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#!/bin/bash

set -e

set -u

set -o pipefail

ROOT=$(cd "$(dirname "$0")" && pwd)

TARGET=${1:?Specify 8000 the target filename}

DIST=${2:-stable}

SNAPSHOT_ID=${3:-}

LOGFILE=${TARGET}.log

:>"$LOGFILE"

exec > >(tee -ia "$LOGFILE")

exec 2> >(tee -ia "$LOGFILE" >&2)

DEBOOTSTRAP_DIR=$(mktemp -d)

cp -a /usr/share/debootstrap/* "$DEBOOTSTRAP_DIR"

cp -a /usr/share/keyrings/debian-archive-keyring.gpg "$DEBOOTSTRAP_DIR"

cp -a "${ROOT}/debootstrap/"* "${DEBOOTSTRAP_DIR}/scripts"

KEYRING=$DEBOOTSTRAP_DIR/debian-archive-keyring.gpg

if [ -f "${ROOT}/keys/${DIST}.gpg" ]; then

gpg --no-default-keyring --keyring "$KEYRING" --import "${ROOT}/keys/${DIST}.gpg"

export DEBIAN_FRONTEND=noninteractive

DIRS_TO_TRIM="/usr/share/man

/var/cache/apt

/var/lib/apt/lists

/usr/share/locale

/var/log

/usr/share/info

rootfsDir=$(mktemp -d)

echo "Building base in $rootfsDir"

DEBOOTSTRAP_DIR="$DEBOOTSTRAP_DIR" debootstrap --keyring "$KEYRING" --variant container --foreign "${DIST}" "$rootfsDir"

chroot "$rootfsDir" bash debootstrap/debootstrap --second-stage

repo_url="http://deb.debian.org/debian"

sec_repo_url="http://security.debian.org/"

if [ -n "$SNAPSHOT_ID" ]; then

repo_url="http://snapshot.debian.org/archive/debian/${SNAPSHOT_ID}/"

sec_repo_url="http://snapshot.debian.org/archive/debian-security/${SNAPSHOT_ID}/"

echo -e "deb ${repo_url} $DIST main" > "$rootfsDir/etc/apt/sources.list"

if [ "$DIST" != "unstable" ]; then

echo "deb ${sec_repo_url} $DIST/updates main" >> "$rootfsDir/etc/apt/sources.list"

chroot "$rootfsDir" apt-get update

chroot "$rootfsDir" apt-get upgrade -y -o Dpkg::Options::="--force-confdef"

chroot "$rootfsDir" dpkg -l | tee "$TARGET.manifest"

echo "Applying docker-specific tweaks"

# These are copied from the docker contrib/mkimage/debootstrap script.

# Modifications:

# - remove `strings` check for applying the --force-unsafe-io tweak.

# This was sometimes wrongly detected as not applying, and we aren't

# interested in building versions that this guard would apply to,

# so simply apply the tweak unconditionally.

# get path to "chroot" in our current PATH

chrootPath="$(type -P chroot)"

rootfs_chroot() {

# "chroot" doesn't set PATH, so we need to set it explicitly to something our new debootstrap chroot can use appropriately!

# set PATH and chroot away!

PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin' \

"$chrootPath" "$rootfsDir" "$@"

}

# prevent init scripts from running during install/update

echo >&2 "+ echo exit 101 > '$rootfsDir/usr/sbin/policy-rc.d'"

cat > "$rootfsDir/usr/sbin/policy-rc.d" <<-'EOF'

#!/bin/sh

# For most Docker users, "apt-get install" only happens during "docker build",

# where starting services doesn't work and often fails in humorous ways. This

# prevents those failures by stopping the services from attempting to start.

exit 101

EOF

chmod +x "$rootfsDir/usr/sbin/policy-rc.d"

# prevent upstart scripts from running during install/update

(

set -x

rootfs_chroot dpkg-divert --local --rename --add /sbin/initctl

cp -a "$rootfsDir/usr/sbin/policy-rc.d" "$rootfsDir/sbin/initctl"

sed -i 's/^exit.*/exit 0/' "$rootfsDir/sbin/initctl"

)

# shrink a little, since apt makes us cache-fat (wheezy: ~157.5MB vs ~120MB)

( set -x; rootfs_chroot apt-get clean )

# this file is one APT creates to make sure we don't "autoremove" our currently

# in-use kernel, which doesn't really apply to debootstraps/Docker images that

# don't even have kernels installed

rm -f "$rootfsDir/etc/apt/apt.conf.d/01autoremove-kernels"

# force dpkg not to call sync() after package extraction (speeding up installs)

echo >&2 "+ echo force-unsafe-io > '$rootfsDir/etc/dpkg/dpkg.cfg.d/docker-apt-speedup'"

cat > "$rootfsDir/etc/dpkg/dpkg.cfg.d/docker-apt-speedup" <<-'EOF'

# For most Docker users, package installs happen during "docker build", which

# doesn't survive power loss and gets restarted clean afterwards anyhow, so

# this minor tweak gives us a nice speedup (much nicer on spinning disks,

# obviously).

force-unsafe-io

EOF

if [ -d "$rootfsDir/etc/apt/apt.conf.d" ]; then

# _keep_ us lean by effectively running "apt-get clean" after every install

aptGetClean='"rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true";'

echo >&2 "+ cat > '$rootfsDir/etc/apt/apt.conf.d/docker-clean'"

cat > "$rootfsDir/etc/apt/apt.conf.d/docker-clean" <<-EOF

# Since for most Docker users, package installs happen in "docker build" steps,

# they essentially become individual layers due to the way Docker handles

# layering, especially using CoW filesystems. What this means for us is that

# the caches that APT keeps end up just wasting space in those layers, making

# our layers unnecessarily large (especially since we'll normally never use

# these caches again and will instead just "docker build" again and make a brand

# new image).

# Ideally, these would just be invoking "apt-get clean", but in our testing,

# that ended up being cyclic and we got stuck on APT's lock, so we get this fun

# creation that's essentially just "apt-get clean".

DPkg::Post-Invoke { ${aptGetClean} };

APT::Update::Post-Invoke { ${aptGetClean} };

Dir::Cache::pkgcache "";

Dir::Cache::srcpkgcache "";

# Note that we do realize this isn't the ideal way to do this, and are always

# open to better suggestions (https://github.com/docker/docker/issues).

EOF

# remove apt-cache translations for fast "apt-get update"

echo >&2 "+ echo Acquire::Languages 'none' > '$rootfsDir/etc/apt/apt.conf.d/docker-no-languages'"

cat > "$rootfsDir/etc/apt/apt.conf.d/docker-no-languages" <<-'EOF'

# In Docker, we don't often need the "Translations" files, so we're just wasting

# time and space by downloading them, and this inhibits that. For users that do

# need them, it's a simple matter to delete this file and "apt-get update". :)

Acquire::Languages "none";

EOF

echo >&2 "+ echo Acquire::GzipIndexes 'true' > '$rootfsDir/etc/apt/apt.conf.d/docker-gzip-indexes'"

cat > "$rootfsDir/etc/apt/apt.conf.d/docker-gzip-indexes" <<-'EOF'

# Since Docker users using "RUN apt-get update && apt-get install -y ..." in

# their Dockerfiles don't go delete the lists files afterwards, we want them to

# be as small as possible on-disk, so we explicitly request "gz" versions and

# tell Apt to keep them gzipped on-disk.

# For comparison, an "apt-get update" layer without this on a pristine

# "debian:wheezy" base image was "29.88 MB", where with this it was only

# "8.273 MB".

Acquire::GzipIndexes "true";

Acquire::CompressionTypes::Order:: "gz";

EOF

# update "autoremove" configuration to be aggressive about removing suggests deps that weren't manually installed

echo >&2 "+ echo Apt::AutoRemove::SuggestsImportant 'false' > '$rootfsDir/etc/apt/apt.conf.d/docker-autoremove-suggests'"

cat > "$rootfsDir/etc/apt/apt.conf.d/docker-autoremove-suggests" <<-'EOF'

# Since Docker users are looking for the smallest possible final images, the

# following emerges as a very common pattern:

# RUN apt-get update \

# && apt-get install -y <packages> \

# && <do some compilation work> \

# && apt-get purge -y --auto-remove <packages>

# By default, APT will actually _keep_ packages installed via Recommends or

# Depends if another package Suggests them, even and including if the package

# that originally caused them to be installed is removed. Setting this to

# "false" ensures that APT is appropriately aggressive about removing the

# packages it added.

# https://aptitude.alioth.debian.org/doc/en/ch02s05s05.html#configApt-AutoRemove-SuggestsImportant

Apt::AutoRemove::SuggestsImportant "false";

EOF

cat > "$rootfsDir/usr/sbin/install_packages" <<-'EOF'

#!/bin/sh

set -e

set -u

export DEBIAN_FRONTEND=noninteractive

n=0

max=2

until [ $n -gt $max ]; do

set +e

(

apt-get update -qq &&

apt-get install -y --no-install-recommends "$@"

)

CODE=$?

set -e

if [ $CODE -eq 0 ]; then

break

if [ $n -eq $max ]; then

exit $CODE

echo "apt failed, retrying"

n=$(($n + 1))

done

rm -r /var/lib/apt/lists /var/cache/apt/archives

EOF

chmod 0755 "$rootfsDir/usr/sbin/install_packages"

# Set the password change date to a fixed date, otherwise it defaults to the current

# date, so we get a different image every day. SOURCE_DATE_EPOCH is designed to do this, but

# was only implemented recently, so we can't rely on it for all versions we want to build

# We also have to copy over the backup at /etc/shadow- so that it doesn't change

chroot "$rootfsDir" getent passwd | cut -d: -f1 | xargs -n 1 chroot "$rootfsDir" chage -d 17885 && cp "$rootfsDir/etc/shadow" "$rootfsDir/etc/shadow-"

# Clean /etc/hostname and /etc/resolv.conf as they are based on the current env, so make

# the chroot different. Docker doesn't care about them, as it fills them when starting

# a container

echo "" > "$rootfsDir/etc/resolv.conf"

echo "host" > "$rootfsDir/etc/hostname"

# Capture the most recent date that a package in the image was changed.

# We don't care about the particular date, or which package it comes from,

# we just need a date that isn't very far in the past.

BUILD_DATE="$(find "$rootfsDir/usr/share/doc" -name changelog.Debian.gz -print0 | xargs -0 -n1 -I{} dpkg-parsechangelog -SDate -l'{}' | xargs -l -i date --date="{}" +%s | sort -n | tail -n 1)"

echo "Trimming down"

for DIR in $DIRS_TO_TRIM; do

rm -r "${rootfsDir:?rootfsDir cannot be empty}/$DIR"/*

done

# Remove the aux-cache as it isn't reproducible. It doesn't seem to

# cause any problems to remove it.

rm "$rootfsDir/var/cache/ldconfig/aux-cache"

# Remove /usr/share/doc, but leave copyright files to be sure that we

# comply with all licenses.

# `mindepth 2` as we only want to remove files within the per-package

# directories. Crucially some packages use a symlink to another package

# dir (e.g. libgcc1), and we don't want to remove those.

find "$rootfsDir/usr/share/doc" -mindepth 2 -not -name copyright -not -type d -delete

find "$rootfsDir/usr/share/doc" -mindepth 1 -type d -empty -delete

# Set the mtime on all files to be no older than $BUILD_DATE.

# This is required to have the same metadata on files so that the

# same tarball is produced. We assume that it is not important

# that any file have a newer mtime than this.

find "$rootfsDir" -depth -newermt "@$BUILD_DATE" -print0 | xargs -0r touch --no-dereference --date="@$BUILD_DATE"

echo "Total size"

du -skh "$rootfsDir"

echo "Package sizes"

# these aren't shell variables, this is a template, so override sc thinking these are the wrong type of quotes

# shellcheck disable=SC2016

chroot "$rootfsDir" dpkg-query -W -f '${Package} ${Installed-Size}\n'

echo "Largest dirs"

du "$rootfsDir" | sort -n | tail -n 20

echo "Built in $rootfsDir"

tar cf "$TARGET" -C "$rootfsDir" .

rm -r "$rootfsDir"

rm -r "$DEBOOTSTRAP_DIR"

echo "Image built at ${TARGET}"

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