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Components of UNIX

Important Components:

  • a. Shell
  • b. Kernel

a. Shell:

It is the outer layer of the UNIX operating system.
Shell reads commands, whether they are valid or not.
Shell checks if the command is used properly.
If everything is correct, the shell interprets the command into a kernel-understandable form and hands it over to the kernel.
Shell acts as an interface between the user and the kernel.

b. Kernel:

It is the core component of the UNIX operating system.
It is responsible for executing commands with the help of hardware components.
Memory allocation and process allocation are managed by the kernel.
It acts as an interface between the shell and hardware components.

Shell Script Example:

To perform a big task, multiple commands may be required.
Create a new shell script file using the command:

gedit test.sh

Make the shell script executable with the command:

chmod u+x test.sh

Execute the shell script using the command:

./test.sh

Types of Users in a Linux System:

  • Normal user: $ prompt
  • Super user/Root user/Admin user: # prompt

Example session:

akshay@Ubuntu:~/Documents/DurgaSoft_Linux$ whoami
akshay
akshay@Ubuntu:~/Documents/DurgaSoft_Linux$ sudo -i
root@Ubuntu:~# whoami
root
root@Ubuntu:~# exit
logout
akshay@Ubuntu:~/Documents/DurgaSoft_Linux$
  • sudo -i: Switch to superuser
  • exit: Return to the normal user

Online UNIX Terminal:

http://masswerk.at/jsuix

Most Commonly Used Linux Commands:

  • pwd : Print working directory
  • ls : List all files and directories
  • mkdir : Create a directory
  • cd : Change directory
  • touch : Create an empty file
  • rmdir : Remove the directory
  • rm : Remove a file
  • date : Display current date and time
  • help : Display available commands
  • exit : Log out of the session
  • clear : Clear the terminal
  • hello : Display brief system information

/ : Root directory in Linux

  • User home directory for Durga: /home/durga
  • User home directory for Akshay: /home/akshay

More Commands in Linux:

  • alias : Sets an alias for a (complex) command
  • apropos : Displays a short description of a command
  • browse : Opens a web page in a new browser window
  • cal : Displays a monthly calendar
  • cat : Concatenates and outputs files
  • chmod : Changes a file's permissions
  • cp : Copies files from source to target
  • echo : Writes all arguments back to the terminal
  • man : Displays manual pages for a command
  • mv : Moves (renames) files from source to target
  • ps : Displays current processes
  • uname : Displays the system identification
  • vi : Visual editor (simpler version of standard UNIX vi)
  • which : Evaluates which command will be executed
  • web : Opens a web page in a new browser window

For more commands, try http://masswerk.at/jsuix.