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<title>Debugging with GDB: Signaling</title>
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<a name="Signaling"></a>
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<div class="header">
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<p>
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Next: <a href="Returning.html#Returning" accesskey="n" rel="next">Returning</a>, Previous: <a href="Jumping.html#Jumping" accesskey="p" rel="previous">Jumping</a>, Up: <a href="Altering.html#Altering" accesskey="u" rel="up">Altering</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
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<a name="Giving-Your-Program-a-Signal"></a>
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<h3 class="section">17.3 Giving Your Program a Signal</h3>
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<a name="index-deliver-a-signal-to-a-program"></a>
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<dl compact="compact">
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<dd><a name="index-signal"></a>
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</dd>
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<dt><code>signal <var>signal</var></code></dt>
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<dd><p>Resume execution where your program is stopped, but immediately give it the
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signal <var>signal</var>. The <var>signal</var> can be the name or the number of a
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signal. For example, on many systems <code>signal 2</code> and <code>signal
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SIGINT</code> are both ways of sending an interrupt signal.
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</p>
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<p>Alternatively, if <var>signal</var> is zero, continue execution without
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giving a signal. This is useful when your program stopped on account of
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a signal and would ordinarily see the signal when resumed with the
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<code>continue</code> command; ‘<samp>signal 0</samp>’ causes it to resume without a
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signal.
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</p>
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<p><em>Note:</em> When resuming a multi-threaded program, <var>signal</var> is
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delivered to the currently selected thread, not the thread that last
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reported a stop. This includes the situation where a thread was
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stopped due to a signal. So if you want to continue execution
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suppressing the signal that stopped a thread, you should select that
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same thread before issuing the ‘<samp>signal 0</samp>’ command. If you issue
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the ‘<samp>signal 0</samp>’ command with another thread as the selected one,
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<small>GDB</small> detects that and asks for confirmation.
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</p>
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<p>Invoking the <code>signal</code> command is not the same as invoking the
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<code>kill</code> utility from the shell. Sending a signal with <code>kill</code>
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causes <small>GDB</small> to decide what to do with the signal depending on
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the signal handling tables (see <a href="Signals.html#Signals">Signals</a>). The <code>signal</code> command
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passes the signal directly to your program.
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</p>
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<p><code>signal</code> does not repeat when you press <tt class="key">RET</tt> a second time
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after executing the command.
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</p>
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<a name="index-queue_002dsignal"></a>
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</dd>
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<dt><code>queue-signal <var>signal</var></code></dt>
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<dd><p>Queue <var>signal</var> to be delivered immediately to the current thread
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when execution of the thread resumes. The <var>signal</var> can be the name or
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the number of a signal. For example, on many systems <code>signal 2</code> and
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<code>signal SIGINT</code> are both ways of sending an interrupt signal.
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The handling of the signal must be set to pass the signal to the program,
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otherwise <small>GDB</small> will report an error.
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You can control the handling of signals from <small>GDB</small> with the
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<code>handle</code> command (see <a href="Signals.html#Signals">Signals</a>).
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</p>
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<p>Alternatively, if <var>signal</var> is zero, any currently queued signal
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for the current thread is discarded and when execution resumes no signal
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will be delivered. This is useful when your program stopped on account
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of a signal and would ordinarily see the signal when resumed with the
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<code>continue</code> command.
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</p>
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<p>This command differs from the <code>signal</code> command in that the signal
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is just queued, execution is not resumed. And <code>queue-signal</code> cannot
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be used to pass a signal whose handling state has been set to <code>nopass</code>
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(see <a href="Signals.html#Signals">Signals</a>).
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</p></dd>
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</dl>
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<p>See <a href="Signals.html#stepping-into-signal-handlers">stepping into signal handlers</a>, for information on how stepping
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commands behave when the thread has a signal queued.
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</p>
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<hr>
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<div class="header">
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Next: <a href="Returning.html#Returning" accesskey="n" rel="next">Returning</a>, Previous: <a href="Jumping.html#Jumping" accesskey="p" rel="previous">Jumping</a>, Up: <a href="Altering.html#Altering" accesskey="u" rel="up">Altering</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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