CSMBAC Technical Resource
Website errors
Errors that stop a site loading, from redirect loops to internal server failures.
Articles
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PHP allow_url_fopen disabled breaks plugins and remote requests
How allow_url_fopen controls remote file reads, the errors it causes when disabled, and safe ways to fetch remote data.
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Browser showing old or stale website content
Browser showing old website content explained: the browser, CDN and server cache layers, how to clear each, and how to prove the source is new.
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Chrome Aw, snap page crash
Fix the Chrome Aw, snap crashed tab warning, from memory and GPU causes to extensions and site code that kill a renderer process.
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Connection refused vs connection timed out
Connection refused vs timed out, how each maps to a firewall, dead server or slow app, with the test that separates them.
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Connection timed out error
Connection timed out error explained: DNS, TCP route, firewall and origin causes with the ordered tests that fix each timeout type.
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DNS_PROBE_FINISHED_NXDOMAIN error explained
DNS_PROBE_FINISHED_NXDOMAIN means the domain has no DNS record: check the registrar, zone, nameservers and your own resolver in order.
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DNS server not responding error
DNS server not responding error explained: locate the error, flush the resolver, check hosts and firewall rules, and reset router DNS.
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Domain expired and website is down
Domain expired website down explained: confirm the expiry, renew and restore the domain, verify records, and prevent the next lapse.
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ERR_ABORTED website error explained
Understand the ERR_ABORTED Chrome error, the many reasons a request is cancelled, and how to diagnose it.
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ERR_BLOCKED_BY_CLIENT website error explained
ERR_BLOCKED_BY_CLIENT in Chrome: an extension blocks the request before the server is reached, so test in incognito, rename the resource, or allowlist the site.
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ERR_CERT_AUTHORITY_INVALID website error explained
ERR_CERT_AUTHORITY_INVALID in Chrome: the browser does not recognise who signed the certificate, usually a missing intermediate or a self-signed cert.
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ERR_CERT_REVOKED website error explained
NET::ERR_CERT_REVOKED means the CA invalidated the certificate early, often a compromised key. Reissue and install a fresh certificate with a new key.
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ERR_CONNECTION_RESET in Chrome explained
ERR_CONNECTION_RESET explained: what TCP reset means, server and client causes, and the debugging order that fixes it.
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ERR_INSECURE_RESPONSE website error explained
ERR_INSECURE_RESPONSE in Chrome means a response failed the browser's security checks. Find the expired, mismatched or weak certificate and fix the chain.
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ERR_INTERNET_DISCONNECTED website error explained
ERR_INTERNET_DISCONNECTED in Chrome means the device reports no active internet path. Check Wi-Fi, modem, adapter and VPN before blaming the site.
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ERR_NAME_NOT_RESOLVED troubleshooting
ERR_NAME_NOT_RESOLVED troubleshooting, from wrong DNS servers and missing records to typos, with ordered tests for each cause.
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Fix ERR_SPDY_PROTOCOL_ERROR and ERR_HTTP2_PROTOCOL_ERROR
Diagnose and fix ERR_SPDY_PROTOCOL_ERROR, retitled ERR_HTTP2_PROTOCOL_ERROR, a Chrome HTTP/2 framing error.
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Fix ERR_SSL_PROTOCOL_ERROR in the browser
Diagnose ERR_SSL_PROTOCOL_ERROR, a failed TLS handshake, across browser cache, certificates, protocols, and network.
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ERR_TOO_MANY_REDIRECTS redirect loop
Why a browser reports ERR_TOO_MANY_REDIRECTS, how to trace the redirect chain, and how to stop double HTTPS, plugin and cookie redirect loops.
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Contact form not sending email
Contact form not sending email: test the SMTP path, check MTA and plugin settings, and fix the settings that route mail reliably.
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Read website error logs
Read website error logs: find the log, map the entry to the page, and use Apache, nginx and PHP lines to fix a failing site.
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.htaccess internal server error
.htaccess 500 error diagnosis and fix: syntax, encoding, permissions and Apache modules behind the internal server error.
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Remove malware from a website
Website malware removal checklist: isolate, find the entry point, clean files and database, then secure the site against reinfection.
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MySQL "server has gone away" error
MySQL server has gone away: raise wait_timeout and max_allowed_packet, close idle connections, and find the restart that ends the error.
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MySQL too many connections error
MySQL too many connections explained: the connection limit, persistent and leaked connections, and the fixes that keep apps within it.
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Nginx 502 and 504 with PHP-FPM
Diagnose and fix Nginx 502 and 504 errors caused by a down, slow or exhausted PHP-FPM pool.
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Node.js JavaScript heap out of memory
Fix the Node.js fatal JavaScript heap out of memory error, V8 default limits and --max-old-space-size.
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PHP fatal error stops the site
PHP fatal error diagnosis and fix for blank pages and 500s, from the error log to memory limits and safe rollback.
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PHP max execution time and fatal timeout errors
PHP max execution time explained: the fatal timeout error, memory and I/O causes, and safe ways to raise or avoid the limit.
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Plugin activation boot loop
Fix a plugin activation boot loop where enabling an add-on sends WordPress into an instant 500, redirect, or fatal repeat loop.
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Server disk full stopping the website
Server disk full stopping the website: how a full disk breaks services, find the biggest files, clear logs and caches safely, and prevent it.
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Website loads but shows a blank page
Website blank page explained: tell a 200 with empty output from a 200 with hidden content, then fix the render or the source in order.
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Website unreachable in one region
Website unreachable in one region: test DNS answers, CDN edges and geo rules, and fix a region that times out or errors for real visitors.
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Build user facing error pages
User facing error pages: plan on-brand 404, 500 and 503 pages, know the server settings, and ship a good experience during downtimes.
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Web server log rotation setup
Why web server logs grow to fill disk and how to configure logrotate to rotate, compress and prune them.
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Website error and symptom reference
Website error meaning reference that maps messages to causes and fixes for loading, connection, DNS, HTTP status, blank page and cache errors.
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Website errors: ERR_CERT_DATE_INVALID before the certificate start date
Fix ERR_CERT_DATE_INVALID from a clock set before a certificate start date, covering device and server clock fixes.
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ERR_CERT_DATE_INVALID error
Fix ERR_CERT_DATE_INVALID: check your device date and time, then verify whether the site's certificate is genuinely expired.
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ERR_UNSAFE_PORT error
ERR_UNSAFE_PORT appears when a URL uses a port Chrome blocks for security. Use a safe port or allow it for local development only.
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Website redirection to spam or scam pages
Stop a website redirecting to spam or scam pages: find the injected redirect, check providers and plugins, and clean the payload.
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Website not loading at all
Diagnose why a website will not load at all: walk DNS, connection, server and TLS in order, and separate a not loading site from a blank page.
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Website under maintenance
Website under maintenance explained: what the status means, how long maintenance should last, and the ordered steps to bring the site back online.
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WordPress cron requests returning 502
Diagnose WordPress cron 502 bad gateway errors from PHP timeouts, web server limits, and overlapping cron runs.
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X-Frame-Options vs CSP frame-ancestors
X-Frame-Options vs CSP frame-ancestors, why frame-ancestors wins when both are set, and how to send both headers safely.