monline

Having a bootable DOS partition on an USB drive can be necessary for flashing the BIOS of your motherboard or RAID controller (since most recent PCs come without a floppy drive). However the official way to do this requires you to have already a DOS bootable partition. Fortunately there're a couple of solutions in case you've only a running linux system. The linked page has the best description of the qemu+FreeDOS method (the one that I prefer) and lists various other approaches as well. To keep the instructions safe, I made a copy of them here.

Prerequisites:

• dd
• qemu
• a DOS floppy image, e.g. balder10.img

Procedure (assumptions for this description: balder10.img is in CWD, stick appears as /dev/sdc):

• Insert memory stick (Caution: all data on this stick will be destroyed)
• Find out device name (e.g. /dev/sdc)
• Make sure it's not mounted (check with mount command)
• Clear the MBR:
  
  dd if=/dev/zero of=/dev/sdc bs=1012 count=2
• Boot qemu:
  
  qemu -curses -boot a -fda ./balder10.img -hda /dev/sdc
  The -curses option will make it run in text mode.
  (This way you can run qemu easily eg. over an ssh connection.)
• Answer all questions with their default values
• At the A:\> prompt:
  
  fdisk
  (create a bootable, primary DOS partition)
• Stop qemu
• Remove memory stick and re-insert it.
• Make sure it's still /dev/sdc, otherwise use new name in the next steps.
• Make sure again that it is not mounted.
• Boot qemu:
  
  qemu -curses -boot a -fda ./balder10.img -hda /dev/sdc
• At the A:\> prompt:
  
  format c: /s
• At the A:\> prompt:
  
  xcopy a: c: /n /e
• Stop qemu

Done! Now you can mount the stick again and copy any required utilities on it ...

P.S.: of course you can use an MS bootdisk image too, but FreeDOS is usually up to the task (and in some aspects it's even better).