#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE* fp = fopen("/dev/uptime", "r");
    if (!fp)
    {
        perror("fopen");
        return 1;
    }

    char buf[32];
    fgets(buf, sizeof(buf), fp);

    if (ferror(fp))
    {
        perror("fgets");
        return 1;
    }

    long ms_uptime = atol(buf);

    printf("up for %ld seconds\n", ms_uptime / 1000);

    fclose(fp);
}