If by chance you understand German this is an excellent beginner course: https://www.math.uni-bielefeld.de/~frettloe/teach/unix20.html otherwise I would grab a book; but I have no specific book to recommend. However, to name some I found interesting after a quick search:
How Linux Works: What Every Super-User Should Know
If by chance you understand German this is an excellent beginner course: https://www.math.uni-bielefeld.de/~frettloe/teach/unix20.html otherwise I would grab a book; but I have no specific book to recommend. However, to name some I found interesting after a quick search: