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Reboot
In computing, rebooting is the process by which a running computer system is restarted, either intentionally or unintentionally. Reboots can be either a cold reboot (alternatively known as a hard reboot) in which the power to the system is physically turned off and back on again (causing an initial boot of the machine); or a warm reboot (or soft reboot) in which the system restarts while still powered up. The term restart (as a system command) is used to refer to a reboot when the operating system closes all programs and finalizes all pending input and output operations before initiating a soft reboot. Terminology Etymology Early electronic computers (like the IBM 1401) had no operating system and little internal memory. The input was often a stack of punch cards or via a switch register. On systems with cards, the computer was initiated by pressing a start button that performed a single command - "read a card". This first card then instructed the machine to read more card ...
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Control-Alt-Delete
Control-Alt-Delete (often abbreviated to Ctrl+Alt+Del and sometimes called the "three-finger salute" or "Security Keys") is a computer keyboard command on IBM PC compatible computers, invoked by pressing the Delete key while holding the Control and Alt keys: . The function of the key combination differs depending on the context but it generally interrupts or facilitates interrupting a function. For instance, in pre-boot environment (before an operating system starts) or in MS-DOS, Windows 3.0 and earlier versions of Windows or OS/2, the key combination reboots the computer. Starting with Windows 95, the key combination invokes a task manager or security related component that facilitates ending a Windows session or killing a frozen application. History The soft reboot function via keyboard was originally designed by David Bradley. Bradley, as the chief engineer of the IBM PC project and developer of the machine's ROM-BIOS, had originally used , but found it was too ea ...
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Booting
In computing, booting is the process of starting a computer as initiated via Computer hardware, hardware such as a physical button on the computer or by a software command. After it is switched on, a computer's central processing unit (CPU) has no software in its main memory, so some process must load software into memory before it can be executed. This may be done by hardware or firmware in the CPU, or by a separate processor in the computer system. On some systems a power-on reset (POR) does not initiate booting and the operator must initiate booting after POR completes. IBM uses the term Initial Program Load (IPL) on someE.g., System/360 through IBM Z, RS/6000 and System/38 through IBM Power Systems product lines. Restarting a computer also is called Reboot (computing), ''rebooting'', which can be "hard", e.g. after electrical power to the CPU is switched from off to on, or "soft", where the power is not cut. On some systems, a soft boot may optionally clear RAM to zero. Bo ...
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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 during the booting process (power-on startup). The firmware comes pre-installed on the computer's motherboard. The name originates from the Basic Input/Output System used in the CP/M operating system in 1975. The BIOS firmware was originally proprietary to the IBM PC; it was reverse engineered by some companies (such as Phoenix Technologies) looking to create compatible systems. The interface of that original system serves as a ''de facto'' standard. The BIOS in older PCs initializes and tests the system hardware components ( power-on self-test or POST for short), and loads a boot loader from a mass storage device which then initializes a kernel. In the era of DOS, the BIOS provided BIOS interrupt calls for the keyboard, display, st ...
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Kernel Panic
A kernel panic (sometimes abbreviated as KP) is a safety measure taken by an operating system's Kernel (operating system), kernel upon detecting an internal Fatal system error, fatal error in which either it is unable to safely recover or continuing to run the system would have a higher risk of major data loss. The term is largely specific to Unix and Unix-like systems. The equivalent on Microsoft Windows operating systems is a Blue screen of death, stop error, often called a "blue screen of death". The Kernel (operating system), kernel routines that handle panics, known as panic() in AT&T Corporation, AT&T-derived and Berkeley Software Distribution, BSD Unix source code, are generally designed to output an error message to the system console, console, dump an image of kernel memory to disk for post-mortem debugging, and then either wait for the system to be manually rebooted, or initiate an automatic reboot. The information provided is of a highly technical nature and aims t ...
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Kexec
kexec (kernel execute), analogous to the Unix/Linux kernel call Exec (system call), exec, is a mechanism of the Linux kernel that allows booting of a new kernel (operating system), kernel from the currently running one. Details Essentially, kexec skips the bootloader stage and computer hardware, hardware initialization phase performed by the system firmware (BIOS or UEFI), and directly loads the new kernel into main memory and starts executing it immediately. This avoids the long times associated with a full reboot, and can help systems to meet high-availability requirements by minimizing downtime. While feasible, implementing a mechanism such as kexec raises two major challenges: * Memory of the currently running kernel is overwritten by the new kernel, while the old one is still executing. * The new kernel will usually expect all hardware devices to be in a well defined state, in which they are after a system reboot because the system firmware resets them to a "sane" state. B ...
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Reset (computing)
In a computer or data transmission system, a reset clears any pending errors or events and brings a system to normal condition or an 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 to proceed and all error recovery mechanisms fail. A computer storage program would normally perform a "reset" if a command times out and error recovery schemes like retry or abort also fail. Software reset A software reset (or soft reset) is initiated by the software, for example, Control-Alt-Delete key combination have been pressed, or execute restart in Microsoft Windows. Hardware reset Most computers have a reset line that brings the device into the startup state and is active for a short time after powering on. For example, in the x86 architecture, asserting the RESET line halts the CPU; this is done after the system is switched on and before the power supply has asserted "p ...
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Power-on Self-test
A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on. POST processes may set the initial state of the device from firmware and detect if any hardware components are non-functional. The results of the POST may be displayed on a panel that is part of the device, output to an external device, or stored for future retrieval by a diagnostic tool. In some computers, an indicator lamp or a PC speaker, speaker may be provided to show error codes as a sequence of flashes or Beep (sound), beeps in the event that a computer display malfunctions. POST routines are part of a computer's pre-boot sequence. If they complete successfully, the bootstrap loader code is invoked to load an operating system. In IBM PC compatible computers, the main duties of POST are handled by the BIOS or UEFI. IBM-compatible PC POST In IBM PC compatible computers, the main duties of POST are handled by ...
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Memory Leak
In computer science, a memory leak is a type of resource leak that occurs when a computer program incorrectly manages memory allocations in a way that memory which is no longer needed is not released. A memory leak may also happen when an object is stored in memory but cannot be accessed by the running code (i.e. unreachable memory). A memory leak has symptoms similar to a number of other problems and generally can only be diagnosed by a programmer with access to the program's source code. A related concept is the "space leak", which is when a program consumes excessive memory but does eventually release it. Because they can exhaust available system memory as an application runs, memory leaks are often the cause of or a contributing factor to software aging. Effects Minor leaks If a program has a memory leak and its memory usage is steadily increasing, there will not usually be an immediate symptom. In modern operating systems, normal memory used by an application is releas ...
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Power Cycling
Power cycling is the act of turning a piece of equipment, usually a computer, off and then on again. Reasons for power cycling include having an electronic device reinitialize its set of configuration parameters or recover from an unresponsive state of its mission critical functionality, such as in a crash or hang situation. Power cycling can also be used to reset network activity inside a modem. It can also be among the first steps for troubleshooting an issue. Overview Power cycling can be done manually, usually using the power switch on the device, or remotely, through some type of external device connected to the power input. In the data center environment, remote control power cycling can usually be done through a power distribution unit, over the network. In the home environment, this can be done through home automation powerline communications. Most Internet Service Providers publish a "how-to" on their website showing their customers the correct procedure to power cycle ...
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Cold Boot Attack
In computer security, a cold boot attack (or to a lesser extent, a platform reset attack) is a type of side channel attack in which an attacker with physical access to a computer performs a memory dump of a computer's random-access memory (RAM) by performing a hard reset of the target machine. Typically, cold boot attacks are used for retrieving encryption keys from a running operating system for malicious or criminal investigative reasons. The attack relies on the data remanence property of DRAM and SRAM to retrieve memory contents that remain readable in the seconds to minutes following a power switch-off. An attacker with physical access to a running computer typically executes a cold boot attack by cold-booting the machine and booting a lightweight operating system from a removable disk to dump the contents of pre-boot physical memory to a file. An attacker is then free to analyze the data dumped from memory to find sensitive data, such as the keys, using various forms ...
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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, packaged as a Linux distribution (distro), which includes the kernel and supporting system software and library (computing), libraries—most of which are provided by third parties—to create a complete operating system, designed as a clone of Unix and released under the copyleft GPL license. List of Linux distributions, Thousands of Linux distributions exist, many based directly or indirectly on other distributions; popular Linux distributions include Debian, Fedora Linux, Linux Mint, Arch Linux, and Ubuntu, while commercial distributions include Red Hat Enterprise Linux, SUSE Linux Enterprise, and ChromeOS. Linux distributions are frequently used in server platforms. Many Linux distributions use the word "Linux" in their name, but the Free ...
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