README
¶
img
Standalone, daemon-less, unprivileged Dockerfile and OCI compatible container image builder.
img is more cache-efficient than Docker and can also execute multiple build stages concurrently,
as it internally uses BuildKit's DAG solver.
The commands/UX are the same as docker {build,tag,push,pull,login,logout,save} so all you
have to do is replace docker with img in your scripts, command line, and/or life.
Table of Contents
- Goals - Upstream Patches - Benchmarks
- Installation
- Usage
- How It Works
- Contributing
- Acknowledgements
Goals
This a glorified cli tool built on top of buildkit. The goal of this project is to be able to build container images as an unprivileged user.
Running unprivileged allows companies who use LDAP and other login mechanisms
to use img without needing root. This is very important in HPC environments
and academia as well.
Currently this works out of the box on a Linux machine if you install via
the directions covered in installing from binaries. This
installation will ensure you have the correct version of img and also runc.
The ultimate goal is to also have this work inside a container. There are patches being made to container runtimes and Kubernetes to make this possible. For the on-going work toward getting patches into container runtimes and Kubernetes, see:
- moby/moby#36644 merged
- docker/cli#1347 merged
- kubernetes/community#1934 merged
- kubernetes/kubernetes#64283 merged
The patches for runc has been merged into the upstream since ecd55a4135e0a26de884ce436442914f945b1e76 (May 30, 2018).
The upstream BuildKit can also run in rootless mode since 65b526438b86a17cf35042011051ce15c8bfb92a (June 1, 2018).
You might also be interested in reading:
If you are curious about benchmarks comparing various container builders, check out @AkihiroSuda's buildbench results.
Installation
You need to have newuidmap installed. On Ubuntu, newuidmap is provided by the uidmap package.
You also need to have seccomp installed. On Ubuntu, seccomp is provided by the libseccomp-dev package.
runc will be installed on start from an embedded binary if it is not already
available locally. If you would like to disable the embedded runc you can use BUILDTAGS="seccomp noembed" while building from source with make. Or the environment variable
IMG_DISABLE_EMBEDDED_RUNC=1 on execution of the img binary.
NOTE: These steps work only for Linux. Compile and run in a container (explained below) if you're on Windows or MacOS.
Binaries
For installation instructions from binaries please visit the Releases Page.
From Source
$ mkdir -p $GOPATH/src/github.com/genuinetools
$ git clone https://github.com/genuinetools/img $GOPATH/src/github.com/genuinetools/img
$ cd !$
$ make
$ sudo make install
# For packagers if you would like to disable the embedded `runc`, please use:
$ make BUILDTAGS="seccomp noembed"
Alpine Linux
There is an APKBUILD.
$ apk add img --repository=http://dl-cdn.alpinelinux.org/alpine/edge/testing
Arch Linux
There is an AUR build.
# Use whichever AUR helper you prefer
$ yay -S img
# Or build from the source PKGBUILD
$ git clone https://aur.archlinux.org/packages/img.git
$ cd img
$ makepkg -si
Gentoo
There is an ebuild.
$ sudo emerge -a app-emulation/img
Running with Docker
Docker image r.j3ss.co/img is configured to be executed as an unprivileged user with UID 1000 and it does not need --privileged since img v0.5.11.
$ docker run --rm -it \
--name img \
--volume $(pwd):/home/user/src:ro \ # for the build context and dockerfile, can be read-only since we won't modify it
--workdir /home/user/src \ # set the builder working directory
--volume "${HOME}/.docker:/root/.docker:ro" \ # for credentials to push to docker hub or a registry
--security-opt seccomp=unconfined --security-opt apparmor=unconfined \ # required by runc
r.j3ss.co/img build -t user/myimage .
To enable PID namespace isolation (which disallows build containers to kill(2) the img process), you need to specify
--privileged so that build containers can mount /proc with unshared PID namespaces.
Note that even with --privileged, img works as an unprivileged user with UID 1000.
See docker/cli patch for how to allow mounting /proc without --privileged.
Running with Kubernetes
Since img v0.5.11, you don't need to specify any securityContext for running img as a Kubernetes container.
However the following security annotations are needed:
container.apparmor.security.beta.kubernetes.io/img: unconfined
container.seccomp.security.alpha.kubernetes.io/img: unconfined
To enable PID namespace isolation, you need to set securityContext.procMount to Unmasked (or simply set
securityContext.privileged to true).
securityContext.procMount is available since Kubernetes 1.12 with Docker 18.06/containerd 1.2/CRI-O 1.12.
Usage
Make sure you have user namespace support enabled. On some distros (Debian and
Arch Linux) this requires running echo 1 > /proc/sys/kernel/unprivileged_userns_clone.
$ img -h
img - Standalone, daemon-less, unprivileged Dockerfile and OCI compatible container image builder
Usage: img [OPTIONS] COMMAND [ARG...]
Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-h, --help help for img
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
-v, --version Print version information and quit
Commands:
build Build an image from a Dockerfile
du Show image disk usage.
help Help about any command
login Log in to a Docker registry.
logout Log out from a Docker registry.
ls List images and digests.
prune Prune and clean up the build cache.
pull Pull an image or a repository from a registry.
push Push an image or a repository to a registry.
rm Remove one or more images.
save Save an image to a tar archive (streamed to STDOUT by default).
tag Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE.
unpack Unpack an image to a rootfs directory.
version Show the version information.
Use "img [command] --help" for more information about a command.
Build an Image
$ img build -h
build - Build an image from a Dockerfile
Usage: img build [OPTIONS] PATH
Flags:
--build-arg list Set build-time variables
--cache-from list Buildkit import-cache or Buildx cache-from specification
--cache-to list Buildx cache-to specification
-f, --file string Name of the Dockerfile (Default is 'PATH/Dockerfile')
-h, --help help for build
--label list Set metadata for an image
--no-cache Do not use cache when building the image
--no-console Use non-console progress UI
-o, --output string BuildKit output specification (e.g. type=tar,dest=build.tar)
--platform list Set platforms for which the image should be built
-t, --tag list Name and optionally a tag in the 'name:tag' format
--target string Set the target build stage to build
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
Use just like you would docker build.
$ img build -t r.j3ss.co/img .
Building r.j3ss.co/img:latest
Setting up the rootfs... this may take a bit.
[+] Building 44.7s (16/16) FINISHED
=> local://dockerfile (Dockerfile) 0.0s
=> => transferring dockerfile: 1.15kB 0.0s
=> local://context (.dockerignore) 0.0s
=> => transferring context: 02B 0.0s
=> CACHED docker-image://docker.io/tonistiigi/copy:v0.1.1@sha256:854cee92ccab4c6d63 0.0s
=> => resolve docker.io/tonistiigi/copy:v0.1.1@sha256:854cee92ccab4c6d63183d147389e 0.0s
=> CACHED docker-image://docker.io/library/alpine@sha256:e1871801d30885a610511c867d 0.0s
=> => resolve docker.io/library/alpine@sha256:e1871801d30885a610511c867de0d6baca7ed 0.0s
=> docker-image://docker.io/library/golang:1.10-alpine@sha256:98c1f3458b21f50ac2e58 5.5s
=> => resolve docker.io/library/golang:1.10-alpine@sha256:98c1f3458b21f50ac2e5896d1 0.0s
=> => sha256:866414f805391b58973d4e3d76e5d32ae51baecb1c93762c9751b9d6c5 126B / 126B 0.0s
=> => sha256:ae8dbf6f23bf1c326de78fc780c6a870bf11eb86b45a7dc567 308.02kB / 308.02kB 0.0s
=> => sha256:44ccce322b34208317d748e998212cd677c16f1a58c2ff5e59578c 3.86kB / 3.86kB 0.0s
=> => sha256:0d01df27c53e651ecfa5c689dafb8c63c759761a757cc37e30eccc5e3a 153B / 153B 0.0s
=> => sha256:ff3a5c916c92643ff77519ffa742d3ec61b7f591b6b7504599d95a 2.07MB / 2.07MB 0.0s
=> => sha256:4be696a8d726150ed9636ea7156edcaa9ba8293df1aae49f9e 113.26MB / 113.26MB 0.0s
=> => sha256:98c1f3458b21f50ac2e5896d14a644eadb3adcae5afdceac0cc9c2 2.04kB / 2.04kB 0.0s
=> => sha256:bb31085d5c5db578edf3d4e5541cfb949b713bb7018bbac4dfd407 1.36kB / 1.36kB 0.0s
=> => unpacking docker.io/library/golang:1.10-alpine@sha256:98c1f3458b21f50ac2e5896 5.4s
=> local://context 0.8s
=> => transferring context: 116.83MB 0.8s
=> /bin/sh -c apk add --no-cache bash build-base gcc git libseccomp-dev linux 3.8s
=> copy /src-0 go/src/github.com/genuinetools/img/ 1.5s
=> /bin/sh -c go get -u github.com/jteeuwen/go-bindata/... 7.3s
=> /bin/sh -c make static && mv img /usr/bin/img 15.2s
=> /bin/sh -c git clone https://github.com/opencontainers/runc.git "$GOPATH/src/git 7.6s
=> /bin/sh -c apk add --no-cache bash git shadow shadow-uidmap strace 2.3s
=> copy /src-0/img usr/bin/img 0.5s
=> copy /src-0/runc usr/bin/runc 0.4s
=> /bin/sh -c useradd --create-home --home-dir $HOME user && chown -R user:user $H 0.4s
=> exporting to image 1.5s
=> => exporting layers 1.4s
=> => exporting manifest sha256:03e034afb839fe6399a271efc972da823b1b6297ea792ec94fa 0.0s
=> => exporting config sha256:92d033f9575176046db41f4f1feacc0602c8f2811f59d59f8e7b6 0.0s
=> => naming to r.j3ss.co/img:latest 0.0s
Successfully built r.j3ss.co/img:latest
Cross Platform
img and the underlying buildkit library support building containers for arbitrary platforms (OS and architecture combinations). In img this can be achieved using the --platform option, but note that
using the RUN command during a build requires installing support for the desired platform, and any FROM images used must exist for the target platform as well.
Some common platforms include:
- linux/amd64
- linux/arm64
- linux/arm/v7
- linux/arm/v6
- linux/s390x
- linux/ppc64le
- darwin/amd64
- windows/amd64
If you use multiple --platform options for the same build, they will be included into a manifest and should work for the different platforms built for.
The most common way to get RUN working in cross-platform builds is to install an emulator such as QEMU on the host system (static bindings are recommended to avoid shared library loading issues). To properly use the emulator inside the build environment, the kernel binfmt_misc parameters must be set with the following flags: OCF.
You can check the settings in /proc to ensure they are set correctly.
$ cat /proc/sys/fs/binfmt_misc/qemu-arm | grep flags
flags: OCF
On Debian/Ubuntu the above should be available with the qemu-user-static package >= 1:2.12+dfsg-3
NOTE: cross-OS builds are slightly more complicated to get RUN commands working, but follow from the same principle.
Exporter Types
img can also use buildkit's exporter types directly to output the
resulting image to a Docker-type bundle or a rootfs tar without saving the image
itself locally. Builds will still benefit from caching.
The output type and destination are specified with the --output flag. The list
of valid output specifications includes:
| flag | description |
|---|---|
-o type=tar,dest=rootfs.tar |
export rootfs of target image to a tar archive |
-o type=tar |
output a rootfs tar to stdout, for use in piped commands |
-o type=docker,dest=image.tar |
save a Docker-type bundle of the image |
-o type=oci,dest=image.tar |
save an OCI-type bundle of the image |
-o type=local,dest=rootfs/ |
export the target image to this directory |
-o type=image,name=r.j3ss.co/img |
build and tag an image and store it locally |
When used in conjunction with a Dockerfile which has a final FROM scratch stage and
only copies files of interest from earlier stages with COPY --from=..., this can be
utilized to output arbitrary build artifacts for example.
List Image Layers
$ img ls -h
ls - List images and digests.
Usage: img ls [OPTIONS]
Flags:
-f, --filter list Filter output based on conditions provided
-h, --help help for ls
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img ls
NAME SIZE CREATED AT UPDATED AT DIGEST
jess/img:latest 1.534KiB 9 seconds ago 9 seconds ago sha256:27d862ac32022946d61afbb91ddfc6a1fa2341a78a0da11ff9595a85f651d51e
jess/thing:latest 591B 30 minutes ago 30 minutes ago sha256:d664b4e9b9cd8b3067e122ef68180e95dd4494fd4cb01d05632b6e77ce19118e
Pull an Image
If you need to use self-signed certs with your registry, see Using Self-Signed Certs with a Registry.
$ img pull -h
pull - Pull an image or a repository from a registry.
Usage: img pull [OPTIONS] NAME[:TAG|@DIGEST]
Flags:
-h, --help help for pull
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img pull r.j3ss.co/stress
Pulling r.j3ss.co/stress:latest...
Snapshot ref: sha256:2bb7a0a5f074ffe898b1ef64b3761e7f5062c3bdfe9947960e6db48a998ae1d6
Size: 365.9KiB
Push an Image
If you need to use self-signed certs with your registry, see Using Self-Signed Certs with a Registry.
$ img push -h
push - Push an image or a repository to a registry.
Usage: img push [OPTIONS] NAME[:TAG]
Flags:
-h, --help help for push
--insecure-registry Push to insecure registry
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img push jess/thing
Pushing jess/thing:latest...
Successfully pushed jess/thing:latest
Tag an Image
$ img tag -h
tag - Create a tag TARGET_IMAGE that refers to SOURCE_IMAGE.
Usage: img tag SOURCE_IMAGE[:TAG] TARGET_IMAGE[:TAG]
Flags:
-h, --help help for tag
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img tag jess/thing jess/otherthing
Successfully tagged jess/thing as jess/otherthing
Export an Image to Docker
$ img save -h
save - Save an image to a tar archive (streamed to STDOUT by default).
Usage: img save [OPTIONS] IMAGE [IMAGE...]
Flags:
--format string image output format (docker|oci) (default "docker")
-h, --help help for save
-o, --output string write to a file, instead of STDOUT
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img save jess/thing | docker load
6c3d70c8619c: Loading layer [==================================================>] 9.927MB/9.927MB
7e336c441b5e: Loading layer [==================================================>] 5.287MB/5.287MB
533fecff21a8: Loading layer [==================================================>] 2.56MB/2.56MB
3db7019eac28: Loading layer [==================================================>] 1.679kB/1.679kB
Loaded image: jess/thing
Unpack an Image to a rootfs
$ img unpack -h
unpack - Unpack an image to a rootfs directory.
Usage: img unpack [OPTIONS] IMAGE
Flags:
-h, --help help for unpack
-o, --output string Directory to unpack the rootfs to. (defaults to rootfs/ in the current working directory)
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img unpack busybox
Successfully unpacked rootfs for busybox to: /home/user/rootfs
Remove an Image
$ img rm -h
rm - Remove one or more images.
Usage: img rm [OPTIONS] IMAGE [IMAGE...]
Flags:
-h, --help help for rm
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
Disk Usage
$ img du -h
du - Show image disk usage.
Usage: img du [OPTIONS]
Flags:
-f, --filter list Filter output based on conditions provided
-h, --help help for du
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img du
ID RECLAIMABLE SIZE DESCRIPTION
sha256:d9a48086f223d28a838263a6c04705c8009fab1dd67cc82c0ee821545de3bf7c true 911.8KiB pulled from docker.io/tonistiigi/copy@sha256:476e0a67a1e4650c6adaf213269a2913deb7c52cbc77f954026f769d51e1a14e
7ia86xm2e4hzn2u947iqh9ph2 true 203.2MiB mount /dest from exec copy /src-0 /dest/go/src/github.com/genuinetools/img
...
sha256:9f131fba0383a6aaf25ecd78bd5f37003e41a4385d7f38c3b0cde352ad7676da true 958.6KiB pulled from docker.io/library/golang:alpine@sha256:a0045fbb52a7ef318937e84cf7ad3301b4d2ba6cecc2d01804f428a1e39d1dfc
sha256:c4151b5a5de5b7e272b2b6a3a4518c980d6e7f580f39c85370330a1bff5821f1 true 472.3KiB pulled from docker.io/tonistiigi/copy@sha256:476e0a67a1e4650c6adaf213269a2913deb7c52cbc77f954026f769d51e1a14e
sha256:ae4ecac23119cc920f9e44847334815d32bdf82f6678069d8a8be103c1ee2891 true 148.9MiB pulled from docker.io/library/debian:buster@sha256:a7789365b226786a0cb9e0f142c515f9f2ede7164a6f6be4a1dc4bfe19d5ec9c
bkrjrzv3nvp7lvzd5cw9vzut7* true 4.879KiB local source for dockerfile
sha256:db193011cbfc238d622d65c4099750758df83d74571e8d7498392b17df381207 true 467.2MiB pulled from docker.io/library/golang:alpine@sha256:a0045fbb52a7ef318937e84cf7ad3301b4d2ba6cecc2d01804f428a1e39d1dfc
wn4m5i5swdcjvt1ud5bvtr75h* true 4.204KiB local source for dockerfile
Reclaimable: 1.08GiB
Total: 1.08GiB
Prune and Cleanup the Build Cache
$ img prune -h
prune - Prune and clean up the build cache.
Usage: img prune [OPTIONS]
Flags:
-h, --help help for prune
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
$ img prune
ID RECLAIMABLE SIZE DESCRIPTION
j1yil8bdz35eyxp0m17tggknd true 5.08KiB local source for dockerfile
je23wfyz2apii1au38occ8zag true 52.95MiB mount / from exec /bin/sh -c useradd --create-home...
sha256:74906c0186257f2897c5fba99e1ea87eb8b2ee0bb03b611f5e866232bfbf6739 true 2.238MiB pulled from docker.io/tonistiigi/copy:v0.1.1@sha25...
vr2pvhmrt1sjs8n7jodesrvnz* true 572.6MiB mount / from exec /bin/sh -c git clone https://git...
afn0clz11yphlv6g8golv59c8 true 4KiB local source for context
qx5yql370piuscuczutrnansv* true 692.4MiB mount / from exec /bin/sh -c make static && mv img...
uxocruvniojl1jqlm8gs3ds1e* true 113.8MiB local source for context
sha256:0b9cfed6a170b357c528cd9dfc104d8b404d08d84152b38e98c60f50d2ae718b true 1.449MiB pulled from docker.io/tonistiigi/copy:v0.1.1@sha25...
vz0716utmnlmya1vhkojyxd4o true 55.39MiB mount /dest from exec copy /src-0/runc usr/bin/run...
a0om6hwulbf9gd2jfgmxsyaoa true 646.5MiB mount / from exec /bin/sh -c go get -u github.com/...
ys8y9ixi3didtbpvwbxuptdfq true 641.2MiB mount /dest from exec copy /src-0 go/src/github.co...
sha256:f64a552a56ce93b6e389328602f2cd830280fd543ade026905e69895b5696b7a true 1.234MiB pulled from docker.io/tonistiigi/copy:v0.1.1@sha25...
05wxxnq6yu5nssn3bojsz2mii true 52.4MiB mount /dest from exec copy /src-0/img usr/bin/img
wlrp1nxsa37cixf127bh6w2sv true 35.11MiB mount / from exec /bin/sh -c apk add --no-cache b...
wy0173xa6rkoq49tf9g092r4z true 527.4MiB mount / from exec /bin/sh -c apk add --no-cache b...
Reclaimed: 4.148GiB
Total: 4.148GiB
Login to a Registry
If you need to use self-signed certs with your registry, see Using Self-Signed Certs with a Registry.
$ img login -h
login - Log in to a Docker registry.
Usage: img login [OPTIONS] [SERVER]
Flags:
-h, --help help for login
-p, --password string Password
--password-stdin Take the password from stdin
-u, --user string Username
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
Logout from a Registry
$ img logout -h
logout - Log out from a Docker registry.
Usage: img logout [SERVER]
Flags:
-h, --help help for logout
Global Flags:
-b, --backend string backend for snapshots ([auto native overlayfs]) (default "auto")
-d, --debug enable debug logging
-s, --state string directory to hold the global state (default "/home/user/.local/share/img")
Using Self-Signed Certs with a Registry
We do not allow users to pass all the custom certificate flags on commands because it is unnecessarily messy and can be handled through Linux itself. Which we believe is a better user experience than having to pass three different flags just to communicate with a registry using self-signed or private certificates.
Below are instructions on adding a self-signed or private certificate to your trusted ca-certificates on Linux.
Make sure you have the package ca-certificates installed.
Copy the public half of your CA certificate (the one user to sign the CSR) into the CA certificate directory (as root):
$ cp cacert.pem /usr/share/ca-certificates
Rebuild the directory with your certificate included, run as root:
# On debian, this will bring up a menu.
# Select the ask option, scroll to the certificate you are adding,
# mark it for inclusion, and select ok.
$ dpkg-reconfigure ca-certificates
# On other distros...
$ update-ca-certificates
How It Works
Unprivileged Mounting
To mount a filesystem without root accsess, img automatically invokes
newuidmap(1)/newgidmap(1)
SUID binaries to prepare SUBUIDs/SUBGIDs, which is typically required by apt.
Make sure you have sufficient entries (typically >=65536) in your
/etc/subuid and /etc/subgid.
High Level
Low Level
Snapshotter Backends
auto (default)
The auto backend is resolved into either native or overlayfs, depending on
the availability of overlayfs on the system.
native
The native backends creates image layers by simply copying files.
copy_file_range(2) is used when available.
overlayfs
You can also use overlayfs
backend, but that requires a kernel patch from Ubuntu to be unprivileged,
see #22.
Contributing
Please do! This is a new project and can use some love <3. Check out the issues.
The local directories are mostly re-implementations of buildkit interfaces to
be unprivileged.
Acknowledgements
A lot of this is based on the work of moby/buildkit. Thanks @tonistiigi and @AkihiroSuda!
Documentation
¶
There is no documentation for this package.
Source Files
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