Linux | file + directory breakdown *

Linux File / Directory Structure

file hierarchyDirectory Structuremore ...

https://www.geeksforgeeks.org/linux-file-hierarchy-structure/

The Linux File Hierarchy Structure or the Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Unix-like operating systems. It is maintained by the Linux Foundation.

In the FHS, all files and directories appear under the root directory /, even if they are stored on different physical or virtual devices.
Some of these directories only exist on a particular system if certain subsystems, such as the X Window System, are installed.
Most of these directories exist in all UNIX operating systems and are generally used in much the same way; however, the descriptions here are those used specifically for the FHS and are not considered authoritative for platforms other than Linux.

linux-directory

1. / (Root):

Primary hierarchy root and root directory of the entire file system hierarchy.

Every single file and directory start from the root directory.
The only root user has the right to write under this directory.
/root is the root user’s home directory, which is not the same as /

root-linux-directory

2. /bin :

Essential command binaries that need to be available in single-user mode; for all users, e.g., cat, ls, cp.

Contains binary executables.
Common linux commands you need to use in single-user modes are located under this directory.
Commands used by all the users of the system are located here e.g. ps, ls, ping, grep, cp

bin-linux-directory

3. /boot :

Boot loader files, e.g., kernels, initrd.

Kernel initrd, vmlinux, grub files are located under /boot
Example: initrd.img-2.6.32-24-generic, vmlinuz-2.6.32-24-generic

boot-linux-directory

4. /dev :

Essential device files, e.g., /dev/null.

These include terminal devices, usb, or any device attached to the system.
Example: /dev/tty1, /dev/usbmon0

dev-linux-directory

5. /etc :

Host-specific system-wide configuration files.

Contains configuration files required by all programs.
This also contains startup and shutdown shell scripts used to start/stop individual programs.
Example: /etc/resolv.conf, /etc/logrotate.conf.

etc-linux-directory

6. /home :

Users’ home directories, containing saved files, personal settings, etc.

Play

Unmute

Home directories for all users to store their personal files.
example: /home/kishlay, /home/kv

home-linux-directory

7. /lib:

Libraries essential for the binaries in /bin/ and /sbin/.

Library filenames are either ld* or lib.so.
Example: ld-2.11.1.so, libncurses.so.5.7

lib-linux-directory

8. /media:

Mount points for removable media such as CD-ROMs (appeared in FHS-2.3).

Temporary mount directory for removable devices.
Examples, /media/cdrom for CD-ROM; /media/floppy for floppy drives; /media/cdrecorder for CD writer

media-linux-directory

9. /mnt :

Temporarily mounted filesystems.

Temporary mount directory where sysadmins can mount filesystems.

mnt-linux-directory

10. /opt :

Optional application software packages.

Contains add-on applications from individual vendors.
Add-on applications should be installed under either /opt/ or /opt/ sub-directory.

opt-linux-directory.

11. /sbin :

Essential system binaries, e.g., fsck, init, route.

Just like /bin, /sbin also contains binary executables.
The linux commands located under this directory are used typically by system administrators, for system maintenance purposes.
Example: iptables, reboot, fdisk, ifconfig, swapon

sbin-linux-directory

12. /srv :

Site-specific data served by this system, such as data and scripts for web servers, data offered by FTP servers, and repositories for version control systems.

srv stands for service.
Contains server specific services related data.
Example, /srv/cvs contains CVS related data.

srv-linux-directory

13. /tmp :

Temporary files. Often not preserved between system reboots and may be severely size restricted.

Directory that contains temporary files created by system and users.
Files under this directory are deleted when the system is rebooted.

tmp-linux-directory

14. /usr :

Secondary hierarchy for read-only user data; contains the majority of (multi-)user utilities and applications.

Contains binaries, libraries, documentation, and source-code for second level programs.
/usr/bin contains binary files for user programs. If you can’t find a user binary under /bin, look under /usr/bin. For example: at, awk, cc, less, scp
/usr/sbin contains binary files for system administrators. If you can’t find a system binary under /sbin, look under /usr/sbin. For example: atd, cron, sshd, useradd, userdel
/usr/lib contains libraries for /usr/bin and /usr/sbin
/usr/local contains user’s programs that you install from source. For example, when you install apache from source, it goes under /usr/local/apache2
/usr/src holds the Linux kernel sources, header-files and documentation.

usr_bin-linux-directory

usr_sbin-linux-directory

usr_lib-linux-dirctory

usr_local-linux-directory

usr_src-linux-directory

15. /proc:

Virtual filesystem providing process and kernel information as files. In Linux, it corresponds to a procs mount. Generally, automatically generated and populated by the system, on the fly.

Contains information about system process.
This is a pseudo filesystem that contains information about running processes. For example: /proc/{pid} directory contains information about the process with that particular pid.
This is a virtual filesystem with text information about system resources. For example: /proc/uptime

proc-linux-directory

Modern Linux distributions include a /run directory as a temporary filesystem (tmpfs) which stores volatile runtime data, following the FHS version 3.0. According to the FHS version 2.3, such data were stored in /var/run but this was a problem in some cases because this directory is not always available at early boot. As a result, these programs have had to resort to trickery, such as using /dev/.udev, /dev/.mdadm, /dev/.systems or /dev/.mount directories, even though the device directory isn’t intended for such data.Among other advantages, this makes the system easier to use normally with the root filesystem mounted read-only. For example, below are the changes Debian made in its 2013 Wheezy release:

/dev/.* ? /run/*
/dev/shm ? /run/shm
/dev/shm/* ? /run/*
/etc/* (writable files) ? /run/*
/lib/init/rw ? /run
/var/lock ? /run/lock
/var/run ? /run
/tmp ? /run/tmp

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https://www.geeksforgeeks.org/linux-directory-structure/

In Linux/Unix operating system everything is a file even directories are files, files are files, and devices like mouse, keyboard, printer, etc are also files. Here we are going to see the Directory Structure in Linux.

Types of files in the Linux system.

General Files – It is also called ordinary files. It may be an image, video, program, or simple text file. These types of files can be in ASCII or Binary format. It is the most commonly used file in the Linux system.
Directory Files – These types of files are a warehouse for other file types. It may be a directory file within a directory (subdirectory).
Device Files – In a Windows-like operating system, devices like CD-ROM, and hard drives are represented as drive letters like F: G: H whereas in the Linux system devices are represented as files. As for example, /dev/sda1, /dev/sda2, and so on.

We know that in a Windows-like operating system, files are stored in different folders on different data drives like C: D: E: whereas in the Linux/Unix operating system files are stored in a tree-like structure starting with the root directory as shown in the below diagram.

data storage in Linux/Unix operating systems

The Linux/Unix file system hierarchy base begins at the root and everything starts with the root directory.

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	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	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.

To check the Linux directories, open the terminal and execute sudo -s followed by system password to give root privilege. Then after changing the current home directory to the root directory and check the list of all available directories in the base directory as shown below.

Linux directories

Conclusion

If we understand the Linux directory’s structure correctly, it would be so easy to effectively navigate and manage our filesystem, locate important configuration files, and access system information. One must know that the directory structure and specific file mentioned in this article are based on standard Linux conventions. We must consider that the different Linux distributions may have variations in the directory structure and specific file locations, but overall concept and organization remain similar.