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A headless computer is a computer system or device that has been configured to operate without a
monitor Monitor or monitor may refer to: Places * Monitor, Alberta * Monitor, Indiana, town in the United States * Monitor, Kentucky * Monitor, Oregon, unincorporated community in the United States * Monitor, Washington * Monitor, Logan County, We ...
(the missing "head"),
keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Mus ...
, and
mouse A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...
. A headless system is typically controlled over a network connection, although some headless system devices require a serial connection to be made over
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...
for administration of the device. Headless operation of a server is typically employed to reduce operating costs.


PC BIOS limitations

During bootup, some (especially older) PC
BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during th ...
versions will wait indefinitely for a user to press a key before proceeding. If some basic device, such as a
video card A graphics card (also called a video card, display card, graphics adapter, VGA card/VGA, video adapter, display adapter, or mistakenly GPU) is an expansion card which generates a feed of output images to a display device, such as a computer moni ...
or
keyboard Keyboard may refer to: Text input * Keyboard, part of a typewriter * Computer keyboard ** Keyboard layout, the software control of computer keyboards and their mapping ** Keyboard technology, computer keyboard hardware and firmware Music * Mus ...
, are not installed or connected, this could effectively halt an unattended system. On more modern systems, the BIOS factory setting will typically be configured to behave this way as well, but this setting can be changed with a BIOS setup utility to proceed without user intervention. Even in cases where a system has been set up to be managed remotely, a local keyboard and video card may still be needed from time to time; for example, to diagnose boot problems that occur before a remote access application is initialized.


Hardware remote control

Some servers provide for remote control with an internal
network card A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter or physical network interface, and by similar terms) is a computer hardware component that connects a computer to a computer network. Ear ...
and hardware that mirrors the console screen. For example, HP offers a system called Integrated Lights-Out (iLO) that provides this function. Remote access to the system is gained using a secure web connection to an IP address assigned to the iLO adapter, and allows for monitoring of the system during start-up, before the operating system is loaded. Another hardware solution is to use a KVM-over-IP switch. Such a switch is a traditional Keyboard-Video-Mouse device with the added ability to provide remote control sessions over IP. Connection to the KVM device is gained using a web browser, which allows for remote monitoring of the connected system console port.


Software remote control

Administration of a headless system typically takes place with a text-based interface such as a
command line A command-line interpreter or command-line processor uses a command-line interface (CLI) to receive commands from a user in the form of lines of text. This provides a means of setting parameters for the environment, invoking executables and pro ...
in
Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, an ...
or in
Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, whic ...
. These interfaces, often called "
virtual terminal In open systems, a virtual terminal (VT) is an application service that: # Allows host terminals on a multi-user network to interact with other hosts regardless of terminal type and characteristics, # Allows remote log-on by local area network ...
s" or "
terminal emulator A terminal emulator, or terminal application, is a computer program that emulates a video terminal within some other display architecture. Though typically synonymous with a shell or text terminal, the term ''terminal'' covers all remote termin ...
s", attempt to simulate the behavior of "real" interface terminals like the
Digital Equipment Corporation Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unti ...
's
VT100 The VT100 is a video terminal, introduced in August 1978 by Digital Equipment Corporation (DEC). It was one of the first terminals to support ANSI escape codes for cursor control and other tasks, and added a number of extended codes for special ...
, but over networks, usually using protocols such as
Secure Shell The Secure Shell Protocol (SSH) is a cryptographic network protocol for operating network services securely over an unsecured network. Its most notable applications are remote login and command-line execution. SSH applications are based on ...
. One can also use systems such as
X Window System The X Window System (X11, or simply X) is a windowing system for bitmap displays, common on Unix-like operating systems. X provides the basic framework for a GUI environment: drawing and moving windows on the display device and interacting wi ...
and
VNC Virtual Network Computing (VNC) is a graphical desktop-sharing system that uses the Remote Frame Buffer protocol (RFB) to remotely control another computer. It transmits the keyboard and mouse input from one computer to another, relaying the g ...
combined with virtual
display driver In electronics/ computer hardware, a display driver is usually a semiconductor integrated circuit (but may alternatively comprise a state machine made of discrete logic and other components) which provides an interface function between a micropr ...
s - this setup allows remote connections to headless machines through ordinary
graphical user interface The GUI ( "UI" by itself is still usually pronounced . or ), graphical user interface, is a form of user interface that allows users to interact with electronic devices through graphical icons and audio indicator such as primary notation, inst ...
s, often running over network protocols like
TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the su ...
.


See also

*
Xvfb Xvfb or X virtual framebuffer is a display server implementing the X11 display server protocol. In contrast to other display servers, Xvfb performs all graphical operations in virtual memory without showing any screen output. From the point of ...
*
x11vnc x11vnc is a Virtual Network Computing (VNC) server program. It allows remote access from a remote client to a computer hosting an X Window session and the x11vnc software, continuously polling the X server's frame buffer for changes. This allo ...
* Headless software *
Embedded system An embedded system is a computer system—a combination of a computer processor, computer memory, and input/output peripheral devices—that has a dedicated function within a larger mechanical or electronic system. It is ''embedded'' a ...
s


References

{{reflist Classes of computers System administration