tokibi/undocker

Go library and command line tool for decomposing docker images.

undocker

Go library and command line tool for decomposing docker images.

Command Use

Usage

NAME:
   undocker - Decompose docker images.

USAGE:
   undocker [global options] command [command options] [arguments...]

VERSION:
   0.1.3

COMMANDS:
     extract, e  Extract to rootfs.
     show, s     Show image informations
     help, h     Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --registry-url value, -r value   docker registry url [$REGISTRY_URL]
   --registry-user value, -u value  docker registry login username [$REGISTRY_USER]
   --registry-pass value, -p value  docker registry login password [$REGISTRY_PASS]
   --help, -h                       show help
   --version, -v                    print the version

Installation

homebrew tap:

$ brew install tokibi/tap/undocker

manually:

Download binany from releases page

go get:

$ go get github.com/tokibi/undocker/cmd/undocker

Extract

Extract from local images.

$ undocker extract busybox:latest ./image
$ ls ./image
bin/  dev/  etc/  home/  root/	tmp/  usr/  var/

Extract directly from docker registry.

$ export REGISTRY_USER=xxx # optional
$ export REGISTRY_PASS=xxx # optional
$ undocker -r "https://registry-1.docker.io/" extract busybox:latest ./image

Config

Show image config.

$ undocker show config busybox:latest | jq
{
  "architecture": "amd64",
  "config": {
    "Hostname": "",
    "Domainname": "",
    "User": "",
    "AttachStdin": false,
    "AttachStdout": false,
    "AttachStderr": false,
    "Tty": false,
    "OpenStdin": false,
    "StdinOnce": false,
    "Env": [
      "PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
    ],
    "Cmd": [
      "sh"
    ],
...

Library Use

Extract

Extract from local images.

func main() {
    dst := "./image"

    api, err := undocker.NewDockerAPI()
    if err != nil {
        log.Fatal(err)
    }
    api.Image("busybox", "latest").Extract(dst, false)
}

Extract directly from docker registry.

func main() {
    url := "https://registry-1.docker.io/"
    username := ""
    password := ""
    dst := "./image"

    registry, err := undocker.NewRegistry(url, username, password)
    if err != nil {
        log.Fatal(err)
    }
    registry.Image("busybox", "latest").Extract(dst, false)
}

Config

func main() {
    api, _ := undocker.NewDockerAPI()
    config, err := api.Image("busybox", "latest").Config()
    if err != nil {
        return err
    }
    fmt.Println(config.architecture)
}

undocker's Issues

Build static binary with alpine environment

Hi,

instead of download the latest (static) release it would be easier to build by go get / go build, but the binary still have dependencies.

Step 10/19 : RUN     ldd $BDIR/undocker
 ---> Running in d5d820f05f47
        /lib/ld-musl-x86_64.so.1 (0x7efdc0b4d000)
        libc.musl-x86_64.so.1 => /lib/ld-musl-x86_64.so.1 (0x7efdc0b4d000)

How to build a static binary with alpine?
Tried with that dockerfile:

ARG     GOBUILD_IMG=golang:alpine

FROM    $GOBUILD_IMG AS gobuild

RUN     apk --update --no-cache add \
        build-base \
        git

ENV     BDIR=/build

WORKDIR $BDIR

RUN     git clone https://github.com/tokibi/undocker.git $BDIR

RUN     go build --ldflags "-s -w -extldflags -static" github.com/tokibi/undocker/cmd/undocker

RUN     ls -lh $BDIR/undocker

RUN     strip $BDIR/undocker

RUN     ldd $BDIR/undocker
RUN     ls -lh $BDIR/undocker

Add symlink absolute to relative conversion

First, thanks for the awesome tool, I originally looked at undocked.py but the Go implementation looks more elaborate and can be installed with a single executable, which is nice.

I have a small feature request that would make a huge difference: I am working on using docker images to produce sysroots meant for cross-compilation outside of a docker container. The main issue I encounter when using the "raw" docker container contents are absolute symlinks that can point to invalid locations on the build host, while they really should be pointing inside the sysroot directory.

One instance of such a problem I encountered is with libgcc_s.so which can often be a symlink to the real .so, unfortunately often set with an absolute path:

$ file ./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so
./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so: broken symbolic link to /lib/i386-linux-gnu/libgcc_s.so.1
$ rm ./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so
$ ln -s ../../../../../lib/i386-linux-gnu/libgcc_s.so.1 ./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so
$ file ./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so
./usr/lib/gcc/i686-linux-gnu/5/libgcc_s.so: ELF 32-bit LSB shared object Intel 80386, version 1 (SYSV), dynamically linked, BuildID[sha1]=50f0704a5c669c096642b2c5b08b4867bbc9303f, stripped

In the above example, the 32-bit ubuntu sysroot has a libgcc_s.so symlink to '/lib/i386-linux-gnu/libgcc_s.so.1', which obviously makes no sense when outside of the container. Replacing the symlink by '../../../../../lib/i386-linux-gnu/libgcc_s.so.1' (relative) fixes the symlink such that it can point to the right location again.

The Dockerfile I used for this example is simple, it's just an ubuntu environment with a few development packages:

FROM i386/ubuntu:16.04
LABEL maintainer "Devolutions Inc."

ARG DEBIAN_FRONTEND=noninteractive

RUN apt-get update -y
RUN apt-get install -y \
    libx11-dev \
    libxtst-dev \
    libxcursor-dev \
    libxrandr-dev \
    libgtk-3-dev \
    libglib2.0-dev \
    libappindicator3-dev \
    libnotify-dev \
    libssl-dev

I then built and extracted its contents this way:

docker build . -t ubuntu-16.04-i386-sysroot
undocker extract ubuntu-16.04-i386-sysroot ./sysroot

Let me know if this could be done, thanks a lot!

Default registry url

Hi @tokibi,

undocker binary is great for some usecases and the smallest binary I found to download and unpack images! Thanks!

You shoult add default registriy url to docker hub and replace if needed with -r?

-r https://registry-1.docker.io/  # should be default