alpine-linux-headless-boots.../make.sh

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#!/bin/busybox sh
# SPDX-FileCopyrightText: Copyright 2022-2023, macmpi
# SPDX-License-Identifier: MIT
# Script meant to be run on Alpine (busybox) or on Ubuntu.
# Check busybox version & options if eventually using other platforms.
# Ubuntu LTS busybox 1.30.1 tar does NOT support setting owner/group/mtime
# probably available after busybox 1.31.1, following 2019-08-01 change:
# https://git.busybox.net/busybox/commit/?id=e6a87e74837ba5f2f2207a75cd825acf8cf28afb
# This limitation requires copying files and setting owner/group/mtime before archiving.
command -v doas > /dev/null || alias doas="/usr/bin/sudo"
build_path="$(mktemp -d)"
if [ -n "$build_path" ]; then
# prefer timestamp option for touch as it works on directories too
t_stamp="$( TZ=UTC date +%Y%m%d0000.00 )"
cp -a overlay "$build_path"/.
find "$build_path"/overlay/ -exec sh -c 'TZ=UTC touch -chm -t "$0" "$1"' "$t_stamp" {} \;
# setting modes and owner/groups for runtime (won't affect mtime)
find "$build_path"/overlay/etc -type d -exec chmod 755 {} \;
chmod 755 "$build_path"/overlay/etc/init.d/*
chmod 755 "$build_path"/overlay/etc/runlevels/default/*
chmod 777 "$build_path"/overlay/tmp
chmod 700 "$build_path"/overlay/tmp/.trash
chmod -R 600 "$build_path"/overlay/tmp/.trash/ssh_host_*_key
find "$build_path"/overlay/usr -type d -exec chmod 755 {} \;
chmod 755 "$build_path"/overlay/usr/local/bin/*
doas chown -Rh 0:0 "$build_path"/overlay/*
# busybox config on Alpine & Ubuntu has FEATURE_TAR_GNU_EXTENSIONS
# (will preserve user/group/modes & mtime) and FEATURE_TAR_LONG_OPTIONS
# shellcheck disable=SC2046 # we want word splitting as result of find
doas tar cv -C "$build_path"/overlay --no-recursion \
$(doas find "$build_path"/overlay/ | sed "s|$build_path/overlay/||" | sort | xargs ) | \
gzip -c9n > headless.apkovl.tar.gz
sha512sum headless.apkovl.tar.gz > headless.apkovl.tar.gz.sha512
TZ=UTC touch -cm -t "$t_stamp" headless.apkovl.tar.gz*
doas rm -rf "$build_path"
fi