[root@home tmp]# ping www.baidu.com > /dev/null &
[1] 2759
[root@home tmp]# pstree -p
systemd(1)-+-agetty(157)
      |-agetty(163)
      |-avahi-daemon(129)---avahi-daemon(134)
      |-avahi-dnsconfd(125)
      |-crond(121)
      |-dbus-daemon(130)
      |-haveged(128)
      |-ifplugd(126)
      |-nginx(226)---nginx(227)
      |-ntpd(223)
      |-python(2727)
      |-rngd(124)
      |-sshd(216)---sshd(2683)---bash(2690)-+-ping(2759)
      |                   `-pstree(2760)
      |-systemd(2687)---(sd-pam)(2688)
      |-systemd-journal(76)
      |-systemd-logind(127)
      |-systemd-udevd(89)
      `-wpa_supplicant(153)

#!/usr/bin/env python
import os
import signal
import time
logfile="/tmp/daemon.log"
pid=os.fork()
#exit parent process
if pid: exit()
#get the pid of subprocess
daeid=os.getpid()
os.setsid()
os.umask(0)
os.chdir("/")
#Redirection file descriptor
fd=open("/dev/null","a+")
os.dup2(fd.fileno(),0)
os.dup2(fd.fileno(),1)
os.dup2(fd.fileno(),2)
fd.close()
log=open(logfile,'a')
log.write('Daemon start up at %s\n'%(time.strftime('%Y:%m:%d',time.localtime(time.time()))))
log.close()
def reload(a,b):
  log=open(logfile,'a')
  log.write('Daemon reload at %s\n'%(time.strftime('%Y:%m:%d',time.localtime(time.time()))))
  log.close()
while True:
  signal.signal(signal.SIGHUP,reload)
  time.sleep(2)