This is a list of resources and challenges to learn and understand the Linux command line
TryHackMe room for linux fundamentals Part 1
TryHackMe room for linux fundamentals Part 2
TryHackMe room for linux fundamentals Part 3
The Linux command line for beginners | Ubuntu
Tutorial on Linux Command line
Video guide on Bash Terminal
Linux Commands Cheat Sheet
Bash Scripting (Advanced)
COPS Infosec Video
Attempt as many levels as you can from the following online wargame which tests your skills on finding flags using basic Linux commands and also the 3 challenges from PicoCTF
OverTheWire: Bandit
PicoCTF challenge 1
PicoCTF challenge 2
PicoCTF challenge 3