How to run armhf docker on x86

Docker Desktop
1

Hi,
i found a few setups on the web on how to get a armhf docker running on x86. I followed for example this:
https://matchboxdorry.gitbooks.io/matchboxblog/content/blogs/build_and_run_arm_images.html
and this

in short i created a debian12 VM an ran:

    sudo apt-get update && sudo apt-get install -y --no-install-recommends qemu-user-static binfmt-support
    sudo update-binfmts --enable qemu-arm
    sudo update-binfmts --display qemu-arm
    sudo apt-get install ca-certificates curl
    sudo install -m 0755 -d /etc/apt/keyrings
    sudo curl -fsSL https://download.docker.com/linux/debian/gpg -o /etc/apt/keyrings/docker.asc
    sudo chmod a+r /etc/apt/keyrings/docker.asc
    echo   "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/debian $(. /etc/os-release && echo "$VERSION_CODENAME") stable" |   sudo tee etc/apt/sources.list.d/docker.list > /dev/null
    sudo apt-get update
    sudo apt-get install docker
    sudo groupadd docker
    sudo usermod -aG docker $USER
    docker run --rm --privileged multiarch/qemu-user-static --reset -p yes -c yes

which succeded, i then try to run:

docker run -it --rm -v /usr/bin/qemu-arm-static:/usr/bin/qemu-arm-static arm32v7/debian /bin/sh

and

docker run -it --restart always     -v /usr/bin/qemu-arm-static:/usr/bin/qemu-arm-static     arm32v7/debian /bin/sh

which both wont run with the note that:

Unable to find image 'arm32v7/debian:latest' locally
latest: Pulling from arm32v7/debian
docker: no matching manifest for linux/amd64 in the manifest list entries.
See 'docker run --help'.

Iā€™d expect it not to use linux/amd64 but the armv7 stuff but it doesnā€™t.

ls /proc/sys/fs/binfmt_misc
python3.11       qemu-alpha  qemu-hexagon  qemu-microblaze    qemu-mips64    qemu-mipsn32    qemu-ppc      qemu-riscv32  qemu-sh4    qemu-sparc32plus  qemu-xtensaeb
qemu-aarch64     qemu-arm    qemu-hppa     qemu-microblazeel  qemu-mips64el  qemu-mipsn32el  qemu-ppc64    qemu-riscv64  qemu-sh4eb  qemu-sparc64      register
qemu-aarch64_be  qemu-armeb  qemu-m68k     qemu-mips          qemu-mipsel    qemu-or1k       qemu-ppc64le  qemu-s390x    qemu-sparc  qemu-xtensa       status

ls /usr/bin/qemu-arm-static 
/usr/bin/qemu-arm-static

I obviously am doing something wrong but can currently not see what. Can someone spot it?
Thanks

2

Use Dockerā€™s --platform option. You donā€™t need to mount any emulator into the container.

2 Likes
3

That is absolutely rigth, i just missed the --platform :slight_smile: thanks. Now when i run:

 docker run --platform=linux/arm64/v8 --rm debian:latest uname -m

its output is:

aarch64

But it seems to be VERY slow when trying to get a shell. Is that to be expected? For example when i run above command it returns almost immediately but when i try to get a bash in the container like

docker run --platform=linux/armhf --rm -t debian:latest /bin/bash
root@211244bce976:/# ls

it seems to be stuck. Allthough when ran directly it just returns fineā€¦

docker run --platform=linux/armhf --rm debian:latest ls
bin
boot
dev
etc
home
lib
media
mnt
opt
proc
root
run
sbin
srv
sys
tmp
usr
var
4

Emulation is never perfect and the performance will be worse than when you donā€™t emulate. Some applications cannot even run emulated.

When you run the ls command in the container, that indeed runs in a shell. When you run it directly through the docker run command, ls runs the /usr/bin/ls binary, directly. So it seems that the emulation of the armhf-based bash shell is slow on x86_64 systems.

1 Like
5

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