https://stackoverflow.com/questions/23133362
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RussianYou should flush stdout or any other output streams before calling os.fork. This question has a lot of usefull information about daemons in Python. Also check out this gist
Python: Strange stdout behaviour after fork()
Question
I am developing a python program, which contains a Daemon starting a subprocess for different users and services. Here's the code of interest:
'''
Created on 13.02.2014
@author: Richard Neumann
'''
import os, zmq, signal, threading, time, sys
from homie import Syslog, Config
from homie.lib.files import FieldsFile
from homie.service import Service
from homie.lib.user import User
from homie.lib.log import LogLvl, ErrLvl, LogEntry
from homie.lib.ipc import SocketClient
class Daemon():
'''
Class to represent the system service
'''
def __get_user(self, user_name):
'''
Gets a user securely
'''
user = False
try:
user = User(user_name)
except:
self.log('No such user "' + user_name + '"', LogLvl.DEFAULT, ErrLvl.ERROR)
return user
def __get_service_data(self, user, service_name):
'''
Returns the PID and the listening port of a service of a user
'''
service_data = user.get_runfile().get_data(service_name)
''' Runfile file contains "<service_name>=<pid>[tab]<port>" '''
service_data = service_data.split('\t')
pid = service_data[0] if len(service_data) >= 1 else None
port = service_data[1] if len(service_data) >= 2 else None
return pid, port
def __get_pid(self, user, service_name):
'''
Returns the PID of a service of a user
'''
pid, __ = self.__get_service_data(user, service_name)
if pid:
try:
pid = int(pid)
return pid
except:
self.log('No PID for service "' + service_name + '" for user "' + str(user) + '"', LogLvl.DEFAULT, ErrLvl.ERROR)
return None
def __get_port(self, user, service_name):
'''
Returns the listening port of a service of a user
'''
__, port = self.__get_service_data(user, service_name)
if port:
try:
port = int(port)
return port
except:
self.log('No listening port for service "' + service_name + '" for user "' + str(user) + '"', LogLvl.DEFAULT, ErrLvl.ERROR)
return None
def __start(self, user_name, service_name):
'''
Starts a service for a user
'''
print('Starting service "' + service_name + '" for user "' + user_name + '"\t\t'),
if self.__status(user_name, service_name):
''' Service is already running for user '''
print('[ALREADY RUNNING]')
return True
else:
user = self.__get_user(user_name)
if user:
''' We have a valid user '''
if service_name in user.get_services():
''' The service is enabled for the user '''
try:
ServiceClass = Service.by_classname(service_name)
except:
print('[NO SUCH SERVICE]')
return False
pid = os.fork()
if pid != 0:
''' Daemon: Return OK '''
print('[OK]')
return True
else:
''' Child: Start new service '''
os.setuid(user.get_uid()) # Do this first!
service_instance = ServiceClass(user)
service_instance.init()
service_instance.start()
return True
else:
print('[NOT ENABLED]')
return False
else:
print('[NO SUCH USER]')
return False
print('[FAILED]')
return False
def __stop(self, user_name, service_name):
'''
Stops a service for a user
'''
print('Stopping service "' + service_name + '" for user "' + user_name + '"\t\t'),
if self.__status(user_name, service_name):
pid = self.__get_pid(self.__get_user(user_name), service_name)
''' Kill the process '''
try:
os.kill(pid, signal.SIGTERM)
''' And remove runfile entry '''
user = self.__get_user(user_name)
runfile = user.get_runfile()
runfile.remove(service_name)
print('[OK]')
return True
except:
print('[FAILED]')
return False
else:
print('[NOT RUNNING]')
return True
def __status(self, user_name, service_name, quiet=True):
'''
Determines status of the daemon
'''
if not quiet: print('Service "' + service_name + '" for user "' + user_name + '" is\t\t'),
user = self.__get_user(user_name)
if user:
pid = self.__get_pid(user, service_name)
try:
os.kill(pid, 0)
status = '[UP'
try:
port = self.__get_port(self.__get_user(user_name), service_name)
sc = SocketClient(port)
if sc.query('status') == 'RUNNING':
status += ' & RUNNING]'
else:
status += ' & STOPPED]'
except:
status += ' & UNDETERMINED]'
if not quiet: print(status)
except:
if not quiet: print('[DOWN]')
return False
return True
else:
if not quiet: print('[NO SUCH USER]')
return False
def start(self, user_name=None, service_name=None):
'''
Starts the daemons
'''
if user_name:
''' Start user's services '''
if service_name:
self.__start(user_name, service_name)
else:
user = self.__get_user(user_name)
if user:
for service_name in user.get_services():
self.start(user_name, service_name)
else:
print('No such user: ' + user_name)
else:
for user in User.fetch(Config.CUSTOMERS_GROUP):
self.start(str(user), service_name)
def stop(self, user_name=None, service_name=None):
'''
Stops the daemons
'''
if user_name:
''' Start user's services '''
if service_name:
self.__stop(user_name, service_name)
else:
user = self.__get_user(user_name)
if user:
for service_name in user.get_services():
self.stop(user_name, service_name)
else:
print('No such user: ' + user_name)
else:
for user in User.fetch(Config.CUSTOMERS_GROUP):
self.stop(user.get_name(), service_name)
def status(self, user_name=None, service_name=None):
'''
Determines status of the daemons
'''
if user_name:
''' Start user's services '''
if service_name:
self.__status(user_name, service_name, quiet=False)
else:
user = self.__get_user(user_name)
if user:
for service_name in user.get_services():
self.status(user_name, service_name)
else:
print('No such user: ' + user_name)
else:
for user in User.fetch(Config.CUSTOMERS_GROUP):
self.status(user.get_name(), service_name)
def restart(self, user_name=None, service_name=None):
'''
Restarts the daemons
'''
self.stop(user_name, service_name)
self.start(user_name, service_name)
def reload(self, user_name=None, service_name=None):
'''
Reloads the deamons
'''
# TODO: Just reload
self.restart(user_name, service_name)
def log(self, message, loglvl, errlvl):
'''
Logging
'''
entry = LogEntry(self, message, loglvl, errlvl)
Syslog.log(entry)
The strange thing now is, that if I run this program when one user has more than one service configured, it will write the output twice and the second time to the same line as here for user test2 in the last line:
# /etc/init.d/homied start
Starting service "ExposeAgent" for user "test" [OK]
Starting service "ExposeAgent" for user "test2" [OK]
Starting service "Someservice" for user "test2" [NO SUCH SERVICE]
Starting service "ExposeAgent" for user "test3" [OK]
Starting service "ExposeAgent" for user "test4" [OK]
Starting service "ExposeAgent" for user "test5" [OK]
Starting service "ExposeAgent" for user "test6" [OK]
Starting service "ExposeAgent" for user "test7" [OK]
Starting service "ExposeAgent" for user "test8" [OK]
Starting service "ExposeAgent" for user "test9" [OK]
Starting service "ExposeAgent" for user "test2" Starting service "Someservice" for user "test2" [NO SUCH SERVICE]
I suspect the error is somewhere in the __start() method:
def __start(self, user_name, service_name):
'''
Starts a service for a user
'''
print('Starting service "' + service_name + '" for user "' + user_name + '"\t\t'),
if self.__status(user_name, service_name):
''' Service is already running for user '''
print('[ALREADY RUNNING]')
return True
else:
user = self.__get_user(user_name)
if user:
''' We have a valid user '''
if service_name in user.get_services():
''' The service is enabled for the user '''
try:
ServiceClass = Service.by_classname(service_name)
except:
print('[NO SUCH SERVICE]')
return False
pid = os.fork()
if pid != 0:
''' Daemon: Return OK '''
print('[OK]')
return True
else:
''' Child: Start new service '''
os.setuid(user.get_uid()) # Do this first!
service_instance = ServiceClass(user)
service_instance.init()
service_instance.start()
return True
else:
print('[NOT ENABLED]')
return False
else:
print('[NO SUCH USER]')
return False
print('[FAILED]')
return False
But I don't understand where stuff is going wrong. I'd appreciate any hint.
Regards,
Richard
Solution
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