Catching Signal, with fork

Today, I will demonstrate signals, by forking a child. 

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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("Inside the signal function %d PID=%d\n", sig_num,getpid()); fflush(stdout); } int main() { pid_t child_pid; int status; // Registering the Signal Handler signal(SIGINT,catch_signal); child_pid=fork(); if (child_pid == 0) { //This is Child Section 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>>pid=%d Ppid=%d Waiting for Ctrl+C\n",getpid(),getppid()); fflush(stdout); pause(); printf("PARENT>>Caught the signal\n"); wait(&status); } return 0; }

Summary of what I did:

1.  Created a signal handling function
2. Registered signal
3. Forked the process
4. Child, waits for the signal Ctrl+C
5. parent also waits for the signal Ctrl+C

 After I executed

root@kali:/media/root/persistence# ./a.out
PARENT>>pid=2869 Ppid=2344 Waiting for Ctrl+C
CHILD>>pid=2870 Ppid=2869 Waiting for Ctrl+C

Execution 1:

When I hit Ctrl+C in the terminal, Parent and Child got terminated at the same time.

root@kali:/media/root/persistence# ./a.out
PARENT>>pid=2869 Ppid=2344 Waiting for Ctrl+C
CHILD>>pid=2870 Ppid=2869 Waiting for Ctrl+C
Inside the signal function 2 PID=2870
CHILD>>Caught the signal
Inside the signal function 2 PID=2869
PARENT>>Caught the signal

Execution 2:

From another terminal if I pass SIGINT individually to parent and child. They catch signal

root@kali:/media/root/persistence# ./a.out
PARENT>>pid=3119 Ppid=2344 Waiting for Ctrl+C
CHILD>>pid=3120 Ppid=3119 Waiting for Ctrl+C

From another terminal, I issue 'kill -s 2 3119' to the parent process. Parent executes the signal handling function.

root@kali:/media/root/persistence# ./a.out
PARENT>>pid=3119 Ppid=2344 Waiting for Ctrl+C
CHILD>>pid=3120 Ppid=3119 Waiting for Ctrl+C
Inside the signal function 2 PID=3119
PARENT>>Caught the signal

 
Then I issue 'kill -s 2 3120'

root@kali:/media/root/persistence# ./a.out
PARENT>>pid=3119 Ppid=2344 Waiting for Ctrl+C
CHILD>>pid=3120 Ppid=3119 Waiting for Ctrl+C
Inside the signal function 2 PID=3119
PARENT>>Caught the signal
Inside the signal function 2 PID=3120
CHILD>>Caught the signal