Using signals between unrelated processes (C)

[sauronnikko]

Hi. I'm having quite a headache trying to communicate two processes which have no relation (one is not the child of the other). I use SIGUSR1 for this purpose. i just want to send one signal from process 1 to process 2 so that this last process prints something in the console. Instead, it prints "User defined signal 1" and exits. I know this is the default behaviour but i'm installing a signal handler which supposedly just prints something. Any help'll be appreciated. Thanks

[SagaciousKJB]

Well, it would be helpful to see your source. It should look something like so

#include <signal.h>

...

static void handler(int sig, siginfo_t *si, void *unused)
{
           printf("%.2lf cps\n", (float)count/(time(0) - start));
}

...

struct sigaction sa;

        sa.sa_flags = SA_SIGINFO;
        sigemptyset(&sa.sa_mask);
        sa.sa_sigaction = handler;

if (sigaction(SIGUSR1, &sa, NULL) == -1)
                        ;

The "struct sigaction" is defined in signal.h, so sa.sa_flags is defined as such in there. sa.sa_sigaction is just a pointer to a function which is the signal handler.

As far as sending a SIGUSR1 to another process, I'm not sure how one would do this in C, I have just done it with the "kill" application".

[Rubberman]

Do note that to set a signal on another process, you either have to be the owner of that process, or root. This keeps one user from killing processes of another user.

[tetsujin]

As far as sending a SIGUSR1 to another process, I'm not sure how one would do this in C, I have just done it with the "kill" application".

The "kill" system call, of course.