getloadavg —
get system load averages
Standard C Library (libc, -lc)
#include <stdlib.h>
int
  
  getloadavg(double
    loadavg[], int
    nelem);
The getloadavg() function returns the number of
  processes in the system run queue averaged over various periods of time. Up to
  nelem samples are retrieved and assigned to successive
  elements of loadavg[]. The system imposes a maximum of 3
  samples, representing averages over the last 1, 5, and 15 minutes,
  respectively.
If the load average was unobtainable, -1 is returned; otherwise, the number of
  samples actually retrieved is returned.
The getloadavg() function appeared in
  4.3BSD-Reno.