Error map
accept4() failed (24: Too many open files) Nginx: [crit] accept4() failed (24: Too many open files) / open() failed (24: Too many open files)
Nginx / Apache · layer 3, Edge & web server
Centre: this error. First ring: errors it is linked with (12). 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 (12)
Cloudflare Error 1025: Please check back later (Workers request limit)
The site’s Cloudflare Workers plan exceeded its daily request limit (free plan: 100,000 requests/day).
Cloudflare Error 1102: Worker exceeded resource limits (CPU time / memory)
The Worker used more CPU time or memory than its plan allows for a single request.
Cloudflare 413 Request Entity Too Large (upload over the plan limit)
The request body is larger than Cloudflare allows through the proxy — 100 MB on Free/Pro, 200 MB Business, 500 MB Enterprise defa…
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.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
Nginx: [info] client prematurely closed connection while reading response header from upstream / access log status 499
The client (browser, mobile app, load balancer) disconnected before Nginx finished the response; Nginx logs status 499.
Go: accept tcp [::]:8080: accept4: too many open files / open x: too many open files
The process reached its file-descriptor limit — usually leaked connections, files or response bodies.
Nginx/Apache: ModSecurity: Access denied with code 403 (phase 2). Matched "Operator GE matched 5 at TX:anomaly_score"
The ModSecurity WAF (OWASP Core Rule Set) blocked the request as suspicious.
Nginx: [error] client intended to send too large body: 5242880 bytes (413 Request Entity Too Large)
A request body exceeded `client_max_body_size` (default 1 MB), so Nginx returned 413 before reaching your app.
Nginx: [alert] 1234#1234: *987 1024 worker_connections are not enough while connecting to upstream
Nginx ran out of simultaneous connection slots in a worker.
Nginx: nginx: [warn] the "listen ... http2" directive is deprecated, use the "http2" directive instead
Since Nginx 1.25.1 HTTP/2 is enabled with a separate `http2 on;` directive instead of `listen 443 ssl http2;`.
Nginx: [error] limiting requests, excess: 5.370 by zone "perip", client: 203.0.113.5
`limit_req` rejected requests because the client exceeded the configured rate (burst) — response 503 (or 429).
Two steps away (36)
Lambda: Request must be smaller than 6291456 bytes for the InvokeFunction operation (RequestEntityTooLargeException)
The event payload (or response) is over Lambda’s 6 MB synchronous limit (256 KB for async invocations).
Lambda: Unzipped size must be smaller than 262144000 bytes
The function code plus layers exceed Lambda’s 250 MB unzipped limit for zip deployments.
Cloudflare Error 1015: You are being rate limited
The site’s Cloudflare rate-limiting rule blocked you for sending too many requests in a short time.
Cloudflare Error 1019: Compute server error (Workers)
A Cloudflare Worker routed the request to a loop or hit an internal compute error.
Cloudflare Error 1101: Worker threw exception
The Cloudflare Worker serving this route threw an uncaught JavaScript exception.
Cloudflare Error 1104: A variation of this script was not found (Worker route to deleted script)
A Worker route points to a script that no longer exists (deleted, renamed or not deployed to that environment).
HTTP 413 Content Too Large (Request Entity Too Large)
The request body is bigger than the server is willing to accept — usually a file upload over the configured limit.
WordPress: The link you followed has expired
Usually an upload (theme, plugin, media) larger than PHP’s upload/post limits — WordPress receives an empty request and shows thi…
Upload error: File type not allowed / unsupported file type
The upload was rejected because the file’s type — extension, MIME type or actual content — isn’t on the allowed list.
Error: listen EADDRINUSE: address already in use :::3000
Another process is already listening on that port.
Error: write EPIPE
Node wrote to a pipe or socket whose other end was already closed.
RangeError [ERR_CHILD_PROCESS_STDIO_MAXBUFFER]: stdout maxBuffer length exceeded
child_process.exec/execSync produced more output than its buffer allows (default 1 MB).
Error: ENOENT: no such file or directory
A file or directory the program tried to open doesn’t exist at that path.
Error: socket hang up / read ECONNRESET
The other side closed the TCP connection abruptly while your client was still using it.
MySQL ERROR 1040 (08004): Too many connections
MySQL reached `max_connections` and refuses new clients.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
Error response from daemon: network X not found
The container or Compose project refers to a Docker network that doesn’t exist (any more).
Error response from daemon: Pool overlaps with other one on this address space
Docker tried to create a network whose subnet clashes with an existing Docker network (or a VPN/host route).
driver failed programming external connectivity on endpoint: iptables: No chain/target/match by that name
Docker’s iptables rules were wiped (firewalld/ufw reload, iptables flush) while Docker was running, so it can’t publish ports.
HTTP 403 Forbidden
The server understood the request but refuses to authorize it — you (or the server process) are not allowed to access this resour…
Cloudflare Error 1020: Access Denied
A Cloudflare firewall/WAF custom rule blocked the request — the visitor’s IP, country, user agent or request pattern matched a bl…
nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)
Nginx (or another server) can’t listen on the port because another process already holds it — often Apache, another Nginx, or a s…
HTTP 100 Continue
An interim response telling the client to go ahead and send the request body — normal when the client sent Expect: 100-continue.
HTTP 417 Expectation Failed
The server or a proxy can’t meet the Expect header in the request — almost always Expect: 100-continue.
WordPress: Sorry, you are not allowed to upload this file type / Sorry, this file type is not permitted for security reasons
WordPress blocked the upload because the file extension/MIME type isn’t in its allowed list (SVG, JSON, WEBP on old versions, fon…
Nginx: upstream timed out (110: Connection timed out) while reading response header from upstream
Nginx waited longer than proxy_read_timeout (60 s default) for the backend (app server, PHP-FPM) to respond, then returned 504.
Nginx: 400 Bad Request — Request Header Or Cookie Too Large / client sent too long header line
The request line or headers (often cookies) exceed `large_client_header_buffers`.
Apache: [mpm_event:error] AH00484: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
Apache used all its worker slots, so new requests queue or time out.
HTTP 410 Gone
The resource used to exist but was intentionally and permanently removed, with no forwarding address.
Nginx: nginx: [emerg] unknown directive "x" in /etc/nginx/sites-enabled/x:12 — configuration file test failed
Nginx found a directive it doesn’t know — a typo, a missing semicolon on the previous line, a directive from a module that isn’t…
Nginx: [emerg] SSL_CTX_set_tmp_dh("/etc/ssl/dhparam.pem") failed (SSL: error:1401E0A8:SSL routines:... dh key too small)
The Diffie-Hellman parameters file is too weak (e.g. 512 or 768 bit) for the current OpenSSL security level.
HTTP 429 Too Many Requests
You’ve hit a rate limit — too many requests in a given time window. Slow down and retry later.
API/app requests get 403 with cf-mitigated: challenge (Bot Fight Mode / challenge on non-browser clients)
Cloudflare is answering API calls, webhooks or mobile-app requests with a challenge page (HTML 403) because bot protection treats…
Let's Encrypt: urn:ietf:params:acme:error:rateLimited :: too many certificates (5) already issued for this exact set of identifiers in the last 168 hours
You hit a Let's Encrypt rate limit — too many certificates, failed validations or new orders in a period.
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