Just a memory dump for important files and directories.

~/.bashrc

runs on interactive login

~/.bash_aliases

runs from .bashrc (if uncommented…)

~/.emacs

Emacs settings

/etc/crontab

file that controls scheduled running of scripts

/etc/cron.d/hourly, daily, weekly, monthly

for running scripts on a scheduled basis

/etc/group

groups in the system

/etc/hosts

hard-coded hosts like in Windows.

/etc/motd

the greetings text when logging into the system

/etc/resolv.conf

DNS hosts

/etc/sudoers

users and groups that can do sudo. Edit via sudo visudo.

/etc/syslog.conf

log configuration (cron etc)

/etc/init.d/

daemon control files. To remove from startup, use sudo /etc/init.d/XYZ stop, sudo update-rc.d -f XYZ remove. To start manually: sudo /etc/init.d/XYZ start

/etc/init.d/gdm

Gnome Desktop Manager.

/etc/rcS

file run at system start. Runs the files in /etc/rcX.d depending on run level

/etc/rcX.d/

files that are run from /etc/rcS depending on run level. See The Linux Boot Process Explained

/var/log/

log files

/var/run/

lock files and run-time information

/etc/apt/sources.list

the list of URLs for apt-get for upgrading / installing packages

Also see Filesystem Hierarchy Standard.