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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <meta name="generator" content="HTML Tidy, see www.w3.org"> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <link type="text/css" rel="stylesheet" href="style.css"> <!-- Generated by The Open Group's rhtm tool v1.2.1 --> <!-- Copyright (c) 2001-2004 IEEE and The Open Group, All Rights Reserved --> <title>exit</title> </head> <body bgcolor="white"> <script type="text/javascript" language="JavaScript" src="../jscript/codes.js"> </script> <basefont size="3"> <a name="exit"></a> <a name="tag_03_131"></a><!-- exit --> <!--header start--> <center><font size="2">The Open Group Base Specifications Issue 6<br> IEEE Std 1003.1, 2004 Edition<br> Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.</font></center><center><font color="red">A newer edition of this document exists <a href="http://pubs.opengroup.org/onlinepubs/9699919799/" target="_parent">here</a></font></center> <!--header end--> <hr size="2" noshade> <h4><a name="tag_03_131_01"></a>NAME</h4> <blockquote>exit, _Exit, _exit - terminate a process</blockquote> <h4><a name="tag_03_131_02"></a>SYNOPSIS</h4> <blockquote class="synopsis"> <p><code><tt>#include <<a href="../basedefs/stdlib.h.html">stdlib.h</a>><br> <br> void exit(int</tt> <i>status</i><tt>);<br> void _Exit(int</tt> <i>status</i><tt>);<br> <br> <br> #include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br> void _exit(int</tt> <i>status</i><tt>);<br> </tt></code></p> </blockquote> <h4><a name="tag_03_131_03"></a>DESCRIPTION</h4> <blockquote> <p>For <i>exit</i>() and <i>_Exit</i>(): <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src= "../images/opt-start.gif" alt="[Option Start]" border="0"> 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. <img src="../images/opt-end.gif" alt="[Option End]" border= "0"></p> <p>The value of <i>status</i> may be 0, EXIT_SUCCESS, EXIT_FAILURE, <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> or any other value, though only the least significant 8 bits (that is, <i>status</i> & 0377) shall be available to a waiting parent process. <img src="../images/opt-end.gif" alt= "[Option End]" border="0"></p> <p>The <i>exit</i>() function shall first call all functions registered by <a href="../functions/atexit.html"><i>atexit</i>()</a>, 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 <a href="../functions/longjmp.html"><i>longjmp</i>()</a> function is made that would terminate the call to the registered function, the behavior is undefined.</p> <p>If a function registered by a call to <a href="../functions/atexit.html"><i>atexit</i>()</a> fails to return, the remaining registered functions shall not be called and the rest of the <i>exit</i>() processing shall not be completed. If <i>exit</i>() is called more than once, the behavior is undefined.</p> <p>The <i>exit</i>() function shall then flush all open streams with unwritten buffered data, close all open streams, and remove all files created by <a href="../functions/tmpfile.html"><i>tmpfile</i>()</a>. Finally, control shall be terminated with the consequences described below.</p> <p><sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The <i>_Exit</i>() and <i>_exit</i>() functions shall be functionally equivalent. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> <p>The <i>_Exit</i>() <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src="../images/opt-start.gif" alt= "[Option Start]" border="0"> and <i>_exit</i>() <img src="../images/opt-end.gif" alt="[Option End]" border="0"> functions shall not call functions registered with <a href="../functions/atexit.html"><i>atexit</i>()</a> 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.</p> <p>These functions shall terminate the calling process <sup>[<a href="javascript:open_code('CX')">CX</a>]</sup> <img src= "../images/opt-start.gif" alt="[Option Start]" border="0"> with the following consequences: <img src="../images/opt-end.gif" alt="[Option End]" border="0"> <basefont size="2"></p> <dl> <dt><b>Note:</b></dt> <dd>These consequences are all extensions to the ISO C standard and are not further CX shaded. However, XSI extensions are shaded.</dd> </dl> <basefont size="3"> <ul> <li> <p>All of the file descriptors, directory streams, <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src= "../images/opt-start.gif" alt="[Option Start]" border="0"> conversion descriptors, and message catalog descriptors <img src= "../images/opt-end.gif" alt="[Option End]" border="0"> open in the calling process shall be closed.</p> </li> <li> <p>If the parent process of the calling process is executing a <a href="../functions/wait.html"><i>wait</i>()</a> or <a href= "../functions/waitpid.html"><i>waitpid</i>()</a>, <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src= "../images/opt-start.gif" alt="[Option Start]" border="0"> and has neither set its SA_NOCLDWAIT flag nor set SIGCHLD to SIG_IGN, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> it shall be notified of the calling process' termination and the low-order eight bits (that is, bits 0377) of <i>status</i> 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 <a href= "../functions/wait.html"><i>wait</i>()</a> or <a href="../functions/waitpid.html"><i>waitpid</i>()</a>.</p> <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The semantics of the <a href="../functions/waitid.html"><i>waitid</i>()</a> function shall be equivalent to <a href= "../functions/wait.html"><i>wait</i>()</a>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p>If the parent process of the calling process is not executing a <a href="../functions/wait.html"><i>wait</i>()</a> or <a href= "../functions/waitpid.html"><i>waitpid</i>()</a>, <sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src= "../images/opt-start.gif" alt="[Option Start]" border="0"> and has neither set its SA_NOCLDWAIT flag nor set SIGCHLD to SIG_IGN, <img src="../images/opt-end.gif" alt="[Option End]" border="0"> the calling process shall be transformed into a <i>zombie process</i>. A <i>zombie process</i> is an inactive process and it shall be deleted at some later time when its parent process executes <a href="../functions/wait.html"><i>wait</i>()</a> or <a href="../functions/waitpid.html"><i>waitpid</i>()</a>.</p> <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> The semantics of the <a href="../functions/waitid.html"><i>waitid</i>()</a> function shall be equivalent to <a href= "../functions/wait.html"><i>wait</i>()</a>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p>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.</p> </li> <li> <p>Either:</p> <p>If the implementation supports the SIGCHLD signal, a SIGCHLD shall be sent to the parent process.</p> <p>Or:</p> <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> 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. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p>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.</p> </li> <li> <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Each attached shared-memory segment is detached and the value of <i>shm_nattch</i> (see <a href= "../functions/shmget.html"><i>shmget</i>()</a>) in the data structure associated with its shared memory ID shall be decremented by 1. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> For each semaphore for which the calling process has set a <i>semadj</i> value (see <a href="semop.html"><i>semop</i>()</a> ), that value shall be added to the <i>semval</i> of the specified semaphore. <img src="../images/opt-end.gif" alt="[Option End]" border= "0"></p> </li> <li> <p>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.</p> </li> <li> <p>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.</p> </li> <li> <p>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.</p> </li> <li> <p><sup>[<a href="javascript:open_code('SEM')">SEM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> All open named semaphores in the calling process shall be closed as if by appropriate calls to <a href= "../functions/sem_close.html"><i>sem_close</i>()</a>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('ML')">ML</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Any memory locks established by the process via calls to <a href="../functions/mlockall.html"><i>mlockall</i>()</a> or <a href= "../functions/mlock.html"><i>mlock</i>()</a> 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 <i>_Exit</i>() or <i>_exit</i>(). <img src="../images/opt-end.gif" alt= "[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('MF')">MF|SHM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Memory mappings that were created in the process shall be unmapped before the process is destroyed. <img src= "../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('TYM')">TYM</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Any blocks of typed memory that were mapped in the calling process shall be unmapped, as if <a href= "../functions/munmap.html"><i>munmap</i>()</a> was implicitly called to unmap them. <img src="../images/opt-end.gif" alt= "[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('MSG')">MSG</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> All open message queue descriptors in the calling process shall be closed as if by appropriate calls to <a href= "../functions/mq_close.html"><i>mq_close</i>()</a>. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p><sup>[<a href="javascript:open_code('AIO')">AIO</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> Any outstanding cancelable asynchronous I/O operations may be canceled. Those asynchronous I/O operations that are not canceled shall complete as if the <i>_Exit</i>() or <i>_exit</i>() operation had not yet occurred, but any associated signal notifications shall be suppressed. The <i>_Exit</i>() or <i>_exit</i>() operation may block awaiting such I/O completion. Whether any I/O is canceled, and which I/O may be canceled upon <i>_Exit</i>() or <i>_exit</i>(), is implementation-defined. <img src= "../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> <li> <p>Threads terminated by a call to <i>_Exit</i>() or <i>_exit</i>() shall not invoke their cancellation cleanup handlers or per-thread data destructors.</p> </li> <li> <p><sup>[<a href="javascript:open_code('TRC')">TRC</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> 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 <a href="../functions/posix_trace_shutdown.html"><i>posix_trace_shutdown</i>()</a> function, and any process' mapping of trace event names to trace event type identifiers built for these trace streams may be deallocated. <img src= "../images/opt-end.gif" alt="[Option End]" border="0"></p> </li> </ul> </blockquote> <h4><a name="tag_03_131_04"></a>RETURN VALUE</h4> <blockquote> <p>These functions do not return.</p> </blockquote> <h4><a name="tag_03_131_05"></a>ERRORS</h4> <blockquote> <p>No errors are defined.</p> </blockquote> <hr> <div class="box"><em>The following sections are informative.</em></div> <h4><a name="tag_03_131_06"></a>EXAMPLES</h4> <blockquote> <p>None.</p> </blockquote> <h4><a name="tag_03_131_07"></a>APPLICATION USAGE</h4> <blockquote> <p>Normally applications should use <i>exit</i>() rather than <i>_Exit</i>() or <i>_exit</i>().</p> </blockquote> <h4><a name="tag_03_131_08"></a>RATIONALE</h4> <blockquote> <h5><a name="tag_03_131_08_01"></a>Process Termination</h5> <p>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: <i>normal termination</i> (as in the current specification), <i>simple abnormal termination</i>, and <i>abnormal termination with actions</i>. 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.</p> <p>The implementation-defined actions usually include, in most historical implementations, the creation of a file named <b>core</b> 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.</p> <p>There is a potential security problem in creating a <b>core</b> 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 <b>core</b> file or should make it unreadable by the user.</p> <p>Despite the silence of this volume of IEEE Std 1003.1-2001 on this feature, applications are advised not to create files named <b>core</b> because of potential conflicts in many implementations. Some implementations use a name other than <b>core</b> for the file; for example, by appending the process ID to the filename.</p> <h5><a name="tag_03_131_08_02"></a>Terminating a Process</h5> <p>It is important that the consequences of process termination as described occur regardless of whether the process called <i>_exit</i>() (perhaps indirectly through <i>exit</i>()) or instead was terminated due to a signal or for some other reason. Note that in the specific case of <i>exit</i>() this means that the <i>status</i> argument to <i>exit</i>() is treated in the same way as the <i>status</i> argument to <i>_exit</i>().</p> <p>A language other than C may have other termination primitives than the C-language <i>exit</i>() 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 <i>_exit</i>() 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.</p> <p>As required by the ISO C standard, using <b>return</b> from <i>main</i>() has the same behavior (other than with respect to language scope issues) as calling <i>exit</i>() with the returned value. Reaching the end of the <i>main</i>() function has the same behavior as calling <i>exit</i>(0).</p> <p>A value of zero (or EXIT_SUCCESS, which is required to be zero) for the argument <i>status</i> conventionally indicates successful termination. This corresponds to the specification for <i>exit</i>() in the ISO C standard. The convention is followed by utilities such as <a href="../utilities/make.html"><i>make</i></a> and various shells, which interpret a zero status from a child process as success. For this reason, applications should not call <i>exit</i>(0) or <i>_exit</i>(0) when they terminate unsuccessfully; for example, in signal-catching functions.</p> <p>Historically, the implementation-defined process that inherits children whose parents have terminated without waiting on them is called <i>init</i> and has a process ID of 1.</p> <p>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 <i>vhangup</i>() 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 <i>_exit</i>() behave this way in such systems should not cause problems with existing applications.</p> <p>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.</p> <p>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 <i>_exit</i>() must consider processes other than child processes.</p> <p>It is possible for a process group to be orphaned by a call to <a href="../functions/setpgid.html"><i>setpgid</i>()</a> or <a href="../functions/setsid.html"><i>setsid</i>()</a>, 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 <a href= "../basedefs/signal.h.html"><i><signal.h></i></a>.</p> <p>The ISO/IEC 9899:1999 standard adds the <i>_Exit</i>() function that results in immediate program termination without triggering signals or <a href="../functions/atexit.html"><i>atexit</i>()</a>-registered functions. In IEEE Std 1003.1-2001, this is equivalent to the <i>_exit</i>() function.</p> </blockquote> <h4><a name="tag_03_131_09"></a>FUTURE DIRECTIONS</h4> <blockquote> <p>None.</p> </blockquote> <h4><a name="tag_03_131_10"></a>SEE ALSO</h4> <blockquote> <p><a href="atexit.html"><i>atexit</i>()</a>, <a href="close.html"><i>close</i>()</a>, <a href="fclose.html"><i>fclose</i>()</a> , <a href="longjmp.html"><i>longjmp</i>()</a>, <a href="posix_trace_shutdown.html"><i>posix_trace_shutdown</i>()</a>, <a href= "posix_trace_trid_eventid_open.html"><i>posix_trace_trid_eventid_open</i>()</a>, <a href="semop.html"><i>semop</i>()</a>, <a href="shmget.html"><i>shmget</i>()</a>, <a href="sigaction.html"><i>sigaction</i>()</a>, <a href="wait.html"><i>wait</i>()</a>, <a href="waitid.html"><i>waitid</i>()</a>, <a href="waitpid.html"><i>waitpid</i>()</a>, the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/stdlib.h.html"><i><stdlib.h></i></a>, <a href= "../basedefs/unistd.h.html"><i><unistd.h></i></a></p> </blockquote> <h4><a name="tag_03_131_11"></a>CHANGE HISTORY</h4> <blockquote> <p>First released in Issue 1. Derived from Issue 1 of the SVID.</p> </blockquote> <h4><a name="tag_03_131_12"></a>Issue 5</h4> <blockquote> <p>The DESCRIPTION is updated for alignment with the POSIX Realtime Extension and the POSIX Threads Extension.</p> <p>Interactions with the SA_NOCLDWAIT flag and SIGCHLD signal are further clarified.</p> <p>The values of <i>status</i> from <i>exit</i>() are better described.</p> </blockquote> <h4><a name="tag_03_131_13"></a>Issue 6</h4> <blockquote> <p>Extensions beyond the ISO C standard are marked.</p> <p>The DESCRIPTION is updated for alignment with IEEE Std 1003.1j-2000 by adding semantics for typed memory.</p> <p>The following changes are made for alignment with the ISO/IEC 9899:1999 standard:</p> <ul> <li> <p>The <i>_Exit</i>() function is included.</p> </li> <li> <p>The DESCRIPTION is updated.</p> </li> </ul> <p>The description of tracing semantics is added for alignment with IEEE Std 1003.1q-2000.</p> <p>References to the <i>wait3</i>() function are removed.</p> <p>IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/16 is applied, correcting grammar in the DESCRIPTION.</p> </blockquote> <div class="box"><em>End of informative text.</em></div> <hr size="2" noshade> <center><font size="2"><!--footer start--> UNIX ® is a registered Trademark of The Open Group.<br> POSIX ® is a registered Trademark of The IEEE.<br> [ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href= "../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a> ]</font></center> <!--footer end--> <hr size="2" noshade> </body> </html>