diff --git a/elements/ubuntu-core/root.d/10-cache-ubuntu-image b/elements/ubuntu-core/root.d/10-cache-ubuntu-image
index 550fdc2e..aaa2f673 100755
--- a/elements/ubuntu-core/root.d/10-cache-ubuntu-image
+++ b/elements/ubuntu-core/root.d/10-cache-ubuntu-image
@@ -12,74 +12,58 @@ set -o pipefail
 
 shopt -s extglob
 
-DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cdimage.ubuntu.com/ubuntu-core/preview}
-DIB_RELEASE=${DIB_RELEASE:-alpha-01}
-BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-ubuntu-core-$DIB_RELEASE.img}
-BASE_IMAGE_TAR=$DIB_RELEASE-ubuntu-core.tgz
+DIB_RELEASE=${DIB_RELEASE:-trusty}
+
+declare -A release_numbers
+release_numbers[precise]=12.04
+release_numbers[trusty]=14.04
+release_numbers[vivid]=15.04
+release_numbers[wily]=15.10
+
+numeric_release=${release_numbers[$DIB_RELEASE]}
+DIB_CLOUD_IMAGES=${DIB_CLOUD_IMAGES:-http://cdimage.ubuntu.com/ubuntu-core/releases/$numeric_release/release}
+BASE_IMAGE_FILE=${BASE_IMAGE_FILE:-ubuntu-core-$numeric_release-core-$ARCH.tar.gz}
 SHA256SUMS=${SHA256SUMS:-$DIB_CLOUD_IMAGES/SHA256SUMS}
 CACHED_FILE=$DIB_IMAGE_CACHE/$BASE_IMAGE_FILE
-CACHED_TAR=$DIB_IMAGE_CACHE/$BASE_IMAGE_TAR
-CACHED_SUMS=$DIB_IMAGE_CACHE/SHA256SUMS.ubuntu-core.$DIB_RELEASE
+CACHED_FILE_LOCK=$DIB_IMAGE_CACHE/$BASE_IMAGE_FILE.lock
+CACHED_SUMS=$DIB_IMAGE_CACHE/SHA256SUMS.ubuntu-core.$DIB_RELEASE.$ARCH
 
-if [ -n "$DIB_OFFLINE" -a -f "$CACHED_TAR" ] ; then
-    echo "Not checking freshness of cached $CACHED_TAR"
-else
-    echo "Fetching Base Image"
-    $TMP_HOOKS_PATH/bin/cache-url $SHA256SUMS $CACHED_SUMS
-    $TMP_HOOKS_PATH/bin/cache-url $DIB_CLOUD_IMAGES/$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 skewed
-        # result - either a cached SHA file or a cached image. Use cache-busting
-        # to get (as long as caches are compliant...) fresh files.
-        # Try the sha256sum first, just in case that is the stale one (avoiding
-        # downloading the larger image), and then if the sums still fail retry
-        # the image.
-        $TMP_HOOKS_PATH/bin/cache-url -f $SHA256SUMS $CACHED_SUMS
+function get_ubuntu_tarball() {
+    if [ -n "$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 \
+            $DIB_CLOUD_IMAGES/$BASE_IMAGE_FILE $CACHED_FILE
+        pushd $DIB_IMAGE_CACHE
         if ! grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check - ; then
-            $TMP_HOOKS_PATH/bin/cache-url -f \
-                $DIB_CLOUD_IMAGES/$BASE_IMAGE_FILE $CACHED_FILE
-            grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check -
+            # It is likely that an upstream http(s) proxy has given us a skewed
+            # result - either a cached SHA file or a cached image. Use cache-busting
+            # to get (as long as caches are compliant...) fresh files.
+            # Try the sha256sum first, just in case that is the stale one (avoiding
+            # downloading the larger image), and then if the sums still fail retry
+            # the image.
+            $TMP_HOOKS_PATH/bin/cache-url -f $SHA256SUMS $CACHED_SUMS
+            if ! grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check - ; then
+                $TMP_HOOKS_PATH/bin/cache-url -f \
+                    $DIB_CLOUD_IMAGES/$BASE_IMAGE_FILE $CACHED_FILE
+                grep "$BASE_IMAGE_FILE" $CACHED_SUMS | sha256sum --check -
+            fi
         fi
+        popd
     fi
-    popd
+    # 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 [ ! -f $CACHED_TAR -o \
-        $DIB_IMAGE_CACHE/$BASE_IMAGE_FILE -nt $CACHED_TAR ] ; then
-
-        echo "Repacking base image as tarball."
-        WORKING=$(mktemp -d)
-        EACTION="rm -r $WORKING"
-        trap "$EACTION" EXIT
-        RAW_FILE=$(mktemp --tmpdir=$WORKING XXXXXX.raw)
-        qemu-img convert -f qcow2 -O raw $CACHED_FILE $RAW_FILE
-        MAGIC_BIT=p1
-        # NOTE: On RHEL, partprobe of /dev/loop0 does not create /dev/loop0p2,
-        # while kpartx at least creates /dev/mapper/loop0p2.
-        LOOPDEV=$(sudo kpartx -av $RAW_FILE | awk "/loop[0-9]+$MAGIC_BIT/ {print \$3}")
-        # If running inside Docker, make our nodes manually, because udev will not be working.
-        if [ -f /.dockerenv ]; then
-            sudo dmsetup --noudevsync mknodes
-        fi
-        export LOOPDEV=$LOOPDEV
-        echo "Loop device is set to: $LOOPDEV"
-        if ! timeout 5 sh -c "while ! [ -e /dev/mapper/$LOOPDEV ]; do sleep 1; done"; then
-            echo "Error: Could not find /dev/mapper/$LOOPDEV"
-            exit 1
-        fi
-        EACTION="sudo kpartx -d $RAW_FILE;$EACTION"
-        trap "$EACTION" EXIT
-        mkdir $WORKING/mnt
-        sudo mount /dev/mapper/$LOOPDEV $WORKING/mnt
-        EACTION="sudo umount -f $WORKING/mnt;$EACTION"
-        trap "$EACTION" EXIT
-        # Chroot in so that we get the correct uid/gid
-        sudo chroot $WORKING/mnt bin/tar -cz . > $WORKING/tmp.tar
-        mv $WORKING/tmp.tar $DIB_IMAGE_CACHE/$BASE_IMAGE_TAR
+(
+    echo "Getting $CACHED_FILE_LOCK: $(date)"
+    # Wait up to 20 minutes for another process to download
+    if ! flock -w 1200 9 ; then
+        echo "Did not get $CACHED_FILE_LOCK: $(date)"
+        exit 1
     fi
-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_TAR
+    get_ubuntu_tarball
+) 9> $CACHED_FILE_LOCK