I got to set up the lDebug development environment on a new Debian 12 installation on the amd64 machine. (The SSD seems to have caused crashes recently, and it had the root file system of the prior Debian installation.) Here's how I installed dosemu2 (from source), FreeDOS (from packages plus my recent kernel and FreeCOM builds), and lDebug (from assembly source).

Install the following packages using synaptic: (many based on dosemu2's current INSTALL file)

• git
• gitk
• gcc
• autoconf
• bison
• flex
• libjson-c-dev
• libc6-dev
• libfluidsynth-dev
• libsdl2-dev
• libslang2-dev
• libslirp-dev
• libgpm-dev
• alsa-oss
• alsa-tools
• ladspa-sdk
• libao-dev
• libudev-dev
• libxext-dev
• make
• gawk
• libbsd-dev

Install these packages too:

• mercurial
• diffuse
• mercurial-crecord
• tortoisehg
• tortoisehg-caja
• mtools
• halibut
• nasm
• dos2unix
• qemu-system-x86
• python3-tqdm (needed for install-freedos)
• clang (needed to build lzsa)
• lrzsz
• picocom
• socat

Clone the following from the directory ~/proj:

• hg clone https://hg.pushbx.org/ecm/ldebug
• hg clone https://hg.pushbx.org/ecm/lmacros
• hg clone https://hg.pushbx.org/ecm/ldosboot
• hg clone https://hg.pushbx.org/ecm/inicomp
• hg clone https://hg.pushbx.org/ecm/bootimg
• hg clone https://hg.pushbx.org/ecm/crc16-t
• hg clone https://hg.pushbx.org/ecm/symsnip
• hg clone https://hg.pushbx.org/ecm/mktmpinc
• hg clone https://hg.pushbx.org/ecm/tellsize
• hg clone https://hg.pushbx.org/ecm/tractest
• hg clone https://hg.pushbx.org/ecm/instsect
• hg clone https://hg.pushbx.org/ecm/scanptab
• git clone https://github.com/emmanuel-marty/lzsa
• git clone https://github.com/dosemu2/dosemu2
• git clone https://github.com/dosemu2/install-freedos

Enter directory ~/proj/dosemu2 and run:

./autogen.sh
./default-configure --disable-fdpp
make
sudo make install

Make directory ~/.dosemu/drive_c and download:

• wget https://pushbx.org/ecm/download/freecom.zip
• wget https://pushbx.org/ecm/download/fdkernel.zip
• unzip freecom.zip command.com
• unzip -j fdkernel.zip bin/kernel.sys
• unzip -j fdkernel.zip bin/sys.com

Enter directory ~/proj/install-freedos/ and enter commands: (Probably not all needed, this is just what worked for me.)

cd src
./dosemu-downloaddos -o freedos13
./dosemu-downloaddos -o freedos13userspace
./dosemu-setupfreedos
./dosemu-installfreedosuserspace

In directory ~/.dosemu/drive_c create symlinks:

ln -s ../command.com bin/command.com
ln -s ../sys.com bin/sys.com

Enter directory /usr/local/share/dosemu/dosemu2-cmds-0.3/ and run:

cp -ia fdppconf.sys ~/.dosemu/drive_c/fdconfig.sys
cp -ia fdautoem.bat ~/.dosemu/drive_c
nano ~/.dosemu/drive_c/fdconfig.sys
nano ~/.dosemu/drive_c/fdautoem.bat

Contents of file fdconfig.sys edited to read:

device=d:\dosemu\umb.sys
devicehigh=d:\dosemu\ems.sys
SWITCHES=/F
DOS=UMB
dosdata=umb
fileshigh=128
lastdrive=Z
rem emufs.sys /all replaces emufs.com
devicehigh=d:\dosemu\emufs.sys /all
devicehigh=d:\dosemu\cdrom.sys
set SHELL_ALLOW_EXIT=1
shellhigh=c:\command.com /p:fdautoem.bat

Contents of file fdautoem.bat (not edited):

@echo off
rem autoexec.bat for DOSEMU + FreeDOS
path d:\dosemu
rem this is needed when booting from dosemu-freedos-bin
if exist f:\gnu\nul path %PATH%;f:\bin;f:\gnu
if exist c:\bin\nul path %PATH%;c:\bin
set HELPPATH=f:\help
if exist c:\help\nul set HELPPATH=c:\help
if exist e:\tmp\nul call swapdrv.bat c: e:
set TEMP=c:\tmp
if not exist %TEMP%\nul mkdir %TEMP%
emusound -e
emumouse c 1
prompt $P$G
rem uncomment to load another bitmap font
rem lh display con=(vga,437,2)
rem mode con codepage prepare=((850) f:\cpi\ega.cpx)
rem mode con codepage select 850
rem chcp 850
echo Welcome to dosemu2!
system -s DOSEMU_VERSION
echo     Build %DOSEMU_VERSION%
call exechlp.bat -ep

Setup ~/.hgrc

In ~/proj/lzsa run make and symlink lzsa executable into path.

In ~/proj/tellsize compile program and place executable tellsize in path.

In ~/proj/ldebug/source copy cfg.sh to ovr.sh and edit line setting INICOMP_METHOD to set it to only lzsa2.

Build several lDebug builds:

./mak.sh
./makerd
build_name=cdebugx build_options="-D_DEBUG -D_DEBUG_COND -D_PM" ./mak.sh
build_name=cdebug build_options="-D_DEBUG -D_DEBUG_COND -D_PM=0" ./mak.sh

Enter directory ~/.dosemu/drive_c/bin and create symlinks:

ln -s ../../../proj/ldebug/bin/ldebug.com
ln -s ../../../proj/ldebug/bin/ldebugu.com
ln -s ../../../proj/ldebug/bin/lddebugu.com
ln -s ../../../proj/ldebug/bin/lddebug.com
ln -s ../../../proj/ldebug/bin/lcdebug.com
ln -s ../../../proj/ldebug/bin/lcdebugu.com
ln -s ../../../proj/ldebug/bin/lcdebugx.com

Create a configuration with the following contents (also in ~/.dosemu/drive_c/bin):

@:applicationstartup
@:devicestartup
@install getinput
@?version

Using these commands:

nano ldebug.sld
ln -s ldebug.sld lcdebug.sld
ln -s ldebug.sld lddebug.sld

In DOS run sys config c:\kernel.sys checkdebugger=1

Symlink ~/.dosemu/drive_c/rxdos.com to an lDebug executable in order to bootload the debugger.

This is the output of booting (dosemu -t):

dosemu2 2.0pre9-dev-20230704-1320-g3b250d8d0 Configured: 2023-07-06 10:08:54 +0000
Get the latest code at http://dosemu2.github.io/dosemu2
Submit Bugs via https://github.com/dosemu2/dosemu2/issues
Ask for help in mail list: linux-msdos@vger.kernel.org
This program comes with ABSOLUTELY NO WARRANTY.
This is free software, GPL v2 (or any later version) distribution conditions.

FreeDOS kernel - GIT (build 2043 OEM:0xfd) [compiled Jul  3 2023]
Kernel compatibility 7.10 - GNUC - FAT32 support

(C) Copyright 1995-2022 Pasquale J. Villani and The FreeDOS Project.
All Rights Reserved. This is free software and comes with ABSOLUTELY NO
WARRANTY; you can redistribute it and/or modify it under the terms of the
GNU General Public License as published by the Free Software Foundation;
either version 2, or (at your option) any later version.
C: HD1, Pri[ 1], CHS=    0-1-1, start=     0 MB, size=  2000 MB
D: HD2, Pri[ 1], CHS=    0-1-1, start=     0 MB, size=  2000 MB
dosemu XMS 3.0 & UMB support enabled
UMBs unavailable!
dosemu EMS driver rev 0.9 installed.
UMBs unavailable!
EMUFS host file and print access available
dosemu CDROM driver installed (V0.2)

FreeCom version 0.85a - GNUC - XMS_Swap [Mar 31 2023 23:40:37]
BLASTER=A220 I5 D1 H5 P300 T6
MIDI=SYNTH:2 MAP:E MODE:0
Welcome to dosemu2!
    Build 2.0pre9-dev-20230704-1320-g3b250d8d0
C:\>

I don't know what exactly displays the two "UMBs unavailable!" lines and why. If I boot into the debugger then enter boot protocol freedos then q, these lines do not appear. Regardless whether they appear, DOS UMBs are set up and used properly.