In the middle of the desert you can say anything you want

03 Aug 2022

Slurm pyxis using a docker

If I sent you a link to this you probably want the TL;DR at the bottom


Previously: 220712-2208 Slurm creating modifiable persistent container

Problem: I have a docker image in a private docker registry that needs user/pass.

I need to use it in slurm’s pyxis.

The default srun --container-image .. syntax has no obvious place for a Docker registry user/pass.

Trying to use an image from a private registry does this:

$ srun --mem=16384 -c2 --gres=gpu:v100:2 --container-image comp/myimage:latest

slurmstepd: error: pyxis: child 2505947 failed with error code: 1
slurmstepd: error: pyxis: failed to import docker image
slurmstepd: error: pyxis: printing contents of log file ...
slurmstepd: error: pyxis:     [INFO] Querying registry for permission grant
slurmstepd: error: pyxis:     [INFO] Authenticating with user: <anonymous>
slurmstepd: error: pyxis:     [INFO] Authentication succeeded
slurmstepd: error: pyxis:     [INFO] Fetching image manifest list
slurmstepd: error: pyxis:     [INFO] Fetching image manifest
slurmstepd: error: pyxis:     [ERROR] URL[...] returned error code: 401 Unauthorized

Slurm’s pyxis1 uses enroot2 to do the container magic that includes interfacing with Docker.

enroot is installed on the box, Docker isn’t, I have no root access.

Option/attempt 1: Using enroot config to pass a credentials file

I need to pass through srun configs to enroot, so it can access the docker registry.

To pass credentials to it, create a credentials file in $ENROOT_CONFIG_PATH/.credentials:

# DockerHub
machine login <login> password <password>

That env var is not set in the base system, set it to /home/me/enroot/ and put the file there - same (no) result.

After googling, found this really detailed thread about the way pyxis handles environment variables: enroot/ at master · NVIDIA/enroot Especially this specific comment: pyxis doesn’t use environment variables defined in enroot .env files · Issue #46 · NVIDIA/pyxis

So basically, enroot and pyxis are behaving in opposite ways:

  • if a ‘dynamic’ env var is defined in enroot conf files, enroot passes it to the container, but not pyxis
  • if it’s not defined in enroot conf files, enroot doesn’t pass it to the container, but pyxis does.

I don’t have write access to the enroot config files, but the $ENROOT_CONFIG_PATH isn’t set there, I should be able to change it. No effect though.

Giving up for now, though that would’ve been the most beautiful solution.

Attempt 2: Get the image separately through enroot

I could use pure enroot to get the docker image, then pass the file to srun.

Run “Docker” Containers with NVIDIA Enroot

To use a oath authentication and a token you would need to sign-up/sign-in and create a token (which you can save for reuse) and then do the container import as,

enroot import 'docker://$'

Awesome, let’s create a token and try:

… okay, what’s the address of the docker hub? The one that’s default and ergo not used anywhere, but I need to pass it explicitly?..

Anyway let’s try to get bitnami/minideb from a public repo to pin the syntax down. returned 404s, trial and error led me to

[INFO] Querying registry for permission grant
[INFO] Permission granted
[INFO] Fetching image manifest list
[ERROR] Could not process JSON input
curl: (23) Failed writing body (1011 != 4220) actually asked me for a password!

enroot import 'docker://$'
[INFO] Querying registry for permission grant
[INFO] Authenticating with user: $token
Enter host password for user '$token':
[ERROR] URL returned error code: 401 Unauthorized

Without providing the token the image gets downloaded! Then I found index.docker.io3 that seems to be the correct one.

Okay, let’s get my private one

me@slurm-box:/slurm/me$ ENROOT_CONFIG_PATH=/home/me/enroot enroot import 'docker://' 

401 error unauthorized, still ignoring my .credentials or env variable pointing to it.

Docker username only:

enroot import 'docker://' 

Asks me for a password and then imports correctly! And creates a file called myimage.sqsh in the current dir.

Woohoo, working way to get docker images from private registry!

$ enroot start myimage.sqsh

enroot-nsenter: failed to create user namespace: Operation not permitted

Okay, so I’m not allowed to start them with enroot - not that I had any reason to.

 srun --mem=16384 -c4 --gres=gpu:v100:2 --container-image ./Docker/myimage.sqsh --container-mounts=/slurm/$(id -u -n)/data:/data --container-workdir /data  --pty bash

Drops me inside a shell in the container - it works!

Next step - using the Docker token.

Docker seems to see it as password replacement, this conflicts with official docus:

# Import Tensorflow 19.01 from NVIDIA GPU Cloud
$ enroot import --output tensorflow.sqsh 'docker://$'

On further googling - that’s a thing specific for, Docker Hub uses Docker stuff and I use that token as password replacement, period. Okay.

Had issues with mounting stuff as /data by default, but that specific bit is used in the docker image too - used something else.

The Dockerfile also has an ENTRYPOINT and sbin wants something to execute, true can be passed. Couldn’t get this to work, no true means sbin refuses to start, passing true makes it ignore the entrypoint altogether. --[no-]container-entrypoint from docu didn’t help - leaving for later.

Final line:

srun  --mem=16384 -c4 --gres=gpu:v100:2 --container-image ./Docker/myimage.sqsh --container-mounts=/slurm/$(id -u -n)/data:/SLURMdata --container-writable python3 -m trainer_module -i /data/ -o /SLURMdata/Checkpoints/ --config-file /SLURMdata/config.yaml


  • makes the image writable, so huggingface and friends can download stuff
  • makes /slurm/me/data available as /SLURMdata inside the image;
  • passes a config file to it that I have inside /data/config.yaml to the trainer (that accesses it as /SLURMdata/config.yaml)
  • runs the training on a dataset inside the directory that the Dockerfile puts inside /data in the image itself (the one that conflicted with mine earlier),
  • puts training results in a directory inside /SLURMdata which means it’s available to me after sbin is done in my /slurm/me/data directory.

TODO / for later

  • Try again to find a way to use a .credentials file, one command less to run then
  • How to run my docker image’s ENTRYPOINT

(More) resources


Two ways I found, passing credentials for the docker registry didn’t work, separately downloading the image and then running it did. Read the entire post if you want details on most of this.

Getting the image:

enroot import 'docker://' 

Replace mydockerusername with your docker username, comp with companyname and myimage with the name of the image.

It will ask you for your Docker pass or Personal Access Token.

Will download the image into a *.sqsh file in the current directory or whatever you pass through the -o parameter.

Running the image

srun  --mem=16384 -c4 --gres=gpu:v100:2 --container-image ./Docker/myimage.sqsh --container-mounts=/slurm/$(id -u -n)/data:/SLURMdata --container-writable your_command_to_run

# or - if you are running the thing I'm running - ...

srun  --mem=16384 -c4 --gres=gpu:v100:2 --container-image ./Docker/myimage.sqsh --container-mounts=/slurm/$(id -u -n)/data:/SLURMdata --container-writable python3 -m trainer_module -i /data/ -o /SLURMdata/Checkpoints/ --config-file /SLURMdata/config.yaml

In decreasing order of interest/generality:

  • pass the downloaded *.sqsh file to --container-image.
  • Environment variables get passed as-is in most cases. If you’d do docker run --env ENV_VAR_NAME, here you’d say ENV_VAR_NAME=whatever srun ... or just export ... it before running and it should work.
  • --container-writable is needed to make the filesystem writable, huggingface needs that to write cache files
  • --container-mounts
    • are /dir_in_your_fs:/dir_inside_docker_image
    • Make sure the Docker itself doesn’t have anything unexpected located at /dir_inside_docker_image

  1. NVIDIA/pyxis: Container plugin for Slurm Workload Manager ↩︎

  2. NVIDIA/enroot: A simple yet powerful tool to turn traditional container/OS images into unprivileged sandboxes. ↩︎

  3. How to change the default docker registry from to my private registry? - Stack Overflow ↩︎

Nel mezzo del deserto posso dire tutto quello che voglio.