LOADLIN

LOADLIN is a program that can boot Linux from DOS. Since the advent of Windows ME and Windows XP, it is no longer natural that PC users have DOS installed on their PCs. Windows versions up to and including Windows 98 came with a DOS version that was usable for LOADLIN. In my opinion LOADLIN is primarily of historical interest for this reason. The primary reasons to use LOADLIN were the following:

• Getting devices working under Linux after loading their DOS device drivers. Some PC devices (mostly sound cards) were supposed to be fully compatible with a standard product (that Linux had a device driver for), but only after they were initialized by their DOS device drivers. So you needed to run a DOS device driver first before Linux would be able to access that device. Therefore it made sense to boot Linux from DOS.
• Booting from a Linux CD without the need to create boot floppies. Bootable CDs are a comparatively recent invention and most BIOS-es did not support it before 1998. Without the ability to boot directly from the CD you either needed boot floppies or you could start Linux on the CD from DOS using LOADLIN.
• Installing Linux without the need to tamper with the hard disk. With LOADLIN it is not necessary to install anything into the MBR in order to get Linux booted from the hard disk. A loadlin entry could easily be added to the DOS boot menu in CONFIG.SYS.

  Linux could even be installed without repartitioning the disk. For this very purpose the UMSDOS file system was added to the Linux kernel. It still exists, though it sees very little usage today. The Linux file systems lived in the LINUX directory on the DOS partition and it contained special files to translate long file names into DOS 8+3 file names and to specify attributes such as users, groups, permissions and device files. Linux could be installed just by unpacking a bunch of ZIP files, just as one would install a large DOS application. LOADLIN made booting Linux just as easy as running a DOS application, hence it fit nicely into the DOS mindset.

Loadlin can be downloaded from Hans Lermen's home page. Download the file lodln16.tgz and unpack it. We will use only the file loadlin.exe.

In order to run LOADLIN, we need DOS. Create a bootable DOS diskette with just the bare system and COMMAND.COM on it. For those of you who have either Windows NT/ME/2000/XP or no Microsoft OS at all, you can use Freedos. Download the file FDB8_144.DSK (the rawrite image) and transfer it to a diskette

dd if=FDB8_144.DSK of=/dev/fd0

Next remove everything but KERNEL.SYS and COMMAND.COM from this diskette.

mount /dev/fd0 /mnt
cd /mnt
rm -rf config.sys *.bat kernel32.sys kernel16.sys readme\
    docs fdos games install util
cd
umount /mnt

Now that we have a minimal DOS diskette, copy LOADLIN.EXE, the linux kernel and the initial RAM disk to it:

mount /dev/fd0 /mnt
cd /home/lennartb/myboot
cp loadlin.exe /mnt
cp zImage /mnt/zimage
cp root.img.gz /mnt/root.gz
umount /mnt

Next try to boot from the diskette. You should boot into DOS. As there is no AUTOEXEC.BAT, you will be prompted for date and time. Press enter twice. Now you should be at the A> prompt. Type the following line to boot Linux:

loadlin zimage initrd=root.gz

Of course you can put this line in a batch file or even in AUTOEXEC.BAT.