My python daemon is run through systemd, with stderr logging on a file.
A simplified version of the systemd service file is this:
[Unit]
Description=Test
[Service]
ExecStart=/path/to/test.py
StandardError=file:/path/to/error.log
[Install]
WantedBy=multi-user.target
The python daemon instantiates a threaded TCP server and runs serve_forever on it. The problem is any error happening after the thread start is not logged on the error.log file. Any error happening before is logged.
A simplified version of the python daemon is this:
import threading, socketserver
class ThreadedTCPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
pass
class TCPHandler(socketserver.BaseRequestHandler):
def handle(self):
pass
#barfoo
TCPServer = ThreadedTCPServer(("127.0.0.1", 12345), TCPHandler)
TCPThread = threading.Thread(target=TCPServer.serve_forever)
TCPThread.start()
#foobar
If I uncomment "barfoo", a "name not defined" is logged in the error.log file.
If I uncomment "foobar", nothing is logged.
Also, since the TCP server thread is still running, the systemd daemon is shown as running, so I can't even detect the error from there.
If I run the daemon from command line, both errors are correctly logged on stderr (and redirected if I redirect stderr on a file). Trying the same redirect in the systemd script, instead of the StandardError directive, has the same effect as the latter.
EDIT: I tested the same thing with a generic infinite looping thread, for the same effect:
import threading
def run():
while True:
pass
#aaaaaa # logs an error on systemd's stderr
test_thread = threading.Thread(target=run)
test_thread.start()
#foobar # doesn't log an error on systemd's stderr
