Find file
Fetching contributors…
Cannot retrieve contributors at this time
507 lines (435 sloc) 15 KB
storeDir ? builtins.storeDir,
# WARNING: this API is unstable and may be subject to backwards-incompatible changes in the future.
rec {
examples = import ./examples.nix {
inherit pkgs buildImage pullImage shadowSetup;
pullImage = callPackage ./pull.nix {};
# We need to sum layer.tar, not a directory, hence tarsum instead of nix-hash.
# And we cannot untar it, because then we cannot preserve permissions ecc.
tarsum = runCommand "tarsum" {
buildInputs = [ go ];
} ''
mkdir tarsum
cd tarsum
cp ${./tarsum.go} tarsum.go
export GOPATH=$(pwd)
mkdir src
ln -sT ${docker.src}/pkg/tarsum src/tarsum
go build
cp tarsum $out
# buildEnv creates symlinks to dirs, which is hard to edit inside the overlay VM
mergeDrvs = {
onlyDeps ? false
runCommand "merge-drvs" {
inherit derivations onlyDeps;
} ''
if [[ -n "$onlyDeps" ]]; then
echo $derivations > $out
exit 0
mkdir $out
for derivation in $derivations; do
echo "Merging $derivation..."
if [[ -d "$derivation" ]]; then
# If it's a directory, copy all of its contents into $out.
cp -drf --preserve=mode -f $derivation/* $out/
# Otherwise treat the derivation as a tarball and extract it
# into $out.
tar -C $out -xpf $drv || true
# Helper for setting up the base files for managing users and
# groups, only if such files don't exist already. It is suitable for
# being used in a runAsRoot script.
shadowSetup = ''
export PATH=${shadow}/bin:$PATH
mkdir -p /etc/pam.d
if [[ ! -f /etc/passwd ]]; then
echo "root:x:0:0::/root:/bin/sh" > /etc/passwd
echo "root:!x:::::::" > /etc/shadow
if [[ ! -f /etc/group ]]; then
echo "root:x:0:" > /etc/group
echo "root:x::" > /etc/gshadow
if [[ ! -f /etc/pam.d/other ]]; then
cat > /etc/pam.d/other <<EOF
account sufficient
auth sufficient
password requisite nullok sha512
session required
if [[ ! -f /etc/login.defs ]]; then
touch /etc/login.defs
# Run commands in a virtual machine.
runWithOverlay = {
fromImage ? null,
fromImageName ? null,
fromImageTag ? null,
diskSize ? 1024,
preMount ? "",
postMount ? "",
postUmount ? ""
vmTools.runInLinuxVM (
runCommand name {
preVM = vmTools.createEmptyImage {
size = diskSize;
fullName = "docker-run-disk";
inherit fromImage fromImageName fromImageTag;
buildInputs = [ utillinux e2fsprogs jshon rsync ];
} ''
rm -rf $out
mkdir disk
mkfs /dev/${vmTools.hd}
mount /dev/${vmTools.hd} disk
cd disk
if [[ -n "$fromImage" ]]; then
echo "Unpacking base image..."
mkdir image
tar -C image -xpf "$fromImage"
# If the image name isn't set, read it from the image repository json.
if [[ -z "$fromImageName" ]]; then
fromImageName=$(jshon -k < image/repositories | head -n 1)
echo "From-image name wasn't set. Read $fromImageName."
# If the tag isn't set, use the name as an index into the json
# and read the first key found.
if [[ -z "$fromImageTag" ]]; then
fromImageTag=$(jshon -e $fromImageName -k < image/repositories \
| head -n1)
echo "From-image tag wasn't set. Read $fromImageTag."
# Use the name and tag to get the parent ID field.
parentID=$(jshon -e $fromImageName -e $fromImageTag -u \
< image/repositories)
# Unpack all of the parent layers into the image.
while [[ -n "$parentID" ]]; do
echo "Unpacking layer $parentID"
mkdir -p image/$parentID/layer
tar -C image/$parentID/layer -xpf image/$parentID/layer.tar
rm image/$parentID/layer.tar
find image/$parentID/layer -name ".wh.*" -exec bash -c 'name="$(basename {}|sed "s/^.wh.//")"; mknod "$(dirname {})/$name" c 0 0; rm {}' \;
# Get the next lower directory and continue the loop.
parentID=$(cat image/$parentID/json \
| (jshon -e parent -u 2>/dev/null || true))
mkdir work
mkdir layer
mkdir mnt
${lib.optionalString (preMount != "") ''
# Execute pre-mount steps
echo "Executing pre-mount steps..."
if [ -n "$lowerdir" ]; then
mount -t overlay overlay -olowerdir=$lowerdir,workdir=work,upperdir=layer mnt
mount --bind layer mnt
${lib.optionalString (postMount != "") ''
# Execute post-mount steps
echo "Executing post-mount steps..."
umount mnt
cd layer
cmd='name="$(basename {})"; touch "$(dirname {})/.wh.$name"; rm "{}"'
find . -type c -exec bash -c "$cmd" \;
exportImage = { name ?, fromImage, fromImageName ? null, fromImageTag ? null, diskSize ? 1024 }:
runWithOverlay {
inherit name fromImage fromImageName fromImageTag diskSize;
postMount = ''
echo "Packing raw image..."
tar -C mnt --mtime=0 -cf $out .
# Create an executable shell script which has the coreutils in its
# PATH. Since root scripts are executed in a blank environment, even
# things like `ls` or `echo` will be missing.
shellScript = name: text:
writeScript name ''
set -e
export PATH=${coreutils}/bin:/bin
# Create a "layer" (set of files).
mkPureLayer = {
# Name of the layer
# JSON containing configuration and metadata for this layer.
# Files to add to the layer.
contents ? null,
# Additional commands to run on the layer before it is tar'd up.
extraCommands ? ""
runCommand "docker-layer-${name}" {
inherit baseJson contents extraCommands;
buildInputs = [ jshon rsync ];
mkdir layer
if [[ -n "$contents" ]]; then
echo "Adding contents..."
for item in $contents; do
echo "Adding $item"
rsync -ak $item/ layer/
echo "No contents to add to layer."
if [[ -n $extraCommands ]]; then
(cd layer; eval "$extraCommands")
# Tar up the layer and throw it into 'layer.tar'.
echo "Packing layer..."
mkdir $out
tar -C layer --mtime=0 -cf $out/layer.tar .
# Compute a checksum of the tarball.
echo "Computing layer checksum..."
tarsum=$(${tarsum} < $out/layer.tar)
# Add a 'checksum' field to the JSON, with the value set to the
# checksum of the tarball.
cat ${baseJson} | jshon -s "$tarsum" -i checksum > $out/json
# Indicate to docker that we're using schema version 1.0.
echo -n "1.0" > $out/VERSION
echo "Finished building layer '${name}'"
# Make a "root" layer; required if we need to execute commands as a
# privileged user on the image. The commands themselves will be
# performed in a virtual machine sandbox.
mkRootLayer = {
# Name of the image.
# Script to run as root. Bash.
# Files to add to the layer. If null, an empty layer will be created.
contents ? null,
# JSON containing configuration and metadata for this layer.
# Existing image onto which to append the new layer.
fromImage ? null,
# Name of the image we're appending onto.
fromImageName ? null,
# Tag of the image we're appending onto.
fromImageTag ? null,
# How much disk to allocate for the temporary virtual machine.
diskSize ? 1024,
# Commands (bash) to run on the layer; these do not require sudo.
extraCommands ? ""
# Generate an executable script from the `runAsRoot` text.
let runAsRootScript = shellScript "" runAsRoot;
in runWithOverlay {
name = "docker-layer-${name}";
inherit fromImage fromImageName fromImageTag diskSize;
preMount = lib.optionalString (contents != null && contents != []) ''
echo "Adding contents..."
for item in ${toString contents}; do
echo "Adding $item..."
rsync -ak $item/ layer/
postMount = ''
mkdir -p mnt/{dev,proc,sys} mnt${storeDir}
# Mount /dev, /sys and the nix store as shared folders.
mount --rbind /dev mnt/dev
mount --rbind /sys mnt/sys
mount --rbind ${storeDir} mnt${storeDir}
# Execute the run as root script. See 'man unshare' for
# details on what's going on here; basically this command
# means that the runAsRootScript will be executed in a nearly
# completely isolated environment.
unshare -imnpuf --mount-proc chroot mnt ${runAsRootScript}
# Unmount directories and remove them.
umount -R mnt/dev mnt/sys mnt${storeDir}
rmdir --ignore-fail-on-non-empty \
mnt/dev mnt/proc mnt/sys mnt${storeDir} \
mnt$(dirname ${storeDir})
postUmount = ''
(cd layer; eval "${extraCommands}")
echo "Packing layer..."
mkdir $out
tar -C layer --mtime=0 -cf $out/layer.tar .
# Compute the tar checksum and add it to the output json.
echo "Computing checksum..."
ts=$(${tarsum} < $out/layer.tar)
cat ${baseJson} | jshon -s "$ts" -i checksum > $out/json
# Indicate to docker that we're using schema version 1.0.
echo -n "1.0" > $out/VERSION
echo "Finished building layer '${name}'"
# 1. extract the base image
# 2. create the layer
# 3. add layer deps to the layer itself, diffing with the base image
# 4. compute the layer id
# 5. put the layer in the image
# 6. repack the image
buildImage = args@{
# Image name.
# Image tag.
tag ? "latest",
# Parent image, to append to.
fromImage ? null,
# Name of the parent image; will be read from the image otherwise.
fromImageName ? null,
# Tag of the parent image; will be read from the image otherwise.
fromImageTag ? null,
# Files to put on the image (a nix store path or list of paths).
contents ? null,
# Docker config; e.g. what command to run on the container.
config ? null,
# Optional bash script to run on the files prior to fixturizing the layer.
extraCommands ? "",
# Optional bash script to run as root on the image when provisioning.
runAsRoot ? null,
# Size of the virtual machine disk to provision when building the image.
diskSize ? 1024,
baseName = baseNameOf name;
# Create a JSON blob of the configuration. Set the date to unix zero.
baseJson = writeText "${baseName}-config.json" (builtins.toJSON {
created = "1970-01-01T00:00:01Z";
architecture = "amd64";
os = "linux";
config = config;
layer =
if runAsRoot == null
then mkPureLayer {
name = baseName;
inherit baseJson contents extraCommands;
} else mkRootLayer {
name = baseName;
inherit baseJson fromImage fromImageName fromImageTag
contents runAsRoot diskSize extraCommands;
result = runCommand "docker-image-${baseName}.tar.gz" {
buildInputs = [ jshon pigz coreutils findutils ];
imageName = name;
imageTag = tag;
inherit fromImage baseJson;
layerClosure = writeReferencesToFile layer;
passthru.buildArgs = args;
passthru.layer = layer;
} ''
# Print tar contents:
# 1: Interpreted as relative to the root directory
# 2: With no trailing slashes on directories
# This is useful for ensuring that the output matches the
# values generated by the "find" command
ls_tar() {
for f in $(tar -tf $1 | xargs realpath -ms --relative-to=.); do
if [[ "$f" != "." ]]; then
echo "/$f"
mkdir image
touch baseFiles
if [[ -n "$fromImage" ]]; then
echo "Unpacking base image..."
tar -C image -xpf "$fromImage"
if [[ -z "$fromImageName" ]]; then
fromImageName=$(jshon -k < image/repositories|head -n1)
if [[ -z "$fromImageTag" ]]; then
fromImageTag=$(jshon -e $fromImageName -k \
< image/repositories|head -n1)
parentID=$(jshon -e $fromImageName -e $fromImageTag -u \
< image/repositories)
for l in image/*/layer.tar; do
ls_tar $l >> baseFiles
chmod -R ug+rw image
mkdir temp
cp ${layer}/* temp/
chmod ug+w temp/*
echo "$(dirname ${storeDir})" >> layerFiles
echo '${storeDir}' >> layerFiles
for dep in $(cat $layerClosure); do
find $dep >> layerFiles
echo "Adding layer..."
# Record the contents of the tarball with ls_tar.
ls_tar temp/layer.tar >> baseFiles
# Get the files in the new layer which were *not* present in
# the old layer, and record them as newFiles.
comm <(sort -n baseFiles|uniq) \
<(sort -n layerFiles|uniq|grep -v ${layer}) -1 -3 > newFiles
# Append the new files to the layer.
tar -rpf temp/layer.tar --mtime=0 --no-recursion --files-from newFiles
echo "Adding meta..."
# If we have a parentID, add it to the json metadata.
if [[ -n "$parentID" ]]; then
cat temp/json | jshon -s "$parentID" -i parent > tmpjson
mv tmpjson temp/json
# Take the sha256 sum of the generated json and use it as the layer ID.
# Compute the size and add it to the json under the 'Size' field.
layerID=$(sha256sum temp/json|cut -d ' ' -f 1)
size=$(stat --printf="%s" temp/layer.tar)
cat temp/json | jshon -s "$layerID" -i id -n $size -i Size > tmpjson
mv tmpjson temp/json
# Use the temp folder we've been working on to create a new image.
mv temp image/$layerID
# Store the json under the name image/repositories.
jshon -n object \
-n object -s "$layerID" -i "$imageTag" \
-i "$imageName" > image/repositories
# Make the image read-only.
chmod -R a-w image
echo "Cooking the image..."
tar -C image --mtime=0 -c . | pigz -nT > $out
echo "Finished."