Humble Bundle just started a countdown for a Linux ebook bundle here (https://www.humblebundle.com/books/linux-wiley-books?linkID=&mcID=102:5c7db48b382c29441a7b6043:ot:5a0e5ff71c7d4cd39aeb5822:1&utm_source=Humble+Bundle+Newsletter&utm_medium=email&utm_campaign=2019_03_11_linuxwiley_bookbundle&linkID=&utm_content=cta_button). Get 4 books for only a buck. Makes a great gift too for that person you know that is curious about Linux.
Thanks for posting, Jason! A very good offering!
You can't beat the price, but I should point out the all of the books are pretty old except for Linux For Dummies (that one is 2018). There is a slightly more expensive bundle that includes the Linux Bible. I had an old hard copy version of that, and it was quite good. Unfortunately this one is also quite old (2015), though it is the most recent edition. (A 10th edition is coming out shortly.) That isn't to say that there is no value in these books since a lot of the information is still relevant, but it's nice to have a version that covers the present distro offerings.
Though a little dated, the first two books in the $1 bundle are about Linux commands which don't really hasn't changed much since 2013/2015 and now. So I think there is a LOT of value in them if you're interested in the terminal. Also both of those books are being sold on Amazon right now and they are the most recent editions.
The programming book is dated 2007 so is probably not very useful except that it could probably get you started with the basics of C and shell programming. The GTK stuff is going to be pretty outdated although APIs usually backwards compatible so the old code would likely work, there'd just be different ways of doing it now.
And with the way distros change, it's pretty difficult to have to hate updated books on Linux seeing how long it can take a book to be written to being published (unless it's a self-published ebook).