CODEWITHSUNDEEP
python
user192082107
user192082107

Reputation: 1367

About signals in python with os module

I was studying the signals topic in python and came across this example

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)

Now he is sending the signal using this

I ran signal_signal.py in one window, then kill -USR1 $pid, kill -USR2 $pid, and kill -INT $pid in another.

I have few problems

  1. how can linux kill command is way of sending siganls . i dont get it
  2. what is kill -USR1 from where did USR came from , what parameter is kill command expecting

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

Upvotes: 2

Views: 1098

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1121614

The kill command is a little bit misnamed. It sends signals to processes, and the default signal is SIGTERM, process termination. Using kill for sending SIGUSR* signals is perfectly correct.

When you have questions about a UNIX command, your best bet is to type in man <commandname> on the command line. man kill would have told you all this and more.

Try running kill -l for a list of supported signals. You can specify signals by number, by symbolic name and by symbolic name prepended by SIG. You can use kill -10, kill -USR1 or kill -SIGUSR1, all would send the same signal. See the kill manpage for more details.

Upvotes: 6

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