podman build --ssh default on windows

[dominoplayer84]

I tried to build an image that requires pulling external Git dependencies over SSH. When I was building this image on Docker, it was working. I'm wondering if it's supposed to work on Podman on Windows using WSL2 as well.

I did a simple image test:

ARG DEBIAN_FRONTEND=noninteractive
FROM ubuntu:24.04

RUN apt update && apt install -y ssh

RUN mkdir -p -m 0600 ~/.ssh && ssh-keyscan github.com >> ~/.ssh/known_hosts
RUN --mount=type=ssh ssh -T git@github.com

I use this command to run it on Podman: $env:DOCKER_BUILDKIT=1; podman build --ssh default -t github-ssh-test:latest -f ./Dockerfile .

I tried looking around the documentation and different GitHub issues related to SSH, but I didn't find a clear response.

[manimovassagh]

The --ssh default flag with Podman on Windows/WSL2 should work, but there are a few gotchas compared to Docker that are easy to miss.

1. Make sure your SSH agent is running and has keys loaded

Inside your WSL2 session (not PowerShell), check:

ssh-add -l

If you get "Could not open a connection to your authentication agent", start it first:

eval $(ssh-agent -s)
ssh-add ~/.ssh/id_ed25519   # or whichever key you use for GitHub

The --ssh default flag forwards $SSH_AUTH_SOCK into the build. If the agent is not running or has no keys, the mount is empty.

2. Run the build from WSL2, not PowerShell

When you run Podman from PowerShell with WSL2 backend, the SSH agent socket forwarding can break because the socket path does not translate cleanly between Windows and the WSL2 VM. Run the build directly from your WSL2 terminal instead:

# Inside WSL2
podman build --ssh default -t github-ssh-test:latest -f ./Dockerfile .

3. Drop the DOCKER_BUILDKIT env var

DOCKER_BUILDKIT=1 is a Docker-specific variable. Podman uses Buildah under the hood and does not read this variable. It should not cause harm, but it is not doing anything either -- remove it to avoid confusion.

4. Verify the Dockerfile syntax

Your Dockerfile looks correct, but make sure the RUN --mount=type=ssh syntax is being processed. This requires the Buildah version that ships with Podman 4.x+. Check your version:

podman version
buildah version

If you are on a recent Podman (4.x or 5.x), the syntax is supported.

5. Debug the SSH connection

If it still fails, add verbose output to the SSH command in your Dockerfile to see what is happening:

RUN --mount=type=ssh ssh -vvv -T git@github.com 2>&1 || true

This will show you whether the SSH socket is being mounted and whether keys are available inside the build context.