Catching Signal, Child to Parent

Now, I am sending a signal(Ctrl+C) from Child to Parent, using 'kill' command. 'Kill' needs pid of the process & Signal to be sent.

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#include <stdio.h> #include <unistd.h> #include <signal.h> #include <sys/wait.h> // Function telling what to do when we catch CTRL+C void catch_signal (int sig_num) { printf("SIGNAL FUNCTION>> Caught the signal %d by process with PID=%d\n",sig_num,getpid()); fflush(stdout); } int main() { pid_t child_pid; int status; child_pid=fork(); if (child_pid == 0) { //This is Child Section //Registering the Signal Handler signal(SIGINT,catch_signal); printf("CHILD>>pid=%d Ppid=%d Waiting for Ctrl+C\n",getpid(),getppid()); fflush(stdout); pause(); printf("CHILD>>Caught the signal\n"); } else { //This is Parent Section printf("PARENT>>Waiting couple of seconds to make sure, child waits for SIGINT\n"); sleep(2); kill(child_pid,SIGINT); printf("PARENT>>Sent the SIGINT signal to child with pid=%d\n",child_pid); wait(&status); } return 0; }

Steps can be defined as:

1. Process is forked
2. Child registers signal handler
3. Child waits for Ctrl+C
4. Parent sleeps.
5. Parent sends Ctrl+C using Kill command.
6. Parent waits for Child to complete

In step 4, if Parent did not sleep, sometimes parents will send Ctrl+C, even before Child executes 'pause'.  Then by the time Child needs Ctrl+C, parent will not be in a position to send Ctrl+C because Parent had already sent it.
When we execute the program

root@kali:/media/root/persistence# ./a.out
PARENT>>Waiting couple of seconds to make sure, child waits for SIGINT
CHILD>>pid=3722 Ppid=3721 Waiting for Ctrl+C

Child waits for Ctrl+C, as Parent is sleeping.  Within moments, the rest of the program executes

root@kali:/media/root/persistence# ./a.out
PARENT>>Waiting couple of seconds to make sure, child waits for SIGINT
CHILD>>pid=3722 Ppid=3721 Waiting for Ctrl+C
SIGNAL FUNCTION>> Caught the signal 2 by process with PID=3722
PARENT>>Sent the SIGINT signal to child with pid=3722
CHILD>>Caught the signal