uptime.c

#include <stdio.h>
#include <time.h>
#include <sys/param.h>
#include <sys/sysctl.h>


int
main()
{
    time_t uptime;
    time_t now;
    size_t size;
    int mib[2];

    struct timeval boottime;

    time(&now);
    size = sizeof(boottime);

    mib[0] = CTL_KERN;
    mib[1] = KERN_BOOTTIME;

    if (sysctl(mib, 2, &boottime, &size, NULL, 0) != -1) {
        uptime = now - boottime.tv_sec;
        printf("%d\n", uptime);
    }

    return 0;
}