Sorry if this is a stupid and/or widely known question.
I've written a docker that basically just runs a single process then exits. It runs fine on my ubuntu machine 16.04 and its been tested on another ubuntu machine. However, someone else has tested out the docker on macos and the docker did not run to completion.
Is this a known limitation of docker? i.e. can linux dockers only run on linux, macos dockers only run on macos, etc... Or is it even more restrictive in that is only works on the same OS (i.e. ubuntu dockers should only be run on ubuntu).
The docker itself is an image processing pipeline. We run it by mounting a directory that contains the image and then mount an output directory as well and just run a process inside the container. I'll post more details of the docker if that's important to the answer.
Since docker runs as a vm on macos, you have to specify the memory. The docker uses 8 gigs of ram and was running out of memory. The solution was to boost the vm memory to 8 gigs and it worked fine...
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As i understand, docker use linux VM even i install it on windows OS.
So i agree that windows docker can execute linux container.
But then, how windows docker executes windows container?
Can i make container with other OS?
In other words, can i make container(having windows & windows app) and run it on linux docker?
As i know, docker does not support other OS in image, but it looks like some people is saying it is possible that make windows container and run it on linux.
Docker container shares just one kernel, is it possible?
To answer your questions:
That first statement is incorrect. Docker uses the underlying OS feature (container) to run its stack/daemon. The OS is responsible for instantiating the container itself. That means a Linux OS will instantiate a Linux container and Windows host will instantiate a Windows container. So, if you install Docker on Windows you don't have a Linux VM. Instead, you have the ability to instantiate Windows containers directly without the need to run Linux at all. To answer the question itself: The process is pretty much the same as Linux. You pull images with docker pull and then run them with docker run. You can also build images with docker build and everything else.
Windows containers can only run on Windows hosts (either Windows 10/11 or Windows Server). For Linux containers, that's not so strict. You can run Linux containers on Windows for development purposes, by leveraging the Windows Subsystem for Linux (WSL).
There's much more details on these on the Microsoft documentation page: https://cda.ms/4nN
I installed Docker for windows on a windows 10 box. It required me to enable the HyperV feature on it. Everything installed correctly and is running fine.
Although one thing took me by surprise. I am actually able to run a linux container on docker windows. I thought cross-containerization is not possible conceptually. Can anyone please help me understand how does this work?
HyperV is used to spin up a Linux VM to run containers. Docker is still running Linux containers under the covers, the native Windows containers are still being developed.
Basically, you are running a Linux Container on a Linux Machine rather than Windows. Windows runs a VM in Hyper-V when you download the Docker for Windows. You can open Hyper-V Manager and see a Linux VM will be running. Currently Docker for Windows is in beta which supports the Docker natively which needs Windows 10 build no. greater than 14393.222 or a Windows Server 2016.
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.