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Power cycling refers to the act of turning a device or piece of electrical or electronic equipment off, or otherwise disconnecting it from its power source, and then turning it back on again. Often this is done to computers, modems (to reset network activity) or other electronic equipment to correct a frozen, hung or otherwise malfunctioning device. Depending on the device, manufacturers often recommend leaving the device powered off for five to 30 seconds (sometimes longer) before restarting.
Power cycling is also known as off-on test or power cycle. Similar or associated terms include soft reboot, random reboot, automatic reboot and quick boot.
Power cycling can be done manually by using a switch on the device, or automatically through another device, system, network management control or network monitoring system. Power cycling can also be done remotely or through a communication channel. This is often done over TCP/IP in a data center environment through a power distribution unit, panel or system.
In relation to servers, personal computers, desktop computers and laptop computers, power cycling is synonymous with rebooting the computer. For servers, some IT personnel refer to it as bouncing the server.
Hard reboot is a similar term describing abruptly turning a computer off without going through the normal shutdown procedure. Especially with operating systems that use disk caches, a hard reboot may leave files in an unclean state (temporary files not deleted or moved as normally would be done before a system shutdown). This may require a scan, of the file system structures before normal operations can resume after restarting.