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| <h4 class="subsection">24.2.2 Termination Signals</h4> |
| |
| <p><a name="index-program-termination-signals-2848"></a> |
| These signals are all used to tell a process to terminate, in one way |
| or another. They have different names because they're used for slightly |
| different purposes, and programs might want to handle them differently. |
| |
| <p>The reason for handling these signals is usually so your program can |
| tidy up as appropriate before actually terminating. For example, you |
| might want to save state information, delete temporary files, or restore |
| the previous terminal modes. Such a handler should end by specifying |
| the default action for the signal that happened and then reraising it; |
| this will cause the program to terminate with that signal, as if it had |
| not had a handler. (See <a href="Termination-in-Handler.html#Termination-in-Handler">Termination in Handler</a>.) |
| |
| <p>The (obvious) default action for all of these signals is to cause the |
| process to terminate. |
| |
| <!-- signal.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>SIGTERM</b><var><a name="index-SIGTERM-2849"></a></var><br> |
| <blockquote><p><a name="index-termination-signal-2850"></a>The <code>SIGTERM</code> signal is a generic signal used to cause program |
| termination. Unlike <code>SIGKILL</code>, this signal can be blocked, |
| handled, and ignored. It is the normal way to politely ask a program to |
| terminate. |
| |
| <p>The shell command <code>kill</code> generates <code>SIGTERM</code> by default. |
| <a name="index-kill-2851"></a></p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- ISO --> |
| <div class="defun"> |
| — Macro: int <b>SIGINT</b><var><a name="index-SIGINT-2852"></a></var><br> |
| <blockquote><p><a name="index-interrupt-signal-2853"></a>The <code>SIGINT</code> (“program interrupt”) signal is sent when the user |
| types the INTR character (normally <kbd>C-c</kbd>). See <a href="Special-Characters.html#Special-Characters">Special Characters</a>, for information about terminal driver support for |
| <kbd>C-c</kbd>. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>SIGQUIT</b><var><a name="index-SIGQUIT-2854"></a></var><br> |
| <blockquote><p><a name="index-quit-signal-2855"></a><a name="index-quit-signal-2856"></a>The <code>SIGQUIT</code> signal is similar to <code>SIGINT</code>, except that it's |
| controlled by a different key—the QUIT character, usually |
| <kbd>C-\</kbd>—and produces a core dump when it terminates the process, |
| just like a program error signal. You can think of this as a |
| program error condition “detected” by the user. |
| |
| <p>See <a href="Program-Error-Signals.html#Program-Error-Signals">Program Error Signals</a>, for information about core dumps. |
| See <a href="Special-Characters.html#Special-Characters">Special Characters</a>, for information about terminal driver |
| support. |
| |
| <p>Certain kinds of cleanups are best omitted in handling <code>SIGQUIT</code>. |
| For example, if the program creates temporary files, it should handle |
| the other termination requests by deleting the temporary files. But it |
| is better for <code>SIGQUIT</code> not to delete them, so that the user can |
| examine them in conjunction with the core dump. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>SIGKILL</b><var><a name="index-SIGKILL-2857"></a></var><br> |
| <blockquote><p>The <code>SIGKILL</code> signal is used to cause immediate program termination. |
| It cannot be handled or ignored, and is therefore always fatal. It is |
| also not possible to block this signal. |
| |
| <p>This signal is usually generated only by explicit request. Since it |
| cannot be handled, you should generate it only as a last resort, after |
| first trying a less drastic method such as <kbd>C-c</kbd> or <code>SIGTERM</code>. |
| If a process does not respond to any other termination signals, sending |
| it a <code>SIGKILL</code> signal will almost always cause it to go away. |
| |
| <p>In fact, if <code>SIGKILL</code> fails to terminate a process, that by itself |
| constitutes an operating system bug which you should report. |
| |
| <p>The system will generate <code>SIGKILL</code> for a process itself under some |
| unusual conditions where the program cannot possibly continue to run |
| (even to run a signal handler). |
| </p></blockquote></div> |
| <a name="index-kill-signal-2858"></a> |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| |
| <div class="defun"> |
| — Macro: int <b>SIGHUP</b><var><a name="index-SIGHUP-2859"></a></var><br> |
| <blockquote><p><a name="index-hangup-signal-2860"></a>The <code>SIGHUP</code> (“hang-up”) signal is used to report that the user's |
| terminal is disconnected, perhaps because a network or telephone |
| connection was broken. For more information about this, see <a href="Control-Modes.html#Control-Modes">Control Modes</a>. |
| |
| <p>This signal is also used to report the termination of the controlling |
| process on a terminal to jobs associated with that session; this |
| termination effectively disconnects all processes in the session from |
| the controlling terminal. For more information, see <a href="Termination-Internals.html#Termination-Internals">Termination Internals</a>. |
| </p></blockquote></div> |
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