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| <h4 class="subsection">24.1.1 Some Kinds of Signals</h4> |
| |
| <p>A signal reports the occurrence of an exceptional event. These are some |
| of the events that can cause (or <dfn>generate</dfn>, or <dfn>raise</dfn>) a |
| signal: |
| |
| <ul> |
| <li>A program error such as dividing by zero or issuing an address outside |
| the valid range. |
| |
| <li>A user request to interrupt or terminate the program. Most environments |
| are set up to let a user suspend the program by typing <kbd>C-z</kbd>, or |
| terminate it with <kbd>C-c</kbd>. Whatever key sequence is used, the |
| operating system sends the proper signal to interrupt the process. |
| |
| <li>The termination of a child process. |
| |
| <li>Expiration of a timer or alarm. |
| |
| <li>A call to <code>kill</code> or <code>raise</code> by the same process. |
| |
| <li>A call to <code>kill</code> from another process. Signals are a limited but |
| useful form of interprocess communication. |
| |
| <li>An attempt to perform an I/O operation that cannot be done. Examples |
| are reading from a pipe that has no writer (see <a href="Pipes-and-FIFOs.html#Pipes-and-FIFOs">Pipes and FIFOs</a>), |
| and reading or writing to a terminal in certain situations (see <a href="Job-Control.html#Job-Control">Job Control</a>). |
| </ul> |
| |
| <p>Each of these kinds of events (excepting explicit calls to <code>kill</code> |
| and <code>raise</code>) generates its own particular kind of signal. The |
| various kinds of signals are listed and described in detail in |
| <a href="Standard-Signals.html#Standard-Signals">Standard Signals</a>. |
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