https://www.amazon.com/Modern-Linux-Administration-Cutting-E... (General Linux)

https://landing.google.com/sre/book.html (SRE)

https://www.amazon.com/Ansible-DevOps-Server-configuration-m... (Ansible)

https://www.amazon.com/Puppet-4-10-Beginners-Guide-Second/dp... (Puppet, beginner)

https://www.amazon.com/Learning-Puppet-Configuration-Managem... (Puppet, intermediate)

https://www.amazon.com/Learning-SaltStack-Second-Colton-Myer... (SaltStack)

https://www.amazon.com/Networking-Systems-Administrators-Mas... (Networking)

https://leanpub.com/serversforhackers (SysAdmin)

https://leanpub.com/scalingphp (Scaling)

https://debian-handbook.info/get/ (Debian Linux)