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Magic SysRq Key
The magic SysRq key is a key combination understood by the Linux kernel, which allows the user to perform various low-level commands regardless of the system's state. It is often used to recover from freeze (computing), freezes, or to booting, reboot a computer without corrupting the filesystem. This key combination provides access to features for disaster recovery. In this sense, it can be considered a form of escape sequence. Principal among the offered commands are means to forcibly unmount file systems, kill processes, recover keyboard state, and write unwritten data to disk. The magic SysRq key cannot work under certain conditions, such as a kernel panic or a hardware failure preventing the kernel from running properly. Implementation The Linux kernel contains sysrq.c, which implements magic SysRq functionality. Magic SysRq functionality is called by serial devices at a low level in the driver code. Commands The key combination consists of and another key, which c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lock (computer Science)
In computer science, a lock or mutex (from mutual exclusion) is a synchronization primitive that prevents state from being modified or accessed by multiple threads of execution at once. Locks enforce mutual exclusion concurrency control policies, and with a variety of possible methods there exist multiple unique implementations for different applications. Types Generally, locks are ''advisory locks'', where each thread cooperates by acquiring the lock before accessing the corresponding data. Some systems also implement ''mandatory locks'', where attempting unauthorized access to a locked resource will force an exception in the entity attempting to make the access. The simplest type of lock is a binary semaphore. It provides exclusive access to the locked data. Other schemes also provide shared access for reading data. Other widely implemented access modes are exclusive, intend-to-exclude and intend-to-upgrade. Another way to classify locks is by what happens when the lock st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SPARC64 V
The SPARC64 V (''Zeus'') is a SPARC, SPARC V9 microprocessor designed by Fujitsu. The SPARC64 V was the basis for a series of successive processors designed for servers, and later, supercomputers. The servers series are the SPARC64 V+, VI, VI+, VII, VII+, X, X+ and XII. The SPARC64 VI and its successors up to the VII+ were used in the Fujitsu and Sun (later Oracle Corporation, Oracle) SPARC Enterprise, SPARC Enterprise M-Series servers. In addition to servers, a version of the SPARC64 VII was also used in the commercially available Fujitsu FX1 supercomputer. As of October 2017, the SPARC64 XII is the latest server processor, and it is used in the Fujitsu and Oracle M12 servers. The supercomputer series was based on the SPARC64 VII, and are the SPARC64 VIIfx, IXfx, and XIfx. The SPARC64 VIIIfx was used in the K computer, and the SPARC64 IXfx in the commercially available PRIMEHPC FX10. As of July 2016, the SPARC64 XIfx is the latest supercomputer processor, and it is used in the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PowerPC
PowerPC (with the backronym Performance Optimization With Enhanced RISC – Performance Computing, sometimes abbreviated as PPC) is a reduced instruction set computer (RISC) instruction set architecture (ISA) created by the 1991 Apple Inc., Apple–IBM–Motorola alliance, known as AIM alliance, AIM. PowerPC, as an evolving instruction set, has been named Power ISA since 2006, while the old name lives on as a trademark for some implementations of Power Architecture–based processors. Originally intended for personal computers, the architecture is well known for being used by Apple's desktop and laptop lines from 1994 until 2006, and in several videogame consoles including Microsoft's Xbox 360, Sony's PlayStation 3, and Nintendo's GameCube, Wii, and Wii U. PowerPC was also used for the Curiosity (rover), Curiosity and Perseverance (rover), Perseverance rovers on Mars and a variety of satellites. It has since become a niche architecture for personal computers, particularly with A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
File System Permissions
Typically, a file system maintains permission settings for each stored item commonly files and directories that either grant or deny the ability to manipulate file system items. Often the settings allow controlling access based on function such as read, change, navigate, and execute and to different users and groups of users. One well-established technology was developed for Unix and later codified by POSIX. Another common technology is an access-control list (ACL) with multiple variants implemented in file systems and one codified by POSIX. Since POSIX defines both the older Unix-based technology as well as ACLs, the former is called ''traditional POSIX permissions'' for clarity even though it is not a well-known term. A permission-driven user interface tailors the functionality available to the user based on file system item permissions. For example, the interface might hide menu options that are not allowed based on the permissions stored for an item. Examples File sy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Real-time Computing
Real-time computing (RTC) is the computer science term for Computer hardware, hardware and software systems subject to a "real-time constraint", for example from Event (synchronization primitive), event to Event (computing), system response. Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines".Mordechai Ben-Ari, Ben-Ari, Mordechai; "Principles of Concurrent and Distributed Programming", ch. 16, Prentice Hall, 1990, , p. 164 The term "real-time" is also used in Computer simulation, simulation to mean that the simulation's clock runs at the same speed as a real clock. Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. A system not specified as operating in real time cannot usually ''guarantee'' a response within any timeframe, although ''typical'' or ''expected'' response times may be given. Real-time processing ''fails'' if not completed within a specified deadline rela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nice (Unix)
nice is a program found on Unix and Unix-like operating systems such as Linux. It directly maps to a kernel call of the same name. nice is used to invoke a utility or shell script with a particular CPU priority, thus giving the process more or less CPU time than other processes. A niceness of -20 is the lowest niceness, or highest priority. The default niceness for processes is inherited from its parent process and is usually 0. Systems have diverged on what priority is the lowest. Linux systems document a niceness of 19 as the lowest priority, BSD systems document 20 as the lowest priority. In both cases, the "lowest" priority is documented as running only when nothing else wants to. Etymology ''Niceness value'' is a number attached to processes in *nix systems, that is used along with other data (such as the amount of I/O done by each process) by the kernel process scheduler to calculate a process' 'true priority'which is used to decide how much CPU time is allocated t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Secure Attention Key
A secure attention key (SAK), special attention key, or secure attention sequence (SAS) is a special key, key combination or sequence to be pressed on a computer keyboard before a login screen which must, to the user, be completely trustworthy. The operating system kernel, which interacts directly with the hardware, or init system is able to detect whether the secure attention key has been pressed. When this event is detected, the trusted login processing is started. The secure attention key is designed to make login spoofing impossible, as the kernel will suspend any program, including those masquerading as the computer's login process, before starting a trustable login operation. Examples Some examples are: * : Introduced in systemd v257 as a more reliable SAK for Linux distributions but may require support from the currently running desktop environment. It is implemented as of gdm (GNOME display manager) 47. * on X Window System immediately kills the X server (although ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
SIGKILL
Signals are standardized messages sent to a running program to trigger specific behavior, such as quitting or error handling. They are a limited form of inter-process communication (IPC), typically used in Unix, Unix-like, and other POSIX-compliant operating systems. A signal is an asynchronous notification sent to a process or to a specific thread within the same process to notify it of an event. Common uses of signals are to interrupt, suspend, terminate or kill a process. Signals originated in 1970s Bell Labs Unix and were later specified in the POSIX standard. When a signal is sent, the operating system interrupts the target process's normal flow of execution to deliver the signal. Execution can be interrupted during any non-atomic instruction. If the process has previously registered a signal handler, that routine is executed. Otherwise, the default signal handler is executed. Embedded programs may find signals useful for inter-process communications, as signals ar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Direct Rendering Manager
The Direct Rendering Manager (DRM) is a subsystem of the Linux kernel responsible for interfacing with Graphics processing unit, GPUs of modern video cards. DRM exposes an Application programming interface, API that user-space programs can use to send commands and data to the GPU and perform operations such as configuring the mode setting of the display. DRM was first developed as the kernel-space component of the X.Org Server, X Server Direct Rendering Infrastructure, but since then it has been used by other graphic stack alternatives such as Wayland (display server protocol), Wayland and standalone applications and libraries such as Simple DirectMedia Layer , SDL2 and Kodi (software) , Kodi. User-space programs can use the DRM API to command the GPU to do hardware acceleration, hardware-accelerated 3D rendering and video decoding, as well as General-purpose computing on graphics processing units, GPGPU computing. Overview The Linux kernel already had an Application program ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
