It has been mentioned that when employing x86_64 Docker images on an M1 Mac, when no ARM64 image is available, that container will start under qemu
emulation for compatibility. (At the cost of performance.)
Often times when I'm running a collection of containers (and integration tests against the lot), I'll see qemu-system-aarch64
pegging a few cores.
My question: How can I determine, for a given list of running containers (ie. docker ps
), which ones are running natively and which are being emulated?
This is true also for Docker running on amd64
CPU, when the image is build for arm64
, and the whole mechanism is explained in this SO
The mechanism for emulation is using the information in the elf
to recognize the architecture for which the process is build, and if the architecture of the binary differs from the architecture of the CPU, it starts the qemu
emulation. Though the recognizing of the architecture is more related to the process, there is still information about the targeted architecture of the docker image. The targeted architecture is determined from the "Architecture" flag on the image which was set when the image was build. Any of the containers that will run the image will be associated (trough the image) with this flag.
It should be noted that the "Architecture" flag on the image will not prevent a single process inside the image, which is compiled for a different architecture than the flagged one to run. The reason for this is that bitfmt
(which is the underlying mechanism sitting inside the linux kernel) will always try to recognize the architecture from the magic
numbers of the elf
and will start the the emulation if the magic
number is recognized.
To list the architecture of the containers, you can use the following "quick" query:
for i in `docker ps --format "{{.Image}}"` ; do docker image inspect $i --format "$i -> {{.Architecture}} : {{.Os}}" ;done
The command will print the container name, the architecture and the os of the image.
To avoid typing this command multiple times, you can add alias in .bashrc
as follows:
alias docker-arch-ps='for i in `docker ps --format "{{.Image}}"` ; do docker image inspect $i --format "$i -> {{.Architecture}} : {{.Os}}" ;done';
After this, you can use simple docker-arch-ps
to get the list of the containers and their architecture.
As an improvement of the @jordanvrtanoski's answer, I've done two additional commands
docker-ps-arch
:
#!/bin/bash
OPT=$@
set -euo pipefail
docker container ls $OPT --format "{{.ID}}\t{{.Image}}\t{{.Command}}\t{{.Status}}\t{{.Names}}" |
awk -F '\t' 'BEGIN {OFS=FS} { "docker image inspect --format \"{{.Os}}/{{.Architecture}}\" "$2" #"NR | getline $6; print }' |
column --table --table-columns "CONTAINER ID,IMAGE,COMMAND,STATUS,NAME,ARCH" -o ' ' -s $'\t'
and docker-images-arch
:
#!/bin/bash
OPT=$@
set -euo pipefail
docker image ls $OPT --format "{{.Repository}}\t{{.Tag}}\t{{.ID}}\t{{.Size}}" |
awk -F '\t' 'BEGIN {OFS=FS} { "docker image inspect --format \"{{.Os}}/{{.Architecture}}\" "$3" #"NR | getline $5; print }' |
column --table --table-columns "REPOSITORY,TAG,IMAGE ID,SIZE,ARCH" -o ' ' -s $'\t'
They produce outputs close to the original commands and support options of docker container ls
and docker image ls
.
$ docker-ps-arch -a
CONTAINER ID IMAGE COMMAND STATUS NAME ARCH
261767e38db2 hello-world "/hello" Exited (0) About an hour ago practical_moore linux/amd64
16e364572d08 18e5af790473 "/hello" Exited (0) 3 hours ago peaceful_lalande linux/arm64
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