Docker Windows

Docker on Windows (MINGW/MSYS2/Git Bash)

The Problem

Running Docker from Git Bash / MINGW on Windows silently breaks commands in three ways:

1. Path mangling: MINGW converts anything that looks like a Unix path to a Windows path. -w /work becomes -w C:/Program Files/Git/work — Docker gets a nonsensical Windows path.

2. Flag conversion: Single-letter flags like -i (for MOOSE input files) get eaten by MINGW's path-conversion heuristic when followed by a filename. -i input.i may be silently mangled.

3. Volume mount paths: Forward slashes in volume source paths can trigger path conversion. -v /c/Users/... may be rewritten to -v C:/Program Files/Git/c/Users/....

These failures are silent — Docker may start, mount an empty volume, or pass garbled flags, and the command appears to "work" while producing no output or wrong results.

The Solution

Always prefix Docker commands with MSYS_NO_PATHCONV=1 to disable all MINGW path conversion.

Canonical Docker Run Pattern

MSYS_NO_PATHCONV=1 docker run --rm \
  -v "C:/Users/USER/path/to/host/dir:/container/mount" \
  -w /container/mount/subdir \
  --entrypoint /bin/bash \
  IMAGE_NAME:TAG \
  -c 'COMMAND_TO_RUN 2>&1 | tail -N'

Key Rules

What NOT to Do

# BAD: No MSYS_NO_PATHCONV — paths will be mangled
docker run --rm -v "C:/mydir:/work" -w /work image:tag command

# BAD: Using -i flag directly — MINGW may eat it
docker run --rm -v "..." -w /work image:tag combined-opt -i input.i

# BAD: Using double quotes around -c — host shell expands paths
docker run --rm --entrypoint /bin/bash image:tag -c "cd /work && run"

# BAD: Using NUL instead of /dev/null inside container
# (The container is Linux even though the host is Windows)

MOOSE-Specific Pattern

The MOOSE Docker image idaholab/moose:latest has combined-opt at /opt/moose/bin/combined-opt.

Running a MOOSE Input File

MSYS_NO_PATHCONV=1 docker run --rm \
  -v "C:/Users/simon/Downloads/moose-next/quickstart-runs:/work" \
  -w /work/case01-1d-steady-diffusion \
  --entrypoint /bin/bash \
  idaholab/moose:latest \
  -c '/opt/moose/bin/combined-opt -i case01_diffusion_1d.i 2>&1 | tail -30'

Running Multiple Cases in Sequence

MSYS_NO_PATHCONV=1 docker run --rm \
  -v "C:/Users/simon/Downloads/moose-next/quickstart-runs:/work" \
  --entrypoint /bin/bash \
  idaholab/moose:latest \
  -c '
    for dir in case14-thermoelasticity case15-lid-driven-cavity; do
      echo "=== $dir ==="
      cd /work/$dir
      ifile=$(ls *.i | head -1)
      /opt/moose/bin/combined-opt -i $ifile 2>&1 | tail -5
      echo
    done
  '

MOOSE-Specific Gotchas

Debugging Checklist

If a Docker command produces no output or wrong results on Windows:

1. Check MSYS_NO_PATHCONV=1 — is it set before the docker command?
2. Check volume mount — run ls inside the container to verify files are visible:

   MSYS_NO_PATHCONV=1 docker run --rm \
     -v "C:/Users/simon/mydir:/work" \
     --entrypoint /bin/bash image:tag \
     -c 'ls -la /work'
   

3. Check Docker Desktop is running — docker info should succeed
4. Check entrypoint pattern — use --entrypoint /bin/bash + -c '...' to avoid flag mangling
5. Check output persistence — files written inside the container only persist if they're in the mounted volume path

General Docker Commands (Windows-Safe)

# Check Docker is running
docker info > /dev/null 2>&1 && echo "Docker OK" || echo "Start Docker Desktop"

# Pull an image
MSYS_NO_PATHCONV=1 docker pull idaholab/moose:latest

# Interactive shell (for debugging)
MSYS_NO_PATHCONV=1 docker run --rm -it \
  -v "C:/Users/simon/mydir:/work" \
  -w /work \
  idaholab/moose:latest \
  /bin/bash

# Run with resource limits (CPU-only machine)
MSYS_NO_PATHCONV=1 docker run --rm --cpus=4 --memory=8g \
  -v "C:/Users/simon/mydir:/work" \
  -w /work \
  --entrypoint /bin/bash \
  idaholab/moose:latest \
  -c 'command here'