Introduction to Linux Shell and basic commands:

Kernel:

• The kernel is a computer program that is the core of a computer’s operating system, with complete control over everything in the system.
• Think of it as as Chef working in a hotel. You as a coustmer can’t see the chef working but get your order (output).

Shell:

• Shell is a special user program that provides an interface for the user to use operating system services.
• Using the same scenario, think of shell as a waiter, who takes your order (input) and gives it to the chef (Kernel).

Shell is divided into two categories-

1. Command Line Shell:

   

2. Graphical shell:

   

Types of shell:

• BASH (Bourne Again SHell)
• CSH (C SHell)
• KSH (Korn SHell)

### File system structure:

NAME	DESCRIPTION
/	The slash / character denotes the root of the filesystem tree. exp: Trunk of a tree.
/home	Contains personal directories of user.
/lib	Contains system libraries and critical file.
/bin	Contains user executable files.
/boot	Contains all the files that are required for booting.
/dev	Contains hardware and development files.
/media	Mount points for removable media.
/mnt	Temporarily mounted filesystems.
/opt	Contains optional files.

Commands:

• date: Returns current date.
• whoami: Returns the current domain and user name.
• ls (list): Returns content of a specified Directory
• cd: Changes directory.

• mkdir: Creates a new directory.
• pwd: Prints the current working directory.

• touch: Creates empty file.
• cat: Creates file with content.

• whereis: Finds the location of specified file.

• mv: To move or rename a file.

  

• cp: To copy content of a file to the other.

  

• whatis: Gives short description of a command.

Issues faced:

Running whatis command always returns “nothing appropriate”

Solution found:

whatis uses an index created and maintained by mandb to locate the documentation you’re looking for. If said index doesn’t exist, or if the command you’re looking for isn’t in the existing index, you’ll see Nothing appropriate. If your setup doesn’t have a mandb index yet, you can create one by running sudo mandb