Unix - File System Basics

Linux file hierarchy System

file system is a logical collection of files on a partition or disk. A partition is a container for information and can span an entire hard drive if desired.
Your hard drive can have various partitions which usually contains only one file system, such as one file system housing the / file system or another containing the /home file system.
One file system per partition allows for the logical maintenance and management of differing file systems.
Everything in Unix is considered to be a file, including physical devices such as DVD-ROMs, USB devices, floppy drives, and so forth.

Directory Structure:

Unix uses a hierarchical file system structure, much like an upside-down tree, with root (/) at the base of the file system and all other directories spreading from there.
A UNIX filesystem is a collection of files and directories that has the following properties:

• It has a root directory (/) that contains other files and directories.
• Each file or directory is uniquely identified by its name, the directory in which it resides, and a unique identifier, typically called an inode.
• By convention, the root directory has an inode number of 2 and the lost+found directory has an inode number of 3. Inode numbers 0 and 1 are not used. File inode numbers can be seen by specifying the -i option to ls command.
• It is self contained. There are no dependencies between one filesystem and any other.

The directories have specific purposes and generally hold the same types of information for easily locating files. Following are the directories that exist on the major versions of Unix:

Directory	Description
/	This is the root directory which should contain only the directories needed at the top level of the file structure.
/bin	This is where the executable files are located. They are available to all user.
/dev	These are device drivers.
/etc	Supervisor directory commands, configuration files, disk configuration files, valid user lists, groups, ethernet, hosts, where to send critical messages.
/lib	Contains shared library files and sometimes other kernel-related files.
/boot	Contains files for booting the system.
/home	Contains the home directory for users and other accounts.
/mnt	Used to mount other temporary file systems, such as cdrom and floppy for the CD-ROM drive and floppy diskette drive, respectively
/proc	Contains all processes marked as a file by process number or other information that is dynamic to the system.
/tmp	Holds temporary files used between system boots
/usr	Used for miscellaneous purposes, or can be used by many users. Includes administrative commands, shared files, library files, and others
/var	Typically contains variable-length files such as log and print files and any other type of file that may contain a variable amount of data
/sbin	Contains binary (executable) files, usually for system administration. For example fdisk and ifconfig utlities.
/kernel	Contains kernel files

Navigating the File System:

Now that you understand the basics of the file system, you can begin navigating to the files you need. The following are commands you'll use to navigate the system:

Command	Description
cat filename	Displays a filename.
cd dirname	Moves you to the directory identified.
cp file1 file2	Copies one file/directory to specified location.
file filename	Identifies the file type (binary, text, etc).
find filename dir	Finds a file/directory.
head filename	Shows the beginning of a file.
less filename	Browses through a file from end or beginning.
ls dirname	Shows the contents of the directory specified.
mkdir dirname	Creates the specified directory.
more filename	Browses through a file from beginning to end.
mv file1 file2	Moves the location of or renames a file/directory.
pwd	Shows the current directory the user is in.
rm filename	Removes a file.
rmdir dirname	Removes a directory.
tail filename	Shows the end of a file.
touch filename	Creates a blank file or modifies an existing file.s attributes.
whereis filename	Shows the location of a file.
which filename	Shows the location of a file if it is in your PATH.