If you ever wonder and would like to know about basic file-system architecture / organization of debain or ubuntu based system than here you go:
- ./: is root directory.
- under root there will be home directory which will be having directory for each user under it.
- under root "/" there will be following directories:
etc, dev, home, usr, var
- /boot: This folder contains important files required to boot machine including bootloader files.
- /dev: Each device on your system has an entry in this folder. Each application accesses the device by using the relevant items inside /dev.
- /etc: This directory stores files for system-wide configuration. Apart from configuration files for all programs or system itself, this directory will also contain files for each user under the system.
- /lib: Important system software libraries are stored inside.
- /media: Media devices such as CD or USB sticks are referenced here when they are plugged in.
- /mnt: other mountable devices.
- /opt: Optional software can be installed here. This folder is optionally used when you want to build your own software.
- /proc/sys: Information about the current running status of the system is stored here.
- /root: Home directory for the main superuser.
- /bin: Software that is vital for the system to be able to boot is stored here.
- /sbin: Software that should be run by superuser is stored here.
- /usr: General software is installed here.
- /var: contains log files about the software on your computer.
Including debian, ubuntu and many other Linux operating system follows Filesystem Hierarchy Standard which you can refer here on Wikipedia. You can read more about Linux or Ubuntu File System Tree overview here on Ubuntu online documentation/help.