CheatSheet
Linux
Debian: Debian refcard (pdf) (people.debian.org/~debacle/)
Unix/Linux Command Cheat Sheet by Jacob (pdf) (fosswire.net)
The One Page Linux Manual by Squadron (pdf) (digilife.be)
Linux Administrator’s Quick Reference by Jialong He (pdf) (tiger.la.asu.edu)
Linux System Calls Quick Reference by Jialong He (pdf) (tiger.la.asu.edu)
Linux Security Quick Reference by Dave Wreski & Benjamin Thomas (pdf) (digilife.be)
MySQL
MySQL Cheat Sheet by Dave Child (pdf) (addedbytes.com)
MySQL Database Quick Reference by DeepX (pdf) (tiger.la.asu.edu)
Oracle
Oracle SQL quick reference by EM Group (pdf) (tiger.la.asu.edu)
Oracle Server Architecture by Dr. Lars Ditzel (pdf) (digilife.be)
ORACLE Server 8i Quick Reference Card by Dr. Lars Ditzel (pdf) (digilife.be)
Oracle Server 9i – Quick Reference Guide (pdf) (digilife.be)
OpenSSH
OpenSSH Configuration Quick Reference by Jialong He (pdf) (tiger.la.asu.edu)
GDB
GDB Quick Reference (pdf)