Reboot
It has been suggested that this article be merged with Power cycling. (Discuss) Proposed since February 2024. |
In
Terminology
Etymology
Early electronic computers (like the
Cold versus warm reboot
This article's factual accuracy may be compromised due to out-of-date information. The reason given is: The described differences between a cold and a warm reboot aren't universally applicable. Also, "BIOS" is not the firmware of a PC, it is just a long-obsolete API for such a firmware, and this API is usually no longer involved in the boot process.. (December 2023) |
For IBM PC compatible computers, a cold boot is a boot process in which the computer starts from a powerless state, in which the system performs a complete power-on self-test (POST).[1][2][3][4] Both the operating system and third-party software can initiate a cold boot; the restart command in Windows 9x initiates a cold reboot, unless Shift key is held.[1]: 509
A warm boot is initiated by the BIOS, either as a result of the Control-Alt-Delete key combination[1][2][3][4] or directly through BIOS interrupt INT 19h.[5] It may not perform a complete POST - for example, it may skip the memory test - and may not perform a POST at all.[1][2][4] Malware may prevent or subvert a warm boot by intercepting the Ctrl + Alt + Delete key combination and prevent it from reaching BIOS.[6] The Windows NT family of operating systems also does the same and reserves the key combination for its own use.[7][8]
The Linux family of operating systems supports an alternative to warm boot; the Linux kernel has optional support for kexec, a system call which transfers execution to a new kernel and skips hardware or firmware reset. The entire process occurs independently of the system firmware. The kernel being executed does not have to be a Linux kernel.[citation needed]
Outside the domain of IBM PC compatible computers, the types of boot may not be as clear. According to Sue Loh of
Hard reboot
A hard reboot means that the system is not shut down in an orderly manner, skipping file system synchronisation and other activities that would occur on an orderly shutdown. This can be achieved by either applying a reset, by cycling power, by issuing the halt -q
command in most Unix-like systems, or by triggering a kernel panic.
Hard reboots are used in the cold boot attack.
Restart
The term "restart" is used by the Microsoft Windows and Linux families of operating systems to denote an operating system-assisted reboot. In a restart, the operating system ensures that all pending I/O operations are gracefully ended before commencing a reboot.
Causes
Deliberate
Users may deliberately initiate a reboot. Rationale for such action may include:
- Troubleshooting: Rebooting may be used by users, support staff or system administrators as a technique to work around bugs in software,[10] for example memory leaks or processes that hog resources to the detriment of the overall system, or to terminate malware. While this approach does not address the root cause of the issue, resetting a system back to a good, known state may allow it to be used again for some period until the issue next occurs.
- Switching operating systems: On a multi-boot system without a hypervisor, a reboot is required to switch between installed operating systems.
- Offensive: As stated earlier, components lose power during a cold reboot; therefore, components such as RAM that require power lose the data they hold. However, in a cold boot attack, special configurations may allow for part of the system state, like a RAM disk, to be preserved through the reboot.[11]
The means of performing a deliberate reboot also vary and may include:
- Manual, hardware-based: A power switch or
- Manual, software-based: Computer software and operating system can trigger a reboot as well; more specifically, Microsoft Windows operating systems are outfitted with a restart command that closes open programs and eliminates data loss due to reboot.[1]: 509
- Automated: Software can be scheduled to run at a certain time and date; therefore, it is possible to schedule a reboot.[13]
Power failure
Unexpected loss of power for any reason (including power outage, power supply failure or depletion of battery on a mobile device) forces the system user to perform a cold boot once the power is restored. Some BIOSes have an option to automatically boot the system after a power failure.[14][15] An uninterruptible power supply (UPS), backup battery or redundant power supply can prevent such circumstances.
Random reboot
"Random reboot" is a non-technical term referring to an unintended (and often undesired) reboot following a
Systems may be configured to reboot automatically after a power failure, or a
Hibernation
The introduction of
Simulated reboot
A reboot may be simulated by software running on an operating system. For example: the Sysinternals BlueScreen utility, which is used for pranking; or some modes of the bsod XScreenSaver "hack", for entertainment (albeit possibly concerning at first glance). Malware may also simulate a reboot, and thereby deceive a computer user for some nefarious purpose.[6]
Microsoft App-V sequencing tool captures all the file system operations of an installer in order to create a virtualized software package for users. As part of the sequencing process, it will detect when an installer requires a reboot, interrupt the triggered reboot, and instead simulate the required reboot by restarting services and loading/unloading libraries.[16]
Windows deviations and labeling criticism
Windows 8 & 10 enable (by default) a hibernation-like "Fast Startup" (a.k.a. "Fast Boot") which can cause problems (including confusion) for users accustomed to turning off computers to (cold) reboot them.[17][18][19]
See also
- Booting
- Cold start (computing)
- Local reboot
- Power cycling
- Reset (computing)
References
- ^ ISBN 9780789728678.
- ^ ISBN 9780789725738.
- ^ ISBN 0-7356-1378-8.
- ^ ISBN 9780789730626.
- ^ "Hardware Troubleshooting: Cold Booting Versus Warm Booting". Support. Microsoft. 7 July 2005. Archived from the original on 21 February 2015.
- ^ ISBN 9781565926820.
- ^ "Using CTRL+ALT+DEL key combination to open Windows Security opens Task Manager". Microsoft Support. Microsoft. 15 January 2006. Retrieved 19 January 2013.
- MSDN Blogs. Retrieved 15 March 2007.
- ^ Loh, Sue (22 June 2005). "Boot Persistence Terminology". Windows CE Base Team Blog. Microsoft. Retrieved 3 March 2013.
- ^ Debogue, Jean. "Did you reboot". WeDebugYou.
- ^ Ken Freeze (28 October 1985), "Jram-3 Rivals Persyst Stretch In RAM Race of Add-On Boards", InfoWorld
- ISBN 9781133598312.
- ISBN 9781449309350.
- ^ "AsRock 775i65G User Manual" (PDF). p. 32.
- ^ "Supermicro C7Q67 User's Manual" (PDF). p. 69.[permanent dead link]
- ^ Microsoft App-V 4.6 SP1 Sequencing Guide
- ^ Walter Glenn (3 March 2016). "The Pros and Cons of Windows 10's "Fast Startup" Mode". How-To Geek.
- ^ Oliver Niehus (14 December 2012). "Windows 8: Fast Boot". MSDN - Oliver's Blog.
- ^ "Distinguishing Fast Startup from Wake-from-Hibernation". Microsoft Hardware Dev Center. 15 December 2021.