To set "global" options affecting all buildouts, create a directory .buildout (note leading dot) in your home directory, and add a file there called default.cfg. Any option set here will be applied to the corresponding section in any buildout.cfg that you run, unless it is overridden by a more specific option in the buildout.cfg file itself.

The most common options are:

executable

Specify a python interpreter other than the system default. This is useful if you have Python 2.5 installed, say, but you want your buildouts to use another installation of Python 2.4.

eggs-directory

Specify a directory where eggs will be downloaded. This allows multiple buildouts to share the same eggs, saving disk space and download time. Note that only those eggs explicitly required by a particular buildout will be activated. The eggs directory may contain many more eggs (or many different versions of the same package) than what is used at any one time.

download-directory

Specify a shared directory for downloaded archives. Again, this can save disk space and download time.

Here is an example ~/.buildout/default.cfg setting all three:

[buildout]
executable = /opt/python24/bin/python
eggs-directory = /home/username/.buildout/eggs
download-cache = /home/username/.buildout/downloads

This assumes Python 2.4 is installed in /opt/python2.4. For the last two options to work, you would need to create the directories eggs and downloads inside the ~/.buildout directory.