The origins of Unix directory structure
Unix (includes Linux) beginner, often very confused, do not understand the meaning of what directory structure.
For example, there is a subdirectory of the root directory / bin, for storing binary program. However, / usr subdirectory there is / usr / bin, and / usr / local / bin, but also for storing binary program; some systems even / opt / bin. What's the difference between them?
For a long time, and I am very hard to understand, do not understand why this design. Like most people, I'm just based on "Unix file system structure Standard" (Filesystem Hierarchy Standard), rote different directories difference.
Yesterday, I read Rob Landley of brief explanation , suddenly realized that the Unix directory structure is history.
Saying 1969, Ken Thompson and Dennis Ritchie on a PDP-7 minicomputer invented Unix. In 1971, they will host upgrade to the PDP-11.
At that time, they used a technique called RK05 storage disk, a capacity is about 1.5MB.
没过多久，操作系统（根目录）变得越来越大，一块盘已经装不下了。于是，他们加上了第二盘RK05，并且规定第一块盘专门放系统程序，第二块盘专门放用户自己的程序，因此挂载的目录点取名为/usr。也就是说，根目录"/"挂载在第一块盘，"/usr"目录挂载在第二块盘。除此之外，两块盘的目录结构完全相同，第一块盘的目录（/bin, /sbin, /lib, /tmp...）都在/usr目录下重新出现一次。
后来，第二块盘也满了，他们只好又加了第三盘RK05，挂载的目录点取名为/home，并且规定/usr用于存放用户的程序，/home用于存放用户的数据。
从此，这种目录结构就延续了下来。随着硬盘容量越来越大，各个目录的含义进一步得到明确。
/：存放系统程序，也就是At&t开发的Unix程序。
/usr：存放Unix系统商（比如IBM和HP）开发的程序。
/usr/local：存放用户自己安装的程序。
/opt：在某些系统，用于存放第三方厂商开发的程序，所以取名为option，意为"选装"。
（完）