Normally the cat command is applied for basically three things in particular:

• Display the contents of a file
• Copy text files to another text file
• Append a text file’s contents to another text file

Being a UNIX command it is ported to all GNU/LINUX distributions and of course, it has options to expand and vary the power of the command itself.  Let’s see the output at the terminal if we do the following command:

cat --help

The command shows us a quick help on the cat command including its options.

The basic usage syntax is:

cat [OPTION] [FILE]…

And the list of commands is shown in this table:

Don’t worry; we’ll examine the most useful options with several examples.

Display Content of File

If we want to show the content of a text file, the syntax would be:

cat path_of_the_archive

I’m going to show the content of a file called file1.txt located in the Example folder. Run below command to display file1.txt content.

cat file1.txt

And there we have the content of the file shown on the terminal in above image.

If you would like to display the contents of several files, simply place them next. Run below command to display contents of two files file1.txt and file2.txt.

cat file1.txt file2.txt

The exit at the terminal would be as follows:

You can see the contents of both files one by one in above image.

Identify Specific File Content

As we can see in above image, it simply shows the contents of file 1 and when it ends, it immediately shows the content of file 2 as if they were “concatenated”. If you would like to know where the content of each file ends, then use the -e option to show a $ at the end of the file.

cat –e file1.txt file2.txt

Add Number of Lines in Output

If you want to display the number of lines along with the file content then you can show it by adding -n option. Run below command to display the line numbers while displaying the file content.

cat –n file1.txt file2.txt

Copy Contents of One file to Another

We can also copy the content of one text file to another using CAT command. Run below command to copy content of file1.txt to file4.txt.

cat file1.txt > file4.txt

In this case, the command reads the contents of file1.txt and overwrites the contents of the new file. If it does not exist, it is simply created. Now we can validate above command whether contents have been copied to not. Now we proceed to show the contents of file4.txt to verify that it made the “copy”. Display content of file4.txt by running below command.

cat file4.txt

We can see the content is same as file1.txt in above image.

Combine or Append the Content of One File to Another

The cat command also allows us to combine or append a text file data to another one, thanks to the operator >>

In this case, we will combine the content of file1.txt with that of file2.txt

cat file1.txt >> file2.txt

And then we check the contents of the file2.txt file to validate it.

cat file2.txt

We can see contents have been combined in to this file. Basically the command takes the content of file1.txt and places it at the end of the file2.txt file

As a conclusion we can say that the cat command is a useful and important command to work with text files in GNU/LINUX and everything about the terminal. It is very useful for managing service configuration files on a server.

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Read More:

• 11 Examples of ls command to List Files in Linux
• Add, Delete & Modify Linux User Accounts
• How to Reset or Change Linux User Passwords?
• How to Change Linux Server Name?

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LIST FILES IN LINUX: “ls” COMMAND 

As it was said, the command ls allows you to list files and folders of a specific path, is easy to use and is very useful and used in the daily work. The command has several options to improve the listings. In a terminal, we can invoke the help of the command ls in this way.

ls --help 

Above command will display all options available for ls command to list the files and folders. In this way we get the syntax of usage and options as output per terminal.

As all options will not cover in one single screenshot so i have scrolled the above screen and taken another screenshots to cover all options in screenshots that has been displayed below.

As we can see the documentation is extensive, but don’t worry we will examine the most useful and used options. The basic syntax of the command is:

ls [options] [file|dir]

Although it is possible to use ls from the most basic form only by typing:

#List files from your given directory.
ls

With this we only list the files that are in the directory where we are located in the terminal. For example, if we wanted to list everything in the root directory of our GNU/LINUX distribution it would be with the command:

#List everything in the root directory
ls /

It was easy, wasn’t it?

Most Important Options of the Command “ls”

ls as well as all GNU/LINUX commands have options that modify the basic command execution result. Here is a list of the most outstanding ones for this command.

 Examples of Command “ls”

Here i have given different examples of command ls that you can use to fulfill different requirements.

List Hidden Files 

We can use option -a if we want to list the hidden files of a specific folder, it would be enough to write:

ls –a path

In my case it would be something like that:

ls –a /home/angelo/

You can see all hidden files as well in above screenshot. We can identify hidden files by looking at the output as such files or folders start with dot (.).

Display Files with their Index Number

We can list files with their index number by running below command. To show files/folders with their index number we will use the option –i along with command ls. You can see i have used below command and output is showing in below image.

ls -i /home/angelo/
 

List Files with full Details (Permissions, Index no, Owner, Create Date etc.)

We can use ls command to display information such as permissions and owner of the folder or file. We will be using option -I to show complete information about files and folders as shown in below screenshot.

ls -l /home/angelo/

This output shows us more specific information about what we have in the folder: First it shows the permissions on the folder, its index number, the owner of the folder, who created the folder, its size in kb, the date it was modified and the folder name.

List Files or Folders in a Reverse Order

ls command also gives an option to sort files and folders in reverse order. We can use -r option to show files and folders in a reverse order as shown in below screenshot after running below command.

ls –r  /home/angelo/

List Subdirectories Recursively

We can List subdirectories recursively by adding the -R option with ls command.  It will display the contents of the directory subfolders. Run below command to display the result.

ls –R /home/angelo/

 Display list of Directories Only

We can use -d and an asterisk option to list and show only the directories. Have a look at below command that has displayed the list of directories under /home/angelo.

ls –d */home/angelo/

Display Files Sort by their File Size

Run below command to display files sort by file size. It is possible with the option –S.

ls -S /home/angelo/

Sort by Date/Time

We can option -t to display files sort by date/time. Run below command to see the output that is also showing in below screenshot.

ls –t /home/angelo/

Display Files as they were Created

Use option -U to show folders and files in no order at all. It will display just as they are created.

ls –U /home/angelo/

Sort by File Extension

We can use option -X with ls command to sort files by their extension names. You can see this in below screenshot.

ls –X /home/angelo/

Sort by Modified Files

We can use combination of options -ltr to show last modification file or directory date. Simply run below command to display the output.

ls -lrt

ls -lrt [path]

In conclusion we can say that the ls command, even when it is relatively easy to use, is one of the tools most used by system administrators.

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Read More:

• RHEL Interview Questions & Answers
• Linux User Administration – Add, Delete & Modify User Accounts
• Install HTop and Use it to Monitor Linux Processes
• How to Change Host Name of RHEL system?
• How to Reset or Change Linux User Account Passwords?

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USERS IN GNU/LINUX 

The first thing we need to know is that, in GNU/LINUX there are different types of users already predefined and each of them have different characteristics for the correct functioning of the system. The first of these is the root user.

Root user

The Root user is the administrator of the operating system, with all options and permissions to perform operations and changes in the system. Its main features are:

• It is the only user account with system-wide privileges.
• In charge of controlling the administration of user accounts.
• It is the only user that can stop the system.
• The root user can install, uninstall and update basic system programs and libraries.

In other words, the root user is the all-powerful user of the system.

Special Users 

They are also called users without login. Their roles in the system are determined by the addition of installed programs. They are distinguished by:

• They are created (usually) automatically at the time of Linux or application installation.
• It does not have all the privileges of the root user, but depending on the account they assume different root privileges.
• They are created when installing the system or any of its extra components.
• Some of them are: bin, daemon, adm, lp, sync, shutdown, mail, operator, squid, apache

Common Users 

These last users are us. That is, they are accounts that are created to use all accessible parts of the system, such as assigned programs and directories. They have a Home directory where they can easily access their documents and files.

• Such users have only full privileges in their working directory or HOME.
• They are used for individual users.
• These users do not have privileges to manage the system or install software. 

How to Create or Add USERS TO Linux Systems?

The adduser command is a “new” alternative to the useradd binary that allows us to add common users to our GNU/LINUX distribution. It is much more “friendly” and intuitive than useradd and allows us to add additional information about the new user. Here we will learn how to create user on Linux system.

In order to use the adduser command we must be root users, for that reason write the following command in a terminal

#Connect using su.
su

You need to write the root password then we can use adduser. The most basic way to use the adduser command is:

adduser new_user 

where new_user is the name of user account. With this “basic” form a new user is created and by giving Enter we are asked to enter the new password for this new user account.

Type the password for your new user account and press Enter. Prompt will ask you to reenter the same password. Re-enter the password and press enter button.

After that you will be asked for any additional information such as Full Name, phone number etc.

At the end, prompt will ask us to confirm the information provided. Type Y to proceed if all information is correct.

Now, as mentioned above, that is the most basic way to create a user but adduser also has options and alternatives to create users. These alternatives are given by the options that can be added to the command, some of them are:

adduser [--home DIR] [--shell SHELL] [--no-create-home] [--uid ID]
[--firstuid ID] [--lastuid ID] [--gecos GECOS] [--ingroup GROUP | --gid ID]
[--disabled-password] [--disabled-login] [--add_extra_groups] USER

You can see various options available with adduser command in above screenshot. Let’s look at example. If you would like to add a user named angelob, and set their home directory to /opt/angelob/ the the command will be as follows.

adduser --home /opt/angelob/ angelob

And then it will ask us for the new password and basic user information. This way you can add user to Linux system.

How to Delete Linux User Accounts? 

As in above section we have learnt how to create user on Linux system. Here i will explain how remove user from Linux system. Removing users from the Linux system is simple and the command to do so is userdel and has many fewer options to make the task. You can see the descriptions for this command in below image.

The easiest way to delete a user is to remove it by running below command. Here user is the name of user account.

#user is the name of user account.
userdel user

We can also delete your entire personal directory with the -r option. Run below command to do this.

userdel -r user

How to Modify Linux User Accounts? 

I have shown how to remove Linux user  in above section. Here, i will explain how to modify a Linux user. To modify users in the GNU/LINUX system we use the command usermod. We can see in the following image the possibilities shown in command:

For example, if we wanted to change the password of a created user, it would be as follows.

#user is the name of Linux user account.
usermod -p ‘new_password’ user

Obviously this method is not recommended because it leaves the password visible. Be careful. Read below article if you want to change your Linux user account password.

• How to Reset or Change User Password on RHEL?

Another useful example is to move the personal folder of the desired user to another one, for it we must combine the options -d and -m in the following way.

usermod -d /opt/angelob1/ -m angelob

With the rest of the options, we only have to place them according to our needs.

In conclusion we can say that the administration of GNU/LINUX users is a matter for system administrators, the subject is wide and with many options to take into account for the creation of them.

Adduser simplifies the creation of user accounts and usermod allows us to modify them in a very fast and dynamic way. And if a user has already completed his life cycle in the system, we can remove it with userdel.

I hope this small guide has been useful to understand a little bit about GNU/LINUX users, clarifying that the commands explained in the article can be used in all popular distributions such as Ubuntu, Red Hat, Suse, Debian and others.
I hope you like this article. Please follow our Facebook page and Twitter handle to get latest updates.

Read More:

• RHEL Interview Questions and Answers
• How to Change Hostname of RHEL system?
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• Install Debian 9 Stretch in Step by Step Process

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Red Hat Linux Interview Questions and Answers

1. What is Red Hat Enterprise Linux?

Answer – It is a GNU/LINUX distribution created and developed by the multinational enterprise oriented company Red Hat, being the basis for deploying cloud applications, servers or data center.

2. Which is the package manager used by RHEL?

Answer – The package manager in RHEL is YUM.

3. How do I install a program in RHEL?

Answer – Installing a package or program in RHEL is simple thanks to YUM. With root permission we type in a terminal.

yum install package_name

4. How can I update the packages in RHEL?

Answer – Run below command to update all packages in your RHEL system.

yum upgrade

5. How can I remove the packages in RHEL?

Answer – Run below command to remove any package from RedHat Linux system.

#Make sure to change the name of package that needs to be removed.
yum remove package_name

6. How can I create a user in RHEL?

Answer – We can create a new user from the terminal with the command:

#Pass the user name in place of user_name 
useradd user_name

7. How can I change the user password?

Answer – The command that allows us to change the password of the active user is passwd. By entering the command in the terminal, you will be prompted for the current password and twice for the new password. Read below article to learn step by step process to change user as well as sudo passwords.

• How to Reset or Change User Password on RHEL?

8. How can I change the system language?

Answer- In RHEL, the system language can be changed using the following command:

localectl set-locale LANG=”xx_XX.utf8”

For example, if the system is in English and we want to change to German

localectl set-locale LANG=de_DE.utf8

Then simply restart the active session (not the system)

9. What is a GNU/LINUX service?

Answer – A service is a program that runs in the background, outside the interactive control of the users of the system.

10. How can I list the services that are running in RHEL?

Answer – This is very useful when managing systems in GNU/LINUX. We can list all the services that are running with the command:

systemctl -t service --state=active

If you want to check specific service running on RHEL then you can pass service name in above command. For example, i want to check SQL Server service running on my RHEL system then i will run below command. This command will show the output for only this service.

systemctl status mssql-server

11. How can I start or stop a service?

Answer – During the administration of a GNU/LINUX based server we will have to initialize and also stop services.

To initialize:

systemctl start name.service 

To Stop:

systemctl stop name.service

To Restart:

systemctl restart name.service

12. How do I know which version of the kernel I am using?

Answer – To know which version of the Linux Kernel we are using, just use the command:

uname –r

13. How can I add and remove kernel modules?

Answer – The kernel modules are small programs or libraries that are added to the kernel so that it can manage hardware devices. To add or remove it we use the command modprobe.

For example, to add a module:

modprobe module_name

And to remove a module

modprobe –r module_name

14. What is the file system RHEL uses?

Answer – The file system used by RHEL is XFS

15. How do I know how much space is available on my hard disk with RHEL?

Answer – This is useful to know when we are reaching the hard disk capacity. With the command:

df –h

16. Can I change hostname in RHEL?

Answer – Yes. There are multiple ways to change hostname of a RHEL system. For example if we want hostname to be example. com, we must write the following command in a terminal:

hostnamectl set-hostname example.com

I have explained it in below article in very details way. Have a look at this article to learn the process to rename or change the hostname of RHEL system.

• How to Change Hostname of RHEL system?

17. How do I know the IP address of the equipment in RHEL?

Answer – With the command:

nmcli dev show

We will not only be able to see the ip address, but also the complete information of all the network interfaces. You can read below article to learn how to check and change the IP address, subnet mask etc of a RHEL system.

• How to Find and Change IP Address, Subnet Mask and Default Gateway of RHEL system?

18. Can I install a Web server in RHEL?

Answer- Of course, we can install the web server we want: Apache, nGix or other.

19. After installing Apache2, where is the default Document Root located?

Answer – By default the apache2 DocumentRoot in RHEL sets it to /var/www/html/

20. How do I know which version of Red Hat Enterprise Linux is running the server?

Answer – Run the command in a terminal to get the RHEL version running on your system.

/etc/redhat-release

I hope you like this set of Linux Interview Questions and Answers. Please follow our Facebook page and Twitter handle to get latest updates.

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HTOP is a process viewer on the terminal created for the entire Unix family but has great popularity within GNU/LINUX. The main advantages of this tool are that we can monitor processes, finalize and explore them all from the terminal which guarantees a minimum expenditure of resources.

How to Install Htop on Various Linux Systems?

We can install Htop from your sources or simply from pre-compiled packages. However, Htop is found in most GNU/LINUX distributions through its main repositories. Please have a look at the step by step process to install Htop on Debian, RHEL, Ubuntu and other Linux systems.

Install Htop on Debian 8 Jessie and Debian 9 Stretch

The first thing we need to do is login as root. Type su on your terminal window and press enter followed by typing its password.

su

Once you will be connected using su account, run below command to install Htop on Debian systems.

apt install htop

Install Htop on Ubuntu 14.04  and Ubuntu 16.04

Here, I will show you how to install Htop on Ubuntu servers. Installation of htop on Ubuntu is very much similar to installing it on Debian as we did in above section. In the case of Ubuntu, we must be root user to install htop. Type su and press enter followed by its password.

su

Once we will be connected using root user, we will proceed to install htop on Ubuntu by running below commands. A set of execution will start and execution will finish with its installation.

apt install htop

Install Htop on Fedora 26 and Fedora 27

There is little different way to install Htop on Fedora systems as we use dnf command to install it on fedora. Fedora users can easily install htop as following below steps. First we connect to root privileges using su account. Type su and its password.

su

Once we will be connected using su account, we can invoke dnf which is Fedora package manager. Run below dnf command to install htop on Fedora systems. A set of execution will start and finish with htop installation.

dnf install htop

Install Htop on Gentoo

For Gentoo we must also be root users. Write in a terminal:

su

Once we connected with root user permissions, we can install Htop by invoking Gentoo’s own package manager emerge. Run below command to start Htop installation on Gentoo system. A series of execution will start and finish with its installation.

emerge sys-process/htop

Install Htop on CentOS 7 and Red Hat Linux Enterprise

In the case of CentOS 7, we must first add the EPEL repository and then install it normally. First we logged in as root user to get installation privileges. Connect using su account by typing below command and its password.

su

Once logged in as root user, we proceed to download the package containing the EPEL repository:

wget http://mirror.pnl.gov/epel/7/x86_64/e/epel-release-7-5.noarch.rpm

And then install the downloaded package to add the EPEL repository:

rpm -Uvh epel-release-7-5.noarch.rpm

The next step is to “validate” the newly added repository by running below command.

yum repolist

And Finally we will install htop on RHEL and Centos by running below command.

yum install htop 

Basic use of HTOP

We have installed Htop on various Linux systems in above section. We must write the command htop To launch it. Here, it is not necessary to do it as root user. You can see i wrote htop on terminal window and press enter to get the Htop task manager screen in below image.

You will get below screen once you execute above command on your terminal screen.

It’s the initial screen. As we can see, it is very simple and easy to understand. We can have fun in three parts that we will study. In this “first part” we see the use of the processor and RAM by all processes along with other details. On the right side a small summary of them: how many tasks are running and the total active time.

“Second part” also you can say middle part is the main view where all the processes are showing. You can see this in below image.

This is where we have the information through columns that contain details about these processes. The columns are:

• PID: Displays the process identifier number.
• User: The user tells us that he has activated this process.
• PRI: It shows the priority with which the process is executed.
• NI: Shows the priority level
• VIRT: The number of virtual memory used by the process.
• RES: Used ram memory (Megabytes)
• SHR: Shared memory used
• S: Process status (Running, sleeping or zombie)
• CPU%: percentage of CPU used by the process
• MEM%: percentage of ram memory used by the process
• TIME+: Active life-time of the process
• Command: The command that executes the process.

So with this we have all the information of the processes that are running at that time.

The “last part” displays the tools provided by Htop for navigation. For example, allows us to search, sort the processes and the best, for me, the “kill” processes by using shortcut keys.

To kill a process we must navigate through the processes with the up and down keys, select it, press the F9 key, and choose the number that corresponds to the option of killing that serves us. I almost always use the 9th showing in below screen.

In conclusion we can say that Htop is a great tool to visualize the active and non-active processes in our Linux systems. Being terminal-based, it has the advantage of consuming virtually nothing in resources and helps us to close very heavy or unnecessary processes.

Here i have shown you how to install Htop on Red Hat, Ubuntu, Fedora and Debian systems and its uses. I hope you like this article. Please follow our Facebook page and Twitter handle to get latest updates.

Read More:

• How to Install Debian 9 Stretch?
• How to Install Zebbix on Ubuntu 16.4?
• How to Install RedHat Enterprise Linux?
• Installing Ubuntu 16.04 in Step by Step Process

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Change Putty Cursor Color or Mouse Pointer Color

You can see background color in my putty console is showing as black and cursor color is showing as green. Now I want to change the putty cursor color or mouse pointer color to red.

1- To start this, we will Right click on the top border of putty console and choose “Change Settings…”

2- You will get below settings window. Now click on Colours tab from left side pane and we need to select an option from right side pane for which we must change the color. As we have to change cursor color or mouse pointer color so we will select Cursor Colour from right side pane. Click on Modify button to select color as per your choice for your cursor or mouse pointer.

Colours->Cursor Colour->Modify

3- Once you click on modify button, you will get custom colors window to choose appropriate color for your putty cursor or mouse pointer. I have selected red color as shown in below screenshot. Click on Ok and then on Apply button to reflect this change.

4- Once you click on apply button, you will see putty cursor color will be changed to red on your putty console. You can see this in below screenshot as well. Now your Putty cursor color has been changed to the color as per your choice in this article.

I have explained step by step method to change putty text color and putty background color for your putty terminal console in attached articles. Read them if you want to change putty text or putty background color. I hope you like this article. Please follow our Facebook page and Twitter handle to get latest updates.

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Related Articles

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• How to Change Putty Cursor or Mouse Pointer Color?

Change Putty Background Color

Please follow below instructions to change background color of your putty console.

1- You can see background color in my putty console is showing as black, now I want to change it to white background. Right click on the top border of putty console and choose “Change Settings…”

2- You will get below settings window. Now click on Colours tab from left side pane and now we need to select an option for which we must change the color. As we have to change putty background color so we will select Default background from right side pane. Click on Modify button to select white color as putty background color. You can choose putty background color as per your choice.

Colours->Default background->Modify

3- Once you click on modify button, you will get custom colors window to choose appropriate color as background in putty console. I have selected white color as shown in below screenshot. Click on Ok and then on Apply button to reflect this change.

4- Once you click on apply button, you will see putty background color will be changed to white on your putty console. You can see that background color for your putty terminal console has been changed to white in below screenshot.

Change Putty Font Color

Now you can see the putty text color is showing very light and it is very difficult to read texts on above terminal console after changing the putty background color. So, your next step would be to change the putty text color or font color so that it can be visible to eyes. This step is optional and not needed if you only want to change putty background color.

I have explained step by step method to change putty text color for your putty terminal console in attached article. You just need to launch settings windows again and click on Colours tab from left side pane followed by Default Foreground option from right side pane and then click on Modify button to choose color for your text. Choose your putty text color accordingly and click on Ok button and finally click on Apply button to reflect the changes.

Now your Putty background color as well as putty text color have been changed as per your choice. I hope you like this article. Please follow our Facebook page and Twitter handle to get latest updates.

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Steps to Change PuTTY Text Color

Please follow below step by step process to change text color of your putty console.

1- You can see text color in my putty console is very light and very difficult to read. You need to put more focus in just reading the texts so I have decided to change putty text color of my console. Right click on the top border of putty console and choose “Change Settings…”

2- You will get below settings window. Click on Colours tab from left side pane and select an option from right side pane for which we must change the color. As we have to change putty text color so we will select Default foreground from right side pane. Now, click on Modify button to select colors for your text.

Colours->Default foreground->Modify

3- Once you click on modify button, you will get custom colors window to choose appropriate color for your text showing in putty console. I have selected black color as shown in below screenshot. Click on Ok and then on Apply button to reflect this change.

4- Once you click on Apply button, you will see the new text color on your putty console. You can see that putty text color has been changed to black in below screenshot.

If you are working for several customers, you can configure distinct colors for each customer so that you easily categories them. You can change the color and save them in your putty profile.

Related Articles

• Fix PuTTY Network Error: Connection Refused While Connecting to Ubuntu Server
• Fix PuTTY Connection Issue Network Error: Connection Timed Out
• How to Change Putty Cursor or Mouse Pointer Color?

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Change User Password in Linux

We will use passwd command to change our own password. Type passwd without specifying a username if you are changing your password. You will be prompted to enter your old password for verification, and then a new password. Below is the high level steps to follow password change process.

1. Open Linux terminal or connect to your server using PuTTY.
2. Type passwd and press Enter.
3. Type your current password and press Enter.
4. Now type your new password and press Enter.
5. Make sure your password is complex and not similar to older one otherwise you will get BAD PASSWORD error as shown in below screenshot.
6. Retype your new password and press Enter.
7. Now you will get notify that your password has been changed.

Change root Password

The “root” account is the most privileged account on a Linux system. When using this account, it is crucial to be very careful. Follow below steps to reset or change the password for your root account.

1. Open Linux terminal or connect to your server using PuTTY.
2. Type su at the command prompt, and press Enter.
3. Type the current root password, then press Enter.
4. Type passwd and press Enter.
5. Type a new password and press Enter.
6. Retype the new password and press Enter.
7. Your password is changed here.

Change other User’s Account Password

To change a password for a user, you need to login using “root” account. Follow below steps to change password on behalf of any user.

1. Open Linux terminal or connect to your server using PuTTY.
2. Type su at the command prompt, and press Enter.
3. Enter current root password, then press Enter.
4. Type passwd LoginName and press Enter. If login account is Manvendra. Type passwd Manvendra.
5. Enter a new password and press Enter.
6. Retype the new password and press Enter.
7. Your password is changed here.

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Related Articles:

• How to Change IP Address, Subnet Mask & Default Gateway of Linux Server
• Fix Error “User is not in sudoers file.
• Installing SQL Server 2017 on Red Hat Linux Server

There are three methods that i will explain here to rename or change hostname of any Redhat Linux server. These three methods that we will use in this article are given below.

1. Edit etc/hostname.
2. nmcli utility.
3. hostnamectl utility.

Change Hostname of RedHat Linux Server by editing etc/hostname

Connect to your Redhat Linux server and check the hostname by running below command.

#Check hostname using any command.
hostname

#You can run below command as well to check the hostname.
cat /etc/hostname

We can see the hostname of this RedHat Linux server is SQLServerRHEL.localdomain. Now we will change this name to TechyazRHEL. If you want to change hostname with fully qualified name then you can write fully qualified name in below command.

#Connect to RHEL as root.
Sudo su

#Change Hostname using /etc/hostname. Make sure to write your new hostname in double quote.
echo "TechyazRHEL" > /etc/hostname

You can see when we check hostname of this linux server using hostname command, it is still showing older name SQLServerRHEL.localdomain whereas when we check using cat /etc/hostname it is showing newly changed hostname.

To reflect new host name, we need to restart service systemd-hostnamed. Once you will restart this service, the output of hostname command will also be same as new hostname as shown in above image.

#Restart service systemd-hostnamed
service systemd-hostnamed restart
 or
systemctl restart systemd-hostnamed 

You can see new hostname after restarting above service in above screenshot. One thing you might notice that command prompt is still showing as older hostname i.e. root@SQLServerRHEL. This will disappear if you close this session and connect to new session. Let’s try this by launching new session, you can see new session is showing new hostname in below image.

Rename Hostname of RedHat Linux Server using nmcli

The nmcli (NetworkManager Command Line Interface) command-line utility is used for controlling Network Manager and reporting network status. nmcli is used to create, display, edit, delete, activate, and deactivate network connections, as well as control and display network device status. Here, we will use nmcli utility to change the hostname of redhat linux server.

Connect to your RedHat Linux server for which you want to change hostname. Run below commands to change hostname of your linux server.

#Connect to RedHat Linux server using root access.
sudo su

#Check existing hostname of RHEL server
hostname

#Change hostname of Redhat Linux server to techyazRHEL-nmCLI. 
#Change your new hostname in place of techyazRHEL-nmCLI.
nmcli general hostname techyazRHEL-nmCLI

#You can also check the hostname of Redhat linux server using nmcli utility.
nmcli general hostname

You can see hostname of RHEL server has been changed to techyazRHEL-nmCLI in above screenshot. Your PuTTY terminal will display new hostname once you open new session.

If new hostname is not showing after running above command then you should restart service systemd-hostnamed to reflect changes as we did in first section. You can see new hostname while launching new session in below screenshot.

Rename Hostname of RedHat Linux Server using hostnamectl

The hostnamectl tool is provided for administering the host names in use on a given system. First we will check the existing hostname of this server by running hostname command. We can also check the hostname using hostnamectl utility.

Connect to your Redhat Linux server using root and check the existing hostname.

#Connect to Linux server using root.
sudo su

#Check existing hostname.
hostname
or 
hostnamectl status

#Change hostname to techyazRHEL.
hostnamectl set-name techyazRHEL

You can check the hostname post renaming it. You can see new hostname in above image. Putty terminal will display new hostname once you open new session as shown in below image.

We can set all three kind of hostnames (Static, Pretty and Transient) using hostnamectl utility. Static name is mandatory whereas remaining two is optional. If you will not pass any hostname type in above command, same name will be set for all three hostnames. I haven’t used any hostname option in above command so all hostname options will have same name. Let’s check this in below image.

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Read More on SQL Server Installation on RHEL

• How to install SQL Server 2017 on RedHat Linux
• How to Install SQL Server on Redhat Linux without Internet – Offline Installation
• Install SQL Tools on RedHat Linux using Internet
• Install SQL Server Agent on RHEL
• Installing SQL tools on RHEL without Internet – Offline Installation

Uninstall SQL Tools on RHEL

As we know sqlcmd and bcp utilities are part of SQL tools so if you want to uninstall these utilities from red hat linux machine you need to uninstall SQL tools package mssql-tools. Follow below steps to uninstall sqlcmd utility from your redhat linux machine.

1- Connect to your RHEL server where SQL tools has been installed and running. Check whether SQL tools are installed on this machine or not by checking sqlcmd or bcp utilities. You can see RedHat Linux is recognizing sqlcmd utility that means SQL tools have been installed on this machine that needs to be uninstalled.

2- We can see sqlcmd utility in above screenshot. Now, we will uninstall SQL tools by running below command.

#Uninstall SQL tools from RHEL
sudo yum remove mssql-tools

You can see the details of SQL tools package that is going to be removed from this machine. We can see mssql-tools package is going to be removed here. Above command will ask us to type y to proceed with the uninstallation of this package mssql-tools and type N to quit this removal.

I entered y to uninstall SQL tools from this machine. This will uninstall both utilities sqlcmd and bcp. You can see SQL tools package mssql-tools has been removed from this machine post entering y in above screenshot.

3- Now, we can check sqlcmd or bcp utility again to validate this uninstallation. I typed sqlcmd as i did in first screenshot and pressed enter. Now we can see red hat linux is not recognizing sqlcmd utility, that means SQL tools have been removed from this machine.

#check sqlcmd utility post SQL tools uninstallation
sqlcmd

Here i have shown step by step process to uninstall SQL Tools sqlcmd and bcp from linux machine.

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Read More on SQL Server Installation on Linux Servers

• Installing SQL Server 2017 on Ubuntu Server
• How to Install SQL Server on Redhat Linux without Internet – Offline Installation
• How to Install SQL Server on Ubuntu without Internet access – Offline Installation
• Installing SQL Tools on RedHat Linux Server

Uninstall SQL Server 2017 on RHEL

Uninstalling SQL Server 2017 that is running on Linux server is totally different process as compared to its windows based SQL Server. Follow below step by step process to uninstall SQL Server 2017 from your RHEL Linux server.

1- Connect to your RHEL server where SQL Server 2017 is running and that needs to be uninstalled from the server. Check whether SQL Server is installed on this machine or not by checking SQL Server service. You can see SQL Server is running on this server.

#Run below command to check SQL Server Service.
systemctl status mssql-server

2- Check SQL Server files along with the database files before removing SQL Server. We will validate SQL Server removal by checking these files post uninstallation.

#Check SQL Server binaries & database files
sudo ls -lrt /var/opt/mssql
sudo ls -lrt /var/opt/mssql/data

Note: Make sure to run full backup of all your databases and keep them in a safer place for future needs.

3- Now, we will uninstall SQL Server by running below command.

#Remove SQL Server from your Linux machine
sudo yum remove mssql-server

You can see details of SQL Server packages that are going to be removed from this machine. These packages are SQL Server and SQL Server Agent that are going to be removed here. Above command will ask us to type y to proceed with the uninstallation and type N to quit this uninstallation. Type y to proceed with the SQL Server removal.

You can see SQL Server and SQL Server Agent both packages have been removed from this machine.

4- Now, remove all SQL Server binaries and database files from its installed location that we checked in second screenshot by running below command.

#Remove database files and SQL binaries.
sudo rm -rf /var/opt/mssql

Here, your SQL Server has been removed from this linux machine. You can check SQL Server binaries and database files by running below commands. We can see no files in these locations because they have been removed now.

#Check database files.
sudo ls -lrt /var/opt/mssql/data

#Check SQL Server files & folders.
sudo ls -lrt /var/opt/mssql

5- Now you can check SQL Server service again by executing below command.

#Check SQL Server Service post SQL Server Removal.
systemctl status mssql-server 

We can see SQL Server is not loaded this time but service is showing as active.

When you will try to restart this service, it will throw you an error that unit not found as shown in below image.

6- Now we need to reboot the server to update SQL Server service status on RHEL. I restarted this linux machine and again checked the SQL Server service. You can see this time it says service could not found.

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Missing Features in SQL Server on Linux

Below is the list of features that are not supported on Linux based SQL Server instances as of now in current GA release of SQL Server 2017.

1. Analysis Services
2. Reporting Services
3. R Services
4. Master Data Services
5. Data Quality Services
6. SQL Server Browser Service
7. Transactional & Merge Replication
8. FILESTREAM
9. FileTables
10. Stretch DB
11. Polybase
12. Third Party Extensions
13. XPs
14. VSS Snapshots
15. Buffer Pool Extension
16. Change Data Capture
17. Alerts
18. Distributed query with 3rd-party connections
19. Database Mirroring
20. AD Authentication for Linked Servers & Availability Groups (AGs)
21. SQL Server Integration Services (SSIS)

The mssql-server-is package (SSIS) is not supported on SUSE Linux in this release. It is currently supported on Ubuntu and on Red Hat Enterprise Linux (RHEL) only.

The following features are not supported in this release when you run SSIS packages on Linux:

o SSIS Catalog database
o Scheduled package execution by SQL Agent
o Windows Authentication
o Third-party components
o Change Data Capture (CDC)
o SSIS Scale Out
o Azure Feature Pack for SSIS
o Hadoop and HDFS support
o Microsoft Connector for SAP BW

For a list of built-in SSIS components that are not currently supported, or that are supported with limitations, see Limitations and known issues for SSIS on Linux

Related Articles:

• Install SQL Server on Ubuntu Server
• How to Install SQL Server on RHEL
• New features Introduced in SQL Server 2017
• Install SQL Server on Ubuntu without Internet Access

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Check IP Address, Subnet Mask & Default Gateway

Launch PuTTY and connect to Linux server. Run ifconfig command.

#Check IP address and Gateway Mask
ifconfig

You will see output of this command like below screenshot.

Focus on the area which is highlighted in red colour. The IP address of this Linux server is 192.168.0.1 which is labeled as inet. You can see the subnet mask of this server which is showing 255.255.255.0 as netmask. We can also see the connection interface name of this machine that is ens33. The connection interface name will be used later in next section during changing IP addresses, subnet mask and gateway details.

Now we knew how to check the IP Address & Subnet Mask of your Linux computer. Now next step is to check the default gateway of this server. Run below command route -n to get the details of default gateway.

#Check Default Gateway
route -n

We can see the gateway IP is given in below screenshot for the same connection interface name ens33.

Change IP Address, Subnet Mask & Default Gateway

We knew how to get the IP address, subnet mask and gateway details of Linux server. Now i will explain how to change these addresses if needed. We will use same command ifconfig to change the IP address and subnet mask. Before proceeding, make sure you have interface name and new IPs. You can get interface name from ipconfig command. The connection interface name of my machine is ens33 as shown in above screenshots. Run below command to change these two values.

#Replace ens33 to your connection interface name. You can get it from ifconfig command.
sudo ifconfig ens33 192.168.209.10 netmask 255.255.255.0

We can see command executed successfully. You can validate the new IP address by running ifconfig command again. I have not changed netmask and kept same. If you want to change it please pass your netmask address.

Now we can see we have changed the IP address and netmask address for this Linux server. Next we can check the gateway address to validate what will be the impact on gateway post changing the IP address and netmask address. Run route -n again to get the details.

We can see gateway address is not set yet and the one showing on first section is not showing now. So let’s change the gateway address for this server. Run below command to change the gateway address.

#change the name of gateway address. Change the connection interface name from ens33 to your name.
sudo route add default gw 192.168.209.250 ens33

Once command will be executed successfully, you can validate this change by running route -n command again.

We can see the new gateway address in above screen. These are the commands that can be used to check and change the IP address, netmask address and gateway address.

Related Articles

• How to Change Hostname of RedHat Linux Server?
• Reset or Change Linux Passwords for users and root?
• How to Change PuTTY Background Color to White?

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Before going ahead, we need to have a RedHat Linux server. If you have no idea about installing Linux server or creating a virtual machine where you can install Linux and SQL Server then i would recommend you to read below articles first.

• How to Create a Virtual Machine.
• Install RedHat Linux 7.3 on a virtual machine.
• How to Install SQL Server on RedHat Linux 7.3

If you have installed SQL Server on Red Hat Linux server, your next step should be to install SQL Server Agent on that server. Make sure you have internet access on the Linux server where we are going to install SQL Server Agent. If your server does not have internet connection then you should read attached article about installing SQL Server Agent on RedHat Linux that are running without Internet.

Install SQL Server Agent on RHEL

As this Linux machine has internet connection so let’s go ahead with Installation on Red Hat Linux server. Installation process is quite similar to the installation of SQL Server on Redhat Linux.

You don’t need to download SQL Server Agent package separately the way we did for SQL Server and SQL Tools installations.The package required to install SQL Server Agent included into SQL Server package repository configuration file.

If you have already downloaded SQL Server package repository configuration file to install SQL Server, you can skip this step and go ahead to install Agent on your server. If you don’t have SQL Server package repository configuration file or you have deleted it then you can run below command to download the package repository configuration file.

#Download Microsoft SQL Server Red Hat repository configuration file
sudo curl -o /etc/yum.repos.d/mssql-server.repo https://packages.microsoft.com/config/rhel/7/mssql-server.repo

This will download Microsoft SQL Server Package Repository Configuration File that are required to install SQL Server and SQL Server Agent.

As we have the Agent repository configuration file now, Let us first check the SQL Server in SSMS to see how SQL Server Agent working.  You can see we are not able to do anything in SQL Server Agent folder.

Now our next step is to install SQL Server Agent to enable its related features. Run below command to start the installation.

#Install SQL Server Agent
sudo yum install mssql-server-agent

You cans see series of executions started to proceed with the installation in below image. It will also ask you to enter Y to proceed.

Enter Y to proceed with the installation, once you press enter it will proceed to install. Now SQL Server Agent will install on your machine.

It will also suggest you to restart SQL Server service. If you will not restart SQL Server service, installation will not be completed so next step is to restart SQL Server service on this server.

#Restart SQL Server Service
systemctl restart mssql-server

You can see SQL Server is online now. Go ahead and connect to SQL Server in SSMS as per below image.

Now you can create Agent jobs to automate database activities on your SQL Server instance.
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