gistfile1.c

#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main()
{
    struct flock fl;
    int fd;

    fl.l_type   = F_RDLCK;  /* F_RDLCK, F_WRLCK, F_UNLCK    */
    fl.l_whence = SEEK_SET; /* SEEK_SET, SEEK_CUR, SEEK_END */
    fl.l_start  = 0;        /* Offset from l_whence         */
    fl.l_len    = 0;        /* length, 0 = to EOF           */
    fl.l_pid    = getpid(); /* our PID                      */

    fd = open("/etc/dfs/sharetab", O_RDONLY);
    fcntl(fd, F_SETLKW, &fl);
    sleep(10);
}