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man pages section 2: System Calls

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Updated: Thursday, June 13, 2019
 
 

_Exit(2)

Name

exit, quick_exit, _Exit, _exit - terminate process

Synopsis

#include <stdlib.h>
void exit(int status);
void quick_exit(int status);
void _Exit(int status);
#include <unistd.h>
void _exit(int status);

Description

A call to exit() results in normal program termination. The exit() function first calls all functions registered by atexit(3C), in the reverse order of their registration, except that a function is called after any previously registered functions that had already been called at the time it was registered. Each function is called as many times as it was registered. If, during the call to any such function, a call to the longjmp(3C) function is made that would terminate the call to the registered function, the behavior is undefined.

If a function registered by a call to atexit(3C) fails to return, the remaining registered functions are not called and the rest of the exit() processing is not completed. If exit() is called more than once, the effects are undefined.

The exit() function then flushes all open streams with unwritten buffered data, closes all open streams, and removes all files created by tmpfile(3C).

Finally, control is returned to the host environment by means of the function call _Exit(status).

The quick_exit() function, and the related at_quick_exit(3C) function are specified in the C11 standard. The quick_exit() function is similar to the exit() function except that no open streams are flushed or closed when control is returned to the host environment. See INCITS/ISO/IEC 9899:2011.

The _Exit() and _exit() functions are functionally equivalent. They do not call functions registered with atexit(3C) or at_quick_exit(3C), do not call any registered signal handlers, and do not flush open streams.

The _exit(), _Exit(), and exit() functions terminate the calling process with the following consequences:

  • All of the file descriptors, directory streams, conversion descriptors and message catalogue descriptors open in the calling process are closed.

  • If the parent process of the calling process is executing a wait(3C), wait3(3C), waitid(2), or waitpid(3C), and has neither set its SA_NOCLDWAIT flag nor set SIGCHLD to SIG_IGN, it is notified of the calling process's termination and the low-order eight bits (that is, bits 0377) of status are made available to it. If the parent is not waiting, the child's status will be made available to it when the parent subsequently executes wait(), wait3(), waitid(), or waitpid().

  • If the parent process of the calling process is not executing a wait(), wait3(), waitid(), or waitpid(), and has not set its SA_NOCLDWAIT flag, or set SIGCHLD to SIG_IGN, the calling process is transformed into a zombie process. A zombie process is an inactive process and it will be deleted at some later time when its parent process executes wait(), wait3(), waitid(), or waitpid(). A zombie process only occupies a slot in the process table; it has no other space allocated either in user or kernel space. The process table slot that it occupies is partially overlaid with time accounting information (see <sys/proc.h>) to be used by the times(2) function.

  • Termination of a process does not directly terminate its children. The sending of a SIGHUP signal as described below indirectly terminates children in some circumstances.

  • A SIGCHLD will be sent to the parent process.

  • The parent process ID of all of the calling process's existing child processes and zombie processes is set to 1. That is, these processes are inherited by the initialization process (see Intro(2)).

  • Each mapped memory object is unmapped.

  • Each attached shared-memory segment is detached and the value of shm_nattch (see shmget(2)) in the data structure associated with its shared memory ID is decremented by 1.

  • For each semaphore for which the calling process has set a semadj value (see semop(2)), that value is added to the semval of the specified semaphore.

  • If the process is a controlling process, the SIGHUP signal will be sent to each process in the foreground process group of the controlling terminal belonging to the calling process.

  • If the process is a controlling process, the controlling terminal associated with the session is disassociated from the session, allowing it to be acquired by a new controlling process.

  • If the exit of the process causes a process group to become orphaned, and if any member of the newly-orphaned process group is stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent to each process in the newly-orphaned process group.

  • If the parent process has set its SA_NOCLDWAIT flag, or set SIGCHLD to SIG_IGN, the status will be discarded, and the lifetime of the calling process will end immediately.

  • If the process has process, text or data locks, an UNLOCK is performed (see plock(3C) and memcntl(2)).

  • All open named semaphores in the process are closed as if by appropriate calls to sem_close(3C). All open message queues in the process are closed as if by appropriate calls to mq_close(3C). Any outstanding asynchronous I/O operations may be cancelled.

  • An accounting record is written on the accounting file if the system's accounting routine is enabled (see acct(2)).

  • An extended accounting record is written to the extended process accounting file if the system's extended process accounting facility is enabled (see acctadm(8)).

  • If the current process is the last process within its task and if the system's extended task accounting facility is enabled (see acctadm(8)), an extended accounting record is written to the extended task accounting file.

Return Values

These functions do not return.

Errors

No errors are defined.

Usage

Normally applications should use exit() rather than _exit().

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
MT-Level
See below.
Standard

The _exit() and _Exit() functions are Async-Signal-Safe.

See Also

acct(2), close(2), Intro(2), memcntl(2), semop(2), shmget(2), sigaction(2), times(2), waitid(2), at_quick_exit(3C), atexit(3C), fclose(3C), mq_close(3C), plock(3C), tmpfile(3C), wait(3C), wait3(3C), waitpid(3C), signal.h(3HEAD), attributes(7), standards(7), acctadm(8)