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5. Other Loopback Root Device Possibilities

Once the principle of booting a filesystem in a file on a DOS partition has been established there are many other things that you can now do.

5.1 DOS Hard-disk Only Installation

If it is possible to boot Linux from a file on a DOS harddisk by using a boot floppy then it is obviously also possible to do it using the harddisk itself.

A configuration boot menu can be used to give the option of running LOADLIN from within the AUTOEXEC.BAT. This will give a much faster boot sequence, but is otherwise identical.

5.2 LILO Booted Installation

Using LOADLIN is only one option for booting a Linux kernel. There is also LILO that does much the same but without needing DOS.

In this case the DOS format floppy disk can be replaced by an ext2fs format one. Otherwise the details are very similar, with the kernel and the initial ramdisk being files on that disk.

The reason that I chose the LOADLIN method is that the arguments that need to be given to LILO are slightly more complex. Also it is more obvious to a casual observer what the floppy disk is since it can be read under DOS.

5.3 VFAT / NTFS Installation

I have tried the NTFS method, and have had no problems with it. The NTFS filesystem driver is not a standard kernel option in version 2.0.x, but is available as a patch from http://www.informatik.hu-berlin.de/~loewis/ntfs/. In version 2.2.x the NTFS driver is included as standard in the kernel.

The only changes for the VFAT or NTFS options are in the initial ramdisk, the file /linuxrc needs to mount a file system of type vfat or ntfs rather that msdos.

I know of no reason why this should not also work on a VFAT partition.

5.4 Installing Linux without Re-partitioning

The process of installing Linux on a PC from a standard distribution requires booting from a floppy disk and re-partitioning the disk. This stage could instead be accomplished by a boot floppy that creates an empty loopback device and swap file. This would allow the installation to proceed as normal, but it would install into the loopback device rather than a partition.

This could be used as an alternative to a UMSDOS installation, it would be more efficient in disk usage since the minimum allocation unit in the ext2 filesystem is 1kB instead of up to 32kB on a DOS partition. It can also be used on VFAT and NTFS formatted disks which are otherwise a problem.

5.5 Booting From a Non-bootable device

This method can also be used to boot a Linux system from a device that is not normally bootable.

Obviously there are many other devices that could be used, NFS root filesystems are already included in the kernel as an option, but the method described here might also be used instead.


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