Reddit mentions of The Official Ubuntu Server Book (3rd Edition)

A few of my favorite books I reference and recommend. Just a note, many of these are older and can be purchased used for much less. Also if you can afford it, get a Safari subscription. I use my work Safari subscription but this alone has saved me from my book buying habit. Now I only buy "must have" books. :)

Official Ubuntu Server book - I really like this book as the writing style helped me "get it" with Linux. Kyle Rankin has a very good method of showing you the technology and then a quick run down to get the server working, followed by some admin tips. It's a just scratching the surface type of book but it's enough to get you started. I rarely use Ubuntu now, but this book helped me understand DNS and other topics that were IMHO harder to grasp from other books.

As a bonus, this book also has an entire chapter dedicated to troubleshooting. While this sounds obvious, it's a great read as it talks about dividing the problem, how to approach the facts, etc. Stuff a seasoned admin would know but might be hard to explain to a new admin.

The Linux Command Line: A Complete Introduction - You can read this book for free on the site, but having a paper copy is nice. As mentioned, you should have a very solid understanding of the command line. In my experience, I have seen co-workers struggle with basic shell scripting and even understanding how to make a single line for loop. This book covers the basics, moving to shell scripting and I think it's a good solid reference guide as well.

DevOps Troubleshooting: Linux Server Best Practices - This book is referenced a few times here but I'll throw another comment for it. Another book from Kyle Rankin and has the same straight to the point writing style. It's very quick reference and simple enough that you could give this to a new sysadmin and he or she could get started with some of the basic tools. While the book covers a good selection of basic services and tools, it's easy to get deeper into a chapter and find it's only discussing a handful of troubleshooting steps. The idea with this book is it's a quick reference guide, and if you want to get deeper into troubleshooting or performance, take a look at other books on the market. Either way, this is a great book I keep on my desk or reference through Safari.

UNIX and Linux System Administration Handbook (4th Edition) - Another popular book based on the comments here. This is a pretty big book, thin pages, but it's like a small brick of UNIX/Linux knowledge. While it's starting to get dated, it does give a great reference to many topics in the system administration world. The chapters can dive deep into the subject and offer more than enough information to get started but also understand the technology. The e-mail chapter I thought was great as well as the DNS. I think of this book as a overall guide and if I want to know more, I would read a book just on the subject, that's if I need more information. One thing to point out is this book makes use of different OS's so it's filled with references to Solaris, different UNIX versions, etc. Not a problem but just keep in mind the author may be talking about something outside the scope of vanilla Linux.

Shell Scripting: Expert Recipes for Linux, Bash and more - I found this book to be a good extenstion of the Linux Command Line book, but there are many many other Bash/Shell scripting books out there. The author has many of the topics discussed on his site but the book is a good reference for scripting. I can't stress enough how important shell scripting is. While it's good to know a more formal language like Python/Perl/etc, you are almost certain bash will be on the machine you are working on.

Systems Performance: Enterprise and the Cloud - I can't comment on this book beyond the first chapter, I'm still reading it now but it's reading similar to Brendan Gregg's site, and that's a great thing. If you don't know who this guy is, he's one of the top performance guys in the Solaris and now Linux world. He has some great infographics on his site, which I use for reference.

Use method for Linux

Linux Performance

Example of Linux performance monitoring tools

Hope this helps!

You might want to start with a book that covers Ubuntu (or even Debian) servers, such as The Official Ubuntu Server Book. There are also books and online resources for MongoDB and Node.js. It might be worth paying your developers for a few hours of tutoring on the basics, too :)