exec format error on M4 Macbook

[mattmacf98]

I have an M4 macbook air and am trying to use python:3.11-slim as my base here is my Dockerfile below

FROM python:3.11-slim

WORKDIR /app


# Install dependencies with uv (parallel downloads, uses pre-built wheels)
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

# Copy application
COPY app.py .

# Expose the sidecar port
EXPOSE 7778

# Bind to 0.0.0.0 so the server is reachable from outside the container
ENV FLASK_APP=app.py
CMD ["flask", "run", "--host=0.0.0.0", "--port=7778"]

running this fails at pip install

 => [internal] load build definition from Dockerfile                                             0.0s
 => => transferring dockerfile: 448B                                                             0.0s
 => [internal] load metadata for docker.io/library/python:3.11-slim                              0.5s
 => [auth] library/python:pull token for registry-1.docker.io                                    0.0s
 => [internal] load .dockerignore                                                                0.0s
 => => transferring context: 2B                                                                  0.0s
 => [1/5] FROM docker.io/library/python:3.11-slim@sha256:d6e4d224f70f9e0172a06a3a2eba2f768eb146  0.0s
 => => resolve docker.io/library/python:3.11-slim@sha256:d6e4d224f70f9e0172a06a3a2eba2f768eb146  0.0s
 => [internal] load build context                                                                0.0s
 => => transferring context: 63B                                                                 0.0s
 => CACHED [2/5] WORKDIR /app                                                                    0.0s
 => CACHED [3/5] COPY requirements.txt .                                                         0.0s
 => ERROR [4/5] RUN pip install --no-cache-dir -r requirements.txt                               0.1s
------                                                                                                
 > [4/5] RUN pip install --no-cache-dir -r requirements.txt:
0.106 exec /bin/sh: exec format error
------
Dockerfile:8
--------------------
   6 |     # Install dependencies with uv (parallel downloads, uses pre-built wheels)
   7 |     COPY requirements.txt .
   8 | >>> RUN pip install --no-cache-dir -r requirements.txt
   9 |     
  10 |     # Copy application
--------------------
ERROR: failed to build: failed to solve: process "/bin/sh -c pip install --no-cache-dir -r requirements.txt" did not complete successfully: exit code: 255

if I swap the FROM to

FROM --platform=linux/amd64 python:3.11-slim then it builds (but with emulation which is not ideal)

System info:
Macbook air M4, 2025, macOS Sequoia 15.3

Thank you in advance if anyone has a fix for this!!

[tianon]

Can you test with something simpler to help narrow down what's going wrong?

$ docker run --rm --pull=always python:3.11-slim python --version
Python 3.11.15

[tianon]

That's weird - I wonder if you've got some corrupted local state or something? Do you have DOCKER_DEFAULT_PLATFORM set, by any chance? (You shouldn't have that set / set that, to be clear, but it's often the cause of folks getting errors like this. 🙈)

I don't personally have an M4, but I have two separate coworkers who have M4 Max machines who tested this same one-liner for me successfully. 😬

[mattmacf98]

running echo $DOCKER_DEFAULT_PLATFORM gives me no output so nothing set, I'll try re-installing docker

[mattmacf98]

That did not work for me unfortunately :/

However, I tried some of the other 3.11 ones and they seemed to work but still not slim

docker run --rm python:3.11-alpine3.23 python --version
Python 3.11.15

docker run --rm python:3.11-trixie python --version    
Python 3.11.15

I am fine just using one of the larger images for my use case since this seems like a very weird my mac issue

[tianon]

I think Docker Desktop has a "reset my VM" option somewhere that is more drastic than just reinstalling and should delete all your local image data, if you wanted to try something more "nuclear" 🙈

[mattmacf98]

oooopphh ok I will give that a go this weekend