404 Not Found
Diagnose a 404 Not Found by checking the URL, deleted files, broken routes, redirects, permalinks, and server configuration.
HTTP Errors and Troubleshooting
Understand HTTP errors such as 404, 500, and 502, then choose the right checks for routes, logs, proxies, redirects, and upstream servers.
Choose by status code
HTTP errors are server responses. They can still be caused by a browser cache, DNS route, CDN, proxy, deployment, plugin, or database dependency, but the status code tells you where to start. First ask whether the failure affects one URL, the whole site, one visitor, every visitor, or only traffic behind a CDN.
| Status or symptom | What it usually means | Best page |
|---|---|---|
| 404 | Resource, route, or redirect target is missing | 404 Not Found |
| 500 | The application failed while processing the request | 500 Internal Server Error |
| 502 | A gateway could not get a valid upstream response | 502 Bad Gateway |
| WordPress 500 | Plugin, theme, PHP, or .htaccess failure likely | WordPress 500 |
| nginx 502 | nginx cannot reach or use an upstream | nginx 502 |
Layer model
Use a simple chain: browser -> DNS -> CDN/cache -> web server -> reverse proxy -> application runtime -> database. A 404 usually sits in routing, redirects, files, or rewrite rules. A 500 usually sits inside the app. A 502 usually sits between the proxy and upstream. If logs are available, start with access and error log matching before applying fixes.
Useful guides
- Check access and error logs for HTTP failures when you need timestamps and log phrases.
- Roll back a website change safely when the first failure follows a deploy or config edit.
- Fix broken redirects, permalinks, and rewrite rules when pages disappear or loop.
- Trace a 502 through proxy, CDN, and upstream layers when the gateway is involved.
Glossary
A route maps a URL to content or code. An upstream is the service a proxy calls. A proxy passes requests to another server. An origin is the server behind a CDN. A redirect sends a browser to a different URL. A cache can serve old responses until purged or expired.
Errors
500 Internal Server Error
Find the cause of a 500 Internal Server Error by checking logs, recent deploys, plugins, PHP failures, permissions, and rollback options.
Aw, Snap! in Chrome
Fix Chrome Aw, Snap! crashes by isolating extensions, profile corruption, cache issues, hardware acceleration, and device-specific problems.
502 Bad Gateway
Diagnose a 502 Bad Gateway by checking the proxy, CDN, upstream app, PHP-FPM, timeouts, and server logs before changing DNS.
500 Internal Server Error in WordPress
Fix a WordPress 500 error by checking plugins, themes, PHP memory, debug logs, .htaccess, permissions, and recent changes.
502 Bad Gateway in nginx
Fix nginx 502 errors by checking upstream health, sockets, proxypass targets, PHP-FPM, timeouts, and nginx error logs.
502 Bad Gateway in WordPress
Troubleshoot a WordPress 502 by checking PHP-FPM, overloaded plugins, theme changes, cache/CDN layers, hosting limits, and logs.
502 Bad Gateway in Chrome
Check a 502 Bad Gateway in Chrome by separating local browser or network symptoms from a real website-side gateway outage.
Guides
Disable plugins in WordPress without admin access
Disable WordPress plugins through files or database access when wp-admin is unavailable because of a 500, 502, or database error.
Check access and error logs for HTTP failures
Learn how to inspect access logs, error logs, status codes, timestamps, upstream failures, and recent changes during HTTP outages.
Roll back a website change safely
Use a safe rollback workflow for website errors by preserving evidence, restoring the smallest change, and verifying recovery.
Fix broken redirects, permalinks, and rewrite rules
Repair redirects, permalink rules, rewrite configuration, and route mismatches that cause 404s or redirect loops after site changes.
Trace 502 through proxy, CDN, and upstream layers
Trace a 502 Bad Gateway across browser, CDN, reverse proxy, origin server, upstream app, and logs to find the failing layer.
Verify nginx upstreams, sockets, and proxy_pass targets
Check nginx upstream definitions, Unix sockets, proxypass targets, service health, permissions, and logs when nginx returns 502.
Stabilize Chrome extensions, profile, cache, and hardware acceleration
Stabilize Chrome when pages crash by testing extensions, profiles, cache, hardware acceleration, browser updates, and device conditions.
Check WordPress file permissions
Check WordPress ownership and permissions when uploads, plugins, themes, cache files, or PHP includes fail after a migration or deploy.
Check WordPress PHP version, extensions, and memory
Check PHP version, required extensions, memory limits, and fatal errors when WordPress fails after hosting, plugin, theme, or core changes.
Clear WordPress page, object, and CDN cache safely
Clear WordPress cache layers in the right order so stale pages, object cache, or CDN responses do not hide the real fix.
Enable WordPress debug log safely
Turn on WP_DEBUG_LOG without displaying errors publicly so WordPress 500, white screen, plugin, theme, and PHP failures leave evidence.
Fix WordPress white screen without wp-admin access
Recover from a WordPress white screen when the admin area is unavailable by checking debug logs, plugins, themes, PHP memory, and recent changes.
Restore WordPress from backup safely
Restore WordPress files and database carefully after a failed update, bad migration, broken plugin, or damaged wp-config.php change.
Understand wp-config.php for WordPress troubleshooting
Use wp-config.php as the starting reference for database credentials, debug logging, salts, table prefixes, and environment-specific WordPress settings.