pyzenkit.daemonizer module

This module contains simple daemonization library, that takes care of all tasks necessary to correctly daemonize a process. Correct daemonization consists of following steps:

# Setup directories and limits # Setup user and group permissions # Terminal detachment with double fork and split session # Setup signal handlers # Close all open file descriptors (except for possible log files) # Redirect stdin, stdout, stderr to /dev/null # Detect current PID and store it to appropriate PID file # Remove PID file at process exit

These steps are performed during full daemonization. For many purposes it is however usefull to be capable of some kind of lite daemonization, in which case almost every step in previous list is done except for terminal detachment, closing all files and redirecting std* to /dev/null. This can be particularly usefull during testing or debugging, or even during production deployments for some kind of stay in foreground feature, which still enables the users to control the running application from outside with signals.

Usage example

Example usage is implemented directly within this module, please refer to source code. To view the result of demonstration please execute the module directly with Python3 interpretter.

pyzenkit.daemonizer.daemonize(chroot_dir=None, work_dir=None, umask=None, uid=None, gid=None, pid_file=None, files_preserve=None, signals=None)[source]

Perform full daemonization of currently running process. All of the function arguments are optinal, so that it is possible to easily turn on/off almost any part of daemonization process. For example omitting the uid and gid arguments will result in process permissions not to be changed.

NOTE: It would be possible to call daemonize_lite() method from within this method, howewer for readability purposes and to maintain correct ordering of the daemonization steps I decided against coding best practices and kept two separate methods with similar contents. It will be necessary to update both when making any improvements, however I do not expect them to change much and often, if ever.

Parameters

  • chroot_dir (str) – Name of the chroot directory (may be None).

  • work_dir (str) – Name of the work directory (may be None).

  • umask (int) – Umask as octal number (eg. 0o002 or 0o022, may be None).

  • uid (int) – User ID to which to drop the permissions (may be None).

  • gid (int) – Group ID to which to drop the permissions (may be None).

  • pid_file (str) – Full path to the PID file (may be None).

  • files_preserve (list) – List of file handles to preserve from closing (may be None).

  • signals (dict) – Desired signals to be handled as keys and their appropriate handlers as values (may be None).

pyzenkit.daemonizer.daemonize_lite(chroot_dir=None, work_dir=None, umask=None, uid=None, gid=None, pid_file=None, signals=None)[source]

Perform lite daemonization of currently running process. All of the function arguments are optinal, so that it is possible to easily turn on/off almost any part of daemonization process. For example omitting the uid and gid arguments will result in process permissions not to be changed.

The lite daemonization does everything full daemonization does but detaching from current session. This can be usefull when debugging daemons, because they can be tested, benchmarked and profiled more easily.

Parameters

  • chroot_dir (str) – Name of the chroot directory (may be None).

  • work_dir (str) – Name of the work directory (may be None).

  • umask (int) – Umask as octal number (eg. 0o002 or 0o022, may be None).

  • uid (int) – User ID to which to drop the permissions (may be None).

  • gid (int) – Group ID to which to drop the permissions (may be None).

  • pid_file (str) – Full path to the PID file (may be None).

  • signals (dict) – Desired signals to be handled as keys and their appropriate handlers as values (may be None).

pyzenkit.daemonizer.get_logger_files(logger)[source]

Return file handlers of all currently active loggers.

Result from this method will be used during daemonization process to close all open file descriptors but those belonging to given logger service.

Warning

This method is hacking internal structure of external module and might stop working, although the related interface has been stable for a long time.

Parameters

logger (logging.Logger) – Logger to be analyzed for open file descriptors.

Returns

List of open file descriptors used by logging service.

Return type

list

pyzenkit.daemonizer.read_pid(pid_file)[source]

Read PID from given PID file.

Parameters

pidfile (str) – Name of the PID file to read from.

Returns

PID from given PID file.

Return type

int

pyzenkit.daemonizer.write_pid(pid_file, pid)[source]

Write given PID into given PID file.

Parameters

  • pidfile (str) – Name of the PID file to write to.

  • pid (int) – PID to write.