Unexpected Behavior Analysis: git fetch origin master:master Does Not Update origin/master
Summary
Executing git fetch origin master:master failed to update origin/master despite fetching new commits
The operation showed ! [rejected] master -> master (non-fast-forward) and created new tags
FETCH_HEAD was successfully updated with the latest commit
Running git fetch origin master later updated origin/master as expected
No recent Git version change or configuration issues were detected
Root Cause
The refspec master:master explicitly targets the local branch named master (not origin/master)
The command attempted an unsafe (non-fast-forward) update to the local master branch, which did not have a direct lineage to the new commit (non-fast-forward rejection)
FETCH_HEAD always updates during fetch operations per Git’s design
origin/master only updates when:
Using git fetch origin (updates all tracking refs)
Or explicitly fetching to the tracking ref (git fetch origin master)
Why This Happens in Real Systems
Refspec misunderstandings are common due to Git’s dual ref concepts:
Remote-tracking refs (origin/master)
Local branches (master)
Production scripts often contain explicit refspecs for “efficiency”
Team members may run commands inconsistently (“fetch to local branch” vs “fetch to tracking ref”)
Infrastructure changes can cause unexpected commit histories (force-pushes, rebases)
