CODEWITHSUNDEEP
c++bashsignals
nicholishiell
nicholishiell

Reputation: 33

Handling signals from child process in Bash Scripts

I am trying to trap a signal raised by a child process. However, my trap callback function is never called. I have the following test code

#include <csignal>
#include <iostream>
#include <thread>
#include <chrono>

int main()
{
    std::this_thread::sleep_for (std::chrono::seconds(5));

    std::cout << ">>> Signal Sent!" << std::endl;
    raise(SIGUSR1);

    return 0;
}

And this bash script

set -bm
set -e 

KEEP_GOING=true

sigusr1()
{
    echo "SIGUSR1 Recieved"
    KEEP_GOING=false
}

trap sigusr1 SIGUSR1

./signalTest  &

while $KEEP_GOING ; do
    sleep 1s
    echo "Waiting for signal"
done

When I run it I get the following 

Waiting for signal
Waiting for signal
Waiting for signal
Waiting for signal
>>> Signal Sent!
[1]+  User defined signal 1   ./signalTest
Waiting for signal
Waiting for signal
Waiting for signal
Waiting for signal
Waiting for signal
^C

From the output I see that the signal is in fact sent, and in some capacity received. However the callback function in my trap is not executed.

Any thoughts?

Upvotes: 3

Views: 178

Answers (1)

Maxim Egorushkin
Maxim Egorushkin

Reputation: 136208

raise sends the signal to the calling thread.

kill sends a signal to the specified process or thread.

To send the signal to the parent process, instead of 

raise(SIGUSR1);

do

#include <unistd.h>
// ...
kill(getppid(), SIGUSR1);

Upvotes: 2

Related Questions