qemu-user-static

multiarch/qemu-user-static is to enable an execution of different multi-architecture containers by QEMU [1] and binfmt_misc [2]. Here are examples with Docker [3].

Getting started

$ uname -m
x86_64

$ docker run --rm -t arm64v8/ubuntu uname -m
standard_init_linux.go:211: exec user process caused "exec format error"

$ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes

$ docker run --rm -t arm64v8/ubuntu uname -m
aarch64

It works on many architectures and OS container images.

$ docker run --rm -t arm32v6/alpine uname -m
armv7l

$ docker run --rm -t ppc64le/debian uname -m
ppc64le

$ docker run --rm -t s390x/ubuntu uname -m
s390x

$ docker run --rm -t arm64v8/fedora uname -m
aarch64

$ docker run --rm -t arm32v7/centos uname -m
armv7l

$ docker run --rm -t ppc64le/busybox uname -m
ppc64le

For 32-bit container image, the result of uname can be the 64-bit's one. But it is 32-bit environment. Please see the example - junaruga/ci-multi-arch-test i386 case on Travis CI.

$ docker run --rm -t i386/ubuntu uname -m
x86_64

Podman [4] also works.

$ sudo podman run --rm --privileged multiarch/qemu-user-static --reset -p yes

$ podman run --rm -t arm64v8/fedora uname -m
aarch64

Singularity [5] also works.

$ sudo singularity run docker://multiarch/qemu-user-static --reset -p yes

$ singularity run --cleanenv docker://arm64v8/fedora uname -m
aarch64

Usage

multiarch/qemu-user-static images

multiarch/qemu-user-static images are managed on the Docker Hub container repository. The images have below tags.

Images

1. multiarch/qemu-user-static image
2. multiarch/qemu-user-static:$version images
3. multiarch/qemu-user-static:$from_arch-$to_arch images
4. multiarch/qemu-user-static:$from_arch-$to_arch-$version images
5. multiarch/qemu-user-static:$to_arch images
6. multiarch/qemu-user-static:$to_arch-$version images
7. multiarch/qemu-user-static:register image

Variables

• $version: Based QEMU's version.
• $from_arch: Host architecture
• $to_arch: Guest architecture

Description

• multiarch/qemu-user-static image container includes both a register script to register binfmt_misc entries and all the /usr/bin/qemu-$arch-static binary files in the container in it. multiarch/qemu-user-static image is an alias of the latest version of multiarch/qemu-user-static:$version images.
• multiarch/qemu-user-static:$to_arch images are aliases of multiarch/qemu-user-static:x86_64-$to_arch. multiarch/qemu-user-static:$to_arch images only include the $to_arch's /usr/bin/qemu-$to_arch-static binary file in it. multiarch/qemu-user-static:$to_arch image is an alias of the latest version of multiarch/qemu-user-static:$to_arch-$version images.
• multiarch/qemu-user-static:register image has only the register script binfmt_misc entries.

multiarch/qemu-user-static and multiarch/qemu-user-static:register images execute the register script that registers below kind of /proc/sys/fs/binfmt_misc/qemu-$arch files for all supported processors except the current one in it when running the container. See binfmt_misc manual [2] for detail of the files. As the /proc/sys/fs/binfmt_misc are common between host and inside of container, the register script modifies the file on host.

$ cat /proc/sys/fs/binfmt_misc/qemu-$arch
enabled
interpreter /usr/bin/qemu-$arch-static
flags: F
offset 0
magic 7f454c460201010000000000000000000200b700
mask ffffffffffffff00fffffffffffffffffeffffff

The --reset option is implemented at the register script that executes find /proc/sys/fs/binfmt_misc -type f -name 'qemu-*' -exec sh -c 'echo -1 > {}' \; to remove binfmt_misc entry files before register the entry. When same name's file /proc/sys/fs/binfmt_misc/qemu-$arch exists, the register command is failed with an error message "sh: write error: File exists".

$ docker run --rm --privileged multiarch/qemu-user-static [--reset][--help][-p yes][options]

On below image, we can not specify -p yes (--persistent yes) option. Because an interpreter's existance is checked when registering a binfmt_misc entry. As the interpreter does not exist in the container, the register script finshes with the error.

$ docker run --rm --privileged multiarch/qemu-user-static:register [--reset][--help][options]

Then the register script executes QEMU's scripts/qemu-binfmt-conf.sh script with options. You can check usage() in the file about the options.

Usage: qemu-binfmt-conf.sh [--qemu-path PATH][--debian][--systemd CPU]
                           [--help][--credential yes|no][--exportdir PATH]
                           [--persistent yes|no][--qemu-suffix SUFFIX]
       Configure binfmt_misc to use qemu interpreter
       --help:        display this usage
       --qemu-path:   set path to qemu interpreter ($QEMU_PATH)
       --qemu-suffix: add a suffix to the default interpreter name
       --debian:      don't write into /proc,
                      instead generate update-binfmts templates
       --systemd:     don't write into /proc,
                      instead generate file for systemd-binfmt.service
                      for the given CPU. If CPU is "ALL", generate a
                      file for all known cpus
       --exportdir:   define where to write configuration files
                      (default: $SYSTEMDDIR or $DEBIANDIR)
       --credential:  if yes, credential and security tokens are
                      calculated according to the binary to interpret
       --persistent:  if yes, the interpreter is loaded when binfmt is
                      configured and remains in memory. All future uses
                      are cloned from the open file.

You can run /usr/bin/qemu-$arch-static binary file` in the container.

$ docker run --rm -t multiarch/qemu-user-static:x86_64-aarch64 /usr/bin/qemu-aarch64-static -help
usage: qemu-aarch64 [options] program [arguments...]
Linux CPU emulator (compiled for aarch64 emulation)
...

$ docker run --rm -t multiarch/qemu-user-static:x86_64-aarch64 /usr/bin/qemu-aarch64-static -version
qemu-aarch64 version 4.0.0 (qemu-4.0.0-5.fc31)
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers


$ docker run --rm -t multiarch/qemu-user-static:aarch64 /usr/bin/qemu-aarch64-static -help
usage: qemu-aarch64 [options] program [arguments...]
Linux CPU emulator (compiled for aarch64 emulation)
...

$ docker run --rm -t multiarch/qemu-user-static:aarch64 /usr/bin/qemu-aarch64-static -version
qemu-aarch64 version 4.0.0 (qemu-4.0.0-5.fc31)
Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers

multiarch/qemu-user-static:$from_arch-$to_arch images are used with multiarch/qemu-user-static:register image. Because when the binfmt_misc entry is registered without -p option, the interpreter needs to be put in the container.

$ docker run --rm --privileged multiarch/qemu-user-static:register --reset

$ docker build --rm -t "test/integration/ubuntu" -<<EOF
FROM multiarch/qemu-user-static:x86_64-aarch64 as qemu
FROM arm64v8/ubuntu
COPY --from=qemu /usr/bin/qemu-aarch64-static /usr/bin
EOF

$ docker run --rm -t "test/integration/ubuntu" uname -m
aarch64

If you have qemu-$arch-static binary files on your local environment, you can set it to the container by docker -v volume mounted file.

$ docker run --rm --privileged multiarch/qemu-user-static:register --reset

$ docker run --rm -t arm64v8/ubuntu uname -m
standard_init_linux.go:211: exec user process caused "no such file or directory"

$ docker run --rm -t -v /usr/bin/qemu-aarch64-static:/usr/bin/qemu-aarch64-static arm64v8/ubuntu uname -m
aarch64

multiarch compatible images [DEPRECATED]

The concept of "compatible images" are deprecated because multiarch/qemu-user-static can build and run standard multi-architecture container images without the multiarch compatible images now. But you can refer the document Compatible images.

The compatible image is the one to add /usr/bin/qemu-$arch-static binary inside of the container based on the standard arch specific container. Last time, we could not register binfmt_misc entry with flags: F (persistent option). When flags: F was not set, the interpreter always needed to be existed inside of the container to run the arch container.

Contributing

We encourage you to contribute to multiarch/qemu-user-static! Please check out the Contributing to multiarch/qemu-user-static guide for guidelines about how to proceed.

See Developers guide for detail.

Supported host architectures

• x86_64

Currently qemu-user-static is not available on other host architectures such as aarch64. Run uname -m to check it on your environment.

Examples & articles

Please note that some examples using compatible images are deprecated.

See Examples & articles.

References

• [1] QEMU: https://www.qemu.org/
• [2] binfmt_misc: https://www.kernel.org/doc/html/latest/admin-guide/binfmt-misc.html
• [3] Docker: https://www.docker.com/
• [4] Podman: https://podman.io/
• [5] Singularity: https://sylabs.io/singularity/