Writing daemons in python

Simple daemon skeleton for Python 3.x

This is a simple daemon skeleton that:

parses CLI arguments
Sets up logging
Daemonizes according to CLI arguments
Captures SIGINT/SIGTERM as termination requests
Captures SIGHUP in case one should re-read the configuration

This does not use PEP-3143 but daemonize

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Redistributions of source code must retain this list of conditions and the following disclaimer.
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THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

	import argparse
	import sys
	import logging

	import signal, lockfile, grp, os

	from pwd import getpwnam
	from daemonize import Daemonize

	class ExampleDaemon:
	def __init__(self, args, logger):
	self.args = args
	self.logger = logger
	self.terminate = False
	self.rereadConfig = True

	def signalSigHup(self, *args):
	self.rereadConfig = True

	def signalTerm(self, *args):
	self.terminate = True

	def __enter__(self):
	return self

	def __exit__(self, type, value, tb):
	pass

	def run(self):
	signal.signal(signal.SIGHUP, self.signalSigHup)
	signal.signal(signal.SIGTERM, self.signalTerm)
	signal.signal(signal.SIGINT, self.signalTerm)

	self.logger.info("Service running")

	while True:
	# Do whatever is required to be done ...
	if self.terminate:
	break

	self.logger.info("Shutting down due to user request")

	def mainDaemon():
	parg = parseArguments()
	args = parg['args']
	logger = parg['logger']

	logger.debug("Daemon starting ...")
	with ExampleDaemon(args, logger) as sampleDaemon:
	sampleDaemon.run()

	def parseArguments():
	ap = argparse.ArgumentParser(description = 'Example daemon')
	ap.add_argument('-f', '--foreground', action='store_true', help="Do not daemonize - stay in foreground and dump debug information to the terminal")

	ap.add_argument('--uid', type=str, required=False, default=None, help="User ID to impersonate when launching as root")
	ap.add_argument('--gid', type=str, required=False, default=None, help="Group ID to impersonate when launching as root")
	ap.add_argument('--chroot', type=str, required=False, default=None, help="Chroot directory that should be switched into")
	ap.add_argument('--pidfile', type=str, required=False, default="/var/run/sampledaemon.pid", help="PID file to keep only one daemon instance running")
	ap.add_argument('--loglevel', type=str, required=False, default="error", help="Loglevel to use (debug, info, warning, error, critical). Default: error")
	ap.add_argument('--logfile', type=str, required=False, default="/var/log/sampledaemon.log", help="Logfile that should be used as target for log messages")

	args = ap.parse_args()
	loglvls = {
	"DEBUG" : logging.DEBUG,
	"INFO" : logging.INFO,
	"WARNING" : logging.WARNING,
	"ERROR" : logging.ERROR,
	"CRITICAL" : logging.CRITICAL
	}
	if not args.loglevel.upper() in loglvls:
	print("Unknown log level {}".format(args.loglevel.upper()))
	sys.exit(1)

	logger = logging.getLogger()
	logger.setLevel(loglvls[args.loglevel.upper()])
	if args.logfile:
	fileHandleLog = logging.FileHandler(args.logfile)
	logger.addHandler(fileHandleLog)

	return { 'args' : args, 'logger' : logger }

	# Entry function for CLI program
	# This also configures the daemon properties

	def mainStartup():
	parg = parseArguments()
	args = parg['args']
	logger = parg['logger']

	daemonPidfile = args.pidfile
	daemonUid = None
	daemonGid = None
	daemonChroot = "/"

	if args.uid:
	try:
	args.uid = int(args.uid)
	except ValueError:
	try:
	args.uid = getpwnam(args.uid).pw_uid
	except KeyError:
	logger.critical("Unknown user {}".format(args.uid))
	print("Unknown user {}".format(args.uid))
	sys.exit(1)
	daemonUid = args.uid
	if args.gid:
	try:
	args.gid = int(args.gid)
	except ValueError:
	try:
	args.gid = grp.getgrnam(args.gid)[2]
	except KeyError:
	logger.critical("Unknown group {}".format(args.gid))
	print("Unknown group {}".format(args.gid))
	sys.exit(1)

	daemonGid = args.gid

	if args.chroot:
	if not os.path.isdir(args.chroot):
	logger.critical("Non existing chroot directors {}".format(args.chroot))
	print("Non existing chroot directors {}".format(args.chroot))
	sys.exit(1)
	daemonChroot = args.chroot

	if args.foreground:
	logger.debug("Launching in foreground")
	with ExampleDaemon(args, logger) as sampleDaemon:
	sampleDaemon.run()
	else:
	logger.debug("Daemonizing ...")
	daemon = Daemonize(
	app="ExampleDaemon",
	action=mainDaemon,
	pid=daemonPidfile,
	user=daemonUid,
	group=daemonGid,
	chdir=daemonChroot
	)
	daemon.start()


	if __name__ == "__main__":
	mainStartup()

Writing daemons in python

The code

Simple daemon skeleton for Python 3.x