#include <stdio.h>
#include <fcntl.h>
#include <errno.h>
#include <stdlib.h>
#include <unistd.h>
main(int argc, char *argv[]) {
	int i, j;
	struct flock fl;

	i = open(argv[1], O_RDWR, 0);
	if (i < 0) {
		fprintf(stderr, "Can't open %s\n", argv[1]);
		exit(1);
	}

	for (j = 0; j < 5; j++) {
		if (fork() != 0)
			sleep(10);
		else {
			fl.l_type = F_WRLCK;
			fl.l_whence = SEEK_SET;
			fl.l_start = 0;
			fl.l_len = 1;
			if (fcntl(i, F_SETLK, &fl) < 0)
				fprintf(stderr, "Failed err=%d\n", errno);
			fl.l_type = F_UNLCK;
			if (fcntl(i, F_SETLK, &fl) < 0)
				fprintf(stderr, "Failed err=%d\n", errno);
			exit(0);
		}
	}
}