Power cycling is the act of turning a piece of equipment, usually a computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

, off and then on again. Reasons for power cycling include having an electronic device reinitialize its configuration or recover from an unresponsive state of its mission critical functionality, such as in a crash

Crash (computing)

A crash in computing is a condition where a computer or a program, either an application or part of the operating system, ceases to function properly, often exiting after encountering errors. Often the offending program may appear to freeze or hang until a crash reporting service documents...

 or hang

Hang (computing)

In computing, a hang or freeze occurs when either a single computer program, or the whole system ceases to respond to inputs. In the most commonly encountered scenario, a workstation with a graphical user interface, all windows belonging to the frozen program become static, and though the mouse...

 situation. Power cycling can also be used to reset network activity inside a modem.

Power cycling can be done manually, usually using a switch on the device to be cycled; automatically, through some type of device, system, or network management

Network management

Network management refers to the activities, methods, procedures, and tools that pertain to the operation, administration, maintenance, and provisioning of networked systems....

 monitoring and control; or by remote control; through a communication channel.

In the data center

Data center

A data center is a facility used to house computer systems and associated components, such as telecommunications and storage systems...

 environment, remote control power cycling can usually be done through a power distribution unit

Power distribution unit

A power distribution unit is a device fitted with multiple outputs designed to distribute electric power, especially to racks of computers and networking equipment located within a data center....

, over TCP/IP. In the home environment, this can be done through home automation

Home automation

Home automation is the residential extension of "building automation". It is automation of the home, housework or household activity. Home automation may include centralized control of lighting, HVAC , appliances, and other systems, to provide improved convenience, comfort, energy efficiency and...

 powerline

Powerline

Powerline or power line may refer to:* Overhead power line, used for electric power transmission* Power line communication, a computer networking technology* Power Line, a political blog* Powerline, a fictional singer in the A Goofy Movie musical...

 communications, via IP protocols (wired or wireless

Wireless

Wireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...

), or by phone line.

Power cycling is dangerous for the hardware like hard drives and is only performed as the last resort, when other attempts to get control on the system fail. Reset

Reset (Computing)

In a computer or data transmission system, to reset means to clear any pending errors or events and bring a system to normal condition or initial state usually in a controlled manner. It is usually done in response to an error condition when it is impossible or undesirable for a processing activity...

has equal effect on the software but may be less problematic for the hardware as power is not interrupted, so it is usually tried first.