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Use DOS Doors with Synchronet on Linux

Instructions for using DOSEMU to run DOS doors on Synchronet-Linux.

Important Note

:!: The maintainer for DOSEMU has been AWOL for some time. Currently, none of the active developers are using this feature, but it is integrated into source code. We are willing to fix problems, but users must be willing to help us debug them.

What is this?

This is functionality that integrates support for the Linux DOS emulator (DOSEMU) into the Synchronet BBS software.

The purpose of such integration is to enable the sysop to install new DOS doors in a simple and straightforward manner, and to be able to easily work around the inevitable emulation-related problems that will occur.

This document was copied (with permission) from

Getting Started

The Linux-DOSEMU support has been integrated but must be enabled at compile time; if you want to enable it, when you go to “make” the BBS, add USE_DOSEMU=1 to the command-line. Example:


Setting up a DOS BBS door



There must be an emusetup.bat in your ctrl directory. This batch file configures the DOS environment, and can be used to load additional TSRs, change drive letters around, or make any other last minute changes to the environment before the door is loaded. It is required to at least load a FOSSIL driver in this batch file.

set PATH=%PATH%;e:\dosutils
REM fossil driver, such as x00, bnu, or dosemu
rem /P1 /L0=11520
rem x00.exe
REM share.exe for multinode file locking
REM for console i/o programs

NOTE: append “eliminate” to x00.exe to skip the 5 second commercial ad when it is invoked (ie; “x00.exe eliminate” instead of just x00.exe). This will prevent a 5 second delay when starting doors and invoking external dos editors.

Drive Letters

The rest of these instructions assume that you are using the default remapped drive letters and haven't changed them around in emusetup.bat. The default drive letters are:

  • D: - The Synchronet node directory, where the dropfile should probably be put. In door configurations, specify this drive (D:\) as the path to the dropfile.
  • E: - Under this drive, the parent of the door's startup directory will be mounted. Example: E:\LORD
  • F: - The Synchronet ctrl directory
  • G: - The Synchronet data directory
  • H: - The Synchronet exec directory

Any necessary utilities that should be loaded before the door starts (like FOSSIL driver, ANSI driver, etc) should be placed in the emusetup.bat with a PATH that points to them. The default location is in a \dosutils directory immediately preceding the door's directory. (For example, if your door is in /sbbs/xtrn/lord, put the dosutils directory as /sbbs/xtrn/dosutils.)

The default dosemu binary is /usr/bin/dosemu.bin. If you have a different one that you would like all DOS programs that Synchronet launches to use, configure DOSemuPath in sbbs.ini.



NOTE: Be sure to point to dosemu.bin and not the dosemu wrapper script.

Ensure that you have a working dosemu setup before trying to set it up with Synchronet! For Debian, simply:

apt-get install dosemu dosemu-freedos

For other distributions, you will need to first install and configure dosemu, and then install FreeDOS (or your DOS of choice) and set it up to work with dosemu. Ensure that you can at least get to a DOS prompt through standalone DOSEMU before even trying to use it with Synchronet.

To configure a DOS BBS door in scfg:

  • Startup Directory: /path/to/the/door (or ../xtrn/mydoor)
  • Program name: program.exe %params (or program.bat %params)
  • Multiuser: Yes/No depending on the program
  • Redirect STDIO: No (instructs Synchronet to use vmodem support)
  • Native Program: No (instructs Synchronet to handle the door through DOSEMU)
  • Dropfile: pick a dropfile type that the door knows how to handle
  • Use Lowercase: Yes
  • Dropfile Dir: Place in Node Directory

You probably want to also add the door's setup program as a standard I/O program (see below for details on standard I/O programs). If you don't want to do this, you will need to enter DOSEMU, redirect the door's parent directory to E: like this assuming the door is in /sbbs/xtrn/doordir:

C:\> lredir E: linux\fs\sbbs\xtrn

then go to E:, change to the door's directory, and run the setup program. If you don't do this redirection and set up through the redirected drive, you will probably set up the door to use wrong paths and it won't work!

When you set up the door, point it to D:\ for the dropfile path. Also, generally it would be a good idea to tell the door to use a fossil driver, unless it doesn't work or produces strange results (like missing lines or dropped characters), in which case you can use the internal comm routines of the door. (DOSEMU's virtual modem support allows both approaches.)

The door's actual directory will be mounted on E:\ with the root of E: being the parent directory of the door. So if your door is in /usr/local/games/tw2002 on the Unix side, it will be in E:\tw2002 on the DOS side. Make sure the door's directory conforms to the DOS 8.3 file format! /usr/local/games/tw2002 would be okay, but /usr/local/games/TradeWars2002 would not. The symptom of a non-conforming directory is a “file not found” when Synchronet tries to change to the DOS door's directory inside DOSEMU.

If the door doesn't start, it's probably a configuration problem of some kind that has left DOSEMU sitting at a DOS prompt. If you have what you think is a hung session, the first thing to try is blindly typing 'exitemu' to see if the session can be exited.

Make SURE that if the door is started with a .bat batch file, that you explicitly name it as such in the “Program Name” field. For instance, LORD's “start.bat” command would be entered as “start.bat %#”, not just “start %#”. Failure to do this will cause the session to be hung inside DOSEMU when the user exits the door. (You can still exit by blindly typing exitemu when this happens.) Setting up a non-door DOS program as a door

For the most part, setting up a non-door DOS program is done following the same procedure as a door. The key difference is that you set Redirect STDIO to Yes for a program that is not designed specifically to run as a BBS door.

You can also set up timed events (e.g. door daily maintenance programs) in this same manner. Just make sure Native Program is set to “No” and it will work fine.

Startup Directory: /path/to/the/door (or ../xtrn/mydoor) 
Program name: program.exe %params 
Multiuser: Yes/No depending on the program 
Redirect STDIO: Yes 
Native Program: No 
Dropfile: pick something if the program wants/needs it. 
Use Lowercase: Yes 
Dropfile Dir: Place in Node Directory 

It would probably be a good idea to set up as an external, so that you can get access to a DOS shell through the board. From there, you can do things like the initial unzipping and setup of door software with ease.

Be careful with the security of these programs! Since they aren't designed to run as doors, a malicious user who has access could probably wipe out your whole BBS system. Customization of your Synchronet DOSEMU setup

File Search Precedence: The following table describes in what order Synchronet will look for various files needed for starting DOSEMU. If a file does not exist in one location or cannot be read, the next location will be tried until there are no more possible locations.

dosemu.bin emusetup.bat dosemu.conf
First startup_dir startup_dir startup_dir
Third /etc/dosemu/dosemu.conf

This is useful because you might want to customize the configuration in order to get a particular balky door working. You might want a custom dosemu binary, emusetup.bat, and/or dosemu config for that particular door, while maintaining a different set of configurations that works for mostly everything else.

make sure you are using a dosemu.conf from the DOSEMU distribution of the particular version you are using. (e.g. if using 1.1.4 release, don't use a dosemu.conf from 1.0.2). If you want to customize a config, start from your distro's release dosemu.conf. Unfortunately, if you upgrade to a newer release of DOSEMU, you will probably have to also forward-port your custom config files since the config file format may change.

The most up-to-date freedos distribution can be found here – this is known to fix problems with Tradewars 2002. You might consider trying DR-DOS if you have problems with FreeDOS. However, be certain that you use the autoexec.bat from the FreeDOS distribution, as the Synchronet integration depends on it (specifically, it depends on the DOSDRIVE_D and unix -e behavior from it). Also remember to copy the DOSEMU support files (usually located in /usr/lib/dosemu/commands) into c:\dosemu in the DR-DOS hdimage.

Known Problems

File locking is dysfunctional with the DOSEMU 1.0.2.x stable releases. File locking problems will manifest themselves as strange error messages related to file opens, long pauses and/or hangs, game data corruption, and other fun stuff. Note that you do not have to be running a multinode BBS to be prone to these issues; most programs detect DOSEMU as a multitasker and thus initiate their lock management regardless of whether or not multiple sessions of the game will be in use. The fix is to upgrade to DOSEMU 1.2 or later, since 1.0.x is obsolete.

There is a file locking hack from Bob Newell which is detailed in this document. Included is a kludge for slow screen draws due to incorrect idling that will occur in some games such as Planets TEOS.

If you are running Debian 'woody', I recommend upgrading to 'sarge' so that you can use DOSEMU 1.2.x that is part of the distribution.

Disabling DOSEMU from opening a window in XWindows

To disable windows being opened when running dosemu:

  • create a shell script for dosemu with the using the following as an example:
  exec /path/to/dosemu/dosemu -T "$@"

If you are having other problems

check the dosemu.log and dosemu_boot.log that will be created in the node directory. They should give you clues to track down a configuration problem. If those files do not exist, then the dosemu.bin is not getting executed properly, so check your sbbs.ini, make sure you have dosemu installed, and check for a stale dosemu.bin symlink in the door's directory. double-check your door's configuration, specifically the paths in scfg and the batch file (if any) that starts it. Also verify that the paths in the door's configuration problem are correct Verify that you have set up enough nodes in the door's configuration to handle all the nodes on your BBS.

If you want help with this, you must send me *at a minimum* the following files:

  • dosemu.log and dosemu_boot.log from the node directory
  • your DOS autoexec.bat and config.sys
  • output of 'find /'
  • emusetup.bat and dosemu.conf (only if you have modified them)

Send problem reports to


The Script Method

There is another way to do this: use a script that launches dosemu. This is the more flexible but non-userfriendly way to use dosemu doors on Synchronet. Example stuff can be found in this tarball.

See Also

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