SOURCES

https://unix.stackexchange.com
https://superuser.com
https://askubuntu.com
https://docs.python.org/2/library/index.html
Debian Manual
Windows Internals, Sixth Edition, Part 1
https://www.webopedia.com
http://wiki.bash-hackers.org/commands/builtin/caller 
https://www.cyberciti.biz/open-source/command-line-hacks/compgen-linux-command/

https://migrationedge.com.au/bg-polygon/ 
https://en.wikipedia.org/wiki/Udev
https://en.wikipedia.org/wiki/Slab_allocation
https://linux.die.net/man/1/ypdomainname
https://en.wikipedia.org/wiki/Network_Information_Service
https://www.geeksforgeeks.org/until-command-in-linux-with-examples/
http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_09_03.html
https://www.computerhope.com/unix/uwait.htm