How-To

A quick reference for enabling verbose Kerberos and Hadoop debug output on the command line, so you can see exactly where authentication is failing.

Enable Kerberos debug logging in a JVM, Spark driver, and Spark executors to troubleshoot SPNEGO and authentication issues. Covers the exact Java system properties, Spark configuration keys, and how to redirect Spark logs to stdout so Kerberos output interleaves with application logs.

A practical walkthrough of how Hadoop maps Kerberos principals to short names via the auth_to_local property, including rule syntax, acceptance filters, and common troubleshooting patterns.

A quick guide to diagnosing and resolving the ‘Key has been revoked’ error in the Linux kernel keyring using keyctl commands.

A quick reference for querying MySQL information_schema to list all foreign key constraints in a given database, including the referencing and referenced columns.

The namei command walks a full path and prints ownership, permissions, and symbolic link resolution for every component. It is a quick way to spot where a permission chain breaks or a symlink redirects unexpectedly.