Error map
AH00288: scoreboard is full, not at MaxRequestWorkers Apache: [mpm_event:error] AH00288: scoreboard is full, not at MaxRequestWorkers. Increase ServerLimit
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)
HTTP 103 Early Hints
An interim response that sends Link headers early so the browser can preload CSS, fonts or scripts while the server is still buil…
HTTP 304 Not Modified
The cached copy is still valid, so the server sends no body and the client reuses its cache.
Cloudflare Error 524: A Timeout Occurred
Cloudflare connected to the origin, but the origin didn’t send an HTTP response within 100 seconds.
Cloudflare not caching: cf-cache-status DYNAMIC / BYPASS / MISS every time
Cloudflare isn’t caching the response — HTML isn’t cached by default, and cookies or Cache-Control headers from the origin preven…
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
Cloudflare Error 1200: Cache connection limit
Too many requests are queued at Cloudflare for the origin — the origin is slow and connections pile up.
Apache: AH00558: apache2: Could not reliably determine the server's fully qualified domain name
A harmless startup warning: Apache has no global ServerName, so it guessed one from the host’s IP.
Apache: (98)Address already in use: AH00072: make_sock: could not bind to address [::]:80 / AH00015: Unable to open logs
Another process (Nginx, another Apache, Skype/IIS-like service) already listens on the port Apache wants.
Apache: AH00091: apache2: could not open error log file /var/log/apache2/error.log. AH00015: Unable to open logs (Permission denied)
Apache can't open its log files — permissions, a missing directory or disk problems.
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.
Apache: AH00526: Syntax error on line 12 of /etc/apache2/sites-enabled/site.conf: Invalid command 'Foo', perhaps misspelled or defined by a module not included in the server configuration
Apache's config has a syntax problem or a directive from a module that isn't loaded.
Apache: [core:error] AH00037: Symbolic link not allowed or link target not accessible: /var/www/html/current
Apache refuses to follow a symlink because `FollowSymLinks`/`SymLinksIfOwnerMatch` isn't allowed or the target isn't readable.
Two steps away (36)
Warning: Cannot modify header information - headers already sent
You called `header()`, `setcookie()` or `session_start()` after output had already been sent to the browser.
CORS Error: No 'Access-Control-Allow-Origin' header is present
The browser blocked a cross-origin request because the server’s response didn’t include the CORS headers allowing your site’s ori…
HTTP 411 Length Required
The server refuses a request with a body but no Content-Length header.
HTTP 301 Moved Permanently
The resource has a new permanent URL; clients and search engines should use the address in the Location header from now on.
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
HTTP 200 OK (but something is still wrong)
The request succeeded at the HTTP level — yet the page is blank, the data is wrong, or an error is hidden inside the response bod…
PHP Fatal error: Maximum execution time of 30 seconds exceeded
The script ran longer than `max_execution_time` and PHP stopped it.
Cloudflare Error 522: Connection Timed Out
Cloudflare’s TCP connection to your origin timed out — the origin didn’t answer at all.
java.util.concurrent.TimeoutException
A Future.get(timeout) or async operation didn’t complete in the allowed time.
ERROR: canceling statement due to statement timeout
A query ran longer than statement_timeout and PostgreSQL cancelled it.
Performance: N+1 query problem (one query per row in a loop)
Code runs one query to load a list, then one more query per item — hundreds of queries per page.
Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. All pooled connections were in use and max pool size was reached.
The application’s connection pool was exhausted — all connections busy or leaked.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP 502 Bad Gateway
A proxy or gateway (Nginx, load balancer, CDN) got an invalid response — or no response — from the upstream server behind it.
HTTP 503 Service Unavailable
The server is temporarily unable to handle the request — overloaded, in maintenance, or has no healthy backends.
Docker build slow: "Sending build context to Docker daemon 2.5GB" / transferring context takes forever
docker build is uploading your whole project folder — node_modules, .git, data files — before building, because there’s no (or a…
Cloudflare-branded 502 Bad Gateway / 504 Gateway Timeout ("cloudflare" footer)
A plain-looking 502/504 page with “cloudflare” at the bottom comes from Cloudflare’s network itself (or an origin response it cou…
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.
OAuth Error: redirect_uri_mismatch
The redirect URI in your OAuth request doesn’t exactly match one registered for the client in the provider’s console.
WordPress: Error Establishing a Database Connection
WordPress can’t connect to its MySQL/MariaDB database with the credentials in wp-config.php, or the database server is down.
Error: listen EADDRINUSE: address already in use :::3000
Another process is already listening on that port.
Error: listen EACCES: permission denied 0.0.0.0:80
Node isn’t allowed to bind that port — ports below 1024 need root on Linux/macOS, and some Windows ports are reserved.
[nodemon] app crashed - waiting for file changes before starting...
Your app threw an error on startup; nodemon is waiting for a file change to retry.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
Apache: AH02240: Server should be SSL-aware but has no certificate configured / SSLCertificateFile: file '/etc/ssl/x.crt' does not exist or is empty
Apache cannot find the certificate or key file named in its configuration, or `SSLEngine on` is set without any certificate.
Apache: [ssl:warn] AH01909: example.com:443:0 server certificate does NOT include an ID which matches the server name
Apache's SSL virtual host name does not match any name inside the certificate it loads.
Too many open files (EMFILE)
The process hit its file-descriptor limit — sockets, files and pipes all count.
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: [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.
PHP Parse error: syntax error, unexpected …
PHP can’t parse the file because of a syntax mistake — the real error is often on the line before the one reported.
Nginx: nginx: [emerg] unexpected end of file, expecting ";" or "}" in /etc/nginx/conf.d/site.conf:42
The config ends while a block or directive is still open — a missing `}` or `;`.
Nginx: nginx: [emerg] directive "proxy_pass" is not terminated by ";" in /etc/nginx/sites-enabled/app:15
A directive's arguments run into the next line because the `;` is missing (or a quote is unbalanced).
Too many levels of symbolic links (ELOOP)
A symlink points to itself, directly or through a chain, so path resolution loops.
Nginx: [error] directory index of "/var/www/html/" is forbidden (403 Forbidden)
A directory was requested but no index file exists (or index is wrong) and autoindex is off, so Nginx returns 403.
Nginx: [error] open() "/home/user/site/index.html" failed (13: Permission denied), 403 Forbidden
The nginx worker user can't read the requested file or traverse a parent directory.
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