Some troubles — especially those happening only sporadically — are not so easy to shoot and call for a deeper understanding of the matter. In the following real-world example this means: SQL*Net Tracing and some knowledge about the inner workings of the server’s operating system, particularly random number generation.
This case was suited well to demonstrate an approach to trouble-shoot connections to Oracle databases.
Recently, I bought the Hypersecu HyperFIDO K5 Key to help me secure access to several websites and services with U2F (“Universal Two-Factor Authorization”).
This works fine and easy on Windows, but with Linux things get a little complicated: The key isn’t accessible to all users by default. This has to be activated using udev rules, which is widely documented on the web, but very often erroneous or outdated. Here’s what I found: