pygame.init() fails when run with systemd

Question

I'm trying to run a python pygame script with systemd and for some reason the script just exits without an error. This is on a Raspberry Pi with Raspian "Jessie lite".

If I run the script manually with "sudo python myscript.py" it works fine.

sudo systemctl status myscript.service reports:

* myscript.service - Python Script
Loaded: loaded    /etc/systemd/system/myscript.service; enabled)    Active: inactive (dead) since Mon 2016-08-29 04:33:19 UTC; 1s ago
Process: 3275> ExecStart=/usr/bin/python /home/pi/myscript.py (code=killed, signal=HUP)
Main PID: 3275 (code=killed, signal=HUP)

If I start the service manually with sudo systemctl start myscript.service the same thing happens.

I've stripped down my script to just the pygame.init() call. This is where it exits.

If I try to initialize the modules manually then "cdrom", "joystick", "threads", and "font" initialize normally but a call to display.init() causes the program to exit. There is no exception raised.

The only resource I could find online is this guy. It seems he ran into the exact same thing I'm seeing. I've tried strace and if I wait long enough (2 minutes), it will work! Obviously I can't run with strace all the time. I think it slows down the execution of the initialization to somehow allow it to work.

EDIT: So the issue appears to be systemd sending a SIGHUP. If this is unhandled in Python the default action is to exit. A quick fix is the catch SIGHUP:

import signal
def handler(signum, frame):
    pass

try:
    signal.signal(signal.SIGHUP, handler)
except AttributeError:
    # Windows compatibility
    pass

So many burning questions. Why does systemd do this? Why does strace fix the issue? Why do some Python scripts get SIGHUP while others don't?

Answer 1

I don't have an answer, but I'm experiencing the same thing, so I'll add some more detail.

Here's the cut-down code:

#!/usr/bin/python2.7

import logging
from pygame import display
import signal
import time

def handler(signum, frame):
  """Why is systemd sending sighups? I DON'T KNOW."""
  logging.warning("Got a {} signal. Doing nothing".format(signum))

signal.signal(signal.SIGHUP, handler)
signal.signal(signal.SIGTERM, handler)
signal.signal(signal.SIGCONT, handler)

logging.warning("About to start display.")
try:
  display.init()   # hups
except Exception as ex:
  logging.warning("Got any exception: %s " % ex)

logging.warning("Quitting in 60")
time.sleep(60)

Here's the log that produces:

Jul  8 22:30:27 beardog systemd[1]: Started PyGame Test.
Jul  8 22:30:27 beardog pygame[17406]: WARNING:root:About to start display.
Jul  8 22:30:27 beardog pygame[17406]: WARNING:root:Got a 1 signal. Doing nothing
Jul  8 22:30:27 beardog pygame[17406]: WARNING:root:Got a 18 signal. Doing nothing
Jul  8 22:30:27 beardog pygame[17406]: WARNING:root:Quitting in 60

It's getting a SIGCONT immediately after the SIGHUP, but no SIGTERM. Systemd claims to only ever send a SIGHUP after a SIGTERM, so maybe it's coming from somewhere else? I can't find anything relevant in the pygame code though.

I've turned on systemd debug logging, but it doesn't print anything interesting.

Here's my systemd config.

[Unit]
Description=PyGame Test
After=syslog.target network.target network-online.target graphical.target

[Service]
Type=simple
WorkingDirectory=/path/to/code/pygame/
ExecStart=/path/to/code/pygame/why.py
Restart=always
RestartSec=5
LimitNOFILE=10000
StandardOutput=syslog
StandardError=syslog
SyslogIdentifier=pygame
SendSIGHUP=no

[Install]
WantedBy=multi-user.target

I've tried this as Type=forking, oneshot and dbus (although it isn't any of them). I've also tried TimeoutStartSec=20, but no change. Tested on an Ubuntu Xenial laptop and on a Raspberry pi running Raspbian. Both python2.7 and python3. Code works fine when run manually, and seems to work when run under strace in systemd. /o\

Like the OP, I can work around it by catching the SIGHUP, but after this much debugging I'd love to know what's going on.

Answer 2

For me the solution was to only init specific modules which I needed.

In my case instead pygame.init() I initialized only pygame.mixer.init() and now systemd can start the service.