# A neutral, distro-agnostic root filesystem laid out per the
# Filesystem Hierarchy Standard 3.0:
#   https://refspecs.linuxfoundation.org/FHS_3.0/fhs/index.html
#
# This is an ordinary CONTAINER build (FROM a base image, not a kernel) on a
# minimal musl/busybox userland. The output image's filesystem *is* the rootfs
# that a downstream bootable build consumes via `ADD <ref> /`. "Neutral"
# = no distro package manager or policy baked in, just the FHS skeleton plus
# busybox.
#
# NB: builds on busybox for its binaries; `FROM scratch` + `ADD <oci-ref> /` is
# equally supported when you assemble the userland yourself.
FROM busybox:1.36-musl

# Build out the full FHS 3.0 hierarchy (busybox ships only a partial layout;
# `mkdir -p` is idempotent). The shell does the work as one logical line —
# UMF strips `#` comments, so the per-section notes live here, above the RUN:
#   §3  root top-level dirs    §4  /usr secondary hierarchy    §5  /var
#   §3.13 private /root        §3.15/§5.15 sticky world-writable temp dirs
#   §5.13 /var/run + /var/lock are runtime (tmpfs) state → symlinks into /run
RUN set -eux; \
    mkdir -p /bin /boot /dev /etc /home /lib /media /mnt /opt /root /run /sbin /srv /sys /tmp /usr /var; \
    mkdir -p /usr/bin /usr/include /usr/lib /usr/libexec /usr/sbin /usr/share /usr/local/bin /usr/local/lib /usr/local/sbin /usr/local/share; \
    mkdir -p /var/cache /var/lib /var/local /var/log /var/opt /var/spool /var/tmp; \
    chmod 1777 /tmp /var/tmp; \
    chmod 0700 /root; \
    mkdir -p /run/lock; \
    rm -rf /var/run /var/lock; \
    ln -s /run /var/run; \
    ln -s /run/lock /var/lock; \
    printf 'root:x:0:0:root:/root:/bin/sh\n' > /etc/passwd; \
    printf 'root:x:0:\n' > /etc/group; \
    printf 'neutral-fhs\n' > /etc/hostname

# Mark the artifact a rootfs so a bootable build can consume it with
# `ADD <ref> /`.
LABEL org.imagilux.umf.type=rootfs
LABEL org.imagilux.umf.rootfs.flavor=busybox-fhs
LABEL org.imagilux.umf.rootfs.standard="FHS-3.0"