Docker + Alpine Linux + Unknown User + Su

General
1

Hello,
I would like run a container with an unknown user (by --user UID) but i need to create this user at runtime

Dockerfile:

FROM alpine:latest
RUN /bin/echo 'root:root' | chpasswd
COPY ./entrypoint.sh /
ENTRYPOINT [ "/bin/sh", "/entrypoint.sh" ]

entrypoint.sh:

#!/bin/sh
su - root -c "adduser -u $(id -u) unknown"
exec "$@"

But the binary “su” gives me the error:

su : Cannot determine your user name.

Do you have any idea so that I can counter this error please?