A headless computer is a computer system or device that has been configured to operate without a monitor (the missing "head"), keyboard, 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 introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a compu ...

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 a type of firmware used to provide runtime services for operating systems and programs and to perform hardware initialization d ...

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 accelerator, graphics adapter, VGA card/VGA, video adapter, display adapter, or colloquially GPU) is a computer expansion card that generates a feed of graphics output to a displa ...

or keyboard, 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 and physical network interface) is a computer hardware component that connects a computer to a computer network. Early network interface ...

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 interface (CLI) is a means of interacting with software via command (computing), commands each formatted as a line of text. Command-line interfaces emerged in the mid-1960s, on computer terminals, as an interactive and more user ...

Unix Unix (, ; trademarked as UNIX) is a family of multitasking, multi-user 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, a ...

or in

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

. These interfaces, often called "

virtual terminal In Open system (computing), open systems, a virtual terminal (VT) is an application service that: # Allows Server (computing), host terminals on a multi-User (computing), user computer network, network to interact with other hosts regardless of ...

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 term ...

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 until ...

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 Protocol) 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 was designed for ...

. 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 originated as part of Project Athena at Massachusetts Institute of Technology (MIT) in 1984. The X protocol has been at ...

and VNC 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 micr ...

s - this setup allows remote connections to headless machines through ordinary

graphical user interface A graphical user interface, or GUI, is a form of user interface that allows user (computing), users to human–computer interaction, interact with electronic devices through Graphics, graphical icon (computing), icons and visual indicators such ...

s, often running over network protocols like

TCP/IP The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suite are ...

References

{{reflist Classes of computers System administration

PC BIOS limitations

Hardware remote control

Software remote control

See also

References