Source code for coloredlogs.syslog

# Easy to use system logging for Python's logging module.
# Author: Peter Odding <>
# Last Change: December 10, 2020
# URL:

Easy to use UNIX system logging for Python's :mod:`logging` module.

Admittedly system logging has little to do with colored terminal output, however:

- The `coloredlogs` package is my attempt to do Python logging right and system
  logging is an important part of that equation.

- I've seen a surprising number of quirks and mistakes in system logging done
  in Python, for example including ``%(asctime)s`` in a format string (the
  system logging daemon is responsible for adding timestamps and thus you end
  up with duplicate timestamps that make the logs awful to read :-).

- The ``%(programname)s`` filter originated in my system logging code and I
  wanted it in `coloredlogs` so the step to include this module wasn't that big.

- As a bonus this Python module now has a test suite and proper documentation.

So there :-P. Go take a look at :func:`enable_system_logging()`.

# Standard library modules.
import logging
import logging.handlers
import os
import socket
import sys

# External dependencies.
from humanfriendly import coerce_boolean
from humanfriendly.compat import on_macos, on_windows

# Modules included in our package.
from coloredlogs import (

LOG_DEVICE_MACOSX = '/var/run/syslog'
"""The pathname of the log device on Mac OS X (a string)."""

LOG_DEVICE_UNIX = '/dev/log'
"""The pathname of the log device on Linux and most other UNIX systems (a string)."""

DEFAULT_LOG_FORMAT = '%(programname)s[%(process)d]: %(levelname)s %(message)s'
The default format for log messages sent to the system log (a string).

The ``%(programname)s`` format requires :class:`~coloredlogs.ProgramNameFilter`
but :func:`enable_system_logging()` takes care of this for you.

The ``name[pid]:`` construct (specifically the colon) in the format allows
rsyslogd_ to extract the ``$programname`` from each log message, which in turn
allows configuration files in ``/etc/rsyslog.d/*.conf`` to filter these log
messages to a separate log file (if the need arises).

.. _rsyslogd:

# Initialize a logger for this module.
logger = logging.getLogger(__name__)

[docs]class SystemLogging(object): """Context manager to enable system logging."""
[docs] def __init__(self, *args, **kw): """ Initialize a :class:`SystemLogging` object. :param args: Positional arguments to :func:`enable_system_logging()`. :param kw: Keyword arguments to :func:`enable_system_logging()`. """ self.args = args = kw self.handler = None
[docs] def __enter__(self): """Enable system logging when entering the context.""" if self.handler is None: self.handler = enable_system_logging(*self.args, ** return self.handler
[docs] def __exit__(self, exc_type=None, exc_value=None, traceback=None): """ Disable system logging when leaving the context. .. note:: If an exception is being handled when we leave the context a warning message including traceback is logged *before* system logging is disabled. """ if self.handler is not None: if exc_type is not None: logger.warning("Disabling system logging due to unhandled exception!", exc_info=True) ('logger') or logging.getLogger()).removeHandler(self.handler) self.handler = None
[docs]def enable_system_logging(programname=None, fmt=None, logger=None, reconfigure=True, **kw): """ Redirect :mod:`logging` messages to the system log (e.g. ``/var/log/syslog``). :param programname: The program name to embed in log messages (a string, defaults to the result of :func:`~coloredlogs.find_program_name()`). :param fmt: The log format for system log messages (a string, defaults to :data:`DEFAULT_LOG_FORMAT`). :param logger: The logger to which the :class:`~logging.handlers.SysLogHandler` should be connected (defaults to the root logger). :param level: The logging level for the :class:`~logging.handlers.SysLogHandler` (defaults to :data:`.DEFAULT_LOG_LEVEL`). This value is coerced using :func:`~coloredlogs.level_to_number()`. :param reconfigure: If :data:`True` (the default) multiple calls to :func:`enable_system_logging()` will each override the previous configuration. :param kw: Refer to :func:`connect_to_syslog()`. :returns: A :class:`~logging.handlers.SysLogHandler` object or :data:`None`. If an existing handler is found and `reconfigure` is :data:`False` the existing handler object is returned. If the connection to the system logging daemon fails :data:`None` is returned. As of release 15.0 this function uses :func:`is_syslog_supported()` to check whether system logging is supported and appropriate before it's enabled. .. note:: When the logger's effective level is too restrictive it is relaxed (refer to `notes about log levels`_ for details). """ # Check whether system logging is supported / appropriate. if not is_syslog_supported(): return None # Provide defaults for omitted arguments. programname = programname or find_program_name() logger = logger or logging.getLogger() fmt = fmt or DEFAULT_LOG_FORMAT level = level_to_number(kw.get('level', DEFAULT_LOG_LEVEL)) # Check whether system logging is already enabled. handler, logger = replace_handler(logger, match_syslog_handler, reconfigure) # Make sure reconfiguration is allowed or not relevant. if not (handler and not reconfigure): # Create a system logging handler. handler = connect_to_syslog(**kw) # Make sure the handler was successfully created. if handler: # Enable the use of %(programname)s. ProgramNameFilter.install(handler=handler, fmt=fmt, programname=programname) # Connect the formatter, handler and logger. handler.setFormatter(logging.Formatter(fmt)) logger.addHandler(handler) # Adjust the level of the selected logger. adjust_level(logger, level) return handler
[docs]def connect_to_syslog(address=None, facility=None, level=None): """ Create a :class:`~logging.handlers.SysLogHandler`. :param address: The device file or network address of the system logging daemon (a string or tuple, defaults to the result of :func:`find_syslog_address()`). :param facility: Refer to :class:`~logging.handlers.SysLogHandler`. Defaults to ``LOG_USER``. :param level: The logging level for the :class:`~logging.handlers.SysLogHandler` (defaults to :data:`.DEFAULT_LOG_LEVEL`). This value is coerced using :func:`~coloredlogs.level_to_number()`. :returns: A :class:`~logging.handlers.SysLogHandler` object or :data:`None` (if the system logging daemon is unavailable). The process of connecting to the system logging daemon goes as follows: - The following two socket types are tried (in decreasing preference): 1. :data:`~socket.SOCK_RAW` avoids truncation of log messages but may not be supported. 2. :data:`~socket.SOCK_STREAM` (TCP) supports longer messages than the default (which is UDP). """ if not address: address = find_syslog_address() if facility is None: facility = logging.handlers.SysLogHandler.LOG_USER if level is None: level = DEFAULT_LOG_LEVEL for socktype in socket.SOCK_RAW, socket.SOCK_STREAM, None: kw = dict(facility=facility, address=address) if socktype is not None: kw['socktype'] = socktype try: handler = logging.handlers.SysLogHandler(**kw) except IOError: # IOError is a superclass of socket.error which can be raised if the system # logging daemon is unavailable. pass else: handler.setLevel(level_to_number(level)) return handler
[docs]def find_syslog_address(): """ Find the most suitable destination for system log messages. :returns: The pathname of a log device (a string) or an address/port tuple as supported by :class:`~logging.handlers.SysLogHandler`. On Mac OS X this prefers :data:`LOG_DEVICE_MACOSX`, after that :data:`LOG_DEVICE_UNIX` is checked for existence. If both of these device files don't exist the default used by :class:`~logging.handlers.SysLogHandler` is returned. """ if sys.platform == 'darwin' and os.path.exists(LOG_DEVICE_MACOSX): return LOG_DEVICE_MACOSX elif os.path.exists(LOG_DEVICE_UNIX): return LOG_DEVICE_UNIX else: return 'localhost', logging.handlers.SYSLOG_UDP_PORT
[docs]def is_syslog_supported(): """ Determine whether system logging is supported. :returns: :data:`True` if system logging is supported and can be enabled, :data:`False` if system logging is not supported or there are good reasons for not enabling it. The decision making process here is as follows: Override If the environment variable ``$COLOREDLOGS_SYSLOG`` is set it is evaluated using :func:`~humanfriendly.coerce_boolean()` and the resulting value overrides the platform detection discussed below, this allows users to override the decision making process if they disagree / know better. Linux / UNIX On systems that are not Windows or MacOS (see below) we assume UNIX which means either syslog is available or sending a bunch of UDP packets to nowhere won't hurt anyone... Microsoft Windows Over the years I've had multiple reports of :pypi:`coloredlogs` spewing extremely verbose errno 10057 warning messages to the console (once for each log message I suppose) so I now assume it a default that "syslog-style system logging" is not generally available on Windows. Apple MacOS There's cPython issue `#38780`_ which seems to result in a fatal exception when the Python interpreter shuts down. This is (way) worse than not having system logging enabled. The error message mentioned in `#38780`_ has actually been following me around for years now, see for example: - mentions Docker images implying Linux, so not strictly the same as `#38780`_. - is definitely related to `#38780`_ and is what eventually prompted me to add the :func:`is_syslog_supported()` logic. .. _#38780: """ override = os.environ.get("COLOREDLOGS_SYSLOG") if override is not None: return coerce_boolean(override) else: return not (on_windows() or on_macos())
[docs]def match_syslog_handler(handler): """ Identify system logging handlers. :param handler: The :class:`~logging.Handler` class to check. :returns: :data:`True` if the handler is a :class:`~logging.handlers.SysLogHandler`, :data:`False` otherwise. This function can be used as a callback for :func:`.find_handler()`. """ return isinstance(handler, logging.handlers.SysLogHandler)