/           The root of the overall file system namespace.
/bin       binary files of standard system commands. (a symbolic link to the /user/bin directory)
/dev      logical device names
/devices physical device names
/etc       host-specific configuration files and databases for system administration
/export  commonly shared file systems, such as user’s home directories, application software, …
/home    the default directory or mount point for a user’s home directory
/kernel   the directory of platform-independent loadable kernel modules that are required as part of the boot process
/mnt      temporary monunt point for file systems
/opt       application packages
/tmp      temporary files
/usr       programs, scripts, and libraries that are used by all system users.
/var       temporary, logging, or status files
/sbin      single-user bin directory

NOTE: /etc/inetd.conf:

inetd will load a network program based on a request from a network. The inetd.conf file tells inetd which ports to listen to and which server to start for each port.

Edit inetd.conf: disable services by commenting them out by adding a # at the beginning of a line, and then sending your inetd process a SIGHUP command to update it to the current inetd.conf file. (It concluds FTP, TELNET, SHELL, LOGIN, TALK, FINGER…etc)

#killall -HUP inetd

etc/nodename, etc/hosts, etc/defaultrouter, etc/netmasks, etc/resolv.conf (it contains the IPs of domain name servers)

etc/init.d contains initialization and termination scripts for changing init states.