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<h3 class="section">4.7 Debugging an Already-running Process</h3>

<p><a name="index-attach-153"></a><a name="index-attach-154"></a>
     <dl>
<dt><code>attach </code><var>process-id</var><dd>This command attaches to a running process&mdash;one that was started
outside <span class="sc">gdb</span>.  (<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><span class="samp">jobs -l</span></samp>&rsquo; shell command.

     <p><code>attach</code> does not repeat if you press &lt;RET&gt; a second time after
executing the command. 
</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>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>The first thing <span class="sc">gdb</span> does after arranging to debug the specified
process is to stop it.  You can examine and modify an attached process
with all the <span class="sc">gdb</span> 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 <span class="sc">gdb</span> to the process.

     
<a name="index-detach-155"></a>
<dl><dt><code>detach</code><dd>When you have finished debugging the attached process, you can use the
<code>detach</code> command to release it from <span class="sc">gdb</span> control.  Detaching
the process continues its execution.  After the <code>detach</code> command,
that process and <span class="sc">gdb</span> 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 &lt;RET&gt; again after
executing the command. 
</dl>

   <p>If you exit <span class="sc">gdb</span> while you have an attached process, you detach
that process.  If you use the <code>run</code> command, you kill that process. 
By default, <span class="sc">gdb</span> 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>).

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