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Linux Directory Structure / File system Hierarchy
Everything in Linux is either a file or a process.
A file is a collection of data. They are created by users using text editors, running compilers etc.
Examples of files:
- a document
- the text of a program written in some high-level programming language
- instructions comprehensible directly to the machine and incomprehensible to a casual user, for example, a collection of binary digits (an executable or binary file);
- a directory, containing information about its contents, which may be a mixture of other directories (subdirectories) and ordinary files.
A process is an executing program identified by a unique PID (process identifier).
File system directory structure in linux
All the files are grouped together in the directory structure. The file-system is arranged in a hierarchical structure, like an inverted tree. The top of the hierarchy is traditionally called root (written as a slash /)
Purpose of the directories
|/||The root directory, the top-level directory in the FHS. All other directories are subdirectories of root, which is always mounted on some partition. All directories that are not mounted on a separate partition are included in the root directory’s partition.|
|/bin||Essential command line utilities. Should not be mounted separately; otherwise, it could be difficult to get to these utilities when using a rescue disk.|
|/boot||Includes Linux startup files, including the Linux kernel. Can be small; 16MB is usually adequate for a typical modular kernel. If you use multiple kernels, such as for testing a kernel upgrade, increase the size of this partition accordingly.|
|/etc||Most basic configuration files.|
|/dev||Hardware and software device drivers for everything from floppy drives to terminals. Do not mount this directory on a separate partition.|
|/home||Home directories for almost every user.|
|/lib||Program libraries for the kernel and various command line utilities. Do not mount this directory on a separate partition.|
|/mnt||The mount point for removable media, including floppy drives, CD-ROMs, and Zip disks.|
|/opt||Applications such as WordPerfect or StarOffice.|
|/proc||Currently running kernel-related processes, including device assignments such as IRQ ports, I/O addresses, and DMA channels.|
|/root||The home directory of the root user.|
|/sbin||System administration commands. Don’t mount this directory separately.|
|/tmp||Temporary files. By default, Red Hat Linux deletes all files in this directory periodically.|
|/usr||Small programs accessible to all users. Includes many system administration commands & utilities.|
|/var||Variable data, including log files and printer spools.|
Types of Files Used by Linux
When working with Linux, you need to be aware of the fact that there are a number of different file types used by the file system. This is another area where the Linux file system differs significantly from the Windows file system. With a Windows file system you basically have two entry types in the file system:
Granted, you can have normal files, hidden files, shortcut files, word processing files, executable files, and so on. However, these are all simple variations of the basic file when working with Windows.
With Linux, however, there are a variety of different file types used by the file system. These include the file types shown in Table
|Regular files||These files are similar to those used by the file systems of other operating systems—for example, executable files, OpenOffice.org files, images, text configuration files, etc.|
|Links||These files are pointers that point to other files in the file system.|
|FIFOs||FIFO stands for First In First Out. These are special files used to move data from one running process on the system to another. A FIFO file is basically a queue where the first chunk of data added to the queue is the first chunk of data removed from the queue. Data can only move in one direction through a FIFO.|
|Sockets||Sockets are similar to FIFOs in that they are used to transfer information between sockets. With a socket, however, data can move bi-directionally.|