You can use also hex editor to write the reboot code directly to the MBR or bootsector. This way the reboot is a bit quicker without the syslinux and FreeDOS bootstrap. Just insert EA 00 00 FF FF, which is the same code you piped into debug to do the same thing. For the MBR, put it in the first five bytes; for the bootsector, the first two bytes will be e.g. EB 58 so add two to the second byte to get your offset within the bootsector e.g. 5A and write the code there. Also with your method using a pipe to debug, FreeDOS will write a temporary file every time.