main.c

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/ipc.h>
#include <sys/sem.h>

typedef void (*sighandler_t)(int);

static void
signal_handler(int sig)
{
  fprintf(stderr, "signal caught\n");
	return;
}

static sighandler_t
install_sighandler(int signum, sighandler_t handler)
{
	struct sigaction act, oact;

	act.sa_handler = handler;
	sigemptyset(&act.sa_mask);
	act.sa_flags = SA_RESTART;
	sigaction(signum, &act, &oact);

	return oact.sa_handler;
}

int
main(int argc, char *argv[])
{
	int		semid, res;
	struct sembuf sem_op;

	install_sighandler(SIGUSR1, signal_handler);

	if ((semid = semget((key_t) 42, 1, 0666|IPC_CREAT)) == -1)
	{
		perror("Failed to create a private semaphore.");
		return 1;
	}
	sem_op.sem_num = 0;
	sem_op.sem_op = -1;
	sem_op.sem_flg = 0;

	res = semop(semid, &sem_op, 1);
	if (res == -1)
	{
		perror("semop failed");
		return 1;
	}

	return 0;
}

Makefile

PROG = run
OBJS = main.o

all: $(PROG)

$(PROG): $(OBJS)
  $(CC) -o $(PROG) $(OBJS)

clean:
	rm -f $(PROG) $(OBJS)