...making Linux just a little more fun!
By Anonymous
GRUB cannot boot the Knoppix CD if booting from the CD-ROM is disabled. This is a feature that the GRUB developers should consider adding. See my previous article in the October 2004 Linux Gazette.
However, GRUB (current version 0.95) can generate a floppy to boot Knoppix after a full install to hard disk - something LILO may have problems with, due to its inability to find files, and due to the kernel and initial RAMdisk growing past diskette size.
Assume Knoppix is installed to hard disk but that its partition is not bootable, for whatever reason. You need a floppy to boot Knoppix, and here is how to make it with GRUB:
You can use a simple GRUB diskette that boots to a GRUB command line. From this command line, you can issue commands to boot your Knoppix on the non-bootable partition.
This simple GRUB boot diskette can be prepared with the
grub-floppy script. It is very quick to prepare, but does not
carry a filesystem, so you cannot do much with it. You cannot write to it,
and you will have to type quite a bit after booting to the GRUB prompt.
A more comfortable solution is given by the script
grub-install, which requires a formatted diskette. A
DOS-formatted diskette will do, and you will be able to modify it from DOS
- quite an advantage. Mount the diskette, e.g., to /floppy, and issue the
command:
grub-install --root-directory=/floppy fd0
The script will create /floppy/boot/grub and copy to it the image files required for booting. Some of them can be deleted, since you do not need support for half a dozen filesystems.
Now, the best part of it is that you can write to /floppy/boot/grub a text
file by the name of menu.lst, which is the configuration file
for GRUB. Here, you put all the instructions you want for booting your
Knoppix, and that's it. (The endline sequence may be DOS-style or
Linux-style.) It boots fairly quickly - or rather, it boots very quickly if
you reduce the timeout to 1 sec and suppress the menu.
Let us now get around to a conjurer trick that looks a bit puzzling.
The hard disk where Knoppix is installed is not visible to the BIOS. Why not? Because the disk is explicitly set to 'none' in the BIOS, for some peculiar reason. Or because the old BIOS cannot see partitions past 8GB.
Wonder: Linux can boot, see the disk even though it is invisible to the BIOS, and plant its root on it.
The preparation of the GRUB diskettes for the trick goes actually the same way as before, but some additional fiddling is required.
Let us focus on the case where a DOS-formatted boot diskette has been
prepared with grub-install.
First, you copy your Linux kernel (name it vmlinuz) to a hard disk visible to the BIOS, e.g., the first hard disk, first partition, which GRUB call (hd0,0).
Second, you must guess the proper Linux designation for the Knoppix partition, when Linux is running. Remember that Linux calls the SCSI disks /dev/sda, dev/sdb, etc., and the IDE disks /dev/hda, /dev/hdb, etc. The partitions are then appended to them as numbers, e.g., /dev/hda1, /dev/hda2, etc. It can get complex, depending on the devices you have in your PC. In any event, you must find the proper designation for the Knoppix partition, since it is invisible to the BIOS and GRUB. Assume for the sake of an example that the correct Linux designation is /dev/hdb1.
Now, write menu.lst to the floppy, directory
/boot/grub, as follows:
# start of menu.lst # GRUB boot for Knoppix 3.6/kernel 2.6.7 # Knoppix is installed to hdb1 # hdb1 is not bootable, indeed not seen by BIOS # By default, boot the first entry default 0 # Boot after 1 second, no menu hiddenmenu timeout 1 # first and unique entry title knoppix36267 kernel (hd0,0)/vmlinuz root=/dev/hdb1 # Should an initial RAMdisk be required, # the last line would be, for instance: # kernel (hd0,0)/vmlinuz root=/dev/hdb1 initrd=/initrd/ird.gz # end of menu.lst
We are not finished yet. GRUB has on the floppy an auto-generated file device.map, listing all devices known to it. In this abnormal case, it is a good idea to check the map file; it may need revision by hand. Indeed, it must include that device unknown to the BIOS but destined to carry the root. Note that the map file is simply a translation between GRUB device names and Linux device names.
That's it. Boot the GRUB diskette and it will pull vmlinuz from your first hard disk: vmlinuz will run and will recognize and use the partition /dev/hdb1 even though /dev/hdb is unknown to the BIOS.
Can anyone explain it? If the kernel can see partitions invisible to the
BIOS, why can't GRUB? GRUB has in the boot sector a tiny program called
stage1 that does nothing but trigger stage2.
Since stage2 is more than 100K, shouldn't it be able to detect
available devices the same way the kernel does?
