Basic Linux Privilege Escalation:
https://blog.g0tmi1k.com/2011/08/basic-linux-privilege-escalation/
Local Linux Enumeration & Privilege Escalation Cheatsheet: an item-by-item list of tests performed by LinEnum:
https://www.rebootuser.com/?p=1623
LinEnum:
https://github.com/rebootuser/LinEnum