Browser errors

Error fix · Browser errorsAw, Snap! in Chrome: Fix Page Crashes and Error CodesChrome's Aw, Snap page means a tab's renderer crashed. Learn what STATUS_ACCESS_VIOLATION and Out of Memory mean and how users and developers fix them.4 min read

Error fix · Browser errorsDNS_PROBE_FINISHED_NO_INTERNET: Meaning and How to Fix ItChrome shows DNS_PROBE_FINISHED_NO_INTERNET when it cannot reach any DNS server. Check the connection, router, DNS settings and firewall step by step.5 min read

Error fix · Browser errorsDNS_PROBE_FINISHED_NXDOMAIN: What It Means and How to Fix ItDNS_PROBE_FINISHED_NXDOMAIN means the resolver says the domain does not exist. Fix local DNS cache problems or the missing records, expiry or typo behind it.4 min read

Error fix · Browser errorsERR_ADDRESS_UNREACHABLE: What It Means and How to Fix ItChrome shows ERR_ADDRESS_UNREACHABLE when there is no route to the server's address. Troubleshoot IPv6, VPN and routing issues, and fix broken AAAA records.5 min read

Error fix · Browser errorsERR_BAD_SSL_CLIENT_AUTH_CERT: Fix Client Certificate ErrorsChrome shows ERR_BAD_SSL_CLIENT_AUTH_CERT when your client certificate is missing, expired or unusable. Repair the cert, key and CA trust for mutual TLS.4 min read

Error fix · Browser errorsERR_BLOCKED_BY_CLIENT: Ad Blockers, Extensions and How to Fix ItERR_BLOCKED_BY_CLIENT means a browser extension or setting stopped a request before it left your device. Find the blocker, or rename the URL as a developer.5 min read

Error fix · Browser errorsERR_CACHE_MISS: "Confirm Form Resubmission" in Chrome ExplainedERR_CACHE_MISS appears when Chrome needs data it no longer has cached, often after a form POST. Learn the visitor fixes and the developer cause.4 min read

Error fix · Browser errorsERR_CERT_AUTHORITY_INVALID: Untrusted Certificate Fix GuideERR_CERT_AUTHORITY_INVALID means the browser does not trust the certificate issuer. Learn the causes, visitor workarounds and how to fix chains and CAs.4 min read

Error fix · Browser errorsERR_CERT_COMMON_NAME_INVALID: Hostname Mismatch Fix GuideERR_CERT_COMMON_NAME_INVALID means the certificate does not cover the address you typed. Find the mismatched name and fix SAN, www, wildcard and SNI issues.5 min read

Error fix · Browser errorsERR_CERT_DATE_INVALID: Expired or Not-Yet-Valid Certificate FixERR_CERT_DATE_INVALID means the certificate is expired or your clock is wrong. See how to tell which, fix it as a visitor, and renew it as a site owner.4 min read

Error fix · Browser errorsERR_CONNECTION_CLOSED: Why the Connection Closed and How to Fix ItERR_CONNECTION_CLOSED means the server or something in between hung up. Fix visitor-side causes, then trace firewalls, TLS, proxies and server limits.5 min read

Error fix · Browser errorsERR_CONNECTION_REFUSED: Why Chrome Can't Connect and How to Fix ItChrome shows ERR_CONNECTION_REFUSED when the server answers but rejects the connection. Fix it as a visitor, or find the closed port or stopped service.4 min read

Error fix · Browser errorsERR_CONNECTION_RESET: What It Means and How to Fix ItChrome's ERR_CONNECTION_RESET means the connection was cut mid-way. Try visitor fixes first, then trace resets from firewalls, proxies and app crashes.4 min read

Error fix · Browser errorsERR_CONNECTION_TIMED_OUT: Causes and Fixes for Visitors and OwnersChrome says the server took too long to respond. Rule out your own network first, then check for dropped packets, firewalls and an overloaded origin.4 min read

Error fix · Browser errorsERR_EMPTY_RESPONSE (Didn't Send Any Data): Causes and FixesERR_EMPTY_RESPONSE means the server closed the connection without sending a reply. Find crashes, nginx 444 rules, WAF drops and PHP failures behind it.5 min read

Error fix · Browser errorsERR_FAILED in Chrome: Generic Error Causes and FixesERR_FAILED is Chrome's catch-all for a request that failed without a specific code. Narrow it down with extensions, network, policy and server checks.4 min read

Error fix · Browser errorsERR_HTTP2_PROTOCOL_ERROR: Causes and Fixes in ChromeERR_HTTP2_PROTOCOL_ERROR means a stream or frame in an HTTP/2 connection was invalid. Test with curl, then fix nginx, Apache, proxy and antivirus causes.4 min read

Error fix · Browser errorsERR_INTERNET_DISCONNECTED: Fix "No Internet" in ChromeERR_INTERNET_DISCONNECTED means Chrome sees no working network. Check Wi-Fi, adapter, proxy and VPN settings, then confirm the problem is not the site.4 min read

Error fix · Browser errorsERR_NAME_NOT_RESOLVED: Causes and Fixes for Visitors and OwnersChrome says the server IP address could not be found. Learn how to flush DNS, change resolvers, and diagnose broken records with dig and our DNS tools.4 min read

Error fix · Browser errorsERR_NETWORK_CHANGED: Why It Happens and How to Stop ItERR_NETWORK_CHANGED means Chrome saw your network change mid-request. Fix Wi-Fi roaming, VPN, IPv6 and adapter issues, and make web apps retry gracefully.5 min read

Error fix · Browser errorsERR_PROXY_CONNECTION_FAILED: Fix Proxy Settings and Proxy ServersChrome cannot reach the configured proxy. Reset Windows, macOS and Linux proxy settings, check VPN leftovers and PAC files, and repair a down proxy service.5 min read

Error fix · Browser errorsERR_SPDY_PROTOCOL_ERROR: Fix Chrome's HTTP/2 Connection FailuresERR_SPDY_PROTOCOL_ERROR is Chrome's older name for an HTTP/2 stream or framing failure. Clear sockets, test without HTTP/2, and fix header or proxy limits.4 min read

Error fix · Browser errorsERR_SSL_PROTOCOL_ERROR: What It Means and How to Fix ItChrome says the site "can't provide a secure connection" and shows ERR_SSL_PROTOCOL_ERROR. Learn the visitor fixes and the server misconfigurations behind it.4 min read

Error fix · Browser errorsERR_SSL_VERSION_OR_CIPHER_MISMATCH: Fix TLS Protocol and Cipher ErrorsThe server and browser share no TLS version or cipher. Update nginx or Apache to TLS 1.2/1.3, and test protocols and ciphers with openssl and nmap.4 min read

Error fix · Browser errorsERR_TOO_MANY_REDIRECTS: Find and Break the Redirect LoopChrome says the site redirected you too many times. Clear cookies as a visitor, or trace and fix the redirect loop in nginx, Apache, a CMS or a CDN.4 min read

Error fix · Browser errorsERR_TUNNEL_CONNECTION_FAILED: Proxy CONNECT Failure ExplainedERR_TUNNEL_CONNECTION_FAILED means your proxy refused to open a tunnel to an HTTPS site. Test with curl -x, check 407 and 403 answers, and fix Squid ACLs.5 min read

Error fix · Browser errorsERR_UNSAFE_PORT: Why Chrome Blocks a Port and What to Use InsteadChrome returns ERR_UNSAFE_PORT for URLs on restricted ports such as 6000 or 6666. See why browsers block them and move your service to a safe port.4 min read

Error fix · Browser errorsFirefox Secure Connection Failed: Error Codes and FixesFirefox's Secure Connection Failed page names a specific error code. Match SSL_ERROR, PR_ and SEC_ERROR codes to their causes and fix them.4 min read

Error fix · Browser errorsSafari Can't Open the Page: Server Unexpectedly Dropped the ConnectionSafari says the server unexpectedly dropped the connection when a TLS or TCP session is cut. Try Private Relay, DNS and content blockers, then fix the server.4 min read

Error fix · Browser errorsSEC_ERROR_EXPIRED_CERTIFICATE in Firefox: Causes and FixesFirefox shows SEC_ERROR_EXPIRED_CERTIFICATE when a certificate in the chain has expired. Check the leaf and intermediates with openssl and fix server renewal.5 min read

Error fix · Browser errorsThis Site Can't Be Reached: Decode the Error and Fix ItChrome's umbrella error for network failures. Use the line under the headline and the ERR_ code to find the real cause, then apply the right fix.5 min read

Error fix · Browser errorsYour Connection Is Not Private Warning: Meaning and FixesTriage the "Your connection is not private" warning in Chrome, Edge and Safari: read the code under Advanced, find the cause, and know when not to proceed.4 min read

Server errors

Error fix · Server errors502 Bad Gateway: Is It the CDN or Your Origin? How to TellWork out whether a 502 Bad Gateway comes from your CDN, a load balancer or your origin server, using response headers, error pages and direct origin tests.5 min read

Error fix · Server errors504 Gateway Timeout by Layer: nginx, Load Balancer, CDN and App TimeoutsA 504 depends on which timer fired first. See default timeouts and settings for nginx, Apache, AWS load balancers, Cloudflare, gunicorn and PHP-FPM.5 min read

Error fix · Server errorsApache .htaccess 500 Internal Server Error: Find the Bad LineA broken .htaccess file makes Apache return 500 for the whole site. Read the error log, find the bad directive, and fix syntax, modules or AllowOverride.4 min read

Error fix · Server errorsApache "(98)Address already in use: could not bind to addressApache fails to start with AH00072 make_sock could not bind to address. Find the process holding port 80 or 443, or the duplicate Listen line, and fix it.4 min read

Error fix · Server errorsApache "client denied by server configuration" (AH01630) FixFix Apache 403 errors logged as "AH01630: client denied by server configuration" by replacing old Order/Allow rules with Require and checking Directory blocks.4 min read

Error fix · Server errorsApache "Forbidden: You don't have permission to access this resourceApache 403 Forbidden on a new site is usually file permissions, a missing index file, SELinux or a Require rule. Use the error log to pick the right fix quickly.4 min read

Error fix · Server errorsApache "Invalid command" in .htaccess: Enable the Missing ModuleFix Apache's "Invalid command perhaps misspelled or defined by a module not included" error by enabling the right module, wrapping rules in IfModule, or removing the line.4 min read

Error fix · Server errorsApache "Premature end of script headers": Causes and FixesApache logs "Premature end of script headers" when a CGI, PHP-CGI or FastCGI script exits before sending valid headers. Check the script, shebang, permissions and limits.4 min read

Error fix · Server errorsApache mod_rewrite Not Working: Rules Ignored or 404? Fix ItWhen RewriteRule seems to do nothing in Apache, check that mod_rewrite is enabled, AllowOverride permits .htaccess, and the rule matches. Includes debug logging.4 min read

Error fix · Server errorsHTTP 400 Bad Request: What It Means and How to Fix ItFix HTTP 400 Bad Request as a visitor (cookies, URL, cache) or as a site owner (malformed headers, oversized cookies, proxy and app validation rules).4 min read

Error fix · Server errorsHTTP 403 Forbidden: Why It Happens and How to Fix ItFix HTTP 403 Forbidden as a visitor or owner: file permissions, missing index, nginx and Apache access rules, WAF and CDN blocks, hotlink and IP restrictions.4 min read

Error fix · Server errorsHTTP 404 Not Found: Find the Cause and Fix Broken URLsFix HTTP 404 Not Found as a visitor or owner: typos, moved pages, rewrite rules for nginx, Apache and WordPress, soft 404s, and redirects that stop lost traffic.4 min read

Error fix · Server errorsHTTP 405 Method Not Allowed: Fix GET, POST and OPTIONS ErrorsFix HTTP 405 Method Not Allowed: read the Allow header, correct form and API methods, nginx static POST, Apache limits, CORS preflight and redirect method changes.4 min read

Error fix · Server errorsHTTP 408 Request Timeout: Causes and Fixes for Slow ClientsFix HTTP 408 Request Timeout: why servers close idle or slow uploads, and how to tune nginx, Apache, load balancer and client timeouts without opening yourself to slowloris.4 min read

Error fix · Server errorsHTTP 410 Gone: What It Means and When to Use It Instead of 404HTTP 410 Gone says content was removed on purpose. Learn how to fix accidental 410s, serve 410 correctly in nginx and Apache, and how Google treats it versus 404.4 min read

Error fix · Server errorsHTTP 415 Unsupported Media Type: Fix Content-Type Errors in APIsFix HTTP 415 Unsupported Media Type: send the correct Content-Type, match what the API accepts, handle charset and multipart uploads, and debug Spring, Express and Laravel.4 min read

Error fix · Server errorsHTTP 422 Unprocessable Content: Fix Validation Errors in APIsFix HTTP 422 Unprocessable Content (Unprocessable Entity): read the validation body, fix field types and rules in Laravel, Rails, FastAPI and Express, and handle CSRF tokens.4 min read

Error fix · Server errorsHTTP 431 Request Header Fields Too Large: Cookie and Header FixesFix HTTP 431 Request Header Fields Too Large: clear bloated cookies, trim headers, and raise nginx, Apache, Node.js and proxy header limits only when needed.4 min read

Error fix · Server errorsHTTP 451 Unavailable For Legal Reasons: What It Means and OptionsHTTP 451 means content is blocked because of a legal demand. Learn what visitors can do, and how site owners should implement and diagnose 451 correctly.4 min read

Error fix · Server errorsHTTP 500 Internal Server Error: Where to Find the Cause in Your LogsFind the real cause of an HTTP 500 by reading the right log for your stack: nginx, Apache, PHP-FPM, WordPress, Laravel, Node.js, Python, Rails and Java.4 min read

Error fix · Server errorsHTTP 503 Retry-After and Maintenance Pages: Doing It RightServe a proper 503 Service Unavailable with a Retry-After header for maintenance windows, with nginx, Apache and CDN examples and notes on SEO and caching.4 min read

Error fix · Server errorsHTTP 505 HTTP Version Not Supported: Causes and FixesFix HTTP 505 Version Not Supported. Learn why a server rejects an HTTP version, from h2c and HTTP/1.0 proxies to malformed request lines, and how to correct it.4 min read

Error fix · Server errorsHTTP 507 Insufficient Storage: Free Disk Space and Fix QuotasHTTP 507 Insufficient Storage means the server cannot store what the request needs. Check disk space, inodes and quotas, then fix WebDAV and upload failures.5 min read

Error fix · Server errorsHTTP 508 Loop Detected and Resource Limit Is Reached: FixesFix HTTP 508 Loop Detected. It means a request cycle on WebDAV, and on CloudLinux hosts it appears as Resource Limit Is Reached. Find the cause and fix it.4 min read

Error fix · Server errorsMySQL "Server Has Gone Away" (Error 2006): Causes and FixesFix MySQL error 2006 "MySQL server has gone away" and 2013 "Lost connection during query" by checking timeouts, max_allowed_packet, crashes and idle connections.4 min read

Error fix · Server errorsMySQL "Too Many Connections" (Error 1040): Causes and FixesFix MySQL and MariaDB error 1040 Too many connections: see who holds the connections, raise max_connections safely, and stop apps from leaking them.4 min read

Error fix · Server errorsMySQL Error 2002: Can't Connect to Local MySQL Server (Fix)Fix MySQL and MariaDB error 2002 "Can't connect to local MySQL server through socket" by checking the service, socket path, bind address and firewall.4 min read

Error fix · Server errorsnginx 'directory index of "/path/" is forbidden' (403) Fixnginx returns 403 with "directory index of is forbidden" when a folder has no index file and autoindex is off. Add the index, fix the root, or enable listings safely.4 min read

Error fix · Server errorsnginx "connect() failed (111: Connection refused)" Upstream FixFix nginx "connect() failed (111: Connection refused) while connecting to upstream" by checking that PHP-FPM or your app listens where nginx expects.4 min read

Error fix · Server errorsnginx "could not build server_names_hash": Increase Bucket SizeFix the nginx emerg error "could not build server_names_hash, you should increase server_names_hash_bucket_size" with the right http-level values and a way to find the cause.4 min read

Error fix · Server errorsnginx "no live upstreams while connecting to upstream" Fixnginx logs no live upstreams when every server in an upstream block is marked failed. Learn why it happens and how to tune max_fails and fail_timeout.4 min read

Error fix · Server errorsnginx "rewrite or internal redirection cycle" (500) FixFix nginx 500 errors logged as rewrite or internal redirection cycle by finding the try_files, rewrite or error_page rule that keeps sending requests back to itself.3 min read

Error fix · Server errorsnginx "socket() failed (24: Too many open files)" FixFix nginx too many open files errors by raising worker_rlimit_nofile, the systemd LimitNOFILE value and system limits, then verify the real limits on workers.4 min read

Error fix · Server errorsnginx "SSL_do_handshake() failed": What Each Variant MeansDecode nginx SSL_do_handshake() failed log lines (wrong version number, no shared cipher, unknown ca, upstream handshakes) and fix client and proxy TLS settings.4 min read

Error fix · Server errorsnginx "upstream sent too big header" 502 FixFix nginx 502 errors caused by upstream sent too big header while reading response header. Raise proxy_buffer_size or fastcgi_buffer_size correctly.4 min read

Error fix · Server errorsnginx "upstream timed out (110: Connection timed out)" FixDecode the nginx log line "upstream timed out (110: Connection timed out)" and set the right timeout directive for PHP-FPM, proxy_pass or uWSGI.4 min read

Error fix · Server errorsnginx "worker_connections are not enough" FixFix the nginx worker_connections are not enough error by sizing worker_connections, worker_rlimit_nofile and the OS file limit, and by cutting wasted connections.4 min read

Error fix · Server errorsnginx 400 Request Header Or Cookie Too Large: How to Fix ItFix nginx 400 Bad Request "Request Header Or Cookie Too Large" by clearing bloated cookies and tuning large_client_header_buffers safely.5 min read

Error fix · Server errorsnginx 403 Forbidden: Diagnose by Error Log Message and FixDiagnose an nginx 403 Forbidden using the exact error log line: permissions, missing index, deny rules, SELinux, symlinks or an upstream. Includes a decision order.4 min read

Error fix · Server errorsnginx 404 for Files That Exist: root, alias and try_files Fixesnginx returns 404 although the file is on disk? Check root versus alias, location matching, try_files order, case, symlinks and the wrong server block, using the error log.4 min read

Error fix · Server errorsnginx 413 Request Entity Too Large: client_max_body_size FixFix nginx 413 Request Entity Too Large by raising client_max_body_size, then check PHP, Apache, ingress and CDN limits that can also reject uploads.4 min read

Error fix · Server errorsnginx 499 Client Closed Request: What It Means and When to Actnginx logs 499 when the client disconnects before the response. Learn the causes, how to find slow upstreams, and how proxy_ignore_client_abort works.4 min read

Error fix · Server errorsPHP "Allowed memory size exhausted" Error: Causes and FixesFix PHP's "Allowed memory size exhausted" fatal error: find the memory_limit actually in effect, raise it in the right place, and fix the memory hog.5 min read

Error fix · Server errorsPHP Parse Error: syntax error, unexpected token (How to Fix)Understand PHP "Parse error: syntax error, unexpected token" messages, find the broken line with php -l, and fix missing semicolons, braces and version mismatches.5 min read

Error fix · Server errorsWordPress "Cookies are blocked due to unexpected output" Login FixFix the WordPress login errors "Cookies are blocked due to unexpected output" and "Cookies are blocked or not supported by your browser" step by step.4 min read

Error fix · Server errorsWordPress "Publishing failed. You are probably offline" FixFix WordPress "Publishing failed" messages, including "You are probably offline" and rest_cookie_invalid_nonce, by checking login state, REST access and caching.4 min read

Error fix · Server errorsWordPress "The link you followed has expired" Error FixFix "The link you followed has expired" in WordPress, usually caused by a theme or plugin upload larger than PHP's post_max_size or upload limits.4 min read

Error fix · Server errorsWordPress "There has been a critical error on this website" FixFix the WordPress message "There has been a critical error on this website" by reading the recovery email, the PHP error log and disabling the failing plugin or theme.4 min read

Error fix · Server errorsWordPress Installation Failed: Could Not Create Directory - FixFix WordPress plugin or theme install errors like Could not create directory by correcting ownership, permissions, disk quota, leftover folders and FS_METHOD.4 min read

Error fix · Server errorsWordPress Posts Return 404 Not Found After Changing PermalinksFix WordPress posts and pages showing 404 Not Found while the home page works: flush rewrite rules, repair .htaccess, enable mod_rewrite or add the nginx try_files line.4 min read

Error fix · Server errorsWordPress Site Health "REST API error" and "Loopback request failedFix the Site Health warnings "The REST API encountered an error" and "Your site could not complete a loopback request" by finding the cURL or HTTP error behind them.4 min read

Cloudflare errors

Error fix · Cloudflare errorsCloudflare Error 1001: DNS Resolution Error (Causes and Fixes)Cloudflare error 1001 is a DNS resolution failure, usually a CNAME to a Cloudflare domain from a non-Cloudflare zone or a CNAME target that does not resolve.4 min read

Error fix · Cloudflare errorsCloudflare Error 1003: Direct IP Access Not Allowed (Fix)Cloudflare error 1003 appears when a browser or script connects to a Cloudflare IP address instead of a domain name. Learn why and how to fix it.4 min read

Error fix · Cloudflare errorsCloudflare Error 1004: Host Not Configured to Serve Web TrafficCloudflare error 1004 means the host is not set up to serve web traffic. Check A records for Cloudflare IPs, DNS propagation and proxy status, then contact support.4 min read

Error fix · Cloudflare errorsCloudflare Error 1009: Country or Region Banned (Fix)Cloudflare error 1009 means the site owner blocked the country or region of your IP address. See visitor options and how owners adjust geo rules safely.4 min read

Error fix · Cloudflare errorsCloudflare Error 1012: Access Denied (Malicious Activity Detected)Cloudflare error 1012 means the site owner blocked your IP or network after detecting malicious activity. Scan for malware, then ask the owner to allow you.4 min read

Error fix · Cloudflare errorsCloudflare Error 1015 "You Are Being Rate Limited": Fix GuideCloudflare error 1015 means a rate limiting rule temporarily blocked you for too many requests. See what to do as a visitor, API client or site owner.4 min read

Error fix · Cloudflare errorsCloudflare Error 1016 "Origin DNS Error": Causes and FixesFix Cloudflare error 1016 Origin DNS error by repairing the DNS record Cloudflare uses to find your origin: a missing A record, broken CNAME or custom hostname.5 min read

Error fix · Cloudflare errorsCloudflare Error 1020 "Access Denied": Meaning and How to Fix ItCloudflare error 1020 means a firewall or WAF rule blocked the request. Use the Ray ID and Security Events to find and fix the rule, as visitor or owner.5 min read

Error fix · Cloudflare errorsCloudflare Error 1033: Argo Tunnel Error (cloudflared Fix)Cloudflare error 1033 means a Tunnel hostname has no healthy cloudflared connector. Check tunnel status, restart the service, and fix firewall rules.3 min read

Error fix · Cloudflare errorsCloudflare Error 520: Web Server Returned an Unknown ErrorCloudflare error 520 means the origin sent an empty, malformed or unexpected response. Learn the real causes, how to test the origin, and what to fix.5 min read

Error fix · Cloudflare errorsCloudflare Error 522: Connection Timed Out (Causes and Fixes)Cloudflare error 522 means the origin did not answer in time. Learn the SYN and 90-second timeouts, firewall causes, and how to test and fix the origin.5 min read

Error fix · Cloudflare errorsCloudflare Error 523: Origin Is Unreachable (How to Fix)Cloudflare error 523 means there is no route from Cloudflare to your origin IP. Check DNS records, routing, the AWS VPC 172.64.0.0/13 trap and your host.5 min read

Error fix · Cloudflare errorsCloudflare Error 524: A Timeout Occurred (125 Second Limit)Cloudflare error 524 means your origin accepted the connection but sent no HTTP response within the 125 second proxy read timeout. Find slow requests and fix them.5 min read

Error fix · Cloudflare errorsCloudflare Error 526: Invalid SSL Certificate (Full Strict Fix)Cloudflare error 526 means the origin certificate failed validation in Full (strict) mode. Fix expired, self-signed, mismatched or incomplete-chain certificates.5 min read

Error fix · Cloudflare errorsCloudflare Error 530: Origin Hostname Cannot Be ResolvedCloudflare error 530 means it could not resolve your origin hostname. Read the 1xxx code in the page body to find the real cause and apply the right fix.4 min read

Error fix · Cloudflare errorsCloudflare Errors 1006, 1007, 1008: Your IP Address Has Been BannedCloudflare errors 1006, 1007, 1008 and 1106 mean a site owner banned your IP address. Learn what to do as a visitor and how owners find the rule and unblock.4 min read

Email errors

Error fix · Email errorsEmail Connection Timed Out on Port 25: Blocked Outbound SMTPEmail stuck with "connection timed out" to port 25? Learn how to confirm your host or ISP blocks outbound SMTP and send through port 587 or a relay.4 min read

Error fix · Email errorsSMTP "535 Authentication Failed" Error: Causes and FixesFix SMTP error 535 5.7.8 "Authentication failed" with checks for credentials, app passwords, TLS port mismatch and provider authentication changes.5 min read

Error fix · Email errorsSMTP "554 5.7.1 Relay access denied": What It Means and FixesFix SMTP "554 5.7.1 Relay access denied" by sending through the right server with authentication, and by correcting Postfix or Exim relay settings and MX records.5 min read

Error fix · Email errorsSMTP 421 Service Not Available: Causes and FixesFix SMTP 421 "service not available, closing transmission channel": rate limits, reputation, connection caps and local server faults, with Postfix log examples.4 min read

Error fix · Email errorsSMTP 450 Mailbox Unavailable and Greylisting ExplainedWhat SMTP 450 and 451 4.7.1 greylisting deferrals mean, how long delays last, and when a 450 signals a real problem such as rate limits or a bad recipient.4 min read

Error fix · Email errorsSMTP 451 Local Error in Processing: Causes and FixesTroubleshoot SMTP "451 requested action aborted: local error in processing" on your own server or a remote one: disk, DNS, content filters and policy daemons.4 min read

Error fix · Email errorsSMTP 452 Insufficient Storage: Server, Mailbox or Recipient LimitsFix SMTP 452 4.2.2 and 4.3.1 insufficient storage errors, including full recipient inboxes, full mail spools and too-many-recipients limits.4 min read

Error fix · Email errorsSMTP 454 TLS Not Available Due to Temporary ReasonFix SMTP 454 4.7.0 "TLS not available due to temporary reason": broken certificates, unreadable key files, expired chains and STARTTLS failures.4 min read

Error fix · Email errorsSMTP 501 Syntax Error in Parameters or ArgumentsFix SMTP 501 5.5.2 and 5.5.4 errors: bad HELO/EHLO names, malformed MAIL FROM or RCPT TO addresses, and broken AUTH responses, with test commands.4 min read

Error fix · Email errorsSMTP 503 Bad Sequence of Commands: Causes and FixesFix SMTP 503 5.5.1 "bad sequence of commands" errors: missing EHLO, RCPT before MAIL, AUTH after mail starts, pipelining and proxy problems.4 min read

Error fix · Email errorsSMTP 550 5.1.1 User Unknown: Mailbox Does Not ExistFix "550 5.1.1 The email account that you tried to reach does not exist": check typos, stale MX records and your own Postfix or Exchange recipient tables.5 min read

Error fix · Email errorsSMTP 550 5.7.1 Message Rejected: Causes and FixesDecode SMTP "550 5.7.1" rejections from Gmail, Microsoft and others, and fix SPF, DKIM, DMARC, blocklist and reverse DNS problems that cause them.4 min read

Error fix · Email errorsSMTP 550 5.7.26 Unauthenticated Email: SPF, DKIM and DMARC FixFix "550 5.7.26 This mail is unauthenticated" bounces from Gmail and similar rejections: read the failed checks, repair SPF and DKIM, align DMARC.5 min read

Error fix · Email errorsSMTP 552 Message Size Exceeded: 5.3.4 and 5.2.3 Limits ExplainedFix SMTP 552 "message size exceeds fixed limit" (5.3.4) and 5.2.3 bounces: attachment limits, base64 overhead, Postfix message_size_limit and filters.5 min read

Error fix · Email errorsSMTP 553 Sender Address Rejected: Causes and FixesFix SMTP 553 sender address rejected errors: from-address mismatches, unverified domains, Postfix login maps and relay rules that block outgoing mail.4 min read

Error fix · Email errorsSMTP 554 5.7.1 Blocklisted: Find the List and Get DelistedMail rejected with 554 5.7.1 and a blocklist name? Identify which DNSBL listed your IP, fix the cause, request delisting and prevent a relisting.4 min read

Developer errors

Error fix · Developer errorsCannot connect to the Docker daemon" Fix: Is the Daemon Running?Fix "Cannot connect to the Docker daemon at unix:///var/run/docker.sock": start the service, fix socket permissions and group, and check DOCKER_HOST.4 min read

Error fix · Developer errorsCertificate Hostname Mismatch: Fix SAN and Name ErrorsFix "certificate is not valid for" and hostname mismatch errors by reading the certificate's SAN list, then reissuing for the right names or serving the right site.4 min read

Error fix · Developer errorsCORS Error: "No Access-Control-Allow-Origin header is present" FixFix the browser CORS error "No Access-Control-Allow-Origin header is present" with server header examples, preflight handling and credentials rules.4 min read

Error fix · Developer errorsCORS Preflight Response Failed: "Does Not Have HTTP OK Status" FixFix CORS preflight failures: OPTIONS requests returning 404, 405, 401 or redirects, missing Allow headers, and auth middleware that runs before CORS.4 min read

Error fix · Developer errorscurl (28) Operation Timed Out: Find Which Phase StalledFix curl error 28 "Operation timed out" and "Connection timed out" by using curl timing variables to see whether DNS, connect, TLS or the server response stalled.5 min read

Error fix · Developer errorscurl (35) SSL connect error: What Each Variant Meanscurl exit code 35 is a generic TLS handshake failure. Read the OpenSSL text after it to separate protocol, cipher, reset and wrong-port causes.4 min read

Error fix · Developer errorscurl (7) Failed to Connect to Host: Port Closed or BlockedFix curl error 7 "Failed to connect to host port 443: Connection refused" by checking the listener, firewall, IPv6 and proxy settings, in a clear order.4 min read

Error fix · Developer errorscurl Error 60: SSL Certificate Problem (Unable to Get Local Issuer)Fix curl error 60 "SSL certificate problem: unable to get local issuer certificate" by finding whether the server chain, CA bundle, proxy or clock is at fault.5 min read

Error fix · Developer errorsDNS SERVFAIL Explained: Causes and How to Diagnose It with digSERVFAIL means a resolver could not get a usable answer. Use dig, +cd and +trace to separate DNSSEC failures, dead nameservers and broken delegation, then fix the right layer.4 min read

Error fix · Developer errorsDocker "bind: address already in use" and "port is already allocatedFix Docker "Bind for 0.0.0.0:80 failed: port is already allocated" and "address already in use": find the process or container holding the port and remap it.4 min read

Error fix · Developer errorsDocker "no space left on device": Find What Filled the DiskFix Docker "no space left on device" during pulls, builds and writes: check disk and inodes, run docker system df, prune safely and move the data root.4 min read

Error fix · Developer errorsGit "SSL certificate problem": unable to get local issuer certificateFix git "SSL certificate problem: unable to get local issuer certificate" and "self signed certificate": find the cause, add the CA, never disable verification.4 min read

Error fix · Developer errorsJava PKIX path building failed: Fix the TruststoreFix Java's "PKIX path building failed: unable to find valid certification path to requested target" with keytool, a custom truststore and the right JDK cacerts file.4 min read

Error fix · Developer errorsKubernetes CrashLoopBackOff: How to Debug a Restarting PodDebug Kubernetes CrashLoopBackOff step by step: read previous logs, check exit codes, OOMKilled, probes, config and commands, then fix and verify the pod.4 min read

Error fix · Developer errorsKubernetes Ingress 502 Bad Gateway and 503 Service UnavailableFix 502 and 503 from a Kubernetes Ingress: check endpoints, selectors, readiness, ports, controller logs and backend protocol, in a clear order.5 min read

Error fix · Developer errorsMongoDB "connect ECONNREFUSED 127.0.0.1:27017": Causes and FixesFix MongoDB ECONNREFUSED on port 27017: start mongod, repair bindIp, handle the IPv6 localhost trap in Node, and fix Docker, Compose and firewall issues.4 min read

Error fix · Developer errorsMongoServerSelectionError: Server Selection Timed Out - FixesFix MongoDB server selection timed out errors. Check Atlas IP access lists, DNS SRV, TLS, bindIp, replica set hostnames, firewalls and serverSelectionTimeoutMS.5 min read

Error fix · Developer errorsMySQL ERROR 1062: Duplicate Entry for Key - Causes and FixesFix MySQL ERROR 1062 Duplicate entry for key. Find the clashing row, use ON DUPLICATE KEY UPDATE or INSERT IGNORE, and repair exhausted AUTO_INCREMENT keys.4 min read

Error fix · Developer errorsMySQL ERROR 1114 (HY000): The Table Is Full - Causes and FixesFix MySQL and MariaDB ERROR 1114 The table is full. Check disk space, tmpdir, max_heap_table_size, tmp_table_size and InnoDB tablespace limits step by step.5 min read

Error fix · Developer errorsMySQL ERROR 1205: Lock Wait Timeout Exceeded - Find the BlockerFix MySQL ERROR 1205 Lock wait timeout exceeded. Find the blocking transaction, tune innodb_lock_wait_timeout, and stop long transactions and missing indexes.4 min read

Error fix · Developer errorsMySQL ERROR 1213: Deadlock Found When Trying to Get LockUnderstand MySQL ERROR 1213 deadlocks. Read the InnoDB deadlock report, fix lock ordering and indexes, log every deadlock, and retry transactions safely.4 min read

Error fix · Developer errorsMySQL ERROR 1215: Cannot Add Foreign Key Constraint - ChecklistFix MySQL ERROR 1215 Cannot add foreign key constraint. Check column types, signedness, collation, indexes, engines, existing data and Laravel foreignId.4 min read

Error fix · Developer errorsMySQL ERROR 1366: Incorrect String Value for Column (utf8mb4 Fix)Fix MySQL ERROR 1366 Incorrect string value for emoji and 4-byte characters. Convert to utf8mb4, set the connection charset, and avoid index length traps.4 min read

Error fix · Developer errorsMySQL ERROR 2013: Lost Connection to Server During QueryFix MySQL ERROR 2013 Lost connection to MySQL server during query. Check net_read_timeout, packet size, crashes and OOM kills, and proxy or firewall idle limits.4 min read

Error fix · Developer errorsNode.js "certificate has expired" (CERT_HAS_EXPIRED) FixFix Node.js "Error: certificate has expired" (CERT_HAS_EXPIRED): renew the server certificate, replace an expired intermediate, or fix the system clock.4 min read

Error fix · Developer errorsNode.js "Error: connect ECONNREFUSED" 127.0.0.1: Causes and FixesFix Node.js ECONNREFUSED errors for databases, APIs and localhost: confirm the service listens, handle IPv6 localhost, Docker networking and startup order.5 min read

Error fix · Developer errorsNode.js "getaddrinfo ENOTFOUND" Error: Causes and FixesFix Node.js "getaddrinfo ENOTFOUND hostname" and EAI_AGAIN by checking the hostname string, DNS, container DNS, proxies and environment variables.5 min read

Error fix · Developer errorsNode.js "JavaScript heap out of memory" Fix and DiagnosisFix "FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory". Raise --max-old-space-size, find leaks and tune builds and containers.4 min read

Error fix · Developer errorsNode.js EADDRINUSE: address already in use :::3000 FixFix Node.js "Error: listen EADDRINUSE: address already in use" by finding the process holding the port with lsof, ss or netstat, then stopping it or changing ports.5 min read

Error fix · Developer errorsNode.js ECONNRESET: read ECONNRESET and "socket hang up" FixFix Node.js "read ECONNRESET" and "socket hang up". Learn why keep-alive reuse, proxies and idle timeouts reset sockets, and how to retry safely.4 min read

Error fix · Developer errorsNode.js ENOMEM "Cannot Allocate Memory": Find What Ran OutFix Node.js spawn ENOMEM and "Cannot allocate memory" errors: tell OS memory exhaustion from heap limits, check the OOM killer, swap and container limits.4 min read

Error fix · Developer errorsNode.js EPIPE: write EPIPE (broken pipe) Causes and FixesFix Node.js "Error: write EPIPE". Understand broken pipes from closed sockets, piped output like head, and dead child processes, and handle them correctly.4 min read

Error fix · Developer errorsNode.js ERR_SSL_WRONG_VERSION_NUMBER: Causes and FixesFix "write EPROTO ... ssl3_get_record:wrong version number" in Node.js. It usually means HTTPS was spoken to a plain HTTP port, or a proxy URL is wrong.4 min read

Error fix · Developer errorsNXDOMAIN vs SERVFAIL vs REFUSED: DNS Response Codes ComparedLearn what the DNS response codes NXDOMAIN, SERVFAIL, REFUSED and NOERROR with no data mean, how to read them in dig, and what to check first for each one.4 min read

Error fix · Developer errorsopenssl s_client "Verify return code": Every Code ExplainedRead openssl s_client output correctly: what Verify return code 0, 10, 18, 19, 20, 21 and 62 mean, the right flags to use, and the fix for each result.5 min read

Error fix · Developer errorsPHP "Call to undefined function": Missing Extension or Removed FunctionFix PHP's "Uncaught Error: Call to undefined function" by checking for a missing extension, a function removed in PHP 7 or 8, or a missing include.4 min read

Error fix · Developer errorsPHP "Class not found" Error: Autoload, Namespace and Case FixesFix PHP's 'Class "App\Foo" not found' error: regenerate the Composer autoloader, correct namespaces and filename case, and install missing extensions.4 min read

Error fix · Developer errorsPHP "Maximum execution time of 30 seconds exceeded" FixFix PHP's "Maximum execution time exceeded" fatal error: raise max_execution_time where it really applies, and find out why the script is slow in the first place.4 min read

Error fix · Developer errorsPHP failed to open stream: Permission denied - Fix OwnershipFix PHP's failed to open stream: Permission denied warning by checking file owner, directory execute bits, the PHP-FPM user, SELinux and open_basedir.4 min read

Error fix · Developer errorsPHP Fatal error: Uncaught TypeError - Causes and FixesFix PHP's Uncaught TypeError by reading the message: wrong argument or return type, null passed to a function, or unsupported operands after a PHP 8 upgrade.4 min read

Error fix · Developer errorsPHP Headers Already Sent: Find the Output and Fix ItFix PHP's headers already sent warning by finding the file and line where output started: BOM, stray whitespace, echo, or notices. Includes ob_start use.4 min read

Error fix · Developer errorsPHP Warning: Undefined array key - What It Means and How to Fix ItFix PHP's Undefined array key warning with isset(), the null coalescing operator and array_key_exists(), and learn why PHP 8 replaced Undefined index.4 min read

Error fix · Developer errorsPHP-FPM Primary Script Unknown: Fix the nginx SCRIPT_FILENAME PathFix the nginx and PHP-FPM Primary script unknown error by correcting root, SCRIPT_FILENAME, try_files, chroot paths and file permissions. Includes tests.4 min read

Error fix · Developer errorsPHP-FPM Server Reached pm.max_children: Size Your Pool CorrectlyFix the PHP-FPM warning server reached pm.max_children by measuring worker memory, setting pm.max_children from real RAM, and finding slow requests.4 min read

Error fix · Developer errorsPostgreSQL "ERROR: deadlock detected" - Find the Cycle and Fix ItUnderstand PostgreSQL deadlock detected (SQLSTATE 40P01). Read the log, tune deadlock_timeout and log_lock_waits, order locks, and add safe retries.5 min read

Error fix · Developer errorsPostgreSQL "sorry, too many clients already" - Causes and FixesFix FATAL sorry, too many clients already in PostgreSQL. Find who holds connections, tune max_connections, use PgBouncer, and stop connection leaks.4 min read

Error fix · Developer errorsRedis "Connection Refused" on Port 6379: Causes and FixesFix Redis Could not connect to Redis at 127.0.0.1:6379 Connection refused: check the service, bind address, protected mode, firewalls and Docker networking.4 min read

Error fix · Developer errorsRedis MISCONF "unable to persist to disk" - Causes and FixesFix the Redis MISCONF error when BGSAVE fails. Check disk space, directory permissions, fork memory and vm.overcommit_memory, then handle stop-writes-on-bgsave-error.4 min read

Error fix · Developer errorsRefused to Display in a Frame: X-Frame-Options Fix (iframe Blocked)Fix "Refused to display in a frame because it set X-Frame-Options" by changing frame-ancestors or X-Frame-Options on the framed site, or by using an embed URL.4 min read

Error fix · Developer errorsself signed certificate in certificate chain: Causes and FixesFix "self signed certificate in certificate chain" in npm, Node, git and curl: identify the proxy or private CA behind it and trust it safely.4 min read

Error fix · Developer errorsSQLite "database is locked" (SQLITE_BUSY) - Causes and FixesFix SQLite database is locked errors. Enable WAL mode, set busy_timeout, use BEGIN IMMEDIATE, shorten transactions, and avoid network filesystems.5 min read

Error fix · Developer errorsSSH "Permission denied (publickey)": How to Fix ItFix SSH Permission denied (publickey) by checking which key is offered, authorized_keys, file permissions, usernames, sshd settings and agent problems.4 min read

Error fix · Developer errorsSSL wrong version number: Why It Happens and How to Fix ItThe OpenSSL error wrong version number means a TLS client got non-TLS bytes back. Find the plain-HTTP port, the HTTPS-to-HTTP proxy setting or STARTTLS mix-up behind it.4 min read