Linux Filesystem Hierarchy Standard (FHS)
Filesystem hierarchy standard describes directory structure and its content in Unix and Unix like operating system. It explains where files and directories should be located and what it should contain.
Its current version is 3.0 released on June 3rd 2015 and is maintained by Free Standards Group. In Unix like operating system everything is considered as a file.
Only Linux distributions follow the FHS and that too partially. Because every distro have their own policy due to which you may notice some differences in the directory tree structure of different distros.
If you want to find out information about your system's FHS, enter the command man hier. It will display directory structure of your system.
Note: GoboLinux and NixOS doesn't follow FHS at all, it has its own and completely different policy.
The Root Directory
All the directories in the Linux system comes under the root directory which is represented by a forward slash (/). Everything in your system can be found under this root directory even if they are stored in different virtual or physical devices.
Look at the above snapshot, we have shown you the root directory of our system i.e; Ubuntu with the help of the command "ls /". Here, we have written (/) to represent root directory.
We have categorize the directories according to the type of file as given below: