ARM on Docker
I'm running ubuntu 14.04.3 on my ARMv7 based devices, which makes it easier to install and run Docker. If you prefer to run a different linux flavor, you might experience little deviations (package naming, etc., if you run Fedora 22 you can continue here). I created my ubuntu userland once from scratch and use it among the different ARMv7 devices. Porting ubuntu to a different device means re-using the userland, then compiling/replacing the vendor specific kernel and bootloader.
You shouldn't be afraid of compiling a customized linux kernel, since the most vendor specific linux kernels don't include support for the aufs filesystem. Although Docker will run on kernels without aufs, it will speed up significantly on aufs enabled platforms. Furthermore some vendors may not include all features needed for Docker to run properly with their default kernel configuration.
Ubuntu 14.04.3 includes a docker.io package (which is actually version 1.6.2).
$ sudo apt-get install lxc aufs-tools cgroup-lite apparmor docker.io
will install the binary, start-up scripts, etc.. But, it is very likely that the Docker service won't start successfully after installing. Usually there is a specific kernel feature not available which Docker relies on. In the meantime, the default ODROID images and kernel packages contain docker enabled kernel images already, so are almost done by installing the packages mentioned above and you might go to the docker upgrade procedure directly.
Running /usr/bin/docker -D -d will give you a clue about the actual reason, why the Docker daemon refuses to start. The Docker developers provide a (bash-) shell script which queries whether all Docker-related requirements are met by a particular kernel config. check-config.sh will either check the config of the running kernel (accessible via /proc/config.gz) or will try to read the kernel source's config file specified on the command line. So
$ curl -L https://raw.githubusercontent.com/docker/docker/master/contrib/check-config.sh | /bin/bash /dev/stdin /path/to/.config
will be your friend.
Many vendors publish their (slightly) modified kernel sources for their ARM devices and instructions how to install the compiled kernel image. I use the following instructions for compiling the kernel sources. To do this, you need to install a compiler tool-chain (make, gcc, ...) and some '3rd party' tools (bc, lzop, u-boot-tools). Be careful, this will overwrite the default kernel image. You may consider to take a backup of your actual kernel.
make menuconfig gives you a much more user-friendly interface then editing the .config with you preferred text editor.
The ODROID kernel sources for XU3 have integrated support for Docker and aufs. There is no need to alter any of the kernel options via make menuconfig.
In the meantime, the default ODROID images and kernel packages contain docker enabled kernel images already, so you may skip this part and go to the docker upgrade procedure directly.
$ git clone --depth 1 --single-branch -b odroidxu3-3.10.y https://github.com/hardkernel/linux
$ cd linux
$ make odroidxu3_defconfig
$ make clean
$ make -j 8
$ sudo make modules_install
$ sudo cp arch/arm/boot/zImage arch/arm/boot/dts/exynos5422-odroidxu3.dtb /media/boot
As I said before, Docker will speed up significantly if the kernel supports the aufs filesystem. I've used the standalone version (kernel module only) so far.
If you have one of the ODROID devices mentioned above, you can skip this part. Their kernel sources have integrated support for aufs already.
$ cd <kernel source directory>
$ git clone git://git.code.sf.net/p/aufs/aufs3-standalone aufs3-standalone.git
$ cd aufs3-standalone.git
$ git checkout origin/aufs3.10 # 3.10 .. 3.10.25
$ git checkout origin/aufs3.10.x # 3.10.26 and above
$ git checkout origin/aufs3.14 # 3.14 .. 3.14.20
$ git checkout origin/aufs3.14.21+ # 3.14.21 .. 3.14.39
$ git checkout origin/aufs3.14.40+ # 3.14.40 and above
$ rm include/uapi/linux/Kbuild # this will keep your kernel sources config management from being damaged
$ cp -rp *.patch fs include Documentation ../
$ cd ..
$ cat aufs3-kbuild.patch aufs3-base.patch aufs3-mmap.patch aufs3-standalone.patch | patch -p1
The aufs release numbering corresponds to the kernel version, so you may checkout origin/aufs3.14 for a linux 3.14.x kernel source code. The 3.10 aufs comes with two branches, 3.10 and 3.10.x. Unfortunately, the aufs developers decided to discontinue the support for kernels below 3.14 with the beginning of 2015 and removed the information that 3.10.x branch has to be used for kernel versions starting with 3.10.26.
$ make oldconfig
...
Aufs (Advanced multi layered unification filesystem) support (AUFS_FS) [N/m/y/?] (NEW) m
Maximum number of branches
> 1. 127 (AUFS_BRANCH_MAX_127) (NEW)
2. 511 (AUFS_BRANCH_MAX_511) (NEW)
3. 1023 (AUFS_BRANCH_MAX_1023) (NEW)
4. 32767 (AUFS_BRANCH_MAX_32767) (NEW)
choice[1-4?]: 1
Detect direct branch access (bypassing aufs) (AUFS_HNOTIFY) [N/y/?] (NEW) y
method
> 1. fsnotify (AUFS_HFSNOTIFY) (NEW)
choice[1]: 1
NFS-exportable aufs (AUFS_EXPORT) [N/y/?] (NEW) y
support for XATTR/EA (including Security Labels) (AUFS_XATTR) [N/y/?] (NEW) y
File-based Hierarchical Storage Management (AUFS_FHSM) [N/y/?] (NEW) y
Readdir in userspace (AUFS_RDU) [N/y/?] (NEW) y
Show whiteouts (AUFS_SHWH) [N/y/?] (NEW) y
Ramfs (initramfs/rootfs) as an aufs branch (AUFS_BR_RAMFS) [N/y/?] (NEW) y
Fuse fs as an aufs branch (AUFS_BR_FUSE) [N/y/?] (NEW) y
Hfsplus as an aufs branch (AUFS_BR_HFSPLUS) [Y/n/?] (NEW) y
Debug aufs (AUFS_DEBUG) [N/y/?] (NEW) n
configuration written to .config
$ make savedefconfig
This will add the aufs related kernel configuration items to your existing config. Please choose 'm' for the aufs support.
Nowadays Docker also supports OverlayFS introduced with the 3.18 Linux kernel. So if you've managed to run linux 3.18 on your arm device OverlayFS could be a replacement for aufs. This article may help you to set up Docker with OverlayFS.
Now it's time to recompile and install the new kernel.
If everything went well the Docker service will run on your device and listens for service requests.
$ sudo docker info
Containers: 0
Images: 0
Storage Driver: aufs
Root Dir: /var/lib/docker/aufs
Backing Filesystem: extfs
Dirs: 0
Execution Driver: native-0.2
Kernel Version: 3.10.66-aufs
Operating System: Ubuntu 14.04.2 LTS
CPUs: 4
Total Memory: 983.4 MiB
Name: odroid-c1
ID: 324D:YXY2:2XQP:CATB:KIQD:AFXA:UZBQ:IEPO:WSB5:3Y2R:O5QU:FRDU
Most of the Docker images are made for the x86 platform and docker itself isn't platform aware, although the Docker images know on which platform they have been created:
$ sudo docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
<none> <none> d8115ff9b785 22 hours ago 301.5 MB
armv7/armhf-ubuntu_core 14.04 c11f1521cacf 2 weeks ago 159 MB
$ sudo docker inspect d8115ff9b785 | jq '.[] | .Architecture'
"arm"
So running
$ sudo docker run ubuntu /bin/echo 'Hello world'
will yield
FATA[0205] Error response from daemon: Cannot start container 9b55520a44ad4c069cc577afa51983713afb8e96ebe55a736e0819706b94f10b: exec format error
Most of the Docker images for ARMv7 devices in the Docker registry have a name starting with armhf-.... You may search for them:
$ sudo docker search armhf-
umiddelb@armh0:~$ sudo docker search armhf-
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
mazzolino/armhf-ubuntu Ubuntu-Core images for armhf (ARMv7) devices 4
armv7/armhf-ubuntu 'official' ubuntu docker images for the AR... 4
mazzolino/armhf-debian Debian Wheezy base image for armhf devices 4
armv7/armhf-archlinux archlinux arm docker image for the ARMv7(a... 3
armv7/armhf-ubuntu_core ubuntu core docker images for the ARMv7(ar... 2
hominidae/armhf-ubuntu ubuntu trusty/14.04 image (minbase) for ar... 2
armv7/armhf-fedora minimal fedora 21, 20 docker images for th... 1
hominidae/armhf-wheezy armhf image of Debian Wheezy, made with de... 1
armbuild/ubuntu-debootstrap ARMHF port of ubuntu-debootstrap 1 [OK]
dpniel/dekko-armhf armhf utopic image to build dekko click pa... 0
troyfontaine/armhf-haproxy HAProxy for ARMHF 0
hominidae/armhf-supervisord ubuntu trusty/14.04 for armhf architecure ... 0
mazzolino/armhf-twister Twister for armhf / armv7 devices 0
hominidae/armhf-archlinux ArchLinux base image for armhf architectur... 0
onlinelabs/armhf-ubuntu 0
chanwit/fedora-armhf Fedora for the armhf architecture 0
moul/armhf-busybox 0 [OK]
armv7/armhf-baseimage ubuntu docker images for the ARMv7(armhf) ... 0
mazzolino/armhf-prosody Secured Prosody XMPP server for armhf (ARM... 0
dehy/armhf-couchdb ARMHF port of klaemo/couchdb 0
mazzolino/armhf-tiddlywiki Tiddywiki5 on NodeJS for armhf (ARMv7) dev... 0
zsoltm/ubuntu-armhf Ubuntu 14.04.1 minimal install, latest upd... 0
mazzolino/armhf-nginx Nginx image for armhf devices 0
troyfontaine/armhf-nginx Nginx for ARMHF 0
rcarmo/armhf-ubuntu Ubuntu 14.04.2 for armhf devices 0
I publish my Docker images using the armv7 profile on dockerhub . So let's try the same with armv7/armhf-ubuntu_core:
$ sudo docker run armv7/armhf-ubuntu_core /bin/echo 'Hello world'
Unable to find image 'armv7/armhf-ubuntu_core:latest' locally
Pulling repository armv7/armhf-ubuntu_core
c3802ac1b0ad: Download complete
Status: Downloaded newer image for armv7/armhf-ubuntu_core:latest
Hello world
This time I've used a different device which hasn't downloaded the image before. It will be part of the local image cache now:
$ sudo docker images
REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE
armv7/armhf-ubuntu_core latest c3802ac1b0ad About an hour ago 163.5 MB
There are lots of excellent resources helping you to get a better understanding of Docker. You may visit
- http://docs.docker.com/userguide/
- https://www.youtube.com/watch?v=pYZPd78F4q4
- https://github.com/veggiemonk/awesome-docker
and subscribe to the weekly Docker newsletter.
You may have experienced a tedious bug in Docker 1.0.1 which will from time to time prevent containers from starting:
$ sudo docker run armv7/armhf-ubuntu_core /bin/echo 'Hello world'
2015/01/15 17:57:10 finalize namespace drop capabilities operation not permitted
This bug seems to be fixed in Docker version 1.4.0. You can build Docker 1.4.0 from source with Docker 1.0.1 but you need patched sources, otherwise the build-in fuse will prevent Docker from starting:
FATA[0000] The Docker runtime currently only supports amd64 (not arm). This will change in the future. Aborting.
The Docker wiki pages will guide you how to build the Docker binary from source.
Starting with release 1.5.0 the Docker developers removed the 'fuse' which explicitly requires the amd64 platform and integrated most of the patches making Docker 32 bit safe. You can build Docker for ARMv7 with the latest original sources now. The only thing you still need is a slightly modified Dockerfile for the armhf/ARMv7 platform and then:
$ git clone -b 'v1.9.1' --depth 1 --single-branch https://github.com/docker/docker.git
$ cd docker
$ curl -L https://github.com/umiddelb/armhf/raw/master/Dockerfile.armv7 > Dockerfile
$ sudo make build
$ sudo make binary
$ sudo service docker.io stop
$ sudo cp bundles/1.9.1/binary/docker-1.9.1 /usr/bin
$ (cd /usr/bin; sudo mv docker _docker; sudo ln -sf docker-1.9.1 docker)
$ sudo service docker.io start
...
It is very likely that the bug mentioned above will interrupt the build process. In this case you have to issue the sudo make build more than once. You may download the final Docker binary here, if you start feeling tired.
The binary itself is linked statically, it will run on other linux flavours as well (e.g. fedora or archlinux):
$ file /usr/bin/docker-1.9.1
docker-1.9.1: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=899c1d9a7227a5d26da60ebc14abf110c26d2318, not stripped
Just replace the existing Docker binary in /usr/bin with the new one and you're done:
$ sudo docker version
Client:
Version: 1.9.1
API version: 1.21
Go version: go1.4.3
Git commit: a34a1d5-dirty
Built: Thu Jan 28 10:28:47 UTC 2016
OS/Arch: linux/arm
Server:
Version: 1.9.1
API version: 1.21
Go version: go1.4.3
Git commit: a34a1d5-dirty
Built: Thu Jan 28 10:28:47 UTC 2016
OS/Arch: linux/arm
The Fedora developers issued a Docker rpm package for armhfp recently, thanks to @vpavlin:
$ sudo yum install lxc bridge-utils device-mapper device-mapper-libs libsqlite3x docker-registry docker-storage-setup docker-io