As a beginner user of Unix or Linux, people would frequently get confused about the use of different directories of the system. For example, there is a /bin directory under root(/), it is used to store binary files. However, there are /usr/bin and /usr/local/bin under /usr which are used for storing binary files as well. Some systems even have /opt/bin. What are the differences among them?Though there are articles explaining different directories in *nix such as Filesystem Hierarchy Standard, it's not clear why these directories are present and their history. Rob Landley filled part ...