If you are new to Linux, then learning some of the tools (especially opensource tools) will be difficult as many of them are only available for Linux or natively running on Linux. And as a DevOps practitioner, you must know the basics of Linux. Here see some of the best Linux training you can start with at no cost; check out and sign up today.
Introduction to Linux (LFS101x)
Develop a good working knowledge of Linux using both the graphical interface and command line across the major Linux distribution families with this free training course from Linux Foundation [from site].
The Linux Foundation | edx.org
Fundamentals of Red Hat Enterprise Linux
Learn practical techniques for using Red Hat Enterprise Linux (RHEL) and how to perform basic system administration tasks from this free training program provided by Red Hat [from site].
Red Hat Enterprise Linux Technical Overview (RH024)
Red Hat Enterprise Linux Technical Overview (RH024) is a series of no-cost, on-demand, online videos that provide a technical introduction to Linux® for IT professionals. This course is based on Red Hat® Enterprise Linux 8 [from site].
Linux Basics: The Command Line Interface
Learn the Linux Command Line interface and become a skilled user of this powerful operating system.
Linux Fundamentals
Learn fundamentals of Linux from this free course offered by LearnQuest.