Introduction

FreeBSD's userland comes with many useful programs, but most users don't even know they exist. doscmd(1) is one of these applications.

doscmd(1) allows you to run DOS programs, and it can even emulate a DOS machine (i.e., boot DOS). It supports text-applications only.

Getting Ready

First, let's find the doscmd(1) binary:

% whereis doscmd
doscmd: /usr/bin/doscmd /usr/share/man/man1/doscmd.1.gz

If whereis gives you an empty result, su to root, install the source tree, and do the following:

# cd /usr/src/usr.bin/doscmd && make clean all install

If this message appears:

make: don't know how to make /usr/obj/usr/src/i386/usr/include/stdio.h. Stop.

It means your /usr/obj directory is empty, and you have to make world to populate it.

To run doscmd(1), you don't need a high-end system. Something along the lines of a P200 with 32MB of RAM running X should be plenty. FreeBSD 3.X users will need to build a kernel with the following options in order to run doscmd(1):

options   "VM86"

To run correctly, doscmd(1) needs a vga font. If you have a recent 4.X source tree (after June 30, 2000), the font is included with the source and you just have to run the following before running doscmd(1):

% xset fp+ /usr/libdata/doscmd/fonts

This command could also be added to your .xinitrc file.

If you don't have a source tree from after June 30, 2000, you'll have to do the following:

1. Fetch this file.

2. Run the following commands as root:
   

   # uudecode cp437-8x16.pcf.gz.uu > cp437-8x16.pcf.gz
   # cp cp437-8x16.pcf.gz /usr/X11R6/lib/X11/fonts/misc/
   # mkfontdir /usr/X11R6/lib/X11/fonts/misc/
   # xset fp rehash

In this case, I didn't create /usr/libdata/doscmd/fonts, I chose to use an existing fonts directory instead.

Configuration

In the following section I'm going to explain how to boot from a floppy disk image and run DOS applications.

First, we need a DOS boot floppy:

• find a box running DOS

• format a: /s

• copy /usr/libdata/doscmd/redir.com onto the floppy

• add a config.sys file on the floppy with the following lines:

  buffers=20
  files=35
  lastdrive=Z

• Add an autoexec.bat file on the floppy with the following lines:

  @echo off
  redir.com
  PATH a:\;

  If you create these files from a FreeBSD machine, you will have to convert them to DOS format (add a carriage return at the end of each line):

  perl -p -e 's/$/\r/' < unixfile > dosfile

• Create a boot floppy:

  dd if=/dev/rfd0 of=/home/user/boot.dos

About the DOS version -- I tried MS-DOS 6.22 and it worked without any problems. FreeDOS, on the other hand, hangs.

The next step is to configure ~/.doscmdrc. Put the following lines in it:

boot A:
assign A: /home/user/boot.dos 1440
assign C: /home/user/dos

The first line is needed to boot on the A: device, the 1440 tells doscmd(1) that the floppy image is a 1.44MB image, and the third line points to a directory that will be seen as C:\. This is the directory where I'd put my DOS programs.

I currently have only managed to run doscmd(1) under X. Even a build with -DNO_X defined won't run on the console.

Now we're ready to launch doscmd(1). From an xterm, do the following:

% doscmd -b -x

You should see a window like this one appear. If execution failed with this message:

doscmd: fatal error X11 support not compiled in

do the following as root:

# cd /usr/src/usr.bin/doscmd && make clean all install

Another thing to note is that each time I ran doscmd(1), I got these messages (however, they can be ignored):

Unknown interrupt 15 function 4101
Unknown interrupt 15 function 87d9

In order to run an application, it's done the same as it is on a real DOS machine -- you simply have to type the name of the executable.

Use and Conclusion

doscmd(1) runs in a small window (640x400 only), but it's sufficient for any text application. I used it to run Turbo C 2.0 from Borland, which you can see here, and PALASM from AMD. PALASM is a program which translates boolean functions and state transition tables into a fuse map for use with a Programmable Array Logic (PAL) device. You can see it in action here, here, and here. I tried to use serial port resident programs without success.

doscmd(1) is quite slow, however it can do the job with old DOS applications quite well.

- Marc Fonvieille

Return to the March 2001 Issue