Fork-Based Daemon Process

daemon.py

# Basic skeleton of Daemon Fork-based daemon service
#
# It will accept a new socket connection, then trigger execute_cmd(). You
# can create a global variable to keep track of the child processes if you
# need to. This approach is sub-optimal, it should use select/poll on the
# accept() function, but this is python not C with a Posix interface. I am
# having the child process just do a simple "/bin/ls" as a proof of concept.
#
# Farhan Khan ([email protected])

import sys, os, socket, signal

def execute_cmd():
   pid = os.fork()
   if pid == 0: # This is the child process
      devnull = os.open('/dev/null', os.O_WRONLY)
      # Uncommented these two to make output go away
#     os.dup2(devnull, 1) # Overwrite stdout
#     os.dup2(devnull, 2) # Overwrite stderr
      os.execv('/bin/ls', ['ls', '/etc/'])
   else:
      pass

def signalHandler(signum, _):
   if signum == signal.SIGCHLD:
      dead_pid, status = os.wait()
      print("The child process %d died"%dead_pid)

def build_socket():
  # Binding on IPv6, w00t w00t!
   sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
   # Binding on port 10000
   sock.bind(('', 10000))
   sock.listen(10)
   return sock

def main():
   sock = build_socket()
   signal.signal(signal.SIGCHLD, signalHandler)

   while True:
      try:
         connection, client_address = sock.accept()

         print "Got a connection, do something"
         connection.send("Send me 10 characters, I'll send you them back and execute the command\r\n")
         data = connection.recv(10)
         connection.send(data)
         connection.close()
         execute_cmd()
      except socket.error, msg:
         continue # This will happen because of the signal interrupt
                  # Interrupt the accept(2) syscall

  print "Server dying, the end"

if __name__ == "__main__":
  main()