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 MonARCH, 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=<YourPartition>

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:k80:2

Available partitions:

Partition

Types of GPU

Per node

comp

P100

2

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 hast 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 go 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

monarch-login1:~ ctan$ smux a

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

Please visit Connecting to MonARCH for more information

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