Built-in checksum tool "cksum" - https://www.freecodecamp.org/news/file-last-modified-in-inux-how-to-check-if-two-files-are-same/

Disable root password - http://www.debianadmin.com/enable-and-disable-ubuntu-root-password.html

How can we fine tune permission more than chmod - http://man-wiki.net/index.php/3:cap_from_text

1. From a shell account on a Unix box behind the firewalled network do this:

	ssh -N -R 3389:localhost:22 user@remote-unix-box.net

2. Leave work and go home. From a shell account on remote-unix-box.net do this:

	ssh 127.0.0.1 -p 3389

http://16systems.com/acls.txt