141 lines
4.9 KiB
Python
141 lines
4.9 KiB
Python
# 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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from types import FrameType, TracebackType
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from typing import NoReturn, Type
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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) 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 OSError:
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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 OSError:
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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: exit.
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# we use os._exit to avoid running the atexit handlers. In particular, that
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# means we don't flush the logs. This is important because if we are using
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# a MemoryHandler, we could have logs buffered which are now buffered in both
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# the main and the child process, so if we let the main process flush the logs,
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# we'll get two copies.
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os._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(
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type_: Type[BaseException], value: BaseException, traceback: TracebackType
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) -> None:
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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 OSError:
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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: signal.Signals, frame: FrameType) -> NoReturn:
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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() -> None:
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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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