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diff --git a/scripts/automation/trex_control_plane/python_lib/python-daemon-2.0.5/doc/FAQ b/scripts/automation/trex_control_plane/python_lib/python-daemon-2.0.5/doc/FAQ new file mode 100755 index 00000000..1fcc4658 --- /dev/null +++ b/scripts/automation/trex_control_plane/python_lib/python-daemon-2.0.5/doc/FAQ @@ -0,0 +1,156 @@ +‘python-daemon’ Frequently Asked Questions +########################################## + +:Author: Ben Finney <ben+python@benfinney.id.au> +:Updated: 2015-01-10 + +.. contents:: +.. + 1 General + 1.1 What is the purpose of the ‘python-daemon’ library? + 1.2 How can I run a service communicating with a separate daemon process? + 2 Security + 2.1 Why is the umask set to 0 by default? + 3 File descriptors + 3.1 Why does the output stop after opening the daemon context? + 3.2 How can I preserve a ‘logging’ handler's file descriptor? + +General +======= + +What is the purpose of the ‘python-daemon’ library? +--------------------------------------------------- + +The ‘python-daemon’ library has a deliberately narrow focus: that of +being a reference implementation for `PEP 3143`_, “Standard daemon +process library”. + +.. _`PEP 3143`: http://www.python.org/dev/peps/pep-3143 + +How can I run a service communicating with a separate daemon process? +--------------------------------------------------------------------- + +As specified in `PEP 3143`_, the ‘python-daemon’ library is +specifically focussed on the goal of having the *current running +program* become a well-behaved Unix daemon process. This leaves open +the question of how this program is started, or about multiple +programs interacting. As detailed in PEP 3143: + + A daemon is not a service + + There is a related concept in many systems, called a “service”. A + service differs from the model in this PEP, in that rather than + having the *current* program continue to run as a daemon process, + a service starts an *additional* process to run in the background, + and the current process communicates with that additional process + via some defined channels. + + The Unix-style daemon model in this PEP can be used, among other + things, to implement the background-process part of a service; but + this PEP does not address the other aspects of setting up and + managing a service. + +A possible starting point for such a “service” model of execution is +in a `message from 2009-01-30`_ to the ``python-ideas`` forum. + +.. _`message from 2009-01-30`: http://mail.python.org/pipermail/python-ideas/2009-January/002606.html + + +Security +======== + +Why is the umask set to 0 by default? +------------------------------------- + +A daemon should not rely on the parent process's umask value, which is +beyond its control and may prevent creating a file with the required +access mode. So when the daemon context opens, the umask is set to an +explicit known value. + +If the conventional value of 0 is too open, consider setting a value +such as 0o022, 0o027, 0o077, or another specific value. Otherwise, +ensure the daemon creates every file with an explicit access mode for +the purpose. + + +File descriptors +================ + +Why does the output stop after opening the daemon context? +---------------------------------------------------------- + +The specified behaviour in `PEP 3143`_ includes the requirement to +detach the process from the controlling terminal (to allow the process +to continue to run as a daemon), and to close all file descriptors not +known to be safe once detached (to ensure any files that continue to +be used are under the control of the daemon process). + +If you want the process to generate output via the system streams +‘sys.stdout’ and ‘sys.stderr’, set the ‘DaemonContext’'s ‘stdout’ +and/or ‘stderr’ options to a file-like object (e.g. the ‘stream’ +attribute of a ‘logging.Handler’ instance). If these objects have file +descriptors, they will be preserved when the daemon context opens. + +How can I preserve a ‘logging’ handler's file descriptor? +--------------------------------------------------------- + +The ‘DaemonContext.open’ method conforms to `PEP 3143`_ by closing all +open file descriptors, but excluding those files specified in the +‘files_preserve’ option. This option is a list of files or file +descriptors. + +The Python standard library ‘logging’ module provides log handlers +that write to streams, including to files via the ‘StreamHandler’ +class and its sub-classes. The documentation (both the online `logging +module documentation`_ and the docstrings for the code) makes no +mention of a way to get at the stream associated with a handler +object. + +However, looking at the source code for ‘StreamHandler’, in Python 2.5 +as ``/usr/lib/python2.5/logging/__init__.py``, shows a ‘stream’ +attribute that is bound to the stream object. The attribute is not +marked private (i.e. it is not named with a leading underscore), so we +can presume it is part of the public API. + +That attribute can then be used to specify that a logging handler's +file descriptor should, when the ‘DaemonContext’ opens, be excluded +from closure:: + + import logging + import daemon + + # any subclass of StreamHandler should provide the ‘stream’ attribute. + lh = logging.handlers.TimedRotatingFileHandler( + "/var/log/foo.log", + # … + ) + + # … do some logging and other activity … + + daemon_context = daemon.DaemonContext() + daemon_context.files_preserve = [lh.stream] + + daemon_context.open() + + # … continue as a daemon process … + +.. _`logging module documentation`: http://docs.python.org/library/logging + + +.. + This is free software: you may copy, modify, and/or distribute this work + under the terms of the Apache License version 2.0 as published by the + Apache Software Foundation. + No warranty expressed or implied. See the file ‘LICENSE.ASF-2’ for details. + +.. + Local variables: + coding: utf-8 + mode: text + mode: rst + time-stamp-format: "%:y-%02m-%02d" + time-stamp-start: "^:Updated:[ ]+" + time-stamp-end: "$" + time-stamp-line-limit: 20 + End: + vim: fileencoding=utf-8 filetype=rst : |