About signals in python with os module
<p>I was studying the signals topic in python and came across this example</p>

<pre><code>import signal
import os
import time

def receive_signal(signum, stack):
    print 'Received:', signum

signal.signal(signal.SIGUSR1, receive_signal)
signal.signal(signal.SIGUSR2, receive_signal)

print 'My PID is:', os.getpid()

while True:
    print 'Waiting...'
    time.sleep(3)
</code></pre>

<p>Now he is sending the signal using this</p>

<pre><code>I ran signal_signal.py in one window, then kill -USR1 $pid, kill -USR2 $pid, and kill -INT $pid in another.
</code></pre>

<p>I have few problems</p>

<ol>
<li>how can linux kill command is way of sending siganls . i dont get it</li>
<li>what is <code>kill -USR1</code> from where did <code>USR</code>  came from , what parameter is kill command expecting</li>
</ol>

<p>i was thinking kill only kills the process id , why are we passing the parameter to kill command for</p>
