Directory structure of Ubuntu Linux

Ubuntu directory structure is a directory tree structure very much similar to directory structure of Unix. There is a resemblance between Unix directory structure and directory structure of Ubuntu Linux. The Ubuntu Linux directory structure contains the root directory  '/'  at the top with the remaining Linux system directories and file structure like hard disk, partition and other data files falling under it. It is a tree like structure and the top of the tree i.e., the highest level in the file system is the root directory '/'.
Some important Ubuntu Linux system directories are

1. /bin: This directory contains important binary application. It would contain the executable file for command like ls, cal, grep etc which are used in everyday Linux environment, directly or indirectly.  
2. /boot: This directory contains the files needed for booting up the operating system. It include the kernel (vmlinux), ramdisk image (initrd.lz) and bootloader configuration files.
3. /dev: This Ubuntu Linux directory does not consume any space on disk and is used to keep track of devices connected to the computer including the ones which are a part of the CPU such as the disks, mouse, display,graphics card etc.
4. /etc: This is the place where you can find the configuration files of the base OS and other installed applications and startup scripts. It contain all the configuration files, ranging from the ones which control the booting of computer to the ones which can change the behavior of installed software and services.
5. /home: It is the user profile folder in Linux similar to the c:/ user folder in Windows. Each user on the system would have a separate directory within this sub-directory.
6. /lib: The system libraries required for the proper functioning of installed software are present in this  Linux directory. 'Library' in context of computing is define as a reusable resource that can be used by more then one software.
7. /lost+found: This contains the lost and found files of your / directory.
8. /media:This directory is not a part of the Linux directory structure. It is the system directory file which help to recognize all the mounted removable media such as CD, external hard drives, USB drives, cameras etc.
9. /mnt: This Linux directory is used to create mount point for other systems which are attached to the computer on boot, e.g. Windows partitions.
10. /opt: This directory provides a location for optional applications to be installed.
11. /proc: This virtual directory does not consume any space on disk but exists only in the system memory. This directory is freely available for browsing only to the 'root' user.
12. root: This is commonly known as the slash-root directory, it refer to '/' as root in Ubuntu Linux.
13. /sbin: This directory is also available to root user. It contains commands to change system wide settings.
14. /srv:  This directory acts as a temporary location for data meant to be used by servers.
15. /sys: This directory contains system-specific information meant as reference for other applications.
16. /tmp: As the mane suggest, it acts as storage for temporary files.
17. /usr: This is where most of your applications and files will be stored, as anything present here is available for all users to acccess. It can be also be called as the program files folder for Linux.
18. /var: This is a directory for variable files such as logs and databases. Notice the contrast with the /tmp directory.