you have to use a real DOS installed on Dosbox. This is done by hard drive images of which you "boot" from within Dosbox. The guides section has a guide on hard drive images.

The MS-DOS or FreeDOS debuggers probably run in DOSBox.

DOSBox can also be compiled to have a built-in debugger, but I don't know the details on that.

Hello,
I downloaded a version of freedos, it has a debug program. But I don't know if it is bootable the way I installed it.

If I change to the directory where I hot freedos, it has an autexec.bat file, but I don't know if the way I installed it makes it bootable.

Does bootable mean, within dosbox you boot freedos? Can you boot it by just cd into the directory?

Reread what I wrote about booting but also what hunterz wrote. The freedos debug and probably the ms dos one run in Dosbox (without booting those DOS OS').

HunterZ wrote:

DOSBox can also be compiled to have a built-in debugger, but I don't know the details on that.

Rather than struggling with compulation, it is much easier to download a precompiled version:
DOSBox debugger

For a more recent version, the debug-enabled DOSBox was also included in ykhwong's build, last time I checked:
http://ykhwong.x-y.net/

MS-DOS debug.exe runs well in DOSBox. Depending on which debug.exe version you use, you might have to set DOSBox to report the right DOS version with the "ver" command, though.