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2. How to do it

  1. Prepare a floppy containing a bootable DOS. I used Caldera's DR-DOS, which is free for personal and charitable uses. (It has been confirmed that DR-DOS 7.03 has changed in some way that netbooting fails; reason is still unknown. 7.02 works.) FreeDOS can also be netbooted and the kernel is loaded from the tagged image rather than from the floppy image, which means more space for applications or data. All the instructions are in the mknbi directory that comes with the Etherboot distribution. You can find a zip file containing the components of a tagged image that runs telnet on the diskless client.
  2. You can do nearly all manipluations on Linux using mtools on a floppy image in a file but you have to get the boot block from DR-DOS first to pass to mformat. You can do this by extracting the first 512 bytes from a formatted and sys'ed floppy. The DOS commands are: format b:, then sys b:. 
    dd if=/dev/fd0 of=dosboot.bin bs=512 count=1
    You also need the kernel files ibmbio.com and ibmdos.com; and command.com. 
    mattrib -rsh a:ibmbio.com a:ibmdos.com
mcopy a:ibmbio.com a:ibmdos.com a:command.com .
  3. Since the RAM available for ramdisk may be limited, in the case of a 286 with 1 MB memory: 384k less the 64 kB High Memory Area, giving 320 kB, you probably want to create a 320kB ramdisk floppy. If you have more extended memory, then you can create larger ramdisks, e.g. 720kB or even 1.44MB.
  4. Set up a mapping between the floppy image and a drive letter by editing .mtoolsrc, see the mtools man pages. 
    drive z: file="/tmp/floppyimage.320"
  5. Create the floppy image and copy the boot block onto it in a file using mformat (adjust the number of tracks, sectors and heads if you are not using a 320kB format). 
    mformat -t 40 -s 8 -h 2 -B dosboot.bin -C z:
    In what follows, when I write floppy, I mean the image in a disk file referred to by z:.
  6. Copy the DOS kernel files onto the floppy. In the case of DR-DOS these are ibmbio.com, ibmdos.com, and command.com. The first two are read-only hidden system files so use mattrib to set these attributes.
  7. Copy all the programs you need to run onto the floppy. Don't forget any configuration files needed. Also include an autoexec.bat (and perhaps config.sys) to start everything up. Don't worry about getting the configuration file contents right at this point, you can replace them at will on the ramdisk floppy.
  8. Get the Etherboot distribution, version 4.4 or higher, and make a boot PROM for the card of your choice. You may want to enable the ASK_BOOT option with a short timeout and ANS_DEFAULT=ANS_NETWORK. This will enable you to boot the 286 normally if you need to fix anything. All network cards, even the very old ones, should accept a 8 kB boot PROM. Most compressed 16 bit images in Etherboot are under 8 kB. Burn it into a PROM or find someone to do it for you. If you are using a larger PROM, make sure you have burnt it in the right portion of the PROM, or burn multiple copies in the address space to be sure. See here for some things to watch out for.
  9. Set up bootp/DHCP and tftp services on the server if you haven't already. Did I mention read the Etherboot documentation already?
  10. In the same Etherboot distribution, compile the mknbi-dos program. Use the program to create a tagged image in the directory that tftpd fetches from, typically /tftpdir. The command is probably: mknbi-dos -x -x -r floppyimage -o /tftpdir/dos.nb. (The two -x flags print out verbose information.) Check that the /etc/bootptab entry or the dhcpd.conf entry for the 286 specifies dos.nb as the file to load. You may need the -f flag to disable checking if mknbi-dos doesn't recognise your DOS version.
  11. On your 286, disable any floppies or hard disks in the CMOS configuration. Also set it to not require a keyboard, if you intend to run keyless. If the CMOS setup doesn't allow you to disable the keyboard, you have a problem. One way out might be to attach an unloved keyboard, one that is just good enough to pass the probe from the BIOS.
  12. Now hit the reset switch and watch the boot PROM take over. It should find the bootp/DHCP server and then the tftp server and load the tagged image. Then DOS will start executing, reading autoexec.bat and running the commands there. Hopefully the last command there is the program you want leave running.
  13. You may wish to look at the contributed program romid.exe in the Etherboot distribution. This is meant to be run from autoexec.bat. It returns the ID of the boot ROM installed in an environment variable so that the appropriate packet driver can be installed.
  14. Another program I like to invoke in autoexec.bat is pdclksml.com, found here which sets the PC clock using bootp and the UDP time service (port 37).

Things that I have netbooted in this fashion are:

You can find these and other suggested applications here.

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