Ascending to the next level on Linux

>Learn CLI
https://www.codecademy.com/en/courses/learn-the-command-line/

>Learn Linux by playing a game
http://www.mprat.org/Terminus/

>10 keyboard shortcuts to improve your Linux experience
http://www.techrepublic.com/blog/10-things/10-keyboard-shortcuts-to-improve-your-linux-experience/

>4 Ways to Teach Yourself Terminal Commands in Linux
http://www.makeuseof.com/tag/4-ways-teach-terminal-commands-linux-si/

>Learn UNIX in 10 minutes
http://freeengineer.org/learnUNIXin10minutes.html

>LinuxCommand.org: Learning the shell.
http://linuxcommand.org/lc3_learning_the_shell.php

>The Cow Says, Have Fun!
http://www.linuxjournal.com/content/cow-says-have-fun

Type "man intro" in the terminal, it shows most commonly used commands and how to use man pages
the intro to section 1 of the manual, same as man 1 intro; man 2 intro through man 8 intro also exist

or type:

whatis command
man command
info command
apropos command

You can also find documentation on your own computer at /usr/share/doc

>Scripting on Linux

>Bash Shell Scripting
https://en.wikibooks.org/wiki/Bash_Shell_Scripting

>Information about scripting
http://wiki.bash-hackers.org/doku.php

>Learn Linux The Hard Way
https://nixsrv.com/llthw

>Linux Basics « Null Byte How-Tos - ACTUALLY FOR (ethical) HACKING
http://null-byte.wonderhowto.com/how-to/linux-basics/

>Learn shells by example

>List of sample code straight to your terminal
http://bropages.org/

>More sample code to your terminal
https://github.com/samirahmed/fu

>Yet more example in your terminal
https://github.com/gleitz/howdoi

>Customizing the CLI

>Customizing Your Bash Command Prompt
http://blog.superuser.com/2011/09/21/customizing-your-bash-command-prompt/

>How to Customize your Bash Prompt on a Linux VPS
https://www.digitalocean.com/community/tutorials/how-to-customize-your-bash-prompt-on-a-linux-vps

>See other people's .bashrc
http://dotshare.it/

>Terminal Color Scheme Designer
http://terminal.sexy/

>Compiling software from source

>How to Compile and Install Software from Source Code on Linux
http://www.howtogeek.com/105413/how-to-compile-and-install-from-source-on-ubuntu/

>Linux Documentation Project Guides
http://www.tldp.org/guides.html

>Single list of HOWTOs
http://www.tldp.org/HOWTO/HOWTO-INDEX/howtos.html

>Go Pro!

>Introduction to Linux - FREE ONLINE COURSE
https://www.edx.org/course/introduction-linux-linuxfoundationx-lfs101x-2

>The Linux Command Line - FREE EBOOK
http://sourceforge.net/projects/linuxcommand/

>Debian's Administrators Handbook - FREE EBOOK
https://debian-handbook.info/get/now/

>Professional resource on Linux
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/

>About exams and certifications for Linux
https://www.lpi.org/study-resources/

>Some other stuffs

>X Window System
https://en.wikipedia.org/wiki/X_Window_System

>X Window System protocols and architecture
https://en.wikipedia.org/wiki/X_Window_System_protocols_and_architecture

>Guide to X11
https://en.wikibooks.org/wiki/Guide_to_X11

>Guide to Unix/Commands/X11
https://en.wikibooks.org/wiki/Guide_to_Unix/Commands/X11

>X Window Programming
https://en.wikibooks.org/wiki/X_Window_Programming

>Make your own kernel. No, seriously.
http://www.linuxfromscratch.org/