I'd like to fully understand the license

I'm thinking of creating a social site (who doesn't? :)), and considering Elgg for it, since it's free and being actively developed. Though I haven't yet tried Elgg, I think that what I have in mind will require some changes or at least a plugin or two. The License page says that the Elgg core is available under an MIT license, but I'm not clear on what's included in the core, and in any case it looks like most (all?) plugins are GPL. So I have some questions:

The features page (http://docs.elgg.org/wiki/Features) describes the core features, then "built-in features". Are the built-in features under an MIT license, or are they separate from the "core" (as the separation on the page might imply)?

My general understanding of the GPL is that if any part of the project is GPL, then the entire project must be offered under the GPL. If that's the case, then using any plug-in (or built-in feature, if these are under GPL) would imply also sharing any core changes, as well as new plugins. Is my understanding correct? If not, what's the real deal, and how exactly do I make sure I'm not stepping on any GPL toes?

I will of course share any changes I might make to a GPL part, but I don't want to have to share everything, including my own plugins, and I don't want to be blamed in the future for breaking the GPL because I thought it allowed me to keep some things to myself and it didn't. So I'd really appreciate some clarification on this.


  • First, the easy part:  The mods that are considered "core" are those in the main SVN repository at http://code.elgg.org/elgg/trunk/mod/  All other modules bundled are not core, and so are GPL only.

    > My general understanding of the GPL is that if any part of the project

    > is GPL, then the entire project must be offered under the GPL.

    This is not the case with GPL 2 :)  Without getting too deep into the murky, murky waters of software licensing, the GPL 2 mainly protects the original application's distribution -- You may freely link against or use the software to provide a service without having to release the source as GPL.  The GPL 2 comes into effect when you are redistributing the product. 

    Basically, if you aren't redistributing a modified version of Elgg, you don't need to worry.  You can make any alterations you need on your own server without having to contribute back, though it's in the spirit OSS and best interest of Elgg if you do!  If you are redistributing Elgg, though, you must make the source code available because of the GPL license.

  • Hi,

    I am a new developer :) So, I have a novice question, I want to ask in a simple way, am I bound to keep the link to elgg, and other footer related to elgg? Coz, my only client seems confused seeing this! And I dont know what to do with this?