How to fix ERR unknown command in Redis

Check the Redis command reference and ensure you're using the exact command name. Common mistakes include case sensitivity issues or typos:

# Incorrect
redis-cli SETT key value      # SETT is not a command, should be SET

# Correct
redis-cli SET key value
redis-cli GET key

Command names in Redis are case-insensitive in redis-cli but must match exactly in client libraries.

Connect to your Redis server and use the COMMAND command to list all available commands:

redis-cli COMMAND

This returns a detailed list of all commands your Redis server supports. Search through this list to verify the command exists. If it doesn't appear, it's either not available in your server version or you're connected to the wrong instance.

Verify you're connecting to the correct Redis instance:

# Connect to your server
redis-cli -h your-host -p 6379

# Once connected, check server info
INFO server

This shows you the Redis version and other details. Ensure you're not accidentally connecting to:
- Redis Sentinel (port 26379) instead of the actual Redis server
- A managed Redis service with limited commands
- An older Redis version that doesn't support your command

If you recently upgraded your Redis client library, it may be trying to use commands not available in your server version.

For example, ioredis and other clients may issue CLIENT SETINFO (Redis 7.2+), HELLO (Redis 6+), or other version-specific commands automatically.

Option 1: Upgrade your Redis server to match the client version.

Option 2: Disable version-specific features in your client:

Node.js (ioredis):

const redis = require('ioredis');
const client = new redis({
  host: 'localhost',
  port: 6379,
  disableClientInfo: true  // Prevents CLIENT SETINFO command
});

Ruby (redis-rb):

require 'redis'
redis = Redis.new(host: 'localhost', port: 6379, protocol: 2)  # Force RESP2

Python (redis-py < 5.0 for RESP2):

import redis
r = redis.Redis(host='localhost', port=6379, protocol=2)

If you're using module-specific commands (like JSON.SET or FT.CREATE), verify the module is installed:

redis-cli INFO modules

If the module isn't listed, you need to install it. For example, to add RedisJSON:

# Using Docker
docker run -d -p 6379:6379 redislabs/rejson:latest

# Or load the module when starting Redis
redis-server --loadmodule /path/to/rejson.so

For Managed Redis (AWS ElastiCache, Azure Cache, etc.), check if the module is available in your service tier. Some providers don't support all modules.

If using EVAL or EVALSHA commands with Lua scripts, ensure the script only calls valid Redis commands:

redis-cli EVAL "return redis.call('GET', KEYS[1])" 1 mykey

Common issues:
- Using incorrect command names inside Lua scripts
- Missing quotes around Lua string literals
- Forgetting to pass the key count and keys/args as separate arguments

# Incorrect
EVAL "redis.call(GET, key)" mykey

# Correct
EVAL "return redis.call('GET', KEYS[1])" 1 mykey