#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <utmp.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

int main(void)
{
        int fd, num, err;
        struct stat fs;
        struct utmp *u0, *u;
        size_t maplen;

        fd = open(_PATH_UTMP, O_RDONLY);
        if (fd < 0) {
                perror(_PATH_UTMP);
                exit(-1);
        }

        if (fstat(fd, &fs) < 0) {
                perror("fstat");
                exit(-1);
        }

        /* The size of a mapped area must be a multiple of pagesize */
        for (maplen = fs.st_size;
             maplen % sysconf(_SC_PAGE_SIZE) != 0;
             maplen++);

        u0 = u = mmap(NULL, maplen, PROT_READ, MAP_PRIVATE, fd, 0);
        if (u == MAP_FAILED) {
                perror("mmap");
                exit(-1);
        }

        num = fs.st_size / sizeof(struct utmp);

        while (num--) {
                if (u->ut_type != DEAD_PROCESS) {
                        time_t t = u->ut_time;
                        printf("%8.8s|%16.16s|%8.8s|%s", u->ut_name,
                               u->ut_host, u->ut_line, ctime(&t));
                }
                u++;
        }

        err = munmap(u0, maplen);
        if (err) {
                perror("munmap");
                exit(-1);
        }
        close(fd);

        return 0;
}