Git submodules

Git Submodules

A submodule pins a specific commit of an external repo. .gitmodules stores URL+path; the super tree records the SHA as a gitlink.

Cloning

git clone --recurse-submodules <url>       # preferred
git submodule update --init --recursive    # after a plain clone

Plain clone creates empty dirs. update without --init silently skips new ones.

Default Update = Detached HEAD

git submodule update checks out the pinned SHA detached. Work there is lost on next update unless committed to a branch.

Proper edit flow:

cd sub && git checkout main
# edit, commit, push from inside sub first
cd .. && git add sub && git commit         # bump super pin

Track a Branch

git config -f .gitmodules submodule.sub.branch main
git submodule update --remote --merge      # fetch + merge
git submodule update --remote --rebase     # fetch + rebase

--remote alone drops to detached HEAD — loses local work.

Global Defaults

git config --global submodule.recurse true         # applies to pull/checkout/reset (NOT clone)
git config --global push.recurseSubmodules check
git config --global status.submodulesummary 1

Push Safety

git push --recurse-submodules=check        # fail if sub commits unpushed
git push --recurse-submodules=on-demand    # push subs first

Without this you push a super pointing to a SHA that doesn't exist remotely.

Batch

git submodule foreach 'git fetch --all'
git submodule foreach --recursive 'git status -sb'

Conflicts & URL Moves

Both sides bumped pin:

cd sub && git merge <their-sha>
cd .. && git add sub && git commit

.gitmodules URL changed upstream:

git submodule sync --recursive
git submodule update --init --recursive

Removing

git submodule deinit -f path/sub
git rm -f path/sub
rm -rf .git/modules/path/sub

Pitfalls

• Forgetting to push the sub before the super — the #1 submodule bug.
• submodule.recurse=true does not affect git clone.
• Converting a subdir to a submodule: git rm -r dir then git submodule add (not rm -rf).