This lesson is being piloted (Beta version)



Teaching: 30 min
Exercises: 15 min
  • How can I handle errors/warnings?

  • Fix a broken recipe

Every user encounters errors. Once you know why you get certain types of errors, they become much easier to fix. The good news is, ESMValTool creates a record of the output messages and stores them in log files. They can be used for debugging or monitoring the process. This lesson helps to understand what the different types of errors are and when you are likely to encounter them.

Log files

Each time we run ESMValTool, it will produce a new output directory. This directory should contain the run folder that is automatically generated by ESMValTool. To examine this, we run a recipe_example.yml that can be found in Setup. Let’s download it to our working directory esmvaltool_tutorial that was created during the Configuration.

In a new terminal, go to our working directory esmvaltool_tutorial where the file recipe_example.yml is located and run the recipe:

  cd esmvaltool_tutorial
  esmvaltool run recipe_example.yml
esmvaltool: command not found

ESMValTool encounters this error because the conda environment esmvaltool has not been activated. To fix the error, before running the recipe, activate the environment:

conda activate esmvaltool

conda environment

More information about the conda environment can be found at Installation.

Let’s change the working directory to the folder run and list its files:

  cd esmvaltool_output/recipe_example_#_#/run
diag_timeseries_temperature  main_log_debug.txt   main_log.txt  recipe_example.yml   resource_usage.txt

In the main_log_debug.txt and main_log.txt, ESMValTool writes the output messages, warnings and possible errors that might happen during pre-processings. To inspect them, we can look inside the files. For example:

  cat main_log.txt

Now, let’s have a look inside the folder diag_timeseries_temperature:

  cd diag_timeseries_temperature/timeseries_diag
log.txt  resource_usage.txt  settings.yml

In the log.txt, ESMValTool writes the output messages, warnings and possible errors that are related to the diagnostic script.

If you encounter an error and don’t know what it means, it is important to read the log information. Sometimes knowing where the error occurred is enough to fix it, even if you don’t entirely understand the message. However, note that you may not always be able to find the error or fix it. In that case, ESMValTool community helps you figure out what went wrong.

Different log files

In the run directory, there are two log files main_log_debug.txt and main_log.txt. What are their differences?


The main_log_debug.txt contains the output messages from the pre-processor whereas the main_log.txt shows general errors and warnings that might happen in running the recipe and diagnostics script.

Let’s change some settings in the recipe to run a regional pre-processor. We use a text editor called nano to open the recipe file:

  cd ~/esmvaltool_tutorial
  nano recipe_example.yml

Text editor side note

No matter what editor you use, you will need to know where it searches for and saves files. If you start it from the shell, it will (probably) use your current working directory as its default location. We use nano in examples here because it is one of the least complex text editors. Press ctrl + O to save the file, and then ctrl + X to exit nano.

See the recipe_example.yml

01    # ESMValTool
02    # recipe_example.yml
03    ---
04    documentation:
05      description: Demonstrate basic ESMValTool example
07      authors:
08        - demora_lee
09        - mueller_benjamin
10        - swaminathan_ranjini
12      maintainer:
13        - demora_lee
15      references:
16        - demora2018gmd
17        # Some plots also appear in ESMValTool paper 2.
19      projects:
20        - ukesm
22    datasets:
23      - {dataset: HadGEM2-ES, project: CMIP5, exp: historical, mip: Omon, ensemble: r1i1p1, start_year: 1859, end_year: 2005}
25    preprocessors:
26      prep_timeseries:  # For 0D fields
27        annual_statistics:
28          operator: mean
30    diagnostics:
31      # --------------------------------------------------
32      # Time series diagnostics
33      # --------------------------------------------------
34      diag_timeseries_temperature:
35        description: simple_time_series
36        variables:
37          timeseries_variable:
38            short_name: thetaoga
39            preprocessor: prep_timeseries
40        scripts:
41          timeseries_diag:
42            script: ocean/

Keys and values in recipe settings

The ESMValTool pre-processors cover a broad range of operations on the input data, like time manipulation, area manipulation, land-sea masking, variable derivation, etc. Let’s add the preprocessor extract_region to the section prep_timeseries:

25    preprocessors:
26      prep_timeseries:  # For 0D fields
27        annual_statistics:
28          operator: mean
29        extract_region:
30          start_longitude: -10
31          end_longitude: 40
32          start_latitude: 27
33          end_latitude: 70

Also, we change the projects value ukesm to tutorial:

19      projects:
20        - tutorial

Then, we save the file and run the recipe:

  esmvaltool run recipe_example.yml
ValueError: Tag 'tutorial' does not exist in section 'projects' of esmvaltool/config-references.yml
2020-06-29 18:09:56,641 UTC [46055] INFO    If you suspect this is a bug or need help,
please open an issue on and
attach the run/recipe_*.yml and run/main_log_debug.txt files from the output directory.

The values for the keys author, maintainer, projects and references in the recipe should be known by ESMValTool:

ESMValTool can’t locate the data

You are assisting a colleague with ESMValTool. The colleague replaces the CMIP5 entry in project: CMIP5 to CMIP6 and runs the recipe. However, ESMValTool encounters an error like:

esmvalcore._recipe_checks.RecipeError: Missing data
2020-06-29 17:26:41,303 UTC [43830] INFO    If you suspect this is a bug or need help,
please open an issue on and
attach the run/recipe_*.yml and run/main_log_debug.txt files from the output directory.

What suggestions would you give the researcher for fixing the error?


  1. Inspect main_log.txt
  2. Check user-config.yml to see if the correct directory for input data is introduced
  3. Check the available data, regarding exp, mip, ensemble, start_year, and end_year
  4. Check the variable name in the diag_timeseries_temperature section in the recipe

Check pre-processed data

The setting save_intermediary_cubes in the configuration file can be used to save the pre-processed data. More information about this setting can be found at Configuration.


Note that this setting should be only used for debugging, as it significantly slows down the recipe and increases disk usage because a lot of output files need to be stored.

Check diagnostic script path

The result of the pre-processor is passed to the script, that is introduced in the recipe as:

40        scripts:
41          timeseries_diag:
42            script: ocean/

The diagnostic scripts are located in the folder diag_scripts in the ESMValTool installation directory <path_to_esmvaltool>. To find where ESMValTool is located on your system, see Installation.

Let’s see what happens if we can change the script path as:

40        scripts:
41          timeseries_diag:
42            script: diag_scripts/ocean/
  esmvaltool run recipe_example.yml
esmvalcore._task.DiagnosticError: Cannot execute script 'diag_scripts/examples/' (esmvaltool/diag_scripts/diag_scripts/examples/ file does not exist.
2020-06-29 20:39:31,669 UTC [53008] INFO    If you suspect this is a bug or need help, please open an issue on and attach the run/recipe_*.yml and run/main_log_debug.txt files from the output directory.

The script path should be relative to diag_scripts directory. It means that the script is located in <path_to_esmvaltool>/diag_scripts/ocean/. Alternatively, the script path can be an absolute path. To examine this, we can download the script from the ESMValTool repository:


One way to get the absolute path is to run:

readlink -f

Then we can update the script path and run the recipe:

40        scripts:
41          timeseries_diag:
42            script: <path_to_script>/
  esmvaltool run recipe_example.yml

Now examine ./esmvaltool_output/recipe_example_#_#/run/diag_timeseries_temperature/timeseries_diag/ to see if it worked!

Available recipe and diagnostic scripts

ESMValTool provides a broad suite of recipes and diagnostic scripts for different disciplines like atmosphere, climate metrics, future projections, IPCC, land, ocean, ….

Re-running a diagnostic

Look at the main_log.txt file and answer the following question: How to re-run the diagnostic script?


The main_log.txt file contains information on how to re-run the diagnostic script without re-running the pre-processors:

2020-06-29 20:36:32,844 UTC [52810] INFO    To re-run this diagnostic script, run:

If you run the command in the next line, you will be able to re-run the diagnostic.

Memory issues

If you run out of memory, try setting max_parallel_tasks to 1 in the configuration file. Then, check the amount of memory you need for that by inspecting the file run/resource_usage.txt in the output directory. Using the number there you can increase the number of parallel tasks again to a reasonable number for the amount of memory available in your system.

Key Points

  • There are three different kinds of log files: main_log.txt, and main_log_debug.txt and log.txt.