create a CD containing the new initrd.gz), that
files _can_ be modified.Therefore, the integrity of the boot files _hav=
e_
to be verified!
e.g.: Use MD5 hashes!

1. Get md5sum.exe for DOS from http://etree.org/md5com.html
   and put it on your config floppy.
2. Create md5 checksums for all files that are on the harddisk,
   e.g. (write on one line):
     md5sum.exe C:\boot\initrd.gz C:\boot\loadlin.exe
                C:\boot\vmlinuz > A:\boot.md5
3. In autoexec.bat of your boot floppy, add the following 2 lines:
     md5sum -vc boot.md5
     if errorlevel 1 exit
4. Don't forget to write-protect your floppy again!

Now, if anyone modifies the files on the harddisk, md5sum fails the
check and the autoexec.bat is aborted.
That's finally it! I just hope that I forgot nothing as I wrote this
mostly from memory...

Anyways, comments *are* welcome!

Regards, Walter

PS: Yes, I know this is a (bad) hack and there are better ways
    (that is, more configurable) to do this.
    However, I had to get the system up and that is what did it.
    You're free to do it any other way you desire! ;-)


--
Walter Haidinger <wal...@gm...>
For contact information or PGP/GPG public key please refer to
http://haidinger.webhop.org/contact.html


(See attached file: linuxrc.diff)

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