Why did you start with two master processes and finally become a worker?

[ygm521]

i am run on vmware, use default conf：
first:
root 4009 1 0 02:25 ? 00:00:00 nginx: master process ./nginx
root 4010 4009 22 02:25 ? 00:00:01 nginx: master process ./nginx

wait a time like this :
root 4010 1 18 02:25 ? 00:00:11 nginx: worker process
What do I need to do whenever I reboot?