Dockerfile w/ volume and correct permissions

Dockerfile

# docker build . -t your:tag
# run the container and mount some directory into /data
# the startup script will create a user and launch CMD w/ the matching the UID:GID
# docker run --rm -it `pwd`:/data your:tag

FROM mhart/alpine-node

ENV GOSU_VERSION 1.10
RUN set -ex; \
	\
	apk add --no-cache --virtual .gosu-deps \
		dpkg \
		gnupg \
		openssl \
	; \
	\
	dpkgArch="$(dpkg --print-architecture | awk -F- '{ print $NF }')"; \
	wget -O /usr/local/bin/gosu "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch"; \
	wget -O /usr/local/bin/gosu.asc "https://github.com/tianon/gosu/releases/download/$GOSU_VERSION/gosu-$dpkgArch.asc"; \
	\
# verify the signature
	export GNUPGHOME="$(mktemp -d)"; \
	gpg --keyserver ha.pool.sks-keyservers.net --recv-keys B42F6819007F00F88E364FD4036A9C25BF357DD4; \
	gpg --batch --verify /usr/local/bin/gosu.asc /usr/local/bin/gosu; \
	rm -r "$GNUPGHOME" /usr/local/bin/gosu.asc; \
	\
	chmod +x /usr/local/bin/gosu; \
# verify that the binary works
	gosu nobody true; \
	\
	apk del .gosu-deps

COPY startup.sh /

ENTRYPOINT ["/startup.sh"]
CMD "/bin/ash"

startup.sh

#!/bin/sh
#
set -e

# create a user using the permissions from the mounted volume at /data
# username: docker
# group:    docker

addgroup -g `stat -c "%g" /data` docker
adduser -D -u `stat -c "%u" /data` -G docker -s /bin/ash docker 
exec gosu docker "$@"