dosdebug(1) run DOS and DOS programs under Linux

Other Alias



dosemu.bin [ -234ABCcdKkmNnOpSstVwX ] [ -h level ] [ -F file ] [ --Fusers file ] [ --Flibdir directory ] [ --Fimagedir directory ] [ -f file ] [ -L dexefile ] [ -u confvar ] [ -D flags ] [ -M size ] [ -e size ] [ -x size ] [ -P file ] [ -o file ] [ 2> debugfile ] [ -I config-options ] [ -i [bootdir] ] [ -U inpipe[:outpipe] ] [ [-E] dos-command ]



dosemu.bin is the binary wrapped by the script dosemu (1) which invokes the Linux dos emulator, also known as DOSEMU.
debugfile is an optional file into which all debugging output will be redirected.

dosdebug is used to control or debug an already running DOSEMU.

Although this program is known as the DOS emulator, it is actually a virtual machine for DOS, allowing DOS and programs written for DOS to operate in an environment similar to a standard IBM PC/AT or compatible with an Intel 80x86 processor in real mode. DOSEMU provides emulation of such services as BIOS video, disk, keyboard, serial, and printer; CMOS memory for configuration information; a real time clock; memory allocation through the XMS 3.0 specification, EMS 4.0 and DPMI 0.9.

Because DOSEMU is not really a DOS emulator, a copy of FreeDos is required, which now is pre-configured and part of the official DOSEMU binary distribution. In addition any currently available proprietary DOS (such as MS-DOS, PC-DOS, DR-DOS) can be booted, when properly configured.


At present, you will need Linux 2.0.28 or above with the SYSV IPC option (System V Inter-Process Communication facilities, see ipc(2)) compiled. SYSV IPC is an option in the configuration setup during a Linux kernel compile.


choose 286, 386, 486 or 586 processor to simulate.
boot from floppy disk A (does not need to be a real floppy disk, see below)
boot from floppy disk B (does not need to be a real floppy disk, see below)
boot from hard disk C (does not need to be a real hard disk or even an msdos filesystem, see below)
use direct Console video (must be at the console, requires special privileges, and -s ).
detach from current virtual console or tty and attach to the first free virtual console
[-E] dos-command
Run DOS command when starting DOSEMU, and, if '-E' is not given, exit DOSEMU after running the command. The command can also be given with a Linux path (for example /home/joeuser/dosemu/freedos/bin/xcopy.exe). Note: this only works if your autoexec.bat contains a "unix -e" command.
use RAW console Keyboard (must be at the console)
Parse this config-script instead of the built-in global.conf file (you need to run as root on suid DOSEMU for this)
Bypass dosemu.users and take this file instead (only accepted when dosemu.bin is not suid-root).
Bypass the default DOSEMU_LIB_DIR (as maybe defined in dosemu.users) and use this directory instead.
Bypass the default directory for bootdirectory and hdimages (DOSEMU_HDIMAGE_DIR) and use this directory instead.
Parse this config-file instead of .dosemurc
Bypass (don't use) dosemu.users and dosemu.conf (only accepted when dosemu.bin is not suid-root).
set a user configuration variable. An u_ is prefixed to the name to avoid name clashes. This variable then can be checked in dosemu.conf or global.conf to do some special configuration.
Load and start a DEXE file (special preconfigured bootable hdimage containing just one DOS application)
Parse the string behind -I with the same syntax as global.conf or .dosemurc such as
                dos ... -I 'video { mda }'

This is useful if you just want to override a given configuration parameter temporary. You also may have a generic configuration by executing a script such as

                dos ... -I "``"

where is a script writing the configuration to stdout. If you have an alternate configuration file besides .dosrc,

                dos ... -I "`cat myother.conf`"

will do the job. Note however, that you have to quote the parameter behind -I because it is expected to be one argument.

launched as part of a systemwide installation, this option (re-)installs a DOS that is used in DOSEMU (this can be the DOSEMU distributed FreeDOS or any proprietary DOS, which is bootable via fatfs). bootdir is the base name of a directory. The symbolic link ~/.dosemu/drives/c will be changed to point to this directory. Re-installing is only rarely necessary, since in practise the symbolic link(s) will automatically point to updated files.
specify which Debugging messages to allow/suppress
dump configuration to stderr and exit (implicit sets -D+c). This is useful for debugging configuration files, you should use -O too to direct the +c type messages to stderr. `level' can be 0, 1 or 2 and controls the amount of configuration parser debug output: No parser debug (0), parser loop debug (1), if_else_endif debug (2).
specify the dosdebug support flags, currently only `1' is is reasonable. with -H1 you force dosemu to wait until the dosdebug terminal has connected. Hence to debug a DOS session from the very beginning you first start dosemu with -H1 and then start dosdebug. DOSEMU will then lock before jumping into the loaded bootsector waiting for dosdebug to connect. Once connected you are in `stopped' state and can set breakpoints or single-step through the bootstrap code.
set base memory to SIZE Kilobytes
toggle internal mouse-support
use stderr for output of Debugging messages
use this file for output of Debugging messages
copy debugging output to FILE
stop for prompting if a non-fatal configuration problem is detected
run using SDL
super-user/full feature mode: enable direct hardware access. Use this switch if you wish to use graphics on the console, need direct port access, hardware interrupts or raw network access. Implies -V and -k by default.


terminal mode: run using the S-Lang library
define inpipe and outpipe for asynchronous control of DOSEMU from another process. The format is (without whitespace in between)

where `:outpipe' can be omitted. In the latter case no feedback from DOSEMU can be expected.

For security reasons DOSEMU does not create the named pipes itself, so the user is responsible to set the permissions of the pipes correctly. Note that when using this options, the foreign process can control your DOSEMU session (such as entering keystrokes). This option should therefor only used by frontends (such as kdos), which first create the proper named pipes and then launch DOSEMU. A special control command ( ack on ) can be used to force DOSEMU returning handshake tags via `outpipe' such that the frontend knows when the control command has started or finished and whether it was successful. The format of this tagging is

                SYN: <commandname>
               <any output from the command>
               ACK: code=n

where n is 0 for success. A tiny control terminal, which can serve as example, is the supplied dosctrl program. It takes just the two pipes as arguments and you may then enter control commands, which of them `help' is the most important one;-) Note that dosctrl does not launch DOSEMU, you have to do it yourself.

use direct console video with VGA graphics and use the native graphics card's BIOS (must be at the console, requires special privileges, and -s ).
toggle windowed/fullscreen mode in X
run in an X Window


DOSEMU supports four methods of supplying DOS with hard disks:
a virtual disk file residing on a Linux filesystem which emulates a hard drive.
direct access to a DOS partition through a raw disk device (i.e. /dev/hda, /dev/hdb, /dev/sdX).
direct access to an DOS partition through single partition access (i.e. /dev/hda1, /dev/hdb2, /dev/sdxx).
access to a Linux filesystem as a "network" drive using the driver emufs.sys supplied with DOSEMU in commands/emufs.sys or lredir.exe.

Configuration of DOSEMU's hard disk resources is done by editing dosemu.conf or .dosemurc before running DOSEMU. Look at /usr/share/doc/dosemu/README.txt.


DOSEMU supports two methods of supplying DOS with floppy disks:
a virtual disk file residing on a Linux filesystem which emulates a floppy drive
direct access to a physical floppy through a raw disk device (i.e. /dev/fd0, /dev/fd1).

This is also explained more thoroughly in README.txt.

Configuration of DOSEMU's floppy disk resources is done by editing the dosemu.conf before running DOSEMU.


DOSEMU may be run on any tty device. However, increased performance and functionality may be had by taking advantage of special features of the Linux console. Those running DOSEMU on the console may wish to investigate the -c, -k, and -V switches, explained more thoroughly in README.txt. There is also some very brief documentation in the file dosemu.conf, which can be edited for your needs.

In brief, proper use of the console device and the corresponding switches allows the user to view a DOS program in its original color and font, with none of the periodic screen update problems with the generic tty output code.


Those using DOSEMU on the Linux console may also wish to use the RAW keyboard support. This mode of operation, selected by the -k switch, provides the user with access to the entire keyboard accessible under DOS. Any combination of ALT, CTRL, and SHIFT keys may be used to generate the odd keycodes expected by many DOS programs.


The BIOS printer services are emulated through standard UNIX file I/O though temporary files which are then periodically spooled by LPR or a different print client, as defined by $_printer_commands in dosemu.conf.


Debug messages can be controlled either at the command line or in the configuration file. Take a look at the documentation inside the config.dist file included with DOSEMU in the examples subdirectory, for debugging options. At the command line, you may specify which classes of messages you wish dos to allow. The syntax of this is DOSEMU takes an option "-D FLAGS", where FLAGS is a string of letters which specify which options to print or suppress. DOSEMU parses this string from left to right.

   +   turns the following options on (initial state)
   -   turns the following options off
   a   turns all the options on/off, depending on flag
   0   turns all options off
   1-9 sets the debug level, the higher, the more output
   #   where # is a letter from the valid class list, 
       turns that option off/on depending on the 
       +/- state.

Message Classes:

 d  disk                        R  disk read            W  disk write

 D  int 21h             C  cdrom                        v  video

 X  X support           k  keyboard             i  port I/O

 s  serial              m  mouse                        #  default ints

 p  printer             g  general              c  configuration

 w  warning             h  hardware             I  IPC

 E  EMS                 x  XMS                  M  DPMI

 n  IPX network P  Pkt-driver           S  SOUND

 r  PIC                 T  IO-tracing           Z  PCI-BIOS

 A  ASPI driver Q  mapping driver

Any debugging classes following a + character, up to a - character, will be turned on (non-suppressed). Any after a - character, up to a + character, will be suppressed. The character a acts like a string of all possible debugging classes, so +a turns on all debugging messages, and -a turns off all debugging messages. The characters 0 and 1-9 are also special: 0 turns off all debugging messages, and 1-9 turns on all debugging messages, but set the debug level too.

There is an assumed + at the beginning of the FLAGS string. Some classes, such as error, can not be turned off. In case you didn't redirect stderr, nearly all output to stderr goes to /dev/null.

Some examples:
  "-D+a-v" or "-D1-v"  : all messages but video
  "-D+kd"              : default + keyboard and disk
  "-D0+RW"             : only disk READ and WRITE

Any option letter can occur in any place. Even pointless combinations, such as -D01-a-1+0, will be parsed without error, so be careful. Some options are set by default, some are clear. This is subject to my whim, and will probably change between releases. You can ensure which are set by always explicitly specifying them.


In RAW keyboard mode (see the -k option), DOSEMU responds to certain key sequences as control functions.

ctrl-scrlock = show 0x32 int vectors
alt-scrlock = show the vm86 registers
rshift-scrlock = generate an int8 (timer)
lshift-scrlock = generate an int9 (keyboard)
ctrl-break = ctrl-break as under DOS.
ctrl-alt-pgup = reboot DOS. Don't trust this!
ctrl-alt-pgdn = exit the emulator

Use <LEFT CTRL>-<LEFT ALT>-<Function key> to switch to another virtual console.


The XMS memory support in DOSEMU conforms to Lotus/Intel/Microsoft/AST extended memory specification 3.0. I have implemented all XMS functions except function 0x12 (Reallocate Upper Memory Block).

DOSEMU also supports EMS 4.0 and implements DPMI 0.9 (1.0 partially).


DOSEMU (comprised of the files dosemu.bin and dosemu ) is based on version 0.4 of the original program written by Matthias Lautner (no current address that I know of).

Robert Sanders <[email protected]> was maintaining and enhancing the incarnation of DOSEMU with which this man page was originally distributed. During about 4 years James B. MacLean <[email protected]> was the restless leader of the dosemu team, implementation of DPMI (which made Windows-3.1, dos4gw, djgpp, etc. running) happened during his 'governement' and brought the project near to Beta-state. Hans Lermen <[email protected]> took over and released the first 1.0 version. Now Bart Oldeman <[email protected]> is maintaining this funny software.


There are too many to count, much less list.

Please report bugs to the author. I'd also like to hear about which programs DO work. Just send me a note detailing what program (and what version) you are using, what works and what doesn't, etc.


The most recent public version of DOSEMU can be obtained from; a fast mirror is at If you want to keep up on private developer pre-releases, join the DOSEMU developer team - even just good detailed debug reports are all you need!


The binary
The wrapper script, it is recommended not to invoke dosemu.bin directly.
Same, but invoking DOS in an X window.
Per user DOSEMU local directory. This will be created silently, if not existing.
All temporary file creation happens here, we do not use /tmp anymore.
Various files used by DOSEMU including debugger pipes.
Bootdirectory containing the FreeDos part.
or (only if /etc/dosemu.users exists) /etc/dosemu.conf Main configuration file for DOSEMU. which is included by global.conf (global.conf is included in dosemu.bin by default).
Per-user configuration file.
For suid-root or sudo running binaries: Defines the access rights to DOSEMU on a per user basis and sets some vital configuration. This is the only fix-location configuration file, DOSEMU first looks for /etc/dosemu.users and, if this is not found, for /etc/dosemu/dosemu.users . Via the keyword default_lib_dir= in dosemu.users the systemwide DOSEMU_LIB_DIR directory may be moved elsewhere. For more information see /usr/share/doc/dosemu/README.txt
IPX configuration file.

To help you hack DOSEMU code.
Various documentation.
QuickStart, README and INSTALL
To set up DOSEMU quickly.
Changes in DOSEMU since the last release.
Information on how to use the DOSEMU/FreeDos ready-to-use binary distribution.
MSDOS mailing list
For more information, mail to
[email protected]