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POHow do I terminate backgrounded ssh instances
 

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  1. POHow do I terminate backgrounded ssh instances
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    <p>I have written C program that uses fork(2) and execl(3) to run ssh for port forwarding purposes. The ssh's are run in the background the -f option.</p> <p>When the C program exits, I want it to send SIGTERM to the ssh instances it spawned.</p> <p>I have tried</p> <pre><code>// creating the ssh process ssh_pid = fork(); if (ssh_pid == 0) execl("/usr/bin/ssh", "/usr/bin/ssh", "-f", other options, NULL) // ... printf("Killing %d\n", ssh_pid); // &lt;--- output the PID kill(ssh_pid, 15); sleep(1); // give it a chance to exit properly if (kill(ssh_pid, 0) == 0) kill(ssh_pid, 9); // the "shotgun" approach </code></pre> <p>However, this doesn't work (even with the SIGKILL).</p> <p>If I run ps <em>before the program exits</em></p> <pre><code>ps aux | grep ssh | grep -v sshd | grep -v grep </code></pre> <p>I see something like this:</p> <pre><code>user 27825 0.2 0.0 0 0 pts/0 Z+ 18:23 0:00 [ssh] &lt;defunct&gt; user 27834 0.0 0.0 41452 1176 ? Ss 18:23 0:00 /usr/bin/ssh -f [other options] </code></pre> <p>When the program prints the PID it is killing, I see this:</p> <pre><code>Killing 27825 </code></pre> <p>Subsequently repeating the ps gives me:</p> <pre><code>user 27834 0.0 0.0 41452 1176 ? Ss 18:23 0:00 /usr/bin/ssh -f [other options] </code></pre> <p>It seems that the original ssh has forked itself in order to become a background process.</p> <p>So I changed my call to kill(2) to attempt to kill all processes spawned by the original ssh:</p> <pre><code>kill(-ssh_pid, 15); </code></pre> <p>But this appears to have no effect. I suspect it is because the original ssh is no longer the parent of the backgrounded ssh.</p> <p>So, how do I safely kill the backgrounded ssh? Is it even possible?</p>
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