# -*- coding: utf-8 -*-
# daemon/daemon.py
# Part of python-daemon, an implementation of PEP 3143.
#
# Copyright © 2008–2010 Ben Finney <ben+python@benfinney.id.au>
# Copyright © 2007–2008 Robert Niederreiter, Jens Klein
# Copyright © 2004–2005 Chad J. Schroeder
# Copyright © 2003 Clark Evans
# Copyright © 2002 Noah Spurrier
# Copyright © 2001 Jürgen Hermann
#
# This is free software: you may copy, modify, and/or distribute this work
# under the terms of the Python Software Foundation License, version 2 or
# later as published by the Python Software Foundation.
# No warranty expressed or implied. See the file LICENSE.PSF-2 for details.
""" Daemon process behaviour.
"""
import os
import sys
import resource
import errno
import signal
import socket
import atexit
class DaemonError(Exception):
""" Base exception class for errors from this module. """
class DaemonOSEnvironmentError(DaemonError, OSError):
""" Exception raised when daemon OS environment setup receives error. """
class DaemonProcessDetachError(DaemonError, OSError):
""" Exception raised when process detach fails. """
class DaemonContext(object):
""" Context for turning the current program into a daemon process.
A `DaemonContext` instance represents the behaviour settings and
process context for the program when it becomes a daemon. The
behaviour and environment is customised by setting options on the
instance, before calling the `open` method.
Each option can be passed as a keyword argument to the `DaemonContext`
constructor, or subsequently altered by assigning to an attribute on
the instance at any time prior to calling `open`. That is, for
options named `wibble` and `wubble`, the following invocation::
foo = daemon.DaemonContext(wibble=bar, wubble=baz)
foo.open()
is equivalent to::
foo = daemon.DaemonContext()
foo.wibble = bar
foo.wubble = baz
foo.open()
The following options are defined.
`files_preserve`
:Default: ``None``
List of files that should *not* be closed when starting the
daemon. If ``None``, all open file descriptors will be closed.
Elements of the list are file descriptors (as returned by a file
object's `fileno()` method) or Python `file` objects. Each
specifies a file that is not to be closed during daemon start.
`chroot_directory`
:Default: ``None``
Full path to a directory to set as the effective root directory of
the process. If ``None``, specifies that the root directory is not
to be changed.
`working_directory`
:Default: ``'/'``
Full path of the working directory to which the process should
change on daemon start.
Since a filesystem cannot be unmounted if a process has its
current working directory on that filesystem, this should either
be left at default or set to a directory that is a sensible “home
directory” for the daemon while it is running.
`umask`
:Default: ``0``
File access creation mask (“umask”) to set for the process on
daemon start.
Since a process inherits its umask from its parent process,
starting the daemon will reset the umask to this value so that
files are created by the daemon with access modes as it expects.
`pidfile`
:Default: ``None``
Context manager for a PID lock file. When the daemon context opens
and closes, it enters and exits the `pidfile` context manager.
`detach_process`
:Default: ``None``
If ``True``, detach the process context when opening the daemon
context; if ``False``, do not detach.
If unspecified (``None``) during initialisation of the instance,
this will be set to ``True`` by default, and ``False`` only if
detaching the process is determined to be redundant; for example,
in the case when the process was started by `init`, by `initd`, or
by `inetd`.
`signal_map`
:Default: system-dependent
Mapping from operating system signals to callback actions.
The mapping is used when the daemon context opens, and determines
the action for each signal's signal handler:
* A value of ``None`` will ignore the signal (by setting the
signal action to ``signal.SIG_IGN``).
* A string value will be used as the name of an attribute on the
``DaemonContext`` instance. The attribute's value will be used
as the action for the signal handler.
* Any other value will be used as the action for the
signal handler. See the ``signal.signal`` documentation
for details of the signal handler interface.
The default value depends on which signals are defined on the
running system. Each item from the list below whose signal is
actually defined in the ``signal`` module will appear in the
default map:
* ``signal.SIGTTIN``: ``None``
* ``signal.SIGTTOU``: ``None``
* ``signal.SIGTSTP``: ``None``
* ``signal.SIGTERM``: ``'terminate'``
Depending on how the program will interact with its child
processes, it may need to specify a signal map that
includes the ``signal.SIGCHLD`` signal (received when a
child process exits). See the specific operating system's
documentation for more detail on how to determine what
circumstances dictate the need for signal handlers.
`uid`
:Default: ``os.getuid()``
`gid`
:Default: ``os.getgid()``
The user ID (“UID”) value and group ID (“GID”) value to switch
the process to on daemon start.
The default values, the real UID and GID of the process, will
relinquish any effective privilege elevation inherited by the
process.
`prevent_core`
:Default: ``True``
If true, prevents the generation of core files, in order to avoid
leaking sensitive information from daemons run as `root`.
`stdin`
:Default: ``None``
`stdout`
:Default: ``None``
`stderr`
:Default: ``None``
Each of `stdin`, `stdout`, and `stderr` is a file-like object
which will be used as the new file for the standard I/O stream
`sys.stdin`, `sys.stdout`, and `sys.stderr` respectively. The file
should therefore be open, with a minimum of mode 'r' in the case
of `stdin`, and mode 'w+' in the case of `stdout` and `stderr`.
If the object has a `fileno()` method that returns a file
descriptor, the corresponding file will be excluded from being
closed during daemon start (that is, it will be treated as though
it were listed in `files_preserve`).
If ``None``, the corresponding system stream is re-bound to the
file named by `os.devnull`.
"""
def __init__(
self,
chroot_directory=None,
working_directory='/',
umask=0,
uid=None,
gid=None,
prevent_core=True,
detach_process=None,
files_preserve=None,
pidfile=None,
stdin=None,
stdout=None,
stderr=None,
signal_map=None,
):
""" Set up a new instance. """
self.chroot_directory = chroot_directory
self.working_directory = working_directory
self.umask = umask
self.prevent_core = prevent_core
self.files_preserve = files_preserve
self.pidfile = pidfile
self.stdin = stdin
self.stdout = stdout
self.stderr = stderr
if uid is None:
uid = os.getuid()
self.uid = uid
if gid is None:
gid = os.getgid()
self.gid = gid
if detach_process is None:
detach_process = is_detach_process_context_required()
self.detach_process = detach_process
if signal_map is None:
signal_map = make_default_signal_map()
self.signal_map = signal_map
self._is_open = False
@property
def is_open(self):
""" ``True`` if the instance is currently open. """
return self._is_open
def open(self):
""" Become a daemon process.
:Return: ``None``
Open the daemon context, turning the current program into a daemon
process. This performs the following steps:
* If this instance's `is_open` property is true, return
immediately. This makes it safe to call `open` multiple times on
an instance.
* If the `prevent_core` attribute is true, set the resource limits
for the process to prevent any core dump from the process.
* If the `chroot_directory` attribute is not ``None``, set the
effective root directory of the process to that directory (via
`os.chroot`).
This allows running the daemon process inside a “chroot gaol”
as a means of limiting the system's exposure to rogue behaviour
by the process. Note that the specified directory needs to
already be set up for this purpose.
* Set the process UID and GID to the `uid` and `gid` attribute
values.
* Close all open file descriptors. This excludes those listed in
the `files_preserve` attribute, and those that correspond to the
`stdin`, `stdout`, or `stderr` attributes.
* Change current working directory to the path specified by the
`working_directory` attribute.
* Reset the file access creation mask to the value specified by
the `umask` attribute.
* If the `detach_process` option is true, detach the current
process into its own process group, and disassociate from any
controlling terminal.
* Set signal handlers as specified by the `signal_map` attribute.
* If any of the attributes `stdin`, `stdout`, `stderr` are not
``None``, bind the system streams `sys.stdin`, `sys.stdout`,
and/or `sys.stderr` to the files represented by the
corresponding attributes. Where the attribute has a file
descriptor, the descriptor is duplicated (instead of re-binding
the name).
* If the `pidfile` attribute is not ``None``, enter its context
manager.
* Mark this instance as open (for the purpose of future `open` and
`close` calls).
* Register the `close` method to be called during Python's exit
processing.
When the function returns, the running program is a daemon
process.
"""
if self.is_open:
return
if self.chroot_directory is not None:
change_root_directory(self.chroot_directory)
if self.prevent_core:
prevent_core_dump()
change_file_creation_mask(self.umask)
change_working_directory(self.working_directory)
change_process_owner(self.uid, self.gid)
if self.detach_process:
detach_process_context()
signal_handler_map = self._make_signal_handler_map()
set_signal_handlers(signal_handler_map)
exclude_fds = self._get_exclude_file_descriptors()
close_all_open_files(exclude=exclude_fds)
redirect_stream(sys.stdin, self.stdin)
redirect_stream(sys.stdout, self.stdout)
redirect_stream(sys.stderr, self.stderr)
if self.pidfile is not None:
self.pidfile.__enter__()
self._is_open = True
register_atexit_function(self.close)
def __enter__(self):
""" Context manager entry point. """
self.open()
return self
def close(self):
""" Exit the daemon process context.
:Return: ``None``
Close the daemon context. This performs the following steps:
* If this instance's `is_open` property is false, return
immediately. This makes it safe to call `close` multiple times
on an instance.
* If the `pidfile` attribute is not ``None``, exit its context
manager.
* Mark this instance as closed (for the purpose of future `open`
and `close` calls).
"""
if not self.is_open:
return
if self.pidfile is not None:
# Follow the interface for telling a context manager to exit,
# <URL:http://docs.python.org/library/stdtypes.html#typecontextmanager>.
self.pidfile.__exit__(None, None, None)
self._is_open = False
def __exit__(self, exc_type, exc_value, traceback):
""" Context manager exit point. """
self.close()
def terminate(self, signal_number, stack_frame):
""" Signal handler for end-process signals.
:Return: ``None``
Signal handler for the ``signal.SIGTERM`` signal. Performs the
following step:
* Raise a ``SystemExit`` exception explaining the signal.
"""
exception = SystemExit(
"Terminating on signal %(signal_number)r"
% vars())
raise exception
def _get_exclude_file_descriptors(self):
""" Return the set of file descriptors to exclude closing.
Returns a set containing the file descriptors for the
items in `files_preserve`, and also each of `stdin`,
`stdout`, and `stderr`:
* If the item is ``None``, it is omitted from the return
set.
* If the item has a ``fileno()`` method, that method's
return value is in the return set.
* Otherwise, the item is in the return set verbatim.
"""
files_preserve = self.files_preserve
if files_preserve is None:
files_preserve = []
files_preserve.extend(
item for item in [self.stdin, self.stdout, self.stderr]
if hasattr(item, 'fileno'))
exclude_descriptors = set()
for item in files_preserve:
if item is None:
continue
if hasattr(item, 'fileno'):
exclude_descriptors.add(item.fileno())
else:
exclude_descriptors.add(item)
return exclude_descriptors
def _make_signal_handler(self, target):
""" Make the signal handler for a specified target object.
If `target` is ``None``, returns ``signal.SIG_IGN``. If
`target` is a string, returns the attribute of this
instance named by that string. Otherwise, returns `target`
itself.
"""
if target is None:
result = signal.SIG_IGN
elif isinstance(target, basestring):
name = target
result = getattr(self, name)
else:
result = target
return result
def _make_signal_handler_map(self):
""" Make the map from signals to handlers for this instance.
Constructs a map from signal numbers to handlers for this
context instance, suitable for passing to
`set_signal_handlers`.
"""
signal_handler_map = dict(
(signal_number, self._make_signal_handler(target))
for (signal_number, target) in self.signal_map.items())
return signal_handler_map
def change_working_directory(directory):
""" Change the working directory of this process.
"""
try:
os.chdir(directory)
except Exception, exc:
error = DaemonOSEnvironmentError(
"Unable to change working directory (%(exc)s)"
% vars())
raise error
def change_root_directory(directory):
""" Change the root directory of this process.
Sets the current working directory, then the process root
directory, to the specified `directory`. Requires appropriate
OS privileges for this process.
"""
try:
os.chdir(directory)
os.chroot(directory)
except Exception, exc:
error = DaemonOSEnvironmentError(
"Unable to change root directory (%(exc)s)"
% vars())
raise error
def change_file_creation_mask(mask):
""" Change the file creation mask for this process.
"""
try:
os.umask(mask)
except Exception, exc:
error = DaemonOSEnvironmentError(
"Unable to change file creation mask (%(exc)s)"
% vars())
raise error
def change_process_owner(uid, gid):
""" Change the owning UID and GID of this process.
Sets the GID then the UID of the process (in that order, to
avoid permission errors) to the specified `gid` and `uid`
values. Requires appropriate OS privileges for this process.
"""
try:
os.setgid(gid)
os.setuid(uid)
except Exception, exc:
error = DaemonOSEnvironmentError(
"Unable to change file creation mask (%(exc)s)"
% vars())
raise error
def prevent_core_dump():
""" Prevent this process from generating a core dump.
Sets the soft and hard limits for core dump size to zero. On
Unix, this prevents the process from creating core dump
altogether.
"""
core_resource = resource.RLIMIT_CORE
try:
# Ensure the resource limit exists on this platform, by requesting
# its current value
core_limit_prev = resource.getrlimit(core_resource)
except ValueError, exc:
error = DaemonOSEnvironmentError(
"System does not support RLIMIT_CORE resource limit (%(exc)s)"
% vars())
raise error
# Set hard and soft limits to zero, i.e. no core dump at all
core_limit = (0, 0)
resource.setrlimit(core_resource, core_limit)
def detach_process_context():
""" Detach the process context from parent and session.
Detach from the parent process and session group, allowing the
parent to exit while this process continues running.
Reference: “Advanced Programming in the Unix Environment”,
section 13.3, by W. Richard Stevens, published 1993 by
Addison-Wesley.
"""
def fork_then_exit_parent(error_message):
""" Fork a child process, then exit the parent process.
If the fork fails, raise a ``DaemonProcessDetachError``
with ``error_message``.
"""
try:
pid = os.fork()
if pid > 0:
os._exit(0)
except OSError, exc:
exc_errno = exc.errno
exc_strerror = exc.strerror
error = DaemonProcessDetachError(
"%(error_message)s: [%(exc_errno)d] %(exc_strerror)s" % vars())
raise error
fork_then_exit_parent(error_message="Failed first fork")
os.setsid()
fork_then_exit_parent(error_message="Failed second fork")
def is_process_started_by_init():
""" Determine if the current process is started by `init`.
The `init` process has the process ID of 1; if that is our
parent process ID, return ``True``, otherwise ``False``.
"""
result = False
init_pid = 1
if os.getppid() == init_pid:
result = True
return result
def is_socket(fd):
""" Determine if the file descriptor is a socket.
Return ``False`` if querying the socket type of `fd` raises an
error; otherwise return ``True``.
"""
result = False
file_socket = socket.fromfd(fd, socket.AF_INET, socket.SOCK_RAW)
try:
socket_type = file_socket.getsockopt(
socket.SOL_SOCKET, socket.SO_TYPE)
except socket.error, exc:
exc_errno = exc.args[0]
if exc_errno == errno.ENOTSOCK:
# Socket operation on non-socket
pass
else:
# Some other socket error
result = True
else:
# No error getting socket type
result = True
return result
def is_process_started_by_superserver():
""" Determine if the current process is started by the superserver.
The internet superserver creates a network socket, and
attaches it to the standard streams of the child process. If
that is the case for this process, return ``True``, otherwise
``False``.
"""
result = False
stdin_fd = sys.__stdin__.fileno()
if is_socket(stdin_fd):
result = True
return result
def is_detach_process_context_required():
""" Determine whether detaching process context is required.
Return ``True`` if the process environment indicates the
process is already detached:
* Process was started by `init`; or
* Process was started by `inetd`.
"""
result = True
if is_process_started_by_init() or is_process_started_by_superserver():
result = False
return result
def close_file_descriptor_if_open(fd):
""" Close a file descriptor if already open.
Close the file descriptor `fd`, suppressing an error in the
case the file was not open.
"""
try:
os.close(fd)
except OSError, exc:
if exc.errno == errno.EBADF:
# File descriptor was not open
pass
else:
error = DaemonOSEnvironmentError(
"Failed to close file descriptor %(fd)d"
" (%(exc)s)"
% vars())
raise error
MAXFD = 2048
def get_maximum_file_descriptors():
""" Return the maximum number of open file descriptors for this process.
Return the process hard resource limit of maximum number of
open file descriptors. If the limit is “infinity”, a default
value of ``MAXFD`` is returned.
"""
limits = resource.getrlimit(resource.RLIMIT_NOFILE)
result = limits[1]
if result == resource.RLIM_INFINITY:
result = MAXFD
return result
def close_all_open_files(exclude=set()):
""" Close all open file descriptors.
Closes every file descriptor (if open) of this process. If
specified, `exclude` is a set of file descriptors to *not*
close.
"""
maxfd = get_maximum_file_descriptors()
for fd in reversed(range(maxfd)):
if fd not in exclude:
close_file_descriptor_if_open(fd)
def redirect_stream(system_stream, target_stream):
""" Redirect a system stream to a specified file.
`system_stream` is a standard system stream such as
``sys.stdout``. `target_stream` is an open file object that
should replace the corresponding system stream object.
If `target_stream` is ``None``, defaults to opening the
operating system's null device and using its file descriptor.
"""
if target_stream is None:
target_fd = os.open(os.devnull, os.O_RDWR)
else:
target_fd = target_stream.fileno()
os.dup2(target_fd, system_stream.fileno())
def make_default_signal_map():
""" Make the default signal map for this system.
The signals available differ by system. The map will not
contain any signals not defined on the running system.
"""
name_map = {
'SIGTSTP': None,
'SIGTTIN': None,
'SIGTTOU': None,
'SIGTERM': 'terminate',
}
signal_map = dict(
(getattr(signal, name), target)
for (name, target) in name_map.items()
if hasattr(signal, name))
return signal_map
def set_signal_handlers(signal_handler_map):
""" Set the signal handlers as specified.
The `signal_handler_map` argument is a map from signal number
to signal handler. See the `signal` module for details.
"""
for (signal_number, handler) in signal_handler_map.items():
signal.signal(signal_number, handler)
def register_atexit_function(func):
""" Register a function for processing at program exit.
The function `func` is registered for a call with no arguments
at program exit.
"""
atexit.register(func)