What is

Memcached SERVER_ERROR failed to listen on UDP port

 ?

Understanding Memcached

Memcached is a high-performance, distributed memory caching system designed to speed up dynamic web applications by alleviating database load. It stores data in memory for quick retrieval, making it an essential tool for applications requiring fast data access.

Identifying the Symptom

When using Memcached, you might encounter the error message: SERVER_ERROR failed to listen on UDP port. This indicates that Memcached is unable to bind to the specified UDP port, which can prevent it from functioning correctly.

Exploring the Issue

What Causes This Error?

The error typically arises when the specified UDP port is already in use or blocked by a firewall. Memcached needs to bind to a port to listen for incoming requests, and if it cannot, it will throw this error.

Understanding UDP Ports

UDP (User Datagram Protocol) is a communication protocol used for time-sensitive transmissions such as video playback or DNS lookups. Memcached can use UDP for faster data retrieval, but it requires an available port to do so.

Steps to Resolve the Issue

Step 1: Check Port Availability

First, ensure that the UDP port Memcached is trying to bind to is not already in use. You can use the following command to check:

netstat -an | grep 'port_number'

Replace port_number with the actual port number Memcached is attempting to use. If the port is in use, you will see it listed in the output.

Step 2: Modify Firewall Rules

If the port is not in use, the issue might be with firewall settings. Ensure that the firewall allows traffic on the specified UDP port. You can adjust firewall settings using:

sudo ufw allow port_number/udp

Replace port_number with the actual port number.

Step 3: Restart Memcached

After ensuring the port is available and not blocked, restart the Memcached service to apply changes:

sudo systemctl restart memcached

Additional Resources

For more information on configuring Memcached, you can refer to the official Memcached documentation. Additionally, for troubleshooting network issues, the DigitalOcean guide on network troubleshooting can be helpful.

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