6.2. Using the sched_setaffinity() System Call to Set Processor Affinity

In addition to the taskset command, processor affinity can also be set using the sched_setaffinity() system call.
The following code excerpt retrieves the CPU affinity information for a specified PID. If the PID passed to it is 0, it will return the affinity information for the current process:
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sched.h>

int main(int argc, char **argv)
  int i, online=0;
  ulong ncores = sysconf(_SC_NPROCESSORS_CONF);
  cpu_set_t *setp = CPU_ALLOC(ncores);
  ulong setsz = CPU_ALLOC_SIZE(ncores);

  CPU_ZERO_S(setsz, setp);

  if (sched_getaffinity(0, setsz, setp) == -1) {
    perror("sched_getaffinity(2) failed");

  for (i=0; i < CPU_COUNT_S(setsz, setp); i++) {
    if (CPU_ISSET_S(i, setsz, setp))
  printf("%d cores configured, %d cpus allowed in affinity mask\n", ncores, online);


For more information, or for further reading, the following man page is related to the information given in this section:
  • sched_setaffinity(2)