I understand that the licensing agreements, or whatever they call them, of commercial distros can limit the number of "units" [which I assume means computers] the customer uses the software or service on. (I was just looking at RHEL's agreement.) How does that mesh with it being free software? Doesn't such an agreement prevent the user from, if not altering the code, then making more copies of the distro? I don't understand this yet. Is it for no other reason that the copies have the company's trademark, which is not free?

I understand only that the companies charge for support, not products.

I believe it does have to do with the trademark. CentOS is just RHEL recompiled without any of the trademark or non-free tools.

As to whether there's another mechanism for keeping you from installing on multiple machines (like a central license server), I can't say.

Nothing about being Open Source software says that everything has to be free. Just the source code. Red Hat makes all of the source code freely available for people to use. Only the Red Hat Logos and such are trademarked. Projects (CentOS) exist to provide binary packages from RHEL without the Red Hat.

Red Hat's software does not actually limit your ability to install it on any number of systems. The roadblock comes into play with updates - an activation key is required to use Red Hat's update servers.

I don't want to speak with 100% certainty, and certainly not for all flavors.

Novell for example will allow you to install SLES (SuSE Linux Enterprise Server)or SLED (SuSE Linux Enterpise, Desktop), but they won't allow even security patches to download / install if you don't buy 'support' for the copy. Of Course OpenSuSE (Novell's 'free offering') does not have this limitation.

Here is a link to their Flyer explaining their Subscription Service


In part from their site:

Your subscription includes:

* Award-winning technical support
* First Look on-demand training
* Maintenance updates, service pack releases, hardware enablement and security and bug fixes Entitlement to the Subscription Management Tool for SUSE Linux Enterprise
* Rights to upgrade to new versions of the SUSE Linux Enterprise family of products
* A generous and predictable lifecycle commitment
* Opportunities to participate in new beta product testing
* Protection under the Novell® Technology Assurance Program, including extensive intellectual property (IP) coverage
* Assurance of compatibility with thousands of hardware and software products Flexible, tiered pricing Access to an extensive global network of resellers and distributors
* Access to Novell Customer Center an online interface where, from one location, you can review the status of all your Novell products, subscriptions and services, and obtain critical Linux updates and support
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Frankly, I think it is a bit of a stretch for them to say they follow the GPL, since they release the updates as well, but only to paying customers. But that is how they attempt to (currently do) get around it. You can download and install it if you want (for free), but if you want updates, security . . . then you have to buy the subscription.

Bottom line for me at least I would rather run SLES, with OES (Open Enterprise Server) and Groupwise, and avoid the Closed source, overpriced world of Microsoft. Though I run a lot of truly free systems too.

I'm not so sure this is even close to a violation of the GPL. Really all the GPL says is that if you distribute changes to a GPL'ed program, you have to provide the source code with the changes you made if someone asks. They are really under no obligation to provide any sort of binary or package of software.