watchdog requires Python 2.6 or above to work. If you are using a Linux/FreeBSD/Mac OS X system, you already have Python installed. However, you may wish to upgrade your system to Python 2.7 at least, because this version comes with updates that can reduce compatibility problems. See a list of Dependencies.

Installing from PyPI using pip

$ pip install watchdog

Installing from source tarballs

$ wget -c
$ tar zxvf watchdog-0.8.2.tar.gz
$ cd watchdog-0.8.2
$ python install

Installing from the code repository

$ git clone --recursive git://
$ cd watchdog
$ python install


watchdog depends on many libraries to do its job. The following is a list of dependencies you need based on the operating system you are using.

Operating system Dependency (row) Windows Linux 2.6
Mac OS X/
XCode     Yes  
PyYAML Yes Yes Yes Yes
argh Yes Yes Yes Yes
argparse Yes Yes Yes Yes
select_backport (Python 2.6)     Yes Yes
pathtools Yes Yes Yes Yes

Installing Dependencies

The watchmedo script depends on PyYAML which links with LibYAML. On Mac OS X, you can use homebrew to install LibYAML:

brew install libyaml

On Linux, use your favorite package manager to install LibYAML. Here’s how you do it on Ubuntu:

sudo aptitude install libyaml-dev

On Windows, please install PyYAML using the binaries they provide.

Supported Platforms (and Caveats)

watchdog uses native APIs as much as possible falling back to polling the disk periodically to compare directory snapshots only when it cannot use an API natively-provided by the underlying operating system. The following operating systems are currently supported:


Differences between behaviors of these native API are noted below.

Linux 2.6+

Linux kernel version 2.6 and later come with an API called inotify that programs can use to monitor file system events.


On most systems the maximum number of watches that can be created per user is limited to 8192. watchdog needs one per directory to monitor. To change this limit, edit /etc/sysctl.conf and add:

Mac OS X

The Darwin kernel/OS X API maintains two ways to monitor directories for file system events:

watchdog can use whichever one is available, preferring FSEvents over kqueue(2). kqueue(2) uses open file descriptors for monitoring and the current implementation uses Mac OS X File System Monitoring Performance Guidelines to open these file descriptors only to monitor events, thus allowing OS X to unmount volumes that are being watched without locking them.


More information about how watchdog uses kqueue(2) is noted in BSD Unix variants. Much of this information applies to Mac OS X as well.

BSD Unix variants

BSD variants come with kqueue which programs can use to monitor changes to open file descriptors. Because of the way kqueue(2) works, watchdog needs to open these files and directories in read-only non-blocking mode and keep books about them.

watchdog will automatically open file descriptors for all new files/directories created and close those for which are deleted.


The maximum number of open file descriptor per process limit on your operating system can hinder watchdog‘s ability to monitor files.

You should ensure this limit is set to at least 1024 (or a value suitable to your usage). The following command appended to your ~/.profile configuration file does this for you:

ulimit -n 1024
Windows Vista and later

The Windows API provides the ReadDirectoryChangesW. watchdog currently contains implementation for a synchronous approach requiring additional API functionality only available in Windows Vista and later.


Since renaming is not the same operation as movement on Windows, watchdog tries hard to convert renames to movement events. Also, because the ReadDirectoryChangesW API function returns rename/movement events for directories even before the underlying I/O is complete, watchdog may not be able to completely scan the moved directory in order to successfully queue movement events for files and directories within it.


Since the Windows API does not provide information about whether an object is a file or a directory, delete events for directories may be reported as a file deleted event.

OS Independent Polling
watchdog also includes a fallback-implementation that polls watched directories for changes by periodically comparing snapshots of the directory tree.