Kill Process Running on a Specific Port

When you encounter "Port X is already in use" errors, you need to find and kill the process occupying that port.

Windows (PowerShell)

Find the process using the port

netstat -ano | findstr :4221

Output example:

TCP    [::1]:4221    [::]:0    LISTENING    3912

The last number (3912) is the Process ID (PID).

Kill the process

taskkill /F /PID 3912

One-liner (find and kill)

# Replace 4221 with your port number
$port = 4221
$pid = (Get-NetTCPConnection -LocalPort $port -ErrorAction SilentlyContinue).OwningProcess
if ($pid) { Stop-Process -Id $pid -Force; Write-Host "Killed process $pid" } else { Write-Host "No process on port $port" }

Linux / macOS (Bash)

Find the process using the port

lsof -i :4221

Or using netstat:

netstat -tulpn | grep :4221

Kill the process

kill -9 3912

One-liner (find and kill)

# Replace 4221 with your port number
kill -9 $(lsof -t -i:4221) 2>/dev/null && echo "Process killed" || echo "No process on port 4221"

Or using fuser:

fuser -k 4221/tcp

Common Use Cases

Dev server conflicts: When Angular/React/Node dev servers don't shut down properly
Docker port binding: When containers leave ports occupied after stopping
Database connections: When database servers (PostgreSQL, MySQL) hold onto ports

Pro Tip

Add these as shell aliases for quick access:

PowerShell (add to $PROFILE):

function killport($port) {
    $p = (Get-NetTCPConnection -LocalPort $port -ErrorAction SilentlyContinue).OwningProcess
    if ($p) { Stop-Process -Id $p -Force; "Killed PID $p on port $port" } else { "No process on port $port" }
}

Bash (add to ~/.bashrc or ~/.zshrc):

killport() { kill -9 $(lsof -t -i:$1) 2>/dev/null && echo "Killed process on port $1" || echo "No process on port $1"; }

Then simply run: killport 4221 This will save you time and frustration when dealing with port conflicts!