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Login Node Guidelines

Login nodes (also called head nodes) are the entry point to the ACE cluster. They are shared among all users and have limited resources. Running computational work on login nodes degrades the experience for everyone and may result in account suspension.

What Login Nodes Are For​

Login nodes are designed for lightweight, preparatory tasks:

  • Editing files - Using text editors like vim, nano, or emacs
  • Compiling code - Small compilation tasks (not parallel builds)
  • Managing files - Organizing directories, moving files
  • Submitting jobs - Using sbatch, squeue, scancel
  • Monitoring jobs - Checking job status and output
  • Small file transfers - Using scp, rsync, or sftp

What NOT to Do on Login Nodes​

Prohibited Activities

The following activities are not allowed on login nodes:

Running Research Applications​

Do not launch computational software directly on login nodes:

# DON'T do this on login nodes
python my_simulation.py
matlab -batch "run_analysis"
R --vanilla < analysis.R
./my_program

Instead, submit these as SLURM batch jobs or request an interactive session.

Parallel Compilation​

Avoid resource-intensive compilation commands:

# DON'T do this on login nodes
make -j 16
ninja -j 8

Instead, use single-threaded compilation on login nodes or submit compilation as a job:

# OK on login nodes
make -j 2

# Better: submit as a job for large builds
sbatch compile_job.sh

Long-Running Processes​

Do not run processes that take more than a few minutes:

# DON'T leave these running on login nodes
nohup long_process &
screen -S mysession  # for computational work

Excessive Resource Monitoring​

Avoid polling job status too frequently:

# DON'T do this
watch -n 1 squeue -u $USER  # Every second is too frequent

# OK - check every few minutes
squeue -u $USER

Using Interactive Sessions​

If you need an interactive environment for testing or development, request compute resources through SLURM:

# Request an interactive session
srun --nodes=1 --ntasks=1 --time=01:00:00 --pty bash

# Or use salloc for more control
salloc --nodes=1 --ntasks=4 --time=02:00:00

This gives you dedicated compute resources without impacting other users.

VSCode and IDEs​

VSCode Users

Running VSCode Remote SSH on login nodes consumes significant resources and can interfere with other users. This may result in account suspension.

Recommended alternatives:

  1. Use VSCode on your local machine - Edit files locally and sync with the cluster
  2. Request an interactive session - Connect VSCode to a compute node
  3. Use terminal-based editors - vim, nano, or emacs on login nodes

How We Monitor Login Node Usage​

The ACE team monitors login node resource usage. Users running prohibited activities may receive:

  1. An automated warning
  2. Process termination
  3. Temporary account suspension for repeated violations