git push: Pushing Commits to a Remote, the -u Flag, and Tracking Branches

Once your local commits exist and a remote is connected (this module's earlier lessons), `git push` is how those commits actually reach a hosted repository like GitHub, making them visible and available to collaborators. This lesson covers the basic push operation, the important `-u` flag that establishes an ongoing tracking relationship, and what that relationship actually enables going forward.

Learning Objectives

Push local commits to a remote repository using git push.
Understand and use the -u (--set-upstream) flag on a branch's first push.
Explain what a tracking branch is and how it simplifies future push/pull commands.
Recognize a common cause of a rejected push and what it signals.

Key Terms to Know Before Learning git push

git push: A command that uploads local commits on a branch to a corresponding branch on a remote repository.
-u / --set-upstream: A flag used with git push that establishes a tracking relationship between a local branch and a remote branch, remembered for future commands.
Tracking branch (upstream branch): A local branch configured to have a direct, remembered association with a specific remote branch, enabling plain git push and git pull without specifying the remote or branch each time.
Rejected push: A push that Git refuses because the remote branch has commits the local branch doesn't have, requiring a pull/merge (or rebase) before pushing can succeed.

How git push Actually Works

The basic form of `git push` explicitly specifies both the remote and the branch:

```
git push origin main
```

This uploads any local commits on `main` that don't yet exist on `origin`'s version of `main`, making them available to anyone else with access to that repository.

The first time you push a *new* local branch that has no corresponding branch yet on the remote, it's standard practice to include the `-u` (or `--set-upstream`) flag:

```
git push -u origin main
```

This does two things: it performs the push exactly as before, and it additionally establishes a **tracking relationship** (also called an upstream) between your local `main` branch and `origin`'s `main` branch. Once this relationship is set, Git remembers it permanently for that branch — meaning every future push or pull for this branch can simply be:

```
git push
git pull
```

with no need to specify `origin main` every single time, since Git already knows, from the established tracking relationship, exactly which remote branch this local branch corresponds to. Without ever setting this relationship (i.e., always omitting `-u`), you'd need to explicitly type `origin main` (or whatever the appropriate remote/branch is) on every single push and pull, which quickly becomes tedious.

A very common situation, especially once collaborators are involved, is a **rejected push**:

```
git push
! [rejected] main -> main (fetch first)
error: failed to push some refs to '...'
hint: Updates were rejected because the remote contains work that you do not have locally.
```

This happens when the remote branch has commits that your local branch doesn't have — typically because a collaborator pushed their own changes since you last synchronized. Git deliberately refuses to overwrite that unknown remote work; the message's hint (`fetch first`) is directing you toward the tools covered in the next lesson (`git fetch` and `git pull`), which retrieve those remote changes so they can be properly incorporated (via merge or rebase) into your local branch before you attempt to push again. This rejection is a *safety feature*, not an error to force past — Git is explicitly protecting against silently overwriting a collaborator's work that you haven't yet seen or reconciled with.

git push and Tracking Branches: Visual Walkthrough

Draw a local branch icon labeled 'main (local)' with an arrow labeled 'git push -u origin main (first time)' pointing to a remote branch icon labeled 'main (origin)'. Beneath, show a small linking icon connecting the two, captioned 'Tracking relationship established — remembered for future pushes/pulls.' Below that, show a simplified second diagram: after the tracking relationship exists, a much shorter arrow labeled simply 'git push' (no arguments needed) pointing the same direction, captioned 'Git already knows which remote branch this corresponds to.'

git push Variants: Quick Reference Table

Command	When to Use	Effect
git push origin main	Any push, remote/branch specified explicitly	Uploads local commits to origin's main branch
git push -u origin main	The FIRST push of a new local branch	Pushes AND establishes a tracking relationship for future use
git push (no arguments)	Any push after a tracking relationship is already set	Uses the remembered remote/branch automatically
Rejected push (fetch first)	Remote has commits your local branch lacks	Git refuses to overwrite unknown remote work — fetch/pull first

git push: Command Syntax and Examples

# First push of a new local branch — establish the tracking relationship
git push -u origin main

# After the tracking relationship exists, future pushes can omit the remote/branch
git push

# Confirm the tracking relationship for the current branch
git branch -vv
# * main  a1b2c3d [origin/main] Latest commit message

# Example of a rejected push (someone else pushed since your last sync)
git push
# ! [rejected]        main -> main (fetch first)
# error: failed to push some refs to '...'
# hint: Updates were rejected because the remote contains work that you do not have locally.

Breaking Down the git push Example

`git push -u origin main` is shown as the correct first-time push for a new branch, both uploading the commits and setting up the tracking relationship. The subsequent plain `git push` demonstrates the convenience this relationship provides — no arguments needed. `git branch -vv` (verbose, twice) is a useful way to directly confirm a branch's tracking relationship, shown here as `[origin/main]` next to `main`. The final block shows a realistic rejected push, with Git's own hint (`fetch first`) pointing toward the correct next step — retrieving and reconciling the remote's unknown commits before attempting to push again, which is exactly the subject of the next lesson.

How git push Is Used on Real Engineering Teams

Nearly every 'getting started' guide for a new GitHub repository explicitly includes the git push -u origin main command as one of the very first steps after creating a project.
Rejected pushes are an extremely common, everyday occurrence on any team with more than one active contributor, making comfort with the fetch-then-integrate workflow a core, practical skill rather than an edge case.
IDE Git integrations (VS Code, IntelliJ) often automatically include the equivalent of the -u flag behind their 'Publish Branch' or similar UI buttons, handling the tracking relationship setup without the developer needing to type the flag manually.
CI/CD systems monitoring specific branches rely on the concept of tracking relationships (and their remote equivalents) to know which local branch state corresponds to which remote branch for triggering builds.

git push Interview Questions and Answers

Q1. What does the -u flag do when used with git push, and why is it typically used on the first push of a new branch?

The -u (or --set-upstream) flag both performs the push and establishes a tracking relationship between the local branch and the specified remote branch. This relationship is remembered by Git, allowing all future push and pull commands on that branch to omit the remote and branch name, since Git already knows the correspondence.

Q2. What does it mean when a git push is rejected with a 'fetch first' message?

It means the remote branch contains commits that your local branch doesn't have, typically because someone else pushed changes since you last synchronized. Git refuses to overwrite this unknown remote work, and the hint directs you to fetch (and then merge or rebase) those changes locally before attempting to push again.

Q3. How can you check whether your current local branch has a tracking relationship set up?

Run git branch -vv, which shows each local branch along with its tracking remote branch (if one is configured), displayed in brackets like [origin/main], confirming the relationship established by a prior git push -u or equivalent.

git push Quiz: Test Your Understanding

1. What does the -u flag in git push -u origin main accomplish?

It deletes the remote branch before pushing
It pushes the commits and establishes a tracking relationship for future push/pull commands
It forces the push even if there are conflicts
It only works for private repositories

Answer: B. It pushes the commits and establishes a tracking relationship for future push/pull commands

Explanation: The -u (--set-upstream) flag both performs the push and remembers the association between the local and remote branch, simplifying all future push/pull commands for that branch.

2. What does a 'rejected push' with a 'fetch first' message indicate?

Your local repository is corrupted
The remote branch has commits your local branch does not have yet
You have not configured a remote at all
Your commit messages are not formatted correctly

Answer: B. The remote branch has commits your local branch does not have yet

Explanation: Git rejects the push specifically to prevent overwriting commits that exist on the remote but not locally, prompting you to fetch and reconcile those changes first.

3. Once a tracking relationship is established for a branch, what can you typically omit from future push commands?

The git command itself
The remote name and branch name (e.g., just running git push)
The commit message
The .git folder

Answer: B. The remote name and branch name (e.g., just running git push)

Explanation: With a tracking relationship in place, Git remembers which remote branch corresponds to the current local branch, allowing plain git push (with no arguments) to work correctly.

Common git push Mistakes Beginners Make

Forgetting the -u flag on a branch's first push, resulting in needing to type the full remote and branch name on every subsequent push and pull.
Treating a rejected push as an error to force past (e.g., with a careless force-push) rather than understanding it as a safety feature protecting unseen remote work.
Not realizing git branch -vv can directly confirm a branch's tracking relationship, and instead guessing or assuming one exists.
Confusing a rejected push (a normal, expected part of collaboration) with a merge conflict — a rejected push happens before any merging is even attempted, simply because the remote has unknown commits.

git push: Exam-Ready Quick Notes

git push origin <branch>: explicit push. git push -u origin <branch>: push + establish tracking relationship.
Once tracking is set, plain git push / git pull work without specifying remote/branch.
Rejected push ('fetch first'): remote has commits the local branch lacks; requires fetch + merge/rebase before pushing again.
git branch -vv: shows each local branch's tracking relationship, if one is configured.

git push: Key Takeaways

git push -u is the standard way to both upload a new branch's commits and set up a lasting tracking relationship for future convenience.
Once established, a tracking relationship lets plain git push and git pull work without repeatedly specifying the remote and branch.
A rejected push is Git's safety mechanism protecting against overwriting unseen remote work, not an error to be forced past carelessly.

Frequently Asked Questions About git push

Q1. What does git push do?

It uploads your local commits on a branch to the corresponding branch on a remote repository, such as GitHub, making them visible and available to anyone else with access to that repository.

Q2. What does the -u flag do in git push -u origin main?

It pushes your commits and also establishes a tracking relationship between your local branch and that specific remote branch. Once set, future pushes and pulls on that branch can simply be git push or git pull, without needing to specify the remote and branch name again.

Q3. Why did my git push get rejected with a message about 'fetch first'?

This means the remote branch has commits that your local branch doesn't have, usually because someone else pushed changes since you last synced. Git refuses to overwrite that unknown work, and you'll need to fetch and merge (or rebase) those changes locally before your push can succeed.

Q4. How can I check if my branch already has a tracking relationship set up?

Run git branch -vv, which lists your local branches along with their tracking remote branch (if configured), shown in brackets like [origin/main].

Q5. Should I always use the -u flag when pushing?

You only need it once per branch, the first time you push it to establish the tracking relationship. After that, Git remembers the association, so plain git push works correctly without needing the flag again for that same branch.

Summary

`git push origin <branch>` uploads local commits to a corresponding branch on a remote repository like GitHub. On a new branch's first push, adding the `-u` (`--set-upstream`) flag both performs the push and establishes a lasting tracking relationship between the local and remote branch, allowing all future `git push` and `git pull` commands on that branch to omit the remote and branch name entirely, since Git remembers the association. A push can be rejected with a 'fetch first' message when the remote branch contains commits the local branch doesn't have — typically from a collaborator's prior push — and this rejection is a deliberate safety feature, prompting a fetch and merge (or rebase, covered in the next lesson) before pushing can succeed, rather than an error to bypass carelessly.