Error map
WARNING: The TCP backlog setting of 511 cannot be enforced Redis: # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128
Redis · layer 5, Data
Centre: this error. First ring: errors it is linked with (9). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (9)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
The kernel booted but couldn’t mount the root filesystem — usually a missing or broken initramfs after a kernel update.
Redis: Client id=12 addr=10.0.0.5:51234 scheduled to be closed ASAP for overcoming of output buffer limits
A client (often a slow subscriber or a replica) couldn't read data fast enough, so Redis disconnected it to protect memory.
Redis: (error) BUSY Redis is busy running a script. You can only call SCRIPT KILL or SHUTDOWN NOSAVE
A long-running Lua script (or function) blocks the single-threaded server, so other commands are rejected.
Celery: Task executed twice / Restoring unacked messages — Redis broker visibility_timeout shorter than task ETA
Celery's Redis transport redelivers a task if it isn't acknowledged within `visibility_timeout` (1 hour by default).
Redis: ERR max number of clients reached
Redis hit its `maxclients` limit (default 10000, lower if the OS limit is low), so new connections are refused.
Redis: # Can't save in background: fork: Cannot allocate memory / WARNING overcommit_memory is set to 0!
Redis couldn't fork to write an RDB/AOF snapshot because the OS refused to allocate memory.
BullMQ: Error: Missing lock for job 42. moveToFinished / job stalled more than allowable limit
A BullMQ worker lost the lock on a job (it took too long or the event loop was blocked), so the job is considered stalled.
Redis: # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis
THP is enabled, which can cause latency spikes and high memory usage with Redis.
Redis::CannotConnectError: Error connecting to Redis on localhost:6379 (Errno::ECONNREFUSED)
Sidekiq or the Rails Redis cache/cable couldn't connect to Redis.
Two steps away (26)
Killed / Out of memory: Killed process (Linux OOM killer)
The kernel ran out of memory and killed a process to recover — the program just prints “Killed” (exit code 137).
EC2 status check failed: Instance reachability check failed (1/2 checks passed)
AWS can reach the host, but the operating system inside the instance isn’t responding — kernel panic, full disk, broken network c…
bash: /bin/rm: Argument list too long
A glob like * expanded to more file names than the kernel allows in one command (ARG_MAX), so the command never ran.
Kubernetes: OOMKilled (exit code 137)
The container used more memory than its limit, and the kernel killed it.
java.lang.OutOfMemoryError: Java heap space
The JVM ran out of heap memory and garbage collection couldn’t free enough.
Segmentation fault (core dumped)
A program accessed memory it wasn’t allowed to, and the kernel killed it with SIGSEGV (exit code 139).
ReplyError: NOAUTH Authentication required.
The Redis server requires a password (or ACL user) but the client didn’t authenticate.
WRONGTYPE Operation against a key holding the wrong kind of value
A Redis command was used on a key of a different type (e.g. HGET on a string key).
Redis: OOM command not allowed when used memory > 'maxmemory'
Redis reached its maxmemory limit and the eviction policy (noeviction) refuses new writes.
Redis: Error: connect ECONNREFUSED 127.0.0.1:6379 / Could not connect to Redis at 127.0.0.1:6379: Connection refused
Nothing is listening on the Redis host/port your client uses.
Redis: DENIED Redis is running in protected mode because protected mode is enabled and no password is set for the default user
Redis refuses connections from non-local clients when it has no password and is bound to all interfaces.
Redis: (error) NOAUTH Authentication required. / WRONGPASS invalid username-password pair or user is disabled
The server requires a password (or ACL user) and the client sent none or the wrong one.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
fork: retry: Resource temporarily unavailable (process/thread limit)
The user or container hit its maximum number of processes/threads (ulimit -u, pids cgroup), so new processes can’t be created.
Redis: Error: read ECONNRESET / redis.exceptions.ConnectionError: Connection reset by peer after idle time
A middlebox or Redis closed an idle connection, and the pooled client reused it.
FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory
The V8 heap hit its limit — a large build (webpack, tsc, Next.js) needs more memory, or the app leaks.
MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 listeners added
More than 10 listeners were added to one event — often a leak where listeners are added repeatedly.
MemoryError (Unable to allocate X GiB for an array)
Python couldn’t allocate memory — the data is larger than available RAM or address space.
Laravel Queue: Illuminate\Queue\MaxAttemptsExceededException: App\Jobs\SendReport has been attempted too many times or run too long
A queued job failed repeatedly or ran past its timeout, so it was marked failed.
Redis: Error: write EPROTO ... SSL routines:ssl3_get_record:wrong version number / Connection reset by peer (TLS vs plaintext)
The client and server disagree about TLS — plaintext client to a TLS port, or TLS client to a plaintext port.
Redis: evicted_keys growing — keys vanish unexpectedly because maxmemory is reached and a volatile/allkeys eviction policy is active
Redis removed keys to stay under `maxmemory` according to the eviction policy.
MongoDB startup: WARNING: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it to 'never'
Transparent Huge Pages are enabled, which can hurt MongoDB performance (latency spikes).
Redis: INFO memory — mem_fragmentation_ratio:2.8 (RSS much larger than used_memory)
The process uses far more RSS than the data size, due to allocator fragmentation or deleted-but-not-returned memory.
Laravel: Predis\Connection\ConnectionException: Connection refused [tcp://127.0.0.1:6379] / RedisException: Connection refused
Laravel can't connect to Redis, which it uses for cache, sessions or queues.
Redis: Could not connect to Redis at 10.0.0.5:6379: Connection timed out
Redis only listens on localhost by default, so remote clients time out or are refused.
Redis: Closing idle client / Connection closed by server after timeout 300
Redis' `timeout` directive closes connections idle longer than N seconds.
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