signal handler with sighup

Question

#include <stdio.h>
#include <stdlib.h>
#include <sys/signal.h>
#include <string.h>

void handler (int sig);
int count;

int main() {

    struct sigaction act;
    memset (&act, 0, sizeof (act));


    act.sa_handler = handler;
    if (sigaction (SIGHUP, &act, NULL) < 0) {
        perror ("sigaction");
        exit (-1);
    }

    int count = 0;
    while(1) {
        sleep(1);
        count++;
    }

}

void handler (int signal_number){
        printf ("count is %d\n", count);
}

I assume i am doing this right, how would I go about call sighup within the command line? It needs to call sighup to print out my count.

why is the output always "count is 0"? Why isnt the count++ processing — DDukesterman, Jul 18 '13 at 21:31
You re-declared count in main. The sig handler is reading the global "count". — aet, Jul 18 '13 at 21:37
@DDukesterman [avoid using printf in a signal handler](http://stackoverflow.com/questions/16891019/how-to-avoid-using-printf-in-a-signal-handler) — Grijesh Chauhan, Jul 18 '13 at 22:14

score 4 · Answer 1 · answered Jul 18 '13 at 21:21

4

Technically it is not safe to do I/O in the signal handler, better to set a flag, watch for it, and print based on the flag. On a posix system, you should be able to "kill -HUP " from the command line to send the signal.

answered Jul 18 '13 at 21:21

aet

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Not only printf, all function do signal interrupts, malloc(), here is [List of authorized functions](http://man7.org/linux/man-pages/man7/signal.7.html) – Grijesh Chauhan Jul 18 '13 at 22:17

score 2 · Accepted Answer · answered Jul 18 '13 at 21:20

2

You can use kill -SIGHUP <pid>, where <pid> is the process ID of your code.

answered Jul 18 '13 at 21:20

Drew McGowen

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score 1 · Answer 3 · edited Jul 18 '13 at 22:18

1

try this in console:

ps -a

read out the pid of your program

kill -s HUP target_pid

Here you have a manual page for kill with a list of signals.

EDIT: even simpler you can use killall:

killall -HUP nameofyourbinary

edited Jul 18 '13 at 22:18

Grijesh Chauhan

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answered Jul 18 '13 at 21:21

nio

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signal handler with sighup

3 Answers3