There's many many sources for education on the Internet that are free or nearly free. Recently I found a few links that are worth sharing.
Linux command line -
Linux the hard way command line - I haven't run through the site yet but this offers a more advanced tutorial than other sites I've seen. This looks really amazing, but I heard there was some issues with certain commands not work correctly. There's even a handy console session to help practice the commands.
The CLI Crash Course - This is a tutorial that is aimed towards the new command line user. The nice thing is a video class is also offered by Udemy for a very reasonable $9.
Learn SQL the hard way - Another "learn the hardway" series, this one focusing on SQL. The examples and screenshots are clear as with the other methods.
Learn Python the hard way - This is another one in the series, but also offers video classes from Udemy for $29.
Invent with Python - I bought the hard copy book recently and enjoy the idea of learning to program while making a game. The book is available for free online but you can order a copy from Amazon as well.
Git Immersion - This is more for coders and developers but it's also handy for the sysadmin or general user. Git is used for checking in code, and updating it as needed. This tutorial is actually very clear and easy to follow.