Error map
AH00526: Syntax error on line of apache config 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
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)
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.
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: 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.
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).
Apache: AH00112: Warning: DocumentRoot [/var/www/example.com/public_html] does not exist
A virtual host points to a directory that doesn't exist.
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: AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary
Rewrite rules loop internally, so Apache aborts with a 500.
Apache: [proxy_http:error] AH01102: error reading status line from remote server 127.0.0.1:3000 / AH00898: Error reading from remote server returned by /api
mod_proxy couldn't read a valid response from the backend, so Apache returned 502/503.
Apache: [proxy:error] AH00957: HTTP: attempt to connect to 127.0.0.1:3000 (127.0.0.1) failed / AH01114: HTTP: failed to make connection to backend: 127.0.0.1
mod_proxy couldn't connect to the backend address, so the client gets 503/502.
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.
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 `;`.
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.
Two steps away (36)
MySQL ERROR 1064 (42000): You have an error in your SQL syntax
MySQL couldn’t parse the query. The text after “near” shows where parsing failed.
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
IndentationError: unexpected indent / expected an indented block
Python’s block structure is broken — inconsistent indentation or mixed tabs and spaces.
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.
ERR_TOO_MANY_REDIRECTS with Cloudflare (Flexible SSL redirect loop)
The page redirects to itself forever — classic cause: Cloudflare SSL mode “Flexible” while the origin redirects HTTP to HTTPS.
ERR_SSL_VERSION_OR_CIPHER_MISMATCH on a Cloudflare site (certificate not issued / multi-level subdomain)
Cloudflare has no edge certificate for the hostname — the Universal SSL cert is still pending, or the hostname is a second-level…
NET::ERR_CERT_AUTHORITY_INVALID with a Cloudflare Origin Certificate (record not proxied)
Cloudflare Origin CA certificates are only trusted by Cloudflare — visitors reaching the origin directly (grey-cloud record, dire…
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] no "ssl_certificate" is defined for the "listen ... ssl" directive in /etc/nginx/sites-enabled/default:3
A server block listens with `ssl` but has no `ssl_certificate` and `ssl_certificate_key`.
Nginx: nginx: [emerg] duplicate location "/" in /etc/nginx/sites-enabled/default:52
Two `location` blocks with the same match exist in one server block (often from two included files).
[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.
Nginx: nginx: [emerg] bind() to 0.0.0.0:80 failed (13: Permission denied)
Nginx isn't allowed to bind that port — a privileged port as non-root, or SELinux restricts it.
Nginx: nginx: [error] invalid PID number "" in "/run/nginx.pid" (when running nginx -s reload)
Nginx can't signal the master process because the PID file is empty, stale or missing.
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.
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…
WordPress: 404 Not Found on every page except the homepage (permalinks / .htaccess / Nginx rules)
Pretty permalinks aren’t being routed to index.php — .htaccess is missing/ignored (Apache) or Nginx lacks try_files.
Nginx: [error] rewrite or internal redirection cycle while internally redirecting to "/index.php" (500 Internal Server Error)
Nginx kept internally redirecting (more than 10 times), typically from a `try_files` or `rewrite` that points back to itself.
Apache: [core:alert] /var/www/html/.htaccess: Invalid command 'php_value', perhaps misspelled or defined by a module not included in the server configuration
A `.htaccess` file uses a directive the server can't handle, causing 500 errors for the whole directory.
HTTP 407 Proxy Authentication Required
A proxy between you and the server requires credentials before it will forward your request.
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 417 Expectation Failed
The server or a proxy can’t meet the Expect header in the request — almost always Expect: 100-continue.
HTTP 503 Service Unavailable
The server is temporarily unable to handle the request — overloaded, in maintenance, or has no healthy backends.
HTTP 511 Network Authentication Required
A captive portal (hotel, airport, office Wi-Fi) is intercepting your traffic until you log in or accept its terms.
Nginx: [error] connect() failed (111: Connection refused) while connecting to upstream, upstream: "http://127.0.0.1:3000/"
Nginx tried to proxy a request but nothing listens on the upstream address, so the client gets 502.
Firefox: Peer's Certificate has expired. Error code: SEC_ERROR_EXPIRED_CERTIFICATE
Firefox found an expired certificate in the chain presented by the server.
Firefox: Websites prove their identity via certificates — the certificate is only valid for other names. Error code: SSL_ERROR_BAD_CERT_DOMAIN
The certificate does not include the hostname you typed.
Node.js: Error: unable to verify the first certificate (code: UNABLE_TO_VERIFY_LEAF_SIGNATURE)
Node could not verify the server's leaf certificate because the intermediate certificates were not provided by the server.
Nginx: nginx: [warn] conflicting server name "example.com" on 0.0.0.0:80, ignored
Two server blocks listen on the same port with the same `server_name`; the second is ignored.
Nginx: nginx: [emerg] open() "/etc/nginx/snippets/fastcgi-php.conf" failed (2: No such file or directory) in /etc/nginx/sites-enabled/app:20
The config includes a file (snippet, certificate, ssl option file) that doesn't exist.
Nginx: nginx: [emerg] could not build the server_names_hash, you should increase server_names_hash_bucket_size: 64
A very long `server_name` (or many names) doesn't fit the hash bucket.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
Apache: [authz_core:error] AH01630: client denied by server configuration: /var/www/html/
Apache 2.4 authorisation denied access to the directory (403) because no `Require all granted` applies.
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.
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