Hi friends,

Currently, I'm working in wake-up issue in my project. I wanna inform android when my host OS windows wakes up. My project leader gave me an idea to send a signal from windows to android in the shell and use that signal to wake android when windows wakes up, like in exam days I keep alarm by 4am, my bad wakes up and give me a kick ;). But I'm zero at LINUX signal concept, as usual i studied it. Now, I'm typing here for my future ref. and other beginner's use.

SIGNAL IN LINUX

Now, we use CTRL + C to terminate something in LINUX. But, we don't wanna let someone to terminate our code with CTRL + C. So, what we have to do now. We have to monitor the user input and we should not let the system to perform any operation when user gives CTRL +C.

But, Instead what we can do in LINUX is, CTRL + C will generate a signal SIGINT in LINUX, so we can register a function to this signal in our code. So that when we user press CTRL + C, it will call our function, so our code won't be terminated.

What is signal in LINUX ? 
 LINUX has a set of signals. One nice example is, kill -9 PID, which we use to kill a process. Here, we are sending KILL signal to a process. Similarly, few other signals are available in LINUX. (SRY, i don't know to explain it, pls ask prof.google :( )

How can we register a function to a signal ?
here is the syntax,

signal(SIGINT, sig_handler)

void sig_handler(int signo) {}

#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void sig_handler(int signo)
{
  if (signo == SIGINT)
    printf("received SIGINT\n");
}

int main(void)
{
  if (signal(SIGINT, sig_handler) == SIG_ERR)
  printf("\ncan't catch SIGINT\n");
  // A long long wait so that we can easily issue a signal to this process
  while(1)
    sleep(1);
  return 0;
}

#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void sig_handler(int signo)
{
  if (signo == SIGUSR1)
    printf("received SIGUSR1\n");
}

int main(void)
{
  if (signal(SIGUSR1, sig_handler) == SIG_ERR)
  printf("\ncan't catch SIGUSR1\n");
  // A long long wait so that we can easily issue a signal to this process
  while(1)
    sleep(1);
  return 0;
}

KILL -USR1 PID