busybox/Dockerfile

FROM frebib/debian-builder as builder

ARG ARCH=x86_64
ARG ARCH_ALT=i686

ARG GLIBC_VER=2.26
ARG BUSYB_VER=1.27.1
ARG SU_EXEC_VER=v0.2
ARG TINI_VER=v0.15.0

ARG PREFIX=/output
WORKDIR $PREFIX

#Set up our dependencies, configure the output filesystem a bit
RUN mkdir -p bin dev etc home lib proc root sbin tmp usr/bin usr/sbin usr/lib var && \
    # This is probably only relevant on 64bit systems?
    ln -sv usr/lib usr/lib64 && \
    ln -sv lib lib64

# Pull tini and su-exec utilities
RUN curl -fL https://github.com/javabean/su-exec/releases/download/${SU_EXEC_VER}/su-exec.amd64 > sbin/su-exec && \
    curl -fL https://github.com/krallin/tini/releases/download/${TINI_VER}/tini-amd64 > sbin/tini && \
    chmod +x sbin/su-exec sbin/tini

WORKDIR /tmp/glibc/build

# Download and build glibc from source
RUN curl -fL https://ftp.gnu.org/gnu/glibc/glibc-${GLIBC_VER}.tar.xz \
        | tar xJ --strip-components=1 -C .. && \
    \
    echo "slibdir=/lib" >> configparms && \
    echo "rtlddir=/lib" >> configparms && \
    echo "sbindir=/bin" >> configparms && \
    echo "rootsbindir=/sbin" >> configparms && \
    echo "build-programs=yes" >> configparms && \
    \
    # Fix debian lib path weirdness
    rm -rf /usr/include/${ARCH}-linux-gnu/c++ && \
    \
    exec >/dev/null && \
    ../configure \
        --prefix= \
        --libdir=/lib \
        --libexecdir=/lib \
        --enable-add-ons \
        --enable-obsolete-rpc \
        --enable-kernel=3.10.0 \
        --enable-bind-now \
        --disable-profile \
        --enable-stackguard-randomization \
        --enable-stack-protector=strong \
        --enable-lock-elision \
        --enable-multi-arch \
        --disable-werror && \
    make -j "$(nproc)" && \
    make -j "$(nproc)" install_root="$(pwd)/out" install

# Strip binaries to reduce their size
RUN apt-get install -y file && \
    find out/{s,}bin -exec file {} \; | grep -i elf \
        | sed 's|^\(.*\):.*|\1|' | xargs strip -s && \
    \
    # Patch ldd to use sh not bash
    sed -i '1s/.*/#!\/bin\/sh/' out/bin/ldd && \
    # Copy glibc libs & generate ld cache
    cp -d out/lib/*.so "${PREFIX}/lib" && \
    cp -d out/bin/ldd "${PREFIX}/bin" && \
    cp -d out/sbin/ldconfig "${PREFIX}/sbin" && \
    \
    echo /usr/lib > "${PREFIX}/etc/ld.so.conf"

WORKDIR /tmp/busybox

# Download and build busybox from source
RUN curl -fL https://busybox.net/downloads/busybox-${BUSYB_VER}.tar.bz2 \
        | tar xj --strip-components=1 && \
    # Use default configuration
    make defconfig && \
    make -j "$(nproc)" && \
    cp busybox "${PREFIX}/bin" && \
    # "Install" busybox, creating symlinks to all binaries it provides
    ./busybox --list-full | xargs -i ln -s /bin/busybox "${PREFIX}/{}"

WORKDIR $PREFIX

# Add default skeleton configuration files
RUN for f in passwd shadow group profile; do \
        curl -fL -o "${PREFIX}/etc/$f" "https://git.busybox.net/buildroot/plain/system/skeleton/etc/$f"; \
    done && \
    \
    # Copy UTC localtime to output
    cp /usr/share/zoneinfo/Etc/UTC etc/

# =============

FROM scratch
WORKDIR /

COPY --from=builder /output/ /
RUN mkdir -p /tmp && \
    chmod 1777 /tmp
RUN ldconfig && \
    ldconfig -p

CMD ["/bin/sh"]