Git Notes

Hub Benefits of Git and GitHub - Why They Matter Git vs GitHub Version Control System What Is Git What Is GitHub Configure Git - User Identity and Settings Create GitHub Account - Sign Up Guide First Git Repository - Getting Started Install Git on Linux - Complete Setup Guide Install Git on macOS - Installation Guide Install Git on Windows - Step-by-Step Guide Git Add - Stage Changes Git Clone - Copy Remote Repositories Locally Git Commit - Save Changes Git Diff - Compare Changes in Your Repository Git Ignore - Exclude Files from Version Control Git Init - Initialize Repository Git Log - View Commit History Git Status - Check Repository State Git Fetch - Download Remote Changes Without Merging Git Pull - Fetch and Merge Remote Changes Git Push - Upload Local Commits to Remote Repository Git Remote - Manage Remote Repository Connections Local Repository - Understanding Your Git Working Environment Remote Repository - Collaborate Through Shared Repositories Sync Local and Remote - Keep Repositories in Harmony Amend Commit - Fix Last Commit Delete Branch - Clean Up Branches Git Reset - Move HEAD and Undo Commits Git Restore - Discard Changes Git Revert - Safely Undo Changes Recover Lost Commits - Reflog Guide Fork Repository GitHub Pages GitHub Profile Setup GitHub Repositories GitHub Stars and Watchers Repository Settings Code Reviews Git Clone Git Fetch Git Pull Git Push GitHub Issues Labels and Milestones Open Source Contributions GitHub Project Boards Pull Requests - Propose and Review Code Changes Team Collaboration with Git and GitHub Automated Testing with GitHub Actions CI/CD with GitHub Actions Deployment Automation with GitHub Actions Introduction to GitHub Actions GitHub Actions Runners GitHub Actions Workflows Enterprise Git Workflows - Scale Git for Large Organizations Feature Branch Workflow - Isolate Development Work GitFlow Workflow - Structured Release Management Monorepo Workflow - Manage Multiple Projects in One Repository Trunk-Based Development - Ship Code Fast and Safely Deployment Workflows GitHub Pages Deployment Netlify Deployment from GitHub Render Deployment from GitHub Vercel Deployment from GitHub Branch Protection Rules - Secure Your Git Branches Personal Access Tokens - Authenticate with GitHub Repository Security Best Practices Secret Scanning - Detect Leaked Credentials in Code Signed Commits - Verify Commit Authenticity with GPG SSH Keys - Secure Git Authentication Without Passwords Git Bisect - Find Bugs with Binary Search Git Cherry-Pick - Apply Specific Commits to Any Branch Git Hooks - Automate Workflows with Git Events Git Internals - Understanding How Git Works Under the Hood Git Stash - Temporarily Save Uncommitted Changes Git Submodules - Manage External Dependencies as Git Repos Git Tag - Mark Important Points in History Git Worktrees - Work on Multiple Branches Simultaneously Collaborative Web App Project Complete Team Workflow Project GitHub Actions Project - Build a CI/CD Pipeline Open Source Project Contribution - Guided Exercise Portfolio Project with Git - Showcase Your Skills Git Command Cheatsheet Git Interview Questions - Comprehensive Preparation Guide GitHub Interview Questions Scenario-Based Git Interview Questions Git Troubleshooting Guide Git Best Practices - Professional Development Habits Common Git Errors and Fixes - Quick Solutions Git Command Reference - Complete Command Guide Learning Resources - Continue Your Git & GitHub Education Branch Strategies - Choosing the Right Git Branching Model Create Branch in Git - Start New Development Lines Fast-Forward Merge in Git - Clean Linear History Git Branch Git Checkout Git Merge Git Rebase Merge Branches in Git - Combine Development Work Merge Conflicts - Resolve Git Conflicts Like a Pro Switch Branch in Git - Navigate Between Branches

Git Troubleshooting Guide

Every developer encounters Git problems — from confusing error messages to accidentally lost work. This guide covers the most common issues you will face,...

Every developer encounters Git problems — from confusing error messages to accidentally lost work. This guide covers the most common issues you will face, their root causes, and step-by-step solutions. Bookmark this page for those moments when Git seems to be working against you rather than for you.

Permission and Authentication Errors

Permission denied (publickey)

bash example

$ git push origin main
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Cause: SSH key is not configured or not added to your GitHub account.

Fix:

bash example

# Check if you have an SSH key
ls ~/.ssh/id_ed25519.pub

# If not, generate one
ssh-keygen -t ed25519 -C "your@email.com"

# Add to SSH agent
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

# Copy public key and add to GitHub Settings → SSH Keys
cat ~/.ssh/id_ed25519.pub

# Test connection
ssh -T git@github.com

Authentication failed (HTTPS)

bash example

remote: Support for password authentication was removed.
fatal: Authentication failed

Fix: Use a Personal Access Token instead of password:

bash example

# Generate token at GitHub → Settings → Developer settings → Personal access tokens
# Use token as password when prompted, or configure credential helper:
git config --global credential.helper store

Merge and Conflict Issues

Merge conflict in file

bash example

CONFLICT (content): Merge conflict in src/app.js
Automatic merge failed; fix conflicts and then commit the result.

Fix:

bash example

# See which files are conflicted
git status

# Open each conflicted file, look for markers:
# <<<<<<< HEAD
# (your changes)
# =======
# (their changes)
# >>>>>>>

# Edit the file to resolve, then:
git add src/app.js
git commit -m "Resolve merge conflict in app.js"

Cannot merge — uncommitted changes

bash example

error: Your local changes would be overwritten by merge.

Fix:

bash example

git stash           # Save changes temporarily
git merge main      # Now merge succeeds
git stash pop       # Restore your changes

Reset and Recovery

Accidentally deleted commits with git reset

bash example

# Find lost commits in reflog
git reflog
# abc1234 HEAD@{2}: commit: The commit you lost

# Recover it
git checkout -b recovery abc1234
# Or reset back to it
git reset --hard abc1234

Committed to wrong branch

bash example

# If not pushed yet:
git checkout correct-branch
git cherry-pick wrong-branch    # Copy the commit
git checkout wrong-branch
git reset --hard HEAD~1          # Remove from wrong branch

Want to undo the last commit but keep changes

bash example

git reset --soft HEAD~1     # Uncommit, keep changes staged
git reset --mixed HEAD~1    # Uncommit, keep changes unstaged
git reset --hard HEAD~1     # Uncommit and DELETE changes (careful!)

Push and Pull Issues

Updates were rejected (non-fast-forward)

Example

! [rejected] main -> main (non-fast-forward)

Cause: Remote has commits you do not have locally.

Fix:

bash example

git pull origin main        # Get remote changes first
git push origin main        # Now push succeeds

# Or with rebase:
git pull --rebase origin main
git push origin main

Detached HEAD state

bash example

You are in 'detached HEAD' state.

Cause: You checked out a specific commit instead of a branch.

Fix:

bash example

# If you want to keep work done in detached state:
git checkout -b save-my-work

# If you just want to go back to a branch:
git checkout main

File and Staging Issues

File too large to push

bash example

remote: error: File large-file.zip is 150 MB; exceeding GitHub's 100 MB limit.

Fix:

bash example

# Remove from current commit
git rm --cached large-file.zip
echo "large-file.zip" >> .gitignore
git commit --amend

# If already in history, remove from all commits:
git filter-branch --tree-filter 'rm -f large-file.zip' HEAD
# Consider using Git LFS for large files

Accidentally staged files

bash example

git restore --staged file.txt         # Unstage specific file
git restore --staged .                # Unstage everything

Gitignore not working for already tracked files

bash example

# Remove from Git tracking (keeps local file)
git rm --cached file-to-ignore.txt
git commit -m "Remove file from tracking"
# Now .gitignore will work for this file

Configuration Issues

Line ending problems (Windows/Mac/Linux)

bash example

# Configure for your OS:
git config --global core.autocrlf true   # Windows
git config --global core.autocrlf input  # Mac/Linux

Wrong author on commits

bash example

# Fix for future commits
git config user.name "Correct Name"
git config user.email "correct@email.com"

# Fix last commit author
git commit --amend --author="Correct Name <correct@email.com>"

Key Takeaways

Most Git problems have straightforward solutions once you understand what caused them. Keep the reflog in mind as your safety net — it preserves history even after destructive operations. When in doubt, git status tells you where you are, and git stash gives you a clean slate to work from. The more you troubleshoot, the more confident you become, and the less these issues disrupt your workflow.

Exam Focus

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Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

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Related Git & GitHub Topics

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Git Notes

Git Troubleshooting Guide

Every developer encounters Git problems — from confusing error messages to accidentally lost work. This guide covers the most common issues you will face,...

Permission and Authentication Errors

Permission denied (publickey)

bash example

$ git push origin main
git@github.com: Permission denied (publickey).
fatal: Could not read from remote repository.

Cause: SSH key is not configured or not added to your GitHub account.

Fix:

bash example

# Check if you have an SSH key
ls ~/.ssh/id_ed25519.pub

# If not, generate one
ssh-keygen -t ed25519 -C "your@email.com"

# Add to SSH agent
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519

# Copy public key and add to GitHub Settings → SSH Keys
cat ~/.ssh/id_ed25519.pub

# Test connection
ssh -T git@github.com

Authentication failed (HTTPS)

bash example

remote: Support for password authentication was removed.
fatal: Authentication failed

Fix: Use a Personal Access Token instead of password:

bash example

# Generate token at GitHub → Settings → Developer settings → Personal access tokens
# Use token as password when prompted, or configure credential helper:
git config --global credential.helper store

Merge and Conflict Issues

Merge conflict in file

bash example

CONFLICT (content): Merge conflict in src/app.js
Automatic merge failed; fix conflicts and then commit the result.

Fix:

bash example

# See which files are conflicted
git status

# Open each conflicted file, look for markers:
# <<<<<<< HEAD
# (your changes)
# =======
# (their changes)
# >>>>>>>

# Edit the file to resolve, then:
git add src/app.js
git commit -m "Resolve merge conflict in app.js"

Cannot merge — uncommitted changes

bash example

error: Your local changes would be overwritten by merge.

Fix:

bash example

git stash           # Save changes temporarily
git merge main      # Now merge succeeds
git stash pop       # Restore your changes

Reset and Recovery

Accidentally deleted commits with git reset

bash example

# Find lost commits in reflog
git reflog
# abc1234 HEAD@{2}: commit: The commit you lost

# Recover it
git checkout -b recovery abc1234
# Or reset back to it
git reset --hard abc1234

Committed to wrong branch

bash example

# If not pushed yet:
git checkout correct-branch
git cherry-pick wrong-branch    # Copy the commit
git checkout wrong-branch
git reset --hard HEAD~1          # Remove from wrong branch

Want to undo the last commit but keep changes

bash example

git reset --soft HEAD~1     # Uncommit, keep changes staged
git reset --mixed HEAD~1    # Uncommit, keep changes unstaged
git reset --hard HEAD~1     # Uncommit and DELETE changes (careful!)

Push and Pull Issues

Updates were rejected (non-fast-forward)

Example

! [rejected] main -> main (non-fast-forward)

Cause: Remote has commits you do not have locally.

Fix:

bash example

git pull origin main        # Get remote changes first
git push origin main        # Now push succeeds

# Or with rebase:
git pull --rebase origin main
git push origin main

Detached HEAD state

bash example

You are in 'detached HEAD' state.

Cause: You checked out a specific commit instead of a branch.

Fix:

bash example

# If you want to keep work done in detached state:
git checkout -b save-my-work

# If you just want to go back to a branch:
git checkout main

File and Staging Issues

File too large to push

bash example

remote: error: File large-file.zip is 150 MB; exceeding GitHub's 100 MB limit.

Fix:

bash example

# Remove from current commit
git rm --cached large-file.zip
echo "large-file.zip" >> .gitignore
git commit --amend

# If already in history, remove from all commits:
git filter-branch --tree-filter 'rm -f large-file.zip' HEAD
# Consider using Git LFS for large files

Accidentally staged files

bash example

git restore --staged file.txt         # Unstage specific file
git restore --staged .                # Unstage everything

Gitignore not working for already tracked files

bash example

# Remove from Git tracking (keeps local file)
git rm --cached file-to-ignore.txt
git commit -m "Remove file from tracking"
# Now .gitignore will work for this file

Configuration Issues

Line ending problems (Windows/Mac/Linux)

bash example

# Configure for your OS:
git config --global core.autocrlf true   # Windows
git config --global core.autocrlf input  # Mac/Linux

Wrong author on commits

bash example

# Fix for future commits
git config user.name "Correct Name"
git config user.email "correct@email.com"

# Fix last commit author
git commit --amend --author="Correct Name <correct@email.com>"

Key Takeaways

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for Git Troubleshooting Guide.

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this Git & GitHub topic.

Search Terms

git-github, git & github, git, github, interview, preparation, troubleshooting, guide

Related Git & GitHub Topics

Continue learning this concept

PreviousScenario-Based Git Interview Questions NextGit Best Practices - Professional Development Habits