exit, atexit, _exit - Terminate a process
#include <stdlib.h>
int atexit(
void (*function)(void) ); void exit(
int status ); #include <unistd.h>
void _exit(
int status );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
exit(), _exit(), atexit(): XSH4.0, XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Indicates the status of the process. Points to a function
that is called at normal process termination for cleanup
processing. The number of exit handlers that can be specified
with the atexit() function is limited by the amount
of available virtual memory.
The atexit() function registers functions to be called at
normal process termination for cleanup processing. The
function adds a single exit handler to a list of handlers
to be called at process termination. The system calls the
functions in reverse order, calling the function at the
top of the list first. Any function that is registered
more than once will be repeated.
The exit() function terminates the calling process after
calling the _cleanup() function to flush any buffered output.
Then it calls any functions registered previously for
the process by the atexit() function, in the reverse order
to that in which they were registered. In addition, the
exit() function flushes all open output streams, closes
all open streams, and removes all files created by the
tmpfile() function. Finally, it calls the _exit() function,
which completes process termination and does not
return.
The _exit() and exit() functions terminate the calling
process and cause the following to occur: All of the file
descriptors and directory streams open in the calling process
are closed. Since the exit() function terminates the
process, any errors encountered during these close operations
go unreported. Message catalog descriptors and conversion
descriptors opened in the calling process are also
closed with no reporting of errors. The parent process ID
of all the calling process' existing child processes and
zombie processes is reset. The child processes continue
executing; however, their parent process ID is set to the
process ID of the init process. The init process thus
adopts each of these processes, catches the SIGCHLD signals
that they generate, and calls the wait() function for
each of them. If the parent process of the calling process
is running a wait() or waitpid() function, that parent
process is notified that the calling process is being
terminated. The low-order 8 bits (that is, bits 0377 or
0xFF) of the status parameter are made available to the
parent process.
[XSH4.2] [XSH5.0] This behavior also applies if
the parent process is running a wait3() or waitid()
function. In addition, this behavior only applies
when the parent process of the calling process has
neither set its SA_NOCLDWAIT flag nor set SIGCHLD
to SIG_IGN. If the parent process is not running a
wait() or waitpid() function when the child process
terminates, the parent process receives a SIGCHLD
signal to notify it that the child process is terminating.
The child process is transformed into a
zombie process.
Once the parent process calls the wait() or waitpid()
routine, the child process completes termination
and the low-order 8 bits (that is, bits 0377
or 0xFF) of the status parameter are made available
to it.
[XSH4.2] [XSH5.0] This behavior also applies to
the wait3() and waitid() functions. In addition,
this behavior only applies when the parent process
has not set its SA_NOCLDWAIT flag or set SIGCHLD to
SIG_IGN. The parent process is sent a SIGCHLD signal
when a child terminates; however, since the
default action for this signal is to ignore it, the
signal usually is not seen. If the process is a
controlling process, the system sends a SIGHUP signal
to each process executing in the foreground on
the terminal that belongs to the calling process.
The terminal is disassociated from the session,
allowing it to be acquired by a new controlling
process. If the termination of a process causes a
process group to become orphaned, and if any member
of the newly orphaned process group is stopped, a
SIGHUP signal, followed by a SIGCONT signal, is
sent to each newly orphaned process.
[XSH4.2] [XSH5.0] If the parent process has set
its SA_NOCLDWAIT flag or set SIGCHLD to SIG_IGN,
the status is discarded, and the lifetime of the
calling process ends immediately.
[XSH4.2] [XSH5.0] Each mapped memory object is
unmapped. Each attached shared memory segment is
detached and the value of shm_nattach in the data
structure associated with its shared memory identifier
is decremented by 1. (See shmget(2) for information
about the data structure.) For each
semaphore for which the calling process has set a
semadj value, that semadj value is added to the
semval of the specified semaphore. (See semop(2)for
information about semaphore operations.) [Tru64
UNIX] If the process has a process lock, text
lock, or data lock, an unlock() is performed. (See
plock(2) for information on locking.) [Tru64
UNIX] An accounting record is written to the
accounting file if the system accounting routine is
enabled. (See acct(2) for information about
enabling accounting routines.) [Tru64 UNIX] Locks
set by the fcntl(), flock(), and lockf() functions
are removed.
[Tru64 UNIX] If a thread calls the _exit() function, the
entire process exits and all threads within the process
are terminated.
[XSH4.2] [XSH5.0] An application should call sysconf()
to obtain the value of ATEXIT_MAX, the number of handlers
that can be registered. There is no way for an application
to tell how many functions have already been registered
with atexit().
To prematurely terminate atexit() handler processing from
within a handler, _exit() can be called. It is not recommended
to call exit() from within an atexit() handler.
The exit() function and _exit() function do not return.
The atexit() function returns 0 (zero) if successful. The
function fails if an application attempts to register more
process cleanup functions than available virtual memory
allows. In this case, the function returns a nonzero
value.
Functions: acct(2), sigaction(2), sigvec(2), wait(2),
ldr_atexit(3), times(3)
Standards: standards(5)
exit(2)
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