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Linux command in DevOps - GeeksforGeeks

DevOps engineers use Linux every day because it’s free, fast, and easy to customize. More importantly, most DevOps tools like Docker, Kubernetes, Ansible, Terraform, and Jenkins are built to run best on Linux.

In DevOps, you often work on cloud servers (like AWS, Azure, or Google Cloud), and most of them run Linux by default. To manage these servers, engineers use Linux commands to move files, check logs, install software, run scripts, and fix problems. That’s why if you want to start a career in DevOps, learning Linux is one of the first and most important steps. It helps you work faster, solve problems easily, and use the tools that DevOps teams rely on every day.

In this article, we will first learn what Linux is, then understand its file system, and after that, we’ll go through some basic and important Linux commands that are useful in DevOps.

In Linux, everything is represented as a file, including a hardware program. The files are stored in a directory, and every directory contains a file with a tree structure. That is called the file system hierarchy. Linux uses a single-rooted, inverted tree-like structure. The root directory is represented with / (forward slash). It is a top-level directory in Linux.

In this section, we are going to discuss the basic commands of Linux:

The 'pwd' command helps you identify your current location in the file system :

   `pwd` - Print Working Directory     

The 'ls' command is used to list the files and directories in the current directory :

  `ls` - List Files and Directories

ls <Path Name>

` any define path` is define after `ls` command, it will display all contain of that location.

ls -l

` -l ` flag is used to display the lists all contents with some extra information like permission of the file or folder , time stamp.

ls - a

` -a ` flag is used to see the hidden files and folder.

The 'uname' command retrieves system information:

   uname - Print System Information

Note : By adding `-r ` flag to the `uname` command , you can display the kernel release version.

uname -r   Print Kernel Release Information

The 'cd' command allows you to navigate the file system by changing your current directory.

cd  -  Change Directory

The 'clear' command clears the terminal screen, providing a clean workspace.

  clear - Clear the Terminal Screen

'whoami' returns the username of the current user logged into the terminal.

 whoami - It returns the username of the current user logged into the terminal

'History' This command is used to display the history of the command that previously executed. history

history

'free' This command is used to check the memory-related detail in your system.

 free

'nslookup' is used to obtain information for DNS server. It stands for Name Server Lookup.

nslookup <domain name>

'ssh-keygen' is used to establish a secure SSH connection from your host machine to any remote server. It generates a public/private key pair.

ssh-keygen -t rsa

'curl' is a tool which is used to fetch data and post the data over the internet. it can used various of protocol like HTTPS , SMTP and FTP.

curl [options] [URL]

'curl -o' flag saves the data into a file on the local machine.

`curl -o` [file_name] [URL...]

apt-get command used to manage packages in the linux. APT stand for the Advanced Packaging Tool , and its main used of install , update , upgrade and remove the packages.

apt-get [options] command

'du' command is used to check disk usage space.

du

'df' command is used to check the available disk space in system.

df -h

ifconfig command is used to view the information about your network interface

ifconfig [OPTIONS] [INTERFACE]

ip command is a modern replacement of ifconfig command. It is used to view and manage network settings. You can check Ip addresses, configure network interfaces, view routing tables by this command.

ip [OPTIONS] OBJECT {COMMAND | help}

In DevOps, creating and managing files and directories is a common task. Here are some essential commands :

1 . For creating a single directory:

 mkdir GFG                                   

2. For creating multiple directories:

 mkdir GFG1 GFG2 GFG3                                                 

3. For creating directory paths (directories inside directories):

mkdir -p   /GFG/GFG1/GFG2

4. For creating a series of numbered directories:

 mkdir gfg{1..3}             

We can create file in linux by using various commands like vi, touch, echo, nano etc. The following table will explain the use case of each command:

The cp command is used for copying and pasting files or directories in Linux. Here are some commonly used options and examples:

1 . For copying a file with verbosity and force (overwrite if necessary):

cp -rvf  gfg1   gfg

To delete files or directories in DevOps, you can use the rm command. Be cautious, as it permanently removes data. Here's an example:

For removing a directory and its contents:

rm -rvf  gfg

The mv command is used to rename files or directories. For example, to rename a directory from "gfg" to "gfg-devops," you can use:

mv gfg  gfg-devops      

User management in Linux is a crucial aspect of DevOps and system administration. Managing users and their permissions ensures that your systems are secure, organized, and meet the needs of your organization. Here's an overview of user management in Linux within a DevOps context:

To create a new user in Linux, you can use the useradd command. For example:

sudo useradd  [usernam]

After creating a user, set a password using the passwd command:

 sudo passwd [username]

To delete a user, use the userdel command :

sudo userdel  [username]

The su command allows you to switch to another user's account by providing the username as an argument. To exit from the user's account and return to your original session, you can simply type 'exit'.

su  [USER NAME]

To change the username from the current name (oldname) to the new name (newname), use the following command.

sudo usermod -l [newname] [oldname]

A group is a collection of user accounts that is very use full to administrators for managing and applying permission to a number users.

sudo groupadd <groupname>

Making a new group

sudo groupdel <groupname>

delete the group

sudo usermod -g <groupname> <username>

Adding a user to a group

A process management is the process of controlling and monitoring the process running on a Linux system.

ps command displays currently running processes.

ps aux

The top command is used for memory monitoring. It shows a real-time view of system processes.

top

The kill command is used to terminate a process using it's PID.

kill 1234

The pidof command is used to gets the PID of a running process by name.

pidof bash

The systemctl command is user to start/stop/restart systemd-managed services (like Docker, Nginx etc.)

sudo systemctl status nginx

In linux , to increase the security of the file and directory. we need to used permission. There are total three type of file permission are Read , Write , Execute.

There are three type of file permission are as follow:

• user ( u ) : Permissions used for the user of the file.
• group( g ) : Permission used by the group member.
• other (o) : Permission used by all other users.

For example, suppose a file has read permissions that are allowed for the user. In this case, the user can only read that file, while the group and others will not be able to read it.

It is used to check the permission of directory

 ls -ld

Permission

Access for a file

Access for a directory

Read (r)

display file contents and copy the file

view contents of directory

Write (w)

modify the file contents

modify the contents of a directory

Execute (x)

execute the file if it an executable permission

allow use of cd command to access the directory

Number

Permission Type

Symbol

0

No permission

---

1

Execute

--x

2

Write

-w-

3

Execute +Write

-wx

4

Read

r--

5

Read + Execute

r-x

6

Read +Write

rw-

7

Read + Write + Execute

rwx

This command is used to change the permission of file and directory.

chmod <permission of user , group , other> {filename }

It is used to change the owner of the file and directory.

chown [owner_name] [file name]

It is used to read and concatenate the text inside the files. with help of this command we can displays the content inside the file.

cat <flag> {filename}

cat -b

This flag adds number to the text line.

cat -E

This flag add $ at the end of each line.

It filter searches a file for a particular pattern of characters , and displays all lines that contain the pattern.

grep <flag or search_word> {file name}

grep -i

Delivers results for case-insensitive strings.

grep -n

Retrieve the corresponding strings and their respective line numbers.

grep -v

Provides the output of lines that do not contain the search string.

It print the output of a file, either alphabetically, numerically or by other specified way.

sort filename

The head command is used to display the first few lines of one or more text files.

head -n 2 gfg

The tail command is used to display the last few lines of one or more text files.

tail -n 3 gfg

The find command is used to search files and directories based on different criteria such as name, size, type and modification date.

find [path] [expression]

The stat command is used to display detailed permission and ownership metadata.

stat data.txt

In conclusion, this article has emphasized the vital role of Linux fundamentals in the toolkit of a DevOps professional. By providing insights into essential Linux commands and concepts, it equips individuals in the field to efficiently navigate file systems, manage users and groups, implement file permissions, and perform a variety of tasks critical for the success of DevOps operations, ultimately contributing to the security and functionality of their systems.

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