fix: resolve macOS/Apple Silicon Docker build failures

[pastudan]

Problem

Building on macOS with Docker Desktop fails in two ways:

1. groupadd: GID '20' already exists (Dockerfile)

macOS passes the host GID (20 = "staff") into the container. That GID already exists in the Debian base image, so groupadd exits with code 4 and the entire build layer fails.

ERROR [6/8] RUN groupadd -g 20 builder && ...
0.035 groupadd: GID '20' already exists

Fix: append 2>/dev/null || true to groupadd so the existing group is silently reused.

---

2. rsync: failed to hard-link … Operation not permitted (Makefile.docker)

Buildroot's per-package isolation uses rsync --hard-links to snapshot the staging tree between packages. Hard links across a Docker bind-mount backed by an APFS volume (macOS host) are not supported by the macOS filesystem layer, causing every package build to fail.

rsync: failed to hard-link … Operation not permitted (1)
make[1]: *** [...] Error 1

Fix: mount the build output directory as a named Docker volume (thingino-build-output) that lives entirely inside the Docker Linux VM, where hard links work normally. The host filesystem is no longer in the rsync path.

A docker-extract-images target is also added to copy the finished thingino-*.bin files back to ./images/ on the host after a successful build.

Testing

Tested on macOS 26.3 (Apple Silicon, M4) with Docker Desktop. Both issues are resolved and a full firmware build completes successfully.

Usage (after this fix)

# Build (output stays in named Docker volume)
CAMERA=your_camera_name ./docker-build.sh build

# Copy finished firmware to ./images/ on the host
make -f Makefile.docker docker-extract-images

Made with Cursor

[alextrical]

I'm also experiencing the same issue as you.
I don't think Fix: append 2>/dev/null || true to groupadd so the existing group is silently reused.
is quite the right solution. the command should be creating the group number 1000, yet somehow the variable is coming through as 20

There where also the following issues on my macbook pro m1:
arm64 not being supported,
gdd instead of dd,
dependencies not being installed with brew
setting user group to 1000
These have been addressed in the branch https://github.com/alextrical/thingino-firmware-mac/tree/fix-macos-docker-build

I do however have an issue with the Podman Volume, on first run it creates the files as expected, however on the second run the system fails due to permissions being unable to remove the files in the volume.
It is only fixable by removing the volume between runs