Interaction with Linux: Shells

Interaction with Linux: Shells

Shell is the interface software between the user and the operating system kernel. The user passes all commands to the operating system via the shell.

The shell program is intended to receive the user's commands and pass them to the operating system. An interface program controlled by the mouse can be used as the shell program. The essential mission is to allow the user to express his wishes. 

Under UNIX, there are many different shell programs for general and special purposes. Bash, ksh, and csh are among the more common general-purpose shell programs. The main difference between these programs is their syntax. In this sense, it can be argued that the shell programs allowed communication with different languages. 

Each user may be using a different shell program. User shells are defined in the /etc/passwd file. 

The most commonly used shell program under Linux is Bash (Bourne Again Shell). This shell, which is preferred due to its advanced features and ease of use, will be examined in more detail as a separate article.

Login and Logout to the System

A computer system running a UNIX operating system can be accessed via the computer's keyboard and screen, or if the computer system provides telnet and/or ssh services, it can also be accessed over the network.

When logged into the system, the shell program satisfies the user and prompts the user to issue commands. The commands issued by the user are executed via the shell.

There is no difference between local access and remote access to a UNIX system. All operations, which can be done in local access and does not require physical action (pressing the power button to open a closing system, etc) can be done remotely.

Users have to inform the system that they are finished using the system. Otherwise the connections will remain open. Exit or logout commands are used at the exit from the system.

New versions of many Linux distributions, if installed with graphical interface support, can meet the user with a graphical user interface rather than text mode.

System Access and Virtual Consoles

On UNIX systems, the system-connected keyboard and display are called "consoles". Each UNIX system has only one console.

Under Linux, "virtual consoles" have been defined to make it easier for users to work through the console. Virtual consoles offer the infrastructure to allow parallel operation even across multiple screens, even when using the same keyboard and screen. For example six Red Hat Linux virtual consoles come pre-defined.

In Linux, Alt + FX key combination can be used to switch between virtual consoles. In this context, Alt + F1 allows the first virtual console, Alt + F3 to pass the third virtual console.

On a Linux system predefined by xwindows, the CTRL + ALT + FX key combination is used to access the console. In this context, CTRL + ALT + F1 allows the first virtual console, CTRL + ALT + F3 to switch to the third virtual console.

Use the Alt + F7 key combination to return to xwindows while in the virtual console.   

To read my previous article: File Hierarchy and Home Directory