These are not typical references you would find online or in handbooks. The emphasis here is on the command line access rather than the graphical interface (GUI). You can accomplish much more via command line than via GUI. The commands listed here have been tested and include typical usage scenarios.
The more you know about each command and its nuances, the more confident you will be using them during security assessments and in real world scenarios. One important point to note is the fact that troubleshooting is often a skill that you need to acquire over time to be able to resolve issues immediately when they occur and often without access to the internet.
Take your time to digest the content, try out different commands in the test environment and when you are ready, the right command will spring to your mind at the right time and in the right place on the production system.
A computer system virtuoso is a person who can operate within any system and any environment with finesse, great skill, freedom and precision. That type of person can defeat all security controls and gain access to even the most secure systems, devices, hardware, applications, databases and environments. The same is true about using above skills to protect systems, anybody with that type of profile can secure and harden mission critical networks, infrastructure and applications.
References:
localectl – Keyboard related settings