Are docker images portable across different linux flavours? Let's say, if I have OEL based docker image with database installed in it, can I run this in boot2docker on a Mac?
Yes, you can archive an image (docker save/docker load), copy it on your mac unless your image and run a container in a boot2docker Tiny Core VM.
The only case where an image might not be portable is if its OS filesystem depends on certain patch level of the kernel.
In that case, a container from that image would only run on the right kernel.
hek2mgl mentions in the comments that a feature like inotify works only on Linux (should work on the TinyCore VM of boot2docker), but would not work when sharing a folder from the (non-Linux) host (ticket VBox 10660 or boot2docker PR 284 comment).
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I configured Windows Subsystem for Linux, installed a Microsoft packaged Ubuntu on Win 10, to get my hands on Docker using Linux. From what I understood, Docker does not need a guest OS, unlike VMWare - that's one of the main advantages.
I browsed the dockerhub and found an official Ubuntu image. What is it for, as there is no need of a guest OS?
Shared OS is probably the wrong term here, because many include the Linux distribution and filesystem as part of the OS. Containers run with a shared Linux kernel, but in isolated namespaces from the host and each other. One of those namespaces is the mount namespace, including your root filesystem. Therefore when you enter a container, the files in /bin and other directories are assembled from the image (plus volume mounts, and changes made within the container).
The Ubuntu docker image is an initial filesystem that includes a minimal Ubuntu environment you can use the create other images for running your containers. If you were to start a container without that, you wouldn't have anything, no /bin/sh, no apt, no libraries, and would have to create every binary and needed libraries to run commands inside the container first.
I installed docker CE on an Ubuntu 16.04, and when I try:
docker pull microsoft/windowsservercore
It fails:
Using default tag: latest
latest: Pulling from microsoft/windowsservercore
3889bb8d808b: Pulling fs layer
da87b55a9b63: Pulling fs layer
image operating system "windows" cannot be used on this platform
Is it possible to run a windows image on a linux host with docker? If yes, how should I do that?
Unlike other Virtual computing systems like Virtual Box or VMWare, Docker images are small and not fully complete stand alone entities.
The Docker image does not include the OS kernel, instead it uses the kernel of the Docker host
This makes the images very light weight, but it also means you won't be able to run a Windows image on a Linux host.
I'm able to run the ARM images (eg. hypriot/rpi-node) in Docker on Windows (64bit), but in all linux x86/64 machines I've tried (Debian, CoreOS, Alpine etc) I get the following error - which makes sense to me but I dont get why it'd run in Docker on Windows then, and I wonder whether I'm missing some opportunity to use an x86 machine as a build server for ARM images (ie. the in google/aws cloud/azure). Any ideas how I might be able to?
docker run -ti hypriot/rpi-node ls
standard_init_linux.go:175: exec user process caused "exec format error"
Docker for windows (and docker for mac) both use a linux vm to host containers. However, the difference between the linux vm they use and your linux machines is the fact that their VM has a kernel system called binfmt_misc setup to call qemu whenever it encounters a binary for a foreign architecture (https://github.com/linuxkit/linuxkit/blob/1c552f7a9db7f0660d3c83362d241e54142323ca/pkg/binfmt/etc/binfmt.d/00_linuxkit.conf )
If you were to configure your linux machine appropriately, it could be used as a build server for ARM images. Google qemu-user-static for some ideas of how to set it up.
Note that the linuxkit vm uses the 'F' flag which doesn't seem to be standard when configuring a typical linux environment. Without it, you need to put the qemu binary inside the container. I'm not sure why it isn't standard practice to use 'F' in more places (there does seem to be a debian bug to do so https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=868030 )
On Windows and Mac docker works under Linux VM. So, I think, that for your container under Windows started ARM Linux VM. But under native Linux used native architecture.
The "exec format error" confirms that you are not running your docker image on the correct architecture.
I had this error trying to run a x86 docker image on a Raspberry Pi 2 (Which works with an ARM architecture). I am pretty sure it might be the same error when you do it the other way round.
So, as Kulti said, Windows/MAC must have started an ARM Linux VM.
If you wish to work with ARM docker images on Linux, you may want to try running a linux docker VM manually. I think you can do it using "docker-machine" even on linux : Docker documentation for docker-machine. (Haven't done it myself so I am not sure)
Hope this helps.
Docker on Windows uses a Linux VM which has been configured such that it can run images of other architectures through Qemu user mode emulation. You can configure native linux in a similar way and it too will then run ARM images. There is a well written three part series that describes it all in detail
Main thing to take away from Part#1 is that any file on Linux is executed through an interpreter (even binary files). The choice of interpreter is configurable, through binfmt_misc, based on byte patterns at the beginning of file or filename extension etc.
Part#2 builds on Part#1 to show how to configure Linux kernel (installed on any architecture) to interpret ARM binaries using Qemu User Emulation.
Finally Part#3 shows how to apply the same trick this time to a linux setup in a docker container which means that linux docker container (which could be for any architecture) will be able to execute ARM binaries.
Important thing to note here is that there is nothing special about docker implementation or containerization that allows docker on Windows to be able to execute ARM binaries. Instead any Linux setup (whether on bare metal or in a container) can be configured to execute ARM binaries through Qemu's user mode emulation of an ARM cpu.
I know this post is old but I will post my solution here in case someone came here through Google.
This happen because your Docker host is not able to run images with AMR architecture. To be enable this in your Docker just run:
docker run --rm --privileged hypriot/qemu-register
More info you can find on this post.
You need the kernel configured for qemu's binfmt_misc module, and the container needs to have the static binaries used by qemu available inside the container filesystem.
You can load the files on the host with the hyperiot/qemu-register image, however I prefer the distribution vendor packages when available (ensures that I get patches when I update). For Debian, the imporant packages is qemu-user-static which you can install as root with:
apt-get update && apt-get install qemu-user-static
Ensure the kernel module is loaded (as root):
modprobe binfmt_misc
Then when running the container, you can mount the static qemu binaries into your container rather than packaging them inside your image, e.g. for the arm arch:
docker run -it --rm \
-v /usr/bin/qemu-arm-static:/usr/bin/qemu-arm-static:ro \
hypriot/rpi-node /bin/sh
Docker includes binfmt_misc in the embedded Linux VM's used on Docker for Desktop, and there appears to be some additional functionality to avoid the need to manually mount the static qemu files inside the container.
I'd love to hear from you some advice on setting up what I'm looking for.
I'm using OSX and I need to develop some code on a Linux machine, the thing is that I was looking for some VM alternative since it takes too much battery power.
The first thing I come across with was a docker container. I know It is not what it was designed for, but I thought it might work anyway. So I tried running a container as
docker run -i -t ubuntu /bin/bash
and it worked well. However all the changes I make are gone and I can't fins a way to solve it. I also tried
docker run -i -v /Users/JaimehRubiks/test:/home/Jaime -t ubuntu /bin/bash
and all files in there are saved (also very interesting because I can share my files with host), but it's kind of boring having to commit to the docker image if I change anything in the config files of my ubuntu.
What I'm looking for is just a simple way to run linux in my mac, and then access to it somehow, like I did in docker or via SSH.
Docker currently does not run natively on osx as Docker relies on the Linux kernel for its isolation features. In fact, the Docker Toolbox uses a Virtual Box virtual machine running the boot2docker Linux distro to run the Docker daemon on osx. See the official documentation on Mac osx installation.
The boot2docker linux image is quite light weight, but I'm not sure you will get much benefit from running Docker on osx for Linux development over simply running a full Virtualbox machine with Ubuntu (or other distro). If you want to run a virtual machine vagrant is a good tool to help you set that up. It lets you easily pull down images from an image repo, setup the image, and ssh into it. It also makes host -> guest-machine folder sharing and port forwarding quite simple.
but it's kind of boring having to commit to the docker image if I change anything in the config files of my ubuntu.
You don't have to docker commit anything: any file change make on the host (/Users/JaimehRubiks/test) will be visible in the container (/home/Jaime)
what about using vagrant to run Ubuntu or CentOS? you can access the system via command vagrant ssh and configure it with configuration file and share it like using docker.
It is known that the docker is a virtualized technology based on Linux kernel, and Windows images can not be run on docker. So when I run docker daemon on centos6.5, does it matter starting a container run on the images of centos7?
No, it doesn't matter very much. The docker image provides the filesystem for your container, while your host os provides the kernel. The only way it could wind up mattering is if the process you are running requires some kernel feature that is not present in the kernel being run on your host system.
You can run docker images based off of all sorts of linux distros without issue. Alpine linux has become pretty popular recently, for example.