GCHP Basic Example Run

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  1. Hardware and Software Requirements
  2. Downloading Source Code
  3. Obtaining a Run Directory
  4. Setting Up the GCHP Environment
  5. Compiling
  6. Basic Example Run
  7. Configuring a Run
  8. Output Data
  9. Developing GCHP
  10. Run Configuration Files


Overview

The default GCHP run directories are configured for a 1-hr simulation at c24 resolution using native resolution meteorology, six cores, and one node. This simple configuration is a good test case to check that GCHP runs on your system. This page presents the basic information needed to run GCHP for this test case.

Run Methods

You can run GCHP by executing the appropriate run command directly on the command line from within your run directory or by submitting your run as a batch job.

Running as a Batch Job (Recommended)

Sample run scripts are included in the runScriptSamples/ subdirectory for submitting your run as a scheduled job. All example run scripts send standard output to file GCHP.log by default and require manually configuring your job-specific resources such as number of cores and nodes. If using versions prior to 12.1.0 then you must also manually add your environment filename to the script. Unless otherwise noted in the run script filename, all sample run scripts assume use of SLURM (simple linux utility for resource management). If your system is not SLURM, you can adapt the sample run scripts to work on your system.

To submit your SLURM batch file, simply type:

 sbatch gchp.run

Job submission is different for other system. For example, to submit a Grid Engine batch file, type:

 qsub gchp.run

If your computational cluster uses a different job scheduler (e.g. LSF or PBS), then check with your IT staff about how to submit batch jobs.

Running Interactively

Before running GCHP interactively, check that your environment is set up properly and you have at least 6 cores available with 6G memory per core. Then execute the following command from within your run directory if using SLURM (you will need to adapt this for other systems):

srun -n 6 --mpi=pmi2 ./geos 2>&1 | tee GCHP.log

This command can be broken down as follows:

Command What it does
srun ... ./geos Runs executable geos as a parallel job
-n 6 Specifies how many individual CPU cores are requested for the run. The number given here should always be the total number of cores, regardless of how many nodes they are spread over. The number of CPUs that you request must be a multiple of 6 (at least one core for each of the cubed-sphere faces, and the same number of cores for each face).
--mpi-pmi2 Specifies usage of the MVAPICH2 implementation of MPI. Do not include this if not using MVAPICH2.
2>&1 | tee GCHP.log Specifies that all MAPL output, both standard and error, be written to both the screen and to file GCHP.log.

You can also adapt a GCHP run script for interactive use. Simply comment out the scheduler-specific code such as #SBATCH headers for SLURM.

Verifying a Successful Run

There are several ways to verify that your run was successful.

  1. NetCDF files are present in the OutputDir subdirectory.
  2. GCHP.log ends with timing information for the run.
  3. Your scheduler log (e.g. output from SLURM) does not contain any obvious errors.
  4. GCHP.log contains text with format "AGCM Date: YYYY/MM/DD Time: HH:mm:ss" for each timestep (e.g. 00:10, 00:20, 00:30, 00:40, 00:50, and 01:00 for a 1-hr run).

If it looks like something went wrong, check all log files (type "ls *.log" in run directory to list them) as well as your scheduler output file (if one exists) to determine where there may have been an error. Beware that if you have a problem in one of your configuration files then you will likely see a MAPL error with traceback to the GCHP/Shared directory. Review all of your configuration files to ensure you have proper setup.

GCHP errors can be cryptic. If you find yourself debugging within MAPL then you may be on the wrong track as most issues can be resolved by updating the run settings. Please send an email to the GEOS-Chem Support Team if you hit a wall deciphering the problem. You can also reach out the GCHP community in the GCHP Slack workspace.


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