1. pwd (Print Working Directory): This command shows you the current directory you are in. It's like asking, "Where am I?" For example, if you're in the "Documents" folder, running pwd will display "/home/user/Documents" to let you know that you're currently in that directory.

   

2. clear: This command clears the terminal screen, giving you a fresh, clean slate. It's like tidying up your workspace by removing all the clutter and starting anew. Just type clear, and all previous output will be cleared from the screen.

3. exit: When you're done working in the terminal, this command lets you gracefully exit or close the terminal session. It's like saying, "I'm finished here, goodbye!" Simply typing exit will close the terminal window or end the session.

4. logout: Similar to the exit command, logout is used to log out of a user session. It's like signing out of your account before leaving a computer. Typing logout will end your current session and return you to the login screen.

5. history: This command shows you a list of the commands you've previously executed in the terminal. It's like viewing a timeline of your past actions. Running history will display a numbered list of your command history, making it easier to recall or reuse commands you've used before.

   

6. history -d <number>: With this command, you can delete a specific command from your command history. For example, if you want to remove command number 7 from your history, you would run history -d 7. It's like selectively erasing a single entry from your command log.

   

7. history -c: This command clears your entire command history. It's like wiping the slate clean and starting fresh. Typing history -c will delete all the entries in your command history, providing a blank history for future commands.

   

System Commands

1. uname -r: This command displays the kernel release version of the operating system. For example, running uname -r might show "4.18.0-305.el8.x86_64" on Red Hat.

   

2. cat: The cat command is short for "concatenate" and is used to display the contents of a file. For instance, running cat file.txt would display the contents of "file.txt" in the terminal.

   

3. uname -s: This command shows the operating system name. For example, running uname -s might display "Linux" on a Red Hat system.

4. uname -n: Running uname -n displays the system's network node hostname. It provides the name of the machine in a network.

5. uname -p: This command displays the processor type or architecture of the machine. For example, it might show "x86_64" on a 64-bit Intel or AMD processor.

6. uname -m: Running uname -m provides information about the machine's hardware architecture. It might display "x86_64" for a 64-bit system.

7. uname -o: This command shows the operating system's vendor or origin. For example, it might display "GNU/Linux" on a Red Hat system.

   

8. cat /proc/cpuinfo: Running this command displays detailed information about the CPU(s) in the system, such as the model, speed, and cache size.

   

9. lscpu: The lscpu command provides comprehensive information about the CPU(s) in a more structured format. It displays details like architecture, cores, threads, and cache sizes.

   

10. lsusb: Running lsusb lists the USB devices connected to the system, providing information about the manufacturer, model, and version of each device. [This you can try on your VM Machines]

11. cat /proc/meminfo: This command displays information about the system's memory usage, including total memory, available memory, and usage statistics.

    

12. free: The free command provides an overview of the system's memory usage and availability, displaying values such as total, used, and free memory.

13. free -m: Running free -m displays the memory usage in megabytes, providing a more human-readable format.

14. free -g: This command shows the memory usage in gigabytes when you run free -g.

15. free -h: Running free -h displays the memory usage in a human-readable format with units like GB, MB, and KB.

    

16. lspci: The lspci command lists the PCI (Peripheral Component Interconnect) devices connected to the system, showing details about the hardware components.

    

17. dmidecode: Running dmidecode displays detailed information about the system's hardware, including BIOS, motherboard, memory, and more.

18. hostname: This command displays the current hostname of the system.

19. hostnamectl: Running hostnamectl provides detailed information about the system's hostname configuration and settings.

    

20. ifconfig: The ifconfig command shows the network interface configuration, including IP addresses, MAC addresses, and other network-related information. Note that this command is being replaced by ip command in newer systems.

    

21. ip addr or ip a s: Running ip addr or ip a s displays detailed information about the network interfaces and their configurations.

    

22. ip a: This command shows the IP addresses assigned to the network interfaces.

    

23. nmcli: The nmcli command is used for network management, allowing you to control and configure network connections, devices, and settings.

24. ping: Running ping followed by an IP address or domain name sends ICMP echo requests to check network connectivity and measure response times.

    

25. du: The du command shows disk usage, displaying the size of files and directories.

26. du -s: Running du -s provides a summary of the disk usage, displaying the total size of a directory.

27. du -h: This command displays disk usage in a human-readable format, using units like GB, MB, and KB.

28. du -sh: Running du -sh shows the summarized disk usage in a human-readable format.

29. lsblk: The lsblk command lists block devices, such as hard drives and partitions, providing information like sizes and mount points.

30. df -h: Running df -h displays disk usage information for file systems in a human-readable format, showing sizes, used space, and available space.

31. df -hT: This command provides a detailed overview of disk usage, including file system types, sizes, used space, available space, and mount points.

    

32. reboot: The reboot command is used to restart the system. It initiates a graceful system restart.

33. init 6: Running init 6 also restarts the system, similar to the reboot command.

34. shutdown: This command initiates a system shutdown, allowing you to safely turn off the computer.

35. init 0: Running init 0 is another way to shut down the system, similar to the shutdown command.

36. shutdown -r: This command shuts down the system and immediately restarts it.

Help Commands

1. man: The man command is used to access the manual pages for various commands and topics. It provides detailed documentation and instructions on how to use specific commands. For example, running man ls will display the manual page for the "ls" command, showing information about its usage, options, and examples.

   

2. help: The help command is a built-in command in many shell environments, such as Bash. It provides a concise overview of the available built-in commands and their usage. Running help without any arguments will display a list of built-in commands, and running help <command> will show information about the specific command.

   

3. which: The which command is used to find the location of an executable file in your system's PATH. For instance, running which ls will display the path to the "ls" command, indicating its location in the system.

4. whereis: The whereis command is used to locate the binary, source, and manual page files for a specific command or program. Running whereis ls will display the paths to the binary, source, and manual page files associated with the "ls" command.

   

5. info: The info command is used to access the documentation in the GNU Info format. It provides comprehensive and structured information about various topics, including commands, utilities, and system configurations. Running info <topic> will display the relevant information in the Info format. For example, info ls will provide detailed documentation on the "ls" command and its options.

   

File Creation

1. touch: The touch command is used to create new files or update the timestamp of existing files. If the file specified doesn't exist, it will be created. For example, running touch file.txt will create a new file called "file.txt" in the current directory or update its timestamp if it already exists.

2. touch -d <date>: With the -d option, you can specify a specific date and time to assign to a file's timestamp. For instance, running touch -d "2022-01-01 12:00:00" file.txt will set the timestamp of "file.txt" to January 1, 2022, at 12:00 PM.

3. touch -a: The -a option updates only the access timestamp of a file, leaving the modification timestamp unchanged. It's useful when you want to indicate that a file was accessed or read without modifying its content. For example, running touch -a file.txt will update the access timestamp of "file.txt".

4. touch -m: The -m option updates only the modification timestamp of a file, leaving the access timestamp unchanged. It's useful when you want to indicate that a file was modified without changing its access status. For example, running touch -m file.txt will update the modification timestamp of "file.txt".

5. touch -r <reference_file>: With the -r option, you can set the timestamp of a file to match that of a reference file. For example, running touch -r reference.txt file.txt will set the timestamps of "file.txt" to match those of "reference.txt".

6. ls: The ls command is used to list the files and directories in a directory. Running ls without any arguments will display the contents of the current directory. For example, running ls will show a list of files and directories in the current directory, including their names and some additional information like permissions and timestamps.

   

The touch command is primarily used for managing file timestamps, while ls is useful for viewing the contents of directories.