Linux Directory Structure

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The Linux directory structure is a standardized layout for organizing files and directories on Linux systems. It is based on the Filesystem Hierarchy Standard (FHS), which defines the recommended placement of files and directories for system-wide consistency.

The Linux directory structure is organized around the root directory, represented by the forward slash (/). All other files and directories reside within the root directory, forming a hierarchical tree structure.

These are the common top-level directories associated with the root directory:

Directories	Description
/bin	binary or executable programs.
/etc	system configuration files.
/home	home directory. It is the default current directory.
/opt	optional or third-party software.
/tmp	temporary space, typically cleared on reboot.
/usr	User related programs.
/var	log files.

Some other directories in the Linux system:

Directories	Description
/boot	It contains all the boot-related information files and folders such as conf, grub, etc.
/dev	It is the location of the device files such as dev/sda1, dev/sda2, etc.
/lib	It contains kernel modules and a shared library.
/lost+found	It is used to find recovered bits of corrupted files.
/media	It contains subdirectories where removal media devices are inserted.
/mnt	It contains temporary mount directories for mounting the file system.
/proc	It is a virtual and pseudo-file system to contains info about the running processes with a specific process ID or PID.
/run	It stores volatile runtime data.
/sbin	binary executable programs for an administrator.
/srv	It contains server-specific and server-related files.
/sys	It is a virtual file system for modern Linux distributions to store and allows modification of the devices connected to the system.

Exploring directories and their usability:

We know that Linux is a very complex system that requires an efficient way to start, stop, maintain and reboot a system, unlike Windows operating system. In the Linux system some well-defined configuration files, binaries, main pages information files are available for every process. 

Linux Kernel File:

• /boot/vmlinux – The Linux kernel file.

Device Files:

• /dev/hda – Device file for the first IDE HDD.
• /dev/hdc – A pseudo-device that output garbage output is redirected to /dev/null.

System Configuration Files:

Configuration Files	Description
/etc/bashrc	It is used by bash shell that contains system defaults and aliases.
/etc/crontab	A shell script to run specified commands on a predefined time interval.
/etc/exports	It contains information on the file system available on the network.
/etc/fstab	Information of the Disk Drive and their mount point.
/etc/group	It is a text file to define Information of Security Group.
/etc/grub.conf	It is the grub bootloader configuration file.
/etc/init.d	Service startup Script.
/etc/lilo.conf	It contains lilo bootloader configuration file.
/etc/hosts	Information of IP and corresponding hostnames
/etc/hosts.allow	It contains a list of hosts allowed accessing services on the local machine.
/etc/host.deny	List of hosts denied accessing services on the local machine.
/etc/inittab	INIT process and their interaction at the various run levels.
/etc/issue	Allows editing the pre-login message.
/etc/modules.conf	It contains the configuration files for the system modules.
/etc/motd	It contains the message of the day.
/etc/mtab	Currently mounted blocks information.
/etc/passwd	It contains username, password of the system, users in a shadow file.
/etc/printcap	It contains printer Information.
/etc/profile	Bash shell defaults.
/etc/profile.d	It contains other scripts like application scripts, executed after login.
/etc/rc.d	It avoids script duplication.
/etc/rc.d/init.d	Run Level Initialisation Script.
/etc/resolv.conf	DNS being used by System.
/etc/security	It contains the name of terminals where root login is possible.
/etc/skel	Script that initiates new user home directory.
/etc/termcap	An ASCII file that defines the behavior of different types of the terminal.
/etc/X11	Directory tree contains all the conf files for the X-window System.

User Related Files:

User Related Files	Descriptions
/usr/bin	It contains most of the executable files.
/usr/bin/X11	Symbolic link of /usr/bin.
/usr/include	It contains standard files used by C program.
/usr/share	It contains architecture independent shareable text files.
/usr/lib	It contains object files and libraries.
/usr/sbin	It contains commands for Super User, for System Administration.

Virtual and Pseudo Process Related Files:

Virtual and Pseudo Process Related Files	Descriptions
/proc/cpuinfo	CPU Information
/proc/filesystems	It keeps useful info about the processes that are currently running.
/proc/interrupts	it keeps the information about the number of interrupts per IRQ.
/proc/ioports	Contains all the Input and Output addresses used by devices on the server
/proc/meminfo	It reports the memory usage information.
/proc/modules	Currently using kernel module.
/proc/mount	Mounted File-system Information.
/proc/stat	It displays the detailed statistics of the current system.
/proc/swaps	It contains swap file information.

Version Information File:

• /version – It displays the Linux version information.

Log Files:

Log Files	Descriptions
/var/log/lastlog	It stores user’s last login info.
/var/log/messages	It has all the global system messages
/var/log/wtmp	It keeps a history of login and logout information.