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Starting an interactive node

Logged in to Bianca via a terminal

Below we describe the general ideas of using an interactive node:

To start an interactive node on specific cluster:

Types of nodes

The UPPMAX HPC clusters have three types of nodes:

What are nodes?

What nodes are, is described in general terms here.

  • login nodes: nodes where a user enters and interacts with the system
  • calculation nodes: nodes that do the calculations
Requesting a calculation to run

Requesting a calculation is described here. This is done by using the Slurm scheduler.

  • interactive nodes: a type of calculation node, where a user can do calculations directly
How can I find out on which node I am?

In a terminal, type hostname:

  • the login node has name rackham[number], where [number] is the number of the login node
  • an interactive node has name r[number], where [number] is the compute node number

As a login is shared with all users, there is a simple rule to use it fairly:

Only do short and light things on the login node

Examples of short and light things are:

  • Editing files
  • Copying, deleting, moving files
  • Scheduling jobs
  • Starting an interactive session

Examples of heavy things are:

  • Running code with big calculations
  • Develop code with big calculations line-by-line
Develop code with big calculations line-by-line

This usage is typically done an interactive node

When to use an interactive node

Some users develop computer code on an HPC cluster in a line-by-line fashion. These users typically want to run a (calculation-heavy) script frequently, to test if the code works.

However, scheduling each new line is too slow, as it can take minutes before the new code is run. Instead, there is a way to directly work with such code: use an interactive node.

An interactive node is a type of calculation node, where one can run heavy calculations directly.

flowchart TD
    UPPMAX(What to run on which node?)
    operation_type[What type of operation/calculation?]
    interaction_type[What type of interaction?]
    login_node(Work on login node)
    interactive_node(Work on interactive node)
    calculation_node(Schedule for calculation node)

    UPPMAX-->operation_type
    operation_type-->|light,short|login_node
    operation_type-->|heavy,long|interaction_type
    interaction_type-->|Direct|interactive_node
    interaction_type-->|Indirect|calculation_node