dosemu2 AppImage

An unofficial AppImage of dosemu2, built from the official sources. dosemu2 is a virtual machine that runs DOS programs under Linux. Download one file, chmod +x, run.

The AppImage carries its own C library and dynamic loader, so it runs on any Linux distribution: glibc or musl, new or old. This is the AnyLinux method (sharun + uruntime + DwarFS).

Upstream project: https://github.com/dosemu2/dosemu2

Download

Builds are published to a rolling latest release, which carries one build at a time, and to a per-commit release that keeps earlier builds reachable. The file name carries the dosemu2 version it was built from.

chmod +x dosemu2-*.AppImage
./dosemu2-*.AppImage

There is an aarch64 build for arm64 hosts.

If appimageupdatetool is installed, the AppImage can update itself in place:

appimageupdatetool dosemu2-*.AppImage

If your distribution does not package it, AM can install it (am -i appimageupdatetool).

Configuration

dosemu2 reads /etc/dosemu/dosemu.conf first, then ~/.dosemu/dosemurc. The AppImage ships neither, so it uses whatever is on the host and your settings survive an update.

Build locally

You need Docker. First build the build environment — Arch, the bundled soundfont, and these, each compiled from a pinned commit or tag:

• binutils
• thunk_gen
• fdpp
• smallerc
• djstub
• dj64dev
• comcom64
• libsearpc
• libmt32emu

docker build -f docker/Dockerfile-appimage -t dosemu2-appimage-build-env .

Then build the AppImage. DOSEMU2_REF is required and can be any dosemu2 commit, tag or branch:

docker run --rm -u 0 -v "$PWD":/workspace -w /workspace \
  -e DOSEMU2_REF=devel -e WORKSPACE=/workspace \
  dosemu2-appimage-build-env sh -c './build-appimage.sh'

The finished .AppImage lands in out/, owned by root because the build runs as root inside the container. out/DOSEMU2_COMMIT records the exact commit it came from.

Proposing a newer dosemu2

The DOSEMU2_REF file in the repository root sets the dosemu2 commit that CI builds and tests. To propose a newer one, edit that file and open a pull request. CI then builds and smoke-tests both architectures against the commit you put there, and publishes nothing.

Releases are never automatic. A maintainer publishes in one of two ways:

• pushes to trunk with [publish] in the message of the last commit pushed
• runs the workflow from the Actions tab with the commit to publish

How it works

build-appimage.sh runs inside the build environment and:

1. Clones dosemu2 at DOSEMU2_REF and builds it with --prefix=/usr --sysconfdir=/etc, installing into the container's own /usr. The sysconfdir is what makes it read /etc/dosemu/dosemu.conf; autoconf would otherwise default it to /usr/etc, which exists on no host.
2. Copies the data dosemu2 looks up by absolute path at runtime into the AppDir: fdpp's kernel, comcom64's command.com, dj64's crt0.elf, dosemu2's keymaps and command utilities, the oldschool TTF fonts, the LADSPA plugins, and the soundfont.
3. Runs quick-sharun over dosemu2.bin, every plugin .so, and alsa-lib's PulseAudio and PipeWire modules, which collects the full library closure including libc and the loader, then packs the result as a DwarFS AppImage.

dosemu2 and its toolchain bake absolute /usr/... paths into their binaries at compile time. quick-sharun rewrites such paths in place, and on libdosemu2.so that corrupts them: DOSEMUCMDS_DEFAULT is a compile-time pointer into the middle of another string literal, so rewriting the literal moves what the pointer reads. The script disables that patcher and uses PATH_MAPPING, an LD_PRELOAD interceptor that redirects the path at runtime instead.

The SDL text plugin asks fontconfig for the fonts by family name and refuses a substitute, so the AppImage ships its own fontconfig configuration pointing at the two bundled fonts.

What is included

dosemu2 is built with every optional plugin its dependencies allow:

• DOS: fdpp, comcom64, dj64
• Video: SDL3 with TrueType text, X11, terminal, console
• Sound: ALSA with the PulseAudio and PipeWire backends, FluidSynth with a bundled soundfont, munt for MT-32, LADSPA
• Other: slirp networking, keyboard maps, parallel port

MIDI plays through GeneralUser GS, which the AppImage carries. If your system has a soundfont in one of the places dosemu2 searches, such as /usr/share/soundfonts/default.sf2, dosemu2 uses that one instead. For a soundfont anywhere else, set $_fluid_sfont in ~/.dosemu/dosemurc:

$_fluid_sfont = "~/.sf2/mysoundfont.sf2"

With a portable home (a <name>.AppImage.home directory next to the AppImage), ~ means that directory, not your real home.

Two things are left out:

• libao output. It loads its backends from a fixed path in /usr that an AppImage cannot supply, so the plugin could only ever report unable to open output device. ALSA and SDL cover sound output.
• MT-32 ROMs. munt is built in, but the ROM files are proprietary. dosemu2 looks for them in ~/.munt_roms; set $_munt_roms to use another directory.

How much Landlock sandboxing you get depends on the kernel. Below ABI 8, startup logs Warning: your kernel is too old, using minimal Landlock protection and runs with a reduced sandbox. Below ABI 2, or with no Landlock at all, it logs landlock_init() failed and runs without one.

License

MIT, see LICENSE. Compatible with dosemu2's GPL-2.0-only: this repo contains build glue, not dosemu2 source.

The AppImage payload is dosemu2 itself under GPL-2.0-only, plus its bundled runtime libraries under their own licenses.