Linux Shell

The shell can be defined as a command interpreter within an operating system like Linux/GNU or Unix. It is a program that runs other programs. The shell facilitates every user of the computer as an interface to the Unix/GNU Linux system. Hence, the user can execute different tools/utilities or commands with a few input data.

Introduction

A bash script is a file containing a sequence of commands that are executed by the bash program line by line. It allows you to perform a series of actions, such as navigating to a specific directory, creating a folder, and launching a process using the command line.

Types of Shell

• Bourne shell (sh)

• Korn shell (ksh)

• Bourne Again shell (bash)

• POSIX shell (sh)

We majorly use BASH scripting

Why do we need shell scripting?

• Shell is a program that acts like a mediator between the kernel and the user.

• Shell scripting is used to automate repetitive tasks. For example- restarting servers or applying patch on to any servers.

• Shell scripts are also used to monitor systems regularly.

• Shell scripts are used to get routine backups by admins.

Users in Linux

Super User:

• This account is also known as the root account. It has previlege to do all the tasks that a root user can perform. We use sudo to switch to root user account or super user account.

  

Normal User:

The general users of the system are assigned in this account.

How to Create a New User in Linux

useradd Command

The general syntax for the useradd command is as follows:

useradd [OPTIONS] USERNAME

Only root or users with sudo privileges can use the useradd command to create new user accounts.

When invoked, useradd creates a new user account according to the options specified on the command line and the default values set in the /etc/default/useradd file.

When executed without any option, useradd creates a new user account using the default settings specified in the /etc/default/useradd file.

System User:

This is the type of account that is created only for a specific purpose or software.

Major Commands used in Linux

1. sudo-With sudo command you can perform tasks with root or administrative previleges

2. cd - Linux command to change directory or navigate through directories

   

3. ls - The most frequently used command in Linux to list directories(ls -lrt used to get long listing of output)

   

4. pwd - To get present working directory using this command

   

5. useradd and usermod - Add new user or change existing users data

   

   

6. mkdir - Command used to create directories in Linux

   

7. mv - Move or rename files in Linux

   

8. cp - Similar usage as mv but for copying files in Linux

   

9. rm - Delete files or directories

   

10. touch - Create blank/empty files

    

11. ln - Create symbolic links (shortcuts) to other files

12. cat - Display file contents on the terminal

    

13. clear - Clear the terminal display

    

14. echo - Print any text that follows the command

    

15. less - Linux command to display paged outputs in the terminal

    

16. man - Access manual pages for all Linux commands

    

    

17. uname - Linux command to get basic information about the OS

    

18. whoami - Get the active username

    

19. tar - Command to extract and compress files in Linux

20. grep - Search for a string within an output

    

21. head - Return the specified number of lines from the top

    

    

22. tail - Return the specified number of lines from the bottom

    

23. diff - Find the difference between two files

    

24. cmp - Allows you to check if two files are identical

    

25. zip - Zip files in Linux

26. unzip - Unzip files in Linux

27. sort - Linux command to sort the content of a file

28. telnet - command to connect to a port on a remote server to verify if the path from our computer to that server is open over that port.

29. passwd - Create or update passwords for existing users

30. ssh - Secure Shell command in Linux

31. service - Linux command to start and stop services

    

32. ps - Display active processes

    

33. kill and killall - Kill active processes by process ID or name

34. df - Display disk filesystem information

    

35. mount - Mount file systems in Linux

    

36. chmod - Command to change file permissions

    

37. chown - Command for granting ownership of files or folders

    

38. ifconfig - Display network interfaces and IP addresses

    

39. traceroute - Trace all the network hops to reach the destination

40. wget - Direct download files from the internet

    

41. ufw - Firewall command

    

42. find-The find command in UNIX is a command line utility for walking a file hierarchy.

    

43. apt, pacman, yum, rpm - Package managers in linux

44. vi -its an editor to add/edit content of a file or script

    

45. cal - View a command-line calendar

    

46. top - View active processes live with their system usage

1. 1. ping -Unix admin command utility used to test the network reachability

2. 48. alias - Create custom shortcuts for your regularly used commands

   

   1. whereis - Locate the binary, source, and manual pages for a command

1. whatis - Find what a command is used for

Conclusion:

I hope this article has given you brief overview about basic commands used in linux. Stay connected for more articles. Happy Learning !!