Linux Unix Filesystem Hierarchy and Structure
Overview of the FHS
Everything in Linux can be reduced to a file. Partitions are associated with files such
as /dev/hda1. Hardware components are associated with files such as /dev/modem.
Detected devices are documented as files in the /proc directory. The Filesystem
Hierarchy Standard (FHS) is the official way to organize files in Unix and Linux
directories.
Linux/Unix Filesystems and Directories
Several major directories are associated with all modern Unix/Linux operating systems.
These directories organize user files, drivers, kernels, logs, programs, utilities, and more
into different categories. The standardization of the FHS makes it easier for users of
other Unix-based operating systems to understand the basics of Linux.
Every FHS starts with the root directory, also known by its label, the single forward
slash (/). All of the other directories shown in Table are subdirectories of the root
directory. Unless they are mounted separately, you can also find their files on the same
partition as the root directory.
| / |
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
and 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
| File Type |
Description |
| 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. |
Some of the Configuration Files in /etc Directory that you should remember
| File |
Function |
| /etc/fstab |
Lists the partitions and file systems that will be automatically mounted when the
system boots. |
| /etc/group |
Contains local group definitions. |
| /etc/grub.conf |
Contains configuration parameters for the GRUB bootloader (assuming it’s being
used on the system). |
| /etc/hosts |
Contains a list of hostname-to-IP address mappings the system can use to resolve
hostnames. |
| /etc/inittab |
Contains configuration parameters for the init process. |
| /etc/init.d/ |
A subdirectory that contains startup scripts for services installed on the system.
On a Fedora or Red Hat system, these are located in /etc/rc.d/init.d. |
| /etc/modules.conf |
Contains configuration parameters for your kernel modules. |
| /etc/passwd |
Contains your system user accounts. |
| /etc/shadow |
Contains encrypted passwords for your user accounts. |
| /etc/X11/ |
Contains configuration files for X Windows. |
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