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Interactive Jobs

Overview

Interactive jobs allow users to directly access a compute node in real time — as if you were working on your personal computer, but with the power of HPC behind it.

Unlike batch jobs, which are queued and run in the background, interactive jobs open a live terminal session on a compute node. This is useful for:

  • Testing code or software modules
  • Debugging runtime issues
  • Running Jupyter notebooks
  • Exploring the system environment or dependencies

You still need to request resources via Slurm, but instead of submitting a script with sbatch, you request an interactive shell using our interative command.

The interactive Command

We provide a built-in shortcut command, interactive, that allows you to quickly and easily request a session in compute node.

The interactive command acts as a convenient wrapper for Slurm’s salloc command. Similar to sbatch, which is used for batch jobs, salloc is specifically designed for interactive jobs. 

$ interactive -h
Usage: interactive -a ACCOUNT -q QOS -j JOB_TYPE
Starts an interactive SLURM job with the required account and QoS settings.

Required options:
  -a ACCOUNT       Specify the account to use.
  -q QOS           Specify the quality of service (QoS).
  -j JOB_TYPE      Specify the type of job: 'cpu' for CPU jobs or 'gpu' for GPU jobs.

Example: Run an interactive GPU job with the 'test' account and 'test' QoS:
  /apps/site/bin/interactive -a test -q test -j gpu

This will launch an interactive job on the 'gpu' partition with the 'test' account and QoS 'test',
using 1 GPU, 1 CPU, and a walltime of 1 hour by default.

Optional parameters to modify resources:
  -n NTASKS        Specify the number of CPU tasks (Default: 1).
  -t WALLTIME      Specify the walltime in hours (Default: 1).
  -g GPU           Specify the number of GPUs (Only for GPU jobs, Default: 1).
  -p PARTITION     Specify the SLURM partition (Default: 'general' for CPU jobs, 'gpu' for GPU jobs).

Use '-h' to display this help message.


$ interactive -a $PI_UCID -q standard -j cpu
Starting an interactive session with the general partition and 1 core for 01:00:00 of walltime in standard priority
salloc: Pending job allocation 466577
salloc: job 466577 queued and waiting for resources
salloc: job 466577 has been allocated resources
salloc: Granted job allocation 466577
salloc: Nodes n0103 are ready for job
Use ssh or srun

srun ./myexe <input/output options> or ssh n0103

$ interactive -a $PI_UCID -q standard -j gpu
Starting an interactive session with the GPU partition, 1 core and 1 GPU for 01:00:00 of walltime in standard priority
salloc: Pending job allocation 466579
salloc: job 466579 queued and waiting for resources
salloc: job 466579 has been allocated resources
salloc: Granted job allocation 466579
salloc: Nodes n0048 are ready for job
Use ssh or srun

srun ./myexe <input/output options> or ssh n0048

$ interactive -a $PI_UCID -q debug -j cpu -p debug
Starting an interactive session with the debug partition and 1 core for 01:00:00 of walltime in debug priority
salloc: Pending job allocation 466581
salloc: job 466581 queued and waiting for resources
salloc: job 466581 has been allocated resources
salloc: Granted job allocation 466581
salloc: Waiting for resource configuration
salloc: Nodes n0127 are ready for job
Use ssh or srun.

srun ./myexe <input/output options> or ssh n0127

Replace $PI_UCID with PI's NJIT UCID. Now, once you get the confirmation of job allocation, you can either use srun or ssh to access the particular node allocated to the job.

Customizing Your Resources

Please note that, by default, this interactive session will request 1 core (for CPU jobs), 1 GPU (for GPU jobs), with a 1-hour walltime. To customize the resources, use the -h option for help. Run interactive -h for more details. Here is an explanation of each flag given below.

Flag Explanation Example
-a Mandatory option. This is followed by your group's name. Use quota_info to check the account/group name. -a $PI_UCID
-q Mandatory option. Used to access the priority -q standard
-j Mandatory option. Specify whether you want CPU or GPU node. -j cpu
-n Optional. The total number of CPUs. Default is 1 core unless specified. -n 1
-t Optional. The amount of walltime to reserve for your job in hours. Default is 1 hour unless specified. -t 1
-g Optional. The total number of GPUs. Default is 1 GPU unless specified. -g 1
-p Optional. Specify the name of the partition. (Default: general for CPU jobs, gpu for GPU jobs). -p debug

Warning

Login nodes are not designed for running computationally intensive jobs. You can use the head node to edit and manage your files, or to run small-scale interactive jobs. The CPU usage is limited per user on the head node. Therefore, for serious computing either submit the job using sbatch command or start an interactive session on the compute node.

Note

Please note that if you are using GPUs, check whether your script is parallelized. If your script is not parallelized and only depends on GPU, then you don't need to request more cores per node. In that case, do not use -n while executing the interactive command, as the default option will request 1 CPU per GPU. It's important to keep in mind that using multiple cores on GPU nodes may result in unnecessary CPU hour charges. Additionally, implementing this practice can make service unit accounting significantly easier.