Convert a docker container image distributed at DockerHub for singularity without installing singularity (but requires Docker)

Dockerfile

FROM amd64/debian:unstable

# disallow services to run for package installation
RUN echo "#!/bin/sh\nexit 101" > /usr/sbin/policy-rc.d && chmod +x /usr/sbin/policy-rc.d

# upgrade already-installed packages
RUN apt update && \
    DEBIAN_FRONTEND=noninteractive apt -y dist-upgrade && \
    DEBIAN_FRONTEND=noninteractive apt install -y singularity-container

# remove apt-related temporary files
RUN apt clean && rm -rf /var/lib/apt/lists/*

# allow services to run
RUN echo "#!/bin/sh\nexit 0" > /usr/sbin/policy-rc.d

Makefile

# -*- Makefile -*-

SOURCE=docker://rocm/pytorch:rocm6.4.1_ubuntu24.04_py3.12_pytorch_release_2.7.1
TARGET=rocm-pytorch.sif

DOCKERNAME=debian-unstable-singularity

$(TARGET): $(DOCKERNAME)
	docker run --name $(DOCKERNAME) -v `pwd`:/output --privileged \
		$(DOCKERNAME) singularity pull /output/$(TARGET) $(SOURCE)
	docker rm $(DOCKERNAME)

$(DOCKERNAME): Dockerfile
	docker build -f Dockerfile -t $(DOCKERNAME) .