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Login Nodes

Opening an SSH connection to NERSC systems results in a connection to a login node. Typically systems will have multiple login nodes which sit behind a load balancer. New connections will be assigned a random node. If an account has recently connected the load balancer will attempt to connect to the same login node as the previous connection.

Usage

Appropriate Use

Do not run compute or memory intensive applications on login nodes. These nodes are a shared resource. NERSC may terminate processes which are having negative impacts on other users or the systems.

  • compile codes (limit to e.g. make -j 8)
  • edit files
  • submit jobs

Some workflows require interactive use of applications such as IDL, MATLAB, NCL, python, and ROOT. For small datasets and short runtimes it is acceptable to run these on login nodes. For extended runtimes or large datasets these should be run in the batch queues.

Tip

An interactive qos is available on Cori for compute and memory intensive interactive work.

Data transfers

If you need to do a large number of data transfers use a dedicated xfer queue.

Guidelines

  • do not use more than 50% of the cores (command: lstopo -p --only core | wc -l)
  • do not use more than 25% of the memory (command: free -m)
  • avoid the watch command
  • avoid long running commands