Login node

A login node is the computer where you arrive after logging in to an UPPMAX HPC cluster.

How does that look like?

Here is how it looks like to be on a login node:

A user on a login node, in this case on a Rackham login node called rackham4. The user used an SSH client and is in a console environment.

A user on a login node, in this case on the Bianca login node of his/her virtual cluster. This user logged in to the Bianca remote desktop via the website

A login node is a shared resource. With this diagram you can determine if you are alone on a login node:

flowchart TD
  question[Are you alone on the login node?]
  which_cluster[Which cluster?]
  alone_in_project[Are you alone in this project?]
  no[No\nYou share the login node with others]
  yes[Yes\nYou have the login node for yourself]
  question --> which_cluster
  which_cluster --> |Rackham| no
  which_cluster --> |Bianca| alone_in_project
  alone_in_project --> |yes| yes
  alone_in_project --> |no| no

Decision tree to determine if you are alone on a login node

Because usually you share a login node with others, this is the rule how to behave on a login node:

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, use the job scheduler instead
• Develop code with big calculations line-by-line, use an interactive node instead

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

Decision tree to determine which type of node you should probably work on

I work alone on a Bianca project. Can I use the login node for heavy things?

Yes!

Or, to be more precise: yes, if the login node is powerful enough for your calculations.

For example, when using RStudio on Bianca it is recommended to use two nodes (but one node does work).

So, if you can, use the login node. If you need more resources, either use the job scheduler or use an interactive node with more nodes than the login node has.