Mukesh Verma Root Cause Diagnosis Hash Sum mismatch occurs when the package index file apt downloaded doesn’t match the SHA256/MD5 checksum listed in the mirror’s Release file, meaning the local copy under /var/lib/apt/lists/ is corrupted or stale relative to what the mirror is currently serving. This happens most often because a transparent caching proxy (ISP-level, corporate, or … Read more
Root Cause Diagnosis Error Code 10 (ConfigManagerErrorCode 10, “This device cannot start”) means Windows successfully loaded a driver for the adapter but the driver’s IRP_MN_START_DEVICE call failed during initialization — the enumeration succeeded, the start did not. For USB-to-RS232 converters this is almost always one of three chipset-specific causes: a genuine Prolific/FTDI/CH340 driver refusing to … Read more
Root Cause Diagnosis WooCommerce tracks a per-webhook failure counter in WC_Webhook::failed_delivery(), incrementing it on every non-2xx response from the receiving endpoint. Once that counter exceeds the value returned by the woocommerce_max_webhook_delivery_failures filter (default 5), WooCommerce sets the webhook’s status to disabled and fires woocommerce_webhook_disabled_due_delivery_failures — after which it stops attempting delivery entirely, even after the … Read more
Root Cause Diagnosis Chromium’s cookie store only writes cookies with an explicit Expires or Max-Age attribute to the on-disk Cookies SQLite database inside the user_data_dir. Cookies issued without either attribute are, per RFC 6265, session cookies — Chromium keeps them in memory only and deliberately purges them on a clean shutdown, regardless of whether you … Read more
Root Cause Diagnosis CyberPanel provisions HTTP/2 at the listener level in OpenLiteSpeed (/usr/local/lsws/conf/httpd_config.conf), but each additional domain — whether added as a new website or a child domain — gets its own SSL context inside its vhost.conf under a vhssl block. That per-vhost block carries its own protocol negotiation setting (enableSpdy, the legacy directive name … Read more
Root Cause Diagnosis /var/lib/docker/overlay2/ accumulates directories named by content-addressable hash for every image layer, stopped container’s writable layer, and build-cache intermediate that Docker has ever created; the daemon does not garbage-collect them automatically. Directories become “dead” (safe to remove) when their owning image, container, or build cache entry no longer exists in Docker’s internal reference … Read more
Root Cause Diagnosis Direct thermal printing works by driving current through a resistive print head to heat individual dots, which trigger a chemical reaction in the paper’s thermosensitive coating; faint or missing print means the head is not reaching the coating’s activation temperature or the paper’s sensitivity has degraded. On printers with a physical darkness/density … Read more
Root Cause Diagnosis A 401 Unauthorized on the WordPress REST API during application password authentication almost always means the Authorization header never reaches PHP, not that the credentials are wrong. Apache with mod_php/mod_fcgid, Nginx with PHP-FPM, and most shared-hosting proxy layers strip the Authorization header by default because it is not passed through by the … Read more
Root Cause Diagnosis cv2.VideoCapture() returns an object whose isOpened() is False (and read() returns (False, None)) when no OpenCV backend can open the source. On a headless Linux server this usually happens for one of four reasons: the source does not exist (no /dev/video* node, or the device is not passed into the container or … Read more
Docker’s default docker0 bridge uses 172.17.0.0/16, and user-defined networks (including those created by docker-compose stacks deployed from aaPanel’s Docker manager) are allocated sequentially from 172.18.0.0/16 upward through 172.31.0.0/16, then 192.168.0.0/20 blocks. When the host, VPN, or LAN uses an overlapping range, the kernel installs a directly connected route for the bridge that takes precedence over … Read more