Dockerfile for building static dropbear, busybox and tcpdump for armv7l

Dockerfile

FROM alpine:latest

# docker build --progress=plain -t arm-tools .
# docker create --name temp-extract arm-tools && docker cp temp-extract:/out . && docker rm temp-extract

# Install build tools
RUN apk add --no-cache \
    build-base \
    curl \
    bash \
    autoconf \
    automake \
    libtool \
    musl-dev \
    linux-headers \
    xz \
    flex \
    bison \
    bzip2

# Target config
ENV TARGET=arm-linux-musleabi
ENV CROSS_DIR=/usr/$TARGET-cross
ENV CROSS_PREFIX=$CROSS_DIR/bin/$TARGET-
ENV PATH=$CROSS_DIR/bin:$PATH

RUN mkdir /out

# Install musl-cross for armv7l
RUN curl -LO https://musl.cc/$TARGET-cross.tgz && \
    tar -xzf $TARGET-cross.tgz -C /usr && \
    rm $TARGET-cross.tgz

WORKDIR /build

# ---- Dropbear ----
RUN curl -LO https://matt.ucc.asn.au/dropbear/releases/dropbear-2025.87.tar.bz2 && \
    tar -xjf dropbear-2025.87.tar.bz2 && \
    rm dropbear-2025.87.tar.bz2

WORKDIR /build/dropbear-2025.87
RUN ./configure --host=$TARGET \
    --disable-zlib \
    --disable-lastlog \
    --disable-utmp \
    --disable-wtmp \
    --disable-loginfunc \
    --disable-pututline \
    --disable-pututxline \
    --enable-static && \
    make PROGRAMS="dropbear dbclient dropbearkey dropbearconvert scp" MULTI=1 STATIC=1

RUN cp dropbearmulti /out/dropbear-armv7l
# ---- BusyBox ----
WORKDIR /build
RUN curl -LO https://www.busybox.net/downloads/busybox-1.36.1.tar.bz2 && \
    tar -xjf busybox-1.36.1.tar.bz2 && \
    rm busybox-1.36.1.tar.bz2

WORKDIR /build/busybox-1.36.1
RUN make defconfig && \
    sed -i 's/.*CONFIG_STATIC.*/CONFIG_STATIC=y/' .config && \
    yes "" | make oldconfig && \
    make CROSS_COMPILE=$CROSS_PREFIX -j$(nproc) && \
    cp busybox /out/busybox-armv7l

# ---- libpcap ----
WORKDIR /build
RUN curl -LO https://www.tcpdump.org/release/libpcap-1.10.5.tar.xz && \
    tar -xJf libpcap-1.10.5.tar.xz && \
    rm libpcap-1.10.5.tar.xz
WORKDIR /build/libpcap-1.10.5
RUN ./configure --host=$TARGET --enable-static --disable-shared && \
    make CC=${CROSS_PREFIX}gcc -j$(nproc)

# ---- tcpdump ----
WORKDIR /build
RUN curl -LO https://www.tcpdump.org/release/tcpdump-4.99.5.tar.xz && \
    tar -xJf tcpdump-4.99.5.tar.xz && \
    rm tcpdump-4.99.5.tar.xz

WORKDIR /build/tcpdump-4.99.5
RUN ./configure --host=$TARGET \
    --with-crypto=no \
    --disable-smb \
    --disable-ipv6 \
    --with-pcap=/build/libpcap-1.10.5 \
    --enable-static
RUN make CC="${CROSS_PREFIX}gcc" \
    CFLAGS="-Os -static" \
    LDFLAGS="-static" \
    -j$(nproc) && \
    cp tcpdump /out/tcpdump-armv7l
# ---- Final output ----

CMD ["sh", "-c", "ls -la /out/ && echo Build complete."]