How do I kill the process using port 11211?

On macOS & Linux, run: "sudo systemctl stop memcached || sudo killall memcached". On Windows PowerShell (as Admin), run: "Stop-Service memcached -Force -ErrorAction SilentlyContinue".

Why am I getting "port 11211 already in use" (EADDRINUSE)?

This occurs when another background instance of memcached or a zombie process is already bound to port 11211. Use the kill commands above to free the port immediately.

Messaging & Cache

Risk: High

Port 11211 — Memcached In-Memory Cache

Q: Is Port 11211 safe to expose to the public internet?

Risk level is High. Exposed UDP port 11211 was historically responsible for the largest DDoS reflection amplification attacks in internet history (>1.3 Tbps). Bind Memcached exclusively to 127.0.0.1 and disable UDP (-U 0).

Port 11211 is the default port for Memcached, a high-performance in-memory key-value caching system used to accelerate database-driven web apps.

PORT NUMBER

11211

PROTOCOL

TCP/UDP

DEFAULT PROCESS

memcached

FIREWALL TARGET

11211/tcp/udp

Instant Terminal Fixes for Port 11211

macOS & Linux Terminal

1. Check who is listening on port 11211:

echo stats | nc localhost 11211 || sudo lsof -i :11211

2. Kill process occupying port 11211 (EADDRINUSE fix):

sudo systemctl stop memcached || sudo killall memcached

3. UFW Firewall Allow rule:

sudo ufw allow from 127.0.0.1 to any port 11211 proto tcp

Windows PowerShell (Admin)

1. Check listening port:

Get-NetTCPConnection -LocalPort 11211

2. Force kill process on port 11211:

Stop-Service memcached -Force -ErrorAction SilentlyContinue

3. Docker Port Forwarding Mapping:

docker run -d -p 11211:11211 memcached:alpine memcached -m 64

Common Error Encountered

Memcached::get(): Failed to connect to server on port 11211: Connection refused.

Security Advisory & Hardening

Exposed UDP port 11211 was historically responsible for the largest DDoS reflection amplification attacks in internet history (>1.3 Tbps). Bind Memcached exclusively to 127.0.0.1 and disable UDP (-U 0).

Frequently Asked Questions

Port 11211 Questions & Answers

Common questions regarding default services, kill commands, and firewall configurations.

Port 11211 is commonly used for Memcached In-Memory Cache. Port 11211 is the default port for Memcached, a high-performance in-memory key-value caching system used to accelerate database-driven web apps.

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