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Virtual console
 
 
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In computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
, some operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
s such as UnixWare
UnixWare

UnixWare is a Unix operating system maintained by The SCO Group . Unixware is typically deployed as a Server rather than Desktop computer. Binary distributions of UnixWare are available for x86 architecture computers....
, Linux
Linux

Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
 and BSD, feature a virtual console (VC, sometimes virtual terminal, VT) — a conceptual combination of the keyboard and the display for a user interface
User interface

The user interface is the aggregate of means by which people—the User s—Interaction with the system—a particular machine, device, computer program or other complex tools....
. The concrete combination is the system console
System console

The system console, root console or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the Kernel , from the init system and from the syslog....
 of the computer, where the user can switch between the virtual consoles to access multiple unrelated user interfaces. Virtual consoles date back at least to Xenix
Xenix

Xenix is a version of the Unix operating system, licensed by Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually began distributing it as SCO UNIX....
 in the 1980s.

Usually in Linux, the first six virtual consoles provide a text terminal with a login prompt to a Unix shell
Unix shell

A Unix shell is a command-line interpreter and script host that provides a traditional user interface for the Unix operating system and for Unix-like systems....
.






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In computing
Computing

Computing is usually defined as the activity of using and developing computer technology, computer hardware and computer software. It is the computer-specific part of information technology....
, some operating system
Operating system

An operating system is an interface between hardware and applications; it is responsible for the management and coordination of activities and the sharing of the limited resources of the computer....
s such as UnixWare
UnixWare

UnixWare is a Unix operating system maintained by The SCO Group . Unixware is typically deployed as a Server rather than Desktop computer. Binary distributions of UnixWare are available for x86 architecture computers....
, Linux
Linux

Linux is a generic term referring to Unix-like computer operating systems based on the Linux kernel. Their development is one of the most prominent examples of free and open source software collaboration; typically all the underlying source code can be used, freely modified, and redistributed by anyone under the terms of the GNU GPL license...
 and BSD, feature a virtual console (VC, sometimes virtual terminal, VT) — a conceptual combination of the keyboard and the display for a user interface
User interface

The user interface is the aggregate of means by which people—the User s—Interaction with the system—a particular machine, device, computer program or other complex tools....
. The concrete combination is the system console
System console

The system console, root console or simply console is the text entry and display device for system administration messages, particularly those from the BIOS or boot loader, the Kernel , from the init system and from the syslog....
 of the computer, where the user can switch between the virtual consoles to access multiple unrelated user interfaces. Virtual consoles date back at least to Xenix
Xenix

Xenix is a version of the Unix operating system, licensed by Microsoft from AT&T in the late 1970s. The Santa Cruz Operation later acquired exclusive rights to the software, and eventually began distributing it as SCO UNIX....
 in the 1980s.

Usually in Linux, the first six virtual consoles provide a text terminal with a login prompt to a Unix shell
Unix shell

A Unix shell is a command-line interpreter and script host that provides a traditional user interface for the Unix operating system and for Unix-like systems....
. The graphical X Window System
X Window System

The X Window System is a computing software system and network protocol that provides a graphical user interface for networked computers. It implements the X Window System protocols and architecture and provides windowing system on raster graphics Visual display units and manages Keyboard and pointing device control functions....
 starts in the seventh virtual console. In Linux, the switching is performed with a key combination of Alt
Alt key

The Alt key on a computer keyboard is used to change the function of other pressed keys. Thus, the Alt key is a modifier key, used in a similar fashion to the Shift key....
 plus a function key
Function key

A function key is a key on a computer or computer terminal computer keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions....
 -- for example Alt+F1
Function key

A function key is a key on a computer or computer terminal computer keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions....
 to access the virtual console number 1. Alt+Left arrow changes to the previous virtual console and Alt+Right arrow to the next virtual console. To switch from the X Window System, Ctrl+Alt+function key works. (Note that users can re-define these default key-combinations.)

The need for virtual consoles has lessened now that most applications work in the graphical framework of the X Window System, where each program has a window and the text mode programs can be run in terminal-emulator
Terminal emulator

A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video Computer terminal within some other display architecture....
 windows. If several sessions
Login session

In computing, a login session is the period of activity between a user Logging and logout of a system.On Unix and Unix-like operating systems, a login session takes one of two main forms:...
 of the X Window System are required to run in parallel, such as in the case of fast user switching
Fast user switching

Fast user switching is a feature on some modern multi-user operating systems such as Windows XP, Windows Vista, Mac OS X, OpenSUSE, Ubuntu and Fedora ....
 or when debugging X programs on a separate X server, each X session usually runs in a separate virtual console. GNU Screen
GNU Screen

GNU Screen is a Free software Computer terminal multiplexer developed by the GNU Project since at least 1995. It allows a user to access multiple separate terminal sessions inside a single terminal window or remote terminal session....
 is a program that can change between several text-mode programs in one textual login. There are also other graphical frameworks such as FrameBuffer UI
FrameBuffer UI

Framebuffer UI is an in-kernel windowing system for Linux that sits on top of the framebuffer subsystem. Unlike the X Window System, FBUI consumes very little memory: the entire subsystem is about 50 kilobytes....
, Y Window System
Y Window System

The Y Window System is a windowing system, consisting of a window Server and a client Library for writing applications. It was written by Mark Thomas as the subject of his Master's thesis at Imperial College, London....
, and Fresco
Fresco (computing)

In computing, Fresco is a windowing system. It was intended as a replacement for the X Window System. As of October 23, 2008, the last activity in was dated June 11, 2004....
.

Interface


The virtual consoles are represented by device special files /dev/tty1, /dev/tty2 etc. There are also special files /dev/console, /dev/tty and /dev/tty0. (Compare the devices using the patterns vcs ("virtual console screen") and vcsa ("virtual console screen with attributes") such as /dev/vcs1 and /dev/vcsa1. ) The virtual consoles can be configured in the file /etc/inittab read by init
Init

init is the program on Unix and Unix-like systems that spawns all other processes. It runs as a daemon and typically has process identifier 1....
 -- typically it starts the text mode login
Logging (computer security)

In computer security, login is the process by which individual access to a computer system is controlled by identification of the User using credentials provided by the user....
 process getty
Getty (Unix)

getty short for "get teletype", is a Unix program running on a host computer that manages physical or virtual Computer_terminal . When it detects a connection, it prompts for a username and runs the 'logging ' program to authenticate the user....
 for several virtual consoles. X Window System
X Window System

The X Window System is a computing software system and network protocol that provides a graphical user interface for networked computers. It implements the X Window System protocols and architecture and provides windowing system on raster graphics Visual display units and manages Keyboard and pointing device control functions....
 can be configured in /etc/inittab or by an X display manager
X display manager

In the X Window System, an X display manager runs as a program, that allows the starting of a login session on an X Server from the same or another computer....
.

Programs used to access the virtual consoles typically include:

  • chvt to switch the current virtual console
  • openvt to run a program on a new virtual console
  • deallocvt to close a currently unused virtual console.


The program startx starts the X Window System
X Window System

The X Window System is a computing software system and network protocol that provides a graphical user interface for networked computers. It implements the X Window System protocols and architecture and provides windowing system on raster graphics Visual display units and manages Keyboard and pointing device control functions....
 on a new virtual console. There are also other graphical programs that can start from the console, such as LinuxTV
LinuxTV

The LinuxTV project is an informal group of volunteers who develop software related to digital television for the Linux operating system. The community develops and maintains the DVB driver subsystem which is part of the Linux 2.6.x kernel....
 and MPlayer
MPlayer

MPlayer is a free software and open source media player . The program is available for all major operating systems, including Linux and other Unix-like systems, Microsoft Windows and Mac OS X....
.

Programs can access the virtual consoles by the device special files. In text mode, writing to the file displays text on the virtual console and reading from the file returns text the user writes to the virtual console. As with other text terminals, there are also special escape sequence
Escape sequence

An escape sequence is a series of character used to change the state of computers and their attached peripheral devices. These are also known as control sequences, reflecting their use in device control....
s, control character
Control character

In computing and telecommunication, a control Grapheme or non-printing character is a code point in a character encoding, that does not in itself represent a written symbol....
s and termios function
System call

In computing, a system call is the mechanism used by an application program to request service from the kernel based on the Monolithic_kernel or to system servers on operating systems based on the microkernel-structure....
s that a program can use, most easily via a library such as ncurses
Ncurses

ncurses is a programming library providing an application programming interface, allowing the programmer to write text user interfaces in a terminal-independent manner....
. For more complex operations, the programs can use console and terminal special ioctl
Ioctl

In computing, an ioctl is part of the userspace-to-kernel interface of a conventional operating system. Short for "Input/output control", ioctls are typically employed to allow userspace code to communicate with hardware devices or kernel components....
 system calls. Graphical programs can use libraries such as DirectFB
DirectFB

DirectFB stands for Direct Frame Buffer. It is a library for the GNU/Linux operating system that provides "hardware graphics acceleration, input device handling and abstraction, integrated windowing system with support for translucent windows and multiple display layers on top of the Linux framebuffer Device." ...
, DRI
Direct Rendering Infrastructure

In computing, the Direct Rendering Infrastructure is an interface and a free software implementation used in the X Window System to securely allow user applications to access the video hardware without requiring data to be passed through the X server....
, SDL
Simple DirectMedia Layer

Simple DirectMedia Layer is a cross-platform, free and open source software multimedia Library written in C that presents a simple interface to various platforms' computer graphics, sound, and input devices, allowing a developer to write a Personal computer game or other multimedia application that can run on many operating systems includi...
 or the earlier SVGALib
SVGALib

SVGAlib is an open-source low-level graphics Library which runs on Linux and FreeBSD and allows programs to change video mode and display full-screen graphics....
.

Unix systems


Unix workstations, such as those manufactured by Sun
Sun Microsystems

Sun Microsystems, Inc. is a multinational corporation vendor of computers, computer components, computer software, and information technology services, founded on February 24, 1982....
 or Silicon Graphics
Silicon Graphics

Silicon Graphics, Inc. is a company manufacturer high-performance computing solutions, including computer hardware and computer software. SGI was founded by James H....
, did not include virtual consoles. The only purpose of console would be fixing the system so that graphical environment could start.

Sun Niagara-based
UltraSPARC T1

Sun Microsystems' UltraSPARC T1 microprocessor, known until its 14 November 2005 announcement by its development codename "Niagara", is a multithreading, multicore central processing unit....
 servers running virtualization
Virtualization

In computing, platform virtualization is a virtualization of computers or operating systems. It hides the physical characteristics of computing platform from the users, instead showing another abstract, emulated computing platform....
 with Logical Domains
Logical Domains

Logical Domains is a technology from Sun Microsystems released in May 2007 which offers a virtualization abstracted from all physical devices....
 get virtual console services from the Control domain.

See also


  • Computer console for the concrete console
  • Text terminal for the textual interface in general
  • Linux framebuffer
    Linux framebuffer

    The Linux framebuffer is a graphic hardware-independent abstraction layer to show computer graphics on a computer console without relying on system-specific libraries such as SVGALib or the heavy overhead of the X Window System....
     for a graphical interface to the console
  • Pseudo terminal
    Pseudo terminal

    In Unix, a pseudo terminal is a pseudo-device pair that provides a text terminal interface without associated Virtual console , computer terminal or serial port hardware....
     for even more virtual consoles
  • Terminal emulator
    Terminal emulator

    A terminal emulator, terminal application, term, or tty for short, is a program that emulates a "dumb" video Computer terminal within some other display architecture....
     for an application program that has the same function as a textual virtual console


External links

  • from The Linux Information Project.