diskimage-builder/elements/ubuntu/root.d/10-cache-ubuntu-tarball

#!/bin/bash
# These are useful, or at worst not harmful, for all images we build.

set -eux
set -o pipefail

[ -n "$ARCH" ]
[ -n "$TARGET_ROOT" ]

shopt -s extglob

DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cloud-images.ubuntu.com}
DIB_RELEASE=${DIB_RELEASE:-trusty}
BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-$DIB_RELEASE-server-cloudimg-$ARCH-root.tar.gz}
SHA256SUMS=${SHA256SUMS:-https://${DIB_CLOUD_IMAGES##http?(s)://}/$DIB_RELEASE/current/SHA256SUMS}
CACHED_FILE=$DIB_IMAGE_CACHE/$BASE_IMAGE_FILE
CACHED_SUMS=$DIB_IMAGE_CACHE/SHA256SUMS.ubuntu.$DIB_RELEASE.$ARCH

if [ -n "$DIB_OFFLINE" -a -f "$CACHED_FILE" ] ; then
    echo "Not checking freshness of cached $CACHED_FILE."
else
    echo "Fetching Base Image"
    $TMP_HOOKS_PATH/bin/cache-url $SHA256SUMS $CACHED_SUMS
    $TMP_HOOKS_PATH/bin/cache-url $DIB_CLOUD_IMAGES/$DIB_RELEASE/current/$BASE_IMAGE_FILE $CACHED_FILE
    pushd $DIB_IMAGE_CACHE
    if ! grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check - ; then
        # It is likely that an upstream http(s) proxy has given us a new image, but stale sha256sums
        # Try again. Harder.
        $TMP_HOOKS_PATH/bin/cache-url -f $SHA256SUMS $CACHED_SUMS
        grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check -
    fi
    popd
fi
# Extract the base image (use --numeric-owner to avoid UID/GID mismatch between
# image tarball and host OS e.g. when building Ubuntu image on an openSUSE host)
sudo tar -C $TARGET_ROOT --numeric-owner -xzf $DIB_IMAGE_CACHE/$BASE_IMAGE_FILE
if [ -e "$TARGET_ROOT/lost+found" ]; then
    sudo rmdir $TARGET_ROOT/lost+found
fi