Redis Errors

This error occurs when the Redis server fails to start or stop within the systemd-configured timeout period. It typically happens with large databases or when system resources are constrained, causing systemd to terminate the startup process prematurely.

This error occurs when the XREAD or XREADGROUP command lacks matching stream IDs for each stream key. Redis requires equal numbers of stream keys and stream IDs in the STREAMS clause.

This error occurs when Redis receives a malformed or invalid command. Common causes include incorrect command syntax, wrong number of arguments, or using a command unsupported in your Redis version. Verify your command syntax matches the Redis documentation.

Redis logs `ERR fsync error` when its persistence thread cannot flush the AOF/RDB file, typically because the disk reports a write or fsync failure. The process pauses writes with `STOP-WRITES-ON-BGSAVE-ERROR` until you fix the underlying storage or OS settings, so gather the fsync logs, check disk health, and tune persistence settings. This guide covers the symptoms, root causes, and ordered steps needed to restore durable writes.

This error occurs when the redis-py client encounters a socket exception while reading data from the Redis server. It typically happens due to connection resets, server-side connection closures, or network issues.

This error occurs when a Redis cluster becomes unavailable due to node failures or missing hash slot coverage. The cluster stops accepting requests until all hash slots are covered again by available nodes.

Redis returned 'ERR unknown command' when you tried to execute a Redis command. This error means the server doesn't recognize the command you sent, usually due to a typo, version mismatch, connecting to the wrong Redis instance, or missing Redis modules.

The ioredis 'Command timed out' error occurs when a Redis command fails to return a response within the configured timeout period. This typically indicates network issues, slow Redis operations, or insufficient timeout configuration.

This error occurs when you call DISCARD without first starting a transaction with MULTI. DISCARD is only valid within an active transaction context, and calling it outside that context causes Redis to return this error.

The Jedis 'Command timed out' error occurs when a Redis command executed through the Jedis Java client fails to complete within the configured timeout period. This typically indicates slow Redis operations, network latency, or insufficient timeout settings.

Redis Sentinel logs "+elected-leader: Won election for epoch" when a Sentinel successfully wins the leader election to perform a failover. This is a normal operational message indicating that the Sentinel has received majority votes and is now authorized to promote a replica to master. Understanding this message helps you monitor failover processes and verify that high availability mechanisms are working correctly.

Redis returns null from EXEC when a watched key was modified between WATCH and EXEC, indicating the optimistic lock failed and the transaction was aborted. This is expected behavior for Redis optimistic locking, ensuring data consistency when multiple clients access the same keys. This guide explains why EXEC returns null, how to implement proper retry logic, and strategies to minimize transaction conflicts.

Redis logs `ERR CONFIG REWRITE failed: Permission denied` when the CONFIG REWRITE command cannot write changes back to the configuration file. This happens due to restrictive file or directory permissions, SELinux policies, systemd service hardening, or incorrect file ownership. This guide covers diagnosing permission issues, fixing file ownership and directory permissions, resolving SELinux conflicts, and updating systemd service files.

Redis Cluster returns -ASK redirects when a hash slot is being migrated between nodes. This is a normal part of cluster rebalancing and requires clients to acknowledge the temporary migration state before retrying commands.

This error occurs when a Redis command receives an incorrect number of arguments. Each Redis command has specific argument requirements, and supplying too few or too many arguments triggers this validation error.

Redis logs `ERR Module failed to load: Permission denied` when it cannot access a module file due to restrictive file permissions, SELinux/AppArmor restrictions, or incorrect ownership. The module fails to initialize, leaving Redis without the expected functionality until you adjust permissions, disable security modules, or relocate the module file. This guide covers the symptoms, root causes, and ordered steps needed to successfully load Redis modules.

The 'OOM command not allowed when used memory exceeds maxmemory' error occurs when a Redis instance reaches its configured memory limit and the maxmemory policy prevents new writes. This happens when the cache is full and Redis cannot store additional data without exceeding the memory threshold.

This error occurs when your application tries to write to a Redis read-only replica instead of the primary master node. Redis replicas are intentionally set to read-only by default to prevent accidental writes and data inconsistency.

The Redis client throws 'ERR Got an unexpected reply from Redis (node-redis pubsub)' when it receives malformed or unexpected responses during pubsub operations. This usually indicates protocol mismatches between client and server versions, network corruption, or Redis server issues during message publishing. Check client-server compatibility, network stability, and Redis server health to resolve the pubsub communication failures.

Redis returns "ERR BGREWRITEAOF scheduled when RDB save in progress" when you try to start an AOF rewrite while a background RDB snapshot is already running. This prevents simultaneous persistence operations that could conflict or overload memory/disk. Wait for the current RDB save to finish, check persistence settings, or manually schedule AOF rewrites during low‑traffic periods.

Redis Cluster returns `CROSSSLOT Keys in request don't hash to the same slot` when you attempt a multi-key operation (like MGET, MSET, or sharded Pub/Sub) on keys that hash to different hash slots. Redis Cluster partitions data across 16384 slots, and multi-key commands require all keys to map to the same slot unless you use hash tags. This guide explains slot hashing, hash tags, and how to structure keys or use client-side routing to avoid cross-slot errors.

Redis Sentinel logs "+try-failover: New failover in progress" when multiple failover attempts overlap, usually because a previous failover is still underway or quorum cannot be reached. This prevents duplicate promotions and ensures only one master election occurs at a time. To resolve, wait for the current failover to complete, verify Sentinel quorum and network connectivity, then retry if needed.

The "ERR invalid password" error occurs when you attempt to authenticate to a Redis server with an incorrect or mismatched password. This is a security measure to protect your Redis instance from unauthorized access.

Redis returns `NOPROTO sorry, this protocol version is not supported` when a client tries to negotiate an unsupported protocol version during the HELLO handshake, typically when requesting RESP3 on a server that only supports RESP2. Modern clients auto-negotiate to RESP3 by default, but older Redis versions or disabled RESP3 configurations reject this upgrade. This guide explains the protocol mismatch, common scenarios, and how to downgrade or enable the correct protocol version.

This error occurs in ioredis when a command cannot complete because the Redis connection has been lost and reconnection attempts have exceeded the configured limit. By default, ioredis will retry each pending command up to 20 times before failing with this error.

This error occurs when the XREADGROUP command is called without the required GROUP keyword and parameters. XREADGROUP is specifically designed for consumer group operations and mandates explicit group and consumer identification.

The MOVED error occurs in Redis Cluster when a client connects to the wrong node for a given hash slot. The cluster returns this error with the correct node address, requiring the client to redirect the query or update its topology knowledge.

This error occurs when attempting write operations (SET, DEL, etc.) inside a Lua script executed with EVAL_RO or by a read-only user. Use EVAL for write operations or ensure your script only performs reads.

This error occurs when a Lua script in Redis Cluster accesses keys without explicitly declaring them in the KEYS array. Redis Cluster requires all key names to be passed as input arguments for proper shard routing.

This error occurs when attempting to use the special $ ID with the XREADGROUP command. While $ represents the last entry in a stream, it cannot be used with XREADGROUP because consumer groups have different semantics for reading messages.

Redis requires authentication when a password is set with the requirepass configuration. Fix this error by either authenticating with your password before running commands or configuring your Redis client to include credentials.

Redis Cluster stops accepting queries when hash slots are not assigned to nodes. This error indicates the cluster is in a partially degraded state where one or more of the 16384 hash slots lack node coverage, preventing normal operations.

Redis rejected your authentication credentials. This occurs when you provide an incorrect password, wrong username, or use an invalid credential format when connecting to a Redis instance with ACL (Access Control List) authentication enabled.

A socket timeout occurs when redis-py cannot read a response from Redis within the configured time limit. This typically happens with slow networks, blocking commands, or idle connections closed by the server.

The 'NOPERM this user has no permissions' error occurs in Redis 6+ when an authenticated user attempts to execute a command, access a key, or publish to a channel they don't have permission for. This happens due to Access Control Lists (ACL) restricting the user's capabilities. Fixing this requires granting appropriate permissions through ACL configuration.

Redis Cluster returns `CROSSSLOT Keys in request don't hash to the same slot` when you attempt a multi-key operation (like MGET, MSET, transactions, or SUNION) on keys that hash to different hash slots. Redis Cluster partitions data across 16384 slots, and multi-key commands require all keys to map to the same slot unless you use hash tags. This guide explains slot hashing, hash tags, and how to fix key design issues.

The NOSCRIPT error occurs when Redis tries to execute a Lua script using EVALSHA but the script isn't cached on the server. Learn how to properly load scripts and handle this common issue.

This error occurs when attempting to restore or migrate a key using Redis commands like RESTORE or MIGRATE, but a key with that name already exists at the destination. It prevents overwriting the existing key unless the REPLACE option is specified.

The 'LOADING Redis is loading the dataset in memory' error occurs when a client attempts to connect to a Redis server that is still initializing and loading persisted data from disk. This is a temporary state during startup or replica resynchronization that prevents commands from executing until the dataset is fully loaded.

In Redis Cluster mode, a multi-key command is being executed while slot migration/rehashing is in progress. The command cannot be executed because the keys are split between the source and destination nodes. This error instructs the client to retry the operation after the resharding completes.

The "NOREPLICAS Not enough good replicas to write" error occurs when a Redis master instance rejects write operations because insufficient replicas are available or synchronized. This is a replication safety feature that prevents data loss.

This error occurs when you try to set a Redis key with an invalid expiration time, typically because the expire duration is negative, zero, or overflowed. Learn how to fix this common SET command issue.

The "ERR EXEC without MULTI" error occurs when attempting to execute EXEC without first starting a transaction with MULTI. This is typically caused by connection switching, premature DISCARD calls, or connection pool issues in client libraries.

Redis "ERR syntax error" occurs when a command violates the Redis Serialization Protocol (RESP) format or uses incorrect command syntax. This typically happens with malformed commands, wrong argument counts, or protocol violations.

The Redis MOVED error indicates that a hash slot has been moved to a different node in a Redis Cluster. This is a client-side redirection issue that occurs when a client connects to a cluster node that no longer owns the requested slot. Fixing requires using cluster-aware Redis clients or enabling cluster mode in your client library.

Redis is configured to require password authentication, but your client connected without providing credentials. This error occurs when the requirepass directive is set on the server and clients attempt to execute commands without first authenticating with the AUTH command.

The "ERR crossed slot boundary" (also displayed as "CROSSSLOT Keys in request don't hash to the same slot") error occurs in Redis Cluster when a multi-key command attempts to operate on keys that hash to different hash slots. Redis Cluster divides data across 16,384 slots, and multi-key operations like MGET, MSET, and Lua scripts require all keys to reside in the same slot. Fix by using hash tags to ensure keys hash to the same slot, or by executing separate commands on each slot.

This error occurs when a Redis client sends malformed commands or receives corrupted responses that violate the RESP (Redis Serialization Protocol) format. The issue typically stems from connection problems, protocol version mismatches, improper connection pooling, or network corruption. Fix by using connection pools, enabling proper authentication, ensuring RESP2/RESP3 compatibility, and validating command formatting.

The 'LOADING Redis is loading the dataset in memory' error occurs when a client attempts to connect to a Redis server that is still initializing and loading persisted data from disk. This is a temporary state during startup or replica resynchronization that prevents commands from executing until the dataset is fully loaded.

This error occurs when connecting to Redis with an incorrect password or invalid authentication credentials. Verify the password matches your Redis configuration, check the authentication format for Redis 6.0+, and ensure special characters are properly encoded.

This error occurs when a Redis command is called with the wrong number of parameters. The GET command requires exactly one argument (the key), but received a different number. Verify your command syntax and the correct argument count for the specific command.

The BUSYKEY error occurs when trying to use the RESTORE command to restore a key that already exists in your Redis database without using the REPLACE option. This prevents accidental data overwrites.

Connection refused errors occur when your application cannot establish a TCP connection to the Redis server. This typically means Redis isn't running, is listening on a different port, or network/firewall rules are blocking the connection.

The "ERR max number of clients reached" error occurs when the number of active client connections exceeds Redis's configured maxclients limit (default 10,000). Common causes include connection leaks, insufficient connection pooling, and undersized Redis instances. Fix by using connection pooling, increasing maxclients, upgrading your Redis instance, or reducing connection usage.

The Redis error "ERR value is not an integer or out of range" occurs when integer operations (INCR, DECR, INCRBY, HINCRBY, etc.) receive invalid values. This happens when the stored value is not a valid integer, exceeds 64-bit signed integer limits, or is a floating-point number. Fixing requires storing valid integers, using INCRBYFLOAT for decimals, or validating input before operations.

The "ERR timeout reading from client" error occurs when Redis cannot read a command or response from a client within the configured timeout period. This commonly happens with long-running Lua scripts, slow commands, network issues, or misconfigured timeouts. Fixing requires optimizing scripts, adjusting timeout values, and investigating network conditions.

This error occurs when a Redis command is executed on a key that holds a different data type than expected. Redis enforces strict type checking—using LPUSH on a string key or HGETALL on a list will fail. Fix by checking the key type with TYPE, using the correct command for that type, or deleting and recreating the key with the proper data type.

This error occurs when a Redis command is blocked by authentication, ACL permissions, or replica mode restrictions. It typically happens when credentials are missing, user permissions are insufficient, or you're trying to write to a read-only replica.

Redis has RDB persistence enabled but cannot write snapshots to disk, blocking write operations. This typically indicates disk space, permission, or memory issues preventing background saves.

This error occurs when your application attempts a write operation on a Redis replica instead of the primary master node. Redis replicas are read-only by default to prevent accidental data corruption.

This error occurs when using XREADGROUP on a Redis Stream consumer group that has not been created yet. Create the consumer group first with XGROUP CREATE before reading messages.

Redis Cluster mode only supports database 0 and disallows the SELECT command. This error occurs when your client attempts to switch databases in cluster mode, which is not supported by design.

This error occurs when attempting to use Redis Cluster commands on a standalone Redis instance. Enable cluster mode in your redis.conf configuration file and restart the instance to resolve it.

The offset value exceeds Redis string size limits (max 536,870,911 bytes). Verify offset is within bounds and your string doesn't exceed 512MB.

This error occurs when EXEC is called without first starting a transaction with MULTI. It typically happens due to connection loss or improper transaction handling in client libraries. Fix it by ensuring MULTI is called before EXEC and using connection pooling.

Redis has hit its maximum client connection limit. Increase the maxclients configuration, fix connection leaks in your application, or use connection pooling to resolve this error.

Redis has RDB snapshots enabled but cannot write to disk due to permission issues, disk space, or memory constraints. This prevents write operations and requires fixing the underlying persistence issue.

This error occurs when a Redis replica attempts to synchronize with a master that is itself a replica but has lost its own master connection. Fixing it requires ensuring proper master configuration and network connectivity in your replication topology.

Redis fails to start when the append-only file (AOF) becomes corrupted. Use redis-check-aof to fix the file, but be aware data loss may occur if corruption is in the early part of the file.

Redis has reached its maxmemory limit and cannot store new data. This occurs when memory usage exceeds the configured limit and the eviction policy cannot free enough space for new operations.

The MASTERDOWN error occurs when a Redis replica loses its connection to the master and replica-serve-stale-data is disabled. This error is common in Redis Sentinel deployments and indicates a replication link failure that prevents the replica from serving requests.

A Redis transaction failed before execution due to syntax errors or command validation issues. Fix by validating all commands in the MULTI block before calling EXEC.

This error occurs when attempting to create a consumer group on a Redis Stream using XGROUP CREATE, but a consumer group with that name already exists on the stream. Redis prevents duplicate group names to avoid overwriting group state and message delivery tracking.

A Redis transaction was aborted due to syntax errors or WATCH key modifications, and you attempted to queue more commands after the abort. Clear the transaction state with DISCARD and verify your commands.

The "ERR Failed to resolve hostname" error occurs when Redis or a Redis client cannot resolve a hostname to its IP address through DNS. This is typically caused by DNS configuration issues, network connectivity problems, or incorrect hostname configuration.

The "NOGOODSLAVE No good slave available for failover" error occurs in Redis Sentinel when attempting a failover but no healthy replica instances are available to promote to master. This typically happens when all replicas are offline, lagging, or unreachable.

This error occurs when your application attempts a write operation on a Redis replica instead of the primary master node. Redis replicas are read-only by design to maintain data consistency across the replication cluster.

The BUSY error occurs when a Lua script is running longer than Redis expects, blocking other clients from executing commands. Clients attempting to send commands receive a BUSY response, indicating they must wait or kill the script.

This error occurs when you try to run a Redis command on a key that stores a different data type than the command expects. For example, using HGETALL (hash command) on a string key will fail. The fix is to check the key's actual type and use the correct command.

Redis detects a checksum mismatch in DUMP payloads or corrupted RDB files, typically during DUMP/RESTORE operations or RDB loading. This happens when data is corrupted during transfer, stored on a bad disk sector, or incompatible with your Redis version. Verify file integrity and restore from backups to recover.

This error occurs when the Jedis Java client loses connection to Redis, usually due to idle timeout, network issues, or stale connection pool entries. The server closes the connection, but the client attempts to use it anyway.