Frequently asked questions

Nested containers

The simplest way to have a containerised job execute containers itself is to define a PROMINENCE task using the Singularity runtime and make use of udocker inside the Singularity container.

Below is a trivial example with a job which installs and runs a udocker container inside a Singularity container:

name: udocker-in-singularity
  nodes: 1
  cpus: 1
  memory: 1
  disk: 10
  - image: centos:7
    runtime: singularity
    cmd: |
      curl -L > udocker-1.3.1.tar.gz
      tar zxf udocker-1.3.1.tar.gz
      export PATH=`pwd`/udocker:$PATH
      udocker -q run eoscprominence/testpi

Of course, for real use cases a container image can be built with udocker pre-installed.

Resources allocated to a job

Using prominence describe it’s possible to see the resources (CPU cores, memory, disk and number of nodes) allocated to a job. This can be done both while a job is running and once it has completed. This information is available in the provisionedResources section of execution, for example:

  "execution": {
    "provisionedResources": {
      "cpus": 32,
      "disk": 10,
      "memory": 64,
      "nodes": 2

This can be particularly useful for jobs where fixed sets of resources were not specified.

Singularity apps

Singularity supports providing multiple apps within a single container (see e.g. this) and this is supported by PROMINENCE with a task app attribute. For example, here is an example running an app called foo:

  "resources": {
    "nodes": 1,
    "disk": 10,
    "cpus": 1,
    "memory": 1
  "name": "singularity-app-test",
  "tasks": [
      "image": "multiapp.sif",
      "runtime": "singularity",
      "app": "foo"