undocker/README.md

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[![godocs.io](http://godocs.io/git.sr.ht/~motiejus/undocker?status.svg)](http://godocs.io/git.sr.ht/~motiejus/undocker)
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[![builds.sr.ht status](https://builds.sr.ht/~motiejus/undocker.svg)](https://builds.sr.ht/~motiejus/undocker?)
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Undocker
--------
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Converts a Docker image (a bunch of layers) to a flattened "rootfs" tarball.
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Why?
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----
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Docker images became a popular way to distribute applications with their
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dependencies; however, Docker is not the best runtime environment. At least not
for everyone. May boring technology run our software.
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Undocker bridges the gap between application images (in docker image format)
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and application isolation ("container") runtimes: once the docker image is
extracted, it can be run with old-fashioned tools: lxc, systemd-nspawn,
systemd, FreeBSD Jails, and many others.
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Undocker has no dependencies outside Golang stdlib.
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Usage: convert docker image to rootfs
-------------------------------------
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Download `busybox` docker image from docker hub and convert it to a rootfs:
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```
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$ skopeo copy docker://docker.io/busybox:latest docker-archive:busybox.tar
$ undocker busybox.tar - | tar -tv | head -10
drwxr-xr-x 0/0 0 2021-05-17 22:07 bin/
-rwxr-xr-x 0/0 1149184 2021-05-17 22:07 bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/[[ link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/acpid link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/add-shell link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/addgroup link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/adduser link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/adjtimex link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/ar link to bin/[
hrwxr-xr-x 0/0 0 2021-05-17 22:07 bin/arch link to bin/[
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```
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You can also refer [here][2] for other ways to download Docker images. There
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are many.
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Converting a [1.1GB Docker image with 77
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layers](https://hub.docker.com/r/homeassistant/home-assistant) takes around 4
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seconds and on a reasonably powerful Intel laptop.
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Usage example: systemd-nspawn
-----------------------------
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Start with systemd-nspawn:
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```
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systemd-nspawn -D $PWD busybox httpd -vfp 8080
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```
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Usage example: plain old systemd
--------------------------------
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```
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systemd-run \
--wait --pty --collect --service-type=exec \
-p PrivateUsers=true \
-p DynamicUser=yes \
-p ProtectProc=invisible \
-p RootDirectory=$PWD \
-- busybox httpd -vfp 8080
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```
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Good things like `PrivateUsers`, `DynamicUser`, `ProtectProc` and other
[systemd protections][1] are available, just like to any systemd unit.
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Similar Projects
----------------
* [rootfs_builder](https://github.com/ForAllSecure/rootfs_builder)
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Changelog
---------
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**1.0.1**
* bugfix: add missing error check when opening the tarball.
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**1.0**
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* initial release: `rootfs.Flatten` and a simple command-line application.
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Contributions
-------------
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The following contributions may be accepted:
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- Pull requests (patchsets) with accompanying tests.
- Regression reports.
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If you found a container that undocker cannot extract, or extracts incorrectly
and you need this that work with undocker, do not submit an issue: submit a
patchset.
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Reports of regression reports must provide examples of "works before" and "does
not work after". Issues without an accompanying patch will most likely be
rejected.
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LICENSE
-------
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MIT
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[1]: https://www.freedesktop.org/software/systemd/man/systemd.exec.html
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[2]: https://fly.io/blog/docker-without-docker/