# job_container/tmpfs

## Overview

job_container/tmpfs is an optional plugin that provides job-specific, private temporary file system space.

When enabled on the cluster, a filesystem namespace will be created for each job with a unique, private instance of /tmp and /dev/shm for the job to use. These directories can be changed with the Dirs= option in job_container.conf. The contents of these directories will be removed at job termination.

## Installation

This plugin is built and installed as part of the default build, no extra installation steps are required.

## Setup

Slurm must be configured to load the job container plugin by adding JobContainerType=job_container/tmpfs and PrologFlags=contain in slurm.conf. Additional configuration must be done in the job_container.conf file, which should be placed in the same directory as slurm.conf.

Job containers can be configured for all nodes, or for a subset of nodes. As an example, if all nodes will be configured the same way, you would put the following in your job_container.conf:

    AutoBasePath=true
    BasePath=/var/nvme/storage

A full description of the parameters available in the job_container.conf file can be found here.

## Initial Testing

An easy way to verify that the container is working is to run a job and ensure that the /tmp directory is empty (since it normally has some other files) and that "." is owned by the user that submitted the job.

    tim@slurm-ctld:~$ srun ls -al /tmp
    total 8
    drwx------  2 tim    root 4096 Feb 10 17:14 .
    drwxr-xr-x 21 root   root 4096 Nov 15 08:46 ..

While a job is running, root should be able to confirm that `/$BasePath/$JobID/_tmp` exists and is empty. This directory is bind mounted into the job. `/$BasePath/$JobID` should be owned by root, and is not intended to be accessible to the user.

## SPANK

This plugin interfaces with the SPANK api, and automatically joins the job's container in the following functions:

- spank_task_init_privileged()
- spank_task_init()

In addition to the job itself, the TaskProlog will also be executed inside the container.