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<a name="Attach"></a>
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Next: <a href="Kill-Process.html#Kill-Process" accesskey="n" rel="next">Kill Process</a>, Previous: <a href="Input_002fOutput.html#Input_002fOutput" accesskey="p" rel="previous">Input/Output</a>, Up: <a href="Running.html#Running" accesskey="u" rel="up">Running</a> &nbsp; [<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>
<a name="Debugging-an-Already_002drunning-Process"></a>
<h3 class="section">4.7 Debugging an Already-running Process</h3>
<a name="index-attach-1"></a>
<a name="index-attach"></a>

<dl compact="compact">
<dt><code>attach <var>process-id</var></code></dt>
<dd><p>This command attaches to a running process&mdash;one that was started
outside <small>GDB</small>.  (<code>info files</code> shows your active
targets.)  The command takes as argument a process ID.  The usual way to
find out the <var>process-id</var> of a Unix process is with the <code>ps</code> utility,
or with the &lsquo;<samp>jobs -l</samp>&rsquo; shell command.
</p>
<p><code>attach</code> does not repeat if you press <tt class="key">RET</tt> a second time after
executing the command.
</p></dd>
</dl>

<p>To use <code>attach</code>, your program must be running in an environment
which supports processes; for example, <code>attach</code> does not work for
programs on bare-board targets that lack an operating system.  You must
also have permission to send the process a signal.
</p>
<p>When you use <code>attach</code>, the debugger finds the program running in
the process first by looking in the current working directory, then (if
the program is not found) by using the source file search path
(see <a href="Source-Path.html#Source-Path">Specifying Source Directories</a>).  You can also use
the <code>file</code> command to load the program.  See <a href="Files.html#Files">Commands to
Specify Files</a>.
</p>
<a name="set-exec_002dfile_002dmismatch"></a><p>If the debugger can determine that the executable file running in the
process it is attaching to does not match the current exec-file loaded
by <small>GDB</small>, the option <code>exec-file-mismatch</code> specifies how to
handle the mismatch.  <small>GDB</small> tries to compare the files by
comparing their build IDs (see <a href="Separate-Debug-Files.html#build-ID">build ID</a>), if available.
</p>
<dl compact="compact">
<dd><a name="index-exec_002dfile_002dmismatch"></a>
<a name="index-set-exec_002dfile_002dmismatch"></a>
</dd>
<dt><code>set exec-file-mismatch &lsquo;<samp>ask|warn|off</samp>&rsquo;</code></dt>
<dd>
<p>Whether to detect mismatch between the current executable file loaded
by <small>GDB</small> and the executable file used to start the process.  If
&lsquo;<samp>ask</samp>&rsquo;, the default, display a warning and ask the user whether to
load the process executable file; if &lsquo;<samp>warn</samp>&rsquo;, just display a
warning; if &lsquo;<samp>off</samp>&rsquo;, don&rsquo;t attempt to detect a mismatch.
If the user confirms loading the process executable file, then its symbols
will be loaded as well.
</p>
<a name="index-show-exec_002dfile_002dmismatch"></a>
</dd>
<dt><code>show exec-file-mismatch</code></dt>
<dd><p>Show the current value of <code>exec-file-mismatch</code>.
</p>
</dd>
</dl>

<p>The first thing <small>GDB</small> does after arranging to debug the specified
process is to stop it.  You can examine and modify an attached process
with all the <small>GDB</small> commands that are ordinarily available when
you start processes with <code>run</code>.  You can insert breakpoints; you
can step and continue; you can modify storage.  If you would rather the
process continue running, you may use the <code>continue</code> command after
attaching <small>GDB</small> to the process.
</p>
<dl compact="compact">
<dd><a name="index-detach"></a>
</dd>
<dt><code>detach</code></dt>
<dd><p>When you have finished debugging the attached process, you can use the
<code>detach</code> command to release it from <small>GDB</small> control.  Detaching
the process continues its execution.  After the <code>detach</code> command,
that process and <small>GDB</small> become completely independent once more, and you
are ready to <code>attach</code> another process or start one with <code>run</code>.
<code>detach</code> does not repeat if you press <tt class="key">RET</tt> again after
executing the command.
</p></dd>
</dl>

<p>If you exit <small>GDB</small> while you have an attached process, you detach
that process.  If you use the <code>run</code> command, you kill that process.
By default, <small>GDB</small> asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the
<code>set confirm</code> command (see <a href="Messages_002fWarnings.html#Messages_002fWarnings">Optional Warnings and
Messages</a>).
</p>
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