man-pages/man3p/exit.3p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "EXIT" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" exit 
.SH NAME
exit, _Exit, _exit \- terminate a process
.SH SYNOPSIS
.LP
\fB#include <stdlib.h>
.br
.sp
void exit(int\fP \fIstatus\fP\fB);
.br
void _Exit(int\fP \fIstatus\fP\fB);
.br
.sp
.sp
#include <unistd.h>
.br
void _exit(int\fP \fIstatus\fP\fB);
.br
\fP
.SH DESCRIPTION
.LP
For \fIexit\fP() and \fI_Exit\fP():   The functionality described
on this reference page is aligned with the
ISO\ C standard. Any conflict between the requirements described here
and the ISO\ C standard is unintentional. This volume
of IEEE\ Std\ 1003.1-2001 defers to the ISO\ C standard. 
.LP
The value of \fIstatus\fP may be 0, EXIT_SUCCESS, EXIT_FAILURE,  
\ or any other value, though only the least significant 8 bits
(that is, \fIstatus\fP & 0377) shall be available to a waiting parent
process. 
.LP
The \fIexit\fP() function shall first call all functions registered
by \fIatexit\fP(),
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 \fIlongjmp\fP() function is made
that would terminate
the call to the registered function, the behavior is undefined.
.LP
If a function registered by a call to \fIatexit\fP() fails to return,
the remaining
registered functions shall not be called and the rest of the \fIexit\fP()
processing shall not be completed. If \fIexit\fP() is
called more than once, the behavior is undefined.
.LP
The \fIexit\fP() function shall then flush all open streams with unwritten
buffered data, close all open streams, and remove
all files created by \fItmpfile\fP(). Finally, control shall be terminated
with the
consequences described below.
.LP
The
\fI_Exit\fP() and \fI_exit\fP() functions shall be functionally equivalent.
.LP
The \fI_Exit\fP()   \ and \fI_exit\fP()  functions
shall not call functions registered with \fIatexit\fP() nor any registered
signal handlers.
Whether open streams are flushed or closed, or temporary files are
removed is implementation-defined. Finally, the calling process
is terminated with the consequences described below.
.LP
These functions shall terminate the calling process   \ with the following
consequences:  
.TP 7
\fBNote:\fP
These consequences are all extensions to the ISO\ C standard and are
not further CX shaded. However, XSI extensions are
shaded.
.sp
.IP " *" 3
All of the file descriptors, directory streams,   \ conversion descriptors,
and message catalog descriptors  \ open in the calling process shall
be closed.
.LP
.IP " *" 3
If the parent process of the calling process is executing a \fIwait\fP()
or \fIwaitpid\fP(),   \ and has neither set its SA_NOCLDWAIT flag
nor set SIGCHLD to
SIG_IGN,  it shall be notified of the calling process' termination
and the low-order eight bits (that is, bits 0377) of \fIstatus\fP
shall be made available to it. If the parent is not waiting, the
child's status shall be made available to it when the parent subsequently
executes \fIwait\fP() or \fIwaitpid\fP().
.LP
The semantics of the \fIwaitid\fP() function shall be equivalent to
\fIwait\fP(). 
.LP
.IP " *" 3
If the parent process of the calling process is not executing a \fIwait\fP()
or \fIwaitpid\fP(),   \ and has neither set its SA_NOCLDWAIT flag
nor set SIGCHLD to
SIG_IGN,  the calling process shall be transformed into a \fIzombie
process\fP. A \fIzombie process\fP is an inactive process and it shall
be deleted at some later time when its parent process
executes \fIwait\fP() or \fIwaitpid\fP().
.LP
The semantics of the \fIwaitid\fP() function shall be equivalent to
\fIwait\fP(). 
.LP
.IP " *" 3
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.
.LP
.IP " *" 3
Either:
.LP
If the implementation supports the SIGCHLD signal, a SIGCHLD shall
be sent to the parent process.
.LP
Or:
.LP
If the parent process has set its SA_NOCLDWAIT flag, or set SIGCHLD
to SIG_IGN, the status shall be discarded, and the lifetime of
the calling process shall end immediately. If SA_NOCLDWAIT is set,
it is implementation-defined whether a SIGCHLD signal is sent to
the parent process. 
.LP
.IP " *" 3
The parent process ID of all of the calling process' existing child
processes and zombie processes shall be set to the process
ID of an implementation-defined system process. That is, these processes
shall be inherited by a special system process.
.LP
.IP " *" 3
Each attached shared-memory segment is detached and the value of \fIshm_nattch\fP
(see \fIshmget\fP()) in the data structure associated with its shared
memory ID shall be decremented by
1. 
.LP
.IP " *" 3
For each semaphore for which the calling process has set a \fIsemadj\fP
value (see \fIsemop\fP() ), that
value shall be added to the \fIsemval\fP of the specified semaphore.
.LP
.IP " *" 3
If the process is a controlling process, the SIGHUP signal shall be
sent to each process in the foreground process group of the
controlling terminal belonging to the calling process.
.LP
.IP " *" 3
If the process is a controlling process, the controlling terminal
associated with the session shall be disassociated from the
session, allowing it to be acquired by a new controlling process.
.LP
.IP " *" 3
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 shall be
sent to each process in the newly-orphaned process group.
.LP
.IP " *" 3
All open named semaphores in the calling process shall be closed as
if by appropriate calls to \fIsem_close\fP(). 
.LP
.IP " *" 3
Any
memory locks established by the process via calls to \fImlockall\fP()
or \fImlock\fP() shall be removed. If locked pages in the address
space of the calling process are also
mapped into the address spaces of other processes and are locked by
those processes, the locks established by the other processes
shall be unaffected by the call by this process to \fI_Exit\fP() or
\fI_exit\fP(). 
.LP
.IP " *" 3
Memory mappings that were created in the process shall be unmapped
before the process is destroyed. 
.LP
.IP " *" 3
Any blocks of typed memory that were mapped in the calling process
shall be unmapped, as if \fImunmap\fP() was implicitly called to unmap
them. 
.LP
.IP " *" 3
All open message queue descriptors in the calling process shall be
closed as if by appropriate calls to \fImq_close\fP(). 
.LP
.IP " *" 3
Any outstanding cancelable asynchronous I/O operations may be canceled.
Those asynchronous I/O operations that are not canceled
shall complete as if the \fI_Exit\fP() or \fI_exit\fP() operation
had not yet occurred, but any associated signal notifications
shall be suppressed. The \fI_Exit\fP() or \fI_exit\fP() operation
may block awaiting such I/O completion. Whether any I/O is
canceled, and which I/O may be canceled upon \fI_Exit\fP() or \fI_exit\fP(),
is implementation-defined. 
.LP
.IP " *" 3
Threads terminated by a call to \fI_Exit\fP() or \fI_exit\fP() shall
not invoke their cancellation cleanup handlers or
per-thread data destructors.
.LP
.IP " *" 3
If the calling process is a trace controller process, any trace streams
that were created by the calling process shall be shut down
as described by the \fIposix_trace_shutdown\fP() function, and any
process'
mapping of trace event names to trace event type identifiers built
for these trace streams may be deallocated. 
.LP
.SH RETURN VALUE
.LP
These functions do not return.
.SH ERRORS
.LP
No errors are defined.
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
Normally applications should use \fIexit\fP() rather than \fI_Exit\fP()
or \fI_exit\fP().
.SH RATIONALE
.SS Process Termination
.LP
Early proposals drew a distinction between normal and abnormal process
termination. Abnormal termination was caused only by
certain signals and resulted in implementation-defined "actions",
as discussed below. Subsequent proposals distinguished three
types of termination: \fInormal termination\fP (as in the current
specification), \fIsimple abnormal termination\fP, and
\fIabnormal termination with actions\fP. Again the distinction between
the two types of abnormal termination was that they were
caused by different signals and that implementation-defined actions
would result in the latter case. Given that these actions were
completely implementation-defined, the early proposals were only saying
when the actions could occur and how their occurrence could
be detected, but not what they were. This was of little or no use
to conforming applications, and thus the distinction is not made
in this volume of IEEE\ Std\ 1003.1-2001.
.LP
The implementation-defined actions usually include, in most historical
implementations, the creation of a file named \fBcore\fP
in the current working directory of the process. This file contains
an image of the memory of the process, together with
descriptive information about the process, perhaps sufficient to reconstruct
the state of the process at the receipt of the
signal.
.LP
There is a potential security problem in creating a \fBcore\fP file
if the process was set-user-ID and the current user is not
the owner of the program, if the process was set-group-ID and none
of the user's groups match the group of the program, or if the
user does not have permission to write in the current directory. In
this situation, an implementation either should not create a
\fBcore\fP file or should make it unreadable by the user.
.LP
Despite the silence of this volume of IEEE\ Std\ 1003.1-2001 on this
feature, applications are advised not to create
files named \fBcore\fP because of potential conflicts in many implementations.
Some implementations use a name other than
\fBcore\fP for the file; for example, by appending the process ID
to the filename.
.SS Terminating a Process
.LP
It is important that the consequences of process termination as described
occur regardless of whether the process called
\fI_exit\fP() (perhaps indirectly through \fIexit\fP()) or instead
was terminated due to a signal or for some other reason. Note
that in the specific case of \fIexit\fP() this means that the \fIstatus\fP
argument to \fIexit\fP() is treated in the same way
as the \fIstatus\fP argument to \fI_exit\fP().
.LP
A language other than C may have other termination primitives than
the C-language \fIexit\fP() function, and programs written
in such a language should use its native termination primitives, but
those should have as part of their function the behavior of
\fI_exit\fP() as described. Implementations in languages other than
C are outside the scope of this version of this volume of
IEEE\ Std\ 1003.1-2001, however.
.LP
As required by the ISO\ C standard, using \fBreturn\fP from \fImain\fP()
has the same behavior (other than with respect to
language scope issues) as calling \fIexit\fP() with the returned value.
Reaching the end of the \fImain\fP() function has the
same behavior as calling \fIexit\fP(0).
.LP
A value of zero (or EXIT_SUCCESS, which is required to be zero) for
the argument \fIstatus\fP conventionally indicates
successful termination. This corresponds to the specification for
\fIexit\fP() in the ISO\ C standard. The convention is
followed by utilities such as \fImake\fP and various shells, which
interpret a zero status
from a child process as success. For this reason, applications should
not call \fIexit\fP(0) or \fI_exit\fP(0) when they
terminate unsuccessfully; for example, in signal-catching functions.
.LP
Historically, the implementation-defined process that inherits children
whose parents have terminated without waiting on them is
called \fIinit\fP and has a process ID of 1.
.LP
The sending of a SIGHUP to the foreground process group when a controlling
process terminates corresponds to somewhat different
historical implementations. In System V, the kernel sends a SIGHUP
on termination of (essentially) a controlling process. In 4.2
BSD, the kernel does not send SIGHUP in a case like this, but the
termination of a controlling process is usually noticed by a
system daemon, which arranges to send a SIGHUP to the foreground process
group with the \fIvhangup\fP() function. However, in 4.2
BSD, due to the behavior of the shells that support job control, the
controlling process is usually a shell with no other processes
in its process group. Thus, a change to make \fI_exit\fP() behave
this way in such systems should not cause problems with existing
applications.
.LP
The termination of a process may cause a process group to become orphaned
in either of two ways. The connection of a process
group to its parent(s) outside of the group depends on both the parents
and their children. Thus, a process group may be orphaned
by the termination of the last connecting parent process outside of
the group or by the termination of the last direct descendant
of the parent process(es). In either case, if the termination of a
process causes a process group to become orphaned, processes
within the group are disconnected from their job control shell, which
no longer has any information on the existence of the process
group. Stopped processes within the group would languish forever.
In order to avoid this problem, newly orphaned process groups
that contain stopped processes are sent a SIGHUP signal and a SIGCONT
signal to indicate that they have been disconnected from
their session. The SIGHUP signal causes the process group members
to terminate unless they are catching or ignoring SIGHUP. Under
most circumstances, all of the members of the process group are stopped
if any of them are stopped.
.LP
The action of sending a SIGHUP and a SIGCONT signal to members of
a newly orphaned process group is similar to the action of 4.2
BSD, which sends SIGHUP and SIGCONT to each stopped child of an exiting
process. If such children exit in response to the SIGHUP,
any additional descendants receive similar treatment at that time.
In this volume of IEEE\ Std\ 1003.1-2001, the signals
are sent to the entire process group at the same time. Also, in this
volume of IEEE\ Std\ 1003.1-2001, but not in 4.2 BSD,
stopped processes may be orphaned, but may be members of a process
group that is not orphaned; therefore, the action taken at
\fI_exit\fP() must consider processes other than child processes.
.LP
It is possible for a process group to be orphaned by a call to \fIsetpgid\fP()
or \fIsetsid\fP(), as well as by process termination. This volume
of
IEEE\ Std\ 1003.1-2001 does not require sending SIGHUP and SIGCONT
in those cases, because, unlike process termination,
those cases are not caused accidentally by applications that are unaware
of job control. An implementation can choose to send
SIGHUP and SIGCONT in those cases as an extension; such an extension
must be documented as required in \fI<signal.h>\fP.
.LP
The ISO/IEC\ 9899:1999 standard adds the \fI_Exit\fP() function that
results in immediate program termination without
triggering signals or \fIatexit\fP()-registered functions. In
IEEE\ Std\ 1003.1-2001, this is equivalent to the \fI_exit\fP() function.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIatexit\fP() , \fIclose\fP() , \fIfclose\fP()
, \fIlongjmp\fP() , \fIposix_trace_shutdown\fP() , \fIposix_trace_trid_eventid_open\fP()
, \fIsemop\fP() , \fIshmget\fP() , \fIsigaction\fP() , \fIwait\fP()
,
\fIwaitid\fP() , \fIwaitpid\fP() , the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<stdlib.h>\fP, \fI<unistd.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .