Fix Next.js Port 3000 Already in Use Error – Quick Solution

The Problem

When running next dev or npm run dev, you might encounter this warning:

⚠ Port 3000 is in use, trying 3001 instead.

Why This Happens

This issue occurs when the Next.js development server doesn’t shut down properly, leaving port 3000 occupied. Common scenarios include:

• Terminal crashes unexpectedly
• Force-quitting the development process
• Previous session still running in background

Quick Solutions

Use either of these commands to kill the process using port 3000:

Method 1: Using lsof (macOS/Linux)

lsof -t -i tcp:3000 | xargs kill

Method 2: For Linux systems without lsof

kill $(ss -lptn 'sport = :3000' | awk 'NR>1 {print $NF}' | sed -E 's/.*pid=([0-9]+).*/\1/')

How These Commands Work

Method 1 breakdown:

• lsof -t -i tcp:3000 – Lists process IDs using TCP port 3000
• xargs kill – Kills the found processes

Method 2 breakdown:

• ss -lptn 'sport = :3000' – Shows socket statistics for port 3000
• awk 'NR>1 {print $NF}' – Extracts the last field from each line (skipping header)
• sed -E 's/.*pid=([0-9]+).*/\1/' – Extracts the process ID from the format
• kill $(...) – Kills the extracted process ID

After running either command, you can start your Next.js development server normally on port 3000.