📚 Developer Reference Library

How-To Guides & Error Fixes
Build, Host, Deploy & Publish

Create websites, host on cloud servers, deploy with Docker, publish apps to Google Play and App Store, and fix common developer errors — all with step-by-step guides.

20
How-To Guides
10
Categories
20+
Topics Covered
Git 5 guides
Git
Understanding 'fatal: refusing to merge unrelated histories' in Git
⚠ fatal: refusing to merge unrelated histories
✓
Read fix
Git
Understanding How to Undo Commits in Git (Tree & Index Architecture)
⚠ Accidentally committed wrong files, wrong branch, or incorrect commit…
✓
Read fix
Git
Understanding 'error: failed to push some refs' in Git
⚠ error: failed to push some refs to 'https://github.com/user/repo.git'…
✓
Read fix
Git
How to Change a Git Commit Message (Clean History Best Practices)
⚠ Typo in commit message, wrong issue ticket reference, or uninformativ…
✓
Read fix
Git
How Git Branching & Deletion Works (Local vs Remote Tracking)
⚠ Managing stale feature branches, unmerged branch warnings, and diverg…
✓
Read fix
Linux 2 guides
Linux
How to Kill a Process on Port 8000, 3000 or 8080 in Linux & Mac
⚠ Error: listen EADDRINUSE: address already in use :::3000 OSError: [Er…
✓ lsof -ti:3000 | xargs kill -9
Read fix
Linux
How to Exit Vim / Vi Editor (Save, Quit Without Saving & Force Quit)
⚠ Stuck inside Vim or Vi editor after running git commit
✓ Press Esc, then type :wq and press Enter
Read fix
Web Development 2 guides
Web Development
How to Fix CORS Error: No 'Access-Control-Allow-Origin' Header
⚠ Access to fetch at 'https://api.example.com' from origin 'http://loca…
✓ # Express: npm install cors && app.use(require('cors')()) #…
Read fix
Web Development
How to Create a Website from Scratch (Complete Curriculum Guide)
✓
Read fix
C Programming 1 guide
C Programming
How to Fix 'Segmentation Fault (core dumped)' in C / C++
⚠ Segmentation fault (core dumped)
✓ gcc -g program.c -o program && gdb ./program (gdb) run (gdb…
Read fix
Python 2 guides
Python
How to Fix 'pip: command not found' on Mac, Ubuntu & Windows
⚠ zsh: command not found: pip bash: pip: command not found
✓ python3 -m pip install <package>
Read fix
Python
How to Fix 'ModuleNotFoundError: No module named' in Python
⚠ ModuleNotFoundError: No module named 'requests' ModuleNotFoundError: …
✓ python3 -m pip install <module_name> && python3 script.py
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JavaScript & React 1 guide
JavaScript & React
How to Fix 'Cannot read properties of undefined (reading map)' in React
⚠ TypeError: Cannot read properties of undefined (reading 'map') TypeEr…
✓ {(items || []).map(item => <Card key={item.id} data={item} …
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Docker 1 guide
Docker
How to Fix 'Cannot connect to the Docker daemon' Error
⚠ Cannot connect to the Docker daemon at unix:///var/run/docker.sock. I…
✓ sudo systemctl start docker
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Database & SQL 1 guide
Database & SQL
SQL Query to Find the Second Highest Salary (3 Methods Explained)
⚠ Write a SQL query to report the second highest salary from the Employ…
✓ SELECT MAX(salary) FROM Employee WHERE salary < (SELECT MAX…
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DevOps & Hosting 2 guides
DevOps & Hosting
How to Host a Website (DNS, Cloud Servers & Infrastructure Guide)
✓
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DevOps & Hosting
How to Deploy a Website to Production (CI/CD, Docker & Cloud Pipelines)
✓
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Mobile Development 3 guides
Mobile Development
How to Create Mobile Apps for iOS and Android (Engineering Curriculum Guide)
✓
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Mobile Development
How to Upload an App to Google Play Store (Publishing & Compliance Guide)
✓
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Mobile Development
How to Upload an App to Apple App Store (iOS App Store Connect Guide)
✓
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