Exit status
Encyclopedia
The exit status or return code of a process in computer programming
is a small number passed from a child process
(or callee) to a parent process
(or caller) when it has finished executing a specific procedure or delegated task. In DOS
, this may be referred to as an errorlevel.
When software programs are run or executed, the operating system
creates an abstract entity called a computer process in which all the book-keeping for that program is accomplished. In multitasking operating systems such as UNIX
or Linux
, new processes can be created by active processes. Such processes are parent processes while those created are child processes. It is common in programming for a parent process to delegate some work to a child process it creates while it may remain busy with something else. When the child has finished executing, it will exit by calling the exit
system call
. This system call facilitates passing a small number back to the parent, which can retrieve this value using the wait
system call. This is the exit status of the child.
may also be available to the parent process.
The specific set of codes returned is unique to the program that sets it. Typically it indicates success or failure. The value of the code returned by the function or program may indicate a specific cause of failure. On many systems, the higher the value, the more severe the cause of the error. Alternatively, each bit may indicate a different condition, which are then ored together to give the final value; for example, fsck
does this.
Sometimes, if the codes are designed with this purpose in mind, they can be used directly as a branch index upon return to the initiating program to avoid additional tests.
programming language allows programs exiting or returning from the main function to signal success or failure by returning an integer, or returning the macros
, the
), SUS specifies that the low-order 8 bits of the status value contain the exit status; this can be retrieved using the WEXITSTATUS macro in wait.h. As such, on Unix exit statuses are restricted to values 0-255, the range of an unsigned 8-bit integer.
Unix-like systems typically use a convention of zero for success and non zero for error. Some conventions have developed as to the relative meanings of various error codes; for example GNU recommend that codes with the high bit set be reserved for serious errors, and FreeBSD have documented an extensive set of preferred interpretations.
exit code
returned by an executable program
or subroutine
. Errorlevels typically range from 0 to 255. In DOS
there are only 256 error codes available.
success is indicated by odd values and failure by even values.
The value is a 32 bit integer with sub-fields: control bits, facility number, message number and severity. Severity values are divided between success (Success, Informational) and failure (Warning, Error, Fatal).OpenVMS Format of Return Status Values
uses 32-bit signed integers as exit codes. If a process fails initialization, a Windows system error code may be returned. Windows system error codes are available online.
Exit codes are directly referenced, for example, by the command line interpreter CMD.exe in the
. .NET Framework
processes and the Windows PowerShell
refer to it as the
Computer programming
Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...
is a small number passed from a child process
Child process
A child process in computing is a process created by another process .A child process inherits most of its attributes, such as open files, from its parent. In UNIX, a child process is in fact created as a copy of the parent...
(or callee) to a parent process
Parent process
In computing, a parent process is a process that has created one or more child processes.- Unix :In the operating system Unix, every process except is created when another process executes the fork system call. The process that invoked fork is the parent process and the newly-created process is...
(or caller) when it has finished executing a specific procedure or delegated task. In DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
, this may be referred to as an errorlevel.
When software programs are run or executed, the operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
creates an abstract entity called a computer process in which all the book-keeping for that program is accomplished. In multitasking operating systems such as UNIX
Unix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
or Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, new processes can be created by active processes. Such processes are parent processes while those created are child processes. It is common in programming for a parent process to delegate some work to a child process it creates while it may remain busy with something else. When the child has finished executing, it will exit by calling the exit
Exit (operating system)
On many computer operating systems, a computer process terminates its execution by making an exit system call. More generally, an exit in a multithreading environment means that a thread of execution has stopped running. The operating system reclaims resources that were used by the process...
system call
System call
In computing, a system call is how a program requests a service from an operating system's kernel. This may include hardware related services , creating and executing new processes, and communicating with integral kernel services...
. This system call facilitates passing a small number back to the parent, which can retrieve this value using the wait
Wait (operating system)
In modern computer operating systems, a process may wait on another process to complete its execution. In most systems, a parent process can create an independently executing child process. The parent process may then issue a wait system call, which suspends the execution of the parent process...
system call. This is the exit status of the child.
Semantics
The parent and the child can have an understanding about the meaning of the exit statuses. For example, it is common programming practice for a child process to return zero to the parent signifying success. Apart from this return value from the child, other information like how the process exited, either normally or by a signalSignal (computing)
A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...
may also be available to the parent process.
The specific set of codes returned is unique to the program that sets it. Typically it indicates success or failure. The value of the code returned by the function or program may indicate a specific cause of failure. On many systems, the higher the value, the more severe the cause of the error. Alternatively, each bit may indicate a different condition, which are then ored together to give the final value; for example, fsck
Fsck
The system utility fsck is a tool for checking the consistency of a file system in Unix and Unix-like operating systems such as Linux.-Use:...
does this.
Sometimes, if the codes are designed with this purpose in mind, they can be used directly as a branch index upon return to the initiating program to avoid additional tests.
C
The CC (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
programming language allows programs exiting or returning from the main function to signal success or failure by returning an integer, or returning the macros
EXIT_SUCCESS and EXIT_FAILURE. On Unix-like systems these evaluate to 0 and 1 respectively. A C program may also use the exit function specifying the integer status or exit macro as the first parameter. The status may be an integer between 0 and 255 and should follow any existing conventions for programs of its type, however typically 0 indicates success and 1 indicates failure.Java
In Java, any method can callSystem.exit(int status), unless a security manager does not permit it. This will terminate the currently running Java Virtual Machine. "The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination." (int status is the errorlevel.)Unix
In UnixUnix
Unix is a multitasking, multi-user computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs, including Ken Thompson, Dennis Ritchie, Brian Kernighan, Douglas McIlroy, and Joe Ossanna...
, the
wait system call sets a status value of type int packed as a bitfield with various types of child termination information. If the child terminated by exiting (as determined by the WIFEXITED macro; the usual alternative being that it died from an uncaught signalSignal (computing)
A signal is a limited form of inter-process communication used in Unix, Unix-like, and other POSIX-compliant operating systems. Essentially it is an asynchronous notification sent to a process in order to notify it of an event that occurred. When a signal is sent to a process, the operating system...
), SUS specifies that the low-order 8 bits of the status value contain the exit status; this can be retrieved using the WEXITSTATUS macro in wait.h. As such, on Unix exit statuses are restricted to values 0-255, the range of an unsigned 8-bit integer.
Unix-like systems typically use a convention of zero for success and non zero for error. Some conventions have developed as to the relative meanings of various error codes; for example GNU recommend that codes with the high bit set be reserved for serious errors, and FreeBSD have documented an extensive set of preferred interpretations.
DOS
In DOS terminology, an errorlevel is an integerInteger
The integers are formed by the natural numbers together with the negatives of the non-zero natural numbers .They are known as Positive and Negative Integers respectively...
exit code
Code
A code is a rule for converting a piece of information into another form or representation , not necessarily of the same type....
returned by an executable program
Executable
In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...
or subroutine
Subroutine
In computer science, a subroutine is a portion of code within a larger program that performs a specific task and is relatively independent of the remaining code....
. Errorlevels typically range from 0 to 255. In DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
there are only 256 error codes available.
OpenVMS
In OpenVMSOpenVMS
OpenVMS , previously known as VAX-11/VMS, VAX/VMS or VMS, is a computer server operating system that runs on VAX, Alpha and Itanium-based families of computers. Contrary to what its name suggests, OpenVMS is not open source software; however, the source listings are available for purchase...
success is indicated by odd values and failure by even values.
The value is a 32 bit integer with sub-fields: control bits, facility number, message number and severity. Severity values are divided between success (Success, Informational) and failure (Warning, Error, Fatal).OpenVMS Format of Return Status Values
Windows
WindowsMicrosoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
uses 32-bit signed integers as exit codes. If a process fails initialization, a Windows system error code may be returned. Windows system error codes are available online.
Exit codes are directly referenced, for example, by the command line interpreter CMD.exe in the
errorlevel terminology inherited from DOSDOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
. .NET Framework
.NET Framework
The .NET Framework is a software framework that runs primarily on Microsoft Windows. It includes a large library and supports several programming languages which allows language interoperability...
processes and the Windows PowerShell
Windows PowerShell
Windows PowerShell is Microsoft's task automation framework, consisting of a command-line shell and associated scripting language built on top of, and integrated with the .NET Framework...
refer to it as the
ExitCode property of the Process object.