Handle a kill signal

Question

I want to handle a kill signal from C program. I'm starting by create an infinite loop and handle the signal

void signal_callback_handler(int signum)
{
   printf("Caught signal %d\n",signum);
   // Cleanup and close up stuff here

   // Terminate program
   exit(signum);
}
 main()
{
    signal(SIGINT, signal_callback_handler);
    printf("pid: %d \n",getpid());
    while(1)
    {

    }

}

When I run this program and make CTRL+C, the kill is handled, and it works. The message Caught signal is printed. However, when I'm trying to kill from another program

int main(int argc, char **argv)
{
    kill(atoi(argv[1]), SIGKILL);

    return 0;

}

The program is stoped but the signal is not handled. In other words, the message Caught signal is not printed. The infinite loop is just stopped.

Answer 1

就是这样：您无法捕获SIGKILL ，它肯定会杀死您的程序，这就是它的创建目的。

Answer 2

You cannot catch or ignore a SIGKILL signal. Also in your code shown below you have created a signal handler only for SIGINT, that is, whenever a SIGINT signal is caught it will call the signal_callback_handler(). All other signals will be caught by the default signal handler.

signal(SIGINT, signal_callback_handler);

For example if you want to catch a SIGHUP signal also in the your program you need to define a signal handler as below:

signal(SIGHUP, signal_callback_handler);

Modified code is shown below:

void signal_callback_handler(int signum)
{   if (signum == SIGINT){
        printf("Caught signal %d\n",signum);
         //Do the action need to be taken when SIGINT is received 
     }
     else if(signum == SIGHUP){
        printf("Caught signal %d\n",signum);
        //Do the action need to be taken when SIGHUP is received
        
     }
}

int main()
{
    signal(SIGINT, signal_callback_handler);
    signal(SIGHUP, signal_callback_handler);
    printf("pid: %d \n",getpid());
    while(1)
    {

    }
    return 0;
}

Answer 3

You need to add

signal(SIGTERM, signal_callback_handler);

As you are only connected to SIGINT (eg Ctrl+C) but for a kill/killall your friend is SIGTERM