Linux Admin - User Management

 When discussing user management, we have three important terms to understand −

• Users
• Groups
• Permissions

We have already discussed in-depth permissions as applied to files and folders. In this chapter, let's discuss about users and groups.

CentOS Users

In CentOS, there are two types accounts −

• System accounts − Used for a daemon or other piece of software.

• Interactive accounts − Usually assigned to a user for accessing system resources.

The main difference between the two user types is −

• System accounts are used by daemons to access files and directories. These will usually be disallowed from interactive login via shell or physical console login.

• Interactive accounts are used by end-users to access computing resources from either a shell or physical console login.

With this basic understanding of users, let's now create a new user for Bob Jones in the Accounting Department. A new user is added with the adduser command.

Following are some adduser common switches −

Switch	Action
-c	Adds comment to the user account
-m	Creates user home directory in default location, if nonexistent
-g	Default group to assign the user
-n	Does not create a private group for the user, usually a group with username
-M	Does not create a home directory
-s	Default shell other than /bin/bash
-u	Specifies UID (otherwise assigned by the system)
-G	Additional groups to assign the user to

When creating a new user, use the -c, -m, -g, -n switches as follows −

[root@localhost Downloads]# useradd -c "Bob Jones  Accounting Dept Manager" 
-m -g accounting -n bjones

Now let's see if our new user has been created −

[root@localhost Downloads]# id bjones 
(bjones) gid = 1001(accounting) groups = 1001(accounting)

[root@localhost Downloads]# grep bjones /etc/passwd 
bjones:x:1001:1001:Bob Jones  Accounting Dept Manager:/home/bjones:/bin/bash

[root@localhost Downloads]#

Now we need to enable the new account using the passwd command −

[root@localhost Downloads]# passwd bjones 
Changing password for user bjones. 
New password:  
Retype new password:  
passwd: all authentication tokens updated successfully.

[root@localhost Downloads]#

The user account is not enabled allowing the user to log into the system.

Disabling User Accounts

There are several methods to disable accounts on a system. These range from editing the /etc/passwd file by hand. Or even using the passwd command with the -lswitch. Both of these methods have one big drawback: if the user has ssh access and uses an RSA key for authentication, they can still login using this method.

Now let’s use the chage command, changing the password expiry date to a previous date. Also, it may be good to make a note on the account as to why we disabled it.

[root@localhost Downloads]# chage -E 2005-10-01 bjones
 
[root@localhost Downloads]# usermod  -c "Disabled Account while Bob out of the country 
for five months" bjones

[root@localhost Downloads]# grep bjones /etc/passwd 
bjones:x:1001:1001:Disabled Account while Bob out of the country for four 
months:/home/bjones:/bin/bash

[root@localhost Downloads]#

Manage Groups

Managing groups in Linux makes it convenient for an administrator to combine the users within containers applying permission-sets applicable to all group members. For example, all users in Accounting may need access to the same files. Thus, we make an accounting group, adding Accounting users.

For the most part, anything requiring special permissions should be done in a group. This approach will usually save time over applying special permissions to just one user. Example, Sally is in-charge of reports and only Sally needs access to certain files for reporting. However, what if Sally is sick one day and Bob does reports? Or the need for reporting grows? When a group is made, an Administrator only needs to do it once. The add users is applied as needs change or expand.

Following are some common commands used for managing groups −

• chgrp
• groupadd
• groups
• usermod

chgrp − Changes the group ownership for a file or directory.

Let's make a directory for people in the accounting group to store files and create directories for files.

[root@localhost Downloads]# mkdir /home/accounting

[root@localhost Downloads]# ls -ld /home/accounting
drwxr-xr-x. 2 root root 6 Jan 13 10:18 /home/accounting

[root@localhost Downloads]#

Next, let's give group ownership to the accounting group.

[root@localhost Downloads]# chgrp -v  accounting /home/accounting/ 
changed group of ‘/home/accounting/’ from root to accounting

[root@localhost Downloads]# ls -ld /home/accounting/ 
drwxr-xr-x. 2 root accounting 6 Jan 13 10:18 /home/accounting/

[root@localhost Downloads]#

Now, everyone in the accounting group has read and execute permissions to /home/accounting. They will need write permissions as well.

[root@localhost Downloads]# chmod g+w /home/accounting/

[root@localhost Downloads]# ls -ld /home/accounting/ 
drwxrwxr-x. 2 root accounting 6 Jan 13 10:18 /home/accounting/

[root@localhost Downloads]#

Since the accounting group may deal with sensitive documents, we need to apply some restrictive permissions for other or world.

[root@localhost Downloads]# chmod o-rx /home/accounting/

[root@localhost Downloads]# ls -ld /home/accounting/ 
drwxrwx---. 2 root accounting 6 Jan 13 10:18 /home/accounting/

[root@localhost Downloads]#

groupadd − Used to make a new group.

Switch	Action
-g	Specifies a GID for the group
-K	Overrides specs for GID in /etc/login.defs
-o	Allows overriding non-unique group id disallowance
-p	Group password, allowing the users to activate themselves

Let's make a new group called secret. We will add a password to the group, allowing the users to add themselves with a known password.

[root@localhost]# groupadd secret

[root@localhost]# gpasswd secret 
Changing the password for group secret 
New Password:  
Re-enter new password:

[root@localhost]# exit 
exit

[centos@localhost ~]$ newgrp secret 
Password:

[centos@localhost ~]$ groups 
secret wheel rdc

[centos@localhost ~]$

In practice, passwords for groups are not used often. Secondary groups are adequate and sharing passwords amongst other users is not a great security practice.

The groups command is used to show which group a user belongs to. We will use this, after making some changes to our current user.

usermod is used to update account attributes.

Following are the common usermod switches.

Switch	Action
-a	Appends, adds user to supplementary groups, only with the -G option
-c	Comment, updatesthe user comment value
-d	Home directory, updates the user's home directory
-G	Groups, adds or removesthe secondary user groups
-g	Group, default primary group of the user

[root@localhost]# groups centos 
centos : accounting secret

[root@localhost]#

[root@localhost]# usermod -a -G wheel centos

[root@localhost]# groups centos
centos : accounting wheel secret

[root@localhost]#

Linux Admin - File / Folder Management

 To introduce permissions as they apply to both directories and files in CentOS Linux, let's look at the following command output.

[centos@centosLocal etc]$ ls -ld /etc/yum* 
drwxr-xr-x. 6 root root 100 Dec  5 06:59 /etc/yum 
-rw-r--r--. 1 root root 970 Nov 15 08:30 /etc/yum.conf 
drwxr-xr-x. 2 root root 187 Nov 15 08:30 /etc/yum.repos.d

Note − The three primary object types you will see are

• "-" − a dash for plain file

• "d" − for a directory

• "l" − for a symbolic link

We will focus on the three blocks of output for each directory and file −

• drwxr-xr-x : root : root
• -rw-r--r-- : root : root
• drwxr-xr-x : root : root

Now let's break this down, to better understand these lines −

d	Means the object type is a directory
rwx	Indicates directory permissions applied to the owner
r-x	Indicates directory permissions applied to the group
r-x	Indicates directory permissions applied to the world
root	The first instance, indicates the owner of the directory
root	The second instance, indicates the group to which group permissions are applied

Understanding the difference between owner, group and world is important. Not understanding this can have big consequences on servers that host services to the Internet.

Before we give a real-world example, let's first understand the permissions as they apply to directories and files.

Please take a look at the following table, then continue with the instruction.

Octal	Symbolic	Perm.	Directory
1	x	Execute	Enter the directory and access files
4	r	Read	List the files within the directory
2	w	Write	Delete or modify the files in a directory

Note − When files should be accessible for reading in a directory, it is common to apply read and execute permissions. Otherwise, the users will have difficulty working with the files. Leaving write disabled will assure files cannot be: renamed, deleted, copied over, or have permissions modified.

Applying Permissions to Directories and Files

When applying permissions, there are two concepts to understand −

• Symbolic Permissions
• Octal Permissions

In essence, each are the same but a different way to referring to, and assigning file permissions. For a quick guide, please study and refer to the following table −

	Read	Write	Execute
Octal	4	2	1
Symbolic	r	w	x

When assigning permissions using the octal method, use a 3 byte number such as: 760. The number 760 translates into: Owner: rwx; Group: rw; Other (or world) no permissions.

Another scenario: 733 would translate to: Owner: rwx; Group: wx; Other: wx.

There is one drawback to permissions using the Octal method. Existing permission sets cannot be modified. It is only possible to reassign the entire permission set of an object.

Now you might wonder, what is wrong with always re-assigning permissions? Imagine a large directory structure, for example /var/www/ on a production web-server. We want to recursively take away the w or write bit on all directories for Other. Thus, forcing it to be pro-actively added only when needed for security measures. If we re-assign the entire permission set, we take away all other custom permissions assigned to every sub-directory.

Hence, it will cause a problem for both the administrator and the user of the system. At some point, a person (or persons) would need to re-assign all the custom permissions that were wiped out by re-assigning the entire permission-set for every directory and object.

In this case, we would want to use the Symbolic method to modify permissions −

chmod -R o-w /var/www/

The above command would not "overwrite permissions" but modify the current permission sets. So get accustomed to using the best practice

• Octal only to assign permissions
• Symbolic to modify permission sets

It is important that a CentOS Administrator be proficient with both Octal and Symbolic permissions as permissions are important for the integrity of data and the entire operating system. If permissions are incorrect, the end result will be both sensitive data and the entire operating system will be compromised.

With that covered, let's look at a few commands for modifying permissions and object owner/members −

• chmod
• chown
• chgrp
• umask

chmod : Change File Mode Permission Bits

Command	Action
-c	Like verbose, but will only report the changes made
-v	Verbose, outputsthe diagnostics for every request made
-R	Recursively applies the operation on files and directories

chmod will allow us to change permissions of directories and files using octal or symbolic permission sets. We will use this to modify our assignment and uploads directories.

chown : Change File Owner and Group

Command	Action
-c	Like verbose, but will only report the changes made
-v	Verbose, outputsthe diagnostics for every request made
-R	Recursively applies the operation on files and directories

chown can modify both owning the user and group of objects. However, unless needing to modify both at the same time, using chgrp is usually used for groups.

chgrp : Change Group Ownership of File or Directory

Command	Action
-c	Like verbose, but will only report the changes
-v	Verbose, outputs the diagnostics for every request made
-R	Recursively, applies the operations on file and directories

chgrp will change the group owner to that supplied.

Real-world practice

Let's change all the subdirectory assignments in /var/www/students/ so the owning group is the students group. Then assign the root of students to the professors group. Later, make Dr. Terry Thomas the owner of the students directory, since he is tasked as being in-charge of all Computer Science academia at the school.

As we can see, when created, the directory is left pretty raw.

[root@centosLocal ~]# ls -ld /var/www/students/ 
drwxr-xr-x. 4 root root 40 Jan  9 22:03 /var/www/students/

[root@centosLocal ~]# ls -l /var/www/students/ 
total 0 
drwxr-xr-x. 2 root root 6 Jan  9 22:03 assignments 
drwxr-xr-x. 2 root root 6 Jan  9 22:03 uploads 

[root@centosLocal ~]#

As Administrators we never want to give our root credentials out to anyone. But at the same time, we need to allow users the ability to do their job. So let's allow Dr. Terry Thomas to take more control of the file structure and limit what students can do.

[root@centosLocal ~]# chown -R drterryt:professors /var/www/students/ 
[root@centosLocal ~]# ls -ld /var/www/students/ 
drwxr-xr-x. 4 drterryt professors 40 Jan  9 22:03 /var/www/students/

[root@centosLocal ~]# ls -ls /var/www/students/ 
total 0 
0 drwxr-xr-x. 2 drterryt professors 6 Jan  9 22:03 assignments 
0 drwxr-xr-x. 2 drterryt professors 6 Jan  9 22:03 uploads

[root@centosLocal ~]#

Now, each directory and subdirectory has an owner of drterryt and the owning group is professors. Since the assignments directory is for students to turn assigned work in, let's take away the ability to list and modify files from the students group.

[root@centosLocal ~]# chgrp students /var/www/students/assignments/ && chmod 
736 /var/www/students/assignments/

[root@centosLocal assignments]# ls -ld /var/www/students/assignments/ 
drwx-wxrw-. 2 drterryt students 44 Jan  9 23:14 /var/www/students/assignments/

[root@centosLocal assignments]#

Students can copy assignments to the assignments directory. But they cannot list contents of the directory, copy over current files, or modify files in the assignments directory. Thus, it just allows the students to submit completed assignments. The CentOS filesystem will provide a date-stamp of when assignments turned in.

As the assignments directory owner −

[drterryt@centosLocal assignments]$ whoami 
drterryt

[drterryt@centosLocal assignments]$ ls -ld /var/www/students/assignment 
drwx-wxrw-. 2 drterryt students 44 Jan  9 23:14 /var/www/students/assignments/

[drterryt@centosLocal assignments]$ ls -l /var/www/students/assignments/ 
total 4 
-rw-r--r--. 1 adama  students  0 Jan  9 23:14 myassign.txt 
-rw-r--r--. 1 tammyr students 16 Jan  9 23:18 terryt.txt

[drterryt@centosLocal assignments]$

We can see, the directory owner can list files as well as modify and remove files.

umask Command: Supplies the Default Modes for File and Directory Permissions As They are Created

umask is an important command that supplies the default modes for File and Directory Permissions as they are created.

umask permissions use unary, negated logic.

Permission	Operation
0	Read, write, execute
1	Read and write
2	Read and execute
3	Read only
4	Read and execute
5	Write only
6	Execute only
7	No permissions

[adama@centosLocal umask_tests]$ ls -l ./ 
-rw-r--r--. 1 adama students 0 Jan 10 00:27 myDir 
-rw-r--r--. 1 adama students 0 Jan 10 00:27 myFile.txt

[adama@centosLocal umask_tests]$ whoami 
adama

[adama@centosLocal umask_tests]$ umask 
0022

[adama@centosLocal umask_tests]$

Now, let’s change the umask for our current user, and make a new file and directory.

[adama@centosLocal umask_tests]$ umask 077

[adama@centosLocal umask_tests]$ touch mynewfile.txt

[adama@centosLocal umask_tests]$ mkdir myNewDir

[adama@centosLocal umask_tests]$ ls -l 
total 0 
-rw-r--r--. 1 adama students 0 Jan 10 00:27 myDir 
-rw-r--r--. 1 adama students 0 Jan 10 00:27 myFile.txt 
drwx------. 2 adama students 6 Jan 10 00:35 myNewDir 
-rw-------. 1 adama students 0 Jan 10 00:35 mynewfile.txt

As we can see, newly created files are a little more restrictive than before.

umask for users must should be changed in either −

• /etc/profile
• ~/bashrc

[root@centosLocal centos]# su adama 
[adama@centosLocal centos]$ umask 
0022 
[adama@centosLocal centos]$

Generally, the default umask in CentOS will be okay. When we run into trouble with a default of 0022, is usually when different departments belonging to different groups need to collaborate on projects.

This is where the role of a system administrator comes in, to balance the operations and design of the CentOS operating system.

Linux Admin - Basic CentOS Linux Commands

 Before learning the tools of a CentOS Linux Administrator, it is important to note the philosophy behind the Linux administration command line.

Linux was designed based on the Unix philosophy of “small, precise tools chained together simplifying larger tasks”. Linux, at its root, does not have large single-purpose applications for one specific use a lot of the time. Instead, there are hundreds of basic utilities that when combined offer great power to accomplish big tasks with efficiency.

Examples of the Linux Philosophy

For example, if an administrator wants a listing of all the current users on a system, the following chained commands can be used to get a list of all system users. On execution of the command, the users are on the system are listed in an alphabetical order.

[root@centosLocal centos]# cut /etc/passwd -d":" -f1 | sort 
abrt 
adm 
avahi 
bin 
centos 
chrony 
colord 
daemon 
dbus

It is easy to export this list into a text file using the following command.

[root@localhost /]# cut /etc/passwd -d ":" -f1 > system_users.txt        
[root@localhost /]# cat ./system_users.txt | sort | wc –l 
40       
[root@localhost /]#

It is also possible to compare the user list with an export at a later date.

[root@centosLocal centos]#  cut /etc/passwd -d ":" -f1 > system_users002.txt && 
   cat system_users002.txt | sort | wc -l 
41 
[root@centosLocal centos]# diff ./system_users.txt ./system_users002.txt  
evilBackdoor [root@centosLocal centos]#

A new user, “evilBackdoor", has been added to the system.

With this approach of small tools chained to accomplish bigger tasks, it is simpler to make a script performing these commands, than automatically email results at regular time intervals.

Basic Commands every Linux Administrator should be proficient in are −

• vim
• grep
• more and less
• tail
• head
• wc
• sort
• uniq
• tee
• cat
• cut
• sed
• tr
• paste

In the Linux world, Administrators use filtering commands every day to parse logs, filter command output, and perform actions with interactive shell scripts. As mentioned, the power of these commands come in their ability to modify one another through a process called piping.

The following command shows how many words begin with the letter a from the CentOS main user dictionary.

[root@centosLocal ~]# egrep '^a.*$' /usr/share/dict/words | wc -l 
25192 
[root@centosLocal ~]#

Linux Admin - CentOS Overview

 Unique among business class Linux distributions, CentOS stays true to the open-source nature that Linux was founded on. The first Linux kernel was developed by a college student at the University of Helsinki (Linus Torvalds) and combined with the GNU utilities founded and promoted by Richard Stallman. CentOS has a proven, open-source licensing that can power today’s business world.

CentOS has quickly become one of the most prolific server platforms in the world. Any Linux Administrator, when seeking employment, is bound to come across the words: “CentOS Linux Experience Preferred”. From startups to Fortune 10 tech titans, CentOS has placed itself amongst the higher echelons of server operating systems worldwide.

What makes CentOS stand out from other Linux distributions is a great combination of −

• Open source licensing

• Dedicated user-base of Linux professionals

• Good hardware support

• Rock-solid stability and reliability

• Focus on security and updates

• Strict adherence to software packaging standards needed in a corporate environment

Before starting the lessons, we assume that the readers have a basic knowledge of Linux and Administration fundamentals such as −

• What is the root user?

• The power of the root user

• Basic concept of security groups and users

• Experience using a Linux terminal emulator

• Fundamental networking concepts

• Fundamental understanding of interpreted programming languages (Perl, Python, Ruby)

• Networking protocols such as HTTP, LDAP, FTP, IMAP, SMTP

• Cores that compose a computer operating system: file system, drivers, and the kerne

 

Advantages of Linux

Linux is an open-source operating system like Windows and MacOS. It is not just limited to the operating system, but nowadays, it is also used as a platform to run desktops, servers, and embedded systems. It provides various distributions and variations as it is open source and has a modular design. The kernel is a core part of the Linux system.

Linux system is used to manage various services such as process scheduling, application scheduling, basic peripheral devices, file system, and more. Linux provides various advantages over other operating systems such as Windows and macOS. So, it is used in almost every field, from cars to home appliances and smartphones to servers (supercomputers).

In this section, we will see some major advantages of the Linux system. Further, we will see the advantages of Linux over other operating systems and will determine why it is better than other operating systems.

Why is Linux better than other operating systems?

There are many features of the Linux operating system that demonstrate that it is better than other operating systems. However, in some prospective other operating systems can be more useful than Linux. Let's see the top 20 advantages of Linux OS.

Top 20 Advantages of Linux

Following are top 20 advantages of the Linux operating system:

1. pen Source

As it is open-source, its source code is easily available. Anyone having programming knowledge can customize the operating system. One can contribute, modify, distribute, and enhance the code for any purpose.

2. Security

The Linux security feature is the main reason that it is the most favorable option for developers. It is not completely safe, but it is less vulnerable than others. Each application needs to authorize by the admin user. The virus is not executed until the administrator provides the access password. Linux systems do not require any antivirus program.

3. Free

Certainly, the biggest advantage of the Linux system is that it is free to use. We can easily download it, and there is no need to buy the license for it. It is distributed under GNU GPL (General Public License). Comparatively, we have to pay a huge amount for the license of the other operating systems.

4. Lightweight

Linux is lightweight. The requirements for running Linux are much less than other operating systems. In Linux, the memory footprint and disk space are also lower. Generally, most of the Linux distributions required as little as 128MB of RAM around the same amount for disk space.

5. Stability

Linux is more stable than other operating systems. Linux does not require to reboot the system to maintain performance levels. It rarely hangs up or slow down. It has big up-times.

6. Performance

Linux system provides high performance over different networks. It is capable of handling a large number of users simultaneously.

7. Flexibility

Linux operating system is very flexible. It can be used for desktop applications, embedded systems, and server applications too. It also provides various restriction options for specific computers. We can install only necessary components for a system.

8. Software Updates

In Linux, the software updates are in user control. We can select the required updates. There a large number of system updates are available. These updates are much faster than other operating systems. So, the system updates can be installed easily without facing any issue.

9. Distributions/ Distros

There are many Linux distributions available in the market. It provides various options and flavors of Linux to the users. We can choose any distros according to our needs. Some popular distros are Ubuntu, Fedora, Debian, Linux Mint, Arch Linux, and many more.

For the beginners, Ubuntu and Linux Mint would be useful and, Debian and Fedora would be good choices for proficient programmers.

10. Live CD/USB

Almost all Linux distributions have a Live CD/USB option. It allows us to try or run the Linux operating system without installing it.

11. Graphical User Interface

Linux is a command-line based OS but, it provides an interactive user interface like Windows.

12. Suitable for programmers

It supports almost all of the most used programming languages such as C/C++, Java, Python, Ruby, and more. Further, it offers a vast range of useful applications for development.

The programmers prefer the Linux terminal over the Windows command line. The package manager on Linux system helps programmers to understand how things are done. Bash scripting is also a functional feature for the programmers. It also provides support for SSH, which helps in managing the servers quickly.

13. Community Support

Linux provides large community support. We can find support from various sources. There are many forums available on the web to assist users. Further, developers from the various opensource communities are ready to help us.

14. Privacy

Linux always takes care of user privacy as it never takes much private data from the user. Comparatively, other operating systems ask for the user's private data.

15. Networking

Linux facilitates with powerful support for networking. The client-server systems can be easily set to a Linux system. It provides various command-line tools such as ssh, ip, mail, telnet, and more for connectivity with the other systems and servers. Tasks such as network backup are much faster than others.

16. Compatibility

Linux is compatible with a large number of file formats as it supports almost all file formats.

17. Installation

Linux installation process takes less time than other operating systems such as Windows. Further, its installation process is much easy as it requires less user input. It does not require much more system configuration even it can be easily installed on old machines having less configuration.

18. Multiple Desktop Support

Linux system provides multiple desktop environment support for its enhanced use. The desktop environment option can be selected during installation. We can select any desktop environment such as GNOME (GNU Network Object Model Environment) or KDE (K Desktop Environment) as both have their specific environment.

19. Multitasking

It is a multitasking operating system as it can run multiple tasks simultaneously without affecting the system speed.

20. Heavily Documented for beginners

There are many command-line options that provide documentation on commands, libraries, standards such as manual pages and info pages. Also, there are plenty of documents available on the internet in different formats, such as Linux tutorials, Linux documentation project, Serverfault, and more. To help the beginners, several communities are available such as Ask Ubuntu, Reddit, and StackOverflow.

What is Linux ? Why Linux?

 

What Is Linux

Linux is an open-source operating system like other operating systems such as Microsoft Windows, Apple Mac OS, iOS, Google android, etc. An operating system is a software that enables the communication between computer hardware and software. It conveys input to get processed by the processor and brings output to the hardware to display it. This is the basic function of an operating system. Although it performs many other important tasks, let's not talk about that.

Linux is around us since the mid-90s. It can be used from wristwatches to supercomputers. It is everywhere in our phones, laptops, PCs, cars and even in refrigerators. It is very much famous among developers and normal computer users.

Evolution of Linux OS

The Linux OS was developed by Linus Torvalds in 1991, which sprouted as an idea to improve the UNIX OS. He suggested improvements but was rejected by UNIX designers. Therefore, he thought of launching an OS, designed in a way that could be modified by its users.

Nowadays, Linux is the fastest-growing OS. It is used from phones to supercomputers by almost all major hardware devices.

Structure Of Linux Operating System

An operating system is a collection of software, each designed for a specific function.

Linux OS has following components:

1) Kernel

Linux kernel is the core part of the operating system. It establishes communication between devices and software. Moreover, it manages system resources. It has four responsibilities:

• device management: A system has many devices connected to it like CPU, a memory device, sound cards, graphic cards, etc. A kernel stores all the data related to all the devices in the device driver (without this kernel won't be able to control the devices). Thus kernel knows what a device can do and how to manipulate it to bring out the best performance. It also manages communication between all the devices. The kernel has certain rules that have to be followed by all the devices.
• Memory management: Another function that kernel has to manage is the memory management. The kernel keeps track of used and unused memory and makes sure that processes shouldn't manipulate data of each other using virtual memory addresses.
• Process management: In the process, management kernel assigns enough time and gives priorities to processes before handling CPU to other processes. It also deals with security and ownership information.
• Handling system calls: Handling system calls means a programmer can write a query or ask the kernel to perform a task.

2) System Libraries

System libraries are special programs that help in accessing the kernel's features. A kernel has to be triggered to perform a task, and this triggering is done by the applications. But applications must know how to place a system call because each kernel has a different set of system calls. Programmers have developed a standard library of procedures to communicate with the kernel. Each operating system supports these standards, and then these are transferred to system calls for that operating system.

The most well-known system library for Linux is Glibc (GNU C library).

3) System Tools

Linux OS has a set of utility tools, which are usually simple commands. It is a software which GNU project has written and publish under their open source license so that software is freely available to everyone.

With the help of commands, you can access your files, edit and manipulate data in your directories or files, change the location of files, or anything.

4) Development Tools

With the above three components, your OS is running and working. But to update your system, you have additional tools and libraries. These additional tools and libraries are written by the programmers and are called toolchain. A toolchain is a vital development tool used by the developers to produce a working application.

5) End User Tools

These end tools make a system unique for a user. End tools are not required for the operating system but are necessary for a user.

Some examples of end tools are graphic design tools, office suites, browsers, multimedia players, etc.

Why use Linux?

This is one of the most asked questions about Linux systems. Why do we use a different and bit complex operating system, if we have a simple operating system like Windows? So there are various features of Linux systems that make it completely different and one of the most used operating systems. Linux may be a perfect operating system if you want to get rid of viruses, malware, slowdowns, crashes, costly repairs, and many more. Further, it provides various advantages over other operating systems, and we don't have to pay for it. Let's have a look at some of its special features that will attract you to switch your operating system.

Free & Open Source Operating System

Most OS come in a compiled format means the main source code has run through a program called a compiler that translates the source code into a language that is known to the computer.

Modifying this compiled code is a tough job.

On the other hand, open-source is completely different. The source code is included with the compiled version and allows modification by anyone having some knowledge. It gives us the freedom to run the program, freedom to change the code according to our use, freedom to redistribute its copies, and freedom to distribute copies, which are modified by us.

In short, Linux is an operating system that is "for the people, by the people."

And we can dive in Linux without paying any cost. We can install it on Multiple machines without paying any cost.

It is secure

Linux supports various security options that will save you from viruses, malware, slowdowns, crashes. Further, it will keep your data protected. Its security feature is the main reason that it is the most favorable option for developers. It is not completely safe, but it is less vulnerable than others. Each application needs to authorize by the admin user. The virus cannot be executed until the administrator provides the access password. Linux systems do not require any antivirus program.

Favorable choice of Developers

Linux is suitable for the developers, as it supports almost all of the most used programming languages such as C/C++, Java, Python, Ruby, and more. Further, it facilitates with a vast range of useful applications for development.

Developers find that the Linux terminal is much better than the Windows command line, So, they prefer terminal over the Windows command line. The package manager on Linux system helps programmers to understand how things are done. Bash scripting is also a functional feature for the programmers. Also, the SSH support helps to manage the servers quickly.

A flexible operating system

Linux is a flexible OS, as, it can be used for desktop applications, embedded systems, and server applications. It can be used from wristwatches to supercomputers. It is everywhere in our phones, laptops, PCs, cars and even in refrigerators. Further, it supports various customization options.

Linux Distributions

Many agencies modified the Linux operating system and makes their Linux distributions. There are many Linux distributions available in the market. It provides a different flavor of the Linux operating system to the users. We can choose any distribution according to our needs. Some popular distros are Ubuntu, Fedora, Debian, Linux Mint, Arch Linux, and many more.

For the beginners, Ubuntu and Linux Mint are considered useful and, for the proficient developer, Debian and Fedora would be a good choice. To Get a list of distributions, visit Linux Distributions.

How does Linux work?

Linux is a UNIX-like operating system, but it supports a range of hardware devices from phones to supercomputers. Every Linux-based operating system has the Linux kernel and set of software packages to manage hardware resources.

Also, Linux OS includes some core GNU tools to provide a way to manage the kernel resources, install software, configure the security setting and performance, and many more. All these tools are packaged together to make a functional operating system.

How to use Linux?

We can use Linux through an interactive user interface as well as from the terminal (Command Line Interface). Different distributions have a slightly different user interface but almost all the commands will have the same behavior for all the distributions. To run Linux from the terminal, press the "CTRL+ALT+T" keys. And, to explore its functionality, press the application button given on the left down corner of your desktop.