https://daniele-michelin.com/en/errors/ New pages in the admin reference: error messages, tech comparisons and command cheat sheets. en https://daniele-michelin.com/en/cheat-sheets/openssl-cheat-sheet/https://daniele-michelin.com/en/cheat-sheets/openssl-cheat-sheet/Fri, 23 Oct 2026 00:00:00 +0000OpenSSL commands for TLS troubleshooting: check certificate chain and expiry, create a CSR, match key and cert, convert PEM/DER/PFX, test STARTTLS. https://daniele-michelin.com/en/cheat-sheets/journalctl-cheat-sheet/https://daniele-michelin.com/en/cheat-sheets/journalctl-cheat-sheet/Fri, 23 Oct 2026 00:00:00 +0000journalctl commands for troubleshooting: filter logs by unit, boot, time and priority, follow live, JSON output and keep journal disk usage in check. https://daniele-michelin.com/en/cheat-sheets/dig-cheat-sheet/https://daniele-michelin.com/en/cheat-sheets/dig-cheat-sheet/Fri, 23 Oct 2026 00:00:00 +0000dig commands for DNS troubleshooting: A, MX, TXT, CAA, +short, +trace, reverse lookups, DNSSEC, SPF/DKIM/DMARC checks and authoritative queries. https://daniele-michelin.com/en/cheat-sheets/nextcloud-occ-cheat-sheet/https://daniele-michelin.com/en/cheat-sheets/nextcloud-occ-cheat-sheet/Fri, 23 Oct 2026 00:00:00 +0000The essential Nextcloud occ commands for admins: maintenance mode, files:scan, users, apps, missing DB indices, cron, trash bin cleanup and 2FA. https://daniele-michelin.com/en/compare/nextcloud-s3-vs-nfs/https://daniele-michelin.com/en/compare/nextcloud-s3-vs-nfs/Fri, 23 Oct 2026 00:00:00 +0000S3 object storage or NFS/block storage as Nextcloud primary storage? Data layout, scaling, backup, migration and pitfalls from real operations. https://daniele-michelin.com/en/compare/systemd-timers-vs-cron/https://daniele-michelin.com/en/compare/systemd-timers-vs-cron/Fri, 23 Oct 2026 00:00:00 +0000systemd timers or cron for scheduled jobs? Logging, missed runs, overlapping jobs, environment and effort compared, with everyday examples. https://daniele-michelin.com/en/compare/nginx-vs-apache-php-fpm/https://daniele-michelin.com/en/compare/nginx-vs-apache-php-fpm/Fri, 23 Oct 2026 00:00:00 +0000nginx or Apache in front of PHP-FPM? .htaccess, configuration, upload limits, timeouts and troubleshooting for Nextcloud, WordPress and other PHP apps. https://daniele-michelin.com/en/compare/nextcloud-aio-vs-manual-install/https://daniele-michelin.com/en/compare/nextcloud-aio-vs-manual-install/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud All-in-One or a classic setup with web server, PHP-FPM and database? Effort, control, updates, backup and troubleshooting compared honestly. https://daniele-michelin.com/en/compare/spf-dkim-dmarc-differences/https://daniele-michelin.com/en/compare/spf-dkim-dmarc-differences/Fri, 23 Oct 2026 00:00:00 +0000What SPF, DKIM and DMARC each check, where they fail and why you need all three. Covers alignment, forwarding and common mistakes from practice. https://daniele-michelin.com/en/compare/http-01-vs-dns-01/https://daniele-michelin.com/en/compare/http-01-vs-dns-01/Fri, 23 Oct 2026 00:00:00 +0000HTTP-01 or DNS-01 challenge for Let's Encrypt? Wildcards, internal hosts, port 80, DNS API access and typical validation failures compared. https://daniele-michelin.com/en/compare/nextcloud-vs-seafile/https://daniele-michelin.com/en/compare/nextcloud-vs-seafile/Fri, 23 Oct 2026 00:00:00 +0000Self-host Nextcloud or Seafile? Storage format, sync, features, updates and backup compared, plainly and from an operations point of view. https://daniele-michelin.com/en/compare/saml-vs-oidc/https://daniele-michelin.com/en/compare/saml-vs-oidc/Fri, 23 Oct 2026 00:00:00 +0000SAML or OpenID Connect for single sign-on? Differences in protocol, clients, certificates and troubleshooting, from running Nextcloud with Keycloak. https://daniele-michelin.com/en/errors/systemd-job-failed-control-process-exited-with-error-code/https://daniele-michelin.com/en/errors/systemd-job-failed-control-process-exited-with-error-code/Fri, 23 Oct 2026 00:00:00 +0000“Job for X.service failed because the control process exited with error code”: how to find the real error message with systemctl status and journalctl. https://daniele-michelin.com/en/errors/linux-out-of-memory-killed-process-oom-killer/https://daniele-michelin.com/en/errors/linux-out-of-memory-killed-process-oom-killer/Fri, 23 Oct 2026 00:00:00 +0000“Out of memory: Killed process” in the kernel log: the OOM killer ended a process. Find the culprit, limit memory per service and stop it happening again. https://daniele-michelin.com/en/errors/linux-too-many-open-files/https://daniele-michelin.com/en/errors/linux-too-many-open-files/Fri, 23 Oct 2026 00:00:00 +0000“Too many open files” (error 24) in nginx, Java or Node: the per-process limit is reached. Check it properly, set LimitNOFILE in systemd, find leaks. https://daniele-michelin.com/en/errors/linux-read-only-file-system/https://daniele-michelin.com/en/errors/linux-read-only-file-system/Fri, 23 Oct 2026 00:00:00 +0000“Read-only file system” on Linux: filesystem errors with remount-ro, a failing disk, ro mount or systemd ProtectSystem. Diagnose it safely and fix it. https://daniele-michelin.com/en/errors/ssh-permission-denied-publickey/https://daniele-michelin.com/en/errors/ssh-permission-denied-publickey/Fri, 23 Oct 2026 00:00:00 +0000SSH says “Permission denied (publickey)”: wrong user, key missing from authorized_keys, wrong permissions or ssh-rsa disabled. Check it step by step. https://daniele-michelin.com/en/errors/dns-cname-at-zone-apex-not-allowed/https://daniele-michelin.com/en/errors/dns-cname-at-zone-apex-not-allowed/Fri, 23 Oct 2026 00:00:00 +0000Error “CNAME and other data” or “CNAME at apex not allowed”: the root domain cannot have a CNAME. Why that is, and which alternatives actually work. https://daniele-michelin.com/en/errors/dns-nxdomain-dns-probe-finished-nxdomain/https://daniele-michelin.com/en/errors/dns-nxdomain-dns-probe-finished-nxdomain/Fri, 23 Oct 2026 00:00:00 +0000NXDOMAIN or DNS_PROBE_FINISHED_NXDOMAIN means DNS says the name does not exist. Find the typo, missing record, broken delegation or negative cache. https://daniele-michelin.com/en/errors/letsencrypt-too-many-certificates-already-issued/https://daniele-michelin.com/en/errors/letsencrypt-too-many-certificates-already-issued/Fri, 23 Oct 2026 00:00:00 +0000Let's Encrypt says “too many certificates already issued”? Which rate limit applies, how to wait it out safely and how to avoid issuance loops in future. https://daniele-michelin.com/en/errors/ssl-certificate-has-expired/https://daniele-michelin.com/en/errors/ssl-certificate-has-expired/Fri, 23 Oct 2026 00:00:00 +0000“certificate has expired” or NET::ERR_CERT_DATE_INVALID: renewal failed, service not reloaded or wrong clock. How to check it and fix it for good. https://daniele-michelin.com/en/errors/net-err-cert-common-name-invalid/https://daniele-michelin.com/en/errors/net-err-cert-common-name-invalid/Fri, 23 Oct 2026 00:00:00 +0000Chrome shows NET::ERR_CERT_COMMON_NAME_INVALID: the hostname is not in the certificate. Check the SAN, find the wrong vhost and expand the certificate. https://daniele-michelin.com/en/errors/ssl-error-rx-record-too-long/https://daniele-michelin.com/en/errors/ssl-error-rx-record-too-long/Fri, 23 Oct 2026 00:00:00 +0000Firefox shows SSL_ERROR_RX_RECORD_TOO_LONG: on port 443 the server answers with plain HTTP. Usually “ssl” is missing from the nginx listen line. https://daniele-michelin.com/en/errors/ssl-unable-to-get-local-issuer-certificate/https://daniele-michelin.com/en/errors/ssl-unable-to-get-local-issuer-certificate/Fri, 23 Oct 2026 00:00:00 +0000“SSL certificate problem: unable to get local issuer certificate” in curl, Python or Git: missing intermediates, CA bundle or TLS inspection. Fixes. https://daniele-michelin.com/en/errors/saml-clock-skew-notbefore-timestamp-not-yet-valid/https://daniele-michelin.com/en/errors/saml-clock-skew-notbefore-timestamp-not-yet-valid/Fri, 23 Oct 2026 00:00:00 +0000SAML error “Could not validate timestamp: not yet valid” or NotBefore/NotOnOrAfter: IdP and SP clocks differ. How to check it and fix it with NTP. https://daniele-michelin.com/en/errors/oidc-redirect-uri-mismatch-invalid-redirect-uri/https://daniele-michelin.com/en/errors/oidc-redirect-uri-mismatch-invalid-redirect-uri/Fri, 23 Oct 2026 00:00:00 +0000OIDC error “redirect_uri_mismatch” or “Invalid parameter: redirect_uri”: the callback URL does not match the IdP registration. How to find the difference. https://daniele-michelin.com/en/errors/oidc-invalid-grant-token-endpoint/https://daniele-michelin.com/en/errors/oidc-invalid-grant-token-endpoint/Fri, 23 Oct 2026 00:00:00 +0000OIDC error “invalid_grant” at the token endpoint: expired or reused code, mismatched redirect_uri, revoked refresh token or clock skew. How to fix it. https://daniele-michelin.com/en/errors/nextcloud-last-background-job-ran-ago-cron/https://daniele-michelin.com/en/errors/nextcloud-last-background-job-ran-ago-cron/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says “Last background job execution ran … ago”? Check cron mode, the www-data crontab and errors in cron.php, then fix it permanently. https://daniele-michelin.com/en/errors/nextcloud-database-is-missing-some-indexes/https://daniele-michelin.com/en/errors/nextcloud-database-is-missing-some-indexes/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says “The database is missing some indexes”. How to add missing indices, columns and primary keys safely with occ, even on large tables. https://daniele-michelin.com/en/errors/nextcloud-memcache-apcu-not-available-for-local-cache/https://daniele-michelin.com/en/errors/nextcloud-memcache-apcu-not-available-for-local-cache/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud shows “Memcache APCu not available for local cache” in occ or cron: usually apc.enable_cli=1 is missing in the CLI php.ini. Check and fix. https://daniele-michelin.com/en/errors/nextcloud-csrf-check-failed/https://daniele-michelin.com/en/errors/nextcloud-csrf-check-failed/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says “CSRF check failed” on login or save? Usually the session is lost: check cookies, reverse proxy, session storage and Redis step by step. https://daniele-michelin.com/en/errors/nextcloud-internal-server-error-request-id/https://daniele-michelin.com/en/errors/nextcloud-internal-server-error-request-id/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud shows “Internal Server Error” with a request ID? How to find the matching entry in nextcloud.log and fix the most common causes directly. https://daniele-michelin.com/en/errors/nextcloud-data-directory-readable-by-other-users/https://daniele-michelin.com/en/errors/nextcloud-data-directory-readable-by-other-users/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says “Your data directory is readable by other users”. How to set 0770 correctly, also on NFS and CIFS mounts, without breaking access. https://daniele-michelin.com/en/errors/nginx-connect-failed-111-connection-refused-upstream/https://daniele-michelin.com/en/errors/nginx-connect-failed-111-connection-refused-upstream/Fri, 23 Oct 2026 00:00:00 +0000nginx logs “connect() failed (111: Connection refused) while connecting to upstream”: the backend is down or listens elsewhere. How to check and fix it. https://daniele-michelin.com/en/errors/http-400-request-header-or-cookie-too-large/https://daniele-michelin.com/en/errors/http-400-request-header-or-cookie-too-large/Fri, 23 Oct 2026 00:00:00 +0000nginx returns 400 “Request Header Or Cookie Too Large”: too many or too big cookies or tokens. Causes, a curl test and safe buffer sizes to set. https://daniele-michelin.com/en/errors/http-503-service-unavailable-nginx/https://daniele-michelin.com/en/errors/http-503-service-unavailable-nginx/Fri, 23 Oct 2026 00:00:00 +0000HTTP 503 Service Unavailable with nginx: rate limit, maintenance mode, overloaded backend or a load balancer without healthy servers. Find the source. https://daniele-michelin.com/en/errors/http-500-internal-server-error-php/https://daniele-michelin.com/en/errors/http-500-internal-server-error-php/Fri, 23 Oct 2026 00:00:00 +0000HTTP 500 Internal Server Error is just the symptom. Find the real cause in nginx and PHP logs: fatal errors, memory limit, permissions, rewrite loops. https://daniele-michelin.com/en/errors/nginx-php-fpm-primary-script-unknown-file-not-found/https://daniele-michelin.com/en/errors/nginx-php-fpm-primary-script-unknown-file-not-found/Fri, 23 Oct 2026 00:00:00 +0000nginx shows “File not found.” and logs “Primary script unknown”: PHP-FPM cannot find the script. Check SCRIPT_FILENAME, root and container paths. https://daniele-michelin.com/en/errors/http-403-forbidden-nginx/https://daniele-michelin.com/en/errors/http-403-forbidden-nginx/Fri, 23 Oct 2026 00:00:00 +0000HTTP 403 Forbidden in nginx: missing index file, file permissions, deny rules or SELinux. How to find the exact cause in error.log and fix it fast. https://daniele-michelin.com/en/errors/dovecot-imap-login-disconnected-auth-failed/https://daniele-michelin.com/en/errors/dovecot-imap-login-disconnected-auth-failed/Fri, 23 Oct 2026 00:00:00 +0000Dovecot logs “imap-login: Disconnected (auth failed)”? How to tell a wrong password from a config error or brute force, and how to fix the cause. https://daniele-michelin.com/en/errors/postfix-hostname-does-not-resolve-to-address/https://daniele-michelin.com/en/errors/postfix-hostname-does-not-resolve-to-address/Fri, 23 Oct 2026 00:00:00 +0000Postfix warning “hostname does not resolve to address”: the client's reverse and forward DNS do not match. When it is harmless and when you must act on it. https://daniele-michelin.com/en/errors/smtp-553-5-7-1-sender-address-rejected/https://daniele-michelin.com/en/errors/smtp-553-5-7-1-sender-address-rejected/Fri, 23 Oct 2026 00:00:00 +0000SMTP 553 5.7.1 means the logged-in user may not send with this sender address. How to check smtpd_sender_login_maps and set up send-as properly. https://daniele-michelin.com/en/errors/smtp-550-5-1-1-user-unknown/https://daniele-michelin.com/en/errors/smtp-550-5-1-1-user-unknown/Fri, 23 Oct 2026 00:00:00 +0000SMTP 550 5.1.1 means the recipient address does not exist on the target server. Check typos, missing mailbox maps and wrong domain class in Postfix. https://daniele-michelin.com/en/errors/smtp-552-5-2-2-mailbox-full/https://daniele-michelin.com/en/errors/smtp-552-5-2-2-mailbox-full/Fri, 23 Oct 2026 00:00:00 +0000SMTP 552 5.2.2 means the recipient's mailbox has reached its storage limit. How to check the Dovecot quota and free space for good, step by step. https://daniele-michelin.com/en/errors/smtp-530-5-7-0-must-issue-starttls/https://daniele-michelin.com/en/errors/smtp-530-5-7-0-must-issue-starttls/Fri, 23 Oct 2026 00:00:00 +0000SMTP 530 5.7.0 means the server wants STARTTLS before it accepts login or mail. Causes, how to check with openssl and the right client settings. https://daniele-michelin.com/en/errors/smtp-535-5-7-8-authentication-failed/https://daniele-michelin.com/en/errors/smtp-535-5-7-8-authentication-failed/Fri, 23 Oct 2026 00:00:00 +0000SMTP 535 5.7.8 means the server rejected the SMTP login. Typical causes with Postfix/Dovecot, Gmail and Microsoft 365 and how to check each one. https://daniele-michelin.com/en/errors/linux-no-space-left-on-device/https://daniele-michelin.com/en/errors/linux-no-space-left-on-device/Fri, 23 Oct 2026 00:00:00 +0000No space left on device but df shows free space? Usually inodes are exhausted or deleted files are still open. Diagnose with df -i and lsof +L1, then fix. https://daniele-michelin.com/en/errors/dns-servfail-dnssec/https://daniele-michelin.com/en/errors/dns-servfail-dnssec/Fri, 23 Oct 2026 00:00:00 +0000dig returns SERVFAIL although the zone looks right? Often DNSSEC is broken, e.g. a stale DS record after a provider move. How to find and fix it. https://daniele-michelin.com/en/errors/letsencrypt-acme-error-unauthorized/https://daniele-michelin.com/en/errors/letsencrypt-acme-error-unauthorized/Fri, 23 Oct 2026 00:00:00 +0000certbot reports urn:ietf:params:acme:error:unauthorized? The HTTP-01 challenge fails, often due to an AAAA record or a redirect. Diagnosis and fix. https://daniele-michelin.com/en/errors/nextcloud-saml-signature-validation-failed/https://daniele-michelin.com/en/errors/nextcloud-saml-signature-validation-failed/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud user_saml says Signature validation failed. SAML Response rejected? Usually a rotated IdP certificate. Causes, checks and the fix. https://daniele-michelin.com/en/errors/nextcloud-trusted-domain-error/https://daniele-michelin.com/en/errors/nextcloud-trusted-domain-error/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says access through untrusted domain: the hostname is missing from trusted_domains. How to add it with occ and check the reverse proxy. https://daniele-michelin.com/en/errors/nextcloud-maintenance-mode-enabled/https://daniele-michelin.com/en/errors/nextcloud-maintenance-mode-enabled/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud stuck in maintenance mode, usually after an aborted update? How to check status with occ, finish the upgrade and turn maintenance off. https://daniele-michelin.com/en/errors/nextcloud-file-is-locked-423/https://daniele-michelin.com/en/errors/nextcloud-file-is-locked-423/Fri, 23 Oct 2026 00:00:00 +0000Nextcloud says is locked or 423 Locked? Stale file locks after aborted requests. How to check Redis locking and cron, and clear old locks safely. https://daniele-michelin.com/en/errors/nginx-upstream-sent-too-big-header/https://daniele-michelin.com/en/errors/nginx-upstream-sent-too-big-header/Fri, 23 Oct 2026 00:00:00 +0000nginx logs upstream sent too big header and returns 502? The backend headers do not fit the buffer. How to raise the fastcgi and proxy buffers. https://daniele-michelin.com/en/errors/http-413-request-entity-too-large/https://daniele-michelin.com/en/errors/http-413-request-entity-too-large/Fri, 23 Oct 2026 00:00:00 +0000413 Request Entity Too Large: nginx or an upstream proxy blocks large uploads. How to set client_max_body_size and the PHP limits correctly. https://daniele-michelin.com/en/errors/http-504-gateway-timeout/https://daniele-michelin.com/en/errors/http-504-gateway-timeout/Fri, 23 Oct 2026 00:00:00 +0000504 Gateway Timeout in nginx: the backend takes longer than allowed. How to find slow scripts, a full PHP-FPM pool and wrong timeouts, and fix them. https://daniele-michelin.com/en/errors/http-502-bad-gateway/https://daniele-michelin.com/en/errors/http-502-bad-gateway/Fri, 23 Oct 2026 00:00:00 +0000502 Bad Gateway in nginx: the backend (PHP-FPM, Node, Gunicorn) is not answering. Common causes, what to look for in error.log and quick fixes. https://daniele-michelin.com/en/errors/smtp-451-4-7-1-greylisting/https://daniele-michelin.com/en/errors/smtp-451-4-7-1-greylisting/Fri, 23 Oct 2026 00:00:00 +0000SMTP 451 4.7.1 Greylisted is an intentional delay. When it is normal, when mail gets stuck and how to tune Postgrey or Rspamd greylisting. https://daniele-michelin.com/en/errors/smtp-554-5-7-1/https://daniele-michelin.com/en/errors/smtp-554-5-7-1/Fri, 23 Oct 2026 00:00:00 +0000SMTP 554 5.7.1 with blocked using: your IP is on a blocklist like Spamhaus. Find the cause, stop the spam and request delisting the right way. https://daniele-michelin.com/en/errors/smtp-421-4-7-0/https://daniele-michelin.com/en/errors/smtp-421-4-7-0/Fri, 23 Oct 2026 00:00:00 +0000SMTP 421 4.7.0 means the receiver is temporarily throttling your IP. Common causes like missing PTR or a spam burst, how to diagnose and fix it. https://daniele-michelin.com/en/errors/smtp-550-5-7-26/https://daniele-michelin.com/en/errors/smtp-550-5-7-26/Fri, 23 Oct 2026 00:00:00 +0000Gmail rejects with 550 5.7.26 or 5.7.23? SPF, DKIM or DMARC alignment is broken. How to check the DNS records and fix the bounce for good. https://daniele-michelin.com/en/errors/smtp-550-5-7-1/https://daniele-michelin.com/en/errors/smtp-550-5-7-1/Fri, 23 Oct 2026 00:00:00 +0000SMTP 550 5.7.1 means the mail server refuses to relay or rejects by policy. Common causes, how to check with postconf and how to fix it for good.