Top books on r/sysadmin

The Practice of System and Network Administration, Second Edition

Time Management for System Administrators

Learn Windows PowerShell in a Month of Lunches

RHCSA/RHCE Red Hat Linux Certification Study Guide

UNIX and Linux System Administration Handbook, 4th Edition

CompTIA A+ Certification All-in-One Exam Guide, 8th Edition

The Phoenix Project

Mastering VMware vSphere 5.5

The Practice of Cloud System Administration

How to Win Friends & Influence People

Windows PowerShell Cookbook

The Visible Ops Handbook

Network Warrior