Get process run time

runtime.c

#include <stdio.h>
#include <stdlib.h>
#include <sys/sysctl.h>
#include <sys/types.h>
#include <time.h>

int main(int argc, char *argv[]) {
    pid_t pid = atoi(argv[1]);
    
    int mib[4] = { CTL_KERN, KERN_PROC, KERN_PROC_PID, pid };
    struct kinfo_proc proc;
    size_t size = sizeof(proc);
    sysctl(mib, 4, &proc, &size, NULL, 0);

    printf("pid %d was started %ld secs ago\n", pid, time(NULL) - proc.kp_proc.p_starttime.tv_sec);
    
    return 0;
}