Why doesn't my python script keep running when I use &

Question

I have my gameServer.py script running remotely through PuTTy.

gameServer.py looks like this:

while True :
  (( listen for packets ))
  (( send all packets to all clients ))

WHEN I execute the script normally:

./gameServer.py

It works perfectly but the terminal is tied up. Naturally quitting PuTTy terminates my script.

I want to be able to close PuTTY and just have this script run perpetually so I tried:

./gameServer.py &

But that actually does not work and I don't understand why. First of all its not receiving or sending any packets when run in that & mode, second of all it will go "+ Stopped" whenever I type enter or ANYTHING into the console.

Answer 1

I don't see why it would be stopping, but try

nohup ./gameServer.py &

This should cause gameServer.py to ignore the hangup signal when you disconnect PuTTY

Answer 2

Try putting it in the background with the command: bg

user@rkt:~$ sleep 10
^z
[1]+  Stopped                 sleep 10
user@rkt:~$ bg
[1]+ sleep 10 &
user@rkt:~$ jobs
[1]+  Running                 sleep 10 &

Answer 3

You can change your process to be a daemon, then you can detouch your tty without having it killed:

def become_daemon():
  pid = os.fork ()
  if pid != 0: # if pid is not child...
    sys.exit(0)

  os.setsid() # Create new session and sets process group.
  pid = os.fork () # Will have INIT (pid 1) as parent process...
  if pid != 0: # if pid is not child...
    sys.exit(0)

and in your script simple invoke this function

You can look at this ActiveState recipe for more about the double-fork mechanism and more precise implementation.

Answer 4

Another way to log off and leave jobs running is with the "disown <jobid>" command. It allows you to unbind jobs from the current login session, so you can logoff.

Answer 5

This isn't aimed at answering your python problem, wouldn't have a clue where to start with that, but a temporary workaround / useful utility is called screen yum install screen or apt-get install screen if you're using either Debian/Ubuntu or Redhat/Centos/Fedora will install it. Screen provides you with a shell session that you can detach from and re-attach from without having to maintain a connection. I pretty much use it on any box I'm connected to because if I get disconnected I don't cut off potentially damaging work in it's flow.

just run screen to spawn a new session, run your command and then press ctrl+a and then d (keep control held down for both letters) To reconnect, run screen -dr from the command line and your screen session will attach itself to your current connection.