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re-implement daemonize (#8011)
This has long been something I've wanted to do. Basically the `Daemonize` code is both too flexible and not flexible enough, in that it offers a bunch of features that we don't use (changing UID, closing FDs in the child, logging to syslog) and doesn't offer a bunch that we could do with (redirecting stdout/err to a file instead of /dev/null; having the parent not exit until the child is running). As a first step, I've lifted the Daemonize code and removed the bits we don't use. This should be a non-functional change. Fixing everything else will come later.
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1
changelog.d/8011.misc
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1
changelog.d/8011.misc
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Replace daemonize library with a local implementation.
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@ -12,7 +12,6 @@
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import gc
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import logging
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import os
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@ -22,7 +21,6 @@ import sys
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import traceback
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from typing import Iterable
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from daemonize import Daemonize
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from typing_extensions import NoReturn
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from twisted.internet import defer, error, reactor
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@ -34,6 +32,7 @@ from synapse.config.server import ListenerConfig
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from synapse.crypto import context_factory
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from synapse.logging.context import PreserveLoggingContext
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from synapse.util.async_helpers import Linearizer
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from synapse.util.daemonize import daemonize_process
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from synapse.util.rlimit import change_resource_limit
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from synapse.util.versionstring import get_version_string
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@ -129,17 +128,8 @@ def start_reactor(
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if print_pidfile:
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print(pid_file)
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daemon = Daemonize(
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app=appname,
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pid=pid_file,
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action=run,
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auto_close_fds=False,
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verbose=True,
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logger=logger,
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)
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daemon.start()
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else:
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run()
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daemonize_process(pid_file, logger)
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run()
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def quit_with_error(error_string: str) -> NoReturn:
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@ -59,7 +59,6 @@ REQUIREMENTS = [
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"pyyaml>=3.11",
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"pyasn1>=0.1.9",
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"pyasn1-modules>=0.0.7",
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"daemonize>=2.3.1",
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"bcrypt>=3.1.0",
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"pillow>=4.3.0",
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"sortedcontainers>=1.4.4",
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131
synapse/util/daemonize.py
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synapse/util/daemonize.py
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# -*- coding: utf-8 -*-
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# Copyright (c) 2012, 2013, 2014 Ilya Otyutskiy <ilya.otyutskiy@icloud.com>
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# Copyright 2020 The Matrix.org Foundation C.I.C.
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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import atexit
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import fcntl
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import logging
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import os
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import signal
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import sys
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def daemonize_process(pid_file: str, logger: logging.Logger, chdir: str = "/") -> None:
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"""daemonize the current process
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This calls fork(), and has the main process exit. When it returns we will be
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running in the child process.
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"""
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# If pidfile already exists, we should read pid from there; to overwrite it, if
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# locking will fail, because locking attempt somehow purges the file contents.
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if os.path.isfile(pid_file):
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with open(pid_file, "r") as pid_fh:
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old_pid = pid_fh.read()
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# Create a lockfile so that only one instance of this daemon is running at any time.
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try:
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lock_fh = open(pid_file, "w")
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except IOError:
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print("Unable to create the pidfile.")
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sys.exit(1)
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try:
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# Try to get an exclusive lock on the file. This will fail if another process
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# has the file locked.
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fcntl.flock(lock_fh, fcntl.LOCK_EX | fcntl.LOCK_NB)
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except IOError:
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print("Unable to lock on the pidfile.")
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# We need to overwrite the pidfile if we got here.
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#
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# XXX better to avoid overwriting it, surely. this looks racey as the pid file
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# could be created between us trying to read it and us trying to lock it.
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with open(pid_file, "w") as pid_fh:
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pid_fh.write(old_pid)
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sys.exit(1)
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# Fork, creating a new process for the child.
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process_id = os.fork()
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if process_id != 0:
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# parent process
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sys.exit(0)
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# This is the child process. Continue.
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# Stop listening for signals that the parent process receives.
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# This is done by getting a new process id.
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# setpgrp() is an alternative to setsid().
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# setsid puts the process in a new parent group and detaches its controlling
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# terminal.
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os.setsid()
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# point stdin, stdout, stderr at /dev/null
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devnull = "/dev/null"
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if hasattr(os, "devnull"):
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# Python has set os.devnull on this system, use it instead as it might be
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# different than /dev/null.
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devnull = os.devnull
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devnull_fd = os.open(devnull, os.O_RDWR)
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os.dup2(devnull_fd, 0)
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os.dup2(devnull_fd, 1)
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os.dup2(devnull_fd, 2)
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os.close(devnull_fd)
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# now that we have redirected stderr to /dev/null, any uncaught exceptions will
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# get sent to /dev/null, so make sure we log them.
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#
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# (we don't normally expect reactor.run to raise any exceptions, but this will
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# also catch any other uncaught exceptions before we get that far.)
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def excepthook(type_, value, traceback):
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logger.critical("Unhanded exception", exc_info=(type_, value, traceback))
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sys.excepthook = excepthook
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# Set umask to default to safe file permissions when running as a root daemon. 027
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# is an octal number which we are typing as 0o27 for Python3 compatibility.
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os.umask(0o27)
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# Change to a known directory. If this isn't done, starting a daemon in a
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# subdirectory that needs to be deleted results in "directory busy" errors.
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os.chdir(chdir)
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try:
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lock_fh.write("%s" % (os.getpid()))
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lock_fh.flush()
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except IOError:
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logger.error("Unable to write pid to the pidfile.")
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print("Unable to write pid to the pidfile.")
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sys.exit(1)
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# write a log line on SIGTERM.
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def sigterm(signum, frame):
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logger.warning("Caught signal %s. Stopping daemon." % signum)
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sys.exit(0)
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signal.signal(signal.SIGTERM, sigterm)
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# Cleanup pid file at exit.
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def exit():
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logger.warning("Stopping daemon.")
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os.remove(pid_file)
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sys.exit(0)
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atexit.register(exit)
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logger.warning("Starting daemon.")
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