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README_GITFLEXIMOD.rst

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Obtaining the full model code and associated scripting infrastructure

CTSM is released via GitHub. You will need some familiarity with git in order to modify the code and commit these changes. However, to simply checkout and run the code, no git knowledge is required other than what is documented in the following steps.

To obtain the CTSM code you need to do the following:

  1. Clone the repository.

    git clone https://github.com/ESCOMP/CTSM.git my_ctsm_sandbox

    This will create a directory my_ctsm_sandbox/ in your current working directory.

  2. Run ./bin/git-fleximod update.

    cd my_ctsm_sandbox
./bin/git-fleximod update
./bin/git-fleximod --help  # for a user's guide

    git-fleximod is a package manager that will populate the ctsm directory with the relevant versions of each of the components along with the CIME infrastructure code. Additional documentation for git-fleximod appears here: https://github.com/ESMCI/git-fleximod?tab=readme-ov-file#git-fleximod

"components" here refers to seperate git repositories for seperable parts of the code (such as the MOSART or mizuRoute river models). Because they are managed with "submodule" in git hereafter we will refer to them as "submodule(s)".

At this point you have a working version of CTSM.

To see full details of how to set up a case, compile and run, see the CIME documentation at http://esmci.github.io/cime/ .

More details on git-fleximod

The file .gitmodules in your top-level CTSM directory tells git-fleximod which tag/branch of each submodule should be brought in to generate your sandbox.

NOTE: If you manually modify a submodule without updating .gitmodules, e.g. switch to a different tag, then rerunning git-fleximod will warn you of local changes you need to resolve. git-fleximod will not change a modified submodule back to what is specified in .gitmodules without the --force option. See below documentation Customizing your CTSM sandbox for more details.

You need to rerun git-fleximod whenever .gitmodules has changed (unless you have already manually updated the relevant submodule(s) to have the correct branch/tag checked out). Common times when this is needed are:

  • After checking out a new CTSM branch/tag
  • After merging some other CTSM branch/tag into your currently checked-out branch

Customizing your CTSM sandbox

There are several use cases to consider when you want to customize or modify your CTSM sandbox.

Switching to a different CTSM branch or tag

If you have already checked out a branch or tag and HAVE NOT MADE ANY MODIFICATIONS it is simple to change your sandbox. Say that you checked out ctsm1.0.0 but really wanted to have ctsm1.1.0; you would simply do the following:

git checkout ctsm1.1.0
./bin/git-fleximod update

You should not use this method if you have made any source code changes, or if you have any ongoing CTSM cases that were created from this sandbox. In these cases, it is often easiest to do a second git clone.

Pointing to a different version of a submodule

Each entry in .gitmodules has the following form (we use CIME as an example below):

[submodule "cime"]
path = cime
url = https://github.com/ESMCI/cime
fxtag = cime6.0.246
fxrequired = ToplevelRequired
fxDONOTUSEurl = https://github.com/ESMCI/cime

Each entry specifies either a tag or a hash. To point to a new tag or hash:

  1. Modify the relevant entry/entries in .gitmodules (e.g., changing cime6.0.246 to cime6.0.247 above)

  2. Checkout the new submodule(s):

    ./bin/git-fleximod update <submodule>

Keep in mind that changing individual submodule from a tag may result in an invalid model (won't compile, won't run, not scientifically meaningful) and is unsupported.

Committing your change to .gitmodules

After making this change, it's a good idea to commit the change in your local CTSM git repository. First create a branch in your local repository, then commit it. Feel free to create whatever local branches you'd like in git. For example:

git checkout -b my_ctsm_branch
git add .gitmodules
git commit -m "Update CIME to cime6.0.247"