Error map
AH00037: Symbolic link not allowed or link target not accessible Apache: [core:error] AH00037: Symbolic link not allowed or link target not accessible: /var/www/html/current
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)
Too many levels of symbolic links (ELOOP)
A symlink points to itself, directly or through a chain, so path resolution loops.
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: 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: [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.
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.
Apache: [core:info] AH00128: File does not exist: /var/www/html/favicon.ico (404)
The requested file isn't in the DocumentRoot — a normal 404 entry in the Apache error log.
Browser shows <?php code or downloads index.php — mod_php / PHP-FPM handler not configured in Apache
Apache serves PHP files as plain text because no PHP handler is active.
systemd: apache2.service: Main process exited, code=exited, status=1/FAILURE — Job for apache2.service failed because the control process exited with error code
systemd couldn't start Apache — the real error is in the journal or `apachectl configtest`.
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.
Two steps away (36)
Linux: Permission denied
Your user (or the service user) lacks read/write/execute permission on a file, directory or one of its parents.
java.nio.file.AccessDeniedException: /path
The OS denied a file operation to the Java process.
No space left on device, but df shows free space (inodes exhausted)
The filesystem has run out of inodes — the slots for files — even though there are gigabytes free, usually because of millions of…
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.
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: 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.
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.
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…
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…
user is not in the sudoers file. This incident will be reported.
Your account isn’t allowed to use sudo.
WordPress: Sorry, you are not allowed to access this page.
Your user role lacks the capability for that admin screen — or the database table prefix / user capabilities are out of sync afte…
HTTP 500 Internal Server Error
The server hit an unexpected condition — usually an unhandled exception or misconfiguration in the application.
HTTP 499 Client Closed Request (Nginx)
Nginx-specific code logged when the client disconnected before the server finished responding.
[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 404 Not Found
The server can’t find anything at the requested URL.
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: AH00112: Warning: DocumentRoot [/var/www/example.com/public_html] does not exist
A virtual host points to a directory that doesn't exist.
FastCGI sent in stderr: "Primary script unknown"
Nginx passed a script path to PHP-FPM that PHP-FPM couldn’t find — usually a wrong SCRIPT_FILENAME or root.
WordPress: Your PHP installation appears to be missing the MySQL extension which is required by WordPress
PHP doesn’t have the mysqli extension loaded, so WordPress can’t talk to the database.
WordPress: Your server is running PHP version 7.2 but WordPress 6.x requires at least 7.4 / This plugin requires a newer version of PHP
WordPress core, a plugin or a theme needs a newer PHP than the server runs.
Job for nginx.service failed because the control process exited with error code
systemd tried to start the service, but its start command failed. The real reason is in the service’s status/journal.
Failed to start x.service: Unit x.service not found
systemd has no unit with that name — the package isn’t installed, the name differs on this distro, or a new unit file wasn’t load…
System has not been booted with systemd as init system (PID 1). Can't operate.
You ran systemctl inside an environment without systemd as PID 1 — a Docker container or older WSL.
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…
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…
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