Running Interactive Jobs

Submitting an Interactive Job

Interactive sessions allow you to connect to a compute node and work on that node directly. This allows you to develop how your jobs might run (i.e. test that commands run as expected before putting them in a script) and do heavy development tasks that cannot be done on the login nodes (i.e. use many cores).

To launch an interactive job on MASSIVE, use the smux new-session command. Please note it will launch the job with the following defaults:

  • --ntasks=1 (1 cpu core)

  • memory=4G

  • time=2 hours

  • no other resources such as GPU

smux has a complete help available by typing smux -h or just smux. Commands such as new-session and attach-session can be abbreviated to n and a. It is designed to mirror the options used by tmux.

If you have a reservation and your reservation nodes are not in the default partition

smux new-session --reservation=hpl --partition=m3c

If you want to change default time to 2 days

smux new-session --time=2-00:00:00

If you need multi-core

smux new-session --ntasks=12

If you need two GPU cards

smux new-session --ntasks=2 --gres=gpu:2 --partition=m3c

Available partitions:


Types of GPU

Per node







If the job launches immediately (as it should most of the time) you will be connected automatically. If it does not launch immediately, you can use smux attach-session or just smux a once it has started.

How long do interactive jobs last for?

Interactive Jobs will remain active until “exit” or the job is cancelled

The mechanism behind the interactive job is:

  • User runs the smux new-session command

  • smux schedules a Slurm batch job to start a tmux session on a compute node

  • Slurm grants the user ssh access to the node

  • smux attach-session connects the user to the node and attaches to the tmux session

  • The job is completed whenever the tmux session ends or the job is cancelled

  • Therefore, an interactive job will not be automatically terminated unless the user manually ends the session.

To end a session:

  • Option 1: Run exit on the compute node. This terminates the smux job and returns you to the login node.

  • Option 2: Cancel the job directly (from compute nodes or login nodes) using scancel [JOBID].

Reconnecting to/Disconnecting from an Active Interactive Job

Since an interactive job is a tmux session, you can reconnect to/disconnect from it at any time. Here is a real-world scenario.

I am in the office and have an interactive job running (ID#70064). Now I plan to to home but I want to leave this job running so I can reconnect to it when I am home. The steps are:

  1. Disconnect the screen session for the existing interactive job. You can either just close your laptop or the terminal and walk away, or type “ctrl-b d” (That is, hold the ctrl key, and press the b key, release both keys then press the d key). ctrl-b is the standard tmux escape sequence, it can be changed.

  2. Now show_job to see if the job is still running:

JOBID          JOB NAME     Project         QOS      STATE    RUNNING      TOTAL   NODE                   DETAILS
                                                                TIME       TIME
70064         _interact     default      normal    Running         7   1-00:00      1                      m3a009
  1. Once I am home, I can reconnect

m3-login1:~ ctan$ smux a

Note: to access to the cluster node, first you need to ssh to the login nodes

Please visit Connecting to M3 for more information

  1. Continue working until the wall-time limit is reached, or I end the job.