Linux information about directory

Unix / Linux — Directory Management

In this chapter, we will discuss in detail about directory management in Unix.

A directory is a file the solo job of which is to store the file names and the related information. All the files, whether ordinary, special, or directory, are contained in directories.

Unix uses a hierarchical structure for organizing files and directories. This structure is often referred to as a directory tree. The tree has a single root node, the slash character (/), and all other directories are contained below it.

Home Directory

The directory in which you find yourself when you first login is called your home directory.

You will be doing much of your work in your home directory and subdirectories that you’ll be creating to organize your files.

You can go in your home directory anytime using the following command −

indicates the home directory. Suppose you have to go in any other user’s home directory, use the following command −

To go in your last directory, you can use the following command −

Absolute/Relative Pathnames

Directories are arranged in a hierarchy with root (/) at the top. The position of any file within the hierarchy is described by its pathname.

Elements of a pathname are separated by a /. A pathname is absolute, if it is described in relation to root, thus absolute pathnames always begin with a /.

Following are some examples of absolute filenames.

A pathname can also be relative to your current working directory. Relative pathnames never begin with /. Relative to user amrood’s home directory, some pathnames might look like this −

To determine where you are within the filesystem hierarchy at any time, enter the command pwd to print the current working directory −

Listing Directories

To list the files in a directory, you can use the following syntax −

Following is the example to list all the files contained in /usr/local directory −

Creating Directories

We will now understand how to create directories. Directories are created by the following command −

Here, directory is the absolute or relative pathname of the directory you want to create. For example, the command −

Creates the directory mydir in the current directory. Here is another example −

This command creates the directory test-dir in the /tmp directory. The mkdir command produces no output if it successfully creates the requested directory.

If you give more than one directory on the command line, mkdir creates each of the directories. For example, −

Creates the directories docs and pub under the current directory.

Creating Parent Directories

We will now understand how to create parent directories. Sometimes when you want to create a directory, its parent directory or directories might not exist. In this case, mkdir issues an error message as follows −

In such cases, you can specify the -p option to the mkdir command. It creates all the necessary directories for you. For example −

The above command creates all the required parent directories.

Removing Directories

Directories can be deleted using the rmdir command as follows −

Note − To remove a directory, make sure it is empty which means there should not be any file or sub-directory inside this directory.

You can remove multiple directories at a time as follows −

The above command removes the directories dirname1, dirname2, and dirname3, if they are empty. The rmdir command produces no output if it is successful.

Changing Directories

You can use the cd command to do more than just change to a home directory. You can use it to change to any directory by specifying a valid absolute or relative path. The syntax is as given below −

Here, dirname is the name of the directory that you want to change to. For example, the command −

Changes to the directory /usr/local/bin. From this directory, you can cd to the directory /usr/home/amrood using the following relative path −

Renaming Directories

The mv (move) command can also be used to rename a directory. The syntax is as follows −

You can rename a directory mydir to yourdir as follows −

The directories . (dot) and .. (dot dot)

The filename . (dot) represents the current working directory; and the filename .. (dot dot) represents the directory one level above the current working directory, often referred to as the parent directory.

If we enter the command to show a listing of the current working directories/files and use the -a option to list all the files and the -l option to provide the long listing, we will receive the following result.

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Linux Directory Structure in Detail

The Linux file directory structure begins at root (/) which looks like a tree. Basically, those are folders on the hard drive where Linux is installed and organized.

You can use ls command to list the file directory structure. Use mkdir command to create directories, mv command to rename directories and cd command to change directory.

Let’s learn the Linux directory structure in detail.

Linux directory structure and compared with windows

If you are coming from Microsoft Windows users, then you will found that Linux directory structure is not different from Microsoft Windows. Here’s the comparison between them.

No	Linux Directory	Function	Comparison with Microsoft Windows 7
1	/	The top directory of Linux	C:\
2	/bin	Store binary files which related to the system such as mount, ls, rm, etc	C:\Windows
3	/boot	Store files related to boot process	C:\Windows
4	/dev	Store information about all devices which connected to your Linux	C:\Windows
5	/etc	Store configuration files about Linux and its application	C:\Windows
6	/home	User directory	My Documents
7	/lib	Store library files	C:\Windows\system
8	/lost+found	lost+found is the directory in which fsck (filesystem check) will put files it restores from orphaned blocks	Found.000
9	/media	Usually used as a moint point for external media such as CD/DVD ROM	D: or E: drives
10	/mnt	Used as a mount point directory, but it more likely a place that “temporarily mounted” device such as network shares.	A mapped drive such as X: , Y:, Z:
11	/opt	Store files which not handled by package manager	None
12	/proc	A virtual filesystem which used to provide information about the system	C:\Windows\system or C:\Windows\System32
13	/root	As root home directory	My Documents for Administrator
14	/sbin	Store a binary files which usually can be run by superuser only	C:\Windows
15	/selinux	Store information about Security Enhanced. Some Linux distributionmay not have this directory	None
16	/srv	Store data services which used by system	None
17	/sys	Store information related about your Linux system	C:\Windows\system or C:\Windows\System32
18	/tmp	Used as a temporary folder for applications	C:\Windows\Temp
19	/usr	Store user utilities and applications	C:\Program Files or C:\ProgramData
20	/var	Store variable data files	None

Below is a screenshot of CentOS 6.4 directory structure look like.

But again, on Debian based Linux, such as Ubuntu, the structure may a little bit different. Below is a screenshot of directory structure on Ubuntu 13.04

On Ubuntu 13.04, we have /cdrom directory while on CentOS 6.4 we don’t have it. But generally, the structure is identical.

Then we see that on Ubuntu 13.04 keeps a symbolic link of initrd.img and vmlinuz files below the / partition while on CentOS 6.4 we don’t find it.

More information about the structure

When you access /usr directory, we will found that /usr directories partly replicate root ( / ) directory. The content of /usr directory of CentOS 6.4 is like this :

• /usr/bin is a directory that store binary files which related to common usage such as clear, gcc, bunzip2
• /usr/etc is a directory that store application configuration files
• /usr/games is a directory that contain of games applications
• /usr/include is a directory that store header files
• /usr/lib is a directory that store library files
• /usr/libexec is a directory that store library files in binary form
• /usr/local is a directory that usually used as a placed for additional user applications
• /usr/sbin is a directory that store user application binary files which require superuser privileges
• /usr/share is a directory that usually keeps documentation files of application that installed in your Linux
• /usr/src is a directory which keeps the source files of the user application
• /usr/tmp is a directory that used as a temporary folder for applications. This folder may point /var/tmp directory

If you dig deeper to /usr/local, then you will found an identical /usr replicate there.

The tmp directory actually is a symbolic link / shortcut to /var/tmp directory.

The above screenshot was captured from CentOS 6.4. On Ubuntu, we found almost identical directory structure inside /usr and /usr local.

Conclusion

Linux may have a lot of distributions. But with a standardized directory structure, it will make it easier for us to understand what’s the function of each directory. If you are a Linux enthusiast who likes to try various Linux distributions, you will not find any trouble in figuring out the usage of each directory. For a Linux Administrator, it will shorten the learning curve for each Linux distributions.

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Linux Directory Structure and Important Files Paths Explained

For any person, who does not have a sound knowledge of Linux Operating System and Linux File System, dealing with the files and their location, their use may be horrible, and a newbie may really mess up.

This article is aimed to provide the information about Linux File System, some of the important files, their usability and location.

Linux Directory Structure Diagram

A standard Linux distribution follows the directory structure as provided below with Diagram and explanation.

Linux Directory Structure

Each of the above directory (which is a file, at the first place) contains important information, required for booting to device drivers, configuration files, etc. Describing briefly the purpose of each directory, we are starting hierarchically.

1. /bin : All the executable binary programs (file) required during booting, repairing, files required to run into single-user-mode, and other important, basic commands viz., cat, du, df, tar, rpm, wc,history, etc.
2. /boot : Holds important files during boot-up process, including Linux Kernel.
3. /dev : Contains device files for all the hardware devices on the machine e.g., cdrom, cpu, etc
4. /etc : Contains Application’s configuration files, startup, shutdown, start, stop script for every individual program.
5. /home : Home directory of the users. Every time a new user is created, a directory in the name of user is created within home directory which contains other directories like Desktop, Downloads, Documents, etc.
6. /lib : The Lib directory contains kernel modules and shared library images required to boot the system and run commands in root file system.
7. /lost+found : This Directory is installed during installation of Linux, useful for recovering files which may be broken due to unexpected shut-down.
8. /media : Temporary mount directory is created for removable devices viz., media/cdrom.
9. /mnt : Temporary mount directory for mounting file system.
10. /opt : Optional is abbreviated as opt. Contains third party application software. Viz., Java, etc.
11. /proc : A virtual and pseudo file-system which contains information about running process with a particular Process-id aka pid.
12. /root : This is the home directory of root user and should never be confused with ‘/‘
13. /run : This directory is the only clean solution for early-runtime-dir problem.
14. /sbin : Contains binary executable programs, required by System Administrator, for Maintenance. Viz., iptables, fdisk, ifconfig, swapon, reboot, etc.
15. /srv : Service is abbreviated as ‘srv‘. This directory contains server specific and service related files.
16. /sys : Modern Linux distributions include a /sys directory as a virtual filesystem, which stores and allows modification of the devices connected to the system.
17. /tmp :System’s Temporary Directory, Accessible by users and root. Stores temporary files for user and system, till next boot.
18. /usr : Contains executable binaries, documentation, source code, libraries for second level program.
19. /var : Stands for variable. The contents of this file is expected to grow. This directory contains log, lock, spool, mail and temp files.

Exploring Important file, their location and their Usability

Linux is a complex system which requires a more complex and efficient way to start, stop, maintain and reboot a system unlike Windows. There is a well defined configuration files, binaries, man pages, info files, etc. for every process in Linux.

1. /boot/vmlinuz : The Linux Kernel file.
2. /dev/hda : Device file for the first IDE HDD (Hard Disk Drive)
3. /dev/hdc : Device file for the IDE Cdrom, commonly
4. /dev/null : A pseudo device, that don’t exist. Sometime garbage output is redirected to /dev/null, so that it gets lost, forever.
5. /etc/bashrc : Contains system defaults and aliases used by bash shell.
6. /etc/crontab : A shell script to run specified commands on a predefined time Interval.
7. /etc/exports : Information of the file system available on network.
8. /etc/fstab : Information of Disk Drive and their mount point.
9. /etc/group : Information of Security Group.
10. /etc/grub.conf : grub bootloader configuration file.
11. /etc/init.d : Service startup Script.
12. /etc/lilo.conf : lilo bootloader configuration file.
13. /etc/hosts : Information of Ip addresses and corresponding host names.
14. /etc/hosts.allow : List of hosts allowed to access services on the local machine.
15. /etc/host.deny : List of hosts denied to access services on the local machine.
16. /etc/inittab : INIT process and their interaction at various run level.
17. /etc/issue : Allows to edit the pre-login message.
18. /etc/modules.conf : Configuration files for system modules.
19. /etc/motd : motd stands for Message Of The Day, The Message users gets upon login.
20. /etc/mtab : Currently mounted blocks information.
21. /etc/passwd : Contains password of system users in a shadow file, a security implementation.
22. /etc/printcap : Printer Information
23. /etc/profile : Bash shell defaults
24. /etc/profile.d : Application script, executed after login.
25. /etc/rc.d : Information about run level specific script.
26. /etc/rc.d/init.d : Run Level Initialisation Script.
27. /etc/resolv.conf : Domain Name Servers (DNS) being used by System.
28. /etc/securetty : Terminal List, where root login is possible.
29. /etc/skel : Script that populates new user home directory.
30. /etc/termcap : An ASCII file that defines the behaviour of Terminal, console and printers.
31. /etc/X11 : Configuration files of X-window System.
32. /usr/bin : Normal user executable commands.
33. /usr/bin/X11 : Binaries of X windows System.
34. /usr/include : Contains include files used by ‘c‘ program.
35. /usr/share : Shared directories of man files, info files, etc.
36. /usr/lib : Library files which are required during program compilation.
37. /usr/sbin : Commands for Super User, for System Administration.
38. /proc/cpuinfo : CPU Information
39. /proc/filesystems : File-system Information being used currently.
40. /proc/interrupts : Information about the current interrupts being utilised currently.
41. /proc/ioports : Contains all the Input/Output addresses used by devices on the server.
42. /proc/meminfo : Memory Usages Information.
43. /proc/modules : Currently using kernel module.
44. /proc/mount : Mounted File-system Information.
45. /proc/stat : Detailed Statistics of the current System.
46. /proc/swaps : Swap File Information.
47. /version : Linux Version Information.
48. /var/log/lastlog : log of last boot process.
49. /var/log/messages : log of messages produced by syslog daemon at boot.
50. /var/log/wtmp : list login time and duration of each user on the system currently.

That’s all for now. Keep connected to Tecmint for any News and post related to Linux and Foss world. Stay healthy and Don’t forget to give your value-able comments in comment section.

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