Linux cannot kill a PID: invalid signal
<p>IN ubuntu Amazon EC2 instances with root access</p>

<p>when do</p>

<pre><code>ps -e
</code></pre>

<p>The process shows up with a valid PID and process name.  The database table also suggests the process is still ongoing.</p>

<pre><code>  PID TTY          TIME CMD
32194 ?        00:00:00 test
32253 ?        00:00:00 mysql
</code></pre>

<p>However, any of the following commands kill the process, but returns nothing or "invalid signal".</p>

<pre><code>top 
kill
Type in PID
y
returns "invalid signal"
</code></pre>

<p>or</p>

<pre><code>kill -9 PID
kill -s PID
etc.
</code></pre>

<p>Could any guru enlighten how to deal with the "ghost jobs"?</p>