filesystem watcher

• Overview
• Requirements
• Installation
  • Debian
  • Pip
• Configuration
• Usage
  • Debug mode
  • Increasing the amount of inotify watchers
  • Increasing the amount of queued events

Overview

Watcher is a daemon that watches specified files/folders for changes and fires commands in response to those changes. It is similar to incron, however, configuration uses a simpler to read ini file instead of a plain text file. Unlike incron it can also recursively monitor directories.

It's written in Python, making it easier to hack.

• Source on GitHub
• Packages on PyPI

This fork is a rewritting of the code using python-daemon implementation of PEP3143 with additional features:

• async commands executing which allows several copies of command can be executed simultaneously for single job
• capturing command output to separate log file
• exclude watching files by regular expression
• perform actions on successful/failure command completion.

Requirements

Watcher supports both Python 2.7 and Python 3.x. It has following dependencies which can be installed with your package manager or pip:

• pyinotify
• python-daemon
• lockfile
• chardet
• future

To install dependencies on Debian:

sudo apt-get install python-pyinotify python-daemon python-lockfile python-chardet python-future

sudo apt-get install python3-pyinotify python3-daemon python3-lockfile python3-chardet python3-future

To install dependencies on Gentoo:

emerge -av dev-python/pyinotify dev-python/python-daemon dev-python/lockfile dev-python/chardet dev-python/future

pip will install dependencies automatically.

Installation

Debian

Download latest deb package from GitHub releases page and install it with dpkg.

sudo dpkg -i fs-watcher_X.Y.Z-0_all.deb

In addition to Watcher itself, it will install:

• sample configuration file to /etc/watcher.ini
• systemd service fs-watcher (in disabled state).

To start using Watcher you must change /etc/watcher.ini to suit your needs and enable/start fs-watcher service.

Pip

System-wide using pip:

sudo pip install fs-watcher

sudo pip3 install fs-watcher

This command will install:

• Python modules for Watcher
• sample configuration file
• samples of startup scripts
• executable to start Watcher

Use following command to check exact locations:

pip show -f fs-watcher

There are samples of startup scripts. Use your init system manual to install them properly. Check/fix path to Watcher executable in samples before using, by default it is assumed to be /usr/sbin/watcher.

For systemd:

cp share/init/fs-watcher.service /etc/systemd/system/fs-watcher.service
systemctl daemon-reload
systemctl enable fs-watcher
systemctl start fs-watcher

For SysV:

cp share/init/fs-watcher.sysvinit /etc/init.d/fs-watcher
update-rc.d fs-watcher defaults
/etc/init.d/fs-watcher start

For OpenRC:

cp share/init/fs-watcher.openrc /etc/init.d/fs-watcher
rc-update add fs-watcher default
/etc/init.d/fs-watcher start

Configuration

Check provided watcher.ini file for an example job configuration. The config file should reside in /etc/watcher.ini or ~/.watcher.ini. You can also specify the path to the config file as a command line parameter using the --config option.

If you edit the ini file you must restart the daemon for it to reload the configuration.

Usage

usage: watcher [-h] [--version] [-c CONFIG] [-v] {start,stop,restart,debug}

positional arguments:
  {start,stop,restart,debug}
                                                What to do.

optional arguments:
  -h, --help            show this help message and exit
  --version             show program's version number and exit
  -c CONFIG, --config CONFIG
                                                Path to the config file (default: None)
  -v, --verbose         verbose output

Debug mode

You can start Watcher with debug positional argument to prevent it from forking to the background and log messages to stdout:

watcher debug

Increasing the amount of inotify watchers

There is a limit of max number of inotify watchers. When this limit is not enough to monitor all jobs, the limit must be increased for Watcher to work properly. You can find following error in log when facing this limit:

add_watch: cannot watch /...... WD=-1, Errno=No space left on device (ENOSPC)

If you are running Debian, RedHat, or another similar Linux distribution, run the following in a terminal to increase this limit:

echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p

Increasing the amount of queued events

There is a limit of max queued events. When this limit is not enough to monitor all jobs, the limit must be increased for Watcher to work properly. You can find following warning in log when facing this limit:

pyinotify - WARNING - Event queue overflowed.

If you are running Debian, RedHat, or another similar Linux distribution, run the following in a terminal to increase this limit:

echo fs.inotify.max_queued_events=65536 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p