Linux Signals – Example C Program to Catch Signal (SIGINT)

What is a signal? Signals are software interrupts.

A robust program need to handle signals. This is because signals are a way to deliver asynchronous events to the application.A user hitting ctrl+c, a process sending a signal to kill another process etc are all such cases where a process needs to do signal handling.

Linux Signals

In Linux, every signal has a name that begins with characters SIG. For example 

 * +--------------------+------------------+

 * |  POSIX signal      |  default action  |

 * +--------------------+------------------+

 * |  SIGHUP               |  terminate |

 * |  SIGINT                  | terminate |

 * |  SIGQUIT                | coredump |

 * |  SIGILL                     | coredump |

 * |  SIGTRAP                | coredump |

 * |  SIGABRT/SIGIOT    | coredump |

 * |  SIGBUS            | coredump |

 * |  SIGFPE            | coredump |

 * |  SIGKILL           | terminate(+) |

 * |  SIGUSR1           | terminate |

 * |  SIGSEGV           | coredump |

 * |  SIGUSR2           | terminate |

 * |  SIGPIPE           | terminate |

 * |  SIGALRM           | terminate |

 * |  SIGTERM           | terminate |

 * |  SIGCHLD           | ignore   |

 * |  SIGCONT           | ignore(*) |

 * |  SIGSTOP           | stop(*)(+)   |

 * |  SIGTSTP           | stop(*)   |

 * |  SIGTTIN           | stop(*)   |

 * |  SIGTTOU           | stop(*)   |

 * |  SIGURG            | ignore   |

 * |  SIGXCPU           | coredump |

 * |  SIGXFSZ           | coredump |

 * |  SIGVTALRM         | terminate |

 * |  SIGPROF           | terminate |

 * |  SIGPOLL/SIGIO     | terminate |

 * |  SIGSYS/SIGUNUSED  | coredump |

 * |  SIGSTKFLT         | terminate |

 * |  SIGWINCH          | ignore   |

 * |  SIGPWR            | terminate |

 * |  SIGRTMIN-SIGRTMAX | terminate       |

 * +--------------------+------------------+

 * |  non-POSIX signal  |  default action  |

 * +--------------------+------------------+

 * |  SIGEMT            |  coredump |

 * +--------------------+------------------+

Example C Program to Catch Signal "SIGINT"

//sigint.c

#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;

}

gcc -o sigint sigint.c

Output: