Troubleshooting
When something is not working: checks and fixes.
127 guides · page 4 of 7
Fix ERR_TOO_MANY_REDIRECTS (redirect loops) on any website
Trace a redirect loop with curl and fix the usual causes: HTTPS behind Cloudflare or a proxy, conflicting www rules, app URL settings and cached redirects.
Fix ERR_TOO_MANY_REDIRECTS: diagnose a redirect loop
Trace an ERR_TOO_MANY_REDIRECTS loop across Nginx, Apache, WordPress and Cloudflare, and find the single rule that keeps sending traffic back to itself.
Fix file upload size errors on cPanel (upload_max_filesize, 413)
Fix 'file exceeds upload_max_filesize', 413 Request Entity Too Large and failed uploads on cPanel by raising PHP limits correctly, or using FTP for very large files.
Fix MySQL or MariaDB error 1045: Access denied for user
Error 1045 means MySQL or MariaDB rejected the login. Find which user and host the client asked for, fix the password or grants, and reset a lost root password safely.
Fix Nginx 404 errors with try_files for pretty URLs
Pretty URLs return 404 on Nginx when nothing routes them to your app. Add the right try_files line for WordPress, Laravel or a single-page app, and avoid root and alias mistakes.
Fix Nginx 413 Request Entity Too Large
Nginx returns 413 Request Entity Too Large when an upload is bigger than client_max_body_size. Raise the limit for one site or the whole server, match PHP's limits, and test.
Fix Nginx failed to start: address already in use
Nginx will not start when another program already holds port 80 or 443. Find what is using the port with ss, stop or move it, fix duplicate listen lines, then start Nginx.
Fix out-of-memory kills: the Linux OOM killer explained
Recognise when the Linux OOM killer stopped MySQL, PHP or Node.js, find which process used the memory, and prevent it with right-sized limits, swap and service settings.
Fix PDOException: could not find driver in PHP
Fix the PHP error "could not find driver" by enabling the right PDO driver (pdo_mysql, pdo_pgsql, pdo_sqlite) for the PHP version your site and CLI actually use.
Fix PHP "Allowed memory size exhausted" fatal error
PHP stops a script when it tries to allocate more memory than memory_limit allows. Find the script that hit the limit, raise the limit in the right place, and fix the cause.
Fix PHP cURL error 28 and other outgoing request errors
Fix cURL error 28 (operation timed out), error 6 (could not resolve host) and error 7 (failed to connect) when PHP, WordPress or Laravel call external APIs.
Fix PHP Fatal error: Call to undefined function
Fix "Call to undefined function" errors in PHP: missing extensions like mysqli, curl, mb_ or gd, functions removed in PHP 8, missing includes and wrong namespaces.
Fix PHP Fatal error: Class not found
Fix "Class not found" errors in PHP apps: Composer autoload not loaded or outdated, missing vendor folder, wrong namespace or case-sensitive file names on Linux, and missing extensions.
Fix PHP max_input_vars exceeded (forms and menus not saving)
Fix the PHP warning Input variables exceeded 1000 and forms or WordPress menus that silently stop saving, by raising max_input_vars on cPanel, a VPS or with .user.ini.
Fix PHP Parse error: syntax error, unexpected
Understand and fix PHP parse errors such as unexpected end of file, unexpected token, unexpected identifier and T_STRING, including errors caused by an old PHP version.
Fix PHP session errors: save path, permissions and lost logins
Fix session_start() errors and users being logged out: session.save_path permissions, full disks, garbage collection, cookie settings, multiple servers and Redis sessions.
Fix pip "externally-managed-environment" on Ubuntu and Debian
Understand why pip refuses to install packages system-wide on Ubuntu 23.04+ and Debian 12, and install Python packages the right way with venv, pipx or apt.
Fix SSH "connection refused", "timed out" and "permission denied"
Work out what each SSH error means, test the port from your computer, and use the control panel's browser console to fix the firewall, the SSH service or key permissions.
Fix SSH "Too many authentication failures" when connecting
Learn why SSH offers too many keys and gets rejected, and fix it with IdentitiesOnly, ssh-agent and a small SSH config entry.
Fix SSH errors: connection refused, timed out and permission denied
Diagnose why you cannot SSH into a server: connection refused, timeouts, host key warnings and permission denied, with the exact checks and fixes for each.
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