Graceful shutdown and hard shutdown are two opposing methods of turning off a computer. A graceful shutdown is when a computer is turned off by software function and the operating system (OS) is allowed to perform its tasks of safely shutting down processes and closing connections. A hard shutdown is when the computer is forcibly shut down by interruption of power.
Graceful shutdowns are generally performed intentionally by users, as a part of their daily routines, at the end of a work day or when finished with home use of a computer. Hard shutdowns maybe unintentional due to power disconnects, electronic protection circuits or hardware failures. In the case of some safety issues like computer fires or security issues like malware or hacked computers, hard shutdowns may be as a safety precaution by users or IT departments.
Generally, a graceful shutdown is preferable in the case of any OS that saves its state. When the standard shutdown procedures are not done with these OSs, the result can be data corruption of program and operating system files. The result of the corruption can be instability, incorrect functioning or failure to boot.
Many modern OSs and other software are fault tolerant and generally handle the odd power interruption without issue. Both bare metal and virtualized systems can be affected by hard shutdowns, so they should be avoided when unnecessary. Virtual machines (VM) may need to be restored from backups, while bare metal systems may even require a full reinstall.