computing Computing is any goal-oriented activity requiring, benefiting from, or creating computing machinery. It includes the study and experimentation of algorithmic processes, and development of both hardware and software. Computing has scientific, ...

, a crash, or system crash, occurs when a computer program such as a software application or an operating system stops functioning properly and exits. On some operating systems or individual applications, a crash reporting service will report the crash and any details relating to it (or give the user the option to do so), usually to the developer(s) of the application. If the program is a critical part of the operating system, the entire system may crash or hang, often resulting in a kernel panic or

fatal system error A fatal system error (also known as a system crash, stop error, kernel error, or bug check) occurs when an operating system halts because it has reached a condition where it can no longer operate safely (''i.e.'' where critical data could be l ...

. Most crashes are the result of a software bug. Typical causes include accessing invalid memory addresses, incorrect

address An address is a collection of information, presented in a mostly fixed format, used to give the location of a building, apartment, or other structure or a plot of land, generally using political boundaries and street names as references, along ...

values in the program counter,

buffer overflow In information security and programming, a buffer overflow, or buffer overrun, is an anomaly whereby a program, while writing data to a buffer, overruns the buffer's boundary and overwrites adjacent memory locations. Buffers are areas of memo ...

, overwriting a portion of the affected program code due to an earlier bug, executing invalid machine instructions (an

illegal opcode An illegal opcode, also called an unimplemented operation, unintended opcode or undocumented instruction, is an instruction to a CPU that is not mentioned in any official documentation released by the CPU's designer or manufacturer, which nev ...

), or triggering an unhandled exception. The original software bug that started this chain of events is typically considered to be the cause of the crash, which is discovered through the process of debugging. The original bug can be far removed from the code that actually triggered the crash. In early personal computers, attempting to write data to hardware addresses outside the system's main memory could cause hardware damage. Some crashes are exploitable and let a malicious program or

hacker A hacker is a person skilled in information technology who uses their technical knowledge to achieve a goal or overcome an obstacle, within a computerized system by non-standard means. Though the term ''hacker'' has become associated in popu ...

execute

arbitrary code In computer security, arbitrary code execution (ACE) is an attacker's ability to run any commands or code of the attacker's choice on a target machine or in a target process. An arbitrary code execution vulnerability is a security flaw in softwa ...

allowing the replication of viruses or the acquisition of data which would normally be inaccessible.

Application crashes

An application typically crashes when it performs an operation that is not allowed by the operating system. The operating system then triggers an exception or

signal In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...

in the application. Unix applications traditionally responded to the signal by dumping core. Most Windows and Unix GUI applications respond by displaying a dialogue box (such as the one shown to the right) with the option to attach a

debugger A debugger or debugging tool is a computer program used to test and debug other programs (the "target" program). The main use of a debugger is to run the target program under controlled conditions that permit the programmer to track its executi ...

if one is installed. Some applications attempt to recover from the error and continue running instead of exiting. An application can also contain code to crash after detecting a severe error. Typical errors that result in application crashes include: *attempting to read or write memory that is not allocated for reading or writing by that application (e.g.,

segmentation fault In computing, a segmentation fault (often shortened to segfault) or access violation is a fault, or failure condition, raised by hardware with memory protection, notifying an operating system (OS) the software has attempted to access a restrict ...

, x86-specific

general protection fault A general protection fault (GPF) in the x86 instruction set architectures (ISAs) is a fault (a type of interrupt) initiated by ISA-defined protection mechanisms in response to an access violation caused by some running code, either in the kernel ...

) *attempting to execute privileged or invalid instructions *attempting to perform I/O operations on hardware devices to which it does not have permission to access *passing invalid arguments to system calls *attempting to access other system resources to which the application does not have permission to access *attempting to execute machine instructions with bad arguments (depending on CPU architecture): divide by zero, operations on

denormal number In computer science, subnormal numbers are the subset of denormalized numbers (sometimes called denormals) that fill the underflow gap around zero in floating-point arithmetic. Any non-zero number with magnitude smaller than the smallest normal ...

NaN Nan or NAN may refer to: Places China * Nan County, Yiyang, Hunan, China * Nan Commandery, historical commandery in Hubei, China Thailand * Nan Province ** Nan, Thailand, the administrative capital of Nan Province * Nan River People Given name ...

(not a number) values, memory access to unaligned addresses, etc.

Crash to desktop

A "crash to desktop" is said to occur when a program (commonly a video game) unexpectedly quits, abruptly taking the user back to the

desktop A desktop traditionally refers to: * The surface of a desk (often to distinguish office appliances that fit on a desk, such as photocopiers and printers, from larger equipment covering its own area on the floor) Desktop may refer to various compu ...

. Usually, the term is applied only to crashes where no error is displayed, hence all the user sees as a result of the crash is the desktop. Many times there is no apparent action that causes a crash to desktop. During normal function, the program may freeze for a shorter period of time, and then close by itself. Also during normal function, the program may become a black screen and repeatedly play the last few seconds of

sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' b ...

(depending on the size of the audio

buffer Buffer may refer to: Science * Buffer gas, an inert or nonflammable gas * Buffer solution, a solution used to prevent changes in pH * Buffering agent, the weak acid or base in a buffer solution * Lysis buffer, in cell biology * Metal ion buffer * ...

) that was being played before it crashes to desktop. Other times it may appear to be triggered by a certain action, such as loading an area. Crash to desktop bugs are considered particularly problematic for users. Since they frequently display no error message, it can be very difficult to track down the source of the problem, especially if the times they occur and the actions taking place right before the crash do not appear to have any pattern or common ground. One way to track down the source of the problem for games is to run them in windowed-mode. Windows Vista has a feature that can help track down the cause of a CTD problem when it occurs on any program. Windows XP included a similar feature as well. Some computer programs, such as '' StepMania'' and BBC's '' Bamzooki'', also crash to desktop if in full-screen, but display the error in a separate window when the user has returned to the desktop.

Web server crashes

The software running the web server behind a website may crash, rendering it inaccessible entirely or providing only an error message instead of normal content. For example: if a site is using an SQL database (such as MySQL) for a script (such as PHP) and that SQL database server crashes, then PHP will display a connection error.

Operating system crashes

An operating system crash commonly occurs when a

hardware exception In computing and computer programming, exception handling is the process of responding to the occurrence of ''exceptions'' – anomalous or exceptional conditions requiring special processing – during the execution of a program. In general, an ...

occurs that cannot be handled. Operating system crashes can also occur when internal sanity-checking logic within the operating system detects that the operating system has lost its internal self-consistency. Modern multi-tasking operating systems, such as

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, w ...

, and macOS, usually remain unharmed when an application program crashes. Some operating systems, e.g.,

z/OS z/OS is a 64-bit operating system for IBM z/Architecture mainframes, introduced by IBM in October 2000. It derives from and is the successor to OS/390, which in turn was preceded by a string of MVS versions.Starting with the earliest: * ...

, have facilities for Reliability, availability and serviceability (RAS) and the OS can recover from the crash of a critical component, whether due to hardware failure, e.g., uncorrectable ECC error, or to software failure, e.g., a reference to an unassigned page.

Security and privacy implications of crashes

Depending on the application, the crash may contain the user's sensitive and private information. Moreover, many software bugs which cause crashes are also exploitable for

arbitrary code execution In computer security, arbitrary code execution (ACE) is an attacker's ability to run any commands or code of the attacker's choice on a target machine or in a target process. An arbitrary code execution vulnerability is a security flaw in softw ...

and other types of

privilege escalation Privilege escalation is the act of exploiting a bug, a design flaw, or a configuration oversight in an operating system or software application to gain elevated access to resources that are normally protected from an application or user. The re ...

. For example, a

stack buffer overflow In software, a stack buffer overflow or stack buffer overrun occurs when a program writes to a memory address on the program's call stack outside of the intended data structure, which is usually a fixed-length buffer. Stack buffer overflow bugs ...

can overwrite the return address of a subroutine with an invalid value, which will cause, e.g., a

, when the subroutine returns. However, if an exploit overwrites the return address with a valid value, the code in that address will be executed.

Crash reproduction

When crashes are collected in the field using a crash reporter, the next step for developers is to be able to reproduce them locally. For this, several techniques exist: STAR uses symbolic execution, MuCrash mutates the test code of the application that has crashed, and EvoCrash performs evolutionary search.

Notes

References

External links

Picking Up The Pieces After A Computer Crash
{{DEFAULTSORT:Crash (Computing) Computer jargon Computer errors Software anomalies