Richard Blum has over 30 years’ experience working as a system and network administrator. He is the bestselling author of the fourth edition of the Linux® Command Line and Shell Scripting Bible and Linux All-In-One For Dummies, 7th Edition. He’s an online Linux instructor and teaches Linux command line and shell scripting courses at Coursera, Udemy, and ed2go.com. Christine Bresnahan is co-author with Richard Blum of previous editions of CompTIA Linux+ Study Guide, Linux Essentials, and the Linux Command Line and Shell Scripting Bible.